1 /*
2 * Copyright (c) 2001, 2015, 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/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc/cms/cmsCollectorPolicy.hpp"
31 #include "gc/cms/cmsOopClosures.inline.hpp"
32 #include "gc/cms/compactibleFreeListSpace.hpp"
33 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
34 #include "gc/cms/concurrentMarkSweepThread.hpp"
35 #include "gc/cms/parNewGeneration.hpp"
36 #include "gc/cms/vmCMSOperations.hpp"
37 #include "gc/serial/genMarkSweep.hpp"
38 #include "gc/serial/tenuredGeneration.hpp"
39 #include "gc/shared/adaptiveSizePolicy.hpp"
40 #include "gc/shared/cardGeneration.inline.hpp"
41 #include "gc/shared/cardTableRS.hpp"
42 #include "gc/shared/collectedHeap.inline.hpp"
43 #include "gc/shared/collectorCounters.hpp"
44 #include "gc/shared/collectorPolicy.hpp"
45 #include "gc/shared/gcLocker.inline.hpp"
46 #include "gc/shared/gcPolicyCounters.hpp"
47 #include "gc/shared/gcTimer.hpp"
48 #include "gc/shared/gcTrace.hpp"
49 #include "gc/shared/gcTraceTime.hpp"
50 #include "gc/shared/genCollectedHeap.hpp"
51 #include "gc/shared/genOopClosures.inline.hpp"
52 #include "gc/shared/isGCActiveMark.hpp"
53 #include "gc/shared/referencePolicy.hpp"
54 #include "gc/shared/strongRootsScope.hpp"
55 #include "gc/shared/taskqueue.inline.hpp"
56 #include "logging/log.hpp"
57 #include "memory/allocation.hpp"
58 #include "memory/iterator.inline.hpp"
59 #include "memory/padded.hpp"
60 #include "memory/resourceArea.hpp"
61 #include "oops/oop.inline.hpp"
62 #include "prims/jvmtiExport.hpp"
63 #include "runtime/atomic.inline.hpp"
64 #include "runtime/globals_extension.hpp"
65 #include "runtime/handles.inline.hpp"
66 #include "runtime/java.hpp"
67 #include "runtime/orderAccess.inline.hpp"
68 #include "runtime/vmThread.hpp"
69 #include "services/memoryService.hpp"
70 #include "services/runtimeService.hpp"
71 #include "utilities/stack.inline.hpp"
72
73 // statics
74 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
75 bool CMSCollector::_full_gc_requested = false;
76 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
77
78 //////////////////////////////////////////////////////////////////
79 // In support of CMS/VM thread synchronization
80 //////////////////////////////////////////////////////////////////
81 // We split use of the CGC_lock into 2 "levels".
82 // The low-level locking is of the usual CGC_lock monitor. We introduce
83 // a higher level "token" (hereafter "CMS token") built on top of the
84 // low level monitor (hereafter "CGC lock").
85 // The token-passing protocol gives priority to the VM thread. The
86 // CMS-lock doesn't provide any fairness guarantees, but clients
87 // should ensure that it is only held for very short, bounded
88 // durations.
89 //
90 // When either of the CMS thread or the VM thread is involved in
91 // collection operations during which it does not want the other
92 // thread to interfere, it obtains the CMS token.
93 //
94 // If either thread tries to get the token while the other has
95 // it, that thread waits. However, if the VM thread and CMS thread
96 // both want the token, then the VM thread gets priority while the
97 // CMS thread waits. This ensures, for instance, that the "concurrent"
98 // phases of the CMS thread's work do not block out the VM thread
99 // for long periods of time as the CMS thread continues to hog
100 // the token. (See bug 4616232).
101 //
102 // The baton-passing functions are, however, controlled by the
103 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
104 // and here the low-level CMS lock, not the high level token,
105 // ensures mutual exclusion.
106 //
107 // Two important conditions that we have to satisfy:
108 // 1. if a thread does a low-level wait on the CMS lock, then it
109 // relinquishes the CMS token if it were holding that token
110 // when it acquired the low-level CMS lock.
111 // 2. any low-level notifications on the low-level lock
112 // should only be sent when a thread has relinquished the token.
113 //
114 // In the absence of either property, we'd have potential deadlock.
115 //
116 // We protect each of the CMS (concurrent and sequential) phases
117 // with the CMS _token_, not the CMS _lock_.
118 //
119 // The only code protected by CMS lock is the token acquisition code
120 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
121 // baton-passing code.
122 //
123 // Unfortunately, i couldn't come up with a good abstraction to factor and
124 // hide the naked CGC_lock manipulation in the baton-passing code
125 // further below. That's something we should try to do. Also, the proof
126 // of correctness of this 2-level locking scheme is far from obvious,
127 // and potentially quite slippery. We have an uneasy suspicion, for instance,
128 // that there may be a theoretical possibility of delay/starvation in the
129 // low-level lock/wait/notify scheme used for the baton-passing because of
130 // potential interference with the priority scheme embodied in the
131 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
132 // invocation further below and marked with "XXX 20011219YSR".
133 // Indeed, as we note elsewhere, this may become yet more slippery
134 // in the presence of multiple CMS and/or multiple VM threads. XXX
135
136 class CMSTokenSync: public StackObj {
137 private:
138 bool _is_cms_thread;
139 public:
140 CMSTokenSync(bool is_cms_thread):
141 _is_cms_thread(is_cms_thread) {
142 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
143 "Incorrect argument to constructor");
144 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
145 }
146
147 ~CMSTokenSync() {
148 assert(_is_cms_thread ?
149 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
150 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
151 "Incorrect state");
152 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
153 }
154 };
155
156 // Convenience class that does a CMSTokenSync, and then acquires
157 // upto three locks.
158 class CMSTokenSyncWithLocks: public CMSTokenSync {
159 private:
160 // Note: locks are acquired in textual declaration order
161 // and released in the opposite order
162 MutexLockerEx _locker1, _locker2, _locker3;
163 public:
164 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
165 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
166 CMSTokenSync(is_cms_thread),
167 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
168 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
169 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
170 { }
171 };
172
173
174 //////////////////////////////////////////////////////////////////
175 // Concurrent Mark-Sweep Generation /////////////////////////////
176 //////////////////////////////////////////////////////////////////
177
178 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
179
180 // This struct contains per-thread things necessary to support parallel
181 // young-gen collection.
182 class CMSParGCThreadState: public CHeapObj<mtGC> {
183 public:
184 CFLS_LAB lab;
185 PromotionInfo promo;
186
187 // Constructor.
188 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
189 promo.setSpace(cfls);
190 }
191 };
192
193 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
194 ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct) :
195 CardGeneration(rs, initial_byte_size, ct),
196 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
197 _did_compact(false)
198 {
199 HeapWord* bottom = (HeapWord*) _virtual_space.low();
200 HeapWord* end = (HeapWord*) _virtual_space.high();
201
202 _direct_allocated_words = 0;
203 NOT_PRODUCT(
204 _numObjectsPromoted = 0;
205 _numWordsPromoted = 0;
206 _numObjectsAllocated = 0;
207 _numWordsAllocated = 0;
208 )
209
210 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end));
211 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
212 _cmsSpace->_old_gen = this;
213
214 _gc_stats = new CMSGCStats();
215
216 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
217 // offsets match. The ability to tell free chunks from objects
218 // depends on this property.
219 debug_only(
220 FreeChunk* junk = NULL;
221 assert(UseCompressedClassPointers ||
222 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
223 "Offset of FreeChunk::_prev within FreeChunk must match"
224 " that of OopDesc::_klass within OopDesc");
225 )
226
227 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
228 for (uint i = 0; i < ParallelGCThreads; i++) {
229 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
230 }
231
232 _incremental_collection_failed = false;
233 // The "dilatation_factor" is the expansion that can occur on
234 // account of the fact that the minimum object size in the CMS
235 // generation may be larger than that in, say, a contiguous young
236 // generation.
237 // Ideally, in the calculation below, we'd compute the dilatation
238 // factor as: MinChunkSize/(promoting_gen's min object size)
239 // Since we do not have such a general query interface for the
240 // promoting generation, we'll instead just use the minimum
241 // object size (which today is a header's worth of space);
242 // note that all arithmetic is in units of HeapWords.
243 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
244 assert(_dilatation_factor >= 1.0, "from previous assert");
245 }
246
247
248 // The field "_initiating_occupancy" represents the occupancy percentage
249 // at which we trigger a new collection cycle. Unless explicitly specified
250 // via CMSInitiatingOccupancyFraction (argument "io" below), it
251 // is calculated by:
252 //
253 // Let "f" be MinHeapFreeRatio in
254 //
255 // _initiating_occupancy = 100-f +
256 // f * (CMSTriggerRatio/100)
257 // where CMSTriggerRatio is the argument "tr" below.
258 //
259 // That is, if we assume the heap is at its desired maximum occupancy at the
260 // end of a collection, we let CMSTriggerRatio of the (purported) free
261 // space be allocated before initiating a new collection cycle.
262 //
263 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
264 assert(io <= 100 && tr <= 100, "Check the arguments");
265 if (io >= 0) {
266 _initiating_occupancy = (double)io / 100.0;
267 } else {
268 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
269 (double)(tr * MinHeapFreeRatio) / 100.0)
270 / 100.0;
271 }
272 }
273
274 void ConcurrentMarkSweepGeneration::ref_processor_init() {
275 assert(collector() != NULL, "no collector");
276 collector()->ref_processor_init();
277 }
278
279 void CMSCollector::ref_processor_init() {
280 if (_ref_processor == NULL) {
281 // Allocate and initialize a reference processor
282 _ref_processor =
283 new ReferenceProcessor(_span, // span
284 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
285 ParallelGCThreads, // mt processing degree
286 _cmsGen->refs_discovery_is_mt(), // mt discovery
287 MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
288 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
289 &_is_alive_closure); // closure for liveness info
290 // Initialize the _ref_processor field of CMSGen
291 _cmsGen->set_ref_processor(_ref_processor);
292
293 }
294 }
295
296 AdaptiveSizePolicy* CMSCollector::size_policy() {
297 GenCollectedHeap* gch = GenCollectedHeap::heap();
298 return gch->gen_policy()->size_policy();
299 }
300
301 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
302
303 const char* gen_name = "old";
304 GenCollectorPolicy* gcp = GenCollectedHeap::heap()->gen_policy();
305 // Generation Counters - generation 1, 1 subspace
306 _gen_counters = new GenerationCounters(gen_name, 1, 1,
307 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
308
309 _space_counters = new GSpaceCounters(gen_name, 0,
310 _virtual_space.reserved_size(),
311 this, _gen_counters);
312 }
313
314 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
315 _cms_gen(cms_gen)
316 {
317 assert(alpha <= 100, "bad value");
318 _saved_alpha = alpha;
319
320 // Initialize the alphas to the bootstrap value of 100.
321 _gc0_alpha = _cms_alpha = 100;
322
323 _cms_begin_time.update();
324 _cms_end_time.update();
325
326 _gc0_duration = 0.0;
327 _gc0_period = 0.0;
328 _gc0_promoted = 0;
329
330 _cms_duration = 0.0;
331 _cms_period = 0.0;
332 _cms_allocated = 0;
333
334 _cms_used_at_gc0_begin = 0;
335 _cms_used_at_gc0_end = 0;
336 _allow_duty_cycle_reduction = false;
337 _valid_bits = 0;
338 }
339
340 double CMSStats::cms_free_adjustment_factor(size_t free) const {
341 // TBD: CR 6909490
342 return 1.0;
343 }
344
345 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
346 }
347
348 // If promotion failure handling is on use
349 // the padded average size of the promotion for each
350 // young generation collection.
351 double CMSStats::time_until_cms_gen_full() const {
352 size_t cms_free = _cms_gen->cmsSpace()->free();
353 GenCollectedHeap* gch = GenCollectedHeap::heap();
354 size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
355 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
356 if (cms_free > expected_promotion) {
357 // Start a cms collection if there isn't enough space to promote
358 // for the next young collection. Use the padded average as
359 // a safety factor.
360 cms_free -= expected_promotion;
361
362 // Adjust by the safety factor.
363 double cms_free_dbl = (double)cms_free;
364 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
365 // Apply a further correction factor which tries to adjust
366 // for recent occurance of concurrent mode failures.
367 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
368 cms_free_dbl = cms_free_dbl * cms_adjustment;
369
370 log_develop(gc, stats)("CMSStats::time_until_cms_gen_full: cms_free " SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
371 cms_free, expected_promotion);
372 log_develop(gc, stats)(" cms_free_dbl %f cms_consumption_rate %f",
373 cms_free_dbl, cms_consumption_rate() + 1.0);
374 // Add 1 in case the consumption rate goes to zero.
375 return cms_free_dbl / (cms_consumption_rate() + 1.0);
376 }
377 return 0.0;
378 }
379
380 // Compare the duration of the cms collection to the
381 // time remaining before the cms generation is empty.
382 // Note that the time from the start of the cms collection
383 // to the start of the cms sweep (less than the total
384 // duration of the cms collection) can be used. This
385 // has been tried and some applications experienced
386 // promotion failures early in execution. This was
387 // possibly because the averages were not accurate
388 // enough at the beginning.
389 double CMSStats::time_until_cms_start() const {
390 // We add "gc0_period" to the "work" calculation
391 // below because this query is done (mostly) at the
392 // end of a scavenge, so we need to conservatively
393 // account for that much possible delay
394 // in the query so as to avoid concurrent mode failures
395 // due to starting the collection just a wee bit too
396 // late.
397 double work = cms_duration() + gc0_period();
398 double deadline = time_until_cms_gen_full();
399 // If a concurrent mode failure occurred recently, we want to be
400 // more conservative and halve our expected time_until_cms_gen_full()
401 if (work > deadline) {
402 log_develop(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ",
403 cms_duration(), gc0_period(), time_until_cms_gen_full());
404 return 0.0;
405 }
406 return work - deadline;
407 }
408
409 #ifndef PRODUCT
410 void CMSStats::print_on(outputStream *st) const {
411 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
412 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
413 gc0_duration(), gc0_period(), gc0_promoted());
414 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
415 cms_duration(), cms_period(), cms_allocated());
416 st->print(",cms_since_beg=%g,cms_since_end=%g",
417 cms_time_since_begin(), cms_time_since_end());
418 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
419 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
420
421 if (valid()) {
422 st->print(",promo_rate=%g,cms_alloc_rate=%g",
423 promotion_rate(), cms_allocation_rate());
424 st->print(",cms_consumption_rate=%g,time_until_full=%g",
425 cms_consumption_rate(), time_until_cms_gen_full());
426 }
427 st->print(" ");
428 }
429 #endif // #ifndef PRODUCT
430
431 CMSCollector::CollectorState CMSCollector::_collectorState =
432 CMSCollector::Idling;
433 bool CMSCollector::_foregroundGCIsActive = false;
434 bool CMSCollector::_foregroundGCShouldWait = false;
435
436 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
437 CardTableRS* ct,
438 ConcurrentMarkSweepPolicy* cp):
439 _cmsGen(cmsGen),
440 _ct(ct),
441 _ref_processor(NULL), // will be set later
442 _conc_workers(NULL), // may be set later
443 _abort_preclean(false),
444 _start_sampling(false),
445 _between_prologue_and_epilogue(false),
446 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
447 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
448 -1 /* lock-free */, "No_lock" /* dummy */),
449 _modUnionClosurePar(&_modUnionTable),
450 // Adjust my span to cover old (cms) gen
451 _span(cmsGen->reserved()),
452 // Construct the is_alive_closure with _span & markBitMap
453 _is_alive_closure(_span, &_markBitMap),
454 _restart_addr(NULL),
455 _overflow_list(NULL),
456 _stats(cmsGen),
457 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
458 //verify that this lock should be acquired with safepoint check.
459 Monitor::_safepoint_check_sometimes)),
460 _eden_chunk_array(NULL), // may be set in ctor body
461 _eden_chunk_capacity(0), // -- ditto --
462 _eden_chunk_index(0), // -- ditto --
463 _survivor_plab_array(NULL), // -- ditto --
464 _survivor_chunk_array(NULL), // -- ditto --
465 _survivor_chunk_capacity(0), // -- ditto --
466 _survivor_chunk_index(0), // -- ditto --
467 _ser_pmc_preclean_ovflw(0),
468 _ser_kac_preclean_ovflw(0),
469 _ser_pmc_remark_ovflw(0),
470 _par_pmc_remark_ovflw(0),
471 _ser_kac_ovflw(0),
472 _par_kac_ovflw(0),
473 #ifndef PRODUCT
474 _num_par_pushes(0),
475 #endif
476 _collection_count_start(0),
477 _verifying(false),
478 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
479 _completed_initialization(false),
480 _collector_policy(cp),
481 _should_unload_classes(CMSClassUnloadingEnabled),
482 _concurrent_cycles_since_last_unload(0),
483 _roots_scanning_options(GenCollectedHeap::SO_None),
484 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
485 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
486 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
487 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
488 _cms_start_registered(false)
489 {
490 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
491 ExplicitGCInvokesConcurrent = true;
492 }
493 // Now expand the span and allocate the collection support structures
494 // (MUT, marking bit map etc.) to cover both generations subject to
495 // collection.
496
497 // For use by dirty card to oop closures.
498 _cmsGen->cmsSpace()->set_collector(this);
499
500 // Allocate MUT and marking bit map
501 {
502 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
503 if (!_markBitMap.allocate(_span)) {
504 warning("Failed to allocate CMS Bit Map");
505 return;
506 }
507 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
508 }
509 {
510 _modUnionTable.allocate(_span);
511 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
512 }
513
514 if (!_markStack.allocate(MarkStackSize)) {
515 warning("Failed to allocate CMS Marking Stack");
516 return;
517 }
518
519 // Support for multi-threaded concurrent phases
520 if (CMSConcurrentMTEnabled) {
521 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
522 // just for now
523 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
524 }
525 if (ConcGCThreads > 1) {
526 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
527 ConcGCThreads, true);
528 if (_conc_workers == NULL) {
529 warning("GC/CMS: _conc_workers allocation failure: "
530 "forcing -CMSConcurrentMTEnabled");
531 CMSConcurrentMTEnabled = false;
532 } else {
533 _conc_workers->initialize_workers();
534 }
535 } else {
536 CMSConcurrentMTEnabled = false;
537 }
538 }
539 if (!CMSConcurrentMTEnabled) {
540 ConcGCThreads = 0;
541 } else {
542 // Turn off CMSCleanOnEnter optimization temporarily for
543 // the MT case where it's not fixed yet; see 6178663.
544 CMSCleanOnEnter = false;
545 }
546 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
547 "Inconsistency");
548
549 // Parallel task queues; these are shared for the
550 // concurrent and stop-world phases of CMS, but
551 // are not shared with parallel scavenge (ParNew).
552 {
553 uint i;
554 uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
555
556 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
557 || ParallelRefProcEnabled)
558 && num_queues > 0) {
559 _task_queues = new OopTaskQueueSet(num_queues);
560 if (_task_queues == NULL) {
561 warning("task_queues allocation failure.");
562 return;
563 }
564 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
565 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
566 for (i = 0; i < num_queues; i++) {
567 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
568 if (q == NULL) {
569 warning("work_queue allocation failure.");
570 return;
571 }
572 _task_queues->register_queue(i, q);
573 }
574 for (i = 0; i < num_queues; i++) {
575 _task_queues->queue(i)->initialize();
576 _hash_seed[i] = 17; // copied from ParNew
577 }
578 }
579 }
580
581 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
582
583 // Clip CMSBootstrapOccupancy between 0 and 100.
584 _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
585
586 // Now tell CMS generations the identity of their collector
587 ConcurrentMarkSweepGeneration::set_collector(this);
588
589 // Create & start a CMS thread for this CMS collector
590 _cmsThread = ConcurrentMarkSweepThread::start(this);
591 assert(cmsThread() != NULL, "CMS Thread should have been created");
592 assert(cmsThread()->collector() == this,
593 "CMS Thread should refer to this gen");
594 assert(CGC_lock != NULL, "Where's the CGC_lock?");
595
596 // Support for parallelizing young gen rescan
597 GenCollectedHeap* gch = GenCollectedHeap::heap();
598 assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
599 _young_gen = (ParNewGeneration*)gch->young_gen();
600 if (gch->supports_inline_contig_alloc()) {
601 _top_addr = gch->top_addr();
602 _end_addr = gch->end_addr();
603 assert(_young_gen != NULL, "no _young_gen");
604 _eden_chunk_index = 0;
605 _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
606 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
607 }
608
609 // Support for parallelizing survivor space rescan
610 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
611 const size_t max_plab_samples =
612 _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
613
614 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
615 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
616 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
617 _survivor_chunk_capacity = max_plab_samples;
618 for (uint i = 0; i < ParallelGCThreads; i++) {
619 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
620 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
621 assert(cur->end() == 0, "Should be 0");
622 assert(cur->array() == vec, "Should be vec");
623 assert(cur->capacity() == max_plab_samples, "Error");
624 }
625 }
626
627 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
628 _gc_counters = new CollectorCounters("CMS", 1);
629 _completed_initialization = true;
630 _inter_sweep_timer.start(); // start of time
631 }
632
633 const char* ConcurrentMarkSweepGeneration::name() const {
634 return "concurrent mark-sweep generation";
635 }
636 void ConcurrentMarkSweepGeneration::update_counters() {
637 if (UsePerfData) {
638 _space_counters->update_all();
639 _gen_counters->update_all();
640 }
641 }
642
643 // this is an optimized version of update_counters(). it takes the
644 // used value as a parameter rather than computing it.
645 //
646 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
647 if (UsePerfData) {
648 _space_counters->update_used(used);
649 _space_counters->update_capacity();
650 _gen_counters->update_all();
651 }
652 }
653
654 void ConcurrentMarkSweepGeneration::print() const {
655 Generation::print();
656 cmsSpace()->print();
657 }
658
659 #ifndef PRODUCT
660 void ConcurrentMarkSweepGeneration::print_statistics() {
661 cmsSpace()->printFLCensus(0);
662 }
663 #endif
664
665 size_t
666 ConcurrentMarkSweepGeneration::contiguous_available() const {
667 // dld proposes an improvement in precision here. If the committed
668 // part of the space ends in a free block we should add that to
669 // uncommitted size in the calculation below. Will make this
670 // change later, staying with the approximation below for the
671 // time being. -- ysr.
672 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
673 }
674
675 size_t
676 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
677 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
678 }
679
680 size_t ConcurrentMarkSweepGeneration::max_available() const {
681 return free() + _virtual_space.uncommitted_size();
682 }
683
684 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
685 size_t available = max_available();
686 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
687 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
688 log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")",
689 res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes);
690 return res;
691 }
692
693 // At a promotion failure dump information on block layout in heap
694 // (cms old generation).
695 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
696 LogHandle(gc, promotion) log;
697 if (log.is_trace()) {
698 ResourceMark rm;
699 cmsSpace()->dump_at_safepoint_with_locks(collector(), log.trace_stream());
700 }
701 }
702
703 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
704 // Clear the promotion information. These pointers can be adjusted
705 // along with all the other pointers into the heap but
706 // compaction is expected to be a rare event with
707 // a heap using cms so don't do it without seeing the need.
708 for (uint i = 0; i < ParallelGCThreads; i++) {
709 _par_gc_thread_states[i]->promo.reset();
710 }
711 }
712
713 void ConcurrentMarkSweepGeneration::compute_new_size() {
714 assert_locked_or_safepoint(Heap_lock);
715
716 // If incremental collection failed, we just want to expand
717 // to the limit.
718 if (incremental_collection_failed()) {
719 clear_incremental_collection_failed();
720 grow_to_reserved();
721 return;
722 }
723
724 // The heap has been compacted but not reset yet.
725 // Any metric such as free() or used() will be incorrect.
726
727 CardGeneration::compute_new_size();
728
729 // Reset again after a possible resizing
730 if (did_compact()) {
731 cmsSpace()->reset_after_compaction();
732 }
733 }
734
735 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
736 assert_locked_or_safepoint(Heap_lock);
737
738 // If incremental collection failed, we just want to expand
739 // to the limit.
740 if (incremental_collection_failed()) {
741 clear_incremental_collection_failed();
742 grow_to_reserved();
743 return;
744 }
745
746 double free_percentage = ((double) free()) / capacity();
747 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
748 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
749
750 // compute expansion delta needed for reaching desired free percentage
751 if (free_percentage < desired_free_percentage) {
752 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
753 assert(desired_capacity >= capacity(), "invalid expansion size");
754 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
755 LogHandle(gc) log;
756 if (log.is_trace()) {
757 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
758 log.trace("From compute_new_size: ");
759 log.trace(" Free fraction %f", free_percentage);
760 log.trace(" Desired free fraction %f", desired_free_percentage);
761 log.trace(" Maximum free fraction %f", maximum_free_percentage);
762 log.trace(" Capacity " SIZE_FORMAT, capacity() / 1000);
763 log.trace(" Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
764 GenCollectedHeap* gch = GenCollectedHeap::heap();
765 assert(gch->is_old_gen(this), "The CMS generation should always be the old generation");
766 size_t young_size = gch->young_gen()->capacity();
767 log.trace(" Young gen size " SIZE_FORMAT, young_size / 1000);
768 log.trace(" unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
769 log.trace(" contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
770 log.trace(" Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
771 }
772 // safe if expansion fails
773 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
774 log.trace(" Expanded free fraction %f", ((double) free()) / capacity());
775 } else {
776 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
777 assert(desired_capacity <= capacity(), "invalid expansion size");
778 size_t shrink_bytes = capacity() - desired_capacity;
779 // Don't shrink unless the delta is greater than the minimum shrink we want
780 if (shrink_bytes >= MinHeapDeltaBytes) {
781 shrink_free_list_by(shrink_bytes);
782 }
783 }
784 }
785
786 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
787 return cmsSpace()->freelistLock();
788 }
789
790 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
791 CMSSynchronousYieldRequest yr;
792 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
793 return have_lock_and_allocate(size, tlab);
794 }
795
796 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
797 bool tlab /* ignored */) {
798 assert_lock_strong(freelistLock());
799 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
800 HeapWord* res = cmsSpace()->allocate(adjustedSize);
801 // Allocate the object live (grey) if the background collector has
802 // started marking. This is necessary because the marker may
803 // have passed this address and consequently this object will
804 // not otherwise be greyed and would be incorrectly swept up.
805 // Note that if this object contains references, the writing
806 // of those references will dirty the card containing this object
807 // allowing the object to be blackened (and its references scanned)
808 // either during a preclean phase or at the final checkpoint.
809 if (res != NULL) {
810 // We may block here with an uninitialized object with
811 // its mark-bit or P-bits not yet set. Such objects need
812 // to be safely navigable by block_start().
813 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
814 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
815 collector()->direct_allocated(res, adjustedSize);
816 _direct_allocated_words += adjustedSize;
817 // allocation counters
818 NOT_PRODUCT(
819 _numObjectsAllocated++;
820 _numWordsAllocated += (int)adjustedSize;
821 )
822 }
823 return res;
824 }
825
826 // In the case of direct allocation by mutators in a generation that
827 // is being concurrently collected, the object must be allocated
828 // live (grey) if the background collector has started marking.
829 // This is necessary because the marker may
830 // have passed this address and consequently this object will
831 // not otherwise be greyed and would be incorrectly swept up.
832 // Note that if this object contains references, the writing
833 // of those references will dirty the card containing this object
834 // allowing the object to be blackened (and its references scanned)
835 // either during a preclean phase or at the final checkpoint.
836 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
837 assert(_markBitMap.covers(start, size), "Out of bounds");
838 if (_collectorState >= Marking) {
839 MutexLockerEx y(_markBitMap.lock(),
840 Mutex::_no_safepoint_check_flag);
841 // [see comments preceding SweepClosure::do_blk() below for details]
842 //
843 // Can the P-bits be deleted now? JJJ
844 //
845 // 1. need to mark the object as live so it isn't collected
846 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
847 // 3. need to mark the end of the object so marking, precleaning or sweeping
848 // can skip over uninitialized or unparsable objects. An allocated
849 // object is considered uninitialized for our purposes as long as
850 // its klass word is NULL. All old gen objects are parsable
851 // as soon as they are initialized.)
852 _markBitMap.mark(start); // object is live
853 _markBitMap.mark(start + 1); // object is potentially uninitialized?
854 _markBitMap.mark(start + size - 1);
855 // mark end of object
856 }
857 // check that oop looks uninitialized
858 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
859 }
860
861 void CMSCollector::promoted(bool par, HeapWord* start,
862 bool is_obj_array, size_t obj_size) {
863 assert(_markBitMap.covers(start), "Out of bounds");
864 // See comment in direct_allocated() about when objects should
865 // be allocated live.
866 if (_collectorState >= Marking) {
867 // we already hold the marking bit map lock, taken in
868 // the prologue
869 if (par) {
870 _markBitMap.par_mark(start);
871 } else {
872 _markBitMap.mark(start);
873 }
874 // We don't need to mark the object as uninitialized (as
875 // in direct_allocated above) because this is being done with the
876 // world stopped and the object will be initialized by the
877 // time the marking, precleaning or sweeping get to look at it.
878 // But see the code for copying objects into the CMS generation,
879 // where we need to ensure that concurrent readers of the
880 // block offset table are able to safely navigate a block that
881 // is in flux from being free to being allocated (and in
882 // transition while being copied into) and subsequently
883 // becoming a bona-fide object when the copy/promotion is complete.
884 assert(SafepointSynchronize::is_at_safepoint(),
885 "expect promotion only at safepoints");
886
887 if (_collectorState < Sweeping) {
888 // Mark the appropriate cards in the modUnionTable, so that
889 // this object gets scanned before the sweep. If this is
890 // not done, CMS generation references in the object might
891 // not get marked.
892 // For the case of arrays, which are otherwise precisely
893 // marked, we need to dirty the entire array, not just its head.
894 if (is_obj_array) {
895 // The [par_]mark_range() method expects mr.end() below to
896 // be aligned to the granularity of a bit's representation
897 // in the heap. In the case of the MUT below, that's a
898 // card size.
899 MemRegion mr(start,
900 (HeapWord*)round_to((intptr_t)(start + obj_size),
901 CardTableModRefBS::card_size /* bytes */));
902 if (par) {
903 _modUnionTable.par_mark_range(mr);
904 } else {
905 _modUnionTable.mark_range(mr);
906 }
907 } else { // not an obj array; we can just mark the head
908 if (par) {
909 _modUnionTable.par_mark(start);
910 } else {
911 _modUnionTable.mark(start);
912 }
913 }
914 }
915 }
916 }
917
918 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
919 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
920 // allocate, copy and if necessary update promoinfo --
921 // delegate to underlying space.
922 assert_lock_strong(freelistLock());
923
924 #ifndef PRODUCT
925 if (GenCollectedHeap::heap()->promotion_should_fail()) {
926 return NULL;
927 }
928 #endif // #ifndef PRODUCT
929
930 oop res = _cmsSpace->promote(obj, obj_size);
931 if (res == NULL) {
932 // expand and retry
933 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
934 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
935 // Since this is the old generation, we don't try to promote
936 // into a more senior generation.
937 res = _cmsSpace->promote(obj, obj_size);
938 }
939 if (res != NULL) {
940 // See comment in allocate() about when objects should
941 // be allocated live.
942 assert(obj->is_oop(), "Will dereference klass pointer below");
943 collector()->promoted(false, // Not parallel
944 (HeapWord*)res, obj->is_objArray(), obj_size);
945 // promotion counters
946 NOT_PRODUCT(
947 _numObjectsPromoted++;
948 _numWordsPromoted +=
949 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
950 )
951 }
952 return res;
953 }
954
955
956 // IMPORTANT: Notes on object size recognition in CMS.
957 // ---------------------------------------------------
958 // A block of storage in the CMS generation is always in
959 // one of three states. A free block (FREE), an allocated
960 // object (OBJECT) whose size() method reports the correct size,
961 // and an intermediate state (TRANSIENT) in which its size cannot
962 // be accurately determined.
963 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
964 // -----------------------------------------------------
965 // FREE: klass_word & 1 == 1; mark_word holds block size
966 //
967 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
968 // obj->size() computes correct size
969 //
970 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
971 //
972 // STATE IDENTIFICATION: (64 bit+COOPS)
973 // ------------------------------------
974 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
975 //
976 // OBJECT: klass_word installed; klass_word != 0;
977 // obj->size() computes correct size
978 //
979 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
980 //
981 //
982 // STATE TRANSITION DIAGRAM
983 //
984 // mut / parnew mut / parnew
985 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
986 // ^ |
987 // |------------------------ DEAD <------------------------------------|
988 // sweep mut
989 //
990 // While a block is in TRANSIENT state its size cannot be determined
991 // so readers will either need to come back later or stall until
992 // the size can be determined. Note that for the case of direct
993 // allocation, P-bits, when available, may be used to determine the
994 // size of an object that may not yet have been initialized.
995
996 // Things to support parallel young-gen collection.
997 oop
998 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
999 oop old, markOop m,
1000 size_t word_sz) {
1001 #ifndef PRODUCT
1002 if (GenCollectedHeap::heap()->promotion_should_fail()) {
1003 return NULL;
1004 }
1005 #endif // #ifndef PRODUCT
1006
1007 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1008 PromotionInfo* promoInfo = &ps->promo;
1009 // if we are tracking promotions, then first ensure space for
1010 // promotion (including spooling space for saving header if necessary).
1011 // then allocate and copy, then track promoted info if needed.
1012 // When tracking (see PromotionInfo::track()), the mark word may
1013 // be displaced and in this case restoration of the mark word
1014 // occurs in the (oop_since_save_marks_)iterate phase.
1015 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1016 // Out of space for allocating spooling buffers;
1017 // try expanding and allocating spooling buffers.
1018 if (!expand_and_ensure_spooling_space(promoInfo)) {
1019 return NULL;
1020 }
1021 }
1022 assert(promoInfo->has_spooling_space(), "Control point invariant");
1023 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1024 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1025 if (obj_ptr == NULL) {
1026 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1027 if (obj_ptr == NULL) {
1028 return NULL;
1029 }
1030 }
1031 oop obj = oop(obj_ptr);
1032 OrderAccess::storestore();
1033 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1034 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1035 // IMPORTANT: See note on object initialization for CMS above.
1036 // Otherwise, copy the object. Here we must be careful to insert the
1037 // klass pointer last, since this marks the block as an allocated object.
1038 // Except with compressed oops it's the mark word.
1039 HeapWord* old_ptr = (HeapWord*)old;
1040 // Restore the mark word copied above.
1041 obj->set_mark(m);
1042 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1043 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1044 OrderAccess::storestore();
1045
1046 if (UseCompressedClassPointers) {
1047 // Copy gap missed by (aligned) header size calculation below
1048 obj->set_klass_gap(old->klass_gap());
1049 }
1050 if (word_sz > (size_t)oopDesc::header_size()) {
1051 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1052 obj_ptr + oopDesc::header_size(),
1053 word_sz - oopDesc::header_size());
1054 }
1055
1056 // Now we can track the promoted object, if necessary. We take care
1057 // to delay the transition from uninitialized to full object
1058 // (i.e., insertion of klass pointer) until after, so that it
1059 // atomically becomes a promoted object.
1060 if (promoInfo->tracking()) {
1061 promoInfo->track((PromotedObject*)obj, old->klass());
1062 }
1063 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1064 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1065 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1066
1067 // Finally, install the klass pointer (this should be volatile).
