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/gcId.hpp"
46 #include "gc/shared/gcLocker.inline.hpp"
47 #include "gc/shared/gcPolicyCounters.hpp"
48 #include "gc/shared/gcTimer.hpp"
49 #include "gc/shared/gcTrace.hpp"
50 #include "gc/shared/gcTraceTime.hpp"
51 #include "gc/shared/genCollectedHeap.hpp"
52 #include "gc/shared/genOopClosures.inline.hpp"
53 #include "gc/shared/isGCActiveMark.hpp"
54 #include "gc/shared/referencePolicy.hpp"
55 #include "gc/shared/strongRootsScope.hpp"
56 #include "gc/shared/taskqueue.inline.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,
195 CardTableRS* ct, bool use_adaptive_freelists,
196 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
197 CardGeneration(rs, initial_byte_size, ct),
198 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
199 _did_compact(false)
200 {
201 HeapWord* bottom = (HeapWord*) _virtual_space.low();
202 HeapWord* end = (HeapWord*) _virtual_space.high();
203
204 _direct_allocated_words = 0;
205 NOT_PRODUCT(
206 _numObjectsPromoted = 0;
207 _numWordsPromoted = 0;
208 _numObjectsAllocated = 0;
209 _numWordsAllocated = 0;
210 )
211
212 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
213 use_adaptive_freelists,
214 dictionaryChoice);
215 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
216 _cmsSpace->_old_gen = this;
217
218 _gc_stats = new CMSGCStats();
219
220 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
221 // offsets match. The ability to tell free chunks from objects
222 // depends on this property.
223 debug_only(
224 FreeChunk* junk = NULL;
225 assert(UseCompressedClassPointers ||
226 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
227 "Offset of FreeChunk::_prev within FreeChunk must match"
228 " that of OopDesc::_klass within OopDesc");
229 )
230
231 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
232 for (uint i = 0; i < ParallelGCThreads; i++) {
233 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
234 }
235
236 _incremental_collection_failed = false;
237 // The "dilatation_factor" is the expansion that can occur on
238 // account of the fact that the minimum object size in the CMS
239 // generation may be larger than that in, say, a contiguous young
240 // generation.
241 // Ideally, in the calculation below, we'd compute the dilatation
242 // factor as: MinChunkSize/(promoting_gen's min object size)
243 // Since we do not have such a general query interface for the
244 // promoting generation, we'll instead just use the minimum
245 // object size (which today is a header's worth of space);
246 // note that all arithmetic is in units of HeapWords.
247 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
248 assert(_dilatation_factor >= 1.0, "from previous assert");
249 }
250
251
252 // The field "_initiating_occupancy" represents the occupancy percentage
253 // at which we trigger a new collection cycle. Unless explicitly specified
254 // via CMSInitiatingOccupancyFraction (argument "io" below), it
255 // is calculated by:
256 //
257 // Let "f" be MinHeapFreeRatio in
258 //
259 // _initiating_occupancy = 100-f +
260 // f * (CMSTriggerRatio/100)
261 // where CMSTriggerRatio is the argument "tr" below.
262 //
263 // That is, if we assume the heap is at its desired maximum occupancy at the
264 // end of a collection, we let CMSTriggerRatio of the (purported) free
265 // space be allocated before initiating a new collection cycle.
266 //
267 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
268 assert(io <= 100 && tr <= 100, "Check the arguments");
269 if (io >= 0) {
270 _initiating_occupancy = (double)io / 100.0;
271 } else {
272 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
273 (double)(tr * MinHeapFreeRatio) / 100.0)
274 / 100.0;
275 }
276 }
277
278 void ConcurrentMarkSweepGeneration::ref_processor_init() {
279 assert(collector() != NULL, "no collector");
280 collector()->ref_processor_init();
281 }
282
283 void CMSCollector::ref_processor_init() {
284 if (_ref_processor == NULL) {
285 // Allocate and initialize a reference processor
286 _ref_processor =
287 new ReferenceProcessor(_span, // span
288 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
289 ParallelGCThreads, // mt processing degree
290 _cmsGen->refs_discovery_is_mt(), // mt discovery
291 MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
292 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
293 &_is_alive_closure); // closure for liveness info
294 // Initialize the _ref_processor field of CMSGen
295 _cmsGen->set_ref_processor(_ref_processor);
296
297 }
298 }
299
300 AdaptiveSizePolicy* CMSCollector::size_policy() {
301 GenCollectedHeap* gch = GenCollectedHeap::heap();
302 return gch->gen_policy()->size_policy();
303 }
304
305 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
306
307 const char* gen_name = "old";
308 GenCollectorPolicy* gcp = GenCollectedHeap::heap()->gen_policy();
309 // Generation Counters - generation 1, 1 subspace
310 _gen_counters = new GenerationCounters(gen_name, 1, 1,
311 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
312
313 _space_counters = new GSpaceCounters(gen_name, 0,
314 _virtual_space.reserved_size(),
315 this, _gen_counters);
316 }
317
318 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
319 _cms_gen(cms_gen)
320 {
321 assert(alpha <= 100, "bad value");
322 _saved_alpha = alpha;
323
324 // Initialize the alphas to the bootstrap value of 100.
325 _gc0_alpha = _cms_alpha = 100;
326
327 _cms_begin_time.update();
328 _cms_end_time.update();
329
330 _gc0_duration = 0.0;
331 _gc0_period = 0.0;
332 _gc0_promoted = 0;
333
334 _cms_duration = 0.0;
335 _cms_period = 0.0;
336 _cms_allocated = 0;
337
338 _cms_used_at_gc0_begin = 0;
339 _cms_used_at_gc0_end = 0;
340 _allow_duty_cycle_reduction = false;
341 _valid_bits = 0;
342 }
343
344 double CMSStats::cms_free_adjustment_factor(size_t free) const {
345 // TBD: CR 6909490
346 return 1.0;
347 }
348
349 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
350 }
351
352 // If promotion failure handling is on use
353 // the padded average size of the promotion for each
354 // young generation collection.
355 double CMSStats::time_until_cms_gen_full() const {
356 size_t cms_free = _cms_gen->cmsSpace()->free();
357 GenCollectedHeap* gch = GenCollectedHeap::heap();
358 size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
359 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
360 if (cms_free > expected_promotion) {
361 // Start a cms collection if there isn't enough space to promote
362 // for the next young collection. Use the padded average as
363 // a safety factor.
364 cms_free -= expected_promotion;
365
366 // Adjust by the safety factor.
367 double cms_free_dbl = (double)cms_free;
368 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
369 // Apply a further correction factor which tries to adjust
370 // for recent occurance of concurrent mode failures.
371 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
372 cms_free_dbl = cms_free_dbl * cms_adjustment;
373
374 if (PrintGCDetails && Verbose) {
375 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
376 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
377 cms_free, expected_promotion);
378 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
379 cms_free_dbl, cms_consumption_rate() + 1.0);
380 }
381 // Add 1 in case the consumption rate goes to zero.
382 return cms_free_dbl / (cms_consumption_rate() + 1.0);
383 }
384 return 0.0;
385 }
386
387 // Compare the duration of the cms collection to the
388 // time remaining before the cms generation is empty.
389 // Note that the time from the start of the cms collection
390 // to the start of the cms sweep (less than the total
391 // duration of the cms collection) can be used. This
392 // has been tried and some applications experienced
393 // promotion failures early in execution. This was
394 // possibly because the averages were not accurate
395 // enough at the beginning.
396 double CMSStats::time_until_cms_start() const {
397 // We add "gc0_period" to the "work" calculation
398 // below because this query is done (mostly) at the
399 // end of a scavenge, so we need to conservatively
400 // account for that much possible delay
401 // in the query so as to avoid concurrent mode failures
402 // due to starting the collection just a wee bit too
403 // late.
404 double work = cms_duration() + gc0_period();
405 double deadline = time_until_cms_gen_full();
406 // If a concurrent mode failure occurred recently, we want to be
407 // more conservative and halve our expected time_until_cms_gen_full()
408 if (work > deadline) {
409 if (Verbose && PrintGCDetails) {
410 gclog_or_tty->print(
411 " CMSCollector: collect because of anticipated promotion "
412 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
413 gc0_period(), time_until_cms_gen_full());
414 }
415 return 0.0;
416 }
417 return work - deadline;
418 }
419
420 #ifndef PRODUCT
421 void CMSStats::print_on(outputStream *st) const {
422 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
423 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
424 gc0_duration(), gc0_period(), gc0_promoted());
425 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
426 cms_duration(), cms_period(), cms_allocated());
427 st->print(",cms_since_beg=%g,cms_since_end=%g",
428 cms_time_since_begin(), cms_time_since_end());
429 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
430 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
431
432 if (valid()) {
433 st->print(",promo_rate=%g,cms_alloc_rate=%g",
434 promotion_rate(), cms_allocation_rate());
435 st->print(",cms_consumption_rate=%g,time_until_full=%g",
436 cms_consumption_rate(), time_until_cms_gen_full());
437 }
438 st->print(" ");
439 }
440 #endif // #ifndef PRODUCT
441
442 CMSCollector::CollectorState CMSCollector::_collectorState =
443 CMSCollector::Idling;
444 bool CMSCollector::_foregroundGCIsActive = false;
445 bool CMSCollector::_foregroundGCShouldWait = false;
446
447 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
448 CardTableRS* ct,
449 ConcurrentMarkSweepPolicy* cp):
450 _cmsGen(cmsGen),
451 _ct(ct),
452 _ref_processor(NULL), // will be set later
453 _conc_workers(NULL), // may be set later
454 _abort_preclean(false),
455 _start_sampling(false),
456 _between_prologue_and_epilogue(false),
457 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
458 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
459 -1 /* lock-free */, "No_lock" /* dummy */),
460 _modUnionClosurePar(&_modUnionTable),
461 // Adjust my span to cover old (cms) gen
462 _span(cmsGen->reserved()),
463 // Construct the is_alive_closure with _span & markBitMap
464 _is_alive_closure(_span, &_markBitMap),
465 _restart_addr(NULL),
466 _overflow_list(NULL),
467 _stats(cmsGen),
468 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
469 //verify that this lock should be acquired with safepoint check.
470 Monitor::_safepoint_check_sometimes)),
471 _eden_chunk_array(NULL), // may be set in ctor body
472 _eden_chunk_capacity(0), // -- ditto --
473 _eden_chunk_index(0), // -- ditto --
474 _survivor_plab_array(NULL), // -- ditto --
475 _survivor_chunk_array(NULL), // -- ditto --
476 _survivor_chunk_capacity(0), // -- ditto --
477 _survivor_chunk_index(0), // -- ditto --
478 _ser_pmc_preclean_ovflw(0),
479 _ser_kac_preclean_ovflw(0),
480 _ser_pmc_remark_ovflw(0),
481 _par_pmc_remark_ovflw(0),
482 _ser_kac_ovflw(0),
483 _par_kac_ovflw(0),
484 #ifndef PRODUCT
485 _num_par_pushes(0),
486 #endif
487 _collection_count_start(0),
488 _verifying(false),
489 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
490 _completed_initialization(false),
491 _collector_policy(cp),
492 _should_unload_classes(CMSClassUnloadingEnabled),
493 _concurrent_cycles_since_last_unload(0),
494 _roots_scanning_options(GenCollectedHeap::SO_None),
495 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
496 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
497 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
498 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
499 _cms_start_registered(false)
500 {
501 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
502 ExplicitGCInvokesConcurrent = true;
503 }
504 // Now expand the span and allocate the collection support structures
505 // (MUT, marking bit map etc.) to cover both generations subject to
506 // collection.
507
508 // For use by dirty card to oop closures.
509 _cmsGen->cmsSpace()->set_collector(this);
510
511 // Allocate MUT and marking bit map
512 {
513 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
514 if (!_markBitMap.allocate(_span)) {
515 warning("Failed to allocate CMS Bit Map");
516 return;
517 }
518 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
519 }
520 {
521 _modUnionTable.allocate(_span);
522 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
523 }
524
525 if (!_markStack.allocate(MarkStackSize)) {
526 warning("Failed to allocate CMS Marking Stack");
527 return;
528 }
529
530 // Support for multi-threaded concurrent phases
531 if (CMSConcurrentMTEnabled) {
532 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
533 // just for now
534 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
535 }
536 if (ConcGCThreads > 1) {
537 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
538 ConcGCThreads, true);
539 if (_conc_workers == NULL) {
540 warning("GC/CMS: _conc_workers allocation failure: "
541 "forcing -CMSConcurrentMTEnabled");
542 CMSConcurrentMTEnabled = false;
543 } else {
544 _conc_workers->initialize_workers();
545 }
546 } else {
547 CMSConcurrentMTEnabled = false;
548 }
549 }
550 if (!CMSConcurrentMTEnabled) {
551 ConcGCThreads = 0;
552 } else {
553 // Turn off CMSCleanOnEnter optimization temporarily for
554 // the MT case where it's not fixed yet; see 6178663.
555 CMSCleanOnEnter = false;
556 }
557 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
558 "Inconsistency");
559
560 // Parallel task queues; these are shared for the
561 // concurrent and stop-world phases of CMS, but
562 // are not shared with parallel scavenge (ParNew).
563 {
564 uint i;
565 uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
566
567 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
568 || ParallelRefProcEnabled)
569 && num_queues > 0) {
570 _task_queues = new OopTaskQueueSet(num_queues);
571 if (_task_queues == NULL) {
572 warning("task_queues allocation failure.");
573 return;
574 }
575 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
576 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
577 for (i = 0; i < num_queues; i++) {
578 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
579 if (q == NULL) {
580 warning("work_queue allocation failure.");
581 return;
582 }
583 _task_queues->register_queue(i, q);
584 }
585 for (i = 0; i < num_queues; i++) {
586 _task_queues->queue(i)->initialize();
587 _hash_seed[i] = 17; // copied from ParNew
588 }
589 }
590 }
591
592 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
593
594 // Clip CMSBootstrapOccupancy between 0 and 100.
595 _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
596
597 // Now tell CMS generations the identity of their collector
598 ConcurrentMarkSweepGeneration::set_collector(this);
599
600 // Create & start a CMS thread for this CMS collector
601 _cmsThread = ConcurrentMarkSweepThread::start(this);
602 assert(cmsThread() != NULL, "CMS Thread should have been created");
603 assert(cmsThread()->collector() == this,
604 "CMS Thread should refer to this gen");
605 assert(CGC_lock != NULL, "Where's the CGC_lock?");
606
607 // Support for parallelizing young gen rescan
608 GenCollectedHeap* gch = GenCollectedHeap::heap();
609 assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
610 _young_gen = (ParNewGeneration*)gch->young_gen();
611 if (gch->supports_inline_contig_alloc()) {
612 _top_addr = gch->top_addr();
613 _end_addr = gch->end_addr();
614 assert(_young_gen != NULL, "no _young_gen");
615 _eden_chunk_index = 0;
616 _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
617 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
618 }
619
620 // Support for parallelizing survivor space rescan
621 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
622 const size_t max_plab_samples =
623 _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
624
625 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
626 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
627 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
628 _survivor_chunk_capacity = max_plab_samples;
629 for (uint i = 0; i < ParallelGCThreads; i++) {
630 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
631 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
632 assert(cur->end() == 0, "Should be 0");
633 assert(cur->array() == vec, "Should be vec");
634 assert(cur->capacity() == max_plab_samples, "Error");
635 }
636 }
637
638 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
639 _gc_counters = new CollectorCounters("CMS", 1);
640 _completed_initialization = true;
641 _inter_sweep_timer.start(); // start of time
642 }
643
644 const char* ConcurrentMarkSweepGeneration::name() const {
645 return "concurrent mark-sweep generation";
646 }
647 void ConcurrentMarkSweepGeneration::update_counters() {
648 if (UsePerfData) {
649 _space_counters->update_all();
650 _gen_counters->update_all();
651 }
652 }
653
654 // this is an optimized version of update_counters(). it takes the
655 // used value as a parameter rather than computing it.
656 //
657 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
658 if (UsePerfData) {
659 _space_counters->update_used(used);
660 _space_counters->update_capacity();
661 _gen_counters->update_all();
662 }
663 }
664
665 void ConcurrentMarkSweepGeneration::print() const {
666 Generation::print();
667 cmsSpace()->print();
668 }
669
670 #ifndef PRODUCT
671 void ConcurrentMarkSweepGeneration::print_statistics() {
672 cmsSpace()->printFLCensus(0);
673 }
674 #endif
675
676 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
677 GenCollectedHeap* gch = GenCollectedHeap::heap();
678 if (PrintGCDetails) {
679 // I didn't want to change the logging when removing the level concept,
680 // but I guess this logging could say "old" or something instead of "1".
681 assert(gch->is_old_gen(this),
682 "The CMS generation should be the old generation");
683 uint level = 1;
684 if (Verbose) {
685 gclog_or_tty->print("[%u %s-%s: " SIZE_FORMAT "(" SIZE_FORMAT ")]",
686 level, short_name(), s, used(), capacity());
687 } else {
688 gclog_or_tty->print("[%u %s-%s: " SIZE_FORMAT "K(" SIZE_FORMAT "K)]",
689 level, short_name(), s, used() / K, capacity() / K);
690 }
691 }
692 if (Verbose) {
693 gclog_or_tty->print(" " SIZE_FORMAT "(" SIZE_FORMAT ")",
694 gch->used(), gch->capacity());
695 } else {
696 gclog_or_tty->print(" " SIZE_FORMAT "K(" SIZE_FORMAT "K)",
697 gch->used() / K, gch->capacity() / K);
698 }
699 }
700
701 size_t
702 ConcurrentMarkSweepGeneration::contiguous_available() const {
703 // dld proposes an improvement in precision here. If the committed
704 // part of the space ends in a free block we should add that to
705 // uncommitted size in the calculation below. Will make this
706 // change later, staying with the approximation below for the
707 // time being. -- ysr.
708 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
709 }
710
711 size_t
712 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
713 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
714 }
715
716 size_t ConcurrentMarkSweepGeneration::max_available() const {
717 return free() + _virtual_space.uncommitted_size();
718 }
719
720 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
721 size_t available = max_available();
722 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
723 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
724 if (Verbose && PrintGCDetails) {
725 gclog_or_tty->print_cr(
726 "CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "),"
727 "max_promo(" SIZE_FORMAT ")",
728 res? "":" not", available, res? ">=":"<",
729 av_promo, max_promotion_in_bytes);
730 }
731 return res;
732 }
733
734 // At a promotion failure dump information on block layout in heap
735 // (cms old generation).
736 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
737 if (CMSDumpAtPromotionFailure) {
738 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
739 }
740 }
741
742 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
743 // Clear the promotion information. These pointers can be adjusted
744 // along with all the other pointers into the heap but
745 // compaction is expected to be a rare event with
746 // a heap using cms so don't do it without seeing the need.
747 for (uint i = 0; i < ParallelGCThreads; i++) {
748 _par_gc_thread_states[i]->promo.reset();
749 }
750 }
751
752 void ConcurrentMarkSweepGeneration::compute_new_size() {
753 assert_locked_or_safepoint(Heap_lock);
754
755 // If incremental collection failed, we just want to expand
756 // to the limit.
757 if (incremental_collection_failed()) {
758 clear_incremental_collection_failed();
759 grow_to_reserved();
760 return;
761 }
762
763 // The heap has been compacted but not reset yet.
764 // Any metric such as free() or used() will be incorrect.
765
766 CardGeneration::compute_new_size();
767
768 // Reset again after a possible resizing
769 if (did_compact()) {
770 cmsSpace()->reset_after_compaction();
771 }
772 }
773
774 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
775 assert_locked_or_safepoint(Heap_lock);
776
777 // If incremental collection failed, we just want to expand
778 // to the limit.
779 if (incremental_collection_failed()) {
780 clear_incremental_collection_failed();
781 grow_to_reserved();
782 return;
783 }
784
785 double free_percentage = ((double) free()) / capacity();
786 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
787 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
788
789 // compute expansion delta needed for reaching desired free percentage
790 if (free_percentage < desired_free_percentage) {
791 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
792 assert(desired_capacity >= capacity(), "invalid expansion size");
793 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
794 if (PrintGCDetails && Verbose) {
795 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
796 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
797 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
798 gclog_or_tty->print_cr(" Desired free fraction %f", desired_free_percentage);
799 gclog_or_tty->print_cr(" Maximum free fraction %f", maximum_free_percentage);
800 gclog_or_tty->print_cr(" Capacity " SIZE_FORMAT, capacity() / 1000);
801 gclog_or_tty->print_cr(" Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
802 GenCollectedHeap* gch = GenCollectedHeap::heap();
803 assert(gch->is_old_gen(this), "The CMS generation should always be the old generation");
804 size_t young_size = gch->young_gen()->capacity();
805 gclog_or_tty->print_cr(" Young gen size " SIZE_FORMAT, young_size / 1000);
806 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
807 gclog_or_tty->print_cr(" contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
808 gclog_or_tty->print_cr(" Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
809 }
810 // safe if expansion fails
811 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
812 if (PrintGCDetails && Verbose) {
813 gclog_or_tty->print_cr(" Expanded free fraction %f", ((double) free()) / capacity());
814 }
815 } else {
816 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
817 assert(desired_capacity <= capacity(), "invalid expansion size");
818 size_t shrink_bytes = capacity() - desired_capacity;
819 // Don't shrink unless the delta is greater than the minimum shrink we want
820 if (shrink_bytes >= MinHeapDeltaBytes) {
821 shrink_free_list_by(shrink_bytes);
822 }
823 }
824 }
825
826 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
827 return cmsSpace()->freelistLock();
828 }
829
830 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
831 CMSSynchronousYieldRequest yr;
832 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
833 return have_lock_and_allocate(size, tlab);
834 }
835
836 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
837 bool tlab /* ignored */) {
838 assert_lock_strong(freelistLock());
839 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
840 HeapWord* res = cmsSpace()->allocate(adjustedSize);
841 // Allocate the object live (grey) if the background collector has
842 // started marking. This is necessary because the marker may
843 // have passed this address and consequently this object will
844 // not otherwise be greyed and would be incorrectly swept up.
845 // Note that if this object contains references, the writing
846 // of those references will dirty the card containing this object
847 // allowing the object to be blackened (and its references scanned)
848 // either during a preclean phase or at the final checkpoint.
849 if (res != NULL) {
850 // We may block here with an uninitialized object with
851 // its mark-bit or P-bits not yet set. Such objects need
852 // to be safely navigable by block_start().
853 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
854 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
855 collector()->direct_allocated(res, adjustedSize);
856 _direct_allocated_words += adjustedSize;
857 // allocation counters
858 NOT_PRODUCT(
859 _numObjectsAllocated++;
860 _numWordsAllocated += (int)adjustedSize;
861 )
862 }
863 return res;
864 }
865
866 // In the case of direct allocation by mutators in a generation that
867 // is being concurrently collected, the object must be allocated
868 // live (grey) if the background collector has started marking.
869 // This is necessary because the marker may
870 // have passed this address and consequently this object will
871 // not otherwise be greyed and would be incorrectly swept up.
872 // Note that if this object contains references, the writing
873 // of those references will dirty the card containing this object
874 // allowing the object to be blackened (and its references scanned)
875 // either during a preclean phase or at the final checkpoint.
876 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
877 assert(_markBitMap.covers(start, size), "Out of bounds");
878 if (_collectorState >= Marking) {
879 MutexLockerEx y(_markBitMap.lock(),
880 Mutex::_no_safepoint_check_flag);
881 // [see comments preceding SweepClosure::do_blk() below for details]
882 //
883 // Can the P-bits be deleted now? JJJ
884 //
885 // 1. need to mark the object as live so it isn't collected
886 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
887 // 3. need to mark the end of the object so marking, precleaning or sweeping
888 // can skip over uninitialized or unparsable objects. An allocated
889 // object is considered uninitialized for our purposes as long as
890 // its klass word is NULL. All old gen objects are parsable
891 // as soon as they are initialized.)
892 _markBitMap.mark(start); // object is live
893 _markBitMap.mark(start + 1); // object is potentially uninitialized?
894 _markBitMap.mark(start + size - 1);
895 // mark end of object
896 }
897 // check that oop looks uninitialized
898 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
899 }
900
901 void CMSCollector::promoted(bool par, HeapWord* start,
902 bool is_obj_array, size_t obj_size) {
903 assert(_markBitMap.covers(start), "Out of bounds");
904 // See comment in direct_allocated() about when objects should
905 // be allocated live.
906 if (_collectorState >= Marking) {
907 // we already hold the marking bit map lock, taken in
908 // the prologue
909 if (par) {
910 _markBitMap.par_mark(start);
911 } else {
912 _markBitMap.mark(start);
913 }
914 // We don't need to mark the object as uninitialized (as
915 // in direct_allocated above) because this is being done with the
916 // world stopped and the object will be initialized by the
917 // time the marking, precleaning or sweeping get to look at it.
918 // But see the code for copying objects into the CMS generation,
919 // where we need to ensure that concurrent readers of the
920 // block offset table are able to safely navigate a block that
921 // is in flux from being free to being allocated (and in
922 // transition while being copied into) and subsequently
923 // becoming a bona-fide object when the copy/promotion is complete.
924 assert(SafepointSynchronize::is_at_safepoint(),
925 "expect promotion only at safepoints");
926
927 if (_collectorState < Sweeping) {
928 // Mark the appropriate cards in the modUnionTable, so that
929 // this object gets scanned before the sweep. If this is
930 // not done, CMS generation references in the object might
931 // not get marked.
932 // For the case of arrays, which are otherwise precisely
933 // marked, we need to dirty the entire array, not just its head.
934 if (is_obj_array) {
935 // The [par_]mark_range() method expects mr.end() below to
936 // be aligned to the granularity of a bit's representation
937 // in the heap. In the case of the MUT below, that's a
938 // card size.
939 MemRegion mr(start,
940 (HeapWord*)round_to((intptr_t)(start + obj_size),
941 CardTableModRefBS::card_size /* bytes */));
942 if (par) {
943 _modUnionTable.par_mark_range(mr);
944 } else {
945 _modUnionTable.mark_range(mr);
946 }
947 } else { // not an obj array; we can just mark the head
948 if (par) {
949 _modUnionTable.par_mark(start);
950 } else {
951 _modUnionTable.mark(start);
952 }
953 }
954 }
955 }
956 }
957
958 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
959 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
960 // allocate, copy and if necessary update promoinfo --
961 // delegate to underlying space.
962 assert_lock_strong(freelistLock());
963
964 #ifndef PRODUCT
965 if (GenCollectedHeap::heap()->promotion_should_fail()) {
966 return NULL;
967 }
968 #endif // #ifndef PRODUCT
969
970 oop res = _cmsSpace->promote(obj, obj_size);
971 if (res == NULL) {
972 // expand and retry
973 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
974 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
975 // Since this is the old generation, we don't try to promote
976 // into a more senior generation.
977 res = _cmsSpace->promote(obj, obj_size);
978 }
979 if (res != NULL) {
980 // See comment in allocate() about when objects should
981 // be allocated live.
982 assert(obj->is_oop(), "Will dereference klass pointer below");
983 collector()->promoted(false, // Not parallel
984 (HeapWord*)res, obj->is_objArray(), obj_size);
985 // promotion counters
986 NOT_PRODUCT(
987 _numObjectsPromoted++;
988 _numWordsPromoted +=
989 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
990 )
991 }
992 return res;
993 }
994
995
996 // IMPORTANT: Notes on object size recognition in CMS.
997 // ---------------------------------------------------
998 // A block of storage in the CMS generation is always in
999 // one of three states. A free block (FREE), an allocated
1000 // object (OBJECT) whose size() method reports the correct size,
1001 // and an intermediate state (TRANSIENT) in which its size cannot
1002 // be accurately determined.
1003 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1004 // -----------------------------------------------------
1005 // FREE: klass_word & 1 == 1; mark_word holds block size
1006 //
1007 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1008 // obj->size() computes correct size
1009 //
1010 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1011 //
1012 // STATE IDENTIFICATION: (64 bit+COOPS)
1013 // ------------------------------------
1014 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1015 //
1016 // OBJECT: klass_word installed; klass_word != 0;
1017 // obj->size() computes correct size
1018 //
1019 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1020 //
1021 //
1022 // STATE TRANSITION DIAGRAM
1023 //
1024 // mut / parnew mut / parnew
1025 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1026 // ^ |
1027 // |------------------------ DEAD <------------------------------------|
1028 // sweep mut
1029 //
1030 // While a block is in TRANSIENT state its size cannot be determined
1031 // so readers will either need to come back later or stall until
1032 // the size can be determined. Note that for the case of direct
1033 // allocation, P-bits, when available, may be used to determine the
1034 // size of an object that may not yet have been initialized.
1035
1036 // Things to support parallel young-gen collection.
1037 oop
1038 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1039 oop old, markOop m,
1040 size_t word_sz) {
1041 #ifndef PRODUCT
1042 if (GenCollectedHeap::heap()->promotion_should_fail()) {
1043 return NULL;
1044 }
1045 #endif // #ifndef PRODUCT
1046
1047 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1048 PromotionInfo* promoInfo = &ps->promo;
1049 // if we are tracking promotions, then first ensure space for
1050 // promotion (including spooling space for saving header if necessary).
1051 // then allocate and copy, then track promoted info if needed.
1052 // When tracking (see PromotionInfo::track()), the mark word may
1053 // be displaced and in this case restoration of the mark word
1054 // occurs in the (oop_since_save_marks_)iterate phase.
1055 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1056 // Out of space for allocating spooling buffers;
1057 // try expanding and allocating spooling buffers.
1058 if (!expand_and_ensure_spooling_space(promoInfo)) {
1059 return NULL;
1060 }
1061 }
1062 assert(promoInfo->has_spooling_space(), "Control point invariant");
1063 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1064 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1065 if (obj_ptr == NULL) {
1066 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1067 if (obj_ptr == NULL) {
1068 return NULL;
1069 }
1070 }
1071 oop obj = oop(obj_ptr);
1072 OrderAccess::storestore();
1073 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1074 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1075 // IMPORTANT: See note on object initialization for CMS above.
1076 // Otherwise, copy the object. Here we must be careful to insert the
1077 // klass pointer last, since this marks the block as an allocated object.
1078 // Except with compressed oops it's the mark word.
1079 HeapWord* old_ptr = (HeapWord*)old;
1080 // Restore the mark word copied above.
1081 obj->set_mark(m);
1082 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1083 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1084 OrderAccess::storestore();
1085
1086 if (UseCompressedClassPointers) {
1087 // Copy gap missed by (aligned) header size calculation below
1088 obj->set_klass_gap(old->klass_gap());
1089 }
1090 if (word_sz > (size_t)oopDesc::header_size()) {
1091 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1092 obj_ptr + oopDesc::header_size(),
1093 word_sz - oopDesc::header_size());
1094 }
1095
1096 // Now we can track the promoted object, if necessary. We take care
1097 // to delay the transition from uninitialized to full object
1098 // (i.e., insertion of klass pointer) until after, so that it
1099 // atomically becomes a promoted object.
1100 if (promoInfo->tracking()) {
1101 promoInfo->track((PromotedObject*)obj, old->klass());
1102 }
1103 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1104 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1105 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1106
1107 // Finally, install the klass pointer (this should be volatile).
1108 OrderAccess::storestore();
1109 obj->set_klass(old->klass());
1110 // We should now be able to calculate the right size for this object
1111 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1112
1113 collector()->promoted(true, // parallel
1114 obj_ptr, old->is_objArray(), word_sz);
1115
1116 NOT_PRODUCT(
1117 Atomic::inc_ptr(&_numObjectsPromoted);
1118 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1119 )
1120
1121 return obj;
1122 }
1123
1124 void
1125 ConcurrentMarkSweepGeneration::
1126 par_promote_alloc_done(int thread_num) {
1127 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1128 ps->lab.retire(thread_num);
1129 }
1130
1131 void
1132 ConcurrentMarkSweepGeneration::
1133 par_oop_since_save_marks_iterate_done(int thread_num) {
1134 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1135 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1136 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1137 }
1138
1139 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1140 size_t size,
1141 bool tlab)
1142 {
1143 // We allow a STW collection only if a full
1144 // collection was requested.
1145 return full || should_allocate(size, tlab); // FIX ME !!!
1146 // This and promotion failure handling are connected at the
1147 // hip and should be fixed by untying them.
1148 }
1149
1150 bool CMSCollector::shouldConcurrentCollect() {
1151 if (_full_gc_requested) {
1152 if (Verbose && PrintGCDetails) {
1153 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1154 " gc request (or gc_locker)");
1155 }
1156 return true;
1157 }
1158
1159 FreelistLocker x(this);
1160 // ------------------------------------------------------------------
1161 // Print out lots of information which affects the initiation of
1162 // a collection.
1163 if (PrintCMSInitiationStatistics && stats().valid()) {
1164 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1165 gclog_or_tty->stamp();
1166 gclog_or_tty->cr();
1167 stats().print_on(gclog_or_tty);
1168 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1169 stats().time_until_cms_gen_full());
1170 gclog_or_tty->print_cr("free=" SIZE_FORMAT, _cmsGen->free());
1171 gclog_or_tty->print_cr("contiguous_available=" SIZE_FORMAT,
1172 _cmsGen->contiguous_available());
1173 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1174 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1175 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1176 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1177 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1178 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1179 gclog_or_tty->print_cr("metadata initialized %d",
1180 MetaspaceGC::should_concurrent_collect());
1181 }
1182 // ------------------------------------------------------------------
1183
1184 // If the estimated time to complete a cms collection (cms_duration())
1185 // is less than the estimated time remaining until the cms generation
1186 // is full, start a collection.
1187 if (!UseCMSInitiatingOccupancyOnly) {
1188 if (stats().valid()) {
1189 if (stats().time_until_cms_start() == 0.0) {
1190 return true;
1191 }
1192 } else {
1193 // We want to conservatively collect somewhat early in order
1194 // to try and "bootstrap" our CMS/promotion statistics;
1195 // this branch will not fire after the first successful CMS
1196 // collection because the stats should then be valid.
1197 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1198 if (Verbose && PrintGCDetails) {
1199 gclog_or_tty->print_cr(
1200 " CMSCollector: collect for bootstrapping statistics:"
1201 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1202 _bootstrap_occupancy);
1203 }
1204 return true;
1205 }
1206 }
1207 }
1208
1209 // Otherwise, we start a collection cycle if
1210 // old gen want a collection cycle started. Each may use
1211 // an appropriate criterion for making this decision.
1212 // XXX We need to make sure that the gen expansion
1213 // criterion dovetails well with this. XXX NEED TO FIX THIS
1214 if (_cmsGen->should_concurrent_collect()) {
1215 if (Verbose && PrintGCDetails) {
1216 gclog_or_tty->print_cr("CMS old gen initiated");
1217 }
1218 return true;
1219 }
1220
1221 // We start a collection if we believe an incremental collection may fail;
1222 // this is not likely to be productive in practice because it's probably too
1223 // late anyway.
1224 GenCollectedHeap* gch = GenCollectedHeap::heap();
1225 assert(gch->collector_policy()->is_generation_policy(),
1226 "You may want to check the correctness of the following");
1227 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1228 if (Verbose && PrintGCDetails) {
1229 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1230 }
1231 return true;
1232 }
1233
1234 if (MetaspaceGC::should_concurrent_collect()) {
1235 if (Verbose && PrintGCDetails) {
1236 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1237 }
1238 return true;
1239 }
1240
1241 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1242 if (CMSTriggerInterval >= 0) {
1243 if (CMSTriggerInterval == 0) {
1244 // Trigger always
1245 return true;
1246 }
1247
1248 // Check the CMS time since begin (we do not check the stats validity
1249 // as we want to be able to trigger the first CMS cycle as well)
1250 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1251 if (Verbose && PrintGCDetails) {
1252 if (stats().valid()) {
1253 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1254 stats().cms_time_since_begin());
1255 } else {
1256 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1257 }
1258 }
1259 return true;
1260 }
1261 }
1262
1263 return false;
1264 }
1265
1266 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1267
1268 // Clear _expansion_cause fields of constituent generations
1269 void CMSCollector::clear_expansion_cause() {
1270 _cmsGen->clear_expansion_cause();
1271 }
1272
1273 // We should be conservative in starting a collection cycle. To
1274 // start too eagerly runs the risk of collecting too often in the
1275 // extreme. To collect too rarely falls back on full collections,
1276 // which works, even if not optimum in terms of concurrent work.
