1 /*
2 * Copyright (c) 2001, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderDataGraph.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/symbolTable.hpp"
29 #include "classfile/systemDictionary.hpp"
30 #include "code/codeCache.hpp"
31 #include "gc/cms/cmsCollectorPolicy.hpp"
32 #include "gc/cms/cmsGCStats.hpp"
33 #include "gc/cms/cmsHeap.hpp"
34 #include "gc/cms/cmsOopClosures.inline.hpp"
35 #include "gc/cms/cmsVMOperations.hpp"
36 #include "gc/cms/compactibleFreeListSpace.hpp"
37 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
38 #include "gc/cms/concurrentMarkSweepThread.hpp"
39 #include "gc/cms/parNewGeneration.hpp"
40 #include "gc/cms/promotionInfo.inline.hpp"
41 #include "gc/serial/genMarkSweep.hpp"
42 #include "gc/serial/tenuredGeneration.hpp"
43 #include "gc/shared/adaptiveSizePolicy.hpp"
44 #include "gc/shared/cardGeneration.inline.hpp"
45 #include "gc/shared/cardTableRS.hpp"
46 #include "gc/shared/collectedHeap.inline.hpp"
47 #include "gc/shared/collectorCounters.hpp"
48 #include "gc/shared/collectorPolicy.hpp"
49 #include "gc/shared/gcLocker.hpp"
50 #include "gc/shared/gcPolicyCounters.hpp"
51 #include "gc/shared/gcTimer.hpp"
52 #include "gc/shared/gcTrace.hpp"
53 #include "gc/shared/gcTraceTime.inline.hpp"
54 #include "gc/shared/genCollectedHeap.hpp"
55 #include "gc/shared/genOopClosures.inline.hpp"
56 #include "gc/shared/isGCActiveMark.hpp"
57 #include "gc/shared/oopStorageParState.hpp"
58 #include "gc/shared/owstTaskTerminator.hpp"
59 #include "gc/shared/referencePolicy.hpp"
60 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
61 #include "gc/shared/space.inline.hpp"
62 #include "gc/shared/strongRootsScope.hpp"
63 #include "gc/shared/taskqueue.inline.hpp"
64 #include "gc/shared/weakProcessor.hpp"
65 #include "gc/shared/workerPolicy.hpp"
66 #include "logging/log.hpp"
67 #include "logging/logStream.hpp"
68 #include "memory/allocation.hpp"
69 #include "memory/binaryTreeDictionary.inline.hpp"
70 #include "memory/iterator.inline.hpp"
71 #include "memory/padded.hpp"
72 #include "memory/resourceArea.hpp"
73 #include "oops/access.inline.hpp"
74 #include "oops/oop.inline.hpp"
75 #include "prims/jvmtiExport.hpp"
76 #include "runtime/atomic.hpp"
77 #include "runtime/flags/flagSetting.hpp"
78 #include "runtime/globals_extension.hpp"
79 #include "runtime/handles.inline.hpp"
80 #include "runtime/java.hpp"
81 #include "runtime/orderAccess.hpp"
82 #include "runtime/timer.hpp"
83 #include "runtime/vmThread.hpp"
84 #include "services/memoryService.hpp"
85 #include "services/runtimeService.hpp"
86 #include "utilities/align.hpp"
87 #include "utilities/stack.inline.hpp"
88 #if INCLUDE_JVMCI
89 #include "jvmci/jvmci.hpp"
90 #endif
91
92 // statics
93 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
94 bool CMSCollector::_full_gc_requested = false;
95 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
96
97 //////////////////////////////////////////////////////////////////
98 // In support of CMS/VM thread synchronization
99 //////////////////////////////////////////////////////////////////
100 // We split use of the CGC_lock into 2 "levels".
101 // The low-level locking is of the usual CGC_lock monitor. We introduce
102 // a higher level "token" (hereafter "CMS token") built on top of the
103 // low level monitor (hereafter "CGC lock").
104 // The token-passing protocol gives priority to the VM thread. The
105 // CMS-lock doesn't provide any fairness guarantees, but clients
106 // should ensure that it is only held for very short, bounded
107 // durations.
108 //
109 // When either of the CMS thread or the VM thread is involved in
110 // collection operations during which it does not want the other
111 // thread to interfere, it obtains the CMS token.
112 //
113 // If either thread tries to get the token while the other has
114 // it, that thread waits. However, if the VM thread and CMS thread
115 // both want the token, then the VM thread gets priority while the
116 // CMS thread waits. This ensures, for instance, that the "concurrent"
117 // phases of the CMS thread's work do not block out the VM thread
118 // for long periods of time as the CMS thread continues to hog
119 // the token. (See bug 4616232).
120 //
121 // The baton-passing functions are, however, controlled by the
122 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
123 // and here the low-level CMS lock, not the high level token,
124 // ensures mutual exclusion.
125 //
126 // Two important conditions that we have to satisfy:
127 // 1. if a thread does a low-level wait on the CMS lock, then it
128 // relinquishes the CMS token if it were holding that token
129 // when it acquired the low-level CMS lock.
130 // 2. any low-level notifications on the low-level lock
131 // should only be sent when a thread has relinquished the token.
132 //
133 // In the absence of either property, we'd have potential deadlock.
134 //
135 // We protect each of the CMS (concurrent and sequential) phases
136 // with the CMS _token_, not the CMS _lock_.
137 //
138 // The only code protected by CMS lock is the token acquisition code
139 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
140 // baton-passing code.
141 //
142 // Unfortunately, i couldn't come up with a good abstraction to factor and
143 // hide the naked CGC_lock manipulation in the baton-passing code
144 // further below. That's something we should try to do. Also, the proof
145 // of correctness of this 2-level locking scheme is far from obvious,
146 // and potentially quite slippery. We have an uneasy suspicion, for instance,
147 // that there may be a theoretical possibility of delay/starvation in the
148 // low-level lock/wait/notify scheme used for the baton-passing because of
149 // potential interference with the priority scheme embodied in the
150 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
151 // invocation further below and marked with "XXX 20011219YSR".
152 // Indeed, as we note elsewhere, this may become yet more slippery
153 // in the presence of multiple CMS and/or multiple VM threads. XXX
154
155 class CMSTokenSync: public StackObj {
156 private:
157 bool _is_cms_thread;
158 public:
159 CMSTokenSync(bool is_cms_thread):
160 _is_cms_thread(is_cms_thread) {
161 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
162 "Incorrect argument to constructor");
163 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
164 }
165
166 ~CMSTokenSync() {
167 assert(_is_cms_thread ?
168 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
169 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
170 "Incorrect state");
171 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
172 }
173 };
174
175 // Convenience class that does a CMSTokenSync, and then acquires
176 // upto three locks.
177 class CMSTokenSyncWithLocks: public CMSTokenSync {
178 private:
179 // Note: locks are acquired in textual declaration order
180 // and released in the opposite order
181 MutexLockerEx _locker1, _locker2, _locker3;
182 public:
183 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
184 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
185 CMSTokenSync(is_cms_thread),
186 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
187 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
188 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
189 { }
190 };
191
192
193 //////////////////////////////////////////////////////////////////
194 // Concurrent Mark-Sweep Generation /////////////////////////////
195 //////////////////////////////////////////////////////////////////
196
197 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
198
199 // This struct contains per-thread things necessary to support parallel
200 // young-gen collection.
201 class CMSParGCThreadState: public CHeapObj<mtGC> {
202 public:
203 CompactibleFreeListSpaceLAB lab;
204 PromotionInfo promo;
205
206 // Constructor.
207 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
208 promo.setSpace(cfls);
209 }
210 };
211
212 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
213 ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct) :
214 CardGeneration(rs, initial_byte_size, ct),
215 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
216 _did_compact(false)
217 {
218 HeapWord* bottom = (HeapWord*) _virtual_space.low();
219 HeapWord* end = (HeapWord*) _virtual_space.high();
220
221 _direct_allocated_words = 0;
222 NOT_PRODUCT(
223 _numObjectsPromoted = 0;
224 _numWordsPromoted = 0;
225 _numObjectsAllocated = 0;
226 _numWordsAllocated = 0;
227 )
228
229 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end));
230 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
231 _cmsSpace->_old_gen = this;
232
233 _gc_stats = new CMSGCStats();
234
235 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
236 // offsets match. The ability to tell free chunks from objects
237 // depends on this property.
238 debug_only(
239 FreeChunk* junk = NULL;
240 assert(UseCompressedClassPointers ||
241 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
242 "Offset of FreeChunk::_prev within FreeChunk must match"
243 " that of OopDesc::_klass within OopDesc");
244 )
245
246 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
247 for (uint i = 0; i < ParallelGCThreads; i++) {
248 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
249 }
250
251 _incremental_collection_failed = false;
252 // The "dilatation_factor" is the expansion that can occur on
253 // account of the fact that the minimum object size in the CMS
254 // generation may be larger than that in, say, a contiguous young
255 // generation.
256 // Ideally, in the calculation below, we'd compute the dilatation
257 // factor as: MinChunkSize/(promoting_gen's min object size)
258 // Since we do not have such a general query interface for the
259 // promoting generation, we'll instead just use the minimum
260 // object size (which today is a header's worth of space);
261 // note that all arithmetic is in units of HeapWords.
262 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
263 assert(_dilatation_factor >= 1.0, "from previous assert");
264 }
265
266
267 // The field "_initiating_occupancy" represents the occupancy percentage
268 // at which we trigger a new collection cycle. Unless explicitly specified
269 // via CMSInitiatingOccupancyFraction (argument "io" below), it
270 // is calculated by:
271 //
272 // Let "f" be MinHeapFreeRatio in
273 //
274 // _initiating_occupancy = 100-f +
275 // f * (CMSTriggerRatio/100)
276 // where CMSTriggerRatio is the argument "tr" below.
277 //
278 // That is, if we assume the heap is at its desired maximum occupancy at the
279 // end of a collection, we let CMSTriggerRatio of the (purported) free
280 // space be allocated before initiating a new collection cycle.
281 //
282 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
283 assert(io <= 100 && tr <= 100, "Check the arguments");
284 if (io >= 0) {
285 _initiating_occupancy = (double)io / 100.0;
286 } else {
287 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
288 (double)(tr * MinHeapFreeRatio) / 100.0)
289 / 100.0;
290 }
291 }
292
293 void ConcurrentMarkSweepGeneration::ref_processor_init() {
294 assert(collector() != NULL, "no collector");
295 collector()->ref_processor_init();
296 }
297
298 void CMSCollector::ref_processor_init() {
299 if (_ref_processor == NULL) {
300 // Allocate and initialize a reference processor
301 _ref_processor =
302 new ReferenceProcessor(&_span_based_discoverer,
303 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
304 ParallelGCThreads, // mt processing degree
305 _cmsGen->refs_discovery_is_mt(), // mt discovery
306 MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
307 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
308 &_is_alive_closure, // closure for liveness info
309 false); // disable adjusting number of processing threads
310 // Initialize the _ref_processor field of CMSGen
311 _cmsGen->set_ref_processor(_ref_processor);
312
313 }
314 }
315
316 AdaptiveSizePolicy* CMSCollector::size_policy() {
317 return CMSHeap::heap()->size_policy();
318 }
319
320 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
321
322 const char* gen_name = "old";
323 GenCollectorPolicy* gcp = CMSHeap::heap()->gen_policy();
324 // Generation Counters - generation 1, 1 subspace
325 _gen_counters = new GenerationCounters(gen_name, 1, 1,
326 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
327
328 _space_counters = new GSpaceCounters(gen_name, 0,
329 _virtual_space.reserved_size(),
330 this, _gen_counters);
331 }
332
333 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
334 _cms_gen(cms_gen)
335 {
336 assert(alpha <= 100, "bad value");
337 _saved_alpha = alpha;
338
339 // Initialize the alphas to the bootstrap value of 100.
340 _gc0_alpha = _cms_alpha = 100;
341
342 _cms_begin_time.update();
343 _cms_end_time.update();
344
345 _gc0_duration = 0.0;
346 _gc0_period = 0.0;
347 _gc0_promoted = 0;
348
349 _cms_duration = 0.0;
350 _cms_period = 0.0;
351 _cms_allocated = 0;
352
353 _cms_used_at_gc0_begin = 0;
354 _cms_used_at_gc0_end = 0;
355 _allow_duty_cycle_reduction = false;
356 _valid_bits = 0;
357 }
358
359 double CMSStats::cms_free_adjustment_factor(size_t free) const {
360 // TBD: CR 6909490
361 return 1.0;
362 }
363
364 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
365 }
366
367 // If promotion failure handling is on use
368 // the padded average size of the promotion for each
369 // young generation collection.
370 double CMSStats::time_until_cms_gen_full() const {
371 size_t cms_free = _cms_gen->cmsSpace()->free();
372 CMSHeap* heap = CMSHeap::heap();
373 size_t expected_promotion = MIN2(heap->young_gen()->capacity(),
374 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
375 if (cms_free > expected_promotion) {
376 // Start a cms collection if there isn't enough space to promote
377 // for the next young collection. Use the padded average as
378 // a safety factor.
379 cms_free -= expected_promotion;
380
381 // Adjust by the safety factor.
382 double cms_free_dbl = (double)cms_free;
383 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
384 // Apply a further correction factor which tries to adjust
385 // for recent occurance of concurrent mode failures.
386 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
387 cms_free_dbl = cms_free_dbl * cms_adjustment;
388
389 log_trace(gc)("CMSStats::time_until_cms_gen_full: cms_free " SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
390 cms_free, expected_promotion);
391 log_trace(gc)(" cms_free_dbl %f cms_consumption_rate %f", cms_free_dbl, cms_consumption_rate() + 1.0);
392 // Add 1 in case the consumption rate goes to zero.
393 return cms_free_dbl / (cms_consumption_rate() + 1.0);
394 }
395 return 0.0;
396 }
397
398 // Compare the duration of the cms collection to the
399 // time remaining before the cms generation is empty.
400 // Note that the time from the start of the cms collection
401 // to the start of the cms sweep (less than the total
402 // duration of the cms collection) can be used. This
403 // has been tried and some applications experienced
404 // promotion failures early in execution. This was
405 // possibly because the averages were not accurate
406 // enough at the beginning.
407 double CMSStats::time_until_cms_start() const {
408 // We add "gc0_period" to the "work" calculation
409 // below because this query is done (mostly) at the
410 // end of a scavenge, so we need to conservatively
411 // account for that much possible delay
412 // in the query so as to avoid concurrent mode failures
413 // due to starting the collection just a wee bit too
414 // late.
415 double work = cms_duration() + gc0_period();
416 double deadline = time_until_cms_gen_full();
417 // If a concurrent mode failure occurred recently, we want to be
418 // more conservative and halve our expected time_until_cms_gen_full()
419 if (work > deadline) {
420 log_develop_trace(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ",
421 cms_duration(), gc0_period(), time_until_cms_gen_full());
422 return 0.0;
423 }
424 return work - deadline;
425 }
426
427 #ifndef PRODUCT
428 void CMSStats::print_on(outputStream *st) const {
429 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
430 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
431 gc0_duration(), gc0_period(), gc0_promoted());
432 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
433 cms_duration(), cms_period(), cms_allocated());
434 st->print(",cms_since_beg=%g,cms_since_end=%g",
435 cms_time_since_begin(), cms_time_since_end());
436 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
437 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
438
439 if (valid()) {
440 st->print(",promo_rate=%g,cms_alloc_rate=%g",
441 promotion_rate(), cms_allocation_rate());
442 st->print(",cms_consumption_rate=%g,time_until_full=%g",
443 cms_consumption_rate(), time_until_cms_gen_full());
444 }
445 st->cr();
446 }
447 #endif // #ifndef PRODUCT
448
449 CMSCollector::CollectorState CMSCollector::_collectorState =
450 CMSCollector::Idling;
451 bool CMSCollector::_foregroundGCIsActive = false;
452 bool CMSCollector::_foregroundGCShouldWait = false;
453
454 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
455 CardTableRS* ct,
456 ConcurrentMarkSweepPolicy* cp):
457 _overflow_list(NULL),
458 _conc_workers(NULL), // may be set later
459 _completed_initialization(false),
460 _collection_count_start(0),
461 _should_unload_classes(CMSClassUnloadingEnabled),
462 _concurrent_cycles_since_last_unload(0),
463 _roots_scanning_options(GenCollectedHeap::SO_None),
464 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
465 _verifying(false),
466 _collector_policy(cp),
467 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
468 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
469 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
470 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
471 _cms_start_registered(false),
472 _cmsGen(cmsGen),
473 // Adjust span to cover old (cms) gen
474 _span(cmsGen->reserved()),
475 _ct(ct),
476 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
477 _modUnionTable((CardTable::card_shift - LogHeapWordSize),
478 -1 /* lock-free */, "No_lock" /* dummy */),
479 _restart_addr(NULL),
480 _ser_pmc_preclean_ovflw(0),
481 _ser_pmc_remark_ovflw(0),
482 _par_pmc_remark_ovflw(0),
483 _ser_kac_preclean_ovflw(0),
484 _ser_kac_ovflw(0),
485 _par_kac_ovflw(0),
486 #ifndef PRODUCT
487 _num_par_pushes(0),
488 #endif
489 _span_based_discoverer(_span),
490 _ref_processor(NULL), // will be set later
491 // Construct the is_alive_closure with _span & markBitMap
492 _is_alive_closure(_span, &_markBitMap),
493 _modUnionClosurePar(&_modUnionTable),
494 _between_prologue_and_epilogue(false),
495 _abort_preclean(false),
496 _start_sampling(false),
497 _stats(cmsGen),
498 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
499 //verify that this lock should be acquired with safepoint check.
500 Monitor::_safepoint_check_sometimes)),
501 _eden_chunk_array(NULL), // may be set in ctor body
502 _eden_chunk_index(0), // -- ditto --
503 _eden_chunk_capacity(0), // -- ditto --
504 _survivor_chunk_array(NULL), // -- ditto --
505 _survivor_chunk_index(0), // -- ditto --
506 _survivor_chunk_capacity(0), // -- ditto --
507 _survivor_plab_array(NULL) // -- ditto --
508 {
509 // Now expand the span and allocate the collection support structures
510 // (MUT, marking bit map etc.) to cover both generations subject to
511 // collection.
512
513 // For use by dirty card to oop closures.
514 _cmsGen->cmsSpace()->set_collector(this);
515
516 // Allocate MUT and marking bit map
517 {
518 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
519 if (!_markBitMap.allocate(_span)) {
520 log_warning(gc)("Failed to allocate CMS Bit Map");
521 return;
522 }
523 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
524 }
525 {
526 _modUnionTable.allocate(_span);
527 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
528 }
529
530 if (!_markStack.allocate(MarkStackSize)) {
531 log_warning(gc)("Failed to allocate CMS Marking Stack");
532 return;
533 }
534
535 // Support for multi-threaded concurrent phases
536 if (CMSConcurrentMTEnabled) {
537 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
538 // just for now
539 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
540 }
541 if (ConcGCThreads > 1) {
542 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
543 ConcGCThreads, true);
544 if (_conc_workers == NULL) {
545 log_warning(gc)("GC/CMS: _conc_workers allocation failure: forcing -CMSConcurrentMTEnabled");
546 CMSConcurrentMTEnabled = false;
547 } else {
548 _conc_workers->initialize_workers();
549 }
550 } else {
551 CMSConcurrentMTEnabled = false;
552 }
553 }
554 if (!CMSConcurrentMTEnabled) {
555 ConcGCThreads = 0;
556 } else {
557 // Turn off CMSCleanOnEnter optimization temporarily for
558 // the MT case where it's not fixed yet; see 6178663.
559 CMSCleanOnEnter = false;
560 }
561 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
562 "Inconsistency");
563 log_debug(gc)("ConcGCThreads: %u", ConcGCThreads);
564 log_debug(gc)("ParallelGCThreads: %u", ParallelGCThreads);
565
566 // Parallel task queues; these are shared for the
567 // concurrent and stop-world phases of CMS, but
568 // are not shared with parallel scavenge (ParNew).
569 {
570 uint i;
571 uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
572
573 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
574 || ParallelRefProcEnabled)
575 && num_queues > 0) {
576 _task_queues = new OopTaskQueueSet(num_queues);
577 if (_task_queues == NULL) {
578 log_warning(gc)("task_queues allocation failure.");
579 return;
580 }
581 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
582 for (i = 0; i < num_queues; i++) {
583 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
584 if (q == NULL) {
585 log_warning(gc)("work_queue allocation failure.");
586 return;
587 }
588 _task_queues->register_queue(i, q);
589 }
590 for (i = 0; i < num_queues; i++) {
591 _task_queues->queue(i)->initialize();
592 }
593 }
594 }
595
596 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
597
598 // Clip CMSBootstrapOccupancy between 0 and 100.
599 _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
600
601 // Now tell CMS generations the identity of their collector
602 ConcurrentMarkSweepGeneration::set_collector(this);
603
604 // Create & start a CMS thread for this CMS collector
605 _cmsThread = ConcurrentMarkSweepThread::start(this);
606 assert(cmsThread() != NULL, "CMS Thread should have been created");
607 assert(cmsThread()->collector() == this,
608 "CMS Thread should refer to this gen");
609 assert(CGC_lock != NULL, "Where's the CGC_lock?");
610
611 // Support for parallelizing young gen rescan
612 CMSHeap* heap = CMSHeap::heap();
613 _young_gen = heap->young_gen();
614 if (heap->supports_inline_contig_alloc()) {
615 _top_addr = heap->top_addr();
616 _end_addr = heap->end_addr();
617 assert(_young_gen != NULL, "no _young_gen");
618 _eden_chunk_index = 0;
619 _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
620 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
621 }
622
623 // Support for parallelizing survivor space rescan
624 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
625 const size_t max_plab_samples =
626 _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
627
628 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
629 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
630 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
631 _survivor_chunk_capacity = max_plab_samples;
632 for (uint i = 0; i < ParallelGCThreads; i++) {
633 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
634 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
635 assert(cur->end() == 0, "Should be 0");
636 assert(cur->array() == vec, "Should be vec");
637 assert(cur->capacity() == max_plab_samples, "Error");
638 }
639 }
640
641 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
642 _gc_counters = new CollectorCounters("CMS full collection pauses", 1);
643 _cgc_counters = new CollectorCounters("CMS concurrent cycle pauses", 2);
644 _completed_initialization = true;
645 _inter_sweep_timer.start(); // start of time
646 }
647
648 const char* ConcurrentMarkSweepGeneration::name() const {
649 return "concurrent mark-sweep generation";
650 }
651 void ConcurrentMarkSweepGeneration::update_counters() {
652 if (UsePerfData) {
653 _space_counters->update_all();
654 _gen_counters->update_all();
655 }
656 }
657
658 // this is an optimized version of update_counters(). it takes the
659 // used value as a parameter rather than computing it.
660 //
661 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
662 if (UsePerfData) {
663 _space_counters->update_used(used);
664 _space_counters->update_capacity();
665 _gen_counters->update_all();
666 }
667 }
668
669 void ConcurrentMarkSweepGeneration::print() const {
670 Generation::print();
671 cmsSpace()->print();
672 }
673
674 #ifndef PRODUCT
675 void ConcurrentMarkSweepGeneration::print_statistics() {
676 cmsSpace()->printFLCensus(0);
677 }
678 #endif
679
680 size_t
681 ConcurrentMarkSweepGeneration::contiguous_available() const {
682 // dld proposes an improvement in precision here. If the committed
683 // part of the space ends in a free block we should add that to
684 // uncommitted size in the calculation below. Will make this
685 // change later, staying with the approximation below for the
686 // time being. -- ysr.
687 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
688 }
689
690 size_t
691 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
692 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
693 }
694
695 size_t ConcurrentMarkSweepGeneration::max_available() const {
696 return free() + _virtual_space.uncommitted_size();
697 }
698
699 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
700 size_t available = max_available();
701 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
702 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
703 log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")",
704 res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes);
705 return res;
706 }
707
708 // At a promotion failure dump information on block layout in heap
709 // (cms old generation).
710 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
711 Log(gc, promotion) log;
712 if (log.is_trace()) {
713 LogStream ls(log.trace());
714 cmsSpace()->dump_at_safepoint_with_locks(collector(), &ls);
715 }
716 }
717
718 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
719 // Clear the promotion information. These pointers can be adjusted
720 // along with all the other pointers into the heap but
721 // compaction is expected to be a rare event with
722 // a heap using cms so don't do it without seeing the need.
723 for (uint i = 0; i < ParallelGCThreads; i++) {
724 _par_gc_thread_states[i]->promo.reset();
725 }
726 }
727
728 void ConcurrentMarkSweepGeneration::compute_new_size() {
729 assert_locked_or_safepoint(Heap_lock);
730
731 // If incremental collection failed, we just want to expand
732 // to the limit.
733 if (incremental_collection_failed()) {
734 clear_incremental_collection_failed();
735 grow_to_reserved();
736 return;
737 }
738
739 // The heap has been compacted but not reset yet.
740 // Any metric such as free() or used() will be incorrect.
741
742 CardGeneration::compute_new_size();
743
744 // Reset again after a possible resizing
745 if (did_compact()) {
746 cmsSpace()->reset_after_compaction();
747 }
748 }
749
750 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
751 assert_locked_or_safepoint(Heap_lock);
752
753 // If incremental collection failed, we just want to expand
754 // to the limit.
755 if (incremental_collection_failed()) {
756 clear_incremental_collection_failed();
757 grow_to_reserved();
758 return;
759 }
760
761 double free_percentage = ((double) free()) / capacity();
762 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
763 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
764
765 // compute expansion delta needed for reaching desired free percentage
766 if (free_percentage < desired_free_percentage) {
767 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
768 assert(desired_capacity >= capacity(), "invalid expansion size");
769 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
770 Log(gc) log;
771 if (log.is_trace()) {
772 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
773 log.trace("From compute_new_size: ");
774 log.trace(" Free fraction %f", free_percentage);
775 log.trace(" Desired free fraction %f", desired_free_percentage);
776 log.trace(" Maximum free fraction %f", maximum_free_percentage);
777 log.trace(" Capacity " SIZE_FORMAT, capacity() / 1000);
778 log.trace(" Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
779 CMSHeap* heap = CMSHeap::heap();
780 size_t young_size = heap->young_gen()->capacity();
781 log.trace(" Young gen size " SIZE_FORMAT, young_size / 1000);
782 log.trace(" unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
783 log.trace(" contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
784 log.trace(" Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
785 }
786 // safe if expansion fails
787 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
788 log.trace(" Expanded free fraction %f", ((double) free()) / capacity());
789 } else {
790 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
791 assert(desired_capacity <= capacity(), "invalid expansion size");
792 size_t shrink_bytes = capacity() - desired_capacity;
793 // Don't shrink unless the delta is greater than the minimum shrink we want
794 if (shrink_bytes >= MinHeapDeltaBytes) {
795 shrink_free_list_by(shrink_bytes);
796 }
797 }
798 }
799
800 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
801 return cmsSpace()->freelistLock();
802 }
803
804 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
805 CMSSynchronousYieldRequest yr;
806 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
807 return have_lock_and_allocate(size, tlab);
808 }
809
810 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
811 bool tlab /* ignored */) {
812 assert_lock_strong(freelistLock());
813 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
814 HeapWord* res = cmsSpace()->allocate(adjustedSize);
815 // Allocate the object live (grey) if the background collector has
816 // started marking. This is necessary because the marker may
817 // have passed this address and consequently this object will
818 // not otherwise be greyed and would be incorrectly swept up.
819 // Note that if this object contains references, the writing
820 // of those references will dirty the card containing this object
821 // allowing the object to be blackened (and its references scanned)
822 // either during a preclean phase or at the final checkpoint.
823 if (res != NULL) {
824 // We may block here with an uninitialized object with
825 // its mark-bit or P-bits not yet set. Such objects need
826 // to be safely navigable by block_start().
827 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
828 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
829 collector()->direct_allocated(res, adjustedSize);
830 _direct_allocated_words += adjustedSize;
831 // allocation counters
832 NOT_PRODUCT(
833 _numObjectsAllocated++;
834 _numWordsAllocated += (int)adjustedSize;
835 )
836 }
837 return res;
838 }
839
840 // In the case of direct allocation by mutators in a generation that
841 // is being concurrently collected, the object must be allocated
842 // live (grey) if the background collector has started marking.
843 // This is necessary because the marker may
844 // have passed this address and consequently this object will
845 // not otherwise be greyed and would be incorrectly swept up.
846 // Note that if this object contains references, the writing
847 // of those references will dirty the card containing this object
848 // allowing the object to be blackened (and its references scanned)
849 // either during a preclean phase or at the final checkpoint.
850 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
851 assert(_markBitMap.covers(start, size), "Out of bounds");
852 if (_collectorState >= Marking) {
853 MutexLockerEx y(_markBitMap.lock(),
854 Mutex::_no_safepoint_check_flag);
855 // [see comments preceding SweepClosure::do_blk() below for details]
856 //
857 // Can the P-bits be deleted now? JJJ
858 //
859 // 1. need to mark the object as live so it isn't collected
860 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
861 // 3. need to mark the end of the object so marking, precleaning or sweeping
862 // can skip over uninitialized or unparsable objects. An allocated
863 // object is considered uninitialized for our purposes as long as
864 // its klass word is NULL. All old gen objects are parsable
865 // as soon as they are initialized.)
866 _markBitMap.mark(start); // object is live
867 _markBitMap.mark(start + 1); // object is potentially uninitialized?
868 _markBitMap.mark(start + size - 1);
869 // mark end of object
870 }
871 // check that oop looks uninitialized
872 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
873 }
874
875 void CMSCollector::promoted(bool par, HeapWord* start,
876 bool is_obj_array, size_t obj_size) {
877 assert(_markBitMap.covers(start), "Out of bounds");
878 // See comment in direct_allocated() about when objects should
879 // be allocated live.
880 if (_collectorState >= Marking) {
881 // we already hold the marking bit map lock, taken in
882 // the prologue
883 if (par) {
884 _markBitMap.par_mark(start);
885 } else {
886 _markBitMap.mark(start);
887 }
888 // We don't need to mark the object as uninitialized (as
889 // in direct_allocated above) because this is being done with the
890 // world stopped and the object will be initialized by the
891 // time the marking, precleaning or sweeping get to look at it.
892 // But see the code for copying objects into the CMS generation,
893 // where we need to ensure that concurrent readers of the
894 // block offset table are able to safely navigate a block that
895 // is in flux from being free to being allocated (and in
896 // transition while being copied into) and subsequently
897 // becoming a bona-fide object when the copy/promotion is complete.
898 assert(SafepointSynchronize::is_at_safepoint(),
899 "expect promotion only at safepoints");
900
901 if (_collectorState < Sweeping) {
902 // Mark the appropriate cards in the modUnionTable, so that
903 // this object gets scanned before the sweep. If this is
904 // not done, CMS generation references in the object might
905 // not get marked.
906 // For the case of arrays, which are otherwise precisely
907 // marked, we need to dirty the entire array, not just its head.
908 if (is_obj_array) {
909 // The [par_]mark_range() method expects mr.end() below to
910 // be aligned to the granularity of a bit's representation
911 // in the heap. In the case of the MUT below, that's a
912 // card size.
913 MemRegion mr(start,
914 align_up(start + obj_size,
915 CardTable::card_size /* bytes */));
916 if (par) {
917 _modUnionTable.par_mark_range(mr);
918 } else {
919 _modUnionTable.mark_range(mr);
920 }
921 } else { // not an obj array; we can just mark the head
922 if (par) {
923 _modUnionTable.par_mark(start);
924 } else {
925 _modUnionTable.mark(start);
926 }
927 }
928 }
929 }
930 }
931
932 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
933 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
934 // allocate, copy and if necessary update promoinfo --
935 // delegate to underlying space.
936 assert_lock_strong(freelistLock());
937
938 #ifndef PRODUCT
939 if (CMSHeap::heap()->promotion_should_fail()) {
940 return NULL;
941 }
942 #endif // #ifndef PRODUCT
943
944 oop res = _cmsSpace->promote(obj, obj_size);
945 if (res == NULL) {
946 // expand and retry
947 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
948 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
949 // Since this is the old generation, we don't try to promote
950 // into a more senior generation.
951 res = _cmsSpace->promote(obj, obj_size);
952 }
953 if (res != NULL) {
954 // See comment in allocate() about when objects should
955 // be allocated live.
956 assert(oopDesc::is_oop(obj), "Will dereference klass pointer below");
957 collector()->promoted(false, // Not parallel
958 (HeapWord*)res, obj->is_objArray(), obj_size);
959 // promotion counters
960 NOT_PRODUCT(
961 _numObjectsPromoted++;
962 _numWordsPromoted +=
963 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
964 )
965 }
966 return res;
967 }
968
969
970 // IMPORTANT: Notes on object size recognition in CMS.
971 // ---------------------------------------------------
972 // A block of storage in the CMS generation is always in
973 // one of three states. A free block (FREE), an allocated
974 // object (OBJECT) whose size() method reports the correct size,
975 // and an intermediate state (TRANSIENT) in which its size cannot
976 // be accurately determined.
977 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
978 // -----------------------------------------------------
979 // FREE: klass_word & 1 == 1; mark_word holds block size
980 //
981 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
982 // obj->size() computes correct size
983 //
984 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
985 //
986 // STATE IDENTIFICATION: (64 bit+COOPS)
987 // ------------------------------------
988 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
989 //
990 // OBJECT: klass_word installed; klass_word != 0;
991 // obj->size() computes correct size
992 //
993 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
994 //
995 //
996 // STATE TRANSITION DIAGRAM
997 //
998 // mut / parnew mut / parnew
999 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1000 // ^ |
1001 // |------------------------ DEAD <------------------------------------|
1002 // sweep mut
1003 //
1004 // While a block is in TRANSIENT state its size cannot be determined
1005 // so readers will either need to come back later or stall until
1006 // the size can be determined. Note that for the case of direct
1007 // allocation, P-bits, when available, may be used to determine the
1008 // size of an object that may not yet have been initialized.
1009
1010 // Things to support parallel young-gen collection.
1011 oop
1012 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1013 oop old, markOop m,
1014 size_t word_sz) {
1015 #ifndef PRODUCT
1016 if (CMSHeap::heap()->promotion_should_fail()) {
1017 return NULL;
1018 }
1019 #endif // #ifndef PRODUCT
1020
1021 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1022 PromotionInfo* promoInfo = &ps->promo;
1023 // if we are tracking promotions, then first ensure space for
1024 // promotion (including spooling space for saving header if necessary).
1025 // then allocate and copy, then track promoted info if needed.
1026 // When tracking (see PromotionInfo::track()), the mark word may
1027 // be displaced and in this case restoration of the mark word
1028 // occurs in the (oop_since_save_marks_)iterate phase.
1029 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1030 // Out of space for allocating spooling buffers;
1031 // try expanding and allocating spooling buffers.
1032 if (!expand_and_ensure_spooling_space(promoInfo)) {
1033 return NULL;
1034 }
1035 }
1036 assert(!promoInfo->tracking() || promoInfo->has_spooling_space(), "Control point invariant");
1037 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1038 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1039 if (obj_ptr == NULL) {
1040 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1041 if (obj_ptr == NULL) {
1042 return NULL;
1043 }
1044 }
1045 oop obj = oop(obj_ptr);
1046 OrderAccess::storestore();
1047 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1048 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1049 // IMPORTANT: See note on object initialization for CMS above.
1050 // Otherwise, copy the object. Here we must be careful to insert the
1051 // klass pointer last, since this marks the block as an allocated object.
1052 // Except with compressed oops it's the mark word.
1053 HeapWord* old_ptr = (HeapWord*)old;
1054 // Restore the mark word copied above.
1055 obj->set_mark_raw(m);
1056 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1057 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1058 OrderAccess::storestore();
1059
1060 if (UseCompressedClassPointers) {
1061 // Copy gap missed by (aligned) header size calculation below
1062 obj->set_klass_gap(old->klass_gap());
1063 }
1064 if (word_sz > (size_t)oopDesc::header_size()) {
1065 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1066 obj_ptr + oopDesc::header_size(),
1067 word_sz - oopDesc::header_size());
1068 }
1069
1070 // Now we can track the promoted object, if necessary. We take care
1071 // to delay the transition from uninitialized to full object
1072 // (i.e., insertion of klass pointer) until after, so that it
1073 // atomically becomes a promoted object.
1074 if (promoInfo->tracking()) {
1075 promoInfo->track((PromotedObject*)obj, old->klass());
1076 }
1077 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1078 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1079 assert(oopDesc::is_oop(old), "Will use and dereference old klass ptr below");
1080
1081 // Finally, install the klass pointer (this should be volatile).