1068 OrderAccess::storestore();
1069 obj->set_klass(old->klass());
1070 // We should now be able to calculate the right size for this object
1071 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1072
1073 collector()->promoted(true, // parallel
1074 obj_ptr, old->is_objArray(), word_sz);
1075
1076 NOT_PRODUCT(
1077 Atomic::inc_ptr(&_numObjectsPromoted);
1078 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1079 )
1080
1081 return obj;
1082 }
1083
1084 void
1085 ConcurrentMarkSweepGeneration::
1086 par_promote_alloc_done(int thread_num) {
1087 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1088 ps->lab.retire(thread_num);
1089 }
1090
1091 void
1092 ConcurrentMarkSweepGeneration::
1093 par_oop_since_save_marks_iterate_done(int thread_num) {
1094 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1095 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1096 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1097 }
1098
1099 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1100 size_t size,
1101 bool tlab)
1102 {
1103 // We allow a STW collection only if a full
1104 // collection was requested.
1105 return full || should_allocate(size, tlab); // FIX ME !!!
1106 // This and promotion failure handling are connected at the
1107 // hip and should be fixed by untying them.
1108 }
1109
1110 bool CMSCollector::shouldConcurrentCollect() {
1111 if (_full_gc_requested) {
1112 log_trace(gc, conc)("CMSCollector: collect because of explicit gc request (or gc_locker)");
1113 return true;
1114 }
1115
1116 FreelistLocker x(this);
1117 // ------------------------------------------------------------------
1118 // Print out lots of information which affects the initiation of
1119 // a collection.
1120 LogHandle(gc, conc, stats) log;
1121 if (log.is_debug() && stats().valid()) {
1122 log.debug("CMSCollector shouldConcurrentCollect: ");
1123 ResourceMark rm;
1124 stats().print_on(log.debug_stream());
1125 log.debug("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full());
1126 log.debug("free=" SIZE_FORMAT, _cmsGen->free());
1127 log.debug("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available());
1128 log.debug("promotion_rate=%g", stats().promotion_rate());
1129 log.debug("cms_allocation_rate=%g", stats().cms_allocation_rate());
1130 log.debug("occupancy=%3.7f", _cmsGen->occupancy());
1131 log.debug("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1132 log.debug("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1133 log.debug("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1134 log.debug("metadata initialized %d", MetaspaceGC::should_concurrent_collect());
1135 }
1136 // ------------------------------------------------------------------
1137
1138 // If the estimated time to complete a cms collection (cms_duration())
1139 // is less than the estimated time remaining until the cms generation
1140 // is full, start a collection.
1141 if (!UseCMSInitiatingOccupancyOnly) {
1142 if (stats().valid()) {
1143 if (stats().time_until_cms_start() == 0.0) {
1144 return true;
1145 }
1146 } else {
1147 // We want to conservatively collect somewhat early in order
1148 // to try and "bootstrap" our CMS/promotion statistics;
1149 // this branch will not fire after the first successful CMS
1150 // collection because the stats should then be valid.
1151 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1152 log_debug(gc)(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f",
1153 _cmsGen->occupancy(), _bootstrap_occupancy);
1154 return true;
1155 }
1156 }
1157 }
1158
1159 // Otherwise, we start a collection cycle if
1160 // old gen want a collection cycle started. Each may use
1161 // an appropriate criterion for making this decision.
1162 // XXX We need to make sure that the gen expansion
1163 // criterion dovetails well with this. XXX NEED TO FIX THIS
1164 if (_cmsGen->should_concurrent_collect()) {
1165 log_trace(gc)("CMS old gen initiated");
1166 return true;
1167 }
1168
1169 // We start a collection if we believe an incremental collection may fail;
1170 // this is not likely to be productive in practice because it's probably too
1171 // late anyway.
1172 GenCollectedHeap* gch = GenCollectedHeap::heap();
1173 assert(gch->collector_policy()->is_generation_policy(),
1174 "You may want to check the correctness of the following");
1175 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1176 log_trace(gc)("CMSCollector: collect because incremental collection will fail ");
1177 return true;
1178 }
1179
1180 if (MetaspaceGC::should_concurrent_collect()) {
1181 log_trace(gc)("CMSCollector: collect for metadata allocation ");
1182 return true;
1183 }
1184
1185 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1186 if (CMSTriggerInterval >= 0) {
1187 if (CMSTriggerInterval == 0) {
1188 // Trigger always
1189 return true;
1190 }
1191
1192 // Check the CMS time since begin (we do not check the stats validity
1193 // as we want to be able to trigger the first CMS cycle as well)
1194 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1195 if (stats().valid()) {
1196 log_trace(gc)("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1197 stats().cms_time_since_begin());
1198 } else {
1199 log_trace(gc)("CMSCollector: collect because of trigger interval (first collection)");
1200 }
1201 return true;
1202 }
1203 }
1204
1205 return false;
1206 }
1207
1208 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1209
1210 // Clear _expansion_cause fields of constituent generations
1211 void CMSCollector::clear_expansion_cause() {
1212 _cmsGen->clear_expansion_cause();
1213 }
1214
1215 // We should be conservative in starting a collection cycle. To
1216 // start too eagerly runs the risk of collecting too often in the
1217 // extreme. To collect too rarely falls back on full collections,
1218 // which works, even if not optimum in terms of concurrent work.
1219 // As a work around for too eagerly collecting, use the flag
1220 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1221 // giving the user an easily understandable way of controlling the
1222 // collections.
1223 // We want to start a new collection cycle if any of the following
1224 // conditions hold:
1225 // . our current occupancy exceeds the configured initiating occupancy
1226 // for this generation, or
1227 // . we recently needed to expand this space and have not, since that
1228 // expansion, done a collection of this generation, or
1229 // . the underlying space believes that it may be a good idea to initiate
1230 // a concurrent collection (this may be based on criteria such as the
1231 // following: the space uses linear allocation and linear allocation is
1232 // going to fail, or there is believed to be excessive fragmentation in
1233 // the generation, etc... or ...
1234 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1235 // the case of the old generation; see CR 6543076):
1236 // we may be approaching a point at which allocation requests may fail because
1237 // we will be out of sufficient free space given allocation rate estimates.]
1238 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1239
1240 assert_lock_strong(freelistLock());
1241 if (occupancy() > initiating_occupancy()) {
1242 log_trace(gc)(" %s: collect because of occupancy %f / %f ",
1243 short_name(), occupancy(), initiating_occupancy());
1244 return true;
1245 }
1246 if (UseCMSInitiatingOccupancyOnly) {
1247 return false;
1248 }
1249 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1250 log_trace(gc)(" %s: collect because expanded for allocation ", short_name());
1251 return true;
1252 }
1253 return false;
1254 }
1255
1256 void ConcurrentMarkSweepGeneration::collect(bool full,
1257 bool clear_all_soft_refs,
1258 size_t size,
1259 bool tlab)
1260 {
1261 collector()->collect(full, clear_all_soft_refs, size, tlab);
1262 }
1263
1264 void CMSCollector::collect(bool full,
1265 bool clear_all_soft_refs,
1266 size_t size,
1267 bool tlab)
1268 {
1269 // The following "if" branch is present for defensive reasons.
1270 // In the current uses of this interface, it can be replaced with:
1271 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1272 // But I am not placing that assert here to allow future
1273 // generality in invoking this interface.
1274 if (GC_locker::is_active()) {
1275 // A consistency test for GC_locker
1276 assert(GC_locker::needs_gc(), "Should have been set already");
1277 // Skip this foreground collection, instead
1278 // expanding the heap if necessary.
1279 // Need the free list locks for the call to free() in compute_new_size()
1280 compute_new_size();
1281 return;
1282 }
1283 acquire_control_and_collect(full, clear_all_soft_refs);
1284 }
1285
1286 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1287 GenCollectedHeap* gch = GenCollectedHeap::heap();
1288 unsigned int gc_count = gch->total_full_collections();
1289 if (gc_count == full_gc_count) {
1290 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1291 _full_gc_requested = true;
1292 _full_gc_cause = cause;
1293 CGC_lock->notify(); // nudge CMS thread
1294 } else {
1295 assert(gc_count > full_gc_count, "Error: causal loop");
1296 }
1297 }
1298
1299 bool CMSCollector::is_external_interruption() {
1300 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1301 return GCCause::is_user_requested_gc(cause) ||
1302 GCCause::is_serviceability_requested_gc(cause);
1303 }
1304
1305 void CMSCollector::report_concurrent_mode_interruption() {
1306 if (is_external_interruption()) {
1307 log_debug(gc)("Concurrent mode interrupted");
1308 } else {
1309 log_debug(gc)("Concurrent mode failure");
1310 _gc_tracer_cm->report_concurrent_mode_failure();
1311 }
1312 }
1313
1314
1315 // The foreground and background collectors need to coordinate in order
1316 // to make sure that they do not mutually interfere with CMS collections.
1317 // When a background collection is active,
1318 // the foreground collector may need to take over (preempt) and
1319 // synchronously complete an ongoing collection. Depending on the
1320 // frequency of the background collections and the heap usage
1321 // of the application, this preemption can be seldom or frequent.
1322 // There are only certain
1323 // points in the background collection that the "collection-baton"
1324 // can be passed to the foreground collector.
1325 //
1326 // The foreground collector will wait for the baton before
1327 // starting any part of the collection. The foreground collector
1328 // will only wait at one location.
1329 //
1330 // The background collector will yield the baton before starting a new
1331 // phase of the collection (e.g., before initial marking, marking from roots,
1332 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1333 // of the loop which switches the phases. The background collector does some
1334 // of the phases (initial mark, final re-mark) with the world stopped.
1335 // Because of locking involved in stopping the world,
1336 // the foreground collector should not block waiting for the background
1337 // collector when it is doing a stop-the-world phase. The background
1338 // collector will yield the baton at an additional point just before
1339 // it enters a stop-the-world phase. Once the world is stopped, the
1340 // background collector checks the phase of the collection. If the
1341 // phase has not changed, it proceeds with the collection. If the
1342 // phase has changed, it skips that phase of the collection. See
1343 // the comments on the use of the Heap_lock in collect_in_background().
1344 //
1345 // Variable used in baton passing.
1346 // _foregroundGCIsActive - Set to true by the foreground collector when
1347 // it wants the baton. The foreground clears it when it has finished
1348 // the collection.
1349 // _foregroundGCShouldWait - Set to true by the background collector
1350 // when it is running. The foreground collector waits while
1351 // _foregroundGCShouldWait is true.
1352 // CGC_lock - monitor used to protect access to the above variables
1353 // and to notify the foreground and background collectors.
1354 // _collectorState - current state of the CMS collection.
1355 //
1356 // The foreground collector
1357 // acquires the CGC_lock
1358 // sets _foregroundGCIsActive
1359 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1360 // various locks acquired in preparation for the collection
1361 // are released so as not to block the background collector
1362 // that is in the midst of a collection
1363 // proceeds with the collection
1364 // clears _foregroundGCIsActive
1365 // returns
1366 //
1367 // The background collector in a loop iterating on the phases of the
1368 // collection
1369 // acquires the CGC_lock
1370 // sets _foregroundGCShouldWait
1371 // if _foregroundGCIsActive is set
1372 // clears _foregroundGCShouldWait, notifies _CGC_lock
1373 // waits on _CGC_lock for _foregroundGCIsActive to become false
1374 // and exits the loop.
1375 // otherwise
1376 // proceed with that phase of the collection
1377 // if the phase is a stop-the-world phase,
1378 // yield the baton once more just before enqueueing
1379 // the stop-world CMS operation (executed by the VM thread).
1380 // returns after all phases of the collection are done
1381 //
1382
1383 void CMSCollector::acquire_control_and_collect(bool full,
1384 bool clear_all_soft_refs) {
1385 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1386 assert(!Thread::current()->is_ConcurrentGC_thread(),
1387 "shouldn't try to acquire control from self!");
1388
1389 // Start the protocol for acquiring control of the
1390 // collection from the background collector (aka CMS thread).
1391 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1392 "VM thread should have CMS token");
1393 // Remember the possibly interrupted state of an ongoing
1394 // concurrent collection
1395 CollectorState first_state = _collectorState;
1396
1397 // Signal to a possibly ongoing concurrent collection that
1398 // we want to do a foreground collection.
1399 _foregroundGCIsActive = true;
1400
1401 // release locks and wait for a notify from the background collector
1402 // releasing the locks in only necessary for phases which
1403 // do yields to improve the granularity of the collection.
1404 assert_lock_strong(bitMapLock());
1405 // We need to lock the Free list lock for the space that we are
1406 // currently collecting.
1407 assert(haveFreelistLocks(), "Must be holding free list locks");
1408 bitMapLock()->unlock();
1409 releaseFreelistLocks();
1410 {
1411 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1412 if (_foregroundGCShouldWait) {
1413 // We are going to be waiting for action for the CMS thread;
1414 // it had better not be gone (for instance at shutdown)!
1415 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1416 "CMS thread must be running");
1417 // Wait here until the background collector gives us the go-ahead
1418 ConcurrentMarkSweepThread::clear_CMS_flag(
1419 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1420 // Get a possibly blocked CMS thread going:
1421 // Note that we set _foregroundGCIsActive true above,
1422 // without protection of the CGC_lock.
1423 CGC_lock->notify();
1424 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1425 "Possible deadlock");
1426 while (_foregroundGCShouldWait) {
1427 // wait for notification
1428 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1429 // Possibility of delay/starvation here, since CMS token does
1430 // not know to give priority to VM thread? Actually, i think
1431 // there wouldn't be any delay/starvation, but the proof of
1432 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1433 }
1434 ConcurrentMarkSweepThread::set_CMS_flag(
1435 ConcurrentMarkSweepThread::CMS_vm_has_token);
1436 }
1437 }
1438 // The CMS_token is already held. Get back the other locks.
1439 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1440 "VM thread should have CMS token");
1441 getFreelistLocks();
1442 bitMapLock()->lock_without_safepoint_check();
1443 log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d",
1444 p2i(Thread::current()), first_state);
1445 log_debug(gc, state)(" gets control with state %d", _collectorState);
1446
1447 // Inform cms gen if this was due to partial collection failing.
1448 // The CMS gen may use this fact to determine its expansion policy.
1449 GenCollectedHeap* gch = GenCollectedHeap::heap();
1450 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1451 assert(!_cmsGen->incremental_collection_failed(),
1452 "Should have been noticed, reacted to and cleared");
1453 _cmsGen->set_incremental_collection_failed();
1454 }
1455
1456 if (first_state > Idling) {
1457 report_concurrent_mode_interruption();
1458 }
1459
1460 set_did_compact(true);
1461
1462 // If the collection is being acquired from the background
1463 // collector, there may be references on the discovered
1464 // references lists. Abandon those references, since some
1465 // of them may have become unreachable after concurrent
1466 // discovery; the STW compacting collector will redo discovery
1467 // more precisely, without being subject to floating garbage.
1468 // Leaving otherwise unreachable references in the discovered
1469 // lists would require special handling.
1470 ref_processor()->disable_discovery();
1471 ref_processor()->abandon_partial_discovery();
1472 ref_processor()->verify_no_references_recorded();
1473
1474 if (first_state > Idling) {
1475 save_heap_summary();
1476 }
1477
1478 do_compaction_work(clear_all_soft_refs);
1479
1480 // Has the GC time limit been exceeded?
1481 size_t max_eden_size = _young_gen->max_eden_size();
1482 GCCause::Cause gc_cause = gch->gc_cause();
1483 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1484 _young_gen->eden()->used(),
1485 _cmsGen->max_capacity(),
1486 max_eden_size,
1487 full,
1488 gc_cause,
1489 gch->collector_policy());
1490
1491 // Reset the expansion cause, now that we just completed
1492 // a collection cycle.
1493 clear_expansion_cause();
1494 _foregroundGCIsActive = false;
1495 return;
1496 }
1497
1498 // Resize the tenured generation
1499 // after obtaining the free list locks for the
1500 // two generations.
1501 void CMSCollector::compute_new_size() {
1502 assert_locked_or_safepoint(Heap_lock);
1503 FreelistLocker z(this);
1504 MetaspaceGC::compute_new_size();
1505 _cmsGen->compute_new_size_free_list();
1506 }
1507
1508 // A work method used by the foreground collector to do
1509 // a mark-sweep-compact.
1510 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1511 GenCollectedHeap* gch = GenCollectedHeap::heap();
1512
1513 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1514 gc_timer->register_gc_start();
1515
1516 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1517 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1518
1519 GCTraceTime(Trace, gc) t("CMS:MSC");
1520
1521 // Temporarily widen the span of the weak reference processing to
1522 // the entire heap.
1523 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1524 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1525 // Temporarily, clear the "is_alive_non_header" field of the
1526 // reference processor.
1527 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1528 // Temporarily make reference _processing_ single threaded (non-MT).
1529 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1530 // Temporarily make refs discovery atomic
1531 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1532 // Temporarily make reference _discovery_ single threaded (non-MT)
1533 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1534
1535 ref_processor()->set_enqueuing_is_done(false);
1536 ref_processor()->enable_discovery();
1537 ref_processor()->setup_policy(clear_all_soft_refs);
1538 // If an asynchronous collection finishes, the _modUnionTable is
1539 // all clear. If we are assuming the collection from an asynchronous
1540 // collection, clear the _modUnionTable.
1541 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1542 "_modUnionTable should be clear if the baton was not passed");
1543 _modUnionTable.clear_all();
1544 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1545 "mod union for klasses should be clear if the baton was passed");
1546 _ct->klass_rem_set()->clear_mod_union();
1547
1548 // We must adjust the allocation statistics being maintained
1549 // in the free list space. We do so by reading and clearing
1550 // the sweep timer and updating the block flux rate estimates below.
1551 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1552 if (_inter_sweep_timer.is_active()) {
1553 _inter_sweep_timer.stop();
1554 // Note that we do not use this sample to update the _inter_sweep_estimate.
1555 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1556 _inter_sweep_estimate.padded_average(),
1557 _intra_sweep_estimate.padded_average());
1558 }
1559
1560 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1561 #ifdef ASSERT
1562 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1563 size_t free_size = cms_space->free();
1564 assert(free_size ==
1565 pointer_delta(cms_space->end(), cms_space->compaction_top())
1566 * HeapWordSize,
1567 "All the free space should be compacted into one chunk at top");
1568 assert(cms_space->dictionary()->total_chunk_size(
1569 debug_only(cms_space->freelistLock())) == 0 ||
1570 cms_space->totalSizeInIndexedFreeLists() == 0,
1571 "All the free space should be in a single chunk");
1572 size_t num = cms_space->totalCount();
1573 assert((free_size == 0 && num == 0) ||
1574 (free_size > 0 && (num == 1 || num == 2)),
1575 "There should be at most 2 free chunks after compaction");
1576 #endif // ASSERT
1577 _collectorState = Resetting;
1578 assert(_restart_addr == NULL,
1579 "Should have been NULL'd before baton was passed");
1580 reset_stw();
1581 _cmsGen->reset_after_compaction();
1582 _concurrent_cycles_since_last_unload = 0;
1583
1584 // Clear any data recorded in the PLAB chunk arrays.
1585 if (_survivor_plab_array != NULL) {
1586 reset_survivor_plab_arrays();
1587 }
1588
1589 // Adjust the per-size allocation stats for the next epoch.
1590 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1591 // Restart the "inter sweep timer" for the next epoch.
1592 _inter_sweep_timer.reset();
1593 _inter_sweep_timer.start();
1594
1595 gc_timer->register_gc_end();
1596
1597 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1598
1599 // For a mark-sweep-compact, compute_new_size() will be called
1600 // in the heap's do_collection() method.
1601 }
1602
1603 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1604 LogHandle(gc, heap) log;
1605 if (!log.is_trace()) {
1606 return;
1607 }
1608
1609 ContiguousSpace* eden_space = _young_gen->eden();
1610 ContiguousSpace* from_space = _young_gen->from();
1611 ContiguousSpace* to_space = _young_gen->to();
1612 // Eden
1613 if (_eden_chunk_array != NULL) {
1614 log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1615 p2i(eden_space->bottom()), p2i(eden_space->top()),
1616 p2i(eden_space->end()), eden_space->capacity());
1617 log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT,
1618 _eden_chunk_index, _eden_chunk_capacity);
1619 for (size_t i = 0; i < _eden_chunk_index; i++) {
1620 log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i]));
1621 }
1622 }
1623 // Survivor
1624 if (_survivor_chunk_array != NULL) {
1625 log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1626 p2i(from_space->bottom()), p2i(from_space->top()),
1627 p2i(from_space->end()), from_space->capacity());
1628 log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT,
1629 _survivor_chunk_index, _survivor_chunk_capacity);
1630 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1631 log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i]));
1632 }
1633 }
1634 }
1635
1636 void CMSCollector::getFreelistLocks() const {
1637 // Get locks for all free lists in all generations that this
1638 // collector is responsible for
1639 _cmsGen->freelistLock()->lock_without_safepoint_check();
1640 }
1641
1642 void CMSCollector::releaseFreelistLocks() const {
1643 // Release locks for all free lists in all generations that this
1644 // collector is responsible for
1645 _cmsGen->freelistLock()->unlock();
1646 }
1647
1648 bool CMSCollector::haveFreelistLocks() const {
1649 // Check locks for all free lists in all generations that this
1650 // collector is responsible for
1651 assert_lock_strong(_cmsGen->freelistLock());
1652 PRODUCT_ONLY(ShouldNotReachHere());
1653 return true;
1654 }
1655
1656 // A utility class that is used by the CMS collector to
1657 // temporarily "release" the foreground collector from its
1658 // usual obligation to wait for the background collector to
1659 // complete an ongoing phase before proceeding.
1660 class ReleaseForegroundGC: public StackObj {
1661 private:
1662 CMSCollector* _c;
1663 public:
1664 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1665 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1666 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1667 // allow a potentially blocked foreground collector to proceed
1668 _c->_foregroundGCShouldWait = false;
1669 if (_c->_foregroundGCIsActive) {
1670 CGC_lock->notify();
1671 }
1672 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1673 "Possible deadlock");
1674 }
1675
1676 ~ReleaseForegroundGC() {
1677 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1678 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1679 _c->_foregroundGCShouldWait = true;
1680 }
1681 };
1682
1683 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1684 assert(Thread::current()->is_ConcurrentGC_thread(),
1685 "A CMS asynchronous collection is only allowed on a CMS thread.");
1686
1687 GenCollectedHeap* gch = GenCollectedHeap::heap();
1688 {
1689 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1690 MutexLockerEx hl(Heap_lock, safepoint_check);
1691 FreelistLocker fll(this);
1692 MutexLockerEx x(CGC_lock, safepoint_check);
1693 if (_foregroundGCIsActive) {
1694 // The foreground collector is. Skip this
1695 // background collection.
1696 assert(!_foregroundGCShouldWait, "Should be clear");
1697 return;
1698 } else {
1699 assert(_collectorState == Idling, "Should be idling before start.");
1700 _collectorState = InitialMarking;
1701 register_gc_start(cause);
1702 // Reset the expansion cause, now that we are about to begin
1703 // a new cycle.
1704 clear_expansion_cause();
1705
1706 // Clear the MetaspaceGC flag since a concurrent collection
1707 // is starting but also clear it after the collection.
1708 MetaspaceGC::set_should_concurrent_collect(false);
1709 }
1710 // Decide if we want to enable class unloading as part of the
1711 // ensuing concurrent GC cycle.
1712 update_should_unload_classes();
1713 _full_gc_requested = false; // acks all outstanding full gc requests
1714 _full_gc_cause = GCCause::_no_gc;
1715 // Signal that we are about to start a collection
1716 gch->increment_total_full_collections(); // ... starting a collection cycle
1717 _collection_count_start = gch->total_full_collections();
1718 }
1719
1720 // Used for PrintGC
1721 size_t prev_used = 0;
1722 if (PrintGC && Verbose) {
1723 prev_used = _cmsGen->used();
1724 }
1725
1726 // The change of the collection state is normally done at this level;
1727 // the exceptions are phases that are executed while the world is
1728 // stopped. For those phases the change of state is done while the
1729 // world is stopped. For baton passing purposes this allows the
1730 // background collector to finish the phase and change state atomically.
1731 // The foreground collector cannot wait on a phase that is done
1732 // while the world is stopped because the foreground collector already
1733 // has the world stopped and would deadlock.
1734 while (_collectorState != Idling) {
1735 log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d",
1736 p2i(Thread::current()), _collectorState);
1737 // The foreground collector
1738 // holds the Heap_lock throughout its collection.
1739 // holds the CMS token (but not the lock)
1740 // except while it is waiting for the background collector to yield.
1741 //
1742 // The foreground collector should be blocked (not for long)
1743 // if the background collector is about to start a phase
1744 // executed with world stopped. If the background
1745 // collector has already started such a phase, the
1746 // foreground collector is blocked waiting for the
1747 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1748 // are executed in the VM thread.
1749 //
1750 // The locking order is
1751 // PendingListLock (PLL) -- if applicable (FinalMarking)
1752 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1753 // CMS token (claimed in
1754 // stop_world_and_do() -->
1755 // safepoint_synchronize() -->
1756 // CMSThread::synchronize())
1757
1758 {
1759 // Check if the FG collector wants us to yield.
1760 CMSTokenSync x(true); // is cms thread
1761 if (waitForForegroundGC()) {
1762 // We yielded to a foreground GC, nothing more to be
1763 // done this round.
1764 assert(_foregroundGCShouldWait == false, "We set it to false in "
1765 "waitForForegroundGC()");
1766 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1767 p2i(Thread::current()), _collectorState);
1768 return;
1769 } else {
1770 // The background collector can run but check to see if the
1771 // foreground collector has done a collection while the
1772 // background collector was waiting to get the CGC_lock
1773 // above. If yes, break so that _foregroundGCShouldWait
1774 // is cleared before returning.
1775 if (_collectorState == Idling) {
1776 break;
1777 }
1778 }
1779 }
1780
1781 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1782 "should be waiting");
1783
1784 switch (_collectorState) {
1785 case InitialMarking:
1786 {
1787 ReleaseForegroundGC x(this);
1788 stats().record_cms_begin();
1789 VM_CMS_Initial_Mark initial_mark_op(this);
1790 VMThread::execute(&initial_mark_op);
1791 }
1792 // The collector state may be any legal state at this point
1793 // since the background collector may have yielded to the
1794 // foreground collector.
1795 break;
1796 case Marking:
1797 // initial marking in checkpointRootsInitialWork has been completed
1798 if (markFromRoots()) { // we were successful
1799 assert(_collectorState == Precleaning, "Collector state should "
1800 "have changed");
1801 } else {
1802 assert(_foregroundGCIsActive, "Internal state inconsistency");
1803 }
1804 break;
1805 case Precleaning:
1806 // marking from roots in markFromRoots has been completed
1807 preclean();
1808 assert(_collectorState == AbortablePreclean ||
1809 _collectorState == FinalMarking,
1810 "Collector state should have changed");
1811 break;
1812 case AbortablePreclean:
1813 abortable_preclean();
1814 assert(_collectorState == FinalMarking, "Collector state should "
1815 "have changed");
1816 break;
1817 case FinalMarking:
1818 {
1819 ReleaseForegroundGC x(this);
1820
1821 VM_CMS_Final_Remark final_remark_op(this);
1822 VMThread::execute(&final_remark_op);
1823 }
1824 assert(_foregroundGCShouldWait, "block post-condition");
1825 break;
1826 case Sweeping:
1827 // final marking in checkpointRootsFinal has been completed
1828 sweep();
1829 assert(_collectorState == Resizing, "Collector state change "
1830 "to Resizing must be done under the free_list_lock");
1831
1832 case Resizing: {
1833 // Sweeping has been completed...
1834 // At this point the background collection has completed.
1835 // Don't move the call to compute_new_size() down
1836 // into code that might be executed if the background
1837 // collection was preempted.
1838 {
1839 ReleaseForegroundGC x(this); // unblock FG collection
1840 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1841 CMSTokenSync z(true); // not strictly needed.
1842 if (_collectorState == Resizing) {
1843 compute_new_size();
1844 save_heap_summary();
1845 _collectorState = Resetting;
1846 } else {
1847 assert(_collectorState == Idling, "The state should only change"
1848 " because the foreground collector has finished the collection");
1849 }
1850 }
1851 break;
1852 }
1853 case Resetting:
1854 // CMS heap resizing has been completed
1855 reset_concurrent();
1856 assert(_collectorState == Idling, "Collector state should "
1857 "have changed");
1858
1859 MetaspaceGC::set_should_concurrent_collect(false);
1860
1861 stats().record_cms_end();
1862 // Don't move the concurrent_phases_end() and compute_new_size()
1863 // calls to here because a preempted background collection
1864 // has it's state set to "Resetting".
1865 break;
1866 case Idling:
1867 default:
1868 ShouldNotReachHere();
1869 break;
1870 }
1871 log_debug(gc, state)(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1872 p2i(Thread::current()), _collectorState);
1873 assert(_foregroundGCShouldWait, "block post-condition");
1874 }
1875
1876 // Should this be in gc_epilogue?
1877 collector_policy()->counters()->update_counters();
1878
1879 {
1880 // Clear _foregroundGCShouldWait and, in the event that the
1881 // foreground collector is waiting, notify it, before
1882 // returning.
1883 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1884 _foregroundGCShouldWait = false;
1885 if (_foregroundGCIsActive) {
1886 CGC_lock->notify();
1887 }
1888 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1889 "Possible deadlock");
1890 }
1891 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1892 p2i(Thread::current()), _collectorState);
1893 log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K(" SIZE_FORMAT "K)",
1894 prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K);
1895 }
1896
1897 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1898 _cms_start_registered = true;
1899 _gc_timer_cm->register_gc_start();
1900 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1901 }
1902
1903 void CMSCollector::register_gc_end() {
1904 if (_cms_start_registered) {
1905 report_heap_summary(GCWhen::AfterGC);
1906
1907 _gc_timer_cm->register_gc_end();
1908 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1909 _cms_start_registered = false;
1910 }
1911 }
1912
1913 void CMSCollector::save_heap_summary() {
1914 GenCollectedHeap* gch = GenCollectedHeap::heap();
1915 _last_heap_summary = gch->create_heap_summary();
1916 _last_metaspace_summary = gch->create_metaspace_summary();
1917 }
1918
1919 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1920 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1921 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1922 }
1923
1924 bool CMSCollector::waitForForegroundGC() {
1925 bool res = false;
1926 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1927 "CMS thread should have CMS token");
1928 // Block the foreground collector until the
1929 // background collectors decides whether to
1930 // yield.
1931 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1932 _foregroundGCShouldWait = true;
1933 if (_foregroundGCIsActive) {
1934 // The background collector yields to the
1935 // foreground collector and returns a value
1936 // indicating that it has yielded. The foreground
1937 // collector can proceed.
1938 res = true;
1939 _foregroundGCShouldWait = false;
1940 ConcurrentMarkSweepThread::clear_CMS_flag(
1941 ConcurrentMarkSweepThread::CMS_cms_has_token);
1942 ConcurrentMarkSweepThread::set_CMS_flag(
1943 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1944 // Get a possibly blocked foreground thread going
1945 CGC_lock->notify();
1946 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
1947 p2i(Thread::current()), _collectorState);
1948 while (_foregroundGCIsActive) {
1949 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1950 }
1951 ConcurrentMarkSweepThread::set_CMS_flag(
1952 ConcurrentMarkSweepThread::CMS_cms_has_token);
1953 ConcurrentMarkSweepThread::clear_CMS_flag(
1954 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1955 }
1956 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
1957 p2i(Thread::current()), _collectorState);
1958 return res;
1959 }
1960
1961 // Because of the need to lock the free lists and other structures in
1962 // the collector, common to all the generations that the collector is
1963 // collecting, we need the gc_prologues of individual CMS generations
1964 // delegate to their collector. It may have been simpler had the
1965 // current infrastructure allowed one to call a prologue on a
1966 // collector. In the absence of that we have the generation's
1967 // prologue delegate to the collector, which delegates back
1968 // some "local" work to a worker method in the individual generations
1969 // that it's responsible for collecting, while itself doing any
1970 // work common to all generations it's responsible for. A similar
1971 // comment applies to the gc_epilogue()'s.
1972 // The role of the variable _between_prologue_and_epilogue is to
1973 // enforce the invocation protocol.
1974 void CMSCollector::gc_prologue(bool full) {
1975 // Call gc_prologue_work() for the CMSGen
1976 // we are responsible for.
1977
1978 // The following locking discipline assumes that we are only called
1979 // when the world is stopped.
1980 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
1981
1982 // The CMSCollector prologue must call the gc_prologues for the
1983 // "generations" that it's responsible
1984 // for.
1985
1986 assert( Thread::current()->is_VM_thread()
1987 || ( CMSScavengeBeforeRemark
1988 && Thread::current()->is_ConcurrentGC_thread()),
1989 "Incorrect thread type for prologue execution");
1990
1991 if (_between_prologue_and_epilogue) {
1992 // We have already been invoked; this is a gc_prologue delegation
1993 // from yet another CMS generation that we are responsible for, just
1994 // ignore it since all relevant work has already been done.
1995 return;
1996 }
1997
1998 // set a bit saying prologue has been called; cleared in epilogue
1999 _between_prologue_and_epilogue = true;
2000 // Claim locks for common data structures, then call gc_prologue_work()
2001 // for each CMSGen.
2002
2003 getFreelistLocks(); // gets free list locks on constituent spaces
2004 bitMapLock()->lock_without_safepoint_check();
2005
2006 // Should call gc_prologue_work() for all cms gens we are responsible for
2007 bool duringMarking = _collectorState >= Marking
2008 && _collectorState < Sweeping;
2009
2010 // The young collections clear the modified oops state, which tells if
2011 // there are any modified oops in the class. The remark phase also needs
2012 // that information. Tell the young collection to save the union of all
2013 // modified klasses.
2014 if (duringMarking) {
2015 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2016 }
2017
2018 bool registerClosure = duringMarking;
2019
2020 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2021
2022 if (!full) {
2023 stats().record_gc0_begin();
2024 }
2025 }
2026
2027 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2028
2029 _capacity_at_prologue = capacity();
2030 _used_at_prologue = used();
2031
2032 // Delegate to CMScollector which knows how to coordinate between
2033 // this and any other CMS generations that it is responsible for
2034 // collecting.
2035 collector()->gc_prologue(full);
2036 }
2037
2038 // This is a "private" interface for use by this generation's CMSCollector.
2039 // Not to be called directly by any other entity (for instance,
2040 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2041 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2042 bool registerClosure, ModUnionClosure* modUnionClosure) {
2043 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2044 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2045 "Should be NULL");
2046 if (registerClosure) {
2047 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2048 }
2049 cmsSpace()->gc_prologue();
2050 // Clear stat counters
2051 NOT_PRODUCT(
2052 assert(_numObjectsPromoted == 0, "check");
2053 assert(_numWordsPromoted == 0, "check");
2054 log_develop(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently",
2055 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2056 _numObjectsAllocated = 0;
2057 _numWordsAllocated = 0;
2058 )
2059 }
2060
2061 void CMSCollector::gc_epilogue(bool full) {
2062 // The following locking discipline assumes that we are only called
2063 // when the world is stopped.
2064 assert(SafepointSynchronize::is_at_safepoint(),
2065 "world is stopped assumption");
2066
2067 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2068 // if linear allocation blocks need to be appropriately marked to allow the
2069 // the blocks to be parsable. We also check here whether we need to nudge the
2070 // CMS collector thread to start a new cycle (if it's not already active).