1277 // As a work around for too eagerly collecting, use the flag
1278 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1279 // giving the user an easily understandable way of controlling the
1280 // collections.
1281 // We want to start a new collection cycle if any of the following
1282 // conditions hold:
1283 // . our current occupancy exceeds the configured initiating occupancy
1284 // for this generation, or
1285 // . we recently needed to expand this space and have not, since that
1286 // expansion, done a collection of this generation, or
1287 // . the underlying space believes that it may be a good idea to initiate
1288 // a concurrent collection (this may be based on criteria such as the
1289 // following: the space uses linear allocation and linear allocation is
1290 // going to fail, or there is believed to be excessive fragmentation in
1291 // the generation, etc... or ...
1292 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1293 // the case of the old generation; see CR 6543076):
1294 // we may be approaching a point at which allocation requests may fail because
1295 // we will be out of sufficient free space given allocation rate estimates.]
1296 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1297
1298 assert_lock_strong(freelistLock());
1299 if (occupancy() > initiating_occupancy()) {
1300 if (PrintGCDetails && Verbose) {
1301 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1302 short_name(), occupancy(), initiating_occupancy());
1303 }
1304 return true;
1305 }
1306 if (UseCMSInitiatingOccupancyOnly) {
1307 return false;
1308 }
1309 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1310 if (PrintGCDetails && Verbose) {
1311 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1312 short_name());
1313 }
1314 return true;
1315 }
1316 if (_cmsSpace->should_concurrent_collect()) {
1317 if (PrintGCDetails && Verbose) {
1318 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1319 short_name());
1320 }
1321 return true;
1322 }
1323 return false;
1324 }
1325
1326 void ConcurrentMarkSweepGeneration::collect(bool full,
1327 bool clear_all_soft_refs,
1328 size_t size,
1329 bool tlab)
1330 {
1331 collector()->collect(full, clear_all_soft_refs, size, tlab);
1332 }
1333
1334 void CMSCollector::collect(bool full,
1335 bool clear_all_soft_refs,
1336 size_t size,
1337 bool tlab)
1338 {
1339 // The following "if" branch is present for defensive reasons.
1340 // In the current uses of this interface, it can be replaced with:
1341 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1342 // But I am not placing that assert here to allow future
1343 // generality in invoking this interface.
1344 if (GC_locker::is_active()) {
1345 // A consistency test for GC_locker
1346 assert(GC_locker::needs_gc(), "Should have been set already");
1347 // Skip this foreground collection, instead
1348 // expanding the heap if necessary.
1349 // Need the free list locks for the call to free() in compute_new_size()
1350 compute_new_size();
1351 return;
1352 }
1353 acquire_control_and_collect(full, clear_all_soft_refs);
1354 }
1355
1356 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1357 GenCollectedHeap* gch = GenCollectedHeap::heap();
1358 unsigned int gc_count = gch->total_full_collections();
1359 if (gc_count == full_gc_count) {
1360 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1361 _full_gc_requested = true;
1362 _full_gc_cause = cause;
1363 CGC_lock->notify(); // nudge CMS thread
1364 } else {
1365 assert(gc_count > full_gc_count, "Error: causal loop");
1366 }
1367 }
1368
1369 bool CMSCollector::is_external_interruption() {
1370 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1371 return GCCause::is_user_requested_gc(cause) ||
1372 GCCause::is_serviceability_requested_gc(cause);
1373 }
1374
1375 void CMSCollector::report_concurrent_mode_interruption() {
1376 if (is_external_interruption()) {
1377 if (PrintGCDetails) {
1378 gclog_or_tty->print(" (concurrent mode interrupted)");
1379 }
1380 } else {
1381 if (PrintGCDetails) {
1382 gclog_or_tty->print(" (concurrent mode failure)");
1383 }
1384 _gc_tracer_cm->report_concurrent_mode_failure();
1385 }
1386 }
1387
1388
1389 // The foreground and background collectors need to coordinate in order
1390 // to make sure that they do not mutually interfere with CMS collections.
1391 // When a background collection is active,
1392 // the foreground collector may need to take over (preempt) and
1393 // synchronously complete an ongoing collection. Depending on the
1394 // frequency of the background collections and the heap usage
1395 // of the application, this preemption can be seldom or frequent.
1396 // There are only certain
1397 // points in the background collection that the "collection-baton"
1398 // can be passed to the foreground collector.
1399 //
1400 // The foreground collector will wait for the baton before
1401 // starting any part of the collection. The foreground collector
1402 // will only wait at one location.
1403 //
1404 // The background collector will yield the baton before starting a new
1405 // phase of the collection (e.g., before initial marking, marking from roots,
1406 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1407 // of the loop which switches the phases. The background collector does some
1408 // of the phases (initial mark, final re-mark) with the world stopped.
1409 // Because of locking involved in stopping the world,
1410 // the foreground collector should not block waiting for the background
1411 // collector when it is doing a stop-the-world phase. The background
1412 // collector will yield the baton at an additional point just before
1413 // it enters a stop-the-world phase. Once the world is stopped, the
1414 // background collector checks the phase of the collection. If the
1415 // phase has not changed, it proceeds with the collection. If the
1416 // phase has changed, it skips that phase of the collection. See
1417 // the comments on the use of the Heap_lock in collect_in_background().
1418 //
1419 // Variable used in baton passing.
1420 // _foregroundGCIsActive - Set to true by the foreground collector when
1421 // it wants the baton. The foreground clears it when it has finished
1422 // the collection.
1423 // _foregroundGCShouldWait - Set to true by the background collector
1424 // when it is running. The foreground collector waits while
1425 // _foregroundGCShouldWait is true.
1426 // CGC_lock - monitor used to protect access to the above variables
1427 // and to notify the foreground and background collectors.
1428 // _collectorState - current state of the CMS collection.
1429 //
1430 // The foreground collector
1431 // acquires the CGC_lock
1432 // sets _foregroundGCIsActive
1433 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1434 // various locks acquired in preparation for the collection
1435 // are released so as not to block the background collector
1436 // that is in the midst of a collection
1437 // proceeds with the collection
1438 // clears _foregroundGCIsActive
1439 // returns
1440 //
1441 // The background collector in a loop iterating on the phases of the
1442 // collection
1443 // acquires the CGC_lock
1444 // sets _foregroundGCShouldWait
1445 // if _foregroundGCIsActive is set
1446 // clears _foregroundGCShouldWait, notifies _CGC_lock
1447 // waits on _CGC_lock for _foregroundGCIsActive to become false
1448 // and exits the loop.
1449 // otherwise
1450 // proceed with that phase of the collection
1451 // if the phase is a stop-the-world phase,
1452 // yield the baton once more just before enqueueing
1453 // the stop-world CMS operation (executed by the VM thread).
1454 // returns after all phases of the collection are done
1455 //
1456
1457 void CMSCollector::acquire_control_and_collect(bool full,
1458 bool clear_all_soft_refs) {
1459 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1460 assert(!Thread::current()->is_ConcurrentGC_thread(),
1461 "shouldn't try to acquire control from self!");
1462
1463 // Start the protocol for acquiring control of the
1464 // collection from the background collector (aka CMS thread).
1465 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1466 "VM thread should have CMS token");
1467 // Remember the possibly interrupted state of an ongoing
1468 // concurrent collection
1469 CollectorState first_state = _collectorState;
1470
1471 // Signal to a possibly ongoing concurrent collection that
1472 // we want to do a foreground collection.
1473 _foregroundGCIsActive = true;
1474
1475 // release locks and wait for a notify from the background collector
1476 // releasing the locks in only necessary for phases which
1477 // do yields to improve the granularity of the collection.
1478 assert_lock_strong(bitMapLock());
1479 // We need to lock the Free list lock for the space that we are
1480 // currently collecting.
1481 assert(haveFreelistLocks(), "Must be holding free list locks");
1482 bitMapLock()->unlock();
1483 releaseFreelistLocks();
1484 {
1485 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1486 if (_foregroundGCShouldWait) {
1487 // We are going to be waiting for action for the CMS thread;
1488 // it had better not be gone (for instance at shutdown)!
1489 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1490 "CMS thread must be running");
1491 // Wait here until the background collector gives us the go-ahead
1492 ConcurrentMarkSweepThread::clear_CMS_flag(
1493 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1494 // Get a possibly blocked CMS thread going:
1495 // Note that we set _foregroundGCIsActive true above,
1496 // without protection of the CGC_lock.
1497 CGC_lock->notify();
1498 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1499 "Possible deadlock");
1500 while (_foregroundGCShouldWait) {
1501 // wait for notification
1502 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1503 // Possibility of delay/starvation here, since CMS token does
1504 // not know to give priority to VM thread? Actually, i think
1505 // there wouldn't be any delay/starvation, but the proof of
1506 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1507 }
1508 ConcurrentMarkSweepThread::set_CMS_flag(
1509 ConcurrentMarkSweepThread::CMS_vm_has_token);
1510 }
1511 }
1512 // The CMS_token is already held. Get back the other locks.
1513 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1514 "VM thread should have CMS token");
1515 getFreelistLocks();
1516 bitMapLock()->lock_without_safepoint_check();
1517 if (TraceCMSState) {
1518 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1519 INTPTR_FORMAT " with first state %d", p2i(Thread::current()), first_state);
1520 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1521 }
1522
1523 // Inform cms gen if this was due to partial collection failing.
1524 // The CMS gen may use this fact to determine its expansion policy.
1525 GenCollectedHeap* gch = GenCollectedHeap::heap();
1526 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1527 assert(!_cmsGen->incremental_collection_failed(),
1528 "Should have been noticed, reacted to and cleared");
1529 _cmsGen->set_incremental_collection_failed();
1530 }
1531
1532 if (first_state > Idling) {
1533 report_concurrent_mode_interruption();
1534 }
1535
1536 set_did_compact(true);
1537
1538 // If the collection is being acquired from the background
1539 // collector, there may be references on the discovered
1540 // references lists. Abandon those references, since some
1541 // of them may have become unreachable after concurrent
1542 // discovery; the STW compacting collector will redo discovery
1543 // more precisely, without being subject to floating garbage.
1544 // Leaving otherwise unreachable references in the discovered
1545 // lists would require special handling.
1546 ref_processor()->disable_discovery();
1547 ref_processor()->abandon_partial_discovery();
1548 ref_processor()->verify_no_references_recorded();
1549
1550 if (first_state > Idling) {
1551 save_heap_summary();
1552 }
1553
1554 do_compaction_work(clear_all_soft_refs);
1555
1556 // Has the GC time limit been exceeded?
1557 size_t max_eden_size = _young_gen->max_capacity() -
1558 _young_gen->to()->capacity() -
1559 _young_gen->from()->capacity();
1560 GCCause::Cause gc_cause = gch->gc_cause();
1561 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1562 _young_gen->eden()->used(),
1563 _cmsGen->max_capacity(),
1564 max_eden_size,
1565 full,
1566 gc_cause,
1567 gch->collector_policy());
1568
1569 // Reset the expansion cause, now that we just completed
1570 // a collection cycle.
1571 clear_expansion_cause();
1572 _foregroundGCIsActive = false;
1573 return;
1574 }
1575
1576 // Resize the tenured generation
1577 // after obtaining the free list locks for the
1578 // two generations.
1579 void CMSCollector::compute_new_size() {
1580 assert_locked_or_safepoint(Heap_lock);
1581 FreelistLocker z(this);
1582 MetaspaceGC::compute_new_size();
1583 _cmsGen->compute_new_size_free_list();
1584 }
1585
1586 // A work method used by the foreground collector to do
1587 // a mark-sweep-compact.
1588 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1589 GenCollectedHeap* gch = GenCollectedHeap::heap();
1590
1591 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1592 gc_timer->register_gc_start();
1593
1594 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1595 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1596
1597 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL);
1598
1599 // Temporarily widen the span of the weak reference processing to
1600 // the entire heap.
1601 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1602 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1603 // Temporarily, clear the "is_alive_non_header" field of the
1604 // reference processor.
1605 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1606 // Temporarily make reference _processing_ single threaded (non-MT).
1607 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1608 // Temporarily make refs discovery atomic
1609 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1610 // Temporarily make reference _discovery_ single threaded (non-MT)
1611 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1612
1613 ref_processor()->set_enqueuing_is_done(false);
1614 ref_processor()->enable_discovery();
1615 ref_processor()->setup_policy(clear_all_soft_refs);
1616 // If an asynchronous collection finishes, the _modUnionTable is
1617 // all clear. If we are assuming the collection from an asynchronous
1618 // collection, clear the _modUnionTable.
1619 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1620 "_modUnionTable should be clear if the baton was not passed");
1621 _modUnionTable.clear_all();
1622 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1623 "mod union for klasses should be clear if the baton was passed");
1624 _ct->klass_rem_set()->clear_mod_union();
1625
1626 // We must adjust the allocation statistics being maintained
1627 // in the free list space. We do so by reading and clearing
1628 // the sweep timer and updating the block flux rate estimates below.
1629 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1630 if (_inter_sweep_timer.is_active()) {
1631 _inter_sweep_timer.stop();
1632 // Note that we do not use this sample to update the _inter_sweep_estimate.
1633 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1634 _inter_sweep_estimate.padded_average(),
1635 _intra_sweep_estimate.padded_average());
1636 }
1637
1638 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1639 #ifdef ASSERT
1640 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1641 size_t free_size = cms_space->free();
1642 assert(free_size ==
1643 pointer_delta(cms_space->end(), cms_space->compaction_top())
1644 * HeapWordSize,
1645 "All the free space should be compacted into one chunk at top");
1646 assert(cms_space->dictionary()->total_chunk_size(
1647 debug_only(cms_space->freelistLock())) == 0 ||
1648 cms_space->totalSizeInIndexedFreeLists() == 0,
1649 "All the free space should be in a single chunk");
1650 size_t num = cms_space->totalCount();
1651 assert((free_size == 0 && num == 0) ||
1652 (free_size > 0 && (num == 1 || num == 2)),
1653 "There should be at most 2 free chunks after compaction");
1654 #endif // ASSERT
1655 _collectorState = Resetting;
1656 assert(_restart_addr == NULL,
1657 "Should have been NULL'd before baton was passed");
1658 reset(false /* == !concurrent */);
1659 _cmsGen->reset_after_compaction();
1660 _concurrent_cycles_since_last_unload = 0;
1661
1662 // Clear any data recorded in the PLAB chunk arrays.
1663 if (_survivor_plab_array != NULL) {
1664 reset_survivor_plab_arrays();
1665 }
1666
1667 // Adjust the per-size allocation stats for the next epoch.
1668 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1669 // Restart the "inter sweep timer" for the next epoch.
1670 _inter_sweep_timer.reset();
1671 _inter_sweep_timer.start();
1672
1673 gc_timer->register_gc_end();
1674
1675 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1676
1677 // For a mark-sweep-compact, compute_new_size() will be called
1678 // in the heap's do_collection() method.
1679 }
1680
1681 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1682 ContiguousSpace* eden_space = _young_gen->eden();
1683 ContiguousSpace* from_space = _young_gen->from();
1684 ContiguousSpace* to_space = _young_gen->to();
1685 // Eden
1686 if (_eden_chunk_array != NULL) {
1687 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1688 p2i(eden_space->bottom()), p2i(eden_space->top()),
1689 p2i(eden_space->end()), eden_space->capacity());
1690 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1691 "_eden_chunk_capacity=" SIZE_FORMAT,
1692 _eden_chunk_index, _eden_chunk_capacity);
1693 for (size_t i = 0; i < _eden_chunk_index; i++) {
1694 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1695 i, p2i(_eden_chunk_array[i]));
1696 }
1697 }
1698 // Survivor
1699 if (_survivor_chunk_array != NULL) {
1700 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1701 p2i(from_space->bottom()), p2i(from_space->top()),
1702 p2i(from_space->end()), from_space->capacity());
1703 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1704 "_survivor_chunk_capacity=" SIZE_FORMAT,
1705 _survivor_chunk_index, _survivor_chunk_capacity);
1706 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1707 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1708 i, p2i(_survivor_chunk_array[i]));
1709 }
1710 }
1711 }
1712
1713 void CMSCollector::getFreelistLocks() const {
1714 // Get locks for all free lists in all generations that this
1715 // collector is responsible for
1716 _cmsGen->freelistLock()->lock_without_safepoint_check();
1717 }
1718
1719 void CMSCollector::releaseFreelistLocks() const {
1720 // Release locks for all free lists in all generations that this
1721 // collector is responsible for
1722 _cmsGen->freelistLock()->unlock();
1723 }
1724
1725 bool CMSCollector::haveFreelistLocks() const {
1726 // Check locks for all free lists in all generations that this
1727 // collector is responsible for
1728 assert_lock_strong(_cmsGen->freelistLock());
1729 PRODUCT_ONLY(ShouldNotReachHere());
1730 return true;
1731 }
1732
1733 // A utility class that is used by the CMS collector to
1734 // temporarily "release" the foreground collector from its
1735 // usual obligation to wait for the background collector to
1736 // complete an ongoing phase before proceeding.
1737 class ReleaseForegroundGC: public StackObj {
1738 private:
1739 CMSCollector* _c;
1740 public:
1741 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1742 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1743 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1744 // allow a potentially blocked foreground collector to proceed
1745 _c->_foregroundGCShouldWait = false;
1746 if (_c->_foregroundGCIsActive) {
1747 CGC_lock->notify();
1748 }
1749 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1750 "Possible deadlock");
1751 }
1752
1753 ~ReleaseForegroundGC() {
1754 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1755 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1756 _c->_foregroundGCShouldWait = true;
1757 }
1758 };
1759
1760 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1761 assert(Thread::current()->is_ConcurrentGC_thread(),
1762 "A CMS asynchronous collection is only allowed on a CMS thread.");
1763
1764 GenCollectedHeap* gch = GenCollectedHeap::heap();
1765 {
1766 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1767 MutexLockerEx hl(Heap_lock, safepoint_check);
1768 FreelistLocker fll(this);
1769 MutexLockerEx x(CGC_lock, safepoint_check);
1770 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
1771 // The foreground collector is active or we're
1772 // not using asynchronous collections. Skip this
1773 // background collection.
1774 assert(!_foregroundGCShouldWait, "Should be clear");
1775 return;
1776 } else {
1777 assert(_collectorState == Idling, "Should be idling before start.");
1778 _collectorState = InitialMarking;
1779 register_gc_start(cause);
1780 // Reset the expansion cause, now that we are about to begin
1781 // a new cycle.
1782 clear_expansion_cause();
1783
1784 // Clear the MetaspaceGC flag since a concurrent collection
1785 // is starting but also clear it after the collection.
1786 MetaspaceGC::set_should_concurrent_collect(false);
1787 }
1788 // Decide if we want to enable class unloading as part of the
1789 // ensuing concurrent GC cycle.
1790 update_should_unload_classes();
1791 _full_gc_requested = false; // acks all outstanding full gc requests
1792 _full_gc_cause = GCCause::_no_gc;
1793 // Signal that we are about to start a collection
1794 gch->increment_total_full_collections(); // ... starting a collection cycle
1795 _collection_count_start = gch->total_full_collections();
1796 }
1797
1798 // Used for PrintGC
1799 size_t prev_used;
1800 if (PrintGC && Verbose) {
1801 prev_used = _cmsGen->used();
1802 }
1803
1804 // The change of the collection state is normally done at this level;
1805 // the exceptions are phases that are executed while the world is
1806 // stopped. For those phases the change of state is done while the
1807 // world is stopped. For baton passing purposes this allows the
1808 // background collector to finish the phase and change state atomically.
1809 // The foreground collector cannot wait on a phase that is done
1810 // while the world is stopped because the foreground collector already
1811 // has the world stopped and would deadlock.
1812 while (_collectorState != Idling) {
1813 if (TraceCMSState) {
1814 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
1815 p2i(Thread::current()), _collectorState);
1816 }
1817 // The foreground collector
1818 // holds the Heap_lock throughout its collection.
1819 // holds the CMS token (but not the lock)
1820 // except while it is waiting for the background collector to yield.
1821 //
1822 // The foreground collector should be blocked (not for long)
1823 // if the background collector is about to start a phase
1824 // executed with world stopped. If the background
1825 // collector has already started such a phase, the
1826 // foreground collector is blocked waiting for the
1827 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1828 // are executed in the VM thread.
1829 //
1830 // The locking order is
1831 // PendingListLock (PLL) -- if applicable (FinalMarking)
1832 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1833 // CMS token (claimed in
1834 // stop_world_and_do() -->
1835 // safepoint_synchronize() -->
1836 // CMSThread::synchronize())
1837
1838 {
1839 // Check if the FG collector wants us to yield.
1840 CMSTokenSync x(true); // is cms thread
1841 if (waitForForegroundGC()) {
1842 // We yielded to a foreground GC, nothing more to be
1843 // done this round.
1844 assert(_foregroundGCShouldWait == false, "We set it to false in "
1845 "waitForForegroundGC()");
1846 if (TraceCMSState) {
1847 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1848 " exiting collection CMS state %d",
1849 p2i(Thread::current()), _collectorState);
1850 }
1851 return;
1852 } else {
1853 // The background collector can run but check to see if the
1854 // foreground collector has done a collection while the
1855 // background collector was waiting to get the CGC_lock
1856 // above. If yes, break so that _foregroundGCShouldWait
1857 // is cleared before returning.
1858 if (_collectorState == Idling) {
1859 break;
1860 }
1861 }
1862 }
1863
1864 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1865 "should be waiting");
1866
1867 switch (_collectorState) {
1868 case InitialMarking:
1869 {
1870 ReleaseForegroundGC x(this);
1871 stats().record_cms_begin();
1872 VM_CMS_Initial_Mark initial_mark_op(this);
1873 VMThread::execute(&initial_mark_op);
1874 }
1875 // The collector state may be any legal state at this point
1876 // since the background collector may have yielded to the
1877 // foreground collector.
1878 break;
1879 case Marking:
1880 // initial marking in checkpointRootsInitialWork has been completed
1881 if (markFromRoots()) { // we were successful
1882 assert(_collectorState == Precleaning, "Collector state should "
1883 "have changed");
1884 } else {
1885 assert(_foregroundGCIsActive, "Internal state inconsistency");
1886 }
1887 break;
1888 case Precleaning:
1889 // marking from roots in markFromRoots has been completed
1890 preclean();
1891 assert(_collectorState == AbortablePreclean ||
1892 _collectorState == FinalMarking,
1893 "Collector state should have changed");
1894 break;
1895 case AbortablePreclean:
1896 abortable_preclean();
1897 assert(_collectorState == FinalMarking, "Collector state should "
1898 "have changed");
1899 break;
1900 case FinalMarking:
1901 {
1902 ReleaseForegroundGC x(this);
1903
1904 VM_CMS_Final_Remark final_remark_op(this);
1905 VMThread::execute(&final_remark_op);
1906 }
1907 assert(_foregroundGCShouldWait, "block post-condition");
1908 break;
1909 case Sweeping:
1910 // final marking in checkpointRootsFinal has been completed
1911 sweep();
1912 assert(_collectorState == Resizing, "Collector state change "
1913 "to Resizing must be done under the free_list_lock");
1914
1915 case Resizing: {
1916 // Sweeping has been completed...
1917 // At this point the background collection has completed.
1918 // Don't move the call to compute_new_size() down
1919 // into code that might be executed if the background
1920 // collection was preempted.
1921 {
1922 ReleaseForegroundGC x(this); // unblock FG collection
1923 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1924 CMSTokenSync z(true); // not strictly needed.
1925 if (_collectorState == Resizing) {
1926 compute_new_size();
1927 save_heap_summary();
1928 _collectorState = Resetting;
1929 } else {
1930 assert(_collectorState == Idling, "The state should only change"
1931 " because the foreground collector has finished the collection");
1932 }
1933 }
1934 break;
1935 }
1936 case Resetting:
1937 // CMS heap resizing has been completed
1938 reset(true);
1939 assert(_collectorState == Idling, "Collector state should "
1940 "have changed");
1941
1942 MetaspaceGC::set_should_concurrent_collect(false);
1943
1944 stats().record_cms_end();
1945 // Don't move the concurrent_phases_end() and compute_new_size()
1946 // calls to here because a preempted background collection
1947 // has it's state set to "Resetting".
1948 break;
1949 case Idling:
1950 default:
1951 ShouldNotReachHere();
1952 break;
1953 }
1954 if (TraceCMSState) {
1955 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1956 p2i(Thread::current()), _collectorState);
1957 }
1958 assert(_foregroundGCShouldWait, "block post-condition");
1959 }
1960
1961 // Should this be in gc_epilogue?
1962 collector_policy()->counters()->update_counters();
1963
1964 {
1965 // Clear _foregroundGCShouldWait and, in the event that the
1966 // foreground collector is waiting, notify it, before
1967 // returning.
1968 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1969 _foregroundGCShouldWait = false;
1970 if (_foregroundGCIsActive) {
1971 CGC_lock->notify();
1972 }
1973 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1974 "Possible deadlock");
1975 }
1976 if (TraceCMSState) {
1977 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1978 " exiting collection CMS state %d",
1979 p2i(Thread::current()), _collectorState);
1980 }
1981 if (PrintGC && Verbose) {
1982 _cmsGen->print_heap_change(prev_used);
1983 }
1984 }
1985
1986 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1987 _cms_start_registered = true;
1988 _gc_timer_cm->register_gc_start();
1989 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1990 }
1991
1992 void CMSCollector::register_gc_end() {
1993 if (_cms_start_registered) {
1994 report_heap_summary(GCWhen::AfterGC);
1995
1996 _gc_timer_cm->register_gc_end();
1997 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1998 _cms_start_registered = false;
1999 }
2000 }
2001
2002 void CMSCollector::save_heap_summary() {
2003 GenCollectedHeap* gch = GenCollectedHeap::heap();
2004 _last_heap_summary = gch->create_heap_summary();
2005 _last_metaspace_summary = gch->create_metaspace_summary();
2006 }
2007
2008 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2009 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2010 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2011 }
2012
2013 bool CMSCollector::waitForForegroundGC() {
2014 bool res = false;
2015 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2016 "CMS thread should have CMS token");
2017 // Block the foreground collector until the
2018 // background collectors decides whether to
2019 // yield.
2020 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2021 _foregroundGCShouldWait = true;
2022 if (_foregroundGCIsActive) {
2023 // The background collector yields to the
2024 // foreground collector and returns a value
2025 // indicating that it has yielded. The foreground
2026 // collector can proceed.
2027 res = true;
2028 _foregroundGCShouldWait = false;
2029 ConcurrentMarkSweepThread::clear_CMS_flag(
2030 ConcurrentMarkSweepThread::CMS_cms_has_token);
2031 ConcurrentMarkSweepThread::set_CMS_flag(
2032 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2033 // Get a possibly blocked foreground thread going
2034 CGC_lock->notify();
2035 if (TraceCMSState) {
2036 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2037 p2i(Thread::current()), _collectorState);
2038 }
2039 while (_foregroundGCIsActive) {
2040 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2041 }
2042 ConcurrentMarkSweepThread::set_CMS_flag(
2043 ConcurrentMarkSweepThread::CMS_cms_has_token);
2044 ConcurrentMarkSweepThread::clear_CMS_flag(
2045 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2046 }
2047 if (TraceCMSState) {
2048 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2049 p2i(Thread::current()), _collectorState);
2050 }
2051 return res;
2052 }
2053
2054 // Because of the need to lock the free lists and other structures in
2055 // the collector, common to all the generations that the collector is
2056 // collecting, we need the gc_prologues of individual CMS generations
2057 // delegate to their collector. It may have been simpler had the
2058 // current infrastructure allowed one to call a prologue on a
2059 // collector. In the absence of that we have the generation's
2060 // prologue delegate to the collector, which delegates back
2061 // some "local" work to a worker method in the individual generations
2062 // that it's responsible for collecting, while itself doing any
2063 // work common to all generations it's responsible for. A similar
2064 // comment applies to the gc_epilogue()'s.
2065 // The role of the variable _between_prologue_and_epilogue is to
2066 // enforce the invocation protocol.
2067 void CMSCollector::gc_prologue(bool full) {
2068 // Call gc_prologue_work() for the CMSGen
2069 // we are responsible for.
2070
2071 // The following locking discipline assumes that we are only called
2072 // when the world is stopped.
2073 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2074
2075 // The CMSCollector prologue must call the gc_prologues for the
2076 // "generations" that it's responsible
2077 // for.
2078
2079 assert( Thread::current()->is_VM_thread()
2080 || ( CMSScavengeBeforeRemark
2081 && Thread::current()->is_ConcurrentGC_thread()),
2082 "Incorrect thread type for prologue execution");
2083
2084 if (_between_prologue_and_epilogue) {
2085 // We have already been invoked; this is a gc_prologue delegation
2086 // from yet another CMS generation that we are responsible for, just
2087 // ignore it since all relevant work has already been done.
2088 return;
2089 }
2090
2091 // set a bit saying prologue has been called; cleared in epilogue
2092 _between_prologue_and_epilogue = true;
2093 // Claim locks for common data structures, then call gc_prologue_work()
2094 // for each CMSGen.
2095
2096 getFreelistLocks(); // gets free list locks on constituent spaces
2097 bitMapLock()->lock_without_safepoint_check();
2098
2099 // Should call gc_prologue_work() for all cms gens we are responsible for
2100 bool duringMarking = _collectorState >= Marking
2101 && _collectorState < Sweeping;
2102
2103 // The young collections clear the modified oops state, which tells if
2104 // there are any modified oops in the class. The remark phase also needs
2105 // that information. Tell the young collection to save the union of all
2106 // modified klasses.
2107 if (duringMarking) {
2108 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2109 }
2110
2111 bool registerClosure = duringMarking;
2112
2113 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2114
2115 if (!full) {
2116 stats().record_gc0_begin();
2117 }
2118 }
2119
2120 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2121
2122 _capacity_at_prologue = capacity();
2123 _used_at_prologue = used();
2124
2125 // Delegate to CMScollector which knows how to coordinate between
2126 // this and any other CMS generations that it is responsible for
2127 // collecting.
2128 collector()->gc_prologue(full);
2129 }
2130
2131 // This is a "private" interface for use by this generation's CMSCollector.
2132 // Not to be called directly by any other entity (for instance,
2133 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2134 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2135 bool registerClosure, ModUnionClosure* modUnionClosure) {
2136 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2137 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2138 "Should be NULL");
2139 if (registerClosure) {
2140 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2141 }
2142 cmsSpace()->gc_prologue();
2143 // Clear stat counters
2144 NOT_PRODUCT(
2145 assert(_numObjectsPromoted == 0, "check");
2146 assert(_numWordsPromoted == 0, "check");
2147 if (Verbose && PrintGC) {
2148 gclog_or_tty->print("Allocated " SIZE_FORMAT " objects, "
2149 SIZE_FORMAT " bytes concurrently",
2150 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2151 }
2152 _numObjectsAllocated = 0;
2153 _numWordsAllocated = 0;
2154 )
2155 }
2156
2157 void CMSCollector::gc_epilogue(bool full) {
2158 // The following locking discipline assumes that we are only called
2159 // when the world is stopped.
2160 assert(SafepointSynchronize::is_at_safepoint(),
2161 "world is stopped assumption");
2162
2163 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2164 // if linear allocation blocks need to be appropriately marked to allow the
2165 // the blocks to be parsable. We also check here whether we need to nudge the
2166 // CMS collector thread to start a new cycle (if it's not already active).
2167 assert( Thread::current()->is_VM_thread()
2168 || ( CMSScavengeBeforeRemark
2169 && Thread::current()->is_ConcurrentGC_thread()),
2170 "Incorrect thread type for epilogue execution");
2171
2172 if (!_between_prologue_and_epilogue) {
2173 // We have already been invoked; this is a gc_epilogue delegation
2174 // from yet another CMS generation that we are responsible for, just
2175 // ignore it since all relevant work has already been done.
2176 return;
2177 }
2178 assert(haveFreelistLocks(), "must have freelist locks");
2179 assert_lock_strong(bitMapLock());
2180
2181 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2182
2183 _cmsGen->gc_epilogue_work(full);
2184
2185 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2186 // in case sampling was not already enabled, enable it
2187 _start_sampling = true;
2188 }
2189 // reset _eden_chunk_array so sampling starts afresh
2190 _eden_chunk_index = 0;
2191
2192 size_t cms_used = _cmsGen->cmsSpace()->used();
2193
2194 // update performance counters - this uses a special version of
2195 // update_counters() that allows the utilization to be passed as a
2196 // parameter, avoiding multiple calls to used().
2197 //
2198 _cmsGen->update_counters(cms_used);
2199
2200 bitMapLock()->unlock();
2201 releaseFreelistLocks();
2202
2203 if (!CleanChunkPoolAsync) {
2204 Chunk::clean_chunk_pool();
2205 }
2206
2207 set_did_compact(false);
2208 _between_prologue_and_epilogue = false; // ready for next cycle
2209 }
2210
2211 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2212 collector()->gc_epilogue(full);
2213
2214 // Also reset promotion tracking in par gc thread states.
2215 for (uint i = 0; i < ParallelGCThreads; i++) {
2216 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2217 }
2218 }
2219
2220 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2221 assert(!incremental_collection_failed(), "Should have been cleared");
2222 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2223 cmsSpace()->gc_epilogue();
2224 // Print stat counters
2225 NOT_PRODUCT(
2226 assert(_numObjectsAllocated == 0, "check");
2227 assert(_numWordsAllocated == 0, "check");
2228 if (Verbose && PrintGC) {
2229 gclog_or_tty->print("Promoted " SIZE_FORMAT " objects, "
2230 SIZE_FORMAT " bytes",
2231 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2232 }
2233 _numObjectsPromoted = 0;
2234 _numWordsPromoted = 0;
2235 )
2236
2237 if (PrintGC && Verbose) {
2238 // Call down the chain in contiguous_available needs the freelistLock
2239 // so print this out before releasing the freeListLock.
2240 gclog_or_tty->print(" Contiguous available " SIZE_FORMAT " bytes ",
2241 contiguous_available());
2242 }
2243 }
2244
2245 #ifndef PRODUCT
2246 bool CMSCollector::have_cms_token() {
2247 Thread* thr = Thread::current();
2248 if (thr->is_VM_thread()) {
2249 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2250 } else if (thr->is_ConcurrentGC_thread()) {
2251 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2252 } else if (thr->is_GC_task_thread()) {
2253 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2254 ParGCRareEvent_lock->owned_by_self();
2255 }
2256 return false;
2257 }
2258 #endif
2259
2260 // Check reachability of the given heap address in CMS generation,
2261 // treating all other generations as roots.
2262 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2263 // We could "guarantee" below, rather than assert, but I'll
2264 // leave these as "asserts" so that an adventurous debugger
2265 // could try this in the product build provided some subset of
2266 // the conditions were met, provided they were interested in the
2267 // results and knew that the computation below wouldn't interfere
2268 // with other concurrent computations mutating the structures
2269 // being read or written.
2270 assert(SafepointSynchronize::is_at_safepoint(),
2271 "Else mutations in object graph will make answer suspect");
2272 assert(have_cms_token(), "Should hold cms token");
2273 assert(haveFreelistLocks(), "must hold free list locks");
2274 assert_lock_strong(bitMapLock());
2275
2276 // Clear the marking bit map array before starting, but, just
2277 // for kicks, first report if the given address is already marked
2278 gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2279 _markBitMap.isMarked(addr) ? "" : " not");
2280
2281 if (verify_after_remark()) {
2282 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2283 bool result = verification_mark_bm()->isMarked(addr);
2284 gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2285 result ? "IS" : "is NOT");
2286 return result;
2287 } else {
2288 gclog_or_tty->print_cr("Could not compute result");
2289 return false;
2290 }
2291 }
2292
2293
2294 void
2295 CMSCollector::print_on_error(outputStream* st) {
2296 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2297 if (collector != NULL) {
2298 CMSBitMap* bitmap = &collector->_markBitMap;
2299 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2300 bitmap->print_on_error(st, " Bits: ");
2301
2302 st->cr();
2303
2304 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2305 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2306 mut_bitmap->print_on_error(st, " Bits: ");
2307 }
2308 }
2309
2310 ////////////////////////////////////////////////////////
2311 // CMS Verification Support
2312 ////////////////////////////////////////////////////////
2313 // Following the remark phase, the following invariant
2314 // should hold -- each object in the CMS heap which is
2315 // marked in markBitMap() should be marked in the verification_mark_bm().
