1 /*
2 * Copyright (c) 2001, 2018, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/symbolTable.hpp"
29 #include "classfile/systemDictionary.hpp"
30 #include "code/codeCache.hpp"
31 #include "gc/cms/cmsCollectorPolicy.hpp"
32 #include "gc/cms/cmsGCStats.hpp"
33 #include "gc/cms/cmsHeap.hpp"
34 #include "gc/cms/cmsOopClosures.inline.hpp"
35 #include "gc/cms/compactibleFreeListSpace.hpp"
36 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
37 #include "gc/cms/concurrentMarkSweepThread.hpp"
38 #include "gc/cms/parNewGeneration.hpp"
39 #include "gc/cms/vmCMSOperations.hpp"
40 #include "gc/serial/genMarkSweep.hpp"
41 #include "gc/serial/tenuredGeneration.hpp"
42 #include "gc/shared/adaptiveSizePolicy.hpp"
43 #include "gc/shared/cardGeneration.inline.hpp"
44 #include "gc/shared/cardTableRS.hpp"
45 #include "gc/shared/collectedHeap.inline.hpp"
46 #include "gc/shared/collectorCounters.hpp"
47 #include "gc/shared/collectorPolicy.hpp"
48 #include "gc/shared/gcLocker.hpp"
49 #include "gc/shared/gcPolicyCounters.hpp"
50 #include "gc/shared/gcTimer.hpp"
51 #include "gc/shared/gcTrace.hpp"
52 #include "gc/shared/gcTraceTime.inline.hpp"
53 #include "gc/shared/genCollectedHeap.hpp"
54 #include "gc/shared/genOopClosures.inline.hpp"
55 #include "gc/shared/isGCActiveMark.hpp"
56 #include "gc/shared/referencePolicy.hpp"
57 #include "gc/shared/strongRootsScope.hpp"
58 #include "gc/shared/taskqueue.inline.hpp"
59 #include "gc/shared/weakProcessor.hpp"
60 #include "logging/log.hpp"
61 #include "logging/logStream.hpp"
62 #include "memory/allocation.hpp"
63 #include "memory/binaryTreeDictionary.inline.hpp"
64 #include "memory/iterator.inline.hpp"
65 #include "memory/padded.hpp"
66 #include "memory/resourceArea.hpp"
67 #include "oops/access.inline.hpp"
68 #include "oops/oop.inline.hpp"
69 #include "prims/jvmtiExport.hpp"
70 #include "runtime/atomic.hpp"
71 #include "runtime/flags/flagSetting.hpp"
72 #include "runtime/globals_extension.hpp"
73 #include "runtime/handles.inline.hpp"
74 #include "runtime/java.hpp"
75 #include "runtime/orderAccess.inline.hpp"
76 #include "runtime/timer.hpp"
77 #include "runtime/vmThread.hpp"
78 #include "services/memoryService.hpp"
79 #include "services/runtimeService.hpp"
80 #include "utilities/align.hpp"
81 #include "utilities/stack.inline.hpp"
82
83 // statics
84 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
85 bool CMSCollector::_full_gc_requested = false;
86 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
87
88 //////////////////////////////////////////////////////////////////
89 // In support of CMS/VM thread synchronization
90 //////////////////////////////////////////////////////////////////
91 // We split use of the CGC_lock into 2 "levels".
92 // The low-level locking is of the usual CGC_lock monitor. We introduce
93 // a higher level "token" (hereafter "CMS token") built on top of the
94 // low level monitor (hereafter "CGC lock").
95 // The token-passing protocol gives priority to the VM thread. The
96 // CMS-lock doesn't provide any fairness guarantees, but clients
97 // should ensure that it is only held for very short, bounded
98 // durations.
99 //
100 // When either of the CMS thread or the VM thread is involved in
101 // collection operations during which it does not want the other
102 // thread to interfere, it obtains the CMS token.
103 //
104 // If either thread tries to get the token while the other has
105 // it, that thread waits. However, if the VM thread and CMS thread
106 // both want the token, then the VM thread gets priority while the
107 // CMS thread waits. This ensures, for instance, that the "concurrent"
108 // phases of the CMS thread's work do not block out the VM thread
109 // for long periods of time as the CMS thread continues to hog
110 // the token. (See bug 4616232).
111 //
112 // The baton-passing functions are, however, controlled by the
113 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
114 // and here the low-level CMS lock, not the high level token,
115 // ensures mutual exclusion.
116 //
117 // Two important conditions that we have to satisfy:
118 // 1. if a thread does a low-level wait on the CMS lock, then it
119 // relinquishes the CMS token if it were holding that token
120 // when it acquired the low-level CMS lock.
121 // 2. any low-level notifications on the low-level lock
122 // should only be sent when a thread has relinquished the token.
123 //
124 // In the absence of either property, we'd have potential deadlock.
125 //
126 // We protect each of the CMS (concurrent and sequential) phases
127 // with the CMS _token_, not the CMS _lock_.
128 //
129 // The only code protected by CMS lock is the token acquisition code
130 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
131 // baton-passing code.
132 //
133 // Unfortunately, i couldn't come up with a good abstraction to factor and
134 // hide the naked CGC_lock manipulation in the baton-passing code
135 // further below. That's something we should try to do. Also, the proof
136 // of correctness of this 2-level locking scheme is far from obvious,
137 // and potentially quite slippery. We have an uneasy suspicion, for instance,
138 // that there may be a theoretical possibility of delay/starvation in the
139 // low-level lock/wait/notify scheme used for the baton-passing because of
140 // potential interference with the priority scheme embodied in the
141 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
142 // invocation further below and marked with "XXX 20011219YSR".
143 // Indeed, as we note elsewhere, this may become yet more slippery
144 // in the presence of multiple CMS and/or multiple VM threads. XXX
145
146 class CMSTokenSync: public StackObj {
147 private:
148 bool _is_cms_thread;
149 public:
150 CMSTokenSync(bool is_cms_thread):
151 _is_cms_thread(is_cms_thread) {
152 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
153 "Incorrect argument to constructor");
154 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
155 }
156
157 ~CMSTokenSync() {
158 assert(_is_cms_thread ?
159 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
160 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
161 "Incorrect state");
162 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
163 }
164 };
165
166 // Convenience class that does a CMSTokenSync, and then acquires
167 // upto three locks.
168 class CMSTokenSyncWithLocks: public CMSTokenSync {
169 private:
170 // Note: locks are acquired in textual declaration order
171 // and released in the opposite order
172 MutexLockerEx _locker1, _locker2, _locker3;
173 public:
174 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
175 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
176 CMSTokenSync(is_cms_thread),
177 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
178 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
179 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
180 { }
181 };
182
183
184 //////////////////////////////////////////////////////////////////
185 // Concurrent Mark-Sweep Generation /////////////////////////////
186 //////////////////////////////////////////////////////////////////
187
188 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
189
190 // This struct contains per-thread things necessary to support parallel
191 // young-gen collection.
192 class CMSParGCThreadState: public CHeapObj<mtGC> {
193 public:
194 CompactibleFreeListSpaceLAB lab;
195 PromotionInfo promo;
196
197 // Constructor.
198 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
199 promo.setSpace(cfls);
200 }
201 };
202
203 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
204 ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct) :
205 CardGeneration(rs, initial_byte_size, ct),
206 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
207 _did_compact(false)
208 {
209 HeapWord* bottom = (HeapWord*) _virtual_space.low();
210 HeapWord* end = (HeapWord*) _virtual_space.high();
211
212 _direct_allocated_words = 0;
213 NOT_PRODUCT(
214 _numObjectsPromoted = 0;
215 _numWordsPromoted = 0;
216 _numObjectsAllocated = 0;
217 _numWordsAllocated = 0;
218 )
219
220 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end));
221 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
222 _cmsSpace->_old_gen = this;
223
224 _gc_stats = new CMSGCStats();
225
226 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
227 // offsets match. The ability to tell free chunks from objects
228 // depends on this property.
229 debug_only(
230 FreeChunk* junk = NULL;
231 assert(UseCompressedClassPointers ||
232 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
233 "Offset of FreeChunk::_prev within FreeChunk must match"
234 " that of OopDesc::_klass within OopDesc");
235 )
236
237 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
238 for (uint i = 0; i < ParallelGCThreads; i++) {
239 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
240 }
241
242 _incremental_collection_failed = false;
243 // The "dilatation_factor" is the expansion that can occur on
244 // account of the fact that the minimum object size in the CMS
245 // generation may be larger than that in, say, a contiguous young
246 // generation.
247 // Ideally, in the calculation below, we'd compute the dilatation
248 // factor as: MinChunkSize/(promoting_gen's min object size)
249 // Since we do not have such a general query interface for the
250 // promoting generation, we'll instead just use the minimum
251 // object size (which today is a header's worth of space);
252 // note that all arithmetic is in units of HeapWords.
253 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
254 assert(_dilatation_factor >= 1.0, "from previous assert");
255 }
256
257
258 // The field "_initiating_occupancy" represents the occupancy percentage
259 // at which we trigger a new collection cycle. Unless explicitly specified
260 // via CMSInitiatingOccupancyFraction (argument "io" below), it
261 // is calculated by:
262 //
263 // Let "f" be MinHeapFreeRatio in
264 //
265 // _initiating_occupancy = 100-f +
266 // f * (CMSTriggerRatio/100)
267 // where CMSTriggerRatio is the argument "tr" below.
268 //
269 // That is, if we assume the heap is at its desired maximum occupancy at the
270 // end of a collection, we let CMSTriggerRatio of the (purported) free
271 // space be allocated before initiating a new collection cycle.
272 //
273 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
274 assert(io <= 100 && tr <= 100, "Check the arguments");
275 if (io >= 0) {
276 _initiating_occupancy = (double)io / 100.0;
277 } else {
278 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
279 (double)(tr * MinHeapFreeRatio) / 100.0)
280 / 100.0;
281 }
282 }
283
284 void ConcurrentMarkSweepGeneration::ref_processor_init() {
285 assert(collector() != NULL, "no collector");
286 collector()->ref_processor_init();
287 }
288
289 void CMSCollector::ref_processor_init() {
290 if (_ref_processor == NULL) {
291 // Allocate and initialize a reference processor
292 _ref_processor =
293 new ReferenceProcessor(_span, // span
294 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
295 ParallelGCThreads, // mt processing degree
296 _cmsGen->refs_discovery_is_mt(), // mt discovery
297 MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
298 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
299 &_is_alive_closure); // closure for liveness info
300 // Initialize the _ref_processor field of CMSGen
301 _cmsGen->set_ref_processor(_ref_processor);
302
303 }
304 }
305
306 AdaptiveSizePolicy* CMSCollector::size_policy() {
307 return CMSHeap::heap()->size_policy();
308 }
309
310 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
311
312 const char* gen_name = "old";
313 GenCollectorPolicy* gcp = CMSHeap::heap()->gen_policy();
314 // Generation Counters - generation 1, 1 subspace
315 _gen_counters = new GenerationCounters(gen_name, 1, 1,
316 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
317
318 _space_counters = new GSpaceCounters(gen_name, 0,
319 _virtual_space.reserved_size(),
320 this, _gen_counters);
321 }
322
323 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
324 _cms_gen(cms_gen)
325 {
326 assert(alpha <= 100, "bad value");
327 _saved_alpha = alpha;
328
329 // Initialize the alphas to the bootstrap value of 100.
330 _gc0_alpha = _cms_alpha = 100;
331
332 _cms_begin_time.update();
333 _cms_end_time.update();
334
335 _gc0_duration = 0.0;
336 _gc0_period = 0.0;
337 _gc0_promoted = 0;
338
339 _cms_duration = 0.0;
340 _cms_period = 0.0;
341 _cms_allocated = 0;
342
343 _cms_used_at_gc0_begin = 0;
344 _cms_used_at_gc0_end = 0;
345 _allow_duty_cycle_reduction = false;
346 _valid_bits = 0;
347 }
348
349 double CMSStats::cms_free_adjustment_factor(size_t free) const {
350 // TBD: CR 6909490
351 return 1.0;
352 }
353
354 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
355 }
356
357 // If promotion failure handling is on use
358 // the padded average size of the promotion for each
359 // young generation collection.
360 double CMSStats::time_until_cms_gen_full() const {
361 size_t cms_free = _cms_gen->cmsSpace()->free();
362 CMSHeap* heap = CMSHeap::heap();
363 size_t expected_promotion = MIN2(heap->young_gen()->capacity(),
364 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
365 if (cms_free > expected_promotion) {
366 // Start a cms collection if there isn't enough space to promote
367 // for the next young collection. Use the padded average as
368 // a safety factor.
369 cms_free -= expected_promotion;
370
371 // Adjust by the safety factor.
372 double cms_free_dbl = (double)cms_free;
373 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
374 // Apply a further correction factor which tries to adjust
375 // for recent occurance of concurrent mode failures.
376 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
377 cms_free_dbl = cms_free_dbl * cms_adjustment;
378
379 log_trace(gc)("CMSStats::time_until_cms_gen_full: cms_free " SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
380 cms_free, expected_promotion);
381 log_trace(gc)(" cms_free_dbl %f cms_consumption_rate %f", cms_free_dbl, cms_consumption_rate() + 1.0);
382 // Add 1 in case the consumption rate goes to zero.
383 return cms_free_dbl / (cms_consumption_rate() + 1.0);
384 }
385 return 0.0;
386 }
387
388 // Compare the duration of the cms collection to the
389 // time remaining before the cms generation is empty.
390 // Note that the time from the start of the cms collection
391 // to the start of the cms sweep (less than the total
392 // duration of the cms collection) can be used. This
393 // has been tried and some applications experienced
394 // promotion failures early in execution. This was
395 // possibly because the averages were not accurate
396 // enough at the beginning.
397 double CMSStats::time_until_cms_start() const {
398 // We add "gc0_period" to the "work" calculation
399 // below because this query is done (mostly) at the
400 // end of a scavenge, so we need to conservatively
401 // account for that much possible delay
402 // in the query so as to avoid concurrent mode failures
403 // due to starting the collection just a wee bit too
404 // late.
405 double work = cms_duration() + gc0_period();
406 double deadline = time_until_cms_gen_full();
407 // If a concurrent mode failure occurred recently, we want to be
408 // more conservative and halve our expected time_until_cms_gen_full()
409 if (work > deadline) {
410 log_develop_trace(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ",
411 cms_duration(), gc0_period(), time_until_cms_gen_full());
412 return 0.0;
413 }
414 return work - deadline;
415 }
416
417 #ifndef PRODUCT
418 void CMSStats::print_on(outputStream *st) const {
419 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
420 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
421 gc0_duration(), gc0_period(), gc0_promoted());
422 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
423 cms_duration(), cms_period(), cms_allocated());
424 st->print(",cms_since_beg=%g,cms_since_end=%g",
425 cms_time_since_begin(), cms_time_since_end());
426 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
427 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
428
429 if (valid()) {
430 st->print(",promo_rate=%g,cms_alloc_rate=%g",
431 promotion_rate(), cms_allocation_rate());
432 st->print(",cms_consumption_rate=%g,time_until_full=%g",
433 cms_consumption_rate(), time_until_cms_gen_full());
434 }
435 st->cr();
436 }
437 #endif // #ifndef PRODUCT
438
439 CMSCollector::CollectorState CMSCollector::_collectorState =
440 CMSCollector::Idling;
441 bool CMSCollector::_foregroundGCIsActive = false;
442 bool CMSCollector::_foregroundGCShouldWait = false;
443
444 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
445 CardTableRS* ct,
446 ConcurrentMarkSweepPolicy* cp):
447 _cmsGen(cmsGen),
448 _ct(ct),
449 _ref_processor(NULL), // will be set later
450 _conc_workers(NULL), // may be set later
451 _abort_preclean(false),
452 _start_sampling(false),
453 _between_prologue_and_epilogue(false),
454 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
455 _modUnionTable((CardTable::card_shift - LogHeapWordSize),
456 -1 /* lock-free */, "No_lock" /* dummy */),
457 _modUnionClosurePar(&_modUnionTable),
458 // Adjust my span to cover old (cms) gen
459 _span(cmsGen->reserved()),
460 // Construct the is_alive_closure with _span & markBitMap
461 _is_alive_closure(_span, &_markBitMap),
462 _restart_addr(NULL),
463 _overflow_list(NULL),
464 _stats(cmsGen),
465 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
466 //verify that this lock should be acquired with safepoint check.
467 Monitor::_safepoint_check_sometimes)),
468 _eden_chunk_array(NULL), // may be set in ctor body
469 _eden_chunk_capacity(0), // -- ditto --
470 _eden_chunk_index(0), // -- ditto --
471 _survivor_plab_array(NULL), // -- ditto --
472 _survivor_chunk_array(NULL), // -- ditto --
473 _survivor_chunk_capacity(0), // -- ditto --
474 _survivor_chunk_index(0), // -- ditto --
475 _ser_pmc_preclean_ovflw(0),
476 _ser_kac_preclean_ovflw(0),
477 _ser_pmc_remark_ovflw(0),
478 _par_pmc_remark_ovflw(0),
479 _ser_kac_ovflw(0),
480 _par_kac_ovflw(0),
481 #ifndef PRODUCT
482 _num_par_pushes(0),
483 #endif
484 _collection_count_start(0),
485 _verifying(false),
486 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
487 _completed_initialization(false),
488 _collector_policy(cp),
489 _should_unload_classes(CMSClassUnloadingEnabled),
490 _concurrent_cycles_since_last_unload(0),
491 _roots_scanning_options(GenCollectedHeap::SO_None),
492 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
493 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
494 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
495 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
496 _cms_start_registered(false)
497 {
498 // Now expand the span and allocate the collection support structures
499 // (MUT, marking bit map etc.) to cover both generations subject to
500 // collection.
501
502 // For use by dirty card to oop closures.
503 _cmsGen->cmsSpace()->set_collector(this);
504
505 // Allocate MUT and marking bit map
506 {
507 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
508 if (!_markBitMap.allocate(_span)) {
509 log_warning(gc)("Failed to allocate CMS Bit Map");
510 return;
511 }
512 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
513 }
514 {
515 _modUnionTable.allocate(_span);
516 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
517 }
518
519 if (!_markStack.allocate(MarkStackSize)) {
520 log_warning(gc)("Failed to allocate CMS Marking Stack");
521 return;
522 }
523
524 // Support for multi-threaded concurrent phases
525 if (CMSConcurrentMTEnabled) {
526 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
527 // just for now
528 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
529 }
530 if (ConcGCThreads > 1) {
531 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
532 ConcGCThreads, true);
533 if (_conc_workers == NULL) {
534 log_warning(gc)("GC/CMS: _conc_workers allocation failure: forcing -CMSConcurrentMTEnabled");
535 CMSConcurrentMTEnabled = false;
536 } else {
537 _conc_workers->initialize_workers();
538 }
539 } else {
540 CMSConcurrentMTEnabled = false;
541 }
542 }
543 if (!CMSConcurrentMTEnabled) {
544 ConcGCThreads = 0;
545 } else {
546 // Turn off CMSCleanOnEnter optimization temporarily for
547 // the MT case where it's not fixed yet; see 6178663.
548 CMSCleanOnEnter = false;
549 }
550 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
551 "Inconsistency");
552 log_debug(gc)("ConcGCThreads: %u", ConcGCThreads);
553 log_debug(gc)("ParallelGCThreads: %u", ParallelGCThreads);
554
555 // Parallel task queues; these are shared for the
556 // concurrent and stop-world phases of CMS, but
557 // are not shared with parallel scavenge (ParNew).
558 {
559 uint i;
560 uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
561
562 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
563 || ParallelRefProcEnabled)
564 && num_queues > 0) {
565 _task_queues = new OopTaskQueueSet(num_queues);
566 if (_task_queues == NULL) {
567 log_warning(gc)("task_queues allocation failure.");
568 return;
569 }
570 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
571 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
572 for (i = 0; i < num_queues; i++) {
573 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
574 if (q == NULL) {
575 log_warning(gc)("work_queue allocation failure.");
576 return;
577 }
578 _task_queues->register_queue(i, q);
579 }
580 for (i = 0; i < num_queues; i++) {
581 _task_queues->queue(i)->initialize();
582 _hash_seed[i] = 17; // copied from ParNew
583 }
584 }
585 }
586
587 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
588
589 // Clip CMSBootstrapOccupancy between 0 and 100.
590 _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
591
592 // Now tell CMS generations the identity of their collector
593 ConcurrentMarkSweepGeneration::set_collector(this);
594
595 // Create & start a CMS thread for this CMS collector
596 _cmsThread = ConcurrentMarkSweepThread::start(this);
597 assert(cmsThread() != NULL, "CMS Thread should have been created");
598 assert(cmsThread()->collector() == this,
599 "CMS Thread should refer to this gen");
600 assert(CGC_lock != NULL, "Where's the CGC_lock?");
601
602 // Support for parallelizing young gen rescan
603 CMSHeap* heap = CMSHeap::heap();
604 assert(heap->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
605 _young_gen = (ParNewGeneration*)heap->young_gen();
606 if (heap->supports_inline_contig_alloc()) {
607 _top_addr = heap->top_addr();
608 _end_addr = heap->end_addr();
609 assert(_young_gen != NULL, "no _young_gen");
610 _eden_chunk_index = 0;
611 _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
612 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
613 }
614
615 // Support for parallelizing survivor space rescan
616 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
617 const size_t max_plab_samples =
618 _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
619
620 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
621 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
622 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
623 _survivor_chunk_capacity = max_plab_samples;
624 for (uint i = 0; i < ParallelGCThreads; i++) {
625 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
626 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
627 assert(cur->end() == 0, "Should be 0");
628 assert(cur->array() == vec, "Should be vec");
629 assert(cur->capacity() == max_plab_samples, "Error");
630 }
631 }
632
633 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
634 _gc_counters = new CollectorCounters("CMS", 1);
635 _cgc_counters = new CollectorCounters("CMS stop-the-world phases", 2);
636 _completed_initialization = true;
637 _inter_sweep_timer.start(); // start of time
638 }
639
640 const char* ConcurrentMarkSweepGeneration::name() const {
641 return "concurrent mark-sweep generation";
642 }
643 void ConcurrentMarkSweepGeneration::update_counters() {
644 if (UsePerfData) {
645 _space_counters->update_all();
646 _gen_counters->update_all();
647 }
648 }
649
650 // this is an optimized version of update_counters(). it takes the
651 // used value as a parameter rather than computing it.
652 //
653 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
654 if (UsePerfData) {
655 _space_counters->update_used(used);
656 _space_counters->update_capacity();
657 _gen_counters->update_all();
658 }
659 }
660
661 void ConcurrentMarkSweepGeneration::print() const {
662 Generation::print();
663 cmsSpace()->print();
664 }
665
666 #ifndef PRODUCT
667 void ConcurrentMarkSweepGeneration::print_statistics() {
668 cmsSpace()->printFLCensus(0);
669 }
670 #endif
671
672 size_t
673 ConcurrentMarkSweepGeneration::contiguous_available() const {
674 // dld proposes an improvement in precision here. If the committed
675 // part of the space ends in a free block we should add that to
676 // uncommitted size in the calculation below. Will make this
677 // change later, staying with the approximation below for the
678 // time being. -- ysr.
679 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
680 }
681
682 size_t
683 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
684 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
685 }
686
687 size_t ConcurrentMarkSweepGeneration::max_available() const {
688 return free() + _virtual_space.uncommitted_size();
689 }
690
691 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
692 size_t available = max_available();
693 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
694 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
695 log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")",
696 res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes);
697 return res;
698 }
699
700 // At a promotion failure dump information on block layout in heap
701 // (cms old generation).
702 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
703 Log(gc, promotion) log;
704 if (log.is_trace()) {
705 LogStream ls(log.trace());
706 cmsSpace()->dump_at_safepoint_with_locks(collector(), &ls);
707 }
708 }
709
710 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
711 // Clear the promotion information. These pointers can be adjusted
712 // along with all the other pointers into the heap but
713 // compaction is expected to be a rare event with
714 // a heap using cms so don't do it without seeing the need.
715 for (uint i = 0; i < ParallelGCThreads; i++) {
716 _par_gc_thread_states[i]->promo.reset();
717 }
718 }
719
720 void ConcurrentMarkSweepGeneration::compute_new_size() {
721 assert_locked_or_safepoint(Heap_lock);
722
723 // If incremental collection failed, we just want to expand
724 // to the limit.
725 if (incremental_collection_failed()) {
726 clear_incremental_collection_failed();
727 grow_to_reserved();
728 return;
729 }
730
731 // The heap has been compacted but not reset yet.
732 // Any metric such as free() or used() will be incorrect.
733
734 CardGeneration::compute_new_size();
735
736 // Reset again after a possible resizing
737 if (did_compact()) {
738 cmsSpace()->reset_after_compaction();
739 }
740 }
741
742 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
743 assert_locked_or_safepoint(Heap_lock);
744
745 // If incremental collection failed, we just want to expand
746 // to the limit.
747 if (incremental_collection_failed()) {
748 clear_incremental_collection_failed();
749 grow_to_reserved();
750 return;
751 }
752
753 double free_percentage = ((double) free()) / capacity();
754 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
755 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
756
757 // compute expansion delta needed for reaching desired free percentage
758 if (free_percentage < desired_free_percentage) {
759 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
760 assert(desired_capacity >= capacity(), "invalid expansion size");
761 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
762 Log(gc) log;
763 if (log.is_trace()) {
764 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
765 log.trace("From compute_new_size: ");
766 log.trace(" Free fraction %f", free_percentage);
767 log.trace(" Desired free fraction %f", desired_free_percentage);
768 log.trace(" Maximum free fraction %f", maximum_free_percentage);
769 log.trace(" Capacity " SIZE_FORMAT, capacity() / 1000);
770 log.trace(" Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
771 CMSHeap* heap = CMSHeap::heap();
772 assert(heap->is_old_gen(this), "The CMS generation should always be the old generation");
773 size_t young_size = heap->young_gen()->capacity();
774 log.trace(" Young gen size " SIZE_FORMAT, young_size / 1000);
775 log.trace(" unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
776 log.trace(" contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
777 log.trace(" Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
778 }
779 // safe if expansion fails
780 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
781 log.trace(" Expanded free fraction %f", ((double) free()) / capacity());
782 } else {
783 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
784 assert(desired_capacity <= capacity(), "invalid expansion size");
785 size_t shrink_bytes = capacity() - desired_capacity;
786 // Don't shrink unless the delta is greater than the minimum shrink we want
787 if (shrink_bytes >= MinHeapDeltaBytes) {
788 shrink_free_list_by(shrink_bytes);
789 }
790 }
791 }
792
793 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
794 return cmsSpace()->freelistLock();
795 }
796
797 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
798 CMSSynchronousYieldRequest yr;
799 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
800 return have_lock_and_allocate(size, tlab);
801 }
802
803 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
804 bool tlab /* ignored */) {
805 assert_lock_strong(freelistLock());
806 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
807 HeapWord* res = cmsSpace()->allocate(adjustedSize);
808 // Allocate the object live (grey) if the background collector has
809 // started marking. This is necessary because the marker may
810 // have passed this address and consequently this object will
811 // not otherwise be greyed and would be incorrectly swept up.
812 // Note that if this object contains references, the writing
813 // of those references will dirty the card containing this object
814 // allowing the object to be blackened (and its references scanned)
815 // either during a preclean phase or at the final checkpoint.
816 if (res != NULL) {
817 // We may block here with an uninitialized object with
818 // its mark-bit or P-bits not yet set. Such objects need
819 // to be safely navigable by block_start().
820 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
821 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
822 collector()->direct_allocated(res, adjustedSize);
823 _direct_allocated_words += adjustedSize;
824 // allocation counters
825 NOT_PRODUCT(
826 _numObjectsAllocated++;
827 _numWordsAllocated += (int)adjustedSize;
828 )
829 }
830 return res;
831 }
832
833 // In the case of direct allocation by mutators in a generation that
834 // is being concurrently collected, the object must be allocated
835 // live (grey) if the background collector has started marking.
836 // This is necessary because the marker may
837 // have passed this address and consequently this object will
838 // not otherwise be greyed and would be incorrectly swept up.
839 // Note that if this object contains references, the writing
840 // of those references will dirty the card containing this object
841 // allowing the object to be blackened (and its references scanned)
842 // either during a preclean phase or at the final checkpoint.
843 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
844 assert(_markBitMap.covers(start, size), "Out of bounds");
845 if (_collectorState >= Marking) {
846 MutexLockerEx y(_markBitMap.lock(),
847 Mutex::_no_safepoint_check_flag);
848 // [see comments preceding SweepClosure::do_blk() below for details]
849 //
850 // Can the P-bits be deleted now? JJJ
851 //
852 // 1. need to mark the object as live so it isn't collected
853 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
854 // 3. need to mark the end of the object so marking, precleaning or sweeping
855 // can skip over uninitialized or unparsable objects. An allocated
856 // object is considered uninitialized for our purposes as long as
857 // its klass word is NULL. All old gen objects are parsable
858 // as soon as they are initialized.)
859 _markBitMap.mark(start); // object is live
860 _markBitMap.mark(start + 1); // object is potentially uninitialized?
861 _markBitMap.mark(start + size - 1);
862 // mark end of object
863 }
864 // check that oop looks uninitialized
865 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
866 }
867
868 void CMSCollector::promoted(bool par, HeapWord* start,
869 bool is_obj_array, size_t obj_size) {
870 assert(_markBitMap.covers(start), "Out of bounds");
871 // See comment in direct_allocated() about when objects should
872 // be allocated live.
873 if (_collectorState >= Marking) {
874 // we already hold the marking bit map lock, taken in
875 // the prologue
876 if (par) {
877 _markBitMap.par_mark(start);
878 } else {
879 _markBitMap.mark(start);
880 }
881 // We don't need to mark the object as uninitialized (as
882 // in direct_allocated above) because this is being done with the
883 // world stopped and the object will be initialized by the
884 // time the marking, precleaning or sweeping get to look at it.
885 // But see the code for copying objects into the CMS generation,
886 // where we need to ensure that concurrent readers of the
887 // block offset table are able to safely navigate a block that
888 // is in flux from being free to being allocated (and in
889 // transition while being copied into) and subsequently
890 // becoming a bona-fide object when the copy/promotion is complete.
891 assert(SafepointSynchronize::is_at_safepoint(),
892 "expect promotion only at safepoints");
893
894 if (_collectorState < Sweeping) {
895 // Mark the appropriate cards in the modUnionTable, so that
896 // this object gets scanned before the sweep. If this is
897 // not done, CMS generation references in the object might
898 // not get marked.
899 // For the case of arrays, which are otherwise precisely
900 // marked, we need to dirty the entire array, not just its head.
901 if (is_obj_array) {
902 // The [par_]mark_range() method expects mr.end() below to
903 // be aligned to the granularity of a bit's representation
904 // in the heap. In the case of the MUT below, that's a
905 // card size.
906 MemRegion mr(start,
907 align_up(start + obj_size,
908 CardTable::card_size /* bytes */));
909 if (par) {
910 _modUnionTable.par_mark_range(mr);
911 } else {
912 _modUnionTable.mark_range(mr);
913 }
914 } else { // not an obj array; we can just mark the head
915 if (par) {
916 _modUnionTable.par_mark(start);
917 } else {
918 _modUnionTable.mark(start);
919 }
920 }
921 }
922 }
923 }
924
925 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
926 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
927 // allocate, copy and if necessary update promoinfo --
928 // delegate to underlying space.
929 assert_lock_strong(freelistLock());
930
931 #ifndef PRODUCT
932 if (CMSHeap::heap()->promotion_should_fail()) {
933 return NULL;
934 }
935 #endif // #ifndef PRODUCT
936
937 oop res = _cmsSpace->promote(obj, obj_size);
938 if (res == NULL) {
939 // expand and retry
940 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
941 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
942 // Since this is the old generation, we don't try to promote
943 // into a more senior generation.
944 res = _cmsSpace->promote(obj, obj_size);
945 }
946 if (res != NULL) {
947 // See comment in allocate() about when objects should
948 // be allocated live.
949 assert(oopDesc::is_oop(obj), "Will dereference klass pointer below");
950 collector()->promoted(false, // Not parallel
951 (HeapWord*)res, obj->is_objArray(), obj_size);
952 // promotion counters
953 NOT_PRODUCT(
954 _numObjectsPromoted++;
955 _numWordsPromoted +=
956 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
957 )
958 }
959 return res;
960 }
961
962
963 // IMPORTANT: Notes on object size recognition in CMS.
964 // ---------------------------------------------------
965 // A block of storage in the CMS generation is always in
966 // one of three states. A free block (FREE), an allocated
967 // object (OBJECT) whose size() method reports the correct size,
968 // and an intermediate state (TRANSIENT) in which its size cannot
969 // be accurately determined.
970 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
971 // -----------------------------------------------------
972 // FREE: klass_word & 1 == 1; mark_word holds block size
973 //
974 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
975 // obj->size() computes correct size
976 //
977 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
978 //
979 // STATE IDENTIFICATION: (64 bit+COOPS)
980 // ------------------------------------
981 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
982 //
983 // OBJECT: klass_word installed; klass_word != 0;
984 // obj->size() computes correct size
985 //
986 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
987 //
988 //
989 // STATE TRANSITION DIAGRAM
990 //
991 // mut / parnew mut / parnew
992 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
993 // ^ |
994 // |------------------------ DEAD <------------------------------------|
995 // sweep mut
996 //
997 // While a block is in TRANSIENT state its size cannot be determined
998 // so readers will either need to come back later or stall until
999 // the size can be determined. Note that for the case of direct
1000 // allocation, P-bits, when available, may be used to determine the
1001 // size of an object that may not yet have been initialized.
1002
1003 // Things to support parallel young-gen collection.
1004 oop
1005 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1006 oop old, markOop m,
1007 size_t word_sz) {
1008 #ifndef PRODUCT
1009 if (CMSHeap::heap()->promotion_should_fail()) {
1010 return NULL;
1011 }
1012 #endif // #ifndef PRODUCT
1013
1014 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1015 PromotionInfo* promoInfo = &ps->promo;
1016 // if we are tracking promotions, then first ensure space for
1017 // promotion (including spooling space for saving header if necessary).
1018 // then allocate and copy, then track promoted info if needed.
1019 // When tracking (see PromotionInfo::track()), the mark word may
1020 // be displaced and in this case restoration of the mark word
1021 // occurs in the (oop_since_save_marks_)iterate phase.
1022 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1023 // Out of space for allocating spooling buffers;
1024 // try expanding and allocating spooling buffers.
1025 if (!expand_and_ensure_spooling_space(promoInfo)) {
1026 return NULL;
1027 }
1028 }
1029 assert(!promoInfo->tracking() || promoInfo->has_spooling_space(), "Control point invariant");
1030 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1031 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1032 if (obj_ptr == NULL) {
1033 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1034 if (obj_ptr == NULL) {
1035 return NULL;
1036 }
1037 }
1038 oop obj = oop(obj_ptr);
1039 OrderAccess::storestore();
1040 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1041 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1042 // IMPORTANT: See note on object initialization for CMS above.
1043 // Otherwise, copy the object. Here we must be careful to insert the
1044 // klass pointer last, since this marks the block as an allocated object.
1045 // Except with compressed oops it's the mark word.
1046 HeapWord* old_ptr = (HeapWord*)old;
1047 // Restore the mark word copied above.
1048 obj->set_mark_raw(m);
1049 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1050 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1051 OrderAccess::storestore();
1052
1053 if (UseCompressedClassPointers) {
1054 // Copy gap missed by (aligned) header size calculation below
1055 obj->set_klass_gap(old->klass_gap());
1056 }
1057 if (word_sz > (size_t)oopDesc::header_size()) {
1058 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1059 obj_ptr + oopDesc::header_size(),
1060 word_sz - oopDesc::header_size());
1061 }
1062
1063 // Now we can track the promoted object, if necessary. We take care
1064 // to delay the transition from uninitialized to full object
1065 // (i.e., insertion of klass pointer) until after, so that it
1066 // atomically becomes a promoted object.
1067 if (promoInfo->tracking()) {
1068 promoInfo->track((PromotedObject*)obj, old->klass());
1069 }
1070 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1071 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1072 assert(oopDesc::is_oop(old), "Will use and dereference old klass ptr below");
1073
1074 // Finally, install the klass pointer (this should be volatile).
