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/classLoaderData.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/referencePolicy.hpp"
58 #include "gc/shared/space.inline.hpp"
59 #include "gc/shared/strongRootsScope.hpp"
60 #include "gc/shared/taskqueue.inline.hpp"
61 #include "gc/shared/weakProcessor.hpp"
62 #include "logging/log.hpp"
63 #include "logging/logStream.hpp"
64 #include "memory/allocation.hpp"
65 #include "memory/binaryTreeDictionary.inline.hpp"
66 #include "memory/iterator.inline.hpp"
67 #include "memory/padded.hpp"
68 #include "memory/resourceArea.hpp"
69 #include "oops/access.inline.hpp"
70 #include "oops/oop.inline.hpp"
71 #include "prims/jvmtiExport.hpp"
72 #include "runtime/atomic.hpp"
73 #include "runtime/flags/flagSetting.hpp"
74 #include "runtime/globals_extension.hpp"
75 #include "runtime/handles.inline.hpp"
76 #include "runtime/java.hpp"
77 #include "runtime/orderAccess.inline.hpp"
78 #include "runtime/timer.hpp"
79 #include "runtime/vmThread.hpp"
80 #include "services/memoryService.hpp"
81 #include "services/runtimeService.hpp"
82 #include "utilities/align.hpp"
83 #include "utilities/stack.inline.hpp"
84
85 // statics
86 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
87 bool CMSCollector::_full_gc_requested = false;
88 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
89
90 //////////////////////////////////////////////////////////////////
91 // In support of CMS/VM thread synchronization
92 //////////////////////////////////////////////////////////////////
93 // We split use of the CGC_lock into 2 "levels".
94 // The low-level locking is of the usual CGC_lock monitor. We introduce
95 // a higher level "token" (hereafter "CMS token") built on top of the
96 // low level monitor (hereafter "CGC lock").
97 // The token-passing protocol gives priority to the VM thread. The
98 // CMS-lock doesn't provide any fairness guarantees, but clients
99 // should ensure that it is only held for very short, bounded
100 // durations.
101 //
102 // When either of the CMS thread or the VM thread is involved in
103 // collection operations during which it does not want the other
104 // thread to interfere, it obtains the CMS token.
105 //
106 // If either thread tries to get the token while the other has
107 // it, that thread waits. However, if the VM thread and CMS thread
108 // both want the token, then the VM thread gets priority while the
109 // CMS thread waits. This ensures, for instance, that the "concurrent"
110 // phases of the CMS thread's work do not block out the VM thread
111 // for long periods of time as the CMS thread continues to hog
112 // the token. (See bug 4616232).
113 //
114 // The baton-passing functions are, however, controlled by the
115 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
116 // and here the low-level CMS lock, not the high level token,
117 // ensures mutual exclusion.
118 //
119 // Two important conditions that we have to satisfy:
120 // 1. if a thread does a low-level wait on the CMS lock, then it
121 // relinquishes the CMS token if it were holding that token
122 // when it acquired the low-level CMS lock.
123 // 2. any low-level notifications on the low-level lock
124 // should only be sent when a thread has relinquished the token.
125 //
126 // In the absence of either property, we'd have potential deadlock.
127 //
128 // We protect each of the CMS (concurrent and sequential) phases
129 // with the CMS _token_, not the CMS _lock_.
130 //
131 // The only code protected by CMS lock is the token acquisition code
132 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
133 // baton-passing code.
134 //
135 // Unfortunately, i couldn't come up with a good abstraction to factor and
136 // hide the naked CGC_lock manipulation in the baton-passing code
137 // further below. That's something we should try to do. Also, the proof
138 // of correctness of this 2-level locking scheme is far from obvious,
139 // and potentially quite slippery. We have an uneasy suspicion, for instance,
140 // that there may be a theoretical possibility of delay/starvation in the
141 // low-level lock/wait/notify scheme used for the baton-passing because of
142 // potential interference with the priority scheme embodied in the
143 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
144 // invocation further below and marked with "XXX 20011219YSR".
145 // Indeed, as we note elsewhere, this may become yet more slippery
146 // in the presence of multiple CMS and/or multiple VM threads. XXX
147
148 class CMSTokenSync: public StackObj {
149 private:
150 bool _is_cms_thread;
151 public:
152 CMSTokenSync(bool is_cms_thread):
153 _is_cms_thread(is_cms_thread) {
154 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
155 "Incorrect argument to constructor");
156 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
157 }
158
159 ~CMSTokenSync() {
160 assert(_is_cms_thread ?
161 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
162 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
163 "Incorrect state");
164 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
165 }
166 };
167
168 // Convenience class that does a CMSTokenSync, and then acquires
169 // upto three locks.
170 class CMSTokenSyncWithLocks: public CMSTokenSync {
171 private:
172 // Note: locks are acquired in textual declaration order
173 // and released in the opposite order
174 MutexLockerEx _locker1, _locker2, _locker3;
175 public:
176 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
177 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
178 CMSTokenSync(is_cms_thread),
179 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
180 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
181 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
182 { }
183 };
184
185
186 //////////////////////////////////////////////////////////////////
187 // Concurrent Mark-Sweep Generation /////////////////////////////
188 //////////////////////////////////////////////////////////////////
189
190 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
191
192 // This struct contains per-thread things necessary to support parallel
193 // young-gen collection.
194 class CMSParGCThreadState: public CHeapObj<mtGC> {
195 public:
196 CompactibleFreeListSpaceLAB lab;
197 PromotionInfo promo;
198
199 // Constructor.
200 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
201 promo.setSpace(cfls);
202 }
203 };
204
205 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
206 ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct) :
207 CardGeneration(rs, initial_byte_size, ct),
208 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
209 _did_compact(false)
210 {
211 HeapWord* bottom = (HeapWord*) _virtual_space.low();
212 HeapWord* end = (HeapWord*) _virtual_space.high();
213
214 _direct_allocated_words = 0;
215 NOT_PRODUCT(
216 _numObjectsPromoted = 0;
217 _numWordsPromoted = 0;
218 _numObjectsAllocated = 0;
219 _numWordsAllocated = 0;
220 )
221
222 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end));
223 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
224 _cmsSpace->_old_gen = this;
225
226 _gc_stats = new CMSGCStats();
227
228 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
229 // offsets match. The ability to tell free chunks from objects
230 // depends on this property.
231 debug_only(
232 FreeChunk* junk = NULL;
233 assert(UseCompressedClassPointers ||
234 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
235 "Offset of FreeChunk::_prev within FreeChunk must match"
236 " that of OopDesc::_klass within OopDesc");
237 )
238
239 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
240 for (uint i = 0; i < ParallelGCThreads; i++) {
241 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
242 }
243
244 _incremental_collection_failed = false;
245 // The "dilatation_factor" is the expansion that can occur on
246 // account of the fact that the minimum object size in the CMS
247 // generation may be larger than that in, say, a contiguous young
248 // generation.
249 // Ideally, in the calculation below, we'd compute the dilatation
250 // factor as: MinChunkSize/(promoting_gen's min object size)
251 // Since we do not have such a general query interface for the
252 // promoting generation, we'll instead just use the minimum
253 // object size (which today is a header's worth of space);
254 // note that all arithmetic is in units of HeapWords.
255 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
256 assert(_dilatation_factor >= 1.0, "from previous assert");
257 }
258
259
260 // The field "_initiating_occupancy" represents the occupancy percentage
261 // at which we trigger a new collection cycle. Unless explicitly specified
262 // via CMSInitiatingOccupancyFraction (argument "io" below), it
263 // is calculated by:
264 //
265 // Let "f" be MinHeapFreeRatio in
266 //
267 // _initiating_occupancy = 100-f +
268 // f * (CMSTriggerRatio/100)
269 // where CMSTriggerRatio is the argument "tr" below.
270 //
271 // That is, if we assume the heap is at its desired maximum occupancy at the
272 // end of a collection, we let CMSTriggerRatio of the (purported) free
273 // space be allocated before initiating a new collection cycle.
274 //
275 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
276 assert(io <= 100 && tr <= 100, "Check the arguments");
277 if (io >= 0) {
278 _initiating_occupancy = (double)io / 100.0;
279 } else {
280 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
281 (double)(tr * MinHeapFreeRatio) / 100.0)
282 / 100.0;
283 }
284 }
285
286 void ConcurrentMarkSweepGeneration::ref_processor_init() {
287 assert(collector() != NULL, "no collector");
288 collector()->ref_processor_init();
289 }
290
291 void CMSCollector::ref_processor_init() {
292 if (_ref_processor == NULL) {
293 // Allocate and initialize a reference processor
294 _ref_processor =
295 new ReferenceProcessor(&_span_based_discoverer,
296 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
297 ParallelGCThreads, // mt processing degree
298 _cmsGen->refs_discovery_is_mt(), // mt discovery
299 MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
300 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
301 &_is_alive_closure); // closure for liveness info
302 // Initialize the _ref_processor field of CMSGen
303 _cmsGen->set_ref_processor(_ref_processor);
304
305 }
306 }
307
308 AdaptiveSizePolicy* CMSCollector::size_policy() {
309 return CMSHeap::heap()->size_policy();
310 }
311
312 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
313
314 const char* gen_name = "old";
315 GenCollectorPolicy* gcp = CMSHeap::heap()->gen_policy();
316 // Generation Counters - generation 1, 1 subspace
317 _gen_counters = new GenerationCounters(gen_name, 1, 1,
318 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
319
320 _space_counters = new GSpaceCounters(gen_name, 0,
321 _virtual_space.reserved_size(),
322 this, _gen_counters);
323 }
324
325 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
326 _cms_gen(cms_gen)
327 {
328 assert(alpha <= 100, "bad value");
329 _saved_alpha = alpha;
330
331 // Initialize the alphas to the bootstrap value of 100.
332 _gc0_alpha = _cms_alpha = 100;
333
334 _cms_begin_time.update();
335 _cms_end_time.update();
336
337 _gc0_duration = 0.0;
338 _gc0_period = 0.0;
339 _gc0_promoted = 0;
340
341 _cms_duration = 0.0;
342 _cms_period = 0.0;
343 _cms_allocated = 0;
344
345 _cms_used_at_gc0_begin = 0;
346 _cms_used_at_gc0_end = 0;
347 _allow_duty_cycle_reduction = false;
348 _valid_bits = 0;
349 }
350
351 double CMSStats::cms_free_adjustment_factor(size_t free) const {
352 // TBD: CR 6909490
353 return 1.0;
354 }
355
356 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
357 }
358
359 // If promotion failure handling is on use
360 // the padded average size of the promotion for each
361 // young generation collection.
362 double CMSStats::time_until_cms_gen_full() const {
363 size_t cms_free = _cms_gen->cmsSpace()->free();
364 CMSHeap* heap = CMSHeap::heap();
365 size_t expected_promotion = MIN2(heap->young_gen()->capacity(),
366 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
367 if (cms_free > expected_promotion) {
368 // Start a cms collection if there isn't enough space to promote
369 // for the next young collection. Use the padded average as
370 // a safety factor.
371 cms_free -= expected_promotion;
372
373 // Adjust by the safety factor.
374 double cms_free_dbl = (double)cms_free;
375 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
376 // Apply a further correction factor which tries to adjust
377 // for recent occurance of concurrent mode failures.
378 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
379 cms_free_dbl = cms_free_dbl * cms_adjustment;
380
381 log_trace(gc)("CMSStats::time_until_cms_gen_full: cms_free " SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
382 cms_free, expected_promotion);
383 log_trace(gc)(" cms_free_dbl %f cms_consumption_rate %f", cms_free_dbl, cms_consumption_rate() + 1.0);
384 // Add 1 in case the consumption rate goes to zero.
385 return cms_free_dbl / (cms_consumption_rate() + 1.0);
386 }
387 return 0.0;
388 }
389
390 // Compare the duration of the cms collection to the
391 // time remaining before the cms generation is empty.
392 // Note that the time from the start of the cms collection
393 // to the start of the cms sweep (less than the total
394 // duration of the cms collection) can be used. This
395 // has been tried and some applications experienced
396 // promotion failures early in execution. This was
397 // possibly because the averages were not accurate
398 // enough at the beginning.
399 double CMSStats::time_until_cms_start() const {
400 // We add "gc0_period" to the "work" calculation
401 // below because this query is done (mostly) at the
402 // end of a scavenge, so we need to conservatively
403 // account for that much possible delay
404 // in the query so as to avoid concurrent mode failures
405 // due to starting the collection just a wee bit too
406 // late.
407 double work = cms_duration() + gc0_period();
408 double deadline = time_until_cms_gen_full();
409 // If a concurrent mode failure occurred recently, we want to be
410 // more conservative and halve our expected time_until_cms_gen_full()
411 if (work > deadline) {
412 log_develop_trace(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ",
413 cms_duration(), gc0_period(), time_until_cms_gen_full());
414 return 0.0;
415 }
416 return work - deadline;
417 }
418
419 #ifndef PRODUCT
420 void CMSStats::print_on(outputStream *st) const {
421 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
422 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
423 gc0_duration(), gc0_period(), gc0_promoted());
424 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
425 cms_duration(), cms_period(), cms_allocated());
426 st->print(",cms_since_beg=%g,cms_since_end=%g",
427 cms_time_since_begin(), cms_time_since_end());
428 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
429 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
430
431 if (valid()) {
432 st->print(",promo_rate=%g,cms_alloc_rate=%g",
433 promotion_rate(), cms_allocation_rate());
434 st->print(",cms_consumption_rate=%g,time_until_full=%g",
435 cms_consumption_rate(), time_until_cms_gen_full());
436 }
437 st->cr();
438 }
439 #endif // #ifndef PRODUCT
440
441 CMSCollector::CollectorState CMSCollector::_collectorState =
442 CMSCollector::Idling;
443 bool CMSCollector::_foregroundGCIsActive = false;
444 bool CMSCollector::_foregroundGCShouldWait = false;
445
446 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
447 CardTableRS* ct,
448 ConcurrentMarkSweepPolicy* cp):
449 _cmsGen(cmsGen),
450 // Adjust span to cover old (cms) gen
451 _span(cmsGen->reserved()),
452 _ct(ct),
453 _span_based_discoverer(_span),
454 _ref_processor(NULL), // will be set later
455 _conc_workers(NULL), // may be set later
456 _abort_preclean(false),
457 _start_sampling(false),
458 _between_prologue_and_epilogue(false),
459 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
460 _modUnionTable((CardTable::card_shift - LogHeapWordSize),
461 -1 /* lock-free */, "No_lock" /* dummy */),
462 _modUnionClosurePar(&_modUnionTable),
463 // Construct the is_alive_closure with _span & markBitMap
464 _is_alive_closure(_span, &_markBitMap),
465 _restart_addr(NULL),
466 _overflow_list(NULL),
467 _stats(cmsGen),
468 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
469 //verify that this lock should be acquired with safepoint check.
470 Monitor::_safepoint_check_sometimes)),
471 _eden_chunk_array(NULL), // may be set in ctor body
472 _eden_chunk_capacity(0), // -- ditto --
473 _eden_chunk_index(0), // -- ditto --
474 _survivor_plab_array(NULL), // -- ditto --
475 _survivor_chunk_array(NULL), // -- ditto --
476 _survivor_chunk_capacity(0), // -- ditto --
477 _survivor_chunk_index(0), // -- ditto --
478 _ser_pmc_preclean_ovflw(0),
479 _ser_kac_preclean_ovflw(0),
480 _ser_pmc_remark_ovflw(0),
481 _par_pmc_remark_ovflw(0),
482 _ser_kac_ovflw(0),
483 _par_kac_ovflw(0),
484 #ifndef PRODUCT
485 _num_par_pushes(0),
486 #endif
487 _collection_count_start(0),
488 _verifying(false),
489 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
490 _completed_initialization(false),
491 _collector_policy(cp),
492 _should_unload_classes(CMSClassUnloadingEnabled),
493 _concurrent_cycles_since_last_unload(0),
494 _roots_scanning_options(GenCollectedHeap::SO_None),
495 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
496 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
497 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
498 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
499 _cms_start_registered(false)
500 {
501 // Now expand the span and allocate the collection support structures
502 // (MUT, marking bit map etc.) to cover both generations subject to
503 // collection.
504
505 // For use by dirty card to oop closures.
506 _cmsGen->cmsSpace()->set_collector(this);
507
508 // Allocate MUT and marking bit map
509 {
510 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
511 if (!_markBitMap.allocate(_span)) {
512 log_warning(gc)("Failed to allocate CMS Bit Map");
513 return;
514 }
515 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
516 }
517 {
518 _modUnionTable.allocate(_span);
519 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
520 }
521
522 if (!_markStack.allocate(MarkStackSize)) {
523 log_warning(gc)("Failed to allocate CMS Marking Stack");
524 return;
525 }
526
527 // Support for multi-threaded concurrent phases
528 if (CMSConcurrentMTEnabled) {
529 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
530 // just for now
531 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
532 }
533 if (ConcGCThreads > 1) {
534 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
535 ConcGCThreads, true);
536 if (_conc_workers == NULL) {
537 log_warning(gc)("GC/CMS: _conc_workers allocation failure: forcing -CMSConcurrentMTEnabled");
538 CMSConcurrentMTEnabled = false;
539 } else {
540 _conc_workers->initialize_workers();
541 }
542 } else {
543 CMSConcurrentMTEnabled = false;
544 }
545 }
546 if (!CMSConcurrentMTEnabled) {
547 ConcGCThreads = 0;
548 } else {
549 // Turn off CMSCleanOnEnter optimization temporarily for
550 // the MT case where it's not fixed yet; see 6178663.
551 CMSCleanOnEnter = false;
552 }
553 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
554 "Inconsistency");
555 log_debug(gc)("ConcGCThreads: %u", ConcGCThreads);
556 log_debug(gc)("ParallelGCThreads: %u", ParallelGCThreads);
557
558 // Parallel task queues; these are shared for the
559 // concurrent and stop-world phases of CMS, but
560 // are not shared with parallel scavenge (ParNew).
561 {
562 uint i;
563 uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
564
565 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
566 || ParallelRefProcEnabled)
567 && num_queues > 0) {
568 _task_queues = new OopTaskQueueSet(num_queues);
569 if (_task_queues == NULL) {
570 log_warning(gc)("task_queues allocation failure.");
571 return;
572 }
573 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
574 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
575 for (i = 0; i < num_queues; i++) {
576 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
577 if (q == NULL) {
578 log_warning(gc)("work_queue allocation failure.");
579 return;
580 }
581 _task_queues->register_queue(i, q);
582 }
583 for (i = 0; i < num_queues; i++) {
584 _task_queues->queue(i)->initialize();
585 _hash_seed[i] = 17; // copied from ParNew
586 }
587 }
588 }
589
590 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
591
592 // Clip CMSBootstrapOccupancy between 0 and 100.
593 _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
594
595 // Now tell CMS generations the identity of their collector
596 ConcurrentMarkSweepGeneration::set_collector(this);
597
598 // Create & start a CMS thread for this CMS collector
599 _cmsThread = ConcurrentMarkSweepThread::start(this);
600 assert(cmsThread() != NULL, "CMS Thread should have been created");
601 assert(cmsThread()->collector() == this,
602 "CMS Thread should refer to this gen");
603 assert(CGC_lock != NULL, "Where's the CGC_lock?");
604
605 // Support for parallelizing young gen rescan
606 CMSHeap* heap = CMSHeap::heap();
607 _young_gen = heap->young_gen();
608 if (heap->supports_inline_contig_alloc()) {
609 _top_addr = heap->top_addr();
610 _end_addr = heap->end_addr();
611 assert(_young_gen != NULL, "no _young_gen");
612 _eden_chunk_index = 0;
613 _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
614 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
615 }
616
617 // Support for parallelizing survivor space rescan
618 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
619 const size_t max_plab_samples =
620 _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
621
622 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
623 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
624 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
625 _survivor_chunk_capacity = max_plab_samples;
626 for (uint i = 0; i < ParallelGCThreads; i++) {
627 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
628 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
629 assert(cur->end() == 0, "Should be 0");
630 assert(cur->array() == vec, "Should be vec");
631 assert(cur->capacity() == max_plab_samples, "Error");
632 }
633 }
634
635 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
636 _gc_counters = new CollectorCounters("CMS", 1);
637 _cgc_counters = new CollectorCounters("CMS stop-the-world phases", 2);
638 _completed_initialization = true;
639 _inter_sweep_timer.start(); // start of time
640 }
641
642 const char* ConcurrentMarkSweepGeneration::name() const {
643 return "concurrent mark-sweep generation";
644 }
645 void ConcurrentMarkSweepGeneration::update_counters() {
646 if (UsePerfData) {
647 _space_counters->update_all();
648 _gen_counters->update_all();
649 }
650 }
651
652 // this is an optimized version of update_counters(). it takes the
653 // used value as a parameter rather than computing it.
654 //
655 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
656 if (UsePerfData) {
657 _space_counters->update_used(used);
658 _space_counters->update_capacity();
659 _gen_counters->update_all();
660 }
661 }
662
663 void ConcurrentMarkSweepGeneration::print() const {
664 Generation::print();
665 cmsSpace()->print();
666 }
667
668 #ifndef PRODUCT
669 void ConcurrentMarkSweepGeneration::print_statistics() {
670 cmsSpace()->printFLCensus(0);
671 }
672 #endif
673
674 size_t
675 ConcurrentMarkSweepGeneration::contiguous_available() const {
676 // dld proposes an improvement in precision here. If the committed
677 // part of the space ends in a free block we should add that to
678 // uncommitted size in the calculation below. Will make this
679 // change later, staying with the approximation below for the
680 // time being. -- ysr.
681 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
682 }
683
684 size_t
685 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
686 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
687 }
688
689 size_t ConcurrentMarkSweepGeneration::max_available() const {
690 return free() + _virtual_space.uncommitted_size();
691 }
692
693 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
694 size_t available = max_available();
695 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
696 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
697 log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")",
698 res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes);
699 return res;
700 }
701
702 // At a promotion failure dump information on block layout in heap
703 // (cms old generation).
704 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
705 Log(gc, promotion) log;
706 if (log.is_trace()) {
707 LogStream ls(log.trace());
708 cmsSpace()->dump_at_safepoint_with_locks(collector(), &ls);
709 }
710 }
711
712 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
713 // Clear the promotion information. These pointers can be adjusted
714 // along with all the other pointers into the heap but
715 // compaction is expected to be a rare event with
716 // a heap using cms so don't do it without seeing the need.
717 for (uint i = 0; i < ParallelGCThreads; i++) {
718 _par_gc_thread_states[i]->promo.reset();
719 }
720 }
721
722 void ConcurrentMarkSweepGeneration::compute_new_size() {
723 assert_locked_or_safepoint(Heap_lock);
724
725 // If incremental collection failed, we just want to expand
726 // to the limit.
727 if (incremental_collection_failed()) {
728 clear_incremental_collection_failed();
729 grow_to_reserved();
730 return;
731 }
732
733 // The heap has been compacted but not reset yet.
734 // Any metric such as free() or used() will be incorrect.
735
736 CardGeneration::compute_new_size();
737
738 // Reset again after a possible resizing
739 if (did_compact()) {
740 cmsSpace()->reset_after_compaction();
741 }
742 }
743
744 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
745 assert_locked_or_safepoint(Heap_lock);
746
747 // If incremental collection failed, we just want to expand
748 // to the limit.
749 if (incremental_collection_failed()) {
750 clear_incremental_collection_failed();
751 grow_to_reserved();
752 return;
753 }
754
755 double free_percentage = ((double) free()) / capacity();
756 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
757 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
758
759 // compute expansion delta needed for reaching desired free percentage
760 if (free_percentage < desired_free_percentage) {
761 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
762 assert(desired_capacity >= capacity(), "invalid expansion size");
763 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
764 Log(gc) log;
765 if (log.is_trace()) {
766 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
767 log.trace("From compute_new_size: ");
768 log.trace(" Free fraction %f", free_percentage);
769 log.trace(" Desired free fraction %f", desired_free_percentage);
770 log.trace(" Maximum free fraction %f", maximum_free_percentage);
771 log.trace(" Capacity " SIZE_FORMAT, capacity() / 1000);
772 log.trace(" Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
773 CMSHeap* heap = CMSHeap::heap();
774 size_t young_size = heap->young_gen()->capacity();
775 log.trace(" Young gen size " SIZE_FORMAT, young_size / 1000);
776 log.trace(" unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
777 log.trace(" contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
778 log.trace(" Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
779 }
780 // safe if expansion fails
781 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
782 log.trace(" Expanded free fraction %f", ((double) free()) / capacity());
783 } else {
784 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
785 assert(desired_capacity <= capacity(), "invalid expansion size");
786 size_t shrink_bytes = capacity() - desired_capacity;
787 // Don't shrink unless the delta is greater than the minimum shrink we want
788 if (shrink_bytes >= MinHeapDeltaBytes) {
789 shrink_free_list_by(shrink_bytes);
790 }
791 }
792 }
793
794 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
795 return cmsSpace()->freelistLock();
796 }
797
798 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
799 CMSSynchronousYieldRequest yr;
800 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
801 return have_lock_and_allocate(size, tlab);
802 }
803
804 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
805 bool tlab /* ignored */) {
806 assert_lock_strong(freelistLock());
807 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
808 HeapWord* res = cmsSpace()->allocate(adjustedSize);
809 // Allocate the object live (grey) if the background collector has
810 // started marking. This is necessary because the marker may
811 // have passed this address and consequently this object will
812 // not otherwise be greyed and would be incorrectly swept up.
813 // Note that if this object contains references, the writing
814 // of those references will dirty the card containing this object
815 // allowing the object to be blackened (and its references scanned)
816 // either during a preclean phase or at the final checkpoint.
817 if (res != NULL) {
818 // We may block here with an uninitialized object with
819 // its mark-bit or P-bits not yet set. Such objects need
820 // to be safely navigable by block_start().
821 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
822 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
823 collector()->direct_allocated(res, adjustedSize);
824 _direct_allocated_words += adjustedSize;
825 // allocation counters
826 NOT_PRODUCT(
827 _numObjectsAllocated++;
828 _numWordsAllocated += (int)adjustedSize;
829 )
830 }
831 return res;
832 }
833
834 // In the case of direct allocation by mutators in a generation that
835 // is being concurrently collected, the object must be allocated
836 // live (grey) if the background collector has started marking.
837 // This is necessary because the marker may
838 // have passed this address and consequently this object will
839 // not otherwise be greyed and would be incorrectly swept up.
840 // Note that if this object contains references, the writing
841 // of those references will dirty the card containing this object
842 // allowing the object to be blackened (and its references scanned)
843 // either during a preclean phase or at the final checkpoint.
844 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
845 assert(_markBitMap.covers(start, size), "Out of bounds");
846 if (_collectorState >= Marking) {
847 MutexLockerEx y(_markBitMap.lock(),
848 Mutex::_no_safepoint_check_flag);
849 // [see comments preceding SweepClosure::do_blk() below for details]
850 //
851 // Can the P-bits be deleted now? JJJ
852 //
853 // 1. need to mark the object as live so it isn't collected
854 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
855 // 3. need to mark the end of the object so marking, precleaning or sweeping
856 // can skip over uninitialized or unparsable objects. An allocated
857 // object is considered uninitialized for our purposes as long as
858 // its klass word is NULL. All old gen objects are parsable
859 // as soon as they are initialized.)
860 _markBitMap.mark(start); // object is live
861 _markBitMap.mark(start + 1); // object is potentially uninitialized?
862 _markBitMap.mark(start + size - 1);
863 // mark end of object
864 }
865 // check that oop looks uninitialized
866 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
867 }
868
869 void CMSCollector::promoted(bool par, HeapWord* start,
870 bool is_obj_array, size_t obj_size) {
871 assert(_markBitMap.covers(start), "Out of bounds");
872 // See comment in direct_allocated() about when objects should
873 // be allocated live.
874 if (_collectorState >= Marking) {
875 // we already hold the marking bit map lock, taken in
876 // the prologue
877 if (par) {
878 _markBitMap.par_mark(start);
879 } else {
880 _markBitMap.mark(start);
881 }
882 // We don't need to mark the object as uninitialized (as
883 // in direct_allocated above) because this is being done with the
884 // world stopped and the object will be initialized by the
885 // time the marking, precleaning or sweeping get to look at it.
886 // But see the code for copying objects into the CMS generation,
887 // where we need to ensure that concurrent readers of the
888 // block offset table are able to safely navigate a block that
889 // is in flux from being free to being allocated (and in
890 // transition while being copied into) and subsequently
891 // becoming a bona-fide object when the copy/promotion is complete.
892 assert(SafepointSynchronize::is_at_safepoint(),
893 "expect promotion only at safepoints");
894
895 if (_collectorState < Sweeping) {
896 // Mark the appropriate cards in the modUnionTable, so that
897 // this object gets scanned before the sweep. If this is
898 // not done, CMS generation references in the object might
899 // not get marked.
900 // For the case of arrays, which are otherwise precisely
901 // marked, we need to dirty the entire array, not just its head.
902 if (is_obj_array) {
903 // The [par_]mark_range() method expects mr.end() below to
904 // be aligned to the granularity of a bit's representation
905 // in the heap. In the case of the MUT below, that's a
906 // card size.
907 MemRegion mr(start,
908 align_up(start + obj_size,
909 CardTable::card_size /* bytes */));
910 if (par) {
911 _modUnionTable.par_mark_range(mr);
912 } else {
913 _modUnionTable.mark_range(mr);
914 }
915 } else { // not an obj array; we can just mark the head
916 if (par) {
917 _modUnionTable.par_mark(start);
918 } else {
919 _modUnionTable.mark(start);
920 }
921 }
922 }
923 }
924 }
925
926 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
927 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
928 // allocate, copy and if necessary update promoinfo --
929 // delegate to underlying space.
930 assert_lock_strong(freelistLock());
931
932 #ifndef PRODUCT
933 if (CMSHeap::heap()->promotion_should_fail()) {
934 return NULL;
935 }
936 #endif // #ifndef PRODUCT
937
938 oop res = _cmsSpace->promote(obj, obj_size);
939 if (res == NULL) {
940 // expand and retry
941 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
942 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
943 // Since this is the old generation, we don't try to promote
944 // into a more senior generation.
945 res = _cmsSpace->promote(obj, obj_size);
946 }
947 if (res != NULL) {
948 // See comment in allocate() about when objects should
949 // be allocated live.
950 assert(oopDesc::is_oop(obj), "Will dereference klass pointer below");
951 collector()->promoted(false, // Not parallel
952 (HeapWord*)res, obj->is_objArray(), obj_size);
953 // promotion counters
954 NOT_PRODUCT(
955 _numObjectsPromoted++;
956 _numWordsPromoted +=
957 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
958 )
959 }
960 return res;
961 }
962
963
964 // IMPORTANT: Notes on object size recognition in CMS.
965 // ---------------------------------------------------
966 // A block of storage in the CMS generation is always in
967 // one of three states. A free block (FREE), an allocated
968 // object (OBJECT) whose size() method reports the correct size,
969 // and an intermediate state (TRANSIENT) in which its size cannot
970 // be accurately determined.
971 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
972 // -----------------------------------------------------
973 // FREE: klass_word & 1 == 1; mark_word holds block size
974 //
975 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
976 // obj->size() computes correct size
977 //
978 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
979 //
980 // STATE IDENTIFICATION: (64 bit+COOPS)
981 // ------------------------------------
982 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
983 //
984 // OBJECT: klass_word installed; klass_word != 0;
985 // obj->size() computes correct size
986 //
987 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
988 //
989 //
990 // STATE TRANSITION DIAGRAM
991 //
992 // mut / parnew mut / parnew
993 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
994 // ^ |
995 // |------------------------ DEAD <------------------------------------|
996 // sweep mut
997 //
998 // While a block is in TRANSIENT state its size cannot be determined
999 // so readers will either need to come back later or stall until
1000 // the size can be determined. Note that for the case of direct
1001 // allocation, P-bits, when available, may be used to determine the
1002 // size of an object that may not yet have been initialized.
1003
1004 // Things to support parallel young-gen collection.
1005 oop
1006 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1007 oop old, markOop m,
1008 size_t word_sz) {
1009 #ifndef PRODUCT
1010 if (CMSHeap::heap()->promotion_should_fail()) {
1011 return NULL;
1012 }
1013 #endif // #ifndef PRODUCT
1014
1015 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1016 PromotionInfo* promoInfo = &ps->promo;
1017 // if we are tracking promotions, then first ensure space for
1018 // promotion (including spooling space for saving header if necessary).
1019 // then allocate and copy, then track promoted info if needed.
1020 // When tracking (see PromotionInfo::track()), the mark word may
1021 // be displaced and in this case restoration of the mark word
1022 // occurs in the (oop_since_save_marks_)iterate phase.
1023 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1024 // Out of space for allocating spooling buffers;
1025 // try expanding and allocating spooling buffers.
1026 if (!expand_and_ensure_spooling_space(promoInfo)) {
1027 return NULL;
1028 }
1029 }
1030 assert(!promoInfo->tracking() || promoInfo->has_spooling_space(), "Control point invariant");
1031 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1032 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1033 if (obj_ptr == NULL) {
1034 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1035 if (obj_ptr == NULL) {
1036 return NULL;
1037 }
1038 }
1039 oop obj = oop(obj_ptr);
1040 OrderAccess::storestore();
1041 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1042 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1043 // IMPORTANT: See note on object initialization for CMS above.
1044 // Otherwise, copy the object. Here we must be careful to insert the
1045 // klass pointer last, since this marks the block as an allocated object.
1046 // Except with compressed oops it's the mark word.
1047 HeapWord* old_ptr = (HeapWord*)old;
1048 // Restore the mark word copied above.
1049 obj->set_mark_raw(m);
1050 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1051 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1052 OrderAccess::storestore();
1053
1054 if (UseCompressedClassPointers) {
1055 // Copy gap missed by (aligned) header size calculation below
1056 obj->set_klass_gap(old->klass_gap());
1057 }
1058 if (word_sz > (size_t)oopDesc::header_size()) {
1059 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1060 obj_ptr + oopDesc::header_size(),
1061 word_sz - oopDesc::header_size());
1062 }
1063
1064 // Now we can track the promoted object, if necessary. We take care
1065 // to delay the transition from uninitialized to full object
1066 // (i.e., insertion of klass pointer) until after, so that it
1067 // atomically becomes a promoted object.
1068 if (promoInfo->tracking()) {
1069 promoInfo->track((PromotedObject*)obj, old->klass());
1070 }
1071 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1072 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1073 assert(oopDesc::is_oop(old), "Will use and dereference old klass ptr below");
1074
1075 // Finally, install the klass pointer (this should be volatile).
1076 OrderAccess::storestore();
1077 obj->set_klass(old->klass());
1078 // We should now be able to calculate the right size for this object
1079 assert(oopDesc::is_oop(obj) && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1080
1081 collector()->promoted(true, // parallel
1082 obj_ptr, old->is_objArray(), word_sz);
1083
1084 NOT_PRODUCT(
1085 Atomic::inc(&_numObjectsPromoted);
1086 Atomic::add(alloc_sz, &_numWordsPromoted);
1087 )
1088
1089 return obj;
1090 }
1091
1092 void
1093 ConcurrentMarkSweepGeneration::
1094 par_promote_alloc_done(int thread_num) {
1095 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1096 ps->lab.retire(thread_num);
1097 }
1098
1099 void
1100 ConcurrentMarkSweepGeneration::
1101 par_oop_since_save_marks_iterate_done(int thread_num) {
1102 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1103 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1104 ps->promo.promoted_oops_iterate(dummy_cl);
1105
1106 // Because card-scanning has been completed, subsequent phases
1107 // (e.g., reference processing) will not need to recognize which
1108 // objects have been promoted during this GC. So, we can now disable
1109 // promotion tracking.
1110 ps->promo.stopTrackingPromotions();
1111 }
1112
1113 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1114 size_t size,
1115 bool tlab)
1116 {
1117 // We allow a STW collection only if a full
1118 // collection was requested.