2316
2317 class VerifyMarkedClosure: public BitMapClosure {
2318 CMSBitMap* _marks;
2319 bool _failed;
2320
2321 public:
2322 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2323
2324 bool do_bit(size_t offset) {
2325 HeapWord* addr = _marks->offsetToHeapWord(offset);
2326 if (!_marks->isMarked(addr)) {
2327 oop(addr)->print_on(gclog_or_tty);
2328 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2329 _failed = true;
2330 }
2331 return true;
2332 }
2333
2334 bool failed() { return _failed; }
2335 };
2336
2337 bool CMSCollector::verify_after_remark(bool silent) {
2338 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2339 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2340 static bool init = false;
2341
2342 assert(SafepointSynchronize::is_at_safepoint(),
2343 "Else mutations in object graph will make answer suspect");
2344 assert(have_cms_token(),
2345 "Else there may be mutual interference in use of "
2346 " verification data structures");
2347 assert(_collectorState > Marking && _collectorState <= Sweeping,
2348 "Else marking info checked here may be obsolete");
2349 assert(haveFreelistLocks(), "must hold free list locks");
2350 assert_lock_strong(bitMapLock());
2351
2352
2353 // Allocate marking bit map if not already allocated
2354 if (!init) { // first time
2355 if (!verification_mark_bm()->allocate(_span)) {
2356 return false;
2357 }
2358 init = true;
2359 }
2360
2361 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2362
2363 // Turn off refs discovery -- so we will be tracing through refs.
2364 // This is as intended, because by this time
2365 // GC must already have cleared any refs that need to be cleared,
2366 // and traced those that need to be marked; moreover,
2367 // the marking done here is not going to interfere in any
2368 // way with the marking information used by GC.
2369 NoRefDiscovery no_discovery(ref_processor());
2370
2371 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2372
2373 // Clear any marks from a previous round
2374 verification_mark_bm()->clear_all();
2375 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2376 verify_work_stacks_empty();
2377
2378 GenCollectedHeap* gch = GenCollectedHeap::heap();
2379 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2380 // Update the saved marks which may affect the root scans.
2381 gch->save_marks();
2382
2383 if (CMSRemarkVerifyVariant == 1) {
2384 // In this first variant of verification, we complete
2385 // all marking, then check if the new marks-vector is
2386 // a subset of the CMS marks-vector.
2387 verify_after_remark_work_1();
2388 } else if (CMSRemarkVerifyVariant == 2) {
2389 // In this second variant of verification, we flag an error
2390 // (i.e. an object reachable in the new marks-vector not reachable
2391 // in the CMS marks-vector) immediately, also indicating the
2392 // identify of an object (A) that references the unmarked object (B) --
2393 // presumably, a mutation to A failed to be picked up by preclean/remark?
2394 verify_after_remark_work_2();
2395 } else {
2396 warning("Unrecognized value " UINTX_FORMAT " for CMSRemarkVerifyVariant",
2397 CMSRemarkVerifyVariant);
2398 }
2399 if (!silent) gclog_or_tty->print(" done] ");
2400 return true;
2401 }
2402
2403 void CMSCollector::verify_after_remark_work_1() {
2404 ResourceMark rm;
2405 HandleMark hm;
2406 GenCollectedHeap* gch = GenCollectedHeap::heap();
2407
2408 // Get a clear set of claim bits for the roots processing to work with.
2409 ClassLoaderDataGraph::clear_claimed_marks();
2410
2411 // Mark from roots one level into CMS
2412 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2413 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2414
2415 {
2416 StrongRootsScope srs(1);
2417
2418 gch->gen_process_roots(&srs,
2419 GenCollectedHeap::OldGen,
2420 true, // young gen as roots
2421 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2422 should_unload_classes(),
2423 ¬Older,
2424 NULL,
2425 NULL);
2426 }
2427
2428 // Now mark from the roots
2429 MarkFromRootsClosure markFromRootsClosure(this, _span,
2430 verification_mark_bm(), verification_mark_stack(),
2431 false /* don't yield */, true /* verifying */);
2432 assert(_restart_addr == NULL, "Expected pre-condition");
2433 verification_mark_bm()->iterate(&markFromRootsClosure);
2434 while (_restart_addr != NULL) {
2435 // Deal with stack overflow: by restarting at the indicated
2436 // address.
2437 HeapWord* ra = _restart_addr;
2438 markFromRootsClosure.reset(ra);
2439 _restart_addr = NULL;
2440 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2441 }
2442 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2443 verify_work_stacks_empty();
2444
2445 // Marking completed -- now verify that each bit marked in
2446 // verification_mark_bm() is also marked in markBitMap(); flag all
2447 // errors by printing corresponding objects.
2448 VerifyMarkedClosure vcl(markBitMap());
2449 verification_mark_bm()->iterate(&vcl);
2450 if (vcl.failed()) {
2451 gclog_or_tty->print("Verification failed");
2452 gch->print_on(gclog_or_tty);
2453 fatal("CMS: failed marking verification after remark");
2454 }
2455 }
2456
2457 class VerifyKlassOopsKlassClosure : public KlassClosure {
2458 class VerifyKlassOopsClosure : public OopClosure {
2459 CMSBitMap* _bitmap;
2460 public:
2461 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2462 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2463 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2464 } _oop_closure;
2465 public:
2466 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2467 void do_klass(Klass* k) {
2468 k->oops_do(&_oop_closure);
2469 }
2470 };
2471
2472 void CMSCollector::verify_after_remark_work_2() {
2473 ResourceMark rm;
2474 HandleMark hm;
2475 GenCollectedHeap* gch = GenCollectedHeap::heap();
2476
2477 // Get a clear set of claim bits for the roots processing to work with.
2478 ClassLoaderDataGraph::clear_claimed_marks();
2479
2480 // Mark from roots one level into CMS
2481 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2482 markBitMap());
2483 CLDToOopClosure cld_closure(¬Older, true);
2484
2485 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2486
2487 {
2488 StrongRootsScope srs(1);
2489
2490 gch->gen_process_roots(&srs,
2491 GenCollectedHeap::OldGen,
2492 true, // young gen as roots
2493 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2494 should_unload_classes(),
2495 ¬Older,
2496 NULL,
2497 &cld_closure);
2498 }
2499
2500 // Now mark from the roots
2501 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2502 verification_mark_bm(), markBitMap(), verification_mark_stack());
2503 assert(_restart_addr == NULL, "Expected pre-condition");
2504 verification_mark_bm()->iterate(&markFromRootsClosure);
2505 while (_restart_addr != NULL) {
2506 // Deal with stack overflow: by restarting at the indicated
2507 // address.
2508 HeapWord* ra = _restart_addr;
2509 markFromRootsClosure.reset(ra);
2510 _restart_addr = NULL;
2511 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2512 }
2513 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2514 verify_work_stacks_empty();
2515
2516 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2517 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2518
2519 // Marking completed -- now verify that each bit marked in
2520 // verification_mark_bm() is also marked in markBitMap(); flag all
2521 // errors by printing corresponding objects.
2522 VerifyMarkedClosure vcl(markBitMap());
2523 verification_mark_bm()->iterate(&vcl);
2524 assert(!vcl.failed(), "Else verification above should not have succeeded");
2525 }
2526
2527 void ConcurrentMarkSweepGeneration::save_marks() {
2528 // delegate to CMS space
2529 cmsSpace()->save_marks();
2530 for (uint i = 0; i < ParallelGCThreads; i++) {
2531 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2532 }
2533 }
2534
2535 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2536 return cmsSpace()->no_allocs_since_save_marks();
2537 }
2538
2539 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2540 \
2541 void ConcurrentMarkSweepGeneration:: \
2542 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2543 cl->set_generation(this); \
2544 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2545 cl->reset_generation(); \
2546 save_marks(); \
2547 }
2548
2549 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2550
2551 void
2552 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2553 if (freelistLock()->owned_by_self()) {
2554 Generation::oop_iterate(cl);
2555 } else {
2556 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2557 Generation::oop_iterate(cl);
2558 }
2559 }
2560
2561 void
2562 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2563 if (freelistLock()->owned_by_self()) {
2564 Generation::object_iterate(cl);
2565 } else {
2566 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2567 Generation::object_iterate(cl);
2568 }
2569 }
2570
2571 void
2572 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2573 if (freelistLock()->owned_by_self()) {
2574 Generation::safe_object_iterate(cl);
2575 } else {
2576 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2577 Generation::safe_object_iterate(cl);
2578 }
2579 }
2580
2581 void
2582 ConcurrentMarkSweepGeneration::post_compact() {
2583 }
2584
2585 void
2586 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2587 // Fix the linear allocation blocks to look like free blocks.
2588
2589 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2590 // are not called when the heap is verified during universe initialization and
2591 // at vm shutdown.
2592 if (freelistLock()->owned_by_self()) {
2593 cmsSpace()->prepare_for_verify();
2594 } else {
2595 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2596 cmsSpace()->prepare_for_verify();
2597 }
2598 }
2599
2600 void
2601 ConcurrentMarkSweepGeneration::verify() {
2602 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2603 // are not called when the heap is verified during universe initialization and
2604 // at vm shutdown.
2605 if (freelistLock()->owned_by_self()) {
2606 cmsSpace()->verify();
2607 } else {
2608 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2609 cmsSpace()->verify();
2610 }
2611 }
2612
2613 void CMSCollector::verify() {
2614 _cmsGen->verify();
2615 }
2616
2617 #ifndef PRODUCT
2618 bool CMSCollector::overflow_list_is_empty() const {
2619 assert(_num_par_pushes >= 0, "Inconsistency");
2620 if (_overflow_list == NULL) {
2621 assert(_num_par_pushes == 0, "Inconsistency");
2622 }
2623 return _overflow_list == NULL;
2624 }
2625
2626 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2627 // merely consolidate assertion checks that appear to occur together frequently.
2628 void CMSCollector::verify_work_stacks_empty() const {
2629 assert(_markStack.isEmpty(), "Marking stack should be empty");
2630 assert(overflow_list_is_empty(), "Overflow list should be empty");
2631 }
2632
2633 void CMSCollector::verify_overflow_empty() const {
2634 assert(overflow_list_is_empty(), "Overflow list should be empty");
2635 assert(no_preserved_marks(), "No preserved marks");
2636 }
2637 #endif // PRODUCT
2638
2639 // Decide if we want to enable class unloading as part of the
2640 // ensuing concurrent GC cycle. We will collect and
2641 // unload classes if it's the case that:
2642 // (1) an explicit gc request has been made and the flag
2643 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2644 // (2) (a) class unloading is enabled at the command line, and
2645 // (b) old gen is getting really full
2646 // NOTE: Provided there is no change in the state of the heap between
2647 // calls to this method, it should have idempotent results. Moreover,
2648 // its results should be monotonically increasing (i.e. going from 0 to 1,
2649 // but not 1 to 0) between successive calls between which the heap was
2650 // not collected. For the implementation below, it must thus rely on
2651 // the property that concurrent_cycles_since_last_unload()
2652 // will not decrease unless a collection cycle happened and that
2653 // _cmsGen->is_too_full() are
2654 // themselves also monotonic in that sense. See check_monotonicity()
2655 // below.
2656 void CMSCollector::update_should_unload_classes() {
2657 _should_unload_classes = false;
2658 // Condition 1 above
2659 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2660 _should_unload_classes = true;
2661 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2662 // Disjuncts 2.b.(i,ii,iii) above
2663 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2664 CMSClassUnloadingMaxInterval)
2665 || _cmsGen->is_too_full();
2666 }
2667 }
2668
2669 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2670 bool res = should_concurrent_collect();
2671 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2672 return res;
2673 }
2674
2675 void CMSCollector::setup_cms_unloading_and_verification_state() {
2676 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2677 || VerifyBeforeExit;
2678 const int rso = GenCollectedHeap::SO_AllCodeCache;
2679
2680 // We set the proper root for this CMS cycle here.
2681 if (should_unload_classes()) { // Should unload classes this cycle
2682 remove_root_scanning_option(rso); // Shrink the root set appropriately
2683 set_verifying(should_verify); // Set verification state for this cycle
2684 return; // Nothing else needs to be done at this time
2685 }
2686
2687 // Not unloading classes this cycle
2688 assert(!should_unload_classes(), "Inconsistency!");
2689
2690 // If we are not unloading classes then add SO_AllCodeCache to root
2691 // scanning options.
2692 add_root_scanning_option(rso);
2693
2694 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2695 set_verifying(true);
2696 } else if (verifying() && !should_verify) {
2697 // We were verifying, but some verification flags got disabled.
2698 set_verifying(false);
2699 // Exclude symbols, strings and code cache elements from root scanning to
2700 // reduce IM and RM pauses.
2701 remove_root_scanning_option(rso);
2702 }
2703 }
2704
2705
2706 #ifndef PRODUCT
2707 HeapWord* CMSCollector::block_start(const void* p) const {
2708 const HeapWord* addr = (HeapWord*)p;
2709 if (_span.contains(p)) {
2710 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2711 return _cmsGen->cmsSpace()->block_start(p);
2712 }
2713 }
2714 return NULL;
2715 }
2716 #endif
2717
2718 HeapWord*
2719 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2720 bool tlab,
2721 bool parallel) {
2722 CMSSynchronousYieldRequest yr;
2723 assert(!tlab, "Can't deal with TLAB allocation");
2724 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2725 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2726 if (GCExpandToAllocateDelayMillis > 0) {
2727 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2728 }
2729 return have_lock_and_allocate(word_size, tlab);
2730 }
2731
2732 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2733 size_t bytes,
2734 size_t expand_bytes,
2735 CMSExpansionCause::Cause cause)
2736 {
2737
2738 bool success = expand(bytes, expand_bytes);
2739
2740 // remember why we expanded; this information is used
2741 // by shouldConcurrentCollect() when making decisions on whether to start
2742 // a new CMS cycle.
2743 if (success) {
2744 set_expansion_cause(cause);
2745 if (PrintGCDetails && Verbose) {
2746 gclog_or_tty->print_cr("Expanded CMS gen for %s",
2747 CMSExpansionCause::to_string(cause));
2748 }
2749 }
2750 }
2751
2752 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2753 HeapWord* res = NULL;
2754 MutexLocker x(ParGCRareEvent_lock);
2755 while (true) {
2756 // Expansion by some other thread might make alloc OK now:
2757 res = ps->lab.alloc(word_sz);
2758 if (res != NULL) return res;
2759 // If there's not enough expansion space available, give up.
2760 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2761 return NULL;
2762 }
2763 // Otherwise, we try expansion.
2764 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2765 // Now go around the loop and try alloc again;
2766 // A competing par_promote might beat us to the expansion space,
2767 // so we may go around the loop again if promotion fails again.
2768 if (GCExpandToAllocateDelayMillis > 0) {
2769 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2770 }
2771 }
2772 }
2773
2774
2775 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2776 PromotionInfo* promo) {
2777 MutexLocker x(ParGCRareEvent_lock);
2778 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2779 while (true) {
2780 // Expansion by some other thread might make alloc OK now:
2781 if (promo->ensure_spooling_space()) {
2782 assert(promo->has_spooling_space(),
2783 "Post-condition of successful ensure_spooling_space()");
2784 return true;
2785 }
2786 // If there's not enough expansion space available, give up.
2787 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2788 return false;
2789 }
2790 // Otherwise, we try expansion.
2791 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2792 // Now go around the loop and try alloc again;
2793 // A competing allocation might beat us to the expansion space,
2794 // so we may go around the loop again if allocation fails again.
2795 if (GCExpandToAllocateDelayMillis > 0) {
2796 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2797 }
2798 }
2799 }
2800
2801 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2802 // Only shrink if a compaction was done so that all the free space
2803 // in the generation is in a contiguous block at the end.
2804 if (did_compact()) {
2805 CardGeneration::shrink(bytes);
2806 }
2807 }
2808
2809 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2810 assert_locked_or_safepoint(Heap_lock);
2811 }
2812
2813 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2814 assert_locked_or_safepoint(Heap_lock);
2815 assert_lock_strong(freelistLock());
2816 if (PrintGCDetails && Verbose) {
2817 warning("Shrinking of CMS not yet implemented");
2818 }
2819 return;
2820 }
2821
2822
2823 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2824 // phases.
2825 class CMSPhaseAccounting: public StackObj {
2826 public:
2827 CMSPhaseAccounting(CMSCollector *collector,
2828 const char *phase,
2829 bool print_cr = true);
2830 ~CMSPhaseAccounting();
2831
2832 private:
2833 CMSCollector *_collector;
2834 const char *_phase;
2835 elapsedTimer _wallclock;
2836 bool _print_cr;
2837
2838 public:
2839 // Not MT-safe; so do not pass around these StackObj's
2840 // where they may be accessed by other threads.
2841 jlong wallclock_millis() {
2842 assert(_wallclock.is_active(), "Wall clock should not stop");
2843 _wallclock.stop(); // to record time
2844 jlong ret = _wallclock.milliseconds();
2845 _wallclock.start(); // restart
2846 return ret;
2847 }
2848 };
2849
2850 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2851 const char *phase,
2852 bool print_cr) :
2853 _collector(collector), _phase(phase), _print_cr(print_cr) {
2854
2855 if (PrintCMSStatistics != 0) {
2856 _collector->resetYields();
2857 }
2858 if (PrintGCDetails) {
2859 gclog_or_tty->gclog_stamp();
2860 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
2861 _collector->cmsGen()->short_name(), _phase);
2862 }
2863 _collector->resetTimer();
2864 _wallclock.start();
2865 _collector->startTimer();
2866 }
2867
2868 CMSPhaseAccounting::~CMSPhaseAccounting() {
2869 assert(_wallclock.is_active(), "Wall clock should not have stopped");
2870 _collector->stopTimer();
2871 _wallclock.stop();
2872 if (PrintGCDetails) {
2873 gclog_or_tty->gclog_stamp();
2874 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
2875 _collector->cmsGen()->short_name(),
2876 _phase, _collector->timerValue(), _wallclock.seconds());
2877 if (_print_cr) {
2878 gclog_or_tty->cr();
2879 }
2880 if (PrintCMSStatistics != 0) {
2881 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
2882 _collector->yields());
2883 }
2884 }
2885 }
2886
2887 // CMS work
2888
2889 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2890 class CMSParMarkTask : public AbstractGangTask {
2891 protected:
2892 CMSCollector* _collector;
2893 uint _n_workers;
2894 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2895 AbstractGangTask(name),
2896 _collector(collector),
2897 _n_workers(n_workers) {}
2898 // Work method in support of parallel rescan ... of young gen spaces
2899 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2900 ContiguousSpace* space,
2901 HeapWord** chunk_array, size_t chunk_top);
2902 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2903 };
2904
2905 // Parallel initial mark task
2906 class CMSParInitialMarkTask: public CMSParMarkTask {
2907 StrongRootsScope* _strong_roots_scope;
2908 public:
2909 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2910 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2911 _strong_roots_scope(strong_roots_scope) {}
2912 void work(uint worker_id);
2913 };
2914
2915 // Checkpoint the roots into this generation from outside
2916 // this generation. [Note this initial checkpoint need only
2917 // be approximate -- we'll do a catch up phase subsequently.]
2918 void CMSCollector::checkpointRootsInitial() {
2919 assert(_collectorState == InitialMarking, "Wrong collector state");
2920 check_correct_thread_executing();
2921 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2922
2923 save_heap_summary();
2924 report_heap_summary(GCWhen::BeforeGC);
2925
2926 ReferenceProcessor* rp = ref_processor();
2927 assert(_restart_addr == NULL, "Control point invariant");
2928 {
2929 // acquire locks for subsequent manipulations
2930 MutexLockerEx x(bitMapLock(),
2931 Mutex::_no_safepoint_check_flag);
2932 checkpointRootsInitialWork();
2933 // enable ("weak") refs discovery
2934 rp->enable_discovery();
2935 _collectorState = Marking;
2936 }
2937 }
2938
2939 void CMSCollector::checkpointRootsInitialWork() {
2940 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2941 assert(_collectorState == InitialMarking, "just checking");
2942
2943 // Already have locks.
2944 assert_lock_strong(bitMapLock());
2945 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2946
2947 // Setup the verification and class unloading state for this
2948 // CMS collection cycle.
2949 setup_cms_unloading_and_verification_state();
2950
2951 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
2952 PrintGCDetails && Verbose, true, _gc_timer_cm);)
2953
2954 // Reset all the PLAB chunk arrays if necessary.
2955 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2956 reset_survivor_plab_arrays();
2957 }
2958
2959 ResourceMark rm;
2960 HandleMark hm;
2961
2962 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2963 GenCollectedHeap* gch = GenCollectedHeap::heap();
2964
2965 verify_work_stacks_empty();
2966 verify_overflow_empty();
2967
2968 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2969 // Update the saved marks which may affect the root scans.
2970 gch->save_marks();
2971
2972 // weak reference processing has not started yet.
2973 ref_processor()->set_enqueuing_is_done(false);
2974
2975 // Need to remember all newly created CLDs,
2976 // so that we can guarantee that the remark finds them.
2977 ClassLoaderDataGraph::remember_new_clds(true);
2978
2979 // Whenever a CLD is found, it will be claimed before proceeding to mark
2980 // the klasses. The claimed marks need to be cleared before marking starts.
2981 ClassLoaderDataGraph::clear_claimed_marks();
2982
2983 if (CMSPrintEdenSurvivorChunks) {
2984 print_eden_and_survivor_chunk_arrays();
2985 }
2986
2987 {
2988 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2989 if (CMSParallelInitialMarkEnabled) {
2990 // The parallel version.
2991 WorkGang* workers = gch->workers();
2992 assert(workers != NULL, "Need parallel worker threads.");
2993 uint n_workers = workers->active_workers();
2994
2995 StrongRootsScope srs(n_workers);
2996
2997 CMSParInitialMarkTask tsk(this, &srs, n_workers);
2998 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2999 if (n_workers > 1) {
3000 workers->run_task(&tsk);
3001 } else {
3002 tsk.work(0);
3003 }
3004 } else {
3005 // The serial version.
3006 CLDToOopClosure cld_closure(¬Older, true);
3007 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3008
3009 StrongRootsScope srs(1);
3010
3011 gch->gen_process_roots(&srs,
3012 GenCollectedHeap::OldGen,
3013 true, // young gen as roots
3014 GenCollectedHeap::ScanningOption(roots_scanning_options()),
3015 should_unload_classes(),
3016 ¬Older,
3017 NULL,
3018 &cld_closure);
3019 }
3020 }
3021
3022 // Clear mod-union table; it will be dirtied in the prologue of
3023 // CMS generation per each young generation collection.
3024
3025 assert(_modUnionTable.isAllClear(),
3026 "Was cleared in most recent final checkpoint phase"
3027 " or no bits are set in the gc_prologue before the start of the next "
3028 "subsequent marking phase.");
3029
3030 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3031
3032 // Save the end of the used_region of the constituent generations
3033 // to be used to limit the extent of sweep in each generation.
3034 save_sweep_limits();
3035 verify_overflow_empty();
3036 }
3037
3038 bool CMSCollector::markFromRoots() {
3039 // we might be tempted to assert that:
3040 // assert(!SafepointSynchronize::is_at_safepoint(),
3041 // "inconsistent argument?");
3042 // However that wouldn't be right, because it's possible that
3043 // a safepoint is indeed in progress as a young generation
3044 // stop-the-world GC happens even as we mark in this generation.
3045 assert(_collectorState == Marking, "inconsistent state?");
3046 check_correct_thread_executing();
3047 verify_overflow_empty();
3048
3049 // Weak ref discovery note: We may be discovering weak
3050 // refs in this generation concurrent (but interleaved) with
3051 // weak ref discovery by the young generation collector.
3052
3053 CMSTokenSyncWithLocks ts(true, bitMapLock());
3054 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3055 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3056 bool res = markFromRootsWork();
3057 if (res) {
3058 _collectorState = Precleaning;
3059 } else { // We failed and a foreground collection wants to take over
3060 assert(_foregroundGCIsActive, "internal state inconsistency");
3061 assert(_restart_addr == NULL, "foreground will restart from scratch");
3062 if (PrintGCDetails) {
3063 gclog_or_tty->print_cr("bailing out to foreground collection");
3064 }
3065 }
3066 verify_overflow_empty();
3067 return res;
3068 }
3069
3070 bool CMSCollector::markFromRootsWork() {
3071 // iterate over marked bits in bit map, doing a full scan and mark
3072 // from these roots using the following algorithm:
3073 // . if oop is to the right of the current scan pointer,
3074 // mark corresponding bit (we'll process it later)
3075 // . else (oop is to left of current scan pointer)
3076 // push oop on marking stack
3077 // . drain the marking stack
3078
3079 // Note that when we do a marking step we need to hold the
3080 // bit map lock -- recall that direct allocation (by mutators)
3081 // and promotion (by the young generation collector) is also
3082 // marking the bit map. [the so-called allocate live policy.]
3083 // Because the implementation of bit map marking is not
3084 // robust wrt simultaneous marking of bits in the same word,
3085 // we need to make sure that there is no such interference
3086 // between concurrent such updates.
3087
3088 // already have locks
3089 assert_lock_strong(bitMapLock());
3090
3091 verify_work_stacks_empty();
3092 verify_overflow_empty();
3093 bool result = false;
3094 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3095 result = do_marking_mt();
3096 } else {
3097 result = do_marking_st();
3098 }
3099 return result;
3100 }
3101
3102 // Forward decl
3103 class CMSConcMarkingTask;
3104
3105 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3106 CMSCollector* _collector;
3107 CMSConcMarkingTask* _task;
3108 public:
3109 virtual void yield();
3110
3111 // "n_threads" is the number of threads to be terminated.
3112 // "queue_set" is a set of work queues of other threads.
3113 // "collector" is the CMS collector associated with this task terminator.
3114 // "yield" indicates whether we need the gang as a whole to yield.
3115 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3116 ParallelTaskTerminator(n_threads, queue_set),
3117 _collector(collector) { }
3118
3119 void set_task(CMSConcMarkingTask* task) {
3120 _task = task;
3121 }
3122 };
3123
3124 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3125 CMSConcMarkingTask* _task;
3126 public:
3127 bool should_exit_termination();
3128 void set_task(CMSConcMarkingTask* task) {
3129 _task = task;
3130 }
3131 };
3132
3133 // MT Concurrent Marking Task
3134 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3135 CMSCollector* _collector;
3136 uint _n_workers; // requested/desired # workers
3137 bool _result;
3138 CompactibleFreeListSpace* _cms_space;
3139 char _pad_front[64]; // padding to ...
3140 HeapWord* _global_finger; // ... avoid sharing cache line
3141 char _pad_back[64];
3142 HeapWord* _restart_addr;
3143
3144 // Exposed here for yielding support
3145 Mutex* const _bit_map_lock;
3146
3147 // The per thread work queues, available here for stealing
3148 OopTaskQueueSet* _task_queues;
3149
3150 // Termination (and yielding) support
3151 CMSConcMarkingTerminator _term;
3152 CMSConcMarkingTerminatorTerminator _term_term;
3153
3154 public:
3155 CMSConcMarkingTask(CMSCollector* collector,
3156 CompactibleFreeListSpace* cms_space,
3157 YieldingFlexibleWorkGang* workers,
3158 OopTaskQueueSet* task_queues):
3159 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3160 _collector(collector),
3161 _cms_space(cms_space),
3162 _n_workers(0), _result(true),
3163 _task_queues(task_queues),
3164 _term(_n_workers, task_queues, _collector),
3165 _bit_map_lock(collector->bitMapLock())
3166 {
3167 _requested_size = _n_workers;
3168 _term.set_task(this);
3169 _term_term.set_task(this);
3170 _restart_addr = _global_finger = _cms_space->bottom();
3171 }
3172
3173
3174 OopTaskQueueSet* task_queues() { return _task_queues; }
3175
3176 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3177
3178 HeapWord** global_finger_addr() { return &_global_finger; }
3179
3180 CMSConcMarkingTerminator* terminator() { return &_term; }
3181
3182 virtual void set_for_termination(uint active_workers) {
3183 terminator()->reset_for_reuse(active_workers);
3184 }
3185
3186 void work(uint worker_id);
3187 bool should_yield() {
3188 return ConcurrentMarkSweepThread::should_yield()
3189 && !_collector->foregroundGCIsActive();
3190 }
3191
3192 virtual void coordinator_yield(); // stuff done by coordinator
3193 bool result() { return _result; }
3194
3195 void reset(HeapWord* ra) {
3196 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3197 _restart_addr = _global_finger = ra;
3198 _term.reset_for_reuse();
3199 }
3200
3201 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3202 OopTaskQueue* work_q);
3203
3204 private:
3205 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3206 void do_work_steal(int i);
3207 void bump_global_finger(HeapWord* f);
3208 };
3209
3210 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3211 assert(_task != NULL, "Error");
3212 return _task->yielding();
3213 // Note that we do not need the disjunct || _task->should_yield() above
3214 // because we want terminating threads to yield only if the task
3215 // is already in the midst of yielding, which happens only after at least one
3216 // thread has yielded.
3217 }
3218
3219 void CMSConcMarkingTerminator::yield() {
3220 if (_task->should_yield()) {
3221 _task->yield();
3222 } else {
3223 ParallelTaskTerminator::yield();
3224 }
3225 }
3226
3227 ////////////////////////////////////////////////////////////////
3228 // Concurrent Marking Algorithm Sketch
3229 ////////////////////////////////////////////////////////////////
3230 // Until all tasks exhausted (both spaces):
3231 // -- claim next available chunk
3232 // -- bump global finger via CAS
3233 // -- find first object that starts in this chunk
3234 // and start scanning bitmap from that position
3235 // -- scan marked objects for oops
3236 // -- CAS-mark target, and if successful:
3237 // . if target oop is above global finger (volatile read)
3238 // nothing to do
3239 // . if target oop is in chunk and above local finger
3240 // then nothing to do
3241 // . else push on work-queue
3242 // -- Deal with possible overflow issues:
3243 // . local work-queue overflow causes stuff to be pushed on
3244 // global (common) overflow queue
3245 // . always first empty local work queue
3246 // . then get a batch of oops from global work queue if any
3247 // . then do work stealing
3248 // -- When all tasks claimed (both spaces)
3249 // and local work queue empty,
3250 // then in a loop do:
3251 // . check global overflow stack; steal a batch of oops and trace
3252 // . try to steal from other threads oif GOS is empty
3253 // . if neither is available, offer termination
3254 // -- Terminate and return result
3255 //
3256 void CMSConcMarkingTask::work(uint worker_id) {
3257 elapsedTimer _timer;
3258 ResourceMark rm;
3259 HandleMark hm;
3260
3261 DEBUG_ONLY(_collector->verify_overflow_empty();)
3262
3263 // Before we begin work, our work queue should be empty
3264 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3265 // Scan the bitmap covering _cms_space, tracing through grey objects.
3266 _timer.start();
3267 do_scan_and_mark(worker_id, _cms_space);
3268 _timer.stop();
3269 if (PrintCMSStatistics != 0) {
3270 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3271 worker_id, _timer.seconds());
3272 // XXX: need xxx/xxx type of notation, two timers
3273 }
3274
3275 // ... do work stealing
3276 _timer.reset();
3277 _timer.start();
3278 do_work_steal(worker_id);
3279 _timer.stop();
3280 if (PrintCMSStatistics != 0) {
3281 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3282 worker_id, _timer.seconds());
3283 // XXX: need xxx/xxx type of notation, two timers
3284 }
3285 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3286 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3287 // Note that under the current task protocol, the
3288 // following assertion is true even of the spaces
3289 // expanded since the completion of the concurrent
3290 // marking. XXX This will likely change under a strict
3291 // ABORT semantics.
3292 // After perm removal the comparison was changed to
3293 // greater than or equal to from strictly greater than.
3294 // Before perm removal the highest address sweep would
3295 // have been at the end of perm gen but now is at the
3296 // end of the tenured gen.
3297 assert(_global_finger >= _cms_space->end(),
3298 "All tasks have been completed");
3299 DEBUG_ONLY(_collector->verify_overflow_empty();)
3300 }
3301
3302 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3303 HeapWord* read = _global_finger;
3304 HeapWord* cur = read;
3305 while (f > read) {
3306 cur = read;
3307 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3308 if (cur == read) {
3309 // our cas succeeded
3310 assert(_global_finger >= f, "protocol consistency");
3311 break;
3312 }
3313 }
3314 }
3315
3316 // This is really inefficient, and should be redone by
3317 // using (not yet available) block-read and -write interfaces to the
3318 // stack and the work_queue. XXX FIX ME !!!
3319 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3320 OopTaskQueue* work_q) {
3321 // Fast lock-free check
3322 if (ovflw_stk->length() == 0) {
3323 return false;
3324 }
3325 assert(work_q->size() == 0, "Shouldn't steal");
3326 MutexLockerEx ml(ovflw_stk->par_lock(),
3327 Mutex::_no_safepoint_check_flag);
3328 // Grab up to 1/4 the size of the work queue
3329 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3330 (size_t)ParGCDesiredObjsFromOverflowList);
3331 num = MIN2(num, ovflw_stk->length());
3332 for (int i = (int) num; i > 0; i--) {
3333 oop cur = ovflw_stk->pop();
3334 assert(cur != NULL, "Counted wrong?");
3335 work_q->push(cur);
3336 }
3337 return num > 0;
3338 }
3339
3340 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3341 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3342 int n_tasks = pst->n_tasks();
3343 // We allow that there may be no tasks to do here because
3344 // we are restarting after a stack overflow.
3345 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3346 uint nth_task = 0;
3347
3348 HeapWord* aligned_start = sp->bottom();
3349 if (sp->used_region().contains(_restart_addr)) {
3350 // Align down to a card boundary for the start of 0th task
3351 // for this space.
3352 aligned_start =
3353 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3354 CardTableModRefBS::card_size);
3355 }
3356
3357 size_t chunk_size = sp->marking_task_size();
3358 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3359 // Having claimed the nth task in this space,
3360 // compute the chunk that it corresponds to:
3361 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3362 aligned_start + (nth_task+1)*chunk_size);
3363 // Try and bump the global finger via a CAS;
3364 // note that we need to do the global finger bump
3365 // _before_ taking the intersection below, because
3366 // the task corresponding to that region will be
3367 // deemed done even if the used_region() expands
3368 // because of allocation -- as it almost certainly will
3369 // during start-up while the threads yield in the
3370 // closure below.
3371 HeapWord* finger = span.end();
3372 bump_global_finger(finger); // atomically
3373 // There are null tasks here corresponding to chunks
3374 // beyond the "top" address of the space.
3375 span = span.intersection(sp->used_region());
3376 if (!span.is_empty()) { // Non-null task
3377 HeapWord* prev_obj;
3378 assert(!span.contains(_restart_addr) || nth_task == 0,
3379 "Inconsistency");
3380 if (nth_task == 0) {
3381 // For the 0th task, we'll not need to compute a block_start.
3382 if (span.contains(_restart_addr)) {
3383 // In the case of a restart because of stack overflow,
3384 // we might additionally skip a chunk prefix.
3385 prev_obj = _restart_addr;
3386 } else {
3387 prev_obj = span.start();
3388 }
3389 } else {
3390 // We want to skip the first object because
3391 // the protocol is to scan any object in its entirety
3392 // that _starts_ in this span; a fortiori, any
3393 // object starting in an earlier span is scanned
3394 // as part of an earlier claimed task.
3395 // Below we use the "careful" version of block_start
3396 // so we do not try to navigate uninitialized objects.
3397 prev_obj = sp->block_start_careful(span.start());
3398 // Below we use a variant of block_size that uses the
3399 // Printezis bits to avoid waiting for allocated
3400 // objects to become initialized/parsable.
