1 /*
2 * Copyright (c) 2001, 2018, 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
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderDataGraph.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/symbolTable.hpp"
29 #include "classfile/systemDictionary.hpp"
30 #include "code/codeCache.hpp"
31 #include "gc/cms/cmsCollectorPolicy.hpp"
32 #include "gc/cms/cmsGCStats.hpp"
33 #include "gc/cms/cmsHeap.hpp"
34 #include "gc/cms/cmsOopClosures.inline.hpp"
35 #include "gc/cms/compactibleFreeListSpace.hpp"
36 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
37 #include "gc/cms/concurrentMarkSweepThread.hpp"
38 #include "gc/cms/parNewGeneration.hpp"
39 #include "gc/cms/promotionInfo.inline.hpp"
40 #include "gc/cms/vmCMSOperations.hpp"
41 #include "gc/serial/genMarkSweep.hpp"
42 #include "gc/serial/tenuredGeneration.hpp"
43 #include "gc/shared/adaptiveSizePolicy.hpp"
44 #include "gc/shared/cardGeneration.inline.hpp"
45 #include "gc/shared/cardTableRS.hpp"
46 #include "gc/shared/collectedHeap.inline.hpp"
47 #include "gc/shared/collectorCounters.hpp"
48 #include "gc/shared/collectorPolicy.hpp"
49 #include "gc/shared/gcLocker.hpp"
50 #include "gc/shared/gcPolicyCounters.hpp"
51 #include "gc/shared/gcTimer.hpp"
52 #include "gc/shared/gcTrace.hpp"
53 #include "gc/shared/gcTraceTime.inline.hpp"
54 #include "gc/shared/genCollectedHeap.hpp"
55 #include "gc/shared/genOopClosures.inline.hpp"
56 #include "gc/shared/isGCActiveMark.hpp"
57 #include "gc/shared/oopStorageParState.hpp"
58 #include "gc/shared/referencePolicy.hpp"
59 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
60 #include "gc/shared/space.inline.hpp"
61 #include "gc/shared/strongRootsScope.hpp"
62 #include "gc/shared/taskqueue.inline.hpp"
63 #include "gc/shared/weakProcessor.hpp"
64 #include "gc/shared/workerPolicy.hpp"
65 #include "logging/log.hpp"
66 #include "logging/logStream.hpp"
67 #include "memory/allocation.hpp"
68 #include "memory/binaryTreeDictionary.inline.hpp"
69 #include "memory/iterator.inline.hpp"
70 #include "memory/padded.hpp"
71 #include "memory/resourceArea.hpp"
72 #include "oops/access.inline.hpp"
73 #include "oops/oop.inline.hpp"
74 #include "prims/jvmtiExport.hpp"
75 #include "runtime/atomic.hpp"
76 #include "runtime/flags/flagSetting.hpp"
77 #include "runtime/globals_extension.hpp"
78 #include "runtime/handles.inline.hpp"
79 #include "runtime/java.hpp"
80 #include "runtime/orderAccess.hpp"
81 #include "runtime/timer.hpp"
82 #include "runtime/vmThread.hpp"
83 #include "services/memoryService.hpp"
84 #include "services/runtimeService.hpp"
85 #include "utilities/align.hpp"
86 #include "utilities/stack.inline.hpp"
87
88 // statics
89 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
90 bool CMSCollector::_full_gc_requested = false;
91 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
92
93 //////////////////////////////////////////////////////////////////
94 // In support of CMS/VM thread synchronization
95 //////////////////////////////////////////////////////////////////
96 // We split use of the CGC_lock into 2 "levels".
97 // The low-level locking is of the usual CGC_lock monitor. We introduce
98 // a higher level "token" (hereafter "CMS token") built on top of the
99 // low level monitor (hereafter "CGC lock").
100 // The token-passing protocol gives priority to the VM thread. The
101 // CMS-lock doesn't provide any fairness guarantees, but clients
102 // should ensure that it is only held for very short, bounded
103 // durations.
104 //
105 // When either of the CMS thread or the VM thread is involved in
106 // collection operations during which it does not want the other
107 // thread to interfere, it obtains the CMS token.
108 //
109 // If either thread tries to get the token while the other has
110 // it, that thread waits. However, if the VM thread and CMS thread
111 // both want the token, then the VM thread gets priority while the
112 // CMS thread waits. This ensures, for instance, that the "concurrent"
113 // phases of the CMS thread's work do not block out the VM thread
114 // for long periods of time as the CMS thread continues to hog
115 // the token. (See bug 4616232).
116 //
117 // The baton-passing functions are, however, controlled by the
118 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
119 // and here the low-level CMS lock, not the high level token,
120 // ensures mutual exclusion.
121 //
122 // Two important conditions that we have to satisfy:
123 // 1. if a thread does a low-level wait on the CMS lock, then it
124 // relinquishes the CMS token if it were holding that token
125 // when it acquired the low-level CMS lock.
126 // 2. any low-level notifications on the low-level lock
127 // should only be sent when a thread has relinquished the token.
128 //
129 // In the absence of either property, we'd have potential deadlock.
130 //
131 // We protect each of the CMS (concurrent and sequential) phases
132 // with the CMS _token_, not the CMS _lock_.
133 //
134 // The only code protected by CMS lock is the token acquisition code
135 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
136 // baton-passing code.
137 //
138 // Unfortunately, i couldn't come up with a good abstraction to factor and
139 // hide the naked CGC_lock manipulation in the baton-passing code
140 // further below. That's something we should try to do. Also, the proof
141 // of correctness of this 2-level locking scheme is far from obvious,
142 // and potentially quite slippery. We have an uneasy suspicion, for instance,
143 // that there may be a theoretical possibility of delay/starvation in the
144 // low-level lock/wait/notify scheme used for the baton-passing because of
145 // potential interference with the priority scheme embodied in the
146 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
147 // invocation further below and marked with "XXX 20011219YSR".
148 // Indeed, as we note elsewhere, this may become yet more slippery
149 // in the presence of multiple CMS and/or multiple VM threads. XXX
150
151 class CMSTokenSync: public StackObj {
152 private:
153 bool _is_cms_thread;
154 public:
155 CMSTokenSync(bool is_cms_thread):
156 _is_cms_thread(is_cms_thread) {
157 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
158 "Incorrect argument to constructor");
159 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
160 }
161
162 ~CMSTokenSync() {
163 assert(_is_cms_thread ?
164 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
165 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
166 "Incorrect state");
167 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
168 }
169 };
170
171 // Convenience class that does a CMSTokenSync, and then acquires
172 // upto three locks.
173 class CMSTokenSyncWithLocks: public CMSTokenSync {
174 private:
175 // Note: locks are acquired in textual declaration order
176 // and released in the opposite order
177 MutexLockerEx _locker1, _locker2, _locker3;
178 public:
179 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
180 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
181 CMSTokenSync(is_cms_thread),
182 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
183 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
184 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
185 { }
186 };
187
188
189 //////////////////////////////////////////////////////////////////
190 // Concurrent Mark-Sweep Generation /////////////////////////////
191 //////////////////////////////////////////////////////////////////
192
193 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
194
195 // This struct contains per-thread things necessary to support parallel
196 // young-gen collection.
197 class CMSParGCThreadState: public CHeapObj<mtGC> {
198 public:
199 CompactibleFreeListSpaceLAB lab;
200 PromotionInfo promo;
201
202 // Constructor.
203 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
204 promo.setSpace(cfls);
205 }
206 };
207
208 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
209 ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct) :
210 CardGeneration(rs, initial_byte_size, ct),
211 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
212 _did_compact(false)
213 {
214 HeapWord* bottom = (HeapWord*) _virtual_space.low();
215 HeapWord* end = (HeapWord*) _virtual_space.high();
216
217 _direct_allocated_words = 0;
218 NOT_PRODUCT(
219 _numObjectsPromoted = 0;
220 _numWordsPromoted = 0;
221 _numObjectsAllocated = 0;
222 _numWordsAllocated = 0;
223 )
224
225 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end));
226 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
227 _cmsSpace->_old_gen = this;
228
229 _gc_stats = new CMSGCStats();
230
231 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
232 // offsets match. The ability to tell free chunks from objects
233 // depends on this property.
234 debug_only(
235 FreeChunk* junk = NULL;
236 assert(UseCompressedClassPointers ||
237 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
238 "Offset of FreeChunk::_prev within FreeChunk must match"
239 " that of OopDesc::_klass within OopDesc");
240 )
241
242 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
243 for (uint i = 0; i < ParallelGCThreads; i++) {
244 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
245 }
246
247 _incremental_collection_failed = false;
248 // The "dilatation_factor" is the expansion that can occur on
249 // account of the fact that the minimum object size in the CMS
250 // generation may be larger than that in, say, a contiguous young
251 // generation.
252 // Ideally, in the calculation below, we'd compute the dilatation
253 // factor as: MinChunkSize/(promoting_gen's min object size)
254 // Since we do not have such a general query interface for the
255 // promoting generation, we'll instead just use the minimum
256 // object size (which today is a header's worth of space);
257 // note that all arithmetic is in units of HeapWords.
258 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
259 assert(_dilatation_factor >= 1.0, "from previous assert");
260 }
261
262
263 // The field "_initiating_occupancy" represents the occupancy percentage
264 // at which we trigger a new collection cycle. Unless explicitly specified
265 // via CMSInitiatingOccupancyFraction (argument "io" below), it
266 // is calculated by:
267 //
268 // Let "f" be MinHeapFreeRatio in
269 //
270 // _initiating_occupancy = 100-f +
271 // f * (CMSTriggerRatio/100)
272 // where CMSTriggerRatio is the argument "tr" below.
273 //
274 // That is, if we assume the heap is at its desired maximum occupancy at the
275 // end of a collection, we let CMSTriggerRatio of the (purported) free
276 // space be allocated before initiating a new collection cycle.
277 //
278 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
279 assert(io <= 100 && tr <= 100, "Check the arguments");
280 if (io >= 0) {
281 _initiating_occupancy = (double)io / 100.0;
282 } else {
283 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
284 (double)(tr * MinHeapFreeRatio) / 100.0)
285 / 100.0;
286 }
287 }
288
289 void ConcurrentMarkSweepGeneration::ref_processor_init() {
290 assert(collector() != NULL, "no collector");
291 collector()->ref_processor_init();
292 }
293
294 void CMSCollector::ref_processor_init() {
295 if (_ref_processor == NULL) {
296 // Allocate and initialize a reference processor
297 _ref_processor =
298 new ReferenceProcessor(&_span_based_discoverer,
299 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
300 ParallelGCThreads, // mt processing degree
301 _cmsGen->refs_discovery_is_mt(), // mt discovery
302 MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
303 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
304 &_is_alive_closure, // closure for liveness info
305 false); // disable adjusting number of processing threads
306 // Initialize the _ref_processor field of CMSGen
307 _cmsGen->set_ref_processor(_ref_processor);
308
309 }
310 }
311
312 AdaptiveSizePolicy* CMSCollector::size_policy() {
313 return CMSHeap::heap()->size_policy();
314 }
315
316 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
317
318 const char* gen_name = "old";
319 GenCollectorPolicy* gcp = CMSHeap::heap()->gen_policy();
320 // Generation Counters - generation 1, 1 subspace
321 _gen_counters = new GenerationCounters(gen_name, 1, 1,
322 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
323
324 _space_counters = new GSpaceCounters(gen_name, 0,
325 _virtual_space.reserved_size(),
326 this, _gen_counters);
327 }
328
329 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
330 _cms_gen(cms_gen)
331 {
332 assert(alpha <= 100, "bad value");
333 _saved_alpha = alpha;
334
335 // Initialize the alphas to the bootstrap value of 100.
336 _gc0_alpha = _cms_alpha = 100;
337
338 _cms_begin_time.update();
339 _cms_end_time.update();
340
341 _gc0_duration = 0.0;
342 _gc0_period = 0.0;
343 _gc0_promoted = 0;
344
345 _cms_duration = 0.0;
346 _cms_period = 0.0;
347 _cms_allocated = 0;
348
349 _cms_used_at_gc0_begin = 0;
350 _cms_used_at_gc0_end = 0;
351 _allow_duty_cycle_reduction = false;
352 _valid_bits = 0;
353 }
354
355 double CMSStats::cms_free_adjustment_factor(size_t free) const {
356 // TBD: CR 6909490
357 return 1.0;
358 }
359
360 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
361 }
362
363 // If promotion failure handling is on use
364 // the padded average size of the promotion for each
365 // young generation collection.
366 double CMSStats::time_until_cms_gen_full() const {
367 size_t cms_free = _cms_gen->cmsSpace()->free();
368 CMSHeap* heap = CMSHeap::heap();
369 size_t expected_promotion = MIN2(heap->young_gen()->capacity(),
370 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
371 if (cms_free > expected_promotion) {
372 // Start a cms collection if there isn't enough space to promote
373 // for the next young collection. Use the padded average as
374 // a safety factor.
375 cms_free -= expected_promotion;
376
377 // Adjust by the safety factor.
378 double cms_free_dbl = (double)cms_free;
379 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
380 // Apply a further correction factor which tries to adjust
381 // for recent occurance of concurrent mode failures.
382 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
383 cms_free_dbl = cms_free_dbl * cms_adjustment;
384
385 log_trace(gc)("CMSStats::time_until_cms_gen_full: cms_free " SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
386 cms_free, expected_promotion);
387 log_trace(gc)(" cms_free_dbl %f cms_consumption_rate %f", cms_free_dbl, cms_consumption_rate() + 1.0);
388 // Add 1 in case the consumption rate goes to zero.
389 return cms_free_dbl / (cms_consumption_rate() + 1.0);
390 }
391 return 0.0;
392 }
393
394 // Compare the duration of the cms collection to the
395 // time remaining before the cms generation is empty.
396 // Note that the time from the start of the cms collection
397 // to the start of the cms sweep (less than the total
398 // duration of the cms collection) can be used. This
399 // has been tried and some applications experienced
400 // promotion failures early in execution. This was
401 // possibly because the averages were not accurate
402 // enough at the beginning.
403 double CMSStats::time_until_cms_start() const {
404 // We add "gc0_period" to the "work" calculation
405 // below because this query is done (mostly) at the
406 // end of a scavenge, so we need to conservatively
407 // account for that much possible delay
408 // in the query so as to avoid concurrent mode failures
409 // due to starting the collection just a wee bit too
410 // late.
411 double work = cms_duration() + gc0_period();
412 double deadline = time_until_cms_gen_full();
413 // If a concurrent mode failure occurred recently, we want to be
414 // more conservative and halve our expected time_until_cms_gen_full()
415 if (work > deadline) {
416 log_develop_trace(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ",
417 cms_duration(), gc0_period(), time_until_cms_gen_full());
418 return 0.0;
419 }
420 return work - deadline;
421 }
422
423 #ifndef PRODUCT
424 void CMSStats::print_on(outputStream *st) const {
425 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
426 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
427 gc0_duration(), gc0_period(), gc0_promoted());
428 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
429 cms_duration(), cms_period(), cms_allocated());
430 st->print(",cms_since_beg=%g,cms_since_end=%g",
431 cms_time_since_begin(), cms_time_since_end());
432 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
433 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
434
435 if (valid()) {
436 st->print(",promo_rate=%g,cms_alloc_rate=%g",
437 promotion_rate(), cms_allocation_rate());
438 st->print(",cms_consumption_rate=%g,time_until_full=%g",
439 cms_consumption_rate(), time_until_cms_gen_full());
440 }
441 st->cr();
442 }
443 #endif // #ifndef PRODUCT
444
445 CMSCollector::CollectorState CMSCollector::_collectorState =
446 CMSCollector::Idling;
447 bool CMSCollector::_foregroundGCIsActive = false;
448 bool CMSCollector::_foregroundGCShouldWait = false;
449
450 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
451 CardTableRS* ct,
452 ConcurrentMarkSweepPolicy* cp):
453 _overflow_list(NULL),
454 _conc_workers(NULL), // may be set later
455 _completed_initialization(false),
456 _collection_count_start(0),
457 _should_unload_classes(CMSClassUnloadingEnabled),
458 _concurrent_cycles_since_last_unload(0),
459 _roots_scanning_options(GenCollectedHeap::SO_None),
460 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
461 _verifying(false),
462 _collector_policy(cp),
463 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
464 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
465 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
466 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
467 _cms_start_registered(false),
468 _cmsGen(cmsGen),
469 // Adjust span to cover old (cms) gen
470 _span(cmsGen->reserved()),
471 _ct(ct),
472 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
473 _modUnionTable((CardTable::card_shift - LogHeapWordSize),
474 -1 /* lock-free */, "No_lock" /* dummy */),
475 _restart_addr(NULL),
476 _ser_pmc_preclean_ovflw(0),
477 _ser_pmc_remark_ovflw(0),
478 _par_pmc_remark_ovflw(0),
479 _ser_kac_preclean_ovflw(0),
480 _ser_kac_ovflw(0),
481 _par_kac_ovflw(0),
482 #ifndef PRODUCT
483 _num_par_pushes(0),
484 #endif
485 _span_based_discoverer(_span),
486 _ref_processor(NULL), // will be set later
487 // Construct the is_alive_closure with _span & markBitMap
488 _is_alive_closure(_span, &_markBitMap),
489 _modUnionClosurePar(&_modUnionTable),
490 _between_prologue_and_epilogue(false),
491 _abort_preclean(false),
492 _start_sampling(false),
493 _stats(cmsGen),
494 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
495 //verify that this lock should be acquired with safepoint check.
496 Monitor::_safepoint_check_sometimes)),
497 _eden_chunk_array(NULL), // may be set in ctor body
498 _eden_chunk_index(0), // -- ditto --
499 _eden_chunk_capacity(0), // -- ditto --
500 _survivor_chunk_array(NULL), // -- ditto --
501 _survivor_chunk_index(0), // -- ditto --
502 _survivor_chunk_capacity(0), // -- ditto --
503 _survivor_plab_array(NULL) // -- ditto --
504 {
505 // Now expand the span and allocate the collection support structures
506 // (MUT, marking bit map etc.) to cover both generations subject to
507 // collection.
508
509 // For use by dirty card to oop closures.
510 _cmsGen->cmsSpace()->set_collector(this);
511
512 // Allocate MUT and marking bit map
513 {
514 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
515 if (!_markBitMap.allocate(_span)) {
516 log_warning(gc)("Failed to allocate CMS Bit Map");
517 return;
518 }
519 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
520 }
521 {
522 _modUnionTable.allocate(_span);
523 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
524 }
525
526 if (!_markStack.allocate(MarkStackSize)) {
527 log_warning(gc)("Failed to allocate CMS Marking Stack");
528 return;
529 }
530
531 // Support for multi-threaded concurrent phases
532 if (CMSConcurrentMTEnabled) {
533 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
534 // just for now
535 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
536 }
537 if (ConcGCThreads > 1) {
538 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
539 ConcGCThreads, true);
540 if (_conc_workers == NULL) {
541 log_warning(gc)("GC/CMS: _conc_workers allocation failure: forcing -CMSConcurrentMTEnabled");
542 CMSConcurrentMTEnabled = false;
543 } else {
544 _conc_workers->initialize_workers();
545 }
546 } else {
547 CMSConcurrentMTEnabled = false;
548 }
549 }
550 if (!CMSConcurrentMTEnabled) {
551 ConcGCThreads = 0;
552 } else {
553 // Turn off CMSCleanOnEnter optimization temporarily for
554 // the MT case where it's not fixed yet; see 6178663.
555 CMSCleanOnEnter = false;
556 }
557 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
558 "Inconsistency");
559 log_debug(gc)("ConcGCThreads: %u", ConcGCThreads);
560 log_debug(gc)("ParallelGCThreads: %u", ParallelGCThreads);
561
562 // Parallel task queues; these are shared for the
563 // concurrent and stop-world phases of CMS, but
564 // are not shared with parallel scavenge (ParNew).
565 {
566 uint i;
567 uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
568
569 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
570 || ParallelRefProcEnabled)
571 && num_queues > 0) {
572 _task_queues = new OopTaskQueueSet(num_queues);
573 if (_task_queues == NULL) {
574 log_warning(gc)("task_queues allocation failure.");
575 return;
576 }
577 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
578 for (i = 0; i < num_queues; i++) {
579 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
580 if (q == NULL) {
581 log_warning(gc)("work_queue allocation failure.");
582 return;
583 }
584 _task_queues->register_queue(i, q);
585 }
586 for (i = 0; i < num_queues; i++) {
587 _task_queues->queue(i)->initialize();
588 }
589 }
590 }
591
592 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
593
594 // Clip CMSBootstrapOccupancy between 0 and 100.
595 _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
596
597 // Now tell CMS generations the identity of their collector
598 ConcurrentMarkSweepGeneration::set_collector(this);
599
600 // Create & start a CMS thread for this CMS collector
601 _cmsThread = ConcurrentMarkSweepThread::start(this);
602 assert(cmsThread() != NULL, "CMS Thread should have been created");
603 assert(cmsThread()->collector() == this,
604 "CMS Thread should refer to this gen");
605 assert(CGC_lock != NULL, "Where's the CGC_lock?");
606
607 // Support for parallelizing young gen rescan
608 CMSHeap* heap = CMSHeap::heap();
609 _young_gen = heap->young_gen();
610 if (heap->supports_inline_contig_alloc()) {
611 _top_addr = heap->top_addr();
612 _end_addr = heap->end_addr();
613 assert(_young_gen != NULL, "no _young_gen");
614 _eden_chunk_index = 0;
615 _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
616 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
617 }
618
619 // Support for parallelizing survivor space rescan
620 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
621 const size_t max_plab_samples =
622 _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
623
624 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
625 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
626 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
627 _survivor_chunk_capacity = max_plab_samples;
628 for (uint i = 0; i < ParallelGCThreads; i++) {
629 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
630 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
631 assert(cur->end() == 0, "Should be 0");
632 assert(cur->array() == vec, "Should be vec");
633 assert(cur->capacity() == max_plab_samples, "Error");
634 }
635 }
636
637 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
638 _gc_counters = new CollectorCounters("CMS", 1);
639 _cgc_counters = new CollectorCounters("CMS stop-the-world phases", 2);
640 _completed_initialization = true;
641 _inter_sweep_timer.start(); // start of time
642 }
643
644 const char* ConcurrentMarkSweepGeneration::name() const {
645 return "concurrent mark-sweep generation";
646 }
647 void ConcurrentMarkSweepGeneration::update_counters() {
648 if (UsePerfData) {
649 _space_counters->update_all();
650 _gen_counters->update_all();
651 }
652 }
653
654 // this is an optimized version of update_counters(). it takes the
655 // used value as a parameter rather than computing it.
656 //
657 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
658 if (UsePerfData) {
659 _space_counters->update_used(used);
660 _space_counters->update_capacity();
661 _gen_counters->update_all();
662 }
663 }
664
665 void ConcurrentMarkSweepGeneration::print() const {
666 Generation::print();
667 cmsSpace()->print();
668 }
669
670 #ifndef PRODUCT
671 void ConcurrentMarkSweepGeneration::print_statistics() {
672 cmsSpace()->printFLCensus(0);
673 }
674 #endif
675
676 size_t
677 ConcurrentMarkSweepGeneration::contiguous_available() const {
678 // dld proposes an improvement in precision here. If the committed
679 // part of the space ends in a free block we should add that to
680 // uncommitted size in the calculation below. Will make this
681 // change later, staying with the approximation below for the
682 // time being. -- ysr.
683 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
684 }
685
686 size_t
687 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
688 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
689 }
690
691 size_t ConcurrentMarkSweepGeneration::max_available() const {
692 return free() + _virtual_space.uncommitted_size();
693 }
694
695 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
696 size_t available = max_available();
697 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
698 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
699 log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")",
700 res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes);
701 return res;
702 }
703
704 // At a promotion failure dump information on block layout in heap
705 // (cms old generation).
706 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
707 Log(gc, promotion) log;
708 if (log.is_trace()) {
709 LogStream ls(log.trace());
710 cmsSpace()->dump_at_safepoint_with_locks(collector(), &ls);
711 }
712 }
713
714 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
715 // Clear the promotion information. These pointers can be adjusted
716 // along with all the other pointers into the heap but
717 // compaction is expected to be a rare event with
718 // a heap using cms so don't do it without seeing the need.
719 for (uint i = 0; i < ParallelGCThreads; i++) {
720 _par_gc_thread_states[i]->promo.reset();
721 }
722 }
723
724 void ConcurrentMarkSweepGeneration::compute_new_size() {
725 assert_locked_or_safepoint(Heap_lock);
726
727 // If incremental collection failed, we just want to expand
728 // to the limit.
729 if (incremental_collection_failed()) {
730 clear_incremental_collection_failed();
731 grow_to_reserved();
732 return;
733 }
734
735 // The heap has been compacted but not reset yet.
736 // Any metric such as free() or used() will be incorrect.
737
738 CardGeneration::compute_new_size();
739
740 // Reset again after a possible resizing
741 if (did_compact()) {
742 cmsSpace()->reset_after_compaction();
743 }
744 }
745
746 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
747 assert_locked_or_safepoint(Heap_lock);
748
749 // If incremental collection failed, we just want to expand
750 // to the limit.
751 if (incremental_collection_failed()) {
752 clear_incremental_collection_failed();
753 grow_to_reserved();
754 return;
755 }
756
757 double free_percentage = ((double) free()) / capacity();
758 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
759 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
760
761 // compute expansion delta needed for reaching desired free percentage
762 if (free_percentage < desired_free_percentage) {
763 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
764 assert(desired_capacity >= capacity(), "invalid expansion size");
765 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
766 Log(gc) log;
767 if (log.is_trace()) {
768 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
769 log.trace("From compute_new_size: ");
770 log.trace(" Free fraction %f", free_percentage);
771 log.trace(" Desired free fraction %f", desired_free_percentage);
772 log.trace(" Maximum free fraction %f", maximum_free_percentage);
773 log.trace(" Capacity " SIZE_FORMAT, capacity() / 1000);
774 log.trace(" Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
775 CMSHeap* heap = CMSHeap::heap();
776 size_t young_size = heap->young_gen()->capacity();
777 log.trace(" Young gen size " SIZE_FORMAT, young_size / 1000);
778 log.trace(" unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
779 log.trace(" contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
780 log.trace(" Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
781 }
782 // safe if expansion fails
783 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
784 log.trace(" Expanded free fraction %f", ((double) free()) / capacity());
785 } else {
786 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
787 assert(desired_capacity <= capacity(), "invalid expansion size");
788 size_t shrink_bytes = capacity() - desired_capacity;
789 // Don't shrink unless the delta is greater than the minimum shrink we want
790 if (shrink_bytes >= MinHeapDeltaBytes) {
791 shrink_free_list_by(shrink_bytes);
792 }
793 }
794 }
795
796 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
797 return cmsSpace()->freelistLock();
798 }
799
800 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
801 CMSSynchronousYieldRequest yr;
802 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
803 return have_lock_and_allocate(size, tlab);
804 }
805
806 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
807 bool tlab /* ignored */) {
808 assert_lock_strong(freelistLock());
809 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
810 HeapWord* res = cmsSpace()->allocate(adjustedSize);
811 // Allocate the object live (grey) if the background collector has
812 // started marking. This is necessary because the marker may
813 // have passed this address and consequently this object will
814 // not otherwise be greyed and would be incorrectly swept up.
815 // Note that if this object contains references, the writing
816 // of those references will dirty the card containing this object
817 // allowing the object to be blackened (and its references scanned)
818 // either during a preclean phase or at the final checkpoint.
819 if (res != NULL) {
820 // We may block here with an uninitialized object with
821 // its mark-bit or P-bits not yet set. Such objects need
822 // to be safely navigable by block_start().
823 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
824 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
825 collector()->direct_allocated(res, adjustedSize);
826 _direct_allocated_words += adjustedSize;
827 // allocation counters
828 NOT_PRODUCT(
829 _numObjectsAllocated++;
830 _numWordsAllocated += (int)adjustedSize;
831 )
832 }
833 return res;
834 }
835
836 // In the case of direct allocation by mutators in a generation that
837 // is being concurrently collected, the object must be allocated
838 // live (grey) if the background collector has started marking.
839 // This is necessary because the marker may
840 // have passed this address and consequently this object will
841 // not otherwise be greyed and would be incorrectly swept up.
842 // Note that if this object contains references, the writing
843 // of those references will dirty the card containing this object
844 // allowing the object to be blackened (and its references scanned)
845 // either during a preclean phase or at the final checkpoint.
846 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
847 assert(_markBitMap.covers(start, size), "Out of bounds");
848 if (_collectorState >= Marking) {
849 MutexLockerEx y(_markBitMap.lock(),
850 Mutex::_no_safepoint_check_flag);
851 // [see comments preceding SweepClosure::do_blk() below for details]
852 //
853 // Can the P-bits be deleted now? JJJ
854 //
855 // 1. need to mark the object as live so it isn't collected
856 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
857 // 3. need to mark the end of the object so marking, precleaning or sweeping
858 // can skip over uninitialized or unparsable objects. An allocated
859 // object is considered uninitialized for our purposes as long as
860 // its klass word is NULL. All old gen objects are parsable
861 // as soon as they are initialized.)
862 _markBitMap.mark(start); // object is live
863 _markBitMap.mark(start + 1); // object is potentially uninitialized?
864 _markBitMap.mark(start + size - 1);
865 // mark end of object
866 }
867 // check that oop looks uninitialized
868 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
869 }
870
871 void CMSCollector::promoted(bool par, HeapWord* start,
872 bool is_obj_array, size_t obj_size) {
873 assert(_markBitMap.covers(start), "Out of bounds");
874 // See comment in direct_allocated() about when objects should
875 // be allocated live.
876 if (_collectorState >= Marking) {
877 // we already hold the marking bit map lock, taken in
878 // the prologue
879 if (par) {
880 _markBitMap.par_mark(start);
881 } else {
882 _markBitMap.mark(start);
883 }
884 // We don't need to mark the object as uninitialized (as
885 // in direct_allocated above) because this is being done with the
886 // world stopped and the object will be initialized by the
887 // time the marking, precleaning or sweeping get to look at it.
888 // But see the code for copying objects into the CMS generation,
889 // where we need to ensure that concurrent readers of the
890 // block offset table are able to safely navigate a block that
891 // is in flux from being free to being allocated (and in
892 // transition while being copied into) and subsequently
893 // becoming a bona-fide object when the copy/promotion is complete.
894 assert(SafepointSynchronize::is_at_safepoint(),
895 "expect promotion only at safepoints");
896
897 if (_collectorState < Sweeping) {
898 // Mark the appropriate cards in the modUnionTable, so that
899 // this object gets scanned before the sweep. If this is
900 // not done, CMS generation references in the object might
901 // not get marked.
902 // For the case of arrays, which are otherwise precisely
903 // marked, we need to dirty the entire array, not just its head.
904 if (is_obj_array) {
905 // The [par_]mark_range() method expects mr.end() below to
906 // be aligned to the granularity of a bit's representation
907 // in the heap. In the case of the MUT below, that's a
908 // card size.
909 MemRegion mr(start,
910 align_up(start + obj_size,
911 CardTable::card_size /* bytes */));
912 if (par) {
913 _modUnionTable.par_mark_range(mr);
914 } else {
915 _modUnionTable.mark_range(mr);
916 }
917 } else { // not an obj array; we can just mark the head
918 if (par) {
919 _modUnionTable.par_mark(start);
920 } else {
921 _modUnionTable.mark(start);
922 }
923 }
924 }
925 }
926 }
927
928 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
929 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
930 // allocate, copy and if necessary update promoinfo --
931 // delegate to underlying space.
932 assert_lock_strong(freelistLock());
933
934 #ifndef PRODUCT
935 if (CMSHeap::heap()->promotion_should_fail()) {
936 return NULL;
937 }
938 #endif // #ifndef PRODUCT
939
940 oop res = _cmsSpace->promote(obj, obj_size);
941 if (res == NULL) {
942 // expand and retry
943 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
944 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
945 // Since this is the old generation, we don't try to promote
946 // into a more senior generation.
947 res = _cmsSpace->promote(obj, obj_size);
948 }
949 if (res != NULL) {
950 // See comment in allocate() about when objects should
951 // be allocated live.
952 assert(oopDesc::is_oop(obj), "Will dereference klass pointer below");
953 collector()->promoted(false, // Not parallel
954 (HeapWord*)res, obj->is_objArray(), obj_size);
955 // promotion counters
956 NOT_PRODUCT(
957 _numObjectsPromoted++;
958 _numWordsPromoted +=
959 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
960 )
961 }
962 return res;
963 }
964
965
966 // IMPORTANT: Notes on object size recognition in CMS.
967 // ---------------------------------------------------
968 // A block of storage in the CMS generation is always in
969 // one of three states. A free block (FREE), an allocated
970 // object (OBJECT) whose size() method reports the correct size,
971 // and an intermediate state (TRANSIENT) in which its size cannot
972 // be accurately determined.
973 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
974 // -----------------------------------------------------
975 // FREE: klass_word & 1 == 1; mark_word holds block size
976 //
977 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
978 // obj->size() computes correct size
979 //
980 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
981 //
982 // STATE IDENTIFICATION: (64 bit+COOPS)
983 // ------------------------------------
984 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
985 //
986 // OBJECT: klass_word installed; klass_word != 0;
987 // obj->size() computes correct size
988 //
989 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
990 //
991 //
992 // STATE TRANSITION DIAGRAM
993 //
994 // mut / parnew mut / parnew
995 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
996 // ^ |
997 // |------------------------ DEAD <------------------------------------|
998 // sweep mut
999 //
1000 // While a block is in TRANSIENT state its size cannot be determined
1001 // so readers will either need to come back later or stall until
1002 // the size can be determined. Note that for the case of direct
1003 // allocation, P-bits, when available, may be used to determine the
1004 // size of an object that may not yet have been initialized.
1005
1006 // Things to support parallel young-gen collection.
1007 oop
1008 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1009 oop old, markOop m,
1010 size_t word_sz) {
1011 #ifndef PRODUCT
1012 if (CMSHeap::heap()->promotion_should_fail()) {
1013 return NULL;
1014 }
1015 #endif // #ifndef PRODUCT
1016
1017 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1018 PromotionInfo* promoInfo = &ps->promo;
1019 // if we are tracking promotions, then first ensure space for
1020 // promotion (including spooling space for saving header if necessary).
1021 // then allocate and copy, then track promoted info if needed.
1022 // When tracking (see PromotionInfo::track()), the mark word may
1023 // be displaced and in this case restoration of the mark word
1024 // occurs in the (oop_since_save_marks_)iterate phase.
1025 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1026 // Out of space for allocating spooling buffers;
1027 // try expanding and allocating spooling buffers.
1028 if (!expand_and_ensure_spooling_space(promoInfo)) {
1029 return NULL;
1030 }
1031 }
1032 assert(!promoInfo->tracking() || promoInfo->has_spooling_space(), "Control point invariant");
1033 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1034 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1035 if (obj_ptr == NULL) {
1036 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1037 if (obj_ptr == NULL) {
1038 return NULL;
1039 }
1040 }
1041 oop obj = oop(obj_ptr);
1042 OrderAccess::storestore();
1043 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1044 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1045 // IMPORTANT: See note on object initialization for CMS above.
1046 // Otherwise, copy the object. Here we must be careful to insert the
1047 // klass pointer last, since this marks the block as an allocated object.
1048 // Except with compressed oops it's the mark word.
1049 HeapWord* old_ptr = (HeapWord*)old;
1050 // Restore the mark word copied above.
1051 obj->set_mark_raw(m);
1052 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1053 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1054 OrderAccess::storestore();
1055
1056 if (UseCompressedClassPointers) {
1057 // Copy gap missed by (aligned) header size calculation below
1058 obj->set_klass_gap(old->klass_gap());
1059 }
1060 if (word_sz > (size_t)oopDesc::header_size()) {
1061 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1062 obj_ptr + oopDesc::header_size(),
1063 word_sz - oopDesc::header_size());
1064 }
1065
1066 // Now we can track the promoted object, if necessary. We take care
1067 // to delay the transition from uninitialized to full object
1068 // (i.e., insertion of klass pointer) until after, so that it
1069 // atomically becomes a promoted object.