1119 return full || should_allocate(size, tlab); // FIX ME !!!
1120 // This and promotion failure handling are connected at the
1121 // hip and should be fixed by untying them.
1122 }
1123
1124 bool CMSCollector::shouldConcurrentCollect() {
1125 LogTarget(Trace, gc) log;
1126
1127 if (_full_gc_requested) {
1128 log.print("CMSCollector: collect because of explicit gc request (or GCLocker)");
1129 return true;
1130 }
1131
1132 FreelistLocker x(this);
1133 // ------------------------------------------------------------------
1134 // Print out lots of information which affects the initiation of
1135 // a collection.
1136 if (log.is_enabled() && stats().valid()) {
1137 log.print("CMSCollector shouldConcurrentCollect: ");
1138
1139 LogStream out(log);
1140 stats().print_on(&out);
1141
1142 log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full());
1143 log.print("free=" SIZE_FORMAT, _cmsGen->free());
1144 log.print("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available());
1145 log.print("promotion_rate=%g", stats().promotion_rate());
1146 log.print("cms_allocation_rate=%g", stats().cms_allocation_rate());
1147 log.print("occupancy=%3.7f", _cmsGen->occupancy());
1148 log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1149 log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1150 log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1151 log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect());
1152 }
1153 // ------------------------------------------------------------------
1154
1155 // If the estimated time to complete a cms collection (cms_duration())
1156 // is less than the estimated time remaining until the cms generation
1157 // is full, start a collection.
1158 if (!UseCMSInitiatingOccupancyOnly) {
1159 if (stats().valid()) {
1160 if (stats().time_until_cms_start() == 0.0) {
1161 return true;
1162 }
1163 } else {
1164 // We want to conservatively collect somewhat early in order
1165 // to try and "bootstrap" our CMS/promotion statistics;
1166 // this branch will not fire after the first successful CMS
1167 // collection because the stats should then be valid.
1168 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1169 log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f",
1170 _cmsGen->occupancy(), _bootstrap_occupancy);
1171 return true;
1172 }
1173 }
1174 }
1175
1176 // Otherwise, we start a collection cycle if
1177 // old gen want a collection cycle started. Each may use
1178 // an appropriate criterion for making this decision.
1179 // XXX We need to make sure that the gen expansion
1180 // criterion dovetails well with this. XXX NEED TO FIX THIS
1181 if (_cmsGen->should_concurrent_collect()) {
1182 log.print("CMS old gen initiated");
1183 return true;
1184 }
1185
1186 // We start a collection if we believe an incremental collection may fail;
1187 // this is not likely to be productive in practice because it's probably too
1188 // late anyway.
1189 CMSHeap* heap = CMSHeap::heap();
1190 if (heap->incremental_collection_will_fail(true /* consult_young */)) {
1191 log.print("CMSCollector: collect because incremental collection will fail ");
1192 return true;
1193 }
1194
1195 if (MetaspaceGC::should_concurrent_collect()) {
1196 log.print("CMSCollector: collect for metadata allocation ");
1197 return true;
1198 }
1199
1200 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1201 if (CMSTriggerInterval >= 0) {
1202 if (CMSTriggerInterval == 0) {
1203 // Trigger always
1204 return true;
1205 }
1206
1207 // Check the CMS time since begin (we do not check the stats validity
1208 // as we want to be able to trigger the first CMS cycle as well)
1209 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1210 if (stats().valid()) {
1211 log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1212 stats().cms_time_since_begin());
1213 } else {
1214 log.print("CMSCollector: collect because of trigger interval (first collection)");
1215 }
1216 return true;
1217 }
1218 }
1219
1220 return false;
1221 }
1222
1223 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1224
1225 // Clear _expansion_cause fields of constituent generations
1226 void CMSCollector::clear_expansion_cause() {
1227 _cmsGen->clear_expansion_cause();
1228 }
1229
1230 // We should be conservative in starting a collection cycle. To
1231 // start too eagerly runs the risk of collecting too often in the
1232 // extreme. To collect too rarely falls back on full collections,
1233 // which works, even if not optimum in terms of concurrent work.
1234 // As a work around for too eagerly collecting, use the flag
1235 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1236 // giving the user an easily understandable way of controlling the
1237 // collections.
1238 // We want to start a new collection cycle if any of the following
1239 // conditions hold:
1240 // . our current occupancy exceeds the configured initiating occupancy
1241 // for this generation, or
1242 // . we recently needed to expand this space and have not, since that
1243 // expansion, done a collection of this generation, or
1244 // . the underlying space believes that it may be a good idea to initiate
1245 // a concurrent collection (this may be based on criteria such as the
1246 // following: the space uses linear allocation and linear allocation is
1247 // going to fail, or there is believed to be excessive fragmentation in
1248 // the generation, etc... or ...
1249 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1250 // the case of the old generation; see CR 6543076):
1251 // we may be approaching a point at which allocation requests may fail because
1252 // we will be out of sufficient free space given allocation rate estimates.]
1253 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1254
1255 assert_lock_strong(freelistLock());
1256 if (occupancy() > initiating_occupancy()) {
1257 log_trace(gc)(" %s: collect because of occupancy %f / %f ",
1258 short_name(), occupancy(), initiating_occupancy());
1259 return true;
1260 }
1261 if (UseCMSInitiatingOccupancyOnly) {
1262 return false;
1263 }
1264 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1265 log_trace(gc)(" %s: collect because expanded for allocation ", short_name());
1266 return true;
1267 }
1268 return false;
1269 }
1270
1271 void ConcurrentMarkSweepGeneration::collect(bool full,
1272 bool clear_all_soft_refs,
1273 size_t size,
1274 bool tlab)
1275 {
1276 collector()->collect(full, clear_all_soft_refs, size, tlab);
1277 }
1278
1279 void CMSCollector::collect(bool full,
1280 bool clear_all_soft_refs,
1281 size_t size,
1282 bool tlab)
1283 {
1284 // The following "if" branch is present for defensive reasons.
1285 // In the current uses of this interface, it can be replaced with:
1286 // assert(!GCLocker.is_active(), "Can't be called otherwise");
1287 // But I am not placing that assert here to allow future
1288 // generality in invoking this interface.
1289 if (GCLocker::is_active()) {
1290 // A consistency test for GCLocker
1291 assert(GCLocker::needs_gc(), "Should have been set already");
1292 // Skip this foreground collection, instead
1293 // expanding the heap if necessary.
1294 // Need the free list locks for the call to free() in compute_new_size()
1295 compute_new_size();
1296 return;
1297 }
1298 acquire_control_and_collect(full, clear_all_soft_refs);
1299 }
1300
1301 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1302 CMSHeap* heap = CMSHeap::heap();
1303 unsigned int gc_count = heap->total_full_collections();
1304 if (gc_count == full_gc_count) {
1305 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1306 _full_gc_requested = true;
1307 _full_gc_cause = cause;
1308 CGC_lock->notify(); // nudge CMS thread
1309 } else {
1310 assert(gc_count > full_gc_count, "Error: causal loop");
1311 }
1312 }
1313
1314 bool CMSCollector::is_external_interruption() {
1315 GCCause::Cause cause = CMSHeap::heap()->gc_cause();
1316 return GCCause::is_user_requested_gc(cause) ||
1317 GCCause::is_serviceability_requested_gc(cause);
1318 }
1319
1320 void CMSCollector::report_concurrent_mode_interruption() {
1321 if (is_external_interruption()) {
1322 log_debug(gc)("Concurrent mode interrupted");
1323 } else {
1324 log_debug(gc)("Concurrent mode failure");
1325 _gc_tracer_cm->report_concurrent_mode_failure();
1326 }
1327 }
1328
1329
1330 // The foreground and background collectors need to coordinate in order
1331 // to make sure that they do not mutually interfere with CMS collections.
1332 // When a background collection is active,
1333 // the foreground collector may need to take over (preempt) and
1334 // synchronously complete an ongoing collection. Depending on the
1335 // frequency of the background collections and the heap usage
1336 // of the application, this preemption can be seldom or frequent.
1337 // There are only certain
1338 // points in the background collection that the "collection-baton"
1339 // can be passed to the foreground collector.
1340 //
1341 // The foreground collector will wait for the baton before
1342 // starting any part of the collection. The foreground collector
1343 // will only wait at one location.
1344 //
1345 // The background collector will yield the baton before starting a new
1346 // phase of the collection (e.g., before initial marking, marking from roots,
1347 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1348 // of the loop which switches the phases. The background collector does some
1349 // of the phases (initial mark, final re-mark) with the world stopped.
1350 // Because of locking involved in stopping the world,
1351 // the foreground collector should not block waiting for the background
1352 // collector when it is doing a stop-the-world phase. The background
1353 // collector will yield the baton at an additional point just before
1354 // it enters a stop-the-world phase. Once the world is stopped, the
1355 // background collector checks the phase of the collection. If the
1356 // phase has not changed, it proceeds with the collection. If the
1357 // phase has changed, it skips that phase of the collection. See
1358 // the comments on the use of the Heap_lock in collect_in_background().
1359 //
1360 // Variable used in baton passing.
1361 // _foregroundGCIsActive - Set to true by the foreground collector when
1362 // it wants the baton. The foreground clears it when it has finished
1363 // the collection.
1364 // _foregroundGCShouldWait - Set to true by the background collector
1365 // when it is running. The foreground collector waits while
1366 // _foregroundGCShouldWait is true.
1367 // CGC_lock - monitor used to protect access to the above variables
1368 // and to notify the foreground and background collectors.
1369 // _collectorState - current state of the CMS collection.
1370 //
1371 // The foreground collector
1372 // acquires the CGC_lock
1373 // sets _foregroundGCIsActive
1374 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1375 // various locks acquired in preparation for the collection
1376 // are released so as not to block the background collector
1377 // that is in the midst of a collection
1378 // proceeds with the collection
1379 // clears _foregroundGCIsActive
1380 // returns
1381 //
1382 // The background collector in a loop iterating on the phases of the
1383 // collection
1384 // acquires the CGC_lock
1385 // sets _foregroundGCShouldWait
1386 // if _foregroundGCIsActive is set
1387 // clears _foregroundGCShouldWait, notifies _CGC_lock
1388 // waits on _CGC_lock for _foregroundGCIsActive to become false
1389 // and exits the loop.
1390 // otherwise
1391 // proceed with that phase of the collection
1392 // if the phase is a stop-the-world phase,
1393 // yield the baton once more just before enqueueing
1394 // the stop-world CMS operation (executed by the VM thread).
1395 // returns after all phases of the collection are done
1396 //
1397
1398 void CMSCollector::acquire_control_and_collect(bool full,
1399 bool clear_all_soft_refs) {
1400 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1401 assert(!Thread::current()->is_ConcurrentGC_thread(),
1402 "shouldn't try to acquire control from self!");
1403
1404 // Start the protocol for acquiring control of the
1405 // collection from the background collector (aka CMS thread).
1406 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1407 "VM thread should have CMS token");
1408 // Remember the possibly interrupted state of an ongoing
1409 // concurrent collection
1410 CollectorState first_state = _collectorState;
1411
1412 // Signal to a possibly ongoing concurrent collection that
1413 // we want to do a foreground collection.
1414 _foregroundGCIsActive = true;
1415
1416 // release locks and wait for a notify from the background collector
1417 // releasing the locks in only necessary for phases which
1418 // do yields to improve the granularity of the collection.
1419 assert_lock_strong(bitMapLock());
1420 // We need to lock the Free list lock for the space that we are
1421 // currently collecting.
1422 assert(haveFreelistLocks(), "Must be holding free list locks");
1423 bitMapLock()->unlock();
1424 releaseFreelistLocks();
1425 {
1426 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1427 if (_foregroundGCShouldWait) {
1428 // We are going to be waiting for action for the CMS thread;
1429 // it had better not be gone (for instance at shutdown)!
1430 assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(),
1431 "CMS thread must be running");
1432 // Wait here until the background collector gives us the go-ahead
1433 ConcurrentMarkSweepThread::clear_CMS_flag(
1434 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1435 // Get a possibly blocked CMS thread going:
1436 // Note that we set _foregroundGCIsActive true above,
1437 // without protection of the CGC_lock.
1438 CGC_lock->notify();
1439 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1440 "Possible deadlock");
1441 while (_foregroundGCShouldWait) {
1442 // wait for notification
1443 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1444 // Possibility of delay/starvation here, since CMS token does
1445 // not know to give priority to VM thread? Actually, i think
1446 // there wouldn't be any delay/starvation, but the proof of
1447 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1448 }
1449 ConcurrentMarkSweepThread::set_CMS_flag(
1450 ConcurrentMarkSweepThread::CMS_vm_has_token);
1451 }
1452 }
1453 // The CMS_token is already held. Get back the other locks.
1454 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1455 "VM thread should have CMS token");
1456 getFreelistLocks();
1457 bitMapLock()->lock_without_safepoint_check();
1458 log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d",
1459 p2i(Thread::current()), first_state);
1460 log_debug(gc, state)(" gets control with state %d", _collectorState);
1461
1462 // Inform cms gen if this was due to partial collection failing.
1463 // The CMS gen may use this fact to determine its expansion policy.
1464 CMSHeap* heap = CMSHeap::heap();
1465 if (heap->incremental_collection_will_fail(false /* don't consult_young */)) {
1466 assert(!_cmsGen->incremental_collection_failed(),
1467 "Should have been noticed, reacted to and cleared");
1468 _cmsGen->set_incremental_collection_failed();
1469 }
1470
1471 if (first_state > Idling) {
1472 report_concurrent_mode_interruption();
1473 }
1474
1475 set_did_compact(true);
1476
1477 // If the collection is being acquired from the background
1478 // collector, there may be references on the discovered
1479 // references lists. Abandon those references, since some
1480 // of them may have become unreachable after concurrent
1481 // discovery; the STW compacting collector will redo discovery
1482 // more precisely, without being subject to floating garbage.
1483 // Leaving otherwise unreachable references in the discovered
1484 // lists would require special handling.
1485 ref_processor()->disable_discovery();
1486 ref_processor()->abandon_partial_discovery();
1487 ref_processor()->verify_no_references_recorded();
1488
1489 if (first_state > Idling) {
1490 save_heap_summary();
1491 }
1492
1493 do_compaction_work(clear_all_soft_refs);
1494
1495 // Has the GC time limit been exceeded?
1496 size_t max_eden_size = _young_gen->max_eden_size();
1497 GCCause::Cause gc_cause = heap->gc_cause();
1498 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1499 _young_gen->eden()->used(),
1500 _cmsGen->max_capacity(),
1501 max_eden_size,
1502 full,
1503 gc_cause,
1504 heap->soft_ref_policy());
1505
1506 // Reset the expansion cause, now that we just completed
1507 // a collection cycle.
1508 clear_expansion_cause();
1509 _foregroundGCIsActive = false;
1510 return;
1511 }
1512
1513 // Resize the tenured generation
1514 // after obtaining the free list locks for the
1515 // two generations.
1516 void CMSCollector::compute_new_size() {
1517 assert_locked_or_safepoint(Heap_lock);
1518 FreelistLocker z(this);
1519 MetaspaceGC::compute_new_size();
1520 _cmsGen->compute_new_size_free_list();
1521 }
1522
1523 // A work method used by the foreground collector to do
1524 // a mark-sweep-compact.
1525 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1526 CMSHeap* heap = CMSHeap::heap();
1527
1528 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1529 gc_timer->register_gc_start();
1530
1531 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1532 gc_tracer->report_gc_start(heap->gc_cause(), gc_timer->gc_start());
1533
1534 heap->pre_full_gc_dump(gc_timer);
1535
1536 GCTraceTime(Trace, gc, phases) t("CMS:MSC");
1537
1538 // Temporarily widen the span of the weak reference processing to
1539 // the entire heap.
1540 MemRegion new_span(CMSHeap::heap()->reserved_region());
1541 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1542 // Temporarily, clear the "is_alive_non_header" field of the
1543 // reference processor.
1544 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1545 // Temporarily make reference _processing_ single threaded (non-MT).
1546 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1547 // Temporarily make refs discovery atomic
1548 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1549 // Temporarily make reference _discovery_ single threaded (non-MT)
1550 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1551
1552 ref_processor()->set_enqueuing_is_done(false);
1553 ref_processor()->enable_discovery();
1554 ref_processor()->setup_policy(clear_all_soft_refs);
1555 // If an asynchronous collection finishes, the _modUnionTable is
1556 // all clear. If we are assuming the collection from an asynchronous
1557 // collection, clear the _modUnionTable.
1558 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1559 "_modUnionTable should be clear if the baton was not passed");
1560 _modUnionTable.clear_all();
1561 assert(_collectorState != Idling || _ct->cld_rem_set()->mod_union_is_clear(),
1562 "mod union for klasses should be clear if the baton was passed");
1563 _ct->cld_rem_set()->clear_mod_union();
1564
1565
1566 // We must adjust the allocation statistics being maintained
1567 // in the free list space. We do so by reading and clearing
1568 // the sweep timer and updating the block flux rate estimates below.
1569 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1570 if (_inter_sweep_timer.is_active()) {
1571 _inter_sweep_timer.stop();
1572 // Note that we do not use this sample to update the _inter_sweep_estimate.
1573 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1574 _inter_sweep_estimate.padded_average(),
1575 _intra_sweep_estimate.padded_average());
1576 }
1577
1578 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1579 #ifdef ASSERT
1580 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1581 size_t free_size = cms_space->free();
1582 assert(free_size ==
1583 pointer_delta(cms_space->end(), cms_space->compaction_top())
1584 * HeapWordSize,
1585 "All the free space should be compacted into one chunk at top");
1586 assert(cms_space->dictionary()->total_chunk_size(
1587 debug_only(cms_space->freelistLock())) == 0 ||
1588 cms_space->totalSizeInIndexedFreeLists() == 0,
1589 "All the free space should be in a single chunk");
1590 size_t num = cms_space->totalCount();
1591 assert((free_size == 0 && num == 0) ||
1592 (free_size > 0 && (num == 1 || num == 2)),
1593 "There should be at most 2 free chunks after compaction");
1594 #endif // ASSERT
1595 _collectorState = Resetting;
1596 assert(_restart_addr == NULL,
1597 "Should have been NULL'd before baton was passed");
1598 reset_stw();
1599 _cmsGen->reset_after_compaction();
1600 _concurrent_cycles_since_last_unload = 0;
1601
1602 // Clear any data recorded in the PLAB chunk arrays.
1603 if (_survivor_plab_array != NULL) {
1604 reset_survivor_plab_arrays();
1605 }
1606
1607 // Adjust the per-size allocation stats for the next epoch.
1608 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1609 // Restart the "inter sweep timer" for the next epoch.
1610 _inter_sweep_timer.reset();
1611 _inter_sweep_timer.start();
1612
1613 // No longer a need to do a concurrent collection for Metaspace.
1614 MetaspaceGC::set_should_concurrent_collect(false);
1615
1616 heap->post_full_gc_dump(gc_timer);
1617
1618 gc_timer->register_gc_end();
1619
1620 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1621
1622 // For a mark-sweep-compact, compute_new_size() will be called
1623 // in the heap's do_collection() method.
1624 }
1625
1626 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1627 Log(gc, heap) log;
1628 if (!log.is_trace()) {
1629 return;
1630 }
1631
1632 ContiguousSpace* eden_space = _young_gen->eden();
1633 ContiguousSpace* from_space = _young_gen->from();
1634 ContiguousSpace* to_space = _young_gen->to();
1635 // Eden
1636 if (_eden_chunk_array != NULL) {
1637 log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1638 p2i(eden_space->bottom()), p2i(eden_space->top()),
1639 p2i(eden_space->end()), eden_space->capacity());
1640 log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT,
1641 _eden_chunk_index, _eden_chunk_capacity);
1642 for (size_t i = 0; i < _eden_chunk_index; i++) {
1643 log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i]));
1644 }
1645 }
1646 // Survivor
1647 if (_survivor_chunk_array != NULL) {
1648 log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1649 p2i(from_space->bottom()), p2i(from_space->top()),
1650 p2i(from_space->end()), from_space->capacity());
1651 log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT,
1652 _survivor_chunk_index, _survivor_chunk_capacity);
1653 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1654 log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i]));
1655 }
1656 }
1657 }
1658
1659 void CMSCollector::getFreelistLocks() const {
1660 // Get locks for all free lists in all generations that this
1661 // collector is responsible for
1662 _cmsGen->freelistLock()->lock_without_safepoint_check();
1663 }
1664
1665 void CMSCollector::releaseFreelistLocks() const {
1666 // Release locks for all free lists in all generations that this
1667 // collector is responsible for
1668 _cmsGen->freelistLock()->unlock();
1669 }
1670
1671 bool CMSCollector::haveFreelistLocks() const {
1672 // Check locks for all free lists in all generations that this
1673 // collector is responsible for
1674 assert_lock_strong(_cmsGen->freelistLock());
1675 PRODUCT_ONLY(ShouldNotReachHere());
1676 return true;
1677 }
1678
1679 // A utility class that is used by the CMS collector to
1680 // temporarily "release" the foreground collector from its
1681 // usual obligation to wait for the background collector to
1682 // complete an ongoing phase before proceeding.
1683 class ReleaseForegroundGC: public StackObj {
1684 private:
1685 CMSCollector* _c;
1686 public:
1687 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1688 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1689 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1690 // allow a potentially blocked foreground collector to proceed
1691 _c->_foregroundGCShouldWait = false;
1692 if (_c->_foregroundGCIsActive) {
1693 CGC_lock->notify();
1694 }
1695 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1696 "Possible deadlock");
1697 }
1698
1699 ~ReleaseForegroundGC() {
1700 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1701 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1702 _c->_foregroundGCShouldWait = true;
1703 }
1704 };
1705
1706 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1707 assert(Thread::current()->is_ConcurrentGC_thread(),
1708 "A CMS asynchronous collection is only allowed on a CMS thread.");
1709
1710 CMSHeap* heap = CMSHeap::heap();
1711 {
1712 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1713 MutexLockerEx hl(Heap_lock, safepoint_check);
1714 FreelistLocker fll(this);
1715 MutexLockerEx x(CGC_lock, safepoint_check);
1716 if (_foregroundGCIsActive) {
1717 // The foreground collector is. Skip this
1718 // background collection.
1719 assert(!_foregroundGCShouldWait, "Should be clear");
1720 return;
1721 } else {
1722 assert(_collectorState == Idling, "Should be idling before start.");
1723 _collectorState = InitialMarking;
1724 register_gc_start(cause);
1725 // Reset the expansion cause, now that we are about to begin
1726 // a new cycle.
1727 clear_expansion_cause();
1728
1729 // Clear the MetaspaceGC flag since a concurrent collection
1730 // is starting but also clear it after the collection.
1731 MetaspaceGC::set_should_concurrent_collect(false);
1732 }
1733 // Decide if we want to enable class unloading as part of the
1734 // ensuing concurrent GC cycle.
1735 update_should_unload_classes();
1736 _full_gc_requested = false; // acks all outstanding full gc requests
1737 _full_gc_cause = GCCause::_no_gc;
1738 // Signal that we are about to start a collection
1739 heap->increment_total_full_collections(); // ... starting a collection cycle
1740 _collection_count_start = heap->total_full_collections();
1741 }
1742
1743 size_t prev_used = _cmsGen->used();
1744
1745 // The change of the collection state is normally done at this level;
1746 // the exceptions are phases that are executed while the world is
1747 // stopped. For those phases the change of state is done while the
1748 // world is stopped. For baton passing purposes this allows the
1749 // background collector to finish the phase and change state atomically.
1750 // The foreground collector cannot wait on a phase that is done
1751 // while the world is stopped because the foreground collector already
1752 // has the world stopped and would deadlock.
1753 while (_collectorState != Idling) {
1754 log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d",
1755 p2i(Thread::current()), _collectorState);
1756 // The foreground collector
1757 // holds the Heap_lock throughout its collection.
1758 // holds the CMS token (but not the lock)
1759 // except while it is waiting for the background collector to yield.
1760 //
1761 // The foreground collector should be blocked (not for long)
1762 // if the background collector is about to start a phase
1763 // executed with world stopped. If the background
1764 // collector has already started such a phase, the
1765 // foreground collector is blocked waiting for the
1766 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1767 // are executed in the VM thread.
1768 //
1769 // The locking order is
1770 // PendingListLock (PLL) -- if applicable (FinalMarking)
1771 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1772 // CMS token (claimed in
1773 // stop_world_and_do() -->
1774 // safepoint_synchronize() -->
1775 // CMSThread::synchronize())
1776
1777 {
1778 // Check if the FG collector wants us to yield.
1779 CMSTokenSync x(true); // is cms thread
1780 if (waitForForegroundGC()) {
1781 // We yielded to a foreground GC, nothing more to be
1782 // done this round.
1783 assert(_foregroundGCShouldWait == false, "We set it to false in "
1784 "waitForForegroundGC()");
1785 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1786 p2i(Thread::current()), _collectorState);
1787 return;
1788 } else {
1789 // The background collector can run but check to see if the
1790 // foreground collector has done a collection while the
1791 // background collector was waiting to get the CGC_lock
1792 // above. If yes, break so that _foregroundGCShouldWait
1793 // is cleared before returning.
1794 if (_collectorState == Idling) {
1795 break;
1796 }
1797 }
1798 }
1799
1800 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1801 "should be waiting");
1802
1803 switch (_collectorState) {
1804 case InitialMarking:
1805 {
1806 ReleaseForegroundGC x(this);
1807 stats().record_cms_begin();
1808 VM_CMS_Initial_Mark initial_mark_op(this);
1809 VMThread::execute(&initial_mark_op);
1810 }
1811 // The collector state may be any legal state at this point
1812 // since the background collector may have yielded to the
1813 // foreground collector.
1814 break;
1815 case Marking:
1816 // initial marking in checkpointRootsInitialWork has been completed
1817 if (markFromRoots()) { // we were successful
1818 assert(_collectorState == Precleaning, "Collector state should "
1819 "have changed");
1820 } else {
1821 assert(_foregroundGCIsActive, "Internal state inconsistency");
1822 }
1823 break;
1824 case Precleaning:
1825 // marking from roots in markFromRoots has been completed
1826 preclean();
1827 assert(_collectorState == AbortablePreclean ||
1828 _collectorState == FinalMarking,
1829 "Collector state should have changed");
1830 break;
1831 case AbortablePreclean:
1832 abortable_preclean();
1833 assert(_collectorState == FinalMarking, "Collector state should "
1834 "have changed");
1835 break;
1836 case FinalMarking:
1837 {
1838 ReleaseForegroundGC x(this);
1839
1840 VM_CMS_Final_Remark final_remark_op(this);
1841 VMThread::execute(&final_remark_op);
1842 }
1843 assert(_foregroundGCShouldWait, "block post-condition");
1844 break;
1845 case Sweeping:
1846 // final marking in checkpointRootsFinal has been completed
1847 sweep();
1848 assert(_collectorState == Resizing, "Collector state change "
1849 "to Resizing must be done under the free_list_lock");
1850
1851 case Resizing: {
1852 // Sweeping has been completed...
1853 // At this point the background collection has completed.
1854 // Don't move the call to compute_new_size() down
1855 // into code that might be executed if the background
1856 // collection was preempted.
1857 {
1858 ReleaseForegroundGC x(this); // unblock FG collection
1859 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1860 CMSTokenSync z(true); // not strictly needed.
1861 if (_collectorState == Resizing) {
1862 compute_new_size();
1863 save_heap_summary();
1864 _collectorState = Resetting;
1865 } else {
1866 assert(_collectorState == Idling, "The state should only change"
1867 " because the foreground collector has finished the collection");
1868 }
1869 }
1870 break;
1871 }
1872 case Resetting:
1873 // CMS heap resizing has been completed
1874 reset_concurrent();
1875 assert(_collectorState == Idling, "Collector state should "
1876 "have changed");
1877
1878 MetaspaceGC::set_should_concurrent_collect(false);
1879
1880 stats().record_cms_end();
1881 // Don't move the concurrent_phases_end() and compute_new_size()
1882 // calls to here because a preempted background collection
1883 // has it's state set to "Resetting".
1884 break;
1885 case Idling:
1886 default:
1887 ShouldNotReachHere();
1888 break;
1889 }
1890 log_debug(gc, state)(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1891 p2i(Thread::current()), _collectorState);
1892 assert(_foregroundGCShouldWait, "block post-condition");
1893 }
1894
1895 // Should this be in gc_epilogue?
1896 heap->counters()->update_counters();
1897
1898 {
1899 // Clear _foregroundGCShouldWait and, in the event that the
1900 // foreground collector is waiting, notify it, before
1901 // returning.
1902 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1903 _foregroundGCShouldWait = false;
1904 if (_foregroundGCIsActive) {
1905 CGC_lock->notify();
1906 }
1907 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1908 "Possible deadlock");
1909 }
1910 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1911 p2i(Thread::current()), _collectorState);
1912 log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K(" SIZE_FORMAT "K)",
1913 prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K);
1914 }
1915
1916 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1917 _cms_start_registered = true;
1918 _gc_timer_cm->register_gc_start();
1919 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1920 }
1921
1922 void CMSCollector::register_gc_end() {
1923 if (_cms_start_registered) {
1924 report_heap_summary(GCWhen::AfterGC);
1925
1926 _gc_timer_cm->register_gc_end();
1927 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1928 _cms_start_registered = false;
1929 }
1930 }
1931
1932 void CMSCollector::save_heap_summary() {
1933 CMSHeap* heap = CMSHeap::heap();
1934 _last_heap_summary = heap->create_heap_summary();
1935 _last_metaspace_summary = heap->create_metaspace_summary();
1936 }
1937
1938 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1939 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1940 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1941 }
1942
1943 bool CMSCollector::waitForForegroundGC() {
1944 bool res = false;
1945 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1946 "CMS thread should have CMS token");
1947 // Block the foreground collector until the
1948 // background collectors decides whether to
1949 // yield.
1950 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1951 _foregroundGCShouldWait = true;
1952 if (_foregroundGCIsActive) {
1953 // The background collector yields to the
1954 // foreground collector and returns a value
1955 // indicating that it has yielded. The foreground
1956 // collector can proceed.
1957 res = true;
1958 _foregroundGCShouldWait = false;
1959 ConcurrentMarkSweepThread::clear_CMS_flag(
1960 ConcurrentMarkSweepThread::CMS_cms_has_token);
1961 ConcurrentMarkSweepThread::set_CMS_flag(
1962 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1963 // Get a possibly blocked foreground thread going
1964 CGC_lock->notify();
1965 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
1966 p2i(Thread::current()), _collectorState);
1967 while (_foregroundGCIsActive) {
1968 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1969 }
1970 ConcurrentMarkSweepThread::set_CMS_flag(
1971 ConcurrentMarkSweepThread::CMS_cms_has_token);
1972 ConcurrentMarkSweepThread::clear_CMS_flag(
1973 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1974 }
1975 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
1976 p2i(Thread::current()), _collectorState);
1977 return res;
1978 }
1979
1980 // Because of the need to lock the free lists and other structures in
1981 // the collector, common to all the generations that the collector is
1982 // collecting, we need the gc_prologues of individual CMS generations
1983 // delegate to their collector. It may have been simpler had the
1984 // current infrastructure allowed one to call a prologue on a
1985 // collector. In the absence of that we have the generation's
1986 // prologue delegate to the collector, which delegates back
1987 // some "local" work to a worker method in the individual generations
1988 // that it's responsible for collecting, while itself doing any
1989 // work common to all generations it's responsible for. A similar
1990 // comment applies to the gc_epilogue()'s.
1991 // The role of the variable _between_prologue_and_epilogue is to
1992 // enforce the invocation protocol.
1993 void CMSCollector::gc_prologue(bool full) {
1994 // Call gc_prologue_work() for the CMSGen
1995 // we are responsible for.
1996
1997 // The following locking discipline assumes that we are only called
1998 // when the world is stopped.
1999 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2000
2001 // The CMSCollector prologue must call the gc_prologues for the
2002 // "generations" that it's responsible
2003 // for.
2004
2005 assert( Thread::current()->is_VM_thread()
2006 || ( CMSScavengeBeforeRemark
2007 && Thread::current()->is_ConcurrentGC_thread()),
2008 "Incorrect thread type for prologue execution");
2009
2010 if (_between_prologue_and_epilogue) {
2011 // We have already been invoked; this is a gc_prologue delegation
2012 // from yet another CMS generation that we are responsible for, just
2013 // ignore it since all relevant work has already been done.
2014 return;
2015 }
2016
2017 // set a bit saying prologue has been called; cleared in epilogue
2018 _between_prologue_and_epilogue = true;
2019 // Claim locks for common data structures, then call gc_prologue_work()
2020 // for each CMSGen.
2021
2022 getFreelistLocks(); // gets free list locks on constituent spaces
2023 bitMapLock()->lock_without_safepoint_check();
2024
2025 // Should call gc_prologue_work() for all cms gens we are responsible for
2026 bool duringMarking = _collectorState >= Marking
2027 && _collectorState < Sweeping;
2028
2029 // The young collections clear the modified oops state, which tells if
2030 // there are any modified oops in the class. The remark phase also needs
2031 // that information. Tell the young collection to save the union of all
2032 // modified klasses.
2033 if (duringMarking) {
2034 _ct->cld_rem_set()->set_accumulate_modified_oops(true);
2035 }
2036
2037 bool registerClosure = duringMarking;
2038
2039 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2040
2041 if (!full) {
2042 stats().record_gc0_begin();
2043 }
2044 }
2045
2046 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2047
2048 _capacity_at_prologue = capacity();
2049 _used_at_prologue = used();
2050
2051 // We enable promotion tracking so that card-scanning can recognize
2052 // which objects have been promoted during this GC and skip them.
2053 for (uint i = 0; i < ParallelGCThreads; i++) {
2054 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2055 }
2056
2057 // Delegate to CMScollector which knows how to coordinate between
2058 // this and any other CMS generations that it is responsible for
2059 // collecting.
2060 collector()->gc_prologue(full);
2061 }
2062
2063 // This is a "private" interface for use by this generation's CMSCollector.
2064 // Not to be called directly by any other entity (for instance,
2065 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2066 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2067 bool registerClosure, ModUnionClosure* modUnionClosure) {
2068 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2069 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2070 "Should be NULL");
2071 if (registerClosure) {
2072 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2073 }
2074 cmsSpace()->gc_prologue();
2075 // Clear stat counters
2076 NOT_PRODUCT(
2077 assert(_numObjectsPromoted == 0, "check");
2078 assert(_numWordsPromoted == 0, "check");
2079 log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently",
2080 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2081 _numObjectsAllocated = 0;
2082 _numWordsAllocated = 0;
2083 )
2084 }
2085
2086 void CMSCollector::gc_epilogue(bool full) {
2087 // The following locking discipline assumes that we are only called
2088 // when the world is stopped.
2089 assert(SafepointSynchronize::is_at_safepoint(),
2090 "world is stopped assumption");
2091
2092 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2093 // if linear allocation blocks need to be appropriately marked to allow the
2094 // the blocks to be parsable. We also check here whether we need to nudge the
2095 // CMS collector thread to start a new cycle (if it's not already active).
2096 assert( Thread::current()->is_VM_thread()
2097 || ( CMSScavengeBeforeRemark
2098 && Thread::current()->is_ConcurrentGC_thread()),
2099 "Incorrect thread type for epilogue execution");
2100
2101 if (!_between_prologue_and_epilogue) {
2102 // We have already been invoked; this is a gc_epilogue delegation
2103 // from yet another CMS generation that we are responsible for, just
2104 // ignore it since all relevant work has already been done.