1082 OrderAccess::storestore();
1083 obj->set_klass(old->klass());
1084 // We should now be able to calculate the right size for this object
1085 assert(oopDesc::is_oop(obj) && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1086
1087 collector()->promoted(true, // parallel
1088 obj_ptr, old->is_objArray(), word_sz);
1089
1090 NOT_PRODUCT(
1091 Atomic::inc(&_numObjectsPromoted);
1092 Atomic::add(alloc_sz, &_numWordsPromoted);
1093 )
1094
1095 return obj;
1096 }
1097
1098 void
1099 ConcurrentMarkSweepGeneration::
1100 par_promote_alloc_done(int thread_num) {
1101 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1102 ps->lab.retire(thread_num);
1103 }
1104
1105 void
1106 ConcurrentMarkSweepGeneration::
1107 par_oop_since_save_marks_iterate_done(int thread_num) {
1108 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1109 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1110 ps->promo.promoted_oops_iterate(dummy_cl);
1111
1112 // Because card-scanning has been completed, subsequent phases
1113 // (e.g., reference processing) will not need to recognize which
1114 // objects have been promoted during this GC. So, we can now disable
1115 // promotion tracking.
1116 ps->promo.stopTrackingPromotions();
1117 }
1118
1119 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1120 size_t size,
1121 bool tlab)
1122 {
1123 // We allow a STW collection only if a full
1124 // collection was requested.
1125 return full || should_allocate(size, tlab); // FIX ME !!!
1126 // This and promotion failure handling are connected at the
1127 // hip and should be fixed by untying them.
1128 }
1129
1130 bool CMSCollector::shouldConcurrentCollect() {
1131 LogTarget(Trace, gc) log;
1132
1133 if (_full_gc_requested) {
1134 log.print("CMSCollector: collect because of explicit gc request (or GCLocker)");
1135 return true;
1136 }
1137
1138 FreelistLocker x(this);
1139 // ------------------------------------------------------------------
1140 // Print out lots of information which affects the initiation of
1141 // a collection.
1142 if (log.is_enabled() && stats().valid()) {
1143 log.print("CMSCollector shouldConcurrentCollect: ");
1144
1145 LogStream out(log);
1146 stats().print_on(&out);
1147
1148 log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full());
1149 log.print("free=" SIZE_FORMAT, _cmsGen->free());
1150 log.print("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available());
1151 log.print("promotion_rate=%g", stats().promotion_rate());
1152 log.print("cms_allocation_rate=%g", stats().cms_allocation_rate());
1153 log.print("occupancy=%3.7f", _cmsGen->occupancy());
1154 log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1155 log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1156 log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1157 log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect());
1158 }
1159 // ------------------------------------------------------------------
1160
1161 // If the estimated time to complete a cms collection (cms_duration())
1162 // is less than the estimated time remaining until the cms generation
1163 // is full, start a collection.
1164 if (!UseCMSInitiatingOccupancyOnly) {
1165 if (stats().valid()) {
1166 if (stats().time_until_cms_start() == 0.0) {
1167 return true;
1168 }
1169 } else {
1170 // We want to conservatively collect somewhat early in order
1171 // to try and "bootstrap" our CMS/promotion statistics;
1172 // this branch will not fire after the first successful CMS
1173 // collection because the stats should then be valid.
1174 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1175 log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f",
1176 _cmsGen->occupancy(), _bootstrap_occupancy);
1177 return true;
1178 }
1179 }
1180 }
1181
1182 // Otherwise, we start a collection cycle if
1183 // old gen want a collection cycle started. Each may use
1184 // an appropriate criterion for making this decision.
1185 // XXX We need to make sure that the gen expansion
1186 // criterion dovetails well with this. XXX NEED TO FIX THIS
1187 if (_cmsGen->should_concurrent_collect()) {
1188 log.print("CMS old gen initiated");
1189 return true;
1190 }
1191
1192 // We start a collection if we believe an incremental collection may fail;
1193 // this is not likely to be productive in practice because it's probably too
1194 // late anyway.
1195 CMSHeap* heap = CMSHeap::heap();
1196 if (heap->incremental_collection_will_fail(true /* consult_young */)) {
1197 log.print("CMSCollector: collect because incremental collection will fail ");
1198 return true;
1199 }
1200
1201 if (MetaspaceGC::should_concurrent_collect()) {
1202 log.print("CMSCollector: collect for metadata allocation ");
1203 return true;
1204 }
1205
1206 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1207 if (CMSTriggerInterval >= 0) {
1208 if (CMSTriggerInterval == 0) {
1209 // Trigger always
1210 return true;
1211 }
1212
1213 // Check the CMS time since begin (we do not check the stats validity
1214 // as we want to be able to trigger the first CMS cycle as well)
1215 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1216 if (stats().valid()) {
1217 log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1218 stats().cms_time_since_begin());
1219 } else {
1220 log.print("CMSCollector: collect because of trigger interval (first collection)");
1221 }
1222 return true;
1223 }
1224 }
1225
1226 return false;
1227 }
1228
1229 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1230
1231 // Clear _expansion_cause fields of constituent generations
1232 void CMSCollector::clear_expansion_cause() {
1233 _cmsGen->clear_expansion_cause();
1234 }
1235
1236 // We should be conservative in starting a collection cycle. To
1237 // start too eagerly runs the risk of collecting too often in the
1238 // extreme. To collect too rarely falls back on full collections,
1239 // which works, even if not optimum in terms of concurrent work.
1240 // As a work around for too eagerly collecting, use the flag
1241 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1242 // giving the user an easily understandable way of controlling the
1243 // collections.
1244 // We want to start a new collection cycle if any of the following
1245 // conditions hold:
1246 // . our current occupancy exceeds the configured initiating occupancy
1247 // for this generation, or
1248 // . we recently needed to expand this space and have not, since that
1249 // expansion, done a collection of this generation, or
1250 // . the underlying space believes that it may be a good idea to initiate
1251 // a concurrent collection (this may be based on criteria such as the
1252 // following: the space uses linear allocation and linear allocation is
1253 // going to fail, or there is believed to be excessive fragmentation in
1254 // the generation, etc... or ...
1255 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1256 // the case of the old generation; see CR 6543076):
1257 // we may be approaching a point at which allocation requests may fail because
1258 // we will be out of sufficient free space given allocation rate estimates.]
1259 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1260
1261 assert_lock_strong(freelistLock());
1262 if (occupancy() > initiating_occupancy()) {
1263 log_trace(gc)(" %s: collect because of occupancy %f / %f ",
1264 short_name(), occupancy(), initiating_occupancy());
1265 return true;
1266 }
1267 if (UseCMSInitiatingOccupancyOnly) {
1268 return false;
1269 }
1270 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1271 log_trace(gc)(" %s: collect because expanded for allocation ", short_name());
1272 return true;
1273 }
1274 return false;
1275 }
1276
1277 void ConcurrentMarkSweepGeneration::collect(bool full,
1278 bool clear_all_soft_refs,
1279 size_t size,
1280 bool tlab)
1281 {
1282 collector()->collect(full, clear_all_soft_refs, size, tlab);
1283 }
1284
1285 void CMSCollector::collect(bool full,
1286 bool clear_all_soft_refs,
1287 size_t size,
1288 bool tlab)
1289 {
1290 // The following "if" branch is present for defensive reasons.
1291 // In the current uses of this interface, it can be replaced with:
1292 // assert(!GCLocker.is_active(), "Can't be called otherwise");
1293 // But I am not placing that assert here to allow future
1294 // generality in invoking this interface.
1295 if (GCLocker::is_active()) {
1296 // A consistency test for GCLocker
1297 assert(GCLocker::needs_gc(), "Should have been set already");
1298 // Skip this foreground collection, instead
1299 // expanding the heap if necessary.
1300 // Need the free list locks for the call to free() in compute_new_size()
1301 compute_new_size();
1302 return;
1303 }
1304 acquire_control_and_collect(full, clear_all_soft_refs);
1305 }
1306
1307 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1308 CMSHeap* heap = CMSHeap::heap();
1309 unsigned int gc_count = heap->total_full_collections();
1310 if (gc_count == full_gc_count) {
1311 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1312 _full_gc_requested = true;
1313 _full_gc_cause = cause;
1314 CGC_lock->notify(); // nudge CMS thread
1315 } else {
1316 assert(gc_count > full_gc_count, "Error: causal loop");
1317 }
1318 }
1319
1320 bool CMSCollector::is_external_interruption() {
1321 GCCause::Cause cause = CMSHeap::heap()->gc_cause();
1322 return GCCause::is_user_requested_gc(cause) ||
1323 GCCause::is_serviceability_requested_gc(cause);
1324 }
1325
1326 void CMSCollector::report_concurrent_mode_interruption() {
1327 if (is_external_interruption()) {
1328 log_debug(gc)("Concurrent mode interrupted");
1329 } else {
1330 log_debug(gc)("Concurrent mode failure");
1331 _gc_tracer_cm->report_concurrent_mode_failure();
1332 }
1333 }
1334
1335
1336 // The foreground and background collectors need to coordinate in order
1337 // to make sure that they do not mutually interfere with CMS collections.
1338 // When a background collection is active,
1339 // the foreground collector may need to take over (preempt) and
1340 // synchronously complete an ongoing collection. Depending on the
1341 // frequency of the background collections and the heap usage
1342 // of the application, this preemption can be seldom or frequent.
1343 // There are only certain
1344 // points in the background collection that the "collection-baton"
1345 // can be passed to the foreground collector.
1346 //
1347 // The foreground collector will wait for the baton before
1348 // starting any part of the collection. The foreground collector
1349 // will only wait at one location.
1350 //
1351 // The background collector will yield the baton before starting a new
1352 // phase of the collection (e.g., before initial marking, marking from roots,
1353 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1354 // of the loop which switches the phases. The background collector does some
1355 // of the phases (initial mark, final re-mark) with the world stopped.
1356 // Because of locking involved in stopping the world,
1357 // the foreground collector should not block waiting for the background
1358 // collector when it is doing a stop-the-world phase. The background
1359 // collector will yield the baton at an additional point just before
1360 // it enters a stop-the-world phase. Once the world is stopped, the
1361 // background collector checks the phase of the collection. If the
1362 // phase has not changed, it proceeds with the collection. If the
1363 // phase has changed, it skips that phase of the collection. See
1364 // the comments on the use of the Heap_lock in collect_in_background().
1365 //
1366 // Variable used in baton passing.
1367 // _foregroundGCIsActive - Set to true by the foreground collector when
1368 // it wants the baton. The foreground clears it when it has finished
1369 // the collection.
1370 // _foregroundGCShouldWait - Set to true by the background collector
1371 // when it is running. The foreground collector waits while
1372 // _foregroundGCShouldWait is true.
1373 // CGC_lock - monitor used to protect access to the above variables
1374 // and to notify the foreground and background collectors.
1375 // _collectorState - current state of the CMS collection.
1376 //
1377 // The foreground collector
1378 // acquires the CGC_lock
1379 // sets _foregroundGCIsActive
1380 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1381 // various locks acquired in preparation for the collection
1382 // are released so as not to block the background collector
1383 // that is in the midst of a collection
1384 // proceeds with the collection
1385 // clears _foregroundGCIsActive
1386 // returns
1387 //
1388 // The background collector in a loop iterating on the phases of the
1389 // collection
1390 // acquires the CGC_lock
1391 // sets _foregroundGCShouldWait
1392 // if _foregroundGCIsActive is set
1393 // clears _foregroundGCShouldWait, notifies _CGC_lock
1394 // waits on _CGC_lock for _foregroundGCIsActive to become false
1395 // and exits the loop.
1396 // otherwise
1397 // proceed with that phase of the collection
1398 // if the phase is a stop-the-world phase,
1399 // yield the baton once more just before enqueueing
1400 // the stop-world CMS operation (executed by the VM thread).
1401 // returns after all phases of the collection are done
1402 //
1403
1404 void CMSCollector::acquire_control_and_collect(bool full,
1405 bool clear_all_soft_refs) {
1406 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1407 assert(!Thread::current()->is_ConcurrentGC_thread(),
1408 "shouldn't try to acquire control from self!");
1409
1410 // Start the protocol for acquiring control of the
1411 // collection from the background collector (aka CMS thread).
1412 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1413 "VM thread should have CMS token");
1414 // Remember the possibly interrupted state of an ongoing
1415 // concurrent collection
1416 CollectorState first_state = _collectorState;
1417
1418 // Signal to a possibly ongoing concurrent collection that
1419 // we want to do a foreground collection.
1420 _foregroundGCIsActive = true;
1421
1422 // release locks and wait for a notify from the background collector
1423 // releasing the locks in only necessary for phases which
1424 // do yields to improve the granularity of the collection.
1425 assert_lock_strong(bitMapLock());
1426 // We need to lock the Free list lock for the space that we are
1427 // currently collecting.
1428 assert(haveFreelistLocks(), "Must be holding free list locks");
1429 bitMapLock()->unlock();
1430 releaseFreelistLocks();
1431 {
1432 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1433 if (_foregroundGCShouldWait) {
1434 // We are going to be waiting for action for the CMS thread;
1435 // it had better not be gone (for instance at shutdown)!
1436 assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(),
1437 "CMS thread must be running");
1438 // Wait here until the background collector gives us the go-ahead
1439 ConcurrentMarkSweepThread::clear_CMS_flag(
1440 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1441 // Get a possibly blocked CMS thread going:
1442 // Note that we set _foregroundGCIsActive true above,
1443 // without protection of the CGC_lock.
1444 CGC_lock->notify();
1445 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1446 "Possible deadlock");
1447 while (_foregroundGCShouldWait) {
1448 // wait for notification
1449 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1450 // Possibility of delay/starvation here, since CMS token does
1451 // not know to give priority to VM thread? Actually, i think
1452 // there wouldn't be any delay/starvation, but the proof of
1453 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1454 }
1455 ConcurrentMarkSweepThread::set_CMS_flag(
1456 ConcurrentMarkSweepThread::CMS_vm_has_token);
1457 }
1458 }
1459 // The CMS_token is already held. Get back the other locks.
1460 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1461 "VM thread should have CMS token");
1462 getFreelistLocks();
1463 bitMapLock()->lock_without_safepoint_check();
1464 log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d",
1465 p2i(Thread::current()), first_state);
1466 log_debug(gc, state)(" gets control with state %d", _collectorState);
1467
1468 // Inform cms gen if this was due to partial collection failing.
1469 // The CMS gen may use this fact to determine its expansion policy.
1470 CMSHeap* heap = CMSHeap::heap();
1471 if (heap->incremental_collection_will_fail(false /* don't consult_young */)) {
1472 assert(!_cmsGen->incremental_collection_failed(),
1473 "Should have been noticed, reacted to and cleared");
1474 _cmsGen->set_incremental_collection_failed();
1475 }
1476
1477 if (first_state > Idling) {
1478 report_concurrent_mode_interruption();
1479 }
1480
1481 set_did_compact(true);
1482
1483 // If the collection is being acquired from the background
1484 // collector, there may be references on the discovered
1485 // references lists. Abandon those references, since some
1486 // of them may have become unreachable after concurrent
1487 // discovery; the STW compacting collector will redo discovery
1488 // more precisely, without being subject to floating garbage.
1489 // Leaving otherwise unreachable references in the discovered
1490 // lists would require special handling.
1491 ref_processor()->disable_discovery();
1492 ref_processor()->abandon_partial_discovery();
1493 ref_processor()->verify_no_references_recorded();
1494
1495 if (first_state > Idling) {
1496 save_heap_summary();
1497 }
1498
1499 do_compaction_work(clear_all_soft_refs);
1500
1501 // Has the GC time limit been exceeded?
1502 size_t max_eden_size = _young_gen->max_eden_size();
1503 GCCause::Cause gc_cause = heap->gc_cause();
1504 size_policy()->check_gc_overhead_limit(_young_gen->eden()->used(),
1505 _cmsGen->max_capacity(),
1506 max_eden_size,
1507 full,
1508 gc_cause,
1509 heap->soft_ref_policy());
1510
1511 // Reset the expansion cause, now that we just completed
1512 // a collection cycle.
1513 clear_expansion_cause();
1514 _foregroundGCIsActive = false;
1515 return;
1516 }
1517
1518 // Resize the tenured generation
1519 // after obtaining the free list locks for the
1520 // two generations.
1521 void CMSCollector::compute_new_size() {
1522 assert_locked_or_safepoint(Heap_lock);
1523 FreelistLocker z(this);
1524 MetaspaceGC::compute_new_size();
1525 _cmsGen->compute_new_size_free_list();
1526 }
1527
1528 // A work method used by the foreground collector to do
1529 // a mark-sweep-compact.
1530 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1531 CMSHeap* heap = CMSHeap::heap();
1532
1533 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1534 gc_timer->register_gc_start();
1535
1536 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1537 gc_tracer->report_gc_start(heap->gc_cause(), gc_timer->gc_start());
1538
1539 heap->pre_full_gc_dump(gc_timer);
1540
1541 GCTraceTime(Trace, gc, phases) t("CMS:MSC");
1542
1543 // Temporarily widen the span of the weak reference processing to
1544 // the entire heap.
1545 MemRegion new_span(CMSHeap::heap()->reserved_region());
1546 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1547 // Temporarily, clear the "is_alive_non_header" field of the
1548 // reference processor.
1549 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1550 // Temporarily make reference _processing_ single threaded (non-MT).
1551 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1552 // Temporarily make refs discovery atomic
1553 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1554 // Temporarily make reference _discovery_ single threaded (non-MT)
1555 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1556
1557 ref_processor()->set_enqueuing_is_done(false);
1558 ref_processor()->enable_discovery();
1559 ref_processor()->setup_policy(clear_all_soft_refs);
1560 // If an asynchronous collection finishes, the _modUnionTable is
1561 // all clear. If we are assuming the collection from an asynchronous
1562 // collection, clear the _modUnionTable.
1563 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1564 "_modUnionTable should be clear if the baton was not passed");
1565 _modUnionTable.clear_all();
1566 assert(_collectorState != Idling || _ct->cld_rem_set()->mod_union_is_clear(),
1567 "mod union for klasses should be clear if the baton was passed");
1568 _ct->cld_rem_set()->clear_mod_union();
1569
1570
1571 // We must adjust the allocation statistics being maintained
1572 // in the free list space. We do so by reading and clearing
1573 // the sweep timer and updating the block flux rate estimates below.
1574 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1575 if (_inter_sweep_timer.is_active()) {
1576 _inter_sweep_timer.stop();
1577 // Note that we do not use this sample to update the _inter_sweep_estimate.
1578 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1579 _inter_sweep_estimate.padded_average(),
1580 _intra_sweep_estimate.padded_average());
1581 }
1582
1583 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1584 #ifdef ASSERT
1585 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1586 size_t free_size = cms_space->free();
1587 assert(free_size ==
1588 pointer_delta(cms_space->end(), cms_space->compaction_top())
1589 * HeapWordSize,
1590 "All the free space should be compacted into one chunk at top");
1591 assert(cms_space->dictionary()->total_chunk_size(
1592 debug_only(cms_space->freelistLock())) == 0 ||
1593 cms_space->totalSizeInIndexedFreeLists() == 0,
1594 "All the free space should be in a single chunk");
1595 size_t num = cms_space->totalCount();
1596 assert((free_size == 0 && num == 0) ||
1597 (free_size > 0 && (num == 1 || num == 2)),
1598 "There should be at most 2 free chunks after compaction");
1599 #endif // ASSERT
1600 _collectorState = Resetting;
1601 assert(_restart_addr == NULL,
1602 "Should have been NULL'd before baton was passed");
1603 reset_stw();
1604 _cmsGen->reset_after_compaction();
1605 _concurrent_cycles_since_last_unload = 0;
1606
1607 // Clear any data recorded in the PLAB chunk arrays.
1608 if (_survivor_plab_array != NULL) {
1609 reset_survivor_plab_arrays();
1610 }
1611
1612 // Adjust the per-size allocation stats for the next epoch.
1613 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1614 // Restart the "inter sweep timer" for the next epoch.
1615 _inter_sweep_timer.reset();
1616 _inter_sweep_timer.start();
1617
1618 // No longer a need to do a concurrent collection for Metaspace.
1619 MetaspaceGC::set_should_concurrent_collect(false);
1620
1621 heap->post_full_gc_dump(gc_timer);
1622
1623 gc_timer->register_gc_end();
1624
1625 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1626
1627 // For a mark-sweep-compact, compute_new_size() will be called
1628 // in the heap's do_collection() method.
1629 }
1630
1631 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1632 Log(gc, heap) log;
1633 if (!log.is_trace()) {
1634 return;
1635 }
1636
1637 ContiguousSpace* eden_space = _young_gen->eden();
1638 ContiguousSpace* from_space = _young_gen->from();
1639 ContiguousSpace* to_space = _young_gen->to();
1640 // Eden
1641 if (_eden_chunk_array != NULL) {
1642 log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1643 p2i(eden_space->bottom()), p2i(eden_space->top()),
1644 p2i(eden_space->end()), eden_space->capacity());
1645 log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT,
1646 _eden_chunk_index, _eden_chunk_capacity);
1647 for (size_t i = 0; i < _eden_chunk_index; i++) {
1648 log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i]));
1649 }
1650 }
1651 // Survivor
1652 if (_survivor_chunk_array != NULL) {
1653 log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1654 p2i(from_space->bottom()), p2i(from_space->top()),
1655 p2i(from_space->end()), from_space->capacity());
1656 log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT,
1657 _survivor_chunk_index, _survivor_chunk_capacity);
1658 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1659 log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i]));
1660 }
1661 }
1662 }
1663
1664 void CMSCollector::getFreelistLocks() const {
1665 // Get locks for all free lists in all generations that this
1666 // collector is responsible for
1667 _cmsGen->freelistLock()->lock_without_safepoint_check();
1668 }
1669
1670 void CMSCollector::releaseFreelistLocks() const {
1671 // Release locks for all free lists in all generations that this
1672 // collector is responsible for
1673 _cmsGen->freelistLock()->unlock();
1674 }
1675
1676 bool CMSCollector::haveFreelistLocks() const {
1677 // Check locks for all free lists in all generations that this
1678 // collector is responsible for
1679 assert_lock_strong(_cmsGen->freelistLock());
1680 PRODUCT_ONLY(ShouldNotReachHere());
1681 return true;
1682 }
1683
1684 // A utility class that is used by the CMS collector to
1685 // temporarily "release" the foreground collector from its
1686 // usual obligation to wait for the background collector to
1687 // complete an ongoing phase before proceeding.
1688 class ReleaseForegroundGC: public StackObj {
1689 private:
1690 CMSCollector* _c;
1691 public:
1692 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1693 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1694 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1695 // allow a potentially blocked foreground collector to proceed
1696 _c->_foregroundGCShouldWait = false;
1697 if (_c->_foregroundGCIsActive) {
1698 CGC_lock->notify();
1699 }
1700 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1701 "Possible deadlock");
1702 }
1703
1704 ~ReleaseForegroundGC() {
1705 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1706 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1707 _c->_foregroundGCShouldWait = true;
1708 }
1709 };
1710
1711 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1712 assert(Thread::current()->is_ConcurrentGC_thread(),
1713 "A CMS asynchronous collection is only allowed on a CMS thread.");
1714
1715 CMSHeap* heap = CMSHeap::heap();
1716 {
1717 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1718 MutexLockerEx hl(Heap_lock, safepoint_check);
1719 FreelistLocker fll(this);
1720 MutexLockerEx x(CGC_lock, safepoint_check);
1721 if (_foregroundGCIsActive) {
1722 // The foreground collector is. Skip this
1723 // background collection.
1724 assert(!_foregroundGCShouldWait, "Should be clear");
1725 return;
1726 } else {
1727 assert(_collectorState == Idling, "Should be idling before start.");
1728 _collectorState = InitialMarking;
1729 register_gc_start(cause);
1730 // Reset the expansion cause, now that we are about to begin
1731 // a new cycle.
1732 clear_expansion_cause();
1733
1734 // Clear the MetaspaceGC flag since a concurrent collection
1735 // is starting but also clear it after the collection.
1736 MetaspaceGC::set_should_concurrent_collect(false);
1737 }
1738 // Decide if we want to enable class unloading as part of the
1739 // ensuing concurrent GC cycle.
1740 update_should_unload_classes();
1741 _full_gc_requested = false; // acks all outstanding full gc requests
1742 _full_gc_cause = GCCause::_no_gc;
1743 // Signal that we are about to start a collection
1744 heap->increment_total_full_collections(); // ... starting a collection cycle
1745 _collection_count_start = heap->total_full_collections();
1746 }
1747
1748 size_t prev_used = _cmsGen->used();
1749
1750 // The change of the collection state is normally done at this level;
1751 // the exceptions are phases that are executed while the world is
1752 // stopped. For those phases the change of state is done while the
1753 // world is stopped. For baton passing purposes this allows the
1754 // background collector to finish the phase and change state atomically.
1755 // The foreground collector cannot wait on a phase that is done
1756 // while the world is stopped because the foreground collector already
1757 // has the world stopped and would deadlock.
1758 while (_collectorState != Idling) {
1759 log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d",
1760 p2i(Thread::current()), _collectorState);
1761 // The foreground collector
1762 // holds the Heap_lock throughout its collection.
1763 // holds the CMS token (but not the lock)
1764 // except while it is waiting for the background collector to yield.
1765 //
1766 // The foreground collector should be blocked (not for long)
1767 // if the background collector is about to start a phase
1768 // executed with world stopped. If the background
1769 // collector has already started such a phase, the
1770 // foreground collector is blocked waiting for the
1771 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1772 // are executed in the VM thread.
1773 //
1774 // The locking order is
1775 // PendingListLock (PLL) -- if applicable (FinalMarking)
1776 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1777 // CMS token (claimed in
1778 // stop_world_and_do() -->
1779 // safepoint_synchronize() -->
1780 // CMSThread::synchronize())
1781
1782 {
1783 // Check if the FG collector wants us to yield.
1784 CMSTokenSync x(true); // is cms thread
1785 if (waitForForegroundGC()) {
1786 // We yielded to a foreground GC, nothing more to be
1787 // done this round.
1788 assert(_foregroundGCShouldWait == false, "We set it to false in "
1789 "waitForForegroundGC()");
1790 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1791 p2i(Thread::current()), _collectorState);
1792 return;
1793 } else {
1794 // The background collector can run but check to see if the
1795 // foreground collector has done a collection while the
1796 // background collector was waiting to get the CGC_lock
1797 // above. If yes, break so that _foregroundGCShouldWait
1798 // is cleared before returning.
1799 if (_collectorState == Idling) {
1800 break;
1801 }
1802 }
1803 }
1804
1805 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1806 "should be waiting");
1807
1808 switch (_collectorState) {
1809 case InitialMarking:
1810 {
1811 ReleaseForegroundGC x(this);
1812 stats().record_cms_begin();
1813 VM_CMS_Initial_Mark initial_mark_op(this);
1814 VMThread::execute(&initial_mark_op);
1815 }
1816 // The collector state may be any legal state at this point
1817 // since the background collector may have yielded to the
1818 // foreground collector.
1819 break;
1820 case Marking:
1821 // initial marking in checkpointRootsInitialWork has been completed
1822 if (markFromRoots()) { // we were successful
1823 assert(_collectorState == Precleaning, "Collector state should "
1824 "have changed");
1825 } else {
1826 assert(_foregroundGCIsActive, "Internal state inconsistency");
1827 }
1828 break;
1829 case Precleaning:
1830 // marking from roots in markFromRoots has been completed
1831 preclean();
1832 assert(_collectorState == AbortablePreclean ||
1833 _collectorState == FinalMarking,
1834 "Collector state should have changed");
1835 break;
1836 case AbortablePreclean:
1837 abortable_preclean();
1838 assert(_collectorState == FinalMarking, "Collector state should "
1839 "have changed");
1840 break;
1841 case FinalMarking:
1842 {
1843 ReleaseForegroundGC x(this);
1844
1845 VM_CMS_Final_Remark final_remark_op(this);
1846 VMThread::execute(&final_remark_op);
1847 }
1848 assert(_foregroundGCShouldWait, "block post-condition");
1849 break;
1850 case Sweeping:
1851 // final marking in checkpointRootsFinal has been completed
1852 sweep();
1853 assert(_collectorState == Resizing, "Collector state change "
1854 "to Resizing must be done under the free_list_lock");
1855
1856 case Resizing: {
1857 // Sweeping has been completed...
1858 // At this point the background collection has completed.
1859 // Don't move the call to compute_new_size() down
1860 // into code that might be executed if the background
1861 // collection was preempted.
1862 {
1863 ReleaseForegroundGC x(this); // unblock FG collection
1864 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1865 CMSTokenSync z(true); // not strictly needed.
1866 if (_collectorState == Resizing) {
1867 compute_new_size();
1868 save_heap_summary();
1869 _collectorState = Resetting;
1870 } else {
1871 assert(_collectorState == Idling, "The state should only change"
1872 " because the foreground collector has finished the collection");
1873 }
1874 }
1875 break;
1876 }
1877 case Resetting:
1878 // CMS heap resizing has been completed
1879 reset_concurrent();
1880 assert(_collectorState == Idling, "Collector state should "
1881 "have changed");
1882
1883 MetaspaceGC::set_should_concurrent_collect(false);
1884
1885 stats().record_cms_end();
1886 // Don't move the concurrent_phases_end() and compute_new_size()
1887 // calls to here because a preempted background collection
1888 // has it's state set to "Resetting".
1889 break;
1890 case Idling:
1891 default:
1892 ShouldNotReachHere();
1893 break;
1894 }
1895 log_debug(gc, state)(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1896 p2i(Thread::current()), _collectorState);
1897 assert(_foregroundGCShouldWait, "block post-condition");
1898 }
1899
1900 // Should this be in gc_epilogue?
1901 heap->counters()->update_counters();
1902
1903 {
1904 // Clear _foregroundGCShouldWait and, in the event that the
1905 // foreground collector is waiting, notify it, before
1906 // returning.
1907 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1908 _foregroundGCShouldWait = false;
1909 if (_foregroundGCIsActive) {
1910 CGC_lock->notify();
1911 }
1912 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1913 "Possible deadlock");
1914 }
1915 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1916 p2i(Thread::current()), _collectorState);
1917 log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K(" SIZE_FORMAT "K)",
1918 prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K);
1919 }
1920
1921 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1922 _cms_start_registered = true;
1923 _gc_timer_cm->register_gc_start();
1924 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1925 }
1926
1927 void CMSCollector::register_gc_end() {
1928 if (_cms_start_registered) {
1929 report_heap_summary(GCWhen::AfterGC);
1930
1931 _gc_timer_cm->register_gc_end();
1932 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1933 _cms_start_registered = false;
1934 }
1935 }
1936
1937 void CMSCollector::save_heap_summary() {
1938 CMSHeap* heap = CMSHeap::heap();
1939 _last_heap_summary = heap->create_heap_summary();
1940 _last_metaspace_summary = heap->create_metaspace_summary();
1941 }
1942
1943 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1944 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1945 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1946 }
1947
1948 bool CMSCollector::waitForForegroundGC() {
1949 bool res = false;
1950 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1951 "CMS thread should have CMS token");
1952 // Block the foreground collector until the
1953 // background collectors decides whether to
1954 // yield.
1955 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1956 _foregroundGCShouldWait = true;
1957 if (_foregroundGCIsActive) {
1958 // The background collector yields to the
1959 // foreground collector and returns a value
1960 // indicating that it has yielded. The foreground
1961 // collector can proceed.
1962 res = true;
1963 _foregroundGCShouldWait = false;
1964 ConcurrentMarkSweepThread::clear_CMS_flag(
1965 ConcurrentMarkSweepThread::CMS_cms_has_token);
1966 ConcurrentMarkSweepThread::set_CMS_flag(
1967 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1968 // Get a possibly blocked foreground thread going
1969 CGC_lock->notify();
1970 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
1971 p2i(Thread::current()), _collectorState);
1972 while (_foregroundGCIsActive) {
1973 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1974 }
1975 ConcurrentMarkSweepThread::set_CMS_flag(
1976 ConcurrentMarkSweepThread::CMS_cms_has_token);
1977 ConcurrentMarkSweepThread::clear_CMS_flag(
1978 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1979 }
1980 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
1981 p2i(Thread::current()), _collectorState);
1982 return res;
1983 }
1984
1985 // Because of the need to lock the free lists and other structures in
1986 // the collector, common to all the generations that the collector is
1987 // collecting, we need the gc_prologues of individual CMS generations
1988 // delegate to their collector. It may have been simpler had the
1989 // current infrastructure allowed one to call a prologue on a
1990 // collector. In the absence of that we have the generation's
1991 // prologue delegate to the collector, which delegates back
1992 // some "local" work to a worker method in the individual generations
1993 // that it's responsible for collecting, while itself doing any
1994 // work common to all generations it's responsible for. A similar
1995 // comment applies to the gc_epilogue()'s.
1996 // The role of the variable _between_prologue_and_epilogue is to
1997 // enforce the invocation protocol.
1998 void CMSCollector::gc_prologue(bool full) {
1999 // Call gc_prologue_work() for the CMSGen
2000 // we are responsible for.
2001
2002 // The following locking discipline assumes that we are only called
2003 // when the world is stopped.
2004 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2005
2006 // The CMSCollector prologue must call the gc_prologues for the
2007 // "generations" that it's responsible
2008 // for.
2009
2010 assert( Thread::current()->is_VM_thread()
2011 || ( CMSScavengeBeforeRemark
2012 && Thread::current()->is_ConcurrentGC_thread()),
2013 "Incorrect thread type for prologue execution");
2014
2015 if (_between_prologue_and_epilogue) {
2016 // We have already been invoked; this is a gc_prologue delegation
2017 // from yet another CMS generation that we are responsible for, just
2018 // ignore it since all relevant work has already been done.
2019 return;
2020 }
2021
2022 // set a bit saying prologue has been called; cleared in epilogue
2023 _between_prologue_and_epilogue = true;
2024 // Claim locks for common data structures, then call gc_prologue_work()
2025 // for each CMSGen.
2026
2027 getFreelistLocks(); // gets free list locks on constituent spaces
2028 bitMapLock()->lock_without_safepoint_check();
2029
2030 // Should call gc_prologue_work() for all cms gens we are responsible for
2031 bool duringMarking = _collectorState >= Marking
2032 && _collectorState < Sweeping;
2033
2034 // The young collections clear the modified oops state, which tells if
2035 // there are any modified oops in the class. The remark phase also needs
2036 // that information. Tell the young collection to save the union of all
2037 // modified klasses.
2038 if (duringMarking) {
2039 _ct->cld_rem_set()->set_accumulate_modified_oops(true);
2040 }
2041
2042 bool registerClosure = duringMarking;
2043
2044 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2045
2046 if (!full) {
2047 stats().record_gc0_begin();
2048 }
2049 }
2050
2051 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2052
2053 _capacity_at_prologue = capacity();
2054 _used_at_prologue = used();
2055
2056 // We enable promotion tracking so that card-scanning can recognize
2057 // which objects have been promoted during this GC and skip them.
2058 for (uint i = 0; i < ParallelGCThreads; i++) {
2059 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2060 }
2061
2062 // Delegate to CMScollector which knows how to coordinate between
2063 // this and any other CMS generations that it is responsible for
2064 // collecting.
2065 collector()->gc_prologue(full);
2066 }
2067
2068 // This is a "private" interface for use by this generation's CMSCollector.
2069 // Not to be called directly by any other entity (for instance,
2070 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2071 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2072 bool registerClosure, ModUnionClosure* modUnionClosure) {
2073 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2074 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2075 "Should be NULL");
2076 if (registerClosure) {
2077 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2078 }
2079 cmsSpace()->gc_prologue();
2080 // Clear stat counters
2081 NOT_PRODUCT(
2082 assert(_numObjectsPromoted == 0, "check");
2083 assert(_numWordsPromoted == 0, "check");
2084 log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently",
2085 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2086 _numObjectsAllocated = 0;
2087 _numWordsAllocated = 0;
2088 )
2089 }
2090
2091 void CMSCollector::gc_epilogue(bool full) {
2092 // The following locking discipline assumes that we are only called
2093 // when the world is stopped.
2094 assert(SafepointSynchronize::is_at_safepoint(),
2095 "world is stopped assumption");
2096
2097 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2098 // if linear allocation blocks need to be appropriately marked to allow the
2099 // the blocks to be parsable. We also check here whether we need to nudge the
2100 // CMS collector thread to start a new cycle (if it's not already active).