1075 OrderAccess::storestore();
1076 obj->set_klass(old->klass());
1077 // We should now be able to calculate the right size for this object
1078 assert(oopDesc::is_oop(obj) && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1079
1080 collector()->promoted(true, // parallel
1081 obj_ptr, old->is_objArray(), word_sz);
1082
1083 NOT_PRODUCT(
1084 Atomic::inc(&_numObjectsPromoted);
1085 Atomic::add(alloc_sz, &_numWordsPromoted);
1086 )
1087
1088 return obj;
1089 }
1090
1091 void
1092 ConcurrentMarkSweepGeneration::
1093 par_promote_alloc_done(int thread_num) {
1094 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1095 ps->lab.retire(thread_num);
1096 }
1097
1098 void
1099 ConcurrentMarkSweepGeneration::
1100 par_oop_since_save_marks_iterate_done(int thread_num) {
1101 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1102 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1103 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1104
1105 // Because card-scanning has been completed, subsequent phases
1106 // (e.g., reference processing) will not need to recognize which
1107 // objects have been promoted during this GC. So, we can now disable
1108 // promotion tracking.
1109 ps->promo.stopTrackingPromotions();
1110 }
1111
1112 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1113 size_t size,
1114 bool tlab)
1115 {
1116 // We allow a STW collection only if a full
1117 // collection was requested.
1118 return full || should_allocate(size, tlab); // FIX ME !!!
1119 // This and promotion failure handling are connected at the
1120 // hip and should be fixed by untying them.
1121 }
1122
1123 bool CMSCollector::shouldConcurrentCollect() {
1124 LogTarget(Trace, gc) log;
1125
1126 if (_full_gc_requested) {
1127 log.print("CMSCollector: collect because of explicit gc request (or GCLocker)");
1128 return true;
1129 }
1130
1131 FreelistLocker x(this);
1132 // ------------------------------------------------------------------
1133 // Print out lots of information which affects the initiation of
1134 // a collection.
1135 if (log.is_enabled() && stats().valid()) {
1136 log.print("CMSCollector shouldConcurrentCollect: ");
1137
1138 LogStream out(log);
1139 stats().print_on(&out);
1140
1141 log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full());
1142 log.print("free=" SIZE_FORMAT, _cmsGen->free());
1143 log.print("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available());
1144 log.print("promotion_rate=%g", stats().promotion_rate());
1145 log.print("cms_allocation_rate=%g", stats().cms_allocation_rate());
1146 log.print("occupancy=%3.7f", _cmsGen->occupancy());
1147 log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1148 log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1149 log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1150 log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect());
1151 }
1152 // ------------------------------------------------------------------
1153
1154 // If the estimated time to complete a cms collection (cms_duration())
1155 // is less than the estimated time remaining until the cms generation
1156 // is full, start a collection.
1157 if (!UseCMSInitiatingOccupancyOnly) {
1158 if (stats().valid()) {
1159 if (stats().time_until_cms_start() == 0.0) {
1160 return true;
1161 }
1162 } else {
1163 // We want to conservatively collect somewhat early in order
1164 // to try and "bootstrap" our CMS/promotion statistics;
1165 // this branch will not fire after the first successful CMS
1166 // collection because the stats should then be valid.
1167 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1168 log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f",
1169 _cmsGen->occupancy(), _bootstrap_occupancy);
1170 return true;
1171 }
1172 }
1173 }
1174
1175 // Otherwise, we start a collection cycle if
1176 // old gen want a collection cycle started. Each may use
1177 // an appropriate criterion for making this decision.
1178 // XXX We need to make sure that the gen expansion
1179 // criterion dovetails well with this. XXX NEED TO FIX THIS
1180 if (_cmsGen->should_concurrent_collect()) {
1181 log.print("CMS old gen initiated");
1182 return true;
1183 }
1184
1185 // We start a collection if we believe an incremental collection may fail;
1186 // this is not likely to be productive in practice because it's probably too
1187 // late anyway.
1188 CMSHeap* heap = CMSHeap::heap();
1189 if (heap->incremental_collection_will_fail(true /* consult_young */)) {
1190 log.print("CMSCollector: collect because incremental collection will fail ");
1191 return true;
1192 }
1193
1194 if (MetaspaceGC::should_concurrent_collect()) {
1195 log.print("CMSCollector: collect for metadata allocation ");
1196 return true;
1197 }
1198
1199 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1200 if (CMSTriggerInterval >= 0) {
1201 if (CMSTriggerInterval == 0) {
1202 // Trigger always
1203 return true;
1204 }
1205
1206 // Check the CMS time since begin (we do not check the stats validity
1207 // as we want to be able to trigger the first CMS cycle as well)
1208 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1209 if (stats().valid()) {
1210 log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1211 stats().cms_time_since_begin());
1212 } else {
1213 log.print("CMSCollector: collect because of trigger interval (first collection)");
1214 }
1215 return true;
1216 }
1217 }
1218
1219 return false;
1220 }
1221
1222 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1223
1224 // Clear _expansion_cause fields of constituent generations
1225 void CMSCollector::clear_expansion_cause() {
1226 _cmsGen->clear_expansion_cause();
1227 }
1228
1229 // We should be conservative in starting a collection cycle. To
1230 // start too eagerly runs the risk of collecting too often in the
1231 // extreme. To collect too rarely falls back on full collections,
1232 // which works, even if not optimum in terms of concurrent work.
1233 // As a work around for too eagerly collecting, use the flag
1234 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1235 // giving the user an easily understandable way of controlling the
1236 // collections.
1237 // We want to start a new collection cycle if any of the following
1238 // conditions hold:
1239 // . our current occupancy exceeds the configured initiating occupancy
1240 // for this generation, or
1241 // . we recently needed to expand this space and have not, since that
1242 // expansion, done a collection of this generation, or
1243 // . the underlying space believes that it may be a good idea to initiate
1244 // a concurrent collection (this may be based on criteria such as the
1245 // following: the space uses linear allocation and linear allocation is
1246 // going to fail, or there is believed to be excessive fragmentation in
1247 // the generation, etc... or ...
1248 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1249 // the case of the old generation; see CR 6543076):
1250 // we may be approaching a point at which allocation requests may fail because
1251 // we will be out of sufficient free space given allocation rate estimates.]
1252 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1253
1254 assert_lock_strong(freelistLock());
1255 if (occupancy() > initiating_occupancy()) {
1256 log_trace(gc)(" %s: collect because of occupancy %f / %f ",
1257 short_name(), occupancy(), initiating_occupancy());
1258 return true;
1259 }
1260 if (UseCMSInitiatingOccupancyOnly) {
1261 return false;
1262 }
1263 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1264 log_trace(gc)(" %s: collect because expanded for allocation ", short_name());
1265 return true;
1266 }
1267 return false;
1268 }
1269
1270 void ConcurrentMarkSweepGeneration::collect(bool full,
1271 bool clear_all_soft_refs,
1272 size_t size,
1273 bool tlab)
1274 {
1275 collector()->collect(full, clear_all_soft_refs, size, tlab);
1276 }
1277
1278 void CMSCollector::collect(bool full,
1279 bool clear_all_soft_refs,
1280 size_t size,
1281 bool tlab)
1282 {
1283 // The following "if" branch is present for defensive reasons.
1284 // In the current uses of this interface, it can be replaced with:
1285 // assert(!GCLocker.is_active(), "Can't be called otherwise");
1286 // But I am not placing that assert here to allow future
1287 // generality in invoking this interface.
1288 if (GCLocker::is_active()) {
1289 // A consistency test for GCLocker
1290 assert(GCLocker::needs_gc(), "Should have been set already");
1291 // Skip this foreground collection, instead
1292 // expanding the heap if necessary.
1293 // Need the free list locks for the call to free() in compute_new_size()
1294 compute_new_size();
1295 return;
1296 }
1297 acquire_control_and_collect(full, clear_all_soft_refs);
1298 }
1299
1300 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1301 CMSHeap* heap = CMSHeap::heap();
1302 unsigned int gc_count = heap->total_full_collections();
1303 if (gc_count == full_gc_count) {
1304 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1305 _full_gc_requested = true;
1306 _full_gc_cause = cause;
1307 CGC_lock->notify(); // nudge CMS thread
1308 } else {
1309 assert(gc_count > full_gc_count, "Error: causal loop");
1310 }
1311 }
1312
1313 bool CMSCollector::is_external_interruption() {
1314 GCCause::Cause cause = CMSHeap::heap()->gc_cause();
1315 return GCCause::is_user_requested_gc(cause) ||
1316 GCCause::is_serviceability_requested_gc(cause);
1317 }
1318
1319 void CMSCollector::report_concurrent_mode_interruption() {
1320 if (is_external_interruption()) {
1321 log_debug(gc)("Concurrent mode interrupted");
1322 } else {
1323 log_debug(gc)("Concurrent mode failure");
1324 _gc_tracer_cm->report_concurrent_mode_failure();
1325 }
1326 }
1327
1328
1329 // The foreground and background collectors need to coordinate in order
1330 // to make sure that they do not mutually interfere with CMS collections.
1331 // When a background collection is active,
1332 // the foreground collector may need to take over (preempt) and
1333 // synchronously complete an ongoing collection. Depending on the
1334 // frequency of the background collections and the heap usage
1335 // of the application, this preemption can be seldom or frequent.
1336 // There are only certain
1337 // points in the background collection that the "collection-baton"
1338 // can be passed to the foreground collector.
1339 //
1340 // The foreground collector will wait for the baton before
1341 // starting any part of the collection. The foreground collector
1342 // will only wait at one location.
1343 //
1344 // The background collector will yield the baton before starting a new
1345 // phase of the collection (e.g., before initial marking, marking from roots,
1346 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1347 // of the loop which switches the phases. The background collector does some
1348 // of the phases (initial mark, final re-mark) with the world stopped.
1349 // Because of locking involved in stopping the world,
1350 // the foreground collector should not block waiting for the background
1351 // collector when it is doing a stop-the-world phase. The background
1352 // collector will yield the baton at an additional point just before
1353 // it enters a stop-the-world phase. Once the world is stopped, the
1354 // background collector checks the phase of the collection. If the
1355 // phase has not changed, it proceeds with the collection. If the
1356 // phase has changed, it skips that phase of the collection. See
1357 // the comments on the use of the Heap_lock in collect_in_background().
1358 //
1359 // Variable used in baton passing.
1360 // _foregroundGCIsActive - Set to true by the foreground collector when
1361 // it wants the baton. The foreground clears it when it has finished
1362 // the collection.
1363 // _foregroundGCShouldWait - Set to true by the background collector
1364 // when it is running. The foreground collector waits while
1365 // _foregroundGCShouldWait is true.
1366 // CGC_lock - monitor used to protect access to the above variables
1367 // and to notify the foreground and background collectors.
1368 // _collectorState - current state of the CMS collection.
1369 //
1370 // The foreground collector
1371 // acquires the CGC_lock
1372 // sets _foregroundGCIsActive
1373 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1374 // various locks acquired in preparation for the collection
1375 // are released so as not to block the background collector
1376 // that is in the midst of a collection
1377 // proceeds with the collection
1378 // clears _foregroundGCIsActive
1379 // returns
1380 //
1381 // The background collector in a loop iterating on the phases of the
1382 // collection
1383 // acquires the CGC_lock
1384 // sets _foregroundGCShouldWait
1385 // if _foregroundGCIsActive is set
1386 // clears _foregroundGCShouldWait, notifies _CGC_lock
1387 // waits on _CGC_lock for _foregroundGCIsActive to become false
1388 // and exits the loop.
1389 // otherwise
1390 // proceed with that phase of the collection
1391 // if the phase is a stop-the-world phase,
1392 // yield the baton once more just before enqueueing
1393 // the stop-world CMS operation (executed by the VM thread).
1394 // returns after all phases of the collection are done
1395 //
1396
1397 void CMSCollector::acquire_control_and_collect(bool full,
1398 bool clear_all_soft_refs) {
1399 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1400 assert(!Thread::current()->is_ConcurrentGC_thread(),
1401 "shouldn't try to acquire control from self!");
1402
1403 // Start the protocol for acquiring control of the
1404 // collection from the background collector (aka CMS thread).
1405 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1406 "VM thread should have CMS token");
1407 // Remember the possibly interrupted state of an ongoing
1408 // concurrent collection
1409 CollectorState first_state = _collectorState;
1410
1411 // Signal to a possibly ongoing concurrent collection that
1412 // we want to do a foreground collection.
1413 _foregroundGCIsActive = true;
1414
1415 // release locks and wait for a notify from the background collector
1416 // releasing the locks in only necessary for phases which
1417 // do yields to improve the granularity of the collection.
1418 assert_lock_strong(bitMapLock());
1419 // We need to lock the Free list lock for the space that we are
1420 // currently collecting.
1421 assert(haveFreelistLocks(), "Must be holding free list locks");
1422 bitMapLock()->unlock();
1423 releaseFreelistLocks();
1424 {
1425 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1426 if (_foregroundGCShouldWait) {
1427 // We are going to be waiting for action for the CMS thread;
1428 // it had better not be gone (for instance at shutdown)!
1429 assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(),
1430 "CMS thread must be running");
1431 // Wait here until the background collector gives us the go-ahead
1432 ConcurrentMarkSweepThread::clear_CMS_flag(
1433 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1434 // Get a possibly blocked CMS thread going:
1435 // Note that we set _foregroundGCIsActive true above,
1436 // without protection of the CGC_lock.
1437 CGC_lock->notify();
1438 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1439 "Possible deadlock");
1440 while (_foregroundGCShouldWait) {
1441 // wait for notification
1442 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1443 // Possibility of delay/starvation here, since CMS token does
1444 // not know to give priority to VM thread? Actually, i think
1445 // there wouldn't be any delay/starvation, but the proof of
1446 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1447 }
1448 ConcurrentMarkSweepThread::set_CMS_flag(
1449 ConcurrentMarkSweepThread::CMS_vm_has_token);
1450 }
1451 }
1452 // The CMS_token is already held. Get back the other locks.
1453 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1454 "VM thread should have CMS token");
1455 getFreelistLocks();
1456 bitMapLock()->lock_without_safepoint_check();
1457 log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d",
1458 p2i(Thread::current()), first_state);
1459 log_debug(gc, state)(" gets control with state %d", _collectorState);
1460
1461 // Inform cms gen if this was due to partial collection failing.
1462 // The CMS gen may use this fact to determine its expansion policy.
1463 CMSHeap* heap = CMSHeap::heap();
1464 if (heap->incremental_collection_will_fail(false /* don't consult_young */)) {
1465 assert(!_cmsGen->incremental_collection_failed(),
1466 "Should have been noticed, reacted to and cleared");
1467 _cmsGen->set_incremental_collection_failed();
1468 }
1469
1470 if (first_state > Idling) {
1471 report_concurrent_mode_interruption();
1472 }
1473
1474 set_did_compact(true);
1475
1476 // If the collection is being acquired from the background
1477 // collector, there may be references on the discovered
1478 // references lists. Abandon those references, since some
1479 // of them may have become unreachable after concurrent
1480 // discovery; the STW compacting collector will redo discovery
1481 // more precisely, without being subject to floating garbage.
1482 // Leaving otherwise unreachable references in the discovered
1483 // lists would require special handling.
1484 ref_processor()->disable_discovery();
1485 ref_processor()->abandon_partial_discovery();
1486 ref_processor()->verify_no_references_recorded();
1487
1488 if (first_state > Idling) {
1489 save_heap_summary();
1490 }
1491
1492 do_compaction_work(clear_all_soft_refs);
1493
1494 // Has the GC time limit been exceeded?
1495 size_t max_eden_size = _young_gen->max_eden_size();
1496 GCCause::Cause gc_cause = heap->gc_cause();
1497 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1498 _young_gen->eden()->used(),
1499 _cmsGen->max_capacity(),
1500 max_eden_size,
1501 full,
1502 gc_cause,
1503 heap->soft_ref_policy());
1504
1505 // Reset the expansion cause, now that we just completed
1506 // a collection cycle.
1507 clear_expansion_cause();
1508 _foregroundGCIsActive = false;
1509 return;
1510 }
1511
1512 // Resize the tenured generation
1513 // after obtaining the free list locks for the
1514 // two generations.
1515 void CMSCollector::compute_new_size() {
1516 assert_locked_or_safepoint(Heap_lock);
1517 FreelistLocker z(this);
1518 MetaspaceGC::compute_new_size();
1519 _cmsGen->compute_new_size_free_list();
1520 }
1521
1522 // A work method used by the foreground collector to do
1523 // a mark-sweep-compact.
1524 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1525 CMSHeap* heap = CMSHeap::heap();
1526
1527 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1528 gc_timer->register_gc_start();
1529
1530 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1531 gc_tracer->report_gc_start(heap->gc_cause(), gc_timer->gc_start());
1532
1533 heap->pre_full_gc_dump(gc_timer);
1534
1535 GCTraceTime(Trace, gc, phases) t("CMS:MSC");
1536
1537 // Temporarily widen the span of the weak reference processing to
1538 // the entire heap.
1539 MemRegion new_span(CMSHeap::heap()->reserved_region());
1540 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1541 // Temporarily, clear the "is_alive_non_header" field of the
1542 // reference processor.
1543 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1544 // Temporarily make reference _processing_ single threaded (non-MT).
1545 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1546 // Temporarily make refs discovery atomic
1547 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1548 // Temporarily make reference _discovery_ single threaded (non-MT)
1549 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1550
1551 ref_processor()->set_enqueuing_is_done(false);
1552 ref_processor()->enable_discovery();
1553 ref_processor()->setup_policy(clear_all_soft_refs);
1554 // If an asynchronous collection finishes, the _modUnionTable is
1555 // all clear. If we are assuming the collection from an asynchronous
1556 // collection, clear the _modUnionTable.
1557 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1558 "_modUnionTable should be clear if the baton was not passed");
1559 _modUnionTable.clear_all();
1560 assert(_collectorState != Idling || _ct->cld_rem_set()->mod_union_is_clear(),
1561 "mod union for klasses should be clear if the baton was passed");
1562 _ct->cld_rem_set()->clear_mod_union();
1563
1564
1565 // We must adjust the allocation statistics being maintained
1566 // in the free list space. We do so by reading and clearing
1567 // the sweep timer and updating the block flux rate estimates below.
1568 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1569 if (_inter_sweep_timer.is_active()) {
1570 _inter_sweep_timer.stop();
1571 // Note that we do not use this sample to update the _inter_sweep_estimate.
1572 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1573 _inter_sweep_estimate.padded_average(),
1574 _intra_sweep_estimate.padded_average());
1575 }
1576
1577 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1578 #ifdef ASSERT
1579 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1580 size_t free_size = cms_space->free();
1581 assert(free_size ==
1582 pointer_delta(cms_space->end(), cms_space->compaction_top())
1583 * HeapWordSize,
1584 "All the free space should be compacted into one chunk at top");
1585 assert(cms_space->dictionary()->total_chunk_size(
1586 debug_only(cms_space->freelistLock())) == 0 ||
1587 cms_space->totalSizeInIndexedFreeLists() == 0,
1588 "All the free space should be in a single chunk");
1589 size_t num = cms_space->totalCount();
1590 assert((free_size == 0 && num == 0) ||
1591 (free_size > 0 && (num == 1 || num == 2)),
1592 "There should be at most 2 free chunks after compaction");
1593 #endif // ASSERT
1594 _collectorState = Resetting;
1595 assert(_restart_addr == NULL,
1596 "Should have been NULL'd before baton was passed");
1597 reset_stw();
1598 _cmsGen->reset_after_compaction();
1599 _concurrent_cycles_since_last_unload = 0;
1600
1601 // Clear any data recorded in the PLAB chunk arrays.
1602 if (_survivor_plab_array != NULL) {
1603 reset_survivor_plab_arrays();
1604 }
1605
1606 // Adjust the per-size allocation stats for the next epoch.
1607 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1608 // Restart the "inter sweep timer" for the next epoch.
1609 _inter_sweep_timer.reset();
1610 _inter_sweep_timer.start();
1611
1612 // No longer a need to do a concurrent collection for Metaspace.
1613 MetaspaceGC::set_should_concurrent_collect(false);
1614
1615 heap->post_full_gc_dump(gc_timer);
1616
1617 gc_timer->register_gc_end();
1618
1619 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1620
1621 // For a mark-sweep-compact, compute_new_size() will be called
1622 // in the heap's do_collection() method.
1623 }
1624
1625 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1626 Log(gc, heap) log;
1627 if (!log.is_trace()) {
1628 return;
1629 }
1630
1631 ContiguousSpace* eden_space = _young_gen->eden();
1632 ContiguousSpace* from_space = _young_gen->from();
1633 ContiguousSpace* to_space = _young_gen->to();
1634 // Eden
1635 if (_eden_chunk_array != NULL) {
1636 log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1637 p2i(eden_space->bottom()), p2i(eden_space->top()),
1638 p2i(eden_space->end()), eden_space->capacity());
1639 log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT,
1640 _eden_chunk_index, _eden_chunk_capacity);
1641 for (size_t i = 0; i < _eden_chunk_index; i++) {
1642 log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i]));
1643 }
1644 }
1645 // Survivor
1646 if (_survivor_chunk_array != NULL) {
1647 log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1648 p2i(from_space->bottom()), p2i(from_space->top()),
1649 p2i(from_space->end()), from_space->capacity());
1650 log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT,
1651 _survivor_chunk_index, _survivor_chunk_capacity);
1652 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1653 log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i]));
1654 }
1655 }
1656 }
1657
1658 void CMSCollector::getFreelistLocks() const {
1659 // Get locks for all free lists in all generations that this
1660 // collector is responsible for
1661 _cmsGen->freelistLock()->lock_without_safepoint_check();
1662 }
1663
1664 void CMSCollector::releaseFreelistLocks() const {
1665 // Release locks for all free lists in all generations that this
1666 // collector is responsible for
1667 _cmsGen->freelistLock()->unlock();
1668 }
1669
1670 bool CMSCollector::haveFreelistLocks() const {
1671 // Check locks for all free lists in all generations that this
1672 // collector is responsible for
1673 assert_lock_strong(_cmsGen->freelistLock());
1674 PRODUCT_ONLY(ShouldNotReachHere());
1675 return true;
1676 }
1677
1678 // A utility class that is used by the CMS collector to
1679 // temporarily "release" the foreground collector from its
1680 // usual obligation to wait for the background collector to
1681 // complete an ongoing phase before proceeding.
1682 class ReleaseForegroundGC: public StackObj {
1683 private:
1684 CMSCollector* _c;
1685 public:
1686 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1687 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1688 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1689 // allow a potentially blocked foreground collector to proceed
1690 _c->_foregroundGCShouldWait = false;
1691 if (_c->_foregroundGCIsActive) {
1692 CGC_lock->notify();
1693 }
1694 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1695 "Possible deadlock");
1696 }
1697
1698 ~ReleaseForegroundGC() {
1699 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1700 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1701 _c->_foregroundGCShouldWait = true;
1702 }
1703 };
1704
1705 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1706 assert(Thread::current()->is_ConcurrentGC_thread(),
1707 "A CMS asynchronous collection is only allowed on a CMS thread.");
1708
1709 CMSHeap* heap = CMSHeap::heap();
1710 {
1711 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1712 MutexLockerEx hl(Heap_lock, safepoint_check);
1713 FreelistLocker fll(this);
1714 MutexLockerEx x(CGC_lock, safepoint_check);
1715 if (_foregroundGCIsActive) {
1716 // The foreground collector is. Skip this
1717 // background collection.
1718 assert(!_foregroundGCShouldWait, "Should be clear");
1719 return;
1720 } else {
1721 assert(_collectorState == Idling, "Should be idling before start.");
1722 _collectorState = InitialMarking;
1723 register_gc_start(cause);
1724 // Reset the expansion cause, now that we are about to begin
1725 // a new cycle.
1726 clear_expansion_cause();
1727
1728 // Clear the MetaspaceGC flag since a concurrent collection
1729 // is starting but also clear it after the collection.
1730 MetaspaceGC::set_should_concurrent_collect(false);
1731 }
1732 // Decide if we want to enable class unloading as part of the
1733 // ensuing concurrent GC cycle.
1734 update_should_unload_classes();
1735 _full_gc_requested = false; // acks all outstanding full gc requests
1736 _full_gc_cause = GCCause::_no_gc;
1737 // Signal that we are about to start a collection
1738 heap->increment_total_full_collections(); // ... starting a collection cycle
1739 _collection_count_start = heap->total_full_collections();
1740 }
1741
1742 size_t prev_used = _cmsGen->used();
1743
1744 // The change of the collection state is normally done at this level;
1745 // the exceptions are phases that are executed while the world is
1746 // stopped. For those phases the change of state is done while the
1747 // world is stopped. For baton passing purposes this allows the
1748 // background collector to finish the phase and change state atomically.
1749 // The foreground collector cannot wait on a phase that is done
1750 // while the world is stopped because the foreground collector already
1751 // has the world stopped and would deadlock.
1752 while (_collectorState != Idling) {
1753 log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d",
1754 p2i(Thread::current()), _collectorState);
1755 // The foreground collector
1756 // holds the Heap_lock throughout its collection.
1757 // holds the CMS token (but not the lock)
1758 // except while it is waiting for the background collector to yield.
1759 //
1760 // The foreground collector should be blocked (not for long)
1761 // if the background collector is about to start a phase
1762 // executed with world stopped. If the background
1763 // collector has already started such a phase, the
1764 // foreground collector is blocked waiting for the
1765 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1766 // are executed in the VM thread.
1767 //
1768 // The locking order is
1769 // PendingListLock (PLL) -- if applicable (FinalMarking)
1770 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1771 // CMS token (claimed in
1772 // stop_world_and_do() -->
1773 // safepoint_synchronize() -->
1774 // CMSThread::synchronize())
1775
1776 {
1777 // Check if the FG collector wants us to yield.
1778 CMSTokenSync x(true); // is cms thread
1779 if (waitForForegroundGC()) {
1780 // We yielded to a foreground GC, nothing more to be
1781 // done this round.
1782 assert(_foregroundGCShouldWait == false, "We set it to false in "
1783 "waitForForegroundGC()");
1784 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1785 p2i(Thread::current()), _collectorState);
1786 return;
1787 } else {
1788 // The background collector can run but check to see if the
1789 // foreground collector has done a collection while the
1790 // background collector was waiting to get the CGC_lock
1791 // above. If yes, break so that _foregroundGCShouldWait
1792 // is cleared before returning.
1793 if (_collectorState == Idling) {
1794 break;
1795 }
1796 }
1797 }
1798
1799 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1800 "should be waiting");
1801
1802 switch (_collectorState) {
1803 case InitialMarking:
1804 {
1805 ReleaseForegroundGC x(this);
1806 stats().record_cms_begin();
1807 VM_CMS_Initial_Mark initial_mark_op(this);
1808 VMThread::execute(&initial_mark_op);
1809 }
1810 // The collector state may be any legal state at this point
1811 // since the background collector may have yielded to the
1812 // foreground collector.
1813 break;
1814 case Marking:
1815 // initial marking in checkpointRootsInitialWork has been completed
1816 if (markFromRoots()) { // we were successful
1817 assert(_collectorState == Precleaning, "Collector state should "
1818 "have changed");
1819 } else {
1820 assert(_foregroundGCIsActive, "Internal state inconsistency");
1821 }
1822 break;
1823 case Precleaning:
1824 // marking from roots in markFromRoots has been completed
1825 preclean();
1826 assert(_collectorState == AbortablePreclean ||
1827 _collectorState == FinalMarking,
1828 "Collector state should have changed");
1829 break;
1830 case AbortablePreclean:
1831 abortable_preclean();
1832 assert(_collectorState == FinalMarking, "Collector state should "
1833 "have changed");
1834 break;
1835 case FinalMarking:
1836 {
1837 ReleaseForegroundGC x(this);
1838
1839 VM_CMS_Final_Remark final_remark_op(this);
1840 VMThread::execute(&final_remark_op);
1841 }
1842 assert(_foregroundGCShouldWait, "block post-condition");
1843 break;
1844 case Sweeping:
1845 // final marking in checkpointRootsFinal has been completed
1846 sweep();
1847 assert(_collectorState == Resizing, "Collector state change "
1848 "to Resizing must be done under the free_list_lock");
1849
1850 case Resizing: {
1851 // Sweeping has been completed...
1852 // At this point the background collection has completed.
1853 // Don't move the call to compute_new_size() down
1854 // into code that might be executed if the background
1855 // collection was preempted.
1856 {
1857 ReleaseForegroundGC x(this); // unblock FG collection
1858 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1859 CMSTokenSync z(true); // not strictly needed.
1860 if (_collectorState == Resizing) {
1861 compute_new_size();
1862 save_heap_summary();
1863 _collectorState = Resetting;
1864 } else {
1865 assert(_collectorState == Idling, "The state should only change"
1866 " because the foreground collector has finished the collection");
1867 }
1868 }
1869 break;
1870 }
1871 case Resetting:
1872 // CMS heap resizing has been completed
1873 reset_concurrent();
1874 assert(_collectorState == Idling, "Collector state should "
1875 "have changed");
1876
1877 MetaspaceGC::set_should_concurrent_collect(false);
1878
1879 stats().record_cms_end();
1880 // Don't move the concurrent_phases_end() and compute_new_size()
1881 // calls to here because a preempted background collection
1882 // has it's state set to "Resetting".
1883 break;
1884 case Idling:
1885 default:
1886 ShouldNotReachHere();
1887 break;
1888 }
1889 log_debug(gc, state)(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1890 p2i(Thread::current()), _collectorState);
1891 assert(_foregroundGCShouldWait, "block post-condition");
1892 }
1893
1894 // Should this be in gc_epilogue?
1895 heap->counters()->update_counters();
1896
1897 {
1898 // Clear _foregroundGCShouldWait and, in the event that the
1899 // foreground collector is waiting, notify it, before
1900 // returning.
1901 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1902 _foregroundGCShouldWait = false;
1903 if (_foregroundGCIsActive) {
1904 CGC_lock->notify();
1905 }
1906 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1907 "Possible deadlock");
1908 }
1909 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1910 p2i(Thread::current()), _collectorState);
1911 log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K(" SIZE_FORMAT "K)",
1912 prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K);
1913 }
1914
1915 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1916 _cms_start_registered = true;
1917 _gc_timer_cm->register_gc_start();
1918 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1919 }
1920
1921 void CMSCollector::register_gc_end() {
1922 if (_cms_start_registered) {
1923 report_heap_summary(GCWhen::AfterGC);
1924
1925 _gc_timer_cm->register_gc_end();
1926 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1927 _cms_start_registered = false;
1928 }
1929 }
1930
1931 void CMSCollector::save_heap_summary() {
1932 CMSHeap* heap = CMSHeap::heap();
1933 _last_heap_summary = heap->create_heap_summary();
1934 _last_metaspace_summary = heap->create_metaspace_summary();
1935 }
1936
1937 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1938 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1939 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1940 }
1941
1942 bool CMSCollector::waitForForegroundGC() {
1943 bool res = false;
1944 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1945 "CMS thread should have CMS token");
1946 // Block the foreground collector until the
1947 // background collectors decides whether to
1948 // yield.
1949 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1950 _foregroundGCShouldWait = true;
1951 if (_foregroundGCIsActive) {
1952 // The background collector yields to the
1953 // foreground collector and returns a value
1954 // indicating that it has yielded. The foreground
1955 // collector can proceed.
1956 res = true;
1957 _foregroundGCShouldWait = false;
1958 ConcurrentMarkSweepThread::clear_CMS_flag(
1959 ConcurrentMarkSweepThread::CMS_cms_has_token);
1960 ConcurrentMarkSweepThread::set_CMS_flag(
1961 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1962 // Get a possibly blocked foreground thread going
1963 CGC_lock->notify();
1964 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
1965 p2i(Thread::current()), _collectorState);
1966 while (_foregroundGCIsActive) {
1967 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1968 }
1969 ConcurrentMarkSweepThread::set_CMS_flag(
1970 ConcurrentMarkSweepThread::CMS_cms_has_token);
1971 ConcurrentMarkSweepThread::clear_CMS_flag(
1972 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1973 }
1974 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
1975 p2i(Thread::current()), _collectorState);
1976 return res;
1977 }
1978
1979 // Because of the need to lock the free lists and other structures in
1980 // the collector, common to all the generations that the collector is
1981 // collecting, we need the gc_prologues of individual CMS generations
1982 // delegate to their collector. It may have been simpler had the
1983 // current infrastructure allowed one to call a prologue on a
1984 // collector. In the absence of that we have the generation's
1985 // prologue delegate to the collector, which delegates back
1986 // some "local" work to a worker method in the individual generations
1987 // that it's responsible for collecting, while itself doing any
1988 // work common to all generations it's responsible for. A similar
1989 // comment applies to the gc_epilogue()'s.
1990 // The role of the variable _between_prologue_and_epilogue is to
1991 // enforce the invocation protocol.
1992 void CMSCollector::gc_prologue(bool full) {
1993 // Call gc_prologue_work() for the CMSGen
1994 // we are responsible for.
1995
1996 // The following locking discipline assumes that we are only called
1997 // when the world is stopped.
1998 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
1999
2000 // The CMSCollector prologue must call the gc_prologues for the
2001 // "generations" that it's responsible
2002 // for.
2003
2004 assert( Thread::current()->is_VM_thread()
2005 || ( CMSScavengeBeforeRemark
2006 && Thread::current()->is_ConcurrentGC_thread()),
2007 "Incorrect thread type for prologue execution");
2008
2009 if (_between_prologue_and_epilogue) {
2010 // We have already been invoked; this is a gc_prologue delegation
2011 // from yet another CMS generation that we are responsible for, just
2012 // ignore it since all relevant work has already been done.
2013 return;
2014 }
2015
2016 // set a bit saying prologue has been called; cleared in epilogue
2017 _between_prologue_and_epilogue = true;
2018 // Claim locks for common data structures, then call gc_prologue_work()
2019 // for each CMSGen.
2020
2021 getFreelistLocks(); // gets free list locks on constituent spaces
2022 bitMapLock()->lock_without_safepoint_check();
2023
2024 // Should call gc_prologue_work() for all cms gens we are responsible for
2025 bool duringMarking = _collectorState >= Marking
2026 && _collectorState < Sweeping;
2027
2028 // The young collections clear the modified oops state, which tells if
2029 // there are any modified oops in the class. The remark phase also needs
2030 // that information. Tell the young collection to save the union of all
2031 // modified klasses.
2032 if (duringMarking) {
2033 _ct->cld_rem_set()->set_accumulate_modified_oops(true);
2034 }
2035
2036 bool registerClosure = duringMarking;
2037
2038 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2039
2040 if (!full) {
2041 stats().record_gc0_begin();
2042 }
2043 }
2044
2045 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2046
2047 _capacity_at_prologue = capacity();
2048 _used_at_prologue = used();
2049
2050 // We enable promotion tracking so that card-scanning can recognize
2051 // which objects have been promoted during this GC and skip them.
2052 for (uint i = 0; i < ParallelGCThreads; i++) {
2053 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2054 }
2055
2056 // Delegate to CMScollector which knows how to coordinate between
2057 // this and any other CMS generations that it is responsible for
2058 // collecting.
2059 collector()->gc_prologue(full);
2060 }
2061
2062 // This is a "private" interface for use by this generation's CMSCollector.
2063 // Not to be called directly by any other entity (for instance,
2064 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2065 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2066 bool registerClosure, ModUnionClosure* modUnionClosure) {
2067 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2068 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2069 "Should be NULL");
2070 if (registerClosure) {
2071 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2072 }
2073 cmsSpace()->gc_prologue();
2074 // Clear stat counters
2075 NOT_PRODUCT(
2076 assert(_numObjectsPromoted == 0, "check");
2077 assert(_numWordsPromoted == 0, "check");
2078 log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently",
2079 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2080 _numObjectsAllocated = 0;
2081 _numWordsAllocated = 0;
2082 )
2083 }
2084
2085 void CMSCollector::gc_epilogue(bool full) {
2086 // The following locking discipline assumes that we are only called
2087 // when the world is stopped.
2088 assert(SafepointSynchronize::is_at_safepoint(),
2089 "world is stopped assumption");
2090
2091 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2092 // if linear allocation blocks need to be appropriately marked to allow the
2093 // the blocks to be parsable. We also check here whether we need to nudge the
2094 // CMS collector thread to start a new cycle (if it's not already active).
