Fri, 21 Mar 2014 10:31:51 +0100
8036703: Add trace event with statistics for the metaspace chunk free lists
Reviewed-by: stefank, mgerdin, coleenp, egahlin
1 /*
2 * Copyright (c) 2001, 2013, 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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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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/vmThread.hpp"
63 #include "services/memoryService.hpp"
64 #include "services/runtimeService.hpp"
66 // statics
67 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
68 bool CMSCollector::_full_gc_requested = false;
69 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
71 //////////////////////////////////////////////////////////////////
72 // In support of CMS/VM thread synchronization
73 //////////////////////////////////////////////////////////////////
74 // We split use of the CGC_lock into 2 "levels".
75 // The low-level locking is of the usual CGC_lock monitor. We introduce
76 // a higher level "token" (hereafter "CMS token") built on top of the
77 // low level monitor (hereafter "CGC lock").
78 // The token-passing protocol gives priority to the VM thread. The
79 // CMS-lock doesn't provide any fairness guarantees, but clients
80 // should ensure that it is only held for very short, bounded
81 // durations.
82 //
83 // When either of the CMS thread or the VM thread is involved in
84 // collection operations during which it does not want the other
85 // thread to interfere, it obtains the CMS token.
86 //
87 // If either thread tries to get the token while the other has
88 // it, that thread waits. However, if the VM thread and CMS thread
89 // both want the token, then the VM thread gets priority while the
90 // CMS thread waits. This ensures, for instance, that the "concurrent"
91 // phases of the CMS thread's work do not block out the VM thread
92 // for long periods of time as the CMS thread continues to hog
93 // the token. (See bug 4616232).
94 //
95 // The baton-passing functions are, however, controlled by the
96 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
97 // and here the low-level CMS lock, not the high level token,
98 // ensures mutual exclusion.
99 //
100 // Two important conditions that we have to satisfy:
101 // 1. if a thread does a low-level wait on the CMS lock, then it
102 // relinquishes the CMS token if it were holding that token
103 // when it acquired the low-level CMS lock.
104 // 2. any low-level notifications on the low-level lock
105 // should only be sent when a thread has relinquished the token.
106 //
107 // In the absence of either property, we'd have potential deadlock.
108 //
109 // We protect each of the CMS (concurrent and sequential) phases
110 // with the CMS _token_, not the CMS _lock_.
111 //
112 // The only code protected by CMS lock is the token acquisition code
113 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
114 // baton-passing code.
115 //
116 // Unfortunately, i couldn't come up with a good abstraction to factor and
117 // hide the naked CGC_lock manipulation in the baton-passing code
118 // further below. That's something we should try to do. Also, the proof
119 // of correctness of this 2-level locking scheme is far from obvious,
120 // and potentially quite slippery. We have an uneasy supsicion, for instance,
121 // that there may be a theoretical possibility of delay/starvation in the
122 // low-level lock/wait/notify scheme used for the baton-passing because of
123 // potential intereference with the priority scheme embodied in the
124 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
125 // invocation further below and marked with "XXX 20011219YSR".
126 // Indeed, as we note elsewhere, this may become yet more slippery
127 // in the presence of multiple CMS and/or multiple VM threads. XXX
129 class CMSTokenSync: public StackObj {
130 private:
131 bool _is_cms_thread;
132 public:
133 CMSTokenSync(bool is_cms_thread):
134 _is_cms_thread(is_cms_thread) {
135 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
136 "Incorrect argument to constructor");
137 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
138 }
140 ~CMSTokenSync() {
141 assert(_is_cms_thread ?
142 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
143 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
144 "Incorrect state");
145 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
146 }
147 };
149 // Convenience class that does a CMSTokenSync, and then acquires
150 // upto three locks.
151 class CMSTokenSyncWithLocks: public CMSTokenSync {
152 private:
153 // Note: locks are acquired in textual declaration order
154 // and released in the opposite order
155 MutexLockerEx _locker1, _locker2, _locker3;
156 public:
157 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
158 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
159 CMSTokenSync(is_cms_thread),
160 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
161 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
162 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
163 { }
164 };
167 // Wrapper class to temporarily disable icms during a foreground cms collection.
168 class ICMSDisabler: public StackObj {
169 public:
170 // The ctor disables icms and wakes up the thread so it notices the change;
171 // the dtor re-enables icms. Note that the CMSCollector methods will check
172 // CMSIncrementalMode.
173 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
174 ~ICMSDisabler() { CMSCollector::enable_icms(); }
175 };
177 //////////////////////////////////////////////////////////////////
178 // Concurrent Mark-Sweep Generation /////////////////////////////
179 //////////////////////////////////////////////////////////////////
181 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
183 // This struct contains per-thread things necessary to support parallel
184 // young-gen collection.
185 class CMSParGCThreadState: public CHeapObj<mtGC> {
186 public:
187 CFLS_LAB lab;
188 PromotionInfo promo;
190 // Constructor.
191 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
192 promo.setSpace(cfls);
193 }
194 };
196 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
197 ReservedSpace rs, size_t initial_byte_size, int level,
198 CardTableRS* ct, bool use_adaptive_freelists,
199 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
200 CardGeneration(rs, initial_byte_size, level, ct),
201 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
202 _debug_collection_type(Concurrent_collection_type),
203 _did_compact(false)
204 {
205 HeapWord* bottom = (HeapWord*) _virtual_space.low();
206 HeapWord* end = (HeapWord*) _virtual_space.high();
208 _direct_allocated_words = 0;
209 NOT_PRODUCT(
210 _numObjectsPromoted = 0;
211 _numWordsPromoted = 0;
212 _numObjectsAllocated = 0;
213 _numWordsAllocated = 0;
214 )
216 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
217 use_adaptive_freelists,
218 dictionaryChoice);
219 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
220 if (_cmsSpace == NULL) {
221 vm_exit_during_initialization(
222 "CompactibleFreeListSpace allocation failure");
223 }
224 _cmsSpace->_gen = this;
226 _gc_stats = new CMSGCStats();
228 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
229 // offsets match. The ability to tell free chunks from objects
230 // depends on this property.
231 debug_only(
232 FreeChunk* junk = NULL;
233 assert(UseCompressedClassPointers ||
234 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
235 "Offset of FreeChunk::_prev within FreeChunk must match"
236 " that of OopDesc::_klass within OopDesc");
237 )
238 if (CollectedHeap::use_parallel_gc_threads()) {
239 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
240 _par_gc_thread_states =
241 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
242 if (_par_gc_thread_states == NULL) {
243 vm_exit_during_initialization("Could not allocate par gc structs");
244 }
245 for (uint i = 0; i < ParallelGCThreads; i++) {
246 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
247 if (_par_gc_thread_states[i] == NULL) {
248 vm_exit_during_initialization("Could not allocate par gc structs");
249 }
250 }
251 } else {
252 _par_gc_thread_states = NULL;
253 }
254 _incremental_collection_failed = false;
255 // The "dilatation_factor" is the expansion that can occur on
256 // account of the fact that the minimum object size in the CMS
257 // generation may be larger than that in, say, a contiguous young
258 // generation.
259 // Ideally, in the calculation below, we'd compute the dilatation
260 // factor as: MinChunkSize/(promoting_gen's min object size)
261 // Since we do not have such a general query interface for the
262 // promoting generation, we'll instead just use the mimimum
263 // object size (which today is a header's worth of space);
264 // note that all arithmetic is in units of HeapWords.
265 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
266 assert(_dilatation_factor >= 1.0, "from previous assert");
267 }
270 // The field "_initiating_occupancy" represents the occupancy percentage
271 // at which we trigger a new collection cycle. Unless explicitly specified
272 // via CMSInitiatingOccupancyFraction (argument "io" below), it
273 // is calculated by:
274 //
275 // Let "f" be MinHeapFreeRatio in
276 //
277 // _intiating_occupancy = 100-f +
278 // f * (CMSTriggerRatio/100)
279 // where CMSTriggerRatio is the argument "tr" below.
280 //
281 // That is, if we assume the heap is at its desired maximum occupancy at the
282 // end of a collection, we let CMSTriggerRatio of the (purported) free
283 // space be allocated before initiating a new collection cycle.
284 //
285 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
286 assert(io <= 100 && tr <= 100, "Check the arguments");
287 if (io >= 0) {
288 _initiating_occupancy = (double)io / 100.0;
289 } else {
290 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
291 (double)(tr * MinHeapFreeRatio) / 100.0)
292 / 100.0;
293 }
294 }
296 void ConcurrentMarkSweepGeneration::ref_processor_init() {
297 assert(collector() != NULL, "no collector");
298 collector()->ref_processor_init();
299 }
301 void CMSCollector::ref_processor_init() {
302 if (_ref_processor == NULL) {
303 // Allocate and initialize a reference processor
304 _ref_processor =
305 new ReferenceProcessor(_span, // span
306 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
307 (int) ParallelGCThreads, // mt processing degree
308 _cmsGen->refs_discovery_is_mt(), // mt discovery
309 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
310 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
311 &_is_alive_closure, // closure for liveness info
312 false); // next field updates do not need write barrier
313 // Initialize the _ref_processor field of CMSGen
314 _cmsGen->set_ref_processor(_ref_processor);
316 }
317 }
319 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
320 GenCollectedHeap* gch = GenCollectedHeap::heap();
321 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
322 "Wrong type of heap");
323 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
324 gch->gen_policy()->size_policy();
325 assert(sp->is_gc_cms_adaptive_size_policy(),
326 "Wrong type of size policy");
327 return sp;
328 }
330 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
331 CMSGCAdaptivePolicyCounters* results =
332 (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
333 assert(
334 results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
335 "Wrong gc policy counter kind");
336 return results;
337 }
340 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
342 const char* gen_name = "old";
344 // Generation Counters - generation 1, 1 subspace
345 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
347 _space_counters = new GSpaceCounters(gen_name, 0,
348 _virtual_space.reserved_size(),
349 this, _gen_counters);
350 }
352 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
353 _cms_gen(cms_gen)
354 {
355 assert(alpha <= 100, "bad value");
356 _saved_alpha = alpha;
358 // Initialize the alphas to the bootstrap value of 100.
359 _gc0_alpha = _cms_alpha = 100;
361 _cms_begin_time.update();
362 _cms_end_time.update();
364 _gc0_duration = 0.0;
365 _gc0_period = 0.0;
366 _gc0_promoted = 0;
368 _cms_duration = 0.0;
369 _cms_period = 0.0;
370 _cms_allocated = 0;
372 _cms_used_at_gc0_begin = 0;
373 _cms_used_at_gc0_end = 0;
374 _allow_duty_cycle_reduction = false;
375 _valid_bits = 0;
376 _icms_duty_cycle = CMSIncrementalDutyCycle;
377 }
379 double CMSStats::cms_free_adjustment_factor(size_t free) const {
380 // TBD: CR 6909490
381 return 1.0;
382 }
384 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
385 }
387 // If promotion failure handling is on use
388 // the padded average size of the promotion for each
389 // young generation collection.
390 double CMSStats::time_until_cms_gen_full() const {
391 size_t cms_free = _cms_gen->cmsSpace()->free();
392 GenCollectedHeap* gch = GenCollectedHeap::heap();
393 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
394 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
395 if (cms_free > expected_promotion) {
396 // Start a cms collection if there isn't enough space to promote
397 // for the next minor collection. Use the padded average as
398 // a safety factor.
399 cms_free -= expected_promotion;
401 // Adjust by the safety factor.
402 double cms_free_dbl = (double)cms_free;
403 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
404 // Apply a further correction factor which tries to adjust
405 // for recent occurance of concurrent mode failures.
406 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
407 cms_free_dbl = cms_free_dbl * cms_adjustment;
409 if (PrintGCDetails && Verbose) {
410 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
411 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
412 cms_free, expected_promotion);
413 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
414 cms_free_dbl, cms_consumption_rate() + 1.0);
415 }
416 // Add 1 in case the consumption rate goes to zero.
417 return cms_free_dbl / (cms_consumption_rate() + 1.0);
418 }
419 return 0.0;
420 }
422 // Compare the duration of the cms collection to the
423 // time remaining before the cms generation is empty.
424 // Note that the time from the start of the cms collection
425 // to the start of the cms sweep (less than the total
426 // duration of the cms collection) can be used. This
427 // has been tried and some applications experienced
428 // promotion failures early in execution. This was
429 // possibly because the averages were not accurate
430 // enough at the beginning.
431 double CMSStats::time_until_cms_start() const {
432 // We add "gc0_period" to the "work" calculation
433 // below because this query is done (mostly) at the
434 // end of a scavenge, so we need to conservatively
435 // account for that much possible delay
436 // in the query so as to avoid concurrent mode failures
437 // due to starting the collection just a wee bit too
438 // late.
439 double work = cms_duration() + gc0_period();
440 double deadline = time_until_cms_gen_full();
441 // If a concurrent mode failure occurred recently, we want to be
442 // more conservative and halve our expected time_until_cms_gen_full()
443 if (work > deadline) {
444 if (Verbose && PrintGCDetails) {
445 gclog_or_tty->print(
446 " CMSCollector: collect because of anticipated promotion "
447 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
448 gc0_period(), time_until_cms_gen_full());
449 }
450 return 0.0;
451 }
452 return work - deadline;
453 }
455 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
456 // amount of change to prevent wild oscillation.
457 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
458 unsigned int new_duty_cycle) {
459 assert(old_duty_cycle <= 100, "bad input value");
460 assert(new_duty_cycle <= 100, "bad input value");
462 // Note: use subtraction with caution since it may underflow (values are
463 // unsigned). Addition is safe since we're in the range 0-100.
464 unsigned int damped_duty_cycle = new_duty_cycle;
465 if (new_duty_cycle < old_duty_cycle) {
466 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
467 if (new_duty_cycle + largest_delta < old_duty_cycle) {
468 damped_duty_cycle = old_duty_cycle - largest_delta;
469 }
470 } else if (new_duty_cycle > old_duty_cycle) {
471 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
472 if (new_duty_cycle > old_duty_cycle + largest_delta) {
473 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
474 }
475 }
476 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
478 if (CMSTraceIncrementalPacing) {
479 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
480 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
481 }
482 return damped_duty_cycle;
483 }
485 unsigned int CMSStats::icms_update_duty_cycle_impl() {
486 assert(CMSIncrementalPacing && valid(),
487 "should be handled in icms_update_duty_cycle()");
489 double cms_time_so_far = cms_timer().seconds();
490 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
491 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
493 // Avoid division by 0.
494 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
495 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
497 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
498 if (new_duty_cycle > _icms_duty_cycle) {
499 // Avoid very small duty cycles (1 or 2); 0 is allowed.
500 if (new_duty_cycle > 2) {
501 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
502 new_duty_cycle);
503 }
504 } else if (_allow_duty_cycle_reduction) {
505 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
506 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
507 // Respect the minimum duty cycle.
508 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
509 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
510 }
512 if (PrintGCDetails || CMSTraceIncrementalPacing) {
513 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
514 }
516 _allow_duty_cycle_reduction = false;
517 return _icms_duty_cycle;
518 }
520 #ifndef PRODUCT
521 void CMSStats::print_on(outputStream *st) const {
522 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
523 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
524 gc0_duration(), gc0_period(), gc0_promoted());
525 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
526 cms_duration(), cms_duration_per_mb(),
527 cms_period(), cms_allocated());
528 st->print(",cms_since_beg=%g,cms_since_end=%g",
529 cms_time_since_begin(), cms_time_since_end());
530 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
531 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
532 if (CMSIncrementalMode) {
533 st->print(",dc=%d", icms_duty_cycle());
534 }
536 if (valid()) {
537 st->print(",promo_rate=%g,cms_alloc_rate=%g",
538 promotion_rate(), cms_allocation_rate());
539 st->print(",cms_consumption_rate=%g,time_until_full=%g",
540 cms_consumption_rate(), time_until_cms_gen_full());
541 }
542 st->print(" ");
543 }
544 #endif // #ifndef PRODUCT
546 CMSCollector::CollectorState CMSCollector::_collectorState =
547 CMSCollector::Idling;
548 bool CMSCollector::_foregroundGCIsActive = false;
549 bool CMSCollector::_foregroundGCShouldWait = false;
551 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
552 CardTableRS* ct,
553 ConcurrentMarkSweepPolicy* cp):
554 _cmsGen(cmsGen),
555 _ct(ct),
556 _ref_processor(NULL), // will be set later
557 _conc_workers(NULL), // may be set later
558 _abort_preclean(false),
559 _start_sampling(false),
560 _between_prologue_and_epilogue(false),
561 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
562 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
563 -1 /* lock-free */, "No_lock" /* dummy */),
564 _modUnionClosure(&_modUnionTable),
565 _modUnionClosurePar(&_modUnionTable),
566 // Adjust my span to cover old (cms) gen
567 _span(cmsGen->reserved()),
568 // Construct the is_alive_closure with _span & markBitMap
569 _is_alive_closure(_span, &_markBitMap),
570 _restart_addr(NULL),
571 _overflow_list(NULL),
572 _stats(cmsGen),
573 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true)),
574 _eden_chunk_array(NULL), // may be set in ctor body
575 _eden_chunk_capacity(0), // -- ditto --
576 _eden_chunk_index(0), // -- ditto --
577 _survivor_plab_array(NULL), // -- ditto --
578 _survivor_chunk_array(NULL), // -- ditto --
579 _survivor_chunk_capacity(0), // -- ditto --
580 _survivor_chunk_index(0), // -- ditto --
581 _ser_pmc_preclean_ovflw(0),
582 _ser_kac_preclean_ovflw(0),
583 _ser_pmc_remark_ovflw(0),
584 _par_pmc_remark_ovflw(0),
585 _ser_kac_ovflw(0),
586 _par_kac_ovflw(0),
587 #ifndef PRODUCT
588 _num_par_pushes(0),
589 #endif
590 _collection_count_start(0),
591 _verifying(false),
592 _icms_start_limit(NULL),
593 _icms_stop_limit(NULL),
594 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
595 _completed_initialization(false),
596 _collector_policy(cp),
597 _should_unload_classes(CMSClassUnloadingEnabled),
598 _concurrent_cycles_since_last_unload(0),
599 _roots_scanning_options(SharedHeap::SO_None),
600 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
601 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
602 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
603 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
604 _cms_start_registered(false)
605 {
606 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
607 ExplicitGCInvokesConcurrent = true;
608 }
609 // Now expand the span and allocate the collection support structures
610 // (MUT, marking bit map etc.) to cover both generations subject to
611 // collection.
613 // For use by dirty card to oop closures.
614 _cmsGen->cmsSpace()->set_collector(this);
616 // Allocate MUT and marking bit map
617 {
618 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
619 if (!_markBitMap.allocate(_span)) {
620 warning("Failed to allocate CMS Bit Map");
621 return;
622 }
623 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
624 }
625 {
626 _modUnionTable.allocate(_span);
627 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
628 }
630 if (!_markStack.allocate(MarkStackSize)) {
631 warning("Failed to allocate CMS Marking Stack");
632 return;
633 }
635 // Support for multi-threaded concurrent phases
636 if (CMSConcurrentMTEnabled) {
637 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
638 // just for now
639 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
640 }
641 if (ConcGCThreads > 1) {
642 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
643 ConcGCThreads, true);
644 if (_conc_workers == NULL) {
645 warning("GC/CMS: _conc_workers allocation failure: "
646 "forcing -CMSConcurrentMTEnabled");
647 CMSConcurrentMTEnabled = false;
648 } else {
649 _conc_workers->initialize_workers();
650 }
651 } else {
652 CMSConcurrentMTEnabled = false;
653 }
654 }
655 if (!CMSConcurrentMTEnabled) {
656 ConcGCThreads = 0;
657 } else {
658 // Turn off CMSCleanOnEnter optimization temporarily for
659 // the MT case where it's not fixed yet; see 6178663.
660 CMSCleanOnEnter = false;
661 }
662 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
663 "Inconsistency");
665 // Parallel task queues; these are shared for the
666 // concurrent and stop-world phases of CMS, but
667 // are not shared with parallel scavenge (ParNew).
668 {
669 uint i;
670 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
672 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
673 || ParallelRefProcEnabled)
674 && num_queues > 0) {
675 _task_queues = new OopTaskQueueSet(num_queues);
676 if (_task_queues == NULL) {
677 warning("task_queues allocation failure.");
678 return;
679 }
680 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
681 if (_hash_seed == NULL) {
682 warning("_hash_seed array allocation failure");
683 return;
684 }
686 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
687 for (i = 0; i < num_queues; i++) {
688 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
689 if (q == NULL) {
690 warning("work_queue allocation failure.");
691 return;
692 }
693 _task_queues->register_queue(i, q);
694 }
695 for (i = 0; i < num_queues; i++) {
696 _task_queues->queue(i)->initialize();
697 _hash_seed[i] = 17; // copied from ParNew
698 }
699 }
700 }
702 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
704 // Clip CMSBootstrapOccupancy between 0 and 100.
705 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
707 _full_gcs_since_conc_gc = 0;
709 // Now tell CMS generations the identity of their collector
710 ConcurrentMarkSweepGeneration::set_collector(this);
712 // Create & start a CMS thread for this CMS collector
713 _cmsThread = ConcurrentMarkSweepThread::start(this);
714 assert(cmsThread() != NULL, "CMS Thread should have been created");
715 assert(cmsThread()->collector() == this,
716 "CMS Thread should refer to this gen");
717 assert(CGC_lock != NULL, "Where's the CGC_lock?");
719 // Support for parallelizing young gen rescan
720 GenCollectedHeap* gch = GenCollectedHeap::heap();
721 _young_gen = gch->prev_gen(_cmsGen);
722 if (gch->supports_inline_contig_alloc()) {
723 _top_addr = gch->top_addr();
724 _end_addr = gch->end_addr();
725 assert(_young_gen != NULL, "no _young_gen");
726 _eden_chunk_index = 0;
727 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
728 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
729 if (_eden_chunk_array == NULL) {
730 _eden_chunk_capacity = 0;
731 warning("GC/CMS: _eden_chunk_array allocation failure");
732 }
733 }
734 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
736 // Support for parallelizing survivor space rescan
737 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
738 const size_t max_plab_samples =
739 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
741 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
742 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
743 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
744 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
745 || _cursor == NULL) {
746 warning("Failed to allocate survivor plab/chunk array");
747 if (_survivor_plab_array != NULL) {
748 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
749 _survivor_plab_array = NULL;
750 }
751 if (_survivor_chunk_array != NULL) {
752 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
753 _survivor_chunk_array = NULL;
754 }
755 if (_cursor != NULL) {
756 FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
757 _cursor = NULL;
758 }
759 } else {
760 _survivor_chunk_capacity = 2*max_plab_samples;
761 for (uint i = 0; i < ParallelGCThreads; i++) {
762 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
763 if (vec == NULL) {
764 warning("Failed to allocate survivor plab array");
765 for (int j = i; j > 0; j--) {
766 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
767 }
768 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
769 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
770 _survivor_plab_array = NULL;
771 _survivor_chunk_array = NULL;
772 _survivor_chunk_capacity = 0;
773 break;
774 } else {
775 ChunkArray* cur =
776 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
777 max_plab_samples);
778 assert(cur->end() == 0, "Should be 0");
779 assert(cur->array() == vec, "Should be vec");
780 assert(cur->capacity() == max_plab_samples, "Error");
781 }
782 }
783 }
784 }
785 assert( ( _survivor_plab_array != NULL
786 && _survivor_chunk_array != NULL)
787 || ( _survivor_chunk_capacity == 0
788 && _survivor_chunk_index == 0),
789 "Error");
791 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
792 _gc_counters = new CollectorCounters("CMS", 1);
793 _completed_initialization = true;
794 _inter_sweep_timer.start(); // start of time
795 }
797 const char* ConcurrentMarkSweepGeneration::name() const {
798 return "concurrent mark-sweep generation";
799 }
800 void ConcurrentMarkSweepGeneration::update_counters() {
801 if (UsePerfData) {
802 _space_counters->update_all();
803 _gen_counters->update_all();
804 }
805 }
807 // this is an optimized version of update_counters(). it takes the
808 // used value as a parameter rather than computing it.
809 //
810 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
811 if (UsePerfData) {
812 _space_counters->update_used(used);
813 _space_counters->update_capacity();
814 _gen_counters->update_all();
815 }
816 }
818 void ConcurrentMarkSweepGeneration::print() const {
819 Generation::print();
820 cmsSpace()->print();
821 }
823 #ifndef PRODUCT
824 void ConcurrentMarkSweepGeneration::print_statistics() {
825 cmsSpace()->printFLCensus(0);
826 }
827 #endif
829 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
830 GenCollectedHeap* gch = GenCollectedHeap::heap();
831 if (PrintGCDetails) {
832 if (Verbose) {
833 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
834 level(), short_name(), s, used(), capacity());
835 } else {
836 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
837 level(), short_name(), s, used() / K, capacity() / K);
838 }
839 }
840 if (Verbose) {
841 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
842 gch->used(), gch->capacity());
843 } else {
844 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
845 gch->used() / K, gch->capacity() / K);
846 }
847 }
849 size_t
850 ConcurrentMarkSweepGeneration::contiguous_available() const {
851 // dld proposes an improvement in precision here. If the committed
852 // part of the space ends in a free block we should add that to
853 // uncommitted size in the calculation below. Will make this
854 // change later, staying with the approximation below for the
855 // time being. -- ysr.
856 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
857 }
859 size_t
860 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
861 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
862 }
864 size_t ConcurrentMarkSweepGeneration::max_available() const {
865 return free() + _virtual_space.uncommitted_size();
866 }
868 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
869 size_t available = max_available();
870 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
871 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
872 if (Verbose && PrintGCDetails) {
873 gclog_or_tty->print_cr(
874 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
875 "max_promo("SIZE_FORMAT")",
876 res? "":" not", available, res? ">=":"<",
877 av_promo, max_promotion_in_bytes);
878 }
879 return res;
880 }
882 // At a promotion failure dump information on block layout in heap
883 // (cms old generation).
884 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
885 if (CMSDumpAtPromotionFailure) {
886 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
887 }
888 }
890 CompactibleSpace*
891 ConcurrentMarkSweepGeneration::first_compaction_space() const {
892 return _cmsSpace;
893 }
895 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
896 // Clear the promotion information. These pointers can be adjusted
897 // along with all the other pointers into the heap but
898 // compaction is expected to be a rare event with
899 // a heap using cms so don't do it without seeing the need.
900 if (CollectedHeap::use_parallel_gc_threads()) {
901 for (uint i = 0; i < ParallelGCThreads; i++) {
902 _par_gc_thread_states[i]->promo.reset();
903 }
904 }
905 }
907 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
908 blk->do_space(_cmsSpace);
909 }
911 void ConcurrentMarkSweepGeneration::compute_new_size() {
912 assert_locked_or_safepoint(Heap_lock);
914 // If incremental collection failed, we just want to expand
915 // to the limit.
916 if (incremental_collection_failed()) {
917 clear_incremental_collection_failed();
918 grow_to_reserved();
919 return;
920 }
922 // The heap has been compacted but not reset yet.
923 // Any metric such as free() or used() will be incorrect.
925 CardGeneration::compute_new_size();
927 // Reset again after a possible resizing
928 if (did_compact()) {
929 cmsSpace()->reset_after_compaction();
930 }
931 }
933 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
934 assert_locked_or_safepoint(Heap_lock);
936 // If incremental collection failed, we just want to expand
937 // to the limit.
938 if (incremental_collection_failed()) {
939 clear_incremental_collection_failed();
940 grow_to_reserved();
941 return;
942 }
944 double free_percentage = ((double) free()) / capacity();
945 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
946 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
948 // compute expansion delta needed for reaching desired free percentage
949 if (free_percentage < desired_free_percentage) {
950 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
951 assert(desired_capacity >= capacity(), "invalid expansion size");
952 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
953 if (PrintGCDetails && Verbose) {
954 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
955 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
956 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
957 gclog_or_tty->print_cr(" Desired free fraction %f",
958 desired_free_percentage);
959 gclog_or_tty->print_cr(" Maximum free fraction %f",
960 maximum_free_percentage);
961 gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000);
962 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
963 desired_capacity/1000);
964 int prev_level = level() - 1;
965 if (prev_level >= 0) {
966 size_t prev_size = 0;
967 GenCollectedHeap* gch = GenCollectedHeap::heap();
968 Generation* prev_gen = gch->_gens[prev_level];
969 prev_size = prev_gen->capacity();
970 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
971 prev_size/1000);
972 }
973 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
974 unsafe_max_alloc_nogc()/1000);
975 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
976 contiguous_available()/1000);
977 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
978 expand_bytes);
979 }
980 // safe if expansion fails
981 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
982 if (PrintGCDetails && Verbose) {
983 gclog_or_tty->print_cr(" Expanded free fraction %f",
984 ((double) free()) / capacity());
985 }
986 } else {
987 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
988 assert(desired_capacity <= capacity(), "invalid expansion size");
989 size_t shrink_bytes = capacity() - desired_capacity;
990 // Don't shrink unless the delta is greater than the minimum shrink we want
991 if (shrink_bytes >= MinHeapDeltaBytes) {
992 shrink_free_list_by(shrink_bytes);
993 }
994 }
995 }
997 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
998 return cmsSpace()->freelistLock();
999 }
1001 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
1002 bool tlab) {
1003 CMSSynchronousYieldRequest yr;
1004 MutexLockerEx x(freelistLock(),
1005 Mutex::_no_safepoint_check_flag);
1006 return have_lock_and_allocate(size, tlab);
1007 }
1009 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
1010 bool tlab /* ignored */) {
1011 assert_lock_strong(freelistLock());
1012 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1013 HeapWord* res = cmsSpace()->allocate(adjustedSize);
1014 // Allocate the object live (grey) if the background collector has
1015 // started marking. This is necessary because the marker may
1016 // have passed this address and consequently this object will
1017 // not otherwise be greyed and would be incorrectly swept up.
1018 // Note that if this object contains references, the writing
1019 // of those references will dirty the card containing this object
1020 // allowing the object to be blackened (and its references scanned)
1021 // either during a preclean phase or at the final checkpoint.
1022 if (res != NULL) {
1023 // We may block here with an uninitialized object with
1024 // its mark-bit or P-bits not yet set. Such objects need
1025 // to be safely navigable by block_start().
1026 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1027 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1028 collector()->direct_allocated(res, adjustedSize);
1029 _direct_allocated_words += adjustedSize;
1030 // allocation counters
1031 NOT_PRODUCT(
1032 _numObjectsAllocated++;
1033 _numWordsAllocated += (int)adjustedSize;
1034 )
1035 }
1036 return res;
1037 }
1039 // In the case of direct allocation by mutators in a generation that
1040 // is being concurrently collected, the object must be allocated
1041 // live (grey) if the background collector has started marking.
1042 // This is necessary because the marker may
1043 // have passed this address and consequently this object will
1044 // not otherwise be greyed and would be incorrectly swept up.
1045 // Note that if this object contains references, the writing
1046 // of those references will dirty the card containing this object
1047 // allowing the object to be blackened (and its references scanned)
1048 // either during a preclean phase or at the final checkpoint.
1049 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1050 assert(_markBitMap.covers(start, size), "Out of bounds");
1051 if (_collectorState >= Marking) {
1052 MutexLockerEx y(_markBitMap.lock(),
1053 Mutex::_no_safepoint_check_flag);
1054 // [see comments preceding SweepClosure::do_blk() below for details]
1055 //
1056 // Can the P-bits be deleted now? JJJ
1057 //
1058 // 1. need to mark the object as live so it isn't collected
1059 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1060 // 3. need to mark the end of the object so marking, precleaning or sweeping
1061 // can skip over uninitialized or unparsable objects. An allocated
1062 // object is considered uninitialized for our purposes as long as
1063 // its klass word is NULL. All old gen objects are parsable
1064 // as soon as they are initialized.)
1065 _markBitMap.mark(start); // object is live
1066 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1067 _markBitMap.mark(start + size - 1);
1068 // mark end of object
1069 }
1070 // check that oop looks uninitialized
1071 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1072 }
1074 void CMSCollector::promoted(bool par, HeapWord* start,
1075 bool is_obj_array, size_t obj_size) {
1076 assert(_markBitMap.covers(start), "Out of bounds");
1077 // See comment in direct_allocated() about when objects should
1078 // be allocated live.
1079 if (_collectorState >= Marking) {
1080 // we already hold the marking bit map lock, taken in
1081 // the prologue
1082 if (par) {
1083 _markBitMap.par_mark(start);
1084 } else {
1085 _markBitMap.mark(start);
1086 }
1087 // We don't need to mark the object as uninitialized (as
1088 // in direct_allocated above) because this is being done with the
1089 // world stopped and the object will be initialized by the
1090 // time the marking, precleaning or sweeping get to look at it.
1091 // But see the code for copying objects into the CMS generation,
1092 // where we need to ensure that concurrent readers of the
1093 // block offset table are able to safely navigate a block that
1094 // is in flux from being free to being allocated (and in
1095 // transition while being copied into) and subsequently
1096 // becoming a bona-fide object when the copy/promotion is complete.
1097 assert(SafepointSynchronize::is_at_safepoint(),
1098 "expect promotion only at safepoints");
1100 if (_collectorState < Sweeping) {
1101 // Mark the appropriate cards in the modUnionTable, so that
1102 // this object gets scanned before the sweep. If this is
1103 // not done, CMS generation references in the object might
1104 // not get marked.
1105 // For the case of arrays, which are otherwise precisely
1106 // marked, we need to dirty the entire array, not just its head.
1107 if (is_obj_array) {
1108 // The [par_]mark_range() method expects mr.end() below to
1109 // be aligned to the granularity of a bit's representation
1110 // in the heap. In the case of the MUT below, that's a
1111 // card size.
1112 MemRegion mr(start,
1113 (HeapWord*)round_to((intptr_t)(start + obj_size),
1114 CardTableModRefBS::card_size /* bytes */));
1115 if (par) {
1116 _modUnionTable.par_mark_range(mr);
1117 } else {
1118 _modUnionTable.mark_range(mr);
1119 }
1120 } else { // not an obj array; we can just mark the head
1121 if (par) {
1122 _modUnionTable.par_mark(start);
1123 } else {
1124 _modUnionTable.mark(start);
1125 }
1126 }
1127 }
1128 }
1129 }
1131 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1132 {
1133 size_t delta = pointer_delta(addr, space->bottom());
1134 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1135 }
1137 void CMSCollector::icms_update_allocation_limits()
1138 {
1139 Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1140 EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1142 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1143 if (CMSTraceIncrementalPacing) {
1144 stats().print();
1145 }
1147 assert(duty_cycle <= 100, "invalid duty cycle");
1148 if (duty_cycle != 0) {
1149 // The duty_cycle is a percentage between 0 and 100; convert to words and
1150 // then compute the offset from the endpoints of the space.
1151 size_t free_words = eden->free() / HeapWordSize;
1152 double free_words_dbl = (double)free_words;
1153 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1154 size_t offset_words = (free_words - duty_cycle_words) / 2;
1156 _icms_start_limit = eden->top() + offset_words;
1157 _icms_stop_limit = eden->end() - offset_words;
1159 // The limits may be adjusted (shifted to the right) by
1160 // CMSIncrementalOffset, to allow the application more mutator time after a
1161 // young gen gc (when all mutators were stopped) and before CMS starts and
1162 // takes away one or more cpus.
1163 if (CMSIncrementalOffset != 0) {
1164 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1165 size_t adjustment = (size_t)adjustment_dbl;
1166 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1167 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1168 _icms_start_limit += adjustment;
1169 _icms_stop_limit = tmp_stop;
1170 }
1171 }
1172 }
1173 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1174 _icms_start_limit = _icms_stop_limit = eden->end();
1175 }
1177 // Install the new start limit.
1178 eden->set_soft_end(_icms_start_limit);
1180 if (CMSTraceIncrementalMode) {
1181 gclog_or_tty->print(" icms alloc limits: "
1182 PTR_FORMAT "," PTR_FORMAT
1183 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1184 _icms_start_limit, _icms_stop_limit,
1185 percent_of_space(eden, _icms_start_limit),
1186 percent_of_space(eden, _icms_stop_limit));
1187 if (Verbose) {
1188 gclog_or_tty->print("eden: ");
1189 eden->print_on(gclog_or_tty);
1190 }
1191 }
1192 }
1194 // Any changes here should try to maintain the invariant
1195 // that if this method is called with _icms_start_limit
1196 // and _icms_stop_limit both NULL, then it should return NULL
1197 // and not notify the icms thread.
1198 HeapWord*
1199 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1200 size_t word_size)
1201 {
1202 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1203 // nop.
1204 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1205 if (top <= _icms_start_limit) {
1206 if (CMSTraceIncrementalMode) {
1207 space->print_on(gclog_or_tty);
1208 gclog_or_tty->stamp();
1209 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1210 ", new limit=" PTR_FORMAT
1211 " (" SIZE_FORMAT "%%)",
1212 top, _icms_stop_limit,
1213 percent_of_space(space, _icms_stop_limit));
1214 }
1215 ConcurrentMarkSweepThread::start_icms();
1216 assert(top < _icms_stop_limit, "Tautology");
1217 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1218 return _icms_stop_limit;
1219 }
1221 // The allocation will cross both the _start and _stop limits, so do the
1222 // stop notification also and return end().
