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_implementation/shared/adaptiveSizePolicy.hpp"
31 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
32 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
33 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
34 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
36 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
37 #include "gc_implementation/parNew/parNewGeneration.hpp"
38 #include "gc_implementation/shared/collectorCounters.hpp"
39 #include "gc_implementation/shared/gcTimer.hpp"
40 #include "gc_implementation/shared/gcTrace.hpp"
41 #include "gc_implementation/shared/gcTraceTime.hpp"
42 #include "gc_implementation/shared/isGCActiveMark.hpp"
43 #include "gc_interface/collectedHeap.inline.hpp"
44 #include "memory/allocation.hpp"
45 #include "memory/cardGeneration.inline.hpp"
46 #include "memory/cardTableRS.hpp"
47 #include "memory/collectorPolicy.hpp"
48 #include "memory/gcLocker.inline.hpp"
49 #include "memory/genCollectedHeap.hpp"
50 #include "memory/genMarkSweep.hpp"
51 #include "memory/genOopClosures.inline.hpp"
52 #include "memory/iterator.inline.hpp"
53 #include "memory/padded.hpp"
54 #include "memory/referencePolicy.hpp"
55 #include "memory/resourceArea.hpp"
56 #include "memory/tenuredGeneration.hpp"
57 #include "oops/oop.inline.hpp"
58 #include "prims/jvmtiExport.hpp"
59 #include "runtime/atomic.inline.hpp"
60 #include "runtime/globals_extension.hpp"
61 #include "runtime/handles.inline.hpp"
62 #include "runtime/java.hpp"
63 #include "runtime/orderAccess.inline.hpp"
64 #include "runtime/vmThread.hpp"
65 #include "services/memoryService.hpp"
66 #include "services/runtimeService.hpp"
67
68 // statics
69 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
70 bool CMSCollector::_full_gc_requested = false;
71 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
72
73 //////////////////////////////////////////////////////////////////
74 // In support of CMS/VM thread synchronization
75 //////////////////////////////////////////////////////////////////
76 // We split use of the CGC_lock into 2 "levels".
77 // The low-level locking is of the usual CGC_lock monitor. We introduce
78 // a higher level "token" (hereafter "CMS token") built on top of the
79 // low level monitor (hereafter "CGC lock").
80 // The token-passing protocol gives priority to the VM thread. The
81 // CMS-lock doesn't provide any fairness guarantees, but clients
82 // should ensure that it is only held for very short, bounded
83 // durations.
84 //
85 // When either of the CMS thread or the VM thread is involved in
86 // collection operations during which it does not want the other
87 // thread to interfere, it obtains the CMS token.
88 //
89 // If either thread tries to get the token while the other has
90 // it, that thread waits. However, if the VM thread and CMS thread
91 // both want the token, then the VM thread gets priority while the
92 // CMS thread waits. This ensures, for instance, that the "concurrent"
93 // phases of the CMS thread's work do not block out the VM thread
94 // for long periods of time as the CMS thread continues to hog
95 // the token. (See bug 4616232).
96 //
97 // The baton-passing functions are, however, controlled by the
98 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
99 // and here the low-level CMS lock, not the high level token,
100 // ensures mutual exclusion.
101 //
102 // Two important conditions that we have to satisfy:
103 // 1. if a thread does a low-level wait on the CMS lock, then it
104 // relinquishes the CMS token if it were holding that token
105 // when it acquired the low-level CMS lock.
106 // 2. any low-level notifications on the low-level lock
107 // should only be sent when a thread has relinquished the token.
108 //
109 // In the absence of either property, we'd have potential deadlock.
110 //
111 // We protect each of the CMS (concurrent and sequential) phases
112 // with the CMS _token_, not the CMS _lock_.
113 //
114 // The only code protected by CMS lock is the token acquisition code
115 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
116 // baton-passing code.
117 //
118 // Unfortunately, i couldn't come up with a good abstraction to factor and
119 // hide the naked CGC_lock manipulation in the baton-passing code
120 // further below. That's something we should try to do. Also, the proof
121 // of correctness of this 2-level locking scheme is far from obvious,
122 // and potentially quite slippery. We have an uneasy suspicion, for instance,
123 // that there may be a theoretical possibility of delay/starvation in the
124 // low-level lock/wait/notify scheme used for the baton-passing because of
125 // potential interference with the priority scheme embodied in the
126 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
127 // invocation further below and marked with "XXX 20011219YSR".
128 // Indeed, as we note elsewhere, this may become yet more slippery
129 // in the presence of multiple CMS and/or multiple VM threads. XXX
130
131 class CMSTokenSync: public StackObj {
132 private:
133 bool _is_cms_thread;
134 public:
135 CMSTokenSync(bool is_cms_thread):
136 _is_cms_thread(is_cms_thread) {
137 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
138 "Incorrect argument to constructor");
139 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
140 }
141
142 ~CMSTokenSync() {
143 assert(_is_cms_thread ?
144 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
145 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
146 "Incorrect state");
147 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
148 }
149 };
150
151 // Convenience class that does a CMSTokenSync, and then acquires
152 // upto three locks.
153 class CMSTokenSyncWithLocks: public CMSTokenSync {
154 private:
155 // Note: locks are acquired in textual declaration order
156 // and released in the opposite order
157 MutexLockerEx _locker1, _locker2, _locker3;
158 public:
159 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
160 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
161 CMSTokenSync(is_cms_thread),
162 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
163 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
164 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
165 { }
166 };
167
168
169 //////////////////////////////////////////////////////////////////
170 // Concurrent Mark-Sweep Generation /////////////////////////////
171 //////////////////////////////////////////////////////////////////
172
173 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
174
175 // This struct contains per-thread things necessary to support parallel
176 // young-gen collection.
177 class CMSParGCThreadState: public CHeapObj<mtGC> {
178 public:
179 CFLS_LAB lab;
180 PromotionInfo promo;
181
182 // Constructor.
183 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
184 promo.setSpace(cfls);
185 }
186 };
187
188 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
189 ReservedSpace rs, size_t initial_byte_size, int level,
190 CardTableRS* ct, bool use_adaptive_freelists,
191 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
192 CardGeneration(rs, initial_byte_size, level, ct),
193 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
194 _did_compact(false)
195 {
196 HeapWord* bottom = (HeapWord*) _virtual_space.low();
197 HeapWord* end = (HeapWord*) _virtual_space.high();
198
199 _direct_allocated_words = 0;
200 NOT_PRODUCT(
201 _numObjectsPromoted = 0;
202 _numWordsPromoted = 0;
203 _numObjectsAllocated = 0;
204 _numWordsAllocated = 0;
205 )
206
207 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
208 use_adaptive_freelists,
209 dictionaryChoice);
210 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
211 _cmsSpace->_gen = this;
212
213 _gc_stats = new CMSGCStats();
214
215 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
216 // offsets match. The ability to tell free chunks from objects
217 // depends on this property.
218 debug_only(
219 FreeChunk* junk = NULL;
220 assert(UseCompressedClassPointers ||
221 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
222 "Offset of FreeChunk::_prev within FreeChunk must match"
223 " that of OopDesc::_klass within OopDesc");
224 )
225 if (CollectedHeap::use_parallel_gc_threads()) {
226 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
227 _par_gc_thread_states =
228 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
229 for (uint i = 0; i < ParallelGCThreads; i++) {
230 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
231 }
232 } else {
233 _par_gc_thread_states = NULL;
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 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
302 "Wrong type of heap");
303 return gch->gen_policy()->size_policy();
304 }
305
306 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
307
308 const char* gen_name = "old";
309 GenCollectorPolicy* gcp = (GenCollectorPolicy*) GenCollectedHeap::heap()->collector_policy();
310
311 // Generation Counters - generation 1, 1 subspace
312 _gen_counters = new GenerationCounters(gen_name, 1, 1,
313 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
314
315 _space_counters = new GSpaceCounters(gen_name, 0,
316 _virtual_space.reserved_size(),
317 this, _gen_counters);
318 }
319
320 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
321 _cms_gen(cms_gen)
322 {
323 assert(alpha <= 100, "bad value");
324 _saved_alpha = alpha;
325
326 // Initialize the alphas to the bootstrap value of 100.
327 _gc0_alpha = _cms_alpha = 100;
328
329 _cms_begin_time.update();
330 _cms_end_time.update();
331
332 _gc0_duration = 0.0;
333 _gc0_period = 0.0;
334 _gc0_promoted = 0;
335
336 _cms_duration = 0.0;
337 _cms_period = 0.0;
338 _cms_allocated = 0;
339
340 _cms_used_at_gc0_begin = 0;
341 _cms_used_at_gc0_end = 0;
342 _allow_duty_cycle_reduction = false;
343 _valid_bits = 0;
344 }
345
346 double CMSStats::cms_free_adjustment_factor(size_t free) const {
347 // TBD: CR 6909490
348 return 1.0;
349 }
350
351 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
352 }
353
354 // If promotion failure handling is on use
355 // the padded average size of the promotion for each
356 // young generation collection.
357 double CMSStats::time_until_cms_gen_full() const {
358 size_t cms_free = _cms_gen->cmsSpace()->free();
359 GenCollectedHeap* gch = GenCollectedHeap::heap();
360 size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
361 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
362 if (cms_free > expected_promotion) {
363 // Start a cms collection if there isn't enough space to promote
364 // for the next minor collection. Use the padded average as
365 // a safety factor.
366 cms_free -= expected_promotion;
367
368 // Adjust by the safety factor.
369 double cms_free_dbl = (double)cms_free;
370 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
371 // Apply a further correction factor which tries to adjust
372 // for recent occurance of concurrent mode failures.
373 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
374 cms_free_dbl = cms_free_dbl * cms_adjustment;
375
376 if (PrintGCDetails && Verbose) {
377 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
378 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
379 cms_free, expected_promotion);
380 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
381 cms_free_dbl, cms_consumption_rate() + 1.0);
382 }
383 // Add 1 in case the consumption rate goes to zero.
384 return cms_free_dbl / (cms_consumption_rate() + 1.0);
385 }
386 return 0.0;
387 }
388
389 // Compare the duration of the cms collection to the
390 // time remaining before the cms generation is empty.
391 // Note that the time from the start of the cms collection
392 // to the start of the cms sweep (less than the total
393 // duration of the cms collection) can be used. This
394 // has been tried and some applications experienced
395 // promotion failures early in execution. This was
396 // possibly because the averages were not accurate
397 // enough at the beginning.
398 double CMSStats::time_until_cms_start() const {
399 // We add "gc0_period" to the "work" calculation
400 // below because this query is done (mostly) at the
401 // end of a scavenge, so we need to conservatively
402 // account for that much possible delay
403 // in the query so as to avoid concurrent mode failures
404 // due to starting the collection just a wee bit too
405 // late.
406 double work = cms_duration() + gc0_period();
407 double deadline = time_until_cms_gen_full();
408 // If a concurrent mode failure occurred recently, we want to be
409 // more conservative and halve our expected time_until_cms_gen_full()
410 if (work > deadline) {
411 if (Verbose && PrintGCDetails) {
412 gclog_or_tty->print(
413 " CMSCollector: collect because of anticipated promotion "
414 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
415 gc0_period(), time_until_cms_gen_full());
416 }
417 return 0.0;
418 }
419 return work - deadline;
420 }
421
422 #ifndef PRODUCT
423 void CMSStats::print_on(outputStream *st) const {
424 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
425 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
426 gc0_duration(), gc0_period(), gc0_promoted());
427 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
428 cms_duration(), cms_period(), cms_allocated());
429 st->print(",cms_since_beg=%g,cms_since_end=%g",
430 cms_time_since_begin(), cms_time_since_end());
431 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
432 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
433
434 if (valid()) {
435 st->print(",promo_rate=%g,cms_alloc_rate=%g",
436 promotion_rate(), cms_allocation_rate());
437 st->print(",cms_consumption_rate=%g,time_until_full=%g",
438 cms_consumption_rate(), time_until_cms_gen_full());
439 }
440 st->print(" ");
441 }
442 #endif // #ifndef PRODUCT
443
444 CMSCollector::CollectorState CMSCollector::_collectorState =
445 CMSCollector::Idling;
446 bool CMSCollector::_foregroundGCIsActive = false;
447 bool CMSCollector::_foregroundGCShouldWait = false;
448
449 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
450 CardTableRS* ct,
451 ConcurrentMarkSweepPolicy* cp):
452 _cmsGen(cmsGen),
453 _ct(ct),
454 _ref_processor(NULL), // will be set later
455 _conc_workers(NULL), // may be set later
456 _abort_preclean(false),
457 _start_sampling(false),
458 _between_prologue_and_epilogue(false),
459 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
460 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
461 -1 /* lock-free */, "No_lock" /* dummy */),
462 _modUnionClosure(&_modUnionTable),
463 _modUnionClosurePar(&_modUnionTable),
464 // Adjust my span to cover old (cms) gen
465 _span(cmsGen->reserved()),
466 // Construct the is_alive_closure with _span & markBitMap
467 _is_alive_closure(_span, &_markBitMap),
468 _restart_addr(NULL),
469 _overflow_list(NULL),
470 _stats(cmsGen),
471 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
472 //verify that this lock should be acquired with safepoint check.
473 Monitor::_safepoint_check_sometimes)),
474 _eden_chunk_array(NULL), // may be set in ctor body
475 _eden_chunk_capacity(0), // -- ditto --
476 _eden_chunk_index(0), // -- ditto --
477 _survivor_plab_array(NULL), // -- ditto --
478 _survivor_chunk_array(NULL), // -- ditto --
479 _survivor_chunk_capacity(0), // -- ditto --
480 _survivor_chunk_index(0), // -- ditto --
481 _ser_pmc_preclean_ovflw(0),
482 _ser_kac_preclean_ovflw(0),
483 _ser_pmc_remark_ovflw(0),
484 _par_pmc_remark_ovflw(0),
485 _ser_kac_ovflw(0),
486 _par_kac_ovflw(0),
487 #ifndef PRODUCT
488 _num_par_pushes(0),
489 #endif
490 _collection_count_start(0),
491 _verifying(false),
492 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
493 _completed_initialization(false),
494 _collector_policy(cp),
495 _should_unload_classes(CMSClassUnloadingEnabled),
496 _concurrent_cycles_since_last_unload(0),
497 _roots_scanning_options(GenCollectedHeap::SO_None),
498 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
499 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
500 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
501 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
502 _cms_start_registered(false)
503 {
504 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
505 ExplicitGCInvokesConcurrent = true;
506 }
507 // Now expand the span and allocate the collection support structures
508 // (MUT, marking bit map etc.) to cover both generations subject to
509 // collection.
510
511 // For use by dirty card to oop closures.
512 _cmsGen->cmsSpace()->set_collector(this);
513
514 // Allocate MUT and marking bit map
515 {
516 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
517 if (!_markBitMap.allocate(_span)) {
518 warning("Failed to allocate CMS Bit Map");
519 return;
520 }
521 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
522 }
523 {
524 _modUnionTable.allocate(_span);
525 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
526 }
527
528 if (!_markStack.allocate(MarkStackSize)) {
529 warning("Failed to allocate CMS Marking Stack");
530 return;
531 }
532
533 // Support for multi-threaded concurrent phases
534 if (CMSConcurrentMTEnabled) {
535 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
536 // just for now
537 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
538 }
539 if (ConcGCThreads > 1) {
540 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
541 ConcGCThreads, true);
542 if (_conc_workers == NULL) {
543 warning("GC/CMS: _conc_workers allocation failure: "
544 "forcing -CMSConcurrentMTEnabled");
545 CMSConcurrentMTEnabled = false;
546 } else {
547 _conc_workers->initialize_workers();
548 }
549 } else {
550 CMSConcurrentMTEnabled = false;
551 }
552 }
553 if (!CMSConcurrentMTEnabled) {
554 ConcGCThreads = 0;
555 } else {
556 // Turn off CMSCleanOnEnter optimization temporarily for
557 // the MT case where it's not fixed yet; see 6178663.
558 CMSCleanOnEnter = false;
559 }
560 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
561 "Inconsistency");
562
563 // Parallel task queues; these are shared for the
564 // concurrent and stop-world phases of CMS, but
565 // are not shared with parallel scavenge (ParNew).
566 {
567 uint i;
568 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
569
570 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
571 || ParallelRefProcEnabled)
572 && num_queues > 0) {
573 _task_queues = new OopTaskQueueSet(num_queues);
574 if (_task_queues == NULL) {
575 warning("task_queues allocation failure.");
576 return;
577 }
578 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
579 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
580 for (i = 0; i < num_queues; i++) {
581 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
582 if (q == NULL) {
583 warning("work_queue allocation failure.");
584 return;
585 }
586 _task_queues->register_queue(i, q);
587 }
588 for (i = 0; i < num_queues; i++) {
589 _task_queues->queue(i)->initialize();
590 _hash_seed[i] = 17; // copied from ParNew
591 }
592 }
593 }
594
595 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
596
597 // Clip CMSBootstrapOccupancy between 0 and 100.
598 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
599
600 // Now tell CMS generations the identity of their collector
601 ConcurrentMarkSweepGeneration::set_collector(this);
602
603 // Create & start a CMS thread for this CMS collector
604 _cmsThread = ConcurrentMarkSweepThread::start(this);
605 assert(cmsThread() != NULL, "CMS Thread should have been created");
606 assert(cmsThread()->collector() == this,
607 "CMS Thread should refer to this gen");
608 assert(CGC_lock != NULL, "Where's the CGC_lock?");
609
610 // Support for parallelizing young gen rescan
611 GenCollectedHeap* gch = GenCollectedHeap::heap();
612 assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
613 _young_gen = (ParNewGeneration*)gch->young_gen();
614 if (gch->supports_inline_contig_alloc()) {
615 _top_addr = gch->top_addr();
616 _end_addr = gch->end_addr();
617 assert(_young_gen != NULL, "no _young_gen");
618 _eden_chunk_index = 0;
619 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
620 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
621 }
622
623 // Support for parallelizing survivor space rescan
624 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
625 const size_t max_plab_samples =
626 ((DefNewGeneration*)_young_gen)->max_survivor_size() / plab_sample_minimum_size();
627
628 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
629 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
630 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
631 _survivor_chunk_capacity = 2*max_plab_samples;
632 for (uint i = 0; i < ParallelGCThreads; i++) {
633 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
634 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
635 assert(cur->end() == 0, "Should be 0");
636 assert(cur->array() == vec, "Should be vec");
637 assert(cur->capacity() == max_plab_samples, "Error");
638 }
639 }
640
641 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
642 _gc_counters = new CollectorCounters("CMS", 1);
643 _completed_initialization = true;
644 _inter_sweep_timer.start(); // start of time
645 }
646
647 size_t CMSCollector::plab_sample_minimum_size() {
648 // The default value of MinTLABSize is 2k, but there is
649 // no way to get the default value if the flag has been overridden.
650 return MAX2(ThreadLocalAllocBuffer::min_size() * HeapWordSize, 2 * K);
651 }
652
653 const char* ConcurrentMarkSweepGeneration::name() const {
654 return "concurrent mark-sweep generation";
655 }
656 void ConcurrentMarkSweepGeneration::update_counters() {
657 if (UsePerfData) {
658 _space_counters->update_all();
659 _gen_counters->update_all();
660 }
661 }
662
663 // this is an optimized version of update_counters(). it takes the
664 // used value as a parameter rather than computing it.
665 //
666 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
667 if (UsePerfData) {
668 _space_counters->update_used(used);
669 _space_counters->update_capacity();
670 _gen_counters->update_all();
671 }
672 }
673
674 void ConcurrentMarkSweepGeneration::print() const {
675 Generation::print();
676 cmsSpace()->print();
677 }
678
679 #ifndef PRODUCT
680 void ConcurrentMarkSweepGeneration::print_statistics() {
681 cmsSpace()->printFLCensus(0);
682 }
683 #endif
684
685 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
686 GenCollectedHeap* gch = GenCollectedHeap::heap();
687 if (PrintGCDetails) {
688 if (Verbose) {
689 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
690 level(), short_name(), s, used(), capacity());
691 } else {
692 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
693 level(), short_name(), s, used() / K, capacity() / K);
694 }
695 }
696 if (Verbose) {
697 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
698 gch->used(), gch->capacity());
699 } else {
700 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
701 gch->used() / K, gch->capacity() / K);
702 }
703 }
704
705 size_t
706 ConcurrentMarkSweepGeneration::contiguous_available() const {
707 // dld proposes an improvement in precision here. If the committed
708 // part of the space ends in a free block we should add that to
709 // uncommitted size in the calculation below. Will make this
710 // change later, staying with the approximation below for the
711 // time being. -- ysr.
712 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
713 }
714
715 size_t
716 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
717 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
718 }
719
720 size_t ConcurrentMarkSweepGeneration::max_available() const {
721 return free() + _virtual_space.uncommitted_size();
722 }
723
724 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
725 size_t available = max_available();
726 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
727 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
728 if (Verbose && PrintGCDetails) {
729 gclog_or_tty->print_cr(
730 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
731 "max_promo("SIZE_FORMAT")",
732 res? "":" not", available, res? ">=":"<",
733 av_promo, max_promotion_in_bytes);
734 }
735 return res;
736 }
737
738 // At a promotion failure dump information on block layout in heap
739 // (cms old generation).
740 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
741 if (CMSDumpAtPromotionFailure) {
742 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
743 }
744 }
745
746 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
747 // Clear the promotion information. These pointers can be adjusted
748 // along with all the other pointers into the heap but
749 // compaction is expected to be a rare event with
750 // a heap using cms so don't do it without seeing the need.
751 for (uint i = 0; i < ParallelGCThreads; i++) {
752 _par_gc_thread_states[i]->promo.reset();
753 }
754 }
755
756 void ConcurrentMarkSweepGeneration::compute_new_size() {
757 assert_locked_or_safepoint(Heap_lock);
758
759 // If incremental collection failed, we just want to expand
760 // to the limit.
761 if (incremental_collection_failed()) {
762 clear_incremental_collection_failed();
763 grow_to_reserved();
764 return;
765 }
766
767 // The heap has been compacted but not reset yet.
768 // Any metric such as free() or used() will be incorrect.
769
770 CardGeneration::compute_new_size();
771
772 // Reset again after a possible resizing
773 if (did_compact()) {
774 cmsSpace()->reset_after_compaction();
775 }
776 }
777
778 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
779 assert_locked_or_safepoint(Heap_lock);
780
781 // If incremental collection failed, we just want to expand
782 // to the limit.
783 if (incremental_collection_failed()) {
784 clear_incremental_collection_failed();
785 grow_to_reserved();
786 return;
787 }
788
789 double free_percentage = ((double) free()) / capacity();
790 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
791 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
792
793 // compute expansion delta needed for reaching desired free percentage
794 if (free_percentage < desired_free_percentage) {
795 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
796 assert(desired_capacity >= capacity(), "invalid expansion size");
797 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
798 if (PrintGCDetails && Verbose) {
799 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
800 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
801 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
802 gclog_or_tty->print_cr(" Desired free fraction %f",
803 desired_free_percentage);
804 gclog_or_tty->print_cr(" Maximum free fraction %f",
805 maximum_free_percentage);
806 gclog_or_tty->print_cr(" Capacity "SIZE_FORMAT, capacity()/1000);
807 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
808 desired_capacity/1000);
809 int prev_level = level() - 1;
810 if (prev_level >= 0) {
811 size_t prev_size = 0;
812 GenCollectedHeap* gch = GenCollectedHeap::heap();
813 Generation* prev_gen = gch->young_gen();
814 prev_size = prev_gen->capacity();
815 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
816 prev_size/1000);
817 }
818 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
819 unsafe_max_alloc_nogc()/1000);
820 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
821 contiguous_available()/1000);
822 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
823 expand_bytes);
824 }
825 // safe if expansion fails
826 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
827 if (PrintGCDetails && Verbose) {
828 gclog_or_tty->print_cr(" Expanded free fraction %f",
829 ((double) free()) / capacity());
830 }
831 } else {
832 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
833 assert(desired_capacity <= capacity(), "invalid expansion size");
834 size_t shrink_bytes = capacity() - desired_capacity;
835 // Don't shrink unless the delta is greater than the minimum shrink we want
836 if (shrink_bytes >= MinHeapDeltaBytes) {
837 shrink_free_list_by(shrink_bytes);
838 }
839 }
840 }
841
842 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
843 return cmsSpace()->freelistLock();
844 }
845
846 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
847 bool tlab) {
848 CMSSynchronousYieldRequest yr;
849 MutexLockerEx x(freelistLock(),
850 Mutex::_no_safepoint_check_flag);
851 return have_lock_and_allocate(size, tlab);
852 }
853
854 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
855 bool tlab /* ignored */) {
856 assert_lock_strong(freelistLock());
857 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
858 HeapWord* res = cmsSpace()->allocate(adjustedSize);
859 // Allocate the object live (grey) if the background collector has
860 // started marking. This is necessary because the marker may
861 // have passed this address and consequently this object will
862 // not otherwise be greyed and would be incorrectly swept up.
863 // Note that if this object contains references, the writing
864 // of those references will dirty the card containing this object
865 // allowing the object to be blackened (and its references scanned)
866 // either during a preclean phase or at the final checkpoint.
867 if (res != NULL) {
868 // We may block here with an uninitialized object with
869 // its mark-bit or P-bits not yet set. Such objects need
870 // to be safely navigable by block_start().
871 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
872 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
873 collector()->direct_allocated(res, adjustedSize);
874 _direct_allocated_words += adjustedSize;
875 // allocation counters
876 NOT_PRODUCT(
877 _numObjectsAllocated++;
878 _numWordsAllocated += (int)adjustedSize;
879 )
880 }
881 return res;
882 }
883
884 // In the case of direct allocation by mutators in a generation that
885 // is being concurrently collected, the object must be allocated
886 // live (grey) if the background collector has started marking.
887 // This is necessary because the marker may
888 // have passed this address and consequently this object will
889 // not otherwise be greyed and would be incorrectly swept up.
890 // Note that if this object contains references, the writing
891 // of those references will dirty the card containing this object
892 // allowing the object to be blackened (and its references scanned)
893 // either during a preclean phase or at the final checkpoint.
894 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
895 assert(_markBitMap.covers(start, size), "Out of bounds");
896 if (_collectorState >= Marking) {
897 MutexLockerEx y(_markBitMap.lock(),
898 Mutex::_no_safepoint_check_flag);
899 // [see comments preceding SweepClosure::do_blk() below for details]
900 //
901 // Can the P-bits be deleted now? JJJ
902 //
903 // 1. need to mark the object as live so it isn't collected
904 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
905 // 3. need to mark the end of the object so marking, precleaning or sweeping
906 // can skip over uninitialized or unparsable objects. An allocated
907 // object is considered uninitialized for our purposes as long as
908 // its klass word is NULL. All old gen objects are parsable
909 // as soon as they are initialized.)
910 _markBitMap.mark(start); // object is live
911 _markBitMap.mark(start + 1); // object is potentially uninitialized?
912 _markBitMap.mark(start + size - 1);
913 // mark end of object
914 }
915 // check that oop looks uninitialized
916 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
917 }
918
919 void CMSCollector::promoted(bool par, HeapWord* start,
920 bool is_obj_array, size_t obj_size) {
921 assert(_markBitMap.covers(start), "Out of bounds");
922 // See comment in direct_allocated() about when objects should
923 // be allocated live.
924 if (_collectorState >= Marking) {
925 // we already hold the marking bit map lock, taken in
926 // the prologue
927 if (par) {
928 _markBitMap.par_mark(start);
929 } else {
930 _markBitMap.mark(start);
931 }
932 // We don't need to mark the object as uninitialized (as
933 // in direct_allocated above) because this is being done with the
934 // world stopped and the object will be initialized by the
935 // time the marking, precleaning or sweeping get to look at it.
936 // But see the code for copying objects into the CMS generation,
937 // where we need to ensure that concurrent readers of the
938 // block offset table are able to safely navigate a block that
939 // is in flux from being free to being allocated (and in
940 // transition while being copied into) and subsequently
941 // becoming a bona-fide object when the copy/promotion is complete.
942 assert(SafepointSynchronize::is_at_safepoint(),
943 "expect promotion only at safepoints");
944
945 if (_collectorState < Sweeping) {
946 // Mark the appropriate cards in the modUnionTable, so that
947 // this object gets scanned before the sweep. If this is
948 // not done, CMS generation references in the object might
949 // not get marked.
950 // For the case of arrays, which are otherwise precisely
951 // marked, we need to dirty the entire array, not just its head.
952 if (is_obj_array) {
953 // The [par_]mark_range() method expects mr.end() below to
954 // be aligned to the granularity of a bit's representation
955 // in the heap. In the case of the MUT below, that's a
956 // card size.
957 MemRegion mr(start,
958 (HeapWord*)round_to((intptr_t)(start + obj_size),
959 CardTableModRefBS::card_size /* bytes */));
960 if (par) {
961 _modUnionTable.par_mark_range(mr);
962 } else {
963 _modUnionTable.mark_range(mr);
964 }
965 } else { // not an obj array; we can just mark the head
966 if (par) {
967 _modUnionTable.par_mark(start);
968 } else {
969 _modUnionTable.mark(start);
970 }
971 }
972 }
973 }
974 }
975
976 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
977 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
978 // allocate, copy and if necessary update promoinfo --
979 // delegate to underlying space.
980 assert_lock_strong(freelistLock());
981
982 #ifndef PRODUCT
983 if (Universe::heap()->promotion_should_fail()) {
984 return NULL;
985 }
986 #endif // #ifndef PRODUCT
987
988 oop res = _cmsSpace->promote(obj, obj_size);
989 if (res == NULL) {
990 // expand and retry
991 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
992 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
993 // Since this is the old generation, we don't try to promote
994 // into a more senior generation.
995 res = _cmsSpace->promote(obj, obj_size);
996 }
997 if (res != NULL) {
998 // See comment in allocate() about when objects should
999 // be allocated live.
1000 assert(obj->is_oop(), "Will dereference klass pointer below");
1001 collector()->promoted(false, // Not parallel
1002 (HeapWord*)res, obj->is_objArray(), obj_size);
1003 // promotion counters
1004 NOT_PRODUCT(
1005 _numObjectsPromoted++;
1006 _numWordsPromoted +=
1007 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1008 )
1009 }
1010 return res;
1011 }
1012
1013
1014 // IMPORTANT: Notes on object size recognition in CMS.
1015 // ---------------------------------------------------
1016 // A block of storage in the CMS generation is always in
1017 // one of three states. A free block (FREE), an allocated
1018 // object (OBJECT) whose size() method reports the correct size,
1019 // and an intermediate state (TRANSIENT) in which its size cannot
1020 // be accurately determined.
1021 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1022 // -----------------------------------------------------
1023 // FREE: klass_word & 1 == 1; mark_word holds block size
1024 //
1025 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1026 // obj->size() computes correct size
1027 //
1028 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1029 //
1030 // STATE IDENTIFICATION: (64 bit+COOPS)
1031 // ------------------------------------
1032 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1033 //
1034 // OBJECT: klass_word installed; klass_word != 0;
1035 // obj->size() computes correct size
1036 //
1037 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1038 //
1039 //
1040 // STATE TRANSITION DIAGRAM
1041 //
1042 // mut / parnew mut / parnew
1043 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1044 // ^ |
1045 // |------------------------ DEAD <------------------------------------|
1046 // sweep mut
1047 //
1048 // While a block is in TRANSIENT state its size cannot be determined
1049 // so readers will either need to come back later or stall until
1050 // the size can be determined. Note that for the case of direct
1051 // allocation, P-bits, when available, may be used to determine the
1052 // size of an object that may not yet have been initialized.
1053
1054 // Things to support parallel young-gen collection.
1055 oop
1056 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1057 oop old, markOop m,
1058 size_t word_sz) {
1059 #ifndef PRODUCT
1060 if (Universe::heap()->promotion_should_fail()) {
1061 return NULL;
1062 }
1063 #endif // #ifndef PRODUCT
1064
1065 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1066 PromotionInfo* promoInfo = &ps->promo;
1067 // if we are tracking promotions, then first ensure space for
1068 // promotion (including spooling space for saving header if necessary).
1069 // then allocate and copy, then track promoted info if needed.
1070 // When tracking (see PromotionInfo::track()), the mark word may
1071 // be displaced and in this case restoration of the mark word
1072 // occurs in the (oop_since_save_marks_)iterate phase.
1073 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1074 // Out of space for allocating spooling buffers;
1075 // try expanding and allocating spooling buffers.
1076 if (!expand_and_ensure_spooling_space(promoInfo)) {
1077 return NULL;
1078 }
1079 }
1080 assert(promoInfo->has_spooling_space(), "Control point invariant");
1081 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1082 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1083 if (obj_ptr == NULL) {
1084 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1085 if (obj_ptr == NULL) {
1086 return NULL;
1087 }
1088 }
1089 oop obj = oop(obj_ptr);
1090 OrderAccess::storestore();
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 // IMPORTANT: See note on object initialization for CMS above.
1094 // Otherwise, copy the object. Here we must be careful to insert the
1095 // klass pointer last, since this marks the block as an allocated object.
1096 // Except with compressed oops it's the mark word.
1097 HeapWord* old_ptr = (HeapWord*)old;
1098 // Restore the mark word copied above.
1099 obj->set_mark(m);
1100 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1101 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1102 OrderAccess::storestore();
1103
1104 if (UseCompressedClassPointers) {
1105 // Copy gap missed by (aligned) header size calculation below
1106 obj->set_klass_gap(old->klass_gap());
1107 }
1108 if (word_sz > (size_t)oopDesc::header_size()) {
1109 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1110 obj_ptr + oopDesc::header_size(),
1111 word_sz - oopDesc::header_size());
1112 }
1113
1114 // Now we can track the promoted object, if necessary. We take care
1115 // to delay the transition from uninitialized to full object
1116 // (i.e., insertion of klass pointer) until after, so that it
1117 // atomically becomes a promoted object.
1118 if (promoInfo->tracking()) {
1119 promoInfo->track((PromotedObject*)obj, old->klass());
1120 }
1121 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1122 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1123 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1124
1125 // Finally, install the klass pointer (this should be volatile).
1126 OrderAccess::storestore();
1127 obj->set_klass(old->klass());
1128 // We should now be able to calculate the right size for this object
1129 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1130
1131 collector()->promoted(true, // parallel
1132 obj_ptr, old->is_objArray(), word_sz);
1133
1134 NOT_PRODUCT(
1135 Atomic::inc_ptr(&_numObjectsPromoted);
1136 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1137 )
1138
1139 return obj;
1140 }
1141
1142 void
1143 ConcurrentMarkSweepGeneration::
1144 par_promote_alloc_done(int thread_num) {
1145 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1146 ps->lab.retire(thread_num);
1147 }
1148
1149 void
1150 ConcurrentMarkSweepGeneration::
1151 par_oop_since_save_marks_iterate_done(int thread_num) {
1152 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1153 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1154 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1155 }
1156
1157 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1158 size_t size,
1159 bool tlab)
1160 {
1161 // We allow a STW collection only if a full
1162 // collection was requested.
1163 return full || should_allocate(size, tlab); // FIX ME !!!
1164 // This and promotion failure handling are connected at the
1165 // hip and should be fixed by untying them.
1166 }
1167
1168 bool CMSCollector::shouldConcurrentCollect() {
1169 if (_full_gc_requested) {
1170 if (Verbose && PrintGCDetails) {
1171 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1172 " gc request (or gc_locker)");
1173 }
1174 return true;
1175 }
1176
1177 FreelistLocker x(this);
1178 // ------------------------------------------------------------------
1179 // Print out lots of information which affects the initiation of
1180 // a collection.
1181 if (PrintCMSInitiationStatistics && stats().valid()) {
1182 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1183 gclog_or_tty->stamp();
1184 gclog_or_tty->cr();
1185 stats().print_on(gclog_or_tty);
1186 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1187 stats().time_until_cms_gen_full());
1188 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1189 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1190 _cmsGen->contiguous_available());
1191 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1192 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1193 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1194 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1195 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1196 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1197 gclog_or_tty->print_cr("metadata initialized %d",
1198 MetaspaceGC::should_concurrent_collect());
1199 }
1200 // ------------------------------------------------------------------
1201
1202 // If the estimated time to complete a cms collection (cms_duration())
1203 // is less than the estimated time remaining until the cms generation
1204 // is full, start a collection.
