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/strongRootsScope.hpp"
57 #include "memory/tenuredGeneration.hpp"
58 #include "oops/oop.inline.hpp"
59 #include "prims/jvmtiExport.hpp"
60 #include "runtime/atomic.inline.hpp"
61 #include "runtime/globals_extension.hpp"
62 #include "runtime/handles.inline.hpp"
63 #include "runtime/java.hpp"
64 #include "runtime/orderAccess.inline.hpp"
65 #include "runtime/vmThread.hpp"
66 #include "services/memoryService.hpp"
67 #include "services/runtimeService.hpp"
68
69 // statics
70 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
71 bool CMSCollector::_full_gc_requested = false;
72 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
73
74 //////////////////////////////////////////////////////////////////
75 // In support of CMS/VM thread synchronization
76 //////////////////////////////////////////////////////////////////
77 // We split use of the CGC_lock into 2 "levels".
78 // The low-level locking is of the usual CGC_lock monitor. We introduce
79 // a higher level "token" (hereafter "CMS token") built on top of the
80 // low level monitor (hereafter "CGC lock").
81 // The token-passing protocol gives priority to the VM thread. The
82 // CMS-lock doesn't provide any fairness guarantees, but clients
83 // should ensure that it is only held for very short, bounded
84 // durations.
85 //
86 // When either of the CMS thread or the VM thread is involved in
87 // collection operations during which it does not want the other
88 // thread to interfere, it obtains the CMS token.
89 //
90 // If either thread tries to get the token while the other has
91 // it, that thread waits. However, if the VM thread and CMS thread
92 // both want the token, then the VM thread gets priority while the
93 // CMS thread waits. This ensures, for instance, that the "concurrent"
94 // phases of the CMS thread's work do not block out the VM thread
95 // for long periods of time as the CMS thread continues to hog
96 // the token. (See bug 4616232).
97 //
98 // The baton-passing functions are, however, controlled by the
99 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
100 // and here the low-level CMS lock, not the high level token,
101 // ensures mutual exclusion.
102 //
103 // Two important conditions that we have to satisfy:
104 // 1. if a thread does a low-level wait on the CMS lock, then it
105 // relinquishes the CMS token if it were holding that token
106 // when it acquired the low-level CMS lock.
107 // 2. any low-level notifications on the low-level lock
108 // should only be sent when a thread has relinquished the token.
109 //
110 // In the absence of either property, we'd have potential deadlock.
111 //
112 // We protect each of the CMS (concurrent and sequential) phases
113 // with the CMS _token_, not the CMS _lock_.
114 //
115 // The only code protected by CMS lock is the token acquisition code
116 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
117 // baton-passing code.
118 //
119 // Unfortunately, i couldn't come up with a good abstraction to factor and
120 // hide the naked CGC_lock manipulation in the baton-passing code
121 // further below. That's something we should try to do. Also, the proof
122 // of correctness of this 2-level locking scheme is far from obvious,
123 // and potentially quite slippery. We have an uneasy suspicion, for instance,
124 // that there may be a theoretical possibility of delay/starvation in the
125 // low-level lock/wait/notify scheme used for the baton-passing because of
126 // potential interference with the priority scheme embodied in the
127 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
128 // invocation further below and marked with "XXX 20011219YSR".
129 // Indeed, as we note elsewhere, this may become yet more slippery
130 // in the presence of multiple CMS and/or multiple VM threads. XXX
131
132 class CMSTokenSync: public StackObj {
133 private:
134 bool _is_cms_thread;
135 public:
136 CMSTokenSync(bool is_cms_thread):
137 _is_cms_thread(is_cms_thread) {
138 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
139 "Incorrect argument to constructor");
140 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
141 }
142
143 ~CMSTokenSync() {
144 assert(_is_cms_thread ?
145 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
146 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
147 "Incorrect state");
148 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
149 }
150 };
151
152 // Convenience class that does a CMSTokenSync, and then acquires
153 // upto three locks.
154 class CMSTokenSyncWithLocks: public CMSTokenSync {
155 private:
156 // Note: locks are acquired in textual declaration order
157 // and released in the opposite order
158 MutexLockerEx _locker1, _locker2, _locker3;
159 public:
160 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
161 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
162 CMSTokenSync(is_cms_thread),
163 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
164 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
165 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
166 { }
167 };
168
169
170 //////////////////////////////////////////////////////////////////
171 // Concurrent Mark-Sweep Generation /////////////////////////////
172 //////////////////////////////////////////////////////////////////
173
174 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
175
176 // This struct contains per-thread things necessary to support parallel
177 // young-gen collection.
178 class CMSParGCThreadState: public CHeapObj<mtGC> {
179 public:
180 CFLS_LAB lab;
181 PromotionInfo promo;
182
183 // Constructor.
184 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
185 promo.setSpace(cfls);
186 }
187 };
188
189 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
190 ReservedSpace rs, size_t initial_byte_size, int level,
191 CardTableRS* ct, bool use_adaptive_freelists,
192 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
193 CardGeneration(rs, initial_byte_size, level, ct),
194 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
195 _did_compact(false)
196 {
197 HeapWord* bottom = (HeapWord*) _virtual_space.low();
198 HeapWord* end = (HeapWord*) _virtual_space.high();
199
200 _direct_allocated_words = 0;
201 NOT_PRODUCT(
202 _numObjectsPromoted = 0;
203 _numWordsPromoted = 0;
204 _numObjectsAllocated = 0;
205 _numWordsAllocated = 0;
206 )
207
208 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
209 use_adaptive_freelists,
210 dictionaryChoice);
211 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
212 if (_cmsSpace == NULL) {
213 vm_exit_during_initialization(
214 "CompactibleFreeListSpace allocation failure");
215 }
216 _cmsSpace->_gen = this;
217
218 _gc_stats = new CMSGCStats();
219
220 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
221 // offsets match. The ability to tell free chunks from objects
222 // depends on this property.
223 debug_only(
224 FreeChunk* junk = NULL;
225 assert(UseCompressedClassPointers ||
226 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
227 "Offset of FreeChunk::_prev within FreeChunk must match"
228 " that of OopDesc::_klass within OopDesc");
229 )
230 if (CollectedHeap::use_parallel_gc_threads()) {
231 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
232 _par_gc_thread_states =
233 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
234 if (_par_gc_thread_states == NULL) {
235 vm_exit_during_initialization("Could not allocate par gc structs");
236 }
237 for (uint i = 0; i < ParallelGCThreads; i++) {
238 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
239 if (_par_gc_thread_states[i] == NULL) {
240 vm_exit_during_initialization("Could not allocate par gc structs");
241 }
242 }
243 } else {
244 _par_gc_thread_states = NULL;
245 }
246 _incremental_collection_failed = false;
247 // The "dilatation_factor" is the expansion that can occur on
248 // account of the fact that the minimum object size in the CMS
249 // generation may be larger than that in, say, a contiguous young
250 // generation.
251 // Ideally, in the calculation below, we'd compute the dilatation
252 // factor as: MinChunkSize/(promoting_gen's min object size)
253 // Since we do not have such a general query interface for the
254 // promoting generation, we'll instead just use the minimum
255 // object size (which today is a header's worth of space);
256 // note that all arithmetic is in units of HeapWords.
257 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
258 assert(_dilatation_factor >= 1.0, "from previous assert");
259 }
260
261
262 // The field "_initiating_occupancy" represents the occupancy percentage
263 // at which we trigger a new collection cycle. Unless explicitly specified
264 // via CMSInitiatingOccupancyFraction (argument "io" below), it
265 // is calculated by:
266 //
267 // Let "f" be MinHeapFreeRatio in
268 //
269 // _initiating_occupancy = 100-f +
270 // f * (CMSTriggerRatio/100)
271 // where CMSTriggerRatio is the argument "tr" below.
272 //
273 // That is, if we assume the heap is at its desired maximum occupancy at the
274 // end of a collection, we let CMSTriggerRatio of the (purported) free
275 // space be allocated before initiating a new collection cycle.
276 //
277 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
278 assert(io <= 100 && tr <= 100, "Check the arguments");
279 if (io >= 0) {
280 _initiating_occupancy = (double)io / 100.0;
281 } else {
282 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
283 (double)(tr * MinHeapFreeRatio) / 100.0)
284 / 100.0;
285 }
286 }
287
288 void ConcurrentMarkSweepGeneration::ref_processor_init() {
289 assert(collector() != NULL, "no collector");
290 collector()->ref_processor_init();
291 }
292
293 void CMSCollector::ref_processor_init() {
294 if (_ref_processor == NULL) {
295 // Allocate and initialize a reference processor
296 _ref_processor =
297 new ReferenceProcessor(_span, // span
298 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
299 (int) ParallelGCThreads, // mt processing degree
300 _cmsGen->refs_discovery_is_mt(), // mt discovery
301 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
302 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
303 &_is_alive_closure); // closure for liveness info
304 // Initialize the _ref_processor field of CMSGen
305 _cmsGen->set_ref_processor(_ref_processor);
306
307 }
308 }
309
310 AdaptiveSizePolicy* CMSCollector::size_policy() {
311 GenCollectedHeap* gch = GenCollectedHeap::heap();
312 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
313 "Wrong type of heap");
314 return gch->gen_policy()->size_policy();
315 }
316
317 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
318
319 const char* gen_name = "old";
320 GenCollectorPolicy* gcp = (GenCollectorPolicy*) GenCollectedHeap::heap()->collector_policy();
321
322 // Generation Counters - generation 1, 1 subspace
323 _gen_counters = new GenerationCounters(gen_name, 1, 1,
324 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
325
326 _space_counters = new GSpaceCounters(gen_name, 0,
327 _virtual_space.reserved_size(),
328 this, _gen_counters);
329 }
330
331 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
332 _cms_gen(cms_gen)
333 {
334 assert(alpha <= 100, "bad value");
335 _saved_alpha = alpha;
336
337 // Initialize the alphas to the bootstrap value of 100.
338 _gc0_alpha = _cms_alpha = 100;
339
340 _cms_begin_time.update();
341 _cms_end_time.update();
342
343 _gc0_duration = 0.0;
344 _gc0_period = 0.0;
345 _gc0_promoted = 0;
346
347 _cms_duration = 0.0;
348 _cms_period = 0.0;
349 _cms_allocated = 0;
350
351 _cms_used_at_gc0_begin = 0;
352 _cms_used_at_gc0_end = 0;
353 _allow_duty_cycle_reduction = false;
354 _valid_bits = 0;
355 }
356
357 double CMSStats::cms_free_adjustment_factor(size_t free) const {
358 // TBD: CR 6909490
359 return 1.0;
360 }
361
362 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
363 }
364
365 // If promotion failure handling is on use
366 // the padded average size of the promotion for each
367 // young generation collection.
368 double CMSStats::time_until_cms_gen_full() const {
369 size_t cms_free = _cms_gen->cmsSpace()->free();
370 GenCollectedHeap* gch = GenCollectedHeap::heap();
371 size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
372 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
373 if (cms_free > expected_promotion) {
374 // Start a cms collection if there isn't enough space to promote
375 // for the next minor collection. Use the padded average as
376 // a safety factor.
377 cms_free -= expected_promotion;
378
379 // Adjust by the safety factor.
380 double cms_free_dbl = (double)cms_free;
381 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
382 // Apply a further correction factor which tries to adjust
383 // for recent occurance of concurrent mode failures.
384 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
385 cms_free_dbl = cms_free_dbl * cms_adjustment;
386
387 if (PrintGCDetails && Verbose) {
388 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
389 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
390 cms_free, expected_promotion);
391 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
392 cms_free_dbl, cms_consumption_rate() + 1.0);
393 }
394 // Add 1 in case the consumption rate goes to zero.
395 return cms_free_dbl / (cms_consumption_rate() + 1.0);
396 }
397 return 0.0;
398 }
399
400 // Compare the duration of the cms collection to the
401 // time remaining before the cms generation is empty.
402 // Note that the time from the start of the cms collection
403 // to the start of the cms sweep (less than the total
404 // duration of the cms collection) can be used. This
405 // has been tried and some applications experienced
406 // promotion failures early in execution. This was
407 // possibly because the averages were not accurate
408 // enough at the beginning.
409 double CMSStats::time_until_cms_start() const {
410 // We add "gc0_period" to the "work" calculation
411 // below because this query is done (mostly) at the
412 // end of a scavenge, so we need to conservatively
413 // account for that much possible delay
414 // in the query so as to avoid concurrent mode failures
415 // due to starting the collection just a wee bit too
416 // late.
417 double work = cms_duration() + gc0_period();
418 double deadline = time_until_cms_gen_full();
419 // If a concurrent mode failure occurred recently, we want to be
420 // more conservative and halve our expected time_until_cms_gen_full()
421 if (work > deadline) {
422 if (Verbose && PrintGCDetails) {
423 gclog_or_tty->print(
424 " CMSCollector: collect because of anticipated promotion "
425 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
426 gc0_period(), time_until_cms_gen_full());
427 }
428 return 0.0;
429 }
430 return work - deadline;
431 }
432
433 #ifndef PRODUCT
434 void CMSStats::print_on(outputStream *st) const {
435 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
436 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
437 gc0_duration(), gc0_period(), gc0_promoted());
438 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
439 cms_duration(), cms_period(), cms_allocated());
440 st->print(",cms_since_beg=%g,cms_since_end=%g",
441 cms_time_since_begin(), cms_time_since_end());
442 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
443 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
444
445 if (valid()) {
446 st->print(",promo_rate=%g,cms_alloc_rate=%g",
447 promotion_rate(), cms_allocation_rate());
448 st->print(",cms_consumption_rate=%g,time_until_full=%g",
449 cms_consumption_rate(), time_until_cms_gen_full());
450 }
451 st->print(" ");
452 }
453 #endif // #ifndef PRODUCT
454
455 CMSCollector::CollectorState CMSCollector::_collectorState =
456 CMSCollector::Idling;
457 bool CMSCollector::_foregroundGCIsActive = false;
458 bool CMSCollector::_foregroundGCShouldWait = false;
459
460 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
461 CardTableRS* ct,
462 ConcurrentMarkSweepPolicy* cp):
463 _cmsGen(cmsGen),
464 _ct(ct),
465 _ref_processor(NULL), // will be set later
466 _conc_workers(NULL), // may be set later
467 _abort_preclean(false),
468 _start_sampling(false),
469 _between_prologue_and_epilogue(false),
470 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
471 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
472 -1 /* lock-free */, "No_lock" /* dummy */),
473 _modUnionClosure(&_modUnionTable),
474 _modUnionClosurePar(&_modUnionTable),
475 // Adjust my span to cover old (cms) gen
476 _span(cmsGen->reserved()),
477 // Construct the is_alive_closure with _span & markBitMap
478 _is_alive_closure(_span, &_markBitMap),
479 _restart_addr(NULL),
480 _overflow_list(NULL),
481 _stats(cmsGen),
482 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
483 //verify that this lock should be acquired with safepoint check.
484 Monitor::_safepoint_check_sometimes)),
485 _eden_chunk_array(NULL), // may be set in ctor body
486 _eden_chunk_capacity(0), // -- ditto --
487 _eden_chunk_index(0), // -- ditto --
488 _survivor_plab_array(NULL), // -- ditto --
489 _survivor_chunk_array(NULL), // -- ditto --
490 _survivor_chunk_capacity(0), // -- ditto --
491 _survivor_chunk_index(0), // -- ditto --
492 _ser_pmc_preclean_ovflw(0),
493 _ser_kac_preclean_ovflw(0),
494 _ser_pmc_remark_ovflw(0),
495 _par_pmc_remark_ovflw(0),
496 _ser_kac_ovflw(0),
497 _par_kac_ovflw(0),
498 #ifndef PRODUCT
499 _num_par_pushes(0),
500 #endif
501 _collection_count_start(0),
502 _verifying(false),
503 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
504 _completed_initialization(false),
505 _collector_policy(cp),
506 _should_unload_classes(CMSClassUnloadingEnabled),
507 _concurrent_cycles_since_last_unload(0),
508 _roots_scanning_options(GenCollectedHeap::SO_None),
509 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
510 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
511 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
512 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
513 _cms_start_registered(false)
514 {
515 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
516 ExplicitGCInvokesConcurrent = true;
517 }
518 // Now expand the span and allocate the collection support structures
519 // (MUT, marking bit map etc.) to cover both generations subject to
520 // collection.
521
522 // For use by dirty card to oop closures.
523 _cmsGen->cmsSpace()->set_collector(this);
524
525 // Allocate MUT and marking bit map
526 {
527 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
528 if (!_markBitMap.allocate(_span)) {
529 warning("Failed to allocate CMS Bit Map");
530 return;
531 }
532 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
533 }
534 {
535 _modUnionTable.allocate(_span);
536 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
537 }
538
539 if (!_markStack.allocate(MarkStackSize)) {
540 warning("Failed to allocate CMS Marking Stack");
541 return;
542 }
543
544 // Support for multi-threaded concurrent phases
545 if (CMSConcurrentMTEnabled) {
546 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
547 // just for now
548 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
549 }
550 if (ConcGCThreads > 1) {
551 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
552 ConcGCThreads, true);
553 if (_conc_workers == NULL) {
554 warning("GC/CMS: _conc_workers allocation failure: "
555 "forcing -CMSConcurrentMTEnabled");
556 CMSConcurrentMTEnabled = false;
557 } else {
558 _conc_workers->initialize_workers();
559 }
560 } else {
561 CMSConcurrentMTEnabled = false;
562 }
563 }
564 if (!CMSConcurrentMTEnabled) {
565 ConcGCThreads = 0;
566 } else {
567 // Turn off CMSCleanOnEnter optimization temporarily for
568 // the MT case where it's not fixed yet; see 6178663.
569 CMSCleanOnEnter = false;
570 }
571 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
572 "Inconsistency");
573
574 // Parallel task queues; these are shared for the
575 // concurrent and stop-world phases of CMS, but
576 // are not shared with parallel scavenge (ParNew).
577 {
578 uint i;
579 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
580
581 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
582 || ParallelRefProcEnabled)
583 && num_queues > 0) {
584 _task_queues = new OopTaskQueueSet(num_queues);
585 if (_task_queues == NULL) {
586 warning("task_queues allocation failure.");
587 return;
588 }
589 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
590 if (_hash_seed == NULL) {
591 warning("_hash_seed array allocation failure");
592 return;
593 }
594
595 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
596 for (i = 0; i < num_queues; i++) {
597 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
598 if (q == NULL) {
599 warning("work_queue allocation failure.");
600 return;
601 }
602 _task_queues->register_queue(i, q);
603 }
604 for (i = 0; i < num_queues; i++) {
605 _task_queues->queue(i)->initialize();
606 _hash_seed[i] = 17; // copied from ParNew
607 }
608 }
609 }
610
611 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
612
613 // Clip CMSBootstrapOccupancy between 0 and 100.
614 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
615
616 // Now tell CMS generations the identity of their collector
617 ConcurrentMarkSweepGeneration::set_collector(this);
618
619 // Create & start a CMS thread for this CMS collector
620 _cmsThread = ConcurrentMarkSweepThread::start(this);
621 assert(cmsThread() != NULL, "CMS Thread should have been created");
622 assert(cmsThread()->collector() == this,
623 "CMS Thread should refer to this gen");
624 assert(CGC_lock != NULL, "Where's the CGC_lock?");
625
626 // Support for parallelizing young gen rescan
627 GenCollectedHeap* gch = GenCollectedHeap::heap();
628 assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
629 _young_gen = (ParNewGeneration*)gch->young_gen();
630 if (gch->supports_inline_contig_alloc()) {
631 _top_addr = gch->top_addr();
632 _end_addr = gch->end_addr();
633 assert(_young_gen != NULL, "no _young_gen");
634 _eden_chunk_index = 0;
635 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
636 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
637 if (_eden_chunk_array == NULL) {
638 _eden_chunk_capacity = 0;
639 warning("GC/CMS: _eden_chunk_array allocation failure");
640 }
641 }
642 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
643
644 // Support for parallelizing survivor space rescan
645 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
646 const size_t max_plab_samples =
647 ((DefNewGeneration*)_young_gen)->max_survivor_size() / plab_sample_minimum_size();
648
649 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
650 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
651 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
652 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
653 || _cursor == NULL) {
654 warning("Failed to allocate survivor plab/chunk array");
655 if (_survivor_plab_array != NULL) {
656 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
657 _survivor_plab_array = NULL;
658 }
659 if (_survivor_chunk_array != NULL) {
660 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
661 _survivor_chunk_array = NULL;
662 }
663 if (_cursor != NULL) {
664 FREE_C_HEAP_ARRAY(size_t, _cursor);
665 _cursor = NULL;
666 }
667 } else {
668 _survivor_chunk_capacity = 2*max_plab_samples;
669 for (uint i = 0; i < ParallelGCThreads; i++) {
670 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
671 if (vec == NULL) {
672 warning("Failed to allocate survivor plab array");
673 for (int j = i; j > 0; j--) {
674 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array());
675 }
676 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
677 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
678 _survivor_plab_array = NULL;
679 _survivor_chunk_array = NULL;
680 _survivor_chunk_capacity = 0;
681 break;
682 } else {
683 ChunkArray* cur =
684 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
685 max_plab_samples);
686 assert(cur->end() == 0, "Should be 0");
687 assert(cur->array() == vec, "Should be vec");
688 assert(cur->capacity() == max_plab_samples, "Error");
689 }
690 }
691 }
692 }
693 assert( ( _survivor_plab_array != NULL
694 && _survivor_chunk_array != NULL)
695 || ( _survivor_chunk_capacity == 0
696 && _survivor_chunk_index == 0),
697 "Error");
698
699 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
700 _gc_counters = new CollectorCounters("CMS", 1);
701 _completed_initialization = true;
702 _inter_sweep_timer.start(); // start of time
703 }
704
705 size_t CMSCollector::plab_sample_minimum_size() {
706 // The default value of MinTLABSize is 2k, but there is
707 // no way to get the default value if the flag has been overridden.