1223 if (CMSTraceIncrementalMode) {
1224 space->print_on(gclog_or_tty);
1225 gclog_or_tty->stamp();
1226 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1227 ", new limit=" PTR_FORMAT
1228 " (" SIZE_FORMAT "%%)",
1229 top, space->end(),
1230 percent_of_space(space, space->end()));
1231 }
1232 ConcurrentMarkSweepThread::stop_icms();
1233 return space->end();
1234 }
1236 if (top <= _icms_stop_limit) {
1237 if (CMSTraceIncrementalMode) {
1238 space->print_on(gclog_or_tty);
1239 gclog_or_tty->stamp();
1240 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1241 ", new limit=" PTR_FORMAT
1242 " (" SIZE_FORMAT "%%)",
1243 top, space->end(),
1244 percent_of_space(space, space->end()));
1245 }
1246 ConcurrentMarkSweepThread::stop_icms();
1247 return space->end();
1248 }
1250 if (CMSTraceIncrementalMode) {
1251 space->print_on(gclog_or_tty);
1252 gclog_or_tty->stamp();
1253 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1254 ", new limit=" PTR_FORMAT,
1255 top, NULL);
1256 }
1257 }
1259 return NULL;
1260 }
1262 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1263 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1264 // allocate, copy and if necessary update promoinfo --
1265 // delegate to underlying space.
1266 assert_lock_strong(freelistLock());
1268 #ifndef PRODUCT
1269 if (Universe::heap()->promotion_should_fail()) {
1270 return NULL;
1271 }
1272 #endif // #ifndef PRODUCT
1274 oop res = _cmsSpace->promote(obj, obj_size);
1275 if (res == NULL) {
1276 // expand and retry
1277 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1278 expand(s*HeapWordSize, MinHeapDeltaBytes,
1279 CMSExpansionCause::_satisfy_promotion);
1280 // Since there's currently no next generation, we don't try to promote
1281 // into a more senior generation.
1282 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1283 "is made to pass on a possibly failing "
1284 "promotion to next generation");
1285 res = _cmsSpace->promote(obj, obj_size);
1286 }
1287 if (res != NULL) {
1288 // See comment in allocate() about when objects should
1289 // be allocated live.
1290 assert(obj->is_oop(), "Will dereference klass pointer below");
1291 collector()->promoted(false, // Not parallel
1292 (HeapWord*)res, obj->is_objArray(), obj_size);
1293 // promotion counters
1294 NOT_PRODUCT(
1295 _numObjectsPromoted++;
1296 _numWordsPromoted +=
1297 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1298 )
1299 }
1300 return res;
1301 }
1304 HeapWord*
1305 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1306 HeapWord* top,
1307 size_t word_sz)
1308 {
1309 return collector()->allocation_limit_reached(space, top, word_sz);
1310 }
1312 // IMPORTANT: Notes on object size recognition in CMS.
1313 // ---------------------------------------------------
1314 // A block of storage in the CMS generation is always in
1315 // one of three states. A free block (FREE), an allocated
1316 // object (OBJECT) whose size() method reports the correct size,
1317 // and an intermediate state (TRANSIENT) in which its size cannot
1318 // be accurately determined.
1319 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1320 // -----------------------------------------------------
1321 // FREE: klass_word & 1 == 1; mark_word holds block size
1322 //
1323 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1324 // obj->size() computes correct size
1325 //
1326 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1327 //
1328 // STATE IDENTIFICATION: (64 bit+COOPS)
1329 // ------------------------------------
1330 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1331 //
1332 // OBJECT: klass_word installed; klass_word != 0;
1333 // obj->size() computes correct size
1334 //
1335 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1336 //
1337 //
1338 // STATE TRANSITION DIAGRAM
1339 //
1340 // mut / parnew mut / parnew
1341 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1342 // ^ |
1343 // |------------------------ DEAD <------------------------------------|
1344 // sweep mut
1345 //
1346 // While a block is in TRANSIENT state its size cannot be determined
1347 // so readers will either need to come back later or stall until
1348 // the size can be determined. Note that for the case of direct
1349 // allocation, P-bits, when available, may be used to determine the
1350 // size of an object that may not yet have been initialized.
1352 // Things to support parallel young-gen collection.
1353 oop
1354 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1355 oop old, markOop m,
1356 size_t word_sz) {
1357 #ifndef PRODUCT
1358 if (Universe::heap()->promotion_should_fail()) {
1359 return NULL;
1360 }
1361 #endif // #ifndef PRODUCT
1363 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1364 PromotionInfo* promoInfo = &ps->promo;
1365 // if we are tracking promotions, then first ensure space for
1366 // promotion (including spooling space for saving header if necessary).
1367 // then allocate and copy, then track promoted info if needed.
1368 // When tracking (see PromotionInfo::track()), the mark word may
1369 // be displaced and in this case restoration of the mark word
1370 // occurs in the (oop_since_save_marks_)iterate phase.
1371 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1372 // Out of space for allocating spooling buffers;
1373 // try expanding and allocating spooling buffers.
1374 if (!expand_and_ensure_spooling_space(promoInfo)) {
1375 return NULL;
1376 }
1377 }
1378 assert(promoInfo->has_spooling_space(), "Control point invariant");
1379 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1380 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1381 if (obj_ptr == NULL) {
1382 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1383 if (obj_ptr == NULL) {
1384 return NULL;
1385 }
1386 }
1387 oop obj = oop(obj_ptr);
1388 OrderAccess::storestore();
1389 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1390 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1391 // IMPORTANT: See note on object initialization for CMS above.
1392 // Otherwise, copy the object. Here we must be careful to insert the
1393 // klass pointer last, since this marks the block as an allocated object.
1394 // Except with compressed oops it's the mark word.
1395 HeapWord* old_ptr = (HeapWord*)old;
1396 // Restore the mark word copied above.
1397 obj->set_mark(m);
1398 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1399 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1400 OrderAccess::storestore();
1402 if (UseCompressedClassPointers) {
1403 // Copy gap missed by (aligned) header size calculation below
1404 obj->set_klass_gap(old->klass_gap());
1405 }
1406 if (word_sz > (size_t)oopDesc::header_size()) {
1407 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1408 obj_ptr + oopDesc::header_size(),
1409 word_sz - oopDesc::header_size());
1410 }
1412 // Now we can track the promoted object, if necessary. We take care
1413 // to delay the transition from uninitialized to full object
1414 // (i.e., insertion of klass pointer) until after, so that it
1415 // atomically becomes a promoted object.
1416 if (promoInfo->tracking()) {
1417 promoInfo->track((PromotedObject*)obj, old->klass());
1418 }
1419 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1420 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1421 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1423 // Finally, install the klass pointer (this should be volatile).
1424 OrderAccess::storestore();
1425 obj->set_klass(old->klass());
1426 // We should now be able to calculate the right size for this object
1427 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1429 collector()->promoted(true, // parallel
1430 obj_ptr, old->is_objArray(), word_sz);
1432 NOT_PRODUCT(
1433 Atomic::inc_ptr(&_numObjectsPromoted);
1434 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1435 )
1437 return obj;
1438 }
1440 void
1441 ConcurrentMarkSweepGeneration::
1442 par_promote_alloc_undo(int thread_num,
1443 HeapWord* obj, size_t word_sz) {
1444 // CMS does not support promotion undo.
1445 ShouldNotReachHere();
1446 }
1448 void
1449 ConcurrentMarkSweepGeneration::
1450 par_promote_alloc_done(int thread_num) {
1451 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1452 ps->lab.retire(thread_num);
1453 }
1455 void
1456 ConcurrentMarkSweepGeneration::
1457 par_oop_since_save_marks_iterate_done(int thread_num) {
1458 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1459 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1460 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1461 }
1463 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1464 size_t size,
1465 bool tlab)
1466 {
1467 // We allow a STW collection only if a full
1468 // collection was requested.
1469 return full || should_allocate(size, tlab); // FIX ME !!!
1470 // This and promotion failure handling are connected at the
1471 // hip and should be fixed by untying them.
1472 }
1474 bool CMSCollector::shouldConcurrentCollect() {
1475 if (_full_gc_requested) {
1476 if (Verbose && PrintGCDetails) {
1477 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1478 " gc request (or gc_locker)");
1479 }
1480 return true;
1481 }
1483 // For debugging purposes, change the type of collection.
1484 // If the rotation is not on the concurrent collection
1485 // type, don't start a concurrent collection.
1486 NOT_PRODUCT(
1487 if (RotateCMSCollectionTypes &&
1488 (_cmsGen->debug_collection_type() !=
1489 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1490 assert(_cmsGen->debug_collection_type() !=
1491 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1492 "Bad cms collection type");
1493 return false;
1494 }
1495 )
1497 FreelistLocker x(this);
1498 // ------------------------------------------------------------------
1499 // Print out lots of information which affects the initiation of
1500 // a collection.
1501 if (PrintCMSInitiationStatistics && stats().valid()) {
1502 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1503 gclog_or_tty->stamp();
1504 gclog_or_tty->print_cr("");
1505 stats().print_on(gclog_or_tty);
1506 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1507 stats().time_until_cms_gen_full());
1508 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1509 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1510 _cmsGen->contiguous_available());
1511 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1512 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1513 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1514 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1515 gclog_or_tty->print_cr("metadata initialized %d",
1516 MetaspaceGC::should_concurrent_collect());
1517 }
1518 // ------------------------------------------------------------------
1520 // If the estimated time to complete a cms collection (cms_duration())
1521 // is less than the estimated time remaining until the cms generation
1522 // is full, start a collection.
1523 if (!UseCMSInitiatingOccupancyOnly) {
1524 if (stats().valid()) {
1525 if (stats().time_until_cms_start() == 0.0) {
1526 return true;
1527 }
1528 } else {
1529 // We want to conservatively collect somewhat early in order
1530 // to try and "bootstrap" our CMS/promotion statistics;
1531 // this branch will not fire after the first successful CMS
1532 // collection because the stats should then be valid.
1533 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1534 if (Verbose && PrintGCDetails) {
1535 gclog_or_tty->print_cr(
1536 " CMSCollector: collect for bootstrapping statistics:"
1537 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1538 _bootstrap_occupancy);
1539 }
1540 return true;
1541 }
1542 }
1543 }
1545 // Otherwise, we start a collection cycle if
1546 // old gen want a collection cycle started. Each may use
1547 // an appropriate criterion for making this decision.
1548 // XXX We need to make sure that the gen expansion
1549 // criterion dovetails well with this. XXX NEED TO FIX THIS
1550 if (_cmsGen->should_concurrent_collect()) {
1551 if (Verbose && PrintGCDetails) {
1552 gclog_or_tty->print_cr("CMS old gen initiated");
1553 }
1554 return true;
1555 }
1557 // We start a collection if we believe an incremental collection may fail;
1558 // this is not likely to be productive in practice because it's probably too
1559 // late anyway.
1560 GenCollectedHeap* gch = GenCollectedHeap::heap();
1561 assert(gch->collector_policy()->is_two_generation_policy(),
1562 "You may want to check the correctness of the following");
1563 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1564 if (Verbose && PrintGCDetails) {
1565 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1566 }
1567 return true;
1568 }
1570 if (MetaspaceGC::should_concurrent_collect()) {
1571 if (Verbose && PrintGCDetails) {
1572 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1573 }
1574 return true;
1575 }
1577 return false;
1578 }
1580 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1582 // Clear _expansion_cause fields of constituent generations
1583 void CMSCollector::clear_expansion_cause() {
1584 _cmsGen->clear_expansion_cause();
1585 }
1587 // We should be conservative in starting a collection cycle. To
1588 // start too eagerly runs the risk of collecting too often in the
1589 // extreme. To collect too rarely falls back on full collections,
1590 // which works, even if not optimum in terms of concurrent work.
1591 // As a work around for too eagerly collecting, use the flag
1592 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1593 // giving the user an easily understandable way of controlling the
1594 // collections.
1595 // We want to start a new collection cycle if any of the following
1596 // conditions hold:
1597 // . our current occupancy exceeds the configured initiating occupancy
1598 // for this generation, or
1599 // . we recently needed to expand this space and have not, since that
1600 // expansion, done a collection of this generation, or
1601 // . the underlying space believes that it may be a good idea to initiate
1602 // a concurrent collection (this may be based on criteria such as the
1603 // following: the space uses linear allocation and linear allocation is
1604 // going to fail, or there is believed to be excessive fragmentation in
1605 // the generation, etc... or ...
1606 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1607 // the case of the old generation; see CR 6543076):
1608 // we may be approaching a point at which allocation requests may fail because
1609 // we will be out of sufficient free space given allocation rate estimates.]
1610 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1612 assert_lock_strong(freelistLock());
1613 if (occupancy() > initiating_occupancy()) {
1614 if (PrintGCDetails && Verbose) {
1615 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1616 short_name(), occupancy(), initiating_occupancy());
1617 }
1618 return true;
1619 }
1620 if (UseCMSInitiatingOccupancyOnly) {
1621 return false;
1622 }
1623 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1624 if (PrintGCDetails && Verbose) {
1625 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1626 short_name());
1627 }
1628 return true;
1629 }
1630 if (_cmsSpace->should_concurrent_collect()) {
1631 if (PrintGCDetails && Verbose) {
1632 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1633 short_name());
1634 }
1635 return true;
1636 }
1637 return false;
1638 }
1640 void ConcurrentMarkSweepGeneration::collect(bool full,
1641 bool clear_all_soft_refs,
1642 size_t size,
1643 bool tlab)
1644 {
1645 collector()->collect(full, clear_all_soft_refs, size, tlab);
1646 }
1648 void CMSCollector::collect(bool full,
1649 bool clear_all_soft_refs,
1650 size_t size,
1651 bool tlab)
1652 {
1653 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1654 // For debugging purposes skip the collection if the state
1655 // is not currently idle
1656 if (TraceCMSState) {
1657 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1658 Thread::current(), full, _collectorState);
1659 }
1660 return;
1661 }
1663 // The following "if" branch is present for defensive reasons.
1664 // In the current uses of this interface, it can be replaced with:
1665 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1666 // But I am not placing that assert here to allow future
1667 // generality in invoking this interface.
1668 if (GC_locker::is_active()) {
1669 // A consistency test for GC_locker
1670 assert(GC_locker::needs_gc(), "Should have been set already");
1671 // Skip this foreground collection, instead
1672 // expanding the heap if necessary.
1673 // Need the free list locks for the call to free() in compute_new_size()
1674 compute_new_size();
1675 return;
1676 }
1677 acquire_control_and_collect(full, clear_all_soft_refs);
1678 _full_gcs_since_conc_gc++;
1679 }
1681 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1682 GenCollectedHeap* gch = GenCollectedHeap::heap();
1683 unsigned int gc_count = gch->total_full_collections();
1684 if (gc_count == full_gc_count) {
1685 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1686 _full_gc_requested = true;
1687 _full_gc_cause = cause;
1688 CGC_lock->notify(); // nudge CMS thread
1689 } else {
1690 assert(gc_count > full_gc_count, "Error: causal loop");
1691 }
1692 }
1694 bool CMSCollector::is_external_interruption() {
1695 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1696 return GCCause::is_user_requested_gc(cause) ||
1697 GCCause::is_serviceability_requested_gc(cause);
1698 }
1700 void CMSCollector::report_concurrent_mode_interruption() {
1701 if (is_external_interruption()) {
1702 if (PrintGCDetails) {
1703 gclog_or_tty->print(" (concurrent mode interrupted)");
1704 }
1705 } else {
1706 if (PrintGCDetails) {
1707 gclog_or_tty->print(" (concurrent mode failure)");
1708 }
1709 _gc_tracer_cm->report_concurrent_mode_failure();
1710 }
1711 }
1714 // The foreground and background collectors need to coordinate in order
1715 // to make sure that they do not mutually interfere with CMS collections.
1716 // When a background collection is active,
1717 // the foreground collector may need to take over (preempt) and
1718 // synchronously complete an ongoing collection. Depending on the
1719 // frequency of the background collections and the heap usage
1720 // of the application, this preemption can be seldom or frequent.
1721 // There are only certain
1722 // points in the background collection that the "collection-baton"
1723 // can be passed to the foreground collector.
1724 //
1725 // The foreground collector will wait for the baton before
1726 // starting any part of the collection. The foreground collector
1727 // will only wait at one location.
1728 //
1729 // The background collector will yield the baton before starting a new
1730 // phase of the collection (e.g., before initial marking, marking from roots,
1731 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1732 // of the loop which switches the phases. The background collector does some
1733 // of the phases (initial mark, final re-mark) with the world stopped.
1734 // Because of locking involved in stopping the world,
1735 // the foreground collector should not block waiting for the background
1736 // collector when it is doing a stop-the-world phase. The background
1737 // collector will yield the baton at an additional point just before
1738 // it enters a stop-the-world phase. Once the world is stopped, the
1739 // background collector checks the phase of the collection. If the
1740 // phase has not changed, it proceeds with the collection. If the
1741 // phase has changed, it skips that phase of the collection. See
1742 // the comments on the use of the Heap_lock in collect_in_background().
1743 //
1744 // Variable used in baton passing.
1745 // _foregroundGCIsActive - Set to true by the foreground collector when
1746 // it wants the baton. The foreground clears it when it has finished
1747 // the collection.
1748 // _foregroundGCShouldWait - Set to true by the background collector
1749 // when it is running. The foreground collector waits while
1750 // _foregroundGCShouldWait is true.
1751 // CGC_lock - monitor used to protect access to the above variables
1752 // and to notify the foreground and background collectors.
1753 // _collectorState - current state of the CMS collection.
1754 //
1755 // The foreground collector
1756 // acquires the CGC_lock
1757 // sets _foregroundGCIsActive
1758 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1759 // various locks acquired in preparation for the collection
1760 // are released so as not to block the background collector
1761 // that is in the midst of a collection
1762 // proceeds with the collection
1763 // clears _foregroundGCIsActive
1764 // returns
1765 //
1766 // The background collector in a loop iterating on the phases of the
1767 // collection
1768 // acquires the CGC_lock
1769 // sets _foregroundGCShouldWait
1770 // if _foregroundGCIsActive is set
1771 // clears _foregroundGCShouldWait, notifies _CGC_lock
1772 // waits on _CGC_lock for _foregroundGCIsActive to become false
1773 // and exits the loop.
1774 // otherwise
1775 // proceed with that phase of the collection
1776 // if the phase is a stop-the-world phase,
1777 // yield the baton once more just before enqueueing
1778 // the stop-world CMS operation (executed by the VM thread).
1779 // returns after all phases of the collection are done
1780 //
1782 void CMSCollector::acquire_control_and_collect(bool full,
1783 bool clear_all_soft_refs) {
1784 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1785 assert(!Thread::current()->is_ConcurrentGC_thread(),
1786 "shouldn't try to acquire control from self!");
1788 // Start the protocol for acquiring control of the
1789 // collection from the background collector (aka CMS thread).
1790 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1791 "VM thread should have CMS token");
1792 // Remember the possibly interrupted state of an ongoing
1793 // concurrent collection
1794 CollectorState first_state = _collectorState;
1796 // Signal to a possibly ongoing concurrent collection that
1797 // we want to do a foreground collection.
1798 _foregroundGCIsActive = true;
1800 // Disable incremental mode during a foreground collection.
1801 ICMSDisabler icms_disabler;
1803 // release locks and wait for a notify from the background collector
1804 // releasing the locks in only necessary for phases which
1805 // do yields to improve the granularity of the collection.
1806 assert_lock_strong(bitMapLock());
1807 // We need to lock the Free list lock for the space that we are
1808 // currently collecting.
1809 assert(haveFreelistLocks(), "Must be holding free list locks");
1810 bitMapLock()->unlock();
1811 releaseFreelistLocks();
1812 {
1813 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1814 if (_foregroundGCShouldWait) {
1815 // We are going to be waiting for action for the CMS thread;
1816 // it had better not be gone (for instance at shutdown)!
1817 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1818 "CMS thread must be running");
1819 // Wait here until the background collector gives us the go-ahead
1820 ConcurrentMarkSweepThread::clear_CMS_flag(
1821 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1822 // Get a possibly blocked CMS thread going:
1823 // Note that we set _foregroundGCIsActive true above,
1824 // without protection of the CGC_lock.
1825 CGC_lock->notify();
1826 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1827 "Possible deadlock");
1828 while (_foregroundGCShouldWait) {
1829 // wait for notification
1830 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1831 // Possibility of delay/starvation here, since CMS token does
1832 // not know to give priority to VM thread? Actually, i think
1833 // there wouldn't be any delay/starvation, but the proof of
1834 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1835 }
1836 ConcurrentMarkSweepThread::set_CMS_flag(
1837 ConcurrentMarkSweepThread::CMS_vm_has_token);
1838 }
1839 }
1840 // The CMS_token is already held. Get back the other locks.
1841 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1842 "VM thread should have CMS token");
1843 getFreelistLocks();
1844 bitMapLock()->lock_without_safepoint_check();
1845 if (TraceCMSState) {
1846 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1847 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1848 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1849 }
1851 // Check if we need to do a compaction, or if not, whether
1852 // we need to start the mark-sweep from scratch.
1853 bool should_compact = false;
1854 bool should_start_over = false;
1855 decide_foreground_collection_type(clear_all_soft_refs,
1856 &should_compact, &should_start_over);
1858 NOT_PRODUCT(
1859 if (RotateCMSCollectionTypes) {
1860 if (_cmsGen->debug_collection_type() ==
1861 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1862 should_compact = true;
1863 } else if (_cmsGen->debug_collection_type() ==
1864 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1865 should_compact = false;
1866 }
1867 }
1868 )
1870 if (first_state > Idling) {
1871 report_concurrent_mode_interruption();
1872 }
1874 set_did_compact(should_compact);
1875 if (should_compact) {
1876 // If the collection is being acquired from the background
1877 // collector, there may be references on the discovered
1878 // references lists that have NULL referents (being those
1879 // that were concurrently cleared by a mutator) or
1880 // that are no longer active (having been enqueued concurrently
1881 // by the mutator).
1882 // Scrub the list of those references because Mark-Sweep-Compact
1883 // code assumes referents are not NULL and that all discovered
1884 // Reference objects are active.
1885 ref_processor()->clean_up_discovered_references();
1887 if (first_state > Idling) {
1888 save_heap_summary();
1889 }
1891 do_compaction_work(clear_all_soft_refs);
1893 // Has the GC time limit been exceeded?
1894 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1895 size_t max_eden_size = young_gen->max_capacity() -
1896 young_gen->to()->capacity() -
1897 young_gen->from()->capacity();
1898 GenCollectedHeap* gch = GenCollectedHeap::heap();
1899 GCCause::Cause gc_cause = gch->gc_cause();
1900 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1901 young_gen->eden()->used(),
1902 _cmsGen->max_capacity(),
1903 max_eden_size,
1904 full,
1905 gc_cause,
1906 gch->collector_policy());
1907 } else {
1908 do_mark_sweep_work(clear_all_soft_refs, first_state,
1909 should_start_over);
1910 }
1911 // Reset the expansion cause, now that we just completed
1912 // a collection cycle.
1913 clear_expansion_cause();
1914 _foregroundGCIsActive = false;
1915 return;
1916 }
1918 // Resize the tenured generation
1919 // after obtaining the free list locks for the
1920 // two generations.
1921 void CMSCollector::compute_new_size() {
1922 assert_locked_or_safepoint(Heap_lock);
1923 FreelistLocker z(this);
1924 MetaspaceGC::compute_new_size();
1925 _cmsGen->compute_new_size_free_list();
1926 }
1928 // A work method used by foreground collection to determine
1929 // what type of collection (compacting or not, continuing or fresh)
1930 // it should do.
1931 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1932 // and CMSCompactWhenClearAllSoftRefs the default in the future
1933 // and do away with the flags after a suitable period.
1934 void CMSCollector::decide_foreground_collection_type(
1935 bool clear_all_soft_refs, bool* should_compact,
1936 bool* should_start_over) {
1937 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1938 // flag is set, and we have either requested a System.gc() or
1939 // the number of full gc's since the last concurrent cycle
1940 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1941 // or if an incremental collection has failed
1942 GenCollectedHeap* gch = GenCollectedHeap::heap();
1943 assert(gch->collector_policy()->is_two_generation_policy(),
1944 "You may want to check the correctness of the following");
1945 // Inform cms gen if this was due to partial collection failing.
1946 // The CMS gen may use this fact to determine its expansion policy.
1947 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1948 assert(!_cmsGen->incremental_collection_failed(),
1949 "Should have been noticed, reacted to and cleared");
1950 _cmsGen->set_incremental_collection_failed();
1951 }
1952 *should_compact =
1953 UseCMSCompactAtFullCollection &&
1954 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1955 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1956 gch->incremental_collection_will_fail(true /* consult_young */));
1957 *should_start_over = false;
1958 if (clear_all_soft_refs && !*should_compact) {
1959 // We are about to do a last ditch collection attempt
1960 // so it would normally make sense to do a compaction
1961 // to reclaim as much space as possible.
1962 if (CMSCompactWhenClearAllSoftRefs) {
1963 // Default: The rationale is that in this case either
1964 // we are past the final marking phase, in which case
1965 // we'd have to start over, or so little has been done
1966 // that there's little point in saving that work. Compaction
1967 // appears to be the sensible choice in either case.
1968 *should_compact = true;
1969 } else {
1970 // We have been asked to clear all soft refs, but not to
1971 // compact. Make sure that we aren't past the final checkpoint
1972 // phase, for that is where we process soft refs. If we are already
1973 // past that phase, we'll need to redo the refs discovery phase and
1974 // if necessary clear soft refs that weren't previously
1975 // cleared. We do so by remembering the phase in which
1976 // we came in, and if we are past the refs processing
1977 // phase, we'll choose to just redo the mark-sweep
1978 // collection from scratch.
1979 if (_collectorState > FinalMarking) {
1980 // We are past the refs processing phase;
1981 // start over and do a fresh synchronous CMS cycle
1982 _collectorState = Resetting; // skip to reset to start new cycle
1983 reset(false /* == !asynch */);
1984 *should_start_over = true;
1985 } // else we can continue a possibly ongoing current cycle
1986 }
1987 }
1988 }
1990 // A work method used by the foreground collector to do
1991 // a mark-sweep-compact.
1992 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1993 GenCollectedHeap* gch = GenCollectedHeap::heap();
1995 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1996 gc_timer->register_gc_start();
1998 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1999 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
2001 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL);
2002 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
2003 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
2004 "collections passed to foreground collector", _full_gcs_since_conc_gc);
2005 }
2007 // Sample collection interval time and reset for collection pause.
2008 if (UseAdaptiveSizePolicy) {
2009 size_policy()->msc_collection_begin();
2010 }
2012 // Temporarily widen the span of the weak reference processing to
2013 // the entire heap.
2014 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
2015 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
2016 // Temporarily, clear the "is_alive_non_header" field of the
2017 // reference processor.
2018 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
2019 // Temporarily make reference _processing_ single threaded (non-MT).
2020 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
2021 // Temporarily make refs discovery atomic
2022 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
2023 // Temporarily make reference _discovery_ single threaded (non-MT)
2024 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
2026 ref_processor()->set_enqueuing_is_done(false);
2027 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
2028 ref_processor()->setup_policy(clear_all_soft_refs);
2029 // If an asynchronous collection finishes, the _modUnionTable is
2030 // all clear. If we are assuming the collection from an asynchronous
2031 // collection, clear the _modUnionTable.
2032 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
2033 "_modUnionTable should be clear if the baton was not passed");
2034 _modUnionTable.clear_all();
2035 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
2036 "mod union for klasses should be clear if the baton was passed");
2037 _ct->klass_rem_set()->clear_mod_union();
2039 // We must adjust the allocation statistics being maintained
2040 // in the free list space. We do so by reading and clearing
2041 // the sweep timer and updating the block flux rate estimates below.
2042 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
2043 if (_inter_sweep_timer.is_active()) {
2044 _inter_sweep_timer.stop();
2045 // Note that we do not use this sample to update the _inter_sweep_estimate.
2046 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
2047 _inter_sweep_estimate.padded_average(),
2048 _intra_sweep_estimate.padded_average());
2049 }
2051 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2052 ref_processor(), clear_all_soft_refs);
2053 #ifdef ASSERT
2054 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2055 size_t free_size = cms_space->free();
2056 assert(free_size ==
2057 pointer_delta(cms_space->end(), cms_space->compaction_top())
2058 * HeapWordSize,
2059 "All the free space should be compacted into one chunk at top");
2060 assert(cms_space->dictionary()->total_chunk_size(
2061 debug_only(cms_space->freelistLock())) == 0 ||
2062 cms_space->totalSizeInIndexedFreeLists() == 0,
2063 "All the free space should be in a single chunk");
2064 size_t num = cms_space->totalCount();
2065 assert((free_size == 0 && num == 0) ||
2066 (free_size > 0 && (num == 1 || num == 2)),
2067 "There should be at most 2 free chunks after compaction");
2068 #endif // ASSERT
2069 _collectorState = Resetting;
2070 assert(_restart_addr == NULL,
2071 "Should have been NULL'd before baton was passed");
2072 reset(false /* == !asynch */);
2073 _cmsGen->reset_after_compaction();
2074 _concurrent_cycles_since_last_unload = 0;
2076 // Clear any data recorded in the PLAB chunk arrays.
2077 if (_survivor_plab_array != NULL) {
2078 reset_survivor_plab_arrays();
2079 }
2081 // Adjust the per-size allocation stats for the next epoch.
2082 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2083 // Restart the "inter sweep timer" for the next epoch.
2084 _inter_sweep_timer.reset();
2085 _inter_sweep_timer.start();
2087 // Sample collection pause time and reset for collection interval.
2088 if (UseAdaptiveSizePolicy) {
2089 size_policy()->msc_collection_end(gch->gc_cause());
2090 }
2092 gc_timer->register_gc_end();
2094 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
2096 // For a mark-sweep-compact, compute_new_size() will be called
2097 // in the heap's do_collection() method.
2098 }
2100 // A work method used by the foreground collector to do
2101 // a mark-sweep, after taking over from a possibly on-going
2102 // concurrent mark-sweep collection.
2103 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2104 CollectorState first_state, bool should_start_over) {
2105 if (PrintGC && Verbose) {
2106 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2107 "collector with count %d",
2108 _full_gcs_since_conc_gc);
2109 }
2110 switch (_collectorState) {
2111 case Idling:
2112 if (first_state == Idling || should_start_over) {
2113 // The background GC was not active, or should
2114 // restarted from scratch; start the cycle.
2115 _collectorState = InitialMarking;
2116 }
2117 // If first_state was not Idling, then a background GC
2118 // was in progress and has now finished. No need to do it
2119 // again. Leave the state as Idling.
2120 break;
2121 case Precleaning:
2122 // In the foreground case don't do the precleaning since
2123 // it is not done concurrently and there is extra work
2124 // required.
2125 _collectorState = FinalMarking;
2126 }
2127 collect_in_foreground(clear_all_soft_refs, GenCollectedHeap::heap()->gc_cause());
2129 // For a mark-sweep, compute_new_size() will be called
2130 // in the heap's do_collection() method.
2131 }
2134 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
2135 DefNewGeneration* dng = _young_gen->as_DefNewGeneration();
2136 EdenSpace* eden_space = dng->eden();
2137 ContiguousSpace* from_space = dng->from();
2138 ContiguousSpace* to_space = dng->to();
2139 // Eden
2140 if (_eden_chunk_array != NULL) {
2141 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2142 eden_space->bottom(), eden_space->top(),
2143 eden_space->end(), eden_space->capacity());
2144 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
2145 "_eden_chunk_capacity=" SIZE_FORMAT,
2146 _eden_chunk_index, _eden_chunk_capacity);
2147 for (size_t i = 0; i < _eden_chunk_index; i++) {
2148 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2149 i, _eden_chunk_array[i]);
2150 }
2151 }
2152 // Survivor
2153 if (_survivor_chunk_array != NULL) {
2154 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2155 from_space->bottom(), from_space->top(),
2156 from_space->end(), from_space->capacity());
2157 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
2158 "_survivor_chunk_capacity=" SIZE_FORMAT,
2159 _survivor_chunk_index, _survivor_chunk_capacity);
2160 for (size_t i = 0; i < _survivor_chunk_index; i++) {
2161 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2162 i, _survivor_chunk_array[i]);
2163 }
2164 }
2165 }
2167 void CMSCollector::getFreelistLocks() const {
2168 // Get locks for all free lists in all generations that this
2169 // collector is responsible for
2170 _cmsGen->freelistLock()->lock_without_safepoint_check();
2171 }
2173 void CMSCollector::releaseFreelistLocks() const {
2174 // Release locks for all free lists in all generations that this
2175 // collector is responsible for
2176 _cmsGen->freelistLock()->unlock();
2177 }
2179 bool CMSCollector::haveFreelistLocks() const {
2180 // Check locks for all free lists in all generations that this
2181 // collector is responsible for
2182 assert_lock_strong(_cmsGen->freelistLock());
2183 PRODUCT_ONLY(ShouldNotReachHere());
2184 return true;
2185 }
2187 // A utility class that is used by the CMS collector to
2188 // temporarily "release" the foreground collector from its
2189 // usual obligation to wait for the background collector to
2190 // complete an ongoing phase before proceeding.
2191 class ReleaseForegroundGC: public StackObj {
2192 private:
2193 CMSCollector* _c;
2194 public:
2195 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2196 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2197 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2198 // allow a potentially blocked foreground collector to proceed
2199 _c->_foregroundGCShouldWait = false;
2200 if (_c->_foregroundGCIsActive) {
2201 CGC_lock->notify();
2202 }
2203 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2204 "Possible deadlock");
2205 }
2207 ~ReleaseForegroundGC() {
2208 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2209 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2210 _c->_foregroundGCShouldWait = true;
2211 }
2212 };
2214 // There are separate collect_in_background and collect_in_foreground because of
2215 // the different locking requirements of the background collector and the
2216 // foreground collector. There was originally an attempt to share
2217 // one "collect" method between the background collector and the foreground
2218 // collector but the if-then-else required made it cleaner to have
2219 // separate methods.
2220 void CMSCollector::collect_in_background(bool clear_all_soft_refs, GCCause::Cause cause) {
2221 assert(Thread::current()->is_ConcurrentGC_thread(),
2222 "A CMS asynchronous collection is only allowed on a CMS thread.");
2224 GenCollectedHeap* gch = GenCollectedHeap::heap();
2225 {
2226 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2227 MutexLockerEx hl(Heap_lock, safepoint_check);
2228 FreelistLocker fll(this);
2229 MutexLockerEx x(CGC_lock, safepoint_check);
2230 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2231 // The foreground collector is active or we're
2232 // not using asynchronous collections. Skip this
2233 // background collection.
2234 assert(!_foregroundGCShouldWait, "Should be clear");
2235 return;
2236 } else {
2237 assert(_collectorState == Idling, "Should be idling before start.");
2238 _collectorState = InitialMarking;
2239 register_gc_start(cause);
2240 // Reset the expansion cause, now that we are about to begin
2241 // a new cycle.
2242 clear_expansion_cause();
2244 // Clear the MetaspaceGC flag since a concurrent collection
2245 // is starting but also clear it after the collection.
2246 MetaspaceGC::set_should_concurrent_collect(false);
2247 }
2248 // Decide if we want to enable class unloading as part of the
2249 // ensuing concurrent GC cycle.
2250 update_should_unload_classes();
2251 _full_gc_requested = false; // acks all outstanding full gc requests
2252 _full_gc_cause = GCCause::_no_gc;
2253 // Signal that we are about to start a collection
2254 gch->increment_total_full_collections(); // ... starting a collection cycle
2255 _collection_count_start = gch->total_full_collections();
2256 }
2258 // Used for PrintGC
2259 size_t prev_used;
2260 if (PrintGC && Verbose) {
2261 prev_used = _cmsGen->used(); // XXXPERM
2262 }
2264 // The change of the collection state is normally done at this level;
2265 // the exceptions are phases that are executed while the world is
2266 // stopped. For those phases the change of state is done while the
2267 // world is stopped. For baton passing purposes this allows the
2268 // background collector to finish the phase and change state atomically.
2269 // The foreground collector cannot wait on a phase that is done
2270 // while the world is stopped because the foreground collector already
2271 // has the world stopped and would deadlock.
2272 while (_collectorState != Idling) {
2273 if (TraceCMSState) {
2274 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2275 Thread::current(), _collectorState);
2276 }
2277 // The foreground collector
2278 // holds the Heap_lock throughout its collection.
2279 // holds the CMS token (but not the lock)
2280 // except while it is waiting for the background collector to yield.
2281 //
2282 // The foreground collector should be blocked (not for long)
2283 // if the background collector is about to start a phase
2284 // executed with world stopped. If the background
2285 // collector has already started such a phase, the
2286 // foreground collector is blocked waiting for the
2287 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2288 // are executed in the VM thread.
2289 //
2290 // The locking order is
2291 // PendingListLock (PLL) -- if applicable (FinalMarking)
2292 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2293 // CMS token (claimed in
2294 // stop_world_and_do() -->
2295 // safepoint_synchronize() -->
2296 // CMSThread::synchronize())
2298 {
2299 // Check if the FG collector wants us to yield.
2300 CMSTokenSync x(true); // is cms thread
2301 if (waitForForegroundGC()) {
2302 // We yielded to a foreground GC, nothing more to be
2303 // done this round.
2304 assert(_foregroundGCShouldWait == false, "We set it to false in "
2305 "waitForForegroundGC()");
2306 if (TraceCMSState) {
2307 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2308 " exiting collection CMS state %d",
2309 Thread::current(), _collectorState);
2310 }
2311 return;
2312 } else {
2313 // The background collector can run but check to see if the
2314 // foreground collector has done a collection while the
2315 // background collector was waiting to get the CGC_lock
2316 // above. If yes, break so that _foregroundGCShouldWait
2317 // is cleared before returning.
2318 if (_collectorState == Idling) {
2319 break;
2320 }
2321 }
2322 }
2324 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2325 "should be waiting");
2327 switch (_collectorState) {
2328 case InitialMarking:
2329 {
2330 ReleaseForegroundGC x(this);
2331 stats().record_cms_begin();
2332 VM_CMS_Initial_Mark initial_mark_op(this);
2333 VMThread::execute(&initial_mark_op);
2334 }
2335 // The collector state may be any legal state at this point
2336 // since the background collector may have yielded to the
2337 // foreground collector.