3401 while (prev_obj < span.start()) {
3402 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3403 if (sz > 0) {
3404 prev_obj += sz;
3405 } else {
3406 // In this case we may end up doing a bit of redundant
3407 // scanning, but that appears unavoidable, short of
3408 // locking the free list locks; see bug 6324141.
3409 break;
3410 }
3411 }
3412 }
3413 if (prev_obj < span.end()) {
3414 MemRegion my_span = MemRegion(prev_obj, span.end());
3415 // Do the marking work within a non-empty span --
3416 // the last argument to the constructor indicates whether the
3417 // iteration should be incremental with periodic yields.
3418 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3419 &_collector->_markBitMap,
3420 work_queue(i),
3421 &_collector->_markStack);
3422 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3423 } // else nothing to do for this task
3424 } // else nothing to do for this task
3425 }
3426 // We'd be tempted to assert here that since there are no
3427 // more tasks left to claim in this space, the global_finger
3428 // must exceed space->top() and a fortiori space->end(). However,
3429 // that would not quite be correct because the bumping of
3430 // global_finger occurs strictly after the claiming of a task,
3431 // so by the time we reach here the global finger may not yet
3432 // have been bumped up by the thread that claimed the last
3433 // task.
3434 pst->all_tasks_completed();
3435 }
3436
3437 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3438 private:
3439 CMSCollector* _collector;
3440 CMSConcMarkingTask* _task;
3441 MemRegion _span;
3442 CMSBitMap* _bit_map;
3443 CMSMarkStack* _overflow_stack;
3444 OopTaskQueue* _work_queue;
3445 protected:
3446 DO_OOP_WORK_DEFN
3447 public:
3448 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3449 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3450 MetadataAwareOopClosure(collector->ref_processor()),
3451 _collector(collector),
3452 _task(task),
3453 _span(collector->_span),
3454 _work_queue(work_queue),
3455 _bit_map(bit_map),
3456 _overflow_stack(overflow_stack)
3457 { }
3458 virtual void do_oop(oop* p);
3459 virtual void do_oop(narrowOop* p);
3460
3461 void trim_queue(size_t max);
3462 void handle_stack_overflow(HeapWord* lost);
3463 void do_yield_check() {
3464 if (_task->should_yield()) {
3465 _task->yield();
3466 }
3467 }
3468 };
3469
3470 // Grey object scanning during work stealing phase --
3471 // the salient assumption here is that any references
3472 // that are in these stolen objects being scanned must
3473 // already have been initialized (else they would not have
3474 // been published), so we do not need to check for
3475 // uninitialized objects before pushing here.
3476 void Par_ConcMarkingClosure::do_oop(oop obj) {
3477 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
3478 HeapWord* addr = (HeapWord*)obj;
3479 // Check if oop points into the CMS generation
3480 // and is not marked
3481 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3482 // a white object ...
3483 // If we manage to "claim" the object, by being the
3484 // first thread to mark it, then we push it on our
3485 // marking stack
3486 if (_bit_map->par_mark(addr)) { // ... now grey
3487 // push on work queue (grey set)
3488 bool simulate_overflow = false;
3489 NOT_PRODUCT(
3490 if (CMSMarkStackOverflowALot &&
3491 _collector->simulate_overflow()) {
3492 // simulate a stack overflow
3493 simulate_overflow = true;
3494 }
3495 )
3496 if (simulate_overflow ||
3497 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3498 // stack overflow
3499 if (PrintCMSStatistics != 0) {
3500 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3501 SIZE_FORMAT, _overflow_stack->capacity());
3502 }
3503 // We cannot assert that the overflow stack is full because
3504 // it may have been emptied since.
3505 assert(simulate_overflow ||
3506 _work_queue->size() == _work_queue->max_elems(),
3507 "Else push should have succeeded");
3508 handle_stack_overflow(addr);
3509 }
3510 } // Else, some other thread got there first
3511 do_yield_check();
3512 }
3513 }
3514
3515 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3516 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3517
3518 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3519 while (_work_queue->size() > max) {
3520 oop new_oop;
3521 if (_work_queue->pop_local(new_oop)) {
3522 assert(new_oop->is_oop(), "Should be an oop");
3523 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3524 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3525 new_oop->oop_iterate(this); // do_oop() above
3526 do_yield_check();
3527 }
3528 }
3529 }
3530
3531 // Upon stack overflow, we discard (part of) the stack,
3532 // remembering the least address amongst those discarded
3533 // in CMSCollector's _restart_address.
3534 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3535 // We need to do this under a mutex to prevent other
3536 // workers from interfering with the work done below.
3537 MutexLockerEx ml(_overflow_stack->par_lock(),
3538 Mutex::_no_safepoint_check_flag);
3539 // Remember the least grey address discarded
3540 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3541 _collector->lower_restart_addr(ra);
3542 _overflow_stack->reset(); // discard stack contents
3543 _overflow_stack->expand(); // expand the stack if possible
3544 }
3545
3546
3547 void CMSConcMarkingTask::do_work_steal(int i) {
3548 OopTaskQueue* work_q = work_queue(i);
3549 oop obj_to_scan;
3550 CMSBitMap* bm = &(_collector->_markBitMap);
3551 CMSMarkStack* ovflw = &(_collector->_markStack);
3552 int* seed = _collector->hash_seed(i);
3553 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3554 while (true) {
3555 cl.trim_queue(0);
3556 assert(work_q->size() == 0, "Should have been emptied above");
3557 if (get_work_from_overflow_stack(ovflw, work_q)) {
3558 // Can't assert below because the work obtained from the
3559 // overflow stack may already have been stolen from us.
3560 // assert(work_q->size() > 0, "Work from overflow stack");
3561 continue;
3562 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3563 assert(obj_to_scan->is_oop(), "Should be an oop");
3564 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3565 obj_to_scan->oop_iterate(&cl);
3566 } else if (terminator()->offer_termination(&_term_term)) {
3567 assert(work_q->size() == 0, "Impossible!");
3568 break;
3569 } else if (yielding() || should_yield()) {
3570 yield();
3571 }
3572 }
3573 }
3574
3575 // This is run by the CMS (coordinator) thread.
3576 void CMSConcMarkingTask::coordinator_yield() {
3577 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3578 "CMS thread should hold CMS token");
3579 // First give up the locks, then yield, then re-lock
3580 // We should probably use a constructor/destructor idiom to
3581 // do this unlock/lock or modify the MutexUnlocker class to
3582 // serve our purpose. XXX
3583 assert_lock_strong(_bit_map_lock);
3584 _bit_map_lock->unlock();
3585 ConcurrentMarkSweepThread::desynchronize(true);
3586 _collector->stopTimer();
3587 if (PrintCMSStatistics != 0) {
3588 _collector->incrementYields();
3589 }
3590
3591 // It is possible for whichever thread initiated the yield request
3592 // not to get a chance to wake up and take the bitmap lock between
3593 // this thread releasing it and reacquiring it. So, while the
3594 // should_yield() flag is on, let's sleep for a bit to give the
3595 // other thread a chance to wake up. The limit imposed on the number
3596 // of iterations is defensive, to avoid any unforseen circumstances
3597 // putting us into an infinite loop. Since it's always been this
3598 // (coordinator_yield()) method that was observed to cause the
3599 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3600 // which is by default non-zero. For the other seven methods that
3601 // also perform the yield operation, as are using a different
3602 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3603 // can enable the sleeping for those methods too, if necessary.
3604 // See 6442774.
3605 //
3606 // We really need to reconsider the synchronization between the GC
3607 // thread and the yield-requesting threads in the future and we
3608 // should really use wait/notify, which is the recommended
3609 // way of doing this type of interaction. Additionally, we should
3610 // consolidate the eight methods that do the yield operation and they
3611 // are almost identical into one for better maintainability and
3612 // readability. See 6445193.
3613 //
3614 // Tony 2006.06.29
3615 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3616 ConcurrentMarkSweepThread::should_yield() &&
3617 !CMSCollector::foregroundGCIsActive(); ++i) {
3618 os::sleep(Thread::current(), 1, false);
3619 }
3620
3621 ConcurrentMarkSweepThread::synchronize(true);
3622 _bit_map_lock->lock_without_safepoint_check();
3623 _collector->startTimer();
3624 }
3625
3626 bool CMSCollector::do_marking_mt() {
3627 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3628 uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3629 conc_workers()->active_workers(),
3630 Threads::number_of_non_daemon_threads());
3631 conc_workers()->set_active_workers(num_workers);
3632
3633 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3634
3635 CMSConcMarkingTask tsk(this,
3636 cms_space,
3637 conc_workers(),
3638 task_queues());
3639
3640 // Since the actual number of workers we get may be different
3641 // from the number we requested above, do we need to do anything different
3642 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3643 // class?? XXX
3644 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3645
3646 // Refs discovery is already non-atomic.
3647 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3648 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3649 conc_workers()->start_task(&tsk);
3650 while (tsk.yielded()) {
3651 tsk.coordinator_yield();
3652 conc_workers()->continue_task(&tsk);
3653 }
3654 // If the task was aborted, _restart_addr will be non-NULL
3655 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3656 while (_restart_addr != NULL) {
3657 // XXX For now we do not make use of ABORTED state and have not
3658 // yet implemented the right abort semantics (even in the original
3659 // single-threaded CMS case). That needs some more investigation
3660 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3661 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3662 // If _restart_addr is non-NULL, a marking stack overflow
3663 // occurred; we need to do a fresh marking iteration from the
3664 // indicated restart address.
3665 if (_foregroundGCIsActive) {
3666 // We may be running into repeated stack overflows, having
3667 // reached the limit of the stack size, while making very
3668 // slow forward progress. It may be best to bail out and
3669 // let the foreground collector do its job.
3670 // Clear _restart_addr, so that foreground GC
3671 // works from scratch. This avoids the headache of
3672 // a "rescan" which would otherwise be needed because
3673 // of the dirty mod union table & card table.
3674 _restart_addr = NULL;
3675 return false;
3676 }
3677 // Adjust the task to restart from _restart_addr
3678 tsk.reset(_restart_addr);
3679 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3680 _restart_addr);
3681 _restart_addr = NULL;
3682 // Get the workers going again
3683 conc_workers()->start_task(&tsk);
3684 while (tsk.yielded()) {
3685 tsk.coordinator_yield();
3686 conc_workers()->continue_task(&tsk);
3687 }
3688 }
3689 assert(tsk.completed(), "Inconsistency");
3690 assert(tsk.result() == true, "Inconsistency");
3691 return true;
3692 }
3693
3694 bool CMSCollector::do_marking_st() {
3695 ResourceMark rm;
3696 HandleMark hm;
3697
3698 // Temporarily make refs discovery single threaded (non-MT)
3699 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3700 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3701 &_markStack, CMSYield);
3702 // the last argument to iterate indicates whether the iteration
3703 // should be incremental with periodic yields.
3704 _markBitMap.iterate(&markFromRootsClosure);
3705 // If _restart_addr is non-NULL, a marking stack overflow
3706 // occurred; we need to do a fresh iteration from the
3707 // indicated restart address.
3708 while (_restart_addr != NULL) {
3709 if (_foregroundGCIsActive) {
3710 // We may be running into repeated stack overflows, having
3711 // reached the limit of the stack size, while making very
3712 // slow forward progress. It may be best to bail out and
3713 // let the foreground collector do its job.
3714 // Clear _restart_addr, so that foreground GC
3715 // works from scratch. This avoids the headache of
3716 // a "rescan" which would otherwise be needed because
3717 // of the dirty mod union table & card table.
3718 _restart_addr = NULL;
3719 return false; // indicating failure to complete marking
3720 }
3721 // Deal with stack overflow:
3722 // we restart marking from _restart_addr
3723 HeapWord* ra = _restart_addr;
3724 markFromRootsClosure.reset(ra);
3725 _restart_addr = NULL;
3726 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3727 }
3728 return true;
3729 }
3730
3731 void CMSCollector::preclean() {
3732 check_correct_thread_executing();
3733 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3734 verify_work_stacks_empty();
3735 verify_overflow_empty();
3736 _abort_preclean = false;
3737 if (CMSPrecleaningEnabled) {
3738 if (!CMSEdenChunksRecordAlways) {
3739 _eden_chunk_index = 0;
3740 }
3741 size_t used = get_eden_used();
3742 size_t capacity = get_eden_capacity();
3743 // Don't start sampling unless we will get sufficiently
3744 // many samples.
3745 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3746 * CMSScheduleRemarkEdenPenetration)) {
3747 _start_sampling = true;
3748 } else {
3749 _start_sampling = false;
3750 }
3751 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3752 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
3753 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3754 }
3755 CMSTokenSync x(true); // is cms thread
3756 if (CMSPrecleaningEnabled) {
3757 sample_eden();
3758 _collectorState = AbortablePreclean;
3759 } else {
3760 _collectorState = FinalMarking;
3761 }
3762 verify_work_stacks_empty();
3763 verify_overflow_empty();
3764 }
3765
3766 // Try and schedule the remark such that young gen
3767 // occupancy is CMSScheduleRemarkEdenPenetration %.
3768 void CMSCollector::abortable_preclean() {
3769 check_correct_thread_executing();
3770 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3771 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3772
3773 // If Eden's current occupancy is below this threshold,
3774 // immediately schedule the remark; else preclean
3775 // past the next scavenge in an effort to
3776 // schedule the pause as described above. By choosing
3777 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3778 // we will never do an actual abortable preclean cycle.
3779 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3780 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3781 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
3782 // We need more smarts in the abortable preclean
3783 // loop below to deal with cases where allocation
3784 // in young gen is very very slow, and our precleaning
3785 // is running a losing race against a horde of
3786 // mutators intent on flooding us with CMS updates
3787 // (dirty cards).
3788 // One, admittedly dumb, strategy is to give up
3789 // after a certain number of abortable precleaning loops
3790 // or after a certain maximum time. We want to make
3791 // this smarter in the next iteration.
3792 // XXX FIX ME!!! YSR
3793 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3794 while (!(should_abort_preclean() ||
3795 ConcurrentMarkSweepThread::should_terminate())) {
3796 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3797 cumworkdone += workdone;
3798 loops++;
3799 // Voluntarily terminate abortable preclean phase if we have
3800 // been at it for too long.
3801 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3802 loops >= CMSMaxAbortablePrecleanLoops) {
3803 if (PrintGCDetails) {
3804 gclog_or_tty->print(" CMS: abort preclean due to loops ");
3805 }
3806 break;
3807 }
3808 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3809 if (PrintGCDetails) {
3810 gclog_or_tty->print(" CMS: abort preclean due to time ");
3811 }
3812 break;
3813 }
3814 // If we are doing little work each iteration, we should
3815 // take a short break.
3816 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3817 // Sleep for some time, waiting for work to accumulate
3818 stopTimer();
3819 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3820 startTimer();
3821 waited++;
3822 }
3823 }
3824 if (PrintCMSStatistics > 0) {
3825 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3826 loops, waited, cumworkdone);
3827 }
3828 }
3829 CMSTokenSync x(true); // is cms thread
3830 if (_collectorState != Idling) {
3831 assert(_collectorState == AbortablePreclean,
3832 "Spontaneous state transition?");
3833 _collectorState = FinalMarking;
3834 } // Else, a foreground collection completed this CMS cycle.
3835 return;
3836 }
3837
3838 // Respond to an Eden sampling opportunity
3839 void CMSCollector::sample_eden() {
3840 // Make sure a young gc cannot sneak in between our
3841 // reading and recording of a sample.
3842 assert(Thread::current()->is_ConcurrentGC_thread(),
3843 "Only the cms thread may collect Eden samples");
3844 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3845 "Should collect samples while holding CMS token");
3846 if (!_start_sampling) {
3847 return;
3848 }
3849 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3850 // is populated by the young generation.
3851 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3852 if (_eden_chunk_index < _eden_chunk_capacity) {
3853 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3854 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3855 "Unexpected state of Eden");
3856 // We'd like to check that what we just sampled is an oop-start address;
3857 // however, we cannot do that here since the object may not yet have been
3858 // initialized. So we'll instead do the check when we _use_ this sample
3859 // later.
3860 if (_eden_chunk_index == 0 ||
3861 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3862 _eden_chunk_array[_eden_chunk_index-1])
3863 >= CMSSamplingGrain)) {
3864 _eden_chunk_index++; // commit sample
3865 }
3866 }
3867 }
3868 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3869 size_t used = get_eden_used();
3870 size_t capacity = get_eden_capacity();
3871 assert(used <= capacity, "Unexpected state of Eden");
3872 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3873 _abort_preclean = true;
3874 }
3875 }
3876 }
3877
3878
3879 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3880 assert(_collectorState == Precleaning ||
3881 _collectorState == AbortablePreclean, "incorrect state");
3882 ResourceMark rm;
3883 HandleMark hm;
3884
3885 // Precleaning is currently not MT but the reference processor
3886 // may be set for MT. Disable it temporarily here.
3887 ReferenceProcessor* rp = ref_processor();
3888 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3889
3890 // Do one pass of scrubbing the discovered reference lists
3891 // to remove any reference objects with strongly-reachable
3892 // referents.
3893 if (clean_refs) {
3894 CMSPrecleanRefsYieldClosure yield_cl(this);
3895 assert(rp->span().equals(_span), "Spans should be equal");
3896 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3897 &_markStack, true /* preclean */);
3898 CMSDrainMarkingStackClosure complete_trace(this,
3899 _span, &_markBitMap, &_markStack,
3900 &keep_alive, true /* preclean */);
3901
3902 // We don't want this step to interfere with a young
3903 // collection because we don't want to take CPU
3904 // or memory bandwidth away from the young GC threads
3905 // (which may be as many as there are CPUs).
3906 // Note that we don't need to protect ourselves from
3907 // interference with mutators because they can't
3908 // manipulate the discovered reference lists nor affect
3909 // the computed reachability of the referents, the
3910 // only properties manipulated by the precleaning
3911 // of these reference lists.
3912 stopTimer();
3913 CMSTokenSyncWithLocks x(true /* is cms thread */,
3914 bitMapLock());
3915 startTimer();
3916 sample_eden();
3917
3918 // The following will yield to allow foreground
3919 // collection to proceed promptly. XXX YSR:
3920 // The code in this method may need further
3921 // tweaking for better performance and some restructuring
3922 // for cleaner interfaces.
3923 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3924 rp->preclean_discovered_references(
3925 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3926 gc_timer);
3927 }
3928
3929 if (clean_survivor) { // preclean the active survivor space(s)
3930 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3931 &_markBitMap, &_modUnionTable,
3932 &_markStack, true /* precleaning phase */);
3933 stopTimer();
3934 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3935 bitMapLock());
3936 startTimer();
3937 unsigned int before_count =
3938 GenCollectedHeap::heap()->total_collections();
3939 SurvivorSpacePrecleanClosure
3940 sss_cl(this, _span, &_markBitMap, &_markStack,
3941 &pam_cl, before_count, CMSYield);
3942 _young_gen->from()->object_iterate_careful(&sss_cl);
3943 _young_gen->to()->object_iterate_careful(&sss_cl);
3944 }
3945 MarkRefsIntoAndScanClosure
3946 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3947 &_markStack, this, CMSYield,
3948 true /* precleaning phase */);
3949 // CAUTION: The following closure has persistent state that may need to
3950 // be reset upon a decrease in the sequence of addresses it
3951 // processes.
3952 ScanMarkedObjectsAgainCarefullyClosure
3953 smoac_cl(this, _span,
3954 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3955
3956 // Preclean dirty cards in ModUnionTable and CardTable using
3957 // appropriate convergence criterion;
3958 // repeat CMSPrecleanIter times unless we find that
3959 // we are losing.
3960 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3961 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3962 "Bad convergence multiplier");
3963 assert(CMSPrecleanThreshold >= 100,
3964 "Unreasonably low CMSPrecleanThreshold");
3965
3966 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3967 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3968 numIter < CMSPrecleanIter;
3969 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3970 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3971 if (Verbose && PrintGCDetails) {
3972 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3973 }
3974 // Either there are very few dirty cards, so re-mark
3975 // pause will be small anyway, or our pre-cleaning isn't
3976 // that much faster than the rate at which cards are being
3977 // dirtied, so we might as well stop and re-mark since
3978 // precleaning won't improve our re-mark time by much.
3979 if (curNumCards <= CMSPrecleanThreshold ||
3980 (numIter > 0 &&
3981 (curNumCards * CMSPrecleanDenominator >
3982 lastNumCards * CMSPrecleanNumerator))) {
3983 numIter++;
3984 cumNumCards += curNumCards;
3985 break;
3986 }
3987 }
3988
3989 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
3990
3991 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3992 cumNumCards += curNumCards;
3993 if (PrintGCDetails && PrintCMSStatistics != 0) {
3994 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3995 curNumCards, cumNumCards, numIter);
3996 }
3997 return cumNumCards; // as a measure of useful work done
3998 }
3999
4000 // PRECLEANING NOTES:
4001 // Precleaning involves:
4002 // . reading the bits of the modUnionTable and clearing the set bits.
4003 // . For the cards corresponding to the set bits, we scan the
4004 // objects on those cards. This means we need the free_list_lock
4005 // so that we can safely iterate over the CMS space when scanning
4006 // for oops.
4007 // . When we scan the objects, we'll be both reading and setting
4008 // marks in the marking bit map, so we'll need the marking bit map.
4009 // . For protecting _collector_state transitions, we take the CGC_lock.
4010 // Note that any races in the reading of of card table entries by the
4011 // CMS thread on the one hand and the clearing of those entries by the
4012 // VM thread or the setting of those entries by the mutator threads on the
4013 // other are quite benign. However, for efficiency it makes sense to keep
4014 // the VM thread from racing with the CMS thread while the latter is
4015 // dirty card info to the modUnionTable. We therefore also use the
4016 // CGC_lock to protect the reading of the card table and the mod union
4017 // table by the CM thread.
4018 // . We run concurrently with mutator updates, so scanning
4019 // needs to be done carefully -- we should not try to scan
4020 // potentially uninitialized objects.
4021 //
4022 // Locking strategy: While holding the CGC_lock, we scan over and
4023 // reset a maximal dirty range of the mod union / card tables, then lock
4024 // the free_list_lock and bitmap lock to do a full marking, then
4025 // release these locks; and repeat the cycle. This allows for a
4026 // certain amount of fairness in the sharing of these locks between
4027 // the CMS collector on the one hand, and the VM thread and the
4028 // mutators on the other.
4029
4030 // NOTE: preclean_mod_union_table() and preclean_card_table()
4031 // further below are largely identical; if you need to modify
4032 // one of these methods, please check the other method too.
4033
4034 size_t CMSCollector::preclean_mod_union_table(
4035 ConcurrentMarkSweepGeneration* old_gen,
4036 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4037 verify_work_stacks_empty();
4038 verify_overflow_empty();
4039
4040 // strategy: starting with the first card, accumulate contiguous
4041 // ranges of dirty cards; clear these cards, then scan the region
4042 // covered by these cards.
4043
4044 // Since all of the MUT is committed ahead, we can just use
4045 // that, in case the generations expand while we are precleaning.
4046 // It might also be fine to just use the committed part of the
4047 // generation, but we might potentially miss cards when the
4048 // generation is rapidly expanding while we are in the midst
4049 // of precleaning.
4050 HeapWord* startAddr = old_gen->reserved().start();
4051 HeapWord* endAddr = old_gen->reserved().end();
4052
4053 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4054
4055 size_t numDirtyCards, cumNumDirtyCards;
4056 HeapWord *nextAddr, *lastAddr;
4057 for (cumNumDirtyCards = numDirtyCards = 0,
4058 nextAddr = lastAddr = startAddr;
4059 nextAddr < endAddr;
4060 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4061
4062 ResourceMark rm;
4063 HandleMark hm;
4064
4065 MemRegion dirtyRegion;
4066 {
4067 stopTimer();
4068 // Potential yield point
4069 CMSTokenSync ts(true);
4070 startTimer();
4071 sample_eden();
4072 // Get dirty region starting at nextOffset (inclusive),
4073 // simultaneously clearing it.
4074 dirtyRegion =
4075 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4076 assert(dirtyRegion.start() >= nextAddr,
4077 "returned region inconsistent?");
4078 }
4079 // Remember where the next search should begin.
4080 // The returned region (if non-empty) is a right open interval,
4081 // so lastOffset is obtained from the right end of that
4082 // interval.
4083 lastAddr = dirtyRegion.end();
4084 // Should do something more transparent and less hacky XXX
4085 numDirtyCards =
4086 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4087
4088 // We'll scan the cards in the dirty region (with periodic
4089 // yields for foreground GC as needed).
4090 if (!dirtyRegion.is_empty()) {
4091 assert(numDirtyCards > 0, "consistency check");
4092 HeapWord* stop_point = NULL;
4093 stopTimer();
4094 // Potential yield point
4095 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
4096 bitMapLock());
4097 startTimer();
4098 {
4099 verify_work_stacks_empty();
4100 verify_overflow_empty();
4101 sample_eden();
4102 stop_point =
4103 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4104 }
4105 if (stop_point != NULL) {
4106 // The careful iteration stopped early either because it found an
4107 // uninitialized object, or because we were in the midst of an
4108 // "abortable preclean", which should now be aborted. Redirty
4109 // the bits corresponding to the partially-scanned or unscanned
4110 // cards. We'll either restart at the next block boundary or
4111 // abort the preclean.
4112 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4113 "Should only be AbortablePreclean.");
4114 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4115 if (should_abort_preclean()) {
4116 break; // out of preclean loop
4117 } else {
4118 // Compute the next address at which preclean should pick up;
4119 // might need bitMapLock in order to read P-bits.
4120 lastAddr = next_card_start_after_block(stop_point);
4121 }
4122 }
4123 } else {
4124 assert(lastAddr == endAddr, "consistency check");
4125 assert(numDirtyCards == 0, "consistency check");
4126 break;
4127 }
4128 }
4129 verify_work_stacks_empty();
4130 verify_overflow_empty();
4131 return cumNumDirtyCards;
4132 }
4133
4134 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4135 // below are largely identical; if you need to modify
4136 // one of these methods, please check the other method too.
4137
4138 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
4139 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4140 // strategy: it's similar to precleamModUnionTable above, in that
4141 // we accumulate contiguous ranges of dirty cards, mark these cards
4142 // precleaned, then scan the region covered by these cards.
4143 HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high());
4144 HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4145
4146 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4147
4148 size_t numDirtyCards, cumNumDirtyCards;
4149 HeapWord *lastAddr, *nextAddr;
4150
4151 for (cumNumDirtyCards = numDirtyCards = 0,
4152 nextAddr = lastAddr = startAddr;
4153 nextAddr < endAddr;
4154 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4155
4156 ResourceMark rm;
4157 HandleMark hm;
4158
4159 MemRegion dirtyRegion;
4160 {
4161 // See comments in "Precleaning notes" above on why we
4162 // do this locking. XXX Could the locking overheads be
4163 // too high when dirty cards are sparse? [I don't think so.]
4164 stopTimer();
4165 CMSTokenSync x(true); // is cms thread
4166 startTimer();
4167 sample_eden();
4168 // Get and clear dirty region from card table
4169 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4170 MemRegion(nextAddr, endAddr),
4171 true,
4172 CardTableModRefBS::precleaned_card_val());
4173
4174 assert(dirtyRegion.start() >= nextAddr,
4175 "returned region inconsistent?");
4176 }
4177 lastAddr = dirtyRegion.end();
4178 numDirtyCards =
4179 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4180
4181 if (!dirtyRegion.is_empty()) {
4182 stopTimer();
4183 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4184 startTimer();
4185 sample_eden();
4186 verify_work_stacks_empty();
4187 verify_overflow_empty();
4188 HeapWord* stop_point =
4189 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4190 if (stop_point != NULL) {
4191 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4192 "Should only be AbortablePreclean.");
4193 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4194 if (should_abort_preclean()) {
4195 break; // out of preclean loop
4196 } else {
4197 // Compute the next address at which preclean should pick up.
4198 lastAddr = next_card_start_after_block(stop_point);
4199 }
4200 }
4201 } else {
4202 break;
4203 }
4204 }
4205 verify_work_stacks_empty();
4206 verify_overflow_empty();
4207 return cumNumDirtyCards;
4208 }
4209
4210 class PrecleanKlassClosure : public KlassClosure {
4211 KlassToOopClosure _cm_klass_closure;
4212 public:
4213 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4214 void do_klass(Klass* k) {
4215 if (k->has_accumulated_modified_oops()) {
4216 k->clear_accumulated_modified_oops();
4217
4218 _cm_klass_closure.do_klass(k);
4219 }
4220 }
4221 };
4222
4223 // The freelist lock is needed to prevent asserts, is it really needed?
4224 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4225
4226 cl->set_freelistLock(freelistLock);
4227
4228 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4229
4230 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4231 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4232 PrecleanKlassClosure preclean_klass_closure(cl);
4233 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4234
4235 verify_work_stacks_empty();
4236 verify_overflow_empty();
4237 }
4238
4239 void CMSCollector::checkpointRootsFinal() {
4240 assert(_collectorState == FinalMarking, "incorrect state transition?");
4241 check_correct_thread_executing();
4242 // world is stopped at this checkpoint
4243 assert(SafepointSynchronize::is_at_safepoint(),
4244 "world should be stopped");
4245 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4246
4247 verify_work_stacks_empty();
4248 verify_overflow_empty();
4249
4250 if (PrintGCDetails) {
4251 gclog_or_tty->print("[YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)]",
4252 _young_gen->used() / K,
4253 _young_gen->capacity() / K);
4254 }
4255 {
4256 if (CMSScavengeBeforeRemark) {
4257 GenCollectedHeap* gch = GenCollectedHeap::heap();
4258 // Temporarily set flag to false, GCH->do_collection will
4259 // expect it to be false and set to true
4260 FlagSetting fl(gch->_is_gc_active, false);
4261 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4262 PrintGCDetails && Verbose, true, _gc_timer_cm);)
4263 gch->do_collection(true, // full (i.e. force, see below)
4264 false, // !clear_all_soft_refs
4265 0, // size
4266 false, // is_tlab
4267 GenCollectedHeap::YoungGen // type
4268 );
4269 }
4270 FreelistLocker x(this);
4271 MutexLockerEx y(bitMapLock(),
4272 Mutex::_no_safepoint_check_flag);
4273 checkpointRootsFinalWork();
4274 }
4275 verify_work_stacks_empty();
4276 verify_overflow_empty();
4277 }
4278
4279 void CMSCollector::checkpointRootsFinalWork() {
4280 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm);)
4281
4282 assert(haveFreelistLocks(), "must have free list locks");
4283 assert_lock_strong(bitMapLock());
4284
4285 ResourceMark rm;
4286 HandleMark hm;
4287
4288 GenCollectedHeap* gch = GenCollectedHeap::heap();
4289
4290 if (should_unload_classes()) {
4291 CodeCache::gc_prologue();
4292 }
4293 assert(haveFreelistLocks(), "must have free list locks");
4294 assert_lock_strong(bitMapLock());
4295
4296 // We might assume that we need not fill TLAB's when
4297 // CMSScavengeBeforeRemark is set, because we may have just done
4298 // a scavenge which would have filled all TLAB's -- and besides
4299 // Eden would be empty. This however may not always be the case --
4300 // for instance although we asked for a scavenge, it may not have
4301 // happened because of a JNI critical section. We probably need
4302 // a policy for deciding whether we can in that case wait until
4303 // the critical section releases and then do the remark following
4304 // the scavenge, and skip it here. In the absence of that policy,
4305 // or of an indication of whether the scavenge did indeed occur,
4306 // we cannot rely on TLAB's having been filled and must do
4307 // so here just in case a scavenge did not happen.
4308 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4309 // Update the saved marks which may affect the root scans.
4310 gch->save_marks();
4311
4312 if (CMSPrintEdenSurvivorChunks) {
4313 print_eden_and_survivor_chunk_arrays();
4314 }
4315
4316 {
4317 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4318
4319 // Note on the role of the mod union table:
4320 // Since the marker in "markFromRoots" marks concurrently with
4321 // mutators, it is possible for some reachable objects not to have been
4322 // scanned. For instance, an only reference to an object A was
4323 // placed in object B after the marker scanned B. Unless B is rescanned,
4324 // A would be collected. Such updates to references in marked objects
4325 // are detected via the mod union table which is the set of all cards
4326 // dirtied since the first checkpoint in this GC cycle and prior to
4327 // the most recent young generation GC, minus those cleaned up by the
4328 // concurrent precleaning.
4329 if (CMSParallelRemarkEnabled) {
4330 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm);
4331 do_remark_parallel();
4332 } else {
4333 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false, _gc_timer_cm);
4334 do_remark_non_parallel();
4335 }
4336 }
4337 verify_work_stacks_empty();
4338 verify_overflow_empty();
4339
4340 {
4341 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm);)
4342 refProcessingWork();
4343 }
4344 verify_work_stacks_empty();
4345 verify_overflow_empty();
4346
4347 if (should_unload_classes()) {
4348 CodeCache::gc_epilogue();
4349 }
4350 JvmtiExport::gc_epilogue();
4351
4352 // If we encountered any (marking stack / work queue) overflow
4353 // events during the current CMS cycle, take appropriate
4354 // remedial measures, where possible, so as to try and avoid
4355 // recurrence of that condition.
4356 assert(_markStack.isEmpty(), "No grey objects");
4357 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4358 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4359 if (ser_ovflw > 0) {
4360 if (PrintCMSStatistics != 0) {
4361 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4362 "(pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT
4363 ", kac_preclean=" SIZE_FORMAT ")",
4364 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4365 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4366 }
4367 _markStack.expand();
4368 _ser_pmc_remark_ovflw = 0;
4369 _ser_pmc_preclean_ovflw = 0;
4370 _ser_kac_preclean_ovflw = 0;
4371 _ser_kac_ovflw = 0;
4372 }
4373 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4374 if (PrintCMSStatistics != 0) {
4375 gclog_or_tty->print_cr("Work queue overflow (benign) "
4376 "(pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4377 _par_pmc_remark_ovflw, _par_kac_ovflw);
4378 }
4379 _par_pmc_remark_ovflw = 0;
4380 _par_kac_ovflw = 0;
4381 }
4382 if (PrintCMSStatistics != 0) {
4383 if (_markStack._hit_limit > 0) {
4384 gclog_or_tty->print_cr(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4385 _markStack._hit_limit);
4386 }
4387 if (_markStack._failed_double > 0) {
4388 gclog_or_tty->print_cr(" (benign) Failed stack doubling (" SIZE_FORMAT "),"
4389 " current capacity " SIZE_FORMAT,
4390 _markStack._failed_double,
4391 _markStack.capacity());
4392 }
4393 }
4394 _markStack._hit_limit = 0;
4395 _markStack._failed_double = 0;
4396
4397 if ((VerifyAfterGC || VerifyDuringGC) &&
4398 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4399 verify_after_remark();
4400 }
4401
4402 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4403
4404 // Change under the freelistLocks.
4405 _collectorState = Sweeping;
4406 // Call isAllClear() under bitMapLock
4407 assert(_modUnionTable.isAllClear(),
4408 "Should be clear by end of the final marking");
4409 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4410 "Should be clear by end of the final marking");
4411 }
4412
4413 void CMSParInitialMarkTask::work(uint worker_id) {
4414 elapsedTimer _timer;
4415 ResourceMark rm;
4416 HandleMark hm;
4417
4418 // ---------- scan from roots --------------
4419 _timer.start();
4420 GenCollectedHeap* gch = GenCollectedHeap::heap();
4421 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4422
4423 // ---------- young gen roots --------------
4424 {
4425 work_on_young_gen_roots(worker_id, &par_mri_cl);
4426 _timer.stop();
4427 if (PrintCMSStatistics != 0) {
4428 gclog_or_tty->print_cr(
4429 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4430 worker_id, _timer.seconds());
4431 }
4432 }
4433
4434 // ---------- remaining roots --------------
4435 _timer.reset();
4436 _timer.start();
4437
4438 CLDToOopClosure cld_closure(&par_mri_cl, true);
4439
4440 gch->gen_process_roots(_strong_roots_scope,
4441 GenCollectedHeap::OldGen,
4442 false, // yg was scanned above
4443 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4444 _collector->should_unload_classes(),
4445 &par_mri_cl,
4446 NULL,
4447 &cld_closure);
4448 assert(_collector->should_unload_classes()
4449 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4450 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4451 _timer.stop();
4452 if (PrintCMSStatistics != 0) {
4453 gclog_or_tty->print_cr(
4454 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4455 worker_id, _timer.seconds());
4456 }
4457 }
4458
4459 // Parallel remark task
4460 class CMSParRemarkTask: public CMSParMarkTask {
4461 CompactibleFreeListSpace* _cms_space;
4462
4463 // The per-thread work queues, available here for stealing.