2071 assert( Thread::current()->is_VM_thread()
2072 || ( CMSScavengeBeforeRemark
2073 && Thread::current()->is_ConcurrentGC_thread()),
2074 "Incorrect thread type for epilogue execution");
2075
2076 if (!_between_prologue_and_epilogue) {
2077 // We have already been invoked; this is a gc_epilogue delegation
2078 // from yet another CMS generation that we are responsible for, just
2079 // ignore it since all relevant work has already been done.
2080 return;
2081 }
2082 assert(haveFreelistLocks(), "must have freelist locks");
2083 assert_lock_strong(bitMapLock());
2084
2085 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2086
2087 _cmsGen->gc_epilogue_work(full);
2088
2089 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2090 // in case sampling was not already enabled, enable it
2091 _start_sampling = true;
2092 }
2093 // reset _eden_chunk_array so sampling starts afresh
2094 _eden_chunk_index = 0;
2095
2096 size_t cms_used = _cmsGen->cmsSpace()->used();
2097
2098 // update performance counters - this uses a special version of
2099 // update_counters() that allows the utilization to be passed as a
2100 // parameter, avoiding multiple calls to used().
2101 //
2102 _cmsGen->update_counters(cms_used);
2103
2104 bitMapLock()->unlock();
2105 releaseFreelistLocks();
2106
2107 if (!CleanChunkPoolAsync) {
2108 Chunk::clean_chunk_pool();
2109 }
2110
2111 set_did_compact(false);
2112 _between_prologue_and_epilogue = false; // ready for next cycle
2113 }
2114
2115 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2116 collector()->gc_epilogue(full);
2117
2118 // Also reset promotion tracking in par gc thread states.
2119 for (uint i = 0; i < ParallelGCThreads; i++) {
2120 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2121 }
2122 }
2123
2124 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2125 assert(!incremental_collection_failed(), "Should have been cleared");
2126 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2127 cmsSpace()->gc_epilogue();
2128 // Print stat counters
2129 NOT_PRODUCT(
2130 assert(_numObjectsAllocated == 0, "check");
2131 assert(_numWordsAllocated == 0, "check");
2132 log_develop(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
2133 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2134 _numObjectsPromoted = 0;
2135 _numWordsPromoted = 0;
2136 )
2137
2138 // Call down the chain in contiguous_available needs the freelistLock
2139 // so print this out before releasing the freeListLock.
2140 log_develop(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available());
2141 }
2142
2143 #ifndef PRODUCT
2144 bool CMSCollector::have_cms_token() {
2145 Thread* thr = Thread::current();
2146 if (thr->is_VM_thread()) {
2147 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2148 } else if (thr->is_ConcurrentGC_thread()) {
2149 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2150 } else if (thr->is_GC_task_thread()) {
2151 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2152 ParGCRareEvent_lock->owned_by_self();
2153 }
2154 return false;
2155 }
2156 #endif
2157
2158 void
2159 CMSCollector::print_on_error(outputStream* st) {
2160 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2161 if (collector != NULL) {
2162 CMSBitMap* bitmap = &collector->_markBitMap;
2163 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2164 bitmap->print_on_error(st, " Bits: ");
2165
2166 st->cr();
2167
2168 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2169 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2170 mut_bitmap->print_on_error(st, " Bits: ");
2171 }
2172 }
2173
2174 ////////////////////////////////////////////////////////
2175 // CMS Verification Support
2176 ////////////////////////////////////////////////////////
2177 // Following the remark phase, the following invariant
2178 // should hold -- each object in the CMS heap which is
2179 // marked in markBitMap() should be marked in the verification_mark_bm().
2180
2181 class VerifyMarkedClosure: public BitMapClosure {
2182 CMSBitMap* _marks;
2183 bool _failed;
2184
2185 public:
2186 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2187
2188 bool do_bit(size_t offset) {
2189 HeapWord* addr = _marks->offsetToHeapWord(offset);
2190 if (!_marks->isMarked(addr)) {
2191 LogHandle(gc, verify) log;
2192 ResourceMark rm;
2193 oop(addr)->print_on(log.info_stream());
2194 log.info(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2195 _failed = true;
2196 }
2197 return true;
2198 }
2199
2200 bool failed() { return _failed; }
2201 };
2202
2203 bool CMSCollector::verify_after_remark() {
2204 GCTraceTime(Info, gc, verify) tm("Verifying CMS Marking.");
2205 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2206 static bool init = false;
2207
2208 assert(SafepointSynchronize::is_at_safepoint(),
2209 "Else mutations in object graph will make answer suspect");
2210 assert(have_cms_token(),
2211 "Else there may be mutual interference in use of "
2212 " verification data structures");
2213 assert(_collectorState > Marking && _collectorState <= Sweeping,
2214 "Else marking info checked here may be obsolete");
2215 assert(haveFreelistLocks(), "must hold free list locks");
2216 assert_lock_strong(bitMapLock());
2217
2218
2219 // Allocate marking bit map if not already allocated
2220 if (!init) { // first time
2221 if (!verification_mark_bm()->allocate(_span)) {
2222 return false;
2223 }
2224 init = true;
2225 }
2226
2227 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2228
2229 // Turn off refs discovery -- so we will be tracing through refs.
2230 // This is as intended, because by this time
2231 // GC must already have cleared any refs that need to be cleared,
2232 // and traced those that need to be marked; moreover,
2233 // the marking done here is not going to interfere in any
2234 // way with the marking information used by GC.
2235 NoRefDiscovery no_discovery(ref_processor());
2236
2237 #if defined(COMPILER2) || INCLUDE_JVMCI
2238 DerivedPointerTableDeactivate dpt_deact;
2239 #endif
2240
2241 // Clear any marks from a previous round
2242 verification_mark_bm()->clear_all();
2243 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2244 verify_work_stacks_empty();
2245
2246 GenCollectedHeap* gch = GenCollectedHeap::heap();
2247 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2248 // Update the saved marks which may affect the root scans.
2249 gch->save_marks();
2250
2251 if (CMSRemarkVerifyVariant == 1) {
2252 // In this first variant of verification, we complete
2253 // all marking, then check if the new marks-vector is
2254 // a subset of the CMS marks-vector.
2255 verify_after_remark_work_1();
2256 } else if (CMSRemarkVerifyVariant == 2) {
2257 // In this second variant of verification, we flag an error
2258 // (i.e. an object reachable in the new marks-vector not reachable
2259 // in the CMS marks-vector) immediately, also indicating the
2260 // identify of an object (A) that references the unmarked object (B) --
2261 // presumably, a mutation to A failed to be picked up by preclean/remark?
2262 verify_after_remark_work_2();
2263 } else {
2264 warning("Unrecognized value " UINTX_FORMAT " for CMSRemarkVerifyVariant",
2265 CMSRemarkVerifyVariant);
2266 }
2267 return true;
2268 }
2269
2270 void CMSCollector::verify_after_remark_work_1() {
2271 ResourceMark rm;
2272 HandleMark hm;
2273 GenCollectedHeap* gch = GenCollectedHeap::heap();
2274
2275 // Get a clear set of claim bits for the roots processing to work with.
2276 ClassLoaderDataGraph::clear_claimed_marks();
2277
2278 // Mark from roots one level into CMS
2279 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2280 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2281
2282 {
2283 StrongRootsScope srs(1);
2284
2285 gch->gen_process_roots(&srs,
2286 GenCollectedHeap::OldGen,
2287 true, // young gen as roots
2288 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2289 should_unload_classes(),
2290 ¬Older,
2291 NULL,
2292 NULL);
2293 }
2294
2295 // Now mark from the roots
2296 MarkFromRootsClosure markFromRootsClosure(this, _span,
2297 verification_mark_bm(), verification_mark_stack(),
2298 false /* don't yield */, true /* verifying */);
2299 assert(_restart_addr == NULL, "Expected pre-condition");
2300 verification_mark_bm()->iterate(&markFromRootsClosure);
2301 while (_restart_addr != NULL) {
2302 // Deal with stack overflow: by restarting at the indicated
2303 // address.
2304 HeapWord* ra = _restart_addr;
2305 markFromRootsClosure.reset(ra);
2306 _restart_addr = NULL;
2307 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2308 }
2309 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2310 verify_work_stacks_empty();
2311
2312 // Marking completed -- now verify that each bit marked in
2313 // verification_mark_bm() is also marked in markBitMap(); flag all
2314 // errors by printing corresponding objects.
2315 VerifyMarkedClosure vcl(markBitMap());
2316 verification_mark_bm()->iterate(&vcl);
2317 if (vcl.failed()) {
2318 LogHandle(gc, verify) log;
2319 log.info("Verification failed");
2320 ResourceMark rm;
2321 gch->print_on(log.info_stream());
2322 fatal("CMS: failed marking verification after remark");
2323 }
2324 }
2325
2326 class VerifyKlassOopsKlassClosure : public KlassClosure {
2327 class VerifyKlassOopsClosure : public OopClosure {
2328 CMSBitMap* _bitmap;
2329 public:
2330 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2331 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2332 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2333 } _oop_closure;
2334 public:
2335 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2336 void do_klass(Klass* k) {
2337 k->oops_do(&_oop_closure);
2338 }
2339 };
2340
2341 void CMSCollector::verify_after_remark_work_2() {
2342 ResourceMark rm;
2343 HandleMark hm;
2344 GenCollectedHeap* gch = GenCollectedHeap::heap();
2345
2346 // Get a clear set of claim bits for the roots processing to work with.
2347 ClassLoaderDataGraph::clear_claimed_marks();
2348
2349 // Mark from roots one level into CMS
2350 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2351 markBitMap());
2352 CLDToOopClosure cld_closure(¬Older, true);
2353
2354 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2355
2356 {
2357 StrongRootsScope srs(1);
2358
2359 gch->gen_process_roots(&srs,
2360 GenCollectedHeap::OldGen,
2361 true, // young gen as roots
2362 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2363 should_unload_classes(),
2364 ¬Older,
2365 NULL,
2366 &cld_closure);
2367 }
2368
2369 // Now mark from the roots
2370 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2371 verification_mark_bm(), markBitMap(), verification_mark_stack());
2372 assert(_restart_addr == NULL, "Expected pre-condition");
2373 verification_mark_bm()->iterate(&markFromRootsClosure);
2374 while (_restart_addr != NULL) {
2375 // Deal with stack overflow: by restarting at the indicated
2376 // address.
2377 HeapWord* ra = _restart_addr;
2378 markFromRootsClosure.reset(ra);
2379 _restart_addr = NULL;
2380 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2381 }
2382 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2383 verify_work_stacks_empty();
2384
2385 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2386 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2387
2388 // Marking completed -- now verify that each bit marked in
2389 // verification_mark_bm() is also marked in markBitMap(); flag all
2390 // errors by printing corresponding objects.
2391 VerifyMarkedClosure vcl(markBitMap());
2392 verification_mark_bm()->iterate(&vcl);
2393 assert(!vcl.failed(), "Else verification above should not have succeeded");
2394 }
2395
2396 void ConcurrentMarkSweepGeneration::save_marks() {
2397 // delegate to CMS space
2398 cmsSpace()->save_marks();
2399 for (uint i = 0; i < ParallelGCThreads; i++) {
2400 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2401 }
2402 }
2403
2404 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2405 return cmsSpace()->no_allocs_since_save_marks();
2406 }
2407
2408 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2409 \
2410 void ConcurrentMarkSweepGeneration:: \
2411 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2412 cl->set_generation(this); \
2413 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2414 cl->reset_generation(); \
2415 save_marks(); \
2416 }
2417
2418 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2419
2420 void
2421 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2422 if (freelistLock()->owned_by_self()) {
2423 Generation::oop_iterate(cl);
2424 } else {
2425 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2426 Generation::oop_iterate(cl);
2427 }
2428 }
2429
2430 void
2431 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2432 if (freelistLock()->owned_by_self()) {
2433 Generation::object_iterate(cl);
2434 } else {
2435 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2436 Generation::object_iterate(cl);
2437 }
2438 }
2439
2440 void
2441 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2442 if (freelistLock()->owned_by_self()) {
2443 Generation::safe_object_iterate(cl);
2444 } else {
2445 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2446 Generation::safe_object_iterate(cl);
2447 }
2448 }
2449
2450 void
2451 ConcurrentMarkSweepGeneration::post_compact() {
2452 }
2453
2454 void
2455 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2456 // Fix the linear allocation blocks to look like free blocks.
2457
2458 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2459 // are not called when the heap is verified during universe initialization and
2460 // at vm shutdown.
2461 if (freelistLock()->owned_by_self()) {
2462 cmsSpace()->prepare_for_verify();
2463 } else {
2464 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2465 cmsSpace()->prepare_for_verify();
2466 }
2467 }
2468
2469 void
2470 ConcurrentMarkSweepGeneration::verify() {
2471 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2472 // are not called when the heap is verified during universe initialization and
2473 // at vm shutdown.
2474 if (freelistLock()->owned_by_self()) {
2475 cmsSpace()->verify();
2476 } else {
2477 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2478 cmsSpace()->verify();
2479 }
2480 }
2481
2482 void CMSCollector::verify() {
2483 _cmsGen->verify();
2484 }
2485
2486 #ifndef PRODUCT
2487 bool CMSCollector::overflow_list_is_empty() const {
2488 assert(_num_par_pushes >= 0, "Inconsistency");
2489 if (_overflow_list == NULL) {
2490 assert(_num_par_pushes == 0, "Inconsistency");
2491 }
2492 return _overflow_list == NULL;
2493 }
2494
2495 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2496 // merely consolidate assertion checks that appear to occur together frequently.
2497 void CMSCollector::verify_work_stacks_empty() const {
2498 assert(_markStack.isEmpty(), "Marking stack should be empty");
2499 assert(overflow_list_is_empty(), "Overflow list should be empty");
2500 }
2501
2502 void CMSCollector::verify_overflow_empty() const {
2503 assert(overflow_list_is_empty(), "Overflow list should be empty");
2504 assert(no_preserved_marks(), "No preserved marks");
2505 }
2506 #endif // PRODUCT
2507
2508 // Decide if we want to enable class unloading as part of the
2509 // ensuing concurrent GC cycle. We will collect and
2510 // unload classes if it's the case that:
2511 // (1) an explicit gc request has been made and the flag
2512 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2513 // (2) (a) class unloading is enabled at the command line, and
2514 // (b) old gen is getting really full
2515 // NOTE: Provided there is no change in the state of the heap between
2516 // calls to this method, it should have idempotent results. Moreover,
2517 // its results should be monotonically increasing (i.e. going from 0 to 1,
2518 // but not 1 to 0) between successive calls between which the heap was
2519 // not collected. For the implementation below, it must thus rely on
2520 // the property that concurrent_cycles_since_last_unload()
2521 // will not decrease unless a collection cycle happened and that
2522 // _cmsGen->is_too_full() are
2523 // themselves also monotonic in that sense. See check_monotonicity()
2524 // below.
2525 void CMSCollector::update_should_unload_classes() {
2526 _should_unload_classes = false;
2527 // Condition 1 above
2528 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2529 _should_unload_classes = true;
2530 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2531 // Disjuncts 2.b.(i,ii,iii) above
2532 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2533 CMSClassUnloadingMaxInterval)
2534 || _cmsGen->is_too_full();
2535 }
2536 }
2537
2538 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2539 bool res = should_concurrent_collect();
2540 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2541 return res;
2542 }
2543
2544 void CMSCollector::setup_cms_unloading_and_verification_state() {
2545 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2546 || VerifyBeforeExit;
2547 const int rso = GenCollectedHeap::SO_AllCodeCache;
2548
2549 // We set the proper root for this CMS cycle here.
2550 if (should_unload_classes()) { // Should unload classes this cycle
2551 remove_root_scanning_option(rso); // Shrink the root set appropriately
2552 set_verifying(should_verify); // Set verification state for this cycle
2553 return; // Nothing else needs to be done at this time
2554 }
2555
2556 // Not unloading classes this cycle
2557 assert(!should_unload_classes(), "Inconsistency!");
2558
2559 // If we are not unloading classes then add SO_AllCodeCache to root
2560 // scanning options.
2561 add_root_scanning_option(rso);
2562
2563 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2564 set_verifying(true);
2565 } else if (verifying() && !should_verify) {
2566 // We were verifying, but some verification flags got disabled.
2567 set_verifying(false);
2568 // Exclude symbols, strings and code cache elements from root scanning to
2569 // reduce IM and RM pauses.
2570 remove_root_scanning_option(rso);
2571 }
2572 }
2573
2574
2575 #ifndef PRODUCT
2576 HeapWord* CMSCollector::block_start(const void* p) const {
2577 const HeapWord* addr = (HeapWord*)p;
2578 if (_span.contains(p)) {
2579 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2580 return _cmsGen->cmsSpace()->block_start(p);
2581 }
2582 }
2583 return NULL;
2584 }
2585 #endif
2586
2587 HeapWord*
2588 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2589 bool tlab,
2590 bool parallel) {
2591 CMSSynchronousYieldRequest yr;
2592 assert(!tlab, "Can't deal with TLAB allocation");
2593 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2594 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2595 if (GCExpandToAllocateDelayMillis > 0) {
2596 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2597 }
2598 return have_lock_and_allocate(word_size, tlab);
2599 }
2600
2601 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2602 size_t bytes,
2603 size_t expand_bytes,
2604 CMSExpansionCause::Cause cause)
2605 {
2606
2607 bool success = expand(bytes, expand_bytes);
2608
2609 // remember why we expanded; this information is used
2610 // by shouldConcurrentCollect() when making decisions on whether to start
2611 // a new CMS cycle.
2612 if (success) {
2613 set_expansion_cause(cause);
2614 log_trace(gc)("Expanded CMS gen for %s", CMSExpansionCause::to_string(cause));
2615 }
2616 }
2617
2618 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2619 HeapWord* res = NULL;
2620 MutexLocker x(ParGCRareEvent_lock);
2621 while (true) {
2622 // Expansion by some other thread might make alloc OK now:
2623 res = ps->lab.alloc(word_sz);
2624 if (res != NULL) return res;
2625 // If there's not enough expansion space available, give up.
2626 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2627 return NULL;
2628 }
2629 // Otherwise, we try expansion.
2630 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2631 // Now go around the loop and try alloc again;
2632 // A competing par_promote might beat us to the expansion space,
2633 // so we may go around the loop again if promotion fails again.
2634 if (GCExpandToAllocateDelayMillis > 0) {
2635 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2636 }
2637 }
2638 }
2639
2640
2641 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2642 PromotionInfo* promo) {
2643 MutexLocker x(ParGCRareEvent_lock);
2644 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2645 while (true) {
2646 // Expansion by some other thread might make alloc OK now:
2647 if (promo->ensure_spooling_space()) {
2648 assert(promo->has_spooling_space(),
2649 "Post-condition of successful ensure_spooling_space()");
2650 return true;
2651 }
2652 // If there's not enough expansion space available, give up.
2653 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2654 return false;
2655 }
2656 // Otherwise, we try expansion.
2657 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2658 // Now go around the loop and try alloc again;
2659 // A competing allocation might beat us to the expansion space,
2660 // so we may go around the loop again if allocation fails again.
2661 if (GCExpandToAllocateDelayMillis > 0) {
2662 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2663 }
2664 }
2665 }
2666
2667 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2668 // Only shrink if a compaction was done so that all the free space
2669 // in the generation is in a contiguous block at the end.
2670 if (did_compact()) {
2671 CardGeneration::shrink(bytes);
2672 }
2673 }
2674
2675 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2676 assert_locked_or_safepoint(Heap_lock);
2677 }
2678
2679 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2680 assert_locked_or_safepoint(Heap_lock);
2681 assert_lock_strong(freelistLock());
2682 if (PrintGCDetails && Verbose) {
2683 warning("Shrinking of CMS not yet implemented");
2684 }
2685 return;
2686 }
2687
2688
2689 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2690 // phases.
2691 class CMSPhaseAccounting: public StackObj {
2692 public:
2693 CMSPhaseAccounting(CMSCollector *collector,
2694 const char *phase,
2695 bool print_cr = true);
2696 ~CMSPhaseAccounting();
2697
2698 private:
2699 CMSCollector *_collector;
2700 const char *_phase;
2701 jlong _start_counter;
2702 bool _print_cr;
2703
2704 public:
2705 // Not MT-safe; so do not pass around these StackObj's
2706 // where they may be accessed by other threads.
2707 jlong wallclock_millis() {
2708 return TimeHelper::counter_to_millis(os::elapsed_counter() - _start_counter);
2709 }
2710 };
2711
2712 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2713 const char *phase,
2714 bool print_cr) :
2715 _collector(collector), _phase(phase), _print_cr(print_cr) {
2716
2717 _collector->resetYields();
2718 _collector->resetTimer();
2719 _start_counter = os::elapsed_counter();
2720 _collector->startTimer();
2721 log_info(gc)("Concurrent %s (%.3f)", _phase, TimeHelper::counter_to_seconds(_start_counter));
2722 }
2723
2724 CMSPhaseAccounting::~CMSPhaseAccounting() {
2725 _collector->stopTimer();
2726 jlong end_counter = os::elapsed_counter();
2727 log_debug(gc)("Concurrent active time: %.3fms", _collector->timerValue());
2728 log_info(gc)("Concurrent %s (%.3fs, %.3fs) %.3fms",
2729 _phase,
2730 TimeHelper::counter_to_seconds(_start_counter),
2731 TimeHelper::counter_to_seconds(end_counter),
2732 TimeHelper::counter_to_millis(end_counter - _start_counter));
2733 log_debug(gc, conc, stats)(" (CMS-concurrent-%s yielded %d times)", _phase, _collector->yields());
2734 }
2735
2736 // CMS work
2737
2738 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2739 class CMSParMarkTask : public AbstractGangTask {
2740 protected:
2741 CMSCollector* _collector;
2742 uint _n_workers;
2743 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2744 AbstractGangTask(name),
2745 _collector(collector),
2746 _n_workers(n_workers) {}
2747 // Work method in support of parallel rescan ... of young gen spaces
2748 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2749 ContiguousSpace* space,
2750 HeapWord** chunk_array, size_t chunk_top);
2751 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2752 };
2753
2754 // Parallel initial mark task
2755 class CMSParInitialMarkTask: public CMSParMarkTask {
2756 StrongRootsScope* _strong_roots_scope;
2757 public:
2758 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2759 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2760 _strong_roots_scope(strong_roots_scope) {}
2761 void work(uint worker_id);
2762 };
2763
2764 // Checkpoint the roots into this generation from outside
2765 // this generation. [Note this initial checkpoint need only
2766 // be approximate -- we'll do a catch up phase subsequently.]
2767 void CMSCollector::checkpointRootsInitial() {
2768 assert(_collectorState == InitialMarking, "Wrong collector state");
2769 check_correct_thread_executing();
2770 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2771
2772 save_heap_summary();
2773 report_heap_summary(GCWhen::BeforeGC);
2774
2775 ReferenceProcessor* rp = ref_processor();
2776 assert(_restart_addr == NULL, "Control point invariant");
2777 {
2778 // acquire locks for subsequent manipulations
2779 MutexLockerEx x(bitMapLock(),
2780 Mutex::_no_safepoint_check_flag);
2781 checkpointRootsInitialWork();
2782 // enable ("weak") refs discovery
2783 rp->enable_discovery();
2784 _collectorState = Marking;
2785 }
2786 }
2787
2788 void CMSCollector::checkpointRootsInitialWork() {
2789 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2790 assert(_collectorState == InitialMarking, "just checking");
2791
2792 // Already have locks.
2793 assert_lock_strong(bitMapLock());
2794 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2795
2796 // Setup the verification and class unloading state for this
2797 // CMS collection cycle.
2798 setup_cms_unloading_and_verification_state();
2799
2800 GCTraceTime(Trace, gc) ts("checkpointRootsInitialWork", _gc_timer_cm);
2801
2802 // Reset all the PLAB chunk arrays if necessary.
2803 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2804 reset_survivor_plab_arrays();
2805 }
2806
2807 ResourceMark rm;
2808 HandleMark hm;
2809
2810 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2811 GenCollectedHeap* gch = GenCollectedHeap::heap();
2812
2813 verify_work_stacks_empty();
2814 verify_overflow_empty();
2815
2816 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2817 // Update the saved marks which may affect the root scans.
2818 gch->save_marks();
2819
2820 // weak reference processing has not started yet.
2821 ref_processor()->set_enqueuing_is_done(false);
2822
2823 // Need to remember all newly created CLDs,
2824 // so that we can guarantee that the remark finds them.
2825 ClassLoaderDataGraph::remember_new_clds(true);
2826
2827 // Whenever a CLD is found, it will be claimed before proceeding to mark
2828 // the klasses. The claimed marks need to be cleared before marking starts.
2829 ClassLoaderDataGraph::clear_claimed_marks();
2830
2831 print_eden_and_survivor_chunk_arrays();
2832
2833 {
2834 #if defined(COMPILER2) || INCLUDE_JVMCI
2835 DerivedPointerTableDeactivate dpt_deact;
2836 #endif
2837 if (CMSParallelInitialMarkEnabled) {
2838 // The parallel version.
2839 WorkGang* workers = gch->workers();
2840 assert(workers != NULL, "Need parallel worker threads.");
2841 uint n_workers = workers->active_workers();
2842
2843 StrongRootsScope srs(n_workers);
2844
2845 CMSParInitialMarkTask tsk(this, &srs, n_workers);
2846 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2847 if (n_workers > 1) {
2848 workers->run_task(&tsk);
2849 } else {
2850 tsk.work(0);
2851 }
2852 } else {
2853 // The serial version.
2854 CLDToOopClosure cld_closure(¬Older, true);
2855 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2856
2857 StrongRootsScope srs(1);
2858
2859 gch->gen_process_roots(&srs,
2860 GenCollectedHeap::OldGen,
2861 true, // young gen as roots
2862 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2863 should_unload_classes(),
2864 ¬Older,
2865 NULL,
2866 &cld_closure);
2867 }
2868 }
2869
2870 // Clear mod-union table; it will be dirtied in the prologue of
2871 // CMS generation per each young generation collection.
2872
2873 assert(_modUnionTable.isAllClear(),
2874 "Was cleared in most recent final checkpoint phase"
2875 " or no bits are set in the gc_prologue before the start of the next "
2876 "subsequent marking phase.");
2877
2878 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
2879
2880 // Save the end of the used_region of the constituent generations
2881 // to be used to limit the extent of sweep in each generation.
2882 save_sweep_limits();
2883 verify_overflow_empty();
2884 }
2885
2886 bool CMSCollector::markFromRoots() {
2887 // we might be tempted to assert that:
2888 // assert(!SafepointSynchronize::is_at_safepoint(),
2889 // "inconsistent argument?");
2890 // However that wouldn't be right, because it's possible that
2891 // a safepoint is indeed in progress as a young generation
2892 // stop-the-world GC happens even as we mark in this generation.
2893 assert(_collectorState == Marking, "inconsistent state?");
2894 check_correct_thread_executing();
2895 verify_overflow_empty();
2896
2897 // Weak ref discovery note: We may be discovering weak
2898 // refs in this generation concurrent (but interleaved) with
2899 // weak ref discovery by the young generation collector.
2900
2901 CMSTokenSyncWithLocks ts(true, bitMapLock());
2902 GCTraceCPUTime tcpu;
2903 CMSPhaseAccounting pa(this, "Mark", !PrintGCDetails);
2904 bool res = markFromRootsWork();
2905 if (res) {
2906 _collectorState = Precleaning;
2907 } else { // We failed and a foreground collection wants to take over
2908 assert(_foregroundGCIsActive, "internal state inconsistency");
2909 assert(_restart_addr == NULL, "foreground will restart from scratch");
2910 log_debug(gc, conc)("bailing out to foreground collection");
2911 }
2912 verify_overflow_empty();
2913 return res;
2914 }
2915
2916 bool CMSCollector::markFromRootsWork() {
2917 // iterate over marked bits in bit map, doing a full scan and mark
2918 // from these roots using the following algorithm:
2919 // . if oop is to the right of the current scan pointer,
2920 // mark corresponding bit (we'll process it later)
2921 // . else (oop is to left of current scan pointer)
2922 // push oop on marking stack
2923 // . drain the marking stack
2924
2925 // Note that when we do a marking step we need to hold the
2926 // bit map lock -- recall that direct allocation (by mutators)
2927 // and promotion (by the young generation collector) is also
2928 // marking the bit map. [the so-called allocate live policy.]
2929 // Because the implementation of bit map marking is not
2930 // robust wrt simultaneous marking of bits in the same word,
2931 // we need to make sure that there is no such interference
2932 // between concurrent such updates.
2933
2934 // already have locks
2935 assert_lock_strong(bitMapLock());
2936
2937 verify_work_stacks_empty();
2938 verify_overflow_empty();
2939 bool result = false;
2940 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2941 result = do_marking_mt();
2942 } else {
2943 result = do_marking_st();
2944 }
2945 return result;
2946 }
2947
2948 // Forward decl
2949 class CMSConcMarkingTask;
2950
2951 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
2952 CMSCollector* _collector;
2953 CMSConcMarkingTask* _task;
2954 public:
2955 virtual void yield();
2956
2957 // "n_threads" is the number of threads to be terminated.
2958 // "queue_set" is a set of work queues of other threads.
2959 // "collector" is the CMS collector associated with this task terminator.
2960 // "yield" indicates whether we need the gang as a whole to yield.
2961 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
2962 ParallelTaskTerminator(n_threads, queue_set),
2963 _collector(collector) { }
2964
2965 void set_task(CMSConcMarkingTask* task) {
2966 _task = task;
2967 }
2968 };
2969
2970 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
2971 CMSConcMarkingTask* _task;
2972 public:
2973 bool should_exit_termination();
2974 void set_task(CMSConcMarkingTask* task) {
2975 _task = task;
2976 }
2977 };
2978
2979 // MT Concurrent Marking Task
2980 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
2981 CMSCollector* _collector;
2982 uint _n_workers; // requested/desired # workers
2983 bool _result;
2984 CompactibleFreeListSpace* _cms_space;
2985 char _pad_front[64]; // padding to ...
2986 HeapWord* _global_finger; // ... avoid sharing cache line
2987 char _pad_back[64];
2988 HeapWord* _restart_addr;
2989
2990 // Exposed here for yielding support
2991 Mutex* const _bit_map_lock;
2992
2993 // The per thread work queues, available here for stealing
2994 OopTaskQueueSet* _task_queues;
2995
2996 // Termination (and yielding) support
2997 CMSConcMarkingTerminator _term;
2998 CMSConcMarkingTerminatorTerminator _term_term;
2999
3000 public:
3001 CMSConcMarkingTask(CMSCollector* collector,
3002 CompactibleFreeListSpace* cms_space,
3003 YieldingFlexibleWorkGang* workers,
3004 OopTaskQueueSet* task_queues):
3005 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3006 _collector(collector),
3007 _cms_space(cms_space),
3008 _n_workers(0), _result(true),
3009 _task_queues(task_queues),
3010 _term(_n_workers, task_queues, _collector),
3011 _bit_map_lock(collector->bitMapLock())
3012 {
3013 _requested_size = _n_workers;
3014 _term.set_task(this);
3015 _term_term.set_task(this);
3016 _restart_addr = _global_finger = _cms_space->bottom();
3017 }
3018
3019
3020 OopTaskQueueSet* task_queues() { return _task_queues; }
3021
3022 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3023
3024 HeapWord** global_finger_addr() { return &_global_finger; }
3025
3026 CMSConcMarkingTerminator* terminator() { return &_term; }
3027
3028 virtual void set_for_termination(uint active_workers) {
3029 terminator()->reset_for_reuse(active_workers);
3030 }
3031
3032 void work(uint worker_id);
3033 bool should_yield() {
3034 return ConcurrentMarkSweepThread::should_yield()
3035 && !_collector->foregroundGCIsActive();
3036 }
3037
3038 virtual void coordinator_yield(); // stuff done by coordinator
3039 bool result() { return _result; }
3040
3041 void reset(HeapWord* ra) {
3042 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3043 _restart_addr = _global_finger = ra;
3044 _term.reset_for_reuse();
3045 }
3046
3047 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3048 OopTaskQueue* work_q);
3049
3050 private:
3051 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3052 void do_work_steal(int i);
3053 void bump_global_finger(HeapWord* f);
3054 };
3055
3056 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3057 assert(_task != NULL, "Error");
3058 return _task->yielding();
3059 // Note that we do not need the disjunct || _task->should_yield() above
3060 // because we want terminating threads to yield only if the task
3061 // is already in the midst of yielding, which happens only after at least one
3062 // thread has yielded.
3063 }
3064
3065 void CMSConcMarkingTerminator::yield() {
3066 if (_task->should_yield()) {
3067 _task->yield();
3068 } else {
3069 ParallelTaskTerminator::yield();
3070 }
3071 }
3072
3073 ////////////////////////////////////////////////////////////////
3074 // Concurrent Marking Algorithm Sketch
3075 ////////////////////////////////////////////////////////////////
3076 // Until all tasks exhausted (both spaces):
3077 // -- claim next available chunk
3078 // -- bump global finger via CAS
3079 // -- find first object that starts in this chunk
3080 // and start scanning bitmap from that position
3081 // -- scan marked objects for oops
3082 // -- CAS-mark target, and if successful:
3083 // . if target oop is above global finger (volatile read)
3084 // nothing to do
3085 // . if target oop is in chunk and above local finger
3086 // then nothing to do
3087 // . else push on work-queue
3088 // -- Deal with possible overflow issues:
3089 // . local work-queue overflow causes stuff to be pushed on
3090 // global (common) overflow queue
3091 // . always first empty local work queue
3092 // . then get a batch of oops from global work queue if any
3093 // . then do work stealing
3094 // -- When all tasks claimed (both spaces)
3095 // and local work queue empty,
3096 // then in a loop do:
3097 // . check global overflow stack; steal a batch of oops and trace
3098 // . try to steal from other threads oif GOS is empty
3099 // . if neither is available, offer termination
3100 // -- Terminate and return result
3101 //
3102 void CMSConcMarkingTask::work(uint worker_id) {
3103 elapsedTimer _timer;
3104 ResourceMark rm;
3105 HandleMark hm;
3106
3107 DEBUG_ONLY(_collector->verify_overflow_empty();)
3108
3109 // Before we begin work, our work queue should be empty
3110 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3111 // Scan the bitmap covering _cms_space, tracing through grey objects.
3112 _timer.start();
3113 do_scan_and_mark(worker_id, _cms_space);
3114 _timer.stop();
3115 log_debug(gc, conc, stats)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3116
3117 // ... do work stealing
3118 _timer.reset();
3119 _timer.start();
3120 do_work_steal(worker_id);
3121 _timer.stop();
3122 log_debug(gc, conc, stats)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3123 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3124 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3125 // Note that under the current task protocol, the
3126 // following assertion is true even of the spaces
3127 // expanded since the completion of the concurrent
3128 // marking. XXX This will likely change under a strict
3129 // ABORT semantics.
3130 // After perm removal the comparison was changed to
3131 // greater than or equal to from strictly greater than.
3132 // Before perm removal the highest address sweep would
3133 // have been at the end of perm gen but now is at the
3134 // end of the tenured gen.
3135 assert(_global_finger >= _cms_space->end(),
3136 "All tasks have been completed");
3137 DEBUG_ONLY(_collector->verify_overflow_empty();)
3138 }
3139
3140 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3141 HeapWord* read = _global_finger;
3142 HeapWord* cur = read;
3143 while (f > read) {
3144 cur = read;
3145 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3146 if (cur == read) {
3147 // our cas succeeded
3148 assert(_global_finger >= f, "protocol consistency");
3149 break;
3150 }
3151 }
3152 }
3153
3154 // This is really inefficient, and should be redone by
3155 // using (not yet available) block-read and -write interfaces to the
3156 // stack and the work_queue. XXX FIX ME !!!