2338 break;
2339 case Marking:
2340 // initial marking in checkpointRootsInitialWork has been completed
2341 if (markFromRoots(true)) { // we were successful
2342 assert(_collectorState == Precleaning, "Collector state should "
2343 "have changed");
2344 } else {
2345 assert(_foregroundGCIsActive, "Internal state inconsistency");
2346 }
2347 break;
2348 case Precleaning:
2349 if (UseAdaptiveSizePolicy) {
2350 size_policy()->concurrent_precleaning_begin();
2351 }
2352 // marking from roots in markFromRoots has been completed
2353 preclean();
2354 if (UseAdaptiveSizePolicy) {
2355 size_policy()->concurrent_precleaning_end();
2356 }
2357 assert(_collectorState == AbortablePreclean ||
2358 _collectorState == FinalMarking,
2359 "Collector state should have changed");
2360 break;
2361 case AbortablePreclean:
2362 if (UseAdaptiveSizePolicy) {
2363 size_policy()->concurrent_phases_resume();
2364 }
2365 abortable_preclean();
2366 if (UseAdaptiveSizePolicy) {
2367 size_policy()->concurrent_precleaning_end();
2368 }
2369 assert(_collectorState == FinalMarking, "Collector state should "
2370 "have changed");
2371 break;
2372 case FinalMarking:
2373 {
2374 ReleaseForegroundGC x(this);
2376 VM_CMS_Final_Remark final_remark_op(this);
2377 VMThread::execute(&final_remark_op);
2378 }
2379 assert(_foregroundGCShouldWait, "block post-condition");
2380 break;
2381 case Sweeping:
2382 if (UseAdaptiveSizePolicy) {
2383 size_policy()->concurrent_sweeping_begin();
2384 }
2385 // final marking in checkpointRootsFinal has been completed
2386 sweep(true);
2387 assert(_collectorState == Resizing, "Collector state change "
2388 "to Resizing must be done under the free_list_lock");
2389 _full_gcs_since_conc_gc = 0;
2391 // Stop the timers for adaptive size policy for the concurrent phases
2392 if (UseAdaptiveSizePolicy) {
2393 size_policy()->concurrent_sweeping_end();
2394 size_policy()->concurrent_phases_end(gch->gc_cause(),
2395 gch->prev_gen(_cmsGen)->capacity(),
2396 _cmsGen->free());
2397 }
2399 case Resizing: {
2400 // Sweeping has been completed...
2401 // At this point the background collection has completed.
2402 // Don't move the call to compute_new_size() down
2403 // into code that might be executed if the background
2404 // collection was preempted.
2405 {
2406 ReleaseForegroundGC x(this); // unblock FG collection
2407 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2408 CMSTokenSync z(true); // not strictly needed.
2409 if (_collectorState == Resizing) {
2410 compute_new_size();
2411 save_heap_summary();
2412 _collectorState = Resetting;
2413 } else {
2414 assert(_collectorState == Idling, "The state should only change"
2415 " because the foreground collector has finished the collection");
2416 }
2417 }
2418 break;
2419 }
2420 case Resetting:
2421 // CMS heap resizing has been completed
2422 reset(true);
2423 assert(_collectorState == Idling, "Collector state should "
2424 "have changed");
2426 MetaspaceGC::set_should_concurrent_collect(false);
2428 stats().record_cms_end();
2429 // Don't move the concurrent_phases_end() and compute_new_size()
2430 // calls to here because a preempted background collection
2431 // has it's state set to "Resetting".
2432 break;
2433 case Idling:
2434 default:
2435 ShouldNotReachHere();
2436 break;
2437 }
2438 if (TraceCMSState) {
2439 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2440 Thread::current(), _collectorState);
2441 }
2442 assert(_foregroundGCShouldWait, "block post-condition");
2443 }
2445 // Should this be in gc_epilogue?
2446 collector_policy()->counters()->update_counters();
2448 {
2449 // Clear _foregroundGCShouldWait and, in the event that the
2450 // foreground collector is waiting, notify it, before
2451 // returning.
2452 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2453 _foregroundGCShouldWait = false;
2454 if (_foregroundGCIsActive) {
2455 CGC_lock->notify();
2456 }
2457 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2458 "Possible deadlock");
2459 }
2460 if (TraceCMSState) {
2461 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2462 " exiting collection CMS state %d",
2463 Thread::current(), _collectorState);
2464 }
2465 if (PrintGC && Verbose) {
2466 _cmsGen->print_heap_change(prev_used);
2467 }
2468 }
2470 void CMSCollector::register_foreground_gc_start(GCCause::Cause cause) {
2471 if (!_cms_start_registered) {
2472 register_gc_start(cause);
2473 }
2474 }
2476 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2477 _cms_start_registered = true;
2478 _gc_timer_cm->register_gc_start();
2479 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2480 }
2482 void CMSCollector::register_gc_end() {
2483 if (_cms_start_registered) {
2484 report_heap_summary(GCWhen::AfterGC);
2486 _gc_timer_cm->register_gc_end();
2487 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2488 _cms_start_registered = false;
2489 }
2490 }
2492 void CMSCollector::save_heap_summary() {
2493 GenCollectedHeap* gch = GenCollectedHeap::heap();
2494 _last_heap_summary = gch->create_heap_summary();
2495 _last_metaspace_summary = gch->create_metaspace_summary();
2496 }
2498 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2499 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2500 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2501 }
2503 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs, GCCause::Cause cause) {
2504 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2505 "Foreground collector should be waiting, not executing");
2506 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2507 "may only be done by the VM Thread with the world stopped");
2508 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2509 "VM thread should have CMS token");
2511 NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2512 true, NULL);)
2513 if (UseAdaptiveSizePolicy) {
2514 size_policy()->ms_collection_begin();
2515 }
2516 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2518 HandleMark hm; // Discard invalid handles created during verification
2520 if (VerifyBeforeGC &&
2521 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2522 Universe::verify();
2523 }
2525 // Snapshot the soft reference policy to be used in this collection cycle.
2526 ref_processor()->setup_policy(clear_all_soft_refs);
2528 // Decide if class unloading should be done
2529 update_should_unload_classes();
2531 bool init_mark_was_synchronous = false; // until proven otherwise
2532 while (_collectorState != Idling) {
2533 if (TraceCMSState) {
2534 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2535 Thread::current(), _collectorState);
2536 }
2537 switch (_collectorState) {
2538 case InitialMarking:
2539 register_foreground_gc_start(cause);
2540 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2541 checkpointRootsInitial(false);
2542 assert(_collectorState == Marking, "Collector state should have changed"
2543 " within checkpointRootsInitial()");
2544 break;
2545 case Marking:
2546 // initial marking in checkpointRootsInitialWork has been completed
2547 if (VerifyDuringGC &&
2548 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2549 Universe::verify("Verify before initial mark: ");
2550 }
2551 {
2552 bool res = markFromRoots(false);
2553 assert(res && _collectorState == FinalMarking, "Collector state should "
2554 "have changed");
2555 break;
2556 }
2557 case FinalMarking:
2558 if (VerifyDuringGC &&
2559 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2560 Universe::verify("Verify before re-mark: ");
2561 }
2562 checkpointRootsFinal(false, clear_all_soft_refs,
2563 init_mark_was_synchronous);
2564 assert(_collectorState == Sweeping, "Collector state should not "
2565 "have changed within checkpointRootsFinal()");
2566 break;
2567 case Sweeping:
2568 // final marking in checkpointRootsFinal has been completed
2569 if (VerifyDuringGC &&
2570 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2571 Universe::verify("Verify before sweep: ");
2572 }
2573 sweep(false);
2574 assert(_collectorState == Resizing, "Incorrect state");
2575 break;
2576 case Resizing: {
2577 // Sweeping has been completed; the actual resize in this case
2578 // is done separately; nothing to be done in this state.
2579 _collectorState = Resetting;
2580 break;
2581 }
2582 case Resetting:
2583 // The heap has been resized.
2584 if (VerifyDuringGC &&
2585 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2586 Universe::verify("Verify before reset: ");
2587 }
2588 save_heap_summary();
2589 reset(false);
2590 assert(_collectorState == Idling, "Collector state should "
2591 "have changed");
2592 break;
2593 case Precleaning:
2594 case AbortablePreclean:
2595 // Elide the preclean phase
2596 _collectorState = FinalMarking;
2597 break;
2598 default:
2599 ShouldNotReachHere();
2600 }
2601 if (TraceCMSState) {
2602 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2603 Thread::current(), _collectorState);
2604 }
2605 }
2607 if (UseAdaptiveSizePolicy) {
2608 GenCollectedHeap* gch = GenCollectedHeap::heap();
2609 size_policy()->ms_collection_end(gch->gc_cause());
2610 }
2612 if (VerifyAfterGC &&
2613 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2614 Universe::verify();
2615 }
2616 if (TraceCMSState) {
2617 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2618 " exiting collection CMS state %d",
2619 Thread::current(), _collectorState);
2620 }
2621 }
2623 bool CMSCollector::waitForForegroundGC() {
2624 bool res = false;
2625 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2626 "CMS thread should have CMS token");
2627 // Block the foreground collector until the
2628 // background collectors decides whether to
2629 // yield.
2630 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2631 _foregroundGCShouldWait = true;
2632 if (_foregroundGCIsActive) {
2633 // The background collector yields to the
2634 // foreground collector and returns a value
2635 // indicating that it has yielded. The foreground
2636 // collector can proceed.
2637 res = true;
2638 _foregroundGCShouldWait = false;
2639 ConcurrentMarkSweepThread::clear_CMS_flag(
2640 ConcurrentMarkSweepThread::CMS_cms_has_token);
2641 ConcurrentMarkSweepThread::set_CMS_flag(
2642 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2643 // Get a possibly blocked foreground thread going
2644 CGC_lock->notify();
2645 if (TraceCMSState) {
2646 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2647 Thread::current(), _collectorState);
2648 }
2649 while (_foregroundGCIsActive) {
2650 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2651 }
2652 ConcurrentMarkSweepThread::set_CMS_flag(
2653 ConcurrentMarkSweepThread::CMS_cms_has_token);
2654 ConcurrentMarkSweepThread::clear_CMS_flag(
2655 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2656 }
2657 if (TraceCMSState) {
2658 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2659 Thread::current(), _collectorState);
2660 }
2661 return res;
2662 }
2664 // Because of the need to lock the free lists and other structures in
2665 // the collector, common to all the generations that the collector is
2666 // collecting, we need the gc_prologues of individual CMS generations
2667 // delegate to their collector. It may have been simpler had the
2668 // current infrastructure allowed one to call a prologue on a
2669 // collector. In the absence of that we have the generation's
2670 // prologue delegate to the collector, which delegates back
2671 // some "local" work to a worker method in the individual generations
2672 // that it's responsible for collecting, while itself doing any
2673 // work common to all generations it's responsible for. A similar
2674 // comment applies to the gc_epilogue()'s.
2675 // The role of the varaible _between_prologue_and_epilogue is to
2676 // enforce the invocation protocol.
2677 void CMSCollector::gc_prologue(bool full) {
2678 // Call gc_prologue_work() for the CMSGen
2679 // we are responsible for.
2681 // The following locking discipline assumes that we are only called
2682 // when the world is stopped.
2683 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2685 // The CMSCollector prologue must call the gc_prologues for the
2686 // "generations" that it's responsible
2687 // for.
2689 assert( Thread::current()->is_VM_thread()
2690 || ( CMSScavengeBeforeRemark
2691 && Thread::current()->is_ConcurrentGC_thread()),
2692 "Incorrect thread type for prologue execution");
2694 if (_between_prologue_and_epilogue) {
2695 // We have already been invoked; this is a gc_prologue delegation
2696 // from yet another CMS generation that we are responsible for, just
2697 // ignore it since all relevant work has already been done.
2698 return;
2699 }
2701 // set a bit saying prologue has been called; cleared in epilogue
2702 _between_prologue_and_epilogue = true;
2703 // Claim locks for common data structures, then call gc_prologue_work()
2704 // for each CMSGen.
2706 getFreelistLocks(); // gets free list locks on constituent spaces
2707 bitMapLock()->lock_without_safepoint_check();
2709 // Should call gc_prologue_work() for all cms gens we are responsible for
2710 bool duringMarking = _collectorState >= Marking
2711 && _collectorState < Sweeping;
2713 // The young collections clear the modified oops state, which tells if
2714 // there are any modified oops in the class. The remark phase also needs
2715 // that information. Tell the young collection to save the union of all
2716 // modified klasses.
2717 if (duringMarking) {
2718 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2719 }
2721 bool registerClosure = duringMarking;
2723 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2724 &_modUnionClosurePar
2725 : &_modUnionClosure;
2726 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2728 if (!full) {
2729 stats().record_gc0_begin();
2730 }
2731 }
2733 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2735 _capacity_at_prologue = capacity();
2736 _used_at_prologue = used();
2738 // Delegate to CMScollector which knows how to coordinate between
2739 // this and any other CMS generations that it is responsible for
2740 // collecting.
2741 collector()->gc_prologue(full);
2742 }
2744 // This is a "private" interface for use by this generation's CMSCollector.
2745 // Not to be called directly by any other entity (for instance,
2746 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2747 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2748 bool registerClosure, ModUnionClosure* modUnionClosure) {
2749 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2750 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2751 "Should be NULL");
2752 if (registerClosure) {
2753 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2754 }
2755 cmsSpace()->gc_prologue();
2756 // Clear stat counters
2757 NOT_PRODUCT(
2758 assert(_numObjectsPromoted == 0, "check");
2759 assert(_numWordsPromoted == 0, "check");
2760 if (Verbose && PrintGC) {
2761 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2762 SIZE_FORMAT" bytes concurrently",
2763 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2764 }
2765 _numObjectsAllocated = 0;
2766 _numWordsAllocated = 0;
2767 )
2768 }
2770 void CMSCollector::gc_epilogue(bool full) {
2771 // The following locking discipline assumes that we are only called
2772 // when the world is stopped.
2773 assert(SafepointSynchronize::is_at_safepoint(),
2774 "world is stopped assumption");
2776 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2777 // if linear allocation blocks need to be appropriately marked to allow the
2778 // the blocks to be parsable. We also check here whether we need to nudge the
2779 // CMS collector thread to start a new cycle (if it's not already active).
2780 assert( Thread::current()->is_VM_thread()
2781 || ( CMSScavengeBeforeRemark
2782 && Thread::current()->is_ConcurrentGC_thread()),
2783 "Incorrect thread type for epilogue execution");
2785 if (!_between_prologue_and_epilogue) {
2786 // We have already been invoked; this is a gc_epilogue delegation
2787 // from yet another CMS generation that we are responsible for, just
2788 // ignore it since all relevant work has already been done.
2789 return;
2790 }
2791 assert(haveFreelistLocks(), "must have freelist locks");
2792 assert_lock_strong(bitMapLock());
2794 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2796 _cmsGen->gc_epilogue_work(full);
2798 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2799 // in case sampling was not already enabled, enable it
2800 _start_sampling = true;
2801 }
2802 // reset _eden_chunk_array so sampling starts afresh
2803 _eden_chunk_index = 0;
2805 size_t cms_used = _cmsGen->cmsSpace()->used();
2807 // update performance counters - this uses a special version of
2808 // update_counters() that allows the utilization to be passed as a
2809 // parameter, avoiding multiple calls to used().
2810 //
2811 _cmsGen->update_counters(cms_used);
2813 if (CMSIncrementalMode) {
2814 icms_update_allocation_limits();
2815 }
2817 bitMapLock()->unlock();
2818 releaseFreelistLocks();
2820 if (!CleanChunkPoolAsync) {
2821 Chunk::clean_chunk_pool();
2822 }
2824 set_did_compact(false);
2825 _between_prologue_and_epilogue = false; // ready for next cycle
2826 }
2828 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2829 collector()->gc_epilogue(full);
2831 // Also reset promotion tracking in par gc thread states.
2832 if (CollectedHeap::use_parallel_gc_threads()) {
2833 for (uint i = 0; i < ParallelGCThreads; i++) {
2834 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2835 }
2836 }
2837 }
2839 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2840 assert(!incremental_collection_failed(), "Should have been cleared");
2841 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2842 cmsSpace()->gc_epilogue();
2843 // Print stat counters
2844 NOT_PRODUCT(
2845 assert(_numObjectsAllocated == 0, "check");
2846 assert(_numWordsAllocated == 0, "check");
2847 if (Verbose && PrintGC) {
2848 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2849 SIZE_FORMAT" bytes",
2850 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2851 }
2852 _numObjectsPromoted = 0;
2853 _numWordsPromoted = 0;
2854 )
2856 if (PrintGC && Verbose) {
2857 // Call down the chain in contiguous_available needs the freelistLock
2858 // so print this out before releasing the freeListLock.
2859 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2860 contiguous_available());
2861 }
2862 }
2864 #ifndef PRODUCT
2865 bool CMSCollector::have_cms_token() {
2866 Thread* thr = Thread::current();
2867 if (thr->is_VM_thread()) {
2868 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2869 } else if (thr->is_ConcurrentGC_thread()) {
2870 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2871 } else if (thr->is_GC_task_thread()) {
2872 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2873 ParGCRareEvent_lock->owned_by_self();
2874 }
2875 return false;
2876 }
2877 #endif
2879 // Check reachability of the given heap address in CMS generation,
2880 // treating all other generations as roots.
2881 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2882 // We could "guarantee" below, rather than assert, but i'll
2883 // leave these as "asserts" so that an adventurous debugger
2884 // could try this in the product build provided some subset of
2885 // the conditions were met, provided they were intersted in the
2886 // results and knew that the computation below wouldn't interfere
2887 // with other concurrent computations mutating the structures
2888 // being read or written.
2889 assert(SafepointSynchronize::is_at_safepoint(),
2890 "Else mutations in object graph will make answer suspect");
2891 assert(have_cms_token(), "Should hold cms token");
2892 assert(haveFreelistLocks(), "must hold free list locks");
2893 assert_lock_strong(bitMapLock());
2895 // Clear the marking bit map array before starting, but, just
2896 // for kicks, first report if the given address is already marked
2897 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2898 _markBitMap.isMarked(addr) ? "" : " not");
2900 if (verify_after_remark()) {
2901 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2902 bool result = verification_mark_bm()->isMarked(addr);
2903 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2904 result ? "IS" : "is NOT");
2905 return result;
2906 } else {
2907 gclog_or_tty->print_cr("Could not compute result");
2908 return false;
2909 }
2910 }
2913 void
2914 CMSCollector::print_on_error(outputStream* st) {
2915 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2916 if (collector != NULL) {
2917 CMSBitMap* bitmap = &collector->_markBitMap;
2918 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, bitmap);
2919 bitmap->print_on_error(st, " Bits: ");
2921 st->cr();
2923 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2924 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, mut_bitmap);
2925 mut_bitmap->print_on_error(st, " Bits: ");
2926 }
2927 }
2929 ////////////////////////////////////////////////////////
2930 // CMS Verification Support
2931 ////////////////////////////////////////////////////////
2932 // Following the remark phase, the following invariant
2933 // should hold -- each object in the CMS heap which is
2934 // marked in markBitMap() should be marked in the verification_mark_bm().
2936 class VerifyMarkedClosure: public BitMapClosure {
2937 CMSBitMap* _marks;
2938 bool _failed;
2940 public:
2941 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2943 bool do_bit(size_t offset) {
2944 HeapWord* addr = _marks->offsetToHeapWord(offset);
2945 if (!_marks->isMarked(addr)) {
2946 oop(addr)->print_on(gclog_or_tty);
2947 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2948 _failed = true;
2949 }
2950 return true;
2951 }
2953 bool failed() { return _failed; }
2954 };
2956 bool CMSCollector::verify_after_remark(bool silent) {
2957 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2958 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2959 static bool init = false;
2961 assert(SafepointSynchronize::is_at_safepoint(),
2962 "Else mutations in object graph will make answer suspect");
2963 assert(have_cms_token(),
2964 "Else there may be mutual interference in use of "
2965 " verification data structures");
2966 assert(_collectorState > Marking && _collectorState <= Sweeping,
2967 "Else marking info checked here may be obsolete");
2968 assert(haveFreelistLocks(), "must hold free list locks");
2969 assert_lock_strong(bitMapLock());
2972 // Allocate marking bit map if not already allocated
2973 if (!init) { // first time
2974 if (!verification_mark_bm()->allocate(_span)) {
2975 return false;
2976 }
2977 init = true;
2978 }
2980 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2982 // Turn off refs discovery -- so we will be tracing through refs.
2983 // This is as intended, because by this time
2984 // GC must already have cleared any refs that need to be cleared,
2985 // and traced those that need to be marked; moreover,
2986 // the marking done here is not going to intefere in any
2987 // way with the marking information used by GC.
2988 NoRefDiscovery no_discovery(ref_processor());
2990 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2992 // Clear any marks from a previous round
2993 verification_mark_bm()->clear_all();
2994 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2995 verify_work_stacks_empty();
2997 GenCollectedHeap* gch = GenCollectedHeap::heap();
2998 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2999 // Update the saved marks which may affect the root scans.
3000 gch->save_marks();
3002 if (CMSRemarkVerifyVariant == 1) {
3003 // In this first variant of verification, we complete
3004 // all marking, then check if the new marks-verctor is
3005 // a subset of the CMS marks-vector.
3006 verify_after_remark_work_1();
3007 } else if (CMSRemarkVerifyVariant == 2) {
3008 // In this second variant of verification, we flag an error
3009 // (i.e. an object reachable in the new marks-vector not reachable
3010 // in the CMS marks-vector) immediately, also indicating the
3011 // identify of an object (A) that references the unmarked object (B) --
3012 // presumably, a mutation to A failed to be picked up by preclean/remark?
3013 verify_after_remark_work_2();
3014 } else {
3015 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
3016 CMSRemarkVerifyVariant);
3017 }
3018 if (!silent) gclog_or_tty->print(" done] ");
3019 return true;
3020 }
3022 void CMSCollector::verify_after_remark_work_1() {
3023 ResourceMark rm;
3024 HandleMark hm;
3025 GenCollectedHeap* gch = GenCollectedHeap::heap();
3027 // Get a clear set of claim bits for the strong roots processing to work with.
3028 ClassLoaderDataGraph::clear_claimed_marks();
3030 // Mark from roots one level into CMS
3031 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
3032 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3034 gch->gen_process_strong_roots(_cmsGen->level(),
3035 true, // younger gens are roots
3036 true, // activate StrongRootsScope
3037 false, // not scavenging
3038 SharedHeap::ScanningOption(roots_scanning_options()),
3039 ¬Older,
3040 true, // walk code active on stacks
3041 NULL,
3042 NULL); // SSS: Provide correct closure
3044 // Now mark from the roots
3045 MarkFromRootsClosure markFromRootsClosure(this, _span,
3046 verification_mark_bm(), verification_mark_stack(),
3047 false /* don't yield */, true /* verifying */);
3048 assert(_restart_addr == NULL, "Expected pre-condition");
3049 verification_mark_bm()->iterate(&markFromRootsClosure);
3050 while (_restart_addr != NULL) {
3051 // Deal with stack overflow: by restarting at the indicated
3052 // address.
3053 HeapWord* ra = _restart_addr;
3054 markFromRootsClosure.reset(ra);
3055 _restart_addr = NULL;
3056 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3057 }
3058 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3059 verify_work_stacks_empty();
3061 // Marking completed -- now verify that each bit marked in
3062 // verification_mark_bm() is also marked in markBitMap(); flag all
3063 // errors by printing corresponding objects.
3064 VerifyMarkedClosure vcl(markBitMap());
3065 verification_mark_bm()->iterate(&vcl);
3066 if (vcl.failed()) {
3067 gclog_or_tty->print("Verification failed");
3068 Universe::heap()->print_on(gclog_or_tty);
3069 fatal("CMS: failed marking verification after remark");
3070 }
3071 }
3073 class VerifyKlassOopsKlassClosure : public KlassClosure {
3074 class VerifyKlassOopsClosure : public OopClosure {
3075 CMSBitMap* _bitmap;
3076 public:
3077 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
3078 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
3079 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
3080 } _oop_closure;
3081 public:
3082 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
3083 void do_klass(Klass* k) {
3084 k->oops_do(&_oop_closure);
3085 }
3086 };
3088 void CMSCollector::verify_after_remark_work_2() {
3089 ResourceMark rm;
3090 HandleMark hm;
3091 GenCollectedHeap* gch = GenCollectedHeap::heap();
3093 // Get a clear set of claim bits for the strong roots processing to work with.
3094 ClassLoaderDataGraph::clear_claimed_marks();
3096 // Mark from roots one level into CMS
3097 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
3098 markBitMap());
3099 CMKlassClosure klass_closure(¬Older);
3101 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3102 gch->gen_process_strong_roots(_cmsGen->level(),
3103 true, // younger gens are roots
3104 true, // activate StrongRootsScope
3105 false, // not scavenging
3106 SharedHeap::ScanningOption(roots_scanning_options()),
3107 ¬Older,
3108 true, // walk code active on stacks
3109 NULL,
3110 &klass_closure);
3112 // Now mark from the roots
3113 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
3114 verification_mark_bm(), markBitMap(), verification_mark_stack());
3115 assert(_restart_addr == NULL, "Expected pre-condition");
3116 verification_mark_bm()->iterate(&markFromRootsClosure);
3117 while (_restart_addr != NULL) {
3118 // Deal with stack overflow: by restarting at the indicated
3119 // address.
3120 HeapWord* ra = _restart_addr;
3121 markFromRootsClosure.reset(ra);
3122 _restart_addr = NULL;
3123 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3124 }
3125 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3126 verify_work_stacks_empty();
3128 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
3129 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
3131 // Marking completed -- now verify that each bit marked in
3132 // verification_mark_bm() is also marked in markBitMap(); flag all
3133 // errors by printing corresponding objects.
3134 VerifyMarkedClosure vcl(markBitMap());
3135 verification_mark_bm()->iterate(&vcl);
3136 assert(!vcl.failed(), "Else verification above should not have succeeded");
3137 }
3139 void ConcurrentMarkSweepGeneration::save_marks() {
3140 // delegate to CMS space
3141 cmsSpace()->save_marks();
3142 for (uint i = 0; i < ParallelGCThreads; i++) {
3143 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3144 }
3145 }
3147 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3148 return cmsSpace()->no_allocs_since_save_marks();
3149 }
3151 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3152 \
3153 void ConcurrentMarkSweepGeneration:: \
3154 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3155 cl->set_generation(this); \
3156 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3157 cl->reset_generation(); \
3158 save_marks(); \
3159 }
3161 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3163 void
3164 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3165 cl->set_generation(this);
3166 younger_refs_in_space_iterate(_cmsSpace, cl);
3167 cl->reset_generation();
3168 }
3170 void
3171 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, ExtendedOopClosure* cl) {
3172 if (freelistLock()->owned_by_self()) {
3173 Generation::oop_iterate(mr, cl);
3174 } else {
3175 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3176 Generation::oop_iterate(mr, cl);
3177 }
3178 }
3180 void
3181 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
3182 if (freelistLock()->owned_by_self()) {
3183 Generation::oop_iterate(cl);
3184 } else {
3185 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3186 Generation::oop_iterate(cl);
3187 }
3188 }
3190 void
3191 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3192 if (freelistLock()->owned_by_self()) {
3193 Generation::object_iterate(cl);
3194 } else {
3195 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3196 Generation::object_iterate(cl);
3197 }
3198 }
3200 void
3201 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3202 if (freelistLock()->owned_by_self()) {
3203 Generation::safe_object_iterate(cl);
3204 } else {
3205 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3206 Generation::safe_object_iterate(cl);
3207 }
3208 }
3210 void
3211 ConcurrentMarkSweepGeneration::post_compact() {
3212 }
3214 void
3215 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3216 // Fix the linear allocation blocks to look like free blocks.
3218 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3219 // are not called when the heap is verified during universe initialization and
3220 // at vm shutdown.
3221 if (freelistLock()->owned_by_self()) {
3222 cmsSpace()->prepare_for_verify();
3223 } else {
3224 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3225 cmsSpace()->prepare_for_verify();
3226 }
3227 }
3229 void
3230 ConcurrentMarkSweepGeneration::verify() {
3231 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3232 // are not called when the heap is verified during universe initialization and
3233 // at vm shutdown.
3234 if (freelistLock()->owned_by_self()) {
3235 cmsSpace()->verify();
3236 } else {
3237 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3238 cmsSpace()->verify();
3239 }
3240 }
3242 void CMSCollector::verify() {
3243 _cmsGen->verify();
3244 }
3246 #ifndef PRODUCT
3247 bool CMSCollector::overflow_list_is_empty() const {
3248 assert(_num_par_pushes >= 0, "Inconsistency");
3249 if (_overflow_list == NULL) {
3250 assert(_num_par_pushes == 0, "Inconsistency");
3251 }
3252 return _overflow_list == NULL;
3253 }
3255 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3256 // merely consolidate assertion checks that appear to occur together frequently.
3257 void CMSCollector::verify_work_stacks_empty() const {
3258 assert(_markStack.isEmpty(), "Marking stack should be empty");
3259 assert(overflow_list_is_empty(), "Overflow list should be empty");
3260 }
3262 void CMSCollector::verify_overflow_empty() const {
3263 assert(overflow_list_is_empty(), "Overflow list should be empty");
3264 assert(no_preserved_marks(), "No preserved marks");
3265 }
3266 #endif // PRODUCT
3268 // Decide if we want to enable class unloading as part of the
3269 // ensuing concurrent GC cycle. We will collect and
3270 // unload classes if it's the case that:
3271 // (1) an explicit gc request has been made and the flag
3272 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3273 // (2) (a) class unloading is enabled at the command line, and
3274 // (b) old gen is getting really full
3275 // NOTE: Provided there is no change in the state of the heap between
3276 // calls to this method, it should have idempotent results. Moreover,
3277 // its results should be monotonically increasing (i.e. going from 0 to 1,
3278 // but not 1 to 0) between successive calls between which the heap was
3279 // not collected. For the implementation below, it must thus rely on
3280 // the property that concurrent_cycles_since_last_unload()
3281 // will not decrease unless a collection cycle happened and that
3282 // _cmsGen->is_too_full() are
3283 // themselves also monotonic in that sense. See check_monotonicity()
3284 // below.
3285 void CMSCollector::update_should_unload_classes() {
3286 _should_unload_classes = false;
3287 // Condition 1 above
3288 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3289 _should_unload_classes = true;
3290 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3291 // Disjuncts 2.b.(i,ii,iii) above
3292 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3293 CMSClassUnloadingMaxInterval)
3294 || _cmsGen->is_too_full();
3295 }
3296 }
3298 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3299 bool res = should_concurrent_collect();
3300 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3301 return res;
3302 }
3304 void CMSCollector::setup_cms_unloading_and_verification_state() {
3305 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3306 || VerifyBeforeExit;
3307 const int rso = SharedHeap::SO_Strings | SharedHeap::SO_CodeCache;
3309 // We set the proper root for this CMS cycle here.
3310 if (should_unload_classes()) { // Should unload classes this cycle
3311 remove_root_scanning_option(SharedHeap::SO_AllClasses);
3312 add_root_scanning_option(SharedHeap::SO_SystemClasses);
3313 remove_root_scanning_option(rso); // Shrink the root set appropriately
3314 set_verifying(should_verify); // Set verification state for this cycle
3315 return; // Nothing else needs to be done at this time
3316 }
3318 // Not unloading classes this cycle
3319 assert(!should_unload_classes(), "Inconsitency!");
3320 remove_root_scanning_option(SharedHeap::SO_SystemClasses);
3321 add_root_scanning_option(SharedHeap::SO_AllClasses);
3323 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3324 // Include symbols, strings and code cache elements to prevent their resurrection.
3325 add_root_scanning_option(rso);
3326 set_verifying(true);
3327 } else if (verifying() && !should_verify) {
3328 // We were verifying, but some verification flags got disabled.
3329 set_verifying(false);
3330 // Exclude symbols, strings and code cache elements from root scanning to
3331 // reduce IM and RM pauses.
3332 remove_root_scanning_option(rso);
3333 }
3334 }
3337 #ifndef PRODUCT
3338 HeapWord* CMSCollector::block_start(const void* p) const {
3339 const HeapWord* addr = (HeapWord*)p;
3340 if (_span.contains(p)) {
3341 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3342 return _cmsGen->cmsSpace()->block_start(p);
3343 }
3344 }
3345 return NULL;
3346 }
3347 #endif
3349 HeapWord*
3350 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3351 bool tlab,
3352 bool parallel) {
3353 CMSSynchronousYieldRequest yr;
3354 assert(!tlab, "Can't deal with TLAB allocation");
3355 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3356 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3357 CMSExpansionCause::_satisfy_allocation);
3358 if (GCExpandToAllocateDelayMillis > 0) {
3359 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3360 }
3361 return have_lock_and_allocate(word_size, tlab);
3362 }
3364 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3365 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3366 // to CardGeneration and share it...
3367 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3368 return CardGeneration::expand(bytes, expand_bytes);
3369 }
3371 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3372 CMSExpansionCause::Cause cause)
3373 {
3375 bool success = expand(bytes, expand_bytes);
3377 // remember why we expanded; this information is used
3378 // by shouldConcurrentCollect() when making decisions on whether to start
3379 // a new CMS cycle.
3380 if (success) {
3381 set_expansion_cause(cause);
3382 if (PrintGCDetails && Verbose) {
3383 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3384 CMSExpansionCause::to_string(cause));
3385 }
3386 }
3387 }
3389 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3390 HeapWord* res = NULL;
3391 MutexLocker x(ParGCRareEvent_lock);
3392 while (true) {
3393 // Expansion by some other thread might make alloc OK now:
3394 res = ps->lab.alloc(word_sz);
3395 if (res != NULL) return res;
3396 // If there's not enough expansion space available, give up.
3397 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3398 return NULL;
3399 }
3400 // Otherwise, we try expansion.
3401 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3402 CMSExpansionCause::_allocate_par_lab);
3403 // Now go around the loop and try alloc again;
3404 // A competing par_promote might beat us to the expansion space,
3405 // so we may go around the loop again if promotion fails agaion.
3406 if (GCExpandToAllocateDelayMillis > 0) {
3407 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3408 }
3409 }
3410 }
3413 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3414 PromotionInfo* promo) {
3415 MutexLocker x(ParGCRareEvent_lock);
3416 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3417 while (true) {
3418 // Expansion by some other thread might make alloc OK now:
3419 if (promo->ensure_spooling_space()) {
3420 assert(promo->has_spooling_space(),
3421 "Post-condition of successful ensure_spooling_space()");
3422 return true;
3423 }
3424 // If there's not enough expansion space available, give up.
3425 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3426 return false;
3427 }
3428 // Otherwise, we try expansion.
3429 expand(refill_size_bytes, MinHeapDeltaBytes,
3430 CMSExpansionCause::_allocate_par_spooling_space);
3431 // Now go around the loop and try alloc again;
3432 // A competing allocation might beat us to the expansion space,
3433 // so we may go around the loop again if allocation fails again.
3434 if (GCExpandToAllocateDelayMillis > 0) {
3435 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3436 }
3437 }
3438 }
3441 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3442 assert_locked_or_safepoint(ExpandHeap_lock);
3443 // Shrink committed space
3444 _virtual_space.shrink_by(bytes);
3445 // Shrink space; this also shrinks the space's BOT
3446 _cmsSpace->set_end((HeapWord*) _virtual_space.high());
3447 size_t new_word_size = heap_word_size(_cmsSpace->capacity());
3448 // Shrink the shared block offset array
3449 _bts->resize(new_word_size);
3450 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3451 // Shrink the card table
3452 Universe::heap()->barrier_set()->resize_covered_region(mr);
3454 if (Verbose && PrintGC) {
3455 size_t new_mem_size = _virtual_space.committed_size();
3456 size_t old_mem_size = new_mem_size + bytes;
3457 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3458 name(), old_mem_size/K, new_mem_size/K);
3459 }
3460 }
3462 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3463 assert_locked_or_safepoint(Heap_lock);
3464 size_t size = ReservedSpace::page_align_size_down(bytes);
3465 // Only shrink if a compaction was done so that all the free space
3466 // in the generation is in a contiguous block at the end.
3467 if (size > 0 && did_compact()) {
3468 shrink_by(size);
3469 }
3470 }
3472 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3473 assert_locked_or_safepoint(Heap_lock);
3474 bool result = _virtual_space.expand_by(bytes);
3475 if (result) {
3476 size_t new_word_size =
3477 heap_word_size(_virtual_space.committed_size());
3478 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3479 _bts->resize(new_word_size); // resize the block offset shared array
3480 Universe::heap()->barrier_set()->resize_covered_region(mr);
3481 // Hmmmm... why doesn't CFLS::set_end verify locking?
3482 // This is quite ugly; FIX ME XXX
3483 _cmsSpace->assert_locked(freelistLock());
3484 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3486 // update the space and generation capacity counters
3487 if (UsePerfData) {
3488 _space_counters->update_capacity();
3489 _gen_counters->update_all();
3490 }
3492 if (Verbose && PrintGC) {
3493 size_t new_mem_size = _virtual_space.committed_size();
3494 size_t old_mem_size = new_mem_size - bytes;
3495 gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3496 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3497 }
3498 }
3499 return result;
3500 }
3502 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3503 assert_locked_or_safepoint(Heap_lock);
3504 bool success = true;
3505 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3506 if (remaining_bytes > 0) {
3507 success = grow_by(remaining_bytes);
3508 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3509 }
3510 return success;
3511 }
3513 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
3514 assert_locked_or_safepoint(Heap_lock);
3515 assert_lock_strong(freelistLock());
3516 if (PrintGCDetails && Verbose) {
3517 warning("Shrinking of CMS not yet implemented");
3518 }
3519 return;
3520 }
3523 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3524 // phases.
