1 /*
2 * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc/cms/cmsCollectorPolicy.hpp"
31 #include "gc/cms/cmsOopClosures.inline.hpp"
32 #include "gc/cms/compactibleFreeListSpace.hpp"
33 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
34 #include "gc/cms/concurrentMarkSweepThread.hpp"
35 #include "gc/cms/parNewGeneration.hpp"
36 #include "gc/cms/vmCMSOperations.hpp"
37 #include "gc/serial/genMarkSweep.hpp"
38 #include "gc/serial/tenuredGeneration.hpp"
39 #include "gc/shared/adaptiveSizePolicy.hpp"
40 #include "gc/shared/cardGeneration.inline.hpp"
41 #include "gc/shared/cardTableRS.hpp"
42 #include "gc/shared/collectedHeap.inline.hpp"
43 #include "gc/shared/collectorCounters.hpp"
44 #include "gc/shared/collectorPolicy.hpp"
45 #include "gc/shared/gcLocker.inline.hpp"
46 #include "gc/shared/gcPolicyCounters.hpp"
47 #include "gc/shared/gcTimer.hpp"
48 #include "gc/shared/gcTrace.hpp"
49 #include "gc/shared/gcTraceTime.hpp"
50 #include "gc/shared/genCollectedHeap.hpp"
51 #include "gc/shared/genOopClosures.inline.hpp"
52 #include "gc/shared/isGCActiveMark.hpp"
53 #include "gc/shared/referencePolicy.hpp"
54 #include "gc/shared/strongRootsScope.hpp"
55 #include "gc/shared/taskqueue.inline.hpp"
56 #include "memory/allocation.hpp"
57 #include "memory/iterator.inline.hpp"
58 #include "memory/padded.hpp"
59 #include "memory/resourceArea.hpp"
60 #include "oops/oop.inline.hpp"
61 #include "prims/jvmtiExport.hpp"
62 #include "runtime/atomic.inline.hpp"
63 #include "runtime/globals_extension.hpp"
64 #include "runtime/handles.inline.hpp"
65 #include "runtime/java.hpp"
66 #include "runtime/orderAccess.inline.hpp"
67 #include "runtime/vmThread.hpp"
68 #include "services/memoryService.hpp"
69 #include "services/runtimeService.hpp"
70 #include "utilities/stack.inline.hpp"
71
72 // statics
73 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
74 bool CMSCollector::_full_gc_requested = false;
75 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
76
77 //////////////////////////////////////////////////////////////////
78 // In support of CMS/VM thread synchronization
79 //////////////////////////////////////////////////////////////////
80 // We split use of the CGC_lock into 2 "levels".
81 // The low-level locking is of the usual CGC_lock monitor. We introduce
82 // a higher level "token" (hereafter "CMS token") built on top of the
83 // low level monitor (hereafter "CGC lock").
84 // The token-passing protocol gives priority to the VM thread. The
85 // CMS-lock doesn't provide any fairness guarantees, but clients
86 // should ensure that it is only held for very short, bounded
87 // durations.
88 //
89 // When either of the CMS thread or the VM thread is involved in
90 // collection operations during which it does not want the other
91 // thread to interfere, it obtains the CMS token.
92 //
93 // If either thread tries to get the token while the other has
94 // it, that thread waits. However, if the VM thread and CMS thread
95 // both want the token, then the VM thread gets priority while the
96 // CMS thread waits. This ensures, for instance, that the "concurrent"
97 // phases of the CMS thread's work do not block out the VM thread
98 // for long periods of time as the CMS thread continues to hog
99 // the token. (See bug 4616232).
100 //
101 // The baton-passing functions are, however, controlled by the
102 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
103 // and here the low-level CMS lock, not the high level token,
104 // ensures mutual exclusion.
105 //
106 // Two important conditions that we have to satisfy:
107 // 1. if a thread does a low-level wait on the CMS lock, then it
108 // relinquishes the CMS token if it were holding that token
109 // when it acquired the low-level CMS lock.
110 // 2. any low-level notifications on the low-level lock
111 // should only be sent when a thread has relinquished the token.
112 //
113 // In the absence of either property, we'd have potential deadlock.
114 //
115 // We protect each of the CMS (concurrent and sequential) phases
116 // with the CMS _token_, not the CMS _lock_.
117 //
118 // The only code protected by CMS lock is the token acquisition code
119 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
120 // baton-passing code.
121 //
122 // Unfortunately, i couldn't come up with a good abstraction to factor and
123 // hide the naked CGC_lock manipulation in the baton-passing code
124 // further below. That's something we should try to do. Also, the proof
125 // of correctness of this 2-level locking scheme is far from obvious,
126 // and potentially quite slippery. We have an uneasy suspicion, for instance,
127 // that there may be a theoretical possibility of delay/starvation in the
128 // low-level lock/wait/notify scheme used for the baton-passing because of
129 // potential interference with the priority scheme embodied in the
130 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
131 // invocation further below and marked with "XXX 20011219YSR".
132 // Indeed, as we note elsewhere, this may become yet more slippery
133 // in the presence of multiple CMS and/or multiple VM threads. XXX
134
135 class CMSTokenSync: public StackObj {
136 private:
137 bool _is_cms_thread;
138 public:
139 CMSTokenSync(bool is_cms_thread):
140 _is_cms_thread(is_cms_thread) {
141 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
142 "Incorrect argument to constructor");
143 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
144 }
145
146 ~CMSTokenSync() {
147 assert(_is_cms_thread ?
148 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
149 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
150 "Incorrect state");
151 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
152 }
153 };
154
155 // Convenience class that does a CMSTokenSync, and then acquires
156 // upto three locks.
157 class CMSTokenSyncWithLocks: public CMSTokenSync {
158 private:
159 // Note: locks are acquired in textual declaration order
160 // and released in the opposite order
161 MutexLockerEx _locker1, _locker2, _locker3;
162 public:
163 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
164 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
165 CMSTokenSync(is_cms_thread),
166 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
167 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
168 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
169 { }
170 };
171
172
173 //////////////////////////////////////////////////////////////////
174 // Concurrent Mark-Sweep Generation /////////////////////////////
175 //////////////////////////////////////////////////////////////////
176
177 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
178
179 // This struct contains per-thread things necessary to support parallel
180 // young-gen collection.
181 class CMSParGCThreadState: public CHeapObj<mtGC> {
182 public:
183 CFLS_LAB lab;
184 PromotionInfo promo;
185
186 // Constructor.
187 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
188 promo.setSpace(cfls);
189 }
190 };
191
192 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
193 ReservedSpace rs, size_t initial_byte_size,
194 CardTableRS* ct, bool use_adaptive_freelists,
195 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
196 CardGeneration(rs, initial_byte_size, ct),
197 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
198 _did_compact(false)
199 {
200 HeapWord* bottom = (HeapWord*) _virtual_space.low();
201 HeapWord* end = (HeapWord*) _virtual_space.high();
202
203 _direct_allocated_words = 0;
204 NOT_PRODUCT(
205 _numObjectsPromoted = 0;
206 _numWordsPromoted = 0;
207 _numObjectsAllocated = 0;
208 _numWordsAllocated = 0;
209 )
210
211 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
212 use_adaptive_freelists,
213 dictionaryChoice);
214 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
215 _cmsSpace->_gen = this;
216
217 _gc_stats = new CMSGCStats();
218
219 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
220 // offsets match. The ability to tell free chunks from objects
221 // depends on this property.
222 debug_only(
223 FreeChunk* junk = NULL;
224 assert(UseCompressedClassPointers ||
225 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
226 "Offset of FreeChunk::_prev within FreeChunk must match"
227 " that of OopDesc::_klass within OopDesc");
228 )
229
230 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
231 for (uint i = 0; i < ParallelGCThreads; i++) {
232 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
233 }
234
235 _incremental_collection_failed = false;
236 // The "dilatation_factor" is the expansion that can occur on
237 // account of the fact that the minimum object size in the CMS
238 // generation may be larger than that in, say, a contiguous young
239 // generation.
240 // Ideally, in the calculation below, we'd compute the dilatation
241 // factor as: MinChunkSize/(promoting_gen's min object size)
242 // Since we do not have such a general query interface for the
243 // promoting generation, we'll instead just use the minimum
244 // object size (which today is a header's worth of space);
245 // note that all arithmetic is in units of HeapWords.
246 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
247 assert(_dilatation_factor >= 1.0, "from previous assert");
248 }
249
250
251 // The field "_initiating_occupancy" represents the occupancy percentage
252 // at which we trigger a new collection cycle. Unless explicitly specified
253 // via CMSInitiatingOccupancyFraction (argument "io" below), it
254 // is calculated by:
255 //
256 // Let "f" be MinHeapFreeRatio in
257 //
258 // _initiating_occupancy = 100-f +
259 // f * (CMSTriggerRatio/100)
260 // where CMSTriggerRatio is the argument "tr" below.
261 //
262 // That is, if we assume the heap is at its desired maximum occupancy at the
263 // end of a collection, we let CMSTriggerRatio of the (purported) free
264 // space be allocated before initiating a new collection cycle.
265 //
266 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
267 assert(io <= 100 && tr <= 100, "Check the arguments");
268 if (io >= 0) {
269 _initiating_occupancy = (double)io / 100.0;
270 } else {
271 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
272 (double)(tr * MinHeapFreeRatio) / 100.0)
273 / 100.0;
274 }
275 }
276
277 void ConcurrentMarkSweepGeneration::ref_processor_init() {
278 assert(collector() != NULL, "no collector");
279 collector()->ref_processor_init();
280 }
281
282 void CMSCollector::ref_processor_init() {
283 if (_ref_processor == NULL) {
284 // Allocate and initialize a reference processor
285 _ref_processor =
286 new ReferenceProcessor(_span, // span
287 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
288 (int) ParallelGCThreads, // mt processing degree
289 _cmsGen->refs_discovery_is_mt(), // mt discovery
290 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
291 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
292 &_is_alive_closure); // closure for liveness info
293 // Initialize the _ref_processor field of CMSGen
294 _cmsGen->set_ref_processor(_ref_processor);
295
296 }
297 }
298
299 AdaptiveSizePolicy* CMSCollector::size_policy() {
300 GenCollectedHeap* gch = GenCollectedHeap::heap();
301 return gch->gen_policy()->size_policy();
302 }
303
304 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
305
306 const char* gen_name = "old";
307 GenCollectorPolicy* gcp = (GenCollectorPolicy*) GenCollectedHeap::heap()->collector_policy();
308
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 minor 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 = (uint) 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 = ((double)CMSBootstrapOccupancy)/(double)100;
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 ((DefNewGeneration*)_young_gen)->max_survivor_size() / plab_sample_minimum_size();
624
625 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
626 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
627 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
628 _survivor_chunk_capacity = 2*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 size_t CMSCollector::plab_sample_minimum_size() {
645 // The default value of MinTLABSize is 2k, but there is
646 // no way to get the default value if the flag has been overridden.
647 return MAX2(ThreadLocalAllocBuffer::min_size() * HeapWordSize, 2 * K);
648 }
649
650 const char* ConcurrentMarkSweepGeneration::name() const {
651 return "concurrent mark-sweep generation";
652 }
653 void ConcurrentMarkSweepGeneration::update_counters() {
654 if (UsePerfData) {
655 _space_counters->update_all();
656 _gen_counters->update_all();
657 }
658 }
659
660 // this is an optimized version of update_counters(). it takes the
661 // used value as a parameter rather than computing it.
662 //
663 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
664 if (UsePerfData) {
665 _space_counters->update_used(used);
666 _space_counters->update_capacity();
667 _gen_counters->update_all();
668 }
669 }
670
671 void ConcurrentMarkSweepGeneration::print() const {
672 Generation::print();
673 cmsSpace()->print();
674 }
675
676 #ifndef PRODUCT
677 void ConcurrentMarkSweepGeneration::print_statistics() {
678 cmsSpace()->printFLCensus(0);
679 }
680 #endif
681
682 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
683 GenCollectedHeap* gch = GenCollectedHeap::heap();
684 if (PrintGCDetails) {
685 // I didn't want to change the logging when removing the level concept,
686 // but I guess this logging could say "old" or something instead of "1".
687 assert(this == gch->old_gen(),
688 "The CMS generation should be the old generation");
689 uint level = 1;
690 if (Verbose) {
691 gclog_or_tty->print("[%u %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
692 level, short_name(), s, used(), capacity());
693 } else {
694 gclog_or_tty->print("[%u %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
695 level, short_name(), s, used() / K, capacity() / K);
696 }
697 }
698 if (Verbose) {
699 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
700 gch->used(), gch->capacity());
701 } else {
702 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
703 gch->used() / K, gch->capacity() / K);
704 }
705 }
706
707 size_t
708 ConcurrentMarkSweepGeneration::contiguous_available() const {
709 // dld proposes an improvement in precision here. If the committed
710 // part of the space ends in a free block we should add that to
711 // uncommitted size in the calculation below. Will make this
712 // change later, staying with the approximation below for the
713 // time being. -- ysr.
714 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
715 }
716
717 size_t
718 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
719 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
720 }
721
722 size_t ConcurrentMarkSweepGeneration::max_available() const {
723 return free() + _virtual_space.uncommitted_size();
724 }
725
726 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
727 size_t available = max_available();
728 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
729 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
730 if (Verbose && PrintGCDetails) {
731 gclog_or_tty->print_cr(
732 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
733 "max_promo("SIZE_FORMAT")",
734 res? "":" not", available, res? ">=":"<",
735 av_promo, max_promotion_in_bytes);
736 }
737 return res;
738 }
739
740 // At a promotion failure dump information on block layout in heap
741 // (cms old generation).
742 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
743 if (CMSDumpAtPromotionFailure) {
744 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
745 }
746 }
747
748 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
749 // Clear the promotion information. These pointers can be adjusted
750 // along with all the other pointers into the heap but
751 // compaction is expected to be a rare event with
752 // a heap using cms so don't do it without seeing the need.
753 for (uint i = 0; i < ParallelGCThreads; i++) {
754 _par_gc_thread_states[i]->promo.reset();
755 }
756 }
757
758 void ConcurrentMarkSweepGeneration::compute_new_size() {
759 assert_locked_or_safepoint(Heap_lock);
760
761 // If incremental collection failed, we just want to expand
762 // to the limit.
763 if (incremental_collection_failed()) {
764 clear_incremental_collection_failed();
765 grow_to_reserved();
766 return;
767 }
768
769 // The heap has been compacted but not reset yet.
770 // Any metric such as free() or used() will be incorrect.
771
772 CardGeneration::compute_new_size();
773
774 // Reset again after a possible resizing
775 if (did_compact()) {
776 cmsSpace()->reset_after_compaction();
777 }
778 }
779
780 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
781 assert_locked_or_safepoint(Heap_lock);
782
783 // If incremental collection failed, we just want to expand
784 // to the limit.
785 if (incremental_collection_failed()) {
786 clear_incremental_collection_failed();
787 grow_to_reserved();
788 return;
789 }
790
791 double free_percentage = ((double) free()) / capacity();
792 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
793 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
794
795 // compute expansion delta needed for reaching desired free percentage
796 if (free_percentage < desired_free_percentage) {
797 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
798 assert(desired_capacity >= capacity(), "invalid expansion size");
799 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
800 if (PrintGCDetails && Verbose) {
801 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
802 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
803 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
804 gclog_or_tty->print_cr(" Desired free fraction %f", desired_free_percentage);
805 gclog_or_tty->print_cr(" Maximum free fraction %f", maximum_free_percentage);
806 gclog_or_tty->print_cr(" Capacity "SIZE_FORMAT, capacity() / 1000);
807 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT, desired_capacity / 1000);
808 GenCollectedHeap* gch = GenCollectedHeap::heap();
809 assert(this == gch->_old_gen, "The CMS generation should always be the old generation");
810 size_t young_size = gch->_young_gen->capacity();
811 gclog_or_tty->print_cr(" Young gen size "SIZE_FORMAT, young_size / 1000);
812 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
813 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT, contiguous_available() / 1000);
814 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)", expand_bytes);
815 }
816 // safe if expansion fails
817 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
818 if (PrintGCDetails && Verbose) {
819 gclog_or_tty->print_cr(" Expanded free fraction %f",
820 ((double) free()) / capacity());
821 }
822 } else {
823 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
824 assert(desired_capacity <= capacity(), "invalid expansion size");
825 size_t shrink_bytes = capacity() - desired_capacity;
826 // Don't shrink unless the delta is greater than the minimum shrink we want
827 if (shrink_bytes >= MinHeapDeltaBytes) {
828 shrink_free_list_by(shrink_bytes);
829 }
830 }
831 }
832
833 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
834 return cmsSpace()->freelistLock();
835 }
836
837 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
838 bool tlab) {
839 CMSSynchronousYieldRequest yr;
840 MutexLockerEx x(freelistLock(),
841 Mutex::_no_safepoint_check_flag);
842 return have_lock_and_allocate(size, tlab);
843 }
844
845 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
846 bool tlab /* ignored */) {
847 assert_lock_strong(freelistLock());
848 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
849 HeapWord* res = cmsSpace()->allocate(adjustedSize);
850 // Allocate the object live (grey) if the background collector has
851 // started marking. This is necessary because the marker may
852 // have passed this address and consequently this object will
853 // not otherwise be greyed and would be incorrectly swept up.
854 // Note that if this object contains references, the writing
855 // of those references will dirty the card containing this object
856 // allowing the object to be blackened (and its references scanned)
857 // either during a preclean phase or at the final checkpoint.
858 if (res != NULL) {
859 // We may block here with an uninitialized object with
860 // its mark-bit or P-bits not yet set. Such objects need
861 // to be safely navigable by block_start().
862 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
863 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
864 collector()->direct_allocated(res, adjustedSize);
865 _direct_allocated_words += adjustedSize;
866 // allocation counters
867 NOT_PRODUCT(
868 _numObjectsAllocated++;
869 _numWordsAllocated += (int)adjustedSize;
870 )
871 }
872 return res;
873 }
874
875 // In the case of direct allocation by mutators in a generation that
876 // is being concurrently collected, the object must be allocated
877 // live (grey) if the background collector has started marking.
878 // This is necessary because the marker may
879 // have passed this address and consequently this object will
880 // not otherwise be greyed and would be incorrectly swept up.
881 // Note that if this object contains references, the writing
882 // of those references will dirty the card containing this object
883 // allowing the object to be blackened (and its references scanned)
884 // either during a preclean phase or at the final checkpoint.
885 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
886 assert(_markBitMap.covers(start, size), "Out of bounds");
887 if (_collectorState >= Marking) {
888 MutexLockerEx y(_markBitMap.lock(),
889 Mutex::_no_safepoint_check_flag);
890 // [see comments preceding SweepClosure::do_blk() below for details]
891 //
892 // Can the P-bits be deleted now? JJJ
893 //
894 // 1. need to mark the object as live so it isn't collected
895 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
896 // 3. need to mark the end of the object so marking, precleaning or sweeping
897 // can skip over uninitialized or unparsable objects. An allocated
898 // object is considered uninitialized for our purposes as long as
899 // its klass word is NULL. All old gen objects are parsable
900 // as soon as they are initialized.)
901 _markBitMap.mark(start); // object is live
902 _markBitMap.mark(start + 1); // object is potentially uninitialized?
903 _markBitMap.mark(start + size - 1);
904 // mark end of object
905 }
906 // check that oop looks uninitialized
907 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
908 }
909
910 void CMSCollector::promoted(bool par, HeapWord* start,
911 bool is_obj_array, size_t obj_size) {
912 assert(_markBitMap.covers(start), "Out of bounds");
913 // See comment in direct_allocated() about when objects should
914 // be allocated live.
915 if (_collectorState >= Marking) {
916 // we already hold the marking bit map lock, taken in
917 // the prologue
918 if (par) {
919 _markBitMap.par_mark(start);
920 } else {
921 _markBitMap.mark(start);
922 }
923 // We don't need to mark the object as uninitialized (as
924 // in direct_allocated above) because this is being done with the
925 // world stopped and the object will be initialized by the
926 // time the marking, precleaning or sweeping get to look at it.
927 // But see the code for copying objects into the CMS generation,
928 // where we need to ensure that concurrent readers of the
929 // block offset table are able to safely navigate a block that
930 // is in flux from being free to being allocated (and in
931 // transition while being copied into) and subsequently
932 // becoming a bona-fide object when the copy/promotion is complete.
933 assert(SafepointSynchronize::is_at_safepoint(),
934 "expect promotion only at safepoints");
935
936 if (_collectorState < Sweeping) {
937 // Mark the appropriate cards in the modUnionTable, so that
938 // this object gets scanned before the sweep. If this is
939 // not done, CMS generation references in the object might
940 // not get marked.
941 // For the case of arrays, which are otherwise precisely
942 // marked, we need to dirty the entire array, not just its head.
943 if (is_obj_array) {
944 // The [par_]mark_range() method expects mr.end() below to
945 // be aligned to the granularity of a bit's representation
946 // in the heap. In the case of the MUT below, that's a
947 // card size.
948 MemRegion mr(start,
949 (HeapWord*)round_to((intptr_t)(start + obj_size),
950 CardTableModRefBS::card_size /* bytes */));
951 if (par) {
952 _modUnionTable.par_mark_range(mr);
953 } else {
954 _modUnionTable.mark_range(mr);
955 }
956 } else { // not an obj array; we can just mark the head
957 if (par) {
958 _modUnionTable.par_mark(start);
959 } else {
960 _modUnionTable.mark(start);
961 }
962 }
963 }
964 }
965 }
966
967 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
968 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
969 // allocate, copy and if necessary update promoinfo --
970 // delegate to underlying space.
971 assert_lock_strong(freelistLock());
972
973 #ifndef PRODUCT
974 if (GenCollectedHeap::heap()->promotion_should_fail()) {
975 return NULL;
976 }
977 #endif // #ifndef PRODUCT
978
979 oop res = _cmsSpace->promote(obj, obj_size);
980 if (res == NULL) {
981 // expand and retry
982 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
983 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
984 // Since this is the old generation, we don't try to promote
985 // into a more senior generation.
986 res = _cmsSpace->promote(obj, obj_size);
987 }
988 if (res != NULL) {
989 // See comment in allocate() about when objects should
990 // be allocated live.
991 assert(obj->is_oop(), "Will dereference klass pointer below");
992 collector()->promoted(false, // Not parallel
993 (HeapWord*)res, obj->is_objArray(), obj_size);
994 // promotion counters
995 NOT_PRODUCT(
996 _numObjectsPromoted++;
997 _numWordsPromoted +=
998 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
999 )
1000 }
1001 return res;
1002 }
1003
1004
1005 // IMPORTANT: Notes on object size recognition in CMS.
1006 // ---------------------------------------------------
1007 // A block of storage in the CMS generation is always in
1008 // one of three states. A free block (FREE), an allocated
1009 // object (OBJECT) whose size() method reports the correct size,
1010 // and an intermediate state (TRANSIENT) in which its size cannot
1011 // be accurately determined.
1012 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1013 // -----------------------------------------------------
1014 // FREE: klass_word & 1 == 1; mark_word holds block size
1015 //
1016 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1017 // obj->size() computes correct size
1018 //
1019 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1020 //
1021 // STATE IDENTIFICATION: (64 bit+COOPS)
1022 // ------------------------------------
1023 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1024 //
1025 // OBJECT: klass_word installed; klass_word != 0;
1026 // obj->size() computes correct size
1027 //
1028 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1029 //
1030 //
1031 // STATE TRANSITION DIAGRAM
1032 //
1033 // mut / parnew mut / parnew
1034 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1035 // ^ |
1036 // |------------------------ DEAD <------------------------------------|
1037 // sweep mut
1038 //
1039 // While a block is in TRANSIENT state its size cannot be determined
1040 // so readers will either need to come back later or stall until
1041 // the size can be determined. Note that for the case of direct
1042 // allocation, P-bits, when available, may be used to determine the
1043 // size of an object that may not yet have been initialized.
1044
1045 // Things to support parallel young-gen collection.
1046 oop
1047 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1048 oop old, markOop m,
1049 size_t word_sz) {
1050 #ifndef PRODUCT
1051 if (GenCollectedHeap::heap()->promotion_should_fail()) {
1052 return NULL;
1053 }
1054 #endif // #ifndef PRODUCT
1055
1056 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1057 PromotionInfo* promoInfo = &ps->promo;
1058 // if we are tracking promotions, then first ensure space for
1059 // promotion (including spooling space for saving header if necessary).
1060 // then allocate and copy, then track promoted info if needed.
1061 // When tracking (see PromotionInfo::track()), the mark word may
1062 // be displaced and in this case restoration of the mark word
1063 // occurs in the (oop_since_save_marks_)iterate phase.
1064 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1065 // Out of space for allocating spooling buffers;
1066 // try expanding and allocating spooling buffers.
1067 if (!expand_and_ensure_spooling_space(promoInfo)) {
1068 return NULL;
1069 }
1070 }
1071 assert(promoInfo->has_spooling_space(), "Control point invariant");
1072 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1073 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1074 if (obj_ptr == NULL) {
1075 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1076 if (obj_ptr == NULL) {
1077 return NULL;
1078 }
1079 }
1080 oop obj = oop(obj_ptr);
1081 OrderAccess::storestore();
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 // IMPORTANT: See note on object initialization for CMS above.
1085 // Otherwise, copy the object. Here we must be careful to insert the
1086 // klass pointer last, since this marks the block as an allocated object.
1087 // Except with compressed oops it's the mark word.
1088 HeapWord* old_ptr = (HeapWord*)old;
1089 // Restore the mark word copied above.
1090 obj->set_mark(m);
1091 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1092 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1093 OrderAccess::storestore();
1094
1095 if (UseCompressedClassPointers) {
1096 // Copy gap missed by (aligned) header size calculation below
1097 obj->set_klass_gap(old->klass_gap());
1098 }
1099 if (word_sz > (size_t)oopDesc::header_size()) {
1100 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1101 obj_ptr + oopDesc::header_size(),
1102 word_sz - oopDesc::header_size());
1103 }
1104
1105 // Now we can track the promoted object, if necessary. We take care
1106 // to delay the transition from uninitialized to full object
1107 // (i.e., insertion of klass pointer) until after, so that it
1108 // atomically becomes a promoted object.
1109 if (promoInfo->tracking()) {
1110 promoInfo->track((PromotedObject*)obj, old->klass());
1111 }
1112 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1113 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1114 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1115
1116 // Finally, install the klass pointer (this should be volatile).
1117 OrderAccess::storestore();
1118 obj->set_klass(old->klass());
1119 // We should now be able to calculate the right size for this object
1120 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1121
1122 collector()->promoted(true, // parallel
1123 obj_ptr, old->is_objArray(), word_sz);
1124
1125 NOT_PRODUCT(
1126 Atomic::inc_ptr(&_numObjectsPromoted);
1127 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1128 )
1129
1130 return obj;
1131 }
1132
1133 void
1134 ConcurrentMarkSweepGeneration::
1135 par_promote_alloc_done(int thread_num) {
1136 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1137 ps->lab.retire(thread_num);
1138 }
1139
1140 void
1141 ConcurrentMarkSweepGeneration::
1142 par_oop_since_save_marks_iterate_done(int thread_num) {
1143 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1144 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1145 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1146 }
1147
1148 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1149 size_t size,
1150 bool tlab)
1151 {
1152 // We allow a STW collection only if a full
1153 // collection was requested.
1154 return full || should_allocate(size, tlab); // FIX ME !!!
1155 // This and promotion failure handling are connected at the
1156 // hip and should be fixed by untying them.
1157 }
1158
1159 bool CMSCollector::shouldConcurrentCollect() {
1160 if (_full_gc_requested) {
1161 if (Verbose && PrintGCDetails) {
1162 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1163 " gc request (or gc_locker)");
1164 }
1165 return true;
1166 }
1167
1168 FreelistLocker x(this);
1169 // ------------------------------------------------------------------
1170 // Print out lots of information which affects the initiation of
1171 // a collection.
1172 if (PrintCMSInitiationStatistics && stats().valid()) {
1173 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1174 gclog_or_tty->stamp();
1175 gclog_or_tty->cr();
1176 stats().print_on(gclog_or_tty);
1177 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1178 stats().time_until_cms_gen_full());
1179 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1180 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1181 _cmsGen->contiguous_available());
1182 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1183 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1184 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1185 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1186 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1187 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1188 gclog_or_tty->print_cr("metadata initialized %d",
1189 MetaspaceGC::should_concurrent_collect());
1190 }
1191 // ------------------------------------------------------------------
1192
1193 // If the estimated time to complete a cms collection (cms_duration())
1194 // is less than the estimated time remaining until the cms generation
1195 // is full, start a collection.
1196 if (!UseCMSInitiatingOccupancyOnly) {
1197 if (stats().valid()) {
1198 if (stats().time_until_cms_start() == 0.0) {
1199 return true;
1200 }
1201 } else {
1202 // We want to conservatively collect somewhat early in order
1203 // to try and "bootstrap" our CMS/promotion statistics;
1204 // this branch will not fire after the first successful CMS
1205 // collection because the stats should then be valid.
1206 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1207 if (Verbose && PrintGCDetails) {
1208 gclog_or_tty->print_cr(
1209 " CMSCollector: collect for bootstrapping statistics:"
1210 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1211 _bootstrap_occupancy);
1212 }
1213 return true;
1214 }
1215 }
1216 }
1217
1218 // Otherwise, we start a collection cycle if
1219 // old gen want a collection cycle started. Each may use
1220 // an appropriate criterion for making this decision.
1221 // XXX We need to make sure that the gen expansion
1222 // criterion dovetails well with this. XXX NEED TO FIX THIS
1223 if (_cmsGen->should_concurrent_collect()) {
1224 if (Verbose && PrintGCDetails) {
1225 gclog_or_tty->print_cr("CMS old gen initiated");
1226 }
1227 return true;
1228 }
1229
1230 // We start a collection if we believe an incremental collection may fail;
1231 // this is not likely to be productive in practice because it's probably too
1232 // late anyway.
1233 GenCollectedHeap* gch = GenCollectedHeap::heap();
1234 assert(gch->collector_policy()->is_generation_policy(),
1235 "You may want to check the correctness of the following");
1236 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1237 if (Verbose && PrintGCDetails) {
1238 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1239 }
1240 return true;
1241 }
1242
1243 if (MetaspaceGC::should_concurrent_collect()) {
1244 if (Verbose && PrintGCDetails) {
1245 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1246 }
1247 return true;
1248 }
1249
1250 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1251 if (CMSTriggerInterval >= 0) {
1252 if (CMSTriggerInterval == 0) {
1253 // Trigger always
1254 return true;
1255 }
1256
1257 // Check the CMS time since begin (we do not check the stats validity
1258 // as we want to be able to trigger the first CMS cycle as well)
1259 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1260 if (Verbose && PrintGCDetails) {
1261 if (stats().valid()) {
1262 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1263 stats().cms_time_since_begin());
1264 } else {
1265 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1266 }
1267 }
1268 return true;
1269 }
1270 }
1271
1272 return false;
1273 }
1274
1275 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1276
1277 // Clear _expansion_cause fields of constituent generations
1278 void CMSCollector::clear_expansion_cause() {
1279 _cmsGen->clear_expansion_cause();
1280 }
1281
1282 // We should be conservative in starting a collection cycle. To
1283 // start too eagerly runs the risk of collecting too often in the
1284 // extreme. To collect too rarely falls back on full collections,
1285 // which works, even if not optimum in terms of concurrent work.
1286 // As a work around for too eagerly collecting, use the flag
1287 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1288 // giving the user an easily understandable way of controlling the
1289 // collections.
1290 // We want to start a new collection cycle if any of the following
1291 // conditions hold:
1292 // . our current occupancy exceeds the configured initiating occupancy
1293 // for this generation, or
1294 // . we recently needed to expand this space and have not, since that
1295 // expansion, done a collection of this generation, or
1296 // . the underlying space believes that it may be a good idea to initiate
1297 // a concurrent collection (this may be based on criteria such as the
1298 // following: the space uses linear allocation and linear allocation is
1299 // going to fail, or there is believed to be excessive fragmentation in
1300 // the generation, etc... or ...
1301 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1302 // the case of the old generation; see CR 6543076):
1303 // we may be approaching a point at which allocation requests may fail because
1304 // we will be out of sufficient free space given allocation rate estimates.]
1305 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1306
1307 assert_lock_strong(freelistLock());
1308 if (occupancy() > initiating_occupancy()) {
1309 if (PrintGCDetails && Verbose) {
1310 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1311 short_name(), occupancy(), initiating_occupancy());
1312 }
1313 return true;
1314 }
1315 if (UseCMSInitiatingOccupancyOnly) {
1316 return false;
1317 }
1318 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1319 if (PrintGCDetails && Verbose) {
1320 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1321 short_name());
1322 }
1323 return true;
1324 }
1325 if (_cmsSpace->should_concurrent_collect()) {
1326 if (PrintGCDetails && Verbose) {
1327 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1328 short_name());
1329 }
1330 return true;
1331 }
1332 return false;
1333 }
1334
1335 void ConcurrentMarkSweepGeneration::collect(bool full,
1336 bool clear_all_soft_refs,
1337 size_t size,
1338 bool tlab)
1339 {
1340 collector()->collect(full, clear_all_soft_refs, size, tlab);
1341 }
1342
1343 void CMSCollector::collect(bool full,
1344 bool clear_all_soft_refs,
1345 size_t size,
1346 bool tlab)
1347 {
1348 // The following "if" branch is present for defensive reasons.
1349 // In the current uses of this interface, it can be replaced with:
1350 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1351 // But I am not placing that assert here to allow future
1352 // generality in invoking this interface.
1353 if (GC_locker::is_active()) {
1354 // A consistency test for GC_locker
1355 assert(GC_locker::needs_gc(), "Should have been set already");
1356 // Skip this foreground collection, instead
1357 // expanding the heap if necessary.
1358 // Need the free list locks for the call to free() in compute_new_size()
1359 compute_new_size();
1360 return;
1361 }
1362 acquire_control_and_collect(full, clear_all_soft_refs);
1363 }
1364
1365 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1366 GenCollectedHeap* gch = GenCollectedHeap::heap();
1367 unsigned int gc_count = gch->total_full_collections();
1368 if (gc_count == full_gc_count) {
1369 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1370 _full_gc_requested = true;
1371 _full_gc_cause = cause;
1372 CGC_lock->notify(); // nudge CMS thread
1373 } else {
1374 assert(gc_count > full_gc_count, "Error: causal loop");
1375 }
1376 }
1377
1378 bool CMSCollector::is_external_interruption() {
1379 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1380 return GCCause::is_user_requested_gc(cause) ||
1381 GCCause::is_serviceability_requested_gc(cause);
1382 }
1383
1384 void CMSCollector::report_concurrent_mode_interruption() {
1385 if (is_external_interruption()) {
1386 if (PrintGCDetails) {
1387 gclog_or_tty->print(" (concurrent mode interrupted)");
1388 }
1389 } else {
1390 if (PrintGCDetails) {
1391 gclog_or_tty->print(" (concurrent mode failure)");
1392 }
1393 _gc_tracer_cm->report_concurrent_mode_failure();
1394 }
1395 }
1396
1397
1398 // The foreground and background collectors need to coordinate in order
1399 // to make sure that they do not mutually interfere with CMS collections.
