Sat, 23 Nov 2013 12:25:13 +0100
8028128: Add a type safe alternative for working with counter based data
Reviewed-by: dholmes, 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.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
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).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
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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, _last_metaspace_summary);
2500 }
2502 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs, GCCause::Cause cause) {
2503 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2504 "Foreground collector should be waiting, not executing");
2505 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2506 "may only be done by the VM Thread with the world stopped");
2507 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2508 "VM thread should have CMS token");
2510 NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2511 true, NULL);)
2512 if (UseAdaptiveSizePolicy) {
2513 size_policy()->ms_collection_begin();
2514 }
2515 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2517 HandleMark hm; // Discard invalid handles created during verification
2519 if (VerifyBeforeGC &&
2520 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2521 Universe::verify();
2522 }
2524 // Snapshot the soft reference policy to be used in this collection cycle.
2525 ref_processor()->setup_policy(clear_all_soft_refs);
2527 // Decide if class unloading should be done
2528 update_should_unload_classes();
2530 bool init_mark_was_synchronous = false; // until proven otherwise
2531 while (_collectorState != Idling) {
2532 if (TraceCMSState) {
2533 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2534 Thread::current(), _collectorState);
2535 }
2536 switch (_collectorState) {
2537 case InitialMarking:
2538 register_foreground_gc_start(cause);
2539 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2540 checkpointRootsInitial(false);
2541 assert(_collectorState == Marking, "Collector state should have changed"
2542 " within checkpointRootsInitial()");
2543 break;
2544 case Marking:
2545 // initial marking in checkpointRootsInitialWork has been completed
2546 if (VerifyDuringGC &&
2547 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2548 Universe::verify("Verify before initial mark: ");
2549 }
2550 {
2551 bool res = markFromRoots(false);
2552 assert(res && _collectorState == FinalMarking, "Collector state should "
2553 "have changed");
2554 break;
2555 }
2556 case FinalMarking:
2557 if (VerifyDuringGC &&
2558 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2559 Universe::verify("Verify before re-mark: ");
2560 }
2561 checkpointRootsFinal(false, clear_all_soft_refs,
2562 init_mark_was_synchronous);
2563 assert(_collectorState == Sweeping, "Collector state should not "
2564 "have changed within checkpointRootsFinal()");
2565 break;
2566 case Sweeping:
2567 // final marking in checkpointRootsFinal has been completed
2568 if (VerifyDuringGC &&
2569 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2570 Universe::verify("Verify before sweep: ");
2571 }
2572 sweep(false);
2573 assert(_collectorState == Resizing, "Incorrect state");
2574 break;
2575 case Resizing: {
2576 // Sweeping has been completed; the actual resize in this case
2577 // is done separately; nothing to be done in this state.
2578 _collectorState = Resetting;
2579 break;
2580 }
2581 case Resetting:
2582 // The heap has been resized.
2583 if (VerifyDuringGC &&
2584 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2585 Universe::verify("Verify before reset: ");
2586 }
2587 save_heap_summary();
2588 reset(false);
2589 assert(_collectorState == Idling, "Collector state should "
2590 "have changed");
2591 break;
2592 case Precleaning:
2593 case AbortablePreclean:
2594 // Elide the preclean phase
2595 _collectorState = FinalMarking;
2596 break;
2597 default:
2598 ShouldNotReachHere();
2599 }
2600 if (TraceCMSState) {
2601 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2602 Thread::current(), _collectorState);
2603 }
2604 }
2606 if (UseAdaptiveSizePolicy) {
2607 GenCollectedHeap* gch = GenCollectedHeap::heap();
2608 size_policy()->ms_collection_end(gch->gc_cause());
2609 }
2611 if (VerifyAfterGC &&
2612 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2613 Universe::verify();
2614 }
2615 if (TraceCMSState) {
2616 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2617 " exiting collection CMS state %d",
2618 Thread::current(), _collectorState);
2619 }
2620 }
2622 bool CMSCollector::waitForForegroundGC() {
2623 bool res = false;
2624 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2625 "CMS thread should have CMS token");
2626 // Block the foreground collector until the
2627 // background collectors decides whether to
2628 // yield.
2629 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2630 _foregroundGCShouldWait = true;
2631 if (_foregroundGCIsActive) {
2632 // The background collector yields to the
2633 // foreground collector and returns a value
2634 // indicating that it has yielded. The foreground
2635 // collector can proceed.
2636 res = true;
2637 _foregroundGCShouldWait = false;
2638 ConcurrentMarkSweepThread::clear_CMS_flag(
2639 ConcurrentMarkSweepThread::CMS_cms_has_token);
2640 ConcurrentMarkSweepThread::set_CMS_flag(
2641 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2642 // Get a possibly blocked foreground thread going
2643 CGC_lock->notify();
2644 if (TraceCMSState) {
2645 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2646 Thread::current(), _collectorState);
2647 }
2648 while (_foregroundGCIsActive) {
2649 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2650 }
2651 ConcurrentMarkSweepThread::set_CMS_flag(
2652 ConcurrentMarkSweepThread::CMS_cms_has_token);
2653 ConcurrentMarkSweepThread::clear_CMS_flag(
2654 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2655 }
2656 if (TraceCMSState) {
2657 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2658 Thread::current(), _collectorState);
2659 }
2660 return res;
2661 }
2663 // Because of the need to lock the free lists and other structures in
2664 // the collector, common to all the generations that the collector is
2665 // collecting, we need the gc_prologues of individual CMS generations
2666 // delegate to their collector. It may have been simpler had the
2667 // current infrastructure allowed one to call a prologue on a
2668 // collector. In the absence of that we have the generation's
2669 // prologue delegate to the collector, which delegates back
2670 // some "local" work to a worker method in the individual generations
2671 // that it's responsible for collecting, while itself doing any
2672 // work common to all generations it's responsible for. A similar
2673 // comment applies to the gc_epilogue()'s.
2674 // The role of the varaible _between_prologue_and_epilogue is to
2675 // enforce the invocation protocol.
2676 void CMSCollector::gc_prologue(bool full) {
2677 // Call gc_prologue_work() for the CMSGen
2678 // we are responsible for.
2680 // The following locking discipline assumes that we are only called
2681 // when the world is stopped.
2682 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2684 // The CMSCollector prologue must call the gc_prologues for the
2685 // "generations" that it's responsible
2686 // for.
2688 assert( Thread::current()->is_VM_thread()
2689 || ( CMSScavengeBeforeRemark
2690 && Thread::current()->is_ConcurrentGC_thread()),
2691 "Incorrect thread type for prologue execution");
2693 if (_between_prologue_and_epilogue) {
2694 // We have already been invoked; this is a gc_prologue delegation
2695 // from yet another CMS generation that we are responsible for, just
2696 // ignore it since all relevant work has already been done.
2697 return;
2698 }
2700 // set a bit saying prologue has been called; cleared in epilogue
2701 _between_prologue_and_epilogue = true;
2702 // Claim locks for common data structures, then call gc_prologue_work()
2703 // for each CMSGen.
2705 getFreelistLocks(); // gets free list locks on constituent spaces
2706 bitMapLock()->lock_without_safepoint_check();
2708 // Should call gc_prologue_work() for all cms gens we are responsible for
2709 bool duringMarking = _collectorState >= Marking
2710 && _collectorState < Sweeping;
2712 // The young collections clear the modified oops state, which tells if
2713 // there are any modified oops in the class. The remark phase also needs
2714 // that information. Tell the young collection to save the union of all
2715 // modified klasses.
2716 if (duringMarking) {
2717 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2718 }
2720 bool registerClosure = duringMarking;
2722 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2723 &_modUnionClosurePar
2724 : &_modUnionClosure;
2725 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2727 if (!full) {
2728 stats().record_gc0_begin();
2729 }
2730 }
2732 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2734 _capacity_at_prologue = capacity();
2735 _used_at_prologue = used();
2737 // Delegate to CMScollector which knows how to coordinate between
2738 // this and any other CMS generations that it is responsible for
2739 // collecting.
2740 collector()->gc_prologue(full);
2741 }
2743 // This is a "private" interface for use by this generation's CMSCollector.
2744 // Not to be called directly by any other entity (for instance,
2745 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2746 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2747 bool registerClosure, ModUnionClosure* modUnionClosure) {
2748 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2749 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2750 "Should be NULL");
2751 if (registerClosure) {
2752 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2753 }
2754 cmsSpace()->gc_prologue();
2755 // Clear stat counters
2756 NOT_PRODUCT(
2757 assert(_numObjectsPromoted == 0, "check");
2758 assert(_numWordsPromoted == 0, "check");
2759 if (Verbose && PrintGC) {
2760 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2761 SIZE_FORMAT" bytes concurrently",
2762 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2763 }
2764 _numObjectsAllocated = 0;
2765 _numWordsAllocated = 0;
2766 )
2767 }
2769 void CMSCollector::gc_epilogue(bool full) {
2770 // The following locking discipline assumes that we are only called
2771 // when the world is stopped.
2772 assert(SafepointSynchronize::is_at_safepoint(),
2773 "world is stopped assumption");
2775 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2776 // if linear allocation blocks need to be appropriately marked to allow the
2777 // the blocks to be parsable. We also check here whether we need to nudge the
2778 // CMS collector thread to start a new cycle (if it's not already active).
2779 assert( Thread::current()->is_VM_thread()
2780 || ( CMSScavengeBeforeRemark
2781 && Thread::current()->is_ConcurrentGC_thread()),
2782 "Incorrect thread type for epilogue execution");
2784 if (!_between_prologue_and_epilogue) {
2785 // We have already been invoked; this is a gc_epilogue delegation
2786 // from yet another CMS generation that we are responsible for, just
2787 // ignore it since all relevant work has already been done.
2788 return;
2789 }
2790 assert(haveFreelistLocks(), "must have freelist locks");
2791 assert_lock_strong(bitMapLock());
2793 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2795 _cmsGen->gc_epilogue_work(full);
2797 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2798 // in case sampling was not already enabled, enable it
2799 _start_sampling = true;
2800 }
2801 // reset _eden_chunk_array so sampling starts afresh
2802 _eden_chunk_index = 0;
2804 size_t cms_used = _cmsGen->cmsSpace()->used();
2806 // update performance counters - this uses a special version of
2807 // update_counters() that allows the utilization to be passed as a
2808 // parameter, avoiding multiple calls to used().
2809 //
2810 _cmsGen->update_counters(cms_used);
2812 if (CMSIncrementalMode) {
2813 icms_update_allocation_limits();
2814 }
2816 bitMapLock()->unlock();
2817 releaseFreelistLocks();
2819 if (!CleanChunkPoolAsync) {
2820 Chunk::clean_chunk_pool();
2821 }
2823 set_did_compact(false);
2824 _between_prologue_and_epilogue = false; // ready for next cycle
2825 }
2827 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2828 collector()->gc_epilogue(full);
2830 // Also reset promotion tracking in par gc thread states.
2831 if (CollectedHeap::use_parallel_gc_threads()) {
2832 for (uint i = 0; i < ParallelGCThreads; i++) {
2833 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2834 }
2835 }
2836 }
2838 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2839 assert(!incremental_collection_failed(), "Should have been cleared");
2840 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2841 cmsSpace()->gc_epilogue();
2842 // Print stat counters
2843 NOT_PRODUCT(
2844 assert(_numObjectsAllocated == 0, "check");
2845 assert(_numWordsAllocated == 0, "check");
2846 if (Verbose && PrintGC) {
2847 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2848 SIZE_FORMAT" bytes",
2849 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2850 }
2851 _numObjectsPromoted = 0;
2852 _numWordsPromoted = 0;
2853 )
2855 if (PrintGC && Verbose) {
2856 // Call down the chain in contiguous_available needs the freelistLock
2857 // so print this out before releasing the freeListLock.
2858 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2859 contiguous_available());
2860 }
2861 }
2863 #ifndef PRODUCT
2864 bool CMSCollector::have_cms_token() {
2865 Thread* thr = Thread::current();
2866 if (thr->is_VM_thread()) {
2867 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2868 } else if (thr->is_ConcurrentGC_thread()) {
2869 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2870 } else if (thr->is_GC_task_thread()) {
2871 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2872 ParGCRareEvent_lock->owned_by_self();
2873 }
2874 return false;
2875 }
2876 #endif
2878 // Check reachability of the given heap address in CMS generation,
2879 // treating all other generations as roots.
2880 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2881 // We could "guarantee" below, rather than assert, but i'll
2882 // leave these as "asserts" so that an adventurous debugger
2883 // could try this in the product build provided some subset of
2884 // the conditions were met, provided they were intersted in the
2885 // results and knew that the computation below wouldn't interfere
2886 // with other concurrent computations mutating the structures
2887 // being read or written.
2888 assert(SafepointSynchronize::is_at_safepoint(),
2889 "Else mutations in object graph will make answer suspect");
2890 assert(have_cms_token(), "Should hold cms token");
2891 assert(haveFreelistLocks(), "must hold free list locks");
2892 assert_lock_strong(bitMapLock());
2894 // Clear the marking bit map array before starting, but, just
2895 // for kicks, first report if the given address is already marked
2896 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2897 _markBitMap.isMarked(addr) ? "" : " not");
2899 if (verify_after_remark()) {
2900 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2901 bool result = verification_mark_bm()->isMarked(addr);
2902 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2903 result ? "IS" : "is NOT");
2904 return result;
2905 } else {
2906 gclog_or_tty->print_cr("Could not compute result");
2907 return false;
2908 }
2909 }
2912 void
2913 CMSCollector::print_on_error(outputStream* st) {
2914 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2915 if (collector != NULL) {
2916 CMSBitMap* bitmap = &collector->_markBitMap;
2917 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, bitmap);
2918 bitmap->print_on_error(st, " Bits: ");
2920 st->cr();
2922 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2923 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, mut_bitmap);
2924 mut_bitmap->print_on_error(st, " Bits: ");
2925 }
2926 }
2928 ////////////////////////////////////////////////////////
2929 // CMS Verification Support
2930 ////////////////////////////////////////////////////////
2931 // Following the remark phase, the following invariant
2932 // should hold -- each object in the CMS heap which is
2933 // marked in markBitMap() should be marked in the verification_mark_bm().
2935 class VerifyMarkedClosure: public BitMapClosure {
2936 CMSBitMap* _marks;
2937 bool _failed;
2939 public:
2940 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2942 bool do_bit(size_t offset) {
2943 HeapWord* addr = _marks->offsetToHeapWord(offset);
2944 if (!_marks->isMarked(addr)) {
2945 oop(addr)->print_on(gclog_or_tty);
2946 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2947 _failed = true;
2948 }
2949 return true;
2950 }
2952 bool failed() { return _failed; }
2953 };
2955 bool CMSCollector::verify_after_remark(bool silent) {
2956 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2957 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2958 static bool init = false;
2960 assert(SafepointSynchronize::is_at_safepoint(),
2961 "Else mutations in object graph will make answer suspect");
2962 assert(have_cms_token(),
2963 "Else there may be mutual interference in use of "
2964 " verification data structures");
2965 assert(_collectorState > Marking && _collectorState <= Sweeping,
2966 "Else marking info checked here may be obsolete");
2967 assert(haveFreelistLocks(), "must hold free list locks");
2968 assert_lock_strong(bitMapLock());
2971 // Allocate marking bit map if not already allocated
2972 if (!init) { // first time
2973 if (!verification_mark_bm()->allocate(_span)) {
2974 return false;
2975 }
2976 init = true;
2977 }
2979 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2981 // Turn off refs discovery -- so we will be tracing through refs.
2982 // This is as intended, because by this time
2983 // GC must already have cleared any refs that need to be cleared,
2984 // and traced those that need to be marked; moreover,
2985 // the marking done here is not going to intefere in any
2986 // way with the marking information used by GC.
2987 NoRefDiscovery no_discovery(ref_processor());
2989 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2991 // Clear any marks from a previous round
2992 verification_mark_bm()->clear_all();
2993 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2994 verify_work_stacks_empty();
2996 GenCollectedHeap* gch = GenCollectedHeap::heap();
2997 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2998 // Update the saved marks which may affect the root scans.
2999 gch->save_marks();
3001 if (CMSRemarkVerifyVariant == 1) {
3002 // In this first variant of verification, we complete
3003 // all marking, then check if the new marks-verctor is
3004 // a subset of the CMS marks-vector.
3005 verify_after_remark_work_1();
3006 } else if (CMSRemarkVerifyVariant == 2) {
3007 // In this second variant of verification, we flag an error
3008 // (i.e. an object reachable in the new marks-vector not reachable
3009 // in the CMS marks-vector) immediately, also indicating the
3010 // identify of an object (A) that references the unmarked object (B) --
3011 // presumably, a mutation to A failed to be picked up by preclean/remark?
3012 verify_after_remark_work_2();
3013 } else {
3014 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
3015 CMSRemarkVerifyVariant);
3016 }
3017 if (!silent) gclog_or_tty->print(" done] ");
3018 return true;
3019 }
3021 void CMSCollector::verify_after_remark_work_1() {
3022 ResourceMark rm;
3023 HandleMark hm;
3024 GenCollectedHeap* gch = GenCollectedHeap::heap();
3026 // Get a clear set of claim bits for the strong roots processing to work with.
3027 ClassLoaderDataGraph::clear_claimed_marks();
3029 // Mark from roots one level into CMS
3030 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
3031 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3033 gch->gen_process_strong_roots(_cmsGen->level(),
3034 true, // younger gens are roots
3035 true, // activate StrongRootsScope
3036 false, // not scavenging
3037 SharedHeap::ScanningOption(roots_scanning_options()),
3038 ¬Older,
3039 true, // walk code active on stacks
3040 NULL,
3041 NULL); // SSS: Provide correct closure
3043 // Now mark from the roots
3044 MarkFromRootsClosure markFromRootsClosure(this, _span,
3045 verification_mark_bm(), verification_mark_stack(),
3046 false /* don't yield */, true /* verifying */);
3047 assert(_restart_addr == NULL, "Expected pre-condition");
3048 verification_mark_bm()->iterate(&markFromRootsClosure);
3049 while (_restart_addr != NULL) {
3050 // Deal with stack overflow: by restarting at the indicated
3051 // address.
3052 HeapWord* ra = _restart_addr;
3053 markFromRootsClosure.reset(ra);
3054 _restart_addr = NULL;
3055 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3056 }
3057 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3058 verify_work_stacks_empty();
3060 // Marking completed -- now verify that each bit marked in
3061 // verification_mark_bm() is also marked in markBitMap(); flag all
3062 // errors by printing corresponding objects.
3063 VerifyMarkedClosure vcl(markBitMap());
3064 verification_mark_bm()->iterate(&vcl);
3065 if (vcl.failed()) {
3066 gclog_or_tty->print("Verification failed");
3067 Universe::heap()->print_on(gclog_or_tty);
3068 fatal("CMS: failed marking verification after remark");
3069 }
3070 }
3072 class VerifyKlassOopsKlassClosure : public KlassClosure {
3073 class VerifyKlassOopsClosure : public OopClosure {
3074 CMSBitMap* _bitmap;
3075 public:
3076 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
3077 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
3078 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
3079 } _oop_closure;
3080 public:
3081 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
3082 void do_klass(Klass* k) {
3083 k->oops_do(&_oop_closure);
3084 }
3085 };
3087 void CMSCollector::verify_after_remark_work_2() {
3088 ResourceMark rm;
3089 HandleMark hm;
3090 GenCollectedHeap* gch = GenCollectedHeap::heap();
3092 // Get a clear set of claim bits for the strong roots processing to work with.
3093 ClassLoaderDataGraph::clear_claimed_marks();
3095 // Mark from roots one level into CMS
3096 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
3097 markBitMap());
3098 CMKlassClosure klass_closure(¬Older);
3100 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3101 gch->gen_process_strong_roots(_cmsGen->level(),
3102 true, // younger gens are roots
3103 true, // activate StrongRootsScope
3104 false, // not scavenging
3105 SharedHeap::ScanningOption(roots_scanning_options()),
3106 ¬Older,
3107 true, // walk code active on stacks
3108 NULL,
3109 &klass_closure);
3111 // Now mark from the roots
3112 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
3113 verification_mark_bm(), markBitMap(), verification_mark_stack());
3114 assert(_restart_addr == NULL, "Expected pre-condition");
3115 verification_mark_bm()->iterate(&markFromRootsClosure);
3116 while (_restart_addr != NULL) {
3117 // Deal with stack overflow: by restarting at the indicated
3118 // address.
3119 HeapWord* ra = _restart_addr;
3120 markFromRootsClosure.reset(ra);
3121 _restart_addr = NULL;
3122 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3123 }
3124 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3125 verify_work_stacks_empty();
3127 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
3128 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
3130 // Marking completed -- now verify that each bit marked in
3131 // verification_mark_bm() is also marked in markBitMap(); flag all
3132 // errors by printing corresponding objects.
3133 VerifyMarkedClosure vcl(markBitMap());
3134 verification_mark_bm()->iterate(&vcl);
3135 assert(!vcl.failed(), "Else verification above should not have succeeded");
3136 }
3138 void ConcurrentMarkSweepGeneration::save_marks() {
3139 // delegate to CMS space
3140 cmsSpace()->save_marks();
3141 for (uint i = 0; i < ParallelGCThreads; i++) {
3142 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3143 }
3144 }
3146 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3147 return cmsSpace()->no_allocs_since_save_marks();
3148 }
3150 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3151 \
3152 void ConcurrentMarkSweepGeneration:: \
3153 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3154 cl->set_generation(this); \
3155 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3156 cl->reset_generation(); \
3157 save_marks(); \
3158 }
3160 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3162 void
3163 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3164 cl->set_generation(this);
3165 younger_refs_in_space_iterate(_cmsSpace, cl);
3166 cl->reset_generation();
3167 }
3169 void
3170 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, ExtendedOopClosure* cl) {
3171 if (freelistLock()->owned_by_self()) {
3172 Generation::oop_iterate(mr, cl);
3173 } else {
3174 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3175 Generation::oop_iterate(mr, cl);
3176 }
3177 }
3179 void
3180 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
3181 if (freelistLock()->owned_by_self()) {
3182 Generation::oop_iterate(cl);
3183 } else {
3184 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3185 Generation::oop_iterate(cl);
3186 }
3187 }
3189 void
3190 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3191 if (freelistLock()->owned_by_self()) {
3192 Generation::object_iterate(cl);
3193 } else {
3194 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3195 Generation::object_iterate(cl);
3196 }
3197 }
3199 void
3200 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3201 if (freelistLock()->owned_by_self()) {
3202 Generation::safe_object_iterate(cl);
3203 } else {
3204 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3205 Generation::safe_object_iterate(cl);
3206 }
3207 }
3209 void
3210 ConcurrentMarkSweepGeneration::post_compact() {
3211 }
3213 void
3214 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3215 // Fix the linear allocation blocks to look like free blocks.
3217 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3218 // are not called when the heap is verified during universe initialization and
3219 // at vm shutdown.
3220 if (freelistLock()->owned_by_self()) {
3221 cmsSpace()->prepare_for_verify();
3222 } else {
3223 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3224 cmsSpace()->prepare_for_verify();
3225 }
3226 }
3228 void
3229 ConcurrentMarkSweepGeneration::verify() {
3230 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3231 // are not called when the heap is verified during universe initialization and
3232 // at vm shutdown.
3233 if (freelistLock()->owned_by_self()) {
3234 cmsSpace()->verify();
3235 } else {
3236 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3237 cmsSpace()->verify();
3238 }
3239 }
3241 void CMSCollector::verify() {
3242 _cmsGen->verify();
3243 }
3245 #ifndef PRODUCT
3246 bool CMSCollector::overflow_list_is_empty() const {
3247 assert(_num_par_pushes >= 0, "Inconsistency");
3248 if (_overflow_list == NULL) {
3249 assert(_num_par_pushes == 0, "Inconsistency");
3250 }
3251 return _overflow_list == NULL;
3252 }
3254 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3255 // merely consolidate assertion checks that appear to occur together frequently.
3256 void CMSCollector::verify_work_stacks_empty() const {
3257 assert(_markStack.isEmpty(), "Marking stack should be empty");
3258 assert(overflow_list_is_empty(), "Overflow list should be empty");
3259 }
3261 void CMSCollector::verify_overflow_empty() const {
3262 assert(overflow_list_is_empty(), "Overflow list should be empty");
3263 assert(no_preserved_marks(), "No preserved marks");
3264 }
3265 #endif // PRODUCT
3267 // Decide if we want to enable class unloading as part of the
3268 // ensuing concurrent GC cycle. We will collect and
3269 // unload classes if it's the case that:
3270 // (1) an explicit gc request has been made and the flag
3271 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3272 // (2) (a) class unloading is enabled at the command line, and
3273 // (b) old gen is getting really full
3274 // NOTE: Provided there is no change in the state of the heap between
3275 // calls to this method, it should have idempotent results. Moreover,
3276 // its results should be monotonically increasing (i.e. going from 0 to 1,
3277 // but not 1 to 0) between successive calls between which the heap was
3278 // not collected. For the implementation below, it must thus rely on
3279 // the property that concurrent_cycles_since_last_unload()
3280 // will not decrease unless a collection cycle happened and that
3281 // _cmsGen->is_too_full() are
3282 // themselves also monotonic in that sense. See check_monotonicity()
3283 // below.
3284 void CMSCollector::update_should_unload_classes() {
3285 _should_unload_classes = false;
3286 // Condition 1 above
3287 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3288 _should_unload_classes = true;
3289 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3290 // Disjuncts 2.b.(i,ii,iii) above
3291 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3292 CMSClassUnloadingMaxInterval)
3293 || _cmsGen->is_too_full();
3294 }
3295 }
3297 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3298 bool res = should_concurrent_collect();
3299 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3300 return res;
3301 }
3303 void CMSCollector::setup_cms_unloading_and_verification_state() {
3304 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3305 || VerifyBeforeExit;
3306 const int rso = SharedHeap::SO_Strings | SharedHeap::SO_CodeCache;
3308 // We set the proper root for this CMS cycle here.
3309 if (should_unload_classes()) { // Should unload classes this cycle
3310 remove_root_scanning_option(SharedHeap::SO_AllClasses);
3311 add_root_scanning_option(SharedHeap::SO_SystemClasses);
3312 remove_root_scanning_option(rso); // Shrink the root set appropriately
3313 set_verifying(should_verify); // Set verification state for this cycle
3314 return; // Nothing else needs to be done at this time
3315 }
3317 // Not unloading classes this cycle
3318 assert(!should_unload_classes(), "Inconsitency!");
3319 remove_root_scanning_option(SharedHeap::SO_SystemClasses);
3320 add_root_scanning_option(SharedHeap::SO_AllClasses);
3322 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3323 // Include symbols, strings and code cache elements to prevent their resurrection.
3324 add_root_scanning_option(rso);
3325 set_verifying(true);
3326 } else if (verifying() && !should_verify) {
3327 // We were verifying, but some verification flags got disabled.
3328 set_verifying(false);
3329 // Exclude symbols, strings and code cache elements from root scanning to
3330 // reduce IM and RM pauses.
3331 remove_root_scanning_option(rso);
3332 }
3333 }
3336 #ifndef PRODUCT
3337 HeapWord* CMSCollector::block_start(const void* p) const {
3338 const HeapWord* addr = (HeapWord*)p;
3339 if (_span.contains(p)) {
3340 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3341 return _cmsGen->cmsSpace()->block_start(p);
3342 }
3343 }
3344 return NULL;
3345 }
3346 #endif
3348 HeapWord*
3349 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3350 bool tlab,
3351 bool parallel) {
3352 CMSSynchronousYieldRequest yr;
3353 assert(!tlab, "Can't deal with TLAB allocation");
3354 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3355 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3356 CMSExpansionCause::_satisfy_allocation);
3357 if (GCExpandToAllocateDelayMillis > 0) {
3358 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3359 }
3360 return have_lock_and_allocate(word_size, tlab);
3361 }
3363 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3364 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3365 // to CardGeneration and share it...
3366 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3367 return CardGeneration::expand(bytes, expand_bytes);
3368 }
3370 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3371 CMSExpansionCause::Cause cause)
3372 {
3374 bool success = expand(bytes, expand_bytes);
3376 // remember why we expanded; this information is used
3377 // by shouldConcurrentCollect() when making decisions on whether to start
3378 // a new CMS cycle.
3379 if (success) {
3380 set_expansion_cause(cause);
3381 if (PrintGCDetails && Verbose) {
3382 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3383 CMSExpansionCause::to_string(cause));
3384 }
3385 }
3386 }
3388 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3389 HeapWord* res = NULL;
3390 MutexLocker x(ParGCRareEvent_lock);
3391 while (true) {
3392 // Expansion by some other thread might make alloc OK now:
3393 res = ps->lab.alloc(word_sz);
3394 if (res != NULL) return res;
3395 // If there's not enough expansion space available, give up.
3396 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3397 return NULL;
3398 }
3399 // Otherwise, we try expansion.
3400 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3401 CMSExpansionCause::_allocate_par_lab);
3402 // Now go around the loop and try alloc again;
3403 // A competing par_promote might beat us to the expansion space,
3404 // so we may go around the loop again if promotion fails agaion.
3405 if (GCExpandToAllocateDelayMillis > 0) {
3406 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3407 }
3408 }
3409 }
3412 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3413 PromotionInfo* promo) {
3414 MutexLocker x(ParGCRareEvent_lock);
3415 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3416 while (true) {
3417 // Expansion by some other thread might make alloc OK now:
3418 if (promo->ensure_spooling_space()) {
3419 assert(promo->has_spooling_space(),
3420 "Post-condition of successful ensure_spooling_space()");
3421 return true;
3422 }
3423 // If there's not enough expansion space available, give up.
3424 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3425 return false;
3426 }
3427 // Otherwise, we try expansion.
3428 expand(refill_size_bytes, MinHeapDeltaBytes,
3429 CMSExpansionCause::_allocate_par_spooling_space);
3430 // Now go around the loop and try alloc again;
3431 // A competing allocation might beat us to the expansion space,
3432 // so we may go around the loop again if allocation fails again.