2095 assert( Thread::current()->is_VM_thread()
2096 || ( CMSScavengeBeforeRemark
2097 && Thread::current()->is_ConcurrentGC_thread()),
2098 "Incorrect thread type for epilogue execution");
2099
2100 if (!_between_prologue_and_epilogue) {
2101 // We have already been invoked; this is a gc_epilogue delegation
2102 // from yet another CMS generation that we are responsible for, just
2103 // ignore it since all relevant work has already been done.
2104 return;
2105 }
2106 assert(haveFreelistLocks(), "must have freelist locks");
2107 assert_lock_strong(bitMapLock());
2108
2109 _ct->cld_rem_set()->set_accumulate_modified_oops(false);
2110
2111 _cmsGen->gc_epilogue_work(full);
2112
2113 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2114 // in case sampling was not already enabled, enable it
2115 _start_sampling = true;
2116 }
2117 // reset _eden_chunk_array so sampling starts afresh
2118 _eden_chunk_index = 0;
2119
2120 size_t cms_used = _cmsGen->cmsSpace()->used();
2121
2122 // update performance counters - this uses a special version of
2123 // update_counters() that allows the utilization to be passed as a
2124 // parameter, avoiding multiple calls to used().
2125 //
2126 _cmsGen->update_counters(cms_used);
2127
2128 bitMapLock()->unlock();
2129 releaseFreelistLocks();
2130
2131 if (!CleanChunkPoolAsync) {
2132 Chunk::clean_chunk_pool();
2133 }
2134
2135 set_did_compact(false);
2136 _between_prologue_and_epilogue = false; // ready for next cycle
2137 }
2138
2139 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2140 collector()->gc_epilogue(full);
2141
2142 // When using ParNew, promotion tracking should have already been
2143 // disabled. However, the prologue (which enables promotion
2144 // tracking) and epilogue are called irrespective of the type of
2145 // GC. So they will also be called before and after Full GCs, during
2146 // which promotion tracking will not be explicitly disabled. So,
2147 // it's safer to also disable it here too (to be symmetric with
2148 // enabling it in the prologue).
2149 for (uint i = 0; i < ParallelGCThreads; i++) {
2150 _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2151 }
2152 }
2153
2154 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2155 assert(!incremental_collection_failed(), "Should have been cleared");
2156 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2157 cmsSpace()->gc_epilogue();
2158 // Print stat counters
2159 NOT_PRODUCT(
2160 assert(_numObjectsAllocated == 0, "check");
2161 assert(_numWordsAllocated == 0, "check");
2162 log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
2163 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2164 _numObjectsPromoted = 0;
2165 _numWordsPromoted = 0;
2166 )
2167
2168 // Call down the chain in contiguous_available needs the freelistLock
2169 // so print this out before releasing the freeListLock.
2170 log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available());
2171 }
2172
2173 #ifndef PRODUCT
2174 bool CMSCollector::have_cms_token() {
2175 Thread* thr = Thread::current();
2176 if (thr->is_VM_thread()) {
2177 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2178 } else if (thr->is_ConcurrentGC_thread()) {
2179 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2180 } else if (thr->is_GC_task_thread()) {
2181 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2182 ParGCRareEvent_lock->owned_by_self();
2183 }
2184 return false;
2185 }
2186
2187 // Check reachability of the given heap address in CMS generation,
2188 // treating all other generations as roots.
2189 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2190 // We could "guarantee" below, rather than assert, but I'll
2191 // leave these as "asserts" so that an adventurous debugger
2192 // could try this in the product build provided some subset of
2193 // the conditions were met, provided they were interested in the
2194 // results and knew that the computation below wouldn't interfere
2195 // with other concurrent computations mutating the structures
2196 // being read or written.
2197 assert(SafepointSynchronize::is_at_safepoint(),
2198 "Else mutations in object graph will make answer suspect");
2199 assert(have_cms_token(), "Should hold cms token");
2200 assert(haveFreelistLocks(), "must hold free list locks");
2201 assert_lock_strong(bitMapLock());
2202
2203 // Clear the marking bit map array before starting, but, just
2204 // for kicks, first report if the given address is already marked
2205 tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2206 _markBitMap.isMarked(addr) ? "" : " not");
2207
2208 if (verify_after_remark()) {
2209 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2210 bool result = verification_mark_bm()->isMarked(addr);
2211 tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2212 result ? "IS" : "is NOT");
2213 return result;
2214 } else {
2215 tty->print_cr("Could not compute result");
2216 return false;
2217 }
2218 }
2219 #endif
2220
2221 void
2222 CMSCollector::print_on_error(outputStream* st) {
2223 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2224 if (collector != NULL) {
2225 CMSBitMap* bitmap = &collector->_markBitMap;
2226 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2227 bitmap->print_on_error(st, " Bits: ");
2228
2229 st->cr();
2230
2231 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2232 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2233 mut_bitmap->print_on_error(st, " Bits: ");
2234 }
2235 }
2236
2237 ////////////////////////////////////////////////////////
2238 // CMS Verification Support
2239 ////////////////////////////////////////////////////////
2240 // Following the remark phase, the following invariant
2241 // should hold -- each object in the CMS heap which is
2242 // marked in markBitMap() should be marked in the verification_mark_bm().
2243
2244 class VerifyMarkedClosure: public BitMapClosure {
2245 CMSBitMap* _marks;
2246 bool _failed;
2247
2248 public:
2249 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2250
2251 bool do_bit(size_t offset) {
2252 HeapWord* addr = _marks->offsetToHeapWord(offset);
2253 if (!_marks->isMarked(addr)) {
2254 Log(gc, verify) log;
2255 ResourceMark rm;
2256 LogStream ls(log.error());
2257 oop(addr)->print_on(&ls);
2258 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2259 _failed = true;
2260 }
2261 return true;
2262 }
2263
2264 bool failed() { return _failed; }
2265 };
2266
2267 bool CMSCollector::verify_after_remark() {
2268 GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking.");
2269 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2270 static bool init = false;
2271
2272 assert(SafepointSynchronize::is_at_safepoint(),
2273 "Else mutations in object graph will make answer suspect");
2274 assert(have_cms_token(),
2275 "Else there may be mutual interference in use of "
2276 " verification data structures");
2277 assert(_collectorState > Marking && _collectorState <= Sweeping,
2278 "Else marking info checked here may be obsolete");
2279 assert(haveFreelistLocks(), "must hold free list locks");
2280 assert_lock_strong(bitMapLock());
2281
2282
2283 // Allocate marking bit map if not already allocated
2284 if (!init) { // first time
2285 if (!verification_mark_bm()->allocate(_span)) {
2286 return false;
2287 }
2288 init = true;
2289 }
2290
2291 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2292
2293 // Turn off refs discovery -- so we will be tracing through refs.
2294 // This is as intended, because by this time
2295 // GC must already have cleared any refs that need to be cleared,
2296 // and traced those that need to be marked; moreover,
2297 // the marking done here is not going to interfere in any
2298 // way with the marking information used by GC.
2299 NoRefDiscovery no_discovery(ref_processor());
2300
2301 #if COMPILER2_OR_JVMCI
2302 DerivedPointerTableDeactivate dpt_deact;
2303 #endif
2304
2305 // Clear any marks from a previous round
2306 verification_mark_bm()->clear_all();
2307 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2308 verify_work_stacks_empty();
2309
2310 CMSHeap* heap = CMSHeap::heap();
2311 heap->ensure_parsability(false); // fill TLABs, but no need to retire them
2312 // Update the saved marks which may affect the root scans.
2313 heap->save_marks();
2314
2315 if (CMSRemarkVerifyVariant == 1) {
2316 // In this first variant of verification, we complete
2317 // all marking, then check if the new marks-vector is
2318 // a subset of the CMS marks-vector.
2319 verify_after_remark_work_1();
2320 } else {
2321 guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2");
2322 // In this second variant of verification, we flag an error
2323 // (i.e. an object reachable in the new marks-vector not reachable
2324 // in the CMS marks-vector) immediately, also indicating the
2325 // identify of an object (A) that references the unmarked object (B) --
2326 // presumably, a mutation to A failed to be picked up by preclean/remark?
2327 verify_after_remark_work_2();
2328 }
2329
2330 return true;
2331 }
2332
2333 void CMSCollector::verify_after_remark_work_1() {
2334 ResourceMark rm;
2335 HandleMark hm;
2336 CMSHeap* heap = CMSHeap::heap();
2337
2338 // Get a clear set of claim bits for the roots processing to work with.
2339 ClassLoaderDataGraph::clear_claimed_marks();
2340
2341 // Mark from roots one level into CMS
2342 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2343 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2344
2345 {
2346 StrongRootsScope srs(1);
2347
2348 heap->cms_process_roots(&srs,
2349 true, // young gen as roots
2350 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2351 should_unload_classes(),
2352 ¬Older,
2353 NULL);
2354 }
2355
2356 // Now mark from the roots
2357 MarkFromRootsClosure markFromRootsClosure(this, _span,
2358 verification_mark_bm(), verification_mark_stack(),
2359 false /* don't yield */, true /* verifying */);
2360 assert(_restart_addr == NULL, "Expected pre-condition");
2361 verification_mark_bm()->iterate(&markFromRootsClosure);
2362 while (_restart_addr != NULL) {
2363 // Deal with stack overflow: by restarting at the indicated
2364 // address.
2365 HeapWord* ra = _restart_addr;
2366 markFromRootsClosure.reset(ra);
2367 _restart_addr = NULL;
2368 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2369 }
2370 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2371 verify_work_stacks_empty();
2372
2373 // Marking completed -- now verify that each bit marked in
2374 // verification_mark_bm() is also marked in markBitMap(); flag all
2375 // errors by printing corresponding objects.
2376 VerifyMarkedClosure vcl(markBitMap());
2377 verification_mark_bm()->iterate(&vcl);
2378 if (vcl.failed()) {
2379 Log(gc, verify) log;
2380 log.error("Failed marking verification after remark");
2381 ResourceMark rm;
2382 LogStream ls(log.error());
2383 heap->print_on(&ls);
2384 fatal("CMS: failed marking verification after remark");
2385 }
2386 }
2387
2388 class VerifyCLDOopsCLDClosure : public CLDClosure {
2389 class VerifyCLDOopsClosure : public OopClosure {
2390 CMSBitMap* _bitmap;
2391 public:
2392 VerifyCLDOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2393 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2394 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2395 } _oop_closure;
2396 public:
2397 VerifyCLDOopsCLDClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2398 void do_cld(ClassLoaderData* cld) {
2399 cld->oops_do(&_oop_closure, false, false);
2400 }
2401 };
2402
2403 void CMSCollector::verify_after_remark_work_2() {
2404 ResourceMark rm;
2405 HandleMark hm;
2406 CMSHeap* heap = CMSHeap::heap();
2407
2408 // Get a clear set of claim bits for the roots processing to work with.
2409 ClassLoaderDataGraph::clear_claimed_marks();
2410
2411 // Mark from roots one level into CMS
2412 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2413 markBitMap());
2414 CLDToOopClosure cld_closure(¬Older, true);
2415
2416 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2417
2418 {
2419 StrongRootsScope srs(1);
2420
2421 heap->cms_process_roots(&srs,
2422 true, // young gen as roots
2423 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2424 should_unload_classes(),
2425 ¬Older,
2426 &cld_closure);
2427 }
2428
2429 // Now mark from the roots
2430 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2431 verification_mark_bm(), markBitMap(), verification_mark_stack());
2432 assert(_restart_addr == NULL, "Expected pre-condition");
2433 verification_mark_bm()->iterate(&markFromRootsClosure);
2434 while (_restart_addr != NULL) {
2435 // Deal with stack overflow: by restarting at the indicated
2436 // address.
2437 HeapWord* ra = _restart_addr;
2438 markFromRootsClosure.reset(ra);
2439 _restart_addr = NULL;
2440 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2441 }
2442 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2443 verify_work_stacks_empty();
2444
2445 VerifyCLDOopsCLDClosure verify_cld_oops(verification_mark_bm());
2446 ClassLoaderDataGraph::cld_do(&verify_cld_oops);
2447
2448 // Marking completed -- now verify that each bit marked in
2449 // verification_mark_bm() is also marked in markBitMap(); flag all
2450 // errors by printing corresponding objects.
2451 VerifyMarkedClosure vcl(markBitMap());
2452 verification_mark_bm()->iterate(&vcl);
2453 assert(!vcl.failed(), "Else verification above should not have succeeded");
2454 }
2455
2456 void ConcurrentMarkSweepGeneration::save_marks() {
2457 // delegate to CMS space
2458 cmsSpace()->save_marks();
2459 }
2460
2461 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2462 return cmsSpace()->no_allocs_since_save_marks();
2463 }
2464
2465 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2466 \
2467 void ConcurrentMarkSweepGeneration:: \
2468 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2469 cl->set_generation(this); \
2470 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2471 cl->reset_generation(); \
2472 save_marks(); \
2473 }
2474
2475 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2476
2477 void
2478 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2479 if (freelistLock()->owned_by_self()) {
2480 Generation::oop_iterate(cl);
2481 } else {
2482 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2483 Generation::oop_iterate(cl);
2484 }
2485 }
2486
2487 void
2488 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2489 if (freelistLock()->owned_by_self()) {
2490 Generation::object_iterate(cl);
2491 } else {
2492 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2493 Generation::object_iterate(cl);
2494 }
2495 }
2496
2497 void
2498 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2499 if (freelistLock()->owned_by_self()) {
2500 Generation::safe_object_iterate(cl);
2501 } else {
2502 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2503 Generation::safe_object_iterate(cl);
2504 }
2505 }
2506
2507 void
2508 ConcurrentMarkSweepGeneration::post_compact() {
2509 }
2510
2511 void
2512 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2513 // Fix the linear allocation blocks to look like free blocks.
2514
2515 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2516 // are not called when the heap is verified during universe initialization and
2517 // at vm shutdown.
2518 if (freelistLock()->owned_by_self()) {
2519 cmsSpace()->prepare_for_verify();
2520 } else {
2521 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2522 cmsSpace()->prepare_for_verify();
2523 }
2524 }
2525
2526 void
2527 ConcurrentMarkSweepGeneration::verify() {
2528 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2529 // are not called when the heap is verified during universe initialization and
2530 // at vm shutdown.
2531 if (freelistLock()->owned_by_self()) {
2532 cmsSpace()->verify();
2533 } else {
2534 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2535 cmsSpace()->verify();
2536 }
2537 }
2538
2539 void CMSCollector::verify() {
2540 _cmsGen->verify();
2541 }
2542
2543 #ifndef PRODUCT
2544 bool CMSCollector::overflow_list_is_empty() const {
2545 assert(_num_par_pushes >= 0, "Inconsistency");
2546 if (_overflow_list == NULL) {
2547 assert(_num_par_pushes == 0, "Inconsistency");
2548 }
2549 return _overflow_list == NULL;
2550 }
2551
2552 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2553 // merely consolidate assertion checks that appear to occur together frequently.
2554 void CMSCollector::verify_work_stacks_empty() const {
2555 assert(_markStack.isEmpty(), "Marking stack should be empty");
2556 assert(overflow_list_is_empty(), "Overflow list should be empty");
2557 }
2558
2559 void CMSCollector::verify_overflow_empty() const {
2560 assert(overflow_list_is_empty(), "Overflow list should be empty");
2561 assert(no_preserved_marks(), "No preserved marks");
2562 }
2563 #endif // PRODUCT
2564
2565 // Decide if we want to enable class unloading as part of the
2566 // ensuing concurrent GC cycle. We will collect and
2567 // unload classes if it's the case that:
2568 // (a) class unloading is enabled at the command line, and
2569 // (b) old gen is getting really full
2570 // NOTE: Provided there is no change in the state of the heap between
2571 // calls to this method, it should have idempotent results. Moreover,
2572 // its results should be monotonically increasing (i.e. going from 0 to 1,
2573 // but not 1 to 0) between successive calls between which the heap was
2574 // not collected. For the implementation below, it must thus rely on
2575 // the property that concurrent_cycles_since_last_unload()
2576 // will not decrease unless a collection cycle happened and that
2577 // _cmsGen->is_too_full() are
2578 // themselves also monotonic in that sense. See check_monotonicity()
2579 // below.
2580 void CMSCollector::update_should_unload_classes() {
2581 _should_unload_classes = false;
2582 if (CMSClassUnloadingEnabled) {
2583 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2584 CMSClassUnloadingMaxInterval)
2585 || _cmsGen->is_too_full();
2586 }
2587 }
2588
2589 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2590 bool res = should_concurrent_collect();
2591 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2592 return res;
2593 }
2594
2595 void CMSCollector::setup_cms_unloading_and_verification_state() {
2596 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2597 || VerifyBeforeExit;
2598 const int rso = GenCollectedHeap::SO_AllCodeCache;
2599
2600 // We set the proper root for this CMS cycle here.
2601 if (should_unload_classes()) { // Should unload classes this cycle
2602 remove_root_scanning_option(rso); // Shrink the root set appropriately
2603 set_verifying(should_verify); // Set verification state for this cycle
2604 return; // Nothing else needs to be done at this time
2605 }
2606
2607 // Not unloading classes this cycle
2608 assert(!should_unload_classes(), "Inconsistency!");
2609
2610 // If we are not unloading classes then add SO_AllCodeCache to root
2611 // scanning options.
2612 add_root_scanning_option(rso);
2613
2614 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2615 set_verifying(true);
2616 } else if (verifying() && !should_verify) {
2617 // We were verifying, but some verification flags got disabled.
2618 set_verifying(false);
2619 // Exclude symbols, strings and code cache elements from root scanning to
2620 // reduce IM and RM pauses.
2621 remove_root_scanning_option(rso);
2622 }
2623 }
2624
2625
2626 #ifndef PRODUCT
2627 HeapWord* CMSCollector::block_start(const void* p) const {
2628 const HeapWord* addr = (HeapWord*)p;
2629 if (_span.contains(p)) {
2630 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2631 return _cmsGen->cmsSpace()->block_start(p);
2632 }
2633 }
2634 return NULL;
2635 }
2636 #endif
2637
2638 HeapWord*
2639 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2640 bool tlab,
2641 bool parallel) {
2642 CMSSynchronousYieldRequest yr;
2643 assert(!tlab, "Can't deal with TLAB allocation");
2644 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2645 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2646 if (GCExpandToAllocateDelayMillis > 0) {
2647 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2648 }
2649 return have_lock_and_allocate(word_size, tlab);
2650 }
2651
2652 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2653 size_t bytes,
2654 size_t expand_bytes,
2655 CMSExpansionCause::Cause cause)
2656 {
2657
2658 bool success = expand(bytes, expand_bytes);
2659
2660 // remember why we expanded; this information is used
2661 // by shouldConcurrentCollect() when making decisions on whether to start
2662 // a new CMS cycle.
2663 if (success) {
2664 set_expansion_cause(cause);
2665 log_trace(gc)("Expanded CMS gen for %s", CMSExpansionCause::to_string(cause));
2666 }
2667 }
2668
2669 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2670 HeapWord* res = NULL;
2671 MutexLocker x(ParGCRareEvent_lock);
2672 while (true) {
2673 // Expansion by some other thread might make alloc OK now:
2674 res = ps->lab.alloc(word_sz);
2675 if (res != NULL) return res;
2676 // If there's not enough expansion space available, give up.
2677 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2678 return NULL;
2679 }
2680 // Otherwise, we try expansion.
2681 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2682 // Now go around the loop and try alloc again;
2683 // A competing par_promote might beat us to the expansion space,
2684 // so we may go around the loop again if promotion fails again.
2685 if (GCExpandToAllocateDelayMillis > 0) {
2686 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2687 }
2688 }
2689 }
2690
2691
2692 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2693 PromotionInfo* promo) {
2694 MutexLocker x(ParGCRareEvent_lock);
2695 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2696 while (true) {
2697 // Expansion by some other thread might make alloc OK now:
2698 if (promo->ensure_spooling_space()) {
2699 assert(promo->has_spooling_space(),
2700 "Post-condition of successful ensure_spooling_space()");
2701 return true;
2702 }
2703 // If there's not enough expansion space available, give up.
2704 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2705 return false;
2706 }
2707 // Otherwise, we try expansion.
2708 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2709 // Now go around the loop and try alloc again;
2710 // A competing allocation might beat us to the expansion space,
2711 // so we may go around the loop again if allocation fails again.
2712 if (GCExpandToAllocateDelayMillis > 0) {
2713 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2714 }
2715 }
2716 }
2717
2718 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2719 // Only shrink if a compaction was done so that all the free space
2720 // in the generation is in a contiguous block at the end.
2721 if (did_compact()) {
2722 CardGeneration::shrink(bytes);
2723 }
2724 }
2725
2726 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2727 assert_locked_or_safepoint(Heap_lock);
2728 }
2729
2730 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2731 assert_locked_or_safepoint(Heap_lock);
2732 assert_lock_strong(freelistLock());
2733 log_trace(gc)("Shrinking of CMS not yet implemented");
2734 return;
2735 }
2736
2737
2738 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2739 // phases.
2740 class CMSPhaseAccounting: public StackObj {
2741 public:
2742 CMSPhaseAccounting(CMSCollector *collector,
2743 const char *title);
2744 ~CMSPhaseAccounting();
2745
2746 private:
2747 CMSCollector *_collector;
2748 const char *_title;
2749 GCTraceConcTime(Info, gc) _trace_time;
2750
2751 public:
2752 // Not MT-safe; so do not pass around these StackObj's
2753 // where they may be accessed by other threads.
2754 double wallclock_millis() {
2755 return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time());
2756 }
2757 };
2758
2759 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2760 const char *title) :
2761 _collector(collector), _title(title), _trace_time(title) {
2762
2763 _collector->resetYields();
2764 _collector->resetTimer();
2765 _collector->startTimer();
2766 _collector->gc_timer_cm()->register_gc_concurrent_start(title);
2767 }
2768
2769 CMSPhaseAccounting::~CMSPhaseAccounting() {
2770 _collector->gc_timer_cm()->register_gc_concurrent_end();
2771 _collector->stopTimer();
2772 log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_seconds(_collector->timerTicks()));
2773 log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields());
2774 }
2775
2776 // CMS work
2777
2778 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2779 class CMSParMarkTask : public AbstractGangTask {
2780 protected:
2781 CMSCollector* _collector;
2782 uint _n_workers;
2783 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2784 AbstractGangTask(name),
2785 _collector(collector),
2786 _n_workers(n_workers) {}
2787 // Work method in support of parallel rescan ... of young gen spaces
2788 void do_young_space_rescan(OopsInGenClosure* cl,
2789 ContiguousSpace* space,
2790 HeapWord** chunk_array, size_t chunk_top);
2791 void work_on_young_gen_roots(OopsInGenClosure* cl);
2792 };
2793
2794 // Parallel initial mark task
2795 class CMSParInitialMarkTask: public CMSParMarkTask {
2796 StrongRootsScope* _strong_roots_scope;
2797 public:
2798 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2799 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2800 _strong_roots_scope(strong_roots_scope) {}
2801 void work(uint worker_id);
2802 };
2803
2804 // Checkpoint the roots into this generation from outside
2805 // this generation. [Note this initial checkpoint need only
2806 // be approximate -- we'll do a catch up phase subsequently.]
2807 void CMSCollector::checkpointRootsInitial() {
2808 assert(_collectorState == InitialMarking, "Wrong collector state");
2809 check_correct_thread_executing();
2810 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
2811
2812 save_heap_summary();
2813 report_heap_summary(GCWhen::BeforeGC);
2814
2815 ReferenceProcessor* rp = ref_processor();
2816 assert(_restart_addr == NULL, "Control point invariant");
2817 {
2818 // acquire locks for subsequent manipulations
2819 MutexLockerEx x(bitMapLock(),
2820 Mutex::_no_safepoint_check_flag);
2821 checkpointRootsInitialWork();
2822 // enable ("weak") refs discovery
2823 rp->enable_discovery();
2824 _collectorState = Marking;
2825 }
2826 }
2827
2828 void CMSCollector::checkpointRootsInitialWork() {
2829 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2830 assert(_collectorState == InitialMarking, "just checking");
2831
2832 // Already have locks.
2833 assert_lock_strong(bitMapLock());
2834 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2835
2836 // Setup the verification and class unloading state for this
2837 // CMS collection cycle.
2838 setup_cms_unloading_and_verification_state();
2839
2840 GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm);
2841
2842 // Reset all the PLAB chunk arrays if necessary.
2843 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2844 reset_survivor_plab_arrays();
2845 }
2846
2847 ResourceMark rm;
2848 HandleMark hm;
2849
2850 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2851 CMSHeap* heap = CMSHeap::heap();
2852
2853 verify_work_stacks_empty();
2854 verify_overflow_empty();
2855
2856 heap->ensure_parsability(false); // fill TLABs, but no need to retire them
2857 // Update the saved marks which may affect the root scans.
2858 heap->save_marks();
2859
2860 // weak reference processing has not started yet.
2861 ref_processor()->set_enqueuing_is_done(false);
2862
2863 // Need to remember all newly created CLDs,
2864 // so that we can guarantee that the remark finds them.
2865 ClassLoaderDataGraph::remember_new_clds(true);
2866
2867 // Whenever a CLD is found, it will be claimed before proceeding to mark
2868 // the klasses. The claimed marks need to be cleared before marking starts.
2869 ClassLoaderDataGraph::clear_claimed_marks();
2870
2871 print_eden_and_survivor_chunk_arrays();
2872
2873 {
2874 #if COMPILER2_OR_JVMCI
2875 DerivedPointerTableDeactivate dpt_deact;
2876 #endif
2877 if (CMSParallelInitialMarkEnabled) {
2878 // The parallel version.
2879 WorkGang* workers = heap->workers();
2880 assert(workers != NULL, "Need parallel worker threads.");
2881 uint n_workers = workers->active_workers();
2882
2883 StrongRootsScope srs(n_workers);
2884
2885 CMSParInitialMarkTask tsk(this, &srs, n_workers);
2886 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2887 // If the total workers is greater than 1, then multiple workers
2888 // may be used at some time and the initialization has been set
2889 // such that the single threaded path cannot be used.
2890 if (workers->total_workers() > 1) {
2891 workers->run_task(&tsk);
2892 } else {
2893 tsk.work(0);
2894 }
2895 } else {
2896 // The serial version.
2897 CLDToOopClosure cld_closure(¬Older, true);
2898 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2899
2900 StrongRootsScope srs(1);
2901
2902 heap->cms_process_roots(&srs,
2903 true, // young gen as roots
2904 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2905 should_unload_classes(),
2906 ¬Older,
2907 &cld_closure);
2908 }
2909 }
2910
2911 // Clear mod-union table; it will be dirtied in the prologue of
2912 // CMS generation per each young generation collection.
2913
2914 assert(_modUnionTable.isAllClear(),
2915 "Was cleared in most recent final checkpoint phase"
2916 " or no bits are set in the gc_prologue before the start of the next "
2917 "subsequent marking phase.");
2918
2919 assert(_ct->cld_rem_set()->mod_union_is_clear(), "Must be");
2920
2921 // Save the end of the used_region of the constituent generations
2922 // to be used to limit the extent of sweep in each generation.
2923 save_sweep_limits();
2924 verify_overflow_empty();
2925 }
2926
2927 bool CMSCollector::markFromRoots() {
2928 // we might be tempted to assert that:
2929 // assert(!SafepointSynchronize::is_at_safepoint(),
2930 // "inconsistent argument?");
2931 // However that wouldn't be right, because it's possible that
2932 // a safepoint is indeed in progress as a young generation
2933 // stop-the-world GC happens even as we mark in this generation.
2934 assert(_collectorState == Marking, "inconsistent state?");
2935 check_correct_thread_executing();
2936 verify_overflow_empty();
2937
2938 // Weak ref discovery note: We may be discovering weak
2939 // refs in this generation concurrent (but interleaved) with
2940 // weak ref discovery by the young generation collector.
2941
2942 CMSTokenSyncWithLocks ts(true, bitMapLock());
2943 GCTraceCPUTime tcpu;
2944 CMSPhaseAccounting pa(this, "Concurrent Mark");
2945 bool res = markFromRootsWork();
2946 if (res) {
2947 _collectorState = Precleaning;
2948 } else { // We failed and a foreground collection wants to take over
2949 assert(_foregroundGCIsActive, "internal state inconsistency");
2950 assert(_restart_addr == NULL, "foreground will restart from scratch");
2951 log_debug(gc)("bailing out to foreground collection");
2952 }
2953 verify_overflow_empty();
2954 return res;
2955 }
2956
2957 bool CMSCollector::markFromRootsWork() {
2958 // iterate over marked bits in bit map, doing a full scan and mark
2959 // from these roots using the following algorithm:
2960 // . if oop is to the right of the current scan pointer,
2961 // mark corresponding bit (we'll process it later)
2962 // . else (oop is to left of current scan pointer)
2963 // push oop on marking stack
2964 // . drain the marking stack
2965
2966 // Note that when we do a marking step we need to hold the
2967 // bit map lock -- recall that direct allocation (by mutators)
2968 // and promotion (by the young generation collector) is also
2969 // marking the bit map. [the so-called allocate live policy.]
2970 // Because the implementation of bit map marking is not
2971 // robust wrt simultaneous marking of bits in the same word,
2972 // we need to make sure that there is no such interference
2973 // between concurrent such updates.
2974
2975 // already have locks
2976 assert_lock_strong(bitMapLock());
2977
2978 verify_work_stacks_empty();
2979 verify_overflow_empty();
2980 bool result = false;
2981 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2982 result = do_marking_mt();
2983 } else {
2984 result = do_marking_st();
2985 }
2986 return result;
2987 }
2988
2989 // Forward decl
2990 class CMSConcMarkingTask;
2991
2992 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
2993 CMSCollector* _collector;
2994 CMSConcMarkingTask* _task;
2995 public:
2996 virtual void yield();
2997
2998 // "n_threads" is the number of threads to be terminated.
2999 // "queue_set" is a set of work queues of other threads.
3000 // "collector" is the CMS collector associated with this task terminator.
3001 // "yield" indicates whether we need the gang as a whole to yield.
3002 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3003 ParallelTaskTerminator(n_threads, queue_set),
3004 _collector(collector) { }
3005
3006 void set_task(CMSConcMarkingTask* task) {
3007 _task = task;
3008 }
3009 };
3010
3011 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3012 CMSConcMarkingTask* _task;
3013 public:
3014 bool should_exit_termination();
3015 void set_task(CMSConcMarkingTask* task) {
3016 _task = task;
3017 }
3018 };
3019
3020 // MT Concurrent Marking Task
3021 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3022 CMSCollector* _collector;
3023 uint _n_workers; // requested/desired # workers
3024 bool _result;
3025 CompactibleFreeListSpace* _cms_space;
3026 char _pad_front[64]; // padding to ...
3027 HeapWord* volatile _global_finger; // ... avoid sharing cache line
3028 char _pad_back[64];
3029 HeapWord* _restart_addr;
3030
3031 // Exposed here for yielding support
3032 Mutex* const _bit_map_lock;
3033
3034 // The per thread work queues, available here for stealing
3035 OopTaskQueueSet* _task_queues;
3036
3037 // Termination (and yielding) support
3038 CMSConcMarkingTerminator _term;
3039 CMSConcMarkingTerminatorTerminator _term_term;
3040
3041 public:
3042 CMSConcMarkingTask(CMSCollector* collector,
3043 CompactibleFreeListSpace* cms_space,
3044 YieldingFlexibleWorkGang* workers,
3045 OopTaskQueueSet* task_queues):
3046 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3047 _collector(collector),
3048 _cms_space(cms_space),
3049 _n_workers(0), _result(true),
3050 _task_queues(task_queues),
3051 _term(_n_workers, task_queues, _collector),
3052 _bit_map_lock(collector->bitMapLock())
3053 {
3054 _requested_size = _n_workers;
3055 _term.set_task(this);
3056 _term_term.set_task(this);
3057 _restart_addr = _global_finger = _cms_space->bottom();
3058 }
3059
3060
3061 OopTaskQueueSet* task_queues() { return _task_queues; }
3062
3063 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3064
3065 HeapWord* volatile* global_finger_addr() { return &_global_finger; }
3066
3067 CMSConcMarkingTerminator* terminator() { return &_term; }
3068
3069 virtual void set_for_termination(uint active_workers) {
3070 terminator()->reset_for_reuse(active_workers);
3071 }
3072
3073 void work(uint worker_id);
3074 bool should_yield() {
3075 return ConcurrentMarkSweepThread::should_yield()
3076 && !_collector->foregroundGCIsActive();
3077 }
3078
3079 virtual void coordinator_yield(); // stuff done by coordinator
3080 bool result() { return _result; }
3081
3082 void reset(HeapWord* ra) {
3083 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3084 _restart_addr = _global_finger = ra;
3085 _term.reset_for_reuse();
3086 }
3087
3088 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3089 OopTaskQueue* work_q);
3090
3091 private:
3092 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3093 void do_work_steal(int i);
3094 void bump_global_finger(HeapWord* f);
3095 };
3096
3097 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3098 assert(_task != NULL, "Error");
3099 return _task->yielding();
3100 // Note that we do not need the disjunct || _task->should_yield() above
3101 // because we want terminating threads to yield only if the task
3102 // is already in the midst of yielding, which happens only after at least one
3103 // thread has yielded.
3104 }
3105
3106 void CMSConcMarkingTerminator::yield() {
3107 if (_task->should_yield()) {
3108 _task->yield();
3109 } else {
3110 ParallelTaskTerminator::yield();
3111 }
3112 }
3113
3114 ////////////////////////////////////////////////////////////////
3115 // Concurrent Marking Algorithm Sketch
3116 ////////////////////////////////////////////////////////////////
3117 // Until all tasks exhausted (both spaces):
3118 // -- claim next available chunk
3119 // -- bump global finger via CAS
3120 // -- find first object that starts in this chunk
3121 // and start scanning bitmap from that position
3122 // -- scan marked objects for oops
3123 // -- CAS-mark target, and if successful:
3124 // . if target oop is above global finger (volatile read)
3125 // nothing to do
3126 // . if target oop is in chunk and above local finger
3127 // then nothing to do
3128 // . else push on work-queue
3129 // -- Deal with possible overflow issues:
3130 // . local work-queue overflow causes stuff to be pushed on
3131 // global (common) overflow queue
3132 // . always first empty local work queue
3133 // . then get a batch of oops from global work queue if any
3134 // . then do work stealing
3135 // -- When all tasks claimed (both spaces)
3136 // and local work queue empty,
3137 // then in a loop do:
3138 // . check global overflow stack; steal a batch of oops and trace
3139 // . try to steal from other threads oif GOS is empty
3140 // . if neither is available, offer termination
3141 // -- Terminate and return result
3142 //
3143 void CMSConcMarkingTask::work(uint worker_id) {
3144 elapsedTimer _timer;
3145 ResourceMark rm;
3146 HandleMark hm;
3147
3148 DEBUG_ONLY(_collector->verify_overflow_empty();)
3149
3150 // Before we begin work, our work queue should be empty
3151 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3152 // Scan the bitmap covering _cms_space, tracing through grey objects.
3153 _timer.start();
3154 do_scan_and_mark(worker_id, _cms_space);
3155 _timer.stop();
3156 log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3157
3158 // ... do work stealing
3159 _timer.reset();
3160 _timer.start();
3161 do_work_steal(worker_id);
3162 _timer.stop();
3163 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3164 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3165 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3166 // Note that under the current task protocol, the
3167 // following assertion is true even of the spaces
3168 // expanded since the completion of the concurrent
3169 // marking. XXX This will likely change under a strict
3170 // ABORT semantics.
3171 // After perm removal the comparison was changed to
3172 // greater than or equal to from strictly greater than.
3173 // Before perm removal the highest address sweep would
3174 // have been at the end of perm gen but now is at the
3175 // end of the tenured gen.
3176 assert(_global_finger >= _cms_space->end(),
3177 "All tasks have been completed");
3178 DEBUG_ONLY(_collector->verify_overflow_empty();)
3179 }
3180
3181 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3182 HeapWord* read = _global_finger;
3183 HeapWord* cur = read;
3184 while (f > read) {
3185 cur = read;
3186 read = Atomic::cmpxchg(f, &_global_finger, cur);
3187 if (cur == read) {
3188 // our cas succeeded
3189 assert(_global_finger >= f, "protocol consistency");
3190 break;
3191 }
3192 }
3193 }
3194
3195 // This is really inefficient, and should be redone by
3196 // using (not yet available) block-read and -write interfaces to the
3197 // stack and the work_queue. XXX FIX ME !!!
