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 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
69
70 // statics
71 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
72 bool CMSCollector::_full_gc_requested = false;
73 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
74
75 //////////////////////////////////////////////////////////////////
76 // In support of CMS/VM thread synchronization
77 //////////////////////////////////////////////////////////////////
78 // We split use of the CGC_lock into 2 "levels".
79 // The low-level locking is of the usual CGC_lock monitor. We introduce
80 // a higher level "token" (hereafter "CMS token") built on top of the
81 // low level monitor (hereafter "CGC lock").
82 // The token-passing protocol gives priority to the VM thread. The
83 // CMS-lock doesn't provide any fairness guarantees, but clients
84 // should ensure that it is only held for very short, bounded
85 // durations.
86 //
87 // When either of the CMS thread or the VM thread is involved in
88 // collection operations during which it does not want the other
89 // thread to interfere, it obtains the CMS token.
90 //
91 // If either thread tries to get the token while the other has
92 // it, that thread waits. However, if the VM thread and CMS thread
93 // both want the token, then the VM thread gets priority while the
94 // CMS thread waits. This ensures, for instance, that the "concurrent"
95 // phases of the CMS thread's work do not block out the VM thread
96 // for long periods of time as the CMS thread continues to hog
97 // the token. (See bug 4616232).
98 //
99 // The baton-passing functions are, however, controlled by the
100 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
101 // and here the low-level CMS lock, not the high level token,
102 // ensures mutual exclusion.
103 //
104 // Two important conditions that we have to satisfy:
105 // 1. if a thread does a low-level wait on the CMS lock, then it
106 // relinquishes the CMS token if it were holding that token
107 // when it acquired the low-level CMS lock.
108 // 2. any low-level notifications on the low-level lock
109 // should only be sent when a thread has relinquished the token.
110 //
111 // In the absence of either property, we'd have potential deadlock.
112 //
113 // We protect each of the CMS (concurrent and sequential) phases
114 // with the CMS _token_, not the CMS _lock_.
115 //
116 // The only code protected by CMS lock is the token acquisition code
117 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
118 // baton-passing code.
119 //
120 // Unfortunately, i couldn't come up with a good abstraction to factor and
121 // hide the naked CGC_lock manipulation in the baton-passing code
122 // further below. That's something we should try to do. Also, the proof
123 // of correctness of this 2-level locking scheme is far from obvious,
124 // and potentially quite slippery. We have an uneasy suspicion, for instance,
125 // that there may be a theoretical possibility of delay/starvation in the
126 // low-level lock/wait/notify scheme used for the baton-passing because of
127 // potential interference with the priority scheme embodied in the
128 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
129 // invocation further below and marked with "XXX 20011219YSR".
130 // Indeed, as we note elsewhere, this may become yet more slippery
131 // in the presence of multiple CMS and/or multiple VM threads. XXX
132
133 class CMSTokenSync: public StackObj {
134 private:
135 bool _is_cms_thread;
136 public:
137 CMSTokenSync(bool is_cms_thread):
138 _is_cms_thread(is_cms_thread) {
139 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
140 "Incorrect argument to constructor");
141 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
142 }
143
144 ~CMSTokenSync() {
145 assert(_is_cms_thread ?
146 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
147 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
148 "Incorrect state");
149 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
150 }
151 };
152
153 // Convenience class that does a CMSTokenSync, and then acquires
154 // upto three locks.
155 class CMSTokenSyncWithLocks: public CMSTokenSync {
156 private:
157 // Note: locks are acquired in textual declaration order
158 // and released in the opposite order
159 MutexLockerEx _locker1, _locker2, _locker3;
160 public:
161 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
162 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
163 CMSTokenSync(is_cms_thread),
164 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
165 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
166 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
167 { }
168 };
169
170
171 //////////////////////////////////////////////////////////////////
172 // Concurrent Mark-Sweep Generation /////////////////////////////
173 //////////////////////////////////////////////////////////////////
174
175 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
176
177 // This struct contains per-thread things necessary to support parallel
178 // young-gen collection.
179 class CMSParGCThreadState: public CHeapObj<mtGC> {
180 public:
181 CFLS_LAB lab;
182 PromotionInfo promo;
183
184 // Constructor.
185 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
186 promo.setSpace(cfls);
187 }
188 };
189
190 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
191 ReservedSpace rs, size_t initial_byte_size, int level,
192 CardTableRS* ct, bool use_adaptive_freelists,
193 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
194 CardGeneration(rs, initial_byte_size, level, ct),
195 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
196 _did_compact(false)
197 {
198 HeapWord* bottom = (HeapWord*) _virtual_space.low();
199 HeapWord* end = (HeapWord*) _virtual_space.high();
200
201 _direct_allocated_words = 0;
202 NOT_PRODUCT(
203 _numObjectsPromoted = 0;
204 _numWordsPromoted = 0;
205 _numObjectsAllocated = 0;
206 _numWordsAllocated = 0;
207 )
208
209 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
210 use_adaptive_freelists,
211 dictionaryChoice);
212 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
213 if (_cmsSpace == NULL) {
214 vm_exit_during_initialization(
215 "CompactibleFreeListSpace allocation failure");
216 }
217 _cmsSpace->_gen = this;
218
219 _gc_stats = new CMSGCStats();
220
221 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
222 // offsets match. The ability to tell free chunks from objects
223 // depends on this property.
224 debug_only(
225 FreeChunk* junk = NULL;
226 assert(UseCompressedClassPointers ||
227 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
228 "Offset of FreeChunk::_prev within FreeChunk must match"
229 " that of OopDesc::_klass within OopDesc");
230 )
231 if (CollectedHeap::use_parallel_gc_threads()) {
232 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
233 _par_gc_thread_states =
234 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
235 if (_par_gc_thread_states == NULL) {
236 vm_exit_during_initialization("Could not allocate par gc structs");
237 }
238 for (uint i = 0; i < ParallelGCThreads; i++) {
239 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
240 if (_par_gc_thread_states[i] == NULL) {
241 vm_exit_during_initialization("Could not allocate par gc structs");
242 }
243 }
244 } else {
245 _par_gc_thread_states = NULL;
246 }
247 _incremental_collection_failed = false;
248 // The "dilatation_factor" is the expansion that can occur on
249 // account of the fact that the minimum object size in the CMS
250 // generation may be larger than that in, say, a contiguous young
251 // generation.
252 // Ideally, in the calculation below, we'd compute the dilatation
253 // factor as: MinChunkSize/(promoting_gen's min object size)
254 // Since we do not have such a general query interface for the
255 // promoting generation, we'll instead just use the minimum
256 // object size (which today is a header's worth of space);
257 // note that all arithmetic is in units of HeapWords.
258 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
259 assert(_dilatation_factor >= 1.0, "from previous assert");
260 }
261
262
263 // The field "_initiating_occupancy" represents the occupancy percentage
264 // at which we trigger a new collection cycle. Unless explicitly specified
265 // via CMSInitiatingOccupancyFraction (argument "io" below), it
266 // is calculated by:
267 //
268 // Let "f" be MinHeapFreeRatio in
269 //
270 // _initiating_occupancy = 100-f +
271 // f * (CMSTriggerRatio/100)
272 // where CMSTriggerRatio is the argument "tr" below.
273 //
274 // That is, if we assume the heap is at its desired maximum occupancy at the
275 // end of a collection, we let CMSTriggerRatio of the (purported) free
276 // space be allocated before initiating a new collection cycle.
277 //
278 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
279 assert(io <= 100 && tr <= 100, "Check the arguments");
280 if (io >= 0) {
281 _initiating_occupancy = (double)io / 100.0;
282 } else {
283 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
284 (double)(tr * MinHeapFreeRatio) / 100.0)
285 / 100.0;
286 }
287 }
288
289 void ConcurrentMarkSweepGeneration::ref_processor_init() {
290 assert(collector() != NULL, "no collector");
291 collector()->ref_processor_init();
292 }
293
294 void CMSCollector::ref_processor_init() {
295 if (_ref_processor == NULL) {
296 // Allocate and initialize a reference processor
297 _ref_processor =
298 new ReferenceProcessor(_span, // span
299 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
300 (int) ParallelGCThreads, // mt processing degree
301 _cmsGen->refs_discovery_is_mt(), // mt discovery
302 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
303 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
304 &_is_alive_closure); // closure for liveness info
305 // Initialize the _ref_processor field of CMSGen
306 _cmsGen->set_ref_processor(_ref_processor);
307
308 }
309 }
310
311 AdaptiveSizePolicy* CMSCollector::size_policy() {
312 GenCollectedHeap* gch = GenCollectedHeap::heap();
313 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
314 "Wrong type of heap");
315 return gch->gen_policy()->size_policy();
316 }
317
318 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
319
320 const char* gen_name = "old";
321 GenCollectorPolicy* gcp = (GenCollectorPolicy*) GenCollectedHeap::heap()->collector_policy();
322
323 // Generation Counters - generation 1, 1 subspace
324 _gen_counters = new GenerationCounters(gen_name, 1, 1,
325 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
326
327 _space_counters = new GSpaceCounters(gen_name, 0,
328 _virtual_space.reserved_size(),
329 this, _gen_counters);
330 }
331
332 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
333 _cms_gen(cms_gen)
334 {
335 assert(alpha <= 100, "bad value");
336 _saved_alpha = alpha;
337
338 // Initialize the alphas to the bootstrap value of 100.
339 _gc0_alpha = _cms_alpha = 100;
340
341 _cms_begin_time.update();
342 _cms_end_time.update();
343
344 _gc0_duration = 0.0;
345 _gc0_period = 0.0;
346 _gc0_promoted = 0;
347
348 _cms_duration = 0.0;
349 _cms_period = 0.0;
350 _cms_allocated = 0;
351
352 _cms_used_at_gc0_begin = 0;
353 _cms_used_at_gc0_end = 0;
354 _allow_duty_cycle_reduction = false;
355 _valid_bits = 0;
356 }
357
358 double CMSStats::cms_free_adjustment_factor(size_t free) const {
359 // TBD: CR 6909490
360 return 1.0;
361 }
362
363 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
364 }
365
366 // If promotion failure handling is on use
367 // the padded average size of the promotion for each
368 // young generation collection.
369 double CMSStats::time_until_cms_gen_full() const {
370 size_t cms_free = _cms_gen->cmsSpace()->free();
371 GenCollectedHeap* gch = GenCollectedHeap::heap();
372 size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
373 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
374 if (cms_free > expected_promotion) {
375 // Start a cms collection if there isn't enough space to promote
376 // for the next minor collection. Use the padded average as
377 // a safety factor.
378 cms_free -= expected_promotion;
379
380 // Adjust by the safety factor.
381 double cms_free_dbl = (double)cms_free;
382 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
383 // Apply a further correction factor which tries to adjust
384 // for recent occurance of concurrent mode failures.
385 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
386 cms_free_dbl = cms_free_dbl * cms_adjustment;
387
388 if (PrintGCDetails && Verbose) {
389 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
390 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
391 cms_free, expected_promotion);
392 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
393 cms_free_dbl, cms_consumption_rate() + 1.0);
394 }
395 // Add 1 in case the consumption rate goes to zero.
396 return cms_free_dbl / (cms_consumption_rate() + 1.0);
397 }
398 return 0.0;
399 }
400
401 // Compare the duration of the cms collection to the
402 // time remaining before the cms generation is empty.
403 // Note that the time from the start of the cms collection
404 // to the start of the cms sweep (less than the total
405 // duration of the cms collection) can be used. This
406 // has been tried and some applications experienced
407 // promotion failures early in execution. This was
408 // possibly because the averages were not accurate
409 // enough at the beginning.
410 double CMSStats::time_until_cms_start() const {
411 // We add "gc0_period" to the "work" calculation
412 // below because this query is done (mostly) at the
413 // end of a scavenge, so we need to conservatively
414 // account for that much possible delay
415 // in the query so as to avoid concurrent mode failures
416 // due to starting the collection just a wee bit too
417 // late.
418 double work = cms_duration() + gc0_period();
419 double deadline = time_until_cms_gen_full();
420 // If a concurrent mode failure occurred recently, we want to be
421 // more conservative and halve our expected time_until_cms_gen_full()
422 if (work > deadline) {
423 if (Verbose && PrintGCDetails) {
424 gclog_or_tty->print(
425 " CMSCollector: collect because of anticipated promotion "
426 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
427 gc0_period(), time_until_cms_gen_full());
428 }
429 return 0.0;
430 }
431 return work - deadline;
432 }
433
434 #ifndef PRODUCT
435 void CMSStats::print_on(outputStream *st) const {
436 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
437 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
438 gc0_duration(), gc0_period(), gc0_promoted());
439 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
440 cms_duration(), cms_period(), cms_allocated());
441 st->print(",cms_since_beg=%g,cms_since_end=%g",
442 cms_time_since_begin(), cms_time_since_end());
443 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
444 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
445
446 if (valid()) {
447 st->print(",promo_rate=%g,cms_alloc_rate=%g",
448 promotion_rate(), cms_allocation_rate());
449 st->print(",cms_consumption_rate=%g,time_until_full=%g",
450 cms_consumption_rate(), time_until_cms_gen_full());
451 }
452 st->print(" ");
453 }
454 #endif // #ifndef PRODUCT
455
456 CMSCollector::CollectorState CMSCollector::_collectorState =
457 CMSCollector::Idling;
458 bool CMSCollector::_foregroundGCIsActive = false;
459 bool CMSCollector::_foregroundGCShouldWait = false;
460
461 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
462 CardTableRS* ct,
463 ConcurrentMarkSweepPolicy* cp):
464 _cmsGen(cmsGen),
465 _ct(ct),
466 _ref_processor(NULL), // will be set later
467 _conc_workers(NULL), // may be set later
468 _abort_preclean(false),
469 _start_sampling(false),
470 _between_prologue_and_epilogue(false),
471 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
472 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
473 -1 /* lock-free */, "No_lock" /* dummy */),
474 _modUnionClosure(&_modUnionTable),
475 _modUnionClosurePar(&_modUnionTable),
476 // Adjust my span to cover old (cms) gen
477 _span(cmsGen->reserved()),
478 // Construct the is_alive_closure with _span & markBitMap
479 _is_alive_closure(_span, &_markBitMap),
480 _restart_addr(NULL),
481 _overflow_list(NULL),
482 _stats(cmsGen),
483 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
484 //verify that this lock should be acquired with safepoint check.
485 Monitor::_safepoint_check_sometimes)),
486 _eden_chunk_array(NULL), // may be set in ctor body
487 _eden_chunk_capacity(0), // -- ditto --
488 _eden_chunk_index(0), // -- ditto --
489 _survivor_plab_array(NULL), // -- ditto --
490 _survivor_chunk_array(NULL), // -- ditto --
491 _survivor_chunk_capacity(0), // -- ditto --
492 _survivor_chunk_index(0), // -- ditto --
493 _ser_pmc_preclean_ovflw(0),
494 _ser_kac_preclean_ovflw(0),
495 _ser_pmc_remark_ovflw(0),
496 _par_pmc_remark_ovflw(0),
497 _ser_kac_ovflw(0),
498 _par_kac_ovflw(0),
499 #ifndef PRODUCT
500 _num_par_pushes(0),
501 #endif
502 _collection_count_start(0),
503 _verifying(false),
504 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
505 _completed_initialization(false),
506 _collector_policy(cp),
507 _should_unload_classes(CMSClassUnloadingEnabled),
508 _concurrent_cycles_since_last_unload(0),
509 _roots_scanning_options(SharedHeap::SO_None),
510 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
511 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
512 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
513 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
514 _cms_start_registered(false)
515 {
516 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
517 ExplicitGCInvokesConcurrent = true;
518 }
519 // Now expand the span and allocate the collection support structures
520 // (MUT, marking bit map etc.) to cover both generations subject to
521 // collection.
522
523 // For use by dirty card to oop closures.
524 _cmsGen->cmsSpace()->set_collector(this);
525
526 // Allocate MUT and marking bit map
527 {
528 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
529 if (!_markBitMap.allocate(_span)) {
530 warning("Failed to allocate CMS Bit Map");
531 return;
532 }
533 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
534 }
535 {
536 _modUnionTable.allocate(_span);
537 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
538 }
539
540 if (!_markStack.allocate(MarkStackSize)) {
541 warning("Failed to allocate CMS Marking Stack");
542 return;
543 }
544
545 // Support for multi-threaded concurrent phases
546 if (CMSConcurrentMTEnabled) {
547 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
548 // just for now
549 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
550 }
551 if (ConcGCThreads > 1) {
552 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
553 ConcGCThreads, true);
554 if (_conc_workers == NULL) {
555 warning("GC/CMS: _conc_workers allocation failure: "
556 "forcing -CMSConcurrentMTEnabled");
557 CMSConcurrentMTEnabled = false;
558 } else {
559 _conc_workers->initialize_workers();
560 }
561 } else {
562 CMSConcurrentMTEnabled = false;
563 }
564 }
565 if (!CMSConcurrentMTEnabled) {
566 ConcGCThreads = 0;
567 } else {
568 // Turn off CMSCleanOnEnter optimization temporarily for
569 // the MT case where it's not fixed yet; see 6178663.
570 CMSCleanOnEnter = false;
571 }
572 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
573 "Inconsistency");
574
575 // Parallel task queues; these are shared for the
576 // concurrent and stop-world phases of CMS, but
577 // are not shared with parallel scavenge (ParNew).
578 {
579 uint i;
580 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
581
582 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
583 || ParallelRefProcEnabled)
584 && num_queues > 0) {
585 _task_queues = new OopTaskQueueSet(num_queues);
586 if (_task_queues == NULL) {
587 warning("task_queues allocation failure.");
588 return;
589 }
590 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
591 if (_hash_seed == NULL) {
592 warning("_hash_seed array allocation failure");
593 return;
594 }
595
596 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
597 for (i = 0; i < num_queues; i++) {
598 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
599 if (q == NULL) {
600 warning("work_queue allocation failure.");
601 return;
602 }
603 _task_queues->register_queue(i, q);
604 }
605 for (i = 0; i < num_queues; i++) {
606 _task_queues->queue(i)->initialize();
607 _hash_seed[i] = 17; // copied from ParNew
608 }
609 }
610 }
611
612 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
613
614 // Clip CMSBootstrapOccupancy between 0 and 100.
615 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
616
617 // Now tell CMS generations the identity of their collector
618 ConcurrentMarkSweepGeneration::set_collector(this);
619
620 // Create & start a CMS thread for this CMS collector
621 _cmsThread = ConcurrentMarkSweepThread::start(this);
622 assert(cmsThread() != NULL, "CMS Thread should have been created");
623 assert(cmsThread()->collector() == this,
624 "CMS Thread should refer to this gen");
625 assert(CGC_lock != NULL, "Where's the CGC_lock?");
626
627 // Support for parallelizing young gen rescan
628 GenCollectedHeap* gch = GenCollectedHeap::heap();
629 assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
630 _young_gen = (ParNewGeneration*)gch->young_gen();
631 if (gch->supports_inline_contig_alloc()) {
632 _top_addr = gch->top_addr();
633 _end_addr = gch->end_addr();
634 assert(_young_gen != NULL, "no _young_gen");
635 _eden_chunk_index = 0;
636 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
637 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
638 if (_eden_chunk_array == NULL) {
639 _eden_chunk_capacity = 0;
640 warning("GC/CMS: _eden_chunk_array allocation failure");
641 }
642 }
643 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
644
645 // Support for parallelizing survivor space rescan
646 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
647 const size_t max_plab_samples =
648 ((DefNewGeneration*)_young_gen)->max_survivor_size() / plab_sample_minimum_size();
649
650 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
651 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
652 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
653 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
654 || _cursor == NULL) {
655 warning("Failed to allocate survivor plab/chunk array");
656 if (_survivor_plab_array != NULL) {
657 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
658 _survivor_plab_array = NULL;
659 }
660 if (_survivor_chunk_array != NULL) {
661 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
662 _survivor_chunk_array = NULL;
663 }
664 if (_cursor != NULL) {
665 FREE_C_HEAP_ARRAY(size_t, _cursor);
666 _cursor = NULL;
667 }
668 } else {
669 _survivor_chunk_capacity = 2*max_plab_samples;
670 for (uint i = 0; i < ParallelGCThreads; i++) {
671 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
672 if (vec == NULL) {
673 warning("Failed to allocate survivor plab array");
674 for (int j = i; j > 0; j--) {
675 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array());
676 }
677 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
678 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
679 _survivor_plab_array = NULL;
680 _survivor_chunk_array = NULL;
681 _survivor_chunk_capacity = 0;
682 break;
683 } else {
684 ChunkArray* cur =
685 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
686 max_plab_samples);
687 assert(cur->end() == 0, "Should be 0");
688 assert(cur->array() == vec, "Should be vec");
689 assert(cur->capacity() == max_plab_samples, "Error");
690 }
691 }
692 }
693 }
694 assert( ( _survivor_plab_array != NULL
695 && _survivor_chunk_array != NULL)
696 || ( _survivor_chunk_capacity == 0
697 && _survivor_chunk_index == 0),
698 "Error");
699
700 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
701 _gc_counters = new CollectorCounters("CMS", 1);
702 _completed_initialization = true;
703 _inter_sweep_timer.start(); // start of time
704 }
705
706 size_t CMSCollector::plab_sample_minimum_size() {
707 // The default value of MinTLABSize is 2k, but there is
708 // no way to get the default value if the flag has been overridden.
709 return MAX2(ThreadLocalAllocBuffer::min_size() * HeapWordSize, 2 * K);
710 }
711
712 const char* ConcurrentMarkSweepGeneration::name() const {
713 return "concurrent mark-sweep generation";
714 }
715 void ConcurrentMarkSweepGeneration::update_counters() {
716 if (UsePerfData) {
717 _space_counters->update_all();
718 _gen_counters->update_all();
719 }
720 }
721
722 // this is an optimized version of update_counters(). it takes the
723 // used value as a parameter rather than computing it.
724 //
725 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
726 if (UsePerfData) {
727 _space_counters->update_used(used);
728 _space_counters->update_capacity();
729 _gen_counters->update_all();
730 }
731 }
732
733 void ConcurrentMarkSweepGeneration::print() const {
734 Generation::print();
735 cmsSpace()->print();
736 }
737
738 #ifndef PRODUCT
739 void ConcurrentMarkSweepGeneration::print_statistics() {
740 cmsSpace()->printFLCensus(0);
741 }
742 #endif
743
744 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
745 GenCollectedHeap* gch = GenCollectedHeap::heap();
746 if (PrintGCDetails) {
747 if (Verbose) {
748 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
749 level(), short_name(), s, used(), capacity());
750 } else {
751 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
752 level(), short_name(), s, used() / K, capacity() / K);
753 }
754 }
755 if (Verbose) {
756 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
757 gch->used(), gch->capacity());
758 } else {
759 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
760 gch->used() / K, gch->capacity() / K);
761 }
762 }
763
764 size_t
765 ConcurrentMarkSweepGeneration::contiguous_available() const {
766 // dld proposes an improvement in precision here. If the committed
767 // part of the space ends in a free block we should add that to
768 // uncommitted size in the calculation below. Will make this
769 // change later, staying with the approximation below for the
770 // time being. -- ysr.
771 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
772 }
773
774 size_t
775 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
776 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
777 }
778
779 size_t ConcurrentMarkSweepGeneration::max_available() const {
780 return free() + _virtual_space.uncommitted_size();
781 }
782
783 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
784 size_t available = max_available();
785 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
786 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
787 if (Verbose && PrintGCDetails) {
788 gclog_or_tty->print_cr(
789 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
790 "max_promo("SIZE_FORMAT")",
791 res? "":" not", available, res? ">=":"<",
792 av_promo, max_promotion_in_bytes);
793 }
794 return res;
795 }
796
797 // At a promotion failure dump information on block layout in heap
798 // (cms old generation).
799 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
800 if (CMSDumpAtPromotionFailure) {
801 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
802 }
803 }
804
805 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
806 // Clear the promotion information. These pointers can be adjusted
807 // along with all the other pointers into the heap but
808 // compaction is expected to be a rare event with
809 // a heap using cms so don't do it without seeing the need.
810 for (uint i = 0; i < ParallelGCThreads; i++) {
811 _par_gc_thread_states[i]->promo.reset();
812 }
813 }
814
815 void ConcurrentMarkSweepGeneration::compute_new_size() {
816 assert_locked_or_safepoint(Heap_lock);
817
818 // If incremental collection failed, we just want to expand
819 // to the limit.
820 if (incremental_collection_failed()) {
821 clear_incremental_collection_failed();
822 grow_to_reserved();
823 return;
824 }
825
826 // The heap has been compacted but not reset yet.
827 // Any metric such as free() or used() will be incorrect.
828
829 CardGeneration::compute_new_size();
830
831 // Reset again after a possible resizing
832 if (did_compact()) {
833 cmsSpace()->reset_after_compaction();
834 }
835 }
836
837 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
838 assert_locked_or_safepoint(Heap_lock);
839
840 // If incremental collection failed, we just want to expand
841 // to the limit.
842 if (incremental_collection_failed()) {
843 clear_incremental_collection_failed();
844 grow_to_reserved();
845 return;
846 }
847
848 double free_percentage = ((double) free()) / capacity();
849 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
850 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
851
852 // compute expansion delta needed for reaching desired free percentage
853 if (free_percentage < desired_free_percentage) {
854 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
855 assert(desired_capacity >= capacity(), "invalid expansion size");
856 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
857 if (PrintGCDetails && Verbose) {
858 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
859 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
860 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
861 gclog_or_tty->print_cr(" Desired free fraction %f",
862 desired_free_percentage);
863 gclog_or_tty->print_cr(" Maximum free fraction %f",
864 maximum_free_percentage);
865 gclog_or_tty->print_cr(" Capacity "SIZE_FORMAT, capacity()/1000);
866 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
867 desired_capacity/1000);
868 int prev_level = level() - 1;
869 if (prev_level >= 0) {
870 size_t prev_size = 0;
871 GenCollectedHeap* gch = GenCollectedHeap::heap();
872 Generation* prev_gen = gch->young_gen();
873 prev_size = prev_gen->capacity();
874 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
875 prev_size/1000);
876 }
877 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
878 unsafe_max_alloc_nogc()/1000);
879 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
880 contiguous_available()/1000);
881 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
882 expand_bytes);
883 }
884 // safe if expansion fails
885 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
886 if (PrintGCDetails && Verbose) {
887 gclog_or_tty->print_cr(" Expanded free fraction %f",
888 ((double) free()) / capacity());
889 }
890 } else {
891 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
892 assert(desired_capacity <= capacity(), "invalid expansion size");
893 size_t shrink_bytes = capacity() - desired_capacity;
894 // Don't shrink unless the delta is greater than the minimum shrink we want
895 if (shrink_bytes >= MinHeapDeltaBytes) {
896 shrink_free_list_by(shrink_bytes);
897 }
898 }
899 }
900
901 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
902 return cmsSpace()->freelistLock();
903 }
904
905 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
906 bool tlab) {
907 CMSSynchronousYieldRequest yr;
908 MutexLockerEx x(freelistLock(),
909 Mutex::_no_safepoint_check_flag);
910 return have_lock_and_allocate(size, tlab);
911 }
912
913 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
914 bool tlab /* ignored */) {
915 assert_lock_strong(freelistLock());
916 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
917 HeapWord* res = cmsSpace()->allocate(adjustedSize);
918 // Allocate the object live (grey) if the background collector has
919 // started marking. This is necessary because the marker may
920 // have passed this address and consequently this object will
921 // not otherwise be greyed and would be incorrectly swept up.
922 // Note that if this object contains references, the writing
923 // of those references will dirty the card containing this object
924 // allowing the object to be blackened (and its references scanned)
925 // either during a preclean phase or at the final checkpoint.
926 if (res != NULL) {
927 // We may block here with an uninitialized object with
928 // its mark-bit or P-bits not yet set. Such objects need
929 // to be safely navigable by block_start().
930 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
931 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
932 collector()->direct_allocated(res, adjustedSize);
933 _direct_allocated_words += adjustedSize;
934 // allocation counters
935 NOT_PRODUCT(
936 _numObjectsAllocated++;
937 _numWordsAllocated += (int)adjustedSize;
938 )
939 }
940 return res;
941 }
942
943 // In the case of direct allocation by mutators in a generation that
944 // is being concurrently collected, the object must be allocated
945 // live (grey) if the background collector has started marking.
946 // This is necessary because the marker may
947 // have passed this address and consequently this object will
948 // not otherwise be greyed and would be incorrectly swept up.
949 // Note that if this object contains references, the writing
950 // of those references will dirty the card containing this object
951 // allowing the object to be blackened (and its references scanned)
952 // either during a preclean phase or at the final checkpoint.
953 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
954 assert(_markBitMap.covers(start, size), "Out of bounds");
955 if (_collectorState >= Marking) {
956 MutexLockerEx y(_markBitMap.lock(),
957 Mutex::_no_safepoint_check_flag);
958 // [see comments preceding SweepClosure::do_blk() below for details]
959 //
960 // Can the P-bits be deleted now? JJJ
961 //
962 // 1. need to mark the object as live so it isn't collected
963 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
964 // 3. need to mark the end of the object so marking, precleaning or sweeping
965 // can skip over uninitialized or unparsable objects. An allocated
966 // object is considered uninitialized for our purposes as long as
967 // its klass word is NULL. All old gen objects are parsable
968 // as soon as they are initialized.)
969 _markBitMap.mark(start); // object is live
970 _markBitMap.mark(start + 1); // object is potentially uninitialized?
971 _markBitMap.mark(start + size - 1);
972 // mark end of object
973 }
974 // check that oop looks uninitialized
975 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
976 }
977
978 void CMSCollector::promoted(bool par, HeapWord* start,
979 bool is_obj_array, size_t obj_size) {
980 assert(_markBitMap.covers(start), "Out of bounds");
981 // See comment in direct_allocated() about when objects should
982 // be allocated live.
983 if (_collectorState >= Marking) {
984 // we already hold the marking bit map lock, taken in
985 // the prologue
986 if (par) {
987 _markBitMap.par_mark(start);
988 } else {
989 _markBitMap.mark(start);
990 }
991 // We don't need to mark the object as uninitialized (as
992 // in direct_allocated above) because this is being done with the
993 // world stopped and the object will be initialized by the
994 // time the marking, precleaning or sweeping get to look at it.
995 // But see the code for copying objects into the CMS generation,
996 // where we need to ensure that concurrent readers of the
997 // block offset table are able to safely navigate a block that
998 // is in flux from being free to being allocated (and in
999 // transition while being copied into) and subsequently
1000 // becoming a bona-fide object when the copy/promotion is complete.
1001 assert(SafepointSynchronize::is_at_safepoint(),
1002 "expect promotion only at safepoints");
1003
1004 if (_collectorState < Sweeping) {
1005 // Mark the appropriate cards in the modUnionTable, so that
1006 // this object gets scanned before the sweep. If this is
1007 // not done, CMS generation references in the object might
1008 // not get marked.
1009 // For the case of arrays, which are otherwise precisely
1010 // marked, we need to dirty the entire array, not just its head.
1011 if (is_obj_array) {
1012 // The [par_]mark_range() method expects mr.end() below to
1013 // be aligned to the granularity of a bit's representation
1014 // in the heap. In the case of the MUT below, that's a
1015 // card size.
1016 MemRegion mr(start,
1017 (HeapWord*)round_to((intptr_t)(start + obj_size),
1018 CardTableModRefBS::card_size /* bytes */));
1019 if (par) {
1020 _modUnionTable.par_mark_range(mr);
1021 } else {
1022 _modUnionTable.mark_range(mr);
1023 }
1024 } else { // not an obj array; we can just mark the head
1025 if (par) {
1026 _modUnionTable.par_mark(start);
1027 } else {
1028 _modUnionTable.mark(start);
1029 }
1030 }
1031 }
1032 }
1033 }
1034
1035 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1036 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1037 // allocate, copy and if necessary update promoinfo --
1038 // delegate to underlying space.
1039 assert_lock_strong(freelistLock());
1040
1041 #ifndef PRODUCT
1042 if (Universe::heap()->promotion_should_fail()) {
1043 return NULL;
1044 }
1045 #endif // #ifndef PRODUCT
1046
1047 oop res = _cmsSpace->promote(obj, obj_size);
1048 if (res == NULL) {
1049 // expand and retry
1050 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1051 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
1052 // Since this is the old generation, we don't try to promote
1053 // into a more senior generation.
1054 res = _cmsSpace->promote(obj, obj_size);
1055 }
1056 if (res != NULL) {
1057 // See comment in allocate() about when objects should
1058 // be allocated live.
1059 assert(obj->is_oop(), "Will dereference klass pointer below");
1060 collector()->promoted(false, // Not parallel
1061 (HeapWord*)res, obj->is_objArray(), obj_size);
1062 // promotion counters
1063 NOT_PRODUCT(
1064 _numObjectsPromoted++;
1065 _numWordsPromoted +=
1066 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1067 )
1068 }
1069 return res;
1070 }
1071
1072
1073 // IMPORTANT: Notes on object size recognition in CMS.
1074 // ---------------------------------------------------
1075 // A block of storage in the CMS generation is always in
1076 // one of three states. A free block (FREE), an allocated
1077 // object (OBJECT) whose size() method reports the correct size,
1078 // and an intermediate state (TRANSIENT) in which its size cannot
1079 // be accurately determined.
1080 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1081 // -----------------------------------------------------
1082 // FREE: klass_word & 1 == 1; mark_word holds block size
1083 //
1084 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1085 // obj->size() computes correct size
1086 //
1087 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1088 //
1089 // STATE IDENTIFICATION: (64 bit+COOPS)
1090 // ------------------------------------
1091 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1092 //
1093 // OBJECT: klass_word installed; klass_word != 0;
1094 // obj->size() computes correct size
1095 //
1096 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1097 //
1098 //
1099 // STATE TRANSITION DIAGRAM
1100 //
1101 // mut / parnew mut / parnew
1102 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1103 // ^ |
1104 // |------------------------ DEAD <------------------------------------|
1105 // sweep mut
1106 //
1107 // While a block is in TRANSIENT state its size cannot be determined
1108 // so readers will either need to come back later or stall until
1109 // the size can be determined. Note that for the case of direct
1110 // allocation, P-bits, when available, may be used to determine the
1111 // size of an object that may not yet have been initialized.
1112
1113 // Things to support parallel young-gen collection.
1114 oop
1115 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1116 oop old, markOop m,
1117 size_t word_sz) {
1118 #ifndef PRODUCT
1119 if (Universe::heap()->promotion_should_fail()) {
1120 return NULL;
1121 }
1122 #endif // #ifndef PRODUCT
1123
1124 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1125 PromotionInfo* promoInfo = &ps->promo;
1126 // if we are tracking promotions, then first ensure space for
1127 // promotion (including spooling space for saving header if necessary).
1128 // then allocate and copy, then track promoted info if needed.
1129 // When tracking (see PromotionInfo::track()), the mark word may
1130 // be displaced and in this case restoration of the mark word
1131 // occurs in the (oop_since_save_marks_)iterate phase.
1132 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1133 // Out of space for allocating spooling buffers;
1134 // try expanding and allocating spooling buffers.
1135 if (!expand_and_ensure_spooling_space(promoInfo)) {
1136 return NULL;
1137 }
1138 }
1139 assert(promoInfo->has_spooling_space(), "Control point invariant");
1140 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1141 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1142 if (obj_ptr == NULL) {
1143 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1144 if (obj_ptr == NULL) {
1145 return NULL;
1146 }
1147 }
1148 oop obj = oop(obj_ptr);
1149 OrderAccess::storestore();
1150 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1151 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1152 // IMPORTANT: See note on object initialization for CMS above.
1153 // Otherwise, copy the object. Here we must be careful to insert the
1154 // klass pointer last, since this marks the block as an allocated object.
1155 // Except with compressed oops it's the mark word.
1156 HeapWord* old_ptr = (HeapWord*)old;
1157 // Restore the mark word copied above.
1158 obj->set_mark(m);
1159 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1160 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1161 OrderAccess::storestore();
1162
1163 if (UseCompressedClassPointers) {
1164 // Copy gap missed by (aligned) header size calculation below
1165 obj->set_klass_gap(old->klass_gap());
1166 }
1167 if (word_sz > (size_t)oopDesc::header_size()) {
1168 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1169 obj_ptr + oopDesc::header_size(),
1170 word_sz - oopDesc::header_size());
1171 }
1172
1173 // Now we can track the promoted object, if necessary. We take care
1174 // to delay the transition from uninitialized to full object
1175 // (i.e., insertion of klass pointer) until after, so that it
1176 // atomically becomes a promoted object.