4464 OopTaskQueueSet* _task_queues;
4465 ParallelTaskTerminator _term;
4466 StrongRootsScope* _strong_roots_scope;
4467
4468 public:
4469 // A value of 0 passed to n_workers will cause the number of
4470 // workers to be taken from the active workers in the work gang.
4471 CMSParRemarkTask(CMSCollector* collector,
4472 CompactibleFreeListSpace* cms_space,
4473 uint n_workers, WorkGang* workers,
4474 OopTaskQueueSet* task_queues,
4475 StrongRootsScope* strong_roots_scope):
4476 CMSParMarkTask("Rescan roots and grey objects in parallel",
4477 collector, n_workers),
4478 _cms_space(cms_space),
4479 _task_queues(task_queues),
4480 _term(n_workers, task_queues),
4481 _strong_roots_scope(strong_roots_scope) { }
4482
4483 OopTaskQueueSet* task_queues() { return _task_queues; }
4484
4485 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4486
4487 ParallelTaskTerminator* terminator() { return &_term; }
4488 uint n_workers() { return _n_workers; }
4489
4490 void work(uint worker_id);
4491
4492 private:
4493 // ... of dirty cards in old space
4494 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4495 Par_MarkRefsIntoAndScanClosure* cl);
4496
4497 // ... work stealing for the above
4498 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4499 };
4500
4501 class RemarkKlassClosure : public KlassClosure {
4502 KlassToOopClosure _cm_klass_closure;
4503 public:
4504 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4505 void do_klass(Klass* k) {
4506 // Check if we have modified any oops in the Klass during the concurrent marking.
4507 if (k->has_accumulated_modified_oops()) {
4508 k->clear_accumulated_modified_oops();
4509
4510 // We could have transfered the current modified marks to the accumulated marks,
4511 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4512 } else if (k->has_modified_oops()) {
4513 // Don't clear anything, this info is needed by the next young collection.
4514 } else {
4515 // No modified oops in the Klass.
4516 return;
4517 }
4518
4519 // The klass has modified fields, need to scan the klass.
4520 _cm_klass_closure.do_klass(k);
4521 }
4522 };
4523
4524 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4525 ParNewGeneration* young_gen = _collector->_young_gen;
4526 ContiguousSpace* eden_space = young_gen->eden();
4527 ContiguousSpace* from_space = young_gen->from();
4528 ContiguousSpace* to_space = young_gen->to();
4529
4530 HeapWord** eca = _collector->_eden_chunk_array;
4531 size_t ect = _collector->_eden_chunk_index;
4532 HeapWord** sca = _collector->_survivor_chunk_array;
4533 size_t sct = _collector->_survivor_chunk_index;
4534
4535 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4536 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4537
4538 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4539 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4540 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4541 }
4542
4543 // work_queue(i) is passed to the closure
4544 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
4545 // also is passed to do_dirty_card_rescan_tasks() and to
4546 // do_work_steal() to select the i-th task_queue.
4547
4548 void CMSParRemarkTask::work(uint worker_id) {
4549 elapsedTimer _timer;
4550 ResourceMark rm;
4551 HandleMark hm;
4552
4553 // ---------- rescan from roots --------------
4554 _timer.start();
4555 GenCollectedHeap* gch = GenCollectedHeap::heap();
4556 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4557 _collector->_span, _collector->ref_processor(),
4558 &(_collector->_markBitMap),
4559 work_queue(worker_id));
4560
4561 // Rescan young gen roots first since these are likely
4562 // coarsely partitioned and may, on that account, constitute
4563 // the critical path; thus, it's best to start off that
4564 // work first.
4565 // ---------- young gen roots --------------
4566 {
4567 work_on_young_gen_roots(worker_id, &par_mrias_cl);
4568 _timer.stop();
4569 if (PrintCMSStatistics != 0) {
4570 gclog_or_tty->print_cr(
4571 "Finished young gen rescan work in %dth thread: %3.3f sec",
4572 worker_id, _timer.seconds());
4573 }
4574 }
4575
4576 // ---------- remaining roots --------------
4577 _timer.reset();
4578 _timer.start();
4579 gch->gen_process_roots(_strong_roots_scope,
4580 GenCollectedHeap::OldGen,
4581 false, // yg was scanned above
4582 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4583 _collector->should_unload_classes(),
4584 &par_mrias_cl,
4585 NULL,
4586 NULL); // The dirty klasses will be handled below
4587
4588 assert(_collector->should_unload_classes()
4589 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4590 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4591 _timer.stop();
4592 if (PrintCMSStatistics != 0) {
4593 gclog_or_tty->print_cr(
4594 "Finished remaining root rescan work in %dth thread: %3.3f sec",
4595 worker_id, _timer.seconds());
4596 }
4597
4598 // ---------- unhandled CLD scanning ----------
4599 if (worker_id == 0) { // Single threaded at the moment.
4600 _timer.reset();
4601 _timer.start();
4602
4603 // Scan all new class loader data objects and new dependencies that were
4604 // introduced during concurrent marking.
4605 ResourceMark rm;
4606 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4607 for (int i = 0; i < array->length(); i++) {
4608 par_mrias_cl.do_cld_nv(array->at(i));
4609 }
4610
4611 // We don't need to keep track of new CLDs anymore.
4612 ClassLoaderDataGraph::remember_new_clds(false);
4613
4614 _timer.stop();
4615 if (PrintCMSStatistics != 0) {
4616 gclog_or_tty->print_cr(
4617 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4618 worker_id, _timer.seconds());
4619 }
4620 }
4621
4622 // ---------- dirty klass scanning ----------
4623 if (worker_id == 0) { // Single threaded at the moment.
4624 _timer.reset();
4625 _timer.start();
4626
4627 // Scan all classes that was dirtied during the concurrent marking phase.
4628 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4629 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4630
4631 _timer.stop();
4632 if (PrintCMSStatistics != 0) {
4633 gclog_or_tty->print_cr(
4634 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4635 worker_id, _timer.seconds());
4636 }
4637 }
4638
4639 // We might have added oops to ClassLoaderData::_handles during the
4640 // concurrent marking phase. These oops point to newly allocated objects
4641 // that are guaranteed to be kept alive. Either by the direct allocation
4642 // code, or when the young collector processes the roots. Hence,
4643 // we don't have to revisit the _handles block during the remark phase.
4644
4645 // ---------- rescan dirty cards ------------
4646 _timer.reset();
4647 _timer.start();
4648
4649 // Do the rescan tasks for each of the two spaces
4650 // (cms_space) in turn.
4651 // "worker_id" is passed to select the task_queue for "worker_id"
4652 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4653 _timer.stop();
4654 if (PrintCMSStatistics != 0) {
4655 gclog_or_tty->print_cr(
4656 "Finished dirty card rescan work in %dth thread: %3.3f sec",
4657 worker_id, _timer.seconds());
4658 }
4659
4660 // ---------- steal work from other threads ...
4661 // ---------- ... and drain overflow list.
4662 _timer.reset();
4663 _timer.start();
4664 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4665 _timer.stop();
4666 if (PrintCMSStatistics != 0) {
4667 gclog_or_tty->print_cr(
4668 "Finished work stealing in %dth thread: %3.3f sec",
4669 worker_id, _timer.seconds());
4670 }
4671 }
4672
4673 // Note that parameter "i" is not used.
4674 void
4675 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4676 OopsInGenClosure* cl, ContiguousSpace* space,
4677 HeapWord** chunk_array, size_t chunk_top) {
4678 // Until all tasks completed:
4679 // . claim an unclaimed task
4680 // . compute region boundaries corresponding to task claimed
4681 // using chunk_array
4682 // . par_oop_iterate(cl) over that region
4683
4684 ResourceMark rm;
4685 HandleMark hm;
4686
4687 SequentialSubTasksDone* pst = space->par_seq_tasks();
4688
4689 uint nth_task = 0;
4690 uint n_tasks = pst->n_tasks();
4691
4692 if (n_tasks > 0) {
4693 assert(pst->valid(), "Uninitialized use?");
4694 HeapWord *start, *end;
4695 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4696 // We claimed task # nth_task; compute its boundaries.
4697 if (chunk_top == 0) { // no samples were taken
4698 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4699 start = space->bottom();
4700 end = space->top();
4701 } else if (nth_task == 0) {
4702 start = space->bottom();
4703 end = chunk_array[nth_task];
4704 } else if (nth_task < (uint)chunk_top) {
4705 assert(nth_task >= 1, "Control point invariant");
4706 start = chunk_array[nth_task - 1];
4707 end = chunk_array[nth_task];
4708 } else {
4709 assert(nth_task == (uint)chunk_top, "Control point invariant");
4710 start = chunk_array[chunk_top - 1];
4711 end = space->top();
4712 }
4713 MemRegion mr(start, end);
4714 // Verify that mr is in space
4715 assert(mr.is_empty() || space->used_region().contains(mr),
4716 "Should be in space");
4717 // Verify that "start" is an object boundary
4718 assert(mr.is_empty() || oop(mr.start())->is_oop(),
4719 "Should be an oop");
4720 space->par_oop_iterate(mr, cl);
4721 }
4722 pst->all_tasks_completed();
4723 }
4724 }
4725
4726 void
4727 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4728 CompactibleFreeListSpace* sp, int i,
4729 Par_MarkRefsIntoAndScanClosure* cl) {
4730 // Until all tasks completed:
4731 // . claim an unclaimed task
4732 // . compute region boundaries corresponding to task claimed
4733 // . transfer dirty bits ct->mut for that region
4734 // . apply rescanclosure to dirty mut bits for that region
4735
4736 ResourceMark rm;
4737 HandleMark hm;
4738
4739 OopTaskQueue* work_q = work_queue(i);
4740 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4741 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4742 // CAUTION: This closure has state that persists across calls to
4743 // the work method dirty_range_iterate_clear() in that it has
4744 // embedded in it a (subtype of) UpwardsObjectClosure. The
4745 // use of that state in the embedded UpwardsObjectClosure instance
4746 // assumes that the cards are always iterated (even if in parallel
4747 // by several threads) in monotonically increasing order per each
4748 // thread. This is true of the implementation below which picks
4749 // card ranges (chunks) in monotonically increasing order globally
4750 // and, a-fortiori, in monotonically increasing order per thread
4751 // (the latter order being a subsequence of the former).
4752 // If the work code below is ever reorganized into a more chaotic
4753 // work-partitioning form than the current "sequential tasks"
4754 // paradigm, the use of that persistent state will have to be
4755 // revisited and modified appropriately. See also related
4756 // bug 4756801 work on which should examine this code to make
4757 // sure that the changes there do not run counter to the
4758 // assumptions made here and necessary for correctness and
4759 // efficiency. Note also that this code might yield inefficient
4760 // behavior in the case of very large objects that span one or
4761 // more work chunks. Such objects would potentially be scanned
4762 // several times redundantly. Work on 4756801 should try and
4763 // address that performance anomaly if at all possible. XXX
4764 MemRegion full_span = _collector->_span;
4765 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4766 MarkFromDirtyCardsClosure
4767 greyRescanClosure(_collector, full_span, // entire span of interest
4768 sp, bm, work_q, cl);
4769
4770 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4771 assert(pst->valid(), "Uninitialized use?");
4772 uint nth_task = 0;
4773 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4774 MemRegion span = sp->used_region();
4775 HeapWord* start_addr = span.start();
4776 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4777 alignment);
4778 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4779 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4780 start_addr, "Check alignment");
4781 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4782 chunk_size, "Check alignment");
4783
4784 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4785 // Having claimed the nth_task, compute corresponding mem-region,
4786 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4787 // The alignment restriction ensures that we do not need any
4788 // synchronization with other gang-workers while setting or
4789 // clearing bits in thus chunk of the MUT.
4790 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4791 start_addr + (nth_task+1)*chunk_size);
4792 // The last chunk's end might be way beyond end of the
4793 // used region. In that case pull back appropriately.
4794 if (this_span.end() > end_addr) {
4795 this_span.set_end(end_addr);
4796 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4797 }
4798 // Iterate over the dirty cards covering this chunk, marking them
4799 // precleaned, and setting the corresponding bits in the mod union
4800 // table. Since we have been careful to partition at Card and MUT-word
4801 // boundaries no synchronization is needed between parallel threads.
4802 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4803 &modUnionClosure);
4804
4805 // Having transferred these marks into the modUnionTable,
4806 // rescan the marked objects on the dirty cards in the modUnionTable.
4807 // Even if this is at a synchronous collection, the initial marking
4808 // may have been done during an asynchronous collection so there
4809 // may be dirty bits in the mod-union table.
4810 _collector->_modUnionTable.dirty_range_iterate_clear(
4811 this_span, &greyRescanClosure);
4812 _collector->_modUnionTable.verifyNoOneBitsInRange(
4813 this_span.start(),
4814 this_span.end());
4815 }
4816 pst->all_tasks_completed(); // declare that i am done
4817 }
4818
4819 // . see if we can share work_queues with ParNew? XXX
4820 void
4821 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4822 int* seed) {
4823 OopTaskQueue* work_q = work_queue(i);
4824 NOT_PRODUCT(int num_steals = 0;)
4825 oop obj_to_scan;
4826 CMSBitMap* bm = &(_collector->_markBitMap);
4827
4828 while (true) {
4829 // Completely finish any left over work from (an) earlier round(s)
4830 cl->trim_queue(0);
4831 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4832 (size_t)ParGCDesiredObjsFromOverflowList);
4833 // Now check if there's any work in the overflow list
4834 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4835 // only affects the number of attempts made to get work from the
4836 // overflow list and does not affect the number of workers. Just
4837 // pass ParallelGCThreads so this behavior is unchanged.
4838 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4839 work_q,
4840 ParallelGCThreads)) {
4841 // found something in global overflow list;
4842 // not yet ready to go stealing work from others.
4843 // We'd like to assert(work_q->size() != 0, ...)
4844 // because we just took work from the overflow list,
4845 // but of course we can't since all of that could have
4846 // been already stolen from us.
4847 // "He giveth and He taketh away."
4848 continue;
4849 }
4850 // Verify that we have no work before we resort to stealing
4851 assert(work_q->size() == 0, "Have work, shouldn't steal");
4852 // Try to steal from other queues that have work
4853 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4854 NOT_PRODUCT(num_steals++;)
4855 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4856 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4857 // Do scanning work
4858 obj_to_scan->oop_iterate(cl);
4859 // Loop around, finish this work, and try to steal some more
4860 } else if (terminator()->offer_termination()) {
4861 break; // nirvana from the infinite cycle
4862 }
4863 }
4864 NOT_PRODUCT(
4865 if (PrintCMSStatistics != 0) {
4866 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
4867 }
4868 )
4869 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4870 "Else our work is not yet done");
4871 }
4872
4873 // Record object boundaries in _eden_chunk_array by sampling the eden
4874 // top in the slow-path eden object allocation code path and record
4875 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4876 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4877 // sampling in sample_eden() that activates during the part of the
4878 // preclean phase.
4879 void CMSCollector::sample_eden_chunk() {
4880 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4881 if (_eden_chunk_lock->try_lock()) {
4882 // Record a sample. This is the critical section. The contents
4883 // of the _eden_chunk_array have to be non-decreasing in the
4884 // address order.
4885 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4886 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4887 "Unexpected state of Eden");
4888 if (_eden_chunk_index == 0 ||
4889 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4890 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4891 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4892 _eden_chunk_index++; // commit sample
4893 }
4894 _eden_chunk_lock->unlock();
4895 }
4896 }
4897 }
4898
4899 // Return a thread-local PLAB recording array, as appropriate.
4900 void* CMSCollector::get_data_recorder(int thr_num) {
4901 if (_survivor_plab_array != NULL &&
4902 (CMSPLABRecordAlways ||
4903 (_collectorState > Marking && _collectorState < FinalMarking))) {
4904 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4905 ChunkArray* ca = &_survivor_plab_array[thr_num];
4906 ca->reset(); // clear it so that fresh data is recorded
4907 return (void*) ca;
4908 } else {
4909 return NULL;
4910 }
4911 }
4912
4913 // Reset all the thread-local PLAB recording arrays
4914 void CMSCollector::reset_survivor_plab_arrays() {
4915 for (uint i = 0; i < ParallelGCThreads; i++) {
4916 _survivor_plab_array[i].reset();
4917 }
4918 }
4919
4920 // Merge the per-thread plab arrays into the global survivor chunk
4921 // array which will provide the partitioning of the survivor space
4922 // for CMS initial scan and rescan.
4923 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4924 int no_of_gc_threads) {
4925 assert(_survivor_plab_array != NULL, "Error");
4926 assert(_survivor_chunk_array != NULL, "Error");
4927 assert(_collectorState == FinalMarking ||
4928 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4929 for (int j = 0; j < no_of_gc_threads; j++) {
4930 _cursor[j] = 0;
4931 }
4932 HeapWord* top = surv->top();
4933 size_t i;
4934 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4935 HeapWord* min_val = top; // Higher than any PLAB address
4936 uint min_tid = 0; // position of min_val this round
4937 for (int j = 0; j < no_of_gc_threads; j++) {
4938 ChunkArray* cur_sca = &_survivor_plab_array[j];
4939 if (_cursor[j] == cur_sca->end()) {
4940 continue;
4941 }
4942 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4943 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4944 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4945 if (cur_val < min_val) {
4946 min_tid = j;
4947 min_val = cur_val;
4948 } else {
4949 assert(cur_val < top, "All recorded addresses should be less");
4950 }
4951 }
4952 // At this point min_val and min_tid are respectively
4953 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4954 // and the thread (j) that witnesses that address.
4955 // We record this address in the _survivor_chunk_array[i]
4956 // and increment _cursor[min_tid] prior to the next round i.
4957 if (min_val == top) {
4958 break;
4959 }
4960 _survivor_chunk_array[i] = min_val;
4961 _cursor[min_tid]++;
4962 }
4963 // We are all done; record the size of the _survivor_chunk_array
4964 _survivor_chunk_index = i; // exclusive: [0, i)
4965 if (PrintCMSStatistics > 0) {
4966 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4967 }
4968 // Verify that we used up all the recorded entries
4969 #ifdef ASSERT
4970 size_t total = 0;
4971 for (int j = 0; j < no_of_gc_threads; j++) {
4972 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4973 total += _cursor[j];
4974 }
4975 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4976 // Check that the merged array is in sorted order
4977 if (total > 0) {
4978 for (size_t i = 0; i < total - 1; i++) {
4979 if (PrintCMSStatistics > 0) {
4980 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4981 i, p2i(_survivor_chunk_array[i]));
4982 }
4983 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4984 "Not sorted");
4985 }
4986 }
4987 #endif // ASSERT
4988 }
4989
4990 // Set up the space's par_seq_tasks structure for work claiming
4991 // for parallel initial scan and rescan of young gen.
4992 // See ParRescanTask where this is currently used.
4993 void
4994 CMSCollector::
4995 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4996 assert(n_threads > 0, "Unexpected n_threads argument");
4997
4998 // Eden space
4999 if (!_young_gen->eden()->is_empty()) {
5000 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
5001 assert(!pst->valid(), "Clobbering existing data?");
5002 // Each valid entry in [0, _eden_chunk_index) represents a task.
5003 size_t n_tasks = _eden_chunk_index + 1;
5004 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5005 // Sets the condition for completion of the subtask (how many threads
5006 // need to finish in order to be done).
5007 pst->set_n_threads(n_threads);
5008 pst->set_n_tasks((int)n_tasks);
5009 }
5010
5011 // Merge the survivor plab arrays into _survivor_chunk_array
5012 if (_survivor_plab_array != NULL) {
5013 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5014 } else {
5015 assert(_survivor_chunk_index == 0, "Error");
5016 }
5017
5018 // To space
5019 {
5020 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5021 assert(!pst->valid(), "Clobbering existing data?");
5022 // Sets the condition for completion of the subtask (how many threads
5023 // need to finish in order to be done).
5024 pst->set_n_threads(n_threads);
5025 pst->set_n_tasks(1);
5026 assert(pst->valid(), "Error");
5027 }
5028
5029 // From space
5030 {
5031 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5032 assert(!pst->valid(), "Clobbering existing data?");
5033 size_t n_tasks = _survivor_chunk_index + 1;
5034 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5035 // Sets the condition for completion of the subtask (how many threads
5036 // need to finish in order to be done).
5037 pst->set_n_threads(n_threads);
5038 pst->set_n_tasks((int)n_tasks);
5039 assert(pst->valid(), "Error");
5040 }
5041 }
5042
5043 // Parallel version of remark
5044 void CMSCollector::do_remark_parallel() {
5045 GenCollectedHeap* gch = GenCollectedHeap::heap();
5046 WorkGang* workers = gch->workers();
5047 assert(workers != NULL, "Need parallel worker threads.");
5048 // Choose to use the number of GC workers most recently set
5049 // into "active_workers".
5050 uint n_workers = workers->active_workers();
5051
5052 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5053
5054 StrongRootsScope srs(n_workers);
5055
5056 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
5057
5058 // We won't be iterating over the cards in the card table updating
5059 // the younger_gen cards, so we shouldn't call the following else
5060 // the verification code as well as subsequent younger_refs_iterate
5061 // code would get confused. XXX
5062 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5063
5064 // The young gen rescan work will not be done as part of
5065 // process_roots (which currently doesn't know how to
5066 // parallelize such a scan), but rather will be broken up into
5067 // a set of parallel tasks (via the sampling that the [abortable]
5068 // preclean phase did of eden, plus the [two] tasks of
5069 // scanning the [two] survivor spaces. Further fine-grain
5070 // parallelization of the scanning of the survivor spaces
5071 // themselves, and of precleaning of the young gen itself
5072 // is deferred to the future.
5073 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5074
5075 // The dirty card rescan work is broken up into a "sequence"
5076 // of parallel tasks (per constituent space) that are dynamically
5077 // claimed by the parallel threads.
5078 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5079
5080 // It turns out that even when we're using 1 thread, doing the work in a
5081 // separate thread causes wide variance in run times. We can't help this
5082 // in the multi-threaded case, but we special-case n=1 here to get
5083 // repeatable measurements of the 1-thread overhead of the parallel code.
5084 if (n_workers > 1) {
5085 // Make refs discovery MT-safe, if it isn't already: it may not
5086 // necessarily be so, since it's possible that we are doing
5087 // ST marking.
5088 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5089 workers->run_task(&tsk);
5090 } else {
5091 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5092 tsk.work(0);
5093 }
5094
5095 // restore, single-threaded for now, any preserved marks
5096 // as a result of work_q overflow
5097 restore_preserved_marks_if_any();
5098 }
5099
5100 // Non-parallel version of remark
5101 void CMSCollector::do_remark_non_parallel() {
5102 ResourceMark rm;
5103 HandleMark hm;
5104 GenCollectedHeap* gch = GenCollectedHeap::heap();
5105 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5106
5107 MarkRefsIntoAndScanClosure
5108 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5109 &_markStack, this,
5110 false /* should_yield */, false /* not precleaning */);
5111 MarkFromDirtyCardsClosure
5112 markFromDirtyCardsClosure(this, _span,
5113 NULL, // space is set further below
5114 &_markBitMap, &_markStack, &mrias_cl);
5115 {
5116 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm);
5117 // Iterate over the dirty cards, setting the corresponding bits in the
5118 // mod union table.
5119 {
5120 ModUnionClosure modUnionClosure(&_modUnionTable);
5121 _ct->ct_bs()->dirty_card_iterate(
5122 _cmsGen->used_region(),
5123 &modUnionClosure);
5124 }
5125 // Having transferred these marks into the modUnionTable, we just need
5126 // to rescan the marked objects on the dirty cards in the modUnionTable.
5127 // The initial marking may have been done during an asynchronous
5128 // collection so there may be dirty bits in the mod-union table.
5129 const int alignment =
5130 CardTableModRefBS::card_size * BitsPerWord;
5131 {
5132 // ... First handle dirty cards in CMS gen
5133 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5134 MemRegion ur = _cmsGen->used_region();
5135 HeapWord* lb = ur.start();
5136 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5137 MemRegion cms_span(lb, ub);
5138 _modUnionTable.dirty_range_iterate_clear(cms_span,
5139 &markFromDirtyCardsClosure);
5140 verify_work_stacks_empty();
5141 if (PrintCMSStatistics != 0) {
5142 gclog_or_tty->print(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ",
5143 markFromDirtyCardsClosure.num_dirty_cards());
5144 }
5145 }
5146 }
5147 if (VerifyDuringGC &&
5148 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5149 HandleMark hm; // Discard invalid handles created during verification
5150 Universe::verify();
5151 }
5152 {
5153 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm);
5154
5155 verify_work_stacks_empty();
5156
5157 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5158 StrongRootsScope srs(1);
5159
5160 gch->gen_process_roots(&srs,
5161 GenCollectedHeap::OldGen,
5162 true, // young gen as roots
5163 GenCollectedHeap::ScanningOption(roots_scanning_options()),
5164 should_unload_classes(),
5165 &mrias_cl,
5166 NULL,
5167 NULL); // The dirty klasses will be handled below
5168
5169 assert(should_unload_classes()
5170 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5171 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5172 }
5173
5174 {
5175 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm);
5176
5177 verify_work_stacks_empty();
5178
5179 // Scan all class loader data objects that might have been introduced
5180 // during concurrent marking.
5181 ResourceMark rm;
5182 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5183 for (int i = 0; i < array->length(); i++) {
5184 mrias_cl.do_cld_nv(array->at(i));
5185 }
5186
5187 // We don't need to keep track of new CLDs anymore.
5188 ClassLoaderDataGraph::remember_new_clds(false);
5189
5190 verify_work_stacks_empty();
5191 }
5192
5193 {
5194 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm);
5195
5196 verify_work_stacks_empty();
5197
5198 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5199 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5200
5201 verify_work_stacks_empty();
5202 }
5203
5204 // We might have added oops to ClassLoaderData::_handles during the
5205 // concurrent marking phase. These oops point to newly allocated objects
5206 // that are guaranteed to be kept alive. Either by the direct allocation
5207 // code, or when the young collector processes the roots. Hence,
5208 // we don't have to revisit the _handles block during the remark phase.
5209
5210 verify_work_stacks_empty();
5211 // Restore evacuated mark words, if any, used for overflow list links
5212 if (!CMSOverflowEarlyRestoration) {
5213 restore_preserved_marks_if_any();
5214 }
5215 verify_overflow_empty();
5216 }
5217
5218 ////////////////////////////////////////////////////////
5219 // Parallel Reference Processing Task Proxy Class
5220 ////////////////////////////////////////////////////////
5221 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5222 OopTaskQueueSet* _queues;
5223 ParallelTaskTerminator _terminator;
5224 public:
5225 AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5226 AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5227 ParallelTaskTerminator* terminator() { return &_terminator; }
5228 OopTaskQueueSet* queues() { return _queues; }
5229 };
5230
5231 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5232 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5233 CMSCollector* _collector;
5234 CMSBitMap* _mark_bit_map;
5235 const MemRegion _span;
5236 ProcessTask& _task;
5237
5238 public:
5239 CMSRefProcTaskProxy(ProcessTask& task,
5240 CMSCollector* collector,
5241 const MemRegion& span,
5242 CMSBitMap* mark_bit_map,
5243 AbstractWorkGang* workers,
5244 OopTaskQueueSet* task_queues):
5245 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5246 task_queues,
5247 workers->active_workers()),
5248 _task(task),
5249 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5250 {
5251 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5252 "Inconsistency in _span");
5253 }
5254
5255 OopTaskQueueSet* task_queues() { return queues(); }
5256
5257 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5258
5259 void do_work_steal(int i,
5260 CMSParDrainMarkingStackClosure* drain,
5261 CMSParKeepAliveClosure* keep_alive,
5262 int* seed);
5263
5264 virtual void work(uint worker_id);
5265 };
5266
5267 void CMSRefProcTaskProxy::work(uint worker_id) {
5268 ResourceMark rm;
5269 HandleMark hm;
5270 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5271 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5272 _mark_bit_map,
5273 work_queue(worker_id));
5274 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5275 _mark_bit_map,
5276 work_queue(worker_id));
5277 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5278 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5279 if (_task.marks_oops_alive()) {
5280 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5281 _collector->hash_seed(worker_id));
5282 }
5283 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5284 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5285 }
5286
5287 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5288 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5289 EnqueueTask& _task;
5290
5291 public:
5292 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5293 : AbstractGangTask("Enqueue reference objects in parallel"),
5294 _task(task)
5295 { }
5296
5297 virtual void work(uint worker_id)
5298 {
5299 _task.work(worker_id);
5300 }
5301 };
5302
5303 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5304 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5305 _span(span),
5306 _bit_map(bit_map),
5307 _work_queue(work_queue),
5308 _mark_and_push(collector, span, bit_map, work_queue),
5309 _low_water_mark(MIN2((work_queue->max_elems()/4),
5310 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5311 { }
5312
5313 // . see if we can share work_queues with ParNew? XXX
5314 void CMSRefProcTaskProxy::do_work_steal(int i,
5315 CMSParDrainMarkingStackClosure* drain,
5316 CMSParKeepAliveClosure* keep_alive,
5317 int* seed) {
5318 OopTaskQueue* work_q = work_queue(i);
5319 NOT_PRODUCT(int num_steals = 0;)
5320 oop obj_to_scan;
5321
5322 while (true) {
5323 // Completely finish any left over work from (an) earlier round(s)
5324 drain->trim_queue(0);
5325 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5326 (size_t)ParGCDesiredObjsFromOverflowList);
5327 // Now check if there's any work in the overflow list
5328 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5329 // only affects the number of attempts made to get work from the
5330 // overflow list and does not affect the number of workers. Just
5331 // pass ParallelGCThreads so this behavior is unchanged.
5332 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5333 work_q,
5334 ParallelGCThreads)) {
5335 // Found something in global overflow list;
5336 // not yet ready to go stealing work from others.
5337 // We'd like to assert(work_q->size() != 0, ...)
5338 // because we just took work from the overflow list,
5339 // but of course we can't, since all of that might have
5340 // been already stolen from us.
5341 continue;
5342 }
5343 // Verify that we have no work before we resort to stealing
5344 assert(work_q->size() == 0, "Have work, shouldn't steal");
5345 // Try to steal from other queues that have work
5346 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5347 NOT_PRODUCT(num_steals++;)
5348 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5349 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5350 // Do scanning work
5351 obj_to_scan->oop_iterate(keep_alive);
5352 // Loop around, finish this work, and try to steal some more
5353 } else if (terminator()->offer_termination()) {
5354 break; // nirvana from the infinite cycle
5355 }
5356 }
5357 NOT_PRODUCT(
5358 if (PrintCMSStatistics != 0) {
5359 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5360 }
5361 )
5362 }
5363
5364 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5365 {
5366 GenCollectedHeap* gch = GenCollectedHeap::heap();
5367 WorkGang* workers = gch->workers();
5368 assert(workers != NULL, "Need parallel worker threads.");
5369 CMSRefProcTaskProxy rp_task(task, &_collector,
5370 _collector.ref_processor()->span(),
5371 _collector.markBitMap(),
5372 workers, _collector.task_queues());
5373 workers->run_task(&rp_task);
5374 }
5375
5376 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5377 {
5378
5379 GenCollectedHeap* gch = GenCollectedHeap::heap();
5380 WorkGang* workers = gch->workers();
5381 assert(workers != NULL, "Need parallel worker threads.");
5382 CMSRefEnqueueTaskProxy enq_task(task);
5383 workers->run_task(&enq_task);
5384 }
5385
5386 void CMSCollector::refProcessingWork() {
5387 ResourceMark rm;
5388 HandleMark hm;
5389
5390 ReferenceProcessor* rp = ref_processor();
5391 assert(rp->span().equals(_span), "Spans should be equal");
5392 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5393 // Process weak references.
5394 rp->setup_policy(false);
5395 verify_work_stacks_empty();
5396
5397 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5398 &_markStack, false /* !preclean */);
5399 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5400 _span, &_markBitMap, &_markStack,
5401 &cmsKeepAliveClosure, false /* !preclean */);
5402 {
5403 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm);
5404
5405 ReferenceProcessorStats stats;
5406 if (rp->processing_is_mt()) {
5407 // Set the degree of MT here. If the discovery is done MT, there
5408 // may have been a different number of threads doing the discovery
5409 // and a different number of discovered lists may have Ref objects.
5410 // That is OK as long as the Reference lists are balanced (see
5411 // balance_all_queues() and balance_queues()).
5412 GenCollectedHeap* gch = GenCollectedHeap::heap();
5413 uint active_workers = ParallelGCThreads;
5414 WorkGang* workers = gch->workers();
5415 if (workers != NULL) {
5416 active_workers = workers->active_workers();
5417 // The expectation is that active_workers will have already
5418 // been set to a reasonable value. If it has not been set,
5419 // investigate.
5420 assert(active_workers > 0, "Should have been set during scavenge");
5421 }
5422 rp->set_active_mt_degree(active_workers);
5423 CMSRefProcTaskExecutor task_executor(*this);
5424 stats = rp->process_discovered_references(&_is_alive_closure,
5425 &cmsKeepAliveClosure,
5426 &cmsDrainMarkingStackClosure,
5427 &task_executor,
5428 _gc_timer_cm);
5429 } else {
5430 stats = rp->process_discovered_references(&_is_alive_closure,
5431 &cmsKeepAliveClosure,
5432 &cmsDrainMarkingStackClosure,
5433 NULL,
5434 _gc_timer_cm);
5435 }
5436 _gc_tracer_cm->report_gc_reference_stats(stats);
5437
5438 }
5439
5440 // This is the point where the entire marking should have completed.
5441 verify_work_stacks_empty();
5442
5443 if (should_unload_classes()) {
5444 {
5445 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm);
5446
5447 // Unload classes and purge the SystemDictionary.
5448 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5449
5450 // Unload nmethods.
5451 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5452
5453 // Prune dead klasses from subklass/sibling/implementor lists.
5454 Klass::clean_weak_klass_links(&_is_alive_closure);
5455 }
5456
5457 {
5458 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm);
5459 // Clean up unreferenced symbols in symbol table.
5460 SymbolTable::unlink();
5461 }
5462
5463 {
5464 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm);
5465 // Delete entries for dead interned strings.
5466 StringTable::unlink(&_is_alive_closure);
5467 }
5468 }
5469
5470
5471 // Restore any preserved marks as a result of mark stack or
5472 // work queue overflow
5473 restore_preserved_marks_if_any(); // done single-threaded for now
5474
5475 rp->set_enqueuing_is_done(true);
5476 if (rp->processing_is_mt()) {
5477 rp->balance_all_queues();
5478 CMSRefProcTaskExecutor task_executor(*this);
5479 rp->enqueue_discovered_references(&task_executor);
5480 } else {
5481 rp->enqueue_discovered_references(NULL);
5482 }
5483 rp->verify_no_references_recorded();
5484 assert(!rp->discovery_enabled(), "should have been disabled");
5485 }
5486
5487 #ifndef PRODUCT
5488 void CMSCollector::check_correct_thread_executing() {
5489 Thread* t = Thread::current();
5490 // Only the VM thread or the CMS thread should be here.
5491 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5492 "Unexpected thread type");
5493 // If this is the vm thread, the foreground process
5494 // should not be waiting. Note that _foregroundGCIsActive is
5495 // true while the foreground collector is waiting.
5496 if (_foregroundGCShouldWait) {
5497 // We cannot be the VM thread
5498 assert(t->is_ConcurrentGC_thread(),
5499 "Should be CMS thread");
5500 } else {
5501 // We can be the CMS thread only if we are in a stop-world
5502 // phase of CMS collection.