1400 // When a background collection is active,
1401 // the foreground collector may need to take over (preempt) and
1402 // synchronously complete an ongoing collection. Depending on the
1403 // frequency of the background collections and the heap usage
1404 // of the application, this preemption can be seldom or frequent.
1405 // There are only certain
1406 // points in the background collection that the "collection-baton"
1407 // can be passed to the foreground collector.
1408 //
1409 // The foreground collector will wait for the baton before
1410 // starting any part of the collection. The foreground collector
1411 // will only wait at one location.
1412 //
1413 // The background collector will yield the baton before starting a new
1414 // phase of the collection (e.g., before initial marking, marking from roots,
1415 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1416 // of the loop which switches the phases. The background collector does some
1417 // of the phases (initial mark, final re-mark) with the world stopped.
1418 // Because of locking involved in stopping the world,
1419 // the foreground collector should not block waiting for the background
1420 // collector when it is doing a stop-the-world phase. The background
1421 // collector will yield the baton at an additional point just before
1422 // it enters a stop-the-world phase. Once the world is stopped, the
1423 // background collector checks the phase of the collection. If the
1424 // phase has not changed, it proceeds with the collection. If the
1425 // phase has changed, it skips that phase of the collection. See
1426 // the comments on the use of the Heap_lock in collect_in_background().
1427 //
1428 // Variable used in baton passing.
1429 // _foregroundGCIsActive - Set to true by the foreground collector when
1430 // it wants the baton. The foreground clears it when it has finished
1431 // the collection.
1432 // _foregroundGCShouldWait - Set to true by the background collector
1433 // when it is running. The foreground collector waits while
1434 // _foregroundGCShouldWait is true.
1435 // CGC_lock - monitor used to protect access to the above variables
1436 // and to notify the foreground and background collectors.
1437 // _collectorState - current state of the CMS collection.
1438 //
1439 // The foreground collector
1440 // acquires the CGC_lock
1441 // sets _foregroundGCIsActive
1442 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1443 // various locks acquired in preparation for the collection
1444 // are released so as not to block the background collector
1445 // that is in the midst of a collection
1446 // proceeds with the collection
1447 // clears _foregroundGCIsActive
1448 // returns
1449 //
1450 // The background collector in a loop iterating on the phases of the
1451 // collection
1452 // acquires the CGC_lock
1453 // sets _foregroundGCShouldWait
1454 // if _foregroundGCIsActive is set
1455 // clears _foregroundGCShouldWait, notifies _CGC_lock
1456 // waits on _CGC_lock for _foregroundGCIsActive to become false
1457 // and exits the loop.
1458 // otherwise
1459 // proceed with that phase of the collection
1460 // if the phase is a stop-the-world phase,
1461 // yield the baton once more just before enqueueing
1462 // the stop-world CMS operation (executed by the VM thread).
1463 // returns after all phases of the collection are done
1464 //
1465
1466 void CMSCollector::acquire_control_and_collect(bool full,
1467 bool clear_all_soft_refs) {
1468 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1469 assert(!Thread::current()->is_ConcurrentGC_thread(),
1470 "shouldn't try to acquire control from self!");
1471
1472 // Start the protocol for acquiring control of the
1473 // collection from the background collector (aka CMS thread).
1474 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1475 "VM thread should have CMS token");
1476 // Remember the possibly interrupted state of an ongoing
1477 // concurrent collection
1478 CollectorState first_state = _collectorState;
1479
1480 // Signal to a possibly ongoing concurrent collection that
1481 // we want to do a foreground collection.
1482 _foregroundGCIsActive = true;
1483
1484 // release locks and wait for a notify from the background collector
1485 // releasing the locks in only necessary for phases which
1486 // do yields to improve the granularity of the collection.
1487 assert_lock_strong(bitMapLock());
1488 // We need to lock the Free list lock for the space that we are
1489 // currently collecting.
1490 assert(haveFreelistLocks(), "Must be holding free list locks");
1491 bitMapLock()->unlock();
1492 releaseFreelistLocks();
1493 {
1494 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1495 if (_foregroundGCShouldWait) {
1496 // We are going to be waiting for action for the CMS thread;
1497 // it had better not be gone (for instance at shutdown)!
1498 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1499 "CMS thread must be running");
1500 // Wait here until the background collector gives us the go-ahead
1501 ConcurrentMarkSweepThread::clear_CMS_flag(
1502 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1503 // Get a possibly blocked CMS thread going:
1504 // Note that we set _foregroundGCIsActive true above,
1505 // without protection of the CGC_lock.
1506 CGC_lock->notify();
1507 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1508 "Possible deadlock");
1509 while (_foregroundGCShouldWait) {
1510 // wait for notification
1511 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1512 // Possibility of delay/starvation here, since CMS token does
1513 // not know to give priority to VM thread? Actually, i think
1514 // there wouldn't be any delay/starvation, but the proof of
1515 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1516 }
1517 ConcurrentMarkSweepThread::set_CMS_flag(
1518 ConcurrentMarkSweepThread::CMS_vm_has_token);
1519 }
1520 }
1521 // The CMS_token is already held. Get back the other locks.
1522 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1523 "VM thread should have CMS token");
1524 getFreelistLocks();
1525 bitMapLock()->lock_without_safepoint_check();
1526 if (TraceCMSState) {
1527 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1528 INTPTR_FORMAT " with first state %d", p2i(Thread::current()), first_state);
1529 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1530 }
1531
1532 // Inform cms gen if this was due to partial collection failing.
1533 // The CMS gen may use this fact to determine its expansion policy.
1534 GenCollectedHeap* gch = GenCollectedHeap::heap();
1535 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1536 assert(!_cmsGen->incremental_collection_failed(),
1537 "Should have been noticed, reacted to and cleared");
1538 _cmsGen->set_incremental_collection_failed();
1539 }
1540
1541 if (first_state > Idling) {
1542 report_concurrent_mode_interruption();
1543 }
1544
1545 set_did_compact(true);
1546
1547 // If the collection is being acquired from the background
1548 // collector, there may be references on the discovered
1549 // references lists. Abandon those references, since some
1550 // of them may have become unreachable after concurrent
1551 // discovery; the STW compacting collector will redo discovery
1552 // more precisely, without being subject to floating garbage.
1553 // Leaving otherwise unreachable references in the discovered
1554 // lists would require special handling.
1555 ref_processor()->disable_discovery();
1556 ref_processor()->abandon_partial_discovery();
1557 ref_processor()->verify_no_references_recorded();
1558
1559 if (first_state > Idling) {
1560 save_heap_summary();
1561 }
1562
1563 do_compaction_work(clear_all_soft_refs);
1564
1565 // Has the GC time limit been exceeded?
1566 size_t max_eden_size = _young_gen->max_capacity() -
1567 _young_gen->to()->capacity() -
1568 _young_gen->from()->capacity();
1569 GCCause::Cause gc_cause = gch->gc_cause();
1570 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1571 _young_gen->eden()->used(),
1572 _cmsGen->max_capacity(),
1573 max_eden_size,
1574 full,
1575 gc_cause,
1576 gch->collector_policy());
1577
1578 // Reset the expansion cause, now that we just completed
1579 // a collection cycle.
1580 clear_expansion_cause();
1581 _foregroundGCIsActive = false;
1582 return;
1583 }
1584
1585 // Resize the tenured generation
1586 // after obtaining the free list locks for the
1587 // two generations.
1588 void CMSCollector::compute_new_size() {
1589 assert_locked_or_safepoint(Heap_lock);
1590 FreelistLocker z(this);
1591 MetaspaceGC::compute_new_size();
1592 _cmsGen->compute_new_size_free_list();
1593 }
1594
1595 // A work method used by the foreground collector to do
1596 // a mark-sweep-compact.
1597 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1598 GenCollectedHeap* gch = GenCollectedHeap::heap();
1599
1600 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1601 gc_timer->register_gc_start();
1602
1603 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1604 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1605
1606 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
1607
1608 // Temporarily widen the span of the weak reference processing to
1609 // the entire heap.
1610 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1611 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1612 // Temporarily, clear the "is_alive_non_header" field of the
1613 // reference processor.
1614 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1615 // Temporarily make reference _processing_ single threaded (non-MT).
1616 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1617 // Temporarily make refs discovery atomic
1618 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1619 // Temporarily make reference _discovery_ single threaded (non-MT)
1620 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1621
1622 ref_processor()->set_enqueuing_is_done(false);
1623 ref_processor()->enable_discovery();
1624 ref_processor()->setup_policy(clear_all_soft_refs);
1625 // If an asynchronous collection finishes, the _modUnionTable is
1626 // all clear. If we are assuming the collection from an asynchronous
1627 // collection, clear the _modUnionTable.
1628 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1629 "_modUnionTable should be clear if the baton was not passed");
1630 _modUnionTable.clear_all();
1631 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1632 "mod union for klasses should be clear if the baton was passed");
1633 _ct->klass_rem_set()->clear_mod_union();
1634
1635 // We must adjust the allocation statistics being maintained
1636 // in the free list space. We do so by reading and clearing
1637 // the sweep timer and updating the block flux rate estimates below.
1638 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1639 if (_inter_sweep_timer.is_active()) {
1640 _inter_sweep_timer.stop();
1641 // Note that we do not use this sample to update the _inter_sweep_estimate.
1642 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1643 _inter_sweep_estimate.padded_average(),
1644 _intra_sweep_estimate.padded_average());
1645 }
1646
1647 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1648 #ifdef ASSERT
1649 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1650 size_t free_size = cms_space->free();
1651 assert(free_size ==
1652 pointer_delta(cms_space->end(), cms_space->compaction_top())
1653 * HeapWordSize,
1654 "All the free space should be compacted into one chunk at top");
1655 assert(cms_space->dictionary()->total_chunk_size(
1656 debug_only(cms_space->freelistLock())) == 0 ||
1657 cms_space->totalSizeInIndexedFreeLists() == 0,
1658 "All the free space should be in a single chunk");
1659 size_t num = cms_space->totalCount();
1660 assert((free_size == 0 && num == 0) ||
1661 (free_size > 0 && (num == 1 || num == 2)),
1662 "There should be at most 2 free chunks after compaction");
1663 #endif // ASSERT
1664 _collectorState = Resetting;
1665 assert(_restart_addr == NULL,
1666 "Should have been NULL'd before baton was passed");
1667 reset(false /* == !concurrent */);
1668 _cmsGen->reset_after_compaction();
1669 _concurrent_cycles_since_last_unload = 0;
1670
1671 // Clear any data recorded in the PLAB chunk arrays.
1672 if (_survivor_plab_array != NULL) {
1673 reset_survivor_plab_arrays();
1674 }
1675
1676 // Adjust the per-size allocation stats for the next epoch.
1677 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1678 // Restart the "inter sweep timer" for the next epoch.
1679 _inter_sweep_timer.reset();
1680 _inter_sweep_timer.start();
1681
1682 gc_timer->register_gc_end();
1683
1684 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1685
1686 // For a mark-sweep-compact, compute_new_size() will be called
1687 // in the heap's do_collection() method.
1688 }
1689
1690 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1691 ContiguousSpace* eden_space = _young_gen->eden();
1692 ContiguousSpace* from_space = _young_gen->from();
1693 ContiguousSpace* to_space = _young_gen->to();
1694 // Eden
1695 if (_eden_chunk_array != NULL) {
1696 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1697 p2i(eden_space->bottom()), p2i(eden_space->top()),
1698 p2i(eden_space->end()), eden_space->capacity());
1699 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1700 "_eden_chunk_capacity=" SIZE_FORMAT,
1701 _eden_chunk_index, _eden_chunk_capacity);
1702 for (size_t i = 0; i < _eden_chunk_index; i++) {
1703 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1704 i, p2i(_eden_chunk_array[i]));
1705 }
1706 }
1707 // Survivor
1708 if (_survivor_chunk_array != NULL) {
1709 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1710 p2i(from_space->bottom()), p2i(from_space->top()),
1711 p2i(from_space->end()), from_space->capacity());
1712 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1713 "_survivor_chunk_capacity=" SIZE_FORMAT,
1714 _survivor_chunk_index, _survivor_chunk_capacity);
1715 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1716 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1717 i, p2i(_survivor_chunk_array[i]));
1718 }
1719 }
1720 }
1721
1722 void CMSCollector::getFreelistLocks() const {
1723 // Get locks for all free lists in all generations that this
1724 // collector is responsible for
1725 _cmsGen->freelistLock()->lock_without_safepoint_check();
1726 }
1727
1728 void CMSCollector::releaseFreelistLocks() const {
1729 // Release locks for all free lists in all generations that this
1730 // collector is responsible for
1731 _cmsGen->freelistLock()->unlock();
1732 }
1733
1734 bool CMSCollector::haveFreelistLocks() const {
1735 // Check locks for all free lists in all generations that this
1736 // collector is responsible for
1737 assert_lock_strong(_cmsGen->freelistLock());
1738 PRODUCT_ONLY(ShouldNotReachHere());
1739 return true;
1740 }
1741
1742 // A utility class that is used by the CMS collector to
1743 // temporarily "release" the foreground collector from its
1744 // usual obligation to wait for the background collector to
1745 // complete an ongoing phase before proceeding.
1746 class ReleaseForegroundGC: public StackObj {
1747 private:
1748 CMSCollector* _c;
1749 public:
1750 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1751 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1752 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1753 // allow a potentially blocked foreground collector to proceed
1754 _c->_foregroundGCShouldWait = false;
1755 if (_c->_foregroundGCIsActive) {
1756 CGC_lock->notify();
1757 }
1758 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1759 "Possible deadlock");
1760 }
1761
1762 ~ReleaseForegroundGC() {
1763 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1764 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1765 _c->_foregroundGCShouldWait = true;
1766 }
1767 };
1768
1769 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1770 assert(Thread::current()->is_ConcurrentGC_thread(),
1771 "A CMS asynchronous collection is only allowed on a CMS thread.");
1772
1773 GenCollectedHeap* gch = GenCollectedHeap::heap();
1774 {
1775 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1776 MutexLockerEx hl(Heap_lock, safepoint_check);
1777 FreelistLocker fll(this);
1778 MutexLockerEx x(CGC_lock, safepoint_check);
1779 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
1780 // The foreground collector is active or we're
1781 // not using asynchronous collections. Skip this
1782 // background collection.
1783 assert(!_foregroundGCShouldWait, "Should be clear");
1784 return;
1785 } else {
1786 assert(_collectorState == Idling, "Should be idling before start.");
1787 _collectorState = InitialMarking;
1788 register_gc_start(cause);
1789 // Reset the expansion cause, now that we are about to begin
1790 // a new cycle.
1791 clear_expansion_cause();
1792
1793 // Clear the MetaspaceGC flag since a concurrent collection
1794 // is starting but also clear it after the collection.
1795 MetaspaceGC::set_should_concurrent_collect(false);
1796 }
1797 // Decide if we want to enable class unloading as part of the
1798 // ensuing concurrent GC cycle.
1799 update_should_unload_classes();
1800 _full_gc_requested = false; // acks all outstanding full gc requests
1801 _full_gc_cause = GCCause::_no_gc;
1802 // Signal that we are about to start a collection
1803 gch->increment_total_full_collections(); // ... starting a collection cycle
1804 _collection_count_start = gch->total_full_collections();
1805 }
1806
1807 // Used for PrintGC
1808 size_t prev_used;
1809 if (PrintGC && Verbose) {
1810 prev_used = _cmsGen->used();
1811 }
1812
1813 // The change of the collection state is normally done at this level;
1814 // the exceptions are phases that are executed while the world is
1815 // stopped. For those phases the change of state is done while the
1816 // world is stopped. For baton passing purposes this allows the
1817 // background collector to finish the phase and change state atomically.
1818 // The foreground collector cannot wait on a phase that is done
1819 // while the world is stopped because the foreground collector already
1820 // has the world stopped and would deadlock.
1821 while (_collectorState != Idling) {
1822 if (TraceCMSState) {
1823 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
1824 p2i(Thread::current()), _collectorState);
1825 }
1826 // The foreground collector
1827 // holds the Heap_lock throughout its collection.
1828 // holds the CMS token (but not the lock)
1829 // except while it is waiting for the background collector to yield.
1830 //
1831 // The foreground collector should be blocked (not for long)
1832 // if the background collector is about to start a phase
1833 // executed with world stopped. If the background
1834 // collector has already started such a phase, the
1835 // foreground collector is blocked waiting for the
1836 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1837 // are executed in the VM thread.
1838 //
1839 // The locking order is
1840 // PendingListLock (PLL) -- if applicable (FinalMarking)
1841 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1842 // CMS token (claimed in
1843 // stop_world_and_do() -->
1844 // safepoint_synchronize() -->
1845 // CMSThread::synchronize())
1846
1847 {
1848 // Check if the FG collector wants us to yield.
1849 CMSTokenSync x(true); // is cms thread
1850 if (waitForForegroundGC()) {
1851 // We yielded to a foreground GC, nothing more to be
1852 // done this round.
1853 assert(_foregroundGCShouldWait == false, "We set it to false in "
1854 "waitForForegroundGC()");
1855 if (TraceCMSState) {
1856 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1857 " exiting collection CMS state %d",
1858 p2i(Thread::current()), _collectorState);
1859 }
1860 return;
1861 } else {
1862 // The background collector can run but check to see if the
1863 // foreground collector has done a collection while the
1864 // background collector was waiting to get the CGC_lock
1865 // above. If yes, break so that _foregroundGCShouldWait
1866 // is cleared before returning.
1867 if (_collectorState == Idling) {
1868 break;
1869 }
1870 }
1871 }
1872
1873 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1874 "should be waiting");
1875
1876 switch (_collectorState) {
1877 case InitialMarking:
1878 {
1879 ReleaseForegroundGC x(this);
1880 stats().record_cms_begin();
1881 VM_CMS_Initial_Mark initial_mark_op(this);
1882 VMThread::execute(&initial_mark_op);
1883 }
1884 // The collector state may be any legal state at this point
1885 // since the background collector may have yielded to the
1886 // foreground collector.
1887 break;
1888 case Marking:
1889 // initial marking in checkpointRootsInitialWork has been completed
1890 if (markFromRoots()) { // we were successful
1891 assert(_collectorState == Precleaning, "Collector state should "
1892 "have changed");
1893 } else {
1894 assert(_foregroundGCIsActive, "Internal state inconsistency");
1895 }
1896 break;
1897 case Precleaning:
1898 // marking from roots in markFromRoots has been completed
1899 preclean();
1900 assert(_collectorState == AbortablePreclean ||
1901 _collectorState == FinalMarking,
1902 "Collector state should have changed");
1903 break;
1904 case AbortablePreclean:
1905 abortable_preclean();
1906 assert(_collectorState == FinalMarking, "Collector state should "
1907 "have changed");
1908 break;
1909 case FinalMarking:
1910 {
1911 ReleaseForegroundGC x(this);
1912
1913 VM_CMS_Final_Remark final_remark_op(this);
1914 VMThread::execute(&final_remark_op);
1915 }
1916 assert(_foregroundGCShouldWait, "block post-condition");
1917 break;
1918 case Sweeping:
1919 // final marking in checkpointRootsFinal has been completed
1920 sweep();
1921 assert(_collectorState == Resizing, "Collector state change "
1922 "to Resizing must be done under the free_list_lock");
1923
1924 case Resizing: {
1925 // Sweeping has been completed...
1926 // At this point the background collection has completed.
1927 // Don't move the call to compute_new_size() down
1928 // into code that might be executed if the background
1929 // collection was preempted.
1930 {
1931 ReleaseForegroundGC x(this); // unblock FG collection
1932 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1933 CMSTokenSync z(true); // not strictly needed.
1934 if (_collectorState == Resizing) {
1935 compute_new_size();
1936 save_heap_summary();
1937 _collectorState = Resetting;
1938 } else {
1939 assert(_collectorState == Idling, "The state should only change"
1940 " because the foreground collector has finished the collection");
1941 }
1942 }
1943 break;
1944 }
1945 case Resetting:
1946 // CMS heap resizing has been completed
1947 reset(true);
1948 assert(_collectorState == Idling, "Collector state should "
1949 "have changed");
1950
1951 MetaspaceGC::set_should_concurrent_collect(false);
1952
1953 stats().record_cms_end();
1954 // Don't move the concurrent_phases_end() and compute_new_size()
1955 // calls to here because a preempted background collection
1956 // has it's state set to "Resetting".
1957 break;
1958 case Idling:
1959 default:
1960 ShouldNotReachHere();
1961 break;
1962 }
1963 if (TraceCMSState) {
1964 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1965 p2i(Thread::current()), _collectorState);
1966 }
1967 assert(_foregroundGCShouldWait, "block post-condition");
1968 }
1969
1970 // Should this be in gc_epilogue?
1971 collector_policy()->counters()->update_counters();
1972
1973 {
1974 // Clear _foregroundGCShouldWait and, in the event that the
1975 // foreground collector is waiting, notify it, before
1976 // returning.
1977 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1978 _foregroundGCShouldWait = false;
1979 if (_foregroundGCIsActive) {
1980 CGC_lock->notify();
1981 }
1982 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1983 "Possible deadlock");
1984 }
1985 if (TraceCMSState) {
1986 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1987 " exiting collection CMS state %d",
1988 p2i(Thread::current()), _collectorState);
1989 }
1990 if (PrintGC && Verbose) {
1991 _cmsGen->print_heap_change(prev_used);
1992 }
1993 }
1994
1995 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1996 _cms_start_registered = true;
1997 _gc_timer_cm->register_gc_start();
1998 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1999 }
2000
2001 void CMSCollector::register_gc_end() {
2002 if (_cms_start_registered) {
2003 report_heap_summary(GCWhen::AfterGC);
2004
2005 _gc_timer_cm->register_gc_end();
2006 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2007 _cms_start_registered = false;
2008 }
2009 }
2010
2011 void CMSCollector::save_heap_summary() {
2012 GenCollectedHeap* gch = GenCollectedHeap::heap();
2013 _last_heap_summary = gch->create_heap_summary();
2014 _last_metaspace_summary = gch->create_metaspace_summary();
2015 }
2016
2017 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2018 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2019 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2020 }
2021
2022 bool CMSCollector::waitForForegroundGC() {
2023 bool res = false;
2024 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2025 "CMS thread should have CMS token");
2026 // Block the foreground collector until the
2027 // background collectors decides whether to
2028 // yield.
2029 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2030 _foregroundGCShouldWait = true;
2031 if (_foregroundGCIsActive) {
2032 // The background collector yields to the
2033 // foreground collector and returns a value
2034 // indicating that it has yielded. The foreground
2035 // collector can proceed.
2036 res = true;
2037 _foregroundGCShouldWait = false;
2038 ConcurrentMarkSweepThread::clear_CMS_flag(
2039 ConcurrentMarkSweepThread::CMS_cms_has_token);
2040 ConcurrentMarkSweepThread::set_CMS_flag(
2041 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2042 // Get a possibly blocked foreground thread going
2043 CGC_lock->notify();
2044 if (TraceCMSState) {
2045 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2046 p2i(Thread::current()), _collectorState);
2047 }
2048 while (_foregroundGCIsActive) {
2049 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2050 }
2051 ConcurrentMarkSweepThread::set_CMS_flag(
2052 ConcurrentMarkSweepThread::CMS_cms_has_token);
2053 ConcurrentMarkSweepThread::clear_CMS_flag(
2054 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2055 }
2056 if (TraceCMSState) {
2057 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2058 p2i(Thread::current()), _collectorState);
2059 }
2060 return res;
2061 }
2062
2063 // Because of the need to lock the free lists and other structures in
2064 // the collector, common to all the generations that the collector is
2065 // collecting, we need the gc_prologues of individual CMS generations
2066 // delegate to their collector. It may have been simpler had the
2067 // current infrastructure allowed one to call a prologue on a
2068 // collector. In the absence of that we have the generation's
2069 // prologue delegate to the collector, which delegates back
2070 // some "local" work to a worker method in the individual generations
2071 // that it's responsible for collecting, while itself doing any
2072 // work common to all generations it's responsible for. A similar
2073 // comment applies to the gc_epilogue()'s.
2074 // The role of the variable _between_prologue_and_epilogue is to
2075 // enforce the invocation protocol.
2076 void CMSCollector::gc_prologue(bool full) {
2077 // Call gc_prologue_work() for the CMSGen
2078 // we are responsible for.
2079
2080 // The following locking discipline assumes that we are only called
2081 // when the world is stopped.
2082 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2083
2084 // The CMSCollector prologue must call the gc_prologues for the
2085 // "generations" that it's responsible
2086 // for.
2087
2088 assert( Thread::current()->is_VM_thread()
2089 || ( CMSScavengeBeforeRemark
2090 && Thread::current()->is_ConcurrentGC_thread()),
2091 "Incorrect thread type for prologue execution");
2092
2093 if (_between_prologue_and_epilogue) {
2094 // We have already been invoked; this is a gc_prologue delegation
2095 // from yet another CMS generation that we are responsible for, just
2096 // ignore it since all relevant work has already been done.
2097 return;
2098 }
2099
2100 // set a bit saying prologue has been called; cleared in epilogue
2101 _between_prologue_and_epilogue = true;
2102 // Claim locks for common data structures, then call gc_prologue_work()
2103 // for each CMSGen.
2104
2105 getFreelistLocks(); // gets free list locks on constituent spaces
2106 bitMapLock()->lock_without_safepoint_check();
2107
2108 // Should call gc_prologue_work() for all cms gens we are responsible for
2109 bool duringMarking = _collectorState >= Marking
2110 && _collectorState < Sweeping;
2111
2112 // The young collections clear the modified oops state, which tells if
2113 // there are any modified oops in the class. The remark phase also needs
2114 // that information. Tell the young collection to save the union of all
2115 // modified klasses.
2116 if (duringMarking) {
2117 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2118 }
2119
2120 bool registerClosure = duringMarking;
2121
2122 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2123
2124 if (!full) {
2125 stats().record_gc0_begin();
2126 }
2127 }
2128
2129 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2130
2131 _capacity_at_prologue = capacity();
2132 _used_at_prologue = used();
2133
2134 // Delegate to CMScollector which knows how to coordinate between
2135 // this and any other CMS generations that it is responsible for
2136 // collecting.
2137 collector()->gc_prologue(full);
2138 }
2139
2140 // This is a "private" interface for use by this generation's CMSCollector.
2141 // Not to be called directly by any other entity (for instance,
2142 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2143 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2144 bool registerClosure, ModUnionClosure* modUnionClosure) {
2145 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2146 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2147 "Should be NULL");
2148 if (registerClosure) {
2149 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2150 }
2151 cmsSpace()->gc_prologue();
2152 // Clear stat counters
2153 NOT_PRODUCT(
2154 assert(_numObjectsPromoted == 0, "check");
2155 assert(_numWordsPromoted == 0, "check");
2156 if (Verbose && PrintGC) {
2157 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2158 SIZE_FORMAT" bytes concurrently",
2159 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2160 }
2161 _numObjectsAllocated = 0;
2162 _numWordsAllocated = 0;
2163 )
2164 }
2165
2166 void CMSCollector::gc_epilogue(bool full) {
2167 // The following locking discipline assumes that we are only called
2168 // when the world is stopped.
2169 assert(SafepointSynchronize::is_at_safepoint(),
2170 "world is stopped assumption");
2171
2172 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2173 // if linear allocation blocks need to be appropriately marked to allow the
2174 // the blocks to be parsable. We also check here whether we need to nudge the
2175 // CMS collector thread to start a new cycle (if it's not already active).
2176 assert( Thread::current()->is_VM_thread()
2177 || ( CMSScavengeBeforeRemark
2178 && Thread::current()->is_ConcurrentGC_thread()),
2179 "Incorrect thread type for epilogue execution");
2180
2181 if (!_between_prologue_and_epilogue) {
2182 // We have already been invoked; this is a gc_epilogue delegation
2183 // from yet another CMS generation that we are responsible for, just
2184 // ignore it since all relevant work has already been done.
2185 return;
2186 }
2187 assert(haveFreelistLocks(), "must have freelist locks");
2188 assert_lock_strong(bitMapLock());
2189
2190 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2191
2192 _cmsGen->gc_epilogue_work(full);
2193
2194 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2195 // in case sampling was not already enabled, enable it
2196 _start_sampling = true;
2197 }
2198 // reset _eden_chunk_array so sampling starts afresh
2199 _eden_chunk_index = 0;
2200
2201 size_t cms_used = _cmsGen->cmsSpace()->used();
2202
2203 // update performance counters - this uses a special version of
2204 // update_counters() that allows the utilization to be passed as a
2205 // parameter, avoiding multiple calls to used().
2206 //
2207 _cmsGen->update_counters(cms_used);
2208
2209 bitMapLock()->unlock();
2210 releaseFreelistLocks();
2211
2212 if (!CleanChunkPoolAsync) {
2213 Chunk::clean_chunk_pool();
2214 }
2215
2216 set_did_compact(false);
2217 _between_prologue_and_epilogue = false; // ready for next cycle
2218 }
2219
2220 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2221 collector()->gc_epilogue(full);
2222
2223 // Also reset promotion tracking in par gc thread states.
2224 for (uint i = 0; i < ParallelGCThreads; i++) {
2225 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2226 }
2227 }
2228
2229 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2230 assert(!incremental_collection_failed(), "Should have been cleared");
2231 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2232 cmsSpace()->gc_epilogue();
2233 // Print stat counters
2234 NOT_PRODUCT(
2235 assert(_numObjectsAllocated == 0, "check");
2236 assert(_numWordsAllocated == 0, "check");
2237 if (Verbose && PrintGC) {
2238 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2239 SIZE_FORMAT" bytes",
2240 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2241 }
2242 _numObjectsPromoted = 0;
2243 _numWordsPromoted = 0;
2244 )
2245
2246 if (PrintGC && Verbose) {
2247 // Call down the chain in contiguous_available needs the freelistLock
2248 // so print this out before releasing the freeListLock.
2249 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2250 contiguous_available());
2251 }
2252 }
2253
2254 #ifndef PRODUCT
2255 bool CMSCollector::have_cms_token() {
2256 Thread* thr = Thread::current();
2257 if (thr->is_VM_thread()) {
2258 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2259 } else if (thr->is_ConcurrentGC_thread()) {
2260 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2261 } else if (thr->is_GC_task_thread()) {
2262 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2263 ParGCRareEvent_lock->owned_by_self();
2264 }
2265 return false;
2266 }
2267 #endif
2268
2269 // Check reachability of the given heap address in CMS generation,
2270 // treating all other generations as roots.
2271 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2272 // We could "guarantee" below, rather than assert, but I'll
2273 // leave these as "asserts" so that an adventurous debugger
2274 // could try this in the product build provided some subset of
2275 // the conditions were met, provided they were interested in the
2276 // results and knew that the computation below wouldn't interfere
2277 // with other concurrent computations mutating the structures
2278 // being read or written.
2279 assert(SafepointSynchronize::is_at_safepoint(),
2280 "Else mutations in object graph will make answer suspect");
2281 assert(have_cms_token(), "Should hold cms token");
2282 assert(haveFreelistLocks(), "must hold free list locks");
2283 assert_lock_strong(bitMapLock());
2284
2285 // Clear the marking bit map array before starting, but, just
2286 // for kicks, first report if the given address is already marked
2287 gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2288 _markBitMap.isMarked(addr) ? "" : " not");
2289
2290 if (verify_after_remark()) {
2291 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2292 bool result = verification_mark_bm()->isMarked(addr);
2293 gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2294 result ? "IS" : "is NOT");
2295 return result;
2296 } else {
2297 gclog_or_tty->print_cr("Could not compute result");
2298 return false;
2299 }
2300 }
2301
2302
2303 void
2304 CMSCollector::print_on_error(outputStream* st) {
2305 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2306 if (collector != NULL) {
2307 CMSBitMap* bitmap = &collector->_markBitMap;
2308 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2309 bitmap->print_on_error(st, " Bits: ");
2310
2311 st->cr();
2312
2313 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2314 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2315 mut_bitmap->print_on_error(st, " Bits: ");
2316 }
2317 }
2318
2319 ////////////////////////////////////////////////////////
2320 // CMS Verification Support
2321 ////////////////////////////////////////////////////////
2322 // Following the remark phase, the following invariant
2323 // should hold -- each object in the CMS heap which is
2324 // marked in markBitMap() should be marked in the verification_mark_bm().
2325
2326 class VerifyMarkedClosure: public BitMapClosure {
2327 CMSBitMap* _marks;
2328 bool _failed;
2329
2330 public:
2331 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2332
2333 bool do_bit(size_t offset) {
2334 HeapWord* addr = _marks->offsetToHeapWord(offset);
2335 if (!_marks->isMarked(addr)) {
2336 oop(addr)->print_on(gclog_or_tty);
2337 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", p2i(addr));
2338 _failed = true;
2339 }
2340 return true;
2341 }
2342
2343 bool failed() { return _failed; }
2344 };
2345
2346 bool CMSCollector::verify_after_remark(bool silent) {
2347 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2348 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2349 static bool init = false;
2350
2351 assert(SafepointSynchronize::is_at_safepoint(),
2352 "Else mutations in object graph will make answer suspect");
2353 assert(have_cms_token(),
2354 "Else there may be mutual interference in use of "
2355 " verification data structures");
2356 assert(_collectorState > Marking && _collectorState <= Sweeping,
2357 "Else marking info checked here may be obsolete");
2358 assert(haveFreelistLocks(), "must hold free list locks");
2359 assert_lock_strong(bitMapLock());
2360
2361
2362 // Allocate marking bit map if not already allocated
2363 if (!init) { // first time
2364 if (!verification_mark_bm()->allocate(_span)) {
2365 return false;
2366 }
2367 init = true;
2368 }
2369
2370 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2371
2372 // Turn off refs discovery -- so we will be tracing through refs.
2373 // This is as intended, because by this time
2374 // GC must already have cleared any refs that need to be cleared,
2375 // and traced those that need to be marked; moreover,
2376 // the marking done here is not going to interfere in any
2377 // way with the marking information used by GC.
2378 NoRefDiscovery no_discovery(ref_processor());
2379
2380 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2381
2382 // Clear any marks from a previous round
2383 verification_mark_bm()->clear_all();
2384 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2385 verify_work_stacks_empty();
2386
2387 GenCollectedHeap* gch = GenCollectedHeap::heap();
2388 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2389 // Update the saved marks which may affect the root scans.
2390 gch->save_marks();
2391
2392 if (CMSRemarkVerifyVariant == 1) {
2393 // In this first variant of verification, we complete
2394 // all marking, then check if the new marks-vector is
2395 // a subset of the CMS marks-vector.
2396 verify_after_remark_work_1();
2397 } else if (CMSRemarkVerifyVariant == 2) {
2398 // In this second variant of verification, we flag an error
2399 // (i.e. an object reachable in the new marks-vector not reachable
2400 // in the CMS marks-vector) immediately, also indicating the
2401 // identify of an object (A) that references the unmarked object (B) --
2402 // presumably, a mutation to A failed to be picked up by preclean/remark?
2403 verify_after_remark_work_2();
2404 } else {
2405 warning("Unrecognized value " UINTX_FORMAT " for CMSRemarkVerifyVariant",
2406 CMSRemarkVerifyVariant);
2407 }
2408 if (!silent) gclog_or_tty->print(" done] ");
2409 return true;
2410 }
2411
2412 void CMSCollector::verify_after_remark_work_1() {
2413 ResourceMark rm;
2414 HandleMark hm;
2415 GenCollectedHeap* gch = GenCollectedHeap::heap();
2416
2417 // Get a clear set of claim bits for the roots processing to work with.