3198 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3199 OopTaskQueue* work_q) {
3200 // Fast lock-free check
3201 if (ovflw_stk->length() == 0) {
3202 return false;
3203 }
3204 assert(work_q->size() == 0, "Shouldn't steal");
3205 MutexLockerEx ml(ovflw_stk->par_lock(),
3206 Mutex::_no_safepoint_check_flag);
3207 // Grab up to 1/4 the size of the work queue
3208 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3209 (size_t)ParGCDesiredObjsFromOverflowList);
3210 num = MIN2(num, ovflw_stk->length());
3211 for (int i = (int) num; i > 0; i--) {
3212 oop cur = ovflw_stk->pop();
3213 assert(cur != NULL, "Counted wrong?");
3214 work_q->push(cur);
3215 }
3216 return num > 0;
3217 }
3218
3219 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3220 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3221 int n_tasks = pst->n_tasks();
3222 // We allow that there may be no tasks to do here because
3223 // we are restarting after a stack overflow.
3224 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3225 uint nth_task = 0;
3226
3227 HeapWord* aligned_start = sp->bottom();
3228 if (sp->used_region().contains(_restart_addr)) {
3229 // Align down to a card boundary for the start of 0th task
3230 // for this space.
3231 aligned_start = align_down(_restart_addr, CardTable::card_size);
3232 }
3233
3234 size_t chunk_size = sp->marking_task_size();
3235 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3236 // Having claimed the nth task in this space,
3237 // compute the chunk that it corresponds to:
3238 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3239 aligned_start + (nth_task+1)*chunk_size);
3240 // Try and bump the global finger via a CAS;
3241 // note that we need to do the global finger bump
3242 // _before_ taking the intersection below, because
3243 // the task corresponding to that region will be
3244 // deemed done even if the used_region() expands
3245 // because of allocation -- as it almost certainly will
3246 // during start-up while the threads yield in the
3247 // closure below.
3248 HeapWord* finger = span.end();
3249 bump_global_finger(finger); // atomically
3250 // There are null tasks here corresponding to chunks
3251 // beyond the "top" address of the space.
3252 span = span.intersection(sp->used_region());
3253 if (!span.is_empty()) { // Non-null task
3254 HeapWord* prev_obj;
3255 assert(!span.contains(_restart_addr) || nth_task == 0,
3256 "Inconsistency");
3257 if (nth_task == 0) {
3258 // For the 0th task, we'll not need to compute a block_start.
3259 if (span.contains(_restart_addr)) {
3260 // In the case of a restart because of stack overflow,
3261 // we might additionally skip a chunk prefix.
3262 prev_obj = _restart_addr;
3263 } else {
3264 prev_obj = span.start();
3265 }
3266 } else {
3267 // We want to skip the first object because
3268 // the protocol is to scan any object in its entirety
3269 // that _starts_ in this span; a fortiori, any
3270 // object starting in an earlier span is scanned
3271 // as part of an earlier claimed task.
3272 // Below we use the "careful" version of block_start
3273 // so we do not try to navigate uninitialized objects.
3274 prev_obj = sp->block_start_careful(span.start());
3275 // Below we use a variant of block_size that uses the
3276 // Printezis bits to avoid waiting for allocated
3277 // objects to become initialized/parsable.
3278 while (prev_obj < span.start()) {
3279 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3280 if (sz > 0) {
3281 prev_obj += sz;
3282 } else {
3283 // In this case we may end up doing a bit of redundant
3284 // scanning, but that appears unavoidable, short of
3285 // locking the free list locks; see bug 6324141.
3286 break;
3287 }
3288 }
3289 }
3290 if (prev_obj < span.end()) {
3291 MemRegion my_span = MemRegion(prev_obj, span.end());
3292 // Do the marking work within a non-empty span --
3293 // the last argument to the constructor indicates whether the
3294 // iteration should be incremental with periodic yields.
3295 ParMarkFromRootsClosure cl(this, _collector, my_span,
3296 &_collector->_markBitMap,
3297 work_queue(i),
3298 &_collector->_markStack);
3299 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3300 } // else nothing to do for this task
3301 } // else nothing to do for this task
3302 }
3303 // We'd be tempted to assert here that since there are no
3304 // more tasks left to claim in this space, the global_finger
3305 // must exceed space->top() and a fortiori space->end(). However,
3306 // that would not quite be correct because the bumping of
3307 // global_finger occurs strictly after the claiming of a task,
3308 // so by the time we reach here the global finger may not yet
3309 // have been bumped up by the thread that claimed the last
3310 // task.
3311 pst->all_tasks_completed();
3312 }
3313
3314 class ParConcMarkingClosure: public MetadataAwareOopClosure {
3315 private:
3316 CMSCollector* _collector;
3317 CMSConcMarkingTask* _task;
3318 MemRegion _span;
3319 CMSBitMap* _bit_map;
3320 CMSMarkStack* _overflow_stack;
3321 OopTaskQueue* _work_queue;
3322 protected:
3323 DO_OOP_WORK_DEFN
3324 public:
3325 ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3326 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3327 MetadataAwareOopClosure(collector->ref_processor()),
3328 _collector(collector),
3329 _task(task),
3330 _span(collector->_span),
3331 _work_queue(work_queue),
3332 _bit_map(bit_map),
3333 _overflow_stack(overflow_stack)
3334 { }
3335 virtual void do_oop(oop* p);
3336 virtual void do_oop(narrowOop* p);
3337
3338 void trim_queue(size_t max);
3339 void handle_stack_overflow(HeapWord* lost);
3340 void do_yield_check() {
3341 if (_task->should_yield()) {
3342 _task->yield();
3343 }
3344 }
3345 };
3346
3347 DO_OOP_WORK_IMPL(ParConcMarkingClosure)
3348
3349 // Grey object scanning during work stealing phase --
3350 // the salient assumption here is that any references
3351 // that are in these stolen objects being scanned must
3352 // already have been initialized (else they would not have
3353 // been published), so we do not need to check for
3354 // uninitialized objects before pushing here.
3355 void ParConcMarkingClosure::do_oop(oop obj) {
3356 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3357 HeapWord* addr = (HeapWord*)obj;
3358 // Check if oop points into the CMS generation
3359 // and is not marked
3360 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3361 // a white object ...
3362 // If we manage to "claim" the object, by being the
3363 // first thread to mark it, then we push it on our
3364 // marking stack
3365 if (_bit_map->par_mark(addr)) { // ... now grey
3366 // push on work queue (grey set)
3367 bool simulate_overflow = false;
3368 NOT_PRODUCT(
3369 if (CMSMarkStackOverflowALot &&
3370 _collector->simulate_overflow()) {
3371 // simulate a stack overflow
3372 simulate_overflow = true;
3373 }
3374 )
3375 if (simulate_overflow ||
3376 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3377 // stack overflow
3378 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3379 // We cannot assert that the overflow stack is full because
3380 // it may have been emptied since.
3381 assert(simulate_overflow ||
3382 _work_queue->size() == _work_queue->max_elems(),
3383 "Else push should have succeeded");
3384 handle_stack_overflow(addr);
3385 }
3386 } // Else, some other thread got there first
3387 do_yield_check();
3388 }
3389 }
3390
3391 void ParConcMarkingClosure::do_oop(oop* p) { ParConcMarkingClosure::do_oop_work(p); }
3392 void ParConcMarkingClosure::do_oop(narrowOop* p) { ParConcMarkingClosure::do_oop_work(p); }
3393
3394 void ParConcMarkingClosure::trim_queue(size_t max) {
3395 while (_work_queue->size() > max) {
3396 oop new_oop;
3397 if (_work_queue->pop_local(new_oop)) {
3398 assert(oopDesc::is_oop(new_oop), "Should be an oop");
3399 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3400 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3401 new_oop->oop_iterate(this); // do_oop() above
3402 do_yield_check();
3403 }
3404 }
3405 }
3406
3407 // Upon stack overflow, we discard (part of) the stack,
3408 // remembering the least address amongst those discarded
3409 // in CMSCollector's _restart_address.
3410 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3411 // We need to do this under a mutex to prevent other
3412 // workers from interfering with the work done below.
3413 MutexLockerEx ml(_overflow_stack->par_lock(),
3414 Mutex::_no_safepoint_check_flag);
3415 // Remember the least grey address discarded
3416 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3417 _collector->lower_restart_addr(ra);
3418 _overflow_stack->reset(); // discard stack contents
3419 _overflow_stack->expand(); // expand the stack if possible
3420 }
3421
3422
3423 void CMSConcMarkingTask::do_work_steal(int i) {
3424 OopTaskQueue* work_q = work_queue(i);
3425 oop obj_to_scan;
3426 CMSBitMap* bm = &(_collector->_markBitMap);
3427 CMSMarkStack* ovflw = &(_collector->_markStack);
3428 int* seed = _collector->hash_seed(i);
3429 ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3430 while (true) {
3431 cl.trim_queue(0);
3432 assert(work_q->size() == 0, "Should have been emptied above");
3433 if (get_work_from_overflow_stack(ovflw, work_q)) {
3434 // Can't assert below because the work obtained from the
3435 // overflow stack may already have been stolen from us.
3436 // assert(work_q->size() > 0, "Work from overflow stack");
3437 continue;
3438 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3439 assert(oopDesc::is_oop(obj_to_scan), "Should be an oop");
3440 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3441 obj_to_scan->oop_iterate(&cl);
3442 } else if (terminator()->offer_termination(&_term_term)) {
3443 assert(work_q->size() == 0, "Impossible!");
3444 break;
3445 } else if (yielding() || should_yield()) {
3446 yield();
3447 }
3448 }
3449 }
3450
3451 // This is run by the CMS (coordinator) thread.
3452 void CMSConcMarkingTask::coordinator_yield() {
3453 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3454 "CMS thread should hold CMS token");
3455 // First give up the locks, then yield, then re-lock
3456 // We should probably use a constructor/destructor idiom to
3457 // do this unlock/lock or modify the MutexUnlocker class to
3458 // serve our purpose. XXX
3459 assert_lock_strong(_bit_map_lock);
3460 _bit_map_lock->unlock();
3461 ConcurrentMarkSweepThread::desynchronize(true);
3462 _collector->stopTimer();
3463 _collector->incrementYields();
3464
3465 // It is possible for whichever thread initiated the yield request
3466 // not to get a chance to wake up and take the bitmap lock between
3467 // this thread releasing it and reacquiring it. So, while the
3468 // should_yield() flag is on, let's sleep for a bit to give the
3469 // other thread a chance to wake up. The limit imposed on the number
3470 // of iterations is defensive, to avoid any unforseen circumstances
3471 // putting us into an infinite loop. Since it's always been this
3472 // (coordinator_yield()) method that was observed to cause the
3473 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3474 // which is by default non-zero. For the other seven methods that
3475 // also perform the yield operation, as are using a different
3476 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3477 // can enable the sleeping for those methods too, if necessary.
3478 // See 6442774.
3479 //
3480 // We really need to reconsider the synchronization between the GC
3481 // thread and the yield-requesting threads in the future and we
3482 // should really use wait/notify, which is the recommended
3483 // way of doing this type of interaction. Additionally, we should
3484 // consolidate the eight methods that do the yield operation and they
3485 // are almost identical into one for better maintainability and
3486 // readability. See 6445193.
3487 //
3488 // Tony 2006.06.29
3489 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3490 ConcurrentMarkSweepThread::should_yield() &&
3491 !CMSCollector::foregroundGCIsActive(); ++i) {
3492 os::sleep(Thread::current(), 1, false);
3493 }
3494
3495 ConcurrentMarkSweepThread::synchronize(true);
3496 _bit_map_lock->lock_without_safepoint_check();
3497 _collector->startTimer();
3498 }
3499
3500 bool CMSCollector::do_marking_mt() {
3501 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3502 uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3503 conc_workers()->active_workers(),
3504 Threads::number_of_non_daemon_threads());
3505 num_workers = conc_workers()->update_active_workers(num_workers);
3506 log_info(gc,task)("Using %u workers of %u for marking", num_workers, conc_workers()->total_workers());
3507
3508 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3509
3510 CMSConcMarkingTask tsk(this,
3511 cms_space,
3512 conc_workers(),
3513 task_queues());
3514
3515 // Since the actual number of workers we get may be different
3516 // from the number we requested above, do we need to do anything different
3517 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3518 // class?? XXX
3519 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3520
3521 // Refs discovery is already non-atomic.
3522 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3523 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3524 conc_workers()->start_task(&tsk);
3525 while (tsk.yielded()) {
3526 tsk.coordinator_yield();
3527 conc_workers()->continue_task(&tsk);
3528 }
3529 // If the task was aborted, _restart_addr will be non-NULL
3530 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3531 while (_restart_addr != NULL) {
3532 // XXX For now we do not make use of ABORTED state and have not
3533 // yet implemented the right abort semantics (even in the original
3534 // single-threaded CMS case). That needs some more investigation
3535 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3536 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3537 // If _restart_addr is non-NULL, a marking stack overflow
3538 // occurred; we need to do a fresh marking iteration from the
3539 // indicated restart address.
3540 if (_foregroundGCIsActive) {
3541 // We may be running into repeated stack overflows, having
3542 // reached the limit of the stack size, while making very
3543 // slow forward progress. It may be best to bail out and
3544 // let the foreground collector do its job.
3545 // Clear _restart_addr, so that foreground GC
3546 // works from scratch. This avoids the headache of
3547 // a "rescan" which would otherwise be needed because
3548 // of the dirty mod union table & card table.
3549 _restart_addr = NULL;
3550 return false;
3551 }
3552 // Adjust the task to restart from _restart_addr
3553 tsk.reset(_restart_addr);
3554 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3555 _restart_addr);
3556 _restart_addr = NULL;
3557 // Get the workers going again
3558 conc_workers()->start_task(&tsk);
3559 while (tsk.yielded()) {
3560 tsk.coordinator_yield();
3561 conc_workers()->continue_task(&tsk);
3562 }
3563 }
3564 assert(tsk.completed(), "Inconsistency");
3565 assert(tsk.result() == true, "Inconsistency");
3566 return true;
3567 }
3568
3569 bool CMSCollector::do_marking_st() {
3570 ResourceMark rm;
3571 HandleMark hm;
3572
3573 // Temporarily make refs discovery single threaded (non-MT)
3574 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3575 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3576 &_markStack, CMSYield);
3577 // the last argument to iterate indicates whether the iteration
3578 // should be incremental with periodic yields.
3579 _markBitMap.iterate(&markFromRootsClosure);
3580 // If _restart_addr is non-NULL, a marking stack overflow
3581 // occurred; we need to do a fresh iteration from the
3582 // indicated restart address.
3583 while (_restart_addr != NULL) {
3584 if (_foregroundGCIsActive) {
3585 // We may be running into repeated stack overflows, having
3586 // reached the limit of the stack size, while making very
3587 // slow forward progress. It may be best to bail out and
3588 // let the foreground collector do its job.
3589 // Clear _restart_addr, so that foreground GC
3590 // works from scratch. This avoids the headache of
3591 // a "rescan" which would otherwise be needed because
3592 // of the dirty mod union table & card table.
3593 _restart_addr = NULL;
3594 return false; // indicating failure to complete marking
3595 }
3596 // Deal with stack overflow:
3597 // we restart marking from _restart_addr
3598 HeapWord* ra = _restart_addr;
3599 markFromRootsClosure.reset(ra);
3600 _restart_addr = NULL;
3601 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3602 }
3603 return true;
3604 }
3605
3606 void CMSCollector::preclean() {
3607 check_correct_thread_executing();
3608 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3609 verify_work_stacks_empty();
3610 verify_overflow_empty();
3611 _abort_preclean = false;
3612 if (CMSPrecleaningEnabled) {
3613 if (!CMSEdenChunksRecordAlways) {
3614 _eden_chunk_index = 0;
3615 }
3616 size_t used = get_eden_used();
3617 size_t capacity = get_eden_capacity();
3618 // Don't start sampling unless we will get sufficiently
3619 // many samples.
3620 if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100)
3621 * CMSScheduleRemarkEdenPenetration)) {
3622 _start_sampling = true;
3623 } else {
3624 _start_sampling = false;
3625 }
3626 GCTraceCPUTime tcpu;
3627 CMSPhaseAccounting pa(this, "Concurrent Preclean");
3628 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3629 }
3630 CMSTokenSync x(true); // is cms thread
3631 if (CMSPrecleaningEnabled) {
3632 sample_eden();
3633 _collectorState = AbortablePreclean;
3634 } else {
3635 _collectorState = FinalMarking;
3636 }
3637 verify_work_stacks_empty();
3638 verify_overflow_empty();
3639 }
3640
3641 // Try and schedule the remark such that young gen
3642 // occupancy is CMSScheduleRemarkEdenPenetration %.
3643 void CMSCollector::abortable_preclean() {
3644 check_correct_thread_executing();
3645 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3646 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3647
3648 // If Eden's current occupancy is below this threshold,
3649 // immediately schedule the remark; else preclean
3650 // past the next scavenge in an effort to
3651 // schedule the pause as described above. By choosing
3652 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3653 // we will never do an actual abortable preclean cycle.
3654 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3655 GCTraceCPUTime tcpu;
3656 CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean");
3657 // We need more smarts in the abortable preclean
3658 // loop below to deal with cases where allocation
3659 // in young gen is very very slow, and our precleaning
3660 // is running a losing race against a horde of
3661 // mutators intent on flooding us with CMS updates
3662 // (dirty cards).
3663 // One, admittedly dumb, strategy is to give up
3664 // after a certain number of abortable precleaning loops
3665 // or after a certain maximum time. We want to make
3666 // this smarter in the next iteration.
3667 // XXX FIX ME!!! YSR
3668 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3669 while (!(should_abort_preclean() ||
3670 ConcurrentMarkSweepThread::cmst()->should_terminate())) {
3671 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3672 cumworkdone += workdone;
3673 loops++;
3674 // Voluntarily terminate abortable preclean phase if we have
3675 // been at it for too long.
3676 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3677 loops >= CMSMaxAbortablePrecleanLoops) {
3678 log_debug(gc)(" CMS: abort preclean due to loops ");
3679 break;
3680 }
3681 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3682 log_debug(gc)(" CMS: abort preclean due to time ");
3683 break;
3684 }
3685 // If we are doing little work each iteration, we should
3686 // take a short break.
3687 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3688 // Sleep for some time, waiting for work to accumulate
3689 stopTimer();
3690 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3691 startTimer();
3692 waited++;
3693 }
3694 }
3695 log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3696 loops, waited, cumworkdone);
3697 }
3698 CMSTokenSync x(true); // is cms thread
3699 if (_collectorState != Idling) {
3700 assert(_collectorState == AbortablePreclean,
3701 "Spontaneous state transition?");
3702 _collectorState = FinalMarking;
3703 } // Else, a foreground collection completed this CMS cycle.
3704 return;
3705 }
3706
3707 // Respond to an Eden sampling opportunity
3708 void CMSCollector::sample_eden() {
3709 // Make sure a young gc cannot sneak in between our
3710 // reading and recording of a sample.
3711 assert(Thread::current()->is_ConcurrentGC_thread(),
3712 "Only the cms thread may collect Eden samples");
3713 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3714 "Should collect samples while holding CMS token");
3715 if (!_start_sampling) {
3716 return;
3717 }
3718 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3719 // is populated by the young generation.
3720 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3721 if (_eden_chunk_index < _eden_chunk_capacity) {
3722 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3723 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3724 "Unexpected state of Eden");
3725 // We'd like to check that what we just sampled is an oop-start address;
3726 // however, we cannot do that here since the object may not yet have been
3727 // initialized. So we'll instead do the check when we _use_ this sample
3728 // later.
3729 if (_eden_chunk_index == 0 ||
3730 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3731 _eden_chunk_array[_eden_chunk_index-1])
3732 >= CMSSamplingGrain)) {
3733 _eden_chunk_index++; // commit sample
3734 }
3735 }
3736 }
3737 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3738 size_t used = get_eden_used();
3739 size_t capacity = get_eden_capacity();
3740 assert(used <= capacity, "Unexpected state of Eden");
3741 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3742 _abort_preclean = true;
3743 }
3744 }
3745 }
3746
3747
3748 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3749 assert(_collectorState == Precleaning ||
3750 _collectorState == AbortablePreclean, "incorrect state");
3751 ResourceMark rm;
3752 HandleMark hm;
3753
3754 // Precleaning is currently not MT but the reference processor
3755 // may be set for MT. Disable it temporarily here.
3756 ReferenceProcessor* rp = ref_processor();
3757 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3758
3759 // Do one pass of scrubbing the discovered reference lists
3760 // to remove any reference objects with strongly-reachable
3761 // referents.
3762 if (clean_refs) {
3763 CMSPrecleanRefsYieldClosure yield_cl(this);
3764 assert(rp->span().equals(_span), "Spans should be equal");
3765 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3766 &_markStack, true /* preclean */);
3767 CMSDrainMarkingStackClosure complete_trace(this,
3768 _span, &_markBitMap, &_markStack,
3769 &keep_alive, true /* preclean */);
3770
3771 // We don't want this step to interfere with a young
3772 // collection because we don't want to take CPU
3773 // or memory bandwidth away from the young GC threads
3774 // (which may be as many as there are CPUs).
3775 // Note that we don't need to protect ourselves from
3776 // interference with mutators because they can't
3777 // manipulate the discovered reference lists nor affect
3778 // the computed reachability of the referents, the
3779 // only properties manipulated by the precleaning
3780 // of these reference lists.
3781 stopTimer();
3782 CMSTokenSyncWithLocks x(true /* is cms thread */,
3783 bitMapLock());
3784 startTimer();
3785 sample_eden();
3786
3787 // The following will yield to allow foreground
3788 // collection to proceed promptly. XXX YSR:
3789 // The code in this method may need further
3790 // tweaking for better performance and some restructuring
3791 // for cleaner interfaces.
3792 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3793 rp->preclean_discovered_references(
3794 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3795 gc_timer);
3796 }
3797
3798 if (clean_survivor) { // preclean the active survivor space(s)
3799 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3800 &_markBitMap, &_modUnionTable,
3801 &_markStack, true /* precleaning phase */);
3802 stopTimer();
3803 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3804 bitMapLock());
3805 startTimer();
3806 unsigned int before_count =
3807 CMSHeap::heap()->total_collections();
3808 SurvivorSpacePrecleanClosure
3809 sss_cl(this, _span, &_markBitMap, &_markStack,
3810 &pam_cl, before_count, CMSYield);
3811 _young_gen->from()->object_iterate_careful(&sss_cl);
3812 _young_gen->to()->object_iterate_careful(&sss_cl);
3813 }
3814 MarkRefsIntoAndScanClosure
3815 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3816 &_markStack, this, CMSYield,
3817 true /* precleaning phase */);
3818 // CAUTION: The following closure has persistent state that may need to
3819 // be reset upon a decrease in the sequence of addresses it
3820 // processes.
3821 ScanMarkedObjectsAgainCarefullyClosure
3822 smoac_cl(this, _span,
3823 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3824
3825 // Preclean dirty cards in ModUnionTable and CardTable using
3826 // appropriate convergence criterion;
3827 // repeat CMSPrecleanIter times unless we find that
3828 // we are losing.
3829 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3830 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3831 "Bad convergence multiplier");
3832 assert(CMSPrecleanThreshold >= 100,
3833 "Unreasonably low CMSPrecleanThreshold");
3834
3835 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3836 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3837 numIter < CMSPrecleanIter;
3838 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3839 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3840 log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3841 // Either there are very few dirty cards, so re-mark
3842 // pause will be small anyway, or our pre-cleaning isn't
3843 // that much faster than the rate at which cards are being
3844 // dirtied, so we might as well stop and re-mark since
3845 // precleaning won't improve our re-mark time by much.
3846 if (curNumCards <= CMSPrecleanThreshold ||
3847 (numIter > 0 &&
3848 (curNumCards * CMSPrecleanDenominator >
3849 lastNumCards * CMSPrecleanNumerator))) {
3850 numIter++;
3851 cumNumCards += curNumCards;
3852 break;
3853 }
3854 }
3855
3856 preclean_cld(&mrias_cl, _cmsGen->freelistLock());
3857
3858 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3859 cumNumCards += curNumCards;
3860 log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3861 curNumCards, cumNumCards, numIter);
3862 return cumNumCards; // as a measure of useful work done
3863 }
3864
3865 // PRECLEANING NOTES:
3866 // Precleaning involves:
3867 // . reading the bits of the modUnionTable and clearing the set bits.
3868 // . For the cards corresponding to the set bits, we scan the
3869 // objects on those cards. This means we need the free_list_lock
3870 // so that we can safely iterate over the CMS space when scanning
3871 // for oops.
3872 // . When we scan the objects, we'll be both reading and setting
3873 // marks in the marking bit map, so we'll need the marking bit map.
3874 // . For protecting _collector_state transitions, we take the CGC_lock.
3875 // Note that any races in the reading of of card table entries by the
3876 // CMS thread on the one hand and the clearing of those entries by the
3877 // VM thread or the setting of those entries by the mutator threads on the
3878 // other are quite benign. However, for efficiency it makes sense to keep
3879 // the VM thread from racing with the CMS thread while the latter is
3880 // dirty card info to the modUnionTable. We therefore also use the
3881 // CGC_lock to protect the reading of the card table and the mod union
3882 // table by the CM thread.
3883 // . We run concurrently with mutator updates, so scanning
3884 // needs to be done carefully -- we should not try to scan
3885 // potentially uninitialized objects.
3886 //
3887 // Locking strategy: While holding the CGC_lock, we scan over and
3888 // reset a maximal dirty range of the mod union / card tables, then lock
3889 // the free_list_lock and bitmap lock to do a full marking, then
3890 // release these locks; and repeat the cycle. This allows for a
3891 // certain amount of fairness in the sharing of these locks between
3892 // the CMS collector on the one hand, and the VM thread and the
3893 // mutators on the other.
3894
3895 // NOTE: preclean_mod_union_table() and preclean_card_table()
3896 // further below are largely identical; if you need to modify
3897 // one of these methods, please check the other method too.
3898
3899 size_t CMSCollector::preclean_mod_union_table(
3900 ConcurrentMarkSweepGeneration* old_gen,
3901 ScanMarkedObjectsAgainCarefullyClosure* cl) {
3902 verify_work_stacks_empty();
3903 verify_overflow_empty();
3904
3905 // strategy: starting with the first card, accumulate contiguous
3906 // ranges of dirty cards; clear these cards, then scan the region
3907 // covered by these cards.
3908
3909 // Since all of the MUT is committed ahead, we can just use
3910 // that, in case the generations expand while we are precleaning.
3911 // It might also be fine to just use the committed part of the
3912 // generation, but we might potentially miss cards when the
3913 // generation is rapidly expanding while we are in the midst
3914 // of precleaning.
3915 HeapWord* startAddr = old_gen->reserved().start();
3916 HeapWord* endAddr = old_gen->reserved().end();
3917
3918 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
3919
3920 size_t numDirtyCards, cumNumDirtyCards;
3921 HeapWord *nextAddr, *lastAddr;
3922 for (cumNumDirtyCards = numDirtyCards = 0,
3923 nextAddr = lastAddr = startAddr;
3924 nextAddr < endAddr;
3925 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3926
3927 ResourceMark rm;
3928 HandleMark hm;
3929
3930 MemRegion dirtyRegion;
3931 {
3932 stopTimer();
3933 // Potential yield point
3934 CMSTokenSync ts(true);
3935 startTimer();
3936 sample_eden();
3937 // Get dirty region starting at nextOffset (inclusive),
3938 // simultaneously clearing it.
3939 dirtyRegion =
3940 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3941 assert(dirtyRegion.start() >= nextAddr,
3942 "returned region inconsistent?");
3943 }
3944 // Remember where the next search should begin.
3945 // The returned region (if non-empty) is a right open interval,
3946 // so lastOffset is obtained from the right end of that
3947 // interval.
3948 lastAddr = dirtyRegion.end();
3949 // Should do something more transparent and less hacky XXX
3950 numDirtyCards =
3951 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
3952
3953 // We'll scan the cards in the dirty region (with periodic
3954 // yields for foreground GC as needed).
3955 if (!dirtyRegion.is_empty()) {
3956 assert(numDirtyCards > 0, "consistency check");
3957 HeapWord* stop_point = NULL;
3958 stopTimer();
3959 // Potential yield point
3960 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
3961 bitMapLock());
3962 startTimer();
3963 {
3964 verify_work_stacks_empty();
3965 verify_overflow_empty();
3966 sample_eden();
3967 stop_point =
3968 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
3969 }
3970 if (stop_point != NULL) {
3971 // The careful iteration stopped early either because it found an
3972 // uninitialized object, or because we were in the midst of an
3973 // "abortable preclean", which should now be aborted. Redirty
3974 // the bits corresponding to the partially-scanned or unscanned
3975 // cards. We'll either restart at the next block boundary or
3976 // abort the preclean.
3977 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
3978 "Should only be AbortablePreclean.");
3979 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
3980 if (should_abort_preclean()) {
3981 break; // out of preclean loop
3982 } else {
3983 // Compute the next address at which preclean should pick up;
3984 // might need bitMapLock in order to read P-bits.
3985 lastAddr = next_card_start_after_block(stop_point);
3986 }
3987 }
3988 } else {
3989 assert(lastAddr == endAddr, "consistency check");
3990 assert(numDirtyCards == 0, "consistency check");
3991 break;
3992 }
3993 }
3994 verify_work_stacks_empty();
3995 verify_overflow_empty();
3996 return cumNumDirtyCards;
3997 }
3998
3999 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4000 // below are largely identical; if you need to modify
4001 // one of these methods, please check the other method too.
4002
4003 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
4004 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4005 // strategy: it's similar to precleamModUnionTable above, in that
4006 // we accumulate contiguous ranges of dirty cards, mark these cards
4007 // precleaned, then scan the region covered by these cards.
4008 HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high());
4009 HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4010
4011 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4012
4013 size_t numDirtyCards, cumNumDirtyCards;
4014 HeapWord *lastAddr, *nextAddr;
4015
4016 for (cumNumDirtyCards = numDirtyCards = 0,
4017 nextAddr = lastAddr = startAddr;
4018 nextAddr < endAddr;
4019 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4020
4021 ResourceMark rm;
4022 HandleMark hm;
4023
4024 MemRegion dirtyRegion;
4025 {
4026 // See comments in "Precleaning notes" above on why we
4027 // do this locking. XXX Could the locking overheads be
4028 // too high when dirty cards are sparse? [I don't think so.]
4029 stopTimer();
4030 CMSTokenSync x(true); // is cms thread
4031 startTimer();
4032 sample_eden();
4033 // Get and clear dirty region from card table
4034 dirtyRegion = _ct->dirty_card_range_after_reset(MemRegion(nextAddr, endAddr),
4035 true,
4036 CardTable::precleaned_card_val());
4037
4038 assert(dirtyRegion.start() >= nextAddr,
4039 "returned region inconsistent?");
4040 }
4041 lastAddr = dirtyRegion.end();
4042 numDirtyCards =
4043 dirtyRegion.word_size()/CardTable::card_size_in_words;
4044
4045 if (!dirtyRegion.is_empty()) {
4046 stopTimer();
4047 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4048 startTimer();
4049 sample_eden();
4050 verify_work_stacks_empty();
4051 verify_overflow_empty();
4052 HeapWord* stop_point =
4053 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4054 if (stop_point != NULL) {
4055 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4056 "Should only be AbortablePreclean.");
4057 _ct->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4058 if (should_abort_preclean()) {
4059 break; // out of preclean loop
4060 } else {
4061 // Compute the next address at which preclean should pick up.
4062 lastAddr = next_card_start_after_block(stop_point);
4063 }
4064 }
4065 } else {
4066 break;
4067 }
4068 }
4069 verify_work_stacks_empty();
4070 verify_overflow_empty();
4071 return cumNumDirtyCards;
4072 }
4073
4074 class PrecleanCLDClosure : public CLDClosure {
4075 MetadataAwareOopsInGenClosure* _cm_closure;
4076 public:
4077 PrecleanCLDClosure(MetadataAwareOopsInGenClosure* oop_closure) : _cm_closure(oop_closure) {}
4078 void do_cld(ClassLoaderData* cld) {
4079 if (cld->has_accumulated_modified_oops()) {
4080 cld->clear_accumulated_modified_oops();
4081
4082 _cm_closure->do_cld(cld);
4083 }
4084 }
4085 };
4086
4087 // The freelist lock is needed to prevent asserts, is it really needed?
4088 void CMSCollector::preclean_cld(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4089
4090 cl->set_freelistLock(freelistLock);
4091
4092 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4093
4094 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4095 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4096 PrecleanCLDClosure preclean_closure(cl);
4097 ClassLoaderDataGraph::cld_do(&preclean_closure);
4098
4099 verify_work_stacks_empty();
4100 verify_overflow_empty();
4101 }
4102
4103 void CMSCollector::checkpointRootsFinal() {
4104 assert(_collectorState == FinalMarking, "incorrect state transition?");
4105 check_correct_thread_executing();
4106 // world is stopped at this checkpoint
4107 assert(SafepointSynchronize::is_at_safepoint(),
4108 "world should be stopped");
4109 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
4110
4111 verify_work_stacks_empty();
4112 verify_overflow_empty();
4113
4114 log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4115 _young_gen->used() / K, _young_gen->capacity() / K);
4116 {
4117 if (CMSScavengeBeforeRemark) {
4118 CMSHeap* heap = CMSHeap::heap();
4119 // Temporarily set flag to false, GCH->do_collection will
4120 // expect it to be false and set to true
4121 FlagSetting fl(heap->_is_gc_active, false);
4122
4123 heap->do_collection(true, // full (i.e. force, see below)
4124 false, // !clear_all_soft_refs
4125 0, // size
4126 false, // is_tlab
4127 GenCollectedHeap::YoungGen // type
4128 );
4129 }
4130 FreelistLocker x(this);
4131 MutexLockerEx y(bitMapLock(),
4132 Mutex::_no_safepoint_check_flag);
4133 checkpointRootsFinalWork();
4134 }
4135 verify_work_stacks_empty();
4136 verify_overflow_empty();
4137 }
4138
4139 void CMSCollector::checkpointRootsFinalWork() {
4140 GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm);
4141
4142 assert(haveFreelistLocks(), "must have free list locks");
4143 assert_lock_strong(bitMapLock());
4144
4145 ResourceMark rm;
4146 HandleMark hm;
4147
4148 CMSHeap* heap = CMSHeap::heap();
4149
4150 if (should_unload_classes()) {
4151 CodeCache::gc_prologue();
4152 }
4153 assert(haveFreelistLocks(), "must have free list locks");
4154 assert_lock_strong(bitMapLock());
4155
4156 // We might assume that we need not fill TLAB's when
4157 // CMSScavengeBeforeRemark is set, because we may have just done
4158 // a scavenge which would have filled all TLAB's -- and besides
4159 // Eden would be empty. This however may not always be the case --
4160 // for instance although we asked for a scavenge, it may not have
4161 // happened because of a JNI critical section. We probably need
4162 // a policy for deciding whether we can in that case wait until
4163 // the critical section releases and then do the remark following
4164 // the scavenge, and skip it here. In the absence of that policy,
4165 // or of an indication of whether the scavenge did indeed occur,
4166 // we cannot rely on TLAB's having been filled and must do
4167 // so here just in case a scavenge did not happen.
4168 heap->ensure_parsability(false); // fill TLAB's, but no need to retire them
4169 // Update the saved marks which may affect the root scans.
4170 heap->save_marks();
4171
4172 print_eden_and_survivor_chunk_arrays();
4173
4174 {
4175 #if COMPILER2_OR_JVMCI
4176 DerivedPointerTableDeactivate dpt_deact;
4177 #endif
4178
4179 // Note on the role of the mod union table:
4180 // Since the marker in "markFromRoots" marks concurrently with
4181 // mutators, it is possible for some reachable objects not to have been
4182 // scanned. For instance, an only reference to an object A was
4183 // placed in object B after the marker scanned B. Unless B is rescanned,
4184 // A would be collected. Such updates to references in marked objects
4185 // are detected via the mod union table which is the set of all cards
4186 // dirtied since the first checkpoint in this GC cycle and prior to
4187 // the most recent young generation GC, minus those cleaned up by the
4188 // concurrent precleaning.