2105 return;
2106 }
2107 assert(haveFreelistLocks(), "must have freelist locks");
2108 assert_lock_strong(bitMapLock());
2109
2110 _ct->cld_rem_set()->set_accumulate_modified_oops(false);
2111
2112 _cmsGen->gc_epilogue_work(full);
2113
2114 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2115 // in case sampling was not already enabled, enable it
2116 _start_sampling = true;
2117 }
2118 // reset _eden_chunk_array so sampling starts afresh
2119 _eden_chunk_index = 0;
2120
2121 size_t cms_used = _cmsGen->cmsSpace()->used();
2122
2123 // update performance counters - this uses a special version of
2124 // update_counters() that allows the utilization to be passed as a
2125 // parameter, avoiding multiple calls to used().
2126 //
2127 _cmsGen->update_counters(cms_used);
2128
2129 bitMapLock()->unlock();
2130 releaseFreelistLocks();
2131
2132 if (!CleanChunkPoolAsync) {
2133 Chunk::clean_chunk_pool();
2134 }
2135
2136 set_did_compact(false);
2137 _between_prologue_and_epilogue = false; // ready for next cycle
2138 }
2139
2140 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2141 collector()->gc_epilogue(full);
2142
2143 // When using ParNew, promotion tracking should have already been
2144 // disabled. However, the prologue (which enables promotion
2145 // tracking) and epilogue are called irrespective of the type of
2146 // GC. So they will also be called before and after Full GCs, during
2147 // which promotion tracking will not be explicitly disabled. So,
2148 // it's safer to also disable it here too (to be symmetric with
2149 // enabling it in the prologue).
2150 for (uint i = 0; i < ParallelGCThreads; i++) {
2151 _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2152 }
2153 }
2154
2155 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2156 assert(!incremental_collection_failed(), "Should have been cleared");
2157 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2158 cmsSpace()->gc_epilogue();
2159 // Print stat counters
2160 NOT_PRODUCT(
2161 assert(_numObjectsAllocated == 0, "check");
2162 assert(_numWordsAllocated == 0, "check");
2163 log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
2164 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2165 _numObjectsPromoted = 0;
2166 _numWordsPromoted = 0;
2167 )
2168
2169 // Call down the chain in contiguous_available needs the freelistLock
2170 // so print this out before releasing the freeListLock.
2171 log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available());
2172 }
2173
2174 #ifndef PRODUCT
2175 bool CMSCollector::have_cms_token() {
2176 Thread* thr = Thread::current();
2177 if (thr->is_VM_thread()) {
2178 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2179 } else if (thr->is_ConcurrentGC_thread()) {
2180 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2181 } else if (thr->is_GC_task_thread()) {
2182 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2183 ParGCRareEvent_lock->owned_by_self();
2184 }
2185 return false;
2186 }
2187
2188 // Check reachability of the given heap address in CMS generation,
2189 // treating all other generations as roots.
2190 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2191 // We could "guarantee" below, rather than assert, but I'll
2192 // leave these as "asserts" so that an adventurous debugger
2193 // could try this in the product build provided some subset of
2194 // the conditions were met, provided they were interested in the
2195 // results and knew that the computation below wouldn't interfere
2196 // with other concurrent computations mutating the structures
2197 // being read or written.
2198 assert(SafepointSynchronize::is_at_safepoint(),
2199 "Else mutations in object graph will make answer suspect");
2200 assert(have_cms_token(), "Should hold cms token");
2201 assert(haveFreelistLocks(), "must hold free list locks");
2202 assert_lock_strong(bitMapLock());
2203
2204 // Clear the marking bit map array before starting, but, just
2205 // for kicks, first report if the given address is already marked
2206 tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2207 _markBitMap.isMarked(addr) ? "" : " not");
2208
2209 if (verify_after_remark()) {
2210 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2211 bool result = verification_mark_bm()->isMarked(addr);
2212 tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2213 result ? "IS" : "is NOT");
2214 return result;
2215 } else {
2216 tty->print_cr("Could not compute result");
2217 return false;
2218 }
2219 }
2220 #endif
2221
2222 void
2223 CMSCollector::print_on_error(outputStream* st) {
2224 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2225 if (collector != NULL) {
2226 CMSBitMap* bitmap = &collector->_markBitMap;
2227 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2228 bitmap->print_on_error(st, " Bits: ");
2229
2230 st->cr();
2231
2232 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2233 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2234 mut_bitmap->print_on_error(st, " Bits: ");
2235 }
2236 }
2237
2238 ////////////////////////////////////////////////////////
2239 // CMS Verification Support
2240 ////////////////////////////////////////////////////////
2241 // Following the remark phase, the following invariant
2242 // should hold -- each object in the CMS heap which is
2243 // marked in markBitMap() should be marked in the verification_mark_bm().
2244
2245 class VerifyMarkedClosure: public BitMapClosure {
2246 CMSBitMap* _marks;
2247 bool _failed;
2248
2249 public:
2250 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2251
2252 bool do_bit(size_t offset) {
2253 HeapWord* addr = _marks->offsetToHeapWord(offset);
2254 if (!_marks->isMarked(addr)) {
2255 Log(gc, verify) log;
2256 ResourceMark rm;
2257 LogStream ls(log.error());
2258 oop(addr)->print_on(&ls);
2259 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2260 _failed = true;
2261 }
2262 return true;
2263 }
2264
2265 bool failed() { return _failed; }
2266 };
2267
2268 bool CMSCollector::verify_after_remark() {
2269 GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking.");
2270 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2271 static bool init = false;
2272
2273 assert(SafepointSynchronize::is_at_safepoint(),
2274 "Else mutations in object graph will make answer suspect");
2275 assert(have_cms_token(),
2276 "Else there may be mutual interference in use of "
2277 " verification data structures");
2278 assert(_collectorState > Marking && _collectorState <= Sweeping,
2279 "Else marking info checked here may be obsolete");
2280 assert(haveFreelistLocks(), "must hold free list locks");
2281 assert_lock_strong(bitMapLock());
2282
2283
2284 // Allocate marking bit map if not already allocated
2285 if (!init) { // first time
2286 if (!verification_mark_bm()->allocate(_span)) {
2287 return false;
2288 }
2289 init = true;
2290 }
2291
2292 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2293
2294 // Turn off refs discovery -- so we will be tracing through refs.
2295 // This is as intended, because by this time
2296 // GC must already have cleared any refs that need to be cleared,
2297 // and traced those that need to be marked; moreover,
2298 // the marking done here is not going to interfere in any
2299 // way with the marking information used by GC.
2300 NoRefDiscovery no_discovery(ref_processor());
2301
2302 #if COMPILER2_OR_JVMCI
2303 DerivedPointerTableDeactivate dpt_deact;
2304 #endif
2305
2306 // Clear any marks from a previous round
2307 verification_mark_bm()->clear_all();
2308 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2309 verify_work_stacks_empty();
2310
2311 CMSHeap* heap = CMSHeap::heap();
2312 heap->ensure_parsability(false); // fill TLABs, but no need to retire them
2313 // Update the saved marks which may affect the root scans.
2314 heap->save_marks();
2315
2316 if (CMSRemarkVerifyVariant == 1) {
2317 // In this first variant of verification, we complete
2318 // all marking, then check if the new marks-vector is
2319 // a subset of the CMS marks-vector.
2320 verify_after_remark_work_1();
2321 } else {
2322 guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2");
2323 // In this second variant of verification, we flag an error
2324 // (i.e. an object reachable in the new marks-vector not reachable
2325 // in the CMS marks-vector) immediately, also indicating the
2326 // identify of an object (A) that references the unmarked object (B) --
2327 // presumably, a mutation to A failed to be picked up by preclean/remark?
2328 verify_after_remark_work_2();
2329 }
2330
2331 return true;
2332 }
2333
2334 void CMSCollector::verify_after_remark_work_1() {
2335 ResourceMark rm;
2336 HandleMark hm;
2337 CMSHeap* heap = CMSHeap::heap();
2338
2339 // Get a clear set of claim bits for the roots processing to work with.
2340 ClassLoaderDataGraph::clear_claimed_marks();
2341
2342 // Mark from roots one level into CMS
2343 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2344 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2345
2346 {
2347 StrongRootsScope srs(1);
2348
2349 heap->cms_process_roots(&srs,
2350 true, // young gen as roots
2351 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2352 should_unload_classes(),
2353 ¬Older,
2354 NULL);
2355 }
2356
2357 // Now mark from the roots
2358 MarkFromRootsClosure markFromRootsClosure(this, _span,
2359 verification_mark_bm(), verification_mark_stack(),
2360 false /* don't yield */, true /* verifying */);
2361 assert(_restart_addr == NULL, "Expected pre-condition");
2362 verification_mark_bm()->iterate(&markFromRootsClosure);
2363 while (_restart_addr != NULL) {
2364 // Deal with stack overflow: by restarting at the indicated
2365 // address.
2366 HeapWord* ra = _restart_addr;
2367 markFromRootsClosure.reset(ra);
2368 _restart_addr = NULL;
2369 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2370 }
2371 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2372 verify_work_stacks_empty();
2373
2374 // Marking completed -- now verify that each bit marked in
2375 // verification_mark_bm() is also marked in markBitMap(); flag all
2376 // errors by printing corresponding objects.
2377 VerifyMarkedClosure vcl(markBitMap());
2378 verification_mark_bm()->iterate(&vcl);
2379 if (vcl.failed()) {
2380 Log(gc, verify) log;
2381 log.error("Failed marking verification after remark");
2382 ResourceMark rm;
2383 LogStream ls(log.error());
2384 heap->print_on(&ls);
2385 fatal("CMS: failed marking verification after remark");
2386 }
2387 }
2388
2389 class VerifyCLDOopsCLDClosure : public CLDClosure {
2390 class VerifyCLDOopsClosure : public OopClosure {
2391 CMSBitMap* _bitmap;
2392 public:
2393 VerifyCLDOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2394 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2395 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2396 } _oop_closure;
2397 public:
2398 VerifyCLDOopsCLDClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2399 void do_cld(ClassLoaderData* cld) {
2400 cld->oops_do(&_oop_closure, false, false);
2401 }
2402 };
2403
2404 void CMSCollector::verify_after_remark_work_2() {
2405 ResourceMark rm;
2406 HandleMark hm;
2407 CMSHeap* heap = CMSHeap::heap();
2408
2409 // Get a clear set of claim bits for the roots processing to work with.
2410 ClassLoaderDataGraph::clear_claimed_marks();
2411
2412 // Mark from roots one level into CMS
2413 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2414 markBitMap());
2415 CLDToOopClosure cld_closure(¬Older, true);
2416
2417 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2418
2419 {
2420 StrongRootsScope srs(1);
2421
2422 heap->cms_process_roots(&srs,
2423 true, // young gen as roots
2424 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2425 should_unload_classes(),
2426 ¬Older,
2427 &cld_closure);
2428 }
2429
2430 // Now mark from the roots
2431 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2432 verification_mark_bm(), markBitMap(), verification_mark_stack());
2433 assert(_restart_addr == NULL, "Expected pre-condition");
2434 verification_mark_bm()->iterate(&markFromRootsClosure);
2435 while (_restart_addr != NULL) {
2436 // Deal with stack overflow: by restarting at the indicated
2437 // address.
2438 HeapWord* ra = _restart_addr;
2439 markFromRootsClosure.reset(ra);
2440 _restart_addr = NULL;
2441 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2442 }
2443 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2444 verify_work_stacks_empty();
2445
2446 VerifyCLDOopsCLDClosure verify_cld_oops(verification_mark_bm());
2447 ClassLoaderDataGraph::cld_do(&verify_cld_oops);
2448
2449 // Marking completed -- now verify that each bit marked in
2450 // verification_mark_bm() is also marked in markBitMap(); flag all
2451 // errors by printing corresponding objects.
2452 VerifyMarkedClosure vcl(markBitMap());
2453 verification_mark_bm()->iterate(&vcl);
2454 assert(!vcl.failed(), "Else verification above should not have succeeded");
2455 }
2456
2457 void ConcurrentMarkSweepGeneration::save_marks() {
2458 // delegate to CMS space
2459 cmsSpace()->save_marks();
2460 }
2461
2462 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2463 return cmsSpace()->no_allocs_since_save_marks();
2464 }
2465
2466 void
2467 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2468 if (freelistLock()->owned_by_self()) {
2469 Generation::oop_iterate(cl);
2470 } else {
2471 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2472 Generation::oop_iterate(cl);
2473 }
2474 }
2475
2476 void
2477 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2478 if (freelistLock()->owned_by_self()) {
2479 Generation::object_iterate(cl);
2480 } else {
2481 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2482 Generation::object_iterate(cl);
2483 }
2484 }
2485
2486 void
2487 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2488 if (freelistLock()->owned_by_self()) {
2489 Generation::safe_object_iterate(cl);
2490 } else {
2491 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2492 Generation::safe_object_iterate(cl);
2493 }
2494 }
2495
2496 void
2497 ConcurrentMarkSweepGeneration::post_compact() {
2498 }
2499
2500 void
2501 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2502 // Fix the linear allocation blocks to look like free blocks.
2503
2504 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2505 // are not called when the heap is verified during universe initialization and
2506 // at vm shutdown.
2507 if (freelistLock()->owned_by_self()) {
2508 cmsSpace()->prepare_for_verify();
2509 } else {
2510 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2511 cmsSpace()->prepare_for_verify();
2512 }
2513 }
2514
2515 void
2516 ConcurrentMarkSweepGeneration::verify() {
2517 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2518 // are not called when the heap is verified during universe initialization and
2519 // at vm shutdown.
2520 if (freelistLock()->owned_by_self()) {
2521 cmsSpace()->verify();
2522 } else {
2523 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2524 cmsSpace()->verify();
2525 }
2526 }
2527
2528 void CMSCollector::verify() {
2529 _cmsGen->verify();
2530 }
2531
2532 #ifndef PRODUCT
2533 bool CMSCollector::overflow_list_is_empty() const {
2534 assert(_num_par_pushes >= 0, "Inconsistency");
2535 if (_overflow_list == NULL) {
2536 assert(_num_par_pushes == 0, "Inconsistency");
2537 }
2538 return _overflow_list == NULL;
2539 }
2540
2541 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2542 // merely consolidate assertion checks that appear to occur together frequently.
2543 void CMSCollector::verify_work_stacks_empty() const {
2544 assert(_markStack.isEmpty(), "Marking stack should be empty");
2545 assert(overflow_list_is_empty(), "Overflow list should be empty");
2546 }
2547
2548 void CMSCollector::verify_overflow_empty() const {
2549 assert(overflow_list_is_empty(), "Overflow list should be empty");
2550 assert(no_preserved_marks(), "No preserved marks");
2551 }
2552 #endif // PRODUCT
2553
2554 // Decide if we want to enable class unloading as part of the
2555 // ensuing concurrent GC cycle. We will collect and
2556 // unload classes if it's the case that:
2557 // (a) class unloading is enabled at the command line, and
2558 // (b) old gen is getting really full
2559 // NOTE: Provided there is no change in the state of the heap between
2560 // calls to this method, it should have idempotent results. Moreover,
2561 // its results should be monotonically increasing (i.e. going from 0 to 1,
2562 // but not 1 to 0) between successive calls between which the heap was
2563 // not collected. For the implementation below, it must thus rely on
2564 // the property that concurrent_cycles_since_last_unload()
2565 // will not decrease unless a collection cycle happened and that
2566 // _cmsGen->is_too_full() are
2567 // themselves also monotonic in that sense. See check_monotonicity()
2568 // below.
2569 void CMSCollector::update_should_unload_classes() {
2570 _should_unload_classes = false;
2571 if (CMSClassUnloadingEnabled) {
2572 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2573 CMSClassUnloadingMaxInterval)
2574 || _cmsGen->is_too_full();
2575 }
2576 }
2577
2578 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2579 bool res = should_concurrent_collect();
2580 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2581 return res;
2582 }
2583
2584 void CMSCollector::setup_cms_unloading_and_verification_state() {
2585 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2586 || VerifyBeforeExit;
2587 const int rso = GenCollectedHeap::SO_AllCodeCache;
2588
2589 // We set the proper root for this CMS cycle here.
2590 if (should_unload_classes()) { // Should unload classes this cycle
2591 remove_root_scanning_option(rso); // Shrink the root set appropriately
2592 set_verifying(should_verify); // Set verification state for this cycle
2593 return; // Nothing else needs to be done at this time
2594 }
2595
2596 // Not unloading classes this cycle
2597 assert(!should_unload_classes(), "Inconsistency!");
2598
2599 // If we are not unloading classes then add SO_AllCodeCache to root
2600 // scanning options.
2601 add_root_scanning_option(rso);
2602
2603 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2604 set_verifying(true);
2605 } else if (verifying() && !should_verify) {
2606 // We were verifying, but some verification flags got disabled.
2607 set_verifying(false);
2608 // Exclude symbols, strings and code cache elements from root scanning to
2609 // reduce IM and RM pauses.
2610 remove_root_scanning_option(rso);
2611 }
2612 }
2613
2614
2615 #ifndef PRODUCT
2616 HeapWord* CMSCollector::block_start(const void* p) const {
2617 const HeapWord* addr = (HeapWord*)p;
2618 if (_span.contains(p)) {
2619 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2620 return _cmsGen->cmsSpace()->block_start(p);
2621 }
2622 }
2623 return NULL;
2624 }
2625 #endif
2626
2627 HeapWord*
2628 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2629 bool tlab,
2630 bool parallel) {
2631 CMSSynchronousYieldRequest yr;
2632 assert(!tlab, "Can't deal with TLAB allocation");
2633 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2634 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2635 if (GCExpandToAllocateDelayMillis > 0) {
2636 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2637 }
2638 return have_lock_and_allocate(word_size, tlab);
2639 }
2640
2641 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2642 size_t bytes,
2643 size_t expand_bytes,
2644 CMSExpansionCause::Cause cause)
2645 {
2646
2647 bool success = expand(bytes, expand_bytes);
2648
2649 // remember why we expanded; this information is used
2650 // by shouldConcurrentCollect() when making decisions on whether to start
2651 // a new CMS cycle.
2652 if (success) {
2653 set_expansion_cause(cause);
2654 log_trace(gc)("Expanded CMS gen for %s", CMSExpansionCause::to_string(cause));
2655 }
2656 }
2657
2658 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2659 HeapWord* res = NULL;
2660 MutexLocker x(ParGCRareEvent_lock);
2661 while (true) {
2662 // Expansion by some other thread might make alloc OK now:
2663 res = ps->lab.alloc(word_sz);
2664 if (res != NULL) return res;
2665 // If there's not enough expansion space available, give up.
2666 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2667 return NULL;
2668 }
2669 // Otherwise, we try expansion.
2670 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2671 // Now go around the loop and try alloc again;
2672 // A competing par_promote might beat us to the expansion space,
2673 // so we may go around the loop again if promotion fails again.
2674 if (GCExpandToAllocateDelayMillis > 0) {
2675 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2676 }
2677 }
2678 }
2679
2680
2681 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2682 PromotionInfo* promo) {
2683 MutexLocker x(ParGCRareEvent_lock);
2684 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2685 while (true) {
2686 // Expansion by some other thread might make alloc OK now:
2687 if (promo->ensure_spooling_space()) {
2688 assert(promo->has_spooling_space(),
2689 "Post-condition of successful ensure_spooling_space()");
2690 return true;
2691 }
2692 // If there's not enough expansion space available, give up.
2693 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2694 return false;
2695 }
2696 // Otherwise, we try expansion.
2697 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2698 // Now go around the loop and try alloc again;
2699 // A competing allocation might beat us to the expansion space,
2700 // so we may go around the loop again if allocation fails again.
2701 if (GCExpandToAllocateDelayMillis > 0) {
2702 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2703 }
2704 }
2705 }
2706
2707 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2708 // Only shrink if a compaction was done so that all the free space
2709 // in the generation is in a contiguous block at the end.
2710 if (did_compact()) {
2711 CardGeneration::shrink(bytes);
2712 }
2713 }
2714
2715 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2716 assert_locked_or_safepoint(Heap_lock);
2717 }
2718
2719 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2720 assert_locked_or_safepoint(Heap_lock);
2721 assert_lock_strong(freelistLock());
2722 log_trace(gc)("Shrinking of CMS not yet implemented");
2723 return;
2724 }
2725
2726
2727 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2728 // phases.
2729 class CMSPhaseAccounting: public StackObj {
2730 public:
2731 CMSPhaseAccounting(CMSCollector *collector,
2732 const char *title);
2733 ~CMSPhaseAccounting();
2734
2735 private:
2736 CMSCollector *_collector;
2737 const char *_title;
2738 GCTraceConcTime(Info, gc) _trace_time;
2739
2740 public:
2741 // Not MT-safe; so do not pass around these StackObj's
2742 // where they may be accessed by other threads.
2743 double wallclock_millis() {
2744 return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time());
2745 }
2746 };
2747
2748 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2749 const char *title) :
2750 _collector(collector), _title(title), _trace_time(title) {
2751
2752 _collector->resetYields();
2753 _collector->resetTimer();
2754 _collector->startTimer();
2755 _collector->gc_timer_cm()->register_gc_concurrent_start(title);
2756 }
2757
2758 CMSPhaseAccounting::~CMSPhaseAccounting() {
2759 _collector->gc_timer_cm()->register_gc_concurrent_end();
2760 _collector->stopTimer();
2761 log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_seconds(_collector->timerTicks()));
2762 log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields());
2763 }
2764
2765 // CMS work
2766
2767 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2768 class CMSParMarkTask : public AbstractGangTask {
2769 protected:
2770 CMSCollector* _collector;
2771 uint _n_workers;
2772 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2773 AbstractGangTask(name),
2774 _collector(collector),
2775 _n_workers(n_workers) {}
2776 // Work method in support of parallel rescan ... of young gen spaces
2777 void do_young_space_rescan(OopsInGenClosure* cl,
2778 ContiguousSpace* space,
2779 HeapWord** chunk_array, size_t chunk_top);
2780 void work_on_young_gen_roots(OopsInGenClosure* cl);
2781 };
2782
2783 // Parallel initial mark task
2784 class CMSParInitialMarkTask: public CMSParMarkTask {
2785 StrongRootsScope* _strong_roots_scope;
2786 public:
2787 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2788 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2789 _strong_roots_scope(strong_roots_scope) {}
2790 void work(uint worker_id);
2791 };
2792
2793 // Checkpoint the roots into this generation from outside
2794 // this generation. [Note this initial checkpoint need only
2795 // be approximate -- we'll do a catch up phase subsequently.]
2796 void CMSCollector::checkpointRootsInitial() {
2797 assert(_collectorState == InitialMarking, "Wrong collector state");
2798 check_correct_thread_executing();
2799 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
2800
2801 save_heap_summary();
2802 report_heap_summary(GCWhen::BeforeGC);
2803
2804 ReferenceProcessor* rp = ref_processor();
2805 assert(_restart_addr == NULL, "Control point invariant");
2806 {
2807 // acquire locks for subsequent manipulations
2808 MutexLockerEx x(bitMapLock(),
2809 Mutex::_no_safepoint_check_flag);
2810 checkpointRootsInitialWork();
2811 // enable ("weak") refs discovery
2812 rp->enable_discovery();
2813 _collectorState = Marking;
2814 }
2815 }
2816
2817 void CMSCollector::checkpointRootsInitialWork() {
2818 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2819 assert(_collectorState == InitialMarking, "just checking");
2820
2821 // Already have locks.
2822 assert_lock_strong(bitMapLock());
2823 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2824
2825 // Setup the verification and class unloading state for this
2826 // CMS collection cycle.
2827 setup_cms_unloading_and_verification_state();
2828
2829 GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm);
2830
2831 // Reset all the PLAB chunk arrays if necessary.
2832 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2833 reset_survivor_plab_arrays();
2834 }
2835
2836 ResourceMark rm;
2837 HandleMark hm;
2838
2839 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2840 CMSHeap* heap = CMSHeap::heap();
2841
2842 verify_work_stacks_empty();
2843 verify_overflow_empty();
2844
2845 heap->ensure_parsability(false); // fill TLABs, but no need to retire them
2846 // Update the saved marks which may affect the root scans.
2847 heap->save_marks();
2848
2849 // weak reference processing has not started yet.
2850 ref_processor()->set_enqueuing_is_done(false);
2851
2852 // Need to remember all newly created CLDs,
2853 // so that we can guarantee that the remark finds them.
2854 ClassLoaderDataGraph::remember_new_clds(true);
2855
2856 // Whenever a CLD is found, it will be claimed before proceeding to mark
2857 // the klasses. The claimed marks need to be cleared before marking starts.
2858 ClassLoaderDataGraph::clear_claimed_marks();
2859
2860 print_eden_and_survivor_chunk_arrays();
2861
2862 {
2863 #if COMPILER2_OR_JVMCI
2864 DerivedPointerTableDeactivate dpt_deact;
2865 #endif
2866 if (CMSParallelInitialMarkEnabled) {
2867 // The parallel version.
2868 WorkGang* workers = heap->workers();
2869 assert(workers != NULL, "Need parallel worker threads.");
2870 uint n_workers = workers->active_workers();
2871
2872 StrongRootsScope srs(n_workers);
2873
2874 CMSParInitialMarkTask tsk(this, &srs, n_workers);
2875 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2876 // If the total workers is greater than 1, then multiple workers
2877 // may be used at some time and the initialization has been set
2878 // such that the single threaded path cannot be used.
2879 if (workers->total_workers() > 1) {
2880 workers->run_task(&tsk);
2881 } else {
2882 tsk.work(0);
2883 }
2884 } else {
2885 // The serial version.
2886 CLDToOopClosure cld_closure(¬Older, true);
2887 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2888
2889 StrongRootsScope srs(1);
2890
2891 heap->cms_process_roots(&srs,
2892 true, // young gen as roots
2893 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2894 should_unload_classes(),
2895 ¬Older,
2896 &cld_closure);
2897 }
2898 }
2899
2900 // Clear mod-union table; it will be dirtied in the prologue of
2901 // CMS generation per each young generation collection.
2902
2903 assert(_modUnionTable.isAllClear(),
2904 "Was cleared in most recent final checkpoint phase"
2905 " or no bits are set in the gc_prologue before the start of the next "
2906 "subsequent marking phase.");
2907
2908 assert(_ct->cld_rem_set()->mod_union_is_clear(), "Must be");
2909
2910 // Save the end of the used_region of the constituent generations
2911 // to be used to limit the extent of sweep in each generation.
2912 save_sweep_limits();
2913 verify_overflow_empty();
2914 }
2915
2916 bool CMSCollector::markFromRoots() {
2917 // we might be tempted to assert that:
2918 // assert(!SafepointSynchronize::is_at_safepoint(),
2919 // "inconsistent argument?");
2920 // However that wouldn't be right, because it's possible that
2921 // a safepoint is indeed in progress as a young generation
2922 // stop-the-world GC happens even as we mark in this generation.
2923 assert(_collectorState == Marking, "inconsistent state?");
2924 check_correct_thread_executing();
2925 verify_overflow_empty();
2926
2927 // Weak ref discovery note: We may be discovering weak
2928 // refs in this generation concurrent (but interleaved) with
2929 // weak ref discovery by the young generation collector.
2930
2931 CMSTokenSyncWithLocks ts(true, bitMapLock());
2932 GCTraceCPUTime tcpu;
2933 CMSPhaseAccounting pa(this, "Concurrent Mark");
2934 bool res = markFromRootsWork();
2935 if (res) {
2936 _collectorState = Precleaning;
2937 } else { // We failed and a foreground collection wants to take over
2938 assert(_foregroundGCIsActive, "internal state inconsistency");
2939 assert(_restart_addr == NULL, "foreground will restart from scratch");
2940 log_debug(gc)("bailing out to foreground collection");
2941 }
2942 verify_overflow_empty();
2943 return res;
2944 }
2945
2946 bool CMSCollector::markFromRootsWork() {
2947 // iterate over marked bits in bit map, doing a full scan and mark
2948 // from these roots using the following algorithm:
2949 // . if oop is to the right of the current scan pointer,
2950 // mark corresponding bit (we'll process it later)
2951 // . else (oop is to left of current scan pointer)
2952 // push oop on marking stack
2953 // . drain the marking stack
2954
2955 // Note that when we do a marking step we need to hold the
2956 // bit map lock -- recall that direct allocation (by mutators)
2957 // and promotion (by the young generation collector) is also
2958 // marking the bit map. [the so-called allocate live policy.]
2959 // Because the implementation of bit map marking is not
2960 // robust wrt simultaneous marking of bits in the same word,
2961 // we need to make sure that there is no such interference
2962 // between concurrent such updates.
2963
2964 // already have locks
2965 assert_lock_strong(bitMapLock());
2966
2967 verify_work_stacks_empty();
2968 verify_overflow_empty();
2969 bool result = false;
2970 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2971 result = do_marking_mt();
2972 } else {
2973 result = do_marking_st();
2974 }
2975 return result;
2976 }
2977
2978 // Forward decl
2979 class CMSConcMarkingTask;
2980
2981 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
2982 CMSCollector* _collector;
2983 CMSConcMarkingTask* _task;
2984 public:
2985 virtual void yield();
2986
2987 // "n_threads" is the number of threads to be terminated.
2988 // "queue_set" is a set of work queues of other threads.
2989 // "collector" is the CMS collector associated with this task terminator.
2990 // "yield" indicates whether we need the gang as a whole to yield.
2991 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
2992 ParallelTaskTerminator(n_threads, queue_set),
2993 _collector(collector) { }
2994
2995 void set_task(CMSConcMarkingTask* task) {
2996 _task = task;
2997 }
2998 };
2999
3000 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3001 CMSConcMarkingTask* _task;
3002 public:
3003 bool should_exit_termination();
3004 void set_task(CMSConcMarkingTask* task) {
3005 _task = task;
3006 }
3007 };
3008
3009 // MT Concurrent Marking Task
3010 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3011 CMSCollector* _collector;
3012 uint _n_workers; // requested/desired # workers
3013 bool _result;
3014 CompactibleFreeListSpace* _cms_space;
3015 char _pad_front[64]; // padding to ...
3016 HeapWord* volatile _global_finger; // ... avoid sharing cache line
3017 char _pad_back[64];
3018 HeapWord* _restart_addr;
3019
3020 // Exposed here for yielding support
3021 Mutex* const _bit_map_lock;
3022
3023 // The per thread work queues, available here for stealing
3024 OopTaskQueueSet* _task_queues;
3025
3026 // Termination (and yielding) support
3027 CMSConcMarkingTerminator _term;
3028 CMSConcMarkingTerminatorTerminator _term_term;
3029
3030 public:
3031 CMSConcMarkingTask(CMSCollector* collector,
3032 CompactibleFreeListSpace* cms_space,
3033 YieldingFlexibleWorkGang* workers,
3034 OopTaskQueueSet* task_queues):
3035 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3036 _collector(collector),
3037 _cms_space(cms_space),
3038 _n_workers(0), _result(true),
3039 _task_queues(task_queues),
3040 _term(_n_workers, task_queues, _collector),
3041 _bit_map_lock(collector->bitMapLock())
3042 {
3043 _requested_size = _n_workers;
3044 _term.set_task(this);
3045 _term_term.set_task(this);
3046 _restart_addr = _global_finger = _cms_space->bottom();
3047 }
3048
3049
3050 OopTaskQueueSet* task_queues() { return _task_queues; }
3051
3052 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3053
3054 HeapWord* volatile* global_finger_addr() { return &_global_finger; }
3055
3056 CMSConcMarkingTerminator* terminator() { return &_term; }
3057
3058 virtual void set_for_termination(uint active_workers) {
3059 terminator()->reset_for_reuse(active_workers);
3060 }
3061
3062 void work(uint worker_id);
3063 bool should_yield() {
3064 return ConcurrentMarkSweepThread::should_yield()
3065 && !_collector->foregroundGCIsActive();
3066 }
3067
3068 virtual void coordinator_yield(); // stuff done by coordinator
3069 bool result() { return _result; }
3070
3071 void reset(HeapWord* ra) {
3072 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3073 _restart_addr = _global_finger = ra;
3074 _term.reset_for_reuse();
3075 }
3076
3077 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3078 OopTaskQueue* work_q);
3079
3080 private:
3081 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3082 void do_work_steal(int i);
3083 void bump_global_finger(HeapWord* f);
3084 };
3085
3086 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3087 assert(_task != NULL, "Error");
3088 return _task->yielding();
3089 // Note that we do not need the disjunct || _task->should_yield() above
3090 // because we want terminating threads to yield only if the task
3091 // is already in the midst of yielding, which happens only after at least one
3092 // thread has yielded.
3093 }
3094
3095 void CMSConcMarkingTerminator::yield() {
3096 if (_task->should_yield()) {
3097 _task->yield();
3098 } else {
3099 ParallelTaskTerminator::yield();
3100 }
3101 }
3102
3103 ////////////////////////////////////////////////////////////////
3104 // Concurrent Marking Algorithm Sketch
3105 ////////////////////////////////////////////////////////////////
3106 // Until all tasks exhausted (both spaces):
3107 // -- claim next available chunk
3108 // -- bump global finger via CAS
3109 // -- find first object that starts in this chunk
3110 // and start scanning bitmap from that position
3111 // -- scan marked objects for oops
3112 // -- CAS-mark target, and if successful:
3113 // . if target oop is above global finger (volatile read)
3114 // nothing to do
3115 // . if target oop is in chunk and above local finger
3116 // then nothing to do
3117 // . else push on work-queue
3118 // -- Deal with possible overflow issues:
3119 // . local work-queue overflow causes stuff to be pushed on
3120 // global (common) overflow queue
3121 // . always first empty local work queue
3122 // . then get a batch of oops from global work queue if any
3123 // . then do work stealing
3124 // -- When all tasks claimed (both spaces)
3125 // and local work queue empty,
3126 // then in a loop do:
3127 // . check global overflow stack; steal a batch of oops and trace
3128 // . try to steal from other threads oif GOS is empty
3129 // . if neither is available, offer termination
3130 // -- Terminate and return result
3131 //
3132 void CMSConcMarkingTask::work(uint worker_id) {
3133 elapsedTimer _timer;
3134 ResourceMark rm;
3135 HandleMark hm;
3136
3137 DEBUG_ONLY(_collector->verify_overflow_empty();)
3138
3139 // Before we begin work, our work queue should be empty
3140 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3141 // Scan the bitmap covering _cms_space, tracing through grey objects.
3142 _timer.start();
3143 do_scan_and_mark(worker_id, _cms_space);
3144 _timer.stop();
3145 log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3146
3147 // ... do work stealing
3148 _timer.reset();
3149 _timer.start();
3150 do_work_steal(worker_id);
3151 _timer.stop();
3152 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3153 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3154 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3155 // Note that under the current task protocol, the
3156 // following assertion is true even of the spaces
3157 // expanded since the completion of the concurrent
3158 // marking. XXX This will likely change under a strict
3159 // ABORT semantics.
3160 // After perm removal the comparison was changed to
3161 // greater than or equal to from strictly greater than.
3162 // Before perm removal the highest address sweep would
3163 // have been at the end of perm gen but now is at the
3164 // end of the tenured gen.
3165 assert(_global_finger >= _cms_space->end(),
3166 "All tasks have been completed");
3167 DEBUG_ONLY(_collector->verify_overflow_empty();)
3168 }
3169
3170 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3171 HeapWord* read = _global_finger;
3172 HeapWord* cur = read;
3173 while (f > read) {
3174 cur = read;
3175 read = Atomic::cmpxchg(f, &_global_finger, cur);
3176 if (cur == read) {
3177 // our cas succeeded
3178 assert(_global_finger >= f, "protocol consistency");
3179 break;
3180 }
3181 }
3182 }
3183
3184 // This is really inefficient, and should be redone by
3185 // using (not yet available) block-read and -write interfaces to the
3186 // stack and the work_queue. XXX FIX ME !!!