1070 if (promoInfo->tracking()) {
1071 promoInfo->track((PromotedObject*)obj, old->klass());
1072 }
1073 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1074 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1075 assert(oopDesc::is_oop(old), "Will use and dereference old klass ptr below");
1076
1077 // Finally, install the klass pointer (this should be volatile).
1078 OrderAccess::storestore();
1079 obj->set_klass(old->klass());
1080 // We should now be able to calculate the right size for this object
1081 assert(oopDesc::is_oop(obj) && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1082
1083 collector()->promoted(true, // parallel
1084 obj_ptr, old->is_objArray(), word_sz);
1085
1086 NOT_PRODUCT(
1087 Atomic::inc(&_numObjectsPromoted);
1088 Atomic::add(alloc_sz, &_numWordsPromoted);
1089 )
1090
1091 return obj;
1092 }
1093
1094 void
1095 ConcurrentMarkSweepGeneration::
1096 par_promote_alloc_done(int thread_num) {
1097 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1098 ps->lab.retire(thread_num);
1099 }
1100
1101 void
1102 ConcurrentMarkSweepGeneration::
1103 par_oop_since_save_marks_iterate_done(int thread_num) {
1104 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1105 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1106 ps->promo.promoted_oops_iterate(dummy_cl);
1107
1108 // Because card-scanning has been completed, subsequent phases
1109 // (e.g., reference processing) will not need to recognize which
1110 // objects have been promoted during this GC. So, we can now disable
1111 // promotion tracking.
1112 ps->promo.stopTrackingPromotions();
1113 }
1114
1115 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1116 size_t size,
1117 bool tlab)
1118 {
1119 // We allow a STW collection only if a full
1120 // collection was requested.
1121 return full || should_allocate(size, tlab); // FIX ME !!!
1122 // This and promotion failure handling are connected at the
1123 // hip and should be fixed by untying them.
1124 }
1125
1126 bool CMSCollector::shouldConcurrentCollect() {
1127 LogTarget(Trace, gc) log;
1128
1129 if (_full_gc_requested) {
1130 log.print("CMSCollector: collect because of explicit gc request (or GCLocker)");
1131 return true;
1132 }
1133
1134 FreelistLocker x(this);
1135 // ------------------------------------------------------------------
1136 // Print out lots of information which affects the initiation of
1137 // a collection.
1138 if (log.is_enabled() && stats().valid()) {
1139 log.print("CMSCollector shouldConcurrentCollect: ");
1140
1141 LogStream out(log);
1142 stats().print_on(&out);
1143
1144 log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full());
1145 log.print("free=" SIZE_FORMAT, _cmsGen->free());
1146 log.print("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available());
1147 log.print("promotion_rate=%g", stats().promotion_rate());
1148 log.print("cms_allocation_rate=%g", stats().cms_allocation_rate());
1149 log.print("occupancy=%3.7f", _cmsGen->occupancy());
1150 log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1151 log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1152 log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1153 log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect());
1154 }
1155 // ------------------------------------------------------------------
1156
1157 // If the estimated time to complete a cms collection (cms_duration())
1158 // is less than the estimated time remaining until the cms generation
1159 // is full, start a collection.
1160 if (!UseCMSInitiatingOccupancyOnly) {
1161 if (stats().valid()) {
1162 if (stats().time_until_cms_start() == 0.0) {
1163 return true;
1164 }
1165 } else {
1166 // We want to conservatively collect somewhat early in order
1167 // to try and "bootstrap" our CMS/promotion statistics;
1168 // this branch will not fire after the first successful CMS
1169 // collection because the stats should then be valid.
1170 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1171 log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f",
1172 _cmsGen->occupancy(), _bootstrap_occupancy);
1173 return true;
1174 }
1175 }
1176 }
1177
1178 // Otherwise, we start a collection cycle if
1179 // old gen want a collection cycle started. Each may use
1180 // an appropriate criterion for making this decision.
1181 // XXX We need to make sure that the gen expansion
1182 // criterion dovetails well with this. XXX NEED TO FIX THIS
1183 if (_cmsGen->should_concurrent_collect()) {
1184 log.print("CMS old gen initiated");
1185 return true;
1186 }
1187
1188 // We start a collection if we believe an incremental collection may fail;
1189 // this is not likely to be productive in practice because it's probably too
1190 // late anyway.
1191 CMSHeap* heap = CMSHeap::heap();
1192 if (heap->incremental_collection_will_fail(true /* consult_young */)) {
1193 log.print("CMSCollector: collect because incremental collection will fail ");
1194 return true;
1195 }
1196
1197 if (MetaspaceGC::should_concurrent_collect()) {
1198 log.print("CMSCollector: collect for metadata allocation ");
1199 return true;
1200 }
1201
1202 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1203 if (CMSTriggerInterval >= 0) {
1204 if (CMSTriggerInterval == 0) {
1205 // Trigger always
1206 return true;
1207 }
1208
1209 // Check the CMS time since begin (we do not check the stats validity
1210 // as we want to be able to trigger the first CMS cycle as well)
1211 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1212 if (stats().valid()) {
1213 log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1214 stats().cms_time_since_begin());
1215 } else {
1216 log.print("CMSCollector: collect because of trigger interval (first collection)");
1217 }
1218 return true;
1219 }
1220 }
1221
1222 return false;
1223 }
1224
1225 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1226
1227 // Clear _expansion_cause fields of constituent generations
1228 void CMSCollector::clear_expansion_cause() {
1229 _cmsGen->clear_expansion_cause();
1230 }
1231
1232 // We should be conservative in starting a collection cycle. To
1233 // start too eagerly runs the risk of collecting too often in the
1234 // extreme. To collect too rarely falls back on full collections,
1235 // which works, even if not optimum in terms of concurrent work.
1236 // As a work around for too eagerly collecting, use the flag
1237 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1238 // giving the user an easily understandable way of controlling the
1239 // collections.
1240 // We want to start a new collection cycle if any of the following
1241 // conditions hold:
1242 // . our current occupancy exceeds the configured initiating occupancy
1243 // for this generation, or
1244 // . we recently needed to expand this space and have not, since that
1245 // expansion, done a collection of this generation, or
1246 // . the underlying space believes that it may be a good idea to initiate
1247 // a concurrent collection (this may be based on criteria such as the
1248 // following: the space uses linear allocation and linear allocation is
1249 // going to fail, or there is believed to be excessive fragmentation in
1250 // the generation, etc... or ...
1251 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1252 // the case of the old generation; see CR 6543076):
1253 // we may be approaching a point at which allocation requests may fail because
1254 // we will be out of sufficient free space given allocation rate estimates.]
1255 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1256
1257 assert_lock_strong(freelistLock());
1258 if (occupancy() > initiating_occupancy()) {
1259 log_trace(gc)(" %s: collect because of occupancy %f / %f ",
1260 short_name(), occupancy(), initiating_occupancy());
1261 return true;
1262 }
1263 if (UseCMSInitiatingOccupancyOnly) {
1264 return false;
1265 }
1266 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1267 log_trace(gc)(" %s: collect because expanded for allocation ", short_name());
1268 return true;
1269 }
1270 return false;
1271 }
1272
1273 void ConcurrentMarkSweepGeneration::collect(bool full,
1274 bool clear_all_soft_refs,
1275 size_t size,
1276 bool tlab)
1277 {
1278 collector()->collect(full, clear_all_soft_refs, size, tlab);
1279 }
1280
1281 void CMSCollector::collect(bool full,
1282 bool clear_all_soft_refs,
1283 size_t size,
1284 bool tlab)
1285 {
1286 // The following "if" branch is present for defensive reasons.
1287 // In the current uses of this interface, it can be replaced with:
1288 // assert(!GCLocker.is_active(), "Can't be called otherwise");
1289 // But I am not placing that assert here to allow future
1290 // generality in invoking this interface.
1291 if (GCLocker::is_active()) {
1292 // A consistency test for GCLocker
1293 assert(GCLocker::needs_gc(), "Should have been set already");
1294 // Skip this foreground collection, instead
1295 // expanding the heap if necessary.
1296 // Need the free list locks for the call to free() in compute_new_size()
1297 compute_new_size();
1298 return;
1299 }
1300 acquire_control_and_collect(full, clear_all_soft_refs);
1301 }
1302
1303 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1304 CMSHeap* heap = CMSHeap::heap();
1305 unsigned int gc_count = heap->total_full_collections();
1306 if (gc_count == full_gc_count) {
1307 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1308 _full_gc_requested = true;
1309 _full_gc_cause = cause;
1310 CGC_lock->notify(); // nudge CMS thread
1311 } else {
1312 assert(gc_count > full_gc_count, "Error: causal loop");
1313 }
1314 }
1315
1316 bool CMSCollector::is_external_interruption() {
1317 GCCause::Cause cause = CMSHeap::heap()->gc_cause();
1318 return GCCause::is_user_requested_gc(cause) ||
1319 GCCause::is_serviceability_requested_gc(cause);
1320 }
1321
1322 void CMSCollector::report_concurrent_mode_interruption() {
1323 if (is_external_interruption()) {
1324 log_debug(gc)("Concurrent mode interrupted");
1325 } else {
1326 log_debug(gc)("Concurrent mode failure");
1327 _gc_tracer_cm->report_concurrent_mode_failure();
1328 }
1329 }
1330
1331
1332 // The foreground and background collectors need to coordinate in order
1333 // to make sure that they do not mutually interfere with CMS collections.
1334 // When a background collection is active,
1335 // the foreground collector may need to take over (preempt) and
1336 // synchronously complete an ongoing collection. Depending on the
1337 // frequency of the background collections and the heap usage
1338 // of the application, this preemption can be seldom or frequent.
1339 // There are only certain
1340 // points in the background collection that the "collection-baton"
1341 // can be passed to the foreground collector.
1342 //
1343 // The foreground collector will wait for the baton before
1344 // starting any part of the collection. The foreground collector
1345 // will only wait at one location.
1346 //
1347 // The background collector will yield the baton before starting a new
1348 // phase of the collection (e.g., before initial marking, marking from roots,
1349 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1350 // of the loop which switches the phases. The background collector does some
1351 // of the phases (initial mark, final re-mark) with the world stopped.
1352 // Because of locking involved in stopping the world,
1353 // the foreground collector should not block waiting for the background
1354 // collector when it is doing a stop-the-world phase. The background
1355 // collector will yield the baton at an additional point just before
1356 // it enters a stop-the-world phase. Once the world is stopped, the
1357 // background collector checks the phase of the collection. If the
1358 // phase has not changed, it proceeds with the collection. If the
1359 // phase has changed, it skips that phase of the collection. See
1360 // the comments on the use of the Heap_lock in collect_in_background().
1361 //
1362 // Variable used in baton passing.
1363 // _foregroundGCIsActive - Set to true by the foreground collector when
1364 // it wants the baton. The foreground clears it when it has finished
1365 // the collection.
1366 // _foregroundGCShouldWait - Set to true by the background collector
1367 // when it is running. The foreground collector waits while
1368 // _foregroundGCShouldWait is true.
1369 // CGC_lock - monitor used to protect access to the above variables
1370 // and to notify the foreground and background collectors.
1371 // _collectorState - current state of the CMS collection.
1372 //
1373 // The foreground collector
1374 // acquires the CGC_lock
1375 // sets _foregroundGCIsActive
1376 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1377 // various locks acquired in preparation for the collection
1378 // are released so as not to block the background collector
1379 // that is in the midst of a collection
1380 // proceeds with the collection
1381 // clears _foregroundGCIsActive
1382 // returns
1383 //
1384 // The background collector in a loop iterating on the phases of the
1385 // collection
1386 // acquires the CGC_lock
1387 // sets _foregroundGCShouldWait
1388 // if _foregroundGCIsActive is set
1389 // clears _foregroundGCShouldWait, notifies _CGC_lock
1390 // waits on _CGC_lock for _foregroundGCIsActive to become false
1391 // and exits the loop.
1392 // otherwise
1393 // proceed with that phase of the collection
1394 // if the phase is a stop-the-world phase,
1395 // yield the baton once more just before enqueueing
1396 // the stop-world CMS operation (executed by the VM thread).
1397 // returns after all phases of the collection are done
1398 //
1399
1400 void CMSCollector::acquire_control_and_collect(bool full,
1401 bool clear_all_soft_refs) {
1402 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1403 assert(!Thread::current()->is_ConcurrentGC_thread(),
1404 "shouldn't try to acquire control from self!");
1405
1406 // Start the protocol for acquiring control of the
1407 // collection from the background collector (aka CMS thread).
1408 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1409 "VM thread should have CMS token");
1410 // Remember the possibly interrupted state of an ongoing
1411 // concurrent collection
1412 CollectorState first_state = _collectorState;
1413
1414 // Signal to a possibly ongoing concurrent collection that
1415 // we want to do a foreground collection.
1416 _foregroundGCIsActive = true;
1417
1418 // release locks and wait for a notify from the background collector
1419 // releasing the locks in only necessary for phases which
1420 // do yields to improve the granularity of the collection.
1421 assert_lock_strong(bitMapLock());
1422 // We need to lock the Free list lock for the space that we are
1423 // currently collecting.
1424 assert(haveFreelistLocks(), "Must be holding free list locks");
1425 bitMapLock()->unlock();
1426 releaseFreelistLocks();
1427 {
1428 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1429 if (_foregroundGCShouldWait) {
1430 // We are going to be waiting for action for the CMS thread;
1431 // it had better not be gone (for instance at shutdown)!
1432 assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(),
1433 "CMS thread must be running");
1434 // Wait here until the background collector gives us the go-ahead
1435 ConcurrentMarkSweepThread::clear_CMS_flag(
1436 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1437 // Get a possibly blocked CMS thread going:
1438 // Note that we set _foregroundGCIsActive true above,
1439 // without protection of the CGC_lock.
1440 CGC_lock->notify();
1441 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1442 "Possible deadlock");
1443 while (_foregroundGCShouldWait) {
1444 // wait for notification
1445 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1446 // Possibility of delay/starvation here, since CMS token does
1447 // not know to give priority to VM thread? Actually, i think
1448 // there wouldn't be any delay/starvation, but the proof of
1449 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1450 }
1451 ConcurrentMarkSweepThread::set_CMS_flag(
1452 ConcurrentMarkSweepThread::CMS_vm_has_token);
1453 }
1454 }
1455 // The CMS_token is already held. Get back the other locks.
1456 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1457 "VM thread should have CMS token");
1458 getFreelistLocks();
1459 bitMapLock()->lock_without_safepoint_check();
1460 log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d",
1461 p2i(Thread::current()), first_state);
1462 log_debug(gc, state)(" gets control with state %d", _collectorState);
1463
1464 // Inform cms gen if this was due to partial collection failing.
1465 // The CMS gen may use this fact to determine its expansion policy.
1466 CMSHeap* heap = CMSHeap::heap();
1467 if (heap->incremental_collection_will_fail(false /* don't consult_young */)) {
1468 assert(!_cmsGen->incremental_collection_failed(),
1469 "Should have been noticed, reacted to and cleared");
1470 _cmsGen->set_incremental_collection_failed();
1471 }
1472
1473 if (first_state > Idling) {
1474 report_concurrent_mode_interruption();
1475 }
1476
1477 set_did_compact(true);
1478
1479 // If the collection is being acquired from the background
1480 // collector, there may be references on the discovered
1481 // references lists. Abandon those references, since some
1482 // of them may have become unreachable after concurrent
1483 // discovery; the STW compacting collector will redo discovery
1484 // more precisely, without being subject to floating garbage.
1485 // Leaving otherwise unreachable references in the discovered
1486 // lists would require special handling.
1487 ref_processor()->disable_discovery();
1488 ref_processor()->abandon_partial_discovery();
1489 ref_processor()->verify_no_references_recorded();
1490
1491 if (first_state > Idling) {
1492 save_heap_summary();
1493 }
1494
1495 do_compaction_work(clear_all_soft_refs);
1496
1497 // Has the GC time limit been exceeded?
1498 size_t max_eden_size = _young_gen->max_eden_size();
1499 GCCause::Cause gc_cause = heap->gc_cause();
1500 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1501 _young_gen->eden()->used(),
1502 _cmsGen->max_capacity(),
1503 max_eden_size,
1504 full,
1505 gc_cause,
1506 heap->soft_ref_policy());
1507
1508 // Reset the expansion cause, now that we just completed
1509 // a collection cycle.
1510 clear_expansion_cause();
1511 _foregroundGCIsActive = false;
1512 return;
1513 }
1514
1515 // Resize the tenured generation
1516 // after obtaining the free list locks for the
1517 // two generations.
1518 void CMSCollector::compute_new_size() {
1519 assert_locked_or_safepoint(Heap_lock);
1520 FreelistLocker z(this);
1521 MetaspaceGC::compute_new_size();
1522 _cmsGen->compute_new_size_free_list();
1523 }
1524
1525 // A work method used by the foreground collector to do
1526 // a mark-sweep-compact.
1527 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1528 CMSHeap* heap = CMSHeap::heap();
1529
1530 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1531 gc_timer->register_gc_start();
1532
1533 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1534 gc_tracer->report_gc_start(heap->gc_cause(), gc_timer->gc_start());
1535
1536 heap->pre_full_gc_dump(gc_timer);
1537
1538 GCTraceTime(Trace, gc, phases) t("CMS:MSC");
1539
1540 // Temporarily widen the span of the weak reference processing to
1541 // the entire heap.
1542 MemRegion new_span(CMSHeap::heap()->reserved_region());
1543 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1544 // Temporarily, clear the "is_alive_non_header" field of the
1545 // reference processor.
1546 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1547 // Temporarily make reference _processing_ single threaded (non-MT).
1548 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1549 // Temporarily make refs discovery atomic
1550 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1551 // Temporarily make reference _discovery_ single threaded (non-MT)
1552 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1553
1554 ref_processor()->set_enqueuing_is_done(false);
1555 ref_processor()->enable_discovery();
1556 ref_processor()->setup_policy(clear_all_soft_refs);
1557 // If an asynchronous collection finishes, the _modUnionTable is
1558 // all clear. If we are assuming the collection from an asynchronous
1559 // collection, clear the _modUnionTable.
1560 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1561 "_modUnionTable should be clear if the baton was not passed");
1562 _modUnionTable.clear_all();
1563 assert(_collectorState != Idling || _ct->cld_rem_set()->mod_union_is_clear(),
1564 "mod union for klasses should be clear if the baton was passed");
1565 _ct->cld_rem_set()->clear_mod_union();
1566
1567
1568 // We must adjust the allocation statistics being maintained
1569 // in the free list space. We do so by reading and clearing
1570 // the sweep timer and updating the block flux rate estimates below.
1571 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1572 if (_inter_sweep_timer.is_active()) {
1573 _inter_sweep_timer.stop();
1574 // Note that we do not use this sample to update the _inter_sweep_estimate.
1575 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1576 _inter_sweep_estimate.padded_average(),
1577 _intra_sweep_estimate.padded_average());
1578 }
1579
1580 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1581 #ifdef ASSERT
1582 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1583 size_t free_size = cms_space->free();
1584 assert(free_size ==
1585 pointer_delta(cms_space->end(), cms_space->compaction_top())
1586 * HeapWordSize,
1587 "All the free space should be compacted into one chunk at top");
1588 assert(cms_space->dictionary()->total_chunk_size(
1589 debug_only(cms_space->freelistLock())) == 0 ||
1590 cms_space->totalSizeInIndexedFreeLists() == 0,
1591 "All the free space should be in a single chunk");
1592 size_t num = cms_space->totalCount();
1593 assert((free_size == 0 && num == 0) ||
1594 (free_size > 0 && (num == 1 || num == 2)),
1595 "There should be at most 2 free chunks after compaction");
1596 #endif // ASSERT
1597 _collectorState = Resetting;
1598 assert(_restart_addr == NULL,
1599 "Should have been NULL'd before baton was passed");
1600 reset_stw();
1601 _cmsGen->reset_after_compaction();
1602 _concurrent_cycles_since_last_unload = 0;
1603
1604 // Clear any data recorded in the PLAB chunk arrays.
1605 if (_survivor_plab_array != NULL) {
1606 reset_survivor_plab_arrays();
1607 }
1608
1609 // Adjust the per-size allocation stats for the next epoch.
1610 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1611 // Restart the "inter sweep timer" for the next epoch.
1612 _inter_sweep_timer.reset();
1613 _inter_sweep_timer.start();
1614
1615 // No longer a need to do a concurrent collection for Metaspace.
1616 MetaspaceGC::set_should_concurrent_collect(false);
1617
1618 heap->post_full_gc_dump(gc_timer);
1619
1620 gc_timer->register_gc_end();
1621
1622 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1623
1624 // For a mark-sweep-compact, compute_new_size() will be called
1625 // in the heap's do_collection() method.
1626 }
1627
1628 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1629 Log(gc, heap) log;
1630 if (!log.is_trace()) {
1631 return;
1632 }
1633
1634 ContiguousSpace* eden_space = _young_gen->eden();
1635 ContiguousSpace* from_space = _young_gen->from();
1636 ContiguousSpace* to_space = _young_gen->to();
1637 // Eden
1638 if (_eden_chunk_array != NULL) {
1639 log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1640 p2i(eden_space->bottom()), p2i(eden_space->top()),
1641 p2i(eden_space->end()), eden_space->capacity());
1642 log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT,
1643 _eden_chunk_index, _eden_chunk_capacity);
1644 for (size_t i = 0; i < _eden_chunk_index; i++) {
1645 log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i]));
1646 }
1647 }
1648 // Survivor
1649 if (_survivor_chunk_array != NULL) {
1650 log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1651 p2i(from_space->bottom()), p2i(from_space->top()),
1652 p2i(from_space->end()), from_space->capacity());
1653 log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT,
1654 _survivor_chunk_index, _survivor_chunk_capacity);
1655 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1656 log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i]));
1657 }
1658 }
1659 }
1660
1661 void CMSCollector::getFreelistLocks() const {
1662 // Get locks for all free lists in all generations that this
1663 // collector is responsible for
1664 _cmsGen->freelistLock()->lock_without_safepoint_check();
1665 }
1666
1667 void CMSCollector::releaseFreelistLocks() const {
1668 // Release locks for all free lists in all generations that this
1669 // collector is responsible for
1670 _cmsGen->freelistLock()->unlock();
1671 }
1672
1673 bool CMSCollector::haveFreelistLocks() const {
1674 // Check locks for all free lists in all generations that this
1675 // collector is responsible for
1676 assert_lock_strong(_cmsGen->freelistLock());
1677 PRODUCT_ONLY(ShouldNotReachHere());
1678 return true;
1679 }
1680
1681 // A utility class that is used by the CMS collector to
1682 // temporarily "release" the foreground collector from its
1683 // usual obligation to wait for the background collector to
1684 // complete an ongoing phase before proceeding.
1685 class ReleaseForegroundGC: public StackObj {
1686 private:
1687 CMSCollector* _c;
1688 public:
1689 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1690 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1691 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1692 // allow a potentially blocked foreground collector to proceed
1693 _c->_foregroundGCShouldWait = false;
1694 if (_c->_foregroundGCIsActive) {
1695 CGC_lock->notify();
1696 }
1697 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1698 "Possible deadlock");
1699 }
1700
1701 ~ReleaseForegroundGC() {
1702 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1703 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1704 _c->_foregroundGCShouldWait = true;
1705 }
1706 };
1707
1708 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1709 assert(Thread::current()->is_ConcurrentGC_thread(),
1710 "A CMS asynchronous collection is only allowed on a CMS thread.");
1711
1712 CMSHeap* heap = CMSHeap::heap();
1713 {
1714 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1715 MutexLockerEx hl(Heap_lock, safepoint_check);
1716 FreelistLocker fll(this);
1717 MutexLockerEx x(CGC_lock, safepoint_check);
1718 if (_foregroundGCIsActive) {
1719 // The foreground collector is. Skip this
1720 // background collection.
1721 assert(!_foregroundGCShouldWait, "Should be clear");
1722 return;
1723 } else {
1724 assert(_collectorState == Idling, "Should be idling before start.");
1725 _collectorState = InitialMarking;
1726 register_gc_start(cause);
1727 // Reset the expansion cause, now that we are about to begin
1728 // a new cycle.
1729 clear_expansion_cause();
1730
1731 // Clear the MetaspaceGC flag since a concurrent collection
1732 // is starting but also clear it after the collection.
1733 MetaspaceGC::set_should_concurrent_collect(false);
1734 }
1735 // Decide if we want to enable class unloading as part of the
1736 // ensuing concurrent GC cycle.
1737 update_should_unload_classes();
1738 _full_gc_requested = false; // acks all outstanding full gc requests
1739 _full_gc_cause = GCCause::_no_gc;
1740 // Signal that we are about to start a collection
1741 heap->increment_total_full_collections(); // ... starting a collection cycle
1742 _collection_count_start = heap->total_full_collections();
1743 }
1744
1745 size_t prev_used = _cmsGen->used();
1746
1747 // The change of the collection state is normally done at this level;
1748 // the exceptions are phases that are executed while the world is
1749 // stopped. For those phases the change of state is done while the
1750 // world is stopped. For baton passing purposes this allows the
1751 // background collector to finish the phase and change state atomically.
1752 // The foreground collector cannot wait on a phase that is done
1753 // while the world is stopped because the foreground collector already
1754 // has the world stopped and would deadlock.
1755 while (_collectorState != Idling) {
1756 log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d",
1757 p2i(Thread::current()), _collectorState);
1758 // The foreground collector
1759 // holds the Heap_lock throughout its collection.
1760 // holds the CMS token (but not the lock)
1761 // except while it is waiting for the background collector to yield.
1762 //
1763 // The foreground collector should be blocked (not for long)
1764 // if the background collector is about to start a phase
1765 // executed with world stopped. If the background
1766 // collector has already started such a phase, the
1767 // foreground collector is blocked waiting for the
1768 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1769 // are executed in the VM thread.
1770 //
1771 // The locking order is
1772 // PendingListLock (PLL) -- if applicable (FinalMarking)
1773 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1774 // CMS token (claimed in
1775 // stop_world_and_do() -->
1776 // safepoint_synchronize() -->
1777 // CMSThread::synchronize())
1778
1779 {
1780 // Check if the FG collector wants us to yield.
1781 CMSTokenSync x(true); // is cms thread
1782 if (waitForForegroundGC()) {
1783 // We yielded to a foreground GC, nothing more to be
1784 // done this round.
1785 assert(_foregroundGCShouldWait == false, "We set it to false in "
1786 "waitForForegroundGC()");
1787 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1788 p2i(Thread::current()), _collectorState);
1789 return;
1790 } else {
1791 // The background collector can run but check to see if the
1792 // foreground collector has done a collection while the
1793 // background collector was waiting to get the CGC_lock
1794 // above. If yes, break so that _foregroundGCShouldWait
1795 // is cleared before returning.
1796 if (_collectorState == Idling) {
1797 break;
1798 }
1799 }
1800 }
1801
1802 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1803 "should be waiting");
1804
1805 switch (_collectorState) {
1806 case InitialMarking:
1807 {
1808 ReleaseForegroundGC x(this);
1809 stats().record_cms_begin();
1810 VM_CMS_Initial_Mark initial_mark_op(this);
1811 VMThread::execute(&initial_mark_op);
1812 }
1813 // The collector state may be any legal state at this point
1814 // since the background collector may have yielded to the
1815 // foreground collector.
1816 break;
1817 case Marking:
1818 // initial marking in checkpointRootsInitialWork has been completed
1819 if (markFromRoots()) { // we were successful
1820 assert(_collectorState == Precleaning, "Collector state should "
1821 "have changed");
1822 } else {
1823 assert(_foregroundGCIsActive, "Internal state inconsistency");
1824 }
1825 break;
1826 case Precleaning:
1827 // marking from roots in markFromRoots has been completed
1828 preclean();
1829 assert(_collectorState == AbortablePreclean ||
1830 _collectorState == FinalMarking,
1831 "Collector state should have changed");
1832 break;
1833 case AbortablePreclean:
1834 abortable_preclean();
1835 assert(_collectorState == FinalMarking, "Collector state should "
1836 "have changed");
1837 break;
1838 case FinalMarking:
1839 {
1840 ReleaseForegroundGC x(this);
1841
1842 VM_CMS_Final_Remark final_remark_op(this);
1843 VMThread::execute(&final_remark_op);
1844 }
1845 assert(_foregroundGCShouldWait, "block post-condition");
1846 break;
1847 case Sweeping:
1848 // final marking in checkpointRootsFinal has been completed
1849 sweep();
1850 assert(_collectorState == Resizing, "Collector state change "
1851 "to Resizing must be done under the free_list_lock");
1852
1853 case Resizing: {
1854 // Sweeping has been completed...
1855 // At this point the background collection has completed.
1856 // Don't move the call to compute_new_size() down
1857 // into code that might be executed if the background
1858 // collection was preempted.
1859 {
1860 ReleaseForegroundGC x(this); // unblock FG collection
1861 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1862 CMSTokenSync z(true); // not strictly needed.
1863 if (_collectorState == Resizing) {
1864 compute_new_size();
1865 save_heap_summary();
1866 _collectorState = Resetting;
1867 } else {
1868 assert(_collectorState == Idling, "The state should only change"
1869 " because the foreground collector has finished the collection");
1870 }
1871 }
1872 break;
1873 }
1874 case Resetting:
1875 // CMS heap resizing has been completed
1876 reset_concurrent();
1877 assert(_collectorState == Idling, "Collector state should "
1878 "have changed");
1879
1880 MetaspaceGC::set_should_concurrent_collect(false);
1881
1882 stats().record_cms_end();
1883 // Don't move the concurrent_phases_end() and compute_new_size()
1884 // calls to here because a preempted background collection
1885 // has it's state set to "Resetting".
1886 break;
1887 case Idling:
1888 default:
1889 ShouldNotReachHere();
1890 break;
1891 }
1892 log_debug(gc, state)(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1893 p2i(Thread::current()), _collectorState);
1894 assert(_foregroundGCShouldWait, "block post-condition");
1895 }
1896
1897 // Should this be in gc_epilogue?
1898 heap->counters()->update_counters();
1899
1900 {
1901 // Clear _foregroundGCShouldWait and, in the event that the
1902 // foreground collector is waiting, notify it, before
1903 // returning.
1904 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1905 _foregroundGCShouldWait = false;
1906 if (_foregroundGCIsActive) {
1907 CGC_lock->notify();
1908 }
1909 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1910 "Possible deadlock");
1911 }
1912 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1913 p2i(Thread::current()), _collectorState);
1914 log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K(" SIZE_FORMAT "K)",
1915 prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K);
1916 }
1917
1918 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1919 _cms_start_registered = true;
1920 _gc_timer_cm->register_gc_start();
1921 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1922 }
1923
1924 void CMSCollector::register_gc_end() {
1925 if (_cms_start_registered) {
1926 report_heap_summary(GCWhen::AfterGC);
1927
1928 _gc_timer_cm->register_gc_end();
1929 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1930 _cms_start_registered = false;
1931 }
1932 }
1933
1934 void CMSCollector::save_heap_summary() {
1935 CMSHeap* heap = CMSHeap::heap();
1936 _last_heap_summary = heap->create_heap_summary();
1937 _last_metaspace_summary = heap->create_metaspace_summary();
1938 }
1939
1940 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1941 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1942 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1943 }
1944
1945 bool CMSCollector::waitForForegroundGC() {
1946 bool res = false;
1947 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1948 "CMS thread should have CMS token");
1949 // Block the foreground collector until the
1950 // background collectors decides whether to
1951 // yield.
1952 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1953 _foregroundGCShouldWait = true;
1954 if (_foregroundGCIsActive) {
1955 // The background collector yields to the
1956 // foreground collector and returns a value
1957 // indicating that it has yielded. The foreground
1958 // collector can proceed.
1959 res = true;
1960 _foregroundGCShouldWait = false;
1961 ConcurrentMarkSweepThread::clear_CMS_flag(
1962 ConcurrentMarkSweepThread::CMS_cms_has_token);
1963 ConcurrentMarkSweepThread::set_CMS_flag(
1964 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1965 // Get a possibly blocked foreground thread going
1966 CGC_lock->notify();
1967 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
1968 p2i(Thread::current()), _collectorState);
1969 while (_foregroundGCIsActive) {
1970 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1971 }
1972 ConcurrentMarkSweepThread::set_CMS_flag(
1973 ConcurrentMarkSweepThread::CMS_cms_has_token);
1974 ConcurrentMarkSweepThread::clear_CMS_flag(
1975 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1976 }
1977 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
1978 p2i(Thread::current()), _collectorState);
1979 return res;
1980 }
1981
1982 // Because of the need to lock the free lists and other structures in
1983 // the collector, common to all the generations that the collector is
1984 // collecting, we need the gc_prologues of individual CMS generations
1985 // delegate to their collector. It may have been simpler had the
1986 // current infrastructure allowed one to call a prologue on a
1987 // collector. In the absence of that we have the generation's
1988 // prologue delegate to the collector, which delegates back
1989 // some "local" work to a worker method in the individual generations
1990 // that it's responsible for collecting, while itself doing any
1991 // work common to all generations it's responsible for. A similar
1992 // comment applies to the gc_epilogue()'s.
1993 // The role of the variable _between_prologue_and_epilogue is to
1994 // enforce the invocation protocol.
1995 void CMSCollector::gc_prologue(bool full) {
1996 // Call gc_prologue_work() for the CMSGen
1997 // we are responsible for.
1998
1999 // The following locking discipline assumes that we are only called
2000 // when the world is stopped.
2001 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2002
2003 // The CMSCollector prologue must call the gc_prologues for the
2004 // "generations" that it's responsible
2005 // for.
2006
2007 assert( Thread::current()->is_VM_thread()
2008 || ( CMSScavengeBeforeRemark
2009 && Thread::current()->is_ConcurrentGC_thread()),
2010 "Incorrect thread type for prologue execution");
2011
2012 if (_between_prologue_and_epilogue) {
2013 // We have already been invoked; this is a gc_prologue delegation
2014 // from yet another CMS generation that we are responsible for, just
2015 // ignore it since all relevant work has already been done.
2016 return;
2017 }
2018
2019 // set a bit saying prologue has been called; cleared in epilogue
2020 _between_prologue_and_epilogue = true;
2021 // Claim locks for common data structures, then call gc_prologue_work()
2022 // for each CMSGen.
2023
2024 getFreelistLocks(); // gets free list locks on constituent spaces
2025 bitMapLock()->lock_without_safepoint_check();
2026
2027 // Should call gc_prologue_work() for all cms gens we are responsible for
2028 bool duringMarking = _collectorState >= Marking
2029 && _collectorState < Sweeping;
2030
2031 // The young collections clear the modified oops state, which tells if
2032 // there are any modified oops in the class. The remark phase also needs
2033 // that information. Tell the young collection to save the union of all
2034 // modified klasses.
2035 if (duringMarking) {
2036 _ct->cld_rem_set()->set_accumulate_modified_oops(true);
2037 }
2038
2039 bool registerClosure = duringMarking;
2040
2041 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2042
2043 if (!full) {
2044 stats().record_gc0_begin();
2045 }
2046 }
2047
2048 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2049
2050 _capacity_at_prologue = capacity();
2051 _used_at_prologue = used();
2052
2053 // We enable promotion tracking so that card-scanning can recognize
2054 // which objects have been promoted during this GC and skip them.
2055 for (uint i = 0; i < ParallelGCThreads; i++) {
2056 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2057 }
2058
2059 // Delegate to CMScollector which knows how to coordinate between
2060 // this and any other CMS generations that it is responsible for
2061 // collecting.
2062 collector()->gc_prologue(full);
2063 }
2064
2065 // This is a "private" interface for use by this generation's CMSCollector.
2066 // Not to be called directly by any other entity (for instance,
2067 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2068 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2069 bool registerClosure, ModUnionClosure* modUnionClosure) {
2070 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2071 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2072 "Should be NULL");
2073 if (registerClosure) {
2074 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2075 }
2076 cmsSpace()->gc_prologue();
2077 // Clear stat counters
2078 NOT_PRODUCT(
2079 assert(_numObjectsPromoted == 0, "check");
2080 assert(_numWordsPromoted == 0, "check");
2081 log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently",
2082 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2083 _numObjectsAllocated = 0;
2084 _numWordsAllocated = 0;
2085 )
2086 }
2087
2088 void CMSCollector::gc_epilogue(bool full) {
2089 // The following locking discipline assumes that we are only called
2090 // when the world is stopped.