4189 if (CMSParallelRemarkEnabled) {
4190 GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm);
4191 do_remark_parallel();
4192 } else {
4193 GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm);
4194 do_remark_non_parallel();
4195 }
4196 }
4197 verify_work_stacks_empty();
4198 verify_overflow_empty();
4199
4200 {
4201 GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm);
4202 refProcessingWork();
4203 }
4204 verify_work_stacks_empty();
4205 verify_overflow_empty();
4206
4207 if (should_unload_classes()) {
4208 CodeCache::gc_epilogue();
4209 }
4210 JvmtiExport::gc_epilogue();
4211
4212 // If we encountered any (marking stack / work queue) overflow
4213 // events during the current CMS cycle, take appropriate
4214 // remedial measures, where possible, so as to try and avoid
4215 // recurrence of that condition.
4216 assert(_markStack.isEmpty(), "No grey objects");
4217 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4218 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4219 if (ser_ovflw > 0) {
4220 log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4221 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4222 _markStack.expand();
4223 _ser_pmc_remark_ovflw = 0;
4224 _ser_pmc_preclean_ovflw = 0;
4225 _ser_kac_preclean_ovflw = 0;
4226 _ser_kac_ovflw = 0;
4227 }
4228 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4229 log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4230 _par_pmc_remark_ovflw, _par_kac_ovflw);
4231 _par_pmc_remark_ovflw = 0;
4232 _par_kac_ovflw = 0;
4233 }
4234 if (_markStack._hit_limit > 0) {
4235 log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4236 _markStack._hit_limit);
4237 }
4238 if (_markStack._failed_double > 0) {
4239 log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4240 _markStack._failed_double, _markStack.capacity());
4241 }
4242 _markStack._hit_limit = 0;
4243 _markStack._failed_double = 0;
4244
4245 if ((VerifyAfterGC || VerifyDuringGC) &&
4246 CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4247 verify_after_remark();
4248 }
4249
4250 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4251
4252 // Change under the freelistLocks.
4253 _collectorState = Sweeping;
4254 // Call isAllClear() under bitMapLock
4255 assert(_modUnionTable.isAllClear(),
4256 "Should be clear by end of the final marking");
4257 assert(_ct->cld_rem_set()->mod_union_is_clear(),
4258 "Should be clear by end of the final marking");
4259 }
4260
4261 void CMSParInitialMarkTask::work(uint worker_id) {
4262 elapsedTimer _timer;
4263 ResourceMark rm;
4264 HandleMark hm;
4265
4266 // ---------- scan from roots --------------
4267 _timer.start();
4268 CMSHeap* heap = CMSHeap::heap();
4269 ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4270
4271 // ---------- young gen roots --------------
4272 {
4273 work_on_young_gen_roots(&par_mri_cl);
4274 _timer.stop();
4275 log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4276 }
4277
4278 // ---------- remaining roots --------------
4279 _timer.reset();
4280 _timer.start();
4281
4282 CLDToOopClosure cld_closure(&par_mri_cl, true);
4283
4284 heap->cms_process_roots(_strong_roots_scope,
4285 false, // yg was scanned above
4286 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4287 _collector->should_unload_classes(),
4288 &par_mri_cl,
4289 &cld_closure);
4290 assert(_collector->should_unload_classes()
4291 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4292 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4293 _timer.stop();
4294 log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4295 }
4296
4297 // Parallel remark task
4298 class CMSParRemarkTask: public CMSParMarkTask {
4299 CompactibleFreeListSpace* _cms_space;
4300
4301 // The per-thread work queues, available here for stealing.
4302 OopTaskQueueSet* _task_queues;
4303 ParallelTaskTerminator _term;
4304 StrongRootsScope* _strong_roots_scope;
4305
4306 public:
4307 // A value of 0 passed to n_workers will cause the number of
4308 // workers to be taken from the active workers in the work gang.
4309 CMSParRemarkTask(CMSCollector* collector,
4310 CompactibleFreeListSpace* cms_space,
4311 uint n_workers, WorkGang* workers,
4312 OopTaskQueueSet* task_queues,
4313 StrongRootsScope* strong_roots_scope):
4314 CMSParMarkTask("Rescan roots and grey objects in parallel",
4315 collector, n_workers),
4316 _cms_space(cms_space),
4317 _task_queues(task_queues),
4318 _term(n_workers, task_queues),
4319 _strong_roots_scope(strong_roots_scope) { }
4320
4321 OopTaskQueueSet* task_queues() { return _task_queues; }
4322
4323 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4324
4325 ParallelTaskTerminator* terminator() { return &_term; }
4326 uint n_workers() { return _n_workers; }
4327
4328 void work(uint worker_id);
4329
4330 private:
4331 // ... of dirty cards in old space
4332 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4333 ParMarkRefsIntoAndScanClosure* cl);
4334
4335 // ... work stealing for the above
4336 void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl, int* seed);
4337 };
4338
4339 class RemarkCLDClosure : public CLDClosure {
4340 CLDToOopClosure _cm_closure;
4341 public:
4342 RemarkCLDClosure(OopClosure* oop_closure) : _cm_closure(oop_closure) {}
4343 void do_cld(ClassLoaderData* cld) {
4344 // Check if we have modified any oops in the CLD during the concurrent marking.
4345 if (cld->has_accumulated_modified_oops()) {
4346 cld->clear_accumulated_modified_oops();
4347
4348 // We could have transfered the current modified marks to the accumulated marks,
4349 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4350 } else if (cld->has_modified_oops()) {
4351 // Don't clear anything, this info is needed by the next young collection.
4352 } else {
4353 // No modified oops in the ClassLoaderData.
4354 return;
4355 }
4356
4357 // The klass has modified fields, need to scan the klass.
4358 _cm_closure.do_cld(cld);
4359 }
4360 };
4361
4362 void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) {
4363 ParNewGeneration* young_gen = _collector->_young_gen;
4364 ContiguousSpace* eden_space = young_gen->eden();
4365 ContiguousSpace* from_space = young_gen->from();
4366 ContiguousSpace* to_space = young_gen->to();
4367
4368 HeapWord** eca = _collector->_eden_chunk_array;
4369 size_t ect = _collector->_eden_chunk_index;
4370 HeapWord** sca = _collector->_survivor_chunk_array;
4371 size_t sct = _collector->_survivor_chunk_index;
4372
4373 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4374 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4375
4376 do_young_space_rescan(cl, to_space, NULL, 0);
4377 do_young_space_rescan(cl, from_space, sca, sct);
4378 do_young_space_rescan(cl, eden_space, eca, ect);
4379 }
4380
4381 // work_queue(i) is passed to the closure
4382 // ParMarkRefsIntoAndScanClosure. The "i" parameter
4383 // also is passed to do_dirty_card_rescan_tasks() and to
4384 // do_work_steal() to select the i-th task_queue.
4385
4386 void CMSParRemarkTask::work(uint worker_id) {
4387 elapsedTimer _timer;
4388 ResourceMark rm;
4389 HandleMark hm;
4390
4391 // ---------- rescan from roots --------------
4392 _timer.start();
4393 CMSHeap* heap = CMSHeap::heap();
4394 ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4395 _collector->_span, _collector->ref_processor(),
4396 &(_collector->_markBitMap),
4397 work_queue(worker_id));
4398
4399 // Rescan young gen roots first since these are likely
4400 // coarsely partitioned and may, on that account, constitute
4401 // the critical path; thus, it's best to start off that
4402 // work first.
4403 // ---------- young gen roots --------------
4404 {
4405 work_on_young_gen_roots(&par_mrias_cl);
4406 _timer.stop();
4407 log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4408 }
4409
4410 // ---------- remaining roots --------------
4411 _timer.reset();
4412 _timer.start();
4413 heap->cms_process_roots(_strong_roots_scope,
4414 false, // yg was scanned above
4415 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4416 _collector->should_unload_classes(),
4417 &par_mrias_cl,
4418 NULL); // The dirty klasses will be handled below
4419
4420 assert(_collector->should_unload_classes()
4421 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4422 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4423 _timer.stop();
4424 log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4425
4426 // ---------- unhandled CLD scanning ----------
4427 if (worker_id == 0) { // Single threaded at the moment.
4428 _timer.reset();
4429 _timer.start();
4430
4431 // Scan all new class loader data objects and new dependencies that were
4432 // introduced during concurrent marking.
4433 ResourceMark rm;
4434 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4435 for (int i = 0; i < array->length(); i++) {
4436 par_mrias_cl.do_cld_nv(array->at(i));
4437 }
4438
4439 // We don't need to keep track of new CLDs anymore.
4440 ClassLoaderDataGraph::remember_new_clds(false);
4441
4442 _timer.stop();
4443 log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4444 }
4445
4446 // We might have added oops to ClassLoaderData::_handles during the
4447 // concurrent marking phase. These oops do not always point to newly allocated objects
4448 // that are guaranteed to be kept alive. Hence,
4449 // we do have to revisit the _handles block during the remark phase.
4450
4451 // ---------- dirty CLD scanning ----------
4452 if (worker_id == 0) { // Single threaded at the moment.
4453 _timer.reset();
4454 _timer.start();
4455
4456 // Scan all classes that was dirtied during the concurrent marking phase.
4457 RemarkCLDClosure remark_closure(&par_mrias_cl);
4458 ClassLoaderDataGraph::cld_do(&remark_closure);
4459
4460 _timer.stop();
4461 log_trace(gc, task)("Finished dirty CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4462 }
4463
4464
4465 // ---------- rescan dirty cards ------------
4466 _timer.reset();
4467 _timer.start();
4468
4469 // Do the rescan tasks for each of the two spaces
4470 // (cms_space) in turn.
4471 // "worker_id" is passed to select the task_queue for "worker_id"
4472 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4473 _timer.stop();
4474 log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4475
4476 // ---------- steal work from other threads ...
4477 // ---------- ... and drain overflow list.
4478 _timer.reset();
4479 _timer.start();
4480 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4481 _timer.stop();
4482 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4483 }
4484
4485 void
4486 CMSParMarkTask::do_young_space_rescan(
4487 OopsInGenClosure* cl, ContiguousSpace* space,
4488 HeapWord** chunk_array, size_t chunk_top) {
4489 // Until all tasks completed:
4490 // . claim an unclaimed task
4491 // . compute region boundaries corresponding to task claimed
4492 // using chunk_array
4493 // . par_oop_iterate(cl) over that region
4494
4495 ResourceMark rm;
4496 HandleMark hm;
4497
4498 SequentialSubTasksDone* pst = space->par_seq_tasks();
4499
4500 uint nth_task = 0;
4501 uint n_tasks = pst->n_tasks();
4502
4503 if (n_tasks > 0) {
4504 assert(pst->valid(), "Uninitialized use?");
4505 HeapWord *start, *end;
4506 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4507 // We claimed task # nth_task; compute its boundaries.
4508 if (chunk_top == 0) { // no samples were taken
4509 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4510 start = space->bottom();
4511 end = space->top();
4512 } else if (nth_task == 0) {
4513 start = space->bottom();
4514 end = chunk_array[nth_task];
4515 } else if (nth_task < (uint)chunk_top) {
4516 assert(nth_task >= 1, "Control point invariant");
4517 start = chunk_array[nth_task - 1];
4518 end = chunk_array[nth_task];
4519 } else {
4520 assert(nth_task == (uint)chunk_top, "Control point invariant");
4521 start = chunk_array[chunk_top - 1];
4522 end = space->top();
4523 }
4524 MemRegion mr(start, end);
4525 // Verify that mr is in space
4526 assert(mr.is_empty() || space->used_region().contains(mr),
4527 "Should be in space");
4528 // Verify that "start" is an object boundary
4529 assert(mr.is_empty() || oopDesc::is_oop(oop(mr.start())),
4530 "Should be an oop");
4531 space->par_oop_iterate(mr, cl);
4532 }
4533 pst->all_tasks_completed();
4534 }
4535 }
4536
4537 void
4538 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4539 CompactibleFreeListSpace* sp, int i,
4540 ParMarkRefsIntoAndScanClosure* cl) {
4541 // Until all tasks completed:
4542 // . claim an unclaimed task
4543 // . compute region boundaries corresponding to task claimed
4544 // . transfer dirty bits ct->mut for that region
4545 // . apply rescanclosure to dirty mut bits for that region
4546
4547 ResourceMark rm;
4548 HandleMark hm;
4549
4550 OopTaskQueue* work_q = work_queue(i);
4551 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4552 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4553 // CAUTION: This closure has state that persists across calls to
4554 // the work method dirty_range_iterate_clear() in that it has
4555 // embedded in it a (subtype of) UpwardsObjectClosure. The
4556 // use of that state in the embedded UpwardsObjectClosure instance
4557 // assumes that the cards are always iterated (even if in parallel
4558 // by several threads) in monotonically increasing order per each
4559 // thread. This is true of the implementation below which picks
4560 // card ranges (chunks) in monotonically increasing order globally
4561 // and, a-fortiori, in monotonically increasing order per thread
4562 // (the latter order being a subsequence of the former).
4563 // If the work code below is ever reorganized into a more chaotic
4564 // work-partitioning form than the current "sequential tasks"
4565 // paradigm, the use of that persistent state will have to be
4566 // revisited and modified appropriately. See also related
4567 // bug 4756801 work on which should examine this code to make
4568 // sure that the changes there do not run counter to the
4569 // assumptions made here and necessary for correctness and
4570 // efficiency. Note also that this code might yield inefficient
4571 // behavior in the case of very large objects that span one or
4572 // more work chunks. Such objects would potentially be scanned
4573 // several times redundantly. Work on 4756801 should try and
4574 // address that performance anomaly if at all possible. XXX
4575 MemRegion full_span = _collector->_span;
4576 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4577 MarkFromDirtyCardsClosure
4578 greyRescanClosure(_collector, full_span, // entire span of interest
4579 sp, bm, work_q, cl);
4580
4581 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4582 assert(pst->valid(), "Uninitialized use?");
4583 uint nth_task = 0;
4584 const int alignment = CardTable::card_size * BitsPerWord;
4585 MemRegion span = sp->used_region();
4586 HeapWord* start_addr = span.start();
4587 HeapWord* end_addr = align_up(span.end(), alignment);
4588 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4589 assert(is_aligned(start_addr, alignment), "Check alignment");
4590 assert(is_aligned(chunk_size, alignment), "Check alignment");
4591
4592 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4593 // Having claimed the nth_task, compute corresponding mem-region,
4594 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4595 // The alignment restriction ensures that we do not need any
4596 // synchronization with other gang-workers while setting or
4597 // clearing bits in thus chunk of the MUT.
4598 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4599 start_addr + (nth_task+1)*chunk_size);
4600 // The last chunk's end might be way beyond end of the
4601 // used region. In that case pull back appropriately.
4602 if (this_span.end() > end_addr) {
4603 this_span.set_end(end_addr);
4604 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4605 }
4606 // Iterate over the dirty cards covering this chunk, marking them
4607 // precleaned, and setting the corresponding bits in the mod union
4608 // table. Since we have been careful to partition at Card and MUT-word
4609 // boundaries no synchronization is needed between parallel threads.
4610 _collector->_ct->dirty_card_iterate(this_span,
4611 &modUnionClosure);
4612
4613 // Having transferred these marks into the modUnionTable,
4614 // rescan the marked objects on the dirty cards in the modUnionTable.
4615 // Even if this is at a synchronous collection, the initial marking
4616 // may have been done during an asynchronous collection so there
4617 // may be dirty bits in the mod-union table.
4618 _collector->_modUnionTable.dirty_range_iterate_clear(
4619 this_span, &greyRescanClosure);
4620 _collector->_modUnionTable.verifyNoOneBitsInRange(
4621 this_span.start(),
4622 this_span.end());
4623 }
4624 pst->all_tasks_completed(); // declare that i am done
4625 }
4626
4627 // . see if we can share work_queues with ParNew? XXX
4628 void
4629 CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl,
4630 int* seed) {
4631 OopTaskQueue* work_q = work_queue(i);
4632 NOT_PRODUCT(int num_steals = 0;)
4633 oop obj_to_scan;
4634 CMSBitMap* bm = &(_collector->_markBitMap);
4635
4636 while (true) {
4637 // Completely finish any left over work from (an) earlier round(s)
4638 cl->trim_queue(0);
4639 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4640 (size_t)ParGCDesiredObjsFromOverflowList);
4641 // Now check if there's any work in the overflow list
4642 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4643 // only affects the number of attempts made to get work from the
4644 // overflow list and does not affect the number of workers. Just
4645 // pass ParallelGCThreads so this behavior is unchanged.
4646 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4647 work_q,
4648 ParallelGCThreads)) {
4649 // found something in global overflow list;
4650 // not yet ready to go stealing work from others.
4651 // We'd like to assert(work_q->size() != 0, ...)
4652 // because we just took work from the overflow list,
4653 // but of course we can't since all of that could have
4654 // been already stolen from us.
4655 // "He giveth and He taketh away."
4656 continue;
4657 }
4658 // Verify that we have no work before we resort to stealing
4659 assert(work_q->size() == 0, "Have work, shouldn't steal");
4660 // Try to steal from other queues that have work
4661 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4662 NOT_PRODUCT(num_steals++;)
4663 assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
4664 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4665 // Do scanning work
4666 obj_to_scan->oop_iterate(cl);
4667 // Loop around, finish this work, and try to steal some more
4668 } else if (terminator()->offer_termination()) {
4669 break; // nirvana from the infinite cycle
4670 }
4671 }
4672 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4673 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4674 "Else our work is not yet done");
4675 }
4676
4677 // Record object boundaries in _eden_chunk_array by sampling the eden
4678 // top in the slow-path eden object allocation code path and record
4679 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4680 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4681 // sampling in sample_eden() that activates during the part of the
4682 // preclean phase.
4683 void CMSCollector::sample_eden_chunk() {
4684 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4685 if (_eden_chunk_lock->try_lock()) {
4686 // Record a sample. This is the critical section. The contents
4687 // of the _eden_chunk_array have to be non-decreasing in the
4688 // address order.
4689 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4690 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4691 "Unexpected state of Eden");
4692 if (_eden_chunk_index == 0 ||
4693 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4694 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4695 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4696 _eden_chunk_index++; // commit sample
4697 }
4698 _eden_chunk_lock->unlock();
4699 }
4700 }
4701 }
4702
4703 // Return a thread-local PLAB recording array, as appropriate.
4704 void* CMSCollector::get_data_recorder(int thr_num) {
4705 if (_survivor_plab_array != NULL &&
4706 (CMSPLABRecordAlways ||
4707 (_collectorState > Marking && _collectorState < FinalMarking))) {
4708 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4709 ChunkArray* ca = &_survivor_plab_array[thr_num];
4710 ca->reset(); // clear it so that fresh data is recorded
4711 return (void*) ca;
4712 } else {
4713 return NULL;
4714 }
4715 }
4716
4717 // Reset all the thread-local PLAB recording arrays
4718 void CMSCollector::reset_survivor_plab_arrays() {
4719 for (uint i = 0; i < ParallelGCThreads; i++) {
4720 _survivor_plab_array[i].reset();
4721 }
4722 }
4723
4724 // Merge the per-thread plab arrays into the global survivor chunk
4725 // array which will provide the partitioning of the survivor space
4726 // for CMS initial scan and rescan.
4727 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4728 int no_of_gc_threads) {
4729 assert(_survivor_plab_array != NULL, "Error");
4730 assert(_survivor_chunk_array != NULL, "Error");
4731 assert(_collectorState == FinalMarking ||
4732 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4733 for (int j = 0; j < no_of_gc_threads; j++) {
4734 _cursor[j] = 0;
4735 }
4736 HeapWord* top = surv->top();
4737 size_t i;
4738 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4739 HeapWord* min_val = top; // Higher than any PLAB address
4740 uint min_tid = 0; // position of min_val this round
4741 for (int j = 0; j < no_of_gc_threads; j++) {
4742 ChunkArray* cur_sca = &_survivor_plab_array[j];
4743 if (_cursor[j] == cur_sca->end()) {
4744 continue;
4745 }
4746 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4747 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4748 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4749 if (cur_val < min_val) {
4750 min_tid = j;
4751 min_val = cur_val;
4752 } else {
4753 assert(cur_val < top, "All recorded addresses should be less");
4754 }
4755 }
4756 // At this point min_val and min_tid are respectively
4757 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4758 // and the thread (j) that witnesses that address.
4759 // We record this address in the _survivor_chunk_array[i]
4760 // and increment _cursor[min_tid] prior to the next round i.
4761 if (min_val == top) {
4762 break;
4763 }
4764 _survivor_chunk_array[i] = min_val;
4765 _cursor[min_tid]++;
4766 }
4767 // We are all done; record the size of the _survivor_chunk_array
4768 _survivor_chunk_index = i; // exclusive: [0, i)
4769 log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4770 // Verify that we used up all the recorded entries
4771 #ifdef ASSERT
4772 size_t total = 0;
4773 for (int j = 0; j < no_of_gc_threads; j++) {
4774 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4775 total += _cursor[j];
4776 }
4777 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4778 // Check that the merged array is in sorted order
4779 if (total > 0) {
4780 for (size_t i = 0; i < total - 1; i++) {
4781 log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4782 i, p2i(_survivor_chunk_array[i]));
4783 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4784 "Not sorted");
4785 }
4786 }
4787 #endif // ASSERT
4788 }
4789
4790 // Set up the space's par_seq_tasks structure for work claiming
4791 // for parallel initial scan and rescan of young gen.
4792 // See ParRescanTask where this is currently used.
4793 void
4794 CMSCollector::
4795 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4796 assert(n_threads > 0, "Unexpected n_threads argument");
4797
4798 // Eden space
4799 if (!_young_gen->eden()->is_empty()) {
4800 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4801 assert(!pst->valid(), "Clobbering existing data?");
4802 // Each valid entry in [0, _eden_chunk_index) represents a task.
4803 size_t n_tasks = _eden_chunk_index + 1;
4804 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4805 // Sets the condition for completion of the subtask (how many threads
4806 // need to finish in order to be done).
4807 pst->set_n_threads(n_threads);
4808 pst->set_n_tasks((int)n_tasks);
4809 }
4810
4811 // Merge the survivor plab arrays into _survivor_chunk_array
4812 if (_survivor_plab_array != NULL) {
4813 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4814 } else {
4815 assert(_survivor_chunk_index == 0, "Error");
4816 }
4817
4818 // To space
4819 {
4820 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4821 assert(!pst->valid(), "Clobbering existing data?");
4822 // Sets the condition for completion of the subtask (how many threads
4823 // need to finish in order to be done).
4824 pst->set_n_threads(n_threads);
4825 pst->set_n_tasks(1);
4826 assert(pst->valid(), "Error");
4827 }
4828
4829 // From space
4830 {
4831 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4832 assert(!pst->valid(), "Clobbering existing data?");
4833 size_t n_tasks = _survivor_chunk_index + 1;
4834 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
4835 // Sets the condition for completion of the subtask (how many threads
4836 // need to finish in order to be done).
4837 pst->set_n_threads(n_threads);
4838 pst->set_n_tasks((int)n_tasks);
4839 assert(pst->valid(), "Error");
4840 }
4841 }
4842
4843 // Parallel version of remark
4844 void CMSCollector::do_remark_parallel() {
4845 CMSHeap* heap = CMSHeap::heap();
4846 WorkGang* workers = heap->workers();
4847 assert(workers != NULL, "Need parallel worker threads.");
4848 // Choose to use the number of GC workers most recently set
4849 // into "active_workers".
4850 uint n_workers = workers->active_workers();
4851
4852 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4853
4854 StrongRootsScope srs(n_workers);
4855
4856 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4857
4858 // We won't be iterating over the cards in the card table updating
4859 // the younger_gen cards, so we shouldn't call the following else
4860 // the verification code as well as subsequent younger_refs_iterate
4861 // code would get confused. XXX
4862 // heap->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4863
4864 // The young gen rescan work will not be done as part of
4865 // process_roots (which currently doesn't know how to
4866 // parallelize such a scan), but rather will be broken up into
4867 // a set of parallel tasks (via the sampling that the [abortable]
4868 // preclean phase did of eden, plus the [two] tasks of
4869 // scanning the [two] survivor spaces. Further fine-grain
4870 // parallelization of the scanning of the survivor spaces
4871 // themselves, and of precleaning of the young gen itself
4872 // is deferred to the future.
4873 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4874
4875 // The dirty card rescan work is broken up into a "sequence"
4876 // of parallel tasks (per constituent space) that are dynamically
4877 // claimed by the parallel threads.
4878 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4879
4880 // It turns out that even when we're using 1 thread, doing the work in a
4881 // separate thread causes wide variance in run times. We can't help this
4882 // in the multi-threaded case, but we special-case n=1 here to get
4883 // repeatable measurements of the 1-thread overhead of the parallel code.
4884 if (n_workers > 1) {
4885 // Make refs discovery MT-safe, if it isn't already: it may not
4886 // necessarily be so, since it's possible that we are doing
4887 // ST marking.
4888 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4889 workers->run_task(&tsk);
4890 } else {
4891 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4892 tsk.work(0);
4893 }
4894
4895 // restore, single-threaded for now, any preserved marks
4896 // as a result of work_q overflow
4897 restore_preserved_marks_if_any();
4898 }
4899
4900 // Non-parallel version of remark
4901 void CMSCollector::do_remark_non_parallel() {
4902 ResourceMark rm;
4903 HandleMark hm;
4904 CMSHeap* heap = CMSHeap::heap();
4905 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4906
4907 MarkRefsIntoAndScanClosure
4908 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4909 &_markStack, this,
4910 false /* should_yield */, false /* not precleaning */);
4911 MarkFromDirtyCardsClosure
4912 markFromDirtyCardsClosure(this, _span,
4913 NULL, // space is set further below
4914 &_markBitMap, &_markStack, &mrias_cl);
4915 {
4916 GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm);
4917 // Iterate over the dirty cards, setting the corresponding bits in the
4918 // mod union table.
4919 {
4920 ModUnionClosure modUnionClosure(&_modUnionTable);
4921 _ct->dirty_card_iterate(_cmsGen->used_region(),
4922 &modUnionClosure);
4923 }
4924 // Having transferred these marks into the modUnionTable, we just need
4925 // to rescan the marked objects on the dirty cards in the modUnionTable.
4926 // The initial marking may have been done during an asynchronous
4927 // collection so there may be dirty bits in the mod-union table.
4928 const int alignment = CardTable::card_size * BitsPerWord;
4929 {
4930 // ... First handle dirty cards in CMS gen
4931 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4932 MemRegion ur = _cmsGen->used_region();
4933 HeapWord* lb = ur.start();
4934 HeapWord* ub = align_up(ur.end(), alignment);
4935 MemRegion cms_span(lb, ub);
4936 _modUnionTable.dirty_range_iterate_clear(cms_span,
4937 &markFromDirtyCardsClosure);
4938 verify_work_stacks_empty();
4939 log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4940 }
4941 }
4942 if (VerifyDuringGC &&
4943 CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4944 HandleMark hm; // Discard invalid handles created during verification
4945 Universe::verify();
4946 }
4947 {
4948 GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm);
4949
4950 verify_work_stacks_empty();
4951
4952 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
4953 StrongRootsScope srs(1);
4954
4955 heap->cms_process_roots(&srs,
4956 true, // young gen as roots
4957 GenCollectedHeap::ScanningOption(roots_scanning_options()),
4958 should_unload_classes(),
4959 &mrias_cl,
4960 NULL); // The dirty klasses will be handled below
4961
4962 assert(should_unload_classes()
4963 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4964 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4965 }
4966
4967 {
4968 GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm);
4969
4970 verify_work_stacks_empty();
4971
4972 // Scan all class loader data objects that might have been introduced
4973 // during concurrent marking.
4974 ResourceMark rm;
4975 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4976 for (int i = 0; i < array->length(); i++) {
4977 mrias_cl.do_cld_nv(array->at(i));
4978 }
4979
4980 // We don't need to keep track of new CLDs anymore.
4981 ClassLoaderDataGraph::remember_new_clds(false);
4982
4983 verify_work_stacks_empty();
4984 }
4985
4986 // We might have added oops to ClassLoaderData::_handles during the
4987 // concurrent marking phase. These oops do not point to newly allocated objects
4988 // that are guaranteed to be kept alive. Hence,
4989 // we do have to revisit the _handles block during the remark phase.
4990 {
4991 GCTraceTime(Trace, gc, phases) t("Dirty CLD Scan", _gc_timer_cm);
4992
4993 verify_work_stacks_empty();
4994
4995 RemarkCLDClosure remark_closure(&mrias_cl);
4996 ClassLoaderDataGraph::cld_do(&remark_closure);
4997
4998 verify_work_stacks_empty();
4999 }
5000
5001 verify_work_stacks_empty();
5002 // Restore evacuated mark words, if any, used for overflow list links
5003 restore_preserved_marks_if_any();
5004
5005 verify_overflow_empty();
5006 }
5007
5008 ////////////////////////////////////////////////////////
5009 // Parallel Reference Processing Task Proxy Class
5010 ////////////////////////////////////////////////////////
5011 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5012 OopTaskQueueSet* _queues;
5013 ParallelTaskTerminator _terminator;
5014 public:
5015 AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5016 AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5017 ParallelTaskTerminator* terminator() { return &_terminator; }
5018 OopTaskQueueSet* queues() { return _queues; }
5019 };
5020
5021 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5022 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5023 CMSCollector* _collector;
5024 CMSBitMap* _mark_bit_map;
5025 const MemRegion _span;
5026 ProcessTask& _task;
5027
5028 public:
5029 CMSRefProcTaskProxy(ProcessTask& task,
5030 CMSCollector* collector,
5031 const MemRegion& span,
5032 CMSBitMap* mark_bit_map,
5033 AbstractWorkGang* workers,
5034 OopTaskQueueSet* task_queues):
5035 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5036 task_queues,
5037 workers->active_workers()),
5038 _task(task),
5039 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5040 {
5041 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5042 "Inconsistency in _span");
5043 }
5044
5045 OopTaskQueueSet* task_queues() { return queues(); }
5046
5047 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5048
5049 void do_work_steal(int i,
5050 CMSParDrainMarkingStackClosure* drain,
5051 CMSParKeepAliveClosure* keep_alive,
5052 int* seed);
5053
5054 virtual void work(uint worker_id);
5055 };
5056
5057 void CMSRefProcTaskProxy::work(uint worker_id) {
5058 ResourceMark rm;
5059 HandleMark hm;
5060 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5061 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5062 _mark_bit_map,
5063 work_queue(worker_id));
5064 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5065 _mark_bit_map,
5066 work_queue(worker_id));
5067 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5068 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5069 if (_task.marks_oops_alive()) {
5070 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5071 _collector->hash_seed(worker_id));
5072 }
5073 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5074 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5075 }
5076
5077 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5078 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5079 EnqueueTask& _task;
5080
5081 public:
5082 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5083 : AbstractGangTask("Enqueue reference objects in parallel"),
5084 _task(task)
5085 { }
5086
5087 virtual void work(uint worker_id)
5088 {
5089 _task.work(worker_id);
5090 }
5091 };
5092
5093 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5094 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5095 _span(span),
5096 _bit_map(bit_map),
5097 _work_queue(work_queue),
5098 _mark_and_push(collector, span, bit_map, work_queue),
5099 _low_water_mark(MIN2((work_queue->max_elems()/4),
5100 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5101 { }
5102
5103 // . see if we can share work_queues with ParNew? XXX
5104 void CMSRefProcTaskProxy::do_work_steal(int i,
5105 CMSParDrainMarkingStackClosure* drain,
5106 CMSParKeepAliveClosure* keep_alive,
5107 int* seed) {
5108 OopTaskQueue* work_q = work_queue(i);
5109 NOT_PRODUCT(int num_steals = 0;)
5110 oop obj_to_scan;
5111
5112 while (true) {
5113 // Completely finish any left over work from (an) earlier round(s)
5114 drain->trim_queue(0);
5115 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5116 (size_t)ParGCDesiredObjsFromOverflowList);
5117 // Now check if there's any work in the overflow list
5118 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5119 // only affects the number of attempts made to get work from the
5120 // overflow list and does not affect the number of workers. Just
5121 // pass ParallelGCThreads so this behavior is unchanged.
5122 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5123 work_q,
5124 ParallelGCThreads)) {
5125 // Found something in global overflow list;
5126 // not yet ready to go stealing work from others.
5127 // We'd like to assert(work_q->size() != 0, ...)
5128 // because we just took work from the overflow list,
5129 // but of course we can't, since all of that might have
5130 // been already stolen from us.
5131 continue;
5132 }
5133 // Verify that we have no work before we resort to stealing
5134 assert(work_q->size() == 0, "Have work, shouldn't steal");
5135 // Try to steal from other queues that have work
5136 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5137 NOT_PRODUCT(num_steals++;)
5138 assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
5139 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5140 // Do scanning work
5141 obj_to_scan->oop_iterate(keep_alive);
5142 // Loop around, finish this work, and try to steal some more
5143 } else if (terminator()->offer_termination()) {
5144 break; // nirvana from the infinite cycle
5145 }
5146 }
5147 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5148 }
5149
5150 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5151 {
5152 CMSHeap* heap = CMSHeap::heap();
5153 WorkGang* workers = heap->workers();
5154 assert(workers != NULL, "Need parallel worker threads.");
5155 CMSRefProcTaskProxy rp_task(task, &_collector,
5156 _collector.ref_processor()->span(),
5157 _collector.markBitMap(),
5158 workers, _collector.task_queues());
5159 workers->run_task(&rp_task);
5160 }
5161
5162 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5163 {
5164
5165 CMSHeap* heap = CMSHeap::heap();
5166 WorkGang* workers = heap->workers();
5167 assert(workers != NULL, "Need parallel worker threads.");
5168 CMSRefEnqueueTaskProxy enq_task(task);
5169 workers->run_task(&enq_task);
5170 }
5171
5172 void CMSCollector::refProcessingWork() {
5173 ResourceMark rm;
5174 HandleMark hm;
5175
5176 ReferenceProcessor* rp = ref_processor();
5177 assert(rp->span().equals(_span), "Spans should be equal");
5178 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5179 // Process weak references.
5180 rp->setup_policy(false);
5181 verify_work_stacks_empty();
5182
5183 ReferenceProcessorPhaseTimes pt(_gc_timer_cm, rp->num_q());
5184 {
5185 GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm);
5186
5187 // Setup keep_alive and complete closures.
5188 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5189 &_markStack, false /* !preclean */);
5190 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5191 _span, &_markBitMap, &_markStack,
5192 &cmsKeepAliveClosure, false /* !preclean */);
5193
5194 ReferenceProcessorStats stats;
5195 if (rp->processing_is_mt()) {
5196 // Set the degree of MT here. If the discovery is done MT, there
5197 // may have been a different number of threads doing the discovery
5198 // and a different number of discovered lists may have Ref objects.
5199 // That is OK as long as the Reference lists are balanced (see
5200 // balance_all_queues() and balance_queues()).
5201 CMSHeap* heap = CMSHeap::heap();
5202 uint active_workers = ParallelGCThreads;
5203 WorkGang* workers = heap->workers();
5204 if (workers != NULL) {
5205 active_workers = workers->active_workers();
5206 // The expectation is that active_workers will have already
5207 // been set to a reasonable value. If it has not been set,
5208 // investigate.
5209 assert(active_workers > 0, "Should have been set during scavenge");
5210 }
5211 rp->set_active_mt_degree(active_workers);
5212 CMSRefProcTaskExecutor task_executor(*this);
5213 stats = rp->process_discovered_references(&_is_alive_closure,
5214 &cmsKeepAliveClosure,
5215 &cmsDrainMarkingStackClosure,
5216 &task_executor,
5217 &pt);
5218 } else {
5219 stats = rp->process_discovered_references(&_is_alive_closure,
5220 &cmsKeepAliveClosure,
5221 &cmsDrainMarkingStackClosure,
5222 NULL,
5223 &pt);
5224 }
5225 _gc_tracer_cm->report_gc_reference_stats(stats);
5226 pt.print_all_references();
5227 }
5228
5229 // This is the point where the entire marking should have completed.