3187 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3188 OopTaskQueue* work_q) {
3189 // Fast lock-free check
3190 if (ovflw_stk->length() == 0) {
3191 return false;
3192 }
3193 assert(work_q->size() == 0, "Shouldn't steal");
3194 MutexLockerEx ml(ovflw_stk->par_lock(),
3195 Mutex::_no_safepoint_check_flag);
3196 // Grab up to 1/4 the size of the work queue
3197 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3198 (size_t)ParGCDesiredObjsFromOverflowList);
3199 num = MIN2(num, ovflw_stk->length());
3200 for (int i = (int) num; i > 0; i--) {
3201 oop cur = ovflw_stk->pop();
3202 assert(cur != NULL, "Counted wrong?");
3203 work_q->push(cur);
3204 }
3205 return num > 0;
3206 }
3207
3208 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3209 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3210 int n_tasks = pst->n_tasks();
3211 // We allow that there may be no tasks to do here because
3212 // we are restarting after a stack overflow.
3213 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3214 uint nth_task = 0;
3215
3216 HeapWord* aligned_start = sp->bottom();
3217 if (sp->used_region().contains(_restart_addr)) {
3218 // Align down to a card boundary for the start of 0th task
3219 // for this space.
3220 aligned_start = align_down(_restart_addr, CardTable::card_size);
3221 }
3222
3223 size_t chunk_size = sp->marking_task_size();
3224 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3225 // Having claimed the nth task in this space,
3226 // compute the chunk that it corresponds to:
3227 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3228 aligned_start + (nth_task+1)*chunk_size);
3229 // Try and bump the global finger via a CAS;
3230 // note that we need to do the global finger bump
3231 // _before_ taking the intersection below, because
3232 // the task corresponding to that region will be
3233 // deemed done even if the used_region() expands
3234 // because of allocation -- as it almost certainly will
3235 // during start-up while the threads yield in the
3236 // closure below.
3237 HeapWord* finger = span.end();
3238 bump_global_finger(finger); // atomically
3239 // There are null tasks here corresponding to chunks
3240 // beyond the "top" address of the space.
3241 span = span.intersection(sp->used_region());
3242 if (!span.is_empty()) { // Non-null task
3243 HeapWord* prev_obj;
3244 assert(!span.contains(_restart_addr) || nth_task == 0,
3245 "Inconsistency");
3246 if (nth_task == 0) {
3247 // For the 0th task, we'll not need to compute a block_start.
3248 if (span.contains(_restart_addr)) {
3249 // In the case of a restart because of stack overflow,
3250 // we might additionally skip a chunk prefix.
3251 prev_obj = _restart_addr;
3252 } else {
3253 prev_obj = span.start();
3254 }
3255 } else {
3256 // We want to skip the first object because
3257 // the protocol is to scan any object in its entirety
3258 // that _starts_ in this span; a fortiori, any
3259 // object starting in an earlier span is scanned
3260 // as part of an earlier claimed task.
3261 // Below we use the "careful" version of block_start
3262 // so we do not try to navigate uninitialized objects.
3263 prev_obj = sp->block_start_careful(span.start());
3264 // Below we use a variant of block_size that uses the
3265 // Printezis bits to avoid waiting for allocated
3266 // objects to become initialized/parsable.
3267 while (prev_obj < span.start()) {
3268 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3269 if (sz > 0) {
3270 prev_obj += sz;
3271 } else {
3272 // In this case we may end up doing a bit of redundant
3273 // scanning, but that appears unavoidable, short of
3274 // locking the free list locks; see bug 6324141.
3275 break;
3276 }
3277 }
3278 }
3279 if (prev_obj < span.end()) {
3280 MemRegion my_span = MemRegion(prev_obj, span.end());
3281 // Do the marking work within a non-empty span --
3282 // the last argument to the constructor indicates whether the
3283 // iteration should be incremental with periodic yields.
3284 ParMarkFromRootsClosure cl(this, _collector, my_span,
3285 &_collector->_markBitMap,
3286 work_queue(i),
3287 &_collector->_markStack);
3288 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3289 } // else nothing to do for this task
3290 } // else nothing to do for this task
3291 }
3292 // We'd be tempted to assert here that since there are no
3293 // more tasks left to claim in this space, the global_finger
3294 // must exceed space->top() and a fortiori space->end(). However,
3295 // that would not quite be correct because the bumping of
3296 // global_finger occurs strictly after the claiming of a task,
3297 // so by the time we reach here the global finger may not yet
3298 // have been bumped up by the thread that claimed the last
3299 // task.
3300 pst->all_tasks_completed();
3301 }
3302
3303 class ParConcMarkingClosure: public MetadataAwareOopClosure {
3304 private:
3305 CMSCollector* _collector;
3306 CMSConcMarkingTask* _task;
3307 MemRegion _span;
3308 CMSBitMap* _bit_map;
3309 CMSMarkStack* _overflow_stack;
3310 OopTaskQueue* _work_queue;
3311 protected:
3312 DO_OOP_WORK_DEFN
3313 public:
3314 ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3315 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3316 MetadataAwareOopClosure(collector->ref_processor()),
3317 _collector(collector),
3318 _task(task),
3319 _span(collector->_span),
3320 _work_queue(work_queue),
3321 _bit_map(bit_map),
3322 _overflow_stack(overflow_stack)
3323 { }
3324 virtual void do_oop(oop* p);
3325 virtual void do_oop(narrowOop* p);
3326
3327 void trim_queue(size_t max);
3328 void handle_stack_overflow(HeapWord* lost);
3329 void do_yield_check() {
3330 if (_task->should_yield()) {
3331 _task->yield();
3332 }
3333 }
3334 };
3335
3336 DO_OOP_WORK_IMPL(ParConcMarkingClosure)
3337
3338 // Grey object scanning during work stealing phase --
3339 // the salient assumption here is that any references
3340 // that are in these stolen objects being scanned must
3341 // already have been initialized (else they would not have
3342 // been published), so we do not need to check for
3343 // uninitialized objects before pushing here.
3344 void ParConcMarkingClosure::do_oop(oop obj) {
3345 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3346 HeapWord* addr = (HeapWord*)obj;
3347 // Check if oop points into the CMS generation
3348 // and is not marked
3349 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3350 // a white object ...
3351 // If we manage to "claim" the object, by being the
3352 // first thread to mark it, then we push it on our
3353 // marking stack
3354 if (_bit_map->par_mark(addr)) { // ... now grey
3355 // push on work queue (grey set)
3356 bool simulate_overflow = false;
3357 NOT_PRODUCT(
3358 if (CMSMarkStackOverflowALot &&
3359 _collector->simulate_overflow()) {
3360 // simulate a stack overflow
3361 simulate_overflow = true;
3362 }
3363 )
3364 if (simulate_overflow ||
3365 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3366 // stack overflow
3367 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3368 // We cannot assert that the overflow stack is full because
3369 // it may have been emptied since.
3370 assert(simulate_overflow ||
3371 _work_queue->size() == _work_queue->max_elems(),
3372 "Else push should have succeeded");
3373 handle_stack_overflow(addr);
3374 }
3375 } // Else, some other thread got there first
3376 do_yield_check();
3377 }
3378 }
3379
3380 void ParConcMarkingClosure::do_oop(oop* p) { ParConcMarkingClosure::do_oop_work(p); }
3381 void ParConcMarkingClosure::do_oop(narrowOop* p) { ParConcMarkingClosure::do_oop_work(p); }
3382
3383 void ParConcMarkingClosure::trim_queue(size_t max) {
3384 while (_work_queue->size() > max) {
3385 oop new_oop;
3386 if (_work_queue->pop_local(new_oop)) {
3387 assert(oopDesc::is_oop(new_oop), "Should be an oop");
3388 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3389 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3390 new_oop->oop_iterate(this); // do_oop() above
3391 do_yield_check();
3392 }
3393 }
3394 }
3395
3396 // Upon stack overflow, we discard (part of) the stack,
3397 // remembering the least address amongst those discarded
3398 // in CMSCollector's _restart_address.
3399 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3400 // We need to do this under a mutex to prevent other
3401 // workers from interfering with the work done below.
3402 MutexLockerEx ml(_overflow_stack->par_lock(),
3403 Mutex::_no_safepoint_check_flag);
3404 // Remember the least grey address discarded
3405 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3406 _collector->lower_restart_addr(ra);
3407 _overflow_stack->reset(); // discard stack contents
3408 _overflow_stack->expand(); // expand the stack if possible
3409 }
3410
3411
3412 void CMSConcMarkingTask::do_work_steal(int i) {
3413 OopTaskQueue* work_q = work_queue(i);
3414 oop obj_to_scan;
3415 CMSBitMap* bm = &(_collector->_markBitMap);
3416 CMSMarkStack* ovflw = &(_collector->_markStack);
3417 int* seed = _collector->hash_seed(i);
3418 ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3419 while (true) {
3420 cl.trim_queue(0);
3421 assert(work_q->size() == 0, "Should have been emptied above");
3422 if (get_work_from_overflow_stack(ovflw, work_q)) {
3423 // Can't assert below because the work obtained from the
3424 // overflow stack may already have been stolen from us.
3425 // assert(work_q->size() > 0, "Work from overflow stack");
3426 continue;
3427 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3428 assert(oopDesc::is_oop(obj_to_scan), "Should be an oop");
3429 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3430 obj_to_scan->oop_iterate(&cl);
3431 } else if (terminator()->offer_termination(&_term_term)) {
3432 assert(work_q->size() == 0, "Impossible!");
3433 break;
3434 } else if (yielding() || should_yield()) {
3435 yield();
3436 }
3437 }
3438 }
3439
3440 // This is run by the CMS (coordinator) thread.
3441 void CMSConcMarkingTask::coordinator_yield() {
3442 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3443 "CMS thread should hold CMS token");
3444 // First give up the locks, then yield, then re-lock
3445 // We should probably use a constructor/destructor idiom to
3446 // do this unlock/lock or modify the MutexUnlocker class to
3447 // serve our purpose. XXX
3448 assert_lock_strong(_bit_map_lock);
3449 _bit_map_lock->unlock();
3450 ConcurrentMarkSweepThread::desynchronize(true);
3451 _collector->stopTimer();
3452 _collector->incrementYields();
3453
3454 // It is possible for whichever thread initiated the yield request
3455 // not to get a chance to wake up and take the bitmap lock between
3456 // this thread releasing it and reacquiring it. So, while the
3457 // should_yield() flag is on, let's sleep for a bit to give the
3458 // other thread a chance to wake up. The limit imposed on the number
3459 // of iterations is defensive, to avoid any unforseen circumstances
3460 // putting us into an infinite loop. Since it's always been this
3461 // (coordinator_yield()) method that was observed to cause the
3462 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3463 // which is by default non-zero. For the other seven methods that
3464 // also perform the yield operation, as are using a different
3465 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3466 // can enable the sleeping for those methods too, if necessary.
3467 // See 6442774.
3468 //
3469 // We really need to reconsider the synchronization between the GC
3470 // thread and the yield-requesting threads in the future and we
3471 // should really use wait/notify, which is the recommended
3472 // way of doing this type of interaction. Additionally, we should
3473 // consolidate the eight methods that do the yield operation and they
3474 // are almost identical into one for better maintainability and
3475 // readability. See 6445193.
3476 //
3477 // Tony 2006.06.29
3478 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3479 ConcurrentMarkSweepThread::should_yield() &&
3480 !CMSCollector::foregroundGCIsActive(); ++i) {
3481 os::sleep(Thread::current(), 1, false);
3482 }
3483
3484 ConcurrentMarkSweepThread::synchronize(true);
3485 _bit_map_lock->lock_without_safepoint_check();
3486 _collector->startTimer();
3487 }
3488
3489 bool CMSCollector::do_marking_mt() {
3490 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3491 uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3492 conc_workers()->active_workers(),
3493 Threads::number_of_non_daemon_threads());
3494 num_workers = conc_workers()->update_active_workers(num_workers);
3495 log_info(gc,task)("Using %u workers of %u for marking", num_workers, conc_workers()->total_workers());
3496
3497 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3498
3499 CMSConcMarkingTask tsk(this,
3500 cms_space,
3501 conc_workers(),
3502 task_queues());
3503
3504 // Since the actual number of workers we get may be different
3505 // from the number we requested above, do we need to do anything different
3506 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3507 // class?? XXX
3508 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3509
3510 // Refs discovery is already non-atomic.
3511 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3512 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3513 conc_workers()->start_task(&tsk);
3514 while (tsk.yielded()) {
3515 tsk.coordinator_yield();
3516 conc_workers()->continue_task(&tsk);
3517 }
3518 // If the task was aborted, _restart_addr will be non-NULL
3519 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3520 while (_restart_addr != NULL) {
3521 // XXX For now we do not make use of ABORTED state and have not
3522 // yet implemented the right abort semantics (even in the original
3523 // single-threaded CMS case). That needs some more investigation
3524 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3525 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3526 // If _restart_addr is non-NULL, a marking stack overflow
3527 // occurred; we need to do a fresh marking iteration from the
3528 // indicated restart address.
3529 if (_foregroundGCIsActive) {
3530 // We may be running into repeated stack overflows, having
3531 // reached the limit of the stack size, while making very
3532 // slow forward progress. It may be best to bail out and
3533 // let the foreground collector do its job.
3534 // Clear _restart_addr, so that foreground GC
3535 // works from scratch. This avoids the headache of
3536 // a "rescan" which would otherwise be needed because
3537 // of the dirty mod union table & card table.
3538 _restart_addr = NULL;
3539 return false;
3540 }
3541 // Adjust the task to restart from _restart_addr
3542 tsk.reset(_restart_addr);
3543 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3544 _restart_addr);
3545 _restart_addr = NULL;
3546 // Get the workers going again
3547 conc_workers()->start_task(&tsk);
3548 while (tsk.yielded()) {
3549 tsk.coordinator_yield();
3550 conc_workers()->continue_task(&tsk);
3551 }
3552 }
3553 assert(tsk.completed(), "Inconsistency");
3554 assert(tsk.result() == true, "Inconsistency");
3555 return true;
3556 }
3557
3558 bool CMSCollector::do_marking_st() {
3559 ResourceMark rm;
3560 HandleMark hm;
3561
3562 // Temporarily make refs discovery single threaded (non-MT)
3563 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3564 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3565 &_markStack, CMSYield);
3566 // the last argument to iterate indicates whether the iteration
3567 // should be incremental with periodic yields.
3568 _markBitMap.iterate(&markFromRootsClosure);
3569 // If _restart_addr is non-NULL, a marking stack overflow
3570 // occurred; we need to do a fresh iteration from the
3571 // indicated restart address.
3572 while (_restart_addr != NULL) {
3573 if (_foregroundGCIsActive) {
3574 // We may be running into repeated stack overflows, having
3575 // reached the limit of the stack size, while making very
3576 // slow forward progress. It may be best to bail out and
3577 // let the foreground collector do its job.
3578 // Clear _restart_addr, so that foreground GC
3579 // works from scratch. This avoids the headache of
3580 // a "rescan" which would otherwise be needed because
3581 // of the dirty mod union table & card table.
3582 _restart_addr = NULL;
3583 return false; // indicating failure to complete marking
3584 }
3585 // Deal with stack overflow:
3586 // we restart marking from _restart_addr
3587 HeapWord* ra = _restart_addr;
3588 markFromRootsClosure.reset(ra);
3589 _restart_addr = NULL;
3590 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3591 }
3592 return true;
3593 }
3594
3595 void CMSCollector::preclean() {
3596 check_correct_thread_executing();
3597 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3598 verify_work_stacks_empty();
3599 verify_overflow_empty();
3600 _abort_preclean = false;
3601 if (CMSPrecleaningEnabled) {
3602 if (!CMSEdenChunksRecordAlways) {
3603 _eden_chunk_index = 0;
3604 }
3605 size_t used = get_eden_used();
3606 size_t capacity = get_eden_capacity();
3607 // Don't start sampling unless we will get sufficiently
3608 // many samples.
3609 if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100)
3610 * CMSScheduleRemarkEdenPenetration)) {
3611 _start_sampling = true;
3612 } else {
3613 _start_sampling = false;
3614 }
3615 GCTraceCPUTime tcpu;
3616 CMSPhaseAccounting pa(this, "Concurrent Preclean");
3617 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3618 }
3619 CMSTokenSync x(true); // is cms thread
3620 if (CMSPrecleaningEnabled) {
3621 sample_eden();
3622 _collectorState = AbortablePreclean;
3623 } else {
3624 _collectorState = FinalMarking;
3625 }
3626 verify_work_stacks_empty();
3627 verify_overflow_empty();
3628 }
3629
3630 // Try and schedule the remark such that young gen
3631 // occupancy is CMSScheduleRemarkEdenPenetration %.
3632 void CMSCollector::abortable_preclean() {
3633 check_correct_thread_executing();
3634 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3635 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3636
3637 // If Eden's current occupancy is below this threshold,
3638 // immediately schedule the remark; else preclean
3639 // past the next scavenge in an effort to
3640 // schedule the pause as described above. By choosing
3641 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3642 // we will never do an actual abortable preclean cycle.
3643 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3644 GCTraceCPUTime tcpu;
3645 CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean");
3646 // We need more smarts in the abortable preclean
3647 // loop below to deal with cases where allocation
3648 // in young gen is very very slow, and our precleaning
3649 // is running a losing race against a horde of
3650 // mutators intent on flooding us with CMS updates
3651 // (dirty cards).
3652 // One, admittedly dumb, strategy is to give up
3653 // after a certain number of abortable precleaning loops
3654 // or after a certain maximum time. We want to make
3655 // this smarter in the next iteration.
3656 // XXX FIX ME!!! YSR
3657 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3658 while (!(should_abort_preclean() ||
3659 ConcurrentMarkSweepThread::cmst()->should_terminate())) {
3660 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3661 cumworkdone += workdone;
3662 loops++;
3663 // Voluntarily terminate abortable preclean phase if we have
3664 // been at it for too long.
3665 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3666 loops >= CMSMaxAbortablePrecleanLoops) {
3667 log_debug(gc)(" CMS: abort preclean due to loops ");
3668 break;
3669 }
3670 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3671 log_debug(gc)(" CMS: abort preclean due to time ");
3672 break;
3673 }
3674 // If we are doing little work each iteration, we should
3675 // take a short break.
3676 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3677 // Sleep for some time, waiting for work to accumulate
3678 stopTimer();
3679 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3680 startTimer();
3681 waited++;
3682 }
3683 }
3684 log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3685 loops, waited, cumworkdone);
3686 }
3687 CMSTokenSync x(true); // is cms thread
3688 if (_collectorState != Idling) {
3689 assert(_collectorState == AbortablePreclean,
3690 "Spontaneous state transition?");
3691 _collectorState = FinalMarking;
3692 } // Else, a foreground collection completed this CMS cycle.
3693 return;
3694 }
3695
3696 // Respond to an Eden sampling opportunity
3697 void CMSCollector::sample_eden() {
3698 // Make sure a young gc cannot sneak in between our
3699 // reading and recording of a sample.
3700 assert(Thread::current()->is_ConcurrentGC_thread(),
3701 "Only the cms thread may collect Eden samples");
3702 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3703 "Should collect samples while holding CMS token");
3704 if (!_start_sampling) {
3705 return;
3706 }
3707 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3708 // is populated by the young generation.
3709 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3710 if (_eden_chunk_index < _eden_chunk_capacity) {
3711 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3712 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3713 "Unexpected state of Eden");
3714 // We'd like to check that what we just sampled is an oop-start address;
3715 // however, we cannot do that here since the object may not yet have been
3716 // initialized. So we'll instead do the check when we _use_ this sample
3717 // later.
3718 if (_eden_chunk_index == 0 ||
3719 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3720 _eden_chunk_array[_eden_chunk_index-1])
3721 >= CMSSamplingGrain)) {
3722 _eden_chunk_index++; // commit sample
3723 }
3724 }
3725 }
3726 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3727 size_t used = get_eden_used();
3728 size_t capacity = get_eden_capacity();
3729 assert(used <= capacity, "Unexpected state of Eden");
3730 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3731 _abort_preclean = true;
3732 }
3733 }
3734 }
3735
3736 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3737 assert(_collectorState == Precleaning ||
3738 _collectorState == AbortablePreclean, "incorrect state");
3739 ResourceMark rm;
3740 HandleMark hm;
3741
3742 // Precleaning is currently not MT but the reference processor
3743 // may be set for MT. Disable it temporarily here.
3744 ReferenceProcessor* rp = ref_processor();
3745 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3746
3747 // Do one pass of scrubbing the discovered reference lists
3748 // to remove any reference objects with strongly-reachable
3749 // referents.
3750 if (clean_refs) {
3751 CMSPrecleanRefsYieldClosure yield_cl(this);
3752 assert(_span_based_discoverer.span().equals(_span), "Spans should be equal");
3753 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3754 &_markStack, true /* preclean */);
3755 CMSDrainMarkingStackClosure complete_trace(this,
3756 _span, &_markBitMap, &_markStack,
3757 &keep_alive, true /* preclean */);
3758
3759 // We don't want this step to interfere with a young
3760 // collection because we don't want to take CPU
3761 // or memory bandwidth away from the young GC threads
3762 // (which may be as many as there are CPUs).
3763 // Note that we don't need to protect ourselves from
3764 // interference with mutators because they can't
3765 // manipulate the discovered reference lists nor affect
3766 // the computed reachability of the referents, the
3767 // only properties manipulated by the precleaning
3768 // of these reference lists.
3769 stopTimer();
3770 CMSTokenSyncWithLocks x(true /* is cms thread */,
3771 bitMapLock());
3772 startTimer();
3773 sample_eden();
3774
3775 // The following will yield to allow foreground
3776 // collection to proceed promptly. XXX YSR:
3777 // The code in this method may need further
3778 // tweaking for better performance and some restructuring
3779 // for cleaner interfaces.
3780 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3781 rp->preclean_discovered_references(
3782 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3783 gc_timer);
3784 }
3785
3786 if (clean_survivor) { // preclean the active survivor space(s)
3787 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3788 &_markBitMap, &_modUnionTable,
3789 &_markStack, true /* precleaning phase */);
3790 stopTimer();
3791 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3792 bitMapLock());
3793 startTimer();
3794 unsigned int before_count =
3795 CMSHeap::heap()->total_collections();
3796 SurvivorSpacePrecleanClosure
3797 sss_cl(this, _span, &_markBitMap, &_markStack,
3798 &pam_cl, before_count, CMSYield);
3799 _young_gen->from()->object_iterate_careful(&sss_cl);
3800 _young_gen->to()->object_iterate_careful(&sss_cl);
3801 }
3802 MarkRefsIntoAndScanClosure
3803 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3804 &_markStack, this, CMSYield,
3805 true /* precleaning phase */);
3806 // CAUTION: The following closure has persistent state that may need to
3807 // be reset upon a decrease in the sequence of addresses it
3808 // processes.
3809 ScanMarkedObjectsAgainCarefullyClosure
3810 smoac_cl(this, _span,
3811 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3812
3813 // Preclean dirty cards in ModUnionTable and CardTable using
3814 // appropriate convergence criterion;
3815 // repeat CMSPrecleanIter times unless we find that
3816 // we are losing.
3817 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3818 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3819 "Bad convergence multiplier");
3820 assert(CMSPrecleanThreshold >= 100,
3821 "Unreasonably low CMSPrecleanThreshold");
3822
3823 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3824 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3825 numIter < CMSPrecleanIter;
3826 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3827 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3828 log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3829 // Either there are very few dirty cards, so re-mark
3830 // pause will be small anyway, or our pre-cleaning isn't
3831 // that much faster than the rate at which cards are being
3832 // dirtied, so we might as well stop and re-mark since
3833 // precleaning won't improve our re-mark time by much.
3834 if (curNumCards <= CMSPrecleanThreshold ||
3835 (numIter > 0 &&
3836 (curNumCards * CMSPrecleanDenominator >
3837 lastNumCards * CMSPrecleanNumerator))) {
3838 numIter++;
3839 cumNumCards += curNumCards;
3840 break;
3841 }
3842 }
3843
3844 preclean_cld(&mrias_cl, _cmsGen->freelistLock());
3845
3846 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3847 cumNumCards += curNumCards;
3848 log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3849 curNumCards, cumNumCards, numIter);
3850 return cumNumCards; // as a measure of useful work done
3851 }
3852
3853 // PRECLEANING NOTES:
3854 // Precleaning involves:
3855 // . reading the bits of the modUnionTable and clearing the set bits.
3856 // . For the cards corresponding to the set bits, we scan the
3857 // objects on those cards. This means we need the free_list_lock
3858 // so that we can safely iterate over the CMS space when scanning
3859 // for oops.
3860 // . When we scan the objects, we'll be both reading and setting
3861 // marks in the marking bit map, so we'll need the marking bit map.
3862 // . For protecting _collector_state transitions, we take the CGC_lock.
3863 // Note that any races in the reading of of card table entries by the
3864 // CMS thread on the one hand and the clearing of those entries by the
3865 // VM thread or the setting of those entries by the mutator threads on the
3866 // other are quite benign. However, for efficiency it makes sense to keep
3867 // the VM thread from racing with the CMS thread while the latter is
3868 // dirty card info to the modUnionTable. We therefore also use the
3869 // CGC_lock to protect the reading of the card table and the mod union
3870 // table by the CM thread.
3871 // . We run concurrently with mutator updates, so scanning
3872 // needs to be done carefully -- we should not try to scan
3873 // potentially uninitialized objects.
3874 //
3875 // Locking strategy: While holding the CGC_lock, we scan over and
3876 // reset a maximal dirty range of the mod union / card tables, then lock
3877 // the free_list_lock and bitmap lock to do a full marking, then
3878 // release these locks; and repeat the cycle. This allows for a
3879 // certain amount of fairness in the sharing of these locks between
3880 // the CMS collector on the one hand, and the VM thread and the
3881 // mutators on the other.
3882
3883 // NOTE: preclean_mod_union_table() and preclean_card_table()
3884 // further below are largely identical; if you need to modify
3885 // one of these methods, please check the other method too.
3886
3887 size_t CMSCollector::preclean_mod_union_table(
3888 ConcurrentMarkSweepGeneration* old_gen,
3889 ScanMarkedObjectsAgainCarefullyClosure* cl) {
3890 verify_work_stacks_empty();
3891 verify_overflow_empty();
3892
3893 // strategy: starting with the first card, accumulate contiguous
3894 // ranges of dirty cards; clear these cards, then scan the region
3895 // covered by these cards.
3896
3897 // Since all of the MUT is committed ahead, we can just use
3898 // that, in case the generations expand while we are precleaning.
3899 // It might also be fine to just use the committed part of the
3900 // generation, but we might potentially miss cards when the
3901 // generation is rapidly expanding while we are in the midst
3902 // of precleaning.
3903 HeapWord* startAddr = old_gen->reserved().start();
3904 HeapWord* endAddr = old_gen->reserved().end();
3905
3906 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
3907
3908 size_t numDirtyCards, cumNumDirtyCards;
3909 HeapWord *nextAddr, *lastAddr;
3910 for (cumNumDirtyCards = numDirtyCards = 0,
3911 nextAddr = lastAddr = startAddr;
3912 nextAddr < endAddr;
3913 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3914
3915 ResourceMark rm;
3916 HandleMark hm;
3917
3918 MemRegion dirtyRegion;
3919 {
3920 stopTimer();
3921 // Potential yield point
3922 CMSTokenSync ts(true);
3923 startTimer();
3924 sample_eden();
3925 // Get dirty region starting at nextOffset (inclusive),
3926 // simultaneously clearing it.
3927 dirtyRegion =
3928 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3929 assert(dirtyRegion.start() >= nextAddr,
3930 "returned region inconsistent?");
3931 }
3932 // Remember where the next search should begin.
3933 // The returned region (if non-empty) is a right open interval,
3934 // so lastOffset is obtained from the right end of that
3935 // interval.
3936 lastAddr = dirtyRegion.end();
3937 // Should do something more transparent and less hacky XXX
3938 numDirtyCards =
3939 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
3940
3941 // We'll scan the cards in the dirty region (with periodic
3942 // yields for foreground GC as needed).
3943 if (!dirtyRegion.is_empty()) {
3944 assert(numDirtyCards > 0, "consistency check");
3945 HeapWord* stop_point = NULL;
3946 stopTimer();
3947 // Potential yield point
3948 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
3949 bitMapLock());
3950 startTimer();
3951 {
3952 verify_work_stacks_empty();
3953 verify_overflow_empty();
3954 sample_eden();
3955 stop_point =
3956 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
3957 }
3958 if (stop_point != NULL) {
3959 // The careful iteration stopped early either because it found an
3960 // uninitialized object, or because we were in the midst of an
3961 // "abortable preclean", which should now be aborted. Redirty
3962 // the bits corresponding to the partially-scanned or unscanned
3963 // cards. We'll either restart at the next block boundary or
3964 // abort the preclean.
3965 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
3966 "Should only be AbortablePreclean.");
3967 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
3968 if (should_abort_preclean()) {
3969 break; // out of preclean loop
3970 } else {
3971 // Compute the next address at which preclean should pick up;
3972 // might need bitMapLock in order to read P-bits.
3973 lastAddr = next_card_start_after_block(stop_point);
3974 }
3975 }
3976 } else {
3977 assert(lastAddr == endAddr, "consistency check");
3978 assert(numDirtyCards == 0, "consistency check");
3979 break;
3980 }
3981 }
3982 verify_work_stacks_empty();
3983 verify_overflow_empty();
3984 return cumNumDirtyCards;
3985 }
3986
3987 // NOTE: preclean_mod_union_table() above and preclean_card_table()
3988 // below are largely identical; if you need to modify
3989 // one of these methods, please check the other method too.
3990
3991 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
3992 ScanMarkedObjectsAgainCarefullyClosure* cl) {
3993 // strategy: it's similar to precleamModUnionTable above, in that
3994 // we accumulate contiguous ranges of dirty cards, mark these cards
3995 // precleaned, then scan the region covered by these cards.
3996 HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high());
3997 HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
3998
3999 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4000
4001 size_t numDirtyCards, cumNumDirtyCards;
4002 HeapWord *lastAddr, *nextAddr;
4003
4004 for (cumNumDirtyCards = numDirtyCards = 0,
4005 nextAddr = lastAddr = startAddr;
4006 nextAddr < endAddr;
4007 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4008
4009 ResourceMark rm;
4010 HandleMark hm;
4011
4012 MemRegion dirtyRegion;
4013 {
4014 // See comments in "Precleaning notes" above on why we
4015 // do this locking. XXX Could the locking overheads be
4016 // too high when dirty cards are sparse? [I don't think so.]
4017 stopTimer();
4018 CMSTokenSync x(true); // is cms thread
4019 startTimer();
4020 sample_eden();
4021 // Get and clear dirty region from card table
4022 dirtyRegion = _ct->dirty_card_range_after_reset(MemRegion(nextAddr, endAddr),
4023 true,
4024 CardTable::precleaned_card_val());
4025
4026 assert(dirtyRegion.start() >= nextAddr,
4027 "returned region inconsistent?");
4028 }
4029 lastAddr = dirtyRegion.end();
4030 numDirtyCards =
4031 dirtyRegion.word_size()/CardTable::card_size_in_words;
4032
4033 if (!dirtyRegion.is_empty()) {
4034 stopTimer();
4035 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4036 startTimer();
4037 sample_eden();
4038 verify_work_stacks_empty();
4039 verify_overflow_empty();
4040 HeapWord* stop_point =
4041 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4042 if (stop_point != NULL) {
4043 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4044 "Should only be AbortablePreclean.");
4045 _ct->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4046 if (should_abort_preclean()) {
4047 break; // out of preclean loop
4048 } else {
4049 // Compute the next address at which preclean should pick up.
4050 lastAddr = next_card_start_after_block(stop_point);
4051 }
4052 }
4053 } else {
4054 break;
4055 }
4056 }
4057 verify_work_stacks_empty();
4058 verify_overflow_empty();
4059 return cumNumDirtyCards;
4060 }
4061
4062 class PrecleanCLDClosure : public CLDClosure {
4063 MetadataAwareOopsInGenClosure* _cm_closure;
4064 public:
4065 PrecleanCLDClosure(MetadataAwareOopsInGenClosure* oop_closure) : _cm_closure(oop_closure) {}
4066 void do_cld(ClassLoaderData* cld) {
4067 if (cld->has_accumulated_modified_oops()) {
4068 cld->clear_accumulated_modified_oops();
4069
4070 _cm_closure->do_cld(cld);
4071 }
4072 }
4073 };
4074
4075 // The freelist lock is needed to prevent asserts, is it really needed?
4076 void CMSCollector::preclean_cld(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4077
4078 cl->set_freelistLock(freelistLock);
4079
4080 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4081
4082 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4083 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4084 PrecleanCLDClosure preclean_closure(cl);
4085 ClassLoaderDataGraph::cld_do(&preclean_closure);
4086
4087 verify_work_stacks_empty();
4088 verify_overflow_empty();
4089 }
4090
4091 void CMSCollector::checkpointRootsFinal() {
4092 assert(_collectorState == FinalMarking, "incorrect state transition?");
4093 check_correct_thread_executing();
4094 // world is stopped at this checkpoint
4095 assert(SafepointSynchronize::is_at_safepoint(),
4096 "world should be stopped");
4097 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
4098
4099 verify_work_stacks_empty();
4100 verify_overflow_empty();
4101
4102 log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4103 _young_gen->used() / K, _young_gen->capacity() / K);
4104 {
4105 if (CMSScavengeBeforeRemark) {
4106 CMSHeap* heap = CMSHeap::heap();
4107 // Temporarily set flag to false, GCH->do_collection will
4108 // expect it to be false and set to true
4109 FlagSetting fl(heap->_is_gc_active, false);
4110
4111 heap->do_collection(true, // full (i.e. force, see below)
4112 false, // !clear_all_soft_refs
4113 0, // size
4114 false, // is_tlab
4115 GenCollectedHeap::YoungGen // type
4116 );
4117 }
4118 FreelistLocker x(this);
4119 MutexLockerEx y(bitMapLock(),
4120 Mutex::_no_safepoint_check_flag);
4121 checkpointRootsFinalWork();
4122 }
4123 verify_work_stacks_empty();
4124 verify_overflow_empty();
4125 }
4126
4127 void CMSCollector::checkpointRootsFinalWork() {
4128 GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm);
4129
4130 assert(haveFreelistLocks(), "must have free list locks");
4131 assert_lock_strong(bitMapLock());
4132
4133 ResourceMark rm;
4134 HandleMark hm;
4135
4136 CMSHeap* heap = CMSHeap::heap();
4137
4138 if (should_unload_classes()) {
4139 CodeCache::gc_prologue();
4140 }
4141 assert(haveFreelistLocks(), "must have free list locks");
4142 assert_lock_strong(bitMapLock());
4143
4144 // We might assume that we need not fill TLAB's when
4145 // CMSScavengeBeforeRemark is set, because we may have just done
4146 // a scavenge which would have filled all TLAB's -- and besides
4147 // Eden would be empty. This however may not always be the case --
4148 // for instance although we asked for a scavenge, it may not have
4149 // happened because of a JNI critical section. We probably need
4150 // a policy for deciding whether we can in that case wait until
4151 // the critical section releases and then do the remark following
4152 // the scavenge, and skip it here. In the absence of that policy,
4153 // or of an indication of whether the scavenge did indeed occur,
4154 // we cannot rely on TLAB's having been filled and must do
4155 // so here just in case a scavenge did not happen.
4156 heap->ensure_parsability(false); // fill TLAB's, but no need to retire them
4157 // Update the saved marks which may affect the root scans.
4158 heap->save_marks();
4159
4160 print_eden_and_survivor_chunk_arrays();
4161
4162 {
4163 #if COMPILER2_OR_JVMCI
4164 DerivedPointerTableDeactivate dpt_deact;
4165 #endif
4166
4167 // Note on the role of the mod union table:
4168 // Since the marker in "markFromRoots" marks concurrently with
4169 // mutators, it is possible for some reachable objects not to have been
4170 // scanned. For instance, an only reference to an object A was
4171 // placed in object B after the marker scanned B. Unless B is rescanned,
4172 // A would be collected. Such updates to references in marked objects
4173 // are detected via the mod union table which is the set of all cards
4174 // dirtied since the first checkpoint in this GC cycle and prior to
4175 // the most recent young generation GC, minus those cleaned up by the
4176 // concurrent precleaning.