708 return MAX2(ThreadLocalAllocBuffer::min_size() * HeapWordSize, 2 * K);
709 }
710
711 const char* ConcurrentMarkSweepGeneration::name() const {
712 return "concurrent mark-sweep generation";
713 }
714 void ConcurrentMarkSweepGeneration::update_counters() {
715 if (UsePerfData) {
716 _space_counters->update_all();
717 _gen_counters->update_all();
718 }
719 }
720
721 // this is an optimized version of update_counters(). it takes the
722 // used value as a parameter rather than computing it.
723 //
724 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
725 if (UsePerfData) {
726 _space_counters->update_used(used);
727 _space_counters->update_capacity();
728 _gen_counters->update_all();
729 }
730 }
731
732 void ConcurrentMarkSweepGeneration::print() const {
733 Generation::print();
734 cmsSpace()->print();
735 }
736
737 #ifndef PRODUCT
738 void ConcurrentMarkSweepGeneration::print_statistics() {
739 cmsSpace()->printFLCensus(0);
740 }
741 #endif
742
743 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
744 GenCollectedHeap* gch = GenCollectedHeap::heap();
745 if (PrintGCDetails) {
746 if (Verbose) {
747 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
748 level(), short_name(), s, used(), capacity());
749 } else {
750 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
751 level(), short_name(), s, used() / K, capacity() / K);
752 }
753 }
754 if (Verbose) {
755 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
756 gch->used(), gch->capacity());
757 } else {
758 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
759 gch->used() / K, gch->capacity() / K);
760 }
761 }
762
763 size_t
764 ConcurrentMarkSweepGeneration::contiguous_available() const {
765 // dld proposes an improvement in precision here. If the committed
766 // part of the space ends in a free block we should add that to
767 // uncommitted size in the calculation below. Will make this
768 // change later, staying with the approximation below for the
769 // time being. -- ysr.
770 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
771 }
772
773 size_t
774 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
775 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
776 }
777
778 size_t ConcurrentMarkSweepGeneration::max_available() const {
779 return free() + _virtual_space.uncommitted_size();
780 }
781
782 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
783 size_t available = max_available();
784 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
785 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
786 if (Verbose && PrintGCDetails) {
787 gclog_or_tty->print_cr(
788 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
789 "max_promo("SIZE_FORMAT")",
790 res? "":" not", available, res? ">=":"<",
791 av_promo, max_promotion_in_bytes);
792 }
793 return res;
794 }
795
796 // At a promotion failure dump information on block layout in heap
797 // (cms old generation).
798 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
799 if (CMSDumpAtPromotionFailure) {
800 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
801 }
802 }
803
804 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
805 // Clear the promotion information. These pointers can be adjusted
806 // along with all the other pointers into the heap but
807 // compaction is expected to be a rare event with
808 // a heap using cms so don't do it without seeing the need.
809 for (uint i = 0; i < ParallelGCThreads; i++) {
810 _par_gc_thread_states[i]->promo.reset();
811 }
812 }
813
814 void ConcurrentMarkSweepGeneration::compute_new_size() {
815 assert_locked_or_safepoint(Heap_lock);
816
817 // If incremental collection failed, we just want to expand
818 // to the limit.
819 if (incremental_collection_failed()) {
820 clear_incremental_collection_failed();
821 grow_to_reserved();
822 return;
823 }
824
825 // The heap has been compacted but not reset yet.
826 // Any metric such as free() or used() will be incorrect.
827
828 CardGeneration::compute_new_size();
829
830 // Reset again after a possible resizing
831 if (did_compact()) {
832 cmsSpace()->reset_after_compaction();
833 }
834 }
835
836 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
837 assert_locked_or_safepoint(Heap_lock);
838
839 // If incremental collection failed, we just want to expand
840 // to the limit.
841 if (incremental_collection_failed()) {
842 clear_incremental_collection_failed();
843 grow_to_reserved();
844 return;
845 }
846
847 double free_percentage = ((double) free()) / capacity();
848 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
849 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
850
851 // compute expansion delta needed for reaching desired free percentage
852 if (free_percentage < desired_free_percentage) {
853 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
854 assert(desired_capacity >= capacity(), "invalid expansion size");
855 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
856 if (PrintGCDetails && Verbose) {
857 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
858 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
859 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
860 gclog_or_tty->print_cr(" Desired free fraction %f",
861 desired_free_percentage);
862 gclog_or_tty->print_cr(" Maximum free fraction %f",
863 maximum_free_percentage);
864 gclog_or_tty->print_cr(" Capacity "SIZE_FORMAT, capacity()/1000);
865 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
866 desired_capacity/1000);
867 int prev_level = level() - 1;
868 if (prev_level >= 0) {
869 size_t prev_size = 0;
870 GenCollectedHeap* gch = GenCollectedHeap::heap();
871 Generation* prev_gen = gch->young_gen();
872 prev_size = prev_gen->capacity();
873 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
874 prev_size/1000);
875 }
876 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
877 unsafe_max_alloc_nogc()/1000);
878 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
879 contiguous_available()/1000);
880 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
881 expand_bytes);
882 }
883 // safe if expansion fails
884 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
885 if (PrintGCDetails && Verbose) {
886 gclog_or_tty->print_cr(" Expanded free fraction %f",
887 ((double) free()) / capacity());
888 }
889 } else {
890 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
891 assert(desired_capacity <= capacity(), "invalid expansion size");
892 size_t shrink_bytes = capacity() - desired_capacity;
893 // Don't shrink unless the delta is greater than the minimum shrink we want
894 if (shrink_bytes >= MinHeapDeltaBytes) {
895 shrink_free_list_by(shrink_bytes);
896 }
897 }
898 }
899
900 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
901 return cmsSpace()->freelistLock();
902 }
903
904 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
905 bool tlab) {
906 CMSSynchronousYieldRequest yr;
907 MutexLockerEx x(freelistLock(),
908 Mutex::_no_safepoint_check_flag);
909 return have_lock_and_allocate(size, tlab);
910 }
911
912 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
913 bool tlab /* ignored */) {
914 assert_lock_strong(freelistLock());
915 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
916 HeapWord* res = cmsSpace()->allocate(adjustedSize);
917 // Allocate the object live (grey) if the background collector has
918 // started marking. This is necessary because the marker may
919 // have passed this address and consequently this object will
920 // not otherwise be greyed and would be incorrectly swept up.
921 // Note that if this object contains references, the writing
922 // of those references will dirty the card containing this object
923 // allowing the object to be blackened (and its references scanned)
924 // either during a preclean phase or at the final checkpoint.
925 if (res != NULL) {
926 // We may block here with an uninitialized object with
927 // its mark-bit or P-bits not yet set. Such objects need
928 // to be safely navigable by block_start().
929 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
930 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
931 collector()->direct_allocated(res, adjustedSize);
932 _direct_allocated_words += adjustedSize;
933 // allocation counters
934 NOT_PRODUCT(
935 _numObjectsAllocated++;
936 _numWordsAllocated += (int)adjustedSize;
937 )
938 }
939 return res;
940 }
941
942 // In the case of direct allocation by mutators in a generation that
943 // is being concurrently collected, the object must be allocated
944 // live (grey) if the background collector has started marking.
945 // This is necessary because the marker may
946 // have passed this address and consequently this object will
947 // not otherwise be greyed and would be incorrectly swept up.
948 // Note that if this object contains references, the writing
949 // of those references will dirty the card containing this object
950 // allowing the object to be blackened (and its references scanned)
951 // either during a preclean phase or at the final checkpoint.
952 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
953 assert(_markBitMap.covers(start, size), "Out of bounds");
954 if (_collectorState >= Marking) {
955 MutexLockerEx y(_markBitMap.lock(),
956 Mutex::_no_safepoint_check_flag);
957 // [see comments preceding SweepClosure::do_blk() below for details]
958 //
959 // Can the P-bits be deleted now? JJJ
960 //
961 // 1. need to mark the object as live so it isn't collected
962 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
963 // 3. need to mark the end of the object so marking, precleaning or sweeping
964 // can skip over uninitialized or unparsable objects. An allocated
965 // object is considered uninitialized for our purposes as long as
966 // its klass word is NULL. All old gen objects are parsable
967 // as soon as they are initialized.)
968 _markBitMap.mark(start); // object is live
969 _markBitMap.mark(start + 1); // object is potentially uninitialized?
970 _markBitMap.mark(start + size - 1);
971 // mark end of object
972 }
973 // check that oop looks uninitialized
974 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
975 }
976
977 void CMSCollector::promoted(bool par, HeapWord* start,
978 bool is_obj_array, size_t obj_size) {
979 assert(_markBitMap.covers(start), "Out of bounds");
980 // See comment in direct_allocated() about when objects should
981 // be allocated live.
982 if (_collectorState >= Marking) {
983 // we already hold the marking bit map lock, taken in
984 // the prologue
985 if (par) {
986 _markBitMap.par_mark(start);
987 } else {
988 _markBitMap.mark(start);
989 }
990 // We don't need to mark the object as uninitialized (as
991 // in direct_allocated above) because this is being done with the
992 // world stopped and the object will be initialized by the
993 // time the marking, precleaning or sweeping get to look at it.
994 // But see the code for copying objects into the CMS generation,
995 // where we need to ensure that concurrent readers of the
996 // block offset table are able to safely navigate a block that
997 // is in flux from being free to being allocated (and in
998 // transition while being copied into) and subsequently
999 // becoming a bona-fide object when the copy/promotion is complete.
1000 assert(SafepointSynchronize::is_at_safepoint(),
1001 "expect promotion only at safepoints");
1002
1003 if (_collectorState < Sweeping) {
1004 // Mark the appropriate cards in the modUnionTable, so that
1005 // this object gets scanned before the sweep. If this is
1006 // not done, CMS generation references in the object might
1007 // not get marked.
1008 // For the case of arrays, which are otherwise precisely
1009 // marked, we need to dirty the entire array, not just its head.
1010 if (is_obj_array) {
1011 // The [par_]mark_range() method expects mr.end() below to
1012 // be aligned to the granularity of a bit's representation
1013 // in the heap. In the case of the MUT below, that's a
1014 // card size.
1015 MemRegion mr(start,
1016 (HeapWord*)round_to((intptr_t)(start + obj_size),
1017 CardTableModRefBS::card_size /* bytes */));
1018 if (par) {
1019 _modUnionTable.par_mark_range(mr);
1020 } else {
1021 _modUnionTable.mark_range(mr);
1022 }
1023 } else { // not an obj array; we can just mark the head
1024 if (par) {
1025 _modUnionTable.par_mark(start);
1026 } else {
1027 _modUnionTable.mark(start);
1028 }
1029 }
1030 }
1031 }
1032 }
1033
1034 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1035 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1036 // allocate, copy and if necessary update promoinfo --
1037 // delegate to underlying space.
1038 assert_lock_strong(freelistLock());
1039
1040 #ifndef PRODUCT
1041 if (Universe::heap()->promotion_should_fail()) {
1042 return NULL;
1043 }
1044 #endif // #ifndef PRODUCT
1045
1046 oop res = _cmsSpace->promote(obj, obj_size);
1047 if (res == NULL) {
1048 // expand and retry
1049 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1050 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
1051 // Since this is the old generation, we don't try to promote
1052 // into a more senior generation.
1053 res = _cmsSpace->promote(obj, obj_size);
1054 }
1055 if (res != NULL) {
1056 // See comment in allocate() about when objects should
1057 // be allocated live.
1058 assert(obj->is_oop(), "Will dereference klass pointer below");
1059 collector()->promoted(false, // Not parallel
1060 (HeapWord*)res, obj->is_objArray(), obj_size);
1061 // promotion counters
1062 NOT_PRODUCT(
1063 _numObjectsPromoted++;
1064 _numWordsPromoted +=
1065 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1066 )
1067 }
1068 return res;
1069 }
1070
1071
1072 // IMPORTANT: Notes on object size recognition in CMS.
1073 // ---------------------------------------------------
1074 // A block of storage in the CMS generation is always in
1075 // one of three states. A free block (FREE), an allocated
1076 // object (OBJECT) whose size() method reports the correct size,
1077 // and an intermediate state (TRANSIENT) in which its size cannot
1078 // be accurately determined.
1079 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1080 // -----------------------------------------------------
1081 // FREE: klass_word & 1 == 1; mark_word holds block size
1082 //
1083 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1084 // obj->size() computes correct size
1085 //
1086 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1087 //
1088 // STATE IDENTIFICATION: (64 bit+COOPS)
1089 // ------------------------------------
1090 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1091 //
1092 // OBJECT: klass_word installed; klass_word != 0;
1093 // obj->size() computes correct size
1094 //
1095 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1096 //
1097 //
1098 // STATE TRANSITION DIAGRAM
1099 //
1100 // mut / parnew mut / parnew
1101 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1102 // ^ |
1103 // |------------------------ DEAD <------------------------------------|
1104 // sweep mut
1105 //
1106 // While a block is in TRANSIENT state its size cannot be determined
1107 // so readers will either need to come back later or stall until
1108 // the size can be determined. Note that for the case of direct
1109 // allocation, P-bits, when available, may be used to determine the
1110 // size of an object that may not yet have been initialized.
1111
1112 // Things to support parallel young-gen collection.
1113 oop
1114 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1115 oop old, markOop m,
1116 size_t word_sz) {
1117 #ifndef PRODUCT
1118 if (Universe::heap()->promotion_should_fail()) {
1119 return NULL;
1120 }
1121 #endif // #ifndef PRODUCT
1122
1123 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1124 PromotionInfo* promoInfo = &ps->promo;
1125 // if we are tracking promotions, then first ensure space for
1126 // promotion (including spooling space for saving header if necessary).
1127 // then allocate and copy, then track promoted info if needed.
1128 // When tracking (see PromotionInfo::track()), the mark word may
1129 // be displaced and in this case restoration of the mark word
1130 // occurs in the (oop_since_save_marks_)iterate phase.
1131 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1132 // Out of space for allocating spooling buffers;
1133 // try expanding and allocating spooling buffers.
1134 if (!expand_and_ensure_spooling_space(promoInfo)) {
1135 return NULL;
1136 }
1137 }
1138 assert(promoInfo->has_spooling_space(), "Control point invariant");
1139 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1140 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1141 if (obj_ptr == NULL) {
1142 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1143 if (obj_ptr == NULL) {
1144 return NULL;
1145 }
1146 }
1147 oop obj = oop(obj_ptr);
1148 OrderAccess::storestore();
1149 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1150 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1151 // IMPORTANT: See note on object initialization for CMS above.
1152 // Otherwise, copy the object. Here we must be careful to insert the
1153 // klass pointer last, since this marks the block as an allocated object.
1154 // Except with compressed oops it's the mark word.
1155 HeapWord* old_ptr = (HeapWord*)old;
1156 // Restore the mark word copied above.
1157 obj->set_mark(m);
1158 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1159 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1160 OrderAccess::storestore();
1161
1162 if (UseCompressedClassPointers) {
1163 // Copy gap missed by (aligned) header size calculation below
1164 obj->set_klass_gap(old->klass_gap());
1165 }
1166 if (word_sz > (size_t)oopDesc::header_size()) {
1167 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1168 obj_ptr + oopDesc::header_size(),
1169 word_sz - oopDesc::header_size());
1170 }
1171
1172 // Now we can track the promoted object, if necessary. We take care
1173 // to delay the transition from uninitialized to full object
1174 // (i.e., insertion of klass pointer) until after, so that it
1175 // atomically becomes a promoted object.
1176 if (promoInfo->tracking()) {
1177 promoInfo->track((PromotedObject*)obj, old->klass());
1178 }
1179 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1180 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1181 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1182
1183 // Finally, install the klass pointer (this should be volatile).
1184 OrderAccess::storestore();
1185 obj->set_klass(old->klass());
1186 // We should now be able to calculate the right size for this object
1187 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1188
1189 collector()->promoted(true, // parallel
1190 obj_ptr, old->is_objArray(), word_sz);
1191
1192 NOT_PRODUCT(
1193 Atomic::inc_ptr(&_numObjectsPromoted);
1194 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1195 )
1196
1197 return obj;
1198 }
1199
1200 void
1201 ConcurrentMarkSweepGeneration::
1202 par_promote_alloc_done(int thread_num) {
1203 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1204 ps->lab.retire(thread_num);
1205 }
1206
1207 void
1208 ConcurrentMarkSweepGeneration::
1209 par_oop_since_save_marks_iterate_done(int thread_num) {
1210 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1211 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1212 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1213 }
1214
1215 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1216 size_t size,
1217 bool tlab)
1218 {
1219 // We allow a STW collection only if a full
1220 // collection was requested.
1221 return full || should_allocate(size, tlab); // FIX ME !!!
1222 // This and promotion failure handling are connected at the
1223 // hip and should be fixed by untying them.
1224 }
1225
1226 bool CMSCollector::shouldConcurrentCollect() {
1227 if (_full_gc_requested) {
1228 if (Verbose && PrintGCDetails) {
1229 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1230 " gc request (or gc_locker)");
1231 }
1232 return true;
1233 }
1234
1235 FreelistLocker x(this);
1236 // ------------------------------------------------------------------
1237 // Print out lots of information which affects the initiation of
1238 // a collection.
1239 if (PrintCMSInitiationStatistics && stats().valid()) {
1240 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1241 gclog_or_tty->stamp();
1242 gclog_or_tty->cr();
1243 stats().print_on(gclog_or_tty);
1244 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1245 stats().time_until_cms_gen_full());
1246 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1247 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1248 _cmsGen->contiguous_available());
1249 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1250 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1251 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1252 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1253 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1254 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1255 gclog_or_tty->print_cr("metadata initialized %d",
1256 MetaspaceGC::should_concurrent_collect());
1257 }
1258 // ------------------------------------------------------------------
1259
1260 // If the estimated time to complete a cms collection (cms_duration())
1261 // is less than the estimated time remaining until the cms generation
1262 // is full, start a collection.
1263 if (!UseCMSInitiatingOccupancyOnly) {
1264 if (stats().valid()) {
1265 if (stats().time_until_cms_start() == 0.0) {
1266 return true;
1267 }
1268 } else {
1269 // We want to conservatively collect somewhat early in order
1270 // to try and "bootstrap" our CMS/promotion statistics;
1271 // this branch will not fire after the first successful CMS
1272 // collection because the stats should then be valid.
1273 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1274 if (Verbose && PrintGCDetails) {
1275 gclog_or_tty->print_cr(
1276 " CMSCollector: collect for bootstrapping statistics:"
1277 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1278 _bootstrap_occupancy);
1279 }
1280 return true;
1281 }
1282 }
1283 }
1284
1285 // Otherwise, we start a collection cycle if
1286 // old gen want a collection cycle started. Each may use
1287 // an appropriate criterion for making this decision.
1288 // XXX We need to make sure that the gen expansion
1289 // criterion dovetails well with this. XXX NEED TO FIX THIS
1290 if (_cmsGen->should_concurrent_collect()) {
1291 if (Verbose && PrintGCDetails) {
1292 gclog_or_tty->print_cr("CMS old gen initiated");
1293 }
1294 return true;
1295 }
1296
1297 // We start a collection if we believe an incremental collection may fail;
1298 // this is not likely to be productive in practice because it's probably too
1299 // late anyway.