5230 verify_work_stacks_empty();
5231
5232 {
5233 GCTraceTime(Debug, gc, phases) t("Weak Processing", _gc_timer_cm);
5234 WeakProcessor::weak_oops_do(&_is_alive_closure, &do_nothing_cl);
5235 }
5236
5237 if (should_unload_classes()) {
5238 {
5239 GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm);
5240
5241 // Unload classes and purge the SystemDictionary.
5242 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure, _gc_timer_cm);
5243
5244 // Unload nmethods.
5245 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5246
5247 // Prune dead klasses from subklass/sibling/implementor lists.
5248 Klass::clean_weak_klass_links(purged_class);
5249 }
5250
5251 {
5252 GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer_cm);
5253 // Clean up unreferenced symbols in symbol table.
5254 SymbolTable::unlink();
5255 }
5256
5257 {
5258 GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer_cm);
5259 // Delete entries for dead interned strings.
5260 StringTable::unlink(&_is_alive_closure);
5261 }
5262 }
5263
5264 // Restore any preserved marks as a result of mark stack or
5265 // work queue overflow
5266 restore_preserved_marks_if_any(); // done single-threaded for now
5267
5268 rp->set_enqueuing_is_done(true);
5269 if (rp->processing_is_mt()) {
5270 rp->balance_all_queues();
5271 CMSRefProcTaskExecutor task_executor(*this);
5272 rp->enqueue_discovered_references(&task_executor, &pt);
5273 } else {
5274 rp->enqueue_discovered_references(NULL, &pt);
5275 }
5276 rp->verify_no_references_recorded();
5277 pt.print_enqueue_phase();
5278 assert(!rp->discovery_enabled(), "should have been disabled");
5279 }
5280
5281 #ifndef PRODUCT
5282 void CMSCollector::check_correct_thread_executing() {
5283 Thread* t = Thread::current();
5284 // Only the VM thread or the CMS thread should be here.
5285 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5286 "Unexpected thread type");
5287 // If this is the vm thread, the foreground process
5288 // should not be waiting. Note that _foregroundGCIsActive is
5289 // true while the foreground collector is waiting.
5290 if (_foregroundGCShouldWait) {
5291 // We cannot be the VM thread
5292 assert(t->is_ConcurrentGC_thread(),
5293 "Should be CMS thread");
5294 } else {
5295 // We can be the CMS thread only if we are in a stop-world
5296 // phase of CMS collection.
5297 if (t->is_ConcurrentGC_thread()) {
5298 assert(_collectorState == InitialMarking ||
5299 _collectorState == FinalMarking,
5300 "Should be a stop-world phase");
5301 // The CMS thread should be holding the CMS_token.
5302 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5303 "Potential interference with concurrently "
5304 "executing VM thread");
5305 }
5306 }
5307 }
5308 #endif
5309
5310 void CMSCollector::sweep() {
5311 assert(_collectorState == Sweeping, "just checking");
5312 check_correct_thread_executing();
5313 verify_work_stacks_empty();
5314 verify_overflow_empty();
5315 increment_sweep_count();
5316 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
5317
5318 _inter_sweep_timer.stop();
5319 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5320
5321 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5322 _intra_sweep_timer.reset();
5323 _intra_sweep_timer.start();
5324 {
5325 GCTraceCPUTime tcpu;
5326 CMSPhaseAccounting pa(this, "Concurrent Sweep");
5327 // First sweep the old gen
5328 {
5329 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5330 bitMapLock());
5331 sweepWork(_cmsGen);
5332 }
5333
5334 // Update Universe::_heap_*_at_gc figures.
5335 // We need all the free list locks to make the abstract state
5336 // transition from Sweeping to Resetting. See detailed note
5337 // further below.
5338 {
5339 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5340 // Update heap occupancy information which is used as
5341 // input to soft ref clearing policy at the next gc.
5342 Universe::update_heap_info_at_gc();
5343 _collectorState = Resizing;
5344 }
5345 }
5346 verify_work_stacks_empty();
5347 verify_overflow_empty();
5348
5349 if (should_unload_classes()) {
5350 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5351 // requires that the virtual spaces are stable and not deleted.
5352 ClassLoaderDataGraph::set_should_purge(true);
5353 }
5354
5355 _intra_sweep_timer.stop();
5356 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5357
5358 _inter_sweep_timer.reset();
5359 _inter_sweep_timer.start();
5360
5361 // We need to use a monotonically non-decreasing time in ms
5362 // or we will see time-warp warnings and os::javaTimeMillis()
5363 // does not guarantee monotonicity.
5364 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5365 update_time_of_last_gc(now);
5366
5367 // NOTE on abstract state transitions:
5368 // Mutators allocate-live and/or mark the mod-union table dirty
5369 // based on the state of the collection. The former is done in
5370 // the interval [Marking, Sweeping] and the latter in the interval
5371 // [Marking, Sweeping). Thus the transitions into the Marking state
5372 // and out of the Sweeping state must be synchronously visible
5373 // globally to the mutators.
5374 // The transition into the Marking state happens with the world
5375 // stopped so the mutators will globally see it. Sweeping is
5376 // done asynchronously by the background collector so the transition
5377 // from the Sweeping state to the Resizing state must be done
5378 // under the freelistLock (as is the check for whether to
5379 // allocate-live and whether to dirty the mod-union table).
5380 assert(_collectorState == Resizing, "Change of collector state to"
5381 " Resizing must be done under the freelistLocks (plural)");
5382
5383 // Now that sweeping has been completed, we clear
5384 // the incremental_collection_failed flag,
5385 // thus inviting a younger gen collection to promote into
5386 // this generation. If such a promotion may still fail,
5387 // the flag will be set again when a young collection is
5388 // attempted.
5389 CMSHeap* heap = CMSHeap::heap();
5390 heap->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5391 heap->update_full_collections_completed(_collection_count_start);
5392 }
5393
5394 // FIX ME!!! Looks like this belongs in CFLSpace, with
5395 // CMSGen merely delegating to it.
5396 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5397 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5398 HeapWord* minAddr = _cmsSpace->bottom();
5399 HeapWord* largestAddr =
5400 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5401 if (largestAddr == NULL) {
5402 // The dictionary appears to be empty. In this case
5403 // try to coalesce at the end of the heap.
5404 largestAddr = _cmsSpace->end();
5405 }
5406 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5407 size_t nearLargestOffset =
5408 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5409 log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5410 p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5411 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5412 }
5413
5414 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5415 return addr >= _cmsSpace->nearLargestChunk();
5416 }
5417
5418 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5419 return _cmsSpace->find_chunk_at_end();
5420 }
5421
5422 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5423 bool full) {
5424 // If the young generation has been collected, gather any statistics
5425 // that are of interest at this point.
5426 bool current_is_young = CMSHeap::heap()->is_young_gen(current_generation);
5427 if (!full && current_is_young) {
5428 // Gather statistics on the young generation collection.
5429 collector()->stats().record_gc0_end(used());
5430 }
5431 }
5432
5433 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5434 // We iterate over the space(s) underlying this generation,
5435 // checking the mark bit map to see if the bits corresponding
5436 // to specific blocks are marked or not. Blocks that are
5437 // marked are live and are not swept up. All remaining blocks
5438 // are swept up, with coalescing on-the-fly as we sweep up
5439 // contiguous free and/or garbage blocks:
5440 // We need to ensure that the sweeper synchronizes with allocators
5441 // and stop-the-world collectors. In particular, the following
5442 // locks are used:
5443 // . CMS token: if this is held, a stop the world collection cannot occur
5444 // . freelistLock: if this is held no allocation can occur from this
5445 // generation by another thread
5446 // . bitMapLock: if this is held, no other thread can access or update
5447 //
5448
5449 // Note that we need to hold the freelistLock if we use
5450 // block iterate below; else the iterator might go awry if
5451 // a mutator (or promotion) causes block contents to change
5452 // (for instance if the allocator divvies up a block).
5453 // If we hold the free list lock, for all practical purposes
5454 // young generation GC's can't occur (they'll usually need to
5455 // promote), so we might as well prevent all young generation
5456 // GC's while we do a sweeping step. For the same reason, we might
5457 // as well take the bit map lock for the entire duration
5458
5459 // check that we hold the requisite locks
5460 assert(have_cms_token(), "Should hold cms token");
5461 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5462 assert_lock_strong(old_gen->freelistLock());
5463 assert_lock_strong(bitMapLock());
5464
5465 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5466 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5467 old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5468 _inter_sweep_estimate.padded_average(),
5469 _intra_sweep_estimate.padded_average());
5470 old_gen->setNearLargestChunk();
5471
5472 {
5473 SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5474 old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5475 // We need to free-up/coalesce garbage/blocks from a
5476 // co-terminal free run. This is done in the SweepClosure
5477 // destructor; so, do not remove this scope, else the
5478 // end-of-sweep-census below will be off by a little bit.
5479 }
5480 old_gen->cmsSpace()->sweep_completed();
5481 old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5482 if (should_unload_classes()) { // unloaded classes this cycle,
5483 _concurrent_cycles_since_last_unload = 0; // ... reset count
5484 } else { // did not unload classes,
5485 _concurrent_cycles_since_last_unload++; // ... increment count
5486 }
5487 }
5488
5489 // Reset CMS data structures (for now just the marking bit map)
5490 // preparatory for the next cycle.
5491 void CMSCollector::reset_concurrent() {
5492 CMSTokenSyncWithLocks ts(true, bitMapLock());
5493
5494 // If the state is not "Resetting", the foreground thread
5495 // has done a collection and the resetting.
5496 if (_collectorState != Resetting) {
5497 assert(_collectorState == Idling, "The state should only change"
5498 " because the foreground collector has finished the collection");
5499 return;
5500 }
5501
5502 {
5503 // Clear the mark bitmap (no grey objects to start with)
5504 // for the next cycle.
5505 GCTraceCPUTime tcpu;
5506 CMSPhaseAccounting cmspa(this, "Concurrent Reset");
5507
5508 HeapWord* curAddr = _markBitMap.startWord();
5509 while (curAddr < _markBitMap.endWord()) {
5510 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5511 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5512 _markBitMap.clear_large_range(chunk);
5513 if (ConcurrentMarkSweepThread::should_yield() &&
5514 !foregroundGCIsActive() &&
5515 CMSYield) {
5516 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5517 "CMS thread should hold CMS token");
5518 assert_lock_strong(bitMapLock());
5519 bitMapLock()->unlock();
5520 ConcurrentMarkSweepThread::desynchronize(true);
5521 stopTimer();
5522 incrementYields();
5523
5524 // See the comment in coordinator_yield()
5525 for (unsigned i = 0; i < CMSYieldSleepCount &&
5526 ConcurrentMarkSweepThread::should_yield() &&
5527 !CMSCollector::foregroundGCIsActive(); ++i) {
5528 os::sleep(Thread::current(), 1, false);
5529 }
5530
5531 ConcurrentMarkSweepThread::synchronize(true);
5532 bitMapLock()->lock_without_safepoint_check();
5533 startTimer();
5534 }
5535 curAddr = chunk.end();
5536 }
5537 // A successful mostly concurrent collection has been done.
5538 // Because only the full (i.e., concurrent mode failure) collections
5539 // are being measured for gc overhead limits, clean the "near" flag
5540 // and count.
5541 size_policy()->reset_gc_overhead_limit_count();
5542 _collectorState = Idling;
5543 }
5544
5545 register_gc_end();
5546 }
5547
5548 // Same as above but for STW paths
5549 void CMSCollector::reset_stw() {
5550 // already have the lock
5551 assert(_collectorState == Resetting, "just checking");
5552 assert_lock_strong(bitMapLock());
5553 GCIdMark gc_id_mark(_cmsThread->gc_id());
5554 _markBitMap.clear_all();
5555 _collectorState = Idling;
5556 register_gc_end();
5557 }
5558
5559 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5560 GCTraceCPUTime tcpu;
5561 TraceCollectorStats tcs_cgc(cgc_counters());
5562
5563 switch (op) {
5564 case CMS_op_checkpointRootsInitial: {
5565 GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5566 SvcGCMarker sgcm(SvcGCMarker::CONCURRENT);
5567 checkpointRootsInitial();
5568 break;
5569 }
5570 case CMS_op_checkpointRootsFinal: {
5571 GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5572 SvcGCMarker sgcm(SvcGCMarker::CONCURRENT);
5573 checkpointRootsFinal();
5574 break;
5575 }
5576 default:
5577 fatal("No such CMS_op");
5578 }
5579 }
5580
5581 #ifndef PRODUCT
5582 size_t const CMSCollector::skip_header_HeapWords() {
5583 return FreeChunk::header_size();
5584 }
5585
5586 // Try and collect here conditions that should hold when
5587 // CMS thread is exiting. The idea is that the foreground GC
5588 // thread should not be blocked if it wants to terminate
5589 // the CMS thread and yet continue to run the VM for a while
5590 // after that.
5591 void CMSCollector::verify_ok_to_terminate() const {
5592 assert(Thread::current()->is_ConcurrentGC_thread(),
5593 "should be called by CMS thread");
5594 assert(!_foregroundGCShouldWait, "should be false");
5595 // We could check here that all the various low-level locks
5596 // are not held by the CMS thread, but that is overkill; see
5597 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5598 // is checked.
5599 }
5600 #endif
5601
5602 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5603 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5604 "missing Printezis mark?");
5605 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5606 size_t size = pointer_delta(nextOneAddr + 1, addr);
5607 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5608 "alignment problem");
5609 assert(size >= 3, "Necessary for Printezis marks to work");
5610 return size;
5611 }
5612
5613 // A variant of the above (block_size_using_printezis_bits()) except
5614 // that we return 0 if the P-bits are not yet set.
5615 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5616 if (_markBitMap.isMarked(addr + 1)) {
5617 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5618 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5619 size_t size = pointer_delta(nextOneAddr + 1, addr);
5620 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5621 "alignment problem");
5622 assert(size >= 3, "Necessary for Printezis marks to work");
5623 return size;
5624 }
5625 return 0;
5626 }
5627
5628 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5629 size_t sz = 0;
5630 oop p = (oop)addr;
5631 if (p->klass_or_null_acquire() != NULL) {
5632 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5633 } else {
5634 sz = block_size_using_printezis_bits(addr);
5635 }
5636 assert(sz > 0, "size must be nonzero");
5637 HeapWord* next_block = addr + sz;
5638 HeapWord* next_card = align_up(next_block, CardTable::card_size);
5639 assert(align_down((uintptr_t)addr, CardTable::card_size) <
5640 align_down((uintptr_t)next_card, CardTable::card_size),
5641 "must be different cards");
5642 return next_card;
5643 }
5644
5645
5646 // CMS Bit Map Wrapper /////////////////////////////////////////
5647
5648 // Construct a CMS bit map infrastructure, but don't create the
5649 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5650 // further below.
5651 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5652 _bm(),
5653 _shifter(shifter),
5654 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5655 Monitor::_safepoint_check_sometimes) : NULL)
5656 {
5657 _bmStartWord = 0;
5658 _bmWordSize = 0;
5659 }
5660
5661 bool CMSBitMap::allocate(MemRegion mr) {
5662 _bmStartWord = mr.start();
5663 _bmWordSize = mr.word_size();
5664 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5665 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5666 if (!brs.is_reserved()) {
5667 log_warning(gc)("CMS bit map allocation failure");
5668 return false;
5669 }
5670 // For now we'll just commit all of the bit map up front.
5671 // Later on we'll try to be more parsimonious with swap.
5672 if (!_virtual_space.initialize(brs, brs.size())) {
5673 log_warning(gc)("CMS bit map backing store failure");
5674 return false;
5675 }
5676 assert(_virtual_space.committed_size() == brs.size(),
5677 "didn't reserve backing store for all of CMS bit map?");
5678 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5679 _bmWordSize, "inconsistency in bit map sizing");
5680 _bm = BitMapView((BitMap::bm_word_t*)_virtual_space.low(), _bmWordSize >> _shifter);
5681
5682 // bm.clear(); // can we rely on getting zero'd memory? verify below
5683 assert(isAllClear(),
5684 "Expected zero'd memory from ReservedSpace constructor");
5685 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5686 "consistency check");
5687 return true;
5688 }
5689
5690 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5691 HeapWord *next_addr, *end_addr, *last_addr;
5692 assert_locked();
5693 assert(covers(mr), "out-of-range error");
5694 // XXX assert that start and end are appropriately aligned
5695 for (next_addr = mr.start(), end_addr = mr.end();
5696 next_addr < end_addr; next_addr = last_addr) {
5697 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5698 last_addr = dirty_region.end();
5699 if (!dirty_region.is_empty()) {
5700 cl->do_MemRegion(dirty_region);
5701 } else {
5702 assert(last_addr == end_addr, "program logic");
5703 return;
5704 }
5705 }
5706 }
5707
5708 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5709 _bm.print_on_error(st, prefix);
5710 }
5711
5712 #ifndef PRODUCT
5713 void CMSBitMap::assert_locked() const {
5714 CMSLockVerifier::assert_locked(lock());
5715 }
5716
5717 bool CMSBitMap::covers(MemRegion mr) const {
5718 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5719 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5720 "size inconsistency");
5721 return (mr.start() >= _bmStartWord) &&
5722 (mr.end() <= endWord());
5723 }
5724
5725 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5726 return (start >= _bmStartWord && (start + size) <= endWord());
5727 }
5728
5729 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5730 // verify that there are no 1 bits in the interval [left, right)
5731 FalseBitMapClosure falseBitMapClosure;
5732 iterate(&falseBitMapClosure, left, right);
5733 }
5734
5735 void CMSBitMap::region_invariant(MemRegion mr)
5736 {
5737 assert_locked();
5738 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5739 assert(!mr.is_empty(), "unexpected empty region");
5740 assert(covers(mr), "mr should be covered by bit map");
5741 // convert address range into offset range
5742 size_t start_ofs = heapWordToOffset(mr.start());
5743 // Make sure that end() is appropriately aligned
5744 assert(mr.end() == align_up(mr.end(), (1 << (_shifter+LogHeapWordSize))),
5745 "Misaligned mr.end()");
5746 size_t end_ofs = heapWordToOffset(mr.end());
5747 assert(end_ofs > start_ofs, "Should mark at least one bit");
5748 }
5749
5750 #endif
5751
5752 bool CMSMarkStack::allocate(size_t size) {
5753 // allocate a stack of the requisite depth
5754 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5755 size * sizeof(oop)));
5756 if (!rs.is_reserved()) {
5757 log_warning(gc)("CMSMarkStack allocation failure");
5758 return false;
5759 }
5760 if (!_virtual_space.initialize(rs, rs.size())) {
5761 log_warning(gc)("CMSMarkStack backing store failure");
5762 return false;
5763 }
5764 assert(_virtual_space.committed_size() == rs.size(),
5765 "didn't reserve backing store for all of CMS stack?");
5766 _base = (oop*)(_virtual_space.low());
5767 _index = 0;
5768 _capacity = size;
5769 NOT_PRODUCT(_max_depth = 0);
5770 return true;
5771 }
5772
5773 // XXX FIX ME !!! In the MT case we come in here holding a
5774 // leaf lock. For printing we need to take a further lock
5775 // which has lower rank. We need to recalibrate the two
5776 // lock-ranks involved in order to be able to print the
5777 // messages below. (Or defer the printing to the caller.
5778 // For now we take the expedient path of just disabling the
5779 // messages for the problematic case.)
5780 void CMSMarkStack::expand() {
5781 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5782 if (_capacity == MarkStackSizeMax) {
5783 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5784 // We print a warning message only once per CMS cycle.
5785 log_debug(gc)(" (benign) Hit CMSMarkStack max size limit");
5786 }
5787 return;
5788 }
5789 // Double capacity if possible
5790 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5791 // Do not give up existing stack until we have managed to
5792 // get the double capacity that we desired.
5793 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5794 new_capacity * sizeof(oop)));
5795 if (rs.is_reserved()) {
5796 // Release the backing store associated with old stack
5797 _virtual_space.release();
5798 // Reinitialize virtual space for new stack
5799 if (!_virtual_space.initialize(rs, rs.size())) {
5800 fatal("Not enough swap for expanded marking stack");
5801 }
5802 _base = (oop*)(_virtual_space.low());
5803 _index = 0;
5804 _capacity = new_capacity;
5805 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5806 // Failed to double capacity, continue;
5807 // we print a detail message only once per CMS cycle.
5808 log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5809 _capacity / K, new_capacity / K);
5810 }
5811 }
5812
5813
5814 // Closures
5815 // XXX: there seems to be a lot of code duplication here;
5816 // should refactor and consolidate common code.
5817
5818 // This closure is used to mark refs into the CMS generation in
5819 // the CMS bit map. Called at the first checkpoint. This closure
5820 // assumes that we do not need to re-mark dirty cards; if the CMS
5821 // generation on which this is used is not an oldest
5822 // generation then this will lose younger_gen cards!
5823
5824 MarkRefsIntoClosure::MarkRefsIntoClosure(
5825 MemRegion span, CMSBitMap* bitMap):
5826 _span(span),
5827 _bitMap(bitMap)
5828 {
5829 assert(ref_discoverer() == NULL, "deliberately left NULL");
5830 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5831 }
5832
5833 void MarkRefsIntoClosure::do_oop(oop obj) {
5834 // if p points into _span, then mark corresponding bit in _markBitMap
5835 assert(oopDesc::is_oop(obj), "expected an oop");
5836 HeapWord* addr = (HeapWord*)obj;
5837 if (_span.contains(addr)) {
5838 // this should be made more efficient
5839 _bitMap->mark(addr);
5840 }
5841 }
5842
5843 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5844 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5845
5846 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure(
5847 MemRegion span, CMSBitMap* bitMap):
5848 _span(span),
5849 _bitMap(bitMap)
5850 {
5851 assert(ref_discoverer() == NULL, "deliberately left NULL");
5852 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5853 }
5854
5855 void ParMarkRefsIntoClosure::do_oop(oop obj) {
5856 // if p points into _span, then mark corresponding bit in _markBitMap
5857 assert(oopDesc::is_oop(obj), "expected an oop");
5858 HeapWord* addr = (HeapWord*)obj;
5859 if (_span.contains(addr)) {
5860 // this should be made more efficient
5861 _bitMap->par_mark(addr);
5862 }
5863 }
5864
5865 void ParMarkRefsIntoClosure::do_oop(oop* p) { ParMarkRefsIntoClosure::do_oop_work(p); }
5866 void ParMarkRefsIntoClosure::do_oop(narrowOop* p) { ParMarkRefsIntoClosure::do_oop_work(p); }
5867
5868 // A variant of the above, used for CMS marking verification.
5869 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5870 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5871 _span(span),
5872 _verification_bm(verification_bm),
5873 _cms_bm(cms_bm)
5874 {
5875 assert(ref_discoverer() == NULL, "deliberately left NULL");
5876 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5877 }
5878
5879 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5880 // if p points into _span, then mark corresponding bit in _markBitMap
5881 assert(oopDesc::is_oop(obj), "expected an oop");
5882 HeapWord* addr = (HeapWord*)obj;
5883 if (_span.contains(addr)) {
5884 _verification_bm->mark(addr);
5885 if (!_cms_bm->isMarked(addr)) {
5886 Log(gc, verify) log;
5887 ResourceMark rm;
5888 LogStream ls(log.error());
5889 oop(addr)->print_on(&ls);
5890 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5891 fatal("... aborting");
5892 }
5893 }
5894 }
5895
5896 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5897 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5898
5899 //////////////////////////////////////////////////
5900 // MarkRefsIntoAndScanClosure
5901 //////////////////////////////////////////////////
5902
5903 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5904 ReferenceDiscoverer* rd,
5905 CMSBitMap* bit_map,
5906 CMSBitMap* mod_union_table,
5907 CMSMarkStack* mark_stack,
5908 CMSCollector* collector,
5909 bool should_yield,
5910 bool concurrent_precleaning):
5911 _collector(collector),
5912 _span(span),
5913 _bit_map(bit_map),
5914 _mark_stack(mark_stack),
5915 _pushAndMarkClosure(collector, span, rd, bit_map, mod_union_table,
5916 mark_stack, concurrent_precleaning),
5917 _yield(should_yield),
5918 _concurrent_precleaning(concurrent_precleaning),
5919 _freelistLock(NULL)
5920 {
5921 // FIXME: Should initialize in base class constructor.
5922 assert(rd != NULL, "ref_discoverer shouldn't be NULL");
5923 set_ref_discoverer_internal(rd);
5924 }
5925
5926 // This closure is used to mark refs into the CMS generation at the
5927 // second (final) checkpoint, and to scan and transitively follow
5928 // the unmarked oops. It is also used during the concurrent precleaning
5929 // phase while scanning objects on dirty cards in the CMS generation.
5930 // The marks are made in the marking bit map and the marking stack is
5931 // used for keeping the (newly) grey objects during the scan.
5932 // The parallel version (Par_...) appears further below.
5933 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5934 if (obj != NULL) {
5935 assert(oopDesc::is_oop(obj), "expected an oop");
5936 HeapWord* addr = (HeapWord*)obj;
5937 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5938 assert(_collector->overflow_list_is_empty(),
5939 "overflow list should be empty");
5940 if (_span.contains(addr) &&
5941 !_bit_map->isMarked(addr)) {
5942 // mark bit map (object is now grey)
5943 _bit_map->mark(addr);
5944 // push on marking stack (stack should be empty), and drain the
5945 // stack by applying this closure to the oops in the oops popped
5946 // from the stack (i.e. blacken the grey objects)
5947 bool res = _mark_stack->push(obj);
5948 assert(res, "Should have space to push on empty stack");
5949 do {
5950 oop new_oop = _mark_stack->pop();
5951 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
5952 assert(_bit_map->isMarked((HeapWord*)new_oop),
5953 "only grey objects on this stack");
5954 // iterate over the oops in this oop, marking and pushing
5955 // the ones in CMS heap (i.e. in _span).
5956 new_oop->oop_iterate(&_pushAndMarkClosure);
5957 // check if it's time to yield
5958 do_yield_check();
5959 } while (!_mark_stack->isEmpty() ||
5960 (!_concurrent_precleaning && take_from_overflow_list()));
5961 // if marking stack is empty, and we are not doing this
5962 // during precleaning, then check the overflow list
5963 }
5964 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5965 assert(_collector->overflow_list_is_empty(),
5966 "overflow list was drained above");
5967
5968 assert(_collector->no_preserved_marks(),
5969 "All preserved marks should have been restored above");
5970 }
5971 }
5972
5973 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5974 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5975
5976 void MarkRefsIntoAndScanClosure::do_yield_work() {
5977 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5978 "CMS thread should hold CMS token");
5979 assert_lock_strong(_freelistLock);
5980 assert_lock_strong(_bit_map->lock());
5981 // relinquish the free_list_lock and bitMaplock()
5982 _bit_map->lock()->unlock();
5983 _freelistLock->unlock();
5984 ConcurrentMarkSweepThread::desynchronize(true);
5985 _collector->stopTimer();
5986 _collector->incrementYields();
5987
5988 // See the comment in coordinator_yield()
5989 for (unsigned i = 0;
5990 i < CMSYieldSleepCount &&
5991 ConcurrentMarkSweepThread::should_yield() &&
5992 !CMSCollector::foregroundGCIsActive();
5993 ++i) {
5994 os::sleep(Thread::current(), 1, false);
5995 }
5996
5997 ConcurrentMarkSweepThread::synchronize(true);
5998 _freelistLock->lock_without_safepoint_check();
5999 _bit_map->lock()->lock_without_safepoint_check();
6000 _collector->startTimer();
6001 }
6002
6003 ///////////////////////////////////////////////////////////
6004 // ParMarkRefsIntoAndScanClosure: a parallel version of
6005 // MarkRefsIntoAndScanClosure
6006 ///////////////////////////////////////////////////////////
6007 ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure(
6008 CMSCollector* collector, MemRegion span, ReferenceDiscoverer* rd,
6009 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6010 _span(span),
6011 _bit_map(bit_map),
6012 _work_queue(work_queue),
6013 _low_water_mark(MIN2((work_queue->max_elems()/4),
6014 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6015 _parPushAndMarkClosure(collector, span, rd, bit_map, work_queue)
6016 {
6017 // FIXME: Should initialize in base class constructor.
6018 assert(rd != NULL, "ref_discoverer shouldn't be NULL");
6019 set_ref_discoverer_internal(rd);
6020 }
6021
6022 // This closure is used to mark refs into the CMS generation at the
6023 // second (final) checkpoint, and to scan and transitively follow
6024 // the unmarked oops. The marks are made in the marking bit map and
6025 // the work_queue is used for keeping the (newly) grey objects during
6026 // the scan phase whence they are also available for stealing by parallel
6027 // threads. Since the marking bit map is shared, updates are
6028 // synchronized (via CAS).
6029 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) {
6030 if (obj != NULL) {
6031 // Ignore mark word because this could be an already marked oop
6032 // that may be chained at the end of the overflow list.
6033 assert(oopDesc::is_oop(obj, true), "expected an oop");
6034 HeapWord* addr = (HeapWord*)obj;
6035 if (_span.contains(addr) &&
6036 !_bit_map->isMarked(addr)) {
6037 // mark bit map (object will become grey):
6038 // It is possible for several threads to be
6039 // trying to "claim" this object concurrently;
6040 // the unique thread that succeeds in marking the
6041 // object first will do the subsequent push on
6042 // to the work queue (or overflow list).
6043 if (_bit_map->par_mark(addr)) {
6044 // push on work_queue (which may not be empty), and trim the
6045 // queue to an appropriate length by applying this closure to
6046 // the oops in the oops popped from the stack (i.e. blacken the
6047 // grey objects)
6048 bool res = _work_queue->push(obj);
6049 assert(res, "Low water mark should be less than capacity?");
6050 trim_queue(_low_water_mark);
6051 } // Else, another thread claimed the object
6052 }
6053 }
6054 }
6055
6056 void ParMarkRefsIntoAndScanClosure::do_oop(oop* p) { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6057 void ParMarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6058
6059 // This closure is used to rescan the marked objects on the dirty cards
6060 // in the mod union table and the card table proper.
6061 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6062 oop p, MemRegion mr) {
6063
6064 size_t size = 0;
6065 HeapWord* addr = (HeapWord*)p;
6066 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6067 assert(_span.contains(addr), "we are scanning the CMS generation");
6068 // check if it's time to yield
6069 if (do_yield_check()) {
6070 // We yielded for some foreground stop-world work,
6071 // and we have been asked to abort this ongoing preclean cycle.
6072 return 0;
6073 }
6074 if (_bitMap->isMarked(addr)) {
6075 // it's marked; is it potentially uninitialized?
6076 if (p->klass_or_null_acquire() != NULL) {
6077 // an initialized object; ignore mark word in verification below
6078 // since we are running concurrent with mutators
6079 assert(oopDesc::is_oop(p, true), "should be an oop");
6080 if (p->is_objArray()) {
6081 // objArrays are precisely marked; restrict scanning
6082 // to dirty cards only.
6083 size = CompactibleFreeListSpace::adjustObjectSize(
6084 p->oop_iterate_size(_scanningClosure, mr));
6085 } else {
6086 // A non-array may have been imprecisely marked; we need
6087 // to scan object in its entirety.
6088 size = CompactibleFreeListSpace::adjustObjectSize(
6089 p->oop_iterate_size(_scanningClosure));
6090 }
6091 #ifdef ASSERT
6092 size_t direct_size =
6093 CompactibleFreeListSpace::adjustObjectSize(p->size());
6094 assert(size == direct_size, "Inconsistency in size");
6095 assert(size >= 3, "Necessary for Printezis marks to work");
6096 HeapWord* start_pbit = addr + 1;
6097 HeapWord* end_pbit = addr + size - 1;
6098 assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit),
6099 "inconsistent Printezis mark");
6100 // Verify inner mark bits (between Printezis bits) are clear,
6101 // but don't repeat if there are multiple dirty regions for
6102 // the same object, to avoid potential O(N^2) performance.
6103 if (addr != _last_scanned_object) {
6104 _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit);
6105 _last_scanned_object = addr;
6106 }
6107 #endif // ASSERT
6108 } else {
6109 // An uninitialized object.
6110 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6111 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6112 size = pointer_delta(nextOneAddr + 1, addr);
6113 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6114 "alignment problem");
6115 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6116 // will dirty the card when the klass pointer is installed in the
6117 // object (signaling the completion of initialization).
6118 }
6119 } else {
6120 // Either a not yet marked object or an uninitialized object
6121 if (p->klass_or_null_acquire() == NULL) {
6122 // An uninitialized object, skip to the next card, since
6123 // we may not be able to read its P-bits yet.
6124 assert(size == 0, "Initial value");
6125 } else {
6126 // An object not (yet) reached by marking: we merely need to
6127 // compute its size so as to go look at the next block.
6128 assert(oopDesc::is_oop(p, true), "should be an oop");
6129 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6130 }
6131 }
6132 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6133 return size;
6134 }
6135
6136 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6137 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6138 "CMS thread should hold CMS token");
6139 assert_lock_strong(_freelistLock);
6140 assert_lock_strong(_bitMap->lock());
6141 // relinquish the free_list_lock and bitMaplock()
6142 _bitMap->lock()->unlock();
6143 _freelistLock->unlock();
6144 ConcurrentMarkSweepThread::desynchronize(true);
6145 _collector->stopTimer();
6146 _collector->incrementYields();
6147
6148 // See the comment in coordinator_yield()
6149 for (unsigned i = 0; i < CMSYieldSleepCount &&
6150 ConcurrentMarkSweepThread::should_yield() &&
6151 !CMSCollector::foregroundGCIsActive(); ++i) {
6152 os::sleep(Thread::current(), 1, false);
6153 }
6154
6155 ConcurrentMarkSweepThread::synchronize(true);
6156 _freelistLock->lock_without_safepoint_check();
6157 _bitMap->lock()->lock_without_safepoint_check();
6158 _collector->startTimer();
6159 }
6160
6161
6162 //////////////////////////////////////////////////////////////////
6163 // SurvivorSpacePrecleanClosure
6164 //////////////////////////////////////////////////////////////////
6165 // This (single-threaded) closure is used to preclean the oops in
6166 // the survivor spaces.
6167 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6168
6169 HeapWord* addr = (HeapWord*)p;
6170 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6171 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6172 assert(p->klass_or_null() != NULL, "object should be initialized");
6173 // an initialized object; ignore mark word in verification below
6174 // since we are running concurrent with mutators
6175 assert(oopDesc::is_oop(p, true), "should be an oop");
6176 // Note that we do not yield while we iterate over
6177 // the interior oops of p, pushing the relevant ones
6178 // on our marking stack.
6179 size_t size = p->oop_iterate_size(_scanning_closure);
6180 do_yield_check();
6181 // Observe that below, we do not abandon the preclean
6182 // phase as soon as we should; rather we empty the
6183 // marking stack before returning. This is to satisfy
6184 // some existing assertions. In general, it may be a
6185 // good idea to abort immediately and complete the marking
6186 // from the grey objects at a later time.
6187 while (!_mark_stack->isEmpty()) {
6188 oop new_oop = _mark_stack->pop();
6189 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
6190 assert(_bit_map->isMarked((HeapWord*)new_oop),
6191 "only grey objects on this stack");
6192 // iterate over the oops in this oop, marking and pushing
6193 // the ones in CMS heap (i.e. in _span).
6194 new_oop->oop_iterate(_scanning_closure);
6195 // check if it's time to yield
6196 do_yield_check();
6197 }
6198 unsigned int after_count =
6199 CMSHeap::heap()->total_collections();
6200 bool abort = (_before_count != after_count) ||
6201 _collector->should_abort_preclean();
6202 return abort ? 0 : size;
6203 }
6204
6205 void SurvivorSpacePrecleanClosure::do_yield_work() {
6206 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6207 "CMS thread should hold CMS token");
6208 assert_lock_strong(_bit_map->lock());
6209 // Relinquish the bit map lock
6210 _bit_map->lock()->unlock();
6211 ConcurrentMarkSweepThread::desynchronize(true);
6212 _collector->stopTimer();
6213 _collector->incrementYields();
6214
6215 // See the comment in coordinator_yield()
6216 for (unsigned i = 0; i < CMSYieldSleepCount &&
6217 ConcurrentMarkSweepThread::should_yield() &&
6218 !CMSCollector::foregroundGCIsActive(); ++i) {
6219 os::sleep(Thread::current(), 1, false);
6220 }
6221
6222 ConcurrentMarkSweepThread::synchronize(true);
6223 _bit_map->lock()->lock_without_safepoint_check();
6224 _collector->startTimer();
6225 }
6226
6227 // This closure is used to rescan the marked objects on the dirty cards
6228 // in the mod union table and the card table proper. In the parallel
6229 // case, although the bitMap is shared, we do a single read so the
6230 // isMarked() query is "safe".