3433 if (GCExpandToAllocateDelayMillis > 0) {
3434 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3435 }
3436 }
3437 }
3440 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3441 assert_locked_or_safepoint(ExpandHeap_lock);
3442 // Shrink committed space
3443 _virtual_space.shrink_by(bytes);
3444 // Shrink space; this also shrinks the space's BOT
3445 _cmsSpace->set_end((HeapWord*) _virtual_space.high());
3446 size_t new_word_size = heap_word_size(_cmsSpace->capacity());
3447 // Shrink the shared block offset array
3448 _bts->resize(new_word_size);
3449 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3450 // Shrink the card table
3451 Universe::heap()->barrier_set()->resize_covered_region(mr);
3453 if (Verbose && PrintGC) {
3454 size_t new_mem_size = _virtual_space.committed_size();
3455 size_t old_mem_size = new_mem_size + bytes;
3456 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3457 name(), old_mem_size/K, new_mem_size/K);
3458 }
3459 }
3461 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3462 assert_locked_or_safepoint(Heap_lock);
3463 size_t size = ReservedSpace::page_align_size_down(bytes);
3464 // Only shrink if a compaction was done so that all the free space
3465 // in the generation is in a contiguous block at the end.
3466 if (size > 0 && did_compact()) {
3467 shrink_by(size);
3468 }
3469 }
3471 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3472 assert_locked_or_safepoint(Heap_lock);
3473 bool result = _virtual_space.expand_by(bytes);
3474 if (result) {
3475 size_t new_word_size =
3476 heap_word_size(_virtual_space.committed_size());
3477 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3478 _bts->resize(new_word_size); // resize the block offset shared array
3479 Universe::heap()->barrier_set()->resize_covered_region(mr);
3480 // Hmmmm... why doesn't CFLS::set_end verify locking?
3481 // This is quite ugly; FIX ME XXX
3482 _cmsSpace->assert_locked(freelistLock());
3483 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3485 // update the space and generation capacity counters
3486 if (UsePerfData) {
3487 _space_counters->update_capacity();
3488 _gen_counters->update_all();
3489 }
3491 if (Verbose && PrintGC) {
3492 size_t new_mem_size = _virtual_space.committed_size();
3493 size_t old_mem_size = new_mem_size - bytes;
3494 gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3495 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3496 }
3497 }
3498 return result;
3499 }
3501 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3502 assert_locked_or_safepoint(Heap_lock);
3503 bool success = true;
3504 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3505 if (remaining_bytes > 0) {
3506 success = grow_by(remaining_bytes);
3507 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3508 }
3509 return success;
3510 }
3512 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
3513 assert_locked_or_safepoint(Heap_lock);
3514 assert_lock_strong(freelistLock());
3515 if (PrintGCDetails && Verbose) {
3516 warning("Shrinking of CMS not yet implemented");
3517 }
3518 return;
3519 }
3522 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3523 // phases.
3524 class CMSPhaseAccounting: public StackObj {
3525 public:
3526 CMSPhaseAccounting(CMSCollector *collector,
3527 const char *phase,
3528 bool print_cr = true);
3529 ~CMSPhaseAccounting();
3531 private:
3532 CMSCollector *_collector;
3533 const char *_phase;
3534 elapsedTimer _wallclock;
3535 bool _print_cr;
3537 public:
3538 // Not MT-safe; so do not pass around these StackObj's
3539 // where they may be accessed by other threads.
3540 jlong wallclock_millis() {
3541 assert(_wallclock.is_active(), "Wall clock should not stop");
3542 _wallclock.stop(); // to record time
3543 jlong ret = _wallclock.milliseconds();
3544 _wallclock.start(); // restart
3545 return ret;
3546 }
3547 };
3549 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3550 const char *phase,
3551 bool print_cr) :
3552 _collector(collector), _phase(phase), _print_cr(print_cr) {
3554 if (PrintCMSStatistics != 0) {
3555 _collector->resetYields();
3556 }
3557 if (PrintGCDetails) {
3558 gclog_or_tty->date_stamp(PrintGCDateStamps);
3559 gclog_or_tty->stamp(PrintGCTimeStamps);
3560 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
3561 _collector->cmsGen()->short_name(), _phase);
3562 }
3563 _collector->resetTimer();
3564 _wallclock.start();
3565 _collector->startTimer();
3566 }
3568 CMSPhaseAccounting::~CMSPhaseAccounting() {
3569 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3570 _collector->stopTimer();
3571 _wallclock.stop();
3572 if (PrintGCDetails) {
3573 gclog_or_tty->date_stamp(PrintGCDateStamps);
3574 gclog_or_tty->stamp(PrintGCTimeStamps);
3575 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3576 _collector->cmsGen()->short_name(),
3577 _phase, _collector->timerValue(), _wallclock.seconds());
3578 if (_print_cr) {
3579 gclog_or_tty->print_cr("");
3580 }
3581 if (PrintCMSStatistics != 0) {
3582 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3583 _collector->yields());
3584 }
3585 }
3586 }
3588 // CMS work
3590 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
3591 class CMSParMarkTask : public AbstractGangTask {
3592 protected:
3593 CMSCollector* _collector;
3594 int _n_workers;
3595 CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
3596 AbstractGangTask(name),
3597 _collector(collector),
3598 _n_workers(n_workers) {}
3599 // Work method in support of parallel rescan ... of young gen spaces
3600 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
3601 ContiguousSpace* space,
3602 HeapWord** chunk_array, size_t chunk_top);
3603 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
3604 };
3606 // Parallel initial mark task
3607 class CMSParInitialMarkTask: public CMSParMarkTask {
3608 public:
3609 CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
3610 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
3611 collector, n_workers) {}
3612 void work(uint worker_id);
3613 };
3615 // Checkpoint the roots into this generation from outside
3616 // this generation. [Note this initial checkpoint need only
3617 // be approximate -- we'll do a catch up phase subsequently.]
3618 void CMSCollector::checkpointRootsInitial(bool asynch) {
3619 assert(_collectorState == InitialMarking, "Wrong collector state");
3620 check_correct_thread_executing();
3621 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3623 save_heap_summary();
3624 report_heap_summary(GCWhen::BeforeGC);
3626 ReferenceProcessor* rp = ref_processor();
3627 SpecializationStats::clear();
3628 assert(_restart_addr == NULL, "Control point invariant");
3629 if (asynch) {
3630 // acquire locks for subsequent manipulations
3631 MutexLockerEx x(bitMapLock(),
3632 Mutex::_no_safepoint_check_flag);
3633 checkpointRootsInitialWork(asynch);
3634 // enable ("weak") refs discovery
3635 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3636 _collectorState = Marking;
3637 } else {
3638 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3639 // which recognizes if we are a CMS generation, and doesn't try to turn on
3640 // discovery; verify that they aren't meddling.
3641 assert(!rp->discovery_is_atomic(),
3642 "incorrect setting of discovery predicate");
3643 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3644 "ref discovery for this generation kind");
3645 // already have locks
3646 checkpointRootsInitialWork(asynch);
3647 // now enable ("weak") refs discovery
3648 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3649 _collectorState = Marking;
3650 }
3651 SpecializationStats::print();
3652 }
3654 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3655 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3656 assert(_collectorState == InitialMarking, "just checking");
3658 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3659 // precede our marking with a collection of all
3660 // younger generations to keep floating garbage to a minimum.
3661 // XXX: we won't do this for now -- it's an optimization to be done later.
3663 // already have locks
3664 assert_lock_strong(bitMapLock());
3665 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3667 // Setup the verification and class unloading state for this
3668 // CMS collection cycle.
3669 setup_cms_unloading_and_verification_state();
3671 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3672 PrintGCDetails && Verbose, true, _gc_timer_cm);)
3673 if (UseAdaptiveSizePolicy) {
3674 size_policy()->checkpoint_roots_initial_begin();
3675 }
3677 // Reset all the PLAB chunk arrays if necessary.
3678 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3679 reset_survivor_plab_arrays();
3680 }
3682 ResourceMark rm;
3683 HandleMark hm;
3685 FalseClosure falseClosure;
3686 // In the case of a synchronous collection, we will elide the
3687 // remark step, so it's important to catch all the nmethod oops
3688 // in this step.
3689 // The final 'true' flag to gen_process_strong_roots will ensure this.
3690 // If 'async' is true, we can relax the nmethod tracing.
3691 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3692 GenCollectedHeap* gch = GenCollectedHeap::heap();
3694 verify_work_stacks_empty();
3695 verify_overflow_empty();
3697 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3698 // Update the saved marks which may affect the root scans.
3699 gch->save_marks();
3701 // weak reference processing has not started yet.
3702 ref_processor()->set_enqueuing_is_done(false);
3704 // Need to remember all newly created CLDs,
3705 // so that we can guarantee that the remark finds them.
3706 ClassLoaderDataGraph::remember_new_clds(true);
3708 // Whenever a CLD is found, it will be claimed before proceeding to mark
3709 // the klasses. The claimed marks need to be cleared before marking starts.
3710 ClassLoaderDataGraph::clear_claimed_marks();
3712 if (CMSPrintEdenSurvivorChunks) {
3713 print_eden_and_survivor_chunk_arrays();
3714 }
3716 {
3717 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3718 if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3719 // The parallel version.
3720 FlexibleWorkGang* workers = gch->workers();
3721 assert(workers != NULL, "Need parallel worker threads.");
3722 int n_workers = workers->active_workers();
3723 CMSParInitialMarkTask tsk(this, n_workers);
3724 gch->set_par_threads(n_workers);
3725 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3726 if (n_workers > 1) {
3727 GenCollectedHeap::StrongRootsScope srs(gch);
3728 workers->run_task(&tsk);
3729 } else {
3730 GenCollectedHeap::StrongRootsScope srs(gch);
3731 tsk.work(0);
3732 }
3733 gch->set_par_threads(0);
3734 } else {
3735 // The serial version.
3736 CMKlassClosure klass_closure(¬Older);
3737 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3738 gch->gen_process_strong_roots(_cmsGen->level(),
3739 true, // younger gens are roots
3740 true, // activate StrongRootsScope
3741 false, // not scavenging
3742 SharedHeap::ScanningOption(roots_scanning_options()),
3743 ¬Older,
3744 true, // walk all of code cache if (so & SO_CodeCache)
3745 NULL,
3746 &klass_closure);
3747 }
3748 }
3750 // Clear mod-union table; it will be dirtied in the prologue of
3751 // CMS generation per each younger generation collection.
3753 assert(_modUnionTable.isAllClear(),
3754 "Was cleared in most recent final checkpoint phase"
3755 " or no bits are set in the gc_prologue before the start of the next "
3756 "subsequent marking phase.");
3758 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3760 // Save the end of the used_region of the constituent generations
3761 // to be used to limit the extent of sweep in each generation.
3762 save_sweep_limits();
3763 if (UseAdaptiveSizePolicy) {
3764 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3765 }
3766 verify_overflow_empty();
3767 }
3769 bool CMSCollector::markFromRoots(bool asynch) {
3770 // we might be tempted to assert that:
3771 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3772 // "inconsistent argument?");
3773 // However that wouldn't be right, because it's possible that
3774 // a safepoint is indeed in progress as a younger generation
3775 // stop-the-world GC happens even as we mark in this generation.
3776 assert(_collectorState == Marking, "inconsistent state?");
3777 check_correct_thread_executing();
3778 verify_overflow_empty();
3780 bool res;
3781 if (asynch) {
3783 // Start the timers for adaptive size policy for the concurrent phases
3784 // Do it here so that the foreground MS can use the concurrent
3785 // timer since a foreground MS might has the sweep done concurrently
3786 // or STW.
3787 if (UseAdaptiveSizePolicy) {
3788 size_policy()->concurrent_marking_begin();
3789 }
3791 // Weak ref discovery note: We may be discovering weak
3792 // refs in this generation concurrent (but interleaved) with
3793 // weak ref discovery by a younger generation collector.
3795 CMSTokenSyncWithLocks ts(true, bitMapLock());
3796 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3797 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3798 res = markFromRootsWork(asynch);
3799 if (res) {
3800 _collectorState = Precleaning;
3801 } else { // We failed and a foreground collection wants to take over
3802 assert(_foregroundGCIsActive, "internal state inconsistency");
3803 assert(_restart_addr == NULL, "foreground will restart from scratch");
3804 if (PrintGCDetails) {
3805 gclog_or_tty->print_cr("bailing out to foreground collection");
3806 }
3807 }
3808 if (UseAdaptiveSizePolicy) {
3809 size_policy()->concurrent_marking_end();
3810 }
3811 } else {
3812 assert(SafepointSynchronize::is_at_safepoint(),
3813 "inconsistent with asynch == false");
3814 if (UseAdaptiveSizePolicy) {
3815 size_policy()->ms_collection_marking_begin();
3816 }
3817 // already have locks
3818 res = markFromRootsWork(asynch);
3819 _collectorState = FinalMarking;
3820 if (UseAdaptiveSizePolicy) {
3821 GenCollectedHeap* gch = GenCollectedHeap::heap();
3822 size_policy()->ms_collection_marking_end(gch->gc_cause());
3823 }
3824 }
3825 verify_overflow_empty();
3826 return res;
3827 }
3829 bool CMSCollector::markFromRootsWork(bool asynch) {
3830 // iterate over marked bits in bit map, doing a full scan and mark
3831 // from these roots using the following algorithm:
3832 // . if oop is to the right of the current scan pointer,
3833 // mark corresponding bit (we'll process it later)
3834 // . else (oop is to left of current scan pointer)
3835 // push oop on marking stack
3836 // . drain the marking stack
3838 // Note that when we do a marking step we need to hold the
3839 // bit map lock -- recall that direct allocation (by mutators)
3840 // and promotion (by younger generation collectors) is also
3841 // marking the bit map. [the so-called allocate live policy.]
3842 // Because the implementation of bit map marking is not
3843 // robust wrt simultaneous marking of bits in the same word,
3844 // we need to make sure that there is no such interference
3845 // between concurrent such updates.
3847 // already have locks
3848 assert_lock_strong(bitMapLock());
3850 verify_work_stacks_empty();
3851 verify_overflow_empty();
3852 bool result = false;
3853 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3854 result = do_marking_mt(asynch);
3855 } else {
3856 result = do_marking_st(asynch);
3857 }
3858 return result;
3859 }
3861 // Forward decl
3862 class CMSConcMarkingTask;
3864 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3865 CMSCollector* _collector;
3866 CMSConcMarkingTask* _task;
3867 public:
3868 virtual void yield();
3870 // "n_threads" is the number of threads to be terminated.
3871 // "queue_set" is a set of work queues of other threads.
3872 // "collector" is the CMS collector associated with this task terminator.
3873 // "yield" indicates whether we need the gang as a whole to yield.
3874 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3875 ParallelTaskTerminator(n_threads, queue_set),
3876 _collector(collector) { }
3878 void set_task(CMSConcMarkingTask* task) {
3879 _task = task;
3880 }
3881 };
3883 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3884 CMSConcMarkingTask* _task;
3885 public:
3886 bool should_exit_termination();
3887 void set_task(CMSConcMarkingTask* task) {
3888 _task = task;
3889 }
3890 };
3892 // MT Concurrent Marking Task
3893 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3894 CMSCollector* _collector;
3895 int _n_workers; // requested/desired # workers
3896 bool _asynch;
3897 bool _result;
3898 CompactibleFreeListSpace* _cms_space;
3899 char _pad_front[64]; // padding to ...
3900 HeapWord* _global_finger; // ... avoid sharing cache line
3901 char _pad_back[64];
3902 HeapWord* _restart_addr;
3904 // Exposed here for yielding support
3905 Mutex* const _bit_map_lock;
3907 // The per thread work queues, available here for stealing
3908 OopTaskQueueSet* _task_queues;
3910 // Termination (and yielding) support
3911 CMSConcMarkingTerminator _term;
3912 CMSConcMarkingTerminatorTerminator _term_term;
3914 public:
3915 CMSConcMarkingTask(CMSCollector* collector,
3916 CompactibleFreeListSpace* cms_space,
3917 bool asynch,
3918 YieldingFlexibleWorkGang* workers,
3919 OopTaskQueueSet* task_queues):
3920 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3921 _collector(collector),
3922 _cms_space(cms_space),
3923 _asynch(asynch), _n_workers(0), _result(true),
3924 _task_queues(task_queues),
3925 _term(_n_workers, task_queues, _collector),
3926 _bit_map_lock(collector->bitMapLock())
3927 {
3928 _requested_size = _n_workers;
3929 _term.set_task(this);
3930 _term_term.set_task(this);
3931 _restart_addr = _global_finger = _cms_space->bottom();
3932 }
3935 OopTaskQueueSet* task_queues() { return _task_queues; }
3937 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3939 HeapWord** global_finger_addr() { return &_global_finger; }
3941 CMSConcMarkingTerminator* terminator() { return &_term; }
3943 virtual void set_for_termination(int active_workers) {
3944 terminator()->reset_for_reuse(active_workers);
3945 }
3947 void work(uint worker_id);
3948 bool should_yield() {
3949 return ConcurrentMarkSweepThread::should_yield()
3950 && !_collector->foregroundGCIsActive()
3951 && _asynch;
3952 }
3954 virtual void coordinator_yield(); // stuff done by coordinator
3955 bool result() { return _result; }
3957 void reset(HeapWord* ra) {
3958 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3959 _restart_addr = _global_finger = ra;
3960 _term.reset_for_reuse();
3961 }
3963 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3964 OopTaskQueue* work_q);
3966 private:
3967 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3968 void do_work_steal(int i);
3969 void bump_global_finger(HeapWord* f);
3970 };
3972 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3973 assert(_task != NULL, "Error");
3974 return _task->yielding();
3975 // Note that we do not need the disjunct || _task->should_yield() above
3976 // because we want terminating threads to yield only if the task
3977 // is already in the midst of yielding, which happens only after at least one
3978 // thread has yielded.
3979 }
3981 void CMSConcMarkingTerminator::yield() {
3982 if (_task->should_yield()) {
3983 _task->yield();
3984 } else {
3985 ParallelTaskTerminator::yield();
3986 }
3987 }
3989 ////////////////////////////////////////////////////////////////
3990 // Concurrent Marking Algorithm Sketch
3991 ////////////////////////////////////////////////////////////////
3992 // Until all tasks exhausted (both spaces):
3993 // -- claim next available chunk
3994 // -- bump global finger via CAS
3995 // -- find first object that starts in this chunk
3996 // and start scanning bitmap from that position
3997 // -- scan marked objects for oops
3998 // -- CAS-mark target, and if successful:
3999 // . if target oop is above global finger (volatile read)
4000 // nothing to do
4001 // . if target oop is in chunk and above local finger
4002 // then nothing to do
4003 // . else push on work-queue
4004 // -- Deal with possible overflow issues:
4005 // . local work-queue overflow causes stuff to be pushed on
4006 // global (common) overflow queue
4007 // . always first empty local work queue
4008 // . then get a batch of oops from global work queue if any
4009 // . then do work stealing
4010 // -- When all tasks claimed (both spaces)
4011 // and local work queue empty,
4012 // then in a loop do:
4013 // . check global overflow stack; steal a batch of oops and trace
4014 // . try to steal from other threads oif GOS is empty
4015 // . if neither is available, offer termination
4016 // -- Terminate and return result
4017 //
4018 void CMSConcMarkingTask::work(uint worker_id) {
4019 elapsedTimer _timer;
4020 ResourceMark rm;
4021 HandleMark hm;
4023 DEBUG_ONLY(_collector->verify_overflow_empty();)
4025 // Before we begin work, our work queue should be empty
4026 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
4027 // Scan the bitmap covering _cms_space, tracing through grey objects.
4028 _timer.start();
4029 do_scan_and_mark(worker_id, _cms_space);
4030 _timer.stop();
4031 if (PrintCMSStatistics != 0) {
4032 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
4033 worker_id, _timer.seconds());
4034 // XXX: need xxx/xxx type of notation, two timers
4035 }
4037 // ... do work stealing
4038 _timer.reset();
4039 _timer.start();
4040 do_work_steal(worker_id);
4041 _timer.stop();
4042 if (PrintCMSStatistics != 0) {
4043 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
4044 worker_id, _timer.seconds());
4045 // XXX: need xxx/xxx type of notation, two timers
4046 }
4047 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
4048 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
4049 // Note that under the current task protocol, the
4050 // following assertion is true even of the spaces
4051 // expanded since the completion of the concurrent
4052 // marking. XXX This will likely change under a strict
4053 // ABORT semantics.
4054 // After perm removal the comparison was changed to
4055 // greater than or equal to from strictly greater than.
4056 // Before perm removal the highest address sweep would
4057 // have been at the end of perm gen but now is at the
4058 // end of the tenured gen.
4059 assert(_global_finger >= _cms_space->end(),
4060 "All tasks have been completed");
4061 DEBUG_ONLY(_collector->verify_overflow_empty();)
4062 }
4064 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
4065 HeapWord* read = _global_finger;
4066 HeapWord* cur = read;
4067 while (f > read) {
4068 cur = read;
4069 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
4070 if (cur == read) {
4071 // our cas succeeded
4072 assert(_global_finger >= f, "protocol consistency");
4073 break;
4074 }
4075 }
4076 }
4078 // This is really inefficient, and should be redone by
4079 // using (not yet available) block-read and -write interfaces to the
4080 // stack and the work_queue. XXX FIX ME !!!
4081 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
4082 OopTaskQueue* work_q) {
4083 // Fast lock-free check
4084 if (ovflw_stk->length() == 0) {
4085 return false;
4086 }
4087 assert(work_q->size() == 0, "Shouldn't steal");
4088 MutexLockerEx ml(ovflw_stk->par_lock(),
4089 Mutex::_no_safepoint_check_flag);
4090 // Grab up to 1/4 the size of the work queue
4091 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4092 (size_t)ParGCDesiredObjsFromOverflowList);
4093 num = MIN2(num, ovflw_stk->length());
4094 for (int i = (int) num; i > 0; i--) {
4095 oop cur = ovflw_stk->pop();
4096 assert(cur != NULL, "Counted wrong?");
4097 work_q->push(cur);
4098 }
4099 return num > 0;
4100 }
4102 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
4103 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4104 int n_tasks = pst->n_tasks();
4105 // We allow that there may be no tasks to do here because
4106 // we are restarting after a stack overflow.
4107 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
4108 uint nth_task = 0;
4110 HeapWord* aligned_start = sp->bottom();
4111 if (sp->used_region().contains(_restart_addr)) {
4112 // Align down to a card boundary for the start of 0th task
4113 // for this space.
4114 aligned_start =
4115 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
4116 CardTableModRefBS::card_size);
4117 }
4119 size_t chunk_size = sp->marking_task_size();
4120 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4121 // Having claimed the nth task in this space,
4122 // compute the chunk that it corresponds to:
4123 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
4124 aligned_start + (nth_task+1)*chunk_size);
4125 // Try and bump the global finger via a CAS;
4126 // note that we need to do the global finger bump
4127 // _before_ taking the intersection below, because
4128 // the task corresponding to that region will be
4129 // deemed done even if the used_region() expands
4130 // because of allocation -- as it almost certainly will
4131 // during start-up while the threads yield in the
4132 // closure below.
4133 HeapWord* finger = span.end();
4134 bump_global_finger(finger); // atomically
4135 // There are null tasks here corresponding to chunks
4136 // beyond the "top" address of the space.
4137 span = span.intersection(sp->used_region());
4138 if (!span.is_empty()) { // Non-null task
4139 HeapWord* prev_obj;
4140 assert(!span.contains(_restart_addr) || nth_task == 0,
4141 "Inconsistency");
4142 if (nth_task == 0) {
4143 // For the 0th task, we'll not need to compute a block_start.
4144 if (span.contains(_restart_addr)) {
4145 // In the case of a restart because of stack overflow,
4146 // we might additionally skip a chunk prefix.
4147 prev_obj = _restart_addr;
4148 } else {
4149 prev_obj = span.start();
4150 }
4151 } else {
4152 // We want to skip the first object because
4153 // the protocol is to scan any object in its entirety
4154 // that _starts_ in this span; a fortiori, any
4155 // object starting in an earlier span is scanned
4156 // as part of an earlier claimed task.
4157 // Below we use the "careful" version of block_start
4158 // so we do not try to navigate uninitialized objects.
4159 prev_obj = sp->block_start_careful(span.start());
4160 // Below we use a variant of block_size that uses the
4161 // Printezis bits to avoid waiting for allocated
4162 // objects to become initialized/parsable.
4163 while (prev_obj < span.start()) {
4164 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4165 if (sz > 0) {
4166 prev_obj += sz;
4167 } else {
4168 // In this case we may end up doing a bit of redundant
4169 // scanning, but that appears unavoidable, short of
4170 // locking the free list locks; see bug 6324141.
4171 break;
4172 }
4173 }
4174 }
4175 if (prev_obj < span.end()) {
4176 MemRegion my_span = MemRegion(prev_obj, span.end());
4177 // Do the marking work within a non-empty span --
4178 // the last argument to the constructor indicates whether the
4179 // iteration should be incremental with periodic yields.
4180 Par_MarkFromRootsClosure cl(this, _collector, my_span,
4181 &_collector->_markBitMap,
4182 work_queue(i),
4183 &_collector->_markStack,
4184 _asynch);
4185 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4186 } // else nothing to do for this task
4187 } // else nothing to do for this task
4188 }
4189 // We'd be tempted to assert here that since there are no
4190 // more tasks left to claim in this space, the global_finger
4191 // must exceed space->top() and a fortiori space->end(). However,
4192 // that would not quite be correct because the bumping of
4193 // global_finger occurs strictly after the claiming of a task,
4194 // so by the time we reach here the global finger may not yet
4195 // have been bumped up by the thread that claimed the last
4196 // task.
4197 pst->all_tasks_completed();
4198 }
4200 class Par_ConcMarkingClosure: public CMSOopClosure {
4201 private:
4202 CMSCollector* _collector;
4203 CMSConcMarkingTask* _task;
4204 MemRegion _span;
4205 CMSBitMap* _bit_map;
4206 CMSMarkStack* _overflow_stack;
4207 OopTaskQueue* _work_queue;
4208 protected:
4209 DO_OOP_WORK_DEFN
4210 public:
4211 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4212 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
4213 CMSOopClosure(collector->ref_processor()),
4214 _collector(collector),
4215 _task(task),
4216 _span(collector->_span),
4217 _work_queue(work_queue),
4218 _bit_map(bit_map),
4219 _overflow_stack(overflow_stack)
4220 { }
4221 virtual void do_oop(oop* p);
4222 virtual void do_oop(narrowOop* p);
4224 void trim_queue(size_t max);
4225 void handle_stack_overflow(HeapWord* lost);
4226 void do_yield_check() {
4227 if (_task->should_yield()) {
4228 _task->yield();
4229 }
4230 }
4231 };
4233 // Grey object scanning during work stealing phase --
4234 // the salient assumption here is that any references
4235 // that are in these stolen objects being scanned must
4236 // already have been initialized (else they would not have
4237 // been published), so we do not need to check for
4238 // uninitialized objects before pushing here.
4239 void Par_ConcMarkingClosure::do_oop(oop obj) {
4240 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4241 HeapWord* addr = (HeapWord*)obj;
4242 // Check if oop points into the CMS generation
4243 // and is not marked
4244 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4245 // a white object ...
4246 // If we manage to "claim" the object, by being the
4247 // first thread to mark it, then we push it on our
4248 // marking stack
4249 if (_bit_map->par_mark(addr)) { // ... now grey
4250 // push on work queue (grey set)
4251 bool simulate_overflow = false;
4252 NOT_PRODUCT(
4253 if (CMSMarkStackOverflowALot &&
4254 _collector->simulate_overflow()) {
4255 // simulate a stack overflow
4256 simulate_overflow = true;
4257 }
4258 )
4259 if (simulate_overflow ||
4260 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4261 // stack overflow
4262 if (PrintCMSStatistics != 0) {
4263 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4264 SIZE_FORMAT, _overflow_stack->capacity());
4265 }
4266 // We cannot assert that the overflow stack is full because
4267 // it may have been emptied since.
4268 assert(simulate_overflow ||
4269 _work_queue->size() == _work_queue->max_elems(),
4270 "Else push should have succeeded");
4271 handle_stack_overflow(addr);
4272 }
4273 } // Else, some other thread got there first
4274 do_yield_check();
4275 }
4276 }
4278 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4279 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4281 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4282 while (_work_queue->size() > max) {
4283 oop new_oop;
4284 if (_work_queue->pop_local(new_oop)) {
4285 assert(new_oop->is_oop(), "Should be an oop");
4286 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4287 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4288 new_oop->oop_iterate(this); // do_oop() above
4289 do_yield_check();
4290 }
4291 }
4292 }
4294 // Upon stack overflow, we discard (part of) the stack,
4295 // remembering the least address amongst those discarded
4296 // in CMSCollector's _restart_address.
4297 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4298 // We need to do this under a mutex to prevent other
4299 // workers from interfering with the work done below.
4300 MutexLockerEx ml(_overflow_stack->par_lock(),
4301 Mutex::_no_safepoint_check_flag);
4302 // Remember the least grey address discarded
4303 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4304 _collector->lower_restart_addr(ra);
4305 _overflow_stack->reset(); // discard stack contents
4306 _overflow_stack->expand(); // expand the stack if possible
4307 }
4310 void CMSConcMarkingTask::do_work_steal(int i) {
4311 OopTaskQueue* work_q = work_queue(i);
4312 oop obj_to_scan;
4313 CMSBitMap* bm = &(_collector->_markBitMap);
4314 CMSMarkStack* ovflw = &(_collector->_markStack);
4315 int* seed = _collector->hash_seed(i);
4316 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4317 while (true) {
4318 cl.trim_queue(0);
4319 assert(work_q->size() == 0, "Should have been emptied above");
4320 if (get_work_from_overflow_stack(ovflw, work_q)) {
4321 // Can't assert below because the work obtained from the
4322 // overflow stack may already have been stolen from us.
4323 // assert(work_q->size() > 0, "Work from overflow stack");
4324 continue;
4325 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4326 assert(obj_to_scan->is_oop(), "Should be an oop");
4327 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4328 obj_to_scan->oop_iterate(&cl);
4329 } else if (terminator()->offer_termination(&_term_term)) {
4330 assert(work_q->size() == 0, "Impossible!");
4331 break;
4332 } else if (yielding() || should_yield()) {
4333 yield();
4334 }
4335 }
4336 }
4338 // This is run by the CMS (coordinator) thread.
