Tue, 14 Jan 2014 16:40:33 +0100
8032379: Remove the is_scavenging flag to process_strong_roots
Summary: Refactor the strong root processing to avoid using a boolean in addition to the ScanOption enum.
Reviewed-by: stefank, tschatzl, ehelin, jmasa
1 /*
2 * Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
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23 */
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/symbolTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc_implementation/concurrentMarkSweep/cmsAdaptiveSizePolicy.hpp"
31 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
32 #include "gc_implementation/concurrentMarkSweep/cmsGCAdaptivePolicyCounters.hpp"
33 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
34 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
36 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
37 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
38 #include "gc_implementation/parNew/parNewGeneration.hpp"
39 #include "gc_implementation/shared/collectorCounters.hpp"
40 #include "gc_implementation/shared/gcTimer.hpp"
41 #include "gc_implementation/shared/gcTrace.hpp"
42 #include "gc_implementation/shared/gcTraceTime.hpp"
43 #include "gc_implementation/shared/isGCActiveMark.hpp"
44 #include "gc_interface/collectedHeap.inline.hpp"
45 #include "memory/allocation.hpp"
46 #include "memory/cardTableRS.hpp"
47 #include "memory/collectorPolicy.hpp"
48 #include "memory/gcLocker.inline.hpp"
49 #include "memory/genCollectedHeap.hpp"
50 #include "memory/genMarkSweep.hpp"
51 #include "memory/genOopClosures.inline.hpp"
52 #include "memory/iterator.hpp"
53 #include "memory/padded.hpp"
54 #include "memory/referencePolicy.hpp"
55 #include "memory/resourceArea.hpp"
56 #include "memory/tenuredGeneration.hpp"
57 #include "oops/oop.inline.hpp"
58 #include "prims/jvmtiExport.hpp"
59 #include "runtime/globals_extension.hpp"
60 #include "runtime/handles.inline.hpp"
61 #include "runtime/java.hpp"
62 #include "runtime/orderAccess.inline.hpp"
63 #include "runtime/vmThread.hpp"
64 #include "services/memoryService.hpp"
65 #include "services/runtimeService.hpp"
67 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
69 // statics
70 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
71 bool CMSCollector::_full_gc_requested = false;
72 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
74 //////////////////////////////////////////////////////////////////
75 // In support of CMS/VM thread synchronization
76 //////////////////////////////////////////////////////////////////
77 // We split use of the CGC_lock into 2 "levels".
78 // The low-level locking is of the usual CGC_lock monitor. We introduce
79 // a higher level "token" (hereafter "CMS token") built on top of the
80 // low level monitor (hereafter "CGC lock").
81 // The token-passing protocol gives priority to the VM thread. The
82 // CMS-lock doesn't provide any fairness guarantees, but clients
83 // should ensure that it is only held for very short, bounded
84 // durations.
85 //
86 // When either of the CMS thread or the VM thread is involved in
87 // collection operations during which it does not want the other
88 // thread to interfere, it obtains the CMS token.
89 //
90 // If either thread tries to get the token while the other has
91 // it, that thread waits. However, if the VM thread and CMS thread
92 // both want the token, then the VM thread gets priority while the
93 // CMS thread waits. This ensures, for instance, that the "concurrent"
94 // phases of the CMS thread's work do not block out the VM thread
95 // for long periods of time as the CMS thread continues to hog
96 // the token. (See bug 4616232).
97 //
98 // The baton-passing functions are, however, controlled by the
99 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
100 // and here the low-level CMS lock, not the high level token,
101 // ensures mutual exclusion.
102 //
103 // Two important conditions that we have to satisfy:
104 // 1. if a thread does a low-level wait on the CMS lock, then it
105 // relinquishes the CMS token if it were holding that token
106 // when it acquired the low-level CMS lock.
107 // 2. any low-level notifications on the low-level lock
108 // should only be sent when a thread has relinquished the token.
109 //
110 // In the absence of either property, we'd have potential deadlock.
111 //
112 // We protect each of the CMS (concurrent and sequential) phases
113 // with the CMS _token_, not the CMS _lock_.
114 //
115 // The only code protected by CMS lock is the token acquisition code
116 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
117 // baton-passing code.
118 //
119 // Unfortunately, i couldn't come up with a good abstraction to factor and
120 // hide the naked CGC_lock manipulation in the baton-passing code
121 // further below. That's something we should try to do. Also, the proof
122 // of correctness of this 2-level locking scheme is far from obvious,
123 // and potentially quite slippery. We have an uneasy supsicion, for instance,
124 // that there may be a theoretical possibility of delay/starvation in the
125 // low-level lock/wait/notify scheme used for the baton-passing because of
126 // potential intereference with the priority scheme embodied in the
127 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
128 // invocation further below and marked with "XXX 20011219YSR".
129 // Indeed, as we note elsewhere, this may become yet more slippery
130 // in the presence of multiple CMS and/or multiple VM threads. XXX
132 class CMSTokenSync: public StackObj {
133 private:
134 bool _is_cms_thread;
135 public:
136 CMSTokenSync(bool is_cms_thread):
137 _is_cms_thread(is_cms_thread) {
138 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
139 "Incorrect argument to constructor");
140 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
141 }
143 ~CMSTokenSync() {
144 assert(_is_cms_thread ?
145 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
146 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
147 "Incorrect state");
148 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
149 }
150 };
152 // Convenience class that does a CMSTokenSync, and then acquires
153 // upto three locks.
154 class CMSTokenSyncWithLocks: public CMSTokenSync {
155 private:
156 // Note: locks are acquired in textual declaration order
157 // and released in the opposite order
158 MutexLockerEx _locker1, _locker2, _locker3;
159 public:
160 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
161 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
162 CMSTokenSync(is_cms_thread),
163 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
164 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
165 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
166 { }
167 };
170 // Wrapper class to temporarily disable icms during a foreground cms collection.
171 class ICMSDisabler: public StackObj {
172 public:
173 // The ctor disables icms and wakes up the thread so it notices the change;
174 // the dtor re-enables icms. Note that the CMSCollector methods will check
175 // CMSIncrementalMode.
176 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
177 ~ICMSDisabler() { CMSCollector::enable_icms(); }
178 };
180 //////////////////////////////////////////////////////////////////
181 // Concurrent Mark-Sweep Generation /////////////////////////////
182 //////////////////////////////////////////////////////////////////
184 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
186 // This struct contains per-thread things necessary to support parallel
187 // young-gen collection.
188 class CMSParGCThreadState: public CHeapObj<mtGC> {
189 public:
190 CFLS_LAB lab;
191 PromotionInfo promo;
193 // Constructor.
194 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
195 promo.setSpace(cfls);
196 }
197 };
199 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
200 ReservedSpace rs, size_t initial_byte_size, int level,
201 CardTableRS* ct, bool use_adaptive_freelists,
202 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
203 CardGeneration(rs, initial_byte_size, level, ct),
204 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
205 _debug_collection_type(Concurrent_collection_type),
206 _did_compact(false)
207 {
208 HeapWord* bottom = (HeapWord*) _virtual_space.low();
209 HeapWord* end = (HeapWord*) _virtual_space.high();
211 _direct_allocated_words = 0;
212 NOT_PRODUCT(
213 _numObjectsPromoted = 0;
214 _numWordsPromoted = 0;
215 _numObjectsAllocated = 0;
216 _numWordsAllocated = 0;
217 )
219 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
220 use_adaptive_freelists,
221 dictionaryChoice);
222 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
223 if (_cmsSpace == NULL) {
224 vm_exit_during_initialization(
225 "CompactibleFreeListSpace allocation failure");
226 }
227 _cmsSpace->_gen = this;
229 _gc_stats = new CMSGCStats();
231 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
232 // offsets match. The ability to tell free chunks from objects
233 // depends on this property.
234 debug_only(
235 FreeChunk* junk = NULL;
236 assert(UseCompressedClassPointers ||
237 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
238 "Offset of FreeChunk::_prev within FreeChunk must match"
239 " that of OopDesc::_klass within OopDesc");
240 )
241 if (CollectedHeap::use_parallel_gc_threads()) {
242 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
243 _par_gc_thread_states =
244 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
245 if (_par_gc_thread_states == NULL) {
246 vm_exit_during_initialization("Could not allocate par gc structs");
247 }
248 for (uint i = 0; i < ParallelGCThreads; i++) {
249 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
250 if (_par_gc_thread_states[i] == NULL) {
251 vm_exit_during_initialization("Could not allocate par gc structs");
252 }
253 }
254 } else {
255 _par_gc_thread_states = NULL;
256 }
257 _incremental_collection_failed = false;
258 // The "dilatation_factor" is the expansion that can occur on
259 // account of the fact that the minimum object size in the CMS
260 // generation may be larger than that in, say, a contiguous young
261 // generation.
262 // Ideally, in the calculation below, we'd compute the dilatation
263 // factor as: MinChunkSize/(promoting_gen's min object size)
264 // Since we do not have such a general query interface for the
265 // promoting generation, we'll instead just use the mimimum
266 // object size (which today is a header's worth of space);
267 // note that all arithmetic is in units of HeapWords.
268 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
269 assert(_dilatation_factor >= 1.0, "from previous assert");
270 }
273 // The field "_initiating_occupancy" represents the occupancy percentage
274 // at which we trigger a new collection cycle. Unless explicitly specified
275 // via CMSInitiatingOccupancyFraction (argument "io" below), it
276 // is calculated by:
277 //
278 // Let "f" be MinHeapFreeRatio in
279 //
280 // _intiating_occupancy = 100-f +
281 // f * (CMSTriggerRatio/100)
282 // where CMSTriggerRatio is the argument "tr" below.
283 //
284 // That is, if we assume the heap is at its desired maximum occupancy at the
285 // end of a collection, we let CMSTriggerRatio of the (purported) free
286 // space be allocated before initiating a new collection cycle.
287 //
288 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
289 assert(io <= 100 && tr <= 100, "Check the arguments");
290 if (io >= 0) {
291 _initiating_occupancy = (double)io / 100.0;
292 } else {
293 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
294 (double)(tr * MinHeapFreeRatio) / 100.0)
295 / 100.0;
296 }
297 }
299 void ConcurrentMarkSweepGeneration::ref_processor_init() {
300 assert(collector() != NULL, "no collector");
301 collector()->ref_processor_init();
302 }
304 void CMSCollector::ref_processor_init() {
305 if (_ref_processor == NULL) {
306 // Allocate and initialize a reference processor
307 _ref_processor =
308 new ReferenceProcessor(_span, // span
309 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
310 (int) ParallelGCThreads, // mt processing degree
311 _cmsGen->refs_discovery_is_mt(), // mt discovery
312 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
313 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
314 &_is_alive_closure); // closure for liveness info
315 // Initialize the _ref_processor field of CMSGen
316 _cmsGen->set_ref_processor(_ref_processor);
318 }
319 }
321 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
322 GenCollectedHeap* gch = GenCollectedHeap::heap();
323 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
324 "Wrong type of heap");
325 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
326 gch->gen_policy()->size_policy();
327 assert(sp->is_gc_cms_adaptive_size_policy(),
328 "Wrong type of size policy");
329 return sp;
330 }
332 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
333 CMSGCAdaptivePolicyCounters* results =
334 (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
335 assert(
336 results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
337 "Wrong gc policy counter kind");
338 return results;
339 }
342 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
344 const char* gen_name = "old";
346 // Generation Counters - generation 1, 1 subspace
347 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
349 _space_counters = new GSpaceCounters(gen_name, 0,
350 _virtual_space.reserved_size(),
351 this, _gen_counters);
352 }
354 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
355 _cms_gen(cms_gen)
356 {
357 assert(alpha <= 100, "bad value");
358 _saved_alpha = alpha;
360 // Initialize the alphas to the bootstrap value of 100.
361 _gc0_alpha = _cms_alpha = 100;
363 _cms_begin_time.update();
364 _cms_end_time.update();
366 _gc0_duration = 0.0;
367 _gc0_period = 0.0;
368 _gc0_promoted = 0;
370 _cms_duration = 0.0;
371 _cms_period = 0.0;
372 _cms_allocated = 0;
374 _cms_used_at_gc0_begin = 0;
375 _cms_used_at_gc0_end = 0;
376 _allow_duty_cycle_reduction = false;
377 _valid_bits = 0;
378 _icms_duty_cycle = CMSIncrementalDutyCycle;
379 }
381 double CMSStats::cms_free_adjustment_factor(size_t free) const {
382 // TBD: CR 6909490
383 return 1.0;
384 }
386 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
387 }
389 // If promotion failure handling is on use
390 // the padded average size of the promotion for each
391 // young generation collection.
392 double CMSStats::time_until_cms_gen_full() const {
393 size_t cms_free = _cms_gen->cmsSpace()->free();
394 GenCollectedHeap* gch = GenCollectedHeap::heap();
395 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
396 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
397 if (cms_free > expected_promotion) {
398 // Start a cms collection if there isn't enough space to promote
399 // for the next minor collection. Use the padded average as
400 // a safety factor.
401 cms_free -= expected_promotion;
403 // Adjust by the safety factor.
404 double cms_free_dbl = (double)cms_free;
405 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
406 // Apply a further correction factor which tries to adjust
407 // for recent occurance of concurrent mode failures.
408 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
409 cms_free_dbl = cms_free_dbl * cms_adjustment;
411 if (PrintGCDetails && Verbose) {
412 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
413 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
414 cms_free, expected_promotion);
415 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
416 cms_free_dbl, cms_consumption_rate() + 1.0);
417 }
418 // Add 1 in case the consumption rate goes to zero.
419 return cms_free_dbl / (cms_consumption_rate() + 1.0);
420 }
421 return 0.0;
422 }
424 // Compare the duration of the cms collection to the
425 // time remaining before the cms generation is empty.
426 // Note that the time from the start of the cms collection
427 // to the start of the cms sweep (less than the total
428 // duration of the cms collection) can be used. This
429 // has been tried and some applications experienced
430 // promotion failures early in execution. This was
431 // possibly because the averages were not accurate
432 // enough at the beginning.
433 double CMSStats::time_until_cms_start() const {
434 // We add "gc0_period" to the "work" calculation
435 // below because this query is done (mostly) at the
436 // end of a scavenge, so we need to conservatively
437 // account for that much possible delay
438 // in the query so as to avoid concurrent mode failures
439 // due to starting the collection just a wee bit too
440 // late.
441 double work = cms_duration() + gc0_period();
442 double deadline = time_until_cms_gen_full();
443 // If a concurrent mode failure occurred recently, we want to be
444 // more conservative and halve our expected time_until_cms_gen_full()
445 if (work > deadline) {
446 if (Verbose && PrintGCDetails) {
447 gclog_or_tty->print(
448 " CMSCollector: collect because of anticipated promotion "
449 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
450 gc0_period(), time_until_cms_gen_full());
451 }
452 return 0.0;
453 }
454 return work - deadline;
455 }
457 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
458 // amount of change to prevent wild oscillation.
459 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
460 unsigned int new_duty_cycle) {
461 assert(old_duty_cycle <= 100, "bad input value");
462 assert(new_duty_cycle <= 100, "bad input value");
464 // Note: use subtraction with caution since it may underflow (values are
465 // unsigned). Addition is safe since we're in the range 0-100.
466 unsigned int damped_duty_cycle = new_duty_cycle;
467 if (new_duty_cycle < old_duty_cycle) {
468 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
469 if (new_duty_cycle + largest_delta < old_duty_cycle) {
470 damped_duty_cycle = old_duty_cycle - largest_delta;
471 }
472 } else if (new_duty_cycle > old_duty_cycle) {
473 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
474 if (new_duty_cycle > old_duty_cycle + largest_delta) {
475 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
476 }
477 }
478 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
480 if (CMSTraceIncrementalPacing) {
481 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
482 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
483 }
484 return damped_duty_cycle;
485 }
487 unsigned int CMSStats::icms_update_duty_cycle_impl() {
488 assert(CMSIncrementalPacing && valid(),
489 "should be handled in icms_update_duty_cycle()");
491 double cms_time_so_far = cms_timer().seconds();
492 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
493 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
495 // Avoid division by 0.
496 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
497 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
499 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
500 if (new_duty_cycle > _icms_duty_cycle) {
501 // Avoid very small duty cycles (1 or 2); 0 is allowed.
502 if (new_duty_cycle > 2) {
503 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
504 new_duty_cycle);
505 }
506 } else if (_allow_duty_cycle_reduction) {
507 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
508 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
509 // Respect the minimum duty cycle.
510 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
511 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
512 }
514 if (PrintGCDetails || CMSTraceIncrementalPacing) {
515 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
516 }
518 _allow_duty_cycle_reduction = false;
519 return _icms_duty_cycle;
520 }
522 #ifndef PRODUCT
523 void CMSStats::print_on(outputStream *st) const {
524 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
525 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
526 gc0_duration(), gc0_period(), gc0_promoted());
527 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
528 cms_duration(), cms_duration_per_mb(),
529 cms_period(), cms_allocated());
530 st->print(",cms_since_beg=%g,cms_since_end=%g",
531 cms_time_since_begin(), cms_time_since_end());
532 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
533 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
534 if (CMSIncrementalMode) {
535 st->print(",dc=%d", icms_duty_cycle());
536 }
538 if (valid()) {
539 st->print(",promo_rate=%g,cms_alloc_rate=%g",
540 promotion_rate(), cms_allocation_rate());
541 st->print(",cms_consumption_rate=%g,time_until_full=%g",
542 cms_consumption_rate(), time_until_cms_gen_full());
543 }
544 st->print(" ");
545 }
546 #endif // #ifndef PRODUCT
548 CMSCollector::CollectorState CMSCollector::_collectorState =
549 CMSCollector::Idling;
550 bool CMSCollector::_foregroundGCIsActive = false;
551 bool CMSCollector::_foregroundGCShouldWait = false;
553 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
554 CardTableRS* ct,
555 ConcurrentMarkSweepPolicy* cp):
556 _cmsGen(cmsGen),
557 _ct(ct),
558 _ref_processor(NULL), // will be set later
559 _conc_workers(NULL), // may be set later
560 _abort_preclean(false),
561 _start_sampling(false),
562 _between_prologue_and_epilogue(false),
563 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
564 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
565 -1 /* lock-free */, "No_lock" /* dummy */),
566 _modUnionClosure(&_modUnionTable),
567 _modUnionClosurePar(&_modUnionTable),
568 // Adjust my span to cover old (cms) gen
569 _span(cmsGen->reserved()),
570 // Construct the is_alive_closure with _span & markBitMap
571 _is_alive_closure(_span, &_markBitMap),
572 _restart_addr(NULL),
573 _overflow_list(NULL),
574 _stats(cmsGen),
575 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true)),
576 _eden_chunk_array(NULL), // may be set in ctor body
577 _eden_chunk_capacity(0), // -- ditto --
578 _eden_chunk_index(0), // -- ditto --
579 _survivor_plab_array(NULL), // -- ditto --
580 _survivor_chunk_array(NULL), // -- ditto --
581 _survivor_chunk_capacity(0), // -- ditto --
582 _survivor_chunk_index(0), // -- ditto --
583 _ser_pmc_preclean_ovflw(0),
584 _ser_kac_preclean_ovflw(0),
585 _ser_pmc_remark_ovflw(0),
586 _par_pmc_remark_ovflw(0),
587 _ser_kac_ovflw(0),
588 _par_kac_ovflw(0),
589 #ifndef PRODUCT
590 _num_par_pushes(0),
591 #endif
592 _collection_count_start(0),
593 _verifying(false),
594 _icms_start_limit(NULL),
595 _icms_stop_limit(NULL),
596 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
597 _completed_initialization(false),
598 _collector_policy(cp),
599 _should_unload_classes(CMSClassUnloadingEnabled),
600 _concurrent_cycles_since_last_unload(0),
601 _roots_scanning_options(SharedHeap::SO_None),
602 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
603 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
604 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
605 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
606 _cms_start_registered(false)
607 {
608 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
609 ExplicitGCInvokesConcurrent = true;
610 }
611 // Now expand the span and allocate the collection support structures
612 // (MUT, marking bit map etc.) to cover both generations subject to
613 // collection.
615 // For use by dirty card to oop closures.
616 _cmsGen->cmsSpace()->set_collector(this);
618 // Allocate MUT and marking bit map
619 {
620 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
621 if (!_markBitMap.allocate(_span)) {
622 warning("Failed to allocate CMS Bit Map");
623 return;
624 }
625 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
626 }
627 {
628 _modUnionTable.allocate(_span);
629 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
630 }
632 if (!_markStack.allocate(MarkStackSize)) {
633 warning("Failed to allocate CMS Marking Stack");
634 return;
635 }
637 // Support for multi-threaded concurrent phases
638 if (CMSConcurrentMTEnabled) {
639 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
640 // just for now
641 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
642 }
643 if (ConcGCThreads > 1) {
644 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
645 ConcGCThreads, true);
646 if (_conc_workers == NULL) {
647 warning("GC/CMS: _conc_workers allocation failure: "
648 "forcing -CMSConcurrentMTEnabled");
649 CMSConcurrentMTEnabled = false;
650 } else {
651 _conc_workers->initialize_workers();
652 }
653 } else {
654 CMSConcurrentMTEnabled = false;
655 }
656 }
657 if (!CMSConcurrentMTEnabled) {
658 ConcGCThreads = 0;
659 } else {
660 // Turn off CMSCleanOnEnter optimization temporarily for
661 // the MT case where it's not fixed yet; see 6178663.
662 CMSCleanOnEnter = false;
663 }
664 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
665 "Inconsistency");
667 // Parallel task queues; these are shared for the
668 // concurrent and stop-world phases of CMS, but
669 // are not shared with parallel scavenge (ParNew).
670 {
671 uint i;
672 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
674 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
675 || ParallelRefProcEnabled)
676 && num_queues > 0) {
677 _task_queues = new OopTaskQueueSet(num_queues);
678 if (_task_queues == NULL) {
679 warning("task_queues allocation failure.");
680 return;
681 }
682 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
683 if (_hash_seed == NULL) {
684 warning("_hash_seed array allocation failure");
685 return;
686 }
688 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
689 for (i = 0; i < num_queues; i++) {
690 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
691 if (q == NULL) {
692 warning("work_queue allocation failure.");
693 return;
694 }
695 _task_queues->register_queue(i, q);
696 }
697 for (i = 0; i < num_queues; i++) {
698 _task_queues->queue(i)->initialize();
699 _hash_seed[i] = 17; // copied from ParNew
700 }
701 }
702 }
704 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
706 // Clip CMSBootstrapOccupancy between 0 and 100.
707 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
709 _full_gcs_since_conc_gc = 0;
711 // Now tell CMS generations the identity of their collector
712 ConcurrentMarkSweepGeneration::set_collector(this);
714 // Create & start a CMS thread for this CMS collector
715 _cmsThread = ConcurrentMarkSweepThread::start(this);
716 assert(cmsThread() != NULL, "CMS Thread should have been created");
717 assert(cmsThread()->collector() == this,
718 "CMS Thread should refer to this gen");
719 assert(CGC_lock != NULL, "Where's the CGC_lock?");
721 // Support for parallelizing young gen rescan
722 GenCollectedHeap* gch = GenCollectedHeap::heap();
723 _young_gen = gch->prev_gen(_cmsGen);
724 if (gch->supports_inline_contig_alloc()) {
725 _top_addr = gch->top_addr();
726 _end_addr = gch->end_addr();
727 assert(_young_gen != NULL, "no _young_gen");
728 _eden_chunk_index = 0;
729 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
730 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
731 if (_eden_chunk_array == NULL) {
732 _eden_chunk_capacity = 0;
733 warning("GC/CMS: _eden_chunk_array allocation failure");
734 }
735 }
736 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
738 // Support for parallelizing survivor space rescan
739 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
740 const size_t max_plab_samples =
741 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
743 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
744 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
745 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
746 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
747 || _cursor == NULL) {
748 warning("Failed to allocate survivor plab/chunk array");
749 if (_survivor_plab_array != NULL) {
750 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
751 _survivor_plab_array = NULL;
752 }
753 if (_survivor_chunk_array != NULL) {
754 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
755 _survivor_chunk_array = NULL;
756 }
757 if (_cursor != NULL) {
758 FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
759 _cursor = NULL;
760 }
761 } else {
762 _survivor_chunk_capacity = 2*max_plab_samples;
763 for (uint i = 0; i < ParallelGCThreads; i++) {
764 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
765 if (vec == NULL) {
766 warning("Failed to allocate survivor plab array");
767 for (int j = i; j > 0; j--) {
768 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
769 }
770 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
771 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
772 _survivor_plab_array = NULL;
773 _survivor_chunk_array = NULL;
774 _survivor_chunk_capacity = 0;
775 break;
776 } else {
777 ChunkArray* cur =
778 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
779 max_plab_samples);
780 assert(cur->end() == 0, "Should be 0");
781 assert(cur->array() == vec, "Should be vec");
782 assert(cur->capacity() == max_plab_samples, "Error");
783 }
784 }
785 }
786 }
787 assert( ( _survivor_plab_array != NULL
788 && _survivor_chunk_array != NULL)
789 || ( _survivor_chunk_capacity == 0
790 && _survivor_chunk_index == 0),
791 "Error");
793 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
794 _gc_counters = new CollectorCounters("CMS", 1);
795 _completed_initialization = true;
796 _inter_sweep_timer.start(); // start of time
797 }
799 const char* ConcurrentMarkSweepGeneration::name() const {
800 return "concurrent mark-sweep generation";
801 }
802 void ConcurrentMarkSweepGeneration::update_counters() {
803 if (UsePerfData) {
804 _space_counters->update_all();
805 _gen_counters->update_all();
806 }
807 }
809 // this is an optimized version of update_counters(). it takes the
810 // used value as a parameter rather than computing it.
811 //
812 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
813 if (UsePerfData) {
814 _space_counters->update_used(used);
815 _space_counters->update_capacity();
816 _gen_counters->update_all();
817 }
818 }
820 void ConcurrentMarkSweepGeneration::print() const {
821 Generation::print();
822 cmsSpace()->print();
823 }
825 #ifndef PRODUCT
826 void ConcurrentMarkSweepGeneration::print_statistics() {
827 cmsSpace()->printFLCensus(0);
828 }
829 #endif
831 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
832 GenCollectedHeap* gch = GenCollectedHeap::heap();
833 if (PrintGCDetails) {
834 if (Verbose) {
835 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
836 level(), short_name(), s, used(), capacity());
837 } else {
838 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
839 level(), short_name(), s, used() / K, capacity() / K);
840 }
841 }
842 if (Verbose) {
843 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
844 gch->used(), gch->capacity());
845 } else {
846 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
847 gch->used() / K, gch->capacity() / K);
848 }
849 }
851 size_t
852 ConcurrentMarkSweepGeneration::contiguous_available() const {
853 // dld proposes an improvement in precision here. If the committed
854 // part of the space ends in a free block we should add that to
855 // uncommitted size in the calculation below. Will make this
856 // change later, staying with the approximation below for the
857 // time being. -- ysr.
858 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
859 }
861 size_t
862 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
863 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
864 }
866 size_t ConcurrentMarkSweepGeneration::max_available() const {
867 return free() + _virtual_space.uncommitted_size();
868 }
870 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
871 size_t available = max_available();
872 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
873 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
874 if (Verbose && PrintGCDetails) {
875 gclog_or_tty->print_cr(
876 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
877 "max_promo("SIZE_FORMAT")",
878 res? "":" not", available, res? ">=":"<",
879 av_promo, max_promotion_in_bytes);
880 }
881 return res;
882 }
884 // At a promotion failure dump information on block layout in heap
885 // (cms old generation).
886 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
887 if (CMSDumpAtPromotionFailure) {
888 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
889 }
890 }
892 CompactibleSpace*
893 ConcurrentMarkSweepGeneration::first_compaction_space() const {
894 return _cmsSpace;
895 }
897 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
898 // Clear the promotion information. These pointers can be adjusted
899 // along with all the other pointers into the heap but
900 // compaction is expected to be a rare event with
901 // a heap using cms so don't do it without seeing the need.
902 if (CollectedHeap::use_parallel_gc_threads()) {
903 for (uint i = 0; i < ParallelGCThreads; i++) {
904 _par_gc_thread_states[i]->promo.reset();
905 }
906 }
907 }
909 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
910 blk->do_space(_cmsSpace);
911 }
913 void ConcurrentMarkSweepGeneration::compute_new_size() {
914 assert_locked_or_safepoint(Heap_lock);
916 // If incremental collection failed, we just want to expand
917 // to the limit.
918 if (incremental_collection_failed()) {
919 clear_incremental_collection_failed();
920 grow_to_reserved();
921 return;
922 }
924 // The heap has been compacted but not reset yet.
925 // Any metric such as free() or used() will be incorrect.
927 CardGeneration::compute_new_size();
929 // Reset again after a possible resizing
930 if (did_compact()) {
931 cmsSpace()->reset_after_compaction();
932 }
933 }
935 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
936 assert_locked_or_safepoint(Heap_lock);
938 // If incremental collection failed, we just want to expand
939 // to the limit.
940 if (incremental_collection_failed()) {
941 clear_incremental_collection_failed();
942 grow_to_reserved();
943 return;
944 }
946 double free_percentage = ((double) free()) / capacity();
947 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
948 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
950 // compute expansion delta needed for reaching desired free percentage
951 if (free_percentage < desired_free_percentage) {
952 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
953 assert(desired_capacity >= capacity(), "invalid expansion size");
954 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
955 if (PrintGCDetails && Verbose) {
956 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
957 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
958 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
959 gclog_or_tty->print_cr(" Desired free fraction %f",
960 desired_free_percentage);
961 gclog_or_tty->print_cr(" Maximum free fraction %f",
962 maximum_free_percentage);
963 gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000);
964 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
965 desired_capacity/1000);
966 int prev_level = level() - 1;
967 if (prev_level >= 0) {
968 size_t prev_size = 0;
969 GenCollectedHeap* gch = GenCollectedHeap::heap();
970 Generation* prev_gen = gch->_gens[prev_level];
971 prev_size = prev_gen->capacity();
972 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
973 prev_size/1000);
974 }
975 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
976 unsafe_max_alloc_nogc()/1000);
977 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
978 contiguous_available()/1000);
979 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
980 expand_bytes);
981 }
982 // safe if expansion fails
983 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
984 if (PrintGCDetails && Verbose) {
985 gclog_or_tty->print_cr(" Expanded free fraction %f",
986 ((double) free()) / capacity());
987 }
988 } else {
989 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
990 assert(desired_capacity <= capacity(), "invalid expansion size");
991 size_t shrink_bytes = capacity() - desired_capacity;
992 // Don't shrink unless the delta is greater than the minimum shrink we want
993 if (shrink_bytes >= MinHeapDeltaBytes) {
994 shrink_free_list_by(shrink_bytes);
995 }
996 }
997 }
999 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
1000 return cmsSpace()->freelistLock();
1001 }
1003 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
1004 bool tlab) {
1005 CMSSynchronousYieldRequest yr;
1006 MutexLockerEx x(freelistLock(),
1007 Mutex::_no_safepoint_check_flag);
1008 return have_lock_and_allocate(size, tlab);
1009 }
1011 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
1012 bool tlab /* ignored */) {
1013 assert_lock_strong(freelistLock());
1014 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1015 HeapWord* res = cmsSpace()->allocate(adjustedSize);
1016 // Allocate the object live (grey) if the background collector has
1017 // started marking. This is necessary because the marker may
1018 // have passed this address and consequently this object will
1019 // not otherwise be greyed and would be incorrectly swept up.
1020 // Note that if this object contains references, the writing
1021 // of those references will dirty the card containing this object
1022 // allowing the object to be blackened (and its references scanned)
1023 // either during a preclean phase or at the final checkpoint.
1024 if (res != NULL) {
1025 // We may block here with an uninitialized object with
1026 // its mark-bit or P-bits not yet set. Such objects need
1027 // to be safely navigable by block_start().
1028 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1029 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1030 collector()->direct_allocated(res, adjustedSize);
1031 _direct_allocated_words += adjustedSize;
1032 // allocation counters
1033 NOT_PRODUCT(
1034 _numObjectsAllocated++;
1035 _numWordsAllocated += (int)adjustedSize;
1036 )
1037 }
1038 return res;
1039 }
1041 // In the case of direct allocation by mutators in a generation that
1042 // is being concurrently collected, the object must be allocated
1043 // live (grey) if the background collector has started marking.
1044 // This is necessary because the marker may
1045 // have passed this address and consequently this object will
1046 // not otherwise be greyed and would be incorrectly swept up.
1047 // Note that if this object contains references, the writing
1048 // of those references will dirty the card containing this object
1049 // allowing the object to be blackened (and its references scanned)
1050 // either during a preclean phase or at the final checkpoint.
1051 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1052 assert(_markBitMap.covers(start, size), "Out of bounds");
1053 if (_collectorState >= Marking) {
1054 MutexLockerEx y(_markBitMap.lock(),
1055 Mutex::_no_safepoint_check_flag);
1056 // [see comments preceding SweepClosure::do_blk() below for details]
1057 //
1058 // Can the P-bits be deleted now? JJJ
1059 //
1060 // 1. need to mark the object as live so it isn't collected
1061 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1062 // 3. need to mark the end of the object so marking, precleaning or sweeping
1063 // can skip over uninitialized or unparsable objects. An allocated
1064 // object is considered uninitialized for our purposes as long as
1065 // its klass word is NULL. All old gen objects are parsable
1066 // as soon as they are initialized.)
1067 _markBitMap.mark(start); // object is live
1068 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1069 _markBitMap.mark(start + size - 1);
1070 // mark end of object
1071 }
1072 // check that oop looks uninitialized
1073 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1074 }
1076 void CMSCollector::promoted(bool par, HeapWord* start,
1077 bool is_obj_array, size_t obj_size) {
1078 assert(_markBitMap.covers(start), "Out of bounds");
1079 // See comment in direct_allocated() about when objects should
1080 // be allocated live.
1081 if (_collectorState >= Marking) {
1082 // we already hold the marking bit map lock, taken in
1083 // the prologue
1084 if (par) {
1085 _markBitMap.par_mark(start);
1086 } else {
1087 _markBitMap.mark(start);
1088 }
1089 // We don't need to mark the object as uninitialized (as
1090 // in direct_allocated above) because this is being done with the
1091 // world stopped and the object will be initialized by the
1092 // time the marking, precleaning or sweeping get to look at it.
1093 // But see the code for copying objects into the CMS generation,
1094 // where we need to ensure that concurrent readers of the
1095 // block offset table are able to safely navigate a block that
1096 // is in flux from being free to being allocated (and in
1097 // transition while being copied into) and subsequently
1098 // becoming a bona-fide object when the copy/promotion is complete.
1099 assert(SafepointSynchronize::is_at_safepoint(),
1100 "expect promotion only at safepoints");
1102 if (_collectorState < Sweeping) {
1103 // Mark the appropriate cards in the modUnionTable, so that
1104 // this object gets scanned before the sweep. If this is
1105 // not done, CMS generation references in the object might
1106 // not get marked.
1107 // For the case of arrays, which are otherwise precisely
1108 // marked, we need to dirty the entire array, not just its head.
1109 if (is_obj_array) {
1110 // The [par_]mark_range() method expects mr.end() below to
1111 // be aligned to the granularity of a bit's representation
1112 // in the heap. In the case of the MUT below, that's a
1113 // card size.
1114 MemRegion mr(start,
1115 (HeapWord*)round_to((intptr_t)(start + obj_size),
1116 CardTableModRefBS::card_size /* bytes */));
1117 if (par) {
1118 _modUnionTable.par_mark_range(mr);
1119 } else {
1120 _modUnionTable.mark_range(mr);
1121 }
1122 } else { // not an obj array; we can just mark the head
1123 if (par) {
1124 _modUnionTable.par_mark(start);
1125 } else {
1126 _modUnionTable.mark(start);
1127 }
1128 }
1129 }
1130 }
1131 }
1133 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1134 {
1135 size_t delta = pointer_delta(addr, space->bottom());
1136 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1137 }
1139 void CMSCollector::icms_update_allocation_limits()
1140 {
1141 Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1142 EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1144 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1145 if (CMSTraceIncrementalPacing) {
1146 stats().print();
1147 }
1149 assert(duty_cycle <= 100, "invalid duty cycle");
1150 if (duty_cycle != 0) {
1151 // The duty_cycle is a percentage between 0 and 100; convert to words and
1152 // then compute the offset from the endpoints of the space.
1153 size_t free_words = eden->free() / HeapWordSize;
1154 double free_words_dbl = (double)free_words;
1155 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1156 size_t offset_words = (free_words - duty_cycle_words) / 2;
1158 _icms_start_limit = eden->top() + offset_words;
1159 _icms_stop_limit = eden->end() - offset_words;
1161 // The limits may be adjusted (shifted to the right) by
1162 // CMSIncrementalOffset, to allow the application more mutator time after a
1163 // young gen gc (when all mutators were stopped) and before CMS starts and
1164 // takes away one or more cpus.
1165 if (CMSIncrementalOffset != 0) {
1166 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1167 size_t adjustment = (size_t)adjustment_dbl;
1168 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1169 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1170 _icms_start_limit += adjustment;
1171 _icms_stop_limit = tmp_stop;
1172 }
1173 }
1174 }
1175 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1176 _icms_start_limit = _icms_stop_limit = eden->end();
1177 }
1179 // Install the new start limit.
1180 eden->set_soft_end(_icms_start_limit);
1182 if (CMSTraceIncrementalMode) {
1183 gclog_or_tty->print(" icms alloc limits: "
1184 PTR_FORMAT "," PTR_FORMAT
1185 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1186 p2i(_icms_start_limit), p2i(_icms_stop_limit),
1187 percent_of_space(eden, _icms_start_limit),
1188 percent_of_space(eden, _icms_stop_limit));
1189 if (Verbose) {
1190 gclog_or_tty->print("eden: ");
1191 eden->print_on(gclog_or_tty);
1192 }
1193 }
1194 }
1196 // Any changes here should try to maintain the invariant
1197 // that if this method is called with _icms_start_limit
1198 // and _icms_stop_limit both NULL, then it should return NULL
1199 // and not notify the icms thread.
1200 HeapWord*
1201 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1202 size_t word_size)
1203 {
1204 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1205 // nop.
1206 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1207 if (top <= _icms_start_limit) {
1208 if (CMSTraceIncrementalMode) {
1209 space->print_on(gclog_or_tty);
1210 gclog_or_tty->stamp();
1211 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1212 ", new limit=" PTR_FORMAT
1213 " (" SIZE_FORMAT "%%)",
1214 p2i(top), p2i(_icms_stop_limit),
1215 percent_of_space(space, _icms_stop_limit));
1216 }
1217 ConcurrentMarkSweepThread::start_icms();
1218 assert(top < _icms_stop_limit, "Tautology");
1219 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1220 return _icms_stop_limit;
1221 }
1223 // The allocation will cross both the _start and _stop limits, so do the
1224 // stop notification also and return end().
1225 if (CMSTraceIncrementalMode) {
1226 space->print_on(gclog_or_tty);
1227 gclog_or_tty->stamp();
1228 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1229 ", new limit=" PTR_FORMAT
1230 " (" SIZE_FORMAT "%%)",
1231 p2i(top), p2i(space->end()),
1232 percent_of_space(space, space->end()));
1233 }
1234 ConcurrentMarkSweepThread::stop_icms();
1235 return space->end();
1236 }
1238 if (top <= _icms_stop_limit) {
1239 if (CMSTraceIncrementalMode) {
1240 space->print_on(gclog_or_tty);
1241 gclog_or_tty->stamp();
1242 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1243 ", new limit=" PTR_FORMAT
1244 " (" SIZE_FORMAT "%%)",
1245 top, space->end(),
1246 percent_of_space(space, space->end()));
1247 }
1248 ConcurrentMarkSweepThread::stop_icms();
1249 return space->end();
1250 }
1252 if (CMSTraceIncrementalMode) {
1253 space->print_on(gclog_or_tty);
1254 gclog_or_tty->stamp();
1255 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1256 ", new limit=" PTR_FORMAT,
1257 top, NULL);
1258 }
1259 }
1261 return NULL;
1262 }
1264 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1265 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1266 // allocate, copy and if necessary update promoinfo --
1267 // delegate to underlying space.
1268 assert_lock_strong(freelistLock());
1270 #ifndef PRODUCT
1271 if (Universe::heap()->promotion_should_fail()) {
1272 return NULL;
1273 }
1274 #endif // #ifndef PRODUCT
1276 oop res = _cmsSpace->promote(obj, obj_size);
1277 if (res == NULL) {
1278 // expand and retry
1279 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1280 expand(s*HeapWordSize, MinHeapDeltaBytes,
1281 CMSExpansionCause::_satisfy_promotion);
1282 // Since there's currently no next generation, we don't try to promote
1283 // into a more senior generation.