3525 class CMSPhaseAccounting: public StackObj {
3526 public:
3527 CMSPhaseAccounting(CMSCollector *collector,
3528 const char *phase,
3529 bool print_cr = true);
3530 ~CMSPhaseAccounting();
3532 private:
3533 CMSCollector *_collector;
3534 const char *_phase;
3535 elapsedTimer _wallclock;
3536 bool _print_cr;
3538 public:
3539 // Not MT-safe; so do not pass around these StackObj's
3540 // where they may be accessed by other threads.
3541 jlong wallclock_millis() {
3542 assert(_wallclock.is_active(), "Wall clock should not stop");
3543 _wallclock.stop(); // to record time
3544 jlong ret = _wallclock.milliseconds();
3545 _wallclock.start(); // restart
3546 return ret;
3547 }
3548 };
3550 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3551 const char *phase,
3552 bool print_cr) :
3553 _collector(collector), _phase(phase), _print_cr(print_cr) {
3555 if (PrintCMSStatistics != 0) {
3556 _collector->resetYields();
3557 }
3558 if (PrintGCDetails) {
3559 gclog_or_tty->date_stamp(PrintGCDateStamps);
3560 gclog_or_tty->stamp(PrintGCTimeStamps);
3561 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
3562 _collector->cmsGen()->short_name(), _phase);
3563 }
3564 _collector->resetTimer();
3565 _wallclock.start();
3566 _collector->startTimer();
3567 }
3569 CMSPhaseAccounting::~CMSPhaseAccounting() {
3570 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3571 _collector->stopTimer();
3572 _wallclock.stop();
3573 if (PrintGCDetails) {
3574 gclog_or_tty->date_stamp(PrintGCDateStamps);
3575 gclog_or_tty->stamp(PrintGCTimeStamps);
3576 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3577 _collector->cmsGen()->short_name(),
3578 _phase, _collector->timerValue(), _wallclock.seconds());
3579 if (_print_cr) {
3580 gclog_or_tty->print_cr("");
3581 }
3582 if (PrintCMSStatistics != 0) {
3583 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3584 _collector->yields());
3585 }
3586 }
3587 }
3589 // CMS work
3591 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
3592 class CMSParMarkTask : public AbstractGangTask {
3593 protected:
3594 CMSCollector* _collector;
3595 int _n_workers;
3596 CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
3597 AbstractGangTask(name),
3598 _collector(collector),
3599 _n_workers(n_workers) {}
3600 // Work method in support of parallel rescan ... of young gen spaces
3601 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
3602 ContiguousSpace* space,
3603 HeapWord** chunk_array, size_t chunk_top);
3604 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
3605 };
3607 // Parallel initial mark task
3608 class CMSParInitialMarkTask: public CMSParMarkTask {
3609 public:
3610 CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
3611 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
3612 collector, n_workers) {}
3613 void work(uint worker_id);
3614 };
3616 // Checkpoint the roots into this generation from outside
3617 // this generation. [Note this initial checkpoint need only
3618 // be approximate -- we'll do a catch up phase subsequently.]
3619 void CMSCollector::checkpointRootsInitial(bool asynch) {
3620 assert(_collectorState == InitialMarking, "Wrong collector state");
3621 check_correct_thread_executing();
3622 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3624 save_heap_summary();
3625 report_heap_summary(GCWhen::BeforeGC);
3627 ReferenceProcessor* rp = ref_processor();
3628 SpecializationStats::clear();
3629 assert(_restart_addr == NULL, "Control point invariant");
3630 if (asynch) {
3631 // acquire locks for subsequent manipulations
3632 MutexLockerEx x(bitMapLock(),
3633 Mutex::_no_safepoint_check_flag);
3634 checkpointRootsInitialWork(asynch);
3635 // enable ("weak") refs discovery
3636 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3637 _collectorState = Marking;
3638 } else {
3639 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3640 // which recognizes if we are a CMS generation, and doesn't try to turn on
3641 // discovery; verify that they aren't meddling.
3642 assert(!rp->discovery_is_atomic(),
3643 "incorrect setting of discovery predicate");
3644 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3645 "ref discovery for this generation kind");
3646 // already have locks
3647 checkpointRootsInitialWork(asynch);
3648 // now enable ("weak") refs discovery
3649 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3650 _collectorState = Marking;
3651 }
3652 SpecializationStats::print();
3653 }
3655 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3656 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3657 assert(_collectorState == InitialMarking, "just checking");
3659 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3660 // precede our marking with a collection of all
3661 // younger generations to keep floating garbage to a minimum.
3662 // XXX: we won't do this for now -- it's an optimization to be done later.
3664 // already have locks
3665 assert_lock_strong(bitMapLock());
3666 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3668 // Setup the verification and class unloading state for this
3669 // CMS collection cycle.
3670 setup_cms_unloading_and_verification_state();
3672 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3673 PrintGCDetails && Verbose, true, _gc_timer_cm);)
3674 if (UseAdaptiveSizePolicy) {
3675 size_policy()->checkpoint_roots_initial_begin();
3676 }
3678 // Reset all the PLAB chunk arrays if necessary.
3679 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3680 reset_survivor_plab_arrays();
3681 }
3683 ResourceMark rm;
3684 HandleMark hm;
3686 FalseClosure falseClosure;
3687 // In the case of a synchronous collection, we will elide the
3688 // remark step, so it's important to catch all the nmethod oops
3689 // in this step.
3690 // The final 'true' flag to gen_process_strong_roots will ensure this.
3691 // If 'async' is true, we can relax the nmethod tracing.
3692 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3693 GenCollectedHeap* gch = GenCollectedHeap::heap();
3695 verify_work_stacks_empty();
3696 verify_overflow_empty();
3698 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3699 // Update the saved marks which may affect the root scans.
3700 gch->save_marks();
3702 // weak reference processing has not started yet.
3703 ref_processor()->set_enqueuing_is_done(false);
3705 // Need to remember all newly created CLDs,
3706 // so that we can guarantee that the remark finds them.
3707 ClassLoaderDataGraph::remember_new_clds(true);
3709 // Whenever a CLD is found, it will be claimed before proceeding to mark
3710 // the klasses. The claimed marks need to be cleared before marking starts.
3711 ClassLoaderDataGraph::clear_claimed_marks();
3713 if (CMSPrintEdenSurvivorChunks) {
3714 print_eden_and_survivor_chunk_arrays();
3715 }
3717 {
3718 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3719 if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3720 // The parallel version.
3721 FlexibleWorkGang* workers = gch->workers();
3722 assert(workers != NULL, "Need parallel worker threads.");
3723 int n_workers = workers->active_workers();
3724 CMSParInitialMarkTask tsk(this, n_workers);
3725 gch->set_par_threads(n_workers);
3726 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3727 if (n_workers > 1) {
3728 GenCollectedHeap::StrongRootsScope srs(gch);
3729 workers->run_task(&tsk);
3730 } else {
3731 GenCollectedHeap::StrongRootsScope srs(gch);
3732 tsk.work(0);
3733 }
3734 gch->set_par_threads(0);
3735 } else {
3736 // The serial version.
3737 CMKlassClosure klass_closure(¬Older);
3738 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3739 gch->gen_process_strong_roots(_cmsGen->level(),
3740 true, // younger gens are roots
3741 true, // activate StrongRootsScope
3742 false, // not scavenging
3743 SharedHeap::ScanningOption(roots_scanning_options()),
3744 ¬Older,
3745 true, // walk all of code cache if (so & SO_CodeCache)
3746 NULL,
3747 &klass_closure);
3748 }
3749 }
3751 // Clear mod-union table; it will be dirtied in the prologue of
3752 // CMS generation per each younger generation collection.
3754 assert(_modUnionTable.isAllClear(),
3755 "Was cleared in most recent final checkpoint phase"
3756 " or no bits are set in the gc_prologue before the start of the next "
3757 "subsequent marking phase.");
3759 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3761 // Save the end of the used_region of the constituent generations
3762 // to be used to limit the extent of sweep in each generation.
3763 save_sweep_limits();
3764 if (UseAdaptiveSizePolicy) {
3765 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3766 }
3767 verify_overflow_empty();
3768 }
3770 bool CMSCollector::markFromRoots(bool asynch) {
3771 // we might be tempted to assert that:
3772 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3773 // "inconsistent argument?");
3774 // However that wouldn't be right, because it's possible that
3775 // a safepoint is indeed in progress as a younger generation
3776 // stop-the-world GC happens even as we mark in this generation.
3777 assert(_collectorState == Marking, "inconsistent state?");
3778 check_correct_thread_executing();
3779 verify_overflow_empty();
3781 bool res;
3782 if (asynch) {
3784 // Start the timers for adaptive size policy for the concurrent phases
3785 // Do it here so that the foreground MS can use the concurrent
3786 // timer since a foreground MS might has the sweep done concurrently
3787 // or STW.
3788 if (UseAdaptiveSizePolicy) {
3789 size_policy()->concurrent_marking_begin();
3790 }
3792 // Weak ref discovery note: We may be discovering weak
3793 // refs in this generation concurrent (but interleaved) with
3794 // weak ref discovery by a younger generation collector.
3796 CMSTokenSyncWithLocks ts(true, bitMapLock());
3797 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3798 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3799 res = markFromRootsWork(asynch);
3800 if (res) {
3801 _collectorState = Precleaning;
3802 } else { // We failed and a foreground collection wants to take over
3803 assert(_foregroundGCIsActive, "internal state inconsistency");
3804 assert(_restart_addr == NULL, "foreground will restart from scratch");
3805 if (PrintGCDetails) {
3806 gclog_or_tty->print_cr("bailing out to foreground collection");
3807 }
3808 }
3809 if (UseAdaptiveSizePolicy) {
3810 size_policy()->concurrent_marking_end();
3811 }
3812 } else {
3813 assert(SafepointSynchronize::is_at_safepoint(),
3814 "inconsistent with asynch == false");
3815 if (UseAdaptiveSizePolicy) {
3816 size_policy()->ms_collection_marking_begin();
3817 }
3818 // already have locks
3819 res = markFromRootsWork(asynch);
3820 _collectorState = FinalMarking;
3821 if (UseAdaptiveSizePolicy) {
3822 GenCollectedHeap* gch = GenCollectedHeap::heap();
3823 size_policy()->ms_collection_marking_end(gch->gc_cause());
3824 }
3825 }
3826 verify_overflow_empty();
3827 return res;
3828 }
3830 bool CMSCollector::markFromRootsWork(bool asynch) {
3831 // iterate over marked bits in bit map, doing a full scan and mark
3832 // from these roots using the following algorithm:
3833 // . if oop is to the right of the current scan pointer,
3834 // mark corresponding bit (we'll process it later)
3835 // . else (oop is to left of current scan pointer)
3836 // push oop on marking stack
3837 // . drain the marking stack
3839 // Note that when we do a marking step we need to hold the
3840 // bit map lock -- recall that direct allocation (by mutators)
3841 // and promotion (by younger generation collectors) is also
3842 // marking the bit map. [the so-called allocate live policy.]
3843 // Because the implementation of bit map marking is not
3844 // robust wrt simultaneous marking of bits in the same word,
3845 // we need to make sure that there is no such interference
3846 // between concurrent such updates.
3848 // already have locks
3849 assert_lock_strong(bitMapLock());
3851 verify_work_stacks_empty();
3852 verify_overflow_empty();
3853 bool result = false;
3854 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3855 result = do_marking_mt(asynch);
3856 } else {
3857 result = do_marking_st(asynch);
3858 }
3859 return result;
3860 }
3862 // Forward decl
3863 class CMSConcMarkingTask;
3865 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3866 CMSCollector* _collector;
3867 CMSConcMarkingTask* _task;
3868 public:
3869 virtual void yield();
3871 // "n_threads" is the number of threads to be terminated.
3872 // "queue_set" is a set of work queues of other threads.
3873 // "collector" is the CMS collector associated with this task terminator.
3874 // "yield" indicates whether we need the gang as a whole to yield.
3875 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3876 ParallelTaskTerminator(n_threads, queue_set),
3877 _collector(collector) { }
3879 void set_task(CMSConcMarkingTask* task) {
3880 _task = task;
3881 }
3882 };
3884 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3885 CMSConcMarkingTask* _task;
3886 public:
3887 bool should_exit_termination();
3888 void set_task(CMSConcMarkingTask* task) {
3889 _task = task;
3890 }
3891 };
3893 // MT Concurrent Marking Task
3894 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3895 CMSCollector* _collector;
3896 int _n_workers; // requested/desired # workers
3897 bool _asynch;
3898 bool _result;
3899 CompactibleFreeListSpace* _cms_space;
3900 char _pad_front[64]; // padding to ...
3901 HeapWord* _global_finger; // ... avoid sharing cache line
3902 char _pad_back[64];
3903 HeapWord* _restart_addr;
3905 // Exposed here for yielding support
3906 Mutex* const _bit_map_lock;
3908 // The per thread work queues, available here for stealing
3909 OopTaskQueueSet* _task_queues;
3911 // Termination (and yielding) support
3912 CMSConcMarkingTerminator _term;
3913 CMSConcMarkingTerminatorTerminator _term_term;
3915 public:
3916 CMSConcMarkingTask(CMSCollector* collector,
3917 CompactibleFreeListSpace* cms_space,
3918 bool asynch,
3919 YieldingFlexibleWorkGang* workers,
3920 OopTaskQueueSet* task_queues):
3921 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3922 _collector(collector),
3923 _cms_space(cms_space),
3924 _asynch(asynch), _n_workers(0), _result(true),
3925 _task_queues(task_queues),
3926 _term(_n_workers, task_queues, _collector),
3927 _bit_map_lock(collector->bitMapLock())
3928 {
3929 _requested_size = _n_workers;
3930 _term.set_task(this);
3931 _term_term.set_task(this);
3932 _restart_addr = _global_finger = _cms_space->bottom();
3933 }
3936 OopTaskQueueSet* task_queues() { return _task_queues; }
3938 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3940 HeapWord** global_finger_addr() { return &_global_finger; }
3942 CMSConcMarkingTerminator* terminator() { return &_term; }
3944 virtual void set_for_termination(int active_workers) {
3945 terminator()->reset_for_reuse(active_workers);
3946 }
3948 void work(uint worker_id);
3949 bool should_yield() {
3950 return ConcurrentMarkSweepThread::should_yield()
3951 && !_collector->foregroundGCIsActive()
3952 && _asynch;
3953 }
3955 virtual void coordinator_yield(); // stuff done by coordinator
3956 bool result() { return _result; }
3958 void reset(HeapWord* ra) {
3959 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3960 _restart_addr = _global_finger = ra;
3961 _term.reset_for_reuse();
3962 }
3964 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3965 OopTaskQueue* work_q);
3967 private:
3968 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3969 void do_work_steal(int i);
3970 void bump_global_finger(HeapWord* f);
3971 };
3973 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3974 assert(_task != NULL, "Error");
3975 return _task->yielding();
3976 // Note that we do not need the disjunct || _task->should_yield() above
3977 // because we want terminating threads to yield only if the task
3978 // is already in the midst of yielding, which happens only after at least one
3979 // thread has yielded.
3980 }
3982 void CMSConcMarkingTerminator::yield() {
3983 if (_task->should_yield()) {
3984 _task->yield();
3985 } else {
3986 ParallelTaskTerminator::yield();
3987 }
3988 }
3990 ////////////////////////////////////////////////////////////////
3991 // Concurrent Marking Algorithm Sketch
3992 ////////////////////////////////////////////////////////////////
3993 // Until all tasks exhausted (both spaces):
3994 // -- claim next available chunk
3995 // -- bump global finger via CAS
3996 // -- find first object that starts in this chunk
3997 // and start scanning bitmap from that position
3998 // -- scan marked objects for oops
3999 // -- CAS-mark target, and if successful:
4000 // . if target oop is above global finger (volatile read)
4001 // nothing to do
4002 // . if target oop is in chunk and above local finger
4003 // then nothing to do
4004 // . else push on work-queue
4005 // -- Deal with possible overflow issues:
4006 // . local work-queue overflow causes stuff to be pushed on
4007 // global (common) overflow queue
4008 // . always first empty local work queue
4009 // . then get a batch of oops from global work queue if any
4010 // . then do work stealing
4011 // -- When all tasks claimed (both spaces)
4012 // and local work queue empty,
4013 // then in a loop do:
4014 // . check global overflow stack; steal a batch of oops and trace
4015 // . try to steal from other threads oif GOS is empty
4016 // . if neither is available, offer termination
4017 // -- Terminate and return result
4018 //
4019 void CMSConcMarkingTask::work(uint worker_id) {
4020 elapsedTimer _timer;
4021 ResourceMark rm;
4022 HandleMark hm;
4024 DEBUG_ONLY(_collector->verify_overflow_empty();)
4026 // Before we begin work, our work queue should be empty
4027 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
4028 // Scan the bitmap covering _cms_space, tracing through grey objects.
4029 _timer.start();
4030 do_scan_and_mark(worker_id, _cms_space);
4031 _timer.stop();
4032 if (PrintCMSStatistics != 0) {
4033 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
4034 worker_id, _timer.seconds());
4035 // XXX: need xxx/xxx type of notation, two timers
4036 }
4038 // ... do work stealing
4039 _timer.reset();
4040 _timer.start();
4041 do_work_steal(worker_id);
4042 _timer.stop();
4043 if (PrintCMSStatistics != 0) {
4044 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
4045 worker_id, _timer.seconds());
4046 // XXX: need xxx/xxx type of notation, two timers
4047 }
4048 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
4049 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
4050 // Note that under the current task protocol, the
4051 // following assertion is true even of the spaces
4052 // expanded since the completion of the concurrent
4053 // marking. XXX This will likely change under a strict
4054 // ABORT semantics.
4055 // After perm removal the comparison was changed to
4056 // greater than or equal to from strictly greater than.
4057 // Before perm removal the highest address sweep would
4058 // have been at the end of perm gen but now is at the
4059 // end of the tenured gen.
4060 assert(_global_finger >= _cms_space->end(),
4061 "All tasks have been completed");
4062 DEBUG_ONLY(_collector->verify_overflow_empty();)
4063 }
4065 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
4066 HeapWord* read = _global_finger;
4067 HeapWord* cur = read;
4068 while (f > read) {
4069 cur = read;
4070 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
4071 if (cur == read) {
4072 // our cas succeeded
4073 assert(_global_finger >= f, "protocol consistency");
4074 break;
4075 }
4076 }
4077 }
4079 // This is really inefficient, and should be redone by
4080 // using (not yet available) block-read and -write interfaces to the
4081 // stack and the work_queue. XXX FIX ME !!!
4082 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
4083 OopTaskQueue* work_q) {
4084 // Fast lock-free check
4085 if (ovflw_stk->length() == 0) {
4086 return false;
4087 }
4088 assert(work_q->size() == 0, "Shouldn't steal");
4089 MutexLockerEx ml(ovflw_stk->par_lock(),
4090 Mutex::_no_safepoint_check_flag);
4091 // Grab up to 1/4 the size of the work queue
4092 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4093 (size_t)ParGCDesiredObjsFromOverflowList);
4094 num = MIN2(num, ovflw_stk->length());
4095 for (int i = (int) num; i > 0; i--) {
4096 oop cur = ovflw_stk->pop();
4097 assert(cur != NULL, "Counted wrong?");
4098 work_q->push(cur);
4099 }
4100 return num > 0;
4101 }
4103 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
4104 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4105 int n_tasks = pst->n_tasks();
4106 // We allow that there may be no tasks to do here because
4107 // we are restarting after a stack overflow.
4108 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
4109 uint nth_task = 0;
4111 HeapWord* aligned_start = sp->bottom();
4112 if (sp->used_region().contains(_restart_addr)) {
4113 // Align down to a card boundary for the start of 0th task
4114 // for this space.
4115 aligned_start =
4116 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
4117 CardTableModRefBS::card_size);
4118 }
4120 size_t chunk_size = sp->marking_task_size();
4121 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4122 // Having claimed the nth task in this space,
4123 // compute the chunk that it corresponds to:
4124 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
4125 aligned_start + (nth_task+1)*chunk_size);
4126 // Try and bump the global finger via a CAS;
4127 // note that we need to do the global finger bump
4128 // _before_ taking the intersection below, because
4129 // the task corresponding to that region will be
4130 // deemed done even if the used_region() expands
4131 // because of allocation -- as it almost certainly will
4132 // during start-up while the threads yield in the
4133 // closure below.
4134 HeapWord* finger = span.end();
4135 bump_global_finger(finger); // atomically
4136 // There are null tasks here corresponding to chunks
4137 // beyond the "top" address of the space.
4138 span = span.intersection(sp->used_region());
4139 if (!span.is_empty()) { // Non-null task
4140 HeapWord* prev_obj;
4141 assert(!span.contains(_restart_addr) || nth_task == 0,
4142 "Inconsistency");
4143 if (nth_task == 0) {
4144 // For the 0th task, we'll not need to compute a block_start.
4145 if (span.contains(_restart_addr)) {
4146 // In the case of a restart because of stack overflow,
4147 // we might additionally skip a chunk prefix.
4148 prev_obj = _restart_addr;
4149 } else {
4150 prev_obj = span.start();
4151 }
4152 } else {
4153 // We want to skip the first object because
4154 // the protocol is to scan any object in its entirety
4155 // that _starts_ in this span; a fortiori, any
4156 // object starting in an earlier span is scanned
4157 // as part of an earlier claimed task.
4158 // Below we use the "careful" version of block_start
4159 // so we do not try to navigate uninitialized objects.
4160 prev_obj = sp->block_start_careful(span.start());
4161 // Below we use a variant of block_size that uses the
4162 // Printezis bits to avoid waiting for allocated
4163 // objects to become initialized/parsable.
4164 while (prev_obj < span.start()) {
4165 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4166 if (sz > 0) {
4167 prev_obj += sz;
4168 } else {
4169 // In this case we may end up doing a bit of redundant
4170 // scanning, but that appears unavoidable, short of
4171 // locking the free list locks; see bug 6324141.
4172 break;
4173 }
4174 }
4175 }
4176 if (prev_obj < span.end()) {
4177 MemRegion my_span = MemRegion(prev_obj, span.end());
4178 // Do the marking work within a non-empty span --
4179 // the last argument to the constructor indicates whether the
4180 // iteration should be incremental with periodic yields.
4181 Par_MarkFromRootsClosure cl(this, _collector, my_span,
4182 &_collector->_markBitMap,
4183 work_queue(i),
4184 &_collector->_markStack,
4185 _asynch);
4186 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4187 } // else nothing to do for this task
4188 } // else nothing to do for this task
4189 }
4190 // We'd be tempted to assert here that since there are no
4191 // more tasks left to claim in this space, the global_finger
4192 // must exceed space->top() and a fortiori space->end(). However,
4193 // that would not quite be correct because the bumping of
4194 // global_finger occurs strictly after the claiming of a task,
4195 // so by the time we reach here the global finger may not yet
4196 // have been bumped up by the thread that claimed the last
4197 // task.
4198 pst->all_tasks_completed();
4199 }
4201 class Par_ConcMarkingClosure: public CMSOopClosure {
4202 private:
4203 CMSCollector* _collector;
4204 CMSConcMarkingTask* _task;
4205 MemRegion _span;
4206 CMSBitMap* _bit_map;
4207 CMSMarkStack* _overflow_stack;
4208 OopTaskQueue* _work_queue;
4209 protected:
4210 DO_OOP_WORK_DEFN
4211 public:
4212 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4213 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
4214 CMSOopClosure(collector->ref_processor()),
4215 _collector(collector),
4216 _task(task),
4217 _span(collector->_span),
4218 _work_queue(work_queue),
4219 _bit_map(bit_map),
4220 _overflow_stack(overflow_stack)
4221 { }
4222 virtual void do_oop(oop* p);
4223 virtual void do_oop(narrowOop* p);
4225 void trim_queue(size_t max);
4226 void handle_stack_overflow(HeapWord* lost);
4227 void do_yield_check() {
4228 if (_task->should_yield()) {
4229 _task->yield();
4230 }
4231 }
4232 };
4234 // Grey object scanning during work stealing phase --
4235 // the salient assumption here is that any references
4236 // that are in these stolen objects being scanned must
4237 // already have been initialized (else they would not have
4238 // been published), so we do not need to check for
4239 // uninitialized objects before pushing here.
4240 void Par_ConcMarkingClosure::do_oop(oop obj) {
4241 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4242 HeapWord* addr = (HeapWord*)obj;
4243 // Check if oop points into the CMS generation
4244 // and is not marked
4245 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4246 // a white object ...
4247 // If we manage to "claim" the object, by being the
4248 // first thread to mark it, then we push it on our
4249 // marking stack
4250 if (_bit_map->par_mark(addr)) { // ... now grey
4251 // push on work queue (grey set)
4252 bool simulate_overflow = false;
4253 NOT_PRODUCT(
4254 if (CMSMarkStackOverflowALot &&
4255 _collector->simulate_overflow()) {
4256 // simulate a stack overflow
4257 simulate_overflow = true;
4258 }
4259 )
4260 if (simulate_overflow ||
4261 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4262 // stack overflow
4263 if (PrintCMSStatistics != 0) {
4264 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4265 SIZE_FORMAT, _overflow_stack->capacity());
4266 }
4267 // We cannot assert that the overflow stack is full because
4268 // it may have been emptied since.
4269 assert(simulate_overflow ||
4270 _work_queue->size() == _work_queue->max_elems(),
4271 "Else push should have succeeded");
4272 handle_stack_overflow(addr);
4273 }
4274 } // Else, some other thread got there first
4275 do_yield_check();
4276 }
4277 }
4279 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4280 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4282 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4283 while (_work_queue->size() > max) {
4284 oop new_oop;
4285 if (_work_queue->pop_local(new_oop)) {
4286 assert(new_oop->is_oop(), "Should be an oop");
4287 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4288 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4289 new_oop->oop_iterate(this); // do_oop() above
4290 do_yield_check();
4291 }
4292 }
4293 }
4295 // Upon stack overflow, we discard (part of) the stack,
4296 // remembering the least address amongst those discarded
4297 // in CMSCollector's _restart_address.
4298 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4299 // We need to do this under a mutex to prevent other
4300 // workers from interfering with the work done below.
4301 MutexLockerEx ml(_overflow_stack->par_lock(),
4302 Mutex::_no_safepoint_check_flag);
4303 // Remember the least grey address discarded
4304 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4305 _collector->lower_restart_addr(ra);
4306 _overflow_stack->reset(); // discard stack contents
4307 _overflow_stack->expand(); // expand the stack if possible
4308 }
4311 void CMSConcMarkingTask::do_work_steal(int i) {
4312 OopTaskQueue* work_q = work_queue(i);
4313 oop obj_to_scan;
4314 CMSBitMap* bm = &(_collector->_markBitMap);
4315 CMSMarkStack* ovflw = &(_collector->_markStack);
4316 int* seed = _collector->hash_seed(i);
4317 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4318 while (true) {
4319 cl.trim_queue(0);
4320 assert(work_q->size() == 0, "Should have been emptied above");
4321 if (get_work_from_overflow_stack(ovflw, work_q)) {
4322 // Can't assert below because the work obtained from the
4323 // overflow stack may already have been stolen from us.
4324 // assert(work_q->size() > 0, "Work from overflow stack");
4325 continue;
4326 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4327 assert(obj_to_scan->is_oop(), "Should be an oop");
4328 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4329 obj_to_scan->oop_iterate(&cl);
4330 } else if (terminator()->offer_termination(&_term_term)) {
4331 assert(work_q->size() == 0, "Impossible!");
4332 break;
4333 } else if (yielding() || should_yield()) {
4334 yield();
4335 }
4336 }
4337 }
4339 // This is run by the CMS (coordinator) thread.
4340 void CMSConcMarkingTask::coordinator_yield() {
4341 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4342 "CMS thread should hold CMS token");
4343 // First give up the locks, then yield, then re-lock
4344 // We should probably use a constructor/destructor idiom to
4345 // do this unlock/lock or modify the MutexUnlocker class to
4346 // serve our purpose. XXX
4347 assert_lock_strong(_bit_map_lock);
4348 _bit_map_lock->unlock();
4349 ConcurrentMarkSweepThread::desynchronize(true);
4350 ConcurrentMarkSweepThread::acknowledge_yield_request();
4351 _collector->stopTimer();
4352 if (PrintCMSStatistics != 0) {
4353 _collector->incrementYields();
4354 }
4355 _collector->icms_wait();
4357 // It is possible for whichever thread initiated the yield request
4358 // not to get a chance to wake up and take the bitmap lock between
4359 // this thread releasing it and reacquiring it. So, while the
4360 // should_yield() flag is on, let's sleep for a bit to give the
4361 // other thread a chance to wake up. The limit imposed on the number
4362 // of iterations is defensive, to avoid any unforseen circumstances
4363 // putting us into an infinite loop. Since it's always been this
4364 // (coordinator_yield()) method that was observed to cause the
4365 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4366 // which is by default non-zero. For the other seven methods that
4367 // also perform the yield operation, as are using a different
4368 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4369 // can enable the sleeping for those methods too, if necessary.
4370 // See 6442774.
4371 //
4372 // We really need to reconsider the synchronization between the GC
4373 // thread and the yield-requesting threads in the future and we
4374 // should really use wait/notify, which is the recommended
4375 // way of doing this type of interaction. Additionally, we should
4376 // consolidate the eight methods that do the yield operation and they
4377 // are almost identical into one for better maintenability and
4378 // readability. See 6445193.
4379 //
4380 // Tony 2006.06.29
4381 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4382 ConcurrentMarkSweepThread::should_yield() &&
4383 !CMSCollector::foregroundGCIsActive(); ++i) {
4384 os::sleep(Thread::current(), 1, false);
4385 ConcurrentMarkSweepThread::acknowledge_yield_request();
4386 }
4388 ConcurrentMarkSweepThread::synchronize(true);
4389 _bit_map_lock->lock_without_safepoint_check();
4390 _collector->startTimer();
4391 }
4393 bool CMSCollector::do_marking_mt(bool asynch) {
4394 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4395 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4396 conc_workers()->total_workers(),
4397 conc_workers()->active_workers(),
4398 Threads::number_of_non_daemon_threads());
4399 conc_workers()->set_active_workers(num_workers);
4401 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4403 CMSConcMarkingTask tsk(this,
4404 cms_space,
4405 asynch,
4406 conc_workers(),
4407 task_queues());
4409 // Since the actual number of workers we get may be different
4410 // from the number we requested above, do we need to do anything different
4411 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4412 // class?? XXX
4413 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4415 // Refs discovery is already non-atomic.
4416 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4417 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4418 conc_workers()->start_task(&tsk);
4419 while (tsk.yielded()) {
4420 tsk.coordinator_yield();
4421 conc_workers()->continue_task(&tsk);
4422 }
4423 // If the task was aborted, _restart_addr will be non-NULL
4424 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4425 while (_restart_addr != NULL) {
4426 // XXX For now we do not make use of ABORTED state and have not
4427 // yet implemented the right abort semantics (even in the original
4428 // single-threaded CMS case). That needs some more investigation
4429 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4430 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4431 // If _restart_addr is non-NULL, a marking stack overflow
4432 // occurred; we need to do a fresh marking iteration from the
4433 // indicated restart address.
4434 if (_foregroundGCIsActive && asynch) {
4435 // We may be running into repeated stack overflows, having
4436 // reached the limit of the stack size, while making very
4437 // slow forward progress. It may be best to bail out and
4438 // let the foreground collector do its job.
4439 // Clear _restart_addr, so that foreground GC
4440 // works from scratch. This avoids the headache of
4441 // a "rescan" which would otherwise be needed because
4442 // of the dirty mod union table & card table.
4443 _restart_addr = NULL;
4444 return false;
4445 }
4446 // Adjust the task to restart from _restart_addr
4447 tsk.reset(_restart_addr);
4448 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4449 _restart_addr);
4450 _restart_addr = NULL;
4451 // Get the workers going again
4452 conc_workers()->start_task(&tsk);
4453 while (tsk.yielded()) {
4454 tsk.coordinator_yield();
4455 conc_workers()->continue_task(&tsk);
4456 }
4457 }
4458 assert(tsk.completed(), "Inconsistency");
4459 assert(tsk.result() == true, "Inconsistency");
4460 return true;
4461 }
4463 bool CMSCollector::do_marking_st(bool asynch) {
4464 ResourceMark rm;
4465 HandleMark hm;
4467 // Temporarily make refs discovery single threaded (non-MT)
4468 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4469 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4470 &_markStack, CMSYield && asynch);
4471 // the last argument to iterate indicates whether the iteration
4472 // should be incremental with periodic yields.
4473 _markBitMap.iterate(&markFromRootsClosure);
4474 // If _restart_addr is non-NULL, a marking stack overflow
4475 // occurred; we need to do a fresh iteration from the
4476 // indicated restart address.
4477 while (_restart_addr != NULL) {
4478 if (_foregroundGCIsActive && asynch) {
4479 // We may be running into repeated stack overflows, having
4480 // reached the limit of the stack size, while making very
4481 // slow forward progress. It may be best to bail out and
4482 // let the foreground collector do its job.
4483 // Clear _restart_addr, so that foreground GC
4484 // works from scratch. This avoids the headache of
4485 // a "rescan" which would otherwise be needed because
4486 // of the dirty mod union table & card table.
4487 _restart_addr = NULL;
4488 return false; // indicating failure to complete marking
4489 }
4490 // Deal with stack overflow:
4491 // we restart marking from _restart_addr
4492 HeapWord* ra = _restart_addr;
4493 markFromRootsClosure.reset(ra);
4494 _restart_addr = NULL;
4495 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4496 }
4497 return true;
4498 }
4500 void CMSCollector::preclean() {
4501 check_correct_thread_executing();
4502 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4503 verify_work_stacks_empty();
4504 verify_overflow_empty();
4505 _abort_preclean = false;
4506 if (CMSPrecleaningEnabled) {
4507 if (!CMSEdenChunksRecordAlways) {
4508 _eden_chunk_index = 0;
4509 }
4510 size_t used = get_eden_used();
4511 size_t capacity = get_eden_capacity();
4512 // Don't start sampling unless we will get sufficiently
4513 // many samples.
4514 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4515 * CMSScheduleRemarkEdenPenetration)) {
4516 _start_sampling = true;
4517 } else {
4518 _start_sampling = false;
4519 }
4520 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4521 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4522 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4523 }
4524 CMSTokenSync x(true); // is cms thread
4525 if (CMSPrecleaningEnabled) {
4526 sample_eden();
4527 _collectorState = AbortablePreclean;
4528 } else {
4529 _collectorState = FinalMarking;
4530 }
4531 verify_work_stacks_empty();
4532 verify_overflow_empty();
4533 }
4535 // Try and schedule the remark such that young gen
4536 // occupancy is CMSScheduleRemarkEdenPenetration %.
4537 void CMSCollector::abortable_preclean() {
4538 check_correct_thread_executing();
4539 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4540 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4542 // If Eden's current occupancy is below this threshold,
4543 // immediately schedule the remark; else preclean
4544 // past the next scavenge in an effort to
4545 // schedule the pause as described avove. By choosing
4546 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4547 // we will never do an actual abortable preclean cycle.
4548 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4549 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4550 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4551 // We need more smarts in the abortable preclean
4552 // loop below to deal with cases where allocation
4553 // in young gen is very very slow, and our precleaning
4554 // is running a losing race against a horde of
4555 // mutators intent on flooding us with CMS updates
4556 // (dirty cards).
4557 // One, admittedly dumb, strategy is to give up
4558 // after a certain number of abortable precleaning loops
4559 // or after a certain maximum time. We want to make
4560 // this smarter in the next iteration.
4561 // XXX FIX ME!!! YSR
4562 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4563 while (!(should_abort_preclean() ||
4564 ConcurrentMarkSweepThread::should_terminate())) {
4565 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4566 cumworkdone += workdone;
4567 loops++;
4568 // Voluntarily terminate abortable preclean phase if we have
4569 // been at it for too long.
4570 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4571 loops >= CMSMaxAbortablePrecleanLoops) {
4572 if (PrintGCDetails) {
4573 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4574 }
4575 break;
4576 }
4577 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4578 if (PrintGCDetails) {
4579 gclog_or_tty->print(" CMS: abort preclean due to time ");
4580 }
4581 break;
4582 }
4583 // If we are doing little work each iteration, we should
4584 // take a short break.
4585 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4586 // Sleep for some time, waiting for work to accumulate
4587 stopTimer();
4588 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4589 startTimer();
4590 waited++;
4591 }
4592 }
4593 if (PrintCMSStatistics > 0) {
4594 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4595 loops, waited, cumworkdone);
4596 }
4597 }
4598 CMSTokenSync x(true); // is cms thread
4599 if (_collectorState != Idling) {
4600 assert(_collectorState == AbortablePreclean,
4601 "Spontaneous state transition?");
4602 _collectorState = FinalMarking;
4603 } // Else, a foreground collection completed this CMS cycle.
4604 return;
4605 }
4607 // Respond to an Eden sampling opportunity
4608 void CMSCollector::sample_eden() {
4609 // Make sure a young gc cannot sneak in between our
4610 // reading and recording of a sample.
4611 assert(Thread::current()->is_ConcurrentGC_thread(),
4612 "Only the cms thread may collect Eden samples");
4613 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4614 "Should collect samples while holding CMS token");
4615 if (!_start_sampling) {
4616 return;
4617 }
4618 // When CMSEdenChunksRecordAlways is true, the eden chunk array
4619 // is populated by the young generation.
4620 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
4621 if (_eden_chunk_index < _eden_chunk_capacity) {
4622 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4623 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4624 "Unexpected state of Eden");
4625 // We'd like to check that what we just sampled is an oop-start address;
4626 // however, we cannot do that here since the object may not yet have been
4627 // initialized. So we'll instead do the check when we _use_ this sample
4628 // later.