4339 void CMSConcMarkingTask::coordinator_yield() {
4340 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4341 "CMS thread should hold CMS token");
4342 // First give up the locks, then yield, then re-lock
4343 // We should probably use a constructor/destructor idiom to
4344 // do this unlock/lock or modify the MutexUnlocker class to
4345 // serve our purpose. XXX
4346 assert_lock_strong(_bit_map_lock);
4347 _bit_map_lock->unlock();
4348 ConcurrentMarkSweepThread::desynchronize(true);
4349 ConcurrentMarkSweepThread::acknowledge_yield_request();
4350 _collector->stopTimer();
4351 if (PrintCMSStatistics != 0) {
4352 _collector->incrementYields();
4353 }
4354 _collector->icms_wait();
4356 // It is possible for whichever thread initiated the yield request
4357 // not to get a chance to wake up and take the bitmap lock between
4358 // this thread releasing it and reacquiring it. So, while the
4359 // should_yield() flag is on, let's sleep for a bit to give the
4360 // other thread a chance to wake up. The limit imposed on the number
4361 // of iterations is defensive, to avoid any unforseen circumstances
4362 // putting us into an infinite loop. Since it's always been this
4363 // (coordinator_yield()) method that was observed to cause the
4364 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4365 // which is by default non-zero. For the other seven methods that
4366 // also perform the yield operation, as are using a different
4367 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4368 // can enable the sleeping for those methods too, if necessary.
4369 // See 6442774.
4370 //
4371 // We really need to reconsider the synchronization between the GC
4372 // thread and the yield-requesting threads in the future and we
4373 // should really use wait/notify, which is the recommended
4374 // way of doing this type of interaction. Additionally, we should
4375 // consolidate the eight methods that do the yield operation and they
4376 // are almost identical into one for better maintenability and
4377 // readability. See 6445193.
4378 //
4379 // Tony 2006.06.29
4380 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4381 ConcurrentMarkSweepThread::should_yield() &&
4382 !CMSCollector::foregroundGCIsActive(); ++i) {
4383 os::sleep(Thread::current(), 1, false);
4384 ConcurrentMarkSweepThread::acknowledge_yield_request();
4385 }
4387 ConcurrentMarkSweepThread::synchronize(true);
4388 _bit_map_lock->lock_without_safepoint_check();
4389 _collector->startTimer();
4390 }
4392 bool CMSCollector::do_marking_mt(bool asynch) {
4393 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4394 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4395 conc_workers()->total_workers(),
4396 conc_workers()->active_workers(),
4397 Threads::number_of_non_daemon_threads());
4398 conc_workers()->set_active_workers(num_workers);
4400 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4402 CMSConcMarkingTask tsk(this,
4403 cms_space,
4404 asynch,
4405 conc_workers(),
4406 task_queues());
4408 // Since the actual number of workers we get may be different
4409 // from the number we requested above, do we need to do anything different
4410 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4411 // class?? XXX
4412 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4414 // Refs discovery is already non-atomic.
4415 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4416 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4417 conc_workers()->start_task(&tsk);
4418 while (tsk.yielded()) {
4419 tsk.coordinator_yield();
4420 conc_workers()->continue_task(&tsk);
4421 }
4422 // If the task was aborted, _restart_addr will be non-NULL
4423 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4424 while (_restart_addr != NULL) {
4425 // XXX For now we do not make use of ABORTED state and have not
4426 // yet implemented the right abort semantics (even in the original
4427 // single-threaded CMS case). That needs some more investigation
4428 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4429 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4430 // If _restart_addr is non-NULL, a marking stack overflow
4431 // occurred; we need to do a fresh marking iteration from the
4432 // indicated restart address.
4433 if (_foregroundGCIsActive && asynch) {
4434 // We may be running into repeated stack overflows, having
4435 // reached the limit of the stack size, while making very
4436 // slow forward progress. It may be best to bail out and
4437 // let the foreground collector do its job.
4438 // Clear _restart_addr, so that foreground GC
4439 // works from scratch. This avoids the headache of
4440 // a "rescan" which would otherwise be needed because
4441 // of the dirty mod union table & card table.
4442 _restart_addr = NULL;
4443 return false;
4444 }
4445 // Adjust the task to restart from _restart_addr
4446 tsk.reset(_restart_addr);
4447 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4448 _restart_addr);
4449 _restart_addr = NULL;
4450 // Get the workers going again
4451 conc_workers()->start_task(&tsk);
4452 while (tsk.yielded()) {
4453 tsk.coordinator_yield();
4454 conc_workers()->continue_task(&tsk);
4455 }
4456 }
4457 assert(tsk.completed(), "Inconsistency");
4458 assert(tsk.result() == true, "Inconsistency");
4459 return true;
4460 }
4462 bool CMSCollector::do_marking_st(bool asynch) {
4463 ResourceMark rm;
4464 HandleMark hm;
4466 // Temporarily make refs discovery single threaded (non-MT)
4467 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4468 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4469 &_markStack, CMSYield && asynch);
4470 // the last argument to iterate indicates whether the iteration
4471 // should be incremental with periodic yields.
4472 _markBitMap.iterate(&markFromRootsClosure);
4473 // If _restart_addr is non-NULL, a marking stack overflow
4474 // occurred; we need to do a fresh iteration from the
4475 // indicated restart address.
4476 while (_restart_addr != NULL) {
4477 if (_foregroundGCIsActive && asynch) {
4478 // We may be running into repeated stack overflows, having
4479 // reached the limit of the stack size, while making very
4480 // slow forward progress. It may be best to bail out and
4481 // let the foreground collector do its job.
4482 // Clear _restart_addr, so that foreground GC
4483 // works from scratch. This avoids the headache of
4484 // a "rescan" which would otherwise be needed because
4485 // of the dirty mod union table & card table.
4486 _restart_addr = NULL;
4487 return false; // indicating failure to complete marking
4488 }
4489 // Deal with stack overflow:
4490 // we restart marking from _restart_addr
4491 HeapWord* ra = _restart_addr;
4492 markFromRootsClosure.reset(ra);
4493 _restart_addr = NULL;
4494 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4495 }
4496 return true;
4497 }
4499 void CMSCollector::preclean() {
4500 check_correct_thread_executing();
4501 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4502 verify_work_stacks_empty();
4503 verify_overflow_empty();
4504 _abort_preclean = false;
4505 if (CMSPrecleaningEnabled) {
4506 if (!CMSEdenChunksRecordAlways) {
4507 _eden_chunk_index = 0;
4508 }
4509 size_t used = get_eden_used();
4510 size_t capacity = get_eden_capacity();
4511 // Don't start sampling unless we will get sufficiently
4512 // many samples.
4513 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4514 * CMSScheduleRemarkEdenPenetration)) {
4515 _start_sampling = true;
4516 } else {
4517 _start_sampling = false;
4518 }
4519 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4520 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4521 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4522 }
4523 CMSTokenSync x(true); // is cms thread
4524 if (CMSPrecleaningEnabled) {
4525 sample_eden();
4526 _collectorState = AbortablePreclean;
4527 } else {
4528 _collectorState = FinalMarking;
4529 }
4530 verify_work_stacks_empty();
4531 verify_overflow_empty();
4532 }
4534 // Try and schedule the remark such that young gen
4535 // occupancy is CMSScheduleRemarkEdenPenetration %.
4536 void CMSCollector::abortable_preclean() {
4537 check_correct_thread_executing();
4538 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4539 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4541 // If Eden's current occupancy is below this threshold,
4542 // immediately schedule the remark; else preclean
4543 // past the next scavenge in an effort to
4544 // schedule the pause as described avove. By choosing
4545 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4546 // we will never do an actual abortable preclean cycle.
4547 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4548 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4549 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4550 // We need more smarts in the abortable preclean
4551 // loop below to deal with cases where allocation
4552 // in young gen is very very slow, and our precleaning
4553 // is running a losing race against a horde of
4554 // mutators intent on flooding us with CMS updates
4555 // (dirty cards).
4556 // One, admittedly dumb, strategy is to give up
4557 // after a certain number of abortable precleaning loops
4558 // or after a certain maximum time. We want to make
4559 // this smarter in the next iteration.
4560 // XXX FIX ME!!! YSR
4561 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4562 while (!(should_abort_preclean() ||
4563 ConcurrentMarkSweepThread::should_terminate())) {
4564 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4565 cumworkdone += workdone;
4566 loops++;
4567 // Voluntarily terminate abortable preclean phase if we have
4568 // been at it for too long.
4569 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4570 loops >= CMSMaxAbortablePrecleanLoops) {
4571 if (PrintGCDetails) {
4572 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4573 }
4574 break;
4575 }
4576 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4577 if (PrintGCDetails) {
4578 gclog_or_tty->print(" CMS: abort preclean due to time ");
4579 }
4580 break;
4581 }
4582 // If we are doing little work each iteration, we should
4583 // take a short break.
4584 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4585 // Sleep for some time, waiting for work to accumulate
4586 stopTimer();
4587 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4588 startTimer();
4589 waited++;
4590 }
4591 }
4592 if (PrintCMSStatistics > 0) {
4593 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4594 loops, waited, cumworkdone);
4595 }
4596 }
4597 CMSTokenSync x(true); // is cms thread
4598 if (_collectorState != Idling) {
4599 assert(_collectorState == AbortablePreclean,
4600 "Spontaneous state transition?");
4601 _collectorState = FinalMarking;
4602 } // Else, a foreground collection completed this CMS cycle.
4603 return;
4604 }
4606 // Respond to an Eden sampling opportunity
4607 void CMSCollector::sample_eden() {
4608 // Make sure a young gc cannot sneak in between our
4609 // reading and recording of a sample.
4610 assert(Thread::current()->is_ConcurrentGC_thread(),
4611 "Only the cms thread may collect Eden samples");
4612 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4613 "Should collect samples while holding CMS token");
4614 if (!_start_sampling) {
4615 return;
4616 }
4617 // When CMSEdenChunksRecordAlways is true, the eden chunk array
4618 // is populated by the young generation.
4619 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
4620 if (_eden_chunk_index < _eden_chunk_capacity) {
4621 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4622 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4623 "Unexpected state of Eden");
4624 // We'd like to check that what we just sampled is an oop-start address;
4625 // however, we cannot do that here since the object may not yet have been
4626 // initialized. So we'll instead do the check when we _use_ this sample
4627 // later.
4628 if (_eden_chunk_index == 0 ||
4629 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4630 _eden_chunk_array[_eden_chunk_index-1])
4631 >= CMSSamplingGrain)) {
4632 _eden_chunk_index++; // commit sample
4633 }
4634 }
4635 }
4636 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4637 size_t used = get_eden_used();
4638 size_t capacity = get_eden_capacity();
4639 assert(used <= capacity, "Unexpected state of Eden");
4640 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4641 _abort_preclean = true;
4642 }
4643 }
4644 }
4647 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4648 assert(_collectorState == Precleaning ||
4649 _collectorState == AbortablePreclean, "incorrect state");
4650 ResourceMark rm;
4651 HandleMark hm;
4653 // Precleaning is currently not MT but the reference processor
4654 // may be set for MT. Disable it temporarily here.
4655 ReferenceProcessor* rp = ref_processor();
4656 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4658 // Do one pass of scrubbing the discovered reference lists
4659 // to remove any reference objects with strongly-reachable
4660 // referents.
4661 if (clean_refs) {
4662 CMSPrecleanRefsYieldClosure yield_cl(this);
4663 assert(rp->span().equals(_span), "Spans should be equal");
4664 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4665 &_markStack, true /* preclean */);
4666 CMSDrainMarkingStackClosure complete_trace(this,
4667 _span, &_markBitMap, &_markStack,
4668 &keep_alive, true /* preclean */);
4670 // We don't want this step to interfere with a young
4671 // collection because we don't want to take CPU
4672 // or memory bandwidth away from the young GC threads
4673 // (which may be as many as there are CPUs).
4674 // Note that we don't need to protect ourselves from
4675 // interference with mutators because they can't
4676 // manipulate the discovered reference lists nor affect
4677 // the computed reachability of the referents, the
4678 // only properties manipulated by the precleaning
4679 // of these reference lists.
4680 stopTimer();
4681 CMSTokenSyncWithLocks x(true /* is cms thread */,
4682 bitMapLock());
4683 startTimer();
4684 sample_eden();
4686 // The following will yield to allow foreground
4687 // collection to proceed promptly. XXX YSR:
4688 // The code in this method may need further
4689 // tweaking for better performance and some restructuring
4690 // for cleaner interfaces.
4691 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4692 rp->preclean_discovered_references(
4693 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
4694 gc_timer);
4695 }
4697 if (clean_survivor) { // preclean the active survivor space(s)
4698 assert(_young_gen->kind() == Generation::DefNew ||
4699 _young_gen->kind() == Generation::ParNew ||
4700 _young_gen->kind() == Generation::ASParNew,
4701 "incorrect type for cast");
4702 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4703 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4704 &_markBitMap, &_modUnionTable,
4705 &_markStack, true /* precleaning phase */);
4706 stopTimer();
4707 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4708 bitMapLock());
4709 startTimer();
4710 unsigned int before_count =
4711 GenCollectedHeap::heap()->total_collections();
4712 SurvivorSpacePrecleanClosure
4713 sss_cl(this, _span, &_markBitMap, &_markStack,
4714 &pam_cl, before_count, CMSYield);
4715 dng->from()->object_iterate_careful(&sss_cl);
4716 dng->to()->object_iterate_careful(&sss_cl);
4717 }
4718 MarkRefsIntoAndScanClosure
4719 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4720 &_markStack, this, CMSYield,
4721 true /* precleaning phase */);
4722 // CAUTION: The following closure has persistent state that may need to
4723 // be reset upon a decrease in the sequence of addresses it
4724 // processes.
4725 ScanMarkedObjectsAgainCarefullyClosure
4726 smoac_cl(this, _span,
4727 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4729 // Preclean dirty cards in ModUnionTable and CardTable using
4730 // appropriate convergence criterion;
4731 // repeat CMSPrecleanIter times unless we find that
4732 // we are losing.
4733 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4734 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4735 "Bad convergence multiplier");
4736 assert(CMSPrecleanThreshold >= 100,
4737 "Unreasonably low CMSPrecleanThreshold");
4739 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4740 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4741 numIter < CMSPrecleanIter;
4742 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4743 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4744 if (Verbose && PrintGCDetails) {
4745 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4746 }
4747 // Either there are very few dirty cards, so re-mark
4748 // pause will be small anyway, or our pre-cleaning isn't
4749 // that much faster than the rate at which cards are being
4750 // dirtied, so we might as well stop and re-mark since
4751 // precleaning won't improve our re-mark time by much.
4752 if (curNumCards <= CMSPrecleanThreshold ||
4753 (numIter > 0 &&
4754 (curNumCards * CMSPrecleanDenominator >
4755 lastNumCards * CMSPrecleanNumerator))) {
4756 numIter++;
4757 cumNumCards += curNumCards;
4758 break;
4759 }
4760 }
4762 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4764 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4765 cumNumCards += curNumCards;
4766 if (PrintGCDetails && PrintCMSStatistics != 0) {
4767 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4768 curNumCards, cumNumCards, numIter);
4769 }
4770 return cumNumCards; // as a measure of useful work done
4771 }
4773 // PRECLEANING NOTES:
4774 // Precleaning involves:
4775 // . reading the bits of the modUnionTable and clearing the set bits.
4776 // . For the cards corresponding to the set bits, we scan the
4777 // objects on those cards. This means we need the free_list_lock
4778 // so that we can safely iterate over the CMS space when scanning
4779 // for oops.
4780 // . When we scan the objects, we'll be both reading and setting
4781 // marks in the marking bit map, so we'll need the marking bit map.
4782 // . For protecting _collector_state transitions, we take the CGC_lock.
4783 // Note that any races in the reading of of card table entries by the
4784 // CMS thread on the one hand and the clearing of those entries by the
4785 // VM thread or the setting of those entries by the mutator threads on the
4786 // other are quite benign. However, for efficiency it makes sense to keep
4787 // the VM thread from racing with the CMS thread while the latter is
4788 // dirty card info to the modUnionTable. We therefore also use the
4789 // CGC_lock to protect the reading of the card table and the mod union
4790 // table by the CM thread.
4791 // . We run concurrently with mutator updates, so scanning
4792 // needs to be done carefully -- we should not try to scan
4793 // potentially uninitialized objects.
4794 //
4795 // Locking strategy: While holding the CGC_lock, we scan over and
4796 // reset a maximal dirty range of the mod union / card tables, then lock
4797 // the free_list_lock and bitmap lock to do a full marking, then
4798 // release these locks; and repeat the cycle. This allows for a
4799 // certain amount of fairness in the sharing of these locks between
4800 // the CMS collector on the one hand, and the VM thread and the
4801 // mutators on the other.
4803 // NOTE: preclean_mod_union_table() and preclean_card_table()
4804 // further below are largely identical; if you need to modify
4805 // one of these methods, please check the other method too.
4807 size_t CMSCollector::preclean_mod_union_table(
4808 ConcurrentMarkSweepGeneration* gen,
4809 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4810 verify_work_stacks_empty();
4811 verify_overflow_empty();
4813 // strategy: starting with the first card, accumulate contiguous
4814 // ranges of dirty cards; clear these cards, then scan the region
4815 // covered by these cards.
4817 // Since all of the MUT is committed ahead, we can just use
4818 // that, in case the generations expand while we are precleaning.
4819 // It might also be fine to just use the committed part of the
4820 // generation, but we might potentially miss cards when the
4821 // generation is rapidly expanding while we are in the midst
4822 // of precleaning.
4823 HeapWord* startAddr = gen->reserved().start();
4824 HeapWord* endAddr = gen->reserved().end();
4826 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4828 size_t numDirtyCards, cumNumDirtyCards;
4829 HeapWord *nextAddr, *lastAddr;
4830 for (cumNumDirtyCards = numDirtyCards = 0,
4831 nextAddr = lastAddr = startAddr;
4832 nextAddr < endAddr;
4833 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4835 ResourceMark rm;
4836 HandleMark hm;
4838 MemRegion dirtyRegion;
4839 {
4840 stopTimer();
4841 // Potential yield point
4842 CMSTokenSync ts(true);
4843 startTimer();
4844 sample_eden();
4845 // Get dirty region starting at nextOffset (inclusive),
4846 // simultaneously clearing it.
4847 dirtyRegion =
4848 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4849 assert(dirtyRegion.start() >= nextAddr,
4850 "returned region inconsistent?");
4851 }
4852 // Remember where the next search should begin.
4853 // The returned region (if non-empty) is a right open interval,
4854 // so lastOffset is obtained from the right end of that
4855 // interval.
4856 lastAddr = dirtyRegion.end();
4857 // Should do something more transparent and less hacky XXX
4858 numDirtyCards =
4859 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4861 // We'll scan the cards in the dirty region (with periodic
4862 // yields for foreground GC as needed).
4863 if (!dirtyRegion.is_empty()) {
4864 assert(numDirtyCards > 0, "consistency check");
4865 HeapWord* stop_point = NULL;
4866 stopTimer();
4867 // Potential yield point
4868 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4869 bitMapLock());
4870 startTimer();
4871 {
4872 verify_work_stacks_empty();
4873 verify_overflow_empty();
4874 sample_eden();
4875 stop_point =
4876 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4877 }
4878 if (stop_point != NULL) {
4879 // The careful iteration stopped early either because it found an
4880 // uninitialized object, or because we were in the midst of an
4881 // "abortable preclean", which should now be aborted. Redirty
4882 // the bits corresponding to the partially-scanned or unscanned
4883 // cards. We'll either restart at the next block boundary or
4884 // abort the preclean.
4885 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4886 "Should only be AbortablePreclean.");
4887 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4888 if (should_abort_preclean()) {
4889 break; // out of preclean loop
4890 } else {
4891 // Compute the next address at which preclean should pick up;
4892 // might need bitMapLock in order to read P-bits.
4893 lastAddr = next_card_start_after_block(stop_point);
4894 }
4895 }
4896 } else {
4897 assert(lastAddr == endAddr, "consistency check");
4898 assert(numDirtyCards == 0, "consistency check");
4899 break;
4900 }
4901 }
4902 verify_work_stacks_empty();
4903 verify_overflow_empty();
4904 return cumNumDirtyCards;
4905 }
4907 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4908 // below are largely identical; if you need to modify
4909 // one of these methods, please check the other method too.
4911 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4912 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4913 // strategy: it's similar to precleamModUnionTable above, in that
4914 // we accumulate contiguous ranges of dirty cards, mark these cards
4915 // precleaned, then scan the region covered by these cards.
4916 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4917 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4919 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4921 size_t numDirtyCards, cumNumDirtyCards;
4922 HeapWord *lastAddr, *nextAddr;
4924 for (cumNumDirtyCards = numDirtyCards = 0,
4925 nextAddr = lastAddr = startAddr;
4926 nextAddr < endAddr;
4927 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4929 ResourceMark rm;
4930 HandleMark hm;
4932 MemRegion dirtyRegion;
4933 {
4934 // See comments in "Precleaning notes" above on why we
4935 // do this locking. XXX Could the locking overheads be
4936 // too high when dirty cards are sparse? [I don't think so.]
4937 stopTimer();
4938 CMSTokenSync x(true); // is cms thread
4939 startTimer();
4940 sample_eden();
4941 // Get and clear dirty region from card table
4942 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4943 MemRegion(nextAddr, endAddr),
4944 true,
4945 CardTableModRefBS::precleaned_card_val());
4947 assert(dirtyRegion.start() >= nextAddr,
4948 "returned region inconsistent?");
4949 }
4950 lastAddr = dirtyRegion.end();
4951 numDirtyCards =
4952 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4954 if (!dirtyRegion.is_empty()) {
4955 stopTimer();
4956 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4957 startTimer();
4958 sample_eden();
4959 verify_work_stacks_empty();
4960 verify_overflow_empty();
4961 HeapWord* stop_point =
4962 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4963 if (stop_point != NULL) {
4964 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4965 "Should only be AbortablePreclean.");
4966 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4967 if (should_abort_preclean()) {
4968 break; // out of preclean loop
4969 } else {
4970 // Compute the next address at which preclean should pick up.
4971 lastAddr = next_card_start_after_block(stop_point);
4972 }
4973 }
4974 } else {
4975 break;
4976 }
4977 }
4978 verify_work_stacks_empty();
4979 verify_overflow_empty();
4980 return cumNumDirtyCards;
4981 }
4983 class PrecleanKlassClosure : public KlassClosure {
4984 CMKlassClosure _cm_klass_closure;
4985 public:
4986 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4987 void do_klass(Klass* k) {
4988 if (k->has_accumulated_modified_oops()) {
4989 k->clear_accumulated_modified_oops();
4991 _cm_klass_closure.do_klass(k);
4992 }
4993 }
4994 };
4996 // The freelist lock is needed to prevent asserts, is it really needed?
4997 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4999 cl->set_freelistLock(freelistLock);
5001 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
5003 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
5004 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
5005 PrecleanKlassClosure preclean_klass_closure(cl);
5006 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
5008 verify_work_stacks_empty();
5009 verify_overflow_empty();
5010 }
5012 void CMSCollector::checkpointRootsFinal(bool asynch,
5013 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
5014 assert(_collectorState == FinalMarking, "incorrect state transition?");
5015 check_correct_thread_executing();
5016 // world is stopped at this checkpoint
5017 assert(SafepointSynchronize::is_at_safepoint(),
5018 "world should be stopped");
5019 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5021 verify_work_stacks_empty();
5022 verify_overflow_empty();
5024 SpecializationStats::clear();
5025 if (PrintGCDetails) {
5026 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
5027 _young_gen->used() / K,
5028 _young_gen->capacity() / K);
5029 }
5030 if (asynch) {
5031 if (CMSScavengeBeforeRemark) {
5032 GenCollectedHeap* gch = GenCollectedHeap::heap();
5033 // Temporarily set flag to false, GCH->do_collection will
5034 // expect it to be false and set to true
5035 FlagSetting fl(gch->_is_gc_active, false);
5036 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
5037 PrintGCDetails && Verbose, true, _gc_timer_cm);)
5038 int level = _cmsGen->level() - 1;
5039 if (level >= 0) {
5040 gch->do_collection(true, // full (i.e. force, see below)
5041 false, // !clear_all_soft_refs
5042 0, // size
5043 false, // is_tlab
5044 level // max_level
5045 );
5046 }
5047 }
5048 FreelistLocker x(this);
5049 MutexLockerEx y(bitMapLock(),
5050 Mutex::_no_safepoint_check_flag);
5051 assert(!init_mark_was_synchronous, "but that's impossible!");
5052 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
5053 } else {
5054 // already have all the locks
5055 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
5056 init_mark_was_synchronous);
5057 }
5058 verify_work_stacks_empty();
5059 verify_overflow_empty();
5060 SpecializationStats::print();
5061 }
5063 void CMSCollector::checkpointRootsFinalWork(bool asynch,
5064 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
5066 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm);)
5068 assert(haveFreelistLocks(), "must have free list locks");
5069 assert_lock_strong(bitMapLock());
5071 if (UseAdaptiveSizePolicy) {
5072 size_policy()->checkpoint_roots_final_begin();
5073 }
5075 ResourceMark rm;
5076 HandleMark hm;
5078 GenCollectedHeap* gch = GenCollectedHeap::heap();
5080 if (should_unload_classes()) {
5081 CodeCache::gc_prologue();
5082 }
5083 assert(haveFreelistLocks(), "must have free list locks");
5084 assert_lock_strong(bitMapLock());
5086 if (!init_mark_was_synchronous) {
5087 // We might assume that we need not fill TLAB's when
5088 // CMSScavengeBeforeRemark is set, because we may have just done
5089 // a scavenge which would have filled all TLAB's -- and besides
5090 // Eden would be empty. This however may not always be the case --
5091 // for instance although we asked for a scavenge, it may not have
5092 // happened because of a JNI critical section. We probably need
5093 // a policy for deciding whether we can in that case wait until
5094 // the critical section releases and then do the remark following
5095 // the scavenge, and skip it here. In the absence of that policy,
5096 // or of an indication of whether the scavenge did indeed occur,
5097 // we cannot rely on TLAB's having been filled and must do
5098 // so here just in case a scavenge did not happen.
5099 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
5100 // Update the saved marks which may affect the root scans.
5101 gch->save_marks();
5103 if (CMSPrintEdenSurvivorChunks) {
5104 print_eden_and_survivor_chunk_arrays();
5105 }
5107 {
5108 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
5110 // Note on the role of the mod union table:
5111 // Since the marker in "markFromRoots" marks concurrently with
5112 // mutators, it is possible for some reachable objects not to have been
5113 // scanned. For instance, an only reference to an object A was
5114 // placed in object B after the marker scanned B. Unless B is rescanned,
5115 // A would be collected. Such updates to references in marked objects
5116 // are detected via the mod union table which is the set of all cards
5117 // dirtied since the first checkpoint in this GC cycle and prior to
5118 // the most recent young generation GC, minus those cleaned up by the
5119 // concurrent precleaning.
5120 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
5121 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm);
5122 do_remark_parallel();
5123 } else {
5124 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
5125 _gc_timer_cm);
5126 do_remark_non_parallel();
5127 }
5128 }
5129 } else {
5130 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
5131 // The initial mark was stop-world, so there's no rescanning to
5132 // do; go straight on to the next step below.
5133 }
5134 verify_work_stacks_empty();
5135 verify_overflow_empty();
5137 {
5138 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm);)
5139 refProcessingWork(asynch, clear_all_soft_refs);
5140 }
5141 verify_work_stacks_empty();
5142 verify_overflow_empty();
5144 if (should_unload_classes()) {
5145 CodeCache::gc_epilogue();
5146 }
5147 JvmtiExport::gc_epilogue();
5149 // If we encountered any (marking stack / work queue) overflow
5150 // events during the current CMS cycle, take appropriate
5151 // remedial measures, where possible, so as to try and avoid
5152 // recurrence of that condition.
5153 assert(_markStack.isEmpty(), "No grey objects");
5154 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5155 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
5156 if (ser_ovflw > 0) {
5157 if (PrintCMSStatistics != 0) {
5158 gclog_or_tty->print_cr("Marking stack overflow (benign) "
5159 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5160 ", kac_preclean="SIZE_FORMAT")",
5161 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5162 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5163 }
5164 _markStack.expand();
5165 _ser_pmc_remark_ovflw = 0;
5166 _ser_pmc_preclean_ovflw = 0;
5167 _ser_kac_preclean_ovflw = 0;
5168 _ser_kac_ovflw = 0;
5169 }
5170 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5171 if (PrintCMSStatistics != 0) {
5172 gclog_or_tty->print_cr("Work queue overflow (benign) "
5173 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5174 _par_pmc_remark_ovflw, _par_kac_ovflw);
5175 }
5176 _par_pmc_remark_ovflw = 0;
5177 _par_kac_ovflw = 0;
5178 }
5179 if (PrintCMSStatistics != 0) {
5180 if (_markStack._hit_limit > 0) {
5181 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5182 _markStack._hit_limit);
5183 }
5184 if (_markStack._failed_double > 0) {
5185 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5186 " current capacity "SIZE_FORMAT,
5187 _markStack._failed_double,
5188 _markStack.capacity());
5189 }
5190 }
5191 _markStack._hit_limit = 0;
5192 _markStack._failed_double = 0;
5194 if ((VerifyAfterGC || VerifyDuringGC) &&
5195 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5196 verify_after_remark();
5197 }
5199 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
5201 // Change under the freelistLocks.
5202 _collectorState = Sweeping;
5203 // Call isAllClear() under bitMapLock
5204 assert(_modUnionTable.isAllClear(),
5205 "Should be clear by end of the final marking");
5206 assert(_ct->klass_rem_set()->mod_union_is_clear(),
5207 "Should be clear by end of the final marking");
5208 if (UseAdaptiveSizePolicy) {
5209 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
5210 }
5211 }
5213 void CMSParInitialMarkTask::work(uint worker_id) {
5214 elapsedTimer _timer;
5215 ResourceMark rm;
5216 HandleMark hm;
5218 // ---------- scan from roots --------------
5219 _timer.start();
5220 GenCollectedHeap* gch = GenCollectedHeap::heap();
5221 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
5222 CMKlassClosure klass_closure(&par_mri_cl);
5224 // ---------- young gen roots --------------
5225 {
5226 work_on_young_gen_roots(worker_id, &par_mri_cl);
5227 _timer.stop();
5228 if (PrintCMSStatistics != 0) {
5229 gclog_or_tty->print_cr(
5230 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
5231 worker_id, _timer.seconds());
5232 }
5233 }
5235 // ---------- remaining roots --------------
5236 _timer.reset();
5237 _timer.start();
5238 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5239 false, // yg was scanned above
5240 false, // this is parallel code
5241 false, // not scavenging
5242 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5243 &par_mri_cl,
5244 true, // walk all of code cache if (so & SO_CodeCache)
5245 NULL,
5246 &klass_closure);
5247 assert(_collector->should_unload_classes()
5248 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache),
5249 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5250 _timer.stop();
5251 if (PrintCMSStatistics != 0) {
5252 gclog_or_tty->print_cr(
5253 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
5254 worker_id, _timer.seconds());
5255 }
5256 }
5258 // Parallel remark task
5259 class CMSParRemarkTask: public CMSParMarkTask {
5260 CompactibleFreeListSpace* _cms_space;
5262 // The per-thread work queues, available here for stealing.