2418 ClassLoaderDataGraph::clear_claimed_marks();
2419
2420 // Mark from roots one level into CMS
2421 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2422 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2423
2424 {
2425 StrongRootsScope srs(1);
2426
2427 gch->gen_process_roots(&srs,
2428 Generation::Old,
2429 true, // younger gens are roots
2430 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2431 should_unload_classes(),
2432 ¬Older,
2433 NULL,
2434 NULL);
2435 }
2436
2437 // Now mark from the roots
2438 MarkFromRootsClosure markFromRootsClosure(this, _span,
2439 verification_mark_bm(), verification_mark_stack(),
2440 false /* don't yield */, true /* verifying */);
2441 assert(_restart_addr == NULL, "Expected pre-condition");
2442 verification_mark_bm()->iterate(&markFromRootsClosure);
2443 while (_restart_addr != NULL) {
2444 // Deal with stack overflow: by restarting at the indicated
2445 // address.
2446 HeapWord* ra = _restart_addr;
2447 markFromRootsClosure.reset(ra);
2448 _restart_addr = NULL;
2449 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2450 }
2451 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2452 verify_work_stacks_empty();
2453
2454 // Marking completed -- now verify that each bit marked in
2455 // verification_mark_bm() is also marked in markBitMap(); flag all
2456 // errors by printing corresponding objects.
2457 VerifyMarkedClosure vcl(markBitMap());
2458 verification_mark_bm()->iterate(&vcl);
2459 if (vcl.failed()) {
2460 gclog_or_tty->print("Verification failed");
2461 gch->print_on(gclog_or_tty);
2462 fatal("CMS: failed marking verification after remark");
2463 }
2464 }
2465
2466 class VerifyKlassOopsKlassClosure : public KlassClosure {
2467 class VerifyKlassOopsClosure : public OopClosure {
2468 CMSBitMap* _bitmap;
2469 public:
2470 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2471 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2472 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2473 } _oop_closure;
2474 public:
2475 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2476 void do_klass(Klass* k) {
2477 k->oops_do(&_oop_closure);
2478 }
2479 };
2480
2481 void CMSCollector::verify_after_remark_work_2() {
2482 ResourceMark rm;
2483 HandleMark hm;
2484 GenCollectedHeap* gch = GenCollectedHeap::heap();
2485
2486 // Get a clear set of claim bits for the roots processing to work with.
2487 ClassLoaderDataGraph::clear_claimed_marks();
2488
2489 // Mark from roots one level into CMS
2490 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2491 markBitMap());
2492 CLDToOopClosure cld_closure(¬Older, true);
2493
2494 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2495
2496 {
2497 StrongRootsScope srs(1);
2498
2499 gch->gen_process_roots(&srs,
2500 Generation::Old,
2501 true, // younger gens are roots
2502 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2503 should_unload_classes(),
2504 ¬Older,
2505 NULL,
2506 &cld_closure);
2507 }
2508
2509 // Now mark from the roots
2510 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2511 verification_mark_bm(), markBitMap(), verification_mark_stack());
2512 assert(_restart_addr == NULL, "Expected pre-condition");
2513 verification_mark_bm()->iterate(&markFromRootsClosure);
2514 while (_restart_addr != NULL) {
2515 // Deal with stack overflow: by restarting at the indicated
2516 // address.
2517 HeapWord* ra = _restart_addr;
2518 markFromRootsClosure.reset(ra);
2519 _restart_addr = NULL;
2520 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2521 }
2522 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2523 verify_work_stacks_empty();
2524
2525 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2526 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2527
2528 // Marking completed -- now verify that each bit marked in
2529 // verification_mark_bm() is also marked in markBitMap(); flag all
2530 // errors by printing corresponding objects.
2531 VerifyMarkedClosure vcl(markBitMap());
2532 verification_mark_bm()->iterate(&vcl);
2533 assert(!vcl.failed(), "Else verification above should not have succeeded");
2534 }
2535
2536 void ConcurrentMarkSweepGeneration::save_marks() {
2537 // delegate to CMS space
2538 cmsSpace()->save_marks();
2539 for (uint i = 0; i < ParallelGCThreads; i++) {
2540 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2541 }
2542 }
2543
2544 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2545 return cmsSpace()->no_allocs_since_save_marks();
2546 }
2547
2548 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2549 \
2550 void ConcurrentMarkSweepGeneration:: \
2551 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2552 cl->set_generation(this); \
2553 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2554 cl->reset_generation(); \
2555 save_marks(); \
2556 }
2557
2558 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2559
2560 void
2561 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2562 if (freelistLock()->owned_by_self()) {
2563 Generation::oop_iterate(cl);
2564 } else {
2565 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2566 Generation::oop_iterate(cl);
2567 }
2568 }
2569
2570 void
2571 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2572 if (freelistLock()->owned_by_self()) {
2573 Generation::object_iterate(cl);
2574 } else {
2575 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2576 Generation::object_iterate(cl);
2577 }
2578 }
2579
2580 void
2581 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2582 if (freelistLock()->owned_by_self()) {
2583 Generation::safe_object_iterate(cl);
2584 } else {
2585 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2586 Generation::safe_object_iterate(cl);
2587 }
2588 }
2589
2590 void
2591 ConcurrentMarkSweepGeneration::post_compact() {
2592 }
2593
2594 void
2595 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2596 // Fix the linear allocation blocks to look like free blocks.
2597
2598 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2599 // are not called when the heap is verified during universe initialization and
2600 // at vm shutdown.
2601 if (freelistLock()->owned_by_self()) {
2602 cmsSpace()->prepare_for_verify();
2603 } else {
2604 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2605 cmsSpace()->prepare_for_verify();
2606 }
2607 }
2608
2609 void
2610 ConcurrentMarkSweepGeneration::verify() {
2611 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2612 // are not called when the heap is verified during universe initialization and
2613 // at vm shutdown.
2614 if (freelistLock()->owned_by_self()) {
2615 cmsSpace()->verify();
2616 } else {
2617 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2618 cmsSpace()->verify();
2619 }
2620 }
2621
2622 void CMSCollector::verify() {
2623 _cmsGen->verify();
2624 }
2625
2626 #ifndef PRODUCT
2627 bool CMSCollector::overflow_list_is_empty() const {
2628 assert(_num_par_pushes >= 0, "Inconsistency");
2629 if (_overflow_list == NULL) {
2630 assert(_num_par_pushes == 0, "Inconsistency");
2631 }
2632 return _overflow_list == NULL;
2633 }
2634
2635 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2636 // merely consolidate assertion checks that appear to occur together frequently.
2637 void CMSCollector::verify_work_stacks_empty() const {
2638 assert(_markStack.isEmpty(), "Marking stack should be empty");
2639 assert(overflow_list_is_empty(), "Overflow list should be empty");
2640 }
2641
2642 void CMSCollector::verify_overflow_empty() const {
2643 assert(overflow_list_is_empty(), "Overflow list should be empty");
2644 assert(no_preserved_marks(), "No preserved marks");
2645 }
2646 #endif // PRODUCT
2647
2648 // Decide if we want to enable class unloading as part of the
2649 // ensuing concurrent GC cycle. We will collect and
2650 // unload classes if it's the case that:
2651 // (1) an explicit gc request has been made and the flag
2652 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2653 // (2) (a) class unloading is enabled at the command line, and
2654 // (b) old gen is getting really full
2655 // NOTE: Provided there is no change in the state of the heap between
2656 // calls to this method, it should have idempotent results. Moreover,
2657 // its results should be monotonically increasing (i.e. going from 0 to 1,
2658 // but not 1 to 0) between successive calls between which the heap was
2659 // not collected. For the implementation below, it must thus rely on
2660 // the property that concurrent_cycles_since_last_unload()
2661 // will not decrease unless a collection cycle happened and that
2662 // _cmsGen->is_too_full() are
2663 // themselves also monotonic in that sense. See check_monotonicity()
2664 // below.
2665 void CMSCollector::update_should_unload_classes() {
2666 _should_unload_classes = false;
2667 // Condition 1 above
2668 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2669 _should_unload_classes = true;
2670 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2671 // Disjuncts 2.b.(i,ii,iii) above
2672 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2673 CMSClassUnloadingMaxInterval)
2674 || _cmsGen->is_too_full();
2675 }
2676 }
2677
2678 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2679 bool res = should_concurrent_collect();
2680 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2681 return res;
2682 }
2683
2684 void CMSCollector::setup_cms_unloading_and_verification_state() {
2685 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2686 || VerifyBeforeExit;
2687 const int rso = GenCollectedHeap::SO_AllCodeCache;
2688
2689 // We set the proper root for this CMS cycle here.
2690 if (should_unload_classes()) { // Should unload classes this cycle
2691 remove_root_scanning_option(rso); // Shrink the root set appropriately
2692 set_verifying(should_verify); // Set verification state for this cycle
2693 return; // Nothing else needs to be done at this time
2694 }
2695
2696 // Not unloading classes this cycle
2697 assert(!should_unload_classes(), "Inconsistency!");
2698
2699 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2700 // Include symbols, strings and code cache elements to prevent their resurrection.
2701 add_root_scanning_option(rso);
2702 set_verifying(true);
2703 } else if (verifying() && !should_verify) {
2704 // We were verifying, but some verification flags got disabled.
2705 set_verifying(false);
2706 // Exclude symbols, strings and code cache elements from root scanning to
2707 // reduce IM and RM pauses.
2708 remove_root_scanning_option(rso);
2709 }
2710 }
2711
2712
2713 #ifndef PRODUCT
2714 HeapWord* CMSCollector::block_start(const void* p) const {
2715 const HeapWord* addr = (HeapWord*)p;
2716 if (_span.contains(p)) {
2717 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2718 return _cmsGen->cmsSpace()->block_start(p);
2719 }
2720 }
2721 return NULL;
2722 }
2723 #endif
2724
2725 HeapWord*
2726 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2727 bool tlab,
2728 bool parallel) {
2729 CMSSynchronousYieldRequest yr;
2730 assert(!tlab, "Can't deal with TLAB allocation");
2731 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2732 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2733 if (GCExpandToAllocateDelayMillis > 0) {
2734 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2735 }
2736 return have_lock_and_allocate(word_size, tlab);
2737 }
2738
2739 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2740 size_t bytes,
2741 size_t expand_bytes,
2742 CMSExpansionCause::Cause cause)
2743 {
2744
2745 bool success = expand(bytes, expand_bytes);
2746
2747 // remember why we expanded; this information is used
2748 // by shouldConcurrentCollect() when making decisions on whether to start
2749 // a new CMS cycle.
2750 if (success) {
2751 set_expansion_cause(cause);
2752 if (PrintGCDetails && Verbose) {
2753 gclog_or_tty->print_cr("Expanded CMS gen for %s",
2754 CMSExpansionCause::to_string(cause));
2755 }
2756 }
2757 }
2758
2759 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2760 HeapWord* res = NULL;
2761 MutexLocker x(ParGCRareEvent_lock);
2762 while (true) {
2763 // Expansion by some other thread might make alloc OK now:
2764 res = ps->lab.alloc(word_sz);
2765 if (res != NULL) return res;
2766 // If there's not enough expansion space available, give up.
2767 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2768 return NULL;
2769 }
2770 // Otherwise, we try expansion.
2771 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2772 // Now go around the loop and try alloc again;
2773 // A competing par_promote might beat us to the expansion space,
2774 // so we may go around the loop again if promotion fails again.
2775 if (GCExpandToAllocateDelayMillis > 0) {
2776 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2777 }
2778 }
2779 }
2780
2781
2782 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2783 PromotionInfo* promo) {
2784 MutexLocker x(ParGCRareEvent_lock);
2785 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2786 while (true) {
2787 // Expansion by some other thread might make alloc OK now:
2788 if (promo->ensure_spooling_space()) {
2789 assert(promo->has_spooling_space(),
2790 "Post-condition of successful ensure_spooling_space()");
2791 return true;
2792 }
2793 // If there's not enough expansion space available, give up.
2794 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2795 return false;
2796 }
2797 // Otherwise, we try expansion.
2798 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2799 // Now go around the loop and try alloc again;
2800 // A competing allocation might beat us to the expansion space,
2801 // so we may go around the loop again if allocation fails again.
2802 if (GCExpandToAllocateDelayMillis > 0) {
2803 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2804 }
2805 }
2806 }
2807
2808 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2809 // Only shrink if a compaction was done so that all the free space
2810 // in the generation is in a contiguous block at the end.
2811 if (did_compact()) {
2812 CardGeneration::shrink(bytes);
2813 }
2814 }
2815
2816 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2817 assert_locked_or_safepoint(Heap_lock);
2818 }
2819
2820 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2821 assert_locked_or_safepoint(Heap_lock);
2822 assert_lock_strong(freelistLock());
2823 if (PrintGCDetails && Verbose) {
2824 warning("Shrinking of CMS not yet implemented");
2825 }
2826 return;
2827 }
2828
2829
2830 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2831 // phases.
2832 class CMSPhaseAccounting: public StackObj {
2833 public:
2834 CMSPhaseAccounting(CMSCollector *collector,
2835 const char *phase,
2836 const GCId gc_id,
2837 bool print_cr = true);
2838 ~CMSPhaseAccounting();
2839
2840 private:
2841 CMSCollector *_collector;
2842 const char *_phase;
2843 elapsedTimer _wallclock;
2844 bool _print_cr;
2845 const GCId _gc_id;
2846
2847 public:
2848 // Not MT-safe; so do not pass around these StackObj's
2849 // where they may be accessed by other threads.
2850 jlong wallclock_millis() {
2851 assert(_wallclock.is_active(), "Wall clock should not stop");
2852 _wallclock.stop(); // to record time
2853 jlong ret = _wallclock.milliseconds();
2854 _wallclock.start(); // restart
2855 return ret;
2856 }
2857 };
2858
2859 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2860 const char *phase,
2861 const GCId gc_id,
2862 bool print_cr) :
2863 _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
2864
2865 if (PrintCMSStatistics != 0) {
2866 _collector->resetYields();
2867 }
2868 if (PrintGCDetails) {
2869 gclog_or_tty->gclog_stamp(_gc_id);
2870 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
2871 _collector->cmsGen()->short_name(), _phase);
2872 }
2873 _collector->resetTimer();
2874 _wallclock.start();
2875 _collector->startTimer();
2876 }
2877
2878 CMSPhaseAccounting::~CMSPhaseAccounting() {
2879 assert(_wallclock.is_active(), "Wall clock should not have stopped");
2880 _collector->stopTimer();
2881 _wallclock.stop();
2882 if (PrintGCDetails) {
2883 gclog_or_tty->gclog_stamp(_gc_id);
2884 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
2885 _collector->cmsGen()->short_name(),
2886 _phase, _collector->timerValue(), _wallclock.seconds());
2887 if (_print_cr) {
2888 gclog_or_tty->cr();
2889 }
2890 if (PrintCMSStatistics != 0) {
2891 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
2892 _collector->yields());
2893 }
2894 }
2895 }
2896
2897 // CMS work
2898
2899 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2900 class CMSParMarkTask : public AbstractGangTask {
2901 protected:
2902 CMSCollector* _collector;
2903 uint _n_workers;
2904 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2905 AbstractGangTask(name),
2906 _collector(collector),
2907 _n_workers(n_workers) {}
2908 // Work method in support of parallel rescan ... of young gen spaces
2909 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2910 ContiguousSpace* space,
2911 HeapWord** chunk_array, size_t chunk_top);
2912 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2913 };
2914
2915 // Parallel initial mark task
2916 class CMSParInitialMarkTask: public CMSParMarkTask {
2917 StrongRootsScope* _strong_roots_scope;
2918 public:
2919 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2920 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2921 _strong_roots_scope(strong_roots_scope) {}
2922 void work(uint worker_id);
2923 };
2924
2925 // Checkpoint the roots into this generation from outside
2926 // this generation. [Note this initial checkpoint need only
2927 // be approximate -- we'll do a catch up phase subsequently.]
2928 void CMSCollector::checkpointRootsInitial() {
2929 assert(_collectorState == InitialMarking, "Wrong collector state");
2930 check_correct_thread_executing();
2931 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2932
2933 save_heap_summary();
2934 report_heap_summary(GCWhen::BeforeGC);
2935
2936 ReferenceProcessor* rp = ref_processor();
2937 assert(_restart_addr == NULL, "Control point invariant");
2938 {
2939 // acquire locks for subsequent manipulations
2940 MutexLockerEx x(bitMapLock(),
2941 Mutex::_no_safepoint_check_flag);
2942 checkpointRootsInitialWork();
2943 // enable ("weak") refs discovery
2944 rp->enable_discovery();
2945 _collectorState = Marking;
2946 }
2947 }
2948
2949 void CMSCollector::checkpointRootsInitialWork() {
2950 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2951 assert(_collectorState == InitialMarking, "just checking");
2952
2953 // If there has not been a GC[n-1] since last GC[n] cycle completed,
2954 // precede our marking with a collection of all
2955 // younger generations to keep floating garbage to a minimum.
2956 // XXX: we won't do this for now -- it's an optimization to be done later.
2957
2958 // already have locks
2959 assert_lock_strong(bitMapLock());
2960 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2961
2962 // Setup the verification and class unloading state for this
2963 // CMS collection cycle.
2964 setup_cms_unloading_and_verification_state();
2965
2966 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
2967 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
2968
2969 // Reset all the PLAB chunk arrays if necessary.
2970 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2971 reset_survivor_plab_arrays();
2972 }
2973
2974 ResourceMark rm;
2975 HandleMark hm;
2976
2977 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2978 GenCollectedHeap* gch = GenCollectedHeap::heap();
2979
2980 verify_work_stacks_empty();
2981 verify_overflow_empty();
2982
2983 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2984 // Update the saved marks which may affect the root scans.
2985 gch->save_marks();
2986
2987 // weak reference processing has not started yet.
2988 ref_processor()->set_enqueuing_is_done(false);
2989
2990 // Need to remember all newly created CLDs,
2991 // so that we can guarantee that the remark finds them.
2992 ClassLoaderDataGraph::remember_new_clds(true);
2993
2994 // Whenever a CLD is found, it will be claimed before proceeding to mark
2995 // the klasses. The claimed marks need to be cleared before marking starts.
2996 ClassLoaderDataGraph::clear_claimed_marks();
2997
2998 if (CMSPrintEdenSurvivorChunks) {
2999 print_eden_and_survivor_chunk_arrays();
3000 }
3001
3002 {
3003 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3004 if (CMSParallelInitialMarkEnabled) {
3005 // The parallel version.
3006 FlexibleWorkGang* workers = gch->workers();
3007 assert(workers != NULL, "Need parallel worker threads.");
3008 uint n_workers = workers->active_workers();
3009
3010 StrongRootsScope srs(n_workers);
3011
3012 CMSParInitialMarkTask tsk(this, &srs, n_workers);
3013 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3014 if (n_workers > 1) {
3015 workers->run_task(&tsk);
3016 } else {
3017 tsk.work(0);
3018 }
3019 } else {
3020 // The serial version.
3021 CLDToOopClosure cld_closure(¬Older, true);
3022 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3023
3024 StrongRootsScope srs(1);
3025
3026 gch->gen_process_roots(&srs,
3027 Generation::Old,
3028 true, // younger gens are roots
3029 GenCollectedHeap::ScanningOption(roots_scanning_options()),
3030 should_unload_classes(),
3031 ¬Older,
3032 NULL,
3033 &cld_closure);
3034 }
3035 }
3036
3037 // Clear mod-union table; it will be dirtied in the prologue of
3038 // CMS generation per each younger generation collection.
3039
3040 assert(_modUnionTable.isAllClear(),
3041 "Was cleared in most recent final checkpoint phase"
3042 " or no bits are set in the gc_prologue before the start of the next "
3043 "subsequent marking phase.");
3044
3045 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3046
3047 // Save the end of the used_region of the constituent generations
3048 // to be used to limit the extent of sweep in each generation.
3049 save_sweep_limits();
3050 verify_overflow_empty();
3051 }
3052
3053 bool CMSCollector::markFromRoots() {
3054 // we might be tempted to assert that:
3055 // assert(!SafepointSynchronize::is_at_safepoint(),
3056 // "inconsistent argument?");
3057 // However that wouldn't be right, because it's possible that
3058 // a safepoint is indeed in progress as a younger generation
3059 // stop-the-world GC happens even as we mark in this generation.
3060 assert(_collectorState == Marking, "inconsistent state?");
3061 check_correct_thread_executing();
3062 verify_overflow_empty();
3063
3064 // Weak ref discovery note: We may be discovering weak
3065 // refs in this generation concurrent (but interleaved) with
3066 // weak ref discovery by a younger generation collector.
3067
3068 CMSTokenSyncWithLocks ts(true, bitMapLock());
3069 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3070 CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3071 bool res = markFromRootsWork();
3072 if (res) {
3073 _collectorState = Precleaning;
3074 } else { // We failed and a foreground collection wants to take over
3075 assert(_foregroundGCIsActive, "internal state inconsistency");
3076 assert(_restart_addr == NULL, "foreground will restart from scratch");
3077 if (PrintGCDetails) {
3078 gclog_or_tty->print_cr("bailing out to foreground collection");
3079 }
3080 }
3081 verify_overflow_empty();
3082 return res;
3083 }
3084
3085 bool CMSCollector::markFromRootsWork() {
3086 // iterate over marked bits in bit map, doing a full scan and mark
3087 // from these roots using the following algorithm:
3088 // . if oop is to the right of the current scan pointer,
3089 // mark corresponding bit (we'll process it later)
3090 // . else (oop is to left of current scan pointer)
3091 // push oop on marking stack
3092 // . drain the marking stack
3093
3094 // Note that when we do a marking step we need to hold the
3095 // bit map lock -- recall that direct allocation (by mutators)
3096 // and promotion (by younger generation collectors) is also
3097 // marking the bit map. [the so-called allocate live policy.]
3098 // Because the implementation of bit map marking is not
3099 // robust wrt simultaneous marking of bits in the same word,
3100 // we need to make sure that there is no such interference
3101 // between concurrent such updates.
3102
3103 // already have locks
3104 assert_lock_strong(bitMapLock());
3105
3106 verify_work_stacks_empty();
3107 verify_overflow_empty();
3108 bool result = false;
3109 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3110 result = do_marking_mt();
3111 } else {
3112 result = do_marking_st();
3113 }
3114 return result;
3115 }
3116
3117 // Forward decl
3118 class CMSConcMarkingTask;
3119
3120 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3121 CMSCollector* _collector;
3122 CMSConcMarkingTask* _task;
3123 public:
3124 virtual void yield();
3125
3126 // "n_threads" is the number of threads to be terminated.
3127 // "queue_set" is a set of work queues of other threads.
3128 // "collector" is the CMS collector associated with this task terminator.
3129 // "yield" indicates whether we need the gang as a whole to yield.
3130 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3131 ParallelTaskTerminator(n_threads, queue_set),
3132 _collector(collector) { }
3133
3134 void set_task(CMSConcMarkingTask* task) {
3135 _task = task;
3136 }
3137 };
3138
3139 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3140 CMSConcMarkingTask* _task;
3141 public:
3142 bool should_exit_termination();
3143 void set_task(CMSConcMarkingTask* task) {
3144 _task = task;
3145 }
3146 };
3147
3148 // MT Concurrent Marking Task
3149 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3150 CMSCollector* _collector;
3151 uint _n_workers; // requested/desired # workers
3152 bool _result;
3153 CompactibleFreeListSpace* _cms_space;
3154 char _pad_front[64]; // padding to ...
3155 HeapWord* _global_finger; // ... avoid sharing cache line
3156 char _pad_back[64];
3157 HeapWord* _restart_addr;
3158
3159 // Exposed here for yielding support
3160 Mutex* const _bit_map_lock;
3161
3162 // The per thread work queues, available here for stealing
3163 OopTaskQueueSet* _task_queues;
3164
3165 // Termination (and yielding) support
3166 CMSConcMarkingTerminator _term;
3167 CMSConcMarkingTerminatorTerminator _term_term;
3168
3169 public:
3170 CMSConcMarkingTask(CMSCollector* collector,
3171 CompactibleFreeListSpace* cms_space,
3172 YieldingFlexibleWorkGang* workers,
3173 OopTaskQueueSet* task_queues):
3174 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3175 _collector(collector),
3176 _cms_space(cms_space),
3177 _n_workers(0), _result(true),
3178 _task_queues(task_queues),
3179 _term(_n_workers, task_queues, _collector),
3180 _bit_map_lock(collector->bitMapLock())
3181 {
3182 _requested_size = _n_workers;
3183 _term.set_task(this);
3184 _term_term.set_task(this);
3185 _restart_addr = _global_finger = _cms_space->bottom();
3186 }
3187
3188
3189 OopTaskQueueSet* task_queues() { return _task_queues; }
3190
3191 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3192
3193 HeapWord** global_finger_addr() { return &_global_finger; }
3194
3195 CMSConcMarkingTerminator* terminator() { return &_term; }
3196
3197 virtual void set_for_termination(uint active_workers) {
3198 terminator()->reset_for_reuse(active_workers);
3199 }
3200
3201 void work(uint worker_id);
3202 bool should_yield() {
3203 return ConcurrentMarkSweepThread::should_yield()
3204 && !_collector->foregroundGCIsActive();
3205 }
3206
3207 virtual void coordinator_yield(); // stuff done by coordinator
3208 bool result() { return _result; }
3209
3210 void reset(HeapWord* ra) {
3211 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3212 _restart_addr = _global_finger = ra;
3213 _term.reset_for_reuse();
3214 }
3215
3216 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3217 OopTaskQueue* work_q);
3218
3219 private:
3220 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3221 void do_work_steal(int i);
3222 void bump_global_finger(HeapWord* f);
3223 };
3224
3225 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3226 assert(_task != NULL, "Error");
3227 return _task->yielding();
3228 // Note that we do not need the disjunct || _task->should_yield() above
3229 // because we want terminating threads to yield only if the task
3230 // is already in the midst of yielding, which happens only after at least one
3231 // thread has yielded.
3232 }
3233
3234 void CMSConcMarkingTerminator::yield() {
3235 if (_task->should_yield()) {
3236 _task->yield();
3237 } else {
3238 ParallelTaskTerminator::yield();
3239 }
3240 }
3241
3242 ////////////////////////////////////////////////////////////////
3243 // Concurrent Marking Algorithm Sketch
3244 ////////////////////////////////////////////////////////////////
3245 // Until all tasks exhausted (both spaces):
3246 // -- claim next available chunk
3247 // -- bump global finger via CAS
3248 // -- find first object that starts in this chunk
3249 // and start scanning bitmap from that position
3250 // -- scan marked objects for oops
3251 // -- CAS-mark target, and if successful:
3252 // . if target oop is above global finger (volatile read)
3253 // nothing to do
3254 // . if target oop is in chunk and above local finger
3255 // then nothing to do
3256 // . else push on work-queue
3257 // -- Deal with possible overflow issues:
3258 // . local work-queue overflow causes stuff to be pushed on
3259 // global (common) overflow queue
3260 // . always first empty local work queue
3261 // . then get a batch of oops from global work queue if any
3262 // . then do work stealing
3263 // -- When all tasks claimed (both spaces)
3264 // and local work queue empty,
3265 // then in a loop do:
3266 // . check global overflow stack; steal a batch of oops and trace
3267 // . try to steal from other threads oif GOS is empty
3268 // . if neither is available, offer termination
3269 // -- Terminate and return result
3270 //
3271 void CMSConcMarkingTask::work(uint worker_id) {
3272 elapsedTimer _timer;
3273 ResourceMark rm;
3274 HandleMark hm;
3275
3276 DEBUG_ONLY(_collector->verify_overflow_empty();)
3277
3278 // Before we begin work, our work queue should be empty
3279 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3280 // Scan the bitmap covering _cms_space, tracing through grey objects.
3281 _timer.start();
3282 do_scan_and_mark(worker_id, _cms_space);
3283 _timer.stop();
3284 if (PrintCMSStatistics != 0) {
3285 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3286 worker_id, _timer.seconds());
3287 // XXX: need xxx/xxx type of notation, two timers
3288 }
3289
3290 // ... do work stealing
3291 _timer.reset();
3292 _timer.start();
3293 do_work_steal(worker_id);
3294 _timer.stop();
3295 if (PrintCMSStatistics != 0) {
3296 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3297 worker_id, _timer.seconds());
3298 // XXX: need xxx/xxx type of notation, two timers
3299 }
3300 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3301 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3302 // Note that under the current task protocol, the
3303 // following assertion is true even of the spaces
3304 // expanded since the completion of the concurrent
3305 // marking. XXX This will likely change under a strict
3306 // ABORT semantics.
3307 // After perm removal the comparison was changed to
3308 // greater than or equal to from strictly greater than.
3309 // Before perm removal the highest address sweep would
3310 // have been at the end of perm gen but now is at the
3311 // end of the tenured gen.
3312 assert(_global_finger >= _cms_space->end(),
3313 "All tasks have been completed");
3314 DEBUG_ONLY(_collector->verify_overflow_empty();)
3315 }
3316
3317 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3318 HeapWord* read = _global_finger;
3319 HeapWord* cur = read;
3320 while (f > read) {
3321 cur = read;
3322 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3323 if (cur == read) {
3324 // our cas succeeded
3325 assert(_global_finger >= f, "protocol consistency");
3326 break;
3327 }
3328 }
3329 }
3330
3331 // This is really inefficient, and should be redone by
3332 // using (not yet available) block-read and -write interfaces to the
3333 // stack and the work_queue. XXX FIX ME !!!
3334 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3335 OopTaskQueue* work_q) {
3336 // Fast lock-free check
3337 if (ovflw_stk->length() == 0) {
3338 return false;
3339 }
3340 assert(work_q->size() == 0, "Shouldn't steal");
3341 MutexLockerEx ml(ovflw_stk->par_lock(),
3342 Mutex::_no_safepoint_check_flag);
3343 // Grab up to 1/4 the size of the work queue
3344 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3345 (size_t)ParGCDesiredObjsFromOverflowList);
3346 num = MIN2(num, ovflw_stk->length());
3347 for (int i = (int) num; i > 0; i--) {
3348 oop cur = ovflw_stk->pop();
3349 assert(cur != NULL, "Counted wrong?");
3350 work_q->push(cur);
3351 }
3352 return num > 0;
3353 }
3354
3355 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3356 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3357 int n_tasks = pst->n_tasks();
3358 // We allow that there may be no tasks to do here because
3359 // we are restarting after a stack overflow.
3360 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3361 uint nth_task = 0;
3362
3363 HeapWord* aligned_start = sp->bottom();
3364 if (sp->used_region().contains(_restart_addr)) {
3365 // Align down to a card boundary for the start of 0th task
3366 // for this space.
3367 aligned_start =
3368 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3369 CardTableModRefBS::card_size);
3370 }
3371
3372 size_t chunk_size = sp->marking_task_size();
3373 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3374 // Having claimed the nth task in this space,
3375 // compute the chunk that it corresponds to:
3376 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3377 aligned_start + (nth_task+1)*chunk_size);
3378 // Try and bump the global finger via a CAS;
3379 // note that we need to do the global finger bump
3380 // _before_ taking the intersection below, because
3381 // the task corresponding to that region will be
3382 // deemed done even if the used_region() expands
3383 // because of allocation -- as it almost certainly will
3384 // during start-up while the threads yield in the
3385 // closure below.
3386 HeapWord* finger = span.end();
3387 bump_global_finger(finger); // atomically
3388 // There are null tasks here corresponding to chunks
3389 // beyond the "top" address of the space.
3390 span = span.intersection(sp->used_region());
3391 if (!span.is_empty()) { // Non-null task
3392 HeapWord* prev_obj;
3393 assert(!span.contains(_restart_addr) || nth_task == 0,
3394 "Inconsistency");
3395 if (nth_task == 0) {
3396 // For the 0th task, we'll not need to compute a block_start.
3397 if (span.contains(_restart_addr)) {
3398 // In the case of a restart because of stack overflow,
3399 // we might additionally skip a chunk prefix.
3400 prev_obj = _restart_addr;
3401 } else {
3402 prev_obj = span.start();
3403 }
3404 } else {
3405 // We want to skip the first object because
3406 // the protocol is to scan any object in its entirety
3407 // that _starts_ in this span; a fortiori, any
3408 // object starting in an earlier span is scanned
3409 // as part of an earlier claimed task.
3410 // Below we use the "careful" version of block_start
3411 // so we do not try to navigate uninitialized objects.
3412 prev_obj = sp->block_start_careful(span.start());
3413 // Below we use a variant of block_size that uses the
3414 // Printezis bits to avoid waiting for allocated
3415 // objects to become initialized/parsable.
3416 while (prev_obj < span.start()) {
3417 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3418 if (sz > 0) {
3419 prev_obj += sz;
3420 } else {
3421 // In this case we may end up doing a bit of redundant
3422 // scanning, but that appears unavoidable, short of
3423 // locking the free list locks; see bug 6324141.
3424 break;
3425 }
3426 }
3427 }
3428 if (prev_obj < span.end()) {
3429 MemRegion my_span = MemRegion(prev_obj, span.end());
3430 // Do the marking work within a non-empty span --
3431 // the last argument to the constructor indicates whether the
3432 // iteration should be incremental with periodic yields.
3433 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3434 &_collector->_markBitMap,
3435 work_queue(i),
3436 &_collector->_markStack);
3437 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3438 } // else nothing to do for this task
3439 } // else nothing to do for this task
3440 }
3441 // We'd be tempted to assert here that since there are no
3442 // more tasks left to claim in this space, the global_finger
3443 // must exceed space->top() and a fortiori space->end(). However,
3444 // that would not quite be correct because the bumping of
3445 // global_finger occurs strictly after the claiming of a task,
3446 // so by the time we reach here the global finger may not yet
3447 // have been bumped up by the thread that claimed the last
3448 // task.
3449 pst->all_tasks_completed();
3450 }
3451
3452 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3453 private:
3454 CMSCollector* _collector;
3455 CMSConcMarkingTask* _task;
3456 MemRegion _span;
3457 CMSBitMap* _bit_map;
3458 CMSMarkStack* _overflow_stack;
3459 OopTaskQueue* _work_queue;
3460 protected:
3461 DO_OOP_WORK_DEFN
3462 public:
3463 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3464 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3465 MetadataAwareOopClosure(collector->ref_processor()),
3466 _collector(collector),
3467 _task(task),
3468 _span(collector->_span),
3469 _work_queue(work_queue),
3470 _bit_map(bit_map),
3471 _overflow_stack(overflow_stack)
3472 { }
3473 virtual void do_oop(oop* p);
3474 virtual void do_oop(narrowOop* p);
3475
3476 void trim_queue(size_t max);
3477 void handle_stack_overflow(HeapWord* lost);
3478 void do_yield_check() {
3479 if (_task->should_yield()) {
3480 _task->yield();
3481 }
3482 }
3483 };
3484
3485 // Grey object scanning during work stealing phase --
3486 // the salient assumption here is that any references
3487 // that are in these stolen objects being scanned must
3488 // already have been initialized (else they would not have
3489 // been published), so we do not need to check for
3490 // uninitialized objects before pushing here.
3491 void Par_ConcMarkingClosure::do_oop(oop obj) {
3492 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
3493 HeapWord* addr = (HeapWord*)obj;
3494 // Check if oop points into the CMS generation
3495 // and is not marked
3496 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3497 // a white object ...