1205 if (!UseCMSInitiatingOccupancyOnly) {
1206 if (stats().valid()) {
1207 if (stats().time_until_cms_start() == 0.0) {
1208 return true;
1209 }
1210 } else {
1211 // We want to conservatively collect somewhat early in order
1212 // to try and "bootstrap" our CMS/promotion statistics;
1213 // this branch will not fire after the first successful CMS
1214 // collection because the stats should then be valid.
1215 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1216 if (Verbose && PrintGCDetails) {
1217 gclog_or_tty->print_cr(
1218 " CMSCollector: collect for bootstrapping statistics:"
1219 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1220 _bootstrap_occupancy);
1221 }
1222 return true;
1223 }
1224 }
1225 }
1226
1227 // Otherwise, we start a collection cycle if
1228 // old gen want a collection cycle started. Each may use
1229 // an appropriate criterion for making this decision.
1230 // XXX We need to make sure that the gen expansion
1231 // criterion dovetails well with this. XXX NEED TO FIX THIS
1232 if (_cmsGen->should_concurrent_collect()) {
1233 if (Verbose && PrintGCDetails) {
1234 gclog_or_tty->print_cr("CMS old gen initiated");
1235 }
1236 return true;
1237 }
1238
1239 // We start a collection if we believe an incremental collection may fail;
1240 // this is not likely to be productive in practice because it's probably too
1241 // late anyway.
1242 GenCollectedHeap* gch = GenCollectedHeap::heap();
1243 assert(gch->collector_policy()->is_generation_policy(),
1244 "You may want to check the correctness of the following");
1245 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1246 if (Verbose && PrintGCDetails) {
1247 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1248 }
1249 return true;
1250 }
1251
1252 if (MetaspaceGC::should_concurrent_collect()) {
1253 if (Verbose && PrintGCDetails) {
1254 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1255 }
1256 return true;
1257 }
1258
1259 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1260 if (CMSTriggerInterval >= 0) {
1261 if (CMSTriggerInterval == 0) {
1262 // Trigger always
1263 return true;
1264 }
1265
1266 // Check the CMS time since begin (we do not check the stats validity
1267 // as we want to be able to trigger the first CMS cycle as well)
1268 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1269 if (Verbose && PrintGCDetails) {
1270 if (stats().valid()) {
1271 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1272 stats().cms_time_since_begin());
1273 } else {
1274 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1275 }
1276 }
1277 return true;
1278 }
1279 }
1280
1281 return false;
1282 }
1283
1284 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1285
1286 // Clear _expansion_cause fields of constituent generations
1287 void CMSCollector::clear_expansion_cause() {
1288 _cmsGen->clear_expansion_cause();
1289 }
1290
1291 // We should be conservative in starting a collection cycle. To
1292 // start too eagerly runs the risk of collecting too often in the
1293 // extreme. To collect too rarely falls back on full collections,
1294 // which works, even if not optimum in terms of concurrent work.
1295 // As a work around for too eagerly collecting, use the flag
1296 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1297 // giving the user an easily understandable way of controlling the
1298 // collections.
1299 // We want to start a new collection cycle if any of the following
1300 // conditions hold:
1301 // . our current occupancy exceeds the configured initiating occupancy
1302 // for this generation, or
1303 // . we recently needed to expand this space and have not, since that
1304 // expansion, done a collection of this generation, or
1305 // . the underlying space believes that it may be a good idea to initiate
1306 // a concurrent collection (this may be based on criteria such as the
1307 // following: the space uses linear allocation and linear allocation is
1308 // going to fail, or there is believed to be excessive fragmentation in
1309 // the generation, etc... or ...
1310 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1311 // the case of the old generation; see CR 6543076):
1312 // we may be approaching a point at which allocation requests may fail because
1313 // we will be out of sufficient free space given allocation rate estimates.]
1314 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1315
1316 assert_lock_strong(freelistLock());
1317 if (occupancy() > initiating_occupancy()) {
1318 if (PrintGCDetails && Verbose) {
1319 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1320 short_name(), occupancy(), initiating_occupancy());
1321 }
1322 return true;
1323 }
1324 if (UseCMSInitiatingOccupancyOnly) {
1325 return false;
1326 }
1327 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1328 if (PrintGCDetails && Verbose) {
1329 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1330 short_name());
1331 }
1332 return true;
1333 }
1334 if (_cmsSpace->should_concurrent_collect()) {
1335 if (PrintGCDetails && Verbose) {
1336 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1337 short_name());
1338 }
1339 return true;
1340 }
1341 return false;
1342 }
1343
1344 void ConcurrentMarkSweepGeneration::collect(bool full,
1345 bool clear_all_soft_refs,
1346 size_t size,
1347 bool tlab)
1348 {
1349 collector()->collect(full, clear_all_soft_refs, size, tlab);
1350 }
1351
1352 void CMSCollector::collect(bool full,
1353 bool clear_all_soft_refs,
1354 size_t size,
1355 bool tlab)
1356 {
1357 // The following "if" branch is present for defensive reasons.
1358 // In the current uses of this interface, it can be replaced with:
1359 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1360 // But I am not placing that assert here to allow future
1361 // generality in invoking this interface.
1362 if (GC_locker::is_active()) {
1363 // A consistency test for GC_locker
1364 assert(GC_locker::needs_gc(), "Should have been set already");
1365 // Skip this foreground collection, instead
1366 // expanding the heap if necessary.
1367 // Need the free list locks for the call to free() in compute_new_size()
1368 compute_new_size();
1369 return;
1370 }
1371 acquire_control_and_collect(full, clear_all_soft_refs);
1372 }
1373
1374 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1375 GenCollectedHeap* gch = GenCollectedHeap::heap();
1376 unsigned int gc_count = gch->total_full_collections();
1377 if (gc_count == full_gc_count) {
1378 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1379 _full_gc_requested = true;
1380 _full_gc_cause = cause;
1381 CGC_lock->notify(); // nudge CMS thread
1382 } else {
1383 assert(gc_count > full_gc_count, "Error: causal loop");
1384 }
1385 }
1386
1387 bool CMSCollector::is_external_interruption() {
1388 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1389 return GCCause::is_user_requested_gc(cause) ||
1390 GCCause::is_serviceability_requested_gc(cause);
1391 }
1392
1393 void CMSCollector::report_concurrent_mode_interruption() {
1394 if (is_external_interruption()) {
1395 if (PrintGCDetails) {
1396 gclog_or_tty->print(" (concurrent mode interrupted)");
1397 }
1398 } else {
1399 if (PrintGCDetails) {
1400 gclog_or_tty->print(" (concurrent mode failure)");
1401 }
1402 _gc_tracer_cm->report_concurrent_mode_failure();
1403 }
1404 }
1405
1406
1407 // The foreground and background collectors need to coordinate in order
1408 // to make sure that they do not mutually interfere with CMS collections.
1409 // When a background collection is active,
1410 // the foreground collector may need to take over (preempt) and
1411 // synchronously complete an ongoing collection. Depending on the
1412 // frequency of the background collections and the heap usage
1413 // of the application, this preemption can be seldom or frequent.
1414 // There are only certain
1415 // points in the background collection that the "collection-baton"
1416 // can be passed to the foreground collector.
1417 //
1418 // The foreground collector will wait for the baton before
1419 // starting any part of the collection. The foreground collector
1420 // will only wait at one location.
1421 //
1422 // The background collector will yield the baton before starting a new
1423 // phase of the collection (e.g., before initial marking, marking from roots,
1424 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1425 // of the loop which switches the phases. The background collector does some
1426 // of the phases (initial mark, final re-mark) with the world stopped.
1427 // Because of locking involved in stopping the world,
1428 // the foreground collector should not block waiting for the background
1429 // collector when it is doing a stop-the-world phase. The background
1430 // collector will yield the baton at an additional point just before
1431 // it enters a stop-the-world phase. Once the world is stopped, the
1432 // background collector checks the phase of the collection. If the
1433 // phase has not changed, it proceeds with the collection. If the
1434 // phase has changed, it skips that phase of the collection. See
1435 // the comments on the use of the Heap_lock in collect_in_background().
1436 //
1437 // Variable used in baton passing.
1438 // _foregroundGCIsActive - Set to true by the foreground collector when
1439 // it wants the baton. The foreground clears it when it has finished
1440 // the collection.
1441 // _foregroundGCShouldWait - Set to true by the background collector
1442 // when it is running. The foreground collector waits while
1443 // _foregroundGCShouldWait is true.
1444 // CGC_lock - monitor used to protect access to the above variables
1445 // and to notify the foreground and background collectors.
1446 // _collectorState - current state of the CMS collection.
1447 //
1448 // The foreground collector
1449 // acquires the CGC_lock
1450 // sets _foregroundGCIsActive
1451 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1452 // various locks acquired in preparation for the collection
1453 // are released so as not to block the background collector
1454 // that is in the midst of a collection
1455 // proceeds with the collection
1456 // clears _foregroundGCIsActive
1457 // returns
1458 //
1459 // The background collector in a loop iterating on the phases of the
1460 // collection
1461 // acquires the CGC_lock
1462 // sets _foregroundGCShouldWait
1463 // if _foregroundGCIsActive is set
1464 // clears _foregroundGCShouldWait, notifies _CGC_lock
1465 // waits on _CGC_lock for _foregroundGCIsActive to become false
1466 // and exits the loop.
1467 // otherwise
1468 // proceed with that phase of the collection
1469 // if the phase is a stop-the-world phase,
1470 // yield the baton once more just before enqueueing
1471 // the stop-world CMS operation (executed by the VM thread).
1472 // returns after all phases of the collection are done
1473 //
1474
1475 void CMSCollector::acquire_control_and_collect(bool full,
1476 bool clear_all_soft_refs) {
1477 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1478 assert(!Thread::current()->is_ConcurrentGC_thread(),
1479 "shouldn't try to acquire control from self!");
1480
1481 // Start the protocol for acquiring control of the
1482 // collection from the background collector (aka CMS thread).
1483 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1484 "VM thread should have CMS token");
1485 // Remember the possibly interrupted state of an ongoing
1486 // concurrent collection
1487 CollectorState first_state = _collectorState;
1488
1489 // Signal to a possibly ongoing concurrent collection that
1490 // we want to do a foreground collection.
1491 _foregroundGCIsActive = true;
1492
1493 // release locks and wait for a notify from the background collector
1494 // releasing the locks in only necessary for phases which
1495 // do yields to improve the granularity of the collection.
1496 assert_lock_strong(bitMapLock());
1497 // We need to lock the Free list lock for the space that we are
1498 // currently collecting.
1499 assert(haveFreelistLocks(), "Must be holding free list locks");
1500 bitMapLock()->unlock();
1501 releaseFreelistLocks();
1502 {
1503 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1504 if (_foregroundGCShouldWait) {
1505 // We are going to be waiting for action for the CMS thread;
1506 // it had better not be gone (for instance at shutdown)!
1507 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1508 "CMS thread must be running");
1509 // Wait here until the background collector gives us the go-ahead
1510 ConcurrentMarkSweepThread::clear_CMS_flag(
1511 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1512 // Get a possibly blocked CMS thread going:
1513 // Note that we set _foregroundGCIsActive true above,
1514 // without protection of the CGC_lock.
1515 CGC_lock->notify();
1516 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1517 "Possible deadlock");
1518 while (_foregroundGCShouldWait) {
1519 // wait for notification
1520 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1521 // Possibility of delay/starvation here, since CMS token does
1522 // not know to give priority to VM thread? Actually, i think
1523 // there wouldn't be any delay/starvation, but the proof of
1524 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1525 }
1526 ConcurrentMarkSweepThread::set_CMS_flag(
1527 ConcurrentMarkSweepThread::CMS_vm_has_token);
1528 }
1529 }
1530 // The CMS_token is already held. Get back the other locks.
1531 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1532 "VM thread should have CMS token");
1533 getFreelistLocks();
1534 bitMapLock()->lock_without_safepoint_check();
1535 if (TraceCMSState) {
1536 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1537 INTPTR_FORMAT " with first state %d", p2i(Thread::current()), first_state);
1538 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1539 }
1540
1541 // Inform cms gen if this was due to partial collection failing.
1542 // The CMS gen may use this fact to determine its expansion policy.
1543 GenCollectedHeap* gch = GenCollectedHeap::heap();
1544 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1545 assert(!_cmsGen->incremental_collection_failed(),
1546 "Should have been noticed, reacted to and cleared");
1547 _cmsGen->set_incremental_collection_failed();
1548 }
1549
1550 if (first_state > Idling) {
1551 report_concurrent_mode_interruption();
1552 }
1553
1554 set_did_compact(true);
1555
1556 // If the collection is being acquired from the background
1557 // collector, there may be references on the discovered
1558 // references lists. Abandon those references, since some
1559 // of them may have become unreachable after concurrent
1560 // discovery; the STW compacting collector will redo discovery
1561 // more precisely, without being subject to floating garbage.
1562 // Leaving otherwise unreachable references in the discovered
1563 // lists would require special handling.
1564 ref_processor()->disable_discovery();
1565 ref_processor()->abandon_partial_discovery();
1566 ref_processor()->verify_no_references_recorded();
1567
1568 if (first_state > Idling) {
1569 save_heap_summary();
1570 }
1571
1572 do_compaction_work(clear_all_soft_refs);
1573
1574 // Has the GC time limit been exceeded?
1575 size_t max_eden_size = _young_gen->max_capacity() -
1576 _young_gen->to()->capacity() -
1577 _young_gen->from()->capacity();
1578 GCCause::Cause gc_cause = gch->gc_cause();
1579 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1580 _young_gen->eden()->used(),
1581 _cmsGen->max_capacity(),
1582 max_eden_size,
1583 full,
1584 gc_cause,
1585 gch->collector_policy());
1586
1587 // Reset the expansion cause, now that we just completed
1588 // a collection cycle.
1589 clear_expansion_cause();
1590 _foregroundGCIsActive = false;
1591 return;
1592 }
1593
1594 // Resize the tenured generation
1595 // after obtaining the free list locks for the
1596 // two generations.
1597 void CMSCollector::compute_new_size() {
1598 assert_locked_or_safepoint(Heap_lock);
1599 FreelistLocker z(this);
1600 MetaspaceGC::compute_new_size();
1601 _cmsGen->compute_new_size_free_list();
1602 }
1603
1604 // A work method used by the foreground collector to do
1605 // a mark-sweep-compact.
1606 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1607 GenCollectedHeap* gch = GenCollectedHeap::heap();
1608
1609 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1610 gc_timer->register_gc_start();
1611
1612 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1613 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1614
1615 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
1616
1617 // Temporarily widen the span of the weak reference processing to
1618 // the entire heap.
1619 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1620 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1621 // Temporarily, clear the "is_alive_non_header" field of the
1622 // reference processor.
1623 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1624 // Temporarily make reference _processing_ single threaded (non-MT).
1625 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1626 // Temporarily make refs discovery atomic
1627 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1628 // Temporarily make reference _discovery_ single threaded (non-MT)
1629 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1630
1631 ref_processor()->set_enqueuing_is_done(false);
1632 ref_processor()->enable_discovery();
1633 ref_processor()->setup_policy(clear_all_soft_refs);
1634 // If an asynchronous collection finishes, the _modUnionTable is
1635 // all clear. If we are assuming the collection from an asynchronous
1636 // collection, clear the _modUnionTable.
1637 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1638 "_modUnionTable should be clear if the baton was not passed");
1639 _modUnionTable.clear_all();
1640 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1641 "mod union for klasses should be clear if the baton was passed");
1642 _ct->klass_rem_set()->clear_mod_union();
1643
1644 // We must adjust the allocation statistics being maintained
1645 // in the free list space. We do so by reading and clearing
1646 // the sweep timer and updating the block flux rate estimates below.
1647 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1648 if (_inter_sweep_timer.is_active()) {
1649 _inter_sweep_timer.stop();
1650 // Note that we do not use this sample to update the _inter_sweep_estimate.
1651 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1652 _inter_sweep_estimate.padded_average(),
1653 _intra_sweep_estimate.padded_average());
1654 }
1655
1656 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1657 ref_processor(), clear_all_soft_refs);
1658 #ifdef ASSERT
1659 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1660 size_t free_size = cms_space->free();
1661 assert(free_size ==
1662 pointer_delta(cms_space->end(), cms_space->compaction_top())
1663 * HeapWordSize,
1664 "All the free space should be compacted into one chunk at top");
1665 assert(cms_space->dictionary()->total_chunk_size(
1666 debug_only(cms_space->freelistLock())) == 0 ||
1667 cms_space->totalSizeInIndexedFreeLists() == 0,
1668 "All the free space should be in a single chunk");
1669 size_t num = cms_space->totalCount();
1670 assert((free_size == 0 && num == 0) ||
1671 (free_size > 0 && (num == 1 || num == 2)),
1672 "There should be at most 2 free chunks after compaction");
1673 #endif // ASSERT
1674 _collectorState = Resetting;
1675 assert(_restart_addr == NULL,
1676 "Should have been NULL'd before baton was passed");
1677 reset(false /* == !concurrent */);
1678 _cmsGen->reset_after_compaction();
1679 _concurrent_cycles_since_last_unload = 0;
1680
1681 // Clear any data recorded in the PLAB chunk arrays.
1682 if (_survivor_plab_array != NULL) {
1683 reset_survivor_plab_arrays();
1684 }
1685
1686 // Adjust the per-size allocation stats for the next epoch.
1687 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1688 // Restart the "inter sweep timer" for the next epoch.
1689 _inter_sweep_timer.reset();
1690 _inter_sweep_timer.start();
1691
1692 gc_timer->register_gc_end();
1693
1694 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1695
1696 // For a mark-sweep-compact, compute_new_size() will be called
1697 // in the heap's do_collection() method.
1698 }
1699
1700 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1701 ContiguousSpace* eden_space = _young_gen->eden();
1702 ContiguousSpace* from_space = _young_gen->from();
1703 ContiguousSpace* to_space = _young_gen->to();
1704 // Eden
1705 if (_eden_chunk_array != NULL) {
1706 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1707 p2i(eden_space->bottom()), p2i(eden_space->top()),
1708 p2i(eden_space->end()), eden_space->capacity());
1709 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1710 "_eden_chunk_capacity=" SIZE_FORMAT,
1711 _eden_chunk_index, _eden_chunk_capacity);
1712 for (size_t i = 0; i < _eden_chunk_index; i++) {
1713 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1714 i, p2i(_eden_chunk_array[i]));
1715 }
1716 }
1717 // Survivor
1718 if (_survivor_chunk_array != NULL) {
1719 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1720 p2i(from_space->bottom()), p2i(from_space->top()),
1721 p2i(from_space->end()), from_space->capacity());
1722 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1723 "_survivor_chunk_capacity=" SIZE_FORMAT,
1724 _survivor_chunk_index, _survivor_chunk_capacity);
1725 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1726 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1727 i, p2i(_survivor_chunk_array[i]));
1728 }
1729 }
1730 }
1731
1732 void CMSCollector::getFreelistLocks() const {
1733 // Get locks for all free lists in all generations that this
1734 // collector is responsible for
1735 _cmsGen->freelistLock()->lock_without_safepoint_check();
1736 }
1737
1738 void CMSCollector::releaseFreelistLocks() const {
1739 // Release locks for all free lists in all generations that this
1740 // collector is responsible for
1741 _cmsGen->freelistLock()->unlock();
1742 }
1743
1744 bool CMSCollector::haveFreelistLocks() const {
1745 // Check locks for all free lists in all generations that this
1746 // collector is responsible for
1747 assert_lock_strong(_cmsGen->freelistLock());
1748 PRODUCT_ONLY(ShouldNotReachHere());
1749 return true;
1750 }
1751
1752 // A utility class that is used by the CMS collector to
1753 // temporarily "release" the foreground collector from its
1754 // usual obligation to wait for the background collector to
1755 // complete an ongoing phase before proceeding.
1756 class ReleaseForegroundGC: public StackObj {
1757 private:
1758 CMSCollector* _c;
1759 public:
1760 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1761 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1762 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1763 // allow a potentially blocked foreground collector to proceed
1764 _c->_foregroundGCShouldWait = false;
1765 if (_c->_foregroundGCIsActive) {
1766 CGC_lock->notify();
1767 }
1768 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1769 "Possible deadlock");
1770 }
1771
1772 ~ReleaseForegroundGC() {
1773 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1774 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1775 _c->_foregroundGCShouldWait = true;
1776 }
1777 };
1778
1779 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1780 assert(Thread::current()->is_ConcurrentGC_thread(),
1781 "A CMS asynchronous collection is only allowed on a CMS thread.");
1782
1783 GenCollectedHeap* gch = GenCollectedHeap::heap();
1784 {
1785 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1786 MutexLockerEx hl(Heap_lock, safepoint_check);
1787 FreelistLocker fll(this);
1788 MutexLockerEx x(CGC_lock, safepoint_check);
1789 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
1790 // The foreground collector is active or we're
1791 // not using asynchronous collections. Skip this
1792 // background collection.
1793 assert(!_foregroundGCShouldWait, "Should be clear");
1794 return;
1795 } else {
1796 assert(_collectorState == Idling, "Should be idling before start.");
1797 _collectorState = InitialMarking;
1798 register_gc_start(cause);
1799 // Reset the expansion cause, now that we are about to begin
1800 // a new cycle.
1801 clear_expansion_cause();
1802
1803 // Clear the MetaspaceGC flag since a concurrent collection
1804 // is starting but also clear it after the collection.
1805 MetaspaceGC::set_should_concurrent_collect(false);
1806 }
1807 // Decide if we want to enable class unloading as part of the
1808 // ensuing concurrent GC cycle.
1809 update_should_unload_classes();
1810 _full_gc_requested = false; // acks all outstanding full gc requests
1811 _full_gc_cause = GCCause::_no_gc;
1812 // Signal that we are about to start a collection
1813 gch->increment_total_full_collections(); // ... starting a collection cycle
1814 _collection_count_start = gch->total_full_collections();
1815 }
1816
1817 // Used for PrintGC
1818 size_t prev_used;
1819 if (PrintGC && Verbose) {
1820 prev_used = _cmsGen->used();
1821 }
1822
1823 // The change of the collection state is normally done at this level;
1824 // the exceptions are phases that are executed while the world is
1825 // stopped. For those phases the change of state is done while the
1826 // world is stopped. For baton passing purposes this allows the
1827 // background collector to finish the phase and change state atomically.
1828 // The foreground collector cannot wait on a phase that is done
1829 // while the world is stopped because the foreground collector already
1830 // has the world stopped and would deadlock.
1831 while (_collectorState != Idling) {
1832 if (TraceCMSState) {
1833 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
1834 p2i(Thread::current()), _collectorState);
1835 }
1836 // The foreground collector
1837 // holds the Heap_lock throughout its collection.
1838 // holds the CMS token (but not the lock)
1839 // except while it is waiting for the background collector to yield.
1840 //
1841 // The foreground collector should be blocked (not for long)
1842 // if the background collector is about to start a phase
1843 // executed with world stopped. If the background
1844 // collector has already started such a phase, the
1845 // foreground collector is blocked waiting for the
1846 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1847 // are executed in the VM thread.
1848 //
1849 // The locking order is
1850 // PendingListLock (PLL) -- if applicable (FinalMarking)
1851 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1852 // CMS token (claimed in
1853 // stop_world_and_do() -->
1854 // safepoint_synchronize() -->
1855 // CMSThread::synchronize())
1856
1857 {
1858 // Check if the FG collector wants us to yield.
1859 CMSTokenSync x(true); // is cms thread
1860 if (waitForForegroundGC()) {
1861 // We yielded to a foreground GC, nothing more to be
1862 // done this round.
1863 assert(_foregroundGCShouldWait == false, "We set it to false in "
1864 "waitForForegroundGC()");
1865 if (TraceCMSState) {
1866 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1867 " exiting collection CMS state %d",
1868 p2i(Thread::current()), _collectorState);
1869 }
1870 return;
1871 } else {
1872 // The background collector can run but check to see if the
1873 // foreground collector has done a collection while the
1874 // background collector was waiting to get the CGC_lock
1875 // above. If yes, break so that _foregroundGCShouldWait
1876 // is cleared before returning.
1877 if (_collectorState == Idling) {
1878 break;
1879 }
1880 }
1881 }
1882
1883 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1884 "should be waiting");
1885
1886 switch (_collectorState) {
1887 case InitialMarking:
1888 {
1889 ReleaseForegroundGC x(this);
1890 stats().record_cms_begin();
1891 VM_CMS_Initial_Mark initial_mark_op(this);
1892 VMThread::execute(&initial_mark_op);
1893 }
1894 // The collector state may be any legal state at this point
1895 // since the background collector may have yielded to the
1896 // foreground collector.
1897 break;
1898 case Marking:
1899 // initial marking in checkpointRootsInitialWork has been completed
1900 if (markFromRoots()) { // we were successful
1901 assert(_collectorState == Precleaning, "Collector state should "
1902 "have changed");
1903 } else {
1904 assert(_foregroundGCIsActive, "Internal state inconsistency");
1905 }
1906 break;
1907 case Precleaning:
1908 // marking from roots in markFromRoots has been completed
1909 preclean();
1910 assert(_collectorState == AbortablePreclean ||
1911 _collectorState == FinalMarking,
1912 "Collector state should have changed");
1913 break;
1914 case AbortablePreclean:
1915 abortable_preclean();
1916 assert(_collectorState == FinalMarking, "Collector state should "
1917 "have changed");
1918 break;
1919 case FinalMarking:
1920 {
1921 ReleaseForegroundGC x(this);
1922
1923 VM_CMS_Final_Remark final_remark_op(this);
1924 VMThread::execute(&final_remark_op);
1925 }
1926 assert(_foregroundGCShouldWait, "block post-condition");
1927 break;
1928 case Sweeping:
1929 // final marking in checkpointRootsFinal has been completed
1930 sweep();
1931 assert(_collectorState == Resizing, "Collector state change "
1932 "to Resizing must be done under the free_list_lock");
1933
1934 case Resizing: {
1935 // Sweeping has been completed...
1936 // At this point the background collection has completed.
1937 // Don't move the call to compute_new_size() down
1938 // into code that might be executed if the background
1939 // collection was preempted.
1940 {
1941 ReleaseForegroundGC x(this); // unblock FG collection
1942 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1943 CMSTokenSync z(true); // not strictly needed.
1944 if (_collectorState == Resizing) {
1945 compute_new_size();
1946 save_heap_summary();
1947 _collectorState = Resetting;
1948 } else {
1949 assert(_collectorState == Idling, "The state should only change"
1950 " because the foreground collector has finished the collection");
1951 }
1952 }
1953 break;
1954 }
1955 case Resetting:
1956 // CMS heap resizing has been completed
1957 reset(true);
1958 assert(_collectorState == Idling, "Collector state should "
1959 "have changed");
1960
1961 MetaspaceGC::set_should_concurrent_collect(false);
1962
1963 stats().record_cms_end();
1964 // Don't move the concurrent_phases_end() and compute_new_size()
1965 // calls to here because a preempted background collection
1966 // has it's state set to "Resetting".
1967 break;
1968 case Idling:
1969 default:
1970 ShouldNotReachHere();
1971 break;
1972 }
1973 if (TraceCMSState) {
1974 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1975 p2i(Thread::current()), _collectorState);
1976 }
1977 assert(_foregroundGCShouldWait, "block post-condition");
1978 }
1979
1980 // Should this be in gc_epilogue?
1981 collector_policy()->counters()->update_counters();
1982
1983 {
1984 // Clear _foregroundGCShouldWait and, in the event that the
1985 // foreground collector is waiting, notify it, before
1986 // returning.
1987 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1988 _foregroundGCShouldWait = false;
1989 if (_foregroundGCIsActive) {
1990 CGC_lock->notify();
1991 }
1992 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1993 "Possible deadlock");
1994 }
1995 if (TraceCMSState) {
1996 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1997 " exiting collection CMS state %d",
1998 p2i(Thread::current()), _collectorState);
1999 }
2000 if (PrintGC && Verbose) {
2001 _cmsGen->print_heap_change(prev_used);
2002 }
2003 }
2004
2005 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2006 _cms_start_registered = true;
2007 _gc_timer_cm->register_gc_start();
2008 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2009 }
2010
2011 void CMSCollector::register_gc_end() {
2012 if (_cms_start_registered) {
2013 report_heap_summary(GCWhen::AfterGC);
2014
2015 _gc_timer_cm->register_gc_end();
2016 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2017 _cms_start_registered = false;
2018 }
2019 }
2020
2021 void CMSCollector::save_heap_summary() {
2022 GenCollectedHeap* gch = GenCollectedHeap::heap();
2023 _last_heap_summary = gch->create_heap_summary();
2024 _last_metaspace_summary = gch->create_metaspace_summary();
2025 }
2026
2027 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2028 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2029 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2030 }
2031
2032 bool CMSCollector::waitForForegroundGC() {
2033 bool res = false;
2034 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2035 "CMS thread should have CMS token");
2036 // Block the foreground collector until the
2037 // background collectors decides whether to
2038 // yield.
2039 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2040 _foregroundGCShouldWait = true;
2041 if (_foregroundGCIsActive) {
2042 // The background collector yields to the
2043 // foreground collector and returns a value
2044 // indicating that it has yielded. The foreground
2045 // collector can proceed.
2046 res = true;
2047 _foregroundGCShouldWait = false;
2048 ConcurrentMarkSweepThread::clear_CMS_flag(
2049 ConcurrentMarkSweepThread::CMS_cms_has_token);
2050 ConcurrentMarkSweepThread::set_CMS_flag(
2051 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2052 // Get a possibly blocked foreground thread going
2053 CGC_lock->notify();
2054 if (TraceCMSState) {
2055 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2056 p2i(Thread::current()), _collectorState);
2057 }
2058 while (_foregroundGCIsActive) {
2059 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2060 }
2061 ConcurrentMarkSweepThread::set_CMS_flag(
2062 ConcurrentMarkSweepThread::CMS_cms_has_token);
2063 ConcurrentMarkSweepThread::clear_CMS_flag(
2064 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2065 }
2066 if (TraceCMSState) {
2067 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2068 p2i(Thread::current()), _collectorState);
2069 }
2070 return res;
2071 }
2072
2073 // Because of the need to lock the free lists and other structures in
2074 // the collector, common to all the generations that the collector is
2075 // collecting, we need the gc_prologues of individual CMS generations
2076 // delegate to their collector. It may have been simpler had the
2077 // current infrastructure allowed one to call a prologue on a
2078 // collector. In the absence of that we have the generation's
2079 // prologue delegate to the collector, which delegates back
2080 // some "local" work to a worker method in the individual generations
2081 // that it's responsible for collecting, while itself doing any
2082 // work common to all generations it's responsible for. A similar
2083 // comment applies to the gc_epilogue()'s.
2084 // The role of the variable _between_prologue_and_epilogue is to
2085 // enforce the invocation protocol.
2086 void CMSCollector::gc_prologue(bool full) {
2087 // Call gc_prologue_work() for the CMSGen
2088 // we are responsible for.
2089
2090 // The following locking discipline assumes that we are only called
2091 // when the world is stopped.
2092 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2093
2094 // The CMSCollector prologue must call the gc_prologues for the
2095 // "generations" that it's responsible
2096 // for.
2097
2098 assert( Thread::current()->is_VM_thread()
2099 || ( CMSScavengeBeforeRemark
2100 && Thread::current()->is_ConcurrentGC_thread()),
2101 "Incorrect thread type for prologue execution");
2102
2103 if (_between_prologue_and_epilogue) {
2104 // We have already been invoked; this is a gc_prologue delegation
2105 // from yet another CMS generation that we are responsible for, just
2106 // ignore it since all relevant work has already been done.
2107 return;
2108 }
2109
2110 // set a bit saying prologue has been called; cleared in epilogue
2111 _between_prologue_and_epilogue = true;
2112 // Claim locks for common data structures, then call gc_prologue_work()
2113 // for each CMSGen.
2114
2115 getFreelistLocks(); // gets free list locks on constituent spaces
2116 bitMapLock()->lock_without_safepoint_check();
2117
2118 // Should call gc_prologue_work() for all cms gens we are responsible for
2119 bool duringMarking = _collectorState >= Marking
2120 && _collectorState < Sweeping;
2121
2122 // The young collections clear the modified oops state, which tells if
2123 // there are any modified oops in the class. The remark phase also needs
2124 // that information. Tell the young collection to save the union of all
2125 // modified klasses.
2126 if (duringMarking) {
2127 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2128 }
2129
2130 bool registerClosure = duringMarking;
2131
2132 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2133 &_modUnionClosurePar
2134 : &_modUnionClosure;
2135 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2136
2137 if (!full) {
2138 stats().record_gc0_begin();
2139 }
2140 }
2141
2142 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2143
2144 _capacity_at_prologue = capacity();
2145 _used_at_prologue = used();
2146
2147 // Delegate to CMScollector which knows how to coordinate between
2148 // this and any other CMS generations that it is responsible for
2149 // collecting.
2150 collector()->gc_prologue(full);
2151 }
2152
2153 // This is a "private" interface for use by this generation's CMSCollector.
2154 // Not to be called directly by any other entity (for instance,
2155 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2156 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2157 bool registerClosure, ModUnionClosure* modUnionClosure) {
2158 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2159 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2160 "Should be NULL");
2161 if (registerClosure) {
2162 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2163 }
2164 cmsSpace()->gc_prologue();
2165 // Clear stat counters
2166 NOT_PRODUCT(
2167 assert(_numObjectsPromoted == 0, "check");
2168 assert(_numWordsPromoted == 0, "check");
2169 if (Verbose && PrintGC) {
2170 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2171 SIZE_FORMAT" bytes concurrently",
2172 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2173 }
2174 _numObjectsAllocated = 0;
2175 _numWordsAllocated = 0;
2176 )
2177 }
2178
2179 void CMSCollector::gc_epilogue(bool full) {
2180 // The following locking discipline assumes that we are only called
2181 // when the world is stopped.
2182 assert(SafepointSynchronize::is_at_safepoint(),
2183 "world is stopped assumption");
2184
2185 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2186 // if linear allocation blocks need to be appropriately marked to allow the
2187 // the blocks to be parsable. We also check here whether we need to nudge the
2188 // CMS collector thread to start a new cycle (if it's not already active).
2189 assert( Thread::current()->is_VM_thread()
2190 || ( CMSScavengeBeforeRemark
2191 && Thread::current()->is_ConcurrentGC_thread()),
2192 "Incorrect thread type for epilogue execution");
2193
2194 if (!_between_prologue_and_epilogue) {
2195 // We have already been invoked; this is a gc_epilogue delegation
2196 // from yet another CMS generation that we are responsible for, just
2197 // ignore it since all relevant work has already been done.
2198 return;
2199 }
2200 assert(haveFreelistLocks(), "must have freelist locks");
2201 assert_lock_strong(bitMapLock());
2202
2203 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2204
2205 _cmsGen->gc_epilogue_work(full);
2206
2207 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2208 // in case sampling was not already enabled, enable it
2209 _start_sampling = true;
2210 }
2211 // reset _eden_chunk_array so sampling starts afresh
2212 _eden_chunk_index = 0;
2213
2214 size_t cms_used = _cmsGen->cmsSpace()->used();
2215
2216 // update performance counters - this uses a special version of
2217 // update_counters() that allows the utilization to be passed as a
2218 // parameter, avoiding multiple calls to used().
2219 //
2220 _cmsGen->update_counters(cms_used);
2221
2222 bitMapLock()->unlock();
2223 releaseFreelistLocks();
2224
2225 if (!CleanChunkPoolAsync) {
2226 Chunk::clean_chunk_pool();
2227 }
2228
2229 set_did_compact(false);
2230 _between_prologue_and_epilogue = false; // ready for next cycle
2231 }
2232
2233 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2234 collector()->gc_epilogue(full);
2235
2236 // Also reset promotion tracking in par gc thread states.
2237 for (uint i = 0; i < ParallelGCThreads; i++) {
2238 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2239 }
2240 }
2241
2242 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2243 assert(!incremental_collection_failed(), "Should have been cleared");
2244 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2245 cmsSpace()->gc_epilogue();
2246 // Print stat counters
2247 NOT_PRODUCT(
2248 assert(_numObjectsAllocated == 0, "check");
2249 assert(_numWordsAllocated == 0, "check");
2250 if (Verbose && PrintGC) {
2251 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2252 SIZE_FORMAT" bytes",
2253 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2254 }
2255 _numObjectsPromoted = 0;
2256 _numWordsPromoted = 0;
2257 )
2258
2259 if (PrintGC && Verbose) {
2260 // Call down the chain in contiguous_available needs the freelistLock
2261 // so print this out before releasing the freeListLock.