1177 if (promoInfo->tracking()) {
1178 promoInfo->track((PromotedObject*)obj, old->klass());
1179 }
1180 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1181 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1182 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1183
1184 // Finally, install the klass pointer (this should be volatile).
1185 OrderAccess::storestore();
1186 obj->set_klass(old->klass());
1187 // We should now be able to calculate the right size for this object
1188 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1189
1190 collector()->promoted(true, // parallel
1191 obj_ptr, old->is_objArray(), word_sz);
1192
1193 NOT_PRODUCT(
1194 Atomic::inc_ptr(&_numObjectsPromoted);
1195 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1196 )
1197
1198 return obj;
1199 }
1200
1201 void
1202 ConcurrentMarkSweepGeneration::
1203 par_promote_alloc_done(int thread_num) {
1204 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1205 ps->lab.retire(thread_num);
1206 }
1207
1208 void
1209 ConcurrentMarkSweepGeneration::
1210 par_oop_since_save_marks_iterate_done(int thread_num) {
1211 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1212 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1213 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1214 }
1215
1216 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1217 size_t size,
1218 bool tlab)
1219 {
1220 // We allow a STW collection only if a full
1221 // collection was requested.
1222 return full || should_allocate(size, tlab); // FIX ME !!!
1223 // This and promotion failure handling are connected at the
1224 // hip and should be fixed by untying them.
1225 }
1226
1227 bool CMSCollector::shouldConcurrentCollect() {
1228 if (_full_gc_requested) {
1229 if (Verbose && PrintGCDetails) {
1230 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1231 " gc request (or gc_locker)");
1232 }
1233 return true;
1234 }
1235
1236 FreelistLocker x(this);
1237 // ------------------------------------------------------------------
1238 // Print out lots of information which affects the initiation of
1239 // a collection.
1240 if (PrintCMSInitiationStatistics && stats().valid()) {
1241 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1242 gclog_or_tty->stamp();
1243 gclog_or_tty->cr();
1244 stats().print_on(gclog_or_tty);
1245 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1246 stats().time_until_cms_gen_full());
1247 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1248 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1249 _cmsGen->contiguous_available());
1250 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1251 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1252 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1253 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1254 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1255 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1256 gclog_or_tty->print_cr("metadata initialized %d",
1257 MetaspaceGC::should_concurrent_collect());
1258 }
1259 // ------------------------------------------------------------------
1260
1261 // If the estimated time to complete a cms collection (cms_duration())
1262 // is less than the estimated time remaining until the cms generation
1263 // is full, start a collection.
1264 if (!UseCMSInitiatingOccupancyOnly) {
1265 if (stats().valid()) {
1266 if (stats().time_until_cms_start() == 0.0) {
1267 return true;
1268 }
1269 } else {
1270 // We want to conservatively collect somewhat early in order
1271 // to try and "bootstrap" our CMS/promotion statistics;
1272 // this branch will not fire after the first successful CMS
1273 // collection because the stats should then be valid.
1274 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1275 if (Verbose && PrintGCDetails) {
1276 gclog_or_tty->print_cr(
1277 " CMSCollector: collect for bootstrapping statistics:"
1278 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1279 _bootstrap_occupancy);
1280 }
1281 return true;
1282 }
1283 }
1284 }
1285
1286 // Otherwise, we start a collection cycle if
1287 // old gen want a collection cycle started. Each may use
1288 // an appropriate criterion for making this decision.
1289 // XXX We need to make sure that the gen expansion
1290 // criterion dovetails well with this. XXX NEED TO FIX THIS
1291 if (_cmsGen->should_concurrent_collect()) {
1292 if (Verbose && PrintGCDetails) {
1293 gclog_or_tty->print_cr("CMS old gen initiated");
1294 }
1295 return true;
1296 }
1297
1298 // We start a collection if we believe an incremental collection may fail;
1299 // this is not likely to be productive in practice because it's probably too
1300 // late anyway.
1301 GenCollectedHeap* gch = GenCollectedHeap::heap();
1302 assert(gch->collector_policy()->is_generation_policy(),
1303 "You may want to check the correctness of the following");
1304 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1305 if (Verbose && PrintGCDetails) {
1306 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1307 }
1308 return true;
1309 }
1310
1311 if (MetaspaceGC::should_concurrent_collect()) {
1312 if (Verbose && PrintGCDetails) {
1313 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1314 }
1315 return true;
1316 }
1317
1318 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1319 if (CMSTriggerInterval >= 0) {
1320 if (CMSTriggerInterval == 0) {
1321 // Trigger always
1322 return true;
1323 }
1324
1325 // Check the CMS time since begin (we do not check the stats validity
1326 // as we want to be able to trigger the first CMS cycle as well)
1327 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1328 if (Verbose && PrintGCDetails) {
1329 if (stats().valid()) {
1330 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1331 stats().cms_time_since_begin());
1332 } else {
1333 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1334 }
1335 }
1336 return true;
1337 }
1338 }
1339
1340 return false;
1341 }
1342
1343 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1344
1345 // Clear _expansion_cause fields of constituent generations
1346 void CMSCollector::clear_expansion_cause() {
1347 _cmsGen->clear_expansion_cause();
1348 }
1349
1350 // We should be conservative in starting a collection cycle. To
1351 // start too eagerly runs the risk of collecting too often in the
1352 // extreme. To collect too rarely falls back on full collections,
1353 // which works, even if not optimum in terms of concurrent work.
1354 // As a work around for too eagerly collecting, use the flag
1355 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1356 // giving the user an easily understandable way of controlling the
1357 // collections.
1358 // We want to start a new collection cycle if any of the following
1359 // conditions hold:
1360 // . our current occupancy exceeds the configured initiating occupancy
1361 // for this generation, or
1362 // . we recently needed to expand this space and have not, since that
1363 // expansion, done a collection of this generation, or
1364 // . the underlying space believes that it may be a good idea to initiate
1365 // a concurrent collection (this may be based on criteria such as the
1366 // following: the space uses linear allocation and linear allocation is
1367 // going to fail, or there is believed to be excessive fragmentation in
1368 // the generation, etc... or ...
1369 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1370 // the case of the old generation; see CR 6543076):
1371 // we may be approaching a point at which allocation requests may fail because
1372 // we will be out of sufficient free space given allocation rate estimates.]
1373 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1374
1375 assert_lock_strong(freelistLock());
1376 if (occupancy() > initiating_occupancy()) {
1377 if (PrintGCDetails && Verbose) {
1378 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1379 short_name(), occupancy(), initiating_occupancy());
1380 }
1381 return true;
1382 }
1383 if (UseCMSInitiatingOccupancyOnly) {
1384 return false;
1385 }
1386 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1387 if (PrintGCDetails && Verbose) {
1388 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1389 short_name());
1390 }
1391 return true;
1392 }
1393 if (_cmsSpace->should_concurrent_collect()) {
1394 if (PrintGCDetails && Verbose) {
1395 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1396 short_name());
1397 }
1398 return true;
1399 }
1400 return false;
1401 }
1402
1403 void ConcurrentMarkSweepGeneration::collect(bool full,
1404 bool clear_all_soft_refs,
1405 size_t size,
1406 bool tlab)
1407 {
1408 collector()->collect(full, clear_all_soft_refs, size, tlab);
1409 }
1410
1411 void CMSCollector::collect(bool full,
1412 bool clear_all_soft_refs,
1413 size_t size,
1414 bool tlab)
1415 {
1416 // The following "if" branch is present for defensive reasons.
1417 // In the current uses of this interface, it can be replaced with:
1418 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1419 // But I am not placing that assert here to allow future
1420 // generality in invoking this interface.
1421 if (GC_locker::is_active()) {
1422 // A consistency test for GC_locker
1423 assert(GC_locker::needs_gc(), "Should have been set already");
1424 // Skip this foreground collection, instead
1425 // expanding the heap if necessary.
1426 // Need the free list locks for the call to free() in compute_new_size()
1427 compute_new_size();
1428 return;
1429 }
1430 acquire_control_and_collect(full, clear_all_soft_refs);
1431 }
1432
1433 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1434 GenCollectedHeap* gch = GenCollectedHeap::heap();
1435 unsigned int gc_count = gch->total_full_collections();
1436 if (gc_count == full_gc_count) {
1437 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1438 _full_gc_requested = true;
1439 _full_gc_cause = cause;
1440 CGC_lock->notify(); // nudge CMS thread
1441 } else {
1442 assert(gc_count > full_gc_count, "Error: causal loop");
1443 }
1444 }
1445
1446 bool CMSCollector::is_external_interruption() {
1447 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1448 return GCCause::is_user_requested_gc(cause) ||
1449 GCCause::is_serviceability_requested_gc(cause);
1450 }
1451
1452 void CMSCollector::report_concurrent_mode_interruption() {
1453 if (is_external_interruption()) {
1454 if (PrintGCDetails) {
1455 gclog_or_tty->print(" (concurrent mode interrupted)");
1456 }
1457 } else {
1458 if (PrintGCDetails) {
1459 gclog_or_tty->print(" (concurrent mode failure)");
1460 }
1461 _gc_tracer_cm->report_concurrent_mode_failure();
1462 }
1463 }
1464
1465
1466 // The foreground and background collectors need to coordinate in order
1467 // to make sure that they do not mutually interfere with CMS collections.
1468 // When a background collection is active,
1469 // the foreground collector may need to take over (preempt) and
1470 // synchronously complete an ongoing collection. Depending on the
1471 // frequency of the background collections and the heap usage
1472 // of the application, this preemption can be seldom or frequent.
1473 // There are only certain
1474 // points in the background collection that the "collection-baton"
1475 // can be passed to the foreground collector.
1476 //
1477 // The foreground collector will wait for the baton before
1478 // starting any part of the collection. The foreground collector
1479 // will only wait at one location.
1480 //
1481 // The background collector will yield the baton before starting a new
1482 // phase of the collection (e.g., before initial marking, marking from roots,
1483 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1484 // of the loop which switches the phases. The background collector does some
1485 // of the phases (initial mark, final re-mark) with the world stopped.
1486 // Because of locking involved in stopping the world,
1487 // the foreground collector should not block waiting for the background
1488 // collector when it is doing a stop-the-world phase. The background
1489 // collector will yield the baton at an additional point just before
1490 // it enters a stop-the-world phase. Once the world is stopped, the
1491 // background collector checks the phase of the collection. If the
1492 // phase has not changed, it proceeds with the collection. If the
1493 // phase has changed, it skips that phase of the collection. See
1494 // the comments on the use of the Heap_lock in collect_in_background().
1495 //
1496 // Variable used in baton passing.
1497 // _foregroundGCIsActive - Set to true by the foreground collector when
1498 // it wants the baton. The foreground clears it when it has finished
1499 // the collection.
1500 // _foregroundGCShouldWait - Set to true by the background collector
1501 // when it is running. The foreground collector waits while
1502 // _foregroundGCShouldWait is true.
1503 // CGC_lock - monitor used to protect access to the above variables
1504 // and to notify the foreground and background collectors.
1505 // _collectorState - current state of the CMS collection.
1506 //
1507 // The foreground collector
1508 // acquires the CGC_lock
1509 // sets _foregroundGCIsActive
1510 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1511 // various locks acquired in preparation for the collection
1512 // are released so as not to block the background collector
1513 // that is in the midst of a collection
1514 // proceeds with the collection
1515 // clears _foregroundGCIsActive
1516 // returns
1517 //
1518 // The background collector in a loop iterating on the phases of the
1519 // collection
1520 // acquires the CGC_lock
1521 // sets _foregroundGCShouldWait
1522 // if _foregroundGCIsActive is set
1523 // clears _foregroundGCShouldWait, notifies _CGC_lock
1524 // waits on _CGC_lock for _foregroundGCIsActive to become false
1525 // and exits the loop.
1526 // otherwise
1527 // proceed with that phase of the collection
1528 // if the phase is a stop-the-world phase,
1529 // yield the baton once more just before enqueueing
1530 // the stop-world CMS operation (executed by the VM thread).
1531 // returns after all phases of the collection are done
1532 //
1533
1534 void CMSCollector::acquire_control_and_collect(bool full,
1535 bool clear_all_soft_refs) {
1536 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1537 assert(!Thread::current()->is_ConcurrentGC_thread(),
1538 "shouldn't try to acquire control from self!");
1539
1540 // Start the protocol for acquiring control of the
1541 // collection from the background collector (aka CMS thread).
1542 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1543 "VM thread should have CMS token");
1544 // Remember the possibly interrupted state of an ongoing
1545 // concurrent collection
1546 CollectorState first_state = _collectorState;
1547
1548 // Signal to a possibly ongoing concurrent collection that
1549 // we want to do a foreground collection.
1550 _foregroundGCIsActive = true;
1551
1552 // release locks and wait for a notify from the background collector
1553 // releasing the locks in only necessary for phases which
1554 // do yields to improve the granularity of the collection.
1555 assert_lock_strong(bitMapLock());
1556 // We need to lock the Free list lock for the space that we are
1557 // currently collecting.
1558 assert(haveFreelistLocks(), "Must be holding free list locks");
1559 bitMapLock()->unlock();
1560 releaseFreelistLocks();
1561 {
1562 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1563 if (_foregroundGCShouldWait) {
1564 // We are going to be waiting for action for the CMS thread;
1565 // it had better not be gone (for instance at shutdown)!
1566 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1567 "CMS thread must be running");
1568 // Wait here until the background collector gives us the go-ahead
1569 ConcurrentMarkSweepThread::clear_CMS_flag(
1570 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1571 // Get a possibly blocked CMS thread going:
1572 // Note that we set _foregroundGCIsActive true above,
1573 // without protection of the CGC_lock.
1574 CGC_lock->notify();
1575 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1576 "Possible deadlock");
1577 while (_foregroundGCShouldWait) {
1578 // wait for notification
1579 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1580 // Possibility of delay/starvation here, since CMS token does
1581 // not know to give priority to VM thread? Actually, i think
1582 // there wouldn't be any delay/starvation, but the proof of
1583 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1584 }
1585 ConcurrentMarkSweepThread::set_CMS_flag(
1586 ConcurrentMarkSweepThread::CMS_vm_has_token);
1587 }
1588 }
1589 // The CMS_token is already held. Get back the other locks.
1590 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1591 "VM thread should have CMS token");
1592 getFreelistLocks();
1593 bitMapLock()->lock_without_safepoint_check();
1594 if (TraceCMSState) {
1595 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1596 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1597 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1598 }
1599
1600 // Inform cms gen if this was due to partial collection failing.
1601 // The CMS gen may use this fact to determine its expansion policy.
1602 GenCollectedHeap* gch = GenCollectedHeap::heap();
1603 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1604 assert(!_cmsGen->incremental_collection_failed(),
1605 "Should have been noticed, reacted to and cleared");
1606 _cmsGen->set_incremental_collection_failed();
1607 }
1608
1609 if (first_state > Idling) {
1610 report_concurrent_mode_interruption();
1611 }
1612
1613 set_did_compact(true);
1614
1615 // If the collection is being acquired from the background
1616 // collector, there may be references on the discovered
1617 // references lists. Abandon those references, since some
1618 // of them may have become unreachable after concurrent
1619 // discovery; the STW compacting collector will redo discovery
1620 // more precisely, without being subject to floating garbage.
1621 // Leaving otherwise unreachable references in the discovered
1622 // lists would require special handling.
1623 ref_processor()->disable_discovery();
1624 ref_processor()->abandon_partial_discovery();
1625 ref_processor()->verify_no_references_recorded();
1626
1627 if (first_state > Idling) {
1628 save_heap_summary();
1629 }
1630
1631 do_compaction_work(clear_all_soft_refs);
1632
1633 // Has the GC time limit been exceeded?
1634 size_t max_eden_size = _young_gen->max_capacity() -
1635 _young_gen->to()->capacity() -
1636 _young_gen->from()->capacity();
1637 GCCause::Cause gc_cause = gch->gc_cause();
1638 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1639 _young_gen->eden()->used(),
1640 _cmsGen->max_capacity(),
1641 max_eden_size,
1642 full,
1643 gc_cause,
1644 gch->collector_policy());
1645
1646 // Reset the expansion cause, now that we just completed
1647 // a collection cycle.
1648 clear_expansion_cause();
1649 _foregroundGCIsActive = false;
1650 return;
1651 }
1652
1653 // Resize the tenured generation
1654 // after obtaining the free list locks for the
1655 // two generations.
1656 void CMSCollector::compute_new_size() {
1657 assert_locked_or_safepoint(Heap_lock);
1658 FreelistLocker z(this);
1659 MetaspaceGC::compute_new_size();
1660 _cmsGen->compute_new_size_free_list();
1661 }
1662
1663 // A work method used by the foreground collector to do
1664 // a mark-sweep-compact.
1665 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1666 GenCollectedHeap* gch = GenCollectedHeap::heap();
1667
1668 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1669 gc_timer->register_gc_start();
1670
1671 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1672 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1673
1674 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
1675
1676 // Temporarily widen the span of the weak reference processing to
1677 // the entire heap.
1678 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1679 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1680 // Temporarily, clear the "is_alive_non_header" field of the
1681 // reference processor.
1682 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1683 // Temporarily make reference _processing_ single threaded (non-MT).
1684 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1685 // Temporarily make refs discovery atomic
1686 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1687 // Temporarily make reference _discovery_ single threaded (non-MT)
1688 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1689
1690 ref_processor()->set_enqueuing_is_done(false);
1691 ref_processor()->enable_discovery();
1692 ref_processor()->setup_policy(clear_all_soft_refs);
1693 // If an asynchronous collection finishes, the _modUnionTable is
1694 // all clear. If we are assuming the collection from an asynchronous
1695 // collection, clear the _modUnionTable.
1696 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1697 "_modUnionTable should be clear if the baton was not passed");
1698 _modUnionTable.clear_all();
1699 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1700 "mod union for klasses should be clear if the baton was passed");
1701 _ct->klass_rem_set()->clear_mod_union();
1702
1703 // We must adjust the allocation statistics being maintained
1704 // in the free list space. We do so by reading and clearing
1705 // the sweep timer and updating the block flux rate estimates below.
1706 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1707 if (_inter_sweep_timer.is_active()) {
1708 _inter_sweep_timer.stop();
1709 // Note that we do not use this sample to update the _inter_sweep_estimate.
1710 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1711 _inter_sweep_estimate.padded_average(),
1712 _intra_sweep_estimate.padded_average());
1713 }
1714
1715 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1716 ref_processor(), clear_all_soft_refs);
1717 #ifdef ASSERT
1718 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1719 size_t free_size = cms_space->free();
1720 assert(free_size ==
1721 pointer_delta(cms_space->end(), cms_space->compaction_top())
1722 * HeapWordSize,
1723 "All the free space should be compacted into one chunk at top");
1724 assert(cms_space->dictionary()->total_chunk_size(
1725 debug_only(cms_space->freelistLock())) == 0 ||
1726 cms_space->totalSizeInIndexedFreeLists() == 0,
1727 "All the free space should be in a single chunk");
1728 size_t num = cms_space->totalCount();
1729 assert((free_size == 0 && num == 0) ||
1730 (free_size > 0 && (num == 1 || num == 2)),
1731 "There should be at most 2 free chunks after compaction");
1732 #endif // ASSERT
1733 _collectorState = Resetting;
1734 assert(_restart_addr == NULL,
1735 "Should have been NULL'd before baton was passed");
1736 reset(false /* == !concurrent */);
1737 _cmsGen->reset_after_compaction();
1738 _concurrent_cycles_since_last_unload = 0;
1739
1740 // Clear any data recorded in the PLAB chunk arrays.
1741 if (_survivor_plab_array != NULL) {
1742 reset_survivor_plab_arrays();
1743 }
1744
1745 // Adjust the per-size allocation stats for the next epoch.
1746 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1747 // Restart the "inter sweep timer" for the next epoch.
1748 _inter_sweep_timer.reset();
1749 _inter_sweep_timer.start();
1750
1751 gc_timer->register_gc_end();
1752
1753 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1754
1755 // For a mark-sweep-compact, compute_new_size() will be called
1756 // in the heap's do_collection() method.
1757 }
1758
1759 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1760 ContiguousSpace* eden_space = _young_gen->eden();
1761 ContiguousSpace* from_space = _young_gen->from();
1762 ContiguousSpace* to_space = _young_gen->to();
1763 // Eden
1764 if (_eden_chunk_array != NULL) {
1765 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1766 eden_space->bottom(), eden_space->top(),
1767 eden_space->end(), eden_space->capacity());
1768 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1769 "_eden_chunk_capacity=" SIZE_FORMAT,
1770 _eden_chunk_index, _eden_chunk_capacity);
1771 for (size_t i = 0; i < _eden_chunk_index; i++) {
1772 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1773 i, _eden_chunk_array[i]);
1774 }
1775 }
1776 // Survivor
1777 if (_survivor_chunk_array != NULL) {
1778 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1779 from_space->bottom(), from_space->top(),
1780 from_space->end(), from_space->capacity());
1781 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1782 "_survivor_chunk_capacity=" SIZE_FORMAT,
1783 _survivor_chunk_index, _survivor_chunk_capacity);
1784 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1785 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1786 i, _survivor_chunk_array[i]);
1787 }
1788 }
1789 }
1790
1791 void CMSCollector::getFreelistLocks() const {
1792 // Get locks for all free lists in all generations that this
1793 // collector is responsible for
1794 _cmsGen->freelistLock()->lock_without_safepoint_check();
1795 }
1796
1797 void CMSCollector::releaseFreelistLocks() const {
1798 // Release locks for all free lists in all generations that this
1799 // collector is responsible for
1800 _cmsGen->freelistLock()->unlock();
1801 }
1802
1803 bool CMSCollector::haveFreelistLocks() const {
1804 // Check locks for all free lists in all generations that this
1805 // collector is responsible for
1806 assert_lock_strong(_cmsGen->freelistLock());
1807 PRODUCT_ONLY(ShouldNotReachHere());
1808 return true;
1809 }
1810
1811 // A utility class that is used by the CMS collector to
1812 // temporarily "release" the foreground collector from its
1813 // usual obligation to wait for the background collector to
1814 // complete an ongoing phase before proceeding.
1815 class ReleaseForegroundGC: public StackObj {
1816 private:
1817 CMSCollector* _c;
1818 public:
1819 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1820 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1821 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1822 // allow a potentially blocked foreground collector to proceed
1823 _c->_foregroundGCShouldWait = false;
1824 if (_c->_foregroundGCIsActive) {
1825 CGC_lock->notify();
1826 }
1827 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1828 "Possible deadlock");
1829 }
1830
1831 ~ReleaseForegroundGC() {
1832 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1833 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1834 _c->_foregroundGCShouldWait = true;
1835 }
1836 };
1837
1838 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1839 assert(Thread::current()->is_ConcurrentGC_thread(),
1840 "A CMS asynchronous collection is only allowed on a CMS thread.");
1841
1842 GenCollectedHeap* gch = GenCollectedHeap::heap();
1843 {
1844 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1845 MutexLockerEx hl(Heap_lock, safepoint_check);
1846 FreelistLocker fll(this);
1847 MutexLockerEx x(CGC_lock, safepoint_check);
1848 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
1849 // The foreground collector is active or we're
1850 // not using asynchronous collections. Skip this
1851 // background collection.
1852 assert(!_foregroundGCShouldWait, "Should be clear");
1853 return;
1854 } else {
1855 assert(_collectorState == Idling, "Should be idling before start.");
1856 _collectorState = InitialMarking;
1857 register_gc_start(cause);
1858 // Reset the expansion cause, now that we are about to begin
1859 // a new cycle.
1860 clear_expansion_cause();
1861
1862 // Clear the MetaspaceGC flag since a concurrent collection
1863 // is starting but also clear it after the collection.
1864 MetaspaceGC::set_should_concurrent_collect(false);
1865 }
1866 // Decide if we want to enable class unloading as part of the
1867 // ensuing concurrent GC cycle.
1868 update_should_unload_classes();
1869 _full_gc_requested = false; // acks all outstanding full gc requests
1870 _full_gc_cause = GCCause::_no_gc;
1871 // Signal that we are about to start a collection
1872 gch->increment_total_full_collections(); // ... starting a collection cycle
1873 _collection_count_start = gch->total_full_collections();
1874 }
1875
1876 // Used for PrintGC
1877 size_t prev_used;
1878 if (PrintGC && Verbose) {
1879 prev_used = _cmsGen->used();
1880 }
1881
1882 // The change of the collection state is normally done at this level;
1883 // the exceptions are phases that are executed while the world is
1884 // stopped. For those phases the change of state is done while the
1885 // world is stopped. For baton passing purposes this allows the
1886 // background collector to finish the phase and change state atomically.
1887 // The foreground collector cannot wait on a phase that is done
1888 // while the world is stopped because the foreground collector already
1889 // has the world stopped and would deadlock.
1890 while (_collectorState != Idling) {
1891 if (TraceCMSState) {
1892 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
1893 Thread::current(), _collectorState);
1894 }
1895 // The foreground collector
1896 // holds the Heap_lock throughout its collection.
1897 // holds the CMS token (but not the lock)
1898 // except while it is waiting for the background collector to yield.
1899 //
1900 // The foreground collector should be blocked (not for long)
1901 // if the background collector is about to start a phase
1902 // executed with world stopped. If the background
1903 // collector has already started such a phase, the
1904 // foreground collector is blocked waiting for the
1905 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1906 // are executed in the VM thread.
1907 //
1908 // The locking order is
1909 // PendingListLock (PLL) -- if applicable (FinalMarking)
1910 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1911 // CMS token (claimed in
1912 // stop_world_and_do() -->
1913 // safepoint_synchronize() -->
1914 // CMSThread::synchronize())
1915
1916 {
1917 // Check if the FG collector wants us to yield.
1918 CMSTokenSync x(true); // is cms thread
1919 if (waitForForegroundGC()) {
1920 // We yielded to a foreground GC, nothing more to be
1921 // done this round.
1922 assert(_foregroundGCShouldWait == false, "We set it to false in "
1923 "waitForForegroundGC()");
1924 if (TraceCMSState) {
1925 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1926 " exiting collection CMS state %d",
1927 Thread::current(), _collectorState);
1928 }
1929 return;
1930 } else {
1931 // The background collector can run but check to see if the
1932 // foreground collector has done a collection while the
1933 // background collector was waiting to get the CGC_lock
1934 // above. If yes, break so that _foregroundGCShouldWait
1935 // is cleared before returning.
1936 if (_collectorState == Idling) {
1937 break;
1938 }
1939 }
1940 }
1941
1942 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1943 "should be waiting");
1944
1945 switch (_collectorState) {
1946 case InitialMarking:
1947 {
1948 ReleaseForegroundGC x(this);
1949 stats().record_cms_begin();
1950 VM_CMS_Initial_Mark initial_mark_op(this);
1951 VMThread::execute(&initial_mark_op);
1952 }
1953 // The collector state may be any legal state at this point
1954 // since the background collector may have yielded to the
1955 // foreground collector.
1956 break;
1957 case Marking:
1958 // initial marking in checkpointRootsInitialWork has been completed
1959 if (markFromRoots()) { // we were successful
1960 assert(_collectorState == Precleaning, "Collector state should "
1961 "have changed");
1962 } else {
1963 assert(_foregroundGCIsActive, "Internal state inconsistency");
1964 }
1965 break;
1966 case Precleaning:
1967 // marking from roots in markFromRoots has been completed
1968 preclean();
1969 assert(_collectorState == AbortablePreclean ||
1970 _collectorState == FinalMarking,
1971 "Collector state should have changed");
1972 break;
1973 case AbortablePreclean:
1974 abortable_preclean();
1975 assert(_collectorState == FinalMarking, "Collector state should "
1976 "have changed");
1977 break;
1978 case FinalMarking:
1979 {
1980 ReleaseForegroundGC x(this);
1981
1982 VM_CMS_Final_Remark final_remark_op(this);
1983 VMThread::execute(&final_remark_op);
1984 }
1985 assert(_foregroundGCShouldWait, "block post-condition");
1986 break;
1987 case Sweeping:
1988 // final marking in checkpointRootsFinal has been completed
1989 sweep();
1990 assert(_collectorState == Resizing, "Collector state change "
1991 "to Resizing must be done under the free_list_lock");
1992
1993 case Resizing: {
1994 // Sweeping has been completed...
1995 // At this point the background collection has completed.
1996 // Don't move the call to compute_new_size() down
1997 // into code that might be executed if the background
1998 // collection was preempted.
1999 {
2000 ReleaseForegroundGC x(this); // unblock FG collection
2001 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2002 CMSTokenSync z(true); // not strictly needed.
2003 if (_collectorState == Resizing) {
2004 compute_new_size();
2005 save_heap_summary();
2006 _collectorState = Resetting;
2007 } else {
2008 assert(_collectorState == Idling, "The state should only change"
2009 " because the foreground collector has finished the collection");
2010 }
2011 }
2012 break;
2013 }
2014 case Resetting:
2015 // CMS heap resizing has been completed
2016 reset(true);
2017 assert(_collectorState == Idling, "Collector state should "
2018 "have changed");
2019
2020 MetaspaceGC::set_should_concurrent_collect(false);
2021
2022 stats().record_cms_end();
2023 // Don't move the concurrent_phases_end() and compute_new_size()
2024 // calls to here because a preempted background collection
2025 // has it's state set to "Resetting".
2026 break;
2027 case Idling:
2028 default:
2029 ShouldNotReachHere();
2030 break;
2031 }
2032 if (TraceCMSState) {
2033 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2034 Thread::current(), _collectorState);
2035 }
2036 assert(_foregroundGCShouldWait, "block post-condition");
2037 }
2038
2039 // Should this be in gc_epilogue?
2040 collector_policy()->counters()->update_counters();
2041
2042 {
2043 // Clear _foregroundGCShouldWait and, in the event that the
2044 // foreground collector is waiting, notify it, before
2045 // returning.
2046 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2047 _foregroundGCShouldWait = false;
2048 if (_foregroundGCIsActive) {
2049 CGC_lock->notify();
2050 }
2051 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2052 "Possible deadlock");
2053 }
2054 if (TraceCMSState) {
2055 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2056 " exiting collection CMS state %d",
2057 Thread::current(), _collectorState);
2058 }
2059 if (PrintGC && Verbose) {
2060 _cmsGen->print_heap_change(prev_used);
2061 }
2062 }
2063
2064 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2065 _cms_start_registered = true;
2066 _gc_timer_cm->register_gc_start();
2067 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2068 }
2069
2070 void CMSCollector::register_gc_end() {
2071 if (_cms_start_registered) {
2072 report_heap_summary(GCWhen::AfterGC);
2073
2074 _gc_timer_cm->register_gc_end();
2075 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2076 _cms_start_registered = false;
2077 }
2078 }
2079
2080 void CMSCollector::save_heap_summary() {
2081 GenCollectedHeap* gch = GenCollectedHeap::heap();
2082 _last_heap_summary = gch->create_heap_summary();
2083 _last_metaspace_summary = gch->create_metaspace_summary();
2084 }
2085
2086 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2087 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2088 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2089 }
2090
2091 bool CMSCollector::waitForForegroundGC() {
2092 bool res = false;
2093 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2094 "CMS thread should have CMS token");
2095 // Block the foreground collector until the
2096 // background collectors decides whether to
2097 // yield.
2098 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2099 _foregroundGCShouldWait = true;
2100 if (_foregroundGCIsActive) {
2101 // The background collector yields to the
2102 // foreground collector and returns a value
2103 // indicating that it has yielded. The foreground
2104 // collector can proceed.
2105 res = true;
2106 _foregroundGCShouldWait = false;
2107 ConcurrentMarkSweepThread::clear_CMS_flag(
2108 ConcurrentMarkSweepThread::CMS_cms_has_token);
2109 ConcurrentMarkSweepThread::set_CMS_flag(
2110 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2111 // Get a possibly blocked foreground thread going
2112 CGC_lock->notify();
2113 if (TraceCMSState) {
2114 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2115 Thread::current(), _collectorState);
2116 }
2117 while (_foregroundGCIsActive) {
2118 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2119 }
2120 ConcurrentMarkSweepThread::set_CMS_flag(
2121 ConcurrentMarkSweepThread::CMS_cms_has_token);
2122 ConcurrentMarkSweepThread::clear_CMS_flag(
2123 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2124 }
2125 if (TraceCMSState) {
2126 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2127 Thread::current(), _collectorState);
2128 }
2129 return res;
2130 }
2131
2132 // Because of the need to lock the free lists and other structures in
2133 // the collector, common to all the generations that the collector is
2134 // collecting, we need the gc_prologues of individual CMS generations
2135 // delegate to their collector. It may have been simpler had the
2136 // current infrastructure allowed one to call a prologue on a
2137 // collector. In the absence of that we have the generation's
2138 // prologue delegate to the collector, which delegates back
2139 // some "local" work to a worker method in the individual generations
2140 // that it's responsible for collecting, while itself doing any
2141 // work common to all generations it's responsible for. A similar
2142 // comment applies to the gc_epilogue()'s.
2143 // The role of the variable _between_prologue_and_epilogue is to
2144 // enforce the invocation protocol.
2145 void CMSCollector::gc_prologue(bool full) {
2146 // Call gc_prologue_work() for the CMSGen
2147 // we are responsible for.
2148
2149 // The following locking discipline assumes that we are only called
2150 // when the world is stopped.
2151 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2152
2153 // The CMSCollector prologue must call the gc_prologues for the
2154 // "generations" that it's responsible
2155 // for.
2156
2157 assert( Thread::current()->is_VM_thread()
2158 || ( CMSScavengeBeforeRemark
2159 && Thread::current()->is_ConcurrentGC_thread()),
2160 "Incorrect thread type for prologue execution");
2161
2162 if (_between_prologue_and_epilogue) {
2163 // We have already been invoked; this is a gc_prologue delegation
2164 // from yet another CMS generation that we are responsible for, just
2165 // ignore it since all relevant work has already been done.
2166 return;
2167 }
2168
2169 // set a bit saying prologue has been called; cleared in epilogue
2170 _between_prologue_and_epilogue = true;
2171 // Claim locks for common data structures, then call gc_prologue_work()
2172 // for each CMSGen.
2173
2174 getFreelistLocks(); // gets free list locks on constituent spaces
2175 bitMapLock()->lock_without_safepoint_check();
2176
2177 // Should call gc_prologue_work() for all cms gens we are responsible for
2178 bool duringMarking = _collectorState >= Marking
2179 && _collectorState < Sweeping;
2180
2181 // The young collections clear the modified oops state, which tells if
2182 // there are any modified oops in the class. The remark phase also needs
2183 // that information. Tell the young collection to save the union of all
2184 // modified klasses.
2185 if (duringMarking) {
2186 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2187 }
2188
2189 bool registerClosure = duringMarking;
2190
2191 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2192 &_modUnionClosurePar
2193 : &_modUnionClosure;
2194 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2195
2196 if (!full) {
2197 stats().record_gc0_begin();
2198 }
2199 }
2200
2201 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2202
2203 _capacity_at_prologue = capacity();
2204 _used_at_prologue = used();
2205
2206 // Delegate to CMScollector which knows how to coordinate between
2207 // this and any other CMS generations that it is responsible for
2208 // collecting.
2209 collector()->gc_prologue(full);
2210 }
2211
2212 // This is a "private" interface for use by this generation's CMSCollector.
2213 // Not to be called directly by any other entity (for instance,
2214 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2215 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2216 bool registerClosure, ModUnionClosure* modUnionClosure) {
2217 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2218 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2219 "Should be NULL");
2220 if (registerClosure) {
2221 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2222 }
2223 cmsSpace()->gc_prologue();
2224 // Clear stat counters
2225 NOT_PRODUCT(
2226 assert(_numObjectsPromoted == 0, "check");
2227 assert(_numWordsPromoted == 0, "check");
2228 if (Verbose && PrintGC) {
2229 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2230 SIZE_FORMAT" bytes concurrently",
2231 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2232 }
2233 _numObjectsAllocated = 0;
2234 _numWordsAllocated = 0;
2235 )
2236 }
2237
2238 void CMSCollector::gc_epilogue(bool full) {
2239 // The following locking discipline assumes that we are only called
2240 // when the world is stopped.
2241 assert(SafepointSynchronize::is_at_safepoint(),
2242 "world is stopped assumption");
2243
2244 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2245 // if linear allocation blocks need to be appropriately marked to allow the
2246 // the blocks to be parsable. We also check here whether we need to nudge the
2247 // CMS collector thread to start a new cycle (if it's not already active).
2248 assert( Thread::current()->is_VM_thread()
2249 || ( CMSScavengeBeforeRemark
2250 && Thread::current()->is_ConcurrentGC_thread()),
2251 "Incorrect thread type for epilogue execution");
2252
2253 if (!_between_prologue_and_epilogue) {
2254 // We have already been invoked; this is a gc_epilogue delegation
2255 // from yet another CMS generation that we are responsible for, just
2256 // ignore it since all relevant work has already been done.