2101 assert( Thread::current()->is_VM_thread()
2102 || ( CMSScavengeBeforeRemark
2103 && Thread::current()->is_ConcurrentGC_thread()),
2104 "Incorrect thread type for epilogue execution");
2105
2106 if (!_between_prologue_and_epilogue) {
2107 // We have already been invoked; this is a gc_epilogue delegation
2108 // from yet another CMS generation that we are responsible for, just
2109 // ignore it since all relevant work has already been done.
2110 return;
2111 }
2112 assert(haveFreelistLocks(), "must have freelist locks");
2113 assert_lock_strong(bitMapLock());
2114
2115 _ct->cld_rem_set()->set_accumulate_modified_oops(false);
2116
2117 _cmsGen->gc_epilogue_work(full);
2118
2119 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2120 // in case sampling was not already enabled, enable it
2121 _start_sampling = true;
2122 }
2123 // reset _eden_chunk_array so sampling starts afresh
2124 _eden_chunk_index = 0;
2125
2126 size_t cms_used = _cmsGen->cmsSpace()->used();
2127
2128 // update performance counters - this uses a special version of
2129 // update_counters() that allows the utilization to be passed as a
2130 // parameter, avoiding multiple calls to used().
2131 //
2132 _cmsGen->update_counters(cms_used);
2133
2134 bitMapLock()->unlock();
2135 releaseFreelistLocks();
2136
2137 if (!CleanChunkPoolAsync) {
2138 Chunk::clean_chunk_pool();
2139 }
2140
2141 set_did_compact(false);
2142 _between_prologue_and_epilogue = false; // ready for next cycle
2143 }
2144
2145 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2146 collector()->gc_epilogue(full);
2147
2148 // When using ParNew, promotion tracking should have already been
2149 // disabled. However, the prologue (which enables promotion
2150 // tracking) and epilogue are called irrespective of the type of
2151 // GC. So they will also be called before and after Full GCs, during
2152 // which promotion tracking will not be explicitly disabled. So,
2153 // it's safer to also disable it here too (to be symmetric with
2154 // enabling it in the prologue).
2155 for (uint i = 0; i < ParallelGCThreads; i++) {
2156 _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2157 }
2158 }
2159
2160 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2161 assert(!incremental_collection_failed(), "Should have been cleared");
2162 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2163 cmsSpace()->gc_epilogue();
2164 // Print stat counters
2165 NOT_PRODUCT(
2166 assert(_numObjectsAllocated == 0, "check");
2167 assert(_numWordsAllocated == 0, "check");
2168 log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
2169 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2170 _numObjectsPromoted = 0;
2171 _numWordsPromoted = 0;
2172 )
2173
2174 // Call down the chain in contiguous_available needs the freelistLock
2175 // so print this out before releasing the freeListLock.
2176 log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available());
2177 }
2178
2179 #ifndef PRODUCT
2180 bool CMSCollector::have_cms_token() {
2181 Thread* thr = Thread::current();
2182 if (thr->is_VM_thread()) {
2183 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2184 } else if (thr->is_ConcurrentGC_thread()) {
2185 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2186 } else if (thr->is_GC_task_thread()) {
2187 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2188 ParGCRareEvent_lock->owned_by_self();
2189 }
2190 return false;
2191 }
2192
2193 // Check reachability of the given heap address in CMS generation,
2194 // treating all other generations as roots.
2195 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2196 // We could "guarantee" below, rather than assert, but I'll
2197 // leave these as "asserts" so that an adventurous debugger
2198 // could try this in the product build provided some subset of
2199 // the conditions were met, provided they were interested in the
2200 // results and knew that the computation below wouldn't interfere
2201 // with other concurrent computations mutating the structures
2202 // being read or written.
2203 assert(SafepointSynchronize::is_at_safepoint(),
2204 "Else mutations in object graph will make answer suspect");
2205 assert(have_cms_token(), "Should hold cms token");
2206 assert(haveFreelistLocks(), "must hold free list locks");
2207 assert_lock_strong(bitMapLock());
2208
2209 // Clear the marking bit map array before starting, but, just
2210 // for kicks, first report if the given address is already marked
2211 tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2212 _markBitMap.isMarked(addr) ? "" : " not");
2213
2214 if (verify_after_remark()) {
2215 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2216 bool result = verification_mark_bm()->isMarked(addr);
2217 tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2218 result ? "IS" : "is NOT");
2219 return result;
2220 } else {
2221 tty->print_cr("Could not compute result");
2222 return false;
2223 }
2224 }
2225 #endif
2226
2227 void
2228 CMSCollector::print_on_error(outputStream* st) {
2229 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2230 if (collector != NULL) {
2231 CMSBitMap* bitmap = &collector->_markBitMap;
2232 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2233 bitmap->print_on_error(st, " Bits: ");
2234
2235 st->cr();
2236
2237 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2238 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2239 mut_bitmap->print_on_error(st, " Bits: ");
2240 }
2241 }
2242
2243 ////////////////////////////////////////////////////////
2244 // CMS Verification Support
2245 ////////////////////////////////////////////////////////
2246 // Following the remark phase, the following invariant
2247 // should hold -- each object in the CMS heap which is
2248 // marked in markBitMap() should be marked in the verification_mark_bm().
2249
2250 class VerifyMarkedClosure: public BitMapClosure {
2251 CMSBitMap* _marks;
2252 bool _failed;
2253
2254 public:
2255 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2256
2257 bool do_bit(size_t offset) {
2258 HeapWord* addr = _marks->offsetToHeapWord(offset);
2259 if (!_marks->isMarked(addr)) {
2260 Log(gc, verify) log;
2261 ResourceMark rm;
2262 LogStream ls(log.error());
2263 oop(addr)->print_on(&ls);
2264 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2265 _failed = true;
2266 }
2267 return true;
2268 }
2269
2270 bool failed() { return _failed; }
2271 };
2272
2273 bool CMSCollector::verify_after_remark() {
2274 GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking.");
2275 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2276 static bool init = false;
2277
2278 assert(SafepointSynchronize::is_at_safepoint(),
2279 "Else mutations in object graph will make answer suspect");
2280 assert(have_cms_token(),
2281 "Else there may be mutual interference in use of "
2282 " verification data structures");
2283 assert(_collectorState > Marking && _collectorState <= Sweeping,
2284 "Else marking info checked here may be obsolete");
2285 assert(haveFreelistLocks(), "must hold free list locks");
2286 assert_lock_strong(bitMapLock());
2287
2288
2289 // Allocate marking bit map if not already allocated
2290 if (!init) { // first time
2291 if (!verification_mark_bm()->allocate(_span)) {
2292 return false;
2293 }
2294 init = true;
2295 }
2296
2297 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2298
2299 // Turn off refs discovery -- so we will be tracing through refs.
2300 // This is as intended, because by this time
2301 // GC must already have cleared any refs that need to be cleared,
2302 // and traced those that need to be marked; moreover,
2303 // the marking done here is not going to interfere in any
2304 // way with the marking information used by GC.
2305 NoRefDiscovery no_discovery(ref_processor());
2306
2307 #if COMPILER2_OR_JVMCI
2308 DerivedPointerTableDeactivate dpt_deact;
2309 #endif
2310
2311 // Clear any marks from a previous round
2312 verification_mark_bm()->clear_all();
2313 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2314 verify_work_stacks_empty();
2315
2316 CMSHeap* heap = CMSHeap::heap();
2317 heap->ensure_parsability(false); // fill TLABs, but no need to retire them
2318 // Update the saved marks which may affect the root scans.
2319 heap->save_marks();
2320
2321 if (CMSRemarkVerifyVariant == 1) {
2322 // In this first variant of verification, we complete
2323 // all marking, then check if the new marks-vector is
2324 // a subset of the CMS marks-vector.
2325 verify_after_remark_work_1();
2326 } else {
2327 guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2");
2328 // In this second variant of verification, we flag an error
2329 // (i.e. an object reachable in the new marks-vector not reachable
2330 // in the CMS marks-vector) immediately, also indicating the
2331 // identify of an object (A) that references the unmarked object (B) --
2332 // presumably, a mutation to A failed to be picked up by preclean/remark?
2333 verify_after_remark_work_2();
2334 }
2335
2336 return true;
2337 }
2338
2339 void CMSCollector::verify_after_remark_work_1() {
2340 ResourceMark rm;
2341 HandleMark hm;
2342 CMSHeap* heap = CMSHeap::heap();
2343
2344 // Get a clear set of claim bits for the roots processing to work with.
2345 ClassLoaderDataGraph::clear_claimed_marks();
2346
2347 // Mark from roots one level into CMS
2348 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2349 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2350
2351 {
2352 StrongRootsScope srs(1);
2353
2354 heap->cms_process_roots(&srs,
2355 true, // young gen as roots
2356 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2357 should_unload_classes(),
2358 ¬Older,
2359 NULL);
2360 }
2361
2362 // Now mark from the roots
2363 MarkFromRootsClosure markFromRootsClosure(this, _span,
2364 verification_mark_bm(), verification_mark_stack(),
2365 false /* don't yield */, true /* verifying */);
2366 assert(_restart_addr == NULL, "Expected pre-condition");
2367 verification_mark_bm()->iterate(&markFromRootsClosure);
2368 while (_restart_addr != NULL) {
2369 // Deal with stack overflow: by restarting at the indicated
2370 // address.
2371 HeapWord* ra = _restart_addr;
2372 markFromRootsClosure.reset(ra);
2373 _restart_addr = NULL;
2374 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2375 }
2376 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2377 verify_work_stacks_empty();
2378
2379 // Marking completed -- now verify that each bit marked in
2380 // verification_mark_bm() is also marked in markBitMap(); flag all
2381 // errors by printing corresponding objects.
2382 VerifyMarkedClosure vcl(markBitMap());
2383 verification_mark_bm()->iterate(&vcl);
2384 if (vcl.failed()) {
2385 Log(gc, verify) log;
2386 log.error("Failed marking verification after remark");
2387 ResourceMark rm;
2388 LogStream ls(log.error());
2389 heap->print_on(&ls);
2390 fatal("CMS: failed marking verification after remark");
2391 }
2392 }
2393
2394 class VerifyCLDOopsCLDClosure : public CLDClosure {
2395 class VerifyCLDOopsClosure : public OopClosure {
2396 CMSBitMap* _bitmap;
2397 public:
2398 VerifyCLDOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2399 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2400 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2401 } _oop_closure;
2402 public:
2403 VerifyCLDOopsCLDClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2404 void do_cld(ClassLoaderData* cld) {
2405 cld->oops_do(&_oop_closure, ClassLoaderData::_claim_none, false);
2406 }
2407 };
2408
2409 void CMSCollector::verify_after_remark_work_2() {
2410 ResourceMark rm;
2411 HandleMark hm;
2412 CMSHeap* heap = CMSHeap::heap();
2413
2414 // Get a clear set of claim bits for the roots processing to work with.
2415 ClassLoaderDataGraph::clear_claimed_marks();
2416
2417 // Mark from roots one level into CMS
2418 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2419 markBitMap());
2420 CLDToOopClosure cld_closure(¬Older, ClassLoaderData::_claim_strong);
2421
2422 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2423
2424 {
2425 StrongRootsScope srs(1);
2426
2427 heap->cms_process_roots(&srs,
2428 true, // young gen as roots
2429 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2430 should_unload_classes(),
2431 ¬Older,
2432 &cld_closure);
2433 }
2434
2435 // Now mark from the roots
2436 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2437 verification_mark_bm(), markBitMap(), verification_mark_stack());
2438 assert(_restart_addr == NULL, "Expected pre-condition");
2439 verification_mark_bm()->iterate(&markFromRootsClosure);
2440 while (_restart_addr != NULL) {
2441 // Deal with stack overflow: by restarting at the indicated
2442 // address.
2443 HeapWord* ra = _restart_addr;
2444 markFromRootsClosure.reset(ra);
2445 _restart_addr = NULL;
2446 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2447 }
2448 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2449 verify_work_stacks_empty();
2450
2451 VerifyCLDOopsCLDClosure verify_cld_oops(verification_mark_bm());
2452 ClassLoaderDataGraph::cld_do(&verify_cld_oops);
2453
2454 // Marking completed -- now verify that each bit marked in
2455 // verification_mark_bm() is also marked in markBitMap(); flag all
2456 // errors by printing corresponding objects.
2457 VerifyMarkedClosure vcl(markBitMap());
2458 verification_mark_bm()->iterate(&vcl);
2459 assert(!vcl.failed(), "Else verification above should not have succeeded");
2460 }
2461
2462 void ConcurrentMarkSweepGeneration::save_marks() {
2463 // delegate to CMS space
2464 cmsSpace()->save_marks();
2465 }
2466
2467 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2468 return cmsSpace()->no_allocs_since_save_marks();
2469 }
2470
2471 void
2472 ConcurrentMarkSweepGeneration::oop_iterate(OopIterateClosure* cl) {
2473 if (freelistLock()->owned_by_self()) {
2474 Generation::oop_iterate(cl);
2475 } else {
2476 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2477 Generation::oop_iterate(cl);
2478 }
2479 }
2480
2481 void
2482 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2483 if (freelistLock()->owned_by_self()) {
2484 Generation::object_iterate(cl);
2485 } else {
2486 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2487 Generation::object_iterate(cl);
2488 }
2489 }
2490
2491 void
2492 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2493 if (freelistLock()->owned_by_self()) {
2494 Generation::safe_object_iterate(cl);
2495 } else {
2496 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2497 Generation::safe_object_iterate(cl);
2498 }
2499 }
2500
2501 void
2502 ConcurrentMarkSweepGeneration::post_compact() {
2503 }
2504
2505 void
2506 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2507 // Fix the linear allocation blocks to look like free blocks.
2508
2509 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2510 // are not called when the heap is verified during universe initialization and
2511 // at vm shutdown.
2512 if (freelistLock()->owned_by_self()) {
2513 cmsSpace()->prepare_for_verify();
2514 } else {
2515 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2516 cmsSpace()->prepare_for_verify();
2517 }
2518 }
2519
2520 void
2521 ConcurrentMarkSweepGeneration::verify() {
2522 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2523 // are not called when the heap is verified during universe initialization and
2524 // at vm shutdown.
2525 if (freelistLock()->owned_by_self()) {
2526 cmsSpace()->verify();
2527 } else {
2528 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2529 cmsSpace()->verify();
2530 }
2531 }
2532
2533 void CMSCollector::verify() {
2534 _cmsGen->verify();
2535 }
2536
2537 #ifndef PRODUCT
2538 bool CMSCollector::overflow_list_is_empty() const {
2539 assert(_num_par_pushes >= 0, "Inconsistency");
2540 if (_overflow_list == NULL) {
2541 assert(_num_par_pushes == 0, "Inconsistency");
2542 }
2543 return _overflow_list == NULL;
2544 }
2545
2546 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2547 // merely consolidate assertion checks that appear to occur together frequently.
2548 void CMSCollector::verify_work_stacks_empty() const {
2549 assert(_markStack.isEmpty(), "Marking stack should be empty");
2550 assert(overflow_list_is_empty(), "Overflow list should be empty");
2551 }
2552
2553 void CMSCollector::verify_overflow_empty() const {
2554 assert(overflow_list_is_empty(), "Overflow list should be empty");
2555 assert(no_preserved_marks(), "No preserved marks");
2556 }
2557 #endif // PRODUCT
2558
2559 // Decide if we want to enable class unloading as part of the
2560 // ensuing concurrent GC cycle. We will collect and
2561 // unload classes if it's the case that:
2562 // (a) class unloading is enabled at the command line, and
2563 // (b) old gen is getting really full
2564 // NOTE: Provided there is no change in the state of the heap between
2565 // calls to this method, it should have idempotent results. Moreover,
2566 // its results should be monotonically increasing (i.e. going from 0 to 1,
2567 // but not 1 to 0) between successive calls between which the heap was
2568 // not collected. For the implementation below, it must thus rely on
2569 // the property that concurrent_cycles_since_last_unload()
2570 // will not decrease unless a collection cycle happened and that
2571 // _cmsGen->is_too_full() are
2572 // themselves also monotonic in that sense. See check_monotonicity()
2573 // below.
2574 void CMSCollector::update_should_unload_classes() {
2575 _should_unload_classes = false;
2576 if (CMSClassUnloadingEnabled) {
2577 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2578 CMSClassUnloadingMaxInterval)
2579 || _cmsGen->is_too_full();
2580 }
2581 }
2582
2583 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2584 bool res = should_concurrent_collect();
2585 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2586 return res;
2587 }
2588
2589 void CMSCollector::setup_cms_unloading_and_verification_state() {
2590 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2591 || VerifyBeforeExit;
2592 const int rso = GenCollectedHeap::SO_AllCodeCache;
2593
2594 // We set the proper root for this CMS cycle here.
2595 if (should_unload_classes()) { // Should unload classes this cycle
2596 remove_root_scanning_option(rso); // Shrink the root set appropriately
2597 set_verifying(should_verify); // Set verification state for this cycle
2598 return; // Nothing else needs to be done at this time
2599 }
2600
2601 // Not unloading classes this cycle
2602 assert(!should_unload_classes(), "Inconsistency!");
2603
2604 // If we are not unloading classes then add SO_AllCodeCache to root
2605 // scanning options.
2606 add_root_scanning_option(rso);
2607
2608 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2609 set_verifying(true);
2610 } else if (verifying() && !should_verify) {
2611 // We were verifying, but some verification flags got disabled.
2612 set_verifying(false);
2613 // Exclude symbols, strings and code cache elements from root scanning to
2614 // reduce IM and RM pauses.
2615 remove_root_scanning_option(rso);
2616 }
2617 }
2618
2619
2620 #ifndef PRODUCT
2621 HeapWord* CMSCollector::block_start(const void* p) const {
2622 const HeapWord* addr = (HeapWord*)p;
2623 if (_span.contains(p)) {
2624 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2625 return _cmsGen->cmsSpace()->block_start(p);
2626 }
2627 }
2628 return NULL;
2629 }
2630 #endif
2631
2632 HeapWord*
2633 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2634 bool tlab,
2635 bool parallel) {
2636 CMSSynchronousYieldRequest yr;
2637 assert(!tlab, "Can't deal with TLAB allocation");
2638 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2639 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2640 if (GCExpandToAllocateDelayMillis > 0) {
2641 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2642 }
2643 return have_lock_and_allocate(word_size, tlab);
2644 }
2645
2646 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2647 size_t bytes,
2648 size_t expand_bytes,
2649 CMSExpansionCause::Cause cause)
2650 {
2651
2652 bool success = expand(bytes, expand_bytes);
2653
2654 // remember why we expanded; this information is used
2655 // by shouldConcurrentCollect() when making decisions on whether to start
2656 // a new CMS cycle.
2657 if (success) {
2658 set_expansion_cause(cause);
2659 log_trace(gc)("Expanded CMS gen for %s", CMSExpansionCause::to_string(cause));
2660 }
2661 }
2662
2663 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2664 HeapWord* res = NULL;
2665 MutexLocker x(ParGCRareEvent_lock);
2666 while (true) {
2667 // Expansion by some other thread might make alloc OK now:
2668 res = ps->lab.alloc(word_sz);
2669 if (res != NULL) return res;
2670 // If there's not enough expansion space available, give up.
2671 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2672 return NULL;
2673 }
2674 // Otherwise, we try expansion.
2675 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2676 // Now go around the loop and try alloc again;
2677 // A competing par_promote might beat us to the expansion space,
2678 // so we may go around the loop again if promotion fails again.
2679 if (GCExpandToAllocateDelayMillis > 0) {
2680 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2681 }
2682 }
2683 }
2684
2685
2686 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2687 PromotionInfo* promo) {
2688 MutexLocker x(ParGCRareEvent_lock);
2689 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2690 while (true) {
2691 // Expansion by some other thread might make alloc OK now:
2692 if (promo->ensure_spooling_space()) {
2693 assert(promo->has_spooling_space(),
2694 "Post-condition of successful ensure_spooling_space()");
2695 return true;
2696 }
2697 // If there's not enough expansion space available, give up.
2698 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2699 return false;
2700 }
2701 // Otherwise, we try expansion.
2702 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2703 // Now go around the loop and try alloc again;
2704 // A competing allocation might beat us to the expansion space,
2705 // so we may go around the loop again if allocation fails again.
2706 if (GCExpandToAllocateDelayMillis > 0) {
2707 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2708 }
2709 }
2710 }
2711
2712 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2713 // Only shrink if a compaction was done so that all the free space
2714 // in the generation is in a contiguous block at the end.
2715 if (did_compact()) {
2716 CardGeneration::shrink(bytes);
2717 }
2718 }
2719
2720 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2721 assert_locked_or_safepoint(Heap_lock);
2722 }
2723
2724 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2725 assert_locked_or_safepoint(Heap_lock);
2726 assert_lock_strong(freelistLock());
2727 log_trace(gc)("Shrinking of CMS not yet implemented");
2728 return;
2729 }
2730
2731
2732 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2733 // phases.
2734 class CMSPhaseAccounting: public StackObj {
2735 public:
2736 CMSPhaseAccounting(CMSCollector *collector,
2737 const char *title);
2738 ~CMSPhaseAccounting();
2739
2740 private:
2741 CMSCollector *_collector;
2742 const char *_title;
2743 GCTraceConcTime(Info, gc) _trace_time;
2744
2745 public:
2746 // Not MT-safe; so do not pass around these StackObj's
2747 // where they may be accessed by other threads.
2748 double wallclock_millis() {
2749 return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time());
2750 }
2751 };
2752
2753 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2754 const char *title) :
2755 _collector(collector), _title(title), _trace_time(title) {
2756
2757 _collector->resetYields();
2758 _collector->resetTimer();
2759 _collector->startTimer();
2760 _collector->gc_timer_cm()->register_gc_concurrent_start(title);
2761 }
2762
2763 CMSPhaseAccounting::~CMSPhaseAccounting() {
2764 _collector->gc_timer_cm()->register_gc_concurrent_end();
2765 _collector->stopTimer();
2766 log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_millis(_collector->timerTicks()));
2767 log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields());
2768 }
2769
2770 // CMS work
2771
2772 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2773 class CMSParMarkTask : public AbstractGangTask {
2774 protected:
2775 CMSCollector* _collector;
2776 uint _n_workers;
2777 OopStorage::ParState<false, false> _par_state_string;
2778 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2779 AbstractGangTask(name),
2780 _collector(collector),
2781 _n_workers(n_workers),
2782 _par_state_string(StringTable::weak_storage()) {}
2783 // Work method in support of parallel rescan ... of young gen spaces
2784 void do_young_space_rescan(OopsInGenClosure* cl,
2785 ContiguousSpace* space,
2786 HeapWord** chunk_array, size_t chunk_top);
2787 void work_on_young_gen_roots(OopsInGenClosure* cl);
2788 };
2789
2790 // Parallel initial mark task
2791 class CMSParInitialMarkTask: public CMSParMarkTask {
2792 StrongRootsScope* _strong_roots_scope;
2793 public:
2794 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2795 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2796 _strong_roots_scope(strong_roots_scope) {}
2797 void work(uint worker_id);
2798 };
2799
2800 // Checkpoint the roots into this generation from outside
2801 // this generation. [Note this initial checkpoint need only
2802 // be approximate -- we'll do a catch up phase subsequently.]
2803 void CMSCollector::checkpointRootsInitial() {
2804 assert(_collectorState == InitialMarking, "Wrong collector state");
2805 check_correct_thread_executing();
2806 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
2807
2808 save_heap_summary();
2809 report_heap_summary(GCWhen::BeforeGC);
2810
2811 ReferenceProcessor* rp = ref_processor();
2812 assert(_restart_addr == NULL, "Control point invariant");
2813 {
2814 // acquire locks for subsequent manipulations
2815 MutexLockerEx x(bitMapLock(),
2816 Mutex::_no_safepoint_check_flag);
2817 checkpointRootsInitialWork();
2818 // enable ("weak") refs discovery
2819 rp->enable_discovery();
2820 _collectorState = Marking;
2821 }
2822 }
2823
2824 void CMSCollector::checkpointRootsInitialWork() {
2825 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2826 assert(_collectorState == InitialMarking, "just checking");
2827
2828 // Already have locks.
2829 assert_lock_strong(bitMapLock());
2830 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2831
2832 // Setup the verification and class unloading state for this
2833 // CMS collection cycle.
2834 setup_cms_unloading_and_verification_state();
2835
2836 GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm);
2837
2838 // Reset all the PLAB chunk arrays if necessary.
2839 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2840 reset_survivor_plab_arrays();
2841 }
2842
2843 ResourceMark rm;
2844 HandleMark hm;
2845
2846 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2847 CMSHeap* heap = CMSHeap::heap();
2848
2849 verify_work_stacks_empty();
2850 verify_overflow_empty();
2851
2852 heap->ensure_parsability(false); // fill TLABs, but no need to retire them
2853 // Update the saved marks which may affect the root scans.
2854 heap->save_marks();
2855
2856 // weak reference processing has not started yet.
2857 ref_processor()->set_enqueuing_is_done(false);
2858
2859 // Need to remember all newly created CLDs,
2860 // so that we can guarantee that the remark finds them.
2861 ClassLoaderDataGraph::remember_new_clds(true);
2862
2863 // Whenever a CLD is found, it will be claimed before proceeding to mark
2864 // the klasses. The claimed marks need to be cleared before marking starts.
2865 ClassLoaderDataGraph::clear_claimed_marks();
2866
2867 print_eden_and_survivor_chunk_arrays();
2868
2869 {
2870 #if COMPILER2_OR_JVMCI
2871 DerivedPointerTableDeactivate dpt_deact;
2872 #endif
2873 if (CMSParallelInitialMarkEnabled) {
2874 // The parallel version.
2875 WorkGang* workers = heap->workers();
2876 assert(workers != NULL, "Need parallel worker threads.");
2877 uint n_workers = workers->active_workers();
2878
2879 StrongRootsScope srs(n_workers);
2880
2881 CMSParInitialMarkTask tsk(this, &srs, n_workers);
2882 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2883 // If the total workers is greater than 1, then multiple workers
2884 // may be used at some time and the initialization has been set
2885 // such that the single threaded path cannot be used.
2886 if (workers->total_workers() > 1) {
2887 workers->run_task(&tsk);
2888 } else {
2889 tsk.work(0);
2890 }
2891 } else {
2892 // The serial version.
2893 CLDToOopClosure cld_closure(¬Older, ClassLoaderData::_claim_strong);
2894 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2895
2896 StrongRootsScope srs(1);
2897
2898 heap->cms_process_roots(&srs,
2899 true, // young gen as roots
2900 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2901 should_unload_classes(),
2902 ¬Older,
2903 &cld_closure);
2904 }
2905 }
2906
2907 // Clear mod-union table; it will be dirtied in the prologue of
2908 // CMS generation per each young generation collection.
2909
2910 assert(_modUnionTable.isAllClear(),
2911 "Was cleared in most recent final checkpoint phase"
2912 " or no bits are set in the gc_prologue before the start of the next "
2913 "subsequent marking phase.");
2914
2915 assert(_ct->cld_rem_set()->mod_union_is_clear(), "Must be");
2916
2917 // Save the end of the used_region of the constituent generations
2918 // to be used to limit the extent of sweep in each generation.
2919 save_sweep_limits();
2920 verify_overflow_empty();
2921 }
2922
2923 bool CMSCollector::markFromRoots() {
2924 // we might be tempted to assert that:
2925 // assert(!SafepointSynchronize::is_at_safepoint(),
2926 // "inconsistent argument?");
2927 // However that wouldn't be right, because it's possible that
2928 // a safepoint is indeed in progress as a young generation
2929 // stop-the-world GC happens even as we mark in this generation.
2930 assert(_collectorState == Marking, "inconsistent state?");
2931 check_correct_thread_executing();
2932 verify_overflow_empty();
2933
2934 // Weak ref discovery note: We may be discovering weak
2935 // refs in this generation concurrent (but interleaved) with
2936 // weak ref discovery by the young generation collector.
2937
2938 CMSTokenSyncWithLocks ts(true, bitMapLock());
2939 GCTraceCPUTime tcpu;
2940 CMSPhaseAccounting pa(this, "Concurrent Mark");
2941 bool res = markFromRootsWork();
2942 if (res) {
2943 _collectorState = Precleaning;
2944 } else { // We failed and a foreground collection wants to take over
2945 assert(_foregroundGCIsActive, "internal state inconsistency");
2946 assert(_restart_addr == NULL, "foreground will restart from scratch");
2947 log_debug(gc)("bailing out to foreground collection");
2948 }
2949 verify_overflow_empty();
2950 return res;
2951 }
2952
2953 bool CMSCollector::markFromRootsWork() {
2954 // iterate over marked bits in bit map, doing a full scan and mark
2955 // from these roots using the following algorithm:
2956 // . if oop is to the right of the current scan pointer,
2957 // mark corresponding bit (we'll process it later)
2958 // . else (oop is to left of current scan pointer)
2959 // push oop on marking stack
2960 // . drain the marking stack
2961
2962 // Note that when we do a marking step we need to hold the
2963 // bit map lock -- recall that direct allocation (by mutators)
2964 // and promotion (by the young generation collector) is also
2965 // marking the bit map. [the so-called allocate live policy.]
2966 // Because the implementation of bit map marking is not
2967 // robust wrt simultaneous marking of bits in the same word,
2968 // we need to make sure that there is no such interference
2969 // between concurrent such updates.
2970
2971 // already have locks
2972 assert_lock_strong(bitMapLock());
2973
2974 verify_work_stacks_empty();
2975 verify_overflow_empty();
2976 bool result = false;
2977 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2978 result = do_marking_mt();
2979 } else {
2980 result = do_marking_st();
2981 }
2982 return result;
2983 }
2984
2985 // Forward decl
2986 class CMSConcMarkingTask;
2987
2988 class CMSConcMarkingParallelTerminator: public ParallelTaskTerminator {
2989 CMSCollector* _collector;
2990 CMSConcMarkingTask* _task;
2991 public:
2992 virtual void yield();
2993
2994 // "n_threads" is the number of threads to be terminated.
2995 // "queue_set" is a set of work queues of other threads.
2996 // "collector" is the CMS collector associated with this task terminator.
2997 // "yield" indicates whether we need the gang as a whole to yield.
2998 CMSConcMarkingParallelTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
2999 ParallelTaskTerminator(n_threads, queue_set),
3000 _collector(collector) { }
3001
3002 void set_task(CMSConcMarkingTask* task) {
3003 _task = task;
3004 }
3005 };
3006
3007 class CMSConcMarkingOWSTTerminator: public OWSTTaskTerminator {
3008 CMSCollector* _collector;
3009 CMSConcMarkingTask* _task;
3010 public:
3011 virtual void yield();
3012
3013 // "n_threads" is the number of threads to be terminated.
3014 // "queue_set" is a set of work queues of other threads.
3015 // "collector" is the CMS collector associated with this task terminator.
3016 // "yield" indicates whether we need the gang as a whole to yield.
3017 CMSConcMarkingOWSTTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3018 OWSTTaskTerminator(n_threads, queue_set),
3019 _collector(collector) { }
3020
3021 void set_task(CMSConcMarkingTask* task) {
3022 _task = task;
3023 }
3024 };
3025
3026 class CMSConcMarkingTaskTerminator {
3027 private:
3028 ParallelTaskTerminator* _term;
3029 public:
3030 CMSConcMarkingTaskTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) {
3031 if (UseOWSTTaskTerminator) {
3032 _term = new CMSConcMarkingOWSTTerminator(n_threads, queue_set, collector);
3033 } else {
3034 _term = new CMSConcMarkingParallelTerminator(n_threads, queue_set, collector);
3035 }
3036 }
3037 ~CMSConcMarkingTaskTerminator() {
3038 assert(_term != NULL, "Must not be NULL");
3039 delete _term;
3040 }
3041
3042 void set_task(CMSConcMarkingTask* task);
3043 ParallelTaskTerminator* terminator() const { return _term; }
3044 };
3045
3046 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3047 CMSConcMarkingTask* _task;
3048 public:
3049 bool should_exit_termination();
3050 void set_task(CMSConcMarkingTask* task) {
3051 _task = task;
3052 }
3053 };
3054
3055 // MT Concurrent Marking Task
3056 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3057 CMSCollector* _collector;
3058 uint _n_workers; // requested/desired # workers
3059 bool _result;
3060 CompactibleFreeListSpace* _cms_space;
3061 char _pad_front[64]; // padding to ...
3062 HeapWord* volatile _global_finger; // ... avoid sharing cache line
3063 char _pad_back[64];
3064 HeapWord* _restart_addr;
3065
3066 // Exposed here for yielding support
3067 Mutex* const _bit_map_lock;
3068
3069 // The per thread work queues, available here for stealing
3070 OopTaskQueueSet* _task_queues;
3071
3072 // Termination (and yielding) support
3073 CMSConcMarkingTaskTerminator _term;
3074 CMSConcMarkingTerminatorTerminator _term_term;
3075
3076 public:
3077 CMSConcMarkingTask(CMSCollector* collector,
3078 CompactibleFreeListSpace* cms_space,
3079 YieldingFlexibleWorkGang* workers,
3080 OopTaskQueueSet* task_queues):
3081 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3082 _collector(collector),
3083 _n_workers(0),
3084 _result(true),
3085 _cms_space(cms_space),
3086 _bit_map_lock(collector->bitMapLock()),
3087 _task_queues(task_queues),
3088 _term(_n_workers, task_queues, _collector)
3089 {
3090 _requested_size = _n_workers;
3091 _term.set_task(this);
3092 _term_term.set_task(this);
3093 _restart_addr = _global_finger = _cms_space->bottom();
3094 }
3095
3096
3097 OopTaskQueueSet* task_queues() { return _task_queues; }
3098
3099 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3100
3101 HeapWord* volatile* global_finger_addr() { return &_global_finger; }
3102
3103 ParallelTaskTerminator* terminator() { return _term.terminator(); }
3104
3105 virtual void set_for_termination(uint active_workers) {
3106 terminator()->reset_for_reuse(active_workers);
3107 }
3108
3109 void work(uint worker_id);
3110 bool should_yield() {
3111 return ConcurrentMarkSweepThread::should_yield()
3112 && !_collector->foregroundGCIsActive();
3113 }
3114
3115 virtual void coordinator_yield(); // stuff done by coordinator
3116 bool result() { return _result; }
3117
3118 void reset(HeapWord* ra) {
3119 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3120 _restart_addr = _global_finger = ra;
3121 _term.terminator()->reset_for_reuse();
3122 }
3123
3124 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3125 OopTaskQueue* work_q);
3126
3127 private:
3128 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3129 void do_work_steal(int i);
3130 void bump_global_finger(HeapWord* f);
3131 };
3132
3133 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3134 assert(_task != NULL, "Error");
3135 return _task->yielding();
3136 // Note that we do not need the disjunct || _task->should_yield() above
3137 // because we want terminating threads to yield only if the task
3138 // is already in the midst of yielding, which happens only after at least one
3139 // thread has yielded.
3140 }
3141
3142 void CMSConcMarkingParallelTerminator::yield() {
3143 if (_task->should_yield()) {
3144 _task->yield();
3145 } else {
3146 ParallelTaskTerminator::yield();
3147 }
3148 }
3149
3150 void CMSConcMarkingOWSTTerminator::yield() {
3151 if (_task->should_yield()) {
3152 _task->yield();
3153 } else {
3154 OWSTTaskTerminator::yield();
3155 }
3156 }
3157
3158 void CMSConcMarkingTaskTerminator::set_task(CMSConcMarkingTask* task) {
3159 if (UseOWSTTaskTerminator) {
3160 ((CMSConcMarkingOWSTTerminator*)_term)->set_task(task);
3161 } else {
3162 ((CMSConcMarkingParallelTerminator*)_term)->set_task(task);
3163 }
3164 }
3165
3166 ////////////////////////////////////////////////////////////////
3167 // Concurrent Marking Algorithm Sketch
3168 ////////////////////////////////////////////////////////////////
3169 // Until all tasks exhausted (both spaces):
3170 // -- claim next available chunk
3171 // -- bump global finger via CAS
3172 // -- find first object that starts in this chunk
3173 // and start scanning bitmap from that position
3174 // -- scan marked objects for oops
3175 // -- CAS-mark target, and if successful:
3176 // . if target oop is above global finger (volatile read)
3177 // nothing to do
3178 // . if target oop is in chunk and above local finger
3179 // then nothing to do
3180 // . else push on work-queue
3181 // -- Deal with possible overflow issues:
3182 // . local work-queue overflow causes stuff to be pushed on
3183 // global (common) overflow queue
3184 // . always first empty local work queue
3185 // . then get a batch of oops from global work queue if any
3186 // . then do work stealing
3187 // -- When all tasks claimed (both spaces)
3188 // and local work queue empty,
3189 // then in a loop do:
3190 // . check global overflow stack; steal a batch of oops and trace
3191 // . try to steal from other threads oif GOS is empty
3192 // . if neither is available, offer termination
3193 // -- Terminate and return result
3194 //
3195 void CMSConcMarkingTask::work(uint worker_id) {
3196 elapsedTimer _timer;
3197 ResourceMark rm;
3198 HandleMark hm;
3199
3200 DEBUG_ONLY(_collector->verify_overflow_empty();)
3201
3202 // Before we begin work, our work queue should be empty
3203 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3204 // Scan the bitmap covering _cms_space, tracing through grey objects.