2262 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2263 contiguous_available());
2264 }
2265 }
2266
2267 #ifndef PRODUCT
2268 bool CMSCollector::have_cms_token() {
2269 Thread* thr = Thread::current();
2270 if (thr->is_VM_thread()) {
2271 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2272 } else if (thr->is_ConcurrentGC_thread()) {
2273 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2274 } else if (thr->is_GC_task_thread()) {
2275 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2276 ParGCRareEvent_lock->owned_by_self();
2277 }
2278 return false;
2279 }
2280 #endif
2281
2282 // Check reachability of the given heap address in CMS generation,
2283 // treating all other generations as roots.
2284 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2285 // We could "guarantee" below, rather than assert, but I'll
2286 // leave these as "asserts" so that an adventurous debugger
2287 // could try this in the product build provided some subset of
2288 // the conditions were met, provided they were interested in the
2289 // results and knew that the computation below wouldn't interfere
2290 // with other concurrent computations mutating the structures
2291 // being read or written.
2292 assert(SafepointSynchronize::is_at_safepoint(),
2293 "Else mutations in object graph will make answer suspect");
2294 assert(have_cms_token(), "Should hold cms token");
2295 assert(haveFreelistLocks(), "must hold free list locks");
2296 assert_lock_strong(bitMapLock());
2297
2298 // Clear the marking bit map array before starting, but, just
2299 // for kicks, first report if the given address is already marked
2300 gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2301 _markBitMap.isMarked(addr) ? "" : " not");
2302
2303 if (verify_after_remark()) {
2304 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2305 bool result = verification_mark_bm()->isMarked(addr);
2306 gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2307 result ? "IS" : "is NOT");
2308 return result;
2309 } else {
2310 gclog_or_tty->print_cr("Could not compute result");
2311 return false;
2312 }
2313 }
2314
2315
2316 void
2317 CMSCollector::print_on_error(outputStream* st) {
2318 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2319 if (collector != NULL) {
2320 CMSBitMap* bitmap = &collector->_markBitMap;
2321 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2322 bitmap->print_on_error(st, " Bits: ");
2323
2324 st->cr();
2325
2326 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2327 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2328 mut_bitmap->print_on_error(st, " Bits: ");
2329 }
2330 }
2331
2332 ////////////////////////////////////////////////////////
2333 // CMS Verification Support
2334 ////////////////////////////////////////////////////////
2335 // Following the remark phase, the following invariant
2336 // should hold -- each object in the CMS heap which is
2337 // marked in markBitMap() should be marked in the verification_mark_bm().
2338
2339 class VerifyMarkedClosure: public BitMapClosure {
2340 CMSBitMap* _marks;
2341 bool _failed;
2342
2343 public:
2344 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2345
2346 bool do_bit(size_t offset) {
2347 HeapWord* addr = _marks->offsetToHeapWord(offset);
2348 if (!_marks->isMarked(addr)) {
2349 oop(addr)->print_on(gclog_or_tty);
2350 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", p2i(addr));
2351 _failed = true;
2352 }
2353 return true;
2354 }
2355
2356 bool failed() { return _failed; }
2357 };
2358
2359 bool CMSCollector::verify_after_remark(bool silent) {
2360 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2361 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2362 static bool init = false;
2363
2364 assert(SafepointSynchronize::is_at_safepoint(),
2365 "Else mutations in object graph will make answer suspect");
2366 assert(have_cms_token(),
2367 "Else there may be mutual interference in use of "
2368 " verification data structures");
2369 assert(_collectorState > Marking && _collectorState <= Sweeping,
2370 "Else marking info checked here may be obsolete");
2371 assert(haveFreelistLocks(), "must hold free list locks");
2372 assert_lock_strong(bitMapLock());
2373
2374
2375 // Allocate marking bit map if not already allocated
2376 if (!init) { // first time
2377 if (!verification_mark_bm()->allocate(_span)) {
2378 return false;
2379 }
2380 init = true;
2381 }
2382
2383 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2384
2385 // Turn off refs discovery -- so we will be tracing through refs.
2386 // This is as intended, because by this time
2387 // GC must already have cleared any refs that need to be cleared,
2388 // and traced those that need to be marked; moreover,
2389 // the marking done here is not going to interfere in any
2390 // way with the marking information used by GC.
2391 NoRefDiscovery no_discovery(ref_processor());
2392
2393 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2394
2395 // Clear any marks from a previous round
2396 verification_mark_bm()->clear_all();
2397 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2398 verify_work_stacks_empty();
2399
2400 GenCollectedHeap* gch = GenCollectedHeap::heap();
2401 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2402 // Update the saved marks which may affect the root scans.
2403 gch->save_marks();
2404
2405 if (CMSRemarkVerifyVariant == 1) {
2406 // In this first variant of verification, we complete
2407 // all marking, then check if the new marks-vector is
2408 // a subset of the CMS marks-vector.
2409 verify_after_remark_work_1();
2410 } else if (CMSRemarkVerifyVariant == 2) {
2411 // In this second variant of verification, we flag an error
2412 // (i.e. an object reachable in the new marks-vector not reachable
2413 // in the CMS marks-vector) immediately, also indicating the
2414 // identify of an object (A) that references the unmarked object (B) --
2415 // presumably, a mutation to A failed to be picked up by preclean/remark?
2416 verify_after_remark_work_2();
2417 } else {
2418 warning("Unrecognized value " UINTX_FORMAT " for CMSRemarkVerifyVariant",
2419 CMSRemarkVerifyVariant);
2420 }
2421 if (!silent) gclog_or_tty->print(" done] ");
2422 return true;
2423 }
2424
2425 void CMSCollector::verify_after_remark_work_1() {
2426 ResourceMark rm;
2427 HandleMark hm;
2428 GenCollectedHeap* gch = GenCollectedHeap::heap();
2429
2430 // Get a clear set of claim bits for the roots processing to work with.
2431 ClassLoaderDataGraph::clear_claimed_marks();
2432
2433 // Mark from roots one level into CMS
2434 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2435 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2436
2437 gch->gen_process_roots(_cmsGen->level(),
2438 true, // younger gens are roots
2439 true, // activate StrongRootsScope
2440 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2441 should_unload_classes(),
2442 ¬Older,
2443 NULL,
2444 NULL); // SSS: Provide correct closure
2445
2446 // Now mark from the roots
2447 MarkFromRootsClosure markFromRootsClosure(this, _span,
2448 verification_mark_bm(), verification_mark_stack(),
2449 false /* don't yield */, true /* verifying */);
2450 assert(_restart_addr == NULL, "Expected pre-condition");
2451 verification_mark_bm()->iterate(&markFromRootsClosure);
2452 while (_restart_addr != NULL) {
2453 // Deal with stack overflow: by restarting at the indicated
2454 // address.
2455 HeapWord* ra = _restart_addr;
2456 markFromRootsClosure.reset(ra);
2457 _restart_addr = NULL;
2458 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2459 }
2460 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2461 verify_work_stacks_empty();
2462
2463 // Marking completed -- now verify that each bit marked in
2464 // verification_mark_bm() is also marked in markBitMap(); flag all
2465 // errors by printing corresponding objects.
2466 VerifyMarkedClosure vcl(markBitMap());
2467 verification_mark_bm()->iterate(&vcl);
2468 if (vcl.failed()) {
2469 gclog_or_tty->print("Verification failed");
2470 Universe::heap()->print_on(gclog_or_tty);
2471 fatal("CMS: failed marking verification after remark");
2472 }
2473 }
2474
2475 class VerifyKlassOopsKlassClosure : public KlassClosure {
2476 class VerifyKlassOopsClosure : public OopClosure {
2477 CMSBitMap* _bitmap;
2478 public:
2479 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2480 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2481 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2482 } _oop_closure;
2483 public:
2484 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2485 void do_klass(Klass* k) {
2486 k->oops_do(&_oop_closure);
2487 }
2488 };
2489
2490 void CMSCollector::verify_after_remark_work_2() {
2491 ResourceMark rm;
2492 HandleMark hm;
2493 GenCollectedHeap* gch = GenCollectedHeap::heap();
2494
2495 // Get a clear set of claim bits for the roots processing to work with.
2496 ClassLoaderDataGraph::clear_claimed_marks();
2497
2498 // Mark from roots one level into CMS
2499 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2500 markBitMap());
2501 CLDToOopClosure cld_closure(¬Older, true);
2502
2503 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2504
2505 gch->gen_process_roots(_cmsGen->level(),
2506 true, // younger gens are roots
2507 true, // activate StrongRootsScope
2508 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2509 should_unload_classes(),
2510 ¬Older,
2511 NULL,
2512 &cld_closure);
2513
2514 // Now mark from the roots
2515 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2516 verification_mark_bm(), markBitMap(), verification_mark_stack());
2517 assert(_restart_addr == NULL, "Expected pre-condition");
2518 verification_mark_bm()->iterate(&markFromRootsClosure);
2519 while (_restart_addr != NULL) {
2520 // Deal with stack overflow: by restarting at the indicated
2521 // address.
2522 HeapWord* ra = _restart_addr;
2523 markFromRootsClosure.reset(ra);
2524 _restart_addr = NULL;
2525 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2526 }
2527 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2528 verify_work_stacks_empty();
2529
2530 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2531 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2532
2533 // Marking completed -- now verify that each bit marked in
2534 // verification_mark_bm() is also marked in markBitMap(); flag all
2535 // errors by printing corresponding objects.
2536 VerifyMarkedClosure vcl(markBitMap());
2537 verification_mark_bm()->iterate(&vcl);
2538 assert(!vcl.failed(), "Else verification above should not have succeeded");
2539 }
2540
2541 void ConcurrentMarkSweepGeneration::save_marks() {
2542 // delegate to CMS space
2543 cmsSpace()->save_marks();
2544 for (uint i = 0; i < ParallelGCThreads; i++) {
2545 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2546 }
2547 }
2548
2549 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2550 return cmsSpace()->no_allocs_since_save_marks();
2551 }
2552
2553 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2554 \
2555 void ConcurrentMarkSweepGeneration:: \
2556 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2557 cl->set_generation(this); \
2558 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2559 cl->reset_generation(); \
2560 save_marks(); \
2561 }
2562
2563 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2564
2565 void
2566 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2567 if (freelistLock()->owned_by_self()) {
2568 Generation::oop_iterate(cl);
2569 } else {
2570 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2571 Generation::oop_iterate(cl);
2572 }
2573 }
2574
2575 void
2576 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2577 if (freelistLock()->owned_by_self()) {
2578 Generation::object_iterate(cl);
2579 } else {
2580 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2581 Generation::object_iterate(cl);
2582 }
2583 }
2584
2585 void
2586 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2587 if (freelistLock()->owned_by_self()) {
2588 Generation::safe_object_iterate(cl);
2589 } else {
2590 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2591 Generation::safe_object_iterate(cl);
2592 }
2593 }
2594
2595 void
2596 ConcurrentMarkSweepGeneration::post_compact() {
2597 }
2598
2599 void
2600 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2601 // Fix the linear allocation blocks to look like free blocks.
2602
2603 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2604 // are not called when the heap is verified during universe initialization and
2605 // at vm shutdown.
2606 if (freelistLock()->owned_by_self()) {
2607 cmsSpace()->prepare_for_verify();
2608 } else {
2609 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2610 cmsSpace()->prepare_for_verify();
2611 }
2612 }
2613
2614 void
2615 ConcurrentMarkSweepGeneration::verify() {
2616 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2617 // are not called when the heap is verified during universe initialization and
2618 // at vm shutdown.
2619 if (freelistLock()->owned_by_self()) {
2620 cmsSpace()->verify();
2621 } else {
2622 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2623 cmsSpace()->verify();
2624 }
2625 }
2626
2627 void CMSCollector::verify() {
2628 _cmsGen->verify();
2629 }
2630
2631 #ifndef PRODUCT
2632 bool CMSCollector::overflow_list_is_empty() const {
2633 assert(_num_par_pushes >= 0, "Inconsistency");
2634 if (_overflow_list == NULL) {
2635 assert(_num_par_pushes == 0, "Inconsistency");
2636 }
2637 return _overflow_list == NULL;
2638 }
2639
2640 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2641 // merely consolidate assertion checks that appear to occur together frequently.
2642 void CMSCollector::verify_work_stacks_empty() const {
2643 assert(_markStack.isEmpty(), "Marking stack should be empty");
2644 assert(overflow_list_is_empty(), "Overflow list should be empty");
2645 }
2646
2647 void CMSCollector::verify_overflow_empty() const {
2648 assert(overflow_list_is_empty(), "Overflow list should be empty");
2649 assert(no_preserved_marks(), "No preserved marks");
2650 }
2651 #endif // PRODUCT
2652
2653 // Decide if we want to enable class unloading as part of the
2654 // ensuing concurrent GC cycle. We will collect and
2655 // unload classes if it's the case that:
2656 // (1) an explicit gc request has been made and the flag
2657 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2658 // (2) (a) class unloading is enabled at the command line, and
2659 // (b) old gen is getting really full
2660 // NOTE: Provided there is no change in the state of the heap between
2661 // calls to this method, it should have idempotent results. Moreover,
2662 // its results should be monotonically increasing (i.e. going from 0 to 1,
2663 // but not 1 to 0) between successive calls between which the heap was
2664 // not collected. For the implementation below, it must thus rely on
2665 // the property that concurrent_cycles_since_last_unload()
2666 // will not decrease unless a collection cycle happened and that
2667 // _cmsGen->is_too_full() are
2668 // themselves also monotonic in that sense. See check_monotonicity()
2669 // below.
2670 void CMSCollector::update_should_unload_classes() {
2671 _should_unload_classes = false;
2672 // Condition 1 above
2673 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2674 _should_unload_classes = true;
2675 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2676 // Disjuncts 2.b.(i,ii,iii) above
2677 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2678 CMSClassUnloadingMaxInterval)
2679 || _cmsGen->is_too_full();
2680 }
2681 }
2682
2683 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2684 bool res = should_concurrent_collect();
2685 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2686 return res;
2687 }
2688
2689 void CMSCollector::setup_cms_unloading_and_verification_state() {
2690 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2691 || VerifyBeforeExit;
2692 const int rso = GenCollectedHeap::SO_AllCodeCache;
2693
2694 // We set the proper root for this CMS cycle here.
2695 if (should_unload_classes()) { // Should unload classes this cycle
2696 remove_root_scanning_option(rso); // Shrink the root set appropriately
2697 set_verifying(should_verify); // Set verification state for this cycle
2698 return; // Nothing else needs to be done at this time
2699 }
2700
2701 // Not unloading classes this cycle
2702 assert(!should_unload_classes(), "Inconsistency!");
2703
2704 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2705 // Include symbols, strings and code cache elements to prevent their resurrection.
2706 add_root_scanning_option(rso);
2707 set_verifying(true);
2708 } else if (verifying() && !should_verify) {
2709 // We were verifying, but some verification flags got disabled.
2710 set_verifying(false);
2711 // Exclude symbols, strings and code cache elements from root scanning to
2712 // reduce IM and RM pauses.
2713 remove_root_scanning_option(rso);
2714 }
2715 }
2716
2717
2718 #ifndef PRODUCT
2719 HeapWord* CMSCollector::block_start(const void* p) const {
2720 const HeapWord* addr = (HeapWord*)p;
2721 if (_span.contains(p)) {
2722 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2723 return _cmsGen->cmsSpace()->block_start(p);
2724 }
2725 }
2726 return NULL;
2727 }
2728 #endif
2729
2730 HeapWord*
2731 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2732 bool tlab,
2733 bool parallel) {
2734 CMSSynchronousYieldRequest yr;
2735 assert(!tlab, "Can't deal with TLAB allocation");
2736 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2737 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2738 if (GCExpandToAllocateDelayMillis > 0) {
2739 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2740 }
2741 return have_lock_and_allocate(word_size, tlab);
2742 }
2743
2744 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2745 size_t bytes,
2746 size_t expand_bytes,
2747 CMSExpansionCause::Cause cause)
2748 {
2749
2750 bool success = expand(bytes, expand_bytes);
2751
2752 // remember why we expanded; this information is used
2753 // by shouldConcurrentCollect() when making decisions on whether to start
2754 // a new CMS cycle.
2755 if (success) {
2756 set_expansion_cause(cause);
2757 if (PrintGCDetails && Verbose) {
2758 gclog_or_tty->print_cr("Expanded CMS gen for %s",
2759 CMSExpansionCause::to_string(cause));
2760 }
2761 }
2762 }
2763
2764 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2765 HeapWord* res = NULL;
2766 MutexLocker x(ParGCRareEvent_lock);
2767 while (true) {
2768 // Expansion by some other thread might make alloc OK now:
2769 res = ps->lab.alloc(word_sz);
2770 if (res != NULL) return res;
2771 // If there's not enough expansion space available, give up.
2772 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2773 return NULL;
2774 }
2775 // Otherwise, we try expansion.
2776 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2777 // Now go around the loop and try alloc again;
2778 // A competing par_promote might beat us to the expansion space,
2779 // so we may go around the loop again if promotion fails again.
2780 if (GCExpandToAllocateDelayMillis > 0) {
2781 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2782 }
2783 }
2784 }
2785
2786
2787 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2788 PromotionInfo* promo) {
2789 MutexLocker x(ParGCRareEvent_lock);
2790 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2791 while (true) {
2792 // Expansion by some other thread might make alloc OK now:
2793 if (promo->ensure_spooling_space()) {
2794 assert(promo->has_spooling_space(),
2795 "Post-condition of successful ensure_spooling_space()");
2796 return true;
2797 }
2798 // If there's not enough expansion space available, give up.
2799 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2800 return false;
2801 }
2802 // Otherwise, we try expansion.
2803 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2804 // Now go around the loop and try alloc again;
2805 // A competing allocation might beat us to the expansion space,
2806 // so we may go around the loop again if allocation fails again.
2807 if (GCExpandToAllocateDelayMillis > 0) {
2808 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2809 }
2810 }
2811 }
2812
2813 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2814 // Only shrink if a compaction was done so that all the free space
2815 // in the generation is in a contiguous block at the end.
2816 if (did_compact()) {
2817 CardGeneration::shrink(bytes);
2818 }
2819 }
2820
2821 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2822 assert_locked_or_safepoint(Heap_lock);
2823 }
2824
2825 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2826 assert_locked_or_safepoint(Heap_lock);
2827 assert_lock_strong(freelistLock());
2828 if (PrintGCDetails && Verbose) {
2829 warning("Shrinking of CMS not yet implemented");
2830 }
2831 return;
2832 }
2833
2834
2835 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2836 // phases.
2837 class CMSPhaseAccounting: public StackObj {
2838 public:
2839 CMSPhaseAccounting(CMSCollector *collector,
2840 const char *phase,
2841 const GCId gc_id,
2842 bool print_cr = true);
2843 ~CMSPhaseAccounting();
2844
2845 private:
2846 CMSCollector *_collector;
2847 const char *_phase;
2848 elapsedTimer _wallclock;
2849 bool _print_cr;
2850 const GCId _gc_id;
2851
2852 public:
2853 // Not MT-safe; so do not pass around these StackObj's
2854 // where they may be accessed by other threads.
2855 jlong wallclock_millis() {
2856 assert(_wallclock.is_active(), "Wall clock should not stop");
2857 _wallclock.stop(); // to record time
2858 jlong ret = _wallclock.milliseconds();
2859 _wallclock.start(); // restart
2860 return ret;
2861 }
2862 };
2863
2864 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2865 const char *phase,
2866 const GCId gc_id,
2867 bool print_cr) :
2868 _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
2869
2870 if (PrintCMSStatistics != 0) {
2871 _collector->resetYields();
2872 }
2873 if (PrintGCDetails) {
2874 gclog_or_tty->gclog_stamp(_gc_id);
2875 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
2876 _collector->cmsGen()->short_name(), _phase);
2877 }
2878 _collector->resetTimer();
2879 _wallclock.start();
2880 _collector->startTimer();
2881 }
2882
2883 CMSPhaseAccounting::~CMSPhaseAccounting() {
2884 assert(_wallclock.is_active(), "Wall clock should not have stopped");
2885 _collector->stopTimer();
2886 _wallclock.stop();
2887 if (PrintGCDetails) {
2888 gclog_or_tty->gclog_stamp(_gc_id);
2889 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
2890 _collector->cmsGen()->short_name(),
2891 _phase, _collector->timerValue(), _wallclock.seconds());
2892 if (_print_cr) {
2893 gclog_or_tty->cr();
2894 }
2895 if (PrintCMSStatistics != 0) {
2896 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
2897 _collector->yields());
2898 }
2899 }
2900 }
2901
2902 // CMS work
2903
2904 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2905 class CMSParMarkTask : public AbstractGangTask {
2906 protected:
2907 CMSCollector* _collector;
2908 int _n_workers;
2909 CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
2910 AbstractGangTask(name),
2911 _collector(collector),
2912 _n_workers(n_workers) {}
2913 // Work method in support of parallel rescan ... of young gen spaces
2914 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2915 ContiguousSpace* space,
2916 HeapWord** chunk_array, size_t chunk_top);
2917 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2918 };
2919
2920 // Parallel initial mark task
2921 class CMSParInitialMarkTask: public CMSParMarkTask {
2922 public:
2923 CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
2924 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
2925 collector, n_workers) {}
2926 void work(uint worker_id);
2927 };
2928
2929 // Checkpoint the roots into this generation from outside
2930 // this generation. [Note this initial checkpoint need only
2931 // be approximate -- we'll do a catch up phase subsequently.]
2932 void CMSCollector::checkpointRootsInitial() {
2933 assert(_collectorState == InitialMarking, "Wrong collector state");
2934 check_correct_thread_executing();
2935 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2936
2937 save_heap_summary();
2938 report_heap_summary(GCWhen::BeforeGC);
2939
2940 ReferenceProcessor* rp = ref_processor();
2941 assert(_restart_addr == NULL, "Control point invariant");
2942 {
2943 // acquire locks for subsequent manipulations
2944 MutexLockerEx x(bitMapLock(),
2945 Mutex::_no_safepoint_check_flag);
2946 checkpointRootsInitialWork();
2947 // enable ("weak") refs discovery
2948 rp->enable_discovery();
2949 _collectorState = Marking;
2950 }
2951 }
2952
2953 void CMSCollector::checkpointRootsInitialWork() {
2954 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2955 assert(_collectorState == InitialMarking, "just checking");
2956
2957 // If there has not been a GC[n-1] since last GC[n] cycle completed,
2958 // precede our marking with a collection of all
2959 // younger generations to keep floating garbage to a minimum.
2960 // XXX: we won't do this for now -- it's an optimization to be done later.
2961
2962 // already have locks
2963 assert_lock_strong(bitMapLock());
2964 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2965
2966 // Setup the verification and class unloading state for this
2967 // CMS collection cycle.
2968 setup_cms_unloading_and_verification_state();
2969
2970 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
2971 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
2972
2973 // Reset all the PLAB chunk arrays if necessary.
2974 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2975 reset_survivor_plab_arrays();
2976 }
2977
2978 ResourceMark rm;
2979 HandleMark hm;
2980
2981 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2982 GenCollectedHeap* gch = GenCollectedHeap::heap();
2983
2984 verify_work_stacks_empty();
2985 verify_overflow_empty();
2986
2987 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2988 // Update the saved marks which may affect the root scans.
2989 gch->save_marks();
2990
2991 // weak reference processing has not started yet.
2992 ref_processor()->set_enqueuing_is_done(false);
2993
2994 // Need to remember all newly created CLDs,
2995 // so that we can guarantee that the remark finds them.
2996 ClassLoaderDataGraph::remember_new_clds(true);
2997
2998 // Whenever a CLD is found, it will be claimed before proceeding to mark
2999 // the klasses. The claimed marks need to be cleared before marking starts.
3000 ClassLoaderDataGraph::clear_claimed_marks();
3001
3002 if (CMSPrintEdenSurvivorChunks) {
3003 print_eden_and_survivor_chunk_arrays();
3004 }
3005
3006 {
3007 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3008 if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3009 // The parallel version.
3010 FlexibleWorkGang* workers = gch->workers();
3011 assert(workers != NULL, "Need parallel worker threads.");
3012 int n_workers = workers->active_workers();
3013 CMSParInitialMarkTask tsk(this, n_workers);
3014 gch->set_par_threads(n_workers);
3015 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3016 if (n_workers > 1) {
3017 GenCollectedHeap::StrongRootsScope srs(gch);
3018 workers->run_task(&tsk);
3019 } else {
3020 GenCollectedHeap::StrongRootsScope srs(gch);
3021 tsk.work(0);
3022 }
3023 gch->set_par_threads(0);
3024 } else {
3025 // The serial version.
3026 CLDToOopClosure cld_closure(¬Older, true);
3027 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3028 gch->gen_process_roots(_cmsGen->level(),
3029 true, // younger gens are roots
3030 true, // activate StrongRootsScope
3031 GenCollectedHeap::ScanningOption(roots_scanning_options()),
3032 should_unload_classes(),
3033 ¬Older,
3034 NULL,
3035 &cld_closure);
3036 }
3037 }
3038
3039 // Clear mod-union table; it will be dirtied in the prologue of
3040 // CMS generation per each younger generation collection.
3041
3042 assert(_modUnionTable.isAllClear(),
3043 "Was cleared in most recent final checkpoint phase"
3044 " or no bits are set in the gc_prologue before the start of the next "
3045 "subsequent marking phase.");
3046
3047 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3048
3049 // Save the end of the used_region of the constituent generations
3050 // to be used to limit the extent of sweep in each generation.
3051 save_sweep_limits();
3052 verify_overflow_empty();
3053 }
3054
3055 bool CMSCollector::markFromRoots() {
3056 // we might be tempted to assert that:
3057 // assert(!SafepointSynchronize::is_at_safepoint(),
3058 // "inconsistent argument?");
3059 // However that wouldn't be right, because it's possible that
3060 // a safepoint is indeed in progress as a younger generation
3061 // stop-the-world GC happens even as we mark in this generation.
3062 assert(_collectorState == Marking, "inconsistent state?");
3063 check_correct_thread_executing();
3064 verify_overflow_empty();
3065
3066 // Weak ref discovery note: We may be discovering weak
3067 // refs in this generation concurrent (but interleaved) with
3068 // weak ref discovery by a younger generation collector.
3069
3070 CMSTokenSyncWithLocks ts(true, bitMapLock());
3071 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3072 CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3073 bool res = markFromRootsWork();
3074 if (res) {
3075 _collectorState = Precleaning;
3076 } else { // We failed and a foreground collection wants to take over
3077 assert(_foregroundGCIsActive, "internal state inconsistency");
3078 assert(_restart_addr == NULL, "foreground will restart from scratch");
3079 if (PrintGCDetails) {
3080 gclog_or_tty->print_cr("bailing out to foreground collection");
3081 }
3082 }
3083 verify_overflow_empty();
3084 return res;
3085 }
3086
3087 bool CMSCollector::markFromRootsWork() {
3088 // iterate over marked bits in bit map, doing a full scan and mark
3089 // from these roots using the following algorithm:
3090 // . if oop is to the right of the current scan pointer,
3091 // mark corresponding bit (we'll process it later)
3092 // . else (oop is to left of current scan pointer)
3093 // push oop on marking stack
3094 // . drain the marking stack
3095
3096 // Note that when we do a marking step we need to hold the
3097 // bit map lock -- recall that direct allocation (by mutators)
3098 // and promotion (by younger generation collectors) is also
3099 // marking the bit map. [the so-called allocate live policy.]
3100 // Because the implementation of bit map marking is not
3101 // robust wrt simultaneous marking of bits in the same word,
3102 // we need to make sure that there is no such interference
3103 // between concurrent such updates.
3104
3105 // already have locks
3106 assert_lock_strong(bitMapLock());
3107
3108 verify_work_stacks_empty();
3109 verify_overflow_empty();
3110 bool result = false;
3111 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3112 result = do_marking_mt();
3113 } else {
3114 result = do_marking_st();
3115 }
3116 return result;
3117 }
3118
3119 // Forward decl
3120 class CMSConcMarkingTask;
3121
3122 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3123 CMSCollector* _collector;
3124 CMSConcMarkingTask* _task;
3125 public:
3126 virtual void yield();
3127
3128 // "n_threads" is the number of threads to be terminated.
3129 // "queue_set" is a set of work queues of other threads.
3130 // "collector" is the CMS collector associated with this task terminator.
3131 // "yield" indicates whether we need the gang as a whole to yield.
3132 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3133 ParallelTaskTerminator(n_threads, queue_set),
3134 _collector(collector) { }
3135
3136 void set_task(CMSConcMarkingTask* task) {
3137 _task = task;
3138 }
3139 };
3140
3141 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3142 CMSConcMarkingTask* _task;
3143 public:
3144 bool should_exit_termination();
3145 void set_task(CMSConcMarkingTask* task) {
3146 _task = task;
3147 }
3148 };
3149
3150 // MT Concurrent Marking Task
3151 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3152 CMSCollector* _collector;
3153 int _n_workers; // requested/desired # workers
3154 bool _result;
3155 CompactibleFreeListSpace* _cms_space;
3156 char _pad_front[64]; // padding to ...
3157 HeapWord* _global_finger; // ... avoid sharing cache line
3158 char _pad_back[64];
3159 HeapWord* _restart_addr;
3160
3161 // Exposed here for yielding support
3162 Mutex* const _bit_map_lock;
3163
3164 // The per thread work queues, available here for stealing
3165 OopTaskQueueSet* _task_queues;
3166
3167 // Termination (and yielding) support
3168 CMSConcMarkingTerminator _term;
3169 CMSConcMarkingTerminatorTerminator _term_term;
3170
3171 public:
3172 CMSConcMarkingTask(CMSCollector* collector,
3173 CompactibleFreeListSpace* cms_space,
3174 YieldingFlexibleWorkGang* workers,
3175 OopTaskQueueSet* task_queues):
3176 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3177 _collector(collector),
3178 _cms_space(cms_space),
3179 _n_workers(0), _result(true),
3180 _task_queues(task_queues),
3181 _term(_n_workers, task_queues, _collector),
3182 _bit_map_lock(collector->bitMapLock())
3183 {
3184 _requested_size = _n_workers;
3185 _term.set_task(this);
3186 _term_term.set_task(this);
3187 _restart_addr = _global_finger = _cms_space->bottom();
3188 }
3189
3190
3191 OopTaskQueueSet* task_queues() { return _task_queues; }
3192
3193 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3194
3195 HeapWord** global_finger_addr() { return &_global_finger; }
3196
3197 CMSConcMarkingTerminator* terminator() { return &_term; }
3198
3199 virtual void set_for_termination(int active_workers) {
3200 terminator()->reset_for_reuse(active_workers);
3201 }
3202
3203 void work(uint worker_id);
3204 bool should_yield() {
3205 return ConcurrentMarkSweepThread::should_yield()
3206 && !_collector->foregroundGCIsActive();
3207 }
3208
3209 virtual void coordinator_yield(); // stuff done by coordinator
3210 bool result() { return _result; }
3211
3212 void reset(HeapWord* ra) {
3213 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3214 _restart_addr = _global_finger = ra;
3215 _term.reset_for_reuse();
3216 }
3217
3218 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3219 OopTaskQueue* work_q);
3220
3221 private:
3222 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3223 void do_work_steal(int i);
3224 void bump_global_finger(HeapWord* f);
3225 };
3226
3227 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3228 assert(_task != NULL, "Error");
3229 return _task->yielding();
3230 // Note that we do not need the disjunct || _task->should_yield() above
3231 // because we want terminating threads to yield only if the task
3232 // is already in the midst of yielding, which happens only after at least one
3233 // thread has yielded.
3234 }
3235
3236 void CMSConcMarkingTerminator::yield() {
3237 if (_task->should_yield()) {
3238 _task->yield();
3239 } else {
3240 ParallelTaskTerminator::yield();
3241 }
3242 }
3243
3244 ////////////////////////////////////////////////////////////////
3245 // Concurrent Marking Algorithm Sketch
3246 ////////////////////////////////////////////////////////////////
3247 // Until all tasks exhausted (both spaces):
3248 // -- claim next available chunk
3249 // -- bump global finger via CAS
3250 // -- find first object that starts in this chunk
3251 // and start scanning bitmap from that position
3252 // -- scan marked objects for oops
3253 // -- CAS-mark target, and if successful:
3254 // . if target oop is above global finger (volatile read)
3255 // nothing to do
3256 // . if target oop is in chunk and above local finger
3257 // then nothing to do
3258 // . else push on work-queue
3259 // -- Deal with possible overflow issues:
3260 // . local work-queue overflow causes stuff to be pushed on
3261 // global (common) overflow queue
3262 // . always first empty local work queue
3263 // . then get a batch of oops from global work queue if any
3264 // . then do work stealing
3265 // -- When all tasks claimed (both spaces)
3266 // and local work queue empty,
3267 // then in a loop do:
3268 // . check global overflow stack; steal a batch of oops and trace
3269 // . try to steal from other threads oif GOS is empty
3270 // . if neither is available, offer termination
3271 // -- Terminate and return result
3272 //
3273 void CMSConcMarkingTask::work(uint worker_id) {
3274 elapsedTimer _timer;
3275 ResourceMark rm;
3276 HandleMark hm;
3277
3278 DEBUG_ONLY(_collector->verify_overflow_empty();)
3279
3280 // Before we begin work, our work queue should be empty
3281 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3282 // Scan the bitmap covering _cms_space, tracing through grey objects.
3283 _timer.start();
3284 do_scan_and_mark(worker_id, _cms_space);
3285 _timer.stop();
3286 if (PrintCMSStatistics != 0) {
3287 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3288 worker_id, _timer.seconds());
3289 // XXX: need xxx/xxx type of notation, two timers
3290 }
3291
3292 // ... do work stealing
3293 _timer.reset();
3294 _timer.start();
3295 do_work_steal(worker_id);
3296 _timer.stop();
3297 if (PrintCMSStatistics != 0) {
3298 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3299 worker_id, _timer.seconds());
3300 // XXX: need xxx/xxx type of notation, two timers
3301 }
3302 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3303 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3304 // Note that under the current task protocol, the
3305 // following assertion is true even of the spaces
3306 // expanded since the completion of the concurrent
3307 // marking. XXX This will likely change under a strict
3308 // ABORT semantics.
3309 // After perm removal the comparison was changed to
3310 // greater than or equal to from strictly greater than.
3311 // Before perm removal the highest address sweep would
3312 // have been at the end of perm gen but now is at the
3313 // end of the tenured gen.
3314 assert(_global_finger >= _cms_space->end(),
3315 "All tasks have been completed");
3316 DEBUG_ONLY(_collector->verify_overflow_empty();)
3317 }
3318
3319 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3320 HeapWord* read = _global_finger;
3321 HeapWord* cur = read;
3322 while (f > read) {
3323 cur = read;
3324 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3325 if (cur == read) {
3326 // our cas succeeded
3327 assert(_global_finger >= f, "protocol consistency");
3328 break;
3329 }
3330 }
3331 }
3332
3333 // This is really inefficient, and should be redone by
3334 // using (not yet available) block-read and -write interfaces to the
3335 // stack and the work_queue. XXX FIX ME !!!
3336 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3337 OopTaskQueue* work_q) {
3338 // Fast lock-free check
3339 if (ovflw_stk->length() == 0) {
3340 return false;
3341 }
3342 assert(work_q->size() == 0, "Shouldn't steal");
3343 MutexLockerEx ml(ovflw_stk->par_lock(),
3344 Mutex::_no_safepoint_check_flag);
3345 // Grab up to 1/4 the size of the work queue
3346 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3347 (size_t)ParGCDesiredObjsFromOverflowList);
3348 num = MIN2(num, ovflw_stk->length());
3349 for (int i = (int) num; i > 0; i--) {
3350 oop cur = ovflw_stk->pop();
3351 assert(cur != NULL, "Counted wrong?");
3352 work_q->push(cur);
3353 }
3354 return num > 0;
3355 }
3356
3357 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3358 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3359 int n_tasks = pst->n_tasks();
3360 // We allow that there may be no tasks to do here because
3361 // we are restarting after a stack overflow.
3362 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3363 uint nth_task = 0;
3364
3365 HeapWord* aligned_start = sp->bottom();
3366 if (sp->used_region().contains(_restart_addr)) {
3367 // Align down to a card boundary for the start of 0th task
3368 // for this space.