5263 OopTaskQueueSet* _task_queues;
5264 ParallelTaskTerminator _term;
5266 public:
5267 // A value of 0 passed to n_workers will cause the number of
5268 // workers to be taken from the active workers in the work gang.
5269 CMSParRemarkTask(CMSCollector* collector,
5270 CompactibleFreeListSpace* cms_space,
5271 int n_workers, FlexibleWorkGang* workers,
5272 OopTaskQueueSet* task_queues):
5273 CMSParMarkTask("Rescan roots and grey objects in parallel",
5274 collector, n_workers),
5275 _cms_space(cms_space),
5276 _task_queues(task_queues),
5277 _term(n_workers, task_queues) { }
5279 OopTaskQueueSet* task_queues() { return _task_queues; }
5281 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5283 ParallelTaskTerminator* terminator() { return &_term; }
5284 int n_workers() { return _n_workers; }
5286 void work(uint worker_id);
5288 private:
5289 // ... of dirty cards in old space
5290 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5291 Par_MarkRefsIntoAndScanClosure* cl);
5293 // ... work stealing for the above
5294 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5295 };
5297 class RemarkKlassClosure : public KlassClosure {
5298 CMKlassClosure _cm_klass_closure;
5299 public:
5300 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
5301 void do_klass(Klass* k) {
5302 // Check if we have modified any oops in the Klass during the concurrent marking.
5303 if (k->has_accumulated_modified_oops()) {
5304 k->clear_accumulated_modified_oops();
5306 // We could have transfered the current modified marks to the accumulated marks,
5307 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
5308 } else if (k->has_modified_oops()) {
5309 // Don't clear anything, this info is needed by the next young collection.
5310 } else {
5311 // No modified oops in the Klass.
5312 return;
5313 }
5315 // The klass has modified fields, need to scan the klass.
5316 _cm_klass_closure.do_klass(k);
5317 }
5318 };
5320 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
5321 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5322 EdenSpace* eden_space = dng->eden();
5323 ContiguousSpace* from_space = dng->from();
5324 ContiguousSpace* to_space = dng->to();
5326 HeapWord** eca = _collector->_eden_chunk_array;
5327 size_t ect = _collector->_eden_chunk_index;
5328 HeapWord** sca = _collector->_survivor_chunk_array;
5329 size_t sct = _collector->_survivor_chunk_index;
5331 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5332 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5334 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
5335 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
5336 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
5337 }
5339 // work_queue(i) is passed to the closure
5340 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5341 // also is passed to do_dirty_card_rescan_tasks() and to
5342 // do_work_steal() to select the i-th task_queue.
5344 void CMSParRemarkTask::work(uint worker_id) {
5345 elapsedTimer _timer;
5346 ResourceMark rm;
5347 HandleMark hm;
5349 // ---------- rescan from roots --------------
5350 _timer.start();
5351 GenCollectedHeap* gch = GenCollectedHeap::heap();
5352 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5353 _collector->_span, _collector->ref_processor(),
5354 &(_collector->_markBitMap),
5355 work_queue(worker_id));
5357 // Rescan young gen roots first since these are likely
5358 // coarsely partitioned and may, on that account, constitute
5359 // the critical path; thus, it's best to start off that
5360 // work first.
5361 // ---------- young gen roots --------------
5362 {
5363 work_on_young_gen_roots(worker_id, &par_mrias_cl);
5364 _timer.stop();
5365 if (PrintCMSStatistics != 0) {
5366 gclog_or_tty->print_cr(
5367 "Finished young gen rescan work in %dth thread: %3.3f sec",
5368 worker_id, _timer.seconds());
5369 }
5370 }
5372 // ---------- remaining roots --------------
5373 _timer.reset();
5374 _timer.start();
5375 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5376 false, // yg was scanned above
5377 false, // this is parallel code
5378 false, // not scavenging
5379 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5380 &par_mrias_cl,
5381 true, // walk all of code cache if (so & SO_CodeCache)
5382 NULL,
5383 NULL); // The dirty klasses will be handled below
5384 assert(_collector->should_unload_classes()
5385 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache),
5386 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5387 _timer.stop();
5388 if (PrintCMSStatistics != 0) {
5389 gclog_or_tty->print_cr(
5390 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5391 worker_id, _timer.seconds());
5392 }
5394 // ---------- unhandled CLD scanning ----------
5395 if (worker_id == 0) { // Single threaded at the moment.
5396 _timer.reset();
5397 _timer.start();
5399 // Scan all new class loader data objects and new dependencies that were
5400 // introduced during concurrent marking.
5401 ResourceMark rm;
5402 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5403 for (int i = 0; i < array->length(); i++) {
5404 par_mrias_cl.do_class_loader_data(array->at(i));
5405 }
5407 // We don't need to keep track of new CLDs anymore.
5408 ClassLoaderDataGraph::remember_new_clds(false);
5410 _timer.stop();
5411 if (PrintCMSStatistics != 0) {
5412 gclog_or_tty->print_cr(
5413 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
5414 worker_id, _timer.seconds());
5415 }
5416 }
5418 // ---------- dirty klass scanning ----------
5419 if (worker_id == 0) { // Single threaded at the moment.
5420 _timer.reset();
5421 _timer.start();
5423 // Scan all classes that was dirtied during the concurrent marking phase.
5424 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
5425 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5427 _timer.stop();
5428 if (PrintCMSStatistics != 0) {
5429 gclog_or_tty->print_cr(
5430 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
5431 worker_id, _timer.seconds());
5432 }
5433 }
5435 // We might have added oops to ClassLoaderData::_handles during the
5436 // concurrent marking phase. These oops point to newly allocated objects
5437 // that are guaranteed to be kept alive. Either by the direct allocation
5438 // code, or when the young collector processes the strong roots. Hence,
5439 // we don't have to revisit the _handles block during the remark phase.
5441 // ---------- rescan dirty cards ------------
5442 _timer.reset();
5443 _timer.start();
5445 // Do the rescan tasks for each of the two spaces
5446 // (cms_space) in turn.
5447 // "worker_id" is passed to select the task_queue for "worker_id"
5448 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5449 _timer.stop();
5450 if (PrintCMSStatistics != 0) {
5451 gclog_or_tty->print_cr(
5452 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5453 worker_id, _timer.seconds());
5454 }
5456 // ---------- steal work from other threads ...
5457 // ---------- ... and drain overflow list.
5458 _timer.reset();
5459 _timer.start();
5460 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5461 _timer.stop();
5462 if (PrintCMSStatistics != 0) {
5463 gclog_or_tty->print_cr(
5464 "Finished work stealing in %dth thread: %3.3f sec",
5465 worker_id, _timer.seconds());
5466 }
5467 }
5469 // Note that parameter "i" is not used.
5470 void
5471 CMSParMarkTask::do_young_space_rescan(uint worker_id,
5472 OopsInGenClosure* cl, ContiguousSpace* space,
5473 HeapWord** chunk_array, size_t chunk_top) {
5474 // Until all tasks completed:
5475 // . claim an unclaimed task
5476 // . compute region boundaries corresponding to task claimed
5477 // using chunk_array
5478 // . par_oop_iterate(cl) over that region
5480 ResourceMark rm;
5481 HandleMark hm;
5483 SequentialSubTasksDone* pst = space->par_seq_tasks();
5485 uint nth_task = 0;
5486 uint n_tasks = pst->n_tasks();
5488 if (n_tasks > 0) {
5489 assert(pst->valid(), "Uninitialized use?");
5490 HeapWord *start, *end;
5491 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5492 // We claimed task # nth_task; compute its boundaries.
5493 if (chunk_top == 0) { // no samples were taken
5494 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5495 start = space->bottom();
5496 end = space->top();
5497 } else if (nth_task == 0) {
5498 start = space->bottom();
5499 end = chunk_array[nth_task];
5500 } else if (nth_task < (uint)chunk_top) {
5501 assert(nth_task >= 1, "Control point invariant");
5502 start = chunk_array[nth_task - 1];
5503 end = chunk_array[nth_task];
5504 } else {
5505 assert(nth_task == (uint)chunk_top, "Control point invariant");
5506 start = chunk_array[chunk_top - 1];
5507 end = space->top();
5508 }
5509 MemRegion mr(start, end);
5510 // Verify that mr is in space
5511 assert(mr.is_empty() || space->used_region().contains(mr),
5512 "Should be in space");
5513 // Verify that "start" is an object boundary
5514 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5515 "Should be an oop");
5516 space->par_oop_iterate(mr, cl);
5517 }
5518 pst->all_tasks_completed();
5519 }
5520 }
5522 void
5523 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5524 CompactibleFreeListSpace* sp, int i,
5525 Par_MarkRefsIntoAndScanClosure* cl) {
5526 // Until all tasks completed:
5527 // . claim an unclaimed task
5528 // . compute region boundaries corresponding to task claimed
5529 // . transfer dirty bits ct->mut for that region
5530 // . apply rescanclosure to dirty mut bits for that region
5532 ResourceMark rm;
5533 HandleMark hm;
5535 OopTaskQueue* work_q = work_queue(i);
5536 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5537 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5538 // CAUTION: This closure has state that persists across calls to
5539 // the work method dirty_range_iterate_clear() in that it has
5540 // imbedded in it a (subtype of) UpwardsObjectClosure. The
5541 // use of that state in the imbedded UpwardsObjectClosure instance
5542 // assumes that the cards are always iterated (even if in parallel
5543 // by several threads) in monotonically increasing order per each
5544 // thread. This is true of the implementation below which picks
5545 // card ranges (chunks) in monotonically increasing order globally
5546 // and, a-fortiori, in monotonically increasing order per thread
5547 // (the latter order being a subsequence of the former).
5548 // If the work code below is ever reorganized into a more chaotic
5549 // work-partitioning form than the current "sequential tasks"
5550 // paradigm, the use of that persistent state will have to be
5551 // revisited and modified appropriately. See also related
5552 // bug 4756801 work on which should examine this code to make
5553 // sure that the changes there do not run counter to the
5554 // assumptions made here and necessary for correctness and
5555 // efficiency. Note also that this code might yield inefficient
5556 // behaviour in the case of very large objects that span one or
5557 // more work chunks. Such objects would potentially be scanned
5558 // several times redundantly. Work on 4756801 should try and
5559 // address that performance anomaly if at all possible. XXX
5560 MemRegion full_span = _collector->_span;
5561 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5562 MarkFromDirtyCardsClosure
5563 greyRescanClosure(_collector, full_span, // entire span of interest
5564 sp, bm, work_q, cl);
5566 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5567 assert(pst->valid(), "Uninitialized use?");
5568 uint nth_task = 0;
5569 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5570 MemRegion span = sp->used_region();
5571 HeapWord* start_addr = span.start();
5572 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5573 alignment);
5574 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5575 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5576 start_addr, "Check alignment");
5577 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5578 chunk_size, "Check alignment");
5580 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5581 // Having claimed the nth_task, compute corresponding mem-region,
5582 // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5583 // The alignment restriction ensures that we do not need any
5584 // synchronization with other gang-workers while setting or
5585 // clearing bits in thus chunk of the MUT.
5586 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5587 start_addr + (nth_task+1)*chunk_size);
5588 // The last chunk's end might be way beyond end of the
5589 // used region. In that case pull back appropriately.
5590 if (this_span.end() > end_addr) {
5591 this_span.set_end(end_addr);
5592 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5593 }
5594 // Iterate over the dirty cards covering this chunk, marking them
5595 // precleaned, and setting the corresponding bits in the mod union
5596 // table. Since we have been careful to partition at Card and MUT-word
5597 // boundaries no synchronization is needed between parallel threads.
5598 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5599 &modUnionClosure);
5601 // Having transferred these marks into the modUnionTable,
5602 // rescan the marked objects on the dirty cards in the modUnionTable.
5603 // Even if this is at a synchronous collection, the initial marking
5604 // may have been done during an asynchronous collection so there
5605 // may be dirty bits in the mod-union table.
5606 _collector->_modUnionTable.dirty_range_iterate_clear(
5607 this_span, &greyRescanClosure);
5608 _collector->_modUnionTable.verifyNoOneBitsInRange(
5609 this_span.start(),
5610 this_span.end());
5611 }
5612 pst->all_tasks_completed(); // declare that i am done
5613 }
5615 // . see if we can share work_queues with ParNew? XXX
5616 void
5617 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5618 int* seed) {
5619 OopTaskQueue* work_q = work_queue(i);
5620 NOT_PRODUCT(int num_steals = 0;)
5621 oop obj_to_scan;
5622 CMSBitMap* bm = &(_collector->_markBitMap);
5624 while (true) {
5625 // Completely finish any left over work from (an) earlier round(s)
5626 cl->trim_queue(0);
5627 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5628 (size_t)ParGCDesiredObjsFromOverflowList);
5629 // Now check if there's any work in the overflow list
5630 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5631 // only affects the number of attempts made to get work from the
5632 // overflow list and does not affect the number of workers. Just
5633 // pass ParallelGCThreads so this behavior is unchanged.
5634 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5635 work_q,
5636 ParallelGCThreads)) {
5637 // found something in global overflow list;
5638 // not yet ready to go stealing work from others.
5639 // We'd like to assert(work_q->size() != 0, ...)
5640 // because we just took work from the overflow list,
5641 // but of course we can't since all of that could have
5642 // been already stolen from us.
5643 // "He giveth and He taketh away."
5644 continue;
5645 }
5646 // Verify that we have no work before we resort to stealing
5647 assert(work_q->size() == 0, "Have work, shouldn't steal");
5648 // Try to steal from other queues that have work
5649 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5650 NOT_PRODUCT(num_steals++;)
5651 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5652 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5653 // Do scanning work
5654 obj_to_scan->oop_iterate(cl);
5655 // Loop around, finish this work, and try to steal some more
5656 } else if (terminator()->offer_termination()) {
5657 break; // nirvana from the infinite cycle
5658 }
5659 }
5660 NOT_PRODUCT(
5661 if (PrintCMSStatistics != 0) {
5662 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5663 }
5664 )
5665 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5666 "Else our work is not yet done");
5667 }
5669 // Record object boundaries in _eden_chunk_array by sampling the eden
5670 // top in the slow-path eden object allocation code path and record
5671 // the boundaries, if CMSEdenChunksRecordAlways is true. If
5672 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
5673 // sampling in sample_eden() that activates during the part of the
5674 // preclean phase.
5675 void CMSCollector::sample_eden_chunk() {
5676 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
5677 if (_eden_chunk_lock->try_lock()) {
5678 // Record a sample. This is the critical section. The contents
5679 // of the _eden_chunk_array have to be non-decreasing in the
5680 // address order.
5681 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
5682 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
5683 "Unexpected state of Eden");
5684 if (_eden_chunk_index == 0 ||
5685 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
5686 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
5687 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
5688 _eden_chunk_index++; // commit sample
5689 }
5690 _eden_chunk_lock->unlock();
5691 }
5692 }
5693 }
5695 // Return a thread-local PLAB recording array, as appropriate.
5696 void* CMSCollector::get_data_recorder(int thr_num) {
5697 if (_survivor_plab_array != NULL &&
5698 (CMSPLABRecordAlways ||
5699 (_collectorState > Marking && _collectorState < FinalMarking))) {
5700 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5701 ChunkArray* ca = &_survivor_plab_array[thr_num];
5702 ca->reset(); // clear it so that fresh data is recorded
5703 return (void*) ca;
5704 } else {
5705 return NULL;
5706 }
5707 }
5709 // Reset all the thread-local PLAB recording arrays
5710 void CMSCollector::reset_survivor_plab_arrays() {
5711 for (uint i = 0; i < ParallelGCThreads; i++) {
5712 _survivor_plab_array[i].reset();
5713 }
5714 }
5716 // Merge the per-thread plab arrays into the global survivor chunk
5717 // array which will provide the partitioning of the survivor space
5718 // for CMS initial scan and rescan.
5719 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5720 int no_of_gc_threads) {
5721 assert(_survivor_plab_array != NULL, "Error");
5722 assert(_survivor_chunk_array != NULL, "Error");
5723 assert(_collectorState == FinalMarking ||
5724 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
5725 for (int j = 0; j < no_of_gc_threads; j++) {
5726 _cursor[j] = 0;
5727 }
5728 HeapWord* top = surv->top();
5729 size_t i;
5730 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5731 HeapWord* min_val = top; // Higher than any PLAB address
5732 uint min_tid = 0; // position of min_val this round
5733 for (int j = 0; j < no_of_gc_threads; j++) {
5734 ChunkArray* cur_sca = &_survivor_plab_array[j];
5735 if (_cursor[j] == cur_sca->end()) {
5736 continue;
5737 }
5738 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5739 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5740 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5741 if (cur_val < min_val) {
5742 min_tid = j;
5743 min_val = cur_val;
5744 } else {
5745 assert(cur_val < top, "All recorded addresses should be less");
5746 }
5747 }
5748 // At this point min_val and min_tid are respectively
5749 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5750 // and the thread (j) that witnesses that address.
5751 // We record this address in the _survivor_chunk_array[i]
5752 // and increment _cursor[min_tid] prior to the next round i.
5753 if (min_val == top) {
5754 break;
5755 }
5756 _survivor_chunk_array[i] = min_val;
5757 _cursor[min_tid]++;
5758 }
5759 // We are all done; record the size of the _survivor_chunk_array
5760 _survivor_chunk_index = i; // exclusive: [0, i)
5761 if (PrintCMSStatistics > 0) {
5762 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5763 }
5764 // Verify that we used up all the recorded entries
5765 #ifdef ASSERT
5766 size_t total = 0;
5767 for (int j = 0; j < no_of_gc_threads; j++) {
5768 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5769 total += _cursor[j];
5770 }
5771 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5772 // Check that the merged array is in sorted order
5773 if (total > 0) {
5774 for (size_t i = 0; i < total - 1; i++) {
5775 if (PrintCMSStatistics > 0) {
5776 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5777 i, _survivor_chunk_array[i]);
5778 }
5779 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5780 "Not sorted");
5781 }
5782 }
5783 #endif // ASSERT
5784 }
5786 // Set up the space's par_seq_tasks structure for work claiming
5787 // for parallel initial scan and rescan of young gen.
5788 // See ParRescanTask where this is currently used.
5789 void
5790 CMSCollector::
5791 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5792 assert(n_threads > 0, "Unexpected n_threads argument");
5793 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5795 // Eden space
5796 if (!dng->eden()->is_empty()) {
5797 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5798 assert(!pst->valid(), "Clobbering existing data?");
5799 // Each valid entry in [0, _eden_chunk_index) represents a task.
5800 size_t n_tasks = _eden_chunk_index + 1;
5801 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5802 // Sets the condition for completion of the subtask (how many threads
5803 // need to finish in order to be done).
5804 pst->set_n_threads(n_threads);
5805 pst->set_n_tasks((int)n_tasks);
5806 }
5808 // Merge the survivor plab arrays into _survivor_chunk_array
5809 if (_survivor_plab_array != NULL) {
5810 merge_survivor_plab_arrays(dng->from(), n_threads);
5811 } else {
5812 assert(_survivor_chunk_index == 0, "Error");
5813 }
5815 // To space
5816 {
5817 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5818 assert(!pst->valid(), "Clobbering existing data?");
5819 // Sets the condition for completion of the subtask (how many threads
5820 // need to finish in order to be done).
5821 pst->set_n_threads(n_threads);
5822 pst->set_n_tasks(1);
5823 assert(pst->valid(), "Error");
5824 }
5826 // From space
5827 {
5828 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5829 assert(!pst->valid(), "Clobbering existing data?");
5830 size_t n_tasks = _survivor_chunk_index + 1;
5831 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5832 // Sets the condition for completion of the subtask (how many threads
5833 // need to finish in order to be done).
5834 pst->set_n_threads(n_threads);
5835 pst->set_n_tasks((int)n_tasks);
5836 assert(pst->valid(), "Error");
5837 }
5838 }
5840 // Parallel version of remark
5841 void CMSCollector::do_remark_parallel() {
5842 GenCollectedHeap* gch = GenCollectedHeap::heap();
5843 FlexibleWorkGang* workers = gch->workers();
5844 assert(workers != NULL, "Need parallel worker threads.");
5845 // Choose to use the number of GC workers most recently set
5846 // into "active_workers". If active_workers is not set, set it
5847 // to ParallelGCThreads.
5848 int n_workers = workers->active_workers();
5849 if (n_workers == 0) {
5850 assert(n_workers > 0, "Should have been set during scavenge");
5851 n_workers = ParallelGCThreads;
5852 workers->set_active_workers(n_workers);
5853 }
5854 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5856 CMSParRemarkTask tsk(this,
5857 cms_space,
5858 n_workers, workers, task_queues());
5860 // Set up for parallel process_strong_roots work.
5861 gch->set_par_threads(n_workers);
5862 // We won't be iterating over the cards in the card table updating
5863 // the younger_gen cards, so we shouldn't call the following else
5864 // the verification code as well as subsequent younger_refs_iterate
5865 // code would get confused. XXX
5866 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5868 // The young gen rescan work will not be done as part of
5869 // process_strong_roots (which currently doesn't knw how to
5870 // parallelize such a scan), but rather will be broken up into
5871 // a set of parallel tasks (via the sampling that the [abortable]
5872 // preclean phase did of EdenSpace, plus the [two] tasks of
5873 // scanning the [two] survivor spaces. Further fine-grain
5874 // parallelization of the scanning of the survivor spaces
5875 // themselves, and of precleaning of the younger gen itself
5876 // is deferred to the future.
5877 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5879 // The dirty card rescan work is broken up into a "sequence"
5880 // of parallel tasks (per constituent space) that are dynamically
5881 // claimed by the parallel threads.
5882 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5884 // It turns out that even when we're using 1 thread, doing the work in a
5885 // separate thread causes wide variance in run times. We can't help this
5886 // in the multi-threaded case, but we special-case n=1 here to get
5887 // repeatable measurements of the 1-thread overhead of the parallel code.
5888 if (n_workers > 1) {
5889 // Make refs discovery MT-safe, if it isn't already: it may not
5890 // necessarily be so, since it's possible that we are doing
5891 // ST marking.
5892 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5893 GenCollectedHeap::StrongRootsScope srs(gch);
5894 workers->run_task(&tsk);
5895 } else {
5896 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5897 GenCollectedHeap::StrongRootsScope srs(gch);
5898 tsk.work(0);
5899 }
5901 gch->set_par_threads(0); // 0 ==> non-parallel.
5902 // restore, single-threaded for now, any preserved marks
5903 // as a result of work_q overflow
5904 restore_preserved_marks_if_any();
5905 }
5907 // Non-parallel version of remark
5908 void CMSCollector::do_remark_non_parallel() {
5909 ResourceMark rm;
5910 HandleMark hm;
5911 GenCollectedHeap* gch = GenCollectedHeap::heap();
5912 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5914 MarkRefsIntoAndScanClosure
5915 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5916 &_markStack, this,
5917 false /* should_yield */, false /* not precleaning */);
5918 MarkFromDirtyCardsClosure
5919 markFromDirtyCardsClosure(this, _span,
5920 NULL, // space is set further below
5921 &_markBitMap, &_markStack, &mrias_cl);
5922 {
5923 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm);
5924 // Iterate over the dirty cards, setting the corresponding bits in the
5925 // mod union table.
5926 {
5927 ModUnionClosure modUnionClosure(&_modUnionTable);
5928 _ct->ct_bs()->dirty_card_iterate(
5929 _cmsGen->used_region(),
5930 &modUnionClosure);
5931 }
5932 // Having transferred these marks into the modUnionTable, we just need
5933 // to rescan the marked objects on the dirty cards in the modUnionTable.
5934 // The initial marking may have been done during an asynchronous
5935 // collection so there may be dirty bits in the mod-union table.
5936 const int alignment =
5937 CardTableModRefBS::card_size * BitsPerWord;
5938 {
5939 // ... First handle dirty cards in CMS gen
5940 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5941 MemRegion ur = _cmsGen->used_region();
5942 HeapWord* lb = ur.start();
5943 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5944 MemRegion cms_span(lb, ub);
5945 _modUnionTable.dirty_range_iterate_clear(cms_span,
5946 &markFromDirtyCardsClosure);
5947 verify_work_stacks_empty();
5948 if (PrintCMSStatistics != 0) {
5949 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5950 markFromDirtyCardsClosure.num_dirty_cards());
5951 }
5952 }
5953 }
5954 if (VerifyDuringGC &&
5955 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5956 HandleMark hm; // Discard invalid handles created during verification
5957 Universe::verify();
5958 }
5959 {
5960 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm);
5962 verify_work_stacks_empty();
5964 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5965 GenCollectedHeap::StrongRootsScope srs(gch);
5966 gch->gen_process_strong_roots(_cmsGen->level(),
5967 true, // younger gens as roots
5968 false, // use the local StrongRootsScope
5969 false, // not scavenging
5970 SharedHeap::ScanningOption(roots_scanning_options()),
5971 &mrias_cl,
5972 true, // walk code active on stacks
5973 NULL,
5974 NULL); // The dirty klasses will be handled below
5976 assert(should_unload_classes()
5977 || (roots_scanning_options() & SharedHeap::SO_CodeCache),
5978 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5979 }
5981 {
5982 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm);
5984 verify_work_stacks_empty();
5986 // Scan all class loader data objects that might have been introduced
5987 // during concurrent marking.
5988 ResourceMark rm;
5989 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5990 for (int i = 0; i < array->length(); i++) {
5991 mrias_cl.do_class_loader_data(array->at(i));
5992 }
5994 // We don't need to keep track of new CLDs anymore.
5995 ClassLoaderDataGraph::remember_new_clds(false);
5997 verify_work_stacks_empty();
5998 }
6000 {
6001 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm);
6003 verify_work_stacks_empty();
6005 RemarkKlassClosure remark_klass_closure(&mrias_cl);
6006 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
6008 verify_work_stacks_empty();
6009 }
6011 // We might have added oops to ClassLoaderData::_handles during the
6012 // concurrent marking phase. These oops point to newly allocated objects
6013 // that are guaranteed to be kept alive. Either by the direct allocation
6014 // code, or when the young collector processes the strong roots. Hence,
6015 // we don't have to revisit the _handles block during the remark phase.
6017 verify_work_stacks_empty();
6018 // Restore evacuated mark words, if any, used for overflow list links
6019 if (!CMSOverflowEarlyRestoration) {
6020 restore_preserved_marks_if_any();
6021 }
6022 verify_overflow_empty();
6023 }
6025 ////////////////////////////////////////////////////////
6026 // Parallel Reference Processing Task Proxy Class
6027 ////////////////////////////////////////////////////////
6028 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
6029 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
6030 CMSCollector* _collector;
6031 CMSBitMap* _mark_bit_map;
6032 const MemRegion _span;
6033 ProcessTask& _task;
6035 public:
6036 CMSRefProcTaskProxy(ProcessTask& task,
6037 CMSCollector* collector,
6038 const MemRegion& span,
6039 CMSBitMap* mark_bit_map,
6040 AbstractWorkGang* workers,
6041 OopTaskQueueSet* task_queues):
6042 // XXX Should superclass AGTWOQ also know about AWG since it knows
6043 // about the task_queues used by the AWG? Then it could initialize
6044 // the terminator() object. See 6984287. The set_for_termination()
6045 // below is a temporary band-aid for the regression in 6984287.
6046 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
6047 task_queues),
6048 _task(task),
6049 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
6050 {
6051 assert(_collector->_span.equals(_span) && !_span.is_empty(),
6052 "Inconsistency in _span");
6053 set_for_termination(workers->active_workers());
6054 }
6056 OopTaskQueueSet* task_queues() { return queues(); }
6058 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
6060 void do_work_steal(int i,
6061 CMSParDrainMarkingStackClosure* drain,
6062 CMSParKeepAliveClosure* keep_alive,
6063 int* seed);
6065 virtual void work(uint worker_id);
6066 };
6068 void CMSRefProcTaskProxy::work(uint worker_id) {
6069 assert(_collector->_span.equals(_span), "Inconsistency in _span");
6070 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
6071 _mark_bit_map,
6072 work_queue(worker_id));
6073 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
6074 _mark_bit_map,
6075 work_queue(worker_id));
6076 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
6077 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
6078 if (_task.marks_oops_alive()) {
6079 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
6080 _collector->hash_seed(worker_id));
6081 }
6082 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
6083 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
6084 }
6086 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
6087 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
6088 EnqueueTask& _task;
6090 public:
6091 CMSRefEnqueueTaskProxy(EnqueueTask& task)
6092 : AbstractGangTask("Enqueue reference objects in parallel"),
6093 _task(task)
6094 { }
6096 virtual void work(uint worker_id)
6097 {
6098 _task.work(worker_id);
6099 }
6100 };
6102 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
6103 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
6104 _span(span),
6105 _bit_map(bit_map),
6106 _work_queue(work_queue),
6107 _mark_and_push(collector, span, bit_map, work_queue),
6108 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6109 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
6110 { }
6112 // . see if we can share work_queues with ParNew? XXX
6113 void CMSRefProcTaskProxy::do_work_steal(int i,
6114 CMSParDrainMarkingStackClosure* drain,
6115 CMSParKeepAliveClosure* keep_alive,
6116 int* seed) {
6117 OopTaskQueue* work_q = work_queue(i);
6118 NOT_PRODUCT(int num_steals = 0;)
6119 oop obj_to_scan;
6121 while (true) {
6122 // Completely finish any left over work from (an) earlier round(s)
6123 drain->trim_queue(0);
6124 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
6125 (size_t)ParGCDesiredObjsFromOverflowList);
6126 // Now check if there's any work in the overflow list
6127 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
6128 // only affects the number of attempts made to get work from the
6129 // overflow list and does not affect the number of workers. Just
6130 // pass ParallelGCThreads so this behavior is unchanged.