1284 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1285 "is made to pass on a possibly failing "
1286 "promotion to next generation");
1287 res = _cmsSpace->promote(obj, obj_size);
1288 }
1289 if (res != NULL) {
1290 // See comment in allocate() about when objects should
1291 // be allocated live.
1292 assert(obj->is_oop(), "Will dereference klass pointer below");
1293 collector()->promoted(false, // Not parallel
1294 (HeapWord*)res, obj->is_objArray(), obj_size);
1295 // promotion counters
1296 NOT_PRODUCT(
1297 _numObjectsPromoted++;
1298 _numWordsPromoted +=
1299 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1300 )
1301 }
1302 return res;
1303 }
1306 HeapWord*
1307 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1308 HeapWord* top,
1309 size_t word_sz)
1310 {
1311 return collector()->allocation_limit_reached(space, top, word_sz);
1312 }
1314 // IMPORTANT: Notes on object size recognition in CMS.
1315 // ---------------------------------------------------
1316 // A block of storage in the CMS generation is always in
1317 // one of three states. A free block (FREE), an allocated
1318 // object (OBJECT) whose size() method reports the correct size,
1319 // and an intermediate state (TRANSIENT) in which its size cannot
1320 // be accurately determined.
1321 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1322 // -----------------------------------------------------
1323 // FREE: klass_word & 1 == 1; mark_word holds block size
1324 //
1325 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1326 // obj->size() computes correct size
1327 //
1328 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1329 //
1330 // STATE IDENTIFICATION: (64 bit+COOPS)
1331 // ------------------------------------
1332 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1333 //
1334 // OBJECT: klass_word installed; klass_word != 0;
1335 // obj->size() computes correct size
1336 //
1337 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1338 //
1339 //
1340 // STATE TRANSITION DIAGRAM
1341 //
1342 // mut / parnew mut / parnew
1343 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1344 // ^ |
1345 // |------------------------ DEAD <------------------------------------|
1346 // sweep mut
1347 //
1348 // While a block is in TRANSIENT state its size cannot be determined
1349 // so readers will either need to come back later or stall until
1350 // the size can be determined. Note that for the case of direct
1351 // allocation, P-bits, when available, may be used to determine the
1352 // size of an object that may not yet have been initialized.
1354 // Things to support parallel young-gen collection.
1355 oop
1356 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1357 oop old, markOop m,
1358 size_t word_sz) {
1359 #ifndef PRODUCT
1360 if (Universe::heap()->promotion_should_fail()) {
1361 return NULL;
1362 }
1363 #endif // #ifndef PRODUCT
1365 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1366 PromotionInfo* promoInfo = &ps->promo;
1367 // if we are tracking promotions, then first ensure space for
1368 // promotion (including spooling space for saving header if necessary).
1369 // then allocate and copy, then track promoted info if needed.
1370 // When tracking (see PromotionInfo::track()), the mark word may
1371 // be displaced and in this case restoration of the mark word
1372 // occurs in the (oop_since_save_marks_)iterate phase.
1373 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1374 // Out of space for allocating spooling buffers;
1375 // try expanding and allocating spooling buffers.
1376 if (!expand_and_ensure_spooling_space(promoInfo)) {
1377 return NULL;
1378 }
1379 }
1380 assert(promoInfo->has_spooling_space(), "Control point invariant");
1381 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1382 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1383 if (obj_ptr == NULL) {
1384 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1385 if (obj_ptr == NULL) {
1386 return NULL;
1387 }
1388 }
1389 oop obj = oop(obj_ptr);
1390 OrderAccess::storestore();
1391 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1392 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1393 // IMPORTANT: See note on object initialization for CMS above.
1394 // Otherwise, copy the object. Here we must be careful to insert the
1395 // klass pointer last, since this marks the block as an allocated object.
1396 // Except with compressed oops it's the mark word.
1397 HeapWord* old_ptr = (HeapWord*)old;
1398 // Restore the mark word copied above.
1399 obj->set_mark(m);
1400 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1401 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1402 OrderAccess::storestore();
1404 if (UseCompressedClassPointers) {
1405 // Copy gap missed by (aligned) header size calculation below
1406 obj->set_klass_gap(old->klass_gap());
1407 }
1408 if (word_sz > (size_t)oopDesc::header_size()) {
1409 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1410 obj_ptr + oopDesc::header_size(),
1411 word_sz - oopDesc::header_size());
1412 }
1414 // Now we can track the promoted object, if necessary. We take care
1415 // to delay the transition from uninitialized to full object
1416 // (i.e., insertion of klass pointer) until after, so that it
1417 // atomically becomes a promoted object.
1418 if (promoInfo->tracking()) {
1419 promoInfo->track((PromotedObject*)obj, old->klass());
1420 }
1421 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1422 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1423 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1425 // Finally, install the klass pointer (this should be volatile).
1426 OrderAccess::storestore();
1427 obj->set_klass(old->klass());
1428 // We should now be able to calculate the right size for this object
1429 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1431 collector()->promoted(true, // parallel
1432 obj_ptr, old->is_objArray(), word_sz);
1434 NOT_PRODUCT(
1435 Atomic::inc_ptr(&_numObjectsPromoted);
1436 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1437 )
1439 return obj;
1440 }
1442 void
1443 ConcurrentMarkSweepGeneration::
1444 par_promote_alloc_undo(int thread_num,
1445 HeapWord* obj, size_t word_sz) {
1446 // CMS does not support promotion undo.
1447 ShouldNotReachHere();
1448 }
1450 void
1451 ConcurrentMarkSweepGeneration::
1452 par_promote_alloc_done(int thread_num) {
1453 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1454 ps->lab.retire(thread_num);
1455 }
1457 void
1458 ConcurrentMarkSweepGeneration::
1459 par_oop_since_save_marks_iterate_done(int thread_num) {
1460 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1461 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1462 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1463 }
1465 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1466 size_t size,
1467 bool tlab)
1468 {
1469 // We allow a STW collection only if a full
1470 // collection was requested.
1471 return full || should_allocate(size, tlab); // FIX ME !!!
1472 // This and promotion failure handling are connected at the
1473 // hip and should be fixed by untying them.
1474 }
1476 bool CMSCollector::shouldConcurrentCollect() {
1477 if (_full_gc_requested) {
1478 if (Verbose && PrintGCDetails) {
1479 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1480 " gc request (or gc_locker)");
1481 }
1482 return true;
1483 }
1485 // For debugging purposes, change the type of collection.
1486 // If the rotation is not on the concurrent collection
1487 // type, don't start a concurrent collection.
1488 NOT_PRODUCT(
1489 if (RotateCMSCollectionTypes &&
1490 (_cmsGen->debug_collection_type() !=
1491 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1492 assert(_cmsGen->debug_collection_type() !=
1493 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1494 "Bad cms collection type");
1495 return false;
1496 }
1497 )
1499 FreelistLocker x(this);
1500 // ------------------------------------------------------------------
1501 // Print out lots of information which affects the initiation of
1502 // a collection.
1503 if (PrintCMSInitiationStatistics && stats().valid()) {
1504 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1505 gclog_or_tty->stamp();
1506 gclog_or_tty->cr();
1507 stats().print_on(gclog_or_tty);
1508 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1509 stats().time_until_cms_gen_full());
1510 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1511 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1512 _cmsGen->contiguous_available());
1513 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1514 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1515 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1516 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1517 gclog_or_tty->print_cr("metadata initialized %d",
1518 MetaspaceGC::should_concurrent_collect());
1519 }
1520 // ------------------------------------------------------------------
1522 // If the estimated time to complete a cms collection (cms_duration())
1523 // is less than the estimated time remaining until the cms generation
1524 // is full, start a collection.
1525 if (!UseCMSInitiatingOccupancyOnly) {
1526 if (stats().valid()) {
1527 if (stats().time_until_cms_start() == 0.0) {
1528 return true;
1529 }
1530 } else {
1531 // We want to conservatively collect somewhat early in order
1532 // to try and "bootstrap" our CMS/promotion statistics;
1533 // this branch will not fire after the first successful CMS
1534 // collection because the stats should then be valid.
1535 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1536 if (Verbose && PrintGCDetails) {
1537 gclog_or_tty->print_cr(
1538 " CMSCollector: collect for bootstrapping statistics:"
1539 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1540 _bootstrap_occupancy);
1541 }
1542 return true;
1543 }
1544 }
1545 }
1547 // Otherwise, we start a collection cycle if
1548 // old gen want a collection cycle started. Each may use
1549 // an appropriate criterion for making this decision.
1550 // XXX We need to make sure that the gen expansion
1551 // criterion dovetails well with this. XXX NEED TO FIX THIS
1552 if (_cmsGen->should_concurrent_collect()) {
1553 if (Verbose && PrintGCDetails) {
1554 gclog_or_tty->print_cr("CMS old gen initiated");
1555 }
1556 return true;
1557 }
1559 // We start a collection if we believe an incremental collection may fail;
1560 // this is not likely to be productive in practice because it's probably too
1561 // late anyway.
1562 GenCollectedHeap* gch = GenCollectedHeap::heap();
1563 assert(gch->collector_policy()->is_two_generation_policy(),
1564 "You may want to check the correctness of the following");
1565 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1566 if (Verbose && PrintGCDetails) {
1567 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1568 }
1569 return true;
1570 }
1572 if (MetaspaceGC::should_concurrent_collect()) {
1573 if (Verbose && PrintGCDetails) {
1574 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1575 }
1576 return true;
1577 }
1579 return false;
1580 }
1582 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1584 // Clear _expansion_cause fields of constituent generations
1585 void CMSCollector::clear_expansion_cause() {
1586 _cmsGen->clear_expansion_cause();
1587 }
1589 // We should be conservative in starting a collection cycle. To
1590 // start too eagerly runs the risk of collecting too often in the
1591 // extreme. To collect too rarely falls back on full collections,
1592 // which works, even if not optimum in terms of concurrent work.
1593 // As a work around for too eagerly collecting, use the flag
1594 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1595 // giving the user an easily understandable way of controlling the
1596 // collections.
1597 // We want to start a new collection cycle if any of the following
1598 // conditions hold:
1599 // . our current occupancy exceeds the configured initiating occupancy
1600 // for this generation, or
1601 // . we recently needed to expand this space and have not, since that
1602 // expansion, done a collection of this generation, or
1603 // . the underlying space believes that it may be a good idea to initiate
1604 // a concurrent collection (this may be based on criteria such as the
1605 // following: the space uses linear allocation and linear allocation is
1606 // going to fail, or there is believed to be excessive fragmentation in
1607 // the generation, etc... or ...
1608 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1609 // the case of the old generation; see CR 6543076):
1610 // we may be approaching a point at which allocation requests may fail because
1611 // we will be out of sufficient free space given allocation rate estimates.]
1612 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1614 assert_lock_strong(freelistLock());
1615 if (occupancy() > initiating_occupancy()) {
1616 if (PrintGCDetails && Verbose) {
1617 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1618 short_name(), occupancy(), initiating_occupancy());
1619 }
1620 return true;
1621 }
1622 if (UseCMSInitiatingOccupancyOnly) {
1623 return false;
1624 }
1625 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1626 if (PrintGCDetails && Verbose) {
1627 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1628 short_name());
1629 }
1630 return true;
1631 }
1632 if (_cmsSpace->should_concurrent_collect()) {
1633 if (PrintGCDetails && Verbose) {
1634 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1635 short_name());
1636 }
1637 return true;
1638 }
1639 return false;
1640 }
1642 void ConcurrentMarkSweepGeneration::collect(bool full,
1643 bool clear_all_soft_refs,
1644 size_t size,
1645 bool tlab)
1646 {
1647 collector()->collect(full, clear_all_soft_refs, size, tlab);
1648 }
1650 void CMSCollector::collect(bool full,
1651 bool clear_all_soft_refs,
1652 size_t size,
1653 bool tlab)
1654 {
1655 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1656 // For debugging purposes skip the collection if the state
1657 // is not currently idle
1658 if (TraceCMSState) {
1659 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1660 Thread::current(), full, _collectorState);
1661 }
1662 return;
1663 }
1665 // The following "if" branch is present for defensive reasons.
1666 // In the current uses of this interface, it can be replaced with:
1667 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1668 // But I am not placing that assert here to allow future
1669 // generality in invoking this interface.
1670 if (GC_locker::is_active()) {
1671 // A consistency test for GC_locker
1672 assert(GC_locker::needs_gc(), "Should have been set already");
1673 // Skip this foreground collection, instead
1674 // expanding the heap if necessary.
1675 // Need the free list locks for the call to free() in compute_new_size()
1676 compute_new_size();
1677 return;
1678 }
1679 acquire_control_and_collect(full, clear_all_soft_refs);
1680 _full_gcs_since_conc_gc++;
1681 }
1683 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1684 GenCollectedHeap* gch = GenCollectedHeap::heap();
1685 unsigned int gc_count = gch->total_full_collections();
1686 if (gc_count == full_gc_count) {
1687 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1688 _full_gc_requested = true;
1689 _full_gc_cause = cause;
1690 CGC_lock->notify(); // nudge CMS thread
1691 } else {
1692 assert(gc_count > full_gc_count, "Error: causal loop");
1693 }
1694 }
1696 bool CMSCollector::is_external_interruption() {
1697 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1698 return GCCause::is_user_requested_gc(cause) ||
1699 GCCause::is_serviceability_requested_gc(cause);
1700 }
1702 void CMSCollector::report_concurrent_mode_interruption() {
1703 if (is_external_interruption()) {
1704 if (PrintGCDetails) {
1705 gclog_or_tty->print(" (concurrent mode interrupted)");
1706 }
1707 } else {
1708 if (PrintGCDetails) {
1709 gclog_or_tty->print(" (concurrent mode failure)");
1710 }
1711 _gc_tracer_cm->report_concurrent_mode_failure();
1712 }
1713 }
1716 // The foreground and background collectors need to coordinate in order
1717 // to make sure that they do not mutually interfere with CMS collections.
1718 // When a background collection is active,
1719 // the foreground collector may need to take over (preempt) and
1720 // synchronously complete an ongoing collection. Depending on the
1721 // frequency of the background collections and the heap usage
1722 // of the application, this preemption can be seldom or frequent.
1723 // There are only certain
1724 // points in the background collection that the "collection-baton"
1725 // can be passed to the foreground collector.
1726 //
1727 // The foreground collector will wait for the baton before
1728 // starting any part of the collection. The foreground collector
1729 // will only wait at one location.
1730 //
1731 // The background collector will yield the baton before starting a new
1732 // phase of the collection (e.g., before initial marking, marking from roots,
1733 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1734 // of the loop which switches the phases. The background collector does some
1735 // of the phases (initial mark, final re-mark) with the world stopped.
1736 // Because of locking involved in stopping the world,
1737 // the foreground collector should not block waiting for the background
1738 // collector when it is doing a stop-the-world phase. The background
1739 // collector will yield the baton at an additional point just before
1740 // it enters a stop-the-world phase. Once the world is stopped, the
1741 // background collector checks the phase of the collection. If the
1742 // phase has not changed, it proceeds with the collection. If the
1743 // phase has changed, it skips that phase of the collection. See
1744 // the comments on the use of the Heap_lock in collect_in_background().
1745 //
1746 // Variable used in baton passing.
1747 // _foregroundGCIsActive - Set to true by the foreground collector when
1748 // it wants the baton. The foreground clears it when it has finished
1749 // the collection.
1750 // _foregroundGCShouldWait - Set to true by the background collector
1751 // when it is running. The foreground collector waits while
1752 // _foregroundGCShouldWait is true.
1753 // CGC_lock - monitor used to protect access to the above variables
1754 // and to notify the foreground and background collectors.
1755 // _collectorState - current state of the CMS collection.
1756 //
1757 // The foreground collector
1758 // acquires the CGC_lock
1759 // sets _foregroundGCIsActive
1760 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1761 // various locks acquired in preparation for the collection
1762 // are released so as not to block the background collector
1763 // that is in the midst of a collection
1764 // proceeds with the collection
1765 // clears _foregroundGCIsActive
1766 // returns
1767 //
1768 // The background collector in a loop iterating on the phases of the
1769 // collection
1770 // acquires the CGC_lock
1771 // sets _foregroundGCShouldWait
1772 // if _foregroundGCIsActive is set
1773 // clears _foregroundGCShouldWait, notifies _CGC_lock
1774 // waits on _CGC_lock for _foregroundGCIsActive to become false
1775 // and exits the loop.
1776 // otherwise
1777 // proceed with that phase of the collection
1778 // if the phase is a stop-the-world phase,
1779 // yield the baton once more just before enqueueing
1780 // the stop-world CMS operation (executed by the VM thread).
1781 // returns after all phases of the collection are done
1782 //
1784 void CMSCollector::acquire_control_and_collect(bool full,
1785 bool clear_all_soft_refs) {
1786 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1787 assert(!Thread::current()->is_ConcurrentGC_thread(),
1788 "shouldn't try to acquire control from self!");
1790 // Start the protocol for acquiring control of the
1791 // collection from the background collector (aka CMS thread).
1792 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1793 "VM thread should have CMS token");
1794 // Remember the possibly interrupted state of an ongoing
1795 // concurrent collection
1796 CollectorState first_state = _collectorState;
1798 // Signal to a possibly ongoing concurrent collection that
1799 // we want to do a foreground collection.
1800 _foregroundGCIsActive = true;
1802 // Disable incremental mode during a foreground collection.
1803 ICMSDisabler icms_disabler;
1805 // release locks and wait for a notify from the background collector
1806 // releasing the locks in only necessary for phases which
1807 // do yields to improve the granularity of the collection.
1808 assert_lock_strong(bitMapLock());
1809 // We need to lock the Free list lock for the space that we are
1810 // currently collecting.
1811 assert(haveFreelistLocks(), "Must be holding free list locks");
1812 bitMapLock()->unlock();
1813 releaseFreelistLocks();
1814 {
1815 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1816 if (_foregroundGCShouldWait) {
1817 // We are going to be waiting for action for the CMS thread;
1818 // it had better not be gone (for instance at shutdown)!
1819 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1820 "CMS thread must be running");
1821 // Wait here until the background collector gives us the go-ahead
1822 ConcurrentMarkSweepThread::clear_CMS_flag(
1823 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1824 // Get a possibly blocked CMS thread going:
1825 // Note that we set _foregroundGCIsActive true above,
1826 // without protection of the CGC_lock.
1827 CGC_lock->notify();
1828 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1829 "Possible deadlock");
1830 while (_foregroundGCShouldWait) {
1831 // wait for notification
1832 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1833 // Possibility of delay/starvation here, since CMS token does
1834 // not know to give priority to VM thread? Actually, i think
1835 // there wouldn't be any delay/starvation, but the proof of
1836 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1837 }
1838 ConcurrentMarkSweepThread::set_CMS_flag(
1839 ConcurrentMarkSweepThread::CMS_vm_has_token);
1840 }
1841 }
1842 // The CMS_token is already held. Get back the other locks.
1843 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1844 "VM thread should have CMS token");
1845 getFreelistLocks();
1846 bitMapLock()->lock_without_safepoint_check();
1847 if (TraceCMSState) {
1848 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1849 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1850 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1851 }
1853 // Check if we need to do a compaction, or if not, whether
1854 // we need to start the mark-sweep from scratch.
1855 bool should_compact = false;
1856 bool should_start_over = false;
1857 decide_foreground_collection_type(clear_all_soft_refs,
1858 &should_compact, &should_start_over);
1860 NOT_PRODUCT(
1861 if (RotateCMSCollectionTypes) {
1862 if (_cmsGen->debug_collection_type() ==
1863 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1864 should_compact = true;
1865 } else if (_cmsGen->debug_collection_type() ==
1866 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1867 should_compact = false;
1868 }
1869 }
1870 )
1872 if (first_state > Idling) {
1873 report_concurrent_mode_interruption();
1874 }
1876 set_did_compact(should_compact);
1877 if (should_compact) {
1878 // If the collection is being acquired from the background
1879 // collector, there may be references on the discovered
1880 // references lists that have NULL referents (being those
1881 // that were concurrently cleared by a mutator) or
1882 // that are no longer active (having been enqueued concurrently
1883 // by the mutator).
1884 // Scrub the list of those references because Mark-Sweep-Compact
1885 // code assumes referents are not NULL and that all discovered
1886 // Reference objects are active.
1887 ref_processor()->clean_up_discovered_references();
1889 if (first_state > Idling) {
1890 save_heap_summary();
1891 }
1893 do_compaction_work(clear_all_soft_refs);
1895 // Has the GC time limit been exceeded?
1896 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1897 size_t max_eden_size = young_gen->max_capacity() -
1898 young_gen->to()->capacity() -
1899 young_gen->from()->capacity();
1900 GenCollectedHeap* gch = GenCollectedHeap::heap();
1901 GCCause::Cause gc_cause = gch->gc_cause();
1902 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1903 young_gen->eden()->used(),
1904 _cmsGen->max_capacity(),
1905 max_eden_size,
1906 full,
1907 gc_cause,
1908 gch->collector_policy());
1909 } else {
1910 do_mark_sweep_work(clear_all_soft_refs, first_state,
1911 should_start_over);
1912 }
1913 // Reset the expansion cause, now that we just completed
1914 // a collection cycle.
1915 clear_expansion_cause();
1916 _foregroundGCIsActive = false;
1917 return;
1918 }
1920 // Resize the tenured generation
1921 // after obtaining the free list locks for the
1922 // two generations.
1923 void CMSCollector::compute_new_size() {
1924 assert_locked_or_safepoint(Heap_lock);
1925 FreelistLocker z(this);
1926 MetaspaceGC::compute_new_size();
1927 _cmsGen->compute_new_size_free_list();
1928 }
1930 // A work method used by foreground collection to determine
1931 // what type of collection (compacting or not, continuing or fresh)
1932 // it should do.
1933 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1934 // and CMSCompactWhenClearAllSoftRefs the default in the future
1935 // and do away with the flags after a suitable period.
1936 void CMSCollector::decide_foreground_collection_type(
1937 bool clear_all_soft_refs, bool* should_compact,
1938 bool* should_start_over) {
1939 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1940 // flag is set, and we have either requested a System.gc() or
1941 // the number of full gc's since the last concurrent cycle
1942 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1943 // or if an incremental collection has failed
1944 GenCollectedHeap* gch = GenCollectedHeap::heap();
1945 assert(gch->collector_policy()->is_two_generation_policy(),
1946 "You may want to check the correctness of the following");
1947 // Inform cms gen if this was due to partial collection failing.
1948 // The CMS gen may use this fact to determine its expansion policy.
1949 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1950 assert(!_cmsGen->incremental_collection_failed(),
1951 "Should have been noticed, reacted to and cleared");
1952 _cmsGen->set_incremental_collection_failed();
1953 }
1954 *should_compact =
1955 UseCMSCompactAtFullCollection &&
1956 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1957 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1958 gch->incremental_collection_will_fail(true /* consult_young */));
1959 *should_start_over = false;
1960 if (clear_all_soft_refs && !*should_compact) {
1961 // We are about to do a last ditch collection attempt
1962 // so it would normally make sense to do a compaction
1963 // to reclaim as much space as possible.
1964 if (CMSCompactWhenClearAllSoftRefs) {
1965 // Default: The rationale is that in this case either
1966 // we are past the final marking phase, in which case
1967 // we'd have to start over, or so little has been done
1968 // that there's little point in saving that work. Compaction
1969 // appears to be the sensible choice in either case.
1970 *should_compact = true;
1971 } else {
1972 // We have been asked to clear all soft refs, but not to
1973 // compact. Make sure that we aren't past the final checkpoint
1974 // phase, for that is where we process soft refs. If we are already
1975 // past that phase, we'll need to redo the refs discovery phase and
1976 // if necessary clear soft refs that weren't previously
1977 // cleared. We do so by remembering the phase in which
1978 // we came in, and if we are past the refs processing
1979 // phase, we'll choose to just redo the mark-sweep
1980 // collection from scratch.
1981 if (_collectorState > FinalMarking) {
1982 // We are past the refs processing phase;
1983 // start over and do a fresh synchronous CMS cycle
1984 _collectorState = Resetting; // skip to reset to start new cycle
1985 reset(false /* == !asynch */);
1986 *should_start_over = true;
1987 } // else we can continue a possibly ongoing current cycle
1988 }
1989 }
1990 }
1992 // A work method used by the foreground collector to do
1993 // a mark-sweep-compact.
1994 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1995 GenCollectedHeap* gch = GenCollectedHeap::heap();
1997 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1998 gc_timer->register_gc_start();
2000 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
2001 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
2003 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
2004 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
2005 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
2006 "collections passed to foreground collector", _full_gcs_since_conc_gc);
2007 }
2009 // Sample collection interval time and reset for collection pause.
2010 if (UseAdaptiveSizePolicy) {
2011 size_policy()->msc_collection_begin();
2012 }
2014 // Temporarily widen the span of the weak reference processing to
2015 // the entire heap.
2016 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
2017 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
2018 // Temporarily, clear the "is_alive_non_header" field of the
2019 // reference processor.
2020 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
2021 // Temporarily make reference _processing_ single threaded (non-MT).
2022 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
2023 // Temporarily make refs discovery atomic
2024 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
2025 // Temporarily make reference _discovery_ single threaded (non-MT)
2026 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
2028 ref_processor()->set_enqueuing_is_done(false);
2029 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
2030 ref_processor()->setup_policy(clear_all_soft_refs);
2031 // If an asynchronous collection finishes, the _modUnionTable is
2032 // all clear. If we are assuming the collection from an asynchronous
2033 // collection, clear the _modUnionTable.
2034 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
2035 "_modUnionTable should be clear if the baton was not passed");
2036 _modUnionTable.clear_all();
2037 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
2038 "mod union for klasses should be clear if the baton was passed");
2039 _ct->klass_rem_set()->clear_mod_union();
2041 // We must adjust the allocation statistics being maintained
2042 // in the free list space. We do so by reading and clearing
2043 // the sweep timer and updating the block flux rate estimates below.
2044 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
2045 if (_inter_sweep_timer.is_active()) {
2046 _inter_sweep_timer.stop();
2047 // Note that we do not use this sample to update the _inter_sweep_estimate.
2048 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
2049 _inter_sweep_estimate.padded_average(),
2050 _intra_sweep_estimate.padded_average());
2051 }
2053 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2054 ref_processor(), clear_all_soft_refs);
2055 #ifdef ASSERT
2056 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2057 size_t free_size = cms_space->free();
2058 assert(free_size ==
2059 pointer_delta(cms_space->end(), cms_space->compaction_top())
2060 * HeapWordSize,
2061 "All the free space should be compacted into one chunk at top");
2062 assert(cms_space->dictionary()->total_chunk_size(
2063 debug_only(cms_space->freelistLock())) == 0 ||
2064 cms_space->totalSizeInIndexedFreeLists() == 0,
2065 "All the free space should be in a single chunk");
2066 size_t num = cms_space->totalCount();
2067 assert((free_size == 0 && num == 0) ||
2068 (free_size > 0 && (num == 1 || num == 2)),
2069 "There should be at most 2 free chunks after compaction");
2070 #endif // ASSERT
2071 _collectorState = Resetting;
2072 assert(_restart_addr == NULL,
2073 "Should have been NULL'd before baton was passed");
2074 reset(false /* == !asynch */);
2075 _cmsGen->reset_after_compaction();
2076 _concurrent_cycles_since_last_unload = 0;
2078 // Clear any data recorded in the PLAB chunk arrays.
2079 if (_survivor_plab_array != NULL) {
2080 reset_survivor_plab_arrays();
2081 }
2083 // Adjust the per-size allocation stats for the next epoch.
2084 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2085 // Restart the "inter sweep timer" for the next epoch.
2086 _inter_sweep_timer.reset();
2087 _inter_sweep_timer.start();
2089 // Sample collection pause time and reset for collection interval.
2090 if (UseAdaptiveSizePolicy) {
2091 size_policy()->msc_collection_end(gch->gc_cause());
2092 }
2094 gc_timer->register_gc_end();
2096 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
2098 // For a mark-sweep-compact, compute_new_size() will be called
2099 // in the heap's do_collection() method.
2100 }
2102 // A work method used by the foreground collector to do
2103 // a mark-sweep, after taking over from a possibly on-going
2104 // concurrent mark-sweep collection.
2105 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2106 CollectorState first_state, bool should_start_over) {
2107 if (PrintGC && Verbose) {
2108 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2109 "collector with count %d",
2110 _full_gcs_since_conc_gc);
2111 }
2112 switch (_collectorState) {
2113 case Idling:
2114 if (first_state == Idling || should_start_over) {
2115 // The background GC was not active, or should
2116 // restarted from scratch; start the cycle.
2117 _collectorState = InitialMarking;
2118 }
2119 // If first_state was not Idling, then a background GC
2120 // was in progress and has now finished. No need to do it
2121 // again. Leave the state as Idling.
2122 break;
2123 case Precleaning:
2124 // In the foreground case don't do the precleaning since
2125 // it is not done concurrently and there is extra work
2126 // required.
2127 _collectorState = FinalMarking;
2128 }
2129 collect_in_foreground(clear_all_soft_refs, GenCollectedHeap::heap()->gc_cause());
2131 // For a mark-sweep, compute_new_size() will be called
2132 // in the heap's do_collection() method.
2133 }
2136 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
2137 DefNewGeneration* dng = _young_gen->as_DefNewGeneration();
2138 EdenSpace* eden_space = dng->eden();
2139 ContiguousSpace* from_space = dng->from();
2140 ContiguousSpace* to_space = dng->to();
2141 // Eden
2142 if (_eden_chunk_array != NULL) {
2143 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2144 eden_space->bottom(), eden_space->top(),
2145 eden_space->end(), eden_space->capacity());
2146 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
2147 "_eden_chunk_capacity=" SIZE_FORMAT,
2148 _eden_chunk_index, _eden_chunk_capacity);
2149 for (size_t i = 0; i < _eden_chunk_index; i++) {
2150 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2151 i, _eden_chunk_array[i]);
2152 }
2153 }
2154 // Survivor
2155 if (_survivor_chunk_array != NULL) {
2156 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2157 from_space->bottom(), from_space->top(),
2158 from_space->end(), from_space->capacity());
2159 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
2160 "_survivor_chunk_capacity=" SIZE_FORMAT,
2161 _survivor_chunk_index, _survivor_chunk_capacity);
2162 for (size_t i = 0; i < _survivor_chunk_index; i++) {
2163 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2164 i, _survivor_chunk_array[i]);
2165 }
2166 }
2167 }
2169 void CMSCollector::getFreelistLocks() const {
2170 // Get locks for all free lists in all generations that this
2171 // collector is responsible for
2172 _cmsGen->freelistLock()->lock_without_safepoint_check();
2173 }
2175 void CMSCollector::releaseFreelistLocks() const {
2176 // Release locks for all free lists in all generations that this
2177 // collector is responsible for
2178 _cmsGen->freelistLock()->unlock();
2179 }
2181 bool CMSCollector::haveFreelistLocks() const {
2182 // Check locks for all free lists in all generations that this
2183 // collector is responsible for
2184 assert_lock_strong(_cmsGen->freelistLock());
2185 PRODUCT_ONLY(ShouldNotReachHere());
2186 return true;
2187 }
2189 // A utility class that is used by the CMS collector to
2190 // temporarily "release" the foreground collector from its
2191 // usual obligation to wait for the background collector to
2192 // complete an ongoing phase before proceeding.
2193 class ReleaseForegroundGC: public StackObj {
2194 private:
2195 CMSCollector* _c;
2196 public:
2197 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2198 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2199 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2200 // allow a potentially blocked foreground collector to proceed
2201 _c->_foregroundGCShouldWait = false;
2202 if (_c->_foregroundGCIsActive) {
2203 CGC_lock->notify();
2204 }
2205 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2206 "Possible deadlock");
2207 }
2209 ~ReleaseForegroundGC() {
2210 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2211 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2212 _c->_foregroundGCShouldWait = true;
2213 }
2214 };
2216 // There are separate collect_in_background and collect_in_foreground because of
2217 // the different locking requirements of the background collector and the
2218 // foreground collector. There was originally an attempt to share
2219 // one "collect" method between the background collector and the foreground
2220 // collector but the if-then-else required made it cleaner to have
2221 // separate methods.
2222 void CMSCollector::collect_in_background(bool clear_all_soft_refs, GCCause::Cause cause) {
2223 assert(Thread::current()->is_ConcurrentGC_thread(),
2224 "A CMS asynchronous collection is only allowed on a CMS thread.");
2226 GenCollectedHeap* gch = GenCollectedHeap::heap();
2227 {
2228 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2229 MutexLockerEx hl(Heap_lock, safepoint_check);
2230 FreelistLocker fll(this);
2231 MutexLockerEx x(CGC_lock, safepoint_check);
2232 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2233 // The foreground collector is active or we're
2234 // not using asynchronous collections. Skip this
2235 // background collection.
2236 assert(!_foregroundGCShouldWait, "Should be clear");
2237 return;
2238 } else {
2239 assert(_collectorState == Idling, "Should be idling before start.");
2240 _collectorState = InitialMarking;
2241 register_gc_start(cause);
2242 // Reset the expansion cause, now that we are about to begin
2243 // a new cycle.
2244 clear_expansion_cause();
2246 // Clear the MetaspaceGC flag since a concurrent collection
2247 // is starting but also clear it after the collection.
2248 MetaspaceGC::set_should_concurrent_collect(false);
2249 }
2250 // Decide if we want to enable class unloading as part of the
2251 // ensuing concurrent GC cycle.
2252 update_should_unload_classes();
2253 _full_gc_requested = false; // acks all outstanding full gc requests
2254 _full_gc_cause = GCCause::_no_gc;
2255 // Signal that we are about to start a collection
2256 gch->increment_total_full_collections(); // ... starting a collection cycle
2257 _collection_count_start = gch->total_full_collections();
2258 }
2260 // Used for PrintGC
2261 size_t prev_used;
2262 if (PrintGC && Verbose) {
2263 prev_used = _cmsGen->used(); // XXXPERM
2264 }
2266 // The change of the collection state is normally done at this level;
2267 // the exceptions are phases that are executed while the world is
2268 // stopped. For those phases the change of state is done while the
2269 // world is stopped. For baton passing purposes this allows the
2270 // background collector to finish the phase and change state atomically.
2271 // The foreground collector cannot wait on a phase that is done
2272 // while the world is stopped because the foreground collector already
2273 // has the world stopped and would deadlock.
2274 while (_collectorState != Idling) {
2275 if (TraceCMSState) {
2276 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2277 Thread::current(), _collectorState);
2278 }
2279 // The foreground collector
2280 // holds the Heap_lock throughout its collection.
2281 // holds the CMS token (but not the lock)
2282 // except while it is waiting for the background collector to yield.
2283 //
2284 // The foreground collector should be blocked (not for long)
2285 // if the background collector is about to start a phase
2286 // executed with world stopped. If the background
2287 // collector has already started such a phase, the
2288 // foreground collector is blocked waiting for the
2289 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2290 // are executed in the VM thread.
2291 //
2292 // The locking order is
2293 // PendingListLock (PLL) -- if applicable (FinalMarking)
2294 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2295 // CMS token (claimed in
2296 // stop_world_and_do() -->
2297 // safepoint_synchronize() -->
2298 // CMSThread::synchronize())
2300 {
2301 // Check if the FG collector wants us to yield.
2302 CMSTokenSync x(true); // is cms thread
2303 if (waitForForegroundGC()) {
2304 // We yielded to a foreground GC, nothing more to be
2305 // done this round.
2306 assert(_foregroundGCShouldWait == false, "We set it to false in "
2307 "waitForForegroundGC()");
2308 if (TraceCMSState) {
2309 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2310 " exiting collection CMS state %d",
2311 Thread::current(), _collectorState);
2312 }
2313 return;
2314 } else {
2315 // The background collector can run but check to see if the
2316 // foreground collector has done a collection while the
2317 // background collector was waiting to get the CGC_lock
2318 // above. If yes, break so that _foregroundGCShouldWait
2319 // is cleared before returning.
2320 if (_collectorState == Idling) {
2321 break;
2322 }
2323 }
2324 }
2326 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2327 "should be waiting");
2329 switch (_collectorState) {
2330 case InitialMarking:
2331 {
2332 ReleaseForegroundGC x(this);
2333 stats().record_cms_begin();
2334 VM_CMS_Initial_Mark initial_mark_op(this);
2335 VMThread::execute(&initial_mark_op);
2336 }
2337 // The collector state may be any legal state at this point
2338 // since the background collector may have yielded to the
2339 // foreground collector.
2340 break;
2341 case Marking:
2342 // initial marking in checkpointRootsInitialWork has been completed
2343 if (markFromRoots(true)) { // we were successful
2344 assert(_collectorState == Precleaning, "Collector state should "
2345 "have changed");
2346 } else {
2347 assert(_foregroundGCIsActive, "Internal state inconsistency");
2348 }
2349 break;
2350 case Precleaning:
2351 if (UseAdaptiveSizePolicy) {
2352 size_policy()->concurrent_precleaning_begin();
2353 }
2354 // marking from roots in markFromRoots has been completed
2355 preclean();
2356 if (UseAdaptiveSizePolicy) {
2357 size_policy()->concurrent_precleaning_end();
2358 }
2359 assert(_collectorState == AbortablePreclean ||
2360 _collectorState == FinalMarking,
2361 "Collector state should have changed");
2362 break;
2363 case AbortablePreclean:
2364 if (UseAdaptiveSizePolicy) {
2365 size_policy()->concurrent_phases_resume();
2366 }
2367 abortable_preclean();
2368 if (UseAdaptiveSizePolicy) {
2369 size_policy()->concurrent_precleaning_end();
2370 }
2371 assert(_collectorState == FinalMarking, "Collector state should "
2372 "have changed");
2373 break;
2374 case FinalMarking:
2375 {
2376 ReleaseForegroundGC x(this);
2378 VM_CMS_Final_Remark final_remark_op(this);
2379 VMThread::execute(&final_remark_op);
2380 }
2381 assert(_foregroundGCShouldWait, "block post-condition");
2382 break;
2383 case Sweeping:
2384 if (UseAdaptiveSizePolicy) {
2385 size_policy()->concurrent_sweeping_begin();
2386 }
2387 // final marking in checkpointRootsFinal has been completed
2388 sweep(true);
2389 assert(_collectorState == Resizing, "Collector state change "
2390 "to Resizing must be done under the free_list_lock");
2391 _full_gcs_since_conc_gc = 0;
2393 // Stop the timers for adaptive size policy for the concurrent phases
2394 if (UseAdaptiveSizePolicy) {
2395 size_policy()->concurrent_sweeping_end();
2396 size_policy()->concurrent_phases_end(gch->gc_cause(),
2397 gch->prev_gen(_cmsGen)->capacity(),
2398 _cmsGen->free());
2399 }
2401 case Resizing: {
2402 // Sweeping has been completed...
2403 // At this point the background collection has completed.
2404 // Don't move the call to compute_new_size() down
2405 // into code that might be executed if the background
2406 // collection was preempted.
2407 {
2408 ReleaseForegroundGC x(this); // unblock FG collection
2409 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2410 CMSTokenSync z(true); // not strictly needed.
2411 if (_collectorState == Resizing) {
2412 compute_new_size();
2413 save_heap_summary();
2414 _collectorState = Resetting;
2415 } else {
2416 assert(_collectorState == Idling, "The state should only change"
2417 " because the foreground collector has finished the collection");
2418 }
2419 }
2420 break;
2421 }
2422 case Resetting:
2423 // CMS heap resizing has been completed
2424 reset(true);
2425 assert(_collectorState == Idling, "Collector state should "
2426 "have changed");
2428 MetaspaceGC::set_should_concurrent_collect(false);
2430 stats().record_cms_end();
2431 // Don't move the concurrent_phases_end() and compute_new_size()
2432 // calls to here because a preempted background collection
2433 // has it's state set to "Resetting".
2434 break;
2435 case Idling:
2436 default:
2437 ShouldNotReachHere();
2438 break;
2439 }
2440 if (TraceCMSState) {
2441 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2442 Thread::current(), _collectorState);
2443 }
2444 assert(_foregroundGCShouldWait, "block post-condition");
2445 }
2447 // Should this be in gc_epilogue?
2448 collector_policy()->counters()->update_counters();
2450 {
2451 // Clear _foregroundGCShouldWait and, in the event that the
2452 // foreground collector is waiting, notify it, before
2453 // returning.