3157 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3158 OopTaskQueue* work_q) {
3159 // Fast lock-free check
3160 if (ovflw_stk->length() == 0) {
3161 return false;
3162 }
3163 assert(work_q->size() == 0, "Shouldn't steal");
3164 MutexLockerEx ml(ovflw_stk->par_lock(),
3165 Mutex::_no_safepoint_check_flag);
3166 // Grab up to 1/4 the size of the work queue
3167 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3168 (size_t)ParGCDesiredObjsFromOverflowList);
3169 num = MIN2(num, ovflw_stk->length());
3170 for (int i = (int) num; i > 0; i--) {
3171 oop cur = ovflw_stk->pop();
3172 assert(cur != NULL, "Counted wrong?");
3173 work_q->push(cur);
3174 }
3175 return num > 0;
3176 }
3177
3178 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3179 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3180 int n_tasks = pst->n_tasks();
3181 // We allow that there may be no tasks to do here because
3182 // we are restarting after a stack overflow.
3183 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3184 uint nth_task = 0;
3185
3186 HeapWord* aligned_start = sp->bottom();
3187 if (sp->used_region().contains(_restart_addr)) {
3188 // Align down to a card boundary for the start of 0th task
3189 // for this space.
3190 aligned_start =
3191 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3192 CardTableModRefBS::card_size);
3193 }
3194
3195 size_t chunk_size = sp->marking_task_size();
3196 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3197 // Having claimed the nth task in this space,
3198 // compute the chunk that it corresponds to:
3199 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3200 aligned_start + (nth_task+1)*chunk_size);
3201 // Try and bump the global finger via a CAS;
3202 // note that we need to do the global finger bump
3203 // _before_ taking the intersection below, because
3204 // the task corresponding to that region will be
3205 // deemed done even if the used_region() expands
3206 // because of allocation -- as it almost certainly will
3207 // during start-up while the threads yield in the
3208 // closure below.
3209 HeapWord* finger = span.end();
3210 bump_global_finger(finger); // atomically
3211 // There are null tasks here corresponding to chunks
3212 // beyond the "top" address of the space.
3213 span = span.intersection(sp->used_region());
3214 if (!span.is_empty()) { // Non-null task
3215 HeapWord* prev_obj;
3216 assert(!span.contains(_restart_addr) || nth_task == 0,
3217 "Inconsistency");
3218 if (nth_task == 0) {
3219 // For the 0th task, we'll not need to compute a block_start.
3220 if (span.contains(_restart_addr)) {
3221 // In the case of a restart because of stack overflow,
3222 // we might additionally skip a chunk prefix.
3223 prev_obj = _restart_addr;
3224 } else {
3225 prev_obj = span.start();
3226 }
3227 } else {
3228 // We want to skip the first object because
3229 // the protocol is to scan any object in its entirety
3230 // that _starts_ in this span; a fortiori, any
3231 // object starting in an earlier span is scanned
3232 // as part of an earlier claimed task.
3233 // Below we use the "careful" version of block_start
3234 // so we do not try to navigate uninitialized objects.
3235 prev_obj = sp->block_start_careful(span.start());
3236 // Below we use a variant of block_size that uses the
3237 // Printezis bits to avoid waiting for allocated
3238 // objects to become initialized/parsable.
3239 while (prev_obj < span.start()) {
3240 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3241 if (sz > 0) {
3242 prev_obj += sz;
3243 } else {
3244 // In this case we may end up doing a bit of redundant
3245 // scanning, but that appears unavoidable, short of
3246 // locking the free list locks; see bug 6324141.
3247 break;
3248 }
3249 }
3250 }
3251 if (prev_obj < span.end()) {
3252 MemRegion my_span = MemRegion(prev_obj, span.end());
3253 // Do the marking work within a non-empty span --
3254 // the last argument to the constructor indicates whether the
3255 // iteration should be incremental with periodic yields.
3256 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3257 &_collector->_markBitMap,
3258 work_queue(i),
3259 &_collector->_markStack);
3260 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3261 } // else nothing to do for this task
3262 } // else nothing to do for this task
3263 }
3264 // We'd be tempted to assert here that since there are no
3265 // more tasks left to claim in this space, the global_finger
3266 // must exceed space->top() and a fortiori space->end(). However,
3267 // that would not quite be correct because the bumping of
3268 // global_finger occurs strictly after the claiming of a task,
3269 // so by the time we reach here the global finger may not yet
3270 // have been bumped up by the thread that claimed the last
3271 // task.
3272 pst->all_tasks_completed();
3273 }
3274
3275 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3276 private:
3277 CMSCollector* _collector;
3278 CMSConcMarkingTask* _task;
3279 MemRegion _span;
3280 CMSBitMap* _bit_map;
3281 CMSMarkStack* _overflow_stack;
3282 OopTaskQueue* _work_queue;
3283 protected:
3284 DO_OOP_WORK_DEFN
3285 public:
3286 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3287 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3288 MetadataAwareOopClosure(collector->ref_processor()),
3289 _collector(collector),
3290 _task(task),
3291 _span(collector->_span),
3292 _work_queue(work_queue),
3293 _bit_map(bit_map),
3294 _overflow_stack(overflow_stack)
3295 { }
3296 virtual void do_oop(oop* p);
3297 virtual void do_oop(narrowOop* p);
3298
3299 void trim_queue(size_t max);
3300 void handle_stack_overflow(HeapWord* lost);
3301 void do_yield_check() {
3302 if (_task->should_yield()) {
3303 _task->yield();
3304 }
3305 }
3306 };
3307
3308 // Grey object scanning during work stealing phase --
3309 // the salient assumption here is that any references
3310 // that are in these stolen objects being scanned must
3311 // already have been initialized (else they would not have
3312 // been published), so we do not need to check for
3313 // uninitialized objects before pushing here.
3314 void Par_ConcMarkingClosure::do_oop(oop obj) {
3315 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3316 HeapWord* addr = (HeapWord*)obj;
3317 // Check if oop points into the CMS generation
3318 // and is not marked
3319 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3320 // a white object ...
3321 // If we manage to "claim" the object, by being the
3322 // first thread to mark it, then we push it on our
3323 // marking stack
3324 if (_bit_map->par_mark(addr)) { // ... now grey
3325 // push on work queue (grey set)
3326 bool simulate_overflow = false;
3327 NOT_PRODUCT(
3328 if (CMSMarkStackOverflowALot &&
3329 _collector->simulate_overflow()) {
3330 // simulate a stack overflow
3331 simulate_overflow = true;
3332 }
3333 )
3334 if (simulate_overflow ||
3335 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3336 // stack overflow
3337 log_debug(gc, conc, stats)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3338 // We cannot assert that the overflow stack is full because
3339 // it may have been emptied since.
3340 assert(simulate_overflow ||
3341 _work_queue->size() == _work_queue->max_elems(),
3342 "Else push should have succeeded");
3343 handle_stack_overflow(addr);
3344 }
3345 } // Else, some other thread got there first
3346 do_yield_check();
3347 }
3348 }
3349
3350 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3351 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3352
3353 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3354 while (_work_queue->size() > max) {
3355 oop new_oop;
3356 if (_work_queue->pop_local(new_oop)) {
3357 assert(new_oop->is_oop(), "Should be an oop");
3358 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3359 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3360 new_oop->oop_iterate(this); // do_oop() above
3361 do_yield_check();
3362 }
3363 }
3364 }
3365
3366 // Upon stack overflow, we discard (part of) the stack,
3367 // remembering the least address amongst those discarded
3368 // in CMSCollector's _restart_address.
3369 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3370 // We need to do this under a mutex to prevent other
3371 // workers from interfering with the work done below.
3372 MutexLockerEx ml(_overflow_stack->par_lock(),
3373 Mutex::_no_safepoint_check_flag);
3374 // Remember the least grey address discarded
3375 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3376 _collector->lower_restart_addr(ra);
3377 _overflow_stack->reset(); // discard stack contents
3378 _overflow_stack->expand(); // expand the stack if possible
3379 }
3380
3381
3382 void CMSConcMarkingTask::do_work_steal(int i) {
3383 OopTaskQueue* work_q = work_queue(i);
3384 oop obj_to_scan;
3385 CMSBitMap* bm = &(_collector->_markBitMap);
3386 CMSMarkStack* ovflw = &(_collector->_markStack);
3387 int* seed = _collector->hash_seed(i);
3388 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3389 while (true) {
3390 cl.trim_queue(0);
3391 assert(work_q->size() == 0, "Should have been emptied above");
3392 if (get_work_from_overflow_stack(ovflw, work_q)) {
3393 // Can't assert below because the work obtained from the
3394 // overflow stack may already have been stolen from us.
3395 // assert(work_q->size() > 0, "Work from overflow stack");
3396 continue;
3397 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3398 assert(obj_to_scan->is_oop(), "Should be an oop");
3399 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3400 obj_to_scan->oop_iterate(&cl);
3401 } else if (terminator()->offer_termination(&_term_term)) {
3402 assert(work_q->size() == 0, "Impossible!");
3403 break;
3404 } else if (yielding() || should_yield()) {
3405 yield();
3406 }
3407 }
3408 }
3409
3410 // This is run by the CMS (coordinator) thread.
3411 void CMSConcMarkingTask::coordinator_yield() {
3412 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3413 "CMS thread should hold CMS token");
3414 // First give up the locks, then yield, then re-lock
3415 // We should probably use a constructor/destructor idiom to
3416 // do this unlock/lock or modify the MutexUnlocker class to
3417 // serve our purpose. XXX
3418 assert_lock_strong(_bit_map_lock);
3419 _bit_map_lock->unlock();
3420 ConcurrentMarkSweepThread::desynchronize(true);
3421 _collector->stopTimer();
3422 _collector->incrementYields();
3423
3424 // It is possible for whichever thread initiated the yield request
3425 // not to get a chance to wake up and take the bitmap lock between
3426 // this thread releasing it and reacquiring it. So, while the
3427 // should_yield() flag is on, let's sleep for a bit to give the
3428 // other thread a chance to wake up. The limit imposed on the number
3429 // of iterations is defensive, to avoid any unforseen circumstances
3430 // putting us into an infinite loop. Since it's always been this
3431 // (coordinator_yield()) method that was observed to cause the
3432 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3433 // which is by default non-zero. For the other seven methods that
3434 // also perform the yield operation, as are using a different
3435 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3436 // can enable the sleeping for those methods too, if necessary.
3437 // See 6442774.
3438 //
3439 // We really need to reconsider the synchronization between the GC
3440 // thread and the yield-requesting threads in the future and we
3441 // should really use wait/notify, which is the recommended
3442 // way of doing this type of interaction. Additionally, we should
3443 // consolidate the eight methods that do the yield operation and they
3444 // are almost identical into one for better maintainability and
3445 // readability. See 6445193.
3446 //
3447 // Tony 2006.06.29
3448 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3449 ConcurrentMarkSweepThread::should_yield() &&
3450 !CMSCollector::foregroundGCIsActive(); ++i) {
3451 os::sleep(Thread::current(), 1, false);
3452 }
3453
3454 ConcurrentMarkSweepThread::synchronize(true);
3455 _bit_map_lock->lock_without_safepoint_check();
3456 _collector->startTimer();
3457 }
3458
3459 bool CMSCollector::do_marking_mt() {
3460 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3461 uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3462 conc_workers()->active_workers(),
3463 Threads::number_of_non_daemon_threads());
3464 conc_workers()->set_active_workers(num_workers);
3465
3466 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3467
3468 CMSConcMarkingTask tsk(this,
3469 cms_space,
3470 conc_workers(),
3471 task_queues());
3472
3473 // Since the actual number of workers we get may be different
3474 // from the number we requested above, do we need to do anything different
3475 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3476 // class?? XXX
3477 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3478
3479 // Refs discovery is already non-atomic.
3480 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3481 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3482 conc_workers()->start_task(&tsk);
3483 while (tsk.yielded()) {
3484 tsk.coordinator_yield();
3485 conc_workers()->continue_task(&tsk);
3486 }
3487 // If the task was aborted, _restart_addr will be non-NULL
3488 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3489 while (_restart_addr != NULL) {
3490 // XXX For now we do not make use of ABORTED state and have not
3491 // yet implemented the right abort semantics (even in the original
3492 // single-threaded CMS case). That needs some more investigation
3493 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3494 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3495 // If _restart_addr is non-NULL, a marking stack overflow
3496 // occurred; we need to do a fresh marking iteration from the
3497 // indicated restart address.
3498 if (_foregroundGCIsActive) {
3499 // We may be running into repeated stack overflows, having
3500 // reached the limit of the stack size, while making very
3501 // slow forward progress. It may be best to bail out and
3502 // let the foreground collector do its job.
3503 // Clear _restart_addr, so that foreground GC
3504 // works from scratch. This avoids the headache of
3505 // a "rescan" which would otherwise be needed because
3506 // of the dirty mod union table & card table.
3507 _restart_addr = NULL;
3508 return false;
3509 }
3510 // Adjust the task to restart from _restart_addr
3511 tsk.reset(_restart_addr);
3512 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3513 _restart_addr);
3514 _restart_addr = NULL;
3515 // Get the workers going again
3516 conc_workers()->start_task(&tsk);
3517 while (tsk.yielded()) {
3518 tsk.coordinator_yield();
3519 conc_workers()->continue_task(&tsk);
3520 }
3521 }
3522 assert(tsk.completed(), "Inconsistency");
3523 assert(tsk.result() == true, "Inconsistency");
3524 return true;
3525 }
3526
3527 bool CMSCollector::do_marking_st() {
3528 ResourceMark rm;
3529 HandleMark hm;
3530
3531 // Temporarily make refs discovery single threaded (non-MT)
3532 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3533 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3534 &_markStack, CMSYield);
3535 // the last argument to iterate indicates whether the iteration
3536 // should be incremental with periodic yields.
3537 _markBitMap.iterate(&markFromRootsClosure);
3538 // If _restart_addr is non-NULL, a marking stack overflow
3539 // occurred; we need to do a fresh iteration from the
3540 // indicated restart address.
3541 while (_restart_addr != NULL) {
3542 if (_foregroundGCIsActive) {
3543 // We may be running into repeated stack overflows, having
3544 // reached the limit of the stack size, while making very
3545 // slow forward progress. It may be best to bail out and
3546 // let the foreground collector do its job.
3547 // Clear _restart_addr, so that foreground GC
3548 // works from scratch. This avoids the headache of
3549 // a "rescan" which would otherwise be needed because
3550 // of the dirty mod union table & card table.
3551 _restart_addr = NULL;
3552 return false; // indicating failure to complete marking
3553 }
3554 // Deal with stack overflow:
3555 // we restart marking from _restart_addr
3556 HeapWord* ra = _restart_addr;
3557 markFromRootsClosure.reset(ra);
3558 _restart_addr = NULL;
3559 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3560 }
3561 return true;
3562 }
3563
3564 void CMSCollector::preclean() {
3565 check_correct_thread_executing();
3566 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3567 verify_work_stacks_empty();
3568 verify_overflow_empty();
3569 _abort_preclean = false;
3570 if (CMSPrecleaningEnabled) {
3571 if (!CMSEdenChunksRecordAlways) {
3572 _eden_chunk_index = 0;
3573 }
3574 size_t used = get_eden_used();
3575 size_t capacity = get_eden_capacity();
3576 // Don't start sampling unless we will get sufficiently
3577 // many samples.
3578 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3579 * CMSScheduleRemarkEdenPenetration)) {
3580 _start_sampling = true;
3581 } else {
3582 _start_sampling = false;
3583 }
3584 GCTraceCPUTime tcpu;
3585 CMSPhaseAccounting pa(this, "Preclean", !PrintGCDetails);
3586 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3587 }
3588 CMSTokenSync x(true); // is cms thread
3589 if (CMSPrecleaningEnabled) {
3590 sample_eden();
3591 _collectorState = AbortablePreclean;
3592 } else {
3593 _collectorState = FinalMarking;
3594 }
3595 verify_work_stacks_empty();
3596 verify_overflow_empty();
3597 }
3598
3599 // Try and schedule the remark such that young gen
3600 // occupancy is CMSScheduleRemarkEdenPenetration %.
3601 void CMSCollector::abortable_preclean() {
3602 check_correct_thread_executing();
3603 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3604 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3605
3606 // If Eden's current occupancy is below this threshold,
3607 // immediately schedule the remark; else preclean
3608 // past the next scavenge in an effort to
3609 // schedule the pause as described above. By choosing
3610 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3611 // we will never do an actual abortable preclean cycle.
3612 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3613 GCTraceCPUTime tcpu;
3614 CMSPhaseAccounting pa(this, "Abortable Preclean", !PrintGCDetails);
3615 // We need more smarts in the abortable preclean
3616 // loop below to deal with cases where allocation
3617 // in young gen is very very slow, and our precleaning
3618 // is running a losing race against a horde of
3619 // mutators intent on flooding us with CMS updates
3620 // (dirty cards).
3621 // One, admittedly dumb, strategy is to give up
3622 // after a certain number of abortable precleaning loops
3623 // or after a certain maximum time. We want to make
3624 // this smarter in the next iteration.
3625 // XXX FIX ME!!! YSR
3626 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3627 while (!(should_abort_preclean() ||
3628 ConcurrentMarkSweepThread::should_terminate())) {
3629 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3630 cumworkdone += workdone;
3631 loops++;
3632 // Voluntarily terminate abortable preclean phase if we have
3633 // been at it for too long.
3634 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3635 loops >= CMSMaxAbortablePrecleanLoops) {
3636 log_debug(gc, conc)(" CMS: abort preclean due to loops ");
3637 break;
3638 }
3639 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3640 log_debug(gc, conc)(" CMS: abort preclean due to time ");
3641 break;
3642 }
3643 // If we are doing little work each iteration, we should
3644 // take a short break.
3645 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3646 // Sleep for some time, waiting for work to accumulate
3647 stopTimer();
3648 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3649 startTimer();
3650 waited++;
3651 }
3652 }
3653 log_debug(gc, conc, stats)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3654 loops, waited, cumworkdone);
3655 }
3656 CMSTokenSync x(true); // is cms thread
3657 if (_collectorState != Idling) {
3658 assert(_collectorState == AbortablePreclean,
3659 "Spontaneous state transition?");
3660 _collectorState = FinalMarking;
3661 } // Else, a foreground collection completed this CMS cycle.
3662 return;
3663 }
3664
3665 // Respond to an Eden sampling opportunity
3666 void CMSCollector::sample_eden() {
3667 // Make sure a young gc cannot sneak in between our
3668 // reading and recording of a sample.
3669 assert(Thread::current()->is_ConcurrentGC_thread(),
3670 "Only the cms thread may collect Eden samples");
3671 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3672 "Should collect samples while holding CMS token");
3673 if (!_start_sampling) {
3674 return;
3675 }
3676 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3677 // is populated by the young generation.
3678 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3679 if (_eden_chunk_index < _eden_chunk_capacity) {
3680 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3681 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3682 "Unexpected state of Eden");
3683 // We'd like to check that what we just sampled is an oop-start address;
3684 // however, we cannot do that here since the object may not yet have been
3685 // initialized. So we'll instead do the check when we _use_ this sample
3686 // later.
3687 if (_eden_chunk_index == 0 ||
3688 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3689 _eden_chunk_array[_eden_chunk_index-1])
3690 >= CMSSamplingGrain)) {
3691 _eden_chunk_index++; // commit sample
3692 }
3693 }
3694 }
3695 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3696 size_t used = get_eden_used();
3697 size_t capacity = get_eden_capacity();
3698 assert(used <= capacity, "Unexpected state of Eden");
3699 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3700 _abort_preclean = true;
3701 }
3702 }
3703 }
3704
3705
3706 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3707 assert(_collectorState == Precleaning ||
3708 _collectorState == AbortablePreclean, "incorrect state");
3709 ResourceMark rm;
3710 HandleMark hm;
3711
3712 // Precleaning is currently not MT but the reference processor
3713 // may be set for MT. Disable it temporarily here.
3714 ReferenceProcessor* rp = ref_processor();
3715 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3716
3717 // Do one pass of scrubbing the discovered reference lists
3718 // to remove any reference objects with strongly-reachable
3719 // referents.
3720 if (clean_refs) {
3721 CMSPrecleanRefsYieldClosure yield_cl(this);
3722 assert(rp->span().equals(_span), "Spans should be equal");
3723 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3724 &_markStack, true /* preclean */);
3725 CMSDrainMarkingStackClosure complete_trace(this,
3726 _span, &_markBitMap, &_markStack,
3727 &keep_alive, true /* preclean */);
3728
3729 // We don't want this step to interfere with a young
3730 // collection because we don't want to take CPU
3731 // or memory bandwidth away from the young GC threads
3732 // (which may be as many as there are CPUs).
3733 // Note that we don't need to protect ourselves from
3734 // interference with mutators because they can't
3735 // manipulate the discovered reference lists nor affect
3736 // the computed reachability of the referents, the
3737 // only properties manipulated by the precleaning
3738 // of these reference lists.
3739 stopTimer();
3740 CMSTokenSyncWithLocks x(true /* is cms thread */,
3741 bitMapLock());
3742 startTimer();
3743 sample_eden();
3744
3745 // The following will yield to allow foreground
3746 // collection to proceed promptly. XXX YSR:
3747 // The code in this method may need further
3748 // tweaking for better performance and some restructuring
3749 // for cleaner interfaces.
3750 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3751 rp->preclean_discovered_references(
3752 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3753 gc_timer);
3754 }
3755
3756 if (clean_survivor) { // preclean the active survivor space(s)
3757 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3758 &_markBitMap, &_modUnionTable,
3759 &_markStack, true /* precleaning phase */);
3760 stopTimer();
3761 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3762 bitMapLock());
3763 startTimer();
3764 unsigned int before_count =
3765 GenCollectedHeap::heap()->total_collections();
3766 SurvivorSpacePrecleanClosure
3767 sss_cl(this, _span, &_markBitMap, &_markStack,
3768 &pam_cl, before_count, CMSYield);
3769 _young_gen->from()->object_iterate_careful(&sss_cl);
3770 _young_gen->to()->object_iterate_careful(&sss_cl);
3771 }
3772 MarkRefsIntoAndScanClosure
3773 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3774 &_markStack, this, CMSYield,
3775 true /* precleaning phase */);
3776 // CAUTION: The following closure has persistent state that may need to
3777 // be reset upon a decrease in the sequence of addresses it
3778 // processes.
3779 ScanMarkedObjectsAgainCarefullyClosure
3780 smoac_cl(this, _span,
3781 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3782
3783 // Preclean dirty cards in ModUnionTable and CardTable using
3784 // appropriate convergence criterion;
3785 // repeat CMSPrecleanIter times unless we find that
3786 // we are losing.
3787 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3788 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3789 "Bad convergence multiplier");
3790 assert(CMSPrecleanThreshold >= 100,
3791 "Unreasonably low CMSPrecleanThreshold");
3792
3793 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3794 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3795 numIter < CMSPrecleanIter;
3796 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3797 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3798 log_trace(gc, conc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3799 // Either there are very few dirty cards, so re-mark
3800 // pause will be small anyway, or our pre-cleaning isn't
3801 // that much faster than the rate at which cards are being
3802 // dirtied, so we might as well stop and re-mark since
3803 // precleaning won't improve our re-mark time by much.
3804 if (curNumCards <= CMSPrecleanThreshold ||
3805 (numIter > 0 &&
3806 (curNumCards * CMSPrecleanDenominator >
3807 lastNumCards * CMSPrecleanNumerator))) {
3808 numIter++;
3809 cumNumCards += curNumCards;
3810 break;
3811 }
3812 }
3813
3814 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
3815
3816 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3817 cumNumCards += curNumCards;
3818 log_trace(gc, conc, stats)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3819 curNumCards, cumNumCards, numIter);
3820 return cumNumCards; // as a measure of useful work done
3821 }
3822
3823 // PRECLEANING NOTES:
3824 // Precleaning involves:
3825 // . reading the bits of the modUnionTable and clearing the set bits.
3826 // . For the cards corresponding to the set bits, we scan the
3827 // objects on those cards. This means we need the free_list_lock
3828 // so that we can safely iterate over the CMS space when scanning
3829 // for oops.
3830 // . When we scan the objects, we'll be both reading and setting
3831 // marks in the marking bit map, so we'll need the marking bit map.
3832 // . For protecting _collector_state transitions, we take the CGC_lock.
3833 // Note that any races in the reading of of card table entries by the
3834 // CMS thread on the one hand and the clearing of those entries by the
3835 // VM thread or the setting of those entries by the mutator threads on the
3836 // other are quite benign. However, for efficiency it makes sense to keep
3837 // the VM thread from racing with the CMS thread while the latter is
3838 // dirty card info to the modUnionTable. We therefore also use the
3839 // CGC_lock to protect the reading of the card table and the mod union
3840 // table by the CM thread.
3841 // . We run concurrently with mutator updates, so scanning
3842 // needs to be done carefully -- we should not try to scan
3843 // potentially uninitialized objects.
3844 //
3845 // Locking strategy: While holding the CGC_lock, we scan over and
3846 // reset a maximal dirty range of the mod union / card tables, then lock
3847 // the free_list_lock and bitmap lock to do a full marking, then
3848 // release these locks; and repeat the cycle. This allows for a
3849 // certain amount of fairness in the sharing of these locks between
3850 // the CMS collector on the one hand, and the VM thread and the
3851 // mutators on the other.
3852
3853 // NOTE: preclean_mod_union_table() and preclean_card_table()
3854 // further below are largely identical; if you need to modify
3855 // one of these methods, please check the other method too.
3856
3857 size_t CMSCollector::preclean_mod_union_table(
3858 ConcurrentMarkSweepGeneration* old_gen,
3859 ScanMarkedObjectsAgainCarefullyClosure* cl) {
3860 verify_work_stacks_empty();
3861 verify_overflow_empty();
3862
3863 // strategy: starting with the first card, accumulate contiguous
3864 // ranges of dirty cards; clear these cards, then scan the region
3865 // covered by these cards.
3866
3867 // Since all of the MUT is committed ahead, we can just use
3868 // that, in case the generations expand while we are precleaning.
3869 // It might also be fine to just use the committed part of the
3870 // generation, but we might potentially miss cards when the
3871 // generation is rapidly expanding while we are in the midst
3872 // of precleaning.
3873 HeapWord* startAddr = old_gen->reserved().start();
3874 HeapWord* endAddr = old_gen->reserved().end();
3875
3876 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
3877
3878 size_t numDirtyCards, cumNumDirtyCards;
3879 HeapWord *nextAddr, *lastAddr;
3880 for (cumNumDirtyCards = numDirtyCards = 0,
3881 nextAddr = lastAddr = startAddr;
3882 nextAddr < endAddr;
3883 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3884
3885 ResourceMark rm;
3886 HandleMark hm;
3887
3888 MemRegion dirtyRegion;
3889 {
3890 stopTimer();
3891 // Potential yield point
3892 CMSTokenSync ts(true);
3893 startTimer();
3894 sample_eden();
3895 // Get dirty region starting at nextOffset (inclusive),
3896 // simultaneously clearing it.
3897 dirtyRegion =
3898 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3899 assert(dirtyRegion.start() >= nextAddr,
3900 "returned region inconsistent?");
3901 }
3902 // Remember where the next search should begin.
3903 // The returned region (if non-empty) is a right open interval,
3904 // so lastOffset is obtained from the right end of that
3905 // interval.
3906 lastAddr = dirtyRegion.end();
3907 // Should do something more transparent and less hacky XXX
3908 numDirtyCards =
3909 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
3910
3911 // We'll scan the cards in the dirty region (with periodic
3912 // yields for foreground GC as needed).
3913 if (!dirtyRegion.is_empty()) {
3914 assert(numDirtyCards > 0, "consistency check");
3915 HeapWord* stop_point = NULL;
3916 stopTimer();
3917 // Potential yield point
3918 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
3919 bitMapLock());
3920 startTimer();
3921 {
3922 verify_work_stacks_empty();
3923 verify_overflow_empty();
3924 sample_eden();
3925 stop_point =
3926 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
3927 }
3928 if (stop_point != NULL) {
3929 // The careful iteration stopped early either because it found an
3930 // uninitialized object, or because we were in the midst of an
3931 // "abortable preclean", which should now be aborted. Redirty
3932 // the bits corresponding to the partially-scanned or unscanned
3933 // cards. We'll either restart at the next block boundary or
3934 // abort the preclean.
3935 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
3936 "Should only be AbortablePreclean.");
3937 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
3938 if (should_abort_preclean()) {
3939 break; // out of preclean loop
3940 } else {
3941 // Compute the next address at which preclean should pick up;
3942 // might need bitMapLock in order to read P-bits.
3943 lastAddr = next_card_start_after_block(stop_point);
3944 }
3945 }
3946 } else {
3947 assert(lastAddr == endAddr, "consistency check");
3948 assert(numDirtyCards == 0, "consistency check");
3949 break;
3950 }
3951 }
3952 verify_work_stacks_empty();
3953 verify_overflow_empty();
3954 return cumNumDirtyCards;
3955 }
3956
3957 // NOTE: preclean_mod_union_table() above and preclean_card_table()
3958 // below are largely identical; if you need to modify
3959 // one of these methods, please check the other method too.
3960
3961 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
3962 ScanMarkedObjectsAgainCarefullyClosure* cl) {
3963 // strategy: it's similar to precleamModUnionTable above, in that
3964 // we accumulate contiguous ranges of dirty cards, mark these cards
3965 // precleaned, then scan the region covered by these cards.
3966 HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high());
3967 HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
3968
3969 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
3970
3971 size_t numDirtyCards, cumNumDirtyCards;
3972 HeapWord *lastAddr, *nextAddr;
3973
3974 for (cumNumDirtyCards = numDirtyCards = 0,
3975 nextAddr = lastAddr = startAddr;
3976 nextAddr < endAddr;
3977 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3978
3979 ResourceMark rm;
3980 HandleMark hm;
3981
3982 MemRegion dirtyRegion;
3983 {
3984 // See comments in "Precleaning notes" above on why we
3985 // do this locking. XXX Could the locking overheads be
3986 // too high when dirty cards are sparse? [I don't think so.]
3987 stopTimer();
3988 CMSTokenSync x(true); // is cms thread
3989 startTimer();
3990 sample_eden();
3991 // Get and clear dirty region from card table
3992 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
3993 MemRegion(nextAddr, endAddr),
3994 true,
3995 CardTableModRefBS::precleaned_card_val());
3996
3997 assert(dirtyRegion.start() >= nextAddr,
3998 "returned region inconsistent?");
3999 }
4000 lastAddr = dirtyRegion.end();
4001 numDirtyCards =
4002 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4003
4004 if (!dirtyRegion.is_empty()) {
4005 stopTimer();
4006 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4007 startTimer();
4008 sample_eden();
4009 verify_work_stacks_empty();
4010 verify_overflow_empty();
4011 HeapWord* stop_point =
4012 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4013 if (stop_point != NULL) {
4014 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4015 "Should only be AbortablePreclean.");
4016 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4017 if (should_abort_preclean()) {
4018 break; // out of preclean loop
4019 } else {
4020 // Compute the next address at which preclean should pick up.
4021 lastAddr = next_card_start_after_block(stop_point);
4022 }
4023 }
4024 } else {
4025 break;
4026 }
4027 }
4028 verify_work_stacks_empty();
4029 verify_overflow_empty();
4030 return cumNumDirtyCards;
4031 }
4032
4033 class PrecleanKlassClosure : public KlassClosure {
4034 KlassToOopClosure _cm_klass_closure;
4035 public:
4036 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4037 void do_klass(Klass* k) {
4038 if (k->has_accumulated_modified_oops()) {
4039 k->clear_accumulated_modified_oops();
4040
4041 _cm_klass_closure.do_klass(k);
4042 }
4043 }
4044 };
4045
4046 // The freelist lock is needed to prevent asserts, is it really needed?
4047 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4048
4049 cl->set_freelistLock(freelistLock);
4050
4051 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4052
4053 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4054 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4055 PrecleanKlassClosure preclean_klass_closure(cl);
4056 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4057
4058 verify_work_stacks_empty();
4059 verify_overflow_empty();
4060 }
4061
4062 void CMSCollector::checkpointRootsFinal() {
4063 assert(_collectorState == FinalMarking, "incorrect state transition?");
4064 check_correct_thread_executing();
4065 // world is stopped at this checkpoint
4066 assert(SafepointSynchronize::is_at_safepoint(),
4067 "world should be stopped");
4068 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4069
4070 verify_work_stacks_empty();
4071 verify_overflow_empty();
4072
4073 log_debug(gc, conc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4074 _young_gen->used() / K, _young_gen->capacity() / K);
4075 {
4076 if (CMSScavengeBeforeRemark) {
4077 GenCollectedHeap* gch = GenCollectedHeap::heap();
4078 // Temporarily set flag to false, GCH->do_collection will
4079 // expect it to be false and set to true
4080 FlagSetting fl(gch->_is_gc_active, false);
4081
4082 GCTraceTime(Trace, gc) tm("Scavenge-Before-Remark", _gc_timer_cm);
4083
4084 gch->do_collection(true, // full (i.e. force, see below)
4085 false, // !clear_all_soft_refs
4086 0, // size
4087 false, // is_tlab
4088 GenCollectedHeap::YoungGen // type
4089 );
4090 }
4091 FreelistLocker x(this);
4092 MutexLockerEx y(bitMapLock(),
4093 Mutex::_no_safepoint_check_flag);
4094 checkpointRootsFinalWork();
4095 }
4096 verify_work_stacks_empty();
4097 verify_overflow_empty();
4098 }
4099
4100 void CMSCollector::checkpointRootsFinalWork() {
4101 GCTraceTime(Trace, gc) tm("checkpointRootsFinalWork", _gc_timer_cm);
4102
4103 assert(haveFreelistLocks(), "must have free list locks");
4104 assert_lock_strong(bitMapLock());
4105
4106 ResourceMark rm;
4107 HandleMark hm;
4108
4109 GenCollectedHeap* gch = GenCollectedHeap::heap();
4110
4111 if (should_unload_classes()) {
4112 CodeCache::gc_prologue();
4113 }
4114 assert(haveFreelistLocks(), "must have free list locks");
4115 assert_lock_strong(bitMapLock());
4116
4117 // We might assume that we need not fill TLAB's when
4118 // CMSScavengeBeforeRemark is set, because we may have just done
4119 // a scavenge which would have filled all TLAB's -- and besides
4120 // Eden would be empty. This however may not always be the case --
4121 // for instance although we asked for a scavenge, it may not have
4122 // happened because of a JNI critical section. We probably need
4123 // a policy for deciding whether we can in that case wait until
4124 // the critical section releases and then do the remark following
4125 // the scavenge, and skip it here. In the absence of that policy,
4126 // or of an indication of whether the scavenge did indeed occur,
4127 // we cannot rely on TLAB's having been filled and must do
4128 // so here just in case a scavenge did not happen.
4129 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4130 // Update the saved marks which may affect the root scans.
4131 gch->save_marks();
4132
4133 print_eden_and_survivor_chunk_arrays();
4134
4135 {
4136 #if defined(COMPILER2) || INCLUDE_JVMCI
4137 DerivedPointerTableDeactivate dpt_deact;
4138 #endif
4139
4140 // Note on the role of the mod union table:
4141 // Since the marker in "markFromRoots" marks concurrently with
4142 // mutators, it is possible for some reachable objects not to have been
4143 // scanned. For instance, an only reference to an object A was
4144 // placed in object B after the marker scanned B. Unless B is rescanned,
4145 // A would be collected. Such updates to references in marked objects
4146 // are detected via the mod union table which is the set of all cards
4147 // dirtied since the first checkpoint in this GC cycle and prior to
4148 // the most recent young generation GC, minus those cleaned up by the
4149 // concurrent precleaning.