2091 assert(SafepointSynchronize::is_at_safepoint(),
2092 "world is stopped assumption");
2093
2094 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2095 // if linear allocation blocks need to be appropriately marked to allow the
2096 // the blocks to be parsable. We also check here whether we need to nudge the
2097 // CMS collector thread to start a new cycle (if it's not already active).
2098 assert( Thread::current()->is_VM_thread()
2099 || ( CMSScavengeBeforeRemark
2100 && Thread::current()->is_ConcurrentGC_thread()),
2101 "Incorrect thread type for epilogue execution");
2102
2103 if (!_between_prologue_and_epilogue) {
2104 // We have already been invoked; this is a gc_epilogue delegation
2105 // from yet another CMS generation that we are responsible for, just
2106 // ignore it since all relevant work has already been done.
2107 return;
2108 }
2109 assert(haveFreelistLocks(), "must have freelist locks");
2110 assert_lock_strong(bitMapLock());
2111
2112 _ct->cld_rem_set()->set_accumulate_modified_oops(false);
2113
2114 _cmsGen->gc_epilogue_work(full);
2115
2116 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2117 // in case sampling was not already enabled, enable it
2118 _start_sampling = true;
2119 }
2120 // reset _eden_chunk_array so sampling starts afresh
2121 _eden_chunk_index = 0;
2122
2123 size_t cms_used = _cmsGen->cmsSpace()->used();
2124
2125 // update performance counters - this uses a special version of
2126 // update_counters() that allows the utilization to be passed as a
2127 // parameter, avoiding multiple calls to used().
2128 //
2129 _cmsGen->update_counters(cms_used);
2130
2131 bitMapLock()->unlock();
2132 releaseFreelistLocks();
2133
2134 if (!CleanChunkPoolAsync) {
2135 Chunk::clean_chunk_pool();
2136 }
2137
2138 set_did_compact(false);
2139 _between_prologue_and_epilogue = false; // ready for next cycle
2140 }
2141
2142 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2143 collector()->gc_epilogue(full);
2144
2145 // When using ParNew, promotion tracking should have already been
2146 // disabled. However, the prologue (which enables promotion
2147 // tracking) and epilogue are called irrespective of the type of
2148 // GC. So they will also be called before and after Full GCs, during
2149 // which promotion tracking will not be explicitly disabled. So,
2150 // it's safer to also disable it here too (to be symmetric with
2151 // enabling it in the prologue).
2152 for (uint i = 0; i < ParallelGCThreads; i++) {
2153 _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2154 }
2155 }
2156
2157 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2158 assert(!incremental_collection_failed(), "Should have been cleared");
2159 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2160 cmsSpace()->gc_epilogue();
2161 // Print stat counters
2162 NOT_PRODUCT(
2163 assert(_numObjectsAllocated == 0, "check");
2164 assert(_numWordsAllocated == 0, "check");
2165 log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
2166 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2167 _numObjectsPromoted = 0;
2168 _numWordsPromoted = 0;
2169 )
2170
2171 // Call down the chain in contiguous_available needs the freelistLock
2172 // so print this out before releasing the freeListLock.
2173 log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available());
2174 }
2175
2176 #ifndef PRODUCT
2177 bool CMSCollector::have_cms_token() {
2178 Thread* thr = Thread::current();
2179 if (thr->is_VM_thread()) {
2180 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2181 } else if (thr->is_ConcurrentGC_thread()) {
2182 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2183 } else if (thr->is_GC_task_thread()) {
2184 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2185 ParGCRareEvent_lock->owned_by_self();
2186 }
2187 return false;
2188 }
2189
2190 // Check reachability of the given heap address in CMS generation,
2191 // treating all other generations as roots.
2192 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2193 // We could "guarantee" below, rather than assert, but I'll
2194 // leave these as "asserts" so that an adventurous debugger
2195 // could try this in the product build provided some subset of
2196 // the conditions were met, provided they were interested in the
2197 // results and knew that the computation below wouldn't interfere
2198 // with other concurrent computations mutating the structures
2199 // being read or written.
2200 assert(SafepointSynchronize::is_at_safepoint(),
2201 "Else mutations in object graph will make answer suspect");
2202 assert(have_cms_token(), "Should hold cms token");
2203 assert(haveFreelistLocks(), "must hold free list locks");
2204 assert_lock_strong(bitMapLock());
2205
2206 // Clear the marking bit map array before starting, but, just
2207 // for kicks, first report if the given address is already marked
2208 tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2209 _markBitMap.isMarked(addr) ? "" : " not");
2210
2211 if (verify_after_remark()) {
2212 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2213 bool result = verification_mark_bm()->isMarked(addr);
2214 tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2215 result ? "IS" : "is NOT");
2216 return result;
2217 } else {
2218 tty->print_cr("Could not compute result");
2219 return false;
2220 }
2221 }
2222 #endif
2223
2224 void
2225 CMSCollector::print_on_error(outputStream* st) {
2226 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2227 if (collector != NULL) {
2228 CMSBitMap* bitmap = &collector->_markBitMap;
2229 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2230 bitmap->print_on_error(st, " Bits: ");
2231
2232 st->cr();
2233
2234 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2235 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2236 mut_bitmap->print_on_error(st, " Bits: ");
2237 }
2238 }
2239
2240 ////////////////////////////////////////////////////////
2241 // CMS Verification Support
2242 ////////////////////////////////////////////////////////
2243 // Following the remark phase, the following invariant
2244 // should hold -- each object in the CMS heap which is
2245 // marked in markBitMap() should be marked in the verification_mark_bm().
2246
2247 class VerifyMarkedClosure: public BitMapClosure {
2248 CMSBitMap* _marks;
2249 bool _failed;
2250
2251 public:
2252 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2253
2254 bool do_bit(size_t offset) {
2255 HeapWord* addr = _marks->offsetToHeapWord(offset);
2256 if (!_marks->isMarked(addr)) {
2257 Log(gc, verify) log;
2258 ResourceMark rm;
2259 LogStream ls(log.error());
2260 oop(addr)->print_on(&ls);
2261 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2262 _failed = true;
2263 }
2264 return true;
2265 }
2266
2267 bool failed() { return _failed; }
2268 };
2269
2270 bool CMSCollector::verify_after_remark() {
2271 GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking.");
2272 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2273 static bool init = false;
2274
2275 assert(SafepointSynchronize::is_at_safepoint(),
2276 "Else mutations in object graph will make answer suspect");
2277 assert(have_cms_token(),
2278 "Else there may be mutual interference in use of "
2279 " verification data structures");
2280 assert(_collectorState > Marking && _collectorState <= Sweeping,
2281 "Else marking info checked here may be obsolete");
2282 assert(haveFreelistLocks(), "must hold free list locks");
2283 assert_lock_strong(bitMapLock());
2284
2285
2286 // Allocate marking bit map if not already allocated
2287 if (!init) { // first time
2288 if (!verification_mark_bm()->allocate(_span)) {
2289 return false;
2290 }
2291 init = true;
2292 }
2293
2294 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2295
2296 // Turn off refs discovery -- so we will be tracing through refs.
2297 // This is as intended, because by this time
2298 // GC must already have cleared any refs that need to be cleared,
2299 // and traced those that need to be marked; moreover,
2300 // the marking done here is not going to interfere in any
2301 // way with the marking information used by GC.
2302 NoRefDiscovery no_discovery(ref_processor());
2303
2304 #if COMPILER2_OR_JVMCI
2305 DerivedPointerTableDeactivate dpt_deact;
2306 #endif
2307
2308 // Clear any marks from a previous round
2309 verification_mark_bm()->clear_all();
2310 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2311 verify_work_stacks_empty();
2312
2313 CMSHeap* heap = CMSHeap::heap();
2314 heap->ensure_parsability(false); // fill TLABs, but no need to retire them
2315 // Update the saved marks which may affect the root scans.
2316 heap->save_marks();
2317
2318 if (CMSRemarkVerifyVariant == 1) {
2319 // In this first variant of verification, we complete
2320 // all marking, then check if the new marks-vector is
2321 // a subset of the CMS marks-vector.
2322 verify_after_remark_work_1();
2323 } else {
2324 guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2");
2325 // In this second variant of verification, we flag an error
2326 // (i.e. an object reachable in the new marks-vector not reachable
2327 // in the CMS marks-vector) immediately, also indicating the
2328 // identify of an object (A) that references the unmarked object (B) --
2329 // presumably, a mutation to A failed to be picked up by preclean/remark?
2330 verify_after_remark_work_2();
2331 }
2332
2333 return true;
2334 }
2335
2336 void CMSCollector::verify_after_remark_work_1() {
2337 ResourceMark rm;
2338 HandleMark hm;
2339 CMSHeap* heap = CMSHeap::heap();
2340
2341 // Get a clear set of claim bits for the roots processing to work with.
2342 ClassLoaderDataGraph::clear_claimed_marks();
2343
2344 // Mark from roots one level into CMS
2345 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2346 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2347
2348 {
2349 StrongRootsScope srs(1);
2350
2351 heap->cms_process_roots(&srs,
2352 true, // young gen as roots
2353 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2354 should_unload_classes(),
2355 ¬Older,
2356 NULL);
2357 }
2358
2359 // Now mark from the roots
2360 MarkFromRootsClosure markFromRootsClosure(this, _span,
2361 verification_mark_bm(), verification_mark_stack(),
2362 false /* don't yield */, true /* verifying */);
2363 assert(_restart_addr == NULL, "Expected pre-condition");
2364 verification_mark_bm()->iterate(&markFromRootsClosure);
2365 while (_restart_addr != NULL) {
2366 // Deal with stack overflow: by restarting at the indicated
2367 // address.
2368 HeapWord* ra = _restart_addr;
2369 markFromRootsClosure.reset(ra);
2370 _restart_addr = NULL;
2371 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2372 }
2373 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2374 verify_work_stacks_empty();
2375
2376 // Marking completed -- now verify that each bit marked in
2377 // verification_mark_bm() is also marked in markBitMap(); flag all
2378 // errors by printing corresponding objects.
2379 VerifyMarkedClosure vcl(markBitMap());
2380 verification_mark_bm()->iterate(&vcl);
2381 if (vcl.failed()) {
2382 Log(gc, verify) log;
2383 log.error("Failed marking verification after remark");
2384 ResourceMark rm;
2385 LogStream ls(log.error());
2386 heap->print_on(&ls);
2387 fatal("CMS: failed marking verification after remark");
2388 }
2389 }
2390
2391 class VerifyCLDOopsCLDClosure : public CLDClosure {
2392 class VerifyCLDOopsClosure : public OopClosure {
2393 CMSBitMap* _bitmap;
2394 public:
2395 VerifyCLDOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2396 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2397 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2398 } _oop_closure;
2399 public:
2400 VerifyCLDOopsCLDClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2401 void do_cld(ClassLoaderData* cld) {
2402 cld->oops_do(&_oop_closure, ClassLoaderData::_claim_none, false);
2403 }
2404 };
2405
2406 void CMSCollector::verify_after_remark_work_2() {
2407 ResourceMark rm;
2408 HandleMark hm;
2409 CMSHeap* heap = CMSHeap::heap();
2410
2411 // Get a clear set of claim bits for the roots processing to work with.
2412 ClassLoaderDataGraph::clear_claimed_marks();
2413
2414 // Mark from roots one level into CMS
2415 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2416 markBitMap());
2417 CLDToOopClosure cld_closure(¬Older, ClassLoaderData::_claim_strong);
2418
2419 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2420
2421 {
2422 StrongRootsScope srs(1);
2423
2424 heap->cms_process_roots(&srs,
2425 true, // young gen as roots
2426 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2427 should_unload_classes(),
2428 ¬Older,
2429 &cld_closure);
2430 }
2431
2432 // Now mark from the roots
2433 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2434 verification_mark_bm(), markBitMap(), verification_mark_stack());
2435 assert(_restart_addr == NULL, "Expected pre-condition");
2436 verification_mark_bm()->iterate(&markFromRootsClosure);
2437 while (_restart_addr != NULL) {
2438 // Deal with stack overflow: by restarting at the indicated
2439 // address.
2440 HeapWord* ra = _restart_addr;
2441 markFromRootsClosure.reset(ra);
2442 _restart_addr = NULL;
2443 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2444 }
2445 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2446 verify_work_stacks_empty();
2447
2448 VerifyCLDOopsCLDClosure verify_cld_oops(verification_mark_bm());
2449 ClassLoaderDataGraph::cld_do(&verify_cld_oops);
2450
2451 // Marking completed -- now verify that each bit marked in
2452 // verification_mark_bm() is also marked in markBitMap(); flag all
2453 // errors by printing corresponding objects.
2454 VerifyMarkedClosure vcl(markBitMap());
2455 verification_mark_bm()->iterate(&vcl);
2456 assert(!vcl.failed(), "Else verification above should not have succeeded");
2457 }
2458
2459 void ConcurrentMarkSweepGeneration::save_marks() {
2460 // delegate to CMS space
2461 cmsSpace()->save_marks();
2462 }
2463
2464 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2465 return cmsSpace()->no_allocs_since_save_marks();
2466 }
2467
2468 void
2469 ConcurrentMarkSweepGeneration::oop_iterate(OopIterateClosure* cl) {
2470 if (freelistLock()->owned_by_self()) {
2471 Generation::oop_iterate(cl);
2472 } else {
2473 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2474 Generation::oop_iterate(cl);
2475 }
2476 }
2477
2478 void
2479 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2480 if (freelistLock()->owned_by_self()) {
2481 Generation::object_iterate(cl);
2482 } else {
2483 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2484 Generation::object_iterate(cl);
2485 }
2486 }
2487
2488 void
2489 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2490 if (freelistLock()->owned_by_self()) {
2491 Generation::safe_object_iterate(cl);
2492 } else {
2493 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2494 Generation::safe_object_iterate(cl);
2495 }
2496 }
2497
2498 void
2499 ConcurrentMarkSweepGeneration::post_compact() {
2500 }
2501
2502 void
2503 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2504 // Fix the linear allocation blocks to look like free blocks.
2505
2506 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2507 // are not called when the heap is verified during universe initialization and
2508 // at vm shutdown.
2509 if (freelistLock()->owned_by_self()) {
2510 cmsSpace()->prepare_for_verify();
2511 } else {
2512 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2513 cmsSpace()->prepare_for_verify();
2514 }
2515 }
2516
2517 void
2518 ConcurrentMarkSweepGeneration::verify() {
2519 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2520 // are not called when the heap is verified during universe initialization and
2521 // at vm shutdown.
2522 if (freelistLock()->owned_by_self()) {
2523 cmsSpace()->verify();
2524 } else {
2525 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2526 cmsSpace()->verify();
2527 }
2528 }
2529
2530 void CMSCollector::verify() {
2531 _cmsGen->verify();
2532 }
2533
2534 #ifndef PRODUCT
2535 bool CMSCollector::overflow_list_is_empty() const {
2536 assert(_num_par_pushes >= 0, "Inconsistency");
2537 if (_overflow_list == NULL) {
2538 assert(_num_par_pushes == 0, "Inconsistency");
2539 }
2540 return _overflow_list == NULL;
2541 }
2542
2543 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2544 // merely consolidate assertion checks that appear to occur together frequently.
2545 void CMSCollector::verify_work_stacks_empty() const {
2546 assert(_markStack.isEmpty(), "Marking stack should be empty");
2547 assert(overflow_list_is_empty(), "Overflow list should be empty");
2548 }
2549
2550 void CMSCollector::verify_overflow_empty() const {
2551 assert(overflow_list_is_empty(), "Overflow list should be empty");
2552 assert(no_preserved_marks(), "No preserved marks");
2553 }
2554 #endif // PRODUCT
2555
2556 // Decide if we want to enable class unloading as part of the
2557 // ensuing concurrent GC cycle. We will collect and
2558 // unload classes if it's the case that:
2559 // (a) class unloading is enabled at the command line, and
2560 // (b) old gen is getting really full
2561 // NOTE: Provided there is no change in the state of the heap between
2562 // calls to this method, it should have idempotent results. Moreover,
2563 // its results should be monotonically increasing (i.e. going from 0 to 1,
2564 // but not 1 to 0) between successive calls between which the heap was
2565 // not collected. For the implementation below, it must thus rely on
2566 // the property that concurrent_cycles_since_last_unload()
2567 // will not decrease unless a collection cycle happened and that
2568 // _cmsGen->is_too_full() are
2569 // themselves also monotonic in that sense. See check_monotonicity()
2570 // below.
2571 void CMSCollector::update_should_unload_classes() {
2572 _should_unload_classes = false;
2573 if (CMSClassUnloadingEnabled) {
2574 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2575 CMSClassUnloadingMaxInterval)
2576 || _cmsGen->is_too_full();
2577 }
2578 }
2579
2580 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2581 bool res = should_concurrent_collect();
2582 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2583 return res;
2584 }
2585
2586 void CMSCollector::setup_cms_unloading_and_verification_state() {
2587 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2588 || VerifyBeforeExit;
2589 const int rso = GenCollectedHeap::SO_AllCodeCache;
2590
2591 // We set the proper root for this CMS cycle here.
2592 if (should_unload_classes()) { // Should unload classes this cycle
2593 remove_root_scanning_option(rso); // Shrink the root set appropriately
2594 set_verifying(should_verify); // Set verification state for this cycle
2595 return; // Nothing else needs to be done at this time
2596 }
2597
2598 // Not unloading classes this cycle
2599 assert(!should_unload_classes(), "Inconsistency!");
2600
2601 // If we are not unloading classes then add SO_AllCodeCache to root
2602 // scanning options.
2603 add_root_scanning_option(rso);
2604
2605 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2606 set_verifying(true);
2607 } else if (verifying() && !should_verify) {
2608 // We were verifying, but some verification flags got disabled.
2609 set_verifying(false);
2610 // Exclude symbols, strings and code cache elements from root scanning to
2611 // reduce IM and RM pauses.
2612 remove_root_scanning_option(rso);
2613 }
2614 }
2615
2616
2617 #ifndef PRODUCT
2618 HeapWord* CMSCollector::block_start(const void* p) const {
2619 const HeapWord* addr = (HeapWord*)p;
2620 if (_span.contains(p)) {
2621 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2622 return _cmsGen->cmsSpace()->block_start(p);
2623 }
2624 }
2625 return NULL;
2626 }
2627 #endif
2628
2629 HeapWord*
2630 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2631 bool tlab,
2632 bool parallel) {
2633 CMSSynchronousYieldRequest yr;
2634 assert(!tlab, "Can't deal with TLAB allocation");
2635 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2636 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2637 if (GCExpandToAllocateDelayMillis > 0) {
2638 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2639 }
2640 return have_lock_and_allocate(word_size, tlab);
2641 }
2642
2643 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2644 size_t bytes,
2645 size_t expand_bytes,
2646 CMSExpansionCause::Cause cause)
2647 {
2648
2649 bool success = expand(bytes, expand_bytes);
2650
2651 // remember why we expanded; this information is used
2652 // by shouldConcurrentCollect() when making decisions on whether to start
2653 // a new CMS cycle.
2654 if (success) {
2655 set_expansion_cause(cause);
2656 log_trace(gc)("Expanded CMS gen for %s", CMSExpansionCause::to_string(cause));
2657 }
2658 }
2659
2660 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2661 HeapWord* res = NULL;
2662 MutexLocker x(ParGCRareEvent_lock);
2663 while (true) {
2664 // Expansion by some other thread might make alloc OK now:
2665 res = ps->lab.alloc(word_sz);
2666 if (res != NULL) return res;
2667 // If there's not enough expansion space available, give up.
2668 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2669 return NULL;
2670 }
2671 // Otherwise, we try expansion.
2672 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2673 // Now go around the loop and try alloc again;
2674 // A competing par_promote might beat us to the expansion space,
2675 // so we may go around the loop again if promotion fails again.
2676 if (GCExpandToAllocateDelayMillis > 0) {
2677 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2678 }
2679 }
2680 }
2681
2682
2683 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2684 PromotionInfo* promo) {
2685 MutexLocker x(ParGCRareEvent_lock);
2686 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2687 while (true) {
2688 // Expansion by some other thread might make alloc OK now:
2689 if (promo->ensure_spooling_space()) {
2690 assert(promo->has_spooling_space(),
2691 "Post-condition of successful ensure_spooling_space()");
2692 return true;
2693 }
2694 // If there's not enough expansion space available, give up.
2695 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2696 return false;
2697 }
2698 // Otherwise, we try expansion.
2699 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2700 // Now go around the loop and try alloc again;
2701 // A competing allocation might beat us to the expansion space,
2702 // so we may go around the loop again if allocation fails again.
2703 if (GCExpandToAllocateDelayMillis > 0) {
2704 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2705 }
2706 }
2707 }
2708
2709 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2710 // Only shrink if a compaction was done so that all the free space
2711 // in the generation is in a contiguous block at the end.
2712 if (did_compact()) {
2713 CardGeneration::shrink(bytes);
2714 }
2715 }
2716
2717 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2718 assert_locked_or_safepoint(Heap_lock);
2719 }
2720
2721 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2722 assert_locked_or_safepoint(Heap_lock);
2723 assert_lock_strong(freelistLock());
2724 log_trace(gc)("Shrinking of CMS not yet implemented");
2725 return;
2726 }
2727
2728
2729 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2730 // phases.
2731 class CMSPhaseAccounting: public StackObj {
2732 public:
2733 CMSPhaseAccounting(CMSCollector *collector,
2734 const char *title);
2735 ~CMSPhaseAccounting();
2736
2737 private:
2738 CMSCollector *_collector;
2739 const char *_title;
2740 GCTraceConcTime(Info, gc) _trace_time;
2741
2742 public:
2743 // Not MT-safe; so do not pass around these StackObj's
2744 // where they may be accessed by other threads.
2745 double wallclock_millis() {
2746 return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time());
2747 }
2748 };
2749
2750 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2751 const char *title) :
2752 _collector(collector), _title(title), _trace_time(title) {
2753
2754 _collector->resetYields();
2755 _collector->resetTimer();
2756 _collector->startTimer();
2757 _collector->gc_timer_cm()->register_gc_concurrent_start(title);
2758 }
2759
2760 CMSPhaseAccounting::~CMSPhaseAccounting() {
2761 _collector->gc_timer_cm()->register_gc_concurrent_end();
2762 _collector->stopTimer();
2763 log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_seconds(_collector->timerTicks()));
2764 log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields());
2765 }
2766
2767 // CMS work
2768
2769 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2770 class CMSParMarkTask : public AbstractGangTask {
2771 protected:
2772 CMSCollector* _collector;
2773 uint _n_workers;
2774 OopStorage::ParState<false, false> _par_state_string;
2775 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2776 AbstractGangTask(name),
2777 _collector(collector),
2778 _n_workers(n_workers),
2779 _par_state_string(StringTable::weak_storage()) {}
2780 // Work method in support of parallel rescan ... of young gen spaces
2781 void do_young_space_rescan(OopsInGenClosure* cl,
2782 ContiguousSpace* space,
2783 HeapWord** chunk_array, size_t chunk_top);
2784 void work_on_young_gen_roots(OopsInGenClosure* cl);
2785 };
2786
2787 // Parallel initial mark task
2788 class CMSParInitialMarkTask: public CMSParMarkTask {
2789 StrongRootsScope* _strong_roots_scope;
2790 public:
2791 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2792 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2793 _strong_roots_scope(strong_roots_scope) {}
2794 void work(uint worker_id);
2795 };
2796
2797 // Checkpoint the roots into this generation from outside
2798 // this generation. [Note this initial checkpoint need only
2799 // be approximate -- we'll do a catch up phase subsequently.]
2800 void CMSCollector::checkpointRootsInitial() {
2801 assert(_collectorState == InitialMarking, "Wrong collector state");
2802 check_correct_thread_executing();
2803 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
2804
2805 save_heap_summary();
2806 report_heap_summary(GCWhen::BeforeGC);
2807
2808 ReferenceProcessor* rp = ref_processor();
2809 assert(_restart_addr == NULL, "Control point invariant");
2810 {
2811 // acquire locks for subsequent manipulations
2812 MutexLockerEx x(bitMapLock(),
2813 Mutex::_no_safepoint_check_flag);
2814 checkpointRootsInitialWork();
2815 // enable ("weak") refs discovery
2816 rp->enable_discovery();
2817 _collectorState = Marking;
2818 }
2819 }
2820
2821 void CMSCollector::checkpointRootsInitialWork() {
2822 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2823 assert(_collectorState == InitialMarking, "just checking");
2824
2825 // Already have locks.
2826 assert_lock_strong(bitMapLock());
2827 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2828
2829 // Setup the verification and class unloading state for this
2830 // CMS collection cycle.
2831 setup_cms_unloading_and_verification_state();
2832
2833 GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm);
2834
2835 // Reset all the PLAB chunk arrays if necessary.
2836 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2837 reset_survivor_plab_arrays();
2838 }
2839
2840 ResourceMark rm;
2841 HandleMark hm;
2842
2843 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2844 CMSHeap* heap = CMSHeap::heap();
2845
2846 verify_work_stacks_empty();
2847 verify_overflow_empty();
2848
2849 heap->ensure_parsability(false); // fill TLABs, but no need to retire them
2850 // Update the saved marks which may affect the root scans.
2851 heap->save_marks();
2852
2853 // weak reference processing has not started yet.
2854 ref_processor()->set_enqueuing_is_done(false);
2855
2856 // Need to remember all newly created CLDs,
2857 // so that we can guarantee that the remark finds them.
2858 ClassLoaderDataGraph::remember_new_clds(true);
2859
2860 // Whenever a CLD is found, it will be claimed before proceeding to mark
2861 // the klasses. The claimed marks need to be cleared before marking starts.
2862 ClassLoaderDataGraph::clear_claimed_marks();
2863
2864 print_eden_and_survivor_chunk_arrays();
2865
2866 {
2867 #if COMPILER2_OR_JVMCI
2868 DerivedPointerTableDeactivate dpt_deact;
2869 #endif
2870 if (CMSParallelInitialMarkEnabled) {
2871 // The parallel version.
2872 WorkGang* workers = heap->workers();
2873 assert(workers != NULL, "Need parallel worker threads.");
2874 uint n_workers = workers->active_workers();
2875
2876 StrongRootsScope srs(n_workers);
2877
2878 CMSParInitialMarkTask tsk(this, &srs, n_workers);
2879 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2880 // If the total workers is greater than 1, then multiple workers
2881 // may be used at some time and the initialization has been set
2882 // such that the single threaded path cannot be used.
2883 if (workers->total_workers() > 1) {
2884 workers->run_task(&tsk);
2885 } else {
2886 tsk.work(0);
2887 }
2888 } else {
2889 // The serial version.
2890 CLDToOopClosure cld_closure(¬Older, ClassLoaderData::_claim_strong);
2891 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2892
2893 StrongRootsScope srs(1);
2894
2895 heap->cms_process_roots(&srs,
2896 true, // young gen as roots
2897 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2898 should_unload_classes(),
2899 ¬Older,
2900 &cld_closure);
2901 }
2902 }
2903
2904 // Clear mod-union table; it will be dirtied in the prologue of
2905 // CMS generation per each young generation collection.
2906
2907 assert(_modUnionTable.isAllClear(),
2908 "Was cleared in most recent final checkpoint phase"
2909 " or no bits are set in the gc_prologue before the start of the next "
2910 "subsequent marking phase.");
2911
2912 assert(_ct->cld_rem_set()->mod_union_is_clear(), "Must be");
2913
2914 // Save the end of the used_region of the constituent generations
2915 // to be used to limit the extent of sweep in each generation.
2916 save_sweep_limits();
2917 verify_overflow_empty();
2918 }
2919
2920 bool CMSCollector::markFromRoots() {
2921 // we might be tempted to assert that:
2922 // assert(!SafepointSynchronize::is_at_safepoint(),
2923 // "inconsistent argument?");
2924 // However that wouldn't be right, because it's possible that
2925 // a safepoint is indeed in progress as a young generation
2926 // stop-the-world GC happens even as we mark in this generation.
2927 assert(_collectorState == Marking, "inconsistent state?");
2928 check_correct_thread_executing();
2929 verify_overflow_empty();
2930
2931 // Weak ref discovery note: We may be discovering weak
2932 // refs in this generation concurrent (but interleaved) with
2933 // weak ref discovery by the young generation collector.
2934
2935 CMSTokenSyncWithLocks ts(true, bitMapLock());
2936 GCTraceCPUTime tcpu;
2937 CMSPhaseAccounting pa(this, "Concurrent Mark");
2938 bool res = markFromRootsWork();
2939 if (res) {
2940 _collectorState = Precleaning;
2941 } else { // We failed and a foreground collection wants to take over
2942 assert(_foregroundGCIsActive, "internal state inconsistency");
2943 assert(_restart_addr == NULL, "foreground will restart from scratch");
2944 log_debug(gc)("bailing out to foreground collection");
2945 }
2946 verify_overflow_empty();
2947 return res;
2948 }
2949
2950 bool CMSCollector::markFromRootsWork() {
2951 // iterate over marked bits in bit map, doing a full scan and mark
2952 // from these roots using the following algorithm:
2953 // . if oop is to the right of the current scan pointer,
2954 // mark corresponding bit (we'll process it later)
2955 // . else (oop is to left of current scan pointer)
2956 // push oop on marking stack
2957 // . drain the marking stack
2958
2959 // Note that when we do a marking step we need to hold the
2960 // bit map lock -- recall that direct allocation (by mutators)
2961 // and promotion (by the young generation collector) is also
2962 // marking the bit map. [the so-called allocate live policy.]
2963 // Because the implementation of bit map marking is not
2964 // robust wrt simultaneous marking of bits in the same word,
2965 // we need to make sure that there is no such interference
2966 // between concurrent such updates.
2967
2968 // already have locks
2969 assert_lock_strong(bitMapLock());
2970
2971 verify_work_stacks_empty();
2972 verify_overflow_empty();
2973 bool result = false;
2974 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2975 result = do_marking_mt();
2976 } else {
2977 result = do_marking_st();
2978 }
2979 return result;
2980 }
2981
2982 // Forward decl
2983 class CMSConcMarkingTask;
2984
2985 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
2986 CMSCollector* _collector;
2987 CMSConcMarkingTask* _task;
2988 public:
2989 virtual void yield();
2990
2991 // "n_threads" is the number of threads to be terminated.
2992 // "queue_set" is a set of work queues of other threads.
2993 // "collector" is the CMS collector associated with this task terminator.
2994 // "yield" indicates whether we need the gang as a whole to yield.
2995 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
2996 ParallelTaskTerminator(n_threads, queue_set),
2997 _collector(collector) { }
2998
2999 void set_task(CMSConcMarkingTask* task) {
3000 _task = task;
3001 }
3002 };
3003
3004 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3005 CMSConcMarkingTask* _task;
3006 public:
3007 bool should_exit_termination();
3008 void set_task(CMSConcMarkingTask* task) {
3009 _task = task;
3010 }
3011 };
3012
3013 // MT Concurrent Marking Task
3014 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3015 CMSCollector* _collector;
3016 uint _n_workers; // requested/desired # workers
3017 bool _result;
3018 CompactibleFreeListSpace* _cms_space;
3019 char _pad_front[64]; // padding to ...
3020 HeapWord* volatile _global_finger; // ... avoid sharing cache line
3021 char _pad_back[64];
3022 HeapWord* _restart_addr;
3023
3024 // Exposed here for yielding support
3025 Mutex* const _bit_map_lock;
3026
3027 // The per thread work queues, available here for stealing
3028 OopTaskQueueSet* _task_queues;
3029
3030 // Termination (and yielding) support
3031 CMSConcMarkingTerminator _term;
3032 CMSConcMarkingTerminatorTerminator _term_term;
3033
3034 public:
3035 CMSConcMarkingTask(CMSCollector* collector,
3036 CompactibleFreeListSpace* cms_space,
3037 YieldingFlexibleWorkGang* workers,
3038 OopTaskQueueSet* task_queues):
3039 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3040 _collector(collector),
3041 _n_workers(0),
3042 _result(true),
3043 _cms_space(cms_space),
3044 _bit_map_lock(collector->bitMapLock()),
3045 _task_queues(task_queues),
3046 _term(_n_workers, task_queues, _collector)
3047 {
3048 _requested_size = _n_workers;
3049 _term.set_task(this);
3050 _term_term.set_task(this);
3051 _restart_addr = _global_finger = _cms_space->bottom();
3052 }
3053
3054
3055 OopTaskQueueSet* task_queues() { return _task_queues; }
3056
3057 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3058
3059 HeapWord* volatile* global_finger_addr() { return &_global_finger; }
3060
3061 CMSConcMarkingTerminator* terminator() { return &_term; }
3062
3063 virtual void set_for_termination(uint active_workers) {
3064 terminator()->reset_for_reuse(active_workers);
3065 }
3066
3067 void work(uint worker_id);
3068 bool should_yield() {
3069 return ConcurrentMarkSweepThread::should_yield()
3070 && !_collector->foregroundGCIsActive();
3071 }
3072
3073 virtual void coordinator_yield(); // stuff done by coordinator
3074 bool result() { return _result; }
3075
3076 void reset(HeapWord* ra) {
3077 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3078 _restart_addr = _global_finger = ra;
3079 _term.reset_for_reuse();
3080 }
3081
3082 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3083 OopTaskQueue* work_q);
3084
3085 private:
3086 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3087 void do_work_steal(int i);
3088 void bump_global_finger(HeapWord* f);
3089 };
3090
3091 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3092 assert(_task != NULL, "Error");
3093 return _task->yielding();
3094 // Note that we do not need the disjunct || _task->should_yield() above
3095 // because we want terminating threads to yield only if the task
3096 // is already in the midst of yielding, which happens only after at least one
3097 // thread has yielded.
3098 }
3099
3100 void CMSConcMarkingTerminator::yield() {
3101 if (_task->should_yield()) {
3102 _task->yield();
3103 } else {
3104 ParallelTaskTerminator::yield();
3105 }
3106 }
3107
3108 ////////////////////////////////////////////////////////////////
3109 // Concurrent Marking Algorithm Sketch
3110 ////////////////////////////////////////////////////////////////
3111 // Until all tasks exhausted (both spaces):
3112 // -- claim next available chunk
3113 // -- bump global finger via CAS
3114 // -- find first object that starts in this chunk
3115 // and start scanning bitmap from that position
3116 // -- scan marked objects for oops
3117 // -- CAS-mark target, and if successful:
3118 // . if target oop is above global finger (volatile read)
3119 // nothing to do
3120 // . if target oop is in chunk and above local finger
3121 // then nothing to do
3122 // . else push on work-queue
3123 // -- Deal with possible overflow issues:
3124 // . local work-queue overflow causes stuff to be pushed on
3125 // global (common) overflow queue
3126 // . always first empty local work queue
3127 // . then get a batch of oops from global work queue if any
3128 // . then do work stealing
3129 // -- When all tasks claimed (both spaces)
3130 // and local work queue empty,
3131 // then in a loop do:
3132 // . check global overflow stack; steal a batch of oops and trace
3133 // . try to steal from other threads oif GOS is empty
3134 // . if neither is available, offer termination
3135 // -- Terminate and return result
3136 //
3137 void CMSConcMarkingTask::work(uint worker_id) {
3138 elapsedTimer _timer;
3139 ResourceMark rm;
3140 HandleMark hm;
3141
3142 DEBUG_ONLY(_collector->verify_overflow_empty();)
3143
3144 // Before we begin work, our work queue should be empty
3145 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3146 // Scan the bitmap covering _cms_space, tracing through grey objects.
3147 _timer.start();
3148 do_scan_and_mark(worker_id, _cms_space);
3149 _timer.stop();
3150 log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3151
3152 // ... do work stealing
3153 _timer.reset();
3154 _timer.start();
3155 do_work_steal(worker_id);
3156 _timer.stop();
3157 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3158 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3159 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3160 // Note that under the current task protocol, the
3161 // following assertion is true even of the spaces
3162 // expanded since the completion of the concurrent
3163 // marking. XXX This will likely change under a strict
3164 // ABORT semantics.
3165 // After perm removal the comparison was changed to
3166 // greater than or equal to from strictly greater than.
3167 // Before perm removal the highest address sweep would
3168 // have been at the end of perm gen but now is at the
3169 // end of the tenured gen.