2454 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2455 _foregroundGCShouldWait = false;
2456 if (_foregroundGCIsActive) {
2457 CGC_lock->notify();
2458 }
2459 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2460 "Possible deadlock");
2461 }
2462 if (TraceCMSState) {
2463 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2464 " exiting collection CMS state %d",
2465 Thread::current(), _collectorState);
2466 }
2467 if (PrintGC && Verbose) {
2468 _cmsGen->print_heap_change(prev_used);
2469 }
2470 }
2472 void CMSCollector::register_foreground_gc_start(GCCause::Cause cause) {
2473 if (!_cms_start_registered) {
2474 register_gc_start(cause);
2475 }
2476 }
2478 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2479 _cms_start_registered = true;
2480 _gc_timer_cm->register_gc_start();
2481 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2482 }
2484 void CMSCollector::register_gc_end() {
2485 if (_cms_start_registered) {
2486 report_heap_summary(GCWhen::AfterGC);
2488 _gc_timer_cm->register_gc_end();
2489 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2490 _cms_start_registered = false;
2491 }
2492 }
2494 void CMSCollector::save_heap_summary() {
2495 GenCollectedHeap* gch = GenCollectedHeap::heap();
2496 _last_heap_summary = gch->create_heap_summary();
2497 _last_metaspace_summary = gch->create_metaspace_summary();
2498 }
2500 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2501 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2502 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2503 }
2505 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs, GCCause::Cause cause) {
2506 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2507 "Foreground collector should be waiting, not executing");
2508 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2509 "may only be done by the VM Thread with the world stopped");
2510 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2511 "VM thread should have CMS token");
2513 // The gc id is created in register_foreground_gc_start if this collection is synchronous
2514 const GCId gc_id = _collectorState == InitialMarking ? GCId::peek() : _gc_tracer_cm->gc_id();
2515 NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2516 true, NULL, gc_id);)
2517 if (UseAdaptiveSizePolicy) {
2518 size_policy()->ms_collection_begin();
2519 }
2520 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2522 HandleMark hm; // Discard invalid handles created during verification
2524 if (VerifyBeforeGC &&
2525 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2526 Universe::verify();
2527 }
2529 // Snapshot the soft reference policy to be used in this collection cycle.
2530 ref_processor()->setup_policy(clear_all_soft_refs);
2532 // Decide if class unloading should be done
2533 update_should_unload_classes();
2535 bool init_mark_was_synchronous = false; // until proven otherwise
2536 while (_collectorState != Idling) {
2537 if (TraceCMSState) {
2538 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2539 Thread::current(), _collectorState);
2540 }
2541 switch (_collectorState) {
2542 case InitialMarking:
2543 register_foreground_gc_start(cause);
2544 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2545 checkpointRootsInitial(false);
2546 assert(_collectorState == Marking, "Collector state should have changed"
2547 " within checkpointRootsInitial()");
2548 break;
2549 case Marking:
2550 // initial marking in checkpointRootsInitialWork has been completed
2551 if (VerifyDuringGC &&
2552 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2553 Universe::verify("Verify before initial mark: ");
2554 }
2555 {
2556 bool res = markFromRoots(false);
2557 assert(res && _collectorState == FinalMarking, "Collector state should "
2558 "have changed");
2559 break;
2560 }
2561 case FinalMarking:
2562 if (VerifyDuringGC &&
2563 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2564 Universe::verify("Verify before re-mark: ");
2565 }
2566 checkpointRootsFinal(false, clear_all_soft_refs,
2567 init_mark_was_synchronous);
2568 assert(_collectorState == Sweeping, "Collector state should not "
2569 "have changed within checkpointRootsFinal()");
2570 break;
2571 case Sweeping:
2572 // final marking in checkpointRootsFinal has been completed
2573 if (VerifyDuringGC &&
2574 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2575 Universe::verify("Verify before sweep: ");
2576 }
2577 sweep(false);
2578 assert(_collectorState == Resizing, "Incorrect state");
2579 break;
2580 case Resizing: {
2581 // Sweeping has been completed; the actual resize in this case
2582 // is done separately; nothing to be done in this state.
2583 _collectorState = Resetting;
2584 break;
2585 }
2586 case Resetting:
2587 // The heap has been resized.
2588 if (VerifyDuringGC &&
2589 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2590 Universe::verify("Verify before reset: ");
2591 }
2592 save_heap_summary();
2593 reset(false);
2594 assert(_collectorState == Idling, "Collector state should "
2595 "have changed");
2596 break;
2597 case Precleaning:
2598 case AbortablePreclean:
2599 // Elide the preclean phase
2600 _collectorState = FinalMarking;
2601 break;
2602 default:
2603 ShouldNotReachHere();
2604 }
2605 if (TraceCMSState) {
2606 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2607 Thread::current(), _collectorState);
2608 }
2609 }
2611 if (UseAdaptiveSizePolicy) {
2612 GenCollectedHeap* gch = GenCollectedHeap::heap();
2613 size_policy()->ms_collection_end(gch->gc_cause());
2614 }
2616 if (VerifyAfterGC &&
2617 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2618 Universe::verify();
2619 }
2620 if (TraceCMSState) {
2621 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2622 " exiting collection CMS state %d",
2623 Thread::current(), _collectorState);
2624 }
2625 }
2627 bool CMSCollector::waitForForegroundGC() {
2628 bool res = false;
2629 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2630 "CMS thread should have CMS token");
2631 // Block the foreground collector until the
2632 // background collectors decides whether to
2633 // yield.
2634 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2635 _foregroundGCShouldWait = true;
2636 if (_foregroundGCIsActive) {
2637 // The background collector yields to the
2638 // foreground collector and returns a value
2639 // indicating that it has yielded. The foreground
2640 // collector can proceed.
2641 res = true;
2642 _foregroundGCShouldWait = false;
2643 ConcurrentMarkSweepThread::clear_CMS_flag(
2644 ConcurrentMarkSweepThread::CMS_cms_has_token);
2645 ConcurrentMarkSweepThread::set_CMS_flag(
2646 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2647 // Get a possibly blocked foreground thread going
2648 CGC_lock->notify();
2649 if (TraceCMSState) {
2650 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2651 Thread::current(), _collectorState);
2652 }
2653 while (_foregroundGCIsActive) {
2654 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2655 }
2656 ConcurrentMarkSweepThread::set_CMS_flag(
2657 ConcurrentMarkSweepThread::CMS_cms_has_token);
2658 ConcurrentMarkSweepThread::clear_CMS_flag(
2659 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2660 }
2661 if (TraceCMSState) {
2662 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2663 Thread::current(), _collectorState);
2664 }
2665 return res;
2666 }
2668 // Because of the need to lock the free lists and other structures in
2669 // the collector, common to all the generations that the collector is
2670 // collecting, we need the gc_prologues of individual CMS generations
2671 // delegate to their collector. It may have been simpler had the
2672 // current infrastructure allowed one to call a prologue on a
2673 // collector. In the absence of that we have the generation's
2674 // prologue delegate to the collector, which delegates back
2675 // some "local" work to a worker method in the individual generations
2676 // that it's responsible for collecting, while itself doing any
2677 // work common to all generations it's responsible for. A similar
2678 // comment applies to the gc_epilogue()'s.
2679 // The role of the varaible _between_prologue_and_epilogue is to
2680 // enforce the invocation protocol.
2681 void CMSCollector::gc_prologue(bool full) {
2682 // Call gc_prologue_work() for the CMSGen
2683 // we are responsible for.
2685 // The following locking discipline assumes that we are only called
2686 // when the world is stopped.
2687 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2689 // The CMSCollector prologue must call the gc_prologues for the
2690 // "generations" that it's responsible
2691 // for.
2693 assert( Thread::current()->is_VM_thread()
2694 || ( CMSScavengeBeforeRemark
2695 && Thread::current()->is_ConcurrentGC_thread()),
2696 "Incorrect thread type for prologue execution");
2698 if (_between_prologue_and_epilogue) {
2699 // We have already been invoked; this is a gc_prologue delegation
2700 // from yet another CMS generation that we are responsible for, just
2701 // ignore it since all relevant work has already been done.
2702 return;
2703 }
2705 // set a bit saying prologue has been called; cleared in epilogue
2706 _between_prologue_and_epilogue = true;
2707 // Claim locks for common data structures, then call gc_prologue_work()
2708 // for each CMSGen.
2710 getFreelistLocks(); // gets free list locks on constituent spaces
2711 bitMapLock()->lock_without_safepoint_check();
2713 // Should call gc_prologue_work() for all cms gens we are responsible for
2714 bool duringMarking = _collectorState >= Marking
2715 && _collectorState < Sweeping;
2717 // The young collections clear the modified oops state, which tells if
2718 // there are any modified oops in the class. The remark phase also needs
2719 // that information. Tell the young collection to save the union of all
2720 // modified klasses.
2721 if (duringMarking) {
2722 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2723 }
2725 bool registerClosure = duringMarking;
2727 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2728 &_modUnionClosurePar
2729 : &_modUnionClosure;
2730 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2732 if (!full) {
2733 stats().record_gc0_begin();
2734 }
2735 }
2737 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2739 _capacity_at_prologue = capacity();
2740 _used_at_prologue = used();
2742 // Delegate to CMScollector which knows how to coordinate between
2743 // this and any other CMS generations that it is responsible for
2744 // collecting.
2745 collector()->gc_prologue(full);
2746 }
2748 // This is a "private" interface for use by this generation's CMSCollector.
2749 // Not to be called directly by any other entity (for instance,
2750 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2751 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2752 bool registerClosure, ModUnionClosure* modUnionClosure) {
2753 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2754 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2755 "Should be NULL");
2756 if (registerClosure) {
2757 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2758 }
2759 cmsSpace()->gc_prologue();
2760 // Clear stat counters
2761 NOT_PRODUCT(
2762 assert(_numObjectsPromoted == 0, "check");
2763 assert(_numWordsPromoted == 0, "check");
2764 if (Verbose && PrintGC) {
2765 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2766 SIZE_FORMAT" bytes concurrently",
2767 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2768 }
2769 _numObjectsAllocated = 0;
2770 _numWordsAllocated = 0;
2771 )
2772 }
2774 void CMSCollector::gc_epilogue(bool full) {
2775 // The following locking discipline assumes that we are only called
2776 // when the world is stopped.
2777 assert(SafepointSynchronize::is_at_safepoint(),
2778 "world is stopped assumption");
2780 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2781 // if linear allocation blocks need to be appropriately marked to allow the
2782 // the blocks to be parsable. We also check here whether we need to nudge the
2783 // CMS collector thread to start a new cycle (if it's not already active).
2784 assert( Thread::current()->is_VM_thread()
2785 || ( CMSScavengeBeforeRemark
2786 && Thread::current()->is_ConcurrentGC_thread()),
2787 "Incorrect thread type for epilogue execution");
2789 if (!_between_prologue_and_epilogue) {
2790 // We have already been invoked; this is a gc_epilogue delegation
2791 // from yet another CMS generation that we are responsible for, just
2792 // ignore it since all relevant work has already been done.
2793 return;
2794 }
2795 assert(haveFreelistLocks(), "must have freelist locks");
2796 assert_lock_strong(bitMapLock());
2798 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2800 _cmsGen->gc_epilogue_work(full);
2802 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2803 // in case sampling was not already enabled, enable it
2804 _start_sampling = true;
2805 }
2806 // reset _eden_chunk_array so sampling starts afresh
2807 _eden_chunk_index = 0;
2809 size_t cms_used = _cmsGen->cmsSpace()->used();
2811 // update performance counters - this uses a special version of
2812 // update_counters() that allows the utilization to be passed as a
2813 // parameter, avoiding multiple calls to used().
2814 //
2815 _cmsGen->update_counters(cms_used);
2817 if (CMSIncrementalMode) {
2818 icms_update_allocation_limits();
2819 }
2821 bitMapLock()->unlock();
2822 releaseFreelistLocks();
2824 if (!CleanChunkPoolAsync) {
2825 Chunk::clean_chunk_pool();
2826 }
2828 set_did_compact(false);
2829 _between_prologue_and_epilogue = false; // ready for next cycle
2830 }
2832 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2833 collector()->gc_epilogue(full);
2835 // Also reset promotion tracking in par gc thread states.
2836 if (CollectedHeap::use_parallel_gc_threads()) {
2837 for (uint i = 0; i < ParallelGCThreads; i++) {
2838 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2839 }
2840 }
2841 }
2843 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2844 assert(!incremental_collection_failed(), "Should have been cleared");
2845 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2846 cmsSpace()->gc_epilogue();
2847 // Print stat counters
2848 NOT_PRODUCT(
2849 assert(_numObjectsAllocated == 0, "check");
2850 assert(_numWordsAllocated == 0, "check");
2851 if (Verbose && PrintGC) {
2852 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2853 SIZE_FORMAT" bytes",
2854 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2855 }
2856 _numObjectsPromoted = 0;
2857 _numWordsPromoted = 0;
2858 )
2860 if (PrintGC && Verbose) {
2861 // Call down the chain in contiguous_available needs the freelistLock
2862 // so print this out before releasing the freeListLock.
2863 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2864 contiguous_available());
2865 }
2866 }
2868 #ifndef PRODUCT
2869 bool CMSCollector::have_cms_token() {
2870 Thread* thr = Thread::current();
2871 if (thr->is_VM_thread()) {
2872 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2873 } else if (thr->is_ConcurrentGC_thread()) {
2874 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2875 } else if (thr->is_GC_task_thread()) {
2876 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2877 ParGCRareEvent_lock->owned_by_self();
2878 }
2879 return false;
2880 }
2881 #endif
2883 // Check reachability of the given heap address in CMS generation,
2884 // treating all other generations as roots.
2885 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2886 // We could "guarantee" below, rather than assert, but i'll
2887 // leave these as "asserts" so that an adventurous debugger
2888 // could try this in the product build provided some subset of
2889 // the conditions were met, provided they were intersted in the
2890 // results and knew that the computation below wouldn't interfere
2891 // with other concurrent computations mutating the structures
2892 // being read or written.
2893 assert(SafepointSynchronize::is_at_safepoint(),
2894 "Else mutations in object graph will make answer suspect");
2895 assert(have_cms_token(), "Should hold cms token");
2896 assert(haveFreelistLocks(), "must hold free list locks");
2897 assert_lock_strong(bitMapLock());
2899 // Clear the marking bit map array before starting, but, just
2900 // for kicks, first report if the given address is already marked
2901 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2902 _markBitMap.isMarked(addr) ? "" : " not");
2904 if (verify_after_remark()) {
2905 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2906 bool result = verification_mark_bm()->isMarked(addr);
2907 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2908 result ? "IS" : "is NOT");
2909 return result;
2910 } else {
2911 gclog_or_tty->print_cr("Could not compute result");
2912 return false;
2913 }
2914 }
2917 void
2918 CMSCollector::print_on_error(outputStream* st) {
2919 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2920 if (collector != NULL) {
2921 CMSBitMap* bitmap = &collector->_markBitMap;
2922 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, bitmap);
2923 bitmap->print_on_error(st, " Bits: ");
2925 st->cr();
2927 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2928 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, mut_bitmap);
2929 mut_bitmap->print_on_error(st, " Bits: ");
2930 }
2931 }
2933 ////////////////////////////////////////////////////////
2934 // CMS Verification Support
2935 ////////////////////////////////////////////////////////
2936 // Following the remark phase, the following invariant
2937 // should hold -- each object in the CMS heap which is
2938 // marked in markBitMap() should be marked in the verification_mark_bm().
2940 class VerifyMarkedClosure: public BitMapClosure {
2941 CMSBitMap* _marks;
2942 bool _failed;
2944 public:
2945 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2947 bool do_bit(size_t offset) {
2948 HeapWord* addr = _marks->offsetToHeapWord(offset);
2949 if (!_marks->isMarked(addr)) {
2950 oop(addr)->print_on(gclog_or_tty);
2951 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2952 _failed = true;
2953 }
2954 return true;
2955 }
2957 bool failed() { return _failed; }
2958 };
2960 bool CMSCollector::verify_after_remark(bool silent) {
2961 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2962 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2963 static bool init = false;
2965 assert(SafepointSynchronize::is_at_safepoint(),
2966 "Else mutations in object graph will make answer suspect");
2967 assert(have_cms_token(),
2968 "Else there may be mutual interference in use of "
2969 " verification data structures");
2970 assert(_collectorState > Marking && _collectorState <= Sweeping,
2971 "Else marking info checked here may be obsolete");
2972 assert(haveFreelistLocks(), "must hold free list locks");
2973 assert_lock_strong(bitMapLock());
2976 // Allocate marking bit map if not already allocated
2977 if (!init) { // first time
2978 if (!verification_mark_bm()->allocate(_span)) {
2979 return false;
2980 }
2981 init = true;
2982 }
2984 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2986 // Turn off refs discovery -- so we will be tracing through refs.
2987 // This is as intended, because by this time
2988 // GC must already have cleared any refs that need to be cleared,
2989 // and traced those that need to be marked; moreover,
2990 // the marking done here is not going to intefere in any
2991 // way with the marking information used by GC.
2992 NoRefDiscovery no_discovery(ref_processor());
2994 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2996 // Clear any marks from a previous round
2997 verification_mark_bm()->clear_all();
2998 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2999 verify_work_stacks_empty();
3001 GenCollectedHeap* gch = GenCollectedHeap::heap();
3002 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3003 // Update the saved marks which may affect the root scans.
3004 gch->save_marks();
3006 if (CMSRemarkVerifyVariant == 1) {
3007 // In this first variant of verification, we complete
3008 // all marking, then check if the new marks-verctor is
3009 // a subset of the CMS marks-vector.
3010 verify_after_remark_work_1();
3011 } else if (CMSRemarkVerifyVariant == 2) {
3012 // In this second variant of verification, we flag an error
3013 // (i.e. an object reachable in the new marks-vector not reachable
3014 // in the CMS marks-vector) immediately, also indicating the
3015 // identify of an object (A) that references the unmarked object (B) --
3016 // presumably, a mutation to A failed to be picked up by preclean/remark?
3017 verify_after_remark_work_2();
3018 } else {
3019 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
3020 CMSRemarkVerifyVariant);
3021 }
3022 if (!silent) gclog_or_tty->print(" done] ");
3023 return true;
3024 }
3026 void CMSCollector::verify_after_remark_work_1() {
3027 ResourceMark rm;
3028 HandleMark hm;
3029 GenCollectedHeap* gch = GenCollectedHeap::heap();
3031 // Get a clear set of claim bits for the strong roots processing to work with.
3032 ClassLoaderDataGraph::clear_claimed_marks();
3034 // Mark from roots one level into CMS
3035 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
3036 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3038 gch->gen_process_strong_roots(_cmsGen->level(),
3039 true, // younger gens are roots
3040 true, // activate StrongRootsScope
3041 SharedHeap::ScanningOption(roots_scanning_options()),
3042 ¬Older,
3043 true, // walk code active on stacks
3044 NULL,
3045 NULL); // SSS: Provide correct closure
3047 // Now mark from the roots
3048 MarkFromRootsClosure markFromRootsClosure(this, _span,
3049 verification_mark_bm(), verification_mark_stack(),
3050 false /* don't yield */, true /* verifying */);
3051 assert(_restart_addr == NULL, "Expected pre-condition");
3052 verification_mark_bm()->iterate(&markFromRootsClosure);
3053 while (_restart_addr != NULL) {
3054 // Deal with stack overflow: by restarting at the indicated
3055 // address.
3056 HeapWord* ra = _restart_addr;
3057 markFromRootsClosure.reset(ra);
3058 _restart_addr = NULL;
3059 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3060 }
3061 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3062 verify_work_stacks_empty();
3064 // Marking completed -- now verify that each bit marked in
3065 // verification_mark_bm() is also marked in markBitMap(); flag all
3066 // errors by printing corresponding objects.
3067 VerifyMarkedClosure vcl(markBitMap());
3068 verification_mark_bm()->iterate(&vcl);
3069 if (vcl.failed()) {
3070 gclog_or_tty->print("Verification failed");
3071 Universe::heap()->print_on(gclog_or_tty);
3072 fatal("CMS: failed marking verification after remark");
3073 }
3074 }
3076 class VerifyKlassOopsKlassClosure : public KlassClosure {
3077 class VerifyKlassOopsClosure : public OopClosure {
3078 CMSBitMap* _bitmap;
3079 public:
3080 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
3081 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
3082 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
3083 } _oop_closure;
3084 public:
3085 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
3086 void do_klass(Klass* k) {
3087 k->oops_do(&_oop_closure);
3088 }
3089 };
3091 void CMSCollector::verify_after_remark_work_2() {
3092 ResourceMark rm;
3093 HandleMark hm;
3094 GenCollectedHeap* gch = GenCollectedHeap::heap();
3096 // Get a clear set of claim bits for the strong roots processing to work with.
3097 ClassLoaderDataGraph::clear_claimed_marks();
3099 // Mark from roots one level into CMS
3100 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
3101 markBitMap());
3102 CMKlassClosure klass_closure(¬Older);
3104 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3105 gch->gen_process_strong_roots(_cmsGen->level(),
3106 true, // younger gens are roots
3107 true, // activate StrongRootsScope
3108 SharedHeap::ScanningOption(roots_scanning_options()),
3109 ¬Older,
3110 true, // walk code active on stacks
3111 NULL,
3112 &klass_closure);
3114 // Now mark from the roots
3115 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
3116 verification_mark_bm(), markBitMap(), verification_mark_stack());
3117 assert(_restart_addr == NULL, "Expected pre-condition");
3118 verification_mark_bm()->iterate(&markFromRootsClosure);
3119 while (_restart_addr != NULL) {
3120 // Deal with stack overflow: by restarting at the indicated
3121 // address.
3122 HeapWord* ra = _restart_addr;
3123 markFromRootsClosure.reset(ra);
3124 _restart_addr = NULL;
3125 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3126 }
3127 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3128 verify_work_stacks_empty();
3130 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
3131 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
3133 // Marking completed -- now verify that each bit marked in
3134 // verification_mark_bm() is also marked in markBitMap(); flag all
3135 // errors by printing corresponding objects.
3136 VerifyMarkedClosure vcl(markBitMap());
3137 verification_mark_bm()->iterate(&vcl);
3138 assert(!vcl.failed(), "Else verification above should not have succeeded");
3139 }
3141 void ConcurrentMarkSweepGeneration::save_marks() {
3142 // delegate to CMS space
3143 cmsSpace()->save_marks();
3144 for (uint i = 0; i < ParallelGCThreads; i++) {
3145 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3146 }
3147 }
3149 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3150 return cmsSpace()->no_allocs_since_save_marks();
3151 }
3153 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3154 \
3155 void ConcurrentMarkSweepGeneration:: \
3156 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3157 cl->set_generation(this); \
3158 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3159 cl->reset_generation(); \
3160 save_marks(); \
3161 }
3163 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3165 void
3166 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3167 cl->set_generation(this);
3168 younger_refs_in_space_iterate(_cmsSpace, cl);
3169 cl->reset_generation();
3170 }
3172 void
3173 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, ExtendedOopClosure* cl) {
3174 if (freelistLock()->owned_by_self()) {
3175 Generation::oop_iterate(mr, cl);
3176 } else {
3177 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3178 Generation::oop_iterate(mr, cl);
3179 }
3180 }
3182 void
3183 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
3184 if (freelistLock()->owned_by_self()) {
3185 Generation::oop_iterate(cl);
3186 } else {
3187 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3188 Generation::oop_iterate(cl);
3189 }
3190 }
3192 void
3193 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3194 if (freelistLock()->owned_by_self()) {
3195 Generation::object_iterate(cl);
3196 } else {
3197 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3198 Generation::object_iterate(cl);
3199 }
3200 }
3202 void
3203 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3204 if (freelistLock()->owned_by_self()) {
3205 Generation::safe_object_iterate(cl);
3206 } else {
3207 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3208 Generation::safe_object_iterate(cl);
3209 }
3210 }
3212 void
3213 ConcurrentMarkSweepGeneration::post_compact() {
3214 }
3216 void
3217 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3218 // Fix the linear allocation blocks to look like free blocks.
3220 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3221 // are not called when the heap is verified during universe initialization and
3222 // at vm shutdown.
3223 if (freelistLock()->owned_by_self()) {
3224 cmsSpace()->prepare_for_verify();
3225 } else {
3226 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3227 cmsSpace()->prepare_for_verify();
3228 }
3229 }
3231 void
3232 ConcurrentMarkSweepGeneration::verify() {
3233 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3234 // are not called when the heap is verified during universe initialization and
3235 // at vm shutdown.
3236 if (freelistLock()->owned_by_self()) {
3237 cmsSpace()->verify();
3238 } else {
3239 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3240 cmsSpace()->verify();
3241 }
3242 }
3244 void CMSCollector::verify() {
3245 _cmsGen->verify();
3246 }
3248 #ifndef PRODUCT
3249 bool CMSCollector::overflow_list_is_empty() const {
3250 assert(_num_par_pushes >= 0, "Inconsistency");
3251 if (_overflow_list == NULL) {
3252 assert(_num_par_pushes == 0, "Inconsistency");
3253 }
3254 return _overflow_list == NULL;
3255 }
3257 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3258 // merely consolidate assertion checks that appear to occur together frequently.
3259 void CMSCollector::verify_work_stacks_empty() const {
3260 assert(_markStack.isEmpty(), "Marking stack should be empty");
3261 assert(overflow_list_is_empty(), "Overflow list should be empty");
3262 }
3264 void CMSCollector::verify_overflow_empty() const {
3265 assert(overflow_list_is_empty(), "Overflow list should be empty");
3266 assert(no_preserved_marks(), "No preserved marks");
3267 }
3268 #endif // PRODUCT
3270 // Decide if we want to enable class unloading as part of the
3271 // ensuing concurrent GC cycle. We will collect and
3272 // unload classes if it's the case that:
3273 // (1) an explicit gc request has been made and the flag
3274 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3275 // (2) (a) class unloading is enabled at the command line, and
3276 // (b) old gen is getting really full
3277 // NOTE: Provided there is no change in the state of the heap between
3278 // calls to this method, it should have idempotent results. Moreover,
3279 // its results should be monotonically increasing (i.e. going from 0 to 1,
3280 // but not 1 to 0) between successive calls between which the heap was
3281 // not collected. For the implementation below, it must thus rely on
3282 // the property that concurrent_cycles_since_last_unload()
3283 // will not decrease unless a collection cycle happened and that
3284 // _cmsGen->is_too_full() are
3285 // themselves also monotonic in that sense. See check_monotonicity()
3286 // below.
3287 void CMSCollector::update_should_unload_classes() {
3288 _should_unload_classes = false;
3289 // Condition 1 above
3290 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3291 _should_unload_classes = true;
3292 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3293 // Disjuncts 2.b.(i,ii,iii) above
3294 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3295 CMSClassUnloadingMaxInterval)
3296 || _cmsGen->is_too_full();
3297 }
3298 }
3300 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3301 bool res = should_concurrent_collect();
3302 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3303 return res;
3304 }
3306 void CMSCollector::setup_cms_unloading_and_verification_state() {
3307 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3308 || VerifyBeforeExit;
3309 const int rso = SharedHeap::SO_Strings | SharedHeap::SO_AllCodeCache;
3311 // We set the proper root for this CMS cycle here.
3312 if (should_unload_classes()) { // Should unload classes this cycle
3313 remove_root_scanning_option(SharedHeap::SO_AllClasses);
3314 add_root_scanning_option(SharedHeap::SO_SystemClasses);
3315 remove_root_scanning_option(rso); // Shrink the root set appropriately
3316 set_verifying(should_verify); // Set verification state for this cycle
3317 return; // Nothing else needs to be done at this time
3318 }
3320 // Not unloading classes this cycle
3321 assert(!should_unload_classes(), "Inconsitency!");
3322 remove_root_scanning_option(SharedHeap::SO_SystemClasses);
3323 add_root_scanning_option(SharedHeap::SO_AllClasses);
3325 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3326 // Include symbols, strings and code cache elements to prevent their resurrection.
3327 add_root_scanning_option(rso);
3328 set_verifying(true);
3329 } else if (verifying() && !should_verify) {
3330 // We were verifying, but some verification flags got disabled.
3331 set_verifying(false);
3332 // Exclude symbols, strings and code cache elements from root scanning to
3333 // reduce IM and RM pauses.
3334 remove_root_scanning_option(rso);
3335 }
3336 }
3339 #ifndef PRODUCT
3340 HeapWord* CMSCollector::block_start(const void* p) const {
3341 const HeapWord* addr = (HeapWord*)p;
3342 if (_span.contains(p)) {
3343 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3344 return _cmsGen->cmsSpace()->block_start(p);
3345 }
3346 }
3347 return NULL;
3348 }
3349 #endif
3351 HeapWord*
3352 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3353 bool tlab,
3354 bool parallel) {
3355 CMSSynchronousYieldRequest yr;
3356 assert(!tlab, "Can't deal with TLAB allocation");
3357 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3358 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3359 CMSExpansionCause::_satisfy_allocation);
3360 if (GCExpandToAllocateDelayMillis > 0) {
3361 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3362 }
3363 return have_lock_and_allocate(word_size, tlab);
3364 }
3366 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3367 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3368 // to CardGeneration and share it...
3369 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3370 return CardGeneration::expand(bytes, expand_bytes);
3371 }
3373 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3374 CMSExpansionCause::Cause cause)
3375 {
3377 bool success = expand(bytes, expand_bytes);
3379 // remember why we expanded; this information is used
3380 // by shouldConcurrentCollect() when making decisions on whether to start
3381 // a new CMS cycle.
3382 if (success) {
3383 set_expansion_cause(cause);
3384 if (PrintGCDetails && Verbose) {
3385 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3386 CMSExpansionCause::to_string(cause));
3387 }
3388 }
3389 }
3391 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3392 HeapWord* res = NULL;
3393 MutexLocker x(ParGCRareEvent_lock);
3394 while (true) {
3395 // Expansion by some other thread might make alloc OK now:
3396 res = ps->lab.alloc(word_sz);
3397 if (res != NULL) return res;
3398 // If there's not enough expansion space available, give up.
3399 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3400 return NULL;
3401 }
3402 // Otherwise, we try expansion.
3403 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3404 CMSExpansionCause::_allocate_par_lab);
3405 // Now go around the loop and try alloc again;
3406 // A competing par_promote might beat us to the expansion space,
3407 // so we may go around the loop again if promotion fails agaion.
3408 if (GCExpandToAllocateDelayMillis > 0) {
3409 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3410 }
3411 }
3412 }
3415 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3416 PromotionInfo* promo) {
3417 MutexLocker x(ParGCRareEvent_lock);
3418 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3419 while (true) {
3420 // Expansion by some other thread might make alloc OK now:
3421 if (promo->ensure_spooling_space()) {
3422 assert(promo->has_spooling_space(),
3423 "Post-condition of successful ensure_spooling_space()");
3424 return true;
3425 }
3426 // If there's not enough expansion space available, give up.
3427 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3428 return false;
3429 }
3430 // Otherwise, we try expansion.
3431 expand(refill_size_bytes, MinHeapDeltaBytes,
3432 CMSExpansionCause::_allocate_par_spooling_space);
3433 // Now go around the loop and try alloc again;
3434 // A competing allocation might beat us to the expansion space,
3435 // so we may go around the loop again if allocation fails again.
3436 if (GCExpandToAllocateDelayMillis > 0) {
3437 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3438 }
3439 }
3440 }
3443 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3444 assert_locked_or_safepoint(ExpandHeap_lock);
3445 // Shrink committed space
3446 _virtual_space.shrink_by(bytes);
3447 // Shrink space; this also shrinks the space's BOT
3448 _cmsSpace->set_end((HeapWord*) _virtual_space.high());
3449 size_t new_word_size = heap_word_size(_cmsSpace->capacity());
3450 // Shrink the shared block offset array
3451 _bts->resize(new_word_size);
3452 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3453 // Shrink the card table
3454 Universe::heap()->barrier_set()->resize_covered_region(mr);
3456 if (Verbose && PrintGC) {
3457 size_t new_mem_size = _virtual_space.committed_size();
3458 size_t old_mem_size = new_mem_size + bytes;
3459 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3460 name(), old_mem_size/K, new_mem_size/K);
3461 }
3462 }
3464 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3465 assert_locked_or_safepoint(Heap_lock);
3466 size_t size = ReservedSpace::page_align_size_down(bytes);
3467 // Only shrink if a compaction was done so that all the free space
3468 // in the generation is in a contiguous block at the end.
3469 if (size > 0 && did_compact()) {
3470 shrink_by(size);
3471 }
3472 }
3474 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3475 assert_locked_or_safepoint(Heap_lock);
3476 bool result = _virtual_space.expand_by(bytes);
3477 if (result) {
3478 size_t new_word_size =
3479 heap_word_size(_virtual_space.committed_size());
3480 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3481 _bts->resize(new_word_size); // resize the block offset shared array
3482 Universe::heap()->barrier_set()->resize_covered_region(mr);
3483 // Hmmmm... why doesn't CFLS::set_end verify locking?
3484 // This is quite ugly; FIX ME XXX
3485 _cmsSpace->assert_locked(freelistLock());
3486 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3488 // update the space and generation capacity counters
3489 if (UsePerfData) {
3490 _space_counters->update_capacity();
3491 _gen_counters->update_all();
3492 }
3494 if (Verbose && PrintGC) {
3495 size_t new_mem_size = _virtual_space.committed_size();
3496 size_t old_mem_size = new_mem_size - bytes;
3497 gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3498 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3499 }
3500 }
3501 return result;
3502 }
3504 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3505 assert_locked_or_safepoint(Heap_lock);
3506 bool success = true;
3507 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3508 if (remaining_bytes > 0) {
3509 success = grow_by(remaining_bytes);
3510 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3511 }
3512 return success;
3513 }
3515 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
3516 assert_locked_or_safepoint(Heap_lock);
3517 assert_lock_strong(freelistLock());
3518 if (PrintGCDetails && Verbose) {
3519 warning("Shrinking of CMS not yet implemented");
3520 }
3521 return;
3522 }
3525 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3526 // phases.
3527 class CMSPhaseAccounting: public StackObj {
3528 public:
3529 CMSPhaseAccounting(CMSCollector *collector,
3530 const char *phase,
3531 const GCId gc_id,
3532 bool print_cr = true);
3533 ~CMSPhaseAccounting();
3535 private:
3536 CMSCollector *_collector;
3537 const char *_phase;
3538 elapsedTimer _wallclock;
3539 bool _print_cr;
3540 const GCId _gc_id;
3542 public:
3543 // Not MT-safe; so do not pass around these StackObj's
3544 // where they may be accessed by other threads.
3545 jlong wallclock_millis() {
3546 assert(_wallclock.is_active(), "Wall clock should not stop");
3547 _wallclock.stop(); // to record time
3548 jlong ret = _wallclock.milliseconds();
3549 _wallclock.start(); // restart
3550 return ret;
3551 }
3552 };
3554 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3555 const char *phase,
3556 const GCId gc_id,
3557 bool print_cr) :
3558 _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
3560 if (PrintCMSStatistics != 0) {
3561 _collector->resetYields();
3562 }
3563 if (PrintGCDetails) {
3564 gclog_or_tty->gclog_stamp(_gc_id);
3565 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
3566 _collector->cmsGen()->short_name(), _phase);
3567 }
3568 _collector->resetTimer();
3569 _wallclock.start();
3570 _collector->startTimer();
3571 }
3573 CMSPhaseAccounting::~CMSPhaseAccounting() {
3574 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3575 _collector->stopTimer();
3576 _wallclock.stop();
3577 if (PrintGCDetails) {
3578 gclog_or_tty->gclog_stamp(_gc_id);
3579 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3580 _collector->cmsGen()->short_name(),
3581 _phase, _collector->timerValue(), _wallclock.seconds());
3582 if (_print_cr) {
3583 gclog_or_tty->cr();
3584 }
3585 if (PrintCMSStatistics != 0) {
3586 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3587 _collector->yields());
3588 }
3589 }
3590 }
3592 // CMS work
3594 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
3595 class CMSParMarkTask : public AbstractGangTask {
3596 protected:
3597 CMSCollector* _collector;
3598 int _n_workers;
3599 CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
3600 AbstractGangTask(name),
3601 _collector(collector),
3602 _n_workers(n_workers) {}
3603 // Work method in support of parallel rescan ... of young gen spaces
3604 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
3605 ContiguousSpace* space,
3606 HeapWord** chunk_array, size_t chunk_top);
3607 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
3608 };
3610 // Parallel initial mark task
3611 class CMSParInitialMarkTask: public CMSParMarkTask {
3612 public:
3613 CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
3614 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
3615 collector, n_workers) {}
3616 void work(uint worker_id);
3617 };
3619 // Checkpoint the roots into this generation from outside
3620 // this generation. [Note this initial checkpoint need only
3621 // be approximate -- we'll do a catch up phase subsequently.]
3622 void CMSCollector::checkpointRootsInitial(bool asynch) {
3623 assert(_collectorState == InitialMarking, "Wrong collector state");
3624 check_correct_thread_executing();
3625 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3627 save_heap_summary();
3628 report_heap_summary(GCWhen::BeforeGC);
3630 ReferenceProcessor* rp = ref_processor();
3631 SpecializationStats::clear();
3632 assert(_restart_addr == NULL, "Control point invariant");
3633 if (asynch) {
3634 // acquire locks for subsequent manipulations
3635 MutexLockerEx x(bitMapLock(),
3636 Mutex::_no_safepoint_check_flag);
3637 checkpointRootsInitialWork(asynch);
3638 // enable ("weak") refs discovery
3639 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3640 _collectorState = Marking;
3641 } else {
3642 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3643 // which recognizes if we are a CMS generation, and doesn't try to turn on
3644 // discovery; verify that they aren't meddling.
3645 assert(!rp->discovery_is_atomic(),
3646 "incorrect setting of discovery predicate");
3647 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3648 "ref discovery for this generation kind");
3649 // already have locks
3650 checkpointRootsInitialWork(asynch);
3651 // now enable ("weak") refs discovery
3652 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3653 _collectorState = Marking;
3654 }
3655 SpecializationStats::print();
3656 }
3658 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3659 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3660 assert(_collectorState == InitialMarking, "just checking");
3662 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3663 // precede our marking with a collection of all
3664 // younger generations to keep floating garbage to a minimum.
3665 // XXX: we won't do this for now -- it's an optimization to be done later.
3667 // already have locks
3668 assert_lock_strong(bitMapLock());
3669 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3671 // Setup the verification and class unloading state for this
3672 // CMS collection cycle.
3673 setup_cms_unloading_and_verification_state();
3675 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3676 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
3677 if (UseAdaptiveSizePolicy) {
3678 size_policy()->checkpoint_roots_initial_begin();
3679 }
3681 // Reset all the PLAB chunk arrays if necessary.
3682 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3683 reset_survivor_plab_arrays();
3684 }
3686 ResourceMark rm;
3687 HandleMark hm;
3689 FalseClosure falseClosure;
3690 // In the case of a synchronous collection, we will elide the
3691 // remark step, so it's important to catch all the nmethod oops
3692 // in this step.
3693 // The final 'true' flag to gen_process_strong_roots will ensure this.
3694 // If 'async' is true, we can relax the nmethod tracing.
3695 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3696 GenCollectedHeap* gch = GenCollectedHeap::heap();
3698 verify_work_stacks_empty();
3699 verify_overflow_empty();
3701 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3702 // Update the saved marks which may affect the root scans.
3703 gch->save_marks();
3705 // weak reference processing has not started yet.
3706 ref_processor()->set_enqueuing_is_done(false);
3708 // Need to remember all newly created CLDs,
3709 // so that we can guarantee that the remark finds them.
3710 ClassLoaderDataGraph::remember_new_clds(true);
3712 // Whenever a CLD is found, it will be claimed before proceeding to mark
3713 // the klasses. The claimed marks need to be cleared before marking starts.
3714 ClassLoaderDataGraph::clear_claimed_marks();
3716 if (CMSPrintEdenSurvivorChunks) {
3717 print_eden_and_survivor_chunk_arrays();
3718 }
3720 {
3721 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3722 if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3723 // The parallel version.
3724 FlexibleWorkGang* workers = gch->workers();
3725 assert(workers != NULL, "Need parallel worker threads.");
3726 int n_workers = workers->active_workers();
3727 CMSParInitialMarkTask tsk(this, n_workers);
3728 gch->set_par_threads(n_workers);
3729 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3730 if (n_workers > 1) {
3731 GenCollectedHeap::StrongRootsScope srs(gch);
3732 workers->run_task(&tsk);
3733 } else {
3734 GenCollectedHeap::StrongRootsScope srs(gch);
3735 tsk.work(0);
3736 }
3737 gch->set_par_threads(0);
3738 } else {
3739 // The serial version.