4150 if (CMSParallelRemarkEnabled) {
4151 GCTraceTime(Debug, gc) t("Rescan (parallel)", _gc_timer_cm);
4152 do_remark_parallel();
4153 } else {
4154 GCTraceTime(Debug, gc) t("Rescan (non-parallel)", _gc_timer_cm);
4155 do_remark_non_parallel();
4156 }
4157 }
4158 verify_work_stacks_empty();
4159 verify_overflow_empty();
4160
4161 {
4162 GCTraceTime(Trace, gc) ts("refProcessingWork", _gc_timer_cm);
4163 refProcessingWork();
4164 }
4165 verify_work_stacks_empty();
4166 verify_overflow_empty();
4167
4168 if (should_unload_classes()) {
4169 CodeCache::gc_epilogue();
4170 }
4171 JvmtiExport::gc_epilogue();
4172
4173 // If we encountered any (marking stack / work queue) overflow
4174 // events during the current CMS cycle, take appropriate
4175 // remedial measures, where possible, so as to try and avoid
4176 // recurrence of that condition.
4177 assert(_markStack.isEmpty(), "No grey objects");
4178 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4179 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4180 if (ser_ovflw > 0) {
4181 log_debug(gc, conc, stats)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4182 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4183 _markStack.expand();
4184 _ser_pmc_remark_ovflw = 0;
4185 _ser_pmc_preclean_ovflw = 0;
4186 _ser_kac_preclean_ovflw = 0;
4187 _ser_kac_ovflw = 0;
4188 }
4189 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4190 log_debug(gc, conc, stats)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4191 _par_pmc_remark_ovflw, _par_kac_ovflw);
4192 _par_pmc_remark_ovflw = 0;
4193 _par_kac_ovflw = 0;
4194 }
4195 if (_markStack._hit_limit > 0) {
4196 log_debug(gc, conc, stats)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4197 _markStack._hit_limit);
4198 }
4199 if (_markStack._failed_double > 0) {
4200 log_debug(gc, conc, stats)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4201 _markStack._failed_double, _markStack.capacity());
4202 }
4203 _markStack._hit_limit = 0;
4204 _markStack._failed_double = 0;
4205
4206 if ((VerifyAfterGC || VerifyDuringGC) &&
4207 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4208 verify_after_remark();
4209 }
4210
4211 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4212
4213 // Change under the freelistLocks.
4214 _collectorState = Sweeping;
4215 // Call isAllClear() under bitMapLock
4216 assert(_modUnionTable.isAllClear(),
4217 "Should be clear by end of the final marking");
4218 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4219 "Should be clear by end of the final marking");
4220 }
4221
4222 void CMSParInitialMarkTask::work(uint worker_id) {
4223 elapsedTimer _timer;
4224 ResourceMark rm;
4225 HandleMark hm;
4226
4227 // ---------- scan from roots --------------
4228 _timer.start();
4229 GenCollectedHeap* gch = GenCollectedHeap::heap();
4230 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4231
4232 // ---------- young gen roots --------------
4233 {
4234 work_on_young_gen_roots(worker_id, &par_mri_cl);
4235 _timer.stop();
4236 log_debug(gc, conc, stats)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4237 }
4238
4239 // ---------- remaining roots --------------
4240 _timer.reset();
4241 _timer.start();
4242
4243 CLDToOopClosure cld_closure(&par_mri_cl, true);
4244
4245 gch->gen_process_roots(_strong_roots_scope,
4246 GenCollectedHeap::OldGen,
4247 false, // yg was scanned above
4248 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4249 _collector->should_unload_classes(),
4250 &par_mri_cl,
4251 NULL,
4252 &cld_closure);
4253 assert(_collector->should_unload_classes()
4254 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4255 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4256 _timer.stop();
4257 log_debug(gc, conc, stats)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4258 }
4259
4260 // Parallel remark task
4261 class CMSParRemarkTask: public CMSParMarkTask {
4262 CompactibleFreeListSpace* _cms_space;
4263
4264 // The per-thread work queues, available here for stealing.
4265 OopTaskQueueSet* _task_queues;
4266 ParallelTaskTerminator _term;
4267 StrongRootsScope* _strong_roots_scope;
4268
4269 public:
4270 // A value of 0 passed to n_workers will cause the number of
4271 // workers to be taken from the active workers in the work gang.
4272 CMSParRemarkTask(CMSCollector* collector,
4273 CompactibleFreeListSpace* cms_space,
4274 uint n_workers, WorkGang* workers,
4275 OopTaskQueueSet* task_queues,
4276 StrongRootsScope* strong_roots_scope):
4277 CMSParMarkTask("Rescan roots and grey objects in parallel",
4278 collector, n_workers),
4279 _cms_space(cms_space),
4280 _task_queues(task_queues),
4281 _term(n_workers, task_queues),
4282 _strong_roots_scope(strong_roots_scope) { }
4283
4284 OopTaskQueueSet* task_queues() { return _task_queues; }
4285
4286 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4287
4288 ParallelTaskTerminator* terminator() { return &_term; }
4289 uint n_workers() { return _n_workers; }
4290
4291 void work(uint worker_id);
4292
4293 private:
4294 // ... of dirty cards in old space
4295 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4296 Par_MarkRefsIntoAndScanClosure* cl);
4297
4298 // ... work stealing for the above
4299 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4300 };
4301
4302 class RemarkKlassClosure : public KlassClosure {
4303 KlassToOopClosure _cm_klass_closure;
4304 public:
4305 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4306 void do_klass(Klass* k) {
4307 // Check if we have modified any oops in the Klass during the concurrent marking.
4308 if (k->has_accumulated_modified_oops()) {
4309 k->clear_accumulated_modified_oops();
4310
4311 // We could have transfered the current modified marks to the accumulated marks,
4312 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4313 } else if (k->has_modified_oops()) {
4314 // Don't clear anything, this info is needed by the next young collection.
4315 } else {
4316 // No modified oops in the Klass.
4317 return;
4318 }
4319
4320 // The klass has modified fields, need to scan the klass.
4321 _cm_klass_closure.do_klass(k);
4322 }
4323 };
4324
4325 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4326 ParNewGeneration* young_gen = _collector->_young_gen;
4327 ContiguousSpace* eden_space = young_gen->eden();
4328 ContiguousSpace* from_space = young_gen->from();
4329 ContiguousSpace* to_space = young_gen->to();
4330
4331 HeapWord** eca = _collector->_eden_chunk_array;
4332 size_t ect = _collector->_eden_chunk_index;
4333 HeapWord** sca = _collector->_survivor_chunk_array;
4334 size_t sct = _collector->_survivor_chunk_index;
4335
4336 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4337 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4338
4339 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4340 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4341 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4342 }
4343
4344 // work_queue(i) is passed to the closure
4345 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
4346 // also is passed to do_dirty_card_rescan_tasks() and to
4347 // do_work_steal() to select the i-th task_queue.
4348
4349 void CMSParRemarkTask::work(uint worker_id) {
4350 elapsedTimer _timer;
4351 ResourceMark rm;
4352 HandleMark hm;
4353
4354 // ---------- rescan from roots --------------
4355 _timer.start();
4356 GenCollectedHeap* gch = GenCollectedHeap::heap();
4357 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4358 _collector->_span, _collector->ref_processor(),
4359 &(_collector->_markBitMap),
4360 work_queue(worker_id));
4361
4362 // Rescan young gen roots first since these are likely
4363 // coarsely partitioned and may, on that account, constitute
4364 // the critical path; thus, it's best to start off that
4365 // work first.
4366 // ---------- young gen roots --------------
4367 {
4368 work_on_young_gen_roots(worker_id, &par_mrias_cl);
4369 _timer.stop();
4370 log_debug(gc, conc, stats)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4371 }
4372
4373 // ---------- remaining roots --------------
4374 _timer.reset();
4375 _timer.start();
4376 gch->gen_process_roots(_strong_roots_scope,
4377 GenCollectedHeap::OldGen,
4378 false, // yg was scanned above
4379 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4380 _collector->should_unload_classes(),
4381 &par_mrias_cl,
4382 NULL,
4383 NULL); // The dirty klasses will be handled below
4384
4385 assert(_collector->should_unload_classes()
4386 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4387 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4388 _timer.stop();
4389 log_debug(gc, conc, stats)("Finished remaining root rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4390
4391 // ---------- unhandled CLD scanning ----------
4392 if (worker_id == 0) { // Single threaded at the moment.
4393 _timer.reset();
4394 _timer.start();
4395
4396 // Scan all new class loader data objects and new dependencies that were
4397 // introduced during concurrent marking.
4398 ResourceMark rm;
4399 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4400 for (int i = 0; i < array->length(); i++) {
4401 par_mrias_cl.do_cld_nv(array->at(i));
4402 }
4403
4404 // We don't need to keep track of new CLDs anymore.
4405 ClassLoaderDataGraph::remember_new_clds(false);
4406
4407 _timer.stop();
4408 log_debug(gc, conc, stats)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4409 }
4410
4411 // ---------- dirty klass scanning ----------
4412 if (worker_id == 0) { // Single threaded at the moment.
4413 _timer.reset();
4414 _timer.start();
4415
4416 // Scan all classes that was dirtied during the concurrent marking phase.
4417 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4418 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4419
4420 _timer.stop();
4421 log_debug(gc, conc, stats)("Finished dirty klass scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4422 }
4423
4424 // We might have added oops to ClassLoaderData::_handles during the
4425 // concurrent marking phase. These oops point to newly allocated objects
4426 // that are guaranteed to be kept alive. Either by the direct allocation
4427 // code, or when the young collector processes the roots. Hence,
4428 // we don't have to revisit the _handles block during the remark phase.
4429
4430 // ---------- rescan dirty cards ------------
4431 _timer.reset();
4432 _timer.start();
4433
4434 // Do the rescan tasks for each of the two spaces
4435 // (cms_space) in turn.
4436 // "worker_id" is passed to select the task_queue for "worker_id"
4437 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4438 _timer.stop();
4439 log_debug(gc, conc, stats)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4440
4441 // ---------- steal work from other threads ...
4442 // ---------- ... and drain overflow list.
4443 _timer.reset();
4444 _timer.start();
4445 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4446 _timer.stop();
4447 log_debug(gc, conc, stats)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4448 }
4449
4450 // Note that parameter "i" is not used.
4451 void
4452 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4453 OopsInGenClosure* cl, ContiguousSpace* space,
4454 HeapWord** chunk_array, size_t chunk_top) {
4455 // Until all tasks completed:
4456 // . claim an unclaimed task
4457 // . compute region boundaries corresponding to task claimed
4458 // using chunk_array
4459 // . par_oop_iterate(cl) over that region
4460
4461 ResourceMark rm;
4462 HandleMark hm;
4463
4464 SequentialSubTasksDone* pst = space->par_seq_tasks();
4465
4466 uint nth_task = 0;
4467 uint n_tasks = pst->n_tasks();
4468
4469 if (n_tasks > 0) {
4470 assert(pst->valid(), "Uninitialized use?");
4471 HeapWord *start, *end;
4472 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4473 // We claimed task # nth_task; compute its boundaries.
4474 if (chunk_top == 0) { // no samples were taken
4475 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4476 start = space->bottom();
4477 end = space->top();
4478 } else if (nth_task == 0) {
4479 start = space->bottom();
4480 end = chunk_array[nth_task];
4481 } else if (nth_task < (uint)chunk_top) {
4482 assert(nth_task >= 1, "Control point invariant");
4483 start = chunk_array[nth_task - 1];
4484 end = chunk_array[nth_task];
4485 } else {
4486 assert(nth_task == (uint)chunk_top, "Control point invariant");
4487 start = chunk_array[chunk_top - 1];
4488 end = space->top();
4489 }
4490 MemRegion mr(start, end);
4491 // Verify that mr is in space
4492 assert(mr.is_empty() || space->used_region().contains(mr),
4493 "Should be in space");
4494 // Verify that "start" is an object boundary
4495 assert(mr.is_empty() || oop(mr.start())->is_oop(),
4496 "Should be an oop");
4497 space->par_oop_iterate(mr, cl);
4498 }
4499 pst->all_tasks_completed();
4500 }
4501 }
4502
4503 void
4504 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4505 CompactibleFreeListSpace* sp, int i,
4506 Par_MarkRefsIntoAndScanClosure* cl) {
4507 // Until all tasks completed:
4508 // . claim an unclaimed task
4509 // . compute region boundaries corresponding to task claimed
4510 // . transfer dirty bits ct->mut for that region
4511 // . apply rescanclosure to dirty mut bits for that region
4512
4513 ResourceMark rm;
4514 HandleMark hm;
4515
4516 OopTaskQueue* work_q = work_queue(i);
4517 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4518 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4519 // CAUTION: This closure has state that persists across calls to
4520 // the work method dirty_range_iterate_clear() in that it has
4521 // embedded in it a (subtype of) UpwardsObjectClosure. The
4522 // use of that state in the embedded UpwardsObjectClosure instance
4523 // assumes that the cards are always iterated (even if in parallel
4524 // by several threads) in monotonically increasing order per each
4525 // thread. This is true of the implementation below which picks
4526 // card ranges (chunks) in monotonically increasing order globally
4527 // and, a-fortiori, in monotonically increasing order per thread
4528 // (the latter order being a subsequence of the former).
4529 // If the work code below is ever reorganized into a more chaotic
4530 // work-partitioning form than the current "sequential tasks"
4531 // paradigm, the use of that persistent state will have to be
4532 // revisited and modified appropriately. See also related
4533 // bug 4756801 work on which should examine this code to make
4534 // sure that the changes there do not run counter to the
4535 // assumptions made here and necessary for correctness and
4536 // efficiency. Note also that this code might yield inefficient
4537 // behavior in the case of very large objects that span one or
4538 // more work chunks. Such objects would potentially be scanned
4539 // several times redundantly. Work on 4756801 should try and
4540 // address that performance anomaly if at all possible. XXX
4541 MemRegion full_span = _collector->_span;
4542 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4543 MarkFromDirtyCardsClosure
4544 greyRescanClosure(_collector, full_span, // entire span of interest
4545 sp, bm, work_q, cl);
4546
4547 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4548 assert(pst->valid(), "Uninitialized use?");
4549 uint nth_task = 0;
4550 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4551 MemRegion span = sp->used_region();
4552 HeapWord* start_addr = span.start();
4553 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4554 alignment);
4555 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4556 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4557 start_addr, "Check alignment");
4558 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4559 chunk_size, "Check alignment");
4560
4561 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4562 // Having claimed the nth_task, compute corresponding mem-region,
4563 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4564 // The alignment restriction ensures that we do not need any
4565 // synchronization with other gang-workers while setting or
4566 // clearing bits in thus chunk of the MUT.
4567 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4568 start_addr + (nth_task+1)*chunk_size);
4569 // The last chunk's end might be way beyond end of the
4570 // used region. In that case pull back appropriately.
4571 if (this_span.end() > end_addr) {
4572 this_span.set_end(end_addr);
4573 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4574 }
4575 // Iterate over the dirty cards covering this chunk, marking them
4576 // precleaned, and setting the corresponding bits in the mod union
4577 // table. Since we have been careful to partition at Card and MUT-word
4578 // boundaries no synchronization is needed between parallel threads.
4579 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4580 &modUnionClosure);
4581
4582 // Having transferred these marks into the modUnionTable,
4583 // rescan the marked objects on the dirty cards in the modUnionTable.
4584 // Even if this is at a synchronous collection, the initial marking
4585 // may have been done during an asynchronous collection so there
4586 // may be dirty bits in the mod-union table.
4587 _collector->_modUnionTable.dirty_range_iterate_clear(
4588 this_span, &greyRescanClosure);
4589 _collector->_modUnionTable.verifyNoOneBitsInRange(
4590 this_span.start(),
4591 this_span.end());
4592 }
4593 pst->all_tasks_completed(); // declare that i am done
4594 }
4595
4596 // . see if we can share work_queues with ParNew? XXX
4597 void
4598 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4599 int* seed) {
4600 OopTaskQueue* work_q = work_queue(i);
4601 NOT_PRODUCT(int num_steals = 0;)
4602 oop obj_to_scan;
4603 CMSBitMap* bm = &(_collector->_markBitMap);
4604
4605 while (true) {
4606 // Completely finish any left over work from (an) earlier round(s)
4607 cl->trim_queue(0);
4608 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4609 (size_t)ParGCDesiredObjsFromOverflowList);
4610 // Now check if there's any work in the overflow list
4611 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4612 // only affects the number of attempts made to get work from the
4613 // overflow list and does not affect the number of workers. Just
4614 // pass ParallelGCThreads so this behavior is unchanged.
4615 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4616 work_q,
4617 ParallelGCThreads)) {
4618 // found something in global overflow list;
4619 // not yet ready to go stealing work from others.
4620 // We'd like to assert(work_q->size() != 0, ...)
4621 // because we just took work from the overflow list,
4622 // but of course we can't since all of that could have
4623 // been already stolen from us.
4624 // "He giveth and He taketh away."
4625 continue;
4626 }
4627 // Verify that we have no work before we resort to stealing
4628 assert(work_q->size() == 0, "Have work, shouldn't steal");
4629 // Try to steal from other queues that have work
4630 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4631 NOT_PRODUCT(num_steals++;)
4632 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4633 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4634 // Do scanning work
4635 obj_to_scan->oop_iterate(cl);
4636 // Loop around, finish this work, and try to steal some more
4637 } else if (terminator()->offer_termination()) {
4638 break; // nirvana from the infinite cycle
4639 }
4640 }
4641 log_develop(gc, conc, stats)("\t(%d: stole %d oops)", i, num_steals);
4642 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4643 "Else our work is not yet done");
4644 }
4645
4646 // Record object boundaries in _eden_chunk_array by sampling the eden
4647 // top in the slow-path eden object allocation code path and record
4648 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4649 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4650 // sampling in sample_eden() that activates during the part of the
4651 // preclean phase.
4652 void CMSCollector::sample_eden_chunk() {
4653 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4654 if (_eden_chunk_lock->try_lock()) {
4655 // Record a sample. This is the critical section. The contents
4656 // of the _eden_chunk_array have to be non-decreasing in the
4657 // address order.
4658 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4659 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4660 "Unexpected state of Eden");
4661 if (_eden_chunk_index == 0 ||
4662 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4663 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4664 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4665 _eden_chunk_index++; // commit sample
4666 }
4667 _eden_chunk_lock->unlock();
4668 }
4669 }
4670 }
4671
4672 // Return a thread-local PLAB recording array, as appropriate.
4673 void* CMSCollector::get_data_recorder(int thr_num) {
4674 if (_survivor_plab_array != NULL &&
4675 (CMSPLABRecordAlways ||
4676 (_collectorState > Marking && _collectorState < FinalMarking))) {
4677 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4678 ChunkArray* ca = &_survivor_plab_array[thr_num];
4679 ca->reset(); // clear it so that fresh data is recorded
4680 return (void*) ca;
4681 } else {
4682 return NULL;
4683 }
4684 }
4685
4686 // Reset all the thread-local PLAB recording arrays
4687 void CMSCollector::reset_survivor_plab_arrays() {
4688 for (uint i = 0; i < ParallelGCThreads; i++) {
4689 _survivor_plab_array[i].reset();
4690 }
4691 }
4692
4693 // Merge the per-thread plab arrays into the global survivor chunk
4694 // array which will provide the partitioning of the survivor space
4695 // for CMS initial scan and rescan.
4696 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4697 int no_of_gc_threads) {
4698 assert(_survivor_plab_array != NULL, "Error");
4699 assert(_survivor_chunk_array != NULL, "Error");
4700 assert(_collectorState == FinalMarking ||
4701 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4702 for (int j = 0; j < no_of_gc_threads; j++) {
4703 _cursor[j] = 0;
4704 }
4705 HeapWord* top = surv->top();
4706 size_t i;
4707 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4708 HeapWord* min_val = top; // Higher than any PLAB address
4709 uint min_tid = 0; // position of min_val this round
4710 for (int j = 0; j < no_of_gc_threads; j++) {
4711 ChunkArray* cur_sca = &_survivor_plab_array[j];
4712 if (_cursor[j] == cur_sca->end()) {
4713 continue;
4714 }
4715 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4716 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4717 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4718 if (cur_val < min_val) {
4719 min_tid = j;
4720 min_val = cur_val;
4721 } else {
4722 assert(cur_val < top, "All recorded addresses should be less");
4723 }
4724 }
4725 // At this point min_val and min_tid are respectively
4726 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4727 // and the thread (j) that witnesses that address.
4728 // We record this address in the _survivor_chunk_array[i]
4729 // and increment _cursor[min_tid] prior to the next round i.
4730 if (min_val == top) {
4731 break;
4732 }
4733 _survivor_chunk_array[i] = min_val;
4734 _cursor[min_tid]++;
4735 }
4736 // We are all done; record the size of the _survivor_chunk_array
4737 _survivor_chunk_index = i; // exclusive: [0, i)
4738 log_debug(gc, conc, stats)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4739 // Verify that we used up all the recorded entries
4740 #ifdef ASSERT
4741 size_t total = 0;
4742 for (int j = 0; j < no_of_gc_threads; j++) {
4743 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4744 total += _cursor[j];
4745 }
4746 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4747 // Check that the merged array is in sorted order
4748 if (total > 0) {
4749 for (size_t i = 0; i < total - 1; i++) {
4750 log_develop(gc, conc, stats)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4751 i, p2i(_survivor_chunk_array[i]));
4752 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4753 "Not sorted");
4754 }
4755 }
4756 #endif // ASSERT
4757 }
4758
4759 // Set up the space's par_seq_tasks structure for work claiming
4760 // for parallel initial scan and rescan of young gen.
4761 // See ParRescanTask where this is currently used.
4762 void
4763 CMSCollector::
4764 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4765 assert(n_threads > 0, "Unexpected n_threads argument");
4766
4767 // Eden space
4768 if (!_young_gen->eden()->is_empty()) {
4769 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4770 assert(!pst->valid(), "Clobbering existing data?");
4771 // Each valid entry in [0, _eden_chunk_index) represents a task.
4772 size_t n_tasks = _eden_chunk_index + 1;
4773 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4774 // Sets the condition for completion of the subtask (how many threads
4775 // need to finish in order to be done).
4776 pst->set_n_threads(n_threads);
4777 pst->set_n_tasks((int)n_tasks);
4778 }
4779
4780 // Merge the survivor plab arrays into _survivor_chunk_array
4781 if (_survivor_plab_array != NULL) {
4782 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4783 } else {
4784 assert(_survivor_chunk_index == 0, "Error");
4785 }
4786
4787 // To space
4788 {
4789 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4790 assert(!pst->valid(), "Clobbering existing data?");
4791 // Sets the condition for completion of the subtask (how many threads
4792 // need to finish in order to be done).
4793 pst->set_n_threads(n_threads);
4794 pst->set_n_tasks(1);
4795 assert(pst->valid(), "Error");
4796 }
4797
4798 // From space
4799 {
4800 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4801 assert(!pst->valid(), "Clobbering existing data?");
4802 size_t n_tasks = _survivor_chunk_index + 1;
4803 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
4804 // Sets the condition for completion of the subtask (how many threads
4805 // need to finish in order to be done).
4806 pst->set_n_threads(n_threads);
4807 pst->set_n_tasks((int)n_tasks);
4808 assert(pst->valid(), "Error");
4809 }
4810 }
4811
4812 // Parallel version of remark
4813 void CMSCollector::do_remark_parallel() {
4814 GenCollectedHeap* gch = GenCollectedHeap::heap();
4815 WorkGang* workers = gch->workers();
4816 assert(workers != NULL, "Need parallel worker threads.");
4817 // Choose to use the number of GC workers most recently set
4818 // into "active_workers".
4819 uint n_workers = workers->active_workers();
4820
4821 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4822
4823 StrongRootsScope srs(n_workers);
4824
4825 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4826
4827 // We won't be iterating over the cards in the card table updating
4828 // the younger_gen cards, so we shouldn't call the following else
4829 // the verification code as well as subsequent younger_refs_iterate
4830 // code would get confused. XXX
4831 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4832
4833 // The young gen rescan work will not be done as part of
4834 // process_roots (which currently doesn't know how to
4835 // parallelize such a scan), but rather will be broken up into
4836 // a set of parallel tasks (via the sampling that the [abortable]
4837 // preclean phase did of eden, plus the [two] tasks of
4838 // scanning the [two] survivor spaces. Further fine-grain
4839 // parallelization of the scanning of the survivor spaces
4840 // themselves, and of precleaning of the young gen itself
4841 // is deferred to the future.
4842 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4843
4844 // The dirty card rescan work is broken up into a "sequence"
4845 // of parallel tasks (per constituent space) that are dynamically
4846 // claimed by the parallel threads.
4847 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4848
4849 // It turns out that even when we're using 1 thread, doing the work in a
4850 // separate thread causes wide variance in run times. We can't help this
4851 // in the multi-threaded case, but we special-case n=1 here to get
4852 // repeatable measurements of the 1-thread overhead of the parallel code.
4853 if (n_workers > 1) {
4854 // Make refs discovery MT-safe, if it isn't already: it may not
4855 // necessarily be so, since it's possible that we are doing
4856 // ST marking.
4857 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4858 workers->run_task(&tsk);
4859 } else {
4860 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4861 tsk.work(0);
4862 }
4863
4864 // restore, single-threaded for now, any preserved marks
4865 // as a result of work_q overflow
4866 restore_preserved_marks_if_any();
4867 }
4868
4869 // Non-parallel version of remark
4870 void CMSCollector::do_remark_non_parallel() {
4871 ResourceMark rm;
4872 HandleMark hm;
4873 GenCollectedHeap* gch = GenCollectedHeap::heap();
4874 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4875
4876 MarkRefsIntoAndScanClosure
4877 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4878 &_markStack, this,
4879 false /* should_yield */, false /* not precleaning */);
4880 MarkFromDirtyCardsClosure
4881 markFromDirtyCardsClosure(this, _span,
4882 NULL, // space is set further below
4883 &_markBitMap, &_markStack, &mrias_cl);
4884 {
4885 GCTraceTime(Trace, gc) t("grey object rescan", _gc_timer_cm);
4886 // Iterate over the dirty cards, setting the corresponding bits in the
4887 // mod union table.
4888 {
4889 ModUnionClosure modUnionClosure(&_modUnionTable);
4890 _ct->ct_bs()->dirty_card_iterate(
4891 _cmsGen->used_region(),
4892 &modUnionClosure);
4893 }
4894 // Having transferred these marks into the modUnionTable, we just need
4895 // to rescan the marked objects on the dirty cards in the modUnionTable.
4896 // The initial marking may have been done during an asynchronous
4897 // collection so there may be dirty bits in the mod-union table.
4898 const int alignment =
4899 CardTableModRefBS::card_size * BitsPerWord;
4900 {
4901 // ... First handle dirty cards in CMS gen
4902 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4903 MemRegion ur = _cmsGen->used_region();
4904 HeapWord* lb = ur.start();
4905 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
4906 MemRegion cms_span(lb, ub);
4907 _modUnionTable.dirty_range_iterate_clear(cms_span,
4908 &markFromDirtyCardsClosure);
4909 verify_work_stacks_empty();
4910 log_debug(gc, conc, stats)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4911 }
4912 }
4913 if (VerifyDuringGC &&
4914 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4915 HandleMark hm; // Discard invalid handles created during verification
4916 Universe::verify();
4917 }
4918 {
4919 GCTraceTime(Trace, gc) t("root rescan", _gc_timer_cm);
4920
4921 verify_work_stacks_empty();
4922
4923 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
4924 StrongRootsScope srs(1);
4925
4926 gch->gen_process_roots(&srs,
4927 GenCollectedHeap::OldGen,
4928 true, // young gen as roots
4929 GenCollectedHeap::ScanningOption(roots_scanning_options()),
4930 should_unload_classes(),
4931 &mrias_cl,
4932 NULL,
4933 NULL); // The dirty klasses will be handled below
4934
4935 assert(should_unload_classes()
4936 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4937 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4938 }
4939
4940 {
4941 GCTraceTime(Trace, gc) t("visit unhandled CLDs", _gc_timer_cm);
4942
4943 verify_work_stacks_empty();
4944
4945 // Scan all class loader data objects that might have been introduced
4946 // during concurrent marking.
4947 ResourceMark rm;
4948 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4949 for (int i = 0; i < array->length(); i++) {
4950 mrias_cl.do_cld_nv(array->at(i));
4951 }
4952
4953 // We don't need to keep track of new CLDs anymore.
4954 ClassLoaderDataGraph::remember_new_clds(false);
4955
4956 verify_work_stacks_empty();
4957 }
4958
4959 {
4960 GCTraceTime(Trace, gc) t("dirty klass scan", _gc_timer_cm);
4961
4962 verify_work_stacks_empty();
4963
4964 RemarkKlassClosure remark_klass_closure(&mrias_cl);
4965 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4966
4967 verify_work_stacks_empty();
4968 }
4969
4970 // We might have added oops to ClassLoaderData::_handles during the
4971 // concurrent marking phase. These oops point to newly allocated objects
4972 // that are guaranteed to be kept alive. Either by the direct allocation
4973 // code, or when the young collector processes the roots. Hence,
4974 // we don't have to revisit the _handles block during the remark phase.
4975
4976 verify_work_stacks_empty();
4977 // Restore evacuated mark words, if any, used for overflow list links
4978 restore_preserved_marks_if_any();
4979
4980 verify_overflow_empty();
4981 }
4982
4983 ////////////////////////////////////////////////////////
4984 // Parallel Reference Processing Task Proxy Class
4985 ////////////////////////////////////////////////////////
4986 class AbstractGangTaskWOopQueues : public AbstractGangTask {
4987 OopTaskQueueSet* _queues;
4988 ParallelTaskTerminator _terminator;
4989 public:
4990 AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
4991 AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
4992 ParallelTaskTerminator* terminator() { return &_terminator; }
4993 OopTaskQueueSet* queues() { return _queues; }
4994 };
4995
4996 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
4997 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
4998 CMSCollector* _collector;
4999 CMSBitMap* _mark_bit_map;
5000 const MemRegion _span;
5001 ProcessTask& _task;
5002
5003 public:
5004 CMSRefProcTaskProxy(ProcessTask& task,
5005 CMSCollector* collector,
5006 const MemRegion& span,
5007 CMSBitMap* mark_bit_map,
5008 AbstractWorkGang* workers,
5009 OopTaskQueueSet* task_queues):
5010 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5011 task_queues,
5012 workers->active_workers()),
5013 _task(task),
5014 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5015 {
5016 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5017 "Inconsistency in _span");
5018 }
5019
5020 OopTaskQueueSet* task_queues() { return queues(); }
5021
5022 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5023
5024 void do_work_steal(int i,
5025 CMSParDrainMarkingStackClosure* drain,
5026 CMSParKeepAliveClosure* keep_alive,
5027 int* seed);
5028
5029 virtual void work(uint worker_id);
5030 };
5031
5032 void CMSRefProcTaskProxy::work(uint worker_id) {
5033 ResourceMark rm;
5034 HandleMark hm;
5035 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5036 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5037 _mark_bit_map,
5038 work_queue(worker_id));
5039 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5040 _mark_bit_map,
5041 work_queue(worker_id));
5042 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5043 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5044 if (_task.marks_oops_alive()) {
5045 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5046 _collector->hash_seed(worker_id));
5047 }
5048 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5049 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5050 }
5051
5052 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5053 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5054 EnqueueTask& _task;
5055
5056 public:
5057 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5058 : AbstractGangTask("Enqueue reference objects in parallel"),
5059 _task(task)
5060 { }
5061
5062 virtual void work(uint worker_id)
5063 {
5064 _task.work(worker_id);
5065 }
5066 };
5067
5068 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5069 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5070 _span(span),
5071 _bit_map(bit_map),
5072 _work_queue(work_queue),
5073 _mark_and_push(collector, span, bit_map, work_queue),
5074 _low_water_mark(MIN2((work_queue->max_elems()/4),
5075 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5076 { }
5077
5078 // . see if we can share work_queues with ParNew? XXX
5079 void CMSRefProcTaskProxy::do_work_steal(int i,
5080 CMSParDrainMarkingStackClosure* drain,
5081 CMSParKeepAliveClosure* keep_alive,
5082 int* seed) {
5083 OopTaskQueue* work_q = work_queue(i);
5084 NOT_PRODUCT(int num_steals = 0;)
5085 oop obj_to_scan;
5086
5087 while (true) {
5088 // Completely finish any left over work from (an) earlier round(s)
5089 drain->trim_queue(0);
5090 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5091 (size_t)ParGCDesiredObjsFromOverflowList);
5092 // Now check if there's any work in the overflow list
5093 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5094 // only affects the number of attempts made to get work from the
5095 // overflow list and does not affect the number of workers. Just
5096 // pass ParallelGCThreads so this behavior is unchanged.
5097 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5098 work_q,
5099 ParallelGCThreads)) {
5100 // Found something in global overflow list;
5101 // not yet ready to go stealing work from others.
5102 // We'd like to assert(work_q->size() != 0, ...)
5103 // because we just took work from the overflow list,
5104 // but of course we can't, since all of that might have
5105 // been already stolen from us.
5106 continue;
5107 }
5108 // Verify that we have no work before we resort to stealing
5109 assert(work_q->size() == 0, "Have work, shouldn't steal");
5110 // Try to steal from other queues that have work
5111 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5112 NOT_PRODUCT(num_steals++;)
5113 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5114 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5115 // Do scanning work
5116 obj_to_scan->oop_iterate(keep_alive);
5117 // Loop around, finish this work, and try to steal some more
5118 } else if (terminator()->offer_termination()) {
5119 break; // nirvana from the infinite cycle
5120 }
5121 }
5122 log_develop(gc, conc, stats)("\n\t(%d: stole %d oops)", i, num_steals);
5123 }
5124
5125 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5126 {
5127 GenCollectedHeap* gch = GenCollectedHeap::heap();
5128 WorkGang* workers = gch->workers();
5129 assert(workers != NULL, "Need parallel worker threads.");
5130 CMSRefProcTaskProxy rp_task(task, &_collector,
5131 _collector.ref_processor()->span(),
5132 _collector.markBitMap(),
5133 workers, _collector.task_queues());
5134 workers->run_task(&rp_task);
5135 }
5136
5137 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5138 {
5139
5140 GenCollectedHeap* gch = GenCollectedHeap::heap();
5141 WorkGang* workers = gch->workers();
5142 assert(workers != NULL, "Need parallel worker threads.");
5143 CMSRefEnqueueTaskProxy enq_task(task);
5144 workers->run_task(&enq_task);
5145 }
5146
5147 void CMSCollector::refProcessingWork() {
5148 ResourceMark rm;
5149 HandleMark hm;
5150
5151 ReferenceProcessor* rp = ref_processor();
5152 assert(rp->span().equals(_span), "Spans should be equal");
5153 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5154 // Process weak references.
5155 rp->setup_policy(false);
5156 verify_work_stacks_empty();
5157
5158 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5159 &_markStack, false /* !preclean */);
5160 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5161 _span, &_markBitMap, &_markStack,
5162 &cmsKeepAliveClosure, false /* !preclean */);
5163 {
5164 GCTraceTime(Debug, gc) t("weak refs processing", _gc_timer_cm);
5165
5166 ReferenceProcessorStats stats;
5167 if (rp->processing_is_mt()) {
5168 // Set the degree of MT here. If the discovery is done MT, there
5169 // may have been a different number of threads doing the discovery
5170 // and a different number of discovered lists may have Ref objects.