6131 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
6132 work_q,
6133 ParallelGCThreads)) {
6134 // Found something in global overflow list;
6135 // not yet ready to go stealing work from others.
6136 // We'd like to assert(work_q->size() != 0, ...)
6137 // because we just took work from the overflow list,
6138 // but of course we can't, since all of that might have
6139 // been already stolen from us.
6140 continue;
6141 }
6142 // Verify that we have no work before we resort to stealing
6143 assert(work_q->size() == 0, "Have work, shouldn't steal");
6144 // Try to steal from other queues that have work
6145 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
6146 NOT_PRODUCT(num_steals++;)
6147 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
6148 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
6149 // Do scanning work
6150 obj_to_scan->oop_iterate(keep_alive);
6151 // Loop around, finish this work, and try to steal some more
6152 } else if (terminator()->offer_termination()) {
6153 break; // nirvana from the infinite cycle
6154 }
6155 }
6156 NOT_PRODUCT(
6157 if (PrintCMSStatistics != 0) {
6158 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
6159 }
6160 )
6161 }
6163 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
6164 {
6165 GenCollectedHeap* gch = GenCollectedHeap::heap();
6166 FlexibleWorkGang* workers = gch->workers();
6167 assert(workers != NULL, "Need parallel worker threads.");
6168 CMSRefProcTaskProxy rp_task(task, &_collector,
6169 _collector.ref_processor()->span(),
6170 _collector.markBitMap(),
6171 workers, _collector.task_queues());
6172 workers->run_task(&rp_task);
6173 }
6175 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
6176 {
6178 GenCollectedHeap* gch = GenCollectedHeap::heap();
6179 FlexibleWorkGang* workers = gch->workers();
6180 assert(workers != NULL, "Need parallel worker threads.");
6181 CMSRefEnqueueTaskProxy enq_task(task);
6182 workers->run_task(&enq_task);
6183 }
6185 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
6187 ResourceMark rm;
6188 HandleMark hm;
6190 ReferenceProcessor* rp = ref_processor();
6191 assert(rp->span().equals(_span), "Spans should be equal");
6192 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
6193 // Process weak references.
6194 rp->setup_policy(clear_all_soft_refs);
6195 verify_work_stacks_empty();
6197 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
6198 &_markStack, false /* !preclean */);
6199 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
6200 _span, &_markBitMap, &_markStack,
6201 &cmsKeepAliveClosure, false /* !preclean */);
6202 {
6203 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm);
6205 ReferenceProcessorStats stats;
6206 if (rp->processing_is_mt()) {
6207 // Set the degree of MT here. If the discovery is done MT, there
6208 // may have been a different number of threads doing the discovery
6209 // and a different number of discovered lists may have Ref objects.
6210 // That is OK as long as the Reference lists are balanced (see
6211 // balance_all_queues() and balance_queues()).
6212 GenCollectedHeap* gch = GenCollectedHeap::heap();
6213 int active_workers = ParallelGCThreads;
6214 FlexibleWorkGang* workers = gch->workers();
6215 if (workers != NULL) {
6216 active_workers = workers->active_workers();
6217 // The expectation is that active_workers will have already
6218 // been set to a reasonable value. If it has not been set,
6219 // investigate.
6220 assert(active_workers > 0, "Should have been set during scavenge");
6221 }
6222 rp->set_active_mt_degree(active_workers);
6223 CMSRefProcTaskExecutor task_executor(*this);
6224 stats = rp->process_discovered_references(&_is_alive_closure,
6225 &cmsKeepAliveClosure,
6226 &cmsDrainMarkingStackClosure,
6227 &task_executor,
6228 _gc_timer_cm);
6229 } else {
6230 stats = rp->process_discovered_references(&_is_alive_closure,
6231 &cmsKeepAliveClosure,
6232 &cmsDrainMarkingStackClosure,
6233 NULL,
6234 _gc_timer_cm);
6235 }
6236 _gc_tracer_cm->report_gc_reference_stats(stats);
6238 }
6240 // This is the point where the entire marking should have completed.
6241 verify_work_stacks_empty();
6243 if (should_unload_classes()) {
6244 {
6245 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm);
6247 // Unload classes and purge the SystemDictionary.
6248 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
6250 // Unload nmethods.
6251 CodeCache::do_unloading(&_is_alive_closure, purged_class);
6253 // Prune dead klasses from subklass/sibling/implementor lists.
6254 Klass::clean_weak_klass_links(&_is_alive_closure);
6255 }
6257 {
6258 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm);
6259 // Clean up unreferenced symbols in symbol table.
6260 SymbolTable::unlink();
6261 }
6262 }
6264 // CMS doesn't use the StringTable as hard roots when class unloading is turned off.
6265 // Need to check if we really scanned the StringTable.
6266 if ((roots_scanning_options() & SharedHeap::SO_Strings) == 0) {
6267 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm);
6268 // Delete entries for dead interned strings.
6269 StringTable::unlink(&_is_alive_closure);
6270 }
6272 // Restore any preserved marks as a result of mark stack or
6273 // work queue overflow
6274 restore_preserved_marks_if_any(); // done single-threaded for now
6276 rp->set_enqueuing_is_done(true);
6277 if (rp->processing_is_mt()) {
6278 rp->balance_all_queues();
6279 CMSRefProcTaskExecutor task_executor(*this);
6280 rp->enqueue_discovered_references(&task_executor);
6281 } else {
6282 rp->enqueue_discovered_references(NULL);
6283 }
6284 rp->verify_no_references_recorded();
6285 assert(!rp->discovery_enabled(), "should have been disabled");
6286 }
6288 #ifndef PRODUCT
6289 void CMSCollector::check_correct_thread_executing() {
6290 Thread* t = Thread::current();
6291 // Only the VM thread or the CMS thread should be here.
6292 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6293 "Unexpected thread type");
6294 // If this is the vm thread, the foreground process
6295 // should not be waiting. Note that _foregroundGCIsActive is
6296 // true while the foreground collector is waiting.
6297 if (_foregroundGCShouldWait) {
6298 // We cannot be the VM thread
6299 assert(t->is_ConcurrentGC_thread(),
6300 "Should be CMS thread");
6301 } else {
6302 // We can be the CMS thread only if we are in a stop-world
6303 // phase of CMS collection.
6304 if (t->is_ConcurrentGC_thread()) {
6305 assert(_collectorState == InitialMarking ||
6306 _collectorState == FinalMarking,
6307 "Should be a stop-world phase");
6308 // The CMS thread should be holding the CMS_token.
6309 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6310 "Potential interference with concurrently "
6311 "executing VM thread");
6312 }
6313 }
6314 }
6315 #endif
6317 void CMSCollector::sweep(bool asynch) {
6318 assert(_collectorState == Sweeping, "just checking");
6319 check_correct_thread_executing();
6320 verify_work_stacks_empty();
6321 verify_overflow_empty();
6322 increment_sweep_count();
6323 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6325 _inter_sweep_timer.stop();
6326 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6327 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
6329 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6330 _intra_sweep_timer.reset();
6331 _intra_sweep_timer.start();
6332 if (asynch) {
6333 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6334 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
6335 // First sweep the old gen
6336 {
6337 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6338 bitMapLock());
6339 sweepWork(_cmsGen, asynch);
6340 }
6342 // Update Universe::_heap_*_at_gc figures.
6343 // We need all the free list locks to make the abstract state
6344 // transition from Sweeping to Resetting. See detailed note
6345 // further below.
6346 {
6347 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6348 // Update heap occupancy information which is used as
6349 // input to soft ref clearing policy at the next gc.
6350 Universe::update_heap_info_at_gc();
6351 _collectorState = Resizing;
6352 }
6353 } else {
6354 // already have needed locks
6355 sweepWork(_cmsGen, asynch);
6356 // Update heap occupancy information which is used as
6357 // input to soft ref clearing policy at the next gc.
6358 Universe::update_heap_info_at_gc();
6359 _collectorState = Resizing;
6360 }
6361 verify_work_stacks_empty();
6362 verify_overflow_empty();
6364 if (should_unload_classes()) {
6365 ClassLoaderDataGraph::purge();
6366 }
6368 _intra_sweep_timer.stop();
6369 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6371 _inter_sweep_timer.reset();
6372 _inter_sweep_timer.start();
6374 // We need to use a monotonically non-deccreasing time in ms
6375 // or we will see time-warp warnings and os::javaTimeMillis()
6376 // does not guarantee monotonicity.
6377 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6378 update_time_of_last_gc(now);
6380 // NOTE on abstract state transitions:
6381 // Mutators allocate-live and/or mark the mod-union table dirty
6382 // based on the state of the collection. The former is done in
6383 // the interval [Marking, Sweeping] and the latter in the interval
6384 // [Marking, Sweeping). Thus the transitions into the Marking state
6385 // and out of the Sweeping state must be synchronously visible
6386 // globally to the mutators.
6387 // The transition into the Marking state happens with the world
6388 // stopped so the mutators will globally see it. Sweeping is
6389 // done asynchronously by the background collector so the transition
6390 // from the Sweeping state to the Resizing state must be done
6391 // under the freelistLock (as is the check for whether to
6392 // allocate-live and whether to dirty the mod-union table).
6393 assert(_collectorState == Resizing, "Change of collector state to"
6394 " Resizing must be done under the freelistLocks (plural)");
6396 // Now that sweeping has been completed, we clear
6397 // the incremental_collection_failed flag,
6398 // thus inviting a younger gen collection to promote into
6399 // this generation. If such a promotion may still fail,
6400 // the flag will be set again when a young collection is
6401 // attempted.
6402 GenCollectedHeap* gch = GenCollectedHeap::heap();
6403 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6404 gch->update_full_collections_completed(_collection_count_start);
6405 }
6407 // FIX ME!!! Looks like this belongs in CFLSpace, with
6408 // CMSGen merely delegating to it.
6409 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6410 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6411 HeapWord* minAddr = _cmsSpace->bottom();
6412 HeapWord* largestAddr =
6413 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6414 if (largestAddr == NULL) {
6415 // The dictionary appears to be empty. In this case
6416 // try to coalesce at the end of the heap.
6417 largestAddr = _cmsSpace->end();
6418 }
6419 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6420 size_t nearLargestOffset =
6421 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6422 if (PrintFLSStatistics != 0) {
6423 gclog_or_tty->print_cr(
6424 "CMS: Large Block: " PTR_FORMAT ";"
6425 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6426 largestAddr,
6427 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6428 }
6429 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6430 }
6432 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6433 return addr >= _cmsSpace->nearLargestChunk();
6434 }
6436 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6437 return _cmsSpace->find_chunk_at_end();
6438 }
6440 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6441 bool full) {
6442 // The next lower level has been collected. Gather any statistics
6443 // that are of interest at this point.
6444 if (!full && (current_level + 1) == level()) {
6445 // Gather statistics on the young generation collection.
6446 collector()->stats().record_gc0_end(used());
6447 }
6448 }
6450 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6451 GenCollectedHeap* gch = GenCollectedHeap::heap();
6452 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6453 "Wrong type of heap");
6454 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6455 gch->gen_policy()->size_policy();
6456 assert(sp->is_gc_cms_adaptive_size_policy(),
6457 "Wrong type of size policy");
6458 return sp;
6459 }
6461 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6462 if (PrintGCDetails && Verbose) {
6463 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6464 }
6465 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6466 _debug_collection_type =
6467 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6468 if (PrintGCDetails && Verbose) {
6469 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6470 }
6471 }
6473 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6474 bool asynch) {
6475 // We iterate over the space(s) underlying this generation,
6476 // checking the mark bit map to see if the bits corresponding
6477 // to specific blocks are marked or not. Blocks that are
6478 // marked are live and are not swept up. All remaining blocks
6479 // are swept up, with coalescing on-the-fly as we sweep up
6480 // contiguous free and/or garbage blocks:
6481 // We need to ensure that the sweeper synchronizes with allocators
6482 // and stop-the-world collectors. In particular, the following
6483 // locks are used:
6484 // . CMS token: if this is held, a stop the world collection cannot occur
6485 // . freelistLock: if this is held no allocation can occur from this
6486 // generation by another thread
6487 // . bitMapLock: if this is held, no other thread can access or update
6488 //
6490 // Note that we need to hold the freelistLock if we use
6491 // block iterate below; else the iterator might go awry if
6492 // a mutator (or promotion) causes block contents to change
6493 // (for instance if the allocator divvies up a block).
6494 // If we hold the free list lock, for all practical purposes
6495 // young generation GC's can't occur (they'll usually need to
6496 // promote), so we might as well prevent all young generation
6497 // GC's while we do a sweeping step. For the same reason, we might
6498 // as well take the bit map lock for the entire duration
6500 // check that we hold the requisite locks
6501 assert(have_cms_token(), "Should hold cms token");
6502 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6503 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6504 "Should possess CMS token to sweep");
6505 assert_lock_strong(gen->freelistLock());
6506 assert_lock_strong(bitMapLock());
6508 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6509 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6510 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6511 _inter_sweep_estimate.padded_average(),
6512 _intra_sweep_estimate.padded_average());
6513 gen->setNearLargestChunk();
6515 {
6516 SweepClosure sweepClosure(this, gen, &_markBitMap,
6517 CMSYield && asynch);
6518 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6519 // We need to free-up/coalesce garbage/blocks from a
6520 // co-terminal free run. This is done in the SweepClosure
6521 // destructor; so, do not remove this scope, else the
6522 // end-of-sweep-census below will be off by a little bit.
6523 }
6524 gen->cmsSpace()->sweep_completed();
6525 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6526 if (should_unload_classes()) { // unloaded classes this cycle,
6527 _concurrent_cycles_since_last_unload = 0; // ... reset count
6528 } else { // did not unload classes,
6529 _concurrent_cycles_since_last_unload++; // ... increment count
6530 }
6531 }
6533 // Reset CMS data structures (for now just the marking bit map)
6534 // preparatory for the next cycle.
6535 void CMSCollector::reset(bool asynch) {
6536 GenCollectedHeap* gch = GenCollectedHeap::heap();
6537 CMSAdaptiveSizePolicy* sp = size_policy();
6538 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6539 if (asynch) {
6540 CMSTokenSyncWithLocks ts(true, bitMapLock());
6542 // If the state is not "Resetting", the foreground thread
6543 // has done a collection and the resetting.
6544 if (_collectorState != Resetting) {
6545 assert(_collectorState == Idling, "The state should only change"
6546 " because the foreground collector has finished the collection");
6547 return;
6548 }
6550 // Clear the mark bitmap (no grey objects to start with)
6551 // for the next cycle.
6552 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6553 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6555 HeapWord* curAddr = _markBitMap.startWord();
6556 while (curAddr < _markBitMap.endWord()) {
6557 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6558 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6559 _markBitMap.clear_large_range(chunk);
6560 if (ConcurrentMarkSweepThread::should_yield() &&
6561 !foregroundGCIsActive() &&
6562 CMSYield) {
6563 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6564 "CMS thread should hold CMS token");
6565 assert_lock_strong(bitMapLock());
6566 bitMapLock()->unlock();
6567 ConcurrentMarkSweepThread::desynchronize(true);
6568 ConcurrentMarkSweepThread::acknowledge_yield_request();
6569 stopTimer();
6570 if (PrintCMSStatistics != 0) {
6571 incrementYields();
6572 }
6573 icms_wait();
6575 // See the comment in coordinator_yield()
6576 for (unsigned i = 0; i < CMSYieldSleepCount &&
6577 ConcurrentMarkSweepThread::should_yield() &&
6578 !CMSCollector::foregroundGCIsActive(); ++i) {
6579 os::sleep(Thread::current(), 1, false);
6580 ConcurrentMarkSweepThread::acknowledge_yield_request();
6581 }
6583 ConcurrentMarkSweepThread::synchronize(true);
6584 bitMapLock()->lock_without_safepoint_check();
6585 startTimer();
6586 }
6587 curAddr = chunk.end();
6588 }
6589 // A successful mostly concurrent collection has been done.
6590 // Because only the full (i.e., concurrent mode failure) collections
6591 // are being measured for gc overhead limits, clean the "near" flag
6592 // and count.
6593 sp->reset_gc_overhead_limit_count();
6594 _collectorState = Idling;
6595 } else {
6596 // already have the lock
6597 assert(_collectorState == Resetting, "just checking");
6598 assert_lock_strong(bitMapLock());
6599 _markBitMap.clear_all();
6600 _collectorState = Idling;
6601 }
6603 // Stop incremental mode after a cycle completes, so that any future cycles
6604 // are triggered by allocation.
6605 stop_icms();
6607 NOT_PRODUCT(
6608 if (RotateCMSCollectionTypes) {
6609 _cmsGen->rotate_debug_collection_type();
6610 }
6611 )
6613 register_gc_end();
6614 }
6616 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6617 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6618 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6619 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL);
6620 TraceCollectorStats tcs(counters());
6622 switch (op) {
6623 case CMS_op_checkpointRootsInitial: {
6624 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6625 checkpointRootsInitial(true); // asynch
6626 if (PrintGC) {
6627 _cmsGen->printOccupancy("initial-mark");
6628 }
6629 break;
6630 }
6631 case CMS_op_checkpointRootsFinal: {
6632 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6633 checkpointRootsFinal(true, // asynch
6634 false, // !clear_all_soft_refs
6635 false); // !init_mark_was_synchronous
6636 if (PrintGC) {
6637 _cmsGen->printOccupancy("remark");
6638 }
6639 break;
6640 }
6641 default:
6642 fatal("No such CMS_op");
6643 }
6644 }
6646 #ifndef PRODUCT
6647 size_t const CMSCollector::skip_header_HeapWords() {
6648 return FreeChunk::header_size();
6649 }
6651 // Try and collect here conditions that should hold when
6652 // CMS thread is exiting. The idea is that the foreground GC
6653 // thread should not be blocked if it wants to terminate
6654 // the CMS thread and yet continue to run the VM for a while
6655 // after that.
6656 void CMSCollector::verify_ok_to_terminate() const {
6657 assert(Thread::current()->is_ConcurrentGC_thread(),
6658 "should be called by CMS thread");
6659 assert(!_foregroundGCShouldWait, "should be false");
6660 // We could check here that all the various low-level locks
6661 // are not held by the CMS thread, but that is overkill; see
6662 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6663 // is checked.
6664 }
6665 #endif
6667 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6668 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6669 "missing Printezis mark?");
6670 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6671 size_t size = pointer_delta(nextOneAddr + 1, addr);
6672 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6673 "alignment problem");
6674 assert(size >= 3, "Necessary for Printezis marks to work");
6675 return size;
6676 }
6678 // A variant of the above (block_size_using_printezis_bits()) except
6679 // that we return 0 if the P-bits are not yet set.
6680 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6681 if (_markBitMap.isMarked(addr + 1)) {
6682 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6683 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6684 size_t size = pointer_delta(nextOneAddr + 1, addr);
6685 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6686 "alignment problem");
6687 assert(size >= 3, "Necessary for Printezis marks to work");
6688 return size;
6689 }
6690 return 0;
6691 }
6693 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6694 size_t sz = 0;
6695 oop p = (oop)addr;
6696 if (p->klass_or_null() != NULL) {
6697 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6698 } else {
6699 sz = block_size_using_printezis_bits(addr);
6700 }
6701 assert(sz > 0, "size must be nonzero");
6702 HeapWord* next_block = addr + sz;
6703 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6704 CardTableModRefBS::card_size);
6705 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6706 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6707 "must be different cards");
6708 return next_card;
6709 }
6712 // CMS Bit Map Wrapper /////////////////////////////////////////
6714 // Construct a CMS bit map infrastructure, but don't create the
6715 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6716 // further below.
6717 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6718 _bm(),
6719 _shifter(shifter),
6720 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6721 {
6722 _bmStartWord = 0;
6723 _bmWordSize = 0;
6724 }
6726 bool CMSBitMap::allocate(MemRegion mr) {
6727 _bmStartWord = mr.start();
6728 _bmWordSize = mr.word_size();
6729 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6730 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6731 if (!brs.is_reserved()) {
6732 warning("CMS bit map allocation failure");
6733 return false;
6734 }
6735 // For now we'll just commit all of the bit map up fromt.
6736 // Later on we'll try to be more parsimonious with swap.
6737 if (!_virtual_space.initialize(brs, brs.size())) {
6738 warning("CMS bit map backing store failure");
6739 return false;
6740 }
6741 assert(_virtual_space.committed_size() == brs.size(),
6742 "didn't reserve backing store for all of CMS bit map?");
6743 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6744 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6745 _bmWordSize, "inconsistency in bit map sizing");
6746 _bm.set_size(_bmWordSize >> _shifter);
6748 // bm.clear(); // can we rely on getting zero'd memory? verify below
6749 assert(isAllClear(),
6750 "Expected zero'd memory from ReservedSpace constructor");
6751 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6752 "consistency check");
6753 return true;
6754 }
6756 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6757 HeapWord *next_addr, *end_addr, *last_addr;
6758 assert_locked();
6759 assert(covers(mr), "out-of-range error");
6760 // XXX assert that start and end are appropriately aligned
6761 for (next_addr = mr.start(), end_addr = mr.end();
6762 next_addr < end_addr; next_addr = last_addr) {
6763 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6764 last_addr = dirty_region.end();
6765 if (!dirty_region.is_empty()) {
6766 cl->do_MemRegion(dirty_region);
6767 } else {
6768 assert(last_addr == end_addr, "program logic");
6769 return;
6770 }
6771 }
6772 }
6774 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6775 _bm.print_on_error(st, prefix);
6776 }
6778 #ifndef PRODUCT
6779 void CMSBitMap::assert_locked() const {
6780 CMSLockVerifier::assert_locked(lock());
6781 }
6783 bool CMSBitMap::covers(MemRegion mr) const {
6784 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6785 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6786 "size inconsistency");
6787 return (mr.start() >= _bmStartWord) &&
6788 (mr.end() <= endWord());
6789 }
6791 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6792 return (start >= _bmStartWord && (start + size) <= endWord());
6793 }
6795 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6796 // verify that there are no 1 bits in the interval [left, right)
6797 FalseBitMapClosure falseBitMapClosure;
6798 iterate(&falseBitMapClosure, left, right);
6799 }
6801 void CMSBitMap::region_invariant(MemRegion mr)
6802 {
6803 assert_locked();
6804 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6805 assert(!mr.is_empty(), "unexpected empty region");
6806 assert(covers(mr), "mr should be covered by bit map");
6807 // convert address range into offset range
6808 size_t start_ofs = heapWordToOffset(mr.start());
6809 // Make sure that end() is appropriately aligned
6810 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6811 (1 << (_shifter+LogHeapWordSize))),
6812 "Misaligned mr.end()");
6813 size_t end_ofs = heapWordToOffset(mr.end());
6814 assert(end_ofs > start_ofs, "Should mark at least one bit");
6815 }
6817 #endif
6819 bool CMSMarkStack::allocate(size_t size) {
6820 // allocate a stack of the requisite depth
6821 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6822 size * sizeof(oop)));
6823 if (!rs.is_reserved()) {
6824 warning("CMSMarkStack allocation failure");
6825 return false;
6826 }
6827 if (!_virtual_space.initialize(rs, rs.size())) {
6828 warning("CMSMarkStack backing store failure");
6829 return false;
6830 }
6831 assert(_virtual_space.committed_size() == rs.size(),
6832 "didn't reserve backing store for all of CMS stack?");
6833 _base = (oop*)(_virtual_space.low());
6834 _index = 0;
6835 _capacity = size;
6836 NOT_PRODUCT(_max_depth = 0);
6837 return true;
6838 }
6840 // XXX FIX ME !!! In the MT case we come in here holding a
6841 // leaf lock. For printing we need to take a further lock
6842 // which has lower rank. We need to recallibrate the two
6843 // lock-ranks involved in order to be able to rpint the
6844 // messages below. (Or defer the printing to the caller.
6845 // For now we take the expedient path of just disabling the
6846 // messages for the problematic case.)
6847 void CMSMarkStack::expand() {
6848 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6849 if (_capacity == MarkStackSizeMax) {
6850 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6851 // We print a warning message only once per CMS cycle.
6852 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6853 }
6854 return;
6855 }
6856 // Double capacity if possible
6857 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6858 // Do not give up existing stack until we have managed to
6859 // get the double capacity that we desired.
6860 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6861 new_capacity * sizeof(oop)));
6862 if (rs.is_reserved()) {
6863 // Release the backing store associated with old stack
6864 _virtual_space.release();
6865 // Reinitialize virtual space for new stack
6866 if (!_virtual_space.initialize(rs, rs.size())) {
6867 fatal("Not enough swap for expanded marking stack");
6868 }
6869 _base = (oop*)(_virtual_space.low());
6870 _index = 0;
6871 _capacity = new_capacity;
6872 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6873 // Failed to double capacity, continue;
6874 // we print a detail message only once per CMS cycle.
6875 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6876 SIZE_FORMAT"K",
6877 _capacity / K, new_capacity / K);
6878 }
6879 }
6882 // Closures
6883 // XXX: there seems to be a lot of code duplication here;
6884 // should refactor and consolidate common code.
6886 // This closure is used to mark refs into the CMS generation in
6887 // the CMS bit map. Called at the first checkpoint. This closure
6888 // assumes that we do not need to re-mark dirty cards; if the CMS
6889 // generation on which this is used is not an oldest
6890 // generation then this will lose younger_gen cards!
6892 MarkRefsIntoClosure::MarkRefsIntoClosure(
6893 MemRegion span, CMSBitMap* bitMap):
6894 _span(span),
6895 _bitMap(bitMap)
6896 {
6897 assert(_ref_processor == NULL, "deliberately left NULL");
6898 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6899 }
6901 void MarkRefsIntoClosure::do_oop(oop obj) {
6902 // if p points into _span, then mark corresponding bit in _markBitMap
6903 assert(obj->is_oop(), "expected an oop");
6904 HeapWord* addr = (HeapWord*)obj;
6905 if (_span.contains(addr)) {
6906 // this should be made more efficient
6907 _bitMap->mark(addr);
6908 }
6909 }
6911 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6912 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6914 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6915 MemRegion span, CMSBitMap* bitMap):
6916 _span(span),
6917 _bitMap(bitMap)
6918 {
6919 assert(_ref_processor == NULL, "deliberately left NULL");
6920 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6921 }
6923 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6924 // if p points into _span, then mark corresponding bit in _markBitMap
6925 assert(obj->is_oop(), "expected an oop");
6926 HeapWord* addr = (HeapWord*)obj;
6927 if (_span.contains(addr)) {
6928 // this should be made more efficient
6929 _bitMap->par_mark(addr);
6930 }
6931 }
6933 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6934 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6936 // A variant of the above, used for CMS marking verification.
6937 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6938 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6939 _span(span),
6940 _verification_bm(verification_bm),
6941 _cms_bm(cms_bm)
6942 {
6943 assert(_ref_processor == NULL, "deliberately left NULL");
6944 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6945 }
6947 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6948 // if p points into _span, then mark corresponding bit in _markBitMap
6949 assert(obj->is_oop(), "expected an oop");
6950 HeapWord* addr = (HeapWord*)obj;
6951 if (_span.contains(addr)) {
6952 _verification_bm->mark(addr);
6953 if (!_cms_bm->isMarked(addr)) {
6954 oop(addr)->print();
6955 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6956 fatal("... aborting");
6957 }
6958 }
6959 }
6961 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6962 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6964 //////////////////////////////////////////////////
6965 // MarkRefsIntoAndScanClosure
6966 //////////////////////////////////////////////////
6968 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6969 ReferenceProcessor* rp,
6970 CMSBitMap* bit_map,
6971 CMSBitMap* mod_union_table,
6972 CMSMarkStack* mark_stack,
6973 CMSCollector* collector,
6974 bool should_yield,
6975 bool concurrent_precleaning):
6976 _collector(collector),
6977 _span(span),
6978 _bit_map(bit_map),
6979 _mark_stack(mark_stack),
6980 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6981 mark_stack, concurrent_precleaning),
6982 _yield(should_yield),
6983 _concurrent_precleaning(concurrent_precleaning),
6984 _freelistLock(NULL)
6985 {
6986 _ref_processor = rp;
6987 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6988 }
6990 // This closure is used to mark refs into the CMS generation at the
6991 // second (final) checkpoint, and to scan and transitively follow
6992 // the unmarked oops. It is also used during the concurrent precleaning
6993 // phase while scanning objects on dirty cards in the CMS generation.
6994 // The marks are made in the marking bit map and the marking stack is
6995 // used for keeping the (newly) grey objects during the scan.
6996 // The parallel version (Par_...) appears further below.
6997 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6998 if (obj != NULL) {
6999 assert(obj->is_oop(), "expected an oop");
7000 HeapWord* addr = (HeapWord*)obj;
7001 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7002 assert(_collector->overflow_list_is_empty(),
7003 "overflow list should be empty");
7004 if (_span.contains(addr) &&
7005 !_bit_map->isMarked(addr)) {
7006 // mark bit map (object is now grey)
7007 _bit_map->mark(addr);
7008 // push on marking stack (stack should be empty), and drain the
7009 // stack by applying this closure to the oops in the oops popped
7010 // from the stack (i.e. blacken the grey objects)
7011 bool res = _mark_stack->push(obj);
7012 assert(res, "Should have space to push on empty stack");
7013 do {
7014 oop new_oop = _mark_stack->pop();
7015 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7016 assert(_bit_map->isMarked((HeapWord*)new_oop),
7017 "only grey objects on this stack");
7018 // iterate over the oops in this oop, marking and pushing
7019 // the ones in CMS heap (i.e. in _span).
7020 new_oop->oop_iterate(&_pushAndMarkClosure);
7021 // check if it's time to yield
7022 do_yield_check();
7023 } while (!_mark_stack->isEmpty() ||
7024 (!_concurrent_precleaning && take_from_overflow_list()));
7025 // if marking stack is empty, and we are not doing this
7026 // during precleaning, then check the overflow list
7027 }
7028 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7029 assert(_collector->overflow_list_is_empty(),
7030 "overflow list was drained above");
7031 // We could restore evacuated mark words, if any, used for
7032 // overflow list links here because the overflow list is
7033 // provably empty here. That would reduce the maximum
7034 // size requirements for preserved_{oop,mark}_stack.
7035 // But we'll just postpone it until we are all done
7036 // so we can just stream through.