3170 assert(_global_finger >= _cms_space->end(),
3171 "All tasks have been completed");
3172 DEBUG_ONLY(_collector->verify_overflow_empty();)
3173 }
3174
3175 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3176 HeapWord* read = _global_finger;
3177 HeapWord* cur = read;
3178 while (f > read) {
3179 cur = read;
3180 read = Atomic::cmpxchg(f, &_global_finger, cur);
3181 if (cur == read) {
3182 // our cas succeeded
3183 assert(_global_finger >= f, "protocol consistency");
3184 break;
3185 }
3186 }
3187 }
3188
3189 // This is really inefficient, and should be redone by
3190 // using (not yet available) block-read and -write interfaces to the
3191 // stack and the work_queue. XXX FIX ME !!!
3192 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3193 OopTaskQueue* work_q) {
3194 // Fast lock-free check
3195 if (ovflw_stk->length() == 0) {
3196 return false;
3197 }
3198 assert(work_q->size() == 0, "Shouldn't steal");
3199 MutexLockerEx ml(ovflw_stk->par_lock(),
3200 Mutex::_no_safepoint_check_flag);
3201 // Grab up to 1/4 the size of the work queue
3202 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3203 (size_t)ParGCDesiredObjsFromOverflowList);
3204 num = MIN2(num, ovflw_stk->length());
3205 for (int i = (int) num; i > 0; i--) {
3206 oop cur = ovflw_stk->pop();
3207 assert(cur != NULL, "Counted wrong?");
3208 work_q->push(cur);
3209 }
3210 return num > 0;
3211 }
3212
3213 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3214 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3215 int n_tasks = pst->n_tasks();
3216 // We allow that there may be no tasks to do here because
3217 // we are restarting after a stack overflow.
3218 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3219 uint nth_task = 0;
3220
3221 HeapWord* aligned_start = sp->bottom();
3222 if (sp->used_region().contains(_restart_addr)) {
3223 // Align down to a card boundary for the start of 0th task
3224 // for this space.
3225 aligned_start = align_down(_restart_addr, CardTable::card_size);
3226 }
3227
3228 size_t chunk_size = sp->marking_task_size();
3229 while (pst->try_claim_task(/* reference */ nth_task)) {
3230 // Having claimed the nth task in this space,
3231 // compute the chunk that it corresponds to:
3232 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3233 aligned_start + (nth_task+1)*chunk_size);
3234 // Try and bump the global finger via a CAS;
3235 // note that we need to do the global finger bump
3236 // _before_ taking the intersection below, because
3237 // the task corresponding to that region will be
3238 // deemed done even if the used_region() expands
3239 // because of allocation -- as it almost certainly will
3240 // during start-up while the threads yield in the
3241 // closure below.
3242 HeapWord* finger = span.end();
3243 bump_global_finger(finger); // atomically
3244 // There are null tasks here corresponding to chunks
3245 // beyond the "top" address of the space.
3246 span = span.intersection(sp->used_region());
3247 if (!span.is_empty()) { // Non-null task
3248 HeapWord* prev_obj;
3249 assert(!span.contains(_restart_addr) || nth_task == 0,
3250 "Inconsistency");
3251 if (nth_task == 0) {
3252 // For the 0th task, we'll not need to compute a block_start.
3253 if (span.contains(_restart_addr)) {
3254 // In the case of a restart because of stack overflow,
3255 // we might additionally skip a chunk prefix.
3256 prev_obj = _restart_addr;
3257 } else {
3258 prev_obj = span.start();
3259 }
3260 } else {
3261 // We want to skip the first object because
3262 // the protocol is to scan any object in its entirety
3263 // that _starts_ in this span; a fortiori, any
3264 // object starting in an earlier span is scanned
3265 // as part of an earlier claimed task.
3266 // Below we use the "careful" version of block_start
3267 // so we do not try to navigate uninitialized objects.
3268 prev_obj = sp->block_start_careful(span.start());
3269 // Below we use a variant of block_size that uses the
3270 // Printezis bits to avoid waiting for allocated
3271 // objects to become initialized/parsable.
3272 while (prev_obj < span.start()) {
3273 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3274 if (sz > 0) {
3275 prev_obj += sz;
3276 } else {
3277 // In this case we may end up doing a bit of redundant
3278 // scanning, but that appears unavoidable, short of
3279 // locking the free list locks; see bug 6324141.
3280 break;
3281 }
3282 }
3283 }
3284 if (prev_obj < span.end()) {
3285 MemRegion my_span = MemRegion(prev_obj, span.end());
3286 // Do the marking work within a non-empty span --
3287 // the last argument to the constructor indicates whether the
3288 // iteration should be incremental with periodic yields.
3289 ParMarkFromRootsClosure cl(this, _collector, my_span,
3290 &_collector->_markBitMap,
3291 work_queue(i),
3292 &_collector->_markStack);
3293 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3294 } // else nothing to do for this task
3295 } // else nothing to do for this task
3296 }
3297 // We'd be tempted to assert here that since there are no
3298 // more tasks left to claim in this space, the global_finger
3299 // must exceed space->top() and a fortiori space->end(). However,
3300 // that would not quite be correct because the bumping of
3301 // global_finger occurs strictly after the claiming of a task,
3302 // so by the time we reach here the global finger may not yet
3303 // have been bumped up by the thread that claimed the last
3304 // task.
3305 pst->all_tasks_completed();
3306 }
3307
3308 class ParConcMarkingClosure: public MetadataVisitingOopIterateClosure {
3309 private:
3310 CMSCollector* _collector;
3311 CMSConcMarkingTask* _task;
3312 MemRegion _span;
3313 CMSBitMap* _bit_map;
3314 CMSMarkStack* _overflow_stack;
3315 OopTaskQueue* _work_queue;
3316 protected:
3317 DO_OOP_WORK_DEFN
3318 public:
3319 ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3320 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3321 MetadataVisitingOopIterateClosure(collector->ref_processor()),
3322 _collector(collector),
3323 _task(task),
3324 _span(collector->_span),
3325 _bit_map(bit_map),
3326 _overflow_stack(overflow_stack),
3327 _work_queue(work_queue)
3328 { }
3329 virtual void do_oop(oop* p);
3330 virtual void do_oop(narrowOop* p);
3331
3332 void trim_queue(size_t max);
3333 void handle_stack_overflow(HeapWord* lost);
3334 void do_yield_check() {
3335 if (_task->should_yield()) {
3336 _task->yield();
3337 }
3338 }
3339 };
3340
3341 DO_OOP_WORK_IMPL(ParConcMarkingClosure)
3342
3343 // Grey object scanning during work stealing phase --
3344 // the salient assumption here is that any references
3345 // that are in these stolen objects being scanned must
3346 // already have been initialized (else they would not have
3347 // been published), so we do not need to check for
3348 // uninitialized objects before pushing here.
3349 void ParConcMarkingClosure::do_oop(oop obj) {
3350 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3351 HeapWord* addr = (HeapWord*)obj;
3352 // Check if oop points into the CMS generation
3353 // and is not marked
3354 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3355 // a white object ...
3356 // If we manage to "claim" the object, by being the
3357 // first thread to mark it, then we push it on our
3358 // marking stack
3359 if (_bit_map->par_mark(addr)) { // ... now grey
3360 // push on work queue (grey set)
3361 bool simulate_overflow = false;
3362 NOT_PRODUCT(
3363 if (CMSMarkStackOverflowALot &&
3364 _collector->simulate_overflow()) {
3365 // simulate a stack overflow
3366 simulate_overflow = true;
3367 }
3368 )
3369 if (simulate_overflow ||
3370 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3371 // stack overflow
3372 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3373 // We cannot assert that the overflow stack is full because
3374 // it may have been emptied since.
3375 assert(simulate_overflow ||
3376 _work_queue->size() == _work_queue->max_elems(),
3377 "Else push should have succeeded");
3378 handle_stack_overflow(addr);
3379 }
3380 } // Else, some other thread got there first
3381 do_yield_check();
3382 }
3383 }
3384
3385 void ParConcMarkingClosure::trim_queue(size_t max) {
3386 while (_work_queue->size() > max) {
3387 oop new_oop;
3388 if (_work_queue->pop_local(new_oop)) {
3389 assert(oopDesc::is_oop(new_oop), "Should be an oop");
3390 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3391 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3392 new_oop->oop_iterate(this); // do_oop() above
3393 do_yield_check();
3394 }
3395 }
3396 }
3397
3398 // Upon stack overflow, we discard (part of) the stack,
3399 // remembering the least address amongst those discarded
3400 // in CMSCollector's _restart_address.
3401 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3402 // We need to do this under a mutex to prevent other
3403 // workers from interfering with the work done below.
3404 MutexLockerEx ml(_overflow_stack->par_lock(),
3405 Mutex::_no_safepoint_check_flag);
3406 // Remember the least grey address discarded
3407 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3408 _collector->lower_restart_addr(ra);
3409 _overflow_stack->reset(); // discard stack contents
3410 _overflow_stack->expand(); // expand the stack if possible
3411 }
3412
3413
3414 void CMSConcMarkingTask::do_work_steal(int i) {
3415 OopTaskQueue* work_q = work_queue(i);
3416 oop obj_to_scan;
3417 CMSBitMap* bm = &(_collector->_markBitMap);
3418 CMSMarkStack* ovflw = &(_collector->_markStack);
3419 ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3420 while (true) {
3421 cl.trim_queue(0);
3422 assert(work_q->size() == 0, "Should have been emptied above");
3423 if (get_work_from_overflow_stack(ovflw, work_q)) {
3424 // Can't assert below because the work obtained from the
3425 // overflow stack may already have been stolen from us.
3426 // assert(work_q->size() > 0, "Work from overflow stack");
3427 continue;
3428 } else if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
3429 assert(oopDesc::is_oop(obj_to_scan), "Should be an oop");
3430 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3431 obj_to_scan->oop_iterate(&cl);
3432 } else if (terminator()->offer_termination(&_term_term)) {
3433 assert(work_q->size() == 0, "Impossible!");
3434 break;
3435 } else if (yielding() || should_yield()) {
3436 yield();
3437 }
3438 }
3439 }
3440
3441 // This is run by the CMS (coordinator) thread.
3442 void CMSConcMarkingTask::coordinator_yield() {
3443 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3444 "CMS thread should hold CMS token");
3445 // First give up the locks, then yield, then re-lock
3446 // We should probably use a constructor/destructor idiom to
3447 // do this unlock/lock or modify the MutexUnlocker class to
3448 // serve our purpose. XXX
3449 assert_lock_strong(_bit_map_lock);
3450 _bit_map_lock->unlock();
3451 ConcurrentMarkSweepThread::desynchronize(true);
3452 _collector->stopTimer();
3453 _collector->incrementYields();
3454
3455 // It is possible for whichever thread initiated the yield request
3456 // not to get a chance to wake up and take the bitmap lock between
3457 // this thread releasing it and reacquiring it. So, while the
3458 // should_yield() flag is on, let's sleep for a bit to give the
3459 // other thread a chance to wake up. The limit imposed on the number
3460 // of iterations is defensive, to avoid any unforseen circumstances
3461 // putting us into an infinite loop. Since it's always been this
3462 // (coordinator_yield()) method that was observed to cause the
3463 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3464 // which is by default non-zero. For the other seven methods that
3465 // also perform the yield operation, as are using a different
3466 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3467 // can enable the sleeping for those methods too, if necessary.
3468 // See 6442774.
3469 //
3470 // We really need to reconsider the synchronization between the GC
3471 // thread and the yield-requesting threads in the future and we
3472 // should really use wait/notify, which is the recommended
3473 // way of doing this type of interaction. Additionally, we should
3474 // consolidate the eight methods that do the yield operation and they
3475 // are almost identical into one for better maintainability and
3476 // readability. See 6445193.
3477 //
3478 // Tony 2006.06.29
3479 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3480 ConcurrentMarkSweepThread::should_yield() &&
3481 !CMSCollector::foregroundGCIsActive(); ++i) {
3482 os::sleep(Thread::current(), 1, false);
3483 }
3484
3485 ConcurrentMarkSweepThread::synchronize(true);
3486 _bit_map_lock->lock_without_safepoint_check();
3487 _collector->startTimer();
3488 }
3489
3490 bool CMSCollector::do_marking_mt() {
3491 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3492 uint num_workers = WorkerPolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3493 conc_workers()->active_workers(),
3494 Threads::number_of_non_daemon_threads());
3495 num_workers = conc_workers()->update_active_workers(num_workers);
3496 log_info(gc,task)("Using %u workers of %u for marking", num_workers, conc_workers()->total_workers());
3497
3498 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3499
3500 CMSConcMarkingTask tsk(this,
3501 cms_space,
3502 conc_workers(),
3503 task_queues());
3504
3505 // Since the actual number of workers we get may be different
3506 // from the number we requested above, do we need to do anything different
3507 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3508 // class?? XXX
3509 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3510
3511 // Refs discovery is already non-atomic.
3512 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3513 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3514 conc_workers()->start_task(&tsk);
3515 while (tsk.yielded()) {
3516 tsk.coordinator_yield();
3517 conc_workers()->continue_task(&tsk);
3518 }
3519 // If the task was aborted, _restart_addr will be non-NULL
3520 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3521 while (_restart_addr != NULL) {
3522 // XXX For now we do not make use of ABORTED state and have not
3523 // yet implemented the right abort semantics (even in the original
3524 // single-threaded CMS case). That needs some more investigation
3525 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3526 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3527 // If _restart_addr is non-NULL, a marking stack overflow
3528 // occurred; we need to do a fresh marking iteration from the
3529 // indicated restart address.
3530 if (_foregroundGCIsActive) {
3531 // We may be running into repeated stack overflows, having
3532 // reached the limit of the stack size, while making very
3533 // slow forward progress. It may be best to bail out and
3534 // let the foreground collector do its job.
3535 // Clear _restart_addr, so that foreground GC
3536 // works from scratch. This avoids the headache of
3537 // a "rescan" which would otherwise be needed because
3538 // of the dirty mod union table & card table.
3539 _restart_addr = NULL;
3540 return false;
3541 }
3542 // Adjust the task to restart from _restart_addr
3543 tsk.reset(_restart_addr);
3544 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3545 _restart_addr);
3546 _restart_addr = NULL;
3547 // Get the workers going again
3548 conc_workers()->start_task(&tsk);
3549 while (tsk.yielded()) {
3550 tsk.coordinator_yield();
3551 conc_workers()->continue_task(&tsk);
3552 }
3553 }
3554 assert(tsk.completed(), "Inconsistency");
3555 assert(tsk.result() == true, "Inconsistency");
3556 return true;
3557 }
3558
3559 bool CMSCollector::do_marking_st() {
3560 ResourceMark rm;
3561 HandleMark hm;
3562
3563 // Temporarily make refs discovery single threaded (non-MT)
3564 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3565 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3566 &_markStack, CMSYield);
3567 // the last argument to iterate indicates whether the iteration
3568 // should be incremental with periodic yields.
3569 _markBitMap.iterate(&markFromRootsClosure);
3570 // If _restart_addr is non-NULL, a marking stack overflow
3571 // occurred; we need to do a fresh iteration from the
3572 // indicated restart address.
3573 while (_restart_addr != NULL) {
3574 if (_foregroundGCIsActive) {
3575 // We may be running into repeated stack overflows, having
3576 // reached the limit of the stack size, while making very
3577 // slow forward progress. It may be best to bail out and
3578 // let the foreground collector do its job.
3579 // Clear _restart_addr, so that foreground GC
3580 // works from scratch. This avoids the headache of
3581 // a "rescan" which would otherwise be needed because
3582 // of the dirty mod union table & card table.
3583 _restart_addr = NULL;
3584 return false; // indicating failure to complete marking
3585 }
3586 // Deal with stack overflow:
3587 // we restart marking from _restart_addr
3588 HeapWord* ra = _restart_addr;
3589 markFromRootsClosure.reset(ra);
3590 _restart_addr = NULL;
3591 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3592 }
3593 return true;
3594 }
3595
3596 void CMSCollector::preclean() {
3597 check_correct_thread_executing();
3598 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3599 verify_work_stacks_empty();
3600 verify_overflow_empty();
3601 _abort_preclean = false;
3602 if (CMSPrecleaningEnabled) {
3603 if (!CMSEdenChunksRecordAlways) {
3604 _eden_chunk_index = 0;
3605 }
3606 size_t used = get_eden_used();
3607 size_t capacity = get_eden_capacity();
3608 // Don't start sampling unless we will get sufficiently
3609 // many samples.
3610 if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100)
3611 * CMSScheduleRemarkEdenPenetration)) {
3612 _start_sampling = true;
3613 } else {
3614 _start_sampling = false;
3615 }
3616 GCTraceCPUTime tcpu;
3617 CMSPhaseAccounting pa(this, "Concurrent Preclean");
3618 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3619 }
3620 CMSTokenSync x(true); // is cms thread
3621 if (CMSPrecleaningEnabled) {
3622 sample_eden();
3623 _collectorState = AbortablePreclean;
3624 } else {
3625 _collectorState = FinalMarking;
3626 }
3627 verify_work_stacks_empty();
3628 verify_overflow_empty();
3629 }
3630
3631 // Try and schedule the remark such that young gen
3632 // occupancy is CMSScheduleRemarkEdenPenetration %.
3633 void CMSCollector::abortable_preclean() {
3634 check_correct_thread_executing();
3635 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3636 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3637
3638 // If Eden's current occupancy is below this threshold,
3639 // immediately schedule the remark; else preclean
3640 // past the next scavenge in an effort to
3641 // schedule the pause as described above. By choosing
3642 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3643 // we will never do an actual abortable preclean cycle.
3644 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3645 GCTraceCPUTime tcpu;
3646 CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean");
3647 // We need more smarts in the abortable preclean
3648 // loop below to deal with cases where allocation
3649 // in young gen is very very slow, and our precleaning
3650 // is running a losing race against a horde of
3651 // mutators intent on flooding us with CMS updates
3652 // (dirty cards).
3653 // One, admittedly dumb, strategy is to give up
3654 // after a certain number of abortable precleaning loops
3655 // or after a certain maximum time. We want to make
3656 // this smarter in the next iteration.
3657 // XXX FIX ME!!! YSR
3658 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3659 while (!(should_abort_preclean() ||
3660 ConcurrentMarkSweepThread::cmst()->should_terminate())) {
3661 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3662 cumworkdone += workdone;
3663 loops++;
3664 // Voluntarily terminate abortable preclean phase if we have
3665 // been at it for too long.
3666 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3667 loops >= CMSMaxAbortablePrecleanLoops) {
3668 log_debug(gc)(" CMS: abort preclean due to loops ");
3669 break;
3670 }
3671 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3672 log_debug(gc)(" CMS: abort preclean due to time ");
3673 break;
3674 }
3675 // If we are doing little work each iteration, we should
3676 // take a short break.
3677 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3678 // Sleep for some time, waiting for work to accumulate
3679 stopTimer();
3680 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3681 startTimer();
3682 waited++;
3683 }
3684 }
3685 log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3686 loops, waited, cumworkdone);
3687 }
3688 CMSTokenSync x(true); // is cms thread
3689 if (_collectorState != Idling) {
3690 assert(_collectorState == AbortablePreclean,
3691 "Spontaneous state transition?");
3692 _collectorState = FinalMarking;
3693 } // Else, a foreground collection completed this CMS cycle.
3694 return;
3695 }
3696
3697 // Respond to an Eden sampling opportunity
3698 void CMSCollector::sample_eden() {
3699 // Make sure a young gc cannot sneak in between our
3700 // reading and recording of a sample.
3701 assert(Thread::current()->is_ConcurrentGC_thread(),
3702 "Only the cms thread may collect Eden samples");
3703 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3704 "Should collect samples while holding CMS token");
3705 if (!_start_sampling) {
3706 return;
3707 }
3708 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3709 // is populated by the young generation.
3710 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3711 if (_eden_chunk_index < _eden_chunk_capacity) {
3712 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3713 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3714 "Unexpected state of Eden");
3715 // We'd like to check that what we just sampled is an oop-start address;
3716 // however, we cannot do that here since the object may not yet have been
3717 // initialized. So we'll instead do the check when we _use_ this sample
3718 // later.
3719 if (_eden_chunk_index == 0 ||
3720 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3721 _eden_chunk_array[_eden_chunk_index-1])
3722 >= CMSSamplingGrain)) {
3723 _eden_chunk_index++; // commit sample
3724 }
3725 }
3726 }
3727 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3728 size_t used = get_eden_used();
3729 size_t capacity = get_eden_capacity();
3730 assert(used <= capacity, "Unexpected state of Eden");
3731 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3732 _abort_preclean = true;
3733 }
3734 }
3735 }
3736
3737 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3738 assert(_collectorState == Precleaning ||
3739 _collectorState == AbortablePreclean, "incorrect state");
3740 ResourceMark rm;
3741 HandleMark hm;
3742
3743 // Precleaning is currently not MT but the reference processor
3744 // may be set for MT. Disable it temporarily here.
3745 ReferenceProcessor* rp = ref_processor();
3746 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3747
3748 // Do one pass of scrubbing the discovered reference lists
3749 // to remove any reference objects with strongly-reachable
3750 // referents.
3751 if (clean_refs) {
3752 CMSPrecleanRefsYieldClosure yield_cl(this);
3753 assert(_span_based_discoverer.span().equals(_span), "Spans should be equal");
3754 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3755 &_markStack, true /* preclean */);
3756 CMSDrainMarkingStackClosure complete_trace(this,
3757 _span, &_markBitMap, &_markStack,
3758 &keep_alive, true /* preclean */);
3759
3760 // We don't want this step to interfere with a young
3761 // collection because we don't want to take CPU
3762 // or memory bandwidth away from the young GC threads
3763 // (which may be as many as there are CPUs).
3764 // Note that we don't need to protect ourselves from
3765 // interference with mutators because they can't
3766 // manipulate the discovered reference lists nor affect
3767 // the computed reachability of the referents, the
3768 // only properties manipulated by the precleaning
3769 // of these reference lists.
3770 stopTimer();
3771 CMSTokenSyncWithLocks x(true /* is cms thread */,
3772 bitMapLock());
3773 startTimer();
3774 sample_eden();
3775
3776 // The following will yield to allow foreground
3777 // collection to proceed promptly. XXX YSR:
3778 // The code in this method may need further
3779 // tweaking for better performance and some restructuring
3780 // for cleaner interfaces.
3781 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3782 rp->preclean_discovered_references(
3783 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3784 gc_timer);
3785 }
3786
3787 if (clean_survivor) { // preclean the active survivor space(s)
3788 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3789 &_markBitMap, &_modUnionTable,
3790 &_markStack, true /* precleaning phase */);
3791 stopTimer();
3792 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3793 bitMapLock());
3794 startTimer();
3795 unsigned int before_count =
3796 CMSHeap::heap()->total_collections();
3797 SurvivorSpacePrecleanClosure
3798 sss_cl(this, _span, &_markBitMap, &_markStack,
3799 &pam_cl, before_count, CMSYield);
3800 _young_gen->from()->object_iterate_careful(&sss_cl);
3801 _young_gen->to()->object_iterate_careful(&sss_cl);
3802 }
3803 MarkRefsIntoAndScanClosure
3804 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3805 &_markStack, this, CMSYield,
3806 true /* precleaning phase */);
3807 // CAUTION: The following closure has persistent state that may need to
3808 // be reset upon a decrease in the sequence of addresses it
3809 // processes.
3810 ScanMarkedObjectsAgainCarefullyClosure
3811 smoac_cl(this, _span,
3812 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3813
3814 // Preclean dirty cards in ModUnionTable and CardTable using
3815 // appropriate convergence criterion;
3816 // repeat CMSPrecleanIter times unless we find that
3817 // we are losing.
3818 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3819 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3820 "Bad convergence multiplier");
3821 assert(CMSPrecleanThreshold >= 100,
3822 "Unreasonably low CMSPrecleanThreshold");
3823
3824 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3825 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3826 numIter < CMSPrecleanIter;
3827 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3828 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3829 log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3830 // Either there are very few dirty cards, so re-mark
3831 // pause will be small anyway, or our pre-cleaning isn't
3832 // that much faster than the rate at which cards are being
3833 // dirtied, so we might as well stop and re-mark since
3834 // precleaning won't improve our re-mark time by much.
3835 if (curNumCards <= CMSPrecleanThreshold ||
3836 (numIter > 0 &&
3837 (curNumCards * CMSPrecleanDenominator >
3838 lastNumCards * CMSPrecleanNumerator))) {
3839 numIter++;
3840 cumNumCards += curNumCards;
3841 break;
3842 }
3843 }
3844
3845 preclean_cld(&mrias_cl, _cmsGen->freelistLock());
3846
3847 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3848 cumNumCards += curNumCards;
3849 log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3850 curNumCards, cumNumCards, numIter);
3851 return cumNumCards; // as a measure of useful work done
3852 }
3853
3854 // PRECLEANING NOTES:
3855 // Precleaning involves:
3856 // . reading the bits of the modUnionTable and clearing the set bits.
3857 // . For the cards corresponding to the set bits, we scan the
3858 // objects on those cards. This means we need the free_list_lock
3859 // so that we can safely iterate over the CMS space when scanning
3860 // for oops.
3861 // . When we scan the objects, we'll be both reading and setting
3862 // marks in the marking bit map, so we'll need the marking bit map.
3863 // . For protecting _collector_state transitions, we take the CGC_lock.
3864 // Note that any races in the reading of of card table entries by the
3865 // CMS thread on the one hand and the clearing of those entries by the
3866 // VM thread or the setting of those entries by the mutator threads on the
3867 // other are quite benign. However, for efficiency it makes sense to keep
3868 // the VM thread from racing with the CMS thread while the latter is
3869 // dirty card info to the modUnionTable. We therefore also use the
3870 // CGC_lock to protect the reading of the card table and the mod union
3871 // table by the CM thread.
3872 // . We run concurrently with mutator updates, so scanning
3873 // needs to be done carefully -- we should not try to scan
3874 // potentially uninitialized objects.
3875 //
3876 // Locking strategy: While holding the CGC_lock, we scan over and
3877 // reset a maximal dirty range of the mod union / card tables, then lock
3878 // the free_list_lock and bitmap lock to do a full marking, then
3879 // release these locks; and repeat the cycle. This allows for a
3880 // certain amount of fairness in the sharing of these locks between
3881 // the CMS collector on the one hand, and the VM thread and the
3882 // mutators on the other.
3883
3884 // NOTE: preclean_mod_union_table() and preclean_card_table()
3885 // further below are largely identical; if you need to modify
3886 // one of these methods, please check the other method too.
3887
3888 size_t CMSCollector::preclean_mod_union_table(
3889 ConcurrentMarkSweepGeneration* old_gen,
3890 ScanMarkedObjectsAgainCarefullyClosure* cl) {
3891 verify_work_stacks_empty();
3892 verify_overflow_empty();
3893
3894 // strategy: starting with the first card, accumulate contiguous
3895 // ranges of dirty cards; clear these cards, then scan the region
3896 // covered by these cards.
3897
3898 // Since all of the MUT is committed ahead, we can just use
3899 // that, in case the generations expand while we are precleaning.
3900 // It might also be fine to just use the committed part of the
3901 // generation, but we might potentially miss cards when the
3902 // generation is rapidly expanding while we are in the midst
3903 // of precleaning.
3904 HeapWord* startAddr = old_gen->reserved().start();
3905 HeapWord* endAddr = old_gen->reserved().end();
3906
3907 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
3908
3909 size_t numDirtyCards, cumNumDirtyCards;
3910 HeapWord *nextAddr, *lastAddr;
3911 for (cumNumDirtyCards = numDirtyCards = 0,
3912 nextAddr = lastAddr = startAddr;
3913 nextAddr < endAddr;
3914 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3915
3916 ResourceMark rm;
3917 HandleMark hm;
3918
3919 MemRegion dirtyRegion;
3920 {
3921 stopTimer();
3922 // Potential yield point
3923 CMSTokenSync ts(true);
3924 startTimer();
3925 sample_eden();
3926 // Get dirty region starting at nextOffset (inclusive),
3927 // simultaneously clearing it.
3928 dirtyRegion =
3929 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3930 assert(dirtyRegion.start() >= nextAddr,
3931 "returned region inconsistent?");
3932 }
3933 // Remember where the next search should begin.
3934 // The returned region (if non-empty) is a right open interval,
3935 // so lastOffset is obtained from the right end of that
3936 // interval.
3937 lastAddr = dirtyRegion.end();
3938 // Should do something more transparent and less hacky XXX
3939 numDirtyCards =
3940 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
3941
3942 // We'll scan the cards in the dirty region (with periodic
3943 // yields for foreground GC as needed).
3944 if (!dirtyRegion.is_empty()) {
3945 assert(numDirtyCards > 0, "consistency check");
3946 HeapWord* stop_point = NULL;
3947 stopTimer();
3948 // Potential yield point
3949 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
3950 bitMapLock());
3951 startTimer();
3952 {
3953 verify_work_stacks_empty();
3954 verify_overflow_empty();
3955 sample_eden();
3956 stop_point =
3957 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
3958 }
3959 if (stop_point != NULL) {
3960 // The careful iteration stopped early either because it found an
3961 // uninitialized object, or because we were in the midst of an
3962 // "abortable preclean", which should now be aborted. Redirty
3963 // the bits corresponding to the partially-scanned or unscanned
3964 // cards. We'll either restart at the next block boundary or
3965 // abort the preclean.
3966 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
3967 "Should only be AbortablePreclean.");
3968 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
3969 if (should_abort_preclean()) {
3970 break; // out of preclean loop
3971 } else {
3972 // Compute the next address at which preclean should pick up;
3973 // might need bitMapLock in order to read P-bits.
3974 lastAddr = next_card_start_after_block(stop_point);
3975 }
3976 }
3977 } else {
3978 assert(lastAddr == endAddr, "consistency check");
3979 assert(numDirtyCards == 0, "consistency check");
3980 break;
3981 }
3982 }
3983 verify_work_stacks_empty();
3984 verify_overflow_empty();
3985 return cumNumDirtyCards;
3986 }
3987
3988 // NOTE: preclean_mod_union_table() above and preclean_card_table()
3989 // below are largely identical; if you need to modify
3990 // one of these methods, please check the other method too.
3991
3992 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
3993 ScanMarkedObjectsAgainCarefullyClosure* cl) {
3994 // strategy: it's similar to precleamModUnionTable above, in that
3995 // we accumulate contiguous ranges of dirty cards, mark these cards
3996 // precleaned, then scan the region covered by these cards.
3997 HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high());
3998 HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
3999
4000 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4001
4002 size_t numDirtyCards, cumNumDirtyCards;
4003 HeapWord *lastAddr, *nextAddr;
4004
4005 for (cumNumDirtyCards = numDirtyCards = 0,
4006 nextAddr = lastAddr = startAddr;
4007 nextAddr < endAddr;
4008 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4009
4010 ResourceMark rm;
4011 HandleMark hm;
4012
4013 MemRegion dirtyRegion;
4014 {
4015 // See comments in "Precleaning notes" above on why we
4016 // do this locking. XXX Could the locking overheads be
4017 // too high when dirty cards are sparse? [I don't think so.]
4018 stopTimer();
4019 CMSTokenSync x(true); // is cms thread
4020 startTimer();
4021 sample_eden();
4022 // Get and clear dirty region from card table
4023 dirtyRegion = _ct->dirty_card_range_after_reset(MemRegion(nextAddr, endAddr),
4024 true,
4025 CardTable::precleaned_card_val());
4026
4027 assert(dirtyRegion.start() >= nextAddr,
4028 "returned region inconsistent?");
4029 }
4030 lastAddr = dirtyRegion.end();
4031 numDirtyCards =
4032 dirtyRegion.word_size()/CardTable::card_size_in_words;
4033
4034 if (!dirtyRegion.is_empty()) {
4035 stopTimer();
4036 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4037 startTimer();
4038 sample_eden();
4039 verify_work_stacks_empty();
4040 verify_overflow_empty();
4041 HeapWord* stop_point =
4042 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4043 if (stop_point != NULL) {
4044 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4045 "Should only be AbortablePreclean.");
4046 _ct->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4047 if (should_abort_preclean()) {
4048 break; // out of preclean loop
4049 } else {
4050 // Compute the next address at which preclean should pick up.
4051 lastAddr = next_card_start_after_block(stop_point);
4052 }
4053 }
4054 } else {
4055 break;
4056 }
4057 }
4058 verify_work_stacks_empty();
4059 verify_overflow_empty();
4060 return cumNumDirtyCards;
4061 }
4062
4063 class PrecleanCLDClosure : public CLDClosure {
4064 MetadataVisitingOopsInGenClosure* _cm_closure;
4065 public:
4066 PrecleanCLDClosure(MetadataVisitingOopsInGenClosure* oop_closure) : _cm_closure(oop_closure) {}
4067 void do_cld(ClassLoaderData* cld) {
4068 if (cld->has_accumulated_modified_oops()) {
4069 cld->clear_accumulated_modified_oops();
4070
4071 _cm_closure->do_cld(cld);
4072 }
4073 }
4074 };
4075
4076 // The freelist lock is needed to prevent asserts, is it really needed?
4077 void CMSCollector::preclean_cld(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4078 // Needed to walk CLDG
4079 MutexLocker ml(ClassLoaderDataGraph_lock);
4080
4081 cl->set_freelistLock(freelistLock);
4082
4083 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4084
4085 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4086 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4087 PrecleanCLDClosure preclean_closure(cl);
4088 ClassLoaderDataGraph::cld_do(&preclean_closure);
4089
4090 verify_work_stacks_empty();
4091 verify_overflow_empty();
4092 }
4093
4094 void CMSCollector::checkpointRootsFinal() {
4095 assert(_collectorState == FinalMarking, "incorrect state transition?");
4096 check_correct_thread_executing();
4097 // world is stopped at this checkpoint
4098 assert(SafepointSynchronize::is_at_safepoint(),
4099 "world should be stopped");
4100 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
4101
4102 verify_work_stacks_empty();
4103 verify_overflow_empty();
4104
4105 log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4106 _young_gen->used() / K, _young_gen->capacity() / K);
4107 {
4108 if (CMSScavengeBeforeRemark) {
4109 CMSHeap* heap = CMSHeap::heap();
4110 // Temporarily set flag to false, GCH->do_collection will
4111 // expect it to be false and set to true
4112 FlagSetting fl(heap->_is_gc_active, false);
4113
4114 heap->do_collection(true, // full (i.e. force, see below)
4115 false, // !clear_all_soft_refs
4116 0, // size
4117 false, // is_tlab
4118 GenCollectedHeap::YoungGen // type
4119 );
4120 }
4121 FreelistLocker x(this);
4122 MutexLockerEx y(bitMapLock(),
4123 Mutex::_no_safepoint_check_flag);
4124 checkpointRootsFinalWork();
4125 }
4126 verify_work_stacks_empty();
4127 verify_overflow_empty();
4128 }
4129
4130 void CMSCollector::checkpointRootsFinalWork() {
4131 GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm);
4132
4133 assert(haveFreelistLocks(), "must have free list locks");
4134 assert_lock_strong(bitMapLock());
4135
4136 ResourceMark rm;
4137 HandleMark hm;
4138
4139 CMSHeap* heap = CMSHeap::heap();
4140
4141 if (should_unload_classes()) {
4142 CodeCache::gc_prologue();
4143 }
4144 assert(haveFreelistLocks(), "must have free list locks");
4145 assert_lock_strong(bitMapLock());
4146
4147 // We might assume that we need not fill TLAB's when
4148 // CMSScavengeBeforeRemark is set, because we may have just done
4149 // a scavenge which would have filled all TLAB's -- and besides
4150 // Eden would be empty. This however may not always be the case --
4151 // for instance although we asked for a scavenge, it may not have
4152 // happened because of a JNI critical section. We probably need
4153 // a policy for deciding whether we can in that case wait until
4154 // the critical section releases and then do the remark following
4155 // the scavenge, and skip it here. In the absence of that policy,
4156 // or of an indication of whether the scavenge did indeed occur,
4157 // we cannot rely on TLAB's having been filled and must do
4158 // so here just in case a scavenge did not happen.
4159 heap->ensure_parsability(false); // fill TLAB's, but no need to retire them
4160 // Update the saved marks which may affect the root scans.