1300 GenCollectedHeap* gch = GenCollectedHeap::heap();
1301 assert(gch->collector_policy()->is_generation_policy(),
1302 "You may want to check the correctness of the following");
1303 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1304 if (Verbose && PrintGCDetails) {
1305 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1306 }
1307 return true;
1308 }
1309
1310 if (MetaspaceGC::should_concurrent_collect()) {
1311 if (Verbose && PrintGCDetails) {
1312 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1313 }
1314 return true;
1315 }
1316
1317 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1318 if (CMSTriggerInterval >= 0) {
1319 if (CMSTriggerInterval == 0) {
1320 // Trigger always
1321 return true;
1322 }
1323
1324 // Check the CMS time since begin (we do not check the stats validity
1325 // as we want to be able to trigger the first CMS cycle as well)
1326 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1327 if (Verbose && PrintGCDetails) {
1328 if (stats().valid()) {
1329 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1330 stats().cms_time_since_begin());
1331 } else {
1332 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1333 }
1334 }
1335 return true;
1336 }
1337 }
1338
1339 return false;
1340 }
1341
1342 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1343
1344 // Clear _expansion_cause fields of constituent generations
1345 void CMSCollector::clear_expansion_cause() {
1346 _cmsGen->clear_expansion_cause();
1347 }
1348
1349 // We should be conservative in starting a collection cycle. To
1350 // start too eagerly runs the risk of collecting too often in the
1351 // extreme. To collect too rarely falls back on full collections,
1352 // which works, even if not optimum in terms of concurrent work.
1353 // As a work around for too eagerly collecting, use the flag
1354 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1355 // giving the user an easily understandable way of controlling the
1356 // collections.
1357 // We want to start a new collection cycle if any of the following
1358 // conditions hold:
1359 // . our current occupancy exceeds the configured initiating occupancy
1360 // for this generation, or
1361 // . we recently needed to expand this space and have not, since that
1362 // expansion, done a collection of this generation, or
1363 // . the underlying space believes that it may be a good idea to initiate
1364 // a concurrent collection (this may be based on criteria such as the
1365 // following: the space uses linear allocation and linear allocation is
1366 // going to fail, or there is believed to be excessive fragmentation in
1367 // the generation, etc... or ...
1368 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1369 // the case of the old generation; see CR 6543076):
1370 // we may be approaching a point at which allocation requests may fail because
1371 // we will be out of sufficient free space given allocation rate estimates.]
1372 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1373
1374 assert_lock_strong(freelistLock());
1375 if (occupancy() > initiating_occupancy()) {
1376 if (PrintGCDetails && Verbose) {
1377 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1378 short_name(), occupancy(), initiating_occupancy());
1379 }
1380 return true;
1381 }
1382 if (UseCMSInitiatingOccupancyOnly) {
1383 return false;
1384 }
1385 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1386 if (PrintGCDetails && Verbose) {
1387 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1388 short_name());
1389 }
1390 return true;
1391 }
1392 if (_cmsSpace->should_concurrent_collect()) {
1393 if (PrintGCDetails && Verbose) {
1394 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1395 short_name());
1396 }
1397 return true;
1398 }
1399 return false;
1400 }
1401
1402 void ConcurrentMarkSweepGeneration::collect(bool full,
1403 bool clear_all_soft_refs,
1404 size_t size,
1405 bool tlab)
1406 {
1407 collector()->collect(full, clear_all_soft_refs, size, tlab);
1408 }
1409
1410 void CMSCollector::collect(bool full,
1411 bool clear_all_soft_refs,
1412 size_t size,
1413 bool tlab)
1414 {
1415 // The following "if" branch is present for defensive reasons.
1416 // In the current uses of this interface, it can be replaced with:
1417 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1418 // But I am not placing that assert here to allow future
1419 // generality in invoking this interface.
1420 if (GC_locker::is_active()) {
1421 // A consistency test for GC_locker
1422 assert(GC_locker::needs_gc(), "Should have been set already");
1423 // Skip this foreground collection, instead
1424 // expanding the heap if necessary.
1425 // Need the free list locks for the call to free() in compute_new_size()
1426 compute_new_size();
1427 return;
1428 }
1429 acquire_control_and_collect(full, clear_all_soft_refs);
1430 }
1431
1432 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1433 GenCollectedHeap* gch = GenCollectedHeap::heap();
1434 unsigned int gc_count = gch->total_full_collections();
1435 if (gc_count == full_gc_count) {
1436 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1437 _full_gc_requested = true;
1438 _full_gc_cause = cause;
1439 CGC_lock->notify(); // nudge CMS thread
1440 } else {
1441 assert(gc_count > full_gc_count, "Error: causal loop");
1442 }
1443 }
1444
1445 bool CMSCollector::is_external_interruption() {
1446 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1447 return GCCause::is_user_requested_gc(cause) ||
1448 GCCause::is_serviceability_requested_gc(cause);
1449 }
1450
1451 void CMSCollector::report_concurrent_mode_interruption() {
1452 if (is_external_interruption()) {
1453 if (PrintGCDetails) {
1454 gclog_or_tty->print(" (concurrent mode interrupted)");
1455 }
1456 } else {
1457 if (PrintGCDetails) {
1458 gclog_or_tty->print(" (concurrent mode failure)");
1459 }
1460 _gc_tracer_cm->report_concurrent_mode_failure();
1461 }
1462 }
1463
1464
1465 // The foreground and background collectors need to coordinate in order
1466 // to make sure that they do not mutually interfere with CMS collections.
1467 // When a background collection is active,
1468 // the foreground collector may need to take over (preempt) and
1469 // synchronously complete an ongoing collection. Depending on the
1470 // frequency of the background collections and the heap usage
1471 // of the application, this preemption can be seldom or frequent.
1472 // There are only certain
1473 // points in the background collection that the "collection-baton"
1474 // can be passed to the foreground collector.
1475 //
1476 // The foreground collector will wait for the baton before
1477 // starting any part of the collection. The foreground collector
1478 // will only wait at one location.
1479 //
1480 // The background collector will yield the baton before starting a new
1481 // phase of the collection (e.g., before initial marking, marking from roots,
1482 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1483 // of the loop which switches the phases. The background collector does some
1484 // of the phases (initial mark, final re-mark) with the world stopped.
1485 // Because of locking involved in stopping the world,
1486 // the foreground collector should not block waiting for the background
1487 // collector when it is doing a stop-the-world phase. The background
1488 // collector will yield the baton at an additional point just before
1489 // it enters a stop-the-world phase. Once the world is stopped, the
1490 // background collector checks the phase of the collection. If the
1491 // phase has not changed, it proceeds with the collection. If the
1492 // phase has changed, it skips that phase of the collection. See
1493 // the comments on the use of the Heap_lock in collect_in_background().
1494 //
1495 // Variable used in baton passing.
1496 // _foregroundGCIsActive - Set to true by the foreground collector when
1497 // it wants the baton. The foreground clears it when it has finished
1498 // the collection.
1499 // _foregroundGCShouldWait - Set to true by the background collector
1500 // when it is running. The foreground collector waits while
1501 // _foregroundGCShouldWait is true.
1502 // CGC_lock - monitor used to protect access to the above variables
1503 // and to notify the foreground and background collectors.
1504 // _collectorState - current state of the CMS collection.
1505 //
1506 // The foreground collector
1507 // acquires the CGC_lock
1508 // sets _foregroundGCIsActive
1509 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1510 // various locks acquired in preparation for the collection
1511 // are released so as not to block the background collector
1512 // that is in the midst of a collection
1513 // proceeds with the collection
1514 // clears _foregroundGCIsActive
1515 // returns
1516 //
1517 // The background collector in a loop iterating on the phases of the
1518 // collection
1519 // acquires the CGC_lock
1520 // sets _foregroundGCShouldWait
1521 // if _foregroundGCIsActive is set
1522 // clears _foregroundGCShouldWait, notifies _CGC_lock
1523 // waits on _CGC_lock for _foregroundGCIsActive to become false
1524 // and exits the loop.
1525 // otherwise
1526 // proceed with that phase of the collection
1527 // if the phase is a stop-the-world phase,
1528 // yield the baton once more just before enqueueing
1529 // the stop-world CMS operation (executed by the VM thread).
1530 // returns after all phases of the collection are done
1531 //
1532
1533 void CMSCollector::acquire_control_and_collect(bool full,
1534 bool clear_all_soft_refs) {
1535 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1536 assert(!Thread::current()->is_ConcurrentGC_thread(),
1537 "shouldn't try to acquire control from self!");
1538
1539 // Start the protocol for acquiring control of the
1540 // collection from the background collector (aka CMS thread).
1541 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1542 "VM thread should have CMS token");
1543 // Remember the possibly interrupted state of an ongoing
1544 // concurrent collection
1545 CollectorState first_state = _collectorState;
1546
1547 // Signal to a possibly ongoing concurrent collection that
1548 // we want to do a foreground collection.
1549 _foregroundGCIsActive = true;
1550
1551 // release locks and wait for a notify from the background collector
1552 // releasing the locks in only necessary for phases which
1553 // do yields to improve the granularity of the collection.
1554 assert_lock_strong(bitMapLock());
1555 // We need to lock the Free list lock for the space that we are
1556 // currently collecting.
1557 assert(haveFreelistLocks(), "Must be holding free list locks");
1558 bitMapLock()->unlock();
1559 releaseFreelistLocks();
1560 {
1561 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1562 if (_foregroundGCShouldWait) {
1563 // We are going to be waiting for action for the CMS thread;
1564 // it had better not be gone (for instance at shutdown)!
1565 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1566 "CMS thread must be running");
1567 // Wait here until the background collector gives us the go-ahead
1568 ConcurrentMarkSweepThread::clear_CMS_flag(
1569 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1570 // Get a possibly blocked CMS thread going:
1571 // Note that we set _foregroundGCIsActive true above,
1572 // without protection of the CGC_lock.
1573 CGC_lock->notify();
1574 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1575 "Possible deadlock");
1576 while (_foregroundGCShouldWait) {
1577 // wait for notification
1578 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1579 // Possibility of delay/starvation here, since CMS token does
1580 // not know to give priority to VM thread? Actually, i think
1581 // there wouldn't be any delay/starvation, but the proof of
1582 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1583 }
1584 ConcurrentMarkSweepThread::set_CMS_flag(
1585 ConcurrentMarkSweepThread::CMS_vm_has_token);
1586 }
1587 }
1588 // The CMS_token is already held. Get back the other locks.
1589 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1590 "VM thread should have CMS token");
1591 getFreelistLocks();
1592 bitMapLock()->lock_without_safepoint_check();
1593 if (TraceCMSState) {
1594 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1595 INTPTR_FORMAT " with first state %d", p2i(Thread::current()), first_state);
1596 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1597 }
1598
1599 // Inform cms gen if this was due to partial collection failing.
1600 // The CMS gen may use this fact to determine its expansion policy.
1601 GenCollectedHeap* gch = GenCollectedHeap::heap();
1602 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1603 assert(!_cmsGen->incremental_collection_failed(),
1604 "Should have been noticed, reacted to and cleared");
1605 _cmsGen->set_incremental_collection_failed();
1606 }
1607
1608 if (first_state > Idling) {
1609 report_concurrent_mode_interruption();
1610 }
1611
1612 set_did_compact(true);
1613
1614 // If the collection is being acquired from the background
1615 // collector, there may be references on the discovered
1616 // references lists. Abandon those references, since some
1617 // of them may have become unreachable after concurrent
1618 // discovery; the STW compacting collector will redo discovery
1619 // more precisely, without being subject to floating garbage.
1620 // Leaving otherwise unreachable references in the discovered
1621 // lists would require special handling.
1622 ref_processor()->disable_discovery();
1623 ref_processor()->abandon_partial_discovery();
1624 ref_processor()->verify_no_references_recorded();
1625
1626 if (first_state > Idling) {
1627 save_heap_summary();
1628 }
1629
1630 do_compaction_work(clear_all_soft_refs);
1631
1632 // Has the GC time limit been exceeded?
1633 size_t max_eden_size = _young_gen->max_capacity() -
1634 _young_gen->to()->capacity() -
1635 _young_gen->from()->capacity();
1636 GCCause::Cause gc_cause = gch->gc_cause();
1637 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1638 _young_gen->eden()->used(),
1639 _cmsGen->max_capacity(),
1640 max_eden_size,
1641 full,
1642 gc_cause,
1643 gch->collector_policy());
1644
1645 // Reset the expansion cause, now that we just completed
1646 // a collection cycle.
1647 clear_expansion_cause();
1648 _foregroundGCIsActive = false;
1649 return;
1650 }
1651
1652 // Resize the tenured generation
1653 // after obtaining the free list locks for the
1654 // two generations.
1655 void CMSCollector::compute_new_size() {
1656 assert_locked_or_safepoint(Heap_lock);
1657 FreelistLocker z(this);
1658 MetaspaceGC::compute_new_size();
1659 _cmsGen->compute_new_size_free_list();
1660 }
1661
1662 // A work method used by the foreground collector to do
1663 // a mark-sweep-compact.
1664 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1665 GenCollectedHeap* gch = GenCollectedHeap::heap();
1666
1667 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1668 gc_timer->register_gc_start();
1669
1670 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1671 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1672
1673 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
1674
1675 // Temporarily widen the span of the weak reference processing to
1676 // the entire heap.
1677 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1678 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1679 // Temporarily, clear the "is_alive_non_header" field of the
1680 // reference processor.
1681 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1682 // Temporarily make reference _processing_ single threaded (non-MT).
1683 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1684 // Temporarily make refs discovery atomic
1685 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1686 // Temporarily make reference _discovery_ single threaded (non-MT)
1687 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1688
1689 ref_processor()->set_enqueuing_is_done(false);
1690 ref_processor()->enable_discovery();
1691 ref_processor()->setup_policy(clear_all_soft_refs);
1692 // If an asynchronous collection finishes, the _modUnionTable is
1693 // all clear. If we are assuming the collection from an asynchronous
1694 // collection, clear the _modUnionTable.
1695 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1696 "_modUnionTable should be clear if the baton was not passed");
1697 _modUnionTable.clear_all();
1698 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1699 "mod union for klasses should be clear if the baton was passed");
1700 _ct->klass_rem_set()->clear_mod_union();
1701
1702 // We must adjust the allocation statistics being maintained
1703 // in the free list space. We do so by reading and clearing
1704 // the sweep timer and updating the block flux rate estimates below.
1705 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1706 if (_inter_sweep_timer.is_active()) {
1707 _inter_sweep_timer.stop();
1708 // Note that we do not use this sample to update the _inter_sweep_estimate.
1709 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1710 _inter_sweep_estimate.padded_average(),
1711 _intra_sweep_estimate.padded_average());
1712 }
1713
1714 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1715 ref_processor(), clear_all_soft_refs);
1716 #ifdef ASSERT
1717 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1718 size_t free_size = cms_space->free();
1719 assert(free_size ==
1720 pointer_delta(cms_space->end(), cms_space->compaction_top())
1721 * HeapWordSize,
1722 "All the free space should be compacted into one chunk at top");
1723 assert(cms_space->dictionary()->total_chunk_size(
1724 debug_only(cms_space->freelistLock())) == 0 ||
1725 cms_space->totalSizeInIndexedFreeLists() == 0,
1726 "All the free space should be in a single chunk");
1727 size_t num = cms_space->totalCount();
1728 assert((free_size == 0 && num == 0) ||
1729 (free_size > 0 && (num == 1 || num == 2)),
1730 "There should be at most 2 free chunks after compaction");
1731 #endif // ASSERT
1732 _collectorState = Resetting;
1733 assert(_restart_addr == NULL,
1734 "Should have been NULL'd before baton was passed");
1735 reset(false /* == !concurrent */);
1736 _cmsGen->reset_after_compaction();
1737 _concurrent_cycles_since_last_unload = 0;
1738
1739 // Clear any data recorded in the PLAB chunk arrays.
1740 if (_survivor_plab_array != NULL) {
1741 reset_survivor_plab_arrays();
1742 }
1743
1744 // Adjust the per-size allocation stats for the next epoch.
1745 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1746 // Restart the "inter sweep timer" for the next epoch.
1747 _inter_sweep_timer.reset();
1748 _inter_sweep_timer.start();
1749
1750 gc_timer->register_gc_end();
1751
1752 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1753
1754 // For a mark-sweep-compact, compute_new_size() will be called
1755 // in the heap's do_collection() method.
1756 }
1757
1758 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1759 ContiguousSpace* eden_space = _young_gen->eden();
1760 ContiguousSpace* from_space = _young_gen->from();
1761 ContiguousSpace* to_space = _young_gen->to();
1762 // Eden
1763 if (_eden_chunk_array != NULL) {
1764 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1765 p2i(eden_space->bottom()), p2i(eden_space->top()),
1766 p2i(eden_space->end()), eden_space->capacity());
1767 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1768 "_eden_chunk_capacity=" SIZE_FORMAT,
1769 _eden_chunk_index, _eden_chunk_capacity);
1770 for (size_t i = 0; i < _eden_chunk_index; i++) {
1771 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1772 i, p2i(_eden_chunk_array[i]));
1773 }
1774 }
1775 // Survivor
1776 if (_survivor_chunk_array != NULL) {
1777 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1778 p2i(from_space->bottom()), p2i(from_space->top()),
1779 p2i(from_space->end()), from_space->capacity());
1780 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1781 "_survivor_chunk_capacity=" SIZE_FORMAT,
1782 _survivor_chunk_index, _survivor_chunk_capacity);
1783 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1784 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1785 i, p2i(_survivor_chunk_array[i]));
1786 }
1787 }
1788 }
1789
1790 void CMSCollector::getFreelistLocks() const {
1791 // Get locks for all free lists in all generations that this
1792 // collector is responsible for
1793 _cmsGen->freelistLock()->lock_without_safepoint_check();
1794 }
1795
1796 void CMSCollector::releaseFreelistLocks() const {
1797 // Release locks for all free lists in all generations that this
1798 // collector is responsible for
1799 _cmsGen->freelistLock()->unlock();
1800 }
1801
1802 bool CMSCollector::haveFreelistLocks() const {
1803 // Check locks for all free lists in all generations that this
1804 // collector is responsible for
1805 assert_lock_strong(_cmsGen->freelistLock());
1806 PRODUCT_ONLY(ShouldNotReachHere());
1807 return true;
1808 }
1809
1810 // A utility class that is used by the CMS collector to
1811 // temporarily "release" the foreground collector from its
1812 // usual obligation to wait for the background collector to
1813 // complete an ongoing phase before proceeding.
1814 class ReleaseForegroundGC: public StackObj {
1815 private:
1816 CMSCollector* _c;
1817 public:
1818 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1819 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1820 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1821 // allow a potentially blocked foreground collector to proceed
1822 _c->_foregroundGCShouldWait = false;
1823 if (_c->_foregroundGCIsActive) {
1824 CGC_lock->notify();
1825 }
1826 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1827 "Possible deadlock");
1828 }
1829
1830 ~ReleaseForegroundGC() {
1831 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1832 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1833 _c->_foregroundGCShouldWait = true;
1834 }
1835 };
1836
1837 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1838 assert(Thread::current()->is_ConcurrentGC_thread(),
1839 "A CMS asynchronous collection is only allowed on a CMS thread.");
1840
1841 GenCollectedHeap* gch = GenCollectedHeap::heap();
1842 {
1843 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1844 MutexLockerEx hl(Heap_lock, safepoint_check);
1845 FreelistLocker fll(this);
1846 MutexLockerEx x(CGC_lock, safepoint_check);
1847 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
1848 // The foreground collector is active or we're
1849 // not using asynchronous collections. Skip this
1850 // background collection.
1851 assert(!_foregroundGCShouldWait, "Should be clear");
1852 return;
1853 } else {
1854 assert(_collectorState == Idling, "Should be idling before start.");
1855 _collectorState = InitialMarking;
1856 register_gc_start(cause);
1857 // Reset the expansion cause, now that we are about to begin
1858 // a new cycle.
1859 clear_expansion_cause();
1860
1861 // Clear the MetaspaceGC flag since a concurrent collection
1862 // is starting but also clear it after the collection.
1863 MetaspaceGC::set_should_concurrent_collect(false);
1864 }
1865 // Decide if we want to enable class unloading as part of the
1866 // ensuing concurrent GC cycle.
1867 update_should_unload_classes();
1868 _full_gc_requested = false; // acks all outstanding full gc requests
1869 _full_gc_cause = GCCause::_no_gc;
1870 // Signal that we are about to start a collection
1871 gch->increment_total_full_collections(); // ... starting a collection cycle
1872 _collection_count_start = gch->total_full_collections();
1873 }
1874
1875 // Used for PrintGC
1876 size_t prev_used;
1877 if (PrintGC && Verbose) {
1878 prev_used = _cmsGen->used();
1879 }
1880
1881 // The change of the collection state is normally done at this level;
1882 // the exceptions are phases that are executed while the world is
1883 // stopped. For those phases the change of state is done while the
1884 // world is stopped. For baton passing purposes this allows the
1885 // background collector to finish the phase and change state atomically.