7037 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
7038 _collector->restore_preserved_marks_if_any();
7039 assert(_collector->no_preserved_marks(), "No preserved marks");
7040 }
7041 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
7042 "All preserved marks should have been restored above");
7043 }
7044 }
7046 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
7047 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
7049 void MarkRefsIntoAndScanClosure::do_yield_work() {
7050 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7051 "CMS thread should hold CMS token");
7052 assert_lock_strong(_freelistLock);
7053 assert_lock_strong(_bit_map->lock());
7054 // relinquish the free_list_lock and bitMaplock()
7055 _bit_map->lock()->unlock();
7056 _freelistLock->unlock();
7057 ConcurrentMarkSweepThread::desynchronize(true);
7058 ConcurrentMarkSweepThread::acknowledge_yield_request();
7059 _collector->stopTimer();
7060 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7061 if (PrintCMSStatistics != 0) {
7062 _collector->incrementYields();
7063 }
7064 _collector->icms_wait();
7066 // See the comment in coordinator_yield()
7067 for (unsigned i = 0;
7068 i < CMSYieldSleepCount &&
7069 ConcurrentMarkSweepThread::should_yield() &&
7070 !CMSCollector::foregroundGCIsActive();
7071 ++i) {
7072 os::sleep(Thread::current(), 1, false);
7073 ConcurrentMarkSweepThread::acknowledge_yield_request();
7074 }
7076 ConcurrentMarkSweepThread::synchronize(true);
7077 _freelistLock->lock_without_safepoint_check();
7078 _bit_map->lock()->lock_without_safepoint_check();
7079 _collector->startTimer();
7080 }
7082 ///////////////////////////////////////////////////////////
7083 // Par_MarkRefsIntoAndScanClosure: a parallel version of
7084 // MarkRefsIntoAndScanClosure
7085 ///////////////////////////////////////////////////////////
7086 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
7087 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
7088 CMSBitMap* bit_map, OopTaskQueue* work_queue):
7089 _span(span),
7090 _bit_map(bit_map),
7091 _work_queue(work_queue),
7092 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
7093 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
7094 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
7095 {
7096 _ref_processor = rp;
7097 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7098 }
7100 // This closure is used to mark refs into the CMS generation at the
7101 // second (final) checkpoint, and to scan and transitively follow
7102 // the unmarked oops. The marks are made in the marking bit map and
7103 // the work_queue is used for keeping the (newly) grey objects during
7104 // the scan phase whence they are also available for stealing by parallel
7105 // threads. Since the marking bit map is shared, updates are
7106 // synchronized (via CAS).
7107 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
7108 if (obj != NULL) {
7109 // Ignore mark word because this could be an already marked oop
7110 // that may be chained at the end of the overflow list.
7111 assert(obj->is_oop(true), "expected an oop");
7112 HeapWord* addr = (HeapWord*)obj;
7113 if (_span.contains(addr) &&
7114 !_bit_map->isMarked(addr)) {
7115 // mark bit map (object will become grey):
7116 // It is possible for several threads to be
7117 // trying to "claim" this object concurrently;
7118 // the unique thread that succeeds in marking the
7119 // object first will do the subsequent push on
7120 // to the work queue (or overflow list).
7121 if (_bit_map->par_mark(addr)) {
7122 // push on work_queue (which may not be empty), and trim the
7123 // queue to an appropriate length by applying this closure to
7124 // the oops in the oops popped from the stack (i.e. blacken the
7125 // grey objects)
7126 bool res = _work_queue->push(obj);
7127 assert(res, "Low water mark should be less than capacity?");
7128 trim_queue(_low_water_mark);
7129 } // Else, another thread claimed the object
7130 }
7131 }
7132 }
7134 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7135 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7137 // This closure is used to rescan the marked objects on the dirty cards
7138 // in the mod union table and the card table proper.
7139 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
7140 oop p, MemRegion mr) {
7142 size_t size = 0;
7143 HeapWord* addr = (HeapWord*)p;
7144 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7145 assert(_span.contains(addr), "we are scanning the CMS generation");
7146 // check if it's time to yield
7147 if (do_yield_check()) {
7148 // We yielded for some foreground stop-world work,
7149 // and we have been asked to abort this ongoing preclean cycle.
7150 return 0;
7151 }
7152 if (_bitMap->isMarked(addr)) {
7153 // it's marked; is it potentially uninitialized?
7154 if (p->klass_or_null() != NULL) {
7155 // an initialized object; ignore mark word in verification below
7156 // since we are running concurrent with mutators
7157 assert(p->is_oop(true), "should be an oop");
7158 if (p->is_objArray()) {
7159 // objArrays are precisely marked; restrict scanning
7160 // to dirty cards only.
7161 size = CompactibleFreeListSpace::adjustObjectSize(
7162 p->oop_iterate(_scanningClosure, mr));
7163 } else {
7164 // A non-array may have been imprecisely marked; we need
7165 // to scan object in its entirety.
7166 size = CompactibleFreeListSpace::adjustObjectSize(
7167 p->oop_iterate(_scanningClosure));
7168 }
7169 #ifdef ASSERT
7170 size_t direct_size =
7171 CompactibleFreeListSpace::adjustObjectSize(p->size());
7172 assert(size == direct_size, "Inconsistency in size");
7173 assert(size >= 3, "Necessary for Printezis marks to work");
7174 if (!_bitMap->isMarked(addr+1)) {
7175 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
7176 } else {
7177 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
7178 assert(_bitMap->isMarked(addr+size-1),
7179 "inconsistent Printezis mark");
7180 }
7181 #endif // ASSERT
7182 } else {
7183 // an unitialized object
7184 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
7185 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7186 size = pointer_delta(nextOneAddr + 1, addr);
7187 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7188 "alignment problem");
7189 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
7190 // will dirty the card when the klass pointer is installed in the
7191 // object (signalling the completion of initialization).
7192 }
7193 } else {
7194 // Either a not yet marked object or an uninitialized object
7195 if (p->klass_or_null() == NULL) {
7196 // An uninitialized object, skip to the next card, since
7197 // we may not be able to read its P-bits yet.
7198 assert(size == 0, "Initial value");
7199 } else {
7200 // An object not (yet) reached by marking: we merely need to
7201 // compute its size so as to go look at the next block.
7202 assert(p->is_oop(true), "should be an oop");
7203 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
7204 }
7205 }
7206 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7207 return size;
7208 }
7210 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
7211 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7212 "CMS thread should hold CMS token");
7213 assert_lock_strong(_freelistLock);
7214 assert_lock_strong(_bitMap->lock());
7215 // relinquish the free_list_lock and bitMaplock()
7216 _bitMap->lock()->unlock();
7217 _freelistLock->unlock();
7218 ConcurrentMarkSweepThread::desynchronize(true);
7219 ConcurrentMarkSweepThread::acknowledge_yield_request();
7220 _collector->stopTimer();
7221 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7222 if (PrintCMSStatistics != 0) {
7223 _collector->incrementYields();
7224 }
7225 _collector->icms_wait();
7227 // See the comment in coordinator_yield()
7228 for (unsigned i = 0; i < CMSYieldSleepCount &&
7229 ConcurrentMarkSweepThread::should_yield() &&
7230 !CMSCollector::foregroundGCIsActive(); ++i) {
7231 os::sleep(Thread::current(), 1, false);
7232 ConcurrentMarkSweepThread::acknowledge_yield_request();
7233 }
7235 ConcurrentMarkSweepThread::synchronize(true);
7236 _freelistLock->lock_without_safepoint_check();
7237 _bitMap->lock()->lock_without_safepoint_check();
7238 _collector->startTimer();
7239 }
7242 //////////////////////////////////////////////////////////////////
7243 // SurvivorSpacePrecleanClosure
7244 //////////////////////////////////////////////////////////////////
7245 // This (single-threaded) closure is used to preclean the oops in
7246 // the survivor spaces.
7247 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
7249 HeapWord* addr = (HeapWord*)p;
7250 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7251 assert(!_span.contains(addr), "we are scanning the survivor spaces");
7252 assert(p->klass_or_null() != NULL, "object should be initializd");
7253 // an initialized object; ignore mark word in verification below
7254 // since we are running concurrent with mutators
7255 assert(p->is_oop(true), "should be an oop");
7256 // Note that we do not yield while we iterate over
7257 // the interior oops of p, pushing the relevant ones
7258 // on our marking stack.
7259 size_t size = p->oop_iterate(_scanning_closure);
7260 do_yield_check();
7261 // Observe that below, we do not abandon the preclean
7262 // phase as soon as we should; rather we empty the
7263 // marking stack before returning. This is to satisfy
7264 // some existing assertions. In general, it may be a
7265 // good idea to abort immediately and complete the marking
7266 // from the grey objects at a later time.
7267 while (!_mark_stack->isEmpty()) {
7268 oop new_oop = _mark_stack->pop();
7269 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7270 assert(_bit_map->isMarked((HeapWord*)new_oop),
7271 "only grey objects on this stack");
7272 // iterate over the oops in this oop, marking and pushing
7273 // the ones in CMS heap (i.e. in _span).
7274 new_oop->oop_iterate(_scanning_closure);
7275 // check if it's time to yield
7276 do_yield_check();
7277 }
7278 unsigned int after_count =
7279 GenCollectedHeap::heap()->total_collections();
7280 bool abort = (_before_count != after_count) ||
7281 _collector->should_abort_preclean();
7282 return abort ? 0 : size;
7283 }
7285 void SurvivorSpacePrecleanClosure::do_yield_work() {
7286 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7287 "CMS thread should hold CMS token");
7288 assert_lock_strong(_bit_map->lock());
7289 // Relinquish the bit map lock
7290 _bit_map->lock()->unlock();
7291 ConcurrentMarkSweepThread::desynchronize(true);
7292 ConcurrentMarkSweepThread::acknowledge_yield_request();
7293 _collector->stopTimer();
7294 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7295 if (PrintCMSStatistics != 0) {
7296 _collector->incrementYields();
7297 }
7298 _collector->icms_wait();
7300 // See the comment in coordinator_yield()
7301 for (unsigned i = 0; i < CMSYieldSleepCount &&
7302 ConcurrentMarkSweepThread::should_yield() &&
7303 !CMSCollector::foregroundGCIsActive(); ++i) {
7304 os::sleep(Thread::current(), 1, false);
7305 ConcurrentMarkSweepThread::acknowledge_yield_request();
7306 }
7308 ConcurrentMarkSweepThread::synchronize(true);
7309 _bit_map->lock()->lock_without_safepoint_check();
7310 _collector->startTimer();
7311 }
7313 // This closure is used to rescan the marked objects on the dirty cards
7314 // in the mod union table and the card table proper. In the parallel
7315 // case, although the bitMap is shared, we do a single read so the
7316 // isMarked() query is "safe".
7317 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7318 // Ignore mark word because we are running concurrent with mutators
7319 assert(p->is_oop_or_null(true), "expected an oop or null");
7320 HeapWord* addr = (HeapWord*)p;
7321 assert(_span.contains(addr), "we are scanning the CMS generation");
7322 bool is_obj_array = false;
7323 #ifdef ASSERT
7324 if (!_parallel) {
7325 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7326 assert(_collector->overflow_list_is_empty(),
7327 "overflow list should be empty");
7329 }
7330 #endif // ASSERT
7331 if (_bit_map->isMarked(addr)) {
7332 // Obj arrays are precisely marked, non-arrays are not;
7333 // so we scan objArrays precisely and non-arrays in their
7334 // entirety.
7335 if (p->is_objArray()) {
7336 is_obj_array = true;
7337 if (_parallel) {
7338 p->oop_iterate(_par_scan_closure, mr);
7339 } else {
7340 p->oop_iterate(_scan_closure, mr);
7341 }
7342 } else {
7343 if (_parallel) {
7344 p->oop_iterate(_par_scan_closure);
7345 } else {
7346 p->oop_iterate(_scan_closure);
7347 }
7348 }
7349 }
7350 #ifdef ASSERT
7351 if (!_parallel) {
7352 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7353 assert(_collector->overflow_list_is_empty(),
7354 "overflow list should be empty");
7356 }
7357 #endif // ASSERT
7358 return is_obj_array;
7359 }
7361 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7362 MemRegion span,
7363 CMSBitMap* bitMap, CMSMarkStack* markStack,
7364 bool should_yield, bool verifying):
7365 _collector(collector),
7366 _span(span),
7367 _bitMap(bitMap),
7368 _mut(&collector->_modUnionTable),
7369 _markStack(markStack),
7370 _yield(should_yield),
7371 _skipBits(0)
7372 {
7373 assert(_markStack->isEmpty(), "stack should be empty");
7374 _finger = _bitMap->startWord();
7375 _threshold = _finger;
7376 assert(_collector->_restart_addr == NULL, "Sanity check");
7377 assert(_span.contains(_finger), "Out of bounds _finger?");
7378 DEBUG_ONLY(_verifying = verifying;)
7379 }
7381 void MarkFromRootsClosure::reset(HeapWord* addr) {
7382 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7383 assert(_span.contains(addr), "Out of bounds _finger?");
7384 _finger = addr;
7385 _threshold = (HeapWord*)round_to(
7386 (intptr_t)_finger, CardTableModRefBS::card_size);
7387 }
7389 // Should revisit to see if this should be restructured for
7390 // greater efficiency.
7391 bool MarkFromRootsClosure::do_bit(size_t offset) {
7392 if (_skipBits > 0) {
7393 _skipBits--;
7394 return true;
7395 }
7396 // convert offset into a HeapWord*
7397 HeapWord* addr = _bitMap->startWord() + offset;
7398 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7399 "address out of range");
7400 assert(_bitMap->isMarked(addr), "tautology");
7401 if (_bitMap->isMarked(addr+1)) {
7402 // this is an allocated but not yet initialized object
7403 assert(_skipBits == 0, "tautology");
7404 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7405 oop p = oop(addr);
7406 if (p->klass_or_null() == NULL) {
7407 DEBUG_ONLY(if (!_verifying) {)
7408 // We re-dirty the cards on which this object lies and increase
7409 // the _threshold so that we'll come back to scan this object
7410 // during the preclean or remark phase. (CMSCleanOnEnter)
7411 if (CMSCleanOnEnter) {
7412 size_t sz = _collector->block_size_using_printezis_bits(addr);
7413 HeapWord* end_card_addr = (HeapWord*)round_to(
7414 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7415 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7416 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7417 // Bump _threshold to end_card_addr; note that
7418 // _threshold cannot possibly exceed end_card_addr, anyhow.
7419 // This prevents future clearing of the card as the scan proceeds
7420 // to the right.
7421 assert(_threshold <= end_card_addr,
7422 "Because we are just scanning into this object");
7423 if (_threshold < end_card_addr) {
7424 _threshold = end_card_addr;
7425 }
7426 if (p->klass_or_null() != NULL) {
7427 // Redirty the range of cards...
7428 _mut->mark_range(redirty_range);
7429 } // ...else the setting of klass will dirty the card anyway.
7430 }
7431 DEBUG_ONLY(})
7432 return true;
7433 }
7434 }
7435 scanOopsInOop(addr);
7436 return true;
7437 }
7439 // We take a break if we've been at this for a while,
7440 // so as to avoid monopolizing the locks involved.
7441 void MarkFromRootsClosure::do_yield_work() {
7442 // First give up the locks, then yield, then re-lock
7443 // We should probably use a constructor/destructor idiom to
7444 // do this unlock/lock or modify the MutexUnlocker class to
7445 // serve our purpose. XXX
7446 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7447 "CMS thread should hold CMS token");
7448 assert_lock_strong(_bitMap->lock());
7449 _bitMap->lock()->unlock();
7450 ConcurrentMarkSweepThread::desynchronize(true);
7451 ConcurrentMarkSweepThread::acknowledge_yield_request();
7452 _collector->stopTimer();
7453 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7454 if (PrintCMSStatistics != 0) {
7455 _collector->incrementYields();
7456 }
7457 _collector->icms_wait();
7459 // See the comment in coordinator_yield()
7460 for (unsigned i = 0; i < CMSYieldSleepCount &&
7461 ConcurrentMarkSweepThread::should_yield() &&
7462 !CMSCollector::foregroundGCIsActive(); ++i) {
7463 os::sleep(Thread::current(), 1, false);
7464 ConcurrentMarkSweepThread::acknowledge_yield_request();
7465 }
7467 ConcurrentMarkSweepThread::synchronize(true);
7468 _bitMap->lock()->lock_without_safepoint_check();
7469 _collector->startTimer();
7470 }
7472 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7473 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7474 assert(_markStack->isEmpty(),
7475 "should drain stack to limit stack usage");
7476 // convert ptr to an oop preparatory to scanning
7477 oop obj = oop(ptr);
7478 // Ignore mark word in verification below, since we
7479 // may be running concurrent with mutators.
7480 assert(obj->is_oop(true), "should be an oop");
7481 assert(_finger <= ptr, "_finger runneth ahead");
7482 // advance the finger to right end of this object
7483 _finger = ptr + obj->size();
7484 assert(_finger > ptr, "we just incremented it above");
7485 // On large heaps, it may take us some time to get through
7486 // the marking phase (especially if running iCMS). During
7487 // this time it's possible that a lot of mutations have
7488 // accumulated in the card table and the mod union table --
7489 // these mutation records are redundant until we have
7490 // actually traced into the corresponding card.
7491 // Here, we check whether advancing the finger would make
7492 // us cross into a new card, and if so clear corresponding
7493 // cards in the MUT (preclean them in the card-table in the
7494 // future).
7496 DEBUG_ONLY(if (!_verifying) {)
7497 // The clean-on-enter optimization is disabled by default,
7498 // until we fix 6178663.
7499 if (CMSCleanOnEnter && (_finger > _threshold)) {
7500 // [_threshold, _finger) represents the interval
7501 // of cards to be cleared in MUT (or precleaned in card table).
7502 // The set of cards to be cleared is all those that overlap
7503 // with the interval [_threshold, _finger); note that
7504 // _threshold is always kept card-aligned but _finger isn't
7505 // always card-aligned.
7506 HeapWord* old_threshold = _threshold;
7507 assert(old_threshold == (HeapWord*)round_to(
7508 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7509 "_threshold should always be card-aligned");
7510 _threshold = (HeapWord*)round_to(
7511 (intptr_t)_finger, CardTableModRefBS::card_size);
7512 MemRegion mr(old_threshold, _threshold);
7513 assert(!mr.is_empty(), "Control point invariant");
7514 assert(_span.contains(mr), "Should clear within span");
7515 _mut->clear_range(mr);
7516 }
7517 DEBUG_ONLY(})
7518 // Note: the finger doesn't advance while we drain
7519 // the stack below.
7520 PushOrMarkClosure pushOrMarkClosure(_collector,
7521 _span, _bitMap, _markStack,
7522 _finger, this);
7523 bool res = _markStack->push(obj);
7524 assert(res, "Empty non-zero size stack should have space for single push");
7525 while (!_markStack->isEmpty()) {
7526 oop new_oop = _markStack->pop();
7527 // Skip verifying header mark word below because we are
7528 // running concurrent with mutators.
7529 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7530 // now scan this oop's oops
7531 new_oop->oop_iterate(&pushOrMarkClosure);
7532 do_yield_check();
7533 }
7534 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7535 }
7537 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7538 CMSCollector* collector, MemRegion span,
7539 CMSBitMap* bit_map,
7540 OopTaskQueue* work_queue,
7541 CMSMarkStack* overflow_stack,
7542 bool should_yield):
7543 _collector(collector),
7544 _whole_span(collector->_span),
7545 _span(span),
7546 _bit_map(bit_map),
7547 _mut(&collector->_modUnionTable),
7548 _work_queue(work_queue),
7549 _overflow_stack(overflow_stack),
7550 _yield(should_yield),
7551 _skip_bits(0),
7552 _task(task)
7553 {
7554 assert(_work_queue->size() == 0, "work_queue should be empty");
7555 _finger = span.start();
7556 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7557 assert(_span.contains(_finger), "Out of bounds _finger?");
7558 }
7560 // Should revisit to see if this should be restructured for
7561 // greater efficiency.
7562 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7563 if (_skip_bits > 0) {
7564 _skip_bits--;
7565 return true;
7566 }
7567 // convert offset into a HeapWord*
7568 HeapWord* addr = _bit_map->startWord() + offset;
7569 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7570 "address out of range");
7571 assert(_bit_map->isMarked(addr), "tautology");
7572 if (_bit_map->isMarked(addr+1)) {
7573 // this is an allocated object that might not yet be initialized
7574 assert(_skip_bits == 0, "tautology");
7575 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7576 oop p = oop(addr);
7577 if (p->klass_or_null() == NULL) {
7578 // in the case of Clean-on-Enter optimization, redirty card
7579 // and avoid clearing card by increasing the threshold.
7580 return true;
7581 }
7582 }
7583 scan_oops_in_oop(addr);
7584 return true;
7585 }
7587 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7588 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7589 // Should we assert that our work queue is empty or
7590 // below some drain limit?
7591 assert(_work_queue->size() == 0,
7592 "should drain stack to limit stack usage");
7593 // convert ptr to an oop preparatory to scanning
7594 oop obj = oop(ptr);
7595 // Ignore mark word in verification below, since we
7596 // may be running concurrent with mutators.
7597 assert(obj->is_oop(true), "should be an oop");
7598 assert(_finger <= ptr, "_finger runneth ahead");
7599 // advance the finger to right end of this object
7600 _finger = ptr + obj->size();
7601 assert(_finger > ptr, "we just incremented it above");
7602 // On large heaps, it may take us some time to get through
7603 // the marking phase (especially if running iCMS). During
7604 // this time it's possible that a lot of mutations have
7605 // accumulated in the card table and the mod union table --
7606 // these mutation records are redundant until we have
7607 // actually traced into the corresponding card.
7608 // Here, we check whether advancing the finger would make
7609 // us cross into a new card, and if so clear corresponding
7610 // cards in the MUT (preclean them in the card-table in the
7611 // future).
7613 // The clean-on-enter optimization is disabled by default,
7614 // until we fix 6178663.
7615 if (CMSCleanOnEnter && (_finger > _threshold)) {
7616 // [_threshold, _finger) represents the interval
7617 // of cards to be cleared in MUT (or precleaned in card table).
7618 // The set of cards to be cleared is all those that overlap
7619 // with the interval [_threshold, _finger); note that
7620 // _threshold is always kept card-aligned but _finger isn't
7621 // always card-aligned.
7622 HeapWord* old_threshold = _threshold;
7623 assert(old_threshold == (HeapWord*)round_to(
7624 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7625 "_threshold should always be card-aligned");
7626 _threshold = (HeapWord*)round_to(
7627 (intptr_t)_finger, CardTableModRefBS::card_size);
7628 MemRegion mr(old_threshold, _threshold);
7629 assert(!mr.is_empty(), "Control point invariant");
7630 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7631 _mut->clear_range(mr);
7632 }
7634 // Note: the local finger doesn't advance while we drain
7635 // the stack below, but the global finger sure can and will.
7636 HeapWord** gfa = _task->global_finger_addr();
7637 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7638 _span, _bit_map,
7639 _work_queue,
7640 _overflow_stack,
7641 _finger,
7642 gfa, this);
7643 bool res = _work_queue->push(obj); // overflow could occur here
7644 assert(res, "Will hold once we use workqueues");
7645 while (true) {
7646 oop new_oop;
7647 if (!_work_queue->pop_local(new_oop)) {
7648 // We emptied our work_queue; check if there's stuff that can
7649 // be gotten from the overflow stack.
7650 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7651 _overflow_stack, _work_queue)) {
7652 do_yield_check();
7653 continue;
7654 } else { // done
7655 break;
7656 }
7657 }
7658 // Skip verifying header mark word below because we are
7659 // running concurrent with mutators.
7660 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7661 // now scan this oop's oops
7662 new_oop->oop_iterate(&pushOrMarkClosure);
7663 do_yield_check();
7664 }
7665 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7666 }
7668 // Yield in response to a request from VM Thread or
7669 // from mutators.
7670 void Par_MarkFromRootsClosure::do_yield_work() {
7671 assert(_task != NULL, "sanity");
7672 _task->yield();
7673 }
7675 // A variant of the above used for verifying CMS marking work.
7676 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7677 MemRegion span,
7678 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7679 CMSMarkStack* mark_stack):
7680 _collector(collector),
7681 _span(span),
7682 _verification_bm(verification_bm),
7683 _cms_bm(cms_bm),
7684 _mark_stack(mark_stack),
7685 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7686 mark_stack)
7687 {
7688 assert(_mark_stack->isEmpty(), "stack should be empty");
7689 _finger = _verification_bm->startWord();
7690 assert(_collector->_restart_addr == NULL, "Sanity check");
7691 assert(_span.contains(_finger), "Out of bounds _finger?");
7692 }
7694 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7695 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7696 assert(_span.contains(addr), "Out of bounds _finger?");
7697 _finger = addr;
7698 }
7700 // Should revisit to see if this should be restructured for
7701 // greater efficiency.
7702 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7703 // convert offset into a HeapWord*
7704 HeapWord* addr = _verification_bm->startWord() + offset;
7705 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7706 "address out of range");
7707 assert(_verification_bm->isMarked(addr), "tautology");
7708 assert(_cms_bm->isMarked(addr), "tautology");
7710 assert(_mark_stack->isEmpty(),
7711 "should drain stack to limit stack usage");
7712 // convert addr to an oop preparatory to scanning
7713 oop obj = oop(addr);
7714 assert(obj->is_oop(), "should be an oop");
7715 assert(_finger <= addr, "_finger runneth ahead");
7716 // advance the finger to right end of this object
7717 _finger = addr + obj->size();
7718 assert(_finger > addr, "we just incremented it above");
7719 // Note: the finger doesn't advance while we drain
7720 // the stack below.
7721 bool res = _mark_stack->push(obj);
7722 assert(res, "Empty non-zero size stack should have space for single push");
7723 while (!_mark_stack->isEmpty()) {
7724 oop new_oop = _mark_stack->pop();
7725 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7726 // now scan this oop's oops
7727 new_oop->oop_iterate(&_pam_verify_closure);
7728 }
7729 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7730 return true;
7731 }
7733 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7734 CMSCollector* collector, MemRegion span,
7735 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7736 CMSMarkStack* mark_stack):
7737 CMSOopClosure(collector->ref_processor()),
7738 _collector(collector),
7739 _span(span),
7740 _verification_bm(verification_bm),
7741 _cms_bm(cms_bm),
7742 _mark_stack(mark_stack)
7743 { }
7745 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7746 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7748 // Upon stack overflow, we discard (part of) the stack,
7749 // remembering the least address amongst those discarded
7750 // in CMSCollector's _restart_address.
7751 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7752 // Remember the least grey address discarded
7753 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7754 _collector->lower_restart_addr(ra);
7755 _mark_stack->reset(); // discard stack contents
7756 _mark_stack->expand(); // expand the stack if possible
7757 }
7759 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7760 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7761 HeapWord* addr = (HeapWord*)obj;
7762 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7763 // Oop lies in _span and isn't yet grey or black
7764 _verification_bm->mark(addr); // now grey
7765 if (!_cms_bm->isMarked(addr)) {
7766 oop(addr)->print();
7767 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7768 addr);
7769 fatal("... aborting");
7770 }
7772 if (!_mark_stack->push(obj)) { // stack overflow
7773 if (PrintCMSStatistics != 0) {
7774 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7775 SIZE_FORMAT, _mark_stack->capacity());
7776 }
7777 assert(_mark_stack->isFull(), "Else push should have succeeded");
7778 handle_stack_overflow(addr);
7779 }
7780 // anything including and to the right of _finger
7781 // will be scanned as we iterate over the remainder of the
7782 // bit map
7783 }
7784 }
7786 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7787 MemRegion span,
7788 CMSBitMap* bitMap, CMSMarkStack* markStack,
7789 HeapWord* finger, MarkFromRootsClosure* parent) :
7790 CMSOopClosure(collector->ref_processor()),
7791 _collector(collector),
7792 _span(span),
7793 _bitMap(bitMap),
7794 _markStack(markStack),
7795 _finger(finger),
7796 _parent(parent)
7797 { }
7799 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7800 MemRegion span,
7801 CMSBitMap* bit_map,
7802 OopTaskQueue* work_queue,
7803 CMSMarkStack* overflow_stack,
7804 HeapWord* finger,
7805 HeapWord** global_finger_addr,
7806 Par_MarkFromRootsClosure* parent) :
7807 CMSOopClosure(collector->ref_processor()),
7808 _collector(collector),
7809 _whole_span(collector->_span),
7810 _span(span),
7811 _bit_map(bit_map),
7812 _work_queue(work_queue),
7813 _overflow_stack(overflow_stack),
7814 _finger(finger),
7815 _global_finger_addr(global_finger_addr),
7816 _parent(parent)
7817 { }
7819 // Assumes thread-safe access by callers, who are
7820 // responsible for mutual exclusion.
7821 void CMSCollector::lower_restart_addr(HeapWord* low) {
7822 assert(_span.contains(low), "Out of bounds addr");
7823 if (_restart_addr == NULL) {
7824 _restart_addr = low;
7825 } else {
7826 _restart_addr = MIN2(_restart_addr, low);
7827 }
7828 }
7830 // Upon stack overflow, we discard (part of) the stack,
7831 // remembering the least address amongst those discarded
7832 // in CMSCollector's _restart_address.
7833 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7834 // Remember the least grey address discarded
7835 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7836 _collector->lower_restart_addr(ra);
7837 _markStack->reset(); // discard stack contents
7838 _markStack->expand(); // expand the stack if possible
7839 }
7841 // Upon stack overflow, we discard (part of) the stack,
7842 // remembering the least address amongst those discarded
7843 // in CMSCollector's _restart_address.
7844 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7845 // We need to do this under a mutex to prevent other
7846 // workers from interfering with the work done below.
7847 MutexLockerEx ml(_overflow_stack->par_lock(),
7848 Mutex::_no_safepoint_check_flag);
7849 // Remember the least grey address discarded
7850 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7851 _collector->lower_restart_addr(ra);
7852 _overflow_stack->reset(); // discard stack contents
7853 _overflow_stack->expand(); // expand the stack if possible
7854 }
7856 void CMKlassClosure::do_klass(Klass* k) {
7857 assert(_oop_closure != NULL, "Not initialized?");
7858 k->oops_do(_oop_closure);
7859 }
7861 void PushOrMarkClosure::do_oop(oop obj) {
7862 // Ignore mark word because we are running concurrent with mutators.