3205 _timer.start();
3206 do_scan_and_mark(worker_id, _cms_space);
3207 _timer.stop();
3208 log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3209
3210 // ... do work stealing
3211 _timer.reset();
3212 _timer.start();
3213 do_work_steal(worker_id);
3214 _timer.stop();
3215 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3216 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3217 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3218 // Note that under the current task protocol, the
3219 // following assertion is true even of the spaces
3220 // expanded since the completion of the concurrent
3221 // marking. XXX This will likely change under a strict
3222 // ABORT semantics.
3223 // After perm removal the comparison was changed to
3224 // greater than or equal to from strictly greater than.
3225 // Before perm removal the highest address sweep would
3226 // have been at the end of perm gen but now is at the
3227 // end of the tenured gen.
3228 assert(_global_finger >= _cms_space->end(),
3229 "All tasks have been completed");
3230 DEBUG_ONLY(_collector->verify_overflow_empty();)
3231 }
3232
3233 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3234 HeapWord* read = _global_finger;
3235 HeapWord* cur = read;
3236 while (f > read) {
3237 cur = read;
3238 read = Atomic::cmpxchg(f, &_global_finger, cur);
3239 if (cur == read) {
3240 // our cas succeeded
3241 assert(_global_finger >= f, "protocol consistency");
3242 break;
3243 }
3244 }
3245 }
3246
3247 // This is really inefficient, and should be redone by
3248 // using (not yet available) block-read and -write interfaces to the
3249 // stack and the work_queue. XXX FIX ME !!!
3250 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3251 OopTaskQueue* work_q) {
3252 // Fast lock-free check
3253 if (ovflw_stk->length() == 0) {
3254 return false;
3255 }
3256 assert(work_q->size() == 0, "Shouldn't steal");
3257 MutexLockerEx ml(ovflw_stk->par_lock(),
3258 Mutex::_no_safepoint_check_flag);
3259 // Grab up to 1/4 the size of the work queue
3260 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3261 (size_t)ParGCDesiredObjsFromOverflowList);
3262 num = MIN2(num, ovflw_stk->length());
3263 for (int i = (int) num; i > 0; i--) {
3264 oop cur = ovflw_stk->pop();
3265 assert(cur != NULL, "Counted wrong?");
3266 work_q->push(cur);
3267 }
3268 return num > 0;
3269 }
3270
3271 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3272 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3273 int n_tasks = pst->n_tasks();
3274 // We allow that there may be no tasks to do here because
3275 // we are restarting after a stack overflow.
3276 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3277 uint nth_task = 0;
3278
3279 HeapWord* aligned_start = sp->bottom();
3280 if (sp->used_region().contains(_restart_addr)) {
3281 // Align down to a card boundary for the start of 0th task
3282 // for this space.
3283 aligned_start = align_down(_restart_addr, CardTable::card_size);
3284 }
3285
3286 size_t chunk_size = sp->marking_task_size();
3287 while (pst->try_claim_task(/* reference */ nth_task)) {
3288 // Having claimed the nth task in this space,
3289 // compute the chunk that it corresponds to:
3290 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3291 aligned_start + (nth_task+1)*chunk_size);
3292 // Try and bump the global finger via a CAS;
3293 // note that we need to do the global finger bump
3294 // _before_ taking the intersection below, because
3295 // the task corresponding to that region will be
3296 // deemed done even if the used_region() expands
3297 // because of allocation -- as it almost certainly will
3298 // during start-up while the threads yield in the
3299 // closure below.
3300 HeapWord* finger = span.end();
3301 bump_global_finger(finger); // atomically
3302 // There are null tasks here corresponding to chunks
3303 // beyond the "top" address of the space.
3304 span = span.intersection(sp->used_region());
3305 if (!span.is_empty()) { // Non-null task
3306 HeapWord* prev_obj;
3307 assert(!span.contains(_restart_addr) || nth_task == 0,
3308 "Inconsistency");
3309 if (nth_task == 0) {
3310 // For the 0th task, we'll not need to compute a block_start.
3311 if (span.contains(_restart_addr)) {
3312 // In the case of a restart because of stack overflow,
3313 // we might additionally skip a chunk prefix.
3314 prev_obj = _restart_addr;
3315 } else {
3316 prev_obj = span.start();
3317 }
3318 } else {
3319 // We want to skip the first object because
3320 // the protocol is to scan any object in its entirety
3321 // that _starts_ in this span; a fortiori, any
3322 // object starting in an earlier span is scanned
3323 // as part of an earlier claimed task.
3324 // Below we use the "careful" version of block_start
3325 // so we do not try to navigate uninitialized objects.
3326 prev_obj = sp->block_start_careful(span.start());
3327 // Below we use a variant of block_size that uses the
3328 // Printezis bits to avoid waiting for allocated
3329 // objects to become initialized/parsable.
3330 while (prev_obj < span.start()) {
3331 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3332 if (sz > 0) {
3333 prev_obj += sz;
3334 } else {
3335 // In this case we may end up doing a bit of redundant
3336 // scanning, but that appears unavoidable, short of
3337 // locking the free list locks; see bug 6324141.
3338 break;
3339 }
3340 }
3341 }
3342 if (prev_obj < span.end()) {
3343 MemRegion my_span = MemRegion(prev_obj, span.end());
3344 // Do the marking work within a non-empty span --
3345 // the last argument to the constructor indicates whether the
3346 // iteration should be incremental with periodic yields.
3347 ParMarkFromRootsClosure cl(this, _collector, my_span,
3348 &_collector->_markBitMap,
3349 work_queue(i),
3350 &_collector->_markStack);
3351 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3352 } // else nothing to do for this task
3353 } // else nothing to do for this task
3354 }
3355 // We'd be tempted to assert here that since there are no
3356 // more tasks left to claim in this space, the global_finger
3357 // must exceed space->top() and a fortiori space->end(). However,
3358 // that would not quite be correct because the bumping of
3359 // global_finger occurs strictly after the claiming of a task,
3360 // so by the time we reach here the global finger may not yet
3361 // have been bumped up by the thread that claimed the last
3362 // task.
3363 pst->all_tasks_completed();
3364 }
3365
3366 class ParConcMarkingClosure: public MetadataVisitingOopIterateClosure {
3367 private:
3368 CMSCollector* _collector;
3369 CMSConcMarkingTask* _task;
3370 MemRegion _span;
3371 CMSBitMap* _bit_map;
3372 CMSMarkStack* _overflow_stack;
3373 OopTaskQueue* _work_queue;
3374 protected:
3375 DO_OOP_WORK_DEFN
3376 public:
3377 ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3378 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3379 MetadataVisitingOopIterateClosure(collector->ref_processor()),
3380 _collector(collector),
3381 _task(task),
3382 _span(collector->_span),
3383 _bit_map(bit_map),
3384 _overflow_stack(overflow_stack),
3385 _work_queue(work_queue)
3386 { }
3387 virtual void do_oop(oop* p);
3388 virtual void do_oop(narrowOop* p);
3389
3390 void trim_queue(size_t max);
3391 void handle_stack_overflow(HeapWord* lost);
3392 void do_yield_check() {
3393 if (_task->should_yield()) {
3394 _task->yield();
3395 }
3396 }
3397 };
3398
3399 DO_OOP_WORK_IMPL(ParConcMarkingClosure)
3400
3401 // Grey object scanning during work stealing phase --
3402 // the salient assumption here is that any references
3403 // that are in these stolen objects being scanned must
3404 // already have been initialized (else they would not have
3405 // been published), so we do not need to check for
3406 // uninitialized objects before pushing here.
3407 void ParConcMarkingClosure::do_oop(oop obj) {
3408 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3409 HeapWord* addr = (HeapWord*)obj;
3410 // Check if oop points into the CMS generation
3411 // and is not marked
3412 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3413 // a white object ...
3414 // If we manage to "claim" the object, by being the
3415 // first thread to mark it, then we push it on our
3416 // marking stack
3417 if (_bit_map->par_mark(addr)) { // ... now grey
3418 // push on work queue (grey set)
3419 bool simulate_overflow = false;
3420 NOT_PRODUCT(
3421 if (CMSMarkStackOverflowALot &&
3422 _collector->simulate_overflow()) {
3423 // simulate a stack overflow
3424 simulate_overflow = true;
3425 }
3426 )
3427 if (simulate_overflow ||
3428 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3429 // stack overflow
3430 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3431 // We cannot assert that the overflow stack is full because
3432 // it may have been emptied since.
3433 assert(simulate_overflow ||
3434 _work_queue->size() == _work_queue->max_elems(),
3435 "Else push should have succeeded");
3436 handle_stack_overflow(addr);
3437 }
3438 } // Else, some other thread got there first
3439 do_yield_check();
3440 }
3441 }
3442
3443 void ParConcMarkingClosure::trim_queue(size_t max) {
3444 while (_work_queue->size() > max) {
3445 oop new_oop;
3446 if (_work_queue->pop_local(new_oop)) {
3447 assert(oopDesc::is_oop(new_oop), "Should be an oop");
3448 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3449 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3450 new_oop->oop_iterate(this); // do_oop() above
3451 do_yield_check();
3452 }
3453 }
3454 }
3455
3456 // Upon stack overflow, we discard (part of) the stack,
3457 // remembering the least address amongst those discarded
3458 // in CMSCollector's _restart_address.
3459 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3460 // We need to do this under a mutex to prevent other
3461 // workers from interfering with the work done below.
3462 MutexLockerEx ml(_overflow_stack->par_lock(),
3463 Mutex::_no_safepoint_check_flag);
3464 // Remember the least grey address discarded
3465 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3466 _collector->lower_restart_addr(ra);
3467 _overflow_stack->reset(); // discard stack contents
3468 _overflow_stack->expand(); // expand the stack if possible
3469 }
3470
3471
3472 void CMSConcMarkingTask::do_work_steal(int i) {
3473 OopTaskQueue* work_q = work_queue(i);
3474 oop obj_to_scan;
3475 CMSBitMap* bm = &(_collector->_markBitMap);
3476 CMSMarkStack* ovflw = &(_collector->_markStack);
3477 ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3478 while (true) {
3479 cl.trim_queue(0);
3480 assert(work_q->size() == 0, "Should have been emptied above");
3481 if (get_work_from_overflow_stack(ovflw, work_q)) {
3482 // Can't assert below because the work obtained from the
3483 // overflow stack may already have been stolen from us.
3484 // assert(work_q->size() > 0, "Work from overflow stack");
3485 continue;
3486 } else if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
3487 assert(oopDesc::is_oop(obj_to_scan), "Should be an oop");
3488 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3489 obj_to_scan->oop_iterate(&cl);
3490 } else if (terminator()->offer_termination(&_term_term)) {
3491 assert(work_q->size() == 0, "Impossible!");
3492 break;
3493 } else if (yielding() || should_yield()) {
3494 yield();
3495 }
3496 }
3497 }
3498
3499 // This is run by the CMS (coordinator) thread.
3500 void CMSConcMarkingTask::coordinator_yield() {
3501 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3502 "CMS thread should hold CMS token");
3503 // First give up the locks, then yield, then re-lock
3504 // We should probably use a constructor/destructor idiom to
3505 // do this unlock/lock or modify the MutexUnlocker class to
3506 // serve our purpose. XXX
3507 assert_lock_strong(_bit_map_lock);
3508 _bit_map_lock->unlock();
3509 ConcurrentMarkSweepThread::desynchronize(true);
3510 _collector->stopTimer();
3511 _collector->incrementYields();
3512
3513 // It is possible for whichever thread initiated the yield request
3514 // not to get a chance to wake up and take the bitmap lock between
3515 // this thread releasing it and reacquiring it. So, while the
3516 // should_yield() flag is on, let's sleep for a bit to give the
3517 // other thread a chance to wake up. The limit imposed on the number
3518 // of iterations is defensive, to avoid any unforseen circumstances
3519 // putting us into an infinite loop. Since it's always been this
3520 // (coordinator_yield()) method that was observed to cause the
3521 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3522 // which is by default non-zero. For the other seven methods that
3523 // also perform the yield operation, as are using a different
3524 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3525 // can enable the sleeping for those methods too, if necessary.
3526 // See 6442774.
3527 //
3528 // We really need to reconsider the synchronization between the GC
3529 // thread and the yield-requesting threads in the future and we
3530 // should really use wait/notify, which is the recommended
3531 // way of doing this type of interaction. Additionally, we should
3532 // consolidate the eight methods that do the yield operation and they
3533 // are almost identical into one for better maintainability and
3534 // readability. See 6445193.
3535 //
3536 // Tony 2006.06.29
3537 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3538 ConcurrentMarkSweepThread::should_yield() &&
3539 !CMSCollector::foregroundGCIsActive(); ++i) {
3540 os::sleep(Thread::current(), 1, false);
3541 }
3542
3543 ConcurrentMarkSweepThread::synchronize(true);
3544 _bit_map_lock->lock_without_safepoint_check();
3545 _collector->startTimer();
3546 }
3547
3548 bool CMSCollector::do_marking_mt() {
3549 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3550 uint num_workers = WorkerPolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3551 conc_workers()->active_workers(),
3552 Threads::number_of_non_daemon_threads());
3553 num_workers = conc_workers()->update_active_workers(num_workers);
3554 log_info(gc,task)("Using %u workers of %u for marking", num_workers, conc_workers()->total_workers());
3555
3556 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3557
3558 CMSConcMarkingTask tsk(this,
3559 cms_space,
3560 conc_workers(),
3561 task_queues());
3562
3563 // Since the actual number of workers we get may be different
3564 // from the number we requested above, do we need to do anything different
3565 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3566 // class?? XXX
3567 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3568
3569 // Refs discovery is already non-atomic.
3570 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3571 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3572 conc_workers()->start_task(&tsk);
3573 while (tsk.yielded()) {
3574 tsk.coordinator_yield();
3575 conc_workers()->continue_task(&tsk);
3576 }
3577 // If the task was aborted, _restart_addr will be non-NULL
3578 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3579 while (_restart_addr != NULL) {
3580 // XXX For now we do not make use of ABORTED state and have not
3581 // yet implemented the right abort semantics (even in the original
3582 // single-threaded CMS case). That needs some more investigation
3583 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3584 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3585 // If _restart_addr is non-NULL, a marking stack overflow
3586 // occurred; we need to do a fresh marking iteration from the
3587 // indicated restart address.
3588 if (_foregroundGCIsActive) {
3589 // We may be running into repeated stack overflows, having
3590 // reached the limit of the stack size, while making very
3591 // slow forward progress. It may be best to bail out and
3592 // let the foreground collector do its job.
3593 // Clear _restart_addr, so that foreground GC
3594 // works from scratch. This avoids the headache of
3595 // a "rescan" which would otherwise be needed because
3596 // of the dirty mod union table & card table.
3597 _restart_addr = NULL;
3598 return false;
3599 }
3600 // Adjust the task to restart from _restart_addr
3601 tsk.reset(_restart_addr);
3602 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3603 _restart_addr);
3604 _restart_addr = NULL;
3605 // Get the workers going again
3606 conc_workers()->start_task(&tsk);
3607 while (tsk.yielded()) {
3608 tsk.coordinator_yield();
3609 conc_workers()->continue_task(&tsk);
3610 }
3611 }
3612 assert(tsk.completed(), "Inconsistency");
3613 assert(tsk.result() == true, "Inconsistency");
3614 return true;
3615 }
3616
3617 bool CMSCollector::do_marking_st() {
3618 ResourceMark rm;
3619 HandleMark hm;
3620
3621 // Temporarily make refs discovery single threaded (non-MT)
3622 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3623 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3624 &_markStack, CMSYield);
3625 // the last argument to iterate indicates whether the iteration
3626 // should be incremental with periodic yields.
3627 _markBitMap.iterate(&markFromRootsClosure);
3628 // If _restart_addr is non-NULL, a marking stack overflow
3629 // occurred; we need to do a fresh iteration from the
3630 // indicated restart address.
3631 while (_restart_addr != NULL) {
3632 if (_foregroundGCIsActive) {
3633 // We may be running into repeated stack overflows, having
3634 // reached the limit of the stack size, while making very
3635 // slow forward progress. It may be best to bail out and
3636 // let the foreground collector do its job.
3637 // Clear _restart_addr, so that foreground GC
3638 // works from scratch. This avoids the headache of
3639 // a "rescan" which would otherwise be needed because
3640 // of the dirty mod union table & card table.
3641 _restart_addr = NULL;
3642 return false; // indicating failure to complete marking
3643 }
3644 // Deal with stack overflow:
3645 // we restart marking from _restart_addr
3646 HeapWord* ra = _restart_addr;
3647 markFromRootsClosure.reset(ra);
3648 _restart_addr = NULL;
3649 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3650 }
3651 return true;
3652 }
3653
3654 void CMSCollector::preclean() {
3655 check_correct_thread_executing();
3656 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3657 verify_work_stacks_empty();
3658 verify_overflow_empty();
3659 _abort_preclean = false;
3660 if (CMSPrecleaningEnabled) {
3661 if (!CMSEdenChunksRecordAlways) {
3662 _eden_chunk_index = 0;
3663 }
3664 size_t used = get_eden_used();
3665 size_t capacity = get_eden_capacity();
3666 // Don't start sampling unless we will get sufficiently
3667 // many samples.
3668 if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100)
3669 * CMSScheduleRemarkEdenPenetration)) {
3670 _start_sampling = true;
3671 } else {
3672 _start_sampling = false;
3673 }
3674 GCTraceCPUTime tcpu;
3675 CMSPhaseAccounting pa(this, "Concurrent Preclean");
3676 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3677 }
3678 CMSTokenSync x(true); // is cms thread
3679 if (CMSPrecleaningEnabled) {
3680 sample_eden();
3681 _collectorState = AbortablePreclean;
3682 } else {
3683 _collectorState = FinalMarking;
3684 }
3685 verify_work_stacks_empty();
3686 verify_overflow_empty();
3687 }
3688
3689 // Try and schedule the remark such that young gen
3690 // occupancy is CMSScheduleRemarkEdenPenetration %.
3691 void CMSCollector::abortable_preclean() {
3692 check_correct_thread_executing();
3693 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3694 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3695
3696 // If Eden's current occupancy is below this threshold,
3697 // immediately schedule the remark; else preclean
3698 // past the next scavenge in an effort to
3699 // schedule the pause as described above. By choosing
3700 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3701 // we will never do an actual abortable preclean cycle.
3702 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3703 GCTraceCPUTime tcpu;
3704 CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean");
3705 // We need more smarts in the abortable preclean
3706 // loop below to deal with cases where allocation
3707 // in young gen is very very slow, and our precleaning
3708 // is running a losing race against a horde of
3709 // mutators intent on flooding us with CMS updates
3710 // (dirty cards).
3711 // One, admittedly dumb, strategy is to give up
3712 // after a certain number of abortable precleaning loops
3713 // or after a certain maximum time. We want to make
3714 // this smarter in the next iteration.
3715 // XXX FIX ME!!! YSR
3716 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3717 while (!(should_abort_preclean() ||
3718 ConcurrentMarkSweepThread::cmst()->should_terminate())) {
3719 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3720 cumworkdone += workdone;
3721 loops++;
3722 // Voluntarily terminate abortable preclean phase if we have
3723 // been at it for too long.
3724 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3725 loops >= CMSMaxAbortablePrecleanLoops) {
3726 log_debug(gc)(" CMS: abort preclean due to loops ");
3727 break;
3728 }
3729 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3730 log_debug(gc)(" CMS: abort preclean due to time ");
3731 break;
3732 }
3733 // If we are doing little work each iteration, we should
3734 // take a short break.
3735 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3736 // Sleep for some time, waiting for work to accumulate
3737 stopTimer();
3738 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3739 startTimer();
3740 waited++;
3741 }
3742 }
3743 log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3744 loops, waited, cumworkdone);
3745 }
3746 CMSTokenSync x(true); // is cms thread
3747 if (_collectorState != Idling) {
3748 assert(_collectorState == AbortablePreclean,
3749 "Spontaneous state transition?");
3750 _collectorState = FinalMarking;
3751 } // Else, a foreground collection completed this CMS cycle.
3752 return;
3753 }
3754
3755 // Respond to an Eden sampling opportunity
3756 void CMSCollector::sample_eden() {
3757 // Make sure a young gc cannot sneak in between our
3758 // reading and recording of a sample.
3759 assert(Thread::current()->is_ConcurrentGC_thread(),
3760 "Only the cms thread may collect Eden samples");
3761 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3762 "Should collect samples while holding CMS token");
3763 if (!_start_sampling) {
3764 return;
3765 }
3766 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3767 // is populated by the young generation.
3768 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3769 if (_eden_chunk_index < _eden_chunk_capacity) {
3770 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3771 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3772 "Unexpected state of Eden");
3773 // We'd like to check that what we just sampled is an oop-start address;
3774 // however, we cannot do that here since the object may not yet have been
3775 // initialized. So we'll instead do the check when we _use_ this sample
3776 // later.
3777 if (_eden_chunk_index == 0 ||
3778 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3779 _eden_chunk_array[_eden_chunk_index-1])
3780 >= CMSSamplingGrain)) {
3781 _eden_chunk_index++; // commit sample
3782 }
3783 }
3784 }
3785 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3786 size_t used = get_eden_used();
3787 size_t capacity = get_eden_capacity();
3788 assert(used <= capacity, "Unexpected state of Eden");
3789 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3790 _abort_preclean = true;
3791 }
3792 }
3793 }
3794
3795 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3796 assert(_collectorState == Precleaning ||
3797 _collectorState == AbortablePreclean, "incorrect state");
3798 ResourceMark rm;
3799 HandleMark hm;
3800
3801 // Precleaning is currently not MT but the reference processor
3802 // may be set for MT. Disable it temporarily here.
3803 ReferenceProcessor* rp = ref_processor();
3804 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3805
3806 // Do one pass of scrubbing the discovered reference lists
3807 // to remove any reference objects with strongly-reachable
3808 // referents.
3809 if (clean_refs) {
3810 CMSPrecleanRefsYieldClosure yield_cl(this);
3811 assert(_span_based_discoverer.span().equals(_span), "Spans should be equal");
3812 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3813 &_markStack, true /* preclean */);
3814 CMSDrainMarkingStackClosure complete_trace(this,
3815 _span, &_markBitMap, &_markStack,
3816 &keep_alive, true /* preclean */);
3817
3818 // We don't want this step to interfere with a young
3819 // collection because we don't want to take CPU
3820 // or memory bandwidth away from the young GC threads
3821 // (which may be as many as there are CPUs).
3822 // Note that we don't need to protect ourselves from
3823 // interference with mutators because they can't
3824 // manipulate the discovered reference lists nor affect
3825 // the computed reachability of the referents, the
3826 // only properties manipulated by the precleaning
3827 // of these reference lists.
3828 stopTimer();
3829 CMSTokenSyncWithLocks x(true /* is cms thread */,
3830 bitMapLock());
3831 startTimer();
3832 sample_eden();
3833
3834 // The following will yield to allow foreground
3835 // collection to proceed promptly. XXX YSR:
3836 // The code in this method may need further
3837 // tweaking for better performance and some restructuring
3838 // for cleaner interfaces.
3839 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3840 rp->preclean_discovered_references(
3841 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3842 gc_timer);
3843 }
3844
3845 if (clean_survivor) { // preclean the active survivor space(s)
3846 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3847 &_markBitMap, &_modUnionTable,
3848 &_markStack, true /* precleaning phase */);
3849 stopTimer();
3850 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3851 bitMapLock());
3852 startTimer();
3853 unsigned int before_count =
3854 CMSHeap::heap()->total_collections();
3855 SurvivorSpacePrecleanClosure
3856 sss_cl(this, _span, &_markBitMap, &_markStack,
3857 &pam_cl, before_count, CMSYield);
3858 _young_gen->from()->object_iterate_careful(&sss_cl);
3859 _young_gen->to()->object_iterate_careful(&sss_cl);
3860 }
3861 MarkRefsIntoAndScanClosure
3862 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3863 &_markStack, this, CMSYield,
3864 true /* precleaning phase */);
3865 // CAUTION: The following closure has persistent state that may need to
3866 // be reset upon a decrease in the sequence of addresses it
3867 // processes.
3868 ScanMarkedObjectsAgainCarefullyClosure
3869 smoac_cl(this, _span,
3870 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3871
3872 // Preclean dirty cards in ModUnionTable and CardTable using
3873 // appropriate convergence criterion;
3874 // repeat CMSPrecleanIter times unless we find that
3875 // we are losing.
3876 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3877 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3878 "Bad convergence multiplier");
3879 assert(CMSPrecleanThreshold >= 100,
3880 "Unreasonably low CMSPrecleanThreshold");
3881
3882 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3883 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3884 numIter < CMSPrecleanIter;
3885 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3886 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3887 log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3888 // Either there are very few dirty cards, so re-mark
3889 // pause will be small anyway, or our pre-cleaning isn't
3890 // that much faster than the rate at which cards are being
3891 // dirtied, so we might as well stop and re-mark since
3892 // precleaning won't improve our re-mark time by much.
3893 if (curNumCards <= CMSPrecleanThreshold ||
3894 (numIter > 0 &&
3895 (curNumCards * CMSPrecleanDenominator >
3896 lastNumCards * CMSPrecleanNumerator))) {
3897 numIter++;
3898 cumNumCards += curNumCards;
3899 break;
3900 }
3901 }
3902
3903 preclean_cld(&mrias_cl, _cmsGen->freelistLock());
3904
3905 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3906 cumNumCards += curNumCards;
3907 log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3908 curNumCards, cumNumCards, numIter);
3909 return cumNumCards; // as a measure of useful work done
3910 }
3911
3912 // PRECLEANING NOTES:
3913 // Precleaning involves:
3914 // . reading the bits of the modUnionTable and clearing the set bits.
3915 // . For the cards corresponding to the set bits, we scan the
3916 // objects on those cards. This means we need the free_list_lock
3917 // so that we can safely iterate over the CMS space when scanning
3918 // for oops.
3919 // . When we scan the objects, we'll be both reading and setting
3920 // marks in the marking bit map, so we'll need the marking bit map.
3921 // . For protecting _collector_state transitions, we take the CGC_lock.
3922 // Note that any races in the reading of of card table entries by the
3923 // CMS thread on the one hand and the clearing of those entries by the
3924 // VM thread or the setting of those entries by the mutator threads on the
3925 // other are quite benign. However, for efficiency it makes sense to keep
3926 // the VM thread from racing with the CMS thread while the latter is
3927 // dirty card info to the modUnionTable. We therefore also use the
3928 // CGC_lock to protect the reading of the card table and the mod union
3929 // table by the CM thread.
3930 // . We run concurrently with mutator updates, so scanning
3931 // needs to be done carefully -- we should not try to scan
3932 // potentially uninitialized objects.
3933 //
3934 // Locking strategy: While holding the CGC_lock, we scan over and
3935 // reset a maximal dirty range of the mod union / card tables, then lock
3936 // the free_list_lock and bitmap lock to do a full marking, then
3937 // release these locks; and repeat the cycle. This allows for a
3938 // certain amount of fairness in the sharing of these locks between
3939 // the CMS collector on the one hand, and the VM thread and the
3940 // mutators on the other.
3941
3942 // NOTE: preclean_mod_union_table() and preclean_card_table()
3943 // further below are largely identical; if you need to modify
3944 // one of these methods, please check the other method too.
3945
3946 size_t CMSCollector::preclean_mod_union_table(
3947 ConcurrentMarkSweepGeneration* old_gen,
3948 ScanMarkedObjectsAgainCarefullyClosure* cl) {
3949 verify_work_stacks_empty();
3950 verify_overflow_empty();
3951
3952 // strategy: starting with the first card, accumulate contiguous
3953 // ranges of dirty cards; clear these cards, then scan the region
3954 // covered by these cards.
3955
3956 // Since all of the MUT is committed ahead, we can just use
3957 // that, in case the generations expand while we are precleaning.
3958 // It might also be fine to just use the committed part of the
3959 // generation, but we might potentially miss cards when the
3960 // generation is rapidly expanding while we are in the midst
3961 // of precleaning.
3962 HeapWord* startAddr = old_gen->reserved().start();
3963 HeapWord* endAddr = old_gen->reserved().end();
3964
3965 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
3966
3967 size_t numDirtyCards, cumNumDirtyCards;
3968 HeapWord *nextAddr, *lastAddr;
3969 for (cumNumDirtyCards = numDirtyCards = 0,
3970 nextAddr = lastAddr = startAddr;
3971 nextAddr < endAddr;
3972 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3973
3974 ResourceMark rm;
3975 HandleMark hm;
3976
3977 MemRegion dirtyRegion;
3978 {
3979 stopTimer();
3980 // Potential yield point
3981 CMSTokenSync ts(true);
3982 startTimer();
3983 sample_eden();
3984 // Get dirty region starting at nextOffset (inclusive),
3985 // simultaneously clearing it.
3986 dirtyRegion =
3987 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3988 assert(dirtyRegion.start() >= nextAddr,
3989 "returned region inconsistent?");
3990 }
3991 // Remember where the next search should begin.
3992 // The returned region (if non-empty) is a right open interval,
3993 // so lastOffset is obtained from the right end of that
3994 // interval.
3995 lastAddr = dirtyRegion.end();
3996 // Should do something more transparent and less hacky XXX
3997 numDirtyCards =
3998 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
3999
4000 // We'll scan the cards in the dirty region (with periodic
4001 // yields for foreground GC as needed).
4002 if (!dirtyRegion.is_empty()) {
4003 assert(numDirtyCards > 0, "consistency check");
4004 HeapWord* stop_point = NULL;
4005 stopTimer();
4006 // Potential yield point
4007 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
4008 bitMapLock());
4009 startTimer();
4010 {
4011 verify_work_stacks_empty();
4012 verify_overflow_empty();
4013 sample_eden();
4014 stop_point =
4015 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4016 }
4017 if (stop_point != NULL) {
4018 // The careful iteration stopped early either because it found an
4019 // uninitialized object, or because we were in the midst of an
4020 // "abortable preclean", which should now be aborted. Redirty
4021 // the bits corresponding to the partially-scanned or unscanned
4022 // cards. We'll either restart at the next block boundary or
4023 // abort the preclean.
4024 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4025 "Should only be AbortablePreclean.");
4026 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4027 if (should_abort_preclean()) {
4028 break; // out of preclean loop
4029 } else {
4030 // Compute the next address at which preclean should pick up;
4031 // might need bitMapLock in order to read P-bits.
4032 lastAddr = next_card_start_after_block(stop_point);
4033 }
4034 }
4035 } else {
4036 assert(lastAddr == endAddr, "consistency check");
4037 assert(numDirtyCards == 0, "consistency check");
4038 break;
4039 }
4040 }
4041 verify_work_stacks_empty();
4042 verify_overflow_empty();
4043 return cumNumDirtyCards;
4044 }
4045
4046 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4047 // below are largely identical; if you need to modify
4048 // one of these methods, please check the other method too.
4049
4050 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
4051 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4052 // strategy: it's similar to precleamModUnionTable above, in that
4053 // we accumulate contiguous ranges of dirty cards, mark these cards
4054 // precleaned, then scan the region covered by these cards.
4055 HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high());
4056 HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4057
4058 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4059
4060 size_t numDirtyCards, cumNumDirtyCards;
4061 HeapWord *lastAddr, *nextAddr;
4062
4063 for (cumNumDirtyCards = numDirtyCards = 0,
4064 nextAddr = lastAddr = startAddr;
4065 nextAddr < endAddr;
4066 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4067
4068 ResourceMark rm;
4069 HandleMark hm;
4070
4071 MemRegion dirtyRegion;
4072 {
4073 // See comments in "Precleaning notes" above on why we
4074 // do this locking. XXX Could the locking overheads be
4075 // too high when dirty cards are sparse? [I don't think so.]
4076 stopTimer();
4077 CMSTokenSync x(true); // is cms thread
4078 startTimer();
4079 sample_eden();
4080 // Get and clear dirty region from card table
4081 dirtyRegion = _ct->dirty_card_range_after_reset(MemRegion(nextAddr, endAddr),
4082 true,
4083 CardTable::precleaned_card_val());
4084
4085 assert(dirtyRegion.start() >= nextAddr,
4086 "returned region inconsistent?");
4087 }
4088 lastAddr = dirtyRegion.end();
4089 numDirtyCards =
4090 dirtyRegion.word_size()/CardTable::card_size_in_words;
4091
4092 if (!dirtyRegion.is_empty()) {
4093 stopTimer();
4094 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4095 startTimer();
4096 sample_eden();
4097 verify_work_stacks_empty();
4098 verify_overflow_empty();
4099 HeapWord* stop_point =
4100 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4101 if (stop_point != NULL) {
4102 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4103 "Should only be AbortablePreclean.");
4104 _ct->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4105 if (should_abort_preclean()) {
4106 break; // out of preclean loop
4107 } else {
4108 // Compute the next address at which preclean should pick up.
4109 lastAddr = next_card_start_after_block(stop_point);
4110 }
4111 }
4112 } else {
4113 break;
4114 }
4115 }
4116 verify_work_stacks_empty();
4117 verify_overflow_empty();
4118 return cumNumDirtyCards;
4119 }
4120
4121 class PrecleanCLDClosure : public CLDClosure {
4122 MetadataVisitingOopsInGenClosure* _cm_closure;
4123 public:
4124 PrecleanCLDClosure(MetadataVisitingOopsInGenClosure* oop_closure) : _cm_closure(oop_closure) {}
4125 void do_cld(ClassLoaderData* cld) {
4126 if (cld->has_accumulated_modified_oops()) {
4127 cld->clear_accumulated_modified_oops();
4128
4129 _cm_closure->do_cld(cld);
4130 }
4131 }
4132 };
4133
4134 // The freelist lock is needed to prevent asserts, is it really needed?
4135 void CMSCollector::preclean_cld(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4136 // Needed to walk CLDG
4137 MutexLocker ml(ClassLoaderDataGraph_lock);
4138
4139 cl->set_freelistLock(freelistLock);
4140
4141 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4142
4143 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4144 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4145 PrecleanCLDClosure preclean_closure(cl);
4146 ClassLoaderDataGraph::cld_do(&preclean_closure);
4147
4148 verify_work_stacks_empty();
4149 verify_overflow_empty();
4150 }
4151
4152 void CMSCollector::checkpointRootsFinal() {
4153 assert(_collectorState == FinalMarking, "incorrect state transition?");
4154 check_correct_thread_executing();
4155 // world is stopped at this checkpoint
4156 assert(SafepointSynchronize::is_at_safepoint(),
4157 "world should be stopped");
4158 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
4159
4160 verify_work_stacks_empty();
4161 verify_overflow_empty();
4162
4163 log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4164 _young_gen->used() / K, _young_gen->capacity() / K);
4165 {
4166 if (CMSScavengeBeforeRemark) {
4167 CMSHeap* heap = CMSHeap::heap();
4168 // Temporarily set flag to false, GCH->do_collection will
4169 // expect it to be false and set to true
4170 FlagSetting fl(heap->_is_gc_active, false);
4171
4172 heap->do_collection(true, // full (i.e. force, see below)
4173 false, // !clear_all_soft_refs
4174 0, // size
4175 false, // is_tlab
4176 GenCollectedHeap::YoungGen // type
4177 );
4178 }
4179 FreelistLocker x(this);
4180 MutexLockerEx y(bitMapLock(),
4181 Mutex::_no_safepoint_check_flag);
4182 checkpointRootsFinalWork();
4183 }
4184 verify_work_stacks_empty();
4185 verify_overflow_empty();
4186 }
4187
4188 void CMSCollector::checkpointRootsFinalWork() {
4189 GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm);
4190
4191 assert(haveFreelistLocks(), "must have free list locks");
4192 assert_lock_strong(bitMapLock());
4193
4194 ResourceMark rm;
4195 HandleMark hm;
4196
4197 CMSHeap* heap = CMSHeap::heap();
4198
4199 assert(haveFreelistLocks(), "must have free list locks");
4200 assert_lock_strong(bitMapLock());
4201
4202 // We might assume that we need not fill TLAB's when
4203 // CMSScavengeBeforeRemark is set, because we may have just done
4204 // a scavenge which would have filled all TLAB's -- and besides
4205 // Eden would be empty. This however may not always be the case --
4206 // for instance although we asked for a scavenge, it may not have
4207 // happened because of a JNI critical section. We probably need
4208 // a policy for deciding whether we can in that case wait until
4209 // the critical section releases and then do the remark following
4210 // the scavenge, and skip it here. In the absence of that policy,
4211 // or of an indication of whether the scavenge did indeed occur,
4212 // we cannot rely on TLAB's having been filled and must do
4213 // so here just in case a scavenge did not happen.