1886 // The foreground collector cannot wait on a phase that is done
1887 // while the world is stopped because the foreground collector already
1888 // has the world stopped and would deadlock.
1889 while (_collectorState != Idling) {
1890 if (TraceCMSState) {
1891 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
1892 p2i(Thread::current()), _collectorState);
1893 }
1894 // The foreground collector
1895 // holds the Heap_lock throughout its collection.
1896 // holds the CMS token (but not the lock)
1897 // except while it is waiting for the background collector to yield.
1898 //
1899 // The foreground collector should be blocked (not for long)
1900 // if the background collector is about to start a phase
1901 // executed with world stopped. If the background
1902 // collector has already started such a phase, the
1903 // foreground collector is blocked waiting for the
1904 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1905 // are executed in the VM thread.
1906 //
1907 // The locking order is
1908 // PendingListLock (PLL) -- if applicable (FinalMarking)
1909 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1910 // CMS token (claimed in
1911 // stop_world_and_do() -->
1912 // safepoint_synchronize() -->
1913 // CMSThread::synchronize())
1914
1915 {
1916 // Check if the FG collector wants us to yield.
1917 CMSTokenSync x(true); // is cms thread
1918 if (waitForForegroundGC()) {
1919 // We yielded to a foreground GC, nothing more to be
1920 // done this round.
1921 assert(_foregroundGCShouldWait == false, "We set it to false in "
1922 "waitForForegroundGC()");
1923 if (TraceCMSState) {
1924 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1925 " exiting collection CMS state %d",
1926 p2i(Thread::current()), _collectorState);
1927 }
1928 return;
1929 } else {
1930 // The background collector can run but check to see if the
1931 // foreground collector has done a collection while the
1932 // background collector was waiting to get the CGC_lock
1933 // above. If yes, break so that _foregroundGCShouldWait
1934 // is cleared before returning.
1935 if (_collectorState == Idling) {
1936 break;
1937 }
1938 }
1939 }
1940
1941 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1942 "should be waiting");
1943
1944 switch (_collectorState) {
1945 case InitialMarking:
1946 {
1947 ReleaseForegroundGC x(this);
1948 stats().record_cms_begin();
1949 VM_CMS_Initial_Mark initial_mark_op(this);
1950 VMThread::execute(&initial_mark_op);
1951 }
1952 // The collector state may be any legal state at this point
1953 // since the background collector may have yielded to the
1954 // foreground collector.
1955 break;
1956 case Marking:
1957 // initial marking in checkpointRootsInitialWork has been completed
1958 if (markFromRoots()) { // we were successful
1959 assert(_collectorState == Precleaning, "Collector state should "
1960 "have changed");
1961 } else {
1962 assert(_foregroundGCIsActive, "Internal state inconsistency");
1963 }
1964 break;
1965 case Precleaning:
1966 // marking from roots in markFromRoots has been completed
1967 preclean();
1968 assert(_collectorState == AbortablePreclean ||
1969 _collectorState == FinalMarking,
1970 "Collector state should have changed");
1971 break;
1972 case AbortablePreclean:
1973 abortable_preclean();
1974 assert(_collectorState == FinalMarking, "Collector state should "
1975 "have changed");
1976 break;
1977 case FinalMarking:
1978 {
1979 ReleaseForegroundGC x(this);
1980
1981 VM_CMS_Final_Remark final_remark_op(this);
1982 VMThread::execute(&final_remark_op);
1983 }
1984 assert(_foregroundGCShouldWait, "block post-condition");
1985 break;
1986 case Sweeping:
1987 // final marking in checkpointRootsFinal has been completed
1988 sweep();
1989 assert(_collectorState == Resizing, "Collector state change "
1990 "to Resizing must be done under the free_list_lock");
1991
1992 case Resizing: {
1993 // Sweeping has been completed...
1994 // At this point the background collection has completed.
1995 // Don't move the call to compute_new_size() down
1996 // into code that might be executed if the background
1997 // collection was preempted.
1998 {
1999 ReleaseForegroundGC x(this); // unblock FG collection
2000 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2001 CMSTokenSync z(true); // not strictly needed.
2002 if (_collectorState == Resizing) {
2003 compute_new_size();
2004 save_heap_summary();
2005 _collectorState = Resetting;
2006 } else {
2007 assert(_collectorState == Idling, "The state should only change"
2008 " because the foreground collector has finished the collection");
2009 }
2010 }
2011 break;
2012 }
2013 case Resetting:
2014 // CMS heap resizing has been completed
2015 reset(true);
2016 assert(_collectorState == Idling, "Collector state should "
2017 "have changed");
2018
2019 MetaspaceGC::set_should_concurrent_collect(false);
2020
2021 stats().record_cms_end();
2022 // Don't move the concurrent_phases_end() and compute_new_size()
2023 // calls to here because a preempted background collection
2024 // has it's state set to "Resetting".
2025 break;
2026 case Idling:
2027 default:
2028 ShouldNotReachHere();
2029 break;
2030 }
2031 if (TraceCMSState) {
2032 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2033 p2i(Thread::current()), _collectorState);
2034 }
2035 assert(_foregroundGCShouldWait, "block post-condition");
2036 }
2037
2038 // Should this be in gc_epilogue?
2039 collector_policy()->counters()->update_counters();
2040
2041 {
2042 // Clear _foregroundGCShouldWait and, in the event that the
2043 // foreground collector is waiting, notify it, before
2044 // returning.
2045 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2046 _foregroundGCShouldWait = false;
2047 if (_foregroundGCIsActive) {
2048 CGC_lock->notify();
2049 }
2050 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2051 "Possible deadlock");
2052 }
2053 if (TraceCMSState) {
2054 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2055 " exiting collection CMS state %d",
2056 p2i(Thread::current()), _collectorState);
2057 }
2058 if (PrintGC && Verbose) {
2059 _cmsGen->print_heap_change(prev_used);
2060 }
2061 }
2062
2063 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2064 _cms_start_registered = true;
2065 _gc_timer_cm->register_gc_start();
2066 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2067 }
2068
2069 void CMSCollector::register_gc_end() {
2070 if (_cms_start_registered) {
2071 report_heap_summary(GCWhen::AfterGC);
2072
2073 _gc_timer_cm->register_gc_end();
2074 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2075 _cms_start_registered = false;
2076 }
2077 }
2078
2079 void CMSCollector::save_heap_summary() {
2080 GenCollectedHeap* gch = GenCollectedHeap::heap();
2081 _last_heap_summary = gch->create_heap_summary();
2082 _last_metaspace_summary = gch->create_metaspace_summary();
2083 }
2084
2085 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2086 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2087 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2088 }
2089
2090 bool CMSCollector::waitForForegroundGC() {
2091 bool res = false;
2092 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2093 "CMS thread should have CMS token");
2094 // Block the foreground collector until the
2095 // background collectors decides whether to
2096 // yield.
2097 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2098 _foregroundGCShouldWait = true;
2099 if (_foregroundGCIsActive) {
2100 // The background collector yields to the
2101 // foreground collector and returns a value
2102 // indicating that it has yielded. The foreground
2103 // collector can proceed.
2104 res = true;
2105 _foregroundGCShouldWait = false;
2106 ConcurrentMarkSweepThread::clear_CMS_flag(
2107 ConcurrentMarkSweepThread::CMS_cms_has_token);
2108 ConcurrentMarkSweepThread::set_CMS_flag(
2109 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2110 // Get a possibly blocked foreground thread going
2111 CGC_lock->notify();
2112 if (TraceCMSState) {
2113 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2114 p2i(Thread::current()), _collectorState);
2115 }
2116 while (_foregroundGCIsActive) {
2117 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2118 }
2119 ConcurrentMarkSweepThread::set_CMS_flag(
2120 ConcurrentMarkSweepThread::CMS_cms_has_token);
2121 ConcurrentMarkSweepThread::clear_CMS_flag(
2122 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2123 }
2124 if (TraceCMSState) {
2125 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2126 p2i(Thread::current()), _collectorState);
2127 }
2128 return res;
2129 }
2130
2131 // Because of the need to lock the free lists and other structures in
2132 // the collector, common to all the generations that the collector is
2133 // collecting, we need the gc_prologues of individual CMS generations
2134 // delegate to their collector. It may have been simpler had the
2135 // current infrastructure allowed one to call a prologue on a
2136 // collector. In the absence of that we have the generation's
2137 // prologue delegate to the collector, which delegates back
2138 // some "local" work to a worker method in the individual generations
2139 // that it's responsible for collecting, while itself doing any
2140 // work common to all generations it's responsible for. A similar
2141 // comment applies to the gc_epilogue()'s.
2142 // The role of the variable _between_prologue_and_epilogue is to
2143 // enforce the invocation protocol.
2144 void CMSCollector::gc_prologue(bool full) {
2145 // Call gc_prologue_work() for the CMSGen
2146 // we are responsible for.
2147
2148 // The following locking discipline assumes that we are only called
2149 // when the world is stopped.
2150 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2151
2152 // The CMSCollector prologue must call the gc_prologues for the
2153 // "generations" that it's responsible
2154 // for.
2155
2156 assert( Thread::current()->is_VM_thread()
2157 || ( CMSScavengeBeforeRemark
2158 && Thread::current()->is_ConcurrentGC_thread()),
2159 "Incorrect thread type for prologue execution");
2160
2161 if (_between_prologue_and_epilogue) {
2162 // We have already been invoked; this is a gc_prologue delegation
2163 // from yet another CMS generation that we are responsible for, just
2164 // ignore it since all relevant work has already been done.
2165 return;
2166 }
2167
2168 // set a bit saying prologue has been called; cleared in epilogue
2169 _between_prologue_and_epilogue = true;
2170 // Claim locks for common data structures, then call gc_prologue_work()
2171 // for each CMSGen.
2172
2173 getFreelistLocks(); // gets free list locks on constituent spaces
2174 bitMapLock()->lock_without_safepoint_check();
2175
2176 // Should call gc_prologue_work() for all cms gens we are responsible for
2177 bool duringMarking = _collectorState >= Marking
2178 && _collectorState < Sweeping;
2179
2180 // The young collections clear the modified oops state, which tells if
2181 // there are any modified oops in the class. The remark phase also needs
2182 // that information. Tell the young collection to save the union of all
2183 // modified klasses.
2184 if (duringMarking) {
2185 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2186 }
2187
2188 bool registerClosure = duringMarking;
2189
2190 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2191 &_modUnionClosurePar
2192 : &_modUnionClosure;
2193 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2194
2195 if (!full) {
2196 stats().record_gc0_begin();
2197 }
2198 }
2199
2200 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2201
2202 _capacity_at_prologue = capacity();
2203 _used_at_prologue = used();
2204
2205 // Delegate to CMScollector which knows how to coordinate between
2206 // this and any other CMS generations that it is responsible for
2207 // collecting.
2208 collector()->gc_prologue(full);
2209 }
2210
2211 // This is a "private" interface for use by this generation's CMSCollector.
2212 // Not to be called directly by any other entity (for instance,
2213 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2214 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2215 bool registerClosure, ModUnionClosure* modUnionClosure) {
2216 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2217 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2218 "Should be NULL");
2219 if (registerClosure) {
2220 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2221 }
2222 cmsSpace()->gc_prologue();
2223 // Clear stat counters
2224 NOT_PRODUCT(
2225 assert(_numObjectsPromoted == 0, "check");
2226 assert(_numWordsPromoted == 0, "check");
2227 if (Verbose && PrintGC) {
2228 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2229 SIZE_FORMAT" bytes concurrently",
2230 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2231 }
2232 _numObjectsAllocated = 0;
2233 _numWordsAllocated = 0;
2234 )
2235 }
2236
2237 void CMSCollector::gc_epilogue(bool full) {
2238 // The following locking discipline assumes that we are only called
2239 // when the world is stopped.
2240 assert(SafepointSynchronize::is_at_safepoint(),
2241 "world is stopped assumption");
2242
2243 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2244 // if linear allocation blocks need to be appropriately marked to allow the
2245 // the blocks to be parsable. We also check here whether we need to nudge the
2246 // CMS collector thread to start a new cycle (if it's not already active).
2247 assert( Thread::current()->is_VM_thread()
2248 || ( CMSScavengeBeforeRemark
2249 && Thread::current()->is_ConcurrentGC_thread()),
2250 "Incorrect thread type for epilogue execution");
2251
2252 if (!_between_prologue_and_epilogue) {
2253 // We have already been invoked; this is a gc_epilogue delegation
2254 // from yet another CMS generation that we are responsible for, just
2255 // ignore it since all relevant work has already been done.
2256 return;
2257 }
2258 assert(haveFreelistLocks(), "must have freelist locks");
2259 assert_lock_strong(bitMapLock());
2260
2261 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2262
2263 _cmsGen->gc_epilogue_work(full);
2264
2265 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2266 // in case sampling was not already enabled, enable it
2267 _start_sampling = true;
2268 }
2269 // reset _eden_chunk_array so sampling starts afresh
2270 _eden_chunk_index = 0;
2271
2272 size_t cms_used = _cmsGen->cmsSpace()->used();
2273
2274 // update performance counters - this uses a special version of
2275 // update_counters() that allows the utilization to be passed as a
2276 // parameter, avoiding multiple calls to used().
2277 //
2278 _cmsGen->update_counters(cms_used);
2279
2280 bitMapLock()->unlock();
2281 releaseFreelistLocks();
2282
2283 if (!CleanChunkPoolAsync) {
2284 Chunk::clean_chunk_pool();
2285 }
2286
2287 set_did_compact(false);
2288 _between_prologue_and_epilogue = false; // ready for next cycle
2289 }
2290
2291 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2292 collector()->gc_epilogue(full);
2293
2294 // Also reset promotion tracking in par gc thread states.
2295 for (uint i = 0; i < ParallelGCThreads; i++) {
2296 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2297 }
2298 }
2299
2300 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2301 assert(!incremental_collection_failed(), "Should have been cleared");
2302 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2303 cmsSpace()->gc_epilogue();
2304 // Print stat counters
2305 NOT_PRODUCT(
2306 assert(_numObjectsAllocated == 0, "check");
2307 assert(_numWordsAllocated == 0, "check");
2308 if (Verbose && PrintGC) {
2309 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2310 SIZE_FORMAT" bytes",
2311 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2312 }
2313 _numObjectsPromoted = 0;
2314 _numWordsPromoted = 0;
2315 )
2316
2317 if (PrintGC && Verbose) {
2318 // Call down the chain in contiguous_available needs the freelistLock
2319 // so print this out before releasing the freeListLock.
2320 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2321 contiguous_available());
2322 }
2323 }
2324
2325 #ifndef PRODUCT
2326 bool CMSCollector::have_cms_token() {
2327 Thread* thr = Thread::current();
2328 if (thr->is_VM_thread()) {
2329 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2330 } else if (thr->is_ConcurrentGC_thread()) {
2331 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2332 } else if (thr->is_GC_task_thread()) {
2333 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2334 ParGCRareEvent_lock->owned_by_self();
2335 }
2336 return false;
2337 }
2338 #endif
2339
2340 // Check reachability of the given heap address in CMS generation,
2341 // treating all other generations as roots.
2342 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2343 // We could "guarantee" below, rather than assert, but I'll
2344 // leave these as "asserts" so that an adventurous debugger
2345 // could try this in the product build provided some subset of
2346 // the conditions were met, provided they were interested in the
2347 // results and knew that the computation below wouldn't interfere
2348 // with other concurrent computations mutating the structures
2349 // being read or written.
2350 assert(SafepointSynchronize::is_at_safepoint(),
2351 "Else mutations in object graph will make answer suspect");
2352 assert(have_cms_token(), "Should hold cms token");
2353 assert(haveFreelistLocks(), "must hold free list locks");
2354 assert_lock_strong(bitMapLock());
2355
2356 // Clear the marking bit map array before starting, but, just
2357 // for kicks, first report if the given address is already marked
2358 gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2359 _markBitMap.isMarked(addr) ? "" : " not");
2360
2361 if (verify_after_remark()) {
2362 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2363 bool result = verification_mark_bm()->isMarked(addr);
2364 gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2365 result ? "IS" : "is NOT");
2366 return result;
2367 } else {
2368 gclog_or_tty->print_cr("Could not compute result");
2369 return false;
2370 }
2371 }
2372
2373
2374 void
2375 CMSCollector::print_on_error(outputStream* st) {
2376 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2377 if (collector != NULL) {
2378 CMSBitMap* bitmap = &collector->_markBitMap;
2379 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2380 bitmap->print_on_error(st, " Bits: ");
2381
2382 st->cr();
2383
2384 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2385 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2386 mut_bitmap->print_on_error(st, " Bits: ");
2387 }
2388 }
2389
2390 ////////////////////////////////////////////////////////
2391 // CMS Verification Support
2392 ////////////////////////////////////////////////////////
2393 // Following the remark phase, the following invariant
2394 // should hold -- each object in the CMS heap which is
2395 // marked in markBitMap() should be marked in the verification_mark_bm().
2396
2397 class VerifyMarkedClosure: public BitMapClosure {
2398 CMSBitMap* _marks;
2399 bool _failed;
2400
2401 public:
2402 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2403
2404 bool do_bit(size_t offset) {
2405 HeapWord* addr = _marks->offsetToHeapWord(offset);
2406 if (!_marks->isMarked(addr)) {
2407 oop(addr)->print_on(gclog_or_tty);
2408 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", p2i(addr));
2409 _failed = true;
2410 }
2411 return true;
2412 }
2413
2414 bool failed() { return _failed; }
2415 };
2416
2417 bool CMSCollector::verify_after_remark(bool silent) {
2418 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2419 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2420 static bool init = false;
2421
2422 assert(SafepointSynchronize::is_at_safepoint(),
2423 "Else mutations in object graph will make answer suspect");
2424 assert(have_cms_token(),
2425 "Else there may be mutual interference in use of "
2426 " verification data structures");
2427 assert(_collectorState > Marking && _collectorState <= Sweeping,
2428 "Else marking info checked here may be obsolete");
2429 assert(haveFreelistLocks(), "must hold free list locks");
2430 assert_lock_strong(bitMapLock());
2431
2432
2433 // Allocate marking bit map if not already allocated
2434 if (!init) { // first time
2435 if (!verification_mark_bm()->allocate(_span)) {
2436 return false;
2437 }
2438 init = true;
2439 }
2440
2441 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2442
2443 // Turn off refs discovery -- so we will be tracing through refs.
2444 // This is as intended, because by this time
2445 // GC must already have cleared any refs that need to be cleared,
2446 // and traced those that need to be marked; moreover,
2447 // the marking done here is not going to interfere in any
2448 // way with the marking information used by GC.
2449 NoRefDiscovery no_discovery(ref_processor());
2450
2451 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2452
2453 // Clear any marks from a previous round
2454 verification_mark_bm()->clear_all();
2455 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2456 verify_work_stacks_empty();
2457
2458 GenCollectedHeap* gch = GenCollectedHeap::heap();
2459 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2460 // Update the saved marks which may affect the root scans.
2461 gch->save_marks();
2462
2463 if (CMSRemarkVerifyVariant == 1) {
2464 // In this first variant of verification, we complete
2465 // all marking, then check if the new marks-vector is
2466 // a subset of the CMS marks-vector.
2467 verify_after_remark_work_1();
2468 } else if (CMSRemarkVerifyVariant == 2) {
2469 // In this second variant of verification, we flag an error
2470 // (i.e. an object reachable in the new marks-vector not reachable
2471 // in the CMS marks-vector) immediately, also indicating the
2472 // identify of an object (A) that references the unmarked object (B) --
2473 // presumably, a mutation to A failed to be picked up by preclean/remark?
2474 verify_after_remark_work_2();
2475 } else {
2476 warning("Unrecognized value " UINTX_FORMAT " for CMSRemarkVerifyVariant",
2477 CMSRemarkVerifyVariant);
2478 }
2479 if (!silent) gclog_or_tty->print(" done] ");
2480 return true;
2481 }
2482
2483 void CMSCollector::verify_after_remark_work_1() {
2484 ResourceMark rm;
2485 HandleMark hm;
2486 GenCollectedHeap* gch = GenCollectedHeap::heap();
2487
2488 // Get a clear set of claim bits for the roots processing to work with.