4177 if (CMSParallelRemarkEnabled) {
4178 GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm);
4179 do_remark_parallel();
4180 } else {
4181 GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm);
4182 do_remark_non_parallel();
4183 }
4184 }
4185 verify_work_stacks_empty();
4186 verify_overflow_empty();
4187
4188 {
4189 GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm);
4190 refProcessingWork();
4191 }
4192 verify_work_stacks_empty();
4193 verify_overflow_empty();
4194
4195 if (should_unload_classes()) {
4196 CodeCache::gc_epilogue();
4197 }
4198 JvmtiExport::gc_epilogue();
4199
4200 // If we encountered any (marking stack / work queue) overflow
4201 // events during the current CMS cycle, take appropriate
4202 // remedial measures, where possible, so as to try and avoid
4203 // recurrence of that condition.
4204 assert(_markStack.isEmpty(), "No grey objects");
4205 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4206 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4207 if (ser_ovflw > 0) {
4208 log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4209 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4210 _markStack.expand();
4211 _ser_pmc_remark_ovflw = 0;
4212 _ser_pmc_preclean_ovflw = 0;
4213 _ser_kac_preclean_ovflw = 0;
4214 _ser_kac_ovflw = 0;
4215 }
4216 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4217 log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4218 _par_pmc_remark_ovflw, _par_kac_ovflw);
4219 _par_pmc_remark_ovflw = 0;
4220 _par_kac_ovflw = 0;
4221 }
4222 if (_markStack._hit_limit > 0) {
4223 log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4224 _markStack._hit_limit);
4225 }
4226 if (_markStack._failed_double > 0) {
4227 log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4228 _markStack._failed_double, _markStack.capacity());
4229 }
4230 _markStack._hit_limit = 0;
4231 _markStack._failed_double = 0;
4232
4233 if ((VerifyAfterGC || VerifyDuringGC) &&
4234 CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4235 verify_after_remark();
4236 }
4237
4238 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4239
4240 // Change under the freelistLocks.
4241 _collectorState = Sweeping;
4242 // Call isAllClear() under bitMapLock
4243 assert(_modUnionTable.isAllClear(),
4244 "Should be clear by end of the final marking");
4245 assert(_ct->cld_rem_set()->mod_union_is_clear(),
4246 "Should be clear by end of the final marking");
4247 }
4248
4249 void CMSParInitialMarkTask::work(uint worker_id) {
4250 elapsedTimer _timer;
4251 ResourceMark rm;
4252 HandleMark hm;
4253
4254 // ---------- scan from roots --------------
4255 _timer.start();
4256 CMSHeap* heap = CMSHeap::heap();
4257 ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4258
4259 // ---------- young gen roots --------------
4260 {
4261 work_on_young_gen_roots(&par_mri_cl);
4262 _timer.stop();
4263 log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4264 }
4265
4266 // ---------- remaining roots --------------
4267 _timer.reset();
4268 _timer.start();
4269
4270 CLDToOopClosure cld_closure(&par_mri_cl, true);
4271
4272 heap->cms_process_roots(_strong_roots_scope,
4273 false, // yg was scanned above
4274 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4275 _collector->should_unload_classes(),
4276 &par_mri_cl,
4277 &cld_closure);
4278 assert(_collector->should_unload_classes()
4279 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4280 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4281 _timer.stop();
4282 log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4283 }
4284
4285 // Parallel remark task
4286 class CMSParRemarkTask: public CMSParMarkTask {
4287 CompactibleFreeListSpace* _cms_space;
4288
4289 // The per-thread work queues, available here for stealing.
4290 OopTaskQueueSet* _task_queues;
4291 ParallelTaskTerminator _term;
4292 StrongRootsScope* _strong_roots_scope;
4293
4294 public:
4295 // A value of 0 passed to n_workers will cause the number of
4296 // workers to be taken from the active workers in the work gang.
4297 CMSParRemarkTask(CMSCollector* collector,
4298 CompactibleFreeListSpace* cms_space,
4299 uint n_workers, WorkGang* workers,
4300 OopTaskQueueSet* task_queues,
4301 StrongRootsScope* strong_roots_scope):
4302 CMSParMarkTask("Rescan roots and grey objects in parallel",
4303 collector, n_workers),
4304 _cms_space(cms_space),
4305 _task_queues(task_queues),
4306 _term(n_workers, task_queues),
4307 _strong_roots_scope(strong_roots_scope) { }
4308
4309 OopTaskQueueSet* task_queues() { return _task_queues; }
4310
4311 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4312
4313 ParallelTaskTerminator* terminator() { return &_term; }
4314 uint n_workers() { return _n_workers; }
4315
4316 void work(uint worker_id);
4317
4318 private:
4319 // ... of dirty cards in old space
4320 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4321 ParMarkRefsIntoAndScanClosure* cl);
4322
4323 // ... work stealing for the above
4324 void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl, int* seed);
4325 };
4326
4327 class RemarkCLDClosure : public CLDClosure {
4328 CLDToOopClosure _cm_closure;
4329 public:
4330 RemarkCLDClosure(OopClosure* oop_closure) : _cm_closure(oop_closure) {}
4331 void do_cld(ClassLoaderData* cld) {
4332 // Check if we have modified any oops in the CLD during the concurrent marking.
4333 if (cld->has_accumulated_modified_oops()) {
4334 cld->clear_accumulated_modified_oops();
4335
4336 // We could have transfered the current modified marks to the accumulated marks,
4337 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4338 } else if (cld->has_modified_oops()) {
4339 // Don't clear anything, this info is needed by the next young collection.
4340 } else {
4341 // No modified oops in the ClassLoaderData.
4342 return;
4343 }
4344
4345 // The klass has modified fields, need to scan the klass.
4346 _cm_closure.do_cld(cld);
4347 }
4348 };
4349
4350 void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) {
4351 ParNewGeneration* young_gen = _collector->_young_gen;
4352 ContiguousSpace* eden_space = young_gen->eden();
4353 ContiguousSpace* from_space = young_gen->from();
4354 ContiguousSpace* to_space = young_gen->to();
4355
4356 HeapWord** eca = _collector->_eden_chunk_array;
4357 size_t ect = _collector->_eden_chunk_index;
4358 HeapWord** sca = _collector->_survivor_chunk_array;
4359 size_t sct = _collector->_survivor_chunk_index;
4360
4361 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4362 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4363
4364 do_young_space_rescan(cl, to_space, NULL, 0);
4365 do_young_space_rescan(cl, from_space, sca, sct);
4366 do_young_space_rescan(cl, eden_space, eca, ect);
4367 }
4368
4369 // work_queue(i) is passed to the closure
4370 // ParMarkRefsIntoAndScanClosure. The "i" parameter
4371 // also is passed to do_dirty_card_rescan_tasks() and to
4372 // do_work_steal() to select the i-th task_queue.
4373
4374 void CMSParRemarkTask::work(uint worker_id) {
4375 elapsedTimer _timer;
4376 ResourceMark rm;
4377 HandleMark hm;
4378
4379 // ---------- rescan from roots --------------
4380 _timer.start();
4381 CMSHeap* heap = CMSHeap::heap();
4382 ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4383 _collector->_span, _collector->ref_processor(),
4384 &(_collector->_markBitMap),
4385 work_queue(worker_id));
4386
4387 // Rescan young gen roots first since these are likely
4388 // coarsely partitioned and may, on that account, constitute
4389 // the critical path; thus, it's best to start off that
4390 // work first.
4391 // ---------- young gen roots --------------
4392 {
4393 work_on_young_gen_roots(&par_mrias_cl);
4394 _timer.stop();
4395 log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4396 }
4397
4398 // ---------- remaining roots --------------
4399 _timer.reset();
4400 _timer.start();
4401 heap->cms_process_roots(_strong_roots_scope,
4402 false, // yg was scanned above
4403 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4404 _collector->should_unload_classes(),
4405 &par_mrias_cl,
4406 NULL); // The dirty klasses will be handled below
4407
4408 assert(_collector->should_unload_classes()
4409 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4410 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4411 _timer.stop();
4412 log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4413
4414 // ---------- unhandled CLD scanning ----------
4415 if (worker_id == 0) { // Single threaded at the moment.
4416 _timer.reset();
4417 _timer.start();
4418
4419 // Scan all new class loader data objects and new dependencies that were
4420 // introduced during concurrent marking.
4421 ResourceMark rm;
4422 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4423 for (int i = 0; i < array->length(); i++) {
4424 par_mrias_cl.do_cld_nv(array->at(i));
4425 }
4426
4427 // We don't need to keep track of new CLDs anymore.
4428 ClassLoaderDataGraph::remember_new_clds(false);
4429
4430 _timer.stop();
4431 log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4432 }
4433
4434 // We might have added oops to ClassLoaderData::_handles during the
4435 // concurrent marking phase. These oops do not always point to newly allocated objects
4436 // that are guaranteed to be kept alive. Hence,
4437 // we do have to revisit the _handles block during the remark phase.
4438
4439 // ---------- dirty CLD scanning ----------
4440 if (worker_id == 0) { // Single threaded at the moment.
4441 _timer.reset();
4442 _timer.start();
4443
4444 // Scan all classes that was dirtied during the concurrent marking phase.
4445 RemarkCLDClosure remark_closure(&par_mrias_cl);
4446 ClassLoaderDataGraph::cld_do(&remark_closure);
4447
4448 _timer.stop();
4449 log_trace(gc, task)("Finished dirty CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4450 }
4451
4452
4453 // ---------- rescan dirty cards ------------
4454 _timer.reset();
4455 _timer.start();
4456
4457 // Do the rescan tasks for each of the two spaces
4458 // (cms_space) in turn.
4459 // "worker_id" is passed to select the task_queue for "worker_id"
4460 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4461 _timer.stop();
4462 log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4463
4464 // ---------- steal work from other threads ...
4465 // ---------- ... and drain overflow list.
4466 _timer.reset();
4467 _timer.start();
4468 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4469 _timer.stop();
4470 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4471 }
4472
4473 void
4474 CMSParMarkTask::do_young_space_rescan(
4475 OopsInGenClosure* cl, ContiguousSpace* space,
4476 HeapWord** chunk_array, size_t chunk_top) {
4477 // Until all tasks completed:
4478 // . claim an unclaimed task
4479 // . compute region boundaries corresponding to task claimed
4480 // using chunk_array
4481 // . par_oop_iterate(cl) over that region
4482
4483 ResourceMark rm;
4484 HandleMark hm;
4485
4486 SequentialSubTasksDone* pst = space->par_seq_tasks();
4487
4488 uint nth_task = 0;
4489 uint n_tasks = pst->n_tasks();
4490
4491 if (n_tasks > 0) {
4492 assert(pst->valid(), "Uninitialized use?");
4493 HeapWord *start, *end;
4494 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4495 // We claimed task # nth_task; compute its boundaries.
4496 if (chunk_top == 0) { // no samples were taken
4497 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4498 start = space->bottom();
4499 end = space->top();
4500 } else if (nth_task == 0) {
4501 start = space->bottom();
4502 end = chunk_array[nth_task];
4503 } else if (nth_task < (uint)chunk_top) {
4504 assert(nth_task >= 1, "Control point invariant");
4505 start = chunk_array[nth_task - 1];
4506 end = chunk_array[nth_task];
4507 } else {
4508 assert(nth_task == (uint)chunk_top, "Control point invariant");
4509 start = chunk_array[chunk_top - 1];
4510 end = space->top();
4511 }
4512 MemRegion mr(start, end);
4513 // Verify that mr is in space
4514 assert(mr.is_empty() || space->used_region().contains(mr),
4515 "Should be in space");
4516 // Verify that "start" is an object boundary
4517 assert(mr.is_empty() || oopDesc::is_oop(oop(mr.start())),
4518 "Should be an oop");
4519 space->par_oop_iterate(mr, cl);
4520 }
4521 pst->all_tasks_completed();
4522 }
4523 }
4524
4525 void
4526 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4527 CompactibleFreeListSpace* sp, int i,
4528 ParMarkRefsIntoAndScanClosure* cl) {
4529 // Until all tasks completed:
4530 // . claim an unclaimed task
4531 // . compute region boundaries corresponding to task claimed
4532 // . transfer dirty bits ct->mut for that region
4533 // . apply rescanclosure to dirty mut bits for that region
4534
4535 ResourceMark rm;
4536 HandleMark hm;
4537
4538 OopTaskQueue* work_q = work_queue(i);
4539 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4540 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4541 // CAUTION: This closure has state that persists across calls to
4542 // the work method dirty_range_iterate_clear() in that it has
4543 // embedded in it a (subtype of) UpwardsObjectClosure. The
4544 // use of that state in the embedded UpwardsObjectClosure instance
4545 // assumes that the cards are always iterated (even if in parallel
4546 // by several threads) in monotonically increasing order per each
4547 // thread. This is true of the implementation below which picks
4548 // card ranges (chunks) in monotonically increasing order globally
4549 // and, a-fortiori, in monotonically increasing order per thread
4550 // (the latter order being a subsequence of the former).
4551 // If the work code below is ever reorganized into a more chaotic
4552 // work-partitioning form than the current "sequential tasks"
4553 // paradigm, the use of that persistent state will have to be
4554 // revisited and modified appropriately. See also related
4555 // bug 4756801 work on which should examine this code to make
4556 // sure that the changes there do not run counter to the
4557 // assumptions made here and necessary for correctness and
4558 // efficiency. Note also that this code might yield inefficient
4559 // behavior in the case of very large objects that span one or
4560 // more work chunks. Such objects would potentially be scanned
4561 // several times redundantly. Work on 4756801 should try and
4562 // address that performance anomaly if at all possible. XXX
4563 MemRegion full_span = _collector->_span;
4564 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4565 MarkFromDirtyCardsClosure
4566 greyRescanClosure(_collector, full_span, // entire span of interest
4567 sp, bm, work_q, cl);
4568
4569 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4570 assert(pst->valid(), "Uninitialized use?");
4571 uint nth_task = 0;
4572 const int alignment = CardTable::card_size * BitsPerWord;
4573 MemRegion span = sp->used_region();
4574 HeapWord* start_addr = span.start();
4575 HeapWord* end_addr = align_up(span.end(), alignment);
4576 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4577 assert(is_aligned(start_addr, alignment), "Check alignment");
4578 assert(is_aligned(chunk_size, alignment), "Check alignment");
4579
4580 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4581 // Having claimed the nth_task, compute corresponding mem-region,
4582 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4583 // The alignment restriction ensures that we do not need any
4584 // synchronization with other gang-workers while setting or
4585 // clearing bits in thus chunk of the MUT.
4586 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4587 start_addr + (nth_task+1)*chunk_size);
4588 // The last chunk's end might be way beyond end of the
4589 // used region. In that case pull back appropriately.
4590 if (this_span.end() > end_addr) {
4591 this_span.set_end(end_addr);
4592 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4593 }
4594 // Iterate over the dirty cards covering this chunk, marking them
4595 // precleaned, and setting the corresponding bits in the mod union
4596 // table. Since we have been careful to partition at Card and MUT-word
4597 // boundaries no synchronization is needed between parallel threads.
4598 _collector->_ct->dirty_card_iterate(this_span,
4599 &modUnionClosure);
4600
4601 // Having transferred these marks into the modUnionTable,
4602 // rescan the marked objects on the dirty cards in the modUnionTable.
4603 // Even if this is at a synchronous collection, the initial marking
4604 // may have been done during an asynchronous collection so there
4605 // may be dirty bits in the mod-union table.
4606 _collector->_modUnionTable.dirty_range_iterate_clear(
4607 this_span, &greyRescanClosure);
4608 _collector->_modUnionTable.verifyNoOneBitsInRange(
4609 this_span.start(),
4610 this_span.end());
4611 }
4612 pst->all_tasks_completed(); // declare that i am done
4613 }
4614
4615 // . see if we can share work_queues with ParNew? XXX
4616 void
4617 CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl,
4618 int* seed) {
4619 OopTaskQueue* work_q = work_queue(i);
4620 NOT_PRODUCT(int num_steals = 0;)
4621 oop obj_to_scan;
4622 CMSBitMap* bm = &(_collector->_markBitMap);
4623
4624 while (true) {
4625 // Completely finish any left over work from (an) earlier round(s)
4626 cl->trim_queue(0);
4627 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4628 (size_t)ParGCDesiredObjsFromOverflowList);
4629 // Now check if there's any work in the overflow list
4630 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4631 // only affects the number of attempts made to get work from the
4632 // overflow list and does not affect the number of workers. Just
4633 // pass ParallelGCThreads so this behavior is unchanged.
4634 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4635 work_q,
4636 ParallelGCThreads)) {
4637 // found something in global overflow list;
4638 // not yet ready to go stealing work from others.
4639 // We'd like to assert(work_q->size() != 0, ...)
4640 // because we just took work from the overflow list,
4641 // but of course we can't since all of that could have
4642 // been already stolen from us.
4643 // "He giveth and He taketh away."
4644 continue;
4645 }
4646 // Verify that we have no work before we resort to stealing
4647 assert(work_q->size() == 0, "Have work, shouldn't steal");
4648 // Try to steal from other queues that have work
4649 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4650 NOT_PRODUCT(num_steals++;)
4651 assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
4652 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4653 // Do scanning work
4654 obj_to_scan->oop_iterate(cl);
4655 // Loop around, finish this work, and try to steal some more
4656 } else if (terminator()->offer_termination()) {
4657 break; // nirvana from the infinite cycle
4658 }
4659 }
4660 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4661 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4662 "Else our work is not yet done");
4663 }
4664
4665 // Record object boundaries in _eden_chunk_array by sampling the eden
4666 // top in the slow-path eden object allocation code path and record
4667 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4668 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4669 // sampling in sample_eden() that activates during the part of the
4670 // preclean phase.
4671 void CMSCollector::sample_eden_chunk() {
4672 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4673 if (_eden_chunk_lock->try_lock()) {
4674 // Record a sample. This is the critical section. The contents
4675 // of the _eden_chunk_array have to be non-decreasing in the
4676 // address order.
4677 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4678 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4679 "Unexpected state of Eden");
4680 if (_eden_chunk_index == 0 ||
4681 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4682 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4683 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4684 _eden_chunk_index++; // commit sample
4685 }
4686 _eden_chunk_lock->unlock();
4687 }
4688 }
4689 }
4690
4691 // Return a thread-local PLAB recording array, as appropriate.
4692 void* CMSCollector::get_data_recorder(int thr_num) {
4693 if (_survivor_plab_array != NULL &&
4694 (CMSPLABRecordAlways ||
4695 (_collectorState > Marking && _collectorState < FinalMarking))) {
4696 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4697 ChunkArray* ca = &_survivor_plab_array[thr_num];
4698 ca->reset(); // clear it so that fresh data is recorded
4699 return (void*) ca;
4700 } else {
4701 return NULL;
4702 }
4703 }
4704
4705 // Reset all the thread-local PLAB recording arrays
4706 void CMSCollector::reset_survivor_plab_arrays() {
4707 for (uint i = 0; i < ParallelGCThreads; i++) {
4708 _survivor_plab_array[i].reset();
4709 }
4710 }
4711
4712 // Merge the per-thread plab arrays into the global survivor chunk
4713 // array which will provide the partitioning of the survivor space
4714 // for CMS initial scan and rescan.
4715 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4716 int no_of_gc_threads) {
4717 assert(_survivor_plab_array != NULL, "Error");
4718 assert(_survivor_chunk_array != NULL, "Error");
4719 assert(_collectorState == FinalMarking ||
4720 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4721 for (int j = 0; j < no_of_gc_threads; j++) {
4722 _cursor[j] = 0;
4723 }
4724 HeapWord* top = surv->top();
4725 size_t i;
4726 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4727 HeapWord* min_val = top; // Higher than any PLAB address
4728 uint min_tid = 0; // position of min_val this round
4729 for (int j = 0; j < no_of_gc_threads; j++) {
4730 ChunkArray* cur_sca = &_survivor_plab_array[j];
4731 if (_cursor[j] == cur_sca->end()) {
4732 continue;
4733 }
4734 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4735 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4736 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4737 if (cur_val < min_val) {
4738 min_tid = j;
4739 min_val = cur_val;
4740 } else {
4741 assert(cur_val < top, "All recorded addresses should be less");
4742 }
4743 }
4744 // At this point min_val and min_tid are respectively
4745 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4746 // and the thread (j) that witnesses that address.
4747 // We record this address in the _survivor_chunk_array[i]
4748 // and increment _cursor[min_tid] prior to the next round i.
4749 if (min_val == top) {
4750 break;
4751 }
4752 _survivor_chunk_array[i] = min_val;
4753 _cursor[min_tid]++;
4754 }
4755 // We are all done; record the size of the _survivor_chunk_array
4756 _survivor_chunk_index = i; // exclusive: [0, i)
4757 log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4758 // Verify that we used up all the recorded entries
4759 #ifdef ASSERT
4760 size_t total = 0;
4761 for (int j = 0; j < no_of_gc_threads; j++) {
4762 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4763 total += _cursor[j];
4764 }
4765 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4766 // Check that the merged array is in sorted order
4767 if (total > 0) {
4768 for (size_t i = 0; i < total - 1; i++) {
4769 log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4770 i, p2i(_survivor_chunk_array[i]));
4771 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4772 "Not sorted");
4773 }
4774 }
4775 #endif // ASSERT
4776 }
4777
4778 // Set up the space's par_seq_tasks structure for work claiming
4779 // for parallel initial scan and rescan of young gen.
4780 // See ParRescanTask where this is currently used.
4781 void
4782 CMSCollector::
4783 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4784 assert(n_threads > 0, "Unexpected n_threads argument");
4785
4786 // Eden space
4787 if (!_young_gen->eden()->is_empty()) {
4788 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4789 assert(!pst->valid(), "Clobbering existing data?");
4790 // Each valid entry in [0, _eden_chunk_index) represents a task.
4791 size_t n_tasks = _eden_chunk_index + 1;
4792 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4793 // Sets the condition for completion of the subtask (how many threads
4794 // need to finish in order to be done).
4795 pst->set_n_threads(n_threads);
4796 pst->set_n_tasks((int)n_tasks);
4797 }
4798
4799 // Merge the survivor plab arrays into _survivor_chunk_array
4800 if (_survivor_plab_array != NULL) {
4801 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4802 } else {
4803 assert(_survivor_chunk_index == 0, "Error");
4804 }
4805
4806 // To space
4807 {
4808 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4809 assert(!pst->valid(), "Clobbering existing data?");
4810 // Sets the condition for completion of the subtask (how many threads
4811 // need to finish in order to be done).
4812 pst->set_n_threads(n_threads);
4813 pst->set_n_tasks(1);
4814 assert(pst->valid(), "Error");
4815 }
4816
4817 // From space
4818 {
4819 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4820 assert(!pst->valid(), "Clobbering existing data?");
4821 size_t n_tasks = _survivor_chunk_index + 1;
4822 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
4823 // Sets the condition for completion of the subtask (how many threads
4824 // need to finish in order to be done).
4825 pst->set_n_threads(n_threads);
4826 pst->set_n_tasks((int)n_tasks);
4827 assert(pst->valid(), "Error");
4828 }
4829 }
4830
4831 // Parallel version of remark
4832 void CMSCollector::do_remark_parallel() {
4833 CMSHeap* heap = CMSHeap::heap();
4834 WorkGang* workers = heap->workers();
4835 assert(workers != NULL, "Need parallel worker threads.");
4836 // Choose to use the number of GC workers most recently set
4837 // into "active_workers".
4838 uint n_workers = workers->active_workers();
4839
4840 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4841
4842 StrongRootsScope srs(n_workers);
4843
4844 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4845
4846 // We won't be iterating over the cards in the card table updating
4847 // the younger_gen cards, so we shouldn't call the following else
4848 // the verification code as well as subsequent younger_refs_iterate
4849 // code would get confused. XXX
4850 // heap->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4851
4852 // The young gen rescan work will not be done as part of
4853 // process_roots (which currently doesn't know how to
4854 // parallelize such a scan), but rather will be broken up into
4855 // a set of parallel tasks (via the sampling that the [abortable]
4856 // preclean phase did of eden, plus the [two] tasks of
4857 // scanning the [two] survivor spaces. Further fine-grain
4858 // parallelization of the scanning of the survivor spaces
4859 // themselves, and of precleaning of the young gen itself
4860 // is deferred to the future.
4861 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4862
4863 // The dirty card rescan work is broken up into a "sequence"
4864 // of parallel tasks (per constituent space) that are dynamically
4865 // claimed by the parallel threads.
4866 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4867
4868 // It turns out that even when we're using 1 thread, doing the work in a
4869 // separate thread causes wide variance in run times. We can't help this
4870 // in the multi-threaded case, but we special-case n=1 here to get
4871 // repeatable measurements of the 1-thread overhead of the parallel code.
4872 if (n_workers > 1) {
4873 // Make refs discovery MT-safe, if it isn't already: it may not
4874 // necessarily be so, since it's possible that we are doing
4875 // ST marking.
4876 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4877 workers->run_task(&tsk);
4878 } else {
4879 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4880 tsk.work(0);
4881 }
4882
4883 // restore, single-threaded for now, any preserved marks
4884 // as a result of work_q overflow
4885 restore_preserved_marks_if_any();
4886 }
4887
4888 // Non-parallel version of remark
4889 void CMSCollector::do_remark_non_parallel() {
4890 ResourceMark rm;
4891 HandleMark hm;
4892 CMSHeap* heap = CMSHeap::heap();
4893 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4894
4895 MarkRefsIntoAndScanClosure
4896 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4897 &_markStack, this,
4898 false /* should_yield */, false /* not precleaning */);
4899 MarkFromDirtyCardsClosure
4900 markFromDirtyCardsClosure(this, _span,
4901 NULL, // space is set further below
4902 &_markBitMap, &_markStack, &mrias_cl);
4903 {
4904 GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm);
4905 // Iterate over the dirty cards, setting the corresponding bits in the
4906 // mod union table.
4907 {
4908 ModUnionClosure modUnionClosure(&_modUnionTable);
4909 _ct->dirty_card_iterate(_cmsGen->used_region(),
4910 &modUnionClosure);
4911 }
4912 // Having transferred these marks into the modUnionTable, we just need
4913 // to rescan the marked objects on the dirty cards in the modUnionTable.
4914 // The initial marking may have been done during an asynchronous
4915 // collection so there may be dirty bits in the mod-union table.
4916 const int alignment = CardTable::card_size * BitsPerWord;
4917 {
4918 // ... First handle dirty cards in CMS gen
4919 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4920 MemRegion ur = _cmsGen->used_region();
4921 HeapWord* lb = ur.start();
4922 HeapWord* ub = align_up(ur.end(), alignment);
4923 MemRegion cms_span(lb, ub);
4924 _modUnionTable.dirty_range_iterate_clear(cms_span,
4925 &markFromDirtyCardsClosure);
4926 verify_work_stacks_empty();
4927 log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4928 }
4929 }
4930 if (VerifyDuringGC &&
4931 CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4932 HandleMark hm; // Discard invalid handles created during verification
4933 Universe::verify();
4934 }
4935 {
4936 GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm);
4937
4938 verify_work_stacks_empty();
4939
4940 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
4941 StrongRootsScope srs(1);
4942
4943 heap->cms_process_roots(&srs,
4944 true, // young gen as roots
4945 GenCollectedHeap::ScanningOption(roots_scanning_options()),
4946 should_unload_classes(),
4947 &mrias_cl,
4948 NULL); // The dirty klasses will be handled below
4949
4950 assert(should_unload_classes()
4951 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4952 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4953 }
4954
4955 {
4956 GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm);
4957
4958 verify_work_stacks_empty();
4959
4960 // Scan all class loader data objects that might have been introduced
4961 // during concurrent marking.
4962 ResourceMark rm;
4963 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4964 for (int i = 0; i < array->length(); i++) {
4965 mrias_cl.do_cld_nv(array->at(i));
4966 }
4967
4968 // We don't need to keep track of new CLDs anymore.
4969 ClassLoaderDataGraph::remember_new_clds(false);
4970
4971 verify_work_stacks_empty();
4972 }
4973
4974 // We might have added oops to ClassLoaderData::_handles during the
4975 // concurrent marking phase. These oops do not point to newly allocated objects
4976 // that are guaranteed to be kept alive. Hence,
4977 // we do have to revisit the _handles block during the remark phase.
4978 {
4979 GCTraceTime(Trace, gc, phases) t("Dirty CLD Scan", _gc_timer_cm);
4980
4981 verify_work_stacks_empty();
4982
4983 RemarkCLDClosure remark_closure(&mrias_cl);
4984 ClassLoaderDataGraph::cld_do(&remark_closure);
4985
4986 verify_work_stacks_empty();
4987 }
4988
4989 verify_work_stacks_empty();
4990 // Restore evacuated mark words, if any, used for overflow list links
4991 restore_preserved_marks_if_any();
4992
4993 verify_overflow_empty();
4994 }
4995
4996 ////////////////////////////////////////////////////////
4997 // Parallel Reference Processing Task Proxy Class
4998 ////////////////////////////////////////////////////////
4999 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5000 OopTaskQueueSet* _queues;
5001 ParallelTaskTerminator _terminator;
5002 public:
5003 AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5004 AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5005 ParallelTaskTerminator* terminator() { return &_terminator; }
5006 OopTaskQueueSet* queues() { return _queues; }
5007 };
5008
5009 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5010 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5011 CMSCollector* _collector;
5012 CMSBitMap* _mark_bit_map;
5013 const MemRegion _span;
5014 ProcessTask& _task;
5015
5016 public:
5017 CMSRefProcTaskProxy(ProcessTask& task,
5018 CMSCollector* collector,
5019 const MemRegion& span,
5020 CMSBitMap* mark_bit_map,
5021 AbstractWorkGang* workers,
5022 OopTaskQueueSet* task_queues):
5023 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5024 task_queues,
5025 workers->active_workers()),
5026 _task(task),
5027 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5028 {
5029 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5030 "Inconsistency in _span");
5031 }
5032
5033 OopTaskQueueSet* task_queues() { return queues(); }
5034
5035 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5036
5037 void do_work_steal(int i,
5038 CMSParDrainMarkingStackClosure* drain,
5039 CMSParKeepAliveClosure* keep_alive,
5040 int* seed);
5041
5042 virtual void work(uint worker_id);
5043 };
5044
5045 void CMSRefProcTaskProxy::work(uint worker_id) {
5046 ResourceMark rm;
5047 HandleMark hm;
5048 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5049 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5050 _mark_bit_map,
5051 work_queue(worker_id));
5052 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5053 _mark_bit_map,
5054 work_queue(worker_id));
5055 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5056 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5057 if (_task.marks_oops_alive()) {
5058 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5059 _collector->hash_seed(worker_id));
5060 }
5061 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5062 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5063 }
5064
5065 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5066 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5067 _span(span),
5068 _bit_map(bit_map),
5069 _work_queue(work_queue),
5070 _mark_and_push(collector, span, bit_map, work_queue),
5071 _low_water_mark(MIN2((work_queue->max_elems()/4),
5072 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5073 { }
5074
5075 // . see if we can share work_queues with ParNew? XXX
5076 void CMSRefProcTaskProxy::do_work_steal(int i,
5077 CMSParDrainMarkingStackClosure* drain,
5078 CMSParKeepAliveClosure* keep_alive,
5079 int* seed) {
5080 OopTaskQueue* work_q = work_queue(i);
5081 NOT_PRODUCT(int num_steals = 0;)
5082 oop obj_to_scan;
5083
5084 while (true) {
5085 // Completely finish any left over work from (an) earlier round(s)
5086 drain->trim_queue(0);
5087 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5088 (size_t)ParGCDesiredObjsFromOverflowList);
5089 // Now check if there's any work in the overflow list
5090 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5091 // only affects the number of attempts made to get work from the
5092 // overflow list and does not affect the number of workers. Just
5093 // pass ParallelGCThreads so this behavior is unchanged.
5094 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5095 work_q,
5096 ParallelGCThreads)) {
5097 // Found something in global overflow list;
5098 // not yet ready to go stealing work from others.
5099 // We'd like to assert(work_q->size() != 0, ...)
5100 // because we just took work from the overflow list,
5101 // but of course we can't, since all of that might have
5102 // been already stolen from us.
5103 continue;
5104 }
5105 // Verify that we have no work before we resort to stealing
5106 assert(work_q->size() == 0, "Have work, shouldn't steal");
5107 // Try to steal from other queues that have work
5108 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5109 NOT_PRODUCT(num_steals++;)
5110 assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
5111 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5112 // Do scanning work
5113 obj_to_scan->oop_iterate(keep_alive);
5114 // Loop around, finish this work, and try to steal some more
5115 } else if (terminator()->offer_termination()) {
5116 break; // nirvana from the infinite cycle
5117 }
5118 }
5119 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5120 }
5121
5122 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5123 {
5124 CMSHeap* heap = CMSHeap::heap();
5125 WorkGang* workers = heap->workers();
5126 assert(workers != NULL, "Need parallel worker threads.");
5127 CMSRefProcTaskProxy rp_task(task, &_collector,
5128 _collector.ref_processor_span(),
5129 _collector.markBitMap(),
5130 workers, _collector.task_queues());
5131 workers->run_task(&rp_task);
5132 }
5133
5134 void CMSCollector::refProcessingWork() {
5135 ResourceMark rm;
5136 HandleMark hm;
5137
5138 ReferenceProcessor* rp = ref_processor();
5139 assert(_span_based_discoverer.span().equals(_span), "Spans should be equal");
5140 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5141 // Process weak references.
5142 rp->setup_policy(false);
5143 verify_work_stacks_empty();
5144
5145 ReferenceProcessorPhaseTimes pt(_gc_timer_cm, rp->num_queues());
5146 {
5147 GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm);
5148
5149 // Setup keep_alive and complete closures.
5150 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5151 &_markStack, false /* !preclean */);
5152 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5153 _span, &_markBitMap, &_markStack,
5154 &cmsKeepAliveClosure, false /* !preclean */);
5155
5156 ReferenceProcessorStats stats;
5157 if (rp->processing_is_mt()) {
5158 // Set the degree of MT here. If the discovery is done MT, there
5159 // may have been a different number of threads doing the discovery
5160 // and a different number of discovered lists may have Ref objects.
5161 // That is OK as long as the Reference lists are balanced (see
5162 // balance_all_queues() and balance_queues()).
5163 CMSHeap* heap = CMSHeap::heap();
5164 uint active_workers = ParallelGCThreads;
5165 WorkGang* workers = heap->workers();
5166 if (workers != NULL) {
5167 active_workers = workers->active_workers();
5168 // The expectation is that active_workers will have already
5169 // been set to a reasonable value. If it has not been set,
5170 // investigate.
5171 assert(active_workers > 0, "Should have been set during scavenge");
5172 }
5173 rp->set_active_mt_degree(active_workers);
5174 CMSRefProcTaskExecutor task_executor(*this);
5175 stats = rp->process_discovered_references(&_is_alive_closure,
5176 &cmsKeepAliveClosure,
5177 &cmsDrainMarkingStackClosure,
5178 &task_executor,
5179 &pt);
5180 } else {
5181 stats = rp->process_discovered_references(&_is_alive_closure,
5182 &cmsKeepAliveClosure,
5183 &cmsDrainMarkingStackClosure,
5184 NULL,
5185 &pt);
5186 }
5187 _gc_tracer_cm->report_gc_reference_stats(stats);
5188 pt.print_all_references();
5189 }
5190
5191 // This is the point where the entire marking should have completed.
5192 verify_work_stacks_empty();
5193
5194 {
5195 GCTraceTime(Debug, gc, phases) t("Weak Processing", _gc_timer_cm);
5196 WeakProcessor::weak_oops_do(&_is_alive_closure, &do_nothing_cl);
5197 }
5198
5199 if (should_unload_classes()) {
5200 {
5201 GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm);
5202
5203 // Unload classes and purge the SystemDictionary.