5503 if (t->is_ConcurrentGC_thread()) {
5504 assert(_collectorState == InitialMarking ||
5505 _collectorState == FinalMarking,
5506 "Should be a stop-world phase");
5507 // The CMS thread should be holding the CMS_token.
5508 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5509 "Potential interference with concurrently "
5510 "executing VM thread");
5511 }
5512 }
5513 }
5514 #endif
5515
5516 void CMSCollector::sweep() {
5517 assert(_collectorState == Sweeping, "just checking");
5518 check_correct_thread_executing();
5519 verify_work_stacks_empty();
5520 verify_overflow_empty();
5521 increment_sweep_count();
5522 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5523
5524 _inter_sweep_timer.stop();
5525 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5526
5527 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5528 _intra_sweep_timer.reset();
5529 _intra_sweep_timer.start();
5530 {
5531 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5532 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
5533 // First sweep the old gen
5534 {
5535 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5536 bitMapLock());
5537 sweepWork(_cmsGen);
5538 }
5539
5540 // Update Universe::_heap_*_at_gc figures.
5541 // We need all the free list locks to make the abstract state
5542 // transition from Sweeping to Resetting. See detailed note
5543 // further below.
5544 {
5545 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5546 // Update heap occupancy information which is used as
5547 // input to soft ref clearing policy at the next gc.
5548 Universe::update_heap_info_at_gc();
5549 _collectorState = Resizing;
5550 }
5551 }
5552 verify_work_stacks_empty();
5553 verify_overflow_empty();
5554
5555 if (should_unload_classes()) {
5556 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5557 // requires that the virtual spaces are stable and not deleted.
5558 ClassLoaderDataGraph::set_should_purge(true);
5559 }
5560
5561 _intra_sweep_timer.stop();
5562 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5563
5564 _inter_sweep_timer.reset();
5565 _inter_sweep_timer.start();
5566
5567 // We need to use a monotonically non-decreasing time in ms
5568 // or we will see time-warp warnings and os::javaTimeMillis()
5569 // does not guarantee monotonicity.
5570 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5571 update_time_of_last_gc(now);
5572
5573 // NOTE on abstract state transitions:
5574 // Mutators allocate-live and/or mark the mod-union table dirty
5575 // based on the state of the collection. The former is done in
5576 // the interval [Marking, Sweeping] and the latter in the interval
5577 // [Marking, Sweeping). Thus the transitions into the Marking state
5578 // and out of the Sweeping state must be synchronously visible
5579 // globally to the mutators.
5580 // The transition into the Marking state happens with the world
5581 // stopped so the mutators will globally see it. Sweeping is
5582 // done asynchronously by the background collector so the transition
5583 // from the Sweeping state to the Resizing state must be done
5584 // under the freelistLock (as is the check for whether to
5585 // allocate-live and whether to dirty the mod-union table).
5586 assert(_collectorState == Resizing, "Change of collector state to"
5587 " Resizing must be done under the freelistLocks (plural)");
5588
5589 // Now that sweeping has been completed, we clear
5590 // the incremental_collection_failed flag,
5591 // thus inviting a younger gen collection to promote into
5592 // this generation. If such a promotion may still fail,
5593 // the flag will be set again when a young collection is
5594 // attempted.
5595 GenCollectedHeap* gch = GenCollectedHeap::heap();
5596 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5597 gch->update_full_collections_completed(_collection_count_start);
5598 }
5599
5600 // FIX ME!!! Looks like this belongs in CFLSpace, with
5601 // CMSGen merely delegating to it.
5602 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5603 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5604 HeapWord* minAddr = _cmsSpace->bottom();
5605 HeapWord* largestAddr =
5606 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5607 if (largestAddr == NULL) {
5608 // The dictionary appears to be empty. In this case
5609 // try to coalesce at the end of the heap.
5610 largestAddr = _cmsSpace->end();
5611 }
5612 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5613 size_t nearLargestOffset =
5614 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5615 if (PrintFLSStatistics != 0) {
5616 gclog_or_tty->print_cr(
5617 "CMS: Large Block: " PTR_FORMAT ";"
5618 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5619 p2i(largestAddr),
5620 p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5621 }
5622 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5623 }
5624
5625 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5626 return addr >= _cmsSpace->nearLargestChunk();
5627 }
5628
5629 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5630 return _cmsSpace->find_chunk_at_end();
5631 }
5632
5633 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5634 bool full) {
5635 // If the young generation has been collected, gather any statistics
5636 // that are of interest at this point.
5637 bool current_is_young = GenCollectedHeap::heap()->is_young_gen(current_generation);
5638 if (!full && current_is_young) {
5639 // Gather statistics on the young generation collection.
5640 collector()->stats().record_gc0_end(used());
5641 }
5642 }
5643
5644 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5645 // We iterate over the space(s) underlying this generation,
5646 // checking the mark bit map to see if the bits corresponding
5647 // to specific blocks are marked or not. Blocks that are
5648 // marked are live and are not swept up. All remaining blocks
5649 // are swept up, with coalescing on-the-fly as we sweep up
5650 // contiguous free and/or garbage blocks:
5651 // We need to ensure that the sweeper synchronizes with allocators
5652 // and stop-the-world collectors. In particular, the following
5653 // locks are used:
5654 // . CMS token: if this is held, a stop the world collection cannot occur
5655 // . freelistLock: if this is held no allocation can occur from this
5656 // generation by another thread
5657 // . bitMapLock: if this is held, no other thread can access or update
5658 //
5659
5660 // Note that we need to hold the freelistLock if we use
5661 // block iterate below; else the iterator might go awry if
5662 // a mutator (or promotion) causes block contents to change
5663 // (for instance if the allocator divvies up a block).
5664 // If we hold the free list lock, for all practical purposes
5665 // young generation GC's can't occur (they'll usually need to
5666 // promote), so we might as well prevent all young generation
5667 // GC's while we do a sweeping step. For the same reason, we might
5668 // as well take the bit map lock for the entire duration
5669
5670 // check that we hold the requisite locks
5671 assert(have_cms_token(), "Should hold cms token");
5672 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5673 assert_lock_strong(old_gen->freelistLock());
5674 assert_lock_strong(bitMapLock());
5675
5676 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5677 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5678 old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5679 _inter_sweep_estimate.padded_average(),
5680 _intra_sweep_estimate.padded_average());
5681 old_gen->setNearLargestChunk();
5682
5683 {
5684 SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5685 old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5686 // We need to free-up/coalesce garbage/blocks from a
5687 // co-terminal free run. This is done in the SweepClosure
5688 // destructor; so, do not remove this scope, else the
5689 // end-of-sweep-census below will be off by a little bit.
5690 }
5691 old_gen->cmsSpace()->sweep_completed();
5692 old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5693 if (should_unload_classes()) { // unloaded classes this cycle,
5694 _concurrent_cycles_since_last_unload = 0; // ... reset count
5695 } else { // did not unload classes,
5696 _concurrent_cycles_since_last_unload++; // ... increment count
5697 }
5698 }
5699
5700 // Reset CMS data structures (for now just the marking bit map)
5701 // preparatory for the next cycle.
5702 void CMSCollector::reset(bool concurrent) {
5703 if (concurrent) {
5704 CMSTokenSyncWithLocks ts(true, bitMapLock());
5705
5706 // If the state is not "Resetting", the foreground thread
5707 // has done a collection and the resetting.
5708 if (_collectorState != Resetting) {
5709 assert(_collectorState == Idling, "The state should only change"
5710 " because the foreground collector has finished the collection");
5711 return;
5712 }
5713
5714 // Clear the mark bitmap (no grey objects to start with)
5715 // for the next cycle.
5716 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5717 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
5718
5719 HeapWord* curAddr = _markBitMap.startWord();
5720 while (curAddr < _markBitMap.endWord()) {
5721 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5722 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5723 _markBitMap.clear_large_range(chunk);
5724 if (ConcurrentMarkSweepThread::should_yield() &&
5725 !foregroundGCIsActive() &&
5726 CMSYield) {
5727 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5728 "CMS thread should hold CMS token");
5729 assert_lock_strong(bitMapLock());
5730 bitMapLock()->unlock();
5731 ConcurrentMarkSweepThread::desynchronize(true);
5732 stopTimer();
5733 if (PrintCMSStatistics != 0) {
5734 incrementYields();
5735 }
5736
5737 // See the comment in coordinator_yield()
5738 for (unsigned i = 0; i < CMSYieldSleepCount &&
5739 ConcurrentMarkSweepThread::should_yield() &&
5740 !CMSCollector::foregroundGCIsActive(); ++i) {
5741 os::sleep(Thread::current(), 1, false);
5742 }
5743
5744 ConcurrentMarkSweepThread::synchronize(true);
5745 bitMapLock()->lock_without_safepoint_check();
5746 startTimer();
5747 }
5748 curAddr = chunk.end();
5749 }
5750 // A successful mostly concurrent collection has been done.
5751 // Because only the full (i.e., concurrent mode failure) collections
5752 // are being measured for gc overhead limits, clean the "near" flag
5753 // and count.
5754 size_policy()->reset_gc_overhead_limit_count();
5755 _collectorState = Idling;
5756 } else {
5757 // already have the lock
5758 assert(_collectorState == Resetting, "just checking");
5759 assert_lock_strong(bitMapLock());
5760 _markBitMap.clear_all();
5761 _collectorState = Idling;
5762 }
5763
5764 register_gc_end();
5765 }
5766
5767 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5768 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5769 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL);
5770 TraceCollectorStats tcs(counters());
5771
5772 switch (op) {
5773 case CMS_op_checkpointRootsInitial: {
5774 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5775 checkpointRootsInitial();
5776 if (PrintGC) {
5777 _cmsGen->printOccupancy("initial-mark");
5778 }
5779 break;
5780 }
5781 case CMS_op_checkpointRootsFinal: {
5782 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5783 checkpointRootsFinal();
5784 if (PrintGC) {
5785 _cmsGen->printOccupancy("remark");
5786 }
5787 break;
5788 }
5789 default:
5790 fatal("No such CMS_op");
5791 }
5792 }
5793
5794 #ifndef PRODUCT
5795 size_t const CMSCollector::skip_header_HeapWords() {
5796 return FreeChunk::header_size();
5797 }
5798
5799 // Try and collect here conditions that should hold when
5800 // CMS thread is exiting. The idea is that the foreground GC
5801 // thread should not be blocked if it wants to terminate
5802 // the CMS thread and yet continue to run the VM for a while
5803 // after that.
5804 void CMSCollector::verify_ok_to_terminate() const {
5805 assert(Thread::current()->is_ConcurrentGC_thread(),
5806 "should be called by CMS thread");
5807 assert(!_foregroundGCShouldWait, "should be false");
5808 // We could check here that all the various low-level locks
5809 // are not held by the CMS thread, but that is overkill; see
5810 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5811 // is checked.
5812 }
5813 #endif
5814
5815 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5816 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5817 "missing Printezis mark?");
5818 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5819 size_t size = pointer_delta(nextOneAddr + 1, addr);
5820 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5821 "alignment problem");
5822 assert(size >= 3, "Necessary for Printezis marks to work");
5823 return size;
5824 }
5825
5826 // A variant of the above (block_size_using_printezis_bits()) except
5827 // that we return 0 if the P-bits are not yet set.
5828 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5829 if (_markBitMap.isMarked(addr + 1)) {
5830 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5831 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5832 size_t size = pointer_delta(nextOneAddr + 1, addr);
5833 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5834 "alignment problem");
5835 assert(size >= 3, "Necessary for Printezis marks to work");
5836 return size;
5837 }
5838 return 0;
5839 }
5840
5841 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5842 size_t sz = 0;
5843 oop p = (oop)addr;
5844 if (p->klass_or_null() != NULL) {
5845 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5846 } else {
5847 sz = block_size_using_printezis_bits(addr);
5848 }
5849 assert(sz > 0, "size must be nonzero");
5850 HeapWord* next_block = addr + sz;
5851 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
5852 CardTableModRefBS::card_size);
5853 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
5854 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5855 "must be different cards");
5856 return next_card;
5857 }
5858
5859
5860 // CMS Bit Map Wrapper /////////////////////////////////////////
5861
5862 // Construct a CMS bit map infrastructure, but don't create the
5863 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5864 // further below.
5865 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5866 _bm(),
5867 _shifter(shifter),
5868 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5869 Monitor::_safepoint_check_sometimes) : NULL)
5870 {
5871 _bmStartWord = 0;
5872 _bmWordSize = 0;
5873 }
5874
5875 bool CMSBitMap::allocate(MemRegion mr) {
5876 _bmStartWord = mr.start();
5877 _bmWordSize = mr.word_size();
5878 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5879 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5880 if (!brs.is_reserved()) {
5881 warning("CMS bit map allocation failure");
5882 return false;
5883 }
5884 // For now we'll just commit all of the bit map up front.
5885 // Later on we'll try to be more parsimonious with swap.
5886 if (!_virtual_space.initialize(brs, brs.size())) {
5887 warning("CMS bit map backing store failure");
5888 return false;
5889 }
5890 assert(_virtual_space.committed_size() == brs.size(),
5891 "didn't reserve backing store for all of CMS bit map?");
5892 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5893 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5894 _bmWordSize, "inconsistency in bit map sizing");
5895 _bm.set_size(_bmWordSize >> _shifter);
5896
5897 // bm.clear(); // can we rely on getting zero'd memory? verify below
5898 assert(isAllClear(),
5899 "Expected zero'd memory from ReservedSpace constructor");
5900 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5901 "consistency check");
5902 return true;
5903 }
5904
5905 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5906 HeapWord *next_addr, *end_addr, *last_addr;
5907 assert_locked();
5908 assert(covers(mr), "out-of-range error");
5909 // XXX assert that start and end are appropriately aligned
5910 for (next_addr = mr.start(), end_addr = mr.end();
5911 next_addr < end_addr; next_addr = last_addr) {
5912 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5913 last_addr = dirty_region.end();
5914 if (!dirty_region.is_empty()) {
5915 cl->do_MemRegion(dirty_region);
5916 } else {
5917 assert(last_addr == end_addr, "program logic");
5918 return;
5919 }
5920 }
5921 }
5922
5923 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5924 _bm.print_on_error(st, prefix);
5925 }
5926
5927 #ifndef PRODUCT
5928 void CMSBitMap::assert_locked() const {
5929 CMSLockVerifier::assert_locked(lock());
5930 }
5931
5932 bool CMSBitMap::covers(MemRegion mr) const {
5933 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5934 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5935 "size inconsistency");
5936 return (mr.start() >= _bmStartWord) &&
5937 (mr.end() <= endWord());
5938 }
5939
5940 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5941 return (start >= _bmStartWord && (start + size) <= endWord());
5942 }
5943
5944 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5945 // verify that there are no 1 bits in the interval [left, right)
5946 FalseBitMapClosure falseBitMapClosure;
5947 iterate(&falseBitMapClosure, left, right);
5948 }
5949
5950 void CMSBitMap::region_invariant(MemRegion mr)
5951 {
5952 assert_locked();
5953 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5954 assert(!mr.is_empty(), "unexpected empty region");
5955 assert(covers(mr), "mr should be covered by bit map");
5956 // convert address range into offset range
5957 size_t start_ofs = heapWordToOffset(mr.start());
5958 // Make sure that end() is appropriately aligned
5959 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5960 (1 << (_shifter+LogHeapWordSize))),
5961 "Misaligned mr.end()");
5962 size_t end_ofs = heapWordToOffset(mr.end());
5963 assert(end_ofs > start_ofs, "Should mark at least one bit");
5964 }
5965
5966 #endif
5967
5968 bool CMSMarkStack::allocate(size_t size) {
5969 // allocate a stack of the requisite depth
5970 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5971 size * sizeof(oop)));
5972 if (!rs.is_reserved()) {
5973 warning("CMSMarkStack allocation failure");
5974 return false;
5975 }
5976 if (!_virtual_space.initialize(rs, rs.size())) {
5977 warning("CMSMarkStack backing store failure");
5978 return false;
5979 }
5980 assert(_virtual_space.committed_size() == rs.size(),
5981 "didn't reserve backing store for all of CMS stack?");
5982 _base = (oop*)(_virtual_space.low());
5983 _index = 0;
5984 _capacity = size;
5985 NOT_PRODUCT(_max_depth = 0);
5986 return true;
5987 }
5988
5989 // XXX FIX ME !!! In the MT case we come in here holding a
5990 // leaf lock. For printing we need to take a further lock
5991 // which has lower rank. We need to recalibrate the two
5992 // lock-ranks involved in order to be able to print the
5993 // messages below. (Or defer the printing to the caller.
5994 // For now we take the expedient path of just disabling the
5995 // messages for the problematic case.)
5996 void CMSMarkStack::expand() {
5997 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5998 if (_capacity == MarkStackSizeMax) {
5999 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6000 // We print a warning message only once per CMS cycle.
6001 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6002 }
6003 return;
6004 }
6005 // Double capacity if possible
6006 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6007 // Do not give up existing stack until we have managed to
6008 // get the double capacity that we desired.
6009 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6010 new_capacity * sizeof(oop)));
6011 if (rs.is_reserved()) {
6012 // Release the backing store associated with old stack
6013 _virtual_space.release();
6014 // Reinitialize virtual space for new stack
6015 if (!_virtual_space.initialize(rs, rs.size())) {
6016 fatal("Not enough swap for expanded marking stack");
6017 }
6018 _base = (oop*)(_virtual_space.low());
6019 _index = 0;
6020 _capacity = new_capacity;
6021 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6022 // Failed to double capacity, continue;
6023 // we print a detail message only once per CMS cycle.
6024 gclog_or_tty->print(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to "
6025 SIZE_FORMAT "K",
6026 _capacity / K, new_capacity / K);
6027 }
6028 }
6029
6030
6031 // Closures
6032 // XXX: there seems to be a lot of code duplication here;
6033 // should refactor and consolidate common code.
6034
6035 // This closure is used to mark refs into the CMS generation in
6036 // the CMS bit map. Called at the first checkpoint. This closure
6037 // assumes that we do not need to re-mark dirty cards; if the CMS
6038 // generation on which this is used is not an oldest
6039 // generation then this will lose younger_gen cards!
6040
6041 MarkRefsIntoClosure::MarkRefsIntoClosure(
6042 MemRegion span, CMSBitMap* bitMap):
6043 _span(span),
6044 _bitMap(bitMap)
6045 {
6046 assert(_ref_processor == NULL, "deliberately left NULL");
6047 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6048 }
6049
6050 void MarkRefsIntoClosure::do_oop(oop obj) {
6051 // if p points into _span, then mark corresponding bit in _markBitMap
6052 assert(obj->is_oop(), "expected an oop");
6053 HeapWord* addr = (HeapWord*)obj;
6054 if (_span.contains(addr)) {
6055 // this should be made more efficient
6056 _bitMap->mark(addr);
6057 }
6058 }
6059
6060 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6061 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6062
6063 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6064 MemRegion span, CMSBitMap* bitMap):
6065 _span(span),
6066 _bitMap(bitMap)
6067 {
6068 assert(_ref_processor == NULL, "deliberately left NULL");
6069 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6070 }
6071
6072 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6073 // if p points into _span, then mark corresponding bit in _markBitMap
6074 assert(obj->is_oop(), "expected an oop");
6075 HeapWord* addr = (HeapWord*)obj;
6076 if (_span.contains(addr)) {
6077 // this should be made more efficient
6078 _bitMap->par_mark(addr);
6079 }
6080 }
6081
6082 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6083 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6084
6085 // A variant of the above, used for CMS marking verification.
6086 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6087 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6088 _span(span),
6089 _verification_bm(verification_bm),
6090 _cms_bm(cms_bm)
6091 {
6092 assert(_ref_processor == NULL, "deliberately left NULL");
6093 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6094 }
6095
6096 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6097 // if p points into _span, then mark corresponding bit in _markBitMap
6098 assert(obj->is_oop(), "expected an oop");
6099 HeapWord* addr = (HeapWord*)obj;
6100 if (_span.contains(addr)) {
6101 _verification_bm->mark(addr);
6102 if (!_cms_bm->isMarked(addr)) {
6103 oop(addr)->print();
6104 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6105 fatal("... aborting");
6106 }
6107 }
6108 }
6109
6110 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6111 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6112
6113 //////////////////////////////////////////////////
6114 // MarkRefsIntoAndScanClosure
6115 //////////////////////////////////////////////////
6116
6117 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6118 ReferenceProcessor* rp,
6119 CMSBitMap* bit_map,
6120 CMSBitMap* mod_union_table,
6121 CMSMarkStack* mark_stack,
6122 CMSCollector* collector,
6123 bool should_yield,
6124 bool concurrent_precleaning):
6125 _collector(collector),
6126 _span(span),
6127 _bit_map(bit_map),
6128 _mark_stack(mark_stack),
6129 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6130 mark_stack, concurrent_precleaning),
6131 _yield(should_yield),
6132 _concurrent_precleaning(concurrent_precleaning),
6133 _freelistLock(NULL)
6134 {
6135 _ref_processor = rp;
6136 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6137 }
6138
6139 // This closure is used to mark refs into the CMS generation at the
6140 // second (final) checkpoint, and to scan and transitively follow
6141 // the unmarked oops. It is also used during the concurrent precleaning
6142 // phase while scanning objects on dirty cards in the CMS generation.
6143 // The marks are made in the marking bit map and the marking stack is
6144 // used for keeping the (newly) grey objects during the scan.
6145 // The parallel version (Par_...) appears further below.
6146 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6147 if (obj != NULL) {
6148 assert(obj->is_oop(), "expected an oop");
6149 HeapWord* addr = (HeapWord*)obj;
6150 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6151 assert(_collector->overflow_list_is_empty(),
6152 "overflow list should be empty");
6153 if (_span.contains(addr) &&
6154 !_bit_map->isMarked(addr)) {
6155 // mark bit map (object is now grey)
6156 _bit_map->mark(addr);
6157 // push on marking stack (stack should be empty), and drain the
6158 // stack by applying this closure to the oops in the oops popped
6159 // from the stack (i.e. blacken the grey objects)
6160 bool res = _mark_stack->push(obj);
6161 assert(res, "Should have space to push on empty stack");
6162 do {
6163 oop new_oop = _mark_stack->pop();
6164 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6165 assert(_bit_map->isMarked((HeapWord*)new_oop),
6166 "only grey objects on this stack");
6167 // iterate over the oops in this oop, marking and pushing
6168 // the ones in CMS heap (i.e. in _span).
6169 new_oop->oop_iterate(&_pushAndMarkClosure);
6170 // check if it's time to yield
6171 do_yield_check();
6172 } while (!_mark_stack->isEmpty() ||
6173 (!_concurrent_precleaning && take_from_overflow_list()));
6174 // if marking stack is empty, and we are not doing this
6175 // during precleaning, then check the overflow list
6176 }
6177 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6178 assert(_collector->overflow_list_is_empty(),
6179 "overflow list was drained above");
6180 // We could restore evacuated mark words, if any, used for
6181 // overflow list links here because the overflow list is
6182 // provably empty here. That would reduce the maximum
6183 // size requirements for preserved_{oop,mark}_stack.
6184 // But we'll just postpone it until we are all done
6185 // so we can just stream through.
6186 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6187 _collector->restore_preserved_marks_if_any();
6188 assert(_collector->no_preserved_marks(), "No preserved marks");
6189 }
6190 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6191 "All preserved marks should have been restored above");
6192 }
6193 }
6194
6195 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6196 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6197
6198 void MarkRefsIntoAndScanClosure::do_yield_work() {
6199 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6200 "CMS thread should hold CMS token");
6201 assert_lock_strong(_freelistLock);
6202 assert_lock_strong(_bit_map->lock());
6203 // relinquish the free_list_lock and bitMaplock()
6204 _bit_map->lock()->unlock();
6205 _freelistLock->unlock();
6206 ConcurrentMarkSweepThread::desynchronize(true);
6207 _collector->stopTimer();
6208 if (PrintCMSStatistics != 0) {
6209 _collector->incrementYields();
6210 }
6211
6212 // See the comment in coordinator_yield()
6213 for (unsigned i = 0;
6214 i < CMSYieldSleepCount &&
6215 ConcurrentMarkSweepThread::should_yield() &&
6216 !CMSCollector::foregroundGCIsActive();
6217 ++i) {
6218 os::sleep(Thread::current(), 1, false);
6219 }
6220
6221 ConcurrentMarkSweepThread::synchronize(true);
6222 _freelistLock->lock_without_safepoint_check();
6223 _bit_map->lock()->lock_without_safepoint_check();
6224 _collector->startTimer();
6225 }
6226
6227 ///////////////////////////////////////////////////////////
6228 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6229 // MarkRefsIntoAndScanClosure
6230 ///////////////////////////////////////////////////////////
6231 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6232 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6233 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6234 _span(span),
6235 _bit_map(bit_map),
6236 _work_queue(work_queue),
6237 _low_water_mark(MIN2((work_queue->max_elems()/4),
6238 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6239 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6240 {
6241 _ref_processor = rp;
6242 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6243 }
6244
6245 // This closure is used to mark refs into the CMS generation at the
6246 // second (final) checkpoint, and to scan and transitively follow
6247 // the unmarked oops. The marks are made in the marking bit map and
6248 // the work_queue is used for keeping the (newly) grey objects during
6249 // the scan phase whence they are also available for stealing by parallel
6250 // threads. Since the marking bit map is shared, updates are
6251 // synchronized (via CAS).
6252 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6253 if (obj != NULL) {
6254 // Ignore mark word because this could be an already marked oop
6255 // that may be chained at the end of the overflow list.
6256 assert(obj->is_oop(true), "expected an oop");
6257 HeapWord* addr = (HeapWord*)obj;
6258 if (_span.contains(addr) &&
6259 !_bit_map->isMarked(addr)) {
6260 // mark bit map (object will become grey):
6261 // It is possible for several threads to be
6262 // trying to "claim" this object concurrently;
6263 // the unique thread that succeeds in marking the
6264 // object first will do the subsequent push on
6265 // to the work queue (or overflow list).
6266 if (_bit_map->par_mark(addr)) {
6267 // push on work_queue (which may not be empty), and trim the
6268 // queue to an appropriate length by applying this closure to
6269 // the oops in the oops popped from the stack (i.e. blacken the
6270 // grey objects)
6271 bool res = _work_queue->push(obj);
6272 assert(res, "Low water mark should be less than capacity?");
6273 trim_queue(_low_water_mark);
6274 } // Else, another thread claimed the object
6275 }
6276 }
6277 }
6278
6279 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6280 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6281
6282 // This closure is used to rescan the marked objects on the dirty cards
6283 // in the mod union table and the card table proper.
6284 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6285 oop p, MemRegion mr) {
6286
6287 size_t size = 0;
6288 HeapWord* addr = (HeapWord*)p;
6289 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6290 assert(_span.contains(addr), "we are scanning the CMS generation");
6291 // check if it's time to yield
6292 if (do_yield_check()) {
6293 // We yielded for some foreground stop-world work,
6294 // and we have been asked to abort this ongoing preclean cycle.
6295 return 0;
6296 }
6297 if (_bitMap->isMarked(addr)) {
6298 // it's marked; is it potentially uninitialized?
6299 if (p->klass_or_null() != NULL) {
6300 // an initialized object; ignore mark word in verification below
6301 // since we are running concurrent with mutators
6302 assert(p->is_oop(true), "should be an oop");
6303 if (p->is_objArray()) {
6304 // objArrays are precisely marked; restrict scanning
6305 // to dirty cards only.
6306 size = CompactibleFreeListSpace::adjustObjectSize(
6307 p->oop_iterate_size(_scanningClosure, mr));
6308 } else {
6309 // A non-array may have been imprecisely marked; we need
6310 // to scan object in its entirety.
6311 size = CompactibleFreeListSpace::adjustObjectSize(
6312 p->oop_iterate_size(_scanningClosure));
6313 }
6314 #ifdef ASSERT
6315 size_t direct_size =
6316 CompactibleFreeListSpace::adjustObjectSize(p->size());
6317 assert(size == direct_size, "Inconsistency in size");
6318 assert(size >= 3, "Necessary for Printezis marks to work");
6319 if (!_bitMap->isMarked(addr+1)) {
6320 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6321 } else {
6322 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6323 assert(_bitMap->isMarked(addr+size-1),
6324 "inconsistent Printezis mark");
6325 }
6326 #endif // ASSERT
6327 } else {
6328 // An uninitialized object.
6329 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6330 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6331 size = pointer_delta(nextOneAddr + 1, addr);
6332 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6333 "alignment problem");
6334 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6335 // will dirty the card when the klass pointer is installed in the
6336 // object (signaling the completion of initialization).
6337 }
6338 } else {
6339 // Either a not yet marked object or an uninitialized object
6340 if (p->klass_or_null() == NULL) {
6341 // An uninitialized object, skip to the next card, since
6342 // we may not be able to read its P-bits yet.
6343 assert(size == 0, "Initial value");
6344 } else {
6345 // An object not (yet) reached by marking: we merely need to
6346 // compute its size so as to go look at the next block.
6347 assert(p->is_oop(true), "should be an oop");
6348 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6349 }
6350 }
6351 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6352 return size;
6353 }
6354
6355 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6356 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6357 "CMS thread should hold CMS token");
6358 assert_lock_strong(_freelistLock);
6359 assert_lock_strong(_bitMap->lock());
6360 // relinquish the free_list_lock and bitMaplock()
6361 _bitMap->lock()->unlock();
6362 _freelistLock->unlock();
6363 ConcurrentMarkSweepThread::desynchronize(true);
6364 _collector->stopTimer();
6365 if (PrintCMSStatistics != 0) {
6366 _collector->incrementYields();
6367 }
6368
6369 // See the comment in coordinator_yield()
6370 for (unsigned i = 0; i < CMSYieldSleepCount &&
6371 ConcurrentMarkSweepThread::should_yield() &&
6372 !CMSCollector::foregroundGCIsActive(); ++i) {
6373 os::sleep(Thread::current(), 1, false);
6374 }
6375
6376 ConcurrentMarkSweepThread::synchronize(true);
6377 _freelistLock->lock_without_safepoint_check();
6378 _bitMap->lock()->lock_without_safepoint_check();
6379 _collector->startTimer();
6380 }
6381
6382
6383 //////////////////////////////////////////////////////////////////
6384 // SurvivorSpacePrecleanClosure
6385 //////////////////////////////////////////////////////////////////
6386 // This (single-threaded) closure is used to preclean the oops in
6387 // the survivor spaces.
6388 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6389
6390 HeapWord* addr = (HeapWord*)p;
6391 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6392 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6393 assert(p->klass_or_null() != NULL, "object should be initialized");
6394 // an initialized object; ignore mark word in verification below
6395 // since we are running concurrent with mutators
6396 assert(p->is_oop(true), "should be an oop");
6397 // Note that we do not yield while we iterate over
6398 // the interior oops of p, pushing the relevant ones
6399 // on our marking stack.
6400 size_t size = p->oop_iterate_size(_scanning_closure);
6401 do_yield_check();
6402 // Observe that below, we do not abandon the preclean
6403 // phase as soon as we should; rather we empty the
6404 // marking stack before returning. This is to satisfy
6405 // some existing assertions. In general, it may be a
6406 // good idea to abort immediately and complete the marking
6407 // from the grey objects at a later time.
6408 while (!_mark_stack->isEmpty()) {
6409 oop new_oop = _mark_stack->pop();
6410 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6411 assert(_bit_map->isMarked((HeapWord*)new_oop),
6412 "only grey objects on this stack");
6413 // iterate over the oops in this oop, marking and pushing
6414 // the ones in CMS heap (i.e. in _span).
6415 new_oop->oop_iterate(_scanning_closure);
6416 // check if it's time to yield
6417 do_yield_check();
6418 }
6419 unsigned int after_count =
6420 GenCollectedHeap::heap()->total_collections();
6421 bool abort = (_before_count != after_count) ||
6422 _collector->should_abort_preclean();
6423 return abort ? 0 : size;
6424 }
6425
6426 void SurvivorSpacePrecleanClosure::do_yield_work() {
6427 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6428 "CMS thread should hold CMS token");
6429 assert_lock_strong(_bit_map->lock());
6430 // Relinquish the bit map lock
6431 _bit_map->lock()->unlock();
6432 ConcurrentMarkSweepThread::desynchronize(true);
6433 _collector->stopTimer();
6434 if (PrintCMSStatistics != 0) {
6435 _collector->incrementYields();
6436 }
6437
6438 // See the comment in coordinator_yield()
6439 for (unsigned i = 0; i < CMSYieldSleepCount &&
6440 ConcurrentMarkSweepThread::should_yield() &&
6441 !CMSCollector::foregroundGCIsActive(); ++i) {
6442 os::sleep(Thread::current(), 1, false);
6443 }
6444
6445 ConcurrentMarkSweepThread::synchronize(true);
6446 _bit_map->lock()->lock_without_safepoint_check();
6447 _collector->startTimer();
6448 }
6449
6450 // This closure is used to rescan the marked objects on the dirty cards
6451 // in the mod union table and the card table proper. In the parallel
6452 // case, although the bitMap is shared, we do a single read so the
6453 // isMarked() query is "safe".
6454 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6455 // Ignore mark word because we are running concurrent with mutators
6456 assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
6457 HeapWord* addr = (HeapWord*)p;
6458 assert(_span.contains(addr), "we are scanning the CMS generation");
6459 bool is_obj_array = false;
6460 #ifdef ASSERT
6461 if (!_parallel) {
6462 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6463 assert(_collector->overflow_list_is_empty(),
6464 "overflow list should be empty");
6465
6466 }
6467 #endif // ASSERT
6468 if (_bit_map->isMarked(addr)) {
6469 // Obj arrays are precisely marked, non-arrays are not;
6470 // so we scan objArrays precisely and non-arrays in their
6471 // entirety.
6472 if (p->is_objArray()) {
6473 is_obj_array = true;
6474 if (_parallel) {
6475 p->oop_iterate(_par_scan_closure, mr);
6476 } else {
6477 p->oop_iterate(_scan_closure, mr);
6478 }
6479 } else {
6480 if (_parallel) {
6481 p->oop_iterate(_par_scan_closure);
6482 } else {
6483 p->oop_iterate(_scan_closure);
6484 }
6485 }
6486 }
6487 #ifdef ASSERT
6488 if (!_parallel) {
6489 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6490 assert(_collector->overflow_list_is_empty(),
6491 "overflow list should be empty");
6492
6493 }
6494 #endif // ASSERT
6495 return is_obj_array;
6496 }
6497
6498 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6499 MemRegion span,
6500 CMSBitMap* bitMap, CMSMarkStack* markStack,
6501 bool should_yield, bool verifying):
6502 _collector(collector),
6503 _span(span),
6504 _bitMap(bitMap),
6505 _mut(&collector->_modUnionTable),
6506 _markStack(markStack),
6507 _yield(should_yield),
6508 _skipBits(0)
6509 {
6510 assert(_markStack->isEmpty(), "stack should be empty");
6511 _finger = _bitMap->startWord();
6512 _threshold = _finger;
6513 assert(_collector->_restart_addr == NULL, "Sanity check");
6514 assert(_span.contains(_finger), "Out of bounds _finger?");
6515 DEBUG_ONLY(_verifying = verifying;)
6516 }
6517
6518 void MarkFromRootsClosure::reset(HeapWord* addr) {
6519 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6520 assert(_span.contains(addr), "Out of bounds _finger?");
6521 _finger = addr;
6522 _threshold = (HeapWord*)round_to(
6523 (intptr_t)_finger, CardTableModRefBS::card_size);
6524 }
6525
6526 // Should revisit to see if this should be restructured for
6527 // greater efficiency.