5171 // That is OK as long as the Reference lists are balanced (see
5172 // balance_all_queues() and balance_queues()).
5173 GenCollectedHeap* gch = GenCollectedHeap::heap();
5174 uint active_workers = ParallelGCThreads;
5175 WorkGang* workers = gch->workers();
5176 if (workers != NULL) {
5177 active_workers = workers->active_workers();
5178 // The expectation is that active_workers will have already
5179 // been set to a reasonable value. If it has not been set,
5180 // investigate.
5181 assert(active_workers > 0, "Should have been set during scavenge");
5182 }
5183 rp->set_active_mt_degree(active_workers);
5184 CMSRefProcTaskExecutor task_executor(*this);
5185 stats = rp->process_discovered_references(&_is_alive_closure,
5186 &cmsKeepAliveClosure,
5187 &cmsDrainMarkingStackClosure,
5188 &task_executor,
5189 _gc_timer_cm);
5190 } else {
5191 stats = rp->process_discovered_references(&_is_alive_closure,
5192 &cmsKeepAliveClosure,
5193 &cmsDrainMarkingStackClosure,
5194 NULL,
5195 _gc_timer_cm);
5196 }
5197 _gc_tracer_cm->report_gc_reference_stats(stats);
5198
5199 }
5200
5201 // This is the point where the entire marking should have completed.
5202 verify_work_stacks_empty();
5203
5204 if (should_unload_classes()) {
5205 {
5206 GCTraceTime(Debug, gc) t("class unloading", _gc_timer_cm);
5207
5208 // Unload classes and purge the SystemDictionary.
5209 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5210
5211 // Unload nmethods.
5212 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5213
5214 // Prune dead klasses from subklass/sibling/implementor lists.
5215 Klass::clean_weak_klass_links(&_is_alive_closure);
5216 }
5217
5218 {
5219 GCTraceTime(Debug, gc) t("scrub symbol table", _gc_timer_cm);
5220 // Clean up unreferenced symbols in symbol table.
5221 SymbolTable::unlink();
5222 }
5223
5224 {
5225 GCTraceTime(Debug, gc) t("scrub string table", _gc_timer_cm);
5226 // Delete entries for dead interned strings.
5227 StringTable::unlink(&_is_alive_closure);
5228 }
5229 }
5230
5231
5232 // Restore any preserved marks as a result of mark stack or
5233 // work queue overflow
5234 restore_preserved_marks_if_any(); // done single-threaded for now
5235
5236 rp->set_enqueuing_is_done(true);
5237 if (rp->processing_is_mt()) {
5238 rp->balance_all_queues();
5239 CMSRefProcTaskExecutor task_executor(*this);
5240 rp->enqueue_discovered_references(&task_executor);
5241 } else {
5242 rp->enqueue_discovered_references(NULL);
5243 }
5244 rp->verify_no_references_recorded();
5245 assert(!rp->discovery_enabled(), "should have been disabled");
5246 }
5247
5248 #ifndef PRODUCT
5249 void CMSCollector::check_correct_thread_executing() {
5250 Thread* t = Thread::current();
5251 // Only the VM thread or the CMS thread should be here.
5252 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5253 "Unexpected thread type");
5254 // If this is the vm thread, the foreground process
5255 // should not be waiting. Note that _foregroundGCIsActive is
5256 // true while the foreground collector is waiting.
5257 if (_foregroundGCShouldWait) {
5258 // We cannot be the VM thread
5259 assert(t->is_ConcurrentGC_thread(),
5260 "Should be CMS thread");
5261 } else {
5262 // We can be the CMS thread only if we are in a stop-world
5263 // phase of CMS collection.
5264 if (t->is_ConcurrentGC_thread()) {
5265 assert(_collectorState == InitialMarking ||
5266 _collectorState == FinalMarking,
5267 "Should be a stop-world phase");
5268 // The CMS thread should be holding the CMS_token.
5269 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5270 "Potential interference with concurrently "
5271 "executing VM thread");
5272 }
5273 }
5274 }
5275 #endif
5276
5277 void CMSCollector::sweep() {
5278 assert(_collectorState == Sweeping, "just checking");
5279 check_correct_thread_executing();
5280 verify_work_stacks_empty();
5281 verify_overflow_empty();
5282 increment_sweep_count();
5283 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5284
5285 _inter_sweep_timer.stop();
5286 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5287
5288 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5289 _intra_sweep_timer.reset();
5290 _intra_sweep_timer.start();
5291 {
5292 GCTraceCPUTime tcpu;
5293 CMSPhaseAccounting pa(this, "Sweep", !PrintGCDetails);
5294 // First sweep the old gen
5295 {
5296 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5297 bitMapLock());
5298 sweepWork(_cmsGen);
5299 }
5300
5301 // Update Universe::_heap_*_at_gc figures.
5302 // We need all the free list locks to make the abstract state
5303 // transition from Sweeping to Resetting. See detailed note
5304 // further below.
5305 {
5306 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5307 // Update heap occupancy information which is used as
5308 // input to soft ref clearing policy at the next gc.
5309 Universe::update_heap_info_at_gc();
5310 _collectorState = Resizing;
5311 }
5312 }
5313 verify_work_stacks_empty();
5314 verify_overflow_empty();
5315
5316 if (should_unload_classes()) {
5317 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5318 // requires that the virtual spaces are stable and not deleted.
5319 ClassLoaderDataGraph::set_should_purge(true);
5320 }
5321
5322 _intra_sweep_timer.stop();
5323 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5324
5325 _inter_sweep_timer.reset();
5326 _inter_sweep_timer.start();
5327
5328 // We need to use a monotonically non-decreasing time in ms
5329 // or we will see time-warp warnings and os::javaTimeMillis()
5330 // does not guarantee monotonicity.
5331 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5332 update_time_of_last_gc(now);
5333
5334 // NOTE on abstract state transitions:
5335 // Mutators allocate-live and/or mark the mod-union table dirty
5336 // based on the state of the collection. The former is done in
5337 // the interval [Marking, Sweeping] and the latter in the interval
5338 // [Marking, Sweeping). Thus the transitions into the Marking state
5339 // and out of the Sweeping state must be synchronously visible
5340 // globally to the mutators.
5341 // The transition into the Marking state happens with the world
5342 // stopped so the mutators will globally see it. Sweeping is
5343 // done asynchronously by the background collector so the transition
5344 // from the Sweeping state to the Resizing state must be done
5345 // under the freelistLock (as is the check for whether to
5346 // allocate-live and whether to dirty the mod-union table).
5347 assert(_collectorState == Resizing, "Change of collector state to"
5348 " Resizing must be done under the freelistLocks (plural)");
5349
5350 // Now that sweeping has been completed, we clear
5351 // the incremental_collection_failed flag,
5352 // thus inviting a younger gen collection to promote into
5353 // this generation. If such a promotion may still fail,
5354 // the flag will be set again when a young collection is
5355 // attempted.
5356 GenCollectedHeap* gch = GenCollectedHeap::heap();
5357 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5358 gch->update_full_collections_completed(_collection_count_start);
5359 }
5360
5361 // FIX ME!!! Looks like this belongs in CFLSpace, with
5362 // CMSGen merely delegating to it.
5363 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5364 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5365 HeapWord* minAddr = _cmsSpace->bottom();
5366 HeapWord* largestAddr =
5367 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5368 if (largestAddr == NULL) {
5369 // The dictionary appears to be empty. In this case
5370 // try to coalesce at the end of the heap.
5371 largestAddr = _cmsSpace->end();
5372 }
5373 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5374 size_t nearLargestOffset =
5375 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5376 log_debug(gc, freelist, stats)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5377 p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5378 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5379 }
5380
5381 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5382 return addr >= _cmsSpace->nearLargestChunk();
5383 }
5384
5385 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5386 return _cmsSpace->find_chunk_at_end();
5387 }
5388
5389 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5390 bool full) {
5391 // If the young generation has been collected, gather any statistics
5392 // that are of interest at this point.
5393 bool current_is_young = GenCollectedHeap::heap()->is_young_gen(current_generation);
5394 if (!full && current_is_young) {
5395 // Gather statistics on the young generation collection.
5396 collector()->stats().record_gc0_end(used());
5397 }
5398 }
5399
5400 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5401 // We iterate over the space(s) underlying this generation,
5402 // checking the mark bit map to see if the bits corresponding
5403 // to specific blocks are marked or not. Blocks that are
5404 // marked are live and are not swept up. All remaining blocks
5405 // are swept up, with coalescing on-the-fly as we sweep up
5406 // contiguous free and/or garbage blocks:
5407 // We need to ensure that the sweeper synchronizes with allocators
5408 // and stop-the-world collectors. In particular, the following
5409 // locks are used:
5410 // . CMS token: if this is held, a stop the world collection cannot occur
5411 // . freelistLock: if this is held no allocation can occur from this
5412 // generation by another thread
5413 // . bitMapLock: if this is held, no other thread can access or update
5414 //
5415
5416 // Note that we need to hold the freelistLock if we use
5417 // block iterate below; else the iterator might go awry if
5418 // a mutator (or promotion) causes block contents to change
5419 // (for instance if the allocator divvies up a block).
5420 // If we hold the free list lock, for all practical purposes
5421 // young generation GC's can't occur (they'll usually need to
5422 // promote), so we might as well prevent all young generation
5423 // GC's while we do a sweeping step. For the same reason, we might
5424 // as well take the bit map lock for the entire duration
5425
5426 // check that we hold the requisite locks
5427 assert(have_cms_token(), "Should hold cms token");
5428 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5429 assert_lock_strong(old_gen->freelistLock());
5430 assert_lock_strong(bitMapLock());
5431
5432 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5433 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5434 old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5435 _inter_sweep_estimate.padded_average(),
5436 _intra_sweep_estimate.padded_average());
5437 old_gen->setNearLargestChunk();
5438
5439 {
5440 SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5441 old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5442 // We need to free-up/coalesce garbage/blocks from a
5443 // co-terminal free run. This is done in the SweepClosure
5444 // destructor; so, do not remove this scope, else the
5445 // end-of-sweep-census below will be off by a little bit.
5446 }
5447 old_gen->cmsSpace()->sweep_completed();
5448 old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5449 if (should_unload_classes()) { // unloaded classes this cycle,
5450 _concurrent_cycles_since_last_unload = 0; // ... reset count
5451 } else { // did not unload classes,
5452 _concurrent_cycles_since_last_unload++; // ... increment count
5453 }
5454 }
5455
5456 // Reset CMS data structures (for now just the marking bit map)
5457 // preparatory for the next cycle.
5458 void CMSCollector::reset_concurrent() {
5459 CMSTokenSyncWithLocks ts(true, bitMapLock());
5460
5461 // If the state is not "Resetting", the foreground thread
5462 // has done a collection and the resetting.
5463 if (_collectorState != Resetting) {
5464 assert(_collectorState == Idling, "The state should only change"
5465 " because the foreground collector has finished the collection");
5466 return;
5467 }
5468
5469 // Clear the mark bitmap (no grey objects to start with)
5470 // for the next cycle.
5471 GCTraceCPUTime tcpu;
5472 CMSPhaseAccounting cmspa(this, "Reset", !PrintGCDetails);
5473
5474 HeapWord* curAddr = _markBitMap.startWord();
5475 while (curAddr < _markBitMap.endWord()) {
5476 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5477 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5478 _markBitMap.clear_large_range(chunk);
5479 if (ConcurrentMarkSweepThread::should_yield() &&
5480 !foregroundGCIsActive() &&
5481 CMSYield) {
5482 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5483 "CMS thread should hold CMS token");
5484 assert_lock_strong(bitMapLock());
5485 bitMapLock()->unlock();
5486 ConcurrentMarkSweepThread::desynchronize(true);
5487 stopTimer();
5488 incrementYields();
5489
5490 // See the comment in coordinator_yield()
5491 for (unsigned i = 0; i < CMSYieldSleepCount &&
5492 ConcurrentMarkSweepThread::should_yield() &&
5493 !CMSCollector::foregroundGCIsActive(); ++i) {
5494 os::sleep(Thread::current(), 1, false);
5495 }
5496
5497 ConcurrentMarkSweepThread::synchronize(true);
5498 bitMapLock()->lock_without_safepoint_check();
5499 startTimer();
5500 }
5501 curAddr = chunk.end();
5502 }
5503 // A successful mostly concurrent collection has been done.
5504 // Because only the full (i.e., concurrent mode failure) collections
5505 // are being measured for gc overhead limits, clean the "near" flag
5506 // and count.
5507 size_policy()->reset_gc_overhead_limit_count();
5508 _collectorState = Idling;
5509
5510 register_gc_end();
5511 }
5512
5513 // Same as above but for STW paths
5514 void CMSCollector::reset_stw() {
5515 // already have the lock
5516 assert(_collectorState == Resetting, "just checking");
5517 assert_lock_strong(bitMapLock());
5518 GCIdMarkAndRestore gc_id_mark(_cmsThread->gc_id());
5519 _markBitMap.clear_all();
5520 _collectorState = Idling;
5521 register_gc_end();
5522 }
5523
5524 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5525 GCTraceCPUTime tcpu;
5526 TraceCollectorStats tcs(counters());
5527
5528 switch (op) {
5529 case CMS_op_checkpointRootsInitial: {
5530 GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5531 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5532 checkpointRootsInitial();
5533 break;
5534 }
5535 case CMS_op_checkpointRootsFinal: {
5536 GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5537 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5538 checkpointRootsFinal();
5539 break;
5540 }
5541 default:
5542 fatal("No such CMS_op");
5543 }
5544 }
5545
5546 #ifndef PRODUCT
5547 size_t const CMSCollector::skip_header_HeapWords() {
5548 return FreeChunk::header_size();
5549 }
5550
5551 // Try and collect here conditions that should hold when
5552 // CMS thread is exiting. The idea is that the foreground GC
5553 // thread should not be blocked if it wants to terminate
5554 // the CMS thread and yet continue to run the VM for a while
5555 // after that.
5556 void CMSCollector::verify_ok_to_terminate() const {
5557 assert(Thread::current()->is_ConcurrentGC_thread(),
5558 "should be called by CMS thread");
5559 assert(!_foregroundGCShouldWait, "should be false");
5560 // We could check here that all the various low-level locks
5561 // are not held by the CMS thread, but that is overkill; see
5562 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5563 // is checked.
5564 }
5565 #endif
5566
5567 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5568 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5569 "missing Printezis mark?");
5570 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5571 size_t size = pointer_delta(nextOneAddr + 1, addr);
5572 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5573 "alignment problem");
5574 assert(size >= 3, "Necessary for Printezis marks to work");
5575 return size;
5576 }
5577
5578 // A variant of the above (block_size_using_printezis_bits()) except
5579 // that we return 0 if the P-bits are not yet set.
5580 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5581 if (_markBitMap.isMarked(addr + 1)) {
5582 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5583 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5584 size_t size = pointer_delta(nextOneAddr + 1, addr);
5585 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5586 "alignment problem");
5587 assert(size >= 3, "Necessary for Printezis marks to work");
5588 return size;
5589 }
5590 return 0;
5591 }
5592
5593 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5594 size_t sz = 0;
5595 oop p = (oop)addr;
5596 if (p->klass_or_null() != NULL) {
5597 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5598 } else {
5599 sz = block_size_using_printezis_bits(addr);
5600 }
5601 assert(sz > 0, "size must be nonzero");
5602 HeapWord* next_block = addr + sz;
5603 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
5604 CardTableModRefBS::card_size);
5605 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
5606 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5607 "must be different cards");
5608 return next_card;
5609 }
5610
5611
5612 // CMS Bit Map Wrapper /////////////////////////////////////////
5613
5614 // Construct a CMS bit map infrastructure, but don't create the
5615 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5616 // further below.
5617 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5618 _bm(),
5619 _shifter(shifter),
5620 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5621 Monitor::_safepoint_check_sometimes) : NULL)
5622 {
5623 _bmStartWord = 0;
5624 _bmWordSize = 0;
5625 }
5626
5627 bool CMSBitMap::allocate(MemRegion mr) {
5628 _bmStartWord = mr.start();
5629 _bmWordSize = mr.word_size();
5630 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5631 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5632 if (!brs.is_reserved()) {
5633 warning("CMS bit map allocation failure");
5634 return false;
5635 }
5636 // For now we'll just commit all of the bit map up front.
5637 // Later on we'll try to be more parsimonious with swap.
5638 if (!_virtual_space.initialize(brs, brs.size())) {
5639 warning("CMS bit map backing store failure");
5640 return false;
5641 }
5642 assert(_virtual_space.committed_size() == brs.size(),
5643 "didn't reserve backing store for all of CMS bit map?");
5644 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5645 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5646 _bmWordSize, "inconsistency in bit map sizing");
5647 _bm.set_size(_bmWordSize >> _shifter);
5648
5649 // bm.clear(); // can we rely on getting zero'd memory? verify below
5650 assert(isAllClear(),
5651 "Expected zero'd memory from ReservedSpace constructor");
5652 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5653 "consistency check");
5654 return true;
5655 }
5656
5657 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5658 HeapWord *next_addr, *end_addr, *last_addr;
5659 assert_locked();
5660 assert(covers(mr), "out-of-range error");
5661 // XXX assert that start and end are appropriately aligned
5662 for (next_addr = mr.start(), end_addr = mr.end();
5663 next_addr < end_addr; next_addr = last_addr) {
5664 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5665 last_addr = dirty_region.end();
5666 if (!dirty_region.is_empty()) {
5667 cl->do_MemRegion(dirty_region);
5668 } else {
5669 assert(last_addr == end_addr, "program logic");
5670 return;
5671 }
5672 }
5673 }
5674
5675 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5676 _bm.print_on_error(st, prefix);
5677 }
5678
5679 #ifndef PRODUCT
5680 void CMSBitMap::assert_locked() const {
5681 CMSLockVerifier::assert_locked(lock());
5682 }
5683
5684 bool CMSBitMap::covers(MemRegion mr) const {
5685 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5686 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5687 "size inconsistency");
5688 return (mr.start() >= _bmStartWord) &&
5689 (mr.end() <= endWord());
5690 }
5691
5692 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5693 return (start >= _bmStartWord && (start + size) <= endWord());
5694 }
5695
5696 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5697 // verify that there are no 1 bits in the interval [left, right)
5698 FalseBitMapClosure falseBitMapClosure;
5699 iterate(&falseBitMapClosure, left, right);
5700 }
5701
5702 void CMSBitMap::region_invariant(MemRegion mr)
5703 {
5704 assert_locked();
5705 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5706 assert(!mr.is_empty(), "unexpected empty region");
5707 assert(covers(mr), "mr should be covered by bit map");
5708 // convert address range into offset range
5709 size_t start_ofs = heapWordToOffset(mr.start());
5710 // Make sure that end() is appropriately aligned
5711 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5712 (1 << (_shifter+LogHeapWordSize))),
5713 "Misaligned mr.end()");
5714 size_t end_ofs = heapWordToOffset(mr.end());
5715 assert(end_ofs > start_ofs, "Should mark at least one bit");
5716 }
5717
5718 #endif
5719
5720 bool CMSMarkStack::allocate(size_t size) {
5721 // allocate a stack of the requisite depth
5722 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5723 size * sizeof(oop)));
5724 if (!rs.is_reserved()) {
5725 warning("CMSMarkStack allocation failure");
5726 return false;
5727 }
5728 if (!_virtual_space.initialize(rs, rs.size())) {
5729 warning("CMSMarkStack backing store failure");
5730 return false;
5731 }
5732 assert(_virtual_space.committed_size() == rs.size(),
5733 "didn't reserve backing store for all of CMS stack?");
5734 _base = (oop*)(_virtual_space.low());
5735 _index = 0;
5736 _capacity = size;
5737 NOT_PRODUCT(_max_depth = 0);
5738 return true;
5739 }
5740
5741 // XXX FIX ME !!! In the MT case we come in here holding a
5742 // leaf lock. For printing we need to take a further lock
5743 // which has lower rank. We need to recalibrate the two
5744 // lock-ranks involved in order to be able to print the
5745 // messages below. (Or defer the printing to the caller.
5746 // For now we take the expedient path of just disabling the
5747 // messages for the problematic case.)
5748 void CMSMarkStack::expand() {
5749 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5750 if (_capacity == MarkStackSizeMax) {
5751 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5752 // We print a warning message only once per CMS cycle.
5753 log_debug(gc, conc)(" (benign) Hit CMSMarkStack max size limit");
5754 }
5755 return;
5756 }
5757 // Double capacity if possible
5758 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5759 // Do not give up existing stack until we have managed to
5760 // get the double capacity that we desired.
5761 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5762 new_capacity * sizeof(oop)));
5763 if (rs.is_reserved()) {
5764 // Release the backing store associated with old stack
5765 _virtual_space.release();
5766 // Reinitialize virtual space for new stack
5767 if (!_virtual_space.initialize(rs, rs.size())) {
5768 fatal("Not enough swap for expanded marking stack");
5769 }
5770 _base = (oop*)(_virtual_space.low());
5771 _index = 0;
5772 _capacity = new_capacity;
5773 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5774 // Failed to double capacity, continue;
5775 // we print a detail message only once per CMS cycle.
5776 log_debug(gc, conc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5777 _capacity / K, new_capacity / K);
5778 }
5779 }
5780
5781
5782 // Closures
5783 // XXX: there seems to be a lot of code duplication here;
5784 // should refactor and consolidate common code.
5785
5786 // This closure is used to mark refs into the CMS generation in
5787 // the CMS bit map. Called at the first checkpoint. This closure
5788 // assumes that we do not need to re-mark dirty cards; if the CMS
5789 // generation on which this is used is not an oldest
5790 // generation then this will lose younger_gen cards!
5791
5792 MarkRefsIntoClosure::MarkRefsIntoClosure(
5793 MemRegion span, CMSBitMap* bitMap):
5794 _span(span),
5795 _bitMap(bitMap)
5796 {
5797 assert(ref_processor() == NULL, "deliberately left NULL");
5798 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5799 }
5800
5801 void MarkRefsIntoClosure::do_oop(oop obj) {
5802 // if p points into _span, then mark corresponding bit in _markBitMap
5803 assert(obj->is_oop(), "expected an oop");
5804 HeapWord* addr = (HeapWord*)obj;
5805 if (_span.contains(addr)) {
5806 // this should be made more efficient
5807 _bitMap->mark(addr);
5808 }
5809 }
5810
5811 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5812 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5813
5814 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
5815 MemRegion span, CMSBitMap* bitMap):
5816 _span(span),
5817 _bitMap(bitMap)
5818 {
5819 assert(ref_processor() == NULL, "deliberately left NULL");
5820 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5821 }
5822
5823 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
5824 // if p points into _span, then mark corresponding bit in _markBitMap
5825 assert(obj->is_oop(), "expected an oop");
5826 HeapWord* addr = (HeapWord*)obj;
5827 if (_span.contains(addr)) {
5828 // this should be made more efficient
5829 _bitMap->par_mark(addr);
5830 }
5831 }
5832
5833 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
5834 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
5835
5836 // A variant of the above, used for CMS marking verification.
5837 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5838 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5839 _span(span),
5840 _verification_bm(verification_bm),
5841 _cms_bm(cms_bm)
5842 {
5843 assert(ref_processor() == NULL, "deliberately left NULL");
5844 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5845 }
5846
5847 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5848 // if p points into _span, then mark corresponding bit in _markBitMap
5849 assert(obj->is_oop(), "expected an oop");
5850 HeapWord* addr = (HeapWord*)obj;
5851 if (_span.contains(addr)) {
5852 _verification_bm->mark(addr);
5853 if (!_cms_bm->isMarked(addr)) {
5854 LogHandle(gc, verify) log;
5855 ResourceMark rm;
5856 oop(addr)->print_on(log.info_stream());
5857 log.info(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5858 fatal("... aborting");
5859 }
5860 }
5861 }
5862
5863 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5864 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5865
5866 //////////////////////////////////////////////////
5867 // MarkRefsIntoAndScanClosure
5868 //////////////////////////////////////////////////
5869
5870 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5871 ReferenceProcessor* rp,
5872 CMSBitMap* bit_map,
5873 CMSBitMap* mod_union_table,
5874 CMSMarkStack* mark_stack,
5875 CMSCollector* collector,
5876 bool should_yield,
5877 bool concurrent_precleaning):
5878 _collector(collector),
5879 _span(span),
5880 _bit_map(bit_map),
5881 _mark_stack(mark_stack),
5882 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
5883 mark_stack, concurrent_precleaning),
5884 _yield(should_yield),
5885 _concurrent_precleaning(concurrent_precleaning),
5886 _freelistLock(NULL)
5887 {
5888 // FIXME: Should initialize in base class constructor.
5889 assert(rp != NULL, "ref_processor shouldn't be NULL");
5890 set_ref_processor_internal(rp);
5891 }
5892
5893 // This closure is used to mark refs into the CMS generation at the
5894 // second (final) checkpoint, and to scan and transitively follow
5895 // the unmarked oops. It is also used during the concurrent precleaning
5896 // phase while scanning objects on dirty cards in the CMS generation.
5897 // The marks are made in the marking bit map and the marking stack is
5898 // used for keeping the (newly) grey objects during the scan.
5899 // The parallel version (Par_...) appears further below.
5900 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5901 if (obj != NULL) {
5902 assert(obj->is_oop(), "expected an oop");
5903 HeapWord* addr = (HeapWord*)obj;
5904 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5905 assert(_collector->overflow_list_is_empty(),
5906 "overflow list should be empty");
5907 if (_span.contains(addr) &&
5908 !_bit_map->isMarked(addr)) {
5909 // mark bit map (object is now grey)
5910 _bit_map->mark(addr);
5911 // push on marking stack (stack should be empty), and drain the
5912 // stack by applying this closure to the oops in the oops popped
5913 // from the stack (i.e. blacken the grey objects)
5914 bool res = _mark_stack->push(obj);
5915 assert(res, "Should have space to push on empty stack");
5916 do {
5917 oop new_oop = _mark_stack->pop();
5918 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
5919 assert(_bit_map->isMarked((HeapWord*)new_oop),
5920 "only grey objects on this stack");
5921 // iterate over the oops in this oop, marking and pushing
5922 // the ones in CMS heap (i.e. in _span).
5923 new_oop->oop_iterate(&_pushAndMarkClosure);
5924 // check if it's time to yield
5925 do_yield_check();
5926 } while (!_mark_stack->isEmpty() ||
5927 (!_concurrent_precleaning && take_from_overflow_list()));
5928 // if marking stack is empty, and we are not doing this
5929 // during precleaning, then check the overflow list
5930 }
5931 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5932 assert(_collector->overflow_list_is_empty(),
5933 "overflow list was drained above");
5934
5935 assert(_collector->no_preserved_marks(),
5936 "All preserved marks should have been restored above");
5937 }
5938 }
5939
5940 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5941 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5942
5943 void MarkRefsIntoAndScanClosure::do_yield_work() {
5944 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5945 "CMS thread should hold CMS token");
5946 assert_lock_strong(_freelistLock);
5947 assert_lock_strong(_bit_map->lock());
5948 // relinquish the free_list_lock and bitMaplock()
5949 _bit_map->lock()->unlock();
5950 _freelistLock->unlock();
5951 ConcurrentMarkSweepThread::desynchronize(true);
5952 _collector->stopTimer();
5953 _collector->incrementYields();
5954
5955 // See the comment in coordinator_yield()
5956 for (unsigned i = 0;
5957 i < CMSYieldSleepCount &&
5958 ConcurrentMarkSweepThread::should_yield() &&
5959 !CMSCollector::foregroundGCIsActive();
5960 ++i) {
5961 os::sleep(Thread::current(), 1, false);
5962 }
5963
5964 ConcurrentMarkSweepThread::synchronize(true);
5965 _freelistLock->lock_without_safepoint_check();
5966 _bit_map->lock()->lock_without_safepoint_check();
5967 _collector->startTimer();
5968 }
5969
5970 ///////////////////////////////////////////////////////////
5971 // Par_MarkRefsIntoAndScanClosure: a parallel version of
5972 // MarkRefsIntoAndScanClosure
5973 ///////////////////////////////////////////////////////////
5974 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
5975 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
5976 CMSBitMap* bit_map, OopTaskQueue* work_queue):
5977 _span(span),
5978 _bit_map(bit_map),
5979 _work_queue(work_queue),
5980 _low_water_mark(MIN2((work_queue->max_elems()/4),
5981 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
5982 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
5983 {
5984 // FIXME: Should initialize in base class constructor.
5985 assert(rp != NULL, "ref_processor shouldn't be NULL");
5986 set_ref_processor_internal(rp);
5987 }
5988
5989 // This closure is used to mark refs into the CMS generation at the
5990 // second (final) checkpoint, and to scan and transitively follow
5991 // the unmarked oops. The marks are made in the marking bit map and
5992 // the work_queue is used for keeping the (newly) grey objects during
5993 // the scan phase whence they are also available for stealing by parallel
5994 // threads. Since the marking bit map is shared, updates are
5995 // synchronized (via CAS).
5996 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5997 if (obj != NULL) {
5998 // Ignore mark word because this could be an already marked oop
5999 // that may be chained at the end of the overflow list.
6000 assert(obj->is_oop(true), "expected an oop");
6001 HeapWord* addr = (HeapWord*)obj;
6002 if (_span.contains(addr) &&
6003 !_bit_map->isMarked(addr)) {
6004 // mark bit map (object will become grey):
6005 // It is possible for several threads to be
6006 // trying to "claim" this object concurrently;
6007 // the unique thread that succeeds in marking the
6008 // object first will do the subsequent push on
6009 // to the work queue (or overflow list).
6010 if (_bit_map->par_mark(addr)) {
6011 // push on work_queue (which may not be empty), and trim the
6012 // queue to an appropriate length by applying this closure to
6013 // the oops in the oops popped from the stack (i.e. blacken the
6014 // grey objects)
6015 bool res = _work_queue->push(obj);
6016 assert(res, "Low water mark should be less than capacity?");
6017 trim_queue(_low_water_mark);
6018 } // Else, another thread claimed the object
6019 }
6020 }
6021 }
6022
6023 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6024 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6025
6026 // This closure is used to rescan the marked objects on the dirty cards
6027 // in the mod union table and the card table proper.
6028 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6029 oop p, MemRegion mr) {
6030
6031 size_t size = 0;
6032 HeapWord* addr = (HeapWord*)p;
6033 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6034 assert(_span.contains(addr), "we are scanning the CMS generation");
6035 // check if it's time to yield
6036 if (do_yield_check()) {
6037 // We yielded for some foreground stop-world work,
6038 // and we have been asked to abort this ongoing preclean cycle.
6039 return 0;
6040 }
6041 if (_bitMap->isMarked(addr)) {
6042 // it's marked; is it potentially uninitialized?
6043 if (p->klass_or_null() != NULL) {
6044 // an initialized object; ignore mark word in verification below
6045 // since we are running concurrent with mutators
6046 assert(p->is_oop(true), "should be an oop");
6047 if (p->is_objArray()) {
6048 // objArrays are precisely marked; restrict scanning
6049 // to dirty cards only.
6050 size = CompactibleFreeListSpace::adjustObjectSize(
6051 p->oop_iterate_size(_scanningClosure, mr));
6052 } else {
6053 // A non-array may have been imprecisely marked; we need
6054 // to scan object in its entirety.
6055 size = CompactibleFreeListSpace::adjustObjectSize(
6056 p->oop_iterate_size(_scanningClosure));
6057 }
6058 #ifdef ASSERT
6059 size_t direct_size =
6060 CompactibleFreeListSpace::adjustObjectSize(p->size());
6061 assert(size == direct_size, "Inconsistency in size");
6062 assert(size >= 3, "Necessary for Printezis marks to work");
6063 if (!_bitMap->isMarked(addr+1)) {
6064 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6065 } else {
6066 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6067 assert(_bitMap->isMarked(addr+size-1),
6068 "inconsistent Printezis mark");
6069 }
6070 #endif // ASSERT
6071 } else {
6072 // An uninitialized object.
6073 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6074 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6075 size = pointer_delta(nextOneAddr + 1, addr);
6076 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6077 "alignment problem");
6078 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6079 // will dirty the card when the klass pointer is installed in the
6080 // object (signaling the completion of initialization).
6081 }
6082 } else {
6083 // Either a not yet marked object or an uninitialized object
6084 if (p->klass_or_null() == NULL) {
6085 // An uninitialized object, skip to the next card, since
6086 // we may not be able to read its P-bits yet.
6087 assert(size == 0, "Initial value");
6088 } else {
6089 // An object not (yet) reached by marking: we merely need to
6090 // compute its size so as to go look at the next block.
6091 assert(p->is_oop(true), "should be an oop");
6092 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6093 }
6094 }
6095 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6096 return size;
6097 }
6098
6099 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6100 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6101 "CMS thread should hold CMS token");
6102 assert_lock_strong(_freelistLock);
6103 assert_lock_strong(_bitMap->lock());
6104 // relinquish the free_list_lock and bitMaplock()
6105 _bitMap->lock()->unlock();
6106 _freelistLock->unlock();
6107 ConcurrentMarkSweepThread::desynchronize(true);
6108 _collector->stopTimer();
6109 _collector->incrementYields();
6110
6111 // See the comment in coordinator_yield()
6112 for (unsigned i = 0; i < CMSYieldSleepCount &&
6113 ConcurrentMarkSweepThread::should_yield() &&
6114 !CMSCollector::foregroundGCIsActive(); ++i) {
6115 os::sleep(Thread::current(), 1, false);
6116 }
6117
6118 ConcurrentMarkSweepThread::synchronize(true);
6119 _freelistLock->lock_without_safepoint_check();
6120 _bitMap->lock()->lock_without_safepoint_check();
6121 _collector->startTimer();
6122 }
6123
6124
6125 //////////////////////////////////////////////////////////////////
6126 // SurvivorSpacePrecleanClosure
6127 //////////////////////////////////////////////////////////////////
6128 // This (single-threaded) closure is used to preclean the oops in
6129 // the survivor spaces.
6130 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6131
6132 HeapWord* addr = (HeapWord*)p;
6133 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6134 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6135 assert(p->klass_or_null() != NULL, "object should be initialized");
6136 // an initialized object; ignore mark word in verification below
6137 // since we are running concurrent with mutators
6138 assert(p->is_oop(true), "should be an oop");
6139 // Note that we do not yield while we iterate over
6140 // the interior oops of p, pushing the relevant ones
6141 // on our marking stack.
6142 size_t size = p->oop_iterate_size(_scanning_closure);
6143 do_yield_check();
6144 // Observe that below, we do not abandon the preclean
6145 // phase as soon as we should; rather we empty the
6146 // marking stack before returning. This is to satisfy
6147 // some existing assertions. In general, it may be a
6148 // good idea to abort immediately and complete the marking
6149 // from the grey objects at a later time.
6150 while (!_mark_stack->isEmpty()) {
6151 oop new_oop = _mark_stack->pop();
6152 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6153 assert(_bit_map->isMarked((HeapWord*)new_oop),
6154 "only grey objects on this stack");
6155 // iterate over the oops in this oop, marking and pushing
6156 // the ones in CMS heap (i.e. in _span).