4161 heap->save_marks();
4162
4163 print_eden_and_survivor_chunk_arrays();
4164
4165 {
4166 #if COMPILER2_OR_JVMCI
4167 DerivedPointerTableDeactivate dpt_deact;
4168 #endif
4169
4170 // Note on the role of the mod union table:
4171 // Since the marker in "markFromRoots" marks concurrently with
4172 // mutators, it is possible for some reachable objects not to have been
4173 // scanned. For instance, an only reference to an object A was
4174 // placed in object B after the marker scanned B. Unless B is rescanned,
4175 // A would be collected. Such updates to references in marked objects
4176 // are detected via the mod union table which is the set of all cards
4177 // dirtied since the first checkpoint in this GC cycle and prior to
4178 // the most recent young generation GC, minus those cleaned up by the
4179 // concurrent precleaning.
4180 if (CMSParallelRemarkEnabled) {
4181 GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm);
4182 do_remark_parallel();
4183 } else {
4184 GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm);
4185 do_remark_non_parallel();
4186 }
4187 }
4188 verify_work_stacks_empty();
4189 verify_overflow_empty();
4190
4191 {
4192 GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm);
4193 refProcessingWork();
4194 }
4195 verify_work_stacks_empty();
4196 verify_overflow_empty();
4197
4198 if (should_unload_classes()) {
4199 CodeCache::gc_epilogue();
4200 }
4201 JvmtiExport::gc_epilogue();
4202
4203 // If we encountered any (marking stack / work queue) overflow
4204 // events during the current CMS cycle, take appropriate
4205 // remedial measures, where possible, so as to try and avoid
4206 // recurrence of that condition.
4207 assert(_markStack.isEmpty(), "No grey objects");
4208 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4209 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4210 if (ser_ovflw > 0) {
4211 log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4212 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4213 _markStack.expand();
4214 _ser_pmc_remark_ovflw = 0;
4215 _ser_pmc_preclean_ovflw = 0;
4216 _ser_kac_preclean_ovflw = 0;
4217 _ser_kac_ovflw = 0;
4218 }
4219 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4220 log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4221 _par_pmc_remark_ovflw, _par_kac_ovflw);
4222 _par_pmc_remark_ovflw = 0;
4223 _par_kac_ovflw = 0;
4224 }
4225 if (_markStack._hit_limit > 0) {
4226 log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4227 _markStack._hit_limit);
4228 }
4229 if (_markStack._failed_double > 0) {
4230 log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4231 _markStack._failed_double, _markStack.capacity());
4232 }
4233 _markStack._hit_limit = 0;
4234 _markStack._failed_double = 0;
4235
4236 if ((VerifyAfterGC || VerifyDuringGC) &&
4237 CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4238 verify_after_remark();
4239 }
4240
4241 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4242
4243 // Change under the freelistLocks.
4244 _collectorState = Sweeping;
4245 // Call isAllClear() under bitMapLock
4246 assert(_modUnionTable.isAllClear(),
4247 "Should be clear by end of the final marking");
4248 assert(_ct->cld_rem_set()->mod_union_is_clear(),
4249 "Should be clear by end of the final marking");
4250 }
4251
4252 void CMSParInitialMarkTask::work(uint worker_id) {
4253 elapsedTimer _timer;
4254 ResourceMark rm;
4255 HandleMark hm;
4256
4257 // ---------- scan from roots --------------
4258 _timer.start();
4259 CMSHeap* heap = CMSHeap::heap();
4260 ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4261
4262 // ---------- young gen roots --------------
4263 {
4264 work_on_young_gen_roots(&par_mri_cl);
4265 _timer.stop();
4266 log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4267 }
4268
4269 // ---------- remaining roots --------------
4270 _timer.reset();
4271 _timer.start();
4272
4273 CLDToOopClosure cld_closure(&par_mri_cl, ClassLoaderData::_claim_strong);
4274
4275 heap->cms_process_roots(_strong_roots_scope,
4276 false, // yg was scanned above
4277 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4278 _collector->should_unload_classes(),
4279 &par_mri_cl,
4280 &cld_closure,
4281 &_par_state_string);
4282
4283 assert(_collector->should_unload_classes()
4284 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4285 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4286 _timer.stop();
4287 log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4288 }
4289
4290 // Parallel remark task
4291 class CMSParRemarkTask: public CMSParMarkTask {
4292 CompactibleFreeListSpace* _cms_space;
4293
4294 // The per-thread work queues, available here for stealing.
4295 OopTaskQueueSet* _task_queues;
4296 ParallelTaskTerminator _term;
4297 StrongRootsScope* _strong_roots_scope;
4298
4299 public:
4300 // A value of 0 passed to n_workers will cause the number of
4301 // workers to be taken from the active workers in the work gang.
4302 CMSParRemarkTask(CMSCollector* collector,
4303 CompactibleFreeListSpace* cms_space,
4304 uint n_workers, WorkGang* workers,
4305 OopTaskQueueSet* task_queues,
4306 StrongRootsScope* strong_roots_scope):
4307 CMSParMarkTask("Rescan roots and grey objects in parallel",
4308 collector, n_workers),
4309 _cms_space(cms_space),
4310 _task_queues(task_queues),
4311 _term(n_workers, task_queues),
4312 _strong_roots_scope(strong_roots_scope) { }
4313
4314 OopTaskQueueSet* task_queues() { return _task_queues; }
4315
4316 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4317
4318 ParallelTaskTerminator* terminator() { return &_term; }
4319 uint n_workers() { return _n_workers; }
4320
4321 void work(uint worker_id);
4322
4323 private:
4324 // ... of dirty cards in old space
4325 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4326 ParMarkRefsIntoAndScanClosure* cl);
4327
4328 // ... work stealing for the above
4329 void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl);
4330 };
4331
4332 class RemarkCLDClosure : public CLDClosure {
4333 CLDToOopClosure _cm_closure;
4334 public:
4335 RemarkCLDClosure(OopClosure* oop_closure) : _cm_closure(oop_closure, ClassLoaderData::_claim_strong) {}
4336 void do_cld(ClassLoaderData* cld) {
4337 // Check if we have modified any oops in the CLD during the concurrent marking.
4338 if (cld->has_accumulated_modified_oops()) {
4339 cld->clear_accumulated_modified_oops();
4340
4341 // We could have transfered the current modified marks to the accumulated marks,
4342 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4343 } else if (cld->has_modified_oops()) {
4344 // Don't clear anything, this info is needed by the next young collection.
4345 } else {
4346 // No modified oops in the ClassLoaderData.
4347 return;
4348 }
4349
4350 // The klass has modified fields, need to scan the klass.
4351 _cm_closure.do_cld(cld);
4352 }
4353 };
4354
4355 void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) {
4356 ParNewGeneration* young_gen = _collector->_young_gen;
4357 ContiguousSpace* eden_space = young_gen->eden();
4358 ContiguousSpace* from_space = young_gen->from();
4359 ContiguousSpace* to_space = young_gen->to();
4360
4361 HeapWord** eca = _collector->_eden_chunk_array;
4362 size_t ect = _collector->_eden_chunk_index;
4363 HeapWord** sca = _collector->_survivor_chunk_array;
4364 size_t sct = _collector->_survivor_chunk_index;
4365
4366 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4367 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4368
4369 do_young_space_rescan(cl, to_space, NULL, 0);
4370 do_young_space_rescan(cl, from_space, sca, sct);
4371 do_young_space_rescan(cl, eden_space, eca, ect);
4372 }
4373
4374 // work_queue(i) is passed to the closure
4375 // ParMarkRefsIntoAndScanClosure. The "i" parameter
4376 // also is passed to do_dirty_card_rescan_tasks() and to
4377 // do_work_steal() to select the i-th task_queue.
4378
4379 void CMSParRemarkTask::work(uint worker_id) {
4380 elapsedTimer _timer;
4381 ResourceMark rm;
4382 HandleMark hm;
4383
4384 // ---------- rescan from roots --------------
4385 _timer.start();
4386 CMSHeap* heap = CMSHeap::heap();
4387 ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4388 _collector->_span, _collector->ref_processor(),
4389 &(_collector->_markBitMap),
4390 work_queue(worker_id));
4391
4392 // Rescan young gen roots first since these are likely
4393 // coarsely partitioned and may, on that account, constitute
4394 // the critical path; thus, it's best to start off that
4395 // work first.
4396 // ---------- young gen roots --------------
4397 {
4398 work_on_young_gen_roots(&par_mrias_cl);
4399 _timer.stop();
4400 log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4401 }
4402
4403 // ---------- remaining roots --------------
4404 _timer.reset();
4405 _timer.start();
4406 heap->cms_process_roots(_strong_roots_scope,
4407 false, // yg was scanned above
4408 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4409 _collector->should_unload_classes(),
4410 &par_mrias_cl,
4411 NULL, // The dirty klasses will be handled below
4412 &_par_state_string);
4413
4414 assert(_collector->should_unload_classes()
4415 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4416 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4417 _timer.stop();
4418 log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4419
4420 // ---------- unhandled CLD scanning ----------
4421 if (worker_id == 0) { // Single threaded at the moment.
4422 _timer.reset();
4423 _timer.start();
4424
4425 // Scan all new class loader data objects and new dependencies that were
4426 // introduced during concurrent marking.
4427 ResourceMark rm;
4428 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4429 for (int i = 0; i < array->length(); i++) {
4430 Devirtualizer::do_cld(&par_mrias_cl, array->at(i));
4431 }
4432
4433 // We don't need to keep track of new CLDs anymore.
4434 ClassLoaderDataGraph::remember_new_clds(false);
4435
4436 _timer.stop();
4437 log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4438 }
4439
4440 // We might have added oops to ClassLoaderData::_handles during the
4441 // concurrent marking phase. These oops do not always point to newly allocated objects
4442 // that are guaranteed to be kept alive. Hence,
4443 // we do have to revisit the _handles block during the remark phase.
4444
4445 // ---------- dirty CLD scanning ----------
4446 if (worker_id == 0) { // Single threaded at the moment.
4447 _timer.reset();
4448 _timer.start();
4449
4450 // Scan all classes that was dirtied during the concurrent marking phase.
4451 RemarkCLDClosure remark_closure(&par_mrias_cl);
4452 ClassLoaderDataGraph::cld_do(&remark_closure);
4453
4454 _timer.stop();
4455 log_trace(gc, task)("Finished dirty CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4456 }
4457
4458
4459 // ---------- rescan dirty cards ------------
4460 _timer.reset();
4461 _timer.start();
4462
4463 // Do the rescan tasks for each of the two spaces
4464 // (cms_space) in turn.
4465 // "worker_id" is passed to select the task_queue for "worker_id"
4466 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4467 _timer.stop();
4468 log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4469
4470 // ---------- steal work from other threads ...
4471 // ---------- ... and drain overflow list.
4472 _timer.reset();
4473 _timer.start();
4474 do_work_steal(worker_id, &par_mrias_cl);
4475 _timer.stop();
4476 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4477 }
4478
4479 void
4480 CMSParMarkTask::do_young_space_rescan(
4481 OopsInGenClosure* cl, ContiguousSpace* space,
4482 HeapWord** chunk_array, size_t chunk_top) {
4483 // Until all tasks completed:
4484 // . claim an unclaimed task
4485 // . compute region boundaries corresponding to task claimed
4486 // using chunk_array
4487 // . par_oop_iterate(cl) over that region
4488
4489 ResourceMark rm;
4490 HandleMark hm;
4491
4492 SequentialSubTasksDone* pst = space->par_seq_tasks();
4493
4494 uint nth_task = 0;
4495 uint n_tasks = pst->n_tasks();
4496
4497 if (n_tasks > 0) {
4498 assert(pst->valid(), "Uninitialized use?");
4499 HeapWord *start, *end;
4500 while (pst->try_claim_task(/* reference */ nth_task)) {
4501 // We claimed task # nth_task; compute its boundaries.
4502 if (chunk_top == 0) { // no samples were taken
4503 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4504 start = space->bottom();
4505 end = space->top();
4506 } else if (nth_task == 0) {
4507 start = space->bottom();
4508 end = chunk_array[nth_task];
4509 } else if (nth_task < (uint)chunk_top) {
4510 assert(nth_task >= 1, "Control point invariant");
4511 start = chunk_array[nth_task - 1];
4512 end = chunk_array[nth_task];
4513 } else {
4514 assert(nth_task == (uint)chunk_top, "Control point invariant");
4515 start = chunk_array[chunk_top - 1];
4516 end = space->top();
4517 }
4518 MemRegion mr(start, end);
4519 // Verify that mr is in space
4520 assert(mr.is_empty() || space->used_region().contains(mr),
4521 "Should be in space");
4522 // Verify that "start" is an object boundary
4523 assert(mr.is_empty() || oopDesc::is_oop(oop(mr.start())),
4524 "Should be an oop");
4525 space->par_oop_iterate(mr, cl);
4526 }
4527 pst->all_tasks_completed();
4528 }
4529 }
4530
4531 void
4532 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4533 CompactibleFreeListSpace* sp, int i,
4534 ParMarkRefsIntoAndScanClosure* cl) {
4535 // Until all tasks completed:
4536 // . claim an unclaimed task
4537 // . compute region boundaries corresponding to task claimed
4538 // . transfer dirty bits ct->mut for that region
4539 // . apply rescanclosure to dirty mut bits for that region
4540
4541 ResourceMark rm;
4542 HandleMark hm;
4543
4544 OopTaskQueue* work_q = work_queue(i);
4545 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4546 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4547 // CAUTION: This closure has state that persists across calls to
4548 // the work method dirty_range_iterate_clear() in that it has
4549 // embedded in it a (subtype of) UpwardsObjectClosure. The
4550 // use of that state in the embedded UpwardsObjectClosure instance
4551 // assumes that the cards are always iterated (even if in parallel
4552 // by several threads) in monotonically increasing order per each
4553 // thread. This is true of the implementation below which picks
4554 // card ranges (chunks) in monotonically increasing order globally
4555 // and, a-fortiori, in monotonically increasing order per thread
4556 // (the latter order being a subsequence of the former).
4557 // If the work code below is ever reorganized into a more chaotic
4558 // work-partitioning form than the current "sequential tasks"
4559 // paradigm, the use of that persistent state will have to be
4560 // revisited and modified appropriately. See also related
4561 // bug 4756801 work on which should examine this code to make
4562 // sure that the changes there do not run counter to the
4563 // assumptions made here and necessary for correctness and
4564 // efficiency. Note also that this code might yield inefficient
4565 // behavior in the case of very large objects that span one or
4566 // more work chunks. Such objects would potentially be scanned
4567 // several times redundantly. Work on 4756801 should try and
4568 // address that performance anomaly if at all possible. XXX
4569 MemRegion full_span = _collector->_span;
4570 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4571 MarkFromDirtyCardsClosure
4572 greyRescanClosure(_collector, full_span, // entire span of interest
4573 sp, bm, work_q, cl);
4574
4575 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4576 assert(pst->valid(), "Uninitialized use?");
4577 uint nth_task = 0;
4578 const int alignment = CardTable::card_size * BitsPerWord;
4579 MemRegion span = sp->used_region();
4580 HeapWord* start_addr = span.start();
4581 HeapWord* end_addr = align_up(span.end(), alignment);
4582 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4583 assert(is_aligned(start_addr, alignment), "Check alignment");
4584 assert(is_aligned(chunk_size, alignment), "Check alignment");
4585
4586 while (pst->try_claim_task(/* reference */ nth_task)) {
4587 // Having claimed the nth_task, compute corresponding mem-region,
4588 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4589 // The alignment restriction ensures that we do not need any
4590 // synchronization with other gang-workers while setting or
4591 // clearing bits in thus chunk of the MUT.
4592 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4593 start_addr + (nth_task+1)*chunk_size);
4594 // The last chunk's end might be way beyond end of the
4595 // used region. In that case pull back appropriately.
4596 if (this_span.end() > end_addr) {
4597 this_span.set_end(end_addr);
4598 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4599 }
4600 // Iterate over the dirty cards covering this chunk, marking them
4601 // precleaned, and setting the corresponding bits in the mod union
4602 // table. Since we have been careful to partition at Card and MUT-word
4603 // boundaries no synchronization is needed between parallel threads.
4604 _collector->_ct->dirty_card_iterate(this_span,
4605 &modUnionClosure);
4606
4607 // Having transferred these marks into the modUnionTable,
4608 // rescan the marked objects on the dirty cards in the modUnionTable.
4609 // Even if this is at a synchronous collection, the initial marking
4610 // may have been done during an asynchronous collection so there
4611 // may be dirty bits in the mod-union table.
4612 _collector->_modUnionTable.dirty_range_iterate_clear(
4613 this_span, &greyRescanClosure);
4614 _collector->_modUnionTable.verifyNoOneBitsInRange(
4615 this_span.start(),
4616 this_span.end());
4617 }
4618 pst->all_tasks_completed(); // declare that i am done
4619 }
4620
4621 // . see if we can share work_queues with ParNew? XXX
4622 void
4623 CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl) {
4624 OopTaskQueue* work_q = work_queue(i);
4625 NOT_PRODUCT(int num_steals = 0;)
4626 oop obj_to_scan;
4627 CMSBitMap* bm = &(_collector->_markBitMap);
4628
4629 while (true) {
4630 // Completely finish any left over work from (an) earlier round(s)
4631 cl->trim_queue(0);
4632 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4633 (size_t)ParGCDesiredObjsFromOverflowList);
4634 // Now check if there's any work in the overflow list
4635 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4636 // only affects the number of attempts made to get work from the
4637 // overflow list and does not affect the number of workers. Just
4638 // pass ParallelGCThreads so this behavior is unchanged.
4639 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4640 work_q,
4641 ParallelGCThreads)) {
4642 // found something in global overflow list;
4643 // not yet ready to go stealing work from others.
4644 // We'd like to assert(work_q->size() != 0, ...)
4645 // because we just took work from the overflow list,
4646 // but of course we can't since all of that could have
4647 // been already stolen from us.
4648 // "He giveth and He taketh away."
4649 continue;
4650 }
4651 // Verify that we have no work before we resort to stealing
4652 assert(work_q->size() == 0, "Have work, shouldn't steal");
4653 // Try to steal from other queues that have work
4654 if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
4655 NOT_PRODUCT(num_steals++;)
4656 assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
4657 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4658 // Do scanning work
4659 obj_to_scan->oop_iterate(cl);
4660 // Loop around, finish this work, and try to steal some more
4661 } else if (terminator()->offer_termination()) {
4662 break; // nirvana from the infinite cycle
4663 }
4664 }
4665 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4666 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4667 "Else our work is not yet done");
4668 }
4669
4670 // Record object boundaries in _eden_chunk_array by sampling the eden
4671 // top in the slow-path eden object allocation code path and record
4672 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4673 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4674 // sampling in sample_eden() that activates during the part of the
4675 // preclean phase.
4676 void CMSCollector::sample_eden_chunk() {
4677 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4678 if (_eden_chunk_lock->try_lock()) {
4679 // Record a sample. This is the critical section. The contents
4680 // of the _eden_chunk_array have to be non-decreasing in the
4681 // address order.
4682 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4683 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4684 "Unexpected state of Eden");
4685 if (_eden_chunk_index == 0 ||
4686 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4687 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4688 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4689 _eden_chunk_index++; // commit sample
4690 }
4691 _eden_chunk_lock->unlock();
4692 }
4693 }
4694 }
4695
4696 // Return a thread-local PLAB recording array, as appropriate.
4697 void* CMSCollector::get_data_recorder(int thr_num) {
4698 if (_survivor_plab_array != NULL &&
4699 (CMSPLABRecordAlways ||
4700 (_collectorState > Marking && _collectorState < FinalMarking))) {
4701 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4702 ChunkArray* ca = &_survivor_plab_array[thr_num];
4703 ca->reset(); // clear it so that fresh data is recorded
4704 return (void*) ca;
4705 } else {
4706 return NULL;
4707 }
4708 }
4709
4710 // Reset all the thread-local PLAB recording arrays
4711 void CMSCollector::reset_survivor_plab_arrays() {
4712 for (uint i = 0; i < ParallelGCThreads; i++) {
4713 _survivor_plab_array[i].reset();
4714 }
4715 }
4716
4717 // Merge the per-thread plab arrays into the global survivor chunk
4718 // array which will provide the partitioning of the survivor space
4719 // for CMS initial scan and rescan.
4720 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4721 int no_of_gc_threads) {
4722 assert(_survivor_plab_array != NULL, "Error");
4723 assert(_survivor_chunk_array != NULL, "Error");
4724 assert(_collectorState == FinalMarking ||
4725 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4726 for (int j = 0; j < no_of_gc_threads; j++) {
4727 _cursor[j] = 0;
4728 }
4729 HeapWord* top = surv->top();
4730 size_t i;
4731 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4732 HeapWord* min_val = top; // Higher than any PLAB address
4733 uint min_tid = 0; // position of min_val this round
4734 for (int j = 0; j < no_of_gc_threads; j++) {
4735 ChunkArray* cur_sca = &_survivor_plab_array[j];
4736 if (_cursor[j] == cur_sca->end()) {
4737 continue;
4738 }
4739 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4740 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4741 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4742 if (cur_val < min_val) {
4743 min_tid = j;
4744 min_val = cur_val;
4745 } else {
4746 assert(cur_val < top, "All recorded addresses should be less");
4747 }
4748 }
4749 // At this point min_val and min_tid are respectively
4750 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4751 // and the thread (j) that witnesses that address.
4752 // We record this address in the _survivor_chunk_array[i]
4753 // and increment _cursor[min_tid] prior to the next round i.
4754 if (min_val == top) {
4755 break;
4756 }
4757 _survivor_chunk_array[i] = min_val;
4758 _cursor[min_tid]++;
4759 }
4760 // We are all done; record the size of the _survivor_chunk_array
4761 _survivor_chunk_index = i; // exclusive: [0, i)
4762 log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4763 // Verify that we used up all the recorded entries
4764 #ifdef ASSERT
4765 size_t total = 0;
4766 for (int j = 0; j < no_of_gc_threads; j++) {
4767 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4768 total += _cursor[j];
4769 }
4770 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4771 // Check that the merged array is in sorted order
4772 if (total > 0) {
4773 for (size_t i = 0; i < total - 1; i++) {
4774 log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4775 i, p2i(_survivor_chunk_array[i]));
4776 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4777 "Not sorted");
4778 }
4779 }
4780 #endif // ASSERT
4781 }
4782
4783 // Set up the space's par_seq_tasks structure for work claiming
4784 // for parallel initial scan and rescan of young gen.
4785 // See ParRescanTask where this is currently used.
4786 void
4787 CMSCollector::
4788 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4789 assert(n_threads > 0, "Unexpected n_threads argument");
4790
4791 // Eden space
4792 if (!_young_gen->eden()->is_empty()) {
4793 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4794 assert(!pst->valid(), "Clobbering existing data?");
4795 // Each valid entry in [0, _eden_chunk_index) represents a task.
4796 size_t n_tasks = _eden_chunk_index + 1;
4797 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4798 // Sets the condition for completion of the subtask (how many threads
4799 // need to finish in order to be done).
4800 pst->set_n_threads(n_threads);
4801 pst->set_n_tasks((int)n_tasks);
4802 }
4803
4804 // Merge the survivor plab arrays into _survivor_chunk_array
4805 if (_survivor_plab_array != NULL) {
4806 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4807 } else {
4808 assert(_survivor_chunk_index == 0, "Error");
4809 }
4810
4811 // To space
4812 {
4813 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4814 assert(!pst->valid(), "Clobbering existing data?");
4815 // Sets the condition for completion of the subtask (how many threads
4816 // need to finish in order to be done).
4817 pst->set_n_threads(n_threads);
4818 pst->set_n_tasks(1);
4819 assert(pst->valid(), "Error");
4820 }
4821
4822 // From space
4823 {
4824 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4825 assert(!pst->valid(), "Clobbering existing data?");
4826 size_t n_tasks = _survivor_chunk_index + 1;
4827 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
4828 // Sets the condition for completion of the subtask (how many threads
4829 // need to finish in order to be done).
4830 pst->set_n_threads(n_threads);
4831 pst->set_n_tasks((int)n_tasks);
4832 assert(pst->valid(), "Error");
4833 }
4834 }
4835
4836 // Parallel version of remark
4837 void CMSCollector::do_remark_parallel() {
4838 CMSHeap* heap = CMSHeap::heap();
4839 WorkGang* workers = heap->workers();
4840 assert(workers != NULL, "Need parallel worker threads.");
4841 // Choose to use the number of GC workers most recently set
4842 // into "active_workers".
4843 uint n_workers = workers->active_workers();
4844
4845 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4846
4847 StrongRootsScope srs(n_workers);
4848
4849 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4850
4851 // We won't be iterating over the cards in the card table updating
4852 // the younger_gen cards, so we shouldn't call the following else
4853 // the verification code as well as subsequent younger_refs_iterate
4854 // code would get confused. XXX
4855 // heap->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4856
4857 // The young gen rescan work will not be done as part of
4858 // process_roots (which currently doesn't know how to
4859 // parallelize such a scan), but rather will be broken up into
4860 // a set of parallel tasks (via the sampling that the [abortable]
4861 // preclean phase did of eden, plus the [two] tasks of
4862 // scanning the [two] survivor spaces. Further fine-grain
4863 // parallelization of the scanning of the survivor spaces
4864 // themselves, and of precleaning of the young gen itself
4865 // is deferred to the future.
4866 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4867
4868 // The dirty card rescan work is broken up into a "sequence"
4869 // of parallel tasks (per constituent space) that are dynamically
4870 // claimed by the parallel threads.
4871 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4872
4873 // It turns out that even when we're using 1 thread, doing the work in a
4874 // separate thread causes wide variance in run times. We can't help this
4875 // in the multi-threaded case, but we special-case n=1 here to get
4876 // repeatable measurements of the 1-thread overhead of the parallel code.
4877 if (n_workers > 1) {
4878 // Make refs discovery MT-safe, if it isn't already: it may not
4879 // necessarily be so, since it's possible that we are doing
4880 // ST marking.
4881 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4882 workers->run_task(&tsk);
4883 } else {
4884 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4885 tsk.work(0);
4886 }
4887
4888 // restore, single-threaded for now, any preserved marks
4889 // as a result of work_q overflow
4890 restore_preserved_marks_if_any();
4891 }
4892
4893 // Non-parallel version of remark
4894 void CMSCollector::do_remark_non_parallel() {
4895 ResourceMark rm;
4896 HandleMark hm;
4897 CMSHeap* heap = CMSHeap::heap();
4898 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4899
4900 MarkRefsIntoAndScanClosure
4901 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4902 &_markStack, this,
4903 false /* should_yield */, false /* not precleaning */);
4904 MarkFromDirtyCardsClosure
4905 markFromDirtyCardsClosure(this, _span,
4906 NULL, // space is set further below
4907 &_markBitMap, &_markStack, &mrias_cl);
4908 {
4909 GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm);
4910 // Iterate over the dirty cards, setting the corresponding bits in the
4911 // mod union table.
4912 {
4913 ModUnionClosure modUnionClosure(&_modUnionTable);
4914 _ct->dirty_card_iterate(_cmsGen->used_region(),
4915 &modUnionClosure);
4916 }
4917 // Having transferred these marks into the modUnionTable, we just need
4918 // to rescan the marked objects on the dirty cards in the modUnionTable.
4919 // The initial marking may have been done during an asynchronous
4920 // collection so there may be dirty bits in the mod-union table.
4921 const int alignment = CardTable::card_size * BitsPerWord;
4922 {
4923 // ... First handle dirty cards in CMS gen
4924 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4925 MemRegion ur = _cmsGen->used_region();
4926 HeapWord* lb = ur.start();
4927 HeapWord* ub = align_up(ur.end(), alignment);
4928 MemRegion cms_span(lb, ub);
4929 _modUnionTable.dirty_range_iterate_clear(cms_span,
4930 &markFromDirtyCardsClosure);
4931 verify_work_stacks_empty();
4932 log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4933 }
4934 }
4935 if (VerifyDuringGC &&
4936 CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4937 HandleMark hm; // Discard invalid handles created during verification
4938 Universe::verify();
4939 }
4940 {
4941 GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm);
4942
4943 verify_work_stacks_empty();
4944
4945 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
4946 StrongRootsScope srs(1);
4947
4948 heap->cms_process_roots(&srs,
4949 true, // young gen as roots
4950 GenCollectedHeap::ScanningOption(roots_scanning_options()),
4951 should_unload_classes(),
4952 &mrias_cl,
4953 NULL); // The dirty klasses will be handled below
4954
4955 assert(should_unload_classes()
4956 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4957 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4958 }
4959
4960 {
4961 GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm);
4962
4963 verify_work_stacks_empty();
4964
4965 // Scan all class loader data objects that might have been introduced
4966 // during concurrent marking.
4967 ResourceMark rm;
4968 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4969 for (int i = 0; i < array->length(); i++) {
4970 Devirtualizer::do_cld(&mrias_cl, array->at(i));
4971 }
4972
4973 // We don't need to keep track of new CLDs anymore.
4974 ClassLoaderDataGraph::remember_new_clds(false);
4975
4976 verify_work_stacks_empty();
4977 }
4978
4979 // We might have added oops to ClassLoaderData::_handles during the
4980 // concurrent marking phase. These oops do not point to newly allocated objects
4981 // that are guaranteed to be kept alive. Hence,
4982 // we do have to revisit the _handles block during the remark phase.
4983 {
4984 GCTraceTime(Trace, gc, phases) t("Dirty CLD Scan", _gc_timer_cm);
4985
4986 verify_work_stacks_empty();
4987
4988 RemarkCLDClosure remark_closure(&mrias_cl);
4989 ClassLoaderDataGraph::cld_do(&remark_closure);
4990
4991 verify_work_stacks_empty();
4992 }
4993
4994 verify_work_stacks_empty();
4995 // Restore evacuated mark words, if any, used for overflow list links
4996 restore_preserved_marks_if_any();
4997
4998 verify_overflow_empty();
4999 }
5000
5001 ////////////////////////////////////////////////////////
5002 // Parallel Reference Processing Task Proxy Class
5003 ////////////////////////////////////////////////////////
5004 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5005 OopTaskQueueSet* _queues;
5006 ParallelTaskTerminator _terminator;
5007 public:
5008 AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5009 AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5010 ParallelTaskTerminator* terminator() { return &_terminator; }
5011 OopTaskQueueSet* queues() { return _queues; }
5012 };
5013
5014 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5015 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5016 CMSCollector* _collector;
5017 CMSBitMap* _mark_bit_map;
5018 const MemRegion _span;
5019 ProcessTask& _task;
5020
5021 public:
5022 CMSRefProcTaskProxy(ProcessTask& task,
5023 CMSCollector* collector,
5024 const MemRegion& span,
5025 CMSBitMap* mark_bit_map,
5026 AbstractWorkGang* workers,
5027 OopTaskQueueSet* task_queues):
5028 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5029 task_queues,
5030 workers->active_workers()),
5031 _collector(collector),
5032 _mark_bit_map(mark_bit_map),
5033 _span(span),
5034 _task(task)
5035 {
5036 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5037 "Inconsistency in _span");
5038 }
5039
5040 OopTaskQueueSet* task_queues() { return queues(); }
5041
5042 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5043
5044 void do_work_steal(int i,
5045 CMSParDrainMarkingStackClosure* drain,
5046 CMSParKeepAliveClosure* keep_alive);
5047
5048 virtual void work(uint worker_id);
5049 };
5050
5051 void CMSRefProcTaskProxy::work(uint worker_id) {
5052 ResourceMark rm;
5053 HandleMark hm;
5054 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5055 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5056 _mark_bit_map,
5057 work_queue(worker_id));
5058 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5059 _mark_bit_map,
5060 work_queue(worker_id));
5061 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5062 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5063 if (_task.marks_oops_alive()) {
5064 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive);
5065 }
5066 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5067 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5068 }
5069
5070 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5071 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5072 _span(span),
5073 _work_queue(work_queue),
5074 _bit_map(bit_map),
5075 _mark_and_push(collector, span, bit_map, work_queue),
5076 _low_water_mark(MIN2((work_queue->max_elems()/4),
5077 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5078 { }
5079
5080 // . see if we can share work_queues with ParNew? XXX
5081 void CMSRefProcTaskProxy::do_work_steal(int i,
5082 CMSParDrainMarkingStackClosure* drain,
5083 CMSParKeepAliveClosure* keep_alive) {
5084 OopTaskQueue* work_q = work_queue(i);
5085 NOT_PRODUCT(int num_steals = 0;)
5086 oop obj_to_scan;
5087
5088 while (true) {
5089 // Completely finish any left over work from (an) earlier round(s)
5090 drain->trim_queue(0);
5091 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5092 (size_t)ParGCDesiredObjsFromOverflowList);
5093 // Now check if there's any work in the overflow list
5094 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5095 // only affects the number of attempts made to get work from the
5096 // overflow list and does not affect the number of workers. Just
5097 // pass ParallelGCThreads so this behavior is unchanged.
5098 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5099 work_q,
5100 ParallelGCThreads)) {
5101 // Found something in global overflow list;
5102 // not yet ready to go stealing work from others.
5103 // We'd like to assert(work_q->size() != 0, ...)
5104 // because we just took work from the overflow list,
5105 // but of course we can't, since all of that might have
5106 // been already stolen from us.
5107 continue;
5108 }
5109 // Verify that we have no work before we resort to stealing
5110 assert(work_q->size() == 0, "Have work, shouldn't steal");
5111 // Try to steal from other queues that have work
5112 if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
5113 NOT_PRODUCT(num_steals++;)
5114 assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
5115 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5116 // Do scanning work
5117 obj_to_scan->oop_iterate(keep_alive);
5118 // Loop around, finish this work, and try to steal some more
5119 } else if (terminator()->offer_termination()) {
5120 break; // nirvana from the infinite cycle
5121 }
5122 }
5123 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5124 }
5125
5126 void CMSRefProcTaskExecutor::execute(ProcessTask& task, uint ergo_workers) {
5127 CMSHeap* heap = CMSHeap::heap();
5128 WorkGang* workers = heap->workers();
5129 assert(workers != NULL, "Need parallel worker threads.");
5130 assert(workers->active_workers() == ergo_workers,
5131 "Ergonomically chosen workers (%u) must be equal to active workers (%u)",
5132 ergo_workers, workers->active_workers());
5133 CMSRefProcTaskProxy rp_task(task, &_collector,
5134 _collector.ref_processor_span(),
5135 _collector.markBitMap(),
5136 workers, _collector.task_queues());
5137 workers->run_task(&rp_task, workers->active_workers());
5138 }
5139
5140 void CMSCollector::refProcessingWork() {
5141 ResourceMark rm;
5142 HandleMark hm;
5143
5144 ReferenceProcessor* rp = ref_processor();
5145 assert(_span_based_discoverer.span().equals(_span), "Spans should be equal");
5146 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5147 // Process weak references.
5148 rp->setup_policy(false);
5149 verify_work_stacks_empty();
5150
5151 ReferenceProcessorPhaseTimes pt(_gc_timer_cm, rp->max_num_queues());
5152 {
5153 GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm);
5154
5155 // Setup keep_alive and complete closures.
5156 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5157 &_markStack, false /* !preclean */);
5158 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5159 _span, &_markBitMap, &_markStack,
5160 &cmsKeepAliveClosure, false /* !preclean */);
5161
5162 ReferenceProcessorStats stats;
5163 if (rp->processing_is_mt()) {
5164 // Set the degree of MT here. If the discovery is done MT, there
5165 // may have been a different number of threads doing the discovery
5166 // and a different number of discovered lists may have Ref objects.
5167 // That is OK as long as the Reference lists are balanced (see
5168 // balance_all_queues() and balance_queues()).
5169 CMSHeap* heap = CMSHeap::heap();
5170 uint active_workers = ParallelGCThreads;
5171 WorkGang* workers = heap->workers();
5172 if (workers != NULL) {
5173 active_workers = workers->active_workers();
5174 // The expectation is that active_workers will have already
5175 // been set to a reasonable value. If it has not been set,
5176 // investigate.