4629 if (_eden_chunk_index == 0 ||
4630 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4631 _eden_chunk_array[_eden_chunk_index-1])
4632 >= CMSSamplingGrain)) {
4633 _eden_chunk_index++; // commit sample
4634 }
4635 }
4636 }
4637 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4638 size_t used = get_eden_used();
4639 size_t capacity = get_eden_capacity();
4640 assert(used <= capacity, "Unexpected state of Eden");
4641 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4642 _abort_preclean = true;
4643 }
4644 }
4645 }
4648 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4649 assert(_collectorState == Precleaning ||
4650 _collectorState == AbortablePreclean, "incorrect state");
4651 ResourceMark rm;
4652 HandleMark hm;
4654 // Precleaning is currently not MT but the reference processor
4655 // may be set for MT. Disable it temporarily here.
4656 ReferenceProcessor* rp = ref_processor();
4657 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4659 // Do one pass of scrubbing the discovered reference lists
4660 // to remove any reference objects with strongly-reachable
4661 // referents.
4662 if (clean_refs) {
4663 CMSPrecleanRefsYieldClosure yield_cl(this);
4664 assert(rp->span().equals(_span), "Spans should be equal");
4665 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4666 &_markStack, true /* preclean */);
4667 CMSDrainMarkingStackClosure complete_trace(this,
4668 _span, &_markBitMap, &_markStack,
4669 &keep_alive, true /* preclean */);
4671 // We don't want this step to interfere with a young
4672 // collection because we don't want to take CPU
4673 // or memory bandwidth away from the young GC threads
4674 // (which may be as many as there are CPUs).
4675 // Note that we don't need to protect ourselves from
4676 // interference with mutators because they can't
4677 // manipulate the discovered reference lists nor affect
4678 // the computed reachability of the referents, the
4679 // only properties manipulated by the precleaning
4680 // of these reference lists.
4681 stopTimer();
4682 CMSTokenSyncWithLocks x(true /* is cms thread */,
4683 bitMapLock());
4684 startTimer();
4685 sample_eden();
4687 // The following will yield to allow foreground
4688 // collection to proceed promptly. XXX YSR:
4689 // The code in this method may need further
4690 // tweaking for better performance and some restructuring
4691 // for cleaner interfaces.
4692 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4693 rp->preclean_discovered_references(
4694 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
4695 gc_timer);
4696 }
4698 if (clean_survivor) { // preclean the active survivor space(s)
4699 assert(_young_gen->kind() == Generation::DefNew ||
4700 _young_gen->kind() == Generation::ParNew ||
4701 _young_gen->kind() == Generation::ASParNew,
4702 "incorrect type for cast");
4703 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4704 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4705 &_markBitMap, &_modUnionTable,
4706 &_markStack, true /* precleaning phase */);
4707 stopTimer();
4708 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4709 bitMapLock());
4710 startTimer();
4711 unsigned int before_count =
4712 GenCollectedHeap::heap()->total_collections();
4713 SurvivorSpacePrecleanClosure
4714 sss_cl(this, _span, &_markBitMap, &_markStack,
4715 &pam_cl, before_count, CMSYield);
4716 dng->from()->object_iterate_careful(&sss_cl);
4717 dng->to()->object_iterate_careful(&sss_cl);
4718 }
4719 MarkRefsIntoAndScanClosure
4720 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4721 &_markStack, this, CMSYield,
4722 true /* precleaning phase */);
4723 // CAUTION: The following closure has persistent state that may need to
4724 // be reset upon a decrease in the sequence of addresses it
4725 // processes.
4726 ScanMarkedObjectsAgainCarefullyClosure
4727 smoac_cl(this, _span,
4728 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4730 // Preclean dirty cards in ModUnionTable and CardTable using
4731 // appropriate convergence criterion;
4732 // repeat CMSPrecleanIter times unless we find that
4733 // we are losing.
4734 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4735 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4736 "Bad convergence multiplier");
4737 assert(CMSPrecleanThreshold >= 100,
4738 "Unreasonably low CMSPrecleanThreshold");
4740 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4741 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4742 numIter < CMSPrecleanIter;
4743 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4744 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4745 if (Verbose && PrintGCDetails) {
4746 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4747 }
4748 // Either there are very few dirty cards, so re-mark
4749 // pause will be small anyway, or our pre-cleaning isn't
4750 // that much faster than the rate at which cards are being
4751 // dirtied, so we might as well stop and re-mark since
4752 // precleaning won't improve our re-mark time by much.
4753 if (curNumCards <= CMSPrecleanThreshold ||
4754 (numIter > 0 &&
4755 (curNumCards * CMSPrecleanDenominator >
4756 lastNumCards * CMSPrecleanNumerator))) {
4757 numIter++;
4758 cumNumCards += curNumCards;
4759 break;
4760 }
4761 }
4763 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4765 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4766 cumNumCards += curNumCards;
4767 if (PrintGCDetails && PrintCMSStatistics != 0) {
4768 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4769 curNumCards, cumNumCards, numIter);
4770 }
4771 return cumNumCards; // as a measure of useful work done
4772 }
4774 // PRECLEANING NOTES:
4775 // Precleaning involves:
4776 // . reading the bits of the modUnionTable and clearing the set bits.
4777 // . For the cards corresponding to the set bits, we scan the
4778 // objects on those cards. This means we need the free_list_lock
4779 // so that we can safely iterate over the CMS space when scanning
4780 // for oops.
4781 // . When we scan the objects, we'll be both reading and setting
4782 // marks in the marking bit map, so we'll need the marking bit map.
4783 // . For protecting _collector_state transitions, we take the CGC_lock.
4784 // Note that any races in the reading of of card table entries by the
4785 // CMS thread on the one hand and the clearing of those entries by the
4786 // VM thread or the setting of those entries by the mutator threads on the
4787 // other are quite benign. However, for efficiency it makes sense to keep
4788 // the VM thread from racing with the CMS thread while the latter is
4789 // dirty card info to the modUnionTable. We therefore also use the
4790 // CGC_lock to protect the reading of the card table and the mod union
4791 // table by the CM thread.
4792 // . We run concurrently with mutator updates, so scanning
4793 // needs to be done carefully -- we should not try to scan
4794 // potentially uninitialized objects.
4795 //
4796 // Locking strategy: While holding the CGC_lock, we scan over and
4797 // reset a maximal dirty range of the mod union / card tables, then lock
4798 // the free_list_lock and bitmap lock to do a full marking, then
4799 // release these locks; and repeat the cycle. This allows for a
4800 // certain amount of fairness in the sharing of these locks between
4801 // the CMS collector on the one hand, and the VM thread and the
4802 // mutators on the other.
4804 // NOTE: preclean_mod_union_table() and preclean_card_table()
4805 // further below are largely identical; if you need to modify
4806 // one of these methods, please check the other method too.
4808 size_t CMSCollector::preclean_mod_union_table(
4809 ConcurrentMarkSweepGeneration* gen,
4810 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4811 verify_work_stacks_empty();
4812 verify_overflow_empty();
4814 // strategy: starting with the first card, accumulate contiguous
4815 // ranges of dirty cards; clear these cards, then scan the region
4816 // covered by these cards.
4818 // Since all of the MUT is committed ahead, we can just use
4819 // that, in case the generations expand while we are precleaning.
4820 // It might also be fine to just use the committed part of the
4821 // generation, but we might potentially miss cards when the
4822 // generation is rapidly expanding while we are in the midst
4823 // of precleaning.
4824 HeapWord* startAddr = gen->reserved().start();
4825 HeapWord* endAddr = gen->reserved().end();
4827 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4829 size_t numDirtyCards, cumNumDirtyCards;
4830 HeapWord *nextAddr, *lastAddr;
4831 for (cumNumDirtyCards = numDirtyCards = 0,
4832 nextAddr = lastAddr = startAddr;
4833 nextAddr < endAddr;
4834 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4836 ResourceMark rm;
4837 HandleMark hm;
4839 MemRegion dirtyRegion;
4840 {
4841 stopTimer();
4842 // Potential yield point
4843 CMSTokenSync ts(true);
4844 startTimer();
4845 sample_eden();
4846 // Get dirty region starting at nextOffset (inclusive),
4847 // simultaneously clearing it.
4848 dirtyRegion =
4849 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4850 assert(dirtyRegion.start() >= nextAddr,
4851 "returned region inconsistent?");
4852 }
4853 // Remember where the next search should begin.
4854 // The returned region (if non-empty) is a right open interval,
4855 // so lastOffset is obtained from the right end of that
4856 // interval.
4857 lastAddr = dirtyRegion.end();
4858 // Should do something more transparent and less hacky XXX
4859 numDirtyCards =
4860 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4862 // We'll scan the cards in the dirty region (with periodic
4863 // yields for foreground GC as needed).
4864 if (!dirtyRegion.is_empty()) {
4865 assert(numDirtyCards > 0, "consistency check");
4866 HeapWord* stop_point = NULL;
4867 stopTimer();
4868 // Potential yield point
4869 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4870 bitMapLock());
4871 startTimer();
4872 {
4873 verify_work_stacks_empty();
4874 verify_overflow_empty();
4875 sample_eden();
4876 stop_point =
4877 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4878 }
4879 if (stop_point != NULL) {
4880 // The careful iteration stopped early either because it found an
4881 // uninitialized object, or because we were in the midst of an
4882 // "abortable preclean", which should now be aborted. Redirty
4883 // the bits corresponding to the partially-scanned or unscanned
4884 // cards. We'll either restart at the next block boundary or
4885 // abort the preclean.
4886 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4887 "Should only be AbortablePreclean.");
4888 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4889 if (should_abort_preclean()) {
4890 break; // out of preclean loop
4891 } else {
4892 // Compute the next address at which preclean should pick up;
4893 // might need bitMapLock in order to read P-bits.
4894 lastAddr = next_card_start_after_block(stop_point);
4895 }
4896 }
4897 } else {
4898 assert(lastAddr == endAddr, "consistency check");
4899 assert(numDirtyCards == 0, "consistency check");
4900 break;
4901 }
4902 }
4903 verify_work_stacks_empty();
4904 verify_overflow_empty();
4905 return cumNumDirtyCards;
4906 }
4908 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4909 // below are largely identical; if you need to modify
4910 // one of these methods, please check the other method too.
4912 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4913 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4914 // strategy: it's similar to precleamModUnionTable above, in that
4915 // we accumulate contiguous ranges of dirty cards, mark these cards
4916 // precleaned, then scan the region covered by these cards.
4917 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4918 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4920 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4922 size_t numDirtyCards, cumNumDirtyCards;
4923 HeapWord *lastAddr, *nextAddr;
4925 for (cumNumDirtyCards = numDirtyCards = 0,
4926 nextAddr = lastAddr = startAddr;
4927 nextAddr < endAddr;
4928 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4930 ResourceMark rm;
4931 HandleMark hm;
4933 MemRegion dirtyRegion;
4934 {
4935 // See comments in "Precleaning notes" above on why we
4936 // do this locking. XXX Could the locking overheads be
4937 // too high when dirty cards are sparse? [I don't think so.]
4938 stopTimer();
4939 CMSTokenSync x(true); // is cms thread
4940 startTimer();
4941 sample_eden();
4942 // Get and clear dirty region from card table
4943 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4944 MemRegion(nextAddr, endAddr),
4945 true,
4946 CardTableModRefBS::precleaned_card_val());
4948 assert(dirtyRegion.start() >= nextAddr,
4949 "returned region inconsistent?");
4950 }
4951 lastAddr = dirtyRegion.end();
4952 numDirtyCards =
4953 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4955 if (!dirtyRegion.is_empty()) {
4956 stopTimer();
4957 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4958 startTimer();
4959 sample_eden();
4960 verify_work_stacks_empty();
4961 verify_overflow_empty();
4962 HeapWord* stop_point =
4963 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4964 if (stop_point != NULL) {
4965 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4966 "Should only be AbortablePreclean.");
4967 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4968 if (should_abort_preclean()) {
4969 break; // out of preclean loop
4970 } else {
4971 // Compute the next address at which preclean should pick up.
4972 lastAddr = next_card_start_after_block(stop_point);
4973 }
4974 }
4975 } else {
4976 break;
4977 }
4978 }
4979 verify_work_stacks_empty();
4980 verify_overflow_empty();
4981 return cumNumDirtyCards;
4982 }
4984 class PrecleanKlassClosure : public KlassClosure {
4985 CMKlassClosure _cm_klass_closure;
4986 public:
4987 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4988 void do_klass(Klass* k) {
4989 if (k->has_accumulated_modified_oops()) {
4990 k->clear_accumulated_modified_oops();
4992 _cm_klass_closure.do_klass(k);
4993 }
4994 }
4995 };
4997 // The freelist lock is needed to prevent asserts, is it really needed?
4998 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
5000 cl->set_freelistLock(freelistLock);
5002 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
5004 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
5005 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
5006 PrecleanKlassClosure preclean_klass_closure(cl);
5007 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
5009 verify_work_stacks_empty();
5010 verify_overflow_empty();
5011 }
5013 void CMSCollector::checkpointRootsFinal(bool asynch,
5014 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
5015 assert(_collectorState == FinalMarking, "incorrect state transition?");
5016 check_correct_thread_executing();
5017 // world is stopped at this checkpoint
5018 assert(SafepointSynchronize::is_at_safepoint(),
5019 "world should be stopped");
5020 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5022 verify_work_stacks_empty();
5023 verify_overflow_empty();
5025 SpecializationStats::clear();
5026 if (PrintGCDetails) {
5027 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
5028 _young_gen->used() / K,
5029 _young_gen->capacity() / K);
5030 }
5031 if (asynch) {
5032 if (CMSScavengeBeforeRemark) {
5033 GenCollectedHeap* gch = GenCollectedHeap::heap();
5034 // Temporarily set flag to false, GCH->do_collection will
5035 // expect it to be false and set to true
5036 FlagSetting fl(gch->_is_gc_active, false);
5037 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
5038 PrintGCDetails && Verbose, true, _gc_timer_cm);)
5039 int level = _cmsGen->level() - 1;
5040 if (level >= 0) {
5041 gch->do_collection(true, // full (i.e. force, see below)
5042 false, // !clear_all_soft_refs
5043 0, // size
5044 false, // is_tlab
5045 level // max_level
5046 );
5047 }
5048 }
5049 FreelistLocker x(this);
5050 MutexLockerEx y(bitMapLock(),
5051 Mutex::_no_safepoint_check_flag);
5052 assert(!init_mark_was_synchronous, "but that's impossible!");
5053 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
5054 } else {
5055 // already have all the locks
5056 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
5057 init_mark_was_synchronous);
5058 }
5059 verify_work_stacks_empty();
5060 verify_overflow_empty();
5061 SpecializationStats::print();
5062 }
5064 void CMSCollector::checkpointRootsFinalWork(bool asynch,
5065 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
5067 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm);)
5069 assert(haveFreelistLocks(), "must have free list locks");
5070 assert_lock_strong(bitMapLock());
5072 if (UseAdaptiveSizePolicy) {
5073 size_policy()->checkpoint_roots_final_begin();
5074 }
5076 ResourceMark rm;
5077 HandleMark hm;
5079 GenCollectedHeap* gch = GenCollectedHeap::heap();
5081 if (should_unload_classes()) {
5082 CodeCache::gc_prologue();
5083 }
5084 assert(haveFreelistLocks(), "must have free list locks");
5085 assert_lock_strong(bitMapLock());
5087 if (!init_mark_was_synchronous) {
5088 // We might assume that we need not fill TLAB's when
5089 // CMSScavengeBeforeRemark is set, because we may have just done
5090 // a scavenge which would have filled all TLAB's -- and besides
5091 // Eden would be empty. This however may not always be the case --
5092 // for instance although we asked for a scavenge, it may not have
5093 // happened because of a JNI critical section. We probably need
5094 // a policy for deciding whether we can in that case wait until
5095 // the critical section releases and then do the remark following
5096 // the scavenge, and skip it here. In the absence of that policy,
5097 // or of an indication of whether the scavenge did indeed occur,
5098 // we cannot rely on TLAB's having been filled and must do
5099 // so here just in case a scavenge did not happen.
5100 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
5101 // Update the saved marks which may affect the root scans.
5102 gch->save_marks();
5104 if (CMSPrintEdenSurvivorChunks) {
5105 print_eden_and_survivor_chunk_arrays();
5106 }
5108 {
5109 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
5111 // Note on the role of the mod union table:
5112 // Since the marker in "markFromRoots" marks concurrently with
5113 // mutators, it is possible for some reachable objects not to have been
5114 // scanned. For instance, an only reference to an object A was
5115 // placed in object B after the marker scanned B. Unless B is rescanned,
5116 // A would be collected. Such updates to references in marked objects
5117 // are detected via the mod union table which is the set of all cards
5118 // dirtied since the first checkpoint in this GC cycle and prior to
5119 // the most recent young generation GC, minus those cleaned up by the
5120 // concurrent precleaning.
5121 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
5122 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm);
5123 do_remark_parallel();
5124 } else {
5125 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
5126 _gc_timer_cm);
5127 do_remark_non_parallel();
5128 }
5129 }
5130 } else {
5131 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
5132 // The initial mark was stop-world, so there's no rescanning to
5133 // do; go straight on to the next step below.
5134 }
5135 verify_work_stacks_empty();
5136 verify_overflow_empty();
5138 {
5139 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm);)
5140 refProcessingWork(asynch, clear_all_soft_refs);
5141 }
5142 verify_work_stacks_empty();
5143 verify_overflow_empty();
5145 if (should_unload_classes()) {
5146 CodeCache::gc_epilogue();
5147 }
5148 JvmtiExport::gc_epilogue();
5150 // If we encountered any (marking stack / work queue) overflow
5151 // events during the current CMS cycle, take appropriate
5152 // remedial measures, where possible, so as to try and avoid
5153 // recurrence of that condition.
5154 assert(_markStack.isEmpty(), "No grey objects");
5155 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5156 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
5157 if (ser_ovflw > 0) {
5158 if (PrintCMSStatistics != 0) {
5159 gclog_or_tty->print_cr("Marking stack overflow (benign) "
5160 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5161 ", kac_preclean="SIZE_FORMAT")",
5162 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5163 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5164 }
5165 _markStack.expand();
5166 _ser_pmc_remark_ovflw = 0;
5167 _ser_pmc_preclean_ovflw = 0;
5168 _ser_kac_preclean_ovflw = 0;
5169 _ser_kac_ovflw = 0;
5170 }
5171 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5172 if (PrintCMSStatistics != 0) {
5173 gclog_or_tty->print_cr("Work queue overflow (benign) "
5174 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5175 _par_pmc_remark_ovflw, _par_kac_ovflw);
5176 }
5177 _par_pmc_remark_ovflw = 0;
5178 _par_kac_ovflw = 0;
5179 }
5180 if (PrintCMSStatistics != 0) {
5181 if (_markStack._hit_limit > 0) {
5182 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5183 _markStack._hit_limit);
5184 }
5185 if (_markStack._failed_double > 0) {
5186 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5187 " current capacity "SIZE_FORMAT,
5188 _markStack._failed_double,
5189 _markStack.capacity());
5190 }
5191 }
5192 _markStack._hit_limit = 0;
5193 _markStack._failed_double = 0;
5195 if ((VerifyAfterGC || VerifyDuringGC) &&
5196 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5197 verify_after_remark();
5198 }
5200 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
5202 // Change under the freelistLocks.
5203 _collectorState = Sweeping;
5204 // Call isAllClear() under bitMapLock
5205 assert(_modUnionTable.isAllClear(),
5206 "Should be clear by end of the final marking");
5207 assert(_ct->klass_rem_set()->mod_union_is_clear(),
5208 "Should be clear by end of the final marking");
5209 if (UseAdaptiveSizePolicy) {
5210 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
5211 }
5212 }
5214 void CMSParInitialMarkTask::work(uint worker_id) {
5215 elapsedTimer _timer;
5216 ResourceMark rm;
5217 HandleMark hm;
5219 // ---------- scan from roots --------------
5220 _timer.start();
5221 GenCollectedHeap* gch = GenCollectedHeap::heap();
5222 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
5223 CMKlassClosure klass_closure(&par_mri_cl);
5225 // ---------- young gen roots --------------
5226 {
5227 work_on_young_gen_roots(worker_id, &par_mri_cl);
5228 _timer.stop();
5229 if (PrintCMSStatistics != 0) {
5230 gclog_or_tty->print_cr(
5231 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
5232 worker_id, _timer.seconds());
5233 }
5234 }
5236 // ---------- remaining roots --------------
5237 _timer.reset();
5238 _timer.start();
5239 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5240 false, // yg was scanned above
5241 false, // this is parallel code
5242 false, // not scavenging
5243 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5244 &par_mri_cl,
5245 true, // walk all of code cache if (so & SO_CodeCache)
5246 NULL,
5247 &klass_closure);
5248 assert(_collector->should_unload_classes()
5249 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache),
5250 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5251 _timer.stop();
5252 if (PrintCMSStatistics != 0) {
5253 gclog_or_tty->print_cr(
5254 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
5255 worker_id, _timer.seconds());
5256 }
5257 }
5259 // Parallel remark task
5260 class CMSParRemarkTask: public CMSParMarkTask {
5261 CompactibleFreeListSpace* _cms_space;
5263 // The per-thread work queues, available here for stealing.
5264 OopTaskQueueSet* _task_queues;
5265 ParallelTaskTerminator _term;
5267 public:
5268 // A value of 0 passed to n_workers will cause the number of
5269 // workers to be taken from the active workers in the work gang.
5270 CMSParRemarkTask(CMSCollector* collector,
5271 CompactibleFreeListSpace* cms_space,
5272 int n_workers, FlexibleWorkGang* workers,
5273 OopTaskQueueSet* task_queues):
5274 CMSParMarkTask("Rescan roots and grey objects in parallel",
5275 collector, n_workers),
5276 _cms_space(cms_space),
5277 _task_queues(task_queues),
5278 _term(n_workers, task_queues) { }
5280 OopTaskQueueSet* task_queues() { return _task_queues; }
5282 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5284 ParallelTaskTerminator* terminator() { return &_term; }
5285 int n_workers() { return _n_workers; }
5287 void work(uint worker_id);
5289 private:
5290 // ... of dirty cards in old space
5291 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5292 Par_MarkRefsIntoAndScanClosure* cl);
5294 // ... work stealing for the above
5295 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5296 };
5298 class RemarkKlassClosure : public KlassClosure {
5299 CMKlassClosure _cm_klass_closure;
5300 public:
5301 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
5302 void do_klass(Klass* k) {
5303 // Check if we have modified any oops in the Klass during the concurrent marking.
5304 if (k->has_accumulated_modified_oops()) {
5305 k->clear_accumulated_modified_oops();
5307 // We could have transfered the current modified marks to the accumulated marks,
5308 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
5309 } else if (k->has_modified_oops()) {
5310 // Don't clear anything, this info is needed by the next young collection.
5311 } else {
5312 // No modified oops in the Klass.
5313 return;
5314 }
5316 // The klass has modified fields, need to scan the klass.
5317 _cm_klass_closure.do_klass(k);
5318 }
5319 };
5321 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
5322 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5323 EdenSpace* eden_space = dng->eden();
5324 ContiguousSpace* from_space = dng->from();
5325 ContiguousSpace* to_space = dng->to();
5327 HeapWord** eca = _collector->_eden_chunk_array;
5328 size_t ect = _collector->_eden_chunk_index;
5329 HeapWord** sca = _collector->_survivor_chunk_array;
5330 size_t sct = _collector->_survivor_chunk_index;
5332 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5333 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5335 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
5336 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
5337 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
5338 }
5340 // work_queue(i) is passed to the closure
5341 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5342 // also is passed to do_dirty_card_rescan_tasks() and to
5343 // do_work_steal() to select the i-th task_queue.
5345 void CMSParRemarkTask::work(uint worker_id) {
5346 elapsedTimer _timer;
5347 ResourceMark rm;
5348 HandleMark hm;
5350 // ---------- rescan from roots --------------
5351 _timer.start();
5352 GenCollectedHeap* gch = GenCollectedHeap::heap();
5353 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5354 _collector->_span, _collector->ref_processor(),
5355 &(_collector->_markBitMap),
5356 work_queue(worker_id));
5358 // Rescan young gen roots first since these are likely
5359 // coarsely partitioned and may, on that account, constitute
5360 // the critical path; thus, it's best to start off that
5361 // work first.
5362 // ---------- young gen roots --------------
5363 {
5364 work_on_young_gen_roots(worker_id, &par_mrias_cl);
5365 _timer.stop();
5366 if (PrintCMSStatistics != 0) {
5367 gclog_or_tty->print_cr(
5368 "Finished young gen rescan work in %dth thread: %3.3f sec",
5369 worker_id, _timer.seconds());
5370 }
5371 }
5373 // ---------- remaining roots --------------
5374 _timer.reset();
5375 _timer.start();
5376 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5377 false, // yg was scanned above
5378 false, // this is parallel code
5379 false, // not scavenging
5380 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5381 &par_mrias_cl,
5382 true, // walk all of code cache if (so & SO_CodeCache)
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_CodeCache),
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);
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);
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 false, // not scavenging
5971 SharedHeap::ScanningOption(roots_scanning_options()),
5972 &mrias_cl,
5973 true, // walk code active on stacks
5974 NULL,
5975 NULL); // The dirty klasses will be handled below
5977 assert(should_unload_classes()
5978 || (roots_scanning_options() & SharedHeap::SO_CodeCache),
5979 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5980 }
5982 {
5983 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm);
5985 verify_work_stacks_empty();
5987 // Scan all class loader data objects that might have been introduced
5988 // during concurrent marking.
5989 ResourceMark rm;
5990 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5991 for (int i = 0; i < array->length(); i++) {
5992 mrias_cl.do_class_loader_data(array->at(i));
5993 }
5995 // We don't need to keep track of new CLDs anymore.
5996 ClassLoaderDataGraph::remember_new_clds(false);
5998 verify_work_stacks_empty();
5999 }
6001 {
6002 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm);
6004 verify_work_stacks_empty();
6006 RemarkKlassClosure remark_klass_closure(&mrias_cl);
6007 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
6009 verify_work_stacks_empty();
6010 }
6012 // We might have added oops to ClassLoaderData::_handles during the
6013 // concurrent marking phase. These oops point to newly allocated objects
6014 // that are guaranteed to be kept alive. Either by the direct allocation
6015 // code, or when the young collector processes the strong roots. Hence,
6016 // we don't have to revisit the _handles block during the remark phase.
6018 verify_work_stacks_empty();
6019 // Restore evacuated mark words, if any, used for overflow list links
6020 if (!CMSOverflowEarlyRestoration) {
6021 restore_preserved_marks_if_any();
6022 }
6023 verify_overflow_empty();
6024 }
6026 ////////////////////////////////////////////////////////
6027 // Parallel Reference Processing Task Proxy Class
6028 ////////////////////////////////////////////////////////
6029 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
6030 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
6031 CMSCollector* _collector;
6032 CMSBitMap* _mark_bit_map;
6033 const MemRegion _span;
6034 ProcessTask& _task;
6036 public:
6037 CMSRefProcTaskProxy(ProcessTask& task,
6038 CMSCollector* collector,
6039 const MemRegion& span,
6040 CMSBitMap* mark_bit_map,
6041 AbstractWorkGang* workers,
6042 OopTaskQueueSet* task_queues):
6043 // XXX Should superclass AGTWOQ also know about AWG since it knows
6044 // about the task_queues used by the AWG? Then it could initialize
6045 // the terminator() object. See 6984287. The set_for_termination()
6046 // below is a temporary band-aid for the regression in 6984287.
6047 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
6048 task_queues),
6049 _task(task),
6050 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
6051 {
6052 assert(_collector->_span.equals(_span) && !_span.is_empty(),
6053 "Inconsistency in _span");
6054 set_for_termination(workers->active_workers());
6055 }
6057 OopTaskQueueSet* task_queues() { return queues(); }
6059 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
6061 void do_work_steal(int i,
6062 CMSParDrainMarkingStackClosure* drain,
6063 CMSParKeepAliveClosure* keep_alive,
6064 int* seed);
6066 virtual void work(uint worker_id);
6067 };
6069 void CMSRefProcTaskProxy::work(uint worker_id) {
6070 assert(_collector->_span.equals(_span), "Inconsistency in _span");
6071 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
6072 _mark_bit_map,
6073 work_queue(worker_id));
6074 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
6075 _mark_bit_map,
6076 work_queue(worker_id));
6077 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
6078 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
6079 if (_task.marks_oops_alive()) {
6080 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
6081 _collector->hash_seed(worker_id));
6082 }
6083 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
6084 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
6085 }
6087 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
6088 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
6089 EnqueueTask& _task;
6091 public:
6092 CMSRefEnqueueTaskProxy(EnqueueTask& task)
6093 : AbstractGangTask("Enqueue reference objects in parallel"),
6094 _task(task)
6095 { }
6097 virtual void work(uint worker_id)
6098 {
6099 _task.work(worker_id);
6100 }
6101 };
6103 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
6104 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
6105 _span(span),
6106 _bit_map(bit_map),
6107 _work_queue(work_queue),
6108 _mark_and_push(collector, span, bit_map, work_queue),
6109 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6110 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
6111 { }
6113 // . see if we can share work_queues with ParNew? XXX
6114 void CMSRefProcTaskProxy::do_work_steal(int i,
6115 CMSParDrainMarkingStackClosure* drain,
6116 CMSParKeepAliveClosure* keep_alive,
6117 int* seed) {
6118 OopTaskQueue* work_q = work_queue(i);
6119 NOT_PRODUCT(int num_steals = 0;)
6120 oop obj_to_scan;
6122 while (true) {
6123 // Completely finish any left over work from (an) earlier round(s)
6124 drain->trim_queue(0);
6125 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
6126 (size_t)ParGCDesiredObjsFromOverflowList);
6127 // Now check if there's any work in the overflow list
6128 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
6129 // only affects the number of attempts made to get work from the
6130 // overflow list and does not affect the number of workers. Just
6131 // pass ParallelGCThreads so this behavior is unchanged.
6132 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
6133 work_q,
6134 ParallelGCThreads)) {
6135 // Found something in global overflow list;
6136 // not yet ready to go stealing work from others.
6137 // We'd like to assert(work_q->size() != 0, ...)
6138 // because we just took work from the overflow list,
6139 // but of course we can't, since all of that might have
6140 // been already stolen from us.
6141 continue;
6142 }
6143 // Verify that we have no work before we resort to stealing
6144 assert(work_q->size() == 0, "Have work, shouldn't steal");
6145 // Try to steal from other queues that have work
6146 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
6147 NOT_PRODUCT(num_steals++;)
6148 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
6149 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
6150 // Do scanning work
6151 obj_to_scan->oop_iterate(keep_alive);
6152 // Loop around, finish this work, and try to steal some more
6153 } else if (terminator()->offer_termination()) {
6154 break; // nirvana from the infinite cycle
6155 }
6156 }
6157 NOT_PRODUCT(
6158 if (PrintCMSStatistics != 0) {
6159 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
6160 }
6161 )
6162 }
6164 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
6165 {
6166 GenCollectedHeap* gch = GenCollectedHeap::heap();
6167 FlexibleWorkGang* workers = gch->workers();
6168 assert(workers != NULL, "Need parallel worker threads.");
6169 CMSRefProcTaskProxy rp_task(task, &_collector,
6170 _collector.ref_processor()->span(),
6171 _collector.markBitMap(),
6172 workers, _collector.task_queues());
6173 workers->run_task(&rp_task);
6174 }
6176 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
6177 {
6179 GenCollectedHeap* gch = GenCollectedHeap::heap();
6180 FlexibleWorkGang* workers = gch->workers();
6181 assert(workers != NULL, "Need parallel worker threads.");
6182 CMSRefEnqueueTaskProxy enq_task(task);
6183 workers->run_task(&enq_task);
6184 }
6186 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
6188 ResourceMark rm;
6189 HandleMark hm;
6191 ReferenceProcessor* rp = ref_processor();
6192 assert(rp->span().equals(_span), "Spans should be equal");
6193 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
6194 // Process weak references.
6195 rp->setup_policy(clear_all_soft_refs);
6196 verify_work_stacks_empty();
6198 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
6199 &_markStack, false /* !preclean */);
6200 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
6201 _span, &_markBitMap, &_markStack,
6202 &cmsKeepAliveClosure, false /* !preclean */);
6203 {
6204 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm);
6206 ReferenceProcessorStats stats;
6207 if (rp->processing_is_mt()) {
6208 // Set the degree of MT here. If the discovery is done MT, there
6209 // may have been a different number of threads doing the discovery
6210 // and a different number of discovered lists may have Ref objects.
6211 // That is OK as long as the Reference lists are balanced (see
6212 // balance_all_queues() and balance_queues()).
6213 GenCollectedHeap* gch = GenCollectedHeap::heap();
6214 int active_workers = ParallelGCThreads;
6215 FlexibleWorkGang* workers = gch->workers();
6216 if (workers != NULL) {
6217 active_workers = workers->active_workers();
6218 // The expectation is that active_workers will have already
6219 // been set to a reasonable value. If it has not been set,
6220 // investigate.
6221 assert(active_workers > 0, "Should have been set during scavenge");
6222 }
6223 rp->set_active_mt_degree(active_workers);
6224 CMSRefProcTaskExecutor task_executor(*this);
6225 stats = rp->process_discovered_references(&_is_alive_closure,
6226 &cmsKeepAliveClosure,
6227 &cmsDrainMarkingStackClosure,
6228 &task_executor,
6229 _gc_timer_cm);
6230 } else {
6231 stats = rp->process_discovered_references(&_is_alive_closure,
6232 &cmsKeepAliveClosure,
6233 &cmsDrainMarkingStackClosure,
6234 NULL,
6235 _gc_timer_cm);
6236 }
6237 _gc_tracer_cm->report_gc_reference_stats(stats);
6239 }
6241 // This is the point where the entire marking should have completed.
6242 verify_work_stacks_empty();
6244 if (should_unload_classes()) {
6245 {
6246 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm);
6248 // Unload classes and purge the SystemDictionary.
6249 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
6251 // Unload nmethods.
6252 CodeCache::do_unloading(&_is_alive_closure, purged_class);
6254 // Prune dead klasses from subklass/sibling/implementor lists.
6255 Klass::clean_weak_klass_links(&_is_alive_closure);
6256 }
6258 {
6259 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm);
6260 // Clean up unreferenced symbols in symbol table.
6261 SymbolTable::unlink();
6262 }
6263 }
6265 // CMS doesn't use the StringTable as hard roots when class unloading is turned off.
6266 // Need to check if we really scanned the StringTable.
6267 if ((roots_scanning_options() & SharedHeap::SO_Strings) == 0) {
6268 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm);
6269 // Delete entries for dead interned strings.
6270 StringTable::unlink(&_is_alive_closure);
6271 }
6273 // Restore any preserved marks as a result of mark stack or
6274 // work queue overflow
6275 restore_preserved_marks_if_any(); // done single-threaded for now
6277 rp->set_enqueuing_is_done(true);
6278 if (rp->processing_is_mt()) {
6279 rp->balance_all_queues();
6280 CMSRefProcTaskExecutor task_executor(*this);
6281 rp->enqueue_discovered_references(&task_executor);
6282 } else {
6283 rp->enqueue_discovered_references(NULL);
6284 }
6285 rp->verify_no_references_recorded();
6286 assert(!rp->discovery_enabled(), "should have been disabled");
6287 }
6289 #ifndef PRODUCT
6290 void CMSCollector::check_correct_thread_executing() {
6291 Thread* t = Thread::current();
6292 // Only the VM thread or the CMS thread should be here.
6293 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6294 "Unexpected thread type");
6295 // If this is the vm thread, the foreground process
6296 // should not be waiting. Note that _foregroundGCIsActive is
6297 // true while the foreground collector is waiting.
6298 if (_foregroundGCShouldWait) {
6299 // We cannot be the VM thread
6300 assert(t->is_ConcurrentGC_thread(),
6301 "Should be CMS thread");
6302 } else {
6303 // We can be the CMS thread only if we are in a stop-world
6304 // phase of CMS collection.
6305 if (t->is_ConcurrentGC_thread()) {
6306 assert(_collectorState == InitialMarking ||
6307 _collectorState == FinalMarking,
6308 "Should be a stop-world phase");
6309 // The CMS thread should be holding the CMS_token.
6310 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6311 "Potential interference with concurrently "
6312 "executing VM thread");
6313 }
6314 }
6315 }
6316 #endif
6318 void CMSCollector::sweep(bool asynch) {
6319 assert(_collectorState == Sweeping, "just checking");
6320 check_correct_thread_executing();
6321 verify_work_stacks_empty();
6322 verify_overflow_empty();
6323 increment_sweep_count();
6324 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6326 _inter_sweep_timer.stop();
6327 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6328 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
6330 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6331 _intra_sweep_timer.reset();
6332 _intra_sweep_timer.start();
6333 if (asynch) {
6334 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6335 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
6336 // First sweep the old gen
6337 {
6338 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6339 bitMapLock());
6340 sweepWork(_cmsGen, asynch);
6341 }
6343 // Update Universe::_heap_*_at_gc figures.
6344 // We need all the free list locks to make the abstract state
6345 // transition from Sweeping to Resetting. See detailed note
6346 // further below.
6347 {
6348 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6349 // Update heap occupancy information which is used as
6350 // input to soft ref clearing policy at the next gc.
6351 Universe::update_heap_info_at_gc();
6352 _collectorState = Resizing;
6353 }
6354 } else {
6355 // already have needed locks
6356 sweepWork(_cmsGen, asynch);
6357 // Update heap occupancy information which is used as
6358 // input to soft ref clearing policy at the next gc.