4214 heap->ensure_parsability(false); // fill TLAB's, but no need to retire them
4215 // Update the saved marks which may affect the root scans.
4216 heap->save_marks();
4217
4218 print_eden_and_survivor_chunk_arrays();
4219
4220 {
4221 #if COMPILER2_OR_JVMCI
4222 DerivedPointerTableDeactivate dpt_deact;
4223 #endif
4224
4225 // Note on the role of the mod union table:
4226 // Since the marker in "markFromRoots" marks concurrently with
4227 // mutators, it is possible for some reachable objects not to have been
4228 // scanned. For instance, an only reference to an object A was
4229 // placed in object B after the marker scanned B. Unless B is rescanned,
4230 // A would be collected. Such updates to references in marked objects
4231 // are detected via the mod union table which is the set of all cards
4232 // dirtied since the first checkpoint in this GC cycle and prior to
4233 // the most recent young generation GC, minus those cleaned up by the
4234 // concurrent precleaning.
4235 if (CMSParallelRemarkEnabled) {
4236 GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm);
4237 do_remark_parallel();
4238 } else {
4239 GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm);
4240 do_remark_non_parallel();
4241 }
4242 }
4243 verify_work_stacks_empty();
4244 verify_overflow_empty();
4245
4246 {
4247 GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm);
4248 refProcessingWork();
4249 }
4250 verify_work_stacks_empty();
4251 verify_overflow_empty();
4252
4253 if (should_unload_classes()) {
4254 heap->prune_scavengable_nmethods();
4255 }
4256 JvmtiExport::gc_epilogue();
4257
4258 // If we encountered any (marking stack / work queue) overflow
4259 // events during the current CMS cycle, take appropriate
4260 // remedial measures, where possible, so as to try and avoid
4261 // recurrence of that condition.
4262 assert(_markStack.isEmpty(), "No grey objects");
4263 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4264 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4265 if (ser_ovflw > 0) {
4266 log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4267 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4268 _markStack.expand();
4269 _ser_pmc_remark_ovflw = 0;
4270 _ser_pmc_preclean_ovflw = 0;
4271 _ser_kac_preclean_ovflw = 0;
4272 _ser_kac_ovflw = 0;
4273 }
4274 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4275 log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4276 _par_pmc_remark_ovflw, _par_kac_ovflw);
4277 _par_pmc_remark_ovflw = 0;
4278 _par_kac_ovflw = 0;
4279 }
4280 if (_markStack._hit_limit > 0) {
4281 log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4282 _markStack._hit_limit);
4283 }
4284 if (_markStack._failed_double > 0) {
4285 log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4286 _markStack._failed_double, _markStack.capacity());
4287 }
4288 _markStack._hit_limit = 0;
4289 _markStack._failed_double = 0;
4290
4291 if ((VerifyAfterGC || VerifyDuringGC) &&
4292 CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4293 verify_after_remark();
4294 }
4295
4296 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4297
4298 // Change under the freelistLocks.
4299 _collectorState = Sweeping;
4300 // Call isAllClear() under bitMapLock
4301 assert(_modUnionTable.isAllClear(),
4302 "Should be clear by end of the final marking");
4303 assert(_ct->cld_rem_set()->mod_union_is_clear(),
4304 "Should be clear by end of the final marking");
4305 }
4306
4307 void CMSParInitialMarkTask::work(uint worker_id) {
4308 elapsedTimer _timer;
4309 ResourceMark rm;
4310 HandleMark hm;
4311
4312 // ---------- scan from roots --------------
4313 _timer.start();
4314 CMSHeap* heap = CMSHeap::heap();
4315 ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4316
4317 // ---------- young gen roots --------------
4318 {
4319 work_on_young_gen_roots(&par_mri_cl);
4320 _timer.stop();
4321 log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4322 }
4323
4324 // ---------- remaining roots --------------
4325 _timer.reset();
4326 _timer.start();
4327
4328 CLDToOopClosure cld_closure(&par_mri_cl, ClassLoaderData::_claim_strong);
4329
4330 heap->cms_process_roots(_strong_roots_scope,
4331 false, // yg was scanned above
4332 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4333 _collector->should_unload_classes(),
4334 &par_mri_cl,
4335 &cld_closure);
4336
4337 assert(_collector->should_unload_classes()
4338 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4339 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4340 _timer.stop();
4341 log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4342 }
4343
4344 // Parallel remark task
4345 class CMSParRemarkTask: public CMSParMarkTask {
4346 CompactibleFreeListSpace* _cms_space;
4347
4348 // The per-thread work queues, available here for stealing.
4349 OopTaskQueueSet* _task_queues;
4350 TaskTerminator _term;
4351 StrongRootsScope* _strong_roots_scope;
4352
4353 public:
4354 // A value of 0 passed to n_workers will cause the number of
4355 // workers to be taken from the active workers in the work gang.
4356 CMSParRemarkTask(CMSCollector* collector,
4357 CompactibleFreeListSpace* cms_space,
4358 uint n_workers, WorkGang* workers,
4359 OopTaskQueueSet* task_queues,
4360 StrongRootsScope* strong_roots_scope):
4361 CMSParMarkTask("Rescan roots and grey objects in parallel",
4362 collector, n_workers),
4363 _cms_space(cms_space),
4364 _task_queues(task_queues),
4365 _term(n_workers, task_queues),
4366 _strong_roots_scope(strong_roots_scope) { }
4367
4368 OopTaskQueueSet* task_queues() { return _task_queues; }
4369
4370 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4371
4372 ParallelTaskTerminator* terminator() { return _term.terminator(); }
4373 uint n_workers() { return _n_workers; }
4374
4375 void work(uint worker_id);
4376
4377 private:
4378 // ... of dirty cards in old space
4379 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4380 ParMarkRefsIntoAndScanClosure* cl);
4381
4382 // ... work stealing for the above
4383 void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl);
4384 };
4385
4386 class RemarkCLDClosure : public CLDClosure {
4387 CLDToOopClosure _cm_closure;
4388 public:
4389 RemarkCLDClosure(OopClosure* oop_closure) : _cm_closure(oop_closure, ClassLoaderData::_claim_strong) {}
4390 void do_cld(ClassLoaderData* cld) {
4391 // Check if we have modified any oops in the CLD during the concurrent marking.
4392 if (cld->has_accumulated_modified_oops()) {
4393 cld->clear_accumulated_modified_oops();
4394
4395 // We could have transfered the current modified marks to the accumulated marks,
4396 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4397 } else if (cld->has_modified_oops()) {
4398 // Don't clear anything, this info is needed by the next young collection.
4399 } else {
4400 // No modified oops in the ClassLoaderData.
4401 return;
4402 }
4403
4404 // The klass has modified fields, need to scan the klass.
4405 _cm_closure.do_cld(cld);
4406 }
4407 };
4408
4409 void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) {
4410 ParNewGeneration* young_gen = _collector->_young_gen;
4411 ContiguousSpace* eden_space = young_gen->eden();
4412 ContiguousSpace* from_space = young_gen->from();
4413 ContiguousSpace* to_space = young_gen->to();
4414
4415 HeapWord** eca = _collector->_eden_chunk_array;
4416 size_t ect = _collector->_eden_chunk_index;
4417 HeapWord** sca = _collector->_survivor_chunk_array;
4418 size_t sct = _collector->_survivor_chunk_index;
4419
4420 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4421 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4422
4423 do_young_space_rescan(cl, to_space, NULL, 0);
4424 do_young_space_rescan(cl, from_space, sca, sct);
4425 do_young_space_rescan(cl, eden_space, eca, ect);
4426 }
4427
4428 // work_queue(i) is passed to the closure
4429 // ParMarkRefsIntoAndScanClosure. The "i" parameter
4430 // also is passed to do_dirty_card_rescan_tasks() and to
4431 // do_work_steal() to select the i-th task_queue.
4432
4433 void CMSParRemarkTask::work(uint worker_id) {
4434 elapsedTimer _timer;
4435 ResourceMark rm;
4436 HandleMark hm;
4437
4438 // ---------- rescan from roots --------------
4439 _timer.start();
4440 CMSHeap* heap = CMSHeap::heap();
4441 ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4442 _collector->_span, _collector->ref_processor(),
4443 &(_collector->_markBitMap),
4444 work_queue(worker_id));
4445
4446 // Rescan young gen roots first since these are likely
4447 // coarsely partitioned and may, on that account, constitute
4448 // the critical path; thus, it's best to start off that
4449 // work first.
4450 // ---------- young gen roots --------------
4451 {
4452 work_on_young_gen_roots(&par_mrias_cl);
4453 _timer.stop();
4454 log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4455 }
4456
4457 // ---------- remaining roots --------------
4458 _timer.reset();
4459 _timer.start();
4460 heap->cms_process_roots(_strong_roots_scope,
4461 false, // yg was scanned above
4462 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4463 _collector->should_unload_classes(),
4464 &par_mrias_cl,
4465 NULL); // The dirty klasses will be handled below
4466
4467 assert(_collector->should_unload_classes()
4468 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4469 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4470 _timer.stop();
4471 log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4472
4473 // ---------- unhandled CLD scanning ----------
4474 if (worker_id == 0) { // Single threaded at the moment.
4475 _timer.reset();
4476 _timer.start();
4477
4478 // Scan all new class loader data objects and new dependencies that were
4479 // introduced during concurrent marking.
4480 ResourceMark rm;
4481 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4482 for (int i = 0; i < array->length(); i++) {
4483 Devirtualizer::do_cld(&par_mrias_cl, array->at(i));
4484 }
4485
4486 // We don't need to keep track of new CLDs anymore.
4487 ClassLoaderDataGraph::remember_new_clds(false);
4488
4489 _timer.stop();
4490 log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4491 }
4492
4493 // We might have added oops to ClassLoaderData::_handles during the
4494 // concurrent marking phase. These oops do not always point to newly allocated objects
4495 // that are guaranteed to be kept alive. Hence,
4496 // we do have to revisit the _handles block during the remark phase.
4497
4498 // ---------- dirty CLD scanning ----------
4499 if (worker_id == 0) { // Single threaded at the moment.
4500 _timer.reset();
4501 _timer.start();
4502
4503 // Scan all classes that was dirtied during the concurrent marking phase.
4504 RemarkCLDClosure remark_closure(&par_mrias_cl);
4505 ClassLoaderDataGraph::cld_do(&remark_closure);
4506
4507 _timer.stop();
4508 log_trace(gc, task)("Finished dirty CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4509 }
4510
4511
4512 // ---------- rescan dirty cards ------------
4513 _timer.reset();
4514 _timer.start();
4515
4516 // Do the rescan tasks for each of the two spaces
4517 // (cms_space) in turn.
4518 // "worker_id" is passed to select the task_queue for "worker_id"
4519 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4520 _timer.stop();
4521 log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4522
4523 // ---------- steal work from other threads ...
4524 // ---------- ... and drain overflow list.
4525 _timer.reset();
4526 _timer.start();
4527 do_work_steal(worker_id, &par_mrias_cl);
4528 _timer.stop();
4529 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4530 }
4531
4532 void
4533 CMSParMarkTask::do_young_space_rescan(
4534 OopsInGenClosure* cl, ContiguousSpace* space,
4535 HeapWord** chunk_array, size_t chunk_top) {
4536 // Until all tasks completed:
4537 // . claim an unclaimed task
4538 // . compute region boundaries corresponding to task claimed
4539 // using chunk_array
4540 // . par_oop_iterate(cl) over that region
4541
4542 ResourceMark rm;
4543 HandleMark hm;
4544
4545 SequentialSubTasksDone* pst = space->par_seq_tasks();
4546
4547 uint nth_task = 0;
4548 uint n_tasks = pst->n_tasks();
4549
4550 if (n_tasks > 0) {
4551 assert(pst->valid(), "Uninitialized use?");
4552 HeapWord *start, *end;
4553 while (pst->try_claim_task(/* reference */ nth_task)) {
4554 // We claimed task # nth_task; compute its boundaries.
4555 if (chunk_top == 0) { // no samples were taken
4556 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4557 start = space->bottom();
4558 end = space->top();
4559 } else if (nth_task == 0) {
4560 start = space->bottom();
4561 end = chunk_array[nth_task];
4562 } else if (nth_task < (uint)chunk_top) {
4563 assert(nth_task >= 1, "Control point invariant");
4564 start = chunk_array[nth_task - 1];
4565 end = chunk_array[nth_task];
4566 } else {
4567 assert(nth_task == (uint)chunk_top, "Control point invariant");
4568 start = chunk_array[chunk_top - 1];
4569 end = space->top();
4570 }
4571 MemRegion mr(start, end);
4572 // Verify that mr is in space
4573 assert(mr.is_empty() || space->used_region().contains(mr),
4574 "Should be in space");
4575 // Verify that "start" is an object boundary
4576 assert(mr.is_empty() || oopDesc::is_oop(oop(mr.start())),
4577 "Should be an oop");
4578 space->par_oop_iterate(mr, cl);
4579 }
4580 pst->all_tasks_completed();
4581 }
4582 }
4583
4584 void
4585 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4586 CompactibleFreeListSpace* sp, int i,
4587 ParMarkRefsIntoAndScanClosure* cl) {
4588 // Until all tasks completed:
4589 // . claim an unclaimed task
4590 // . compute region boundaries corresponding to task claimed
4591 // . transfer dirty bits ct->mut for that region
4592 // . apply rescanclosure to dirty mut bits for that region
4593
4594 ResourceMark rm;
4595 HandleMark hm;
4596
4597 OopTaskQueue* work_q = work_queue(i);
4598 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4599 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4600 // CAUTION: This closure has state that persists across calls to
4601 // the work method dirty_range_iterate_clear() in that it has
4602 // embedded in it a (subtype of) UpwardsObjectClosure. The
4603 // use of that state in the embedded UpwardsObjectClosure instance
4604 // assumes that the cards are always iterated (even if in parallel
4605 // by several threads) in monotonically increasing order per each
4606 // thread. This is true of the implementation below which picks
4607 // card ranges (chunks) in monotonically increasing order globally
4608 // and, a-fortiori, in monotonically increasing order per thread
4609 // (the latter order being a subsequence of the former).
4610 // If the work code below is ever reorganized into a more chaotic
4611 // work-partitioning form than the current "sequential tasks"
4612 // paradigm, the use of that persistent state will have to be
4613 // revisited and modified appropriately. See also related
4614 // bug 4756801 work on which should examine this code to make
4615 // sure that the changes there do not run counter to the
4616 // assumptions made here and necessary for correctness and
4617 // efficiency. Note also that this code might yield inefficient
4618 // behavior in the case of very large objects that span one or
4619 // more work chunks. Such objects would potentially be scanned
4620 // several times redundantly. Work on 4756801 should try and
4621 // address that performance anomaly if at all possible. XXX
4622 MemRegion full_span = _collector->_span;
4623 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4624 MarkFromDirtyCardsClosure
4625 greyRescanClosure(_collector, full_span, // entire span of interest
4626 sp, bm, work_q, cl);
4627
4628 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4629 assert(pst->valid(), "Uninitialized use?");
4630 uint nth_task = 0;
4631 const int alignment = CardTable::card_size * BitsPerWord;
4632 MemRegion span = sp->used_region();
4633 HeapWord* start_addr = span.start();
4634 HeapWord* end_addr = align_up(span.end(), alignment);
4635 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4636 assert(is_aligned(start_addr, alignment), "Check alignment");
4637 assert(is_aligned(chunk_size, alignment), "Check alignment");
4638
4639 while (pst->try_claim_task(/* reference */ nth_task)) {
4640 // Having claimed the nth_task, compute corresponding mem-region,
4641 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4642 // The alignment restriction ensures that we do not need any
4643 // synchronization with other gang-workers while setting or
4644 // clearing bits in thus chunk of the MUT.
4645 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4646 start_addr + (nth_task+1)*chunk_size);
4647 // The last chunk's end might be way beyond end of the
4648 // used region. In that case pull back appropriately.
4649 if (this_span.end() > end_addr) {
4650 this_span.set_end(end_addr);
4651 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4652 }
4653 // Iterate over the dirty cards covering this chunk, marking them
4654 // precleaned, and setting the corresponding bits in the mod union
4655 // table. Since we have been careful to partition at Card and MUT-word
4656 // boundaries no synchronization is needed between parallel threads.
4657 _collector->_ct->dirty_card_iterate(this_span,
4658 &modUnionClosure);
4659
4660 // Having transferred these marks into the modUnionTable,
4661 // rescan the marked objects on the dirty cards in the modUnionTable.
4662 // Even if this is at a synchronous collection, the initial marking
4663 // may have been done during an asynchronous collection so there
4664 // may be dirty bits in the mod-union table.
4665 _collector->_modUnionTable.dirty_range_iterate_clear(
4666 this_span, &greyRescanClosure);
4667 _collector->_modUnionTable.verifyNoOneBitsInRange(
4668 this_span.start(),
4669 this_span.end());
4670 }
4671 pst->all_tasks_completed(); // declare that i am done
4672 }
4673
4674 // . see if we can share work_queues with ParNew? XXX
4675 void
4676 CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl) {
4677 OopTaskQueue* work_q = work_queue(i);
4678 NOT_PRODUCT(int num_steals = 0;)
4679 oop obj_to_scan;
4680 CMSBitMap* bm = &(_collector->_markBitMap);
4681
4682 while (true) {
4683 // Completely finish any left over work from (an) earlier round(s)
4684 cl->trim_queue(0);
4685 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4686 (size_t)ParGCDesiredObjsFromOverflowList);
4687 // Now check if there's any work in the overflow list
4688 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4689 // only affects the number of attempts made to get work from the
4690 // overflow list and does not affect the number of workers. Just
4691 // pass ParallelGCThreads so this behavior is unchanged.
4692 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4693 work_q,
4694 ParallelGCThreads)) {
4695 // found something in global overflow list;
4696 // not yet ready to go stealing work from others.
4697 // We'd like to assert(work_q->size() != 0, ...)
4698 // because we just took work from the overflow list,
4699 // but of course we can't since all of that could have
4700 // been already stolen from us.
4701 // "He giveth and He taketh away."
4702 continue;
4703 }
4704 // Verify that we have no work before we resort to stealing
4705 assert(work_q->size() == 0, "Have work, shouldn't steal");
4706 // Try to steal from other queues that have work
4707 if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
4708 NOT_PRODUCT(num_steals++;)
4709 assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
4710 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4711 // Do scanning work
4712 obj_to_scan->oop_iterate(cl);
4713 // Loop around, finish this work, and try to steal some more
4714 } else if (terminator()->offer_termination()) {
4715 break; // nirvana from the infinite cycle
4716 }
4717 }
4718 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4719 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4720 "Else our work is not yet done");
4721 }
4722
4723 // Record object boundaries in _eden_chunk_array by sampling the eden
4724 // top in the slow-path eden object allocation code path and record
4725 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4726 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4727 // sampling in sample_eden() that activates during the part of the
4728 // preclean phase.
4729 void CMSCollector::sample_eden_chunk() {
4730 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4731 if (_eden_chunk_lock->try_lock()) {
4732 // Record a sample. This is the critical section. The contents
4733 // of the _eden_chunk_array have to be non-decreasing in the
4734 // address order.
4735 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4736 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4737 "Unexpected state of Eden");
4738 if (_eden_chunk_index == 0 ||
4739 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4740 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4741 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4742 _eden_chunk_index++; // commit sample
4743 }
4744 _eden_chunk_lock->unlock();
4745 }
4746 }
4747 }
4748
4749 // Return a thread-local PLAB recording array, as appropriate.
4750 void* CMSCollector::get_data_recorder(int thr_num) {
4751 if (_survivor_plab_array != NULL &&
4752 (CMSPLABRecordAlways ||
4753 (_collectorState > Marking && _collectorState < FinalMarking))) {
4754 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4755 ChunkArray* ca = &_survivor_plab_array[thr_num];
4756 ca->reset(); // clear it so that fresh data is recorded
4757 return (void*) ca;
4758 } else {
4759 return NULL;
4760 }
4761 }
4762
4763 // Reset all the thread-local PLAB recording arrays
4764 void CMSCollector::reset_survivor_plab_arrays() {
4765 for (uint i = 0; i < ParallelGCThreads; i++) {
4766 _survivor_plab_array[i].reset();
4767 }
4768 }
4769
4770 // Merge the per-thread plab arrays into the global survivor chunk
4771 // array which will provide the partitioning of the survivor space
4772 // for CMS initial scan and rescan.
4773 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4774 int no_of_gc_threads) {
4775 assert(_survivor_plab_array != NULL, "Error");
4776 assert(_survivor_chunk_array != NULL, "Error");
4777 assert(_collectorState == FinalMarking ||
4778 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4779 for (int j = 0; j < no_of_gc_threads; j++) {
4780 _cursor[j] = 0;
4781 }
4782 HeapWord* top = surv->top();
4783 size_t i;
4784 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4785 HeapWord* min_val = top; // Higher than any PLAB address
4786 uint min_tid = 0; // position of min_val this round
4787 for (int j = 0; j < no_of_gc_threads; j++) {
4788 ChunkArray* cur_sca = &_survivor_plab_array[j];
4789 if (_cursor[j] == cur_sca->end()) {
4790 continue;
4791 }
4792 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4793 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4794 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4795 if (cur_val < min_val) {
4796 min_tid = j;
4797 min_val = cur_val;
4798 } else {
4799 assert(cur_val < top, "All recorded addresses should be less");
4800 }
4801 }
4802 // At this point min_val and min_tid are respectively
4803 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4804 // and the thread (j) that witnesses that address.
4805 // We record this address in the _survivor_chunk_array[i]
4806 // and increment _cursor[min_tid] prior to the next round i.
4807 if (min_val == top) {
4808 break;
4809 }
4810 _survivor_chunk_array[i] = min_val;
4811 _cursor[min_tid]++;
4812 }
4813 // We are all done; record the size of the _survivor_chunk_array
4814 _survivor_chunk_index = i; // exclusive: [0, i)
4815 log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4816 // Verify that we used up all the recorded entries
4817 #ifdef ASSERT
4818 size_t total = 0;
4819 for (int j = 0; j < no_of_gc_threads; j++) {
4820 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4821 total += _cursor[j];
4822 }
4823 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4824 // Check that the merged array is in sorted order
4825 if (total > 0) {
4826 for (size_t i = 0; i < total - 1; i++) {
4827 log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4828 i, p2i(_survivor_chunk_array[i]));
4829 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4830 "Not sorted");
4831 }
4832 }
4833 #endif // ASSERT
4834 }
4835
4836 // Set up the space's par_seq_tasks structure for work claiming
4837 // for parallel initial scan and rescan of young gen.
4838 // See ParRescanTask where this is currently used.
4839 void
4840 CMSCollector::
4841 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4842 assert(n_threads > 0, "Unexpected n_threads argument");
4843
4844 // Eden space
4845 if (!_young_gen->eden()->is_empty()) {
4846 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4847 assert(!pst->valid(), "Clobbering existing data?");
4848 // Each valid entry in [0, _eden_chunk_index) represents a task.
4849 size_t n_tasks = _eden_chunk_index + 1;
4850 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4851 // Sets the condition for completion of the subtask (how many threads
4852 // need to finish in order to be done).
4853 pst->set_n_threads(n_threads);
4854 pst->set_n_tasks((int)n_tasks);
4855 }
4856
4857 // Merge the survivor plab arrays into _survivor_chunk_array
4858 if (_survivor_plab_array != NULL) {
4859 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4860 } else {
4861 assert(_survivor_chunk_index == 0, "Error");
4862 }
4863
4864 // To space
4865 {
4866 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4867 assert(!pst->valid(), "Clobbering existing data?");
4868 // Sets the condition for completion of the subtask (how many threads
4869 // need to finish in order to be done).
4870 pst->set_n_threads(n_threads);
4871 pst->set_n_tasks(1);
4872 assert(pst->valid(), "Error");
4873 }
4874
4875 // From space
4876 {
4877 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4878 assert(!pst->valid(), "Clobbering existing data?");
4879 size_t n_tasks = _survivor_chunk_index + 1;
4880 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
4881 // Sets the condition for completion of the subtask (how many threads
4882 // need to finish in order to be done).
4883 pst->set_n_threads(n_threads);
4884 pst->set_n_tasks((int)n_tasks);
4885 assert(pst->valid(), "Error");
4886 }
4887 }
4888
4889 // Parallel version of remark
4890 void CMSCollector::do_remark_parallel() {
4891 CMSHeap* heap = CMSHeap::heap();
4892 WorkGang* workers = heap->workers();
4893 assert(workers != NULL, "Need parallel worker threads.");
4894 // Choose to use the number of GC workers most recently set
4895 // into "active_workers".
4896 uint n_workers = workers->active_workers();
4897
4898 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4899
4900 StrongRootsScope srs(n_workers);
4901
4902 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4903
4904 // We won't be iterating over the cards in the card table updating
4905 // the younger_gen cards, so we shouldn't call the following else
4906 // the verification code as well as subsequent younger_refs_iterate
4907 // code would get confused. XXX
4908 // heap->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4909
4910 // The young gen rescan work will not be done as part of
4911 // process_roots (which currently doesn't know how to
4912 // parallelize such a scan), but rather will be broken up into
4913 // a set of parallel tasks (via the sampling that the [abortable]
4914 // preclean phase did of eden, plus the [two] tasks of
4915 // scanning the [two] survivor spaces. Further fine-grain
4916 // parallelization of the scanning of the survivor spaces
4917 // themselves, and of precleaning of the young gen itself
4918 // is deferred to the future.
4919 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4920
4921 // The dirty card rescan work is broken up into a "sequence"
4922 // of parallel tasks (per constituent space) that are dynamically
4923 // claimed by the parallel threads.
4924 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4925
4926 // It turns out that even when we're using 1 thread, doing the work in a
4927 // separate thread causes wide variance in run times. We can't help this
4928 // in the multi-threaded case, but we special-case n=1 here to get
4929 // repeatable measurements of the 1-thread overhead of the parallel code.
4930 if (n_workers > 1) {
4931 // Make refs discovery MT-safe, if it isn't already: it may not
4932 // necessarily be so, since it's possible that we are doing
4933 // ST marking.
4934 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4935 workers->run_task(&tsk);
4936 } else {
4937 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4938 tsk.work(0);
4939 }
4940
4941 // restore, single-threaded for now, any preserved marks
4942 // as a result of work_q overflow
4943 restore_preserved_marks_if_any();
4944 }
4945
4946 // Non-parallel version of remark
4947 void CMSCollector::do_remark_non_parallel() {
4948 ResourceMark rm;
4949 HandleMark hm;
4950 CMSHeap* heap = CMSHeap::heap();
4951 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4952
4953 MarkRefsIntoAndScanClosure
4954 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4955 &_markStack, this,
4956 false /* should_yield */, false /* not precleaning */);
4957 MarkFromDirtyCardsClosure
4958 markFromDirtyCardsClosure(this, _span,
4959 NULL, // space is set further below
4960 &_markBitMap, &_markStack, &mrias_cl);
4961 {
4962 GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm);
4963 // Iterate over the dirty cards, setting the corresponding bits in the
4964 // mod union table.
4965 {
4966 ModUnionClosure modUnionClosure(&_modUnionTable);
4967 _ct->dirty_card_iterate(_cmsGen->used_region(),
4968 &modUnionClosure);
4969 }
4970 // Having transferred these marks into the modUnionTable, we just need
4971 // to rescan the marked objects on the dirty cards in the modUnionTable.
4972 // The initial marking may have been done during an asynchronous
4973 // collection so there may be dirty bits in the mod-union table.
4974 const int alignment = CardTable::card_size * BitsPerWord;
4975 {
4976 // ... First handle dirty cards in CMS gen
4977 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4978 MemRegion ur = _cmsGen->used_region();
4979 HeapWord* lb = ur.start();
4980 HeapWord* ub = align_up(ur.end(), alignment);
4981 MemRegion cms_span(lb, ub);
4982 _modUnionTable.dirty_range_iterate_clear(cms_span,
4983 &markFromDirtyCardsClosure);
4984 verify_work_stacks_empty();
4985 log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4986 }
4987 }
4988 if (VerifyDuringGC &&
4989 CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4990 HandleMark hm; // Discard invalid handles created during verification
4991 Universe::verify();
4992 }
4993 {
4994 GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm);
4995
4996 verify_work_stacks_empty();
4997
4998 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
4999 StrongRootsScope srs(1);
5000
5001 heap->cms_process_roots(&srs,
5002 true, // young gen as roots
5003 GenCollectedHeap::ScanningOption(roots_scanning_options()),
5004 should_unload_classes(),
5005 &mrias_cl,
5006 NULL); // The dirty klasses will be handled below
5007
5008 assert(should_unload_classes()
5009 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5010 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5011 }
5012
5013 {
5014 GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm);
5015
5016 verify_work_stacks_empty();
5017
5018 // Scan all class loader data objects that might have been introduced
5019 // during concurrent marking.
5020 ResourceMark rm;
5021 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5022 for (int i = 0; i < array->length(); i++) {
5023 Devirtualizer::do_cld(&mrias_cl, array->at(i));
5024 }
5025
5026 // We don't need to keep track of new CLDs anymore.
5027 ClassLoaderDataGraph::remember_new_clds(false);
5028
5029 verify_work_stacks_empty();
5030 }
5031
5032 // We might have added oops to ClassLoaderData::_handles during the
5033 // concurrent marking phase. These oops do not point to newly allocated objects
5034 // that are guaranteed to be kept alive. Hence,
5035 // we do have to revisit the _handles block during the remark phase.
5036 {
5037 GCTraceTime(Trace, gc, phases) t("Dirty CLD Scan", _gc_timer_cm);
5038
5039 verify_work_stacks_empty();
5040
5041 RemarkCLDClosure remark_closure(&mrias_cl);
5042 ClassLoaderDataGraph::cld_do(&remark_closure);
5043
5044 verify_work_stacks_empty();
5045 }
5046
5047 verify_work_stacks_empty();
5048 // Restore evacuated mark words, if any, used for overflow list links
5049 restore_preserved_marks_if_any();
5050
5051 verify_overflow_empty();
5052 }
5053
5054 ////////////////////////////////////////////////////////
5055 // Parallel Reference Processing Task Proxy Class
5056 ////////////////////////////////////////////////////////
5057 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5058 OopTaskQueueSet* _queues;
5059 TaskTerminator _terminator;
5060 public:
5061 AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5062 AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5063 ParallelTaskTerminator* terminator() { return _terminator.terminator(); }
5064 OopTaskQueueSet* queues() { return _queues; }
5065 };
5066
5067 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5068 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5069 CMSCollector* _collector;
5070 CMSBitMap* _mark_bit_map;
5071 const MemRegion _span;
5072 ProcessTask& _task;
5073
5074 public:
5075 CMSRefProcTaskProxy(ProcessTask& task,
5076 CMSCollector* collector,
5077 const MemRegion& span,
5078 CMSBitMap* mark_bit_map,
5079 AbstractWorkGang* workers,
5080 OopTaskQueueSet* task_queues):
5081 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5082 task_queues,
5083 workers->active_workers()),
5084 _collector(collector),
5085 _mark_bit_map(mark_bit_map),
5086 _span(span),
5087 _task(task)
5088 {
5089 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5090 "Inconsistency in _span");
5091 }
5092
5093 OopTaskQueueSet* task_queues() { return queues(); }
5094
5095 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5096
5097 void do_work_steal(int i,
5098 CMSParDrainMarkingStackClosure* drain,
5099 CMSParKeepAliveClosure* keep_alive);
5100
5101 virtual void work(uint worker_id);
5102 };
5103
5104 void CMSRefProcTaskProxy::work(uint worker_id) {
5105 ResourceMark rm;
5106 HandleMark hm;
5107 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5108 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5109 _mark_bit_map,
5110 work_queue(worker_id));
5111 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5112 _mark_bit_map,
5113 work_queue(worker_id));
5114 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5115 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5116 if (_task.marks_oops_alive()) {
5117 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive);
5118 }
5119 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5120 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5121 }
5122
5123 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5124 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5125 _span(span),
5126 _work_queue(work_queue),
5127 _bit_map(bit_map),
5128 _mark_and_push(collector, span, bit_map, work_queue),
5129 _low_water_mark(MIN2((work_queue->max_elems()/4),
5130 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5131 { }
5132
5133 // . see if we can share work_queues with ParNew? XXX
5134 void CMSRefProcTaskProxy::do_work_steal(int i,
5135 CMSParDrainMarkingStackClosure* drain,
5136 CMSParKeepAliveClosure* keep_alive) {
5137 OopTaskQueue* work_q = work_queue(i);
5138 NOT_PRODUCT(int num_steals = 0;)
5139 oop obj_to_scan;
5140
5141 while (true) {
5142 // Completely finish any left over work from (an) earlier round(s)
5143 drain->trim_queue(0);
5144 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5145 (size_t)ParGCDesiredObjsFromOverflowList);
5146 // Now check if there's any work in the overflow list
5147 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5148 // only affects the number of attempts made to get work from the
5149 // overflow list and does not affect the number of workers. Just
5150 // pass ParallelGCThreads so this behavior is unchanged.
5151 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5152 work_q,
5153 ParallelGCThreads)) {
5154 // Found something in global overflow list;
5155 // not yet ready to go stealing work from others.
5156 // We'd like to assert(work_q->size() != 0, ...)
5157 // because we just took work from the overflow list,
5158 // but of course we can't, since all of that might have
5159 // been already stolen from us.
5160 continue;
5161 }
5162 // Verify that we have no work before we resort to stealing
5163 assert(work_q->size() == 0, "Have work, shouldn't steal");
5164 // Try to steal from other queues that have work
5165 if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
5166 NOT_PRODUCT(num_steals++;)
5167 assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
5168 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5169 // Do scanning work
5170 obj_to_scan->oop_iterate(keep_alive);
5171 // Loop around, finish this work, and try to steal some more
5172 } else if (terminator()->offer_termination()) {
5173 break; // nirvana from the infinite cycle
5174 }
5175 }
5176 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5177 }
5178
5179 void CMSRefProcTaskExecutor::execute(ProcessTask& task, uint ergo_workers) {
5180 CMSHeap* heap = CMSHeap::heap();
5181 WorkGang* workers = heap->workers();
5182 assert(workers != NULL, "Need parallel worker threads.");
5183 assert(workers->active_workers() == ergo_workers,
5184 "Ergonomically chosen workers (%u) must be equal to active workers (%u)",
5185 ergo_workers, workers->active_workers());
5186 CMSRefProcTaskProxy rp_task(task, &_collector,
5187 _collector.ref_processor_span(),
5188 _collector.markBitMap(),
5189 workers, _collector.task_queues());
5190 workers->run_task(&rp_task, workers->active_workers());
5191 }
5192
5193 void CMSCollector::refProcessingWork() {
5194 ResourceMark rm;
5195 HandleMark hm;
5196
5197 ReferenceProcessor* rp = ref_processor();
5198 assert(_span_based_discoverer.span().equals(_span), "Spans should be equal");
5199 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5200 // Process weak references.
5201 rp->setup_policy(false);
5202 verify_work_stacks_empty();
5203
5204 ReferenceProcessorPhaseTimes pt(_gc_timer_cm, rp->max_num_queues());
5205 {
5206 GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm);
5207
5208 // Setup keep_alive and complete closures.