2489 ClassLoaderDataGraph::clear_claimed_marks();
2490
2491 // Mark from roots one level into CMS
2492 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2493 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2494
2495 gch->gen_process_roots(_cmsGen->level(),
2496 true, // younger gens are roots
2497 true, // activate StrongRootsScope
2498 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2499 should_unload_classes(),
2500 ¬Older,
2501 NULL,
2502 NULL); // SSS: Provide correct closure
2503
2504 // Now mark from the roots
2505 MarkFromRootsClosure markFromRootsClosure(this, _span,
2506 verification_mark_bm(), verification_mark_stack(),
2507 false /* don't yield */, true /* verifying */);
2508 assert(_restart_addr == NULL, "Expected pre-condition");
2509 verification_mark_bm()->iterate(&markFromRootsClosure);
2510 while (_restart_addr != NULL) {
2511 // Deal with stack overflow: by restarting at the indicated
2512 // address.
2513 HeapWord* ra = _restart_addr;
2514 markFromRootsClosure.reset(ra);
2515 _restart_addr = NULL;
2516 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2517 }
2518 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2519 verify_work_stacks_empty();
2520
2521 // Marking completed -- now verify that each bit marked in
2522 // verification_mark_bm() is also marked in markBitMap(); flag all
2523 // errors by printing corresponding objects.
2524 VerifyMarkedClosure vcl(markBitMap());
2525 verification_mark_bm()->iterate(&vcl);
2526 if (vcl.failed()) {
2527 gclog_or_tty->print("Verification failed");
2528 Universe::heap()->print_on(gclog_or_tty);
2529 fatal("CMS: failed marking verification after remark");
2530 }
2531 }
2532
2533 class VerifyKlassOopsKlassClosure : public KlassClosure {
2534 class VerifyKlassOopsClosure : public OopClosure {
2535 CMSBitMap* _bitmap;
2536 public:
2537 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2538 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2539 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2540 } _oop_closure;
2541 public:
2542 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2543 void do_klass(Klass* k) {
2544 k->oops_do(&_oop_closure);
2545 }
2546 };
2547
2548 void CMSCollector::verify_after_remark_work_2() {
2549 ResourceMark rm;
2550 HandleMark hm;
2551 GenCollectedHeap* gch = GenCollectedHeap::heap();
2552
2553 // Get a clear set of claim bits for the roots processing to work with.
2554 ClassLoaderDataGraph::clear_claimed_marks();
2555
2556 // Mark from roots one level into CMS
2557 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2558 markBitMap());
2559 CLDToOopClosure cld_closure(¬Older, true);
2560
2561 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2562
2563 gch->gen_process_roots(_cmsGen->level(),
2564 true, // younger gens are roots
2565 true, // activate StrongRootsScope
2566 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2567 should_unload_classes(),
2568 ¬Older,
2569 NULL,
2570 &cld_closure);
2571
2572 // Now mark from the roots
2573 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2574 verification_mark_bm(), markBitMap(), verification_mark_stack());
2575 assert(_restart_addr == NULL, "Expected pre-condition");
2576 verification_mark_bm()->iterate(&markFromRootsClosure);
2577 while (_restart_addr != NULL) {
2578 // Deal with stack overflow: by restarting at the indicated
2579 // address.
2580 HeapWord* ra = _restart_addr;
2581 markFromRootsClosure.reset(ra);
2582 _restart_addr = NULL;
2583 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2584 }
2585 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2586 verify_work_stacks_empty();
2587
2588 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2589 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2590
2591 // Marking completed -- now verify that each bit marked in
2592 // verification_mark_bm() is also marked in markBitMap(); flag all
2593 // errors by printing corresponding objects.
2594 VerifyMarkedClosure vcl(markBitMap());
2595 verification_mark_bm()->iterate(&vcl);
2596 assert(!vcl.failed(), "Else verification above should not have succeeded");
2597 }
2598
2599 void ConcurrentMarkSweepGeneration::save_marks() {
2600 // delegate to CMS space
2601 cmsSpace()->save_marks();
2602 for (uint i = 0; i < ParallelGCThreads; i++) {
2603 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2604 }
2605 }
2606
2607 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2608 return cmsSpace()->no_allocs_since_save_marks();
2609 }
2610
2611 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2612 \
2613 void ConcurrentMarkSweepGeneration:: \
2614 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2615 cl->set_generation(this); \
2616 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2617 cl->reset_generation(); \
2618 save_marks(); \
2619 }
2620
2621 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2622
2623 void
2624 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2625 if (freelistLock()->owned_by_self()) {
2626 Generation::oop_iterate(cl);
2627 } else {
2628 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2629 Generation::oop_iterate(cl);
2630 }
2631 }
2632
2633 void
2634 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2635 if (freelistLock()->owned_by_self()) {
2636 Generation::object_iterate(cl);
2637 } else {
2638 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2639 Generation::object_iterate(cl);
2640 }
2641 }
2642
2643 void
2644 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2645 if (freelistLock()->owned_by_self()) {
2646 Generation::safe_object_iterate(cl);
2647 } else {
2648 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2649 Generation::safe_object_iterate(cl);
2650 }
2651 }
2652
2653 void
2654 ConcurrentMarkSweepGeneration::post_compact() {
2655 }
2656
2657 void
2658 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2659 // Fix the linear allocation blocks to look like free blocks.
2660
2661 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2662 // are not called when the heap is verified during universe initialization and
2663 // at vm shutdown.
2664 if (freelistLock()->owned_by_self()) {
2665 cmsSpace()->prepare_for_verify();
2666 } else {
2667 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2668 cmsSpace()->prepare_for_verify();
2669 }
2670 }
2671
2672 void
2673 ConcurrentMarkSweepGeneration::verify() {
2674 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2675 // are not called when the heap is verified during universe initialization and
2676 // at vm shutdown.
2677 if (freelistLock()->owned_by_self()) {
2678 cmsSpace()->verify();
2679 } else {
2680 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2681 cmsSpace()->verify();
2682 }
2683 }
2684
2685 void CMSCollector::verify() {
2686 _cmsGen->verify();
2687 }
2688
2689 #ifndef PRODUCT
2690 bool CMSCollector::overflow_list_is_empty() const {
2691 assert(_num_par_pushes >= 0, "Inconsistency");
2692 if (_overflow_list == NULL) {
2693 assert(_num_par_pushes == 0, "Inconsistency");
2694 }
2695 return _overflow_list == NULL;
2696 }
2697
2698 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2699 // merely consolidate assertion checks that appear to occur together frequently.
2700 void CMSCollector::verify_work_stacks_empty() const {
2701 assert(_markStack.isEmpty(), "Marking stack should be empty");
2702 assert(overflow_list_is_empty(), "Overflow list should be empty");
2703 }
2704
2705 void CMSCollector::verify_overflow_empty() const {
2706 assert(overflow_list_is_empty(), "Overflow list should be empty");
2707 assert(no_preserved_marks(), "No preserved marks");
2708 }
2709 #endif // PRODUCT
2710
2711 // Decide if we want to enable class unloading as part of the
2712 // ensuing concurrent GC cycle. We will collect and
2713 // unload classes if it's the case that:
2714 // (1) an explicit gc request has been made and the flag
2715 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2716 // (2) (a) class unloading is enabled at the command line, and
2717 // (b) old gen is getting really full
2718 // NOTE: Provided there is no change in the state of the heap between
2719 // calls to this method, it should have idempotent results. Moreover,
2720 // its results should be monotonically increasing (i.e. going from 0 to 1,
2721 // but not 1 to 0) between successive calls between which the heap was
2722 // not collected. For the implementation below, it must thus rely on
2723 // the property that concurrent_cycles_since_last_unload()
2724 // will not decrease unless a collection cycle happened and that
2725 // _cmsGen->is_too_full() are
2726 // themselves also monotonic in that sense. See check_monotonicity()
2727 // below.
2728 void CMSCollector::update_should_unload_classes() {
2729 _should_unload_classes = false;
2730 // Condition 1 above
2731 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2732 _should_unload_classes = true;
2733 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2734 // Disjuncts 2.b.(i,ii,iii) above
2735 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2736 CMSClassUnloadingMaxInterval)
2737 || _cmsGen->is_too_full();
2738 }
2739 }
2740
2741 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2742 bool res = should_concurrent_collect();
2743 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2744 return res;
2745 }
2746
2747 void CMSCollector::setup_cms_unloading_and_verification_state() {
2748 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2749 || VerifyBeforeExit;
2750 const int rso = GenCollectedHeap::SO_AllCodeCache;
2751
2752 // We set the proper root for this CMS cycle here.
2753 if (should_unload_classes()) { // Should unload classes this cycle
2754 remove_root_scanning_option(rso); // Shrink the root set appropriately
2755 set_verifying(should_verify); // Set verification state for this cycle
2756 return; // Nothing else needs to be done at this time
2757 }
2758
2759 // Not unloading classes this cycle
2760 assert(!should_unload_classes(), "Inconsistency!");
2761
2762 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2763 // Include symbols, strings and code cache elements to prevent their resurrection.
2764 add_root_scanning_option(rso);
2765 set_verifying(true);
2766 } else if (verifying() && !should_verify) {
2767 // We were verifying, but some verification flags got disabled.
2768 set_verifying(false);
2769 // Exclude symbols, strings and code cache elements from root scanning to
2770 // reduce IM and RM pauses.
2771 remove_root_scanning_option(rso);
2772 }
2773 }
2774
2775
2776 #ifndef PRODUCT
2777 HeapWord* CMSCollector::block_start(const void* p) const {
2778 const HeapWord* addr = (HeapWord*)p;
2779 if (_span.contains(p)) {
2780 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2781 return _cmsGen->cmsSpace()->block_start(p);
2782 }
2783 }
2784 return NULL;
2785 }
2786 #endif
2787
2788 HeapWord*
2789 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2790 bool tlab,
2791 bool parallel) {
2792 CMSSynchronousYieldRequest yr;
2793 assert(!tlab, "Can't deal with TLAB allocation");
2794 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2795 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2796 if (GCExpandToAllocateDelayMillis > 0) {
2797 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2798 }
2799 return have_lock_and_allocate(word_size, tlab);
2800 }
2801
2802 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2803 size_t bytes,
2804 size_t expand_bytes,
2805 CMSExpansionCause::Cause cause)
2806 {
2807
2808 bool success = expand(bytes, expand_bytes);
2809
2810 // remember why we expanded; this information is used
2811 // by shouldConcurrentCollect() when making decisions on whether to start
2812 // a new CMS cycle.
2813 if (success) {
2814 set_expansion_cause(cause);
2815 if (PrintGCDetails && Verbose) {
2816 gclog_or_tty->print_cr("Expanded CMS gen for %s",
2817 CMSExpansionCause::to_string(cause));
2818 }
2819 }
2820 }
2821
2822 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2823 HeapWord* res = NULL;
2824 MutexLocker x(ParGCRareEvent_lock);
2825 while (true) {
2826 // Expansion by some other thread might make alloc OK now:
2827 res = ps->lab.alloc(word_sz);
2828 if (res != NULL) return res;
2829 // If there's not enough expansion space available, give up.
2830 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2831 return NULL;
2832 }
2833 // Otherwise, we try expansion.
2834 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2835 // Now go around the loop and try alloc again;
2836 // A competing par_promote might beat us to the expansion space,
2837 // so we may go around the loop again if promotion fails again.
2838 if (GCExpandToAllocateDelayMillis > 0) {
2839 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2840 }
2841 }
2842 }
2843
2844
2845 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2846 PromotionInfo* promo) {
2847 MutexLocker x(ParGCRareEvent_lock);
2848 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2849 while (true) {
2850 // Expansion by some other thread might make alloc OK now:
2851 if (promo->ensure_spooling_space()) {
2852 assert(promo->has_spooling_space(),
2853 "Post-condition of successful ensure_spooling_space()");
2854 return true;
2855 }
2856 // If there's not enough expansion space available, give up.
2857 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2858 return false;
2859 }
2860 // Otherwise, we try expansion.
2861 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2862 // Now go around the loop and try alloc again;
2863 // A competing allocation might beat us to the expansion space,
2864 // so we may go around the loop again if allocation fails again.
2865 if (GCExpandToAllocateDelayMillis > 0) {
2866 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2867 }
2868 }
2869 }
2870
2871 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2872 // Only shrink if a compaction was done so that all the free space
2873 // in the generation is in a contiguous block at the end.
2874 if (did_compact()) {
2875 CardGeneration::shrink(bytes);
2876 }
2877 }
2878
2879 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2880 assert_locked_or_safepoint(Heap_lock);
2881 }
2882
2883 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2884 assert_locked_or_safepoint(Heap_lock);
2885 assert_lock_strong(freelistLock());
2886 if (PrintGCDetails && Verbose) {
2887 warning("Shrinking of CMS not yet implemented");
2888 }
2889 return;
2890 }
2891
2892
2893 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2894 // phases.
2895 class CMSPhaseAccounting: public StackObj {
2896 public:
2897 CMSPhaseAccounting(CMSCollector *collector,
2898 const char *phase,
2899 const GCId gc_id,
2900 bool print_cr = true);
2901 ~CMSPhaseAccounting();
2902
2903 private:
2904 CMSCollector *_collector;
2905 const char *_phase;
2906 elapsedTimer _wallclock;
2907 bool _print_cr;
2908 const GCId _gc_id;
2909
2910 public:
2911 // Not MT-safe; so do not pass around these StackObj's
2912 // where they may be accessed by other threads.
2913 jlong wallclock_millis() {
2914 assert(_wallclock.is_active(), "Wall clock should not stop");
2915 _wallclock.stop(); // to record time
2916 jlong ret = _wallclock.milliseconds();
2917 _wallclock.start(); // restart
2918 return ret;
2919 }
2920 };
2921
2922 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2923 const char *phase,
2924 const GCId gc_id,
2925 bool print_cr) :
2926 _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
2927
2928 if (PrintCMSStatistics != 0) {
2929 _collector->resetYields();
2930 }
2931 if (PrintGCDetails) {
2932 gclog_or_tty->gclog_stamp(_gc_id);
2933 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
2934 _collector->cmsGen()->short_name(), _phase);
2935 }
2936 _collector->resetTimer();
2937 _wallclock.start();
2938 _collector->startTimer();
2939 }
2940
2941 CMSPhaseAccounting::~CMSPhaseAccounting() {
2942 assert(_wallclock.is_active(), "Wall clock should not have stopped");
2943 _collector->stopTimer();
2944 _wallclock.stop();
2945 if (PrintGCDetails) {
2946 gclog_or_tty->gclog_stamp(_gc_id);
2947 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
2948 _collector->cmsGen()->short_name(),
2949 _phase, _collector->timerValue(), _wallclock.seconds());
2950 if (_print_cr) {
2951 gclog_or_tty->cr();
2952 }
2953 if (PrintCMSStatistics != 0) {
2954 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
2955 _collector->yields());
2956 }
2957 }
2958 }
2959
2960 // CMS work
2961
2962 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2963 class CMSParMarkTask : public AbstractGangTask {
2964 protected:
2965 CMSCollector* _collector;
2966 int _n_workers;
2967 CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
2968 AbstractGangTask(name),
2969 _collector(collector),
2970 _n_workers(n_workers) {}
2971 // Work method in support of parallel rescan ... of young gen spaces
2972 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2973 ContiguousSpace* space,
2974 HeapWord** chunk_array, size_t chunk_top);
2975 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2976 };
2977
2978 // Parallel initial mark task
2979 class CMSParInitialMarkTask: public CMSParMarkTask {
2980 public:
2981 CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
2982 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
2983 collector, n_workers) {}
2984 void work(uint worker_id);
2985 };
2986
2987 // Checkpoint the roots into this generation from outside
2988 // this generation. [Note this initial checkpoint need only
2989 // be approximate -- we'll do a catch up phase subsequently.]
2990 void CMSCollector::checkpointRootsInitial() {
2991 assert(_collectorState == InitialMarking, "Wrong collector state");
2992 check_correct_thread_executing();
2993 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2994
2995 save_heap_summary();
2996 report_heap_summary(GCWhen::BeforeGC);
2997
2998 ReferenceProcessor* rp = ref_processor();
2999 assert(_restart_addr == NULL, "Control point invariant");
3000 {
3001 // acquire locks for subsequent manipulations
3002 MutexLockerEx x(bitMapLock(),
3003 Mutex::_no_safepoint_check_flag);
3004 checkpointRootsInitialWork();
3005 // enable ("weak") refs discovery
3006 rp->enable_discovery();
3007 _collectorState = Marking;
3008 }
3009 }
3010
3011 void CMSCollector::checkpointRootsInitialWork() {
3012 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3013 assert(_collectorState == InitialMarking, "just checking");
3014
3015 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3016 // precede our marking with a collection of all
3017 // younger generations to keep floating garbage to a minimum.
3018 // XXX: we won't do this for now -- it's an optimization to be done later.
3019
3020 // already have locks
3021 assert_lock_strong(bitMapLock());
3022 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3023
3024 // Setup the verification and class unloading state for this
3025 // CMS collection cycle.
3026 setup_cms_unloading_and_verification_state();
3027
3028 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3029 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
3030
3031 // Reset all the PLAB chunk arrays if necessary.
3032 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3033 reset_survivor_plab_arrays();
3034 }
3035
3036 ResourceMark rm;
3037 HandleMark hm;
3038
3039 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3040 GenCollectedHeap* gch = GenCollectedHeap::heap();
3041
3042 verify_work_stacks_empty();
3043 verify_overflow_empty();
3044
3045 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3046 // Update the saved marks which may affect the root scans.
3047 gch->save_marks();
3048
3049 // weak reference processing has not started yet.
3050 ref_processor()->set_enqueuing_is_done(false);
3051
3052 // Need to remember all newly created CLDs,
3053 // so that we can guarantee that the remark finds them.
3054 ClassLoaderDataGraph::remember_new_clds(true);
3055
3056 // Whenever a CLD is found, it will be claimed before proceeding to mark
3057 // the klasses. The claimed marks need to be cleared before marking starts.
3058 ClassLoaderDataGraph::clear_claimed_marks();
3059
3060 if (CMSPrintEdenSurvivorChunks) {
3061 print_eden_and_survivor_chunk_arrays();
3062 }
3063
3064 {
3065 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3066 if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3067 // The parallel version.
3068 FlexibleWorkGang* workers = gch->workers();
3069 assert(workers != NULL, "Need parallel worker threads.");
3070 int n_workers = workers->active_workers();
3071 CMSParInitialMarkTask tsk(this, n_workers);
3072 gch->set_par_threads(n_workers);
3073 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3074 if (n_workers > 1) {
3075 StrongRootsScope srs;
3076 workers->run_task(&tsk);
3077 } else {
3078 StrongRootsScope srs;
3079 tsk.work(0);
3080 }
3081 gch->set_par_threads(0);
3082 } else {
3083 // The serial version.
3084 CLDToOopClosure cld_closure(¬Older, true);
3085 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3086 gch->gen_process_roots(_cmsGen->level(),
3087 true, // younger gens are roots
3088 true, // activate StrongRootsScope
3089 GenCollectedHeap::ScanningOption(roots_scanning_options()),
3090 should_unload_classes(),
3091 ¬Older,
3092 NULL,
3093 &cld_closure);
3094 }
3095 }
3096
3097 // Clear mod-union table; it will be dirtied in the prologue of
3098 // CMS generation per each younger generation collection.
3099
3100 assert(_modUnionTable.isAllClear(),
3101 "Was cleared in most recent final checkpoint phase"
3102 " or no bits are set in the gc_prologue before the start of the next "
3103 "subsequent marking phase.");
3104
3105 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3106
3107 // Save the end of the used_region of the constituent generations
3108 // to be used to limit the extent of sweep in each generation.
3109 save_sweep_limits();
3110 verify_overflow_empty();
3111 }
3112
3113 bool CMSCollector::markFromRoots() {
3114 // we might be tempted to assert that:
3115 // assert(!SafepointSynchronize::is_at_safepoint(),
3116 // "inconsistent argument?");
3117 // However that wouldn't be right, because it's possible that
3118 // a safepoint is indeed in progress as a younger generation
3119 // stop-the-world GC happens even as we mark in this generation.
3120 assert(_collectorState == Marking, "inconsistent state?");
3121 check_correct_thread_executing();
3122 verify_overflow_empty();
3123
3124 // Weak ref discovery note: We may be discovering weak
3125 // refs in this generation concurrent (but interleaved) with
3126 // weak ref discovery by a younger generation collector.