6359 Universe::update_heap_info_at_gc();
6360 _collectorState = Resizing;
6361 }
6362 verify_work_stacks_empty();
6363 verify_overflow_empty();
6365 if (should_unload_classes()) {
6366 ClassLoaderDataGraph::purge();
6367 }
6369 _intra_sweep_timer.stop();
6370 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6372 _inter_sweep_timer.reset();
6373 _inter_sweep_timer.start();
6375 // We need to use a monotonically non-deccreasing time in ms
6376 // or we will see time-warp warnings and os::javaTimeMillis()
6377 // does not guarantee monotonicity.
6378 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6379 update_time_of_last_gc(now);
6381 // NOTE on abstract state transitions:
6382 // Mutators allocate-live and/or mark the mod-union table dirty
6383 // based on the state of the collection. The former is done in
6384 // the interval [Marking, Sweeping] and the latter in the interval
6385 // [Marking, Sweeping). Thus the transitions into the Marking state
6386 // and out of the Sweeping state must be synchronously visible
6387 // globally to the mutators.
6388 // The transition into the Marking state happens with the world
6389 // stopped so the mutators will globally see it. Sweeping is
6390 // done asynchronously by the background collector so the transition
6391 // from the Sweeping state to the Resizing state must be done
6392 // under the freelistLock (as is the check for whether to
6393 // allocate-live and whether to dirty the mod-union table).
6394 assert(_collectorState == Resizing, "Change of collector state to"
6395 " Resizing must be done under the freelistLocks (plural)");
6397 // Now that sweeping has been completed, we clear
6398 // the incremental_collection_failed flag,
6399 // thus inviting a younger gen collection to promote into
6400 // this generation. If such a promotion may still fail,
6401 // the flag will be set again when a young collection is
6402 // attempted.
6403 GenCollectedHeap* gch = GenCollectedHeap::heap();
6404 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6405 gch->update_full_collections_completed(_collection_count_start);
6406 }
6408 // FIX ME!!! Looks like this belongs in CFLSpace, with
6409 // CMSGen merely delegating to it.
6410 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6411 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6412 HeapWord* minAddr = _cmsSpace->bottom();
6413 HeapWord* largestAddr =
6414 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6415 if (largestAddr == NULL) {
6416 // The dictionary appears to be empty. In this case
6417 // try to coalesce at the end of the heap.
6418 largestAddr = _cmsSpace->end();
6419 }
6420 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6421 size_t nearLargestOffset =
6422 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6423 if (PrintFLSStatistics != 0) {
6424 gclog_or_tty->print_cr(
6425 "CMS: Large Block: " PTR_FORMAT ";"
6426 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6427 largestAddr,
6428 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6429 }
6430 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6431 }
6433 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6434 return addr >= _cmsSpace->nearLargestChunk();
6435 }
6437 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6438 return _cmsSpace->find_chunk_at_end();
6439 }
6441 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6442 bool full) {
6443 // The next lower level has been collected. Gather any statistics
6444 // that are of interest at this point.
6445 if (!full && (current_level + 1) == level()) {
6446 // Gather statistics on the young generation collection.
6447 collector()->stats().record_gc0_end(used());
6448 }
6449 }
6451 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6452 GenCollectedHeap* gch = GenCollectedHeap::heap();
6453 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6454 "Wrong type of heap");
6455 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6456 gch->gen_policy()->size_policy();
6457 assert(sp->is_gc_cms_adaptive_size_policy(),
6458 "Wrong type of size policy");
6459 return sp;
6460 }
6462 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6463 if (PrintGCDetails && Verbose) {
6464 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6465 }
6466 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6467 _debug_collection_type =
6468 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6469 if (PrintGCDetails && Verbose) {
6470 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6471 }
6472 }
6474 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6475 bool asynch) {
6476 // We iterate over the space(s) underlying this generation,
6477 // checking the mark bit map to see if the bits corresponding
6478 // to specific blocks are marked or not. Blocks that are
6479 // marked are live and are not swept up. All remaining blocks
6480 // are swept up, with coalescing on-the-fly as we sweep up
6481 // contiguous free and/or garbage blocks:
6482 // We need to ensure that the sweeper synchronizes with allocators
6483 // and stop-the-world collectors. In particular, the following
6484 // locks are used:
6485 // . CMS token: if this is held, a stop the world collection cannot occur
6486 // . freelistLock: if this is held no allocation can occur from this
6487 // generation by another thread
6488 // . bitMapLock: if this is held, no other thread can access or update
6489 //
6491 // Note that we need to hold the freelistLock if we use
6492 // block iterate below; else the iterator might go awry if
6493 // a mutator (or promotion) causes block contents to change
6494 // (for instance if the allocator divvies up a block).
6495 // If we hold the free list lock, for all practical purposes
6496 // young generation GC's can't occur (they'll usually need to
6497 // promote), so we might as well prevent all young generation
6498 // GC's while we do a sweeping step. For the same reason, we might
6499 // as well take the bit map lock for the entire duration
6501 // check that we hold the requisite locks
6502 assert(have_cms_token(), "Should hold cms token");
6503 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6504 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6505 "Should possess CMS token to sweep");
6506 assert_lock_strong(gen->freelistLock());
6507 assert_lock_strong(bitMapLock());
6509 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6510 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6511 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6512 _inter_sweep_estimate.padded_average(),
6513 _intra_sweep_estimate.padded_average());
6514 gen->setNearLargestChunk();
6516 {
6517 SweepClosure sweepClosure(this, gen, &_markBitMap,
6518 CMSYield && asynch);
6519 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6520 // We need to free-up/coalesce garbage/blocks from a
6521 // co-terminal free run. This is done in the SweepClosure
6522 // destructor; so, do not remove this scope, else the
6523 // end-of-sweep-census below will be off by a little bit.
6524 }
6525 gen->cmsSpace()->sweep_completed();
6526 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6527 if (should_unload_classes()) { // unloaded classes this cycle,
6528 _concurrent_cycles_since_last_unload = 0; // ... reset count
6529 } else { // did not unload classes,
6530 _concurrent_cycles_since_last_unload++; // ... increment count
6531 }
6532 }
6534 // Reset CMS data structures (for now just the marking bit map)
6535 // preparatory for the next cycle.
6536 void CMSCollector::reset(bool asynch) {
6537 GenCollectedHeap* gch = GenCollectedHeap::heap();
6538 CMSAdaptiveSizePolicy* sp = size_policy();
6539 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6540 if (asynch) {
6541 CMSTokenSyncWithLocks ts(true, bitMapLock());
6543 // If the state is not "Resetting", the foreground thread
6544 // has done a collection and the resetting.
6545 if (_collectorState != Resetting) {
6546 assert(_collectorState == Idling, "The state should only change"
6547 " because the foreground collector has finished the collection");
6548 return;
6549 }
6551 // Clear the mark bitmap (no grey objects to start with)
6552 // for the next cycle.
6553 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6554 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6556 HeapWord* curAddr = _markBitMap.startWord();
6557 while (curAddr < _markBitMap.endWord()) {
6558 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6559 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6560 _markBitMap.clear_large_range(chunk);
6561 if (ConcurrentMarkSweepThread::should_yield() &&
6562 !foregroundGCIsActive() &&
6563 CMSYield) {
6564 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6565 "CMS thread should hold CMS token");
6566 assert_lock_strong(bitMapLock());
6567 bitMapLock()->unlock();
6568 ConcurrentMarkSweepThread::desynchronize(true);
6569 ConcurrentMarkSweepThread::acknowledge_yield_request();
6570 stopTimer();
6571 if (PrintCMSStatistics != 0) {
6572 incrementYields();
6573 }
6574 icms_wait();
6576 // See the comment in coordinator_yield()
6577 for (unsigned i = 0; i < CMSYieldSleepCount &&
6578 ConcurrentMarkSweepThread::should_yield() &&
6579 !CMSCollector::foregroundGCIsActive(); ++i) {
6580 os::sleep(Thread::current(), 1, false);
6581 ConcurrentMarkSweepThread::acknowledge_yield_request();
6582 }
6584 ConcurrentMarkSweepThread::synchronize(true);
6585 bitMapLock()->lock_without_safepoint_check();
6586 startTimer();
6587 }
6588 curAddr = chunk.end();
6589 }
6590 // A successful mostly concurrent collection has been done.
6591 // Because only the full (i.e., concurrent mode failure) collections
6592 // are being measured for gc overhead limits, clean the "near" flag
6593 // and count.
6594 sp->reset_gc_overhead_limit_count();
6595 _collectorState = Idling;
6596 } else {
6597 // already have the lock
6598 assert(_collectorState == Resetting, "just checking");
6599 assert_lock_strong(bitMapLock());
6600 _markBitMap.clear_all();
6601 _collectorState = Idling;
6602 }
6604 // Stop incremental mode after a cycle completes, so that any future cycles
6605 // are triggered by allocation.
6606 stop_icms();
6608 NOT_PRODUCT(
6609 if (RotateCMSCollectionTypes) {
6610 _cmsGen->rotate_debug_collection_type();
6611 }
6612 )
6614 register_gc_end();
6615 }
6617 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6618 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6619 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6620 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL);
6621 TraceCollectorStats tcs(counters());
6623 switch (op) {
6624 case CMS_op_checkpointRootsInitial: {
6625 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6626 checkpointRootsInitial(true); // asynch
6627 if (PrintGC) {
6628 _cmsGen->printOccupancy("initial-mark");
6629 }
6630 break;
6631 }
6632 case CMS_op_checkpointRootsFinal: {
6633 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6634 checkpointRootsFinal(true, // asynch
6635 false, // !clear_all_soft_refs
6636 false); // !init_mark_was_synchronous
6637 if (PrintGC) {
6638 _cmsGen->printOccupancy("remark");
6639 }
6640 break;
6641 }
6642 default:
6643 fatal("No such CMS_op");
6644 }
6645 }
6647 #ifndef PRODUCT
6648 size_t const CMSCollector::skip_header_HeapWords() {
6649 return FreeChunk::header_size();
6650 }
6652 // Try and collect here conditions that should hold when
6653 // CMS thread is exiting. The idea is that the foreground GC
6654 // thread should not be blocked if it wants to terminate
6655 // the CMS thread and yet continue to run the VM for a while
6656 // after that.
6657 void CMSCollector::verify_ok_to_terminate() const {
6658 assert(Thread::current()->is_ConcurrentGC_thread(),
6659 "should be called by CMS thread");
6660 assert(!_foregroundGCShouldWait, "should be false");
6661 // We could check here that all the various low-level locks
6662 // are not held by the CMS thread, but that is overkill; see
6663 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6664 // is checked.
6665 }
6666 #endif
6668 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6669 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6670 "missing Printezis mark?");
6671 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6672 size_t size = pointer_delta(nextOneAddr + 1, addr);
6673 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6674 "alignment problem");
6675 assert(size >= 3, "Necessary for Printezis marks to work");
6676 return size;
6677 }
6679 // A variant of the above (block_size_using_printezis_bits()) except
6680 // that we return 0 if the P-bits are not yet set.
6681 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6682 if (_markBitMap.isMarked(addr + 1)) {
6683 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6684 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6685 size_t size = pointer_delta(nextOneAddr + 1, addr);
6686 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6687 "alignment problem");
6688 assert(size >= 3, "Necessary for Printezis marks to work");
6689 return size;
6690 }
6691 return 0;
6692 }
6694 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6695 size_t sz = 0;
6696 oop p = (oop)addr;
6697 if (p->klass_or_null() != NULL) {
6698 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6699 } else {
6700 sz = block_size_using_printezis_bits(addr);
6701 }
6702 assert(sz > 0, "size must be nonzero");
6703 HeapWord* next_block = addr + sz;
6704 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6705 CardTableModRefBS::card_size);
6706 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6707 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6708 "must be different cards");
6709 return next_card;
6710 }
6713 // CMS Bit Map Wrapper /////////////////////////////////////////
6715 // Construct a CMS bit map infrastructure, but don't create the
6716 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6717 // further below.
6718 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6719 _bm(),
6720 _shifter(shifter),
6721 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6722 {
6723 _bmStartWord = 0;
6724 _bmWordSize = 0;
6725 }
6727 bool CMSBitMap::allocate(MemRegion mr) {
6728 _bmStartWord = mr.start();
6729 _bmWordSize = mr.word_size();
6730 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6731 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6732 if (!brs.is_reserved()) {
6733 warning("CMS bit map allocation failure");
6734 return false;
6735 }
6736 // For now we'll just commit all of the bit map up fromt.
6737 // Later on we'll try to be more parsimonious with swap.
6738 if (!_virtual_space.initialize(brs, brs.size())) {
6739 warning("CMS bit map backing store failure");
6740 return false;
6741 }
6742 assert(_virtual_space.committed_size() == brs.size(),
6743 "didn't reserve backing store for all of CMS bit map?");
6744 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6745 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6746 _bmWordSize, "inconsistency in bit map sizing");
6747 _bm.set_size(_bmWordSize >> _shifter);
6749 // bm.clear(); // can we rely on getting zero'd memory? verify below
6750 assert(isAllClear(),
6751 "Expected zero'd memory from ReservedSpace constructor");
6752 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6753 "consistency check");
6754 return true;
6755 }
6757 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6758 HeapWord *next_addr, *end_addr, *last_addr;
6759 assert_locked();
6760 assert(covers(mr), "out-of-range error");
6761 // XXX assert that start and end are appropriately aligned
6762 for (next_addr = mr.start(), end_addr = mr.end();
6763 next_addr < end_addr; next_addr = last_addr) {
6764 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6765 last_addr = dirty_region.end();
6766 if (!dirty_region.is_empty()) {
6767 cl->do_MemRegion(dirty_region);
6768 } else {
6769 assert(last_addr == end_addr, "program logic");
6770 return;
6771 }
6772 }
6773 }
6775 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6776 _bm.print_on_error(st, prefix);
6777 }
6779 #ifndef PRODUCT
6780 void CMSBitMap::assert_locked() const {
6781 CMSLockVerifier::assert_locked(lock());
6782 }
6784 bool CMSBitMap::covers(MemRegion mr) const {
6785 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6786 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6787 "size inconsistency");
6788 return (mr.start() >= _bmStartWord) &&
6789 (mr.end() <= endWord());
6790 }
6792 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6793 return (start >= _bmStartWord && (start + size) <= endWord());
6794 }
6796 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6797 // verify that there are no 1 bits in the interval [left, right)
6798 FalseBitMapClosure falseBitMapClosure;
6799 iterate(&falseBitMapClosure, left, right);
6800 }
6802 void CMSBitMap::region_invariant(MemRegion mr)
6803 {
6804 assert_locked();
6805 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6806 assert(!mr.is_empty(), "unexpected empty region");
6807 assert(covers(mr), "mr should be covered by bit map");
6808 // convert address range into offset range
6809 size_t start_ofs = heapWordToOffset(mr.start());
6810 // Make sure that end() is appropriately aligned
6811 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6812 (1 << (_shifter+LogHeapWordSize))),
6813 "Misaligned mr.end()");
6814 size_t end_ofs = heapWordToOffset(mr.end());
6815 assert(end_ofs > start_ofs, "Should mark at least one bit");
6816 }
6818 #endif
6820 bool CMSMarkStack::allocate(size_t size) {
6821 // allocate a stack of the requisite depth
6822 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6823 size * sizeof(oop)));
6824 if (!rs.is_reserved()) {
6825 warning("CMSMarkStack allocation failure");
6826 return false;
6827 }
6828 if (!_virtual_space.initialize(rs, rs.size())) {
6829 warning("CMSMarkStack backing store failure");
6830 return false;
6831 }
6832 assert(_virtual_space.committed_size() == rs.size(),
6833 "didn't reserve backing store for all of CMS stack?");
6834 _base = (oop*)(_virtual_space.low());
6835 _index = 0;
6836 _capacity = size;
6837 NOT_PRODUCT(_max_depth = 0);
6838 return true;
6839 }
6841 // XXX FIX ME !!! In the MT case we come in here holding a
6842 // leaf lock. For printing we need to take a further lock
6843 // which has lower rank. We need to recallibrate the two
6844 // lock-ranks involved in order to be able to rpint the
6845 // messages below. (Or defer the printing to the caller.
6846 // For now we take the expedient path of just disabling the
6847 // messages for the problematic case.)
6848 void CMSMarkStack::expand() {
6849 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6850 if (_capacity == MarkStackSizeMax) {
6851 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6852 // We print a warning message only once per CMS cycle.
6853 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6854 }
6855 return;
6856 }
6857 // Double capacity if possible
6858 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6859 // Do not give up existing stack until we have managed to
6860 // get the double capacity that we desired.
6861 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6862 new_capacity * sizeof(oop)));
6863 if (rs.is_reserved()) {
6864 // Release the backing store associated with old stack
6865 _virtual_space.release();
6866 // Reinitialize virtual space for new stack
6867 if (!_virtual_space.initialize(rs, rs.size())) {
6868 fatal("Not enough swap for expanded marking stack");
6869 }
6870 _base = (oop*)(_virtual_space.low());
6871 _index = 0;
6872 _capacity = new_capacity;
6873 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6874 // Failed to double capacity, continue;
6875 // we print a detail message only once per CMS cycle.
6876 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6877 SIZE_FORMAT"K",
6878 _capacity / K, new_capacity / K);
6879 }
6880 }
6883 // Closures
6884 // XXX: there seems to be a lot of code duplication here;
6885 // should refactor and consolidate common code.
6887 // This closure is used to mark refs into the CMS generation in
6888 // the CMS bit map. Called at the first checkpoint. This closure
6889 // assumes that we do not need to re-mark dirty cards; if the CMS
6890 // generation on which this is used is not an oldest
6891 // generation then this will lose younger_gen cards!
6893 MarkRefsIntoClosure::MarkRefsIntoClosure(
6894 MemRegion span, CMSBitMap* bitMap):
6895 _span(span),
6896 _bitMap(bitMap)
6897 {
6898 assert(_ref_processor == NULL, "deliberately left NULL");
6899 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6900 }
6902 void MarkRefsIntoClosure::do_oop(oop obj) {
6903 // if p points into _span, then mark corresponding bit in _markBitMap
6904 assert(obj->is_oop(), "expected an oop");
6905 HeapWord* addr = (HeapWord*)obj;
6906 if (_span.contains(addr)) {
6907 // this should be made more efficient
6908 _bitMap->mark(addr);
6909 }
6910 }
6912 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6913 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6915 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6916 MemRegion span, CMSBitMap* bitMap):
6917 _span(span),
6918 _bitMap(bitMap)
6919 {
6920 assert(_ref_processor == NULL, "deliberately left NULL");
6921 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6922 }
6924 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6925 // if p points into _span, then mark corresponding bit in _markBitMap
6926 assert(obj->is_oop(), "expected an oop");
6927 HeapWord* addr = (HeapWord*)obj;
6928 if (_span.contains(addr)) {
6929 // this should be made more efficient
6930 _bitMap->par_mark(addr);
6931 }
6932 }
6934 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6935 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6937 // A variant of the above, used for CMS marking verification.
6938 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6939 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6940 _span(span),
6941 _verification_bm(verification_bm),
6942 _cms_bm(cms_bm)
6943 {
6944 assert(_ref_processor == NULL, "deliberately left NULL");
6945 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6946 }
6948 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6949 // if p points into _span, then mark corresponding bit in _markBitMap
6950 assert(obj->is_oop(), "expected an oop");
6951 HeapWord* addr = (HeapWord*)obj;
6952 if (_span.contains(addr)) {
6953 _verification_bm->mark(addr);
6954 if (!_cms_bm->isMarked(addr)) {
6955 oop(addr)->print();
6956 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6957 fatal("... aborting");
6958 }
6959 }
6960 }
6962 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6963 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6965 //////////////////////////////////////////////////
6966 // MarkRefsIntoAndScanClosure
6967 //////////////////////////////////////////////////
6969 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6970 ReferenceProcessor* rp,
6971 CMSBitMap* bit_map,
6972 CMSBitMap* mod_union_table,
6973 CMSMarkStack* mark_stack,
6974 CMSCollector* collector,
6975 bool should_yield,
6976 bool concurrent_precleaning):
6977 _collector(collector),
6978 _span(span),
6979 _bit_map(bit_map),
6980 _mark_stack(mark_stack),
6981 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6982 mark_stack, concurrent_precleaning),
6983 _yield(should_yield),
6984 _concurrent_precleaning(concurrent_precleaning),
6985 _freelistLock(NULL)
6986 {
6987 _ref_processor = rp;
6988 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6989 }
6991 // This closure is used to mark refs into the CMS generation at the
6992 // second (final) checkpoint, and to scan and transitively follow
6993 // the unmarked oops. It is also used during the concurrent precleaning
6994 // phase while scanning objects on dirty cards in the CMS generation.
6995 // The marks are made in the marking bit map and the marking stack is
6996 // used for keeping the (newly) grey objects during the scan.
6997 // The parallel version (Par_...) appears further below.
6998 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6999 if (obj != NULL) {
7000 assert(obj->is_oop(), "expected an oop");
7001 HeapWord* addr = (HeapWord*)obj;
7002 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7003 assert(_collector->overflow_list_is_empty(),
7004 "overflow list should be empty");
7005 if (_span.contains(addr) &&
7006 !_bit_map->isMarked(addr)) {
7007 // mark bit map (object is now grey)
7008 _bit_map->mark(addr);
7009 // push on marking stack (stack should be empty), and drain the
7010 // stack by applying this closure to the oops in the oops popped
7011 // from the stack (i.e. blacken the grey objects)
7012 bool res = _mark_stack->push(obj);
7013 assert(res, "Should have space to push on empty stack");
7014 do {
7015 oop new_oop = _mark_stack->pop();
7016 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7017 assert(_bit_map->isMarked((HeapWord*)new_oop),
7018 "only grey objects on this stack");
7019 // iterate over the oops in this oop, marking and pushing
7020 // the ones in CMS heap (i.e. in _span).
7021 new_oop->oop_iterate(&_pushAndMarkClosure);
7022 // check if it's time to yield
7023 do_yield_check();
7024 } while (!_mark_stack->isEmpty() ||
7025 (!_concurrent_precleaning && take_from_overflow_list()));
7026 // if marking stack is empty, and we are not doing this
7027 // during precleaning, then check the overflow list
7028 }
7029 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7030 assert(_collector->overflow_list_is_empty(),
7031 "overflow list was drained above");
7032 // We could restore evacuated mark words, if any, used for
7033 // overflow list links here because the overflow list is
7034 // provably empty here. That would reduce the maximum
7035 // size requirements for preserved_{oop,mark}_stack.
7036 // But we'll just postpone it until we are all done
7037 // so we can just stream through.
7038 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
7039 _collector->restore_preserved_marks_if_any();
7040 assert(_collector->no_preserved_marks(), "No preserved marks");
7041 }
7042 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
7043 "All preserved marks should have been restored above");
7044 }
7045 }
7047 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
7048 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
7050 void MarkRefsIntoAndScanClosure::do_yield_work() {
7051 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7052 "CMS thread should hold CMS token");
7053 assert_lock_strong(_freelistLock);
7054 assert_lock_strong(_bit_map->lock());
7055 // relinquish the free_list_lock and bitMaplock()
7056 _bit_map->lock()->unlock();
7057 _freelistLock->unlock();
7058 ConcurrentMarkSweepThread::desynchronize(true);
7059 ConcurrentMarkSweepThread::acknowledge_yield_request();
7060 _collector->stopTimer();
7061 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7062 if (PrintCMSStatistics != 0) {
7063 _collector->incrementYields();
7064 }
7065 _collector->icms_wait();
7067 // See the comment in coordinator_yield()
7068 for (unsigned i = 0;
7069 i < CMSYieldSleepCount &&
7070 ConcurrentMarkSweepThread::should_yield() &&
7071 !CMSCollector::foregroundGCIsActive();
7072 ++i) {
7073 os::sleep(Thread::current(), 1, false);
7074 ConcurrentMarkSweepThread::acknowledge_yield_request();
7075 }
7077 ConcurrentMarkSweepThread::synchronize(true);
7078 _freelistLock->lock_without_safepoint_check();
7079 _bit_map->lock()->lock_without_safepoint_check();
7080 _collector->startTimer();
7081 }
7083 ///////////////////////////////////////////////////////////
7084 // Par_MarkRefsIntoAndScanClosure: a parallel version of
7085 // MarkRefsIntoAndScanClosure
7086 ///////////////////////////////////////////////////////////
7087 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
7088 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
7089 CMSBitMap* bit_map, OopTaskQueue* work_queue):
7090 _span(span),
7091 _bit_map(bit_map),
7092 _work_queue(work_queue),
7093 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
7094 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
7095 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
7096 {
7097 _ref_processor = rp;
7098 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7099 }
7101 // This closure is used to mark refs into the CMS generation at the
7102 // second (final) checkpoint, and to scan and transitively follow
7103 // the unmarked oops. The marks are made in the marking bit map and
7104 // the work_queue is used for keeping the (newly) grey objects during
7105 // the scan phase whence they are also available for stealing by parallel
7106 // threads. Since the marking bit map is shared, updates are
7107 // synchronized (via CAS).
7108 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
7109 if (obj != NULL) {
7110 // Ignore mark word because this could be an already marked oop
7111 // that may be chained at the end of the overflow list.
7112 assert(obj->is_oop(true), "expected an oop");
7113 HeapWord* addr = (HeapWord*)obj;
7114 if (_span.contains(addr) &&
7115 !_bit_map->isMarked(addr)) {
7116 // mark bit map (object will become grey):
7117 // It is possible for several threads to be
7118 // trying to "claim" this object concurrently;
7119 // the unique thread that succeeds in marking the
7120 // object first will do the subsequent push on
7121 // to the work queue (or overflow list).
7122 if (_bit_map->par_mark(addr)) {
7123 // push on work_queue (which may not be empty), and trim the
7124 // queue to an appropriate length by applying this closure to
7125 // the oops in the oops popped from the stack (i.e. blacken the
7126 // grey objects)
7127 bool res = _work_queue->push(obj);
7128 assert(res, "Low water mark should be less than capacity?");
7129 trim_queue(_low_water_mark);
7130 } // Else, another thread claimed the object
7131 }
7132 }
7133 }
7135 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7136 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7138 // This closure is used to rescan the marked objects on the dirty cards
7139 // in the mod union table and the card table proper.
7140 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
7141 oop p, MemRegion mr) {
7143 size_t size = 0;
7144 HeapWord* addr = (HeapWord*)p;
7145 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7146 assert(_span.contains(addr), "we are scanning the CMS generation");
7147 // check if it's time to yield
7148 if (do_yield_check()) {
7149 // We yielded for some foreground stop-world work,
7150 // and we have been asked to abort this ongoing preclean cycle.
7151 return 0;
7152 }
7153 if (_bitMap->isMarked(addr)) {
7154 // it's marked; is it potentially uninitialized?
7155 if (p->klass_or_null() != NULL) {
7156 // an initialized object; ignore mark word in verification below
7157 // since we are running concurrent with mutators
7158 assert(p->is_oop(true), "should be an oop");
7159 if (p->is_objArray()) {
7160 // objArrays are precisely marked; restrict scanning
7161 // to dirty cards only.
7162 size = CompactibleFreeListSpace::adjustObjectSize(
7163 p->oop_iterate(_scanningClosure, mr));
7164 } else {
7165 // A non-array may have been imprecisely marked; we need
7166 // to scan object in its entirety.
7167 size = CompactibleFreeListSpace::adjustObjectSize(
7168 p->oop_iterate(_scanningClosure));
7169 }
7170 #ifdef ASSERT
7171 size_t direct_size =
7172 CompactibleFreeListSpace::adjustObjectSize(p->size());
7173 assert(size == direct_size, "Inconsistency in size");
7174 assert(size >= 3, "Necessary for Printezis marks to work");
7175 if (!_bitMap->isMarked(addr+1)) {
7176 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
7177 } else {
7178 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
7179 assert(_bitMap->isMarked(addr+size-1),
7180 "inconsistent Printezis mark");
7181 }
7182 #endif // ASSERT
7183 } else {
7184 // an unitialized object
7185 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
7186 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7187 size = pointer_delta(nextOneAddr + 1, addr);
7188 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7189 "alignment problem");
7190 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
7191 // will dirty the card when the klass pointer is installed in the
7192 // object (signalling the completion of initialization).
7193 }
7194 } else {
7195 // Either a not yet marked object or an uninitialized object
7196 if (p->klass_or_null() == NULL) {
7197 // An uninitialized object, skip to the next card, since
7198 // we may not be able to read its P-bits yet.
7199 assert(size == 0, "Initial value");
7200 } else {
7201 // An object not (yet) reached by marking: we merely need to
7202 // compute its size so as to go look at the next block.
7203 assert(p->is_oop(true), "should be an oop");
7204 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
7205 }
7206 }
7207 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7208 return size;
7209 }
7211 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
7212 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7213 "CMS thread should hold CMS token");
7214 assert_lock_strong(_freelistLock);
7215 assert_lock_strong(_bitMap->lock());
7216 // relinquish the free_list_lock and bitMaplock()
7217 _bitMap->lock()->unlock();
7218 _freelistLock->unlock();
7219 ConcurrentMarkSweepThread::desynchronize(true);
7220 ConcurrentMarkSweepThread::acknowledge_yield_request();
7221 _collector->stopTimer();
7222 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7223 if (PrintCMSStatistics != 0) {
7224 _collector->incrementYields();
7225 }
7226 _collector->icms_wait();
7228 // See the comment in coordinator_yield()
7229 for (unsigned i = 0; i < CMSYieldSleepCount &&
7230 ConcurrentMarkSweepThread::should_yield() &&
7231 !CMSCollector::foregroundGCIsActive(); ++i) {
7232 os::sleep(Thread::current(), 1, false);
7233 ConcurrentMarkSweepThread::acknowledge_yield_request();
7234 }
7236 ConcurrentMarkSweepThread::synchronize(true);
7237 _freelistLock->lock_without_safepoint_check();
7238 _bitMap->lock()->lock_without_safepoint_check();
7239 _collector->startTimer();
7240 }
7243 //////////////////////////////////////////////////////////////////
7244 // SurvivorSpacePrecleanClosure
7245 //////////////////////////////////////////////////////////////////
7246 // This (single-threaded) closure is used to preclean the oops in
7247 // the survivor spaces.
7248 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
7250 HeapWord* addr = (HeapWord*)p;
7251 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7252 assert(!_span.contains(addr), "we are scanning the survivor spaces");
7253 assert(p->klass_or_null() != NULL, "object should be initializd");
7254 // an initialized object; ignore mark word in verification below
7255 // since we are running concurrent with mutators
7256 assert(p->is_oop(true), "should be an oop");
7257 // Note that we do not yield while we iterate over
7258 // the interior oops of p, pushing the relevant ones
7259 // on our marking stack.
7260 size_t size = p->oop_iterate(_scanning_closure);
7261 do_yield_check();
7262 // Observe that below, we do not abandon the preclean
7263 // phase as soon as we should; rather we empty the
7264 // marking stack before returning. This is to satisfy
7265 // some existing assertions. In general, it may be a
7266 // good idea to abort immediately and complete the marking
7267 // from the grey objects at a later time.
7268 while (!_mark_stack->isEmpty()) {
7269 oop new_oop = _mark_stack->pop();
7270 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7271 assert(_bit_map->isMarked((HeapWord*)new_oop),
7272 "only grey objects on this stack");
7273 // iterate over the oops in this oop, marking and pushing
7274 // the ones in CMS heap (i.e. in _span).
7275 new_oop->oop_iterate(_scanning_closure);
7276 // check if it's time to yield
7277 do_yield_check();
7278 }
7279 unsigned int after_count =
7280 GenCollectedHeap::heap()->total_collections();
7281 bool abort = (_before_count != after_count) ||
7282 _collector->should_abort_preclean();
7283 return abort ? 0 : size;
7284 }
7286 void SurvivorSpacePrecleanClosure::do_yield_work() {
7287 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7288 "CMS thread should hold CMS token");
7289 assert_lock_strong(_bit_map->lock());
7290 // Relinquish the bit map lock
7291 _bit_map->lock()->unlock();
7292 ConcurrentMarkSweepThread::desynchronize(true);
7293 ConcurrentMarkSweepThread::acknowledge_yield_request();
7294 _collector->stopTimer();
7295 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7296 if (PrintCMSStatistics != 0) {
7297 _collector->incrementYields();
7298 }
7299 _collector->icms_wait();
7301 // See the comment in coordinator_yield()
7302 for (unsigned i = 0; i < CMSYieldSleepCount &&
7303 ConcurrentMarkSweepThread::should_yield() &&
7304 !CMSCollector::foregroundGCIsActive(); ++i) {
7305 os::sleep(Thread::current(), 1, false);
7306 ConcurrentMarkSweepThread::acknowledge_yield_request();
7307 }
7309 ConcurrentMarkSweepThread::synchronize(true);
7310 _bit_map->lock()->lock_without_safepoint_check();
7311 _collector->startTimer();
7312 }
7314 // This closure is used to rescan the marked objects on the dirty cards
7315 // in the mod union table and the card table proper. In the parallel
7316 // case, although the bitMap is shared, we do a single read so the
7317 // isMarked() query is "safe".
7318 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7319 // Ignore mark word because we are running concurrent with mutators
7320 assert(p->is_oop_or_null(true), "expected an oop or null");
7321 HeapWord* addr = (HeapWord*)p;
7322 assert(_span.contains(addr), "we are scanning the CMS generation");
7323 bool is_obj_array = false;
7324 #ifdef ASSERT
7325 if (!_parallel) {
7326 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7327 assert(_collector->overflow_list_is_empty(),
7328 "overflow list should be empty");
7330 }
7331 #endif // ASSERT
7332 if (_bit_map->isMarked(addr)) {
7333 // Obj arrays are precisely marked, non-arrays are not;
7334 // so we scan objArrays precisely and non-arrays in their
7335 // entirety.
7336 if (p->is_objArray()) {
7337 is_obj_array = true;
7338 if (_parallel) {
7339 p->oop_iterate(_par_scan_closure, mr);
7340 } else {
7341 p->oop_iterate(_scan_closure, mr);
7342 }
7343 } else {
7344 if (_parallel) {
7345 p->oop_iterate(_par_scan_closure);
7346 } else {
7347 p->oop_iterate(_scan_closure);
7348 }
7349 }
7350 }
7351 #ifdef ASSERT
7352 if (!_parallel) {
7353 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7354 assert(_collector->overflow_list_is_empty(),
7355 "overflow list should be empty");
7357 }
7358 #endif // ASSERT
7359 return is_obj_array;
7360 }
7362 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7363 MemRegion span,
7364 CMSBitMap* bitMap, CMSMarkStack* markStack,
7365 bool should_yield, bool verifying):
7366 _collector(collector),
7367 _span(span),
7368 _bitMap(bitMap),
7369 _mut(&collector->_modUnionTable),
7370 _markStack(markStack),
7371 _yield(should_yield),
7372 _skipBits(0)
7373 {
7374 assert(_markStack->isEmpty(), "stack should be empty");
7375 _finger = _bitMap->startWord();
7376 _threshold = _finger;
7377 assert(_collector->_restart_addr == NULL, "Sanity check");
7378 assert(_span.contains(_finger), "Out of bounds _finger?");
7379 DEBUG_ONLY(_verifying = verifying;)
7380 }
7382 void MarkFromRootsClosure::reset(HeapWord* addr) {
7383 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7384 assert(_span.contains(addr), "Out of bounds _finger?");
7385 _finger = addr;
7386 _threshold = (HeapWord*)round_to(
7387 (intptr_t)_finger, CardTableModRefBS::card_size);
7388 }
7390 // Should revisit to see if this should be restructured for
7391 // greater efficiency.
7392 bool MarkFromRootsClosure::do_bit(size_t offset) {
7393 if (_skipBits > 0) {
7394 _skipBits--;
7395 return true;
7396 }
7397 // convert offset into a HeapWord*
7398 HeapWord* addr = _bitMap->startWord() + offset;
7399 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7400 "address out of range");
7401 assert(_bitMap->isMarked(addr), "tautology");
7402 if (_bitMap->isMarked(addr+1)) {
7403 // this is an allocated but not yet initialized object
7404 assert(_skipBits == 0, "tautology");
7405 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7406 oop p = oop(addr);
7407 if (p->klass_or_null() == NULL) {
7408 DEBUG_ONLY(if (!_verifying) {)
7409 // We re-dirty the cards on which this object lies and increase
7410 // the _threshold so that we'll come back to scan this object
7411 // during the preclean or remark phase. (CMSCleanOnEnter)
7412 if (CMSCleanOnEnter) {
7413 size_t sz = _collector->block_size_using_printezis_bits(addr);
7414 HeapWord* end_card_addr = (HeapWord*)round_to(
7415 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7416 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7417 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7418 // Bump _threshold to end_card_addr; note that
7419 // _threshold cannot possibly exceed end_card_addr, anyhow.
7420 // This prevents future clearing of the card as the scan proceeds
7421 // to the right.
7422 assert(_threshold <= end_card_addr,
7423 "Because we are just scanning into this object");
7424 if (_threshold < end_card_addr) {
7425 _threshold = end_card_addr;
7426 }
7427 if (p->klass_or_null() != NULL) {
7428 // Redirty the range of cards...
7429 _mut->mark_range(redirty_range);
7430 } // ...else the setting of klass will dirty the card anyway.
7431 }
7432 DEBUG_ONLY(})
7433 return true;
7434 }
7435 }
7436 scanOopsInOop(addr);
7437 return true;
7438 }
7440 // We take a break if we've been at this for a while,
7441 // so as to avoid monopolizing the locks involved.