3498 // If we manage to "claim" the object, by being the
3499 // first thread to mark it, then we push it on our
3500 // marking stack
3501 if (_bit_map->par_mark(addr)) { // ... now grey
3502 // push on work queue (grey set)
3503 bool simulate_overflow = false;
3504 NOT_PRODUCT(
3505 if (CMSMarkStackOverflowALot &&
3506 _collector->simulate_overflow()) {
3507 // simulate a stack overflow
3508 simulate_overflow = true;
3509 }
3510 )
3511 if (simulate_overflow ||
3512 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3513 // stack overflow
3514 if (PrintCMSStatistics != 0) {
3515 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3516 SIZE_FORMAT, _overflow_stack->capacity());
3517 }
3518 // We cannot assert that the overflow stack is full because
3519 // it may have been emptied since.
3520 assert(simulate_overflow ||
3521 _work_queue->size() == _work_queue->max_elems(),
3522 "Else push should have succeeded");
3523 handle_stack_overflow(addr);
3524 }
3525 } // Else, some other thread got there first
3526 do_yield_check();
3527 }
3528 }
3529
3530 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3531 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3532
3533 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3534 while (_work_queue->size() > max) {
3535 oop new_oop;
3536 if (_work_queue->pop_local(new_oop)) {
3537 assert(new_oop->is_oop(), "Should be an oop");
3538 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3539 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3540 new_oop->oop_iterate(this); // do_oop() above
3541 do_yield_check();
3542 }
3543 }
3544 }
3545
3546 // Upon stack overflow, we discard (part of) the stack,
3547 // remembering the least address amongst those discarded
3548 // in CMSCollector's _restart_address.
3549 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3550 // We need to do this under a mutex to prevent other
3551 // workers from interfering with the work done below.
3552 MutexLockerEx ml(_overflow_stack->par_lock(),
3553 Mutex::_no_safepoint_check_flag);
3554 // Remember the least grey address discarded
3555 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3556 _collector->lower_restart_addr(ra);
3557 _overflow_stack->reset(); // discard stack contents
3558 _overflow_stack->expand(); // expand the stack if possible
3559 }
3560
3561
3562 void CMSConcMarkingTask::do_work_steal(int i) {
3563 OopTaskQueue* work_q = work_queue(i);
3564 oop obj_to_scan;
3565 CMSBitMap* bm = &(_collector->_markBitMap);
3566 CMSMarkStack* ovflw = &(_collector->_markStack);
3567 int* seed = _collector->hash_seed(i);
3568 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3569 while (true) {
3570 cl.trim_queue(0);
3571 assert(work_q->size() == 0, "Should have been emptied above");
3572 if (get_work_from_overflow_stack(ovflw, work_q)) {
3573 // Can't assert below because the work obtained from the
3574 // overflow stack may already have been stolen from us.
3575 // assert(work_q->size() > 0, "Work from overflow stack");
3576 continue;
3577 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3578 assert(obj_to_scan->is_oop(), "Should be an oop");
3579 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3580 obj_to_scan->oop_iterate(&cl);
3581 } else if (terminator()->offer_termination(&_term_term)) {
3582 assert(work_q->size() == 0, "Impossible!");
3583 break;
3584 } else if (yielding() || should_yield()) {
3585 yield();
3586 }
3587 }
3588 }
3589
3590 // This is run by the CMS (coordinator) thread.
3591 void CMSConcMarkingTask::coordinator_yield() {
3592 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3593 "CMS thread should hold CMS token");
3594 // First give up the locks, then yield, then re-lock
3595 // We should probably use a constructor/destructor idiom to
3596 // do this unlock/lock or modify the MutexUnlocker class to
3597 // serve our purpose. XXX
3598 assert_lock_strong(_bit_map_lock);
3599 _bit_map_lock->unlock();
3600 ConcurrentMarkSweepThread::desynchronize(true);
3601 _collector->stopTimer();
3602 if (PrintCMSStatistics != 0) {
3603 _collector->incrementYields();
3604 }
3605
3606 // It is possible for whichever thread initiated the yield request
3607 // not to get a chance to wake up and take the bitmap lock between
3608 // this thread releasing it and reacquiring it. So, while the
3609 // should_yield() flag is on, let's sleep for a bit to give the
3610 // other thread a chance to wake up. The limit imposed on the number
3611 // of iterations is defensive, to avoid any unforseen circumstances
3612 // putting us into an infinite loop. Since it's always been this
3613 // (coordinator_yield()) method that was observed to cause the
3614 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3615 // which is by default non-zero. For the other seven methods that
3616 // also perform the yield operation, as are using a different
3617 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3618 // can enable the sleeping for those methods too, if necessary.
3619 // See 6442774.
3620 //
3621 // We really need to reconsider the synchronization between the GC
3622 // thread and the yield-requesting threads in the future and we
3623 // should really use wait/notify, which is the recommended
3624 // way of doing this type of interaction. Additionally, we should
3625 // consolidate the eight methods that do the yield operation and they
3626 // are almost identical into one for better maintainability and
3627 // readability. See 6445193.
3628 //
3629 // Tony 2006.06.29
3630 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3631 ConcurrentMarkSweepThread::should_yield() &&
3632 !CMSCollector::foregroundGCIsActive(); ++i) {
3633 os::sleep(Thread::current(), 1, false);
3634 }
3635
3636 ConcurrentMarkSweepThread::synchronize(true);
3637 _bit_map_lock->lock_without_safepoint_check();
3638 _collector->startTimer();
3639 }
3640
3641 bool CMSCollector::do_marking_mt() {
3642 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3643 uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3644 conc_workers()->active_workers(),
3645 Threads::number_of_non_daemon_threads());
3646 conc_workers()->set_active_workers(num_workers);
3647
3648 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3649
3650 CMSConcMarkingTask tsk(this,
3651 cms_space,
3652 conc_workers(),
3653 task_queues());
3654
3655 // Since the actual number of workers we get may be different
3656 // from the number we requested above, do we need to do anything different
3657 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3658 // class?? XXX
3659 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3660
3661 // Refs discovery is already non-atomic.
3662 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3663 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3664 conc_workers()->start_task(&tsk);
3665 while (tsk.yielded()) {
3666 tsk.coordinator_yield();
3667 conc_workers()->continue_task(&tsk);
3668 }
3669 // If the task was aborted, _restart_addr will be non-NULL
3670 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3671 while (_restart_addr != NULL) {
3672 // XXX For now we do not make use of ABORTED state and have not
3673 // yet implemented the right abort semantics (even in the original
3674 // single-threaded CMS case). That needs some more investigation
3675 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3676 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3677 // If _restart_addr is non-NULL, a marking stack overflow
3678 // occurred; we need to do a fresh marking iteration from the
3679 // indicated restart address.
3680 if (_foregroundGCIsActive) {
3681 // We may be running into repeated stack overflows, having
3682 // reached the limit of the stack size, while making very
3683 // slow forward progress. It may be best to bail out and
3684 // let the foreground collector do its job.
3685 // Clear _restart_addr, so that foreground GC
3686 // works from scratch. This avoids the headache of
3687 // a "rescan" which would otherwise be needed because
3688 // of the dirty mod union table & card table.
3689 _restart_addr = NULL;
3690 return false;
3691 }
3692 // Adjust the task to restart from _restart_addr
3693 tsk.reset(_restart_addr);
3694 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3695 _restart_addr);
3696 _restart_addr = NULL;
3697 // Get the workers going again
3698 conc_workers()->start_task(&tsk);
3699 while (tsk.yielded()) {
3700 tsk.coordinator_yield();
3701 conc_workers()->continue_task(&tsk);
3702 }
3703 }
3704 assert(tsk.completed(), "Inconsistency");
3705 assert(tsk.result() == true, "Inconsistency");
3706 return true;
3707 }
3708
3709 bool CMSCollector::do_marking_st() {
3710 ResourceMark rm;
3711 HandleMark hm;
3712
3713 // Temporarily make refs discovery single threaded (non-MT)
3714 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3715 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3716 &_markStack, CMSYield);
3717 // the last argument to iterate indicates whether the iteration
3718 // should be incremental with periodic yields.
3719 _markBitMap.iterate(&markFromRootsClosure);
3720 // If _restart_addr is non-NULL, a marking stack overflow
3721 // occurred; we need to do a fresh iteration from the
3722 // indicated restart address.
3723 while (_restart_addr != NULL) {
3724 if (_foregroundGCIsActive) {
3725 // We may be running into repeated stack overflows, having
3726 // reached the limit of the stack size, while making very
3727 // slow forward progress. It may be best to bail out and
3728 // let the foreground collector do its job.
3729 // Clear _restart_addr, so that foreground GC
3730 // works from scratch. This avoids the headache of
3731 // a "rescan" which would otherwise be needed because
3732 // of the dirty mod union table & card table.
3733 _restart_addr = NULL;
3734 return false; // indicating failure to complete marking
3735 }
3736 // Deal with stack overflow:
3737 // we restart marking from _restart_addr
3738 HeapWord* ra = _restart_addr;
3739 markFromRootsClosure.reset(ra);
3740 _restart_addr = NULL;
3741 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3742 }
3743 return true;
3744 }
3745
3746 void CMSCollector::preclean() {
3747 check_correct_thread_executing();
3748 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3749 verify_work_stacks_empty();
3750 verify_overflow_empty();
3751 _abort_preclean = false;
3752 if (CMSPrecleaningEnabled) {
3753 if (!CMSEdenChunksRecordAlways) {
3754 _eden_chunk_index = 0;
3755 }
3756 size_t used = get_eden_used();
3757 size_t capacity = get_eden_capacity();
3758 // Don't start sampling unless we will get sufficiently
3759 // many samples.
3760 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3761 * CMSScheduleRemarkEdenPenetration)) {
3762 _start_sampling = true;
3763 } else {
3764 _start_sampling = false;
3765 }
3766 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3767 CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3768 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3769 }
3770 CMSTokenSync x(true); // is cms thread
3771 if (CMSPrecleaningEnabled) {
3772 sample_eden();
3773 _collectorState = AbortablePreclean;
3774 } else {
3775 _collectorState = FinalMarking;
3776 }
3777 verify_work_stacks_empty();
3778 verify_overflow_empty();
3779 }
3780
3781 // Try and schedule the remark such that young gen
3782 // occupancy is CMSScheduleRemarkEdenPenetration %.
3783 void CMSCollector::abortable_preclean() {
3784 check_correct_thread_executing();
3785 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3786 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3787
3788 // If Eden's current occupancy is below this threshold,
3789 // immediately schedule the remark; else preclean
3790 // past the next scavenge in an effort to
3791 // schedule the pause as described above. By choosing
3792 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3793 // we will never do an actual abortable preclean cycle.
3794 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3795 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3796 CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3797 // We need more smarts in the abortable preclean
3798 // loop below to deal with cases where allocation
3799 // in young gen is very very slow, and our precleaning
3800 // is running a losing race against a horde of
3801 // mutators intent on flooding us with CMS updates
3802 // (dirty cards).
3803 // One, admittedly dumb, strategy is to give up
3804 // after a certain number of abortable precleaning loops
3805 // or after a certain maximum time. We want to make
3806 // this smarter in the next iteration.
3807 // XXX FIX ME!!! YSR
3808 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3809 while (!(should_abort_preclean() ||
3810 ConcurrentMarkSweepThread::should_terminate())) {
3811 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3812 cumworkdone += workdone;
3813 loops++;
3814 // Voluntarily terminate abortable preclean phase if we have
3815 // been at it for too long.
3816 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3817 loops >= CMSMaxAbortablePrecleanLoops) {
3818 if (PrintGCDetails) {
3819 gclog_or_tty->print(" CMS: abort preclean due to loops ");
3820 }
3821 break;
3822 }
3823 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3824 if (PrintGCDetails) {
3825 gclog_or_tty->print(" CMS: abort preclean due to time ");
3826 }
3827 break;
3828 }
3829 // If we are doing little work each iteration, we should
3830 // take a short break.
3831 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3832 // Sleep for some time, waiting for work to accumulate
3833 stopTimer();
3834 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3835 startTimer();
3836 waited++;
3837 }
3838 }
3839 if (PrintCMSStatistics > 0) {
3840 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3841 loops, waited, cumworkdone);
3842 }
3843 }
3844 CMSTokenSync x(true); // is cms thread
3845 if (_collectorState != Idling) {
3846 assert(_collectorState == AbortablePreclean,
3847 "Spontaneous state transition?");
3848 _collectorState = FinalMarking;
3849 } // Else, a foreground collection completed this CMS cycle.
3850 return;
3851 }
3852
3853 // Respond to an Eden sampling opportunity
3854 void CMSCollector::sample_eden() {
3855 // Make sure a young gc cannot sneak in between our
3856 // reading and recording of a sample.
3857 assert(Thread::current()->is_ConcurrentGC_thread(),
3858 "Only the cms thread may collect Eden samples");
3859 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3860 "Should collect samples while holding CMS token");
3861 if (!_start_sampling) {
3862 return;
3863 }
3864 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3865 // is populated by the young generation.
3866 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3867 if (_eden_chunk_index < _eden_chunk_capacity) {
3868 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3869 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3870 "Unexpected state of Eden");
3871 // We'd like to check that what we just sampled is an oop-start address;
3872 // however, we cannot do that here since the object may not yet have been
3873 // initialized. So we'll instead do the check when we _use_ this sample
3874 // later.
3875 if (_eden_chunk_index == 0 ||
3876 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3877 _eden_chunk_array[_eden_chunk_index-1])
3878 >= CMSSamplingGrain)) {
3879 _eden_chunk_index++; // commit sample
3880 }
3881 }
3882 }
3883 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3884 size_t used = get_eden_used();
3885 size_t capacity = get_eden_capacity();
3886 assert(used <= capacity, "Unexpected state of Eden");
3887 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3888 _abort_preclean = true;
3889 }
3890 }
3891 }
3892
3893
3894 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3895 assert(_collectorState == Precleaning ||
3896 _collectorState == AbortablePreclean, "incorrect state");
3897 ResourceMark rm;
3898 HandleMark hm;
3899
3900 // Precleaning is currently not MT but the reference processor
3901 // may be set for MT. Disable it temporarily here.
3902 ReferenceProcessor* rp = ref_processor();
3903 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3904
3905 // Do one pass of scrubbing the discovered reference lists
3906 // to remove any reference objects with strongly-reachable
3907 // referents.
3908 if (clean_refs) {
3909 CMSPrecleanRefsYieldClosure yield_cl(this);
3910 assert(rp->span().equals(_span), "Spans should be equal");
3911 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3912 &_markStack, true /* preclean */);
3913 CMSDrainMarkingStackClosure complete_trace(this,
3914 _span, &_markBitMap, &_markStack,
3915 &keep_alive, true /* preclean */);
3916
3917 // We don't want this step to interfere with a young
3918 // collection because we don't want to take CPU
3919 // or memory bandwidth away from the young GC threads
3920 // (which may be as many as there are CPUs).
3921 // Note that we don't need to protect ourselves from
3922 // interference with mutators because they can't
3923 // manipulate the discovered reference lists nor affect
3924 // the computed reachability of the referents, the
3925 // only properties manipulated by the precleaning
3926 // of these reference lists.
3927 stopTimer();
3928 CMSTokenSyncWithLocks x(true /* is cms thread */,
3929 bitMapLock());
3930 startTimer();
3931 sample_eden();
3932
3933 // The following will yield to allow foreground
3934 // collection to proceed promptly. XXX YSR:
3935 // The code in this method may need further
3936 // tweaking for better performance and some restructuring
3937 // for cleaner interfaces.
3938 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3939 rp->preclean_discovered_references(
3940 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3941 gc_timer, _gc_tracer_cm->gc_id());
3942 }
3943
3944 if (clean_survivor) { // preclean the active survivor space(s)
3945 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3946 &_markBitMap, &_modUnionTable,
3947 &_markStack, true /* precleaning phase */);
3948 stopTimer();
3949 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3950 bitMapLock());
3951 startTimer();
3952 unsigned int before_count =
3953 GenCollectedHeap::heap()->total_collections();
3954 SurvivorSpacePrecleanClosure
3955 sss_cl(this, _span, &_markBitMap, &_markStack,
3956 &pam_cl, before_count, CMSYield);
3957 _young_gen->from()->object_iterate_careful(&sss_cl);
3958 _young_gen->to()->object_iterate_careful(&sss_cl);
3959 }
3960 MarkRefsIntoAndScanClosure
3961 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3962 &_markStack, this, CMSYield,
3963 true /* precleaning phase */);
3964 // CAUTION: The following closure has persistent state that may need to
3965 // be reset upon a decrease in the sequence of addresses it
3966 // processes.
3967 ScanMarkedObjectsAgainCarefullyClosure
3968 smoac_cl(this, _span,
3969 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3970
3971 // Preclean dirty cards in ModUnionTable and CardTable using
3972 // appropriate convergence criterion;
3973 // repeat CMSPrecleanIter times unless we find that
3974 // we are losing.
3975 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3976 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3977 "Bad convergence multiplier");
3978 assert(CMSPrecleanThreshold >= 100,
3979 "Unreasonably low CMSPrecleanThreshold");
3980
3981 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3982 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3983 numIter < CMSPrecleanIter;
3984 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3985 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3986 if (Verbose && PrintGCDetails) {
3987 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3988 }
3989 // Either there are very few dirty cards, so re-mark
3990 // pause will be small anyway, or our pre-cleaning isn't
3991 // that much faster than the rate at which cards are being
3992 // dirtied, so we might as well stop and re-mark since
3993 // precleaning won't improve our re-mark time by much.
3994 if (curNumCards <= CMSPrecleanThreshold ||
3995 (numIter > 0 &&
3996 (curNumCards * CMSPrecleanDenominator >
3997 lastNumCards * CMSPrecleanNumerator))) {
3998 numIter++;
3999 cumNumCards += curNumCards;
4000 break;
4001 }
4002 }
4003
4004 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4005
4006 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4007 cumNumCards += curNumCards;
4008 if (PrintGCDetails && PrintCMSStatistics != 0) {
4009 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4010 curNumCards, cumNumCards, numIter);
4011 }
4012 return cumNumCards; // as a measure of useful work done
4013 }
4014
4015 // PRECLEANING NOTES:
4016 // Precleaning involves:
4017 // . reading the bits of the modUnionTable and clearing the set bits.
4018 // . For the cards corresponding to the set bits, we scan the
4019 // objects on those cards. This means we need the free_list_lock
4020 // so that we can safely iterate over the CMS space when scanning
4021 // for oops.
4022 // . When we scan the objects, we'll be both reading and setting
4023 // marks in the marking bit map, so we'll need the marking bit map.
4024 // . For protecting _collector_state transitions, we take the CGC_lock.
4025 // Note that any races in the reading of of card table entries by the
4026 // CMS thread on the one hand and the clearing of those entries by the
4027 // VM thread or the setting of those entries by the mutator threads on the
4028 // other are quite benign. However, for efficiency it makes sense to keep
4029 // the VM thread from racing with the CMS thread while the latter is
4030 // dirty card info to the modUnionTable. We therefore also use the
4031 // CGC_lock to protect the reading of the card table and the mod union
4032 // table by the CM thread.
4033 // . We run concurrently with mutator updates, so scanning
4034 // needs to be done carefully -- we should not try to scan
4035 // potentially uninitialized objects.
4036 //
4037 // Locking strategy: While holding the CGC_lock, we scan over and
4038 // reset a maximal dirty range of the mod union / card tables, then lock
4039 // the free_list_lock and bitmap lock to do a full marking, then
4040 // release these locks; and repeat the cycle. This allows for a
4041 // certain amount of fairness in the sharing of these locks between
4042 // the CMS collector on the one hand, and the VM thread and the
4043 // mutators on the other.
4044
4045 // NOTE: preclean_mod_union_table() and preclean_card_table()
4046 // further below are largely identical; if you need to modify
4047 // one of these methods, please check the other method too.
4048
4049 size_t CMSCollector::preclean_mod_union_table(
4050 ConcurrentMarkSweepGeneration* gen,
4051 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4052 verify_work_stacks_empty();
4053 verify_overflow_empty();
4054
4055 // strategy: starting with the first card, accumulate contiguous
4056 // ranges of dirty cards; clear these cards, then scan the region
4057 // covered by these cards.
4058
4059 // Since all of the MUT is committed ahead, we can just use
4060 // that, in case the generations expand while we are precleaning.
4061 // It might also be fine to just use the committed part of the
4062 // generation, but we might potentially miss cards when the
4063 // generation is rapidly expanding while we are in the midst
4064 // of precleaning.
4065 HeapWord* startAddr = gen->reserved().start();
4066 HeapWord* endAddr = gen->reserved().end();
4067
4068 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4069
4070 size_t numDirtyCards, cumNumDirtyCards;
4071 HeapWord *nextAddr, *lastAddr;
4072 for (cumNumDirtyCards = numDirtyCards = 0,
4073 nextAddr = lastAddr = startAddr;
4074 nextAddr < endAddr;
4075 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4076
4077 ResourceMark rm;
4078 HandleMark hm;
4079
4080 MemRegion dirtyRegion;
4081 {
4082 stopTimer();
4083 // Potential yield point
4084 CMSTokenSync ts(true);
4085 startTimer();
4086 sample_eden();
4087 // Get dirty region starting at nextOffset (inclusive),
4088 // simultaneously clearing it.
4089 dirtyRegion =
4090 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4091 assert(dirtyRegion.start() >= nextAddr,
4092 "returned region inconsistent?");
4093 }
4094 // Remember where the next search should begin.
4095 // The returned region (if non-empty) is a right open interval,
4096 // so lastOffset is obtained from the right end of that
4097 // interval.
4098 lastAddr = dirtyRegion.end();
4099 // Should do something more transparent and less hacky XXX
4100 numDirtyCards =
4101 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4102
4103 // We'll scan the cards in the dirty region (with periodic
4104 // yields for foreground GC as needed).
4105 if (!dirtyRegion.is_empty()) {
4106 assert(numDirtyCards > 0, "consistency check");
4107 HeapWord* stop_point = NULL;
4108 stopTimer();
4109 // Potential yield point
4110 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4111 bitMapLock());
4112 startTimer();
4113 {
4114 verify_work_stacks_empty();
4115 verify_overflow_empty();
4116 sample_eden();
4117 stop_point =
4118 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4119 }
4120 if (stop_point != NULL) {
4121 // The careful iteration stopped early either because it found an
4122 // uninitialized object, or because we were in the midst of an
4123 // "abortable preclean", which should now be aborted. Redirty
4124 // the bits corresponding to the partially-scanned or unscanned
4125 // cards. We'll either restart at the next block boundary or
4126 // abort the preclean.
4127 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4128 "Should only be AbortablePreclean.");
4129 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4130 if (should_abort_preclean()) {
4131 break; // out of preclean loop
4132 } else {
4133 // Compute the next address at which preclean should pick up;
4134 // might need bitMapLock in order to read P-bits.
4135 lastAddr = next_card_start_after_block(stop_point);
4136 }
4137 }
4138 } else {
4139 assert(lastAddr == endAddr, "consistency check");
4140 assert(numDirtyCards == 0, "consistency check");
4141 break;
4142 }
4143 }
4144 verify_work_stacks_empty();
4145 verify_overflow_empty();
4146 return cumNumDirtyCards;
4147 }
4148
4149 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4150 // below are largely identical; if you need to modify
4151 // one of these methods, please check the other method too.
4152
4153 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4154 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4155 // strategy: it's similar to precleamModUnionTable above, in that
4156 // we accumulate contiguous ranges of dirty cards, mark these cards
4157 // precleaned, then scan the region covered by these cards.
4158 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4159 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4160
4161 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4162
4163 size_t numDirtyCards, cumNumDirtyCards;
4164 HeapWord *lastAddr, *nextAddr;
4165
4166 for (cumNumDirtyCards = numDirtyCards = 0,
4167 nextAddr = lastAddr = startAddr;
4168 nextAddr < endAddr;
4169 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4170
4171 ResourceMark rm;
4172 HandleMark hm;
4173
4174 MemRegion dirtyRegion;
4175 {
4176 // See comments in "Precleaning notes" above on why we
4177 // do this locking. XXX Could the locking overheads be
4178 // too high when dirty cards are sparse? [I don't think so.]
4179 stopTimer();
4180 CMSTokenSync x(true); // is cms thread
4181 startTimer();
4182 sample_eden();
4183 // Get and clear dirty region from card table
4184 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4185 MemRegion(nextAddr, endAddr),
4186 true,
4187 CardTableModRefBS::precleaned_card_val());
4188
4189 assert(dirtyRegion.start() >= nextAddr,
4190 "returned region inconsistent?");
4191 }
4192 lastAddr = dirtyRegion.end();
4193 numDirtyCards =
4194 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4195
4196 if (!dirtyRegion.is_empty()) {
4197 stopTimer();
4198 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4199 startTimer();
4200 sample_eden();
4201 verify_work_stacks_empty();
4202 verify_overflow_empty();
4203 HeapWord* stop_point =
4204 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4205 if (stop_point != NULL) {
4206 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4207 "Should only be AbortablePreclean.");
4208 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4209 if (should_abort_preclean()) {
4210 break; // out of preclean loop
4211 } else {
4212 // Compute the next address at which preclean should pick up.
4213 lastAddr = next_card_start_after_block(stop_point);
4214 }
4215 }
4216 } else {
4217 break;
4218 }
4219 }
4220 verify_work_stacks_empty();
4221 verify_overflow_empty();
4222 return cumNumDirtyCards;
4223 }
4224
4225 class PrecleanKlassClosure : public KlassClosure {
4226 KlassToOopClosure _cm_klass_closure;
4227 public:
4228 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4229 void do_klass(Klass* k) {
4230 if (k->has_accumulated_modified_oops()) {
4231 k->clear_accumulated_modified_oops();
4232
4233 _cm_klass_closure.do_klass(k);
4234 }
4235 }
4236 };
4237
4238 // The freelist lock is needed to prevent asserts, is it really needed?
4239 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4240
4241 cl->set_freelistLock(freelistLock);
4242
4243 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4244
4245 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4246 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4247 PrecleanKlassClosure preclean_klass_closure(cl);
4248 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4249
4250 verify_work_stacks_empty();
4251 verify_overflow_empty();
4252 }
4253
4254 void CMSCollector::checkpointRootsFinal() {
4255 assert(_collectorState == FinalMarking, "incorrect state transition?");
4256 check_correct_thread_executing();
4257 // world is stopped at this checkpoint
4258 assert(SafepointSynchronize::is_at_safepoint(),
4259 "world should be stopped");
4260 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4261
4262 verify_work_stacks_empty();
4263 verify_overflow_empty();
4264
4265 if (PrintGCDetails) {
4266 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4267 _young_gen->used() / K,
4268 _young_gen->capacity() / K);
4269 }
4270 {
4271 if (CMSScavengeBeforeRemark) {
4272 GenCollectedHeap* gch = GenCollectedHeap::heap();
4273 // Temporarily set flag to false, GCH->do_collection will
4274 // expect it to be false and set to true
4275 FlagSetting fl(gch->_is_gc_active, false);
4276 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4277 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4278 gch->do_collection(true, // full (i.e. force, see below)
4279 false, // !clear_all_soft_refs
4280 0, // size
4281 false, // is_tlab
4282 Generation::Young // type
4283 );
4284 }
4285 FreelistLocker x(this);
4286 MutexLockerEx y(bitMapLock(),
4287 Mutex::_no_safepoint_check_flag);
4288 checkpointRootsFinalWork();
4289 }
4290 verify_work_stacks_empty();
4291 verify_overflow_empty();
4292 }
4293
4294 void CMSCollector::checkpointRootsFinalWork() {
4295 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4296
4297 assert(haveFreelistLocks(), "must have free list locks");
4298 assert_lock_strong(bitMapLock());
4299
4300 ResourceMark rm;
4301 HandleMark hm;
4302
4303 GenCollectedHeap* gch = GenCollectedHeap::heap();
4304
4305 if (should_unload_classes()) {
4306 CodeCache::gc_prologue();
4307 }
4308 assert(haveFreelistLocks(), "must have free list locks");
4309 assert_lock_strong(bitMapLock());
4310
4311 // We might assume that we need not fill TLAB's when
4312 // CMSScavengeBeforeRemark is set, because we may have just done
4313 // a scavenge which would have filled all TLAB's -- and besides
4314 // Eden would be empty. This however may not always be the case --
4315 // for instance although we asked for a scavenge, it may not have
4316 // happened because of a JNI critical section. We probably need
4317 // a policy for deciding whether we can in that case wait until
4318 // the critical section releases and then do the remark following
4319 // the scavenge, and skip it here. In the absence of that policy,
4320 // or of an indication of whether the scavenge did indeed occur,
4321 // we cannot rely on TLAB's having been filled and must do
4322 // so here just in case a scavenge did not happen.
4323 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4324 // Update the saved marks which may affect the root scans.
4325 gch->save_marks();
4326
4327 if (CMSPrintEdenSurvivorChunks) {
4328 print_eden_and_survivor_chunk_arrays();
4329 }
4330
4331 {
4332 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4333
4334 // Note on the role of the mod union table:
4335 // Since the marker in "markFromRoots" marks concurrently with
4336 // mutators, it is possible for some reachable objects not to have been
4337 // scanned. For instance, an only reference to an object A was
4338 // placed in object B after the marker scanned B. Unless B is rescanned,
4339 // A would be collected. Such updates to references in marked objects
4340 // are detected via the mod union table which is the set of all cards
4341 // dirtied since the first checkpoint in this GC cycle and prior to
4342 // the most recent young generation GC, minus those cleaned up by the
4343 // concurrent precleaning.
4344 if (CMSParallelRemarkEnabled) {
4345 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
4346 do_remark_parallel();
4347 } else {
4348 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4349 _gc_timer_cm, _gc_tracer_cm->gc_id());
4350 do_remark_non_parallel();
4351 }
4352 }
4353 verify_work_stacks_empty();
4354 verify_overflow_empty();
4355
4356 {
4357 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4358 refProcessingWork();
4359 }
4360 verify_work_stacks_empty();
4361 verify_overflow_empty();
4362
4363 if (should_unload_classes()) {
4364 CodeCache::gc_epilogue();
4365 }
4366 JvmtiExport::gc_epilogue();
4367
4368 // If we encountered any (marking stack / work queue) overflow
4369 // events during the current CMS cycle, take appropriate
4370 // remedial measures, where possible, so as to try and avoid
4371 // recurrence of that condition.
4372 assert(_markStack.isEmpty(), "No grey objects");
4373 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4374 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4375 if (ser_ovflw > 0) {
4376 if (PrintCMSStatistics != 0) {
4377 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4378 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4379 ", kac_preclean="SIZE_FORMAT")",
4380 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4381 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4382 }
4383 _markStack.expand();
4384 _ser_pmc_remark_ovflw = 0;
4385 _ser_pmc_preclean_ovflw = 0;
4386 _ser_kac_preclean_ovflw = 0;
4387 _ser_kac_ovflw = 0;
4388 }
4389 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4390 if (PrintCMSStatistics != 0) {
4391 gclog_or_tty->print_cr("Work queue overflow (benign) "
4392 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4393 _par_pmc_remark_ovflw, _par_kac_ovflw);
4394 }
4395 _par_pmc_remark_ovflw = 0;
4396 _par_kac_ovflw = 0;
4397 }
4398 if (PrintCMSStatistics != 0) {
4399 if (_markStack._hit_limit > 0) {
4400 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4401 _markStack._hit_limit);
4402 }
4403 if (_markStack._failed_double > 0) {
4404 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4405 " current capacity "SIZE_FORMAT,
4406 _markStack._failed_double,
4407 _markStack.capacity());
4408 }
4409 }
4410 _markStack._hit_limit = 0;
4411 _markStack._failed_double = 0;
4412
4413 if ((VerifyAfterGC || VerifyDuringGC) &&
4414 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4415 verify_after_remark();
4416 }
4417
4418 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4419
4420 // Change under the freelistLocks.
4421 _collectorState = Sweeping;
4422 // Call isAllClear() under bitMapLock
4423 assert(_modUnionTable.isAllClear(),
4424 "Should be clear by end of the final marking");
4425 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4426 "Should be clear by end of the final marking");
4427 }
4428
4429 void CMSParInitialMarkTask::work(uint worker_id) {
4430 elapsedTimer _timer;
4431 ResourceMark rm;
4432 HandleMark hm;
4433
4434 // ---------- scan from roots --------------
4435 _timer.start();
4436 GenCollectedHeap* gch = GenCollectedHeap::heap();
4437 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4438
4439 // ---------- young gen roots --------------
4440 {
4441 work_on_young_gen_roots(worker_id, &par_mri_cl);
4442 _timer.stop();
4443 if (PrintCMSStatistics != 0) {
4444 gclog_or_tty->print_cr(
4445 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4446 worker_id, _timer.seconds());
4447 }
4448 }
4449
4450 // ---------- remaining roots --------------
4451 _timer.reset();
4452 _timer.start();
4453
4454 CLDToOopClosure cld_closure(&par_mri_cl, true);
4455
4456 gch->gen_process_roots(_strong_roots_scope,
4457 Generation::Old,
4458 false, // yg was scanned above
4459 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4460 _collector->should_unload_classes(),
4461 &par_mri_cl,
4462 NULL,
4463 &cld_closure);
4464 assert(_collector->should_unload_classes()
4465 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4466 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4467 _timer.stop();
4468 if (PrintCMSStatistics != 0) {
4469 gclog_or_tty->print_cr(
4470 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4471 worker_id, _timer.seconds());
4472 }
4473 }
4474
4475 // Parallel remark task
4476 class CMSParRemarkTask: public CMSParMarkTask {
4477 CompactibleFreeListSpace* _cms_space;
4478
4479 // The per-thread work queues, available here for stealing.
4480 OopTaskQueueSet* _task_queues;
4481 ParallelTaskTerminator _term;
4482 StrongRootsScope* _strong_roots_scope;
4483
4484 public:
4485 // A value of 0 passed to n_workers will cause the number of
4486 // workers to be taken from the active workers in the work gang.
4487 CMSParRemarkTask(CMSCollector* collector,
4488 CompactibleFreeListSpace* cms_space,
4489 uint n_workers, FlexibleWorkGang* workers,
4490 OopTaskQueueSet* task_queues,
4491 StrongRootsScope* strong_roots_scope):
4492 CMSParMarkTask("Rescan roots and grey objects in parallel",
4493 collector, n_workers),
4494 _cms_space(cms_space),
4495 _task_queues(task_queues),
4496 _term(n_workers, task_queues),
4497 _strong_roots_scope(strong_roots_scope) { }
4498
4499 OopTaskQueueSet* task_queues() { return _task_queues; }
4500
4501 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4502
4503 ParallelTaskTerminator* terminator() { return &_term; }
4504 uint n_workers() { return _n_workers; }
4505
4506 void work(uint worker_id);
4507
4508 private:
4509 // ... of dirty cards in old space
4510 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4511 Par_MarkRefsIntoAndScanClosure* cl);
4512
4513 // ... work stealing for the above
4514 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4515 };
4516
4517 class RemarkKlassClosure : public KlassClosure {
4518 KlassToOopClosure _cm_klass_closure;
4519 public:
4520 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4521 void do_klass(Klass* k) {
4522 // Check if we have modified any oops in the Klass during the concurrent marking.