6157 new_oop->oop_iterate(_scanning_closure);
6158 // check if it's time to yield
6159 do_yield_check();
6160 }
6161 unsigned int after_count =
6162 GenCollectedHeap::heap()->total_collections();
6163 bool abort = (_before_count != after_count) ||
6164 _collector->should_abort_preclean();
6165 return abort ? 0 : size;
6166 }
6167
6168 void SurvivorSpacePrecleanClosure::do_yield_work() {
6169 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6170 "CMS thread should hold CMS token");
6171 assert_lock_strong(_bit_map->lock());
6172 // Relinquish the bit map lock
6173 _bit_map->lock()->unlock();
6174 ConcurrentMarkSweepThread::desynchronize(true);
6175 _collector->stopTimer();
6176 _collector->incrementYields();
6177
6178 // See the comment in coordinator_yield()
6179 for (unsigned i = 0; i < CMSYieldSleepCount &&
6180 ConcurrentMarkSweepThread::should_yield() &&
6181 !CMSCollector::foregroundGCIsActive(); ++i) {
6182 os::sleep(Thread::current(), 1, false);
6183 }
6184
6185 ConcurrentMarkSweepThread::synchronize(true);
6186 _bit_map->lock()->lock_without_safepoint_check();
6187 _collector->startTimer();
6188 }
6189
6190 // This closure is used to rescan the marked objects on the dirty cards
6191 // in the mod union table and the card table proper. In the parallel
6192 // case, although the bitMap is shared, we do a single read so the
6193 // isMarked() query is "safe".
6194 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6195 // Ignore mark word because we are running concurrent with mutators
6196 assert(p->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6197 HeapWord* addr = (HeapWord*)p;
6198 assert(_span.contains(addr), "we are scanning the CMS generation");
6199 bool is_obj_array = false;
6200 #ifdef ASSERT
6201 if (!_parallel) {
6202 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6203 assert(_collector->overflow_list_is_empty(),
6204 "overflow list should be empty");
6205
6206 }
6207 #endif // ASSERT
6208 if (_bit_map->isMarked(addr)) {
6209 // Obj arrays are precisely marked, non-arrays are not;
6210 // so we scan objArrays precisely and non-arrays in their
6211 // entirety.
6212 if (p->is_objArray()) {
6213 is_obj_array = true;
6214 if (_parallel) {
6215 p->oop_iterate(_par_scan_closure, mr);
6216 } else {
6217 p->oop_iterate(_scan_closure, mr);
6218 }
6219 } else {
6220 if (_parallel) {
6221 p->oop_iterate(_par_scan_closure);
6222 } else {
6223 p->oop_iterate(_scan_closure);
6224 }
6225 }
6226 }
6227 #ifdef ASSERT
6228 if (!_parallel) {
6229 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6230 assert(_collector->overflow_list_is_empty(),
6231 "overflow list should be empty");
6232
6233 }
6234 #endif // ASSERT
6235 return is_obj_array;
6236 }
6237
6238 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6239 MemRegion span,
6240 CMSBitMap* bitMap, CMSMarkStack* markStack,
6241 bool should_yield, bool verifying):
6242 _collector(collector),
6243 _span(span),
6244 _bitMap(bitMap),
6245 _mut(&collector->_modUnionTable),
6246 _markStack(markStack),
6247 _yield(should_yield),
6248 _skipBits(0)
6249 {
6250 assert(_markStack->isEmpty(), "stack should be empty");
6251 _finger = _bitMap->startWord();
6252 _threshold = _finger;
6253 assert(_collector->_restart_addr == NULL, "Sanity check");
6254 assert(_span.contains(_finger), "Out of bounds _finger?");
6255 DEBUG_ONLY(_verifying = verifying;)
6256 }
6257
6258 void MarkFromRootsClosure::reset(HeapWord* addr) {
6259 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6260 assert(_span.contains(addr), "Out of bounds _finger?");
6261 _finger = addr;
6262 _threshold = (HeapWord*)round_to(
6263 (intptr_t)_finger, CardTableModRefBS::card_size);
6264 }
6265
6266 // Should revisit to see if this should be restructured for
6267 // greater efficiency.
6268 bool MarkFromRootsClosure::do_bit(size_t offset) {
6269 if (_skipBits > 0) {
6270 _skipBits--;
6271 return true;
6272 }
6273 // convert offset into a HeapWord*
6274 HeapWord* addr = _bitMap->startWord() + offset;
6275 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6276 "address out of range");
6277 assert(_bitMap->isMarked(addr), "tautology");
6278 if (_bitMap->isMarked(addr+1)) {
6279 // this is an allocated but not yet initialized object
6280 assert(_skipBits == 0, "tautology");
6281 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6282 oop p = oop(addr);
6283 if (p->klass_or_null() == NULL) {
6284 DEBUG_ONLY(if (!_verifying) {)
6285 // We re-dirty the cards on which this object lies and increase
6286 // the _threshold so that we'll come back to scan this object
6287 // during the preclean or remark phase. (CMSCleanOnEnter)
6288 if (CMSCleanOnEnter) {
6289 size_t sz = _collector->block_size_using_printezis_bits(addr);
6290 HeapWord* end_card_addr = (HeapWord*)round_to(
6291 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6292 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6293 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6294 // Bump _threshold to end_card_addr; note that
6295 // _threshold cannot possibly exceed end_card_addr, anyhow.
6296 // This prevents future clearing of the card as the scan proceeds
6297 // to the right.
6298 assert(_threshold <= end_card_addr,
6299 "Because we are just scanning into this object");
6300 if (_threshold < end_card_addr) {
6301 _threshold = end_card_addr;
6302 }
6303 if (p->klass_or_null() != NULL) {
6304 // Redirty the range of cards...
6305 _mut->mark_range(redirty_range);
6306 } // ...else the setting of klass will dirty the card anyway.
6307 }
6308 DEBUG_ONLY(})
6309 return true;
6310 }
6311 }
6312 scanOopsInOop(addr);
6313 return true;
6314 }
6315
6316 // We take a break if we've been at this for a while,
6317 // so as to avoid monopolizing the locks involved.
6318 void MarkFromRootsClosure::do_yield_work() {
6319 // First give up the locks, then yield, then re-lock
6320 // We should probably use a constructor/destructor idiom to
6321 // do this unlock/lock or modify the MutexUnlocker class to
6322 // serve our purpose. XXX
6323 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6324 "CMS thread should hold CMS token");
6325 assert_lock_strong(_bitMap->lock());
6326 _bitMap->lock()->unlock();
6327 ConcurrentMarkSweepThread::desynchronize(true);
6328 _collector->stopTimer();
6329 _collector->incrementYields();
6330
6331 // See the comment in coordinator_yield()
6332 for (unsigned i = 0; i < CMSYieldSleepCount &&
6333 ConcurrentMarkSweepThread::should_yield() &&
6334 !CMSCollector::foregroundGCIsActive(); ++i) {
6335 os::sleep(Thread::current(), 1, false);
6336 }
6337
6338 ConcurrentMarkSweepThread::synchronize(true);
6339 _bitMap->lock()->lock_without_safepoint_check();
6340 _collector->startTimer();
6341 }
6342
6343 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6344 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6345 assert(_markStack->isEmpty(),
6346 "should drain stack to limit stack usage");
6347 // convert ptr to an oop preparatory to scanning
6348 oop obj = oop(ptr);
6349 // Ignore mark word in verification below, since we
6350 // may be running concurrent with mutators.
6351 assert(obj->is_oop(true), "should be an oop");
6352 assert(_finger <= ptr, "_finger runneth ahead");
6353 // advance the finger to right end of this object
6354 _finger = ptr + obj->size();
6355 assert(_finger > ptr, "we just incremented it above");
6356 // On large heaps, it may take us some time to get through
6357 // the marking phase. During
6358 // this time it's possible that a lot of mutations have
6359 // accumulated in the card table and the mod union table --
6360 // these mutation records are redundant until we have
6361 // actually traced into the corresponding card.
6362 // Here, we check whether advancing the finger would make
6363 // us cross into a new card, and if so clear corresponding
6364 // cards in the MUT (preclean them in the card-table in the
6365 // future).
6366
6367 DEBUG_ONLY(if (!_verifying) {)
6368 // The clean-on-enter optimization is disabled by default,
6369 // until we fix 6178663.
6370 if (CMSCleanOnEnter && (_finger > _threshold)) {
6371 // [_threshold, _finger) represents the interval
6372 // of cards to be cleared in MUT (or precleaned in card table).
6373 // The set of cards to be cleared is all those that overlap
6374 // with the interval [_threshold, _finger); note that
6375 // _threshold is always kept card-aligned but _finger isn't
6376 // always card-aligned.
6377 HeapWord* old_threshold = _threshold;
6378 assert(old_threshold == (HeapWord*)round_to(
6379 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6380 "_threshold should always be card-aligned");
6381 _threshold = (HeapWord*)round_to(
6382 (intptr_t)_finger, CardTableModRefBS::card_size);
6383 MemRegion mr(old_threshold, _threshold);
6384 assert(!mr.is_empty(), "Control point invariant");
6385 assert(_span.contains(mr), "Should clear within span");
6386 _mut->clear_range(mr);
6387 }
6388 DEBUG_ONLY(})
6389 // Note: the finger doesn't advance while we drain
6390 // the stack below.
6391 PushOrMarkClosure pushOrMarkClosure(_collector,
6392 _span, _bitMap, _markStack,
6393 _finger, this);
6394 bool res = _markStack->push(obj);
6395 assert(res, "Empty non-zero size stack should have space for single push");
6396 while (!_markStack->isEmpty()) {
6397 oop new_oop = _markStack->pop();
6398 // Skip verifying header mark word below because we are
6399 // running concurrent with mutators.
6400 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6401 // now scan this oop's oops
6402 new_oop->oop_iterate(&pushOrMarkClosure);
6403 do_yield_check();
6404 }
6405 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6406 }
6407
6408 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6409 CMSCollector* collector, MemRegion span,
6410 CMSBitMap* bit_map,
6411 OopTaskQueue* work_queue,
6412 CMSMarkStack* overflow_stack):
6413 _collector(collector),
6414 _whole_span(collector->_span),
6415 _span(span),
6416 _bit_map(bit_map),
6417 _mut(&collector->_modUnionTable),
6418 _work_queue(work_queue),
6419 _overflow_stack(overflow_stack),
6420 _skip_bits(0),
6421 _task(task)
6422 {
6423 assert(_work_queue->size() == 0, "work_queue should be empty");
6424 _finger = span.start();
6425 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6426 assert(_span.contains(_finger), "Out of bounds _finger?");
6427 }
6428
6429 // Should revisit to see if this should be restructured for
6430 // greater efficiency.
6431 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6432 if (_skip_bits > 0) {
6433 _skip_bits--;
6434 return true;
6435 }
6436 // convert offset into a HeapWord*
6437 HeapWord* addr = _bit_map->startWord() + offset;
6438 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6439 "address out of range");
6440 assert(_bit_map->isMarked(addr), "tautology");
6441 if (_bit_map->isMarked(addr+1)) {
6442 // this is an allocated object that might not yet be initialized
6443 assert(_skip_bits == 0, "tautology");
6444 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6445 oop p = oop(addr);
6446 if (p->klass_or_null() == NULL) {
6447 // in the case of Clean-on-Enter optimization, redirty card
6448 // and avoid clearing card by increasing the threshold.
6449 return true;
6450 }
6451 }
6452 scan_oops_in_oop(addr);
6453 return true;
6454 }
6455
6456 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6457 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6458 // Should we assert that our work queue is empty or
6459 // below some drain limit?
6460 assert(_work_queue->size() == 0,
6461 "should drain stack to limit stack usage");
6462 // convert ptr to an oop preparatory to scanning
6463 oop obj = oop(ptr);
6464 // Ignore mark word in verification below, since we
6465 // may be running concurrent with mutators.
6466 assert(obj->is_oop(true), "should be an oop");
6467 assert(_finger <= ptr, "_finger runneth ahead");
6468 // advance the finger to right end of this object
6469 _finger = ptr + obj->size();
6470 assert(_finger > ptr, "we just incremented it above");
6471 // On large heaps, it may take us some time to get through
6472 // the marking phase. During
6473 // this time it's possible that a lot of mutations have
6474 // accumulated in the card table and the mod union table --
6475 // these mutation records are redundant until we have
6476 // actually traced into the corresponding card.
6477 // Here, we check whether advancing the finger would make
6478 // us cross into a new card, and if so clear corresponding
6479 // cards in the MUT (preclean them in the card-table in the
6480 // future).
6481
6482 // The clean-on-enter optimization is disabled by default,
6483 // until we fix 6178663.
6484 if (CMSCleanOnEnter && (_finger > _threshold)) {
6485 // [_threshold, _finger) represents the interval
6486 // of cards to be cleared in MUT (or precleaned in card table).
6487 // The set of cards to be cleared is all those that overlap
6488 // with the interval [_threshold, _finger); note that
6489 // _threshold is always kept card-aligned but _finger isn't
6490 // always card-aligned.
6491 HeapWord* old_threshold = _threshold;
6492 assert(old_threshold == (HeapWord*)round_to(
6493 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6494 "_threshold should always be card-aligned");
6495 _threshold = (HeapWord*)round_to(
6496 (intptr_t)_finger, CardTableModRefBS::card_size);
6497 MemRegion mr(old_threshold, _threshold);
6498 assert(!mr.is_empty(), "Control point invariant");
6499 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6500 _mut->clear_range(mr);
6501 }
6502
6503 // Note: the local finger doesn't advance while we drain
6504 // the stack below, but the global finger sure can and will.
6505 HeapWord** gfa = _task->global_finger_addr();
6506 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6507 _span, _bit_map,
6508 _work_queue,
6509 _overflow_stack,
6510 _finger,
6511 gfa, this);
6512 bool res = _work_queue->push(obj); // overflow could occur here
6513 assert(res, "Will hold once we use workqueues");
6514 while (true) {
6515 oop new_oop;
6516 if (!_work_queue->pop_local(new_oop)) {
6517 // We emptied our work_queue; check if there's stuff that can
6518 // be gotten from the overflow stack.
6519 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6520 _overflow_stack, _work_queue)) {
6521 do_yield_check();
6522 continue;
6523 } else { // done
6524 break;
6525 }
6526 }
6527 // Skip verifying header mark word below because we are
6528 // running concurrent with mutators.
6529 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6530 // now scan this oop's oops
6531 new_oop->oop_iterate(&pushOrMarkClosure);
6532 do_yield_check();
6533 }
6534 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6535 }
6536
6537 // Yield in response to a request from VM Thread or
6538 // from mutators.
6539 void Par_MarkFromRootsClosure::do_yield_work() {
6540 assert(_task != NULL, "sanity");
6541 _task->yield();
6542 }
6543
6544 // A variant of the above used for verifying CMS marking work.
6545 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6546 MemRegion span,
6547 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6548 CMSMarkStack* mark_stack):
6549 _collector(collector),
6550 _span(span),
6551 _verification_bm(verification_bm),
6552 _cms_bm(cms_bm),
6553 _mark_stack(mark_stack),
6554 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6555 mark_stack)
6556 {
6557 assert(_mark_stack->isEmpty(), "stack should be empty");
6558 _finger = _verification_bm->startWord();
6559 assert(_collector->_restart_addr == NULL, "Sanity check");
6560 assert(_span.contains(_finger), "Out of bounds _finger?");
6561 }
6562
6563 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6564 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6565 assert(_span.contains(addr), "Out of bounds _finger?");
6566 _finger = addr;
6567 }
6568
6569 // Should revisit to see if this should be restructured for
6570 // greater efficiency.
6571 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6572 // convert offset into a HeapWord*
6573 HeapWord* addr = _verification_bm->startWord() + offset;
6574 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6575 "address out of range");
6576 assert(_verification_bm->isMarked(addr), "tautology");
6577 assert(_cms_bm->isMarked(addr), "tautology");
6578
6579 assert(_mark_stack->isEmpty(),
6580 "should drain stack to limit stack usage");
6581 // convert addr to an oop preparatory to scanning
6582 oop obj = oop(addr);
6583 assert(obj->is_oop(), "should be an oop");
6584 assert(_finger <= addr, "_finger runneth ahead");
6585 // advance the finger to right end of this object
6586 _finger = addr + obj->size();
6587 assert(_finger > addr, "we just incremented it above");
6588 // Note: the finger doesn't advance while we drain
6589 // the stack below.
6590 bool res = _mark_stack->push(obj);
6591 assert(res, "Empty non-zero size stack should have space for single push");
6592 while (!_mark_stack->isEmpty()) {
6593 oop new_oop = _mark_stack->pop();
6594 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6595 // now scan this oop's oops
6596 new_oop->oop_iterate(&_pam_verify_closure);
6597 }
6598 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6599 return true;
6600 }
6601
6602 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6603 CMSCollector* collector, MemRegion span,
6604 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6605 CMSMarkStack* mark_stack):
6606 MetadataAwareOopClosure(collector->ref_processor()),
6607 _collector(collector),
6608 _span(span),
6609 _verification_bm(verification_bm),
6610 _cms_bm(cms_bm),
6611 _mark_stack(mark_stack)
6612 { }
6613
6614 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6615 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6616
6617 // Upon stack overflow, we discard (part of) the stack,
6618 // remembering the least address amongst those discarded
6619 // in CMSCollector's _restart_address.
6620 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6621 // Remember the least grey address discarded
6622 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6623 _collector->lower_restart_addr(ra);
6624 _mark_stack->reset(); // discard stack contents
6625 _mark_stack->expand(); // expand the stack if possible
6626 }
6627
6628 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6629 assert(obj->is_oop_or_null(), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6630 HeapWord* addr = (HeapWord*)obj;
6631 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6632 // Oop lies in _span and isn't yet grey or black
6633 _verification_bm->mark(addr); // now grey
6634 if (!_cms_bm->isMarked(addr)) {
6635 LogHandle(gc, verify) log;
6636 ResourceMark rm;
6637 oop(addr)->print_on(log.info_stream());
6638 log.info(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6639 fatal("... aborting");
6640 }
6641
6642 if (!_mark_stack->push(obj)) { // stack overflow
6643 log_debug(gc, conc, stats)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6644 assert(_mark_stack->isFull(), "Else push should have succeeded");
6645 handle_stack_overflow(addr);
6646 }
6647 // anything including and to the right of _finger
6648 // will be scanned as we iterate over the remainder of the
6649 // bit map
6650 }
6651 }
6652
6653 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6654 MemRegion span,
6655 CMSBitMap* bitMap, CMSMarkStack* markStack,
6656 HeapWord* finger, MarkFromRootsClosure* parent) :
6657 MetadataAwareOopClosure(collector->ref_processor()),
6658 _collector(collector),
6659 _span(span),
6660 _bitMap(bitMap),
6661 _markStack(markStack),
6662 _finger(finger),
6663 _parent(parent)
6664 { }
6665
6666 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
6667 MemRegion span,
6668 CMSBitMap* bit_map,
6669 OopTaskQueue* work_queue,
6670 CMSMarkStack* overflow_stack,
6671 HeapWord* finger,
6672 HeapWord** global_finger_addr,
6673 Par_MarkFromRootsClosure* parent) :
6674 MetadataAwareOopClosure(collector->ref_processor()),
6675 _collector(collector),
6676 _whole_span(collector->_span),
6677 _span(span),
6678 _bit_map(bit_map),
6679 _work_queue(work_queue),
6680 _overflow_stack(overflow_stack),
6681 _finger(finger),
6682 _global_finger_addr(global_finger_addr),
6683 _parent(parent)
6684 { }
6685
6686 // Assumes thread-safe access by callers, who are
6687 // responsible for mutual exclusion.
6688 void CMSCollector::lower_restart_addr(HeapWord* low) {
6689 assert(_span.contains(low), "Out of bounds addr");
6690 if (_restart_addr == NULL) {
6691 _restart_addr = low;
6692 } else {
6693 _restart_addr = MIN2(_restart_addr, low);
6694 }
6695 }
6696
6697 // Upon stack overflow, we discard (part of) the stack,
6698 // remembering the least address amongst those discarded
6699 // in CMSCollector's _restart_address.
6700 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6701 // Remember the least grey address discarded
6702 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6703 _collector->lower_restart_addr(ra);
6704 _markStack->reset(); // discard stack contents
6705 _markStack->expand(); // expand the stack if possible
6706 }
6707
6708 // Upon stack overflow, we discard (part of) the stack,
6709 // remembering the least address amongst those discarded
6710 // in CMSCollector's _restart_address.
6711 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6712 // We need to do this under a mutex to prevent other
6713 // workers from interfering with the work done below.
6714 MutexLockerEx ml(_overflow_stack->par_lock(),
6715 Mutex::_no_safepoint_check_flag);
6716 // Remember the least grey address discarded
6717 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6718 _collector->lower_restart_addr(ra);
6719 _overflow_stack->reset(); // discard stack contents
6720 _overflow_stack->expand(); // expand the stack if possible
6721 }
6722
6723 void PushOrMarkClosure::do_oop(oop obj) {
6724 // Ignore mark word because we are running concurrent with mutators.
6725 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6726 HeapWord* addr = (HeapWord*)obj;
6727 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6728 // Oop lies in _span and isn't yet grey or black
6729 _bitMap->mark(addr); // now grey
6730 if (addr < _finger) {
6731 // the bit map iteration has already either passed, or
6732 // sampled, this bit in the bit map; we'll need to
6733 // use the marking stack to scan this oop's oops.
6734 bool simulate_overflow = false;
6735 NOT_PRODUCT(
6736 if (CMSMarkStackOverflowALot &&
6737 _collector->simulate_overflow()) {
6738 // simulate a stack overflow
6739 simulate_overflow = true;
6740 }
6741 )
6742 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6743 log_debug(gc, conc, stats)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6744 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6745 handle_stack_overflow(addr);
6746 }
6747 }
6748 // anything including and to the right of _finger
6749 // will be scanned as we iterate over the remainder of the
6750 // bit map
6751 do_yield_check();
6752 }
6753 }
6754
6755 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
6756 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
6757
6758 void Par_PushOrMarkClosure::do_oop(oop obj) {
6759 // Ignore mark word because we are running concurrent with mutators.
6760 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6761 HeapWord* addr = (HeapWord*)obj;
6762 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6763 // Oop lies in _span and isn't yet grey or black
6764 // We read the global_finger (volatile read) strictly after marking oop
6765 bool res = _bit_map->par_mark(addr); // now grey
6766 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6767 // Should we push this marked oop on our stack?
6768 // -- if someone else marked it, nothing to do
6769 // -- if target oop is above global finger nothing to do
6770 // -- if target oop is in chunk and above local finger
6771 // then nothing to do
6772 // -- else push on work queue
6773 if ( !res // someone else marked it, they will deal with it
6774 || (addr >= *gfa) // will be scanned in a later task
6775 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6776 return;
6777 }
6778 // the bit map iteration has already either passed, or
6779 // sampled, this bit in the bit map; we'll need to
6780 // use the marking stack to scan this oop's oops.
6781 bool simulate_overflow = false;
6782 NOT_PRODUCT(
6783 if (CMSMarkStackOverflowALot &&
6784 _collector->simulate_overflow()) {
6785 // simulate a stack overflow
6786 simulate_overflow = true;
6787 }
6788 )
6789 if (simulate_overflow ||
6790 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6791 // stack overflow
6792 log_debug(gc, conc, stats)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6793 // We cannot assert that the overflow stack is full because
6794 // it may have been emptied since.
6795 assert(simulate_overflow ||
6796 _work_queue->size() == _work_queue->max_elems(),
6797 "Else push should have succeeded");
6798 handle_stack_overflow(addr);
6799 }
6800 do_yield_check();
6801 }
6802 }
6803
6804 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
6805 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
6806
6807 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6808 MemRegion span,
6809 ReferenceProcessor* rp,
6810 CMSBitMap* bit_map,
6811 CMSBitMap* mod_union_table,
6812 CMSMarkStack* mark_stack,
6813 bool concurrent_precleaning):
6814 MetadataAwareOopClosure(rp),
6815 _collector(collector),
6816 _span(span),
6817 _bit_map(bit_map),
6818 _mod_union_table(mod_union_table),
6819 _mark_stack(mark_stack),
6820 _concurrent_precleaning(concurrent_precleaning)
6821 {
6822 assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6823 }
6824
6825 // Grey object rescan during pre-cleaning and second checkpoint phases --
6826 // the non-parallel version (the parallel version appears further below.)
6827 void PushAndMarkClosure::do_oop(oop obj) {
6828 // Ignore mark word verification. If during concurrent precleaning,
6829 // the object monitor may be locked. If during the checkpoint
6830 // phases, the object may already have been reached by a different
6831 // path and may be at the end of the global overflow list (so
6832 // the mark word may be NULL).
6833 assert(obj->is_oop_or_null(true /* ignore mark word */),
6834 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6835 HeapWord* addr = (HeapWord*)obj;
6836 // Check if oop points into the CMS generation
6837 // and is not marked
6838 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6839 // a white object ...
6840 _bit_map->mark(addr); // ... now grey
6841 // push on the marking stack (grey set)
6842 bool simulate_overflow = false;
6843 NOT_PRODUCT(
6844 if (CMSMarkStackOverflowALot &&
6845 _collector->simulate_overflow()) {
6846 // simulate a stack overflow
6847 simulate_overflow = true;
6848 }
6849 )
6850 if (simulate_overflow || !_mark_stack->push(obj)) {
6851 if (_concurrent_precleaning) {
6852 // During precleaning we can just dirty the appropriate card(s)
6853 // in the mod union table, thus ensuring that the object remains
6854 // in the grey set and continue. In the case of object arrays
6855 // we need to dirty all of the cards that the object spans,
6856 // since the rescan of object arrays will be limited to the
6857 // dirty cards.
6858 // Note that no one can be interfering with us in this action
6859 // of dirtying the mod union table, so no locking or atomics
6860 // are required.
6861 if (obj->is_objArray()) {
6862 size_t sz = obj->size();
6863 HeapWord* end_card_addr = (HeapWord*)round_to(
6864 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6865 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6866 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6867 _mod_union_table->mark_range(redirty_range);
6868 } else {
6869 _mod_union_table->mark(addr);
6870 }
6871 _collector->_ser_pmc_preclean_ovflw++;
6872 } else {
6873 // During the remark phase, we need to remember this oop
6874 // in the overflow list.
6875 _collector->push_on_overflow_list(obj);
6876 _collector->_ser_pmc_remark_ovflw++;
6877 }
6878 }
6879 }
6880 }
6881
6882 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
6883 MemRegion span,
6884 ReferenceProcessor* rp,
6885 CMSBitMap* bit_map,
6886 OopTaskQueue* work_queue):
6887 MetadataAwareOopClosure(rp),
6888 _collector(collector),
6889 _span(span),
6890 _bit_map(bit_map),
6891 _work_queue(work_queue)
6892 {
6893 assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6894 }
6895
6896 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
6897 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
6898
6899 // Grey object rescan during second checkpoint phase --
6900 // the parallel version.
6901 void Par_PushAndMarkClosure::do_oop(oop obj) {
6902 // In the assert below, we ignore the mark word because
6903 // this oop may point to an already visited object that is
6904 // on the overflow stack (in which case the mark word has
6905 // been hijacked for chaining into the overflow stack --
6906 // if this is the last object in the overflow stack then
6907 // its mark word will be NULL). Because this object may
6908 // have been subsequently popped off the global overflow
6909 // stack, and the mark word possibly restored to the prototypical
6910 // value, by the time we get to examined this failing assert in
6911 // the debugger, is_oop_or_null(false) may subsequently start
6912 // to hold.
6913 assert(obj->is_oop_or_null(true),
6914 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6915 HeapWord* addr = (HeapWord*)obj;
6916 // Check if oop points into the CMS generation
6917 // and is not marked
6918 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6919 // a white object ...
6920 // If we manage to "claim" the object, by being the
6921 // first thread to mark it, then we push it on our
6922 // marking stack
6923 if (_bit_map->par_mark(addr)) { // ... now grey
6924 // push on work queue (grey set)
6925 bool simulate_overflow = false;
6926 NOT_PRODUCT(
6927 if (CMSMarkStackOverflowALot &&
6928 _collector->par_simulate_overflow()) {
6929 // simulate a stack overflow
6930 simulate_overflow = true;
6931 }
6932 )
6933 if (simulate_overflow || !_work_queue->push(obj)) {
6934 _collector->par_push_on_overflow_list(obj);
6935 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
6936 }
6937 } // Else, some other thread got there first
6938 }
6939 }
6940
6941 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
6942 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
6943
6944 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6945 Mutex* bml = _collector->bitMapLock();
6946 assert_lock_strong(bml);
6947 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6948 "CMS thread should hold CMS token");
6949
6950 bml->unlock();
6951 ConcurrentMarkSweepThread::desynchronize(true);
6952
6953 _collector->stopTimer();
6954 _collector->incrementYields();
6955
6956 // See the comment in coordinator_yield()
6957 for (unsigned i = 0; i < CMSYieldSleepCount &&
6958 ConcurrentMarkSweepThread::should_yield() &&
6959 !CMSCollector::foregroundGCIsActive(); ++i) {
6960 os::sleep(Thread::current(), 1, false);
6961 }
6962
6963 ConcurrentMarkSweepThread::synchronize(true);
6964 bml->lock();
6965
6966 _collector->startTimer();
6967 }
6968
6969 bool CMSPrecleanRefsYieldClosure::should_return() {
6970 if (ConcurrentMarkSweepThread::should_yield()) {
6971 do_yield_work();
6972 }
6973 return _collector->foregroundGCIsActive();
6974 }
6975
6976 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
6977 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
6978 "mr should be aligned to start at a card boundary");
6979 // We'd like to assert:
6980 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
6981 // "mr should be a range of cards");
6982 // However, that would be too strong in one case -- the last
6983 // partition ends at _unallocated_block which, in general, can be
6984 // an arbitrary boundary, not necessarily card aligned.
6985 _num_dirty_cards += mr.word_size()/CardTableModRefBS::card_size_in_words;
6986 _space->object_iterate_mem(mr, &_scan_cl);
6987 }
6988
6989 SweepClosure::SweepClosure(CMSCollector* collector,
6990 ConcurrentMarkSweepGeneration* g,
6991 CMSBitMap* bitMap, bool should_yield) :
6992 _collector(collector),
6993 _g(g),
6994 _sp(g->cmsSpace()),
6995 _limit(_sp->sweep_limit()),
6996 _freelistLock(_sp->freelistLock()),
6997 _bitMap(bitMap),
6998 _yield(should_yield),
6999 _inFreeRange(false), // No free range at beginning of sweep
7000 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7001 _lastFreeRangeCoalesced(false),
7002 _freeFinger(g->used_region().start())
7003 {
7004 NOT_PRODUCT(
7005 _numObjectsFreed = 0;
7006 _numWordsFreed = 0;
7007 _numObjectsLive = 0;
7008 _numWordsLive = 0;
7009 _numObjectsAlreadyFree = 0;
7010 _numWordsAlreadyFree = 0;
7011 _last_fc = NULL;
7012
7013 _sp->initializeIndexedFreeListArrayReturnedBytes();
7014 _sp->dictionary()->initialize_dict_returned_bytes();
7015 )
7016 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7017 "sweep _limit out of bounds");
7018 log_develop(gc, sweep)("====================");
7019 log_develop(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
7020 }
7021
7022 void SweepClosure::print_on(outputStream* st) const {
7023 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7024 p2i(_sp->bottom()), p2i(_sp->end()));
7025 tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7026 tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7027 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7028 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7029 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7030 }
7031
7032 #ifndef PRODUCT
7033 // Assertion checking only: no useful work in product mode --
7034 // however, if any of the flags below become product flags,
7035 // you may need to review this code to see if it needs to be
7036 // enabled in product mode.
7037 SweepClosure::~SweepClosure() {
7038 assert_lock_strong(_freelistLock);
7039 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7040 "sweep _limit out of bounds");
7041 if (inFreeRange()) {
7042 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7043 print();
7044 ShouldNotReachHere();
7045 }
7046
7047 if (log_is_enabled(Debug, gc, sweep)) {
7048 log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7049 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7050 log_debug(gc, sweep)("Live " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7051 _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7052 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7053 log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7054 }
7055
7056 if (log_is_enabled(Debug, gc, conc, stats) && CMSVerifyReturnedBytes) {
7057 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7058 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7059 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7060 log_debug(gc, conc, stats)("Returned " SIZE_FORMAT " bytes Indexed List Returned " SIZE_FORMAT " bytes Dictionary Returned " SIZE_FORMAT " bytes",
7061 returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7062 }
7063 log_develop(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7064 log_develop(gc, sweep)("================");
7065 }
7066 #endif // PRODUCT
7067
7068 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7069 bool freeRangeInFreeLists) {
7070 log_develop(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7071 p2i(freeFinger), freeRangeInFreeLists);
7072 assert(!inFreeRange(), "Trampling existing free range");
7073 set_inFreeRange(true);
7074 set_lastFreeRangeCoalesced(false);
7075
7076 set_freeFinger(freeFinger);
7077 set_freeRangeInFreeLists(freeRangeInFreeLists);
7078 }
7079
7080 // Note that the sweeper runs concurrently with mutators. Thus,
7081 // it is possible for direct allocation in this generation to happen
7082 // in the middle of the sweep. Note that the sweeper also coalesces
7083 // contiguous free blocks. Thus, unless the sweeper and the allocator
7084 // synchronize appropriately freshly allocated blocks may get swept up.
7085 // This is accomplished by the sweeper locking the free lists while
7086 // it is sweeping. Thus blocks that are determined to be free are
7087 // indeed free. There is however one additional complication:
7088 // blocks that have been allocated since the final checkpoint and
7089 // mark, will not have been marked and so would be treated as
7090 // unreachable and swept up. To prevent this, the allocator marks
7091 // the bit map when allocating during the sweep phase. This leads,
7092 // however, to a further complication -- objects may have been allocated
7093 // but not yet initialized -- in the sense that the header isn't yet
7094 // installed. The sweeper can not then determine the size of the block
7095 // in order to skip over it. To deal with this case, we use a technique
7096 // (due to Printezis) to encode such uninitialized block sizes in the
7097 // bit map. Since the bit map uses a bit per every HeapWord, but the
7098 // CMS generation has a minimum object size of 3 HeapWords, it follows
7099 // that "normal marks" won't be adjacent in the bit map (there will
7100 // always be at least two 0 bits between successive 1 bits). We make use
7101 // of these "unused" bits to represent uninitialized blocks -- the bit
7102 // corresponding to the start of the uninitialized object and the next
7103 // bit are both set. Finally, a 1 bit marks the end of the object that
7104 // started with the two consecutive 1 bits to indicate its potentially
7105 // uninitialized state.
7106
7107 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7108 FreeChunk* fc = (FreeChunk*)addr;
7109 size_t res;
7110
7111 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7112 // than "addr == _limit" because although _limit was a block boundary when
7113 // we started the sweep, it may no longer be one because heap expansion
7114 // may have caused us to coalesce the block ending at the address _limit
7115 // with a newly expanded chunk (this happens when _limit was set to the
7116 // previous _end of the space), so we may have stepped past _limit:
7117 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7118 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7119 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7120 "sweep _limit out of bounds");
7121 assert(addr < _sp->end(), "addr out of bounds");
7122 // Flush any free range we might be holding as a single
7123 // coalesced chunk to the appropriate free list.