6231 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6232 // Ignore mark word because we are running concurrent with mutators
6233 assert(oopDesc::is_oop_or_null(p, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6234 HeapWord* addr = (HeapWord*)p;
6235 assert(_span.contains(addr), "we are scanning the CMS generation");
6236 bool is_obj_array = false;
6237 #ifdef ASSERT
6238 if (!_parallel) {
6239 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6240 assert(_collector->overflow_list_is_empty(),
6241 "overflow list should be empty");
6242
6243 }
6244 #endif // ASSERT
6245 if (_bit_map->isMarked(addr)) {
6246 // Obj arrays are precisely marked, non-arrays are not;
6247 // so we scan objArrays precisely and non-arrays in their
6248 // entirety.
6249 if (p->is_objArray()) {
6250 is_obj_array = true;
6251 if (_parallel) {
6252 p->oop_iterate(_par_scan_closure, mr);
6253 } else {
6254 p->oop_iterate(_scan_closure, mr);
6255 }
6256 } else {
6257 if (_parallel) {
6258 p->oop_iterate(_par_scan_closure);
6259 } else {
6260 p->oop_iterate(_scan_closure);
6261 }
6262 }
6263 }
6264 #ifdef ASSERT
6265 if (!_parallel) {
6266 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6267 assert(_collector->overflow_list_is_empty(),
6268 "overflow list should be empty");
6269
6270 }
6271 #endif // ASSERT
6272 return is_obj_array;
6273 }
6274
6275 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6276 MemRegion span,
6277 CMSBitMap* bitMap, CMSMarkStack* markStack,
6278 bool should_yield, bool verifying):
6279 _collector(collector),
6280 _span(span),
6281 _bitMap(bitMap),
6282 _mut(&collector->_modUnionTable),
6283 _markStack(markStack),
6284 _yield(should_yield),
6285 _skipBits(0)
6286 {
6287 assert(_markStack->isEmpty(), "stack should be empty");
6288 _finger = _bitMap->startWord();
6289 _threshold = _finger;
6290 assert(_collector->_restart_addr == NULL, "Sanity check");
6291 assert(_span.contains(_finger), "Out of bounds _finger?");
6292 DEBUG_ONLY(_verifying = verifying;)
6293 }
6294
6295 void MarkFromRootsClosure::reset(HeapWord* addr) {
6296 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6297 assert(_span.contains(addr), "Out of bounds _finger?");
6298 _finger = addr;
6299 _threshold = align_up(_finger, CardTable::card_size);
6300 }
6301
6302 // Should revisit to see if this should be restructured for
6303 // greater efficiency.
6304 bool MarkFromRootsClosure::do_bit(size_t offset) {
6305 if (_skipBits > 0) {
6306 _skipBits--;
6307 return true;
6308 }
6309 // convert offset into a HeapWord*
6310 HeapWord* addr = _bitMap->startWord() + offset;
6311 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6312 "address out of range");
6313 assert(_bitMap->isMarked(addr), "tautology");
6314 if (_bitMap->isMarked(addr+1)) {
6315 // this is an allocated but not yet initialized object
6316 assert(_skipBits == 0, "tautology");
6317 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6318 oop p = oop(addr);
6319 if (p->klass_or_null_acquire() == NULL) {
6320 DEBUG_ONLY(if (!_verifying) {)
6321 // We re-dirty the cards on which this object lies and increase
6322 // the _threshold so that we'll come back to scan this object
6323 // during the preclean or remark phase. (CMSCleanOnEnter)
6324 if (CMSCleanOnEnter) {
6325 size_t sz = _collector->block_size_using_printezis_bits(addr);
6326 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
6327 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6328 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6329 // Bump _threshold to end_card_addr; note that
6330 // _threshold cannot possibly exceed end_card_addr, anyhow.
6331 // This prevents future clearing of the card as the scan proceeds
6332 // to the right.
6333 assert(_threshold <= end_card_addr,
6334 "Because we are just scanning into this object");
6335 if (_threshold < end_card_addr) {
6336 _threshold = end_card_addr;
6337 }
6338 if (p->klass_or_null_acquire() != NULL) {
6339 // Redirty the range of cards...
6340 _mut->mark_range(redirty_range);
6341 } // ...else the setting of klass will dirty the card anyway.
6342 }
6343 DEBUG_ONLY(})
6344 return true;
6345 }
6346 }
6347 scanOopsInOop(addr);
6348 return true;
6349 }
6350
6351 // We take a break if we've been at this for a while,
6352 // so as to avoid monopolizing the locks involved.
6353 void MarkFromRootsClosure::do_yield_work() {
6354 // First give up the locks, then yield, then re-lock
6355 // We should probably use a constructor/destructor idiom to
6356 // do this unlock/lock or modify the MutexUnlocker class to
6357 // serve our purpose. XXX
6358 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6359 "CMS thread should hold CMS token");
6360 assert_lock_strong(_bitMap->lock());
6361 _bitMap->lock()->unlock();
6362 ConcurrentMarkSweepThread::desynchronize(true);
6363 _collector->stopTimer();
6364 _collector->incrementYields();
6365
6366 // See the comment in coordinator_yield()
6367 for (unsigned i = 0; i < CMSYieldSleepCount &&
6368 ConcurrentMarkSweepThread::should_yield() &&
6369 !CMSCollector::foregroundGCIsActive(); ++i) {
6370 os::sleep(Thread::current(), 1, false);
6371 }
6372
6373 ConcurrentMarkSweepThread::synchronize(true);
6374 _bitMap->lock()->lock_without_safepoint_check();
6375 _collector->startTimer();
6376 }
6377
6378 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6379 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6380 assert(_markStack->isEmpty(),
6381 "should drain stack to limit stack usage");
6382 // convert ptr to an oop preparatory to scanning
6383 oop obj = oop(ptr);
6384 // Ignore mark word in verification below, since we
6385 // may be running concurrent with mutators.
6386 assert(oopDesc::is_oop(obj, true), "should be an oop");
6387 assert(_finger <= ptr, "_finger runneth ahead");
6388 // advance the finger to right end of this object
6389 _finger = ptr + obj->size();
6390 assert(_finger > ptr, "we just incremented it above");
6391 // On large heaps, it may take us some time to get through
6392 // the marking phase. During
6393 // this time it's possible that a lot of mutations have
6394 // accumulated in the card table and the mod union table --
6395 // these mutation records are redundant until we have
6396 // actually traced into the corresponding card.
6397 // Here, we check whether advancing the finger would make
6398 // us cross into a new card, and if so clear corresponding
6399 // cards in the MUT (preclean them in the card-table in the
6400 // future).
6401
6402 DEBUG_ONLY(if (!_verifying) {)
6403 // The clean-on-enter optimization is disabled by default,
6404 // until we fix 6178663.
6405 if (CMSCleanOnEnter && (_finger > _threshold)) {
6406 // [_threshold, _finger) represents the interval
6407 // of cards to be cleared in MUT (or precleaned in card table).
6408 // The set of cards to be cleared is all those that overlap
6409 // with the interval [_threshold, _finger); note that
6410 // _threshold is always kept card-aligned but _finger isn't
6411 // always card-aligned.
6412 HeapWord* old_threshold = _threshold;
6413 assert(is_aligned(old_threshold, CardTable::card_size),
6414 "_threshold should always be card-aligned");
6415 _threshold = align_up(_finger, CardTable::card_size);
6416 MemRegion mr(old_threshold, _threshold);
6417 assert(!mr.is_empty(), "Control point invariant");
6418 assert(_span.contains(mr), "Should clear within span");
6419 _mut->clear_range(mr);
6420 }
6421 DEBUG_ONLY(})
6422 // Note: the finger doesn't advance while we drain
6423 // the stack below.
6424 PushOrMarkClosure pushOrMarkClosure(_collector,
6425 _span, _bitMap, _markStack,
6426 _finger, this);
6427 bool res = _markStack->push(obj);
6428 assert(res, "Empty non-zero size stack should have space for single push");
6429 while (!_markStack->isEmpty()) {
6430 oop new_oop = _markStack->pop();
6431 // Skip verifying header mark word below because we are
6432 // running concurrent with mutators.
6433 assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6434 // now scan this oop's oops
6435 new_oop->oop_iterate(&pushOrMarkClosure);
6436 do_yield_check();
6437 }
6438 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6439 }
6440
6441 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task,
6442 CMSCollector* collector, MemRegion span,
6443 CMSBitMap* bit_map,
6444 OopTaskQueue* work_queue,
6445 CMSMarkStack* overflow_stack):
6446 _collector(collector),
6447 _whole_span(collector->_span),
6448 _span(span),
6449 _bit_map(bit_map),
6450 _mut(&collector->_modUnionTable),
6451 _work_queue(work_queue),
6452 _overflow_stack(overflow_stack),
6453 _skip_bits(0),
6454 _task(task)
6455 {
6456 assert(_work_queue->size() == 0, "work_queue should be empty");
6457 _finger = span.start();
6458 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6459 assert(_span.contains(_finger), "Out of bounds _finger?");
6460 }
6461
6462 // Should revisit to see if this should be restructured for
6463 // greater efficiency.
6464 bool ParMarkFromRootsClosure::do_bit(size_t offset) {
6465 if (_skip_bits > 0) {
6466 _skip_bits--;
6467 return true;
6468 }
6469 // convert offset into a HeapWord*
6470 HeapWord* addr = _bit_map->startWord() + offset;
6471 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6472 "address out of range");
6473 assert(_bit_map->isMarked(addr), "tautology");
6474 if (_bit_map->isMarked(addr+1)) {
6475 // this is an allocated object that might not yet be initialized
6476 assert(_skip_bits == 0, "tautology");
6477 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6478 oop p = oop(addr);
6479 if (p->klass_or_null_acquire() == NULL) {
6480 // in the case of Clean-on-Enter optimization, redirty card
6481 // and avoid clearing card by increasing the threshold.
6482 return true;
6483 }
6484 }
6485 scan_oops_in_oop(addr);
6486 return true;
6487 }
6488
6489 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6490 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6491 // Should we assert that our work queue is empty or
6492 // below some drain limit?
6493 assert(_work_queue->size() == 0,
6494 "should drain stack to limit stack usage");
6495 // convert ptr to an oop preparatory to scanning
6496 oop obj = oop(ptr);
6497 // Ignore mark word in verification below, since we
6498 // may be running concurrent with mutators.
6499 assert(oopDesc::is_oop(obj, true), "should be an oop");
6500 assert(_finger <= ptr, "_finger runneth ahead");
6501 // advance the finger to right end of this object
6502 _finger = ptr + obj->size();
6503 assert(_finger > ptr, "we just incremented it above");
6504 // On large heaps, it may take us some time to get through
6505 // the marking phase. During
6506 // this time it's possible that a lot of mutations have
6507 // accumulated in the card table and the mod union table --
6508 // these mutation records are redundant until we have
6509 // actually traced into the corresponding card.
6510 // Here, we check whether advancing the finger would make
6511 // us cross into a new card, and if so clear corresponding
6512 // cards in the MUT (preclean them in the card-table in the
6513 // future).
6514
6515 // The clean-on-enter optimization is disabled by default,
6516 // until we fix 6178663.
6517 if (CMSCleanOnEnter && (_finger > _threshold)) {
6518 // [_threshold, _finger) represents the interval
6519 // of cards to be cleared in MUT (or precleaned in card table).
6520 // The set of cards to be cleared is all those that overlap
6521 // with the interval [_threshold, _finger); note that
6522 // _threshold is always kept card-aligned but _finger isn't
6523 // always card-aligned.
6524 HeapWord* old_threshold = _threshold;
6525 assert(is_aligned(old_threshold, CardTable::card_size),
6526 "_threshold should always be card-aligned");
6527 _threshold = align_up(_finger, CardTable::card_size);
6528 MemRegion mr(old_threshold, _threshold);
6529 assert(!mr.is_empty(), "Control point invariant");
6530 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6531 _mut->clear_range(mr);
6532 }
6533
6534 // Note: the local finger doesn't advance while we drain
6535 // the stack below, but the global finger sure can and will.
6536 HeapWord* volatile* gfa = _task->global_finger_addr();
6537 ParPushOrMarkClosure pushOrMarkClosure(_collector,
6538 _span, _bit_map,
6539 _work_queue,
6540 _overflow_stack,
6541 _finger,
6542 gfa, this);
6543 bool res = _work_queue->push(obj); // overflow could occur here
6544 assert(res, "Will hold once we use workqueues");
6545 while (true) {
6546 oop new_oop;
6547 if (!_work_queue->pop_local(new_oop)) {
6548 // We emptied our work_queue; check if there's stuff that can
6549 // be gotten from the overflow stack.
6550 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6551 _overflow_stack, _work_queue)) {
6552 do_yield_check();
6553 continue;
6554 } else { // done
6555 break;
6556 }
6557 }
6558 // Skip verifying header mark word below because we are
6559 // running concurrent with mutators.
6560 assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6561 // now scan this oop's oops
6562 new_oop->oop_iterate(&pushOrMarkClosure);
6563 do_yield_check();
6564 }
6565 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6566 }
6567
6568 // Yield in response to a request from VM Thread or
6569 // from mutators.
6570 void ParMarkFromRootsClosure::do_yield_work() {
6571 assert(_task != NULL, "sanity");
6572 _task->yield();
6573 }
6574
6575 // A variant of the above used for verifying CMS marking work.
6576 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6577 MemRegion span,
6578 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6579 CMSMarkStack* mark_stack):
6580 _collector(collector),
6581 _span(span),
6582 _verification_bm(verification_bm),
6583 _cms_bm(cms_bm),
6584 _mark_stack(mark_stack),
6585 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6586 mark_stack)
6587 {
6588 assert(_mark_stack->isEmpty(), "stack should be empty");
6589 _finger = _verification_bm->startWord();
6590 assert(_collector->_restart_addr == NULL, "Sanity check");
6591 assert(_span.contains(_finger), "Out of bounds _finger?");
6592 }
6593
6594 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6595 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6596 assert(_span.contains(addr), "Out of bounds _finger?");
6597 _finger = addr;
6598 }
6599
6600 // Should revisit to see if this should be restructured for
6601 // greater efficiency.
6602 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6603 // convert offset into a HeapWord*
6604 HeapWord* addr = _verification_bm->startWord() + offset;
6605 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6606 "address out of range");
6607 assert(_verification_bm->isMarked(addr), "tautology");
6608 assert(_cms_bm->isMarked(addr), "tautology");
6609
6610 assert(_mark_stack->isEmpty(),
6611 "should drain stack to limit stack usage");
6612 // convert addr to an oop preparatory to scanning
6613 oop obj = oop(addr);
6614 assert(oopDesc::is_oop(obj), "should be an oop");
6615 assert(_finger <= addr, "_finger runneth ahead");
6616 // advance the finger to right end of this object
6617 _finger = addr + obj->size();
6618 assert(_finger > addr, "we just incremented it above");
6619 // Note: the finger doesn't advance while we drain
6620 // the stack below.
6621 bool res = _mark_stack->push(obj);
6622 assert(res, "Empty non-zero size stack should have space for single push");
6623 while (!_mark_stack->isEmpty()) {
6624 oop new_oop = _mark_stack->pop();
6625 assert(oopDesc::is_oop(new_oop), "Oops! expected to pop an oop");
6626 // now scan this oop's oops
6627 new_oop->oop_iterate(&_pam_verify_closure);
6628 }
6629 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6630 return true;
6631 }
6632
6633 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6634 CMSCollector* collector, MemRegion span,
6635 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6636 CMSMarkStack* mark_stack):
6637 MetadataAwareOopClosure(collector->ref_processor()),
6638 _collector(collector),
6639 _span(span),
6640 _verification_bm(verification_bm),
6641 _cms_bm(cms_bm),
6642 _mark_stack(mark_stack)
6643 { }
6644
6645 template <class T> void PushAndMarkVerifyClosure::do_oop_work(T *p) {
6646 oop obj = RawAccess<>::oop_load(p);
6647 do_oop(obj);
6648 }
6649
6650 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6651 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6652
6653 // Upon stack overflow, we discard (part of) the stack,
6654 // remembering the least address amongst those discarded
6655 // in CMSCollector's _restart_address.
6656 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6657 // Remember the least grey address discarded
6658 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6659 _collector->lower_restart_addr(ra);
6660 _mark_stack->reset(); // discard stack contents
6661 _mark_stack->expand(); // expand the stack if possible
6662 }
6663
6664 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6665 assert(oopDesc::is_oop_or_null(obj), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6666 HeapWord* addr = (HeapWord*)obj;
6667 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6668 // Oop lies in _span and isn't yet grey or black
6669 _verification_bm->mark(addr); // now grey
6670 if (!_cms_bm->isMarked(addr)) {
6671 Log(gc, verify) log;
6672 ResourceMark rm;
6673 LogStream ls(log.error());
6674 oop(addr)->print_on(&ls);
6675 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6676 fatal("... aborting");
6677 }
6678
6679 if (!_mark_stack->push(obj)) { // stack overflow
6680 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6681 assert(_mark_stack->isFull(), "Else push should have succeeded");
6682 handle_stack_overflow(addr);
6683 }
6684 // anything including and to the right of _finger
6685 // will be scanned as we iterate over the remainder of the
6686 // bit map
6687 }
6688 }
6689
6690 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6691 MemRegion span,
6692 CMSBitMap* bitMap, CMSMarkStack* markStack,
6693 HeapWord* finger, MarkFromRootsClosure* parent) :
6694 MetadataAwareOopClosure(collector->ref_processor()),
6695 _collector(collector),
6696 _span(span),
6697 _bitMap(bitMap),
6698 _markStack(markStack),
6699 _finger(finger),
6700 _parent(parent)
6701 { }
6702
6703 ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector,
6704 MemRegion span,
6705 CMSBitMap* bit_map,
6706 OopTaskQueue* work_queue,
6707 CMSMarkStack* overflow_stack,
6708 HeapWord* finger,
6709 HeapWord* volatile* global_finger_addr,
6710 ParMarkFromRootsClosure* parent) :
6711 MetadataAwareOopClosure(collector->ref_processor()),
6712 _collector(collector),
6713 _whole_span(collector->_span),
6714 _span(span),
6715 _bit_map(bit_map),
6716 _work_queue(work_queue),
6717 _overflow_stack(overflow_stack),
6718 _finger(finger),
6719 _global_finger_addr(global_finger_addr),
6720 _parent(parent)
6721 { }
6722
6723 // Assumes thread-safe access by callers, who are
6724 // responsible for mutual exclusion.
6725 void CMSCollector::lower_restart_addr(HeapWord* low) {
6726 assert(_span.contains(low), "Out of bounds addr");
6727 if (_restart_addr == NULL) {
6728 _restart_addr = low;
6729 } else {
6730 _restart_addr = MIN2(_restart_addr, low);
6731 }
6732 }
6733
6734 // Upon stack overflow, we discard (part of) the stack,
6735 // remembering the least address amongst those discarded
6736 // in CMSCollector's _restart_address.
6737 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6738 // Remember the least grey address discarded
6739 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6740 _collector->lower_restart_addr(ra);
6741 _markStack->reset(); // discard stack contents
6742 _markStack->expand(); // expand the stack if possible
6743 }
6744
6745 // Upon stack overflow, we discard (part of) the stack,
6746 // remembering the least address amongst those discarded
6747 // in CMSCollector's _restart_address.
6748 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6749 // We need to do this under a mutex to prevent other
6750 // workers from interfering with the work done below.
6751 MutexLockerEx ml(_overflow_stack->par_lock(),
6752 Mutex::_no_safepoint_check_flag);
6753 // Remember the least grey address discarded
6754 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6755 _collector->lower_restart_addr(ra);
6756 _overflow_stack->reset(); // discard stack contents
6757 _overflow_stack->expand(); // expand the stack if possible
6758 }
6759
6760 void PushOrMarkClosure::do_oop(oop obj) {
6761 // Ignore mark word because we are running concurrent with mutators.
6762 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6763 HeapWord* addr = (HeapWord*)obj;
6764 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6765 // Oop lies in _span and isn't yet grey or black
6766 _bitMap->mark(addr); // now grey
6767 if (addr < _finger) {
6768 // the bit map iteration has already either passed, or
6769 // sampled, this bit in the bit map; we'll need to
6770 // use the marking stack to scan this oop's oops.
6771 bool simulate_overflow = false;
6772 NOT_PRODUCT(
6773 if (CMSMarkStackOverflowALot &&
6774 _collector->simulate_overflow()) {
6775 // simulate a stack overflow
6776 simulate_overflow = true;
6777 }
6778 )
6779 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6780 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6781 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6782 handle_stack_overflow(addr);
6783 }
6784 }
6785 // anything including and to the right of _finger
6786 // will be scanned as we iterate over the remainder of the
6787 // bit map
6788 do_yield_check();
6789 }
6790 }
6791
6792 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
6793 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
6794
6795 void ParPushOrMarkClosure::do_oop(oop obj) {
6796 // Ignore mark word because we are running concurrent with mutators.
6797 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6798 HeapWord* addr = (HeapWord*)obj;
6799 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6800 // Oop lies in _span and isn't yet grey or black
6801 // We read the global_finger (volatile read) strictly after marking oop
6802 bool res = _bit_map->par_mark(addr); // now grey
6803 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6804 // Should we push this marked oop on our stack?
6805 // -- if someone else marked it, nothing to do
6806 // -- if target oop is above global finger nothing to do
6807 // -- if target oop is in chunk and above local finger
6808 // then nothing to do
6809 // -- else push on work queue
6810 if ( !res // someone else marked it, they will deal with it
6811 || (addr >= *gfa) // will be scanned in a later task
6812 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6813 return;
6814 }
6815 // the bit map iteration has already either passed, or
6816 // sampled, this bit in the bit map; we'll need to
6817 // use the marking stack to scan this oop's oops.
6818 bool simulate_overflow = false;
6819 NOT_PRODUCT(
6820 if (CMSMarkStackOverflowALot &&
6821 _collector->simulate_overflow()) {
6822 // simulate a stack overflow
6823 simulate_overflow = true;
6824 }
6825 )
6826 if (simulate_overflow ||
6827 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6828 // stack overflow
6829 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6830 // We cannot assert that the overflow stack is full because
6831 // it may have been emptied since.
6832 assert(simulate_overflow ||
6833 _work_queue->size() == _work_queue->max_elems(),
6834 "Else push should have succeeded");
6835 handle_stack_overflow(addr);
6836 }
6837 do_yield_check();
6838 }
6839 }
6840
6841 void ParPushOrMarkClosure::do_oop(oop* p) { ParPushOrMarkClosure::do_oop_work(p); }
6842 void ParPushOrMarkClosure::do_oop(narrowOop* p) { ParPushOrMarkClosure::do_oop_work(p); }
6843
6844 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6845 MemRegion span,
6846 ReferenceDiscoverer* rd,
6847 CMSBitMap* bit_map,
6848 CMSBitMap* mod_union_table,
6849 CMSMarkStack* mark_stack,
6850 bool concurrent_precleaning):
6851 MetadataAwareOopClosure(rd),
6852 _collector(collector),
6853 _span(span),
6854 _bit_map(bit_map),
6855 _mod_union_table(mod_union_table),
6856 _mark_stack(mark_stack),
6857 _concurrent_precleaning(concurrent_precleaning)
6858 {
6859 assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL");
6860 }
6861
6862 // Grey object rescan during pre-cleaning and second checkpoint phases --
6863 // the non-parallel version (the parallel version appears further below.)
6864 void PushAndMarkClosure::do_oop(oop obj) {
6865 // Ignore mark word verification. If during concurrent precleaning,
6866 // the object monitor may be locked. If during the checkpoint
6867 // phases, the object may already have been reached by a different
6868 // path and may be at the end of the global overflow list (so
6869 // the mark word may be NULL).
6870 assert(oopDesc::is_oop_or_null(obj, true /* ignore mark word */),
6871 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6872 HeapWord* addr = (HeapWord*)obj;
6873 // Check if oop points into the CMS generation
6874 // and is not marked
6875 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6876 // a white object ...
6877 _bit_map->mark(addr); // ... now grey
6878 // push on the marking stack (grey set)
6879 bool simulate_overflow = false;
6880 NOT_PRODUCT(
6881 if (CMSMarkStackOverflowALot &&
6882 _collector->simulate_overflow()) {
6883 // simulate a stack overflow
6884 simulate_overflow = true;
6885 }
6886 )
6887 if (simulate_overflow || !_mark_stack->push(obj)) {
6888 if (_concurrent_precleaning) {
6889 // During precleaning we can just dirty the appropriate card(s)
6890 // in the mod union table, thus ensuring that the object remains
6891 // in the grey set and continue. In the case of object arrays
6892 // we need to dirty all of the cards that the object spans,
6893 // since the rescan of object arrays will be limited to the
6894 // dirty cards.
6895 // Note that no one can be interfering with us in this action
6896 // of dirtying the mod union table, so no locking or atomics
6897 // are required.
6898 if (obj->is_objArray()) {
6899 size_t sz = obj->size();
6900 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
6901 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6902 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6903 _mod_union_table->mark_range(redirty_range);
6904 } else {
6905 _mod_union_table->mark(addr);
6906 }
6907 _collector->_ser_pmc_preclean_ovflw++;
6908 } else {
6909 // During the remark phase, we need to remember this oop
6910 // in the overflow list.
6911 _collector->push_on_overflow_list(obj);
6912 _collector->_ser_pmc_remark_ovflw++;
6913 }
6914 }
6915 }
6916 }
6917
6918 ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector,
6919 MemRegion span,
6920 ReferenceDiscoverer* rd,
6921 CMSBitMap* bit_map,
6922 OopTaskQueue* work_queue):
6923 MetadataAwareOopClosure(rd),
6924 _collector(collector),
6925 _span(span),
6926 _bit_map(bit_map),
6927 _work_queue(work_queue)
6928 {
6929 assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL");
6930 }
6931
6932 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
6933 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
6934
6935 // Grey object rescan during second checkpoint phase --
6936 // the parallel version.
6937 void ParPushAndMarkClosure::do_oop(oop obj) {
6938 // In the assert below, we ignore the mark word because
6939 // this oop may point to an already visited object that is
6940 // on the overflow stack (in which case the mark word has
6941 // been hijacked for chaining into the overflow stack --
6942 // if this is the last object in the overflow stack then
6943 // its mark word will be NULL). Because this object may
6944 // have been subsequently popped off the global overflow
6945 // stack, and the mark word possibly restored to the prototypical
6946 // value, by the time we get to examined this failing assert in
6947 // the debugger, is_oop_or_null(false) may subsequently start
6948 // to hold.
6949 assert(oopDesc::is_oop_or_null(obj, true),
6950 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6951 HeapWord* addr = (HeapWord*)obj;
6952 // Check if oop points into the CMS generation
6953 // and is not marked
6954 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6955 // a white object ...
6956 // If we manage to "claim" the object, by being the
6957 // first thread to mark it, then we push it on our
6958 // marking stack
6959 if (_bit_map->par_mark(addr)) { // ... now grey
6960 // push on work queue (grey set)
6961 bool simulate_overflow = false;
6962 NOT_PRODUCT(
6963 if (CMSMarkStackOverflowALot &&
6964 _collector->par_simulate_overflow()) {
6965 // simulate a stack overflow
6966 simulate_overflow = true;
6967 }
6968 )
6969 if (simulate_overflow || !_work_queue->push(obj)) {
6970 _collector->par_push_on_overflow_list(obj);
6971 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
6972 }
6973 } // Else, some other thread got there first
6974 }
6975 }
6976
6977 void ParPushAndMarkClosure::do_oop(oop* p) { ParPushAndMarkClosure::do_oop_work(p); }
6978 void ParPushAndMarkClosure::do_oop(narrowOop* p) { ParPushAndMarkClosure::do_oop_work(p); }
6979
6980 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6981 Mutex* bml = _collector->bitMapLock();
6982 assert_lock_strong(bml);
6983 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6984 "CMS thread should hold CMS token");
6985
6986 bml->unlock();
6987 ConcurrentMarkSweepThread::desynchronize(true);
6988
6989 _collector->stopTimer();
6990 _collector->incrementYields();
6991
6992 // See the comment in coordinator_yield()
6993 for (unsigned i = 0; i < CMSYieldSleepCount &&
6994 ConcurrentMarkSweepThread::should_yield() &&
6995 !CMSCollector::foregroundGCIsActive(); ++i) {
6996 os::sleep(Thread::current(), 1, false);
6997 }
6998
6999 ConcurrentMarkSweepThread::synchronize(true);
7000 bml->lock();
7001
7002 _collector->startTimer();
7003 }
7004
7005 bool CMSPrecleanRefsYieldClosure::should_return() {
7006 if (ConcurrentMarkSweepThread::should_yield()) {
7007 do_yield_work();
7008 }
7009 return _collector->foregroundGCIsActive();
7010 }
7011
7012 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7013 assert(((size_t)mr.start())%CardTable::card_size_in_words == 0,
7014 "mr should be aligned to start at a card boundary");
7015 // We'd like to assert:
7016 // assert(mr.word_size()%CardTable::card_size_in_words == 0,
7017 // "mr should be a range of cards");
7018 // However, that would be too strong in one case -- the last
7019 // partition ends at _unallocated_block which, in general, can be
7020 // an arbitrary boundary, not necessarily card aligned.
7021 _num_dirty_cards += mr.word_size()/CardTable::card_size_in_words;
7022 _space->object_iterate_mem(mr, &_scan_cl);
7023 }
7024
7025 SweepClosure::SweepClosure(CMSCollector* collector,
7026 ConcurrentMarkSweepGeneration* g,
7027 CMSBitMap* bitMap, bool should_yield) :
7028 _collector(collector),
7029 _g(g),
7030 _sp(g->cmsSpace()),
7031 _limit(_sp->sweep_limit()),
7032 _freelistLock(_sp->freelistLock()),
7033 _bitMap(bitMap),
7034 _yield(should_yield),
7035 _inFreeRange(false), // No free range at beginning of sweep
7036 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7037 _lastFreeRangeCoalesced(false),
7038 _freeFinger(g->used_region().start())
7039 {
7040 NOT_PRODUCT(
7041 _numObjectsFreed = 0;
7042 _numWordsFreed = 0;
7043 _numObjectsLive = 0;
7044 _numWordsLive = 0;
7045 _numObjectsAlreadyFree = 0;
7046 _numWordsAlreadyFree = 0;
7047 _last_fc = NULL;
7048
7049 _sp->initializeIndexedFreeListArrayReturnedBytes();
7050 _sp->dictionary()->initialize_dict_returned_bytes();
7051 )
7052 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7053 "sweep _limit out of bounds");
7054 log_develop_trace(gc, sweep)("====================");
7055 log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
7056 }
7057
7058 void SweepClosure::print_on(outputStream* st) const {
7059 st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7060 p2i(_sp->bottom()), p2i(_sp->end()));
7061 st->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7062 st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7063 NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7064 st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7065 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7066 }
7067
7068 #ifndef PRODUCT
7069 // Assertion checking only: no useful work in product mode --
7070 // however, if any of the flags below become product flags,
7071 // you may need to review this code to see if it needs to be
7072 // enabled in product mode.
7073 SweepClosure::~SweepClosure() {
7074 assert_lock_strong(_freelistLock);
7075 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7076 "sweep _limit out of bounds");
7077 if (inFreeRange()) {
7078 Log(gc, sweep) log;
7079 log.error("inFreeRange() should have been reset; dumping state of SweepClosure");
7080 ResourceMark rm;
7081 LogStream ls(log.error());
7082 print_on(&ls);
7083 ShouldNotReachHere();
7084 }
7085
7086 if (log_is_enabled(Debug, gc, sweep)) {
7087 log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7088 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7089 log_debug(gc, sweep)("Live " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7090 _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7091 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7092 log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7093 }
7094
7095 if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) {
7096 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7097 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7098 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7099 log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes Indexed List Returned " SIZE_FORMAT " bytes Dictionary Returned " SIZE_FORMAT " bytes",
7100 returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7101 }
7102 log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7103 log_develop_trace(gc, sweep)("================");
7104 }
7105 #endif // PRODUCT
7106
7107 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7108 bool freeRangeInFreeLists) {
7109 log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7110 p2i(freeFinger), freeRangeInFreeLists);
7111 assert(!inFreeRange(), "Trampling existing free range");
7112 set_inFreeRange(true);
7113 set_lastFreeRangeCoalesced(false);
7114
7115 set_freeFinger(freeFinger);
7116 set_freeRangeInFreeLists(freeRangeInFreeLists);
7117 if (CMSTestInFreeList) {
7118 if (freeRangeInFreeLists) {
7119 FreeChunk* fc = (FreeChunk*) freeFinger;
7120 assert(fc->is_free(), "A chunk on the free list should be free.");
7121 assert(fc->size() > 0, "Free range should have a size");
7122 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7123 }
7124 }
7125 }
7126
7127 // Note that the sweeper runs concurrently with mutators. Thus,
7128 // it is possible for direct allocation in this generation to happen
7129 // in the middle of the sweep. Note that the sweeper also coalesces
7130 // contiguous free blocks. Thus, unless the sweeper and the allocator
7131 // synchronize appropriately freshly allocated blocks may get swept up.
7132 // This is accomplished by the sweeper locking the free lists while
7133 // it is sweeping. Thus blocks that are determined to be free are
7134 // indeed free. There is however one additional complication:
7135 // blocks that have been allocated since the final checkpoint and
7136 // mark, will not have been marked and so would be treated as
7137 // unreachable and swept up. To prevent this, the allocator marks
7138 // the bit map when allocating during the sweep phase. This leads,
7139 // however, to a further complication -- objects may have been allocated
7140 // but not yet initialized -- in the sense that the header isn't yet
7141 // installed. The sweeper can not then determine the size of the block
7142 // in order to skip over it. To deal with this case, we use a technique
7143 // (due to Printezis) to encode such uninitialized block sizes in the
7144 // bit map. Since the bit map uses a bit per every HeapWord, but the
7145 // CMS generation has a minimum object size of 3 HeapWords, it follows
7146 // that "normal marks" won't be adjacent in the bit map (there will
7147 // always be at least two 0 bits between successive 1 bits). We make use
7148 // of these "unused" bits to represent uninitialized blocks -- the bit
7149 // corresponding to the start of the uninitialized object and the next
7150 // bit are both set. Finally, a 1 bit marks the end of the object that
7151 // started with the two consecutive 1 bits to indicate its potentially
7152 // uninitialized state.
7153
7154 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7155 FreeChunk* fc = (FreeChunk*)addr;
7156 size_t res;
7157
7158 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7159 // than "addr == _limit" because although _limit was a block boundary when
7160 // we started the sweep, it may no longer be one because heap expansion
7161 // may have caused us to coalesce the block ending at the address _limit
7162 // with a newly expanded chunk (this happens when _limit was set to the
7163 // previous _end of the space), so we may have stepped past _limit:
7164 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7165 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7166 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7167 "sweep _limit out of bounds");
7168 assert(addr < _sp->end(), "addr out of bounds");
7169 // Flush any free range we might be holding as a single
7170 // coalesced chunk to the appropriate free list.
7171 if (inFreeRange()) {
7172 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7173 "freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger()));
7174 flush_cur_free_chunk(freeFinger(),
7175 pointer_delta(addr, freeFinger()));
7176 log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7177 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7178 lastFreeRangeCoalesced() ? 1 : 0);
7179 }
7180
7181 // help the iterator loop finish
7182 return pointer_delta(_sp->end(), addr);
7183 }
7184
7185 assert(addr < _limit, "sweep invariant");
7186 // check if we should yield
7187 do_yield_check(addr);
7188 if (fc->is_free()) {
7189 // Chunk that is already free
7190 res = fc->size();
7191 do_already_free_chunk(fc);
7192 debug_only(_sp->verifyFreeLists());
7193 // If we flush the chunk at hand in lookahead_and_flush()
7194 // and it's coalesced with a preceding chunk, then the
7195 // process of "mangling" the payload of the coalesced block
7196 // will cause erasure of the size information from the
7197 // (erstwhile) header of all the coalesced blocks but the
7198 // first, so the first disjunct in the assert will not hold
7199 // in that specific case (in which case the second disjunct
7200 // will hold).