4523 if (k->has_accumulated_modified_oops()) {
4524 k->clear_accumulated_modified_oops();
4525
4526 // We could have transfered the current modified marks to the accumulated marks,
4527 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4528 } else if (k->has_modified_oops()) {
4529 // Don't clear anything, this info is needed by the next young collection.
4530 } else {
4531 // No modified oops in the Klass.
4532 return;
4533 }
4534
4535 // The klass has modified fields, need to scan the klass.
4536 _cm_klass_closure.do_klass(k);
4537 }
4538 };
4539
4540 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4541 ParNewGeneration* young_gen = _collector->_young_gen;
4542 ContiguousSpace* eden_space = young_gen->eden();
4543 ContiguousSpace* from_space = young_gen->from();
4544 ContiguousSpace* to_space = young_gen->to();
4545
4546 HeapWord** eca = _collector->_eden_chunk_array;
4547 size_t ect = _collector->_eden_chunk_index;
4548 HeapWord** sca = _collector->_survivor_chunk_array;
4549 size_t sct = _collector->_survivor_chunk_index;
4550
4551 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4552 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4553
4554 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4555 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4556 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4557 }
4558
4559 // work_queue(i) is passed to the closure
4560 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
4561 // also is passed to do_dirty_card_rescan_tasks() and to
4562 // do_work_steal() to select the i-th task_queue.
4563
4564 void CMSParRemarkTask::work(uint worker_id) {
4565 elapsedTimer _timer;
4566 ResourceMark rm;
4567 HandleMark hm;
4568
4569 // ---------- rescan from roots --------------
4570 _timer.start();
4571 GenCollectedHeap* gch = GenCollectedHeap::heap();
4572 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4573 _collector->_span, _collector->ref_processor(),
4574 &(_collector->_markBitMap),
4575 work_queue(worker_id));
4576
4577 // Rescan young gen roots first since these are likely
4578 // coarsely partitioned and may, on that account, constitute
4579 // the critical path; thus, it's best to start off that
4580 // work first.
4581 // ---------- young gen roots --------------
4582 {
4583 work_on_young_gen_roots(worker_id, &par_mrias_cl);
4584 _timer.stop();
4585 if (PrintCMSStatistics != 0) {
4586 gclog_or_tty->print_cr(
4587 "Finished young gen rescan work in %dth thread: %3.3f sec",
4588 worker_id, _timer.seconds());
4589 }
4590 }
4591
4592 // ---------- remaining roots --------------
4593 _timer.reset();
4594 _timer.start();
4595 gch->gen_process_roots(_strong_roots_scope,
4596 Generation::Old,
4597 false, // yg was scanned above
4598 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4599 _collector->should_unload_classes(),
4600 &par_mrias_cl,
4601 NULL,
4602 NULL); // The dirty klasses will be handled below
4603
4604 assert(_collector->should_unload_classes()
4605 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4606 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4607 _timer.stop();
4608 if (PrintCMSStatistics != 0) {
4609 gclog_or_tty->print_cr(
4610 "Finished remaining root rescan work in %dth thread: %3.3f sec",
4611 worker_id, _timer.seconds());
4612 }
4613
4614 // ---------- unhandled CLD scanning ----------
4615 if (worker_id == 0) { // Single threaded at the moment.
4616 _timer.reset();
4617 _timer.start();
4618
4619 // Scan all new class loader data objects and new dependencies that were
4620 // introduced during concurrent marking.
4621 ResourceMark rm;
4622 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4623 for (int i = 0; i < array->length(); i++) {
4624 par_mrias_cl.do_class_loader_data(array->at(i));
4625 }
4626
4627 // We don't need to keep track of new CLDs anymore.
4628 ClassLoaderDataGraph::remember_new_clds(false);
4629
4630 _timer.stop();
4631 if (PrintCMSStatistics != 0) {
4632 gclog_or_tty->print_cr(
4633 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4634 worker_id, _timer.seconds());
4635 }
4636 }
4637
4638 // ---------- dirty klass scanning ----------
4639 if (worker_id == 0) { // Single threaded at the moment.
4640 _timer.reset();
4641 _timer.start();
4642
4643 // Scan all classes that was dirtied during the concurrent marking phase.
4644 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4645 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4646
4647 _timer.stop();
4648 if (PrintCMSStatistics != 0) {
4649 gclog_or_tty->print_cr(
4650 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4651 worker_id, _timer.seconds());
4652 }
4653 }
4654
4655 // We might have added oops to ClassLoaderData::_handles during the
4656 // concurrent marking phase. These oops point to newly allocated objects
4657 // that are guaranteed to be kept alive. Either by the direct allocation
4658 // code, or when the young collector processes the roots. Hence,
4659 // we don't have to revisit the _handles block during the remark phase.
4660
4661 // ---------- rescan dirty cards ------------
4662 _timer.reset();
4663 _timer.start();
4664
4665 // Do the rescan tasks for each of the two spaces
4666 // (cms_space) in turn.
4667 // "worker_id" is passed to select the task_queue for "worker_id"
4668 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4669 _timer.stop();
4670 if (PrintCMSStatistics != 0) {
4671 gclog_or_tty->print_cr(
4672 "Finished dirty card rescan work in %dth thread: %3.3f sec",
4673 worker_id, _timer.seconds());
4674 }
4675
4676 // ---------- steal work from other threads ...
4677 // ---------- ... and drain overflow list.
4678 _timer.reset();
4679 _timer.start();
4680 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4681 _timer.stop();
4682 if (PrintCMSStatistics != 0) {
4683 gclog_or_tty->print_cr(
4684 "Finished work stealing in %dth thread: %3.3f sec",
4685 worker_id, _timer.seconds());
4686 }
4687 }
4688
4689 // Note that parameter "i" is not used.
4690 void
4691 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4692 OopsInGenClosure* cl, ContiguousSpace* space,
4693 HeapWord** chunk_array, size_t chunk_top) {
4694 // Until all tasks completed:
4695 // . claim an unclaimed task
4696 // . compute region boundaries corresponding to task claimed
4697 // using chunk_array
4698 // . par_oop_iterate(cl) over that region
4699
4700 ResourceMark rm;
4701 HandleMark hm;
4702
4703 SequentialSubTasksDone* pst = space->par_seq_tasks();
4704
4705 uint nth_task = 0;
4706 uint n_tasks = pst->n_tasks();
4707
4708 if (n_tasks > 0) {
4709 assert(pst->valid(), "Uninitialized use?");
4710 HeapWord *start, *end;
4711 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4712 // We claimed task # nth_task; compute its boundaries.
4713 if (chunk_top == 0) { // no samples were taken
4714 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4715 start = space->bottom();
4716 end = space->top();
4717 } else if (nth_task == 0) {
4718 start = space->bottom();
4719 end = chunk_array[nth_task];
4720 } else if (nth_task < (uint)chunk_top) {
4721 assert(nth_task >= 1, "Control point invariant");
4722 start = chunk_array[nth_task - 1];
4723 end = chunk_array[nth_task];
4724 } else {
4725 assert(nth_task == (uint)chunk_top, "Control point invariant");
4726 start = chunk_array[chunk_top - 1];
4727 end = space->top();
4728 }
4729 MemRegion mr(start, end);
4730 // Verify that mr is in space
4731 assert(mr.is_empty() || space->used_region().contains(mr),
4732 "Should be in space");
4733 // Verify that "start" is an object boundary
4734 assert(mr.is_empty() || oop(mr.start())->is_oop(),
4735 "Should be an oop");
4736 space->par_oop_iterate(mr, cl);
4737 }
4738 pst->all_tasks_completed();
4739 }
4740 }
4741
4742 void
4743 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4744 CompactibleFreeListSpace* sp, int i,
4745 Par_MarkRefsIntoAndScanClosure* cl) {
4746 // Until all tasks completed:
4747 // . claim an unclaimed task
4748 // . compute region boundaries corresponding to task claimed
4749 // . transfer dirty bits ct->mut for that region
4750 // . apply rescanclosure to dirty mut bits for that region
4751
4752 ResourceMark rm;
4753 HandleMark hm;
4754
4755 OopTaskQueue* work_q = work_queue(i);
4756 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4757 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4758 // CAUTION: This closure has state that persists across calls to
4759 // the work method dirty_range_iterate_clear() in that it has
4760 // embedded in it a (subtype of) UpwardsObjectClosure. The
4761 // use of that state in the embedded UpwardsObjectClosure instance
4762 // assumes that the cards are always iterated (even if in parallel
4763 // by several threads) in monotonically increasing order per each
4764 // thread. This is true of the implementation below which picks
4765 // card ranges (chunks) in monotonically increasing order globally
4766 // and, a-fortiori, in monotonically increasing order per thread
4767 // (the latter order being a subsequence of the former).
4768 // If the work code below is ever reorganized into a more chaotic
4769 // work-partitioning form than the current "sequential tasks"
4770 // paradigm, the use of that persistent state will have to be
4771 // revisited and modified appropriately. See also related
4772 // bug 4756801 work on which should examine this code to make
4773 // sure that the changes there do not run counter to the
4774 // assumptions made here and necessary for correctness and
4775 // efficiency. Note also that this code might yield inefficient
4776 // behavior in the case of very large objects that span one or
4777 // more work chunks. Such objects would potentially be scanned
4778 // several times redundantly. Work on 4756801 should try and
4779 // address that performance anomaly if at all possible. XXX
4780 MemRegion full_span = _collector->_span;
4781 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4782 MarkFromDirtyCardsClosure
4783 greyRescanClosure(_collector, full_span, // entire span of interest
4784 sp, bm, work_q, cl);
4785
4786 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4787 assert(pst->valid(), "Uninitialized use?");
4788 uint nth_task = 0;
4789 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4790 MemRegion span = sp->used_region();
4791 HeapWord* start_addr = span.start();
4792 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4793 alignment);
4794 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4795 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4796 start_addr, "Check alignment");
4797 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4798 chunk_size, "Check alignment");
4799
4800 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4801 // Having claimed the nth_task, compute corresponding mem-region,
4802 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4803 // The alignment restriction ensures that we do not need any
4804 // synchronization with other gang-workers while setting or
4805 // clearing bits in thus chunk of the MUT.
4806 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4807 start_addr + (nth_task+1)*chunk_size);
4808 // The last chunk's end might be way beyond end of the
4809 // used region. In that case pull back appropriately.
4810 if (this_span.end() > end_addr) {
4811 this_span.set_end(end_addr);
4812 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4813 }
4814 // Iterate over the dirty cards covering this chunk, marking them
4815 // precleaned, and setting the corresponding bits in the mod union
4816 // table. Since we have been careful to partition at Card and MUT-word
4817 // boundaries no synchronization is needed between parallel threads.
4818 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4819 &modUnionClosure);
4820
4821 // Having transferred these marks into the modUnionTable,
4822 // rescan the marked objects on the dirty cards in the modUnionTable.
4823 // Even if this is at a synchronous collection, the initial marking
4824 // may have been done during an asynchronous collection so there
4825 // may be dirty bits in the mod-union table.
4826 _collector->_modUnionTable.dirty_range_iterate_clear(
4827 this_span, &greyRescanClosure);
4828 _collector->_modUnionTable.verifyNoOneBitsInRange(
4829 this_span.start(),
4830 this_span.end());
4831 }
4832 pst->all_tasks_completed(); // declare that i am done
4833 }
4834
4835 // . see if we can share work_queues with ParNew? XXX
4836 void
4837 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4838 int* seed) {
4839 OopTaskQueue* work_q = work_queue(i);
4840 NOT_PRODUCT(int num_steals = 0;)
4841 oop obj_to_scan;
4842 CMSBitMap* bm = &(_collector->_markBitMap);
4843
4844 while (true) {
4845 // Completely finish any left over work from (an) earlier round(s)
4846 cl->trim_queue(0);
4847 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4848 (size_t)ParGCDesiredObjsFromOverflowList);
4849 // Now check if there's any work in the overflow list
4850 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4851 // only affects the number of attempts made to get work from the
4852 // overflow list and does not affect the number of workers. Just
4853 // pass ParallelGCThreads so this behavior is unchanged.
4854 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4855 work_q,
4856 ParallelGCThreads)) {
4857 // found something in global overflow list;
4858 // not yet ready to go stealing work from others.
4859 // We'd like to assert(work_q->size() != 0, ...)
4860 // because we just took work from the overflow list,
4861 // but of course we can't since all of that could have
4862 // been already stolen from us.
4863 // "He giveth and He taketh away."
4864 continue;
4865 }
4866 // Verify that we have no work before we resort to stealing
4867 assert(work_q->size() == 0, "Have work, shouldn't steal");
4868 // Try to steal from other queues that have work
4869 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4870 NOT_PRODUCT(num_steals++;)
4871 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4872 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4873 // Do scanning work
4874 obj_to_scan->oop_iterate(cl);
4875 // Loop around, finish this work, and try to steal some more
4876 } else if (terminator()->offer_termination()) {
4877 break; // nirvana from the infinite cycle
4878 }
4879 }
4880 NOT_PRODUCT(
4881 if (PrintCMSStatistics != 0) {
4882 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
4883 }
4884 )
4885 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4886 "Else our work is not yet done");
4887 }
4888
4889 // Record object boundaries in _eden_chunk_array by sampling the eden
4890 // top in the slow-path eden object allocation code path and record
4891 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4892 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4893 // sampling in sample_eden() that activates during the part of the
4894 // preclean phase.
4895 void CMSCollector::sample_eden_chunk() {
4896 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4897 if (_eden_chunk_lock->try_lock()) {
4898 // Record a sample. This is the critical section. The contents
4899 // of the _eden_chunk_array have to be non-decreasing in the
4900 // address order.
4901 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4902 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4903 "Unexpected state of Eden");
4904 if (_eden_chunk_index == 0 ||
4905 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4906 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4907 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4908 _eden_chunk_index++; // commit sample
4909 }
4910 _eden_chunk_lock->unlock();
4911 }
4912 }
4913 }
4914
4915 // Return a thread-local PLAB recording array, as appropriate.
4916 void* CMSCollector::get_data_recorder(int thr_num) {
4917 if (_survivor_plab_array != NULL &&
4918 (CMSPLABRecordAlways ||
4919 (_collectorState > Marking && _collectorState < FinalMarking))) {
4920 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4921 ChunkArray* ca = &_survivor_plab_array[thr_num];
4922 ca->reset(); // clear it so that fresh data is recorded
4923 return (void*) ca;
4924 } else {
4925 return NULL;
4926 }
4927 }
4928
4929 // Reset all the thread-local PLAB recording arrays
4930 void CMSCollector::reset_survivor_plab_arrays() {
4931 for (uint i = 0; i < ParallelGCThreads; i++) {
4932 _survivor_plab_array[i].reset();
4933 }
4934 }
4935
4936 // Merge the per-thread plab arrays into the global survivor chunk
4937 // array which will provide the partitioning of the survivor space
4938 // for CMS initial scan and rescan.
4939 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4940 int no_of_gc_threads) {
4941 assert(_survivor_plab_array != NULL, "Error");
4942 assert(_survivor_chunk_array != NULL, "Error");
4943 assert(_collectorState == FinalMarking ||
4944 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4945 for (int j = 0; j < no_of_gc_threads; j++) {
4946 _cursor[j] = 0;
4947 }
4948 HeapWord* top = surv->top();
4949 size_t i;
4950 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4951 HeapWord* min_val = top; // Higher than any PLAB address
4952 uint min_tid = 0; // position of min_val this round
4953 for (int j = 0; j < no_of_gc_threads; j++) {
4954 ChunkArray* cur_sca = &_survivor_plab_array[j];
4955 if (_cursor[j] == cur_sca->end()) {
4956 continue;
4957 }
4958 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4959 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4960 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4961 if (cur_val < min_val) {
4962 min_tid = j;
4963 min_val = cur_val;
4964 } else {
4965 assert(cur_val < top, "All recorded addresses should be less");
4966 }
4967 }
4968 // At this point min_val and min_tid are respectively
4969 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4970 // and the thread (j) that witnesses that address.
4971 // We record this address in the _survivor_chunk_array[i]
4972 // and increment _cursor[min_tid] prior to the next round i.
4973 if (min_val == top) {
4974 break;
4975 }
4976 _survivor_chunk_array[i] = min_val;
4977 _cursor[min_tid]++;
4978 }
4979 // We are all done; record the size of the _survivor_chunk_array
4980 _survivor_chunk_index = i; // exclusive: [0, i)
4981 if (PrintCMSStatistics > 0) {
4982 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4983 }
4984 // Verify that we used up all the recorded entries
4985 #ifdef ASSERT
4986 size_t total = 0;
4987 for (int j = 0; j < no_of_gc_threads; j++) {
4988 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4989 total += _cursor[j];
4990 }
4991 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4992 // Check that the merged array is in sorted order
4993 if (total > 0) {
4994 for (size_t i = 0; i < total - 1; i++) {
4995 if (PrintCMSStatistics > 0) {
4996 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4997 i, p2i(_survivor_chunk_array[i]));
4998 }
4999 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5000 "Not sorted");
5001 }
5002 }
5003 #endif // ASSERT
5004 }
5005
5006 // Set up the space's par_seq_tasks structure for work claiming
5007 // for parallel initial scan and rescan of young gen.
5008 // See ParRescanTask where this is currently used.
5009 void
5010 CMSCollector::
5011 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5012 assert(n_threads > 0, "Unexpected n_threads argument");
5013
5014 // Eden space
5015 if (!_young_gen->eden()->is_empty()) {
5016 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
5017 assert(!pst->valid(), "Clobbering existing data?");
5018 // Each valid entry in [0, _eden_chunk_index) represents a task.
5019 size_t n_tasks = _eden_chunk_index + 1;
5020 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5021 // Sets the condition for completion of the subtask (how many threads
5022 // need to finish in order to be done).
5023 pst->set_n_threads(n_threads);
5024 pst->set_n_tasks((int)n_tasks);
5025 }
5026
5027 // Merge the survivor plab arrays into _survivor_chunk_array
5028 if (_survivor_plab_array != NULL) {
5029 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5030 } else {
5031 assert(_survivor_chunk_index == 0, "Error");
5032 }
5033
5034 // To space
5035 {
5036 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5037 assert(!pst->valid(), "Clobbering existing data?");
5038 // Sets the condition for completion of the subtask (how many threads
5039 // need to finish in order to be done).
5040 pst->set_n_threads(n_threads);
5041 pst->set_n_tasks(1);
5042 assert(pst->valid(), "Error");
5043 }
5044
5045 // From space
5046 {
5047 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5048 assert(!pst->valid(), "Clobbering existing data?");
5049 size_t n_tasks = _survivor_chunk_index + 1;
5050 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5051 // Sets the condition for completion of the subtask (how many threads
5052 // need to finish in order to be done).
5053 pst->set_n_threads(n_threads);
5054 pst->set_n_tasks((int)n_tasks);
5055 assert(pst->valid(), "Error");
5056 }
5057 }
5058
5059 // Parallel version of remark
5060 void CMSCollector::do_remark_parallel() {
5061 GenCollectedHeap* gch = GenCollectedHeap::heap();
5062 FlexibleWorkGang* workers = gch->workers();
5063 assert(workers != NULL, "Need parallel worker threads.");
5064 // Choose to use the number of GC workers most recently set
5065 // into "active_workers".
5066 uint n_workers = workers->active_workers();
5067
5068 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5069
5070 StrongRootsScope srs(n_workers);
5071
5072 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
5073
5074 // We won't be iterating over the cards in the card table updating
5075 // the younger_gen cards, so we shouldn't call the following else
5076 // the verification code as well as subsequent younger_refs_iterate
5077 // code would get confused. XXX
5078 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5079
5080 // The young gen rescan work will not be done as part of
5081 // process_roots (which currently doesn't know how to
5082 // parallelize such a scan), but rather will be broken up into
5083 // a set of parallel tasks (via the sampling that the [abortable]
5084 // preclean phase did of eden, plus the [two] tasks of
5085 // scanning the [two] survivor spaces. Further fine-grain
5086 // parallelization of the scanning of the survivor spaces
5087 // themselves, and of precleaning of the younger gen itself
5088 // is deferred to the future.
5089 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5090
5091 // The dirty card rescan work is broken up into a "sequence"
5092 // of parallel tasks (per constituent space) that are dynamically
5093 // claimed by the parallel threads.
5094 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5095
5096 // It turns out that even when we're using 1 thread, doing the work in a
5097 // separate thread causes wide variance in run times. We can't help this
5098 // in the multi-threaded case, but we special-case n=1 here to get
5099 // repeatable measurements of the 1-thread overhead of the parallel code.
5100 if (n_workers > 1) {
5101 // Make refs discovery MT-safe, if it isn't already: it may not
5102 // necessarily be so, since it's possible that we are doing
5103 // ST marking.
5104 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5105 workers->run_task(&tsk);
5106 } else {
5107 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5108 tsk.work(0);
5109 }
5110
5111 // restore, single-threaded for now, any preserved marks
5112 // as a result of work_q overflow
5113 restore_preserved_marks_if_any();
5114 }
5115
5116 // Non-parallel version of remark
5117 void CMSCollector::do_remark_non_parallel() {
5118 ResourceMark rm;
5119 HandleMark hm;
5120 GenCollectedHeap* gch = GenCollectedHeap::heap();
5121 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5122
5123 MarkRefsIntoAndScanClosure
5124 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5125 &_markStack, this,
5126 false /* should_yield */, false /* not precleaning */);
5127 MarkFromDirtyCardsClosure
5128 markFromDirtyCardsClosure(this, _span,
5129 NULL, // space is set further below
5130 &_markBitMap, &_markStack, &mrias_cl);
5131 {
5132 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5133 // Iterate over the dirty cards, setting the corresponding bits in the
5134 // mod union table.
5135 {
5136 ModUnionClosure modUnionClosure(&_modUnionTable);
5137 _ct->ct_bs()->dirty_card_iterate(
5138 _cmsGen->used_region(),
5139 &modUnionClosure);
5140 }
5141 // Having transferred these marks into the modUnionTable, we just need
5142 // to rescan the marked objects on the dirty cards in the modUnionTable.
5143 // The initial marking may have been done during an asynchronous
5144 // collection so there may be dirty bits in the mod-union table.
5145 const int alignment =
5146 CardTableModRefBS::card_size * BitsPerWord;
5147 {
5148 // ... First handle dirty cards in CMS gen
5149 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5150 MemRegion ur = _cmsGen->used_region();
5151 HeapWord* lb = ur.start();
5152 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5153 MemRegion cms_span(lb, ub);
5154 _modUnionTable.dirty_range_iterate_clear(cms_span,
5155 &markFromDirtyCardsClosure);
5156 verify_work_stacks_empty();
5157 if (PrintCMSStatistics != 0) {
5158 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5159 markFromDirtyCardsClosure.num_dirty_cards());
5160 }
5161 }
5162 }
5163 if (VerifyDuringGC &&
5164 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5165 HandleMark hm; // Discard invalid handles created during verification
5166 Universe::verify();
5167 }
5168 {
5169 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5170
5171 verify_work_stacks_empty();
5172
5173 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5174 StrongRootsScope srs(1);
5175
5176 gch->gen_process_roots(&srs,
5177 Generation::Old,
5178 true, // younger gens as roots
5179 GenCollectedHeap::ScanningOption(roots_scanning_options()),
5180 should_unload_classes(),
5181 &mrias_cl,
5182 NULL,
5183 NULL); // The dirty klasses will be handled below
5184
5185 assert(should_unload_classes()
5186 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5187 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5188 }
5189
5190 {
5191 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5192
5193 verify_work_stacks_empty();
5194
5195 // Scan all class loader data objects that might have been introduced
5196 // during concurrent marking.
5197 ResourceMark rm;
5198 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5199 for (int i = 0; i < array->length(); i++) {
5200 mrias_cl.do_class_loader_data(array->at(i));
5201 }
5202
5203 // We don't need to keep track of new CLDs anymore.
5204 ClassLoaderDataGraph::remember_new_clds(false);
5205
5206 verify_work_stacks_empty();
5207 }
5208
5209 {
5210 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5211
5212 verify_work_stacks_empty();
5213
5214 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5215 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5216
5217 verify_work_stacks_empty();
5218 }
5219
5220 // We might have added oops to ClassLoaderData::_handles during the
5221 // concurrent marking phase. These oops point to newly allocated objects
5222 // that are guaranteed to be kept alive. Either by the direct allocation
5223 // code, or when the young collector processes the roots. Hence,
5224 // we don't have to revisit the _handles block during the remark phase.
5225
5226 verify_work_stacks_empty();
5227 // Restore evacuated mark words, if any, used for overflow list links
5228 if (!CMSOverflowEarlyRestoration) {
5229 restore_preserved_marks_if_any();
5230 }
5231 verify_overflow_empty();
5232 }
5233
5234 ////////////////////////////////////////////////////////
5235 // Parallel Reference Processing Task Proxy Class
5236 ////////////////////////////////////////////////////////
5237 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5238 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5239 CMSCollector* _collector;
5240 CMSBitMap* _mark_bit_map;
5241 const MemRegion _span;
5242 ProcessTask& _task;
5243
5244 public:
5245 CMSRefProcTaskProxy(ProcessTask& task,
5246 CMSCollector* collector,
5247 const MemRegion& span,
5248 CMSBitMap* mark_bit_map,
5249 AbstractWorkGang* workers,
5250 OopTaskQueueSet* task_queues):
5251 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5252 task_queues,
5253 workers->active_workers()),
5254 _task(task),
5255 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5256 {
5257 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5258 "Inconsistency in _span");
5259 }
5260
5261 OopTaskQueueSet* task_queues() { return queues(); }
5262
5263 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5264
5265 void do_work_steal(int i,
5266 CMSParDrainMarkingStackClosure* drain,
5267 CMSParKeepAliveClosure* keep_alive,
5268 int* seed);
5269
5270 virtual void work(uint worker_id);
5271 };
5272
5273 void CMSRefProcTaskProxy::work(uint worker_id) {
5274 ResourceMark rm;
5275 HandleMark hm;
5276 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5277 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5278 _mark_bit_map,
5279 work_queue(worker_id));
5280 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5281 _mark_bit_map,
5282 work_queue(worker_id));
5283 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5284 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5285 if (_task.marks_oops_alive()) {
5286 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5287 _collector->hash_seed(worker_id));
5288 }
5289 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5290 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5291 }
5292
5293 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5294 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5295 EnqueueTask& _task;
5296
5297 public:
5298 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5299 : AbstractGangTask("Enqueue reference objects in parallel"),
5300 _task(task)
5301 { }
5302
5303 virtual void work(uint worker_id)
5304 {
5305 _task.work(worker_id);
5306 }
5307 };
5308
5309 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5310 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5311 _span(span),
5312 _bit_map(bit_map),
5313 _work_queue(work_queue),
5314 _mark_and_push(collector, span, bit_map, work_queue),
5315 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5316 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5317 { }
5318
5319 // . see if we can share work_queues with ParNew? XXX
5320 void CMSRefProcTaskProxy::do_work_steal(int i,
5321 CMSParDrainMarkingStackClosure* drain,
5322 CMSParKeepAliveClosure* keep_alive,
5323 int* seed) {
5324 OopTaskQueue* work_q = work_queue(i);
5325 NOT_PRODUCT(int num_steals = 0;)
5326 oop obj_to_scan;
5327
5328 while (true) {
5329 // Completely finish any left over work from (an) earlier round(s)
5330 drain->trim_queue(0);
5331 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5332 (size_t)ParGCDesiredObjsFromOverflowList);
5333 // Now check if there's any work in the overflow list
5334 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5335 // only affects the number of attempts made to get work from the
5336 // overflow list and does not affect the number of workers. Just
5337 // pass ParallelGCThreads so this behavior is unchanged.
5338 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5339 work_q,
5340 ParallelGCThreads)) {
5341 // Found something in global overflow list;
5342 // not yet ready to go stealing work from others.
5343 // We'd like to assert(work_q->size() != 0, ...)
5344 // because we just took work from the overflow list,
5345 // but of course we can't, since all of that might have
5346 // been already stolen from us.
5347 continue;
5348 }
5349 // Verify that we have no work before we resort to stealing
5350 assert(work_q->size() == 0, "Have work, shouldn't steal");
5351 // Try to steal from other queues that have work
5352 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5353 NOT_PRODUCT(num_steals++;)
5354 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5355 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5356 // Do scanning work
5357 obj_to_scan->oop_iterate(keep_alive);
5358 // Loop around, finish this work, and try to steal some more
5359 } else if (terminator()->offer_termination()) {
5360 break; // nirvana from the infinite cycle
5361 }
5362 }
5363 NOT_PRODUCT(
5364 if (PrintCMSStatistics != 0) {
5365 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5366 }
5367 )
5368 }
5369
5370 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5371 {
5372 GenCollectedHeap* gch = GenCollectedHeap::heap();
5373 FlexibleWorkGang* workers = gch->workers();
5374 assert(workers != NULL, "Need parallel worker threads.");
5375 CMSRefProcTaskProxy rp_task(task, &_collector,
5376 _collector.ref_processor()->span(),
5377 _collector.markBitMap(),
5378 workers, _collector.task_queues());
5379 workers->run_task(&rp_task);
5380 }
5381
5382 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5383 {
5384
5385 GenCollectedHeap* gch = GenCollectedHeap::heap();
5386 FlexibleWorkGang* workers = gch->workers();
5387 assert(workers != NULL, "Need parallel worker threads.");
5388 CMSRefEnqueueTaskProxy enq_task(task);
5389 workers->run_task(&enq_task);
5390 }
5391
5392 void CMSCollector::refProcessingWork() {
5393 ResourceMark rm;
5394 HandleMark hm;
5395
5396 ReferenceProcessor* rp = ref_processor();
5397 assert(rp->span().equals(_span), "Spans should be equal");
5398 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5399 // Process weak references.
5400 rp->setup_policy(false);
5401 verify_work_stacks_empty();
5402
5403 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5404 &_markStack, false /* !preclean */);
5405 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5406 _span, &_markBitMap, &_markStack,
5407 &cmsKeepAliveClosure, false /* !preclean */);
5408 {
5409 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5410
5411 ReferenceProcessorStats stats;
5412 if (rp->processing_is_mt()) {
5413 // Set the degree of MT here. If the discovery is done MT, there
5414 // may have been a different number of threads doing the discovery
5415 // and a different number of discovered lists may have Ref objects.
5416 // That is OK as long as the Reference lists are balanced (see
5417 // balance_all_queues() and balance_queues()).
5418 GenCollectedHeap* gch = GenCollectedHeap::heap();
5419 uint active_workers = ParallelGCThreads;
5420 FlexibleWorkGang* workers = gch->workers();
5421 if (workers != NULL) {
5422 active_workers = workers->active_workers();
5423 // The expectation is that active_workers will have already
5424 // been set to a reasonable value. If it has not been set,
5425 // investigate.
5426 assert(active_workers > 0, "Should have been set during scavenge");
5427 }
5428 rp->set_active_mt_degree(active_workers);
5429 CMSRefProcTaskExecutor task_executor(*this);
5430 stats = rp->process_discovered_references(&_is_alive_closure,
5431 &cmsKeepAliveClosure,
5432 &cmsDrainMarkingStackClosure,
5433 &task_executor,
5434 _gc_timer_cm,
5435 _gc_tracer_cm->gc_id());
5436 } else {
5437 stats = rp->process_discovered_references(&_is_alive_closure,
5438 &cmsKeepAliveClosure,
5439 &cmsDrainMarkingStackClosure,
5440 NULL,
5441 _gc_timer_cm,
5442 _gc_tracer_cm->gc_id());
5443 }
5444 _gc_tracer_cm->report_gc_reference_stats(stats);
5445
5446 }
5447
5448 // This is the point where the entire marking should have completed.
5449 verify_work_stacks_empty();
5450
5451 if (should_unload_classes()) {
5452 {
5453 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5454
5455 // Unload classes and purge the SystemDictionary.
5456 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5457
5458 // Unload nmethods.
5459 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5460
5461 // Prune dead klasses from subklass/sibling/implementor lists.
5462 Klass::clean_weak_klass_links(&_is_alive_closure);
5463 }
5464
5465 {
5466 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5467 // Clean up unreferenced symbols in symbol table.
5468 SymbolTable::unlink();
5469 }
5470
5471 {
5472 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5473 // Delete entries for dead interned strings.
5474 StringTable::unlink(&_is_alive_closure);
5475 }
5476 }
5477
5478
5479 // Restore any preserved marks as a result of mark stack or
5480 // work queue overflow
5481 restore_preserved_marks_if_any(); // done single-threaded for now
5482
5483 rp->set_enqueuing_is_done(true);
5484 if (rp->processing_is_mt()) {
5485 rp->balance_all_queues();
5486 CMSRefProcTaskExecutor task_executor(*this);
5487 rp->enqueue_discovered_references(&task_executor);
5488 } else {
5489 rp->enqueue_discovered_references(NULL);
5490 }
5491 rp->verify_no_references_recorded();
5492 assert(!rp->discovery_enabled(), "should have been disabled");
5493 }
5494
5495 #ifndef PRODUCT
5496 void CMSCollector::check_correct_thread_executing() {
5497 Thread* t = Thread::current();
5498 // Only the VM thread or the CMS thread should be here.
5499 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5500 "Unexpected thread type");
5501 // If this is the vm thread, the foreground process
5502 // should not be waiting. Note that _foregroundGCIsActive is
5503 // true while the foreground collector is waiting.
5504 if (_foregroundGCShouldWait) {
5505 // We cannot be the VM thread
5506 assert(t->is_ConcurrentGC_thread(),
5507 "Should be CMS thread");
5508 } else {
5509 // We can be the CMS thread only if we are in a stop-world
5510 // phase of CMS collection.
5511 if (t->is_ConcurrentGC_thread()) {
5512 assert(_collectorState == InitialMarking ||
5513 _collectorState == FinalMarking,
5514 "Should be a stop-world phase");
5515 // The CMS thread should be holding the CMS_token.
5516 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5517 "Potential interference with concurrently "
5518 "executing VM thread");
5519 }
5520 }
5521 }
5522 #endif
5523
5524 void CMSCollector::sweep() {
5525 assert(_collectorState == Sweeping, "just checking");
5526 check_correct_thread_executing();
5527 verify_work_stacks_empty();
5528 verify_overflow_empty();
5529 increment_sweep_count();
5530 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5531
5532 _inter_sweep_timer.stop();
5533 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5534
5535 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5536 _intra_sweep_timer.reset();
5537 _intra_sweep_timer.start();
5538 {
5539 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5540 CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5541 // First sweep the old gen
5542 {
5543 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5544 bitMapLock());
5545 sweepWork(_cmsGen);
5546 }
5547
5548 // Update Universe::_heap_*_at_gc figures.
5549 // We need all the free list locks to make the abstract state
5550 // transition from Sweeping to Resetting. See detailed note
5551 // further below.
5552 {
5553 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5554 // Update heap occupancy information which is used as
5555 // input to soft ref clearing policy at the next gc.
5556 Universe::update_heap_info_at_gc();
5557 _collectorState = Resizing;
5558 }
5559 }
5560 verify_work_stacks_empty();
5561 verify_overflow_empty();
5562
5563 if (should_unload_classes()) {
5564 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5565 // requires that the virtual spaces are stable and not deleted.