5204 bool purged_class = SystemDictionary::do_unloading(_gc_timer_cm);
5205
5206 // Unload nmethods.
5207 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5208
5209 // Prune dead klasses from subklass/sibling/implementor lists.
5210 Klass::clean_weak_klass_links(purged_class);
5211 }
5212
5213 {
5214 GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer_cm);
5215 // Clean up unreferenced symbols in symbol table.
5216 SymbolTable::unlink();
5217 }
5218
5219 {
5220 GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer_cm);
5221 // Delete entries for dead interned strings.
5222 StringTable::unlink(&_is_alive_closure);
5223 }
5224 }
5225
5226 // Restore any preserved marks as a result of mark stack or
5227 // work queue overflow
5228 restore_preserved_marks_if_any(); // done single-threaded for now
5229
5230 rp->set_enqueuing_is_done(true);
5231 rp->verify_no_references_recorded();
5232 }
5233
5234 #ifndef PRODUCT
5235 void CMSCollector::check_correct_thread_executing() {
5236 Thread* t = Thread::current();
5237 // Only the VM thread or the CMS thread should be here.
5238 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5239 "Unexpected thread type");
5240 // If this is the vm thread, the foreground process
5241 // should not be waiting. Note that _foregroundGCIsActive is
5242 // true while the foreground collector is waiting.
5243 if (_foregroundGCShouldWait) {
5244 // We cannot be the VM thread
5245 assert(t->is_ConcurrentGC_thread(),
5246 "Should be CMS thread");
5247 } else {
5248 // We can be the CMS thread only if we are in a stop-world
5249 // phase of CMS collection.
5250 if (t->is_ConcurrentGC_thread()) {
5251 assert(_collectorState == InitialMarking ||
5252 _collectorState == FinalMarking,
5253 "Should be a stop-world phase");
5254 // The CMS thread should be holding the CMS_token.
5255 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5256 "Potential interference with concurrently "
5257 "executing VM thread");
5258 }
5259 }
5260 }
5261 #endif
5262
5263 void CMSCollector::sweep() {
5264 assert(_collectorState == Sweeping, "just checking");
5265 check_correct_thread_executing();
5266 verify_work_stacks_empty();
5267 verify_overflow_empty();
5268 increment_sweep_count();
5269 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
5270
5271 _inter_sweep_timer.stop();
5272 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5273
5274 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5275 _intra_sweep_timer.reset();
5276 _intra_sweep_timer.start();
5277 {
5278 GCTraceCPUTime tcpu;
5279 CMSPhaseAccounting pa(this, "Concurrent Sweep");
5280 // First sweep the old gen
5281 {
5282 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5283 bitMapLock());
5284 sweepWork(_cmsGen);
5285 }
5286
5287 // Update Universe::_heap_*_at_gc figures.
5288 // We need all the free list locks to make the abstract state
5289 // transition from Sweeping to Resetting. See detailed note
5290 // further below.
5291 {
5292 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5293 // Update heap occupancy information which is used as
5294 // input to soft ref clearing policy at the next gc.
5295 Universe::update_heap_info_at_gc();
5296 _collectorState = Resizing;
5297 }
5298 }
5299 verify_work_stacks_empty();
5300 verify_overflow_empty();
5301
5302 if (should_unload_classes()) {
5303 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5304 // requires that the virtual spaces are stable and not deleted.
5305 ClassLoaderDataGraph::set_should_purge(true);
5306 }
5307
5308 _intra_sweep_timer.stop();
5309 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5310
5311 _inter_sweep_timer.reset();
5312 _inter_sweep_timer.start();
5313
5314 // We need to use a monotonically non-decreasing time in ms
5315 // or we will see time-warp warnings and os::javaTimeMillis()
5316 // does not guarantee monotonicity.
5317 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5318 update_time_of_last_gc(now);
5319
5320 // NOTE on abstract state transitions:
5321 // Mutators allocate-live and/or mark the mod-union table dirty
5322 // based on the state of the collection. The former is done in
5323 // the interval [Marking, Sweeping] and the latter in the interval
5324 // [Marking, Sweeping). Thus the transitions into the Marking state
5325 // and out of the Sweeping state must be synchronously visible
5326 // globally to the mutators.
5327 // The transition into the Marking state happens with the world
5328 // stopped so the mutators will globally see it. Sweeping is
5329 // done asynchronously by the background collector so the transition
5330 // from the Sweeping state to the Resizing state must be done
5331 // under the freelistLock (as is the check for whether to
5332 // allocate-live and whether to dirty the mod-union table).
5333 assert(_collectorState == Resizing, "Change of collector state to"
5334 " Resizing must be done under the freelistLocks (plural)");
5335
5336 // Now that sweeping has been completed, we clear
5337 // the incremental_collection_failed flag,
5338 // thus inviting a younger gen collection to promote into
5339 // this generation. If such a promotion may still fail,
5340 // the flag will be set again when a young collection is
5341 // attempted.
5342 CMSHeap* heap = CMSHeap::heap();
5343 heap->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5344 heap->update_full_collections_completed(_collection_count_start);
5345 }
5346
5347 // FIX ME!!! Looks like this belongs in CFLSpace, with
5348 // CMSGen merely delegating to it.
5349 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5350 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5351 HeapWord* minAddr = _cmsSpace->bottom();
5352 HeapWord* largestAddr =
5353 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5354 if (largestAddr == NULL) {
5355 // The dictionary appears to be empty. In this case
5356 // try to coalesce at the end of the heap.
5357 largestAddr = _cmsSpace->end();
5358 }
5359 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5360 size_t nearLargestOffset =
5361 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5362 log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5363 p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5364 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5365 }
5366
5367 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5368 return addr >= _cmsSpace->nearLargestChunk();
5369 }
5370
5371 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5372 return _cmsSpace->find_chunk_at_end();
5373 }
5374
5375 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5376 bool full) {
5377 // If the young generation has been collected, gather any statistics
5378 // that are of interest at this point.
5379 bool current_is_young = CMSHeap::heap()->is_young_gen(current_generation);
5380 if (!full && current_is_young) {
5381 // Gather statistics on the young generation collection.
5382 collector()->stats().record_gc0_end(used());
5383 }
5384 }
5385
5386 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5387 // We iterate over the space(s) underlying this generation,
5388 // checking the mark bit map to see if the bits corresponding
5389 // to specific blocks are marked or not. Blocks that are
5390 // marked are live and are not swept up. All remaining blocks
5391 // are swept up, with coalescing on-the-fly as we sweep up
5392 // contiguous free and/or garbage blocks:
5393 // We need to ensure that the sweeper synchronizes with allocators
5394 // and stop-the-world collectors. In particular, the following
5395 // locks are used:
5396 // . CMS token: if this is held, a stop the world collection cannot occur
5397 // . freelistLock: if this is held no allocation can occur from this
5398 // generation by another thread
5399 // . bitMapLock: if this is held, no other thread can access or update
5400 //
5401
5402 // Note that we need to hold the freelistLock if we use
5403 // block iterate below; else the iterator might go awry if
5404 // a mutator (or promotion) causes block contents to change
5405 // (for instance if the allocator divvies up a block).
5406 // If we hold the free list lock, for all practical purposes
5407 // young generation GC's can't occur (they'll usually need to
5408 // promote), so we might as well prevent all young generation
5409 // GC's while we do a sweeping step. For the same reason, we might
5410 // as well take the bit map lock for the entire duration
5411
5412 // check that we hold the requisite locks
5413 assert(have_cms_token(), "Should hold cms token");
5414 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5415 assert_lock_strong(old_gen->freelistLock());
5416 assert_lock_strong(bitMapLock());
5417
5418 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5419 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5420 old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5421 _inter_sweep_estimate.padded_average(),
5422 _intra_sweep_estimate.padded_average());
5423 old_gen->setNearLargestChunk();
5424
5425 {
5426 SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5427 old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5428 // We need to free-up/coalesce garbage/blocks from a
5429 // co-terminal free run. This is done in the SweepClosure
5430 // destructor; so, do not remove this scope, else the
5431 // end-of-sweep-census below will be off by a little bit.
5432 }
5433 old_gen->cmsSpace()->sweep_completed();
5434 old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5435 if (should_unload_classes()) { // unloaded classes this cycle,
5436 _concurrent_cycles_since_last_unload = 0; // ... reset count
5437 } else { // did not unload classes,
5438 _concurrent_cycles_since_last_unload++; // ... increment count
5439 }
5440 }
5441
5442 // Reset CMS data structures (for now just the marking bit map)
5443 // preparatory for the next cycle.
5444 void CMSCollector::reset_concurrent() {
5445 CMSTokenSyncWithLocks ts(true, bitMapLock());
5446
5447 // If the state is not "Resetting", the foreground thread
5448 // has done a collection and the resetting.
5449 if (_collectorState != Resetting) {
5450 assert(_collectorState == Idling, "The state should only change"
5451 " because the foreground collector has finished the collection");
5452 return;
5453 }
5454
5455 {
5456 // Clear the mark bitmap (no grey objects to start with)
5457 // for the next cycle.
5458 GCTraceCPUTime tcpu;
5459 CMSPhaseAccounting cmspa(this, "Concurrent Reset");
5460
5461 HeapWord* curAddr = _markBitMap.startWord();
5462 while (curAddr < _markBitMap.endWord()) {
5463 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5464 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5465 _markBitMap.clear_large_range(chunk);
5466 if (ConcurrentMarkSweepThread::should_yield() &&
5467 !foregroundGCIsActive() &&
5468 CMSYield) {
5469 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5470 "CMS thread should hold CMS token");
5471 assert_lock_strong(bitMapLock());
5472 bitMapLock()->unlock();
5473 ConcurrentMarkSweepThread::desynchronize(true);
5474 stopTimer();
5475 incrementYields();
5476
5477 // See the comment in coordinator_yield()
5478 for (unsigned i = 0; i < CMSYieldSleepCount &&
5479 ConcurrentMarkSweepThread::should_yield() &&
5480 !CMSCollector::foregroundGCIsActive(); ++i) {
5481 os::sleep(Thread::current(), 1, false);
5482 }
5483
5484 ConcurrentMarkSweepThread::synchronize(true);
5485 bitMapLock()->lock_without_safepoint_check();
5486 startTimer();
5487 }
5488 curAddr = chunk.end();
5489 }
5490 // A successful mostly concurrent collection has been done.
5491 // Because only the full (i.e., concurrent mode failure) collections
5492 // are being measured for gc overhead limits, clean the "near" flag
5493 // and count.
5494 size_policy()->reset_gc_overhead_limit_count();
5495 _collectorState = Idling;
5496 }
5497
5498 register_gc_end();
5499 }
5500
5501 // Same as above but for STW paths
5502 void CMSCollector::reset_stw() {
5503 // already have the lock
5504 assert(_collectorState == Resetting, "just checking");
5505 assert_lock_strong(bitMapLock());
5506 GCIdMark gc_id_mark(_cmsThread->gc_id());
5507 _markBitMap.clear_all();
5508 _collectorState = Idling;
5509 register_gc_end();
5510 }
5511
5512 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5513 GCTraceCPUTime tcpu;
5514 TraceCollectorStats tcs_cgc(cgc_counters());
5515
5516 switch (op) {
5517 case CMS_op_checkpointRootsInitial: {
5518 GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5519 SvcGCMarker sgcm(SvcGCMarker::CONCURRENT);
5520 checkpointRootsInitial();
5521 break;
5522 }
5523 case CMS_op_checkpointRootsFinal: {
5524 GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5525 SvcGCMarker sgcm(SvcGCMarker::CONCURRENT);
5526 checkpointRootsFinal();
5527 break;
5528 }
5529 default:
5530 fatal("No such CMS_op");
5531 }
5532 }
5533
5534 #ifndef PRODUCT
5535 size_t const CMSCollector::skip_header_HeapWords() {
5536 return FreeChunk::header_size();
5537 }
5538
5539 // Try and collect here conditions that should hold when
5540 // CMS thread is exiting. The idea is that the foreground GC
5541 // thread should not be blocked if it wants to terminate
5542 // the CMS thread and yet continue to run the VM for a while
5543 // after that.
5544 void CMSCollector::verify_ok_to_terminate() const {
5545 assert(Thread::current()->is_ConcurrentGC_thread(),
5546 "should be called by CMS thread");
5547 assert(!_foregroundGCShouldWait, "should be false");
5548 // We could check here that all the various low-level locks
5549 // are not held by the CMS thread, but that is overkill; see
5550 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5551 // is checked.
5552 }
5553 #endif
5554
5555 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5556 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5557 "missing Printezis mark?");
5558 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5559 size_t size = pointer_delta(nextOneAddr + 1, addr);
5560 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5561 "alignment problem");
5562 assert(size >= 3, "Necessary for Printezis marks to work");
5563 return size;
5564 }
5565
5566 // A variant of the above (block_size_using_printezis_bits()) except
5567 // that we return 0 if the P-bits are not yet set.
5568 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5569 if (_markBitMap.isMarked(addr + 1)) {
5570 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5571 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5572 size_t size = pointer_delta(nextOneAddr + 1, addr);
5573 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5574 "alignment problem");
5575 assert(size >= 3, "Necessary for Printezis marks to work");
5576 return size;
5577 }
5578 return 0;
5579 }
5580
5581 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5582 size_t sz = 0;
5583 oop p = (oop)addr;
5584 if (p->klass_or_null_acquire() != NULL) {
5585 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5586 } else {
5587 sz = block_size_using_printezis_bits(addr);
5588 }
5589 assert(sz > 0, "size must be nonzero");
5590 HeapWord* next_block = addr + sz;
5591 HeapWord* next_card = align_up(next_block, CardTable::card_size);
5592 assert(align_down((uintptr_t)addr, CardTable::card_size) <
5593 align_down((uintptr_t)next_card, CardTable::card_size),
5594 "must be different cards");
5595 return next_card;
5596 }
5597
5598
5599 // CMS Bit Map Wrapper /////////////////////////////////////////
5600
5601 // Construct a CMS bit map infrastructure, but don't create the
5602 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5603 // further below.
5604 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5605 _bm(),
5606 _shifter(shifter),
5607 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5608 Monitor::_safepoint_check_sometimes) : NULL)
5609 {
5610 _bmStartWord = 0;
5611 _bmWordSize = 0;
5612 }
5613
5614 bool CMSBitMap::allocate(MemRegion mr) {
5615 _bmStartWord = mr.start();
5616 _bmWordSize = mr.word_size();
5617 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5618 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5619 if (!brs.is_reserved()) {
5620 log_warning(gc)("CMS bit map allocation failure");
5621 return false;
5622 }
5623 // For now we'll just commit all of the bit map up front.
5624 // Later on we'll try to be more parsimonious with swap.
5625 if (!_virtual_space.initialize(brs, brs.size())) {
5626 log_warning(gc)("CMS bit map backing store failure");
5627 return false;
5628 }
5629 assert(_virtual_space.committed_size() == brs.size(),
5630 "didn't reserve backing store for all of CMS bit map?");
5631 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5632 _bmWordSize, "inconsistency in bit map sizing");
5633 _bm = BitMapView((BitMap::bm_word_t*)_virtual_space.low(), _bmWordSize >> _shifter);
5634
5635 // bm.clear(); // can we rely on getting zero'd memory? verify below
5636 assert(isAllClear(),
5637 "Expected zero'd memory from ReservedSpace constructor");
5638 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5639 "consistency check");
5640 return true;
5641 }
5642
5643 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5644 HeapWord *next_addr, *end_addr, *last_addr;
5645 assert_locked();
5646 assert(covers(mr), "out-of-range error");
5647 // XXX assert that start and end are appropriately aligned
5648 for (next_addr = mr.start(), end_addr = mr.end();
5649 next_addr < end_addr; next_addr = last_addr) {
5650 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5651 last_addr = dirty_region.end();
5652 if (!dirty_region.is_empty()) {
5653 cl->do_MemRegion(dirty_region);
5654 } else {
5655 assert(last_addr == end_addr, "program logic");
5656 return;
5657 }
5658 }
5659 }
5660
5661 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5662 _bm.print_on_error(st, prefix);
5663 }
5664
5665 #ifndef PRODUCT
5666 void CMSBitMap::assert_locked() const {
5667 CMSLockVerifier::assert_locked(lock());
5668 }
5669
5670 bool CMSBitMap::covers(MemRegion mr) const {
5671 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5672 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5673 "size inconsistency");
5674 return (mr.start() >= _bmStartWord) &&
5675 (mr.end() <= endWord());
5676 }
5677
5678 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5679 return (start >= _bmStartWord && (start + size) <= endWord());
5680 }
5681
5682 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5683 // verify that there are no 1 bits in the interval [left, right)
5684 FalseBitMapClosure falseBitMapClosure;
5685 iterate(&falseBitMapClosure, left, right);
5686 }
5687
5688 void CMSBitMap::region_invariant(MemRegion mr)
5689 {
5690 assert_locked();
5691 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5692 assert(!mr.is_empty(), "unexpected empty region");
5693 assert(covers(mr), "mr should be covered by bit map");
5694 // convert address range into offset range
5695 size_t start_ofs = heapWordToOffset(mr.start());
5696 // Make sure that end() is appropriately aligned
5697 assert(mr.end() == align_up(mr.end(), (1 << (_shifter+LogHeapWordSize))),
5698 "Misaligned mr.end()");
5699 size_t end_ofs = heapWordToOffset(mr.end());
5700 assert(end_ofs > start_ofs, "Should mark at least one bit");
5701 }
5702
5703 #endif
5704
5705 bool CMSMarkStack::allocate(size_t size) {
5706 // allocate a stack of the requisite depth
5707 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5708 size * sizeof(oop)));
5709 if (!rs.is_reserved()) {
5710 log_warning(gc)("CMSMarkStack allocation failure");
5711 return false;
5712 }
5713 if (!_virtual_space.initialize(rs, rs.size())) {
5714 log_warning(gc)("CMSMarkStack backing store failure");
5715 return false;
5716 }
5717 assert(_virtual_space.committed_size() == rs.size(),
5718 "didn't reserve backing store for all of CMS stack?");
5719 _base = (oop*)(_virtual_space.low());
5720 _index = 0;
5721 _capacity = size;
5722 NOT_PRODUCT(_max_depth = 0);
5723 return true;
5724 }
5725
5726 // XXX FIX ME !!! In the MT case we come in here holding a
5727 // leaf lock. For printing we need to take a further lock
5728 // which has lower rank. We need to recalibrate the two
5729 // lock-ranks involved in order to be able to print the
5730 // messages below. (Or defer the printing to the caller.
5731 // For now we take the expedient path of just disabling the
5732 // messages for the problematic case.)
5733 void CMSMarkStack::expand() {
5734 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5735 if (_capacity == MarkStackSizeMax) {
5736 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5737 // We print a warning message only once per CMS cycle.
5738 log_debug(gc)(" (benign) Hit CMSMarkStack max size limit");
5739 }
5740 return;
5741 }
5742 // Double capacity if possible
5743 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5744 // Do not give up existing stack until we have managed to
5745 // get the double capacity that we desired.
5746 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5747 new_capacity * sizeof(oop)));
5748 if (rs.is_reserved()) {
5749 // Release the backing store associated with old stack
5750 _virtual_space.release();
5751 // Reinitialize virtual space for new stack
5752 if (!_virtual_space.initialize(rs, rs.size())) {
5753 fatal("Not enough swap for expanded marking stack");
5754 }
5755 _base = (oop*)(_virtual_space.low());
5756 _index = 0;
5757 _capacity = new_capacity;
5758 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5759 // Failed to double capacity, continue;
5760 // we print a detail message only once per CMS cycle.
5761 log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5762 _capacity / K, new_capacity / K);
5763 }
5764 }
5765
5766
5767 // Closures
5768 // XXX: there seems to be a lot of code duplication here;
5769 // should refactor and consolidate common code.
5770
5771 // This closure is used to mark refs into the CMS generation in
5772 // the CMS bit map. Called at the first checkpoint. This closure
5773 // assumes that we do not need to re-mark dirty cards; if the CMS
5774 // generation on which this is used is not an oldest
5775 // generation then this will lose younger_gen cards!
5776
5777 MarkRefsIntoClosure::MarkRefsIntoClosure(
5778 MemRegion span, CMSBitMap* bitMap):
5779 _span(span),
5780 _bitMap(bitMap)
5781 {
5782 assert(ref_discoverer() == NULL, "deliberately left NULL");
5783 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5784 }
5785
5786 void MarkRefsIntoClosure::do_oop(oop obj) {
5787 // if p points into _span, then mark corresponding bit in _markBitMap
5788 assert(oopDesc::is_oop(obj), "expected an oop");
5789 HeapWord* addr = (HeapWord*)obj;
5790 if (_span.contains(addr)) {
5791 // this should be made more efficient
5792 _bitMap->mark(addr);
5793 }
5794 }
5795
5796 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5797 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5798
5799 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure(
5800 MemRegion span, CMSBitMap* bitMap):
5801 _span(span),
5802 _bitMap(bitMap)
5803 {
5804 assert(ref_discoverer() == NULL, "deliberately left NULL");
5805 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5806 }
5807
5808 void ParMarkRefsIntoClosure::do_oop(oop obj) {
5809 // if p points into _span, then mark corresponding bit in _markBitMap
5810 assert(oopDesc::is_oop(obj), "expected an oop");
5811 HeapWord* addr = (HeapWord*)obj;
5812 if (_span.contains(addr)) {
5813 // this should be made more efficient
5814 _bitMap->par_mark(addr);
5815 }
5816 }
5817
5818 void ParMarkRefsIntoClosure::do_oop(oop* p) { ParMarkRefsIntoClosure::do_oop_work(p); }
5819 void ParMarkRefsIntoClosure::do_oop(narrowOop* p) { ParMarkRefsIntoClosure::do_oop_work(p); }
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 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5850 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5851
5852 //////////////////////////////////////////////////
5853 // MarkRefsIntoAndScanClosure
5854 //////////////////////////////////////////////////
5855
5856 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5857 ReferenceDiscoverer* rd,
5858 CMSBitMap* bit_map,
5859 CMSBitMap* mod_union_table,
5860 CMSMarkStack* mark_stack,
5861 CMSCollector* collector,
5862 bool should_yield,
5863 bool concurrent_precleaning):
5864 _collector(collector),
5865 _span(span),
5866 _bit_map(bit_map),
5867 _mark_stack(mark_stack),
5868 _pushAndMarkClosure(collector, span, rd, bit_map, mod_union_table,
5869 mark_stack, concurrent_precleaning),
5870 _yield(should_yield),
5871 _concurrent_precleaning(concurrent_precleaning),
5872 _freelistLock(NULL)
5873 {
5874 // FIXME: Should initialize in base class constructor.
5875 assert(rd != NULL, "ref_discoverer shouldn't be NULL");
5876 set_ref_discoverer_internal(rd);
5877 }
5878
5879 // This closure is used to mark refs into the CMS generation at the
5880 // second (final) checkpoint, and to scan and transitively follow
5881 // the unmarked oops. It is also used during the concurrent precleaning
5882 // phase while scanning objects on dirty cards in the CMS generation.
5883 // The marks are made in the marking bit map and the marking stack is
5884 // used for keeping the (newly) grey objects during the scan.
5885 // The parallel version (Par_...) appears further below.
5886 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5887 if (obj != NULL) {
5888 assert(oopDesc::is_oop(obj), "expected an oop");
5889 HeapWord* addr = (HeapWord*)obj;
5890 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5891 assert(_collector->overflow_list_is_empty(),
5892 "overflow list should be empty");
5893 if (_span.contains(addr) &&
5894 !_bit_map->isMarked(addr)) {
5895 // mark bit map (object is now grey)
5896 _bit_map->mark(addr);
5897 // push on marking stack (stack should be empty), and drain the
5898 // stack by applying this closure to the oops in the oops popped
5899 // from the stack (i.e. blacken the grey objects)
5900 bool res = _mark_stack->push(obj);
5901 assert(res, "Should have space to push on empty stack");
5902 do {
5903 oop new_oop = _mark_stack->pop();
5904 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
5905 assert(_bit_map->isMarked((HeapWord*)new_oop),
5906 "only grey objects on this stack");
5907 // iterate over the oops in this oop, marking and pushing
5908 // the ones in CMS heap (i.e. in _span).
5909 new_oop->oop_iterate(&_pushAndMarkClosure);
5910 // check if it's time to yield
5911 do_yield_check();
5912 } while (!_mark_stack->isEmpty() ||
5913 (!_concurrent_precleaning && take_from_overflow_list()));
5914 // if marking stack is empty, and we are not doing this
5915 // during precleaning, then check the overflow list
5916 }
5917 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5918 assert(_collector->overflow_list_is_empty(),
5919 "overflow list was drained above");
5920
5921 assert(_collector->no_preserved_marks(),
5922 "All preserved marks should have been restored above");
5923 }
5924 }
5925
5926 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5927 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5928
5929 void MarkRefsIntoAndScanClosure::do_yield_work() {
5930 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5931 "CMS thread should hold CMS token");
5932 assert_lock_strong(_freelistLock);
5933 assert_lock_strong(_bit_map->lock());
5934 // relinquish the free_list_lock and bitMaplock()
5935 _bit_map->lock()->unlock();
5936 _freelistLock->unlock();
5937 ConcurrentMarkSweepThread::desynchronize(true);
5938 _collector->stopTimer();
5939 _collector->incrementYields();
5940
5941 // See the comment in coordinator_yield()
5942 for (unsigned i = 0;
5943 i < CMSYieldSleepCount &&
5944 ConcurrentMarkSweepThread::should_yield() &&
5945 !CMSCollector::foregroundGCIsActive();
5946 ++i) {
5947 os::sleep(Thread::current(), 1, false);
5948 }
5949
5950 ConcurrentMarkSweepThread::synchronize(true);
5951 _freelistLock->lock_without_safepoint_check();
5952 _bit_map->lock()->lock_without_safepoint_check();
5953 _collector->startTimer();
5954 }
5955
5956 ///////////////////////////////////////////////////////////
5957 // ParMarkRefsIntoAndScanClosure: a parallel version of
5958 // MarkRefsIntoAndScanClosure
5959 ///////////////////////////////////////////////////////////
5960 ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure(
5961 CMSCollector* collector, MemRegion span, ReferenceDiscoverer* rd,
5962 CMSBitMap* bit_map, OopTaskQueue* work_queue):
5963 _span(span),
5964 _bit_map(bit_map),
5965 _work_queue(work_queue),
5966 _low_water_mark(MIN2((work_queue->max_elems()/4),
5967 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
5968 _parPushAndMarkClosure(collector, span, rd, bit_map, work_queue)
5969 {
5970 // FIXME: Should initialize in base class constructor.
5971 assert(rd != NULL, "ref_discoverer shouldn't be NULL");
5972 set_ref_discoverer_internal(rd);
5973 }
5974
5975 // This closure is used to mark refs into the CMS generation at the
5976 // second (final) checkpoint, and to scan and transitively follow
5977 // the unmarked oops. The marks are made in the marking bit map and
5978 // the work_queue is used for keeping the (newly) grey objects during
5979 // the scan phase whence they are also available for stealing by parallel
5980 // threads. Since the marking bit map is shared, updates are
5981 // synchronized (via CAS).
5982 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) {
5983 if (obj != NULL) {
5984 // Ignore mark word because this could be an already marked oop
5985 // that may be chained at the end of the overflow list.
5986 assert(oopDesc::is_oop(obj, true), "expected an oop");
5987 HeapWord* addr = (HeapWord*)obj;
5988 if (_span.contains(addr) &&
5989 !_bit_map->isMarked(addr)) {
5990 // mark bit map (object will become grey):
5991 // It is possible for several threads to be
5992 // trying to "claim" this object concurrently;
5993 // the unique thread that succeeds in marking the
5994 // object first will do the subsequent push on
5995 // to the work queue (or overflow list).
5996 if (_bit_map->par_mark(addr)) {
5997 // push on work_queue (which may not be empty), and trim the
5998 // queue to an appropriate length by applying this closure to
5999 // the oops in the oops popped from the stack (i.e. blacken the
6000 // grey objects)
6001 bool res = _work_queue->push(obj);
6002 assert(res, "Low water mark should be less than capacity?");
6003 trim_queue(_low_water_mark);
6004 } // Else, another thread claimed the object
6005 }
6006 }
6007 }
6008
6009 void ParMarkRefsIntoAndScanClosure::do_oop(oop* p) { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6010 void ParMarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6011
6012 // This closure is used to rescan the marked objects on the dirty cards
6013 // in the mod union table and the card table proper.
6014 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6015 oop p, MemRegion mr) {
6016
6017 size_t size = 0;
6018 HeapWord* addr = (HeapWord*)p;
6019 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6020 assert(_span.contains(addr), "we are scanning the CMS generation");
6021 // check if it's time to yield
6022 if (do_yield_check()) {
6023 // We yielded for some foreground stop-world work,
6024 // and we have been asked to abort this ongoing preclean cycle.
6025 return 0;
6026 }
6027 if (_bitMap->isMarked(addr)) {
6028 // it's marked; is it potentially uninitialized?
6029 if (p->klass_or_null_acquire() != NULL) {
6030 // an initialized object; ignore mark word in verification below
6031 // since we are running concurrent with mutators
6032 assert(oopDesc::is_oop(p, true), "should be an oop");
6033 if (p->is_objArray()) {
6034 // objArrays are precisely marked; restrict scanning
6035 // to dirty cards only.
6036 size = CompactibleFreeListSpace::adjustObjectSize(
6037 p->oop_iterate_size(_scanningClosure, mr));
6038 } else {
6039 // A non-array may have been imprecisely marked; we need
6040 // to scan object in its entirety.
6041 size = CompactibleFreeListSpace::adjustObjectSize(
6042 p->oop_iterate_size(_scanningClosure));
6043 }
6044 #ifdef ASSERT
6045 size_t direct_size =
6046 CompactibleFreeListSpace::adjustObjectSize(p->size());
6047 assert(size == direct_size, "Inconsistency in size");
6048 assert(size >= 3, "Necessary for Printezis marks to work");
6049 HeapWord* start_pbit = addr + 1;
6050 HeapWord* end_pbit = addr + size - 1;
6051 assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit),
6052 "inconsistent Printezis mark");
6053 // Verify inner mark bits (between Printezis bits) are clear,
6054 // but don't repeat if there are multiple dirty regions for
6055 // the same object, to avoid potential O(N^2) performance.
6056 if (addr != _last_scanned_object) {
6057 _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit);
6058 _last_scanned_object = addr;
6059 }
6060 #endif // ASSERT
6061 } else {
6062 // An uninitialized object.
6063 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6064 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6065 size = pointer_delta(nextOneAddr + 1, addr);
6066 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6067 "alignment problem");
6068 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6069 // will dirty the card when the klass pointer is installed in the
6070 // object (signaling the completion of initialization).
6071 }
6072 } else {
6073 // Either a not yet marked object or an uninitialized object
6074 if (p->klass_or_null_acquire() == NULL) {
6075 // An uninitialized object, skip to the next card, since
6076 // we may not be able to read its P-bits yet.
6077 assert(size == 0, "Initial value");
6078 } else {
6079 // An object not (yet) reached by marking: we merely need to
6080 // compute its size so as to go look at the next block.
6081 assert(oopDesc::is_oop(p, true), "should be an oop");
6082 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6083 }
6084 }
6085 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6086 return size;
6087 }
6088
6089 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6090 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6091 "CMS thread should hold CMS token");
6092 assert_lock_strong(_freelistLock);
6093 assert_lock_strong(_bitMap->lock());
6094 // relinquish the free_list_lock and bitMaplock()
6095 _bitMap->lock()->unlock();
6096 _freelistLock->unlock();
6097 ConcurrentMarkSweepThread::desynchronize(true);
6098 _collector->stopTimer();
6099 _collector->incrementYields();
6100
6101 // See the comment in coordinator_yield()
6102 for (unsigned i = 0; i < CMSYieldSleepCount &&
6103 ConcurrentMarkSweepThread::should_yield() &&
6104 !CMSCollector::foregroundGCIsActive(); ++i) {
6105 os::sleep(Thread::current(), 1, false);
6106 }
6107
6108 ConcurrentMarkSweepThread::synchronize(true);
6109 _freelistLock->lock_without_safepoint_check();
6110 _bitMap->lock()->lock_without_safepoint_check();
6111 _collector->startTimer();
6112 }
6113
6114
6115 //////////////////////////////////////////////////////////////////
6116 // SurvivorSpacePrecleanClosure
6117 //////////////////////////////////////////////////////////////////
6118 // This (single-threaded) closure is used to preclean the oops in
6119 // the survivor spaces.
6120 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6121
6122 HeapWord* addr = (HeapWord*)p;
6123 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6124 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6125 assert(p->klass_or_null() != NULL, "object should be initialized");
6126 // an initialized object; ignore mark word in verification below
6127 // since we are running concurrent with mutators
6128 assert(oopDesc::is_oop(p, true), "should be an oop");
6129 // Note that we do not yield while we iterate over
6130 // the interior oops of p, pushing the relevant ones
6131 // on our marking stack.
6132 size_t size = p->oop_iterate_size(_scanning_closure);
6133 do_yield_check();
6134 // Observe that below, we do not abandon the preclean
6135 // phase as soon as we should; rather we empty the
6136 // marking stack before returning. This is to satisfy
6137 // some existing assertions. In general, it may be a
6138 // good idea to abort immediately and complete the marking
6139 // from the grey objects at a later time.
6140 while (!_mark_stack->isEmpty()) {
6141 oop new_oop = _mark_stack->pop();
6142 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
6143 assert(_bit_map->isMarked((HeapWord*)new_oop),
6144 "only grey objects on this stack");
6145 // iterate over the oops in this oop, marking and pushing
6146 // the ones in CMS heap (i.e. in _span).
6147 new_oop->oop_iterate(_scanning_closure);
6148 // check if it's time to yield
6149 do_yield_check();
6150 }
6151 unsigned int after_count =
6152 CMSHeap::heap()->total_collections();
6153 bool abort = (_before_count != after_count) ||
6154 _collector->should_abort_preclean();
6155 return abort ? 0 : size;
6156 }
6157
6158 void SurvivorSpacePrecleanClosure::do_yield_work() {
6159 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6160 "CMS thread should hold CMS token");
6161 assert_lock_strong(_bit_map->lock());
6162 // Relinquish the bit map lock
6163 _bit_map->lock()->unlock();
6164 ConcurrentMarkSweepThread::desynchronize(true);
6165 _collector->stopTimer();
6166 _collector->incrementYields();
6167
6168 // See the comment in coordinator_yield()
6169 for (unsigned i = 0; i < CMSYieldSleepCount &&
6170 ConcurrentMarkSweepThread::should_yield() &&
6171 !CMSCollector::foregroundGCIsActive(); ++i) {
6172 os::sleep(Thread::current(), 1, false);
6173 }
6174
6175 ConcurrentMarkSweepThread::synchronize(true);
6176 _bit_map->lock()->lock_without_safepoint_check();
6177 _collector->startTimer();
6178 }
6179
6180 // This closure is used to rescan the marked objects on the dirty cards
6181 // in the mod union table and the card table proper. In the parallel
6182 // case, although the bitMap is shared, we do a single read so the
6183 // isMarked() query is "safe".
6184 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6185 // Ignore mark word because we are running concurrent with mutators
6186 assert(oopDesc::is_oop_or_null(p, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6187 HeapWord* addr = (HeapWord*)p;
6188 assert(_span.contains(addr), "we are scanning the CMS generation");
6189 bool is_obj_array = false;
6190 #ifdef ASSERT
6191 if (!_parallel) {
6192 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6193 assert(_collector->overflow_list_is_empty(),
6194 "overflow list should be empty");
6195
6196 }
6197 #endif // ASSERT
6198 if (_bit_map->isMarked(addr)) {
6199 // Obj arrays are precisely marked, non-arrays are not;
6200 // so we scan objArrays precisely and non-arrays in their
6201 // entirety.