2257 return;
2258 }
2259 assert(haveFreelistLocks(), "must have freelist locks");
2260 assert_lock_strong(bitMapLock());
2261
2262 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2263
2264 _cmsGen->gc_epilogue_work(full);
2265
2266 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2267 // in case sampling was not already enabled, enable it
2268 _start_sampling = true;
2269 }
2270 // reset _eden_chunk_array so sampling starts afresh
2271 _eden_chunk_index = 0;
2272
2273 size_t cms_used = _cmsGen->cmsSpace()->used();
2274
2275 // update performance counters - this uses a special version of
2276 // update_counters() that allows the utilization to be passed as a
2277 // parameter, avoiding multiple calls to used().
2278 //
2279 _cmsGen->update_counters(cms_used);
2280
2281 bitMapLock()->unlock();
2282 releaseFreelistLocks();
2283
2284 if (!CleanChunkPoolAsync) {
2285 Chunk::clean_chunk_pool();
2286 }
2287
2288 set_did_compact(false);
2289 _between_prologue_and_epilogue = false; // ready for next cycle
2290 }
2291
2292 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2293 collector()->gc_epilogue(full);
2294
2295 // Also reset promotion tracking in par gc thread states.
2296 for (uint i = 0; i < ParallelGCThreads; i++) {
2297 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2298 }
2299 }
2300
2301 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2302 assert(!incremental_collection_failed(), "Should have been cleared");
2303 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2304 cmsSpace()->gc_epilogue();
2305 // Print stat counters
2306 NOT_PRODUCT(
2307 assert(_numObjectsAllocated == 0, "check");
2308 assert(_numWordsAllocated == 0, "check");
2309 if (Verbose && PrintGC) {
2310 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2311 SIZE_FORMAT" bytes",
2312 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2313 }
2314 _numObjectsPromoted = 0;
2315 _numWordsPromoted = 0;
2316 )
2317
2318 if (PrintGC && Verbose) {
2319 // Call down the chain in contiguous_available needs the freelistLock
2320 // so print this out before releasing the freeListLock.
2321 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2322 contiguous_available());
2323 }
2324 }
2325
2326 #ifndef PRODUCT
2327 bool CMSCollector::have_cms_token() {
2328 Thread* thr = Thread::current();
2329 if (thr->is_VM_thread()) {
2330 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2331 } else if (thr->is_ConcurrentGC_thread()) {
2332 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2333 } else if (thr->is_GC_task_thread()) {
2334 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2335 ParGCRareEvent_lock->owned_by_self();
2336 }
2337 return false;
2338 }
2339 #endif
2340
2341 // Check reachability of the given heap address in CMS generation,
2342 // treating all other generations as roots.
2343 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2344 // We could "guarantee" below, rather than assert, but I'll
2345 // leave these as "asserts" so that an adventurous debugger
2346 // could try this in the product build provided some subset of
2347 // the conditions were met, provided they were interested in the
2348 // results and knew that the computation below wouldn't interfere
2349 // with other concurrent computations mutating the structures
2350 // being read or written.
2351 assert(SafepointSynchronize::is_at_safepoint(),
2352 "Else mutations in object graph will make answer suspect");
2353 assert(have_cms_token(), "Should hold cms token");
2354 assert(haveFreelistLocks(), "must hold free list locks");
2355 assert_lock_strong(bitMapLock());
2356
2357 // Clear the marking bit map array before starting, but, just
2358 // for kicks, first report if the given address is already marked
2359 gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", addr,
2360 _markBitMap.isMarked(addr) ? "" : " not");
2361
2362 if (verify_after_remark()) {
2363 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2364 bool result = verification_mark_bm()->isMarked(addr);
2365 gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", addr,
2366 result ? "IS" : "is NOT");
2367 return result;
2368 } else {
2369 gclog_or_tty->print_cr("Could not compute result");
2370 return false;
2371 }
2372 }
2373
2374
2375 void
2376 CMSCollector::print_on_error(outputStream* st) {
2377 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2378 if (collector != NULL) {
2379 CMSBitMap* bitmap = &collector->_markBitMap;
2380 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, bitmap);
2381 bitmap->print_on_error(st, " Bits: ");
2382
2383 st->cr();
2384
2385 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2386 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, mut_bitmap);
2387 mut_bitmap->print_on_error(st, " Bits: ");
2388 }
2389 }
2390
2391 ////////////////////////////////////////////////////////
2392 // CMS Verification Support
2393 ////////////////////////////////////////////////////////
2394 // Following the remark phase, the following invariant
2395 // should hold -- each object in the CMS heap which is
2396 // marked in markBitMap() should be marked in the verification_mark_bm().
2397
2398 class VerifyMarkedClosure: public BitMapClosure {
2399 CMSBitMap* _marks;
2400 bool _failed;
2401
2402 public:
2403 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2404
2405 bool do_bit(size_t offset) {
2406 HeapWord* addr = _marks->offsetToHeapWord(offset);
2407 if (!_marks->isMarked(addr)) {
2408 oop(addr)->print_on(gclog_or_tty);
2409 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2410 _failed = true;
2411 }
2412 return true;
2413 }
2414
2415 bool failed() { return _failed; }
2416 };
2417
2418 bool CMSCollector::verify_after_remark(bool silent) {
2419 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2420 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2421 static bool init = false;
2422
2423 assert(SafepointSynchronize::is_at_safepoint(),
2424 "Else mutations in object graph will make answer suspect");
2425 assert(have_cms_token(),
2426 "Else there may be mutual interference in use of "
2427 " verification data structures");
2428 assert(_collectorState > Marking && _collectorState <= Sweeping,
2429 "Else marking info checked here may be obsolete");
2430 assert(haveFreelistLocks(), "must hold free list locks");
2431 assert_lock_strong(bitMapLock());
2432
2433
2434 // Allocate marking bit map if not already allocated
2435 if (!init) { // first time
2436 if (!verification_mark_bm()->allocate(_span)) {
2437 return false;
2438 }
2439 init = true;
2440 }
2441
2442 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2443
2444 // Turn off refs discovery -- so we will be tracing through refs.
2445 // This is as intended, because by this time
2446 // GC must already have cleared any refs that need to be cleared,
2447 // and traced those that need to be marked; moreover,
2448 // the marking done here is not going to interfere in any
2449 // way with the marking information used by GC.
2450 NoRefDiscovery no_discovery(ref_processor());
2451
2452 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2453
2454 // Clear any marks from a previous round
2455 verification_mark_bm()->clear_all();
2456 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2457 verify_work_stacks_empty();
2458
2459 GenCollectedHeap* gch = GenCollectedHeap::heap();
2460 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2461 // Update the saved marks which may affect the root scans.
2462 gch->save_marks();
2463
2464 if (CMSRemarkVerifyVariant == 1) {
2465 // In this first variant of verification, we complete
2466 // all marking, then check if the new marks-vector is
2467 // a subset of the CMS marks-vector.
2468 verify_after_remark_work_1();
2469 } else if (CMSRemarkVerifyVariant == 2) {
2470 // In this second variant of verification, we flag an error
2471 // (i.e. an object reachable in the new marks-vector not reachable
2472 // in the CMS marks-vector) immediately, also indicating the
2473 // identify of an object (A) that references the unmarked object (B) --
2474 // presumably, a mutation to A failed to be picked up by preclean/remark?
2475 verify_after_remark_work_2();
2476 } else {
2477 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2478 CMSRemarkVerifyVariant);
2479 }
2480 if (!silent) gclog_or_tty->print(" done] ");
2481 return true;
2482 }
2483
2484 void CMSCollector::verify_after_remark_work_1() {
2485 ResourceMark rm;
2486 HandleMark hm;
2487 GenCollectedHeap* gch = GenCollectedHeap::heap();
2488
2489 // Get a clear set of claim bits for the roots processing to work with.
2490 ClassLoaderDataGraph::clear_claimed_marks();
2491
2492 // Mark from roots one level into CMS
2493 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2494 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2495
2496 gch->gen_process_roots(_cmsGen->level(),
2497 true, // younger gens are roots
2498 true, // activate StrongRootsScope
2499 SharedHeap::ScanningOption(roots_scanning_options()),
2500 should_unload_classes(),
2501 ¬Older,
2502 NULL,
2503 NULL); // SSS: Provide correct closure
2504
2505 // Now mark from the roots
2506 MarkFromRootsClosure markFromRootsClosure(this, _span,
2507 verification_mark_bm(), verification_mark_stack(),
2508 false /* don't yield */, true /* verifying */);
2509 assert(_restart_addr == NULL, "Expected pre-condition");
2510 verification_mark_bm()->iterate(&markFromRootsClosure);
2511 while (_restart_addr != NULL) {
2512 // Deal with stack overflow: by restarting at the indicated
2513 // address.
2514 HeapWord* ra = _restart_addr;
2515 markFromRootsClosure.reset(ra);
2516 _restart_addr = NULL;
2517 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2518 }
2519 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2520 verify_work_stacks_empty();
2521
2522 // Marking completed -- now verify that each bit marked in
2523 // verification_mark_bm() is also marked in markBitMap(); flag all
2524 // errors by printing corresponding objects.
2525 VerifyMarkedClosure vcl(markBitMap());
2526 verification_mark_bm()->iterate(&vcl);
2527 if (vcl.failed()) {
2528 gclog_or_tty->print("Verification failed");
2529 Universe::heap()->print_on(gclog_or_tty);
2530 fatal("CMS: failed marking verification after remark");
2531 }
2532 }
2533
2534 class VerifyKlassOopsKlassClosure : public KlassClosure {
2535 class VerifyKlassOopsClosure : public OopClosure {
2536 CMSBitMap* _bitmap;
2537 public:
2538 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2539 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2540 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2541 } _oop_closure;
2542 public:
2543 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2544 void do_klass(Klass* k) {
2545 k->oops_do(&_oop_closure);
2546 }
2547 };
2548
2549 void CMSCollector::verify_after_remark_work_2() {
2550 ResourceMark rm;
2551 HandleMark hm;
2552 GenCollectedHeap* gch = GenCollectedHeap::heap();
2553
2554 // Get a clear set of claim bits for the roots processing to work with.
2555 ClassLoaderDataGraph::clear_claimed_marks();
2556
2557 // Mark from roots one level into CMS
2558 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2559 markBitMap());
2560 CLDToOopClosure cld_closure(¬Older, true);
2561
2562 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2563
2564 gch->gen_process_roots(_cmsGen->level(),
2565 true, // younger gens are roots
2566 true, // activate StrongRootsScope
2567 SharedHeap::ScanningOption(roots_scanning_options()),
2568 should_unload_classes(),
2569 ¬Older,
2570 NULL,
2571 &cld_closure);
2572
2573 // Now mark from the roots
2574 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2575 verification_mark_bm(), markBitMap(), verification_mark_stack());
2576 assert(_restart_addr == NULL, "Expected pre-condition");
2577 verification_mark_bm()->iterate(&markFromRootsClosure);
2578 while (_restart_addr != NULL) {
2579 // Deal with stack overflow: by restarting at the indicated
2580 // address.
2581 HeapWord* ra = _restart_addr;
2582 markFromRootsClosure.reset(ra);
2583 _restart_addr = NULL;
2584 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2585 }
2586 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2587 verify_work_stacks_empty();
2588
2589 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2590 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2591
2592 // Marking completed -- now verify that each bit marked in
2593 // verification_mark_bm() is also marked in markBitMap(); flag all
2594 // errors by printing corresponding objects.
2595 VerifyMarkedClosure vcl(markBitMap());
2596 verification_mark_bm()->iterate(&vcl);
2597 assert(!vcl.failed(), "Else verification above should not have succeeded");
2598 }
2599
2600 void ConcurrentMarkSweepGeneration::save_marks() {
2601 // delegate to CMS space
2602 cmsSpace()->save_marks();
2603 for (uint i = 0; i < ParallelGCThreads; i++) {
2604 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2605 }
2606 }
2607
2608 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2609 return cmsSpace()->no_allocs_since_save_marks();
2610 }
2611
2612 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2613 \
2614 void ConcurrentMarkSweepGeneration:: \
2615 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2616 cl->set_generation(this); \
2617 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2618 cl->reset_generation(); \
2619 save_marks(); \
2620 }
2621
2622 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2623
2624 void
2625 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2626 if (freelistLock()->owned_by_self()) {
2627 Generation::oop_iterate(cl);
2628 } else {
2629 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2630 Generation::oop_iterate(cl);
2631 }
2632 }
2633
2634 void
2635 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2636 if (freelistLock()->owned_by_self()) {
2637 Generation::object_iterate(cl);
2638 } else {
2639 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2640 Generation::object_iterate(cl);
2641 }
2642 }
2643
2644 void
2645 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2646 if (freelistLock()->owned_by_self()) {
2647 Generation::safe_object_iterate(cl);
2648 } else {
2649 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2650 Generation::safe_object_iterate(cl);
2651 }
2652 }
2653
2654 void
2655 ConcurrentMarkSweepGeneration::post_compact() {
2656 }
2657
2658 void
2659 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2660 // Fix the linear allocation blocks to look like free blocks.
2661
2662 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2663 // are not called when the heap is verified during universe initialization and
2664 // at vm shutdown.
2665 if (freelistLock()->owned_by_self()) {
2666 cmsSpace()->prepare_for_verify();
2667 } else {
2668 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2669 cmsSpace()->prepare_for_verify();
2670 }
2671 }
2672
2673 void
2674 ConcurrentMarkSweepGeneration::verify() {
2675 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2676 // are not called when the heap is verified during universe initialization and
2677 // at vm shutdown.
2678 if (freelistLock()->owned_by_self()) {
2679 cmsSpace()->verify();
2680 } else {
2681 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2682 cmsSpace()->verify();
2683 }
2684 }
2685
2686 void CMSCollector::verify() {
2687 _cmsGen->verify();
2688 }
2689
2690 #ifndef PRODUCT
2691 bool CMSCollector::overflow_list_is_empty() const {
2692 assert(_num_par_pushes >= 0, "Inconsistency");
2693 if (_overflow_list == NULL) {
2694 assert(_num_par_pushes == 0, "Inconsistency");
2695 }
2696 return _overflow_list == NULL;
2697 }
2698
2699 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2700 // merely consolidate assertion checks that appear to occur together frequently.
2701 void CMSCollector::verify_work_stacks_empty() const {
2702 assert(_markStack.isEmpty(), "Marking stack should be empty");
2703 assert(overflow_list_is_empty(), "Overflow list should be empty");
2704 }
2705
2706 void CMSCollector::verify_overflow_empty() const {
2707 assert(overflow_list_is_empty(), "Overflow list should be empty");
2708 assert(no_preserved_marks(), "No preserved marks");
2709 }
2710 #endif // PRODUCT
2711
2712 // Decide if we want to enable class unloading as part of the
2713 // ensuing concurrent GC cycle. We will collect and
2714 // unload classes if it's the case that:
2715 // (1) an explicit gc request has been made and the flag
2716 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2717 // (2) (a) class unloading is enabled at the command line, and
2718 // (b) old gen is getting really full
2719 // NOTE: Provided there is no change in the state of the heap between
2720 // calls to this method, it should have idempotent results. Moreover,
2721 // its results should be monotonically increasing (i.e. going from 0 to 1,
2722 // but not 1 to 0) between successive calls between which the heap was
2723 // not collected. For the implementation below, it must thus rely on
2724 // the property that concurrent_cycles_since_last_unload()
2725 // will not decrease unless a collection cycle happened and that
2726 // _cmsGen->is_too_full() are
2727 // themselves also monotonic in that sense. See check_monotonicity()
2728 // below.
2729 void CMSCollector::update_should_unload_classes() {
2730 _should_unload_classes = false;
2731 // Condition 1 above
2732 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2733 _should_unload_classes = true;
2734 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2735 // Disjuncts 2.b.(i,ii,iii) above
2736 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2737 CMSClassUnloadingMaxInterval)
2738 || _cmsGen->is_too_full();
2739 }
2740 }
2741
2742 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2743 bool res = should_concurrent_collect();
2744 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2745 return res;
2746 }
2747
2748 void CMSCollector::setup_cms_unloading_and_verification_state() {
2749 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2750 || VerifyBeforeExit;
2751 const int rso = SharedHeap::SO_AllCodeCache;
2752
2753 // We set the proper root for this CMS cycle here.
2754 if (should_unload_classes()) { // Should unload classes this cycle
2755 remove_root_scanning_option(rso); // Shrink the root set appropriately
2756 set_verifying(should_verify); // Set verification state for this cycle
2757 return; // Nothing else needs to be done at this time
2758 }
2759
2760 // Not unloading classes this cycle
2761 assert(!should_unload_classes(), "Inconsistency!");
2762
2763 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2764 // Include symbols, strings and code cache elements to prevent their resurrection.
2765 add_root_scanning_option(rso);
2766 set_verifying(true);
2767 } else if (verifying() && !should_verify) {
2768 // We were verifying, but some verification flags got disabled.
2769 set_verifying(false);
2770 // Exclude symbols, strings and code cache elements from root scanning to
2771 // reduce IM and RM pauses.
2772 remove_root_scanning_option(rso);
2773 }
2774 }
2775
2776
2777 #ifndef PRODUCT
2778 HeapWord* CMSCollector::block_start(const void* p) const {
2779 const HeapWord* addr = (HeapWord*)p;
2780 if (_span.contains(p)) {
2781 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2782 return _cmsGen->cmsSpace()->block_start(p);
2783 }
2784 }
2785 return NULL;
2786 }
2787 #endif
2788
2789 HeapWord*
2790 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2791 bool tlab,
2792 bool parallel) {
2793 CMSSynchronousYieldRequest yr;
2794 assert(!tlab, "Can't deal with TLAB allocation");
2795 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2796 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2797 if (GCExpandToAllocateDelayMillis > 0) {
2798 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2799 }
2800 return have_lock_and_allocate(word_size, tlab);
2801 }
2802
2803 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2804 size_t bytes,
2805 size_t expand_bytes,
2806 CMSExpansionCause::Cause cause)
2807 {
2808
2809 bool success = expand(bytes, expand_bytes);
2810
2811 // remember why we expanded; this information is used
2812 // by shouldConcurrentCollect() when making decisions on whether to start
2813 // a new CMS cycle.
2814 if (success) {
2815 set_expansion_cause(cause);
2816 if (PrintGCDetails && Verbose) {
2817 gclog_or_tty->print_cr("Expanded CMS gen for %s",
2818 CMSExpansionCause::to_string(cause));
2819 }
2820 }
2821 }
2822
2823 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2824 HeapWord* res = NULL;
2825 MutexLocker x(ParGCRareEvent_lock);
2826 while (true) {
2827 // Expansion by some other thread might make alloc OK now:
2828 res = ps->lab.alloc(word_sz);
2829 if (res != NULL) return res;
2830 // If there's not enough expansion space available, give up.
2831 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2832 return NULL;
2833 }
2834 // Otherwise, we try expansion.
2835 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2836 // Now go around the loop and try alloc again;
2837 // A competing par_promote might beat us to the expansion space,
2838 // so we may go around the loop again if promotion fails again.
2839 if (GCExpandToAllocateDelayMillis > 0) {
2840 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2841 }
2842 }
2843 }
2844
2845
2846 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2847 PromotionInfo* promo) {
2848 MutexLocker x(ParGCRareEvent_lock);
2849 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2850 while (true) {
2851 // Expansion by some other thread might make alloc OK now:
2852 if (promo->ensure_spooling_space()) {
2853 assert(promo->has_spooling_space(),
2854 "Post-condition of successful ensure_spooling_space()");
2855 return true;
2856 }
2857 // If there's not enough expansion space available, give up.
2858 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2859 return false;
2860 }
2861 // Otherwise, we try expansion.
2862 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2863 // Now go around the loop and try alloc again;
2864 // A competing allocation might beat us to the expansion space,
2865 // so we may go around the loop again if allocation fails again.
2866 if (GCExpandToAllocateDelayMillis > 0) {
2867 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2868 }
2869 }
2870 }
2871
2872 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2873 // Only shrink if a compaction was done so that all the free space
2874 // in the generation is in a contiguous block at the end.
2875 if (did_compact()) {
2876 CardGeneration::shrink(bytes);
2877 }
2878 }
2879
2880 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2881 assert_locked_or_safepoint(Heap_lock);
2882 }
2883
2884 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2885 assert_locked_or_safepoint(Heap_lock);
2886 assert_lock_strong(freelistLock());
2887 if (PrintGCDetails && Verbose) {
2888 warning("Shrinking of CMS not yet implemented");
2889 }
2890 return;
2891 }
2892
2893
2894 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2895 // phases.
2896 class CMSPhaseAccounting: public StackObj {
2897 public:
2898 CMSPhaseAccounting(CMSCollector *collector,
2899 const char *phase,
2900 const GCId gc_id,
2901 bool print_cr = true);
2902 ~CMSPhaseAccounting();
2903
2904 private:
2905 CMSCollector *_collector;
2906 const char *_phase;
2907 elapsedTimer _wallclock;
2908 bool _print_cr;
2909 const GCId _gc_id;
2910
2911 public:
2912 // Not MT-safe; so do not pass around these StackObj's
2913 // where they may be accessed by other threads.
2914 jlong wallclock_millis() {
2915 assert(_wallclock.is_active(), "Wall clock should not stop");
2916 _wallclock.stop(); // to record time
2917 jlong ret = _wallclock.milliseconds();
2918 _wallclock.start(); // restart
2919 return ret;
2920 }
2921 };
2922
2923 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2924 const char *phase,
2925 const GCId gc_id,
2926 bool print_cr) :
2927 _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
2928
2929 if (PrintCMSStatistics != 0) {
2930 _collector->resetYields();
2931 }
2932 if (PrintGCDetails) {
2933 gclog_or_tty->gclog_stamp(_gc_id);
2934 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
2935 _collector->cmsGen()->short_name(), _phase);
2936 }
2937 _collector->resetTimer();
2938 _wallclock.start();
2939 _collector->startTimer();
2940 }
2941
2942 CMSPhaseAccounting::~CMSPhaseAccounting() {
2943 assert(_wallclock.is_active(), "Wall clock should not have stopped");
2944 _collector->stopTimer();
2945 _wallclock.stop();
2946 if (PrintGCDetails) {
2947 gclog_or_tty->gclog_stamp(_gc_id);
2948 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
2949 _collector->cmsGen()->short_name(),
2950 _phase, _collector->timerValue(), _wallclock.seconds());
2951 if (_print_cr) {
2952 gclog_or_tty->cr();
2953 }
2954 if (PrintCMSStatistics != 0) {
2955 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
2956 _collector->yields());
2957 }
2958 }
2959 }
2960
2961 // CMS work
2962
2963 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2964 class CMSParMarkTask : public AbstractGangTask {
2965 protected:
2966 CMSCollector* _collector;
2967 int _n_workers;
2968 CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
2969 AbstractGangTask(name),
2970 _collector(collector),
2971 _n_workers(n_workers) {}
2972 // Work method in support of parallel rescan ... of young gen spaces
2973 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2974 ContiguousSpace* space,
2975 HeapWord** chunk_array, size_t chunk_top);
2976 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2977 };
2978
2979 // Parallel initial mark task
2980 class CMSParInitialMarkTask: public CMSParMarkTask {
2981 public:
2982 CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
2983 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
2984 collector, n_workers) {}
2985 void work(uint worker_id);
2986 };
2987
2988 // Checkpoint the roots into this generation from outside
2989 // this generation. [Note this initial checkpoint need only
2990 // be approximate -- we'll do a catch up phase subsequently.]
2991 void CMSCollector::checkpointRootsInitial() {
2992 assert(_collectorState == InitialMarking, "Wrong collector state");
2993 check_correct_thread_executing();
2994 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2995
2996 save_heap_summary();
2997 report_heap_summary(GCWhen::BeforeGC);
2998
2999 ReferenceProcessor* rp = ref_processor();
3000 assert(_restart_addr == NULL, "Control point invariant");
3001 {
3002 // acquire locks for subsequent manipulations
3003 MutexLockerEx x(bitMapLock(),
3004 Mutex::_no_safepoint_check_flag);
3005 checkpointRootsInitialWork();
3006 // enable ("weak") refs discovery
3007 rp->enable_discovery();
3008 _collectorState = Marking;
3009 }
3010 }
3011
3012 void CMSCollector::checkpointRootsInitialWork() {
3013 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3014 assert(_collectorState == InitialMarking, "just checking");
3015
3016 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3017 // precede our marking with a collection of all
3018 // younger generations to keep floating garbage to a minimum.
3019 // XXX: we won't do this for now -- it's an optimization to be done later.
3020
3021 // already have locks
3022 assert_lock_strong(bitMapLock());
3023 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3024
3025 // Setup the verification and class unloading state for this
3026 // CMS collection cycle.
3027 setup_cms_unloading_and_verification_state();
3028
3029 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3030 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
3031
3032 // Reset all the PLAB chunk arrays if necessary.
3033 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3034 reset_survivor_plab_arrays();
3035 }
3036
3037 ResourceMark rm;
3038 HandleMark hm;
3039
3040 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3041 GenCollectedHeap* gch = GenCollectedHeap::heap();
3042
3043 verify_work_stacks_empty();
3044 verify_overflow_empty();
3045
3046 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3047 // Update the saved marks which may affect the root scans.
3048 gch->save_marks();
3049
3050 // weak reference processing has not started yet.
3051 ref_processor()->set_enqueuing_is_done(false);
3052
3053 // Need to remember all newly created CLDs,
3054 // so that we can guarantee that the remark finds them.
3055 ClassLoaderDataGraph::remember_new_clds(true);
3056
3057 // Whenever a CLD is found, it will be claimed before proceeding to mark
3058 // the klasses. The claimed marks need to be cleared before marking starts.
3059 ClassLoaderDataGraph::clear_claimed_marks();
3060
3061 if (CMSPrintEdenSurvivorChunks) {
3062 print_eden_and_survivor_chunk_arrays();
3063 }
3064
3065 {
3066 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3067 if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3068 // The parallel version.
3069 FlexibleWorkGang* workers = gch->workers();
3070 assert(workers != NULL, "Need parallel worker threads.");
3071 int n_workers = workers->active_workers();
3072 CMSParInitialMarkTask tsk(this, n_workers);
3073 gch->set_par_threads(n_workers);
3074 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3075 if (n_workers > 1) {
3076 GenCollectedHeap::StrongRootsScope srs(gch);
3077 workers->run_task(&tsk);
3078 } else {
3079 GenCollectedHeap::StrongRootsScope srs(gch);
3080 tsk.work(0);
3081 }
3082 gch->set_par_threads(0);
3083 } else {
3084 // The serial version.
3085 CLDToOopClosure cld_closure(¬Older, true);
3086 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3087 gch->gen_process_roots(_cmsGen->level(),
3088 true, // younger gens are roots
3089 true, // activate StrongRootsScope
3090 SharedHeap::ScanningOption(roots_scanning_options()),
3091 should_unload_classes(),
3092 ¬Older,
3093 NULL,
3094 &cld_closure);
3095 }
3096 }
3097
3098 // Clear mod-union table; it will be dirtied in the prologue of
3099 // CMS generation per each younger generation collection.
3100
3101 assert(_modUnionTable.isAllClear(),
3102 "Was cleared in most recent final checkpoint phase"
3103 " or no bits are set in the gc_prologue before the start of the next "
3104 "subsequent marking phase.");
3105
3106 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3107
3108 // Save the end of the used_region of the constituent generations
3109 // to be used to limit the extent of sweep in each generation.
3110 save_sweep_limits();
3111 verify_overflow_empty();
3112 }
3113
3114 bool CMSCollector::markFromRoots() {
3115 // we might be tempted to assert that:
3116 // assert(!SafepointSynchronize::is_at_safepoint(),
3117 // "inconsistent argument?");
3118 // However that wouldn't be right, because it's possible that
3119 // a safepoint is indeed in progress as a younger generation
3120 // stop-the-world GC happens even as we mark in this generation.
3121 assert(_collectorState == Marking, "inconsistent state?");
3122 check_correct_thread_executing();
3123 verify_overflow_empty();
3124
3125 // Weak ref discovery note: We may be discovering weak
3126 // refs in this generation concurrent (but interleaved) with
3127 // weak ref discovery by a younger generation collector.
3128
3129 CMSTokenSyncWithLocks ts(true, bitMapLock());
3130 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3131 CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3132 bool res = markFromRootsWork();
3133 if (res) {
3134 _collectorState = Precleaning;
3135 } else { // We failed and a foreground collection wants to take over
3136 assert(_foregroundGCIsActive, "internal state inconsistency");
3137 assert(_restart_addr == NULL, "foreground will restart from scratch");
3138 if (PrintGCDetails) {
3139 gclog_or_tty->print_cr("bailing out to foreground collection");
3140 }
3141 }
3142 verify_overflow_empty();
3143 return res;
3144 }
3145
3146 bool CMSCollector::markFromRootsWork() {
3147 // iterate over marked bits in bit map, doing a full scan and mark
3148 // from these roots using the following algorithm:
3149 // . if oop is to the right of the current scan pointer,
3150 // mark corresponding bit (we'll process it later)
3151 // . else (oop is to left of current scan pointer)
3152 // push oop on marking stack
3153 // . drain the marking stack
3154
3155 // Note that when we do a marking step we need to hold the
3156 // bit map lock -- recall that direct allocation (by mutators)
3157 // and promotion (by younger generation collectors) is also
3158 // marking the bit map. [the so-called allocate live policy.]
3159 // Because the implementation of bit map marking is not
3160 // robust wrt simultaneous marking of bits in the same word,
3161 // we need to make sure that there is no such interference
3162 // between concurrent such updates.
3163
3164 // already have locks
3165 assert_lock_strong(bitMapLock());
3166
3167 verify_work_stacks_empty();
3168 verify_overflow_empty();
3169 bool result = false;
3170 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3171 result = do_marking_mt();
3172 } else {
3173 result = do_marking_st();
3174 }
3175 return result;
3176 }
3177
3178 // Forward decl
3179 class CMSConcMarkingTask;
3180
3181 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3182 CMSCollector* _collector;
3183 CMSConcMarkingTask* _task;
3184 public:
3185 virtual void yield();
3186
3187 // "n_threads" is the number of threads to be terminated.
3188 // "queue_set" is a set of work queues of other threads.
3189 // "collector" is the CMS collector associated with this task terminator.
3190 // "yield" indicates whether we need the gang as a whole to yield.
3191 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3192 ParallelTaskTerminator(n_threads, queue_set),
3193 _collector(collector) { }
3194
3195 void set_task(CMSConcMarkingTask* task) {
3196 _task = task;
3197 }
3198 };
3199
3200 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3201 CMSConcMarkingTask* _task;
3202 public:
3203 bool should_exit_termination();
3204 void set_task(CMSConcMarkingTask* task) {
3205 _task = task;
3206 }
3207 };
3208
3209 // MT Concurrent Marking Task
3210 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3211 CMSCollector* _collector;
3212 int _n_workers; // requested/desired # workers
3213 bool _result;
3214 CompactibleFreeListSpace* _cms_space;
3215 char _pad_front[64]; // padding to ...
3216 HeapWord* _global_finger; // ... avoid sharing cache line
3217 char _pad_back[64];
3218 HeapWord* _restart_addr;
3219
3220 // Exposed here for yielding support
3221 Mutex* const _bit_map_lock;
3222
3223 // The per thread work queues, available here for stealing
3224 OopTaskQueueSet* _task_queues;
3225
3226 // Termination (and yielding) support
3227 CMSConcMarkingTerminator _term;
3228 CMSConcMarkingTerminatorTerminator _term_term;
3229
3230 public:
3231 CMSConcMarkingTask(CMSCollector* collector,
3232 CompactibleFreeListSpace* cms_space,
3233 YieldingFlexibleWorkGang* workers,
3234 OopTaskQueueSet* task_queues):
3235 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3236 _collector(collector),
3237 _cms_space(cms_space),
3238 _n_workers(0), _result(true),
3239 _task_queues(task_queues),
3240 _term(_n_workers, task_queues, _collector),
3241 _bit_map_lock(collector->bitMapLock())
3242 {
3243 _requested_size = _n_workers;
3244 _term.set_task(this);
3245 _term_term.set_task(this);
3246 _restart_addr = _global_finger = _cms_space->bottom();
3247 }
3248
3249
3250 OopTaskQueueSet* task_queues() { return _task_queues; }
3251
3252 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3253
3254 HeapWord** global_finger_addr() { return &_global_finger; }
3255
3256 CMSConcMarkingTerminator* terminator() { return &_term; }
3257
3258 virtual void set_for_termination(int active_workers) {
3259 terminator()->reset_for_reuse(active_workers);
3260 }
3261
3262 void work(uint worker_id);
3263 bool should_yield() {
3264 return ConcurrentMarkSweepThread::should_yield()
3265 && !_collector->foregroundGCIsActive();
3266 }
3267
3268 virtual void coordinator_yield(); // stuff done by coordinator
3269 bool result() { return _result; }
3270
3271 void reset(HeapWord* ra) {
3272 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3273 _restart_addr = _global_finger = ra;
3274 _term.reset_for_reuse();
3275 }
3276
3277 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3278 OopTaskQueue* work_q);
3279
3280 private:
3281 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3282 void do_work_steal(int i);
3283 void bump_global_finger(HeapWord* f);
3284 };
3285
3286 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3287 assert(_task != NULL, "Error");
3288 return _task->yielding();
3289 // Note that we do not need the disjunct || _task->should_yield() above
3290 // because we want terminating threads to yield only if the task
3291 // is already in the midst of yielding, which happens only after at least one
3292 // thread has yielded.
3293 }
3294
3295 void CMSConcMarkingTerminator::yield() {
3296 if (_task->should_yield()) {
3297 _task->yield();
3298 } else {
3299 ParallelTaskTerminator::yield();
3300 }
3301 }
3302
3303 ////////////////////////////////////////////////////////////////
3304 // Concurrent Marking Algorithm Sketch
3305 ////////////////////////////////////////////////////////////////
3306 // Until all tasks exhausted (both spaces):
3307 // -- claim next available chunk
3308 // -- bump global finger via CAS
3309 // -- find first object that starts in this chunk
3310 // and start scanning bitmap from that position
3311 // -- scan marked objects for oops
3312 // -- CAS-mark target, and if successful:
3313 // . if target oop is above global finger (volatile read)
3314 // nothing to do
3315 // . if target oop is in chunk and above local finger
3316 // then nothing to do
3317 // . else push on work-queue
3318 // -- Deal with possible overflow issues:
3319 // . local work-queue overflow causes stuff to be pushed on
3320 // global (common) overflow queue
3321 // . always first empty local work queue
3322 // . then get a batch of oops from global work queue if any
3323 // . then do work stealing
3324 // -- When all tasks claimed (both spaces)
3325 // and local work queue empty,
3326 // then in a loop do:
3327 // . check global overflow stack; steal a batch of oops and trace
3328 // . try to steal from other threads oif GOS is empty
3329 // . if neither is available, offer termination
3330 // -- Terminate and return result
3331 //
3332 void CMSConcMarkingTask::work(uint worker_id) {
3333 elapsedTimer _timer;
3334 ResourceMark rm;
3335 HandleMark hm;
3336
3337 DEBUG_ONLY(_collector->verify_overflow_empty();)
3338
3339 // Before we begin work, our work queue should be empty
3340 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3341 // Scan the bitmap covering _cms_space, tracing through grey objects.
3342 _timer.start();
3343 do_scan_and_mark(worker_id, _cms_space);
3344 _timer.stop();
3345 if (PrintCMSStatistics != 0) {
3346 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3347 worker_id, _timer.seconds());
3348 // XXX: need xxx/xxx type of notation, two timers
3349 }
3350
3351 // ... do work stealing
3352 _timer.reset();
3353 _timer.start();
3354 do_work_steal(worker_id);
3355 _timer.stop();
3356 if (PrintCMSStatistics != 0) {
3357 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3358 worker_id, _timer.seconds());
3359 // XXX: need xxx/xxx type of notation, two timers
3360 }
3361 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3362 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3363 // Note that under the current task protocol, the
3364 // following assertion is true even of the spaces
3365 // expanded since the completion of the concurrent
3366 // marking. XXX This will likely change under a strict
3367 // ABORT semantics.
3368 // After perm removal the comparison was changed to
3369 // greater than or equal to from strictly greater than.
3370 // Before perm removal the highest address sweep would
3371 // have been at the end of perm gen but now is at the
3372 // end of the tenured gen.