3369 aligned_start =
3370 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3371 CardTableModRefBS::card_size);
3372 }
3373
3374 size_t chunk_size = sp->marking_task_size();
3375 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3376 // Having claimed the nth task in this space,
3377 // compute the chunk that it corresponds to:
3378 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3379 aligned_start + (nth_task+1)*chunk_size);
3380 // Try and bump the global finger via a CAS;
3381 // note that we need to do the global finger bump
3382 // _before_ taking the intersection below, because
3383 // the task corresponding to that region will be
3384 // deemed done even if the used_region() expands
3385 // because of allocation -- as it almost certainly will
3386 // during start-up while the threads yield in the
3387 // closure below.
3388 HeapWord* finger = span.end();
3389 bump_global_finger(finger); // atomically
3390 // There are null tasks here corresponding to chunks
3391 // beyond the "top" address of the space.
3392 span = span.intersection(sp->used_region());
3393 if (!span.is_empty()) { // Non-null task
3394 HeapWord* prev_obj;
3395 assert(!span.contains(_restart_addr) || nth_task == 0,
3396 "Inconsistency");
3397 if (nth_task == 0) {
3398 // For the 0th task, we'll not need to compute a block_start.
3399 if (span.contains(_restart_addr)) {
3400 // In the case of a restart because of stack overflow,
3401 // we might additionally skip a chunk prefix.
3402 prev_obj = _restart_addr;
3403 } else {
3404 prev_obj = span.start();
3405 }
3406 } else {
3407 // We want to skip the first object because
3408 // the protocol is to scan any object in its entirety
3409 // that _starts_ in this span; a fortiori, any
3410 // object starting in an earlier span is scanned
3411 // as part of an earlier claimed task.
3412 // Below we use the "careful" version of block_start
3413 // so we do not try to navigate uninitialized objects.
3414 prev_obj = sp->block_start_careful(span.start());
3415 // Below we use a variant of block_size that uses the
3416 // Printezis bits to avoid waiting for allocated
3417 // objects to become initialized/parsable.
3418 while (prev_obj < span.start()) {
3419 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3420 if (sz > 0) {
3421 prev_obj += sz;
3422 } else {
3423 // In this case we may end up doing a bit of redundant
3424 // scanning, but that appears unavoidable, short of
3425 // locking the free list locks; see bug 6324141.
3426 break;
3427 }
3428 }
3429 }
3430 if (prev_obj < span.end()) {
3431 MemRegion my_span = MemRegion(prev_obj, span.end());
3432 // Do the marking work within a non-empty span --
3433 // the last argument to the constructor indicates whether the
3434 // iteration should be incremental with periodic yields.
3435 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3436 &_collector->_markBitMap,
3437 work_queue(i),
3438 &_collector->_markStack);
3439 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3440 } // else nothing to do for this task
3441 } // else nothing to do for this task
3442 }
3443 // We'd be tempted to assert here that since there are no
3444 // more tasks left to claim in this space, the global_finger
3445 // must exceed space->top() and a fortiori space->end(). However,
3446 // that would not quite be correct because the bumping of
3447 // global_finger occurs strictly after the claiming of a task,
3448 // so by the time we reach here the global finger may not yet
3449 // have been bumped up by the thread that claimed the last
3450 // task.
3451 pst->all_tasks_completed();
3452 }
3453
3454 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3455 private:
3456 CMSCollector* _collector;
3457 CMSConcMarkingTask* _task;
3458 MemRegion _span;
3459 CMSBitMap* _bit_map;
3460 CMSMarkStack* _overflow_stack;
3461 OopTaskQueue* _work_queue;
3462 protected:
3463 DO_OOP_WORK_DEFN
3464 public:
3465 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3466 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3467 MetadataAwareOopClosure(collector->ref_processor()),
3468 _collector(collector),
3469 _task(task),
3470 _span(collector->_span),
3471 _work_queue(work_queue),
3472 _bit_map(bit_map),
3473 _overflow_stack(overflow_stack)
3474 { }
3475 virtual void do_oop(oop* p);
3476 virtual void do_oop(narrowOop* p);
3477
3478 void trim_queue(size_t max);
3479 void handle_stack_overflow(HeapWord* lost);
3480 void do_yield_check() {
3481 if (_task->should_yield()) {
3482 _task->yield();
3483 }
3484 }
3485 };
3486
3487 // Grey object scanning during work stealing phase --
3488 // the salient assumption here is that any references
3489 // that are in these stolen objects being scanned must
3490 // already have been initialized (else they would not have
3491 // been published), so we do not need to check for
3492 // uninitialized objects before pushing here.
3493 void Par_ConcMarkingClosure::do_oop(oop obj) {
3494 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
3495 HeapWord* addr = (HeapWord*)obj;
3496 // Check if oop points into the CMS generation
3497 // and is not marked
3498 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3499 // a white object ...
3500 // If we manage to "claim" the object, by being the
3501 // first thread to mark it, then we push it on our
3502 // marking stack
3503 if (_bit_map->par_mark(addr)) { // ... now grey
3504 // push on work queue (grey set)
3505 bool simulate_overflow = false;
3506 NOT_PRODUCT(
3507 if (CMSMarkStackOverflowALot &&
3508 _collector->simulate_overflow()) {
3509 // simulate a stack overflow
3510 simulate_overflow = true;
3511 }
3512 )
3513 if (simulate_overflow ||
3514 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3515 // stack overflow
3516 if (PrintCMSStatistics != 0) {
3517 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3518 SIZE_FORMAT, _overflow_stack->capacity());
3519 }
3520 // We cannot assert that the overflow stack is full because
3521 // it may have been emptied since.
3522 assert(simulate_overflow ||
3523 _work_queue->size() == _work_queue->max_elems(),
3524 "Else push should have succeeded");
3525 handle_stack_overflow(addr);
3526 }
3527 } // Else, some other thread got there first
3528 do_yield_check();
3529 }
3530 }
3531
3532 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3533 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3534
3535 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3536 while (_work_queue->size() > max) {
3537 oop new_oop;
3538 if (_work_queue->pop_local(new_oop)) {
3539 assert(new_oop->is_oop(), "Should be an oop");
3540 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3541 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3542 new_oop->oop_iterate(this); // do_oop() above
3543 do_yield_check();
3544 }
3545 }
3546 }
3547
3548 // Upon stack overflow, we discard (part of) the stack,
3549 // remembering the least address amongst those discarded
3550 // in CMSCollector's _restart_address.
3551 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3552 // We need to do this under a mutex to prevent other
3553 // workers from interfering with the work done below.
3554 MutexLockerEx ml(_overflow_stack->par_lock(),
3555 Mutex::_no_safepoint_check_flag);
3556 // Remember the least grey address discarded
3557 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3558 _collector->lower_restart_addr(ra);
3559 _overflow_stack->reset(); // discard stack contents
3560 _overflow_stack->expand(); // expand the stack if possible
3561 }
3562
3563
3564 void CMSConcMarkingTask::do_work_steal(int i) {
3565 OopTaskQueue* work_q = work_queue(i);
3566 oop obj_to_scan;
3567 CMSBitMap* bm = &(_collector->_markBitMap);
3568 CMSMarkStack* ovflw = &(_collector->_markStack);
3569 int* seed = _collector->hash_seed(i);
3570 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3571 while (true) {
3572 cl.trim_queue(0);
3573 assert(work_q->size() == 0, "Should have been emptied above");
3574 if (get_work_from_overflow_stack(ovflw, work_q)) {
3575 // Can't assert below because the work obtained from the
3576 // overflow stack may already have been stolen from us.
3577 // assert(work_q->size() > 0, "Work from overflow stack");
3578 continue;
3579 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3580 assert(obj_to_scan->is_oop(), "Should be an oop");
3581 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3582 obj_to_scan->oop_iterate(&cl);
3583 } else if (terminator()->offer_termination(&_term_term)) {
3584 assert(work_q->size() == 0, "Impossible!");
3585 break;
3586 } else if (yielding() || should_yield()) {
3587 yield();
3588 }
3589 }
3590 }
3591
3592 // This is run by the CMS (coordinator) thread.
3593 void CMSConcMarkingTask::coordinator_yield() {
3594 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3595 "CMS thread should hold CMS token");
3596 // First give up the locks, then yield, then re-lock
3597 // We should probably use a constructor/destructor idiom to
3598 // do this unlock/lock or modify the MutexUnlocker class to
3599 // serve our purpose. XXX
3600 assert_lock_strong(_bit_map_lock);
3601 _bit_map_lock->unlock();
3602 ConcurrentMarkSweepThread::desynchronize(true);
3603 _collector->stopTimer();
3604 if (PrintCMSStatistics != 0) {
3605 _collector->incrementYields();
3606 }
3607
3608 // It is possible for whichever thread initiated the yield request
3609 // not to get a chance to wake up and take the bitmap lock between
3610 // this thread releasing it and reacquiring it. So, while the
3611 // should_yield() flag is on, let's sleep for a bit to give the
3612 // other thread a chance to wake up. The limit imposed on the number
3613 // of iterations is defensive, to avoid any unforseen circumstances
3614 // putting us into an infinite loop. Since it's always been this
3615 // (coordinator_yield()) method that was observed to cause the
3616 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3617 // which is by default non-zero. For the other seven methods that
3618 // also perform the yield operation, as are using a different
3619 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3620 // can enable the sleeping for those methods too, if necessary.
3621 // See 6442774.
3622 //
3623 // We really need to reconsider the synchronization between the GC
3624 // thread and the yield-requesting threads in the future and we
3625 // should really use wait/notify, which is the recommended
3626 // way of doing this type of interaction. Additionally, we should
3627 // consolidate the eight methods that do the yield operation and they
3628 // are almost identical into one for better maintainability and
3629 // readability. See 6445193.
3630 //
3631 // Tony 2006.06.29
3632 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3633 ConcurrentMarkSweepThread::should_yield() &&
3634 !CMSCollector::foregroundGCIsActive(); ++i) {
3635 os::sleep(Thread::current(), 1, false);
3636 }
3637
3638 ConcurrentMarkSweepThread::synchronize(true);
3639 _bit_map_lock->lock_without_safepoint_check();
3640 _collector->startTimer();
3641 }
3642
3643 bool CMSCollector::do_marking_mt() {
3644 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3645 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
3646 conc_workers()->total_workers(),
3647 conc_workers()->active_workers(),
3648 Threads::number_of_non_daemon_threads());
3649 conc_workers()->set_active_workers(num_workers);
3650
3651 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3652
3653 CMSConcMarkingTask tsk(this,
3654 cms_space,
3655 conc_workers(),
3656 task_queues());
3657
3658 // Since the actual number of workers we get may be different
3659 // from the number we requested above, do we need to do anything different
3660 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3661 // class?? XXX
3662 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3663
3664 // Refs discovery is already non-atomic.
3665 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3666 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3667 conc_workers()->start_task(&tsk);
3668 while (tsk.yielded()) {
3669 tsk.coordinator_yield();
3670 conc_workers()->continue_task(&tsk);
3671 }
3672 // If the task was aborted, _restart_addr will be non-NULL
3673 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3674 while (_restart_addr != NULL) {
3675 // XXX For now we do not make use of ABORTED state and have not
3676 // yet implemented the right abort semantics (even in the original
3677 // single-threaded CMS case). That needs some more investigation
3678 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3679 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3680 // If _restart_addr is non-NULL, a marking stack overflow
3681 // occurred; we need to do a fresh marking iteration from the
3682 // indicated restart address.
3683 if (_foregroundGCIsActive) {
3684 // We may be running into repeated stack overflows, having
3685 // reached the limit of the stack size, while making very
3686 // slow forward progress. It may be best to bail out and
3687 // let the foreground collector do its job.
3688 // Clear _restart_addr, so that foreground GC
3689 // works from scratch. This avoids the headache of
3690 // a "rescan" which would otherwise be needed because
3691 // of the dirty mod union table & card table.
3692 _restart_addr = NULL;
3693 return false;
3694 }
3695 // Adjust the task to restart from _restart_addr
3696 tsk.reset(_restart_addr);
3697 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3698 _restart_addr);
3699 _restart_addr = NULL;
3700 // Get the workers going again
3701 conc_workers()->start_task(&tsk);
3702 while (tsk.yielded()) {
3703 tsk.coordinator_yield();
3704 conc_workers()->continue_task(&tsk);
3705 }
3706 }
3707 assert(tsk.completed(), "Inconsistency");
3708 assert(tsk.result() == true, "Inconsistency");
3709 return true;
3710 }
3711
3712 bool CMSCollector::do_marking_st() {
3713 ResourceMark rm;
3714 HandleMark hm;
3715
3716 // Temporarily make refs discovery single threaded (non-MT)
3717 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3718 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3719 &_markStack, CMSYield);
3720 // the last argument to iterate indicates whether the iteration
3721 // should be incremental with periodic yields.
3722 _markBitMap.iterate(&markFromRootsClosure);
3723 // If _restart_addr is non-NULL, a marking stack overflow
3724 // occurred; we need to do a fresh iteration from the
3725 // indicated restart address.
3726 while (_restart_addr != NULL) {
3727 if (_foregroundGCIsActive) {
3728 // We may be running into repeated stack overflows, having
3729 // reached the limit of the stack size, while making very
3730 // slow forward progress. It may be best to bail out and
3731 // let the foreground collector do its job.
3732 // Clear _restart_addr, so that foreground GC
3733 // works from scratch. This avoids the headache of
3734 // a "rescan" which would otherwise be needed because
3735 // of the dirty mod union table & card table.
3736 _restart_addr = NULL;
3737 return false; // indicating failure to complete marking
3738 }
3739 // Deal with stack overflow:
3740 // we restart marking from _restart_addr
3741 HeapWord* ra = _restart_addr;
3742 markFromRootsClosure.reset(ra);
3743 _restart_addr = NULL;
3744 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3745 }
3746 return true;
3747 }
3748
3749 void CMSCollector::preclean() {
3750 check_correct_thread_executing();
3751 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3752 verify_work_stacks_empty();
3753 verify_overflow_empty();
3754 _abort_preclean = false;
3755 if (CMSPrecleaningEnabled) {
3756 if (!CMSEdenChunksRecordAlways) {
3757 _eden_chunk_index = 0;
3758 }
3759 size_t used = get_eden_used();
3760 size_t capacity = get_eden_capacity();
3761 // Don't start sampling unless we will get sufficiently
3762 // many samples.
3763 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3764 * CMSScheduleRemarkEdenPenetration)) {
3765 _start_sampling = true;
3766 } else {
3767 _start_sampling = false;
3768 }
3769 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3770 CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3771 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3772 }
3773 CMSTokenSync x(true); // is cms thread
3774 if (CMSPrecleaningEnabled) {
3775 sample_eden();
3776 _collectorState = AbortablePreclean;
3777 } else {
3778 _collectorState = FinalMarking;
3779 }
3780 verify_work_stacks_empty();
3781 verify_overflow_empty();
3782 }
3783
3784 // Try and schedule the remark such that young gen
3785 // occupancy is CMSScheduleRemarkEdenPenetration %.
3786 void CMSCollector::abortable_preclean() {
3787 check_correct_thread_executing();
3788 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3789 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3790
3791 // If Eden's current occupancy is below this threshold,
3792 // immediately schedule the remark; else preclean
3793 // past the next scavenge in an effort to
3794 // schedule the pause as described above. By choosing
3795 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3796 // we will never do an actual abortable preclean cycle.
3797 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3798 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3799 CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3800 // We need more smarts in the abortable preclean
3801 // loop below to deal with cases where allocation
3802 // in young gen is very very slow, and our precleaning
3803 // is running a losing race against a horde of
3804 // mutators intent on flooding us with CMS updates
3805 // (dirty cards).
3806 // One, admittedly dumb, strategy is to give up
3807 // after a certain number of abortable precleaning loops
3808 // or after a certain maximum time. We want to make
3809 // this smarter in the next iteration.
3810 // XXX FIX ME!!! YSR
3811 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3812 while (!(should_abort_preclean() ||
3813 ConcurrentMarkSweepThread::should_terminate())) {
3814 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3815 cumworkdone += workdone;
3816 loops++;
3817 // Voluntarily terminate abortable preclean phase if we have
3818 // been at it for too long.
3819 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3820 loops >= CMSMaxAbortablePrecleanLoops) {
3821 if (PrintGCDetails) {
3822 gclog_or_tty->print(" CMS: abort preclean due to loops ");
3823 }
3824 break;
3825 }
3826 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3827 if (PrintGCDetails) {
3828 gclog_or_tty->print(" CMS: abort preclean due to time ");
3829 }
3830 break;
3831 }
3832 // If we are doing little work each iteration, we should
3833 // take a short break.
3834 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3835 // Sleep for some time, waiting for work to accumulate
3836 stopTimer();
3837 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3838 startTimer();
3839 waited++;
3840 }
3841 }
3842 if (PrintCMSStatistics > 0) {
3843 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3844 loops, waited, cumworkdone);
3845 }
3846 }
3847 CMSTokenSync x(true); // is cms thread
3848 if (_collectorState != Idling) {
3849 assert(_collectorState == AbortablePreclean,
3850 "Spontaneous state transition?");
3851 _collectorState = FinalMarking;
3852 } // Else, a foreground collection completed this CMS cycle.
3853 return;
3854 }
3855
3856 // Respond to an Eden sampling opportunity
3857 void CMSCollector::sample_eden() {
3858 // Make sure a young gc cannot sneak in between our
3859 // reading and recording of a sample.
3860 assert(Thread::current()->is_ConcurrentGC_thread(),
3861 "Only the cms thread may collect Eden samples");
3862 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3863 "Should collect samples while holding CMS token");
3864 if (!_start_sampling) {
3865 return;
3866 }
3867 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3868 // is populated by the young generation.
3869 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3870 if (_eden_chunk_index < _eden_chunk_capacity) {
3871 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3872 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3873 "Unexpected state of Eden");
3874 // We'd like to check that what we just sampled is an oop-start address;
3875 // however, we cannot do that here since the object may not yet have been
3876 // initialized. So we'll instead do the check when we _use_ this sample
3877 // later.
3878 if (_eden_chunk_index == 0 ||
3879 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3880 _eden_chunk_array[_eden_chunk_index-1])
3881 >= CMSSamplingGrain)) {
3882 _eden_chunk_index++; // commit sample
3883 }
3884 }
3885 }
3886 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3887 size_t used = get_eden_used();
3888 size_t capacity = get_eden_capacity();
3889 assert(used <= capacity, "Unexpected state of Eden");
3890 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3891 _abort_preclean = true;
3892 }
3893 }
3894 }
3895
3896
3897 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3898 assert(_collectorState == Precleaning ||
3899 _collectorState == AbortablePreclean, "incorrect state");
3900 ResourceMark rm;
3901 HandleMark hm;
3902
3903 // Precleaning is currently not MT but the reference processor
3904 // may be set for MT. Disable it temporarily here.
3905 ReferenceProcessor* rp = ref_processor();
3906 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3907
3908 // Do one pass of scrubbing the discovered reference lists
3909 // to remove any reference objects with strongly-reachable
3910 // referents.
3911 if (clean_refs) {
3912 CMSPrecleanRefsYieldClosure yield_cl(this);
3913 assert(rp->span().equals(_span), "Spans should be equal");
3914 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3915 &_markStack, true /* preclean */);
3916 CMSDrainMarkingStackClosure complete_trace(this,
3917 _span, &_markBitMap, &_markStack,
3918 &keep_alive, true /* preclean */);
3919
3920 // We don't want this step to interfere with a young
3921 // collection because we don't want to take CPU
3922 // or memory bandwidth away from the young GC threads
3923 // (which may be as many as there are CPUs).
3924 // Note that we don't need to protect ourselves from
3925 // interference with mutators because they can't
3926 // manipulate the discovered reference lists nor affect
3927 // the computed reachability of the referents, the
3928 // only properties manipulated by the precleaning
3929 // of these reference lists.
3930 stopTimer();
3931 CMSTokenSyncWithLocks x(true /* is cms thread */,
3932 bitMapLock());
3933 startTimer();
3934 sample_eden();
3935
3936 // The following will yield to allow foreground
3937 // collection to proceed promptly. XXX YSR:
3938 // The code in this method may need further
3939 // tweaking for better performance and some restructuring
3940 // for cleaner interfaces.
3941 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3942 rp->preclean_discovered_references(
3943 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3944 gc_timer, _gc_tracer_cm->gc_id());
3945 }
3946
3947 if (clean_survivor) { // preclean the active survivor space(s)
3948 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3949 &_markBitMap, &_modUnionTable,
3950 &_markStack, true /* precleaning phase */);
3951 stopTimer();
3952 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3953 bitMapLock());
3954 startTimer();
3955 unsigned int before_count =
3956 GenCollectedHeap::heap()->total_collections();
3957 SurvivorSpacePrecleanClosure
3958 sss_cl(this, _span, &_markBitMap, &_markStack,
3959 &pam_cl, before_count, CMSYield);
3960 _young_gen->from()->object_iterate_careful(&sss_cl);
3961 _young_gen->to()->object_iterate_careful(&sss_cl);
3962 }
3963 MarkRefsIntoAndScanClosure
3964 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3965 &_markStack, this, CMSYield,
3966 true /* precleaning phase */);
3967 // CAUTION: The following closure has persistent state that may need to
3968 // be reset upon a decrease in the sequence of addresses it
3969 // processes.
3970 ScanMarkedObjectsAgainCarefullyClosure
3971 smoac_cl(this, _span,
3972 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3973
3974 // Preclean dirty cards in ModUnionTable and CardTable using
3975 // appropriate convergence criterion;
3976 // repeat CMSPrecleanIter times unless we find that
3977 // we are losing.
3978 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3979 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3980 "Bad convergence multiplier");
3981 assert(CMSPrecleanThreshold >= 100,
3982 "Unreasonably low CMSPrecleanThreshold");
3983
3984 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3985 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3986 numIter < CMSPrecleanIter;
3987 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3988 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3989 if (Verbose && PrintGCDetails) {
3990 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3991 }
3992 // Either there are very few dirty cards, so re-mark
3993 // pause will be small anyway, or our pre-cleaning isn't
3994 // that much faster than the rate at which cards are being
3995 // dirtied, so we might as well stop and re-mark since
3996 // precleaning won't improve our re-mark time by much.
3997 if (curNumCards <= CMSPrecleanThreshold ||
3998 (numIter > 0 &&
3999 (curNumCards * CMSPrecleanDenominator >
4000 lastNumCards * CMSPrecleanNumerator))) {
4001 numIter++;
4002 cumNumCards += curNumCards;
4003 break;
4004 }
4005 }
4006
4007 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4008
4009 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4010 cumNumCards += curNumCards;
4011 if (PrintGCDetails && PrintCMSStatistics != 0) {
4012 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4013 curNumCards, cumNumCards, numIter);
4014 }
4015 return cumNumCards; // as a measure of useful work done
4016 }
4017
4018 // PRECLEANING NOTES:
4019 // Precleaning involves:
4020 // . reading the bits of the modUnionTable and clearing the set bits.
4021 // . For the cards corresponding to the set bits, we scan the
4022 // objects on those cards. This means we need the free_list_lock
4023 // so that we can safely iterate over the CMS space when scanning
4024 // for oops.
4025 // . When we scan the objects, we'll be both reading and setting
4026 // marks in the marking bit map, so we'll need the marking bit map.
4027 // . For protecting _collector_state transitions, we take the CGC_lock.
4028 // Note that any races in the reading of of card table entries by the
4029 // CMS thread on the one hand and the clearing of those entries by the
4030 // VM thread or the setting of those entries by the mutator threads on the
4031 // other are quite benign. However, for efficiency it makes sense to keep
4032 // the VM thread from racing with the CMS thread while the latter is
4033 // dirty card info to the modUnionTable. We therefore also use the
4034 // CGC_lock to protect the reading of the card table and the mod union
4035 // table by the CM thread.
4036 // . We run concurrently with mutator updates, so scanning
4037 // needs to be done carefully -- we should not try to scan
4038 // potentially uninitialized objects.
4039 //
4040 // Locking strategy: While holding the CGC_lock, we scan over and
4041 // reset a maximal dirty range of the mod union / card tables, then lock
4042 // the free_list_lock and bitmap lock to do a full marking, then
4043 // release these locks; and repeat the cycle. This allows for a
4044 // certain amount of fairness in the sharing of these locks between
4045 // the CMS collector on the one hand, and the VM thread and the
4046 // mutators on the other.
4047
4048 // NOTE: preclean_mod_union_table() and preclean_card_table()
4049 // further below are largely identical; if you need to modify
4050 // one of these methods, please check the other method too.
4051
4052 size_t CMSCollector::preclean_mod_union_table(
4053 ConcurrentMarkSweepGeneration* gen,
4054 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4055 verify_work_stacks_empty();
4056 verify_overflow_empty();
4057
4058 // strategy: starting with the first card, accumulate contiguous
4059 // ranges of dirty cards; clear these cards, then scan the region
4060 // covered by these cards.
4061
4062 // Since all of the MUT is committed ahead, we can just use
4063 // that, in case the generations expand while we are precleaning.
4064 // It might also be fine to just use the committed part of the
4065 // generation, but we might potentially miss cards when the
4066 // generation is rapidly expanding while we are in the midst
4067 // of precleaning.
4068 HeapWord* startAddr = gen->reserved().start();
4069 HeapWord* endAddr = gen->reserved().end();
4070
4071 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4072
4073 size_t numDirtyCards, cumNumDirtyCards;
4074 HeapWord *nextAddr, *lastAddr;
4075 for (cumNumDirtyCards = numDirtyCards = 0,
4076 nextAddr = lastAddr = startAddr;
4077 nextAddr < endAddr;
4078 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4079
4080 ResourceMark rm;
4081 HandleMark hm;
4082
4083 MemRegion dirtyRegion;
4084 {
4085 stopTimer();
4086 // Potential yield point
4087 CMSTokenSync ts(true);
4088 startTimer();
4089 sample_eden();
4090 // Get dirty region starting at nextOffset (inclusive),
4091 // simultaneously clearing it.
4092 dirtyRegion =
4093 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4094 assert(dirtyRegion.start() >= nextAddr,
4095 "returned region inconsistent?");
4096 }
4097 // Remember where the next search should begin.
4098 // The returned region (if non-empty) is a right open interval,
4099 // so lastOffset is obtained from the right end of that
4100 // interval.
4101 lastAddr = dirtyRegion.end();
4102 // Should do something more transparent and less hacky XXX
4103 numDirtyCards =
4104 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4105
4106 // We'll scan the cards in the dirty region (with periodic
4107 // yields for foreground GC as needed).
4108 if (!dirtyRegion.is_empty()) {
4109 assert(numDirtyCards > 0, "consistency check");
4110 HeapWord* stop_point = NULL;
4111 stopTimer();
4112 // Potential yield point
4113 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4114 bitMapLock());
4115 startTimer();
4116 {
4117 verify_work_stacks_empty();
4118 verify_overflow_empty();
4119 sample_eden();
4120 stop_point =
4121 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4122 }
4123 if (stop_point != NULL) {
4124 // The careful iteration stopped early either because it found an
4125 // uninitialized object, or because we were in the midst of an
4126 // "abortable preclean", which should now be aborted. Redirty
4127 // the bits corresponding to the partially-scanned or unscanned
4128 // cards. We'll either restart at the next block boundary or
4129 // abort the preclean.
4130 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4131 "Should only be AbortablePreclean.");
4132 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4133 if (should_abort_preclean()) {
4134 break; // out of preclean loop
4135 } else {
4136 // Compute the next address at which preclean should pick up;
4137 // might need bitMapLock in order to read P-bits.
4138 lastAddr = next_card_start_after_block(stop_point);
4139 }
4140 }
4141 } else {
4142 assert(lastAddr == endAddr, "consistency check");
4143 assert(numDirtyCards == 0, "consistency check");
4144 break;
4145 }
4146 }
4147 verify_work_stacks_empty();
4148 verify_overflow_empty();
4149 return cumNumDirtyCards;
4150 }
4151
4152 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4153 // below are largely identical; if you need to modify
4154 // one of these methods, please check the other method too.
4155
4156 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4157 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4158 // strategy: it's similar to precleamModUnionTable above, in that
4159 // we accumulate contiguous ranges of dirty cards, mark these cards
4160 // precleaned, then scan the region covered by these cards.
4161 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4162 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4163
4164 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4165
4166 size_t numDirtyCards, cumNumDirtyCards;
4167 HeapWord *lastAddr, *nextAddr;
4168
4169 for (cumNumDirtyCards = numDirtyCards = 0,
4170 nextAddr = lastAddr = startAddr;
4171 nextAddr < endAddr;
4172 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4173
4174 ResourceMark rm;
4175 HandleMark hm;
4176
4177 MemRegion dirtyRegion;
4178 {
4179 // See comments in "Precleaning notes" above on why we
4180 // do this locking. XXX Could the locking overheads be
4181 // too high when dirty cards are sparse? [I don't think so.]
4182 stopTimer();
4183 CMSTokenSync x(true); // is cms thread
4184 startTimer();
4185 sample_eden();
4186 // Get and clear dirty region from card table
4187 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4188 MemRegion(nextAddr, endAddr),
4189 true,
4190 CardTableModRefBS::precleaned_card_val());
4191
4192 assert(dirtyRegion.start() >= nextAddr,
4193 "returned region inconsistent?");
4194 }
4195 lastAddr = dirtyRegion.end();
4196 numDirtyCards =
4197 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4198
4199 if (!dirtyRegion.is_empty()) {
4200 stopTimer();
4201 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4202 startTimer();
4203 sample_eden();
4204 verify_work_stacks_empty();
4205 verify_overflow_empty();
4206 HeapWord* stop_point =
4207 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4208 if (stop_point != NULL) {
4209 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4210 "Should only be AbortablePreclean.");
4211 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4212 if (should_abort_preclean()) {
4213 break; // out of preclean loop
4214 } else {
4215 // Compute the next address at which preclean should pick up.
4216 lastAddr = next_card_start_after_block(stop_point);
4217 }
4218 }
4219 } else {
4220 break;
4221 }
4222 }
4223 verify_work_stacks_empty();
4224 verify_overflow_empty();
4225 return cumNumDirtyCards;
4226 }
4227
4228 class PrecleanKlassClosure : public KlassClosure {
4229 KlassToOopClosure _cm_klass_closure;
4230 public:
4231 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4232 void do_klass(Klass* k) {
4233 if (k->has_accumulated_modified_oops()) {
4234 k->clear_accumulated_modified_oops();
4235
4236 _cm_klass_closure.do_klass(k);
4237 }
4238 }
4239 };
4240
4241 // The freelist lock is needed to prevent asserts, is it really needed?
4242 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4243
4244 cl->set_freelistLock(freelistLock);
4245
4246 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4247
4248 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4249 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4250 PrecleanKlassClosure preclean_klass_closure(cl);
4251 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4252
4253 verify_work_stacks_empty();
4254 verify_overflow_empty();
4255 }
4256
4257 void CMSCollector::checkpointRootsFinal() {
4258 assert(_collectorState == FinalMarking, "incorrect state transition?");
4259 check_correct_thread_executing();
4260 // world is stopped at this checkpoint
4261 assert(SafepointSynchronize::is_at_safepoint(),
4262 "world should be stopped");
4263 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4264
4265 verify_work_stacks_empty();
4266 verify_overflow_empty();
4267
4268 if (PrintGCDetails) {
4269 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4270 _young_gen->used() / K,
4271 _young_gen->capacity() / K);
4272 }
4273 {
4274 if (CMSScavengeBeforeRemark) {
4275 GenCollectedHeap* gch = GenCollectedHeap::heap();
4276 // Temporarily set flag to false, GCH->do_collection will
4277 // expect it to be false and set to true
4278 FlagSetting fl(gch->_is_gc_active, false);
4279 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4280 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4281 int level = _cmsGen->level() - 1;
4282 if (level >= 0) {
4283 gch->do_collection(true, // full (i.e. force, see below)
4284 false, // !clear_all_soft_refs
4285 0, // size
4286 false, // is_tlab
4287 level // max_level
4288 );
4289 }
4290 }
4291 FreelistLocker x(this);
4292 MutexLockerEx y(bitMapLock(),
4293 Mutex::_no_safepoint_check_flag);
4294 checkpointRootsFinalWork();
4295 }
4296 verify_work_stacks_empty();
4297 verify_overflow_empty();
4298 }
4299
4300 void CMSCollector::checkpointRootsFinalWork() {
4301 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4302
4303 assert(haveFreelistLocks(), "must have free list locks");
4304 assert_lock_strong(bitMapLock());
4305
4306 ResourceMark rm;
4307 HandleMark hm;
4308
4309 GenCollectedHeap* gch = GenCollectedHeap::heap();
4310
4311 if (should_unload_classes()) {
4312 CodeCache::gc_prologue();
4313 }
4314 assert(haveFreelistLocks(), "must have free list locks");
4315 assert_lock_strong(bitMapLock());
4316
4317 // We might assume that we need not fill TLAB's when
4318 // CMSScavengeBeforeRemark is set, because we may have just done
4319 // a scavenge which would have filled all TLAB's -- and besides
4320 // Eden would be empty. This however may not always be the case --
4321 // for instance although we asked for a scavenge, it may not have
4322 // happened because of a JNI critical section. We probably need
4323 // a policy for deciding whether we can in that case wait until
4324 // the critical section releases and then do the remark following
4325 // the scavenge, and skip it here. In the absence of that policy,
4326 // or of an indication of whether the scavenge did indeed occur,
4327 // we cannot rely on TLAB's having been filled and must do
4328 // so here just in case a scavenge did not happen.
4329 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4330 // Update the saved marks which may affect the root scans.
4331 gch->save_marks();
4332
4333 if (CMSPrintEdenSurvivorChunks) {
4334 print_eden_and_survivor_chunk_arrays();
4335 }
4336
4337 {
4338 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4339
4340 // Note on the role of the mod union table:
4341 // Since the marker in "markFromRoots" marks concurrently with
4342 // mutators, it is possible for some reachable objects not to have been
4343 // scanned. For instance, an only reference to an object A was
4344 // placed in object B after the marker scanned B. Unless B is rescanned,
4345 // A would be collected. Such updates to references in marked objects
4346 // are detected via the mod union table which is the set of all cards
4347 // dirtied since the first checkpoint in this GC cycle and prior to
4348 // the most recent young generation GC, minus those cleaned up by the
4349 // concurrent precleaning.
4350 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
4351 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
4352 do_remark_parallel();
4353 } else {
4354 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4355 _gc_timer_cm, _gc_tracer_cm->gc_id());
4356 do_remark_non_parallel();
4357 }
4358 }
4359 verify_work_stacks_empty();
4360 verify_overflow_empty();
4361
4362 {
4363 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4364 refProcessingWork();
4365 }
4366 verify_work_stacks_empty();
4367 verify_overflow_empty();
4368
4369 if (should_unload_classes()) {
4370 CodeCache::gc_epilogue();
4371 }
4372 JvmtiExport::gc_epilogue();
4373
4374 // If we encountered any (marking stack / work queue) overflow
4375 // events during the current CMS cycle, take appropriate
4376 // remedial measures, where possible, so as to try and avoid
4377 // recurrence of that condition.
4378 assert(_markStack.isEmpty(), "No grey objects");
4379 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4380 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4381 if (ser_ovflw > 0) {
4382 if (PrintCMSStatistics != 0) {
4383 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4384 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4385 ", kac_preclean="SIZE_FORMAT")",
4386 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4387 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4388 }
4389 _markStack.expand();
4390 _ser_pmc_remark_ovflw = 0;
4391 _ser_pmc_preclean_ovflw = 0;
4392 _ser_kac_preclean_ovflw = 0;
4393 _ser_kac_ovflw = 0;
4394 }
4395 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4396 if (PrintCMSStatistics != 0) {
4397 gclog_or_tty->print_cr("Work queue overflow (benign) "
4398 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4399 _par_pmc_remark_ovflw, _par_kac_ovflw);
4400 }
4401 _par_pmc_remark_ovflw = 0;
4402 _par_kac_ovflw = 0;
4403 }
4404 if (PrintCMSStatistics != 0) {
4405 if (_markStack._hit_limit > 0) {
4406 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4407 _markStack._hit_limit);
4408 }
4409 if (_markStack._failed_double > 0) {
4410 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4411 " current capacity "SIZE_FORMAT,
4412 _markStack._failed_double,
4413 _markStack.capacity());
4414 }
4415 }
4416 _markStack._hit_limit = 0;
4417 _markStack._failed_double = 0;
4418
4419 if ((VerifyAfterGC || VerifyDuringGC) &&
4420 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4421 verify_after_remark();
4422 }
4423
4424 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4425
4426 // Change under the freelistLocks.