6202 if (p->is_objArray()) {
6203 is_obj_array = true;
6204 if (_parallel) {
6205 p->oop_iterate(_par_scan_closure, mr);
6206 } else {
6207 p->oop_iterate(_scan_closure, mr);
6208 }
6209 } else {
6210 if (_parallel) {
6211 p->oop_iterate(_par_scan_closure);
6212 } else {
6213 p->oop_iterate(_scan_closure);
6214 }
6215 }
6216 }
6217 #ifdef ASSERT
6218 if (!_parallel) {
6219 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6220 assert(_collector->overflow_list_is_empty(),
6221 "overflow list should be empty");
6222
6223 }
6224 #endif // ASSERT
6225 return is_obj_array;
6226 }
6227
6228 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6229 MemRegion span,
6230 CMSBitMap* bitMap, CMSMarkStack* markStack,
6231 bool should_yield, bool verifying):
6232 _collector(collector),
6233 _span(span),
6234 _bitMap(bitMap),
6235 _mut(&collector->_modUnionTable),
6236 _markStack(markStack),
6237 _yield(should_yield),
6238 _skipBits(0)
6239 {
6240 assert(_markStack->isEmpty(), "stack should be empty");
6241 _finger = _bitMap->startWord();
6242 _threshold = _finger;
6243 assert(_collector->_restart_addr == NULL, "Sanity check");
6244 assert(_span.contains(_finger), "Out of bounds _finger?");
6245 DEBUG_ONLY(_verifying = verifying;)
6246 }
6247
6248 void MarkFromRootsClosure::reset(HeapWord* addr) {
6249 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6250 assert(_span.contains(addr), "Out of bounds _finger?");
6251 _finger = addr;
6252 _threshold = align_up(_finger, CardTable::card_size);
6253 }
6254
6255 // Should revisit to see if this should be restructured for
6256 // greater efficiency.
6257 bool MarkFromRootsClosure::do_bit(size_t offset) {
6258 if (_skipBits > 0) {
6259 _skipBits--;
6260 return true;
6261 }
6262 // convert offset into a HeapWord*
6263 HeapWord* addr = _bitMap->startWord() + offset;
6264 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6265 "address out of range");
6266 assert(_bitMap->isMarked(addr), "tautology");
6267 if (_bitMap->isMarked(addr+1)) {
6268 // this is an allocated but not yet initialized object
6269 assert(_skipBits == 0, "tautology");
6270 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6271 oop p = oop(addr);
6272 if (p->klass_or_null_acquire() == NULL) {
6273 DEBUG_ONLY(if (!_verifying) {)
6274 // We re-dirty the cards on which this object lies and increase
6275 // the _threshold so that we'll come back to scan this object
6276 // during the preclean or remark phase. (CMSCleanOnEnter)
6277 if (CMSCleanOnEnter) {
6278 size_t sz = _collector->block_size_using_printezis_bits(addr);
6279 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
6280 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6281 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6282 // Bump _threshold to end_card_addr; note that
6283 // _threshold cannot possibly exceed end_card_addr, anyhow.
6284 // This prevents future clearing of the card as the scan proceeds
6285 // to the right.
6286 assert(_threshold <= end_card_addr,
6287 "Because we are just scanning into this object");
6288 if (_threshold < end_card_addr) {
6289 _threshold = end_card_addr;
6290 }
6291 if (p->klass_or_null_acquire() != NULL) {
6292 // Redirty the range of cards...
6293 _mut->mark_range(redirty_range);
6294 } // ...else the setting of klass will dirty the card anyway.
6295 }
6296 DEBUG_ONLY(})
6297 return true;
6298 }
6299 }
6300 scanOopsInOop(addr);
6301 return true;
6302 }
6303
6304 // We take a break if we've been at this for a while,
6305 // so as to avoid monopolizing the locks involved.
6306 void MarkFromRootsClosure::do_yield_work() {
6307 // First give up the locks, then yield, then re-lock
6308 // We should probably use a constructor/destructor idiom to
6309 // do this unlock/lock or modify the MutexUnlocker class to
6310 // serve our purpose. XXX
6311 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6312 "CMS thread should hold CMS token");
6313 assert_lock_strong(_bitMap->lock());
6314 _bitMap->lock()->unlock();
6315 ConcurrentMarkSweepThread::desynchronize(true);
6316 _collector->stopTimer();
6317 _collector->incrementYields();
6318
6319 // See the comment in coordinator_yield()
6320 for (unsigned i = 0; i < CMSYieldSleepCount &&
6321 ConcurrentMarkSweepThread::should_yield() &&
6322 !CMSCollector::foregroundGCIsActive(); ++i) {
6323 os::sleep(Thread::current(), 1, false);
6324 }
6325
6326 ConcurrentMarkSweepThread::synchronize(true);
6327 _bitMap->lock()->lock_without_safepoint_check();
6328 _collector->startTimer();
6329 }
6330
6331 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6332 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6333 assert(_markStack->isEmpty(),
6334 "should drain stack to limit stack usage");
6335 // convert ptr to an oop preparatory to scanning
6336 oop obj = oop(ptr);
6337 // Ignore mark word in verification below, since we
6338 // may be running concurrent with mutators.
6339 assert(oopDesc::is_oop(obj, true), "should be an oop");
6340 assert(_finger <= ptr, "_finger runneth ahead");
6341 // advance the finger to right end of this object
6342 _finger = ptr + obj->size();
6343 assert(_finger > ptr, "we just incremented it above");
6344 // On large heaps, it may take us some time to get through
6345 // the marking phase. During
6346 // this time it's possible that a lot of mutations have
6347 // accumulated in the card table and the mod union table --
6348 // these mutation records are redundant until we have
6349 // actually traced into the corresponding card.
6350 // Here, we check whether advancing the finger would make
6351 // us cross into a new card, and if so clear corresponding
6352 // cards in the MUT (preclean them in the card-table in the
6353 // future).
6354
6355 DEBUG_ONLY(if (!_verifying) {)
6356 // The clean-on-enter optimization is disabled by default,
6357 // until we fix 6178663.
6358 if (CMSCleanOnEnter && (_finger > _threshold)) {
6359 // [_threshold, _finger) represents the interval
6360 // of cards to be cleared in MUT (or precleaned in card table).
6361 // The set of cards to be cleared is all those that overlap
6362 // with the interval [_threshold, _finger); note that
6363 // _threshold is always kept card-aligned but _finger isn't
6364 // always card-aligned.
6365 HeapWord* old_threshold = _threshold;
6366 assert(is_aligned(old_threshold, CardTable::card_size),
6367 "_threshold should always be card-aligned");
6368 _threshold = align_up(_finger, CardTable::card_size);
6369 MemRegion mr(old_threshold, _threshold);
6370 assert(!mr.is_empty(), "Control point invariant");
6371 assert(_span.contains(mr), "Should clear within span");
6372 _mut->clear_range(mr);
6373 }
6374 DEBUG_ONLY(})
6375 // Note: the finger doesn't advance while we drain
6376 // the stack below.
6377 PushOrMarkClosure pushOrMarkClosure(_collector,
6378 _span, _bitMap, _markStack,
6379 _finger, this);
6380 bool res = _markStack->push(obj);
6381 assert(res, "Empty non-zero size stack should have space for single push");
6382 while (!_markStack->isEmpty()) {
6383 oop new_oop = _markStack->pop();
6384 // Skip verifying header mark word below because we are
6385 // running concurrent with mutators.
6386 assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6387 // now scan this oop's oops
6388 new_oop->oop_iterate(&pushOrMarkClosure);
6389 do_yield_check();
6390 }
6391 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6392 }
6393
6394 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task,
6395 CMSCollector* collector, MemRegion span,
6396 CMSBitMap* bit_map,
6397 OopTaskQueue* work_queue,
6398 CMSMarkStack* overflow_stack):
6399 _collector(collector),
6400 _whole_span(collector->_span),
6401 _span(span),
6402 _bit_map(bit_map),
6403 _mut(&collector->_modUnionTable),
6404 _work_queue(work_queue),
6405 _overflow_stack(overflow_stack),
6406 _skip_bits(0),
6407 _task(task)
6408 {
6409 assert(_work_queue->size() == 0, "work_queue should be empty");
6410 _finger = span.start();
6411 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6412 assert(_span.contains(_finger), "Out of bounds _finger?");
6413 }
6414
6415 // Should revisit to see if this should be restructured for
6416 // greater efficiency.
6417 bool ParMarkFromRootsClosure::do_bit(size_t offset) {
6418 if (_skip_bits > 0) {
6419 _skip_bits--;
6420 return true;
6421 }
6422 // convert offset into a HeapWord*
6423 HeapWord* addr = _bit_map->startWord() + offset;
6424 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6425 "address out of range");
6426 assert(_bit_map->isMarked(addr), "tautology");
6427 if (_bit_map->isMarked(addr+1)) {
6428 // this is an allocated object that might not yet be initialized
6429 assert(_skip_bits == 0, "tautology");
6430 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6431 oop p = oop(addr);
6432 if (p->klass_or_null_acquire() == NULL) {
6433 // in the case of Clean-on-Enter optimization, redirty card
6434 // and avoid clearing card by increasing the threshold.
6435 return true;
6436 }
6437 }
6438 scan_oops_in_oop(addr);
6439 return true;
6440 }
6441
6442 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6443 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6444 // Should we assert that our work queue is empty or
6445 // below some drain limit?
6446 assert(_work_queue->size() == 0,
6447 "should drain stack to limit stack usage");
6448 // convert ptr to an oop preparatory to scanning
6449 oop obj = oop(ptr);
6450 // Ignore mark word in verification below, since we
6451 // may be running concurrent with mutators.
6452 assert(oopDesc::is_oop(obj, true), "should be an oop");
6453 assert(_finger <= ptr, "_finger runneth ahead");
6454 // advance the finger to right end of this object
6455 _finger = ptr + obj->size();
6456 assert(_finger > ptr, "we just incremented it above");
6457 // On large heaps, it may take us some time to get through
6458 // the marking phase. During
6459 // this time it's possible that a lot of mutations have
6460 // accumulated in the card table and the mod union table --
6461 // these mutation records are redundant until we have
6462 // actually traced into the corresponding card.
6463 // Here, we check whether advancing the finger would make
6464 // us cross into a new card, and if so clear corresponding
6465 // cards in the MUT (preclean them in the card-table in the
6466 // future).
6467
6468 // The clean-on-enter optimization is disabled by default,
6469 // until we fix 6178663.
6470 if (CMSCleanOnEnter && (_finger > _threshold)) {
6471 // [_threshold, _finger) represents the interval
6472 // of cards to be cleared in MUT (or precleaned in card table).
6473 // The set of cards to be cleared is all those that overlap
6474 // with the interval [_threshold, _finger); note that
6475 // _threshold is always kept card-aligned but _finger isn't
6476 // always card-aligned.
6477 HeapWord* old_threshold = _threshold;
6478 assert(is_aligned(old_threshold, CardTable::card_size),
6479 "_threshold should always be card-aligned");
6480 _threshold = align_up(_finger, CardTable::card_size);
6481 MemRegion mr(old_threshold, _threshold);
6482 assert(!mr.is_empty(), "Control point invariant");
6483 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6484 _mut->clear_range(mr);
6485 }
6486
6487 // Note: the local finger doesn't advance while we drain
6488 // the stack below, but the global finger sure can and will.
6489 HeapWord* volatile* gfa = _task->global_finger_addr();
6490 ParPushOrMarkClosure pushOrMarkClosure(_collector,
6491 _span, _bit_map,
6492 _work_queue,
6493 _overflow_stack,
6494 _finger,
6495 gfa, this);
6496 bool res = _work_queue->push(obj); // overflow could occur here
6497 assert(res, "Will hold once we use workqueues");
6498 while (true) {
6499 oop new_oop;
6500 if (!_work_queue->pop_local(new_oop)) {
6501 // We emptied our work_queue; check if there's stuff that can
6502 // be gotten from the overflow stack.
6503 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6504 _overflow_stack, _work_queue)) {
6505 do_yield_check();
6506 continue;
6507 } else { // done
6508 break;
6509 }
6510 }
6511 // Skip verifying header mark word below because we are
6512 // running concurrent with mutators.
6513 assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6514 // now scan this oop's oops
6515 new_oop->oop_iterate(&pushOrMarkClosure);
6516 do_yield_check();
6517 }
6518 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6519 }
6520
6521 // Yield in response to a request from VM Thread or
6522 // from mutators.
6523 void ParMarkFromRootsClosure::do_yield_work() {
6524 assert(_task != NULL, "sanity");
6525 _task->yield();
6526 }
6527
6528 // A variant of the above used for verifying CMS marking work.
6529 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6530 MemRegion span,
6531 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6532 CMSMarkStack* mark_stack):
6533 _collector(collector),
6534 _span(span),
6535 _verification_bm(verification_bm),
6536 _cms_bm(cms_bm),
6537 _mark_stack(mark_stack),
6538 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6539 mark_stack)
6540 {
6541 assert(_mark_stack->isEmpty(), "stack should be empty");
6542 _finger = _verification_bm->startWord();
6543 assert(_collector->_restart_addr == NULL, "Sanity check");
6544 assert(_span.contains(_finger), "Out of bounds _finger?");
6545 }
6546
6547 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6548 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6549 assert(_span.contains(addr), "Out of bounds _finger?");
6550 _finger = addr;
6551 }
6552
6553 // Should revisit to see if this should be restructured for
6554 // greater efficiency.
6555 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6556 // convert offset into a HeapWord*
6557 HeapWord* addr = _verification_bm->startWord() + offset;
6558 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6559 "address out of range");
6560 assert(_verification_bm->isMarked(addr), "tautology");
6561 assert(_cms_bm->isMarked(addr), "tautology");
6562
6563 assert(_mark_stack->isEmpty(),
6564 "should drain stack to limit stack usage");
6565 // convert addr to an oop preparatory to scanning
6566 oop obj = oop(addr);
6567 assert(oopDesc::is_oop(obj), "should be an oop");
6568 assert(_finger <= addr, "_finger runneth ahead");
6569 // advance the finger to right end of this object
6570 _finger = addr + obj->size();
6571 assert(_finger > addr, "we just incremented it above");
6572 // Note: the finger doesn't advance while we drain
6573 // the stack below.
6574 bool res = _mark_stack->push(obj);
6575 assert(res, "Empty non-zero size stack should have space for single push");
6576 while (!_mark_stack->isEmpty()) {
6577 oop new_oop = _mark_stack->pop();
6578 assert(oopDesc::is_oop(new_oop), "Oops! expected to pop an oop");
6579 // now scan this oop's oops
6580 new_oop->oop_iterate(&_pam_verify_closure);
6581 }
6582 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6583 return true;
6584 }
6585
6586 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6587 CMSCollector* collector, MemRegion span,
6588 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6589 CMSMarkStack* mark_stack):
6590 MetadataAwareOopClosure(collector->ref_processor()),
6591 _collector(collector),
6592 _span(span),
6593 _verification_bm(verification_bm),
6594 _cms_bm(cms_bm),
6595 _mark_stack(mark_stack)
6596 { }
6597
6598 template <class T> void PushAndMarkVerifyClosure::do_oop_work(T *p) {
6599 oop obj = RawAccess<>::oop_load(p);
6600 do_oop(obj);
6601 }
6602
6603 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6604 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6605
6606 // Upon stack overflow, we discard (part of) the stack,
6607 // remembering the least address amongst those discarded
6608 // in CMSCollector's _restart_address.
6609 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6610 // Remember the least grey address discarded
6611 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6612 _collector->lower_restart_addr(ra);
6613 _mark_stack->reset(); // discard stack contents
6614 _mark_stack->expand(); // expand the stack if possible
6615 }
6616
6617 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6618 assert(oopDesc::is_oop_or_null(obj), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6619 HeapWord* addr = (HeapWord*)obj;
6620 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6621 // Oop lies in _span and isn't yet grey or black
6622 _verification_bm->mark(addr); // now grey
6623 if (!_cms_bm->isMarked(addr)) {
6624 Log(gc, verify) log;
6625 ResourceMark rm;
6626 LogStream ls(log.error());
6627 oop(addr)->print_on(&ls);
6628 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6629 fatal("... aborting");
6630 }
6631
6632 if (!_mark_stack->push(obj)) { // stack overflow
6633 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6634 assert(_mark_stack->isFull(), "Else push should have succeeded");
6635 handle_stack_overflow(addr);
6636 }
6637 // anything including and to the right of _finger
6638 // will be scanned as we iterate over the remainder of the
6639 // bit map
6640 }
6641 }
6642
6643 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6644 MemRegion span,
6645 CMSBitMap* bitMap, CMSMarkStack* markStack,
6646 HeapWord* finger, MarkFromRootsClosure* parent) :
6647 MetadataAwareOopClosure(collector->ref_processor()),
6648 _collector(collector),
6649 _span(span),
6650 _bitMap(bitMap),
6651 _markStack(markStack),
6652 _finger(finger),
6653 _parent(parent)
6654 { }
6655
6656 ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector,
6657 MemRegion span,
6658 CMSBitMap* bit_map,
6659 OopTaskQueue* work_queue,
6660 CMSMarkStack* overflow_stack,
6661 HeapWord* finger,
6662 HeapWord* volatile* global_finger_addr,
6663 ParMarkFromRootsClosure* parent) :
6664 MetadataAwareOopClosure(collector->ref_processor()),
6665 _collector(collector),
6666 _whole_span(collector->_span),
6667 _span(span),
6668 _bit_map(bit_map),
6669 _work_queue(work_queue),
6670 _overflow_stack(overflow_stack),
6671 _finger(finger),
6672 _global_finger_addr(global_finger_addr),
6673 _parent(parent)
6674 { }
6675
6676 // Assumes thread-safe access by callers, who are
6677 // responsible for mutual exclusion.
6678 void CMSCollector::lower_restart_addr(HeapWord* low) {
6679 assert(_span.contains(low), "Out of bounds addr");
6680 if (_restart_addr == NULL) {
6681 _restart_addr = low;
6682 } else {
6683 _restart_addr = MIN2(_restart_addr, low);
6684 }
6685 }
6686
6687 // Upon stack overflow, we discard (part of) the stack,
6688 // remembering the least address amongst those discarded
6689 // in CMSCollector's _restart_address.
6690 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6691 // Remember the least grey address discarded
6692 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6693 _collector->lower_restart_addr(ra);
6694 _markStack->reset(); // discard stack contents
6695 _markStack->expand(); // expand the stack if possible
6696 }
6697
6698 // Upon stack overflow, we discard (part of) the stack,
6699 // remembering the least address amongst those discarded
6700 // in CMSCollector's _restart_address.
6701 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6702 // We need to do this under a mutex to prevent other
6703 // workers from interfering with the work done below.
6704 MutexLockerEx ml(_overflow_stack->par_lock(),
6705 Mutex::_no_safepoint_check_flag);
6706 // Remember the least grey address discarded
6707 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6708 _collector->lower_restart_addr(ra);
6709 _overflow_stack->reset(); // discard stack contents
6710 _overflow_stack->expand(); // expand the stack if possible
6711 }
6712
6713 void PushOrMarkClosure::do_oop(oop obj) {
6714 // Ignore mark word because we are running concurrent with mutators.
6715 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6716 HeapWord* addr = (HeapWord*)obj;
6717 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6718 // Oop lies in _span and isn't yet grey or black
6719 _bitMap->mark(addr); // now grey
6720 if (addr < _finger) {
6721 // the bit map iteration has already either passed, or
6722 // sampled, this bit in the bit map; we'll need to
6723 // use the marking stack to scan this oop's oops.
6724 bool simulate_overflow = false;
6725 NOT_PRODUCT(
6726 if (CMSMarkStackOverflowALot &&
6727 _collector->simulate_overflow()) {
6728 // simulate a stack overflow
6729 simulate_overflow = true;
6730 }
6731 )
6732 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6733 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6734 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6735 handle_stack_overflow(addr);
6736 }
6737 }
6738 // anything including and to the right of _finger
6739 // will be scanned as we iterate over the remainder of the
6740 // bit map
6741 do_yield_check();
6742 }
6743 }
6744
6745 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
6746 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
6747
6748 void ParPushOrMarkClosure::do_oop(oop obj) {
6749 // Ignore mark word because we are running concurrent with mutators.
6750 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6751 HeapWord* addr = (HeapWord*)obj;
6752 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6753 // Oop lies in _span and isn't yet grey or black
6754 // We read the global_finger (volatile read) strictly after marking oop
6755 bool res = _bit_map->par_mark(addr); // now grey
6756 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6757 // Should we push this marked oop on our stack?
6758 // -- if someone else marked it, nothing to do
6759 // -- if target oop is above global finger nothing to do
6760 // -- if target oop is in chunk and above local finger
6761 // then nothing to do
6762 // -- else push on work queue
6763 if ( !res // someone else marked it, they will deal with it
6764 || (addr >= *gfa) // will be scanned in a later task
6765 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6766 return;
6767 }
6768 // the bit map iteration has already either passed, or
6769 // sampled, this bit in the bit map; we'll need to
6770 // use the marking stack to scan this oop's oops.
6771 bool simulate_overflow = false;
6772 NOT_PRODUCT(
6773 if (CMSMarkStackOverflowALot &&
6774 _collector->simulate_overflow()) {
6775 // simulate a stack overflow
6776 simulate_overflow = true;
6777 }
6778 )
6779 if (simulate_overflow ||
6780 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6781 // stack overflow
6782 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6783 // We cannot assert that the overflow stack is full because
6784 // it may have been emptied since.
6785 assert(simulate_overflow ||
6786 _work_queue->size() == _work_queue->max_elems(),
6787 "Else push should have succeeded");
6788 handle_stack_overflow(addr);
6789 }
6790 do_yield_check();
6791 }
6792 }
6793
6794 void ParPushOrMarkClosure::do_oop(oop* p) { ParPushOrMarkClosure::do_oop_work(p); }
6795 void ParPushOrMarkClosure::do_oop(narrowOop* p) { ParPushOrMarkClosure::do_oop_work(p); }
6796
6797 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6798 MemRegion span,
6799 ReferenceDiscoverer* rd,
6800 CMSBitMap* bit_map,
6801 CMSBitMap* mod_union_table,
6802 CMSMarkStack* mark_stack,
6803 bool concurrent_precleaning):
6804 MetadataAwareOopClosure(rd),
6805 _collector(collector),
6806 _span(span),
6807 _bit_map(bit_map),
6808 _mod_union_table(mod_union_table),
6809 _mark_stack(mark_stack),
6810 _concurrent_precleaning(concurrent_precleaning)
6811 {
6812 assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL");
6813 }
6814
6815 // Grey object rescan during pre-cleaning and second checkpoint phases --
6816 // the non-parallel version (the parallel version appears further below.)
6817 void PushAndMarkClosure::do_oop(oop obj) {
6818 // Ignore mark word verification. If during concurrent precleaning,
6819 // the object monitor may be locked. If during the checkpoint
6820 // phases, the object may already have been reached by a different
6821 // path and may be at the end of the global overflow list (so
6822 // the mark word may be NULL).
6823 assert(oopDesc::is_oop_or_null(obj, true /* ignore mark word */),
6824 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6825 HeapWord* addr = (HeapWord*)obj;
6826 // Check if oop points into the CMS generation
6827 // and is not marked
6828 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6829 // a white object ...
6830 _bit_map->mark(addr); // ... now grey
6831 // push on the marking stack (grey set)
6832 bool simulate_overflow = false;
6833 NOT_PRODUCT(
6834 if (CMSMarkStackOverflowALot &&
6835 _collector->simulate_overflow()) {
6836 // simulate a stack overflow
6837 simulate_overflow = true;
6838 }
6839 )
6840 if (simulate_overflow || !_mark_stack->push(obj)) {
6841 if (_concurrent_precleaning) {
6842 // During precleaning we can just dirty the appropriate card(s)
6843 // in the mod union table, thus ensuring that the object remains
6844 // in the grey set and continue. In the case of object arrays
6845 // we need to dirty all of the cards that the object spans,
6846 // since the rescan of object arrays will be limited to the
6847 // dirty cards.
6848 // Note that no one can be interfering with us in this action
6849 // of dirtying the mod union table, so no locking or atomics
6850 // are required.
6851 if (obj->is_objArray()) {
6852 size_t sz = obj->size();
6853 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
6854 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6855 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6856 _mod_union_table->mark_range(redirty_range);
6857 } else {
6858 _mod_union_table->mark(addr);
6859 }
6860 _collector->_ser_pmc_preclean_ovflw++;
6861 } else {
6862 // During the remark phase, we need to remember this oop
6863 // in the overflow list.
6864 _collector->push_on_overflow_list(obj);
6865 _collector->_ser_pmc_remark_ovflw++;
6866 }
6867 }
6868 }
6869 }
6870
6871 ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector,
6872 MemRegion span,
6873 ReferenceDiscoverer* rd,
6874 CMSBitMap* bit_map,
6875 OopTaskQueue* work_queue):
6876 MetadataAwareOopClosure(rd),
6877 _collector(collector),
6878 _span(span),
6879 _bit_map(bit_map),
6880 _work_queue(work_queue)
6881 {
6882 assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL");
6883 }
6884
6885 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
6886 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
6887
6888 // Grey object rescan during second checkpoint phase --
6889 // the parallel version.
6890 void ParPushAndMarkClosure::do_oop(oop obj) {
6891 // In the assert below, we ignore the mark word because
6892 // this oop may point to an already visited object that is
6893 // on the overflow stack (in which case the mark word has
6894 // been hijacked for chaining into the overflow stack --
6895 // if this is the last object in the overflow stack then
6896 // its mark word will be NULL). Because this object may
6897 // have been subsequently popped off the global overflow
6898 // stack, and the mark word possibly restored to the prototypical
6899 // value, by the time we get to examined this failing assert in
6900 // the debugger, is_oop_or_null(false) may subsequently start
6901 // to hold.
6902 assert(oopDesc::is_oop_or_null(obj, true),
6903 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6904 HeapWord* addr = (HeapWord*)obj;
6905 // Check if oop points into the CMS generation
6906 // and is not marked
6907 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6908 // a white object ...
6909 // If we manage to "claim" the object, by being the
6910 // first thread to mark it, then we push it on our
6911 // marking stack
6912 if (_bit_map->par_mark(addr)) { // ... now grey
6913 // push on work queue (grey set)
6914 bool simulate_overflow = false;
6915 NOT_PRODUCT(
6916 if (CMSMarkStackOverflowALot &&
6917 _collector->par_simulate_overflow()) {
6918 // simulate a stack overflow
6919 simulate_overflow = true;
6920 }
6921 )
6922 if (simulate_overflow || !_work_queue->push(obj)) {
6923 _collector->par_push_on_overflow_list(obj);
6924 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
6925 }
6926 } // Else, some other thread got there first
6927 }
6928 }
6929
6930 void ParPushAndMarkClosure::do_oop(oop* p) { ParPushAndMarkClosure::do_oop_work(p); }
6931 void ParPushAndMarkClosure::do_oop(narrowOop* p) { ParPushAndMarkClosure::do_oop_work(p); }
6932
6933 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6934 Mutex* bml = _collector->bitMapLock();
6935 assert_lock_strong(bml);
6936 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6937 "CMS thread should hold CMS token");
6938
6939 bml->unlock();
6940 ConcurrentMarkSweepThread::desynchronize(true);
6941
6942 _collector->stopTimer();
6943 _collector->incrementYields();
6944
6945 // See the comment in coordinator_yield()
6946 for (unsigned i = 0; i < CMSYieldSleepCount &&
6947 ConcurrentMarkSweepThread::should_yield() &&
6948 !CMSCollector::foregroundGCIsActive(); ++i) {
6949 os::sleep(Thread::current(), 1, false);
6950 }
6951
6952 ConcurrentMarkSweepThread::synchronize(true);
6953 bml->lock();
6954
6955 _collector->startTimer();
6956 }
6957
6958 bool CMSPrecleanRefsYieldClosure::should_return() {
6959 if (ConcurrentMarkSweepThread::should_yield()) {
6960 do_yield_work();
6961 }
6962 return _collector->foregroundGCIsActive();
6963 }
6964
6965 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
6966 assert(((size_t)mr.start())%CardTable::card_size_in_words == 0,
6967 "mr should be aligned to start at a card boundary");
6968 // We'd like to assert:
6969 // assert(mr.word_size()%CardTable::card_size_in_words == 0,
6970 // "mr should be a range of cards");
6971 // However, that would be too strong in one case -- the last
6972 // partition ends at _unallocated_block which, in general, can be
6973 // an arbitrary boundary, not necessarily card aligned.
6974 _num_dirty_cards += mr.word_size()/CardTable::card_size_in_words;
6975 _space->object_iterate_mem(mr, &_scan_cl);
6976 }
6977
6978 SweepClosure::SweepClosure(CMSCollector* collector,
6979 ConcurrentMarkSweepGeneration* g,
6980 CMSBitMap* bitMap, bool should_yield) :
6981 _collector(collector),
6982 _g(g),
6983 _sp(g->cmsSpace()),
6984 _limit(_sp->sweep_limit()),
6985 _freelistLock(_sp->freelistLock()),
6986 _bitMap(bitMap),
6987 _yield(should_yield),
6988 _inFreeRange(false), // No free range at beginning of sweep
6989 _freeRangeInFreeLists(false), // No free range at beginning of sweep
6990 _lastFreeRangeCoalesced(false),
6991 _freeFinger(g->used_region().start())
6992 {
6993 NOT_PRODUCT(
6994 _numObjectsFreed = 0;
6995 _numWordsFreed = 0;
6996 _numObjectsLive = 0;
6997 _numWordsLive = 0;
6998 _numObjectsAlreadyFree = 0;
6999 _numWordsAlreadyFree = 0;
7000 _last_fc = NULL;
7001
7002 _sp->initializeIndexedFreeListArrayReturnedBytes();
7003 _sp->dictionary()->initialize_dict_returned_bytes();
7004 )
7005 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7006 "sweep _limit out of bounds");
7007 log_develop_trace(gc, sweep)("====================");
7008 log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
7009 }
7010
7011 void SweepClosure::print_on(outputStream* st) const {
7012 st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7013 p2i(_sp->bottom()), p2i(_sp->end()));
7014 st->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7015 st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7016 NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7017 st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7018 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7019 }
7020
7021 #ifndef PRODUCT
7022 // Assertion checking only: no useful work in product mode --
7023 // however, if any of the flags below become product flags,
7024 // you may need to review this code to see if it needs to be
7025 // enabled in product mode.
7026 SweepClosure::~SweepClosure() {
7027 assert_lock_strong(_freelistLock);
7028 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7029 "sweep _limit out of bounds");
7030 if (inFreeRange()) {
7031 Log(gc, sweep) log;
7032 log.error("inFreeRange() should have been reset; dumping state of SweepClosure");
7033 ResourceMark rm;
7034 LogStream ls(log.error());
7035 print_on(&ls);
7036 ShouldNotReachHere();
7037 }
7038
7039 if (log_is_enabled(Debug, gc, sweep)) {
7040 log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7041 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7042 log_debug(gc, sweep)("Live " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7043 _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7044 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7045 log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7046 }
7047
7048 if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) {
7049 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7050 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7051 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7052 log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes Indexed List Returned " SIZE_FORMAT " bytes Dictionary Returned " SIZE_FORMAT " bytes",
7053 returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7054 }
7055 log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7056 log_develop_trace(gc, sweep)("================");
7057 }
7058 #endif // PRODUCT
7059
7060 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7061 bool freeRangeInFreeLists) {
7062 log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7063 p2i(freeFinger), freeRangeInFreeLists);
7064 assert(!inFreeRange(), "Trampling existing free range");
7065 set_inFreeRange(true);
7066 set_lastFreeRangeCoalesced(false);
7067
7068 set_freeFinger(freeFinger);
7069 set_freeRangeInFreeLists(freeRangeInFreeLists);
7070 if (CMSTestInFreeList) {
7071 if (freeRangeInFreeLists) {
7072 FreeChunk* fc = (FreeChunk*) freeFinger;
7073 assert(fc->is_free(), "A chunk on the free list should be free.");
7074 assert(fc->size() > 0, "Free range should have a size");
7075 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7076 }
7077 }
7078 }
7079
7080 // Note that the sweeper runs concurrently with mutators. Thus,
7081 // it is possible for direct allocation in this generation to happen
7082 // in the middle of the sweep. Note that the sweeper also coalesces
7083 // contiguous free blocks. Thus, unless the sweeper and the allocator
7084 // synchronize appropriately freshly allocated blocks may get swept up.
7085 // This is accomplished by the sweeper locking the free lists while
7086 // it is sweeping. Thus blocks that are determined to be free are
7087 // indeed free. There is however one additional complication:
7088 // blocks that have been allocated since the final checkpoint and
7089 // mark, will not have been marked and so would be treated as
7090 // unreachable and swept up. To prevent this, the allocator marks
7091 // the bit map when allocating during the sweep phase. This leads,
7092 // however, to a further complication -- objects may have been allocated
7093 // but not yet initialized -- in the sense that the header isn't yet
7094 // installed. The sweeper can not then determine the size of the block
7095 // in order to skip over it. To deal with this case, we use a technique
7096 // (due to Printezis) to encode such uninitialized block sizes in the
7097 // bit map. Since the bit map uses a bit per every HeapWord, but the
7098 // CMS generation has a minimum object size of 3 HeapWords, it follows
7099 // that "normal marks" won't be adjacent in the bit map (there will
7100 // always be at least two 0 bits between successive 1 bits). We make use
7101 // of these "unused" bits to represent uninitialized blocks -- the bit
7102 // corresponding to the start of the uninitialized object and the next
7103 // bit are both set. Finally, a 1 bit marks the end of the object that
7104 // started with the two consecutive 1 bits to indicate its potentially
7105 // uninitialized state.
7106
7107 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7108 FreeChunk* fc = (FreeChunk*)addr;
7109 size_t res;
7110
7111 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7112 // than "addr == _limit" because although _limit was a block boundary when
7113 // we started the sweep, it may no longer be one because heap expansion
7114 // may have caused us to coalesce the block ending at the address _limit
7115 // with a newly expanded chunk (this happens when _limit was set to the
7116 // previous _end of the space), so we may have stepped past _limit:
7117 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7118 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7119 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7120 "sweep _limit out of bounds");
7121 assert(addr < _sp->end(), "addr out of bounds");
7122 // Flush any free range we might be holding as a single
7123 // coalesced chunk to the appropriate free list.
7124 if (inFreeRange()) {
7125 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7126 "freeFinger() " PTR_FORMAT " is out of bounds", p2i(freeFinger()));
7127 flush_cur_free_chunk(freeFinger(),
7128 pointer_delta(addr, freeFinger()));
7129 log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7130 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7131 lastFreeRangeCoalesced() ? 1 : 0);
7132 }
7133
7134 // help the iterator loop finish
7135 return pointer_delta(_sp->end(), addr);
7136 }
7137
7138 assert(addr < _limit, "sweep invariant");
7139 // check if we should yield
7140 do_yield_check(addr);
7141 if (fc->is_free()) {
7142 // Chunk that is already free
7143 res = fc->size();
7144 do_already_free_chunk(fc);
7145 debug_only(_sp->verifyFreeLists());
7146 // If we flush the chunk at hand in lookahead_and_flush()
7147 // and it's coalesced with a preceding chunk, then the
7148 // process of "mangling" the payload of the coalesced block
7149 // will cause erasure of the size information from the
7150 // (erstwhile) header of all the coalesced blocks but the
7151 // first, so the first disjunct in the assert will not hold
7152 // in that specific case (in which case the second disjunct
7153 // will hold).
7154 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7155 "Otherwise the size info doesn't change at this step");
7156 NOT_PRODUCT(
7157 _numObjectsAlreadyFree++;
7158 _numWordsAlreadyFree += res;
7159 )
7160 NOT_PRODUCT(_last_fc = fc;)
7161 } else if (!_bitMap->isMarked(addr)) {
7162 // Chunk is fresh garbage
7163 res = do_garbage_chunk(fc);
7164 debug_only(_sp->verifyFreeLists());
7165 NOT_PRODUCT(
7166 _numObjectsFreed++;
7167 _numWordsFreed += res;
7168 )
7169 } else {
7170 // Chunk that is alive.