3373 assert(_global_finger >= _cms_space->end(),
3374 "All tasks have been completed");
3375 DEBUG_ONLY(_collector->verify_overflow_empty();)
3376 }
3377
3378 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3379 HeapWord* read = _global_finger;
3380 HeapWord* cur = read;
3381 while (f > read) {
3382 cur = read;
3383 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3384 if (cur == read) {
3385 // our cas succeeded
3386 assert(_global_finger >= f, "protocol consistency");
3387 break;
3388 }
3389 }
3390 }
3391
3392 // This is really inefficient, and should be redone by
3393 // using (not yet available) block-read and -write interfaces to the
3394 // stack and the work_queue. XXX FIX ME !!!
3395 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3396 OopTaskQueue* work_q) {
3397 // Fast lock-free check
3398 if (ovflw_stk->length() == 0) {
3399 return false;
3400 }
3401 assert(work_q->size() == 0, "Shouldn't steal");
3402 MutexLockerEx ml(ovflw_stk->par_lock(),
3403 Mutex::_no_safepoint_check_flag);
3404 // Grab up to 1/4 the size of the work queue
3405 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3406 (size_t)ParGCDesiredObjsFromOverflowList);
3407 num = MIN2(num, ovflw_stk->length());
3408 for (int i = (int) num; i > 0; i--) {
3409 oop cur = ovflw_stk->pop();
3410 assert(cur != NULL, "Counted wrong?");
3411 work_q->push(cur);
3412 }
3413 return num > 0;
3414 }
3415
3416 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3417 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3418 int n_tasks = pst->n_tasks();
3419 // We allow that there may be no tasks to do here because
3420 // we are restarting after a stack overflow.
3421 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3422 uint nth_task = 0;
3423
3424 HeapWord* aligned_start = sp->bottom();
3425 if (sp->used_region().contains(_restart_addr)) {
3426 // Align down to a card boundary for the start of 0th task
3427 // for this space.
3428 aligned_start =
3429 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3430 CardTableModRefBS::card_size);
3431 }
3432
3433 size_t chunk_size = sp->marking_task_size();
3434 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3435 // Having claimed the nth task in this space,
3436 // compute the chunk that it corresponds to:
3437 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3438 aligned_start + (nth_task+1)*chunk_size);
3439 // Try and bump the global finger via a CAS;
3440 // note that we need to do the global finger bump
3441 // _before_ taking the intersection below, because
3442 // the task corresponding to that region will be
3443 // deemed done even if the used_region() expands
3444 // because of allocation -- as it almost certainly will
3445 // during start-up while the threads yield in the
3446 // closure below.
3447 HeapWord* finger = span.end();
3448 bump_global_finger(finger); // atomically
3449 // There are null tasks here corresponding to chunks
3450 // beyond the "top" address of the space.
3451 span = span.intersection(sp->used_region());
3452 if (!span.is_empty()) { // Non-null task
3453 HeapWord* prev_obj;
3454 assert(!span.contains(_restart_addr) || nth_task == 0,
3455 "Inconsistency");
3456 if (nth_task == 0) {
3457 // For the 0th task, we'll not need to compute a block_start.
3458 if (span.contains(_restart_addr)) {
3459 // In the case of a restart because of stack overflow,
3460 // we might additionally skip a chunk prefix.
3461 prev_obj = _restart_addr;
3462 } else {
3463 prev_obj = span.start();
3464 }
3465 } else {
3466 // We want to skip the first object because
3467 // the protocol is to scan any object in its entirety
3468 // that _starts_ in this span; a fortiori, any
3469 // object starting in an earlier span is scanned
3470 // as part of an earlier claimed task.
3471 // Below we use the "careful" version of block_start
3472 // so we do not try to navigate uninitialized objects.
3473 prev_obj = sp->block_start_careful(span.start());
3474 // Below we use a variant of block_size that uses the
3475 // Printezis bits to avoid waiting for allocated
3476 // objects to become initialized/parsable.
3477 while (prev_obj < span.start()) {
3478 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3479 if (sz > 0) {
3480 prev_obj += sz;
3481 } else {
3482 // In this case we may end up doing a bit of redundant
3483 // scanning, but that appears unavoidable, short of
3484 // locking the free list locks; see bug 6324141.
3485 break;
3486 }
3487 }
3488 }
3489 if (prev_obj < span.end()) {
3490 MemRegion my_span = MemRegion(prev_obj, span.end());
3491 // Do the marking work within a non-empty span --
3492 // the last argument to the constructor indicates whether the
3493 // iteration should be incremental with periodic yields.
3494 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3495 &_collector->_markBitMap,
3496 work_queue(i),
3497 &_collector->_markStack);
3498 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3499 } // else nothing to do for this task
3500 } // else nothing to do for this task
3501 }
3502 // We'd be tempted to assert here that since there are no
3503 // more tasks left to claim in this space, the global_finger
3504 // must exceed space->top() and a fortiori space->end(). However,
3505 // that would not quite be correct because the bumping of
3506 // global_finger occurs strictly after the claiming of a task,
3507 // so by the time we reach here the global finger may not yet
3508 // have been bumped up by the thread that claimed the last
3509 // task.
3510 pst->all_tasks_completed();
3511 }
3512
3513 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3514 private:
3515 CMSCollector* _collector;
3516 CMSConcMarkingTask* _task;
3517 MemRegion _span;
3518 CMSBitMap* _bit_map;
3519 CMSMarkStack* _overflow_stack;
3520 OopTaskQueue* _work_queue;
3521 protected:
3522 DO_OOP_WORK_DEFN
3523 public:
3524 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3525 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3526 MetadataAwareOopClosure(collector->ref_processor()),
3527 _collector(collector),
3528 _task(task),
3529 _span(collector->_span),
3530 _work_queue(work_queue),
3531 _bit_map(bit_map),
3532 _overflow_stack(overflow_stack)
3533 { }
3534 virtual void do_oop(oop* p);
3535 virtual void do_oop(narrowOop* p);
3536
3537 void trim_queue(size_t max);
3538 void handle_stack_overflow(HeapWord* lost);
3539 void do_yield_check() {
3540 if (_task->should_yield()) {
3541 _task->yield();
3542 }
3543 }
3544 };
3545
3546 // Grey object scanning during work stealing phase --
3547 // the salient assumption here is that any references
3548 // that are in these stolen objects being scanned must
3549 // already have been initialized (else they would not have
3550 // been published), so we do not need to check for
3551 // uninitialized objects before pushing here.
3552 void Par_ConcMarkingClosure::do_oop(oop obj) {
3553 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
3554 HeapWord* addr = (HeapWord*)obj;
3555 // Check if oop points into the CMS generation
3556 // and is not marked
3557 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3558 // a white object ...
3559 // If we manage to "claim" the object, by being the
3560 // first thread to mark it, then we push it on our
3561 // marking stack
3562 if (_bit_map->par_mark(addr)) { // ... now grey
3563 // push on work queue (grey set)
3564 bool simulate_overflow = false;
3565 NOT_PRODUCT(
3566 if (CMSMarkStackOverflowALot &&
3567 _collector->simulate_overflow()) {
3568 // simulate a stack overflow
3569 simulate_overflow = true;
3570 }
3571 )
3572 if (simulate_overflow ||
3573 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3574 // stack overflow
3575 if (PrintCMSStatistics != 0) {
3576 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3577 SIZE_FORMAT, _overflow_stack->capacity());
3578 }
3579 // We cannot assert that the overflow stack is full because
3580 // it may have been emptied since.
3581 assert(simulate_overflow ||
3582 _work_queue->size() == _work_queue->max_elems(),
3583 "Else push should have succeeded");
3584 handle_stack_overflow(addr);
3585 }
3586 } // Else, some other thread got there first
3587 do_yield_check();
3588 }
3589 }
3590
3591 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3592 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3593
3594 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3595 while (_work_queue->size() > max) {
3596 oop new_oop;
3597 if (_work_queue->pop_local(new_oop)) {
3598 assert(new_oop->is_oop(), "Should be an oop");
3599 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3600 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3601 new_oop->oop_iterate(this); // do_oop() above
3602 do_yield_check();
3603 }
3604 }
3605 }
3606
3607 // Upon stack overflow, we discard (part of) the stack,
3608 // remembering the least address amongst those discarded
3609 // in CMSCollector's _restart_address.
3610 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3611 // We need to do this under a mutex to prevent other
3612 // workers from interfering with the work done below.
3613 MutexLockerEx ml(_overflow_stack->par_lock(),
3614 Mutex::_no_safepoint_check_flag);
3615 // Remember the least grey address discarded
3616 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3617 _collector->lower_restart_addr(ra);
3618 _overflow_stack->reset(); // discard stack contents
3619 _overflow_stack->expand(); // expand the stack if possible
3620 }
3621
3622
3623 void CMSConcMarkingTask::do_work_steal(int i) {
3624 OopTaskQueue* work_q = work_queue(i);
3625 oop obj_to_scan;
3626 CMSBitMap* bm = &(_collector->_markBitMap);
3627 CMSMarkStack* ovflw = &(_collector->_markStack);
3628 int* seed = _collector->hash_seed(i);
3629 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3630 while (true) {
3631 cl.trim_queue(0);
3632 assert(work_q->size() == 0, "Should have been emptied above");
3633 if (get_work_from_overflow_stack(ovflw, work_q)) {
3634 // Can't assert below because the work obtained from the
3635 // overflow stack may already have been stolen from us.
3636 // assert(work_q->size() > 0, "Work from overflow stack");
3637 continue;
3638 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3639 assert(obj_to_scan->is_oop(), "Should be an oop");
3640 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3641 obj_to_scan->oop_iterate(&cl);
3642 } else if (terminator()->offer_termination(&_term_term)) {
3643 assert(work_q->size() == 0, "Impossible!");
3644 break;
3645 } else if (yielding() || should_yield()) {
3646 yield();
3647 }
3648 }
3649 }
3650
3651 // This is run by the CMS (coordinator) thread.
3652 void CMSConcMarkingTask::coordinator_yield() {
3653 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3654 "CMS thread should hold CMS token");
3655 // First give up the locks, then yield, then re-lock
3656 // We should probably use a constructor/destructor idiom to
3657 // do this unlock/lock or modify the MutexUnlocker class to
3658 // serve our purpose. XXX
3659 assert_lock_strong(_bit_map_lock);
3660 _bit_map_lock->unlock();
3661 ConcurrentMarkSweepThread::desynchronize(true);
3662 _collector->stopTimer();
3663 if (PrintCMSStatistics != 0) {
3664 _collector->incrementYields();
3665 }
3666
3667 // It is possible for whichever thread initiated the yield request
3668 // not to get a chance to wake up and take the bitmap lock between
3669 // this thread releasing it and reacquiring it. So, while the
3670 // should_yield() flag is on, let's sleep for a bit to give the
3671 // other thread a chance to wake up. The limit imposed on the number
3672 // of iterations is defensive, to avoid any unforseen circumstances
3673 // putting us into an infinite loop. Since it's always been this
3674 // (coordinator_yield()) method that was observed to cause the
3675 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3676 // which is by default non-zero. For the other seven methods that
3677 // also perform the yield operation, as are using a different
3678 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3679 // can enable the sleeping for those methods too, if necessary.
3680 // See 6442774.
3681 //
3682 // We really need to reconsider the synchronization between the GC
3683 // thread and the yield-requesting threads in the future and we
3684 // should really use wait/notify, which is the recommended
3685 // way of doing this type of interaction. Additionally, we should
3686 // consolidate the eight methods that do the yield operation and they
3687 // are almost identical into one for better maintainability and
3688 // readability. See 6445193.
3689 //
3690 // Tony 2006.06.29
3691 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3692 ConcurrentMarkSweepThread::should_yield() &&
3693 !CMSCollector::foregroundGCIsActive(); ++i) {
3694 os::sleep(Thread::current(), 1, false);
3695 }
3696
3697 ConcurrentMarkSweepThread::synchronize(true);
3698 _bit_map_lock->lock_without_safepoint_check();
3699 _collector->startTimer();
3700 }
3701
3702 bool CMSCollector::do_marking_mt() {
3703 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3704 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
3705 conc_workers()->total_workers(),
3706 conc_workers()->active_workers(),
3707 Threads::number_of_non_daemon_threads());
3708 conc_workers()->set_active_workers(num_workers);
3709
3710 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3711
3712 CMSConcMarkingTask tsk(this,
3713 cms_space,
3714 conc_workers(),
3715 task_queues());
3716
3717 // Since the actual number of workers we get may be different
3718 // from the number we requested above, do we need to do anything different
3719 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3720 // class?? XXX
3721 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3722
3723 // Refs discovery is already non-atomic.
3724 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3725 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3726 conc_workers()->start_task(&tsk);
3727 while (tsk.yielded()) {
3728 tsk.coordinator_yield();
3729 conc_workers()->continue_task(&tsk);
3730 }
3731 // If the task was aborted, _restart_addr will be non-NULL
3732 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3733 while (_restart_addr != NULL) {
3734 // XXX For now we do not make use of ABORTED state and have not
3735 // yet implemented the right abort semantics (even in the original
3736 // single-threaded CMS case). That needs some more investigation
3737 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3738 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3739 // If _restart_addr is non-NULL, a marking stack overflow
3740 // occurred; we need to do a fresh marking iteration from the
3741 // indicated restart address.
3742 if (_foregroundGCIsActive) {
3743 // We may be running into repeated stack overflows, having
3744 // reached the limit of the stack size, while making very
3745 // slow forward progress. It may be best to bail out and
3746 // let the foreground collector do its job.
3747 // Clear _restart_addr, so that foreground GC
3748 // works from scratch. This avoids the headache of
3749 // a "rescan" which would otherwise be needed because
3750 // of the dirty mod union table & card table.
3751 _restart_addr = NULL;
3752 return false;
3753 }
3754 // Adjust the task to restart from _restart_addr
3755 tsk.reset(_restart_addr);
3756 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3757 _restart_addr);
3758 _restart_addr = NULL;
3759 // Get the workers going again
3760 conc_workers()->start_task(&tsk);
3761 while (tsk.yielded()) {
3762 tsk.coordinator_yield();
3763 conc_workers()->continue_task(&tsk);
3764 }
3765 }
3766 assert(tsk.completed(), "Inconsistency");
3767 assert(tsk.result() == true, "Inconsistency");
3768 return true;
3769 }
3770
3771 bool CMSCollector::do_marking_st() {
3772 ResourceMark rm;
3773 HandleMark hm;
3774
3775 // Temporarily make refs discovery single threaded (non-MT)
3776 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3777 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3778 &_markStack, CMSYield);
3779 // the last argument to iterate indicates whether the iteration
3780 // should be incremental with periodic yields.
3781 _markBitMap.iterate(&markFromRootsClosure);
3782 // If _restart_addr is non-NULL, a marking stack overflow
3783 // occurred; we need to do a fresh iteration from the
3784 // indicated restart address.
3785 while (_restart_addr != NULL) {
3786 if (_foregroundGCIsActive) {
3787 // We may be running into repeated stack overflows, having
3788 // reached the limit of the stack size, while making very
3789 // slow forward progress. It may be best to bail out and
3790 // let the foreground collector do its job.
3791 // Clear _restart_addr, so that foreground GC
3792 // works from scratch. This avoids the headache of
3793 // a "rescan" which would otherwise be needed because
3794 // of the dirty mod union table & card table.
3795 _restart_addr = NULL;
3796 return false; // indicating failure to complete marking
3797 }
3798 // Deal with stack overflow:
3799 // we restart marking from _restart_addr
3800 HeapWord* ra = _restart_addr;
3801 markFromRootsClosure.reset(ra);
3802 _restart_addr = NULL;
3803 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3804 }
3805 return true;
3806 }
3807
3808 void CMSCollector::preclean() {
3809 check_correct_thread_executing();
3810 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3811 verify_work_stacks_empty();
3812 verify_overflow_empty();
3813 _abort_preclean = false;
3814 if (CMSPrecleaningEnabled) {
3815 if (!CMSEdenChunksRecordAlways) {
3816 _eden_chunk_index = 0;
3817 }
3818 size_t used = get_eden_used();
3819 size_t capacity = get_eden_capacity();
3820 // Don't start sampling unless we will get sufficiently
3821 // many samples.
3822 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3823 * CMSScheduleRemarkEdenPenetration)) {
3824 _start_sampling = true;
3825 } else {
3826 _start_sampling = false;
3827 }
3828 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3829 CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3830 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3831 }
3832 CMSTokenSync x(true); // is cms thread
3833 if (CMSPrecleaningEnabled) {
3834 sample_eden();
3835 _collectorState = AbortablePreclean;
3836 } else {
3837 _collectorState = FinalMarking;
3838 }
3839 verify_work_stacks_empty();
3840 verify_overflow_empty();
3841 }
3842
3843 // Try and schedule the remark such that young gen
3844 // occupancy is CMSScheduleRemarkEdenPenetration %.
3845 void CMSCollector::abortable_preclean() {
3846 check_correct_thread_executing();
3847 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3848 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3849
3850 // If Eden's current occupancy is below this threshold,
3851 // immediately schedule the remark; else preclean
3852 // past the next scavenge in an effort to
3853 // schedule the pause as described above. By choosing
3854 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3855 // we will never do an actual abortable preclean cycle.
3856 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3857 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3858 CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3859 // We need more smarts in the abortable preclean
3860 // loop below to deal with cases where allocation
3861 // in young gen is very very slow, and our precleaning
3862 // is running a losing race against a horde of
3863 // mutators intent on flooding us with CMS updates
3864 // (dirty cards).
3865 // One, admittedly dumb, strategy is to give up
3866 // after a certain number of abortable precleaning loops
3867 // or after a certain maximum time. We want to make
3868 // this smarter in the next iteration.
3869 // XXX FIX ME!!! YSR
3870 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3871 while (!(should_abort_preclean() ||
3872 ConcurrentMarkSweepThread::should_terminate())) {
3873 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3874 cumworkdone += workdone;
3875 loops++;
3876 // Voluntarily terminate abortable preclean phase if we have
3877 // been at it for too long.
3878 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3879 loops >= CMSMaxAbortablePrecleanLoops) {
3880 if (PrintGCDetails) {
3881 gclog_or_tty->print(" CMS: abort preclean due to loops ");
3882 }
3883 break;
3884 }
3885 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3886 if (PrintGCDetails) {
3887 gclog_or_tty->print(" CMS: abort preclean due to time ");
3888 }
3889 break;
3890 }
3891 // If we are doing little work each iteration, we should
3892 // take a short break.
3893 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3894 // Sleep for some time, waiting for work to accumulate
3895 stopTimer();
3896 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3897 startTimer();
3898 waited++;
3899 }
3900 }
3901 if (PrintCMSStatistics > 0) {
3902 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3903 loops, waited, cumworkdone);
3904 }
3905 }
3906 CMSTokenSync x(true); // is cms thread
3907 if (_collectorState != Idling) {
3908 assert(_collectorState == AbortablePreclean,
3909 "Spontaneous state transition?");
3910 _collectorState = FinalMarking;
3911 } // Else, a foreground collection completed this CMS cycle.
3912 return;
3913 }
3914
3915 // Respond to an Eden sampling opportunity
3916 void CMSCollector::sample_eden() {
3917 // Make sure a young gc cannot sneak in between our
3918 // reading and recording of a sample.
3919 assert(Thread::current()->is_ConcurrentGC_thread(),
3920 "Only the cms thread may collect Eden samples");
3921 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3922 "Should collect samples while holding CMS token");
3923 if (!_start_sampling) {
3924 return;
3925 }
3926 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3927 // is populated by the young generation.
3928 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3929 if (_eden_chunk_index < _eden_chunk_capacity) {
3930 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3931 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3932 "Unexpected state of Eden");
3933 // We'd like to check that what we just sampled is an oop-start address;
3934 // however, we cannot do that here since the object may not yet have been
3935 // initialized. So we'll instead do the check when we _use_ this sample
3936 // later.
3937 if (_eden_chunk_index == 0 ||
3938 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3939 _eden_chunk_array[_eden_chunk_index-1])
3940 >= CMSSamplingGrain)) {
3941 _eden_chunk_index++; // commit sample
3942 }
3943 }
3944 }
3945 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3946 size_t used = get_eden_used();
3947 size_t capacity = get_eden_capacity();
3948 assert(used <= capacity, "Unexpected state of Eden");
3949 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3950 _abort_preclean = true;
3951 }
3952 }
3953 }
3954
3955
3956 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3957 assert(_collectorState == Precleaning ||
3958 _collectorState == AbortablePreclean, "incorrect state");
3959 ResourceMark rm;
3960 HandleMark hm;
3961
3962 // Precleaning is currently not MT but the reference processor
3963 // may be set for MT. Disable it temporarily here.
3964 ReferenceProcessor* rp = ref_processor();
3965 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3966
3967 // Do one pass of scrubbing the discovered reference lists
3968 // to remove any reference objects with strongly-reachable
3969 // referents.
3970 if (clean_refs) {
3971 CMSPrecleanRefsYieldClosure yield_cl(this);
3972 assert(rp->span().equals(_span), "Spans should be equal");
3973 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3974 &_markStack, true /* preclean */);
3975 CMSDrainMarkingStackClosure complete_trace(this,
3976 _span, &_markBitMap, &_markStack,
3977 &keep_alive, true /* preclean */);
3978
3979 // We don't want this step to interfere with a young
3980 // collection because we don't want to take CPU
3981 // or memory bandwidth away from the young GC threads
3982 // (which may be as many as there are CPUs).
3983 // Note that we don't need to protect ourselves from
3984 // interference with mutators because they can't
3985 // manipulate the discovered reference lists nor affect
3986 // the computed reachability of the referents, the
3987 // only properties manipulated by the precleaning
3988 // of these reference lists.
3989 stopTimer();
3990 CMSTokenSyncWithLocks x(true /* is cms thread */,
3991 bitMapLock());
3992 startTimer();
3993 sample_eden();
3994
3995 // The following will yield to allow foreground
3996 // collection to proceed promptly. XXX YSR:
3997 // The code in this method may need further
3998 // tweaking for better performance and some restructuring
3999 // for cleaner interfaces.
4000 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4001 rp->preclean_discovered_references(
4002 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
4003 gc_timer, _gc_tracer_cm->gc_id());
4004 }
4005
4006 if (clean_survivor) { // preclean the active survivor space(s)
4007 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4008 &_markBitMap, &_modUnionTable,
4009 &_markStack, true /* precleaning phase */);
4010 stopTimer();
4011 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4012 bitMapLock());
4013 startTimer();
4014 unsigned int before_count =
4015 GenCollectedHeap::heap()->total_collections();
4016 SurvivorSpacePrecleanClosure
4017 sss_cl(this, _span, &_markBitMap, &_markStack,
4018 &pam_cl, before_count, CMSYield);
4019 _young_gen->from()->object_iterate_careful(&sss_cl);
4020 _young_gen->to()->object_iterate_careful(&sss_cl);
4021 }
4022 MarkRefsIntoAndScanClosure
4023 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4024 &_markStack, this, CMSYield,
4025 true /* precleaning phase */);
4026 // CAUTION: The following closure has persistent state that may need to
4027 // be reset upon a decrease in the sequence of addresses it
4028 // processes.
4029 ScanMarkedObjectsAgainCarefullyClosure
4030 smoac_cl(this, _span,
4031 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4032
4033 // Preclean dirty cards in ModUnionTable and CardTable using
4034 // appropriate convergence criterion;
4035 // repeat CMSPrecleanIter times unless we find that
4036 // we are losing.
4037 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4038 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4039 "Bad convergence multiplier");
4040 assert(CMSPrecleanThreshold >= 100,
4041 "Unreasonably low CMSPrecleanThreshold");
4042
4043 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4044 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4045 numIter < CMSPrecleanIter;
4046 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4047 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4048 if (Verbose && PrintGCDetails) {
4049 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
4050 }
4051 // Either there are very few dirty cards, so re-mark
4052 // pause will be small anyway, or our pre-cleaning isn't
4053 // that much faster than the rate at which cards are being
4054 // dirtied, so we might as well stop and re-mark since
4055 // precleaning won't improve our re-mark time by much.
4056 if (curNumCards <= CMSPrecleanThreshold ||
4057 (numIter > 0 &&
4058 (curNumCards * CMSPrecleanDenominator >
4059 lastNumCards * CMSPrecleanNumerator))) {
4060 numIter++;
4061 cumNumCards += curNumCards;
4062 break;
4063 }
4064 }
4065
4066 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4067
4068 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4069 cumNumCards += curNumCards;
4070 if (PrintGCDetails && PrintCMSStatistics != 0) {
4071 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4072 curNumCards, cumNumCards, numIter);
4073 }
4074 return cumNumCards; // as a measure of useful work done
4075 }
4076
4077 // PRECLEANING NOTES:
4078 // Precleaning involves:
4079 // . reading the bits of the modUnionTable and clearing the set bits.
4080 // . For the cards corresponding to the set bits, we scan the
4081 // objects on those cards. This means we need the free_list_lock
4082 // so that we can safely iterate over the CMS space when scanning
4083 // for oops.
4084 // . When we scan the objects, we'll be both reading and setting
4085 // marks in the marking bit map, so we'll need the marking bit map.
4086 // . For protecting _collector_state transitions, we take the CGC_lock.
4087 // Note that any races in the reading of of card table entries by the
4088 // CMS thread on the one hand and the clearing of those entries by the
4089 // VM thread or the setting of those entries by the mutator threads on the
4090 // other are quite benign. However, for efficiency it makes sense to keep
4091 // the VM thread from racing with the CMS thread while the latter is
4092 // dirty card info to the modUnionTable. We therefore also use the
4093 // CGC_lock to protect the reading of the card table and the mod union
4094 // table by the CM thread.
4095 // . We run concurrently with mutator updates, so scanning
4096 // needs to be done carefully -- we should not try to scan
4097 // potentially uninitialized objects.
4098 //
4099 // Locking strategy: While holding the CGC_lock, we scan over and
4100 // reset a maximal dirty range of the mod union / card tables, then lock
4101 // the free_list_lock and bitmap lock to do a full marking, then
4102 // release these locks; and repeat the cycle. This allows for a
4103 // certain amount of fairness in the sharing of these locks between
4104 // the CMS collector on the one hand, and the VM thread and the
4105 // mutators on the other.
4106
4107 // NOTE: preclean_mod_union_table() and preclean_card_table()
4108 // further below are largely identical; if you need to modify
4109 // one of these methods, please check the other method too.
4110
4111 size_t CMSCollector::preclean_mod_union_table(
4112 ConcurrentMarkSweepGeneration* gen,
4113 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4114 verify_work_stacks_empty();
4115 verify_overflow_empty();
4116
4117 // strategy: starting with the first card, accumulate contiguous
4118 // ranges of dirty cards; clear these cards, then scan the region
4119 // covered by these cards.
4120
4121 // Since all of the MUT is committed ahead, we can just use
4122 // that, in case the generations expand while we are precleaning.
4123 // It might also be fine to just use the committed part of the
4124 // generation, but we might potentially miss cards when the
4125 // generation is rapidly expanding while we are in the midst
4126 // of precleaning.
4127 HeapWord* startAddr = gen->reserved().start();
4128 HeapWord* endAddr = gen->reserved().end();
4129
4130 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4131
4132 size_t numDirtyCards, cumNumDirtyCards;
4133 HeapWord *nextAddr, *lastAddr;
4134 for (cumNumDirtyCards = numDirtyCards = 0,
4135 nextAddr = lastAddr = startAddr;
4136 nextAddr < endAddr;
4137 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4138
4139 ResourceMark rm;
4140 HandleMark hm;
4141
4142 MemRegion dirtyRegion;
4143 {
4144 stopTimer();
4145 // Potential yield point
4146 CMSTokenSync ts(true);
4147 startTimer();
4148 sample_eden();
4149 // Get dirty region starting at nextOffset (inclusive),
4150 // simultaneously clearing it.
4151 dirtyRegion =
4152 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4153 assert(dirtyRegion.start() >= nextAddr,
4154 "returned region inconsistent?");
4155 }
4156 // Remember where the next search should begin.
4157 // The returned region (if non-empty) is a right open interval,
4158 // so lastOffset is obtained from the right end of that
4159 // interval.
4160 lastAddr = dirtyRegion.end();
4161 // Should do something more transparent and less hacky XXX
4162 numDirtyCards =
4163 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4164
4165 // We'll scan the cards in the dirty region (with periodic
4166 // yields for foreground GC as needed).
4167 if (!dirtyRegion.is_empty()) {
4168 assert(numDirtyCards > 0, "consistency check");
4169 HeapWord* stop_point = NULL;
4170 stopTimer();
4171 // Potential yield point
4172 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4173 bitMapLock());
4174 startTimer();
4175 {
4176 verify_work_stacks_empty();
4177 verify_overflow_empty();
4178 sample_eden();
4179 stop_point =
4180 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4181 }
4182 if (stop_point != NULL) {
4183 // The careful iteration stopped early either because it found an
4184 // uninitialized object, or because we were in the midst of an
4185 // "abortable preclean", which should now be aborted. Redirty
4186 // the bits corresponding to the partially-scanned or unscanned
4187 // cards. We'll either restart at the next block boundary or
4188 // abort the preclean.
4189 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4190 "Should only be AbortablePreclean.");
4191 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4192 if (should_abort_preclean()) {
4193 break; // out of preclean loop
4194 } else {
4195 // Compute the next address at which preclean should pick up;
4196 // might need bitMapLock in order to read P-bits.
4197 lastAddr = next_card_start_after_block(stop_point);
4198 }
4199 }
4200 } else {
4201 assert(lastAddr == endAddr, "consistency check");
4202 assert(numDirtyCards == 0, "consistency check");
4203 break;
4204 }
4205 }
4206 verify_work_stacks_empty();
4207 verify_overflow_empty();
4208 return cumNumDirtyCards;
4209 }
4210
4211 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4212 // below are largely identical; if you need to modify
4213 // one of these methods, please check the other method too.
4214
4215 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4216 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4217 // strategy: it's similar to precleamModUnionTable above, in that
4218 // we accumulate contiguous ranges of dirty cards, mark these cards
4219 // precleaned, then scan the region covered by these cards.
4220 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4221 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4222
4223 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4224
4225 size_t numDirtyCards, cumNumDirtyCards;
4226 HeapWord *lastAddr, *nextAddr;
4227
4228 for (cumNumDirtyCards = numDirtyCards = 0,
4229 nextAddr = lastAddr = startAddr;
4230 nextAddr < endAddr;
4231 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4232
4233 ResourceMark rm;
4234 HandleMark hm;
4235
4236 MemRegion dirtyRegion;
4237 {
4238 // See comments in "Precleaning notes" above on why we
4239 // do this locking. XXX Could the locking overheads be
4240 // too high when dirty cards are sparse? [I don't think so.]
4241 stopTimer();
4242 CMSTokenSync x(true); // is cms thread
4243 startTimer();
4244 sample_eden();
4245 // Get and clear dirty region from card table
4246 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4247 MemRegion(nextAddr, endAddr),
4248 true,
4249 CardTableModRefBS::precleaned_card_val());
4250
4251 assert(dirtyRegion.start() >= nextAddr,
4252 "returned region inconsistent?");
4253 }
4254 lastAddr = dirtyRegion.end();
4255 numDirtyCards =
4256 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4257
4258 if (!dirtyRegion.is_empty()) {
4259 stopTimer();
4260 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4261 startTimer();
4262 sample_eden();
4263 verify_work_stacks_empty();
4264 verify_overflow_empty();
4265 HeapWord* stop_point =
4266 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4267 if (stop_point != NULL) {
4268 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4269 "Should only be AbortablePreclean.");
4270 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4271 if (should_abort_preclean()) {
4272 break; // out of preclean loop
4273 } else {
4274 // Compute the next address at which preclean should pick up.
4275 lastAddr = next_card_start_after_block(stop_point);
4276 }
4277 }
4278 } else {
4279 break;
4280 }
4281 }
4282 verify_work_stacks_empty();
4283 verify_overflow_empty();
4284 return cumNumDirtyCards;
4285 }
4286
4287 class PrecleanKlassClosure : public KlassClosure {
4288 KlassToOopClosure _cm_klass_closure;
4289 public:
4290 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4291 void do_klass(Klass* k) {
4292 if (k->has_accumulated_modified_oops()) {
4293 k->clear_accumulated_modified_oops();
4294
4295 _cm_klass_closure.do_klass(k);
4296 }
4297 }
4298 };
4299
4300 // The freelist lock is needed to prevent asserts, is it really needed?
4301 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4302
4303 cl->set_freelistLock(freelistLock);
4304
4305 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4306
4307 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4308 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4309 PrecleanKlassClosure preclean_klass_closure(cl);
4310 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4311
4312 verify_work_stacks_empty();
4313 verify_overflow_empty();
4314 }
4315
4316 void CMSCollector::checkpointRootsFinal() {
4317 assert(_collectorState == FinalMarking, "incorrect state transition?");
4318 check_correct_thread_executing();
4319 // world is stopped at this checkpoint
4320 assert(SafepointSynchronize::is_at_safepoint(),
4321 "world should be stopped");
4322 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4323
4324 verify_work_stacks_empty();
4325 verify_overflow_empty();
4326
4327 if (PrintGCDetails) {
4328 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4329 _young_gen->used() / K,
4330 _young_gen->capacity() / K);
4331 }
4332 {
4333 if (CMSScavengeBeforeRemark) {
4334 GenCollectedHeap* gch = GenCollectedHeap::heap();
4335 // Temporarily set flag to false, GCH->do_collection will
4336 // expect it to be false and set to true
4337 FlagSetting fl(gch->_is_gc_active, false);
4338 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4339 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4340 int level = _cmsGen->level() - 1;
4341 if (level >= 0) {
4342 gch->do_collection(true, // full (i.e. force, see below)
4343 false, // !clear_all_soft_refs
4344 0, // size
4345 false, // is_tlab
4346 level // max_level
4347 );
4348 }
4349 }
4350 FreelistLocker x(this);
4351 MutexLockerEx y(bitMapLock(),
4352 Mutex::_no_safepoint_check_flag);
4353 checkpointRootsFinalWork();
4354 }
4355 verify_work_stacks_empty();
4356 verify_overflow_empty();
4357 }
4358
4359 void CMSCollector::checkpointRootsFinalWork() {
4360 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4361
4362 assert(haveFreelistLocks(), "must have free list locks");
4363 assert_lock_strong(bitMapLock());
4364
4365 ResourceMark rm;
4366 HandleMark hm;
4367
4368 GenCollectedHeap* gch = GenCollectedHeap::heap();
4369
4370 if (should_unload_classes()) {
4371 CodeCache::gc_prologue();
4372 }
4373 assert(haveFreelistLocks(), "must have free list locks");
4374 assert_lock_strong(bitMapLock());
4375
4376 // We might assume that we need not fill TLAB's when
4377 // CMSScavengeBeforeRemark is set, because we may have just done
4378 // a scavenge which would have filled all TLAB's -- and besides
4379 // Eden would be empty. This however may not always be the case --
4380 // for instance although we asked for a scavenge, it may not have
4381 // happened because of a JNI critical section. We probably need
4382 // a policy for deciding whether we can in that case wait until
4383 // the critical section releases and then do the remark following
4384 // the scavenge, and skip it here. In the absence of that policy,
4385 // or of an indication of whether the scavenge did indeed occur,
4386 // we cannot rely on TLAB's having been filled and must do
4387 // so here just in case a scavenge did not happen.
4388 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4389 // Update the saved marks which may affect the root scans.
4390 gch->save_marks();
4391
4392 if (CMSPrintEdenSurvivorChunks) {
4393 print_eden_and_survivor_chunk_arrays();
4394 }
4395
4396 {
4397 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4398
4399 // Note on the role of the mod union table:
4400 // Since the marker in "markFromRoots" marks concurrently with
4401 // mutators, it is possible for some reachable objects not to have been
4402 // scanned. For instance, an only reference to an object A was
4403 // placed in object B after the marker scanned B. Unless B is rescanned,
4404 // A would be collected. Such updates to references in marked objects
4405 // are detected via the mod union table which is the set of all cards
4406 // dirtied since the first checkpoint in this GC cycle and prior to
4407 // the most recent young generation GC, minus those cleaned up by the
4408 // concurrent precleaning.
4409 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
4410 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
4411 do_remark_parallel();
4412 } else {
4413 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4414 _gc_timer_cm, _gc_tracer_cm->gc_id());
4415 do_remark_non_parallel();
4416 }
4417 }
4418 verify_work_stacks_empty();
4419 verify_overflow_empty();
4420
4421 {
4422 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4423 refProcessingWork();
4424 }
4425 verify_work_stacks_empty();
4426 verify_overflow_empty();
4427
4428 if (should_unload_classes()) {
4429 CodeCache::gc_epilogue();
4430 }
4431 JvmtiExport::gc_epilogue();
4432
4433 // If we encountered any (marking stack / work queue) overflow
4434 // events during the current CMS cycle, take appropriate
4435 // remedial measures, where possible, so as to try and avoid
4436 // recurrence of that condition.