4427 _collectorState = Sweeping;
4428 // Call isAllClear() under bitMapLock
4429 assert(_modUnionTable.isAllClear(),
4430 "Should be clear by end of the final marking");
4431 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4432 "Should be clear by end of the final marking");
4433 }
4434
4435 void CMSParInitialMarkTask::work(uint worker_id) {
4436 elapsedTimer _timer;
4437 ResourceMark rm;
4438 HandleMark hm;
4439
4440 // ---------- scan from roots --------------
4441 _timer.start();
4442 GenCollectedHeap* gch = GenCollectedHeap::heap();
4443 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4444
4445 // ---------- young gen roots --------------
4446 {
4447 work_on_young_gen_roots(worker_id, &par_mri_cl);
4448 _timer.stop();
4449 if (PrintCMSStatistics != 0) {
4450 gclog_or_tty->print_cr(
4451 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4452 worker_id, _timer.seconds());
4453 }
4454 }
4455
4456 // ---------- remaining roots --------------
4457 _timer.reset();
4458 _timer.start();
4459
4460 CLDToOopClosure cld_closure(&par_mri_cl, true);
4461
4462 gch->gen_process_roots(_collector->_cmsGen->level(),
4463 false, // yg was scanned above
4464 false, // this is parallel code
4465 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4466 _collector->should_unload_classes(),
4467 &par_mri_cl,
4468 NULL,
4469 &cld_closure);
4470 assert(_collector->should_unload_classes()
4471 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4472 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4473 _timer.stop();
4474 if (PrintCMSStatistics != 0) {
4475 gclog_or_tty->print_cr(
4476 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4477 worker_id, _timer.seconds());
4478 }
4479 }
4480
4481 // Parallel remark task
4482 class CMSParRemarkTask: public CMSParMarkTask {
4483 CompactibleFreeListSpace* _cms_space;
4484
4485 // The per-thread work queues, available here for stealing.
4486 OopTaskQueueSet* _task_queues;
4487 ParallelTaskTerminator _term;
4488
4489 public:
4490 // A value of 0 passed to n_workers will cause the number of
4491 // workers to be taken from the active workers in the work gang.
4492 CMSParRemarkTask(CMSCollector* collector,
4493 CompactibleFreeListSpace* cms_space,
4494 int n_workers, FlexibleWorkGang* workers,
4495 OopTaskQueueSet* task_queues):
4496 CMSParMarkTask("Rescan roots and grey objects in parallel",
4497 collector, n_workers),
4498 _cms_space(cms_space),
4499 _task_queues(task_queues),
4500 _term(n_workers, task_queues) { }
4501
4502 OopTaskQueueSet* task_queues() { return _task_queues; }
4503
4504 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4505
4506 ParallelTaskTerminator* terminator() { return &_term; }
4507 int n_workers() { return _n_workers; }
4508
4509 void work(uint worker_id);
4510
4511 private:
4512 // ... of dirty cards in old space
4513 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4514 Par_MarkRefsIntoAndScanClosure* cl);
4515
4516 // ... work stealing for the above
4517 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4518 };
4519
4520 class RemarkKlassClosure : public KlassClosure {
4521 KlassToOopClosure _cm_klass_closure;
4522 public:
4523 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4524 void do_klass(Klass* k) {
4525 // Check if we have modified any oops in the Klass during the concurrent marking.
4526 if (k->has_accumulated_modified_oops()) {
4527 k->clear_accumulated_modified_oops();
4528
4529 // We could have transfered the current modified marks to the accumulated marks,
4530 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4531 } else if (k->has_modified_oops()) {
4532 // Don't clear anything, this info is needed by the next young collection.
4533 } else {
4534 // No modified oops in the Klass.
4535 return;
4536 }
4537
4538 // The klass has modified fields, need to scan the klass.
4539 _cm_klass_closure.do_klass(k);
4540 }
4541 };
4542
4543 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4544 ParNewGeneration* young_gen = _collector->_young_gen;
4545 ContiguousSpace* eden_space = young_gen->eden();
4546 ContiguousSpace* from_space = young_gen->from();
4547 ContiguousSpace* to_space = young_gen->to();
4548
4549 HeapWord** eca = _collector->_eden_chunk_array;
4550 size_t ect = _collector->_eden_chunk_index;
4551 HeapWord** sca = _collector->_survivor_chunk_array;
4552 size_t sct = _collector->_survivor_chunk_index;
4553
4554 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4555 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4556
4557 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4558 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4559 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4560 }
4561
4562 // work_queue(i) is passed to the closure
4563 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
4564 // also is passed to do_dirty_card_rescan_tasks() and to
4565 // do_work_steal() to select the i-th task_queue.
4566
4567 void CMSParRemarkTask::work(uint worker_id) {
4568 elapsedTimer _timer;
4569 ResourceMark rm;
4570 HandleMark hm;
4571
4572 // ---------- rescan from roots --------------
4573 _timer.start();
4574 GenCollectedHeap* gch = GenCollectedHeap::heap();
4575 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4576 _collector->_span, _collector->ref_processor(),
4577 &(_collector->_markBitMap),
4578 work_queue(worker_id));
4579
4580 // Rescan young gen roots first since these are likely
4581 // coarsely partitioned and may, on that account, constitute
4582 // the critical path; thus, it's best to start off that
4583 // work first.
4584 // ---------- young gen roots --------------
4585 {
4586 work_on_young_gen_roots(worker_id, &par_mrias_cl);
4587 _timer.stop();
4588 if (PrintCMSStatistics != 0) {
4589 gclog_or_tty->print_cr(
4590 "Finished young gen rescan work in %dth thread: %3.3f sec",
4591 worker_id, _timer.seconds());
4592 }
4593 }
4594
4595 // ---------- remaining roots --------------
4596 _timer.reset();
4597 _timer.start();
4598 gch->gen_process_roots(_collector->_cmsGen->level(),
4599 false, // yg was scanned above
4600 false, // this is parallel code
4601 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4602 _collector->should_unload_classes(),
4603 &par_mrias_cl,
4604 NULL,
4605 NULL); // The dirty klasses will be handled below
4606
4607 assert(_collector->should_unload_classes()
4608 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4609 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4610 _timer.stop();
4611 if (PrintCMSStatistics != 0) {
4612 gclog_or_tty->print_cr(
4613 "Finished remaining root rescan work in %dth thread: %3.3f sec",
4614 worker_id, _timer.seconds());
4615 }
4616
4617 // ---------- unhandled CLD scanning ----------
4618 if (worker_id == 0) { // Single threaded at the moment.
4619 _timer.reset();
4620 _timer.start();
4621
4622 // Scan all new class loader data objects and new dependencies that were
4623 // introduced during concurrent marking.
4624 ResourceMark rm;
4625 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4626 for (int i = 0; i < array->length(); i++) {
4627 par_mrias_cl.do_class_loader_data(array->at(i));
4628 }
4629
4630 // We don't need to keep track of new CLDs anymore.
4631 ClassLoaderDataGraph::remember_new_clds(false);
4632
4633 _timer.stop();
4634 if (PrintCMSStatistics != 0) {
4635 gclog_or_tty->print_cr(
4636 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4637 worker_id, _timer.seconds());
4638 }
4639 }
4640
4641 // ---------- dirty klass scanning ----------
4642 if (worker_id == 0) { // Single threaded at the moment.
4643 _timer.reset();
4644 _timer.start();
4645
4646 // Scan all classes that was dirtied during the concurrent marking phase.
4647 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4648 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4649
4650 _timer.stop();
4651 if (PrintCMSStatistics != 0) {
4652 gclog_or_tty->print_cr(
4653 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4654 worker_id, _timer.seconds());
4655 }
4656 }
4657
4658 // We might have added oops to ClassLoaderData::_handles during the
4659 // concurrent marking phase. These oops point to newly allocated objects
4660 // that are guaranteed to be kept alive. Either by the direct allocation
4661 // code, or when the young collector processes the roots. Hence,
4662 // we don't have to revisit the _handles block during the remark phase.
4663
4664 // ---------- rescan dirty cards ------------
4665 _timer.reset();
4666 _timer.start();
4667
4668 // Do the rescan tasks for each of the two spaces
4669 // (cms_space) in turn.
4670 // "worker_id" is passed to select the task_queue for "worker_id"
4671 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4672 _timer.stop();
4673 if (PrintCMSStatistics != 0) {
4674 gclog_or_tty->print_cr(
4675 "Finished dirty card rescan work in %dth thread: %3.3f sec",
4676 worker_id, _timer.seconds());
4677 }
4678
4679 // ---------- steal work from other threads ...
4680 // ---------- ... and drain overflow list.
4681 _timer.reset();
4682 _timer.start();
4683 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4684 _timer.stop();
4685 if (PrintCMSStatistics != 0) {
4686 gclog_or_tty->print_cr(
4687 "Finished work stealing in %dth thread: %3.3f sec",
4688 worker_id, _timer.seconds());
4689 }
4690 }
4691
4692 // Note that parameter "i" is not used.
4693 void
4694 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4695 OopsInGenClosure* cl, ContiguousSpace* space,
4696 HeapWord** chunk_array, size_t chunk_top) {
4697 // Until all tasks completed:
4698 // . claim an unclaimed task
4699 // . compute region boundaries corresponding to task claimed
4700 // using chunk_array
4701 // . par_oop_iterate(cl) over that region
4702
4703 ResourceMark rm;
4704 HandleMark hm;
4705
4706 SequentialSubTasksDone* pst = space->par_seq_tasks();
4707
4708 uint nth_task = 0;
4709 uint n_tasks = pst->n_tasks();
4710
4711 if (n_tasks > 0) {
4712 assert(pst->valid(), "Uninitialized use?");
4713 HeapWord *start, *end;
4714 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4715 // We claimed task # nth_task; compute its boundaries.
4716 if (chunk_top == 0) { // no samples were taken
4717 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4718 start = space->bottom();
4719 end = space->top();
4720 } else if (nth_task == 0) {
4721 start = space->bottom();
4722 end = chunk_array[nth_task];
4723 } else if (nth_task < (uint)chunk_top) {
4724 assert(nth_task >= 1, "Control point invariant");
4725 start = chunk_array[nth_task - 1];
4726 end = chunk_array[nth_task];
4727 } else {
4728 assert(nth_task == (uint)chunk_top, "Control point invariant");
4729 start = chunk_array[chunk_top - 1];
4730 end = space->top();
4731 }
4732 MemRegion mr(start, end);
4733 // Verify that mr is in space
4734 assert(mr.is_empty() || space->used_region().contains(mr),
4735 "Should be in space");
4736 // Verify that "start" is an object boundary
4737 assert(mr.is_empty() || oop(mr.start())->is_oop(),
4738 "Should be an oop");
4739 space->par_oop_iterate(mr, cl);
4740 }
4741 pst->all_tasks_completed();
4742 }
4743 }
4744
4745 void
4746 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4747 CompactibleFreeListSpace* sp, int i,
4748 Par_MarkRefsIntoAndScanClosure* cl) {
4749 // Until all tasks completed:
4750 // . claim an unclaimed task
4751 // . compute region boundaries corresponding to task claimed
4752 // . transfer dirty bits ct->mut for that region
4753 // . apply rescanclosure to dirty mut bits for that region
4754
4755 ResourceMark rm;
4756 HandleMark hm;
4757
4758 OopTaskQueue* work_q = work_queue(i);
4759 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4760 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4761 // CAUTION: This closure has state that persists across calls to
4762 // the work method dirty_range_iterate_clear() in that it has
4763 // embedded in it a (subtype of) UpwardsObjectClosure. The
4764 // use of that state in the embedded UpwardsObjectClosure instance
4765 // assumes that the cards are always iterated (even if in parallel
4766 // by several threads) in monotonically increasing order per each
4767 // thread. This is true of the implementation below which picks
4768 // card ranges (chunks) in monotonically increasing order globally
4769 // and, a-fortiori, in monotonically increasing order per thread
4770 // (the latter order being a subsequence of the former).
4771 // If the work code below is ever reorganized into a more chaotic
4772 // work-partitioning form than the current "sequential tasks"
4773 // paradigm, the use of that persistent state will have to be
4774 // revisited and modified appropriately. See also related
4775 // bug 4756801 work on which should examine this code to make
4776 // sure that the changes there do not run counter to the
4777 // assumptions made here and necessary for correctness and
4778 // efficiency. Note also that this code might yield inefficient
4779 // behavior in the case of very large objects that span one or
4780 // more work chunks. Such objects would potentially be scanned
4781 // several times redundantly. Work on 4756801 should try and
4782 // address that performance anomaly if at all possible. XXX
4783 MemRegion full_span = _collector->_span;
4784 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4785 MarkFromDirtyCardsClosure
4786 greyRescanClosure(_collector, full_span, // entire span of interest
4787 sp, bm, work_q, cl);
4788
4789 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4790 assert(pst->valid(), "Uninitialized use?");
4791 uint nth_task = 0;
4792 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4793 MemRegion span = sp->used_region();
4794 HeapWord* start_addr = span.start();
4795 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4796 alignment);
4797 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4798 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4799 start_addr, "Check alignment");
4800 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4801 chunk_size, "Check alignment");
4802
4803 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4804 // Having claimed the nth_task, compute corresponding mem-region,
4805 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4806 // The alignment restriction ensures that we do not need any
4807 // synchronization with other gang-workers while setting or
4808 // clearing bits in thus chunk of the MUT.
4809 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4810 start_addr + (nth_task+1)*chunk_size);
4811 // The last chunk's end might be way beyond end of the
4812 // used region. In that case pull back appropriately.
4813 if (this_span.end() > end_addr) {
4814 this_span.set_end(end_addr);
4815 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4816 }
4817 // Iterate over the dirty cards covering this chunk, marking them
4818 // precleaned, and setting the corresponding bits in the mod union
4819 // table. Since we have been careful to partition at Card and MUT-word
4820 // boundaries no synchronization is needed between parallel threads.
4821 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4822 &modUnionClosure);
4823
4824 // Having transferred these marks into the modUnionTable,
4825 // rescan the marked objects on the dirty cards in the modUnionTable.
4826 // Even if this is at a synchronous collection, the initial marking
4827 // may have been done during an asynchronous collection so there
4828 // may be dirty bits in the mod-union table.
4829 _collector->_modUnionTable.dirty_range_iterate_clear(
4830 this_span, &greyRescanClosure);
4831 _collector->_modUnionTable.verifyNoOneBitsInRange(
4832 this_span.start(),
4833 this_span.end());
4834 }
4835 pst->all_tasks_completed(); // declare that i am done
4836 }
4837
4838 // . see if we can share work_queues with ParNew? XXX
4839 void
4840 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4841 int* seed) {
4842 OopTaskQueue* work_q = work_queue(i);
4843 NOT_PRODUCT(int num_steals = 0;)
4844 oop obj_to_scan;
4845 CMSBitMap* bm = &(_collector->_markBitMap);
4846
4847 while (true) {
4848 // Completely finish any left over work from (an) earlier round(s)
4849 cl->trim_queue(0);
4850 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4851 (size_t)ParGCDesiredObjsFromOverflowList);
4852 // Now check if there's any work in the overflow list
4853 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4854 // only affects the number of attempts made to get work from the
4855 // overflow list and does not affect the number of workers. Just
4856 // pass ParallelGCThreads so this behavior is unchanged.
4857 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4858 work_q,
4859 ParallelGCThreads)) {
4860 // found something in global overflow list;
4861 // not yet ready to go stealing work from others.
4862 // We'd like to assert(work_q->size() != 0, ...)
4863 // because we just took work from the overflow list,
4864 // but of course we can't since all of that could have
4865 // been already stolen from us.
4866 // "He giveth and He taketh away."
4867 continue;
4868 }
4869 // Verify that we have no work before we resort to stealing
4870 assert(work_q->size() == 0, "Have work, shouldn't steal");
4871 // Try to steal from other queues that have work
4872 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4873 NOT_PRODUCT(num_steals++;)
4874 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4875 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4876 // Do scanning work
4877 obj_to_scan->oop_iterate(cl);
4878 // Loop around, finish this work, and try to steal some more
4879 } else if (terminator()->offer_termination()) {
4880 break; // nirvana from the infinite cycle
4881 }
4882 }
4883 NOT_PRODUCT(
4884 if (PrintCMSStatistics != 0) {
4885 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
4886 }
4887 )
4888 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4889 "Else our work is not yet done");
4890 }
4891
4892 // Record object boundaries in _eden_chunk_array by sampling the eden
4893 // top in the slow-path eden object allocation code path and record
4894 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4895 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4896 // sampling in sample_eden() that activates during the part of the
4897 // preclean phase.
4898 void CMSCollector::sample_eden_chunk() {
4899 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4900 if (_eden_chunk_lock->try_lock()) {
4901 // Record a sample. This is the critical section. The contents
4902 // of the _eden_chunk_array have to be non-decreasing in the
4903 // address order.
4904 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4905 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4906 "Unexpected state of Eden");
4907 if (_eden_chunk_index == 0 ||
4908 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4909 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4910 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4911 _eden_chunk_index++; // commit sample
4912 }
4913 _eden_chunk_lock->unlock();
4914 }
4915 }
4916 }
4917
4918 // Return a thread-local PLAB recording array, as appropriate.
4919 void* CMSCollector::get_data_recorder(int thr_num) {
4920 if (_survivor_plab_array != NULL &&
4921 (CMSPLABRecordAlways ||
4922 (_collectorState > Marking && _collectorState < FinalMarking))) {
4923 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4924 ChunkArray* ca = &_survivor_plab_array[thr_num];
4925 ca->reset(); // clear it so that fresh data is recorded
4926 return (void*) ca;
4927 } else {
4928 return NULL;
4929 }
4930 }
4931
4932 // Reset all the thread-local PLAB recording arrays
4933 void CMSCollector::reset_survivor_plab_arrays() {
4934 for (uint i = 0; i < ParallelGCThreads; i++) {
4935 _survivor_plab_array[i].reset();
4936 }
4937 }
4938
4939 // Merge the per-thread plab arrays into the global survivor chunk
4940 // array which will provide the partitioning of the survivor space
4941 // for CMS initial scan and rescan.
4942 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4943 int no_of_gc_threads) {
4944 assert(_survivor_plab_array != NULL, "Error");
4945 assert(_survivor_chunk_array != NULL, "Error");
4946 assert(_collectorState == FinalMarking ||
4947 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4948 for (int j = 0; j < no_of_gc_threads; j++) {
4949 _cursor[j] = 0;
4950 }
4951 HeapWord* top = surv->top();
4952 size_t i;
4953 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4954 HeapWord* min_val = top; // Higher than any PLAB address
4955 uint min_tid = 0; // position of min_val this round
4956 for (int j = 0; j < no_of_gc_threads; j++) {
4957 ChunkArray* cur_sca = &_survivor_plab_array[j];
4958 if (_cursor[j] == cur_sca->end()) {
4959 continue;
4960 }
4961 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4962 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4963 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4964 if (cur_val < min_val) {
4965 min_tid = j;
4966 min_val = cur_val;
4967 } else {
4968 assert(cur_val < top, "All recorded addresses should be less");
4969 }
4970 }
4971 // At this point min_val and min_tid are respectively
4972 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4973 // and the thread (j) that witnesses that address.
4974 // We record this address in the _survivor_chunk_array[i]
4975 // and increment _cursor[min_tid] prior to the next round i.
4976 if (min_val == top) {
4977 break;
4978 }
4979 _survivor_chunk_array[i] = min_val;
4980 _cursor[min_tid]++;
4981 }
4982 // We are all done; record the size of the _survivor_chunk_array
4983 _survivor_chunk_index = i; // exclusive: [0, i)
4984 if (PrintCMSStatistics > 0) {
4985 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4986 }
4987 // Verify that we used up all the recorded entries
4988 #ifdef ASSERT
4989 size_t total = 0;
4990 for (int j = 0; j < no_of_gc_threads; j++) {
4991 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4992 total += _cursor[j];
4993 }
4994 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4995 // Check that the merged array is in sorted order
4996 if (total > 0) {
4997 for (size_t i = 0; i < total - 1; i++) {
4998 if (PrintCMSStatistics > 0) {
4999 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5000 i, p2i(_survivor_chunk_array[i]));
5001 }
5002 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5003 "Not sorted");
5004 }
5005 }
5006 #endif // ASSERT
5007 }
5008
5009 // Set up the space's par_seq_tasks structure for work claiming
5010 // for parallel initial scan and rescan of young gen.
5011 // See ParRescanTask where this is currently used.
5012 void
5013 CMSCollector::
5014 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5015 assert(n_threads > 0, "Unexpected n_threads argument");
5016
5017 // Eden space
5018 if (!_young_gen->eden()->is_empty()) {
5019 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
5020 assert(!pst->valid(), "Clobbering existing data?");
5021 // Each valid entry in [0, _eden_chunk_index) represents a task.
5022 size_t n_tasks = _eden_chunk_index + 1;
5023 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5024 // Sets the condition for completion of the subtask (how many threads
5025 // need to finish in order to be done).
5026 pst->set_n_threads(n_threads);
5027 pst->set_n_tasks((int)n_tasks);
5028 }
5029
5030 // Merge the survivor plab arrays into _survivor_chunk_array
5031 if (_survivor_plab_array != NULL) {
5032 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5033 } else {
5034 assert(_survivor_chunk_index == 0, "Error");
5035 }
5036
5037 // To space
5038 {
5039 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5040 assert(!pst->valid(), "Clobbering existing data?");
5041 // Sets the condition for completion of the subtask (how many threads
5042 // need to finish in order to be done).
5043 pst->set_n_threads(n_threads);
5044 pst->set_n_tasks(1);
5045 assert(pst->valid(), "Error");
5046 }
5047
5048 // From space
5049 {
5050 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5051 assert(!pst->valid(), "Clobbering existing data?");
5052 size_t n_tasks = _survivor_chunk_index + 1;
5053 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5054 // Sets the condition for completion of the subtask (how many threads
5055 // need to finish in order to be done).
5056 pst->set_n_threads(n_threads);
5057 pst->set_n_tasks((int)n_tasks);
5058 assert(pst->valid(), "Error");
5059 }
5060 }
5061
5062 // Parallel version of remark
5063 void CMSCollector::do_remark_parallel() {
5064 GenCollectedHeap* gch = GenCollectedHeap::heap();
5065 FlexibleWorkGang* workers = gch->workers();
5066 assert(workers != NULL, "Need parallel worker threads.");
5067 // Choose to use the number of GC workers most recently set
5068 // into "active_workers". If active_workers is not set, set it
5069 // to ParallelGCThreads.
5070 int n_workers = workers->active_workers();
5071 if (n_workers == 0) {
5072 assert(n_workers > 0, "Should have been set during scavenge");
5073 n_workers = ParallelGCThreads;
5074 workers->set_active_workers(n_workers);
5075 }
5076 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5077
5078 CMSParRemarkTask tsk(this,
5079 cms_space,
5080 n_workers, workers, task_queues());
5081
5082 // Set up for parallel process_roots work.
5083 gch->set_par_threads(n_workers);
5084 // We won't be iterating over the cards in the card table updating
5085 // the younger_gen cards, so we shouldn't call the following else
5086 // the verification code as well as subsequent younger_refs_iterate
5087 // code would get confused. XXX
5088 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5089
5090 // The young gen rescan work will not be done as part of
5091 // process_roots (which currently doesn't know how to
5092 // parallelize such a scan), but rather will be broken up into
5093 // a set of parallel tasks (via the sampling that the [abortable]
5094 // preclean phase did of eden, plus the [two] tasks of
5095 // scanning the [two] survivor spaces. Further fine-grain
5096 // parallelization of the scanning of the survivor spaces
5097 // themselves, and of precleaning of the younger gen itself
5098 // is deferred to the future.
5099 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5100
5101 // The dirty card rescan work is broken up into a "sequence"
5102 // of parallel tasks (per constituent space) that are dynamically
5103 // claimed by the parallel threads.
5104 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5105
5106 // It turns out that even when we're using 1 thread, doing the work in a
5107 // separate thread causes wide variance in run times. We can't help this
5108 // in the multi-threaded case, but we special-case n=1 here to get
5109 // repeatable measurements of the 1-thread overhead of the parallel code.
5110 if (n_workers > 1) {
5111 // Make refs discovery MT-safe, if it isn't already: it may not
5112 // necessarily be so, since it's possible that we are doing
5113 // ST marking.
5114 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5115 GenCollectedHeap::StrongRootsScope srs(gch);
5116 workers->run_task(&tsk);
5117 } else {
5118 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5119 GenCollectedHeap::StrongRootsScope srs(gch);
5120 tsk.work(0);
5121 }
5122
5123 gch->set_par_threads(0); // 0 ==> non-parallel.
5124 // restore, single-threaded for now, any preserved marks
5125 // as a result of work_q overflow
5126 restore_preserved_marks_if_any();
5127 }
5128
5129 // Non-parallel version of remark
5130 void CMSCollector::do_remark_non_parallel() {
5131 ResourceMark rm;
5132 HandleMark hm;
5133 GenCollectedHeap* gch = GenCollectedHeap::heap();
5134 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5135
5136 MarkRefsIntoAndScanClosure
5137 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5138 &_markStack, this,
5139 false /* should_yield */, false /* not precleaning */);
5140 MarkFromDirtyCardsClosure
5141 markFromDirtyCardsClosure(this, _span,
5142 NULL, // space is set further below
5143 &_markBitMap, &_markStack, &mrias_cl);
5144 {
5145 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5146 // Iterate over the dirty cards, setting the corresponding bits in the
5147 // mod union table.
5148 {
5149 ModUnionClosure modUnionClosure(&_modUnionTable);
5150 _ct->ct_bs()->dirty_card_iterate(
5151 _cmsGen->used_region(),
5152 &modUnionClosure);
5153 }
5154 // Having transferred these marks into the modUnionTable, we just need
5155 // to rescan the marked objects on the dirty cards in the modUnionTable.
5156 // The initial marking may have been done during an asynchronous
5157 // collection so there may be dirty bits in the mod-union table.
5158 const int alignment =
5159 CardTableModRefBS::card_size * BitsPerWord;
5160 {
5161 // ... First handle dirty cards in CMS gen
5162 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5163 MemRegion ur = _cmsGen->used_region();
5164 HeapWord* lb = ur.start();
5165 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5166 MemRegion cms_span(lb, ub);
5167 _modUnionTable.dirty_range_iterate_clear(cms_span,
5168 &markFromDirtyCardsClosure);
5169 verify_work_stacks_empty();
5170 if (PrintCMSStatistics != 0) {
5171 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5172 markFromDirtyCardsClosure.num_dirty_cards());
5173 }
5174 }
5175 }
5176 if (VerifyDuringGC &&
5177 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5178 HandleMark hm; // Discard invalid handles created during verification
5179 Universe::verify();
5180 }
5181 {
5182 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5183
5184 verify_work_stacks_empty();
5185
5186 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5187 GenCollectedHeap::StrongRootsScope srs(gch);
5188
5189 gch->gen_process_roots(_cmsGen->level(),
5190 true, // younger gens as roots
5191 false, // use the local StrongRootsScope
5192 GenCollectedHeap::ScanningOption(roots_scanning_options()),
5193 should_unload_classes(),
5194 &mrias_cl,
5195 NULL,
5196 NULL); // The dirty klasses will be handled below
5197
5198 assert(should_unload_classes()
5199 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5200 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5201 }
5202
5203 {
5204 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5205
5206 verify_work_stacks_empty();
5207
5208 // Scan all class loader data objects that might have been introduced
5209 // during concurrent marking.
5210 ResourceMark rm;
5211 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5212 for (int i = 0; i < array->length(); i++) {
5213 mrias_cl.do_class_loader_data(array->at(i));
5214 }
5215
5216 // We don't need to keep track of new CLDs anymore.
5217 ClassLoaderDataGraph::remember_new_clds(false);
5218
5219 verify_work_stacks_empty();
5220 }
5221
5222 {
5223 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5224
5225 verify_work_stacks_empty();
5226
5227 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5228 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5229
5230 verify_work_stacks_empty();
5231 }
5232
5233 // We might have added oops to ClassLoaderData::_handles during the
5234 // concurrent marking phase. These oops point to newly allocated objects
5235 // that are guaranteed to be kept alive. Either by the direct allocation
5236 // code, or when the young collector processes the roots. Hence,
5237 // we don't have to revisit the _handles block during the remark phase.
5238
5239 verify_work_stacks_empty();
5240 // Restore evacuated mark words, if any, used for overflow list links
5241 if (!CMSOverflowEarlyRestoration) {
5242 restore_preserved_marks_if_any();
5243 }
5244 verify_overflow_empty();
5245 }
5246
5247 ////////////////////////////////////////////////////////
5248 // Parallel Reference Processing Task Proxy Class
5249 ////////////////////////////////////////////////////////
5250 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5251 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5252 CMSCollector* _collector;
5253 CMSBitMap* _mark_bit_map;
5254 const MemRegion _span;
5255 ProcessTask& _task;
5256
5257 public:
5258 CMSRefProcTaskProxy(ProcessTask& task,
5259 CMSCollector* collector,
5260 const MemRegion& span,
5261 CMSBitMap* mark_bit_map,
5262 AbstractWorkGang* workers,
5263 OopTaskQueueSet* task_queues):
5264 // XXX Should superclass AGTWOQ also know about AWG since it knows
5265 // about the task_queues used by the AWG? Then it could initialize
5266 // the terminator() object. See 6984287. The set_for_termination()
5267 // below is a temporary band-aid for the regression in 6984287.
5268 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5269 task_queues),
5270 _task(task),
5271 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5272 {
5273 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5274 "Inconsistency in _span");
5275 set_for_termination(workers->active_workers());
5276 }
5277
5278 OopTaskQueueSet* task_queues() { return queues(); }
5279
5280 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5281
5282 void do_work_steal(int i,
5283 CMSParDrainMarkingStackClosure* drain,
5284 CMSParKeepAliveClosure* keep_alive,
5285 int* seed);
5286
5287 virtual void work(uint worker_id);
5288 };
5289
5290 void CMSRefProcTaskProxy::work(uint worker_id) {
5291 ResourceMark rm;
5292 HandleMark hm;
5293 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5294 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5295 _mark_bit_map,
5296 work_queue(worker_id));
5297 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5298 _mark_bit_map,
5299 work_queue(worker_id));
5300 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5301 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5302 if (_task.marks_oops_alive()) {
5303 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5304 _collector->hash_seed(worker_id));
5305 }
5306 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5307 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5308 }
5309
5310 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5311 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5312 EnqueueTask& _task;
5313
5314 public:
5315 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5316 : AbstractGangTask("Enqueue reference objects in parallel"),
5317 _task(task)
5318 { }
5319
5320 virtual void work(uint worker_id)
5321 {
5322 _task.work(worker_id);
5323 }
5324 };
5325
5326 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5327 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5328 _span(span),
5329 _bit_map(bit_map),
5330 _work_queue(work_queue),
5331 _mark_and_push(collector, span, bit_map, work_queue),
5332 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5333 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5334 { }
5335
5336 // . see if we can share work_queues with ParNew? XXX
5337 void CMSRefProcTaskProxy::do_work_steal(int i,
5338 CMSParDrainMarkingStackClosure* drain,
5339 CMSParKeepAliveClosure* keep_alive,
5340 int* seed) {
5341 OopTaskQueue* work_q = work_queue(i);
5342 NOT_PRODUCT(int num_steals = 0;)
5343 oop obj_to_scan;
5344
5345 while (true) {
5346 // Completely finish any left over work from (an) earlier round(s)
5347 drain->trim_queue(0);
5348 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5349 (size_t)ParGCDesiredObjsFromOverflowList);
5350 // Now check if there's any work in the overflow list
5351 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5352 // only affects the number of attempts made to get work from the
5353 // overflow list and does not affect the number of workers. Just
5354 // pass ParallelGCThreads so this behavior is unchanged.
5355 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5356 work_q,
5357 ParallelGCThreads)) {
5358 // Found something in global overflow list;
5359 // not yet ready to go stealing work from others.
5360 // We'd like to assert(work_q->size() != 0, ...)
5361 // because we just took work from the overflow list,
5362 // but of course we can't, since all of that might have
5363 // been already stolen from us.
5364 continue;
5365 }
5366 // Verify that we have no work before we resort to stealing
5367 assert(work_q->size() == 0, "Have work, shouldn't steal");
5368 // Try to steal from other queues that have work
5369 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5370 NOT_PRODUCT(num_steals++;)
5371 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5372 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5373 // Do scanning work
5374 obj_to_scan->oop_iterate(keep_alive);
5375 // Loop around, finish this work, and try to steal some more
5376 } else if (terminator()->offer_termination()) {
5377 break; // nirvana from the infinite cycle
5378 }
5379 }
5380 NOT_PRODUCT(
5381 if (PrintCMSStatistics != 0) {
5382 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5383 }
5384 )
5385 }
5386
5387 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5388 {
5389 GenCollectedHeap* gch = GenCollectedHeap::heap();
5390 FlexibleWorkGang* workers = gch->workers();
5391 assert(workers != NULL, "Need parallel worker threads.");
5392 CMSRefProcTaskProxy rp_task(task, &_collector,
5393 _collector.ref_processor()->span(),
5394 _collector.markBitMap(),
5395 workers, _collector.task_queues());
5396 workers->run_task(&rp_task);
5397 }
5398
5399 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5400 {
5401
5402 GenCollectedHeap* gch = GenCollectedHeap::heap();
5403 FlexibleWorkGang* workers = gch->workers();
5404 assert(workers != NULL, "Need parallel worker threads.");
5405 CMSRefEnqueueTaskProxy enq_task(task);
5406 workers->run_task(&enq_task);
5407 }
5408
5409 void CMSCollector::refProcessingWork() {
5410 ResourceMark rm;
5411 HandleMark hm;
5412
5413 ReferenceProcessor* rp = ref_processor();
5414 assert(rp->span().equals(_span), "Spans should be equal");
5415 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5416 // Process weak references.
5417 rp->setup_policy(false);
5418 verify_work_stacks_empty();
5419
5420 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5421 &_markStack, false /* !preclean */);
5422 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5423 _span, &_markBitMap, &_markStack,
5424 &cmsKeepAliveClosure, false /* !preclean */);
5425 {
5426 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5427
5428 ReferenceProcessorStats stats;
5429 if (rp->processing_is_mt()) {
5430 // Set the degree of MT here. If the discovery is done MT, there
5431 // may have been a different number of threads doing the discovery
5432 // and a different number of discovered lists may have Ref objects.
5433 // That is OK as long as the Reference lists are balanced (see
5434 // balance_all_queues() and balance_queues()).
5435 GenCollectedHeap* gch = GenCollectedHeap::heap();
5436 int active_workers = ParallelGCThreads;
5437 FlexibleWorkGang* workers = gch->workers();
5438 if (workers != NULL) {
5439 active_workers = workers->active_workers();
5440 // The expectation is that active_workers will have already
5441 // been set to a reasonable value. If it has not been set,
5442 // investigate.
5443 assert(active_workers > 0, "Should have been set during scavenge");
5444 }
5445 rp->set_active_mt_degree(active_workers);
5446 CMSRefProcTaskExecutor task_executor(*this);
5447 stats = rp->process_discovered_references(&_is_alive_closure,
5448 &cmsKeepAliveClosure,
5449 &cmsDrainMarkingStackClosure,
5450 &task_executor,
5451 _gc_timer_cm,
5452 _gc_tracer_cm->gc_id());
5453 } else {
5454 stats = rp->process_discovered_references(&_is_alive_closure,
5455 &cmsKeepAliveClosure,
5456 &cmsDrainMarkingStackClosure,
5457 NULL,
5458 _gc_timer_cm,
5459 _gc_tracer_cm->gc_id());
5460 }
5461 _gc_tracer_cm->report_gc_reference_stats(stats);
5462
5463 }
5464
5465 // This is the point where the entire marking should have completed.
5466 verify_work_stacks_empty();
5467
5468 if (should_unload_classes()) {
5469 {
5470 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5471
5472 // Unload classes and purge the SystemDictionary.
5473 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5474
5475 // Unload nmethods.
5476 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5477
5478 // Prune dead klasses from subklass/sibling/implementor lists.
5479 Klass::clean_weak_klass_links(&_is_alive_closure);
5480 }
5481
5482 {
5483 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5484 // Clean up unreferenced symbols in symbol table.