5566 ClassLoaderDataGraph::set_should_purge(true);
5567 }
5568
5569 _intra_sweep_timer.stop();
5570 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5571
5572 _inter_sweep_timer.reset();
5573 _inter_sweep_timer.start();
5574
5575 // We need to use a monotonically non-decreasing time in ms
5576 // or we will see time-warp warnings and os::javaTimeMillis()
5577 // does not guarantee monotonicity.
5578 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5579 update_time_of_last_gc(now);
5580
5581 // NOTE on abstract state transitions:
5582 // Mutators allocate-live and/or mark the mod-union table dirty
5583 // based on the state of the collection. The former is done in
5584 // the interval [Marking, Sweeping] and the latter in the interval
5585 // [Marking, Sweeping). Thus the transitions into the Marking state
5586 // and out of the Sweeping state must be synchronously visible
5587 // globally to the mutators.
5588 // The transition into the Marking state happens with the world
5589 // stopped so the mutators will globally see it. Sweeping is
5590 // done asynchronously by the background collector so the transition
5591 // from the Sweeping state to the Resizing state must be done
5592 // under the freelistLock (as is the check for whether to
5593 // allocate-live and whether to dirty the mod-union table).
5594 assert(_collectorState == Resizing, "Change of collector state to"
5595 " Resizing must be done under the freelistLocks (plural)");
5596
5597 // Now that sweeping has been completed, we clear
5598 // the incremental_collection_failed flag,
5599 // thus inviting a younger gen collection to promote into
5600 // this generation. If such a promotion may still fail,
5601 // the flag will be set again when a young collection is
5602 // attempted.
5603 GenCollectedHeap* gch = GenCollectedHeap::heap();
5604 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5605 gch->update_full_collections_completed(_collection_count_start);
5606 }
5607
5608 // FIX ME!!! Looks like this belongs in CFLSpace, with
5609 // CMSGen merely delegating to it.
5610 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5611 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5612 HeapWord* minAddr = _cmsSpace->bottom();
5613 HeapWord* largestAddr =
5614 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5615 if (largestAddr == NULL) {
5616 // The dictionary appears to be empty. In this case
5617 // try to coalesce at the end of the heap.
5618 largestAddr = _cmsSpace->end();
5619 }
5620 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5621 size_t nearLargestOffset =
5622 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5623 if (PrintFLSStatistics != 0) {
5624 gclog_or_tty->print_cr(
5625 "CMS: Large Block: " PTR_FORMAT ";"
5626 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5627 p2i(largestAddr),
5628 p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5629 }
5630 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5631 }
5632
5633 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5634 return addr >= _cmsSpace->nearLargestChunk();
5635 }
5636
5637 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5638 return _cmsSpace->find_chunk_at_end();
5639 }
5640
5641 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5642 bool full) {
5643 // If the young generation has been collected, gather any statistics
5644 // that are of interest at this point.
5645 bool current_is_young = (current_generation == GenCollectedHeap::heap()->young_gen());
5646 if (!full && current_is_young) {
5647 // Gather statistics on the young generation collection.
5648 collector()->stats().record_gc0_end(used());
5649 }
5650 }
5651
5652 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen) {
5653 // We iterate over the space(s) underlying this generation,
5654 // checking the mark bit map to see if the bits corresponding
5655 // to specific blocks are marked or not. Blocks that are
5656 // marked are live and are not swept up. All remaining blocks
5657 // are swept up, with coalescing on-the-fly as we sweep up
5658 // contiguous free and/or garbage blocks:
5659 // We need to ensure that the sweeper synchronizes with allocators
5660 // and stop-the-world collectors. In particular, the following
5661 // locks are used:
5662 // . CMS token: if this is held, a stop the world collection cannot occur
5663 // . freelistLock: if this is held no allocation can occur from this
5664 // generation by another thread
5665 // . bitMapLock: if this is held, no other thread can access or update
5666 //
5667
5668 // Note that we need to hold the freelistLock if we use
5669 // block iterate below; else the iterator might go awry if
5670 // a mutator (or promotion) causes block contents to change
5671 // (for instance if the allocator divvies up a block).
5672 // If we hold the free list lock, for all practical purposes
5673 // young generation GC's can't occur (they'll usually need to
5674 // promote), so we might as well prevent all young generation
5675 // GC's while we do a sweeping step. For the same reason, we might
5676 // as well take the bit map lock for the entire duration
5677
5678 // check that we hold the requisite locks
5679 assert(have_cms_token(), "Should hold cms token");
5680 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5681 assert_lock_strong(gen->freelistLock());
5682 assert_lock_strong(bitMapLock());
5683
5684 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5685 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5686 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5687 _inter_sweep_estimate.padded_average(),
5688 _intra_sweep_estimate.padded_average());
5689 gen->setNearLargestChunk();
5690
5691 {
5692 SweepClosure sweepClosure(this, gen, &_markBitMap, CMSYield);
5693 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5694 // We need to free-up/coalesce garbage/blocks from a
5695 // co-terminal free run. This is done in the SweepClosure
5696 // destructor; so, do not remove this scope, else the
5697 // end-of-sweep-census below will be off by a little bit.
5698 }
5699 gen->cmsSpace()->sweep_completed();
5700 gen->cmsSpace()->endSweepFLCensus(sweep_count());
5701 if (should_unload_classes()) { // unloaded classes this cycle,
5702 _concurrent_cycles_since_last_unload = 0; // ... reset count
5703 } else { // did not unload classes,
5704 _concurrent_cycles_since_last_unload++; // ... increment count
5705 }
5706 }
5707
5708 // Reset CMS data structures (for now just the marking bit map)
5709 // preparatory for the next cycle.
5710 void CMSCollector::reset(bool concurrent) {
5711 if (concurrent) {
5712 CMSTokenSyncWithLocks ts(true, bitMapLock());
5713
5714 // If the state is not "Resetting", the foreground thread
5715 // has done a collection and the resetting.
5716 if (_collectorState != Resetting) {
5717 assert(_collectorState == Idling, "The state should only change"
5718 " because the foreground collector has finished the collection");
5719 return;
5720 }
5721
5722 // Clear the mark bitmap (no grey objects to start with)
5723 // for the next cycle.
5724 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5725 CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5726
5727 HeapWord* curAddr = _markBitMap.startWord();
5728 while (curAddr < _markBitMap.endWord()) {
5729 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5730 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5731 _markBitMap.clear_large_range(chunk);
5732 if (ConcurrentMarkSweepThread::should_yield() &&
5733 !foregroundGCIsActive() &&
5734 CMSYield) {
5735 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5736 "CMS thread should hold CMS token");
5737 assert_lock_strong(bitMapLock());
5738 bitMapLock()->unlock();
5739 ConcurrentMarkSweepThread::desynchronize(true);
5740 stopTimer();
5741 if (PrintCMSStatistics != 0) {
5742 incrementYields();
5743 }
5744
5745 // See the comment in coordinator_yield()
5746 for (unsigned i = 0; i < CMSYieldSleepCount &&
5747 ConcurrentMarkSweepThread::should_yield() &&
5748 !CMSCollector::foregroundGCIsActive(); ++i) {
5749 os::sleep(Thread::current(), 1, false);
5750 }
5751
5752 ConcurrentMarkSweepThread::synchronize(true);
5753 bitMapLock()->lock_without_safepoint_check();
5754 startTimer();
5755 }
5756 curAddr = chunk.end();
5757 }
5758 // A successful mostly concurrent collection has been done.
5759 // Because only the full (i.e., concurrent mode failure) collections
5760 // are being measured for gc overhead limits, clean the "near" flag
5761 // and count.
5762 size_policy()->reset_gc_overhead_limit_count();
5763 _collectorState = Idling;
5764 } else {
5765 // already have the lock
5766 assert(_collectorState == Resetting, "just checking");
5767 assert_lock_strong(bitMapLock());
5768 _markBitMap.clear_all();
5769 _collectorState = Idling;
5770 }
5771
5772 register_gc_end();
5773 }
5774
5775 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5776 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5777 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
5778 TraceCollectorStats tcs(counters());
5779
5780 switch (op) {
5781 case CMS_op_checkpointRootsInitial: {
5782 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5783 checkpointRootsInitial();
5784 if (PrintGC) {
5785 _cmsGen->printOccupancy("initial-mark");
5786 }
5787 break;
5788 }
5789 case CMS_op_checkpointRootsFinal: {
5790 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5791 checkpointRootsFinal();
5792 if (PrintGC) {
5793 _cmsGen->printOccupancy("remark");
5794 }
5795 break;
5796 }
5797 default:
5798 fatal("No such CMS_op");
5799 }
5800 }
5801
5802 #ifndef PRODUCT
5803 size_t const CMSCollector::skip_header_HeapWords() {
5804 return FreeChunk::header_size();
5805 }
5806
5807 // Try and collect here conditions that should hold when
5808 // CMS thread is exiting. The idea is that the foreground GC
5809 // thread should not be blocked if it wants to terminate
5810 // the CMS thread and yet continue to run the VM for a while
5811 // after that.
5812 void CMSCollector::verify_ok_to_terminate() const {
5813 assert(Thread::current()->is_ConcurrentGC_thread(),
5814 "should be called by CMS thread");
5815 assert(!_foregroundGCShouldWait, "should be false");
5816 // We could check here that all the various low-level locks
5817 // are not held by the CMS thread, but that is overkill; see
5818 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5819 // is checked.
5820 }
5821 #endif
5822
5823 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5824 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5825 "missing Printezis mark?");
5826 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5827 size_t size = pointer_delta(nextOneAddr + 1, addr);
5828 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5829 "alignment problem");
5830 assert(size >= 3, "Necessary for Printezis marks to work");
5831 return size;
5832 }
5833
5834 // A variant of the above (block_size_using_printezis_bits()) except
5835 // that we return 0 if the P-bits are not yet set.
5836 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5837 if (_markBitMap.isMarked(addr + 1)) {
5838 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5839 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5840 size_t size = pointer_delta(nextOneAddr + 1, addr);
5841 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5842 "alignment problem");
5843 assert(size >= 3, "Necessary for Printezis marks to work");
5844 return size;
5845 }
5846 return 0;
5847 }
5848
5849 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5850 size_t sz = 0;
5851 oop p = (oop)addr;
5852 if (p->klass_or_null() != NULL) {
5853 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5854 } else {
5855 sz = block_size_using_printezis_bits(addr);
5856 }
5857 assert(sz > 0, "size must be nonzero");
5858 HeapWord* next_block = addr + sz;
5859 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
5860 CardTableModRefBS::card_size);
5861 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
5862 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5863 "must be different cards");
5864 return next_card;
5865 }
5866
5867
5868 // CMS Bit Map Wrapper /////////////////////////////////////////
5869
5870 // Construct a CMS bit map infrastructure, but don't create the
5871 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5872 // further below.
5873 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5874 _bm(),
5875 _shifter(shifter),
5876 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5877 Monitor::_safepoint_check_sometimes) : NULL)
5878 {
5879 _bmStartWord = 0;
5880 _bmWordSize = 0;
5881 }
5882
5883 bool CMSBitMap::allocate(MemRegion mr) {
5884 _bmStartWord = mr.start();
5885 _bmWordSize = mr.word_size();
5886 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5887 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5888 if (!brs.is_reserved()) {
5889 warning("CMS bit map allocation failure");
5890 return false;
5891 }
5892 // For now we'll just commit all of the bit map up front.
5893 // Later on we'll try to be more parsimonious with swap.
5894 if (!_virtual_space.initialize(brs, brs.size())) {
5895 warning("CMS bit map backing store failure");
5896 return false;
5897 }
5898 assert(_virtual_space.committed_size() == brs.size(),
5899 "didn't reserve backing store for all of CMS bit map?");
5900 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5901 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5902 _bmWordSize, "inconsistency in bit map sizing");
5903 _bm.set_size(_bmWordSize >> _shifter);
5904
5905 // bm.clear(); // can we rely on getting zero'd memory? verify below
5906 assert(isAllClear(),
5907 "Expected zero'd memory from ReservedSpace constructor");
5908 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5909 "consistency check");
5910 return true;
5911 }
5912
5913 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5914 HeapWord *next_addr, *end_addr, *last_addr;
5915 assert_locked();
5916 assert(covers(mr), "out-of-range error");
5917 // XXX assert that start and end are appropriately aligned
5918 for (next_addr = mr.start(), end_addr = mr.end();
5919 next_addr < end_addr; next_addr = last_addr) {
5920 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5921 last_addr = dirty_region.end();
5922 if (!dirty_region.is_empty()) {
5923 cl->do_MemRegion(dirty_region);
5924 } else {
5925 assert(last_addr == end_addr, "program logic");
5926 return;
5927 }
5928 }
5929 }
5930
5931 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5932 _bm.print_on_error(st, prefix);
5933 }
5934
5935 #ifndef PRODUCT
5936 void CMSBitMap::assert_locked() const {
5937 CMSLockVerifier::assert_locked(lock());
5938 }
5939
5940 bool CMSBitMap::covers(MemRegion mr) const {
5941 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5942 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5943 "size inconsistency");
5944 return (mr.start() >= _bmStartWord) &&
5945 (mr.end() <= endWord());
5946 }
5947
5948 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5949 return (start >= _bmStartWord && (start + size) <= endWord());
5950 }
5951
5952 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5953 // verify that there are no 1 bits in the interval [left, right)
5954 FalseBitMapClosure falseBitMapClosure;
5955 iterate(&falseBitMapClosure, left, right);
5956 }
5957
5958 void CMSBitMap::region_invariant(MemRegion mr)
5959 {
5960 assert_locked();
5961 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5962 assert(!mr.is_empty(), "unexpected empty region");
5963 assert(covers(mr), "mr should be covered by bit map");
5964 // convert address range into offset range
5965 size_t start_ofs = heapWordToOffset(mr.start());
5966 // Make sure that end() is appropriately aligned
5967 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5968 (1 << (_shifter+LogHeapWordSize))),
5969 "Misaligned mr.end()");
5970 size_t end_ofs = heapWordToOffset(mr.end());
5971 assert(end_ofs > start_ofs, "Should mark at least one bit");
5972 }
5973
5974 #endif
5975
5976 bool CMSMarkStack::allocate(size_t size) {
5977 // allocate a stack of the requisite depth
5978 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5979 size * sizeof(oop)));
5980 if (!rs.is_reserved()) {
5981 warning("CMSMarkStack allocation failure");
5982 return false;
5983 }
5984 if (!_virtual_space.initialize(rs, rs.size())) {
5985 warning("CMSMarkStack backing store failure");
5986 return false;
5987 }
5988 assert(_virtual_space.committed_size() == rs.size(),
5989 "didn't reserve backing store for all of CMS stack?");
5990 _base = (oop*)(_virtual_space.low());
5991 _index = 0;
5992 _capacity = size;
5993 NOT_PRODUCT(_max_depth = 0);
5994 return true;
5995 }
5996
5997 // XXX FIX ME !!! In the MT case we come in here holding a
5998 // leaf lock. For printing we need to take a further lock
5999 // which has lower rank. We need to recalibrate the two
6000 // lock-ranks involved in order to be able to print the
6001 // messages below. (Or defer the printing to the caller.
6002 // For now we take the expedient path of just disabling the
6003 // messages for the problematic case.)
6004 void CMSMarkStack::expand() {
6005 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6006 if (_capacity == MarkStackSizeMax) {
6007 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6008 // We print a warning message only once per CMS cycle.
6009 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6010 }
6011 return;
6012 }
6013 // Double capacity if possible
6014 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6015 // Do not give up existing stack until we have managed to
6016 // get the double capacity that we desired.
6017 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6018 new_capacity * sizeof(oop)));
6019 if (rs.is_reserved()) {
6020 // Release the backing store associated with old stack
6021 _virtual_space.release();
6022 // Reinitialize virtual space for new stack
6023 if (!_virtual_space.initialize(rs, rs.size())) {
6024 fatal("Not enough swap for expanded marking stack");
6025 }
6026 _base = (oop*)(_virtual_space.low());
6027 _index = 0;
6028 _capacity = new_capacity;
6029 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6030 // Failed to double capacity, continue;
6031 // we print a detail message only once per CMS cycle.
6032 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6033 SIZE_FORMAT"K",
6034 _capacity / K, new_capacity / K);
6035 }
6036 }
6037
6038
6039 // Closures
6040 // XXX: there seems to be a lot of code duplication here;
6041 // should refactor and consolidate common code.
6042
6043 // This closure is used to mark refs into the CMS generation in
6044 // the CMS bit map. Called at the first checkpoint. This closure
6045 // assumes that we do not need to re-mark dirty cards; if the CMS
6046 // generation on which this is used is not an oldest
6047 // generation then this will lose younger_gen cards!
6048
6049 MarkRefsIntoClosure::MarkRefsIntoClosure(
6050 MemRegion span, CMSBitMap* bitMap):
6051 _span(span),
6052 _bitMap(bitMap)
6053 {
6054 assert(_ref_processor == NULL, "deliberately left NULL");
6055 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6056 }
6057
6058 void MarkRefsIntoClosure::do_oop(oop obj) {
6059 // if p points into _span, then mark corresponding bit in _markBitMap
6060 assert(obj->is_oop(), "expected an oop");
6061 HeapWord* addr = (HeapWord*)obj;
6062 if (_span.contains(addr)) {
6063 // this should be made more efficient
6064 _bitMap->mark(addr);
6065 }
6066 }
6067
6068 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6069 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6070
6071 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6072 MemRegion span, CMSBitMap* bitMap):
6073 _span(span),
6074 _bitMap(bitMap)
6075 {
6076 assert(_ref_processor == NULL, "deliberately left NULL");
6077 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6078 }
6079
6080 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6081 // if p points into _span, then mark corresponding bit in _markBitMap
6082 assert(obj->is_oop(), "expected an oop");
6083 HeapWord* addr = (HeapWord*)obj;
6084 if (_span.contains(addr)) {
6085 // this should be made more efficient
6086 _bitMap->par_mark(addr);
6087 }
6088 }
6089
6090 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6091 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6092
6093 // A variant of the above, used for CMS marking verification.
6094 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6095 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6096 _span(span),
6097 _verification_bm(verification_bm),
6098 _cms_bm(cms_bm)
6099 {
6100 assert(_ref_processor == NULL, "deliberately left NULL");
6101 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6102 }
6103
6104 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6105 // if p points into _span, then mark corresponding bit in _markBitMap
6106 assert(obj->is_oop(), "expected an oop");
6107 HeapWord* addr = (HeapWord*)obj;
6108 if (_span.contains(addr)) {
6109 _verification_bm->mark(addr);
6110 if (!_cms_bm->isMarked(addr)) {
6111 oop(addr)->print();
6112 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6113 fatal("... aborting");
6114 }
6115 }
6116 }
6117
6118 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6119 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6120
6121 //////////////////////////////////////////////////
6122 // MarkRefsIntoAndScanClosure
6123 //////////////////////////////////////////////////
6124
6125 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6126 ReferenceProcessor* rp,
6127 CMSBitMap* bit_map,
6128 CMSBitMap* mod_union_table,
6129 CMSMarkStack* mark_stack,
6130 CMSCollector* collector,
6131 bool should_yield,
6132 bool concurrent_precleaning):
6133 _collector(collector),
6134 _span(span),
6135 _bit_map(bit_map),
6136 _mark_stack(mark_stack),
6137 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6138 mark_stack, concurrent_precleaning),
6139 _yield(should_yield),
6140 _concurrent_precleaning(concurrent_precleaning),
6141 _freelistLock(NULL)
6142 {
6143 _ref_processor = rp;
6144 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6145 }
6146
6147 // This closure is used to mark refs into the CMS generation at the
6148 // second (final) checkpoint, and to scan and transitively follow
6149 // the unmarked oops. It is also used during the concurrent precleaning
6150 // phase while scanning objects on dirty cards in the CMS generation.
6151 // The marks are made in the marking bit map and the marking stack is
6152 // used for keeping the (newly) grey objects during the scan.
6153 // The parallel version (Par_...) appears further below.
6154 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6155 if (obj != NULL) {
6156 assert(obj->is_oop(), "expected an oop");
6157 HeapWord* addr = (HeapWord*)obj;
6158 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6159 assert(_collector->overflow_list_is_empty(),
6160 "overflow list should be empty");
6161 if (_span.contains(addr) &&
6162 !_bit_map->isMarked(addr)) {
6163 // mark bit map (object is now grey)
6164 _bit_map->mark(addr);
6165 // push on marking stack (stack should be empty), and drain the
6166 // stack by applying this closure to the oops in the oops popped
6167 // from the stack (i.e. blacken the grey objects)
6168 bool res = _mark_stack->push(obj);
6169 assert(res, "Should have space to push on empty stack");
6170 do {
6171 oop new_oop = _mark_stack->pop();
6172 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6173 assert(_bit_map->isMarked((HeapWord*)new_oop),
6174 "only grey objects on this stack");
6175 // iterate over the oops in this oop, marking and pushing
6176 // the ones in CMS heap (i.e. in _span).
6177 new_oop->oop_iterate(&_pushAndMarkClosure);
6178 // check if it's time to yield
6179 do_yield_check();
6180 } while (!_mark_stack->isEmpty() ||
6181 (!_concurrent_precleaning && take_from_overflow_list()));
6182 // if marking stack is empty, and we are not doing this
6183 // during precleaning, then check the overflow list
6184 }
6185 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6186 assert(_collector->overflow_list_is_empty(),
6187 "overflow list was drained above");
6188 // We could restore evacuated mark words, if any, used for
6189 // overflow list links here because the overflow list is
6190 // provably empty here. That would reduce the maximum
6191 // size requirements for preserved_{oop,mark}_stack.
6192 // But we'll just postpone it until we are all done
6193 // so we can just stream through.
6194 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6195 _collector->restore_preserved_marks_if_any();
6196 assert(_collector->no_preserved_marks(), "No preserved marks");
6197 }
6198 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6199 "All preserved marks should have been restored above");
6200 }
6201 }
6202
6203 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6204 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6205
6206 void MarkRefsIntoAndScanClosure::do_yield_work() {
6207 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6208 "CMS thread should hold CMS token");
6209 assert_lock_strong(_freelistLock);
6210 assert_lock_strong(_bit_map->lock());
6211 // relinquish the free_list_lock and bitMaplock()
6212 _bit_map->lock()->unlock();
6213 _freelistLock->unlock();
6214 ConcurrentMarkSweepThread::desynchronize(true);
6215 _collector->stopTimer();
6216 if (PrintCMSStatistics != 0) {
6217 _collector->incrementYields();
6218 }
6219
6220 // See the comment in coordinator_yield()
6221 for (unsigned i = 0;
6222 i < CMSYieldSleepCount &&
6223 ConcurrentMarkSweepThread::should_yield() &&
6224 !CMSCollector::foregroundGCIsActive();
6225 ++i) {
6226 os::sleep(Thread::current(), 1, false);
6227 }
6228
6229 ConcurrentMarkSweepThread::synchronize(true);
6230 _freelistLock->lock_without_safepoint_check();
6231 _bit_map->lock()->lock_without_safepoint_check();
6232 _collector->startTimer();
6233 }
6234
6235 ///////////////////////////////////////////////////////////
6236 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6237 // MarkRefsIntoAndScanClosure
6238 ///////////////////////////////////////////////////////////
6239 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6240 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6241 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6242 _span(span),
6243 _bit_map(bit_map),
6244 _work_queue(work_queue),
6245 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6246 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6247 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6248 {
6249 _ref_processor = rp;
6250 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6251 }
6252
6253 // This closure is used to mark refs into the CMS generation at the
6254 // second (final) checkpoint, and to scan and transitively follow
6255 // the unmarked oops. The marks are made in the marking bit map and
6256 // the work_queue is used for keeping the (newly) grey objects during
6257 // the scan phase whence they are also available for stealing by parallel
6258 // threads. Since the marking bit map is shared, updates are
6259 // synchronized (via CAS).
6260 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6261 if (obj != NULL) {
6262 // Ignore mark word because this could be an already marked oop
6263 // that may be chained at the end of the overflow list.
6264 assert(obj->is_oop(true), "expected an oop");
6265 HeapWord* addr = (HeapWord*)obj;
6266 if (_span.contains(addr) &&
6267 !_bit_map->isMarked(addr)) {
6268 // mark bit map (object will become grey):
6269 // It is possible for several threads to be
6270 // trying to "claim" this object concurrently;
6271 // the unique thread that succeeds in marking the
6272 // object first will do the subsequent push on
6273 // to the work queue (or overflow list).
6274 if (_bit_map->par_mark(addr)) {
6275 // push on work_queue (which may not be empty), and trim the
6276 // queue to an appropriate length by applying this closure to
6277 // the oops in the oops popped from the stack (i.e. blacken the
6278 // grey objects)
6279 bool res = _work_queue->push(obj);
6280 assert(res, "Low water mark should be less than capacity?");
6281 trim_queue(_low_water_mark);
6282 } // Else, another thread claimed the object
6283 }
6284 }
6285 }
6286
6287 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6288 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6289
6290 // This closure is used to rescan the marked objects on the dirty cards
6291 // in the mod union table and the card table proper.
6292 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6293 oop p, MemRegion mr) {
6294
6295 size_t size = 0;
6296 HeapWord* addr = (HeapWord*)p;
6297 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6298 assert(_span.contains(addr), "we are scanning the CMS generation");
6299 // check if it's time to yield
6300 if (do_yield_check()) {
6301 // We yielded for some foreground stop-world work,
6302 // and we have been asked to abort this ongoing preclean cycle.
6303 return 0;
6304 }
6305 if (_bitMap->isMarked(addr)) {
6306 // it's marked; is it potentially uninitialized?
6307 if (p->klass_or_null() != NULL) {
6308 // an initialized object; ignore mark word in verification below
6309 // since we are running concurrent with mutators
6310 assert(p->is_oop(true), "should be an oop");
6311 if (p->is_objArray()) {
6312 // objArrays are precisely marked; restrict scanning
6313 // to dirty cards only.
6314 size = CompactibleFreeListSpace::adjustObjectSize(
6315 p->oop_iterate(_scanningClosure, mr));
6316 } else {
6317 // A non-array may have been imprecisely marked; we need
6318 // to scan object in its entirety.
6319 size = CompactibleFreeListSpace::adjustObjectSize(
6320 p->oop_iterate(_scanningClosure));
6321 }
6322 #ifdef ASSERT
6323 size_t direct_size =
6324 CompactibleFreeListSpace::adjustObjectSize(p->size());
6325 assert(size == direct_size, "Inconsistency in size");
6326 assert(size >= 3, "Necessary for Printezis marks to work");
6327 if (!_bitMap->isMarked(addr+1)) {
6328 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6329 } else {
6330 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6331 assert(_bitMap->isMarked(addr+size-1),
6332 "inconsistent Printezis mark");
6333 }
6334 #endif // ASSERT
6335 } else {
6336 // An uninitialized object.
6337 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6338 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6339 size = pointer_delta(nextOneAddr + 1, addr);
6340 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6341 "alignment problem");
6342 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6343 // will dirty the card when the klass pointer is installed in the
6344 // object (signaling the completion of initialization).
6345 }
6346 } else {
6347 // Either a not yet marked object or an uninitialized object
6348 if (p->klass_or_null() == NULL) {
6349 // An uninitialized object, skip to the next card, since
6350 // we may not be able to read its P-bits yet.
6351 assert(size == 0, "Initial value");
6352 } else {
6353 // An object not (yet) reached by marking: we merely need to
6354 // compute its size so as to go look at the next block.
6355 assert(p->is_oop(true), "should be an oop");
6356 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6357 }
6358 }
6359 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6360 return size;
6361 }
6362
6363 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6364 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6365 "CMS thread should hold CMS token");
6366 assert_lock_strong(_freelistLock);
6367 assert_lock_strong(_bitMap->lock());
6368 // relinquish the free_list_lock and bitMaplock()
6369 _bitMap->lock()->unlock();
6370 _freelistLock->unlock();
6371 ConcurrentMarkSweepThread::desynchronize(true);
6372 _collector->stopTimer();
6373 if (PrintCMSStatistics != 0) {
6374 _collector->incrementYields();
6375 }
6376
6377 // See the comment in coordinator_yield()
6378 for (unsigned i = 0; i < CMSYieldSleepCount &&
6379 ConcurrentMarkSweepThread::should_yield() &&
6380 !CMSCollector::foregroundGCIsActive(); ++i) {
6381 os::sleep(Thread::current(), 1, false);
6382 }
6383
6384 ConcurrentMarkSweepThread::synchronize(true);
6385 _freelistLock->lock_without_safepoint_check();
6386 _bitMap->lock()->lock_without_safepoint_check();
6387 _collector->startTimer();
6388 }
6389
6390
6391 //////////////////////////////////////////////////////////////////
6392 // SurvivorSpacePrecleanClosure
6393 //////////////////////////////////////////////////////////////////
6394 // This (single-threaded) closure is used to preclean the oops in
6395 // the survivor spaces.
6396 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6397
6398 HeapWord* addr = (HeapWord*)p;
6399 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6400 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6401 assert(p->klass_or_null() != NULL, "object should be initialized");
6402 // an initialized object; ignore mark word in verification below
6403 // since we are running concurrent with mutators
6404 assert(p->is_oop(true), "should be an oop");
6405 // Note that we do not yield while we iterate over
6406 // the interior oops of p, pushing the relevant ones
6407 // on our marking stack.
6408 size_t size = p->oop_iterate(_scanning_closure);
6409 do_yield_check();
6410 // Observe that below, we do not abandon the preclean
6411 // phase as soon as we should; rather we empty the
6412 // marking stack before returning. This is to satisfy
6413 // some existing assertions. In general, it may be a
6414 // good idea to abort immediately and complete the marking
6415 // from the grey objects at a later time.
6416 while (!_mark_stack->isEmpty()) {
6417 oop new_oop = _mark_stack->pop();
6418 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6419 assert(_bit_map->isMarked((HeapWord*)new_oop),
6420 "only grey objects on this stack");
6421 // iterate over the oops in this oop, marking and pushing
6422 // the ones in CMS heap (i.e. in _span).
6423 new_oop->oop_iterate(_scanning_closure);
6424 // check if it's time to yield
6425 do_yield_check();
6426 }
6427 unsigned int after_count =
6428 GenCollectedHeap::heap()->total_collections();
6429 bool abort = (_before_count != after_count) ||
6430 _collector->should_abort_preclean();
6431 return abort ? 0 : size;
6432 }
6433
6434 void SurvivorSpacePrecleanClosure::do_yield_work() {
6435 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6436 "CMS thread should hold CMS token");
6437 assert_lock_strong(_bit_map->lock());
6438 // Relinquish the bit map lock
6439 _bit_map->lock()->unlock();
6440 ConcurrentMarkSweepThread::desynchronize(true);
6441 _collector->stopTimer();
6442 if (PrintCMSStatistics != 0) {
6443 _collector->incrementYields();
6444 }
6445
6446 // See the comment in coordinator_yield()
6447 for (unsigned i = 0; i < CMSYieldSleepCount &&
6448 ConcurrentMarkSweepThread::should_yield() &&
6449 !CMSCollector::foregroundGCIsActive(); ++i) {
6450 os::sleep(Thread::current(), 1, false);
6451 }
6452
6453 ConcurrentMarkSweepThread::synchronize(true);
6454 _bit_map->lock()->lock_without_safepoint_check();
6455 _collector->startTimer();
6456 }
6457
6458 // This closure is used to rescan the marked objects on the dirty cards
6459 // in the mod union table and the card table proper. In the parallel
6460 // case, although the bitMap is shared, we do a single read so the
6461 // isMarked() query is "safe".
6462 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6463 // Ignore mark word because we are running concurrent with mutators
6464 assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
6465 HeapWord* addr = (HeapWord*)p;
6466 assert(_span.contains(addr), "we are scanning the CMS generation");
6467 bool is_obj_array = false;
6468 #ifdef ASSERT
6469 if (!_parallel) {
6470 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6471 assert(_collector->overflow_list_is_empty(),
6472 "overflow list should be empty");
6473
6474 }
6475 #endif // ASSERT
6476 if (_bit_map->isMarked(addr)) {
6477 // Obj arrays are precisely marked, non-arrays are not;
6478 // so we scan objArrays precisely and non-arrays in their
6479 // entirety.
6480 if (p->is_objArray()) {
6481 is_obj_array = true;
6482 if (_parallel) {
6483 p->oop_iterate(_par_scan_closure, mr);
6484 } else {
6485 p->oop_iterate(_scan_closure, mr);
6486 }
6487 } else {
6488 if (_parallel) {
6489 p->oop_iterate(_par_scan_closure);
6490 } else {
6491 p->oop_iterate(_scan_closure);
6492 }
6493 }
6494 }
6495 #ifdef ASSERT
6496 if (!_parallel) {
6497 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6498 assert(_collector->overflow_list_is_empty(),
6499 "overflow list should be empty");
6500
6501 }
6502 #endif // ASSERT
6503 return is_obj_array;
6504 }
6505
6506 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6507 MemRegion span,
6508 CMSBitMap* bitMap, CMSMarkStack* markStack,
6509 bool should_yield, bool verifying):
6510 _collector(collector),
6511 _span(span),
6512 _bitMap(bitMap),
6513 _mut(&collector->_modUnionTable),
6514 _markStack(markStack),
6515 _yield(should_yield),
6516 _skipBits(0)
6517 {
6518 assert(_markStack->isEmpty(), "stack should be empty");
6519 _finger = _bitMap->startWord();
6520 _threshold = _finger;
6521 assert(_collector->_restart_addr == NULL, "Sanity check");
6522 assert(_span.contains(_finger), "Out of bounds _finger?");
6523 DEBUG_ONLY(_verifying = verifying;)
6524 }
6525
6526 void MarkFromRootsClosure::reset(HeapWord* addr) {
6527 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6528 assert(_span.contains(addr), "Out of bounds _finger?");
6529 _finger = addr;
6530 _threshold = (HeapWord*)round_to(
6531 (intptr_t)_finger, CardTableModRefBS::card_size);
6532 }
6533
6534 // Should revisit to see if this should be restructured for
6535 // greater efficiency.
6536 bool MarkFromRootsClosure::do_bit(size_t offset) {
6537 if (_skipBits > 0) {
6538 _skipBits--;
6539 return true;
6540 }
6541 // convert offset into a HeapWord*
6542 HeapWord* addr = _bitMap->startWord() + offset;
6543 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6544 "address out of range");
6545 assert(_bitMap->isMarked(addr), "tautology");
6546 if (_bitMap->isMarked(addr+1)) {
6547 // this is an allocated but not yet initialized object
6548 assert(_skipBits == 0, "tautology");
6549 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6550 oop p = oop(addr);
6551 if (p->klass_or_null() == NULL) {
6552 DEBUG_ONLY(if (!_verifying) {)
6553 // We re-dirty the cards on which this object lies and increase
6554 // the _threshold so that we'll come back to scan this object
6555 // during the preclean or remark phase. (CMSCleanOnEnter)
6556 if (CMSCleanOnEnter) {
6557 size_t sz = _collector->block_size_using_printezis_bits(addr);
6558 HeapWord* end_card_addr = (HeapWord*)round_to(
6559 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6560 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6561 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6562 // Bump _threshold to end_card_addr; note that
6563 // _threshold cannot possibly exceed end_card_addr, anyhow.
6564 // This prevents future clearing of the card as the scan proceeds
6565 // to the right.
6566 assert(_threshold <= end_card_addr,
6567 "Because we are just scanning into this object");
6568 if (_threshold < end_card_addr) {
6569 _threshold = end_card_addr;
6570 }
6571 if (p->klass_or_null() != NULL) {
6572 // Redirty the range of cards...