3740 CMKlassClosure klass_closure(¬Older);
3741 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3742 gch->gen_process_strong_roots(_cmsGen->level(),
3743 true, // younger gens are roots
3744 true, // activate StrongRootsScope
3745 SharedHeap::ScanningOption(roots_scanning_options()),
3746 ¬Older,
3747 true, // walk all of code cache if (so & SO_AllCodeCache)
3748 NULL,
3749 &klass_closure);
3750 }
3751 }
3753 // Clear mod-union table; it will be dirtied in the prologue of
3754 // CMS generation per each younger generation collection.
3756 assert(_modUnionTable.isAllClear(),
3757 "Was cleared in most recent final checkpoint phase"
3758 " or no bits are set in the gc_prologue before the start of the next "
3759 "subsequent marking phase.");
3761 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3763 // Save the end of the used_region of the constituent generations
3764 // to be used to limit the extent of sweep in each generation.
3765 save_sweep_limits();
3766 if (UseAdaptiveSizePolicy) {
3767 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3768 }
3769 verify_overflow_empty();
3770 }
3772 bool CMSCollector::markFromRoots(bool asynch) {
3773 // we might be tempted to assert that:
3774 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3775 // "inconsistent argument?");
3776 // However that wouldn't be right, because it's possible that
3777 // a safepoint is indeed in progress as a younger generation
3778 // stop-the-world GC happens even as we mark in this generation.
3779 assert(_collectorState == Marking, "inconsistent state?");
3780 check_correct_thread_executing();
3781 verify_overflow_empty();
3783 bool res;
3784 if (asynch) {
3786 // Start the timers for adaptive size policy for the concurrent phases
3787 // Do it here so that the foreground MS can use the concurrent
3788 // timer since a foreground MS might has the sweep done concurrently
3789 // or STW.
3790 if (UseAdaptiveSizePolicy) {
3791 size_policy()->concurrent_marking_begin();
3792 }
3794 // Weak ref discovery note: We may be discovering weak
3795 // refs in this generation concurrent (but interleaved) with
3796 // weak ref discovery by a younger generation collector.
3798 CMSTokenSyncWithLocks ts(true, bitMapLock());
3799 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3800 CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3801 res = markFromRootsWork(asynch);
3802 if (res) {
3803 _collectorState = Precleaning;
3804 } else { // We failed and a foreground collection wants to take over
3805 assert(_foregroundGCIsActive, "internal state inconsistency");
3806 assert(_restart_addr == NULL, "foreground will restart from scratch");
3807 if (PrintGCDetails) {
3808 gclog_or_tty->print_cr("bailing out to foreground collection");
3809 }
3810 }
3811 if (UseAdaptiveSizePolicy) {
3812 size_policy()->concurrent_marking_end();
3813 }
3814 } else {
3815 assert(SafepointSynchronize::is_at_safepoint(),
3816 "inconsistent with asynch == false");
3817 if (UseAdaptiveSizePolicy) {
3818 size_policy()->ms_collection_marking_begin();
3819 }
3820 // already have locks
3821 res = markFromRootsWork(asynch);
3822 _collectorState = FinalMarking;
3823 if (UseAdaptiveSizePolicy) {
3824 GenCollectedHeap* gch = GenCollectedHeap::heap();
3825 size_policy()->ms_collection_marking_end(gch->gc_cause());
3826 }
3827 }
3828 verify_overflow_empty();
3829 return res;
3830 }
3832 bool CMSCollector::markFromRootsWork(bool asynch) {
3833 // iterate over marked bits in bit map, doing a full scan and mark
3834 // from these roots using the following algorithm:
3835 // . if oop is to the right of the current scan pointer,
3836 // mark corresponding bit (we'll process it later)
3837 // . else (oop is to left of current scan pointer)
3838 // push oop on marking stack
3839 // . drain the marking stack
3841 // Note that when we do a marking step we need to hold the
3842 // bit map lock -- recall that direct allocation (by mutators)
3843 // and promotion (by younger generation collectors) is also
3844 // marking the bit map. [the so-called allocate live policy.]
3845 // Because the implementation of bit map marking is not
3846 // robust wrt simultaneous marking of bits in the same word,
3847 // we need to make sure that there is no such interference
3848 // between concurrent such updates.
3850 // already have locks
3851 assert_lock_strong(bitMapLock());
3853 verify_work_stacks_empty();
3854 verify_overflow_empty();
3855 bool result = false;
3856 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3857 result = do_marking_mt(asynch);
3858 } else {
3859 result = do_marking_st(asynch);
3860 }
3861 return result;
3862 }
3864 // Forward decl
3865 class CMSConcMarkingTask;
3867 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3868 CMSCollector* _collector;
3869 CMSConcMarkingTask* _task;
3870 public:
3871 virtual void yield();
3873 // "n_threads" is the number of threads to be terminated.
3874 // "queue_set" is a set of work queues of other threads.
3875 // "collector" is the CMS collector associated with this task terminator.
3876 // "yield" indicates whether we need the gang as a whole to yield.
3877 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3878 ParallelTaskTerminator(n_threads, queue_set),
3879 _collector(collector) { }
3881 void set_task(CMSConcMarkingTask* task) {
3882 _task = task;
3883 }
3884 };
3886 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3887 CMSConcMarkingTask* _task;
3888 public:
3889 bool should_exit_termination();
3890 void set_task(CMSConcMarkingTask* task) {
3891 _task = task;
3892 }
3893 };
3895 // MT Concurrent Marking Task
3896 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3897 CMSCollector* _collector;
3898 int _n_workers; // requested/desired # workers
3899 bool _asynch;
3900 bool _result;
3901 CompactibleFreeListSpace* _cms_space;
3902 char _pad_front[64]; // padding to ...
3903 HeapWord* _global_finger; // ... avoid sharing cache line
3904 char _pad_back[64];
3905 HeapWord* _restart_addr;
3907 // Exposed here for yielding support
3908 Mutex* const _bit_map_lock;
3910 // The per thread work queues, available here for stealing
3911 OopTaskQueueSet* _task_queues;
3913 // Termination (and yielding) support
3914 CMSConcMarkingTerminator _term;
3915 CMSConcMarkingTerminatorTerminator _term_term;
3917 public:
3918 CMSConcMarkingTask(CMSCollector* collector,
3919 CompactibleFreeListSpace* cms_space,
3920 bool asynch,
3921 YieldingFlexibleWorkGang* workers,
3922 OopTaskQueueSet* task_queues):
3923 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3924 _collector(collector),
3925 _cms_space(cms_space),
3926 _asynch(asynch), _n_workers(0), _result(true),
3927 _task_queues(task_queues),
3928 _term(_n_workers, task_queues, _collector),
3929 _bit_map_lock(collector->bitMapLock())
3930 {
3931 _requested_size = _n_workers;
3932 _term.set_task(this);
3933 _term_term.set_task(this);
3934 _restart_addr = _global_finger = _cms_space->bottom();
3935 }
3938 OopTaskQueueSet* task_queues() { return _task_queues; }
3940 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3942 HeapWord** global_finger_addr() { return &_global_finger; }
3944 CMSConcMarkingTerminator* terminator() { return &_term; }
3946 virtual void set_for_termination(int active_workers) {
3947 terminator()->reset_for_reuse(active_workers);
3948 }
3950 void work(uint worker_id);
3951 bool should_yield() {
3952 return ConcurrentMarkSweepThread::should_yield()
3953 && !_collector->foregroundGCIsActive()
3954 && _asynch;
3955 }
3957 virtual void coordinator_yield(); // stuff done by coordinator
3958 bool result() { return _result; }
3960 void reset(HeapWord* ra) {
3961 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3962 _restart_addr = _global_finger = ra;
3963 _term.reset_for_reuse();
3964 }
3966 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3967 OopTaskQueue* work_q);
3969 private:
3970 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3971 void do_work_steal(int i);
3972 void bump_global_finger(HeapWord* f);
3973 };
3975 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3976 assert(_task != NULL, "Error");
3977 return _task->yielding();
3978 // Note that we do not need the disjunct || _task->should_yield() above
3979 // because we want terminating threads to yield only if the task
3980 // is already in the midst of yielding, which happens only after at least one
3981 // thread has yielded.
3982 }
3984 void CMSConcMarkingTerminator::yield() {
3985 if (_task->should_yield()) {
3986 _task->yield();
3987 } else {
3988 ParallelTaskTerminator::yield();
3989 }
3990 }
3992 ////////////////////////////////////////////////////////////////
3993 // Concurrent Marking Algorithm Sketch
3994 ////////////////////////////////////////////////////////////////
3995 // Until all tasks exhausted (both spaces):
3996 // -- claim next available chunk
3997 // -- bump global finger via CAS
3998 // -- find first object that starts in this chunk
3999 // and start scanning bitmap from that position
4000 // -- scan marked objects for oops
4001 // -- CAS-mark target, and if successful:
4002 // . if target oop is above global finger (volatile read)
4003 // nothing to do
4004 // . if target oop is in chunk and above local finger
4005 // then nothing to do
4006 // . else push on work-queue
4007 // -- Deal with possible overflow issues:
4008 // . local work-queue overflow causes stuff to be pushed on
4009 // global (common) overflow queue
4010 // . always first empty local work queue
4011 // . then get a batch of oops from global work queue if any
4012 // . then do work stealing
4013 // -- When all tasks claimed (both spaces)
4014 // and local work queue empty,
4015 // then in a loop do:
4016 // . check global overflow stack; steal a batch of oops and trace
4017 // . try to steal from other threads oif GOS is empty
4018 // . if neither is available, offer termination
4019 // -- Terminate and return result
4020 //
4021 void CMSConcMarkingTask::work(uint worker_id) {
4022 elapsedTimer _timer;
4023 ResourceMark rm;
4024 HandleMark hm;
4026 DEBUG_ONLY(_collector->verify_overflow_empty();)
4028 // Before we begin work, our work queue should be empty
4029 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
4030 // Scan the bitmap covering _cms_space, tracing through grey objects.
4031 _timer.start();
4032 do_scan_and_mark(worker_id, _cms_space);
4033 _timer.stop();
4034 if (PrintCMSStatistics != 0) {
4035 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
4036 worker_id, _timer.seconds());
4037 // XXX: need xxx/xxx type of notation, two timers
4038 }
4040 // ... do work stealing
4041 _timer.reset();
4042 _timer.start();
4043 do_work_steal(worker_id);
4044 _timer.stop();
4045 if (PrintCMSStatistics != 0) {
4046 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
4047 worker_id, _timer.seconds());
4048 // XXX: need xxx/xxx type of notation, two timers
4049 }
4050 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
4051 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
4052 // Note that under the current task protocol, the
4053 // following assertion is true even of the spaces
4054 // expanded since the completion of the concurrent
4055 // marking. XXX This will likely change under a strict
4056 // ABORT semantics.
4057 // After perm removal the comparison was changed to
4058 // greater than or equal to from strictly greater than.
4059 // Before perm removal the highest address sweep would
4060 // have been at the end of perm gen but now is at the
4061 // end of the tenured gen.
4062 assert(_global_finger >= _cms_space->end(),
4063 "All tasks have been completed");
4064 DEBUG_ONLY(_collector->verify_overflow_empty();)
4065 }
4067 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
4068 HeapWord* read = _global_finger;
4069 HeapWord* cur = read;
4070 while (f > read) {
4071 cur = read;
4072 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
4073 if (cur == read) {
4074 // our cas succeeded
4075 assert(_global_finger >= f, "protocol consistency");
4076 break;
4077 }
4078 }
4079 }
4081 // This is really inefficient, and should be redone by
4082 // using (not yet available) block-read and -write interfaces to the
4083 // stack and the work_queue. XXX FIX ME !!!
4084 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
4085 OopTaskQueue* work_q) {
4086 // Fast lock-free check
4087 if (ovflw_stk->length() == 0) {
4088 return false;
4089 }
4090 assert(work_q->size() == 0, "Shouldn't steal");
4091 MutexLockerEx ml(ovflw_stk->par_lock(),
4092 Mutex::_no_safepoint_check_flag);
4093 // Grab up to 1/4 the size of the work queue
4094 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4095 (size_t)ParGCDesiredObjsFromOverflowList);
4096 num = MIN2(num, ovflw_stk->length());
4097 for (int i = (int) num; i > 0; i--) {
4098 oop cur = ovflw_stk->pop();
4099 assert(cur != NULL, "Counted wrong?");
4100 work_q->push(cur);
4101 }
4102 return num > 0;
4103 }
4105 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
4106 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4107 int n_tasks = pst->n_tasks();
4108 // We allow that there may be no tasks to do here because
4109 // we are restarting after a stack overflow.
4110 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
4111 uint nth_task = 0;
4113 HeapWord* aligned_start = sp->bottom();
4114 if (sp->used_region().contains(_restart_addr)) {
4115 // Align down to a card boundary for the start of 0th task
4116 // for this space.
4117 aligned_start =
4118 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
4119 CardTableModRefBS::card_size);
4120 }
4122 size_t chunk_size = sp->marking_task_size();
4123 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4124 // Having claimed the nth task in this space,
4125 // compute the chunk that it corresponds to:
4126 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
4127 aligned_start + (nth_task+1)*chunk_size);
4128 // Try and bump the global finger via a CAS;
4129 // note that we need to do the global finger bump
4130 // _before_ taking the intersection below, because
4131 // the task corresponding to that region will be
4132 // deemed done even if the used_region() expands
4133 // because of allocation -- as it almost certainly will
4134 // during start-up while the threads yield in the
4135 // closure below.
4136 HeapWord* finger = span.end();
4137 bump_global_finger(finger); // atomically
4138 // There are null tasks here corresponding to chunks
4139 // beyond the "top" address of the space.
4140 span = span.intersection(sp->used_region());
4141 if (!span.is_empty()) { // Non-null task
4142 HeapWord* prev_obj;
4143 assert(!span.contains(_restart_addr) || nth_task == 0,
4144 "Inconsistency");
4145 if (nth_task == 0) {
4146 // For the 0th task, we'll not need to compute a block_start.
4147 if (span.contains(_restart_addr)) {
4148 // In the case of a restart because of stack overflow,
4149 // we might additionally skip a chunk prefix.
4150 prev_obj = _restart_addr;
4151 } else {
4152 prev_obj = span.start();
4153 }
4154 } else {
4155 // We want to skip the first object because
4156 // the protocol is to scan any object in its entirety
4157 // that _starts_ in this span; a fortiori, any
4158 // object starting in an earlier span is scanned
4159 // as part of an earlier claimed task.
4160 // Below we use the "careful" version of block_start
4161 // so we do not try to navigate uninitialized objects.
4162 prev_obj = sp->block_start_careful(span.start());
4163 // Below we use a variant of block_size that uses the
4164 // Printezis bits to avoid waiting for allocated
4165 // objects to become initialized/parsable.
4166 while (prev_obj < span.start()) {
4167 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4168 if (sz > 0) {
4169 prev_obj += sz;
4170 } else {
4171 // In this case we may end up doing a bit of redundant
4172 // scanning, but that appears unavoidable, short of
4173 // locking the free list locks; see bug 6324141.
4174 break;
4175 }
4176 }
4177 }
4178 if (prev_obj < span.end()) {
4179 MemRegion my_span = MemRegion(prev_obj, span.end());
4180 // Do the marking work within a non-empty span --
4181 // the last argument to the constructor indicates whether the
4182 // iteration should be incremental with periodic yields.
4183 Par_MarkFromRootsClosure cl(this, _collector, my_span,
4184 &_collector->_markBitMap,
4185 work_queue(i),
4186 &_collector->_markStack,
4187 _asynch);
4188 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4189 } // else nothing to do for this task
4190 } // else nothing to do for this task
4191 }
4192 // We'd be tempted to assert here that since there are no
4193 // more tasks left to claim in this space, the global_finger
4194 // must exceed space->top() and a fortiori space->end(). However,
4195 // that would not quite be correct because the bumping of
4196 // global_finger occurs strictly after the claiming of a task,
4197 // so by the time we reach here the global finger may not yet
4198 // have been bumped up by the thread that claimed the last
4199 // task.
4200 pst->all_tasks_completed();
4201 }
4203 class Par_ConcMarkingClosure: public CMSOopClosure {
4204 private:
4205 CMSCollector* _collector;
4206 CMSConcMarkingTask* _task;
4207 MemRegion _span;
4208 CMSBitMap* _bit_map;
4209 CMSMarkStack* _overflow_stack;
4210 OopTaskQueue* _work_queue;
4211 protected:
4212 DO_OOP_WORK_DEFN
4213 public:
4214 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4215 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
4216 CMSOopClosure(collector->ref_processor()),
4217 _collector(collector),
4218 _task(task),
4219 _span(collector->_span),
4220 _work_queue(work_queue),
4221 _bit_map(bit_map),
4222 _overflow_stack(overflow_stack)
4223 { }
4224 virtual void do_oop(oop* p);
4225 virtual void do_oop(narrowOop* p);
4227 void trim_queue(size_t max);
4228 void handle_stack_overflow(HeapWord* lost);
4229 void do_yield_check() {
4230 if (_task->should_yield()) {
4231 _task->yield();
4232 }
4233 }
4234 };
4236 // Grey object scanning during work stealing phase --
4237 // the salient assumption here is that any references
4238 // that are in these stolen objects being scanned must
4239 // already have been initialized (else they would not have
4240 // been published), so we do not need to check for
4241 // uninitialized objects before pushing here.
4242 void Par_ConcMarkingClosure::do_oop(oop obj) {
4243 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4244 HeapWord* addr = (HeapWord*)obj;
4245 // Check if oop points into the CMS generation
4246 // and is not marked
4247 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4248 // a white object ...
4249 // If we manage to "claim" the object, by being the
4250 // first thread to mark it, then we push it on our
4251 // marking stack
4252 if (_bit_map->par_mark(addr)) { // ... now grey
4253 // push on work queue (grey set)
4254 bool simulate_overflow = false;
4255 NOT_PRODUCT(
4256 if (CMSMarkStackOverflowALot &&
4257 _collector->simulate_overflow()) {
4258 // simulate a stack overflow
4259 simulate_overflow = true;
4260 }
4261 )
4262 if (simulate_overflow ||
4263 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4264 // stack overflow
4265 if (PrintCMSStatistics != 0) {
4266 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4267 SIZE_FORMAT, _overflow_stack->capacity());
4268 }
4269 // We cannot assert that the overflow stack is full because
4270 // it may have been emptied since.
4271 assert(simulate_overflow ||
4272 _work_queue->size() == _work_queue->max_elems(),
4273 "Else push should have succeeded");
4274 handle_stack_overflow(addr);
4275 }
4276 } // Else, some other thread got there first
4277 do_yield_check();
4278 }
4279 }
4281 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4282 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4284 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4285 while (_work_queue->size() > max) {
4286 oop new_oop;
4287 if (_work_queue->pop_local(new_oop)) {
4288 assert(new_oop->is_oop(), "Should be an oop");
4289 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4290 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4291 new_oop->oop_iterate(this); // do_oop() above
4292 do_yield_check();
4293 }
4294 }
4295 }
4297 // Upon stack overflow, we discard (part of) the stack,
4298 // remembering the least address amongst those discarded
4299 // in CMSCollector's _restart_address.
4300 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4301 // We need to do this under a mutex to prevent other
4302 // workers from interfering with the work done below.
4303 MutexLockerEx ml(_overflow_stack->par_lock(),
4304 Mutex::_no_safepoint_check_flag);
4305 // Remember the least grey address discarded
4306 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4307 _collector->lower_restart_addr(ra);
4308 _overflow_stack->reset(); // discard stack contents
4309 _overflow_stack->expand(); // expand the stack if possible
4310 }
4313 void CMSConcMarkingTask::do_work_steal(int i) {
4314 OopTaskQueue* work_q = work_queue(i);
4315 oop obj_to_scan;
4316 CMSBitMap* bm = &(_collector->_markBitMap);
4317 CMSMarkStack* ovflw = &(_collector->_markStack);
4318 int* seed = _collector->hash_seed(i);
4319 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4320 while (true) {
4321 cl.trim_queue(0);
4322 assert(work_q->size() == 0, "Should have been emptied above");
4323 if (get_work_from_overflow_stack(ovflw, work_q)) {
4324 // Can't assert below because the work obtained from the
4325 // overflow stack may already have been stolen from us.
4326 // assert(work_q->size() > 0, "Work from overflow stack");
4327 continue;
4328 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4329 assert(obj_to_scan->is_oop(), "Should be an oop");
4330 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4331 obj_to_scan->oop_iterate(&cl);
4332 } else if (terminator()->offer_termination(&_term_term)) {
4333 assert(work_q->size() == 0, "Impossible!");
4334 break;
4335 } else if (yielding() || should_yield()) {
4336 yield();
4337 }
4338 }
4339 }
4341 // This is run by the CMS (coordinator) thread.
4342 void CMSConcMarkingTask::coordinator_yield() {
4343 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4344 "CMS thread should hold CMS token");
4345 // First give up the locks, then yield, then re-lock
4346 // We should probably use a constructor/destructor idiom to
4347 // do this unlock/lock or modify the MutexUnlocker class to
4348 // serve our purpose. XXX
4349 assert_lock_strong(_bit_map_lock);
4350 _bit_map_lock->unlock();
4351 ConcurrentMarkSweepThread::desynchronize(true);
4352 ConcurrentMarkSweepThread::acknowledge_yield_request();
4353 _collector->stopTimer();
4354 if (PrintCMSStatistics != 0) {
4355 _collector->incrementYields();
4356 }
4357 _collector->icms_wait();
4359 // It is possible for whichever thread initiated the yield request
4360 // not to get a chance to wake up and take the bitmap lock between
4361 // this thread releasing it and reacquiring it. So, while the
4362 // should_yield() flag is on, let's sleep for a bit to give the
4363 // other thread a chance to wake up. The limit imposed on the number
4364 // of iterations is defensive, to avoid any unforseen circumstances
4365 // putting us into an infinite loop. Since it's always been this
4366 // (coordinator_yield()) method that was observed to cause the
4367 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4368 // which is by default non-zero. For the other seven methods that
4369 // also perform the yield operation, as are using a different
4370 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4371 // can enable the sleeping for those methods too, if necessary.
4372 // See 6442774.
4373 //
4374 // We really need to reconsider the synchronization between the GC
4375 // thread and the yield-requesting threads in the future and we
4376 // should really use wait/notify, which is the recommended
4377 // way of doing this type of interaction. Additionally, we should
4378 // consolidate the eight methods that do the yield operation and they
4379 // are almost identical into one for better maintenability and
4380 // readability. See 6445193.
4381 //
4382 // Tony 2006.06.29
4383 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4384 ConcurrentMarkSweepThread::should_yield() &&
4385 !CMSCollector::foregroundGCIsActive(); ++i) {
4386 os::sleep(Thread::current(), 1, false);
4387 ConcurrentMarkSweepThread::acknowledge_yield_request();
4388 }
4390 ConcurrentMarkSweepThread::synchronize(true);
4391 _bit_map_lock->lock_without_safepoint_check();
4392 _collector->startTimer();
4393 }
4395 bool CMSCollector::do_marking_mt(bool asynch) {
4396 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4397 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4398 conc_workers()->total_workers(),
4399 conc_workers()->active_workers(),
4400 Threads::number_of_non_daemon_threads());
4401 conc_workers()->set_active_workers(num_workers);
4403 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4405 CMSConcMarkingTask tsk(this,
4406 cms_space,
4407 asynch,
4408 conc_workers(),
4409 task_queues());
4411 // Since the actual number of workers we get may be different
4412 // from the number we requested above, do we need to do anything different
4413 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4414 // class?? XXX
4415 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4417 // Refs discovery is already non-atomic.
4418 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4419 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4420 conc_workers()->start_task(&tsk);
4421 while (tsk.yielded()) {
4422 tsk.coordinator_yield();
4423 conc_workers()->continue_task(&tsk);
4424 }
4425 // If the task was aborted, _restart_addr will be non-NULL
4426 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4427 while (_restart_addr != NULL) {
4428 // XXX For now we do not make use of ABORTED state and have not
4429 // yet implemented the right abort semantics (even in the original
4430 // single-threaded CMS case). That needs some more investigation
4431 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4432 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4433 // If _restart_addr is non-NULL, a marking stack overflow
4434 // occurred; we need to do a fresh marking iteration from the
4435 // indicated restart address.
4436 if (_foregroundGCIsActive && asynch) {
4437 // We may be running into repeated stack overflows, having
4438 // reached the limit of the stack size, while making very
4439 // slow forward progress. It may be best to bail out and
4440 // let the foreground collector do its job.
4441 // Clear _restart_addr, so that foreground GC
4442 // works from scratch. This avoids the headache of
4443 // a "rescan" which would otherwise be needed because
4444 // of the dirty mod union table & card table.
4445 _restart_addr = NULL;
4446 return false;
4447 }
4448 // Adjust the task to restart from _restart_addr
4449 tsk.reset(_restart_addr);
4450 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4451 _restart_addr);
4452 _restart_addr = NULL;
4453 // Get the workers going again
4454 conc_workers()->start_task(&tsk);
4455 while (tsk.yielded()) {
4456 tsk.coordinator_yield();
4457 conc_workers()->continue_task(&tsk);
4458 }
4459 }
4460 assert(tsk.completed(), "Inconsistency");
4461 assert(tsk.result() == true, "Inconsistency");
4462 return true;
4463 }
4465 bool CMSCollector::do_marking_st(bool asynch) {
4466 ResourceMark rm;
4467 HandleMark hm;
4469 // Temporarily make refs discovery single threaded (non-MT)
4470 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4471 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4472 &_markStack, CMSYield && asynch);
4473 // the last argument to iterate indicates whether the iteration
4474 // should be incremental with periodic yields.
4475 _markBitMap.iterate(&markFromRootsClosure);
4476 // If _restart_addr is non-NULL, a marking stack overflow
4477 // occurred; we need to do a fresh iteration from the
4478 // indicated restart address.
4479 while (_restart_addr != NULL) {
4480 if (_foregroundGCIsActive && asynch) {
4481 // We may be running into repeated stack overflows, having
4482 // reached the limit of the stack size, while making very
4483 // slow forward progress. It may be best to bail out and
4484 // let the foreground collector do its job.
4485 // Clear _restart_addr, so that foreground GC
4486 // works from scratch. This avoids the headache of
4487 // a "rescan" which would otherwise be needed because
4488 // of the dirty mod union table & card table.
4489 _restart_addr = NULL;
4490 return false; // indicating failure to complete marking
4491 }
4492 // Deal with stack overflow:
4493 // we restart marking from _restart_addr
4494 HeapWord* ra = _restart_addr;
4495 markFromRootsClosure.reset(ra);
4496 _restart_addr = NULL;
4497 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4498 }
4499 return true;
4500 }
4502 void CMSCollector::preclean() {
4503 check_correct_thread_executing();
4504 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4505 verify_work_stacks_empty();
4506 verify_overflow_empty();
4507 _abort_preclean = false;
4508 if (CMSPrecleaningEnabled) {
4509 if (!CMSEdenChunksRecordAlways) {
4510 _eden_chunk_index = 0;
4511 }
4512 size_t used = get_eden_used();
4513 size_t capacity = get_eden_capacity();
4514 // Don't start sampling unless we will get sufficiently
4515 // many samples.
4516 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4517 * CMSScheduleRemarkEdenPenetration)) {
4518 _start_sampling = true;
4519 } else {
4520 _start_sampling = false;
4521 }
4522 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4523 CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
4524 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4525 }
4526 CMSTokenSync x(true); // is cms thread
4527 if (CMSPrecleaningEnabled) {
4528 sample_eden();
4529 _collectorState = AbortablePreclean;
4530 } else {
4531 _collectorState = FinalMarking;
4532 }
4533 verify_work_stacks_empty();
4534 verify_overflow_empty();
4535 }
4537 // Try and schedule the remark such that young gen
4538 // occupancy is CMSScheduleRemarkEdenPenetration %.
4539 void CMSCollector::abortable_preclean() {
4540 check_correct_thread_executing();
4541 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4542 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4544 // If Eden's current occupancy is below this threshold,
4545 // immediately schedule the remark; else preclean
4546 // past the next scavenge in an effort to
4547 // schedule the pause as described avove. By choosing
4548 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4549 // we will never do an actual abortable preclean cycle.
4550 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4551 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4552 CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
4553 // We need more smarts in the abortable preclean
4554 // loop below to deal with cases where allocation
4555 // in young gen is very very slow, and our precleaning
4556 // is running a losing race against a horde of
4557 // mutators intent on flooding us with CMS updates
4558 // (dirty cards).
4559 // One, admittedly dumb, strategy is to give up
4560 // after a certain number of abortable precleaning loops
4561 // or after a certain maximum time. We want to make
4562 // this smarter in the next iteration.
4563 // XXX FIX ME!!! YSR
4564 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4565 while (!(should_abort_preclean() ||
4566 ConcurrentMarkSweepThread::should_terminate())) {
4567 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4568 cumworkdone += workdone;
4569 loops++;
4570 // Voluntarily terminate abortable preclean phase if we have
4571 // been at it for too long.
4572 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4573 loops >= CMSMaxAbortablePrecleanLoops) {
4574 if (PrintGCDetails) {
4575 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4576 }
4577 break;
4578 }
4579 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4580 if (PrintGCDetails) {
4581 gclog_or_tty->print(" CMS: abort preclean due to time ");
4582 }
4583 break;
4584 }
4585 // If we are doing little work each iteration, we should
4586 // take a short break.
4587 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4588 // Sleep for some time, waiting for work to accumulate
4589 stopTimer();
4590 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4591 startTimer();
4592 waited++;
4593 }
4594 }
4595 if (PrintCMSStatistics > 0) {
4596 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4597 loops, waited, cumworkdone);
4598 }
4599 }
4600 CMSTokenSync x(true); // is cms thread
4601 if (_collectorState != Idling) {
4602 assert(_collectorState == AbortablePreclean,
4603 "Spontaneous state transition?");
4604 _collectorState = FinalMarking;
4605 } // Else, a foreground collection completed this CMS cycle.
4606 return;
4607 }
4609 // Respond to an Eden sampling opportunity
4610 void CMSCollector::sample_eden() {
4611 // Make sure a young gc cannot sneak in between our
4612 // reading and recording of a sample.
4613 assert(Thread::current()->is_ConcurrentGC_thread(),
4614 "Only the cms thread may collect Eden samples");
4615 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4616 "Should collect samples while holding CMS token");
4617 if (!_start_sampling) {
4618 return;
4619 }
4620 // When CMSEdenChunksRecordAlways is true, the eden chunk array
4621 // is populated by the young generation.
4622 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
4623 if (_eden_chunk_index < _eden_chunk_capacity) {
4624 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4625 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4626 "Unexpected state of Eden");
4627 // We'd like to check that what we just sampled is an oop-start address;
4628 // however, we cannot do that here since the object may not yet have been
4629 // initialized. So we'll instead do the check when we _use_ this sample
4630 // later.
4631 if (_eden_chunk_index == 0 ||
4632 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4633 _eden_chunk_array[_eden_chunk_index-1])
4634 >= CMSSamplingGrain)) {
4635 _eden_chunk_index++; // commit sample
4636 }
4637 }
4638 }
4639 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4640 size_t used = get_eden_used();
4641 size_t capacity = get_eden_capacity();
4642 assert(used <= capacity, "Unexpected state of Eden");
4643 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4644 _abort_preclean = true;
4645 }
4646 }
4647 }
4650 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4651 assert(_collectorState == Precleaning ||
4652 _collectorState == AbortablePreclean, "incorrect state");
4653 ResourceMark rm;
4654 HandleMark hm;
4656 // Precleaning is currently not MT but the reference processor
4657 // may be set for MT. Disable it temporarily here.
4658 ReferenceProcessor* rp = ref_processor();
4659 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4661 // Do one pass of scrubbing the discovered reference lists
4662 // to remove any reference objects with strongly-reachable
4663 // referents.
4664 if (clean_refs) {
4665 CMSPrecleanRefsYieldClosure yield_cl(this);
4666 assert(rp->span().equals(_span), "Spans should be equal");
4667 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4668 &_markStack, true /* preclean */);
4669 CMSDrainMarkingStackClosure complete_trace(this,
4670 _span, &_markBitMap, &_markStack,
4671 &keep_alive, true /* preclean */);
4673 // We don't want this step to interfere with a young
4674 // collection because we don't want to take CPU
4675 // or memory bandwidth away from the young GC threads
4676 // (which may be as many as there are CPUs).
4677 // Note that we don't need to protect ourselves from
4678 // interference with mutators because they can't
4679 // manipulate the discovered reference lists nor affect
4680 // the computed reachability of the referents, the
4681 // only properties manipulated by the precleaning
4682 // of these reference lists.
4683 stopTimer();
4684 CMSTokenSyncWithLocks x(true /* is cms thread */,
4685 bitMapLock());
4686 startTimer();
4687 sample_eden();
4689 // The following will yield to allow foreground
4690 // collection to proceed promptly. XXX YSR:
4691 // The code in this method may need further
4692 // tweaking for better performance and some restructuring
4693 // for cleaner interfaces.
4694 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4695 rp->preclean_discovered_references(
4696 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
4697 gc_timer, _gc_tracer_cm->gc_id());
4698 }
4700 if (clean_survivor) { // preclean the active survivor space(s)
4701 assert(_young_gen->kind() == Generation::DefNew ||
4702 _young_gen->kind() == Generation::ParNew ||
4703 _young_gen->kind() == Generation::ASParNew,
4704 "incorrect type for cast");
4705 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4706 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4707 &_markBitMap, &_modUnionTable,
4708 &_markStack, true /* precleaning phase */);
4709 stopTimer();
4710 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4711 bitMapLock());
4712 startTimer();
4713 unsigned int before_count =
4714 GenCollectedHeap::heap()->total_collections();
4715 SurvivorSpacePrecleanClosure
4716 sss_cl(this, _span, &_markBitMap, &_markStack,
4717 &pam_cl, before_count, CMSYield);
4718 dng->from()->object_iterate_careful(&sss_cl);
4719 dng->to()->object_iterate_careful(&sss_cl);
4720 }
4721 MarkRefsIntoAndScanClosure
4722 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4723 &_markStack, this, CMSYield,
4724 true /* precleaning phase */);
4725 // CAUTION: The following closure has persistent state that may need to
4726 // be reset upon a decrease in the sequence of addresses it
4727 // processes.
4728 ScanMarkedObjectsAgainCarefullyClosure
4729 smoac_cl(this, _span,
4730 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4732 // Preclean dirty cards in ModUnionTable and CardTable using
4733 // appropriate convergence criterion;
4734 // repeat CMSPrecleanIter times unless we find that
4735 // we are losing.
4736 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4737 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4738 "Bad convergence multiplier");
4739 assert(CMSPrecleanThreshold >= 100,
4740 "Unreasonably low CMSPrecleanThreshold");
4742 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4743 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4744 numIter < CMSPrecleanIter;
4745 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4746 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4747 if (Verbose && PrintGCDetails) {
4748 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4749 }
4750 // Either there are very few dirty cards, so re-mark
4751 // pause will be small anyway, or our pre-cleaning isn't
4752 // that much faster than the rate at which cards are being
4753 // dirtied, so we might as well stop and re-mark since
4754 // precleaning won't improve our re-mark time by much.
4755 if (curNumCards <= CMSPrecleanThreshold ||
4756 (numIter > 0 &&
4757 (curNumCards * CMSPrecleanDenominator >
4758 lastNumCards * CMSPrecleanNumerator))) {
4759 numIter++;
4760 cumNumCards += curNumCards;
4761 break;
4762 }
4763 }
4765 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4767 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4768 cumNumCards += curNumCards;
4769 if (PrintGCDetails && PrintCMSStatistics != 0) {
4770 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4771 curNumCards, cumNumCards, numIter);
4772 }
4773 return cumNumCards; // as a measure of useful work done
4774 }
4776 // PRECLEANING NOTES:
4777 // Precleaning involves:
4778 // . reading the bits of the modUnionTable and clearing the set bits.
4779 // . For the cards corresponding to the set bits, we scan the
4780 // objects on those cards. This means we need the free_list_lock
4781 // so that we can safely iterate over the CMS space when scanning
4782 // for oops.
4783 // . When we scan the objects, we'll be both reading and setting
4784 // marks in the marking bit map, so we'll need the marking bit map.
4785 // . For protecting _collector_state transitions, we take the CGC_lock.
4786 // Note that any races in the reading of of card table entries by the
4787 // CMS thread on the one hand and the clearing of those entries by the
4788 // VM thread or the setting of those entries by the mutator threads on the
4789 // other are quite benign. However, for efficiency it makes sense to keep
4790 // the VM thread from racing with the CMS thread while the latter is
4791 // dirty card info to the modUnionTable. We therefore also use the
4792 // CGC_lock to protect the reading of the card table and the mod union
4793 // table by the CM thread.
4794 // . We run concurrently with mutator updates, so scanning
4795 // needs to be done carefully -- we should not try to scan
4796 // potentially uninitialized objects.
4797 //
4798 // Locking strategy: While holding the CGC_lock, we scan over and
4799 // reset a maximal dirty range of the mod union / card tables, then lock
4800 // the free_list_lock and bitmap lock to do a full marking, then
4801 // release these locks; and repeat the cycle. This allows for a
4802 // certain amount of fairness in the sharing of these locks between
4803 // the CMS collector on the one hand, and the VM thread and the
4804 // mutators on the other.
4806 // NOTE: preclean_mod_union_table() and preclean_card_table()
4807 // further below are largely identical; if you need to modify
4808 // one of these methods, please check the other method too.
4810 size_t CMSCollector::preclean_mod_union_table(
4811 ConcurrentMarkSweepGeneration* gen,
4812 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4813 verify_work_stacks_empty();
4814 verify_overflow_empty();
4816 // strategy: starting with the first card, accumulate contiguous
4817 // ranges of dirty cards; clear these cards, then scan the region
4818 // covered by these cards.
4820 // Since all of the MUT is committed ahead, we can just use
4821 // that, in case the generations expand while we are precleaning.
4822 // It might also be fine to just use the committed part of the
4823 // generation, but we might potentially miss cards when the
4824 // generation is rapidly expanding while we are in the midst
4825 // of precleaning.
4826 HeapWord* startAddr = gen->reserved().start();
4827 HeapWord* endAddr = gen->reserved().end();
4829 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4831 size_t numDirtyCards, cumNumDirtyCards;
4832 HeapWord *nextAddr, *lastAddr;
4833 for (cumNumDirtyCards = numDirtyCards = 0,
4834 nextAddr = lastAddr = startAddr;
4835 nextAddr < endAddr;
4836 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4838 ResourceMark rm;
4839 HandleMark hm;
4841 MemRegion dirtyRegion;
4842 {
4843 stopTimer();
4844 // Potential yield point
4845 CMSTokenSync ts(true);
4846 startTimer();
4847 sample_eden();
4848 // Get dirty region starting at nextOffset (inclusive),
4849 // simultaneously clearing it.
4850 dirtyRegion =
4851 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4852 assert(dirtyRegion.start() >= nextAddr,
4853 "returned region inconsistent?");
4854 }
4855 // Remember where the next search should begin.
4856 // The returned region (if non-empty) is a right open interval,
4857 // so lastOffset is obtained from the right end of that
4858 // interval.
4859 lastAddr = dirtyRegion.end();
4860 // Should do something more transparent and less hacky XXX
4861 numDirtyCards =
4862 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4864 // We'll scan the cards in the dirty region (with periodic
4865 // yields for foreground GC as needed).
4866 if (!dirtyRegion.is_empty()) {
4867 assert(numDirtyCards > 0, "consistency check");
4868 HeapWord* stop_point = NULL;
4869 stopTimer();
4870 // Potential yield point
4871 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4872 bitMapLock());
4873 startTimer();
4874 {
4875 verify_work_stacks_empty();
4876 verify_overflow_empty();
4877 sample_eden();
4878 stop_point =
4879 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4880 }
4881 if (stop_point != NULL) {
4882 // The careful iteration stopped early either because it found an
4883 // uninitialized object, or because we were in the midst of an
4884 // "abortable preclean", which should now be aborted. Redirty
4885 // the bits corresponding to the partially-scanned or unscanned
4886 // cards. We'll either restart at the next block boundary or
4887 // abort the preclean.
4888 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4889 "Should only be AbortablePreclean.");
4890 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4891 if (should_abort_preclean()) {
4892 break; // out of preclean loop
4893 } else {
4894 // Compute the next address at which preclean should pick up;
4895 // might need bitMapLock in order to read P-bits.