5485 SymbolTable::unlink();
5486 }
5487
5488 {
5489 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5490 // Delete entries for dead interned strings.
5491 StringTable::unlink(&_is_alive_closure);
5492 }
5493 }
5494
5495
5496 // Restore any preserved marks as a result of mark stack or
5497 // work queue overflow
5498 restore_preserved_marks_if_any(); // done single-threaded for now
5499
5500 rp->set_enqueuing_is_done(true);
5501 if (rp->processing_is_mt()) {
5502 rp->balance_all_queues();
5503 CMSRefProcTaskExecutor task_executor(*this);
5504 rp->enqueue_discovered_references(&task_executor);
5505 } else {
5506 rp->enqueue_discovered_references(NULL);
5507 }
5508 rp->verify_no_references_recorded();
5509 assert(!rp->discovery_enabled(), "should have been disabled");
5510 }
5511
5512 #ifndef PRODUCT
5513 void CMSCollector::check_correct_thread_executing() {
5514 Thread* t = Thread::current();
5515 // Only the VM thread or the CMS thread should be here.
5516 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5517 "Unexpected thread type");
5518 // If this is the vm thread, the foreground process
5519 // should not be waiting. Note that _foregroundGCIsActive is
5520 // true while the foreground collector is waiting.
5521 if (_foregroundGCShouldWait) {
5522 // We cannot be the VM thread
5523 assert(t->is_ConcurrentGC_thread(),
5524 "Should be CMS thread");
5525 } else {
5526 // We can be the CMS thread only if we are in a stop-world
5527 // phase of CMS collection.
5528 if (t->is_ConcurrentGC_thread()) {
5529 assert(_collectorState == InitialMarking ||
5530 _collectorState == FinalMarking,
5531 "Should be a stop-world phase");
5532 // The CMS thread should be holding the CMS_token.
5533 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5534 "Potential interference with concurrently "
5535 "executing VM thread");
5536 }
5537 }
5538 }
5539 #endif
5540
5541 void CMSCollector::sweep() {
5542 assert(_collectorState == Sweeping, "just checking");
5543 check_correct_thread_executing();
5544 verify_work_stacks_empty();
5545 verify_overflow_empty();
5546 increment_sweep_count();
5547 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5548
5549 _inter_sweep_timer.stop();
5550 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5551
5552 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5553 _intra_sweep_timer.reset();
5554 _intra_sweep_timer.start();
5555 {
5556 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5557 CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5558 // First sweep the old gen
5559 {
5560 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5561 bitMapLock());
5562 sweepWork(_cmsGen);
5563 }
5564
5565 // Update Universe::_heap_*_at_gc figures.
5566 // We need all the free list locks to make the abstract state
5567 // transition from Sweeping to Resetting. See detailed note
5568 // further below.
5569 {
5570 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5571 // Update heap occupancy information which is used as
5572 // input to soft ref clearing policy at the next gc.
5573 Universe::update_heap_info_at_gc();
5574 _collectorState = Resizing;
5575 }
5576 }
5577 verify_work_stacks_empty();
5578 verify_overflow_empty();
5579
5580 if (should_unload_classes()) {
5581 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5582 // requires that the virtual spaces are stable and not deleted.
5583 ClassLoaderDataGraph::set_should_purge(true);
5584 }
5585
5586 _intra_sweep_timer.stop();
5587 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5588
5589 _inter_sweep_timer.reset();
5590 _inter_sweep_timer.start();
5591
5592 // We need to use a monotonically non-decreasing time in ms
5593 // or we will see time-warp warnings and os::javaTimeMillis()
5594 // does not guarantee monotonicity.
5595 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5596 update_time_of_last_gc(now);
5597
5598 // NOTE on abstract state transitions:
5599 // Mutators allocate-live and/or mark the mod-union table dirty
5600 // based on the state of the collection. The former is done in
5601 // the interval [Marking, Sweeping] and the latter in the interval
5602 // [Marking, Sweeping). Thus the transitions into the Marking state
5603 // and out of the Sweeping state must be synchronously visible
5604 // globally to the mutators.
5605 // The transition into the Marking state happens with the world
5606 // stopped so the mutators will globally see it. Sweeping is
5607 // done asynchronously by the background collector so the transition
5608 // from the Sweeping state to the Resizing state must be done
5609 // under the freelistLock (as is the check for whether to
5610 // allocate-live and whether to dirty the mod-union table).
5611 assert(_collectorState == Resizing, "Change of collector state to"
5612 " Resizing must be done under the freelistLocks (plural)");
5613
5614 // Now that sweeping has been completed, we clear
5615 // the incremental_collection_failed flag,
5616 // thus inviting a younger gen collection to promote into
5617 // this generation. If such a promotion may still fail,
5618 // the flag will be set again when a young collection is
5619 // attempted.
5620 GenCollectedHeap* gch = GenCollectedHeap::heap();
5621 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5622 gch->update_full_collections_completed(_collection_count_start);
5623 }
5624
5625 // FIX ME!!! Looks like this belongs in CFLSpace, with
5626 // CMSGen merely delegating to it.
5627 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5628 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5629 HeapWord* minAddr = _cmsSpace->bottom();
5630 HeapWord* largestAddr =
5631 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5632 if (largestAddr == NULL) {
5633 // The dictionary appears to be empty. In this case
5634 // try to coalesce at the end of the heap.
5635 largestAddr = _cmsSpace->end();
5636 }
5637 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5638 size_t nearLargestOffset =
5639 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5640 if (PrintFLSStatistics != 0) {
5641 gclog_or_tty->print_cr(
5642 "CMS: Large Block: " PTR_FORMAT ";"
5643 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5644 p2i(largestAddr),
5645 p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5646 }
5647 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5648 }
5649
5650 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5651 return addr >= _cmsSpace->nearLargestChunk();
5652 }
5653
5654 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5655 return _cmsSpace->find_chunk_at_end();
5656 }
5657
5658 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
5659 bool full) {
5660 // The next lower level has been collected. Gather any statistics
5661 // that are of interest at this point.
5662 if (!full && (current_level + 1) == level()) {
5663 // Gather statistics on the young generation collection.
5664 collector()->stats().record_gc0_end(used());
5665 }
5666 }
5667
5668 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen) {
5669 // We iterate over the space(s) underlying this generation,
5670 // checking the mark bit map to see if the bits corresponding
5671 // to specific blocks are marked or not. Blocks that are
5672 // marked are live and are not swept up. All remaining blocks
5673 // are swept up, with coalescing on-the-fly as we sweep up
5674 // contiguous free and/or garbage blocks:
5675 // We need to ensure that the sweeper synchronizes with allocators
5676 // and stop-the-world collectors. In particular, the following
5677 // locks are used:
5678 // . CMS token: if this is held, a stop the world collection cannot occur
5679 // . freelistLock: if this is held no allocation can occur from this
5680 // generation by another thread
5681 // . bitMapLock: if this is held, no other thread can access or update
5682 //
5683
5684 // Note that we need to hold the freelistLock if we use
5685 // block iterate below; else the iterator might go awry if
5686 // a mutator (or promotion) causes block contents to change
5687 // (for instance if the allocator divvies up a block).
5688 // If we hold the free list lock, for all practical purposes
5689 // young generation GC's can't occur (they'll usually need to
5690 // promote), so we might as well prevent all young generation
5691 // GC's while we do a sweeping step. For the same reason, we might
5692 // as well take the bit map lock for the entire duration
5693
5694 // check that we hold the requisite locks
5695 assert(have_cms_token(), "Should hold cms token");
5696 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5697 assert_lock_strong(gen->freelistLock());
5698 assert_lock_strong(bitMapLock());
5699
5700 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5701 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5702 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5703 _inter_sweep_estimate.padded_average(),
5704 _intra_sweep_estimate.padded_average());
5705 gen->setNearLargestChunk();
5706
5707 {
5708 SweepClosure sweepClosure(this, gen, &_markBitMap, CMSYield);
5709 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5710 // We need to free-up/coalesce garbage/blocks from a
5711 // co-terminal free run. This is done in the SweepClosure
5712 // destructor; so, do not remove this scope, else the
5713 // end-of-sweep-census below will be off by a little bit.
5714 }
5715 gen->cmsSpace()->sweep_completed();
5716 gen->cmsSpace()->endSweepFLCensus(sweep_count());
5717 if (should_unload_classes()) { // unloaded classes this cycle,
5718 _concurrent_cycles_since_last_unload = 0; // ... reset count
5719 } else { // did not unload classes,
5720 _concurrent_cycles_since_last_unload++; // ... increment count
5721 }
5722 }
5723
5724 // Reset CMS data structures (for now just the marking bit map)
5725 // preparatory for the next cycle.
5726 void CMSCollector::reset(bool concurrent) {
5727 if (concurrent) {
5728 CMSTokenSyncWithLocks ts(true, bitMapLock());
5729
5730 // If the state is not "Resetting", the foreground thread
5731 // has done a collection and the resetting.
5732 if (_collectorState != Resetting) {
5733 assert(_collectorState == Idling, "The state should only change"
5734 " because the foreground collector has finished the collection");
5735 return;
5736 }
5737
5738 // Clear the mark bitmap (no grey objects to start with)
5739 // for the next cycle.
5740 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5741 CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5742
5743 HeapWord* curAddr = _markBitMap.startWord();
5744 while (curAddr < _markBitMap.endWord()) {
5745 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5746 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5747 _markBitMap.clear_large_range(chunk);
5748 if (ConcurrentMarkSweepThread::should_yield() &&
5749 !foregroundGCIsActive() &&
5750 CMSYield) {
5751 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5752 "CMS thread should hold CMS token");
5753 assert_lock_strong(bitMapLock());
5754 bitMapLock()->unlock();
5755 ConcurrentMarkSweepThread::desynchronize(true);
5756 stopTimer();
5757 if (PrintCMSStatistics != 0) {
5758 incrementYields();
5759 }
5760
5761 // See the comment in coordinator_yield()
5762 for (unsigned i = 0; i < CMSYieldSleepCount &&
5763 ConcurrentMarkSweepThread::should_yield() &&
5764 !CMSCollector::foregroundGCIsActive(); ++i) {
5765 os::sleep(Thread::current(), 1, false);
5766 }
5767
5768 ConcurrentMarkSweepThread::synchronize(true);
5769 bitMapLock()->lock_without_safepoint_check();
5770 startTimer();
5771 }
5772 curAddr = chunk.end();
5773 }
5774 // A successful mostly concurrent collection has been done.
5775 // Because only the full (i.e., concurrent mode failure) collections
5776 // are being measured for gc overhead limits, clean the "near" flag
5777 // and count.
5778 size_policy()->reset_gc_overhead_limit_count();
5779 _collectorState = Idling;
5780 } else {
5781 // already have the lock
5782 assert(_collectorState == Resetting, "just checking");
5783 assert_lock_strong(bitMapLock());
5784 _markBitMap.clear_all();
5785 _collectorState = Idling;
5786 }
5787
5788 register_gc_end();
5789 }
5790
5791 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5792 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5793 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
5794 TraceCollectorStats tcs(counters());
5795
5796 switch (op) {
5797 case CMS_op_checkpointRootsInitial: {
5798 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5799 checkpointRootsInitial();
5800 if (PrintGC) {
5801 _cmsGen->printOccupancy("initial-mark");
5802 }
5803 break;
5804 }
5805 case CMS_op_checkpointRootsFinal: {
5806 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5807 checkpointRootsFinal();
5808 if (PrintGC) {
5809 _cmsGen->printOccupancy("remark");
5810 }
5811 break;
5812 }
5813 default:
5814 fatal("No such CMS_op");
5815 }
5816 }
5817
5818 #ifndef PRODUCT
5819 size_t const CMSCollector::skip_header_HeapWords() {
5820 return FreeChunk::header_size();
5821 }
5822
5823 // Try and collect here conditions that should hold when
5824 // CMS thread is exiting. The idea is that the foreground GC
5825 // thread should not be blocked if it wants to terminate
5826 // the CMS thread and yet continue to run the VM for a while
5827 // after that.
5828 void CMSCollector::verify_ok_to_terminate() const {
5829 assert(Thread::current()->is_ConcurrentGC_thread(),
5830 "should be called by CMS thread");
5831 assert(!_foregroundGCShouldWait, "should be false");
5832 // We could check here that all the various low-level locks
5833 // are not held by the CMS thread, but that is overkill; see
5834 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5835 // is checked.
5836 }
5837 #endif
5838
5839 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5840 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5841 "missing Printezis mark?");
5842 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5843 size_t size = pointer_delta(nextOneAddr + 1, addr);
5844 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5845 "alignment problem");
5846 assert(size >= 3, "Necessary for Printezis marks to work");
5847 return size;
5848 }
5849
5850 // A variant of the above (block_size_using_printezis_bits()) except
5851 // that we return 0 if the P-bits are not yet set.
5852 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5853 if (_markBitMap.isMarked(addr + 1)) {
5854 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5855 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5856 size_t size = pointer_delta(nextOneAddr + 1, addr);
5857 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5858 "alignment problem");
5859 assert(size >= 3, "Necessary for Printezis marks to work");
5860 return size;
5861 }
5862 return 0;
5863 }
5864
5865 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5866 size_t sz = 0;
5867 oop p = (oop)addr;
5868 if (p->klass_or_null() != NULL) {
5869 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5870 } else {
5871 sz = block_size_using_printezis_bits(addr);
5872 }
5873 assert(sz > 0, "size must be nonzero");
5874 HeapWord* next_block = addr + sz;
5875 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
5876 CardTableModRefBS::card_size);
5877 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
5878 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5879 "must be different cards");
5880 return next_card;
5881 }
5882
5883
5884 // CMS Bit Map Wrapper /////////////////////////////////////////
5885
5886 // Construct a CMS bit map infrastructure, but don't create the
5887 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5888 // further below.
5889 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5890 _bm(),
5891 _shifter(shifter),
5892 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5893 Monitor::_safepoint_check_sometimes) : NULL)
5894 {
5895 _bmStartWord = 0;
5896 _bmWordSize = 0;
5897 }
5898
5899 bool CMSBitMap::allocate(MemRegion mr) {
5900 _bmStartWord = mr.start();
5901 _bmWordSize = mr.word_size();
5902 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5903 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5904 if (!brs.is_reserved()) {
5905 warning("CMS bit map allocation failure");
5906 return false;
5907 }
5908 // For now we'll just commit all of the bit map up front.
5909 // Later on we'll try to be more parsimonious with swap.
5910 if (!_virtual_space.initialize(brs, brs.size())) {
5911 warning("CMS bit map backing store failure");
5912 return false;
5913 }
5914 assert(_virtual_space.committed_size() == brs.size(),
5915 "didn't reserve backing store for all of CMS bit map?");
5916 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5917 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5918 _bmWordSize, "inconsistency in bit map sizing");
5919 _bm.set_size(_bmWordSize >> _shifter);
5920
5921 // bm.clear(); // can we rely on getting zero'd memory? verify below
5922 assert(isAllClear(),
5923 "Expected zero'd memory from ReservedSpace constructor");
5924 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5925 "consistency check");
5926 return true;
5927 }
5928
5929 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5930 HeapWord *next_addr, *end_addr, *last_addr;
5931 assert_locked();
5932 assert(covers(mr), "out-of-range error");
5933 // XXX assert that start and end are appropriately aligned
5934 for (next_addr = mr.start(), end_addr = mr.end();
5935 next_addr < end_addr; next_addr = last_addr) {
5936 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5937 last_addr = dirty_region.end();
5938 if (!dirty_region.is_empty()) {
5939 cl->do_MemRegion(dirty_region);
5940 } else {
5941 assert(last_addr == end_addr, "program logic");
5942 return;
5943 }
5944 }
5945 }
5946
5947 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5948 _bm.print_on_error(st, prefix);
5949 }
5950
5951 #ifndef PRODUCT
5952 void CMSBitMap::assert_locked() const {
5953 CMSLockVerifier::assert_locked(lock());
5954 }
5955
5956 bool CMSBitMap::covers(MemRegion mr) const {
5957 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5958 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5959 "size inconsistency");
5960 return (mr.start() >= _bmStartWord) &&
5961 (mr.end() <= endWord());
5962 }
5963
5964 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5965 return (start >= _bmStartWord && (start + size) <= endWord());
5966 }
5967
5968 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5969 // verify that there are no 1 bits in the interval [left, right)
5970 FalseBitMapClosure falseBitMapClosure;
5971 iterate(&falseBitMapClosure, left, right);
5972 }
5973
5974 void CMSBitMap::region_invariant(MemRegion mr)
5975 {
5976 assert_locked();
5977 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5978 assert(!mr.is_empty(), "unexpected empty region");
5979 assert(covers(mr), "mr should be covered by bit map");
5980 // convert address range into offset range
5981 size_t start_ofs = heapWordToOffset(mr.start());
5982 // Make sure that end() is appropriately aligned
5983 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5984 (1 << (_shifter+LogHeapWordSize))),
5985 "Misaligned mr.end()");
5986 size_t end_ofs = heapWordToOffset(mr.end());
5987 assert(end_ofs > start_ofs, "Should mark at least one bit");
5988 }
5989
5990 #endif
5991
5992 bool CMSMarkStack::allocate(size_t size) {
5993 // allocate a stack of the requisite depth
5994 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5995 size * sizeof(oop)));
5996 if (!rs.is_reserved()) {
5997 warning("CMSMarkStack allocation failure");
5998 return false;
5999 }
6000 if (!_virtual_space.initialize(rs, rs.size())) {
6001 warning("CMSMarkStack backing store failure");
6002 return false;
6003 }
6004 assert(_virtual_space.committed_size() == rs.size(),
6005 "didn't reserve backing store for all of CMS stack?");
6006 _base = (oop*)(_virtual_space.low());
6007 _index = 0;
6008 _capacity = size;
6009 NOT_PRODUCT(_max_depth = 0);
6010 return true;
6011 }
6012
6013 // XXX FIX ME !!! In the MT case we come in here holding a
6014 // leaf lock. For printing we need to take a further lock
6015 // which has lower rank. We need to recalibrate the two
6016 // lock-ranks involved in order to be able to print the
6017 // messages below. (Or defer the printing to the caller.
6018 // For now we take the expedient path of just disabling the
6019 // messages for the problematic case.)
6020 void CMSMarkStack::expand() {
6021 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6022 if (_capacity == MarkStackSizeMax) {
6023 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6024 // We print a warning message only once per CMS cycle.
6025 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6026 }
6027 return;
6028 }
6029 // Double capacity if possible
6030 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6031 // Do not give up existing stack until we have managed to
6032 // get the double capacity that we desired.
6033 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6034 new_capacity * sizeof(oop)));
6035 if (rs.is_reserved()) {
6036 // Release the backing store associated with old stack
6037 _virtual_space.release();
6038 // Reinitialize virtual space for new stack
6039 if (!_virtual_space.initialize(rs, rs.size())) {
6040 fatal("Not enough swap for expanded marking stack");
6041 }
6042 _base = (oop*)(_virtual_space.low());
6043 _index = 0;
6044 _capacity = new_capacity;
6045 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6046 // Failed to double capacity, continue;
6047 // we print a detail message only once per CMS cycle.
6048 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6049 SIZE_FORMAT"K",
6050 _capacity / K, new_capacity / K);
6051 }
6052 }
6053
6054
6055 // Closures
6056 // XXX: there seems to be a lot of code duplication here;
6057 // should refactor and consolidate common code.
6058
6059 // This closure is used to mark refs into the CMS generation in
6060 // the CMS bit map. Called at the first checkpoint. This closure
6061 // assumes that we do not need to re-mark dirty cards; if the CMS
6062 // generation on which this is used is not an oldest
6063 // generation then this will lose younger_gen cards!
6064
6065 MarkRefsIntoClosure::MarkRefsIntoClosure(
6066 MemRegion span, CMSBitMap* bitMap):
6067 _span(span),
6068 _bitMap(bitMap)
6069 {
6070 assert(_ref_processor == NULL, "deliberately left NULL");
6071 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6072 }
6073
6074 void MarkRefsIntoClosure::do_oop(oop obj) {
6075 // if p points into _span, then mark corresponding bit in _markBitMap
6076 assert(obj->is_oop(), "expected an oop");
6077 HeapWord* addr = (HeapWord*)obj;
6078 if (_span.contains(addr)) {
6079 // this should be made more efficient
6080 _bitMap->mark(addr);
6081 }
6082 }
6083
6084 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6085 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6086
6087 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6088 MemRegion span, CMSBitMap* bitMap):
6089 _span(span),
6090 _bitMap(bitMap)
6091 {
6092 assert(_ref_processor == NULL, "deliberately left NULL");
6093 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6094 }
6095
6096 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6097 // if p points into _span, then mark corresponding bit in _markBitMap
6098 assert(obj->is_oop(), "expected an oop");
6099 HeapWord* addr = (HeapWord*)obj;
6100 if (_span.contains(addr)) {
6101 // this should be made more efficient
6102 _bitMap->par_mark(addr);
6103 }
6104 }
6105
6106 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6107 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6108
6109 // A variant of the above, used for CMS marking verification.
6110 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6111 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6112 _span(span),
6113 _verification_bm(verification_bm),
6114 _cms_bm(cms_bm)
6115 {
6116 assert(_ref_processor == NULL, "deliberately left NULL");
6117 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6118 }
6119
6120 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6121 // if p points into _span, then mark corresponding bit in _markBitMap
6122 assert(obj->is_oop(), "expected an oop");
6123 HeapWord* addr = (HeapWord*)obj;
6124 if (_span.contains(addr)) {
6125 _verification_bm->mark(addr);
6126 if (!_cms_bm->isMarked(addr)) {
6127 oop(addr)->print();
6128 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6129 fatal("... aborting");
6130 }
6131 }
6132 }
6133
6134 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6135 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6136
6137 //////////////////////////////////////////////////
6138 // MarkRefsIntoAndScanClosure
6139 //////////////////////////////////////////////////
6140
6141 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6142 ReferenceProcessor* rp,
6143 CMSBitMap* bit_map,
6144 CMSBitMap* mod_union_table,
6145 CMSMarkStack* mark_stack,
6146 CMSCollector* collector,
6147 bool should_yield,
6148 bool concurrent_precleaning):
6149 _collector(collector),
6150 _span(span),
6151 _bit_map(bit_map),
6152 _mark_stack(mark_stack),
6153 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6154 mark_stack, concurrent_precleaning),
6155 _yield(should_yield),
6156 _concurrent_precleaning(concurrent_precleaning),
6157 _freelistLock(NULL)
6158 {
6159 _ref_processor = rp;
6160 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6161 }
6162
6163 // This closure is used to mark refs into the CMS generation at the
6164 // second (final) checkpoint, and to scan and transitively follow
6165 // the unmarked oops. It is also used during the concurrent precleaning
6166 // phase while scanning objects on dirty cards in the CMS generation.
6167 // The marks are made in the marking bit map and the marking stack is
6168 // used for keeping the (newly) grey objects during the scan.
6169 // The parallel version (Par_...) appears further below.
6170 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6171 if (obj != NULL) {
6172 assert(obj->is_oop(), "expected an oop");
6173 HeapWord* addr = (HeapWord*)obj;
6174 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6175 assert(_collector->overflow_list_is_empty(),
6176 "overflow list should be empty");
6177 if (_span.contains(addr) &&
6178 !_bit_map->isMarked(addr)) {
6179 // mark bit map (object is now grey)
6180 _bit_map->mark(addr);
6181 // push on marking stack (stack should be empty), and drain the
6182 // stack by applying this closure to the oops in the oops popped
6183 // from the stack (i.e. blacken the grey objects)
6184 bool res = _mark_stack->push(obj);
6185 assert(res, "Should have space to push on empty stack");
6186 do {
6187 oop new_oop = _mark_stack->pop();
6188 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6189 assert(_bit_map->isMarked((HeapWord*)new_oop),
6190 "only grey objects on this stack");
6191 // iterate over the oops in this oop, marking and pushing
6192 // the ones in CMS heap (i.e. in _span).
6193 new_oop->oop_iterate(&_pushAndMarkClosure);
6194 // check if it's time to yield
6195 do_yield_check();
6196 } while (!_mark_stack->isEmpty() ||
6197 (!_concurrent_precleaning && take_from_overflow_list()));
6198 // if marking stack is empty, and we are not doing this
6199 // during precleaning, then check the overflow list
6200 }
6201 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6202 assert(_collector->overflow_list_is_empty(),
6203 "overflow list was drained above");
6204 // We could restore evacuated mark words, if any, used for
6205 // overflow list links here because the overflow list is
6206 // provably empty here. That would reduce the maximum
6207 // size requirements for preserved_{oop,mark}_stack.
6208 // But we'll just postpone it until we are all done
6209 // so we can just stream through.
6210 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6211 _collector->restore_preserved_marks_if_any();
6212 assert(_collector->no_preserved_marks(), "No preserved marks");
6213 }
6214 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6215 "All preserved marks should have been restored above");
6216 }
6217 }
6218
6219 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6220 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6221
6222 void MarkRefsIntoAndScanClosure::do_yield_work() {
6223 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6224 "CMS thread should hold CMS token");
6225 assert_lock_strong(_freelistLock);
6226 assert_lock_strong(_bit_map->lock());
6227 // relinquish the free_list_lock and bitMaplock()
6228 _bit_map->lock()->unlock();
6229 _freelistLock->unlock();
6230 ConcurrentMarkSweepThread::desynchronize(true);
6231 _collector->stopTimer();
6232 if (PrintCMSStatistics != 0) {
6233 _collector->incrementYields();
6234 }
6235
6236 // See the comment in coordinator_yield()
6237 for (unsigned i = 0;
6238 i < CMSYieldSleepCount &&
6239 ConcurrentMarkSweepThread::should_yield() &&
6240 !CMSCollector::foregroundGCIsActive();
6241 ++i) {
6242 os::sleep(Thread::current(), 1, false);
6243 }
6244
6245 ConcurrentMarkSweepThread::synchronize(true);
6246 _freelistLock->lock_without_safepoint_check();
6247 _bit_map->lock()->lock_without_safepoint_check();
6248 _collector->startTimer();
6249 }
6250
6251 ///////////////////////////////////////////////////////////
6252 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6253 // MarkRefsIntoAndScanClosure
6254 ///////////////////////////////////////////////////////////
6255 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6256 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6257 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6258 _span(span),
6259 _bit_map(bit_map),
6260 _work_queue(work_queue),
6261 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6262 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6263 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6264 {
6265 _ref_processor = rp;
6266 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6267 }
6268
6269 // This closure is used to mark refs into the CMS generation at the
6270 // second (final) checkpoint, and to scan and transitively follow
6271 // the unmarked oops. The marks are made in the marking bit map and
6272 // the work_queue is used for keeping the (newly) grey objects during
6273 // the scan phase whence they are also available for stealing by parallel
6274 // threads. Since the marking bit map is shared, updates are
6275 // synchronized (via CAS).
6276 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6277 if (obj != NULL) {
6278 // Ignore mark word because this could be an already marked oop
6279 // that may be chained at the end of the overflow list.
6280 assert(obj->is_oop(true), "expected an oop");
6281 HeapWord* addr = (HeapWord*)obj;
6282 if (_span.contains(addr) &&
6283 !_bit_map->isMarked(addr)) {
6284 // mark bit map (object will become grey):
6285 // It is possible for several threads to be
6286 // trying to "claim" this object concurrently;
6287 // the unique thread that succeeds in marking the
6288 // object first will do the subsequent push on
6289 // to the work queue (or overflow list).
6290 if (_bit_map->par_mark(addr)) {
6291 // push on work_queue (which may not be empty), and trim the
6292 // queue to an appropriate length by applying this closure to
6293 // the oops in the oops popped from the stack (i.e. blacken the
6294 // grey objects)
6295 bool res = _work_queue->push(obj);
6296 assert(res, "Low water mark should be less than capacity?");
6297 trim_queue(_low_water_mark);
6298 } // Else, another thread claimed the object
6299 }
6300 }
6301 }
6302
6303 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6304 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6305
6306 // This closure is used to rescan the marked objects on the dirty cards
6307 // in the mod union table and the card table proper.
6308 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6309 oop p, MemRegion mr) {
6310
6311 size_t size = 0;
6312 HeapWord* addr = (HeapWord*)p;
6313 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6314 assert(_span.contains(addr), "we are scanning the CMS generation");
6315 // check if it's time to yield
6316 if (do_yield_check()) {
6317 // We yielded for some foreground stop-world work,
6318 // and we have been asked to abort this ongoing preclean cycle.
6319 return 0;
6320 }
6321 if (_bitMap->isMarked(addr)) {
6322 // it's marked; is it potentially uninitialized?
6323 if (p->klass_or_null() != NULL) {
6324 // an initialized object; ignore mark word in verification below
6325 // since we are running concurrent with mutators
6326 assert(p->is_oop(true), "should be an oop");
6327 if (p->is_objArray()) {
6328 // objArrays are precisely marked; restrict scanning
6329 // to dirty cards only.
6330 size = CompactibleFreeListSpace::adjustObjectSize(
6331 p->oop_iterate(_scanningClosure, mr));
6332 } else {
6333 // A non-array may have been imprecisely marked; we need
6334 // to scan object in its entirety.
6335 size = CompactibleFreeListSpace::adjustObjectSize(
6336 p->oop_iterate(_scanningClosure));
6337 }
6338 #ifdef ASSERT
6339 size_t direct_size =
6340 CompactibleFreeListSpace::adjustObjectSize(p->size());
6341 assert(size == direct_size, "Inconsistency in size");
6342 assert(size >= 3, "Necessary for Printezis marks to work");
6343 if (!_bitMap->isMarked(addr+1)) {
6344 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6345 } else {
6346 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6347 assert(_bitMap->isMarked(addr+size-1),
6348 "inconsistent Printezis mark");
6349 }
6350 #endif // ASSERT
6351 } else {
6352 // An uninitialized object.
6353 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6354 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6355 size = pointer_delta(nextOneAddr + 1, addr);
6356 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6357 "alignment problem");
6358 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6359 // will dirty the card when the klass pointer is installed in the
6360 // object (signaling the completion of initialization).
6361 }
6362 } else {
6363 // Either a not yet marked object or an uninitialized object
6364 if (p->klass_or_null() == NULL) {
6365 // An uninitialized object, skip to the next card, since
6366 // we may not be able to read its P-bits yet.
6367 assert(size == 0, "Initial value");
6368 } else {
6369 // An object not (yet) reached by marking: we merely need to
6370 // compute its size so as to go look at the next block.
6371 assert(p->is_oop(true), "should be an oop");
6372 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6373 }
6374 }
6375 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6376 return size;
6377 }
6378
6379 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6380 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6381 "CMS thread should hold CMS token");
6382 assert_lock_strong(_freelistLock);
6383 assert_lock_strong(_bitMap->lock());
6384 // relinquish the free_list_lock and bitMaplock()
6385 _bitMap->lock()->unlock();
6386 _freelistLock->unlock();
6387 ConcurrentMarkSweepThread::desynchronize(true);
6388 _collector->stopTimer();
6389 if (PrintCMSStatistics != 0) {
6390 _collector->incrementYields();
6391 }
6392
6393 // See the comment in coordinator_yield()
6394 for (unsigned i = 0; i < CMSYieldSleepCount &&
6395 ConcurrentMarkSweepThread::should_yield() &&
6396 !CMSCollector::foregroundGCIsActive(); ++i) {
6397 os::sleep(Thread::current(), 1, false);
6398 }
6399
6400 ConcurrentMarkSweepThread::synchronize(true);
6401 _freelistLock->lock_without_safepoint_check();
6402 _bitMap->lock()->lock_without_safepoint_check();
6403 _collector->startTimer();
6404 }
6405
6406
6407 //////////////////////////////////////////////////////////////////
6408 // SurvivorSpacePrecleanClosure
6409 //////////////////////////////////////////////////////////////////
6410 // This (single-threaded) closure is used to preclean the oops in
6411 // the survivor spaces.
6412 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6413
6414 HeapWord* addr = (HeapWord*)p;
6415 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6416 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6417 assert(p->klass_or_null() != NULL, "object should be initialized");
6418 // an initialized object; ignore mark word in verification below
6419 // since we are running concurrent with mutators
6420 assert(p->is_oop(true), "should be an oop");
6421 // Note that we do not yield while we iterate over
6422 // the interior oops of p, pushing the relevant ones
6423 // on our marking stack.
6424 size_t size = p->oop_iterate(_scanning_closure);
6425 do_yield_check();
6426 // Observe that below, we do not abandon the preclean
6427 // phase as soon as we should; rather we empty the
6428 // marking stack before returning. This is to satisfy
6429 // some existing assertions. In general, it may be a
6430 // good idea to abort immediately and complete the marking
6431 // from the grey objects at a later time.
6432 while (!_mark_stack->isEmpty()) {
6433 oop new_oop = _mark_stack->pop();
6434 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6435 assert(_bit_map->isMarked((HeapWord*)new_oop),
6436 "only grey objects on this stack");
6437 // iterate over the oops in this oop, marking and pushing
6438 // the ones in CMS heap (i.e. in _span).
6439 new_oop->oop_iterate(_scanning_closure);
6440 // check if it's time to yield
6441 do_yield_check();
6442 }
6443 unsigned int after_count =
6444 GenCollectedHeap::heap()->total_collections();
6445 bool abort = (_before_count != after_count) ||
6446 _collector->should_abort_preclean();
6447 return abort ? 0 : size;
6448 }
6449
6450 void SurvivorSpacePrecleanClosure::do_yield_work() {
6451 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6452 "CMS thread should hold CMS token");
6453 assert_lock_strong(_bit_map->lock());
6454 // Relinquish the bit map lock
6455 _bit_map->lock()->unlock();
6456 ConcurrentMarkSweepThread::desynchronize(true);
6457 _collector->stopTimer();
6458 if (PrintCMSStatistics != 0) {
6459 _collector->incrementYields();
6460 }
6461
6462 // See the comment in coordinator_yield()
6463 for (unsigned i = 0; i < CMSYieldSleepCount &&
6464 ConcurrentMarkSweepThread::should_yield() &&
6465 !CMSCollector::foregroundGCIsActive(); ++i) {
6466 os::sleep(Thread::current(), 1, false);
6467 }
6468
6469 ConcurrentMarkSweepThread::synchronize(true);
6470 _bit_map->lock()->lock_without_safepoint_check();
6471 _collector->startTimer();
6472 }
6473
6474 // This closure is used to rescan the marked objects on the dirty cards
6475 // in the mod union table and the card table proper. In the parallel
6476 // case, although the bitMap is shared, we do a single read so the
6477 // isMarked() query is "safe".
6478 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6479 // Ignore mark word because we are running concurrent with mutators
6480 assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
6481 HeapWord* addr = (HeapWord*)p;
6482 assert(_span.contains(addr), "we are scanning the CMS generation");
6483 bool is_obj_array = false;
6484 #ifdef ASSERT
6485 if (!_parallel) {
6486 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6487 assert(_collector->overflow_list_is_empty(),
6488 "overflow list should be empty");
6489
6490 }
6491 #endif // ASSERT
6492 if (_bit_map->isMarked(addr)) {
6493 // Obj arrays are precisely marked, non-arrays are not;
6494 // so we scan objArrays precisely and non-arrays in their
6495 // entirety.
6496 if (p->is_objArray()) {
6497 is_obj_array = true;
6498 if (_parallel) {
6499 p->oop_iterate(_par_scan_closure, mr);
6500 } else {
6501 p->oop_iterate(_scan_closure, mr);
6502 }
6503 } else {
6504 if (_parallel) {
6505 p->oop_iterate(_par_scan_closure);
6506 } else {
6507 p->oop_iterate(_scan_closure);
6508 }
6509 }
6510 }
6511 #ifdef ASSERT
6512 if (!_parallel) {
6513 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6514 assert(_collector->overflow_list_is_empty(),
6515 "overflow list should be empty");
6516
6517 }
6518 #endif // ASSERT
6519 return is_obj_array;
6520 }
6521
6522 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6523 MemRegion span,
6524 CMSBitMap* bitMap, CMSMarkStack* markStack,
6525 bool should_yield, bool verifying):
6526 _collector(collector),
6527 _span(span),
6528 _bitMap(bitMap),
6529 _mut(&collector->_modUnionTable),
6530 _markStack(markStack),
6531 _yield(should_yield),
6532 _skipBits(0)
6533 {
6534 assert(_markStack->isEmpty(), "stack should be empty");
6535 _finger = _bitMap->startWord();
6536 _threshold = _finger;
6537 assert(_collector->_restart_addr == NULL, "Sanity check");
6538 assert(_span.contains(_finger), "Out of bounds _finger?");
6539 DEBUG_ONLY(_verifying = verifying;)
6540 }
6541
6542 void MarkFromRootsClosure::reset(HeapWord* addr) {
6543 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6544 assert(_span.contains(addr), "Out of bounds _finger?");
6545 _finger = addr;
6546 _threshold = (HeapWord*)round_to(
6547 (intptr_t)_finger, CardTableModRefBS::card_size);
6548 }
6549
6550 // Should revisit to see if this should be restructured for
6551 // greater efficiency.