6573 _mut->mark_range(redirty_range);
6574 } // ...else the setting of klass will dirty the card anyway.
6575 }
6576 DEBUG_ONLY(})
6577 return true;
6578 }
6579 }
6580 scanOopsInOop(addr);
6581 return true;
6582 }
6583
6584 // We take a break if we've been at this for a while,
6585 // so as to avoid monopolizing the locks involved.
6586 void MarkFromRootsClosure::do_yield_work() {
6587 // First give up the locks, then yield, then re-lock
6588 // We should probably use a constructor/destructor idiom to
6589 // do this unlock/lock or modify the MutexUnlocker class to
6590 // serve our purpose. XXX
6591 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6592 "CMS thread should hold CMS token");
6593 assert_lock_strong(_bitMap->lock());
6594 _bitMap->lock()->unlock();
6595 ConcurrentMarkSweepThread::desynchronize(true);
6596 _collector->stopTimer();
6597 if (PrintCMSStatistics != 0) {
6598 _collector->incrementYields();
6599 }
6600
6601 // See the comment in coordinator_yield()
6602 for (unsigned i = 0; i < CMSYieldSleepCount &&
6603 ConcurrentMarkSweepThread::should_yield() &&
6604 !CMSCollector::foregroundGCIsActive(); ++i) {
6605 os::sleep(Thread::current(), 1, false);
6606 }
6607
6608 ConcurrentMarkSweepThread::synchronize(true);
6609 _bitMap->lock()->lock_without_safepoint_check();
6610 _collector->startTimer();
6611 }
6612
6613 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6614 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6615 assert(_markStack->isEmpty(),
6616 "should drain stack to limit stack usage");
6617 // convert ptr to an oop preparatory to scanning
6618 oop obj = oop(ptr);
6619 // Ignore mark word in verification below, since we
6620 // may be running concurrent with mutators.
6621 assert(obj->is_oop(true), "should be an oop");
6622 assert(_finger <= ptr, "_finger runneth ahead");
6623 // advance the finger to right end of this object
6624 _finger = ptr + obj->size();
6625 assert(_finger > ptr, "we just incremented it above");
6626 // On large heaps, it may take us some time to get through
6627 // the marking phase. During
6628 // this time it's possible that a lot of mutations have
6629 // accumulated in the card table and the mod union table --
6630 // these mutation records are redundant until we have
6631 // actually traced into the corresponding card.
6632 // Here, we check whether advancing the finger would make
6633 // us cross into a new card, and if so clear corresponding
6634 // cards in the MUT (preclean them in the card-table in the
6635 // future).
6636
6637 DEBUG_ONLY(if (!_verifying) {)
6638 // The clean-on-enter optimization is disabled by default,
6639 // until we fix 6178663.
6640 if (CMSCleanOnEnter && (_finger > _threshold)) {
6641 // [_threshold, _finger) represents the interval
6642 // of cards to be cleared in MUT (or precleaned in card table).
6643 // The set of cards to be cleared is all those that overlap
6644 // with the interval [_threshold, _finger); note that
6645 // _threshold is always kept card-aligned but _finger isn't
6646 // always card-aligned.
6647 HeapWord* old_threshold = _threshold;
6648 assert(old_threshold == (HeapWord*)round_to(
6649 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6650 "_threshold should always be card-aligned");
6651 _threshold = (HeapWord*)round_to(
6652 (intptr_t)_finger, CardTableModRefBS::card_size);
6653 MemRegion mr(old_threshold, _threshold);
6654 assert(!mr.is_empty(), "Control point invariant");
6655 assert(_span.contains(mr), "Should clear within span");
6656 _mut->clear_range(mr);
6657 }
6658 DEBUG_ONLY(})
6659 // Note: the finger doesn't advance while we drain
6660 // the stack below.
6661 PushOrMarkClosure pushOrMarkClosure(_collector,
6662 _span, _bitMap, _markStack,
6663 _finger, this);
6664 bool res = _markStack->push(obj);
6665 assert(res, "Empty non-zero size stack should have space for single push");
6666 while (!_markStack->isEmpty()) {
6667 oop new_oop = _markStack->pop();
6668 // Skip verifying header mark word below because we are
6669 // running concurrent with mutators.
6670 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6671 // now scan this oop's oops
6672 new_oop->oop_iterate(&pushOrMarkClosure);
6673 do_yield_check();
6674 }
6675 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6676 }
6677
6678 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6679 CMSCollector* collector, MemRegion span,
6680 CMSBitMap* bit_map,
6681 OopTaskQueue* work_queue,
6682 CMSMarkStack* overflow_stack):
6683 _collector(collector),
6684 _whole_span(collector->_span),
6685 _span(span),
6686 _bit_map(bit_map),
6687 _mut(&collector->_modUnionTable),
6688 _work_queue(work_queue),
6689 _overflow_stack(overflow_stack),
6690 _skip_bits(0),
6691 _task(task)
6692 {
6693 assert(_work_queue->size() == 0, "work_queue should be empty");
6694 _finger = span.start();
6695 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6696 assert(_span.contains(_finger), "Out of bounds _finger?");
6697 }
6698
6699 // Should revisit to see if this should be restructured for
6700 // greater efficiency.
6701 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6702 if (_skip_bits > 0) {
6703 _skip_bits--;
6704 return true;
6705 }
6706 // convert offset into a HeapWord*
6707 HeapWord* addr = _bit_map->startWord() + offset;
6708 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6709 "address out of range");
6710 assert(_bit_map->isMarked(addr), "tautology");
6711 if (_bit_map->isMarked(addr+1)) {
6712 // this is an allocated object that might not yet be initialized
6713 assert(_skip_bits == 0, "tautology");
6714 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6715 oop p = oop(addr);
6716 if (p->klass_or_null() == NULL) {
6717 // in the case of Clean-on-Enter optimization, redirty card
6718 // and avoid clearing card by increasing the threshold.
6719 return true;
6720 }
6721 }
6722 scan_oops_in_oop(addr);
6723 return true;
6724 }
6725
6726 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6727 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6728 // Should we assert that our work queue is empty or
6729 // below some drain limit?
6730 assert(_work_queue->size() == 0,
6731 "should drain stack to limit stack usage");
6732 // convert ptr to an oop preparatory to scanning
6733 oop obj = oop(ptr);
6734 // Ignore mark word in verification below, since we
6735 // may be running concurrent with mutators.
6736 assert(obj->is_oop(true), "should be an oop");
6737 assert(_finger <= ptr, "_finger runneth ahead");
6738 // advance the finger to right end of this object
6739 _finger = ptr + obj->size();
6740 assert(_finger > ptr, "we just incremented it above");
6741 // On large heaps, it may take us some time to get through
6742 // the marking phase. During
6743 // this time it's possible that a lot of mutations have
6744 // accumulated in the card table and the mod union table --
6745 // these mutation records are redundant until we have
6746 // actually traced into the corresponding card.
6747 // Here, we check whether advancing the finger would make
6748 // us cross into a new card, and if so clear corresponding
6749 // cards in the MUT (preclean them in the card-table in the
6750 // future).
6751
6752 // The clean-on-enter optimization is disabled by default,
6753 // until we fix 6178663.
6754 if (CMSCleanOnEnter && (_finger > _threshold)) {
6755 // [_threshold, _finger) represents the interval
6756 // of cards to be cleared in MUT (or precleaned in card table).
6757 // The set of cards to be cleared is all those that overlap
6758 // with the interval [_threshold, _finger); note that
6759 // _threshold is always kept card-aligned but _finger isn't
6760 // always card-aligned.
6761 HeapWord* old_threshold = _threshold;
6762 assert(old_threshold == (HeapWord*)round_to(
6763 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6764 "_threshold should always be card-aligned");
6765 _threshold = (HeapWord*)round_to(
6766 (intptr_t)_finger, CardTableModRefBS::card_size);
6767 MemRegion mr(old_threshold, _threshold);
6768 assert(!mr.is_empty(), "Control point invariant");
6769 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6770 _mut->clear_range(mr);
6771 }
6772
6773 // Note: the local finger doesn't advance while we drain
6774 // the stack below, but the global finger sure can and will.
6775 HeapWord** gfa = _task->global_finger_addr();
6776 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6777 _span, _bit_map,
6778 _work_queue,
6779 _overflow_stack,
6780 _finger,
6781 gfa, this);
6782 bool res = _work_queue->push(obj); // overflow could occur here
6783 assert(res, "Will hold once we use workqueues");
6784 while (true) {
6785 oop new_oop;
6786 if (!_work_queue->pop_local(new_oop)) {
6787 // We emptied our work_queue; check if there's stuff that can
6788 // be gotten from the overflow stack.
6789 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6790 _overflow_stack, _work_queue)) {
6791 do_yield_check();
6792 continue;
6793 } else { // done
6794 break;
6795 }
6796 }
6797 // Skip verifying header mark word below because we are
6798 // running concurrent with mutators.
6799 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6800 // now scan this oop's oops
6801 new_oop->oop_iterate(&pushOrMarkClosure);
6802 do_yield_check();
6803 }
6804 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6805 }
6806
6807 // Yield in response to a request from VM Thread or
6808 // from mutators.
6809 void Par_MarkFromRootsClosure::do_yield_work() {
6810 assert(_task != NULL, "sanity");
6811 _task->yield();
6812 }
6813
6814 // A variant of the above used for verifying CMS marking work.
6815 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6816 MemRegion span,
6817 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6818 CMSMarkStack* mark_stack):
6819 _collector(collector),
6820 _span(span),
6821 _verification_bm(verification_bm),
6822 _cms_bm(cms_bm),
6823 _mark_stack(mark_stack),
6824 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6825 mark_stack)
6826 {
6827 assert(_mark_stack->isEmpty(), "stack should be empty");
6828 _finger = _verification_bm->startWord();
6829 assert(_collector->_restart_addr == NULL, "Sanity check");
6830 assert(_span.contains(_finger), "Out of bounds _finger?");
6831 }
6832
6833 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6834 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6835 assert(_span.contains(addr), "Out of bounds _finger?");
6836 _finger = addr;
6837 }
6838
6839 // Should revisit to see if this should be restructured for
6840 // greater efficiency.
6841 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6842 // convert offset into a HeapWord*
6843 HeapWord* addr = _verification_bm->startWord() + offset;
6844 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6845 "address out of range");
6846 assert(_verification_bm->isMarked(addr), "tautology");
6847 assert(_cms_bm->isMarked(addr), "tautology");
6848
6849 assert(_mark_stack->isEmpty(),
6850 "should drain stack to limit stack usage");
6851 // convert addr to an oop preparatory to scanning
6852 oop obj = oop(addr);
6853 assert(obj->is_oop(), "should be an oop");
6854 assert(_finger <= addr, "_finger runneth ahead");
6855 // advance the finger to right end of this object
6856 _finger = addr + obj->size();
6857 assert(_finger > addr, "we just incremented it above");
6858 // Note: the finger doesn't advance while we drain
6859 // the stack below.
6860 bool res = _mark_stack->push(obj);
6861 assert(res, "Empty non-zero size stack should have space for single push");
6862 while (!_mark_stack->isEmpty()) {
6863 oop new_oop = _mark_stack->pop();
6864 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6865 // now scan this oop's oops
6866 new_oop->oop_iterate(&_pam_verify_closure);
6867 }
6868 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6869 return true;
6870 }
6871
6872 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6873 CMSCollector* collector, MemRegion span,
6874 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6875 CMSMarkStack* mark_stack):
6876 MetadataAwareOopClosure(collector->ref_processor()),
6877 _collector(collector),
6878 _span(span),
6879 _verification_bm(verification_bm),
6880 _cms_bm(cms_bm),
6881 _mark_stack(mark_stack)
6882 { }
6883
6884 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6885 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6886
6887 // Upon stack overflow, we discard (part of) the stack,
6888 // remembering the least address amongst those discarded
6889 // in CMSCollector's _restart_address.
6890 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6891 // Remember the least grey address discarded
6892 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6893 _collector->lower_restart_addr(ra);
6894 _mark_stack->reset(); // discard stack contents
6895 _mark_stack->expand(); // expand the stack if possible
6896 }
6897
6898 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6899 assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
6900 HeapWord* addr = (HeapWord*)obj;
6901 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6902 // Oop lies in _span and isn't yet grey or black
6903 _verification_bm->mark(addr); // now grey
6904 if (!_cms_bm->isMarked(addr)) {
6905 oop(addr)->print();
6906 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
6907 p2i(addr));
6908 fatal("... aborting");
6909 }
6910
6911 if (!_mark_stack->push(obj)) { // stack overflow
6912 if (PrintCMSStatistics != 0) {
6913 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6914 SIZE_FORMAT, _mark_stack->capacity());
6915 }
6916 assert(_mark_stack->isFull(), "Else push should have succeeded");
6917 handle_stack_overflow(addr);
6918 }
6919 // anything including and to the right of _finger
6920 // will be scanned as we iterate over the remainder of the
6921 // bit map
6922 }
6923 }
6924
6925 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6926 MemRegion span,
6927 CMSBitMap* bitMap, CMSMarkStack* markStack,
6928 HeapWord* finger, MarkFromRootsClosure* parent) :
6929 MetadataAwareOopClosure(collector->ref_processor()),
6930 _collector(collector),
6931 _span(span),
6932 _bitMap(bitMap),
6933 _markStack(markStack),
6934 _finger(finger),
6935 _parent(parent)
6936 { }
6937
6938 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
6939 MemRegion span,
6940 CMSBitMap* bit_map,
6941 OopTaskQueue* work_queue,
6942 CMSMarkStack* overflow_stack,
6943 HeapWord* finger,
6944 HeapWord** global_finger_addr,
6945 Par_MarkFromRootsClosure* parent) :
6946 MetadataAwareOopClosure(collector->ref_processor()),
6947 _collector(collector),
6948 _whole_span(collector->_span),
6949 _span(span),
6950 _bit_map(bit_map),
6951 _work_queue(work_queue),
6952 _overflow_stack(overflow_stack),
6953 _finger(finger),
6954 _global_finger_addr(global_finger_addr),
6955 _parent(parent)
6956 { }
6957
6958 // Assumes thread-safe access by callers, who are
6959 // responsible for mutual exclusion.
6960 void CMSCollector::lower_restart_addr(HeapWord* low) {
6961 assert(_span.contains(low), "Out of bounds addr");
6962 if (_restart_addr == NULL) {
6963 _restart_addr = low;
6964 } else {
6965 _restart_addr = MIN2(_restart_addr, low);
6966 }
6967 }
6968
6969 // Upon stack overflow, we discard (part of) the stack,
6970 // remembering the least address amongst those discarded
6971 // in CMSCollector's _restart_address.
6972 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6973 // Remember the least grey address discarded
6974 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6975 _collector->lower_restart_addr(ra);
6976 _markStack->reset(); // discard stack contents
6977 _markStack->expand(); // expand the stack if possible
6978 }
6979
6980 // Upon stack overflow, we discard (part of) the stack,
6981 // remembering the least address amongst those discarded
6982 // in CMSCollector's _restart_address.
6983 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6984 // We need to do this under a mutex to prevent other
6985 // workers from interfering with the work done below.
6986 MutexLockerEx ml(_overflow_stack->par_lock(),
6987 Mutex::_no_safepoint_check_flag);
6988 // Remember the least grey address discarded
6989 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6990 _collector->lower_restart_addr(ra);
6991 _overflow_stack->reset(); // discard stack contents
6992 _overflow_stack->expand(); // expand the stack if possible
6993 }
6994
6995 void PushOrMarkClosure::do_oop(oop obj) {
6996 // Ignore mark word because we are running concurrent with mutators.
6997 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
6998 HeapWord* addr = (HeapWord*)obj;
6999 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7000 // Oop lies in _span and isn't yet grey or black
7001 _bitMap->mark(addr); // now grey
7002 if (addr < _finger) {
7003 // the bit map iteration has already either passed, or
7004 // sampled, this bit in the bit map; we'll need to
7005 // use the marking stack to scan this oop's oops.
7006 bool simulate_overflow = false;
7007 NOT_PRODUCT(
7008 if (CMSMarkStackOverflowALot &&
7009 _collector->simulate_overflow()) {
7010 // simulate a stack overflow
7011 simulate_overflow = true;
7012 }
7013 )
7014 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7015 if (PrintCMSStatistics != 0) {
7016 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7017 SIZE_FORMAT, _markStack->capacity());
7018 }
7019 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7020 handle_stack_overflow(addr);
7021 }
7022 }
7023 // anything including and to the right of _finger
7024 // will be scanned as we iterate over the remainder of the
7025 // bit map
7026 do_yield_check();
7027 }
7028 }
7029
7030 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7031 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7032
7033 void Par_PushOrMarkClosure::do_oop(oop obj) {
7034 // Ignore mark word because we are running concurrent with mutators.
7035 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7036 HeapWord* addr = (HeapWord*)obj;
7037 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7038 // Oop lies in _span and isn't yet grey or black
7039 // We read the global_finger (volatile read) strictly after marking oop
7040 bool res = _bit_map->par_mark(addr); // now grey
7041 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7042 // Should we push this marked oop on our stack?
7043 // -- if someone else marked it, nothing to do
7044 // -- if target oop is above global finger nothing to do
7045 // -- if target oop is in chunk and above local finger
7046 // then nothing to do
7047 // -- else push on work queue
7048 if ( !res // someone else marked it, they will deal with it
7049 || (addr >= *gfa) // will be scanned in a later task
7050 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7051 return;
7052 }
7053 // the bit map iteration has already either passed, or
7054 // sampled, this bit in the bit map; we'll need to
7055 // use the marking stack to scan this oop's oops.
7056 bool simulate_overflow = false;
7057 NOT_PRODUCT(
7058 if (CMSMarkStackOverflowALot &&
7059 _collector->simulate_overflow()) {
7060 // simulate a stack overflow
7061 simulate_overflow = true;
7062 }
7063 )
7064 if (simulate_overflow ||
7065 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7066 // stack overflow
7067 if (PrintCMSStatistics != 0) {
7068 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7069 SIZE_FORMAT, _overflow_stack->capacity());
7070 }
7071 // We cannot assert that the overflow stack is full because
7072 // it may have been emptied since.
7073 assert(simulate_overflow ||
7074 _work_queue->size() == _work_queue->max_elems(),
7075 "Else push should have succeeded");
7076 handle_stack_overflow(addr);
7077 }
7078 do_yield_check();
7079 }
7080 }
7081
7082 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7083 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7084
7085 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7086 MemRegion span,
7087 ReferenceProcessor* rp,
7088 CMSBitMap* bit_map,
7089 CMSBitMap* mod_union_table,
7090 CMSMarkStack* mark_stack,
7091 bool concurrent_precleaning):
7092 MetadataAwareOopClosure(rp),
7093 _collector(collector),
7094 _span(span),
7095 _bit_map(bit_map),
7096 _mod_union_table(mod_union_table),
7097 _mark_stack(mark_stack),
7098 _concurrent_precleaning(concurrent_precleaning)
7099 {
7100 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7101 }
7102
7103 // Grey object rescan during pre-cleaning and second checkpoint phases --
7104 // the non-parallel version (the parallel version appears further below.)
7105 void PushAndMarkClosure::do_oop(oop obj) {
7106 // Ignore mark word verification. If during concurrent precleaning,
7107 // the object monitor may be locked. If during the checkpoint
7108 // phases, the object may already have been reached by a different
7109 // path and may be at the end of the global overflow list (so
7110 // the mark word may be NULL).
7111 assert(obj->is_oop_or_null(true /* ignore mark word */),
7112 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7113 HeapWord* addr = (HeapWord*)obj;
7114 // Check if oop points into the CMS generation
7115 // and is not marked
7116 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7117 // a white object ...
7118 _bit_map->mark(addr); // ... now grey
7119 // push on the marking stack (grey set)
7120 bool simulate_overflow = false;
7121 NOT_PRODUCT(
7122 if (CMSMarkStackOverflowALot &&
7123 _collector->simulate_overflow()) {
7124 // simulate a stack overflow
7125 simulate_overflow = true;
7126 }
7127 )
7128 if (simulate_overflow || !_mark_stack->push(obj)) {
7129 if (_concurrent_precleaning) {
7130 // During precleaning we can just dirty the appropriate card(s)
7131 // in the mod union table, thus ensuring that the object remains
7132 // in the grey set and continue. In the case of object arrays
7133 // we need to dirty all of the cards that the object spans,
7134 // since the rescan of object arrays will be limited to the
7135 // dirty cards.
7136 // Note that no one can be interfering with us in this action
7137 // of dirtying the mod union table, so no locking or atomics
7138 // are required.
7139 if (obj->is_objArray()) {
7140 size_t sz = obj->size();
7141 HeapWord* end_card_addr = (HeapWord*)round_to(
7142 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7143 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7144 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7145 _mod_union_table->mark_range(redirty_range);
7146 } else {
7147 _mod_union_table->mark(addr);
7148 }
7149 _collector->_ser_pmc_preclean_ovflw++;
7150 } else {
7151 // During the remark phase, we need to remember this oop
7152 // in the overflow list.
7153 _collector->push_on_overflow_list(obj);
7154 _collector->_ser_pmc_remark_ovflw++;
7155 }
7156 }
7157 }
7158 }
7159
7160 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7161 MemRegion span,
7162 ReferenceProcessor* rp,
7163 CMSBitMap* bit_map,
7164 OopTaskQueue* work_queue):
7165 MetadataAwareOopClosure(rp),
7166 _collector(collector),
7167 _span(span),
7168 _bit_map(bit_map),
7169 _work_queue(work_queue)
7170 {
7171 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7172 }
7173
7174 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7175 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7176
7177 // Grey object rescan during second checkpoint phase --
7178 // the parallel version.
7179 void Par_PushAndMarkClosure::do_oop(oop obj) {
7180 // In the assert below, we ignore the mark word because
7181 // this oop may point to an already visited object that is
7182 // on the overflow stack (in which case the mark word has
7183 // been hijacked for chaining into the overflow stack --
7184 // if this is the last object in the overflow stack then
7185 // its mark word will be NULL). Because this object may
7186 // have been subsequently popped off the global overflow
7187 // stack, and the mark word possibly restored to the prototypical
7188 // value, by the time we get to examined this failing assert in
7189 // the debugger, is_oop_or_null(false) may subsequently start
7190 // to hold.
7191 assert(obj->is_oop_or_null(true),
7192 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7193 HeapWord* addr = (HeapWord*)obj;
7194 // Check if oop points into the CMS generation
7195 // and is not marked
7196 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7197 // a white object ...
7198 // If we manage to "claim" the object, by being the
7199 // first thread to mark it, then we push it on our
7200 // marking stack
7201 if (_bit_map->par_mark(addr)) { // ... now grey
7202 // push on work queue (grey set)
7203 bool simulate_overflow = false;
7204 NOT_PRODUCT(
7205 if (CMSMarkStackOverflowALot &&
7206 _collector->par_simulate_overflow()) {
7207 // simulate a stack overflow
7208 simulate_overflow = true;
7209 }
7210 )
7211 if (simulate_overflow || !_work_queue->push(obj)) {
7212 _collector->par_push_on_overflow_list(obj);
7213 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7214 }
7215 } // Else, some other thread got there first
7216 }
7217 }
7218
7219 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7220 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7221
7222 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7223 Mutex* bml = _collector->bitMapLock();
7224 assert_lock_strong(bml);
7225 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7226 "CMS thread should hold CMS token");
7227
7228 bml->unlock();
7229 ConcurrentMarkSweepThread::desynchronize(true);
7230
7231 _collector->stopTimer();
7232 if (PrintCMSStatistics != 0) {
7233 _collector->incrementYields();
7234 }
7235
7236 // See the comment in coordinator_yield()
7237 for (unsigned i = 0; i < CMSYieldSleepCount &&
7238 ConcurrentMarkSweepThread::should_yield() &&
7239 !CMSCollector::foregroundGCIsActive(); ++i) {
7240 os::sleep(Thread::current(), 1, false);
7241 }
7242
7243 ConcurrentMarkSweepThread::synchronize(true);
7244 bml->lock();
7245
7246 _collector->startTimer();
7247 }
7248
7249 bool CMSPrecleanRefsYieldClosure::should_return() {
7250 if (ConcurrentMarkSweepThread::should_yield()) {
7251 do_yield_work();
7252 }
7253 return _collector->foregroundGCIsActive();
7254 }
7255
7256 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7257 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7258 "mr should be aligned to start at a card boundary");
7259 // We'd like to assert:
7260 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7261 // "mr should be a range of cards");
7262 // However, that would be too strong in one case -- the last
7263 // partition ends at _unallocated_block which, in general, can be
7264 // an arbitrary boundary, not necessarily card aligned.
7265 if (PrintCMSStatistics != 0) {
7266 _num_dirty_cards +=
7267 mr.word_size()/CardTableModRefBS::card_size_in_words;
7268 }
7269 _space->object_iterate_mem(mr, &_scan_cl);
7270 }
7271
7272 SweepClosure::SweepClosure(CMSCollector* collector,
7273 ConcurrentMarkSweepGeneration* g,
7274 CMSBitMap* bitMap, bool should_yield) :
7275 _collector(collector),
7276 _g(g),
7277 _sp(g->cmsSpace()),
7278 _limit(_sp->sweep_limit()),
7279 _freelistLock(_sp->freelistLock()),
7280 _bitMap(bitMap),
7281 _yield(should_yield),
7282 _inFreeRange(false), // No free range at beginning of sweep
7283 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7284 _lastFreeRangeCoalesced(false),
7285 _freeFinger(g->used_region().start())
7286 {
7287 NOT_PRODUCT(
7288 _numObjectsFreed = 0;
7289 _numWordsFreed = 0;
7290 _numObjectsLive = 0;
7291 _numWordsLive = 0;
7292 _numObjectsAlreadyFree = 0;
7293 _numWordsAlreadyFree = 0;
7294 _last_fc = NULL;
7295
7296 _sp->initializeIndexedFreeListArrayReturnedBytes();
7297 _sp->dictionary()->initialize_dict_returned_bytes();
7298 )
7299 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7300 "sweep _limit out of bounds");
7301 if (CMSTraceSweeper) {
7302 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7303 p2i(_limit));
7304 }
7305 }
7306
7307 void SweepClosure::print_on(outputStream* st) const {
7308 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7309 p2i(_sp->bottom()), p2i(_sp->end()));
7310 tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7311 tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7312 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7313 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7314 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7315 }
7316
7317 #ifndef PRODUCT
7318 // Assertion checking only: no useful work in product mode --
7319 // however, if any of the flags below become product flags,
7320 // you may need to review this code to see if it needs to be
7321 // enabled in product mode.
7322 SweepClosure::~SweepClosure() {
7323 assert_lock_strong(_freelistLock);
7324 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7325 "sweep _limit out of bounds");
7326 if (inFreeRange()) {
7327 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7328 print();
7329 ShouldNotReachHere();
7330 }
7331 if (Verbose && PrintGC) {
7332 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7333 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7334 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7335 SIZE_FORMAT" bytes "
7336 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7337 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7338 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7339 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7340 * sizeof(HeapWord);
7341 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7342
7343 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7344 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7345 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7346 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7347 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7348 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7349 indexListReturnedBytes);
7350 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7351 dict_returned_bytes);
7352 }
7353 }
7354 if (CMSTraceSweeper) {
7355 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7356 p2i(_limit));
7357 }
7358 }
7359 #endif // PRODUCT
7360
7361 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7362 bool freeRangeInFreeLists) {
7363 if (CMSTraceSweeper) {
7364 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7365 p2i(freeFinger), freeRangeInFreeLists);
7366 }
7367 assert(!inFreeRange(), "Trampling existing free range");
7368 set_inFreeRange(true);
7369 set_lastFreeRangeCoalesced(false);
7370
7371 set_freeFinger(freeFinger);
7372 set_freeRangeInFreeLists(freeRangeInFreeLists);
7373 if (CMSTestInFreeList) {
7374 if (freeRangeInFreeLists) {
7375 FreeChunk* fc = (FreeChunk*) freeFinger;
7376 assert(fc->is_free(), "A chunk on the free list should be free.");
7377 assert(fc->size() > 0, "Free range should have a size");
7378 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7379 }
7380 }
7381 }
7382
7383 // Note that the sweeper runs concurrently with mutators. Thus,
7384 // it is possible for direct allocation in this generation to happen
7385 // in the middle of the sweep. Note that the sweeper also coalesces
7386 // contiguous free blocks. Thus, unless the sweeper and the allocator
7387 // synchronize appropriately freshly allocated blocks may get swept up.
7388 // This is accomplished by the sweeper locking the free lists while
7389 // it is sweeping. Thus blocks that are determined to be free are
7390 // indeed free. There is however one additional complication:
7391 // blocks that have been allocated since the final checkpoint and
7392 // mark, will not have been marked and so would be treated as
7393 // unreachable and swept up. To prevent this, the allocator marks
7394 // the bit map when allocating during the sweep phase. This leads,
7395 // however, to a further complication -- objects may have been allocated
7396 // but not yet initialized -- in the sense that the header isn't yet
7397 // installed. The sweeper can not then determine the size of the block
7398 // in order to skip over it. To deal with this case, we use a technique
7399 // (due to Printezis) to encode such uninitialized block sizes in the
7400 // bit map. Since the bit map uses a bit per every HeapWord, but the
7401 // CMS generation has a minimum object size of 3 HeapWords, it follows
7402 // that "normal marks" won't be adjacent in the bit map (there will
7403 // always be at least two 0 bits between successive 1 bits). We make use
7404 // of these "unused" bits to represent uninitialized blocks -- the bit
7405 // corresponding to the start of the uninitialized object and the next
7406 // bit are both set. Finally, a 1 bit marks the end of the object that
7407 // started with the two consecutive 1 bits to indicate its potentially
7408 // uninitialized state.
7409
7410 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7411 FreeChunk* fc = (FreeChunk*)addr;
7412 size_t res;
7413
7414 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7415 // than "addr == _limit" because although _limit was a block boundary when
7416 // we started the sweep, it may no longer be one because heap expansion
7417 // may have caused us to coalesce the block ending at the address _limit
7418 // with a newly expanded chunk (this happens when _limit was set to the
7419 // previous _end of the space), so we may have stepped past _limit:
7420 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7421 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7422 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7423 "sweep _limit out of bounds");
7424 assert(addr < _sp->end(), "addr out of bounds");
7425 // Flush any free range we might be holding as a single
7426 // coalesced chunk to the appropriate free list.
7427 if (inFreeRange()) {
7428 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7429 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", p2i(freeFinger())));
7430 flush_cur_free_chunk(freeFinger(),
7431 pointer_delta(addr, freeFinger()));
7432 if (CMSTraceSweeper) {
7433 gclog_or_tty->print("Sweep: last chunk: ");
7434 gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
7435 "[coalesced:%d]\n",
7436 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7437 lastFreeRangeCoalesced() ? 1 : 0);
7438 }
7439 }
7440
7441 // help the iterator loop finish
7442 return pointer_delta(_sp->end(), addr);
7443 }
7444
7445 assert(addr < _limit, "sweep invariant");
7446 // check if we should yield
7447 do_yield_check(addr);
7448 if (fc->is_free()) {
7449 // Chunk that is already free
7450 res = fc->size();
7451 do_already_free_chunk(fc);
7452 debug_only(_sp->verifyFreeLists());
7453 // If we flush the chunk at hand in lookahead_and_flush()
7454 // and it's coalesced with a preceding chunk, then the
7455 // process of "mangling" the payload of the coalesced block
7456 // will cause erasure of the size information from the
7457 // (erstwhile) header of all the coalesced blocks but the
7458 // first, so the first disjunct in the assert will not hold
7459 // in that specific case (in which case the second disjunct
7460 // will hold).
7461 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7462 "Otherwise the size info doesn't change at this step");
7463 NOT_PRODUCT(
7464 _numObjectsAlreadyFree++;
7465 _numWordsAlreadyFree += res;
7466 )
7467 NOT_PRODUCT(_last_fc = fc;)
7468 } else if (!_bitMap->isMarked(addr)) {
7469 // Chunk is fresh garbage
7470 res = do_garbage_chunk(fc);
7471 debug_only(_sp->verifyFreeLists());
7472 NOT_PRODUCT(
7473 _numObjectsFreed++;
7474 _numWordsFreed += res;
7475 )
7476 } else {
7477 // Chunk that is alive.
7478 res = do_live_chunk(fc);
7479 debug_only(_sp->verifyFreeLists());
7480 NOT_PRODUCT(
7481 _numObjectsLive++;
7482 _numWordsLive += res;
7483 )
7484 }
7485 return res;
7486 }
7487
7488 // For the smart allocation, record following
7489 // split deaths - a free chunk is removed from its free list because
7490 // it is being split into two or more chunks.
7491 // split birth - a free chunk is being added to its free list because
7492 // a larger free chunk has been split and resulted in this free chunk.
7493 // coal death - a free chunk is being removed from its free list because
7494 // it is being coalesced into a large free chunk.
7495 // coal birth - a free chunk is being added to its free list because
7496 // it was created when two or more free chunks where coalesced into
7497 // this free chunk.
7498 //
7499 // These statistics are used to determine the desired number of free
7500 // chunks of a given size. The desired number is chosen to be relative
7501 // to the end of a CMS sweep. The desired number at the end of a sweep
7502 // is the
7503 // count-at-end-of-previous-sweep (an amount that was enough)
7504 // - count-at-beginning-of-current-sweep (the excess)
7505 // + split-births (gains in this size during interval)
7506 // - split-deaths (demands on this size during interval)
7507 // where the interval is from the end of one sweep to the end of the
7508 // next.
7509 //
7510 // When sweeping the sweeper maintains an accumulated chunk which is
7511 // the chunk that is made up of chunks that have been coalesced. That
7512 // will be termed the left-hand chunk. A new chunk of garbage that
7513 // is being considered for coalescing will be referred to as the
7514 // right-hand chunk.
7515 //
7516 // When making a decision on whether to coalesce a right-hand chunk with
7517 // the current left-hand chunk, the current count vs. the desired count
7518 // of the left-hand chunk is considered. Also if the right-hand chunk
7519 // is near the large chunk at the end of the heap (see
7520 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7521 // left-hand chunk is coalesced.
7522 //
7523 // When making a decision about whether to split a chunk, the desired count
7524 // vs. the current count of the candidate to be split is also considered.
7525 // If the candidate is underpopulated (currently fewer chunks than desired)
7526 // a chunk of an overpopulated (currently more chunks than desired) size may
7527 // be chosen. The "hint" associated with a free list, if non-null, points
7528 // to a free list which may be overpopulated.
7529 //
7530
7531 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7532 const size_t size = fc->size();
7533 // Chunks that cannot be coalesced are not in the
7534 // free lists.
7535 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7536 assert(_sp->verify_chunk_in_free_list(fc),
7537 "free chunk should be in free lists");
7538 }
7539 // a chunk that is already free, should not have been
7540 // marked in the bit map
7541 HeapWord* const addr = (HeapWord*) fc;
7542 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7543 // Verify that the bit map has no bits marked between
7544 // addr and purported end of this block.
7545 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7546
7547 // Some chunks cannot be coalesced under any circumstances.
7548 // See the definition of cantCoalesce().
7549 if (!fc->cantCoalesce()) {
7550 // This chunk can potentially be coalesced.