5209 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5210 &_markStack, false /* !preclean */);
5211 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5212 _span, &_markBitMap, &_markStack,
5213 &cmsKeepAliveClosure, false /* !preclean */);
5214
5215 ReferenceProcessorStats stats;
5216 if (rp->processing_is_mt()) {
5217 // Set the degree of MT here. If the discovery is done MT, there
5218 // may have been a different number of threads doing the discovery
5219 // and a different number of discovered lists may have Ref objects.
5220 // That is OK as long as the Reference lists are balanced (see
5221 // balance_all_queues() and balance_queues()).
5222 CMSHeap* heap = CMSHeap::heap();
5223 uint active_workers = ParallelGCThreads;
5224 WorkGang* workers = heap->workers();
5225 if (workers != NULL) {
5226 active_workers = workers->active_workers();
5227 // The expectation is that active_workers will have already
5228 // been set to a reasonable value. If it has not been set,
5229 // investigate.
5230 assert(active_workers > 0, "Should have been set during scavenge");
5231 }
5232 rp->set_active_mt_degree(active_workers);
5233 CMSRefProcTaskExecutor task_executor(*this);
5234 stats = rp->process_discovered_references(&_is_alive_closure,
5235 &cmsKeepAliveClosure,
5236 &cmsDrainMarkingStackClosure,
5237 &task_executor,
5238 &pt);
5239 } else {
5240 stats = rp->process_discovered_references(&_is_alive_closure,
5241 &cmsKeepAliveClosure,
5242 &cmsDrainMarkingStackClosure,
5243 NULL,
5244 &pt);
5245 }
5246 _gc_tracer_cm->report_gc_reference_stats(stats);
5247 pt.print_all_references();
5248 }
5249
5250 // This is the point where the entire marking should have completed.
5251 verify_work_stacks_empty();
5252
5253 {
5254 GCTraceTime(Debug, gc, phases) t("Weak Processing", _gc_timer_cm);
5255 WeakProcessor::weak_oops_do(&_is_alive_closure, &do_nothing_cl);
5256 }
5257
5258 if (should_unload_classes()) {
5259 {
5260 GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm);
5261
5262 // Unload classes and purge the SystemDictionary.
5263 bool purged_class = SystemDictionary::do_unloading(_gc_timer_cm);
5264
5265 // Unload nmethods.
5266 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5267
5268 // Prune dead klasses from subklass/sibling/implementor lists.
5269 Klass::clean_weak_klass_links(purged_class);
5270
5271 #if INCLUDE_JVMCI
5272 // Clean JVMCI metadata handles.
5273 JVMCI::do_unloading(&_is_alive_closure, purged_class);
5274 #endif
5275 }
5276 }
5277
5278 // Restore any preserved marks as a result of mark stack or
5279 // work queue overflow
5280 restore_preserved_marks_if_any(); // done single-threaded for now
5281
5282 rp->set_enqueuing_is_done(true);
5283 rp->verify_no_references_recorded();
5284 }
5285
5286 #ifndef PRODUCT
5287 void CMSCollector::check_correct_thread_executing() {
5288 Thread* t = Thread::current();
5289 // Only the VM thread or the CMS thread should be here.
5290 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5291 "Unexpected thread type");
5292 // If this is the vm thread, the foreground process
5293 // should not be waiting. Note that _foregroundGCIsActive is
5294 // true while the foreground collector is waiting.
5295 if (_foregroundGCShouldWait) {
5296 // We cannot be the VM thread
5297 assert(t->is_ConcurrentGC_thread(),
5298 "Should be CMS thread");
5299 } else {
5300 // We can be the CMS thread only if we are in a stop-world
5301 // phase of CMS collection.
5302 if (t->is_ConcurrentGC_thread()) {
5303 assert(_collectorState == InitialMarking ||
5304 _collectorState == FinalMarking,
5305 "Should be a stop-world phase");
5306 // The CMS thread should be holding the CMS_token.
5307 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5308 "Potential interference with concurrently "
5309 "executing VM thread");
5310 }
5311 }
5312 }
5313 #endif
5314
5315 void CMSCollector::sweep() {
5316 assert(_collectorState == Sweeping, "just checking");
5317 check_correct_thread_executing();
5318 verify_work_stacks_empty();
5319 verify_overflow_empty();
5320 increment_sweep_count();
5321 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
5322
5323 _inter_sweep_timer.stop();
5324 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5325
5326 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5327 _intra_sweep_timer.reset();
5328 _intra_sweep_timer.start();
5329 {
5330 GCTraceCPUTime tcpu;
5331 CMSPhaseAccounting pa(this, "Concurrent Sweep");
5332 // First sweep the old gen
5333 {
5334 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5335 bitMapLock());
5336 sweepWork(_cmsGen);
5337 }
5338
5339 // Update Universe::_heap_*_at_gc figures.
5340 // We need all the free list locks to make the abstract state
5341 // transition from Sweeping to Resetting. See detailed note
5342 // further below.
5343 {
5344 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5345 // Update heap occupancy information which is used as
5346 // input to soft ref clearing policy at the next gc.
5347 Universe::update_heap_info_at_gc();
5348 _collectorState = Resizing;
5349 }
5350 }
5351 verify_work_stacks_empty();
5352 verify_overflow_empty();
5353
5354 if (should_unload_classes()) {
5355 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5356 // requires that the virtual spaces are stable and not deleted.
5357 ClassLoaderDataGraph::set_should_purge(true);
5358 }
5359
5360 _intra_sweep_timer.stop();
5361 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5362
5363 _inter_sweep_timer.reset();
5364 _inter_sweep_timer.start();
5365
5366 // We need to use a monotonically non-decreasing time in ms
5367 // or we will see time-warp warnings and os::javaTimeMillis()
5368 // does not guarantee monotonicity.
5369 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5370 update_time_of_last_gc(now);
5371
5372 // NOTE on abstract state transitions:
5373 // Mutators allocate-live and/or mark the mod-union table dirty
5374 // based on the state of the collection. The former is done in
5375 // the interval [Marking, Sweeping] and the latter in the interval
5376 // [Marking, Sweeping). Thus the transitions into the Marking state
5377 // and out of the Sweeping state must be synchronously visible
5378 // globally to the mutators.
5379 // The transition into the Marking state happens with the world
5380 // stopped so the mutators will globally see it. Sweeping is
5381 // done asynchronously by the background collector so the transition
5382 // from the Sweeping state to the Resizing state must be done
5383 // under the freelistLock (as is the check for whether to
5384 // allocate-live and whether to dirty the mod-union table).
5385 assert(_collectorState == Resizing, "Change of collector state to"
5386 " Resizing must be done under the freelistLocks (plural)");
5387
5388 // Now that sweeping has been completed, we clear
5389 // the incremental_collection_failed flag,
5390 // thus inviting a younger gen collection to promote into
5391 // this generation. If such a promotion may still fail,
5392 // the flag will be set again when a young collection is
5393 // attempted.
5394 CMSHeap* heap = CMSHeap::heap();
5395 heap->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5396 heap->update_full_collections_completed(_collection_count_start);
5397 }
5398
5399 // FIX ME!!! Looks like this belongs in CFLSpace, with
5400 // CMSGen merely delegating to it.
5401 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5402 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5403 HeapWord* minAddr = _cmsSpace->bottom();
5404 HeapWord* largestAddr =
5405 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5406 if (largestAddr == NULL) {
5407 // The dictionary appears to be empty. In this case
5408 // try to coalesce at the end of the heap.
5409 largestAddr = _cmsSpace->end();
5410 }
5411 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5412 size_t nearLargestOffset =
5413 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5414 log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5415 p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5416 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5417 }
5418
5419 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5420 return addr >= _cmsSpace->nearLargestChunk();
5421 }
5422
5423 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5424 return _cmsSpace->find_chunk_at_end();
5425 }
5426
5427 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5428 bool full) {
5429 // If the young generation has been collected, gather any statistics
5430 // that are of interest at this point.
5431 bool current_is_young = CMSHeap::heap()->is_young_gen(current_generation);
5432 if (!full && current_is_young) {
5433 // Gather statistics on the young generation collection.
5434 collector()->stats().record_gc0_end(used());
5435 }
5436 }
5437
5438 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5439 // We iterate over the space(s) underlying this generation,
5440 // checking the mark bit map to see if the bits corresponding
5441 // to specific blocks are marked or not. Blocks that are
5442 // marked are live and are not swept up. All remaining blocks
5443 // are swept up, with coalescing on-the-fly as we sweep up
5444 // contiguous free and/or garbage blocks:
5445 // We need to ensure that the sweeper synchronizes with allocators
5446 // and stop-the-world collectors. In particular, the following
5447 // locks are used:
5448 // . CMS token: if this is held, a stop the world collection cannot occur
5449 // . freelistLock: if this is held no allocation can occur from this
5450 // generation by another thread
5451 // . bitMapLock: if this is held, no other thread can access or update
5452 //
5453
5454 // Note that we need to hold the freelistLock if we use
5455 // block iterate below; else the iterator might go awry if
5456 // a mutator (or promotion) causes block contents to change
5457 // (for instance if the allocator divvies up a block).
5458 // If we hold the free list lock, for all practical purposes
5459 // young generation GC's can't occur (they'll usually need to
5460 // promote), so we might as well prevent all young generation
5461 // GC's while we do a sweeping step. For the same reason, we might
5462 // as well take the bit map lock for the entire duration
5463
5464 // check that we hold the requisite locks
5465 assert(have_cms_token(), "Should hold cms token");
5466 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5467 assert_lock_strong(old_gen->freelistLock());
5468 assert_lock_strong(bitMapLock());
5469
5470 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5471 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5472 old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5473 _inter_sweep_estimate.padded_average(),
5474 _intra_sweep_estimate.padded_average());
5475 old_gen->setNearLargestChunk();
5476
5477 {
5478 SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5479 old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5480 // We need to free-up/coalesce garbage/blocks from a
5481 // co-terminal free run. This is done in the SweepClosure
5482 // destructor; so, do not remove this scope, else the
5483 // end-of-sweep-census below will be off by a little bit.
5484 }
5485 old_gen->cmsSpace()->sweep_completed();
5486 old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5487 if (should_unload_classes()) { // unloaded classes this cycle,
5488 _concurrent_cycles_since_last_unload = 0; // ... reset count
5489 } else { // did not unload classes,
5490 _concurrent_cycles_since_last_unload++; // ... increment count
5491 }
5492 }
5493
5494 // Reset CMS data structures (for now just the marking bit map)
5495 // preparatory for the next cycle.
5496 void CMSCollector::reset_concurrent() {
5497 CMSTokenSyncWithLocks ts(true, bitMapLock());
5498
5499 // If the state is not "Resetting", the foreground thread
5500 // has done a collection and the resetting.
5501 if (_collectorState != Resetting) {
5502 assert(_collectorState == Idling, "The state should only change"
5503 " because the foreground collector has finished the collection");
5504 return;
5505 }
5506
5507 {
5508 // Clear the mark bitmap (no grey objects to start with)
5509 // for the next cycle.
5510 GCTraceCPUTime tcpu;
5511 CMSPhaseAccounting cmspa(this, "Concurrent Reset");
5512
5513 HeapWord* curAddr = _markBitMap.startWord();
5514 while (curAddr < _markBitMap.endWord()) {
5515 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5516 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5517 _markBitMap.clear_large_range(chunk);
5518 if (ConcurrentMarkSweepThread::should_yield() &&
5519 !foregroundGCIsActive() &&
5520 CMSYield) {
5521 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5522 "CMS thread should hold CMS token");
5523 assert_lock_strong(bitMapLock());
5524 bitMapLock()->unlock();
5525 ConcurrentMarkSweepThread::desynchronize(true);
5526 stopTimer();
5527 incrementYields();
5528
5529 // See the comment in coordinator_yield()
5530 for (unsigned i = 0; i < CMSYieldSleepCount &&
5531 ConcurrentMarkSweepThread::should_yield() &&
5532 !CMSCollector::foregroundGCIsActive(); ++i) {
5533 os::sleep(Thread::current(), 1, false);
5534 }
5535
5536 ConcurrentMarkSweepThread::synchronize(true);
5537 bitMapLock()->lock_without_safepoint_check();
5538 startTimer();
5539 }
5540 curAddr = chunk.end();
5541 }
5542 // A successful mostly concurrent collection has been done.
5543 // Because only the full (i.e., concurrent mode failure) collections
5544 // are being measured for gc overhead limits, clean the "near" flag
5545 // and count.
5546 size_policy()->reset_gc_overhead_limit_count();
5547 _collectorState = Idling;
5548 }
5549
5550 register_gc_end();
5551 }
5552
5553 // Same as above but for STW paths
5554 void CMSCollector::reset_stw() {
5555 // already have the lock
5556 assert(_collectorState == Resetting, "just checking");
5557 assert_lock_strong(bitMapLock());
5558 GCIdMark gc_id_mark(_cmsThread->gc_id());
5559 _markBitMap.clear_all();
5560 _collectorState = Idling;
5561 register_gc_end();
5562 }
5563
5564 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5565 GCTraceCPUTime tcpu;
5566 TraceCollectorStats tcs_cgc(cgc_counters());
5567
5568 switch (op) {
5569 case CMS_op_checkpointRootsInitial: {
5570 GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5571 SvcGCMarker sgcm(SvcGCMarker::CONCURRENT);
5572 checkpointRootsInitial();
5573 break;
5574 }
5575 case CMS_op_checkpointRootsFinal: {
5576 GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5577 SvcGCMarker sgcm(SvcGCMarker::CONCURRENT);
5578 checkpointRootsFinal();
5579 break;
5580 }
5581 default:
5582 fatal("No such CMS_op");
5583 }
5584 }
5585
5586 #ifndef PRODUCT
5587 size_t const CMSCollector::skip_header_HeapWords() {
5588 return FreeChunk::header_size();
5589 }
5590
5591 // Try and collect here conditions that should hold when
5592 // CMS thread is exiting. The idea is that the foreground GC
5593 // thread should not be blocked if it wants to terminate
5594 // the CMS thread and yet continue to run the VM for a while
5595 // after that.
5596 void CMSCollector::verify_ok_to_terminate() const {
5597 assert(Thread::current()->is_ConcurrentGC_thread(),
5598 "should be called by CMS thread");
5599 assert(!_foregroundGCShouldWait, "should be false");
5600 // We could check here that all the various low-level locks
5601 // are not held by the CMS thread, but that is overkill; see
5602 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5603 // is checked.
5604 }
5605 #endif
5606
5607 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5608 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5609 "missing Printezis mark?");
5610 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5611 size_t size = pointer_delta(nextOneAddr + 1, addr);
5612 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5613 "alignment problem");
5614 assert(size >= 3, "Necessary for Printezis marks to work");
5615 return size;
5616 }
5617
5618 // A variant of the above (block_size_using_printezis_bits()) except
5619 // that we return 0 if the P-bits are not yet set.
5620 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5621 if (_markBitMap.isMarked(addr + 1)) {
5622 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5623 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5624 size_t size = pointer_delta(nextOneAddr + 1, addr);
5625 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5626 "alignment problem");
5627 assert(size >= 3, "Necessary for Printezis marks to work");
5628 return size;
5629 }
5630 return 0;
5631 }
5632
5633 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5634 size_t sz = 0;
5635 oop p = (oop)addr;
5636 if (p->klass_or_null_acquire() != NULL) {
5637 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5638 } else {
5639 sz = block_size_using_printezis_bits(addr);
5640 }
5641 assert(sz > 0, "size must be nonzero");
5642 HeapWord* next_block = addr + sz;
5643 HeapWord* next_card = align_up(next_block, CardTable::card_size);
5644 assert(align_down((uintptr_t)addr, CardTable::card_size) <
5645 align_down((uintptr_t)next_card, CardTable::card_size),
5646 "must be different cards");
5647 return next_card;
5648 }
5649
5650
5651 // CMS Bit Map Wrapper /////////////////////////////////////////
5652
5653 // Construct a CMS bit map infrastructure, but don't create the
5654 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5655 // further below.
5656 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5657 _shifter(shifter),
5658 _bm(),
5659 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5660 Monitor::_safepoint_check_sometimes) : NULL)
5661 {
5662 _bmStartWord = 0;
5663 _bmWordSize = 0;
5664 }
5665
5666 bool CMSBitMap::allocate(MemRegion mr) {
5667 _bmStartWord = mr.start();
5668 _bmWordSize = mr.word_size();
5669 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5670 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5671 if (!brs.is_reserved()) {
5672 log_warning(gc)("CMS bit map allocation failure");
5673 return false;
5674 }
5675 // For now we'll just commit all of the bit map up front.
5676 // Later on we'll try to be more parsimonious with swap.
5677 if (!_virtual_space.initialize(brs, brs.size())) {
5678 log_warning(gc)("CMS bit map backing store failure");
5679 return false;
5680 }
5681 assert(_virtual_space.committed_size() == brs.size(),
5682 "didn't reserve backing store for all of CMS bit map?");
5683 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5684 _bmWordSize, "inconsistency in bit map sizing");
5685 _bm = BitMapView((BitMap::bm_word_t*)_virtual_space.low(), _bmWordSize >> _shifter);
5686
5687 // bm.clear(); // can we rely on getting zero'd memory? verify below
5688 assert(isAllClear(),
5689 "Expected zero'd memory from ReservedSpace constructor");
5690 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5691 "consistency check");
5692 return true;
5693 }
5694
5695 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5696 HeapWord *next_addr, *end_addr, *last_addr;
5697 assert_locked();
5698 assert(covers(mr), "out-of-range error");
5699 // XXX assert that start and end are appropriately aligned
5700 for (next_addr = mr.start(), end_addr = mr.end();
5701 next_addr < end_addr; next_addr = last_addr) {
5702 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5703 last_addr = dirty_region.end();
5704 if (!dirty_region.is_empty()) {
5705 cl->do_MemRegion(dirty_region);
5706 } else {
5707 assert(last_addr == end_addr, "program logic");
5708 return;
5709 }
5710 }
5711 }
5712
5713 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5714 _bm.print_on_error(st, prefix);
5715 }
5716
5717 #ifndef PRODUCT
5718 void CMSBitMap::assert_locked() const {
5719 CMSLockVerifier::assert_locked(lock());
5720 }
5721
5722 bool CMSBitMap::covers(MemRegion mr) const {
5723 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5724 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5725 "size inconsistency");
5726 return (mr.start() >= _bmStartWord) &&
5727 (mr.end() <= endWord());
5728 }
5729
5730 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5731 return (start >= _bmStartWord && (start + size) <= endWord());
5732 }
5733
5734 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5735 // verify that there are no 1 bits in the interval [left, right)
5736 FalseBitMapClosure falseBitMapClosure;
5737 iterate(&falseBitMapClosure, left, right);
5738 }
5739
5740 void CMSBitMap::region_invariant(MemRegion mr)
5741 {
5742 assert_locked();
5743 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5744 assert(!mr.is_empty(), "unexpected empty region");
5745 assert(covers(mr), "mr should be covered by bit map");
5746 // convert address range into offset range
5747 size_t start_ofs = heapWordToOffset(mr.start());
5748 // Make sure that end() is appropriately aligned
5749 assert(mr.end() == align_up(mr.end(), (1 << (_shifter+LogHeapWordSize))),
5750 "Misaligned mr.end()");
5751 size_t end_ofs = heapWordToOffset(mr.end());
5752 assert(end_ofs > start_ofs, "Should mark at least one bit");
5753 }
5754
5755 #endif
5756
5757 bool CMSMarkStack::allocate(size_t size) {
5758 // allocate a stack of the requisite depth
5759 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5760 size * sizeof(oop)));
5761 if (!rs.is_reserved()) {
5762 log_warning(gc)("CMSMarkStack allocation failure");
5763 return false;
5764 }
5765 if (!_virtual_space.initialize(rs, rs.size())) {
5766 log_warning(gc)("CMSMarkStack backing store failure");
5767 return false;
5768 }
5769 assert(_virtual_space.committed_size() == rs.size(),
5770 "didn't reserve backing store for all of CMS stack?");
5771 _base = (oop*)(_virtual_space.low());
5772 _index = 0;
5773 _capacity = size;
5774 NOT_PRODUCT(_max_depth = 0);
5775 return true;
5776 }
5777
5778 // XXX FIX ME !!! In the MT case we come in here holding a
5779 // leaf lock. For printing we need to take a further lock
5780 // which has lower rank. We need to recalibrate the two
5781 // lock-ranks involved in order to be able to print the
5782 // messages below. (Or defer the printing to the caller.
5783 // For now we take the expedient path of just disabling the
5784 // messages for the problematic case.)
5785 void CMSMarkStack::expand() {
5786 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5787 if (_capacity == MarkStackSizeMax) {
5788 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5789 // We print a warning message only once per CMS cycle.
5790 log_debug(gc)(" (benign) Hit CMSMarkStack max size limit");
5791 }
5792 return;
5793 }
5794 // Double capacity if possible
5795 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5796 // Do not give up existing stack until we have managed to
5797 // get the double capacity that we desired.
5798 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5799 new_capacity * sizeof(oop)));
5800 if (rs.is_reserved()) {
5801 // Release the backing store associated with old stack
5802 _virtual_space.release();
5803 // Reinitialize virtual space for new stack
5804 if (!_virtual_space.initialize(rs, rs.size())) {
5805 fatal("Not enough swap for expanded marking stack");
5806 }
5807 _base = (oop*)(_virtual_space.low());
5808 _index = 0;
5809 _capacity = new_capacity;
5810 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5811 // Failed to double capacity, continue;
5812 // we print a detail message only once per CMS cycle.
5813 log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5814 _capacity / K, new_capacity / K);
5815 }
5816 }
5817
5818
5819 // Closures
5820 // XXX: there seems to be a lot of code duplication here;
5821 // should refactor and consolidate common code.
5822
5823 // This closure is used to mark refs into the CMS generation in
5824 // the CMS bit map. Called at the first checkpoint. This closure
5825 // assumes that we do not need to re-mark dirty cards; if the CMS
5826 // generation on which this is used is not an oldest
5827 // generation then this will lose younger_gen cards!
5828
5829 MarkRefsIntoClosure::MarkRefsIntoClosure(
5830 MemRegion span, CMSBitMap* bitMap):
5831 _span(span),
5832 _bitMap(bitMap)
5833 {
5834 assert(ref_discoverer() == NULL, "deliberately left NULL");
5835 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5836 }
5837
5838 void MarkRefsIntoClosure::do_oop(oop obj) {
5839 // if p points into _span, then mark corresponding bit in _markBitMap
5840 assert(oopDesc::is_oop(obj), "expected an oop");
5841 HeapWord* addr = (HeapWord*)obj;
5842 if (_span.contains(addr)) {
5843 // this should be made more efficient
5844 _bitMap->mark(addr);
5845 }
5846 }
5847
5848 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure(
5849 MemRegion span, CMSBitMap* bitMap):
5850 _span(span),
5851 _bitMap(bitMap)
5852 {
5853 assert(ref_discoverer() == NULL, "deliberately left NULL");
5854 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5855 }
5856
5857 void ParMarkRefsIntoClosure::do_oop(oop obj) {
5858 // if p points into _span, then mark corresponding bit in _markBitMap
5859 assert(oopDesc::is_oop(obj), "expected an oop");
5860 HeapWord* addr = (HeapWord*)obj;
5861 if (_span.contains(addr)) {
5862 // this should be made more efficient
5863 _bitMap->par_mark(addr);
5864 }
5865 }
5866
5867 // A variant of the above, used for CMS marking verification.
5868 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5869 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5870 _span(span),
5871 _verification_bm(verification_bm),
5872 _cms_bm(cms_bm)
5873 {
5874 assert(ref_discoverer() == NULL, "deliberately left NULL");
5875 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5876 }
5877
5878 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5879 // if p points into _span, then mark corresponding bit in _markBitMap
5880 assert(oopDesc::is_oop(obj), "expected an oop");
5881 HeapWord* addr = (HeapWord*)obj;
5882 if (_span.contains(addr)) {
5883 _verification_bm->mark(addr);
5884 if (!_cms_bm->isMarked(addr)) {
5885 Log(gc, verify) log;
5886 ResourceMark rm;
5887 LogStream ls(log.error());
5888 oop(addr)->print_on(&ls);
5889 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5890 fatal("... aborting");
5891 }
5892 }
5893 }
5894
5895 //////////////////////////////////////////////////
5896 // MarkRefsIntoAndScanClosure
5897 //////////////////////////////////////////////////
5898
5899 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5900 ReferenceDiscoverer* rd,
5901 CMSBitMap* bit_map,
5902 CMSBitMap* mod_union_table,
5903 CMSMarkStack* mark_stack,
5904 CMSCollector* collector,
5905 bool should_yield,
5906 bool concurrent_precleaning):
5907 _span(span),
5908 _bit_map(bit_map),
5909 _mark_stack(mark_stack),
5910 _pushAndMarkClosure(collector, span, rd, bit_map, mod_union_table,
5911 mark_stack, concurrent_precleaning),
5912 _collector(collector),
5913 _freelistLock(NULL),
5914 _yield(should_yield),
5915 _concurrent_precleaning(concurrent_precleaning)
5916 {
5917 // FIXME: Should initialize in base class constructor.
5918 assert(rd != NULL, "ref_discoverer shouldn't be NULL");
5919 set_ref_discoverer_internal(rd);
5920 }
5921
5922 // This closure is used to mark refs into the CMS generation at the
5923 // second (final) checkpoint, and to scan and transitively follow
5924 // the unmarked oops. It is also used during the concurrent precleaning
5925 // phase while scanning objects on dirty cards in the CMS generation.
5926 // The marks are made in the marking bit map and the marking stack is
5927 // used for keeping the (newly) grey objects during the scan.
5928 // The parallel version (Par_...) appears further below.
5929 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5930 if (obj != NULL) {
5931 assert(oopDesc::is_oop(obj), "expected an oop");
5932 HeapWord* addr = (HeapWord*)obj;
5933 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5934 assert(_collector->overflow_list_is_empty(),
5935 "overflow list should be empty");
5936 if (_span.contains(addr) &&
5937 !_bit_map->isMarked(addr)) {
5938 // mark bit map (object is now grey)
5939 _bit_map->mark(addr);
5940 // push on marking stack (stack should be empty), and drain the
5941 // stack by applying this closure to the oops in the oops popped
5942 // from the stack (i.e. blacken the grey objects)
5943 bool res = _mark_stack->push(obj);
5944 assert(res, "Should have space to push on empty stack");
5945 do {
5946 oop new_oop = _mark_stack->pop();
5947 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
5948 assert(_bit_map->isMarked((HeapWord*)new_oop),
5949 "only grey objects on this stack");
5950 // iterate over the oops in this oop, marking and pushing
5951 // the ones in CMS heap (i.e. in _span).
5952 new_oop->oop_iterate(&_pushAndMarkClosure);
5953 // check if it's time to yield
5954 do_yield_check();
5955 } while (!_mark_stack->isEmpty() ||
5956 (!_concurrent_precleaning && take_from_overflow_list()));
5957 // if marking stack is empty, and we are not doing this
5958 // during precleaning, then check the overflow list
5959 }
5960 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5961 assert(_collector->overflow_list_is_empty(),
5962 "overflow list was drained above");
5963
5964 assert(_collector->no_preserved_marks(),
5965 "All preserved marks should have been restored above");
5966 }
5967 }
5968
5969 void MarkRefsIntoAndScanClosure::do_yield_work() {
5970 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5971 "CMS thread should hold CMS token");
5972 assert_lock_strong(_freelistLock);
5973 assert_lock_strong(_bit_map->lock());
5974 // relinquish the free_list_lock and bitMaplock()
5975 _bit_map->lock()->unlock();
5976 _freelistLock->unlock();
5977 ConcurrentMarkSweepThread::desynchronize(true);
5978 _collector->stopTimer();
5979 _collector->incrementYields();
5980
5981 // See the comment in coordinator_yield()
5982 for (unsigned i = 0;
5983 i < CMSYieldSleepCount &&
5984 ConcurrentMarkSweepThread::should_yield() &&
5985 !CMSCollector::foregroundGCIsActive();
5986 ++i) {
5987 os::sleep(Thread::current(), 1, false);
5988 }
5989
5990 ConcurrentMarkSweepThread::synchronize(true);
5991 _freelistLock->lock_without_safepoint_check();
5992 _bit_map->lock()->lock_without_safepoint_check();
5993 _collector->startTimer();
5994 }
5995
5996 ///////////////////////////////////////////////////////////
5997 // ParMarkRefsIntoAndScanClosure: a parallel version of
5998 // MarkRefsIntoAndScanClosure
5999 ///////////////////////////////////////////////////////////
6000 ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure(
6001 CMSCollector* collector, MemRegion span, ReferenceDiscoverer* rd,
6002 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6003 _span(span),
6004 _bit_map(bit_map),
6005 _work_queue(work_queue),
6006 _low_water_mark(MIN2((work_queue->max_elems()/4),
6007 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6008 _parPushAndMarkClosure(collector, span, rd, bit_map, work_queue)
6009 {
6010 // FIXME: Should initialize in base class constructor.
6011 assert(rd != NULL, "ref_discoverer shouldn't be NULL");
6012 set_ref_discoverer_internal(rd);
6013 }
6014
6015 // This closure is used to mark refs into the CMS generation at the
6016 // second (final) checkpoint, and to scan and transitively follow
6017 // the unmarked oops. The marks are made in the marking bit map and
6018 // the work_queue is used for keeping the (newly) grey objects during
6019 // the scan phase whence they are also available for stealing by parallel
6020 // threads. Since the marking bit map is shared, updates are
6021 // synchronized (via CAS).
6022 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) {
6023 if (obj != NULL) {
6024 // Ignore mark word because this could be an already marked oop
6025 // that may be chained at the end of the overflow list.
6026 assert(oopDesc::is_oop(obj, true), "expected an oop");
6027 HeapWord* addr = (HeapWord*)obj;
6028 if (_span.contains(addr) &&
6029 !_bit_map->isMarked(addr)) {
6030 // mark bit map (object will become grey):
6031 // It is possible for several threads to be
6032 // trying to "claim" this object concurrently;
6033 // the unique thread that succeeds in marking the
6034 // object first will do the subsequent push on
6035 // to the work queue (or overflow list).
6036 if (_bit_map->par_mark(addr)) {
6037 // push on work_queue (which may not be empty), and trim the
6038 // queue to an appropriate length by applying this closure to
6039 // the oops in the oops popped from the stack (i.e. blacken the
6040 // grey objects)
6041 bool res = _work_queue->push(obj);
6042 assert(res, "Low water mark should be less than capacity?");
6043 trim_queue(_low_water_mark);
6044 } // Else, another thread claimed the object
6045 }
6046 }
6047 }
6048
6049 // This closure is used to rescan the marked objects on the dirty cards
6050 // in the mod union table and the card table proper.
6051 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6052 oop p, MemRegion mr) {
6053
6054 size_t size = 0;
6055 HeapWord* addr = (HeapWord*)p;
6056 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6057 assert(_span.contains(addr), "we are scanning the CMS generation");
6058 // check if it's time to yield
6059 if (do_yield_check()) {
6060 // We yielded for some foreground stop-world work,
6061 // and we have been asked to abort this ongoing preclean cycle.
6062 return 0;
6063 }
6064 if (_bitMap->isMarked(addr)) {
6065 // it's marked; is it potentially uninitialized?
6066 if (p->klass_or_null_acquire() != NULL) {
6067 // an initialized object; ignore mark word in verification below
6068 // since we are running concurrent with mutators
6069 assert(oopDesc::is_oop(p, true), "should be an oop");
6070 if (p->is_objArray()) {
6071 // objArrays are precisely marked; restrict scanning
6072 // to dirty cards only.
6073 size = CompactibleFreeListSpace::adjustObjectSize(
6074 p->oop_iterate_size(_scanningClosure, mr));
6075 } else {
6076 // A non-array may have been imprecisely marked; we need
6077 // to scan object in its entirety.
6078 size = CompactibleFreeListSpace::adjustObjectSize(
6079 p->oop_iterate_size(_scanningClosure));
6080 }
6081 #ifdef ASSERT
6082 size_t direct_size =
6083 CompactibleFreeListSpace::adjustObjectSize(p->size());
6084 assert(size == direct_size, "Inconsistency in size");
6085 assert(size >= 3, "Necessary for Printezis marks to work");
6086 HeapWord* start_pbit = addr + 1;
6087 HeapWord* end_pbit = addr + size - 1;
6088 assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit),
6089 "inconsistent Printezis mark");
6090 // Verify inner mark bits (between Printezis bits) are clear,
6091 // but don't repeat if there are multiple dirty regions for
6092 // the same object, to avoid potential O(N^2) performance.
6093 if (addr != _last_scanned_object) {
6094 _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit);
6095 _last_scanned_object = addr;
6096 }
6097 #endif // ASSERT
6098 } else {
6099 // An uninitialized object.
6100 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6101 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6102 size = pointer_delta(nextOneAddr + 1, addr);
6103 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6104 "alignment problem");
6105 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6106 // will dirty the card when the klass pointer is installed in the
6107 // object (signaling the completion of initialization).
6108 }
6109 } else {
6110 // Either a not yet marked object or an uninitialized object
6111 if (p->klass_or_null_acquire() == NULL) {
6112 // An uninitialized object, skip to the next card, since
6113 // we may not be able to read its P-bits yet.
6114 assert(size == 0, "Initial value");
6115 } else {
6116 // An object not (yet) reached by marking: we merely need to
6117 // compute its size so as to go look at the next block.
6118 assert(oopDesc::is_oop(p, true), "should be an oop");
6119 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6120 }
6121 }
6122 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6123 return size;
6124 }
6125
6126 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6127 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6128 "CMS thread should hold CMS token");
6129 assert_lock_strong(_freelistLock);
6130 assert_lock_strong(_bitMap->lock());
6131 // relinquish the free_list_lock and bitMaplock()
6132 _bitMap->lock()->unlock();
6133 _freelistLock->unlock();
6134 ConcurrentMarkSweepThread::desynchronize(true);
6135 _collector->stopTimer();
6136 _collector->incrementYields();
6137
6138 // See the comment in coordinator_yield()
6139 for (unsigned i = 0; i < CMSYieldSleepCount &&
6140 ConcurrentMarkSweepThread::should_yield() &&
6141 !CMSCollector::foregroundGCIsActive(); ++i) {
6142 os::sleep(Thread::current(), 1, false);
6143 }
6144
6145 ConcurrentMarkSweepThread::synchronize(true);
6146 _freelistLock->lock_without_safepoint_check();
6147 _bitMap->lock()->lock_without_safepoint_check();
6148 _collector->startTimer();
6149 }
6150
6151
6152 //////////////////////////////////////////////////////////////////
6153 // SurvivorSpacePrecleanClosure
6154 //////////////////////////////////////////////////////////////////
6155 // This (single-threaded) closure is used to preclean the oops in
6156 // the survivor spaces.
6157 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6158
6159 HeapWord* addr = (HeapWord*)p;
6160 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6161 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6162 assert(p->klass_or_null() != NULL, "object should be initialized");
6163 // an initialized object; ignore mark word in verification below
6164 // since we are running concurrent with mutators
6165 assert(oopDesc::is_oop(p, true), "should be an oop");
6166 // Note that we do not yield while we iterate over
6167 // the interior oops of p, pushing the relevant ones
6168 // on our marking stack.
6169 size_t size = p->oop_iterate_size(_scanning_closure);
6170 do_yield_check();
6171 // Observe that below, we do not abandon the preclean
6172 // phase as soon as we should; rather we empty the
6173 // marking stack before returning. This is to satisfy
6174 // some existing assertions. In general, it may be a
6175 // good idea to abort immediately and complete the marking
6176 // from the grey objects at a later time.
6177 while (!_mark_stack->isEmpty()) {
6178 oop new_oop = _mark_stack->pop();
6179 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
6180 assert(_bit_map->isMarked((HeapWord*)new_oop),
6181 "only grey objects on this stack");
6182 // iterate over the oops in this oop, marking and pushing
6183 // the ones in CMS heap (i.e. in _span).