3127
3128 CMSTokenSyncWithLocks ts(true, bitMapLock());
3129 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3130 CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3131 bool res = markFromRootsWork();
3132 if (res) {
3133 _collectorState = Precleaning;
3134 } else { // We failed and a foreground collection wants to take over
3135 assert(_foregroundGCIsActive, "internal state inconsistency");
3136 assert(_restart_addr == NULL, "foreground will restart from scratch");
3137 if (PrintGCDetails) {
3138 gclog_or_tty->print_cr("bailing out to foreground collection");
3139 }
3140 }
3141 verify_overflow_empty();
3142 return res;
3143 }
3144
3145 bool CMSCollector::markFromRootsWork() {
3146 // iterate over marked bits in bit map, doing a full scan and mark
3147 // from these roots using the following algorithm:
3148 // . if oop is to the right of the current scan pointer,
3149 // mark corresponding bit (we'll process it later)
3150 // . else (oop is to left of current scan pointer)
3151 // push oop on marking stack
3152 // . drain the marking stack
3153
3154 // Note that when we do a marking step we need to hold the
3155 // bit map lock -- recall that direct allocation (by mutators)
3156 // and promotion (by younger generation collectors) is also
3157 // marking the bit map. [the so-called allocate live policy.]
3158 // Because the implementation of bit map marking is not
3159 // robust wrt simultaneous marking of bits in the same word,
3160 // we need to make sure that there is no such interference
3161 // between concurrent such updates.
3162
3163 // already have locks
3164 assert_lock_strong(bitMapLock());
3165
3166 verify_work_stacks_empty();
3167 verify_overflow_empty();
3168 bool result = false;
3169 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3170 result = do_marking_mt();
3171 } else {
3172 result = do_marking_st();
3173 }
3174 return result;
3175 }
3176
3177 // Forward decl
3178 class CMSConcMarkingTask;
3179
3180 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3181 CMSCollector* _collector;
3182 CMSConcMarkingTask* _task;
3183 public:
3184 virtual void yield();
3185
3186 // "n_threads" is the number of threads to be terminated.
3187 // "queue_set" is a set of work queues of other threads.
3188 // "collector" is the CMS collector associated with this task terminator.
3189 // "yield" indicates whether we need the gang as a whole to yield.
3190 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3191 ParallelTaskTerminator(n_threads, queue_set),
3192 _collector(collector) { }
3193
3194 void set_task(CMSConcMarkingTask* task) {
3195 _task = task;
3196 }
3197 };
3198
3199 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3200 CMSConcMarkingTask* _task;
3201 public:
3202 bool should_exit_termination();
3203 void set_task(CMSConcMarkingTask* task) {
3204 _task = task;
3205 }
3206 };
3207
3208 // MT Concurrent Marking Task
3209 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3210 CMSCollector* _collector;
3211 int _n_workers; // requested/desired # workers
3212 bool _result;
3213 CompactibleFreeListSpace* _cms_space;
3214 char _pad_front[64]; // padding to ...
3215 HeapWord* _global_finger; // ... avoid sharing cache line
3216 char _pad_back[64];
3217 HeapWord* _restart_addr;
3218
3219 // Exposed here for yielding support
3220 Mutex* const _bit_map_lock;
3221
3222 // The per thread work queues, available here for stealing
3223 OopTaskQueueSet* _task_queues;
3224
3225 // Termination (and yielding) support
3226 CMSConcMarkingTerminator _term;
3227 CMSConcMarkingTerminatorTerminator _term_term;
3228
3229 public:
3230 CMSConcMarkingTask(CMSCollector* collector,
3231 CompactibleFreeListSpace* cms_space,
3232 YieldingFlexibleWorkGang* workers,
3233 OopTaskQueueSet* task_queues):
3234 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3235 _collector(collector),
3236 _cms_space(cms_space),
3237 _n_workers(0), _result(true),
3238 _task_queues(task_queues),
3239 _term(_n_workers, task_queues, _collector),
3240 _bit_map_lock(collector->bitMapLock())
3241 {
3242 _requested_size = _n_workers;
3243 _term.set_task(this);
3244 _term_term.set_task(this);
3245 _restart_addr = _global_finger = _cms_space->bottom();
3246 }
3247
3248
3249 OopTaskQueueSet* task_queues() { return _task_queues; }
3250
3251 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3252
3253 HeapWord** global_finger_addr() { return &_global_finger; }
3254
3255 CMSConcMarkingTerminator* terminator() { return &_term; }
3256
3257 virtual void set_for_termination(int active_workers) {
3258 terminator()->reset_for_reuse(active_workers);
3259 }
3260
3261 void work(uint worker_id);
3262 bool should_yield() {
3263 return ConcurrentMarkSweepThread::should_yield()
3264 && !_collector->foregroundGCIsActive();
3265 }
3266
3267 virtual void coordinator_yield(); // stuff done by coordinator
3268 bool result() { return _result; }
3269
3270 void reset(HeapWord* ra) {
3271 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3272 _restart_addr = _global_finger = ra;
3273 _term.reset_for_reuse();
3274 }
3275
3276 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3277 OopTaskQueue* work_q);
3278
3279 private:
3280 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3281 void do_work_steal(int i);
3282 void bump_global_finger(HeapWord* f);
3283 };
3284
3285 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3286 assert(_task != NULL, "Error");
3287 return _task->yielding();
3288 // Note that we do not need the disjunct || _task->should_yield() above
3289 // because we want terminating threads to yield only if the task
3290 // is already in the midst of yielding, which happens only after at least one
3291 // thread has yielded.
3292 }
3293
3294 void CMSConcMarkingTerminator::yield() {
3295 if (_task->should_yield()) {
3296 _task->yield();
3297 } else {
3298 ParallelTaskTerminator::yield();
3299 }
3300 }
3301
3302 ////////////////////////////////////////////////////////////////
3303 // Concurrent Marking Algorithm Sketch
3304 ////////////////////////////////////////////////////////////////
3305 // Until all tasks exhausted (both spaces):
3306 // -- claim next available chunk
3307 // -- bump global finger via CAS
3308 // -- find first object that starts in this chunk
3309 // and start scanning bitmap from that position
3310 // -- scan marked objects for oops
3311 // -- CAS-mark target, and if successful:
3312 // . if target oop is above global finger (volatile read)
3313 // nothing to do
3314 // . if target oop is in chunk and above local finger
3315 // then nothing to do
3316 // . else push on work-queue
3317 // -- Deal with possible overflow issues:
3318 // . local work-queue overflow causes stuff to be pushed on
3319 // global (common) overflow queue
3320 // . always first empty local work queue
3321 // . then get a batch of oops from global work queue if any
3322 // . then do work stealing
3323 // -- When all tasks claimed (both spaces)
3324 // and local work queue empty,
3325 // then in a loop do:
3326 // . check global overflow stack; steal a batch of oops and trace
3327 // . try to steal from other threads oif GOS is empty
3328 // . if neither is available, offer termination
3329 // -- Terminate and return result
3330 //
3331 void CMSConcMarkingTask::work(uint worker_id) {
3332 elapsedTimer _timer;
3333 ResourceMark rm;
3334 HandleMark hm;
3335
3336 DEBUG_ONLY(_collector->verify_overflow_empty();)
3337
3338 // Before we begin work, our work queue should be empty
3339 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3340 // Scan the bitmap covering _cms_space, tracing through grey objects.
3341 _timer.start();
3342 do_scan_and_mark(worker_id, _cms_space);
3343 _timer.stop();
3344 if (PrintCMSStatistics != 0) {
3345 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3346 worker_id, _timer.seconds());
3347 // XXX: need xxx/xxx type of notation, two timers
3348 }
3349
3350 // ... do work stealing
3351 _timer.reset();
3352 _timer.start();
3353 do_work_steal(worker_id);
3354 _timer.stop();
3355 if (PrintCMSStatistics != 0) {
3356 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3357 worker_id, _timer.seconds());
3358 // XXX: need xxx/xxx type of notation, two timers
3359 }
3360 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3361 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3362 // Note that under the current task protocol, the
3363 // following assertion is true even of the spaces
3364 // expanded since the completion of the concurrent
3365 // marking. XXX This will likely change under a strict
3366 // ABORT semantics.
3367 // After perm removal the comparison was changed to
3368 // greater than or equal to from strictly greater than.
3369 // Before perm removal the highest address sweep would
3370 // have been at the end of perm gen but now is at the
3371 // end of the tenured gen.
3372 assert(_global_finger >= _cms_space->end(),
3373 "All tasks have been completed");
3374 DEBUG_ONLY(_collector->verify_overflow_empty();)
3375 }
3376
3377 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3378 HeapWord* read = _global_finger;
3379 HeapWord* cur = read;
3380 while (f > read) {
3381 cur = read;
3382 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3383 if (cur == read) {
3384 // our cas succeeded
3385 assert(_global_finger >= f, "protocol consistency");
3386 break;
3387 }
3388 }
3389 }
3390
3391 // This is really inefficient, and should be redone by
3392 // using (not yet available) block-read and -write interfaces to the
3393 // stack and the work_queue. XXX FIX ME !!!
3394 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3395 OopTaskQueue* work_q) {
3396 // Fast lock-free check
3397 if (ovflw_stk->length() == 0) {
3398 return false;
3399 }
3400 assert(work_q->size() == 0, "Shouldn't steal");
3401 MutexLockerEx ml(ovflw_stk->par_lock(),
3402 Mutex::_no_safepoint_check_flag);
3403 // Grab up to 1/4 the size of the work queue
3404 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3405 (size_t)ParGCDesiredObjsFromOverflowList);
3406 num = MIN2(num, ovflw_stk->length());
3407 for (int i = (int) num; i > 0; i--) {
3408 oop cur = ovflw_stk->pop();
3409 assert(cur != NULL, "Counted wrong?");
3410 work_q->push(cur);
3411 }
3412 return num > 0;
3413 }
3414
3415 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3416 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3417 int n_tasks = pst->n_tasks();
3418 // We allow that there may be no tasks to do here because
3419 // we are restarting after a stack overflow.
3420 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3421 uint nth_task = 0;
3422
3423 HeapWord* aligned_start = sp->bottom();
3424 if (sp->used_region().contains(_restart_addr)) {
3425 // Align down to a card boundary for the start of 0th task
3426 // for this space.
3427 aligned_start =
3428 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3429 CardTableModRefBS::card_size);
3430 }
3431
3432 size_t chunk_size = sp->marking_task_size();
3433 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3434 // Having claimed the nth task in this space,
3435 // compute the chunk that it corresponds to:
3436 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3437 aligned_start + (nth_task+1)*chunk_size);
3438 // Try and bump the global finger via a CAS;
3439 // note that we need to do the global finger bump
3440 // _before_ taking the intersection below, because
3441 // the task corresponding to that region will be
3442 // deemed done even if the used_region() expands
3443 // because of allocation -- as it almost certainly will
3444 // during start-up while the threads yield in the
3445 // closure below.
3446 HeapWord* finger = span.end();
3447 bump_global_finger(finger); // atomically
3448 // There are null tasks here corresponding to chunks
3449 // beyond the "top" address of the space.
3450 span = span.intersection(sp->used_region());
3451 if (!span.is_empty()) { // Non-null task
3452 HeapWord* prev_obj;
3453 assert(!span.contains(_restart_addr) || nth_task == 0,
3454 "Inconsistency");
3455 if (nth_task == 0) {
3456 // For the 0th task, we'll not need to compute a block_start.
3457 if (span.contains(_restart_addr)) {
3458 // In the case of a restart because of stack overflow,
3459 // we might additionally skip a chunk prefix.
3460 prev_obj = _restart_addr;
3461 } else {
3462 prev_obj = span.start();
3463 }
3464 } else {
3465 // We want to skip the first object because
3466 // the protocol is to scan any object in its entirety
3467 // that _starts_ in this span; a fortiori, any
3468 // object starting in an earlier span is scanned
3469 // as part of an earlier claimed task.
3470 // Below we use the "careful" version of block_start
3471 // so we do not try to navigate uninitialized objects.
3472 prev_obj = sp->block_start_careful(span.start());
3473 // Below we use a variant of block_size that uses the
3474 // Printezis bits to avoid waiting for allocated
3475 // objects to become initialized/parsable.
3476 while (prev_obj < span.start()) {
3477 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3478 if (sz > 0) {
3479 prev_obj += sz;
3480 } else {
3481 // In this case we may end up doing a bit of redundant
3482 // scanning, but that appears unavoidable, short of
3483 // locking the free list locks; see bug 6324141.
3484 break;
3485 }
3486 }
3487 }
3488 if (prev_obj < span.end()) {
3489 MemRegion my_span = MemRegion(prev_obj, span.end());
3490 // Do the marking work within a non-empty span --
3491 // the last argument to the constructor indicates whether the
3492 // iteration should be incremental with periodic yields.
3493 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3494 &_collector->_markBitMap,
3495 work_queue(i),
3496 &_collector->_markStack);
3497 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3498 } // else nothing to do for this task
3499 } // else nothing to do for this task
3500 }
3501 // We'd be tempted to assert here that since there are no
3502 // more tasks left to claim in this space, the global_finger
3503 // must exceed space->top() and a fortiori space->end(). However,
3504 // that would not quite be correct because the bumping of
3505 // global_finger occurs strictly after the claiming of a task,
3506 // so by the time we reach here the global finger may not yet
3507 // have been bumped up by the thread that claimed the last
3508 // task.
3509 pst->all_tasks_completed();
3510 }
3511
3512 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3513 private:
3514 CMSCollector* _collector;
3515 CMSConcMarkingTask* _task;
3516 MemRegion _span;
3517 CMSBitMap* _bit_map;
3518 CMSMarkStack* _overflow_stack;
3519 OopTaskQueue* _work_queue;
3520 protected:
3521 DO_OOP_WORK_DEFN
3522 public:
3523 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3524 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3525 MetadataAwareOopClosure(collector->ref_processor()),
3526 _collector(collector),
3527 _task(task),
3528 _span(collector->_span),
3529 _work_queue(work_queue),
3530 _bit_map(bit_map),
3531 _overflow_stack(overflow_stack)
3532 { }
3533 virtual void do_oop(oop* p);
3534 virtual void do_oop(narrowOop* p);
3535
3536 void trim_queue(size_t max);
3537 void handle_stack_overflow(HeapWord* lost);
3538 void do_yield_check() {
3539 if (_task->should_yield()) {
3540 _task->yield();
3541 }
3542 }
3543 };
3544
3545 // Grey object scanning during work stealing phase --
3546 // the salient assumption here is that any references
3547 // that are in these stolen objects being scanned must
3548 // already have been initialized (else they would not have
3549 // been published), so we do not need to check for
3550 // uninitialized objects before pushing here.
3551 void Par_ConcMarkingClosure::do_oop(oop obj) {
3552 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
3553 HeapWord* addr = (HeapWord*)obj;
3554 // Check if oop points into the CMS generation
3555 // and is not marked
3556 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3557 // a white object ...
3558 // If we manage to "claim" the object, by being the
3559 // first thread to mark it, then we push it on our
3560 // marking stack
3561 if (_bit_map->par_mark(addr)) { // ... now grey
3562 // push on work queue (grey set)
3563 bool simulate_overflow = false;
3564 NOT_PRODUCT(
3565 if (CMSMarkStackOverflowALot &&
3566 _collector->simulate_overflow()) {
3567 // simulate a stack overflow
3568 simulate_overflow = true;
3569 }
3570 )
3571 if (simulate_overflow ||
3572 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3573 // stack overflow
3574 if (PrintCMSStatistics != 0) {
3575 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3576 SIZE_FORMAT, _overflow_stack->capacity());
3577 }
3578 // We cannot assert that the overflow stack is full because
3579 // it may have been emptied since.
3580 assert(simulate_overflow ||
3581 _work_queue->size() == _work_queue->max_elems(),
3582 "Else push should have succeeded");
3583 handle_stack_overflow(addr);
3584 }
3585 } // Else, some other thread got there first
3586 do_yield_check();
3587 }
3588 }
3589
3590 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3591 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3592
3593 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3594 while (_work_queue->size() > max) {
3595 oop new_oop;
3596 if (_work_queue->pop_local(new_oop)) {
3597 assert(new_oop->is_oop(), "Should be an oop");
3598 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3599 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3600 new_oop->oop_iterate(this); // do_oop() above
3601 do_yield_check();
3602 }
3603 }
3604 }
3605
3606 // Upon stack overflow, we discard (part of) the stack,
3607 // remembering the least address amongst those discarded
3608 // in CMSCollector's _restart_address.
3609 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3610 // We need to do this under a mutex to prevent other
3611 // workers from interfering with the work done below.
3612 MutexLockerEx ml(_overflow_stack->par_lock(),
3613 Mutex::_no_safepoint_check_flag);
3614 // Remember the least grey address discarded
3615 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3616 _collector->lower_restart_addr(ra);
3617 _overflow_stack->reset(); // discard stack contents
3618 _overflow_stack->expand(); // expand the stack if possible
3619 }
3620
3621
3622 void CMSConcMarkingTask::do_work_steal(int i) {
3623 OopTaskQueue* work_q = work_queue(i);
3624 oop obj_to_scan;
3625 CMSBitMap* bm = &(_collector->_markBitMap);
3626 CMSMarkStack* ovflw = &(_collector->_markStack);
3627 int* seed = _collector->hash_seed(i);
3628 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3629 while (true) {
3630 cl.trim_queue(0);
3631 assert(work_q->size() == 0, "Should have been emptied above");
3632 if (get_work_from_overflow_stack(ovflw, work_q)) {
3633 // Can't assert below because the work obtained from the
3634 // overflow stack may already have been stolen from us.
3635 // assert(work_q->size() > 0, "Work from overflow stack");
3636 continue;
3637 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3638 assert(obj_to_scan->is_oop(), "Should be an oop");
3639 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3640 obj_to_scan->oop_iterate(&cl);
3641 } else if (terminator()->offer_termination(&_term_term)) {
3642 assert(work_q->size() == 0, "Impossible!");
3643 break;
3644 } else if (yielding() || should_yield()) {
3645 yield();
3646 }
3647 }
3648 }
3649
3650 // This is run by the CMS (coordinator) thread.
3651 void CMSConcMarkingTask::coordinator_yield() {
3652 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3653 "CMS thread should hold CMS token");
3654 // First give up the locks, then yield, then re-lock
3655 // We should probably use a constructor/destructor idiom to
3656 // do this unlock/lock or modify the MutexUnlocker class to
3657 // serve our purpose. XXX
3658 assert_lock_strong(_bit_map_lock);
3659 _bit_map_lock->unlock();
3660 ConcurrentMarkSweepThread::desynchronize(true);
3661 _collector->stopTimer();
3662 if (PrintCMSStatistics != 0) {
3663 _collector->incrementYields();
3664 }
3665
3666 // It is possible for whichever thread initiated the yield request
3667 // not to get a chance to wake up and take the bitmap lock between
3668 // this thread releasing it and reacquiring it. So, while the
3669 // should_yield() flag is on, let's sleep for a bit to give the
3670 // other thread a chance to wake up. The limit imposed on the number
3671 // of iterations is defensive, to avoid any unforseen circumstances
3672 // putting us into an infinite loop. Since it's always been this
3673 // (coordinator_yield()) method that was observed to cause the
3674 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3675 // which is by default non-zero. For the other seven methods that
3676 // also perform the yield operation, as are using a different
3677 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3678 // can enable the sleeping for those methods too, if necessary.
3679 // See 6442774.
3680 //
3681 // We really need to reconsider the synchronization between the GC
3682 // thread and the yield-requesting threads in the future and we
3683 // should really use wait/notify, which is the recommended
3684 // way of doing this type of interaction. Additionally, we should
3685 // consolidate the eight methods that do the yield operation and they
3686 // are almost identical into one for better maintainability and
3687 // readability. See 6445193.
3688 //
3689 // Tony 2006.06.29
3690 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3691 ConcurrentMarkSweepThread::should_yield() &&
3692 !CMSCollector::foregroundGCIsActive(); ++i) {
3693 os::sleep(Thread::current(), 1, false);
3694 }
3695
3696 ConcurrentMarkSweepThread::synchronize(true);
3697 _bit_map_lock->lock_without_safepoint_check();
3698 _collector->startTimer();
3699 }
3700
3701 bool CMSCollector::do_marking_mt() {
3702 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3703 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
3704 conc_workers()->total_workers(),
3705 conc_workers()->active_workers(),
3706 Threads::number_of_non_daemon_threads());
3707 conc_workers()->set_active_workers(num_workers);
3708
3709 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3710
3711 CMSConcMarkingTask tsk(this,
3712 cms_space,
3713 conc_workers(),
3714 task_queues());
3715
3716 // Since the actual number of workers we get may be different
3717 // from the number we requested above, do we need to do anything different
3718 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3719 // class?? XXX
3720 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3721
3722 // Refs discovery is already non-atomic.