7201 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7202 "Otherwise the size info doesn't change at this step");
7203 NOT_PRODUCT(
7204 _numObjectsAlreadyFree++;
7205 _numWordsAlreadyFree += res;
7206 )
7207 NOT_PRODUCT(_last_fc = fc;)
7208 } else if (!_bitMap->isMarked(addr)) {
7209 // Chunk is fresh garbage
7210 res = do_garbage_chunk(fc);
7211 debug_only(_sp->verifyFreeLists());
7212 NOT_PRODUCT(
7213 _numObjectsFreed++;
7214 _numWordsFreed += res;
7215 )
7216 } else {
7217 // Chunk that is alive.
7218 res = do_live_chunk(fc);
7219 debug_only(_sp->verifyFreeLists());
7220 NOT_PRODUCT(
7221 _numObjectsLive++;
7222 _numWordsLive += res;
7223 )
7224 }
7225 return res;
7226 }
7227
7228 // For the smart allocation, record following
7229 // split deaths - a free chunk is removed from its free list because
7230 // it is being split into two or more chunks.
7231 // split birth - a free chunk is being added to its free list because
7232 // a larger free chunk has been split and resulted in this free chunk.
7233 // coal death - a free chunk is being removed from its free list because
7234 // it is being coalesced into a large free chunk.
7235 // coal birth - a free chunk is being added to its free list because
7236 // it was created when two or more free chunks where coalesced into
7237 // this free chunk.
7238 //
7239 // These statistics are used to determine the desired number of free
7240 // chunks of a given size. The desired number is chosen to be relative
7241 // to the end of a CMS sweep. The desired number at the end of a sweep
7242 // is the
7243 // count-at-end-of-previous-sweep (an amount that was enough)
7244 // - count-at-beginning-of-current-sweep (the excess)
7245 // + split-births (gains in this size during interval)
7246 // - split-deaths (demands on this size during interval)
7247 // where the interval is from the end of one sweep to the end of the
7248 // next.
7249 //
7250 // When sweeping the sweeper maintains an accumulated chunk which is
7251 // the chunk that is made up of chunks that have been coalesced. That
7252 // will be termed the left-hand chunk. A new chunk of garbage that
7253 // is being considered for coalescing will be referred to as the
7254 // right-hand chunk.
7255 //
7256 // When making a decision on whether to coalesce a right-hand chunk with
7257 // the current left-hand chunk, the current count vs. the desired count
7258 // of the left-hand chunk is considered. Also if the right-hand chunk
7259 // is near the large chunk at the end of the heap (see
7260 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7261 // left-hand chunk is coalesced.
7262 //
7263 // When making a decision about whether to split a chunk, the desired count
7264 // vs. the current count of the candidate to be split is also considered.
7265 // If the candidate is underpopulated (currently fewer chunks than desired)
7266 // a chunk of an overpopulated (currently more chunks than desired) size may
7267 // be chosen. The "hint" associated with a free list, if non-null, points
7268 // to a free list which may be overpopulated.
7269 //
7270
7271 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7272 const size_t size = fc->size();
7273 // Chunks that cannot be coalesced are not in the
7274 // free lists.
7275 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7276 assert(_sp->verify_chunk_in_free_list(fc),
7277 "free chunk should be in free lists");
7278 }
7279 // a chunk that is already free, should not have been
7280 // marked in the bit map
7281 HeapWord* const addr = (HeapWord*) fc;
7282 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7283 // Verify that the bit map has no bits marked between
7284 // addr and purported end of this block.
7285 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7286
7287 // Some chunks cannot be coalesced under any circumstances.
7288 // See the definition of cantCoalesce().
7289 if (!fc->cantCoalesce()) {
7290 // This chunk can potentially be coalesced.
7291 // All the work is done in
7292 do_post_free_or_garbage_chunk(fc, size);
7293 // Note that if the chunk is not coalescable (the else arm
7294 // below), we unconditionally flush, without needing to do
7295 // a "lookahead," as we do below.
7296 if (inFreeRange()) lookahead_and_flush(fc, size);
7297 } else {
7298 // Code path common to both original and adaptive free lists.
7299
7300 // cant coalesce with previous block; this should be treated
7301 // as the end of a free run if any
7302 if (inFreeRange()) {
7303 // we kicked some butt; time to pick up the garbage
7304 assert(freeFinger() < addr, "freeFinger points too high");
7305 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7306 }
7307 // else, nothing to do, just continue
7308 }
7309 }
7310
7311 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7312 // This is a chunk of garbage. It is not in any free list.
7313 // Add it to a free list or let it possibly be coalesced into
7314 // a larger chunk.
7315 HeapWord* const addr = (HeapWord*) fc;
7316 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7317
7318 // Verify that the bit map has no bits marked between
7319 // addr and purported end of just dead object.
7320 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7321 do_post_free_or_garbage_chunk(fc, size);
7322
7323 assert(_limit >= addr + size,
7324 "A freshly garbage chunk can't possibly straddle over _limit");
7325 if (inFreeRange()) lookahead_and_flush(fc, size);
7326 return size;
7327 }
7328
7329 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7330 HeapWord* addr = (HeapWord*) fc;
7331 // The sweeper has just found a live object. Return any accumulated
7332 // left hand chunk to the free lists.
7333 if (inFreeRange()) {
7334 assert(freeFinger() < addr, "freeFinger points too high");
7335 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7336 }
7337
7338 // This object is live: we'd normally expect this to be
7339 // an oop, and like to assert the following:
7340 // assert(oopDesc::is_oop(oop(addr)), "live block should be an oop");
7341 // However, as we commented above, this may be an object whose
7342 // header hasn't yet been initialized.
7343 size_t size;
7344 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7345 if (_bitMap->isMarked(addr + 1)) {
7346 // Determine the size from the bit map, rather than trying to
7347 // compute it from the object header.
7348 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7349 size = pointer_delta(nextOneAddr + 1, addr);
7350 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7351 "alignment problem");
7352
7353 #ifdef ASSERT
7354 if (oop(addr)->klass_or_null_acquire() != NULL) {
7355 // Ignore mark word because we are running concurrent with mutators
7356 assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7357 assert(size ==
7358 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7359 "P-mark and computed size do not agree");
7360 }
7361 #endif
7362
7363 } else {
7364 // This should be an initialized object that's alive.
7365 assert(oop(addr)->klass_or_null_acquire() != NULL,
7366 "Should be an initialized object");
7367 // Ignore mark word because we are running concurrent with mutators
7368 assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7369 // Verify that the bit map has no bits marked between
7370 // addr and purported end of this block.
7371 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7372 assert(size >= 3, "Necessary for Printezis marks to work");
7373 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7374 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7375 }
7376 return size;
7377 }
7378
7379 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7380 size_t chunkSize) {
7381 // do_post_free_or_garbage_chunk() should only be called in the case
7382 // of the adaptive free list allocator.
7383 const bool fcInFreeLists = fc->is_free();
7384 assert((HeapWord*)fc <= _limit, "sweep invariant");
7385 if (CMSTestInFreeList && fcInFreeLists) {
7386 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7387 }
7388
7389 log_develop_trace(gc, sweep)(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7390
7391 HeapWord* const fc_addr = (HeapWord*) fc;
7392
7393 bool coalesce = false;
7394 const size_t left = pointer_delta(fc_addr, freeFinger());
7395 const size_t right = chunkSize;
7396 switch (FLSCoalescePolicy) {
7397 // numeric value forms a coalition aggressiveness metric
7398 case 0: { // never coalesce
7399 coalesce = false;
7400 break;
7401 }
7402 case 1: { // coalesce if left & right chunks on overpopulated lists
7403 coalesce = _sp->coalOverPopulated(left) &&
7404 _sp->coalOverPopulated(right);
7405 break;
7406 }
7407 case 2: { // coalesce if left chunk on overpopulated list (default)
7408 coalesce = _sp->coalOverPopulated(left);
7409 break;
7410 }
7411 case 3: { // coalesce if left OR right chunk on overpopulated list
7412 coalesce = _sp->coalOverPopulated(left) ||
7413 _sp->coalOverPopulated(right);
7414 break;
7415 }
7416 case 4: { // always coalesce
7417 coalesce = true;
7418 break;
7419 }
7420 default:
7421 ShouldNotReachHere();
7422 }
7423
7424 // Should the current free range be coalesced?
7425 // If the chunk is in a free range and either we decided to coalesce above
7426 // or the chunk is near the large block at the end of the heap
7427 // (isNearLargestChunk() returns true), then coalesce this chunk.
7428 const bool doCoalesce = inFreeRange()
7429 && (coalesce || _g->isNearLargestChunk(fc_addr));
7430 if (doCoalesce) {
7431 // Coalesce the current free range on the left with the new
7432 // chunk on the right. If either is on a free list,
7433 // it must be removed from the list and stashed in the closure.
7434 if (freeRangeInFreeLists()) {
7435 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7436 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7437 "Size of free range is inconsistent with chunk size.");
7438 if (CMSTestInFreeList) {
7439 assert(_sp->verify_chunk_in_free_list(ffc),
7440 "Chunk is not in free lists");
7441 }
7442 _sp->coalDeath(ffc->size());
7443 _sp->removeFreeChunkFromFreeLists(ffc);
7444 set_freeRangeInFreeLists(false);
7445 }
7446 if (fcInFreeLists) {
7447 _sp->coalDeath(chunkSize);
7448 assert(fc->size() == chunkSize,
7449 "The chunk has the wrong size or is not in the free lists");
7450 _sp->removeFreeChunkFromFreeLists(fc);
7451 }
7452 set_lastFreeRangeCoalesced(true);
7453 print_free_block_coalesced(fc);
7454 } else { // not in a free range and/or should not coalesce
7455 // Return the current free range and start a new one.
7456 if (inFreeRange()) {
7457 // In a free range but cannot coalesce with the right hand chunk.
7458 // Put the current free range into the free lists.
7459 flush_cur_free_chunk(freeFinger(),
7460 pointer_delta(fc_addr, freeFinger()));
7461 }
7462 // Set up for new free range. Pass along whether the right hand
7463 // chunk is in the free lists.
7464 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7465 }
7466 }
7467
7468 // Lookahead flush:
7469 // If we are tracking a free range, and this is the last chunk that
7470 // we'll look at because its end crosses past _limit, we'll preemptively
7471 // flush it along with any free range we may be holding on to. Note that
7472 // this can be the case only for an already free or freshly garbage
7473 // chunk. If this block is an object, it can never straddle
7474 // over _limit. The "straddling" occurs when _limit is set at
7475 // the previous end of the space when this cycle started, and
7476 // a subsequent heap expansion caused the previously co-terminal
7477 // free block to be coalesced with the newly expanded portion,
7478 // thus rendering _limit a non-block-boundary making it dangerous
7479 // for the sweeper to step over and examine.
7480 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7481 assert(inFreeRange(), "Should only be called if currently in a free range.");
7482 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7483 assert(_sp->used_region().contains(eob - 1),
7484 "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7485 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7486 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7487 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7488 if (eob >= _limit) {
7489 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7490 log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7491 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7492 "[" PTR_FORMAT "," PTR_FORMAT ")",
7493 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7494 // Return the storage we are tracking back into the free lists.
7495 log_develop_trace(gc, sweep)("Flushing ... ");
7496 assert(freeFinger() < eob, "Error");
7497 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7498 }
7499 }
7500
7501 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7502 assert(inFreeRange(), "Should only be called if currently in a free range.");
7503 assert(size > 0,
7504 "A zero sized chunk cannot be added to the free lists.");
7505 if (!freeRangeInFreeLists()) {
7506 if (CMSTestInFreeList) {
7507 FreeChunk* fc = (FreeChunk*) chunk;
7508 fc->set_size(size);
7509 assert(!_sp->verify_chunk_in_free_list(fc),
7510 "chunk should not be in free lists yet");
7511 }
7512 log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size);
7513 // A new free range is going to be starting. The current
7514 // free range has not been added to the free lists yet or
7515 // was removed so add it back.
7516 // If the current free range was coalesced, then the death
7517 // of the free range was recorded. Record a birth now.
7518 if (lastFreeRangeCoalesced()) {
7519 _sp->coalBirth(size);
7520 }
7521 _sp->addChunkAndRepairOffsetTable(chunk, size,
7522 lastFreeRangeCoalesced());
7523 } else {
7524 log_develop_trace(gc, sweep)("Already in free list: nothing to flush");
7525 }
7526 set_inFreeRange(false);
7527 set_freeRangeInFreeLists(false);
7528 }
7529
7530 // We take a break if we've been at this for a while,
7531 // so as to avoid monopolizing the locks involved.
7532 void SweepClosure::do_yield_work(HeapWord* addr) {
7533 // Return current free chunk being used for coalescing (if any)
7534 // to the appropriate freelist. After yielding, the next
7535 // free block encountered will start a coalescing range of
7536 // free blocks. If the next free block is adjacent to the
7537 // chunk just flushed, they will need to wait for the next
7538 // sweep to be coalesced.
7539 if (inFreeRange()) {
7540 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7541 }
7542
7543 // First give up the locks, then yield, then re-lock.
7544 // We should probably use a constructor/destructor idiom to
7545 // do this unlock/lock or modify the MutexUnlocker class to
7546 // serve our purpose. XXX
7547 assert_lock_strong(_bitMap->lock());
7548 assert_lock_strong(_freelistLock);
7549 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7550 "CMS thread should hold CMS token");
7551 _bitMap->lock()->unlock();
7552 _freelistLock->unlock();
7553 ConcurrentMarkSweepThread::desynchronize(true);
7554 _collector->stopTimer();
7555 _collector->incrementYields();
7556
7557 // See the comment in coordinator_yield()
7558 for (unsigned i = 0; i < CMSYieldSleepCount &&
7559 ConcurrentMarkSweepThread::should_yield() &&
7560 !CMSCollector::foregroundGCIsActive(); ++i) {
7561 os::sleep(Thread::current(), 1, false);
7562 }
7563
7564 ConcurrentMarkSweepThread::synchronize(true);
7565 _freelistLock->lock();
7566 _bitMap->lock()->lock_without_safepoint_check();
7567 _collector->startTimer();
7568 }
7569
7570 #ifndef PRODUCT
7571 // This is actually very useful in a product build if it can
7572 // be called from the debugger. Compile it into the product
7573 // as needed.
7574 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7575 return debug_cms_space->verify_chunk_in_free_list(fc);
7576 }
7577 #endif
7578
7579 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7580 log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7581 p2i(fc), fc->size());
7582 }
7583
7584 // CMSIsAliveClosure
7585 bool CMSIsAliveClosure::do_object_b(oop obj) {
7586 HeapWord* addr = (HeapWord*)obj;
7587 return addr != NULL &&
7588 (!_span.contains(addr) || _bit_map->isMarked(addr));
7589 }
7590
7591
7592 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7593 MemRegion span,
7594 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7595 bool cpc):
7596 _collector(collector),
7597 _span(span),
7598 _bit_map(bit_map),
7599 _mark_stack(mark_stack),
7600 _concurrent_precleaning(cpc) {
7601 assert(!_span.is_empty(), "Empty span could spell trouble");
7602 }
7603
7604
7605 // CMSKeepAliveClosure: the serial version
7606 void CMSKeepAliveClosure::do_oop(oop obj) {
7607 HeapWord* addr = (HeapWord*)obj;
7608 if (_span.contains(addr) &&
7609 !_bit_map->isMarked(addr)) {
7610 _bit_map->mark(addr);
7611 bool simulate_overflow = false;
7612 NOT_PRODUCT(
7613 if (CMSMarkStackOverflowALot &&
7614 _collector->simulate_overflow()) {
7615 // simulate a stack overflow
7616 simulate_overflow = true;
7617 }
7618 )
7619 if (simulate_overflow || !_mark_stack->push(obj)) {
7620 if (_concurrent_precleaning) {
7621 // We dirty the overflown object and let the remark
7622 // phase deal with it.
7623 assert(_collector->overflow_list_is_empty(), "Error");
7624 // In the case of object arrays, we need to dirty all of
7625 // the cards that the object spans. No locking or atomics
7626 // are needed since no one else can be mutating the mod union
7627 // table.
7628 if (obj->is_objArray()) {
7629 size_t sz = obj->size();
7630 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
7631 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7632 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7633 _collector->_modUnionTable.mark_range(redirty_range);
7634 } else {
7635 _collector->_modUnionTable.mark(addr);
7636 }
7637 _collector->_ser_kac_preclean_ovflw++;
7638 } else {
7639 _collector->push_on_overflow_list(obj);
7640 _collector->_ser_kac_ovflw++;
7641 }
7642 }
7643 }
7644 }
7645
7646 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7647 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7648
7649 // CMSParKeepAliveClosure: a parallel version of the above.
7650 // The work queues are private to each closure (thread),
7651 // but (may be) available for stealing by other threads.
7652 void CMSParKeepAliveClosure::do_oop(oop obj) {
7653 HeapWord* addr = (HeapWord*)obj;
7654 if (_span.contains(addr) &&
7655 !_bit_map->isMarked(addr)) {
7656 // In general, during recursive tracing, several threads
7657 // may be concurrently getting here; the first one to
7658 // "tag" it, claims it.
7659 if (_bit_map->par_mark(addr)) {
7660 bool res = _work_queue->push(obj);
7661 assert(res, "Low water mark should be much less than capacity");
7662 // Do a recursive trim in the hope that this will keep
7663 // stack usage lower, but leave some oops for potential stealers
7664 trim_queue(_low_water_mark);
7665 } // Else, another thread got there first
7666 }
7667 }
7668
7669 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7670 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7671
7672 void CMSParKeepAliveClosure::trim_queue(uint max) {
7673 while (_work_queue->size() > max) {
7674 oop new_oop;
7675 if (_work_queue->pop_local(new_oop)) {
7676 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
7677 assert(_bit_map->isMarked((HeapWord*)new_oop),
7678 "no white objects on this stack!");
7679 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7680 // iterate over the oops in this oop, marking and pushing
7681 // the ones in CMS heap (i.e. in _span).
7682 new_oop->oop_iterate(&_mark_and_push);
7683 }
7684 }
7685 }
7686
7687 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7688 CMSCollector* collector,
7689 MemRegion span, CMSBitMap* bit_map,
7690 OopTaskQueue* work_queue):
7691 _collector(collector),
7692 _span(span),
7693 _bit_map(bit_map),
7694 _work_queue(work_queue) { }
7695
7696 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7697 HeapWord* addr = (HeapWord*)obj;
7698 if (_span.contains(addr) &&
7699 !_bit_map->isMarked(addr)) {
7700 if (_bit_map->par_mark(addr)) {
7701 bool simulate_overflow = false;
7702 NOT_PRODUCT(
7703 if (CMSMarkStackOverflowALot &&
7704 _collector->par_simulate_overflow()) {
7705 // simulate a stack overflow
7706 simulate_overflow = true;
7707 }
7708 )
7709 if (simulate_overflow || !_work_queue->push(obj)) {
7710 _collector->par_push_on_overflow_list(obj);
7711 _collector->_par_kac_ovflw++;
7712 }
7713 } // Else another thread got there already
7714 }
7715 }
7716
7717 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7718 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7719
7720 //////////////////////////////////////////////////////////////////
7721 // CMSExpansionCause /////////////////////////////
7722 //////////////////////////////////////////////////////////////////
7723 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7724 switch (cause) {
7725 case _no_expansion:
7726 return "No expansion";
7727 case _satisfy_free_ratio:
7728 return "Free ratio";
7729 case _satisfy_promotion:
7730 return "Satisfy promotion";
7731 case _satisfy_allocation:
7732 return "allocation";
7733 case _allocate_par_lab:
7734 return "Par LAB";
7735 case _allocate_par_spooling_space:
7736 return "Par Spooling Space";
7737 case _adaptive_size_policy:
7738 return "Ergonomics";
7739 default:
7740 return "unknown";
7741 }
7742 }
7743
7744 void CMSDrainMarkingStackClosure::do_void() {
7745 // the max number to take from overflow list at a time
7746 const size_t num = _mark_stack->capacity()/4;
7747 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7748 "Overflow list should be NULL during concurrent phases");
7749 while (!_mark_stack->isEmpty() ||
7750 // if stack is empty, check the overflow list
7751 _collector->take_from_overflow_list(num, _mark_stack)) {
7752 oop obj = _mark_stack->pop();
7753 HeapWord* addr = (HeapWord*)obj;
7754 assert(_span.contains(addr), "Should be within span");
7755 assert(_bit_map->isMarked(addr), "Should be marked");
7756 assert(oopDesc::is_oop(obj), "Should be an oop");
7757 obj->oop_iterate(_keep_alive);
7758 }
7759 }
7760
7761 void CMSParDrainMarkingStackClosure::do_void() {
7762 // drain queue
7763 trim_queue(0);
7764 }
7765
7766 // Trim our work_queue so its length is below max at return
7767 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7768 while (_work_queue->size() > max) {
7769 oop new_oop;
7770 if (_work_queue->pop_local(new_oop)) {
7771 assert(oopDesc::is_oop(new_oop), "Expected an oop");
7772 assert(_bit_map->isMarked((HeapWord*)new_oop),
7773 "no white objects on this stack!");
7774 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7775 // iterate over the oops in this oop, marking and pushing
7776 // the ones in CMS heap (i.e. in _span).
7777 new_oop->oop_iterate(&_mark_and_push);
7778 }
7779 }
7780 }
7781
7782 ////////////////////////////////////////////////////////////////////
7783 // Support for Marking Stack Overflow list handling and related code
7784 ////////////////////////////////////////////////////////////////////
7785 // Much of the following code is similar in shape and spirit to the
7786 // code used in ParNewGC. We should try and share that code
7787 // as much as possible in the future.
7788
7789 #ifndef PRODUCT
7790 // Debugging support for CMSStackOverflowALot
7791
7792 // It's OK to call this multi-threaded; the worst thing
7793 // that can happen is that we'll get a bunch of closely
7794 // spaced simulated overflows, but that's OK, in fact
7795 // probably good as it would exercise the overflow code
7796 // under contention.
7797 bool CMSCollector::simulate_overflow() {
7798 if (_overflow_counter-- <= 0) { // just being defensive
7799 _overflow_counter = CMSMarkStackOverflowInterval;
7800 return true;
7801 } else {
7802 return false;
7803 }
7804 }
7805
7806 bool CMSCollector::par_simulate_overflow() {
7807 return simulate_overflow();
7808 }
7809 #endif
7810
7811 // Single-threaded
7812 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7813 assert(stack->isEmpty(), "Expected precondition");
7814 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7815 size_t i = num;
7816 oop cur = _overflow_list;
7817 const markOop proto = markOopDesc::prototype();
7818 NOT_PRODUCT(ssize_t n = 0;)
7819 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7820 next = oop(cur->mark_raw());
7821 cur->set_mark_raw(proto); // until proven otherwise
7822 assert(oopDesc::is_oop(cur), "Should be an oop");
7823 bool res = stack->push(cur);
7824 assert(res, "Bit off more than can chew?");
7825 NOT_PRODUCT(n++;)
7826 }
7827 _overflow_list = cur;
7828 #ifndef PRODUCT
7829 assert(_num_par_pushes >= n, "Too many pops?");
7830 _num_par_pushes -=n;
7831 #endif
7832 return !stack->isEmpty();
7833 }
7834
7835 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
7836 // (MT-safe) Get a prefix of at most "num" from the list.
7837 // The overflow list is chained through the mark word of
7838 // each object in the list. We fetch the entire list,
7839 // break off a prefix of the right size and return the
7840 // remainder. If other threads try to take objects from
7841 // the overflow list at that time, they will wait for
7842 // some time to see if data becomes available. If (and
7843 // only if) another thread places one or more object(s)
7844 // on the global list before we have returned the suffix
7845 // to the global list, we will walk down our local list
7846 // to find its end and append the global list to
7847 // our suffix before returning it. This suffix walk can
7848 // prove to be expensive (quadratic in the amount of traffic)
7849 // when there are many objects in the overflow list and
7850 // there is much producer-consumer contention on the list.
7851 // *NOTE*: The overflow list manipulation code here and
7852 // in ParNewGeneration:: are very similar in shape,
7853 // except that in the ParNew case we use the old (from/eden)
7854 // copy of the object to thread the list via its klass word.
7855 // Because of the common code, if you make any changes in
7856 // the code below, please check the ParNew version to see if
7857 // similar changes might be needed.
7858 // CR 6797058 has been filed to consolidate the common code.
7859 bool CMSCollector::par_take_from_overflow_list(size_t num,
7860 OopTaskQueue* work_q,
7861 int no_of_gc_threads) {
7862 assert(work_q->size() == 0, "First empty local work queue");
7863 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7864 if (_overflow_list == NULL) {
7865 return false;
7866 }
7867 // Grab the entire list; we'll put back a suffix
7868 oop prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7869 Thread* tid = Thread::current();
7870 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7871 // set to ParallelGCThreads.
7872 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7873 size_t sleep_time_millis = MAX2((size_t)1, num/100);
7874 // If the list is busy, we spin for a short while,
7875 // sleeping between attempts to get the list.
7876 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7877 os::sleep(tid, sleep_time_millis, false);
7878 if (_overflow_list == NULL) {
7879 // Nothing left to take
7880 return false;
7881 } else if (_overflow_list != BUSY) {
7882 // Try and grab the prefix
7883 prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7884 }
7885 }
7886 // If the list was found to be empty, or we spun long
7887 // enough, we give up and return empty-handed. If we leave
7888 // the list in the BUSY state below, it must be the case that
7889 // some other thread holds the overflow list and will set it
7890 // to a non-BUSY state in the future.
7891 if (prefix == NULL || prefix == BUSY) {
7892 // Nothing to take or waited long enough
7893 if (prefix == NULL) {
7894 // Write back the NULL in case we overwrote it with BUSY above
7895 // and it is still the same value.
7896 Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7897 }
7898 return false;
7899 }
7900 assert(prefix != NULL && prefix != BUSY, "Error");
7901 size_t i = num;
7902 oop cur = prefix;
7903 // Walk down the first "num" objects, unless we reach the end.
7904 for (; i > 1 && cur->mark_raw() != NULL; cur = oop(cur->mark_raw()), i--);
7905 if (cur->mark_raw() == NULL) {
7906 // We have "num" or fewer elements in the list, so there
7907 // is nothing to return to the global list.
7908 // Write back the NULL in lieu of the BUSY we wrote
7909 // above, if it is still the same value.
7910 if (_overflow_list == BUSY) {
7911 Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7912 }
7913 } else {
7914 // Chop off the suffix and return it to the global list.
7915 assert(cur->mark_raw() != BUSY, "Error");
7916 oop suffix_head = cur->mark_raw(); // suffix will be put back on global list
7917 cur->set_mark_raw(NULL); // break off suffix
7918 // It's possible that the list is still in the empty(busy) state
7919 // we left it in a short while ago; in that case we may be
7920 // able to place back the suffix without incurring the cost
7921 // of a walk down the list.
7922 oop observed_overflow_list = _overflow_list;
7923 oop cur_overflow_list = observed_overflow_list;
7924 bool attached = false;
7925 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7926 observed_overflow_list =
7927 Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7928 if (cur_overflow_list == observed_overflow_list) {
7929 attached = true;
7930 break;
7931 } else cur_overflow_list = observed_overflow_list;
7932 }
7933 if (!attached) {
7934 // Too bad, someone else sneaked in (at least) an element; we'll need
7935 // to do a splice. Find tail of suffix so we can prepend suffix to global
7936 // list.
7937 for (cur = suffix_head; cur->mark_raw() != NULL; cur = (oop)(cur->mark_raw()));
7938 oop suffix_tail = cur;
7939 assert(suffix_tail != NULL && suffix_tail->mark_raw() == NULL,
7940 "Tautology");
7941 observed_overflow_list = _overflow_list;
7942 do {
7943 cur_overflow_list = observed_overflow_list;
7944 if (cur_overflow_list != BUSY) {
7945 // Do the splice ...
7946 suffix_tail->set_mark_raw(markOop(cur_overflow_list));
7947 } else { // cur_overflow_list == BUSY
7948 suffix_tail->set_mark_raw(NULL);
7949 }
7950 // ... and try to place spliced list back on overflow_list ...
7951 observed_overflow_list =
7952 Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7953 } while (cur_overflow_list != observed_overflow_list);
7954 // ... until we have succeeded in doing so.
7955 }
7956 }
7957
7958 // Push the prefix elements on work_q
7959 assert(prefix != NULL, "control point invariant");
7960 const markOop proto = markOopDesc::prototype();
7961 oop next;
7962 NOT_PRODUCT(ssize_t n = 0;)
7963 for (cur = prefix; cur != NULL; cur = next) {
7964 next = oop(cur->mark_raw());
7965 cur->set_mark_raw(proto); // until proven otherwise
7966 assert(oopDesc::is_oop(cur), "Should be an oop");
7967 bool res = work_q->push(cur);
7968 assert(res, "Bit off more than we can chew?");
7969 NOT_PRODUCT(n++;)
7970 }
7971 #ifndef PRODUCT
7972 assert(_num_par_pushes >= n, "Too many pops?");
7973 Atomic::sub(n, &_num_par_pushes);
7974 #endif
7975 return true;
7976 }
7977
7978 // Single-threaded
7979 void CMSCollector::push_on_overflow_list(oop p) {
7980 NOT_PRODUCT(_num_par_pushes++;)
7981 assert(oopDesc::is_oop(p), "Not an oop");
7982 preserve_mark_if_necessary(p);
7983 p->set_mark_raw((markOop)_overflow_list);
7984 _overflow_list = p;
7985 }
7986
7987 // Multi-threaded; use CAS to prepend to overflow list
7988 void CMSCollector::par_push_on_overflow_list(oop p) {
7989 NOT_PRODUCT(Atomic::inc(&_num_par_pushes);)
7990 assert(oopDesc::is_oop(p), "Not an oop");
7991 par_preserve_mark_if_necessary(p);
7992 oop observed_overflow_list = _overflow_list;
7993 oop cur_overflow_list;
7994 do {
7995 cur_overflow_list = observed_overflow_list;
7996 if (cur_overflow_list != BUSY) {
7997 p->set_mark_raw(markOop(cur_overflow_list));
7998 } else {
7999 p->set_mark_raw(NULL);
8000 }
8001 observed_overflow_list =
8002 Atomic::cmpxchg((oopDesc*)p, &_overflow_list, (oopDesc*)cur_overflow_list);
8003 } while (cur_overflow_list != observed_overflow_list);
8004 }
8005 #undef BUSY
8006
8007 // Single threaded
8008 // General Note on GrowableArray: pushes may silently fail
8009 // because we are (temporarily) out of C-heap for expanding
8010 // the stack. The problem is quite ubiquitous and affects
8011 // a lot of code in the JVM. The prudent thing for GrowableArray
8012 // to do (for now) is to exit with an error. However, that may
8013 // be too draconian in some cases because the caller may be
8014 // able to recover without much harm. For such cases, we
8015 // should probably introduce a "soft_push" method which returns
8016 // an indication of success or failure with the assumption that
8017 // the caller may be able to recover from a failure; code in
8018 // the VM can then be changed, incrementally, to deal with such
8019 // failures where possible, thus, incrementally hardening the VM
8020 // in such low resource situations.
8021 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8022 _preserved_oop_stack.push(p);
8023 _preserved_mark_stack.push(m);
8024 assert(m == p->mark_raw(), "Mark word changed");
8025 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8026 "bijection");
8027 }
8028
8029 // Single threaded
8030 void CMSCollector::preserve_mark_if_necessary(oop p) {
8031 markOop m = p->mark_raw();
8032 if (m->must_be_preserved(p)) {
8033 preserve_mark_work(p, m);
8034 }
8035 }
8036
8037 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8038 markOop m = p->mark_raw();
8039 if (m->must_be_preserved(p)) {
8040 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8041 // Even though we read the mark word without holding
8042 // the lock, we are assured that it will not change
8043 // because we "own" this oop, so no other thread can
8044 // be trying to push it on the overflow list; see
8045 // the assertion in preserve_mark_work() that checks
8046 // that m == p->mark_raw().
8047 preserve_mark_work(p, m);
8048 }
8049 }
8050
8051 // We should be able to do this multi-threaded,
8052 // a chunk of stack being a task (this is
8053 // correct because each oop only ever appears
8054 // once in the overflow list. However, it's
8055 // not very easy to completely overlap this with
8056 // other operations, so will generally not be done
8057 // until all work's been completed. Because we
8058 // expect the preserved oop stack (set) to be small,
8059 // it's probably fine to do this single-threaded.
8060 // We can explore cleverer concurrent/overlapped/parallel
8061 // processing of preserved marks if we feel the
8062 // need for this in the future. Stack overflow should
8063 // be so rare in practice and, when it happens, its
8064 // effect on performance so great that this will
8065 // likely just be in the noise anyway.
8066 void CMSCollector::restore_preserved_marks_if_any() {
8067 assert(SafepointSynchronize::is_at_safepoint(),
8068 "world should be stopped");
8069 assert(Thread::current()->is_ConcurrentGC_thread() ||
8070 Thread::current()->is_VM_thread(),
8071 "should be single-threaded");
8072 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8073 "bijection");
8074
8075 while (!_preserved_oop_stack.is_empty()) {
8076 oop p = _preserved_oop_stack.pop();
8077 assert(oopDesc::is_oop(p), "Should be an oop");
8078 assert(_span.contains(p), "oop should be in _span");
8079 assert(p->mark_raw() == markOopDesc::prototype(),
8080 "Set when taken from overflow list");
8081 markOop m = _preserved_mark_stack.pop();
8082 p->set_mark_raw(m);
8083 }
8084 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8085 "stacks were cleared above");
8086 }
8087
8088 #ifndef PRODUCT
8089 bool CMSCollector::no_preserved_marks() const {
8090 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8091 }
8092 #endif
8093
8094 // Transfer some number of overflown objects to usual marking
8095 // stack. Return true if some objects were transferred.
8096 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8097 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8098 (size_t)ParGCDesiredObjsFromOverflowList);
8099
8100 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8101 assert(_collector->overflow_list_is_empty() || res,
8102 "If list is not empty, we should have taken something");
8103 assert(!res || !_mark_stack->isEmpty(),
8104 "If we took something, it should now be on our stack");
8105 return res;
8106 }
8107
8108 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8109 size_t res = _sp->block_size_no_stall(addr, _collector);
8110 if (_sp->block_is_obj(addr)) {
8111 if (_live_bit_map->isMarked(addr)) {
8112 // It can't have been dead in a previous cycle
8113 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8114 } else {
8115 _dead_bit_map->mark(addr); // mark the dead object
8116 }
8117 }
8118 // Could be 0, if the block size could not be computed without stalling.
8119 return res;
8120 }
8121
8122 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8123 GCMemoryManager* manager = CMSHeap::heap()->old_manager();
8124 switch (phase) {
8125 case CMSCollector::InitialMarking:
8126 initialize(manager /* GC manager */ ,
8127 cause /* cause of the GC */,
8128 true /* recordGCBeginTime */,
8129 true /* recordPreGCUsage */,
8130 false /* recordPeakUsage */,
8131 false /* recordPostGCusage */,
8132 true /* recordAccumulatedGCTime */,
8133 false /* recordGCEndTime */,
8134 false /* countCollection */ );
8135 break;
8136
8137 case CMSCollector::FinalMarking:
8138 initialize(manager /* GC manager */ ,
8139 cause /* cause of the GC */,
8140 false /* recordGCBeginTime */,
8141 false /* recordPreGCUsage */,
8142 false /* recordPeakUsage */,
8143 false /* recordPostGCusage */,
8144 true /* recordAccumulatedGCTime */,
8145 false /* recordGCEndTime */,
8146 false /* countCollection */ );
8147 break;
8148
8149 case CMSCollector::Sweeping:
8150 initialize(manager /* GC manager */ ,
8151 cause /* cause of the GC */,
8152 false /* recordGCBeginTime */,
8153 false /* recordPreGCUsage */,
8154 true /* recordPeakUsage */,
8155 true /* recordPostGCusage */,
8156 false /* recordAccumulatedGCTime */,
8157 true /* recordGCEndTime */,
8158 true /* countCollection */ );
8159 break;
8160
8161 default:
8162 ShouldNotReachHere();
8163 }
8164 }
--- EOF ---