7442 void MarkFromRootsClosure::do_yield_work() {
7443 // First give up the locks, then yield, then re-lock
7444 // We should probably use a constructor/destructor idiom to
7445 // do this unlock/lock or modify the MutexUnlocker class to
7446 // serve our purpose. XXX
7447 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7448 "CMS thread should hold CMS token");
7449 assert_lock_strong(_bitMap->lock());
7450 _bitMap->lock()->unlock();
7451 ConcurrentMarkSweepThread::desynchronize(true);
7452 ConcurrentMarkSweepThread::acknowledge_yield_request();
7453 _collector->stopTimer();
7454 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7455 if (PrintCMSStatistics != 0) {
7456 _collector->incrementYields();
7457 }
7458 _collector->icms_wait();
7460 // See the comment in coordinator_yield()
7461 for (unsigned i = 0; i < CMSYieldSleepCount &&
7462 ConcurrentMarkSweepThread::should_yield() &&
7463 !CMSCollector::foregroundGCIsActive(); ++i) {
7464 os::sleep(Thread::current(), 1, false);
7465 ConcurrentMarkSweepThread::acknowledge_yield_request();
7466 }
7468 ConcurrentMarkSweepThread::synchronize(true);
7469 _bitMap->lock()->lock_without_safepoint_check();
7470 _collector->startTimer();
7471 }
7473 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7474 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7475 assert(_markStack->isEmpty(),
7476 "should drain stack to limit stack usage");
7477 // convert ptr to an oop preparatory to scanning
7478 oop obj = oop(ptr);
7479 // Ignore mark word in verification below, since we
7480 // may be running concurrent with mutators.
7481 assert(obj->is_oop(true), "should be an oop");
7482 assert(_finger <= ptr, "_finger runneth ahead");
7483 // advance the finger to right end of this object
7484 _finger = ptr + obj->size();
7485 assert(_finger > ptr, "we just incremented it above");
7486 // On large heaps, it may take us some time to get through
7487 // the marking phase (especially if running iCMS). During
7488 // this time it's possible that a lot of mutations have
7489 // accumulated in the card table and the mod union table --
7490 // these mutation records are redundant until we have
7491 // actually traced into the corresponding card.
7492 // Here, we check whether advancing the finger would make
7493 // us cross into a new card, and if so clear corresponding
7494 // cards in the MUT (preclean them in the card-table in the
7495 // future).
7497 DEBUG_ONLY(if (!_verifying) {)
7498 // The clean-on-enter optimization is disabled by default,
7499 // until we fix 6178663.
7500 if (CMSCleanOnEnter && (_finger > _threshold)) {
7501 // [_threshold, _finger) represents the interval
7502 // of cards to be cleared in MUT (or precleaned in card table).
7503 // The set of cards to be cleared is all those that overlap
7504 // with the interval [_threshold, _finger); note that
7505 // _threshold is always kept card-aligned but _finger isn't
7506 // always card-aligned.
7507 HeapWord* old_threshold = _threshold;
7508 assert(old_threshold == (HeapWord*)round_to(
7509 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7510 "_threshold should always be card-aligned");
7511 _threshold = (HeapWord*)round_to(
7512 (intptr_t)_finger, CardTableModRefBS::card_size);
7513 MemRegion mr(old_threshold, _threshold);
7514 assert(!mr.is_empty(), "Control point invariant");
7515 assert(_span.contains(mr), "Should clear within span");
7516 _mut->clear_range(mr);
7517 }
7518 DEBUG_ONLY(})
7519 // Note: the finger doesn't advance while we drain
7520 // the stack below.
7521 PushOrMarkClosure pushOrMarkClosure(_collector,
7522 _span, _bitMap, _markStack,
7523 _finger, this);
7524 bool res = _markStack->push(obj);
7525 assert(res, "Empty non-zero size stack should have space for single push");
7526 while (!_markStack->isEmpty()) {
7527 oop new_oop = _markStack->pop();
7528 // Skip verifying header mark word below because we are
7529 // running concurrent with mutators.
7530 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7531 // now scan this oop's oops
7532 new_oop->oop_iterate(&pushOrMarkClosure);
7533 do_yield_check();
7534 }
7535 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7536 }
7538 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7539 CMSCollector* collector, MemRegion span,
7540 CMSBitMap* bit_map,
7541 OopTaskQueue* work_queue,
7542 CMSMarkStack* overflow_stack,
7543 bool should_yield):
7544 _collector(collector),
7545 _whole_span(collector->_span),
7546 _span(span),
7547 _bit_map(bit_map),
7548 _mut(&collector->_modUnionTable),
7549 _work_queue(work_queue),
7550 _overflow_stack(overflow_stack),
7551 _yield(should_yield),
7552 _skip_bits(0),
7553 _task(task)
7554 {
7555 assert(_work_queue->size() == 0, "work_queue should be empty");
7556 _finger = span.start();
7557 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7558 assert(_span.contains(_finger), "Out of bounds _finger?");
7559 }
7561 // Should revisit to see if this should be restructured for
7562 // greater efficiency.
7563 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7564 if (_skip_bits > 0) {
7565 _skip_bits--;
7566 return true;
7567 }
7568 // convert offset into a HeapWord*
7569 HeapWord* addr = _bit_map->startWord() + offset;
7570 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7571 "address out of range");
7572 assert(_bit_map->isMarked(addr), "tautology");
7573 if (_bit_map->isMarked(addr+1)) {
7574 // this is an allocated object that might not yet be initialized
7575 assert(_skip_bits == 0, "tautology");
7576 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7577 oop p = oop(addr);
7578 if (p->klass_or_null() == NULL) {
7579 // in the case of Clean-on-Enter optimization, redirty card
7580 // and avoid clearing card by increasing the threshold.
7581 return true;
7582 }
7583 }
7584 scan_oops_in_oop(addr);
7585 return true;
7586 }
7588 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7589 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7590 // Should we assert that our work queue is empty or
7591 // below some drain limit?
7592 assert(_work_queue->size() == 0,
7593 "should drain stack to limit stack usage");
7594 // convert ptr to an oop preparatory to scanning
7595 oop obj = oop(ptr);
7596 // Ignore mark word in verification below, since we
7597 // may be running concurrent with mutators.
7598 assert(obj->is_oop(true), "should be an oop");
7599 assert(_finger <= ptr, "_finger runneth ahead");
7600 // advance the finger to right end of this object
7601 _finger = ptr + obj->size();
7602 assert(_finger > ptr, "we just incremented it above");
7603 // On large heaps, it may take us some time to get through
7604 // the marking phase (especially if running iCMS). During
7605 // this time it's possible that a lot of mutations have
7606 // accumulated in the card table and the mod union table --
7607 // these mutation records are redundant until we have
7608 // actually traced into the corresponding card.
7609 // Here, we check whether advancing the finger would make
7610 // us cross into a new card, and if so clear corresponding
7611 // cards in the MUT (preclean them in the card-table in the
7612 // future).
7614 // The clean-on-enter optimization is disabled by default,
7615 // until we fix 6178663.
7616 if (CMSCleanOnEnter && (_finger > _threshold)) {
7617 // [_threshold, _finger) represents the interval
7618 // of cards to be cleared in MUT (or precleaned in card table).
7619 // The set of cards to be cleared is all those that overlap
7620 // with the interval [_threshold, _finger); note that
7621 // _threshold is always kept card-aligned but _finger isn't
7622 // always card-aligned.
7623 HeapWord* old_threshold = _threshold;
7624 assert(old_threshold == (HeapWord*)round_to(
7625 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7626 "_threshold should always be card-aligned");
7627 _threshold = (HeapWord*)round_to(
7628 (intptr_t)_finger, CardTableModRefBS::card_size);
7629 MemRegion mr(old_threshold, _threshold);
7630 assert(!mr.is_empty(), "Control point invariant");
7631 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7632 _mut->clear_range(mr);
7633 }
7635 // Note: the local finger doesn't advance while we drain
7636 // the stack below, but the global finger sure can and will.
7637 HeapWord** gfa = _task->global_finger_addr();
7638 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7639 _span, _bit_map,
7640 _work_queue,
7641 _overflow_stack,
7642 _finger,
7643 gfa, this);
7644 bool res = _work_queue->push(obj); // overflow could occur here
7645 assert(res, "Will hold once we use workqueues");
7646 while (true) {
7647 oop new_oop;
7648 if (!_work_queue->pop_local(new_oop)) {
7649 // We emptied our work_queue; check if there's stuff that can
7650 // be gotten from the overflow stack.
7651 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7652 _overflow_stack, _work_queue)) {
7653 do_yield_check();
7654 continue;
7655 } else { // done
7656 break;
7657 }
7658 }
7659 // Skip verifying header mark word below because we are
7660 // running concurrent with mutators.
7661 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7662 // now scan this oop's oops
7663 new_oop->oop_iterate(&pushOrMarkClosure);
7664 do_yield_check();
7665 }
7666 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7667 }
7669 // Yield in response to a request from VM Thread or
7670 // from mutators.
7671 void Par_MarkFromRootsClosure::do_yield_work() {
7672 assert(_task != NULL, "sanity");
7673 _task->yield();
7674 }
7676 // A variant of the above used for verifying CMS marking work.
7677 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7678 MemRegion span,
7679 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7680 CMSMarkStack* mark_stack):
7681 _collector(collector),
7682 _span(span),
7683 _verification_bm(verification_bm),
7684 _cms_bm(cms_bm),
7685 _mark_stack(mark_stack),
7686 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7687 mark_stack)
7688 {
7689 assert(_mark_stack->isEmpty(), "stack should be empty");
7690 _finger = _verification_bm->startWord();
7691 assert(_collector->_restart_addr == NULL, "Sanity check");
7692 assert(_span.contains(_finger), "Out of bounds _finger?");
7693 }
7695 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7696 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7697 assert(_span.contains(addr), "Out of bounds _finger?");
7698 _finger = addr;
7699 }
7701 // Should revisit to see if this should be restructured for
7702 // greater efficiency.
7703 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7704 // convert offset into a HeapWord*
7705 HeapWord* addr = _verification_bm->startWord() + offset;
7706 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7707 "address out of range");
7708 assert(_verification_bm->isMarked(addr), "tautology");
7709 assert(_cms_bm->isMarked(addr), "tautology");
7711 assert(_mark_stack->isEmpty(),
7712 "should drain stack to limit stack usage");
7713 // convert addr to an oop preparatory to scanning
7714 oop obj = oop(addr);
7715 assert(obj->is_oop(), "should be an oop");
7716 assert(_finger <= addr, "_finger runneth ahead");
7717 // advance the finger to right end of this object
7718 _finger = addr + obj->size();
7719 assert(_finger > addr, "we just incremented it above");
7720 // Note: the finger doesn't advance while we drain
7721 // the stack below.
7722 bool res = _mark_stack->push(obj);
7723 assert(res, "Empty non-zero size stack should have space for single push");
7724 while (!_mark_stack->isEmpty()) {
7725 oop new_oop = _mark_stack->pop();
7726 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7727 // now scan this oop's oops
7728 new_oop->oop_iterate(&_pam_verify_closure);
7729 }
7730 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7731 return true;
7732 }
7734 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7735 CMSCollector* collector, MemRegion span,
7736 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7737 CMSMarkStack* mark_stack):
7738 CMSOopClosure(collector->ref_processor()),
7739 _collector(collector),
7740 _span(span),
7741 _verification_bm(verification_bm),
7742 _cms_bm(cms_bm),
7743 _mark_stack(mark_stack)
7744 { }
7746 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7747 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7749 // Upon stack overflow, we discard (part of) the stack,
7750 // remembering the least address amongst those discarded
7751 // in CMSCollector's _restart_address.
7752 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7753 // Remember the least grey address discarded
7754 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7755 _collector->lower_restart_addr(ra);
7756 _mark_stack->reset(); // discard stack contents
7757 _mark_stack->expand(); // expand the stack if possible
7758 }
7760 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7761 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7762 HeapWord* addr = (HeapWord*)obj;
7763 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7764 // Oop lies in _span and isn't yet grey or black
7765 _verification_bm->mark(addr); // now grey
7766 if (!_cms_bm->isMarked(addr)) {
7767 oop(addr)->print();
7768 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7769 addr);
7770 fatal("... aborting");
7771 }
7773 if (!_mark_stack->push(obj)) { // stack overflow
7774 if (PrintCMSStatistics != 0) {
7775 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7776 SIZE_FORMAT, _mark_stack->capacity());
7777 }
7778 assert(_mark_stack->isFull(), "Else push should have succeeded");
7779 handle_stack_overflow(addr);
7780 }
7781 // anything including and to the right of _finger
7782 // will be scanned as we iterate over the remainder of the
7783 // bit map
7784 }
7785 }
7787 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7788 MemRegion span,
7789 CMSBitMap* bitMap, CMSMarkStack* markStack,
7790 HeapWord* finger, MarkFromRootsClosure* parent) :
7791 CMSOopClosure(collector->ref_processor()),
7792 _collector(collector),
7793 _span(span),
7794 _bitMap(bitMap),
7795 _markStack(markStack),
7796 _finger(finger),
7797 _parent(parent)
7798 { }
7800 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7801 MemRegion span,
7802 CMSBitMap* bit_map,
7803 OopTaskQueue* work_queue,
7804 CMSMarkStack* overflow_stack,
7805 HeapWord* finger,
7806 HeapWord** global_finger_addr,
7807 Par_MarkFromRootsClosure* parent) :
7808 CMSOopClosure(collector->ref_processor()),
7809 _collector(collector),
7810 _whole_span(collector->_span),
7811 _span(span),
7812 _bit_map(bit_map),
7813 _work_queue(work_queue),
7814 _overflow_stack(overflow_stack),
7815 _finger(finger),
7816 _global_finger_addr(global_finger_addr),
7817 _parent(parent)
7818 { }
7820 // Assumes thread-safe access by callers, who are
7821 // responsible for mutual exclusion.
7822 void CMSCollector::lower_restart_addr(HeapWord* low) {
7823 assert(_span.contains(low), "Out of bounds addr");
7824 if (_restart_addr == NULL) {
7825 _restart_addr = low;
7826 } else {
7827 _restart_addr = MIN2(_restart_addr, low);
7828 }
7829 }
7831 // Upon stack overflow, we discard (part of) the stack,
7832 // remembering the least address amongst those discarded
7833 // in CMSCollector's _restart_address.
7834 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7835 // Remember the least grey address discarded
7836 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7837 _collector->lower_restart_addr(ra);
7838 _markStack->reset(); // discard stack contents
7839 _markStack->expand(); // expand the stack if possible
7840 }
7842 // Upon stack overflow, we discard (part of) the stack,
7843 // remembering the least address amongst those discarded
7844 // in CMSCollector's _restart_address.
7845 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7846 // We need to do this under a mutex to prevent other
7847 // workers from interfering with the work done below.
7848 MutexLockerEx ml(_overflow_stack->par_lock(),
7849 Mutex::_no_safepoint_check_flag);
7850 // Remember the least grey address discarded
7851 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7852 _collector->lower_restart_addr(ra);
7853 _overflow_stack->reset(); // discard stack contents
7854 _overflow_stack->expand(); // expand the stack if possible
7855 }
7857 void CMKlassClosure::do_klass(Klass* k) {
7858 assert(_oop_closure != NULL, "Not initialized?");
7859 k->oops_do(_oop_closure);
7860 }
7862 void PushOrMarkClosure::do_oop(oop obj) {
7863 // Ignore mark word because we are running concurrent with mutators.
7864 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7865 HeapWord* addr = (HeapWord*)obj;
7866 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7867 // Oop lies in _span and isn't yet grey or black
7868 _bitMap->mark(addr); // now grey
7869 if (addr < _finger) {
7870 // the bit map iteration has already either passed, or
7871 // sampled, this bit in the bit map; we'll need to
7872 // use the marking stack to scan this oop's oops.
7873 bool simulate_overflow = false;
7874 NOT_PRODUCT(
7875 if (CMSMarkStackOverflowALot &&
7876 _collector->simulate_overflow()) {
7877 // simulate a stack overflow
7878 simulate_overflow = true;
7879 }
7880 )
7881 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7882 if (PrintCMSStatistics != 0) {
7883 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7884 SIZE_FORMAT, _markStack->capacity());
7885 }
7886 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7887 handle_stack_overflow(addr);
7888 }
7889 }
7890 // anything including and to the right of _finger
7891 // will be scanned as we iterate over the remainder of the
7892 // bit map
7893 do_yield_check();
7894 }
7895 }
7897 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7898 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7900 void Par_PushOrMarkClosure::do_oop(oop obj) {
7901 // Ignore mark word because we are running concurrent with mutators.
7902 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7903 HeapWord* addr = (HeapWord*)obj;
7904 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7905 // Oop lies in _span and isn't yet grey or black
7906 // We read the global_finger (volatile read) strictly after marking oop
7907 bool res = _bit_map->par_mark(addr); // now grey
7908 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7909 // Should we push this marked oop on our stack?
7910 // -- if someone else marked it, nothing to do
7911 // -- if target oop is above global finger nothing to do
7912 // -- if target oop is in chunk and above local finger
7913 // then nothing to do
7914 // -- else push on work queue
7915 if ( !res // someone else marked it, they will deal with it
7916 || (addr >= *gfa) // will be scanned in a later task
7917 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7918 return;
7919 }
7920 // the bit map iteration has already either passed, or
7921 // sampled, this bit in the bit map; we'll need to
7922 // use the marking stack to scan this oop's oops.
7923 bool simulate_overflow = false;
7924 NOT_PRODUCT(
7925 if (CMSMarkStackOverflowALot &&
7926 _collector->simulate_overflow()) {
7927 // simulate a stack overflow
7928 simulate_overflow = true;
7929 }
7930 )
7931 if (simulate_overflow ||
7932 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7933 // stack overflow
7934 if (PrintCMSStatistics != 0) {
7935 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7936 SIZE_FORMAT, _overflow_stack->capacity());
7937 }
7938 // We cannot assert that the overflow stack is full because
7939 // it may have been emptied since.
7940 assert(simulate_overflow ||
7941 _work_queue->size() == _work_queue->max_elems(),
7942 "Else push should have succeeded");
7943 handle_stack_overflow(addr);
7944 }
7945 do_yield_check();
7946 }
7947 }
7949 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7950 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7952 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7953 MemRegion span,
7954 ReferenceProcessor* rp,
7955 CMSBitMap* bit_map,
7956 CMSBitMap* mod_union_table,
7957 CMSMarkStack* mark_stack,
7958 bool concurrent_precleaning):
7959 CMSOopClosure(rp),
7960 _collector(collector),
7961 _span(span),
7962 _bit_map(bit_map),
7963 _mod_union_table(mod_union_table),
7964 _mark_stack(mark_stack),
7965 _concurrent_precleaning(concurrent_precleaning)
7966 {
7967 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7968 }
7970 // Grey object rescan during pre-cleaning and second checkpoint phases --
7971 // the non-parallel version (the parallel version appears further below.)
7972 void PushAndMarkClosure::do_oop(oop obj) {
7973 // Ignore mark word verification. If during concurrent precleaning,
7974 // the object monitor may be locked. If during the checkpoint
7975 // phases, the object may already have been reached by a different
7976 // path and may be at the end of the global overflow list (so
7977 // the mark word may be NULL).
7978 assert(obj->is_oop_or_null(true /* ignore mark word */),
7979 "expected an oop or NULL");
7980 HeapWord* addr = (HeapWord*)obj;
7981 // Check if oop points into the CMS generation
7982 // and is not marked
7983 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7984 // a white object ...
7985 _bit_map->mark(addr); // ... now grey
7986 // push on the marking stack (grey set)
7987 bool simulate_overflow = false;
7988 NOT_PRODUCT(
7989 if (CMSMarkStackOverflowALot &&
7990 _collector->simulate_overflow()) {
7991 // simulate a stack overflow
7992 simulate_overflow = true;
7993 }
7994 )
7995 if (simulate_overflow || !_mark_stack->push(obj)) {
7996 if (_concurrent_precleaning) {
7997 // During precleaning we can just dirty the appropriate card(s)
7998 // in the mod union table, thus ensuring that the object remains
7999 // in the grey set and continue. In the case of object arrays
8000 // we need to dirty all of the cards that the object spans,
8001 // since the rescan of object arrays will be limited to the
8002 // dirty cards.
8003 // Note that no one can be intefering with us in this action
8004 // of dirtying the mod union table, so no locking or atomics
8005 // are required.
8006 if (obj->is_objArray()) {
8007 size_t sz = obj->size();
8008 HeapWord* end_card_addr = (HeapWord*)round_to(
8009 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
8010 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8011 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8012 _mod_union_table->mark_range(redirty_range);
8013 } else {
8014 _mod_union_table->mark(addr);
8015 }
8016 _collector->_ser_pmc_preclean_ovflw++;
8017 } else {
8018 // During the remark phase, we need to remember this oop
8019 // in the overflow list.
8020 _collector->push_on_overflow_list(obj);
8021 _collector->_ser_pmc_remark_ovflw++;
8022 }
8023 }
8024 }
8025 }
8027 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
8028 MemRegion span,
8029 ReferenceProcessor* rp,
8030 CMSBitMap* bit_map,
8031 OopTaskQueue* work_queue):
8032 CMSOopClosure(rp),
8033 _collector(collector),
8034 _span(span),
8035 _bit_map(bit_map),
8036 _work_queue(work_queue)
8037 {
8038 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
8039 }
8041 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
8042 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
8044 // Grey object rescan during second checkpoint phase --
8045 // the parallel version.
8046 void Par_PushAndMarkClosure::do_oop(oop obj) {
8047 // In the assert below, we ignore the mark word because
8048 // this oop may point to an already visited object that is
8049 // on the overflow stack (in which case the mark word has
8050 // been hijacked for chaining into the overflow stack --
8051 // if this is the last object in the overflow stack then
8052 // its mark word will be NULL). Because this object may
8053 // have been subsequently popped off the global overflow
8054 // stack, and the mark word possibly restored to the prototypical
8055 // value, by the time we get to examined this failing assert in
8056 // the debugger, is_oop_or_null(false) may subsequently start
8057 // to hold.
8058 assert(obj->is_oop_or_null(true),
8059 "expected an oop or NULL");
8060 HeapWord* addr = (HeapWord*)obj;
8061 // Check if oop points into the CMS generation
8062 // and is not marked
8063 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
8064 // a white object ...
8065 // If we manage to "claim" the object, by being the
8066 // first thread to mark it, then we push it on our
8067 // marking stack
8068 if (_bit_map->par_mark(addr)) { // ... now grey
8069 // push on work queue (grey set)
8070 bool simulate_overflow = false;
8071 NOT_PRODUCT(
8072 if (CMSMarkStackOverflowALot &&
8073 _collector->par_simulate_overflow()) {
8074 // simulate a stack overflow
8075 simulate_overflow = true;
8076 }
8077 )
8078 if (simulate_overflow || !_work_queue->push(obj)) {
8079 _collector->par_push_on_overflow_list(obj);
8080 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
8081 }
8082 } // Else, some other thread got there first
8083 }
8084 }
8086 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
8087 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
8089 void CMSPrecleanRefsYieldClosure::do_yield_work() {
8090 Mutex* bml = _collector->bitMapLock();
8091 assert_lock_strong(bml);
8092 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8093 "CMS thread should hold CMS token");
8095 bml->unlock();
8096 ConcurrentMarkSweepThread::desynchronize(true);
8098 ConcurrentMarkSweepThread::acknowledge_yield_request();
8100 _collector->stopTimer();
8101 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8102 if (PrintCMSStatistics != 0) {
8103 _collector->incrementYields();
8104 }
8105 _collector->icms_wait();
8107 // See the comment in coordinator_yield()
8108 for (unsigned i = 0; i < CMSYieldSleepCount &&
8109 ConcurrentMarkSweepThread::should_yield() &&
8110 !CMSCollector::foregroundGCIsActive(); ++i) {
8111 os::sleep(Thread::current(), 1, false);
8112 ConcurrentMarkSweepThread::acknowledge_yield_request();
8113 }
8115 ConcurrentMarkSweepThread::synchronize(true);
8116 bml->lock();
8118 _collector->startTimer();
8119 }
8121 bool CMSPrecleanRefsYieldClosure::should_return() {
8122 if (ConcurrentMarkSweepThread::should_yield()) {
8123 do_yield_work();
8124 }
8125 return _collector->foregroundGCIsActive();
8126 }
8128 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
8129 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
8130 "mr should be aligned to start at a card boundary");
8131 // We'd like to assert:
8132 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
8133 // "mr should be a range of cards");
8134 // However, that would be too strong in one case -- the last
8135 // partition ends at _unallocated_block which, in general, can be
8136 // an arbitrary boundary, not necessarily card aligned.
8137 if (PrintCMSStatistics != 0) {
8138 _num_dirty_cards +=
8139 mr.word_size()/CardTableModRefBS::card_size_in_words;
8140 }
8141 _space->object_iterate_mem(mr, &_scan_cl);
8142 }
8144 SweepClosure::SweepClosure(CMSCollector* collector,
8145 ConcurrentMarkSweepGeneration* g,
8146 CMSBitMap* bitMap, bool should_yield) :
8147 _collector(collector),
8148 _g(g),
8149 _sp(g->cmsSpace()),
8150 _limit(_sp->sweep_limit()),
8151 _freelistLock(_sp->freelistLock()),
8152 _bitMap(bitMap),
8153 _yield(should_yield),
8154 _inFreeRange(false), // No free range at beginning of sweep
8155 _freeRangeInFreeLists(false), // No free range at beginning of sweep
8156 _lastFreeRangeCoalesced(false),
8157 _freeFinger(g->used_region().start())
8158 {
8159 NOT_PRODUCT(
8160 _numObjectsFreed = 0;
8161 _numWordsFreed = 0;
8162 _numObjectsLive = 0;
8163 _numWordsLive = 0;
8164 _numObjectsAlreadyFree = 0;
8165 _numWordsAlreadyFree = 0;
8166 _last_fc = NULL;
8168 _sp->initializeIndexedFreeListArrayReturnedBytes();
8169 _sp->dictionary()->initialize_dict_returned_bytes();
8170 )
8171 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8172 "sweep _limit out of bounds");
8173 if (CMSTraceSweeper) {
8174 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
8175 _limit);
8176 }
8177 }
8179 void SweepClosure::print_on(outputStream* st) const {
8180 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
8181 _sp->bottom(), _sp->end());
8182 tty->print_cr("_limit = " PTR_FORMAT, _limit);
8183 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
8184 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
8185 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
8186 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
8187 }
8189 #ifndef PRODUCT
8190 // Assertion checking only: no useful work in product mode --
8191 // however, if any of the flags below become product flags,
8192 // you may need to review this code to see if it needs to be
8193 // enabled in product mode.
8194 SweepClosure::~SweepClosure() {
8195 assert_lock_strong(_freelistLock);
8196 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8197 "sweep _limit out of bounds");
8198 if (inFreeRange()) {
8199 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
8200 print();
8201 ShouldNotReachHere();
8202 }
8203 if (Verbose && PrintGC) {
8204 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
8205 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
8206 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
8207 SIZE_FORMAT" bytes "
8208 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
8209 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
8210 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
8211 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
8212 * sizeof(HeapWord);
8213 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
8215 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
8216 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
8217 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
8218 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
8219 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
8220 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
8221 indexListReturnedBytes);
8222 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
8223 dict_returned_bytes);
8224 }
8225 }
8226 if (CMSTraceSweeper) {
8227 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
8228 _limit);
8229 }
8230 }
8231 #endif // PRODUCT
8233 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
8234 bool freeRangeInFreeLists) {
8235 if (CMSTraceSweeper) {
8236 gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n",
8237 freeFinger, freeRangeInFreeLists);
8238 }
8239 assert(!inFreeRange(), "Trampling existing free range");
8240 set_inFreeRange(true);
8241 set_lastFreeRangeCoalesced(false);
8243 set_freeFinger(freeFinger);
8244 set_freeRangeInFreeLists(freeRangeInFreeLists);
8245 if (CMSTestInFreeList) {
8246 if (freeRangeInFreeLists) {
8247 FreeChunk* fc = (FreeChunk*) freeFinger;
8248 assert(fc->is_free(), "A chunk on the free list should be free.");
8249 assert(fc->size() > 0, "Free range should have a size");
8250 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
8251 }
8252 }
8253 }
8255 // Note that the sweeper runs concurrently with mutators. Thus,
8256 // it is possible for direct allocation in this generation to happen
8257 // in the middle of the sweep. Note that the sweeper also coalesces
8258 // contiguous free blocks. Thus, unless the sweeper and the allocator
8259 // synchronize appropriately freshly allocated blocks may get swept up.
8260 // This is accomplished by the sweeper locking the free lists while
8261 // it is sweeping. Thus blocks that are determined to be free are
8262 // indeed free. There is however one additional complication:
8263 // blocks that have been allocated since the final checkpoint and
8264 // mark, will not have been marked and so would be treated as
8265 // unreachable and swept up. To prevent this, the allocator marks
8266 // the bit map when allocating during the sweep phase. This leads,
8267 // however, to a further complication -- objects may have been allocated
8268 // but not yet initialized -- in the sense that the header isn't yet
8269 // installed. The sweeper can not then determine the size of the block
8270 // in order to skip over it. To deal with this case, we use a technique
8271 // (due to Printezis) to encode such uninitialized block sizes in the
8272 // bit map. Since the bit map uses a bit per every HeapWord, but the
8273 // CMS generation has a minimum object size of 3 HeapWords, it follows
8274 // that "normal marks" won't be adjacent in the bit map (there will
8275 // always be at least two 0 bits between successive 1 bits). We make use
8276 // of these "unused" bits to represent uninitialized blocks -- the bit
8277 // corresponding to the start of the uninitialized object and the next
8278 // bit are both set. Finally, a 1 bit marks the end of the object that
8279 // started with the two consecutive 1 bits to indicate its potentially
8280 // uninitialized state.
8282 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8283 FreeChunk* fc = (FreeChunk*)addr;
8284 size_t res;
8286 // Check if we are done sweeping. Below we check "addr >= _limit" rather
8287 // than "addr == _limit" because although _limit was a block boundary when
8288 // we started the sweep, it may no longer be one because heap expansion
8289 // may have caused us to coalesce the block ending at the address _limit
8290 // with a newly expanded chunk (this happens when _limit was set to the
8291 // previous _end of the space), so we may have stepped past _limit:
8292 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8293 if (addr >= _limit) { // we have swept up to or past the limit: finish up
8294 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8295 "sweep _limit out of bounds");
8296 assert(addr < _sp->end(), "addr out of bounds");
8297 // Flush any free range we might be holding as a single
8298 // coalesced chunk to the appropriate free list.
8299 if (inFreeRange()) {
8300 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8301 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8302 flush_cur_free_chunk(freeFinger(),
8303 pointer_delta(addr, freeFinger()));
8304 if (CMSTraceSweeper) {
8305 gclog_or_tty->print("Sweep: last chunk: ");
8306 gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") "
8307 "[coalesced:"SIZE_FORMAT"]\n",
8308 freeFinger(), pointer_delta(addr, freeFinger()),
8309 lastFreeRangeCoalesced());
8310 }
8311 }
8313 // help the iterator loop finish
8314 return pointer_delta(_sp->end(), addr);
8315 }
8317 assert(addr < _limit, "sweep invariant");
8318 // check if we should yield
8319 do_yield_check(addr);
8320 if (fc->is_free()) {
8321 // Chunk that is already free
8322 res = fc->size();
8323 do_already_free_chunk(fc);
8324 debug_only(_sp->verifyFreeLists());
8325 // If we flush the chunk at hand in lookahead_and_flush()
8326 // and it's coalesced with a preceding chunk, then the
8327 // process of "mangling" the payload of the coalesced block
8328 // will cause erasure of the size information from the
8329 // (erstwhile) header of all the coalesced blocks but the
8330 // first, so the first disjunct in the assert will not hold
8331 // in that specific case (in which case the second disjunct
8332 // will hold).
8333 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8334 "Otherwise the size info doesn't change at this step");
8335 NOT_PRODUCT(
8336 _numObjectsAlreadyFree++;
8337 _numWordsAlreadyFree += res;
8338 )
8339 NOT_PRODUCT(_last_fc = fc;)
8340 } else if (!_bitMap->isMarked(addr)) {
8341 // Chunk is fresh garbage
8342 res = do_garbage_chunk(fc);
8343 debug_only(_sp->verifyFreeLists());
8344 NOT_PRODUCT(
8345 _numObjectsFreed++;
8346 _numWordsFreed += res;
8347 )
8348 } else {
8349 // Chunk that is alive.
8350 res = do_live_chunk(fc);
8351 debug_only(_sp->verifyFreeLists());
8352 NOT_PRODUCT(
8353 _numObjectsLive++;
8354 _numWordsLive += res;
8355 )
8356 }
8357 return res;
8358 }
8360 // For the smart allocation, record following
8361 // split deaths - a free chunk is removed from its free list because
8362 // it is being split into two or more chunks.
8363 // split birth - a free chunk is being added to its free list because
8364 // a larger free chunk has been split and resulted in this free chunk.
8365 // coal death - a free chunk is being removed from its free list because
8366 // it is being coalesced into a large free chunk.
8367 // coal birth - a free chunk is being added to its free list because
8368 // it was created when two or more free chunks where coalesced into
8369 // this free chunk.
8370 //
8371 // These statistics are used to determine the desired number of free
8372 // chunks of a given size. The desired number is chosen to be relative
8373 // to the end of a CMS sweep. The desired number at the end of a sweep
8374 // is the
8375 // count-at-end-of-previous-sweep (an amount that was enough)
8376 // - count-at-beginning-of-current-sweep (the excess)
8377 // + split-births (gains in this size during interval)
8378 // - split-deaths (demands on this size during interval)
8379 // where the interval is from the end of one sweep to the end of the
8380 // next.
8381 //
8382 // When sweeping the sweeper maintains an accumulated chunk which is
8383 // the chunk that is made up of chunks that have been coalesced. That
8384 // will be termed the left-hand chunk. A new chunk of garbage that
8385 // is being considered for coalescing will be referred to as the
8386 // right-hand chunk.
8387 //
8388 // When making a decision on whether to coalesce a right-hand chunk with
8389 // the current left-hand chunk, the current count vs. the desired count
8390 // of the left-hand chunk is considered. Also if the right-hand chunk
8391 // is near the large chunk at the end of the heap (see
8392 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8393 // left-hand chunk is coalesced.
8394 //
8395 // When making a decision about whether to split a chunk, the desired count
8396 // vs. the current count of the candidate to be split is also considered.
8397 // If the candidate is underpopulated (currently fewer chunks than desired)
8398 // a chunk of an overpopulated (currently more chunks than desired) size may
8399 // be chosen. The "hint" associated with a free list, if non-null, points
8400 // to a free list which may be overpopulated.
8401 //
8403 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8404 const size_t size = fc->size();
8405 // Chunks that cannot be coalesced are not in the
8406 // free lists.
8407 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8408 assert(_sp->verify_chunk_in_free_list(fc),
8409 "free chunk should be in free lists");
8410 }
8411 // a chunk that is already free, should not have been
8412 // marked in the bit map
8413 HeapWord* const addr = (HeapWord*) fc;
8414 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8415 // Verify that the bit map has no bits marked between
8416 // addr and purported end of this block.
8417 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8419 // Some chunks cannot be coalesced under any circumstances.
8420 // See the definition of cantCoalesce().
8421 if (!fc->cantCoalesce()) {
8422 // This chunk can potentially be coalesced.
8423 if (_sp->adaptive_freelists()) {
8424 // All the work is done in
8425 do_post_free_or_garbage_chunk(fc, size);
8426 } else { // Not adaptive free lists
8427 // this is a free chunk that can potentially be coalesced by the sweeper;
8428 if (!inFreeRange()) {
8429 // if the next chunk is a free block that can't be coalesced
8430 // it doesn't make sense to remove this chunk from the free lists
8431 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8432 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8433 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8434 nextChunk->is_free() && // ... which is free...
8435 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8436 // nothing to do
8437 } else {
8438 // Potentially the start of a new free range:
8439 // Don't eagerly remove it from the free lists.
8440 // No need to remove it if it will just be put
8441 // back again. (Also from a pragmatic point of view
8442 // if it is a free block in a region that is beyond
8443 // any allocated blocks, an assertion will fail)
8444 // Remember the start of a free run.
8445 initialize_free_range(addr, true);
8446 // end - can coalesce with next chunk
8447 }
8448 } else {
8449 // the midst of a free range, we are coalescing
8450 print_free_block_coalesced(fc);
8451 if (CMSTraceSweeper) {
8452 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
8453 }
8454 // remove it from the free lists
8455 _sp->removeFreeChunkFromFreeLists(fc);
8456 set_lastFreeRangeCoalesced(true);
8457 // If the chunk is being coalesced and the current free range is
8458 // in the free lists, remove the current free range so that it
8459 // will be returned to the free lists in its entirety - all
8460 // the coalesced pieces included.
8461 if (freeRangeInFreeLists()) {
8462 FreeChunk* ffc = (FreeChunk*) freeFinger();
8463 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8464 "Size of free range is inconsistent with chunk size.");
8465 if (CMSTestInFreeList) {
8466 assert(_sp->verify_chunk_in_free_list(ffc),
8467 "free range is not in free lists");
8468 }
8469 _sp->removeFreeChunkFromFreeLists(ffc);
8470 set_freeRangeInFreeLists(false);
8471 }
8472 }
8473 }
8474 // Note that if the chunk is not coalescable (the else arm
8475 // below), we unconditionally flush, without needing to do
8476 // a "lookahead," as we do below.
8477 if (inFreeRange()) lookahead_and_flush(fc, size);
8478 } else {
8479 // Code path common to both original and adaptive free lists.
8481 // cant coalesce with previous block; this should be treated
8482 // as the end of a free run if any
8483 if (inFreeRange()) {
8484 // we kicked some butt; time to pick up the garbage
8485 assert(freeFinger() < addr, "freeFinger points too high");
8486 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8487 }
8488 // else, nothing to do, just continue
8489 }
8490 }
8492 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8493 // This is a chunk of garbage. It is not in any free list.
8494 // Add it to a free list or let it possibly be coalesced into
8495 // a larger chunk.
8496 HeapWord* const addr = (HeapWord*) fc;
8497 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8499 if (_sp->adaptive_freelists()) {
8500 // Verify that the bit map has no bits marked between
8501 // addr and purported end of just dead object.