3723 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3724 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3725 conc_workers()->start_task(&tsk);
3726 while (tsk.yielded()) {
3727 tsk.coordinator_yield();
3728 conc_workers()->continue_task(&tsk);
3729 }
3730 // If the task was aborted, _restart_addr will be non-NULL
3731 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3732 while (_restart_addr != NULL) {
3733 // XXX For now we do not make use of ABORTED state and have not
3734 // yet implemented the right abort semantics (even in the original
3735 // single-threaded CMS case). That needs some more investigation
3736 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3737 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3738 // If _restart_addr is non-NULL, a marking stack overflow
3739 // occurred; we need to do a fresh marking iteration from the
3740 // indicated restart address.
3741 if (_foregroundGCIsActive) {
3742 // We may be running into repeated stack overflows, having
3743 // reached the limit of the stack size, while making very
3744 // slow forward progress. It may be best to bail out and
3745 // let the foreground collector do its job.
3746 // Clear _restart_addr, so that foreground GC
3747 // works from scratch. This avoids the headache of
3748 // a "rescan" which would otherwise be needed because
3749 // of the dirty mod union table & card table.
3750 _restart_addr = NULL;
3751 return false;
3752 }
3753 // Adjust the task to restart from _restart_addr
3754 tsk.reset(_restart_addr);
3755 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3756 _restart_addr);
3757 _restart_addr = NULL;
3758 // Get the workers going again
3759 conc_workers()->start_task(&tsk);
3760 while (tsk.yielded()) {
3761 tsk.coordinator_yield();
3762 conc_workers()->continue_task(&tsk);
3763 }
3764 }
3765 assert(tsk.completed(), "Inconsistency");
3766 assert(tsk.result() == true, "Inconsistency");
3767 return true;
3768 }
3769
3770 bool CMSCollector::do_marking_st() {
3771 ResourceMark rm;
3772 HandleMark hm;
3773
3774 // Temporarily make refs discovery single threaded (non-MT)
3775 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3776 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3777 &_markStack, CMSYield);
3778 // the last argument to iterate indicates whether the iteration
3779 // should be incremental with periodic yields.
3780 _markBitMap.iterate(&markFromRootsClosure);
3781 // If _restart_addr is non-NULL, a marking stack overflow
3782 // occurred; we need to do a fresh iteration from the
3783 // indicated restart address.
3784 while (_restart_addr != NULL) {
3785 if (_foregroundGCIsActive) {
3786 // We may be running into repeated stack overflows, having
3787 // reached the limit of the stack size, while making very
3788 // slow forward progress. It may be best to bail out and
3789 // let the foreground collector do its job.
3790 // Clear _restart_addr, so that foreground GC
3791 // works from scratch. This avoids the headache of
3792 // a "rescan" which would otherwise be needed because
3793 // of the dirty mod union table & card table.
3794 _restart_addr = NULL;
3795 return false; // indicating failure to complete marking
3796 }
3797 // Deal with stack overflow:
3798 // we restart marking from _restart_addr
3799 HeapWord* ra = _restart_addr;
3800 markFromRootsClosure.reset(ra);
3801 _restart_addr = NULL;
3802 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3803 }
3804 return true;
3805 }
3806
3807 void CMSCollector::preclean() {
3808 check_correct_thread_executing();
3809 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3810 verify_work_stacks_empty();
3811 verify_overflow_empty();
3812 _abort_preclean = false;
3813 if (CMSPrecleaningEnabled) {
3814 if (!CMSEdenChunksRecordAlways) {
3815 _eden_chunk_index = 0;
3816 }
3817 size_t used = get_eden_used();
3818 size_t capacity = get_eden_capacity();
3819 // Don't start sampling unless we will get sufficiently
3820 // many samples.
3821 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3822 * CMSScheduleRemarkEdenPenetration)) {
3823 _start_sampling = true;
3824 } else {
3825 _start_sampling = false;
3826 }
3827 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3828 CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3829 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3830 }
3831 CMSTokenSync x(true); // is cms thread
3832 if (CMSPrecleaningEnabled) {
3833 sample_eden();
3834 _collectorState = AbortablePreclean;
3835 } else {
3836 _collectorState = FinalMarking;
3837 }
3838 verify_work_stacks_empty();
3839 verify_overflow_empty();
3840 }
3841
3842 // Try and schedule the remark such that young gen
3843 // occupancy is CMSScheduleRemarkEdenPenetration %.
3844 void CMSCollector::abortable_preclean() {
3845 check_correct_thread_executing();
3846 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3847 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3848
3849 // If Eden's current occupancy is below this threshold,
3850 // immediately schedule the remark; else preclean
3851 // past the next scavenge in an effort to
3852 // schedule the pause as described above. By choosing
3853 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3854 // we will never do an actual abortable preclean cycle.
3855 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3856 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3857 CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3858 // We need more smarts in the abortable preclean
3859 // loop below to deal with cases where allocation
3860 // in young gen is very very slow, and our precleaning
3861 // is running a losing race against a horde of
3862 // mutators intent on flooding us with CMS updates
3863 // (dirty cards).
3864 // One, admittedly dumb, strategy is to give up
3865 // after a certain number of abortable precleaning loops
3866 // or after a certain maximum time. We want to make
3867 // this smarter in the next iteration.
3868 // XXX FIX ME!!! YSR
3869 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3870 while (!(should_abort_preclean() ||
3871 ConcurrentMarkSweepThread::should_terminate())) {
3872 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3873 cumworkdone += workdone;
3874 loops++;
3875 // Voluntarily terminate abortable preclean phase if we have
3876 // been at it for too long.
3877 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3878 loops >= CMSMaxAbortablePrecleanLoops) {
3879 if (PrintGCDetails) {
3880 gclog_or_tty->print(" CMS: abort preclean due to loops ");
3881 }
3882 break;
3883 }
3884 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3885 if (PrintGCDetails) {
3886 gclog_or_tty->print(" CMS: abort preclean due to time ");
3887 }
3888 break;
3889 }
3890 // If we are doing little work each iteration, we should
3891 // take a short break.
3892 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3893 // Sleep for some time, waiting for work to accumulate
3894 stopTimer();
3895 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3896 startTimer();
3897 waited++;
3898 }
3899 }
3900 if (PrintCMSStatistics > 0) {
3901 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3902 loops, waited, cumworkdone);
3903 }
3904 }
3905 CMSTokenSync x(true); // is cms thread
3906 if (_collectorState != Idling) {
3907 assert(_collectorState == AbortablePreclean,
3908 "Spontaneous state transition?");
3909 _collectorState = FinalMarking;
3910 } // Else, a foreground collection completed this CMS cycle.
3911 return;
3912 }
3913
3914 // Respond to an Eden sampling opportunity
3915 void CMSCollector::sample_eden() {
3916 // Make sure a young gc cannot sneak in between our
3917 // reading and recording of a sample.
3918 assert(Thread::current()->is_ConcurrentGC_thread(),
3919 "Only the cms thread may collect Eden samples");
3920 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3921 "Should collect samples while holding CMS token");
3922 if (!_start_sampling) {
3923 return;
3924 }
3925 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3926 // is populated by the young generation.
3927 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3928 if (_eden_chunk_index < _eden_chunk_capacity) {
3929 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3930 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3931 "Unexpected state of Eden");
3932 // We'd like to check that what we just sampled is an oop-start address;
3933 // however, we cannot do that here since the object may not yet have been
3934 // initialized. So we'll instead do the check when we _use_ this sample
3935 // later.
3936 if (_eden_chunk_index == 0 ||
3937 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3938 _eden_chunk_array[_eden_chunk_index-1])
3939 >= CMSSamplingGrain)) {
3940 _eden_chunk_index++; // commit sample
3941 }
3942 }
3943 }
3944 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3945 size_t used = get_eden_used();
3946 size_t capacity = get_eden_capacity();
3947 assert(used <= capacity, "Unexpected state of Eden");
3948 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3949 _abort_preclean = true;
3950 }
3951 }
3952 }
3953
3954
3955 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3956 assert(_collectorState == Precleaning ||
3957 _collectorState == AbortablePreclean, "incorrect state");
3958 ResourceMark rm;
3959 HandleMark hm;
3960
3961 // Precleaning is currently not MT but the reference processor
3962 // may be set for MT. Disable it temporarily here.
3963 ReferenceProcessor* rp = ref_processor();
3964 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3965
3966 // Do one pass of scrubbing the discovered reference lists
3967 // to remove any reference objects with strongly-reachable
3968 // referents.
3969 if (clean_refs) {
3970 CMSPrecleanRefsYieldClosure yield_cl(this);
3971 assert(rp->span().equals(_span), "Spans should be equal");
3972 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3973 &_markStack, true /* preclean */);
3974 CMSDrainMarkingStackClosure complete_trace(this,
3975 _span, &_markBitMap, &_markStack,
3976 &keep_alive, true /* preclean */);
3977
3978 // We don't want this step to interfere with a young
3979 // collection because we don't want to take CPU
3980 // or memory bandwidth away from the young GC threads
3981 // (which may be as many as there are CPUs).
3982 // Note that we don't need to protect ourselves from
3983 // interference with mutators because they can't
3984 // manipulate the discovered reference lists nor affect
3985 // the computed reachability of the referents, the
3986 // only properties manipulated by the precleaning
3987 // of these reference lists.
3988 stopTimer();
3989 CMSTokenSyncWithLocks x(true /* is cms thread */,
3990 bitMapLock());
3991 startTimer();
3992 sample_eden();
3993
3994 // The following will yield to allow foreground
3995 // collection to proceed promptly. XXX YSR:
3996 // The code in this method may need further
3997 // tweaking for better performance and some restructuring
3998 // for cleaner interfaces.
3999 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4000 rp->preclean_discovered_references(
4001 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
4002 gc_timer, _gc_tracer_cm->gc_id());
4003 }
4004
4005 if (clean_survivor) { // preclean the active survivor space(s)
4006 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4007 &_markBitMap, &_modUnionTable,
4008 &_markStack, true /* precleaning phase */);
4009 stopTimer();
4010 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4011 bitMapLock());
4012 startTimer();
4013 unsigned int before_count =
4014 GenCollectedHeap::heap()->total_collections();
4015 SurvivorSpacePrecleanClosure
4016 sss_cl(this, _span, &_markBitMap, &_markStack,
4017 &pam_cl, before_count, CMSYield);
4018 _young_gen->from()->object_iterate_careful(&sss_cl);
4019 _young_gen->to()->object_iterate_careful(&sss_cl);
4020 }
4021 MarkRefsIntoAndScanClosure
4022 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4023 &_markStack, this, CMSYield,
4024 true /* precleaning phase */);
4025 // CAUTION: The following closure has persistent state that may need to
4026 // be reset upon a decrease in the sequence of addresses it
4027 // processes.
4028 ScanMarkedObjectsAgainCarefullyClosure
4029 smoac_cl(this, _span,
4030 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4031
4032 // Preclean dirty cards in ModUnionTable and CardTable using
4033 // appropriate convergence criterion;
4034 // repeat CMSPrecleanIter times unless we find that
4035 // we are losing.
4036 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4037 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4038 "Bad convergence multiplier");
4039 assert(CMSPrecleanThreshold >= 100,
4040 "Unreasonably low CMSPrecleanThreshold");
4041
4042 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4043 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4044 numIter < CMSPrecleanIter;
4045 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4046 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4047 if (Verbose && PrintGCDetails) {
4048 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
4049 }
4050 // Either there are very few dirty cards, so re-mark
4051 // pause will be small anyway, or our pre-cleaning isn't
4052 // that much faster than the rate at which cards are being
4053 // dirtied, so we might as well stop and re-mark since
4054 // precleaning won't improve our re-mark time by much.
4055 if (curNumCards <= CMSPrecleanThreshold ||
4056 (numIter > 0 &&
4057 (curNumCards * CMSPrecleanDenominator >
4058 lastNumCards * CMSPrecleanNumerator))) {
4059 numIter++;
4060 cumNumCards += curNumCards;
4061 break;
4062 }
4063 }
4064
4065 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4066
4067 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4068 cumNumCards += curNumCards;
4069 if (PrintGCDetails && PrintCMSStatistics != 0) {
4070 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4071 curNumCards, cumNumCards, numIter);
4072 }
4073 return cumNumCards; // as a measure of useful work done
4074 }
4075
4076 // PRECLEANING NOTES:
4077 // Precleaning involves:
4078 // . reading the bits of the modUnionTable and clearing the set bits.
4079 // . For the cards corresponding to the set bits, we scan the
4080 // objects on those cards. This means we need the free_list_lock
4081 // so that we can safely iterate over the CMS space when scanning
4082 // for oops.
4083 // . When we scan the objects, we'll be both reading and setting
4084 // marks in the marking bit map, so we'll need the marking bit map.
4085 // . For protecting _collector_state transitions, we take the CGC_lock.
4086 // Note that any races in the reading of of card table entries by the
4087 // CMS thread on the one hand and the clearing of those entries by the
4088 // VM thread or the setting of those entries by the mutator threads on the
4089 // other are quite benign. However, for efficiency it makes sense to keep
4090 // the VM thread from racing with the CMS thread while the latter is
4091 // dirty card info to the modUnionTable. We therefore also use the
4092 // CGC_lock to protect the reading of the card table and the mod union
4093 // table by the CM thread.
4094 // . We run concurrently with mutator updates, so scanning
4095 // needs to be done carefully -- we should not try to scan
4096 // potentially uninitialized objects.
4097 //
4098 // Locking strategy: While holding the CGC_lock, we scan over and
4099 // reset a maximal dirty range of the mod union / card tables, then lock
4100 // the free_list_lock and bitmap lock to do a full marking, then
4101 // release these locks; and repeat the cycle. This allows for a
4102 // certain amount of fairness in the sharing of these locks between
4103 // the CMS collector on the one hand, and the VM thread and the
4104 // mutators on the other.
4105
4106 // NOTE: preclean_mod_union_table() and preclean_card_table()
4107 // further below are largely identical; if you need to modify
4108 // one of these methods, please check the other method too.
4109
4110 size_t CMSCollector::preclean_mod_union_table(
4111 ConcurrentMarkSweepGeneration* gen,
4112 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4113 verify_work_stacks_empty();
4114 verify_overflow_empty();
4115
4116 // strategy: starting with the first card, accumulate contiguous
4117 // ranges of dirty cards; clear these cards, then scan the region
4118 // covered by these cards.
4119
4120 // Since all of the MUT is committed ahead, we can just use
4121 // that, in case the generations expand while we are precleaning.
4122 // It might also be fine to just use the committed part of the
4123 // generation, but we might potentially miss cards when the
4124 // generation is rapidly expanding while we are in the midst
4125 // of precleaning.
4126 HeapWord* startAddr = gen->reserved().start();
4127 HeapWord* endAddr = gen->reserved().end();
4128
4129 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4130
4131 size_t numDirtyCards, cumNumDirtyCards;
4132 HeapWord *nextAddr, *lastAddr;
4133 for (cumNumDirtyCards = numDirtyCards = 0,
4134 nextAddr = lastAddr = startAddr;
4135 nextAddr < endAddr;
4136 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4137
4138 ResourceMark rm;
4139 HandleMark hm;
4140
4141 MemRegion dirtyRegion;
4142 {
4143 stopTimer();
4144 // Potential yield point
4145 CMSTokenSync ts(true);
4146 startTimer();
4147 sample_eden();
4148 // Get dirty region starting at nextOffset (inclusive),
4149 // simultaneously clearing it.
4150 dirtyRegion =
4151 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4152 assert(dirtyRegion.start() >= nextAddr,
4153 "returned region inconsistent?");
4154 }
4155 // Remember where the next search should begin.
4156 // The returned region (if non-empty) is a right open interval,
4157 // so lastOffset is obtained from the right end of that
4158 // interval.
4159 lastAddr = dirtyRegion.end();
4160 // Should do something more transparent and less hacky XXX
4161 numDirtyCards =
4162 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4163
4164 // We'll scan the cards in the dirty region (with periodic
4165 // yields for foreground GC as needed).
4166 if (!dirtyRegion.is_empty()) {
4167 assert(numDirtyCards > 0, "consistency check");
4168 HeapWord* stop_point = NULL;
4169 stopTimer();
4170 // Potential yield point
4171 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4172 bitMapLock());
4173 startTimer();
4174 {
4175 verify_work_stacks_empty();
4176 verify_overflow_empty();
4177 sample_eden();
4178 stop_point =
4179 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4180 }
4181 if (stop_point != NULL) {
4182 // The careful iteration stopped early either because it found an
4183 // uninitialized object, or because we were in the midst of an
4184 // "abortable preclean", which should now be aborted. Redirty
4185 // the bits corresponding to the partially-scanned or unscanned
4186 // cards. We'll either restart at the next block boundary or
4187 // abort the preclean.
4188 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4189 "Should only be AbortablePreclean.");
4190 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4191 if (should_abort_preclean()) {
4192 break; // out of preclean loop
4193 } else {
4194 // Compute the next address at which preclean should pick up;
4195 // might need bitMapLock in order to read P-bits.
4196 lastAddr = next_card_start_after_block(stop_point);
4197 }
4198 }
4199 } else {
4200 assert(lastAddr == endAddr, "consistency check");
4201 assert(numDirtyCards == 0, "consistency check");
4202 break;
4203 }
4204 }
4205 verify_work_stacks_empty();
4206 verify_overflow_empty();
4207 return cumNumDirtyCards;
4208 }
4209
4210 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4211 // below are largely identical; if you need to modify
4212 // one of these methods, please check the other method too.
4213
4214 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4215 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4216 // strategy: it's similar to precleamModUnionTable above, in that
4217 // we accumulate contiguous ranges of dirty cards, mark these cards
4218 // precleaned, then scan the region covered by these cards.
4219 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4220 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4221
4222 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4223
4224 size_t numDirtyCards, cumNumDirtyCards;
4225 HeapWord *lastAddr, *nextAddr;
4226
4227 for (cumNumDirtyCards = numDirtyCards = 0,
4228 nextAddr = lastAddr = startAddr;
4229 nextAddr < endAddr;
4230 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4231
4232 ResourceMark rm;
4233 HandleMark hm;
4234
4235 MemRegion dirtyRegion;
4236 {
4237 // See comments in "Precleaning notes" above on why we
4238 // do this locking. XXX Could the locking overheads be
4239 // too high when dirty cards are sparse? [I don't think so.]
4240 stopTimer();
4241 CMSTokenSync x(true); // is cms thread
4242 startTimer();
4243 sample_eden();
4244 // Get and clear dirty region from card table
4245 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4246 MemRegion(nextAddr, endAddr),
4247 true,
4248 CardTableModRefBS::precleaned_card_val());
4249
4250 assert(dirtyRegion.start() >= nextAddr,
4251 "returned region inconsistent?");
4252 }
4253 lastAddr = dirtyRegion.end();
4254 numDirtyCards =
4255 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4256
4257 if (!dirtyRegion.is_empty()) {
4258 stopTimer();
4259 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4260 startTimer();
4261 sample_eden();
4262 verify_work_stacks_empty();
4263 verify_overflow_empty();
4264 HeapWord* stop_point =
4265 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4266 if (stop_point != NULL) {
4267 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4268 "Should only be AbortablePreclean.");
4269 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4270 if (should_abort_preclean()) {
4271 break; // out of preclean loop
4272 } else {
4273 // Compute the next address at which preclean should pick up.
4274 lastAddr = next_card_start_after_block(stop_point);
4275 }
4276 }
4277 } else {
4278 break;
4279 }
4280 }
4281 verify_work_stacks_empty();
4282 verify_overflow_empty();
4283 return cumNumDirtyCards;
4284 }
4285
4286 class PrecleanKlassClosure : public KlassClosure {
4287 KlassToOopClosure _cm_klass_closure;
4288 public:
4289 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4290 void do_klass(Klass* k) {
4291 if (k->has_accumulated_modified_oops()) {
4292 k->clear_accumulated_modified_oops();
4293
4294 _cm_klass_closure.do_klass(k);
4295 }
4296 }
4297 };
4298
4299 // The freelist lock is needed to prevent asserts, is it really needed?