4896 lastAddr = next_card_start_after_block(stop_point);
4897 }
4898 }
4899 } else {
4900 assert(lastAddr == endAddr, "consistency check");
4901 assert(numDirtyCards == 0, "consistency check");
4902 break;
4903 }
4904 }
4905 verify_work_stacks_empty();
4906 verify_overflow_empty();
4907 return cumNumDirtyCards;
4908 }
4910 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4911 // below are largely identical; if you need to modify
4912 // one of these methods, please check the other method too.
4914 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4915 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4916 // strategy: it's similar to precleamModUnionTable above, in that
4917 // we accumulate contiguous ranges of dirty cards, mark these cards
4918 // precleaned, then scan the region covered by these cards.
4919 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4920 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4922 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4924 size_t numDirtyCards, cumNumDirtyCards;
4925 HeapWord *lastAddr, *nextAddr;
4927 for (cumNumDirtyCards = numDirtyCards = 0,
4928 nextAddr = lastAddr = startAddr;
4929 nextAddr < endAddr;
4930 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4932 ResourceMark rm;
4933 HandleMark hm;
4935 MemRegion dirtyRegion;
4936 {
4937 // See comments in "Precleaning notes" above on why we
4938 // do this locking. XXX Could the locking overheads be
4939 // too high when dirty cards are sparse? [I don't think so.]
4940 stopTimer();
4941 CMSTokenSync x(true); // is cms thread
4942 startTimer();
4943 sample_eden();
4944 // Get and clear dirty region from card table
4945 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4946 MemRegion(nextAddr, endAddr),
4947 true,
4948 CardTableModRefBS::precleaned_card_val());
4950 assert(dirtyRegion.start() >= nextAddr,
4951 "returned region inconsistent?");
4952 }
4953 lastAddr = dirtyRegion.end();
4954 numDirtyCards =
4955 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4957 if (!dirtyRegion.is_empty()) {
4958 stopTimer();
4959 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4960 startTimer();
4961 sample_eden();
4962 verify_work_stacks_empty();
4963 verify_overflow_empty();
4964 HeapWord* stop_point =
4965 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4966 if (stop_point != NULL) {
4967 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4968 "Should only be AbortablePreclean.");
4969 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4970 if (should_abort_preclean()) {
4971 break; // out of preclean loop
4972 } else {
4973 // Compute the next address at which preclean should pick up.
4974 lastAddr = next_card_start_after_block(stop_point);
4975 }
4976 }
4977 } else {
4978 break;
4979 }
4980 }
4981 verify_work_stacks_empty();
4982 verify_overflow_empty();
4983 return cumNumDirtyCards;
4984 }
4986 class PrecleanKlassClosure : public KlassClosure {
4987 CMKlassClosure _cm_klass_closure;
4988 public:
4989 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4990 void do_klass(Klass* k) {
4991 if (k->has_accumulated_modified_oops()) {
4992 k->clear_accumulated_modified_oops();
4994 _cm_klass_closure.do_klass(k);
4995 }
4996 }
4997 };
4999 // The freelist lock is needed to prevent asserts, is it really needed?
5000 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
5002 cl->set_freelistLock(freelistLock);
5004 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
5006 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
5007 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
5008 PrecleanKlassClosure preclean_klass_closure(cl);
5009 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
5011 verify_work_stacks_empty();
5012 verify_overflow_empty();
5013 }
5015 void CMSCollector::checkpointRootsFinal(bool asynch,
5016 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
5017 assert(_collectorState == FinalMarking, "incorrect state transition?");
5018 check_correct_thread_executing();
5019 // world is stopped at this checkpoint
5020 assert(SafepointSynchronize::is_at_safepoint(),
5021 "world should be stopped");
5022 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5024 verify_work_stacks_empty();
5025 verify_overflow_empty();
5027 SpecializationStats::clear();
5028 if (PrintGCDetails) {
5029 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
5030 _young_gen->used() / K,
5031 _young_gen->capacity() / K);
5032 }
5033 if (asynch) {
5034 if (CMSScavengeBeforeRemark) {
5035 GenCollectedHeap* gch = GenCollectedHeap::heap();
5036 // Temporarily set flag to false, GCH->do_collection will
5037 // expect it to be false and set to true
5038 FlagSetting fl(gch->_is_gc_active, false);
5039 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
5040 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
5041 int level = _cmsGen->level() - 1;
5042 if (level >= 0) {
5043 gch->do_collection(true, // full (i.e. force, see below)
5044 false, // !clear_all_soft_refs
5045 0, // size
5046 false, // is_tlab
5047 level // max_level
5048 );
5049 }
5050 }
5051 FreelistLocker x(this);
5052 MutexLockerEx y(bitMapLock(),
5053 Mutex::_no_safepoint_check_flag);
5054 assert(!init_mark_was_synchronous, "but that's impossible!");
5055 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
5056 } else {
5057 // already have all the locks
5058 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
5059 init_mark_was_synchronous);
5060 }
5061 verify_work_stacks_empty();
5062 verify_overflow_empty();
5063 SpecializationStats::print();
5064 }
5066 void CMSCollector::checkpointRootsFinalWork(bool asynch,
5067 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
5069 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
5071 assert(haveFreelistLocks(), "must have free list locks");
5072 assert_lock_strong(bitMapLock());
5074 if (UseAdaptiveSizePolicy) {
5075 size_policy()->checkpoint_roots_final_begin();
5076 }
5078 ResourceMark rm;
5079 HandleMark hm;
5081 GenCollectedHeap* gch = GenCollectedHeap::heap();
5083 if (should_unload_classes()) {
5084 CodeCache::gc_prologue();
5085 }
5086 assert(haveFreelistLocks(), "must have free list locks");
5087 assert_lock_strong(bitMapLock());
5089 if (!init_mark_was_synchronous) {
5090 // We might assume that we need not fill TLAB's when
5091 // CMSScavengeBeforeRemark is set, because we may have just done
5092 // a scavenge which would have filled all TLAB's -- and besides
5093 // Eden would be empty. This however may not always be the case --
5094 // for instance although we asked for a scavenge, it may not have
5095 // happened because of a JNI critical section. We probably need
5096 // a policy for deciding whether we can in that case wait until
5097 // the critical section releases and then do the remark following
5098 // the scavenge, and skip it here. In the absence of that policy,
5099 // or of an indication of whether the scavenge did indeed occur,
5100 // we cannot rely on TLAB's having been filled and must do
5101 // so here just in case a scavenge did not happen.
5102 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
5103 // Update the saved marks which may affect the root scans.
5104 gch->save_marks();
5106 if (CMSPrintEdenSurvivorChunks) {
5107 print_eden_and_survivor_chunk_arrays();
5108 }
5110 {
5111 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
5113 // Note on the role of the mod union table:
5114 // Since the marker in "markFromRoots" marks concurrently with
5115 // mutators, it is possible for some reachable objects not to have been
5116 // scanned. For instance, an only reference to an object A was
5117 // placed in object B after the marker scanned B. Unless B is rescanned,
5118 // A would be collected. Such updates to references in marked objects
5119 // are detected via the mod union table which is the set of all cards
5120 // dirtied since the first checkpoint in this GC cycle and prior to
5121 // the most recent young generation GC, minus those cleaned up by the
5122 // concurrent precleaning.
5123 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
5124 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5125 do_remark_parallel();
5126 } else {
5127 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
5128 _gc_timer_cm, _gc_tracer_cm->gc_id());
5129 do_remark_non_parallel();
5130 }
5131 }
5132 } else {
5133 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
5134 // The initial mark was stop-world, so there's no rescanning to
5135 // do; go straight on to the next step below.
5136 }
5137 verify_work_stacks_empty();
5138 verify_overflow_empty();
5140 {
5141 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
5142 refProcessingWork(asynch, clear_all_soft_refs);
5143 }
5144 verify_work_stacks_empty();
5145 verify_overflow_empty();
5147 if (should_unload_classes()) {
5148 CodeCache::gc_epilogue();
5149 }
5150 JvmtiExport::gc_epilogue();
5152 // If we encountered any (marking stack / work queue) overflow
5153 // events during the current CMS cycle, take appropriate
5154 // remedial measures, where possible, so as to try and avoid
5155 // recurrence of that condition.
5156 assert(_markStack.isEmpty(), "No grey objects");
5157 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5158 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
5159 if (ser_ovflw > 0) {
5160 if (PrintCMSStatistics != 0) {
5161 gclog_or_tty->print_cr("Marking stack overflow (benign) "
5162 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5163 ", kac_preclean="SIZE_FORMAT")",
5164 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5165 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5166 }
5167 _markStack.expand();
5168 _ser_pmc_remark_ovflw = 0;
5169 _ser_pmc_preclean_ovflw = 0;
5170 _ser_kac_preclean_ovflw = 0;
5171 _ser_kac_ovflw = 0;
5172 }
5173 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5174 if (PrintCMSStatistics != 0) {
5175 gclog_or_tty->print_cr("Work queue overflow (benign) "
5176 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5177 _par_pmc_remark_ovflw, _par_kac_ovflw);
5178 }
5179 _par_pmc_remark_ovflw = 0;
5180 _par_kac_ovflw = 0;
5181 }
5182 if (PrintCMSStatistics != 0) {
5183 if (_markStack._hit_limit > 0) {
5184 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5185 _markStack._hit_limit);
5186 }
5187 if (_markStack._failed_double > 0) {
5188 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5189 " current capacity "SIZE_FORMAT,
5190 _markStack._failed_double,
5191 _markStack.capacity());
5192 }
5193 }
5194 _markStack._hit_limit = 0;
5195 _markStack._failed_double = 0;
5197 if ((VerifyAfterGC || VerifyDuringGC) &&
5198 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5199 verify_after_remark();
5200 }
5202 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
5204 // Change under the freelistLocks.
5205 _collectorState = Sweeping;
5206 // Call isAllClear() under bitMapLock
5207 assert(_modUnionTable.isAllClear(),
5208 "Should be clear by end of the final marking");
5209 assert(_ct->klass_rem_set()->mod_union_is_clear(),
5210 "Should be clear by end of the final marking");
5211 if (UseAdaptiveSizePolicy) {
5212 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
5213 }
5214 }
5216 void CMSParInitialMarkTask::work(uint worker_id) {
5217 elapsedTimer _timer;
5218 ResourceMark rm;
5219 HandleMark hm;
5221 // ---------- scan from roots --------------
5222 _timer.start();
5223 GenCollectedHeap* gch = GenCollectedHeap::heap();
5224 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
5225 CMKlassClosure klass_closure(&par_mri_cl);
5227 // ---------- young gen roots --------------
5228 {
5229 work_on_young_gen_roots(worker_id, &par_mri_cl);
5230 _timer.stop();
5231 if (PrintCMSStatistics != 0) {
5232 gclog_or_tty->print_cr(
5233 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
5234 worker_id, _timer.seconds());
5235 }
5236 }
5238 // ---------- remaining roots --------------
5239 _timer.reset();
5240 _timer.start();
5241 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5242 false, // yg was scanned above
5243 false, // this is parallel code
5244 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5245 &par_mri_cl,
5246 true, // walk all of code cache if (so & SO_AllCodeCache)
5247 NULL,
5248 &klass_closure);
5249 assert(_collector->should_unload_classes()
5250 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5251 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5252 _timer.stop();
5253 if (PrintCMSStatistics != 0) {
5254 gclog_or_tty->print_cr(
5255 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
5256 worker_id, _timer.seconds());
5257 }
5258 }
5260 // Parallel remark task
5261 class CMSParRemarkTask: public CMSParMarkTask {
5262 CompactibleFreeListSpace* _cms_space;
5264 // The per-thread work queues, available here for stealing.
5265 OopTaskQueueSet* _task_queues;
5266 ParallelTaskTerminator _term;
5268 public:
5269 // A value of 0 passed to n_workers will cause the number of
5270 // workers to be taken from the active workers in the work gang.
5271 CMSParRemarkTask(CMSCollector* collector,
5272 CompactibleFreeListSpace* cms_space,
5273 int n_workers, FlexibleWorkGang* workers,
5274 OopTaskQueueSet* task_queues):
5275 CMSParMarkTask("Rescan roots and grey objects in parallel",
5276 collector, n_workers),
5277 _cms_space(cms_space),
5278 _task_queues(task_queues),
5279 _term(n_workers, task_queues) { }
5281 OopTaskQueueSet* task_queues() { return _task_queues; }
5283 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5285 ParallelTaskTerminator* terminator() { return &_term; }
5286 int n_workers() { return _n_workers; }
5288 void work(uint worker_id);
5290 private:
5291 // ... of dirty cards in old space
5292 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5293 Par_MarkRefsIntoAndScanClosure* cl);
5295 // ... work stealing for the above
5296 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5297 };
5299 class RemarkKlassClosure : public KlassClosure {
5300 CMKlassClosure _cm_klass_closure;
5301 public:
5302 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
5303 void do_klass(Klass* k) {
5304 // Check if we have modified any oops in the Klass during the concurrent marking.
5305 if (k->has_accumulated_modified_oops()) {
5306 k->clear_accumulated_modified_oops();
5308 // We could have transfered the current modified marks to the accumulated marks,
5309 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
5310 } else if (k->has_modified_oops()) {
5311 // Don't clear anything, this info is needed by the next young collection.
5312 } else {
5313 // No modified oops in the Klass.
5314 return;
5315 }
5317 // The klass has modified fields, need to scan the klass.
5318 _cm_klass_closure.do_klass(k);
5319 }
5320 };
5322 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
5323 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5324 EdenSpace* eden_space = dng->eden();
5325 ContiguousSpace* from_space = dng->from();
5326 ContiguousSpace* to_space = dng->to();
5328 HeapWord** eca = _collector->_eden_chunk_array;
5329 size_t ect = _collector->_eden_chunk_index;
5330 HeapWord** sca = _collector->_survivor_chunk_array;
5331 size_t sct = _collector->_survivor_chunk_index;
5333 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5334 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5336 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
5337 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
5338 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
5339 }
5341 // work_queue(i) is passed to the closure
5342 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5343 // also is passed to do_dirty_card_rescan_tasks() and to
5344 // do_work_steal() to select the i-th task_queue.
5346 void CMSParRemarkTask::work(uint worker_id) {
5347 elapsedTimer _timer;
5348 ResourceMark rm;
5349 HandleMark hm;
5351 // ---------- rescan from roots --------------
5352 _timer.start();
5353 GenCollectedHeap* gch = GenCollectedHeap::heap();
5354 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5355 _collector->_span, _collector->ref_processor(),
5356 &(_collector->_markBitMap),
5357 work_queue(worker_id));
5359 // Rescan young gen roots first since these are likely
5360 // coarsely partitioned and may, on that account, constitute
5361 // the critical path; thus, it's best to start off that
5362 // work first.
5363 // ---------- young gen roots --------------
5364 {
5365 work_on_young_gen_roots(worker_id, &par_mrias_cl);
5366 _timer.stop();
5367 if (PrintCMSStatistics != 0) {
5368 gclog_or_tty->print_cr(
5369 "Finished young gen rescan work in %dth thread: %3.3f sec",
5370 worker_id, _timer.seconds());
5371 }
5372 }
5374 // ---------- remaining roots --------------
5375 _timer.reset();
5376 _timer.start();
5377 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5378 false, // yg was scanned above
5379 false, // this is parallel code
5380 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5381 &par_mrias_cl,
5382 true, // walk all of code cache if (so & SO_AllCodeCache)
5383 NULL,
5384 NULL); // The dirty klasses will be handled below
5385 assert(_collector->should_unload_classes()
5386 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5387 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5388 _timer.stop();
5389 if (PrintCMSStatistics != 0) {
5390 gclog_or_tty->print_cr(
5391 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5392 worker_id, _timer.seconds());
5393 }
5395 // ---------- unhandled CLD scanning ----------
5396 if (worker_id == 0) { // Single threaded at the moment.
5397 _timer.reset();
5398 _timer.start();
5400 // Scan all new class loader data objects and new dependencies that were
5401 // introduced during concurrent marking.
5402 ResourceMark rm;
5403 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5404 for (int i = 0; i < array->length(); i++) {
5405 par_mrias_cl.do_class_loader_data(array->at(i));
5406 }
5408 // We don't need to keep track of new CLDs anymore.
5409 ClassLoaderDataGraph::remember_new_clds(false);
5411 _timer.stop();
5412 if (PrintCMSStatistics != 0) {
5413 gclog_or_tty->print_cr(
5414 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
5415 worker_id, _timer.seconds());
5416 }
5417 }
5419 // ---------- dirty klass scanning ----------
5420 if (worker_id == 0) { // Single threaded at the moment.
5421 _timer.reset();
5422 _timer.start();
5424 // Scan all classes that was dirtied during the concurrent marking phase.
5425 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
5426 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5428 _timer.stop();
5429 if (PrintCMSStatistics != 0) {
5430 gclog_or_tty->print_cr(
5431 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
5432 worker_id, _timer.seconds());
5433 }
5434 }
5436 // We might have added oops to ClassLoaderData::_handles during the
5437 // concurrent marking phase. These oops point to newly allocated objects
5438 // that are guaranteed to be kept alive. Either by the direct allocation
5439 // code, or when the young collector processes the strong roots. Hence,
5440 // we don't have to revisit the _handles block during the remark phase.
5442 // ---------- rescan dirty cards ------------
5443 _timer.reset();
5444 _timer.start();
5446 // Do the rescan tasks for each of the two spaces
5447 // (cms_space) in turn.
5448 // "worker_id" is passed to select the task_queue for "worker_id"
5449 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5450 _timer.stop();
5451 if (PrintCMSStatistics != 0) {
5452 gclog_or_tty->print_cr(
5453 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5454 worker_id, _timer.seconds());
5455 }
5457 // ---------- steal work from other threads ...
5458 // ---------- ... and drain overflow list.
5459 _timer.reset();
5460 _timer.start();
5461 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5462 _timer.stop();
5463 if (PrintCMSStatistics != 0) {
5464 gclog_or_tty->print_cr(
5465 "Finished work stealing in %dth thread: %3.3f sec",
5466 worker_id, _timer.seconds());
5467 }
5468 }
5470 // Note that parameter "i" is not used.
5471 void
5472 CMSParMarkTask::do_young_space_rescan(uint worker_id,
5473 OopsInGenClosure* cl, ContiguousSpace* space,
5474 HeapWord** chunk_array, size_t chunk_top) {
5475 // Until all tasks completed:
5476 // . claim an unclaimed task
5477 // . compute region boundaries corresponding to task claimed
5478 // using chunk_array
5479 // . par_oop_iterate(cl) over that region
5481 ResourceMark rm;
5482 HandleMark hm;
5484 SequentialSubTasksDone* pst = space->par_seq_tasks();
5486 uint nth_task = 0;
5487 uint n_tasks = pst->n_tasks();
5489 if (n_tasks > 0) {
5490 assert(pst->valid(), "Uninitialized use?");
5491 HeapWord *start, *end;
5492 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5493 // We claimed task # nth_task; compute its boundaries.
5494 if (chunk_top == 0) { // no samples were taken
5495 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5496 start = space->bottom();
5497 end = space->top();
5498 } else if (nth_task == 0) {
5499 start = space->bottom();
5500 end = chunk_array[nth_task];
5501 } else if (nth_task < (uint)chunk_top) {
5502 assert(nth_task >= 1, "Control point invariant");
5503 start = chunk_array[nth_task - 1];
5504 end = chunk_array[nth_task];
5505 } else {
5506 assert(nth_task == (uint)chunk_top, "Control point invariant");
5507 start = chunk_array[chunk_top - 1];
5508 end = space->top();
5509 }
5510 MemRegion mr(start, end);
5511 // Verify that mr is in space
5512 assert(mr.is_empty() || space->used_region().contains(mr),
5513 "Should be in space");
5514 // Verify that "start" is an object boundary
5515 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5516 "Should be an oop");
5517 space->par_oop_iterate(mr, cl);
5518 }
5519 pst->all_tasks_completed();
5520 }
5521 }
5523 void
5524 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5525 CompactibleFreeListSpace* sp, int i,
5526 Par_MarkRefsIntoAndScanClosure* cl) {
5527 // Until all tasks completed:
5528 // . claim an unclaimed task
5529 // . compute region boundaries corresponding to task claimed
5530 // . transfer dirty bits ct->mut for that region
5531 // . apply rescanclosure to dirty mut bits for that region
5533 ResourceMark rm;
5534 HandleMark hm;
5536 OopTaskQueue* work_q = work_queue(i);
5537 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5538 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5539 // CAUTION: This closure has state that persists across calls to
5540 // the work method dirty_range_iterate_clear() in that it has
5541 // imbedded in it a (subtype of) UpwardsObjectClosure. The
5542 // use of that state in the imbedded UpwardsObjectClosure instance
5543 // assumes that the cards are always iterated (even if in parallel
5544 // by several threads) in monotonically increasing order per each
5545 // thread. This is true of the implementation below which picks
5546 // card ranges (chunks) in monotonically increasing order globally
5547 // and, a-fortiori, in monotonically increasing order per thread
5548 // (the latter order being a subsequence of the former).
5549 // If the work code below is ever reorganized into a more chaotic
5550 // work-partitioning form than the current "sequential tasks"
5551 // paradigm, the use of that persistent state will have to be
5552 // revisited and modified appropriately. See also related
5553 // bug 4756801 work on which should examine this code to make
5554 // sure that the changes there do not run counter to the
5555 // assumptions made here and necessary for correctness and
5556 // efficiency. Note also that this code might yield inefficient
5557 // behaviour in the case of very large objects that span one or
5558 // more work chunks. Such objects would potentially be scanned
5559 // several times redundantly. Work on 4756801 should try and
5560 // address that performance anomaly if at all possible. XXX
5561 MemRegion full_span = _collector->_span;
5562 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5563 MarkFromDirtyCardsClosure
5564 greyRescanClosure(_collector, full_span, // entire span of interest
5565 sp, bm, work_q, cl);
5567 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5568 assert(pst->valid(), "Uninitialized use?");
5569 uint nth_task = 0;
5570 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5571 MemRegion span = sp->used_region();
5572 HeapWord* start_addr = span.start();
5573 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5574 alignment);
5575 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5576 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5577 start_addr, "Check alignment");
5578 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5579 chunk_size, "Check alignment");
5581 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5582 // Having claimed the nth_task, compute corresponding mem-region,
5583 // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5584 // The alignment restriction ensures that we do not need any
5585 // synchronization with other gang-workers while setting or
5586 // clearing bits in thus chunk of the MUT.
5587 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5588 start_addr + (nth_task+1)*chunk_size);
5589 // The last chunk's end might be way beyond end of the
5590 // used region. In that case pull back appropriately.
5591 if (this_span.end() > end_addr) {
5592 this_span.set_end(end_addr);
5593 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5594 }
5595 // Iterate over the dirty cards covering this chunk, marking them
5596 // precleaned, and setting the corresponding bits in the mod union
5597 // table. Since we have been careful to partition at Card and MUT-word
5598 // boundaries no synchronization is needed between parallel threads.
5599 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5600 &modUnionClosure);
5602 // Having transferred these marks into the modUnionTable,
5603 // rescan the marked objects on the dirty cards in the modUnionTable.
5604 // Even if this is at a synchronous collection, the initial marking
5605 // may have been done during an asynchronous collection so there
5606 // may be dirty bits in the mod-union table.
5607 _collector->_modUnionTable.dirty_range_iterate_clear(
5608 this_span, &greyRescanClosure);
5609 _collector->_modUnionTable.verifyNoOneBitsInRange(
5610 this_span.start(),
5611 this_span.end());
5612 }
5613 pst->all_tasks_completed(); // declare that i am done
5614 }
5616 // . see if we can share work_queues with ParNew? XXX
5617 void
5618 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5619 int* seed) {
5620 OopTaskQueue* work_q = work_queue(i);
5621 NOT_PRODUCT(int num_steals = 0;)
5622 oop obj_to_scan;
5623 CMSBitMap* bm = &(_collector->_markBitMap);
5625 while (true) {
5626 // Completely finish any left over work from (an) earlier round(s)
5627 cl->trim_queue(0);
5628 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5629 (size_t)ParGCDesiredObjsFromOverflowList);
5630 // Now check if there's any work in the overflow list
5631 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5632 // only affects the number of attempts made to get work from the
5633 // overflow list and does not affect the number of workers. Just
5634 // pass ParallelGCThreads so this behavior is unchanged.
5635 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5636 work_q,
5637 ParallelGCThreads)) {
5638 // found something in global overflow list;
5639 // not yet ready to go stealing work from others.
5640 // We'd like to assert(work_q->size() != 0, ...)
5641 // because we just took work from the overflow list,
5642 // but of course we can't since all of that could have
5643 // been already stolen from us.
5644 // "He giveth and He taketh away."
5645 continue;
5646 }
5647 // Verify that we have no work before we resort to stealing
5648 assert(work_q->size() == 0, "Have work, shouldn't steal");
5649 // Try to steal from other queues that have work
5650 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5651 NOT_PRODUCT(num_steals++;)
5652 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5653 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5654 // Do scanning work
5655 obj_to_scan->oop_iterate(cl);
5656 // Loop around, finish this work, and try to steal some more
5657 } else if (terminator()->offer_termination()) {
5658 break; // nirvana from the infinite cycle
5659 }
5660 }
5661 NOT_PRODUCT(
5662 if (PrintCMSStatistics != 0) {
5663 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5664 }
5665 )
5666 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5667 "Else our work is not yet done");
5668 }
5670 // Record object boundaries in _eden_chunk_array by sampling the eden
5671 // top in the slow-path eden object allocation code path and record
5672 // the boundaries, if CMSEdenChunksRecordAlways is true. If
5673 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
5674 // sampling in sample_eden() that activates during the part of the
5675 // preclean phase.
5676 void CMSCollector::sample_eden_chunk() {
5677 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
5678 if (_eden_chunk_lock->try_lock()) {
5679 // Record a sample. This is the critical section. The contents
5680 // of the _eden_chunk_array have to be non-decreasing in the
5681 // address order.
5682 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
5683 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
5684 "Unexpected state of Eden");
5685 if (_eden_chunk_index == 0 ||
5686 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
5687 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
5688 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
5689 _eden_chunk_index++; // commit sample
5690 }
5691 _eden_chunk_lock->unlock();
5692 }
5693 }
5694 }
5696 // Return a thread-local PLAB recording array, as appropriate.
5697 void* CMSCollector::get_data_recorder(int thr_num) {
5698 if (_survivor_plab_array != NULL &&
5699 (CMSPLABRecordAlways ||
5700 (_collectorState > Marking && _collectorState < FinalMarking))) {
5701 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5702 ChunkArray* ca = &_survivor_plab_array[thr_num];
5703 ca->reset(); // clear it so that fresh data is recorded
5704 return (void*) ca;
5705 } else {
5706 return NULL;
5707 }
5708 }
5710 // Reset all the thread-local PLAB recording arrays
5711 void CMSCollector::reset_survivor_plab_arrays() {
5712 for (uint i = 0; i < ParallelGCThreads; i++) {
5713 _survivor_plab_array[i].reset();
5714 }
5715 }
5717 // Merge the per-thread plab arrays into the global survivor chunk
5718 // array which will provide the partitioning of the survivor space
5719 // for CMS initial scan and rescan.
5720 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5721 int no_of_gc_threads) {
5722 assert(_survivor_plab_array != NULL, "Error");
5723 assert(_survivor_chunk_array != NULL, "Error");
5724 assert(_collectorState == FinalMarking ||
5725 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
5726 for (int j = 0; j < no_of_gc_threads; j++) {
5727 _cursor[j] = 0;
5728 }
5729 HeapWord* top = surv->top();
5730 size_t i;
5731 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5732 HeapWord* min_val = top; // Higher than any PLAB address
5733 uint min_tid = 0; // position of min_val this round
5734 for (int j = 0; j < no_of_gc_threads; j++) {
5735 ChunkArray* cur_sca = &_survivor_plab_array[j];
5736 if (_cursor[j] == cur_sca->end()) {
5737 continue;
5738 }
5739 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5740 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5741 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5742 if (cur_val < min_val) {
5743 min_tid = j;
5744 min_val = cur_val;
5745 } else {
5746 assert(cur_val < top, "All recorded addresses should be less");
5747 }
5748 }
5749 // At this point min_val and min_tid are respectively
5750 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5751 // and the thread (j) that witnesses that address.
5752 // We record this address in the _survivor_chunk_array[i]
5753 // and increment _cursor[min_tid] prior to the next round i.
5754 if (min_val == top) {
5755 break;
5756 }
5757 _survivor_chunk_array[i] = min_val;
5758 _cursor[min_tid]++;
5759 }
5760 // We are all done; record the size of the _survivor_chunk_array
5761 _survivor_chunk_index = i; // exclusive: [0, i)
5762 if (PrintCMSStatistics > 0) {
5763 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5764 }
5765 // Verify that we used up all the recorded entries
5766 #ifdef ASSERT
5767 size_t total = 0;
5768 for (int j = 0; j < no_of_gc_threads; j++) {
5769 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5770 total += _cursor[j];
5771 }
5772 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5773 // Check that the merged array is in sorted order
5774 if (total > 0) {
5775 for (size_t i = 0; i < total - 1; i++) {
5776 if (PrintCMSStatistics > 0) {
5777 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5778 i, _survivor_chunk_array[i]);
5779 }
5780 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5781 "Not sorted");
5782 }
5783 }
5784 #endif // ASSERT
5785 }
5787 // Set up the space's par_seq_tasks structure for work claiming
5788 // for parallel initial scan and rescan of young gen.
5789 // See ParRescanTask where this is currently used.
5790 void
5791 CMSCollector::
5792 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5793 assert(n_threads > 0, "Unexpected n_threads argument");
5794 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5796 // Eden space
5797 if (!dng->eden()->is_empty()) {
5798 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5799 assert(!pst->valid(), "Clobbering existing data?");
5800 // Each valid entry in [0, _eden_chunk_index) represents a task.
5801 size_t n_tasks = _eden_chunk_index + 1;
5802 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5803 // Sets the condition for completion of the subtask (how many threads
5804 // need to finish in order to be done).
5805 pst->set_n_threads(n_threads);
5806 pst->set_n_tasks((int)n_tasks);
5807 }
5809 // Merge the survivor plab arrays into _survivor_chunk_array
5810 if (_survivor_plab_array != NULL) {
5811 merge_survivor_plab_arrays(dng->from(), n_threads);
5812 } else {
5813 assert(_survivor_chunk_index == 0, "Error");
5814 }
5816 // To space
5817 {
5818 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5819 assert(!pst->valid(), "Clobbering existing data?");
5820 // Sets the condition for completion of the subtask (how many threads
5821 // need to finish in order to be done).
5822 pst->set_n_threads(n_threads);
5823 pst->set_n_tasks(1);
5824 assert(pst->valid(), "Error");
5825 }
5827 // From space
5828 {
5829 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5830 assert(!pst->valid(), "Clobbering existing data?");
5831 size_t n_tasks = _survivor_chunk_index + 1;
5832 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5833 // Sets the condition for completion of the subtask (how many threads
5834 // need to finish in order to be done).
5835 pst->set_n_threads(n_threads);
5836 pst->set_n_tasks((int)n_tasks);
5837 assert(pst->valid(), "Error");
5838 }
5839 }
5841 // Parallel version of remark
5842 void CMSCollector::do_remark_parallel() {
5843 GenCollectedHeap* gch = GenCollectedHeap::heap();
5844 FlexibleWorkGang* workers = gch->workers();
5845 assert(workers != NULL, "Need parallel worker threads.");
5846 // Choose to use the number of GC workers most recently set
5847 // into "active_workers". If active_workers is not set, set it
5848 // to ParallelGCThreads.
5849 int n_workers = workers->active_workers();
5850 if (n_workers == 0) {
5851 assert(n_workers > 0, "Should have been set during scavenge");
5852 n_workers = ParallelGCThreads;
5853 workers->set_active_workers(n_workers);
5854 }
5855 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5857 CMSParRemarkTask tsk(this,
5858 cms_space,
5859 n_workers, workers, task_queues());
5861 // Set up for parallel process_strong_roots work.
5862 gch->set_par_threads(n_workers);
5863 // We won't be iterating over the cards in the card table updating
5864 // the younger_gen cards, so we shouldn't call the following else
5865 // the verification code as well as subsequent younger_refs_iterate
5866 // code would get confused. XXX
5867 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5869 // The young gen rescan work will not be done as part of
5870 // process_strong_roots (which currently doesn't knw how to
5871 // parallelize such a scan), but rather will be broken up into
5872 // a set of parallel tasks (via the sampling that the [abortable]
5873 // preclean phase did of EdenSpace, plus the [two] tasks of
5874 // scanning the [two] survivor spaces. Further fine-grain
5875 // parallelization of the scanning of the survivor spaces
5876 // themselves, and of precleaning of the younger gen itself
5877 // is deferred to the future.
5878 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5880 // The dirty card rescan work is broken up into a "sequence"
5881 // of parallel tasks (per constituent space) that are dynamically
5882 // claimed by the parallel threads.
5883 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5885 // It turns out that even when we're using 1 thread, doing the work in a
5886 // separate thread causes wide variance in run times. We can't help this
5887 // in the multi-threaded case, but we special-case n=1 here to get
5888 // repeatable measurements of the 1-thread overhead of the parallel code.
5889 if (n_workers > 1) {
5890 // Make refs discovery MT-safe, if it isn't already: it may not
5891 // necessarily be so, since it's possible that we are doing
5892 // ST marking.
5893 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5894 GenCollectedHeap::StrongRootsScope srs(gch);
5895 workers->run_task(&tsk);
5896 } else {
5897 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5898 GenCollectedHeap::StrongRootsScope srs(gch);
5899 tsk.work(0);
5900 }
5902 gch->set_par_threads(0); // 0 ==> non-parallel.
5903 // restore, single-threaded for now, any preserved marks
5904 // as a result of work_q overflow
5905 restore_preserved_marks_if_any();
5906 }
5908 // Non-parallel version of remark
5909 void CMSCollector::do_remark_non_parallel() {
5910 ResourceMark rm;
5911 HandleMark hm;
5912 GenCollectedHeap* gch = GenCollectedHeap::heap();
5913 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5915 MarkRefsIntoAndScanClosure
5916 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5917 &_markStack, this,
5918 false /* should_yield */, false /* not precleaning */);
5919 MarkFromDirtyCardsClosure
5920 markFromDirtyCardsClosure(this, _span,
5921 NULL, // space is set further below
5922 &_markBitMap, &_markStack, &mrias_cl);
5923 {
5924 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5925 // Iterate over the dirty cards, setting the corresponding bits in the
5926 // mod union table.
5927 {
5928 ModUnionClosure modUnionClosure(&_modUnionTable);
5929 _ct->ct_bs()->dirty_card_iterate(
5930 _cmsGen->used_region(),
5931 &modUnionClosure);
5932 }
5933 // Having transferred these marks into the modUnionTable, we just need
5934 // to rescan the marked objects on the dirty cards in the modUnionTable.
5935 // The initial marking may have been done during an asynchronous
5936 // collection so there may be dirty bits in the mod-union table.
5937 const int alignment =
5938 CardTableModRefBS::card_size * BitsPerWord;
5939 {
5940 // ... First handle dirty cards in CMS gen
5941 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5942 MemRegion ur = _cmsGen->used_region();
5943 HeapWord* lb = ur.start();
5944 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5945 MemRegion cms_span(lb, ub);
5946 _modUnionTable.dirty_range_iterate_clear(cms_span,
5947 &markFromDirtyCardsClosure);
5948 verify_work_stacks_empty();
5949 if (PrintCMSStatistics != 0) {
5950 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5951 markFromDirtyCardsClosure.num_dirty_cards());
5952 }
5953 }
5954 }
5955 if (VerifyDuringGC &&
5956 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5957 HandleMark hm; // Discard invalid handles created during verification
5958 Universe::verify();
5959 }
5960 {
5961 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5963 verify_work_stacks_empty();
5965 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5966 GenCollectedHeap::StrongRootsScope srs(gch);
5967 gch->gen_process_strong_roots(_cmsGen->level(),
5968 true, // younger gens as roots
5969 false, // use the local StrongRootsScope
5970 SharedHeap::ScanningOption(roots_scanning_options()),
5971 &mrias_cl,
5972 true, // walk code active on stacks
5973 NULL,
5974 NULL); // The dirty klasses will be handled below
5976 assert(should_unload_classes()
5977 || (roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5978 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5979 }
5981 {
5982 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5984 verify_work_stacks_empty();
5986 // Scan all class loader data objects that might have been introduced
5987 // during concurrent marking.
5988 ResourceMark rm;
5989 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5990 for (int i = 0; i < array->length(); i++) {
5991 mrias_cl.do_class_loader_data(array->at(i));
5992 }
5994 // We don't need to keep track of new CLDs anymore.
5995 ClassLoaderDataGraph::remember_new_clds(false);
5997 verify_work_stacks_empty();
5998 }
6000 {
6001 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6003 verify_work_stacks_empty();
6005 RemarkKlassClosure remark_klass_closure(&mrias_cl);
6006 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
6008 verify_work_stacks_empty();
6009 }
6011 // We might have added oops to ClassLoaderData::_handles during the
6012 // concurrent marking phase. These oops point to newly allocated objects
6013 // that are guaranteed to be kept alive. Either by the direct allocation
6014 // code, or when the young collector processes the strong roots. Hence,
6015 // we don't have to revisit the _handles block during the remark phase.
6017 verify_work_stacks_empty();
6018 // Restore evacuated mark words, if any, used for overflow list links
6019 if (!CMSOverflowEarlyRestoration) {
6020 restore_preserved_marks_if_any();
6021 }
6022 verify_overflow_empty();
6023 }
6025 ////////////////////////////////////////////////////////
6026 // Parallel Reference Processing Task Proxy Class
6027 ////////////////////////////////////////////////////////
6028 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
6029 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
6030 CMSCollector* _collector;
6031 CMSBitMap* _mark_bit_map;
6032 const MemRegion _span;
6033 ProcessTask& _task;
6035 public:
6036 CMSRefProcTaskProxy(ProcessTask& task,
6037 CMSCollector* collector,
6038 const MemRegion& span,
6039 CMSBitMap* mark_bit_map,
6040 AbstractWorkGang* workers,
6041 OopTaskQueueSet* task_queues):
6042 // XXX Should superclass AGTWOQ also know about AWG since it knows
6043 // about the task_queues used by the AWG? Then it could initialize
6044 // the terminator() object. See 6984287. The set_for_termination()
6045 // below is a temporary band-aid for the regression in 6984287.
6046 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
6047 task_queues),
6048 _task(task),
6049 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
6050 {
6051 assert(_collector->_span.equals(_span) && !_span.is_empty(),
6052 "Inconsistency in _span");
6053 set_for_termination(workers->active_workers());
6054 }
6056 OopTaskQueueSet* task_queues() { return queues(); }
6058 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
6060 void do_work_steal(int i,
6061 CMSParDrainMarkingStackClosure* drain,
6062 CMSParKeepAliveClosure* keep_alive,
6063 int* seed);
6065 virtual void work(uint worker_id);
6066 };
6068 void CMSRefProcTaskProxy::work(uint worker_id) {
6069 assert(_collector->_span.equals(_span), "Inconsistency in _span");
6070 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
6071 _mark_bit_map,
6072 work_queue(worker_id));
6073 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
6074 _mark_bit_map,
6075 work_queue(worker_id));
6076 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
6077 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
6078 if (_task.marks_oops_alive()) {
6079 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
6080 _collector->hash_seed(worker_id));
6081 }
6082 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
6083 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
6084 }
6086 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
6087 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
6088 EnqueueTask& _task;
6090 public:
6091 CMSRefEnqueueTaskProxy(EnqueueTask& task)
6092 : AbstractGangTask("Enqueue reference objects in parallel"),
6093 _task(task)
6094 { }
6096 virtual void work(uint worker_id)
6097 {
6098 _task.work(worker_id);
6099 }
6100 };
6102 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
6103 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
6104 _span(span),
6105 _bit_map(bit_map),
6106 _work_queue(work_queue),
6107 _mark_and_push(collector, span, bit_map, work_queue),
6108 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6109 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
6110 { }
6112 // . see if we can share work_queues with ParNew? XXX
6113 void CMSRefProcTaskProxy::do_work_steal(int i,
6114 CMSParDrainMarkingStackClosure* drain,
6115 CMSParKeepAliveClosure* keep_alive,
6116 int* seed) {
6117 OopTaskQueue* work_q = work_queue(i);
6118 NOT_PRODUCT(int num_steals = 0;)
6119 oop obj_to_scan;
6121 while (true) {
6122 // Completely finish any left over work from (an) earlier round(s)
6123 drain->trim_queue(0);
6124 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
6125 (size_t)ParGCDesiredObjsFromOverflowList);
6126 // Now check if there's any work in the overflow list
6127 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
6128 // only affects the number of attempts made to get work from the
6129 // overflow list and does not affect the number of workers. Just
6130 // pass ParallelGCThreads so this behavior is unchanged.