5177 assert(active_workers > 0, "Should have been set during scavenge");
5178 }
5179 rp->set_active_mt_degree(active_workers);
5180 CMSRefProcTaskExecutor task_executor(*this);
5181 stats = rp->process_discovered_references(&_is_alive_closure,
5182 &cmsKeepAliveClosure,
5183 &cmsDrainMarkingStackClosure,
5184 &task_executor,
5185 &pt);
5186 } else {
5187 stats = rp->process_discovered_references(&_is_alive_closure,
5188 &cmsKeepAliveClosure,
5189 &cmsDrainMarkingStackClosure,
5190 NULL,
5191 &pt);
5192 }
5193 _gc_tracer_cm->report_gc_reference_stats(stats);
5194 pt.print_all_references();
5195 }
5196
5197 // This is the point where the entire marking should have completed.
5198 verify_work_stacks_empty();
5199
5200 {
5201 GCTraceTime(Debug, gc, phases) t("Weak Processing", _gc_timer_cm);
5202 WeakProcessor::weak_oops_do(&_is_alive_closure, &do_nothing_cl);
5203 }
5204
5205 if (should_unload_classes()) {
5206 {
5207 GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm);
5208
5209 // Unload classes and purge the SystemDictionary.
5210 bool purged_class = SystemDictionary::do_unloading(_gc_timer_cm);
5211
5212 // Unload nmethods.
5213 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5214
5215 // Prune dead klasses from subklass/sibling/implementor lists.
5216 Klass::clean_weak_klass_links(purged_class);
5217 }
5218
5219 {
5220 GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer_cm);
5221 // Clean up unreferenced symbols in symbol table.
5222 SymbolTable::unlink();
5223 }
5224
5225 {
5226 GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer_cm);
5227 // Delete entries for dead interned strings.
5228 StringTable::unlink(&_is_alive_closure);
5229 }
5230 }
5231
5232 // Restore any preserved marks as a result of mark stack or
5233 // work queue overflow
5234 restore_preserved_marks_if_any(); // done single-threaded for now
5235
5236 rp->set_enqueuing_is_done(true);
5237 rp->verify_no_references_recorded();
5238 }
5239
5240 #ifndef PRODUCT
5241 void CMSCollector::check_correct_thread_executing() {
5242 Thread* t = Thread::current();
5243 // Only the VM thread or the CMS thread should be here.
5244 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5245 "Unexpected thread type");
5246 // If this is the vm thread, the foreground process
5247 // should not be waiting. Note that _foregroundGCIsActive is
5248 // true while the foreground collector is waiting.
5249 if (_foregroundGCShouldWait) {
5250 // We cannot be the VM thread
5251 assert(t->is_ConcurrentGC_thread(),
5252 "Should be CMS thread");
5253 } else {
5254 // We can be the CMS thread only if we are in a stop-world
5255 // phase of CMS collection.
5256 if (t->is_ConcurrentGC_thread()) {
5257 assert(_collectorState == InitialMarking ||
5258 _collectorState == FinalMarking,
5259 "Should be a stop-world phase");
5260 // The CMS thread should be holding the CMS_token.
5261 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5262 "Potential interference with concurrently "
5263 "executing VM thread");
5264 }
5265 }
5266 }
5267 #endif
5268
5269 void CMSCollector::sweep() {
5270 assert(_collectorState == Sweeping, "just checking");
5271 check_correct_thread_executing();
5272 verify_work_stacks_empty();
5273 verify_overflow_empty();
5274 increment_sweep_count();
5275 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
5276
5277 _inter_sweep_timer.stop();
5278 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5279
5280 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5281 _intra_sweep_timer.reset();
5282 _intra_sweep_timer.start();
5283 {
5284 GCTraceCPUTime tcpu;
5285 CMSPhaseAccounting pa(this, "Concurrent Sweep");
5286 // First sweep the old gen
5287 {
5288 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5289 bitMapLock());
5290 sweepWork(_cmsGen);
5291 }
5292
5293 // Update Universe::_heap_*_at_gc figures.
5294 // We need all the free list locks to make the abstract state
5295 // transition from Sweeping to Resetting. See detailed note
5296 // further below.
5297 {
5298 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5299 // Update heap occupancy information which is used as
5300 // input to soft ref clearing policy at the next gc.
5301 Universe::update_heap_info_at_gc();
5302 _collectorState = Resizing;
5303 }
5304 }
5305 verify_work_stacks_empty();
5306 verify_overflow_empty();
5307
5308 if (should_unload_classes()) {
5309 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5310 // requires that the virtual spaces are stable and not deleted.
5311 ClassLoaderDataGraph::set_should_purge(true);
5312 }
5313
5314 _intra_sweep_timer.stop();
5315 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5316
5317 _inter_sweep_timer.reset();
5318 _inter_sweep_timer.start();
5319
5320 // We need to use a monotonically non-decreasing time in ms
5321 // or we will see time-warp warnings and os::javaTimeMillis()
5322 // does not guarantee monotonicity.
5323 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5324 update_time_of_last_gc(now);
5325
5326 // NOTE on abstract state transitions:
5327 // Mutators allocate-live and/or mark the mod-union table dirty
5328 // based on the state of the collection. The former is done in
5329 // the interval [Marking, Sweeping] and the latter in the interval
5330 // [Marking, Sweeping). Thus the transitions into the Marking state
5331 // and out of the Sweeping state must be synchronously visible
5332 // globally to the mutators.
5333 // The transition into the Marking state happens with the world
5334 // stopped so the mutators will globally see it. Sweeping is
5335 // done asynchronously by the background collector so the transition
5336 // from the Sweeping state to the Resizing state must be done
5337 // under the freelistLock (as is the check for whether to
5338 // allocate-live and whether to dirty the mod-union table).
5339 assert(_collectorState == Resizing, "Change of collector state to"
5340 " Resizing must be done under the freelistLocks (plural)");
5341
5342 // Now that sweeping has been completed, we clear
5343 // the incremental_collection_failed flag,
5344 // thus inviting a younger gen collection to promote into
5345 // this generation. If such a promotion may still fail,
5346 // the flag will be set again when a young collection is
5347 // attempted.
5348 CMSHeap* heap = CMSHeap::heap();
5349 heap->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5350 heap->update_full_collections_completed(_collection_count_start);
5351 }
5352
5353 // FIX ME!!! Looks like this belongs in CFLSpace, with
5354 // CMSGen merely delegating to it.
5355 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5356 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5357 HeapWord* minAddr = _cmsSpace->bottom();
5358 HeapWord* largestAddr =
5359 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5360 if (largestAddr == NULL) {
5361 // The dictionary appears to be empty. In this case
5362 // try to coalesce at the end of the heap.
5363 largestAddr = _cmsSpace->end();
5364 }
5365 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5366 size_t nearLargestOffset =
5367 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5368 log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5369 p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5370 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5371 }
5372
5373 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5374 return addr >= _cmsSpace->nearLargestChunk();
5375 }
5376
5377 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5378 return _cmsSpace->find_chunk_at_end();
5379 }
5380
5381 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5382 bool full) {
5383 // If the young generation has been collected, gather any statistics
5384 // that are of interest at this point.
5385 bool current_is_young = CMSHeap::heap()->is_young_gen(current_generation);
5386 if (!full && current_is_young) {
5387 // Gather statistics on the young generation collection.
5388 collector()->stats().record_gc0_end(used());
5389 }
5390 }
5391
5392 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5393 // We iterate over the space(s) underlying this generation,
5394 // checking the mark bit map to see if the bits corresponding
5395 // to specific blocks are marked or not. Blocks that are
5396 // marked are live and are not swept up. All remaining blocks
5397 // are swept up, with coalescing on-the-fly as we sweep up
5398 // contiguous free and/or garbage blocks:
5399 // We need to ensure that the sweeper synchronizes with allocators
5400 // and stop-the-world collectors. In particular, the following
5401 // locks are used:
5402 // . CMS token: if this is held, a stop the world collection cannot occur
5403 // . freelistLock: if this is held no allocation can occur from this
5404 // generation by another thread
5405 // . bitMapLock: if this is held, no other thread can access or update
5406 //
5407
5408 // Note that we need to hold the freelistLock if we use
5409 // block iterate below; else the iterator might go awry if
5410 // a mutator (or promotion) causes block contents to change
5411 // (for instance if the allocator divvies up a block).
5412 // If we hold the free list lock, for all practical purposes
5413 // young generation GC's can't occur (they'll usually need to
5414 // promote), so we might as well prevent all young generation
5415 // GC's while we do a sweeping step. For the same reason, we might
5416 // as well take the bit map lock for the entire duration
5417
5418 // check that we hold the requisite locks
5419 assert(have_cms_token(), "Should hold cms token");
5420 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5421 assert_lock_strong(old_gen->freelistLock());
5422 assert_lock_strong(bitMapLock());
5423
5424 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5425 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5426 old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5427 _inter_sweep_estimate.padded_average(),
5428 _intra_sweep_estimate.padded_average());
5429 old_gen->setNearLargestChunk();
5430
5431 {
5432 SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5433 old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5434 // We need to free-up/coalesce garbage/blocks from a
5435 // co-terminal free run. This is done in the SweepClosure
5436 // destructor; so, do not remove this scope, else the
5437 // end-of-sweep-census below will be off by a little bit.
5438 }
5439 old_gen->cmsSpace()->sweep_completed();
5440 old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5441 if (should_unload_classes()) { // unloaded classes this cycle,
5442 _concurrent_cycles_since_last_unload = 0; // ... reset count
5443 } else { // did not unload classes,
5444 _concurrent_cycles_since_last_unload++; // ... increment count
5445 }
5446 }
5447
5448 // Reset CMS data structures (for now just the marking bit map)
5449 // preparatory for the next cycle.
5450 void CMSCollector::reset_concurrent() {
5451 CMSTokenSyncWithLocks ts(true, bitMapLock());
5452
5453 // If the state is not "Resetting", the foreground thread
5454 // has done a collection and the resetting.
5455 if (_collectorState != Resetting) {
5456 assert(_collectorState == Idling, "The state should only change"
5457 " because the foreground collector has finished the collection");
5458 return;
5459 }
5460
5461 {
5462 // Clear the mark bitmap (no grey objects to start with)
5463 // for the next cycle.
5464 GCTraceCPUTime tcpu;
5465 CMSPhaseAccounting cmspa(this, "Concurrent Reset");
5466
5467 HeapWord* curAddr = _markBitMap.startWord();
5468 while (curAddr < _markBitMap.endWord()) {
5469 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5470 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5471 _markBitMap.clear_large_range(chunk);
5472 if (ConcurrentMarkSweepThread::should_yield() &&
5473 !foregroundGCIsActive() &&
5474 CMSYield) {
5475 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5476 "CMS thread should hold CMS token");
5477 assert_lock_strong(bitMapLock());
5478 bitMapLock()->unlock();
5479 ConcurrentMarkSweepThread::desynchronize(true);
5480 stopTimer();
5481 incrementYields();
5482
5483 // See the comment in coordinator_yield()
5484 for (unsigned i = 0; i < CMSYieldSleepCount &&
5485 ConcurrentMarkSweepThread::should_yield() &&
5486 !CMSCollector::foregroundGCIsActive(); ++i) {
5487 os::sleep(Thread::current(), 1, false);
5488 }
5489
5490 ConcurrentMarkSweepThread::synchronize(true);
5491 bitMapLock()->lock_without_safepoint_check();
5492 startTimer();
5493 }
5494 curAddr = chunk.end();
5495 }
5496 // A successful mostly concurrent collection has been done.
5497 // Because only the full (i.e., concurrent mode failure) collections
5498 // are being measured for gc overhead limits, clean the "near" flag
5499 // and count.
5500 size_policy()->reset_gc_overhead_limit_count();
5501 _collectorState = Idling;
5502 }
5503
5504 register_gc_end();
5505 }
5506
5507 // Same as above but for STW paths
5508 void CMSCollector::reset_stw() {
5509 // already have the lock
5510 assert(_collectorState == Resetting, "just checking");
5511 assert_lock_strong(bitMapLock());
5512 GCIdMark gc_id_mark(_cmsThread->gc_id());
5513 _markBitMap.clear_all();
5514 _collectorState = Idling;
5515 register_gc_end();
5516 }
5517
5518 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5519 GCTraceCPUTime tcpu;
5520 TraceCollectorStats tcs_cgc(cgc_counters());
5521
5522 switch (op) {
5523 case CMS_op_checkpointRootsInitial: {
5524 GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5525 SvcGCMarker sgcm(SvcGCMarker::CONCURRENT);
5526 checkpointRootsInitial();
5527 break;
5528 }
5529 case CMS_op_checkpointRootsFinal: {
5530 GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5531 SvcGCMarker sgcm(SvcGCMarker::CONCURRENT);
5532 checkpointRootsFinal();
5533 break;
5534 }
5535 default:
5536 fatal("No such CMS_op");
5537 }
5538 }
5539
5540 #ifndef PRODUCT
5541 size_t const CMSCollector::skip_header_HeapWords() {
5542 return FreeChunk::header_size();
5543 }
5544
5545 // Try and collect here conditions that should hold when
5546 // CMS thread is exiting. The idea is that the foreground GC
5547 // thread should not be blocked if it wants to terminate
5548 // the CMS thread and yet continue to run the VM for a while
5549 // after that.
5550 void CMSCollector::verify_ok_to_terminate() const {
5551 assert(Thread::current()->is_ConcurrentGC_thread(),
5552 "should be called by CMS thread");
5553 assert(!_foregroundGCShouldWait, "should be false");
5554 // We could check here that all the various low-level locks
5555 // are not held by the CMS thread, but that is overkill; see
5556 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5557 // is checked.
5558 }
5559 #endif
5560
5561 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5562 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5563 "missing Printezis mark?");
5564 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5565 size_t size = pointer_delta(nextOneAddr + 1, addr);
5566 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5567 "alignment problem");
5568 assert(size >= 3, "Necessary for Printezis marks to work");
5569 return size;
5570 }
5571
5572 // A variant of the above (block_size_using_printezis_bits()) except
5573 // that we return 0 if the P-bits are not yet set.
5574 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5575 if (_markBitMap.isMarked(addr + 1)) {
5576 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5577 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5578 size_t size = pointer_delta(nextOneAddr + 1, addr);
5579 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5580 "alignment problem");
5581 assert(size >= 3, "Necessary for Printezis marks to work");
5582 return size;
5583 }
5584 return 0;
5585 }
5586
5587 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5588 size_t sz = 0;
5589 oop p = (oop)addr;
5590 if (p->klass_or_null_acquire() != NULL) {
5591 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5592 } else {
5593 sz = block_size_using_printezis_bits(addr);
5594 }
5595 assert(sz > 0, "size must be nonzero");
5596 HeapWord* next_block = addr + sz;
5597 HeapWord* next_card = align_up(next_block, CardTable::card_size);
5598 assert(align_down((uintptr_t)addr, CardTable::card_size) <
5599 align_down((uintptr_t)next_card, CardTable::card_size),
5600 "must be different cards");
5601 return next_card;
5602 }
5603
5604
5605 // CMS Bit Map Wrapper /////////////////////////////////////////
5606
5607 // Construct a CMS bit map infrastructure, but don't create the
5608 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5609 // further below.
5610 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5611 _shifter(shifter),
5612 _bm(),
5613 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5614 Monitor::_safepoint_check_sometimes) : NULL)
5615 {
5616 _bmStartWord = 0;
5617 _bmWordSize = 0;
5618 }
5619
5620 bool CMSBitMap::allocate(MemRegion mr) {
5621 _bmStartWord = mr.start();
5622 _bmWordSize = mr.word_size();
5623 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5624 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5625 if (!brs.is_reserved()) {
5626 log_warning(gc)("CMS bit map allocation failure");
5627 return false;
5628 }
5629 // For now we'll just commit all of the bit map up front.
5630 // Later on we'll try to be more parsimonious with swap.
5631 if (!_virtual_space.initialize(brs, brs.size())) {
5632 log_warning(gc)("CMS bit map backing store failure");
5633 return false;
5634 }
5635 assert(_virtual_space.committed_size() == brs.size(),
5636 "didn't reserve backing store for all of CMS bit map?");
5637 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5638 _bmWordSize, "inconsistency in bit map sizing");
5639 _bm = BitMapView((BitMap::bm_word_t*)_virtual_space.low(), _bmWordSize >> _shifter);
5640
5641 // bm.clear(); // can we rely on getting zero'd memory? verify below
5642 assert(isAllClear(),
5643 "Expected zero'd memory from ReservedSpace constructor");
5644 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5645 "consistency check");
5646 return true;
5647 }
5648
5649 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5650 HeapWord *next_addr, *end_addr, *last_addr;
5651 assert_locked();
5652 assert(covers(mr), "out-of-range error");
5653 // XXX assert that start and end are appropriately aligned
5654 for (next_addr = mr.start(), end_addr = mr.end();
5655 next_addr < end_addr; next_addr = last_addr) {
5656 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5657 last_addr = dirty_region.end();
5658 if (!dirty_region.is_empty()) {
5659 cl->do_MemRegion(dirty_region);
5660 } else {
5661 assert(last_addr == end_addr, "program logic");
5662 return;
5663 }
5664 }
5665 }
5666
5667 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5668 _bm.print_on_error(st, prefix);
5669 }
5670
5671 #ifndef PRODUCT
5672 void CMSBitMap::assert_locked() const {
5673 CMSLockVerifier::assert_locked(lock());
5674 }
5675
5676 bool CMSBitMap::covers(MemRegion mr) const {
5677 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5678 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5679 "size inconsistency");
5680 return (mr.start() >= _bmStartWord) &&
5681 (mr.end() <= endWord());
5682 }
5683
5684 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5685 return (start >= _bmStartWord && (start + size) <= endWord());
5686 }
5687
5688 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5689 // verify that there are no 1 bits in the interval [left, right)
5690 FalseBitMapClosure falseBitMapClosure;
5691 iterate(&falseBitMapClosure, left, right);
5692 }
5693
5694 void CMSBitMap::region_invariant(MemRegion mr)
5695 {
5696 assert_locked();
5697 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5698 assert(!mr.is_empty(), "unexpected empty region");
5699 assert(covers(mr), "mr should be covered by bit map");
5700 // convert address range into offset range
5701 size_t start_ofs = heapWordToOffset(mr.start());
5702 // Make sure that end() is appropriately aligned
5703 assert(mr.end() == align_up(mr.end(), (1 << (_shifter+LogHeapWordSize))),
5704 "Misaligned mr.end()");
5705 size_t end_ofs = heapWordToOffset(mr.end());
5706 assert(end_ofs > start_ofs, "Should mark at least one bit");
5707 }
5708
5709 #endif
5710
5711 bool CMSMarkStack::allocate(size_t size) {
5712 // allocate a stack of the requisite depth
5713 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5714 size * sizeof(oop)));
5715 if (!rs.is_reserved()) {
5716 log_warning(gc)("CMSMarkStack allocation failure");
5717 return false;
5718 }
5719 if (!_virtual_space.initialize(rs, rs.size())) {
5720 log_warning(gc)("CMSMarkStack backing store failure");
5721 return false;
5722 }
5723 assert(_virtual_space.committed_size() == rs.size(),
5724 "didn't reserve backing store for all of CMS stack?");
5725 _base = (oop*)(_virtual_space.low());
5726 _index = 0;
5727 _capacity = size;
5728 NOT_PRODUCT(_max_depth = 0);
5729 return true;
5730 }
5731
5732 // XXX FIX ME !!! In the MT case we come in here holding a
5733 // leaf lock. For printing we need to take a further lock
5734 // which has lower rank. We need to recalibrate the two
5735 // lock-ranks involved in order to be able to print the
5736 // messages below. (Or defer the printing to the caller.
5737 // For now we take the expedient path of just disabling the
5738 // messages for the problematic case.)
5739 void CMSMarkStack::expand() {
5740 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5741 if (_capacity == MarkStackSizeMax) {
5742 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5743 // We print a warning message only once per CMS cycle.
5744 log_debug(gc)(" (benign) Hit CMSMarkStack max size limit");
5745 }
5746 return;
5747 }
5748 // Double capacity if possible
5749 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5750 // Do not give up existing stack until we have managed to
5751 // get the double capacity that we desired.
5752 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5753 new_capacity * sizeof(oop)));
5754 if (rs.is_reserved()) {
5755 // Release the backing store associated with old stack
5756 _virtual_space.release();
5757 // Reinitialize virtual space for new stack
5758 if (!_virtual_space.initialize(rs, rs.size())) {
5759 fatal("Not enough swap for expanded marking stack");
5760 }
5761 _base = (oop*)(_virtual_space.low());
5762 _index = 0;
5763 _capacity = new_capacity;
5764 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5765 // Failed to double capacity, continue;
5766 // we print a detail message only once per CMS cycle.
5767 log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5768 _capacity / K, new_capacity / K);
5769 }
5770 }
5771
5772
5773 // Closures
5774 // XXX: there seems to be a lot of code duplication here;
5775 // should refactor and consolidate common code.
5776
5777 // This closure is used to mark refs into the CMS generation in
5778 // the CMS bit map. Called at the first checkpoint. This closure
5779 // assumes that we do not need to re-mark dirty cards; if the CMS
5780 // generation on which this is used is not an oldest
5781 // generation then this will lose younger_gen cards!
5782
5783 MarkRefsIntoClosure::MarkRefsIntoClosure(
5784 MemRegion span, CMSBitMap* bitMap):
5785 _span(span),
5786 _bitMap(bitMap)
5787 {
5788 assert(ref_discoverer() == NULL, "deliberately left NULL");
5789 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5790 }
5791
5792 void MarkRefsIntoClosure::do_oop(oop obj) {
5793 // if p points into _span, then mark corresponding bit in _markBitMap
5794 assert(oopDesc::is_oop(obj), "expected an oop");
5795 HeapWord* addr = (HeapWord*)obj;
5796 if (_span.contains(addr)) {
5797 // this should be made more efficient
5798 _bitMap->mark(addr);
5799 }
5800 }
5801
5802 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure(
5803 MemRegion span, CMSBitMap* bitMap):
5804 _span(span),
5805 _bitMap(bitMap)
5806 {
5807 assert(ref_discoverer() == NULL, "deliberately left NULL");
5808 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5809 }
5810
5811 void ParMarkRefsIntoClosure::do_oop(oop obj) {
5812 // if p points into _span, then mark corresponding bit in _markBitMap
5813 assert(oopDesc::is_oop(obj), "expected an oop");
5814 HeapWord* addr = (HeapWord*)obj;
5815 if (_span.contains(addr)) {
5816 // this should be made more efficient
5817 _bitMap->par_mark(addr);
5818 }
5819 }
5820
5821 // A variant of the above, used for CMS marking verification.
5822 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5823 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5824 _span(span),
5825 _verification_bm(verification_bm),
5826 _cms_bm(cms_bm)
5827 {
5828 assert(ref_discoverer() == NULL, "deliberately left NULL");
5829 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5830 }
5831
5832 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5833 // if p points into _span, then mark corresponding bit in _markBitMap
5834 assert(oopDesc::is_oop(obj), "expected an oop");
5835 HeapWord* addr = (HeapWord*)obj;
5836 if (_span.contains(addr)) {
5837 _verification_bm->mark(addr);
5838 if (!_cms_bm->isMarked(addr)) {
5839 Log(gc, verify) log;
5840 ResourceMark rm;
5841 LogStream ls(log.error());
5842 oop(addr)->print_on(&ls);
5843 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5844 fatal("... aborting");
5845 }
5846 }
5847 }
5848
5849 //////////////////////////////////////////////////
5850 // MarkRefsIntoAndScanClosure
5851 //////////////////////////////////////////////////
5852
5853 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5854 ReferenceDiscoverer* rd,
5855 CMSBitMap* bit_map,
5856 CMSBitMap* mod_union_table,
5857 CMSMarkStack* mark_stack,
5858 CMSCollector* collector,
5859 bool should_yield,
5860 bool concurrent_precleaning):
5861 _span(span),
5862 _bit_map(bit_map),
5863 _mark_stack(mark_stack),
5864 _pushAndMarkClosure(collector, span, rd, bit_map, mod_union_table,
5865 mark_stack, concurrent_precleaning),
5866 _collector(collector),
5867 _freelistLock(NULL),
5868 _yield(should_yield),
5869 _concurrent_precleaning(concurrent_precleaning)
5870 {
5871 // FIXME: Should initialize in base class constructor.
5872 assert(rd != NULL, "ref_discoverer shouldn't be NULL");
5873 set_ref_discoverer_internal(rd);
5874 }
5875
5876 // This closure is used to mark refs into the CMS generation at the
5877 // second (final) checkpoint, and to scan and transitively follow
5878 // the unmarked oops. It is also used during the concurrent precleaning
5879 // phase while scanning objects on dirty cards in the CMS generation.
5880 // The marks are made in the marking bit map and the marking stack is
5881 // used for keeping the (newly) grey objects during the scan.
5882 // The parallel version (Par_...) appears further below.
5883 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5884 if (obj != NULL) {
5885 assert(oopDesc::is_oop(obj), "expected an oop");
5886 HeapWord* addr = (HeapWord*)obj;
5887 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5888 assert(_collector->overflow_list_is_empty(),
5889 "overflow list should be empty");
5890 if (_span.contains(addr) &&
5891 !_bit_map->isMarked(addr)) {
5892 // mark bit map (object is now grey)
5893 _bit_map->mark(addr);
5894 // push on marking stack (stack should be empty), and drain the
5895 // stack by applying this closure to the oops in the oops popped
5896 // from the stack (i.e. blacken the grey objects)
5897 bool res = _mark_stack->push(obj);
5898 assert(res, "Should have space to push on empty stack");
5899 do {
5900 oop new_oop = _mark_stack->pop();
5901 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
5902 assert(_bit_map->isMarked((HeapWord*)new_oop),
5903 "only grey objects on this stack");
5904 // iterate over the oops in this oop, marking and pushing
5905 // the ones in CMS heap (i.e. in _span).
5906 new_oop->oop_iterate(&_pushAndMarkClosure);
5907 // check if it's time to yield
5908 do_yield_check();
5909 } while (!_mark_stack->isEmpty() ||
5910 (!_concurrent_precleaning && take_from_overflow_list()));
5911 // if marking stack is empty, and we are not doing this
5912 // during precleaning, then check the overflow list
5913 }
5914 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5915 assert(_collector->overflow_list_is_empty(),
5916 "overflow list was drained above");
5917
5918 assert(_collector->no_preserved_marks(),
5919 "All preserved marks should have been restored above");
5920 }
5921 }
5922
5923 void MarkRefsIntoAndScanClosure::do_yield_work() {
5924 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5925 "CMS thread should hold CMS token");
5926 assert_lock_strong(_freelistLock);
5927 assert_lock_strong(_bit_map->lock());
5928 // relinquish the free_list_lock and bitMaplock()
5929 _bit_map->lock()->unlock();
5930 _freelistLock->unlock();
5931 ConcurrentMarkSweepThread::desynchronize(true);
5932 _collector->stopTimer();
5933 _collector->incrementYields();
5934
5935 // See the comment in coordinator_yield()
5936 for (unsigned i = 0;
5937 i < CMSYieldSleepCount &&
5938 ConcurrentMarkSweepThread::should_yield() &&
5939 !CMSCollector::foregroundGCIsActive();
5940 ++i) {
5941 os::sleep(Thread::current(), 1, false);
5942 }
5943
5944 ConcurrentMarkSweepThread::synchronize(true);
5945 _freelistLock->lock_without_safepoint_check();
5946 _bit_map->lock()->lock_without_safepoint_check();
5947 _collector->startTimer();
5948 }
5949
5950 ///////////////////////////////////////////////////////////
5951 // ParMarkRefsIntoAndScanClosure: a parallel version of
5952 // MarkRefsIntoAndScanClosure
5953 ///////////////////////////////////////////////////////////
5954 ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure(
5955 CMSCollector* collector, MemRegion span, ReferenceDiscoverer* rd,
5956 CMSBitMap* bit_map, OopTaskQueue* work_queue):
5957 _span(span),
5958 _bit_map(bit_map),
5959 _work_queue(work_queue),
5960 _low_water_mark(MIN2((work_queue->max_elems()/4),
5961 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
5962 _parPushAndMarkClosure(collector, span, rd, bit_map, work_queue)
5963 {
5964 // FIXME: Should initialize in base class constructor.
5965 assert(rd != NULL, "ref_discoverer shouldn't be NULL");
5966 set_ref_discoverer_internal(rd);
5967 }
5968
5969 // This closure is used to mark refs into the CMS generation at the
5970 // second (final) checkpoint, and to scan and transitively follow
5971 // the unmarked oops. The marks are made in the marking bit map and
5972 // the work_queue is used for keeping the (newly) grey objects during
5973 // the scan phase whence they are also available for stealing by parallel
5974 // threads. Since the marking bit map is shared, updates are
5975 // synchronized (via CAS).
5976 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) {
5977 if (obj != NULL) {
5978 // Ignore mark word because this could be an already marked oop
5979 // that may be chained at the end of the overflow list.
5980 assert(oopDesc::is_oop(obj, true), "expected an oop");
5981 HeapWord* addr = (HeapWord*)obj;
5982 if (_span.contains(addr) &&
5983 !_bit_map->isMarked(addr)) {
5984 // mark bit map (object will become grey):
5985 // It is possible for several threads to be
5986 // trying to "claim" this object concurrently;
5987 // the unique thread that succeeds in marking the
5988 // object first will do the subsequent push on
5989 // to the work queue (or overflow list).
5990 if (_bit_map->par_mark(addr)) {
5991 // push on work_queue (which may not be empty), and trim the
5992 // queue to an appropriate length by applying this closure to
5993 // the oops in the oops popped from the stack (i.e. blacken the
5994 // grey objects)
5995 bool res = _work_queue->push(obj);
5996 assert(res, "Low water mark should be less than capacity?");
5997 trim_queue(_low_water_mark);
5998 } // Else, another thread claimed the object
5999 }
6000 }
6001 }
6002
6003 // This closure is used to rescan the marked objects on the dirty cards
6004 // in the mod union table and the card table proper.
6005 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6006 oop p, MemRegion mr) {
6007
6008 size_t size = 0;
6009 HeapWord* addr = (HeapWord*)p;
6010 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6011 assert(_span.contains(addr), "we are scanning the CMS generation");
6012 // check if it's time to yield
6013 if (do_yield_check()) {
6014 // We yielded for some foreground stop-world work,
6015 // and we have been asked to abort this ongoing preclean cycle.
6016 return 0;
6017 }
6018 if (_bitMap->isMarked(addr)) {
6019 // it's marked; is it potentially uninitialized?
6020 if (p->klass_or_null_acquire() != NULL) {
6021 // an initialized object; ignore mark word in verification below
6022 // since we are running concurrent with mutators
6023 assert(oopDesc::is_oop(p, true), "should be an oop");
6024 if (p->is_objArray()) {
6025 // objArrays are precisely marked; restrict scanning
6026 // to dirty cards only.
6027 size = CompactibleFreeListSpace::adjustObjectSize(
6028 p->oop_iterate_size(_scanningClosure, mr));
6029 } else {
6030 // A non-array may have been imprecisely marked; we need
6031 // to scan object in its entirety.
6032 size = CompactibleFreeListSpace::adjustObjectSize(
6033 p->oop_iterate_size(_scanningClosure));
6034 }
6035 #ifdef ASSERT
6036 size_t direct_size =
6037 CompactibleFreeListSpace::adjustObjectSize(p->size());
6038 assert(size == direct_size, "Inconsistency in size");
6039 assert(size >= 3, "Necessary for Printezis marks to work");
6040 HeapWord* start_pbit = addr + 1;
6041 HeapWord* end_pbit = addr + size - 1;
6042 assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit),
6043 "inconsistent Printezis mark");
6044 // Verify inner mark bits (between Printezis bits) are clear,
6045 // but don't repeat if there are multiple dirty regions for
6046 // the same object, to avoid potential O(N^2) performance.
6047 if (addr != _last_scanned_object) {
6048 _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit);
6049 _last_scanned_object = addr;
6050 }
6051 #endif // ASSERT
6052 } else {
6053 // An uninitialized object.
6054 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6055 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6056 size = pointer_delta(nextOneAddr + 1, addr);
6057 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6058 "alignment problem");
6059 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6060 // will dirty the card when the klass pointer is installed in the
6061 // object (signaling the completion of initialization).
6062 }
6063 } else {
6064 // Either a not yet marked object or an uninitialized object
6065 if (p->klass_or_null_acquire() == NULL) {
6066 // An uninitialized object, skip to the next card, since
6067 // we may not be able to read its P-bits yet.
6068 assert(size == 0, "Initial value");
6069 } else {
6070 // An object not (yet) reached by marking: we merely need to
6071 // compute its size so as to go look at the next block.
6072 assert(oopDesc::is_oop(p, true), "should be an oop");
6073 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6074 }
6075 }
6076 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6077 return size;
6078 }
6079
6080 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6081 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6082 "CMS thread should hold CMS token");
6083 assert_lock_strong(_freelistLock);
6084 assert_lock_strong(_bitMap->lock());
6085 // relinquish the free_list_lock and bitMaplock()
6086 _bitMap->lock()->unlock();
6087 _freelistLock->unlock();
6088 ConcurrentMarkSweepThread::desynchronize(true);
6089 _collector->stopTimer();
6090 _collector->incrementYields();
6091
6092 // See the comment in coordinator_yield()
6093 for (unsigned i = 0; i < CMSYieldSleepCount &&
6094 ConcurrentMarkSweepThread::should_yield() &&
6095 !CMSCollector::foregroundGCIsActive(); ++i) {
6096 os::sleep(Thread::current(), 1, false);
6097 }
6098
6099 ConcurrentMarkSweepThread::synchronize(true);
6100 _freelistLock->lock_without_safepoint_check();
6101 _bitMap->lock()->lock_without_safepoint_check();
6102 _collector->startTimer();
6103 }
6104
6105
6106 //////////////////////////////////////////////////////////////////
6107 // SurvivorSpacePrecleanClosure
6108 //////////////////////////////////////////////////////////////////
6109 // This (single-threaded) closure is used to preclean the oops in
6110 // the survivor spaces.
6111 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6112
6113 HeapWord* addr = (HeapWord*)p;
6114 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6115 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6116 assert(p->klass_or_null() != NULL, "object should be initialized");
6117 // an initialized object; ignore mark word in verification below
6118 // since we are running concurrent with mutators
6119 assert(oopDesc::is_oop(p, true), "should be an oop");
6120 // Note that we do not yield while we iterate over
6121 // the interior oops of p, pushing the relevant ones
6122 // on our marking stack.
6123 size_t size = p->oop_iterate_size(_scanning_closure);
6124 do_yield_check();
6125 // Observe that below, we do not abandon the preclean
6126 // phase as soon as we should; rather we empty the
6127 // marking stack before returning. This is to satisfy
6128 // some existing assertions. In general, it may be a
6129 // good idea to abort immediately and complete the marking
6130 // from the grey objects at a later time.
6131 while (!_mark_stack->isEmpty()) {
6132 oop new_oop = _mark_stack->pop();
6133 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
6134 assert(_bit_map->isMarked((HeapWord*)new_oop),
6135 "only grey objects on this stack");
6136 // iterate over the oops in this oop, marking and pushing
6137 // the ones in CMS heap (i.e. in _span).
6138 new_oop->oop_iterate(_scanning_closure);
6139 // check if it's time to yield
6140 do_yield_check();
6141 }
6142 unsigned int after_count =
6143 CMSHeap::heap()->total_collections();
6144 bool abort = (_before_count != after_count) ||
6145 _collector->should_abort_preclean();
6146 return abort ? 0 : size;
6147 }
6148
6149 void SurvivorSpacePrecleanClosure::do_yield_work() {
6150 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6151 "CMS thread should hold CMS token");
6152 assert_lock_strong(_bit_map->lock());
6153 // Relinquish the bit map lock
6154 _bit_map->lock()->unlock();
6155 ConcurrentMarkSweepThread::desynchronize(true);
6156 _collector->stopTimer();
6157 _collector->incrementYields();
6158
6159 // See the comment in coordinator_yield()
6160 for (unsigned i = 0; i < CMSYieldSleepCount &&
6161 ConcurrentMarkSweepThread::should_yield() &&
6162 !CMSCollector::foregroundGCIsActive(); ++i) {
6163 os::sleep(Thread::current(), 1, false);
6164 }
6165
6166 ConcurrentMarkSweepThread::synchronize(true);
6167 _bit_map->lock()->lock_without_safepoint_check();
6168 _collector->startTimer();
6169 }
6170
6171 // This closure is used to rescan the marked objects on the dirty cards
6172 // in the mod union table and the card table proper. In the parallel
6173 // case, although the bitMap is shared, we do a single read so the
6174 // isMarked() query is "safe".