4437 assert(_markStack.isEmpty(), "No grey objects");
4438 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4439 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4440 if (ser_ovflw > 0) {
4441 if (PrintCMSStatistics != 0) {
4442 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4443 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4444 ", kac_preclean="SIZE_FORMAT")",
4445 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4446 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4447 }
4448 _markStack.expand();
4449 _ser_pmc_remark_ovflw = 0;
4450 _ser_pmc_preclean_ovflw = 0;
4451 _ser_kac_preclean_ovflw = 0;
4452 _ser_kac_ovflw = 0;
4453 }
4454 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4455 if (PrintCMSStatistics != 0) {
4456 gclog_or_tty->print_cr("Work queue overflow (benign) "
4457 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4458 _par_pmc_remark_ovflw, _par_kac_ovflw);
4459 }
4460 _par_pmc_remark_ovflw = 0;
4461 _par_kac_ovflw = 0;
4462 }
4463 if (PrintCMSStatistics != 0) {
4464 if (_markStack._hit_limit > 0) {
4465 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4466 _markStack._hit_limit);
4467 }
4468 if (_markStack._failed_double > 0) {
4469 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4470 " current capacity "SIZE_FORMAT,
4471 _markStack._failed_double,
4472 _markStack.capacity());
4473 }
4474 }
4475 _markStack._hit_limit = 0;
4476 _markStack._failed_double = 0;
4477
4478 if ((VerifyAfterGC || VerifyDuringGC) &&
4479 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4480 verify_after_remark();
4481 }
4482
4483 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4484
4485 // Change under the freelistLocks.
4486 _collectorState = Sweeping;
4487 // Call isAllClear() under bitMapLock
4488 assert(_modUnionTable.isAllClear(),
4489 "Should be clear by end of the final marking");
4490 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4491 "Should be clear by end of the final marking");
4492 }
4493
4494 void CMSParInitialMarkTask::work(uint worker_id) {
4495 elapsedTimer _timer;
4496 ResourceMark rm;
4497 HandleMark hm;
4498
4499 // ---------- scan from roots --------------
4500 _timer.start();
4501 GenCollectedHeap* gch = GenCollectedHeap::heap();
4502 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4503
4504 // ---------- young gen roots --------------
4505 {
4506 work_on_young_gen_roots(worker_id, &par_mri_cl);
4507 _timer.stop();
4508 if (PrintCMSStatistics != 0) {
4509 gclog_or_tty->print_cr(
4510 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4511 worker_id, _timer.seconds());
4512 }
4513 }
4514
4515 // ---------- remaining roots --------------
4516 _timer.reset();
4517 _timer.start();
4518
4519 CLDToOopClosure cld_closure(&par_mri_cl, true);
4520
4521 gch->gen_process_roots(_collector->_cmsGen->level(),
4522 false, // yg was scanned above
4523 false, // this is parallel code
4524 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4525 _collector->should_unload_classes(),
4526 &par_mri_cl,
4527 NULL,
4528 &cld_closure);
4529 assert(_collector->should_unload_classes()
4530 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
4531 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4532 _timer.stop();
4533 if (PrintCMSStatistics != 0) {
4534 gclog_or_tty->print_cr(
4535 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4536 worker_id, _timer.seconds());
4537 }
4538 }
4539
4540 // Parallel remark task
4541 class CMSParRemarkTask: public CMSParMarkTask {
4542 CompactibleFreeListSpace* _cms_space;
4543
4544 // The per-thread work queues, available here for stealing.
4545 OopTaskQueueSet* _task_queues;
4546 ParallelTaskTerminator _term;
4547
4548 public:
4549 // A value of 0 passed to n_workers will cause the number of
4550 // workers to be taken from the active workers in the work gang.
4551 CMSParRemarkTask(CMSCollector* collector,
4552 CompactibleFreeListSpace* cms_space,
4553 int n_workers, FlexibleWorkGang* workers,
4554 OopTaskQueueSet* task_queues):
4555 CMSParMarkTask("Rescan roots and grey objects in parallel",
4556 collector, n_workers),
4557 _cms_space(cms_space),
4558 _task_queues(task_queues),
4559 _term(n_workers, task_queues) { }
4560
4561 OopTaskQueueSet* task_queues() { return _task_queues; }
4562
4563 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4564
4565 ParallelTaskTerminator* terminator() { return &_term; }
4566 int n_workers() { return _n_workers; }
4567
4568 void work(uint worker_id);
4569
4570 private:
4571 // ... of dirty cards in old space
4572 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4573 Par_MarkRefsIntoAndScanClosure* cl);
4574
4575 // ... work stealing for the above
4576 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4577 };
4578
4579 class RemarkKlassClosure : public KlassClosure {
4580 KlassToOopClosure _cm_klass_closure;
4581 public:
4582 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4583 void do_klass(Klass* k) {
4584 // Check if we have modified any oops in the Klass during the concurrent marking.
4585 if (k->has_accumulated_modified_oops()) {
4586 k->clear_accumulated_modified_oops();
4587
4588 // We could have transfered the current modified marks to the accumulated marks,
4589 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4590 } else if (k->has_modified_oops()) {
4591 // Don't clear anything, this info is needed by the next young collection.
4592 } else {
4593 // No modified oops in the Klass.
4594 return;
4595 }
4596
4597 // The klass has modified fields, need to scan the klass.
4598 _cm_klass_closure.do_klass(k);
4599 }
4600 };
4601
4602 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4603 ParNewGeneration* young_gen = _collector->_young_gen;
4604 ContiguousSpace* eden_space = young_gen->eden();
4605 ContiguousSpace* from_space = young_gen->from();
4606 ContiguousSpace* to_space = young_gen->to();
4607
4608 HeapWord** eca = _collector->_eden_chunk_array;
4609 size_t ect = _collector->_eden_chunk_index;
4610 HeapWord** sca = _collector->_survivor_chunk_array;
4611 size_t sct = _collector->_survivor_chunk_index;
4612
4613 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4614 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4615
4616 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4617 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4618 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4619 }
4620
4621 // work_queue(i) is passed to the closure
4622 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
4623 // also is passed to do_dirty_card_rescan_tasks() and to
4624 // do_work_steal() to select the i-th task_queue.
4625
4626 void CMSParRemarkTask::work(uint worker_id) {
4627 elapsedTimer _timer;
4628 ResourceMark rm;
4629 HandleMark hm;
4630
4631 // ---------- rescan from roots --------------
4632 _timer.start();
4633 GenCollectedHeap* gch = GenCollectedHeap::heap();
4634 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4635 _collector->_span, _collector->ref_processor(),
4636 &(_collector->_markBitMap),
4637 work_queue(worker_id));
4638
4639 // Rescan young gen roots first since these are likely
4640 // coarsely partitioned and may, on that account, constitute
4641 // the critical path; thus, it's best to start off that
4642 // work first.
4643 // ---------- young gen roots --------------
4644 {
4645 work_on_young_gen_roots(worker_id, &par_mrias_cl);
4646 _timer.stop();
4647 if (PrintCMSStatistics != 0) {
4648 gclog_or_tty->print_cr(
4649 "Finished young gen rescan work in %dth thread: %3.3f sec",
4650 worker_id, _timer.seconds());
4651 }
4652 }
4653
4654 // ---------- remaining roots --------------
4655 _timer.reset();
4656 _timer.start();
4657 gch->gen_process_roots(_collector->_cmsGen->level(),
4658 false, // yg was scanned above
4659 false, // this is parallel code
4660 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4661 _collector->should_unload_classes(),
4662 &par_mrias_cl,
4663 NULL,
4664 NULL); // The dirty klasses will be handled below
4665
4666 assert(_collector->should_unload_classes()
4667 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
4668 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4669 _timer.stop();
4670 if (PrintCMSStatistics != 0) {
4671 gclog_or_tty->print_cr(
4672 "Finished remaining root rescan work in %dth thread: %3.3f sec",
4673 worker_id, _timer.seconds());
4674 }
4675
4676 // ---------- unhandled CLD scanning ----------
4677 if (worker_id == 0) { // Single threaded at the moment.
4678 _timer.reset();
4679 _timer.start();
4680
4681 // Scan all new class loader data objects and new dependencies that were
4682 // introduced during concurrent marking.
4683 ResourceMark rm;
4684 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4685 for (int i = 0; i < array->length(); i++) {
4686 par_mrias_cl.do_class_loader_data(array->at(i));
4687 }
4688
4689 // We don't need to keep track of new CLDs anymore.
4690 ClassLoaderDataGraph::remember_new_clds(false);
4691
4692 _timer.stop();
4693 if (PrintCMSStatistics != 0) {
4694 gclog_or_tty->print_cr(
4695 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4696 worker_id, _timer.seconds());
4697 }
4698 }
4699
4700 // ---------- dirty klass scanning ----------
4701 if (worker_id == 0) { // Single threaded at the moment.
4702 _timer.reset();
4703 _timer.start();
4704
4705 // Scan all classes that was dirtied during the concurrent marking phase.
4706 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4707 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4708
4709 _timer.stop();
4710 if (PrintCMSStatistics != 0) {
4711 gclog_or_tty->print_cr(
4712 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4713 worker_id, _timer.seconds());
4714 }
4715 }
4716
4717 // We might have added oops to ClassLoaderData::_handles during the
4718 // concurrent marking phase. These oops point to newly allocated objects
4719 // that are guaranteed to be kept alive. Either by the direct allocation
4720 // code, or when the young collector processes the roots. Hence,
4721 // we don't have to revisit the _handles block during the remark phase.
4722
4723 // ---------- rescan dirty cards ------------
4724 _timer.reset();
4725 _timer.start();
4726
4727 // Do the rescan tasks for each of the two spaces
4728 // (cms_space) in turn.
4729 // "worker_id" is passed to select the task_queue for "worker_id"
4730 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4731 _timer.stop();
4732 if (PrintCMSStatistics != 0) {
4733 gclog_or_tty->print_cr(
4734 "Finished dirty card rescan work in %dth thread: %3.3f sec",
4735 worker_id, _timer.seconds());
4736 }
4737
4738 // ---------- steal work from other threads ...
4739 // ---------- ... and drain overflow list.
4740 _timer.reset();
4741 _timer.start();
4742 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4743 _timer.stop();
4744 if (PrintCMSStatistics != 0) {
4745 gclog_or_tty->print_cr(
4746 "Finished work stealing in %dth thread: %3.3f sec",
4747 worker_id, _timer.seconds());
4748 }
4749 }
4750
4751 // Note that parameter "i" is not used.
4752 void
4753 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4754 OopsInGenClosure* cl, ContiguousSpace* space,
4755 HeapWord** chunk_array, size_t chunk_top) {
4756 // Until all tasks completed:
4757 // . claim an unclaimed task
4758 // . compute region boundaries corresponding to task claimed
4759 // using chunk_array
4760 // . par_oop_iterate(cl) over that region
4761
4762 ResourceMark rm;
4763 HandleMark hm;
4764
4765 SequentialSubTasksDone* pst = space->par_seq_tasks();
4766
4767 uint nth_task = 0;
4768 uint n_tasks = pst->n_tasks();
4769
4770 if (n_tasks > 0) {
4771 assert(pst->valid(), "Uninitialized use?");
4772 HeapWord *start, *end;
4773 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4774 // We claimed task # nth_task; compute its boundaries.
4775 if (chunk_top == 0) { // no samples were taken
4776 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4777 start = space->bottom();
4778 end = space->top();
4779 } else if (nth_task == 0) {
4780 start = space->bottom();
4781 end = chunk_array[nth_task];
4782 } else if (nth_task < (uint)chunk_top) {
4783 assert(nth_task >= 1, "Control point invariant");
4784 start = chunk_array[nth_task - 1];
4785 end = chunk_array[nth_task];
4786 } else {
4787 assert(nth_task == (uint)chunk_top, "Control point invariant");
4788 start = chunk_array[chunk_top - 1];
4789 end = space->top();
4790 }
4791 MemRegion mr(start, end);
4792 // Verify that mr is in space
4793 assert(mr.is_empty() || space->used_region().contains(mr),
4794 "Should be in space");
4795 // Verify that "start" is an object boundary
4796 assert(mr.is_empty() || oop(mr.start())->is_oop(),
4797 "Should be an oop");
4798 space->par_oop_iterate(mr, cl);
4799 }
4800 pst->all_tasks_completed();
4801 }
4802 }
4803
4804 void
4805 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4806 CompactibleFreeListSpace* sp, int i,
4807 Par_MarkRefsIntoAndScanClosure* cl) {
4808 // Until all tasks completed:
4809 // . claim an unclaimed task
4810 // . compute region boundaries corresponding to task claimed
4811 // . transfer dirty bits ct->mut for that region
4812 // . apply rescanclosure to dirty mut bits for that region
4813
4814 ResourceMark rm;
4815 HandleMark hm;
4816
4817 OopTaskQueue* work_q = work_queue(i);
4818 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4819 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4820 // CAUTION: This closure has state that persists across calls to
4821 // the work method dirty_range_iterate_clear() in that it has
4822 // embedded in it a (subtype of) UpwardsObjectClosure. The
4823 // use of that state in the embedded UpwardsObjectClosure instance
4824 // assumes that the cards are always iterated (even if in parallel
4825 // by several threads) in monotonically increasing order per each
4826 // thread. This is true of the implementation below which picks
4827 // card ranges (chunks) in monotonically increasing order globally
4828 // and, a-fortiori, in monotonically increasing order per thread
4829 // (the latter order being a subsequence of the former).
4830 // If the work code below is ever reorganized into a more chaotic
4831 // work-partitioning form than the current "sequential tasks"
4832 // paradigm, the use of that persistent state will have to be
4833 // revisited and modified appropriately. See also related
4834 // bug 4756801 work on which should examine this code to make
4835 // sure that the changes there do not run counter to the
4836 // assumptions made here and necessary for correctness and
4837 // efficiency. Note also that this code might yield inefficient
4838 // behavior in the case of very large objects that span one or
4839 // more work chunks. Such objects would potentially be scanned
4840 // several times redundantly. Work on 4756801 should try and
4841 // address that performance anomaly if at all possible. XXX
4842 MemRegion full_span = _collector->_span;
4843 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4844 MarkFromDirtyCardsClosure
4845 greyRescanClosure(_collector, full_span, // entire span of interest
4846 sp, bm, work_q, cl);
4847
4848 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4849 assert(pst->valid(), "Uninitialized use?");
4850 uint nth_task = 0;
4851 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4852 MemRegion span = sp->used_region();
4853 HeapWord* start_addr = span.start();
4854 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4855 alignment);
4856 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4857 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4858 start_addr, "Check alignment");
4859 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4860 chunk_size, "Check alignment");
4861
4862 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4863 // Having claimed the nth_task, compute corresponding mem-region,
4864 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4865 // The alignment restriction ensures that we do not need any
4866 // synchronization with other gang-workers while setting or
4867 // clearing bits in thus chunk of the MUT.
4868 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4869 start_addr + (nth_task+1)*chunk_size);
4870 // The last chunk's end might be way beyond end of the
4871 // used region. In that case pull back appropriately.
4872 if (this_span.end() > end_addr) {
4873 this_span.set_end(end_addr);
4874 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4875 }
4876 // Iterate over the dirty cards covering this chunk, marking them
4877 // precleaned, and setting the corresponding bits in the mod union
4878 // table. Since we have been careful to partition at Card and MUT-word
4879 // boundaries no synchronization is needed between parallel threads.
4880 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4881 &modUnionClosure);
4882
4883 // Having transferred these marks into the modUnionTable,
4884 // rescan the marked objects on the dirty cards in the modUnionTable.
4885 // Even if this is at a synchronous collection, the initial marking
4886 // may have been done during an asynchronous collection so there
4887 // may be dirty bits in the mod-union table.
4888 _collector->_modUnionTable.dirty_range_iterate_clear(
4889 this_span, &greyRescanClosure);
4890 _collector->_modUnionTable.verifyNoOneBitsInRange(
4891 this_span.start(),
4892 this_span.end());
4893 }
4894 pst->all_tasks_completed(); // declare that i am done
4895 }
4896
4897 // . see if we can share work_queues with ParNew? XXX
4898 void
4899 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4900 int* seed) {
4901 OopTaskQueue* work_q = work_queue(i);
4902 NOT_PRODUCT(int num_steals = 0;)
4903 oop obj_to_scan;
4904 CMSBitMap* bm = &(_collector->_markBitMap);
4905
4906 while (true) {
4907 // Completely finish any left over work from (an) earlier round(s)
4908 cl->trim_queue(0);
4909 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4910 (size_t)ParGCDesiredObjsFromOverflowList);
4911 // Now check if there's any work in the overflow list
4912 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4913 // only affects the number of attempts made to get work from the
4914 // overflow list and does not affect the number of workers. Just
4915 // pass ParallelGCThreads so this behavior is unchanged.
4916 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4917 work_q,
4918 ParallelGCThreads)) {
4919 // found something in global overflow list;
4920 // not yet ready to go stealing work from others.
4921 // We'd like to assert(work_q->size() != 0, ...)
4922 // because we just took work from the overflow list,
4923 // but of course we can't since all of that could have
4924 // been already stolen from us.
4925 // "He giveth and He taketh away."
4926 continue;
4927 }
4928 // Verify that we have no work before we resort to stealing
4929 assert(work_q->size() == 0, "Have work, shouldn't steal");
4930 // Try to steal from other queues that have work
4931 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4932 NOT_PRODUCT(num_steals++;)
4933 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4934 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4935 // Do scanning work
4936 obj_to_scan->oop_iterate(cl);
4937 // Loop around, finish this work, and try to steal some more
4938 } else if (terminator()->offer_termination()) {
4939 break; // nirvana from the infinite cycle
4940 }
4941 }
4942 NOT_PRODUCT(
4943 if (PrintCMSStatistics != 0) {
4944 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
4945 }
4946 )
4947 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4948 "Else our work is not yet done");
4949 }
4950
4951 // Record object boundaries in _eden_chunk_array by sampling the eden
4952 // top in the slow-path eden object allocation code path and record
4953 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4954 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4955 // sampling in sample_eden() that activates during the part of the
4956 // preclean phase.
4957 void CMSCollector::sample_eden_chunk() {
4958 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4959 if (_eden_chunk_lock->try_lock()) {
4960 // Record a sample. This is the critical section. The contents
4961 // of the _eden_chunk_array have to be non-decreasing in the
4962 // address order.
4963 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4964 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4965 "Unexpected state of Eden");
4966 if (_eden_chunk_index == 0 ||
4967 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4968 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4969 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4970 _eden_chunk_index++; // commit sample
4971 }
4972 _eden_chunk_lock->unlock();
4973 }
4974 }
4975 }
4976
4977 // Return a thread-local PLAB recording array, as appropriate.
4978 void* CMSCollector::get_data_recorder(int thr_num) {
4979 if (_survivor_plab_array != NULL &&
4980 (CMSPLABRecordAlways ||
4981 (_collectorState > Marking && _collectorState < FinalMarking))) {
4982 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4983 ChunkArray* ca = &_survivor_plab_array[thr_num];
4984 ca->reset(); // clear it so that fresh data is recorded
4985 return (void*) ca;
4986 } else {
4987 return NULL;
4988 }
4989 }
4990
4991 // Reset all the thread-local PLAB recording arrays
4992 void CMSCollector::reset_survivor_plab_arrays() {
4993 for (uint i = 0; i < ParallelGCThreads; i++) {
4994 _survivor_plab_array[i].reset();
4995 }
4996 }
4997
4998 // Merge the per-thread plab arrays into the global survivor chunk
4999 // array which will provide the partitioning of the survivor space
5000 // for CMS initial scan and rescan.
5001 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5002 int no_of_gc_threads) {
5003 assert(_survivor_plab_array != NULL, "Error");
5004 assert(_survivor_chunk_array != NULL, "Error");
5005 assert(_collectorState == FinalMarking ||
5006 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
5007 for (int j = 0; j < no_of_gc_threads; j++) {
5008 _cursor[j] = 0;
5009 }
5010 HeapWord* top = surv->top();
5011 size_t i;
5012 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5013 HeapWord* min_val = top; // Higher than any PLAB address
5014 uint min_tid = 0; // position of min_val this round
5015 for (int j = 0; j < no_of_gc_threads; j++) {
5016 ChunkArray* cur_sca = &_survivor_plab_array[j];
5017 if (_cursor[j] == cur_sca->end()) {
5018 continue;
5019 }
5020 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5021 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5022 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5023 if (cur_val < min_val) {
5024 min_tid = j;
5025 min_val = cur_val;
5026 } else {
5027 assert(cur_val < top, "All recorded addresses should be less");
5028 }
5029 }
5030 // At this point min_val and min_tid are respectively
5031 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5032 // and the thread (j) that witnesses that address.
5033 // We record this address in the _survivor_chunk_array[i]
5034 // and increment _cursor[min_tid] prior to the next round i.
5035 if (min_val == top) {
5036 break;
5037 }
5038 _survivor_chunk_array[i] = min_val;
5039 _cursor[min_tid]++;
5040 }
5041 // We are all done; record the size of the _survivor_chunk_array
5042 _survivor_chunk_index = i; // exclusive: [0, i)
5043 if (PrintCMSStatistics > 0) {
5044 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5045 }
5046 // Verify that we used up all the recorded entries
5047 #ifdef ASSERT
5048 size_t total = 0;
5049 for (int j = 0; j < no_of_gc_threads; j++) {
5050 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5051 total += _cursor[j];
5052 }
5053 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5054 // Check that the merged array is in sorted order
5055 if (total > 0) {
5056 for (size_t i = 0; i < total - 1; i++) {
5057 if (PrintCMSStatistics > 0) {
5058 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5059 i, _survivor_chunk_array[i]);
5060 }
5061 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5062 "Not sorted");
5063 }
5064 }
5065 #endif // ASSERT
5066 }
5067
5068 // Set up the space's par_seq_tasks structure for work claiming
5069 // for parallel initial scan and rescan of young gen.
5070 // See ParRescanTask where this is currently used.
5071 void
5072 CMSCollector::
5073 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5074 assert(n_threads > 0, "Unexpected n_threads argument");
5075
5076 // Eden space
5077 if (!_young_gen->eden()->is_empty()) {
5078 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
5079 assert(!pst->valid(), "Clobbering existing data?");
5080 // Each valid entry in [0, _eden_chunk_index) represents a task.
5081 size_t n_tasks = _eden_chunk_index + 1;
5082 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5083 // Sets the condition for completion of the subtask (how many threads
5084 // need to finish in order to be done).
5085 pst->set_n_threads(n_threads);
5086 pst->set_n_tasks((int)n_tasks);
5087 }
5088
5089 // Merge the survivor plab arrays into _survivor_chunk_array
5090 if (_survivor_plab_array != NULL) {
5091 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5092 } else {
5093 assert(_survivor_chunk_index == 0, "Error");
5094 }
5095
5096 // To space
5097 {
5098 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5099 assert(!pst->valid(), "Clobbering existing data?");
5100 // Sets the condition for completion of the subtask (how many threads
5101 // need to finish in order to be done).
5102 pst->set_n_threads(n_threads);
5103 pst->set_n_tasks(1);
5104 assert(pst->valid(), "Error");
5105 }
5106
5107 // From space
5108 {
5109 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5110 assert(!pst->valid(), "Clobbering existing data?");
5111 size_t n_tasks = _survivor_chunk_index + 1;
5112 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5113 // Sets the condition for completion of the subtask (how many threads
5114 // need to finish in order to be done).
5115 pst->set_n_threads(n_threads);
5116 pst->set_n_tasks((int)n_tasks);
5117 assert(pst->valid(), "Error");
5118 }
5119 }
5120
5121 // Parallel version of remark
5122 void CMSCollector::do_remark_parallel() {
5123 GenCollectedHeap* gch = GenCollectedHeap::heap();
5124 FlexibleWorkGang* workers = gch->workers();
5125 assert(workers != NULL, "Need parallel worker threads.");
5126 // Choose to use the number of GC workers most recently set
5127 // into "active_workers". If active_workers is not set, set it
5128 // to ParallelGCThreads.
5129 int n_workers = workers->active_workers();
5130 if (n_workers == 0) {
5131 assert(n_workers > 0, "Should have been set during scavenge");
5132 n_workers = ParallelGCThreads;
5133 workers->set_active_workers(n_workers);
5134 }
5135 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5136
5137 CMSParRemarkTask tsk(this,
5138 cms_space,
5139 n_workers, workers, task_queues());
5140
5141 // Set up for parallel process_roots work.
5142 gch->set_par_threads(n_workers);
5143 // We won't be iterating over the cards in the card table updating
5144 // the younger_gen cards, so we shouldn't call the following else
5145 // the verification code as well as subsequent younger_refs_iterate
5146 // code would get confused. XXX
5147 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5148
5149 // The young gen rescan work will not be done as part of
5150 // process_roots (which currently doesn't know how to
5151 // parallelize such a scan), but rather will be broken up into
5152 // a set of parallel tasks (via the sampling that the [abortable]
5153 // preclean phase did of eden, plus the [two] tasks of
5154 // scanning the [two] survivor spaces. Further fine-grain
5155 // parallelization of the scanning of the survivor spaces
5156 // themselves, and of precleaning of the younger gen itself
5157 // is deferred to the future.
5158 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5159
5160 // The dirty card rescan work is broken up into a "sequence"
5161 // of parallel tasks (per constituent space) that are dynamically
5162 // claimed by the parallel threads.
5163 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5164
5165 // It turns out that even when we're using 1 thread, doing the work in a
5166 // separate thread causes wide variance in run times. We can't help this
5167 // in the multi-threaded case, but we special-case n=1 here to get
5168 // repeatable measurements of the 1-thread overhead of the parallel code.
5169 if (n_workers > 1) {
5170 // Make refs discovery MT-safe, if it isn't already: it may not
5171 // necessarily be so, since it's possible that we are doing
5172 // ST marking.
5173 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5174 GenCollectedHeap::StrongRootsScope srs(gch);
5175 workers->run_task(&tsk);
5176 } else {
5177 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5178 GenCollectedHeap::StrongRootsScope srs(gch);
5179 tsk.work(0);
5180 }
5181
5182 gch->set_par_threads(0); // 0 ==> non-parallel.
5183 // restore, single-threaded for now, any preserved marks
5184 // as a result of work_q overflow
5185 restore_preserved_marks_if_any();
5186 }
5187
5188 // Non-parallel version of remark
5189 void CMSCollector::do_remark_non_parallel() {
5190 ResourceMark rm;
5191 HandleMark hm;
5192 GenCollectedHeap* gch = GenCollectedHeap::heap();
5193 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5194
5195 MarkRefsIntoAndScanClosure
5196 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5197 &_markStack, this,
5198 false /* should_yield */, false /* not precleaning */);
5199 MarkFromDirtyCardsClosure
5200 markFromDirtyCardsClosure(this, _span,
5201 NULL, // space is set further below
5202 &_markBitMap, &_markStack, &mrias_cl);
5203 {
5204 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5205 // Iterate over the dirty cards, setting the corresponding bits in the
5206 // mod union table.
5207 {
5208 ModUnionClosure modUnionClosure(&_modUnionTable);
5209 _ct->ct_bs()->dirty_card_iterate(
5210 _cmsGen->used_region(),
5211 &modUnionClosure);
5212 }
5213 // Having transferred these marks into the modUnionTable, we just need
5214 // to rescan the marked objects on the dirty cards in the modUnionTable.
5215 // The initial marking may have been done during an asynchronous
5216 // collection so there may be dirty bits in the mod-union table.
5217 const int alignment =
5218 CardTableModRefBS::card_size * BitsPerWord;
5219 {
5220 // ... First handle dirty cards in CMS gen
5221 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5222 MemRegion ur = _cmsGen->used_region();
5223 HeapWord* lb = ur.start();
5224 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5225 MemRegion cms_span(lb, ub);
5226 _modUnionTable.dirty_range_iterate_clear(cms_span,
5227 &markFromDirtyCardsClosure);
5228 verify_work_stacks_empty();
5229 if (PrintCMSStatistics != 0) {
5230 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5231 markFromDirtyCardsClosure.num_dirty_cards());
5232 }
5233 }
5234 }
5235 if (VerifyDuringGC &&
5236 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5237 HandleMark hm; // Discard invalid handles created during verification
5238 Universe::verify();
5239 }
5240 {
5241 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5242
5243 verify_work_stacks_empty();
5244
5245 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5246 GenCollectedHeap::StrongRootsScope srs(gch);
5247
5248 gch->gen_process_roots(_cmsGen->level(),
5249 true, // younger gens as roots
5250 false, // use the local StrongRootsScope
5251 SharedHeap::ScanningOption(roots_scanning_options()),
5252 should_unload_classes(),
5253 &mrias_cl,
5254 NULL,
5255 NULL); // The dirty klasses will be handled below
5256
5257 assert(should_unload_classes()
5258 || (roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5259 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5260 }
5261
5262 {
5263 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5264
5265 verify_work_stacks_empty();
5266
5267 // Scan all class loader data objects that might have been introduced
5268 // during concurrent marking.
5269 ResourceMark rm;
5270 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5271 for (int i = 0; i < array->length(); i++) {
5272 mrias_cl.do_class_loader_data(array->at(i));
5273 }
5274
5275 // We don't need to keep track of new CLDs anymore.
5276 ClassLoaderDataGraph::remember_new_clds(false);
5277
5278 verify_work_stacks_empty();
5279 }
5280
5281 {
5282 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5283
5284 verify_work_stacks_empty();
5285
5286 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5287 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5288
5289 verify_work_stacks_empty();
5290 }
5291
5292 // We might have added oops to ClassLoaderData::_handles during the
5293 // concurrent marking phase. These oops point to newly allocated objects
5294 // that are guaranteed to be kept alive. Either by the direct allocation
5295 // code, or when the young collector processes the roots. Hence,
5296 // we don't have to revisit the _handles block during the remark phase.
5297
5298 verify_work_stacks_empty();
5299 // Restore evacuated mark words, if any, used for overflow list links
5300 if (!CMSOverflowEarlyRestoration) {
5301 restore_preserved_marks_if_any();
5302 }
5303 verify_overflow_empty();
5304 }
5305
5306 ////////////////////////////////////////////////////////
5307 // Parallel Reference Processing Task Proxy Class
5308 ////////////////////////////////////////////////////////
5309 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5310 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5311 CMSCollector* _collector;
5312 CMSBitMap* _mark_bit_map;
5313 const MemRegion _span;
5314 ProcessTask& _task;
5315
5316 public:
5317 CMSRefProcTaskProxy(ProcessTask& task,
5318 CMSCollector* collector,
5319 const MemRegion& span,
5320 CMSBitMap* mark_bit_map,
5321 AbstractWorkGang* workers,
5322 OopTaskQueueSet* task_queues):
5323 // XXX Should superclass AGTWOQ also know about AWG since it knows
5324 // about the task_queues used by the AWG? Then it could initialize
5325 // the terminator() object. See 6984287. The set_for_termination()
5326 // below is a temporary band-aid for the regression in 6984287.
5327 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5328 task_queues),
5329 _task(task),
5330 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5331 {
5332 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5333 "Inconsistency in _span");
5334 set_for_termination(workers->active_workers());
5335 }
5336
5337 OopTaskQueueSet* task_queues() { return queues(); }
5338
5339 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5340
5341 void do_work_steal(int i,
5342 CMSParDrainMarkingStackClosure* drain,
5343 CMSParKeepAliveClosure* keep_alive,
5344 int* seed);
5345
5346 virtual void work(uint worker_id);
5347 };
5348
5349 void CMSRefProcTaskProxy::work(uint worker_id) {
5350 ResourceMark rm;
5351 HandleMark hm;
5352 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5353 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5354 _mark_bit_map,
5355 work_queue(worker_id));
5356 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5357 _mark_bit_map,
5358 work_queue(worker_id));
5359 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5360 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5361 if (_task.marks_oops_alive()) {
5362 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5363 _collector->hash_seed(worker_id));
5364 }
5365 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5366 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5367 }
5368
5369 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5370 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5371 EnqueueTask& _task;
5372
5373 public:
5374 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5375 : AbstractGangTask("Enqueue reference objects in parallel"),
5376 _task(task)
5377 { }
5378
5379 virtual void work(uint worker_id)
5380 {
5381 _task.work(worker_id);
5382 }
5383 };
5384
5385 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5386 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5387 _span(span),
5388 _bit_map(bit_map),
5389 _work_queue(work_queue),
5390 _mark_and_push(collector, span, bit_map, work_queue),
5391 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5392 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5393 { }
5394
5395 // . see if we can share work_queues with ParNew? XXX
5396 void CMSRefProcTaskProxy::do_work_steal(int i,
5397 CMSParDrainMarkingStackClosure* drain,
5398 CMSParKeepAliveClosure* keep_alive,
5399 int* seed) {
5400 OopTaskQueue* work_q = work_queue(i);
5401 NOT_PRODUCT(int num_steals = 0;)
5402 oop obj_to_scan;
5403
5404 while (true) {
5405 // Completely finish any left over work from (an) earlier round(s)
5406 drain->trim_queue(0);
5407 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5408 (size_t)ParGCDesiredObjsFromOverflowList);
5409 // Now check if there's any work in the overflow list
5410 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5411 // only affects the number of attempts made to get work from the
5412 // overflow list and does not affect the number of workers. Just
5413 // pass ParallelGCThreads so this behavior is unchanged.
5414 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5415 work_q,
5416 ParallelGCThreads)) {
5417 // Found something in global overflow list;
5418 // not yet ready to go stealing work from others.
5419 // We'd like to assert(work_q->size() != 0, ...)
5420 // because we just took work from the overflow list,
5421 // but of course we can't, since all of that might have
5422 // been already stolen from us.
5423 continue;
5424 }
5425 // Verify that we have no work before we resort to stealing
5426 assert(work_q->size() == 0, "Have work, shouldn't steal");
5427 // Try to steal from other queues that have work
5428 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5429 NOT_PRODUCT(num_steals++;)
5430 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5431 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5432 // Do scanning work
5433 obj_to_scan->oop_iterate(keep_alive);
5434 // Loop around, finish this work, and try to steal some more
5435 } else if (terminator()->offer_termination()) {
5436 break; // nirvana from the infinite cycle
5437 }
5438 }
5439 NOT_PRODUCT(
5440 if (PrintCMSStatistics != 0) {
5441 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5442 }
5443 )
5444 }
5445
5446 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5447 {
5448 GenCollectedHeap* gch = GenCollectedHeap::heap();
5449 FlexibleWorkGang* workers = gch->workers();
5450 assert(workers != NULL, "Need parallel worker threads.");
5451 CMSRefProcTaskProxy rp_task(task, &_collector,
5452 _collector.ref_processor()->span(),
5453 _collector.markBitMap(),
5454 workers, _collector.task_queues());
5455 workers->run_task(&rp_task);
5456 }
5457
5458 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5459 {
5460
5461 GenCollectedHeap* gch = GenCollectedHeap::heap();
5462 FlexibleWorkGang* workers = gch->workers();
5463 assert(workers != NULL, "Need parallel worker threads.");
5464 CMSRefEnqueueTaskProxy enq_task(task);
5465 workers->run_task(&enq_task);
5466 }
5467
5468 void CMSCollector::refProcessingWork() {
5469 ResourceMark rm;
5470 HandleMark hm;
5471
5472 ReferenceProcessor* rp = ref_processor();
5473 assert(rp->span().equals(_span), "Spans should be equal");
5474 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5475 // Process weak references.
5476 rp->setup_policy(false);
5477 verify_work_stacks_empty();
5478
5479 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5480 &_markStack, false /* !preclean */);
5481 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5482 _span, &_markBitMap, &_markStack,
5483 &cmsKeepAliveClosure, false /* !preclean */);
5484 {
5485 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5486
5487 ReferenceProcessorStats stats;
5488 if (rp->processing_is_mt()) {
5489 // Set the degree of MT here. If the discovery is done MT, there
5490 // may have been a different number of threads doing the discovery
5491 // and a different number of discovered lists may have Ref objects.
5492 // That is OK as long as the Reference lists are balanced (see
5493 // balance_all_queues() and balance_queues()).
5494 GenCollectedHeap* gch = GenCollectedHeap::heap();
5495 int active_workers = ParallelGCThreads;
5496 FlexibleWorkGang* workers = gch->workers();
5497 if (workers != NULL) {
5498 active_workers = workers->active_workers();
5499 // The expectation is that active_workers will have already
5500 // been set to a reasonable value. If it has not been set,
5501 // investigate.