6131 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
6132 work_q,
6133 ParallelGCThreads)) {
6134 // Found something in global overflow list;
6135 // not yet ready to go stealing work from others.
6136 // We'd like to assert(work_q->size() != 0, ...)
6137 // because we just took work from the overflow list,
6138 // but of course we can't, since all of that might have
6139 // been already stolen from us.
6140 continue;
6141 }
6142 // Verify that we have no work before we resort to stealing
6143 assert(work_q->size() == 0, "Have work, shouldn't steal");
6144 // Try to steal from other queues that have work
6145 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
6146 NOT_PRODUCT(num_steals++;)
6147 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
6148 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
6149 // Do scanning work
6150 obj_to_scan->oop_iterate(keep_alive);
6151 // Loop around, finish this work, and try to steal some more
6152 } else if (terminator()->offer_termination()) {
6153 break; // nirvana from the infinite cycle
6154 }
6155 }
6156 NOT_PRODUCT(
6157 if (PrintCMSStatistics != 0) {
6158 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
6159 }
6160 )
6161 }
6163 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
6164 {
6165 GenCollectedHeap* gch = GenCollectedHeap::heap();
6166 FlexibleWorkGang* workers = gch->workers();
6167 assert(workers != NULL, "Need parallel worker threads.");
6168 CMSRefProcTaskProxy rp_task(task, &_collector,
6169 _collector.ref_processor()->span(),
6170 _collector.markBitMap(),
6171 workers, _collector.task_queues());
6172 workers->run_task(&rp_task);
6173 }
6175 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
6176 {
6178 GenCollectedHeap* gch = GenCollectedHeap::heap();
6179 FlexibleWorkGang* workers = gch->workers();
6180 assert(workers != NULL, "Need parallel worker threads.");
6181 CMSRefEnqueueTaskProxy enq_task(task);
6182 workers->run_task(&enq_task);
6183 }
6185 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
6187 ResourceMark rm;
6188 HandleMark hm;
6190 ReferenceProcessor* rp = ref_processor();
6191 assert(rp->span().equals(_span), "Spans should be equal");
6192 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
6193 // Process weak references.
6194 rp->setup_policy(clear_all_soft_refs);
6195 verify_work_stacks_empty();
6197 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
6198 &_markStack, false /* !preclean */);
6199 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
6200 _span, &_markBitMap, &_markStack,
6201 &cmsKeepAliveClosure, false /* !preclean */);
6202 {
6203 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6205 ReferenceProcessorStats stats;
6206 if (rp->processing_is_mt()) {
6207 // Set the degree of MT here. If the discovery is done MT, there
6208 // may have been a different number of threads doing the discovery
6209 // and a different number of discovered lists may have Ref objects.
6210 // That is OK as long as the Reference lists are balanced (see
6211 // balance_all_queues() and balance_queues()).
6212 GenCollectedHeap* gch = GenCollectedHeap::heap();
6213 int active_workers = ParallelGCThreads;
6214 FlexibleWorkGang* workers = gch->workers();
6215 if (workers != NULL) {
6216 active_workers = workers->active_workers();
6217 // The expectation is that active_workers will have already
6218 // been set to a reasonable value. If it has not been set,
6219 // investigate.
6220 assert(active_workers > 0, "Should have been set during scavenge");
6221 }
6222 rp->set_active_mt_degree(active_workers);
6223 CMSRefProcTaskExecutor task_executor(*this);
6224 stats = rp->process_discovered_references(&_is_alive_closure,
6225 &cmsKeepAliveClosure,
6226 &cmsDrainMarkingStackClosure,
6227 &task_executor,
6228 _gc_timer_cm,
6229 _gc_tracer_cm->gc_id());
6230 } else {
6231 stats = rp->process_discovered_references(&_is_alive_closure,
6232 &cmsKeepAliveClosure,
6233 &cmsDrainMarkingStackClosure,
6234 NULL,
6235 _gc_timer_cm,
6236 _gc_tracer_cm->gc_id());
6237 }
6238 _gc_tracer_cm->report_gc_reference_stats(stats);
6240 }
6242 // This is the point where the entire marking should have completed.
6243 verify_work_stacks_empty();
6245 if (should_unload_classes()) {
6246 {
6247 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6249 // Unload classes and purge the SystemDictionary.
6250 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
6252 // Unload nmethods.
6253 CodeCache::do_unloading(&_is_alive_closure, purged_class);
6255 // Prune dead klasses from subklass/sibling/implementor lists.
6256 Klass::clean_weak_klass_links(&_is_alive_closure);
6257 }
6259 {
6260 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6261 // Clean up unreferenced symbols in symbol table.
6262 SymbolTable::unlink();
6263 }
6264 }
6266 // CMS doesn't use the StringTable as hard roots when class unloading is turned off.
6267 // Need to check if we really scanned the StringTable.
6268 if ((roots_scanning_options() & SharedHeap::SO_Strings) == 0) {
6269 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6270 // Delete entries for dead interned strings.
6271 StringTable::unlink(&_is_alive_closure);
6272 }
6274 // Restore any preserved marks as a result of mark stack or
6275 // work queue overflow
6276 restore_preserved_marks_if_any(); // done single-threaded for now
6278 rp->set_enqueuing_is_done(true);
6279 if (rp->processing_is_mt()) {
6280 rp->balance_all_queues();
6281 CMSRefProcTaskExecutor task_executor(*this);
6282 rp->enqueue_discovered_references(&task_executor);
6283 } else {
6284 rp->enqueue_discovered_references(NULL);
6285 }
6286 rp->verify_no_references_recorded();
6287 assert(!rp->discovery_enabled(), "should have been disabled");
6288 }
6290 #ifndef PRODUCT
6291 void CMSCollector::check_correct_thread_executing() {
6292 Thread* t = Thread::current();
6293 // Only the VM thread or the CMS thread should be here.
6294 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6295 "Unexpected thread type");
6296 // If this is the vm thread, the foreground process
6297 // should not be waiting. Note that _foregroundGCIsActive is
6298 // true while the foreground collector is waiting.
6299 if (_foregroundGCShouldWait) {
6300 // We cannot be the VM thread
6301 assert(t->is_ConcurrentGC_thread(),
6302 "Should be CMS thread");
6303 } else {
6304 // We can be the CMS thread only if we are in a stop-world
6305 // phase of CMS collection.
6306 if (t->is_ConcurrentGC_thread()) {
6307 assert(_collectorState == InitialMarking ||
6308 _collectorState == FinalMarking,
6309 "Should be a stop-world phase");
6310 // The CMS thread should be holding the CMS_token.
6311 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6312 "Potential interference with concurrently "
6313 "executing VM thread");
6314 }
6315 }
6316 }
6317 #endif
6319 void CMSCollector::sweep(bool asynch) {
6320 assert(_collectorState == Sweeping, "just checking");
6321 check_correct_thread_executing();
6322 verify_work_stacks_empty();
6323 verify_overflow_empty();
6324 increment_sweep_count();
6325 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6327 _inter_sweep_timer.stop();
6328 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6329 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
6331 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6332 _intra_sweep_timer.reset();
6333 _intra_sweep_timer.start();
6334 if (asynch) {
6335 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6336 CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
6337 // First sweep the old gen
6338 {
6339 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6340 bitMapLock());
6341 sweepWork(_cmsGen, asynch);
6342 }
6344 // Update Universe::_heap_*_at_gc figures.
6345 // We need all the free list locks to make the abstract state
6346 // transition from Sweeping to Resetting. See detailed note
6347 // further below.
6348 {
6349 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6350 // Update heap occupancy information which is used as
6351 // input to soft ref clearing policy at the next gc.
6352 Universe::update_heap_info_at_gc();
6353 _collectorState = Resizing;
6354 }
6355 } else {
6356 // already have needed locks
6357 sweepWork(_cmsGen, asynch);
6358 // Update heap occupancy information which is used as
6359 // input to soft ref clearing policy at the next gc.
6360 Universe::update_heap_info_at_gc();
6361 _collectorState = Resizing;
6362 }
6363 verify_work_stacks_empty();
6364 verify_overflow_empty();
6366 if (should_unload_classes()) {
6367 // Delay purge to the beginning of the next safepoint. Metaspace::contains
6368 // requires that the virtual spaces are stable and not deleted.
6369 ClassLoaderDataGraph::set_should_purge(true);
6370 }
6372 _intra_sweep_timer.stop();
6373 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6375 _inter_sweep_timer.reset();
6376 _inter_sweep_timer.start();
6378 // We need to use a monotonically non-deccreasing time in ms
6379 // or we will see time-warp warnings and os::javaTimeMillis()
6380 // does not guarantee monotonicity.
6381 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6382 update_time_of_last_gc(now);
6384 // NOTE on abstract state transitions:
6385 // Mutators allocate-live and/or mark the mod-union table dirty
6386 // based on the state of the collection. The former is done in
6387 // the interval [Marking, Sweeping] and the latter in the interval
6388 // [Marking, Sweeping). Thus the transitions into the Marking state
6389 // and out of the Sweeping state must be synchronously visible
6390 // globally to the mutators.
6391 // The transition into the Marking state happens with the world
6392 // stopped so the mutators will globally see it. Sweeping is
6393 // done asynchronously by the background collector so the transition
6394 // from the Sweeping state to the Resizing state must be done
6395 // under the freelistLock (as is the check for whether to
6396 // allocate-live and whether to dirty the mod-union table).
6397 assert(_collectorState == Resizing, "Change of collector state to"
6398 " Resizing must be done under the freelistLocks (plural)");
6400 // Now that sweeping has been completed, we clear
6401 // the incremental_collection_failed flag,
6402 // thus inviting a younger gen collection to promote into
6403 // this generation. If such a promotion may still fail,
6404 // the flag will be set again when a young collection is
6405 // attempted.
6406 GenCollectedHeap* gch = GenCollectedHeap::heap();
6407 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6408 gch->update_full_collections_completed(_collection_count_start);
6409 }
6411 // FIX ME!!! Looks like this belongs in CFLSpace, with
6412 // CMSGen merely delegating to it.
6413 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6414 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6415 HeapWord* minAddr = _cmsSpace->bottom();
6416 HeapWord* largestAddr =
6417 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6418 if (largestAddr == NULL) {
6419 // The dictionary appears to be empty. In this case
6420 // try to coalesce at the end of the heap.
6421 largestAddr = _cmsSpace->end();
6422 }
6423 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6424 size_t nearLargestOffset =
6425 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6426 if (PrintFLSStatistics != 0) {
6427 gclog_or_tty->print_cr(
6428 "CMS: Large Block: " PTR_FORMAT ";"
6429 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6430 largestAddr,
6431 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6432 }
6433 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6434 }
6436 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6437 return addr >= _cmsSpace->nearLargestChunk();
6438 }
6440 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6441 return _cmsSpace->find_chunk_at_end();
6442 }
6444 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6445 bool full) {
6446 // The next lower level has been collected. Gather any statistics
6447 // that are of interest at this point.
6448 if (!full && (current_level + 1) == level()) {
6449 // Gather statistics on the young generation collection.
6450 collector()->stats().record_gc0_end(used());
6451 }
6452 }
6454 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6455 GenCollectedHeap* gch = GenCollectedHeap::heap();
6456 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6457 "Wrong type of heap");
6458 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6459 gch->gen_policy()->size_policy();
6460 assert(sp->is_gc_cms_adaptive_size_policy(),
6461 "Wrong type of size policy");
6462 return sp;
6463 }
6465 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6466 if (PrintGCDetails && Verbose) {
6467 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6468 }
6469 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6470 _debug_collection_type =
6471 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6472 if (PrintGCDetails && Verbose) {
6473 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6474 }
6475 }
6477 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6478 bool asynch) {
6479 // We iterate over the space(s) underlying this generation,
6480 // checking the mark bit map to see if the bits corresponding
6481 // to specific blocks are marked or not. Blocks that are
6482 // marked are live and are not swept up. All remaining blocks
6483 // are swept up, with coalescing on-the-fly as we sweep up
6484 // contiguous free and/or garbage blocks:
6485 // We need to ensure that the sweeper synchronizes with allocators
6486 // and stop-the-world collectors. In particular, the following
6487 // locks are used:
6488 // . CMS token: if this is held, a stop the world collection cannot occur
6489 // . freelistLock: if this is held no allocation can occur from this
6490 // generation by another thread
6491 // . bitMapLock: if this is held, no other thread can access or update
6492 //
6494 // Note that we need to hold the freelistLock if we use
6495 // block iterate below; else the iterator might go awry if
6496 // a mutator (or promotion) causes block contents to change
6497 // (for instance if the allocator divvies up a block).
6498 // If we hold the free list lock, for all practical purposes
6499 // young generation GC's can't occur (they'll usually need to
6500 // promote), so we might as well prevent all young generation
6501 // GC's while we do a sweeping step. For the same reason, we might
6502 // as well take the bit map lock for the entire duration
6504 // check that we hold the requisite locks
6505 assert(have_cms_token(), "Should hold cms token");
6506 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6507 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6508 "Should possess CMS token to sweep");
6509 assert_lock_strong(gen->freelistLock());
6510 assert_lock_strong(bitMapLock());
6512 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6513 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6514 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6515 _inter_sweep_estimate.padded_average(),
6516 _intra_sweep_estimate.padded_average());
6517 gen->setNearLargestChunk();
6519 {
6520 SweepClosure sweepClosure(this, gen, &_markBitMap,
6521 CMSYield && asynch);
6522 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6523 // We need to free-up/coalesce garbage/blocks from a
6524 // co-terminal free run. This is done in the SweepClosure
6525 // destructor; so, do not remove this scope, else the
6526 // end-of-sweep-census below will be off by a little bit.
6527 }
6528 gen->cmsSpace()->sweep_completed();
6529 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6530 if (should_unload_classes()) { // unloaded classes this cycle,
6531 _concurrent_cycles_since_last_unload = 0; // ... reset count
6532 } else { // did not unload classes,
6533 _concurrent_cycles_since_last_unload++; // ... increment count
6534 }
6535 }
6537 // Reset CMS data structures (for now just the marking bit map)
6538 // preparatory for the next cycle.
6539 void CMSCollector::reset(bool asynch) {
6540 GenCollectedHeap* gch = GenCollectedHeap::heap();
6541 CMSAdaptiveSizePolicy* sp = size_policy();
6542 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6543 if (asynch) {
6544 CMSTokenSyncWithLocks ts(true, bitMapLock());
6546 // If the state is not "Resetting", the foreground thread
6547 // has done a collection and the resetting.
6548 if (_collectorState != Resetting) {
6549 assert(_collectorState == Idling, "The state should only change"
6550 " because the foreground collector has finished the collection");
6551 return;
6552 }
6554 // Clear the mark bitmap (no grey objects to start with)
6555 // for the next cycle.
6556 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6557 CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
6559 HeapWord* curAddr = _markBitMap.startWord();
6560 while (curAddr < _markBitMap.endWord()) {
6561 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6562 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6563 _markBitMap.clear_large_range(chunk);
6564 if (ConcurrentMarkSweepThread::should_yield() &&
6565 !foregroundGCIsActive() &&
6566 CMSYield) {
6567 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6568 "CMS thread should hold CMS token");
6569 assert_lock_strong(bitMapLock());
6570 bitMapLock()->unlock();
6571 ConcurrentMarkSweepThread::desynchronize(true);
6572 ConcurrentMarkSweepThread::acknowledge_yield_request();
6573 stopTimer();
6574 if (PrintCMSStatistics != 0) {
6575 incrementYields();
6576 }
6577 icms_wait();
6579 // See the comment in coordinator_yield()
6580 for (unsigned i = 0; i < CMSYieldSleepCount &&
6581 ConcurrentMarkSweepThread::should_yield() &&
6582 !CMSCollector::foregroundGCIsActive(); ++i) {
6583 os::sleep(Thread::current(), 1, false);
6584 ConcurrentMarkSweepThread::acknowledge_yield_request();
6585 }
6587 ConcurrentMarkSweepThread::synchronize(true);
6588 bitMapLock()->lock_without_safepoint_check();
6589 startTimer();
6590 }
6591 curAddr = chunk.end();
6592 }
6593 // A successful mostly concurrent collection has been done.
6594 // Because only the full (i.e., concurrent mode failure) collections
6595 // are being measured for gc overhead limits, clean the "near" flag
6596 // and count.
6597 sp->reset_gc_overhead_limit_count();
6598 _collectorState = Idling;
6599 } else {
6600 // already have the lock
6601 assert(_collectorState == Resetting, "just checking");
6602 assert_lock_strong(bitMapLock());
6603 _markBitMap.clear_all();
6604 _collectorState = Idling;
6605 }
6607 // Stop incremental mode after a cycle completes, so that any future cycles
6608 // are triggered by allocation.
6609 stop_icms();
6611 NOT_PRODUCT(
6612 if (RotateCMSCollectionTypes) {
6613 _cmsGen->rotate_debug_collection_type();
6614 }
6615 )
6617 register_gc_end();
6618 }
6620 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6621 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6622 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6623 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
6624 TraceCollectorStats tcs(counters());
6626 switch (op) {
6627 case CMS_op_checkpointRootsInitial: {
6628 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6629 checkpointRootsInitial(true); // asynch
6630 if (PrintGC) {
6631 _cmsGen->printOccupancy("initial-mark");
6632 }
6633 break;
6634 }
6635 case CMS_op_checkpointRootsFinal: {
6636 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6637 checkpointRootsFinal(true, // asynch
6638 false, // !clear_all_soft_refs
6639 false); // !init_mark_was_synchronous
6640 if (PrintGC) {
6641 _cmsGen->printOccupancy("remark");
6642 }
6643 break;
6644 }
6645 default:
6646 fatal("No such CMS_op");
6647 }
6648 }
6650 #ifndef PRODUCT
6651 size_t const CMSCollector::skip_header_HeapWords() {
6652 return FreeChunk::header_size();
6653 }
6655 // Try and collect here conditions that should hold when
6656 // CMS thread is exiting. The idea is that the foreground GC
6657 // thread should not be blocked if it wants to terminate
6658 // the CMS thread and yet continue to run the VM for a while
6659 // after that.
6660 void CMSCollector::verify_ok_to_terminate() const {
6661 assert(Thread::current()->is_ConcurrentGC_thread(),
6662 "should be called by CMS thread");
6663 assert(!_foregroundGCShouldWait, "should be false");
6664 // We could check here that all the various low-level locks
6665 // are not held by the CMS thread, but that is overkill; see
6666 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6667 // is checked.
6668 }
6669 #endif
6671 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6672 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6673 "missing Printezis mark?");
6674 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6675 size_t size = pointer_delta(nextOneAddr + 1, addr);
6676 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6677 "alignment problem");
6678 assert(size >= 3, "Necessary for Printezis marks to work");
6679 return size;
6680 }
6682 // A variant of the above (block_size_using_printezis_bits()) except
6683 // that we return 0 if the P-bits are not yet set.
6684 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6685 if (_markBitMap.isMarked(addr + 1)) {
6686 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6687 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6688 size_t size = pointer_delta(nextOneAddr + 1, addr);
6689 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6690 "alignment problem");
6691 assert(size >= 3, "Necessary for Printezis marks to work");
6692 return size;
6693 }
6694 return 0;
6695 }
6697 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6698 size_t sz = 0;
6699 oop p = (oop)addr;
6700 if (p->klass_or_null() != NULL) {
6701 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6702 } else {
6703 sz = block_size_using_printezis_bits(addr);
6704 }
6705 assert(sz > 0, "size must be nonzero");
6706 HeapWord* next_block = addr + sz;
6707 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6708 CardTableModRefBS::card_size);
6709 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6710 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6711 "must be different cards");
6712 return next_card;
6713 }
6716 // CMS Bit Map Wrapper /////////////////////////////////////////
6718 // Construct a CMS bit map infrastructure, but don't create the
6719 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6720 // further below.
6721 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6722 _bm(),
6723 _shifter(shifter),
6724 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6725 {
6726 _bmStartWord = 0;
6727 _bmWordSize = 0;
6728 }
6730 bool CMSBitMap::allocate(MemRegion mr) {
6731 _bmStartWord = mr.start();
6732 _bmWordSize = mr.word_size();
6733 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6734 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6735 if (!brs.is_reserved()) {
6736 warning("CMS bit map allocation failure");
6737 return false;
6738 }
6739 // For now we'll just commit all of the bit map up fromt.
6740 // Later on we'll try to be more parsimonious with swap.
6741 if (!_virtual_space.initialize(brs, brs.size())) {
6742 warning("CMS bit map backing store failure");
6743 return false;
6744 }
6745 assert(_virtual_space.committed_size() == brs.size(),
6746 "didn't reserve backing store for all of CMS bit map?");
6747 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6748 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6749 _bmWordSize, "inconsistency in bit map sizing");
6750 _bm.set_size(_bmWordSize >> _shifter);
6752 // bm.clear(); // can we rely on getting zero'd memory? verify below
6753 assert(isAllClear(),
6754 "Expected zero'd memory from ReservedSpace constructor");
6755 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6756 "consistency check");
6757 return true;
6758 }
6760 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6761 HeapWord *next_addr, *end_addr, *last_addr;
6762 assert_locked();
6763 assert(covers(mr), "out-of-range error");
6764 // XXX assert that start and end are appropriately aligned
6765 for (next_addr = mr.start(), end_addr = mr.end();
6766 next_addr < end_addr; next_addr = last_addr) {
6767 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6768 last_addr = dirty_region.end();
6769 if (!dirty_region.is_empty()) {
6770 cl->do_MemRegion(dirty_region);
6771 } else {
6772 assert(last_addr == end_addr, "program logic");
6773 return;
6774 }
6775 }
6776 }
6778 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6779 _bm.print_on_error(st, prefix);
6780 }
6782 #ifndef PRODUCT
6783 void CMSBitMap::assert_locked() const {
6784 CMSLockVerifier::assert_locked(lock());
6785 }
6787 bool CMSBitMap::covers(MemRegion mr) const {
6788 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6789 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6790 "size inconsistency");
6791 return (mr.start() >= _bmStartWord) &&
6792 (mr.end() <= endWord());
6793 }
6795 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6796 return (start >= _bmStartWord && (start + size) <= endWord());
6797 }
6799 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6800 // verify that there are no 1 bits in the interval [left, right)
6801 FalseBitMapClosure falseBitMapClosure;
6802 iterate(&falseBitMapClosure, left, right);
6803 }
6805 void CMSBitMap::region_invariant(MemRegion mr)
6806 {
6807 assert_locked();
6808 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6809 assert(!mr.is_empty(), "unexpected empty region");
6810 assert(covers(mr), "mr should be covered by bit map");
6811 // convert address range into offset range
6812 size_t start_ofs = heapWordToOffset(mr.start());
6813 // Make sure that end() is appropriately aligned
6814 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6815 (1 << (_shifter+LogHeapWordSize))),
6816 "Misaligned mr.end()");
6817 size_t end_ofs = heapWordToOffset(mr.end());
6818 assert(end_ofs > start_ofs, "Should mark at least one bit");
6819 }
6821 #endif
6823 bool CMSMarkStack::allocate(size_t size) {
6824 // allocate a stack of the requisite depth
6825 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6826 size * sizeof(oop)));
6827 if (!rs.is_reserved()) {
6828 warning("CMSMarkStack allocation failure");
6829 return false;
6830 }
6831 if (!_virtual_space.initialize(rs, rs.size())) {
6832 warning("CMSMarkStack backing store failure");
6833 return false;
6834 }
6835 assert(_virtual_space.committed_size() == rs.size(),
6836 "didn't reserve backing store for all of CMS stack?");
6837 _base = (oop*)(_virtual_space.low());
6838 _index = 0;
6839 _capacity = size;
6840 NOT_PRODUCT(_max_depth = 0);
6841 return true;
6842 }
6844 // XXX FIX ME !!! In the MT case we come in here holding a
6845 // leaf lock. For printing we need to take a further lock
6846 // which has lower rank. We need to recallibrate the two
6847 // lock-ranks involved in order to be able to rpint the
6848 // messages below. (Or defer the printing to the caller.
6849 // For now we take the expedient path of just disabling the
6850 // messages for the problematic case.)
6851 void CMSMarkStack::expand() {
6852 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6853 if (_capacity == MarkStackSizeMax) {
6854 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6855 // We print a warning message only once per CMS cycle.
6856 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6857 }
6858 return;
6859 }
6860 // Double capacity if possible
6861 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6862 // Do not give up existing stack until we have managed to
6863 // get the double capacity that we desired.
6864 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6865 new_capacity * sizeof(oop)));
6866 if (rs.is_reserved()) {
6867 // Release the backing store associated with old stack
6868 _virtual_space.release();
6869 // Reinitialize virtual space for new stack
6870 if (!_virtual_space.initialize(rs, rs.size())) {
6871 fatal("Not enough swap for expanded marking stack");
6872 }
6873 _base = (oop*)(_virtual_space.low());
6874 _index = 0;
6875 _capacity = new_capacity;
6876 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6877 // Failed to double capacity, continue;
6878 // we print a detail message only once per CMS cycle.
6879 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6880 SIZE_FORMAT"K",
6881 _capacity / K, new_capacity / K);
6882 }
6883 }
6886 // Closures
6887 // XXX: there seems to be a lot of code duplication here;
6888 // should refactor and consolidate common code.
6890 // This closure is used to mark refs into the CMS generation in
6891 // the CMS bit map. Called at the first checkpoint. This closure
6892 // assumes that we do not need to re-mark dirty cards; if the CMS
6893 // generation on which this is used is not an oldest
6894 // generation then this will lose younger_gen cards!
6896 MarkRefsIntoClosure::MarkRefsIntoClosure(
6897 MemRegion span, CMSBitMap* bitMap):
6898 _span(span),
6899 _bitMap(bitMap)
6900 {
6901 assert(_ref_processor == NULL, "deliberately left NULL");
6902 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6903 }
6905 void MarkRefsIntoClosure::do_oop(oop obj) {
6906 // if p points into _span, then mark corresponding bit in _markBitMap
6907 assert(obj->is_oop(), "expected an oop");
6908 HeapWord* addr = (HeapWord*)obj;
6909 if (_span.contains(addr)) {
6910 // this should be made more efficient
6911 _bitMap->mark(addr);
6912 }
6913 }
6915 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6916 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6918 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6919 MemRegion span, CMSBitMap* bitMap):
6920 _span(span),
6921 _bitMap(bitMap)
6922 {
6923 assert(_ref_processor == NULL, "deliberately left NULL");
6924 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6925 }
6927 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6928 // if p points into _span, then mark corresponding bit in _markBitMap
6929 assert(obj->is_oop(), "expected an oop");
6930 HeapWord* addr = (HeapWord*)obj;
6931 if (_span.contains(addr)) {
6932 // this should be made more efficient
6933 _bitMap->par_mark(addr);
6934 }
6935 }
6937 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6938 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6940 // A variant of the above, used for CMS marking verification.
6941 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6942 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6943 _span(span),
6944 _verification_bm(verification_bm),
6945 _cms_bm(cms_bm)
6946 {
6947 assert(_ref_processor == NULL, "deliberately left NULL");
6948 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6949 }
6951 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6952 // if p points into _span, then mark corresponding bit in _markBitMap
6953 assert(obj->is_oop(), "expected an oop");
6954 HeapWord* addr = (HeapWord*)obj;
6955 if (_span.contains(addr)) {
6956 _verification_bm->mark(addr);
6957 if (!_cms_bm->isMarked(addr)) {
6958 oop(addr)->print();
6959 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6960 fatal("... aborting");
6961 }
6962 }
6963 }
6965 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6966 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6968 //////////////////////////////////////////////////
6969 // MarkRefsIntoAndScanClosure
6970 //////////////////////////////////////////////////
6972 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6973 ReferenceProcessor* rp,
6974 CMSBitMap* bit_map,
6975 CMSBitMap* mod_union_table,
6976 CMSMarkStack* mark_stack,
6977 CMSCollector* collector,
6978 bool should_yield,
6979 bool concurrent_precleaning):
6980 _collector(collector),
6981 _span(span),
6982 _bit_map(bit_map),
6983 _mark_stack(mark_stack),
6984 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6985 mark_stack, concurrent_precleaning),
6986 _yield(should_yield),
6987 _concurrent_precleaning(concurrent_precleaning),
6988 _freelistLock(NULL)
6989 {
6990 _ref_processor = rp;
6991 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6992 }
6994 // This closure is used to mark refs into the CMS generation at the
6995 // second (final) checkpoint, and to scan and transitively follow
6996 // the unmarked oops. It is also used during the concurrent precleaning
6997 // phase while scanning objects on dirty cards in the CMS generation.
6998 // The marks are made in the marking bit map and the marking stack is
6999 // used for keeping the (newly) grey objects during the scan.
7000 // The parallel version (Par_...) appears further below.
7001 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
7002 if (obj != NULL) {
7003 assert(obj->is_oop(), "expected an oop");
7004 HeapWord* addr = (HeapWord*)obj;
7005 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7006 assert(_collector->overflow_list_is_empty(),
7007 "overflow list should be empty");
7008 if (_span.contains(addr) &&
7009 !_bit_map->isMarked(addr)) {
7010 // mark bit map (object is now grey)
7011 _bit_map->mark(addr);
7012 // push on marking stack (stack should be empty), and drain the
7013 // stack by applying this closure to the oops in the oops popped
7014 // from the stack (i.e. blacken the grey objects)
7015 bool res = _mark_stack->push(obj);
7016 assert(res, "Should have space to push on empty stack");
7017 do {
7018 oop new_oop = _mark_stack->pop();
7019 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7020 assert(_bit_map->isMarked((HeapWord*)new_oop),
7021 "only grey objects on this stack");
7022 // iterate over the oops in this oop, marking and pushing
7023 // the ones in CMS heap (i.e. in _span).
7024 new_oop->oop_iterate(&_pushAndMarkClosure);
7025 // check if it's time to yield
7026 do_yield_check();
7027 } while (!_mark_stack->isEmpty() ||
7028 (!_concurrent_precleaning && take_from_overflow_list()));
7029 // if marking stack is empty, and we are not doing this
7030 // during precleaning, then check the overflow list
7031 }
7032 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7033 assert(_collector->overflow_list_is_empty(),
7034 "overflow list was drained above");
7035 // We could restore evacuated mark words, if any, used for
7036 // overflow list links here because the overflow list is
7037 // provably empty here. That would reduce the maximum
7038 // size requirements for preserved_{oop,mark}_stack.
7039 // But we'll just postpone it until we are all done
7040 // so we can just stream through.
7041 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
7042 _collector->restore_preserved_marks_if_any();
7043 assert(_collector->no_preserved_marks(), "No preserved marks");
7044 }
7045 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
7046 "All preserved marks should have been restored above");
7047 }
7048 }
7050 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
7051 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
7053 void MarkRefsIntoAndScanClosure::do_yield_work() {
7054 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7055 "CMS thread should hold CMS token");
7056 assert_lock_strong(_freelistLock);
7057 assert_lock_strong(_bit_map->lock());
7058 // relinquish the free_list_lock and bitMaplock()
7059 _bit_map->lock()->unlock();
7060 _freelistLock->unlock();
7061 ConcurrentMarkSweepThread::desynchronize(true);
7062 ConcurrentMarkSweepThread::acknowledge_yield_request();
7063 _collector->stopTimer();
7064 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7065 if (PrintCMSStatistics != 0) {
7066 _collector->incrementYields();
7067 }
7068 _collector->icms_wait();
7070 // See the comment in coordinator_yield()
7071 for (unsigned i = 0;
7072 i < CMSYieldSleepCount &&
7073 ConcurrentMarkSweepThread::should_yield() &&
7074 !CMSCollector::foregroundGCIsActive();
7075 ++i) {
7076 os::sleep(Thread::current(), 1, false);
7077 ConcurrentMarkSweepThread::acknowledge_yield_request();
7078 }
7080 ConcurrentMarkSweepThread::synchronize(true);
7081 _freelistLock->lock_without_safepoint_check();
7082 _bit_map->lock()->lock_without_safepoint_check();
7083 _collector->startTimer();
7084 }
7086 ///////////////////////////////////////////////////////////
7087 // Par_MarkRefsIntoAndScanClosure: a parallel version of
7088 // MarkRefsIntoAndScanClosure
7089 ///////////////////////////////////////////////////////////
7090 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
7091 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
7092 CMSBitMap* bit_map, OopTaskQueue* work_queue):
7093 _span(span),
7094 _bit_map(bit_map),
7095 _work_queue(work_queue),
7096 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
7097 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
7098 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
7099 {
7100 _ref_processor = rp;
7101 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7102 }
7104 // This closure is used to mark refs into the CMS generation at the
7105 // second (final) checkpoint, and to scan and transitively follow
7106 // the unmarked oops. The marks are made in the marking bit map and
7107 // the work_queue is used for keeping the (newly) grey objects during
7108 // the scan phase whence they are also available for stealing by parallel
7109 // threads. Since the marking bit map is shared, updates are
7110 // synchronized (via CAS).
7111 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
7112 if (obj != NULL) {
7113 // Ignore mark word because this could be an already marked oop
7114 // that may be chained at the end of the overflow list.
7115 assert(obj->is_oop(true), "expected an oop");
7116 HeapWord* addr = (HeapWord*)obj;
7117 if (_span.contains(addr) &&
7118 !_bit_map->isMarked(addr)) {
7119 // mark bit map (object will become grey):
7120 // It is possible for several threads to be
7121 // trying to "claim" this object concurrently;
7122 // the unique thread that succeeds in marking the
7123 // object first will do the subsequent push on
7124 // to the work queue (or overflow list).
7125 if (_bit_map->par_mark(addr)) {
7126 // push on work_queue (which may not be empty), and trim the
7127 // queue to an appropriate length by applying this closure to
7128 // the oops in the oops popped from the stack (i.e. blacken the
7129 // grey objects)
7130 bool res = _work_queue->push(obj);
7131 assert(res, "Low water mark should be less than capacity?");
7132 trim_queue(_low_water_mark);
7133 } // Else, another thread claimed the object
7134 }
7135 }
7136 }
7138 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7139 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7141 // This closure is used to rescan the marked objects on the dirty cards
7142 // in the mod union table and the card table proper.
7143 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
7144 oop p, MemRegion mr) {
7146 size_t size = 0;
7147 HeapWord* addr = (HeapWord*)p;
7148 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7149 assert(_span.contains(addr), "we are scanning the CMS generation");
7150 // check if it's time to yield
7151 if (do_yield_check()) {
7152 // We yielded for some foreground stop-world work,
7153 // and we have been asked to abort this ongoing preclean cycle.
7154 return 0;
7155 }
7156 if (_bitMap->isMarked(addr)) {
7157 // it's marked; is it potentially uninitialized?
7158 if (p->klass_or_null() != NULL) {
7159 // an initialized object; ignore mark word in verification below
7160 // since we are running concurrent with mutators
7161 assert(p->is_oop(true), "should be an oop");
7162 if (p->is_objArray()) {
7163 // objArrays are precisely marked; restrict scanning
7164 // to dirty cards only.
7165 size = CompactibleFreeListSpace::adjustObjectSize(
7166 p->oop_iterate(_scanningClosure, mr));
7167 } else {
7168 // A non-array may have been imprecisely marked; we need
7169 // to scan object in its entirety.
7170 size = CompactibleFreeListSpace::adjustObjectSize(
7171 p->oop_iterate(_scanningClosure));
7172 }
7173 #ifdef ASSERT
7174 size_t direct_size =
7175 CompactibleFreeListSpace::adjustObjectSize(p->size());
7176 assert(size == direct_size, "Inconsistency in size");
7177 assert(size >= 3, "Necessary for Printezis marks to work");
7178 if (!_bitMap->isMarked(addr+1)) {
7179 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
7180 } else {
7181 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
7182 assert(_bitMap->isMarked(addr+size-1),
7183 "inconsistent Printezis mark");
7184 }
7185 #endif // ASSERT
7186 } else {
7187 // an unitialized object
7188 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
7189 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7190 size = pointer_delta(nextOneAddr + 1, addr);
7191 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7192 "alignment problem");
7193 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
7194 // will dirty the card when the klass pointer is installed in the
7195 // object (signalling the completion of initialization).
7196 }
7197 } else {
7198 // Either a not yet marked object or an uninitialized object
7199 if (p->klass_or_null() == NULL) {
7200 // An uninitialized object, skip to the next card, since
7201 // we may not be able to read its P-bits yet.
7202 assert(size == 0, "Initial value");
7203 } else {
7204 // An object not (yet) reached by marking: we merely need to
7205 // compute its size so as to go look at the next block.
7206 assert(p->is_oop(true), "should be an oop");
7207 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
7208 }
7209 }
7210 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7211 return size;
7212 }
7214 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
7215 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7216 "CMS thread should hold CMS token");
7217 assert_lock_strong(_freelistLock);
7218 assert_lock_strong(_bitMap->lock());
7219 // relinquish the free_list_lock and bitMaplock()
7220 _bitMap->lock()->unlock();
7221 _freelistLock->unlock();
7222 ConcurrentMarkSweepThread::desynchronize(true);
7223 ConcurrentMarkSweepThread::acknowledge_yield_request();
7224 _collector->stopTimer();
7225 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7226 if (PrintCMSStatistics != 0) {
7227 _collector->incrementYields();
7228 }
7229 _collector->icms_wait();
7231 // See the comment in coordinator_yield()
7232 for (unsigned i = 0; i < CMSYieldSleepCount &&
7233 ConcurrentMarkSweepThread::should_yield() &&
7234 !CMSCollector::foregroundGCIsActive(); ++i) {
7235 os::sleep(Thread::current(), 1, false);
7236 ConcurrentMarkSweepThread::acknowledge_yield_request();
7237 }
7239 ConcurrentMarkSweepThread::synchronize(true);
7240 _freelistLock->lock_without_safepoint_check();
7241 _bitMap->lock()->lock_without_safepoint_check();
7242 _collector->startTimer();
7243 }
7246 //////////////////////////////////////////////////////////////////
7247 // SurvivorSpacePrecleanClosure
7248 //////////////////////////////////////////////////////////////////
7249 // This (single-threaded) closure is used to preclean the oops in
7250 // the survivor spaces.
7251 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
7253 HeapWord* addr = (HeapWord*)p;
7254 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7255 assert(!_span.contains(addr), "we are scanning the survivor spaces");
7256 assert(p->klass_or_null() != NULL, "object should be initializd");
7257 // an initialized object; ignore mark word in verification below
7258 // since we are running concurrent with mutators
7259 assert(p->is_oop(true), "should be an oop");
7260 // Note that we do not yield while we iterate over
7261 // the interior oops of p, pushing the relevant ones
7262 // on our marking stack.
7263 size_t size = p->oop_iterate(_scanning_closure);
7264 do_yield_check();
7265 // Observe that below, we do not abandon the preclean
7266 // phase as soon as we should; rather we empty the
7267 // marking stack before returning. This is to satisfy
7268 // some existing assertions. In general, it may be a
7269 // good idea to abort immediately and complete the marking
7270 // from the grey objects at a later time.
7271 while (!_mark_stack->isEmpty()) {
7272 oop new_oop = _mark_stack->pop();
7273 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7274 assert(_bit_map->isMarked((HeapWord*)new_oop),
7275 "only grey objects on this stack");
7276 // iterate over the oops in this oop, marking and pushing
7277 // the ones in CMS heap (i.e. in _span).
7278 new_oop->oop_iterate(_scanning_closure);
7279 // check if it's time to yield
7280 do_yield_check();
7281 }
7282 unsigned int after_count =
7283 GenCollectedHeap::heap()->total_collections();
7284 bool abort = (_before_count != after_count) ||
7285 _collector->should_abort_preclean();
7286 return abort ? 0 : size;
7287 }
7289 void SurvivorSpacePrecleanClosure::do_yield_work() {
7290 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7291 "CMS thread should hold CMS token");
7292 assert_lock_strong(_bit_map->lock());
7293 // Relinquish the bit map lock
7294 _bit_map->lock()->unlock();
7295 ConcurrentMarkSweepThread::desynchronize(true);
7296 ConcurrentMarkSweepThread::acknowledge_yield_request();
7297 _collector->stopTimer();
7298 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7299 if (PrintCMSStatistics != 0) {
7300 _collector->incrementYields();
7301 }
7302 _collector->icms_wait();
7304 // See the comment in coordinator_yield()
7305 for (unsigned i = 0; i < CMSYieldSleepCount &&
7306 ConcurrentMarkSweepThread::should_yield() &&
7307 !CMSCollector::foregroundGCIsActive(); ++i) {
7308 os::sleep(Thread::current(), 1, false);
7309 ConcurrentMarkSweepThread::acknowledge_yield_request();
7310 }
7312 ConcurrentMarkSweepThread::synchronize(true);
7313 _bit_map->lock()->lock_without_safepoint_check();
7314 _collector->startTimer();
7315 }
7317 // This closure is used to rescan the marked objects on the dirty cards
7318 // in the mod union table and the card table proper. In the parallel
7319 // case, although the bitMap is shared, we do a single read so the
7320 // isMarked() query is "safe".