6175 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6176 // Ignore mark word because we are running concurrent with mutators
6177 assert(oopDesc::is_oop_or_null(p, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6178 HeapWord* addr = (HeapWord*)p;
6179 assert(_span.contains(addr), "we are scanning the CMS generation");
6180 bool is_obj_array = false;
6181 #ifdef ASSERT
6182 if (!_parallel) {
6183 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6184 assert(_collector->overflow_list_is_empty(),
6185 "overflow list should be empty");
6186
6187 }
6188 #endif // ASSERT
6189 if (_bit_map->isMarked(addr)) {
6190 // Obj arrays are precisely marked, non-arrays are not;
6191 // so we scan objArrays precisely and non-arrays in their
6192 // entirety.
6193 if (p->is_objArray()) {
6194 is_obj_array = true;
6195 if (_parallel) {
6196 p->oop_iterate(_par_scan_closure, mr);
6197 } else {
6198 p->oop_iterate(_scan_closure, mr);
6199 }
6200 } else {
6201 if (_parallel) {
6202 p->oop_iterate(_par_scan_closure);
6203 } else {
6204 p->oop_iterate(_scan_closure);
6205 }
6206 }
6207 }
6208 #ifdef ASSERT
6209 if (!_parallel) {
6210 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6211 assert(_collector->overflow_list_is_empty(),
6212 "overflow list should be empty");
6213
6214 }
6215 #endif // ASSERT
6216 return is_obj_array;
6217 }
6218
6219 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6220 MemRegion span,
6221 CMSBitMap* bitMap, CMSMarkStack* markStack,
6222 bool should_yield, bool verifying):
6223 _collector(collector),
6224 _span(span),
6225 _bitMap(bitMap),
6226 _mut(&collector->_modUnionTable),
6227 _markStack(markStack),
6228 _yield(should_yield),
6229 _skipBits(0)
6230 {
6231 assert(_markStack->isEmpty(), "stack should be empty");
6232 _finger = _bitMap->startWord();
6233 _threshold = _finger;
6234 assert(_collector->_restart_addr == NULL, "Sanity check");
6235 assert(_span.contains(_finger), "Out of bounds _finger?");
6236 DEBUG_ONLY(_verifying = verifying;)
6237 }
6238
6239 void MarkFromRootsClosure::reset(HeapWord* addr) {
6240 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6241 assert(_span.contains(addr), "Out of bounds _finger?");
6242 _finger = addr;
6243 _threshold = align_up(_finger, CardTable::card_size);
6244 }
6245
6246 // Should revisit to see if this should be restructured for
6247 // greater efficiency.
6248 bool MarkFromRootsClosure::do_bit(size_t offset) {
6249 if (_skipBits > 0) {
6250 _skipBits--;
6251 return true;
6252 }
6253 // convert offset into a HeapWord*
6254 HeapWord* addr = _bitMap->startWord() + offset;
6255 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6256 "address out of range");
6257 assert(_bitMap->isMarked(addr), "tautology");
6258 if (_bitMap->isMarked(addr+1)) {
6259 // this is an allocated but not yet initialized object
6260 assert(_skipBits == 0, "tautology");
6261 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6262 oop p = oop(addr);
6263 if (p->klass_or_null_acquire() == NULL) {
6264 DEBUG_ONLY(if (!_verifying) {)
6265 // We re-dirty the cards on which this object lies and increase
6266 // the _threshold so that we'll come back to scan this object
6267 // during the preclean or remark phase. (CMSCleanOnEnter)
6268 if (CMSCleanOnEnter) {
6269 size_t sz = _collector->block_size_using_printezis_bits(addr);
6270 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
6271 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6272 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6273 // Bump _threshold to end_card_addr; note that
6274 // _threshold cannot possibly exceed end_card_addr, anyhow.
6275 // This prevents future clearing of the card as the scan proceeds
6276 // to the right.
6277 assert(_threshold <= end_card_addr,
6278 "Because we are just scanning into this object");
6279 if (_threshold < end_card_addr) {
6280 _threshold = end_card_addr;
6281 }
6282 if (p->klass_or_null_acquire() != NULL) {
6283 // Redirty the range of cards...
6284 _mut->mark_range(redirty_range);
6285 } // ...else the setting of klass will dirty the card anyway.
6286 }
6287 DEBUG_ONLY(})
6288 return true;
6289 }
6290 }
6291 scanOopsInOop(addr);
6292 return true;
6293 }
6294
6295 // We take a break if we've been at this for a while,
6296 // so as to avoid monopolizing the locks involved.
6297 void MarkFromRootsClosure::do_yield_work() {
6298 // First give up the locks, then yield, then re-lock
6299 // We should probably use a constructor/destructor idiom to
6300 // do this unlock/lock or modify the MutexUnlocker class to
6301 // serve our purpose. XXX
6302 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6303 "CMS thread should hold CMS token");
6304 assert_lock_strong(_bitMap->lock());
6305 _bitMap->lock()->unlock();
6306 ConcurrentMarkSweepThread::desynchronize(true);
6307 _collector->stopTimer();
6308 _collector->incrementYields();
6309
6310 // See the comment in coordinator_yield()
6311 for (unsigned i = 0; i < CMSYieldSleepCount &&
6312 ConcurrentMarkSweepThread::should_yield() &&
6313 !CMSCollector::foregroundGCIsActive(); ++i) {
6314 os::sleep(Thread::current(), 1, false);
6315 }
6316
6317 ConcurrentMarkSweepThread::synchronize(true);
6318 _bitMap->lock()->lock_without_safepoint_check();
6319 _collector->startTimer();
6320 }
6321
6322 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6323 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6324 assert(_markStack->isEmpty(),
6325 "should drain stack to limit stack usage");
6326 // convert ptr to an oop preparatory to scanning
6327 oop obj = oop(ptr);
6328 // Ignore mark word in verification below, since we
6329 // may be running concurrent with mutators.
6330 assert(oopDesc::is_oop(obj, true), "should be an oop");
6331 assert(_finger <= ptr, "_finger runneth ahead");
6332 // advance the finger to right end of this object
6333 _finger = ptr + obj->size();
6334 assert(_finger > ptr, "we just incremented it above");
6335 // On large heaps, it may take us some time to get through
6336 // the marking phase. During
6337 // this time it's possible that a lot of mutations have
6338 // accumulated in the card table and the mod union table --
6339 // these mutation records are redundant until we have
6340 // actually traced into the corresponding card.
6341 // Here, we check whether advancing the finger would make
6342 // us cross into a new card, and if so clear corresponding
6343 // cards in the MUT (preclean them in the card-table in the
6344 // future).
6345
6346 DEBUG_ONLY(if (!_verifying) {)
6347 // The clean-on-enter optimization is disabled by default,
6348 // until we fix 6178663.
6349 if (CMSCleanOnEnter && (_finger > _threshold)) {
6350 // [_threshold, _finger) represents the interval
6351 // of cards to be cleared in MUT (or precleaned in card table).
6352 // The set of cards to be cleared is all those that overlap
6353 // with the interval [_threshold, _finger); note that
6354 // _threshold is always kept card-aligned but _finger isn't
6355 // always card-aligned.
6356 HeapWord* old_threshold = _threshold;
6357 assert(is_aligned(old_threshold, CardTable::card_size),
6358 "_threshold should always be card-aligned");
6359 _threshold = align_up(_finger, CardTable::card_size);
6360 MemRegion mr(old_threshold, _threshold);
6361 assert(!mr.is_empty(), "Control point invariant");
6362 assert(_span.contains(mr), "Should clear within span");
6363 _mut->clear_range(mr);
6364 }
6365 DEBUG_ONLY(})
6366 // Note: the finger doesn't advance while we drain
6367 // the stack below.
6368 PushOrMarkClosure pushOrMarkClosure(_collector,
6369 _span, _bitMap, _markStack,
6370 _finger, this);
6371 bool res = _markStack->push(obj);
6372 assert(res, "Empty non-zero size stack should have space for single push");
6373 while (!_markStack->isEmpty()) {
6374 oop new_oop = _markStack->pop();
6375 // Skip verifying header mark word below because we are
6376 // running concurrent with mutators.
6377 assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6378 // now scan this oop's oops
6379 new_oop->oop_iterate(&pushOrMarkClosure);
6380 do_yield_check();
6381 }
6382 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6383 }
6384
6385 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task,
6386 CMSCollector* collector, MemRegion span,
6387 CMSBitMap* bit_map,
6388 OopTaskQueue* work_queue,
6389 CMSMarkStack* overflow_stack):
6390 _collector(collector),
6391 _whole_span(collector->_span),
6392 _span(span),
6393 _bit_map(bit_map),
6394 _mut(&collector->_modUnionTable),
6395 _work_queue(work_queue),
6396 _overflow_stack(overflow_stack),
6397 _skip_bits(0),
6398 _task(task)
6399 {
6400 assert(_work_queue->size() == 0, "work_queue should be empty");
6401 _finger = span.start();
6402 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6403 assert(_span.contains(_finger), "Out of bounds _finger?");
6404 }
6405
6406 // Should revisit to see if this should be restructured for
6407 // greater efficiency.
6408 bool ParMarkFromRootsClosure::do_bit(size_t offset) {
6409 if (_skip_bits > 0) {
6410 _skip_bits--;
6411 return true;
6412 }
6413 // convert offset into a HeapWord*
6414 HeapWord* addr = _bit_map->startWord() + offset;
6415 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6416 "address out of range");
6417 assert(_bit_map->isMarked(addr), "tautology");
6418 if (_bit_map->isMarked(addr+1)) {
6419 // this is an allocated object that might not yet be initialized
6420 assert(_skip_bits == 0, "tautology");
6421 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6422 oop p = oop(addr);
6423 if (p->klass_or_null_acquire() == NULL) {
6424 // in the case of Clean-on-Enter optimization, redirty card
6425 // and avoid clearing card by increasing the threshold.
6426 return true;
6427 }
6428 }
6429 scan_oops_in_oop(addr);
6430 return true;
6431 }
6432
6433 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6434 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6435 // Should we assert that our work queue is empty or
6436 // below some drain limit?
6437 assert(_work_queue->size() == 0,
6438 "should drain stack to limit stack usage");
6439 // convert ptr to an oop preparatory to scanning
6440 oop obj = oop(ptr);
6441 // Ignore mark word in verification below, since we
6442 // may be running concurrent with mutators.
6443 assert(oopDesc::is_oop(obj, true), "should be an oop");
6444 assert(_finger <= ptr, "_finger runneth ahead");
6445 // advance the finger to right end of this object
6446 _finger = ptr + obj->size();
6447 assert(_finger > ptr, "we just incremented it above");
6448 // On large heaps, it may take us some time to get through
6449 // the marking phase. During
6450 // this time it's possible that a lot of mutations have
6451 // accumulated in the card table and the mod union table --
6452 // these mutation records are redundant until we have
6453 // actually traced into the corresponding card.
6454 // Here, we check whether advancing the finger would make
6455 // us cross into a new card, and if so clear corresponding
6456 // cards in the MUT (preclean them in the card-table in the
6457 // future).
6458
6459 // The clean-on-enter optimization is disabled by default,
6460 // until we fix 6178663.
6461 if (CMSCleanOnEnter && (_finger > _threshold)) {
6462 // [_threshold, _finger) represents the interval
6463 // of cards to be cleared in MUT (or precleaned in card table).
6464 // The set of cards to be cleared is all those that overlap
6465 // with the interval [_threshold, _finger); note that
6466 // _threshold is always kept card-aligned but _finger isn't
6467 // always card-aligned.
6468 HeapWord* old_threshold = _threshold;
6469 assert(is_aligned(old_threshold, CardTable::card_size),
6470 "_threshold should always be card-aligned");
6471 _threshold = align_up(_finger, CardTable::card_size);
6472 MemRegion mr(old_threshold, _threshold);
6473 assert(!mr.is_empty(), "Control point invariant");
6474 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6475 _mut->clear_range(mr);
6476 }
6477
6478 // Note: the local finger doesn't advance while we drain
6479 // the stack below, but the global finger sure can and will.
6480 HeapWord* volatile* gfa = _task->global_finger_addr();
6481 ParPushOrMarkClosure pushOrMarkClosure(_collector,
6482 _span, _bit_map,
6483 _work_queue,
6484 _overflow_stack,
6485 _finger,
6486 gfa, this);
6487 bool res = _work_queue->push(obj); // overflow could occur here
6488 assert(res, "Will hold once we use workqueues");
6489 while (true) {
6490 oop new_oop;
6491 if (!_work_queue->pop_local(new_oop)) {
6492 // We emptied our work_queue; check if there's stuff that can
6493 // be gotten from the overflow stack.
6494 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6495 _overflow_stack, _work_queue)) {
6496 do_yield_check();
6497 continue;
6498 } else { // done
6499 break;
6500 }
6501 }
6502 // Skip verifying header mark word below because we are
6503 // running concurrent with mutators.
6504 assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6505 // now scan this oop's oops
6506 new_oop->oop_iterate(&pushOrMarkClosure);
6507 do_yield_check();
6508 }
6509 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6510 }
6511
6512 // Yield in response to a request from VM Thread or
6513 // from mutators.
6514 void ParMarkFromRootsClosure::do_yield_work() {
6515 assert(_task != NULL, "sanity");
6516 _task->yield();
6517 }
6518
6519 // A variant of the above used for verifying CMS marking work.
6520 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6521 MemRegion span,
6522 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6523 CMSMarkStack* mark_stack):
6524 _collector(collector),
6525 _span(span),
6526 _verification_bm(verification_bm),
6527 _cms_bm(cms_bm),
6528 _mark_stack(mark_stack),
6529 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6530 mark_stack)
6531 {
6532 assert(_mark_stack->isEmpty(), "stack should be empty");
6533 _finger = _verification_bm->startWord();
6534 assert(_collector->_restart_addr == NULL, "Sanity check");
6535 assert(_span.contains(_finger), "Out of bounds _finger?");
6536 }
6537
6538 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6539 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6540 assert(_span.contains(addr), "Out of bounds _finger?");
6541 _finger = addr;
6542 }
6543
6544 // Should revisit to see if this should be restructured for
6545 // greater efficiency.
6546 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6547 // convert offset into a HeapWord*
6548 HeapWord* addr = _verification_bm->startWord() + offset;
6549 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6550 "address out of range");
6551 assert(_verification_bm->isMarked(addr), "tautology");
6552 assert(_cms_bm->isMarked(addr), "tautology");
6553
6554 assert(_mark_stack->isEmpty(),
6555 "should drain stack to limit stack usage");
6556 // convert addr to an oop preparatory to scanning
6557 oop obj = oop(addr);
6558 assert(oopDesc::is_oop(obj), "should be an oop");
6559 assert(_finger <= addr, "_finger runneth ahead");
6560 // advance the finger to right end of this object
6561 _finger = addr + obj->size();
6562 assert(_finger > addr, "we just incremented it above");
6563 // Note: the finger doesn't advance while we drain
6564 // the stack below.
6565 bool res = _mark_stack->push(obj);
6566 assert(res, "Empty non-zero size stack should have space for single push");
6567 while (!_mark_stack->isEmpty()) {
6568 oop new_oop = _mark_stack->pop();
6569 assert(oopDesc::is_oop(new_oop), "Oops! expected to pop an oop");
6570 // now scan this oop's oops
6571 new_oop->oop_iterate(&_pam_verify_closure);
6572 }
6573 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6574 return true;
6575 }
6576
6577 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6578 CMSCollector* collector, MemRegion span,
6579 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6580 CMSMarkStack* mark_stack):
6581 MetadataVisitingOopIterateClosure(collector->ref_processor()),
6582 _collector(collector),
6583 _span(span),
6584 _verification_bm(verification_bm),
6585 _cms_bm(cms_bm),
6586 _mark_stack(mark_stack)
6587 { }
6588
6589 template <class T> void PushAndMarkVerifyClosure::do_oop_work(T *p) {
6590 oop obj = RawAccess<>::oop_load(p);
6591 do_oop(obj);
6592 }
6593
6594 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6595 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6596
6597 // Upon stack overflow, we discard (part of) the stack,
6598 // remembering the least address amongst those discarded
6599 // in CMSCollector's _restart_address.
6600 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6601 // Remember the least grey address discarded
6602 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6603 _collector->lower_restart_addr(ra);
6604 _mark_stack->reset(); // discard stack contents
6605 _mark_stack->expand(); // expand the stack if possible
6606 }
6607
6608 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6609 assert(oopDesc::is_oop_or_null(obj), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6610 HeapWord* addr = (HeapWord*)obj;
6611 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6612 // Oop lies in _span and isn't yet grey or black
6613 _verification_bm->mark(addr); // now grey
6614 if (!_cms_bm->isMarked(addr)) {
6615 Log(gc, verify) log;
6616 ResourceMark rm;
6617 LogStream ls(log.error());
6618 oop(addr)->print_on(&ls);
6619 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6620 fatal("... aborting");
6621 }
6622
6623 if (!_mark_stack->push(obj)) { // stack overflow
6624 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6625 assert(_mark_stack->isFull(), "Else push should have succeeded");
6626 handle_stack_overflow(addr);
6627 }
6628 // anything including and to the right of _finger
6629 // will be scanned as we iterate over the remainder of the
6630 // bit map
6631 }
6632 }
6633
6634 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6635 MemRegion span,
6636 CMSBitMap* bitMap, CMSMarkStack* markStack,
6637 HeapWord* finger, MarkFromRootsClosure* parent) :
6638 MetadataVisitingOopIterateClosure(collector->ref_processor()),
6639 _collector(collector),
6640 _span(span),
6641 _bitMap(bitMap),
6642 _markStack(markStack),
6643 _finger(finger),
6644 _parent(parent)
6645 { }
6646
6647 ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector,
6648 MemRegion span,
6649 CMSBitMap* bit_map,
6650 OopTaskQueue* work_queue,
6651 CMSMarkStack* overflow_stack,
6652 HeapWord* finger,
6653 HeapWord* volatile* global_finger_addr,
6654 ParMarkFromRootsClosure* parent) :
6655 MetadataVisitingOopIterateClosure(collector->ref_processor()),
6656 _collector(collector),
6657 _whole_span(collector->_span),
6658 _span(span),
6659 _bit_map(bit_map),
6660 _work_queue(work_queue),
6661 _overflow_stack(overflow_stack),
6662 _finger(finger),
6663 _global_finger_addr(global_finger_addr),
6664 _parent(parent)
6665 { }
6666
6667 // Assumes thread-safe access by callers, who are
6668 // responsible for mutual exclusion.
6669 void CMSCollector::lower_restart_addr(HeapWord* low) {
6670 assert(_span.contains(low), "Out of bounds addr");
6671 if (_restart_addr == NULL) {
6672 _restart_addr = low;
6673 } else {
6674 _restart_addr = MIN2(_restart_addr, low);
6675 }
6676 }
6677
6678 // Upon stack overflow, we discard (part of) the stack,
6679 // remembering the least address amongst those discarded
6680 // in CMSCollector's _restart_address.
6681 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6682 // Remember the least grey address discarded
6683 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6684 _collector->lower_restart_addr(ra);
6685 _markStack->reset(); // discard stack contents
6686 _markStack->expand(); // expand the stack if possible
6687 }
6688
6689 // Upon stack overflow, we discard (part of) the stack,
6690 // remembering the least address amongst those discarded
6691 // in CMSCollector's _restart_address.
6692 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6693 // We need to do this under a mutex to prevent other
6694 // workers from interfering with the work done below.
6695 MutexLockerEx ml(_overflow_stack->par_lock(),
6696 Mutex::_no_safepoint_check_flag);
6697 // Remember the least grey address discarded
6698 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6699 _collector->lower_restart_addr(ra);
6700 _overflow_stack->reset(); // discard stack contents
6701 _overflow_stack->expand(); // expand the stack if possible
6702 }
6703
6704 void PushOrMarkClosure::do_oop(oop obj) {
6705 // Ignore mark word because we are running concurrent with mutators.
6706 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6707 HeapWord* addr = (HeapWord*)obj;
6708 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6709 // Oop lies in _span and isn't yet grey or black
6710 _bitMap->mark(addr); // now grey
6711 if (addr < _finger) {
6712 // the bit map iteration has already either passed, or
6713 // sampled, this bit in the bit map; we'll need to
6714 // use the marking stack to scan this oop's oops.
6715 bool simulate_overflow = false;
6716 NOT_PRODUCT(
6717 if (CMSMarkStackOverflowALot &&
6718 _collector->simulate_overflow()) {
6719 // simulate a stack overflow
6720 simulate_overflow = true;
6721 }
6722 )
6723 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6724 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6725 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6726 handle_stack_overflow(addr);
6727 }
6728 }
6729 // anything including and to the right of _finger
6730 // will be scanned as we iterate over the remainder of the
6731 // bit map
6732 do_yield_check();
6733 }
6734 }
6735
6736 void ParPushOrMarkClosure::do_oop(oop obj) {
6737 // Ignore mark word because we are running concurrent with mutators.
6738 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6739 HeapWord* addr = (HeapWord*)obj;
6740 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6741 // Oop lies in _span and isn't yet grey or black
6742 // We read the global_finger (volatile read) strictly after marking oop
6743 bool res = _bit_map->par_mark(addr); // now grey
6744 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6745 // Should we push this marked oop on our stack?
6746 // -- if someone else marked it, nothing to do
6747 // -- if target oop is above global finger nothing to do
6748 // -- if target oop is in chunk and above local finger
6749 // then nothing to do
6750 // -- else push on work queue
6751 if ( !res // someone else marked it, they will deal with it
6752 || (addr >= *gfa) // will be scanned in a later task
6753 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6754 return;
6755 }
6756 // the bit map iteration has already either passed, or
6757 // sampled, this bit in the bit map; we'll need to
6758 // use the marking stack to scan this oop's oops.
6759 bool simulate_overflow = false;
6760 NOT_PRODUCT(
6761 if (CMSMarkStackOverflowALot &&
6762 _collector->simulate_overflow()) {
6763 // simulate a stack overflow
6764 simulate_overflow = true;
6765 }
6766 )
6767 if (simulate_overflow ||
6768 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6769 // stack overflow
6770 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6771 // We cannot assert that the overflow stack is full because
6772 // it may have been emptied since.
6773 assert(simulate_overflow ||
6774 _work_queue->size() == _work_queue->max_elems(),
6775 "Else push should have succeeded");
6776 handle_stack_overflow(addr);
6777 }
6778 do_yield_check();
6779 }
6780 }
6781
6782 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6783 MemRegion span,
6784 ReferenceDiscoverer* rd,
6785 CMSBitMap* bit_map,
6786 CMSBitMap* mod_union_table,
6787 CMSMarkStack* mark_stack,
6788 bool concurrent_precleaning):
6789 MetadataVisitingOopIterateClosure(rd),
6790 _collector(collector),
6791 _span(span),
6792 _bit_map(bit_map),
6793 _mod_union_table(mod_union_table),
6794 _mark_stack(mark_stack),
6795 _concurrent_precleaning(concurrent_precleaning)
6796 {
6797 assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL");
6798 }
6799
6800 // Grey object rescan during pre-cleaning and second checkpoint phases --
6801 // the non-parallel version (the parallel version appears further below.)
6802 void PushAndMarkClosure::do_oop(oop obj) {
6803 // Ignore mark word verification. If during concurrent precleaning,
6804 // the object monitor may be locked. If during the checkpoint
6805 // phases, the object may already have been reached by a different
6806 // path and may be at the end of the global overflow list (so
6807 // the mark word may be NULL).
6808 assert(oopDesc::is_oop_or_null(obj, true /* ignore mark word */),
6809 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6810 HeapWord* addr = (HeapWord*)obj;
6811 // Check if oop points into the CMS generation
6812 // and is not marked
6813 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6814 // a white object ...
6815 _bit_map->mark(addr); // ... now grey
6816 // push on the marking stack (grey set)
6817 bool simulate_overflow = false;
6818 NOT_PRODUCT(
6819 if (CMSMarkStackOverflowALot &&
6820 _collector->simulate_overflow()) {
6821 // simulate a stack overflow
6822 simulate_overflow = true;
6823 }
6824 )
6825 if (simulate_overflow || !_mark_stack->push(obj)) {
6826 if (_concurrent_precleaning) {
6827 // During precleaning we can just dirty the appropriate card(s)
6828 // in the mod union table, thus ensuring that the object remains
6829 // in the grey set and continue. In the case of object arrays
6830 // we need to dirty all of the cards that the object spans,
6831 // since the rescan of object arrays will be limited to the
6832 // dirty cards.
6833 // Note that no one can be interfering with us in this action
6834 // of dirtying the mod union table, so no locking or atomics
6835 // are required.
6836 if (obj->is_objArray()) {
6837 size_t sz = obj->size();
6838 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
6839 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6840 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6841 _mod_union_table->mark_range(redirty_range);
6842 } else {
6843 _mod_union_table->mark(addr);
6844 }
6845 _collector->_ser_pmc_preclean_ovflw++;
6846 } else {
6847 // During the remark phase, we need to remember this oop
6848 // in the overflow list.
6849 _collector->push_on_overflow_list(obj);
6850 _collector->_ser_pmc_remark_ovflw++;
6851 }
6852 }
6853 }
6854 }
6855
6856 ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector,
6857 MemRegion span,
6858 ReferenceDiscoverer* rd,
6859 CMSBitMap* bit_map,
6860 OopTaskQueue* work_queue):
6861 MetadataVisitingOopIterateClosure(rd),
6862 _collector(collector),
6863 _span(span),
6864 _bit_map(bit_map),
6865 _work_queue(work_queue)
6866 {
6867 assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL");
6868 }
6869
6870 // Grey object rescan during second checkpoint phase --
6871 // the parallel version.
6872 void ParPushAndMarkClosure::do_oop(oop obj) {
6873 // In the assert below, we ignore the mark word because
6874 // this oop may point to an already visited object that is
6875 // on the overflow stack (in which case the mark word has
6876 // been hijacked for chaining into the overflow stack --
6877 // if this is the last object in the overflow stack then
6878 // its mark word will be NULL). Because this object may
6879 // have been subsequently popped off the global overflow
6880 // stack, and the mark word possibly restored to the prototypical
6881 // value, by the time we get to examined this failing assert in
6882 // the debugger, is_oop_or_null(false) may subsequently start
6883 // to hold.
6884 assert(oopDesc::is_oop_or_null(obj, true),
6885 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6886 HeapWord* addr = (HeapWord*)obj;
6887 // Check if oop points into the CMS generation
6888 // and is not marked
6889 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6890 // a white object ...
6891 // If we manage to "claim" the object, by being the
6892 // first thread to mark it, then we push it on our
6893 // marking stack
6894 if (_bit_map->par_mark(addr)) { // ... now grey
6895 // push on work queue (grey set)
6896 bool simulate_overflow = false;
6897 NOT_PRODUCT(
6898 if (CMSMarkStackOverflowALot &&
6899 _collector->par_simulate_overflow()) {
6900 // simulate a stack overflow
6901 simulate_overflow = true;
6902 }
6903 )
6904 if (simulate_overflow || !_work_queue->push(obj)) {
6905 _collector->par_push_on_overflow_list(obj);
6906 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
6907 }
6908 } // Else, some other thread got there first
6909 }
6910 }
6911
6912 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6913 Mutex* bml = _collector->bitMapLock();
6914 assert_lock_strong(bml);
6915 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6916 "CMS thread should hold CMS token");
6917
6918 bml->unlock();
6919 ConcurrentMarkSweepThread::desynchronize(true);
6920
6921 _collector->stopTimer();
6922 _collector->incrementYields();
6923
6924 // See the comment in coordinator_yield()
6925 for (unsigned i = 0; i < CMSYieldSleepCount &&
6926 ConcurrentMarkSweepThread::should_yield() &&
6927 !CMSCollector::foregroundGCIsActive(); ++i) {
6928 os::sleep(Thread::current(), 1, false);
6929 }
6930
6931 ConcurrentMarkSweepThread::synchronize(true);
6932 bml->lock();
6933
6934 _collector->startTimer();
6935 }
6936
6937 bool CMSPrecleanRefsYieldClosure::should_return() {
6938 if (ConcurrentMarkSweepThread::should_yield()) {
6939 do_yield_work();
6940 }
6941 return _collector->foregroundGCIsActive();
6942 }
6943
6944 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
6945 assert(((size_t)mr.start())%CardTable::card_size_in_words == 0,
6946 "mr should be aligned to start at a card boundary");
6947 // We'd like to assert:
6948 // assert(mr.word_size()%CardTable::card_size_in_words == 0,
6949 // "mr should be a range of cards");
6950 // However, that would be too strong in one case -- the last
6951 // partition ends at _unallocated_block which, in general, can be
6952 // an arbitrary boundary, not necessarily card aligned.
6953 _num_dirty_cards += mr.word_size()/CardTable::card_size_in_words;
6954 _space->object_iterate_mem(mr, &_scan_cl);
6955 }
6956
6957 SweepClosure::SweepClosure(CMSCollector* collector,
6958 ConcurrentMarkSweepGeneration* g,
6959 CMSBitMap* bitMap, bool should_yield) :
6960 _collector(collector),
6961 _g(g),
6962 _sp(g->cmsSpace()),
6963 _limit(_sp->sweep_limit()),
6964 _freelistLock(_sp->freelistLock()),
6965 _bitMap(bitMap),
6966 _inFreeRange(false), // No free range at beginning of sweep
6967 _freeRangeInFreeLists(false), // No free range at beginning of sweep
6968 _lastFreeRangeCoalesced(false),
6969 _yield(should_yield),
6970 _freeFinger(g->used_region().start())
6971 {
6972 NOT_PRODUCT(
6973 _numObjectsFreed = 0;
6974 _numWordsFreed = 0;
6975 _numObjectsLive = 0;
6976 _numWordsLive = 0;
6977 _numObjectsAlreadyFree = 0;
6978 _numWordsAlreadyFree = 0;
6979 _last_fc = NULL;
6980
6981 _sp->initializeIndexedFreeListArrayReturnedBytes();
6982 _sp->dictionary()->initialize_dict_returned_bytes();
6983 )
6984 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
6985 "sweep _limit out of bounds");
6986 log_develop_trace(gc, sweep)("====================");
6987 log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
6988 }
6989
6990 void SweepClosure::print_on(outputStream* st) const {
6991 st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
6992 p2i(_sp->bottom()), p2i(_sp->end()));
6993 st->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
6994 st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
6995 NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
6996 st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
6997 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
6998 }
6999
7000 #ifndef PRODUCT
7001 // Assertion checking only: no useful work in product mode --
7002 // however, if any of the flags below become product flags,
7003 // you may need to review this code to see if it needs to be
7004 // enabled in product mode.
7005 SweepClosure::~SweepClosure() {
7006 assert_lock_strong(_freelistLock);
7007 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7008 "sweep _limit out of bounds");
7009 if (inFreeRange()) {
7010 Log(gc, sweep) log;
7011 log.error("inFreeRange() should have been reset; dumping state of SweepClosure");
7012 ResourceMark rm;
7013 LogStream ls(log.error());
7014 print_on(&ls);
7015 ShouldNotReachHere();
7016 }
7017
7018 if (log_is_enabled(Debug, gc, sweep)) {
7019 log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7020 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7021 log_debug(gc, sweep)("Live " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7022 _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7023 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7024 log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7025 }
7026
7027 if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) {
7028 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7029 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7030 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7031 log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes Indexed List Returned " SIZE_FORMAT " bytes Dictionary Returned " SIZE_FORMAT " bytes",
7032 returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7033 }
7034 log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7035 log_develop_trace(gc, sweep)("================");
7036 }
7037 #endif // PRODUCT
7038
7039 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7040 bool freeRangeInFreeLists) {
7041 log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7042 p2i(freeFinger), freeRangeInFreeLists);
7043 assert(!inFreeRange(), "Trampling existing free range");
7044 set_inFreeRange(true);
7045 set_lastFreeRangeCoalesced(false);
7046
7047 set_freeFinger(freeFinger);
7048 set_freeRangeInFreeLists(freeRangeInFreeLists);
7049 if (CMSTestInFreeList) {
7050 if (freeRangeInFreeLists) {
7051 FreeChunk* fc = (FreeChunk*) freeFinger;
7052 assert(fc->is_free(), "A chunk on the free list should be free.");
7053 assert(fc->size() > 0, "Free range should have a size");
7054 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7055 }
7056 }
7057 }
7058
7059 // Note that the sweeper runs concurrently with mutators. Thus,
7060 // it is possible for direct allocation in this generation to happen
7061 // in the middle of the sweep. Note that the sweeper also coalesces
7062 // contiguous free blocks. Thus, unless the sweeper and the allocator
7063 // synchronize appropriately freshly allocated blocks may get swept up.
7064 // This is accomplished by the sweeper locking the free lists while
7065 // it is sweeping. Thus blocks that are determined to be free are
7066 // indeed free. There is however one additional complication:
7067 // blocks that have been allocated since the final checkpoint and
7068 // mark, will not have been marked and so would be treated as
7069 // unreachable and swept up. To prevent this, the allocator marks
7070 // the bit map when allocating during the sweep phase. This leads,
7071 // however, to a further complication -- objects may have been allocated
7072 // but not yet initialized -- in the sense that the header isn't yet
7073 // installed. The sweeper can not then determine the size of the block
7074 // in order to skip over it. To deal with this case, we use a technique
7075 // (due to Printezis) to encode such uninitialized block sizes in the
7076 // bit map. Since the bit map uses a bit per every HeapWord, but the
7077 // CMS generation has a minimum object size of 3 HeapWords, it follows
7078 // that "normal marks" won't be adjacent in the bit map (there will
7079 // always be at least two 0 bits between successive 1 bits). We make use
7080 // of these "unused" bits to represent uninitialized blocks -- the bit
7081 // corresponding to the start of the uninitialized object and the next
7082 // bit are both set. Finally, a 1 bit marks the end of the object that
7083 // started with the two consecutive 1 bits to indicate its potentially
7084 // uninitialized state.
7085
7086 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7087 FreeChunk* fc = (FreeChunk*)addr;
7088 size_t res;
7089
7090 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7091 // than "addr == _limit" because although _limit was a block boundary when
7092 // we started the sweep, it may no longer be one because heap expansion
7093 // may have caused us to coalesce the block ending at the address _limit
7094 // with a newly expanded chunk (this happens when _limit was set to the
7095 // previous _end of the space), so we may have stepped past _limit:
7096 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7097 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7098 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7099 "sweep _limit out of bounds");
7100 assert(addr < _sp->end(), "addr out of bounds");
7101 // Flush any free range we might be holding as a single
7102 // coalesced chunk to the appropriate free list.
7103 if (inFreeRange()) {
7104 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7105 "freeFinger() " PTR_FORMAT " is out of bounds", p2i(freeFinger()));
7106 flush_cur_free_chunk(freeFinger(),
7107 pointer_delta(addr, freeFinger()));
7108 log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7109 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7110 lastFreeRangeCoalesced() ? 1 : 0);
7111 }
7112
7113 // help the iterator loop finish
7114 return pointer_delta(_sp->end(), addr);
7115 }
7116
7117 assert(addr < _limit, "sweep invariant");
7118 // check if we should yield
7119 do_yield_check(addr);
7120 if (fc->is_free()) {
7121 // Chunk that is already free
7122 res = fc->size();
7123 do_already_free_chunk(fc);
7124 debug_only(_sp->verifyFreeLists());
7125 // If we flush the chunk at hand in lookahead_and_flush()
7126 // and it's coalesced with a preceding chunk, then the
7127 // process of "mangling" the payload of the coalesced block
7128 // will cause erasure of the size information from the
7129 // (erstwhile) header of all the coalesced blocks but the
7130 // first, so the first disjunct in the assert will not hold
7131 // in that specific case (in which case the second disjunct
7132 // will hold).