7124 if (inFreeRange()) {
7125 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7126 "freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger()));
7127 flush_cur_free_chunk(freeFinger(),
7128 pointer_delta(addr, freeFinger()));
7129 log_develop(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7130 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7131 lastFreeRangeCoalesced() ? 1 : 0);
7132 }
7133
7134 // help the iterator loop finish
7135 return pointer_delta(_sp->end(), addr);
7136 }
7137
7138 assert(addr < _limit, "sweep invariant");
7139 // check if we should yield
7140 do_yield_check(addr);
7141 if (fc->is_free()) {
7142 // Chunk that is already free
7143 res = fc->size();
7144 do_already_free_chunk(fc);
7145 debug_only(_sp->verifyFreeLists());
7146 // If we flush the chunk at hand in lookahead_and_flush()
7147 // and it's coalesced with a preceding chunk, then the
7148 // process of "mangling" the payload of the coalesced block
7149 // will cause erasure of the size information from the
7150 // (erstwhile) header of all the coalesced blocks but the
7151 // first, so the first disjunct in the assert will not hold
7152 // in that specific case (in which case the second disjunct
7153 // will hold).
7154 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7155 "Otherwise the size info doesn't change at this step");
7156 NOT_PRODUCT(
7157 _numObjectsAlreadyFree++;
7158 _numWordsAlreadyFree += res;
7159 )
7160 NOT_PRODUCT(_last_fc = fc;)
7161 } else if (!_bitMap->isMarked(addr)) {
7162 // Chunk is fresh garbage
7163 res = do_garbage_chunk(fc);
7164 debug_only(_sp->verifyFreeLists());
7165 NOT_PRODUCT(
7166 _numObjectsFreed++;
7167 _numWordsFreed += res;
7168 )
7169 } else {
7170 // Chunk that is alive.
7171 res = do_live_chunk(fc);
7172 debug_only(_sp->verifyFreeLists());
7173 NOT_PRODUCT(
7174 _numObjectsLive++;
7175 _numWordsLive += res;
7176 )
7177 }
7178 return res;
7179 }
7180
7181 // For the smart allocation, record following
7182 // split deaths - a free chunk is removed from its free list because
7183 // it is being split into two or more chunks.
7184 // split birth - a free chunk is being added to its free list because
7185 // a larger free chunk has been split and resulted in this free chunk.
7186 // coal death - a free chunk is being removed from its free list because
7187 // it is being coalesced into a large free chunk.
7188 // coal birth - a free chunk is being added to its free list because
7189 // it was created when two or more free chunks where coalesced into
7190 // this free chunk.
7191 //
7192 // These statistics are used to determine the desired number of free
7193 // chunks of a given size. The desired number is chosen to be relative
7194 // to the end of a CMS sweep. The desired number at the end of a sweep
7195 // is the
7196 // count-at-end-of-previous-sweep (an amount that was enough)
7197 // - count-at-beginning-of-current-sweep (the excess)
7198 // + split-births (gains in this size during interval)
7199 // - split-deaths (demands on this size during interval)
7200 // where the interval is from the end of one sweep to the end of the
7201 // next.
7202 //
7203 // When sweeping the sweeper maintains an accumulated chunk which is
7204 // the chunk that is made up of chunks that have been coalesced. That
7205 // will be termed the left-hand chunk. A new chunk of garbage that
7206 // is being considered for coalescing will be referred to as the
7207 // right-hand chunk.
7208 //
7209 // When making a decision on whether to coalesce a right-hand chunk with
7210 // the current left-hand chunk, the current count vs. the desired count
7211 // of the left-hand chunk is considered. Also if the right-hand chunk
7212 // is near the large chunk at the end of the heap (see
7213 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7214 // left-hand chunk is coalesced.
7215 //
7216 // When making a decision about whether to split a chunk, the desired count
7217 // vs. the current count of the candidate to be split is also considered.
7218 // If the candidate is underpopulated (currently fewer chunks than desired)
7219 // a chunk of an overpopulated (currently more chunks than desired) size may
7220 // be chosen. The "hint" associated with a free list, if non-null, points
7221 // to a free list which may be overpopulated.
7222 //
7223
7224 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7225 const size_t size = fc->size();
7226
7227 // a chunk that is already free, should not have been
7228 // marked in the bit map
7229 HeapWord* const addr = (HeapWord*) fc;
7230 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7231 // Verify that the bit map has no bits marked between
7232 // addr and purported end of this block.
7233 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7234
7235 // Some chunks cannot be coalesced under any circumstances.
7236 // See the definition of cantCoalesce().
7237 if (!fc->cantCoalesce()) {
7238 // This chunk can potentially be coalesced.
7239 // All the work is done in
7240 do_post_free_or_garbage_chunk(fc, size);
7241 // Note that if the chunk is not coalescable (the else arm
7242 // below), we unconditionally flush, without needing to do
7243 // a "lookahead," as we do below.
7244 if (inFreeRange()) lookahead_and_flush(fc, size);
7245 } else {
7246 // Code path common to both original and adaptive free lists.
7247
7248 // cant coalesce with previous block; this should be treated
7249 // as the end of a free run if any
7250 if (inFreeRange()) {
7251 // we kicked some butt; time to pick up the garbage
7252 assert(freeFinger() < addr, "freeFinger points too high");
7253 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7254 }
7255 // else, nothing to do, just continue
7256 }
7257 }
7258
7259 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7260 // This is a chunk of garbage. It is not in any free list.
7261 // Add it to a free list or let it possibly be coalesced into
7262 // a larger chunk.
7263 HeapWord* const addr = (HeapWord*) fc;
7264 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7265
7266 // Verify that the bit map has no bits marked between
7267 // addr and purported end of just dead object.
7268 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7269 do_post_free_or_garbage_chunk(fc, size);
7270
7271 assert(_limit >= addr + size,
7272 "A freshly garbage chunk can't possibly straddle over _limit");
7273 if (inFreeRange()) lookahead_and_flush(fc, size);
7274 return size;
7275 }
7276
7277 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7278 HeapWord* addr = (HeapWord*) fc;
7279 // The sweeper has just found a live object. Return any accumulated
7280 // left hand chunk to the free lists.
7281 if (inFreeRange()) {
7282 assert(freeFinger() < addr, "freeFinger points too high");
7283 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7284 }
7285
7286 // This object is live: we'd normally expect this to be
7287 // an oop, and like to assert the following:
7288 // assert(oop(addr)->is_oop(), "live block should be an oop");
7289 // However, as we commented above, this may be an object whose
7290 // header hasn't yet been initialized.
7291 size_t size;
7292 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7293 if (_bitMap->isMarked(addr + 1)) {
7294 // Determine the size from the bit map, rather than trying to
7295 // compute it from the object header.
7296 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7297 size = pointer_delta(nextOneAddr + 1, addr);
7298 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7299 "alignment problem");
7300
7301 #ifdef ASSERT
7302 if (oop(addr)->klass_or_null() != NULL) {
7303 // Ignore mark word because we are running concurrent with mutators
7304 assert(oop(addr)->is_oop(true), "live block should be an oop");
7305 assert(size ==
7306 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7307 "P-mark and computed size do not agree");
7308 }
7309 #endif
7310
7311 } else {
7312 // This should be an initialized object that's alive.
7313 assert(oop(addr)->klass_or_null() != NULL,
7314 "Should be an initialized object");
7315 // Ignore mark word because we are running concurrent with mutators
7316 assert(oop(addr)->is_oop(true), "live block should be an oop");
7317 // Verify that the bit map has no bits marked between
7318 // addr and purported end of this block.
7319 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7320 assert(size >= 3, "Necessary for Printezis marks to work");
7321 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7322 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7323 }
7324 return size;
7325 }
7326
7327 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7328 size_t chunkSize) {
7329 // do_post_free_or_garbage_chunk() should only be called in the case
7330 // of the adaptive free list allocator.
7331 const bool fcInFreeLists = fc->is_free();
7332 assert((HeapWord*)fc <= _limit, "sweep invariant");
7333
7334 log_develop(gc, sweep)(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7335
7336 HeapWord* const fc_addr = (HeapWord*) fc;
7337
7338 bool coalesce = false;
7339 const size_t left = pointer_delta(fc_addr, freeFinger());
7340 const size_t right = chunkSize;
7341 switch (FLSCoalescePolicy) {
7342 // numeric value forms a coalition aggressiveness metric
7343 case 0: { // never coalesce
7344 coalesce = false;
7345 break;
7346 }
7347 case 1: { // coalesce if left & right chunks on overpopulated lists
7348 coalesce = _sp->coalOverPopulated(left) &&
7349 _sp->coalOverPopulated(right);
7350 break;
7351 }
7352 case 2: { // coalesce if left chunk on overpopulated list (default)
7353 coalesce = _sp->coalOverPopulated(left);
7354 break;
7355 }
7356 case 3: { // coalesce if left OR right chunk on overpopulated list
7357 coalesce = _sp->coalOverPopulated(left) ||
7358 _sp->coalOverPopulated(right);
7359 break;
7360 }
7361 case 4: { // always coalesce
7362 coalesce = true;
7363 break;
7364 }
7365 default:
7366 ShouldNotReachHere();
7367 }
7368
7369 // Should the current free range be coalesced?
7370 // If the chunk is in a free range and either we decided to coalesce above
7371 // or the chunk is near the large block at the end of the heap
7372 // (isNearLargestChunk() returns true), then coalesce this chunk.
7373 const bool doCoalesce = inFreeRange()
7374 && (coalesce || _g->isNearLargestChunk(fc_addr));
7375 if (doCoalesce) {
7376 // Coalesce the current free range on the left with the new
7377 // chunk on the right. If either is on a free list,
7378 // it must be removed from the list and stashed in the closure.
7379 if (freeRangeInFreeLists()) {
7380 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7381 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7382 "Size of free range is inconsistent with chunk size.");
7383 _sp->coalDeath(ffc->size());
7384 _sp->removeFreeChunkFromFreeLists(ffc);
7385 set_freeRangeInFreeLists(false);
7386 }
7387 if (fcInFreeLists) {
7388 _sp->coalDeath(chunkSize);
7389 assert(fc->size() == chunkSize,
7390 "The chunk has the wrong size or is not in the free lists");
7391 _sp->removeFreeChunkFromFreeLists(fc);
7392 }
7393 set_lastFreeRangeCoalesced(true);
7394 print_free_block_coalesced(fc);
7395 } else { // not in a free range and/or should not coalesce
7396 // Return the current free range and start a new one.
7397 if (inFreeRange()) {
7398 // In a free range but cannot coalesce with the right hand chunk.
7399 // Put the current free range into the free lists.
7400 flush_cur_free_chunk(freeFinger(),
7401 pointer_delta(fc_addr, freeFinger()));
7402 }
7403 // Set up for new free range. Pass along whether the right hand
7404 // chunk is in the free lists.
7405 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7406 }
7407 }
7408
7409 // Lookahead flush:
7410 // If we are tracking a free range, and this is the last chunk that
7411 // we'll look at because its end crosses past _limit, we'll preemptively
7412 // flush it along with any free range we may be holding on to. Note that
7413 // this can be the case only for an already free or freshly garbage
7414 // chunk. If this block is an object, it can never straddle
7415 // over _limit. The "straddling" occurs when _limit is set at
7416 // the previous end of the space when this cycle started, and
7417 // a subsequent heap expansion caused the previously co-terminal
7418 // free block to be coalesced with the newly expanded portion,
7419 // thus rendering _limit a non-block-boundary making it dangerous
7420 // for the sweeper to step over and examine.
7421 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7422 assert(inFreeRange(), "Should only be called if currently in a free range.");
7423 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7424 assert(_sp->used_region().contains(eob - 1),
7425 "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7426 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7427 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7428 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7429 if (eob >= _limit) {
7430 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7431 log_develop(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7432 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7433 "[" PTR_FORMAT "," PTR_FORMAT ")",
7434 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7435 // Return the storage we are tracking back into the free lists.
7436 log_develop(gc, sweep)("Flushing ... ");
7437 assert(freeFinger() < eob, "Error");
7438 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7439 }
7440 }
7441
7442 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7443 assert(inFreeRange(), "Should only be called if currently in a free range.");
7444 assert(size > 0,
7445 "A zero sized chunk cannot be added to the free lists.");
7446 if (!freeRangeInFreeLists()) {
7447 log_develop(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7448 p2i(chunk), size);
7449 // A new free range is going to be starting. The current
7450 // free range has not been added to the free lists yet or
7451 // was removed so add it back.
7452 // If the current free range was coalesced, then the death
7453 // of the free range was recorded. Record a birth now.
7454 if (lastFreeRangeCoalesced()) {
7455 _sp->coalBirth(size);
7456 }
7457 _sp->addChunkAndRepairOffsetTable(chunk, size,
7458 lastFreeRangeCoalesced());
7459 } else {
7460 log_develop(gc, sweep)("Already in free list: nothing to flush");
7461 }
7462 set_inFreeRange(false);
7463 set_freeRangeInFreeLists(false);
7464 }
7465
7466 // We take a break if we've been at this for a while,
7467 // so as to avoid monopolizing the locks involved.
7468 void SweepClosure::do_yield_work(HeapWord* addr) {
7469 // Return current free chunk being used for coalescing (if any)
7470 // to the appropriate freelist. After yielding, the next
7471 // free block encountered will start a coalescing range of
7472 // free blocks. If the next free block is adjacent to the
7473 // chunk just flushed, they will need to wait for the next
7474 // sweep to be coalesced.
7475 if (inFreeRange()) {
7476 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7477 }
7478
7479 // First give up the locks, then yield, then re-lock.
7480 // We should probably use a constructor/destructor idiom to
7481 // do this unlock/lock or modify the MutexUnlocker class to
7482 // serve our purpose. XXX
7483 assert_lock_strong(_bitMap->lock());
7484 assert_lock_strong(_freelistLock);
7485 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7486 "CMS thread should hold CMS token");
7487 _bitMap->lock()->unlock();
7488 _freelistLock->unlock();
7489 ConcurrentMarkSweepThread::desynchronize(true);
7490 _collector->stopTimer();
7491 _collector->incrementYields();
7492
7493 // See the comment in coordinator_yield()
7494 for (unsigned i = 0; i < CMSYieldSleepCount &&
7495 ConcurrentMarkSweepThread::should_yield() &&
7496 !CMSCollector::foregroundGCIsActive(); ++i) {
7497 os::sleep(Thread::current(), 1, false);
7498 }
7499
7500 ConcurrentMarkSweepThread::synchronize(true);
7501 _freelistLock->lock();
7502 _bitMap->lock()->lock_without_safepoint_check();
7503 _collector->startTimer();
7504 }
7505
7506 #ifndef PRODUCT
7507 // This is actually very useful in a product build if it can
7508 // be called from the debugger. Compile it into the product
7509 // as needed.
7510 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7511 return debug_cms_space->verify_chunk_in_free_list(fc);
7512 }
7513 #endif
7514
7515 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7516 log_develop(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7517 p2i(fc), fc->size());
7518 }
7519
7520 // CMSIsAliveClosure
7521 bool CMSIsAliveClosure::do_object_b(oop obj) {
7522 HeapWord* addr = (HeapWord*)obj;
7523 return addr != NULL &&
7524 (!_span.contains(addr) || _bit_map->isMarked(addr));
7525 }
7526
7527
7528 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7529 MemRegion span,
7530 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7531 bool cpc):
7532 _collector(collector),
7533 _span(span),
7534 _bit_map(bit_map),
7535 _mark_stack(mark_stack),
7536 _concurrent_precleaning(cpc) {
7537 assert(!_span.is_empty(), "Empty span could spell trouble");
7538 }
7539
7540
7541 // CMSKeepAliveClosure: the serial version
7542 void CMSKeepAliveClosure::do_oop(oop obj) {
7543 HeapWord* addr = (HeapWord*)obj;
7544 if (_span.contains(addr) &&
7545 !_bit_map->isMarked(addr)) {
7546 _bit_map->mark(addr);
7547 bool simulate_overflow = false;
7548 NOT_PRODUCT(
7549 if (CMSMarkStackOverflowALot &&
7550 _collector->simulate_overflow()) {
7551 // simulate a stack overflow
7552 simulate_overflow = true;
7553 }
7554 )
7555 if (simulate_overflow || !_mark_stack->push(obj)) {
7556 if (_concurrent_precleaning) {
7557 // We dirty the overflown object and let the remark
7558 // phase deal with it.
7559 assert(_collector->overflow_list_is_empty(), "Error");
7560 // In the case of object arrays, we need to dirty all of
7561 // the cards that the object spans. No locking or atomics
7562 // are needed since no one else can be mutating the mod union
7563 // table.
7564 if (obj->is_objArray()) {
7565 size_t sz = obj->size();
7566 HeapWord* end_card_addr =
7567 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
7568 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7569 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7570 _collector->_modUnionTable.mark_range(redirty_range);
7571 } else {
7572 _collector->_modUnionTable.mark(addr);
7573 }
7574 _collector->_ser_kac_preclean_ovflw++;
7575 } else {
7576 _collector->push_on_overflow_list(obj);
7577 _collector->_ser_kac_ovflw++;
7578 }
7579 }
7580 }
7581 }
7582
7583 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7584 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7585
7586 // CMSParKeepAliveClosure: a parallel version of the above.
7587 // The work queues are private to each closure (thread),
7588 // but (may be) available for stealing by other threads.
7589 void CMSParKeepAliveClosure::do_oop(oop obj) {
7590 HeapWord* addr = (HeapWord*)obj;
7591 if (_span.contains(addr) &&
7592 !_bit_map->isMarked(addr)) {
7593 // In general, during recursive tracing, several threads
7594 // may be concurrently getting here; the first one to
7595 // "tag" it, claims it.
7596 if (_bit_map->par_mark(addr)) {
7597 bool res = _work_queue->push(obj);
7598 assert(res, "Low water mark should be much less than capacity");
7599 // Do a recursive trim in the hope that this will keep
7600 // stack usage lower, but leave some oops for potential stealers
7601 trim_queue(_low_water_mark);
7602 } // Else, another thread got there first
7603 }
7604 }
7605
7606 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7607 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7608
7609 void CMSParKeepAliveClosure::trim_queue(uint max) {
7610 while (_work_queue->size() > max) {
7611 oop new_oop;
7612 if (_work_queue->pop_local(new_oop)) {
7613 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7614 assert(_bit_map->isMarked((HeapWord*)new_oop),
7615 "no white objects on this stack!");
7616 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7617 // iterate over the oops in this oop, marking and pushing
7618 // the ones in CMS heap (i.e. in _span).
7619 new_oop->oop_iterate(&_mark_and_push);
7620 }
7621 }
7622 }
7623
7624 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7625 CMSCollector* collector,
7626 MemRegion span, CMSBitMap* bit_map,
7627 OopTaskQueue* work_queue):
7628 _collector(collector),
7629 _span(span),
7630 _bit_map(bit_map),
7631 _work_queue(work_queue) { }
7632
7633 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7634 HeapWord* addr = (HeapWord*)obj;
7635 if (_span.contains(addr) &&
7636 !_bit_map->isMarked(addr)) {
7637 if (_bit_map->par_mark(addr)) {
7638 bool simulate_overflow = false;
7639 NOT_PRODUCT(
7640 if (CMSMarkStackOverflowALot &&
7641 _collector->par_simulate_overflow()) {
7642 // simulate a stack overflow
7643 simulate_overflow = true;
7644 }
7645 )
7646 if (simulate_overflow || !_work_queue->push(obj)) {
7647 _collector->par_push_on_overflow_list(obj);
7648 _collector->_par_kac_ovflw++;
7649 }
7650 } // Else another thread got there already
7651 }
7652 }
7653
7654 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7655 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7656
7657 //////////////////////////////////////////////////////////////////
7658 // CMSExpansionCause /////////////////////////////
7659 //////////////////////////////////////////////////////////////////
7660 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7661 switch (cause) {
7662 case _no_expansion:
7663 return "No expansion";
7664 case _satisfy_free_ratio:
7665 return "Free ratio";
7666 case _satisfy_promotion:
7667 return "Satisfy promotion";
7668 case _satisfy_allocation:
7669 return "allocation";
7670 case _allocate_par_lab:
7671 return "Par LAB";
7672 case _allocate_par_spooling_space:
7673 return "Par Spooling Space";
7674 case _adaptive_size_policy:
7675 return "Ergonomics";
7676 default:
7677 return "unknown";
7678 }
7679 }
7680
7681 void CMSDrainMarkingStackClosure::do_void() {
7682 // the max number to take from overflow list at a time
7683 const size_t num = _mark_stack->capacity()/4;
7684 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7685 "Overflow list should be NULL during concurrent phases");
7686 while (!_mark_stack->isEmpty() ||
7687 // if stack is empty, check the overflow list
7688 _collector->take_from_overflow_list(num, _mark_stack)) {
7689 oop obj = _mark_stack->pop();
7690 HeapWord* addr = (HeapWord*)obj;
7691 assert(_span.contains(addr), "Should be within span");
7692 assert(_bit_map->isMarked(addr), "Should be marked");
7693 assert(obj->is_oop(), "Should be an oop");
7694 obj->oop_iterate(_keep_alive);
7695 }
7696 }
7697
7698 void CMSParDrainMarkingStackClosure::do_void() {
7699 // drain queue
7700 trim_queue(0);
7701 }
7702
7703 // Trim our work_queue so its length is below max at return
7704 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7705 while (_work_queue->size() > max) {
7706 oop new_oop;
7707 if (_work_queue->pop_local(new_oop)) {
7708 assert(new_oop->is_oop(), "Expected an oop");
7709 assert(_bit_map->isMarked((HeapWord*)new_oop),
7710 "no white objects on this stack!");
7711 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7712 // iterate over the oops in this oop, marking and pushing
7713 // the ones in CMS heap (i.e. in _span).
7714 new_oop->oop_iterate(&_mark_and_push);
7715 }
7716 }
7717 }
7718
7719 ////////////////////////////////////////////////////////////////////
7720 // Support for Marking Stack Overflow list handling and related code
7721 ////////////////////////////////////////////////////////////////////
7722 // Much of the following code is similar in shape and spirit to the
7723 // code used in ParNewGC. We should try and share that code
7724 // as much as possible in the future.
7725
7726 #ifndef PRODUCT
7727 // Debugging support for CMSStackOverflowALot
7728
7729 // It's OK to call this multi-threaded; the worst thing
7730 // that can happen is that we'll get a bunch of closely
7731 // spaced simulated overflows, but that's OK, in fact
7732 // probably good as it would exercise the overflow code
7733 // under contention.
7734 bool CMSCollector::simulate_overflow() {
7735 if (_overflow_counter-- <= 0) { // just being defensive
7736 _overflow_counter = CMSMarkStackOverflowInterval;
7737 return true;
7738 } else {
7739 return false;
7740 }
7741 }
7742
7743 bool CMSCollector::par_simulate_overflow() {
7744 return simulate_overflow();
7745 }
7746 #endif
7747
7748 // Single-threaded
7749 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7750 assert(stack->isEmpty(), "Expected precondition");
7751 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7752 size_t i = num;
7753 oop cur = _overflow_list;
7754 const markOop proto = markOopDesc::prototype();
7755 NOT_PRODUCT(ssize_t n = 0;)
7756 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7757 next = oop(cur->mark());
7758 cur->set_mark(proto); // until proven otherwise
7759 assert(cur->is_oop(), "Should be an oop");
7760 bool res = stack->push(cur);
7761 assert(res, "Bit off more than can chew?");
7762 NOT_PRODUCT(n++;)
7763 }
7764 _overflow_list = cur;
7765 #ifndef PRODUCT
7766 assert(_num_par_pushes >= n, "Too many pops?");
7767 _num_par_pushes -=n;
7768 #endif
7769 return !stack->isEmpty();
7770 }
7771
7772 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
7773 // (MT-safe) Get a prefix of at most "num" from the list.
7774 // The overflow list is chained through the mark word of
7775 // each object in the list. We fetch the entire list,
7776 // break off a prefix of the right size and return the
7777 // remainder. If other threads try to take objects from
7778 // the overflow list at that time, they will wait for
7779 // some time to see if data becomes available. If (and
7780 // only if) another thread places one or more object(s)
7781 // on the global list before we have returned the suffix
7782 // to the global list, we will walk down our local list
7783 // to find its end and append the global list to
7784 // our suffix before returning it. This suffix walk can
7785 // prove to be expensive (quadratic in the amount of traffic)
7786 // when there are many objects in the overflow list and
7787 // there is much producer-consumer contention on the list.
7788 // *NOTE*: The overflow list manipulation code here and
7789 // in ParNewGeneration:: are very similar in shape,
7790 // except that in the ParNew case we use the old (from/eden)
7791 // copy of the object to thread the list via its klass word.
7792 // Because of the common code, if you make any changes in
7793 // the code below, please check the ParNew version to see if
7794 // similar changes might be needed.
7795 // CR 6797058 has been filed to consolidate the common code.
7796 bool CMSCollector::par_take_from_overflow_list(size_t num,
7797 OopTaskQueue* work_q,
7798 int no_of_gc_threads) {
7799 assert(work_q->size() == 0, "First empty local work queue");
7800 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7801 if (_overflow_list == NULL) {
7802 return false;
7803 }
7804 // Grab the entire list; we'll put back a suffix
7805 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
7806 Thread* tid = Thread::current();
7807 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7808 // set to ParallelGCThreads.
7809 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7810 size_t sleep_time_millis = MAX2((size_t)1, num/100);
7811 // If the list is busy, we spin for a short while,
7812 // sleeping between attempts to get the list.
7813 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7814 os::sleep(tid, sleep_time_millis, false);
7815 if (_overflow_list == NULL) {
7816 // Nothing left to take
7817 return false;
7818 } else if (_overflow_list != BUSY) {
7819 // Try and grab the prefix
7820 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
7821 }
7822 }
7823 // If the list was found to be empty, or we spun long
7824 // enough, we give up and return empty-handed. If we leave
7825 // the list in the BUSY state below, it must be the case that
7826 // some other thread holds the overflow list and will set it
7827 // to a non-BUSY state in the future.
7828 if (prefix == NULL || prefix == BUSY) {
7829 // Nothing to take or waited long enough
7830 if (prefix == NULL) {
7831 // Write back the NULL in case we overwrote it with BUSY above
7832 // and it is still the same value.
7833 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
7834 }
7835 return false;
7836 }
7837 assert(prefix != NULL && prefix != BUSY, "Error");
7838 size_t i = num;
7839 oop cur = prefix;
7840 // Walk down the first "num" objects, unless we reach the end.
7841 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
7842 if (cur->mark() == NULL) {
7843 // We have "num" or fewer elements in the list, so there
7844 // is nothing to return to the global list.
7845 // Write back the NULL in lieu of the BUSY we wrote
7846 // above, if it is still the same value.
7847 if (_overflow_list == BUSY) {
7848 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
7849 }
7850 } else {
7851 // Chop off the suffix and return it to the global list.
7852 assert(cur->mark() != BUSY, "Error");
7853 oop suffix_head = cur->mark(); // suffix will be put back on global list
7854 cur->set_mark(NULL); // break off suffix
7855 // It's possible that the list is still in the empty(busy) state
7856 // we left it in a short while ago; in that case we may be
7857 // able to place back the suffix without incurring the cost
7858 // of a walk down the list.
7859 oop observed_overflow_list = _overflow_list;
7860 oop cur_overflow_list = observed_overflow_list;
7861 bool attached = false;
7862 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7863 observed_overflow_list =
7864 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7865 if (cur_overflow_list == observed_overflow_list) {
7866 attached = true;
7867 break;
7868 } else cur_overflow_list = observed_overflow_list;
7869 }
7870 if (!attached) {
7871 // Too bad, someone else sneaked in (at least) an element; we'll need
7872 // to do a splice. Find tail of suffix so we can prepend suffix to global
7873 // list.
7874 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
7875 oop suffix_tail = cur;
7876 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
7877 "Tautology");
7878 observed_overflow_list = _overflow_list;
7879 do {
7880 cur_overflow_list = observed_overflow_list;
7881 if (cur_overflow_list != BUSY) {
7882 // Do the splice ...
7883 suffix_tail->set_mark(markOop(cur_overflow_list));
7884 } else { // cur_overflow_list == BUSY
7885 suffix_tail->set_mark(NULL);
7886 }
7887 // ... and try to place spliced list back on overflow_list ...
7888 observed_overflow_list =
7889 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7890 } while (cur_overflow_list != observed_overflow_list);
7891 // ... until we have succeeded in doing so.
7892 }
7893 }
7894
7895 // Push the prefix elements on work_q
7896 assert(prefix != NULL, "control point invariant");
7897 const markOop proto = markOopDesc::prototype();
7898 oop next;
7899 NOT_PRODUCT(ssize_t n = 0;)
7900 for (cur = prefix; cur != NULL; cur = next) {
7901 next = oop(cur->mark());
7902 cur->set_mark(proto); // until proven otherwise
7903 assert(cur->is_oop(), "Should be an oop");
7904 bool res = work_q->push(cur);
7905 assert(res, "Bit off more than we can chew?");
7906 NOT_PRODUCT(n++;)
7907 }
7908 #ifndef PRODUCT
7909 assert(_num_par_pushes >= n, "Too many pops?");
7910 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
7911 #endif
7912 return true;
7913 }
7914
7915 // Single-threaded
7916 void CMSCollector::push_on_overflow_list(oop p) {
7917 NOT_PRODUCT(_num_par_pushes++;)
7918 assert(p->is_oop(), "Not an oop");
7919 preserve_mark_if_necessary(p);
7920 p->set_mark((markOop)_overflow_list);
7921 _overflow_list = p;
7922 }
7923
7924 // Multi-threaded; use CAS to prepend to overflow list
7925 void CMSCollector::par_push_on_overflow_list(oop p) {
7926 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
7927 assert(p->is_oop(), "Not an oop");
7928 par_preserve_mark_if_necessary(p);
7929 oop observed_overflow_list = _overflow_list;
7930 oop cur_overflow_list;
7931 do {
7932 cur_overflow_list = observed_overflow_list;
7933 if (cur_overflow_list != BUSY) {
7934 p->set_mark(markOop(cur_overflow_list));
7935 } else {
7936 p->set_mark(NULL);
7937 }
7938 observed_overflow_list =
7939 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
7940 } while (cur_overflow_list != observed_overflow_list);
7941 }
7942 #undef BUSY
7943
7944 // Single threaded
7945 // General Note on GrowableArray: pushes may silently fail
7946 // because we are (temporarily) out of C-heap for expanding
7947 // the stack. The problem is quite ubiquitous and affects
7948 // a lot of code in the JVM. The prudent thing for GrowableArray
7949 // to do (for now) is to exit with an error. However, that may
7950 // be too draconian in some cases because the caller may be
7951 // able to recover without much harm. For such cases, we
7952 // should probably introduce a "soft_push" method which returns
7953 // an indication of success or failure with the assumption that
7954 // the caller may be able to recover from a failure; code in
7955 // the VM can then be changed, incrementally, to deal with such
7956 // failures where possible, thus, incrementally hardening the VM
7957 // in such low resource situations.
7958 void CMSCollector::preserve_mark_work(oop p, markOop m) {
7959 _preserved_oop_stack.push(p);
7960 _preserved_mark_stack.push(m);
7961 assert(m == p->mark(), "Mark word changed");
7962 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
7963 "bijection");
7964 }
7965
7966 // Single threaded
7967 void CMSCollector::preserve_mark_if_necessary(oop p) {
7968 markOop m = p->mark();
7969 if (m->must_be_preserved(p)) {
7970 preserve_mark_work(p, m);
7971 }
7972 }
7973
7974 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
7975 markOop m = p->mark();
7976 if (m->must_be_preserved(p)) {
7977 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
7978 // Even though we read the mark word without holding
7979 // the lock, we are assured that it will not change
7980 // because we "own" this oop, so no other thread can
7981 // be trying to push it on the overflow list; see
7982 // the assertion in preserve_mark_work() that checks
7983 // that m == p->mark().
7984 preserve_mark_work(p, m);
7985 }
7986 }
7987
7988 // We should be able to do this multi-threaded,
7989 // a chunk of stack being a task (this is
7990 // correct because each oop only ever appears
7991 // once in the overflow list. However, it's
7992 // not very easy to completely overlap this with
7993 // other operations, so will generally not be done
7994 // until all work's been completed. Because we
7995 // expect the preserved oop stack (set) to be small,
7996 // it's probably fine to do this single-threaded.
7997 // We can explore cleverer concurrent/overlapped/parallel
7998 // processing of preserved marks if we feel the
7999 // need for this in the future. Stack overflow should
8000 // be so rare in practice and, when it happens, its
8001 // effect on performance so great that this will
8002 // likely just be in the noise anyway.
8003 void CMSCollector::restore_preserved_marks_if_any() {
8004 assert(SafepointSynchronize::is_at_safepoint(),
8005 "world should be stopped");
8006 assert(Thread::current()->is_ConcurrentGC_thread() ||
8007 Thread::current()->is_VM_thread(),
8008 "should be single-threaded");
8009 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8010 "bijection");
8011
8012 while (!_preserved_oop_stack.is_empty()) {
8013 oop p = _preserved_oop_stack.pop();
8014 assert(p->is_oop(), "Should be an oop");
8015 assert(_span.contains(p), "oop should be in _span");
8016 assert(p->mark() == markOopDesc::prototype(),
8017 "Set when taken from overflow list");
8018 markOop m = _preserved_mark_stack.pop();
8019 p->set_mark(m);
8020 }
8021 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8022 "stacks were cleared above");
8023 }
8024
8025 #ifndef PRODUCT
8026 bool CMSCollector::no_preserved_marks() const {
8027 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8028 }
8029 #endif
8030
8031 // Transfer some number of overflown objects to usual marking
8032 // stack. Return true if some objects were transferred.
8033 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8034 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8035 (size_t)ParGCDesiredObjsFromOverflowList);
8036
8037 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8038 assert(_collector->overflow_list_is_empty() || res,
8039 "If list is not empty, we should have taken something");
8040 assert(!res || !_mark_stack->isEmpty(),
8041 "If we took something, it should now be on our stack");
8042 return res;
8043 }
8044
8045 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8046 size_t res = _sp->block_size_no_stall(addr, _collector);
8047 if (_sp->block_is_obj(addr)) {
8048 if (_live_bit_map->isMarked(addr)) {
8049 // It can't have been dead in a previous cycle
8050 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8051 } else {
8052 _dead_bit_map->mark(addr); // mark the dead object
8053 }
8054 }
8055 // Could be 0, if the block size could not be computed without stalling.
8056 return res;
8057 }
8058
8059 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8060
8061 switch (phase) {
8062 case CMSCollector::InitialMarking:
8063 initialize(true /* fullGC */ ,
8064 cause /* cause of the GC */,
8065 true /* recordGCBeginTime */,
8066 true /* recordPreGCUsage */,
8067 false /* recordPeakUsage */,
8068 false /* recordPostGCusage */,
8069 true /* recordAccumulatedGCTime */,
8070 false /* recordGCEndTime */,
8071 false /* countCollection */ );
8072 break;
8073
8074 case CMSCollector::FinalMarking:
8075 initialize(true /* fullGC */ ,
8076 cause /* cause of the GC */,
8077 false /* recordGCBeginTime */,
8078 false /* recordPreGCUsage */,
8079 false /* recordPeakUsage */,
8080 false /* recordPostGCusage */,
8081 true /* recordAccumulatedGCTime */,
8082 false /* recordGCEndTime */,
8083 false /* countCollection */ );
8084 break;
8085
8086 case CMSCollector::Sweeping:
8087 initialize(true /* fullGC */ ,
8088 cause /* cause of the GC */,
8089 false /* recordGCBeginTime */,
8090 false /* recordPreGCUsage */,
8091 true /* recordPeakUsage */,
8092 true /* recordPostGCusage */,
8093 false /* recordAccumulatedGCTime */,
8094 true /* recordGCEndTime */,
8095 true /* countCollection */ );
8096 break;
8097
8098 default:
8099 ShouldNotReachHere();
8100 }
8101 }