6528 bool MarkFromRootsClosure::do_bit(size_t offset) {
6529 if (_skipBits > 0) {
6530 _skipBits--;
6531 return true;
6532 }
6533 // convert offset into a HeapWord*
6534 HeapWord* addr = _bitMap->startWord() + offset;
6535 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6536 "address out of range");
6537 assert(_bitMap->isMarked(addr), "tautology");
6538 if (_bitMap->isMarked(addr+1)) {
6539 // this is an allocated but not yet initialized object
6540 assert(_skipBits == 0, "tautology");
6541 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6542 oop p = oop(addr);
6543 if (p->klass_or_null() == NULL) {
6544 DEBUG_ONLY(if (!_verifying) {)
6545 // We re-dirty the cards on which this object lies and increase
6546 // the _threshold so that we'll come back to scan this object
6547 // during the preclean or remark phase. (CMSCleanOnEnter)
6548 if (CMSCleanOnEnter) {
6549 size_t sz = _collector->block_size_using_printezis_bits(addr);
6550 HeapWord* end_card_addr = (HeapWord*)round_to(
6551 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6552 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6553 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6554 // Bump _threshold to end_card_addr; note that
6555 // _threshold cannot possibly exceed end_card_addr, anyhow.
6556 // This prevents future clearing of the card as the scan proceeds
6557 // to the right.
6558 assert(_threshold <= end_card_addr,
6559 "Because we are just scanning into this object");
6560 if (_threshold < end_card_addr) {
6561 _threshold = end_card_addr;
6562 }
6563 if (p->klass_or_null() != NULL) {
6564 // Redirty the range of cards...
6565 _mut->mark_range(redirty_range);
6566 } // ...else the setting of klass will dirty the card anyway.
6567 }
6568 DEBUG_ONLY(})
6569 return true;
6570 }
6571 }
6572 scanOopsInOop(addr);
6573 return true;
6574 }
6575
6576 // We take a break if we've been at this for a while,
6577 // so as to avoid monopolizing the locks involved.
6578 void MarkFromRootsClosure::do_yield_work() {
6579 // First give up the locks, then yield, then re-lock
6580 // We should probably use a constructor/destructor idiom to
6581 // do this unlock/lock or modify the MutexUnlocker class to
6582 // serve our purpose. XXX
6583 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6584 "CMS thread should hold CMS token");
6585 assert_lock_strong(_bitMap->lock());
6586 _bitMap->lock()->unlock();
6587 ConcurrentMarkSweepThread::desynchronize(true);
6588 _collector->stopTimer();
6589 if (PrintCMSStatistics != 0) {
6590 _collector->incrementYields();
6591 }
6592
6593 // See the comment in coordinator_yield()
6594 for (unsigned i = 0; i < CMSYieldSleepCount &&
6595 ConcurrentMarkSweepThread::should_yield() &&
6596 !CMSCollector::foregroundGCIsActive(); ++i) {
6597 os::sleep(Thread::current(), 1, false);
6598 }
6599
6600 ConcurrentMarkSweepThread::synchronize(true);
6601 _bitMap->lock()->lock_without_safepoint_check();
6602 _collector->startTimer();
6603 }
6604
6605 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6606 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6607 assert(_markStack->isEmpty(),
6608 "should drain stack to limit stack usage");
6609 // convert ptr to an oop preparatory to scanning
6610 oop obj = oop(ptr);
6611 // Ignore mark word in verification below, since we
6612 // may be running concurrent with mutators.
6613 assert(obj->is_oop(true), "should be an oop");
6614 assert(_finger <= ptr, "_finger runneth ahead");
6615 // advance the finger to right end of this object
6616 _finger = ptr + obj->size();
6617 assert(_finger > ptr, "we just incremented it above");
6618 // On large heaps, it may take us some time to get through
6619 // the marking phase. During
6620 // this time it's possible that a lot of mutations have
6621 // accumulated in the card table and the mod union table --
6622 // these mutation records are redundant until we have
6623 // actually traced into the corresponding card.
6624 // Here, we check whether advancing the finger would make
6625 // us cross into a new card, and if so clear corresponding
6626 // cards in the MUT (preclean them in the card-table in the
6627 // future).
6628
6629 DEBUG_ONLY(if (!_verifying) {)
6630 // The clean-on-enter optimization is disabled by default,
6631 // until we fix 6178663.
6632 if (CMSCleanOnEnter && (_finger > _threshold)) {
6633 // [_threshold, _finger) represents the interval
6634 // of cards to be cleared in MUT (or precleaned in card table).
6635 // The set of cards to be cleared is all those that overlap
6636 // with the interval [_threshold, _finger); note that
6637 // _threshold is always kept card-aligned but _finger isn't
6638 // always card-aligned.
6639 HeapWord* old_threshold = _threshold;
6640 assert(old_threshold == (HeapWord*)round_to(
6641 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6642 "_threshold should always be card-aligned");
6643 _threshold = (HeapWord*)round_to(
6644 (intptr_t)_finger, CardTableModRefBS::card_size);
6645 MemRegion mr(old_threshold, _threshold);
6646 assert(!mr.is_empty(), "Control point invariant");
6647 assert(_span.contains(mr), "Should clear within span");
6648 _mut->clear_range(mr);
6649 }
6650 DEBUG_ONLY(})
6651 // Note: the finger doesn't advance while we drain
6652 // the stack below.
6653 PushOrMarkClosure pushOrMarkClosure(_collector,
6654 _span, _bitMap, _markStack,
6655 _finger, this);
6656 bool res = _markStack->push(obj);
6657 assert(res, "Empty non-zero size stack should have space for single push");
6658 while (!_markStack->isEmpty()) {
6659 oop new_oop = _markStack->pop();
6660 // Skip verifying header mark word below because we are
6661 // running concurrent with mutators.
6662 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6663 // now scan this oop's oops
6664 new_oop->oop_iterate(&pushOrMarkClosure);
6665 do_yield_check();
6666 }
6667 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6668 }
6669
6670 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6671 CMSCollector* collector, MemRegion span,
6672 CMSBitMap* bit_map,
6673 OopTaskQueue* work_queue,
6674 CMSMarkStack* overflow_stack):
6675 _collector(collector),
6676 _whole_span(collector->_span),
6677 _span(span),
6678 _bit_map(bit_map),
6679 _mut(&collector->_modUnionTable),
6680 _work_queue(work_queue),
6681 _overflow_stack(overflow_stack),
6682 _skip_bits(0),
6683 _task(task)
6684 {
6685 assert(_work_queue->size() == 0, "work_queue should be empty");
6686 _finger = span.start();
6687 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6688 assert(_span.contains(_finger), "Out of bounds _finger?");
6689 }
6690
6691 // Should revisit to see if this should be restructured for
6692 // greater efficiency.
6693 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6694 if (_skip_bits > 0) {
6695 _skip_bits--;
6696 return true;
6697 }
6698 // convert offset into a HeapWord*
6699 HeapWord* addr = _bit_map->startWord() + offset;
6700 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6701 "address out of range");
6702 assert(_bit_map->isMarked(addr), "tautology");
6703 if (_bit_map->isMarked(addr+1)) {
6704 // this is an allocated object that might not yet be initialized
6705 assert(_skip_bits == 0, "tautology");
6706 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6707 oop p = oop(addr);
6708 if (p->klass_or_null() == NULL) {
6709 // in the case of Clean-on-Enter optimization, redirty card
6710 // and avoid clearing card by increasing the threshold.
6711 return true;
6712 }
6713 }
6714 scan_oops_in_oop(addr);
6715 return true;
6716 }
6717
6718 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6719 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6720 // Should we assert that our work queue is empty or
6721 // below some drain limit?
6722 assert(_work_queue->size() == 0,
6723 "should drain stack to limit stack usage");
6724 // convert ptr to an oop preparatory to scanning
6725 oop obj = oop(ptr);
6726 // Ignore mark word in verification below, since we
6727 // may be running concurrent with mutators.
6728 assert(obj->is_oop(true), "should be an oop");
6729 assert(_finger <= ptr, "_finger runneth ahead");
6730 // advance the finger to right end of this object
6731 _finger = ptr + obj->size();
6732 assert(_finger > ptr, "we just incremented it above");
6733 // On large heaps, it may take us some time to get through
6734 // the marking phase. During
6735 // this time it's possible that a lot of mutations have
6736 // accumulated in the card table and the mod union table --
6737 // these mutation records are redundant until we have
6738 // actually traced into the corresponding card.
6739 // Here, we check whether advancing the finger would make
6740 // us cross into a new card, and if so clear corresponding
6741 // cards in the MUT (preclean them in the card-table in the
6742 // future).
6743
6744 // The clean-on-enter optimization is disabled by default,
6745 // until we fix 6178663.
6746 if (CMSCleanOnEnter && (_finger > _threshold)) {
6747 // [_threshold, _finger) represents the interval
6748 // of cards to be cleared in MUT (or precleaned in card table).
6749 // The set of cards to be cleared is all those that overlap
6750 // with the interval [_threshold, _finger); note that
6751 // _threshold is always kept card-aligned but _finger isn't
6752 // always card-aligned.
6753 HeapWord* old_threshold = _threshold;
6754 assert(old_threshold == (HeapWord*)round_to(
6755 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6756 "_threshold should always be card-aligned");
6757 _threshold = (HeapWord*)round_to(
6758 (intptr_t)_finger, CardTableModRefBS::card_size);
6759 MemRegion mr(old_threshold, _threshold);
6760 assert(!mr.is_empty(), "Control point invariant");
6761 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6762 _mut->clear_range(mr);
6763 }
6764
6765 // Note: the local finger doesn't advance while we drain
6766 // the stack below, but the global finger sure can and will.
6767 HeapWord** gfa = _task->global_finger_addr();
6768 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6769 _span, _bit_map,
6770 _work_queue,
6771 _overflow_stack,
6772 _finger,
6773 gfa, this);
6774 bool res = _work_queue->push(obj); // overflow could occur here
6775 assert(res, "Will hold once we use workqueues");
6776 while (true) {
6777 oop new_oop;
6778 if (!_work_queue->pop_local(new_oop)) {
6779 // We emptied our work_queue; check if there's stuff that can
6780 // be gotten from the overflow stack.
6781 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6782 _overflow_stack, _work_queue)) {
6783 do_yield_check();
6784 continue;
6785 } else { // done
6786 break;
6787 }
6788 }
6789 // Skip verifying header mark word below because we are
6790 // running concurrent with mutators.
6791 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6792 // now scan this oop's oops
6793 new_oop->oop_iterate(&pushOrMarkClosure);
6794 do_yield_check();
6795 }
6796 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6797 }
6798
6799 // Yield in response to a request from VM Thread or
6800 // from mutators.
6801 void Par_MarkFromRootsClosure::do_yield_work() {
6802 assert(_task != NULL, "sanity");
6803 _task->yield();
6804 }
6805
6806 // A variant of the above used for verifying CMS marking work.
6807 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6808 MemRegion span,
6809 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6810 CMSMarkStack* mark_stack):
6811 _collector(collector),
6812 _span(span),
6813 _verification_bm(verification_bm),
6814 _cms_bm(cms_bm),
6815 _mark_stack(mark_stack),
6816 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6817 mark_stack)
6818 {
6819 assert(_mark_stack->isEmpty(), "stack should be empty");
6820 _finger = _verification_bm->startWord();
6821 assert(_collector->_restart_addr == NULL, "Sanity check");
6822 assert(_span.contains(_finger), "Out of bounds _finger?");
6823 }
6824
6825 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6826 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6827 assert(_span.contains(addr), "Out of bounds _finger?");
6828 _finger = addr;
6829 }
6830
6831 // Should revisit to see if this should be restructured for
6832 // greater efficiency.
6833 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6834 // convert offset into a HeapWord*
6835 HeapWord* addr = _verification_bm->startWord() + offset;
6836 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6837 "address out of range");
6838 assert(_verification_bm->isMarked(addr), "tautology");
6839 assert(_cms_bm->isMarked(addr), "tautology");
6840
6841 assert(_mark_stack->isEmpty(),
6842 "should drain stack to limit stack usage");
6843 // convert addr to an oop preparatory to scanning
6844 oop obj = oop(addr);
6845 assert(obj->is_oop(), "should be an oop");
6846 assert(_finger <= addr, "_finger runneth ahead");
6847 // advance the finger to right end of this object
6848 _finger = addr + obj->size();
6849 assert(_finger > addr, "we just incremented it above");
6850 // Note: the finger doesn't advance while we drain
6851 // the stack below.
6852 bool res = _mark_stack->push(obj);
6853 assert(res, "Empty non-zero size stack should have space for single push");
6854 while (!_mark_stack->isEmpty()) {
6855 oop new_oop = _mark_stack->pop();
6856 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6857 // now scan this oop's oops
6858 new_oop->oop_iterate(&_pam_verify_closure);
6859 }
6860 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6861 return true;
6862 }
6863
6864 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6865 CMSCollector* collector, MemRegion span,
6866 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6867 CMSMarkStack* mark_stack):
6868 MetadataAwareOopClosure(collector->ref_processor()),
6869 _collector(collector),
6870 _span(span),
6871 _verification_bm(verification_bm),
6872 _cms_bm(cms_bm),
6873 _mark_stack(mark_stack)
6874 { }
6875
6876 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6877 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6878
6879 // Upon stack overflow, we discard (part of) the stack,
6880 // remembering the least address amongst those discarded
6881 // in CMSCollector's _restart_address.
6882 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6883 // Remember the least grey address discarded
6884 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6885 _collector->lower_restart_addr(ra);
6886 _mark_stack->reset(); // discard stack contents
6887 _mark_stack->expand(); // expand the stack if possible
6888 }
6889
6890 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6891 assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
6892 HeapWord* addr = (HeapWord*)obj;
6893 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6894 // Oop lies in _span and isn't yet grey or black
6895 _verification_bm->mark(addr); // now grey
6896 if (!_cms_bm->isMarked(addr)) {
6897 oop(addr)->print();
6898 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
6899 p2i(addr));
6900 fatal("... aborting");
6901 }
6902
6903 if (!_mark_stack->push(obj)) { // stack overflow
6904 if (PrintCMSStatistics != 0) {
6905 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6906 SIZE_FORMAT, _mark_stack->capacity());
6907 }
6908 assert(_mark_stack->isFull(), "Else push should have succeeded");
6909 handle_stack_overflow(addr);
6910 }
6911 // anything including and to the right of _finger
6912 // will be scanned as we iterate over the remainder of the
6913 // bit map
6914 }
6915 }
6916
6917 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6918 MemRegion span,
6919 CMSBitMap* bitMap, CMSMarkStack* markStack,
6920 HeapWord* finger, MarkFromRootsClosure* parent) :
6921 MetadataAwareOopClosure(collector->ref_processor()),
6922 _collector(collector),
6923 _span(span),
6924 _bitMap(bitMap),
6925 _markStack(markStack),
6926 _finger(finger),
6927 _parent(parent)
6928 { }
6929
6930 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
6931 MemRegion span,
6932 CMSBitMap* bit_map,
6933 OopTaskQueue* work_queue,
6934 CMSMarkStack* overflow_stack,
6935 HeapWord* finger,
6936 HeapWord** global_finger_addr,
6937 Par_MarkFromRootsClosure* parent) :
6938 MetadataAwareOopClosure(collector->ref_processor()),
6939 _collector(collector),
6940 _whole_span(collector->_span),
6941 _span(span),
6942 _bit_map(bit_map),
6943 _work_queue(work_queue),
6944 _overflow_stack(overflow_stack),
6945 _finger(finger),
6946 _global_finger_addr(global_finger_addr),
6947 _parent(parent)
6948 { }
6949
6950 // Assumes thread-safe access by callers, who are
6951 // responsible for mutual exclusion.
6952 void CMSCollector::lower_restart_addr(HeapWord* low) {
6953 assert(_span.contains(low), "Out of bounds addr");
6954 if (_restart_addr == NULL) {
6955 _restart_addr = low;
6956 } else {
6957 _restart_addr = MIN2(_restart_addr, low);
6958 }
6959 }
6960
6961 // Upon stack overflow, we discard (part of) the stack,
6962 // remembering the least address amongst those discarded
6963 // in CMSCollector's _restart_address.
6964 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6965 // Remember the least grey address discarded
6966 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6967 _collector->lower_restart_addr(ra);
6968 _markStack->reset(); // discard stack contents
6969 _markStack->expand(); // expand the stack if possible
6970 }
6971
6972 // Upon stack overflow, we discard (part of) the stack,
6973 // remembering the least address amongst those discarded
6974 // in CMSCollector's _restart_address.
6975 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6976 // We need to do this under a mutex to prevent other
6977 // workers from interfering with the work done below.
6978 MutexLockerEx ml(_overflow_stack->par_lock(),
6979 Mutex::_no_safepoint_check_flag);
6980 // Remember the least grey address discarded
6981 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6982 _collector->lower_restart_addr(ra);
6983 _overflow_stack->reset(); // discard stack contents
6984 _overflow_stack->expand(); // expand the stack if possible
6985 }
6986
6987 void PushOrMarkClosure::do_oop(oop obj) {
6988 // Ignore mark word because we are running concurrent with mutators.
6989 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
6990 HeapWord* addr = (HeapWord*)obj;
6991 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6992 // Oop lies in _span and isn't yet grey or black
6993 _bitMap->mark(addr); // now grey
6994 if (addr < _finger) {
6995 // the bit map iteration has already either passed, or
6996 // sampled, this bit in the bit map; we'll need to
6997 // use the marking stack to scan this oop's oops.
6998 bool simulate_overflow = false;
6999 NOT_PRODUCT(
7000 if (CMSMarkStackOverflowALot &&
7001 _collector->simulate_overflow()) {
7002 // simulate a stack overflow
7003 simulate_overflow = true;
7004 }
7005 )
7006 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7007 if (PrintCMSStatistics != 0) {
7008 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7009 SIZE_FORMAT, _markStack->capacity());
7010 }
7011 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7012 handle_stack_overflow(addr);
7013 }
7014 }
7015 // anything including and to the right of _finger
7016 // will be scanned as we iterate over the remainder of the
7017 // bit map
7018 do_yield_check();
7019 }
7020 }
7021
7022 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7023 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7024
7025 void Par_PushOrMarkClosure::do_oop(oop obj) {
7026 // Ignore mark word because we are running concurrent with mutators.
7027 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7028 HeapWord* addr = (HeapWord*)obj;
7029 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7030 // Oop lies in _span and isn't yet grey or black
7031 // We read the global_finger (volatile read) strictly after marking oop
7032 bool res = _bit_map->par_mark(addr); // now grey
7033 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7034 // Should we push this marked oop on our stack?
7035 // -- if someone else marked it, nothing to do
7036 // -- if target oop is above global finger nothing to do
7037 // -- if target oop is in chunk and above local finger
7038 // then nothing to do
7039 // -- else push on work queue
7040 if ( !res // someone else marked it, they will deal with it
7041 || (addr >= *gfa) // will be scanned in a later task
7042 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7043 return;
7044 }
7045 // the bit map iteration has already either passed, or
7046 // sampled, this bit in the bit map; we'll need to
7047 // use the marking stack to scan this oop's oops.
7048 bool simulate_overflow = false;
7049 NOT_PRODUCT(
7050 if (CMSMarkStackOverflowALot &&
7051 _collector->simulate_overflow()) {
7052 // simulate a stack overflow
7053 simulate_overflow = true;
7054 }
7055 )
7056 if (simulate_overflow ||
7057 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7058 // stack overflow
7059 if (PrintCMSStatistics != 0) {
7060 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7061 SIZE_FORMAT, _overflow_stack->capacity());
7062 }
7063 // We cannot assert that the overflow stack is full because
7064 // it may have been emptied since.
7065 assert(simulate_overflow ||
7066 _work_queue->size() == _work_queue->max_elems(),
7067 "Else push should have succeeded");
7068 handle_stack_overflow(addr);
7069 }
7070 do_yield_check();
7071 }
7072 }
7073
7074 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7075 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7076
7077 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7078 MemRegion span,
7079 ReferenceProcessor* rp,
7080 CMSBitMap* bit_map,
7081 CMSBitMap* mod_union_table,
7082 CMSMarkStack* mark_stack,
7083 bool concurrent_precleaning):
7084 MetadataAwareOopClosure(rp),
7085 _collector(collector),
7086 _span(span),
7087 _bit_map(bit_map),
7088 _mod_union_table(mod_union_table),
7089 _mark_stack(mark_stack),
7090 _concurrent_precleaning(concurrent_precleaning)
7091 {
7092 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7093 }
7094
7095 // Grey object rescan during pre-cleaning and second checkpoint phases --
7096 // the non-parallel version (the parallel version appears further below.)
7097 void PushAndMarkClosure::do_oop(oop obj) {
7098 // Ignore mark word verification. If during concurrent precleaning,
7099 // the object monitor may be locked. If during the checkpoint
7100 // phases, the object may already have been reached by a different
7101 // path and may be at the end of the global overflow list (so
7102 // the mark word may be NULL).
7103 assert(obj->is_oop_or_null(true /* ignore mark word */),
7104 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7105 HeapWord* addr = (HeapWord*)obj;
7106 // Check if oop points into the CMS generation
7107 // and is not marked
7108 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7109 // a white object ...
7110 _bit_map->mark(addr); // ... now grey
7111 // push on the marking stack (grey set)
7112 bool simulate_overflow = false;
7113 NOT_PRODUCT(
7114 if (CMSMarkStackOverflowALot &&
7115 _collector->simulate_overflow()) {
7116 // simulate a stack overflow
7117 simulate_overflow = true;
7118 }
7119 )
7120 if (simulate_overflow || !_mark_stack->push(obj)) {
7121 if (_concurrent_precleaning) {
7122 // During precleaning we can just dirty the appropriate card(s)
7123 // in the mod union table, thus ensuring that the object remains
7124 // in the grey set and continue. In the case of object arrays
7125 // we need to dirty all of the cards that the object spans,
7126 // since the rescan of object arrays will be limited to the
7127 // dirty cards.
7128 // Note that no one can be interfering with us in this action
7129 // of dirtying the mod union table, so no locking or atomics
7130 // are required.
7131 if (obj->is_objArray()) {
7132 size_t sz = obj->size();
7133 HeapWord* end_card_addr = (HeapWord*)round_to(
7134 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7135 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7136 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7137 _mod_union_table->mark_range(redirty_range);
7138 } else {
7139 _mod_union_table->mark(addr);
7140 }
7141 _collector->_ser_pmc_preclean_ovflw++;
7142 } else {
7143 // During the remark phase, we need to remember this oop
7144 // in the overflow list.
7145 _collector->push_on_overflow_list(obj);
7146 _collector->_ser_pmc_remark_ovflw++;
7147 }
7148 }
7149 }
7150 }
7151
7152 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7153 MemRegion span,
7154 ReferenceProcessor* rp,
7155 CMSBitMap* bit_map,
7156 OopTaskQueue* work_queue):
7157 MetadataAwareOopClosure(rp),
7158 _collector(collector),
7159 _span(span),
7160 _bit_map(bit_map),
7161 _work_queue(work_queue)
7162 {
7163 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7164 }
7165
7166 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7167 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7168
7169 // Grey object rescan during second checkpoint phase --
7170 // the parallel version.
7171 void Par_PushAndMarkClosure::do_oop(oop obj) {
7172 // In the assert below, we ignore the mark word because
7173 // this oop may point to an already visited object that is
7174 // on the overflow stack (in which case the mark word has
7175 // been hijacked for chaining into the overflow stack --
7176 // if this is the last object in the overflow stack then
7177 // its mark word will be NULL). Because this object may
7178 // have been subsequently popped off the global overflow
7179 // stack, and the mark word possibly restored to the prototypical
7180 // value, by the time we get to examined this failing assert in
7181 // the debugger, is_oop_or_null(false) may subsequently start
7182 // to hold.
7183 assert(obj->is_oop_or_null(true),
7184 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7185 HeapWord* addr = (HeapWord*)obj;
7186 // Check if oop points into the CMS generation
7187 // and is not marked
7188 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7189 // a white object ...
7190 // If we manage to "claim" the object, by being the
7191 // first thread to mark it, then we push it on our
7192 // marking stack
7193 if (_bit_map->par_mark(addr)) { // ... now grey
7194 // push on work queue (grey set)
7195 bool simulate_overflow = false;
7196 NOT_PRODUCT(
7197 if (CMSMarkStackOverflowALot &&
7198 _collector->par_simulate_overflow()) {
7199 // simulate a stack overflow
7200 simulate_overflow = true;
7201 }
7202 )
7203 if (simulate_overflow || !_work_queue->push(obj)) {
7204 _collector->par_push_on_overflow_list(obj);
7205 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7206 }
7207 } // Else, some other thread got there first
7208 }
7209 }
7210
7211 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7212 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7213
7214 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7215 Mutex* bml = _collector->bitMapLock();
7216 assert_lock_strong(bml);
7217 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7218 "CMS thread should hold CMS token");
7219
7220 bml->unlock();
7221 ConcurrentMarkSweepThread::desynchronize(true);
7222
7223 _collector->stopTimer();
7224 if (PrintCMSStatistics != 0) {
7225 _collector->incrementYields();
7226 }
7227
7228 // See the comment in coordinator_yield()
7229 for (unsigned i = 0; i < CMSYieldSleepCount &&
7230 ConcurrentMarkSweepThread::should_yield() &&
7231 !CMSCollector::foregroundGCIsActive(); ++i) {
7232 os::sleep(Thread::current(), 1, false);
7233 }
7234
7235 ConcurrentMarkSweepThread::synchronize(true);
7236 bml->lock();
7237
7238 _collector->startTimer();
7239 }
7240
7241 bool CMSPrecleanRefsYieldClosure::should_return() {
7242 if (ConcurrentMarkSweepThread::should_yield()) {
7243 do_yield_work();
7244 }
7245 return _collector->foregroundGCIsActive();
7246 }
7247
7248 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7249 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7250 "mr should be aligned to start at a card boundary");
7251 // We'd like to assert:
7252 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7253 // "mr should be a range of cards");
7254 // However, that would be too strong in one case -- the last
7255 // partition ends at _unallocated_block which, in general, can be
7256 // an arbitrary boundary, not necessarily card aligned.
7257 if (PrintCMSStatistics != 0) {
7258 _num_dirty_cards +=
7259 mr.word_size()/CardTableModRefBS::card_size_in_words;
7260 }
7261 _space->object_iterate_mem(mr, &_scan_cl);
7262 }
7263
7264 SweepClosure::SweepClosure(CMSCollector* collector,
7265 ConcurrentMarkSweepGeneration* g,
7266 CMSBitMap* bitMap, bool should_yield) :
7267 _collector(collector),
7268 _g(g),
7269 _sp(g->cmsSpace()),
7270 _limit(_sp->sweep_limit()),
7271 _freelistLock(_sp->freelistLock()),
7272 _bitMap(bitMap),
7273 _yield(should_yield),
7274 _inFreeRange(false), // No free range at beginning of sweep
7275 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7276 _lastFreeRangeCoalesced(false),
7277 _freeFinger(g->used_region().start())
7278 {
7279 NOT_PRODUCT(
7280 _numObjectsFreed = 0;
7281 _numWordsFreed = 0;
7282 _numObjectsLive = 0;
7283 _numWordsLive = 0;
7284 _numObjectsAlreadyFree = 0;
7285 _numWordsAlreadyFree = 0;
7286 _last_fc = NULL;
7287
7288 _sp->initializeIndexedFreeListArrayReturnedBytes();
7289 _sp->dictionary()->initialize_dict_returned_bytes();
7290 )
7291 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7292 "sweep _limit out of bounds");
7293 if (CMSTraceSweeper) {
7294 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7295 p2i(_limit));
7296 }
7297 }
7298
7299 void SweepClosure::print_on(outputStream* st) const {
7300 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7301 p2i(_sp->bottom()), p2i(_sp->end()));
7302 tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7303 tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7304 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7305 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7306 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7307 }
7308
7309 #ifndef PRODUCT
7310 // Assertion checking only: no useful work in product mode --
7311 // however, if any of the flags below become product flags,
7312 // you may need to review this code to see if it needs to be
7313 // enabled in product mode.
7314 SweepClosure::~SweepClosure() {
7315 assert_lock_strong(_freelistLock);
7316 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7317 "sweep _limit out of bounds");
7318 if (inFreeRange()) {
7319 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7320 print();
7321 ShouldNotReachHere();
7322 }
7323 if (Verbose && PrintGC) {
7324 gclog_or_tty->print("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7325 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7326 gclog_or_tty->print_cr("\nLive " SIZE_FORMAT " objects, "
7327 SIZE_FORMAT " bytes "
7328 "Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7329 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7330 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7331 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7332 * sizeof(HeapWord);
7333 gclog_or_tty->print_cr("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7334
7335 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7336 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7337 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7338 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7339 gclog_or_tty->print("Returned " SIZE_FORMAT " bytes", returned_bytes);
7340 gclog_or_tty->print(" Indexed List Returned " SIZE_FORMAT " bytes",
7341 indexListReturnedBytes);
7342 gclog_or_tty->print_cr(" Dictionary Returned " SIZE_FORMAT " bytes",
7343 dict_returned_bytes);
7344 }
7345 }
7346 if (CMSTraceSweeper) {
7347 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7348 p2i(_limit));
7349 }
7350 }
7351 #endif // PRODUCT
7352
7353 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7354 bool freeRangeInFreeLists) {
7355 if (CMSTraceSweeper) {
7356 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7357 p2i(freeFinger), freeRangeInFreeLists);
7358 }
7359 assert(!inFreeRange(), "Trampling existing free range");
7360 set_inFreeRange(true);
7361 set_lastFreeRangeCoalesced(false);
7362
7363 set_freeFinger(freeFinger);
7364 set_freeRangeInFreeLists(freeRangeInFreeLists);
7365 if (CMSTestInFreeList) {
7366 if (freeRangeInFreeLists) {
7367 FreeChunk* fc = (FreeChunk*) freeFinger;
7368 assert(fc->is_free(), "A chunk on the free list should be free.");
7369 assert(fc->size() > 0, "Free range should have a size");
7370 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7371 }
7372 }
7373 }
7374
7375 // Note that the sweeper runs concurrently with mutators. Thus,
7376 // it is possible for direct allocation in this generation to happen
7377 // in the middle of the sweep. Note that the sweeper also coalesces
7378 // contiguous free blocks. Thus, unless the sweeper and the allocator
7379 // synchronize appropriately freshly allocated blocks may get swept up.
7380 // This is accomplished by the sweeper locking the free lists while
7381 // it is sweeping. Thus blocks that are determined to be free are
7382 // indeed free. There is however one additional complication:
7383 // blocks that have been allocated since the final checkpoint and
7384 // mark, will not have been marked and so would be treated as
7385 // unreachable and swept up. To prevent this, the allocator marks
7386 // the bit map when allocating during the sweep phase. This leads,
7387 // however, to a further complication -- objects may have been allocated
7388 // but not yet initialized -- in the sense that the header isn't yet
7389 // installed. The sweeper can not then determine the size of the block
7390 // in order to skip over it. To deal with this case, we use a technique
7391 // (due to Printezis) to encode such uninitialized block sizes in the
7392 // bit map. Since the bit map uses a bit per every HeapWord, but the
7393 // CMS generation has a minimum object size of 3 HeapWords, it follows
7394 // that "normal marks" won't be adjacent in the bit map (there will
7395 // always be at least two 0 bits between successive 1 bits). We make use
7396 // of these "unused" bits to represent uninitialized blocks -- the bit
7397 // corresponding to the start of the uninitialized object and the next
7398 // bit are both set. Finally, a 1 bit marks the end of the object that
7399 // started with the two consecutive 1 bits to indicate its potentially
7400 // uninitialized state.
7401
7402 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7403 FreeChunk* fc = (FreeChunk*)addr;
7404 size_t res;
7405
7406 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7407 // than "addr == _limit" because although _limit was a block boundary when
7408 // we started the sweep, it may no longer be one because heap expansion
7409 // may have caused us to coalesce the block ending at the address _limit
7410 // with a newly expanded chunk (this happens when _limit was set to the
7411 // previous _end of the space), so we may have stepped past _limit:
7412 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7413 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7414 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7415 "sweep _limit out of bounds");
7416 assert(addr < _sp->end(), "addr out of bounds");
7417 // Flush any free range we might be holding as a single
7418 // coalesced chunk to the appropriate free list.
7419 if (inFreeRange()) {
7420 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7421 err_msg("freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger())));
7422 flush_cur_free_chunk(freeFinger(),
7423 pointer_delta(addr, freeFinger()));
7424 if (CMSTraceSweeper) {
7425 gclog_or_tty->print("Sweep: last chunk: ");
7426 gclog_or_tty->print("put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") "
7427 "[coalesced:%d]\n",
7428 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7429 lastFreeRangeCoalesced() ? 1 : 0);
7430 }
7431 }
7432
7433 // help the iterator loop finish
7434 return pointer_delta(_sp->end(), addr);
7435 }
7436
7437 assert(addr < _limit, "sweep invariant");
7438 // check if we should yield
7439 do_yield_check(addr);
7440 if (fc->is_free()) {
7441 // Chunk that is already free
7442 res = fc->size();
7443 do_already_free_chunk(fc);
7444 debug_only(_sp->verifyFreeLists());
7445 // If we flush the chunk at hand in lookahead_and_flush()
7446 // and it's coalesced with a preceding chunk, then the
7447 // process of "mangling" the payload of the coalesced block
7448 // will cause erasure of the size information from the
7449 // (erstwhile) header of all the coalesced blocks but the
7450 // first, so the first disjunct in the assert will not hold
7451 // in that specific case (in which case the second disjunct
7452 // will hold).
7453 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7454 "Otherwise the size info doesn't change at this step");
7455 NOT_PRODUCT(
7456 _numObjectsAlreadyFree++;
7457 _numWordsAlreadyFree += res;
7458 )
7459 NOT_PRODUCT(_last_fc = fc;)
7460 } else if (!_bitMap->isMarked(addr)) {
7461 // Chunk is fresh garbage
7462 res = do_garbage_chunk(fc);
7463 debug_only(_sp->verifyFreeLists());
7464 NOT_PRODUCT(
7465 _numObjectsFreed++;
7466 _numWordsFreed += res;
7467 )
7468 } else {
7469 // Chunk that is alive.
7470 res = do_live_chunk(fc);
7471 debug_only(_sp->verifyFreeLists());
7472 NOT_PRODUCT(
7473 _numObjectsLive++;
7474 _numWordsLive += res;
7475 )
7476 }
7477 return res;
7478 }
7479
7480 // For the smart allocation, record following
7481 // split deaths - a free chunk is removed from its free list because
7482 // it is being split into two or more chunks.
7483 // split birth - a free chunk is being added to its free list because
7484 // a larger free chunk has been split and resulted in this free chunk.
7485 // coal death - a free chunk is being removed from its free list because
7486 // it is being coalesced into a large free chunk.
7487 // coal birth - a free chunk is being added to its free list because
7488 // it was created when two or more free chunks where coalesced into
7489 // this free chunk.
7490 //
7491 // These statistics are used to determine the desired number of free
7492 // chunks of a given size. The desired number is chosen to be relative
7493 // to the end of a CMS sweep. The desired number at the end of a sweep
7494 // is the
7495 // count-at-end-of-previous-sweep (an amount that was enough)
7496 // - count-at-beginning-of-current-sweep (the excess)
7497 // + split-births (gains in this size during interval)
7498 // - split-deaths (demands on this size during interval)
7499 // where the interval is from the end of one sweep to the end of the
7500 // next.
7501 //
7502 // When sweeping the sweeper maintains an accumulated chunk which is
7503 // the chunk that is made up of chunks that have been coalesced. That
7504 // will be termed the left-hand chunk. A new chunk of garbage that
7505 // is being considered for coalescing will be referred to as the
7506 // right-hand chunk.
7507 //
7508 // When making a decision on whether to coalesce a right-hand chunk with
7509 // the current left-hand chunk, the current count vs. the desired count
7510 // of the left-hand chunk is considered. Also if the right-hand chunk
7511 // is near the large chunk at the end of the heap (see
7512 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7513 // left-hand chunk is coalesced.
7514 //
7515 // When making a decision about whether to split a chunk, the desired count
7516 // vs. the current count of the candidate to be split is also considered.
7517 // If the candidate is underpopulated (currently fewer chunks than desired)
7518 // a chunk of an overpopulated (currently more chunks than desired) size may
7519 // be chosen. The "hint" associated with a free list, if non-null, points
7520 // to a free list which may be overpopulated.