7133 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7134 "Otherwise the size info doesn't change at this step");
7135 NOT_PRODUCT(
7136 _numObjectsAlreadyFree++;
7137 _numWordsAlreadyFree += res;
7138 )
7139 NOT_PRODUCT(_last_fc = fc;)
7140 } else if (!_bitMap->isMarked(addr)) {
7141 // Chunk is fresh garbage
7142 res = do_garbage_chunk(fc);
7143 debug_only(_sp->verifyFreeLists());
7144 NOT_PRODUCT(
7145 _numObjectsFreed++;
7146 _numWordsFreed += res;
7147 )
7148 } else {
7149 // Chunk that is alive.
7150 res = do_live_chunk(fc);
7151 debug_only(_sp->verifyFreeLists());
7152 NOT_PRODUCT(
7153 _numObjectsLive++;
7154 _numWordsLive += res;
7155 )
7156 }
7157 return res;
7158 }
7159
7160 // For the smart allocation, record following
7161 // split deaths - a free chunk is removed from its free list because
7162 // it is being split into two or more chunks.
7163 // split birth - a free chunk is being added to its free list because
7164 // a larger free chunk has been split and resulted in this free chunk.
7165 // coal death - a free chunk is being removed from its free list because
7166 // it is being coalesced into a large free chunk.
7167 // coal birth - a free chunk is being added to its free list because
7168 // it was created when two or more free chunks where coalesced into
7169 // this free chunk.
7170 //
7171 // These statistics are used to determine the desired number of free
7172 // chunks of a given size. The desired number is chosen to be relative
7173 // to the end of a CMS sweep. The desired number at the end of a sweep
7174 // is the
7175 // count-at-end-of-previous-sweep (an amount that was enough)
7176 // - count-at-beginning-of-current-sweep (the excess)
7177 // + split-births (gains in this size during interval)
7178 // - split-deaths (demands on this size during interval)
7179 // where the interval is from the end of one sweep to the end of the
7180 // next.
7181 //
7182 // When sweeping the sweeper maintains an accumulated chunk which is
7183 // the chunk that is made up of chunks that have been coalesced. That
7184 // will be termed the left-hand chunk. A new chunk of garbage that
7185 // is being considered for coalescing will be referred to as the
7186 // right-hand chunk.
7187 //
7188 // When making a decision on whether to coalesce a right-hand chunk with
7189 // the current left-hand chunk, the current count vs. the desired count
7190 // of the left-hand chunk is considered. Also if the right-hand chunk
7191 // is near the large chunk at the end of the heap (see
7192 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7193 // left-hand chunk is coalesced.
7194 //
7195 // When making a decision about whether to split a chunk, the desired count
7196 // vs. the current count of the candidate to be split is also considered.
7197 // If the candidate is underpopulated (currently fewer chunks than desired)
7198 // a chunk of an overpopulated (currently more chunks than desired) size may
7199 // be chosen. The "hint" associated with a free list, if non-null, points
7200 // to a free list which may be overpopulated.
7201 //
7202
7203 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7204 const size_t size = fc->size();
7205 // Chunks that cannot be coalesced are not in the
7206 // free lists.
7207 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7208 assert(_sp->verify_chunk_in_free_list(fc),
7209 "free chunk should be in free lists");
7210 }
7211 // a chunk that is already free, should not have been
7212 // marked in the bit map
7213 HeapWord* const addr = (HeapWord*) fc;
7214 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7215 // Verify that the bit map has no bits marked between
7216 // addr and purported end of this block.
7217 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7218
7219 // Some chunks cannot be coalesced under any circumstances.
7220 // See the definition of cantCoalesce().
7221 if (!fc->cantCoalesce()) {
7222 // This chunk can potentially be coalesced.
7223 // All the work is done in
7224 do_post_free_or_garbage_chunk(fc, size);
7225 // Note that if the chunk is not coalescable (the else arm
7226 // below), we unconditionally flush, without needing to do
7227 // a "lookahead," as we do below.
7228 if (inFreeRange()) lookahead_and_flush(fc, size);
7229 } else {
7230 // Code path common to both original and adaptive free lists.
7231
7232 // cant coalesce with previous block; this should be treated
7233 // as the end of a free run if any
7234 if (inFreeRange()) {
7235 // we kicked some butt; time to pick up the garbage
7236 assert(freeFinger() < addr, "freeFinger points too high");
7237 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7238 }
7239 // else, nothing to do, just continue
7240 }
7241 }
7242
7243 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7244 // This is a chunk of garbage. It is not in any free list.
7245 // Add it to a free list or let it possibly be coalesced into
7246 // a larger chunk.
7247 HeapWord* const addr = (HeapWord*) fc;
7248 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7249
7250 // Verify that the bit map has no bits marked between
7251 // addr and purported end of just dead object.
7252 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7253 do_post_free_or_garbage_chunk(fc, size);
7254
7255 assert(_limit >= addr + size,
7256 "A freshly garbage chunk can't possibly straddle over _limit");
7257 if (inFreeRange()) lookahead_and_flush(fc, size);
7258 return size;
7259 }
7260
7261 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7262 HeapWord* addr = (HeapWord*) fc;
7263 // The sweeper has just found a live object. Return any accumulated
7264 // left hand chunk to the free lists.
7265 if (inFreeRange()) {
7266 assert(freeFinger() < addr, "freeFinger points too high");
7267 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7268 }
7269
7270 // This object is live: we'd normally expect this to be
7271 // an oop, and like to assert the following:
7272 // assert(oopDesc::is_oop(oop(addr)), "live block should be an oop");
7273 // However, as we commented above, this may be an object whose
7274 // header hasn't yet been initialized.
7275 size_t size;
7276 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7277 if (_bitMap->isMarked(addr + 1)) {
7278 // Determine the size from the bit map, rather than trying to
7279 // compute it from the object header.
7280 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7281 size = pointer_delta(nextOneAddr + 1, addr);
7282 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7283 "alignment problem");
7284
7285 #ifdef ASSERT
7286 if (oop(addr)->klass_or_null_acquire() != NULL) {
7287 // Ignore mark word because we are running concurrent with mutators
7288 assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7289 assert(size ==
7290 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7291 "P-mark and computed size do not agree");
7292 }
7293 #endif
7294
7295 } else {
7296 // This should be an initialized object that's alive.
7297 assert(oop(addr)->klass_or_null_acquire() != NULL,
7298 "Should be an initialized object");
7299 // Ignore mark word because we are running concurrent with mutators
7300 assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7301 // Verify that the bit map has no bits marked between
7302 // addr and purported end of this block.
7303 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7304 assert(size >= 3, "Necessary for Printezis marks to work");
7305 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7306 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7307 }
7308 return size;
7309 }
7310
7311 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7312 size_t chunkSize) {
7313 // do_post_free_or_garbage_chunk() should only be called in the case
7314 // of the adaptive free list allocator.
7315 const bool fcInFreeLists = fc->is_free();
7316 assert((HeapWord*)fc <= _limit, "sweep invariant");
7317 if (CMSTestInFreeList && fcInFreeLists) {
7318 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7319 }
7320
7321 log_develop_trace(gc, sweep)(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7322
7323 HeapWord* const fc_addr = (HeapWord*) fc;
7324
7325 bool coalesce = false;
7326 const size_t left = pointer_delta(fc_addr, freeFinger());
7327 const size_t right = chunkSize;
7328 switch (FLSCoalescePolicy) {
7329 // numeric value forms a coalition aggressiveness metric
7330 case 0: { // never coalesce
7331 coalesce = false;
7332 break;
7333 }
7334 case 1: { // coalesce if left & right chunks on overpopulated lists
7335 coalesce = _sp->coalOverPopulated(left) &&
7336 _sp->coalOverPopulated(right);
7337 break;
7338 }
7339 case 2: { // coalesce if left chunk on overpopulated list (default)
7340 coalesce = _sp->coalOverPopulated(left);
7341 break;
7342 }
7343 case 3: { // coalesce if left OR right chunk on overpopulated list
7344 coalesce = _sp->coalOverPopulated(left) ||
7345 _sp->coalOverPopulated(right);
7346 break;
7347 }
7348 case 4: { // always coalesce
7349 coalesce = true;
7350 break;
7351 }
7352 default:
7353 ShouldNotReachHere();
7354 }
7355
7356 // Should the current free range be coalesced?
7357 // If the chunk is in a free range and either we decided to coalesce above
7358 // or the chunk is near the large block at the end of the heap
7359 // (isNearLargestChunk() returns true), then coalesce this chunk.
7360 const bool doCoalesce = inFreeRange()
7361 && (coalesce || _g->isNearLargestChunk(fc_addr));
7362 if (doCoalesce) {
7363 // Coalesce the current free range on the left with the new
7364 // chunk on the right. If either is on a free list,
7365 // it must be removed from the list and stashed in the closure.
7366 if (freeRangeInFreeLists()) {
7367 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7368 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7369 "Size of free range is inconsistent with chunk size.");
7370 if (CMSTestInFreeList) {
7371 assert(_sp->verify_chunk_in_free_list(ffc),
7372 "Chunk is not in free lists");
7373 }
7374 _sp->coalDeath(ffc->size());
7375 _sp->removeFreeChunkFromFreeLists(ffc);
7376 set_freeRangeInFreeLists(false);
7377 }
7378 if (fcInFreeLists) {
7379 _sp->coalDeath(chunkSize);
7380 assert(fc->size() == chunkSize,
7381 "The chunk has the wrong size or is not in the free lists");
7382 _sp->removeFreeChunkFromFreeLists(fc);
7383 }
7384 set_lastFreeRangeCoalesced(true);
7385 print_free_block_coalesced(fc);
7386 } else { // not in a free range and/or should not coalesce
7387 // Return the current free range and start a new one.
7388 if (inFreeRange()) {
7389 // In a free range but cannot coalesce with the right hand chunk.
7390 // Put the current free range into the free lists.
7391 flush_cur_free_chunk(freeFinger(),
7392 pointer_delta(fc_addr, freeFinger()));
7393 }
7394 // Set up for new free range. Pass along whether the right hand
7395 // chunk is in the free lists.
7396 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7397 }
7398 }
7399
7400 // Lookahead flush:
7401 // If we are tracking a free range, and this is the last chunk that
7402 // we'll look at because its end crosses past _limit, we'll preemptively
7403 // flush it along with any free range we may be holding on to. Note that
7404 // this can be the case only for an already free or freshly garbage
7405 // chunk. If this block is an object, it can never straddle
7406 // over _limit. The "straddling" occurs when _limit is set at
7407 // the previous end of the space when this cycle started, and
7408 // a subsequent heap expansion caused the previously co-terminal
7409 // free block to be coalesced with the newly expanded portion,
7410 // thus rendering _limit a non-block-boundary making it dangerous
7411 // for the sweeper to step over and examine.
7412 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7413 assert(inFreeRange(), "Should only be called if currently in a free range.");
7414 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7415 assert(_sp->used_region().contains(eob - 1),
7416 "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7417 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7418 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7419 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7420 if (eob >= _limit) {
7421 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7422 log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7423 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7424 "[" PTR_FORMAT "," PTR_FORMAT ")",
7425 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7426 // Return the storage we are tracking back into the free lists.
7427 log_develop_trace(gc, sweep)("Flushing ... ");
7428 assert(freeFinger() < eob, "Error");
7429 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7430 }
7431 }
7432
7433 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7434 assert(inFreeRange(), "Should only be called if currently in a free range.");
7435 assert(size > 0,
7436 "A zero sized chunk cannot be added to the free lists.");
7437 if (!freeRangeInFreeLists()) {
7438 if (CMSTestInFreeList) {
7439 FreeChunk* fc = (FreeChunk*) chunk;
7440 fc->set_size(size);
7441 assert(!_sp->verify_chunk_in_free_list(fc),
7442 "chunk should not be in free lists yet");
7443 }
7444 log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size);
7445 // A new free range is going to be starting. The current
7446 // free range has not been added to the free lists yet or
7447 // was removed so add it back.
7448 // If the current free range was coalesced, then the death
7449 // of the free range was recorded. Record a birth now.
7450 if (lastFreeRangeCoalesced()) {
7451 _sp->coalBirth(size);
7452 }
7453 _sp->addChunkAndRepairOffsetTable(chunk, size,
7454 lastFreeRangeCoalesced());
7455 } else {
7456 log_develop_trace(gc, sweep)("Already in free list: nothing to flush");
7457 }
7458 set_inFreeRange(false);
7459 set_freeRangeInFreeLists(false);
7460 }
7461
7462 // We take a break if we've been at this for a while,
7463 // so as to avoid monopolizing the locks involved.
7464 void SweepClosure::do_yield_work(HeapWord* addr) {
7465 // Return current free chunk being used for coalescing (if any)
7466 // to the appropriate freelist. After yielding, the next
7467 // free block encountered will start a coalescing range of
7468 // free blocks. If the next free block is adjacent to the
7469 // chunk just flushed, they will need to wait for the next
7470 // sweep to be coalesced.
7471 if (inFreeRange()) {
7472 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7473 }
7474
7475 // First give up the locks, then yield, then re-lock.
7476 // We should probably use a constructor/destructor idiom to
7477 // do this unlock/lock or modify the MutexUnlocker class to
7478 // serve our purpose. XXX
7479 assert_lock_strong(_bitMap->lock());
7480 assert_lock_strong(_freelistLock);
7481 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7482 "CMS thread should hold CMS token");
7483 _bitMap->lock()->unlock();
7484 _freelistLock->unlock();
7485 ConcurrentMarkSweepThread::desynchronize(true);
7486 _collector->stopTimer();
7487 _collector->incrementYields();
7488
7489 // See the comment in coordinator_yield()
7490 for (unsigned i = 0; i < CMSYieldSleepCount &&
7491 ConcurrentMarkSweepThread::should_yield() &&
7492 !CMSCollector::foregroundGCIsActive(); ++i) {
7493 os::sleep(Thread::current(), 1, false);
7494 }
7495
7496 ConcurrentMarkSweepThread::synchronize(true);
7497 _freelistLock->lock();
7498 _bitMap->lock()->lock_without_safepoint_check();
7499 _collector->startTimer();
7500 }
7501
7502 #ifndef PRODUCT
7503 // This is actually very useful in a product build if it can
7504 // be called from the debugger. Compile it into the product
7505 // as needed.
7506 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7507 return debug_cms_space->verify_chunk_in_free_list(fc);
7508 }
7509 #endif
7510
7511 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7512 log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7513 p2i(fc), fc->size());
7514 }
7515
7516 // CMSIsAliveClosure
7517 bool CMSIsAliveClosure::do_object_b(oop obj) {
7518 HeapWord* addr = (HeapWord*)obj;
7519 return addr != NULL &&
7520 (!_span.contains(addr) || _bit_map->isMarked(addr));
7521 }
7522
7523 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7524 MemRegion span,
7525 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7526 bool cpc):
7527 _collector(collector),
7528 _span(span),
7529 _mark_stack(mark_stack),
7530 _bit_map(bit_map),
7531 _concurrent_precleaning(cpc) {
7532 assert(!_span.is_empty(), "Empty span could spell trouble");
7533 }
7534
7535
7536 // CMSKeepAliveClosure: the serial version
7537 void CMSKeepAliveClosure::do_oop(oop obj) {
7538 HeapWord* addr = (HeapWord*)obj;
7539 if (_span.contains(addr) &&
7540 !_bit_map->isMarked(addr)) {
7541 _bit_map->mark(addr);
7542 bool simulate_overflow = false;
7543 NOT_PRODUCT(
7544 if (CMSMarkStackOverflowALot &&
7545 _collector->simulate_overflow()) {
7546 // simulate a stack overflow
7547 simulate_overflow = true;
7548 }
7549 )
7550 if (simulate_overflow || !_mark_stack->push(obj)) {
7551 if (_concurrent_precleaning) {
7552 // We dirty the overflown object and let the remark
7553 // phase deal with it.
7554 assert(_collector->overflow_list_is_empty(), "Error");
7555 // In the case of object arrays, we need to dirty all of
7556 // the cards that the object spans. No locking or atomics
7557 // are needed since no one else can be mutating the mod union
7558 // table.
7559 if (obj->is_objArray()) {
7560 size_t sz = obj->size();
7561 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
7562 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7563 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7564 _collector->_modUnionTable.mark_range(redirty_range);
7565 } else {
7566 _collector->_modUnionTable.mark(addr);
7567 }
7568 _collector->_ser_kac_preclean_ovflw++;
7569 } else {
7570 _collector->push_on_overflow_list(obj);
7571 _collector->_ser_kac_ovflw++;
7572 }
7573 }
7574 }
7575 }
7576
7577 // CMSParKeepAliveClosure: a parallel version of the above.
7578 // The work queues are private to each closure (thread),
7579 // but (may be) available for stealing by other threads.
7580 void CMSParKeepAliveClosure::do_oop(oop obj) {
7581 HeapWord* addr = (HeapWord*)obj;
7582 if (_span.contains(addr) &&
7583 !_bit_map->isMarked(addr)) {
7584 // In general, during recursive tracing, several threads
7585 // may be concurrently getting here; the first one to
7586 // "tag" it, claims it.
7587 if (_bit_map->par_mark(addr)) {
7588 bool res = _work_queue->push(obj);
7589 assert(res, "Low water mark should be much less than capacity");
7590 // Do a recursive trim in the hope that this will keep
7591 // stack usage lower, but leave some oops for potential stealers
7592 trim_queue(_low_water_mark);
7593 } // Else, another thread got there first
7594 }
7595 }
7596
7597 void CMSParKeepAliveClosure::trim_queue(uint max) {
7598 while (_work_queue->size() > max) {
7599 oop new_oop;
7600 if (_work_queue->pop_local(new_oop)) {
7601 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
7602 assert(_bit_map->isMarked((HeapWord*)new_oop),
7603 "no white objects on this stack!");
7604 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7605 // iterate over the oops in this oop, marking and pushing
7606 // the ones in CMS heap (i.e. in _span).
7607 new_oop->oop_iterate(&_mark_and_push);
7608 }
7609 }
7610 }
7611
7612 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7613 CMSCollector* collector,
7614 MemRegion span, CMSBitMap* bit_map,
7615 OopTaskQueue* work_queue):
7616 _collector(collector),
7617 _span(span),
7618 _work_queue(work_queue),
7619 _bit_map(bit_map) { }
7620
7621 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7622 HeapWord* addr = (HeapWord*)obj;
7623 if (_span.contains(addr) &&
7624 !_bit_map->isMarked(addr)) {
7625 if (_bit_map->par_mark(addr)) {
7626 bool simulate_overflow = false;
7627 NOT_PRODUCT(
7628 if (CMSMarkStackOverflowALot &&
7629 _collector->par_simulate_overflow()) {
7630 // simulate a stack overflow
7631 simulate_overflow = true;
7632 }
7633 )
7634 if (simulate_overflow || !_work_queue->push(obj)) {
7635 _collector->par_push_on_overflow_list(obj);
7636 _collector->_par_kac_ovflw++;
7637 }
7638 } // Else another thread got there already
7639 }
7640 }
7641
7642 //////////////////////////////////////////////////////////////////
7643 // CMSExpansionCause /////////////////////////////
7644 //////////////////////////////////////////////////////////////////
7645 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7646 switch (cause) {
7647 case _no_expansion:
7648 return "No expansion";
7649 case _satisfy_free_ratio:
7650 return "Free ratio";
7651 case _satisfy_promotion:
7652 return "Satisfy promotion";
7653 case _satisfy_allocation:
7654 return "allocation";
7655 case _allocate_par_lab:
7656 return "Par LAB";
7657 case _allocate_par_spooling_space:
7658 return "Par Spooling Space";
7659 case _adaptive_size_policy:
7660 return "Ergonomics";
7661 default:
7662 return "unknown";
7663 }
7664 }
7665
7666 void CMSDrainMarkingStackClosure::do_void() {
7667 // the max number to take from overflow list at a time
7668 const size_t num = _mark_stack->capacity()/4;
7669 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7670 "Overflow list should be NULL during concurrent phases");
7671 while (!_mark_stack->isEmpty() ||
7672 // if stack is empty, check the overflow list
7673 _collector->take_from_overflow_list(num, _mark_stack)) {
7674 oop obj = _mark_stack->pop();
7675 HeapWord* addr = (HeapWord*)obj;
7676 assert(_span.contains(addr), "Should be within span");
7677 assert(_bit_map->isMarked(addr), "Should be marked");
7678 assert(oopDesc::is_oop(obj), "Should be an oop");
7679 obj->oop_iterate(_keep_alive);
7680 }
7681 }
7682
7683 void CMSParDrainMarkingStackClosure::do_void() {
7684 // drain queue
7685 trim_queue(0);
7686 }
7687
7688 // Trim our work_queue so its length is below max at return
7689 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7690 while (_work_queue->size() > max) {
7691 oop new_oop;
7692 if (_work_queue->pop_local(new_oop)) {
7693 assert(oopDesc::is_oop(new_oop), "Expected an oop");
7694 assert(_bit_map->isMarked((HeapWord*)new_oop),
7695 "no white objects on this stack!");
7696 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7697 // iterate over the oops in this oop, marking and pushing
7698 // the ones in CMS heap (i.e. in _span).
7699 new_oop->oop_iterate(&_mark_and_push);
7700 }
7701 }
7702 }
7703
7704 ////////////////////////////////////////////////////////////////////
7705 // Support for Marking Stack Overflow list handling and related code
7706 ////////////////////////////////////////////////////////////////////
7707 // Much of the following code is similar in shape and spirit to the
7708 // code used in ParNewGC. We should try and share that code
7709 // as much as possible in the future.
7710
7711 #ifndef PRODUCT
7712 // Debugging support for CMSStackOverflowALot
7713
7714 // It's OK to call this multi-threaded; the worst thing
7715 // that can happen is that we'll get a bunch of closely
7716 // spaced simulated overflows, but that's OK, in fact
7717 // probably good as it would exercise the overflow code
7718 // under contention.
7719 bool CMSCollector::simulate_overflow() {
7720 if (_overflow_counter-- <= 0) { // just being defensive
7721 _overflow_counter = CMSMarkStackOverflowInterval;
7722 return true;
7723 } else {
7724 return false;
7725 }
7726 }
7727
7728 bool CMSCollector::par_simulate_overflow() {
7729 return simulate_overflow();
7730 }
7731 #endif
7732
7733 // Single-threaded
7734 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7735 assert(stack->isEmpty(), "Expected precondition");
7736 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7737 size_t i = num;
7738 oop cur = _overflow_list;
7739 const markOop proto = markOopDesc::prototype();
7740 NOT_PRODUCT(ssize_t n = 0;)
7741 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7742 next = oop(cur->mark_raw());
7743 cur->set_mark_raw(proto); // until proven otherwise
7744 assert(oopDesc::is_oop(cur), "Should be an oop");
7745 bool res = stack->push(cur);
7746 assert(res, "Bit off more than can chew?");
7747 NOT_PRODUCT(n++;)
7748 }
7749 _overflow_list = cur;
7750 #ifndef PRODUCT
7751 assert(_num_par_pushes >= n, "Too many pops?");
7752 _num_par_pushes -=n;
7753 #endif
7754 return !stack->isEmpty();
7755 }
7756
7757 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
7758 // (MT-safe) Get a prefix of at most "num" from the list.
7759 // The overflow list is chained through the mark word of
7760 // each object in the list. We fetch the entire list,
7761 // break off a prefix of the right size and return the
7762 // remainder. If other threads try to take objects from
7763 // the overflow list at that time, they will wait for
7764 // some time to see if data becomes available. If (and
7765 // only if) another thread places one or more object(s)
7766 // on the global list before we have returned the suffix
7767 // to the global list, we will walk down our local list
7768 // to find its end and append the global list to
7769 // our suffix before returning it. This suffix walk can
7770 // prove to be expensive (quadratic in the amount of traffic)
7771 // when there are many objects in the overflow list and
7772 // there is much producer-consumer contention on the list.
7773 // *NOTE*: The overflow list manipulation code here and
7774 // in ParNewGeneration:: are very similar in shape,
7775 // except that in the ParNew case we use the old (from/eden)
7776 // copy of the object to thread the list via its klass word.
7777 // Because of the common code, if you make any changes in
7778 // the code below, please check the ParNew version to see if
7779 // similar changes might be needed.
7780 // CR 6797058 has been filed to consolidate the common code.
7781 bool CMSCollector::par_take_from_overflow_list(size_t num,
7782 OopTaskQueue* work_q,
7783 int no_of_gc_threads) {
7784 assert(work_q->size() == 0, "First empty local work queue");
7785 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7786 if (_overflow_list == NULL) {
7787 return false;
7788 }
7789 // Grab the entire list; we'll put back a suffix
7790 oop prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7791 Thread* tid = Thread::current();
7792 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7793 // set to ParallelGCThreads.
7794 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7795 size_t sleep_time_millis = MAX2((size_t)1, num/100);
7796 // If the list is busy, we spin for a short while,
7797 // sleeping between attempts to get the list.
7798 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7799 os::sleep(tid, sleep_time_millis, false);
7800 if (_overflow_list == NULL) {
7801 // Nothing left to take
7802 return false;
7803 } else if (_overflow_list != BUSY) {
7804 // Try and grab the prefix
7805 prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7806 }
7807 }
7808 // If the list was found to be empty, or we spun long
7809 // enough, we give up and return empty-handed. If we leave
7810 // the list in the BUSY state below, it must be the case that
7811 // some other thread holds the overflow list and will set it
7812 // to a non-BUSY state in the future.
7813 if (prefix == NULL || prefix == BUSY) {
7814 // Nothing to take or waited long enough
7815 if (prefix == NULL) {
7816 // Write back the NULL in case we overwrote it with BUSY above
7817 // and it is still the same value.
7818 Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7819 }
7820 return false;
7821 }
7822 assert(prefix != NULL && prefix != BUSY, "Error");
7823 size_t i = num;
7824 oop cur = prefix;
7825 // Walk down the first "num" objects, unless we reach the end.
7826 for (; i > 1 && cur->mark_raw() != NULL; cur = oop(cur->mark_raw()), i--);
7827 if (cur->mark_raw() == NULL) {
7828 // We have "num" or fewer elements in the list, so there
7829 // is nothing to return to the global list.
7830 // Write back the NULL in lieu of the BUSY we wrote
7831 // above, if it is still the same value.
7832 if (_overflow_list == BUSY) {
7833 Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7834 }
7835 } else {
7836 // Chop off the suffix and return it to the global list.
7837 assert(cur->mark_raw() != BUSY, "Error");
7838 oop suffix_head = cur->mark_raw(); // suffix will be put back on global list
7839 cur->set_mark_raw(NULL); // break off suffix
7840 // It's possible that the list is still in the empty(busy) state
7841 // we left it in a short while ago; in that case we may be
7842 // able to place back the suffix without incurring the cost
7843 // of a walk down the list.
7844 oop observed_overflow_list = _overflow_list;
7845 oop cur_overflow_list = observed_overflow_list;
7846 bool attached = false;
7847 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7848 observed_overflow_list =
7849 Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7850 if (cur_overflow_list == observed_overflow_list) {
7851 attached = true;
7852 break;
7853 } else cur_overflow_list = observed_overflow_list;
7854 }
7855 if (!attached) {
7856 // Too bad, someone else sneaked in (at least) an element; we'll need
7857 // to do a splice. Find tail of suffix so we can prepend suffix to global
7858 // list.
7859 for (cur = suffix_head; cur->mark_raw() != NULL; cur = (oop)(cur->mark_raw()));
7860 oop suffix_tail = cur;
7861 assert(suffix_tail != NULL && suffix_tail->mark_raw() == NULL,
7862 "Tautology");
7863 observed_overflow_list = _overflow_list;
7864 do {
7865 cur_overflow_list = observed_overflow_list;
7866 if (cur_overflow_list != BUSY) {
7867 // Do the splice ...
7868 suffix_tail->set_mark_raw(markOop(cur_overflow_list));
7869 } else { // cur_overflow_list == BUSY
7870 suffix_tail->set_mark_raw(NULL);
7871 }
7872 // ... and try to place spliced list back on overflow_list ...
7873 observed_overflow_list =
7874 Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7875 } while (cur_overflow_list != observed_overflow_list);
7876 // ... until we have succeeded in doing so.
7877 }
7878 }
7879
7880 // Push the prefix elements on work_q
7881 assert(prefix != NULL, "control point invariant");
7882 const markOop proto = markOopDesc::prototype();
7883 oop next;
7884 NOT_PRODUCT(ssize_t n = 0;)
7885 for (cur = prefix; cur != NULL; cur = next) {
7886 next = oop(cur->mark_raw());
7887 cur->set_mark_raw(proto); // until proven otherwise
7888 assert(oopDesc::is_oop(cur), "Should be an oop");
7889 bool res = work_q->push(cur);
7890 assert(res, "Bit off more than we can chew?");
7891 NOT_PRODUCT(n++;)
7892 }
7893 #ifndef PRODUCT
7894 assert(_num_par_pushes >= n, "Too many pops?");
7895 Atomic::sub(n, &_num_par_pushes);
7896 #endif
7897 return true;
7898 }
7899
7900 // Single-threaded
7901 void CMSCollector::push_on_overflow_list(oop p) {
7902 NOT_PRODUCT(_num_par_pushes++;)
7903 assert(oopDesc::is_oop(p), "Not an oop");
7904 preserve_mark_if_necessary(p);
7905 p->set_mark_raw((markOop)_overflow_list);
7906 _overflow_list = p;
7907 }
7908
7909 // Multi-threaded; use CAS to prepend to overflow list
7910 void CMSCollector::par_push_on_overflow_list(oop p) {
7911 NOT_PRODUCT(Atomic::inc(&_num_par_pushes);)
7912 assert(oopDesc::is_oop(p), "Not an oop");
7913 par_preserve_mark_if_necessary(p);
7914 oop observed_overflow_list = _overflow_list;
7915 oop cur_overflow_list;
7916 do {
7917 cur_overflow_list = observed_overflow_list;
7918 if (cur_overflow_list != BUSY) {
7919 p->set_mark_raw(markOop(cur_overflow_list));
7920 } else {
7921 p->set_mark_raw(NULL);
7922 }
7923 observed_overflow_list =
7924 Atomic::cmpxchg((oopDesc*)p, &_overflow_list, (oopDesc*)cur_overflow_list);
7925 } while (cur_overflow_list != observed_overflow_list);
7926 }
7927 #undef BUSY
7928
7929 // Single threaded
7930 // General Note on GrowableArray: pushes may silently fail
7931 // because we are (temporarily) out of C-heap for expanding
7932 // the stack. The problem is quite ubiquitous and affects
7933 // a lot of code in the JVM. The prudent thing for GrowableArray
7934 // to do (for now) is to exit with an error. However, that may
7935 // be too draconian in some cases because the caller may be
7936 // able to recover without much harm. For such cases, we
7937 // should probably introduce a "soft_push" method which returns
7938 // an indication of success or failure with the assumption that
7939 // the caller may be able to recover from a failure; code in
7940 // the VM can then be changed, incrementally, to deal with such
7941 // failures where possible, thus, incrementally hardening the VM
7942 // in such low resource situations.
7943 void CMSCollector::preserve_mark_work(oop p, markOop m) {
7944 _preserved_oop_stack.push(p);
7945 _preserved_mark_stack.push(m);
7946 assert(m == p->mark_raw(), "Mark word changed");
7947 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
7948 "bijection");
7949 }
7950
7951 // Single threaded
7952 void CMSCollector::preserve_mark_if_necessary(oop p) {
7953 markOop m = p->mark_raw();
7954 if (m->must_be_preserved(p)) {
7955 preserve_mark_work(p, m);
7956 }
7957 }
7958
7959 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
7960 markOop m = p->mark_raw();
7961 if (m->must_be_preserved(p)) {
7962 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
7963 // Even though we read the mark word without holding
7964 // the lock, we are assured that it will not change
7965 // because we "own" this oop, so no other thread can
7966 // be trying to push it on the overflow list; see
7967 // the assertion in preserve_mark_work() that checks
7968 // that m == p->mark_raw().
7969 preserve_mark_work(p, m);
7970 }
7971 }
7972
7973 // We should be able to do this multi-threaded,
7974 // a chunk of stack being a task (this is
7975 // correct because each oop only ever appears
7976 // once in the overflow list. However, it's
7977 // not very easy to completely overlap this with
7978 // other operations, so will generally not be done
7979 // until all work's been completed. Because we
7980 // expect the preserved oop stack (set) to be small,
7981 // it's probably fine to do this single-threaded.
7982 // We can explore cleverer concurrent/overlapped/parallel
7983 // processing of preserved marks if we feel the
7984 // need for this in the future. Stack overflow should
7985 // be so rare in practice and, when it happens, its
7986 // effect on performance so great that this will
7987 // likely just be in the noise anyway.
7988 void CMSCollector::restore_preserved_marks_if_any() {
7989 assert(SafepointSynchronize::is_at_safepoint(),
7990 "world should be stopped");
7991 assert(Thread::current()->is_ConcurrentGC_thread() ||
7992 Thread::current()->is_VM_thread(),
7993 "should be single-threaded");
7994 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
7995 "bijection");
7996
7997 while (!_preserved_oop_stack.is_empty()) {
7998 oop p = _preserved_oop_stack.pop();
7999 assert(oopDesc::is_oop(p), "Should be an oop");
8000 assert(_span.contains(p), "oop should be in _span");
8001 assert(p->mark_raw() == markOopDesc::prototype(),
8002 "Set when taken from overflow list");
8003 markOop m = _preserved_mark_stack.pop();
8004 p->set_mark_raw(m);
8005 }
8006 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8007 "stacks were cleared above");
8008 }
8009
8010 #ifndef PRODUCT
8011 bool CMSCollector::no_preserved_marks() const {
8012 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8013 }
8014 #endif
8015
8016 // Transfer some number of overflown objects to usual marking
8017 // stack. Return true if some objects were transferred.
8018 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8019 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8020 (size_t)ParGCDesiredObjsFromOverflowList);
8021
8022 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8023 assert(_collector->overflow_list_is_empty() || res,
8024 "If list is not empty, we should have taken something");
8025 assert(!res || !_mark_stack->isEmpty(),
8026 "If we took something, it should now be on our stack");
8027 return res;
8028 }
8029
8030 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8031 size_t res = _sp->block_size_no_stall(addr, _collector);
8032 if (_sp->block_is_obj(addr)) {
8033 if (_live_bit_map->isMarked(addr)) {
8034 // It can't have been dead in a previous cycle
8035 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8036 } else {
8037 _dead_bit_map->mark(addr); // mark the dead object
8038 }
8039 }
8040 // Could be 0, if the block size could not be computed without stalling.
8041 return res;
8042 }
8043
8044 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8045 GCMemoryManager* manager = CMSHeap::heap()->old_manager();
8046 switch (phase) {
8047 case CMSCollector::InitialMarking:
8048 initialize(manager /* GC manager */ ,
8049 cause /* cause of the GC */,
8050 true /* allMemoryPoolsAffected */,
8051 true /* recordGCBeginTime */,
8052 true /* recordPreGCUsage */,
8053 false /* recordPeakUsage */,
8054 false /* recordPostGCusage */,
8055 true /* recordAccumulatedGCTime */,
8056 false /* recordGCEndTime */,
8057 false /* countCollection */ );
8058 break;
8059
8060 case CMSCollector::FinalMarking:
8061 initialize(manager /* GC manager */ ,
8062 cause /* cause of the GC */,
8063 true /* allMemoryPoolsAffected */,
8064 false /* recordGCBeginTime */,
8065 false /* recordPreGCUsage */,
8066 false /* recordPeakUsage */,
8067 false /* recordPostGCusage */,
8068 true /* recordAccumulatedGCTime */,
8069 false /* recordGCEndTime */,
8070 false /* countCollection */ );
8071 break;
8072
8073 case CMSCollector::Sweeping:
8074 initialize(manager /* GC manager */ ,
8075 cause /* cause of the GC */,
8076 true /* allMemoryPoolsAffected */,
8077 false /* recordGCBeginTime */,
8078 false /* recordPreGCUsage */,
8079 true /* recordPeakUsage */,
8080 true /* recordPostGCusage */,
8081 false /* recordAccumulatedGCTime */,
8082 true /* recordGCEndTime */,
8083 true /* countCollection */ );
8084 break;
8085
8086 default:
8087 ShouldNotReachHere();
8088 }
8089 }