5502 assert(active_workers > 0, "Should have been set during scavenge");
5503 }
5504 rp->set_active_mt_degree(active_workers);
5505 CMSRefProcTaskExecutor task_executor(*this);
5506 stats = rp->process_discovered_references(&_is_alive_closure,
5507 &cmsKeepAliveClosure,
5508 &cmsDrainMarkingStackClosure,
5509 &task_executor,
5510 _gc_timer_cm,
5511 _gc_tracer_cm->gc_id());
5512 } else {
5513 stats = rp->process_discovered_references(&_is_alive_closure,
5514 &cmsKeepAliveClosure,
5515 &cmsDrainMarkingStackClosure,
5516 NULL,
5517 _gc_timer_cm,
5518 _gc_tracer_cm->gc_id());
5519 }
5520 _gc_tracer_cm->report_gc_reference_stats(stats);
5521
5522 }
5523
5524 // This is the point where the entire marking should have completed.
5525 verify_work_stacks_empty();
5526
5527 if (should_unload_classes()) {
5528 {
5529 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5530
5531 // Unload classes and purge the SystemDictionary.
5532 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5533
5534 // Unload nmethods.
5535 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5536
5537 // Prune dead klasses from subklass/sibling/implementor lists.
5538 Klass::clean_weak_klass_links(&_is_alive_closure);
5539 }
5540
5541 {
5542 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5543 // Clean up unreferenced symbols in symbol table.
5544 SymbolTable::unlink();
5545 }
5546
5547 {
5548 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5549 // Delete entries for dead interned strings.
5550 StringTable::unlink(&_is_alive_closure);
5551 }
5552 }
5553
5554
5555 // Restore any preserved marks as a result of mark stack or
5556 // work queue overflow
5557 restore_preserved_marks_if_any(); // done single-threaded for now
5558
5559 rp->set_enqueuing_is_done(true);
5560 if (rp->processing_is_mt()) {
5561 rp->balance_all_queues();
5562 CMSRefProcTaskExecutor task_executor(*this);
5563 rp->enqueue_discovered_references(&task_executor);
5564 } else {
5565 rp->enqueue_discovered_references(NULL);
5566 }
5567 rp->verify_no_references_recorded();
5568 assert(!rp->discovery_enabled(), "should have been disabled");
5569 }
5570
5571 #ifndef PRODUCT
5572 void CMSCollector::check_correct_thread_executing() {
5573 Thread* t = Thread::current();
5574 // Only the VM thread or the CMS thread should be here.
5575 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5576 "Unexpected thread type");
5577 // If this is the vm thread, the foreground process
5578 // should not be waiting. Note that _foregroundGCIsActive is
5579 // true while the foreground collector is waiting.
5580 if (_foregroundGCShouldWait) {
5581 // We cannot be the VM thread
5582 assert(t->is_ConcurrentGC_thread(),
5583 "Should be CMS thread");
5584 } else {
5585 // We can be the CMS thread only if we are in a stop-world
5586 // phase of CMS collection.
5587 if (t->is_ConcurrentGC_thread()) {
5588 assert(_collectorState == InitialMarking ||
5589 _collectorState == FinalMarking,
5590 "Should be a stop-world phase");
5591 // The CMS thread should be holding the CMS_token.
5592 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5593 "Potential interference with concurrently "
5594 "executing VM thread");
5595 }
5596 }
5597 }
5598 #endif
5599
5600 void CMSCollector::sweep() {
5601 assert(_collectorState == Sweeping, "just checking");
5602 check_correct_thread_executing();
5603 verify_work_stacks_empty();
5604 verify_overflow_empty();
5605 increment_sweep_count();
5606 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5607
5608 _inter_sweep_timer.stop();
5609 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5610
5611 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5612 _intra_sweep_timer.reset();
5613 _intra_sweep_timer.start();
5614 {
5615 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5616 CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5617 // First sweep the old gen
5618 {
5619 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5620 bitMapLock());
5621 sweepWork(_cmsGen);
5622 }
5623
5624 // Update Universe::_heap_*_at_gc figures.
5625 // We need all the free list locks to make the abstract state
5626 // transition from Sweeping to Resetting. See detailed note
5627 // further below.
5628 {
5629 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5630 // Update heap occupancy information which is used as
5631 // input to soft ref clearing policy at the next gc.
5632 Universe::update_heap_info_at_gc();
5633 _collectorState = Resizing;
5634 }
5635 }
5636 verify_work_stacks_empty();
5637 verify_overflow_empty();
5638
5639 if (should_unload_classes()) {
5640 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5641 // requires that the virtual spaces are stable and not deleted.
5642 ClassLoaderDataGraph::set_should_purge(true);
5643 }
5644
5645 _intra_sweep_timer.stop();
5646 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5647
5648 _inter_sweep_timer.reset();
5649 _inter_sweep_timer.start();
5650
5651 // We need to use a monotonically non-decreasing time in ms
5652 // or we will see time-warp warnings and os::javaTimeMillis()
5653 // does not guarantee monotonicity.
5654 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5655 update_time_of_last_gc(now);
5656
5657 // NOTE on abstract state transitions:
5658 // Mutators allocate-live and/or mark the mod-union table dirty
5659 // based on the state of the collection. The former is done in
5660 // the interval [Marking, Sweeping] and the latter in the interval
5661 // [Marking, Sweeping). Thus the transitions into the Marking state
5662 // and out of the Sweeping state must be synchronously visible
5663 // globally to the mutators.
5664 // The transition into the Marking state happens with the world
5665 // stopped so the mutators will globally see it. Sweeping is
5666 // done asynchronously by the background collector so the transition
5667 // from the Sweeping state to the Resizing state must be done
5668 // under the freelistLock (as is the check for whether to
5669 // allocate-live and whether to dirty the mod-union table).
5670 assert(_collectorState == Resizing, "Change of collector state to"
5671 " Resizing must be done under the freelistLocks (plural)");
5672
5673 // Now that sweeping has been completed, we clear
5674 // the incremental_collection_failed flag,
5675 // thus inviting a younger gen collection to promote into
5676 // this generation. If such a promotion may still fail,
5677 // the flag will be set again when a young collection is
5678 // attempted.
5679 GenCollectedHeap* gch = GenCollectedHeap::heap();
5680 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5681 gch->update_full_collections_completed(_collection_count_start);
5682 }
5683
5684 // FIX ME!!! Looks like this belongs in CFLSpace, with
5685 // CMSGen merely delegating to it.
5686 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5687 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5688 HeapWord* minAddr = _cmsSpace->bottom();
5689 HeapWord* largestAddr =
5690 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5691 if (largestAddr == NULL) {
5692 // The dictionary appears to be empty. In this case
5693 // try to coalesce at the end of the heap.
5694 largestAddr = _cmsSpace->end();
5695 }
5696 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5697 size_t nearLargestOffset =
5698 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5699 if (PrintFLSStatistics != 0) {
5700 gclog_or_tty->print_cr(
5701 "CMS: Large Block: " PTR_FORMAT ";"
5702 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5703 largestAddr,
5704 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
5705 }
5706 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5707 }
5708
5709 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5710 return addr >= _cmsSpace->nearLargestChunk();
5711 }
5712
5713 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5714 return _cmsSpace->find_chunk_at_end();
5715 }
5716
5717 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
5718 bool full) {
5719 // The next lower level has been collected. Gather any statistics
5720 // that are of interest at this point.
5721 if (!full && (current_level + 1) == level()) {
5722 // Gather statistics on the young generation collection.
5723 collector()->stats().record_gc0_end(used());
5724 }
5725 }
5726
5727 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen) {
5728 // We iterate over the space(s) underlying this generation,
5729 // checking the mark bit map to see if the bits corresponding
5730 // to specific blocks are marked or not. Blocks that are
5731 // marked are live and are not swept up. All remaining blocks
5732 // are swept up, with coalescing on-the-fly as we sweep up
5733 // contiguous free and/or garbage blocks:
5734 // We need to ensure that the sweeper synchronizes with allocators
5735 // and stop-the-world collectors. In particular, the following
5736 // locks are used:
5737 // . CMS token: if this is held, a stop the world collection cannot occur
5738 // . freelistLock: if this is held no allocation can occur from this
5739 // generation by another thread
5740 // . bitMapLock: if this is held, no other thread can access or update
5741 //
5742
5743 // Note that we need to hold the freelistLock if we use
5744 // block iterate below; else the iterator might go awry if
5745 // a mutator (or promotion) causes block contents to change
5746 // (for instance if the allocator divvies up a block).
5747 // If we hold the free list lock, for all practical purposes
5748 // young generation GC's can't occur (they'll usually need to
5749 // promote), so we might as well prevent all young generation
5750 // GC's while we do a sweeping step. For the same reason, we might
5751 // as well take the bit map lock for the entire duration
5752
5753 // check that we hold the requisite locks
5754 assert(have_cms_token(), "Should hold cms token");
5755 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5756 assert_lock_strong(gen->freelistLock());
5757 assert_lock_strong(bitMapLock());
5758
5759 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5760 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5761 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5762 _inter_sweep_estimate.padded_average(),
5763 _intra_sweep_estimate.padded_average());
5764 gen->setNearLargestChunk();
5765
5766 {
5767 SweepClosure sweepClosure(this, gen, &_markBitMap, CMSYield);
5768 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5769 // We need to free-up/coalesce garbage/blocks from a
5770 // co-terminal free run. This is done in the SweepClosure
5771 // destructor; so, do not remove this scope, else the
5772 // end-of-sweep-census below will be off by a little bit.
5773 }
5774 gen->cmsSpace()->sweep_completed();
5775 gen->cmsSpace()->endSweepFLCensus(sweep_count());
5776 if (should_unload_classes()) { // unloaded classes this cycle,
5777 _concurrent_cycles_since_last_unload = 0; // ... reset count
5778 } else { // did not unload classes,
5779 _concurrent_cycles_since_last_unload++; // ... increment count
5780 }
5781 }
5782
5783 // Reset CMS data structures (for now just the marking bit map)
5784 // preparatory for the next cycle.
5785 void CMSCollector::reset(bool concurrent) {
5786 if (concurrent) {
5787 CMSTokenSyncWithLocks ts(true, bitMapLock());
5788
5789 // If the state is not "Resetting", the foreground thread
5790 // has done a collection and the resetting.
5791 if (_collectorState != Resetting) {
5792 assert(_collectorState == Idling, "The state should only change"
5793 " because the foreground collector has finished the collection");
5794 return;
5795 }
5796
5797 // Clear the mark bitmap (no grey objects to start with)
5798 // for the next cycle.
5799 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5800 CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5801
5802 HeapWord* curAddr = _markBitMap.startWord();
5803 while (curAddr < _markBitMap.endWord()) {
5804 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5805 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5806 _markBitMap.clear_large_range(chunk);
5807 if (ConcurrentMarkSweepThread::should_yield() &&
5808 !foregroundGCIsActive() &&
5809 CMSYield) {
5810 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5811 "CMS thread should hold CMS token");
5812 assert_lock_strong(bitMapLock());
5813 bitMapLock()->unlock();
5814 ConcurrentMarkSweepThread::desynchronize(true);
5815 stopTimer();
5816 if (PrintCMSStatistics != 0) {
5817 incrementYields();
5818 }
5819
5820 // See the comment in coordinator_yield()
5821 for (unsigned i = 0; i < CMSYieldSleepCount &&
5822 ConcurrentMarkSweepThread::should_yield() &&
5823 !CMSCollector::foregroundGCIsActive(); ++i) {
5824 os::sleep(Thread::current(), 1, false);
5825 }
5826
5827 ConcurrentMarkSweepThread::synchronize(true);
5828 bitMapLock()->lock_without_safepoint_check();
5829 startTimer();
5830 }
5831 curAddr = chunk.end();
5832 }
5833 // A successful mostly concurrent collection has been done.
5834 // Because only the full (i.e., concurrent mode failure) collections
5835 // are being measured for gc overhead limits, clean the "near" flag
5836 // and count.
5837 size_policy()->reset_gc_overhead_limit_count();
5838 _collectorState = Idling;
5839 } else {
5840 // already have the lock
5841 assert(_collectorState == Resetting, "just checking");
5842 assert_lock_strong(bitMapLock());
5843 _markBitMap.clear_all();
5844 _collectorState = Idling;
5845 }
5846
5847 register_gc_end();
5848 }
5849
5850 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5851 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5852 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
5853 TraceCollectorStats tcs(counters());
5854
5855 switch (op) {
5856 case CMS_op_checkpointRootsInitial: {
5857 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5858 checkpointRootsInitial();
5859 if (PrintGC) {
5860 _cmsGen->printOccupancy("initial-mark");
5861 }
5862 break;
5863 }
5864 case CMS_op_checkpointRootsFinal: {
5865 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5866 checkpointRootsFinal();
5867 if (PrintGC) {
5868 _cmsGen->printOccupancy("remark");
5869 }
5870 break;
5871 }
5872 default:
5873 fatal("No such CMS_op");
5874 }
5875 }
5876
5877 #ifndef PRODUCT
5878 size_t const CMSCollector::skip_header_HeapWords() {
5879 return FreeChunk::header_size();
5880 }
5881
5882 // Try and collect here conditions that should hold when
5883 // CMS thread is exiting. The idea is that the foreground GC
5884 // thread should not be blocked if it wants to terminate
5885 // the CMS thread and yet continue to run the VM for a while
5886 // after that.
5887 void CMSCollector::verify_ok_to_terminate() const {
5888 assert(Thread::current()->is_ConcurrentGC_thread(),
5889 "should be called by CMS thread");
5890 assert(!_foregroundGCShouldWait, "should be false");
5891 // We could check here that all the various low-level locks
5892 // are not held by the CMS thread, but that is overkill; see
5893 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5894 // is checked.
5895 }
5896 #endif
5897
5898 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5899 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5900 "missing Printezis mark?");
5901 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5902 size_t size = pointer_delta(nextOneAddr + 1, addr);
5903 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5904 "alignment problem");
5905 assert(size >= 3, "Necessary for Printezis marks to work");
5906 return size;
5907 }
5908
5909 // A variant of the above (block_size_using_printezis_bits()) except
5910 // that we return 0 if the P-bits are not yet set.
5911 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5912 if (_markBitMap.isMarked(addr + 1)) {
5913 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5914 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5915 size_t size = pointer_delta(nextOneAddr + 1, addr);
5916 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5917 "alignment problem");
5918 assert(size >= 3, "Necessary for Printezis marks to work");
5919 return size;
5920 }
5921 return 0;
5922 }
5923
5924 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5925 size_t sz = 0;
5926 oop p = (oop)addr;
5927 if (p->klass_or_null() != NULL) {
5928 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5929 } else {
5930 sz = block_size_using_printezis_bits(addr);
5931 }
5932 assert(sz > 0, "size must be nonzero");
5933 HeapWord* next_block = addr + sz;
5934 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
5935 CardTableModRefBS::card_size);
5936 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
5937 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5938 "must be different cards");
5939 return next_card;
5940 }
5941
5942
5943 // CMS Bit Map Wrapper /////////////////////////////////////////
5944
5945 // Construct a CMS bit map infrastructure, but don't create the
5946 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5947 // further below.
5948 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5949 _bm(),
5950 _shifter(shifter),
5951 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5952 Monitor::_safepoint_check_sometimes) : NULL)
5953 {
5954 _bmStartWord = 0;
5955 _bmWordSize = 0;
5956 }
5957
5958 bool CMSBitMap::allocate(MemRegion mr) {
5959 _bmStartWord = mr.start();
5960 _bmWordSize = mr.word_size();
5961 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5962 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5963 if (!brs.is_reserved()) {
5964 warning("CMS bit map allocation failure");
5965 return false;
5966 }
5967 // For now we'll just commit all of the bit map up front.
5968 // Later on we'll try to be more parsimonious with swap.
5969 if (!_virtual_space.initialize(brs, brs.size())) {
5970 warning("CMS bit map backing store failure");
5971 return false;
5972 }
5973 assert(_virtual_space.committed_size() == brs.size(),
5974 "didn't reserve backing store for all of CMS bit map?");
5975 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5976 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5977 _bmWordSize, "inconsistency in bit map sizing");
5978 _bm.set_size(_bmWordSize >> _shifter);
5979
5980 // bm.clear(); // can we rely on getting zero'd memory? verify below
5981 assert(isAllClear(),
5982 "Expected zero'd memory from ReservedSpace constructor");
5983 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5984 "consistency check");
5985 return true;
5986 }
5987
5988 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5989 HeapWord *next_addr, *end_addr, *last_addr;
5990 assert_locked();
5991 assert(covers(mr), "out-of-range error");
5992 // XXX assert that start and end are appropriately aligned
5993 for (next_addr = mr.start(), end_addr = mr.end();
5994 next_addr < end_addr; next_addr = last_addr) {
5995 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5996 last_addr = dirty_region.end();
5997 if (!dirty_region.is_empty()) {
5998 cl->do_MemRegion(dirty_region);
5999 } else {
6000 assert(last_addr == end_addr, "program logic");
6001 return;
6002 }
6003 }
6004 }
6005
6006 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6007 _bm.print_on_error(st, prefix);
6008 }
6009
6010 #ifndef PRODUCT
6011 void CMSBitMap::assert_locked() const {
6012 CMSLockVerifier::assert_locked(lock());
6013 }
6014
6015 bool CMSBitMap::covers(MemRegion mr) const {
6016 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6017 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6018 "size inconsistency");
6019 return (mr.start() >= _bmStartWord) &&
6020 (mr.end() <= endWord());
6021 }
6022
6023 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6024 return (start >= _bmStartWord && (start + size) <= endWord());
6025 }
6026
6027 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6028 // verify that there are no 1 bits in the interval [left, right)
6029 FalseBitMapClosure falseBitMapClosure;
6030 iterate(&falseBitMapClosure, left, right);
6031 }
6032
6033 void CMSBitMap::region_invariant(MemRegion mr)
6034 {
6035 assert_locked();
6036 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6037 assert(!mr.is_empty(), "unexpected empty region");
6038 assert(covers(mr), "mr should be covered by bit map");
6039 // convert address range into offset range
6040 size_t start_ofs = heapWordToOffset(mr.start());
6041 // Make sure that end() is appropriately aligned
6042 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6043 (1 << (_shifter+LogHeapWordSize))),
6044 "Misaligned mr.end()");
6045 size_t end_ofs = heapWordToOffset(mr.end());
6046 assert(end_ofs > start_ofs, "Should mark at least one bit");
6047 }
6048
6049 #endif
6050
6051 bool CMSMarkStack::allocate(size_t size) {
6052 // allocate a stack of the requisite depth
6053 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6054 size * sizeof(oop)));
6055 if (!rs.is_reserved()) {
6056 warning("CMSMarkStack allocation failure");
6057 return false;
6058 }
6059 if (!_virtual_space.initialize(rs, rs.size())) {
6060 warning("CMSMarkStack backing store failure");
6061 return false;
6062 }
6063 assert(_virtual_space.committed_size() == rs.size(),
6064 "didn't reserve backing store for all of CMS stack?");
6065 _base = (oop*)(_virtual_space.low());
6066 _index = 0;
6067 _capacity = size;
6068 NOT_PRODUCT(_max_depth = 0);
6069 return true;
6070 }
6071
6072 // XXX FIX ME !!! In the MT case we come in here holding a
6073 // leaf lock. For printing we need to take a further lock
6074 // which has lower rank. We need to recalibrate the two
6075 // lock-ranks involved in order to be able to print the
6076 // messages below. (Or defer the printing to the caller.
6077 // For now we take the expedient path of just disabling the
6078 // messages for the problematic case.)
6079 void CMSMarkStack::expand() {
6080 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6081 if (_capacity == MarkStackSizeMax) {
6082 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6083 // We print a warning message only once per CMS cycle.
6084 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6085 }
6086 return;
6087 }
6088 // Double capacity if possible
6089 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6090 // Do not give up existing stack until we have managed to
6091 // get the double capacity that we desired.
6092 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6093 new_capacity * sizeof(oop)));
6094 if (rs.is_reserved()) {
6095 // Release the backing store associated with old stack
6096 _virtual_space.release();
6097 // Reinitialize virtual space for new stack
6098 if (!_virtual_space.initialize(rs, rs.size())) {
6099 fatal("Not enough swap for expanded marking stack");
6100 }
6101 _base = (oop*)(_virtual_space.low());
6102 _index = 0;
6103 _capacity = new_capacity;
6104 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6105 // Failed to double capacity, continue;
6106 // we print a detail message only once per CMS cycle.
6107 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6108 SIZE_FORMAT"K",
6109 _capacity / K, new_capacity / K);
6110 }
6111 }
6112
6113
6114 // Closures
6115 // XXX: there seems to be a lot of code duplication here;
6116 // should refactor and consolidate common code.
6117
6118 // This closure is used to mark refs into the CMS generation in
6119 // the CMS bit map. Called at the first checkpoint. This closure
6120 // assumes that we do not need to re-mark dirty cards; if the CMS
6121 // generation on which this is used is not an oldest
6122 // generation then this will lose younger_gen cards!
6123
6124 MarkRefsIntoClosure::MarkRefsIntoClosure(
6125 MemRegion span, CMSBitMap* bitMap):
6126 _span(span),
6127 _bitMap(bitMap)
6128 {
6129 assert(_ref_processor == NULL, "deliberately left NULL");
6130 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6131 }
6132
6133 void MarkRefsIntoClosure::do_oop(oop obj) {
6134 // if p points into _span, then mark corresponding bit in _markBitMap
6135 assert(obj->is_oop(), "expected an oop");
6136 HeapWord* addr = (HeapWord*)obj;
6137 if (_span.contains(addr)) {
6138 // this should be made more efficient
6139 _bitMap->mark(addr);
6140 }
6141 }
6142
6143 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6144 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6145
6146 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6147 MemRegion span, CMSBitMap* bitMap):
6148 _span(span),
6149 _bitMap(bitMap)
6150 {
6151 assert(_ref_processor == NULL, "deliberately left NULL");
6152 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6153 }
6154
6155 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6156 // if p points into _span, then mark corresponding bit in _markBitMap
6157 assert(obj->is_oop(), "expected an oop");
6158 HeapWord* addr = (HeapWord*)obj;
6159 if (_span.contains(addr)) {
6160 // this should be made more efficient
6161 _bitMap->par_mark(addr);
6162 }
6163 }
6164
6165 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6166 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6167
6168 // A variant of the above, used for CMS marking verification.
6169 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6170 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6171 _span(span),
6172 _verification_bm(verification_bm),
6173 _cms_bm(cms_bm)
6174 {
6175 assert(_ref_processor == NULL, "deliberately left NULL");
6176 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6177 }
6178
6179 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6180 // if p points into _span, then mark corresponding bit in _markBitMap
6181 assert(obj->is_oop(), "expected an oop");
6182 HeapWord* addr = (HeapWord*)obj;
6183 if (_span.contains(addr)) {
6184 _verification_bm->mark(addr);
6185 if (!_cms_bm->isMarked(addr)) {
6186 oop(addr)->print();
6187 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6188 fatal("... aborting");
6189 }
6190 }
6191 }
6192
6193 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6194 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6195
6196 //////////////////////////////////////////////////
6197 // MarkRefsIntoAndScanClosure
6198 //////////////////////////////////////////////////
6199
6200 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6201 ReferenceProcessor* rp,
6202 CMSBitMap* bit_map,
6203 CMSBitMap* mod_union_table,
6204 CMSMarkStack* mark_stack,
6205 CMSCollector* collector,
6206 bool should_yield,
6207 bool concurrent_precleaning):
6208 _collector(collector),
6209 _span(span),
6210 _bit_map(bit_map),
6211 _mark_stack(mark_stack),
6212 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6213 mark_stack, concurrent_precleaning),
6214 _yield(should_yield),
6215 _concurrent_precleaning(concurrent_precleaning),
6216 _freelistLock(NULL)
6217 {
6218 _ref_processor = rp;
6219 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6220 }
6221
6222 // This closure is used to mark refs into the CMS generation at the
6223 // second (final) checkpoint, and to scan and transitively follow
6224 // the unmarked oops. It is also used during the concurrent precleaning
6225 // phase while scanning objects on dirty cards in the CMS generation.
6226 // The marks are made in the marking bit map and the marking stack is
6227 // used for keeping the (newly) grey objects during the scan.
6228 // The parallel version (Par_...) appears further below.
6229 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6230 if (obj != NULL) {
6231 assert(obj->is_oop(), "expected an oop");
6232 HeapWord* addr = (HeapWord*)obj;
6233 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6234 assert(_collector->overflow_list_is_empty(),
6235 "overflow list should be empty");
6236 if (_span.contains(addr) &&
6237 !_bit_map->isMarked(addr)) {
6238 // mark bit map (object is now grey)
6239 _bit_map->mark(addr);
6240 // push on marking stack (stack should be empty), and drain the
6241 // stack by applying this closure to the oops in the oops popped
6242 // from the stack (i.e. blacken the grey objects)
6243 bool res = _mark_stack->push(obj);
6244 assert(res, "Should have space to push on empty stack");
6245 do {
6246 oop new_oop = _mark_stack->pop();
6247 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6248 assert(_bit_map->isMarked((HeapWord*)new_oop),
6249 "only grey objects on this stack");
6250 // iterate over the oops in this oop, marking and pushing
6251 // the ones in CMS heap (i.e. in _span).
6252 new_oop->oop_iterate(&_pushAndMarkClosure);
6253 // check if it's time to yield
6254 do_yield_check();
6255 } while (!_mark_stack->isEmpty() ||
6256 (!_concurrent_precleaning && take_from_overflow_list()));
6257 // if marking stack is empty, and we are not doing this
6258 // during precleaning, then check the overflow list
6259 }
6260 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6261 assert(_collector->overflow_list_is_empty(),
6262 "overflow list was drained above");
6263 // We could restore evacuated mark words, if any, used for
6264 // overflow list links here because the overflow list is
6265 // provably empty here. That would reduce the maximum
6266 // size requirements for preserved_{oop,mark}_stack.
6267 // But we'll just postpone it until we are all done
6268 // so we can just stream through.
6269 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6270 _collector->restore_preserved_marks_if_any();
6271 assert(_collector->no_preserved_marks(), "No preserved marks");
6272 }
6273 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6274 "All preserved marks should have been restored above");
6275 }
6276 }
6277
6278 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6279 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6280
6281 void MarkRefsIntoAndScanClosure::do_yield_work() {
6282 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6283 "CMS thread should hold CMS token");
6284 assert_lock_strong(_freelistLock);
6285 assert_lock_strong(_bit_map->lock());
6286 // relinquish the free_list_lock and bitMaplock()
6287 _bit_map->lock()->unlock();
6288 _freelistLock->unlock();
6289 ConcurrentMarkSweepThread::desynchronize(true);
6290 _collector->stopTimer();
6291 if (PrintCMSStatistics != 0) {
6292 _collector->incrementYields();
6293 }
6294
6295 // See the comment in coordinator_yield()
6296 for (unsigned i = 0;
6297 i < CMSYieldSleepCount &&
6298 ConcurrentMarkSweepThread::should_yield() &&
6299 !CMSCollector::foregroundGCIsActive();
6300 ++i) {
6301 os::sleep(Thread::current(), 1, false);
6302 }
6303
6304 ConcurrentMarkSweepThread::synchronize(true);
6305 _freelistLock->lock_without_safepoint_check();
6306 _bit_map->lock()->lock_without_safepoint_check();
6307 _collector->startTimer();
6308 }
6309
6310 ///////////////////////////////////////////////////////////
6311 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6312 // MarkRefsIntoAndScanClosure
6313 ///////////////////////////////////////////////////////////
6314 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6315 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6316 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6317 _span(span),
6318 _bit_map(bit_map),
6319 _work_queue(work_queue),
6320 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6321 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6322 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6323 {
6324 _ref_processor = rp;
6325 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6326 }
6327
6328 // This closure is used to mark refs into the CMS generation at the
6329 // second (final) checkpoint, and to scan and transitively follow
6330 // the unmarked oops. The marks are made in the marking bit map and
6331 // the work_queue is used for keeping the (newly) grey objects during
6332 // the scan phase whence they are also available for stealing by parallel
6333 // threads. Since the marking bit map is shared, updates are
6334 // synchronized (via CAS).
6335 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6336 if (obj != NULL) {
6337 // Ignore mark word because this could be an already marked oop
6338 // that may be chained at the end of the overflow list.
6339 assert(obj->is_oop(true), "expected an oop");
6340 HeapWord* addr = (HeapWord*)obj;
6341 if (_span.contains(addr) &&
6342 !_bit_map->isMarked(addr)) {
6343 // mark bit map (object will become grey):
6344 // It is possible for several threads to be
6345 // trying to "claim" this object concurrently;
6346 // the unique thread that succeeds in marking the
6347 // object first will do the subsequent push on
6348 // to the work queue (or overflow list).
6349 if (_bit_map->par_mark(addr)) {
6350 // push on work_queue (which may not be empty), and trim the
6351 // queue to an appropriate length by applying this closure to
6352 // the oops in the oops popped from the stack (i.e. blacken the
6353 // grey objects)
6354 bool res = _work_queue->push(obj);
6355 assert(res, "Low water mark should be less than capacity?");
6356 trim_queue(_low_water_mark);
6357 } // Else, another thread claimed the object
6358 }
6359 }
6360 }
6361
6362 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6363 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6364
6365 // This closure is used to rescan the marked objects on the dirty cards
6366 // in the mod union table and the card table proper.
6367 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6368 oop p, MemRegion mr) {
6369
6370 size_t size = 0;
6371 HeapWord* addr = (HeapWord*)p;
6372 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6373 assert(_span.contains(addr), "we are scanning the CMS generation");
6374 // check if it's time to yield
6375 if (do_yield_check()) {
6376 // We yielded for some foreground stop-world work,
6377 // and we have been asked to abort this ongoing preclean cycle.
6378 return 0;
6379 }
6380 if (_bitMap->isMarked(addr)) {
6381 // it's marked; is it potentially uninitialized?
6382 if (p->klass_or_null() != NULL) {
6383 // an initialized object; ignore mark word in verification below
6384 // since we are running concurrent with mutators
6385 assert(p->is_oop(true), "should be an oop");
6386 if (p->is_objArray()) {
6387 // objArrays are precisely marked; restrict scanning
6388 // to dirty cards only.
6389 size = CompactibleFreeListSpace::adjustObjectSize(
6390 p->oop_iterate(_scanningClosure, mr));
6391 } else {
6392 // A non-array may have been imprecisely marked; we need
6393 // to scan object in its entirety.
6394 size = CompactibleFreeListSpace::adjustObjectSize(
6395 p->oop_iterate(_scanningClosure));
6396 }
6397 #ifdef ASSERT
6398 size_t direct_size =
6399 CompactibleFreeListSpace::adjustObjectSize(p->size());
6400 assert(size == direct_size, "Inconsistency in size");
6401 assert(size >= 3, "Necessary for Printezis marks to work");
6402 if (!_bitMap->isMarked(addr+1)) {
6403 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6404 } else {
6405 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6406 assert(_bitMap->isMarked(addr+size-1),
6407 "inconsistent Printezis mark");
6408 }
6409 #endif // ASSERT
6410 } else {
6411 // An uninitialized object.
6412 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6413 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6414 size = pointer_delta(nextOneAddr + 1, addr);
6415 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6416 "alignment problem");
6417 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6418 // will dirty the card when the klass pointer is installed in the
6419 // object (signaling the completion of initialization).
6420 }
6421 } else {
6422 // Either a not yet marked object or an uninitialized object
6423 if (p->klass_or_null() == NULL) {
6424 // An uninitialized object, skip to the next card, since
6425 // we may not be able to read its P-bits yet.
6426 assert(size == 0, "Initial value");
6427 } else {
6428 // An object not (yet) reached by marking: we merely need to
6429 // compute its size so as to go look at the next block.
6430 assert(p->is_oop(true), "should be an oop");
6431 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6432 }
6433 }
6434 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6435 return size;
6436 }
6437
6438 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6439 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6440 "CMS thread should hold CMS token");
6441 assert_lock_strong(_freelistLock);
6442 assert_lock_strong(_bitMap->lock());
6443 // relinquish the free_list_lock and bitMaplock()
6444 _bitMap->lock()->unlock();
6445 _freelistLock->unlock();
6446 ConcurrentMarkSweepThread::desynchronize(true);
6447 _collector->stopTimer();
6448 if (PrintCMSStatistics != 0) {
6449 _collector->incrementYields();
6450 }
6451
6452 // See the comment in coordinator_yield()
6453 for (unsigned i = 0; i < CMSYieldSleepCount &&
6454 ConcurrentMarkSweepThread::should_yield() &&
6455 !CMSCollector::foregroundGCIsActive(); ++i) {
6456 os::sleep(Thread::current(), 1, false);
6457 }
6458
6459 ConcurrentMarkSweepThread::synchronize(true);
6460 _freelistLock->lock_without_safepoint_check();
6461 _bitMap->lock()->lock_without_safepoint_check();
6462 _collector->startTimer();
6463 }
6464
6465
6466 //////////////////////////////////////////////////////////////////
6467 // SurvivorSpacePrecleanClosure
6468 //////////////////////////////////////////////////////////////////
6469 // This (single-threaded) closure is used to preclean the oops in
6470 // the survivor spaces.
6471 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6472
6473 HeapWord* addr = (HeapWord*)p;
6474 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6475 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6476 assert(p->klass_or_null() != NULL, "object should be initialized");
6477 // an initialized object; ignore mark word in verification below
6478 // since we are running concurrent with mutators
6479 assert(p->is_oop(true), "should be an oop");
6480 // Note that we do not yield while we iterate over
6481 // the interior oops of p, pushing the relevant ones
6482 // on our marking stack.
6483 size_t size = p->oop_iterate(_scanning_closure);
6484 do_yield_check();
6485 // Observe that below, we do not abandon the preclean
6486 // phase as soon as we should; rather we empty the
6487 // marking stack before returning. This is to satisfy
6488 // some existing assertions. In general, it may be a
6489 // good idea to abort immediately and complete the marking
6490 // from the grey objects at a later time.
6491 while (!_mark_stack->isEmpty()) {
6492 oop new_oop = _mark_stack->pop();
6493 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6494 assert(_bit_map->isMarked((HeapWord*)new_oop),
6495 "only grey objects on this stack");
6496 // iterate over the oops in this oop, marking and pushing
6497 // the ones in CMS heap (i.e. in _span).
6498 new_oop->oop_iterate(_scanning_closure);
6499 // check if it's time to yield
6500 do_yield_check();
6501 }
6502 unsigned int after_count =
6503 GenCollectedHeap::heap()->total_collections();
6504 bool abort = (_before_count != after_count) ||
6505 _collector->should_abort_preclean();
6506 return abort ? 0 : size;
6507 }
6508
6509 void SurvivorSpacePrecleanClosure::do_yield_work() {
6510 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6511 "CMS thread should hold CMS token");
6512 assert_lock_strong(_bit_map->lock());
6513 // Relinquish the bit map lock
6514 _bit_map->lock()->unlock();
6515 ConcurrentMarkSweepThread::desynchronize(true);
6516 _collector->stopTimer();
6517 if (PrintCMSStatistics != 0) {
6518 _collector->incrementYields();
6519 }
6520
6521 // See the comment in coordinator_yield()
6522 for (unsigned i = 0; i < CMSYieldSleepCount &&
6523 ConcurrentMarkSweepThread::should_yield() &&
6524 !CMSCollector::foregroundGCIsActive(); ++i) {
6525 os::sleep(Thread::current(), 1, false);
6526 }
6527
6528 ConcurrentMarkSweepThread::synchronize(true);
6529 _bit_map->lock()->lock_without_safepoint_check();
6530 _collector->startTimer();
6531 }
6532
6533 // This closure is used to rescan the marked objects on the dirty cards
6534 // in the mod union table and the card table proper. In the parallel
6535 // case, although the bitMap is shared, we do a single read so the
6536 // isMarked() query is "safe".
6537 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6538 // Ignore mark word because we are running concurrent with mutators
6539 assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
6540 HeapWord* addr = (HeapWord*)p;
6541 assert(_span.contains(addr), "we are scanning the CMS generation");
6542 bool is_obj_array = false;
6543 #ifdef ASSERT
6544 if (!_parallel) {
6545 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6546 assert(_collector->overflow_list_is_empty(),
6547 "overflow list should be empty");
6548
6549 }
6550 #endif // ASSERT
6551 if (_bit_map->isMarked(addr)) {
6552 // Obj arrays are precisely marked, non-arrays are not;
6553 // so we scan objArrays precisely and non-arrays in their
6554 // entirety.