7521 //
7522
7523 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7524 const size_t size = fc->size();
7525 // Chunks that cannot be coalesced are not in the
7526 // free lists.
7527 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7528 assert(_sp->verify_chunk_in_free_list(fc),
7529 "free chunk should be in free lists");
7530 }
7531 // a chunk that is already free, should not have been
7532 // marked in the bit map
7533 HeapWord* const addr = (HeapWord*) fc;
7534 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7535 // Verify that the bit map has no bits marked between
7536 // addr and purported end of this block.
7537 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7538
7539 // Some chunks cannot be coalesced under any circumstances.
7540 // See the definition of cantCoalesce().
7541 if (!fc->cantCoalesce()) {
7542 // This chunk can potentially be coalesced.
7543 if (_sp->adaptive_freelists()) {
7544 // All the work is done in
7545 do_post_free_or_garbage_chunk(fc, size);
7546 } else { // Not adaptive free lists
7547 // this is a free chunk that can potentially be coalesced by the sweeper;
7548 if (!inFreeRange()) {
7549 // if the next chunk is a free block that can't be coalesced
7550 // it doesn't make sense to remove this chunk from the free lists
7551 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7552 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
7553 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
7554 nextChunk->is_free() && // ... which is free...
7555 nextChunk->cantCoalesce()) { // ... but can't be coalesced
7556 // nothing to do
7557 } else {
7558 // Potentially the start of a new free range:
7559 // Don't eagerly remove it from the free lists.
7560 // No need to remove it if it will just be put
7561 // back again. (Also from a pragmatic point of view
7562 // if it is a free block in a region that is beyond
7563 // any allocated blocks, an assertion will fail)
7564 // Remember the start of a free run.
7565 initialize_free_range(addr, true);
7566 // end - can coalesce with next chunk
7567 }
7568 } else {
7569 // the midst of a free range, we are coalescing
7570 print_free_block_coalesced(fc);
7571 if (CMSTraceSweeper) {
7572 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7573 }
7574 // remove it from the free lists
7575 _sp->removeFreeChunkFromFreeLists(fc);
7576 set_lastFreeRangeCoalesced(true);
7577 // If the chunk is being coalesced and the current free range is
7578 // in the free lists, remove the current free range so that it
7579 // will be returned to the free lists in its entirety - all
7580 // the coalesced pieces included.
7581 if (freeRangeInFreeLists()) {
7582 FreeChunk* ffc = (FreeChunk*) freeFinger();
7583 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7584 "Size of free range is inconsistent with chunk size.");
7585 if (CMSTestInFreeList) {
7586 assert(_sp->verify_chunk_in_free_list(ffc),
7587 "free range is not in free lists");
7588 }
7589 _sp->removeFreeChunkFromFreeLists(ffc);
7590 set_freeRangeInFreeLists(false);
7591 }
7592 }
7593 }
7594 // Note that if the chunk is not coalescable (the else arm
7595 // below), we unconditionally flush, without needing to do
7596 // a "lookahead," as we do below.
7597 if (inFreeRange()) lookahead_and_flush(fc, size);
7598 } else {
7599 // Code path common to both original and adaptive free lists.
7600
7601 // cant coalesce with previous block; this should be treated
7602 // as the end of a free run if any
7603 if (inFreeRange()) {
7604 // we kicked some butt; time to pick up the garbage
7605 assert(freeFinger() < addr, "freeFinger points too high");
7606 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7607 }
7608 // else, nothing to do, just continue
7609 }
7610 }
7611
7612 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7613 // This is a chunk of garbage. It is not in any free list.
7614 // Add it to a free list or let it possibly be coalesced into
7615 // a larger chunk.
7616 HeapWord* const addr = (HeapWord*) fc;
7617 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7618
7619 if (_sp->adaptive_freelists()) {
7620 // Verify that the bit map has no bits marked between
7621 // addr and purported end of just dead object.
7622 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7623
7624 do_post_free_or_garbage_chunk(fc, size);
7625 } else {
7626 if (!inFreeRange()) {
7627 // start of a new free range
7628 assert(size > 0, "A free range should have a size");
7629 initialize_free_range(addr, false);
7630 } else {
7631 // this will be swept up when we hit the end of the
7632 // free range
7633 if (CMSTraceSweeper) {
7634 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7635 }
7636 // If the chunk is being coalesced and the current free range is
7637 // in the free lists, remove the current free range so that it
7638 // will be returned to the free lists in its entirety - all
7639 // the coalesced pieces included.
7640 if (freeRangeInFreeLists()) {
7641 FreeChunk* ffc = (FreeChunk*)freeFinger();
7642 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7643 "Size of free range is inconsistent with chunk size.");
7644 if (CMSTestInFreeList) {
7645 assert(_sp->verify_chunk_in_free_list(ffc),
7646 "free range is not in free lists");
7647 }
7648 _sp->removeFreeChunkFromFreeLists(ffc);
7649 set_freeRangeInFreeLists(false);
7650 }
7651 set_lastFreeRangeCoalesced(true);
7652 }
7653 // this will be swept up when we hit the end of the free range
7654
7655 // Verify that the bit map has no bits marked between
7656 // addr and purported end of just dead object.
7657 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7658 }
7659 assert(_limit >= addr + size,
7660 "A freshly garbage chunk can't possibly straddle over _limit");
7661 if (inFreeRange()) lookahead_and_flush(fc, size);
7662 return size;
7663 }
7664
7665 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7666 HeapWord* addr = (HeapWord*) fc;
7667 // The sweeper has just found a live object. Return any accumulated
7668 // left hand chunk to the free lists.
7669 if (inFreeRange()) {
7670 assert(freeFinger() < addr, "freeFinger points too high");
7671 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7672 }
7673
7674 // This object is live: we'd normally expect this to be
7675 // an oop, and like to assert the following:
7676 // assert(oop(addr)->is_oop(), "live block should be an oop");
7677 // However, as we commented above, this may be an object whose
7678 // header hasn't yet been initialized.
7679 size_t size;
7680 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7681 if (_bitMap->isMarked(addr + 1)) {
7682 // Determine the size from the bit map, rather than trying to
7683 // compute it from the object header.
7684 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7685 size = pointer_delta(nextOneAddr + 1, addr);
7686 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7687 "alignment problem");
7688
7689 #ifdef ASSERT
7690 if (oop(addr)->klass_or_null() != NULL) {
7691 // Ignore mark word because we are running concurrent with mutators
7692 assert(oop(addr)->is_oop(true), "live block should be an oop");
7693 assert(size ==
7694 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7695 "P-mark and computed size do not agree");
7696 }
7697 #endif
7698
7699 } else {
7700 // This should be an initialized object that's alive.
7701 assert(oop(addr)->klass_or_null() != NULL,
7702 "Should be an initialized object");
7703 // Ignore mark word because we are running concurrent with mutators
7704 assert(oop(addr)->is_oop(true), "live block should be an oop");
7705 // Verify that the bit map has no bits marked between
7706 // addr and purported end of this block.
7707 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7708 assert(size >= 3, "Necessary for Printezis marks to work");
7709 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7710 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7711 }
7712 return size;
7713 }
7714
7715 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7716 size_t chunkSize) {
7717 // do_post_free_or_garbage_chunk() should only be called in the case
7718 // of the adaptive free list allocator.
7719 const bool fcInFreeLists = fc->is_free();
7720 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
7721 assert((HeapWord*)fc <= _limit, "sweep invariant");
7722 if (CMSTestInFreeList && fcInFreeLists) {
7723 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7724 }
7725
7726 if (CMSTraceSweeper) {
7727 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7728 }
7729
7730 HeapWord* const fc_addr = (HeapWord*) fc;
7731
7732 bool coalesce;
7733 const size_t left = pointer_delta(fc_addr, freeFinger());
7734 const size_t right = chunkSize;
7735 switch (FLSCoalescePolicy) {
7736 // numeric value forms a coalition aggressiveness metric
7737 case 0: { // never coalesce
7738 coalesce = false;
7739 break;
7740 }
7741 case 1: { // coalesce if left & right chunks on overpopulated lists
7742 coalesce = _sp->coalOverPopulated(left) &&
7743 _sp->coalOverPopulated(right);
7744 break;
7745 }
7746 case 2: { // coalesce if left chunk on overpopulated list (default)
7747 coalesce = _sp->coalOverPopulated(left);
7748 break;
7749 }
7750 case 3: { // coalesce if left OR right chunk on overpopulated list
7751 coalesce = _sp->coalOverPopulated(left) ||
7752 _sp->coalOverPopulated(right);
7753 break;
7754 }
7755 case 4: { // always coalesce
7756 coalesce = true;
7757 break;
7758 }
7759 default:
7760 ShouldNotReachHere();
7761 }
7762
7763 // Should the current free range be coalesced?
7764 // If the chunk is in a free range and either we decided to coalesce above
7765 // or the chunk is near the large block at the end of the heap
7766 // (isNearLargestChunk() returns true), then coalesce this chunk.
7767 const bool doCoalesce = inFreeRange()
7768 && (coalesce || _g->isNearLargestChunk(fc_addr));
7769 if (doCoalesce) {
7770 // Coalesce the current free range on the left with the new
7771 // chunk on the right. If either is on a free list,
7772 // it must be removed from the list and stashed in the closure.
7773 if (freeRangeInFreeLists()) {
7774 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7775 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7776 "Size of free range is inconsistent with chunk size.");
7777 if (CMSTestInFreeList) {
7778 assert(_sp->verify_chunk_in_free_list(ffc),
7779 "Chunk is not in free lists");
7780 }
7781 _sp->coalDeath(ffc->size());
7782 _sp->removeFreeChunkFromFreeLists(ffc);
7783 set_freeRangeInFreeLists(false);
7784 }
7785 if (fcInFreeLists) {
7786 _sp->coalDeath(chunkSize);
7787 assert(fc->size() == chunkSize,
7788 "The chunk has the wrong size or is not in the free lists");
7789 _sp->removeFreeChunkFromFreeLists(fc);
7790 }
7791 set_lastFreeRangeCoalesced(true);
7792 print_free_block_coalesced(fc);
7793 } else { // not in a free range and/or should not coalesce
7794 // Return the current free range and start a new one.
7795 if (inFreeRange()) {
7796 // In a free range but cannot coalesce with the right hand chunk.
7797 // Put the current free range into the free lists.
7798 flush_cur_free_chunk(freeFinger(),
7799 pointer_delta(fc_addr, freeFinger()));
7800 }
7801 // Set up for new free range. Pass along whether the right hand
7802 // chunk is in the free lists.
7803 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7804 }
7805 }
7806
7807 // Lookahead flush:
7808 // If we are tracking a free range, and this is the last chunk that
7809 // we'll look at because its end crosses past _limit, we'll preemptively
7810 // flush it along with any free range we may be holding on to. Note that
7811 // this can be the case only for an already free or freshly garbage
7812 // chunk. If this block is an object, it can never straddle
7813 // over _limit. The "straddling" occurs when _limit is set at
7814 // the previous end of the space when this cycle started, and
7815 // a subsequent heap expansion caused the previously co-terminal
7816 // free block to be coalesced with the newly expanded portion,
7817 // thus rendering _limit a non-block-boundary making it dangerous
7818 // for the sweeper to step over and examine.
7819 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7820 assert(inFreeRange(), "Should only be called if currently in a free range.");
7821 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7822 assert(_sp->used_region().contains(eob - 1),
7823 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7824 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7825 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7826 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size));
7827 if (eob >= _limit) {
7828 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7829 if (CMSTraceSweeper) {
7830 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7831 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7832 "[" PTR_FORMAT "," PTR_FORMAT ")",
7833 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7834 }
7835 // Return the storage we are tracking back into the free lists.
7836 if (CMSTraceSweeper) {
7837 gclog_or_tty->print_cr("Flushing ... ");
7838 }
7839 assert(freeFinger() < eob, "Error");
7840 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7841 }
7842 }
7843
7844 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7845 assert(inFreeRange(), "Should only be called if currently in a free range.");
7846 assert(size > 0,
7847 "A zero sized chunk cannot be added to the free lists.");
7848 if (!freeRangeInFreeLists()) {
7849 if (CMSTestInFreeList) {
7850 FreeChunk* fc = (FreeChunk*) chunk;
7851 fc->set_size(size);
7852 assert(!_sp->verify_chunk_in_free_list(fc),
7853 "chunk should not be in free lists yet");
7854 }
7855 if (CMSTraceSweeper) {
7856 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7857 p2i(chunk), size);
7858 }
7859 // A new free range is going to be starting. The current
7860 // free range has not been added to the free lists yet or
7861 // was removed so add it back.
7862 // If the current free range was coalesced, then the death
7863 // of the free range was recorded. Record a birth now.
7864 if (lastFreeRangeCoalesced()) {
7865 _sp->coalBirth(size);
7866 }
7867 _sp->addChunkAndRepairOffsetTable(chunk, size,
7868 lastFreeRangeCoalesced());
7869 } else if (CMSTraceSweeper) {
7870 gclog_or_tty->print_cr("Already in free list: nothing to flush");
7871 }
7872 set_inFreeRange(false);
7873 set_freeRangeInFreeLists(false);
7874 }
7875
7876 // We take a break if we've been at this for a while,
7877 // so as to avoid monopolizing the locks involved.
7878 void SweepClosure::do_yield_work(HeapWord* addr) {
7879 // Return current free chunk being used for coalescing (if any)
7880 // to the appropriate freelist. After yielding, the next
7881 // free block encountered will start a coalescing range of
7882 // free blocks. If the next free block is adjacent to the
7883 // chunk just flushed, they will need to wait for the next
7884 // sweep to be coalesced.
7885 if (inFreeRange()) {
7886 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7887 }
7888
7889 // First give up the locks, then yield, then re-lock.
7890 // We should probably use a constructor/destructor idiom to
7891 // do this unlock/lock or modify the MutexUnlocker class to
7892 // serve our purpose. XXX
7893 assert_lock_strong(_bitMap->lock());
7894 assert_lock_strong(_freelistLock);
7895 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7896 "CMS thread should hold CMS token");
7897 _bitMap->lock()->unlock();
7898 _freelistLock->unlock();
7899 ConcurrentMarkSweepThread::desynchronize(true);
7900 _collector->stopTimer();
7901 if (PrintCMSStatistics != 0) {
7902 _collector->incrementYields();
7903 }
7904
7905 // See the comment in coordinator_yield()
7906 for (unsigned i = 0; i < CMSYieldSleepCount &&
7907 ConcurrentMarkSweepThread::should_yield() &&
7908 !CMSCollector::foregroundGCIsActive(); ++i) {
7909 os::sleep(Thread::current(), 1, false);
7910 }
7911
7912 ConcurrentMarkSweepThread::synchronize(true);
7913 _freelistLock->lock();
7914 _bitMap->lock()->lock_without_safepoint_check();
7915 _collector->startTimer();
7916 }
7917
7918 #ifndef PRODUCT
7919 // This is actually very useful in a product build if it can
7920 // be called from the debugger. Compile it into the product
7921 // as needed.
7922 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7923 return debug_cms_space->verify_chunk_in_free_list(fc);
7924 }
7925 #endif
7926
7927 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7928 if (CMSTraceSweeper) {
7929 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7930 p2i(fc), fc->size());
7931 }
7932 }
7933
7934 // CMSIsAliveClosure
7935 bool CMSIsAliveClosure::do_object_b(oop obj) {
7936 HeapWord* addr = (HeapWord*)obj;
7937 return addr != NULL &&
7938 (!_span.contains(addr) || _bit_map->isMarked(addr));
7939 }
7940
7941
7942 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7943 MemRegion span,
7944 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7945 bool cpc):
7946 _collector(collector),
7947 _span(span),
7948 _bit_map(bit_map),
7949 _mark_stack(mark_stack),
7950 _concurrent_precleaning(cpc) {
7951 assert(!_span.is_empty(), "Empty span could spell trouble");
7952 }
7953
7954
7955 // CMSKeepAliveClosure: the serial version
7956 void CMSKeepAliveClosure::do_oop(oop obj) {
7957 HeapWord* addr = (HeapWord*)obj;
7958 if (_span.contains(addr) &&
7959 !_bit_map->isMarked(addr)) {
7960 _bit_map->mark(addr);
7961 bool simulate_overflow = false;
7962 NOT_PRODUCT(
7963 if (CMSMarkStackOverflowALot &&
7964 _collector->simulate_overflow()) {
7965 // simulate a stack overflow
7966 simulate_overflow = true;
7967 }
7968 )
7969 if (simulate_overflow || !_mark_stack->push(obj)) {
7970 if (_concurrent_precleaning) {
7971 // We dirty the overflown object and let the remark
7972 // phase deal with it.
7973 assert(_collector->overflow_list_is_empty(), "Error");
7974 // In the case of object arrays, we need to dirty all of
7975 // the cards that the object spans. No locking or atomics
7976 // are needed since no one else can be mutating the mod union
7977 // table.
7978 if (obj->is_objArray()) {
7979 size_t sz = obj->size();
7980 HeapWord* end_card_addr =
7981 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
7982 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7983 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7984 _collector->_modUnionTable.mark_range(redirty_range);
7985 } else {
7986 _collector->_modUnionTable.mark(addr);
7987 }
7988 _collector->_ser_kac_preclean_ovflw++;
7989 } else {
7990 _collector->push_on_overflow_list(obj);
7991 _collector->_ser_kac_ovflw++;
7992 }
7993 }
7994 }
7995 }
7996
7997 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7998 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7999
8000 // CMSParKeepAliveClosure: a parallel version of the above.
8001 // The work queues are private to each closure (thread),
8002 // but (may be) available for stealing by other threads.
8003 void CMSParKeepAliveClosure::do_oop(oop obj) {
8004 HeapWord* addr = (HeapWord*)obj;
8005 if (_span.contains(addr) &&
8006 !_bit_map->isMarked(addr)) {
8007 // In general, during recursive tracing, several threads
8008 // may be concurrently getting here; the first one to
8009 // "tag" it, claims it.
8010 if (_bit_map->par_mark(addr)) {
8011 bool res = _work_queue->push(obj);
8012 assert(res, "Low water mark should be much less than capacity");
8013 // Do a recursive trim in the hope that this will keep
8014 // stack usage lower, but leave some oops for potential stealers
8015 trim_queue(_low_water_mark);
8016 } // Else, another thread got there first
8017 }
8018 }
8019
8020 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8021 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8022
8023 void CMSParKeepAliveClosure::trim_queue(uint max) {
8024 while (_work_queue->size() > max) {
8025 oop new_oop;
8026 if (_work_queue->pop_local(new_oop)) {
8027 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8028 assert(_bit_map->isMarked((HeapWord*)new_oop),
8029 "no white objects on this stack!");
8030 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8031 // iterate over the oops in this oop, marking and pushing
8032 // the ones in CMS heap (i.e. in _span).
8033 new_oop->oop_iterate(&_mark_and_push);
8034 }
8035 }
8036 }
8037
8038 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8039 CMSCollector* collector,
8040 MemRegion span, CMSBitMap* bit_map,
8041 OopTaskQueue* work_queue):
8042 _collector(collector),
8043 _span(span),
8044 _bit_map(bit_map),
8045 _work_queue(work_queue) { }
8046
8047 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8048 HeapWord* addr = (HeapWord*)obj;
8049 if (_span.contains(addr) &&
8050 !_bit_map->isMarked(addr)) {
8051 if (_bit_map->par_mark(addr)) {
8052 bool simulate_overflow = false;
8053 NOT_PRODUCT(
8054 if (CMSMarkStackOverflowALot &&
8055 _collector->par_simulate_overflow()) {
8056 // simulate a stack overflow
8057 simulate_overflow = true;
8058 }
8059 )
8060 if (simulate_overflow || !_work_queue->push(obj)) {
8061 _collector->par_push_on_overflow_list(obj);
8062 _collector->_par_kac_ovflw++;
8063 }
8064 } // Else another thread got there already
8065 }
8066 }
8067
8068 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8069 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8070
8071 //////////////////////////////////////////////////////////////////
8072 // CMSExpansionCause /////////////////////////////
8073 //////////////////////////////////////////////////////////////////
8074 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8075 switch (cause) {
8076 case _no_expansion:
8077 return "No expansion";
8078 case _satisfy_free_ratio:
8079 return "Free ratio";
8080 case _satisfy_promotion:
8081 return "Satisfy promotion";
8082 case _satisfy_allocation:
8083 return "allocation";
8084 case _allocate_par_lab:
8085 return "Par LAB";
8086 case _allocate_par_spooling_space:
8087 return "Par Spooling Space";
8088 case _adaptive_size_policy:
8089 return "Ergonomics";
8090 default:
8091 return "unknown";
8092 }
8093 }
8094
8095 void CMSDrainMarkingStackClosure::do_void() {
8096 // the max number to take from overflow list at a time
8097 const size_t num = _mark_stack->capacity()/4;
8098 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8099 "Overflow list should be NULL during concurrent phases");
8100 while (!_mark_stack->isEmpty() ||
8101 // if stack is empty, check the overflow list
8102 _collector->take_from_overflow_list(num, _mark_stack)) {
8103 oop obj = _mark_stack->pop();
8104 HeapWord* addr = (HeapWord*)obj;
8105 assert(_span.contains(addr), "Should be within span");
8106 assert(_bit_map->isMarked(addr), "Should be marked");
8107 assert(obj->is_oop(), "Should be an oop");
8108 obj->oop_iterate(_keep_alive);
8109 }
8110 }
8111
8112 void CMSParDrainMarkingStackClosure::do_void() {
8113 // drain queue
8114 trim_queue(0);
8115 }
8116
8117 // Trim our work_queue so its length is below max at return
8118 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8119 while (_work_queue->size() > max) {
8120 oop new_oop;
8121 if (_work_queue->pop_local(new_oop)) {
8122 assert(new_oop->is_oop(), "Expected an oop");
8123 assert(_bit_map->isMarked((HeapWord*)new_oop),
8124 "no white objects on this stack!");
8125 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8126 // iterate over the oops in this oop, marking and pushing
8127 // the ones in CMS heap (i.e. in _span).
8128 new_oop->oop_iterate(&_mark_and_push);
8129 }
8130 }
8131 }
8132
8133 ////////////////////////////////////////////////////////////////////
8134 // Support for Marking Stack Overflow list handling and related code
8135 ////////////////////////////////////////////////////////////////////
8136 // Much of the following code is similar in shape and spirit to the
8137 // code used in ParNewGC. We should try and share that code
8138 // as much as possible in the future.
8139
8140 #ifndef PRODUCT
8141 // Debugging support for CMSStackOverflowALot
8142
8143 // It's OK to call this multi-threaded; the worst thing
8144 // that can happen is that we'll get a bunch of closely
8145 // spaced simulated overflows, but that's OK, in fact
8146 // probably good as it would exercise the overflow code
8147 // under contention.
8148 bool CMSCollector::simulate_overflow() {
8149 if (_overflow_counter-- <= 0) { // just being defensive
8150 _overflow_counter = CMSMarkStackOverflowInterval;
8151 return true;
8152 } else {
8153 return false;
8154 }
8155 }
8156
8157 bool CMSCollector::par_simulate_overflow() {
8158 return simulate_overflow();
8159 }
8160 #endif
8161
8162 // Single-threaded
8163 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8164 assert(stack->isEmpty(), "Expected precondition");
8165 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8166 size_t i = num;
8167 oop cur = _overflow_list;
8168 const markOop proto = markOopDesc::prototype();
8169 NOT_PRODUCT(ssize_t n = 0;)
8170 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8171 next = oop(cur->mark());
8172 cur->set_mark(proto); // until proven otherwise
8173 assert(cur->is_oop(), "Should be an oop");
8174 bool res = stack->push(cur);
8175 assert(res, "Bit off more than can chew?");
8176 NOT_PRODUCT(n++;)
8177 }
8178 _overflow_list = cur;
8179 #ifndef PRODUCT
8180 assert(_num_par_pushes >= n, "Too many pops?");
8181 _num_par_pushes -=n;
8182 #endif
8183 return !stack->isEmpty();
8184 }
8185
8186 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8187 // (MT-safe) Get a prefix of at most "num" from the list.
8188 // The overflow list is chained through the mark word of
8189 // each object in the list. We fetch the entire list,
8190 // break off a prefix of the right size and return the
8191 // remainder. If other threads try to take objects from
8192 // the overflow list at that time, they will wait for
8193 // some time to see if data becomes available. If (and
8194 // only if) another thread places one or more object(s)
8195 // on the global list before we have returned the suffix
8196 // to the global list, we will walk down our local list
8197 // to find its end and append the global list to
8198 // our suffix before returning it. This suffix walk can
8199 // prove to be expensive (quadratic in the amount of traffic)
8200 // when there are many objects in the overflow list and
8201 // there is much producer-consumer contention on the list.
8202 // *NOTE*: The overflow list manipulation code here and
8203 // in ParNewGeneration:: are very similar in shape,
8204 // except that in the ParNew case we use the old (from/eden)
8205 // copy of the object to thread the list via its klass word.
8206 // Because of the common code, if you make any changes in
8207 // the code below, please check the ParNew version to see if
8208 // similar changes might be needed.
8209 // CR 6797058 has been filed to consolidate the common code.
8210 bool CMSCollector::par_take_from_overflow_list(size_t num,
8211 OopTaskQueue* work_q,
8212 int no_of_gc_threads) {
8213 assert(work_q->size() == 0, "First empty local work queue");
8214 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8215 if (_overflow_list == NULL) {
8216 return false;
8217 }
8218 // Grab the entire list; we'll put back a suffix
8219 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8220 Thread* tid = Thread::current();
8221 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8222 // set to ParallelGCThreads.
8223 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8224 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8225 // If the list is busy, we spin for a short while,
8226 // sleeping between attempts to get the list.
8227 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8228 os::sleep(tid, sleep_time_millis, false);
8229 if (_overflow_list == NULL) {
8230 // Nothing left to take
8231 return false;
8232 } else if (_overflow_list != BUSY) {
8233 // Try and grab the prefix
8234 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8235 }
8236 }
8237 // If the list was found to be empty, or we spun long
8238 // enough, we give up and return empty-handed. If we leave
8239 // the list in the BUSY state below, it must be the case that
8240 // some other thread holds the overflow list and will set it
8241 // to a non-BUSY state in the future.
8242 if (prefix == NULL || prefix == BUSY) {
8243 // Nothing to take or waited long enough
8244 if (prefix == NULL) {
8245 // Write back the NULL in case we overwrote it with BUSY above
8246 // and it is still the same value.
8247 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8248 }
8249 return false;
8250 }
8251 assert(prefix != NULL && prefix != BUSY, "Error");
8252 size_t i = num;
8253 oop cur = prefix;
8254 // Walk down the first "num" objects, unless we reach the end.
8255 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8256 if (cur->mark() == NULL) {
8257 // We have "num" or fewer elements in the list, so there
8258 // is nothing to return to the global list.
8259 // Write back the NULL in lieu of the BUSY we wrote
8260 // above, if it is still the same value.
8261 if (_overflow_list == BUSY) {
8262 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8263 }
8264 } else {
8265 // Chop off the suffix and return it to the global list.
8266 assert(cur->mark() != BUSY, "Error");
8267 oop suffix_head = cur->mark(); // suffix will be put back on global list
8268 cur->set_mark(NULL); // break off suffix
8269 // It's possible that the list is still in the empty(busy) state
8270 // we left it in a short while ago; in that case we may be
8271 // able to place back the suffix without incurring the cost
8272 // of a walk down the list.
8273 oop observed_overflow_list = _overflow_list;
8274 oop cur_overflow_list = observed_overflow_list;
8275 bool attached = false;
8276 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8277 observed_overflow_list =
8278 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8279 if (cur_overflow_list == observed_overflow_list) {
8280 attached = true;
8281 break;
8282 } else cur_overflow_list = observed_overflow_list;
8283 }
8284 if (!attached) {
8285 // Too bad, someone else sneaked in (at least) an element; we'll need
8286 // to do a splice. Find tail of suffix so we can prepend suffix to global
8287 // list.
8288 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8289 oop suffix_tail = cur;
8290 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8291 "Tautology");
8292 observed_overflow_list = _overflow_list;
8293 do {
8294 cur_overflow_list = observed_overflow_list;
8295 if (cur_overflow_list != BUSY) {
8296 // Do the splice ...
8297 suffix_tail->set_mark(markOop(cur_overflow_list));
8298 } else { // cur_overflow_list == BUSY
8299 suffix_tail->set_mark(NULL);
8300 }
8301 // ... and try to place spliced list back on overflow_list ...
8302 observed_overflow_list =
8303 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8304 } while (cur_overflow_list != observed_overflow_list);
8305 // ... until we have succeeded in doing so.
8306 }
8307 }
8308
8309 // Push the prefix elements on work_q
8310 assert(prefix != NULL, "control point invariant");
8311 const markOop proto = markOopDesc::prototype();
8312 oop next;
8313 NOT_PRODUCT(ssize_t n = 0;)
8314 for (cur = prefix; cur != NULL; cur = next) {
8315 next = oop(cur->mark());
8316 cur->set_mark(proto); // until proven otherwise
8317 assert(cur->is_oop(), "Should be an oop");
8318 bool res = work_q->push(cur);
8319 assert(res, "Bit off more than we can chew?");
8320 NOT_PRODUCT(n++;)
8321 }
8322 #ifndef PRODUCT
8323 assert(_num_par_pushes >= n, "Too many pops?");
8324 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8325 #endif
8326 return true;
8327 }
8328
8329 // Single-threaded
8330 void CMSCollector::push_on_overflow_list(oop p) {
8331 NOT_PRODUCT(_num_par_pushes++;)
8332 assert(p->is_oop(), "Not an oop");
8333 preserve_mark_if_necessary(p);
8334 p->set_mark((markOop)_overflow_list);
8335 _overflow_list = p;
8336 }
8337
8338 // Multi-threaded; use CAS to prepend to overflow list
8339 void CMSCollector::par_push_on_overflow_list(oop p) {
8340 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8341 assert(p->is_oop(), "Not an oop");
8342 par_preserve_mark_if_necessary(p);
8343 oop observed_overflow_list = _overflow_list;
8344 oop cur_overflow_list;
8345 do {
8346 cur_overflow_list = observed_overflow_list;
8347 if (cur_overflow_list != BUSY) {
8348 p->set_mark(markOop(cur_overflow_list));
8349 } else {
8350 p->set_mark(NULL);
8351 }
8352 observed_overflow_list =
8353 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8354 } while (cur_overflow_list != observed_overflow_list);
8355 }
8356 #undef BUSY
8357
8358 // Single threaded
8359 // General Note on GrowableArray: pushes may silently fail
8360 // because we are (temporarily) out of C-heap for expanding
8361 // the stack. The problem is quite ubiquitous and affects
8362 // a lot of code in the JVM. The prudent thing for GrowableArray
8363 // to do (for now) is to exit with an error. However, that may
8364 // be too draconian in some cases because the caller may be
8365 // able to recover without much harm. For such cases, we
8366 // should probably introduce a "soft_push" method which returns
8367 // an indication of success or failure with the assumption that
8368 // the caller may be able to recover from a failure; code in
8369 // the VM can then be changed, incrementally, to deal with such
8370 // failures where possible, thus, incrementally hardening the VM
8371 // in such low resource situations.
8372 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8373 _preserved_oop_stack.push(p);
8374 _preserved_mark_stack.push(m);
8375 assert(m == p->mark(), "Mark word changed");
8376 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8377 "bijection");
8378 }
8379
8380 // Single threaded
8381 void CMSCollector::preserve_mark_if_necessary(oop p) {
8382 markOop m = p->mark();
8383 if (m->must_be_preserved(p)) {
8384 preserve_mark_work(p, m);
8385 }
8386 }
8387
8388 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8389 markOop m = p->mark();
8390 if (m->must_be_preserved(p)) {
8391 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8392 // Even though we read the mark word without holding
8393 // the lock, we are assured that it will not change
8394 // because we "own" this oop, so no other thread can
8395 // be trying to push it on the overflow list; see
8396 // the assertion in preserve_mark_work() that checks
8397 // that m == p->mark().
8398 preserve_mark_work(p, m);
8399 }
8400 }
8401
8402 // We should be able to do this multi-threaded,
8403 // a chunk of stack being a task (this is
8404 // correct because each oop only ever appears
8405 // once in the overflow list. However, it's
8406 // not very easy to completely overlap this with
8407 // other operations, so will generally not be done
8408 // until all work's been completed. Because we
8409 // expect the preserved oop stack (set) to be small,
8410 // it's probably fine to do this single-threaded.
8411 // We can explore cleverer concurrent/overlapped/parallel
8412 // processing of preserved marks if we feel the
8413 // need for this in the future. Stack overflow should
8414 // be so rare in practice and, when it happens, its
8415 // effect on performance so great that this will
8416 // likely just be in the noise anyway.
8417 void CMSCollector::restore_preserved_marks_if_any() {
8418 assert(SafepointSynchronize::is_at_safepoint(),
8419 "world should be stopped");
8420 assert(Thread::current()->is_ConcurrentGC_thread() ||
8421 Thread::current()->is_VM_thread(),
8422 "should be single-threaded");
8423 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8424 "bijection");
8425
8426 while (!_preserved_oop_stack.is_empty()) {
8427 oop p = _preserved_oop_stack.pop();
8428 assert(p->is_oop(), "Should be an oop");
8429 assert(_span.contains(p), "oop should be in _span");
8430 assert(p->mark() == markOopDesc::prototype(),
8431 "Set when taken from overflow list");
8432 markOop m = _preserved_mark_stack.pop();
8433 p->set_mark(m);
8434 }
8435 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8436 "stacks were cleared above");
8437 }
8438
8439 #ifndef PRODUCT
8440 bool CMSCollector::no_preserved_marks() const {
8441 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8442 }
8443 #endif
8444
8445 // Transfer some number of overflown objects to usual marking
8446 // stack. Return true if some objects were transferred.
8447 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8448 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8449 (size_t)ParGCDesiredObjsFromOverflowList);
8450
8451 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8452 assert(_collector->overflow_list_is_empty() || res,
8453 "If list is not empty, we should have taken something");
8454 assert(!res || !_mark_stack->isEmpty(),
8455 "If we took something, it should now be on our stack");
8456 return res;
8457 }
8458
8459 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8460 size_t res = _sp->block_size_no_stall(addr, _collector);
8461 if (_sp->block_is_obj(addr)) {
8462 if (_live_bit_map->isMarked(addr)) {
8463 // It can't have been dead in a previous cycle
8464 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8465 } else {
8466 _dead_bit_map->mark(addr); // mark the dead object
8467 }
8468 }
8469 // Could be 0, if the block size could not be computed without stalling.
8470 return res;
8471 }
8472
8473 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8474
8475 switch (phase) {
8476 case CMSCollector::InitialMarking:
8477 initialize(true /* fullGC */ ,
8478 cause /* cause of the GC */,
8479 true /* recordGCBeginTime */,
8480 true /* recordPreGCUsage */,
8481 false /* recordPeakUsage */,
8482 false /* recordPostGCusage */,
8483 true /* recordAccumulatedGCTime */,
8484 false /* recordGCEndTime */,
8485 false /* countCollection */ );
8486 break;
8487
8488 case CMSCollector::FinalMarking:
8489 initialize(true /* fullGC */ ,
8490 cause /* cause of the GC */,
8491 false /* recordGCBeginTime */,
8492 false /* recordPreGCUsage */,
8493 false /* recordPeakUsage */,
8494 false /* recordPostGCusage */,
8495 true /* recordAccumulatedGCTime */,
8496 false /* recordGCEndTime */,
8497 false /* countCollection */ );
8498 break;
8499
8500 case CMSCollector::Sweeping:
8501 initialize(true /* fullGC */ ,
8502 cause /* cause of the GC */,
8503 false /* recordGCBeginTime */,
8504 false /* recordPreGCUsage */,
8505 true /* recordPeakUsage */,
8506 true /* recordPostGCusage */,
8507 false /* recordAccumulatedGCTime */,
8508 true /* recordGCEndTime */,
8509 true /* countCollection */ );
8510 break;
8511
8512 default:
8513 ShouldNotReachHere();
8514 }
8515 }