8502 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8504 do_post_free_or_garbage_chunk(fc, size);
8505 } else {
8506 if (!inFreeRange()) {
8507 // start of a new free range
8508 assert(size > 0, "A free range should have a size");
8509 initialize_free_range(addr, false);
8510 } else {
8511 // this will be swept up when we hit the end of the
8512 // free range
8513 if (CMSTraceSweeper) {
8514 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
8515 }
8516 // If the chunk is being coalesced and the current free range is
8517 // in the free lists, remove the current free range so that it
8518 // will be returned to the free lists in its entirety - all
8519 // the coalesced pieces included.
8520 if (freeRangeInFreeLists()) {
8521 FreeChunk* ffc = (FreeChunk*)freeFinger();
8522 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8523 "Size of free range is inconsistent with chunk size.");
8524 if (CMSTestInFreeList) {
8525 assert(_sp->verify_chunk_in_free_list(ffc),
8526 "free range is not in free lists");
8527 }
8528 _sp->removeFreeChunkFromFreeLists(ffc);
8529 set_freeRangeInFreeLists(false);
8530 }
8531 set_lastFreeRangeCoalesced(true);
8532 }
8533 // this will be swept up when we hit the end of the free range
8535 // Verify that the bit map has no bits marked between
8536 // addr and purported end of just dead object.
8537 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8538 }
8539 assert(_limit >= addr + size,
8540 "A freshly garbage chunk can't possibly straddle over _limit");
8541 if (inFreeRange()) lookahead_and_flush(fc, size);
8542 return size;
8543 }
8545 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8546 HeapWord* addr = (HeapWord*) fc;
8547 // The sweeper has just found a live object. Return any accumulated
8548 // left hand chunk to the free lists.
8549 if (inFreeRange()) {
8550 assert(freeFinger() < addr, "freeFinger points too high");
8551 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8552 }
8554 // This object is live: we'd normally expect this to be
8555 // an oop, and like to assert the following:
8556 // assert(oop(addr)->is_oop(), "live block should be an oop");
8557 // However, as we commented above, this may be an object whose
8558 // header hasn't yet been initialized.
8559 size_t size;
8560 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8561 if (_bitMap->isMarked(addr + 1)) {
8562 // Determine the size from the bit map, rather than trying to
8563 // compute it from the object header.
8564 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8565 size = pointer_delta(nextOneAddr + 1, addr);
8566 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8567 "alignment problem");
8569 #ifdef ASSERT
8570 if (oop(addr)->klass_or_null() != NULL) {
8571 // Ignore mark word because we are running concurrent with mutators
8572 assert(oop(addr)->is_oop(true), "live block should be an oop");
8573 assert(size ==
8574 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8575 "P-mark and computed size do not agree");
8576 }
8577 #endif
8579 } else {
8580 // This should be an initialized object that's alive.
8581 assert(oop(addr)->klass_or_null() != NULL,
8582 "Should be an initialized object");
8583 // Ignore mark word because we are running concurrent with mutators
8584 assert(oop(addr)->is_oop(true), "live block should be an oop");
8585 // Verify that the bit map has no bits marked between
8586 // addr and purported end of this block.
8587 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8588 assert(size >= 3, "Necessary for Printezis marks to work");
8589 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8590 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8591 }
8592 return size;
8593 }
8595 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8596 size_t chunkSize) {
8597 // do_post_free_or_garbage_chunk() should only be called in the case
8598 // of the adaptive free list allocator.
8599 const bool fcInFreeLists = fc->is_free();
8600 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8601 assert((HeapWord*)fc <= _limit, "sweep invariant");
8602 if (CMSTestInFreeList && fcInFreeLists) {
8603 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8604 }
8606 if (CMSTraceSweeper) {
8607 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8608 }
8610 HeapWord* const fc_addr = (HeapWord*) fc;
8612 bool coalesce;
8613 const size_t left = pointer_delta(fc_addr, freeFinger());
8614 const size_t right = chunkSize;
8615 switch (FLSCoalescePolicy) {
8616 // numeric value forms a coalition aggressiveness metric
8617 case 0: { // never coalesce
8618 coalesce = false;
8619 break;
8620 }
8621 case 1: { // coalesce if left & right chunks on overpopulated lists
8622 coalesce = _sp->coalOverPopulated(left) &&
8623 _sp->coalOverPopulated(right);
8624 break;
8625 }
8626 case 2: { // coalesce if left chunk on overpopulated list (default)
8627 coalesce = _sp->coalOverPopulated(left);
8628 break;
8629 }
8630 case 3: { // coalesce if left OR right chunk on overpopulated list
8631 coalesce = _sp->coalOverPopulated(left) ||
8632 _sp->coalOverPopulated(right);
8633 break;
8634 }
8635 case 4: { // always coalesce
8636 coalesce = true;
8637 break;
8638 }
8639 default:
8640 ShouldNotReachHere();
8641 }
8643 // Should the current free range be coalesced?
8644 // If the chunk is in a free range and either we decided to coalesce above
8645 // or the chunk is near the large block at the end of the heap
8646 // (isNearLargestChunk() returns true), then coalesce this chunk.
8647 const bool doCoalesce = inFreeRange()
8648 && (coalesce || _g->isNearLargestChunk(fc_addr));
8649 if (doCoalesce) {
8650 // Coalesce the current free range on the left with the new
8651 // chunk on the right. If either is on a free list,
8652 // it must be removed from the list and stashed in the closure.
8653 if (freeRangeInFreeLists()) {
8654 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8655 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8656 "Size of free range is inconsistent with chunk size.");
8657 if (CMSTestInFreeList) {
8658 assert(_sp->verify_chunk_in_free_list(ffc),
8659 "Chunk is not in free lists");
8660 }
8661 _sp->coalDeath(ffc->size());
8662 _sp->removeFreeChunkFromFreeLists(ffc);
8663 set_freeRangeInFreeLists(false);
8664 }
8665 if (fcInFreeLists) {
8666 _sp->coalDeath(chunkSize);
8667 assert(fc->size() == chunkSize,
8668 "The chunk has the wrong size or is not in the free lists");
8669 _sp->removeFreeChunkFromFreeLists(fc);
8670 }
8671 set_lastFreeRangeCoalesced(true);
8672 print_free_block_coalesced(fc);
8673 } else { // not in a free range and/or should not coalesce
8674 // Return the current free range and start a new one.
8675 if (inFreeRange()) {
8676 // In a free range but cannot coalesce with the right hand chunk.
8677 // Put the current free range into the free lists.
8678 flush_cur_free_chunk(freeFinger(),
8679 pointer_delta(fc_addr, freeFinger()));
8680 }
8681 // Set up for new free range. Pass along whether the right hand
8682 // chunk is in the free lists.
8683 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8684 }
8685 }
8687 // Lookahead flush:
8688 // If we are tracking a free range, and this is the last chunk that
8689 // we'll look at because its end crosses past _limit, we'll preemptively
8690 // flush it along with any free range we may be holding on to. Note that
8691 // this can be the case only for an already free or freshly garbage
8692 // chunk. If this block is an object, it can never straddle
8693 // over _limit. The "straddling" occurs when _limit is set at
8694 // the previous end of the space when this cycle started, and
8695 // a subsequent heap expansion caused the previously co-terminal
8696 // free block to be coalesced with the newly expanded portion,
8697 // thus rendering _limit a non-block-boundary making it dangerous
8698 // for the sweeper to step over and examine.
8699 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8700 assert(inFreeRange(), "Should only be called if currently in a free range.");
8701 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8702 assert(_sp->used_region().contains(eob - 1),
8703 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
8704 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8705 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8706 eob, eob-1, _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8707 if (eob >= _limit) {
8708 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8709 if (CMSTraceSweeper) {
8710 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8711 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8712 "[" PTR_FORMAT "," PTR_FORMAT ")",
8713 _limit, fc, eob, _sp->bottom(), _sp->end());
8714 }
8715 // Return the storage we are tracking back into the free lists.
8716 if (CMSTraceSweeper) {
8717 gclog_or_tty->print_cr("Flushing ... ");
8718 }
8719 assert(freeFinger() < eob, "Error");
8720 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8721 }
8722 }
8724 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8725 assert(inFreeRange(), "Should only be called if currently in a free range.");
8726 assert(size > 0,
8727 "A zero sized chunk cannot be added to the free lists.");
8728 if (!freeRangeInFreeLists()) {
8729 if (CMSTestInFreeList) {
8730 FreeChunk* fc = (FreeChunk*) chunk;
8731 fc->set_size(size);
8732 assert(!_sp->verify_chunk_in_free_list(fc),
8733 "chunk should not be in free lists yet");
8734 }
8735 if (CMSTraceSweeper) {
8736 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8737 chunk, size);
8738 }
8739 // A new free range is going to be starting. The current
8740 // free range has not been added to the free lists yet or
8741 // was removed so add it back.
8742 // If the current free range was coalesced, then the death
8743 // of the free range was recorded. Record a birth now.
8744 if (lastFreeRangeCoalesced()) {
8745 _sp->coalBirth(size);
8746 }
8747 _sp->addChunkAndRepairOffsetTable(chunk, size,
8748 lastFreeRangeCoalesced());
8749 } else if (CMSTraceSweeper) {
8750 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8751 }
8752 set_inFreeRange(false);
8753 set_freeRangeInFreeLists(false);
8754 }
8756 // We take a break if we've been at this for a while,
8757 // so as to avoid monopolizing the locks involved.
8758 void SweepClosure::do_yield_work(HeapWord* addr) {
8759 // Return current free chunk being used for coalescing (if any)
8760 // to the appropriate freelist. After yielding, the next
8761 // free block encountered will start a coalescing range of
8762 // free blocks. If the next free block is adjacent to the
8763 // chunk just flushed, they will need to wait for the next
8764 // sweep to be coalesced.
8765 if (inFreeRange()) {
8766 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8767 }
8769 // First give up the locks, then yield, then re-lock.
8770 // We should probably use a constructor/destructor idiom to
8771 // do this unlock/lock or modify the MutexUnlocker class to
8772 // serve our purpose. XXX
8773 assert_lock_strong(_bitMap->lock());
8774 assert_lock_strong(_freelistLock);
8775 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8776 "CMS thread should hold CMS token");
8777 _bitMap->lock()->unlock();
8778 _freelistLock->unlock();
8779 ConcurrentMarkSweepThread::desynchronize(true);
8780 ConcurrentMarkSweepThread::acknowledge_yield_request();
8781 _collector->stopTimer();
8782 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8783 if (PrintCMSStatistics != 0) {
8784 _collector->incrementYields();
8785 }
8786 _collector->icms_wait();
8788 // See the comment in coordinator_yield()
8789 for (unsigned i = 0; i < CMSYieldSleepCount &&
8790 ConcurrentMarkSweepThread::should_yield() &&
8791 !CMSCollector::foregroundGCIsActive(); ++i) {
8792 os::sleep(Thread::current(), 1, false);
8793 ConcurrentMarkSweepThread::acknowledge_yield_request();
8794 }
8796 ConcurrentMarkSweepThread::synchronize(true);
8797 _freelistLock->lock();
8798 _bitMap->lock()->lock_without_safepoint_check();
8799 _collector->startTimer();
8800 }
8802 #ifndef PRODUCT
8803 // This is actually very useful in a product build if it can
8804 // be called from the debugger. Compile it into the product
8805 // as needed.
8806 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8807 return debug_cms_space->verify_chunk_in_free_list(fc);
8808 }
8809 #endif
8811 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8812 if (CMSTraceSweeper) {
8813 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8814 fc, fc->size());
8815 }
8816 }
8818 // CMSIsAliveClosure
8819 bool CMSIsAliveClosure::do_object_b(oop obj) {
8820 HeapWord* addr = (HeapWord*)obj;
8821 return addr != NULL &&
8822 (!_span.contains(addr) || _bit_map->isMarked(addr));
8823 }
8826 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8827 MemRegion span,
8828 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8829 bool cpc):
8830 _collector(collector),
8831 _span(span),
8832 _bit_map(bit_map),
8833 _mark_stack(mark_stack),
8834 _concurrent_precleaning(cpc) {
8835 assert(!_span.is_empty(), "Empty span could spell trouble");
8836 }
8839 // CMSKeepAliveClosure: the serial version
8840 void CMSKeepAliveClosure::do_oop(oop obj) {
8841 HeapWord* addr = (HeapWord*)obj;
8842 if (_span.contains(addr) &&
8843 !_bit_map->isMarked(addr)) {
8844 _bit_map->mark(addr);
8845 bool simulate_overflow = false;
8846 NOT_PRODUCT(
8847 if (CMSMarkStackOverflowALot &&
8848 _collector->simulate_overflow()) {
8849 // simulate a stack overflow
8850 simulate_overflow = true;
8851 }
8852 )
8853 if (simulate_overflow || !_mark_stack->push(obj)) {
8854 if (_concurrent_precleaning) {
8855 // We dirty the overflown object and let the remark
8856 // phase deal with it.
8857 assert(_collector->overflow_list_is_empty(), "Error");
8858 // In the case of object arrays, we need to dirty all of
8859 // the cards that the object spans. No locking or atomics
8860 // are needed since no one else can be mutating the mod union
8861 // table.
8862 if (obj->is_objArray()) {
8863 size_t sz = obj->size();
8864 HeapWord* end_card_addr =
8865 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8866 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8867 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8868 _collector->_modUnionTable.mark_range(redirty_range);
8869 } else {
8870 _collector->_modUnionTable.mark(addr);
8871 }
8872 _collector->_ser_kac_preclean_ovflw++;
8873 } else {
8874 _collector->push_on_overflow_list(obj);
8875 _collector->_ser_kac_ovflw++;
8876 }
8877 }
8878 }
8879 }
8881 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8882 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8884 // CMSParKeepAliveClosure: a parallel version of the above.
8885 // The work queues are private to each closure (thread),
8886 // but (may be) available for stealing by other threads.
8887 void CMSParKeepAliveClosure::do_oop(oop obj) {
8888 HeapWord* addr = (HeapWord*)obj;
8889 if (_span.contains(addr) &&
8890 !_bit_map->isMarked(addr)) {
8891 // In general, during recursive tracing, several threads
8892 // may be concurrently getting here; the first one to
8893 // "tag" it, claims it.
8894 if (_bit_map->par_mark(addr)) {
8895 bool res = _work_queue->push(obj);
8896 assert(res, "Low water mark should be much less than capacity");
8897 // Do a recursive trim in the hope that this will keep
8898 // stack usage lower, but leave some oops for potential stealers
8899 trim_queue(_low_water_mark);
8900 } // Else, another thread got there first
8901 }
8902 }
8904 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8905 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8907 void CMSParKeepAliveClosure::trim_queue(uint max) {
8908 while (_work_queue->size() > max) {
8909 oop new_oop;
8910 if (_work_queue->pop_local(new_oop)) {
8911 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8912 assert(_bit_map->isMarked((HeapWord*)new_oop),
8913 "no white objects on this stack!");
8914 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8915 // iterate over the oops in this oop, marking and pushing
8916 // the ones in CMS heap (i.e. in _span).
8917 new_oop->oop_iterate(&_mark_and_push);
8918 }
8919 }
8920 }
8922 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8923 CMSCollector* collector,
8924 MemRegion span, CMSBitMap* bit_map,
8925 OopTaskQueue* work_queue):
8926 _collector(collector),
8927 _span(span),
8928 _bit_map(bit_map),
8929 _work_queue(work_queue) { }
8931 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8932 HeapWord* addr = (HeapWord*)obj;
8933 if (_span.contains(addr) &&
8934 !_bit_map->isMarked(addr)) {
8935 if (_bit_map->par_mark(addr)) {
8936 bool simulate_overflow = false;
8937 NOT_PRODUCT(
8938 if (CMSMarkStackOverflowALot &&
8939 _collector->par_simulate_overflow()) {
8940 // simulate a stack overflow
8941 simulate_overflow = true;
8942 }
8943 )
8944 if (simulate_overflow || !_work_queue->push(obj)) {
8945 _collector->par_push_on_overflow_list(obj);
8946 _collector->_par_kac_ovflw++;
8947 }
8948 } // Else another thread got there already
8949 }
8950 }
8952 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8953 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8955 //////////////////////////////////////////////////////////////////
8956 // CMSExpansionCause /////////////////////////////
8957 //////////////////////////////////////////////////////////////////
8958 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8959 switch (cause) {
8960 case _no_expansion:
8961 return "No expansion";
8962 case _satisfy_free_ratio:
8963 return "Free ratio";
8964 case _satisfy_promotion:
8965 return "Satisfy promotion";
8966 case _satisfy_allocation:
8967 return "allocation";
8968 case _allocate_par_lab:
8969 return "Par LAB";
8970 case _allocate_par_spooling_space:
8971 return "Par Spooling Space";
8972 case _adaptive_size_policy:
8973 return "Ergonomics";
8974 default:
8975 return "unknown";
8976 }
8977 }
8979 void CMSDrainMarkingStackClosure::do_void() {
8980 // the max number to take from overflow list at a time
8981 const size_t num = _mark_stack->capacity()/4;
8982 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8983 "Overflow list should be NULL during concurrent phases");
8984 while (!_mark_stack->isEmpty() ||
8985 // if stack is empty, check the overflow list
8986 _collector->take_from_overflow_list(num, _mark_stack)) {
8987 oop obj = _mark_stack->pop();
8988 HeapWord* addr = (HeapWord*)obj;
8989 assert(_span.contains(addr), "Should be within span");
8990 assert(_bit_map->isMarked(addr), "Should be marked");
8991 assert(obj->is_oop(), "Should be an oop");
8992 obj->oop_iterate(_keep_alive);
8993 }
8994 }
8996 void CMSParDrainMarkingStackClosure::do_void() {
8997 // drain queue
8998 trim_queue(0);
8999 }
9001 // Trim our work_queue so its length is below max at return
9002 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
9003 while (_work_queue->size() > max) {
9004 oop new_oop;
9005 if (_work_queue->pop_local(new_oop)) {
9006 assert(new_oop->is_oop(), "Expected an oop");
9007 assert(_bit_map->isMarked((HeapWord*)new_oop),
9008 "no white objects on this stack!");
9009 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
9010 // iterate over the oops in this oop, marking and pushing
9011 // the ones in CMS heap (i.e. in _span).
9012 new_oop->oop_iterate(&_mark_and_push);
9013 }
9014 }
9015 }
9017 ////////////////////////////////////////////////////////////////////
9018 // Support for Marking Stack Overflow list handling and related code
9019 ////////////////////////////////////////////////////////////////////
9020 // Much of the following code is similar in shape and spirit to the
9021 // code used in ParNewGC. We should try and share that code
9022 // as much as possible in the future.
9024 #ifndef PRODUCT
9025 // Debugging support for CMSStackOverflowALot
9027 // It's OK to call this multi-threaded; the worst thing
9028 // that can happen is that we'll get a bunch of closely
9029 // spaced simulated oveflows, but that's OK, in fact
9030 // probably good as it would exercise the overflow code
9031 // under contention.
9032 bool CMSCollector::simulate_overflow() {
9033 if (_overflow_counter-- <= 0) { // just being defensive
9034 _overflow_counter = CMSMarkStackOverflowInterval;
9035 return true;
9036 } else {
9037 return false;
9038 }
9039 }
9041 bool CMSCollector::par_simulate_overflow() {
9042 return simulate_overflow();
9043 }
9044 #endif
9046 // Single-threaded
9047 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
9048 assert(stack->isEmpty(), "Expected precondition");
9049 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
9050 size_t i = num;
9051 oop cur = _overflow_list;
9052 const markOop proto = markOopDesc::prototype();
9053 NOT_PRODUCT(ssize_t n = 0;)
9054 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
9055 next = oop(cur->mark());
9056 cur->set_mark(proto); // until proven otherwise
9057 assert(cur->is_oop(), "Should be an oop");
9058 bool res = stack->push(cur);
9059 assert(res, "Bit off more than can chew?");
9060 NOT_PRODUCT(n++;)
9061 }
9062 _overflow_list = cur;
9063 #ifndef PRODUCT
9064 assert(_num_par_pushes >= n, "Too many pops?");
9065 _num_par_pushes -=n;
9066 #endif
9067 return !stack->isEmpty();
9068 }
9070 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
9071 // (MT-safe) Get a prefix of at most "num" from the list.
9072 // The overflow list is chained through the mark word of
9073 // each object in the list. We fetch the entire list,
9074 // break off a prefix of the right size and return the
9075 // remainder. If other threads try to take objects from
9076 // the overflow list at that time, they will wait for
9077 // some time to see if data becomes available. If (and
9078 // only if) another thread places one or more object(s)
9079 // on the global list before we have returned the suffix
9080 // to the global list, we will walk down our local list
9081 // to find its end and append the global list to
9082 // our suffix before returning it. This suffix walk can
9083 // prove to be expensive (quadratic in the amount of traffic)
9084 // when there are many objects in the overflow list and
9085 // there is much producer-consumer contention on the list.
9086 // *NOTE*: The overflow list manipulation code here and
9087 // in ParNewGeneration:: are very similar in shape,
9088 // except that in the ParNew case we use the old (from/eden)
9089 // copy of the object to thread the list via its klass word.
9090 // Because of the common code, if you make any changes in
9091 // the code below, please check the ParNew version to see if
9092 // similar changes might be needed.
9093 // CR 6797058 has been filed to consolidate the common code.
9094 bool CMSCollector::par_take_from_overflow_list(size_t num,
9095 OopTaskQueue* work_q,
9096 int no_of_gc_threads) {
9097 assert(work_q->size() == 0, "First empty local work queue");
9098 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
9099 if (_overflow_list == NULL) {
9100 return false;
9101 }
9102 // Grab the entire list; we'll put back a suffix
9103 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9104 Thread* tid = Thread::current();
9105 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
9106 // set to ParallelGCThreads.
9107 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
9108 size_t sleep_time_millis = MAX2((size_t)1, num/100);
9109 // If the list is busy, we spin for a short while,
9110 // sleeping between attempts to get the list.
9111 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
9112 os::sleep(tid, sleep_time_millis, false);
9113 if (_overflow_list == NULL) {
9114 // Nothing left to take
9115 return false;
9116 } else if (_overflow_list != BUSY) {
9117 // Try and grab the prefix
9118 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9119 }
9120 }
9121 // If the list was found to be empty, or we spun long
9122 // enough, we give up and return empty-handed. If we leave
9123 // the list in the BUSY state below, it must be the case that
9124 // some other thread holds the overflow list and will set it
9125 // to a non-BUSY state in the future.
9126 if (prefix == NULL || prefix == BUSY) {
9127 // Nothing to take or waited long enough
9128 if (prefix == NULL) {
9129 // Write back the NULL in case we overwrote it with BUSY above
9130 // and it is still the same value.
9131 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9132 }
9133 return false;
9134 }
9135 assert(prefix != NULL && prefix != BUSY, "Error");
9136 size_t i = num;
9137 oop cur = prefix;
9138 // Walk down the first "num" objects, unless we reach the end.
9139 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
9140 if (cur->mark() == NULL) {
9141 // We have "num" or fewer elements in the list, so there
9142 // is nothing to return to the global list.
9143 // Write back the NULL in lieu of the BUSY we wrote
9144 // above, if it is still the same value.
9145 if (_overflow_list == BUSY) {
9146 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9147 }
9148 } else {
9149 // Chop off the suffix and rerturn it to the global list.
9150 assert(cur->mark() != BUSY, "Error");
9151 oop suffix_head = cur->mark(); // suffix will be put back on global list
9152 cur->set_mark(NULL); // break off suffix
9153 // It's possible that the list is still in the empty(busy) state
9154 // we left it in a short while ago; in that case we may be
9155 // able to place back the suffix without incurring the cost
9156 // of a walk down the list.
9157 oop observed_overflow_list = _overflow_list;
9158 oop cur_overflow_list = observed_overflow_list;
9159 bool attached = false;
9160 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
9161 observed_overflow_list =
9162 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9163 if (cur_overflow_list == observed_overflow_list) {
9164 attached = true;
9165 break;
9166 } else cur_overflow_list = observed_overflow_list;
9167 }
9168 if (!attached) {
9169 // Too bad, someone else sneaked in (at least) an element; we'll need
9170 // to do a splice. Find tail of suffix so we can prepend suffix to global
9171 // list.
9172 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
9173 oop suffix_tail = cur;
9174 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
9175 "Tautology");
9176 observed_overflow_list = _overflow_list;
9177 do {
9178 cur_overflow_list = observed_overflow_list;
9179 if (cur_overflow_list != BUSY) {
9180 // Do the splice ...
9181 suffix_tail->set_mark(markOop(cur_overflow_list));
9182 } else { // cur_overflow_list == BUSY
9183 suffix_tail->set_mark(NULL);
9184 }
9185 // ... and try to place spliced list back on overflow_list ...
9186 observed_overflow_list =
9187 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9188 } while (cur_overflow_list != observed_overflow_list);
9189 // ... until we have succeeded in doing so.
9190 }
9191 }
9193 // Push the prefix elements on work_q
9194 assert(prefix != NULL, "control point invariant");
9195 const markOop proto = markOopDesc::prototype();
9196 oop next;
9197 NOT_PRODUCT(ssize_t n = 0;)
9198 for (cur = prefix; cur != NULL; cur = next) {
9199 next = oop(cur->mark());
9200 cur->set_mark(proto); // until proven otherwise
9201 assert(cur->is_oop(), "Should be an oop");
9202 bool res = work_q->push(cur);
9203 assert(res, "Bit off more than we can chew?");
9204 NOT_PRODUCT(n++;)
9205 }
9206 #ifndef PRODUCT
9207 assert(_num_par_pushes >= n, "Too many pops?");
9208 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
9209 #endif
9210 return true;
9211 }
9213 // Single-threaded
9214 void CMSCollector::push_on_overflow_list(oop p) {
9215 NOT_PRODUCT(_num_par_pushes++;)
9216 assert(p->is_oop(), "Not an oop");
9217 preserve_mark_if_necessary(p);
9218 p->set_mark((markOop)_overflow_list);
9219 _overflow_list = p;
9220 }
9222 // Multi-threaded; use CAS to prepend to overflow list
9223 void CMSCollector::par_push_on_overflow_list(oop p) {
9224 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
9225 assert(p->is_oop(), "Not an oop");
9226 par_preserve_mark_if_necessary(p);
9227 oop observed_overflow_list = _overflow_list;
9228 oop cur_overflow_list;
9229 do {
9230 cur_overflow_list = observed_overflow_list;
9231 if (cur_overflow_list != BUSY) {
9232 p->set_mark(markOop(cur_overflow_list));
9233 } else {
9234 p->set_mark(NULL);
9235 }
9236 observed_overflow_list =
9237 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
9238 } while (cur_overflow_list != observed_overflow_list);
9239 }
9240 #undef BUSY
9242 // Single threaded
9243 // General Note on GrowableArray: pushes may silently fail
9244 // because we are (temporarily) out of C-heap for expanding
9245 // the stack. The problem is quite ubiquitous and affects
9246 // a lot of code in the JVM. The prudent thing for GrowableArray
9247 // to do (for now) is to exit with an error. However, that may
9248 // be too draconian in some cases because the caller may be
9249 // able to recover without much harm. For such cases, we
9250 // should probably introduce a "soft_push" method which returns
9251 // an indication of success or failure with the assumption that
9252 // the caller may be able to recover from a failure; code in
9253 // the VM can then be changed, incrementally, to deal with such
9254 // failures where possible, thus, incrementally hardening the VM
9255 // in such low resource situations.
9256 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9257 _preserved_oop_stack.push(p);
9258 _preserved_mark_stack.push(m);
9259 assert(m == p->mark(), "Mark word changed");
9260 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9261 "bijection");
9262 }
9264 // Single threaded
9265 void CMSCollector::preserve_mark_if_necessary(oop p) {
9266 markOop m = p->mark();
9267 if (m->must_be_preserved(p)) {
9268 preserve_mark_work(p, m);
9269 }
9270 }
9272 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9273 markOop m = p->mark();
9274 if (m->must_be_preserved(p)) {
9275 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9276 // Even though we read the mark word without holding
9277 // the lock, we are assured that it will not change
9278 // because we "own" this oop, so no other thread can
9279 // be trying to push it on the overflow list; see
9280 // the assertion in preserve_mark_work() that checks
9281 // that m == p->mark().
9282 preserve_mark_work(p, m);
9283 }
9284 }
9286 // We should be able to do this multi-threaded,
9287 // a chunk of stack being a task (this is
9288 // correct because each oop only ever appears
9289 // once in the overflow list. However, it's
9290 // not very easy to completely overlap this with
9291 // other operations, so will generally not be done
9292 // until all work's been completed. Because we
9293 // expect the preserved oop stack (set) to be small,
9294 // it's probably fine to do this single-threaded.
9295 // We can explore cleverer concurrent/overlapped/parallel
9296 // processing of preserved marks if we feel the
9297 // need for this in the future. Stack overflow should
9298 // be so rare in practice and, when it happens, its
9299 // effect on performance so great that this will
9300 // likely just be in the noise anyway.
9301 void CMSCollector::restore_preserved_marks_if_any() {
9302 assert(SafepointSynchronize::is_at_safepoint(),
9303 "world should be stopped");
9304 assert(Thread::current()->is_ConcurrentGC_thread() ||
9305 Thread::current()->is_VM_thread(),
9306 "should be single-threaded");
9307 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9308 "bijection");
9310 while (!_preserved_oop_stack.is_empty()) {
9311 oop p = _preserved_oop_stack.pop();
9312 assert(p->is_oop(), "Should be an oop");
9313 assert(_span.contains(p), "oop should be in _span");
9314 assert(p->mark() == markOopDesc::prototype(),
9315 "Set when taken from overflow list");
9316 markOop m = _preserved_mark_stack.pop();
9317 p->set_mark(m);
9318 }
9319 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9320 "stacks were cleared above");
9321 }
9323 #ifndef PRODUCT
9324 bool CMSCollector::no_preserved_marks() const {
9325 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9326 }
9327 #endif
9329 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
9330 {
9331 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9332 CMSAdaptiveSizePolicy* size_policy =
9333 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
9334 assert(size_policy->is_gc_cms_adaptive_size_policy(),
9335 "Wrong type for size policy");
9336 return size_policy;
9337 }
9339 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
9340 size_t desired_promo_size) {
9341 if (cur_promo_size < desired_promo_size) {
9342 size_t expand_bytes = desired_promo_size - cur_promo_size;
9343 if (PrintAdaptiveSizePolicy && Verbose) {
9344 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9345 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
9346 expand_bytes);
9347 }
9348 expand(expand_bytes,
9349 MinHeapDeltaBytes,
9350 CMSExpansionCause::_adaptive_size_policy);
9351 } else if (desired_promo_size < cur_promo_size) {
9352 size_t shrink_bytes = cur_promo_size - desired_promo_size;
9353 if (PrintAdaptiveSizePolicy && Verbose) {
9354 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9355 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
9356 shrink_bytes);
9357 }
9358 shrink(shrink_bytes);
9359 }
9360 }
9362 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
9363 GenCollectedHeap* gch = GenCollectedHeap::heap();
9364 CMSGCAdaptivePolicyCounters* counters =
9365 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
9366 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
9367 "Wrong kind of counters");
9368 return counters;
9369 }
9372 void ASConcurrentMarkSweepGeneration::update_counters() {
9373 if (UsePerfData) {
9374 _space_counters->update_all();
9375 _gen_counters->update_all();
9376 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9377 GenCollectedHeap* gch = GenCollectedHeap::heap();
9378 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9379 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9380 "Wrong gc statistics type");
9381 counters->update_counters(gc_stats_l);
9382 }
9383 }
9385 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
9386 if (UsePerfData) {
9387 _space_counters->update_used(used);
9388 _space_counters->update_capacity();
9389 _gen_counters->update_all();
9391 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9392 GenCollectedHeap* gch = GenCollectedHeap::heap();
9393 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9394 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9395 "Wrong gc statistics type");
9396 counters->update_counters(gc_stats_l);
9397 }
9398 }
9400 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9401 assert_locked_or_safepoint(Heap_lock);
9402 assert_lock_strong(freelistLock());
9403 HeapWord* old_end = _cmsSpace->end();
9404 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9405 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9406 FreeChunk* chunk_at_end = find_chunk_at_end();
9407 if (chunk_at_end == NULL) {
9408 // No room to shrink
9409 if (PrintGCDetails && Verbose) {
9410 gclog_or_tty->print_cr("No room to shrink: old_end "
9411 PTR_FORMAT " unallocated_start " PTR_FORMAT
9412 " chunk_at_end " PTR_FORMAT,
9413 old_end, unallocated_start, chunk_at_end);
9414 }
9415 return;
9416 } else {
9418 // Find the chunk at the end of the space and determine
9419 // how much it can be shrunk.
9420 size_t shrinkable_size_in_bytes = chunk_at_end->size();
9421 size_t aligned_shrinkable_size_in_bytes =
9422 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9423 assert(unallocated_start <= (HeapWord*) chunk_at_end->end(),
9424 "Inconsistent chunk at end of space");
9425 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9426 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9428 // Shrink the underlying space
9429 _virtual_space.shrink_by(bytes);
9430 if (PrintGCDetails && Verbose) {
9431 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9432 " desired_bytes " SIZE_FORMAT
9433 " shrinkable_size_in_bytes " SIZE_FORMAT
9434 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9435 " bytes " SIZE_FORMAT,
9436 desired_bytes, shrinkable_size_in_bytes,
9437 aligned_shrinkable_size_in_bytes, bytes);
9438 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
9439 " unallocated_start " SIZE_FORMAT,
9440 old_end, unallocated_start);
9441 }
9443 // If the space did shrink (shrinking is not guaranteed),
9444 // shrink the chunk at the end by the appropriate amount.
9445 if (((HeapWord*)_virtual_space.high()) < old_end) {
9446 size_t new_word_size =
9447 heap_word_size(_virtual_space.committed_size());
9449 // Have to remove the chunk from the dictionary because it is changing
9450 // size and might be someplace elsewhere in the dictionary.
9452 // Get the chunk at end, shrink it, and put it
9453 // back.
9454 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9455 size_t word_size_change = word_size_before - new_word_size;
9456 size_t chunk_at_end_old_size = chunk_at_end->size();
9457 assert(chunk_at_end_old_size >= word_size_change,
9458 "Shrink is too large");
9459 chunk_at_end->set_size(chunk_at_end_old_size -
9460 word_size_change);
9461 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9462 word_size_change);
9464 _cmsSpace->returnChunkToDictionary(chunk_at_end);
9466 MemRegion mr(_cmsSpace->bottom(), new_word_size);
9467 _bts->resize(new_word_size); // resize the block offset shared array
9468 Universe::heap()->barrier_set()->resize_covered_region(mr);
9469 _cmsSpace->assert_locked();
9470 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9472 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9474 // update the space and generation capacity counters
9475 if (UsePerfData) {
9476 _space_counters->update_capacity();
9477 _gen_counters->update_all();
9478 }
9480 if (Verbose && PrintGCDetails) {
9481 size_t new_mem_size = _virtual_space.committed_size();
9482 size_t old_mem_size = new_mem_size + bytes;
9483 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
9484 name(), old_mem_size/K, bytes/K, new_mem_size/K);
9485 }
9486 }
9488 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9489 "Inconsistency at end of space");
9490 assert(chunk_at_end->end() == (uintptr_t*) _cmsSpace->end(),
9491 "Shrinking is inconsistent");
9492 return;
9493 }
9494 }
9495 // Transfer some number of overflown objects to usual marking
9496 // stack. Return true if some objects were transferred.
9497 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9498 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9499 (size_t)ParGCDesiredObjsFromOverflowList);
9501 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9502 assert(_collector->overflow_list_is_empty() || res,
9503 "If list is not empty, we should have taken something");
9504 assert(!res || !_mark_stack->isEmpty(),
9505 "If we took something, it should now be on our stack");
9506 return res;
9507 }
9509 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9510 size_t res = _sp->block_size_no_stall(addr, _collector);
9511 if (_sp->block_is_obj(addr)) {
9512 if (_live_bit_map->isMarked(addr)) {
9513 // It can't have been dead in a previous cycle
9514 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9515 } else {
9516 _dead_bit_map->mark(addr); // mark the dead object
9517 }
9518 }
9519 // Could be 0, if the block size could not be computed without stalling.
9520 return res;
9521 }
9523 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9525 switch (phase) {
9526 case CMSCollector::InitialMarking:
9527 initialize(true /* fullGC */ ,
9528 cause /* cause of the GC */,
9529 true /* recordGCBeginTime */,
9530 true /* recordPreGCUsage */,
9531 false /* recordPeakUsage */,
9532 false /* recordPostGCusage */,
9533 true /* recordAccumulatedGCTime */,
9534 false /* recordGCEndTime */,
9535 false /* countCollection */ );
9536 break;
9538 case CMSCollector::FinalMarking:
9539 initialize(true /* fullGC */ ,
9540 cause /* cause of the GC */,
9541 false /* recordGCBeginTime */,
9542 false /* recordPreGCUsage */,
9543 false /* recordPeakUsage */,
9544 false /* recordPostGCusage */,
9545 true /* recordAccumulatedGCTime */,
9546 false /* recordGCEndTime */,
9547 false /* countCollection */ );
9548 break;
9550 case CMSCollector::Sweeping:
9551 initialize(true /* fullGC */ ,
9552 cause /* cause of the GC */,
9553 false /* recordGCBeginTime */,
9554 false /* recordPreGCUsage */,
9555 true /* recordPeakUsage */,
9556 true /* recordPostGCusage */,
9557 false /* recordAccumulatedGCTime */,
9558 true /* recordGCEndTime */,
9559 true /* countCollection */ );
9560 break;
9562 default:
9563 ShouldNotReachHere();
9564 }
9565 }