7321 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7322 // Ignore mark word because we are running concurrent with mutators
7323 assert(p->is_oop_or_null(true), "expected an oop or null");
7324 HeapWord* addr = (HeapWord*)p;
7325 assert(_span.contains(addr), "we are scanning the CMS generation");
7326 bool is_obj_array = false;
7327 #ifdef ASSERT
7328 if (!_parallel) {
7329 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7330 assert(_collector->overflow_list_is_empty(),
7331 "overflow list should be empty");
7333 }
7334 #endif // ASSERT
7335 if (_bit_map->isMarked(addr)) {
7336 // Obj arrays are precisely marked, non-arrays are not;
7337 // so we scan objArrays precisely and non-arrays in their
7338 // entirety.
7339 if (p->is_objArray()) {
7340 is_obj_array = true;
7341 if (_parallel) {
7342 p->oop_iterate(_par_scan_closure, mr);
7343 } else {
7344 p->oop_iterate(_scan_closure, mr);
7345 }
7346 } else {
7347 if (_parallel) {
7348 p->oop_iterate(_par_scan_closure);
7349 } else {
7350 p->oop_iterate(_scan_closure);
7351 }
7352 }
7353 }
7354 #ifdef ASSERT
7355 if (!_parallel) {
7356 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7357 assert(_collector->overflow_list_is_empty(),
7358 "overflow list should be empty");
7360 }
7361 #endif // ASSERT
7362 return is_obj_array;
7363 }
7365 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7366 MemRegion span,
7367 CMSBitMap* bitMap, CMSMarkStack* markStack,
7368 bool should_yield, bool verifying):
7369 _collector(collector),
7370 _span(span),
7371 _bitMap(bitMap),
7372 _mut(&collector->_modUnionTable),
7373 _markStack(markStack),
7374 _yield(should_yield),
7375 _skipBits(0)
7376 {
7377 assert(_markStack->isEmpty(), "stack should be empty");
7378 _finger = _bitMap->startWord();
7379 _threshold = _finger;
7380 assert(_collector->_restart_addr == NULL, "Sanity check");
7381 assert(_span.contains(_finger), "Out of bounds _finger?");
7382 DEBUG_ONLY(_verifying = verifying;)
7383 }
7385 void MarkFromRootsClosure::reset(HeapWord* addr) {
7386 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7387 assert(_span.contains(addr), "Out of bounds _finger?");
7388 _finger = addr;
7389 _threshold = (HeapWord*)round_to(
7390 (intptr_t)_finger, CardTableModRefBS::card_size);
7391 }
7393 // Should revisit to see if this should be restructured for
7394 // greater efficiency.
7395 bool MarkFromRootsClosure::do_bit(size_t offset) {
7396 if (_skipBits > 0) {
7397 _skipBits--;
7398 return true;
7399 }
7400 // convert offset into a HeapWord*
7401 HeapWord* addr = _bitMap->startWord() + offset;
7402 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7403 "address out of range");
7404 assert(_bitMap->isMarked(addr), "tautology");
7405 if (_bitMap->isMarked(addr+1)) {
7406 // this is an allocated but not yet initialized object
7407 assert(_skipBits == 0, "tautology");
7408 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7409 oop p = oop(addr);
7410 if (p->klass_or_null() == NULL) {
7411 DEBUG_ONLY(if (!_verifying) {)
7412 // We re-dirty the cards on which this object lies and increase
7413 // the _threshold so that we'll come back to scan this object
7414 // during the preclean or remark phase. (CMSCleanOnEnter)
7415 if (CMSCleanOnEnter) {
7416 size_t sz = _collector->block_size_using_printezis_bits(addr);
7417 HeapWord* end_card_addr = (HeapWord*)round_to(
7418 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7419 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7420 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7421 // Bump _threshold to end_card_addr; note that
7422 // _threshold cannot possibly exceed end_card_addr, anyhow.
7423 // This prevents future clearing of the card as the scan proceeds
7424 // to the right.
7425 assert(_threshold <= end_card_addr,
7426 "Because we are just scanning into this object");
7427 if (_threshold < end_card_addr) {
7428 _threshold = end_card_addr;
7429 }
7430 if (p->klass_or_null() != NULL) {
7431 // Redirty the range of cards...
7432 _mut->mark_range(redirty_range);
7433 } // ...else the setting of klass will dirty the card anyway.
7434 }
7435 DEBUG_ONLY(})
7436 return true;
7437 }
7438 }
7439 scanOopsInOop(addr);
7440 return true;
7441 }
7443 // We take a break if we've been at this for a while,
7444 // so as to avoid monopolizing the locks involved.
7445 void MarkFromRootsClosure::do_yield_work() {
7446 // First give up the locks, then yield, then re-lock
7447 // We should probably use a constructor/destructor idiom to
7448 // do this unlock/lock or modify the MutexUnlocker class to
7449 // serve our purpose. XXX
7450 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7451 "CMS thread should hold CMS token");
7452 assert_lock_strong(_bitMap->lock());
7453 _bitMap->lock()->unlock();
7454 ConcurrentMarkSweepThread::desynchronize(true);
7455 ConcurrentMarkSweepThread::acknowledge_yield_request();
7456 _collector->stopTimer();
7457 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7458 if (PrintCMSStatistics != 0) {
7459 _collector->incrementYields();
7460 }
7461 _collector->icms_wait();
7463 // See the comment in coordinator_yield()
7464 for (unsigned i = 0; i < CMSYieldSleepCount &&
7465 ConcurrentMarkSweepThread::should_yield() &&
7466 !CMSCollector::foregroundGCIsActive(); ++i) {
7467 os::sleep(Thread::current(), 1, false);
7468 ConcurrentMarkSweepThread::acknowledge_yield_request();
7469 }
7471 ConcurrentMarkSweepThread::synchronize(true);
7472 _bitMap->lock()->lock_without_safepoint_check();
7473 _collector->startTimer();
7474 }
7476 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7477 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7478 assert(_markStack->isEmpty(),
7479 "should drain stack to limit stack usage");
7480 // convert ptr to an oop preparatory to scanning
7481 oop obj = oop(ptr);
7482 // Ignore mark word in verification below, since we
7483 // may be running concurrent with mutators.
7484 assert(obj->is_oop(true), "should be an oop");
7485 assert(_finger <= ptr, "_finger runneth ahead");
7486 // advance the finger to right end of this object
7487 _finger = ptr + obj->size();
7488 assert(_finger > ptr, "we just incremented it above");
7489 // On large heaps, it may take us some time to get through
7490 // the marking phase (especially if running iCMS). During
7491 // this time it's possible that a lot of mutations have
7492 // accumulated in the card table and the mod union table --
7493 // these mutation records are redundant until we have
7494 // actually traced into the corresponding card.
7495 // Here, we check whether advancing the finger would make
7496 // us cross into a new card, and if so clear corresponding
7497 // cards in the MUT (preclean them in the card-table in the
7498 // future).
7500 DEBUG_ONLY(if (!_verifying) {)
7501 // The clean-on-enter optimization is disabled by default,
7502 // until we fix 6178663.
7503 if (CMSCleanOnEnter && (_finger > _threshold)) {
7504 // [_threshold, _finger) represents the interval
7505 // of cards to be cleared in MUT (or precleaned in card table).
7506 // The set of cards to be cleared is all those that overlap
7507 // with the interval [_threshold, _finger); note that
7508 // _threshold is always kept card-aligned but _finger isn't
7509 // always card-aligned.
7510 HeapWord* old_threshold = _threshold;
7511 assert(old_threshold == (HeapWord*)round_to(
7512 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7513 "_threshold should always be card-aligned");
7514 _threshold = (HeapWord*)round_to(
7515 (intptr_t)_finger, CardTableModRefBS::card_size);
7516 MemRegion mr(old_threshold, _threshold);
7517 assert(!mr.is_empty(), "Control point invariant");
7518 assert(_span.contains(mr), "Should clear within span");
7519 _mut->clear_range(mr);
7520 }
7521 DEBUG_ONLY(})
7522 // Note: the finger doesn't advance while we drain
7523 // the stack below.
7524 PushOrMarkClosure pushOrMarkClosure(_collector,
7525 _span, _bitMap, _markStack,
7526 _finger, this);
7527 bool res = _markStack->push(obj);
7528 assert(res, "Empty non-zero size stack should have space for single push");
7529 while (!_markStack->isEmpty()) {
7530 oop new_oop = _markStack->pop();
7531 // Skip verifying header mark word below because we are
7532 // running concurrent with mutators.
7533 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7534 // now scan this oop's oops
7535 new_oop->oop_iterate(&pushOrMarkClosure);
7536 do_yield_check();
7537 }
7538 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7539 }
7541 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7542 CMSCollector* collector, MemRegion span,
7543 CMSBitMap* bit_map,
7544 OopTaskQueue* work_queue,
7545 CMSMarkStack* overflow_stack,
7546 bool should_yield):
7547 _collector(collector),
7548 _whole_span(collector->_span),
7549 _span(span),
7550 _bit_map(bit_map),
7551 _mut(&collector->_modUnionTable),
7552 _work_queue(work_queue),
7553 _overflow_stack(overflow_stack),
7554 _yield(should_yield),
7555 _skip_bits(0),
7556 _task(task)
7557 {
7558 assert(_work_queue->size() == 0, "work_queue should be empty");
7559 _finger = span.start();
7560 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7561 assert(_span.contains(_finger), "Out of bounds _finger?");
7562 }
7564 // Should revisit to see if this should be restructured for
7565 // greater efficiency.
7566 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7567 if (_skip_bits > 0) {
7568 _skip_bits--;
7569 return true;
7570 }
7571 // convert offset into a HeapWord*
7572 HeapWord* addr = _bit_map->startWord() + offset;
7573 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7574 "address out of range");
7575 assert(_bit_map->isMarked(addr), "tautology");
7576 if (_bit_map->isMarked(addr+1)) {
7577 // this is an allocated object that might not yet be initialized
7578 assert(_skip_bits == 0, "tautology");
7579 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7580 oop p = oop(addr);
7581 if (p->klass_or_null() == NULL) {
7582 // in the case of Clean-on-Enter optimization, redirty card
7583 // and avoid clearing card by increasing the threshold.
7584 return true;
7585 }
7586 }
7587 scan_oops_in_oop(addr);
7588 return true;
7589 }
7591 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7592 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7593 // Should we assert that our work queue is empty or
7594 // below some drain limit?
7595 assert(_work_queue->size() == 0,
7596 "should drain stack to limit stack usage");
7597 // convert ptr to an oop preparatory to scanning
7598 oop obj = oop(ptr);
7599 // Ignore mark word in verification below, since we
7600 // may be running concurrent with mutators.
7601 assert(obj->is_oop(true), "should be an oop");
7602 assert(_finger <= ptr, "_finger runneth ahead");
7603 // advance the finger to right end of this object
7604 _finger = ptr + obj->size();
7605 assert(_finger > ptr, "we just incremented it above");
7606 // On large heaps, it may take us some time to get through
7607 // the marking phase (especially if running iCMS). During
7608 // this time it's possible that a lot of mutations have
7609 // accumulated in the card table and the mod union table --
7610 // these mutation records are redundant until we have
7611 // actually traced into the corresponding card.
7612 // Here, we check whether advancing the finger would make
7613 // us cross into a new card, and if so clear corresponding
7614 // cards in the MUT (preclean them in the card-table in the
7615 // future).
7617 // The clean-on-enter optimization is disabled by default,
7618 // until we fix 6178663.
7619 if (CMSCleanOnEnter && (_finger > _threshold)) {
7620 // [_threshold, _finger) represents the interval
7621 // of cards to be cleared in MUT (or precleaned in card table).
7622 // The set of cards to be cleared is all those that overlap
7623 // with the interval [_threshold, _finger); note that
7624 // _threshold is always kept card-aligned but _finger isn't
7625 // always card-aligned.
7626 HeapWord* old_threshold = _threshold;
7627 assert(old_threshold == (HeapWord*)round_to(
7628 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7629 "_threshold should always be card-aligned");
7630 _threshold = (HeapWord*)round_to(
7631 (intptr_t)_finger, CardTableModRefBS::card_size);
7632 MemRegion mr(old_threshold, _threshold);
7633 assert(!mr.is_empty(), "Control point invariant");
7634 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7635 _mut->clear_range(mr);
7636 }
7638 // Note: the local finger doesn't advance while we drain
7639 // the stack below, but the global finger sure can and will.
7640 HeapWord** gfa = _task->global_finger_addr();
7641 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7642 _span, _bit_map,
7643 _work_queue,
7644 _overflow_stack,
7645 _finger,
7646 gfa, this);
7647 bool res = _work_queue->push(obj); // overflow could occur here
7648 assert(res, "Will hold once we use workqueues");
7649 while (true) {
7650 oop new_oop;
7651 if (!_work_queue->pop_local(new_oop)) {
7652 // We emptied our work_queue; check if there's stuff that can
7653 // be gotten from the overflow stack.
7654 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7655 _overflow_stack, _work_queue)) {
7656 do_yield_check();
7657 continue;
7658 } else { // done
7659 break;
7660 }
7661 }
7662 // Skip verifying header mark word below because we are
7663 // running concurrent with mutators.
7664 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7665 // now scan this oop's oops
7666 new_oop->oop_iterate(&pushOrMarkClosure);
7667 do_yield_check();
7668 }
7669 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7670 }
7672 // Yield in response to a request from VM Thread or
7673 // from mutators.
7674 void Par_MarkFromRootsClosure::do_yield_work() {
7675 assert(_task != NULL, "sanity");
7676 _task->yield();
7677 }
7679 // A variant of the above used for verifying CMS marking work.
7680 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7681 MemRegion span,
7682 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7683 CMSMarkStack* mark_stack):
7684 _collector(collector),
7685 _span(span),
7686 _verification_bm(verification_bm),
7687 _cms_bm(cms_bm),
7688 _mark_stack(mark_stack),
7689 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7690 mark_stack)
7691 {
7692 assert(_mark_stack->isEmpty(), "stack should be empty");
7693 _finger = _verification_bm->startWord();
7694 assert(_collector->_restart_addr == NULL, "Sanity check");
7695 assert(_span.contains(_finger), "Out of bounds _finger?");
7696 }
7698 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7699 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7700 assert(_span.contains(addr), "Out of bounds _finger?");
7701 _finger = addr;
7702 }
7704 // Should revisit to see if this should be restructured for
7705 // greater efficiency.
7706 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7707 // convert offset into a HeapWord*
7708 HeapWord* addr = _verification_bm->startWord() + offset;
7709 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7710 "address out of range");
7711 assert(_verification_bm->isMarked(addr), "tautology");
7712 assert(_cms_bm->isMarked(addr), "tautology");
7714 assert(_mark_stack->isEmpty(),
7715 "should drain stack to limit stack usage");
7716 // convert addr to an oop preparatory to scanning
7717 oop obj = oop(addr);
7718 assert(obj->is_oop(), "should be an oop");
7719 assert(_finger <= addr, "_finger runneth ahead");
7720 // advance the finger to right end of this object
7721 _finger = addr + obj->size();
7722 assert(_finger > addr, "we just incremented it above");
7723 // Note: the finger doesn't advance while we drain
7724 // the stack below.
7725 bool res = _mark_stack->push(obj);
7726 assert(res, "Empty non-zero size stack should have space for single push");
7727 while (!_mark_stack->isEmpty()) {
7728 oop new_oop = _mark_stack->pop();
7729 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7730 // now scan this oop's oops
7731 new_oop->oop_iterate(&_pam_verify_closure);
7732 }
7733 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7734 return true;
7735 }
7737 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7738 CMSCollector* collector, MemRegion span,
7739 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7740 CMSMarkStack* mark_stack):
7741 CMSOopClosure(collector->ref_processor()),
7742 _collector(collector),
7743 _span(span),
7744 _verification_bm(verification_bm),
7745 _cms_bm(cms_bm),
7746 _mark_stack(mark_stack)
7747 { }
7749 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7750 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7752 // Upon stack overflow, we discard (part of) the stack,
7753 // remembering the least address amongst those discarded
7754 // in CMSCollector's _restart_address.
7755 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7756 // Remember the least grey address discarded
7757 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7758 _collector->lower_restart_addr(ra);
7759 _mark_stack->reset(); // discard stack contents
7760 _mark_stack->expand(); // expand the stack if possible
7761 }
7763 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7764 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7765 HeapWord* addr = (HeapWord*)obj;
7766 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7767 // Oop lies in _span and isn't yet grey or black
7768 _verification_bm->mark(addr); // now grey
7769 if (!_cms_bm->isMarked(addr)) {
7770 oop(addr)->print();
7771 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7772 addr);
7773 fatal("... aborting");
7774 }
7776 if (!_mark_stack->push(obj)) { // stack overflow
7777 if (PrintCMSStatistics != 0) {
7778 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7779 SIZE_FORMAT, _mark_stack->capacity());
7780 }
7781 assert(_mark_stack->isFull(), "Else push should have succeeded");
7782 handle_stack_overflow(addr);
7783 }
7784 // anything including and to the right of _finger
7785 // will be scanned as we iterate over the remainder of the
7786 // bit map
7787 }
7788 }
7790 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7791 MemRegion span,
7792 CMSBitMap* bitMap, CMSMarkStack* markStack,
7793 HeapWord* finger, MarkFromRootsClosure* parent) :
7794 CMSOopClosure(collector->ref_processor()),
7795 _collector(collector),
7796 _span(span),
7797 _bitMap(bitMap),
7798 _markStack(markStack),
7799 _finger(finger),
7800 _parent(parent)
7801 { }
7803 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7804 MemRegion span,
7805 CMSBitMap* bit_map,
7806 OopTaskQueue* work_queue,
7807 CMSMarkStack* overflow_stack,
7808 HeapWord* finger,
7809 HeapWord** global_finger_addr,
7810 Par_MarkFromRootsClosure* parent) :
7811 CMSOopClosure(collector->ref_processor()),
7812 _collector(collector),
7813 _whole_span(collector->_span),
7814 _span(span),
7815 _bit_map(bit_map),
7816 _work_queue(work_queue),
7817 _overflow_stack(overflow_stack),
7818 _finger(finger),
7819 _global_finger_addr(global_finger_addr),
7820 _parent(parent)
7821 { }
7823 // Assumes thread-safe access by callers, who are
7824 // responsible for mutual exclusion.
7825 void CMSCollector::lower_restart_addr(HeapWord* low) {
7826 assert(_span.contains(low), "Out of bounds addr");
7827 if (_restart_addr == NULL) {
7828 _restart_addr = low;
7829 } else {
7830 _restart_addr = MIN2(_restart_addr, low);
7831 }
7832 }
7834 // Upon stack overflow, we discard (part of) the stack,
7835 // remembering the least address amongst those discarded
7836 // in CMSCollector's _restart_address.
7837 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7838 // Remember the least grey address discarded
7839 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7840 _collector->lower_restart_addr(ra);
7841 _markStack->reset(); // discard stack contents
7842 _markStack->expand(); // expand the stack if possible
7843 }
7845 // Upon stack overflow, we discard (part of) the stack,
7846 // remembering the least address amongst those discarded
7847 // in CMSCollector's _restart_address.
7848 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7849 // We need to do this under a mutex to prevent other
7850 // workers from interfering with the work done below.
7851 MutexLockerEx ml(_overflow_stack->par_lock(),
7852 Mutex::_no_safepoint_check_flag);
7853 // Remember the least grey address discarded
7854 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7855 _collector->lower_restart_addr(ra);
7856 _overflow_stack->reset(); // discard stack contents
7857 _overflow_stack->expand(); // expand the stack if possible
7858 }
7860 void CMKlassClosure::do_klass(Klass* k) {
7861 assert(_oop_closure != NULL, "Not initialized?");
7862 k->oops_do(_oop_closure);
7863 }
7865 void PushOrMarkClosure::do_oop(oop obj) {
7866 // Ignore mark word because we are running concurrent with mutators.
7867 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7868 HeapWord* addr = (HeapWord*)obj;
7869 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7870 // Oop lies in _span and isn't yet grey or black
7871 _bitMap->mark(addr); // now grey
7872 if (addr < _finger) {
7873 // the bit map iteration has already either passed, or
7874 // sampled, this bit in the bit map; we'll need to
7875 // use the marking stack to scan this oop's oops.
7876 bool simulate_overflow = false;
7877 NOT_PRODUCT(
7878 if (CMSMarkStackOverflowALot &&
7879 _collector->simulate_overflow()) {
7880 // simulate a stack overflow
7881 simulate_overflow = true;
7882 }
7883 )
7884 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7885 if (PrintCMSStatistics != 0) {
7886 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7887 SIZE_FORMAT, _markStack->capacity());
7888 }
7889 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7890 handle_stack_overflow(addr);
7891 }
7892 }
7893 // anything including and to the right of _finger
7894 // will be scanned as we iterate over the remainder of the
7895 // bit map
7896 do_yield_check();
7897 }
7898 }
7900 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7901 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7903 void Par_PushOrMarkClosure::do_oop(oop obj) {
7904 // Ignore mark word because we are running concurrent with mutators.
7905 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7906 HeapWord* addr = (HeapWord*)obj;
7907 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7908 // Oop lies in _span and isn't yet grey or black
7909 // We read the global_finger (volatile read) strictly after marking oop
7910 bool res = _bit_map->par_mark(addr); // now grey
7911 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7912 // Should we push this marked oop on our stack?
7913 // -- if someone else marked it, nothing to do
7914 // -- if target oop is above global finger nothing to do
7915 // -- if target oop is in chunk and above local finger
7916 // then nothing to do
7917 // -- else push on work queue
7918 if ( !res // someone else marked it, they will deal with it
7919 || (addr >= *gfa) // will be scanned in a later task
7920 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7921 return;
7922 }
7923 // the bit map iteration has already either passed, or
7924 // sampled, this bit in the bit map; we'll need to
7925 // use the marking stack to scan this oop's oops.
7926 bool simulate_overflow = false;
7927 NOT_PRODUCT(
7928 if (CMSMarkStackOverflowALot &&
7929 _collector->simulate_overflow()) {
7930 // simulate a stack overflow
7931 simulate_overflow = true;
7932 }
7933 )
7934 if (simulate_overflow ||
7935 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7936 // stack overflow
7937 if (PrintCMSStatistics != 0) {
7938 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7939 SIZE_FORMAT, _overflow_stack->capacity());
7940 }
7941 // We cannot assert that the overflow stack is full because
7942 // it may have been emptied since.
7943 assert(simulate_overflow ||
7944 _work_queue->size() == _work_queue->max_elems(),
7945 "Else push should have succeeded");
7946 handle_stack_overflow(addr);
7947 }
7948 do_yield_check();
7949 }
7950 }
7952 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7953 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7955 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7956 MemRegion span,
7957 ReferenceProcessor* rp,
7958 CMSBitMap* bit_map,
7959 CMSBitMap* mod_union_table,
7960 CMSMarkStack* mark_stack,
7961 bool concurrent_precleaning):
7962 CMSOopClosure(rp),
7963 _collector(collector),
7964 _span(span),
7965 _bit_map(bit_map),
7966 _mod_union_table(mod_union_table),
7967 _mark_stack(mark_stack),
7968 _concurrent_precleaning(concurrent_precleaning)
7969 {
7970 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7971 }
7973 // Grey object rescan during pre-cleaning and second checkpoint phases --
7974 // the non-parallel version (the parallel version appears further below.)
7975 void PushAndMarkClosure::do_oop(oop obj) {
7976 // Ignore mark word verification. If during concurrent precleaning,
7977 // the object monitor may be locked. If during the checkpoint
7978 // phases, the object may already have been reached by a different
7979 // path and may be at the end of the global overflow list (so
7980 // the mark word may be NULL).
7981 assert(obj->is_oop_or_null(true /* ignore mark word */),
7982 "expected an oop or NULL");
7983 HeapWord* addr = (HeapWord*)obj;
7984 // Check if oop points into the CMS generation
7985 // and is not marked
7986 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7987 // a white object ...
7988 _bit_map->mark(addr); // ... now grey
7989 // push on the marking stack (grey set)
7990 bool simulate_overflow = false;
7991 NOT_PRODUCT(
7992 if (CMSMarkStackOverflowALot &&
7993 _collector->simulate_overflow()) {
7994 // simulate a stack overflow
7995 simulate_overflow = true;
7996 }
7997 )
7998 if (simulate_overflow || !_mark_stack->push(obj)) {
7999 if (_concurrent_precleaning) {
8000 // During precleaning we can just dirty the appropriate card(s)
8001 // in the mod union table, thus ensuring that the object remains
8002 // in the grey set and continue. In the case of object arrays
8003 // we need to dirty all of the cards that the object spans,
8004 // since the rescan of object arrays will be limited to the
8005 // dirty cards.
8006 // Note that no one can be intefering with us in this action
8007 // of dirtying the mod union table, so no locking or atomics
8008 // are required.
8009 if (obj->is_objArray()) {
8010 size_t sz = obj->size();
8011 HeapWord* end_card_addr = (HeapWord*)round_to(
8012 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
8013 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8014 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8015 _mod_union_table->mark_range(redirty_range);
8016 } else {
8017 _mod_union_table->mark(addr);
8018 }
8019 _collector->_ser_pmc_preclean_ovflw++;
8020 } else {
8021 // During the remark phase, we need to remember this oop
8022 // in the overflow list.
8023 _collector->push_on_overflow_list(obj);
8024 _collector->_ser_pmc_remark_ovflw++;
8025 }
8026 }
8027 }
8028 }
8030 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
8031 MemRegion span,
8032 ReferenceProcessor* rp,
8033 CMSBitMap* bit_map,
8034 OopTaskQueue* work_queue):
8035 CMSOopClosure(rp),
8036 _collector(collector),
8037 _span(span),
8038 _bit_map(bit_map),
8039 _work_queue(work_queue)
8040 {
8041 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
8042 }
8044 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
8045 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
8047 // Grey object rescan during second checkpoint phase --
8048 // the parallel version.
8049 void Par_PushAndMarkClosure::do_oop(oop obj) {
8050 // In the assert below, we ignore the mark word because
8051 // this oop may point to an already visited object that is
8052 // on the overflow stack (in which case the mark word has
8053 // been hijacked for chaining into the overflow stack --
8054 // if this is the last object in the overflow stack then
8055 // its mark word will be NULL). Because this object may
8056 // have been subsequently popped off the global overflow
8057 // stack, and the mark word possibly restored to the prototypical
8058 // value, by the time we get to examined this failing assert in
8059 // the debugger, is_oop_or_null(false) may subsequently start
8060 // to hold.
8061 assert(obj->is_oop_or_null(true),
8062 "expected an oop or NULL");
8063 HeapWord* addr = (HeapWord*)obj;
8064 // Check if oop points into the CMS generation
8065 // and is not marked
8066 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
8067 // a white object ...
8068 // If we manage to "claim" the object, by being the
8069 // first thread to mark it, then we push it on our
8070 // marking stack
8071 if (_bit_map->par_mark(addr)) { // ... now grey
8072 // push on work queue (grey set)
8073 bool simulate_overflow = false;
8074 NOT_PRODUCT(
8075 if (CMSMarkStackOverflowALot &&
8076 _collector->par_simulate_overflow()) {
8077 // simulate a stack overflow
8078 simulate_overflow = true;
8079 }
8080 )
8081 if (simulate_overflow || !_work_queue->push(obj)) {
8082 _collector->par_push_on_overflow_list(obj);
8083 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
8084 }
8085 } // Else, some other thread got there first
8086 }
8087 }
8089 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
8090 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
8092 void CMSPrecleanRefsYieldClosure::do_yield_work() {
8093 Mutex* bml = _collector->bitMapLock();
8094 assert_lock_strong(bml);
8095 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8096 "CMS thread should hold CMS token");
8098 bml->unlock();
8099 ConcurrentMarkSweepThread::desynchronize(true);
8101 ConcurrentMarkSweepThread::acknowledge_yield_request();
8103 _collector->stopTimer();
8104 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8105 if (PrintCMSStatistics != 0) {
8106 _collector->incrementYields();
8107 }
8108 _collector->icms_wait();
8110 // See the comment in coordinator_yield()
8111 for (unsigned i = 0; i < CMSYieldSleepCount &&
8112 ConcurrentMarkSweepThread::should_yield() &&
8113 !CMSCollector::foregroundGCIsActive(); ++i) {
8114 os::sleep(Thread::current(), 1, false);
8115 ConcurrentMarkSweepThread::acknowledge_yield_request();
8116 }
8118 ConcurrentMarkSweepThread::synchronize(true);
8119 bml->lock();
8121 _collector->startTimer();
8122 }
8124 bool CMSPrecleanRefsYieldClosure::should_return() {
8125 if (ConcurrentMarkSweepThread::should_yield()) {
8126 do_yield_work();
8127 }
8128 return _collector->foregroundGCIsActive();
8129 }
8131 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
8132 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
8133 "mr should be aligned to start at a card boundary");
8134 // We'd like to assert:
8135 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
8136 // "mr should be a range of cards");
8137 // However, that would be too strong in one case -- the last
8138 // partition ends at _unallocated_block which, in general, can be
8139 // an arbitrary boundary, not necessarily card aligned.
8140 if (PrintCMSStatistics != 0) {
8141 _num_dirty_cards +=
8142 mr.word_size()/CardTableModRefBS::card_size_in_words;
8143 }
8144 _space->object_iterate_mem(mr, &_scan_cl);
8145 }
8147 SweepClosure::SweepClosure(CMSCollector* collector,
8148 ConcurrentMarkSweepGeneration* g,
8149 CMSBitMap* bitMap, bool should_yield) :
8150 _collector(collector),
8151 _g(g),
8152 _sp(g->cmsSpace()),
8153 _limit(_sp->sweep_limit()),
8154 _freelistLock(_sp->freelistLock()),
8155 _bitMap(bitMap),
8156 _yield(should_yield),
8157 _inFreeRange(false), // No free range at beginning of sweep
8158 _freeRangeInFreeLists(false), // No free range at beginning of sweep
8159 _lastFreeRangeCoalesced(false),
8160 _freeFinger(g->used_region().start())
8161 {
8162 NOT_PRODUCT(
8163 _numObjectsFreed = 0;
8164 _numWordsFreed = 0;
8165 _numObjectsLive = 0;
8166 _numWordsLive = 0;
8167 _numObjectsAlreadyFree = 0;
8168 _numWordsAlreadyFree = 0;
8169 _last_fc = NULL;
8171 _sp->initializeIndexedFreeListArrayReturnedBytes();
8172 _sp->dictionary()->initialize_dict_returned_bytes();
8173 )
8174 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8175 "sweep _limit out of bounds");
8176 if (CMSTraceSweeper) {
8177 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
8178 _limit);
8179 }
8180 }
8182 void SweepClosure::print_on(outputStream* st) const {
8183 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
8184 _sp->bottom(), _sp->end());
8185 tty->print_cr("_limit = " PTR_FORMAT, _limit);
8186 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
8187 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
8188 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
8189 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
8190 }
8192 #ifndef PRODUCT
8193 // Assertion checking only: no useful work in product mode --
8194 // however, if any of the flags below become product flags,
8195 // you may need to review this code to see if it needs to be
8196 // enabled in product mode.
8197 SweepClosure::~SweepClosure() {
8198 assert_lock_strong(_freelistLock);
8199 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8200 "sweep _limit out of bounds");
8201 if (inFreeRange()) {
8202 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
8203 print();
8204 ShouldNotReachHere();
8205 }
8206 if (Verbose && PrintGC) {
8207 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
8208 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
8209 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
8210 SIZE_FORMAT" bytes "
8211 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
8212 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
8213 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
8214 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
8215 * sizeof(HeapWord);
8216 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
8218 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
8219 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
8220 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
8221 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
8222 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
8223 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
8224 indexListReturnedBytes);
8225 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
8226 dict_returned_bytes);
8227 }
8228 }
8229 if (CMSTraceSweeper) {
8230 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
8231 _limit);
8232 }
8233 }
8234 #endif // PRODUCT
8236 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
8237 bool freeRangeInFreeLists) {
8238 if (CMSTraceSweeper) {
8239 gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n",
8240 freeFinger, freeRangeInFreeLists);
8241 }
8242 assert(!inFreeRange(), "Trampling existing free range");
8243 set_inFreeRange(true);
8244 set_lastFreeRangeCoalesced(false);
8246 set_freeFinger(freeFinger);
8247 set_freeRangeInFreeLists(freeRangeInFreeLists);
8248 if (CMSTestInFreeList) {
8249 if (freeRangeInFreeLists) {
8250 FreeChunk* fc = (FreeChunk*) freeFinger;
8251 assert(fc->is_free(), "A chunk on the free list should be free.");
8252 assert(fc->size() > 0, "Free range should have a size");
8253 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
8254 }
8255 }
8256 }
8258 // Note that the sweeper runs concurrently with mutators. Thus,
8259 // it is possible for direct allocation in this generation to happen
8260 // in the middle of the sweep. Note that the sweeper also coalesces
8261 // contiguous free blocks. Thus, unless the sweeper and the allocator
8262 // synchronize appropriately freshly allocated blocks may get swept up.
8263 // This is accomplished by the sweeper locking the free lists while
8264 // it is sweeping. Thus blocks that are determined to be free are
8265 // indeed free. There is however one additional complication:
8266 // blocks that have been allocated since the final checkpoint and
8267 // mark, will not have been marked and so would be treated as
8268 // unreachable and swept up. To prevent this, the allocator marks
8269 // the bit map when allocating during the sweep phase. This leads,
8270 // however, to a further complication -- objects may have been allocated
8271 // but not yet initialized -- in the sense that the header isn't yet
8272 // installed. The sweeper can not then determine the size of the block
8273 // in order to skip over it. To deal with this case, we use a technique
8274 // (due to Printezis) to encode such uninitialized block sizes in the
8275 // bit map. Since the bit map uses a bit per every HeapWord, but the
8276 // CMS generation has a minimum object size of 3 HeapWords, it follows
8277 // that "normal marks" won't be adjacent in the bit map (there will
8278 // always be at least two 0 bits between successive 1 bits). We make use
8279 // of these "unused" bits to represent uninitialized blocks -- the bit
8280 // corresponding to the start of the uninitialized object and the next
8281 // bit are both set. Finally, a 1 bit marks the end of the object that
8282 // started with the two consecutive 1 bits to indicate its potentially
8283 // uninitialized state.
8285 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8286 FreeChunk* fc = (FreeChunk*)addr;
8287 size_t res;
8289 // Check if we are done sweeping. Below we check "addr >= _limit" rather
8290 // than "addr == _limit" because although _limit was a block boundary when
8291 // we started the sweep, it may no longer be one because heap expansion
8292 // may have caused us to coalesce the block ending at the address _limit
8293 // with a newly expanded chunk (this happens when _limit was set to the
8294 // previous _end of the space), so we may have stepped past _limit:
8295 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8296 if (addr >= _limit) { // we have swept up to or past the limit: finish up
8297 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8298 "sweep _limit out of bounds");
8299 assert(addr < _sp->end(), "addr out of bounds");
8300 // Flush any free range we might be holding as a single
8301 // coalesced chunk to the appropriate free list.
8302 if (inFreeRange()) {
8303 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8304 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8305 flush_cur_free_chunk(freeFinger(),
8306 pointer_delta(addr, freeFinger()));
8307 if (CMSTraceSweeper) {
8308 gclog_or_tty->print("Sweep: last chunk: ");
8309 gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") "
8310 "[coalesced:"SIZE_FORMAT"]\n",
8311 freeFinger(), pointer_delta(addr, freeFinger()),
8312 lastFreeRangeCoalesced());
8313 }
8314 }
8316 // help the iterator loop finish
8317 return pointer_delta(_sp->end(), addr);
8318 }
8320 assert(addr < _limit, "sweep invariant");
8321 // check if we should yield
8322 do_yield_check(addr);
8323 if (fc->is_free()) {
8324 // Chunk that is already free
8325 res = fc->size();
8326 do_already_free_chunk(fc);
8327 debug_only(_sp->verifyFreeLists());
8328 // If we flush the chunk at hand in lookahead_and_flush()
8329 // and it's coalesced with a preceding chunk, then the
8330 // process of "mangling" the payload of the coalesced block
8331 // will cause erasure of the size information from the
8332 // (erstwhile) header of all the coalesced blocks but the
8333 // first, so the first disjunct in the assert will not hold
8334 // in that specific case (in which case the second disjunct
8335 // will hold).
8336 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8337 "Otherwise the size info doesn't change at this step");
8338 NOT_PRODUCT(
8339 _numObjectsAlreadyFree++;
8340 _numWordsAlreadyFree += res;
8341 )
8342 NOT_PRODUCT(_last_fc = fc;)
8343 } else if (!_bitMap->isMarked(addr)) {
8344 // Chunk is fresh garbage
8345 res = do_garbage_chunk(fc);
8346 debug_only(_sp->verifyFreeLists());
8347 NOT_PRODUCT(
8348 _numObjectsFreed++;
8349 _numWordsFreed += res;
8350 )
8351 } else {
8352 // Chunk that is alive.
8353 res = do_live_chunk(fc);
8354 debug_only(_sp->verifyFreeLists());
8355 NOT_PRODUCT(
8356 _numObjectsLive++;
8357 _numWordsLive += res;
8358 )
8359 }
8360 return res;
8361 }
8363 // For the smart allocation, record following
8364 // split deaths - a free chunk is removed from its free list because
8365 // it is being split into two or more chunks.
8366 // split birth - a free chunk is being added to its free list because
8367 // a larger free chunk has been split and resulted in this free chunk.
8368 // coal death - a free chunk is being removed from its free list because
8369 // it is being coalesced into a large free chunk.
8370 // coal birth - a free chunk is being added to its free list because
8371 // it was created when two or more free chunks where coalesced into
8372 // this free chunk.
8373 //
8374 // These statistics are used to determine the desired number of free
8375 // chunks of a given size. The desired number is chosen to be relative
8376 // to the end of a CMS sweep. The desired number at the end of a sweep
8377 // is the
8378 // count-at-end-of-previous-sweep (an amount that was enough)
8379 // - count-at-beginning-of-current-sweep (the excess)
8380 // + split-births (gains in this size during interval)
8381 // - split-deaths (demands on this size during interval)
8382 // where the interval is from the end of one sweep to the end of the
8383 // next.
8384 //
8385 // When sweeping the sweeper maintains an accumulated chunk which is
8386 // the chunk that is made up of chunks that have been coalesced. That
8387 // will be termed the left-hand chunk. A new chunk of garbage that
8388 // is being considered for coalescing will be referred to as the
8389 // right-hand chunk.
8390 //
8391 // When making a decision on whether to coalesce a right-hand chunk with
8392 // the current left-hand chunk, the current count vs. the desired count
8393 // of the left-hand chunk is considered. Also if the right-hand chunk
8394 // is near the large chunk at the end of the heap (see
8395 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8396 // left-hand chunk is coalesced.
8397 //
8398 // When making a decision about whether to split a chunk, the desired count
8399 // vs. the current count of the candidate to be split is also considered.
8400 // If the candidate is underpopulated (currently fewer chunks than desired)
8401 // a chunk of an overpopulated (currently more chunks than desired) size may
8402 // be chosen. The "hint" associated with a free list, if non-null, points
8403 // to a free list which may be overpopulated.
8404 //
8406 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8407 const size_t size = fc->size();
8408 // Chunks that cannot be coalesced are not in the
8409 // free lists.
8410 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8411 assert(_sp->verify_chunk_in_free_list(fc),
8412 "free chunk should be in free lists");
8413 }
8414 // a chunk that is already free, should not have been
8415 // marked in the bit map
8416 HeapWord* const addr = (HeapWord*) fc;
8417 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8418 // Verify that the bit map has no bits marked between
8419 // addr and purported end of this block.
8420 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8422 // Some chunks cannot be coalesced under any circumstances.
8423 // See the definition of cantCoalesce().
8424 if (!fc->cantCoalesce()) {
8425 // This chunk can potentially be coalesced.