6184 new_oop->oop_iterate(_scanning_closure);
6185 // check if it's time to yield
6186 do_yield_check();
6187 }
6188 unsigned int after_count =
6189 CMSHeap::heap()->total_collections();
6190 bool abort = (_before_count != after_count) ||
6191 _collector->should_abort_preclean();
6192 return abort ? 0 : size;
6193 }
6194
6195 void SurvivorSpacePrecleanClosure::do_yield_work() {
6196 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6197 "CMS thread should hold CMS token");
6198 assert_lock_strong(_bit_map->lock());
6199 // Relinquish the bit map lock
6200 _bit_map->lock()->unlock();
6201 ConcurrentMarkSweepThread::desynchronize(true);
6202 _collector->stopTimer();
6203 _collector->incrementYields();
6204
6205 // See the comment in coordinator_yield()
6206 for (unsigned i = 0; i < CMSYieldSleepCount &&
6207 ConcurrentMarkSweepThread::should_yield() &&
6208 !CMSCollector::foregroundGCIsActive(); ++i) {
6209 os::sleep(Thread::current(), 1, false);
6210 }
6211
6212 ConcurrentMarkSweepThread::synchronize(true);
6213 _bit_map->lock()->lock_without_safepoint_check();
6214 _collector->startTimer();
6215 }
6216
6217 // This closure is used to rescan the marked objects on the dirty cards
6218 // in the mod union table and the card table proper. In the parallel
6219 // case, although the bitMap is shared, we do a single read so the
6220 // isMarked() query is "safe".
6221 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6222 // Ignore mark word because we are running concurrent with mutators
6223 assert(oopDesc::is_oop_or_null(p, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6224 HeapWord* addr = (HeapWord*)p;
6225 assert(_span.contains(addr), "we are scanning the CMS generation");
6226 bool is_obj_array = false;
6227 #ifdef ASSERT
6228 if (!_parallel) {
6229 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6230 assert(_collector->overflow_list_is_empty(),
6231 "overflow list should be empty");
6232
6233 }
6234 #endif // ASSERT
6235 if (_bit_map->isMarked(addr)) {
6236 // Obj arrays are precisely marked, non-arrays are not;
6237 // so we scan objArrays precisely and non-arrays in their
6238 // entirety.
6239 if (p->is_objArray()) {
6240 is_obj_array = true;
6241 if (_parallel) {
6242 p->oop_iterate(_par_scan_closure, mr);
6243 } else {
6244 p->oop_iterate(_scan_closure, mr);
6245 }
6246 } else {
6247 if (_parallel) {
6248 p->oop_iterate(_par_scan_closure);
6249 } else {
6250 p->oop_iterate(_scan_closure);
6251 }
6252 }
6253 }
6254 #ifdef ASSERT
6255 if (!_parallel) {
6256 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6257 assert(_collector->overflow_list_is_empty(),
6258 "overflow list should be empty");
6259
6260 }
6261 #endif // ASSERT
6262 return is_obj_array;
6263 }
6264
6265 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6266 MemRegion span,
6267 CMSBitMap* bitMap, CMSMarkStack* markStack,
6268 bool should_yield, bool verifying):
6269 _collector(collector),
6270 _span(span),
6271 _bitMap(bitMap),
6272 _mut(&collector->_modUnionTable),
6273 _markStack(markStack),
6274 _yield(should_yield),
6275 _skipBits(0)
6276 {
6277 assert(_markStack->isEmpty(), "stack should be empty");
6278 _finger = _bitMap->startWord();
6279 _threshold = _finger;
6280 assert(_collector->_restart_addr == NULL, "Sanity check");
6281 assert(_span.contains(_finger), "Out of bounds _finger?");
6282 DEBUG_ONLY(_verifying = verifying;)
6283 }
6284
6285 void MarkFromRootsClosure::reset(HeapWord* addr) {
6286 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6287 assert(_span.contains(addr), "Out of bounds _finger?");
6288 _finger = addr;
6289 _threshold = align_up(_finger, CardTable::card_size);
6290 }
6291
6292 // Should revisit to see if this should be restructured for
6293 // greater efficiency.
6294 bool MarkFromRootsClosure::do_bit(size_t offset) {
6295 if (_skipBits > 0) {
6296 _skipBits--;
6297 return true;
6298 }
6299 // convert offset into a HeapWord*
6300 HeapWord* addr = _bitMap->startWord() + offset;
6301 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6302 "address out of range");
6303 assert(_bitMap->isMarked(addr), "tautology");
6304 if (_bitMap->isMarked(addr+1)) {
6305 // this is an allocated but not yet initialized object
6306 assert(_skipBits == 0, "tautology");
6307 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6308 oop p = oop(addr);
6309 if (p->klass_or_null_acquire() == NULL) {
6310 DEBUG_ONLY(if (!_verifying) {)
6311 // We re-dirty the cards on which this object lies and increase
6312 // the _threshold so that we'll come back to scan this object
6313 // during the preclean or remark phase. (CMSCleanOnEnter)
6314 if (CMSCleanOnEnter) {
6315 size_t sz = _collector->block_size_using_printezis_bits(addr);
6316 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
6317 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6318 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6319 // Bump _threshold to end_card_addr; note that
6320 // _threshold cannot possibly exceed end_card_addr, anyhow.
6321 // This prevents future clearing of the card as the scan proceeds
6322 // to the right.
6323 assert(_threshold <= end_card_addr,
6324 "Because we are just scanning into this object");
6325 if (_threshold < end_card_addr) {
6326 _threshold = end_card_addr;
6327 }
6328 if (p->klass_or_null_acquire() != NULL) {
6329 // Redirty the range of cards...
6330 _mut->mark_range(redirty_range);
6331 } // ...else the setting of klass will dirty the card anyway.
6332 }
6333 DEBUG_ONLY(})
6334 return true;
6335 }
6336 }
6337 scanOopsInOop(addr);
6338 return true;
6339 }
6340
6341 // We take a break if we've been at this for a while,
6342 // so as to avoid monopolizing the locks involved.
6343 void MarkFromRootsClosure::do_yield_work() {
6344 // First give up the locks, then yield, then re-lock
6345 // We should probably use a constructor/destructor idiom to
6346 // do this unlock/lock or modify the MutexUnlocker class to
6347 // serve our purpose. XXX
6348 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6349 "CMS thread should hold CMS token");
6350 assert_lock_strong(_bitMap->lock());
6351 _bitMap->lock()->unlock();
6352 ConcurrentMarkSweepThread::desynchronize(true);
6353 _collector->stopTimer();
6354 _collector->incrementYields();
6355
6356 // See the comment in coordinator_yield()
6357 for (unsigned i = 0; i < CMSYieldSleepCount &&
6358 ConcurrentMarkSweepThread::should_yield() &&
6359 !CMSCollector::foregroundGCIsActive(); ++i) {
6360 os::sleep(Thread::current(), 1, false);
6361 }
6362
6363 ConcurrentMarkSweepThread::synchronize(true);
6364 _bitMap->lock()->lock_without_safepoint_check();
6365 _collector->startTimer();
6366 }
6367
6368 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6369 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6370 assert(_markStack->isEmpty(),
6371 "should drain stack to limit stack usage");
6372 // convert ptr to an oop preparatory to scanning
6373 oop obj = oop(ptr);
6374 // Ignore mark word in verification below, since we
6375 // may be running concurrent with mutators.
6376 assert(oopDesc::is_oop(obj, true), "should be an oop");
6377 assert(_finger <= ptr, "_finger runneth ahead");
6378 // advance the finger to right end of this object
6379 _finger = ptr + obj->size();
6380 assert(_finger > ptr, "we just incremented it above");
6381 // On large heaps, it may take us some time to get through
6382 // the marking phase. During
6383 // this time it's possible that a lot of mutations have
6384 // accumulated in the card table and the mod union table --
6385 // these mutation records are redundant until we have
6386 // actually traced into the corresponding card.
6387 // Here, we check whether advancing the finger would make
6388 // us cross into a new card, and if so clear corresponding
6389 // cards in the MUT (preclean them in the card-table in the
6390 // future).
6391
6392 DEBUG_ONLY(if (!_verifying) {)
6393 // The clean-on-enter optimization is disabled by default,
6394 // until we fix 6178663.
6395 if (CMSCleanOnEnter && (_finger > _threshold)) {
6396 // [_threshold, _finger) represents the interval
6397 // of cards to be cleared in MUT (or precleaned in card table).
6398 // The set of cards to be cleared is all those that overlap
6399 // with the interval [_threshold, _finger); note that
6400 // _threshold is always kept card-aligned but _finger isn't
6401 // always card-aligned.
6402 HeapWord* old_threshold = _threshold;
6403 assert(is_aligned(old_threshold, CardTable::card_size),
6404 "_threshold should always be card-aligned");
6405 _threshold = align_up(_finger, CardTable::card_size);
6406 MemRegion mr(old_threshold, _threshold);
6407 assert(!mr.is_empty(), "Control point invariant");
6408 assert(_span.contains(mr), "Should clear within span");
6409 _mut->clear_range(mr);
6410 }
6411 DEBUG_ONLY(})
6412 // Note: the finger doesn't advance while we drain
6413 // the stack below.
6414 PushOrMarkClosure pushOrMarkClosure(_collector,
6415 _span, _bitMap, _markStack,
6416 _finger, this);
6417 bool res = _markStack->push(obj);
6418 assert(res, "Empty non-zero size stack should have space for single push");
6419 while (!_markStack->isEmpty()) {
6420 oop new_oop = _markStack->pop();
6421 // Skip verifying header mark word below because we are
6422 // running concurrent with mutators.
6423 assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6424 // now scan this oop's oops
6425 new_oop->oop_iterate(&pushOrMarkClosure);
6426 do_yield_check();
6427 }
6428 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6429 }
6430
6431 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task,
6432 CMSCollector* collector, MemRegion span,
6433 CMSBitMap* bit_map,
6434 OopTaskQueue* work_queue,
6435 CMSMarkStack* overflow_stack):
6436 _collector(collector),
6437 _whole_span(collector->_span),
6438 _span(span),
6439 _bit_map(bit_map),
6440 _mut(&collector->_modUnionTable),
6441 _work_queue(work_queue),
6442 _overflow_stack(overflow_stack),
6443 _skip_bits(0),
6444 _task(task)
6445 {
6446 assert(_work_queue->size() == 0, "work_queue should be empty");
6447 _finger = span.start();
6448 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6449 assert(_span.contains(_finger), "Out of bounds _finger?");
6450 }
6451
6452 // Should revisit to see if this should be restructured for
6453 // greater efficiency.
6454 bool ParMarkFromRootsClosure::do_bit(size_t offset) {
6455 if (_skip_bits > 0) {
6456 _skip_bits--;
6457 return true;
6458 }
6459 // convert offset into a HeapWord*
6460 HeapWord* addr = _bit_map->startWord() + offset;
6461 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6462 "address out of range");
6463 assert(_bit_map->isMarked(addr), "tautology");
6464 if (_bit_map->isMarked(addr+1)) {
6465 // this is an allocated object that might not yet be initialized
6466 assert(_skip_bits == 0, "tautology");
6467 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6468 oop p = oop(addr);
6469 if (p->klass_or_null_acquire() == NULL) {
6470 // in the case of Clean-on-Enter optimization, redirty card
6471 // and avoid clearing card by increasing the threshold.
6472 return true;
6473 }
6474 }
6475 scan_oops_in_oop(addr);
6476 return true;
6477 }
6478
6479 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6480 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6481 // Should we assert that our work queue is empty or
6482 // below some drain limit?
6483 assert(_work_queue->size() == 0,
6484 "should drain stack to limit stack usage");
6485 // convert ptr to an oop preparatory to scanning
6486 oop obj = oop(ptr);
6487 // Ignore mark word in verification below, since we
6488 // may be running concurrent with mutators.
6489 assert(oopDesc::is_oop(obj, true), "should be an oop");
6490 assert(_finger <= ptr, "_finger runneth ahead");
6491 // advance the finger to right end of this object
6492 _finger = ptr + obj->size();
6493 assert(_finger > ptr, "we just incremented it above");
6494 // On large heaps, it may take us some time to get through
6495 // the marking phase. During
6496 // this time it's possible that a lot of mutations have
6497 // accumulated in the card table and the mod union table --
6498 // these mutation records are redundant until we have
6499 // actually traced into the corresponding card.
6500 // Here, we check whether advancing the finger would make
6501 // us cross into a new card, and if so clear corresponding
6502 // cards in the MUT (preclean them in the card-table in the
6503 // future).
6504
6505 // The clean-on-enter optimization is disabled by default,
6506 // until we fix 6178663.
6507 if (CMSCleanOnEnter && (_finger > _threshold)) {
6508 // [_threshold, _finger) represents the interval
6509 // of cards to be cleared in MUT (or precleaned in card table).
6510 // The set of cards to be cleared is all those that overlap
6511 // with the interval [_threshold, _finger); note that
6512 // _threshold is always kept card-aligned but _finger isn't
6513 // always card-aligned.
6514 HeapWord* old_threshold = _threshold;
6515 assert(is_aligned(old_threshold, CardTable::card_size),
6516 "_threshold should always be card-aligned");
6517 _threshold = align_up(_finger, CardTable::card_size);
6518 MemRegion mr(old_threshold, _threshold);
6519 assert(!mr.is_empty(), "Control point invariant");
6520 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6521 _mut->clear_range(mr);
6522 }
6523
6524 // Note: the local finger doesn't advance while we drain
6525 // the stack below, but the global finger sure can and will.
6526 HeapWord* volatile* gfa = _task->global_finger_addr();
6527 ParPushOrMarkClosure pushOrMarkClosure(_collector,
6528 _span, _bit_map,
6529 _work_queue,
6530 _overflow_stack,
6531 _finger,
6532 gfa, this);
6533 bool res = _work_queue->push(obj); // overflow could occur here
6534 assert(res, "Will hold once we use workqueues");
6535 while (true) {
6536 oop new_oop;
6537 if (!_work_queue->pop_local(new_oop)) {
6538 // We emptied our work_queue; check if there's stuff that can
6539 // be gotten from the overflow stack.
6540 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6541 _overflow_stack, _work_queue)) {
6542 do_yield_check();
6543 continue;
6544 } else { // done
6545 break;
6546 }
6547 }
6548 // Skip verifying header mark word below because we are
6549 // running concurrent with mutators.
6550 assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6551 // now scan this oop's oops
6552 new_oop->oop_iterate(&pushOrMarkClosure);
6553 do_yield_check();
6554 }
6555 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6556 }
6557
6558 // Yield in response to a request from VM Thread or
6559 // from mutators.
6560 void ParMarkFromRootsClosure::do_yield_work() {
6561 assert(_task != NULL, "sanity");
6562 _task->yield();
6563 }
6564
6565 // A variant of the above used for verifying CMS marking work.
6566 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6567 MemRegion span,
6568 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6569 CMSMarkStack* mark_stack):
6570 _collector(collector),
6571 _span(span),
6572 _verification_bm(verification_bm),
6573 _cms_bm(cms_bm),
6574 _mark_stack(mark_stack),
6575 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6576 mark_stack)
6577 {
6578 assert(_mark_stack->isEmpty(), "stack should be empty");
6579 _finger = _verification_bm->startWord();
6580 assert(_collector->_restart_addr == NULL, "Sanity check");
6581 assert(_span.contains(_finger), "Out of bounds _finger?");
6582 }
6583
6584 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6585 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6586 assert(_span.contains(addr), "Out of bounds _finger?");
6587 _finger = addr;
6588 }
6589
6590 // Should revisit to see if this should be restructured for
6591 // greater efficiency.
6592 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6593 // convert offset into a HeapWord*
6594 HeapWord* addr = _verification_bm->startWord() + offset;
6595 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6596 "address out of range");
6597 assert(_verification_bm->isMarked(addr), "tautology");
6598 assert(_cms_bm->isMarked(addr), "tautology");
6599
6600 assert(_mark_stack->isEmpty(),
6601 "should drain stack to limit stack usage");
6602 // convert addr to an oop preparatory to scanning
6603 oop obj = oop(addr);
6604 assert(oopDesc::is_oop(obj), "should be an oop");
6605 assert(_finger <= addr, "_finger runneth ahead");
6606 // advance the finger to right end of this object
6607 _finger = addr + obj->size();
6608 assert(_finger > addr, "we just incremented it above");
6609 // Note: the finger doesn't advance while we drain
6610 // the stack below.
6611 bool res = _mark_stack->push(obj);
6612 assert(res, "Empty non-zero size stack should have space for single push");
6613 while (!_mark_stack->isEmpty()) {
6614 oop new_oop = _mark_stack->pop();
6615 assert(oopDesc::is_oop(new_oop), "Oops! expected to pop an oop");
6616 // now scan this oop's oops
6617 new_oop->oop_iterate(&_pam_verify_closure);
6618 }
6619 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6620 return true;
6621 }
6622
6623 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6624 CMSCollector* collector, MemRegion span,
6625 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6626 CMSMarkStack* mark_stack):
6627 MetadataVisitingOopIterateClosure(collector->ref_processor()),
6628 _collector(collector),
6629 _span(span),
6630 _verification_bm(verification_bm),
6631 _cms_bm(cms_bm),
6632 _mark_stack(mark_stack)
6633 { }
6634
6635 template <class T> void PushAndMarkVerifyClosure::do_oop_work(T *p) {
6636 oop obj = RawAccess<>::oop_load(p);
6637 do_oop(obj);
6638 }
6639
6640 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6641 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6642
6643 // Upon stack overflow, we discard (part of) the stack,
6644 // remembering the least address amongst those discarded
6645 // in CMSCollector's _restart_address.
6646 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6647 // Remember the least grey address discarded
6648 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6649 _collector->lower_restart_addr(ra);
6650 _mark_stack->reset(); // discard stack contents
6651 _mark_stack->expand(); // expand the stack if possible
6652 }
6653
6654 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6655 assert(oopDesc::is_oop_or_null(obj), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6656 HeapWord* addr = (HeapWord*)obj;
6657 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6658 // Oop lies in _span and isn't yet grey or black
6659 _verification_bm->mark(addr); // now grey
6660 if (!_cms_bm->isMarked(addr)) {
6661 Log(gc, verify) log;
6662 ResourceMark rm;
6663 LogStream ls(log.error());
6664 oop(addr)->print_on(&ls);
6665 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6666 fatal("... aborting");
6667 }
6668
6669 if (!_mark_stack->push(obj)) { // stack overflow
6670 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6671 assert(_mark_stack->isFull(), "Else push should have succeeded");
6672 handle_stack_overflow(addr);
6673 }
6674 // anything including and to the right of _finger
6675 // will be scanned as we iterate over the remainder of the
6676 // bit map
6677 }
6678 }
6679
6680 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6681 MemRegion span,
6682 CMSBitMap* bitMap, CMSMarkStack* markStack,
6683 HeapWord* finger, MarkFromRootsClosure* parent) :
6684 MetadataVisitingOopIterateClosure(collector->ref_processor()),
6685 _collector(collector),
6686 _span(span),
6687 _bitMap(bitMap),
6688 _markStack(markStack),
6689 _finger(finger),
6690 _parent(parent)
6691 { }
6692
6693 ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector,
6694 MemRegion span,
6695 CMSBitMap* bit_map,
6696 OopTaskQueue* work_queue,
6697 CMSMarkStack* overflow_stack,
6698 HeapWord* finger,
6699 HeapWord* volatile* global_finger_addr,
6700 ParMarkFromRootsClosure* parent) :
6701 MetadataVisitingOopIterateClosure(collector->ref_processor()),
6702 _collector(collector),
6703 _whole_span(collector->_span),
6704 _span(span),
6705 _bit_map(bit_map),
6706 _work_queue(work_queue),
6707 _overflow_stack(overflow_stack),
6708 _finger(finger),
6709 _global_finger_addr(global_finger_addr),
6710 _parent(parent)
6711 { }
6712
6713 // Assumes thread-safe access by callers, who are
6714 // responsible for mutual exclusion.
6715 void CMSCollector::lower_restart_addr(HeapWord* low) {
6716 assert(_span.contains(low), "Out of bounds addr");
6717 if (_restart_addr == NULL) {
6718 _restart_addr = low;
6719 } else {
6720 _restart_addr = MIN2(_restart_addr, low);
6721 }
6722 }
6723
6724 // Upon stack overflow, we discard (part of) the stack,
6725 // remembering the least address amongst those discarded
6726 // in CMSCollector's _restart_address.
6727 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6728 // Remember the least grey address discarded
6729 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6730 _collector->lower_restart_addr(ra);
6731 _markStack->reset(); // discard stack contents
6732 _markStack->expand(); // expand the stack if possible
6733 }
6734
6735 // Upon stack overflow, we discard (part of) the stack,
6736 // remembering the least address amongst those discarded
6737 // in CMSCollector's _restart_address.
6738 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6739 // We need to do this under a mutex to prevent other
6740 // workers from interfering with the work done below.
6741 MutexLockerEx ml(_overflow_stack->par_lock(),
6742 Mutex::_no_safepoint_check_flag);
6743 // Remember the least grey address discarded
6744 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6745 _collector->lower_restart_addr(ra);
6746 _overflow_stack->reset(); // discard stack contents
6747 _overflow_stack->expand(); // expand the stack if possible
6748 }
6749
6750 void PushOrMarkClosure::do_oop(oop obj) {
6751 // Ignore mark word because we are running concurrent with mutators.
6752 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6753 HeapWord* addr = (HeapWord*)obj;
6754 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6755 // Oop lies in _span and isn't yet grey or black
6756 _bitMap->mark(addr); // now grey
6757 if (addr < _finger) {
6758 // the bit map iteration has already either passed, or
6759 // sampled, this bit in the bit map; we'll need to
6760 // use the marking stack to scan this oop's oops.
6761 bool simulate_overflow = false;
6762 NOT_PRODUCT(
6763 if (CMSMarkStackOverflowALot &&
6764 _collector->simulate_overflow()) {
6765 // simulate a stack overflow
6766 simulate_overflow = true;
6767 }
6768 )
6769 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6770 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6771 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6772 handle_stack_overflow(addr);
6773 }
6774 }
6775 // anything including and to the right of _finger
6776 // will be scanned as we iterate over the remainder of the
6777 // bit map
6778 do_yield_check();
6779 }
6780 }
6781
6782 void ParPushOrMarkClosure::do_oop(oop obj) {
6783 // Ignore mark word because we are running concurrent with mutators.
6784 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6785 HeapWord* addr = (HeapWord*)obj;
6786 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6787 // Oop lies in _span and isn't yet grey or black
6788 // We read the global_finger (volatile read) strictly after marking oop
6789 bool res = _bit_map->par_mark(addr); // now grey
6790 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6791 // Should we push this marked oop on our stack?
6792 // -- if someone else marked it, nothing to do
6793 // -- if target oop is above global finger nothing to do
6794 // -- if target oop is in chunk and above local finger
6795 // then nothing to do
6796 // -- else push on work queue
6797 if ( !res // someone else marked it, they will deal with it
6798 || (addr >= *gfa) // will be scanned in a later task
6799 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6800 return;
6801 }
6802 // the bit map iteration has already either passed, or
6803 // sampled, this bit in the bit map; we'll need to
6804 // use the marking stack to scan this oop's oops.
6805 bool simulate_overflow = false;
6806 NOT_PRODUCT(
6807 if (CMSMarkStackOverflowALot &&
6808 _collector->simulate_overflow()) {
6809 // simulate a stack overflow
6810 simulate_overflow = true;
6811 }
6812 )
6813 if (simulate_overflow ||
6814 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6815 // stack overflow
6816 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6817 // We cannot assert that the overflow stack is full because
6818 // it may have been emptied since.
6819 assert(simulate_overflow ||
6820 _work_queue->size() == _work_queue->max_elems(),
6821 "Else push should have succeeded");
6822 handle_stack_overflow(addr);
6823 }
6824 do_yield_check();
6825 }
6826 }
6827
6828 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6829 MemRegion span,
6830 ReferenceDiscoverer* rd,
6831 CMSBitMap* bit_map,
6832 CMSBitMap* mod_union_table,
6833 CMSMarkStack* mark_stack,
6834 bool concurrent_precleaning):
6835 MetadataVisitingOopIterateClosure(rd),
6836 _collector(collector),
6837 _span(span),
6838 _bit_map(bit_map),
6839 _mod_union_table(mod_union_table),
6840 _mark_stack(mark_stack),
6841 _concurrent_precleaning(concurrent_precleaning)
6842 {
6843 assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL");
6844 }
6845
6846 // Grey object rescan during pre-cleaning and second checkpoint phases --
6847 // the non-parallel version (the parallel version appears further below.)
6848 void PushAndMarkClosure::do_oop(oop obj) {
6849 // Ignore mark word verification. If during concurrent precleaning,
6850 // the object monitor may be locked. If during the checkpoint
6851 // phases, the object may already have been reached by a different
6852 // path and may be at the end of the global overflow list (so
6853 // the mark word may be NULL).
6854 assert(oopDesc::is_oop_or_null(obj, true /* ignore mark word */),
6855 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6856 HeapWord* addr = (HeapWord*)obj;
6857 // Check if oop points into the CMS generation
6858 // and is not marked
6859 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6860 // a white object ...
6861 _bit_map->mark(addr); // ... now grey
6862 // push on the marking stack (grey set)
6863 bool simulate_overflow = false;
6864 NOT_PRODUCT(
6865 if (CMSMarkStackOverflowALot &&
6866 _collector->simulate_overflow()) {
6867 // simulate a stack overflow
6868 simulate_overflow = true;
6869 }
6870 )
6871 if (simulate_overflow || !_mark_stack->push(obj)) {
6872 if (_concurrent_precleaning) {
6873 // During precleaning we can just dirty the appropriate card(s)
6874 // in the mod union table, thus ensuring that the object remains
6875 // in the grey set and continue. In the case of object arrays
6876 // we need to dirty all of the cards that the object spans,
6877 // since the rescan of object arrays will be limited to the
6878 // dirty cards.
6879 // Note that no one can be interfering with us in this action
6880 // of dirtying the mod union table, so no locking or atomics
6881 // are required.
6882 if (obj->is_objArray()) {
6883 size_t sz = obj->size();
6884 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
6885 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6886 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6887 _mod_union_table->mark_range(redirty_range);
6888 } else {
6889 _mod_union_table->mark(addr);
6890 }
6891 _collector->_ser_pmc_preclean_ovflw++;
6892 } else {
6893 // During the remark phase, we need to remember this oop
6894 // in the overflow list.
6895 _collector->push_on_overflow_list(obj);
6896 _collector->_ser_pmc_remark_ovflw++;
6897 }
6898 }
6899 }
6900 }
6901
6902 ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector,
6903 MemRegion span,
6904 ReferenceDiscoverer* rd,
6905 CMSBitMap* bit_map,
6906 OopTaskQueue* work_queue):
6907 MetadataVisitingOopIterateClosure(rd),
6908 _collector(collector),
6909 _span(span),
6910 _bit_map(bit_map),
6911 _work_queue(work_queue)
6912 {
6913 assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL");
6914 }
6915
6916 // Grey object rescan during second checkpoint phase --
6917 // the parallel version.
6918 void ParPushAndMarkClosure::do_oop(oop obj) {
6919 // In the assert below, we ignore the mark word because
6920 // this oop may point to an already visited object that is
6921 // on the overflow stack (in which case the mark word has
6922 // been hijacked for chaining into the overflow stack --
6923 // if this is the last object in the overflow stack then
6924 // its mark word will be NULL). Because this object may
6925 // have been subsequently popped off the global overflow
6926 // stack, and the mark word possibly restored to the prototypical
6927 // value, by the time we get to examined this failing assert in
6928 // the debugger, is_oop_or_null(false) may subsequently start
6929 // to hold.
6930 assert(oopDesc::is_oop_or_null(obj, true),
6931 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6932 HeapWord* addr = (HeapWord*)obj;
6933 // Check if oop points into the CMS generation
6934 // and is not marked
6935 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6936 // a white object ...
6937 // If we manage to "claim" the object, by being the
6938 // first thread to mark it, then we push it on our
6939 // marking stack
6940 if (_bit_map->par_mark(addr)) { // ... now grey
6941 // push on work queue (grey set)
6942 bool simulate_overflow = false;
6943 NOT_PRODUCT(
6944 if (CMSMarkStackOverflowALot &&
6945 _collector->par_simulate_overflow()) {
6946 // simulate a stack overflow
6947 simulate_overflow = true;
6948 }
6949 )
6950 if (simulate_overflow || !_work_queue->push(obj)) {
6951 _collector->par_push_on_overflow_list(obj);
6952 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
6953 }
6954 } // Else, some other thread got there first
6955 }
6956 }
6957
6958 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6959 Mutex* bml = _collector->bitMapLock();
6960 assert_lock_strong(bml);
6961 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6962 "CMS thread should hold CMS token");
6963
6964 bml->unlock();
6965 ConcurrentMarkSweepThread::desynchronize(true);
6966
6967 _collector->stopTimer();
6968 _collector->incrementYields();
6969
6970 // See the comment in coordinator_yield()
6971 for (unsigned i = 0; i < CMSYieldSleepCount &&
6972 ConcurrentMarkSweepThread::should_yield() &&
6973 !CMSCollector::foregroundGCIsActive(); ++i) {
6974 os::sleep(Thread::current(), 1, false);
6975 }
6976
6977 ConcurrentMarkSweepThread::synchronize(true);
6978 bml->lock();
6979
6980 _collector->startTimer();
6981 }
6982
6983 bool CMSPrecleanRefsYieldClosure::should_return() {
6984 if (ConcurrentMarkSweepThread::should_yield()) {
6985 do_yield_work();
6986 }
6987 return _collector->foregroundGCIsActive();
6988 }
6989
6990 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
6991 assert(((size_t)mr.start())%CardTable::card_size_in_words == 0,
6992 "mr should be aligned to start at a card boundary");
6993 // We'd like to assert:
6994 // assert(mr.word_size()%CardTable::card_size_in_words == 0,
6995 // "mr should be a range of cards");
6996 // However, that would be too strong in one case -- the last
6997 // partition ends at _unallocated_block which, in general, can be
6998 // an arbitrary boundary, not necessarily card aligned.
6999 _num_dirty_cards += mr.word_size()/CardTable::card_size_in_words;
7000 _space->object_iterate_mem(mr, &_scan_cl);
7001 }
7002
7003 SweepClosure::SweepClosure(CMSCollector* collector,
7004 ConcurrentMarkSweepGeneration* g,
7005 CMSBitMap* bitMap, bool should_yield) :
7006 _collector(collector),
7007 _g(g),
7008 _sp(g->cmsSpace()),
7009 _limit(_sp->sweep_limit()),
7010 _freelistLock(_sp->freelistLock()),
7011 _bitMap(bitMap),
7012 _inFreeRange(false), // No free range at beginning of sweep
7013 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7014 _lastFreeRangeCoalesced(false),
7015 _yield(should_yield),
7016 _freeFinger(g->used_region().start())
7017 {
7018 NOT_PRODUCT(
7019 _numObjectsFreed = 0;
7020 _numWordsFreed = 0;
7021 _numObjectsLive = 0;
7022 _numWordsLive = 0;
7023 _numObjectsAlreadyFree = 0;
7024 _numWordsAlreadyFree = 0;
7025 _last_fc = NULL;
7026
7027 _sp->initializeIndexedFreeListArrayReturnedBytes();
7028 _sp->dictionary()->initialize_dict_returned_bytes();
7029 )
7030 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7031 "sweep _limit out of bounds");
7032 log_develop_trace(gc, sweep)("====================");
7033 log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
7034 }
7035
7036 void SweepClosure::print_on(outputStream* st) const {
7037 st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7038 p2i(_sp->bottom()), p2i(_sp->end()));
7039 st->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7040 st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7041 NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7042 st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7043 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7044 }
7045
7046 #ifndef PRODUCT
7047 // Assertion checking only: no useful work in product mode --
7048 // however, if any of the flags below become product flags,
7049 // you may need to review this code to see if it needs to be
7050 // enabled in product mode.
7051 SweepClosure::~SweepClosure() {
7052 assert_lock_strong(_freelistLock);
7053 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7054 "sweep _limit out of bounds");
7055 if (inFreeRange()) {
7056 Log(gc, sweep) log;
7057 log.error("inFreeRange() should have been reset; dumping state of SweepClosure");
7058 ResourceMark rm;
7059 LogStream ls(log.error());
7060 print_on(&ls);
7061 ShouldNotReachHere();
7062 }
7063
7064 if (log_is_enabled(Debug, gc, sweep)) {
7065 log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7066 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7067 log_debug(gc, sweep)("Live " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7068 _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7069 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7070 log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7071 }
7072
7073 if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) {
7074 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7075 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7076 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7077 log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes Indexed List Returned " SIZE_FORMAT " bytes Dictionary Returned " SIZE_FORMAT " bytes",
7078 returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7079 }
7080 log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7081 log_develop_trace(gc, sweep)("================");
7082 }
7083 #endif // PRODUCT
7084
7085 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7086 bool freeRangeInFreeLists) {
7087 log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7088 p2i(freeFinger), freeRangeInFreeLists);
7089 assert(!inFreeRange(), "Trampling existing free range");
7090 set_inFreeRange(true);
7091 set_lastFreeRangeCoalesced(false);
7092
7093 set_freeFinger(freeFinger);
7094 set_freeRangeInFreeLists(freeRangeInFreeLists);
7095 if (CMSTestInFreeList) {
7096 if (freeRangeInFreeLists) {
7097 FreeChunk* fc = (FreeChunk*) freeFinger;
7098 assert(fc->is_free(), "A chunk on the free list should be free.");
7099 assert(fc->size() > 0, "Free range should have a size");
7100 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7101 }
7102 }
7103 }
7104
7105 // Note that the sweeper runs concurrently with mutators. Thus,
7106 // it is possible for direct allocation in this generation to happen
7107 // in the middle of the sweep. Note that the sweeper also coalesces
7108 // contiguous free blocks. Thus, unless the sweeper and the allocator
7109 // synchronize appropriately freshly allocated blocks may get swept up.
7110 // This is accomplished by the sweeper locking the free lists while
7111 // it is sweeping. Thus blocks that are determined to be free are
7112 // indeed free. There is however one additional complication:
7113 // blocks that have been allocated since the final checkpoint and
7114 // mark, will not have been marked and so would be treated as
7115 // unreachable and swept up. To prevent this, the allocator marks
7116 // the bit map when allocating during the sweep phase. This leads,
7117 // however, to a further complication -- objects may have been allocated
7118 // but not yet initialized -- in the sense that the header isn't yet
7119 // installed. The sweeper can not then determine the size of the block
7120 // in order to skip over it. To deal with this case, we use a technique
7121 // (due to Printezis) to encode such uninitialized block sizes in the
7122 // bit map. Since the bit map uses a bit per every HeapWord, but the
7123 // CMS generation has a minimum object size of 3 HeapWords, it follows
7124 // that "normal marks" won't be adjacent in the bit map (there will
7125 // always be at least two 0 bits between successive 1 bits). We make use
7126 // of these "unused" bits to represent uninitialized blocks -- the bit
7127 // corresponding to the start of the uninitialized object and the next
7128 // bit are both set. Finally, a 1 bit marks the end of the object that
7129 // started with the two consecutive 1 bits to indicate its potentially
7130 // uninitialized state.
7131
7132 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7133 FreeChunk* fc = (FreeChunk*)addr;
7134 size_t res;
7135
7136 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7137 // than "addr == _limit" because although _limit was a block boundary when
7138 // we started the sweep, it may no longer be one because heap expansion
7139 // may have caused us to coalesce the block ending at the address _limit
7140 // with a newly expanded chunk (this happens when _limit was set to the
7141 // previous _end of the space), so we may have stepped past _limit:
7142 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7143 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7144 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7145 "sweep _limit out of bounds");
7146 assert(addr < _sp->end(), "addr out of bounds");
7147 // Flush any free range we might be holding as a single
7148 // coalesced chunk to the appropriate free list.
7149 if (inFreeRange()) {
7150 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7151 "freeFinger() " PTR_FORMAT " is out of bounds", p2i(freeFinger()));
7152 flush_cur_free_chunk(freeFinger(),
7153 pointer_delta(addr, freeFinger()));
7154 log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7155 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7156 lastFreeRangeCoalesced() ? 1 : 0);
7157 }
7158
7159 // help the iterator loop finish
7160 return pointer_delta(_sp->end(), addr);
7161 }
7162
7163 assert(addr < _limit, "sweep invariant");
7164 // check if we should yield
7165 do_yield_check(addr);
7166 if (fc->is_free()) {
7167 // Chunk that is already free
7168 res = fc->size();
7169 do_already_free_chunk(fc);
7170 debug_only(_sp->verifyFreeLists());
7171 // If we flush the chunk at hand in lookahead_and_flush()
7172 // and it's coalesced with a preceding chunk, then the
7173 // process of "mangling" the payload of the coalesced block
7174 // will cause erasure of the size information from the
7175 // (erstwhile) header of all the coalesced blocks but the
7176 // first, so the first disjunct in the assert will not hold
7177 // in that specific case (in which case the second disjunct
7178 // will hold).