6555 if (p->is_objArray()) {
6556 is_obj_array = true;
6557 if (_parallel) {
6558 p->oop_iterate(_par_scan_closure, mr);
6559 } else {
6560 p->oop_iterate(_scan_closure, mr);
6561 }
6562 } else {
6563 if (_parallel) {
6564 p->oop_iterate(_par_scan_closure);
6565 } else {
6566 p->oop_iterate(_scan_closure);
6567 }
6568 }
6569 }
6570 #ifdef ASSERT
6571 if (!_parallel) {
6572 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6573 assert(_collector->overflow_list_is_empty(),
6574 "overflow list should be empty");
6575
6576 }
6577 #endif // ASSERT
6578 return is_obj_array;
6579 }
6580
6581 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6582 MemRegion span,
6583 CMSBitMap* bitMap, CMSMarkStack* markStack,
6584 bool should_yield, bool verifying):
6585 _collector(collector),
6586 _span(span),
6587 _bitMap(bitMap),
6588 _mut(&collector->_modUnionTable),
6589 _markStack(markStack),
6590 _yield(should_yield),
6591 _skipBits(0)
6592 {
6593 assert(_markStack->isEmpty(), "stack should be empty");
6594 _finger = _bitMap->startWord();
6595 _threshold = _finger;
6596 assert(_collector->_restart_addr == NULL, "Sanity check");
6597 assert(_span.contains(_finger), "Out of bounds _finger?");
6598 DEBUG_ONLY(_verifying = verifying;)
6599 }
6600
6601 void MarkFromRootsClosure::reset(HeapWord* addr) {
6602 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6603 assert(_span.contains(addr), "Out of bounds _finger?");
6604 _finger = addr;
6605 _threshold = (HeapWord*)round_to(
6606 (intptr_t)_finger, CardTableModRefBS::card_size);
6607 }
6608
6609 // Should revisit to see if this should be restructured for
6610 // greater efficiency.
6611 bool MarkFromRootsClosure::do_bit(size_t offset) {
6612 if (_skipBits > 0) {
6613 _skipBits--;
6614 return true;
6615 }
6616 // convert offset into a HeapWord*
6617 HeapWord* addr = _bitMap->startWord() + offset;
6618 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6619 "address out of range");
6620 assert(_bitMap->isMarked(addr), "tautology");
6621 if (_bitMap->isMarked(addr+1)) {
6622 // this is an allocated but not yet initialized object
6623 assert(_skipBits == 0, "tautology");
6624 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6625 oop p = oop(addr);
6626 if (p->klass_or_null() == NULL) {
6627 DEBUG_ONLY(if (!_verifying) {)
6628 // We re-dirty the cards on which this object lies and increase
6629 // the _threshold so that we'll come back to scan this object
6630 // during the preclean or remark phase. (CMSCleanOnEnter)
6631 if (CMSCleanOnEnter) {
6632 size_t sz = _collector->block_size_using_printezis_bits(addr);
6633 HeapWord* end_card_addr = (HeapWord*)round_to(
6634 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6635 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6636 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6637 // Bump _threshold to end_card_addr; note that
6638 // _threshold cannot possibly exceed end_card_addr, anyhow.
6639 // This prevents future clearing of the card as the scan proceeds
6640 // to the right.
6641 assert(_threshold <= end_card_addr,
6642 "Because we are just scanning into this object");
6643 if (_threshold < end_card_addr) {
6644 _threshold = end_card_addr;
6645 }
6646 if (p->klass_or_null() != NULL) {
6647 // Redirty the range of cards...
6648 _mut->mark_range(redirty_range);
6649 } // ...else the setting of klass will dirty the card anyway.
6650 }
6651 DEBUG_ONLY(})
6652 return true;
6653 }
6654 }
6655 scanOopsInOop(addr);
6656 return true;
6657 }
6658
6659 // We take a break if we've been at this for a while,
6660 // so as to avoid monopolizing the locks involved.
6661 void MarkFromRootsClosure::do_yield_work() {
6662 // First give up the locks, then yield, then re-lock
6663 // We should probably use a constructor/destructor idiom to
6664 // do this unlock/lock or modify the MutexUnlocker class to
6665 // serve our purpose. XXX
6666 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6667 "CMS thread should hold CMS token");
6668 assert_lock_strong(_bitMap->lock());
6669 _bitMap->lock()->unlock();
6670 ConcurrentMarkSweepThread::desynchronize(true);
6671 _collector->stopTimer();
6672 if (PrintCMSStatistics != 0) {
6673 _collector->incrementYields();
6674 }
6675
6676 // See the comment in coordinator_yield()
6677 for (unsigned i = 0; i < CMSYieldSleepCount &&
6678 ConcurrentMarkSweepThread::should_yield() &&
6679 !CMSCollector::foregroundGCIsActive(); ++i) {
6680 os::sleep(Thread::current(), 1, false);
6681 }
6682
6683 ConcurrentMarkSweepThread::synchronize(true);
6684 _bitMap->lock()->lock_without_safepoint_check();
6685 _collector->startTimer();
6686 }
6687
6688 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6689 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6690 assert(_markStack->isEmpty(),
6691 "should drain stack to limit stack usage");
6692 // convert ptr to an oop preparatory to scanning
6693 oop obj = oop(ptr);
6694 // Ignore mark word in verification below, since we
6695 // may be running concurrent with mutators.
6696 assert(obj->is_oop(true), "should be an oop");
6697 assert(_finger <= ptr, "_finger runneth ahead");
6698 // advance the finger to right end of this object
6699 _finger = ptr + obj->size();
6700 assert(_finger > ptr, "we just incremented it above");
6701 // On large heaps, it may take us some time to get through
6702 // the marking phase. During
6703 // this time it's possible that a lot of mutations have
6704 // accumulated in the card table and the mod union table --
6705 // these mutation records are redundant until we have
6706 // actually traced into the corresponding card.
6707 // Here, we check whether advancing the finger would make
6708 // us cross into a new card, and if so clear corresponding
6709 // cards in the MUT (preclean them in the card-table in the
6710 // future).
6711
6712 DEBUG_ONLY(if (!_verifying) {)
6713 // The clean-on-enter optimization is disabled by default,
6714 // until we fix 6178663.
6715 if (CMSCleanOnEnter && (_finger > _threshold)) {
6716 // [_threshold, _finger) represents the interval
6717 // of cards to be cleared in MUT (or precleaned in card table).
6718 // The set of cards to be cleared is all those that overlap
6719 // with the interval [_threshold, _finger); note that
6720 // _threshold is always kept card-aligned but _finger isn't
6721 // always card-aligned.
6722 HeapWord* old_threshold = _threshold;
6723 assert(old_threshold == (HeapWord*)round_to(
6724 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6725 "_threshold should always be card-aligned");
6726 _threshold = (HeapWord*)round_to(
6727 (intptr_t)_finger, CardTableModRefBS::card_size);
6728 MemRegion mr(old_threshold, _threshold);
6729 assert(!mr.is_empty(), "Control point invariant");
6730 assert(_span.contains(mr), "Should clear within span");
6731 _mut->clear_range(mr);
6732 }
6733 DEBUG_ONLY(})
6734 // Note: the finger doesn't advance while we drain
6735 // the stack below.
6736 PushOrMarkClosure pushOrMarkClosure(_collector,
6737 _span, _bitMap, _markStack,
6738 _finger, this);
6739 bool res = _markStack->push(obj);
6740 assert(res, "Empty non-zero size stack should have space for single push");
6741 while (!_markStack->isEmpty()) {
6742 oop new_oop = _markStack->pop();
6743 // Skip verifying header mark word below because we are
6744 // running concurrent with mutators.
6745 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6746 // now scan this oop's oops
6747 new_oop->oop_iterate(&pushOrMarkClosure);
6748 do_yield_check();
6749 }
6750 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6751 }
6752
6753 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6754 CMSCollector* collector, MemRegion span,
6755 CMSBitMap* bit_map,
6756 OopTaskQueue* work_queue,
6757 CMSMarkStack* overflow_stack):
6758 _collector(collector),
6759 _whole_span(collector->_span),
6760 _span(span),
6761 _bit_map(bit_map),
6762 _mut(&collector->_modUnionTable),
6763 _work_queue(work_queue),
6764 _overflow_stack(overflow_stack),
6765 _skip_bits(0),
6766 _task(task)
6767 {
6768 assert(_work_queue->size() == 0, "work_queue should be empty");
6769 _finger = span.start();
6770 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6771 assert(_span.contains(_finger), "Out of bounds _finger?");
6772 }
6773
6774 // Should revisit to see if this should be restructured for
6775 // greater efficiency.
6776 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6777 if (_skip_bits > 0) {
6778 _skip_bits--;
6779 return true;
6780 }
6781 // convert offset into a HeapWord*
6782 HeapWord* addr = _bit_map->startWord() + offset;
6783 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6784 "address out of range");
6785 assert(_bit_map->isMarked(addr), "tautology");
6786 if (_bit_map->isMarked(addr+1)) {
6787 // this is an allocated object that might not yet be initialized
6788 assert(_skip_bits == 0, "tautology");
6789 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6790 oop p = oop(addr);
6791 if (p->klass_or_null() == NULL) {
6792 // in the case of Clean-on-Enter optimization, redirty card
6793 // and avoid clearing card by increasing the threshold.
6794 return true;
6795 }
6796 }
6797 scan_oops_in_oop(addr);
6798 return true;
6799 }
6800
6801 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6802 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6803 // Should we assert that our work queue is empty or
6804 // below some drain limit?
6805 assert(_work_queue->size() == 0,
6806 "should drain stack to limit stack usage");
6807 // convert ptr to an oop preparatory to scanning
6808 oop obj = oop(ptr);
6809 // Ignore mark word in verification below, since we
6810 // may be running concurrent with mutators.
6811 assert(obj->is_oop(true), "should be an oop");
6812 assert(_finger <= ptr, "_finger runneth ahead");
6813 // advance the finger to right end of this object
6814 _finger = ptr + obj->size();
6815 assert(_finger > ptr, "we just incremented it above");
6816 // On large heaps, it may take us some time to get through
6817 // the marking phase. During
6818 // this time it's possible that a lot of mutations have
6819 // accumulated in the card table and the mod union table --
6820 // these mutation records are redundant until we have
6821 // actually traced into the corresponding card.
6822 // Here, we check whether advancing the finger would make
6823 // us cross into a new card, and if so clear corresponding
6824 // cards in the MUT (preclean them in the card-table in the
6825 // future).
6826
6827 // The clean-on-enter optimization is disabled by default,
6828 // until we fix 6178663.
6829 if (CMSCleanOnEnter && (_finger > _threshold)) {
6830 // [_threshold, _finger) represents the interval
6831 // of cards to be cleared in MUT (or precleaned in card table).
6832 // The set of cards to be cleared is all those that overlap
6833 // with the interval [_threshold, _finger); note that
6834 // _threshold is always kept card-aligned but _finger isn't
6835 // always card-aligned.
6836 HeapWord* old_threshold = _threshold;
6837 assert(old_threshold == (HeapWord*)round_to(
6838 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6839 "_threshold should always be card-aligned");
6840 _threshold = (HeapWord*)round_to(
6841 (intptr_t)_finger, CardTableModRefBS::card_size);
6842 MemRegion mr(old_threshold, _threshold);
6843 assert(!mr.is_empty(), "Control point invariant");
6844 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6845 _mut->clear_range(mr);
6846 }
6847
6848 // Note: the local finger doesn't advance while we drain
6849 // the stack below, but the global finger sure can and will.
6850 HeapWord** gfa = _task->global_finger_addr();
6851 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6852 _span, _bit_map,
6853 _work_queue,
6854 _overflow_stack,
6855 _finger,
6856 gfa, this);
6857 bool res = _work_queue->push(obj); // overflow could occur here
6858 assert(res, "Will hold once we use workqueues");
6859 while (true) {
6860 oop new_oop;
6861 if (!_work_queue->pop_local(new_oop)) {
6862 // We emptied our work_queue; check if there's stuff that can
6863 // be gotten from the overflow stack.
6864 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6865 _overflow_stack, _work_queue)) {
6866 do_yield_check();
6867 continue;
6868 } else { // done
6869 break;
6870 }
6871 }
6872 // Skip verifying header mark word below because we are
6873 // running concurrent with mutators.
6874 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6875 // now scan this oop's oops
6876 new_oop->oop_iterate(&pushOrMarkClosure);
6877 do_yield_check();
6878 }
6879 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6880 }
6881
6882 // Yield in response to a request from VM Thread or
6883 // from mutators.
6884 void Par_MarkFromRootsClosure::do_yield_work() {
6885 assert(_task != NULL, "sanity");
6886 _task->yield();
6887 }
6888
6889 // A variant of the above used for verifying CMS marking work.
6890 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6891 MemRegion span,
6892 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6893 CMSMarkStack* mark_stack):
6894 _collector(collector),
6895 _span(span),
6896 _verification_bm(verification_bm),
6897 _cms_bm(cms_bm),
6898 _mark_stack(mark_stack),
6899 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6900 mark_stack)
6901 {
6902 assert(_mark_stack->isEmpty(), "stack should be empty");
6903 _finger = _verification_bm->startWord();
6904 assert(_collector->_restart_addr == NULL, "Sanity check");
6905 assert(_span.contains(_finger), "Out of bounds _finger?");
6906 }
6907
6908 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6909 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6910 assert(_span.contains(addr), "Out of bounds _finger?");
6911 _finger = addr;
6912 }
6913
6914 // Should revisit to see if this should be restructured for
6915 // greater efficiency.
6916 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6917 // convert offset into a HeapWord*
6918 HeapWord* addr = _verification_bm->startWord() + offset;
6919 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6920 "address out of range");
6921 assert(_verification_bm->isMarked(addr), "tautology");
6922 assert(_cms_bm->isMarked(addr), "tautology");
6923
6924 assert(_mark_stack->isEmpty(),
6925 "should drain stack to limit stack usage");
6926 // convert addr to an oop preparatory to scanning
6927 oop obj = oop(addr);
6928 assert(obj->is_oop(), "should be an oop");
6929 assert(_finger <= addr, "_finger runneth ahead");
6930 // advance the finger to right end of this object
6931 _finger = addr + obj->size();
6932 assert(_finger > addr, "we just incremented it above");
6933 // Note: the finger doesn't advance while we drain
6934 // the stack below.
6935 bool res = _mark_stack->push(obj);
6936 assert(res, "Empty non-zero size stack should have space for single push");
6937 while (!_mark_stack->isEmpty()) {
6938 oop new_oop = _mark_stack->pop();
6939 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6940 // now scan this oop's oops
6941 new_oop->oop_iterate(&_pam_verify_closure);
6942 }
6943 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6944 return true;
6945 }
6946
6947 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6948 CMSCollector* collector, MemRegion span,
6949 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6950 CMSMarkStack* mark_stack):
6951 MetadataAwareOopClosure(collector->ref_processor()),
6952 _collector(collector),
6953 _span(span),
6954 _verification_bm(verification_bm),
6955 _cms_bm(cms_bm),
6956 _mark_stack(mark_stack)
6957 { }
6958
6959 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6960 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6961
6962 // Upon stack overflow, we discard (part of) the stack,
6963 // remembering the least address amongst those discarded
6964 // in CMSCollector's _restart_address.
6965 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6966 // Remember the least grey address discarded
6967 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6968 _collector->lower_restart_addr(ra);
6969 _mark_stack->reset(); // discard stack contents
6970 _mark_stack->expand(); // expand the stack if possible
6971 }
6972
6973 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6974 assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
6975 HeapWord* addr = (HeapWord*)obj;
6976 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6977 // Oop lies in _span and isn't yet grey or black
6978 _verification_bm->mark(addr); // now grey
6979 if (!_cms_bm->isMarked(addr)) {
6980 oop(addr)->print();
6981 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
6982 addr);
6983 fatal("... aborting");
6984 }
6985
6986 if (!_mark_stack->push(obj)) { // stack overflow
6987 if (PrintCMSStatistics != 0) {
6988 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6989 SIZE_FORMAT, _mark_stack->capacity());
6990 }
6991 assert(_mark_stack->isFull(), "Else push should have succeeded");
6992 handle_stack_overflow(addr);
6993 }
6994 // anything including and to the right of _finger
6995 // will be scanned as we iterate over the remainder of the
6996 // bit map
6997 }
6998 }
6999
7000 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7001 MemRegion span,
7002 CMSBitMap* bitMap, CMSMarkStack* markStack,
7003 HeapWord* finger, MarkFromRootsClosure* parent) :
7004 MetadataAwareOopClosure(collector->ref_processor()),
7005 _collector(collector),
7006 _span(span),
7007 _bitMap(bitMap),
7008 _markStack(markStack),
7009 _finger(finger),
7010 _parent(parent)
7011 { }
7012
7013 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7014 MemRegion span,
7015 CMSBitMap* bit_map,
7016 OopTaskQueue* work_queue,
7017 CMSMarkStack* overflow_stack,
7018 HeapWord* finger,
7019 HeapWord** global_finger_addr,
7020 Par_MarkFromRootsClosure* parent) :
7021 MetadataAwareOopClosure(collector->ref_processor()),
7022 _collector(collector),
7023 _whole_span(collector->_span),
7024 _span(span),
7025 _bit_map(bit_map),
7026 _work_queue(work_queue),
7027 _overflow_stack(overflow_stack),
7028 _finger(finger),
7029 _global_finger_addr(global_finger_addr),
7030 _parent(parent)
7031 { }
7032
7033 // Assumes thread-safe access by callers, who are
7034 // responsible for mutual exclusion.
7035 void CMSCollector::lower_restart_addr(HeapWord* low) {
7036 assert(_span.contains(low), "Out of bounds addr");
7037 if (_restart_addr == NULL) {
7038 _restart_addr = low;
7039 } else {
7040 _restart_addr = MIN2(_restart_addr, low);
7041 }
7042 }
7043
7044 // Upon stack overflow, we discard (part of) the stack,
7045 // remembering the least address amongst those discarded
7046 // in CMSCollector's _restart_address.
7047 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7048 // Remember the least grey address discarded
7049 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7050 _collector->lower_restart_addr(ra);
7051 _markStack->reset(); // discard stack contents
7052 _markStack->expand(); // expand the stack if possible
7053 }
7054
7055 // Upon stack overflow, we discard (part of) the stack,
7056 // remembering the least address amongst those discarded
7057 // in CMSCollector's _restart_address.
7058 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7059 // We need to do this under a mutex to prevent other
7060 // workers from interfering with the work done below.
7061 MutexLockerEx ml(_overflow_stack->par_lock(),
7062 Mutex::_no_safepoint_check_flag);
7063 // Remember the least grey address discarded
7064 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7065 _collector->lower_restart_addr(ra);
7066 _overflow_stack->reset(); // discard stack contents
7067 _overflow_stack->expand(); // expand the stack if possible
7068 }
7069
7070 void PushOrMarkClosure::do_oop(oop obj) {
7071 // Ignore mark word because we are running concurrent with mutators.
7072 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7073 HeapWord* addr = (HeapWord*)obj;
7074 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7075 // Oop lies in _span and isn't yet grey or black
7076 _bitMap->mark(addr); // now grey
7077 if (addr < _finger) {
7078 // the bit map iteration has already either passed, or
7079 // sampled, this bit in the bit map; we'll need to
7080 // use the marking stack to scan this oop's oops.
7081 bool simulate_overflow = false;
7082 NOT_PRODUCT(
7083 if (CMSMarkStackOverflowALot &&
7084 _collector->simulate_overflow()) {
7085 // simulate a stack overflow
7086 simulate_overflow = true;
7087 }
7088 )
7089 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7090 if (PrintCMSStatistics != 0) {
7091 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7092 SIZE_FORMAT, _markStack->capacity());
7093 }
7094 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7095 handle_stack_overflow(addr);
7096 }
7097 }
7098 // anything including and to the right of _finger
7099 // will be scanned as we iterate over the remainder of the
7100 // bit map
7101 do_yield_check();
7102 }
7103 }
7104
7105 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7106 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7107
7108 void Par_PushOrMarkClosure::do_oop(oop obj) {
7109 // Ignore mark word because we are running concurrent with mutators.
7110 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7111 HeapWord* addr = (HeapWord*)obj;
7112 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7113 // Oop lies in _span and isn't yet grey or black
7114 // We read the global_finger (volatile read) strictly after marking oop
7115 bool res = _bit_map->par_mark(addr); // now grey
7116 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7117 // Should we push this marked oop on our stack?
7118 // -- if someone else marked it, nothing to do
7119 // -- if target oop is above global finger nothing to do
7120 // -- if target oop is in chunk and above local finger
7121 // then nothing to do
7122 // -- else push on work queue
7123 if ( !res // someone else marked it, they will deal with it
7124 || (addr >= *gfa) // will be scanned in a later task
7125 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7126 return;
7127 }
7128 // the bit map iteration has already either passed, or
7129 // sampled, this bit in the bit map; we'll need to
7130 // use the marking stack to scan this oop's oops.
7131 bool simulate_overflow = false;
7132 NOT_PRODUCT(
7133 if (CMSMarkStackOverflowALot &&
7134 _collector->simulate_overflow()) {
7135 // simulate a stack overflow
7136 simulate_overflow = true;
7137 }
7138 )
7139 if (simulate_overflow ||
7140 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7141 // stack overflow
7142 if (PrintCMSStatistics != 0) {
7143 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7144 SIZE_FORMAT, _overflow_stack->capacity());
7145 }
7146 // We cannot assert that the overflow stack is full because
7147 // it may have been emptied since.
7148 assert(simulate_overflow ||
7149 _work_queue->size() == _work_queue->max_elems(),
7150 "Else push should have succeeded");
7151 handle_stack_overflow(addr);
7152 }
7153 do_yield_check();
7154 }
7155 }
7156
7157 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7158 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7159
7160 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7161 MemRegion span,
7162 ReferenceProcessor* rp,
7163 CMSBitMap* bit_map,
7164 CMSBitMap* mod_union_table,
7165 CMSMarkStack* mark_stack,
7166 bool concurrent_precleaning):
7167 MetadataAwareOopClosure(rp),
7168 _collector(collector),
7169 _span(span),
7170 _bit_map(bit_map),
7171 _mod_union_table(mod_union_table),
7172 _mark_stack(mark_stack),
7173 _concurrent_precleaning(concurrent_precleaning)
7174 {
7175 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7176 }
7177
7178 // Grey object rescan during pre-cleaning and second checkpoint phases --
7179 // the non-parallel version (the parallel version appears further below.)
7180 void PushAndMarkClosure::do_oop(oop obj) {
7181 // Ignore mark word verification. If during concurrent precleaning,
7182 // the object monitor may be locked. If during the checkpoint
7183 // phases, the object may already have been reached by a different
7184 // path and may be at the end of the global overflow list (so
7185 // the mark word may be NULL).
7186 assert(obj->is_oop_or_null(true /* ignore mark word */),
7187 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7188 HeapWord* addr = (HeapWord*)obj;
7189 // Check if oop points into the CMS generation
7190 // and is not marked
7191 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7192 // a white object ...
7193 _bit_map->mark(addr); // ... now grey
7194 // push on the marking stack (grey set)
7195 bool simulate_overflow = false;
7196 NOT_PRODUCT(
7197 if (CMSMarkStackOverflowALot &&
7198 _collector->simulate_overflow()) {
7199 // simulate a stack overflow
7200 simulate_overflow = true;
7201 }
7202 )
7203 if (simulate_overflow || !_mark_stack->push(obj)) {
7204 if (_concurrent_precleaning) {
7205 // During precleaning we can just dirty the appropriate card(s)
7206 // in the mod union table, thus ensuring that the object remains
7207 // in the grey set and continue. In the case of object arrays
7208 // we need to dirty all of the cards that the object spans,
7209 // since the rescan of object arrays will be limited to the
7210 // dirty cards.
7211 // Note that no one can be interfering with us in this action
7212 // of dirtying the mod union table, so no locking or atomics
7213 // are required.
7214 if (obj->is_objArray()) {
7215 size_t sz = obj->size();
7216 HeapWord* end_card_addr = (HeapWord*)round_to(
7217 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7218 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7219 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7220 _mod_union_table->mark_range(redirty_range);
7221 } else {
7222 _mod_union_table->mark(addr);
7223 }
7224 _collector->_ser_pmc_preclean_ovflw++;
7225 } else {
7226 // During the remark phase, we need to remember this oop
7227 // in the overflow list.
7228 _collector->push_on_overflow_list(obj);
7229 _collector->_ser_pmc_remark_ovflw++;
7230 }
7231 }
7232 }
7233 }
7234
7235 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7236 MemRegion span,
7237 ReferenceProcessor* rp,
7238 CMSBitMap* bit_map,
7239 OopTaskQueue* work_queue):
7240 MetadataAwareOopClosure(rp),
7241 _collector(collector),
7242 _span(span),
7243 _bit_map(bit_map),
7244 _work_queue(work_queue)
7245 {
7246 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7247 }
7248
7249 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7250 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7251
7252 // Grey object rescan during second checkpoint phase --
7253 // the parallel version.
7254 void Par_PushAndMarkClosure::do_oop(oop obj) {
7255 // In the assert below, we ignore the mark word because
7256 // this oop may point to an already visited object that is
7257 // on the overflow stack (in which case the mark word has
7258 // been hijacked for chaining into the overflow stack --
7259 // if this is the last object in the overflow stack then
7260 // its mark word will be NULL). Because this object may
7261 // have been subsequently popped off the global overflow
7262 // stack, and the mark word possibly restored to the prototypical
7263 // value, by the time we get to examined this failing assert in
7264 // the debugger, is_oop_or_null(false) may subsequently start
7265 // to hold.
7266 assert(obj->is_oop_or_null(true),
7267 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7268 HeapWord* addr = (HeapWord*)obj;
7269 // Check if oop points into the CMS generation
7270 // and is not marked
7271 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7272 // a white object ...
7273 // If we manage to "claim" the object, by being the
7274 // first thread to mark it, then we push it on our
7275 // marking stack
7276 if (_bit_map->par_mark(addr)) { // ... now grey
7277 // push on work queue (grey set)
7278 bool simulate_overflow = false;
7279 NOT_PRODUCT(
7280 if (CMSMarkStackOverflowALot &&
7281 _collector->par_simulate_overflow()) {
7282 // simulate a stack overflow
7283 simulate_overflow = true;
7284 }
7285 )
7286 if (simulate_overflow || !_work_queue->push(obj)) {
7287 _collector->par_push_on_overflow_list(obj);
7288 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7289 }
7290 } // Else, some other thread got there first
7291 }
7292 }
7293
7294 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7295 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7296
7297 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7298 Mutex* bml = _collector->bitMapLock();
7299 assert_lock_strong(bml);
7300 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7301 "CMS thread should hold CMS token");
7302
7303 bml->unlock();
7304 ConcurrentMarkSweepThread::desynchronize(true);
7305
7306 _collector->stopTimer();
7307 if (PrintCMSStatistics != 0) {
7308 _collector->incrementYields();
7309 }
7310
7311 // See the comment in coordinator_yield()
7312 for (unsigned i = 0; i < CMSYieldSleepCount &&
7313 ConcurrentMarkSweepThread::should_yield() &&
7314 !CMSCollector::foregroundGCIsActive(); ++i) {
7315 os::sleep(Thread::current(), 1, false);
7316 }
7317
7318 ConcurrentMarkSweepThread::synchronize(true);
7319 bml->lock();
7320
7321 _collector->startTimer();
7322 }
7323
7324 bool CMSPrecleanRefsYieldClosure::should_return() {
7325 if (ConcurrentMarkSweepThread::should_yield()) {
7326 do_yield_work();
7327 }
7328 return _collector->foregroundGCIsActive();
7329 }
7330
7331 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7332 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7333 "mr should be aligned to start at a card boundary");
7334 // We'd like to assert:
7335 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7336 // "mr should be a range of cards");
7337 // However, that would be too strong in one case -- the last
7338 // partition ends at _unallocated_block which, in general, can be
7339 // an arbitrary boundary, not necessarily card aligned.
7340 if (PrintCMSStatistics != 0) {
7341 _num_dirty_cards +=
7342 mr.word_size()/CardTableModRefBS::card_size_in_words;
7343 }
7344 _space->object_iterate_mem(mr, &_scan_cl);
7345 }
7346
7347 SweepClosure::SweepClosure(CMSCollector* collector,
7348 ConcurrentMarkSweepGeneration* g,
7349 CMSBitMap* bitMap, bool should_yield) :
7350 _collector(collector),
7351 _g(g),
7352 _sp(g->cmsSpace()),
7353 _limit(_sp->sweep_limit()),
7354 _freelistLock(_sp->freelistLock()),
7355 _bitMap(bitMap),
7356 _yield(should_yield),
7357 _inFreeRange(false), // No free range at beginning of sweep
7358 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7359 _lastFreeRangeCoalesced(false),
7360 _freeFinger(g->used_region().start())
7361 {
7362 NOT_PRODUCT(
7363 _numObjectsFreed = 0;
7364 _numWordsFreed = 0;
7365 _numObjectsLive = 0;
7366 _numWordsLive = 0;
7367 _numObjectsAlreadyFree = 0;
7368 _numWordsAlreadyFree = 0;
7369 _last_fc = NULL;
7370
7371 _sp->initializeIndexedFreeListArrayReturnedBytes();
7372 _sp->dictionary()->initialize_dict_returned_bytes();
7373 )
7374 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7375 "sweep _limit out of bounds");
7376 if (CMSTraceSweeper) {
7377 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7378 _limit);
7379 }
7380 }
7381
7382 void SweepClosure::print_on(outputStream* st) const {
7383 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7384 _sp->bottom(), _sp->end());
7385 tty->print_cr("_limit = " PTR_FORMAT, _limit);
7386 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
7387 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
7388 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7389 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7390 }
7391
7392 #ifndef PRODUCT
7393 // Assertion checking only: no useful work in product mode --
7394 // however, if any of the flags below become product flags,
7395 // you may need to review this code to see if it needs to be
7396 // enabled in product mode.
7397 SweepClosure::~SweepClosure() {
7398 assert_lock_strong(_freelistLock);
7399 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7400 "sweep _limit out of bounds");
7401 if (inFreeRange()) {
7402 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7403 print();
7404 ShouldNotReachHere();
7405 }
7406 if (Verbose && PrintGC) {
7407 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7408 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7409 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7410 SIZE_FORMAT" bytes "
7411 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7412 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7413 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7414 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7415 * sizeof(HeapWord);
7416 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7417
7418 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7419 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7420 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7421 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7422 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7423 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7424 indexListReturnedBytes);
7425 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7426 dict_returned_bytes);
7427 }
7428 }
7429 if (CMSTraceSweeper) {
7430 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7431 _limit);
7432 }
7433 }
7434 #endif // PRODUCT
7435
7436 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7437 bool freeRangeInFreeLists) {
7438 if (CMSTraceSweeper) {
7439 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7440 freeFinger, freeRangeInFreeLists);
7441 }
7442 assert(!inFreeRange(), "Trampling existing free range");
7443 set_inFreeRange(true);
7444 set_lastFreeRangeCoalesced(false);
7445
7446 set_freeFinger(freeFinger);
7447 set_freeRangeInFreeLists(freeRangeInFreeLists);
7448 if (CMSTestInFreeList) {
7449 if (freeRangeInFreeLists) {
7450 FreeChunk* fc = (FreeChunk*) freeFinger;
7451 assert(fc->is_free(), "A chunk on the free list should be free.");
7452 assert(fc->size() > 0, "Free range should have a size");
7453 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7454 }
7455 }
7456 }
7457
7458 // Note that the sweeper runs concurrently with mutators. Thus,
7459 // it is possible for direct allocation in this generation to happen
7460 // in the middle of the sweep. Note that the sweeper also coalesces
7461 // contiguous free blocks. Thus, unless the sweeper and the allocator
7462 // synchronize appropriately freshly allocated blocks may get swept up.
7463 // This is accomplished by the sweeper locking the free lists while
7464 // it is sweeping. Thus blocks that are determined to be free are
7465 // indeed free. There is however one additional complication:
7466 // blocks that have been allocated since the final checkpoint and
7467 // mark, will not have been marked and so would be treated as
7468 // unreachable and swept up. To prevent this, the allocator marks
7469 // the bit map when allocating during the sweep phase. This leads,
7470 // however, to a further complication -- objects may have been allocated
7471 // but not yet initialized -- in the sense that the header isn't yet
7472 // installed. The sweeper can not then determine the size of the block
7473 // in order to skip over it. To deal with this case, we use a technique
7474 // (due to Printezis) to encode such uninitialized block sizes in the
7475 // bit map. Since the bit map uses a bit per every HeapWord, but the
7476 // CMS generation has a minimum object size of 3 HeapWords, it follows
7477 // that "normal marks" won't be adjacent in the bit map (there will
7478 // always be at least two 0 bits between successive 1 bits). We make use
7479 // of these "unused" bits to represent uninitialized blocks -- the bit
7480 // corresponding to the start of the uninitialized object and the next
7481 // bit are both set. Finally, a 1 bit marks the end of the object that
7482 // started with the two consecutive 1 bits to indicate its potentially
7483 // uninitialized state.
7484
7485 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7486 FreeChunk* fc = (FreeChunk*)addr;
7487 size_t res;
7488
7489 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7490 // than "addr == _limit" because although _limit was a block boundary when
7491 // we started the sweep, it may no longer be one because heap expansion
7492 // may have caused us to coalesce the block ending at the address _limit
7493 // with a newly expanded chunk (this happens when _limit was set to the
7494 // previous _end of the space), so we may have stepped past _limit:
7495 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7496 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7497 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7498 "sweep _limit out of bounds");
7499 assert(addr < _sp->end(), "addr out of bounds");
7500 // Flush any free range we might be holding as a single
7501 // coalesced chunk to the appropriate free list.
7502 if (inFreeRange()) {
7503 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7504 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
7505 flush_cur_free_chunk(freeFinger(),
7506 pointer_delta(addr, freeFinger()));
7507 if (CMSTraceSweeper) {
7508 gclog_or_tty->print("Sweep: last chunk: ");
7509 gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
7510 "[coalesced:%d]\n",
7511 freeFinger(), pointer_delta(addr, freeFinger()),
7512 lastFreeRangeCoalesced() ? 1 : 0);
7513 }
7514 }
7515
7516 // help the iterator loop finish
7517 return pointer_delta(_sp->end(), addr);
7518 }
7519
7520 assert(addr < _limit, "sweep invariant");
7521 // check if we should yield
7522 do_yield_check(addr);
7523 if (fc->is_free()) {
7524 // Chunk that is already free
7525 res = fc->size();
7526 do_already_free_chunk(fc);
7527 debug_only(_sp->verifyFreeLists());
7528 // If we flush the chunk at hand in lookahead_and_flush()
7529 // and it's coalesced with a preceding chunk, then the
7530 // process of "mangling" the payload of the coalesced block
7531 // will cause erasure of the size information from the
7532 // (erstwhile) header of all the coalesced blocks but the
7533 // first, so the first disjunct in the assert will not hold
7534 // in that specific case (in which case the second disjunct
7535 // will hold).
7536 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7537 "Otherwise the size info doesn't change at this step");
7538 NOT_PRODUCT(
7539 _numObjectsAlreadyFree++;
7540 _numWordsAlreadyFree += res;
7541 )
7542 NOT_PRODUCT(_last_fc = fc;)
7543 } else if (!_bitMap->isMarked(addr)) {
7544 // Chunk is fresh garbage
7545 res = do_garbage_chunk(fc);
7546 debug_only(_sp->verifyFreeLists());
7547 NOT_PRODUCT(
7548 _numObjectsFreed++;
7549 _numWordsFreed += res;
7550 )
7551 } else {
7552 // Chunk that is alive.
7553 res = do_live_chunk(fc);
7554 debug_only(_sp->verifyFreeLists());
7555 NOT_PRODUCT(
7556 _numObjectsLive++;
7557 _numWordsLive += res;
7558 )
7559 }
7560 return res;
7561 }
7562
7563 // For the smart allocation, record following
7564 // split deaths - a free chunk is removed from its free list because
7565 // it is being split into two or more chunks.
7566 // split birth - a free chunk is being added to its free list because
7567 // a larger free chunk has been split and resulted in this free chunk.
7568 // coal death - a free chunk is being removed from its free list because
7569 // it is being coalesced into a large free chunk.
7570 // coal birth - a free chunk is being added to its free list because
7571 // it was created when two or more free chunks where coalesced into
7572 // this free chunk.
7573 //
7574 // These statistics are used to determine the desired number of free
7575 // chunks of a given size. The desired number is chosen to be relative
7576 // to the end of a CMS sweep. The desired number at the end of a sweep
7577 // is the
7578 // count-at-end-of-previous-sweep (an amount that was enough)
7579 // - count-at-beginning-of-current-sweep (the excess)
7580 // + split-births (gains in this size during interval)
7581 // - split-deaths (demands on this size during interval)
7582 // where the interval is from the end of one sweep to the end of the
7583 // next.