8426 if (_sp->adaptive_freelists()) {
8427 // All the work is done in
8428 do_post_free_or_garbage_chunk(fc, size);
8429 } else { // Not adaptive free lists
8430 // this is a free chunk that can potentially be coalesced by the sweeper;
8431 if (!inFreeRange()) {
8432 // if the next chunk is a free block that can't be coalesced
8433 // it doesn't make sense to remove this chunk from the free lists
8434 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8435 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8436 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8437 nextChunk->is_free() && // ... which is free...
8438 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8439 // nothing to do
8440 } else {
8441 // Potentially the start of a new free range:
8442 // Don't eagerly remove it from the free lists.
8443 // No need to remove it if it will just be put
8444 // back again. (Also from a pragmatic point of view
8445 // if it is a free block in a region that is beyond
8446 // any allocated blocks, an assertion will fail)
8447 // Remember the start of a free run.
8448 initialize_free_range(addr, true);
8449 // end - can coalesce with next chunk
8450 }
8451 } else {
8452 // the midst of a free range, we are coalescing
8453 print_free_block_coalesced(fc);
8454 if (CMSTraceSweeper) {
8455 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
8456 }
8457 // remove it from the free lists
8458 _sp->removeFreeChunkFromFreeLists(fc);
8459 set_lastFreeRangeCoalesced(true);
8460 // If the chunk is being coalesced and the current free range is
8461 // in the free lists, remove the current free range so that it
8462 // will be returned to the free lists in its entirety - all
8463 // the coalesced pieces included.
8464 if (freeRangeInFreeLists()) {
8465 FreeChunk* ffc = (FreeChunk*) freeFinger();
8466 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8467 "Size of free range is inconsistent with chunk size.");
8468 if (CMSTestInFreeList) {
8469 assert(_sp->verify_chunk_in_free_list(ffc),
8470 "free range is not in free lists");
8471 }
8472 _sp->removeFreeChunkFromFreeLists(ffc);
8473 set_freeRangeInFreeLists(false);
8474 }
8475 }
8476 }
8477 // Note that if the chunk is not coalescable (the else arm
8478 // below), we unconditionally flush, without needing to do
8479 // a "lookahead," as we do below.
8480 if (inFreeRange()) lookahead_and_flush(fc, size);
8481 } else {
8482 // Code path common to both original and adaptive free lists.
8484 // cant coalesce with previous block; this should be treated
8485 // as the end of a free run if any
8486 if (inFreeRange()) {
8487 // we kicked some butt; time to pick up the garbage
8488 assert(freeFinger() < addr, "freeFinger points too high");
8489 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8490 }
8491 // else, nothing to do, just continue
8492 }
8493 }
8495 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8496 // This is a chunk of garbage. It is not in any free list.
8497 // Add it to a free list or let it possibly be coalesced into
8498 // a larger chunk.
8499 HeapWord* const addr = (HeapWord*) fc;
8500 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8502 if (_sp->adaptive_freelists()) {
8503 // Verify that the bit map has no bits marked between
8504 // addr and purported end of just dead object.
8505 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8507 do_post_free_or_garbage_chunk(fc, size);
8508 } else {
8509 if (!inFreeRange()) {
8510 // start of a new free range
8511 assert(size > 0, "A free range should have a size");
8512 initialize_free_range(addr, false);
8513 } else {
8514 // this will be swept up when we hit the end of the
8515 // free range
8516 if (CMSTraceSweeper) {
8517 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
8518 }
8519 // If the chunk is being coalesced and the current free range is
8520 // in the free lists, remove the current free range so that it
8521 // will be returned to the free lists in its entirety - all
8522 // the coalesced pieces included.
8523 if (freeRangeInFreeLists()) {
8524 FreeChunk* ffc = (FreeChunk*)freeFinger();
8525 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8526 "Size of free range is inconsistent with chunk size.");
8527 if (CMSTestInFreeList) {
8528 assert(_sp->verify_chunk_in_free_list(ffc),
8529 "free range is not in free lists");
8530 }
8531 _sp->removeFreeChunkFromFreeLists(ffc);
8532 set_freeRangeInFreeLists(false);
8533 }
8534 set_lastFreeRangeCoalesced(true);
8535 }
8536 // this will be swept up when we hit the end of the free range
8538 // Verify that the bit map has no bits marked between
8539 // addr and purported end of just dead object.
8540 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8541 }
8542 assert(_limit >= addr + size,
8543 "A freshly garbage chunk can't possibly straddle over _limit");
8544 if (inFreeRange()) lookahead_and_flush(fc, size);
8545 return size;
8546 }
8548 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8549 HeapWord* addr = (HeapWord*) fc;
8550 // The sweeper has just found a live object. Return any accumulated
8551 // left hand chunk to the free lists.
8552 if (inFreeRange()) {
8553 assert(freeFinger() < addr, "freeFinger points too high");
8554 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8555 }
8557 // This object is live: we'd normally expect this to be
8558 // an oop, and like to assert the following:
8559 // assert(oop(addr)->is_oop(), "live block should be an oop");
8560 // However, as we commented above, this may be an object whose
8561 // header hasn't yet been initialized.
8562 size_t size;
8563 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8564 if (_bitMap->isMarked(addr + 1)) {
8565 // Determine the size from the bit map, rather than trying to
8566 // compute it from the object header.
8567 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8568 size = pointer_delta(nextOneAddr + 1, addr);
8569 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8570 "alignment problem");
8572 #ifdef ASSERT
8573 if (oop(addr)->klass_or_null() != NULL) {
8574 // Ignore mark word because we are running concurrent with mutators
8575 assert(oop(addr)->is_oop(true), "live block should be an oop");
8576 assert(size ==
8577 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8578 "P-mark and computed size do not agree");
8579 }
8580 #endif
8582 } else {
8583 // This should be an initialized object that's alive.
8584 assert(oop(addr)->klass_or_null() != NULL,
8585 "Should be an initialized object");
8586 // Ignore mark word because we are running concurrent with mutators
8587 assert(oop(addr)->is_oop(true), "live block should be an oop");
8588 // Verify that the bit map has no bits marked between
8589 // addr and purported end of this block.
8590 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8591 assert(size >= 3, "Necessary for Printezis marks to work");
8592 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8593 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8594 }
8595 return size;
8596 }
8598 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8599 size_t chunkSize) {
8600 // do_post_free_or_garbage_chunk() should only be called in the case
8601 // of the adaptive free list allocator.
8602 const bool fcInFreeLists = fc->is_free();
8603 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8604 assert((HeapWord*)fc <= _limit, "sweep invariant");
8605 if (CMSTestInFreeList && fcInFreeLists) {
8606 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8607 }
8609 if (CMSTraceSweeper) {
8610 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8611 }
8613 HeapWord* const fc_addr = (HeapWord*) fc;
8615 bool coalesce;
8616 const size_t left = pointer_delta(fc_addr, freeFinger());
8617 const size_t right = chunkSize;
8618 switch (FLSCoalescePolicy) {
8619 // numeric value forms a coalition aggressiveness metric
8620 case 0: { // never coalesce
8621 coalesce = false;
8622 break;
8623 }
8624 case 1: { // coalesce if left & right chunks on overpopulated lists
8625 coalesce = _sp->coalOverPopulated(left) &&
8626 _sp->coalOverPopulated(right);
8627 break;
8628 }
8629 case 2: { // coalesce if left chunk on overpopulated list (default)
8630 coalesce = _sp->coalOverPopulated(left);
8631 break;
8632 }
8633 case 3: { // coalesce if left OR right chunk on overpopulated list
8634 coalesce = _sp->coalOverPopulated(left) ||
8635 _sp->coalOverPopulated(right);
8636 break;
8637 }
8638 case 4: { // always coalesce
8639 coalesce = true;
8640 break;
8641 }
8642 default:
8643 ShouldNotReachHere();
8644 }
8646 // Should the current free range be coalesced?
8647 // If the chunk is in a free range and either we decided to coalesce above
8648 // or the chunk is near the large block at the end of the heap
8649 // (isNearLargestChunk() returns true), then coalesce this chunk.
8650 const bool doCoalesce = inFreeRange()
8651 && (coalesce || _g->isNearLargestChunk(fc_addr));
8652 if (doCoalesce) {
8653 // Coalesce the current free range on the left with the new
8654 // chunk on the right. If either is on a free list,
8655 // it must be removed from the list and stashed in the closure.
8656 if (freeRangeInFreeLists()) {
8657 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8658 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8659 "Size of free range is inconsistent with chunk size.");
8660 if (CMSTestInFreeList) {
8661 assert(_sp->verify_chunk_in_free_list(ffc),
8662 "Chunk is not in free lists");
8663 }
8664 _sp->coalDeath(ffc->size());
8665 _sp->removeFreeChunkFromFreeLists(ffc);
8666 set_freeRangeInFreeLists(false);
8667 }
8668 if (fcInFreeLists) {
8669 _sp->coalDeath(chunkSize);
8670 assert(fc->size() == chunkSize,
8671 "The chunk has the wrong size or is not in the free lists");
8672 _sp->removeFreeChunkFromFreeLists(fc);
8673 }
8674 set_lastFreeRangeCoalesced(true);
8675 print_free_block_coalesced(fc);
8676 } else { // not in a free range and/or should not coalesce
8677 // Return the current free range and start a new one.
8678 if (inFreeRange()) {
8679 // In a free range but cannot coalesce with the right hand chunk.
8680 // Put the current free range into the free lists.
8681 flush_cur_free_chunk(freeFinger(),
8682 pointer_delta(fc_addr, freeFinger()));
8683 }
8684 // Set up for new free range. Pass along whether the right hand
8685 // chunk is in the free lists.
8686 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8687 }
8688 }
8690 // Lookahead flush:
8691 // If we are tracking a free range, and this is the last chunk that
8692 // we'll look at because its end crosses past _limit, we'll preemptively
8693 // flush it along with any free range we may be holding on to. Note that
8694 // this can be the case only for an already free or freshly garbage
8695 // chunk. If this block is an object, it can never straddle
8696 // over _limit. The "straddling" occurs when _limit is set at
8697 // the previous end of the space when this cycle started, and
8698 // a subsequent heap expansion caused the previously co-terminal
8699 // free block to be coalesced with the newly expanded portion,
8700 // thus rendering _limit a non-block-boundary making it dangerous
8701 // for the sweeper to step over and examine.
8702 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8703 assert(inFreeRange(), "Should only be called if currently in a free range.");
8704 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8705 assert(_sp->used_region().contains(eob - 1),
8706 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
8707 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8708 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8709 eob, eob-1, _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8710 if (eob >= _limit) {
8711 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8712 if (CMSTraceSweeper) {
8713 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8714 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8715 "[" PTR_FORMAT "," PTR_FORMAT ")",
8716 _limit, fc, eob, _sp->bottom(), _sp->end());
8717 }
8718 // Return the storage we are tracking back into the free lists.
8719 if (CMSTraceSweeper) {
8720 gclog_or_tty->print_cr("Flushing ... ");
8721 }
8722 assert(freeFinger() < eob, "Error");
8723 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8724 }
8725 }
8727 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8728 assert(inFreeRange(), "Should only be called if currently in a free range.");
8729 assert(size > 0,
8730 "A zero sized chunk cannot be added to the free lists.");
8731 if (!freeRangeInFreeLists()) {
8732 if (CMSTestInFreeList) {
8733 FreeChunk* fc = (FreeChunk*) chunk;
8734 fc->set_size(size);
8735 assert(!_sp->verify_chunk_in_free_list(fc),
8736 "chunk should not be in free lists yet");
8737 }
8738 if (CMSTraceSweeper) {
8739 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8740 chunk, size);
8741 }
8742 // A new free range is going to be starting. The current
8743 // free range has not been added to the free lists yet or
8744 // was removed so add it back.
8745 // If the current free range was coalesced, then the death
8746 // of the free range was recorded. Record a birth now.
8747 if (lastFreeRangeCoalesced()) {
8748 _sp->coalBirth(size);
8749 }
8750 _sp->addChunkAndRepairOffsetTable(chunk, size,
8751 lastFreeRangeCoalesced());
8752 } else if (CMSTraceSweeper) {
8753 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8754 }
8755 set_inFreeRange(false);
8756 set_freeRangeInFreeLists(false);
8757 }
8759 // We take a break if we've been at this for a while,
8760 // so as to avoid monopolizing the locks involved.
8761 void SweepClosure::do_yield_work(HeapWord* addr) {
8762 // Return current free chunk being used for coalescing (if any)
8763 // to the appropriate freelist. After yielding, the next
8764 // free block encountered will start a coalescing range of
8765 // free blocks. If the next free block is adjacent to the
8766 // chunk just flushed, they will need to wait for the next
8767 // sweep to be coalesced.
8768 if (inFreeRange()) {
8769 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8770 }
8772 // First give up the locks, then yield, then re-lock.
8773 // We should probably use a constructor/destructor idiom to
8774 // do this unlock/lock or modify the MutexUnlocker class to
8775 // serve our purpose. XXX
8776 assert_lock_strong(_bitMap->lock());
8777 assert_lock_strong(_freelistLock);
8778 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8779 "CMS thread should hold CMS token");
8780 _bitMap->lock()->unlock();
8781 _freelistLock->unlock();
8782 ConcurrentMarkSweepThread::desynchronize(true);
8783 ConcurrentMarkSweepThread::acknowledge_yield_request();
8784 _collector->stopTimer();
8785 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8786 if (PrintCMSStatistics != 0) {
8787 _collector->incrementYields();
8788 }
8789 _collector->icms_wait();
8791 // See the comment in coordinator_yield()
8792 for (unsigned i = 0; i < CMSYieldSleepCount &&
8793 ConcurrentMarkSweepThread::should_yield() &&
8794 !CMSCollector::foregroundGCIsActive(); ++i) {
8795 os::sleep(Thread::current(), 1, false);
8796 ConcurrentMarkSweepThread::acknowledge_yield_request();
8797 }
8799 ConcurrentMarkSweepThread::synchronize(true);
8800 _freelistLock->lock();
8801 _bitMap->lock()->lock_without_safepoint_check();
8802 _collector->startTimer();
8803 }
8805 #ifndef PRODUCT
8806 // This is actually very useful in a product build if it can
8807 // be called from the debugger. Compile it into the product
8808 // as needed.
8809 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8810 return debug_cms_space->verify_chunk_in_free_list(fc);
8811 }
8812 #endif
8814 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8815 if (CMSTraceSweeper) {
8816 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8817 fc, fc->size());
8818 }
8819 }
8821 // CMSIsAliveClosure
8822 bool CMSIsAliveClosure::do_object_b(oop obj) {
8823 HeapWord* addr = (HeapWord*)obj;
8824 return addr != NULL &&
8825 (!_span.contains(addr) || _bit_map->isMarked(addr));
8826 }
8829 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8830 MemRegion span,
8831 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8832 bool cpc):
8833 _collector(collector),
8834 _span(span),
8835 _bit_map(bit_map),
8836 _mark_stack(mark_stack),
8837 _concurrent_precleaning(cpc) {
8838 assert(!_span.is_empty(), "Empty span could spell trouble");
8839 }
8842 // CMSKeepAliveClosure: the serial version
8843 void CMSKeepAliveClosure::do_oop(oop obj) {
8844 HeapWord* addr = (HeapWord*)obj;
8845 if (_span.contains(addr) &&
8846 !_bit_map->isMarked(addr)) {
8847 _bit_map->mark(addr);
8848 bool simulate_overflow = false;
8849 NOT_PRODUCT(
8850 if (CMSMarkStackOverflowALot &&
8851 _collector->simulate_overflow()) {
8852 // simulate a stack overflow
8853 simulate_overflow = true;
8854 }
8855 )
8856 if (simulate_overflow || !_mark_stack->push(obj)) {
8857 if (_concurrent_precleaning) {
8858 // We dirty the overflown object and let the remark
8859 // phase deal with it.
8860 assert(_collector->overflow_list_is_empty(), "Error");
8861 // In the case of object arrays, we need to dirty all of
8862 // the cards that the object spans. No locking or atomics
8863 // are needed since no one else can be mutating the mod union
8864 // table.
8865 if (obj->is_objArray()) {
8866 size_t sz = obj->size();
8867 HeapWord* end_card_addr =
8868 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8869 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8870 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8871 _collector->_modUnionTable.mark_range(redirty_range);
8872 } else {
8873 _collector->_modUnionTable.mark(addr);
8874 }
8875 _collector->_ser_kac_preclean_ovflw++;
8876 } else {
8877 _collector->push_on_overflow_list(obj);
8878 _collector->_ser_kac_ovflw++;
8879 }
8880 }
8881 }
8882 }
8884 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8885 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8887 // CMSParKeepAliveClosure: a parallel version of the above.
8888 // The work queues are private to each closure (thread),
8889 // but (may be) available for stealing by other threads.
8890 void CMSParKeepAliveClosure::do_oop(oop obj) {
8891 HeapWord* addr = (HeapWord*)obj;
8892 if (_span.contains(addr) &&
8893 !_bit_map->isMarked(addr)) {
8894 // In general, during recursive tracing, several threads
8895 // may be concurrently getting here; the first one to
8896 // "tag" it, claims it.
8897 if (_bit_map->par_mark(addr)) {
8898 bool res = _work_queue->push(obj);
8899 assert(res, "Low water mark should be much less than capacity");
8900 // Do a recursive trim in the hope that this will keep
8901 // stack usage lower, but leave some oops for potential stealers
8902 trim_queue(_low_water_mark);
8903 } // Else, another thread got there first
8904 }
8905 }
8907 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8908 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8910 void CMSParKeepAliveClosure::trim_queue(uint max) {
8911 while (_work_queue->size() > max) {
8912 oop new_oop;
8913 if (_work_queue->pop_local(new_oop)) {
8914 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8915 assert(_bit_map->isMarked((HeapWord*)new_oop),
8916 "no white objects on this stack!");
8917 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8918 // iterate over the oops in this oop, marking and pushing
8919 // the ones in CMS heap (i.e. in _span).
8920 new_oop->oop_iterate(&_mark_and_push);
8921 }
8922 }
8923 }
8925 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8926 CMSCollector* collector,
8927 MemRegion span, CMSBitMap* bit_map,
8928 OopTaskQueue* work_queue):
8929 _collector(collector),
8930 _span(span),
8931 _bit_map(bit_map),
8932 _work_queue(work_queue) { }
8934 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8935 HeapWord* addr = (HeapWord*)obj;
8936 if (_span.contains(addr) &&
8937 !_bit_map->isMarked(addr)) {
8938 if (_bit_map->par_mark(addr)) {
8939 bool simulate_overflow = false;
8940 NOT_PRODUCT(
8941 if (CMSMarkStackOverflowALot &&
8942 _collector->par_simulate_overflow()) {
8943 // simulate a stack overflow
8944 simulate_overflow = true;
8945 }
8946 )
8947 if (simulate_overflow || !_work_queue->push(obj)) {
8948 _collector->par_push_on_overflow_list(obj);
8949 _collector->_par_kac_ovflw++;
8950 }
8951 } // Else another thread got there already
8952 }
8953 }
8955 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8956 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8958 //////////////////////////////////////////////////////////////////
8959 // CMSExpansionCause /////////////////////////////
8960 //////////////////////////////////////////////////////////////////
8961 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8962 switch (cause) {
8963 case _no_expansion:
8964 return "No expansion";
8965 case _satisfy_free_ratio:
8966 return "Free ratio";
8967 case _satisfy_promotion:
8968 return "Satisfy promotion";
8969 case _satisfy_allocation:
8970 return "allocation";
8971 case _allocate_par_lab:
8972 return "Par LAB";
8973 case _allocate_par_spooling_space:
8974 return "Par Spooling Space";
8975 case _adaptive_size_policy:
8976 return "Ergonomics";
8977 default:
8978 return "unknown";
8979 }
8980 }
8982 void CMSDrainMarkingStackClosure::do_void() {
8983 // the max number to take from overflow list at a time
8984 const size_t num = _mark_stack->capacity()/4;
8985 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8986 "Overflow list should be NULL during concurrent phases");
8987 while (!_mark_stack->isEmpty() ||
8988 // if stack is empty, check the overflow list
8989 _collector->take_from_overflow_list(num, _mark_stack)) {
8990 oop obj = _mark_stack->pop();
8991 HeapWord* addr = (HeapWord*)obj;
8992 assert(_span.contains(addr), "Should be within span");
8993 assert(_bit_map->isMarked(addr), "Should be marked");
8994 assert(obj->is_oop(), "Should be an oop");
8995 obj->oop_iterate(_keep_alive);
8996 }
8997 }
8999 void CMSParDrainMarkingStackClosure::do_void() {
9000 // drain queue
9001 trim_queue(0);
9002 }
9004 // Trim our work_queue so its length is below max at return
9005 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
9006 while (_work_queue->size() > max) {
9007 oop new_oop;
9008 if (_work_queue->pop_local(new_oop)) {
9009 assert(new_oop->is_oop(), "Expected an oop");
9010 assert(_bit_map->isMarked((HeapWord*)new_oop),
9011 "no white objects on this stack!");
9012 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
9013 // iterate over the oops in this oop, marking and pushing
9014 // the ones in CMS heap (i.e. in _span).
9015 new_oop->oop_iterate(&_mark_and_push);
9016 }
9017 }
9018 }
9020 ////////////////////////////////////////////////////////////////////
9021 // Support for Marking Stack Overflow list handling and related code
9022 ////////////////////////////////////////////////////////////////////
9023 // Much of the following code is similar in shape and spirit to the
9024 // code used in ParNewGC. We should try and share that code
9025 // as much as possible in the future.
9027 #ifndef PRODUCT
9028 // Debugging support for CMSStackOverflowALot
9030 // It's OK to call this multi-threaded; the worst thing
9031 // that can happen is that we'll get a bunch of closely
9032 // spaced simulated oveflows, but that's OK, in fact
9033 // probably good as it would exercise the overflow code
9034 // under contention.
9035 bool CMSCollector::simulate_overflow() {
9036 if (_overflow_counter-- <= 0) { // just being defensive
9037 _overflow_counter = CMSMarkStackOverflowInterval;
9038 return true;
9039 } else {
9040 return false;
9041 }
9042 }
9044 bool CMSCollector::par_simulate_overflow() {
9045 return simulate_overflow();
9046 }
9047 #endif
9049 // Single-threaded
9050 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
9051 assert(stack->isEmpty(), "Expected precondition");
9052 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
9053 size_t i = num;
9054 oop cur = _overflow_list;
9055 const markOop proto = markOopDesc::prototype();
9056 NOT_PRODUCT(ssize_t n = 0;)
9057 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
9058 next = oop(cur->mark());
9059 cur->set_mark(proto); // until proven otherwise
9060 assert(cur->is_oop(), "Should be an oop");
9061 bool res = stack->push(cur);
9062 assert(res, "Bit off more than can chew?");
9063 NOT_PRODUCT(n++;)
9064 }
9065 _overflow_list = cur;
9066 #ifndef PRODUCT
9067 assert(_num_par_pushes >= n, "Too many pops?");
9068 _num_par_pushes -=n;
9069 #endif
9070 return !stack->isEmpty();
9071 }
9073 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
9074 // (MT-safe) Get a prefix of at most "num" from the list.
9075 // The overflow list is chained through the mark word of
9076 // each object in the list. We fetch the entire list,
9077 // break off a prefix of the right size and return the
9078 // remainder. If other threads try to take objects from
9079 // the overflow list at that time, they will wait for
9080 // some time to see if data becomes available. If (and
9081 // only if) another thread places one or more object(s)
9082 // on the global list before we have returned the suffix
9083 // to the global list, we will walk down our local list
9084 // to find its end and append the global list to
9085 // our suffix before returning it. This suffix walk can
9086 // prove to be expensive (quadratic in the amount of traffic)
9087 // when there are many objects in the overflow list and
9088 // there is much producer-consumer contention on the list.
9089 // *NOTE*: The overflow list manipulation code here and
9090 // in ParNewGeneration:: are very similar in shape,
9091 // except that in the ParNew case we use the old (from/eden)
9092 // copy of the object to thread the list via its klass word.
9093 // Because of the common code, if you make any changes in
9094 // the code below, please check the ParNew version to see if
9095 // similar changes might be needed.
9096 // CR 6797058 has been filed to consolidate the common code.
9097 bool CMSCollector::par_take_from_overflow_list(size_t num,
9098 OopTaskQueue* work_q,
9099 int no_of_gc_threads) {
9100 assert(work_q->size() == 0, "First empty local work queue");
9101 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
9102 if (_overflow_list == NULL) {
9103 return false;
9104 }
9105 // Grab the entire list; we'll put back a suffix
9106 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9107 Thread* tid = Thread::current();
9108 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
9109 // set to ParallelGCThreads.
9110 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
9111 size_t sleep_time_millis = MAX2((size_t)1, num/100);
9112 // If the list is busy, we spin for a short while,
9113 // sleeping between attempts to get the list.
9114 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
9115 os::sleep(tid, sleep_time_millis, false);
9116 if (_overflow_list == NULL) {
9117 // Nothing left to take
9118 return false;
9119 } else if (_overflow_list != BUSY) {
9120 // Try and grab the prefix
9121 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9122 }
9123 }
9124 // If the list was found to be empty, or we spun long
9125 // enough, we give up and return empty-handed. If we leave
9126 // the list in the BUSY state below, it must be the case that
9127 // some other thread holds the overflow list and will set it
9128 // to a non-BUSY state in the future.
9129 if (prefix == NULL || prefix == BUSY) {
9130 // Nothing to take or waited long enough
9131 if (prefix == NULL) {
9132 // Write back the NULL in case we overwrote it with BUSY above
9133 // and it is still the same value.
9134 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9135 }
9136 return false;
9137 }
9138 assert(prefix != NULL && prefix != BUSY, "Error");
9139 size_t i = num;
9140 oop cur = prefix;
9141 // Walk down the first "num" objects, unless we reach the end.
9142 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
9143 if (cur->mark() == NULL) {
9144 // We have "num" or fewer elements in the list, so there
9145 // is nothing to return to the global list.
9146 // Write back the NULL in lieu of the BUSY we wrote
9147 // above, if it is still the same value.
9148 if (_overflow_list == BUSY) {
9149 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9150 }
9151 } else {
9152 // Chop off the suffix and rerturn it to the global list.
9153 assert(cur->mark() != BUSY, "Error");
9154 oop suffix_head = cur->mark(); // suffix will be put back on global list
9155 cur->set_mark(NULL); // break off suffix
9156 // It's possible that the list is still in the empty(busy) state
9157 // we left it in a short while ago; in that case we may be
9158 // able to place back the suffix without incurring the cost
9159 // of a walk down the list.
9160 oop observed_overflow_list = _overflow_list;
9161 oop cur_overflow_list = observed_overflow_list;
9162 bool attached = false;
9163 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
9164 observed_overflow_list =
9165 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9166 if (cur_overflow_list == observed_overflow_list) {
9167 attached = true;
9168 break;
9169 } else cur_overflow_list = observed_overflow_list;
9170 }
9171 if (!attached) {
9172 // Too bad, someone else sneaked in (at least) an element; we'll need
9173 // to do a splice. Find tail of suffix so we can prepend suffix to global
9174 // list.
9175 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
9176 oop suffix_tail = cur;
9177 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
9178 "Tautology");
9179 observed_overflow_list = _overflow_list;
9180 do {
9181 cur_overflow_list = observed_overflow_list;
9182 if (cur_overflow_list != BUSY) {
9183 // Do the splice ...
9184 suffix_tail->set_mark(markOop(cur_overflow_list));
9185 } else { // cur_overflow_list == BUSY
9186 suffix_tail->set_mark(NULL);
9187 }
9188 // ... and try to place spliced list back on overflow_list ...
9189 observed_overflow_list =
9190 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9191 } while (cur_overflow_list != observed_overflow_list);
9192 // ... until we have succeeded in doing so.
9193 }
9194 }
9196 // Push the prefix elements on work_q
9197 assert(prefix != NULL, "control point invariant");
9198 const markOop proto = markOopDesc::prototype();
9199 oop next;
9200 NOT_PRODUCT(ssize_t n = 0;)
9201 for (cur = prefix; cur != NULL; cur = next) {
9202 next = oop(cur->mark());
9203 cur->set_mark(proto); // until proven otherwise
9204 assert(cur->is_oop(), "Should be an oop");
9205 bool res = work_q->push(cur);
9206 assert(res, "Bit off more than we can chew?");
9207 NOT_PRODUCT(n++;)
9208 }
9209 #ifndef PRODUCT
9210 assert(_num_par_pushes >= n, "Too many pops?");
9211 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
9212 #endif
9213 return true;
9214 }
9216 // Single-threaded
9217 void CMSCollector::push_on_overflow_list(oop p) {
9218 NOT_PRODUCT(_num_par_pushes++;)
9219 assert(p->is_oop(), "Not an oop");
9220 preserve_mark_if_necessary(p);
9221 p->set_mark((markOop)_overflow_list);
9222 _overflow_list = p;
9223 }
9225 // Multi-threaded; use CAS to prepend to overflow list
9226 void CMSCollector::par_push_on_overflow_list(oop p) {
9227 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
9228 assert(p->is_oop(), "Not an oop");
9229 par_preserve_mark_if_necessary(p);
9230 oop observed_overflow_list = _overflow_list;
9231 oop cur_overflow_list;
9232 do {
9233 cur_overflow_list = observed_overflow_list;
9234 if (cur_overflow_list != BUSY) {
9235 p->set_mark(markOop(cur_overflow_list));
9236 } else {
9237 p->set_mark(NULL);
9238 }
9239 observed_overflow_list =
9240 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
9241 } while (cur_overflow_list != observed_overflow_list);
9242 }
9243 #undef BUSY
9245 // Single threaded
9246 // General Note on GrowableArray: pushes may silently fail
9247 // because we are (temporarily) out of C-heap for expanding
9248 // the stack. The problem is quite ubiquitous and affects
9249 // a lot of code in the JVM. The prudent thing for GrowableArray
9250 // to do (for now) is to exit with an error. However, that may
9251 // be too draconian in some cases because the caller may be
9252 // able to recover without much harm. For such cases, we
9253 // should probably introduce a "soft_push" method which returns
9254 // an indication of success or failure with the assumption that
9255 // the caller may be able to recover from a failure; code in
9256 // the VM can then be changed, incrementally, to deal with such
9257 // failures where possible, thus, incrementally hardening the VM
9258 // in such low resource situations.
9259 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9260 _preserved_oop_stack.push(p);
9261 _preserved_mark_stack.push(m);
9262 assert(m == p->mark(), "Mark word changed");
9263 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9264 "bijection");
9265 }
9267 // Single threaded
9268 void CMSCollector::preserve_mark_if_necessary(oop p) {
9269 markOop m = p->mark();
9270 if (m->must_be_preserved(p)) {
9271 preserve_mark_work(p, m);
9272 }
9273 }
9275 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9276 markOop m = p->mark();
9277 if (m->must_be_preserved(p)) {
9278 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9279 // Even though we read the mark word without holding
9280 // the lock, we are assured that it will not change
9281 // because we "own" this oop, so no other thread can
9282 // be trying to push it on the overflow list; see
9283 // the assertion in preserve_mark_work() that checks
9284 // that m == p->mark().
9285 preserve_mark_work(p, m);
9286 }
9287 }
9289 // We should be able to do this multi-threaded,
9290 // a chunk of stack being a task (this is
9291 // correct because each oop only ever appears
9292 // once in the overflow list. However, it's
9293 // not very easy to completely overlap this with
9294 // other operations, so will generally not be done
9295 // until all work's been completed. Because we
9296 // expect the preserved oop stack (set) to be small,
9297 // it's probably fine to do this single-threaded.
9298 // We can explore cleverer concurrent/overlapped/parallel
9299 // processing of preserved marks if we feel the
9300 // need for this in the future. Stack overflow should
9301 // be so rare in practice and, when it happens, its
9302 // effect on performance so great that this will
9303 // likely just be in the noise anyway.
9304 void CMSCollector::restore_preserved_marks_if_any() {
9305 assert(SafepointSynchronize::is_at_safepoint(),
9306 "world should be stopped");
9307 assert(Thread::current()->is_ConcurrentGC_thread() ||
9308 Thread::current()->is_VM_thread(),
9309 "should be single-threaded");
9310 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9311 "bijection");
9313 while (!_preserved_oop_stack.is_empty()) {
9314 oop p = _preserved_oop_stack.pop();
9315 assert(p->is_oop(), "Should be an oop");
9316 assert(_span.contains(p), "oop should be in _span");
9317 assert(p->mark() == markOopDesc::prototype(),
9318 "Set when taken from overflow list");
9319 markOop m = _preserved_mark_stack.pop();
9320 p->set_mark(m);
9321 }
9322 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9323 "stacks were cleared above");
9324 }
9326 #ifndef PRODUCT
9327 bool CMSCollector::no_preserved_marks() const {
9328 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9329 }
9330 #endif
9332 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
9333 {
9334 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9335 CMSAdaptiveSizePolicy* size_policy =
9336 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
9337 assert(size_policy->is_gc_cms_adaptive_size_policy(),
9338 "Wrong type for size policy");
9339 return size_policy;
9340 }
9342 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
9343 size_t desired_promo_size) {
9344 if (cur_promo_size < desired_promo_size) {
9345 size_t expand_bytes = desired_promo_size - cur_promo_size;
9346 if (PrintAdaptiveSizePolicy && Verbose) {
9347 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9348 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
9349 expand_bytes);
9350 }
9351 expand(expand_bytes,
9352 MinHeapDeltaBytes,
9353 CMSExpansionCause::_adaptive_size_policy);
9354 } else if (desired_promo_size < cur_promo_size) {
9355 size_t shrink_bytes = cur_promo_size - desired_promo_size;
9356 if (PrintAdaptiveSizePolicy && Verbose) {
9357 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9358 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
9359 shrink_bytes);
9360 }
9361 shrink(shrink_bytes);
9362 }
9363 }
9365 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
9366 GenCollectedHeap* gch = GenCollectedHeap::heap();
9367 CMSGCAdaptivePolicyCounters* counters =
9368 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
9369 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
9370 "Wrong kind of counters");
9371 return counters;
9372 }
9375 void ASConcurrentMarkSweepGeneration::update_counters() {
9376 if (UsePerfData) {
9377 _space_counters->update_all();
9378 _gen_counters->update_all();
9379 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9380 GenCollectedHeap* gch = GenCollectedHeap::heap();
9381 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9382 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9383 "Wrong gc statistics type");
9384 counters->update_counters(gc_stats_l);
9385 }
9386 }
9388 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
9389 if (UsePerfData) {
9390 _space_counters->update_used(used);
9391 _space_counters->update_capacity();
9392 _gen_counters->update_all();
9394 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9395 GenCollectedHeap* gch = GenCollectedHeap::heap();
9396 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9397 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9398 "Wrong gc statistics type");
9399 counters->update_counters(gc_stats_l);
9400 }
9401 }
9403 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9404 assert_locked_or_safepoint(Heap_lock);
9405 assert_lock_strong(freelistLock());
9406 HeapWord* old_end = _cmsSpace->end();
9407 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9408 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9409 FreeChunk* chunk_at_end = find_chunk_at_end();
9410 if (chunk_at_end == NULL) {
9411 // No room to shrink
9412 if (PrintGCDetails && Verbose) {
9413 gclog_or_tty->print_cr("No room to shrink: old_end "
9414 PTR_FORMAT " unallocated_start " PTR_FORMAT
9415 " chunk_at_end " PTR_FORMAT,
9416 old_end, unallocated_start, chunk_at_end);
9417 }
9418 return;
9419 } else {
9421 // Find the chunk at the end of the space and determine
9422 // how much it can be shrunk.
9423 size_t shrinkable_size_in_bytes = chunk_at_end->size();
9424 size_t aligned_shrinkable_size_in_bytes =
9425 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9426 assert(unallocated_start <= (HeapWord*) chunk_at_end->end(),
9427 "Inconsistent chunk at end of space");
9428 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9429 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9431 // Shrink the underlying space
9432 _virtual_space.shrink_by(bytes);
9433 if (PrintGCDetails && Verbose) {
9434 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9435 " desired_bytes " SIZE_FORMAT
9436 " shrinkable_size_in_bytes " SIZE_FORMAT
9437 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9438 " bytes " SIZE_FORMAT,
9439 desired_bytes, shrinkable_size_in_bytes,
9440 aligned_shrinkable_size_in_bytes, bytes);
9441 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
9442 " unallocated_start " SIZE_FORMAT,
9443 old_end, unallocated_start);
9444 }
9446 // If the space did shrink (shrinking is not guaranteed),
9447 // shrink the chunk at the end by the appropriate amount.
9448 if (((HeapWord*)_virtual_space.high()) < old_end) {
9449 size_t new_word_size =
9450 heap_word_size(_virtual_space.committed_size());
9452 // Have to remove the chunk from the dictionary because it is changing
9453 // size and might be someplace elsewhere in the dictionary.
9455 // Get the chunk at end, shrink it, and put it
9456 // back.
9457 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9458 size_t word_size_change = word_size_before - new_word_size;
9459 size_t chunk_at_end_old_size = chunk_at_end->size();
9460 assert(chunk_at_end_old_size >= word_size_change,
9461 "Shrink is too large");
9462 chunk_at_end->set_size(chunk_at_end_old_size -
9463 word_size_change);
9464 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9465 word_size_change);
9467 _cmsSpace->returnChunkToDictionary(chunk_at_end);
9469 MemRegion mr(_cmsSpace->bottom(), new_word_size);
9470 _bts->resize(new_word_size); // resize the block offset shared array
9471 Universe::heap()->barrier_set()->resize_covered_region(mr);
9472 _cmsSpace->assert_locked();
9473 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9475 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9477 // update the space and generation capacity counters
9478 if (UsePerfData) {
9479 _space_counters->update_capacity();
9480 _gen_counters->update_all();
9481 }
9483 if (Verbose && PrintGCDetails) {
9484 size_t new_mem_size = _virtual_space.committed_size();
9485 size_t old_mem_size = new_mem_size + bytes;
9486 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
9487 name(), old_mem_size/K, bytes/K, new_mem_size/K);
9488 }
9489 }
9491 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9492 "Inconsistency at end of space");
9493 assert(chunk_at_end->end() == (uintptr_t*) _cmsSpace->end(),
9494 "Shrinking is inconsistent");
9495 return;
9496 }
9497 }
9498 // Transfer some number of overflown objects to usual marking
9499 // stack. Return true if some objects were transferred.
9500 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9501 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9502 (size_t)ParGCDesiredObjsFromOverflowList);
9504 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9505 assert(_collector->overflow_list_is_empty() || res,
9506 "If list is not empty, we should have taken something");
9507 assert(!res || !_mark_stack->isEmpty(),
9508 "If we took something, it should now be on our stack");
9509 return res;
9510 }
9512 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9513 size_t res = _sp->block_size_no_stall(addr, _collector);
9514 if (_sp->block_is_obj(addr)) {
9515 if (_live_bit_map->isMarked(addr)) {
9516 // It can't have been dead in a previous cycle
9517 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9518 } else {
9519 _dead_bit_map->mark(addr); // mark the dead object
9520 }
9521 }
9522 // Could be 0, if the block size could not be computed without stalling.
9523 return res;
9524 }
9526 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9528 switch (phase) {
9529 case CMSCollector::InitialMarking:
9530 initialize(true /* fullGC */ ,
9531 cause /* cause of the GC */,
9532 true /* recordGCBeginTime */,
9533 true /* recordPreGCUsage */,
9534 false /* recordPeakUsage */,
9535 false /* recordPostGCusage */,
9536 true /* recordAccumulatedGCTime */,
9537 false /* recordGCEndTime */,
9538 false /* countCollection */ );
9539 break;
9541 case CMSCollector::FinalMarking:
9542 initialize(true /* fullGC */ ,
9543 cause /* cause of the GC */,
9544 false /* recordGCBeginTime */,
9545 false /* recordPreGCUsage */,
9546 false /* recordPeakUsage */,
9547 false /* recordPostGCusage */,
9548 true /* recordAccumulatedGCTime */,
9549 false /* recordGCEndTime */,
9550 false /* countCollection */ );
9551 break;
9553 case CMSCollector::Sweeping:
9554 initialize(true /* fullGC */ ,
9555 cause /* cause of the GC */,
9556 false /* recordGCBeginTime */,
9557 false /* recordPreGCUsage */,
9558 true /* recordPeakUsage */,
9559 true /* recordPostGCusage */,
9560 false /* recordAccumulatedGCTime */,
9561 true /* recordGCEndTime */,
9562 true /* countCollection */ );
9563 break;
9565 default:
9566 ShouldNotReachHere();
9567 }
9568 }