6552 bool MarkFromRootsClosure::do_bit(size_t offset) {
6553 if (_skipBits > 0) {
6554 _skipBits--;
6555 return true;
6556 }
6557 // convert offset into a HeapWord*
6558 HeapWord* addr = _bitMap->startWord() + offset;
6559 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6560 "address out of range");
6561 assert(_bitMap->isMarked(addr), "tautology");
6562 if (_bitMap->isMarked(addr+1)) {
6563 // this is an allocated but not yet initialized object
6564 assert(_skipBits == 0, "tautology");
6565 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6566 oop p = oop(addr);
6567 if (p->klass_or_null() == NULL) {
6568 DEBUG_ONLY(if (!_verifying) {)
6569 // We re-dirty the cards on which this object lies and increase
6570 // the _threshold so that we'll come back to scan this object
6571 // during the preclean or remark phase. (CMSCleanOnEnter)
6572 if (CMSCleanOnEnter) {
6573 size_t sz = _collector->block_size_using_printezis_bits(addr);
6574 HeapWord* end_card_addr = (HeapWord*)round_to(
6575 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6576 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6577 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6578 // Bump _threshold to end_card_addr; note that
6579 // _threshold cannot possibly exceed end_card_addr, anyhow.
6580 // This prevents future clearing of the card as the scan proceeds
6581 // to the right.
6582 assert(_threshold <= end_card_addr,
6583 "Because we are just scanning into this object");
6584 if (_threshold < end_card_addr) {
6585 _threshold = end_card_addr;
6586 }
6587 if (p->klass_or_null() != NULL) {
6588 // Redirty the range of cards...
6589 _mut->mark_range(redirty_range);
6590 } // ...else the setting of klass will dirty the card anyway.
6591 }
6592 DEBUG_ONLY(})
6593 return true;
6594 }
6595 }
6596 scanOopsInOop(addr);
6597 return true;
6598 }
6599
6600 // We take a break if we've been at this for a while,
6601 // so as to avoid monopolizing the locks involved.
6602 void MarkFromRootsClosure::do_yield_work() {
6603 // First give up the locks, then yield, then re-lock
6604 // We should probably use a constructor/destructor idiom to
6605 // do this unlock/lock or modify the MutexUnlocker class to
6606 // serve our purpose. XXX
6607 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6608 "CMS thread should hold CMS token");
6609 assert_lock_strong(_bitMap->lock());
6610 _bitMap->lock()->unlock();
6611 ConcurrentMarkSweepThread::desynchronize(true);
6612 _collector->stopTimer();
6613 if (PrintCMSStatistics != 0) {
6614 _collector->incrementYields();
6615 }
6616
6617 // See the comment in coordinator_yield()
6618 for (unsigned i = 0; i < CMSYieldSleepCount &&
6619 ConcurrentMarkSweepThread::should_yield() &&
6620 !CMSCollector::foregroundGCIsActive(); ++i) {
6621 os::sleep(Thread::current(), 1, false);
6622 }
6623
6624 ConcurrentMarkSweepThread::synchronize(true);
6625 _bitMap->lock()->lock_without_safepoint_check();
6626 _collector->startTimer();
6627 }
6628
6629 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6630 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6631 assert(_markStack->isEmpty(),
6632 "should drain stack to limit stack usage");
6633 // convert ptr to an oop preparatory to scanning
6634 oop obj = oop(ptr);
6635 // Ignore mark word in verification below, since we
6636 // may be running concurrent with mutators.
6637 assert(obj->is_oop(true), "should be an oop");
6638 assert(_finger <= ptr, "_finger runneth ahead");
6639 // advance the finger to right end of this object
6640 _finger = ptr + obj->size();
6641 assert(_finger > ptr, "we just incremented it above");
6642 // On large heaps, it may take us some time to get through
6643 // the marking phase. During
6644 // this time it's possible that a lot of mutations have
6645 // accumulated in the card table and the mod union table --
6646 // these mutation records are redundant until we have
6647 // actually traced into the corresponding card.
6648 // Here, we check whether advancing the finger would make
6649 // us cross into a new card, and if so clear corresponding
6650 // cards in the MUT (preclean them in the card-table in the
6651 // future).
6652
6653 DEBUG_ONLY(if (!_verifying) {)
6654 // The clean-on-enter optimization is disabled by default,
6655 // until we fix 6178663.
6656 if (CMSCleanOnEnter && (_finger > _threshold)) {
6657 // [_threshold, _finger) represents the interval
6658 // of cards to be cleared in MUT (or precleaned in card table).
6659 // The set of cards to be cleared is all those that overlap
6660 // with the interval [_threshold, _finger); note that
6661 // _threshold is always kept card-aligned but _finger isn't
6662 // always card-aligned.
6663 HeapWord* old_threshold = _threshold;
6664 assert(old_threshold == (HeapWord*)round_to(
6665 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6666 "_threshold should always be card-aligned");
6667 _threshold = (HeapWord*)round_to(
6668 (intptr_t)_finger, CardTableModRefBS::card_size);
6669 MemRegion mr(old_threshold, _threshold);
6670 assert(!mr.is_empty(), "Control point invariant");
6671 assert(_span.contains(mr), "Should clear within span");
6672 _mut->clear_range(mr);
6673 }
6674 DEBUG_ONLY(})
6675 // Note: the finger doesn't advance while we drain
6676 // the stack below.
6677 PushOrMarkClosure pushOrMarkClosure(_collector,
6678 _span, _bitMap, _markStack,
6679 _finger, this);
6680 bool res = _markStack->push(obj);
6681 assert(res, "Empty non-zero size stack should have space for single push");
6682 while (!_markStack->isEmpty()) {
6683 oop new_oop = _markStack->pop();
6684 // Skip verifying header mark word below because we are
6685 // running concurrent with mutators.
6686 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6687 // now scan this oop's oops
6688 new_oop->oop_iterate(&pushOrMarkClosure);
6689 do_yield_check();
6690 }
6691 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6692 }
6693
6694 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6695 CMSCollector* collector, MemRegion span,
6696 CMSBitMap* bit_map,
6697 OopTaskQueue* work_queue,
6698 CMSMarkStack* overflow_stack):
6699 _collector(collector),
6700 _whole_span(collector->_span),
6701 _span(span),
6702 _bit_map(bit_map),
6703 _mut(&collector->_modUnionTable),
6704 _work_queue(work_queue),
6705 _overflow_stack(overflow_stack),
6706 _skip_bits(0),
6707 _task(task)
6708 {
6709 assert(_work_queue->size() == 0, "work_queue should be empty");
6710 _finger = span.start();
6711 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6712 assert(_span.contains(_finger), "Out of bounds _finger?");
6713 }
6714
6715 // Should revisit to see if this should be restructured for
6716 // greater efficiency.
6717 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6718 if (_skip_bits > 0) {
6719 _skip_bits--;
6720 return true;
6721 }
6722 // convert offset into a HeapWord*
6723 HeapWord* addr = _bit_map->startWord() + offset;
6724 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6725 "address out of range");
6726 assert(_bit_map->isMarked(addr), "tautology");
6727 if (_bit_map->isMarked(addr+1)) {
6728 // this is an allocated object that might not yet be initialized
6729 assert(_skip_bits == 0, "tautology");
6730 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6731 oop p = oop(addr);
6732 if (p->klass_or_null() == NULL) {
6733 // in the case of Clean-on-Enter optimization, redirty card
6734 // and avoid clearing card by increasing the threshold.
6735 return true;
6736 }
6737 }
6738 scan_oops_in_oop(addr);
6739 return true;
6740 }
6741
6742 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6743 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6744 // Should we assert that our work queue is empty or
6745 // below some drain limit?
6746 assert(_work_queue->size() == 0,
6747 "should drain stack to limit stack usage");
6748 // convert ptr to an oop preparatory to scanning
6749 oop obj = oop(ptr);
6750 // Ignore mark word in verification below, since we
6751 // may be running concurrent with mutators.
6752 assert(obj->is_oop(true), "should be an oop");
6753 assert(_finger <= ptr, "_finger runneth ahead");
6754 // advance the finger to right end of this object
6755 _finger = ptr + obj->size();
6756 assert(_finger > ptr, "we just incremented it above");
6757 // On large heaps, it may take us some time to get through
6758 // the marking phase. During
6759 // this time it's possible that a lot of mutations have
6760 // accumulated in the card table and the mod union table --
6761 // these mutation records are redundant until we have
6762 // actually traced into the corresponding card.
6763 // Here, we check whether advancing the finger would make
6764 // us cross into a new card, and if so clear corresponding
6765 // cards in the MUT (preclean them in the card-table in the
6766 // future).
6767
6768 // The clean-on-enter optimization is disabled by default,
6769 // until we fix 6178663.
6770 if (CMSCleanOnEnter && (_finger > _threshold)) {
6771 // [_threshold, _finger) represents the interval
6772 // of cards to be cleared in MUT (or precleaned in card table).
6773 // The set of cards to be cleared is all those that overlap
6774 // with the interval [_threshold, _finger); note that
6775 // _threshold is always kept card-aligned but _finger isn't
6776 // always card-aligned.
6777 HeapWord* old_threshold = _threshold;
6778 assert(old_threshold == (HeapWord*)round_to(
6779 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6780 "_threshold should always be card-aligned");
6781 _threshold = (HeapWord*)round_to(
6782 (intptr_t)_finger, CardTableModRefBS::card_size);
6783 MemRegion mr(old_threshold, _threshold);
6784 assert(!mr.is_empty(), "Control point invariant");
6785 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6786 _mut->clear_range(mr);
6787 }
6788
6789 // Note: the local finger doesn't advance while we drain
6790 // the stack below, but the global finger sure can and will.
6791 HeapWord** gfa = _task->global_finger_addr();
6792 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6793 _span, _bit_map,
6794 _work_queue,
6795 _overflow_stack,
6796 _finger,
6797 gfa, this);
6798 bool res = _work_queue->push(obj); // overflow could occur here
6799 assert(res, "Will hold once we use workqueues");
6800 while (true) {
6801 oop new_oop;
6802 if (!_work_queue->pop_local(new_oop)) {
6803 // We emptied our work_queue; check if there's stuff that can
6804 // be gotten from the overflow stack.
6805 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6806 _overflow_stack, _work_queue)) {
6807 do_yield_check();
6808 continue;
6809 } else { // done
6810 break;
6811 }
6812 }
6813 // Skip verifying header mark word below because we are
6814 // running concurrent with mutators.
6815 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6816 // now scan this oop's oops
6817 new_oop->oop_iterate(&pushOrMarkClosure);
6818 do_yield_check();
6819 }
6820 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6821 }
6822
6823 // Yield in response to a request from VM Thread or
6824 // from mutators.
6825 void Par_MarkFromRootsClosure::do_yield_work() {
6826 assert(_task != NULL, "sanity");
6827 _task->yield();
6828 }
6829
6830 // A variant of the above used for verifying CMS marking work.
6831 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6832 MemRegion span,
6833 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6834 CMSMarkStack* mark_stack):
6835 _collector(collector),
6836 _span(span),
6837 _verification_bm(verification_bm),
6838 _cms_bm(cms_bm),
6839 _mark_stack(mark_stack),
6840 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6841 mark_stack)
6842 {
6843 assert(_mark_stack->isEmpty(), "stack should be empty");
6844 _finger = _verification_bm->startWord();
6845 assert(_collector->_restart_addr == NULL, "Sanity check");
6846 assert(_span.contains(_finger), "Out of bounds _finger?");
6847 }
6848
6849 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6850 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6851 assert(_span.contains(addr), "Out of bounds _finger?");
6852 _finger = addr;
6853 }
6854
6855 // Should revisit to see if this should be restructured for
6856 // greater efficiency.
6857 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6858 // convert offset into a HeapWord*
6859 HeapWord* addr = _verification_bm->startWord() + offset;
6860 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6861 "address out of range");
6862 assert(_verification_bm->isMarked(addr), "tautology");
6863 assert(_cms_bm->isMarked(addr), "tautology");
6864
6865 assert(_mark_stack->isEmpty(),
6866 "should drain stack to limit stack usage");
6867 // convert addr to an oop preparatory to scanning
6868 oop obj = oop(addr);
6869 assert(obj->is_oop(), "should be an oop");
6870 assert(_finger <= addr, "_finger runneth ahead");
6871 // advance the finger to right end of this object
6872 _finger = addr + obj->size();
6873 assert(_finger > addr, "we just incremented it above");
6874 // Note: the finger doesn't advance while we drain
6875 // the stack below.
6876 bool res = _mark_stack->push(obj);
6877 assert(res, "Empty non-zero size stack should have space for single push");
6878 while (!_mark_stack->isEmpty()) {
6879 oop new_oop = _mark_stack->pop();
6880 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6881 // now scan this oop's oops
6882 new_oop->oop_iterate(&_pam_verify_closure);
6883 }
6884 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6885 return true;
6886 }
6887
6888 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6889 CMSCollector* collector, MemRegion span,
6890 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6891 CMSMarkStack* mark_stack):
6892 MetadataAwareOopClosure(collector->ref_processor()),
6893 _collector(collector),
6894 _span(span),
6895 _verification_bm(verification_bm),
6896 _cms_bm(cms_bm),
6897 _mark_stack(mark_stack)
6898 { }
6899
6900 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6901 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6902
6903 // Upon stack overflow, we discard (part of) the stack,
6904 // remembering the least address amongst those discarded
6905 // in CMSCollector's _restart_address.
6906 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6907 // Remember the least grey address discarded
6908 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6909 _collector->lower_restart_addr(ra);
6910 _mark_stack->reset(); // discard stack contents
6911 _mark_stack->expand(); // expand the stack if possible
6912 }
6913
6914 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6915 assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
6916 HeapWord* addr = (HeapWord*)obj;
6917 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6918 // Oop lies in _span and isn't yet grey or black
6919 _verification_bm->mark(addr); // now grey
6920 if (!_cms_bm->isMarked(addr)) {
6921 oop(addr)->print();
6922 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
6923 p2i(addr));
6924 fatal("... aborting");
6925 }
6926
6927 if (!_mark_stack->push(obj)) { // stack overflow
6928 if (PrintCMSStatistics != 0) {
6929 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6930 SIZE_FORMAT, _mark_stack->capacity());
6931 }
6932 assert(_mark_stack->isFull(), "Else push should have succeeded");
6933 handle_stack_overflow(addr);
6934 }
6935 // anything including and to the right of _finger
6936 // will be scanned as we iterate over the remainder of the
6937 // bit map
6938 }
6939 }
6940
6941 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6942 MemRegion span,
6943 CMSBitMap* bitMap, CMSMarkStack* markStack,
6944 HeapWord* finger, MarkFromRootsClosure* parent) :
6945 MetadataAwareOopClosure(collector->ref_processor()),
6946 _collector(collector),
6947 _span(span),
6948 _bitMap(bitMap),
6949 _markStack(markStack),
6950 _finger(finger),
6951 _parent(parent)
6952 { }
6953
6954 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
6955 MemRegion span,
6956 CMSBitMap* bit_map,
6957 OopTaskQueue* work_queue,
6958 CMSMarkStack* overflow_stack,
6959 HeapWord* finger,
6960 HeapWord** global_finger_addr,
6961 Par_MarkFromRootsClosure* parent) :
6962 MetadataAwareOopClosure(collector->ref_processor()),
6963 _collector(collector),
6964 _whole_span(collector->_span),
6965 _span(span),
6966 _bit_map(bit_map),
6967 _work_queue(work_queue),
6968 _overflow_stack(overflow_stack),
6969 _finger(finger),
6970 _global_finger_addr(global_finger_addr),
6971 _parent(parent)
6972 { }
6973
6974 // Assumes thread-safe access by callers, who are
6975 // responsible for mutual exclusion.
6976 void CMSCollector::lower_restart_addr(HeapWord* low) {
6977 assert(_span.contains(low), "Out of bounds addr");
6978 if (_restart_addr == NULL) {
6979 _restart_addr = low;
6980 } else {
6981 _restart_addr = MIN2(_restart_addr, low);
6982 }
6983 }
6984
6985 // Upon stack overflow, we discard (part of) the stack,
6986 // remembering the least address amongst those discarded
6987 // in CMSCollector's _restart_address.
6988 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6989 // Remember the least grey address discarded
6990 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6991 _collector->lower_restart_addr(ra);
6992 _markStack->reset(); // discard stack contents
6993 _markStack->expand(); // expand the stack if possible
6994 }
6995
6996 // Upon stack overflow, we discard (part of) the stack,
6997 // remembering the least address amongst those discarded
6998 // in CMSCollector's _restart_address.
6999 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7000 // We need to do this under a mutex to prevent other
7001 // workers from interfering with the work done below.
7002 MutexLockerEx ml(_overflow_stack->par_lock(),
7003 Mutex::_no_safepoint_check_flag);
7004 // Remember the least grey address discarded
7005 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7006 _collector->lower_restart_addr(ra);
7007 _overflow_stack->reset(); // discard stack contents
7008 _overflow_stack->expand(); // expand the stack if possible
7009 }
7010
7011 void PushOrMarkClosure::do_oop(oop obj) {
7012 // Ignore mark word because we are running concurrent with mutators.
7013 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7014 HeapWord* addr = (HeapWord*)obj;
7015 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7016 // Oop lies in _span and isn't yet grey or black
7017 _bitMap->mark(addr); // now grey
7018 if (addr < _finger) {
7019 // the bit map iteration has already either passed, or
7020 // sampled, this bit in the bit map; we'll need to
7021 // use the marking stack to scan this oop's oops.
7022 bool simulate_overflow = false;
7023 NOT_PRODUCT(
7024 if (CMSMarkStackOverflowALot &&
7025 _collector->simulate_overflow()) {
7026 // simulate a stack overflow
7027 simulate_overflow = true;
7028 }
7029 )
7030 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7031 if (PrintCMSStatistics != 0) {
7032 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7033 SIZE_FORMAT, _markStack->capacity());
7034 }
7035 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7036 handle_stack_overflow(addr);
7037 }
7038 }
7039 // anything including and to the right of _finger
7040 // will be scanned as we iterate over the remainder of the
7041 // bit map
7042 do_yield_check();
7043 }
7044 }
7045
7046 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7047 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7048
7049 void Par_PushOrMarkClosure::do_oop(oop obj) {
7050 // Ignore mark word because we are running concurrent with mutators.
7051 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7052 HeapWord* addr = (HeapWord*)obj;
7053 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7054 // Oop lies in _span and isn't yet grey or black
7055 // We read the global_finger (volatile read) strictly after marking oop
7056 bool res = _bit_map->par_mark(addr); // now grey
7057 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7058 // Should we push this marked oop on our stack?
7059 // -- if someone else marked it, nothing to do
7060 // -- if target oop is above global finger nothing to do
7061 // -- if target oop is in chunk and above local finger
7062 // then nothing to do
7063 // -- else push on work queue
7064 if ( !res // someone else marked it, they will deal with it
7065 || (addr >= *gfa) // will be scanned in a later task
7066 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7067 return;
7068 }
7069 // the bit map iteration has already either passed, or
7070 // sampled, this bit in the bit map; we'll need to
7071 // use the marking stack to scan this oop's oops.
7072 bool simulate_overflow = false;
7073 NOT_PRODUCT(
7074 if (CMSMarkStackOverflowALot &&
7075 _collector->simulate_overflow()) {
7076 // simulate a stack overflow
7077 simulate_overflow = true;
7078 }
7079 )
7080 if (simulate_overflow ||
7081 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7082 // stack overflow
7083 if (PrintCMSStatistics != 0) {
7084 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7085 SIZE_FORMAT, _overflow_stack->capacity());
7086 }
7087 // We cannot assert that the overflow stack is full because
7088 // it may have been emptied since.
7089 assert(simulate_overflow ||
7090 _work_queue->size() == _work_queue->max_elems(),
7091 "Else push should have succeeded");
7092 handle_stack_overflow(addr);
7093 }
7094 do_yield_check();
7095 }
7096 }
7097
7098 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7099 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7100
7101 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7102 MemRegion span,
7103 ReferenceProcessor* rp,
7104 CMSBitMap* bit_map,
7105 CMSBitMap* mod_union_table,
7106 CMSMarkStack* mark_stack,
7107 bool concurrent_precleaning):
7108 MetadataAwareOopClosure(rp),
7109 _collector(collector),
7110 _span(span),
7111 _bit_map(bit_map),
7112 _mod_union_table(mod_union_table),
7113 _mark_stack(mark_stack),
7114 _concurrent_precleaning(concurrent_precleaning)
7115 {
7116 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7117 }
7118
7119 // Grey object rescan during pre-cleaning and second checkpoint phases --
7120 // the non-parallel version (the parallel version appears further below.)
7121 void PushAndMarkClosure::do_oop(oop obj) {
7122 // Ignore mark word verification. If during concurrent precleaning,
7123 // the object monitor may be locked. If during the checkpoint
7124 // phases, the object may already have been reached by a different
7125 // path and may be at the end of the global overflow list (so
7126 // the mark word may be NULL).
7127 assert(obj->is_oop_or_null(true /* ignore mark word */),
7128 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7129 HeapWord* addr = (HeapWord*)obj;
7130 // Check if oop points into the CMS generation
7131 // and is not marked
7132 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7133 // a white object ...
7134 _bit_map->mark(addr); // ... now grey
7135 // push on the marking stack (grey set)
7136 bool simulate_overflow = false;
7137 NOT_PRODUCT(
7138 if (CMSMarkStackOverflowALot &&
7139 _collector->simulate_overflow()) {
7140 // simulate a stack overflow
7141 simulate_overflow = true;
7142 }
7143 )
7144 if (simulate_overflow || !_mark_stack->push(obj)) {
7145 if (_concurrent_precleaning) {
7146 // During precleaning we can just dirty the appropriate card(s)
7147 // in the mod union table, thus ensuring that the object remains
7148 // in the grey set and continue. In the case of object arrays
7149 // we need to dirty all of the cards that the object spans,
7150 // since the rescan of object arrays will be limited to the
7151 // dirty cards.
7152 // Note that no one can be interfering with us in this action
7153 // of dirtying the mod union table, so no locking or atomics
7154 // are required.
7155 if (obj->is_objArray()) {
7156 size_t sz = obj->size();
7157 HeapWord* end_card_addr = (HeapWord*)round_to(
7158 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7159 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7160 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7161 _mod_union_table->mark_range(redirty_range);
7162 } else {
7163 _mod_union_table->mark(addr);
7164 }
7165 _collector->_ser_pmc_preclean_ovflw++;
7166 } else {
7167 // During the remark phase, we need to remember this oop
7168 // in the overflow list.
7169 _collector->push_on_overflow_list(obj);
7170 _collector->_ser_pmc_remark_ovflw++;
7171 }
7172 }
7173 }
7174 }
7175
7176 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7177 MemRegion span,
7178 ReferenceProcessor* rp,
7179 CMSBitMap* bit_map,
7180 OopTaskQueue* work_queue):
7181 MetadataAwareOopClosure(rp),
7182 _collector(collector),
7183 _span(span),
7184 _bit_map(bit_map),
7185 _work_queue(work_queue)
7186 {
7187 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7188 }
7189
7190 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7191 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7192
7193 // Grey object rescan during second checkpoint phase --
7194 // the parallel version.
7195 void Par_PushAndMarkClosure::do_oop(oop obj) {
7196 // In the assert below, we ignore the mark word because
7197 // this oop may point to an already visited object that is
7198 // on the overflow stack (in which case the mark word has
7199 // been hijacked for chaining into the overflow stack --
7200 // if this is the last object in the overflow stack then
7201 // its mark word will be NULL). Because this object may
7202 // have been subsequently popped off the global overflow
7203 // stack, and the mark word possibly restored to the prototypical
7204 // value, by the time we get to examined this failing assert in
7205 // the debugger, is_oop_or_null(false) may subsequently start
7206 // to hold.
7207 assert(obj->is_oop_or_null(true),
7208 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7209 HeapWord* addr = (HeapWord*)obj;
7210 // Check if oop points into the CMS generation
7211 // and is not marked
7212 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7213 // a white object ...
7214 // If we manage to "claim" the object, by being the
7215 // first thread to mark it, then we push it on our
7216 // marking stack
7217 if (_bit_map->par_mark(addr)) { // ... now grey
7218 // push on work queue (grey set)
7219 bool simulate_overflow = false;
7220 NOT_PRODUCT(
7221 if (CMSMarkStackOverflowALot &&
7222 _collector->par_simulate_overflow()) {
7223 // simulate a stack overflow
7224 simulate_overflow = true;
7225 }
7226 )
7227 if (simulate_overflow || !_work_queue->push(obj)) {
7228 _collector->par_push_on_overflow_list(obj);
7229 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7230 }
7231 } // Else, some other thread got there first
7232 }
7233 }
7234
7235 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7236 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7237
7238 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7239 Mutex* bml = _collector->bitMapLock();
7240 assert_lock_strong(bml);
7241 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7242 "CMS thread should hold CMS token");
7243
7244 bml->unlock();
7245 ConcurrentMarkSweepThread::desynchronize(true);
7246
7247 _collector->stopTimer();
7248 if (PrintCMSStatistics != 0) {
7249 _collector->incrementYields();
7250 }
7251
7252 // See the comment in coordinator_yield()
7253 for (unsigned i = 0; i < CMSYieldSleepCount &&
7254 ConcurrentMarkSweepThread::should_yield() &&
7255 !CMSCollector::foregroundGCIsActive(); ++i) {
7256 os::sleep(Thread::current(), 1, false);
7257 }
7258
7259 ConcurrentMarkSweepThread::synchronize(true);
7260 bml->lock();
7261
7262 _collector->startTimer();
7263 }
7264
7265 bool CMSPrecleanRefsYieldClosure::should_return() {
7266 if (ConcurrentMarkSweepThread::should_yield()) {
7267 do_yield_work();
7268 }
7269 return _collector->foregroundGCIsActive();
7270 }
7271
7272 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7273 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7274 "mr should be aligned to start at a card boundary");
7275 // We'd like to assert:
7276 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7277 // "mr should be a range of cards");
7278 // However, that would be too strong in one case -- the last
7279 // partition ends at _unallocated_block which, in general, can be
7280 // an arbitrary boundary, not necessarily card aligned.
7281 if (PrintCMSStatistics != 0) {
7282 _num_dirty_cards +=
7283 mr.word_size()/CardTableModRefBS::card_size_in_words;
7284 }
7285 _space->object_iterate_mem(mr, &_scan_cl);
7286 }
7287
7288 SweepClosure::SweepClosure(CMSCollector* collector,
7289 ConcurrentMarkSweepGeneration* g,
7290 CMSBitMap* bitMap, bool should_yield) :
7291 _collector(collector),
7292 _g(g),
7293 _sp(g->cmsSpace()),
7294 _limit(_sp->sweep_limit()),
7295 _freelistLock(_sp->freelistLock()),
7296 _bitMap(bitMap),
7297 _yield(should_yield),
7298 _inFreeRange(false), // No free range at beginning of sweep
7299 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7300 _lastFreeRangeCoalesced(false),
7301 _freeFinger(g->used_region().start())
7302 {
7303 NOT_PRODUCT(
7304 _numObjectsFreed = 0;
7305 _numWordsFreed = 0;
7306 _numObjectsLive = 0;
7307 _numWordsLive = 0;
7308 _numObjectsAlreadyFree = 0;
7309 _numWordsAlreadyFree = 0;
7310 _last_fc = NULL;
7311
7312 _sp->initializeIndexedFreeListArrayReturnedBytes();
7313 _sp->dictionary()->initialize_dict_returned_bytes();
7314 )
7315 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7316 "sweep _limit out of bounds");
7317 if (CMSTraceSweeper) {
7318 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7319 p2i(_limit));
7320 }
7321 }
7322
7323 void SweepClosure::print_on(outputStream* st) const {
7324 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7325 p2i(_sp->bottom()), p2i(_sp->end()));
7326 tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7327 tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7328 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7329 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7330 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7331 }
7332
7333 #ifndef PRODUCT
7334 // Assertion checking only: no useful work in product mode --
7335 // however, if any of the flags below become product flags,
7336 // you may need to review this code to see if it needs to be
7337 // enabled in product mode.
7338 SweepClosure::~SweepClosure() {
7339 assert_lock_strong(_freelistLock);
7340 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7341 "sweep _limit out of bounds");
7342 if (inFreeRange()) {
7343 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7344 print();
7345 ShouldNotReachHere();
7346 }
7347 if (Verbose && PrintGC) {
7348 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7349 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7350 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7351 SIZE_FORMAT" bytes "
7352 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7353 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7354 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7355 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7356 * sizeof(HeapWord);
7357 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7358
7359 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7360 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7361 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7362 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7363 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7364 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7365 indexListReturnedBytes);
7366 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7367 dict_returned_bytes);
7368 }
7369 }
7370 if (CMSTraceSweeper) {
7371 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7372 p2i(_limit));
7373 }
7374 }
7375 #endif // PRODUCT
7376
7377 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7378 bool freeRangeInFreeLists) {
7379 if (CMSTraceSweeper) {
7380 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7381 p2i(freeFinger), freeRangeInFreeLists);
7382 }
7383 assert(!inFreeRange(), "Trampling existing free range");
7384 set_inFreeRange(true);
7385 set_lastFreeRangeCoalesced(false);
7386
7387 set_freeFinger(freeFinger);
7388 set_freeRangeInFreeLists(freeRangeInFreeLists);
7389 if (CMSTestInFreeList) {
7390 if (freeRangeInFreeLists) {
7391 FreeChunk* fc = (FreeChunk*) freeFinger;
7392 assert(fc->is_free(), "A chunk on the free list should be free.");
7393 assert(fc->size() > 0, "Free range should have a size");
7394 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7395 }
7396 }
7397 }
7398
7399 // Note that the sweeper runs concurrently with mutators. Thus,
7400 // it is possible for direct allocation in this generation to happen
7401 // in the middle of the sweep. Note that the sweeper also coalesces
7402 // contiguous free blocks. Thus, unless the sweeper and the allocator
7403 // synchronize appropriately freshly allocated blocks may get swept up.
7404 // This is accomplished by the sweeper locking the free lists while
7405 // it is sweeping. Thus blocks that are determined to be free are
7406 // indeed free. There is however one additional complication:
7407 // blocks that have been allocated since the final checkpoint and
7408 // mark, will not have been marked and so would be treated as
7409 // unreachable and swept up. To prevent this, the allocator marks
7410 // the bit map when allocating during the sweep phase. This leads,
7411 // however, to a further complication -- objects may have been allocated
7412 // but not yet initialized -- in the sense that the header isn't yet
7413 // installed. The sweeper can not then determine the size of the block
7414 // in order to skip over it. To deal with this case, we use a technique
7415 // (due to Printezis) to encode such uninitialized block sizes in the
7416 // bit map. Since the bit map uses a bit per every HeapWord, but the
7417 // CMS generation has a minimum object size of 3 HeapWords, it follows
7418 // that "normal marks" won't be adjacent in the bit map (there will
7419 // always be at least two 0 bits between successive 1 bits). We make use
7420 // of these "unused" bits to represent uninitialized blocks -- the bit
7421 // corresponding to the start of the uninitialized object and the next
7422 // bit are both set. Finally, a 1 bit marks the end of the object that
7423 // started with the two consecutive 1 bits to indicate its potentially
7424 // uninitialized state.
7425
7426 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7427 FreeChunk* fc = (FreeChunk*)addr;
7428 size_t res;
7429
7430 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7431 // than "addr == _limit" because although _limit was a block boundary when
7432 // we started the sweep, it may no longer be one because heap expansion
7433 // may have caused us to coalesce the block ending at the address _limit
7434 // with a newly expanded chunk (this happens when _limit was set to the
7435 // previous _end of the space), so we may have stepped past _limit:
7436 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7437 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7438 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7439 "sweep _limit out of bounds");
7440 assert(addr < _sp->end(), "addr out of bounds");
7441 // Flush any free range we might be holding as a single
7442 // coalesced chunk to the appropriate free list.
7443 if (inFreeRange()) {
7444 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7445 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", p2i(freeFinger())));
7446 flush_cur_free_chunk(freeFinger(),
7447 pointer_delta(addr, freeFinger()));
7448 if (CMSTraceSweeper) {
7449 gclog_or_tty->print("Sweep: last chunk: ");
7450 gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
7451 "[coalesced:%d]\n",
7452 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7453 lastFreeRangeCoalesced() ? 1 : 0);
7454 }
7455 }
7456
7457 // help the iterator loop finish
7458 return pointer_delta(_sp->end(), addr);
7459 }
7460
7461 assert(addr < _limit, "sweep invariant");
7462 // check if we should yield
7463 do_yield_check(addr);
7464 if (fc->is_free()) {
7465 // Chunk that is already free
7466 res = fc->size();
7467 do_already_free_chunk(fc);
7468 debug_only(_sp->verifyFreeLists());
7469 // If we flush the chunk at hand in lookahead_and_flush()
7470 // and it's coalesced with a preceding chunk, then the
7471 // process of "mangling" the payload of the coalesced block
7472 // will cause erasure of the size information from the
7473 // (erstwhile) header of all the coalesced blocks but the
7474 // first, so the first disjunct in the assert will not hold
7475 // in that specific case (in which case the second disjunct
7476 // will hold).
7477 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7478 "Otherwise the size info doesn't change at this step");
7479 NOT_PRODUCT(
7480 _numObjectsAlreadyFree++;
7481 _numWordsAlreadyFree += res;
7482 )
7483 NOT_PRODUCT(_last_fc = fc;)
7484 } else if (!_bitMap->isMarked(addr)) {
7485 // Chunk is fresh garbage
7486 res = do_garbage_chunk(fc);
7487 debug_only(_sp->verifyFreeLists());
7488 NOT_PRODUCT(
7489 _numObjectsFreed++;
7490 _numWordsFreed += res;
7491 )
7492 } else {
7493 // Chunk that is alive.
7494 res = do_live_chunk(fc);
7495 debug_only(_sp->verifyFreeLists());
7496 NOT_PRODUCT(
7497 _numObjectsLive++;
7498 _numWordsLive += res;
7499 )
7500 }
7501 return res;
7502 }
7503
7504 // For the smart allocation, record following
7505 // split deaths - a free chunk is removed from its free list because
7506 // it is being split into two or more chunks.
7507 // split birth - a free chunk is being added to its free list because
7508 // a larger free chunk has been split and resulted in this free chunk.
7509 // coal death - a free chunk is being removed from its free list because
7510 // it is being coalesced into a large free chunk.
7511 // coal birth - a free chunk is being added to its free list because
7512 // it was created when two or more free chunks where coalesced into
7513 // this free chunk.
7514 //
7515 // These statistics are used to determine the desired number of free
7516 // chunks of a given size. The desired number is chosen to be relative
7517 // to the end of a CMS sweep. The desired number at the end of a sweep
7518 // is the
7519 // count-at-end-of-previous-sweep (an amount that was enough)
7520 // - count-at-beginning-of-current-sweep (the excess)
7521 // + split-births (gains in this size during interval)
7522 // - split-deaths (demands on this size during interval)
7523 // where the interval is from the end of one sweep to the end of the
7524 // next.
7525 //
7526 // When sweeping the sweeper maintains an accumulated chunk which is
7527 // the chunk that is made up of chunks that have been coalesced. That
7528 // will be termed the left-hand chunk. A new chunk of garbage that
7529 // is being considered for coalescing will be referred to as the
7530 // right-hand chunk.
7531 //
7532 // When making a decision on whether to coalesce a right-hand chunk with
7533 // the current left-hand chunk, the current count vs. the desired count
7534 // of the left-hand chunk is considered. Also if the right-hand chunk
7535 // is near the large chunk at the end of the heap (see
7536 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7537 // left-hand chunk is coalesced.