7863 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7864 HeapWord* addr = (HeapWord*)obj;
7865 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7866 // Oop lies in _span and isn't yet grey or black
7867 _bitMap->mark(addr); // now grey
7868 if (addr < _finger) {
7869 // the bit map iteration has already either passed, or
7870 // sampled, this bit in the bit map; we'll need to
7871 // use the marking stack to scan this oop's oops.
7872 bool simulate_overflow = false;
7873 NOT_PRODUCT(
7874 if (CMSMarkStackOverflowALot &&
7875 _collector->simulate_overflow()) {
7876 // simulate a stack overflow
7877 simulate_overflow = true;
7878 }
7879 )
7880 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7881 if (PrintCMSStatistics != 0) {
7882 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7883 SIZE_FORMAT, _markStack->capacity());
7884 }
7885 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7886 handle_stack_overflow(addr);
7887 }
7888 }
7889 // anything including and to the right of _finger
7890 // will be scanned as we iterate over the remainder of the
7891 // bit map
7892 do_yield_check();
7893 }
7894 }
7896 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7897 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7899 void Par_PushOrMarkClosure::do_oop(oop obj) {
7900 // Ignore mark word because we are running concurrent with mutators.
7901 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7902 HeapWord* addr = (HeapWord*)obj;
7903 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7904 // Oop lies in _span and isn't yet grey or black
7905 // We read the global_finger (volatile read) strictly after marking oop
7906 bool res = _bit_map->par_mark(addr); // now grey
7907 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7908 // Should we push this marked oop on our stack?
7909 // -- if someone else marked it, nothing to do
7910 // -- if target oop is above global finger nothing to do
7911 // -- if target oop is in chunk and above local finger
7912 // then nothing to do
7913 // -- else push on work queue
7914 if ( !res // someone else marked it, they will deal with it
7915 || (addr >= *gfa) // will be scanned in a later task
7916 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7917 return;
7918 }
7919 // the bit map iteration has already either passed, or
7920 // sampled, this bit in the bit map; we'll need to
7921 // use the marking stack to scan this oop's oops.
7922 bool simulate_overflow = false;
7923 NOT_PRODUCT(
7924 if (CMSMarkStackOverflowALot &&
7925 _collector->simulate_overflow()) {
7926 // simulate a stack overflow
7927 simulate_overflow = true;
7928 }
7929 )
7930 if (simulate_overflow ||
7931 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7932 // stack overflow
7933 if (PrintCMSStatistics != 0) {
7934 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7935 SIZE_FORMAT, _overflow_stack->capacity());
7936 }
7937 // We cannot assert that the overflow stack is full because
7938 // it may have been emptied since.
7939 assert(simulate_overflow ||
7940 _work_queue->size() == _work_queue->max_elems(),
7941 "Else push should have succeeded");
7942 handle_stack_overflow(addr);
7943 }
7944 do_yield_check();
7945 }
7946 }
7948 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7949 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7951 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7952 MemRegion span,
7953 ReferenceProcessor* rp,
7954 CMSBitMap* bit_map,
7955 CMSBitMap* mod_union_table,
7956 CMSMarkStack* mark_stack,
7957 bool concurrent_precleaning):
7958 CMSOopClosure(rp),
7959 _collector(collector),
7960 _span(span),
7961 _bit_map(bit_map),
7962 _mod_union_table(mod_union_table),
7963 _mark_stack(mark_stack),
7964 _concurrent_precleaning(concurrent_precleaning)
7965 {
7966 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7967 }
7969 // Grey object rescan during pre-cleaning and second checkpoint phases --
7970 // the non-parallel version (the parallel version appears further below.)
7971 void PushAndMarkClosure::do_oop(oop obj) {
7972 // Ignore mark word verification. If during concurrent precleaning,
7973 // the object monitor may be locked. If during the checkpoint
7974 // phases, the object may already have been reached by a different
7975 // path and may be at the end of the global overflow list (so
7976 // the mark word may be NULL).
7977 assert(obj->is_oop_or_null(true /* ignore mark word */),
7978 "expected an oop or NULL");
7979 HeapWord* addr = (HeapWord*)obj;
7980 // Check if oop points into the CMS generation
7981 // and is not marked
7982 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7983 // a white object ...
7984 _bit_map->mark(addr); // ... now grey
7985 // push on the marking stack (grey set)
7986 bool simulate_overflow = false;
7987 NOT_PRODUCT(
7988 if (CMSMarkStackOverflowALot &&
7989 _collector->simulate_overflow()) {
7990 // simulate a stack overflow
7991 simulate_overflow = true;
7992 }
7993 )
7994 if (simulate_overflow || !_mark_stack->push(obj)) {
7995 if (_concurrent_precleaning) {
7996 // During precleaning we can just dirty the appropriate card(s)
7997 // in the mod union table, thus ensuring that the object remains
7998 // in the grey set and continue. In the case of object arrays
7999 // we need to dirty all of the cards that the object spans,
8000 // since the rescan of object arrays will be limited to the
8001 // dirty cards.
8002 // Note that no one can be intefering with us in this action
8003 // of dirtying the mod union table, so no locking or atomics
8004 // are required.
8005 if (obj->is_objArray()) {
8006 size_t sz = obj->size();
8007 HeapWord* end_card_addr = (HeapWord*)round_to(
8008 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
8009 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8010 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8011 _mod_union_table->mark_range(redirty_range);
8012 } else {
8013 _mod_union_table->mark(addr);
8014 }
8015 _collector->_ser_pmc_preclean_ovflw++;
8016 } else {
8017 // During the remark phase, we need to remember this oop
8018 // in the overflow list.
8019 _collector->push_on_overflow_list(obj);
8020 _collector->_ser_pmc_remark_ovflw++;
8021 }
8022 }
8023 }
8024 }
8026 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
8027 MemRegion span,
8028 ReferenceProcessor* rp,
8029 CMSBitMap* bit_map,
8030 OopTaskQueue* work_queue):
8031 CMSOopClosure(rp),
8032 _collector(collector),
8033 _span(span),
8034 _bit_map(bit_map),
8035 _work_queue(work_queue)
8036 {
8037 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
8038 }
8040 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
8041 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
8043 // Grey object rescan during second checkpoint phase --
8044 // the parallel version.
8045 void Par_PushAndMarkClosure::do_oop(oop obj) {
8046 // In the assert below, we ignore the mark word because
8047 // this oop may point to an already visited object that is
8048 // on the overflow stack (in which case the mark word has
8049 // been hijacked for chaining into the overflow stack --
8050 // if this is the last object in the overflow stack then
8051 // its mark word will be NULL). Because this object may
8052 // have been subsequently popped off the global overflow
8053 // stack, and the mark word possibly restored to the prototypical
8054 // value, by the time we get to examined this failing assert in
8055 // the debugger, is_oop_or_null(false) may subsequently start
8056 // to hold.
8057 assert(obj->is_oop_or_null(true),
8058 "expected an oop or NULL");
8059 HeapWord* addr = (HeapWord*)obj;
8060 // Check if oop points into the CMS generation
8061 // and is not marked
8062 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
8063 // a white object ...
8064 // If we manage to "claim" the object, by being the
8065 // first thread to mark it, then we push it on our
8066 // marking stack
8067 if (_bit_map->par_mark(addr)) { // ... now grey
8068 // push on work queue (grey set)
8069 bool simulate_overflow = false;
8070 NOT_PRODUCT(
8071 if (CMSMarkStackOverflowALot &&
8072 _collector->par_simulate_overflow()) {
8073 // simulate a stack overflow
8074 simulate_overflow = true;
8075 }
8076 )
8077 if (simulate_overflow || !_work_queue->push(obj)) {
8078 _collector->par_push_on_overflow_list(obj);
8079 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
8080 }
8081 } // Else, some other thread got there first
8082 }
8083 }
8085 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
8086 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
8088 void CMSPrecleanRefsYieldClosure::do_yield_work() {
8089 Mutex* bml = _collector->bitMapLock();
8090 assert_lock_strong(bml);
8091 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8092 "CMS thread should hold CMS token");
8094 bml->unlock();
8095 ConcurrentMarkSweepThread::desynchronize(true);
8097 ConcurrentMarkSweepThread::acknowledge_yield_request();
8099 _collector->stopTimer();
8100 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8101 if (PrintCMSStatistics != 0) {
8102 _collector->incrementYields();
8103 }
8104 _collector->icms_wait();
8106 // See the comment in coordinator_yield()
8107 for (unsigned i = 0; i < CMSYieldSleepCount &&
8108 ConcurrentMarkSweepThread::should_yield() &&
8109 !CMSCollector::foregroundGCIsActive(); ++i) {
8110 os::sleep(Thread::current(), 1, false);
8111 ConcurrentMarkSweepThread::acknowledge_yield_request();
8112 }
8114 ConcurrentMarkSweepThread::synchronize(true);
8115 bml->lock();
8117 _collector->startTimer();
8118 }
8120 bool CMSPrecleanRefsYieldClosure::should_return() {
8121 if (ConcurrentMarkSweepThread::should_yield()) {
8122 do_yield_work();
8123 }
8124 return _collector->foregroundGCIsActive();
8125 }
8127 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
8128 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
8129 "mr should be aligned to start at a card boundary");
8130 // We'd like to assert:
8131 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
8132 // "mr should be a range of cards");
8133 // However, that would be too strong in one case -- the last
8134 // partition ends at _unallocated_block which, in general, can be
8135 // an arbitrary boundary, not necessarily card aligned.
8136 if (PrintCMSStatistics != 0) {
8137 _num_dirty_cards +=
8138 mr.word_size()/CardTableModRefBS::card_size_in_words;
8139 }
8140 _space->object_iterate_mem(mr, &_scan_cl);
8141 }
8143 SweepClosure::SweepClosure(CMSCollector* collector,
8144 ConcurrentMarkSweepGeneration* g,
8145 CMSBitMap* bitMap, bool should_yield) :
8146 _collector(collector),
8147 _g(g),
8148 _sp(g->cmsSpace()),
8149 _limit(_sp->sweep_limit()),
8150 _freelistLock(_sp->freelistLock()),
8151 _bitMap(bitMap),
8152 _yield(should_yield),
8153 _inFreeRange(false), // No free range at beginning of sweep
8154 _freeRangeInFreeLists(false), // No free range at beginning of sweep
8155 _lastFreeRangeCoalesced(false),
8156 _freeFinger(g->used_region().start())
8157 {
8158 NOT_PRODUCT(
8159 _numObjectsFreed = 0;
8160 _numWordsFreed = 0;
8161 _numObjectsLive = 0;
8162 _numWordsLive = 0;
8163 _numObjectsAlreadyFree = 0;
8164 _numWordsAlreadyFree = 0;
8165 _last_fc = NULL;
8167 _sp->initializeIndexedFreeListArrayReturnedBytes();
8168 _sp->dictionary()->initialize_dict_returned_bytes();
8169 )
8170 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8171 "sweep _limit out of bounds");
8172 if (CMSTraceSweeper) {
8173 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
8174 _limit);
8175 }
8176 }
8178 void SweepClosure::print_on(outputStream* st) const {
8179 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
8180 _sp->bottom(), _sp->end());
8181 tty->print_cr("_limit = " PTR_FORMAT, _limit);
8182 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
8183 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
8184 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
8185 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
8186 }
8188 #ifndef PRODUCT
8189 // Assertion checking only: no useful work in product mode --
8190 // however, if any of the flags below become product flags,
8191 // you may need to review this code to see if it needs to be
8192 // enabled in product mode.
8193 SweepClosure::~SweepClosure() {
8194 assert_lock_strong(_freelistLock);
8195 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8196 "sweep _limit out of bounds");
8197 if (inFreeRange()) {
8198 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
8199 print();
8200 ShouldNotReachHere();
8201 }
8202 if (Verbose && PrintGC) {
8203 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
8204 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
8205 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
8206 SIZE_FORMAT" bytes "
8207 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
8208 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
8209 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
8210 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
8211 * sizeof(HeapWord);
8212 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
8214 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
8215 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
8216 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
8217 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
8218 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
8219 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
8220 indexListReturnedBytes);
8221 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
8222 dict_returned_bytes);
8223 }
8224 }
8225 if (CMSTraceSweeper) {
8226 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
8227 _limit);
8228 }
8229 }
8230 #endif // PRODUCT
8232 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
8233 bool freeRangeInFreeLists) {
8234 if (CMSTraceSweeper) {
8235 gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n",
8236 freeFinger, freeRangeInFreeLists);
8237 }
8238 assert(!inFreeRange(), "Trampling existing free range");
8239 set_inFreeRange(true);
8240 set_lastFreeRangeCoalesced(false);
8242 set_freeFinger(freeFinger);
8243 set_freeRangeInFreeLists(freeRangeInFreeLists);
8244 if (CMSTestInFreeList) {
8245 if (freeRangeInFreeLists) {
8246 FreeChunk* fc = (FreeChunk*) freeFinger;
8247 assert(fc->is_free(), "A chunk on the free list should be free.");
8248 assert(fc->size() > 0, "Free range should have a size");
8249 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
8250 }
8251 }
8252 }
8254 // Note that the sweeper runs concurrently with mutators. Thus,
8255 // it is possible for direct allocation in this generation to happen
8256 // in the middle of the sweep. Note that the sweeper also coalesces
8257 // contiguous free blocks. Thus, unless the sweeper and the allocator
8258 // synchronize appropriately freshly allocated blocks may get swept up.
8259 // This is accomplished by the sweeper locking the free lists while
8260 // it is sweeping. Thus blocks that are determined to be free are
8261 // indeed free. There is however one additional complication:
8262 // blocks that have been allocated since the final checkpoint and
8263 // mark, will not have been marked and so would be treated as
8264 // unreachable and swept up. To prevent this, the allocator marks
8265 // the bit map when allocating during the sweep phase. This leads,
8266 // however, to a further complication -- objects may have been allocated
8267 // but not yet initialized -- in the sense that the header isn't yet
8268 // installed. The sweeper can not then determine the size of the block
8269 // in order to skip over it. To deal with this case, we use a technique
8270 // (due to Printezis) to encode such uninitialized block sizes in the
8271 // bit map. Since the bit map uses a bit per every HeapWord, but the
8272 // CMS generation has a minimum object size of 3 HeapWords, it follows
8273 // that "normal marks" won't be adjacent in the bit map (there will
8274 // always be at least two 0 bits between successive 1 bits). We make use
8275 // of these "unused" bits to represent uninitialized blocks -- the bit
8276 // corresponding to the start of the uninitialized object and the next
8277 // bit are both set. Finally, a 1 bit marks the end of the object that
8278 // started with the two consecutive 1 bits to indicate its potentially
8279 // uninitialized state.
8281 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8282 FreeChunk* fc = (FreeChunk*)addr;
8283 size_t res;
8285 // Check if we are done sweeping. Below we check "addr >= _limit" rather
8286 // than "addr == _limit" because although _limit was a block boundary when
8287 // we started the sweep, it may no longer be one because heap expansion
8288 // may have caused us to coalesce the block ending at the address _limit
8289 // with a newly expanded chunk (this happens when _limit was set to the
8290 // previous _end of the space), so we may have stepped past _limit:
8291 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8292 if (addr >= _limit) { // we have swept up to or past the limit: finish up
8293 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8294 "sweep _limit out of bounds");
8295 assert(addr < _sp->end(), "addr out of bounds");
8296 // Flush any free range we might be holding as a single
8297 // coalesced chunk to the appropriate free list.
8298 if (inFreeRange()) {
8299 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8300 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8301 flush_cur_free_chunk(freeFinger(),
8302 pointer_delta(addr, freeFinger()));
8303 if (CMSTraceSweeper) {
8304 gclog_or_tty->print("Sweep: last chunk: ");
8305 gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") "
8306 "[coalesced:"SIZE_FORMAT"]\n",
8307 freeFinger(), pointer_delta(addr, freeFinger()),
8308 lastFreeRangeCoalesced());
8309 }
8310 }
8312 // help the iterator loop finish
8313 return pointer_delta(_sp->end(), addr);
8314 }
8316 assert(addr < _limit, "sweep invariant");
8317 // check if we should yield
8318 do_yield_check(addr);
8319 if (fc->is_free()) {
8320 // Chunk that is already free
8321 res = fc->size();
8322 do_already_free_chunk(fc);
8323 debug_only(_sp->verifyFreeLists());
8324 // If we flush the chunk at hand in lookahead_and_flush()
8325 // and it's coalesced with a preceding chunk, then the
8326 // process of "mangling" the payload of the coalesced block
8327 // will cause erasure of the size information from the
8328 // (erstwhile) header of all the coalesced blocks but the
8329 // first, so the first disjunct in the assert will not hold
8330 // in that specific case (in which case the second disjunct
8331 // will hold).
8332 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8333 "Otherwise the size info doesn't change at this step");
8334 NOT_PRODUCT(
8335 _numObjectsAlreadyFree++;
8336 _numWordsAlreadyFree += res;
8337 )
8338 NOT_PRODUCT(_last_fc = fc;)
8339 } else if (!_bitMap->isMarked(addr)) {
8340 // Chunk is fresh garbage
8341 res = do_garbage_chunk(fc);
8342 debug_only(_sp->verifyFreeLists());
8343 NOT_PRODUCT(
8344 _numObjectsFreed++;
8345 _numWordsFreed += res;
8346 )
8347 } else {
8348 // Chunk that is alive.
8349 res = do_live_chunk(fc);
8350 debug_only(_sp->verifyFreeLists());
8351 NOT_PRODUCT(
8352 _numObjectsLive++;
8353 _numWordsLive += res;
8354 )
8355 }
8356 return res;
8357 }
8359 // For the smart allocation, record following
8360 // split deaths - a free chunk is removed from its free list because
8361 // it is being split into two or more chunks.
8362 // split birth - a free chunk is being added to its free list because
8363 // a larger free chunk has been split and resulted in this free chunk.
8364 // coal death - a free chunk is being removed from its free list because
8365 // it is being coalesced into a large free chunk.
8366 // coal birth - a free chunk is being added to its free list because
8367 // it was created when two or more free chunks where coalesced into
8368 // this free chunk.
8369 //
8370 // These statistics are used to determine the desired number of free
8371 // chunks of a given size. The desired number is chosen to be relative
8372 // to the end of a CMS sweep. The desired number at the end of a sweep
8373 // is the
8374 // count-at-end-of-previous-sweep (an amount that was enough)
8375 // - count-at-beginning-of-current-sweep (the excess)
8376 // + split-births (gains in this size during interval)
8377 // - split-deaths (demands on this size during interval)
8378 // where the interval is from the end of one sweep to the end of the
8379 // next.
8380 //
8381 // When sweeping the sweeper maintains an accumulated chunk which is
8382 // the chunk that is made up of chunks that have been coalesced. That
8383 // will be termed the left-hand chunk. A new chunk of garbage that
8384 // is being considered for coalescing will be referred to as the
8385 // right-hand chunk.
8386 //
8387 // When making a decision on whether to coalesce a right-hand chunk with
8388 // the current left-hand chunk, the current count vs. the desired count
8389 // of the left-hand chunk is considered. Also if the right-hand chunk
8390 // is near the large chunk at the end of the heap (see
8391 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8392 // left-hand chunk is coalesced.
8393 //
8394 // When making a decision about whether to split a chunk, the desired count
8395 // vs. the current count of the candidate to be split is also considered.
8396 // If the candidate is underpopulated (currently fewer chunks than desired)
8397 // a chunk of an overpopulated (currently more chunks than desired) size may
8398 // be chosen. The "hint" associated with a free list, if non-null, points
8399 // to a free list which may be overpopulated.
8400 //
8402 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8403 const size_t size = fc->size();
8404 // Chunks that cannot be coalesced are not in the
8405 // free lists.
8406 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8407 assert(_sp->verify_chunk_in_free_list(fc),
8408 "free chunk should be in free lists");
8409 }
8410 // a chunk that is already free, should not have been
8411 // marked in the bit map
8412 HeapWord* const addr = (HeapWord*) fc;
8413 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8414 // Verify that the bit map has no bits marked between
8415 // addr and purported end of this block.
8416 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8418 // Some chunks cannot be coalesced under any circumstances.
8419 // See the definition of cantCoalesce().
8420 if (!fc->cantCoalesce()) {
8421 // This chunk can potentially be coalesced.
8422 if (_sp->adaptive_freelists()) {
8423 // All the work is done in
8424 do_post_free_or_garbage_chunk(fc, size);
8425 } else { // Not adaptive free lists
8426 // this is a free chunk that can potentially be coalesced by the sweeper;
8427 if (!inFreeRange()) {
8428 // if the next chunk is a free block that can't be coalesced
8429 // it doesn't make sense to remove this chunk from the free lists
8430 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8431 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8432 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8433 nextChunk->is_free() && // ... which is free...
8434 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8435 // nothing to do
8436 } else {
8437 // Potentially the start of a new free range:
8438 // Don't eagerly remove it from the free lists.
8439 // No need to remove it if it will just be put
8440 // back again. (Also from a pragmatic point of view
8441 // if it is a free block in a region that is beyond
8442 // any allocated blocks, an assertion will fail)
8443 // Remember the start of a free run.
8444 initialize_free_range(addr, true);
8445 // end - can coalesce with next chunk
8446 }
8447 } else {
8448 // the midst of a free range, we are coalescing
8449 print_free_block_coalesced(fc);
8450 if (CMSTraceSweeper) {
8451 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
8452 }
8453 // remove it from the free lists
8454 _sp->removeFreeChunkFromFreeLists(fc);
8455 set_lastFreeRangeCoalesced(true);
8456 // If the chunk is being coalesced and the current free range is
8457 // in the free lists, remove the current free range so that it
8458 // will be returned to the free lists in its entirety - all
8459 // the coalesced pieces included.
8460 if (freeRangeInFreeLists()) {
8461 FreeChunk* ffc = (FreeChunk*) freeFinger();
8462 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8463 "Size of free range is inconsistent with chunk size.");
8464 if (CMSTestInFreeList) {
8465 assert(_sp->verify_chunk_in_free_list(ffc),
8466 "free range is not in free lists");
8467 }
8468 _sp->removeFreeChunkFromFreeLists(ffc);
8469 set_freeRangeInFreeLists(false);
8470 }
8471 }
8472 }
8473 // Note that if the chunk is not coalescable (the else arm
8474 // below), we unconditionally flush, without needing to do
8475 // a "lookahead," as we do below.
8476 if (inFreeRange()) lookahead_and_flush(fc, size);
8477 } else {
8478 // Code path common to both original and adaptive free lists.
8480 // cant coalesce with previous block; this should be treated
8481 // as the end of a free run if any
8482 if (inFreeRange()) {
8483 // we kicked some butt; time to pick up the garbage
8484 assert(freeFinger() < addr, "freeFinger points too high");
8485 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8486 }
8487 // else, nothing to do, just continue
8488 }
8489 }
8491 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8492 // This is a chunk of garbage. It is not in any free list.
8493 // Add it to a free list or let it possibly be coalesced into
8494 // a larger chunk.
8495 HeapWord* const addr = (HeapWord*) fc;
8496 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8498 if (_sp->adaptive_freelists()) {
8499 // Verify that the bit map has no bits marked between
8500 // addr and purported end of just dead object.
8501 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8503 do_post_free_or_garbage_chunk(fc, size);
8504 } else {
8505 if (!inFreeRange()) {
8506 // start of a new free range
8507 assert(size > 0, "A free range should have a size");
8508 initialize_free_range(addr, false);
8509 } else {
8510 // this will be swept up when we hit the end of the
8511 // free range
8512 if (CMSTraceSweeper) {
8513 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
8514 }
8515 // If the chunk is being coalesced and the current free range is
8516 // in the free lists, remove the current free range so that it
8517 // will be returned to the free lists in its entirety - all
8518 // the coalesced pieces included.
8519 if (freeRangeInFreeLists()) {
8520 FreeChunk* ffc = (FreeChunk*)freeFinger();
8521 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8522 "Size of free range is inconsistent with chunk size.");
8523 if (CMSTestInFreeList) {
8524 assert(_sp->verify_chunk_in_free_list(ffc),
8525 "free range is not in free lists");
8526 }
8527 _sp->removeFreeChunkFromFreeLists(ffc);
8528 set_freeRangeInFreeLists(false);
8529 }
8530 set_lastFreeRangeCoalesced(true);
8531 }
8532 // this will be swept up when we hit the end of the free range
8534 // Verify that the bit map has no bits marked between
8535 // addr and purported end of just dead object.
8536 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8537 }
8538 assert(_limit >= addr + size,
8539 "A freshly garbage chunk can't possibly straddle over _limit");
8540 if (inFreeRange()) lookahead_and_flush(fc, size);
8541 return size;
8542 }
8544 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8545 HeapWord* addr = (HeapWord*) fc;
8546 // The sweeper has just found a live object. Return any accumulated
8547 // left hand chunk to the free lists.
8548 if (inFreeRange()) {
8549 assert(freeFinger() < addr, "freeFinger points too high");
8550 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8551 }
8553 // This object is live: we'd normally expect this to be
8554 // an oop, and like to assert the following:
8555 // assert(oop(addr)->is_oop(), "live block should be an oop");
8556 // However, as we commented above, this may be an object whose
8557 // header hasn't yet been initialized.
8558 size_t size;
8559 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8560 if (_bitMap->isMarked(addr + 1)) {
8561 // Determine the size from the bit map, rather than trying to
8562 // compute it from the object header.
8563 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8564 size = pointer_delta(nextOneAddr + 1, addr);
8565 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8566 "alignment problem");
8568 #ifdef ASSERT
8569 if (oop(addr)->klass_or_null() != NULL) {
8570 // Ignore mark word because we are running concurrent with mutators
8571 assert(oop(addr)->is_oop(true), "live block should be an oop");
8572 assert(size ==
8573 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8574 "P-mark and computed size do not agree");
8575 }
8576 #endif
8578 } else {
8579 // This should be an initialized object that's alive.
8580 assert(oop(addr)->klass_or_null() != NULL,
8581 "Should be an initialized object");
8582 // Ignore mark word because we are running concurrent with mutators
8583 assert(oop(addr)->is_oop(true), "live block should be an oop");
8584 // Verify that the bit map has no bits marked between
8585 // addr and purported end of this block.
8586 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8587 assert(size >= 3, "Necessary for Printezis marks to work");
8588 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8589 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8590 }
8591 return size;
8592 }
8594 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8595 size_t chunkSize) {
8596 // do_post_free_or_garbage_chunk() should only be called in the case
8597 // of the adaptive free list allocator.
8598 const bool fcInFreeLists = fc->is_free();
8599 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8600 assert((HeapWord*)fc <= _limit, "sweep invariant");
8601 if (CMSTestInFreeList && fcInFreeLists) {
8602 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8603 }
8605 if (CMSTraceSweeper) {
8606 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8607 }
8609 HeapWord* const fc_addr = (HeapWord*) fc;
8611 bool coalesce;
8612 const size_t left = pointer_delta(fc_addr, freeFinger());
8613 const size_t right = chunkSize;
8614 switch (FLSCoalescePolicy) {
8615 // numeric value forms a coalition aggressiveness metric
8616 case 0: { // never coalesce
8617 coalesce = false;
8618 break;
8619 }
8620 case 1: { // coalesce if left & right chunks on overpopulated lists
8621 coalesce = _sp->coalOverPopulated(left) &&
8622 _sp->coalOverPopulated(right);
8623 break;
8624 }
8625 case 2: { // coalesce if left chunk on overpopulated list (default)
8626 coalesce = _sp->coalOverPopulated(left);
8627 break;
8628 }
8629 case 3: { // coalesce if left OR right chunk on overpopulated list
8630 coalesce = _sp->coalOverPopulated(left) ||
8631 _sp->coalOverPopulated(right);
8632 break;
8633 }
8634 case 4: { // always coalesce
8635 coalesce = true;
8636 break;
8637 }
8638 default:
8639 ShouldNotReachHere();
8640 }
8642 // Should the current free range be coalesced?
8643 // If the chunk is in a free range and either we decided to coalesce above
8644 // or the chunk is near the large block at the end of the heap
8645 // (isNearLargestChunk() returns true), then coalesce this chunk.
8646 const bool doCoalesce = inFreeRange()
8647 && (coalesce || _g->isNearLargestChunk(fc_addr));
8648 if (doCoalesce) {
8649 // Coalesce the current free range on the left with the new
8650 // chunk on the right. If either is on a free list,
8651 // it must be removed from the list and stashed in the closure.
8652 if (freeRangeInFreeLists()) {
8653 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8654 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8655 "Size of free range is inconsistent with chunk size.");
8656 if (CMSTestInFreeList) {
8657 assert(_sp->verify_chunk_in_free_list(ffc),
8658 "Chunk is not in free lists");
8659 }
8660 _sp->coalDeath(ffc->size());
8661 _sp->removeFreeChunkFromFreeLists(ffc);
8662 set_freeRangeInFreeLists(false);
8663 }
8664 if (fcInFreeLists) {
8665 _sp->coalDeath(chunkSize);
8666 assert(fc->size() == chunkSize,
8667 "The chunk has the wrong size or is not in the free lists");
8668 _sp->removeFreeChunkFromFreeLists(fc);
8669 }
8670 set_lastFreeRangeCoalesced(true);
8671 print_free_block_coalesced(fc);
8672 } else { // not in a free range and/or should not coalesce
8673 // Return the current free range and start a new one.
8674 if (inFreeRange()) {
8675 // In a free range but cannot coalesce with the right hand chunk.
8676 // Put the current free range into the free lists.
8677 flush_cur_free_chunk(freeFinger(),
8678 pointer_delta(fc_addr, freeFinger()));
8679 }
8680 // Set up for new free range. Pass along whether the right hand
8681 // chunk is in the free lists.
8682 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8683 }
8684 }
8686 // Lookahead flush:
8687 // If we are tracking a free range, and this is the last chunk that
8688 // we'll look at because its end crosses past _limit, we'll preemptively
8689 // flush it along with any free range we may be holding on to. Note that
8690 // this can be the case only for an already free or freshly garbage
8691 // chunk. If this block is an object, it can never straddle
8692 // over _limit. The "straddling" occurs when _limit is set at
8693 // the previous end of the space when this cycle started, and
8694 // a subsequent heap expansion caused the previously co-terminal
8695 // free block to be coalesced with the newly expanded portion,
8696 // thus rendering _limit a non-block-boundary making it dangerous
8697 // for the sweeper to step over and examine.