7171 res = do_live_chunk(fc);
7172 debug_only(_sp->verifyFreeLists());
7173 NOT_PRODUCT(
7174 _numObjectsLive++;
7175 _numWordsLive += res;
7176 )
7177 }
7178 return res;
7179 }
7180
7181 // For the smart allocation, record following
7182 // split deaths - a free chunk is removed from its free list because
7183 // it is being split into two or more chunks.
7184 // split birth - a free chunk is being added to its free list because
7185 // a larger free chunk has been split and resulted in this free chunk.
7186 // coal death - a free chunk is being removed from its free list because
7187 // it is being coalesced into a large free chunk.
7188 // coal birth - a free chunk is being added to its free list because
7189 // it was created when two or more free chunks where coalesced into
7190 // this free chunk.
7191 //
7192 // These statistics are used to determine the desired number of free
7193 // chunks of a given size. The desired number is chosen to be relative
7194 // to the end of a CMS sweep. The desired number at the end of a sweep
7195 // is the
7196 // count-at-end-of-previous-sweep (an amount that was enough)
7197 // - count-at-beginning-of-current-sweep (the excess)
7198 // + split-births (gains in this size during interval)
7199 // - split-deaths (demands on this size during interval)
7200 // where the interval is from the end of one sweep to the end of the
7201 // next.
7202 //
7203 // When sweeping the sweeper maintains an accumulated chunk which is
7204 // the chunk that is made up of chunks that have been coalesced. That
7205 // will be termed the left-hand chunk. A new chunk of garbage that
7206 // is being considered for coalescing will be referred to as the
7207 // right-hand chunk.
7208 //
7209 // When making a decision on whether to coalesce a right-hand chunk with
7210 // the current left-hand chunk, the current count vs. the desired count
7211 // of the left-hand chunk is considered. Also if the right-hand chunk
7212 // is near the large chunk at the end of the heap (see
7213 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7214 // left-hand chunk is coalesced.
7215 //
7216 // When making a decision about whether to split a chunk, the desired count
7217 // vs. the current count of the candidate to be split is also considered.
7218 // If the candidate is underpopulated (currently fewer chunks than desired)
7219 // a chunk of an overpopulated (currently more chunks than desired) size may
7220 // be chosen. The "hint" associated with a free list, if non-null, points
7221 // to a free list which may be overpopulated.
7222 //
7223
7224 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7225 const size_t size = fc->size();
7226 // Chunks that cannot be coalesced are not in the
7227 // free lists.
7228 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7229 assert(_sp->verify_chunk_in_free_list(fc),
7230 "free chunk should be in free lists");
7231 }
7232 // a chunk that is already free, should not have been
7233 // marked in the bit map
7234 HeapWord* const addr = (HeapWord*) fc;
7235 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7236 // Verify that the bit map has no bits marked between
7237 // addr and purported end of this block.
7238 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7239
7240 // Some chunks cannot be coalesced under any circumstances.
7241 // See the definition of cantCoalesce().
7242 if (!fc->cantCoalesce()) {
7243 // This chunk can potentially be coalesced.
7244 // All the work is done in
7245 do_post_free_or_garbage_chunk(fc, size);
7246 // Note that if the chunk is not coalescable (the else arm
7247 // below), we unconditionally flush, without needing to do
7248 // a "lookahead," as we do below.
7249 if (inFreeRange()) lookahead_and_flush(fc, size);
7250 } else {
7251 // Code path common to both original and adaptive free lists.
7252
7253 // cant coalesce with previous block; this should be treated
7254 // as the end of a free run if any
7255 if (inFreeRange()) {
7256 // we kicked some butt; time to pick up the garbage
7257 assert(freeFinger() < addr, "freeFinger points too high");
7258 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7259 }
7260 // else, nothing to do, just continue
7261 }
7262 }
7263
7264 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7265 // This is a chunk of garbage. It is not in any free list.
7266 // Add it to a free list or let it possibly be coalesced into
7267 // a larger chunk.
7268 HeapWord* const addr = (HeapWord*) fc;
7269 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7270
7271 // Verify that the bit map has no bits marked between
7272 // addr and purported end of just dead object.
7273 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7274 do_post_free_or_garbage_chunk(fc, size);
7275
7276 assert(_limit >= addr + size,
7277 "A freshly garbage chunk can't possibly straddle over _limit");
7278 if (inFreeRange()) lookahead_and_flush(fc, size);
7279 return size;
7280 }
7281
7282 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7283 HeapWord* addr = (HeapWord*) fc;
7284 // The sweeper has just found a live object. Return any accumulated
7285 // left hand chunk to the free lists.
7286 if (inFreeRange()) {
7287 assert(freeFinger() < addr, "freeFinger points too high");
7288 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7289 }
7290
7291 // This object is live: we'd normally expect this to be
7292 // an oop, and like to assert the following:
7293 // assert(oopDesc::is_oop(oop(addr)), "live block should be an oop");
7294 // However, as we commented above, this may be an object whose
7295 // header hasn't yet been initialized.
7296 size_t size;
7297 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7298 if (_bitMap->isMarked(addr + 1)) {
7299 // Determine the size from the bit map, rather than trying to
7300 // compute it from the object header.
7301 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7302 size = pointer_delta(nextOneAddr + 1, addr);
7303 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7304 "alignment problem");
7305
7306 #ifdef ASSERT
7307 if (oop(addr)->klass_or_null_acquire() != NULL) {
7308 // Ignore mark word because we are running concurrent with mutators
7309 assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7310 assert(size ==
7311 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7312 "P-mark and computed size do not agree");
7313 }
7314 #endif
7315
7316 } else {
7317 // This should be an initialized object that's alive.
7318 assert(oop(addr)->klass_or_null_acquire() != NULL,
7319 "Should be an initialized object");
7320 // Ignore mark word because we are running concurrent with mutators
7321 assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7322 // Verify that the bit map has no bits marked between
7323 // addr and purported end of this block.
7324 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7325 assert(size >= 3, "Necessary for Printezis marks to work");
7326 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7327 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7328 }
7329 return size;
7330 }
7331
7332 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7333 size_t chunkSize) {
7334 // do_post_free_or_garbage_chunk() should only be called in the case
7335 // of the adaptive free list allocator.
7336 const bool fcInFreeLists = fc->is_free();
7337 assert((HeapWord*)fc <= _limit, "sweep invariant");
7338 if (CMSTestInFreeList && fcInFreeLists) {
7339 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7340 }
7341
7342 log_develop_trace(gc, sweep)(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7343
7344 HeapWord* const fc_addr = (HeapWord*) fc;
7345
7346 bool coalesce = false;
7347 const size_t left = pointer_delta(fc_addr, freeFinger());
7348 const size_t right = chunkSize;
7349 switch (FLSCoalescePolicy) {
7350 // numeric value forms a coalition aggressiveness metric
7351 case 0: { // never coalesce
7352 coalesce = false;
7353 break;
7354 }
7355 case 1: { // coalesce if left & right chunks on overpopulated lists
7356 coalesce = _sp->coalOverPopulated(left) &&
7357 _sp->coalOverPopulated(right);
7358 break;
7359 }
7360 case 2: { // coalesce if left chunk on overpopulated list (default)
7361 coalesce = _sp->coalOverPopulated(left);
7362 break;
7363 }
7364 case 3: { // coalesce if left OR right chunk on overpopulated list
7365 coalesce = _sp->coalOverPopulated(left) ||
7366 _sp->coalOverPopulated(right);
7367 break;
7368 }
7369 case 4: { // always coalesce
7370 coalesce = true;
7371 break;
7372 }
7373 default:
7374 ShouldNotReachHere();
7375 }
7376
7377 // Should the current free range be coalesced?
7378 // If the chunk is in a free range and either we decided to coalesce above
7379 // or the chunk is near the large block at the end of the heap
7380 // (isNearLargestChunk() returns true), then coalesce this chunk.
7381 const bool doCoalesce = inFreeRange()
7382 && (coalesce || _g->isNearLargestChunk(fc_addr));
7383 if (doCoalesce) {
7384 // Coalesce the current free range on the left with the new
7385 // chunk on the right. If either is on a free list,
7386 // it must be removed from the list and stashed in the closure.
7387 if (freeRangeInFreeLists()) {
7388 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7389 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7390 "Size of free range is inconsistent with chunk size.");
7391 if (CMSTestInFreeList) {
7392 assert(_sp->verify_chunk_in_free_list(ffc),
7393 "Chunk is not in free lists");
7394 }
7395 _sp->coalDeath(ffc->size());
7396 _sp->removeFreeChunkFromFreeLists(ffc);
7397 set_freeRangeInFreeLists(false);
7398 }
7399 if (fcInFreeLists) {
7400 _sp->coalDeath(chunkSize);
7401 assert(fc->size() == chunkSize,
7402 "The chunk has the wrong size or is not in the free lists");
7403 _sp->removeFreeChunkFromFreeLists(fc);
7404 }
7405 set_lastFreeRangeCoalesced(true);
7406 print_free_block_coalesced(fc);
7407 } else { // not in a free range and/or should not coalesce
7408 // Return the current free range and start a new one.
7409 if (inFreeRange()) {
7410 // In a free range but cannot coalesce with the right hand chunk.
7411 // Put the current free range into the free lists.
7412 flush_cur_free_chunk(freeFinger(),
7413 pointer_delta(fc_addr, freeFinger()));
7414 }
7415 // Set up for new free range. Pass along whether the right hand
7416 // chunk is in the free lists.
7417 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7418 }
7419 }
7420
7421 // Lookahead flush:
7422 // If we are tracking a free range, and this is the last chunk that
7423 // we'll look at because its end crosses past _limit, we'll preemptively
7424 // flush it along with any free range we may be holding on to. Note that
7425 // this can be the case only for an already free or freshly garbage
7426 // chunk. If this block is an object, it can never straddle
7427 // over _limit. The "straddling" occurs when _limit is set at
7428 // the previous end of the space when this cycle started, and
7429 // a subsequent heap expansion caused the previously co-terminal
7430 // free block to be coalesced with the newly expanded portion,
7431 // thus rendering _limit a non-block-boundary making it dangerous
7432 // for the sweeper to step over and examine.
7433 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7434 assert(inFreeRange(), "Should only be called if currently in a free range.");
7435 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7436 assert(_sp->used_region().contains(eob - 1),
7437 "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7438 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7439 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7440 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7441 if (eob >= _limit) {
7442 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7443 log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7444 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7445 "[" PTR_FORMAT "," PTR_FORMAT ")",
7446 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7447 // Return the storage we are tracking back into the free lists.
7448 log_develop_trace(gc, sweep)("Flushing ... ");
7449 assert(freeFinger() < eob, "Error");
7450 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7451 }
7452 }
7453
7454 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7455 assert(inFreeRange(), "Should only be called if currently in a free range.");
7456 assert(size > 0,
7457 "A zero sized chunk cannot be added to the free lists.");
7458 if (!freeRangeInFreeLists()) {
7459 if (CMSTestInFreeList) {
7460 FreeChunk* fc = (FreeChunk*) chunk;
7461 fc->set_size(size);
7462 assert(!_sp->verify_chunk_in_free_list(fc),
7463 "chunk should not be in free lists yet");
7464 }
7465 log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size);
7466 // A new free range is going to be starting. The current
7467 // free range has not been added to the free lists yet or
7468 // was removed so add it back.
7469 // If the current free range was coalesced, then the death
7470 // of the free range was recorded. Record a birth now.
7471 if (lastFreeRangeCoalesced()) {
7472 _sp->coalBirth(size);
7473 }
7474 _sp->addChunkAndRepairOffsetTable(chunk, size,
7475 lastFreeRangeCoalesced());
7476 } else {
7477 log_develop_trace(gc, sweep)("Already in free list: nothing to flush");
7478 }
7479 set_inFreeRange(false);
7480 set_freeRangeInFreeLists(false);
7481 }
7482
7483 // We take a break if we've been at this for a while,
7484 // so as to avoid monopolizing the locks involved.
7485 void SweepClosure::do_yield_work(HeapWord* addr) {
7486 // Return current free chunk being used for coalescing (if any)
7487 // to the appropriate freelist. After yielding, the next
7488 // free block encountered will start a coalescing range of
7489 // free blocks. If the next free block is adjacent to the
7490 // chunk just flushed, they will need to wait for the next
7491 // sweep to be coalesced.
7492 if (inFreeRange()) {
7493 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7494 }
7495
7496 // First give up the locks, then yield, then re-lock.
7497 // We should probably use a constructor/destructor idiom to
7498 // do this unlock/lock or modify the MutexUnlocker class to
7499 // serve our purpose. XXX
7500 assert_lock_strong(_bitMap->lock());
7501 assert_lock_strong(_freelistLock);
7502 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7503 "CMS thread should hold CMS token");
7504 _bitMap->lock()->unlock();
7505 _freelistLock->unlock();
7506 ConcurrentMarkSweepThread::desynchronize(true);
7507 _collector->stopTimer();
7508 _collector->incrementYields();
7509
7510 // See the comment in coordinator_yield()
7511 for (unsigned i = 0; i < CMSYieldSleepCount &&
7512 ConcurrentMarkSweepThread::should_yield() &&
7513 !CMSCollector::foregroundGCIsActive(); ++i) {
7514 os::sleep(Thread::current(), 1, false);
7515 }
7516
7517 ConcurrentMarkSweepThread::synchronize(true);
7518 _freelistLock->lock();
7519 _bitMap->lock()->lock_without_safepoint_check();
7520 _collector->startTimer();
7521 }
7522
7523 #ifndef PRODUCT
7524 // This is actually very useful in a product build if it can
7525 // be called from the debugger. Compile it into the product
7526 // as needed.
7527 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7528 return debug_cms_space->verify_chunk_in_free_list(fc);
7529 }
7530 #endif
7531
7532 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7533 log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7534 p2i(fc), fc->size());
7535 }
7536
7537 // CMSIsAliveClosure
7538 bool CMSIsAliveClosure::do_object_b(oop obj) {
7539 HeapWord* addr = (HeapWord*)obj;
7540 return addr != NULL &&
7541 (!_span.contains(addr) || _bit_map->isMarked(addr));
7542 }
7543
7544
7545 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7546 MemRegion span,
7547 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7548 bool cpc):
7549 _collector(collector),
7550 _span(span),
7551 _bit_map(bit_map),
7552 _mark_stack(mark_stack),
7553 _concurrent_precleaning(cpc) {
7554 assert(!_span.is_empty(), "Empty span could spell trouble");
7555 }
7556
7557
7558 // CMSKeepAliveClosure: the serial version
7559 void CMSKeepAliveClosure::do_oop(oop obj) {
7560 HeapWord* addr = (HeapWord*)obj;
7561 if (_span.contains(addr) &&
7562 !_bit_map->isMarked(addr)) {
7563 _bit_map->mark(addr);
7564 bool simulate_overflow = false;
7565 NOT_PRODUCT(
7566 if (CMSMarkStackOverflowALot &&
7567 _collector->simulate_overflow()) {
7568 // simulate a stack overflow
7569 simulate_overflow = true;
7570 }
7571 )
7572 if (simulate_overflow || !_mark_stack->push(obj)) {
7573 if (_concurrent_precleaning) {
7574 // We dirty the overflown object and let the remark
7575 // phase deal with it.
7576 assert(_collector->overflow_list_is_empty(), "Error");
7577 // In the case of object arrays, we need to dirty all of
7578 // the cards that the object spans. No locking or atomics
7579 // are needed since no one else can be mutating the mod union
7580 // table.
7581 if (obj->is_objArray()) {
7582 size_t sz = obj->size();
7583 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
7584 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7585 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7586 _collector->_modUnionTable.mark_range(redirty_range);
7587 } else {
7588 _collector->_modUnionTable.mark(addr);
7589 }
7590 _collector->_ser_kac_preclean_ovflw++;
7591 } else {
7592 _collector->push_on_overflow_list(obj);
7593 _collector->_ser_kac_ovflw++;
7594 }
7595 }
7596 }
7597 }
7598
7599 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7600 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7601
7602 // CMSParKeepAliveClosure: a parallel version of the above.
7603 // The work queues are private to each closure (thread),
7604 // but (may be) available for stealing by other threads.
7605 void CMSParKeepAliveClosure::do_oop(oop obj) {
7606 HeapWord* addr = (HeapWord*)obj;
7607 if (_span.contains(addr) &&
7608 !_bit_map->isMarked(addr)) {
7609 // In general, during recursive tracing, several threads
7610 // may be concurrently getting here; the first one to
7611 // "tag" it, claims it.
7612 if (_bit_map->par_mark(addr)) {
7613 bool res = _work_queue->push(obj);
7614 assert(res, "Low water mark should be much less than capacity");
7615 // Do a recursive trim in the hope that this will keep
7616 // stack usage lower, but leave some oops for potential stealers
7617 trim_queue(_low_water_mark);
7618 } // Else, another thread got there first
7619 }
7620 }
7621
7622 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7623 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7624
7625 void CMSParKeepAliveClosure::trim_queue(uint max) {
7626 while (_work_queue->size() > max) {
7627 oop new_oop;
7628 if (_work_queue->pop_local(new_oop)) {
7629 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
7630 assert(_bit_map->isMarked((HeapWord*)new_oop),
7631 "no white objects on this stack!");
7632 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7633 // iterate over the oops in this oop, marking and pushing
7634 // the ones in CMS heap (i.e. in _span).
7635 new_oop->oop_iterate(&_mark_and_push);
7636 }
7637 }
7638 }
7639
7640 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7641 CMSCollector* collector,
7642 MemRegion span, CMSBitMap* bit_map,
7643 OopTaskQueue* work_queue):
7644 _collector(collector),
7645 _span(span),
7646 _bit_map(bit_map),
7647 _work_queue(work_queue) { }
7648
7649 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7650 HeapWord* addr = (HeapWord*)obj;
7651 if (_span.contains(addr) &&
7652 !_bit_map->isMarked(addr)) {
7653 if (_bit_map->par_mark(addr)) {
7654 bool simulate_overflow = false;
7655 NOT_PRODUCT(
7656 if (CMSMarkStackOverflowALot &&
7657 _collector->par_simulate_overflow()) {
7658 // simulate a stack overflow
7659 simulate_overflow = true;
7660 }
7661 )
7662 if (simulate_overflow || !_work_queue->push(obj)) {
7663 _collector->par_push_on_overflow_list(obj);
7664 _collector->_par_kac_ovflw++;
7665 }
7666 } // Else another thread got there already
7667 }
7668 }
7669
7670 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7671 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7672
7673 //////////////////////////////////////////////////////////////////
7674 // CMSExpansionCause /////////////////////////////
7675 //////////////////////////////////////////////////////////////////
7676 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7677 switch (cause) {
7678 case _no_expansion:
7679 return "No expansion";
7680 case _satisfy_free_ratio:
7681 return "Free ratio";
7682 case _satisfy_promotion:
7683 return "Satisfy promotion";
7684 case _satisfy_allocation:
7685 return "allocation";
7686 case _allocate_par_lab:
7687 return "Par LAB";
7688 case _allocate_par_spooling_space:
7689 return "Par Spooling Space";
7690 case _adaptive_size_policy:
7691 return "Ergonomics";
7692 default:
7693 return "unknown";
7694 }
7695 }
7696
7697 void CMSDrainMarkingStackClosure::do_void() {
7698 // the max number to take from overflow list at a time
7699 const size_t num = _mark_stack->capacity()/4;
7700 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7701 "Overflow list should be NULL during concurrent phases");
7702 while (!_mark_stack->isEmpty() ||
7703 // if stack is empty, check the overflow list
7704 _collector->take_from_overflow_list(num, _mark_stack)) {
7705 oop obj = _mark_stack->pop();
7706 HeapWord* addr = (HeapWord*)obj;
7707 assert(_span.contains(addr), "Should be within span");
7708 assert(_bit_map->isMarked(addr), "Should be marked");
7709 assert(oopDesc::is_oop(obj), "Should be an oop");
7710 obj->oop_iterate(_keep_alive);
7711 }
7712 }
7713
7714 void CMSParDrainMarkingStackClosure::do_void() {
7715 // drain queue
7716 trim_queue(0);
7717 }
7718
7719 // Trim our work_queue so its length is below max at return
7720 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7721 while (_work_queue->size() > max) {
7722 oop new_oop;
7723 if (_work_queue->pop_local(new_oop)) {
7724 assert(oopDesc::is_oop(new_oop), "Expected an oop");
7725 assert(_bit_map->isMarked((HeapWord*)new_oop),
7726 "no white objects on this stack!");
7727 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7728 // iterate over the oops in this oop, marking and pushing
7729 // the ones in CMS heap (i.e. in _span).
7730 new_oop->oop_iterate(&_mark_and_push);
7731 }
7732 }
7733 }
7734
7735 ////////////////////////////////////////////////////////////////////
7736 // Support for Marking Stack Overflow list handling and related code
7737 ////////////////////////////////////////////////////////////////////
7738 // Much of the following code is similar in shape and spirit to the
7739 // code used in ParNewGC. We should try and share that code
7740 // as much as possible in the future.
7741
7742 #ifndef PRODUCT
7743 // Debugging support for CMSStackOverflowALot
7744
7745 // It's OK to call this multi-threaded; the worst thing
7746 // that can happen is that we'll get a bunch of closely
7747 // spaced simulated overflows, but that's OK, in fact
7748 // probably good as it would exercise the overflow code
7749 // under contention.
7750 bool CMSCollector::simulate_overflow() {
7751 if (_overflow_counter-- <= 0) { // just being defensive
7752 _overflow_counter = CMSMarkStackOverflowInterval;
7753 return true;
7754 } else {
7755 return false;
7756 }
7757 }
7758
7759 bool CMSCollector::par_simulate_overflow() {
7760 return simulate_overflow();
7761 }
7762 #endif
7763
7764 // Single-threaded
7765 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7766 assert(stack->isEmpty(), "Expected precondition");
7767 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7768 size_t i = num;
7769 oop cur = _overflow_list;
7770 const markOop proto = markOopDesc::prototype();
7771 NOT_PRODUCT(ssize_t n = 0;)
7772 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7773 next = oop(cur->mark_raw());
7774 cur->set_mark_raw(proto); // until proven otherwise
7775 assert(oopDesc::is_oop(cur), "Should be an oop");
7776 bool res = stack->push(cur);
7777 assert(res, "Bit off more than can chew?");
7778 NOT_PRODUCT(n++;)
7779 }
7780 _overflow_list = cur;
7781 #ifndef PRODUCT
7782 assert(_num_par_pushes >= n, "Too many pops?");
7783 _num_par_pushes -=n;
7784 #endif
7785 return !stack->isEmpty();
7786 }
7787
7788 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
7789 // (MT-safe) Get a prefix of at most "num" from the list.
7790 // The overflow list is chained through the mark word of
7791 // each object in the list. We fetch the entire list,
7792 // break off a prefix of the right size and return the
7793 // remainder. If other threads try to take objects from
7794 // the overflow list at that time, they will wait for
7795 // some time to see if data becomes available. If (and
7796 // only if) another thread places one or more object(s)
7797 // on the global list before we have returned the suffix
7798 // to the global list, we will walk down our local list
7799 // to find its end and append the global list to
7800 // our suffix before returning it. This suffix walk can
7801 // prove to be expensive (quadratic in the amount of traffic)
7802 // when there are many objects in the overflow list and
7803 // there is much producer-consumer contention on the list.
7804 // *NOTE*: The overflow list manipulation code here and
7805 // in ParNewGeneration:: are very similar in shape,
7806 // except that in the ParNew case we use the old (from/eden)
7807 // copy of the object to thread the list via its klass word.
7808 // Because of the common code, if you make any changes in
7809 // the code below, please check the ParNew version to see if
7810 // similar changes might be needed.
7811 // CR 6797058 has been filed to consolidate the common code.
7812 bool CMSCollector::par_take_from_overflow_list(size_t num,
7813 OopTaskQueue* work_q,
7814 int no_of_gc_threads) {
7815 assert(work_q->size() == 0, "First empty local work queue");
7816 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7817 if (_overflow_list == NULL) {
7818 return false;
7819 }
7820 // Grab the entire list; we'll put back a suffix
7821 oop prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7822 Thread* tid = Thread::current();
7823 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7824 // set to ParallelGCThreads.
7825 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7826 size_t sleep_time_millis = MAX2((size_t)1, num/100);
7827 // If the list is busy, we spin for a short while,
7828 // sleeping between attempts to get the list.
7829 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7830 os::sleep(tid, sleep_time_millis, false);
7831 if (_overflow_list == NULL) {
7832 // Nothing left to take
7833 return false;
7834 } else if (_overflow_list != BUSY) {
7835 // Try and grab the prefix
7836 prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7837 }
7838 }
7839 // If the list was found to be empty, or we spun long
7840 // enough, we give up and return empty-handed. If we leave
7841 // the list in the BUSY state below, it must be the case that
7842 // some other thread holds the overflow list and will set it
7843 // to a non-BUSY state in the future.
7844 if (prefix == NULL || prefix == BUSY) {
7845 // Nothing to take or waited long enough
7846 if (prefix == NULL) {
7847 // Write back the NULL in case we overwrote it with BUSY above
7848 // and it is still the same value.
7849 Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7850 }
7851 return false;
7852 }
7853 assert(prefix != NULL && prefix != BUSY, "Error");
7854 size_t i = num;
7855 oop cur = prefix;
7856 // Walk down the first "num" objects, unless we reach the end.
7857 for (; i > 1 && cur->mark_raw() != NULL; cur = oop(cur->mark_raw()), i--);
7858 if (cur->mark_raw() == NULL) {
7859 // We have "num" or fewer elements in the list, so there
7860 // is nothing to return to the global list.
7861 // Write back the NULL in lieu of the BUSY we wrote
7862 // above, if it is still the same value.
7863 if (_overflow_list == BUSY) {
7864 Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7865 }
7866 } else {
7867 // Chop off the suffix and return it to the global list.
7868 assert(cur->mark_raw() != BUSY, "Error");
7869 oop suffix_head = cur->mark_raw(); // suffix will be put back on global list
7870 cur->set_mark_raw(NULL); // break off suffix
7871 // It's possible that the list is still in the empty(busy) state
7872 // we left it in a short while ago; in that case we may be
7873 // able to place back the suffix without incurring the cost
7874 // of a walk down the list.
7875 oop observed_overflow_list = _overflow_list;
7876 oop cur_overflow_list = observed_overflow_list;
7877 bool attached = false;
7878 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7879 observed_overflow_list =
7880 Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7881 if (cur_overflow_list == observed_overflow_list) {
7882 attached = true;
7883 break;
7884 } else cur_overflow_list = observed_overflow_list;
7885 }
7886 if (!attached) {
7887 // Too bad, someone else sneaked in (at least) an element; we'll need
7888 // to do a splice. Find tail of suffix so we can prepend suffix to global
7889 // list.
7890 for (cur = suffix_head; cur->mark_raw() != NULL; cur = (oop)(cur->mark_raw()));
7891 oop suffix_tail = cur;
7892 assert(suffix_tail != NULL && suffix_tail->mark_raw() == NULL,
7893 "Tautology");
7894 observed_overflow_list = _overflow_list;
7895 do {
7896 cur_overflow_list = observed_overflow_list;
7897 if (cur_overflow_list != BUSY) {
7898 // Do the splice ...
7899 suffix_tail->set_mark_raw(markOop(cur_overflow_list));
7900 } else { // cur_overflow_list == BUSY
7901 suffix_tail->set_mark_raw(NULL);
7902 }
7903 // ... and try to place spliced list back on overflow_list ...
7904 observed_overflow_list =
7905 Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7906 } while (cur_overflow_list != observed_overflow_list);
7907 // ... until we have succeeded in doing so.
7908 }
7909 }
7910
7911 // Push the prefix elements on work_q
7912 assert(prefix != NULL, "control point invariant");
7913 const markOop proto = markOopDesc::prototype();
7914 oop next;
7915 NOT_PRODUCT(ssize_t n = 0;)
7916 for (cur = prefix; cur != NULL; cur = next) {
7917 next = oop(cur->mark_raw());
7918 cur->set_mark_raw(proto); // until proven otherwise
7919 assert(oopDesc::is_oop(cur), "Should be an oop");
7920 bool res = work_q->push(cur);
7921 assert(res, "Bit off more than we can chew?");
7922 NOT_PRODUCT(n++;)
7923 }
7924 #ifndef PRODUCT
7925 assert(_num_par_pushes >= n, "Too many pops?");
7926 Atomic::sub(n, &_num_par_pushes);
7927 #endif
7928 return true;
7929 }
7930
7931 // Single-threaded
7932 void CMSCollector::push_on_overflow_list(oop p) {
7933 NOT_PRODUCT(_num_par_pushes++;)
7934 assert(oopDesc::is_oop(p), "Not an oop");
7935 preserve_mark_if_necessary(p);
7936 p->set_mark_raw((markOop)_overflow_list);
7937 _overflow_list = p;
7938 }
7939
7940 // Multi-threaded; use CAS to prepend to overflow list
7941 void CMSCollector::par_push_on_overflow_list(oop p) {
7942 NOT_PRODUCT(Atomic::inc(&_num_par_pushes);)
7943 assert(oopDesc::is_oop(p), "Not an oop");
7944 par_preserve_mark_if_necessary(p);
7945 oop observed_overflow_list = _overflow_list;
7946 oop cur_overflow_list;
7947 do {
7948 cur_overflow_list = observed_overflow_list;
7949 if (cur_overflow_list != BUSY) {
7950 p->set_mark_raw(markOop(cur_overflow_list));
7951 } else {
7952 p->set_mark_raw(NULL);
7953 }
7954 observed_overflow_list =
7955 Atomic::cmpxchg((oopDesc*)p, &_overflow_list, (oopDesc*)cur_overflow_list);
7956 } while (cur_overflow_list != observed_overflow_list);
7957 }
7958 #undef BUSY
7959
7960 // Single threaded
7961 // General Note on GrowableArray: pushes may silently fail
7962 // because we are (temporarily) out of C-heap for expanding
7963 // the stack. The problem is quite ubiquitous and affects
7964 // a lot of code in the JVM. The prudent thing for GrowableArray
7965 // to do (for now) is to exit with an error. However, that may
7966 // be too draconian in some cases because the caller may be
7967 // able to recover without much harm. For such cases, we
7968 // should probably introduce a "soft_push" method which returns
7969 // an indication of success or failure with the assumption that
7970 // the caller may be able to recover from a failure; code in
7971 // the VM can then be changed, incrementally, to deal with such
7972 // failures where possible, thus, incrementally hardening the VM
7973 // in such low resource situations.
7974 void CMSCollector::preserve_mark_work(oop p, markOop m) {
7975 _preserved_oop_stack.push(p);
7976 _preserved_mark_stack.push(m);
7977 assert(m == p->mark_raw(), "Mark word changed");
7978 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
7979 "bijection");
7980 }
7981
7982 // Single threaded
7983 void CMSCollector::preserve_mark_if_necessary(oop p) {
7984 markOop m = p->mark_raw();
7985 if (m->must_be_preserved(p)) {
7986 preserve_mark_work(p, m);
7987 }
7988 }
7989
7990 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
7991 markOop m = p->mark_raw();
7992 if (m->must_be_preserved(p)) {
7993 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
7994 // Even though we read the mark word without holding
7995 // the lock, we are assured that it will not change
7996 // because we "own" this oop, so no other thread can
7997 // be trying to push it on the overflow list; see
7998 // the assertion in preserve_mark_work() that checks
7999 // that m == p->mark_raw().
8000 preserve_mark_work(p, m);
8001 }
8002 }
8003
8004 // We should be able to do this multi-threaded,
8005 // a chunk of stack being a task (this is
8006 // correct because each oop only ever appears
8007 // once in the overflow list. However, it's
8008 // not very easy to completely overlap this with
8009 // other operations, so will generally not be done
8010 // until all work's been completed. Because we
8011 // expect the preserved oop stack (set) to be small,
8012 // it's probably fine to do this single-threaded.
8013 // We can explore cleverer concurrent/overlapped/parallel
8014 // processing of preserved marks if we feel the
8015 // need for this in the future. Stack overflow should
8016 // be so rare in practice and, when it happens, its
8017 // effect on performance so great that this will
8018 // likely just be in the noise anyway.
8019 void CMSCollector::restore_preserved_marks_if_any() {
8020 assert(SafepointSynchronize::is_at_safepoint(),
8021 "world should be stopped");
8022 assert(Thread::current()->is_ConcurrentGC_thread() ||
8023 Thread::current()->is_VM_thread(),
8024 "should be single-threaded");
8025 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8026 "bijection");
8027
8028 while (!_preserved_oop_stack.is_empty()) {
8029 oop p = _preserved_oop_stack.pop();
8030 assert(oopDesc::is_oop(p), "Should be an oop");
8031 assert(_span.contains(p), "oop should be in _span");
8032 assert(p->mark_raw() == markOopDesc::prototype(),
8033 "Set when taken from overflow list");
8034 markOop m = _preserved_mark_stack.pop();
8035 p->set_mark_raw(m);
8036 }
8037 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8038 "stacks were cleared above");
8039 }
8040
8041 #ifndef PRODUCT
8042 bool CMSCollector::no_preserved_marks() const {
8043 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8044 }
8045 #endif
8046
8047 // Transfer some number of overflown objects to usual marking
8048 // stack. Return true if some objects were transferred.
8049 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8050 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8051 (size_t)ParGCDesiredObjsFromOverflowList);
8052
8053 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8054 assert(_collector->overflow_list_is_empty() || res,
8055 "If list is not empty, we should have taken something");
8056 assert(!res || !_mark_stack->isEmpty(),
8057 "If we took something, it should now be on our stack");
8058 return res;
8059 }
8060
8061 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8062 size_t res = _sp->block_size_no_stall(addr, _collector);
8063 if (_sp->block_is_obj(addr)) {
8064 if (_live_bit_map->isMarked(addr)) {
8065 // It can't have been dead in a previous cycle
8066 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8067 } else {
8068 _dead_bit_map->mark(addr); // mark the dead object
8069 }
8070 }
8071 // Could be 0, if the block size could not be computed without stalling.
8072 return res;
8073 }
8074
8075 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8076 GCMemoryManager* manager = CMSHeap::heap()->old_manager();
8077 switch (phase) {
8078 case CMSCollector::InitialMarking:
8079 initialize(manager /* GC manager */ ,
8080 cause /* cause of the GC */,
8081 true /* recordGCBeginTime */,
8082 true /* recordPreGCUsage */,
8083 false /* recordPeakUsage */,
8084 false /* recordPostGCusage */,
8085 true /* recordAccumulatedGCTime */,
8086 false /* recordGCEndTime */,
8087 false /* countCollection */ );
8088 break;
8089
8090 case CMSCollector::FinalMarking:
8091 initialize(manager /* GC manager */ ,
8092 cause /* cause of the GC */,
8093 false /* recordGCBeginTime */,
8094 false /* recordPreGCUsage */,
8095 false /* recordPeakUsage */,
8096 false /* recordPostGCusage */,
8097 true /* recordAccumulatedGCTime */,
8098 false /* recordGCEndTime */,
8099 false /* countCollection */ );
8100 break;
8101
8102 case CMSCollector::Sweeping:
8103 initialize(manager /* GC manager */ ,
8104 cause /* cause of the GC */,
8105 false /* recordGCBeginTime */,
8106 false /* recordPreGCUsage */,
8107 true /* recordPeakUsage */,
8108 true /* recordPostGCusage */,
8109 false /* recordAccumulatedGCTime */,
8110 true /* recordGCEndTime */,
8111 true /* countCollection */ );
8112 break;
8113
8114 default:
8115 ShouldNotReachHere();
8116 }
8117 }