7179 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7180 "Otherwise the size info doesn't change at this step");
7181 NOT_PRODUCT(
7182 _numObjectsAlreadyFree++;
7183 _numWordsAlreadyFree += res;
7184 )
7185 NOT_PRODUCT(_last_fc = fc;)
7186 } else if (!_bitMap->isMarked(addr)) {
7187 // Chunk is fresh garbage
7188 res = do_garbage_chunk(fc);
7189 debug_only(_sp->verifyFreeLists());
7190 NOT_PRODUCT(
7191 _numObjectsFreed++;
7192 _numWordsFreed += res;
7193 )
7194 } else {
7195 // Chunk that is alive.
7196 res = do_live_chunk(fc);
7197 debug_only(_sp->verifyFreeLists());
7198 NOT_PRODUCT(
7199 _numObjectsLive++;
7200 _numWordsLive += res;
7201 )
7202 }
7203 return res;
7204 }
7205
7206 // For the smart allocation, record following
7207 // split deaths - a free chunk is removed from its free list because
7208 // it is being split into two or more chunks.
7209 // split birth - a free chunk is being added to its free list because
7210 // a larger free chunk has been split and resulted in this free chunk.
7211 // coal death - a free chunk is being removed from its free list because
7212 // it is being coalesced into a large free chunk.
7213 // coal birth - a free chunk is being added to its free list because
7214 // it was created when two or more free chunks where coalesced into
7215 // this free chunk.
7216 //
7217 // These statistics are used to determine the desired number of free
7218 // chunks of a given size. The desired number is chosen to be relative
7219 // to the end of a CMS sweep. The desired number at the end of a sweep
7220 // is the
7221 // count-at-end-of-previous-sweep (an amount that was enough)
7222 // - count-at-beginning-of-current-sweep (the excess)
7223 // + split-births (gains in this size during interval)
7224 // - split-deaths (demands on this size during interval)
7225 // where the interval is from the end of one sweep to the end of the
7226 // next.
7227 //
7228 // When sweeping the sweeper maintains an accumulated chunk which is
7229 // the chunk that is made up of chunks that have been coalesced. That
7230 // will be termed the left-hand chunk. A new chunk of garbage that
7231 // is being considered for coalescing will be referred to as the
7232 // right-hand chunk.
7233 //
7234 // When making a decision on whether to coalesce a right-hand chunk with
7235 // the current left-hand chunk, the current count vs. the desired count
7236 // of the left-hand chunk is considered. Also if the right-hand chunk
7237 // is near the large chunk at the end of the heap (see
7238 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7239 // left-hand chunk is coalesced.
7240 //
7241 // When making a decision about whether to split a chunk, the desired count
7242 // vs. the current count of the candidate to be split is also considered.
7243 // If the candidate is underpopulated (currently fewer chunks than desired)
7244 // a chunk of an overpopulated (currently more chunks than desired) size may
7245 // be chosen. The "hint" associated with a free list, if non-null, points
7246 // to a free list which may be overpopulated.
7247 //
7248
7249 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7250 const size_t size = fc->size();
7251 // Chunks that cannot be coalesced are not in the
7252 // free lists.
7253 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7254 assert(_sp->verify_chunk_in_free_list(fc),
7255 "free chunk should be in free lists");
7256 }
7257 // a chunk that is already free, should not have been
7258 // marked in the bit map
7259 HeapWord* const addr = (HeapWord*) fc;
7260 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7261 // Verify that the bit map has no bits marked between
7262 // addr and purported end of this block.
7263 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7264
7265 // Some chunks cannot be coalesced under any circumstances.
7266 // See the definition of cantCoalesce().
7267 if (!fc->cantCoalesce()) {
7268 // This chunk can potentially be coalesced.
7269 // All the work is done in
7270 do_post_free_or_garbage_chunk(fc, size);
7271 // Note that if the chunk is not coalescable (the else arm
7272 // below), we unconditionally flush, without needing to do
7273 // a "lookahead," as we do below.
7274 if (inFreeRange()) lookahead_and_flush(fc, size);
7275 } else {
7276 // Code path common to both original and adaptive free lists.
7277
7278 // cant coalesce with previous block; this should be treated
7279 // as the end of a free run if any
7280 if (inFreeRange()) {
7281 // we kicked some butt; time to pick up the garbage
7282 assert(freeFinger() < addr, "freeFinger points too high");
7283 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7284 }
7285 // else, nothing to do, just continue
7286 }
7287 }
7288
7289 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7290 // This is a chunk of garbage. It is not in any free list.
7291 // Add it to a free list or let it possibly be coalesced into
7292 // a larger chunk.
7293 HeapWord* const addr = (HeapWord*) fc;
7294 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7295
7296 // Verify that the bit map has no bits marked between
7297 // addr and purported end of just dead object.
7298 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7299 do_post_free_or_garbage_chunk(fc, size);
7300
7301 assert(_limit >= addr + size,
7302 "A freshly garbage chunk can't possibly straddle over _limit");
7303 if (inFreeRange()) lookahead_and_flush(fc, size);
7304 return size;
7305 }
7306
7307 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7308 HeapWord* addr = (HeapWord*) fc;
7309 // The sweeper has just found a live object. Return any accumulated
7310 // left hand chunk to the free lists.
7311 if (inFreeRange()) {
7312 assert(freeFinger() < addr, "freeFinger points too high");
7313 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7314 }
7315
7316 // This object is live: we'd normally expect this to be
7317 // an oop, and like to assert the following:
7318 // assert(oopDesc::is_oop(oop(addr)), "live block should be an oop");
7319 // However, as we commented above, this may be an object whose
7320 // header hasn't yet been initialized.
7321 size_t size;
7322 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7323 if (_bitMap->isMarked(addr + 1)) {
7324 // Determine the size from the bit map, rather than trying to
7325 // compute it from the object header.
7326 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7327 size = pointer_delta(nextOneAddr + 1, addr);
7328 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7329 "alignment problem");
7330
7331 #ifdef ASSERT
7332 if (oop(addr)->klass_or_null_acquire() != NULL) {
7333 // Ignore mark word because we are running concurrent with mutators
7334 assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7335 assert(size ==
7336 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7337 "P-mark and computed size do not agree");
7338 }
7339 #endif
7340
7341 } else {
7342 // This should be an initialized object that's alive.
7343 assert(oop(addr)->klass_or_null_acquire() != NULL,
7344 "Should be an initialized object");
7345 // Ignore mark word because we are running concurrent with mutators
7346 assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7347 // Verify that the bit map has no bits marked between
7348 // addr and purported end of this block.
7349 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7350 assert(size >= 3, "Necessary for Printezis marks to work");
7351 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7352 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7353 }
7354 return size;
7355 }
7356
7357 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7358 size_t chunkSize) {
7359 // do_post_free_or_garbage_chunk() should only be called in the case
7360 // of the adaptive free list allocator.
7361 const bool fcInFreeLists = fc->is_free();
7362 assert((HeapWord*)fc <= _limit, "sweep invariant");
7363 if (CMSTestInFreeList && fcInFreeLists) {
7364 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7365 }
7366
7367 log_develop_trace(gc, sweep)(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7368
7369 HeapWord* const fc_addr = (HeapWord*) fc;
7370
7371 bool coalesce = false;
7372 const size_t left = pointer_delta(fc_addr, freeFinger());
7373 const size_t right = chunkSize;
7374 switch (FLSCoalescePolicy) {
7375 // numeric value forms a coalition aggressiveness metric
7376 case 0: { // never coalesce
7377 coalesce = false;
7378 break;
7379 }
7380 case 1: { // coalesce if left & right chunks on overpopulated lists
7381 coalesce = _sp->coalOverPopulated(left) &&
7382 _sp->coalOverPopulated(right);
7383 break;
7384 }
7385 case 2: { // coalesce if left chunk on overpopulated list (default)
7386 coalesce = _sp->coalOverPopulated(left);
7387 break;
7388 }
7389 case 3: { // coalesce if left OR right chunk on overpopulated list
7390 coalesce = _sp->coalOverPopulated(left) ||
7391 _sp->coalOverPopulated(right);
7392 break;
7393 }
7394 case 4: { // always coalesce
7395 coalesce = true;
7396 break;
7397 }
7398 default:
7399 ShouldNotReachHere();
7400 }
7401
7402 // Should the current free range be coalesced?
7403 // If the chunk is in a free range and either we decided to coalesce above
7404 // or the chunk is near the large block at the end of the heap
7405 // (isNearLargestChunk() returns true), then coalesce this chunk.
7406 const bool doCoalesce = inFreeRange()
7407 && (coalesce || _g->isNearLargestChunk(fc_addr));
7408 if (doCoalesce) {
7409 // Coalesce the current free range on the left with the new
7410 // chunk on the right. If either is on a free list,
7411 // it must be removed from the list and stashed in the closure.
7412 if (freeRangeInFreeLists()) {
7413 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7414 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7415 "Size of free range is inconsistent with chunk size.");
7416 if (CMSTestInFreeList) {
7417 assert(_sp->verify_chunk_in_free_list(ffc),
7418 "Chunk is not in free lists");
7419 }
7420 _sp->coalDeath(ffc->size());
7421 _sp->removeFreeChunkFromFreeLists(ffc);
7422 set_freeRangeInFreeLists(false);
7423 }
7424 if (fcInFreeLists) {
7425 _sp->coalDeath(chunkSize);
7426 assert(fc->size() == chunkSize,
7427 "The chunk has the wrong size or is not in the free lists");
7428 _sp->removeFreeChunkFromFreeLists(fc);
7429 }
7430 set_lastFreeRangeCoalesced(true);
7431 print_free_block_coalesced(fc);
7432 } else { // not in a free range and/or should not coalesce
7433 // Return the current free range and start a new one.
7434 if (inFreeRange()) {
7435 // In a free range but cannot coalesce with the right hand chunk.
7436 // Put the current free range into the free lists.
7437 flush_cur_free_chunk(freeFinger(),
7438 pointer_delta(fc_addr, freeFinger()));
7439 }
7440 // Set up for new free range. Pass along whether the right hand
7441 // chunk is in the free lists.
7442 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7443 }
7444 }
7445
7446 // Lookahead flush:
7447 // If we are tracking a free range, and this is the last chunk that
7448 // we'll look at because its end crosses past _limit, we'll preemptively
7449 // flush it along with any free range we may be holding on to. Note that
7450 // this can be the case only for an already free or freshly garbage
7451 // chunk. If this block is an object, it can never straddle
7452 // over _limit. The "straddling" occurs when _limit is set at
7453 // the previous end of the space when this cycle started, and
7454 // a subsequent heap expansion caused the previously co-terminal
7455 // free block to be coalesced with the newly expanded portion,
7456 // thus rendering _limit a non-block-boundary making it dangerous
7457 // for the sweeper to step over and examine.
7458 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7459 assert(inFreeRange(), "Should only be called if currently in a free range.");
7460 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7461 assert(_sp->used_region().contains(eob - 1),
7462 "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7463 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7464 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7465 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7466 if (eob >= _limit) {
7467 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7468 log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7469 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7470 "[" PTR_FORMAT "," PTR_FORMAT ")",
7471 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7472 // Return the storage we are tracking back into the free lists.
7473 log_develop_trace(gc, sweep)("Flushing ... ");
7474 assert(freeFinger() < eob, "Error");
7475 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7476 }
7477 }
7478
7479 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7480 assert(inFreeRange(), "Should only be called if currently in a free range.");
7481 assert(size > 0,
7482 "A zero sized chunk cannot be added to the free lists.");
7483 if (!freeRangeInFreeLists()) {
7484 if (CMSTestInFreeList) {
7485 FreeChunk* fc = (FreeChunk*) chunk;
7486 fc->set_size(size);
7487 assert(!_sp->verify_chunk_in_free_list(fc),
7488 "chunk should not be in free lists yet");
7489 }
7490 log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size);
7491 // A new free range is going to be starting. The current
7492 // free range has not been added to the free lists yet or
7493 // was removed so add it back.
7494 // If the current free range was coalesced, then the death
7495 // of the free range was recorded. Record a birth now.
7496 if (lastFreeRangeCoalesced()) {
7497 _sp->coalBirth(size);
7498 }
7499 _sp->addChunkAndRepairOffsetTable(chunk, size,
7500 lastFreeRangeCoalesced());
7501 } else {
7502 log_develop_trace(gc, sweep)("Already in free list: nothing to flush");
7503 }
7504 set_inFreeRange(false);
7505 set_freeRangeInFreeLists(false);
7506 }
7507
7508 // We take a break if we've been at this for a while,
7509 // so as to avoid monopolizing the locks involved.
7510 void SweepClosure::do_yield_work(HeapWord* addr) {
7511 // Return current free chunk being used for coalescing (if any)
7512 // to the appropriate freelist. After yielding, the next
7513 // free block encountered will start a coalescing range of
7514 // free blocks. If the next free block is adjacent to the
7515 // chunk just flushed, they will need to wait for the next
7516 // sweep to be coalesced.
7517 if (inFreeRange()) {
7518 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7519 }
7520
7521 // First give up the locks, then yield, then re-lock.
7522 // We should probably use a constructor/destructor idiom to
7523 // do this unlock/lock or modify the MutexUnlocker class to
7524 // serve our purpose. XXX
7525 assert_lock_strong(_bitMap->lock());
7526 assert_lock_strong(_freelistLock);
7527 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7528 "CMS thread should hold CMS token");
7529 _bitMap->lock()->unlock();
7530 _freelistLock->unlock();
7531 ConcurrentMarkSweepThread::desynchronize(true);
7532 _collector->stopTimer();
7533 _collector->incrementYields();
7534
7535 // See the comment in coordinator_yield()
7536 for (unsigned i = 0; i < CMSYieldSleepCount &&
7537 ConcurrentMarkSweepThread::should_yield() &&
7538 !CMSCollector::foregroundGCIsActive(); ++i) {
7539 os::sleep(Thread::current(), 1, false);
7540 }
7541
7542 ConcurrentMarkSweepThread::synchronize(true);
7543 _freelistLock->lock();
7544 _bitMap->lock()->lock_without_safepoint_check();
7545 _collector->startTimer();
7546 }
7547
7548 #ifndef PRODUCT
7549 // This is actually very useful in a product build if it can
7550 // be called from the debugger. Compile it into the product
7551 // as needed.
7552 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7553 return debug_cms_space->verify_chunk_in_free_list(fc);
7554 }
7555 #endif
7556
7557 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7558 log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7559 p2i(fc), fc->size());
7560 }
7561
7562 // CMSIsAliveClosure
7563 bool CMSIsAliveClosure::do_object_b(oop obj) {
7564 HeapWord* addr = (HeapWord*)obj;
7565 return addr != NULL &&
7566 (!_span.contains(addr) || _bit_map->isMarked(addr));
7567 }
7568
7569 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7570 MemRegion span,
7571 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7572 bool cpc):
7573 _collector(collector),
7574 _span(span),
7575 _mark_stack(mark_stack),
7576 _bit_map(bit_map),
7577 _concurrent_precleaning(cpc) {
7578 assert(!_span.is_empty(), "Empty span could spell trouble");
7579 }
7580
7581
7582 // CMSKeepAliveClosure: the serial version
7583 void CMSKeepAliveClosure::do_oop(oop obj) {
7584 HeapWord* addr = (HeapWord*)obj;
7585 if (_span.contains(addr) &&
7586 !_bit_map->isMarked(addr)) {
7587 _bit_map->mark(addr);
7588 bool simulate_overflow = false;
7589 NOT_PRODUCT(
7590 if (CMSMarkStackOverflowALot &&
7591 _collector->simulate_overflow()) {
7592 // simulate a stack overflow
7593 simulate_overflow = true;
7594 }
7595 )
7596 if (simulate_overflow || !_mark_stack->push(obj)) {
7597 if (_concurrent_precleaning) {
7598 // We dirty the overflown object and let the remark
7599 // phase deal with it.
7600 assert(_collector->overflow_list_is_empty(), "Error");
7601 // In the case of object arrays, we need to dirty all of
7602 // the cards that the object spans. No locking or atomics
7603 // are needed since no one else can be mutating the mod union
7604 // table.
7605 if (obj->is_objArray()) {
7606 size_t sz = obj->size();
7607 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
7608 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7609 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7610 _collector->_modUnionTable.mark_range(redirty_range);
7611 } else {
7612 _collector->_modUnionTable.mark(addr);
7613 }
7614 _collector->_ser_kac_preclean_ovflw++;
7615 } else {
7616 _collector->push_on_overflow_list(obj);
7617 _collector->_ser_kac_ovflw++;
7618 }
7619 }
7620 }
7621 }
7622
7623 // CMSParKeepAliveClosure: a parallel version of the above.
7624 // The work queues are private to each closure (thread),
7625 // but (may be) available for stealing by other threads.
7626 void CMSParKeepAliveClosure::do_oop(oop obj) {
7627 HeapWord* addr = (HeapWord*)obj;
7628 if (_span.contains(addr) &&
7629 !_bit_map->isMarked(addr)) {
7630 // In general, during recursive tracing, several threads
7631 // may be concurrently getting here; the first one to
7632 // "tag" it, claims it.
7633 if (_bit_map->par_mark(addr)) {
7634 bool res = _work_queue->push(obj);
7635 assert(res, "Low water mark should be much less than capacity");
7636 // Do a recursive trim in the hope that this will keep
7637 // stack usage lower, but leave some oops for potential stealers
7638 trim_queue(_low_water_mark);
7639 } // Else, another thread got there first
7640 }
7641 }
7642
7643 void CMSParKeepAliveClosure::trim_queue(uint max) {
7644 while (_work_queue->size() > max) {
7645 oop new_oop;
7646 if (_work_queue->pop_local(new_oop)) {
7647 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
7648 assert(_bit_map->isMarked((HeapWord*)new_oop),
7649 "no white objects on this stack!");
7650 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7651 // iterate over the oops in this oop, marking and pushing
7652 // the ones in CMS heap (i.e. in _span).
7653 new_oop->oop_iterate(&_mark_and_push);
7654 }
7655 }
7656 }
7657
7658 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7659 CMSCollector* collector,
7660 MemRegion span, CMSBitMap* bit_map,
7661 OopTaskQueue* work_queue):
7662 _collector(collector),
7663 _span(span),
7664 _work_queue(work_queue),
7665 _bit_map(bit_map) { }
7666
7667 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7668 HeapWord* addr = (HeapWord*)obj;
7669 if (_span.contains(addr) &&
7670 !_bit_map->isMarked(addr)) {
7671 if (_bit_map->par_mark(addr)) {
7672 bool simulate_overflow = false;
7673 NOT_PRODUCT(
7674 if (CMSMarkStackOverflowALot &&
7675 _collector->par_simulate_overflow()) {
7676 // simulate a stack overflow
7677 simulate_overflow = true;
7678 }
7679 )
7680 if (simulate_overflow || !_work_queue->push(obj)) {
7681 _collector->par_push_on_overflow_list(obj);
7682 _collector->_par_kac_ovflw++;
7683 }
7684 } // Else another thread got there already
7685 }
7686 }
7687
7688 //////////////////////////////////////////////////////////////////
7689 // CMSExpansionCause /////////////////////////////
7690 //////////////////////////////////////////////////////////////////
7691 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7692 switch (cause) {
7693 case _no_expansion:
7694 return "No expansion";
7695 case _satisfy_free_ratio:
7696 return "Free ratio";
7697 case _satisfy_promotion:
7698 return "Satisfy promotion";
7699 case _satisfy_allocation:
7700 return "allocation";
7701 case _allocate_par_lab:
7702 return "Par LAB";
7703 case _allocate_par_spooling_space:
7704 return "Par Spooling Space";
7705 case _adaptive_size_policy:
7706 return "Ergonomics";
7707 default:
7708 return "unknown";
7709 }
7710 }
7711
7712 void CMSDrainMarkingStackClosure::do_void() {
7713 // the max number to take from overflow list at a time
7714 const size_t num = _mark_stack->capacity()/4;
7715 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7716 "Overflow list should be NULL during concurrent phases");
7717 while (!_mark_stack->isEmpty() ||
7718 // if stack is empty, check the overflow list
7719 _collector->take_from_overflow_list(num, _mark_stack)) {
7720 oop obj = _mark_stack->pop();
7721 HeapWord* addr = (HeapWord*)obj;
7722 assert(_span.contains(addr), "Should be within span");
7723 assert(_bit_map->isMarked(addr), "Should be marked");
7724 assert(oopDesc::is_oop(obj), "Should be an oop");
7725 obj->oop_iterate(_keep_alive);
7726 }
7727 }
7728
7729 void CMSParDrainMarkingStackClosure::do_void() {
7730 // drain queue
7731 trim_queue(0);
7732 }
7733
7734 // Trim our work_queue so its length is below max at return
7735 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7736 while (_work_queue->size() > max) {
7737 oop new_oop;
7738 if (_work_queue->pop_local(new_oop)) {
7739 assert(oopDesc::is_oop(new_oop), "Expected an oop");
7740 assert(_bit_map->isMarked((HeapWord*)new_oop),
7741 "no white objects on this stack!");
7742 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7743 // iterate over the oops in this oop, marking and pushing
7744 // the ones in CMS heap (i.e. in _span).
7745 new_oop->oop_iterate(&_mark_and_push);
7746 }
7747 }
7748 }
7749
7750 ////////////////////////////////////////////////////////////////////
7751 // Support for Marking Stack Overflow list handling and related code
7752 ////////////////////////////////////////////////////////////////////
7753 // Much of the following code is similar in shape and spirit to the
7754 // code used in ParNewGC. We should try and share that code
7755 // as much as possible in the future.
7756
7757 #ifndef PRODUCT
7758 // Debugging support for CMSStackOverflowALot
7759
7760 // It's OK to call this multi-threaded; the worst thing
7761 // that can happen is that we'll get a bunch of closely
7762 // spaced simulated overflows, but that's OK, in fact
7763 // probably good as it would exercise the overflow code
7764 // under contention.
7765 bool CMSCollector::simulate_overflow() {
7766 if (_overflow_counter-- <= 0) { // just being defensive
7767 _overflow_counter = CMSMarkStackOverflowInterval;
7768 return true;
7769 } else {
7770 return false;
7771 }
7772 }
7773
7774 bool CMSCollector::par_simulate_overflow() {
7775 return simulate_overflow();
7776 }
7777 #endif
7778
7779 // Single-threaded
7780 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7781 assert(stack->isEmpty(), "Expected precondition");
7782 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7783 size_t i = num;
7784 oop cur = _overflow_list;
7785 const markOop proto = markOopDesc::prototype();
7786 NOT_PRODUCT(ssize_t n = 0;)
7787 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7788 next = oop(cur->mark_raw());
7789 cur->set_mark_raw(proto); // until proven otherwise
7790 assert(oopDesc::is_oop(cur), "Should be an oop");
7791 bool res = stack->push(cur);
7792 assert(res, "Bit off more than can chew?");
7793 NOT_PRODUCT(n++;)
7794 }
7795 _overflow_list = cur;
7796 #ifndef PRODUCT
7797 assert(_num_par_pushes >= n, "Too many pops?");
7798 _num_par_pushes -=n;
7799 #endif
7800 return !stack->isEmpty();
7801 }
7802
7803 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
7804 // (MT-safe) Get a prefix of at most "num" from the list.
7805 // The overflow list is chained through the mark word of
7806 // each object in the list. We fetch the entire list,
7807 // break off a prefix of the right size and return the
7808 // remainder. If other threads try to take objects from
7809 // the overflow list at that time, they will wait for
7810 // some time to see if data becomes available. If (and
7811 // only if) another thread places one or more object(s)
7812 // on the global list before we have returned the suffix
7813 // to the global list, we will walk down our local list
7814 // to find its end and append the global list to
7815 // our suffix before returning it. This suffix walk can
7816 // prove to be expensive (quadratic in the amount of traffic)
7817 // when there are many objects in the overflow list and
7818 // there is much producer-consumer contention on the list.
7819 // *NOTE*: The overflow list manipulation code here and
7820 // in ParNewGeneration:: are very similar in shape,
7821 // except that in the ParNew case we use the old (from/eden)
7822 // copy of the object to thread the list via its klass word.
7823 // Because of the common code, if you make any changes in
7824 // the code below, please check the ParNew version to see if
7825 // similar changes might be needed.
7826 // CR 6797058 has been filed to consolidate the common code.
7827 bool CMSCollector::par_take_from_overflow_list(size_t num,
7828 OopTaskQueue* work_q,
7829 int no_of_gc_threads) {
7830 assert(work_q->size() == 0, "First empty local work queue");
7831 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7832 if (_overflow_list == NULL) {
7833 return false;
7834 }
7835 // Grab the entire list; we'll put back a suffix
7836 oop prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7837 Thread* tid = Thread::current();
7838 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7839 // set to ParallelGCThreads.
7840 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7841 size_t sleep_time_millis = MAX2((size_t)1, num/100);
7842 // If the list is busy, we spin for a short while,
7843 // sleeping between attempts to get the list.
7844 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7845 os::sleep(tid, sleep_time_millis, false);
7846 if (_overflow_list == NULL) {
7847 // Nothing left to take
7848 return false;
7849 } else if (_overflow_list != BUSY) {
7850 // Try and grab the prefix
7851 prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7852 }
7853 }
7854 // If the list was found to be empty, or we spun long
7855 // enough, we give up and return empty-handed. If we leave
7856 // the list in the BUSY state below, it must be the case that
7857 // some other thread holds the overflow list and will set it
7858 // to a non-BUSY state in the future.
7859 if (prefix == NULL || prefix == BUSY) {
7860 // Nothing to take or waited long enough
7861 if (prefix == NULL) {
7862 // Write back the NULL in case we overwrote it with BUSY above
7863 // and it is still the same value.
7864 Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7865 }
7866 return false;
7867 }
7868 assert(prefix != NULL && prefix != BUSY, "Error");
7869 size_t i = num;
7870 oop cur = prefix;
7871 // Walk down the first "num" objects, unless we reach the end.
7872 for (; i > 1 && cur->mark_raw() != NULL; cur = oop(cur->mark_raw()), i--);
7873 if (cur->mark_raw() == NULL) {
7874 // We have "num" or fewer elements in the list, so there
7875 // is nothing to return to the global list.
7876 // Write back the NULL in lieu of the BUSY we wrote
7877 // above, if it is still the same value.
7878 if (_overflow_list == BUSY) {
7879 Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7880 }
7881 } else {
7882 // Chop off the suffix and return it to the global list.
7883 assert(cur->mark_raw() != BUSY, "Error");
7884 oop suffix_head = cur->mark_raw(); // suffix will be put back on global list
7885 cur->set_mark_raw(NULL); // break off suffix
7886 // It's possible that the list is still in the empty(busy) state
7887 // we left it in a short while ago; in that case we may be
7888 // able to place back the suffix without incurring the cost
7889 // of a walk down the list.
7890 oop observed_overflow_list = _overflow_list;
7891 oop cur_overflow_list = observed_overflow_list;
7892 bool attached = false;
7893 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7894 observed_overflow_list =
7895 Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7896 if (cur_overflow_list == observed_overflow_list) {
7897 attached = true;
7898 break;
7899 } else cur_overflow_list = observed_overflow_list;
7900 }
7901 if (!attached) {
7902 // Too bad, someone else sneaked in (at least) an element; we'll need
7903 // to do a splice. Find tail of suffix so we can prepend suffix to global
7904 // list.
7905 for (cur = suffix_head; cur->mark_raw() != NULL; cur = (oop)(cur->mark_raw()));
7906 oop suffix_tail = cur;
7907 assert(suffix_tail != NULL && suffix_tail->mark_raw() == NULL,
7908 "Tautology");
7909 observed_overflow_list = _overflow_list;
7910 do {
7911 cur_overflow_list = observed_overflow_list;
7912 if (cur_overflow_list != BUSY) {
7913 // Do the splice ...
7914 suffix_tail->set_mark_raw(markOop(cur_overflow_list));
7915 } else { // cur_overflow_list == BUSY
7916 suffix_tail->set_mark_raw(NULL);
7917 }
7918 // ... and try to place spliced list back on overflow_list ...
7919 observed_overflow_list =
7920 Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7921 } while (cur_overflow_list != observed_overflow_list);
7922 // ... until we have succeeded in doing so.
7923 }
7924 }
7925
7926 // Push the prefix elements on work_q
7927 assert(prefix != NULL, "control point invariant");
7928 const markOop proto = markOopDesc::prototype();
7929 oop next;
7930 NOT_PRODUCT(ssize_t n = 0;)
7931 for (cur = prefix; cur != NULL; cur = next) {
7932 next = oop(cur->mark_raw());
7933 cur->set_mark_raw(proto); // until proven otherwise
7934 assert(oopDesc::is_oop(cur), "Should be an oop");
7935 bool res = work_q->push(cur);
7936 assert(res, "Bit off more than we can chew?");
7937 NOT_PRODUCT(n++;)
7938 }
7939 #ifndef PRODUCT
7940 assert(_num_par_pushes >= n, "Too many pops?");
7941 Atomic::sub(n, &_num_par_pushes);
7942 #endif
7943 return true;
7944 }
7945
7946 // Single-threaded
7947 void CMSCollector::push_on_overflow_list(oop p) {
7948 NOT_PRODUCT(_num_par_pushes++;)
7949 assert(oopDesc::is_oop(p), "Not an oop");
7950 preserve_mark_if_necessary(p);
7951 p->set_mark_raw((markOop)_overflow_list);
7952 _overflow_list = p;
7953 }
7954
7955 // Multi-threaded; use CAS to prepend to overflow list
7956 void CMSCollector::par_push_on_overflow_list(oop p) {
7957 NOT_PRODUCT(Atomic::inc(&_num_par_pushes);)
7958 assert(oopDesc::is_oop(p), "Not an oop");
7959 par_preserve_mark_if_necessary(p);
7960 oop observed_overflow_list = _overflow_list;
7961 oop cur_overflow_list;
7962 do {
7963 cur_overflow_list = observed_overflow_list;
7964 if (cur_overflow_list != BUSY) {
7965 p->set_mark_raw(markOop(cur_overflow_list));
7966 } else {
7967 p->set_mark_raw(NULL);
7968 }
7969 observed_overflow_list =
7970 Atomic::cmpxchg((oopDesc*)p, &_overflow_list, (oopDesc*)cur_overflow_list);
7971 } while (cur_overflow_list != observed_overflow_list);
7972 }
7973 #undef BUSY
7974
7975 // Single threaded
7976 // General Note on GrowableArray: pushes may silently fail
7977 // because we are (temporarily) out of C-heap for expanding
7978 // the stack. The problem is quite ubiquitous and affects
7979 // a lot of code in the JVM. The prudent thing for GrowableArray
7980 // to do (for now) is to exit with an error. However, that may
7981 // be too draconian in some cases because the caller may be
7982 // able to recover without much harm. For such cases, we
7983 // should probably introduce a "soft_push" method which returns
7984 // an indication of success or failure with the assumption that
7985 // the caller may be able to recover from a failure; code in
7986 // the VM can then be changed, incrementally, to deal with such
7987 // failures where possible, thus, incrementally hardening the VM
7988 // in such low resource situations.
7989 void CMSCollector::preserve_mark_work(oop p, markOop m) {
7990 _preserved_oop_stack.push(p);
7991 _preserved_mark_stack.push(m);
7992 assert(m == p->mark_raw(), "Mark word changed");
7993 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
7994 "bijection");
7995 }
7996
7997 // Single threaded
7998 void CMSCollector::preserve_mark_if_necessary(oop p) {
7999 markOop m = p->mark_raw();
8000 if (m->must_be_preserved(p)) {
8001 preserve_mark_work(p, m);
8002 }
8003 }
8004
8005 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8006 markOop m = p->mark_raw();
8007 if (m->must_be_preserved(p)) {
8008 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8009 // Even though we read the mark word without holding
8010 // the lock, we are assured that it will not change
8011 // because we "own" this oop, so no other thread can
8012 // be trying to push it on the overflow list; see
8013 // the assertion in preserve_mark_work() that checks
8014 // that m == p->mark_raw().
8015 preserve_mark_work(p, m);
8016 }
8017 }
8018
8019 // We should be able to do this multi-threaded,
8020 // a chunk of stack being a task (this is
8021 // correct because each oop only ever appears
8022 // once in the overflow list. However, it's
8023 // not very easy to completely overlap this with
8024 // other operations, so will generally not be done
8025 // until all work's been completed. Because we
8026 // expect the preserved oop stack (set) to be small,
8027 // it's probably fine to do this single-threaded.
8028 // We can explore cleverer concurrent/overlapped/parallel
8029 // processing of preserved marks if we feel the
8030 // need for this in the future. Stack overflow should
8031 // be so rare in practice and, when it happens, its
8032 // effect on performance so great that this will
8033 // likely just be in the noise anyway.
8034 void CMSCollector::restore_preserved_marks_if_any() {
8035 assert(SafepointSynchronize::is_at_safepoint(),
8036 "world should be stopped");
8037 assert(Thread::current()->is_ConcurrentGC_thread() ||
8038 Thread::current()->is_VM_thread(),
8039 "should be single-threaded");
8040 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8041 "bijection");
8042
8043 while (!_preserved_oop_stack.is_empty()) {
8044 oop p = _preserved_oop_stack.pop();
8045 assert(oopDesc::is_oop(p), "Should be an oop");
8046 assert(_span.contains(p), "oop should be in _span");
8047 assert(p->mark_raw() == markOopDesc::prototype(),
8048 "Set when taken from overflow list");
8049 markOop m = _preserved_mark_stack.pop();
8050 p->set_mark_raw(m);
8051 }
8052 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8053 "stacks were cleared above");
8054 }
8055
8056 #ifndef PRODUCT
8057 bool CMSCollector::no_preserved_marks() const {
8058 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8059 }
8060 #endif
8061
8062 // Transfer some number of overflown objects to usual marking
8063 // stack. Return true if some objects were transferred.
8064 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8065 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8066 (size_t)ParGCDesiredObjsFromOverflowList);
8067
8068 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8069 assert(_collector->overflow_list_is_empty() || res,
8070 "If list is not empty, we should have taken something");
8071 assert(!res || !_mark_stack->isEmpty(),
8072 "If we took something, it should now be on our stack");
8073 return res;
8074 }
8075
8076 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8077 size_t res = _sp->block_size_no_stall(addr, _collector);
8078 if (_sp->block_is_obj(addr)) {
8079 if (_live_bit_map->isMarked(addr)) {
8080 // It can't have been dead in a previous cycle
8081 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8082 } else {
8083 _dead_bit_map->mark(addr); // mark the dead object
8084 }
8085 }
8086 // Could be 0, if the block size could not be computed without stalling.
8087 return res;
8088 }
8089
8090 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8091 GCMemoryManager* manager = CMSHeap::heap()->old_manager();
8092 switch (phase) {
8093 case CMSCollector::InitialMarking:
8094 initialize(manager /* GC manager */ ,
8095 cause /* cause of the GC */,
8096 true /* allMemoryPoolsAffected */,
8097 true /* recordGCBeginTime */,
8098 true /* recordPreGCUsage */,
8099 false /* recordPeakUsage */,
8100 false /* recordPostGCusage */,
8101 true /* recordAccumulatedGCTime */,
8102 false /* recordGCEndTime */,
8103 false /* countCollection */ );
8104 break;
8105
8106 case CMSCollector::FinalMarking:
8107 initialize(manager /* GC manager */ ,
8108 cause /* cause of the GC */,
8109 true /* allMemoryPoolsAffected */,
8110 false /* recordGCBeginTime */,
8111 false /* recordPreGCUsage */,
8112 false /* recordPeakUsage */,
8113 false /* recordPostGCusage */,
8114 true /* recordAccumulatedGCTime */,
8115 false /* recordGCEndTime */,
8116 false /* countCollection */ );
8117 break;
8118
8119 case CMSCollector::Sweeping:
8120 initialize(manager /* GC manager */ ,
8121 cause /* cause of the GC */,
8122 true /* allMemoryPoolsAffected */,
8123 false /* recordGCBeginTime */,
8124 false /* recordPreGCUsage */,
8125 true /* recordPeakUsage */,
8126 true /* recordPostGCusage */,
8127 false /* recordAccumulatedGCTime */,
8128 true /* recordGCEndTime */,
8129 true /* countCollection */ );
8130 break;
8131
8132 default:
8133 ShouldNotReachHere();
8134 }
8135 }