7551 if (_sp->adaptive_freelists()) {
7552 // All the work is done in
7553 do_post_free_or_garbage_chunk(fc, size);
7554 } else { // Not adaptive free lists
7555 // this is a free chunk that can potentially be coalesced by the sweeper;
7556 if (!inFreeRange()) {
7557 // if the next chunk is a free block that can't be coalesced
7558 // it doesn't make sense to remove this chunk from the free lists
7559 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7560 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
7561 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
7562 nextChunk->is_free() && // ... which is free...
7563 nextChunk->cantCoalesce()) { // ... but can't be coalesced
7564 // nothing to do
7565 } else {
7566 // Potentially the start of a new free range:
7567 // Don't eagerly remove it from the free lists.
7568 // No need to remove it if it will just be put
7569 // back again. (Also from a pragmatic point of view
7570 // if it is a free block in a region that is beyond
7571 // any allocated blocks, an assertion will fail)
7572 // Remember the start of a free run.
7573 initialize_free_range(addr, true);
7574 // end - can coalesce with next chunk
7575 }
7576 } else {
7577 // the midst of a free range, we are coalescing
7578 print_free_block_coalesced(fc);
7579 if (CMSTraceSweeper) {
7580 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7581 }
7582 // remove it from the free lists
7583 _sp->removeFreeChunkFromFreeLists(fc);
7584 set_lastFreeRangeCoalesced(true);
7585 // If the chunk is being coalesced and the current free range is
7586 // in the free lists, remove the current free range so that it
7587 // will be returned to the free lists in its entirety - all
7588 // the coalesced pieces included.
7589 if (freeRangeInFreeLists()) {
7590 FreeChunk* ffc = (FreeChunk*) freeFinger();
7591 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7592 "Size of free range is inconsistent with chunk size.");
7593 if (CMSTestInFreeList) {
7594 assert(_sp->verify_chunk_in_free_list(ffc),
7595 "free range is not in free lists");
7596 }
7597 _sp->removeFreeChunkFromFreeLists(ffc);
7598 set_freeRangeInFreeLists(false);
7599 }
7600 }
7601 }
7602 // Note that if the chunk is not coalescable (the else arm
7603 // below), we unconditionally flush, without needing to do
7604 // a "lookahead," as we do below.
7605 if (inFreeRange()) lookahead_and_flush(fc, size);
7606 } else {
7607 // Code path common to both original and adaptive free lists.
7608
7609 // cant coalesce with previous block; this should be treated
7610 // as the end of a free run if any
7611 if (inFreeRange()) {
7612 // we kicked some butt; time to pick up the garbage
7613 assert(freeFinger() < addr, "freeFinger points too high");
7614 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7615 }
7616 // else, nothing to do, just continue
7617 }
7618 }
7619
7620 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7621 // This is a chunk of garbage. It is not in any free list.
7622 // Add it to a free list or let it possibly be coalesced into
7623 // a larger chunk.
7624 HeapWord* const addr = (HeapWord*) fc;
7625 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7626
7627 if (_sp->adaptive_freelists()) {
7628 // Verify that the bit map has no bits marked between
7629 // addr and purported end of just dead object.
7630 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7631
7632 do_post_free_or_garbage_chunk(fc, size);
7633 } else {
7634 if (!inFreeRange()) {
7635 // start of a new free range
7636 assert(size > 0, "A free range should have a size");
7637 initialize_free_range(addr, false);
7638 } else {
7639 // this will be swept up when we hit the end of the
7640 // free range
7641 if (CMSTraceSweeper) {
7642 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7643 }
7644 // If the chunk is being coalesced and the current free range is
7645 // in the free lists, remove the current free range so that it
7646 // will be returned to the free lists in its entirety - all
7647 // the coalesced pieces included.
7648 if (freeRangeInFreeLists()) {
7649 FreeChunk* ffc = (FreeChunk*)freeFinger();
7650 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7651 "Size of free range is inconsistent with chunk size.");
7652 if (CMSTestInFreeList) {
7653 assert(_sp->verify_chunk_in_free_list(ffc),
7654 "free range is not in free lists");
7655 }
7656 _sp->removeFreeChunkFromFreeLists(ffc);
7657 set_freeRangeInFreeLists(false);
7658 }
7659 set_lastFreeRangeCoalesced(true);
7660 }
7661 // this will be swept up when we hit the end of the free range
7662
7663 // Verify that the bit map has no bits marked between
7664 // addr and purported end of just dead object.
7665 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7666 }
7667 assert(_limit >= addr + size,
7668 "A freshly garbage chunk can't possibly straddle over _limit");
7669 if (inFreeRange()) lookahead_and_flush(fc, size);
7670 return size;
7671 }
7672
7673 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7674 HeapWord* addr = (HeapWord*) fc;
7675 // The sweeper has just found a live object. Return any accumulated
7676 // left hand chunk to the free lists.
7677 if (inFreeRange()) {
7678 assert(freeFinger() < addr, "freeFinger points too high");
7679 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7680 }
7681
7682 // This object is live: we'd normally expect this to be
7683 // an oop, and like to assert the following:
7684 // assert(oop(addr)->is_oop(), "live block should be an oop");
7685 // However, as we commented above, this may be an object whose
7686 // header hasn't yet been initialized.
7687 size_t size;
7688 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7689 if (_bitMap->isMarked(addr + 1)) {
7690 // Determine the size from the bit map, rather than trying to
7691 // compute it from the object header.
7692 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7693 size = pointer_delta(nextOneAddr + 1, addr);
7694 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7695 "alignment problem");
7696
7697 #ifdef ASSERT
7698 if (oop(addr)->klass_or_null() != NULL) {
7699 // Ignore mark word because we are running concurrent with mutators
7700 assert(oop(addr)->is_oop(true), "live block should be an oop");
7701 assert(size ==
7702 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7703 "P-mark and computed size do not agree");
7704 }
7705 #endif
7706
7707 } else {
7708 // This should be an initialized object that's alive.
7709 assert(oop(addr)->klass_or_null() != NULL,
7710 "Should be an initialized object");
7711 // Ignore mark word because we are running concurrent with mutators
7712 assert(oop(addr)->is_oop(true), "live block should be an oop");
7713 // Verify that the bit map has no bits marked between
7714 // addr and purported end of this block.
7715 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7716 assert(size >= 3, "Necessary for Printezis marks to work");
7717 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7718 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7719 }
7720 return size;
7721 }
7722
7723 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7724 size_t chunkSize) {
7725 // do_post_free_or_garbage_chunk() should only be called in the case
7726 // of the adaptive free list allocator.
7727 const bool fcInFreeLists = fc->is_free();
7728 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
7729 assert((HeapWord*)fc <= _limit, "sweep invariant");
7730 if (CMSTestInFreeList && fcInFreeLists) {
7731 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7732 }
7733
7734 if (CMSTraceSweeper) {
7735 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7736 }
7737
7738 HeapWord* const fc_addr = (HeapWord*) fc;
7739
7740 bool coalesce;
7741 const size_t left = pointer_delta(fc_addr, freeFinger());
7742 const size_t right = chunkSize;
7743 switch (FLSCoalescePolicy) {
7744 // numeric value forms a coalition aggressiveness metric
7745 case 0: { // never coalesce
7746 coalesce = false;
7747 break;
7748 }
7749 case 1: { // coalesce if left & right chunks on overpopulated lists
7750 coalesce = _sp->coalOverPopulated(left) &&
7751 _sp->coalOverPopulated(right);
7752 break;
7753 }
7754 case 2: { // coalesce if left chunk on overpopulated list (default)
7755 coalesce = _sp->coalOverPopulated(left);
7756 break;
7757 }
7758 case 3: { // coalesce if left OR right chunk on overpopulated list
7759 coalesce = _sp->coalOverPopulated(left) ||
7760 _sp->coalOverPopulated(right);
7761 break;
7762 }
7763 case 4: { // always coalesce
7764 coalesce = true;
7765 break;
7766 }
7767 default:
7768 ShouldNotReachHere();
7769 }
7770
7771 // Should the current free range be coalesced?
7772 // If the chunk is in a free range and either we decided to coalesce above
7773 // or the chunk is near the large block at the end of the heap
7774 // (isNearLargestChunk() returns true), then coalesce this chunk.
7775 const bool doCoalesce = inFreeRange()
7776 && (coalesce || _g->isNearLargestChunk(fc_addr));
7777 if (doCoalesce) {
7778 // Coalesce the current free range on the left with the new
7779 // chunk on the right. If either is on a free list,
7780 // it must be removed from the list and stashed in the closure.
7781 if (freeRangeInFreeLists()) {
7782 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7783 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7784 "Size of free range is inconsistent with chunk size.");
7785 if (CMSTestInFreeList) {
7786 assert(_sp->verify_chunk_in_free_list(ffc),
7787 "Chunk is not in free lists");
7788 }
7789 _sp->coalDeath(ffc->size());
7790 _sp->removeFreeChunkFromFreeLists(ffc);
7791 set_freeRangeInFreeLists(false);
7792 }
7793 if (fcInFreeLists) {
7794 _sp->coalDeath(chunkSize);
7795 assert(fc->size() == chunkSize,
7796 "The chunk has the wrong size or is not in the free lists");
7797 _sp->removeFreeChunkFromFreeLists(fc);
7798 }
7799 set_lastFreeRangeCoalesced(true);
7800 print_free_block_coalesced(fc);
7801 } else { // not in a free range and/or should not coalesce
7802 // Return the current free range and start a new one.
7803 if (inFreeRange()) {
7804 // In a free range but cannot coalesce with the right hand chunk.
7805 // Put the current free range into the free lists.
7806 flush_cur_free_chunk(freeFinger(),
7807 pointer_delta(fc_addr, freeFinger()));
7808 }
7809 // Set up for new free range. Pass along whether the right hand
7810 // chunk is in the free lists.
7811 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7812 }
7813 }
7814
7815 // Lookahead flush:
7816 // If we are tracking a free range, and this is the last chunk that
7817 // we'll look at because its end crosses past _limit, we'll preemptively
7818 // flush it along with any free range we may be holding on to. Note that
7819 // this can be the case only for an already free or freshly garbage
7820 // chunk. If this block is an object, it can never straddle
7821 // over _limit. The "straddling" occurs when _limit is set at
7822 // the previous end of the space when this cycle started, and
7823 // a subsequent heap expansion caused the previously co-terminal
7824 // free block to be coalesced with the newly expanded portion,
7825 // thus rendering _limit a non-block-boundary making it dangerous
7826 // for the sweeper to step over and examine.
7827 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7828 assert(inFreeRange(), "Should only be called if currently in a free range.");
7829 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7830 assert(_sp->used_region().contains(eob - 1),
7831 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7832 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7833 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7834 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size));
7835 if (eob >= _limit) {
7836 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7837 if (CMSTraceSweeper) {
7838 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7839 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7840 "[" PTR_FORMAT "," PTR_FORMAT ")",
7841 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7842 }
7843 // Return the storage we are tracking back into the free lists.
7844 if (CMSTraceSweeper) {
7845 gclog_or_tty->print_cr("Flushing ... ");
7846 }
7847 assert(freeFinger() < eob, "Error");
7848 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7849 }
7850 }
7851
7852 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7853 assert(inFreeRange(), "Should only be called if currently in a free range.");
7854 assert(size > 0,
7855 "A zero sized chunk cannot be added to the free lists.");
7856 if (!freeRangeInFreeLists()) {
7857 if (CMSTestInFreeList) {
7858 FreeChunk* fc = (FreeChunk*) chunk;
7859 fc->set_size(size);
7860 assert(!_sp->verify_chunk_in_free_list(fc),
7861 "chunk should not be in free lists yet");
7862 }
7863 if (CMSTraceSweeper) {
7864 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7865 p2i(chunk), size);
7866 }
7867 // A new free range is going to be starting. The current
7868 // free range has not been added to the free lists yet or
7869 // was removed so add it back.
7870 // If the current free range was coalesced, then the death
7871 // of the free range was recorded. Record a birth now.
7872 if (lastFreeRangeCoalesced()) {
7873 _sp->coalBirth(size);
7874 }
7875 _sp->addChunkAndRepairOffsetTable(chunk, size,
7876 lastFreeRangeCoalesced());
7877 } else if (CMSTraceSweeper) {
7878 gclog_or_tty->print_cr("Already in free list: nothing to flush");
7879 }
7880 set_inFreeRange(false);
7881 set_freeRangeInFreeLists(false);
7882 }
7883
7884 // We take a break if we've been at this for a while,
7885 // so as to avoid monopolizing the locks involved.
7886 void SweepClosure::do_yield_work(HeapWord* addr) {
7887 // Return current free chunk being used for coalescing (if any)
7888 // to the appropriate freelist. After yielding, the next
7889 // free block encountered will start a coalescing range of
7890 // free blocks. If the next free block is adjacent to the
7891 // chunk just flushed, they will need to wait for the next
7892 // sweep to be coalesced.
7893 if (inFreeRange()) {
7894 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7895 }
7896
7897 // First give up the locks, then yield, then re-lock.
7898 // We should probably use a constructor/destructor idiom to
7899 // do this unlock/lock or modify the MutexUnlocker class to
7900 // serve our purpose. XXX
7901 assert_lock_strong(_bitMap->lock());
7902 assert_lock_strong(_freelistLock);
7903 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7904 "CMS thread should hold CMS token");
7905 _bitMap->lock()->unlock();
7906 _freelistLock->unlock();
7907 ConcurrentMarkSweepThread::desynchronize(true);
7908 _collector->stopTimer();
7909 if (PrintCMSStatistics != 0) {
7910 _collector->incrementYields();
7911 }
7912
7913 // See the comment in coordinator_yield()
7914 for (unsigned i = 0; i < CMSYieldSleepCount &&
7915 ConcurrentMarkSweepThread::should_yield() &&
7916 !CMSCollector::foregroundGCIsActive(); ++i) {
7917 os::sleep(Thread::current(), 1, false);
7918 }
7919
7920 ConcurrentMarkSweepThread::synchronize(true);
7921 _freelistLock->lock();
7922 _bitMap->lock()->lock_without_safepoint_check();
7923 _collector->startTimer();
7924 }
7925
7926 #ifndef PRODUCT
7927 // This is actually very useful in a product build if it can
7928 // be called from the debugger. Compile it into the product
7929 // as needed.
7930 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7931 return debug_cms_space->verify_chunk_in_free_list(fc);
7932 }
7933 #endif
7934
7935 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7936 if (CMSTraceSweeper) {
7937 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7938 p2i(fc), fc->size());
7939 }
7940 }
7941
7942 // CMSIsAliveClosure
7943 bool CMSIsAliveClosure::do_object_b(oop obj) {
7944 HeapWord* addr = (HeapWord*)obj;
7945 return addr != NULL &&
7946 (!_span.contains(addr) || _bit_map->isMarked(addr));
7947 }
7948
7949
7950 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7951 MemRegion span,
7952 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7953 bool cpc):
7954 _collector(collector),
7955 _span(span),
7956 _bit_map(bit_map),
7957 _mark_stack(mark_stack),
7958 _concurrent_precleaning(cpc) {
7959 assert(!_span.is_empty(), "Empty span could spell trouble");
7960 }
7961
7962
7963 // CMSKeepAliveClosure: the serial version
7964 void CMSKeepAliveClosure::do_oop(oop obj) {
7965 HeapWord* addr = (HeapWord*)obj;
7966 if (_span.contains(addr) &&
7967 !_bit_map->isMarked(addr)) {
7968 _bit_map->mark(addr);
7969 bool simulate_overflow = false;
7970 NOT_PRODUCT(
7971 if (CMSMarkStackOverflowALot &&
7972 _collector->simulate_overflow()) {
7973 // simulate a stack overflow
7974 simulate_overflow = true;
7975 }
7976 )
7977 if (simulate_overflow || !_mark_stack->push(obj)) {
7978 if (_concurrent_precleaning) {
7979 // We dirty the overflown object and let the remark
7980 // phase deal with it.
7981 assert(_collector->overflow_list_is_empty(), "Error");
7982 // In the case of object arrays, we need to dirty all of
7983 // the cards that the object spans. No locking or atomics
7984 // are needed since no one else can be mutating the mod union
7985 // table.
7986 if (obj->is_objArray()) {
7987 size_t sz = obj->size();
7988 HeapWord* end_card_addr =
7989 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
7990 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7991 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7992 _collector->_modUnionTable.mark_range(redirty_range);
7993 } else {
7994 _collector->_modUnionTable.mark(addr);
7995 }
7996 _collector->_ser_kac_preclean_ovflw++;
7997 } else {
7998 _collector->push_on_overflow_list(obj);
7999 _collector->_ser_kac_ovflw++;
8000 }
8001 }
8002 }
8003 }
8004
8005 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8006 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8007
8008 // CMSParKeepAliveClosure: a parallel version of the above.
8009 // The work queues are private to each closure (thread),
8010 // but (may be) available for stealing by other threads.
8011 void CMSParKeepAliveClosure::do_oop(oop obj) {
8012 HeapWord* addr = (HeapWord*)obj;
8013 if (_span.contains(addr) &&
8014 !_bit_map->isMarked(addr)) {
8015 // In general, during recursive tracing, several threads
8016 // may be concurrently getting here; the first one to
8017 // "tag" it, claims it.
8018 if (_bit_map->par_mark(addr)) {
8019 bool res = _work_queue->push(obj);
8020 assert(res, "Low water mark should be much less than capacity");
8021 // Do a recursive trim in the hope that this will keep
8022 // stack usage lower, but leave some oops for potential stealers
8023 trim_queue(_low_water_mark);
8024 } // Else, another thread got there first
8025 }
8026 }
8027
8028 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8029 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8030
8031 void CMSParKeepAliveClosure::trim_queue(uint max) {
8032 while (_work_queue->size() > max) {
8033 oop new_oop;
8034 if (_work_queue->pop_local(new_oop)) {
8035 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8036 assert(_bit_map->isMarked((HeapWord*)new_oop),
8037 "no white objects on this stack!");
8038 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8039 // iterate over the oops in this oop, marking and pushing
8040 // the ones in CMS heap (i.e. in _span).
8041 new_oop->oop_iterate(&_mark_and_push);
8042 }
8043 }
8044 }
8045
8046 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8047 CMSCollector* collector,
8048 MemRegion span, CMSBitMap* bit_map,
8049 OopTaskQueue* work_queue):
8050 _collector(collector),
8051 _span(span),
8052 _bit_map(bit_map),
8053 _work_queue(work_queue) { }
8054
8055 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8056 HeapWord* addr = (HeapWord*)obj;
8057 if (_span.contains(addr) &&
8058 !_bit_map->isMarked(addr)) {
8059 if (_bit_map->par_mark(addr)) {
8060 bool simulate_overflow = false;
8061 NOT_PRODUCT(
8062 if (CMSMarkStackOverflowALot &&
8063 _collector->par_simulate_overflow()) {
8064 // simulate a stack overflow
8065 simulate_overflow = true;
8066 }
8067 )
8068 if (simulate_overflow || !_work_queue->push(obj)) {
8069 _collector->par_push_on_overflow_list(obj);
8070 _collector->_par_kac_ovflw++;
8071 }
8072 } // Else another thread got there already
8073 }
8074 }
8075
8076 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8077 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8078
8079 //////////////////////////////////////////////////////////////////
8080 // CMSExpansionCause /////////////////////////////
8081 //////////////////////////////////////////////////////////////////
8082 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8083 switch (cause) {
8084 case _no_expansion:
8085 return "No expansion";
8086 case _satisfy_free_ratio:
8087 return "Free ratio";
8088 case _satisfy_promotion:
8089 return "Satisfy promotion";
8090 case _satisfy_allocation:
8091 return "allocation";
8092 case _allocate_par_lab:
8093 return "Par LAB";
8094 case _allocate_par_spooling_space:
8095 return "Par Spooling Space";
8096 case _adaptive_size_policy:
8097 return "Ergonomics";
8098 default:
8099 return "unknown";
8100 }
8101 }
8102
8103 void CMSDrainMarkingStackClosure::do_void() {
8104 // the max number to take from overflow list at a time
8105 const size_t num = _mark_stack->capacity()/4;
8106 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8107 "Overflow list should be NULL during concurrent phases");
8108 while (!_mark_stack->isEmpty() ||
8109 // if stack is empty, check the overflow list
8110 _collector->take_from_overflow_list(num, _mark_stack)) {
8111 oop obj = _mark_stack->pop();
8112 HeapWord* addr = (HeapWord*)obj;
8113 assert(_span.contains(addr), "Should be within span");
8114 assert(_bit_map->isMarked(addr), "Should be marked");
8115 assert(obj->is_oop(), "Should be an oop");
8116 obj->oop_iterate(_keep_alive);
8117 }
8118 }
8119
8120 void CMSParDrainMarkingStackClosure::do_void() {
8121 // drain queue
8122 trim_queue(0);
8123 }
8124
8125 // Trim our work_queue so its length is below max at return
8126 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8127 while (_work_queue->size() > max) {
8128 oop new_oop;
8129 if (_work_queue->pop_local(new_oop)) {
8130 assert(new_oop->is_oop(), "Expected an oop");
8131 assert(_bit_map->isMarked((HeapWord*)new_oop),
8132 "no white objects on this stack!");
8133 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8134 // iterate over the oops in this oop, marking and pushing
8135 // the ones in CMS heap (i.e. in _span).
8136 new_oop->oop_iterate(&_mark_and_push);
8137 }
8138 }
8139 }
8140
8141 ////////////////////////////////////////////////////////////////////
8142 // Support for Marking Stack Overflow list handling and related code
8143 ////////////////////////////////////////////////////////////////////
8144 // Much of the following code is similar in shape and spirit to the
8145 // code used in ParNewGC. We should try and share that code
8146 // as much as possible in the future.
8147
8148 #ifndef PRODUCT
8149 // Debugging support for CMSStackOverflowALot
8150
8151 // It's OK to call this multi-threaded; the worst thing
8152 // that can happen is that we'll get a bunch of closely
8153 // spaced simulated overflows, but that's OK, in fact
8154 // probably good as it would exercise the overflow code
8155 // under contention.
8156 bool CMSCollector::simulate_overflow() {
8157 if (_overflow_counter-- <= 0) { // just being defensive
8158 _overflow_counter = CMSMarkStackOverflowInterval;
8159 return true;
8160 } else {
8161 return false;
8162 }
8163 }
8164
8165 bool CMSCollector::par_simulate_overflow() {
8166 return simulate_overflow();
8167 }
8168 #endif
8169
8170 // Single-threaded
8171 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8172 assert(stack->isEmpty(), "Expected precondition");
8173 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8174 size_t i = num;
8175 oop cur = _overflow_list;
8176 const markOop proto = markOopDesc::prototype();
8177 NOT_PRODUCT(ssize_t n = 0;)
8178 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8179 next = oop(cur->mark());
8180 cur->set_mark(proto); // until proven otherwise
8181 assert(cur->is_oop(), "Should be an oop");
8182 bool res = stack->push(cur);
8183 assert(res, "Bit off more than can chew?");
8184 NOT_PRODUCT(n++;)
8185 }
8186 _overflow_list = cur;
8187 #ifndef PRODUCT
8188 assert(_num_par_pushes >= n, "Too many pops?");
8189 _num_par_pushes -=n;
8190 #endif
8191 return !stack->isEmpty();
8192 }
8193
8194 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8195 // (MT-safe) Get a prefix of at most "num" from the list.
8196 // The overflow list is chained through the mark word of
8197 // each object in the list. We fetch the entire list,
8198 // break off a prefix of the right size and return the
8199 // remainder. If other threads try to take objects from
8200 // the overflow list at that time, they will wait for
8201 // some time to see if data becomes available. If (and
8202 // only if) another thread places one or more object(s)
8203 // on the global list before we have returned the suffix
8204 // to the global list, we will walk down our local list
8205 // to find its end and append the global list to
8206 // our suffix before returning it. This suffix walk can
8207 // prove to be expensive (quadratic in the amount of traffic)
8208 // when there are many objects in the overflow list and
8209 // there is much producer-consumer contention on the list.
8210 // *NOTE*: The overflow list manipulation code here and
8211 // in ParNewGeneration:: are very similar in shape,
8212 // except that in the ParNew case we use the old (from/eden)
8213 // copy of the object to thread the list via its klass word.
8214 // Because of the common code, if you make any changes in
8215 // the code below, please check the ParNew version to see if
8216 // similar changes might be needed.
8217 // CR 6797058 has been filed to consolidate the common code.
8218 bool CMSCollector::par_take_from_overflow_list(size_t num,
8219 OopTaskQueue* work_q,
8220 int no_of_gc_threads) {
8221 assert(work_q->size() == 0, "First empty local work queue");
8222 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8223 if (_overflow_list == NULL) {
8224 return false;
8225 }
8226 // Grab the entire list; we'll put back a suffix
8227 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8228 Thread* tid = Thread::current();
8229 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8230 // set to ParallelGCThreads.
8231 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8232 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8233 // If the list is busy, we spin for a short while,
8234 // sleeping between attempts to get the list.
8235 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8236 os::sleep(tid, sleep_time_millis, false);
8237 if (_overflow_list == NULL) {
8238 // Nothing left to take
8239 return false;
8240 } else if (_overflow_list != BUSY) {
8241 // Try and grab the prefix
8242 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8243 }
8244 }
8245 // If the list was found to be empty, or we spun long
8246 // enough, we give up and return empty-handed. If we leave
8247 // the list in the BUSY state below, it must be the case that
8248 // some other thread holds the overflow list and will set it
8249 // to a non-BUSY state in the future.
8250 if (prefix == NULL || prefix == BUSY) {
8251 // Nothing to take or waited long enough
8252 if (prefix == NULL) {
8253 // Write back the NULL in case we overwrote it with BUSY above
8254 // and it is still the same value.
8255 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8256 }
8257 return false;
8258 }
8259 assert(prefix != NULL && prefix != BUSY, "Error");
8260 size_t i = num;
8261 oop cur = prefix;
8262 // Walk down the first "num" objects, unless we reach the end.
8263 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8264 if (cur->mark() == NULL) {
8265 // We have "num" or fewer elements in the list, so there
8266 // is nothing to return to the global list.
8267 // Write back the NULL in lieu of the BUSY we wrote
8268 // above, if it is still the same value.
8269 if (_overflow_list == BUSY) {
8270 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8271 }
8272 } else {
8273 // Chop off the suffix and return it to the global list.
8274 assert(cur->mark() != BUSY, "Error");
8275 oop suffix_head = cur->mark(); // suffix will be put back on global list
8276 cur->set_mark(NULL); // break off suffix
8277 // It's possible that the list is still in the empty(busy) state
8278 // we left it in a short while ago; in that case we may be
8279 // able to place back the suffix without incurring the cost
8280 // of a walk down the list.
8281 oop observed_overflow_list = _overflow_list;
8282 oop cur_overflow_list = observed_overflow_list;
8283 bool attached = false;
8284 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8285 observed_overflow_list =
8286 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8287 if (cur_overflow_list == observed_overflow_list) {
8288 attached = true;
8289 break;
8290 } else cur_overflow_list = observed_overflow_list;
8291 }
8292 if (!attached) {
8293 // Too bad, someone else sneaked in (at least) an element; we'll need
8294 // to do a splice. Find tail of suffix so we can prepend suffix to global
8295 // list.
8296 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8297 oop suffix_tail = cur;
8298 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8299 "Tautology");
8300 observed_overflow_list = _overflow_list;
8301 do {
8302 cur_overflow_list = observed_overflow_list;
8303 if (cur_overflow_list != BUSY) {
8304 // Do the splice ...
8305 suffix_tail->set_mark(markOop(cur_overflow_list));
8306 } else { // cur_overflow_list == BUSY
8307 suffix_tail->set_mark(NULL);
8308 }
8309 // ... and try to place spliced list back on overflow_list ...
8310 observed_overflow_list =
8311 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8312 } while (cur_overflow_list != observed_overflow_list);
8313 // ... until we have succeeded in doing so.
8314 }
8315 }
8316
8317 // Push the prefix elements on work_q
8318 assert(prefix != NULL, "control point invariant");
8319 const markOop proto = markOopDesc::prototype();
8320 oop next;
8321 NOT_PRODUCT(ssize_t n = 0;)
8322 for (cur = prefix; cur != NULL; cur = next) {
8323 next = oop(cur->mark());
8324 cur->set_mark(proto); // until proven otherwise
8325 assert(cur->is_oop(), "Should be an oop");
8326 bool res = work_q->push(cur);
8327 assert(res, "Bit off more than we can chew?");
8328 NOT_PRODUCT(n++;)
8329 }
8330 #ifndef PRODUCT
8331 assert(_num_par_pushes >= n, "Too many pops?");
8332 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8333 #endif
8334 return true;
8335 }
8336
8337 // Single-threaded
8338 void CMSCollector::push_on_overflow_list(oop p) {
8339 NOT_PRODUCT(_num_par_pushes++;)
8340 assert(p->is_oop(), "Not an oop");
8341 preserve_mark_if_necessary(p);
8342 p->set_mark((markOop)_overflow_list);
8343 _overflow_list = p;
8344 }
8345
8346 // Multi-threaded; use CAS to prepend to overflow list
8347 void CMSCollector::par_push_on_overflow_list(oop p) {
8348 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8349 assert(p->is_oop(), "Not an oop");
8350 par_preserve_mark_if_necessary(p);
8351 oop observed_overflow_list = _overflow_list;
8352 oop cur_overflow_list;
8353 do {
8354 cur_overflow_list = observed_overflow_list;
8355 if (cur_overflow_list != BUSY) {
8356 p->set_mark(markOop(cur_overflow_list));
8357 } else {
8358 p->set_mark(NULL);
8359 }
8360 observed_overflow_list =
8361 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8362 } while (cur_overflow_list != observed_overflow_list);
8363 }
8364 #undef BUSY
8365
8366 // Single threaded
8367 // General Note on GrowableArray: pushes may silently fail
8368 // because we are (temporarily) out of C-heap for expanding
8369 // the stack. The problem is quite ubiquitous and affects
8370 // a lot of code in the JVM. The prudent thing for GrowableArray
8371 // to do (for now) is to exit with an error. However, that may
8372 // be too draconian in some cases because the caller may be
8373 // able to recover without much harm. For such cases, we
8374 // should probably introduce a "soft_push" method which returns
8375 // an indication of success or failure with the assumption that
8376 // the caller may be able to recover from a failure; code in
8377 // the VM can then be changed, incrementally, to deal with such
8378 // failures where possible, thus, incrementally hardening the VM
8379 // in such low resource situations.
8380 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8381 _preserved_oop_stack.push(p);
8382 _preserved_mark_stack.push(m);
8383 assert(m == p->mark(), "Mark word changed");
8384 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8385 "bijection");
8386 }
8387
8388 // Single threaded
8389 void CMSCollector::preserve_mark_if_necessary(oop p) {
8390 markOop m = p->mark();
8391 if (m->must_be_preserved(p)) {
8392 preserve_mark_work(p, m);
8393 }
8394 }
8395
8396 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8397 markOop m = p->mark();
8398 if (m->must_be_preserved(p)) {
8399 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8400 // Even though we read the mark word without holding
8401 // the lock, we are assured that it will not change
8402 // because we "own" this oop, so no other thread can
8403 // be trying to push it on the overflow list; see
8404 // the assertion in preserve_mark_work() that checks
8405 // that m == p->mark().
8406 preserve_mark_work(p, m);
8407 }
8408 }
8409
8410 // We should be able to do this multi-threaded,
8411 // a chunk of stack being a task (this is
8412 // correct because each oop only ever appears
8413 // once in the overflow list. However, it's
8414 // not very easy to completely overlap this with
8415 // other operations, so will generally not be done
8416 // until all work's been completed. Because we
8417 // expect the preserved oop stack (set) to be small,
8418 // it's probably fine to do this single-threaded.
8419 // We can explore cleverer concurrent/overlapped/parallel
8420 // processing of preserved marks if we feel the
8421 // need for this in the future. Stack overflow should
8422 // be so rare in practice and, when it happens, its
8423 // effect on performance so great that this will
8424 // likely just be in the noise anyway.
8425 void CMSCollector::restore_preserved_marks_if_any() {
8426 assert(SafepointSynchronize::is_at_safepoint(),
8427 "world should be stopped");
8428 assert(Thread::current()->is_ConcurrentGC_thread() ||
8429 Thread::current()->is_VM_thread(),
8430 "should be single-threaded");
8431 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8432 "bijection");
8433
8434 while (!_preserved_oop_stack.is_empty()) {
8435 oop p = _preserved_oop_stack.pop();
8436 assert(p->is_oop(), "Should be an oop");
8437 assert(_span.contains(p), "oop should be in _span");
8438 assert(p->mark() == markOopDesc::prototype(),
8439 "Set when taken from overflow list");
8440 markOop m = _preserved_mark_stack.pop();
8441 p->set_mark(m);
8442 }
8443 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8444 "stacks were cleared above");
8445 }
8446
8447 #ifndef PRODUCT
8448 bool CMSCollector::no_preserved_marks() const {
8449 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8450 }
8451 #endif
8452
8453 // Transfer some number of overflown objects to usual marking
8454 // stack. Return true if some objects were transferred.
8455 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8456 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8457 (size_t)ParGCDesiredObjsFromOverflowList);
8458
8459 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8460 assert(_collector->overflow_list_is_empty() || res,
8461 "If list is not empty, we should have taken something");
8462 assert(!res || !_mark_stack->isEmpty(),
8463 "If we took something, it should now be on our stack");
8464 return res;
8465 }
8466
8467 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8468 size_t res = _sp->block_size_no_stall(addr, _collector);
8469 if (_sp->block_is_obj(addr)) {
8470 if (_live_bit_map->isMarked(addr)) {
8471 // It can't have been dead in a previous cycle
8472 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8473 } else {
8474 _dead_bit_map->mark(addr); // mark the dead object
8475 }
8476 }
8477 // Could be 0, if the block size could not be computed without stalling.
8478 return res;
8479 }
8480
8481 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8482
8483 switch (phase) {
8484 case CMSCollector::InitialMarking:
8485 initialize(true /* fullGC */ ,
8486 cause /* cause of the GC */,
8487 true /* recordGCBeginTime */,
8488 true /* recordPreGCUsage */,
8489 false /* recordPeakUsage */,
8490 false /* recordPostGCusage */,
8491 true /* recordAccumulatedGCTime */,
8492 false /* recordGCEndTime */,
8493 false /* countCollection */ );
8494 break;
8495
8496 case CMSCollector::FinalMarking:
8497 initialize(true /* fullGC */ ,
8498 cause /* cause of the GC */,
8499 false /* recordGCBeginTime */,
8500 false /* recordPreGCUsage */,
8501 false /* recordPeakUsage */,
8502 false /* recordPostGCusage */,
8503 true /* recordAccumulatedGCTime */,
8504 false /* recordGCEndTime */,
8505 false /* countCollection */ );
8506 break;
8507
8508 case CMSCollector::Sweeping:
8509 initialize(true /* fullGC */ ,
8510 cause /* cause of the GC */,
8511 false /* recordGCBeginTime */,
8512 false /* recordPreGCUsage */,
8513 true /* recordPeakUsage */,
8514 true /* recordPostGCusage */,
8515 false /* recordAccumulatedGCTime */,
8516 true /* recordGCEndTime */,
8517 true /* countCollection */ );
8518 break;
8519
8520 default:
8521 ShouldNotReachHere();
8522 }
8523 }