7538 //
7539 // When making a decision about whether to split a chunk, the desired count
7540 // vs. the current count of the candidate to be split is also considered.
7541 // If the candidate is underpopulated (currently fewer chunks than desired)
7542 // a chunk of an overpopulated (currently more chunks than desired) size may
7543 // be chosen. The "hint" associated with a free list, if non-null, points
7544 // to a free list which may be overpopulated.
7545 //
7546
7547 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7548 const size_t size = fc->size();
7549 // Chunks that cannot be coalesced are not in the
7550 // free lists.
7551 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7552 assert(_sp->verify_chunk_in_free_list(fc),
7553 "free chunk should be in free lists");
7554 }
7555 // a chunk that is already free, should not have been
7556 // marked in the bit map
7557 HeapWord* const addr = (HeapWord*) fc;
7558 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7559 // Verify that the bit map has no bits marked between
7560 // addr and purported end of this block.
7561 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7562
7563 // Some chunks cannot be coalesced under any circumstances.
7564 // See the definition of cantCoalesce().
7565 if (!fc->cantCoalesce()) {
7566 // This chunk can potentially be coalesced.
7567 if (_sp->adaptive_freelists()) {
7568 // All the work is done in
7569 do_post_free_or_garbage_chunk(fc, size);
7570 } else { // Not adaptive free lists
7571 // this is a free chunk that can potentially be coalesced by the sweeper;
7572 if (!inFreeRange()) {
7573 // if the next chunk is a free block that can't be coalesced
7574 // it doesn't make sense to remove this chunk from the free lists
7575 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7576 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
7577 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
7578 nextChunk->is_free() && // ... which is free...
7579 nextChunk->cantCoalesce()) { // ... but can't be coalesced
7580 // nothing to do
7581 } else {
7582 // Potentially the start of a new free range:
7583 // Don't eagerly remove it from the free lists.
7584 // No need to remove it if it will just be put
7585 // back again. (Also from a pragmatic point of view
7586 // if it is a free block in a region that is beyond
7587 // any allocated blocks, an assertion will fail)
7588 // Remember the start of a free run.
7589 initialize_free_range(addr, true);
7590 // end - can coalesce with next chunk
7591 }
7592 } else {
7593 // the midst of a free range, we are coalescing
7594 print_free_block_coalesced(fc);
7595 if (CMSTraceSweeper) {
7596 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7597 }
7598 // remove it from the free lists
7599 _sp->removeFreeChunkFromFreeLists(fc);
7600 set_lastFreeRangeCoalesced(true);
7601 // If the chunk is being coalesced and the current free range is
7602 // in the free lists, remove the current free range so that it
7603 // will be returned to the free lists in its entirety - all
7604 // the coalesced pieces included.
7605 if (freeRangeInFreeLists()) {
7606 FreeChunk* ffc = (FreeChunk*) freeFinger();
7607 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7608 "Size of free range is inconsistent with chunk size.");
7609 if (CMSTestInFreeList) {
7610 assert(_sp->verify_chunk_in_free_list(ffc),
7611 "free range is not in free lists");
7612 }
7613 _sp->removeFreeChunkFromFreeLists(ffc);
7614 set_freeRangeInFreeLists(false);
7615 }
7616 }
7617 }
7618 // Note that if the chunk is not coalescable (the else arm
7619 // below), we unconditionally flush, without needing to do
7620 // a "lookahead," as we do below.
7621 if (inFreeRange()) lookahead_and_flush(fc, size);
7622 } else {
7623 // Code path common to both original and adaptive free lists.
7624
7625 // cant coalesce with previous block; this should be treated
7626 // as the end of a free run if any
7627 if (inFreeRange()) {
7628 // we kicked some butt; time to pick up the garbage
7629 assert(freeFinger() < addr, "freeFinger points too high");
7630 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7631 }
7632 // else, nothing to do, just continue
7633 }
7634 }
7635
7636 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7637 // This is a chunk of garbage. It is not in any free list.
7638 // Add it to a free list or let it possibly be coalesced into
7639 // a larger chunk.
7640 HeapWord* const addr = (HeapWord*) fc;
7641 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7642
7643 if (_sp->adaptive_freelists()) {
7644 // Verify that the bit map has no bits marked between
7645 // addr and purported end of just dead object.
7646 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7647
7648 do_post_free_or_garbage_chunk(fc, size);
7649 } else {
7650 if (!inFreeRange()) {
7651 // start of a new free range
7652 assert(size > 0, "A free range should have a size");
7653 initialize_free_range(addr, false);
7654 } else {
7655 // this will be swept up when we hit the end of the
7656 // free range
7657 if (CMSTraceSweeper) {
7658 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7659 }
7660 // If the chunk is being coalesced and the current free range is
7661 // in the free lists, remove the current free range so that it
7662 // will be returned to the free lists in its entirety - all
7663 // the coalesced pieces included.
7664 if (freeRangeInFreeLists()) {
7665 FreeChunk* ffc = (FreeChunk*)freeFinger();
7666 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7667 "Size of free range is inconsistent with chunk size.");
7668 if (CMSTestInFreeList) {
7669 assert(_sp->verify_chunk_in_free_list(ffc),
7670 "free range is not in free lists");
7671 }
7672 _sp->removeFreeChunkFromFreeLists(ffc);
7673 set_freeRangeInFreeLists(false);
7674 }
7675 set_lastFreeRangeCoalesced(true);
7676 }
7677 // this will be swept up when we hit the end of the free range
7678
7679 // Verify that the bit map has no bits marked between
7680 // addr and purported end of just dead object.
7681 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7682 }
7683 assert(_limit >= addr + size,
7684 "A freshly garbage chunk can't possibly straddle over _limit");
7685 if (inFreeRange()) lookahead_and_flush(fc, size);
7686 return size;
7687 }
7688
7689 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7690 HeapWord* addr = (HeapWord*) fc;
7691 // The sweeper has just found a live object. Return any accumulated
7692 // left hand chunk to the free lists.
7693 if (inFreeRange()) {
7694 assert(freeFinger() < addr, "freeFinger points too high");
7695 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7696 }
7697
7698 // This object is live: we'd normally expect this to be
7699 // an oop, and like to assert the following:
7700 // assert(oop(addr)->is_oop(), "live block should be an oop");
7701 // However, as we commented above, this may be an object whose
7702 // header hasn't yet been initialized.
7703 size_t size;
7704 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7705 if (_bitMap->isMarked(addr + 1)) {
7706 // Determine the size from the bit map, rather than trying to
7707 // compute it from the object header.
7708 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7709 size = pointer_delta(nextOneAddr + 1, addr);
7710 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7711 "alignment problem");
7712
7713 #ifdef ASSERT
7714 if (oop(addr)->klass_or_null() != NULL) {
7715 // Ignore mark word because we are running concurrent with mutators
7716 assert(oop(addr)->is_oop(true), "live block should be an oop");
7717 assert(size ==
7718 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7719 "P-mark and computed size do not agree");
7720 }
7721 #endif
7722
7723 } else {
7724 // This should be an initialized object that's alive.
7725 assert(oop(addr)->klass_or_null() != NULL,
7726 "Should be an initialized object");
7727 // Ignore mark word because we are running concurrent with mutators
7728 assert(oop(addr)->is_oop(true), "live block should be an oop");
7729 // Verify that the bit map has no bits marked between
7730 // addr and purported end of this block.
7731 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7732 assert(size >= 3, "Necessary for Printezis marks to work");
7733 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7734 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7735 }
7736 return size;
7737 }
7738
7739 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7740 size_t chunkSize) {
7741 // do_post_free_or_garbage_chunk() should only be called in the case
7742 // of the adaptive free list allocator.
7743 const bool fcInFreeLists = fc->is_free();
7744 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
7745 assert((HeapWord*)fc <= _limit, "sweep invariant");
7746 if (CMSTestInFreeList && fcInFreeLists) {
7747 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7748 }
7749
7750 if (CMSTraceSweeper) {
7751 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7752 }
7753
7754 HeapWord* const fc_addr = (HeapWord*) fc;
7755
7756 bool coalesce;
7757 const size_t left = pointer_delta(fc_addr, freeFinger());
7758 const size_t right = chunkSize;
7759 switch (FLSCoalescePolicy) {
7760 // numeric value forms a coalition aggressiveness metric
7761 case 0: { // never coalesce
7762 coalesce = false;
7763 break;
7764 }
7765 case 1: { // coalesce if left & right chunks on overpopulated lists
7766 coalesce = _sp->coalOverPopulated(left) &&
7767 _sp->coalOverPopulated(right);
7768 break;
7769 }
7770 case 2: { // coalesce if left chunk on overpopulated list (default)
7771 coalesce = _sp->coalOverPopulated(left);
7772 break;
7773 }
7774 case 3: { // coalesce if left OR right chunk on overpopulated list
7775 coalesce = _sp->coalOverPopulated(left) ||
7776 _sp->coalOverPopulated(right);
7777 break;
7778 }
7779 case 4: { // always coalesce
7780 coalesce = true;
7781 break;
7782 }
7783 default:
7784 ShouldNotReachHere();
7785 }
7786
7787 // Should the current free range be coalesced?
7788 // If the chunk is in a free range and either we decided to coalesce above
7789 // or the chunk is near the large block at the end of the heap
7790 // (isNearLargestChunk() returns true), then coalesce this chunk.
7791 const bool doCoalesce = inFreeRange()
7792 && (coalesce || _g->isNearLargestChunk(fc_addr));
7793 if (doCoalesce) {
7794 // Coalesce the current free range on the left with the new
7795 // chunk on the right. If either is on a free list,
7796 // it must be removed from the list and stashed in the closure.
7797 if (freeRangeInFreeLists()) {
7798 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7799 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7800 "Size of free range is inconsistent with chunk size.");
7801 if (CMSTestInFreeList) {
7802 assert(_sp->verify_chunk_in_free_list(ffc),
7803 "Chunk is not in free lists");
7804 }
7805 _sp->coalDeath(ffc->size());
7806 _sp->removeFreeChunkFromFreeLists(ffc);
7807 set_freeRangeInFreeLists(false);
7808 }
7809 if (fcInFreeLists) {
7810 _sp->coalDeath(chunkSize);
7811 assert(fc->size() == chunkSize,
7812 "The chunk has the wrong size or is not in the free lists");
7813 _sp->removeFreeChunkFromFreeLists(fc);
7814 }
7815 set_lastFreeRangeCoalesced(true);
7816 print_free_block_coalesced(fc);
7817 } else { // not in a free range and/or should not coalesce
7818 // Return the current free range and start a new one.
7819 if (inFreeRange()) {
7820 // In a free range but cannot coalesce with the right hand chunk.
7821 // Put the current free range into the free lists.
7822 flush_cur_free_chunk(freeFinger(),
7823 pointer_delta(fc_addr, freeFinger()));
7824 }
7825 // Set up for new free range. Pass along whether the right hand
7826 // chunk is in the free lists.
7827 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7828 }
7829 }
7830
7831 // Lookahead flush:
7832 // If we are tracking a free range, and this is the last chunk that
7833 // we'll look at because its end crosses past _limit, we'll preemptively
7834 // flush it along with any free range we may be holding on to. Note that
7835 // this can be the case only for an already free or freshly garbage
7836 // chunk. If this block is an object, it can never straddle
7837 // over _limit. The "straddling" occurs when _limit is set at
7838 // the previous end of the space when this cycle started, and
7839 // a subsequent heap expansion caused the previously co-terminal
7840 // free block to be coalesced with the newly expanded portion,
7841 // thus rendering _limit a non-block-boundary making it dangerous
7842 // for the sweeper to step over and examine.
7843 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7844 assert(inFreeRange(), "Should only be called if currently in a free range.");
7845 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7846 assert(_sp->used_region().contains(eob - 1),
7847 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7848 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7849 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7850 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size));
7851 if (eob >= _limit) {
7852 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7853 if (CMSTraceSweeper) {
7854 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7855 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7856 "[" PTR_FORMAT "," PTR_FORMAT ")",
7857 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7858 }
7859 // Return the storage we are tracking back into the free lists.
7860 if (CMSTraceSweeper) {
7861 gclog_or_tty->print_cr("Flushing ... ");
7862 }
7863 assert(freeFinger() < eob, "Error");
7864 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7865 }
7866 }
7867
7868 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7869 assert(inFreeRange(), "Should only be called if currently in a free range.");
7870 assert(size > 0,
7871 "A zero sized chunk cannot be added to the free lists.");
7872 if (!freeRangeInFreeLists()) {
7873 if (CMSTestInFreeList) {
7874 FreeChunk* fc = (FreeChunk*) chunk;
7875 fc->set_size(size);
7876 assert(!_sp->verify_chunk_in_free_list(fc),
7877 "chunk should not be in free lists yet");
7878 }
7879 if (CMSTraceSweeper) {
7880 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7881 p2i(chunk), size);
7882 }
7883 // A new free range is going to be starting. The current
7884 // free range has not been added to the free lists yet or
7885 // was removed so add it back.
7886 // If the current free range was coalesced, then the death
7887 // of the free range was recorded. Record a birth now.
7888 if (lastFreeRangeCoalesced()) {
7889 _sp->coalBirth(size);
7890 }
7891 _sp->addChunkAndRepairOffsetTable(chunk, size,
7892 lastFreeRangeCoalesced());
7893 } else if (CMSTraceSweeper) {
7894 gclog_or_tty->print_cr("Already in free list: nothing to flush");
7895 }
7896 set_inFreeRange(false);
7897 set_freeRangeInFreeLists(false);
7898 }
7899
7900 // We take a break if we've been at this for a while,
7901 // so as to avoid monopolizing the locks involved.
7902 void SweepClosure::do_yield_work(HeapWord* addr) {
7903 // Return current free chunk being used for coalescing (if any)
7904 // to the appropriate freelist. After yielding, the next
7905 // free block encountered will start a coalescing range of
7906 // free blocks. If the next free block is adjacent to the
7907 // chunk just flushed, they will need to wait for the next
7908 // sweep to be coalesced.
7909 if (inFreeRange()) {
7910 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7911 }
7912
7913 // First give up the locks, then yield, then re-lock.
7914 // We should probably use a constructor/destructor idiom to
7915 // do this unlock/lock or modify the MutexUnlocker class to
7916 // serve our purpose. XXX
7917 assert_lock_strong(_bitMap->lock());
7918 assert_lock_strong(_freelistLock);
7919 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7920 "CMS thread should hold CMS token");
7921 _bitMap->lock()->unlock();
7922 _freelistLock->unlock();
7923 ConcurrentMarkSweepThread::desynchronize(true);
7924 _collector->stopTimer();
7925 if (PrintCMSStatistics != 0) {
7926 _collector->incrementYields();
7927 }
7928
7929 // See the comment in coordinator_yield()
7930 for (unsigned i = 0; i < CMSYieldSleepCount &&
7931 ConcurrentMarkSweepThread::should_yield() &&
7932 !CMSCollector::foregroundGCIsActive(); ++i) {
7933 os::sleep(Thread::current(), 1, false);
7934 }
7935
7936 ConcurrentMarkSweepThread::synchronize(true);
7937 _freelistLock->lock();
7938 _bitMap->lock()->lock_without_safepoint_check();
7939 _collector->startTimer();
7940 }
7941
7942 #ifndef PRODUCT
7943 // This is actually very useful in a product build if it can
7944 // be called from the debugger. Compile it into the product
7945 // as needed.
7946 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7947 return debug_cms_space->verify_chunk_in_free_list(fc);
7948 }
7949 #endif
7950
7951 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7952 if (CMSTraceSweeper) {
7953 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7954 p2i(fc), fc->size());
7955 }
7956 }
7957
7958 // CMSIsAliveClosure
7959 bool CMSIsAliveClosure::do_object_b(oop obj) {
7960 HeapWord* addr = (HeapWord*)obj;
7961 return addr != NULL &&
7962 (!_span.contains(addr) || _bit_map->isMarked(addr));
7963 }
7964
7965
7966 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7967 MemRegion span,
7968 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7969 bool cpc):
7970 _collector(collector),
7971 _span(span),
7972 _bit_map(bit_map),
7973 _mark_stack(mark_stack),
7974 _concurrent_precleaning(cpc) {
7975 assert(!_span.is_empty(), "Empty span could spell trouble");
7976 }
7977
7978
7979 // CMSKeepAliveClosure: the serial version
7980 void CMSKeepAliveClosure::do_oop(oop obj) {
7981 HeapWord* addr = (HeapWord*)obj;
7982 if (_span.contains(addr) &&
7983 !_bit_map->isMarked(addr)) {
7984 _bit_map->mark(addr);
7985 bool simulate_overflow = false;
7986 NOT_PRODUCT(
7987 if (CMSMarkStackOverflowALot &&
7988 _collector->simulate_overflow()) {
7989 // simulate a stack overflow
7990 simulate_overflow = true;
7991 }
7992 )
7993 if (simulate_overflow || !_mark_stack->push(obj)) {
7994 if (_concurrent_precleaning) {
7995 // We dirty the overflown object and let the remark
7996 // phase deal with it.
7997 assert(_collector->overflow_list_is_empty(), "Error");
7998 // In the case of object arrays, we need to dirty all of
7999 // the cards that the object spans. No locking or atomics
8000 // are needed since no one else can be mutating the mod union
8001 // table.
8002 if (obj->is_objArray()) {
8003 size_t sz = obj->size();
8004 HeapWord* end_card_addr =
8005 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8006 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8007 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8008 _collector->_modUnionTable.mark_range(redirty_range);
8009 } else {
8010 _collector->_modUnionTable.mark(addr);
8011 }
8012 _collector->_ser_kac_preclean_ovflw++;
8013 } else {
8014 _collector->push_on_overflow_list(obj);
8015 _collector->_ser_kac_ovflw++;
8016 }
8017 }
8018 }
8019 }
8020
8021 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8022 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8023
8024 // CMSParKeepAliveClosure: a parallel version of the above.
8025 // The work queues are private to each closure (thread),
8026 // but (may be) available for stealing by other threads.
8027 void CMSParKeepAliveClosure::do_oop(oop obj) {
8028 HeapWord* addr = (HeapWord*)obj;
8029 if (_span.contains(addr) &&
8030 !_bit_map->isMarked(addr)) {
8031 // In general, during recursive tracing, several threads
8032 // may be concurrently getting here; the first one to
8033 // "tag" it, claims it.
8034 if (_bit_map->par_mark(addr)) {
8035 bool res = _work_queue->push(obj);
8036 assert(res, "Low water mark should be much less than capacity");
8037 // Do a recursive trim in the hope that this will keep
8038 // stack usage lower, but leave some oops for potential stealers
8039 trim_queue(_low_water_mark);
8040 } // Else, another thread got there first
8041 }
8042 }
8043
8044 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8045 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8046
8047 void CMSParKeepAliveClosure::trim_queue(uint max) {
8048 while (_work_queue->size() > max) {
8049 oop new_oop;
8050 if (_work_queue->pop_local(new_oop)) {
8051 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8052 assert(_bit_map->isMarked((HeapWord*)new_oop),
8053 "no white objects on this stack!");
8054 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8055 // iterate over the oops in this oop, marking and pushing
8056 // the ones in CMS heap (i.e. in _span).
8057 new_oop->oop_iterate(&_mark_and_push);
8058 }
8059 }
8060 }
8061
8062 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8063 CMSCollector* collector,
8064 MemRegion span, CMSBitMap* bit_map,
8065 OopTaskQueue* work_queue):
8066 _collector(collector),
8067 _span(span),
8068 _bit_map(bit_map),
8069 _work_queue(work_queue) { }
8070
8071 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8072 HeapWord* addr = (HeapWord*)obj;
8073 if (_span.contains(addr) &&
8074 !_bit_map->isMarked(addr)) {
8075 if (_bit_map->par_mark(addr)) {
8076 bool simulate_overflow = false;
8077 NOT_PRODUCT(
8078 if (CMSMarkStackOverflowALot &&
8079 _collector->par_simulate_overflow()) {
8080 // simulate a stack overflow
8081 simulate_overflow = true;
8082 }
8083 )
8084 if (simulate_overflow || !_work_queue->push(obj)) {
8085 _collector->par_push_on_overflow_list(obj);
8086 _collector->_par_kac_ovflw++;
8087 }
8088 } // Else another thread got there already
8089 }
8090 }
8091
8092 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8093 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8094
8095 //////////////////////////////////////////////////////////////////
8096 // CMSExpansionCause /////////////////////////////
8097 //////////////////////////////////////////////////////////////////
8098 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8099 switch (cause) {
8100 case _no_expansion:
8101 return "No expansion";
8102 case _satisfy_free_ratio:
8103 return "Free ratio";
8104 case _satisfy_promotion:
8105 return "Satisfy promotion";
8106 case _satisfy_allocation:
8107 return "allocation";
8108 case _allocate_par_lab:
8109 return "Par LAB";
8110 case _allocate_par_spooling_space:
8111 return "Par Spooling Space";
8112 case _adaptive_size_policy:
8113 return "Ergonomics";
8114 default:
8115 return "unknown";
8116 }
8117 }
8118
8119 void CMSDrainMarkingStackClosure::do_void() {
8120 // the max number to take from overflow list at a time
8121 const size_t num = _mark_stack->capacity()/4;
8122 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8123 "Overflow list should be NULL during concurrent phases");
8124 while (!_mark_stack->isEmpty() ||
8125 // if stack is empty, check the overflow list
8126 _collector->take_from_overflow_list(num, _mark_stack)) {
8127 oop obj = _mark_stack->pop();
8128 HeapWord* addr = (HeapWord*)obj;
8129 assert(_span.contains(addr), "Should be within span");
8130 assert(_bit_map->isMarked(addr), "Should be marked");
8131 assert(obj->is_oop(), "Should be an oop");
8132 obj->oop_iterate(_keep_alive);
8133 }
8134 }
8135
8136 void CMSParDrainMarkingStackClosure::do_void() {
8137 // drain queue
8138 trim_queue(0);
8139 }
8140
8141 // Trim our work_queue so its length is below max at return
8142 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8143 while (_work_queue->size() > max) {
8144 oop new_oop;
8145 if (_work_queue->pop_local(new_oop)) {
8146 assert(new_oop->is_oop(), "Expected an oop");
8147 assert(_bit_map->isMarked((HeapWord*)new_oop),
8148 "no white objects on this stack!");
8149 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8150 // iterate over the oops in this oop, marking and pushing
8151 // the ones in CMS heap (i.e. in _span).
8152 new_oop->oop_iterate(&_mark_and_push);
8153 }
8154 }
8155 }
8156
8157 ////////////////////////////////////////////////////////////////////
8158 // Support for Marking Stack Overflow list handling and related code
8159 ////////////////////////////////////////////////////////////////////
8160 // Much of the following code is similar in shape and spirit to the
8161 // code used in ParNewGC. We should try and share that code
8162 // as much as possible in the future.
8163
8164 #ifndef PRODUCT
8165 // Debugging support for CMSStackOverflowALot
8166
8167 // It's OK to call this multi-threaded; the worst thing
8168 // that can happen is that we'll get a bunch of closely
8169 // spaced simulated overflows, but that's OK, in fact
8170 // probably good as it would exercise the overflow code
8171 // under contention.
8172 bool CMSCollector::simulate_overflow() {
8173 if (_overflow_counter-- <= 0) { // just being defensive
8174 _overflow_counter = CMSMarkStackOverflowInterval;
8175 return true;
8176 } else {
8177 return false;
8178 }
8179 }
8180
8181 bool CMSCollector::par_simulate_overflow() {
8182 return simulate_overflow();
8183 }
8184 #endif
8185
8186 // Single-threaded
8187 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8188 assert(stack->isEmpty(), "Expected precondition");
8189 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8190 size_t i = num;
8191 oop cur = _overflow_list;
8192 const markOop proto = markOopDesc::prototype();
8193 NOT_PRODUCT(ssize_t n = 0;)
8194 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8195 next = oop(cur->mark());
8196 cur->set_mark(proto); // until proven otherwise
8197 assert(cur->is_oop(), "Should be an oop");
8198 bool res = stack->push(cur);
8199 assert(res, "Bit off more than can chew?");
8200 NOT_PRODUCT(n++;)
8201 }
8202 _overflow_list = cur;
8203 #ifndef PRODUCT
8204 assert(_num_par_pushes >= n, "Too many pops?");
8205 _num_par_pushes -=n;
8206 #endif
8207 return !stack->isEmpty();
8208 }
8209
8210 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8211 // (MT-safe) Get a prefix of at most "num" from the list.
8212 // The overflow list is chained through the mark word of
8213 // each object in the list. We fetch the entire list,
8214 // break off a prefix of the right size and return the
8215 // remainder. If other threads try to take objects from
8216 // the overflow list at that time, they will wait for
8217 // some time to see if data becomes available. If (and
8218 // only if) another thread places one or more object(s)
8219 // on the global list before we have returned the suffix
8220 // to the global list, we will walk down our local list
8221 // to find its end and append the global list to
8222 // our suffix before returning it. This suffix walk can
8223 // prove to be expensive (quadratic in the amount of traffic)
8224 // when there are many objects in the overflow list and
8225 // there is much producer-consumer contention on the list.
8226 // *NOTE*: The overflow list manipulation code here and
8227 // in ParNewGeneration:: are very similar in shape,
8228 // except that in the ParNew case we use the old (from/eden)
8229 // copy of the object to thread the list via its klass word.
8230 // Because of the common code, if you make any changes in
8231 // the code below, please check the ParNew version to see if
8232 // similar changes might be needed.
8233 // CR 6797058 has been filed to consolidate the common code.
8234 bool CMSCollector::par_take_from_overflow_list(size_t num,
8235 OopTaskQueue* work_q,
8236 int no_of_gc_threads) {
8237 assert(work_q->size() == 0, "First empty local work queue");
8238 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8239 if (_overflow_list == NULL) {
8240 return false;
8241 }
8242 // Grab the entire list; we'll put back a suffix
8243 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8244 Thread* tid = Thread::current();
8245 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8246 // set to ParallelGCThreads.
8247 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8248 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8249 // If the list is busy, we spin for a short while,
8250 // sleeping between attempts to get the list.
8251 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8252 os::sleep(tid, sleep_time_millis, false);
8253 if (_overflow_list == NULL) {
8254 // Nothing left to take
8255 return false;
8256 } else if (_overflow_list != BUSY) {
8257 // Try and grab the prefix
8258 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8259 }
8260 }
8261 // If the list was found to be empty, or we spun long
8262 // enough, we give up and return empty-handed. If we leave
8263 // the list in the BUSY state below, it must be the case that
8264 // some other thread holds the overflow list and will set it
8265 // to a non-BUSY state in the future.
8266 if (prefix == NULL || prefix == BUSY) {
8267 // Nothing to take or waited long enough
8268 if (prefix == NULL) {
8269 // Write back the NULL in case we overwrote it with BUSY above
8270 // and it is still the same value.
8271 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8272 }
8273 return false;
8274 }
8275 assert(prefix != NULL && prefix != BUSY, "Error");
8276 size_t i = num;
8277 oop cur = prefix;
8278 // Walk down the first "num" objects, unless we reach the end.
8279 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8280 if (cur->mark() == NULL) {
8281 // We have "num" or fewer elements in the list, so there
8282 // is nothing to return to the global list.
8283 // Write back the NULL in lieu of the BUSY we wrote
8284 // above, if it is still the same value.
8285 if (_overflow_list == BUSY) {
8286 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8287 }
8288 } else {
8289 // Chop off the suffix and return it to the global list.
8290 assert(cur->mark() != BUSY, "Error");
8291 oop suffix_head = cur->mark(); // suffix will be put back on global list
8292 cur->set_mark(NULL); // break off suffix
8293 // It's possible that the list is still in the empty(busy) state
8294 // we left it in a short while ago; in that case we may be
8295 // able to place back the suffix without incurring the cost
8296 // of a walk down the list.
8297 oop observed_overflow_list = _overflow_list;
8298 oop cur_overflow_list = observed_overflow_list;
8299 bool attached = false;
8300 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8301 observed_overflow_list =
8302 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8303 if (cur_overflow_list == observed_overflow_list) {
8304 attached = true;
8305 break;
8306 } else cur_overflow_list = observed_overflow_list;
8307 }
8308 if (!attached) {
8309 // Too bad, someone else sneaked in (at least) an element; we'll need
8310 // to do a splice. Find tail of suffix so we can prepend suffix to global
8311 // list.
8312 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8313 oop suffix_tail = cur;
8314 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8315 "Tautology");
8316 observed_overflow_list = _overflow_list;
8317 do {
8318 cur_overflow_list = observed_overflow_list;
8319 if (cur_overflow_list != BUSY) {
8320 // Do the splice ...
8321 suffix_tail->set_mark(markOop(cur_overflow_list));
8322 } else { // cur_overflow_list == BUSY
8323 suffix_tail->set_mark(NULL);
8324 }
8325 // ... and try to place spliced list back on overflow_list ...
8326 observed_overflow_list =
8327 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8328 } while (cur_overflow_list != observed_overflow_list);
8329 // ... until we have succeeded in doing so.
8330 }
8331 }
8332
8333 // Push the prefix elements on work_q
8334 assert(prefix != NULL, "control point invariant");
8335 const markOop proto = markOopDesc::prototype();
8336 oop next;
8337 NOT_PRODUCT(ssize_t n = 0;)
8338 for (cur = prefix; cur != NULL; cur = next) {
8339 next = oop(cur->mark());
8340 cur->set_mark(proto); // until proven otherwise
8341 assert(cur->is_oop(), "Should be an oop");
8342 bool res = work_q->push(cur);
8343 assert(res, "Bit off more than we can chew?");
8344 NOT_PRODUCT(n++;)
8345 }
8346 #ifndef PRODUCT
8347 assert(_num_par_pushes >= n, "Too many pops?");
8348 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8349 #endif
8350 return true;
8351 }
8352
8353 // Single-threaded
8354 void CMSCollector::push_on_overflow_list(oop p) {
8355 NOT_PRODUCT(_num_par_pushes++;)
8356 assert(p->is_oop(), "Not an oop");
8357 preserve_mark_if_necessary(p);
8358 p->set_mark((markOop)_overflow_list);
8359 _overflow_list = p;
8360 }
8361
8362 // Multi-threaded; use CAS to prepend to overflow list
8363 void CMSCollector::par_push_on_overflow_list(oop p) {
8364 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8365 assert(p->is_oop(), "Not an oop");
8366 par_preserve_mark_if_necessary(p);
8367 oop observed_overflow_list = _overflow_list;
8368 oop cur_overflow_list;
8369 do {
8370 cur_overflow_list = observed_overflow_list;
8371 if (cur_overflow_list != BUSY) {
8372 p->set_mark(markOop(cur_overflow_list));
8373 } else {
8374 p->set_mark(NULL);
8375 }
8376 observed_overflow_list =
8377 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8378 } while (cur_overflow_list != observed_overflow_list);
8379 }
8380 #undef BUSY
8381
8382 // Single threaded
8383 // General Note on GrowableArray: pushes may silently fail
8384 // because we are (temporarily) out of C-heap for expanding
8385 // the stack. The problem is quite ubiquitous and affects
8386 // a lot of code in the JVM. The prudent thing for GrowableArray
8387 // to do (for now) is to exit with an error. However, that may
8388 // be too draconian in some cases because the caller may be
8389 // able to recover without much harm. For such cases, we
8390 // should probably introduce a "soft_push" method which returns
8391 // an indication of success or failure with the assumption that
8392 // the caller may be able to recover from a failure; code in
8393 // the VM can then be changed, incrementally, to deal with such
8394 // failures where possible, thus, incrementally hardening the VM
8395 // in such low resource situations.
8396 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8397 _preserved_oop_stack.push(p);
8398 _preserved_mark_stack.push(m);
8399 assert(m == p->mark(), "Mark word changed");
8400 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8401 "bijection");
8402 }
8403
8404 // Single threaded
8405 void CMSCollector::preserve_mark_if_necessary(oop p) {
8406 markOop m = p->mark();
8407 if (m->must_be_preserved(p)) {
8408 preserve_mark_work(p, m);
8409 }
8410 }
8411
8412 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8413 markOop m = p->mark();
8414 if (m->must_be_preserved(p)) {
8415 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8416 // Even though we read the mark word without holding
8417 // the lock, we are assured that it will not change
8418 // because we "own" this oop, so no other thread can
8419 // be trying to push it on the overflow list; see
8420 // the assertion in preserve_mark_work() that checks
8421 // that m == p->mark().
8422 preserve_mark_work(p, m);
8423 }
8424 }
8425
8426 // We should be able to do this multi-threaded,
8427 // a chunk of stack being a task (this is
8428 // correct because each oop only ever appears
8429 // once in the overflow list. However, it's
8430 // not very easy to completely overlap this with
8431 // other operations, so will generally not be done
8432 // until all work's been completed. Because we
8433 // expect the preserved oop stack (set) to be small,
8434 // it's probably fine to do this single-threaded.
8435 // We can explore cleverer concurrent/overlapped/parallel
8436 // processing of preserved marks if we feel the
8437 // need for this in the future. Stack overflow should
8438 // be so rare in practice and, when it happens, its
8439 // effect on performance so great that this will
8440 // likely just be in the noise anyway.
8441 void CMSCollector::restore_preserved_marks_if_any() {
8442 assert(SafepointSynchronize::is_at_safepoint(),
8443 "world should be stopped");
8444 assert(Thread::current()->is_ConcurrentGC_thread() ||
8445 Thread::current()->is_VM_thread(),
8446 "should be single-threaded");
8447 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8448 "bijection");
8449
8450 while (!_preserved_oop_stack.is_empty()) {
8451 oop p = _preserved_oop_stack.pop();
8452 assert(p->is_oop(), "Should be an oop");
8453 assert(_span.contains(p), "oop should be in _span");
8454 assert(p->mark() == markOopDesc::prototype(),
8455 "Set when taken from overflow list");
8456 markOop m = _preserved_mark_stack.pop();
8457 p->set_mark(m);
8458 }
8459 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8460 "stacks were cleared above");
8461 }
8462
8463 #ifndef PRODUCT
8464 bool CMSCollector::no_preserved_marks() const {
8465 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8466 }
8467 #endif
8468
8469 // Transfer some number of overflown objects to usual marking
8470 // stack. Return true if some objects were transferred.
8471 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8472 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8473 (size_t)ParGCDesiredObjsFromOverflowList);
8474
8475 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8476 assert(_collector->overflow_list_is_empty() || res,
8477 "If list is not empty, we should have taken something");
8478 assert(!res || !_mark_stack->isEmpty(),
8479 "If we took something, it should now be on our stack");
8480 return res;
8481 }
8482
8483 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8484 size_t res = _sp->block_size_no_stall(addr, _collector);
8485 if (_sp->block_is_obj(addr)) {
8486 if (_live_bit_map->isMarked(addr)) {
8487 // It can't have been dead in a previous cycle
8488 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8489 } else {
8490 _dead_bit_map->mark(addr); // mark the dead object
8491 }
8492 }
8493 // Could be 0, if the block size could not be computed without stalling.
8494 return res;
8495 }
8496
8497 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8498
8499 switch (phase) {
8500 case CMSCollector::InitialMarking:
8501 initialize(true /* fullGC */ ,
8502 cause /* cause of the GC */,
8503 true /* recordGCBeginTime */,
8504 true /* recordPreGCUsage */,
8505 false /* recordPeakUsage */,
8506 false /* recordPostGCusage */,
8507 true /* recordAccumulatedGCTime */,
8508 false /* recordGCEndTime */,
8509 false /* countCollection */ );
8510 break;
8511
8512 case CMSCollector::FinalMarking:
8513 initialize(true /* fullGC */ ,
8514 cause /* cause of the GC */,
8515 false /* recordGCBeginTime */,
8516 false /* recordPreGCUsage */,
8517 false /* recordPeakUsage */,
8518 false /* recordPostGCusage */,
8519 true /* recordAccumulatedGCTime */,
8520 false /* recordGCEndTime */,
8521 false /* countCollection */ );
8522 break;
8523
8524 case CMSCollector::Sweeping:
8525 initialize(true /* fullGC */ ,
8526 cause /* cause of the GC */,
8527 false /* recordGCBeginTime */,
8528 false /* recordPreGCUsage */,
8529 true /* recordPeakUsage */,
8530 true /* recordPostGCusage */,
8531 false /* recordAccumulatedGCTime */,
8532 true /* recordGCEndTime */,
8533 true /* countCollection */ );
8534 break;
8535
8536 default:
8537 ShouldNotReachHere();
8538 }
8539 }