8698 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8699 assert(inFreeRange(), "Should only be called if currently in a free range.");
8700 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8701 assert(_sp->used_region().contains(eob - 1),
8702 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
8703 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8704 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8705 eob, eob-1, _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8706 if (eob >= _limit) {
8707 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8708 if (CMSTraceSweeper) {
8709 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8710 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8711 "[" PTR_FORMAT "," PTR_FORMAT ")",
8712 _limit, fc, eob, _sp->bottom(), _sp->end());
8713 }
8714 // Return the storage we are tracking back into the free lists.
8715 if (CMSTraceSweeper) {
8716 gclog_or_tty->print_cr("Flushing ... ");
8717 }
8718 assert(freeFinger() < eob, "Error");
8719 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8720 }
8721 }
8723 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8724 assert(inFreeRange(), "Should only be called if currently in a free range.");
8725 assert(size > 0,
8726 "A zero sized chunk cannot be added to the free lists.");
8727 if (!freeRangeInFreeLists()) {
8728 if (CMSTestInFreeList) {
8729 FreeChunk* fc = (FreeChunk*) chunk;
8730 fc->set_size(size);
8731 assert(!_sp->verify_chunk_in_free_list(fc),
8732 "chunk should not be in free lists yet");
8733 }
8734 if (CMSTraceSweeper) {
8735 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8736 chunk, size);
8737 }
8738 // A new free range is going to be starting. The current
8739 // free range has not been added to the free lists yet or
8740 // was removed so add it back.
8741 // If the current free range was coalesced, then the death
8742 // of the free range was recorded. Record a birth now.
8743 if (lastFreeRangeCoalesced()) {
8744 _sp->coalBirth(size);
8745 }
8746 _sp->addChunkAndRepairOffsetTable(chunk, size,
8747 lastFreeRangeCoalesced());
8748 } else if (CMSTraceSweeper) {
8749 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8750 }
8751 set_inFreeRange(false);
8752 set_freeRangeInFreeLists(false);
8753 }
8755 // We take a break if we've been at this for a while,
8756 // so as to avoid monopolizing the locks involved.
8757 void SweepClosure::do_yield_work(HeapWord* addr) {
8758 // Return current free chunk being used for coalescing (if any)
8759 // to the appropriate freelist. After yielding, the next
8760 // free block encountered will start a coalescing range of
8761 // free blocks. If the next free block is adjacent to the
8762 // chunk just flushed, they will need to wait for the next
8763 // sweep to be coalesced.
8764 if (inFreeRange()) {
8765 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8766 }
8768 // First give up the locks, then yield, then re-lock.
8769 // We should probably use a constructor/destructor idiom to
8770 // do this unlock/lock or modify the MutexUnlocker class to
8771 // serve our purpose. XXX
8772 assert_lock_strong(_bitMap->lock());
8773 assert_lock_strong(_freelistLock);
8774 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8775 "CMS thread should hold CMS token");
8776 _bitMap->lock()->unlock();
8777 _freelistLock->unlock();
8778 ConcurrentMarkSweepThread::desynchronize(true);
8779 ConcurrentMarkSweepThread::acknowledge_yield_request();
8780 _collector->stopTimer();
8781 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8782 if (PrintCMSStatistics != 0) {
8783 _collector->incrementYields();
8784 }
8785 _collector->icms_wait();
8787 // See the comment in coordinator_yield()
8788 for (unsigned i = 0; i < CMSYieldSleepCount &&
8789 ConcurrentMarkSweepThread::should_yield() &&
8790 !CMSCollector::foregroundGCIsActive(); ++i) {
8791 os::sleep(Thread::current(), 1, false);
8792 ConcurrentMarkSweepThread::acknowledge_yield_request();
8793 }
8795 ConcurrentMarkSweepThread::synchronize(true);
8796 _freelistLock->lock();
8797 _bitMap->lock()->lock_without_safepoint_check();
8798 _collector->startTimer();
8799 }
8801 #ifndef PRODUCT
8802 // This is actually very useful in a product build if it can
8803 // be called from the debugger. Compile it into the product
8804 // as needed.
8805 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8806 return debug_cms_space->verify_chunk_in_free_list(fc);
8807 }
8808 #endif
8810 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8811 if (CMSTraceSweeper) {
8812 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8813 fc, fc->size());
8814 }
8815 }
8817 // CMSIsAliveClosure
8818 bool CMSIsAliveClosure::do_object_b(oop obj) {
8819 HeapWord* addr = (HeapWord*)obj;
8820 return addr != NULL &&
8821 (!_span.contains(addr) || _bit_map->isMarked(addr));
8822 }
8825 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8826 MemRegion span,
8827 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8828 bool cpc):
8829 _collector(collector),
8830 _span(span),
8831 _bit_map(bit_map),
8832 _mark_stack(mark_stack),
8833 _concurrent_precleaning(cpc) {
8834 assert(!_span.is_empty(), "Empty span could spell trouble");
8835 }
8838 // CMSKeepAliveClosure: the serial version
8839 void CMSKeepAliveClosure::do_oop(oop obj) {
8840 HeapWord* addr = (HeapWord*)obj;
8841 if (_span.contains(addr) &&
8842 !_bit_map->isMarked(addr)) {
8843 _bit_map->mark(addr);
8844 bool simulate_overflow = false;
8845 NOT_PRODUCT(
8846 if (CMSMarkStackOverflowALot &&
8847 _collector->simulate_overflow()) {
8848 // simulate a stack overflow
8849 simulate_overflow = true;
8850 }
8851 )
8852 if (simulate_overflow || !_mark_stack->push(obj)) {
8853 if (_concurrent_precleaning) {
8854 // We dirty the overflown object and let the remark
8855 // phase deal with it.
8856 assert(_collector->overflow_list_is_empty(), "Error");
8857 // In the case of object arrays, we need to dirty all of
8858 // the cards that the object spans. No locking or atomics
8859 // are needed since no one else can be mutating the mod union
8860 // table.
8861 if (obj->is_objArray()) {
8862 size_t sz = obj->size();
8863 HeapWord* end_card_addr =
8864 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8865 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8866 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8867 _collector->_modUnionTable.mark_range(redirty_range);
8868 } else {
8869 _collector->_modUnionTable.mark(addr);
8870 }
8871 _collector->_ser_kac_preclean_ovflw++;
8872 } else {
8873 _collector->push_on_overflow_list(obj);
8874 _collector->_ser_kac_ovflw++;
8875 }
8876 }
8877 }
8878 }
8880 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8881 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8883 // CMSParKeepAliveClosure: a parallel version of the above.
8884 // The work queues are private to each closure (thread),
8885 // but (may be) available for stealing by other threads.
8886 void CMSParKeepAliveClosure::do_oop(oop obj) {
8887 HeapWord* addr = (HeapWord*)obj;
8888 if (_span.contains(addr) &&
8889 !_bit_map->isMarked(addr)) {
8890 // In general, during recursive tracing, several threads
8891 // may be concurrently getting here; the first one to
8892 // "tag" it, claims it.
8893 if (_bit_map->par_mark(addr)) {
8894 bool res = _work_queue->push(obj);
8895 assert(res, "Low water mark should be much less than capacity");
8896 // Do a recursive trim in the hope that this will keep
8897 // stack usage lower, but leave some oops for potential stealers
8898 trim_queue(_low_water_mark);
8899 } // Else, another thread got there first
8900 }
8901 }
8903 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8904 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8906 void CMSParKeepAliveClosure::trim_queue(uint max) {
8907 while (_work_queue->size() > max) {
8908 oop new_oop;
8909 if (_work_queue->pop_local(new_oop)) {
8910 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8911 assert(_bit_map->isMarked((HeapWord*)new_oop),
8912 "no white objects on this stack!");
8913 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8914 // iterate over the oops in this oop, marking and pushing
8915 // the ones in CMS heap (i.e. in _span).
8916 new_oop->oop_iterate(&_mark_and_push);
8917 }
8918 }
8919 }
8921 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8922 CMSCollector* collector,
8923 MemRegion span, CMSBitMap* bit_map,
8924 OopTaskQueue* work_queue):
8925 _collector(collector),
8926 _span(span),
8927 _bit_map(bit_map),
8928 _work_queue(work_queue) { }
8930 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8931 HeapWord* addr = (HeapWord*)obj;
8932 if (_span.contains(addr) &&
8933 !_bit_map->isMarked(addr)) {
8934 if (_bit_map->par_mark(addr)) {
8935 bool simulate_overflow = false;
8936 NOT_PRODUCT(
8937 if (CMSMarkStackOverflowALot &&
8938 _collector->par_simulate_overflow()) {
8939 // simulate a stack overflow
8940 simulate_overflow = true;
8941 }
8942 )
8943 if (simulate_overflow || !_work_queue->push(obj)) {
8944 _collector->par_push_on_overflow_list(obj);
8945 _collector->_par_kac_ovflw++;
8946 }
8947 } // Else another thread got there already
8948 }
8949 }
8951 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8952 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8954 //////////////////////////////////////////////////////////////////
8955 // CMSExpansionCause /////////////////////////////
8956 //////////////////////////////////////////////////////////////////
8957 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8958 switch (cause) {
8959 case _no_expansion:
8960 return "No expansion";
8961 case _satisfy_free_ratio:
8962 return "Free ratio";
8963 case _satisfy_promotion:
8964 return "Satisfy promotion";
8965 case _satisfy_allocation:
8966 return "allocation";
8967 case _allocate_par_lab:
8968 return "Par LAB";
8969 case _allocate_par_spooling_space:
8970 return "Par Spooling Space";
8971 case _adaptive_size_policy:
8972 return "Ergonomics";
8973 default:
8974 return "unknown";
8975 }
8976 }
8978 void CMSDrainMarkingStackClosure::do_void() {
8979 // the max number to take from overflow list at a time
8980 const size_t num = _mark_stack->capacity()/4;
8981 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8982 "Overflow list should be NULL during concurrent phases");
8983 while (!_mark_stack->isEmpty() ||
8984 // if stack is empty, check the overflow list
8985 _collector->take_from_overflow_list(num, _mark_stack)) {
8986 oop obj = _mark_stack->pop();
8987 HeapWord* addr = (HeapWord*)obj;
8988 assert(_span.contains(addr), "Should be within span");
8989 assert(_bit_map->isMarked(addr), "Should be marked");
8990 assert(obj->is_oop(), "Should be an oop");
8991 obj->oop_iterate(_keep_alive);
8992 }
8993 }
8995 void CMSParDrainMarkingStackClosure::do_void() {
8996 // drain queue
8997 trim_queue(0);
8998 }
9000 // Trim our work_queue so its length is below max at return
9001 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
9002 while (_work_queue->size() > max) {
9003 oop new_oop;
9004 if (_work_queue->pop_local(new_oop)) {
9005 assert(new_oop->is_oop(), "Expected an oop");
9006 assert(_bit_map->isMarked((HeapWord*)new_oop),
9007 "no white objects on this stack!");
9008 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
9009 // iterate over the oops in this oop, marking and pushing
9010 // the ones in CMS heap (i.e. in _span).
9011 new_oop->oop_iterate(&_mark_and_push);
9012 }
9013 }
9014 }
9016 ////////////////////////////////////////////////////////////////////
9017 // Support for Marking Stack Overflow list handling and related code
9018 ////////////////////////////////////////////////////////////////////
9019 // Much of the following code is similar in shape and spirit to the
9020 // code used in ParNewGC. We should try and share that code
9021 // as much as possible in the future.
9023 #ifndef PRODUCT
9024 // Debugging support for CMSStackOverflowALot
9026 // It's OK to call this multi-threaded; the worst thing
9027 // that can happen is that we'll get a bunch of closely
9028 // spaced simulated oveflows, but that's OK, in fact
9029 // probably good as it would exercise the overflow code
9030 // under contention.
9031 bool CMSCollector::simulate_overflow() {
9032 if (_overflow_counter-- <= 0) { // just being defensive
9033 _overflow_counter = CMSMarkStackOverflowInterval;
9034 return true;
9035 } else {
9036 return false;
9037 }
9038 }
9040 bool CMSCollector::par_simulate_overflow() {
9041 return simulate_overflow();
9042 }
9043 #endif
9045 // Single-threaded
9046 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
9047 assert(stack->isEmpty(), "Expected precondition");
9048 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
9049 size_t i = num;
9050 oop cur = _overflow_list;
9051 const markOop proto = markOopDesc::prototype();
9052 NOT_PRODUCT(ssize_t n = 0;)
9053 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
9054 next = oop(cur->mark());
9055 cur->set_mark(proto); // until proven otherwise
9056 assert(cur->is_oop(), "Should be an oop");
9057 bool res = stack->push(cur);
9058 assert(res, "Bit off more than can chew?");
9059 NOT_PRODUCT(n++;)
9060 }
9061 _overflow_list = cur;
9062 #ifndef PRODUCT
9063 assert(_num_par_pushes >= n, "Too many pops?");
9064 _num_par_pushes -=n;
9065 #endif
9066 return !stack->isEmpty();
9067 }
9069 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
9070 // (MT-safe) Get a prefix of at most "num" from the list.
9071 // The overflow list is chained through the mark word of
9072 // each object in the list. We fetch the entire list,
9073 // break off a prefix of the right size and return the
9074 // remainder. If other threads try to take objects from
9075 // the overflow list at that time, they will wait for
9076 // some time to see if data becomes available. If (and
9077 // only if) another thread places one or more object(s)
9078 // on the global list before we have returned the suffix
9079 // to the global list, we will walk down our local list
9080 // to find its end and append the global list to
9081 // our suffix before returning it. This suffix walk can
9082 // prove to be expensive (quadratic in the amount of traffic)
9083 // when there are many objects in the overflow list and
9084 // there is much producer-consumer contention on the list.
9085 // *NOTE*: The overflow list manipulation code here and
9086 // in ParNewGeneration:: are very similar in shape,
9087 // except that in the ParNew case we use the old (from/eden)
9088 // copy of the object to thread the list via its klass word.
9089 // Because of the common code, if you make any changes in
9090 // the code below, please check the ParNew version to see if
9091 // similar changes might be needed.
9092 // CR 6797058 has been filed to consolidate the common code.
9093 bool CMSCollector::par_take_from_overflow_list(size_t num,
9094 OopTaskQueue* work_q,
9095 int no_of_gc_threads) {
9096 assert(work_q->size() == 0, "First empty local work queue");
9097 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
9098 if (_overflow_list == NULL) {
9099 return false;
9100 }
9101 // Grab the entire list; we'll put back a suffix
9102 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9103 Thread* tid = Thread::current();
9104 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
9105 // set to ParallelGCThreads.
9106 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
9107 size_t sleep_time_millis = MAX2((size_t)1, num/100);
9108 // If the list is busy, we spin for a short while,
9109 // sleeping between attempts to get the list.
9110 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
9111 os::sleep(tid, sleep_time_millis, false);
9112 if (_overflow_list == NULL) {
9113 // Nothing left to take
9114 return false;
9115 } else if (_overflow_list != BUSY) {
9116 // Try and grab the prefix
9117 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9118 }
9119 }
9120 // If the list was found to be empty, or we spun long
9121 // enough, we give up and return empty-handed. If we leave
9122 // the list in the BUSY state below, it must be the case that
9123 // some other thread holds the overflow list and will set it
9124 // to a non-BUSY state in the future.
9125 if (prefix == NULL || prefix == BUSY) {
9126 // Nothing to take or waited long enough
9127 if (prefix == NULL) {
9128 // Write back the NULL in case we overwrote it with BUSY above
9129 // and it is still the same value.
9130 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9131 }
9132 return false;
9133 }
9134 assert(prefix != NULL && prefix != BUSY, "Error");
9135 size_t i = num;
9136 oop cur = prefix;
9137 // Walk down the first "num" objects, unless we reach the end.
9138 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
9139 if (cur->mark() == NULL) {
9140 // We have "num" or fewer elements in the list, so there
9141 // is nothing to return to the global list.
9142 // Write back the NULL in lieu of the BUSY we wrote
9143 // above, if it is still the same value.
9144 if (_overflow_list == BUSY) {
9145 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9146 }
9147 } else {
9148 // Chop off the suffix and rerturn it to the global list.
9149 assert(cur->mark() != BUSY, "Error");
9150 oop suffix_head = cur->mark(); // suffix will be put back on global list
9151 cur->set_mark(NULL); // break off suffix
9152 // It's possible that the list is still in the empty(busy) state
9153 // we left it in a short while ago; in that case we may be
9154 // able to place back the suffix without incurring the cost
9155 // of a walk down the list.
9156 oop observed_overflow_list = _overflow_list;
9157 oop cur_overflow_list = observed_overflow_list;
9158 bool attached = false;
9159 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
9160 observed_overflow_list =
9161 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9162 if (cur_overflow_list == observed_overflow_list) {
9163 attached = true;
9164 break;
9165 } else cur_overflow_list = observed_overflow_list;
9166 }
9167 if (!attached) {
9168 // Too bad, someone else sneaked in (at least) an element; we'll need
9169 // to do a splice. Find tail of suffix so we can prepend suffix to global
9170 // list.
9171 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
9172 oop suffix_tail = cur;
9173 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
9174 "Tautology");
9175 observed_overflow_list = _overflow_list;
9176 do {
9177 cur_overflow_list = observed_overflow_list;
9178 if (cur_overflow_list != BUSY) {
9179 // Do the splice ...
9180 suffix_tail->set_mark(markOop(cur_overflow_list));
9181 } else { // cur_overflow_list == BUSY
9182 suffix_tail->set_mark(NULL);
9183 }
9184 // ... and try to place spliced list back on overflow_list ...
9185 observed_overflow_list =
9186 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9187 } while (cur_overflow_list != observed_overflow_list);
9188 // ... until we have succeeded in doing so.
9189 }
9190 }
9192 // Push the prefix elements on work_q
9193 assert(prefix != NULL, "control point invariant");
9194 const markOop proto = markOopDesc::prototype();
9195 oop next;
9196 NOT_PRODUCT(ssize_t n = 0;)
9197 for (cur = prefix; cur != NULL; cur = next) {
9198 next = oop(cur->mark());
9199 cur->set_mark(proto); // until proven otherwise
9200 assert(cur->is_oop(), "Should be an oop");
9201 bool res = work_q->push(cur);
9202 assert(res, "Bit off more than we can chew?");
9203 NOT_PRODUCT(n++;)
9204 }
9205 #ifndef PRODUCT
9206 assert(_num_par_pushes >= n, "Too many pops?");
9207 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
9208 #endif
9209 return true;
9210 }
9212 // Single-threaded
9213 void CMSCollector::push_on_overflow_list(oop p) {
9214 NOT_PRODUCT(_num_par_pushes++;)
9215 assert(p->is_oop(), "Not an oop");
9216 preserve_mark_if_necessary(p);
9217 p->set_mark((markOop)_overflow_list);
9218 _overflow_list = p;
9219 }
9221 // Multi-threaded; use CAS to prepend to overflow list
9222 void CMSCollector::par_push_on_overflow_list(oop p) {
9223 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
9224 assert(p->is_oop(), "Not an oop");
9225 par_preserve_mark_if_necessary(p);
9226 oop observed_overflow_list = _overflow_list;
9227 oop cur_overflow_list;
9228 do {
9229 cur_overflow_list = observed_overflow_list;
9230 if (cur_overflow_list != BUSY) {
9231 p->set_mark(markOop(cur_overflow_list));
9232 } else {
9233 p->set_mark(NULL);
9234 }
9235 observed_overflow_list =
9236 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
9237 } while (cur_overflow_list != observed_overflow_list);
9238 }
9239 #undef BUSY
9241 // Single threaded
9242 // General Note on GrowableArray: pushes may silently fail
9243 // because we are (temporarily) out of C-heap for expanding
9244 // the stack. The problem is quite ubiquitous and affects
9245 // a lot of code in the JVM. The prudent thing for GrowableArray
9246 // to do (for now) is to exit with an error. However, that may
9247 // be too draconian in some cases because the caller may be
9248 // able to recover without much harm. For such cases, we
9249 // should probably introduce a "soft_push" method which returns
9250 // an indication of success or failure with the assumption that
9251 // the caller may be able to recover from a failure; code in
9252 // the VM can then be changed, incrementally, to deal with such
9253 // failures where possible, thus, incrementally hardening the VM
9254 // in such low resource situations.
9255 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9256 _preserved_oop_stack.push(p);
9257 _preserved_mark_stack.push(m);
9258 assert(m == p->mark(), "Mark word changed");
9259 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9260 "bijection");
9261 }
9263 // Single threaded
9264 void CMSCollector::preserve_mark_if_necessary(oop p) {
9265 markOop m = p->mark();
9266 if (m->must_be_preserved(p)) {
9267 preserve_mark_work(p, m);
9268 }
9269 }
9271 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9272 markOop m = p->mark();
9273 if (m->must_be_preserved(p)) {
9274 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9275 // Even though we read the mark word without holding
9276 // the lock, we are assured that it will not change
9277 // because we "own" this oop, so no other thread can
9278 // be trying to push it on the overflow list; see
9279 // the assertion in preserve_mark_work() that checks
9280 // that m == p->mark().
9281 preserve_mark_work(p, m);
9282 }
9283 }
9285 // We should be able to do this multi-threaded,
9286 // a chunk of stack being a task (this is
9287 // correct because each oop only ever appears
9288 // once in the overflow list. However, it's
9289 // not very easy to completely overlap this with
9290 // other operations, so will generally not be done
9291 // until all work's been completed. Because we
9292 // expect the preserved oop stack (set) to be small,
9293 // it's probably fine to do this single-threaded.
9294 // We can explore cleverer concurrent/overlapped/parallel
9295 // processing of preserved marks if we feel the
9296 // need for this in the future. Stack overflow should
9297 // be so rare in practice and, when it happens, its
9298 // effect on performance so great that this will
9299 // likely just be in the noise anyway.
9300 void CMSCollector::restore_preserved_marks_if_any() {
9301 assert(SafepointSynchronize::is_at_safepoint(),
9302 "world should be stopped");
9303 assert(Thread::current()->is_ConcurrentGC_thread() ||
9304 Thread::current()->is_VM_thread(),
9305 "should be single-threaded");
9306 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9307 "bijection");
9309 while (!_preserved_oop_stack.is_empty()) {
9310 oop p = _preserved_oop_stack.pop();
9311 assert(p->is_oop(), "Should be an oop");
9312 assert(_span.contains(p), "oop should be in _span");
9313 assert(p->mark() == markOopDesc::prototype(),
9314 "Set when taken from overflow list");
9315 markOop m = _preserved_mark_stack.pop();
9316 p->set_mark(m);
9317 }
9318 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9319 "stacks were cleared above");
9320 }
9322 #ifndef PRODUCT
9323 bool CMSCollector::no_preserved_marks() const {
9324 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9325 }
9326 #endif
9328 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
9329 {
9330 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9331 CMSAdaptiveSizePolicy* size_policy =
9332 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
9333 assert(size_policy->is_gc_cms_adaptive_size_policy(),
9334 "Wrong type for size policy");
9335 return size_policy;
9336 }
9338 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
9339 size_t desired_promo_size) {
9340 if (cur_promo_size < desired_promo_size) {
9341 size_t expand_bytes = desired_promo_size - cur_promo_size;
9342 if (PrintAdaptiveSizePolicy && Verbose) {
9343 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9344 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
9345 expand_bytes);
9346 }
9347 expand(expand_bytes,
9348 MinHeapDeltaBytes,
9349 CMSExpansionCause::_adaptive_size_policy);
9350 } else if (desired_promo_size < cur_promo_size) {
9351 size_t shrink_bytes = cur_promo_size - desired_promo_size;
9352 if (PrintAdaptiveSizePolicy && Verbose) {
9353 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9354 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
9355 shrink_bytes);
9356 }
9357 shrink(shrink_bytes);
9358 }
9359 }
9361 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
9362 GenCollectedHeap* gch = GenCollectedHeap::heap();
9363 CMSGCAdaptivePolicyCounters* counters =
9364 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
9365 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
9366 "Wrong kind of counters");
9367 return counters;
9368 }
9371 void ASConcurrentMarkSweepGeneration::update_counters() {
9372 if (UsePerfData) {
9373 _space_counters->update_all();
9374 _gen_counters->update_all();
9375 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9376 GenCollectedHeap* gch = GenCollectedHeap::heap();
9377 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9378 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9379 "Wrong gc statistics type");
9380 counters->update_counters(gc_stats_l);
9381 }
9382 }
9384 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
9385 if (UsePerfData) {
9386 _space_counters->update_used(used);
9387 _space_counters->update_capacity();
9388 _gen_counters->update_all();
9390 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9391 GenCollectedHeap* gch = GenCollectedHeap::heap();
9392 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9393 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9394 "Wrong gc statistics type");
9395 counters->update_counters(gc_stats_l);
9396 }
9397 }
9399 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9400 assert_locked_or_safepoint(Heap_lock);
9401 assert_lock_strong(freelistLock());
9402 HeapWord* old_end = _cmsSpace->end();
9403 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9404 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9405 FreeChunk* chunk_at_end = find_chunk_at_end();
9406 if (chunk_at_end == NULL) {
9407 // No room to shrink
9408 if (PrintGCDetails && Verbose) {
9409 gclog_or_tty->print_cr("No room to shrink: old_end "
9410 PTR_FORMAT " unallocated_start " PTR_FORMAT
9411 " chunk_at_end " PTR_FORMAT,
9412 old_end, unallocated_start, chunk_at_end);
9413 }
9414 return;
9415 } else {
9417 // Find the chunk at the end of the space and determine
9418 // how much it can be shrunk.
9419 size_t shrinkable_size_in_bytes = chunk_at_end->size();
9420 size_t aligned_shrinkable_size_in_bytes =
9421 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9422 assert(unallocated_start <= (HeapWord*) chunk_at_end->end(),
9423 "Inconsistent chunk at end of space");
9424 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9425 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9427 // Shrink the underlying space
9428 _virtual_space.shrink_by(bytes);
9429 if (PrintGCDetails && Verbose) {
9430 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9431 " desired_bytes " SIZE_FORMAT
9432 " shrinkable_size_in_bytes " SIZE_FORMAT
9433 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9434 " bytes " SIZE_FORMAT,
9435 desired_bytes, shrinkable_size_in_bytes,
9436 aligned_shrinkable_size_in_bytes, bytes);
9437 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
9438 " unallocated_start " SIZE_FORMAT,
9439 old_end, unallocated_start);
9440 }
9442 // If the space did shrink (shrinking is not guaranteed),
9443 // shrink the chunk at the end by the appropriate amount.
9444 if (((HeapWord*)_virtual_space.high()) < old_end) {
9445 size_t new_word_size =
9446 heap_word_size(_virtual_space.committed_size());
9448 // Have to remove the chunk from the dictionary because it is changing
9449 // size and might be someplace elsewhere in the dictionary.
9451 // Get the chunk at end, shrink it, and put it
9452 // back.
9453 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9454 size_t word_size_change = word_size_before - new_word_size;
9455 size_t chunk_at_end_old_size = chunk_at_end->size();
9456 assert(chunk_at_end_old_size >= word_size_change,
9457 "Shrink is too large");
9458 chunk_at_end->set_size(chunk_at_end_old_size -
9459 word_size_change);
9460 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9461 word_size_change);
9463 _cmsSpace->returnChunkToDictionary(chunk_at_end);
9465 MemRegion mr(_cmsSpace->bottom(), new_word_size);
9466 _bts->resize(new_word_size); // resize the block offset shared array
9467 Universe::heap()->barrier_set()->resize_covered_region(mr);
9468 _cmsSpace->assert_locked();
9469 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9471 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9473 // update the space and generation capacity counters
9474 if (UsePerfData) {
9475 _space_counters->update_capacity();
9476 _gen_counters->update_all();
9477 }
9479 if (Verbose && PrintGCDetails) {
9480 size_t new_mem_size = _virtual_space.committed_size();
9481 size_t old_mem_size = new_mem_size + bytes;
9482 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
9483 name(), old_mem_size/K, bytes/K, new_mem_size/K);
9484 }
9485 }
9487 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9488 "Inconsistency at end of space");
9489 assert(chunk_at_end->end() == (uintptr_t*) _cmsSpace->end(),
9490 "Shrinking is inconsistent");
9491 return;
9492 }
9493 }
9494 // Transfer some number of overflown objects to usual marking
9495 // stack. Return true if some objects were transferred.
9496 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9497 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9498 (size_t)ParGCDesiredObjsFromOverflowList);
9500 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9501 assert(_collector->overflow_list_is_empty() || res,
9502 "If list is not empty, we should have taken something");
9503 assert(!res || !_mark_stack->isEmpty(),
9504 "If we took something, it should now be on our stack");
9505 return res;
9506 }
9508 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9509 size_t res = _sp->block_size_no_stall(addr, _collector);
9510 if (_sp->block_is_obj(addr)) {
9511 if (_live_bit_map->isMarked(addr)) {
9512 // It can't have been dead in a previous cycle
9513 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9514 } else {
9515 _dead_bit_map->mark(addr); // mark the dead object
9516 }
9517 }
9518 // Could be 0, if the block size could not be computed without stalling.
9519 return res;
9520 }
9522 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9524 switch (phase) {
9525 case CMSCollector::InitialMarking:
9526 initialize(true /* fullGC */ ,
9527 cause /* cause of the GC */,
9528 true /* recordGCBeginTime */,
9529 true /* recordPreGCUsage */,
9530 false /* recordPeakUsage */,
9531 false /* recordPostGCusage */,
9532 true /* recordAccumulatedGCTime */,
9533 false /* recordGCEndTime */,
9534 false /* countCollection */ );
9535 break;
9537 case CMSCollector::FinalMarking:
9538 initialize(true /* fullGC */ ,
9539 cause /* cause of the GC */,
9540 false /* recordGCBeginTime */,
9541 false /* recordPreGCUsage */,
9542 false /* recordPeakUsage */,
9543 false /* recordPostGCusage */,
9544 true /* recordAccumulatedGCTime */,
9545 false /* recordGCEndTime */,
9546 false /* countCollection */ );
9547 break;
9549 case CMSCollector::Sweeping:
9550 initialize(true /* fullGC */ ,
9551 cause /* cause of the GC */,
9552 false /* recordGCBeginTime */,
9553 false /* recordPreGCUsage */,
9554 true /* recordPeakUsage */,
9555 true /* recordPostGCusage */,
9556 false /* recordAccumulatedGCTime */,
9557 true /* recordGCEndTime */,
9558 true /* countCollection */ );
9559 break;
9561 default:
9562 ShouldNotReachHere();
9563 }
9564 }