7584 //
7585 // When sweeping the sweeper maintains an accumulated chunk which is
7586 // the chunk that is made up of chunks that have been coalesced. That
7587 // will be termed the left-hand chunk. A new chunk of garbage that
7588 // is being considered for coalescing will be referred to as the
7589 // right-hand chunk.
7590 //
7591 // When making a decision on whether to coalesce a right-hand chunk with
7592 // the current left-hand chunk, the current count vs. the desired count
7593 // of the left-hand chunk is considered. Also if the right-hand chunk
7594 // is near the large chunk at the end of the heap (see
7595 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7596 // left-hand chunk is coalesced.
7597 //
7598 // When making a decision about whether to split a chunk, the desired count
7599 // vs. the current count of the candidate to be split is also considered.
7600 // If the candidate is underpopulated (currently fewer chunks than desired)
7601 // a chunk of an overpopulated (currently more chunks than desired) size may
7602 // be chosen. The "hint" associated with a free list, if non-null, points
7603 // to a free list which may be overpopulated.
7604 //
7605
7606 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7607 const size_t size = fc->size();
7608 // Chunks that cannot be coalesced are not in the
7609 // free lists.
7610 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7611 assert(_sp->verify_chunk_in_free_list(fc),
7612 "free chunk should be in free lists");
7613 }
7614 // a chunk that is already free, should not have been
7615 // marked in the bit map
7616 HeapWord* const addr = (HeapWord*) fc;
7617 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7618 // Verify that the bit map has no bits marked between
7619 // addr and purported end of this block.
7620 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7621
7622 // Some chunks cannot be coalesced under any circumstances.
7623 // See the definition of cantCoalesce().
7624 if (!fc->cantCoalesce()) {
7625 // This chunk can potentially be coalesced.
7626 if (_sp->adaptive_freelists()) {
7627 // All the work is done in
7628 do_post_free_or_garbage_chunk(fc, size);
7629 } else { // Not adaptive free lists
7630 // this is a free chunk that can potentially be coalesced by the sweeper;
7631 if (!inFreeRange()) {
7632 // if the next chunk is a free block that can't be coalesced
7633 // it doesn't make sense to remove this chunk from the free lists
7634 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7635 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
7636 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
7637 nextChunk->is_free() && // ... which is free...
7638 nextChunk->cantCoalesce()) { // ... but can't be coalesced
7639 // nothing to do
7640 } else {
7641 // Potentially the start of a new free range:
7642 // Don't eagerly remove it from the free lists.
7643 // No need to remove it if it will just be put
7644 // back again. (Also from a pragmatic point of view
7645 // if it is a free block in a region that is beyond
7646 // any allocated blocks, an assertion will fail)
7647 // Remember the start of a free run.
7648 initialize_free_range(addr, true);
7649 // end - can coalesce with next chunk
7650 }
7651 } else {
7652 // the midst of a free range, we are coalescing
7653 print_free_block_coalesced(fc);
7654 if (CMSTraceSweeper) {
7655 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
7656 }
7657 // remove it from the free lists
7658 _sp->removeFreeChunkFromFreeLists(fc);
7659 set_lastFreeRangeCoalesced(true);
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 }
7676 }
7677 // Note that if the chunk is not coalescable (the else arm
7678 // below), we unconditionally flush, without needing to do
7679 // a "lookahead," as we do below.
7680 if (inFreeRange()) lookahead_and_flush(fc, size);
7681 } else {
7682 // Code path common to both original and adaptive free lists.
7683
7684 // cant coalesce with previous block; this should be treated
7685 // as the end of a free run if any
7686 if (inFreeRange()) {
7687 // we kicked some butt; time to pick up the garbage
7688 assert(freeFinger() < addr, "freeFinger points too high");
7689 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7690 }
7691 // else, nothing to do, just continue
7692 }
7693 }
7694
7695 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7696 // This is a chunk of garbage. It is not in any free list.
7697 // Add it to a free list or let it possibly be coalesced into
7698 // a larger chunk.
7699 HeapWord* const addr = (HeapWord*) fc;
7700 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7701
7702 if (_sp->adaptive_freelists()) {
7703 // Verify that the bit map has no bits marked between
7704 // addr and purported end of just dead object.
7705 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7706
7707 do_post_free_or_garbage_chunk(fc, size);
7708 } else {
7709 if (!inFreeRange()) {
7710 // start of a new free range
7711 assert(size > 0, "A free range should have a size");
7712 initialize_free_range(addr, false);
7713 } else {
7714 // this will be swept up when we hit the end of the
7715 // free range
7716 if (CMSTraceSweeper) {
7717 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
7718 }
7719 // If the chunk is being coalesced and the current free range is
7720 // in the free lists, remove the current free range so that it
7721 // will be returned to the free lists in its entirety - all
7722 // the coalesced pieces included.
7723 if (freeRangeInFreeLists()) {
7724 FreeChunk* ffc = (FreeChunk*)freeFinger();
7725 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7726 "Size of free range is inconsistent with chunk size.");
7727 if (CMSTestInFreeList) {
7728 assert(_sp->verify_chunk_in_free_list(ffc),
7729 "free range is not in free lists");
7730 }
7731 _sp->removeFreeChunkFromFreeLists(ffc);
7732 set_freeRangeInFreeLists(false);
7733 }
7734 set_lastFreeRangeCoalesced(true);
7735 }
7736 // this will be swept up when we hit the end of the free range
7737
7738 // Verify that the bit map has no bits marked between
7739 // addr and purported end of just dead object.
7740 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7741 }
7742 assert(_limit >= addr + size,
7743 "A freshly garbage chunk can't possibly straddle over _limit");
7744 if (inFreeRange()) lookahead_and_flush(fc, size);
7745 return size;
7746 }
7747
7748 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7749 HeapWord* addr = (HeapWord*) fc;
7750 // The sweeper has just found a live object. Return any accumulated
7751 // left hand chunk to the free lists.
7752 if (inFreeRange()) {
7753 assert(freeFinger() < addr, "freeFinger points too high");
7754 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7755 }
7756
7757 // This object is live: we'd normally expect this to be
7758 // an oop, and like to assert the following:
7759 // assert(oop(addr)->is_oop(), "live block should be an oop");
7760 // However, as we commented above, this may be an object whose
7761 // header hasn't yet been initialized.
7762 size_t size;
7763 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7764 if (_bitMap->isMarked(addr + 1)) {
7765 // Determine the size from the bit map, rather than trying to
7766 // compute it from the object header.
7767 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7768 size = pointer_delta(nextOneAddr + 1, addr);
7769 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7770 "alignment problem");
7771
7772 #ifdef ASSERT
7773 if (oop(addr)->klass_or_null() != NULL) {
7774 // Ignore mark word because we are running concurrent with mutators
7775 assert(oop(addr)->is_oop(true), "live block should be an oop");
7776 assert(size ==
7777 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7778 "P-mark and computed size do not agree");
7779 }
7780 #endif
7781
7782 } else {
7783 // This should be an initialized object that's alive.
7784 assert(oop(addr)->klass_or_null() != NULL,
7785 "Should be an initialized object");
7786 // Ignore mark word because we are running concurrent with mutators
7787 assert(oop(addr)->is_oop(true), "live block should be an oop");
7788 // Verify that the bit map has no bits marked between
7789 // addr and purported end of this block.
7790 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7791 assert(size >= 3, "Necessary for Printezis marks to work");
7792 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7793 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7794 }
7795 return size;
7796 }
7797
7798 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7799 size_t chunkSize) {
7800 // do_post_free_or_garbage_chunk() should only be called in the case
7801 // of the adaptive free list allocator.
7802 const bool fcInFreeLists = fc->is_free();
7803 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
7804 assert((HeapWord*)fc <= _limit, "sweep invariant");
7805 if (CMSTestInFreeList && fcInFreeLists) {
7806 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7807 }
7808
7809 if (CMSTraceSweeper) {
7810 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", fc, chunkSize);
7811 }
7812
7813 HeapWord* const fc_addr = (HeapWord*) fc;
7814
7815 bool coalesce;
7816 const size_t left = pointer_delta(fc_addr, freeFinger());
7817 const size_t right = chunkSize;
7818 switch (FLSCoalescePolicy) {
7819 // numeric value forms a coalition aggressiveness metric
7820 case 0: { // never coalesce
7821 coalesce = false;
7822 break;
7823 }
7824 case 1: { // coalesce if left & right chunks on overpopulated lists
7825 coalesce = _sp->coalOverPopulated(left) &&
7826 _sp->coalOverPopulated(right);
7827 break;
7828 }
7829 case 2: { // coalesce if left chunk on overpopulated list (default)
7830 coalesce = _sp->coalOverPopulated(left);
7831 break;
7832 }
7833 case 3: { // coalesce if left OR right chunk on overpopulated list
7834 coalesce = _sp->coalOverPopulated(left) ||
7835 _sp->coalOverPopulated(right);
7836 break;
7837 }
7838 case 4: { // always coalesce
7839 coalesce = true;
7840 break;
7841 }
7842 default:
7843 ShouldNotReachHere();
7844 }
7845
7846 // Should the current free range be coalesced?
7847 // If the chunk is in a free range and either we decided to coalesce above
7848 // or the chunk is near the large block at the end of the heap
7849 // (isNearLargestChunk() returns true), then coalesce this chunk.
7850 const bool doCoalesce = inFreeRange()
7851 && (coalesce || _g->isNearLargestChunk(fc_addr));
7852 if (doCoalesce) {
7853 // Coalesce the current free range on the left with the new
7854 // chunk on the right. If either is on a free list,
7855 // it must be removed from the list and stashed in the closure.
7856 if (freeRangeInFreeLists()) {
7857 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7858 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7859 "Size of free range is inconsistent with chunk size.");
7860 if (CMSTestInFreeList) {
7861 assert(_sp->verify_chunk_in_free_list(ffc),
7862 "Chunk is not in free lists");
7863 }
7864 _sp->coalDeath(ffc->size());
7865 _sp->removeFreeChunkFromFreeLists(ffc);
7866 set_freeRangeInFreeLists(false);
7867 }
7868 if (fcInFreeLists) {
7869 _sp->coalDeath(chunkSize);
7870 assert(fc->size() == chunkSize,
7871 "The chunk has the wrong size or is not in the free lists");
7872 _sp->removeFreeChunkFromFreeLists(fc);
7873 }
7874 set_lastFreeRangeCoalesced(true);
7875 print_free_block_coalesced(fc);
7876 } else { // not in a free range and/or should not coalesce
7877 // Return the current free range and start a new one.
7878 if (inFreeRange()) {
7879 // In a free range but cannot coalesce with the right hand chunk.
7880 // Put the current free range into the free lists.
7881 flush_cur_free_chunk(freeFinger(),
7882 pointer_delta(fc_addr, freeFinger()));
7883 }
7884 // Set up for new free range. Pass along whether the right hand
7885 // chunk is in the free lists.
7886 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7887 }
7888 }
7889
7890 // Lookahead flush:
7891 // If we are tracking a free range, and this is the last chunk that
7892 // we'll look at because its end crosses past _limit, we'll preemptively
7893 // flush it along with any free range we may be holding on to. Note that
7894 // this can be the case only for an already free or freshly garbage
7895 // chunk. If this block is an object, it can never straddle
7896 // over _limit. The "straddling" occurs when _limit is set at
7897 // the previous end of the space when this cycle started, and
7898 // a subsequent heap expansion caused the previously co-terminal
7899 // free block to be coalesced with the newly expanded portion,
7900 // thus rendering _limit a non-block-boundary making it dangerous
7901 // for the sweeper to step over and examine.
7902 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7903 assert(inFreeRange(), "Should only be called if currently in a free range.");
7904 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7905 assert(_sp->used_region().contains(eob - 1),
7906 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7907 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7908 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7909 eob, eob-1, _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
7910 if (eob >= _limit) {
7911 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7912 if (CMSTraceSweeper) {
7913 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7914 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7915 "[" PTR_FORMAT "," PTR_FORMAT ")",
7916 _limit, fc, eob, _sp->bottom(), _sp->end());
7917 }
7918 // Return the storage we are tracking back into the free lists.
7919 if (CMSTraceSweeper) {
7920 gclog_or_tty->print_cr("Flushing ... ");
7921 }
7922 assert(freeFinger() < eob, "Error");
7923 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7924 }
7925 }
7926
7927 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7928 assert(inFreeRange(), "Should only be called if currently in a free range.");
7929 assert(size > 0,
7930 "A zero sized chunk cannot be added to the free lists.");
7931 if (!freeRangeInFreeLists()) {
7932 if (CMSTestInFreeList) {
7933 FreeChunk* fc = (FreeChunk*) chunk;
7934 fc->set_size(size);
7935 assert(!_sp->verify_chunk_in_free_list(fc),
7936 "chunk should not be in free lists yet");
7937 }
7938 if (CMSTraceSweeper) {
7939 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7940 chunk, size);
7941 }
7942 // A new free range is going to be starting. The current
7943 // free range has not been added to the free lists yet or
7944 // was removed so add it back.
7945 // If the current free range was coalesced, then the death
7946 // of the free range was recorded. Record a birth now.
7947 if (lastFreeRangeCoalesced()) {
7948 _sp->coalBirth(size);
7949 }
7950 _sp->addChunkAndRepairOffsetTable(chunk, size,
7951 lastFreeRangeCoalesced());
7952 } else if (CMSTraceSweeper) {
7953 gclog_or_tty->print_cr("Already in free list: nothing to flush");
7954 }
7955 set_inFreeRange(false);
7956 set_freeRangeInFreeLists(false);
7957 }
7958
7959 // We take a break if we've been at this for a while,
7960 // so as to avoid monopolizing the locks involved.
7961 void SweepClosure::do_yield_work(HeapWord* addr) {
7962 // Return current free chunk being used for coalescing (if any)
7963 // to the appropriate freelist. After yielding, the next
7964 // free block encountered will start a coalescing range of
7965 // free blocks. If the next free block is adjacent to the
7966 // chunk just flushed, they will need to wait for the next
7967 // sweep to be coalesced.
7968 if (inFreeRange()) {
7969 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7970 }
7971
7972 // First give up the locks, then yield, then re-lock.
7973 // We should probably use a constructor/destructor idiom to
7974 // do this unlock/lock or modify the MutexUnlocker class to
7975 // serve our purpose. XXX
7976 assert_lock_strong(_bitMap->lock());
7977 assert_lock_strong(_freelistLock);
7978 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7979 "CMS thread should hold CMS token");
7980 _bitMap->lock()->unlock();
7981 _freelistLock->unlock();
7982 ConcurrentMarkSweepThread::desynchronize(true);
7983 _collector->stopTimer();
7984 if (PrintCMSStatistics != 0) {
7985 _collector->incrementYields();
7986 }
7987
7988 // See the comment in coordinator_yield()
7989 for (unsigned i = 0; i < CMSYieldSleepCount &&
7990 ConcurrentMarkSweepThread::should_yield() &&
7991 !CMSCollector::foregroundGCIsActive(); ++i) {
7992 os::sleep(Thread::current(), 1, false);
7993 }
7994
7995 ConcurrentMarkSweepThread::synchronize(true);
7996 _freelistLock->lock();
7997 _bitMap->lock()->lock_without_safepoint_check();
7998 _collector->startTimer();
7999 }
8000
8001 #ifndef PRODUCT
8002 // This is actually very useful in a product build if it can
8003 // be called from the debugger. Compile it into the product
8004 // as needed.
8005 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8006 return debug_cms_space->verify_chunk_in_free_list(fc);
8007 }
8008 #endif
8009
8010 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8011 if (CMSTraceSweeper) {
8012 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8013 fc, fc->size());
8014 }
8015 }
8016
8017 // CMSIsAliveClosure
8018 bool CMSIsAliveClosure::do_object_b(oop obj) {
8019 HeapWord* addr = (HeapWord*)obj;
8020 return addr != NULL &&
8021 (!_span.contains(addr) || _bit_map->isMarked(addr));
8022 }
8023
8024
8025 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8026 MemRegion span,
8027 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8028 bool cpc):
8029 _collector(collector),
8030 _span(span),
8031 _bit_map(bit_map),
8032 _mark_stack(mark_stack),
8033 _concurrent_precleaning(cpc) {
8034 assert(!_span.is_empty(), "Empty span could spell trouble");
8035 }
8036
8037
8038 // CMSKeepAliveClosure: the serial version
8039 void CMSKeepAliveClosure::do_oop(oop obj) {
8040 HeapWord* addr = (HeapWord*)obj;
8041 if (_span.contains(addr) &&
8042 !_bit_map->isMarked(addr)) {
8043 _bit_map->mark(addr);
8044 bool simulate_overflow = false;
8045 NOT_PRODUCT(
8046 if (CMSMarkStackOverflowALot &&
8047 _collector->simulate_overflow()) {
8048 // simulate a stack overflow
8049 simulate_overflow = true;
8050 }
8051 )
8052 if (simulate_overflow || !_mark_stack->push(obj)) {
8053 if (_concurrent_precleaning) {
8054 // We dirty the overflown object and let the remark
8055 // phase deal with it.
8056 assert(_collector->overflow_list_is_empty(), "Error");
8057 // In the case of object arrays, we need to dirty all of
8058 // the cards that the object spans. No locking or atomics
8059 // are needed since no one else can be mutating the mod union
8060 // table.
8061 if (obj->is_objArray()) {
8062 size_t sz = obj->size();
8063 HeapWord* end_card_addr =
8064 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8065 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8066 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8067 _collector->_modUnionTable.mark_range(redirty_range);
8068 } else {
8069 _collector->_modUnionTable.mark(addr);
8070 }
8071 _collector->_ser_kac_preclean_ovflw++;
8072 } else {
8073 _collector->push_on_overflow_list(obj);
8074 _collector->_ser_kac_ovflw++;
8075 }
8076 }
8077 }
8078 }
8079
8080 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8081 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8082
8083 // CMSParKeepAliveClosure: a parallel version of the above.
8084 // The work queues are private to each closure (thread),
8085 // but (may be) available for stealing by other threads.
8086 void CMSParKeepAliveClosure::do_oop(oop obj) {
8087 HeapWord* addr = (HeapWord*)obj;
8088 if (_span.contains(addr) &&
8089 !_bit_map->isMarked(addr)) {
8090 // In general, during recursive tracing, several threads
8091 // may be concurrently getting here; the first one to
8092 // "tag" it, claims it.
8093 if (_bit_map->par_mark(addr)) {
8094 bool res = _work_queue->push(obj);
8095 assert(res, "Low water mark should be much less than capacity");
8096 // Do a recursive trim in the hope that this will keep
8097 // stack usage lower, but leave some oops for potential stealers
8098 trim_queue(_low_water_mark);
8099 } // Else, another thread got there first
8100 }
8101 }
8102
8103 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8104 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8105
8106 void CMSParKeepAliveClosure::trim_queue(uint max) {
8107 while (_work_queue->size() > max) {
8108 oop new_oop;
8109 if (_work_queue->pop_local(new_oop)) {
8110 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8111 assert(_bit_map->isMarked((HeapWord*)new_oop),
8112 "no white objects on this stack!");
8113 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8114 // iterate over the oops in this oop, marking and pushing
8115 // the ones in CMS heap (i.e. in _span).
8116 new_oop->oop_iterate(&_mark_and_push);
8117 }
8118 }
8119 }
8120
8121 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8122 CMSCollector* collector,
8123 MemRegion span, CMSBitMap* bit_map,
8124 OopTaskQueue* work_queue):
8125 _collector(collector),
8126 _span(span),
8127 _bit_map(bit_map),
8128 _work_queue(work_queue) { }
8129
8130 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8131 HeapWord* addr = (HeapWord*)obj;
8132 if (_span.contains(addr) &&
8133 !_bit_map->isMarked(addr)) {
8134 if (_bit_map->par_mark(addr)) {
8135 bool simulate_overflow = false;
8136 NOT_PRODUCT(
8137 if (CMSMarkStackOverflowALot &&
8138 _collector->par_simulate_overflow()) {
8139 // simulate a stack overflow
8140 simulate_overflow = true;
8141 }
8142 )
8143 if (simulate_overflow || !_work_queue->push(obj)) {
8144 _collector->par_push_on_overflow_list(obj);
8145 _collector->_par_kac_ovflw++;
8146 }
8147 } // Else another thread got there already
8148 }
8149 }
8150
8151 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8152 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8153
8154 //////////////////////////////////////////////////////////////////
8155 // CMSExpansionCause /////////////////////////////
8156 //////////////////////////////////////////////////////////////////
8157 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8158 switch (cause) {
8159 case _no_expansion:
8160 return "No expansion";
8161 case _satisfy_free_ratio:
8162 return "Free ratio";
8163 case _satisfy_promotion:
8164 return "Satisfy promotion";
8165 case _satisfy_allocation:
8166 return "allocation";
8167 case _allocate_par_lab:
8168 return "Par LAB";
8169 case _allocate_par_spooling_space:
8170 return "Par Spooling Space";
8171 case _adaptive_size_policy:
8172 return "Ergonomics";
8173 default:
8174 return "unknown";
8175 }
8176 }
8177
8178 void CMSDrainMarkingStackClosure::do_void() {
8179 // the max number to take from overflow list at a time
8180 const size_t num = _mark_stack->capacity()/4;
8181 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8182 "Overflow list should be NULL during concurrent phases");
8183 while (!_mark_stack->isEmpty() ||
8184 // if stack is empty, check the overflow list
8185 _collector->take_from_overflow_list(num, _mark_stack)) {
8186 oop obj = _mark_stack->pop();
8187 HeapWord* addr = (HeapWord*)obj;
8188 assert(_span.contains(addr), "Should be within span");
8189 assert(_bit_map->isMarked(addr), "Should be marked");
8190 assert(obj->is_oop(), "Should be an oop");
8191 obj->oop_iterate(_keep_alive);
8192 }
8193 }
8194
8195 void CMSParDrainMarkingStackClosure::do_void() {
8196 // drain queue
8197 trim_queue(0);
8198 }
8199
8200 // Trim our work_queue so its length is below max at return
8201 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8202 while (_work_queue->size() > max) {
8203 oop new_oop;
8204 if (_work_queue->pop_local(new_oop)) {
8205 assert(new_oop->is_oop(), "Expected an oop");
8206 assert(_bit_map->isMarked((HeapWord*)new_oop),
8207 "no white objects on this stack!");
8208 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8209 // iterate over the oops in this oop, marking and pushing
8210 // the ones in CMS heap (i.e. in _span).
8211 new_oop->oop_iterate(&_mark_and_push);
8212 }
8213 }
8214 }
8215
8216 ////////////////////////////////////////////////////////////////////
8217 // Support for Marking Stack Overflow list handling and related code
8218 ////////////////////////////////////////////////////////////////////
8219 // Much of the following code is similar in shape and spirit to the
8220 // code used in ParNewGC. We should try and share that code
8221 // as much as possible in the future.
8222
8223 #ifndef PRODUCT
8224 // Debugging support for CMSStackOverflowALot
8225
8226 // It's OK to call this multi-threaded; the worst thing
8227 // that can happen is that we'll get a bunch of closely
8228 // spaced simulated overflows, but that's OK, in fact
8229 // probably good as it would exercise the overflow code
8230 // under contention.
8231 bool CMSCollector::simulate_overflow() {
8232 if (_overflow_counter-- <= 0) { // just being defensive
8233 _overflow_counter = CMSMarkStackOverflowInterval;
8234 return true;
8235 } else {
8236 return false;
8237 }
8238 }
8239
8240 bool CMSCollector::par_simulate_overflow() {
8241 return simulate_overflow();
8242 }
8243 #endif
8244
8245 // Single-threaded
8246 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8247 assert(stack->isEmpty(), "Expected precondition");
8248 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8249 size_t i = num;
8250 oop cur = _overflow_list;
8251 const markOop proto = markOopDesc::prototype();
8252 NOT_PRODUCT(ssize_t n = 0;)
8253 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8254 next = oop(cur->mark());
8255 cur->set_mark(proto); // until proven otherwise
8256 assert(cur->is_oop(), "Should be an oop");
8257 bool res = stack->push(cur);
8258 assert(res, "Bit off more than can chew?");
8259 NOT_PRODUCT(n++;)
8260 }
8261 _overflow_list = cur;
8262 #ifndef PRODUCT
8263 assert(_num_par_pushes >= n, "Too many pops?");
8264 _num_par_pushes -=n;
8265 #endif
8266 return !stack->isEmpty();
8267 }
8268
8269 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8270 // (MT-safe) Get a prefix of at most "num" from the list.
8271 // The overflow list is chained through the mark word of
8272 // each object in the list. We fetch the entire list,
8273 // break off a prefix of the right size and return the
8274 // remainder. If other threads try to take objects from
8275 // the overflow list at that time, they will wait for
8276 // some time to see if data becomes available. If (and
8277 // only if) another thread places one or more object(s)
8278 // on the global list before we have returned the suffix
8279 // to the global list, we will walk down our local list
8280 // to find its end and append the global list to
8281 // our suffix before returning it. This suffix walk can
8282 // prove to be expensive (quadratic in the amount of traffic)
8283 // when there are many objects in the overflow list and
8284 // there is much producer-consumer contention on the list.
8285 // *NOTE*: The overflow list manipulation code here and
8286 // in ParNewGeneration:: are very similar in shape,
8287 // except that in the ParNew case we use the old (from/eden)
8288 // copy of the object to thread the list via its klass word.
8289 // Because of the common code, if you make any changes in
8290 // the code below, please check the ParNew version to see if
8291 // similar changes might be needed.
8292 // CR 6797058 has been filed to consolidate the common code.
8293 bool CMSCollector::par_take_from_overflow_list(size_t num,
8294 OopTaskQueue* work_q,
8295 int no_of_gc_threads) {
8296 assert(work_q->size() == 0, "First empty local work queue");
8297 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8298 if (_overflow_list == NULL) {
8299 return false;
8300 }
8301 // Grab the entire list; we'll put back a suffix
8302 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8303 Thread* tid = Thread::current();
8304 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8305 // set to ParallelGCThreads.
8306 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8307 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8308 // If the list is busy, we spin for a short while,
8309 // sleeping between attempts to get the list.
8310 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8311 os::sleep(tid, sleep_time_millis, false);
8312 if (_overflow_list == NULL) {
8313 // Nothing left to take
8314 return false;
8315 } else if (_overflow_list != BUSY) {
8316 // Try and grab the prefix
8317 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8318 }
8319 }
8320 // If the list was found to be empty, or we spun long
8321 // enough, we give up and return empty-handed. If we leave
8322 // the list in the BUSY state below, it must be the case that
8323 // some other thread holds the overflow list and will set it
8324 // to a non-BUSY state in the future.
8325 if (prefix == NULL || prefix == BUSY) {
8326 // Nothing to take or waited long enough
8327 if (prefix == NULL) {
8328 // Write back the NULL in case we overwrote it with BUSY above
8329 // and it is still the same value.
8330 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8331 }
8332 return false;
8333 }
8334 assert(prefix != NULL && prefix != BUSY, "Error");
8335 size_t i = num;
8336 oop cur = prefix;
8337 // Walk down the first "num" objects, unless we reach the end.
8338 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8339 if (cur->mark() == NULL) {
8340 // We have "num" or fewer elements in the list, so there
8341 // is nothing to return to the global list.
8342 // Write back the NULL in lieu of the BUSY we wrote
8343 // above, if it is still the same value.
8344 if (_overflow_list == BUSY) {
8345 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8346 }
8347 } else {
8348 // Chop off the suffix and return it to the global list.
8349 assert(cur->mark() != BUSY, "Error");
8350 oop suffix_head = cur->mark(); // suffix will be put back on global list
8351 cur->set_mark(NULL); // break off suffix
8352 // It's possible that the list is still in the empty(busy) state
8353 // we left it in a short while ago; in that case we may be
8354 // able to place back the suffix without incurring the cost
8355 // of a walk down the list.
8356 oop observed_overflow_list = _overflow_list;
8357 oop cur_overflow_list = observed_overflow_list;
8358 bool attached = false;
8359 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8360 observed_overflow_list =
8361 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8362 if (cur_overflow_list == observed_overflow_list) {
8363 attached = true;
8364 break;
8365 } else cur_overflow_list = observed_overflow_list;
8366 }
8367 if (!attached) {
8368 // Too bad, someone else sneaked in (at least) an element; we'll need
8369 // to do a splice. Find tail of suffix so we can prepend suffix to global
8370 // list.
8371 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8372 oop suffix_tail = cur;
8373 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8374 "Tautology");
8375 observed_overflow_list = _overflow_list;
8376 do {
8377 cur_overflow_list = observed_overflow_list;
8378 if (cur_overflow_list != BUSY) {
8379 // Do the splice ...
8380 suffix_tail->set_mark(markOop(cur_overflow_list));
8381 } else { // cur_overflow_list == BUSY
8382 suffix_tail->set_mark(NULL);
8383 }
8384 // ... and try to place spliced list back on overflow_list ...
8385 observed_overflow_list =
8386 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8387 } while (cur_overflow_list != observed_overflow_list);
8388 // ... until we have succeeded in doing so.
8389 }
8390 }
8391
8392 // Push the prefix elements on work_q
8393 assert(prefix != NULL, "control point invariant");
8394 const markOop proto = markOopDesc::prototype();
8395 oop next;
8396 NOT_PRODUCT(ssize_t n = 0;)
8397 for (cur = prefix; cur != NULL; cur = next) {
8398 next = oop(cur->mark());
8399 cur->set_mark(proto); // until proven otherwise
8400 assert(cur->is_oop(), "Should be an oop");
8401 bool res = work_q->push(cur);
8402 assert(res, "Bit off more than we can chew?");
8403 NOT_PRODUCT(n++;)
8404 }
8405 #ifndef PRODUCT
8406 assert(_num_par_pushes >= n, "Too many pops?");
8407 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8408 #endif
8409 return true;
8410 }
8411
8412 // Single-threaded
8413 void CMSCollector::push_on_overflow_list(oop p) {
8414 NOT_PRODUCT(_num_par_pushes++;)
8415 assert(p->is_oop(), "Not an oop");
8416 preserve_mark_if_necessary(p);
8417 p->set_mark((markOop)_overflow_list);
8418 _overflow_list = p;
8419 }
8420
8421 // Multi-threaded; use CAS to prepend to overflow list
8422 void CMSCollector::par_push_on_overflow_list(oop p) {
8423 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8424 assert(p->is_oop(), "Not an oop");
8425 par_preserve_mark_if_necessary(p);
8426 oop observed_overflow_list = _overflow_list;
8427 oop cur_overflow_list;
8428 do {
8429 cur_overflow_list = observed_overflow_list;
8430 if (cur_overflow_list != BUSY) {
8431 p->set_mark(markOop(cur_overflow_list));
8432 } else {
8433 p->set_mark(NULL);
8434 }
8435 observed_overflow_list =
8436 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8437 } while (cur_overflow_list != observed_overflow_list);
8438 }
8439 #undef BUSY
8440
8441 // Single threaded
8442 // General Note on GrowableArray: pushes may silently fail
8443 // because we are (temporarily) out of C-heap for expanding
8444 // the stack. The problem is quite ubiquitous and affects
8445 // a lot of code in the JVM. The prudent thing for GrowableArray
8446 // to do (for now) is to exit with an error. However, that may
8447 // be too draconian in some cases because the caller may be
8448 // able to recover without much harm. For such cases, we
8449 // should probably introduce a "soft_push" method which returns
8450 // an indication of success or failure with the assumption that
8451 // the caller may be able to recover from a failure; code in
8452 // the VM can then be changed, incrementally, to deal with such
8453 // failures where possible, thus, incrementally hardening the VM
8454 // in such low resource situations.
8455 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8456 _preserved_oop_stack.push(p);
8457 _preserved_mark_stack.push(m);
8458 assert(m == p->mark(), "Mark word changed");
8459 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8460 "bijection");
8461 }
8462
8463 // Single threaded
8464 void CMSCollector::preserve_mark_if_necessary(oop p) {
8465 markOop m = p->mark();
8466 if (m->must_be_preserved(p)) {
8467 preserve_mark_work(p, m);
8468 }
8469 }
8470
8471 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8472 markOop m = p->mark();
8473 if (m->must_be_preserved(p)) {
8474 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8475 // Even though we read the mark word without holding
8476 // the lock, we are assured that it will not change
8477 // because we "own" this oop, so no other thread can
8478 // be trying to push it on the overflow list; see
8479 // the assertion in preserve_mark_work() that checks
8480 // that m == p->mark().
8481 preserve_mark_work(p, m);
8482 }
8483 }
8484
8485 // We should be able to do this multi-threaded,
8486 // a chunk of stack being a task (this is
8487 // correct because each oop only ever appears
8488 // once in the overflow list. However, it's
8489 // not very easy to completely overlap this with
8490 // other operations, so will generally not be done
8491 // until all work's been completed. Because we
8492 // expect the preserved oop stack (set) to be small,
8493 // it's probably fine to do this single-threaded.
8494 // We can explore cleverer concurrent/overlapped/parallel
8495 // processing of preserved marks if we feel the
8496 // need for this in the future. Stack overflow should
8497 // be so rare in practice and, when it happens, its
8498 // effect on performance so great that this will
8499 // likely just be in the noise anyway.
8500 void CMSCollector::restore_preserved_marks_if_any() {
8501 assert(SafepointSynchronize::is_at_safepoint(),
8502 "world should be stopped");
8503 assert(Thread::current()->is_ConcurrentGC_thread() ||
8504 Thread::current()->is_VM_thread(),
8505 "should be single-threaded");
8506 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8507 "bijection");
8508
8509 while (!_preserved_oop_stack.is_empty()) {
8510 oop p = _preserved_oop_stack.pop();
8511 assert(p->is_oop(), "Should be an oop");
8512 assert(_span.contains(p), "oop should be in _span");
8513 assert(p->mark() == markOopDesc::prototype(),
8514 "Set when taken from overflow list");
8515 markOop m = _preserved_mark_stack.pop();
8516 p->set_mark(m);
8517 }
8518 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8519 "stacks were cleared above");
8520 }
8521
8522 #ifndef PRODUCT
8523 bool CMSCollector::no_preserved_marks() const {
8524 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8525 }
8526 #endif
8527
8528 // Transfer some number of overflown objects to usual marking
8529 // stack. Return true if some objects were transferred.
8530 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8531 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8532 (size_t)ParGCDesiredObjsFromOverflowList);
8533
8534 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8535 assert(_collector->overflow_list_is_empty() || res,
8536 "If list is not empty, we should have taken something");
8537 assert(!res || !_mark_stack->isEmpty(),
8538 "If we took something, it should now be on our stack");
8539 return res;
8540 }
8541
8542 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8543 size_t res = _sp->block_size_no_stall(addr, _collector);
8544 if (_sp->block_is_obj(addr)) {
8545 if (_live_bit_map->isMarked(addr)) {
8546 // It can't have been dead in a previous cycle
8547 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8548 } else {
8549 _dead_bit_map->mark(addr); // mark the dead object
8550 }
8551 }
8552 // Could be 0, if the block size could not be computed without stalling.
8553 return res;
8554 }
8555
8556 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8557
8558 switch (phase) {
8559 case CMSCollector::InitialMarking:
8560 initialize(true /* fullGC */ ,
8561 cause /* cause of the GC */,
8562 true /* recordGCBeginTime */,
8563 true /* recordPreGCUsage */,
8564 false /* recordPeakUsage */,
8565 false /* recordPostGCusage */,
8566 true /* recordAccumulatedGCTime */,
8567 false /* recordGCEndTime */,
8568 false /* countCollection */ );
8569 break;
8570
8571 case CMSCollector::FinalMarking:
8572 initialize(true /* fullGC */ ,
8573 cause /* cause of the GC */,
8574 false /* recordGCBeginTime */,
8575 false /* recordPreGCUsage */,
8576 false /* recordPeakUsage */,
8577 false /* recordPostGCusage */,
8578 true /* recordAccumulatedGCTime */,
8579 false /* recordGCEndTime */,
8580 false /* countCollection */ );
8581 break;
8582
8583 case CMSCollector::Sweeping:
8584 initialize(true /* fullGC */ ,
8585 cause /* cause of the GC */,
8586 false /* recordGCBeginTime */,
8587 false /* recordPreGCUsage */,
8588 true /* recordPeakUsage */,
8589 true /* recordPostGCusage */,
8590 false /* recordAccumulatedGCTime */,
8591 true /* recordGCEndTime */,
8592 true /* countCollection */ );
8593 break;
8594
8595 default:
8596 ShouldNotReachHere();
8597 }
8598 }