4300 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4301
4302 cl->set_freelistLock(freelistLock);
4303
4304 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4305
4306 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4307 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4308 PrecleanKlassClosure preclean_klass_closure(cl);
4309 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4310
4311 verify_work_stacks_empty();
4312 verify_overflow_empty();
4313 }
4314
4315 void CMSCollector::checkpointRootsFinal() {
4316 assert(_collectorState == FinalMarking, "incorrect state transition?");
4317 check_correct_thread_executing();
4318 // world is stopped at this checkpoint
4319 assert(SafepointSynchronize::is_at_safepoint(),
4320 "world should be stopped");
4321 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4322
4323 verify_work_stacks_empty();
4324 verify_overflow_empty();
4325
4326 if (PrintGCDetails) {
4327 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4328 _young_gen->used() / K,
4329 _young_gen->capacity() / K);
4330 }
4331 {
4332 if (CMSScavengeBeforeRemark) {
4333 GenCollectedHeap* gch = GenCollectedHeap::heap();
4334 // Temporarily set flag to false, GCH->do_collection will
4335 // expect it to be false and set to true
4336 FlagSetting fl(gch->_is_gc_active, false);
4337 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4338 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4339 int level = _cmsGen->level() - 1;
4340 if (level >= 0) {
4341 gch->do_collection(true, // full (i.e. force, see below)
4342 false, // !clear_all_soft_refs
4343 0, // size
4344 false, // is_tlab
4345 level // max_level
4346 );
4347 }
4348 }
4349 FreelistLocker x(this);
4350 MutexLockerEx y(bitMapLock(),
4351 Mutex::_no_safepoint_check_flag);
4352 checkpointRootsFinalWork();
4353 }
4354 verify_work_stacks_empty();
4355 verify_overflow_empty();
4356 }
4357
4358 void CMSCollector::checkpointRootsFinalWork() {
4359 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4360
4361 assert(haveFreelistLocks(), "must have free list locks");
4362 assert_lock_strong(bitMapLock());
4363
4364 ResourceMark rm;
4365 HandleMark hm;
4366
4367 GenCollectedHeap* gch = GenCollectedHeap::heap();
4368
4369 if (should_unload_classes()) {
4370 CodeCache::gc_prologue();
4371 }
4372 assert(haveFreelistLocks(), "must have free list locks");
4373 assert_lock_strong(bitMapLock());
4374
4375 // We might assume that we need not fill TLAB's when
4376 // CMSScavengeBeforeRemark is set, because we may have just done
4377 // a scavenge which would have filled all TLAB's -- and besides
4378 // Eden would be empty. This however may not always be the case --
4379 // for instance although we asked for a scavenge, it may not have
4380 // happened because of a JNI critical section. We probably need
4381 // a policy for deciding whether we can in that case wait until
4382 // the critical section releases and then do the remark following
4383 // the scavenge, and skip it here. In the absence of that policy,
4384 // or of an indication of whether the scavenge did indeed occur,
4385 // we cannot rely on TLAB's having been filled and must do
4386 // so here just in case a scavenge did not happen.
4387 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4388 // Update the saved marks which may affect the root scans.
4389 gch->save_marks();
4390
4391 if (CMSPrintEdenSurvivorChunks) {
4392 print_eden_and_survivor_chunk_arrays();
4393 }
4394
4395 {
4396 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4397
4398 // Note on the role of the mod union table:
4399 // Since the marker in "markFromRoots" marks concurrently with
4400 // mutators, it is possible for some reachable objects not to have been
4401 // scanned. For instance, an only reference to an object A was
4402 // placed in object B after the marker scanned B. Unless B is rescanned,
4403 // A would be collected. Such updates to references in marked objects
4404 // are detected via the mod union table which is the set of all cards
4405 // dirtied since the first checkpoint in this GC cycle and prior to
4406 // the most recent young generation GC, minus those cleaned up by the
4407 // concurrent precleaning.
4408 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
4409 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
4410 do_remark_parallel();
4411 } else {
4412 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4413 _gc_timer_cm, _gc_tracer_cm->gc_id());
4414 do_remark_non_parallel();
4415 }
4416 }
4417 verify_work_stacks_empty();
4418 verify_overflow_empty();
4419
4420 {
4421 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4422 refProcessingWork();
4423 }
4424 verify_work_stacks_empty();
4425 verify_overflow_empty();
4426
4427 if (should_unload_classes()) {
4428 CodeCache::gc_epilogue();
4429 }
4430 JvmtiExport::gc_epilogue();
4431
4432 // If we encountered any (marking stack / work queue) overflow
4433 // events during the current CMS cycle, take appropriate
4434 // remedial measures, where possible, so as to try and avoid
4435 // recurrence of that condition.
4436 assert(_markStack.isEmpty(), "No grey objects");
4437 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4438 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4439 if (ser_ovflw > 0) {
4440 if (PrintCMSStatistics != 0) {
4441 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4442 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4443 ", kac_preclean="SIZE_FORMAT")",
4444 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4445 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4446 }
4447 _markStack.expand();
4448 _ser_pmc_remark_ovflw = 0;
4449 _ser_pmc_preclean_ovflw = 0;
4450 _ser_kac_preclean_ovflw = 0;
4451 _ser_kac_ovflw = 0;
4452 }
4453 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4454 if (PrintCMSStatistics != 0) {
4455 gclog_or_tty->print_cr("Work queue overflow (benign) "
4456 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4457 _par_pmc_remark_ovflw, _par_kac_ovflw);
4458 }
4459 _par_pmc_remark_ovflw = 0;
4460 _par_kac_ovflw = 0;
4461 }
4462 if (PrintCMSStatistics != 0) {
4463 if (_markStack._hit_limit > 0) {
4464 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4465 _markStack._hit_limit);
4466 }
4467 if (_markStack._failed_double > 0) {
4468 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4469 " current capacity "SIZE_FORMAT,
4470 _markStack._failed_double,
4471 _markStack.capacity());
4472 }
4473 }
4474 _markStack._hit_limit = 0;
4475 _markStack._failed_double = 0;
4476
4477 if ((VerifyAfterGC || VerifyDuringGC) &&
4478 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4479 verify_after_remark();
4480 }
4481
4482 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4483
4484 // Change under the freelistLocks.
4485 _collectorState = Sweeping;
4486 // Call isAllClear() under bitMapLock
4487 assert(_modUnionTable.isAllClear(),
4488 "Should be clear by end of the final marking");
4489 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4490 "Should be clear by end of the final marking");
4491 }
4492
4493 void CMSParInitialMarkTask::work(uint worker_id) {
4494 elapsedTimer _timer;
4495 ResourceMark rm;
4496 HandleMark hm;
4497
4498 // ---------- scan from roots --------------
4499 _timer.start();
4500 GenCollectedHeap* gch = GenCollectedHeap::heap();
4501 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4502
4503 // ---------- young gen roots --------------
4504 {
4505 work_on_young_gen_roots(worker_id, &par_mri_cl);
4506 _timer.stop();
4507 if (PrintCMSStatistics != 0) {
4508 gclog_or_tty->print_cr(
4509 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4510 worker_id, _timer.seconds());
4511 }
4512 }
4513
4514 // ---------- remaining roots --------------
4515 _timer.reset();
4516 _timer.start();
4517
4518 CLDToOopClosure cld_closure(&par_mri_cl, true);
4519
4520 gch->gen_process_roots(_collector->_cmsGen->level(),
4521 false, // yg was scanned above
4522 false, // this is parallel code
4523 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4524 _collector->should_unload_classes(),
4525 &par_mri_cl,
4526 NULL,
4527 &cld_closure);
4528 assert(_collector->should_unload_classes()
4529 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4530 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4531 _timer.stop();
4532 if (PrintCMSStatistics != 0) {
4533 gclog_or_tty->print_cr(
4534 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4535 worker_id, _timer.seconds());
4536 }
4537 }
4538
4539 // Parallel remark task
4540 class CMSParRemarkTask: public CMSParMarkTask {
4541 CompactibleFreeListSpace* _cms_space;
4542
4543 // The per-thread work queues, available here for stealing.
4544 OopTaskQueueSet* _task_queues;
4545 ParallelTaskTerminator _term;
4546
4547 public:
4548 // A value of 0 passed to n_workers will cause the number of
4549 // workers to be taken from the active workers in the work gang.
4550 CMSParRemarkTask(CMSCollector* collector,
4551 CompactibleFreeListSpace* cms_space,
4552 int n_workers, FlexibleWorkGang* workers,
4553 OopTaskQueueSet* task_queues):
4554 CMSParMarkTask("Rescan roots and grey objects in parallel",
4555 collector, n_workers),
4556 _cms_space(cms_space),
4557 _task_queues(task_queues),
4558 _term(n_workers, task_queues) { }
4559
4560 OopTaskQueueSet* task_queues() { return _task_queues; }
4561
4562 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4563
4564 ParallelTaskTerminator* terminator() { return &_term; }
4565 int n_workers() { return _n_workers; }
4566
4567 void work(uint worker_id);
4568
4569 private:
4570 // ... of dirty cards in old space
4571 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4572 Par_MarkRefsIntoAndScanClosure* cl);
4573
4574 // ... work stealing for the above
4575 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4576 };
4577
4578 class RemarkKlassClosure : public KlassClosure {
4579 KlassToOopClosure _cm_klass_closure;
4580 public:
4581 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4582 void do_klass(Klass* k) {
4583 // Check if we have modified any oops in the Klass during the concurrent marking.
4584 if (k->has_accumulated_modified_oops()) {
4585 k->clear_accumulated_modified_oops();
4586
4587 // We could have transfered the current modified marks to the accumulated marks,
4588 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4589 } else if (k->has_modified_oops()) {
4590 // Don't clear anything, this info is needed by the next young collection.
4591 } else {
4592 // No modified oops in the Klass.
4593 return;
4594 }
4595
4596 // The klass has modified fields, need to scan the klass.
4597 _cm_klass_closure.do_klass(k);
4598 }
4599 };
4600
4601 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4602 ParNewGeneration* young_gen = _collector->_young_gen;
4603 ContiguousSpace* eden_space = young_gen->eden();
4604 ContiguousSpace* from_space = young_gen->from();
4605 ContiguousSpace* to_space = young_gen->to();
4606
4607 HeapWord** eca = _collector->_eden_chunk_array;
4608 size_t ect = _collector->_eden_chunk_index;
4609 HeapWord** sca = _collector->_survivor_chunk_array;
4610 size_t sct = _collector->_survivor_chunk_index;
4611
4612 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4613 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4614
4615 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4616 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4617 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4618 }
4619
4620 // work_queue(i) is passed to the closure
4621 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
4622 // also is passed to do_dirty_card_rescan_tasks() and to
4623 // do_work_steal() to select the i-th task_queue.
4624
4625 void CMSParRemarkTask::work(uint worker_id) {
4626 elapsedTimer _timer;
4627 ResourceMark rm;
4628 HandleMark hm;
4629
4630 // ---------- rescan from roots --------------
4631 _timer.start();
4632 GenCollectedHeap* gch = GenCollectedHeap::heap();
4633 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4634 _collector->_span, _collector->ref_processor(),
4635 &(_collector->_markBitMap),
4636 work_queue(worker_id));
4637
4638 // Rescan young gen roots first since these are likely
4639 // coarsely partitioned and may, on that account, constitute
4640 // the critical path; thus, it's best to start off that
4641 // work first.
4642 // ---------- young gen roots --------------
4643 {
4644 work_on_young_gen_roots(worker_id, &par_mrias_cl);
4645 _timer.stop();
4646 if (PrintCMSStatistics != 0) {
4647 gclog_or_tty->print_cr(
4648 "Finished young gen rescan work in %dth thread: %3.3f sec",
4649 worker_id, _timer.seconds());
4650 }
4651 }
4652
4653 // ---------- remaining roots --------------
4654 _timer.reset();
4655 _timer.start();
4656 gch->gen_process_roots(_collector->_cmsGen->level(),
4657 false, // yg was scanned above
4658 false, // this is parallel code
4659 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4660 _collector->should_unload_classes(),
4661 &par_mrias_cl,
4662 NULL,
4663 NULL); // The dirty klasses will be handled below
4664
4665 assert(_collector->should_unload_classes()
4666 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4667 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4668 _timer.stop();
4669 if (PrintCMSStatistics != 0) {
4670 gclog_or_tty->print_cr(
4671 "Finished remaining root rescan work in %dth thread: %3.3f sec",
4672 worker_id, _timer.seconds());
4673 }
4674
4675 // ---------- unhandled CLD scanning ----------
4676 if (worker_id == 0) { // Single threaded at the moment.
4677 _timer.reset();
4678 _timer.start();
4679
4680 // Scan all new class loader data objects and new dependencies that were
4681 // introduced during concurrent marking.
4682 ResourceMark rm;
4683 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4684 for (int i = 0; i < array->length(); i++) {
4685 par_mrias_cl.do_class_loader_data(array->at(i));
4686 }
4687
4688 // We don't need to keep track of new CLDs anymore.
4689 ClassLoaderDataGraph::remember_new_clds(false);
4690
4691 _timer.stop();
4692 if (PrintCMSStatistics != 0) {
4693 gclog_or_tty->print_cr(
4694 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4695 worker_id, _timer.seconds());
4696 }
4697 }
4698
4699 // ---------- dirty klass scanning ----------
4700 if (worker_id == 0) { // Single threaded at the moment.
4701 _timer.reset();
4702 _timer.start();
4703
4704 // Scan all classes that was dirtied during the concurrent marking phase.
4705 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4706 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4707
4708 _timer.stop();
4709 if (PrintCMSStatistics != 0) {
4710 gclog_or_tty->print_cr(
4711 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4712 worker_id, _timer.seconds());
4713 }
4714 }
4715
4716 // We might have added oops to ClassLoaderData::_handles during the
4717 // concurrent marking phase. These oops point to newly allocated objects
4718 // that are guaranteed to be kept alive. Either by the direct allocation
4719 // code, or when the young collector processes the roots. Hence,
4720 // we don't have to revisit the _handles block during the remark phase.
4721
4722 // ---------- rescan dirty cards ------------
4723 _timer.reset();
4724 _timer.start();
4725
4726 // Do the rescan tasks for each of the two spaces
4727 // (cms_space) in turn.
4728 // "worker_id" is passed to select the task_queue for "worker_id"
4729 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4730 _timer.stop();
4731 if (PrintCMSStatistics != 0) {
4732 gclog_or_tty->print_cr(
4733 "Finished dirty card rescan work in %dth thread: %3.3f sec",
4734 worker_id, _timer.seconds());
4735 }
4736
4737 // ---------- steal work from other threads ...
4738 // ---------- ... and drain overflow list.
4739 _timer.reset();
4740 _timer.start();
4741 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4742 _timer.stop();
4743 if (PrintCMSStatistics != 0) {
4744 gclog_or_tty->print_cr(
4745 "Finished work stealing in %dth thread: %3.3f sec",
4746 worker_id, _timer.seconds());
4747 }
4748 }
4749
4750 // Note that parameter "i" is not used.
4751 void
4752 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4753 OopsInGenClosure* cl, ContiguousSpace* space,
4754 HeapWord** chunk_array, size_t chunk_top) {
4755 // Until all tasks completed:
4756 // . claim an unclaimed task
4757 // . compute region boundaries corresponding to task claimed
4758 // using chunk_array
4759 // . par_oop_iterate(cl) over that region
4760
4761 ResourceMark rm;
4762 HandleMark hm;
4763
4764 SequentialSubTasksDone* pst = space->par_seq_tasks();
4765
4766 uint nth_task = 0;
4767 uint n_tasks = pst->n_tasks();
4768
4769 if (n_tasks > 0) {
4770 assert(pst->valid(), "Uninitialized use?");
4771 HeapWord *start, *end;
4772 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4773 // We claimed task # nth_task; compute its boundaries.
4774 if (chunk_top == 0) { // no samples were taken
4775 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4776 start = space->bottom();
4777 end = space->top();
4778 } else if (nth_task == 0) {
4779 start = space->bottom();
4780 end = chunk_array[nth_task];
4781 } else if (nth_task < (uint)chunk_top) {
4782 assert(nth_task >= 1, "Control point invariant");
4783 start = chunk_array[nth_task - 1];
4784 end = chunk_array[nth_task];
4785 } else {
4786 assert(nth_task == (uint)chunk_top, "Control point invariant");
4787 start = chunk_array[chunk_top - 1];
4788 end = space->top();
4789 }
4790 MemRegion mr(start, end);
4791 // Verify that mr is in space
4792 assert(mr.is_empty() || space->used_region().contains(mr),
4793 "Should be in space");
4794 // Verify that "start" is an object boundary
4795 assert(mr.is_empty() || oop(mr.start())->is_oop(),
4796 "Should be an oop");
4797 space->par_oop_iterate(mr, cl);
4798 }
4799 pst->all_tasks_completed();
4800 }
4801 }
4802
4803 void
4804 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4805 CompactibleFreeListSpace* sp, int i,
4806 Par_MarkRefsIntoAndScanClosure* cl) {
4807 // Until all tasks completed:
4808 // . claim an unclaimed task
4809 // . compute region boundaries corresponding to task claimed
4810 // . transfer dirty bits ct->mut for that region
4811 // . apply rescanclosure to dirty mut bits for that region
4812
4813 ResourceMark rm;
4814 HandleMark hm;
4815
4816 OopTaskQueue* work_q = work_queue(i);
4817 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4818 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4819 // CAUTION: This closure has state that persists across calls to
4820 // the work method dirty_range_iterate_clear() in that it has
4821 // embedded in it a (subtype of) UpwardsObjectClosure. The
4822 // use of that state in the embedded UpwardsObjectClosure instance
4823 // assumes that the cards are always iterated (even if in parallel
4824 // by several threads) in monotonically increasing order per each
4825 // thread. This is true of the implementation below which picks
4826 // card ranges (chunks) in monotonically increasing order globally
4827 // and, a-fortiori, in monotonically increasing order per thread
4828 // (the latter order being a subsequence of the former).
4829 // If the work code below is ever reorganized into a more chaotic
4830 // work-partitioning form than the current "sequential tasks"
4831 // paradigm, the use of that persistent state will have to be
4832 // revisited and modified appropriately. See also related
4833 // bug 4756801 work on which should examine this code to make
4834 // sure that the changes there do not run counter to the
4835 // assumptions made here and necessary for correctness and
4836 // efficiency. Note also that this code might yield inefficient
4837 // behavior in the case of very large objects that span one or
4838 // more work chunks. Such objects would potentially be scanned
4839 // several times redundantly. Work on 4756801 should try and
4840 // address that performance anomaly if at all possible. XXX
4841 MemRegion full_span = _collector->_span;
4842 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4843 MarkFromDirtyCardsClosure
4844 greyRescanClosure(_collector, full_span, // entire span of interest
4845 sp, bm, work_q, cl);
4846
4847 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4848 assert(pst->valid(), "Uninitialized use?");
4849 uint nth_task = 0;
4850 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4851 MemRegion span = sp->used_region();
4852 HeapWord* start_addr = span.start();
4853 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4854 alignment);
4855 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4856 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4857 start_addr, "Check alignment");
4858 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4859 chunk_size, "Check alignment");
4860
4861 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4862 // Having claimed the nth_task, compute corresponding mem-region,
4863 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4864 // The alignment restriction ensures that we do not need any
4865 // synchronization with other gang-workers while setting or
4866 // clearing bits in thus chunk of the MUT.
4867 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4868 start_addr + (nth_task+1)*chunk_size);
4869 // The last chunk's end might be way beyond end of the
4870 // used region. In that case pull back appropriately.
4871 if (this_span.end() > end_addr) {
4872 this_span.set_end(end_addr);
4873 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4874 }
4875 // Iterate over the dirty cards covering this chunk, marking them
4876 // precleaned, and setting the corresponding bits in the mod union
4877 // table. Since we have been careful to partition at Card and MUT-word
4878 // boundaries no synchronization is needed between parallel threads.
4879 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4880 &modUnionClosure);
4881
4882 // Having transferred these marks into the modUnionTable,
4883 // rescan the marked objects on the dirty cards in the modUnionTable.
4884 // Even if this is at a synchronous collection, the initial marking
4885 // may have been done during an asynchronous collection so there
4886 // may be dirty bits in the mod-union table.
4887 _collector->_modUnionTable.dirty_range_iterate_clear(
4888 this_span, &greyRescanClosure);
4889 _collector->_modUnionTable.verifyNoOneBitsInRange(
4890 this_span.start(),
4891 this_span.end());
4892 }
4893 pst->all_tasks_completed(); // declare that i am done
4894 }
4895
4896 // . see if we can share work_queues with ParNew? XXX
4897 void
4898 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4899 int* seed) {
4900 OopTaskQueue* work_q = work_queue(i);
4901 NOT_PRODUCT(int num_steals = 0;)
4902 oop obj_to_scan;
4903 CMSBitMap* bm = &(_collector->_markBitMap);
4904
4905 while (true) {
4906 // Completely finish any left over work from (an) earlier round(s)
4907 cl->trim_queue(0);
4908 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4909 (size_t)ParGCDesiredObjsFromOverflowList);
4910 // Now check if there's any work in the overflow list
4911 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4912 // only affects the number of attempts made to get work from the
4913 // overflow list and does not affect the number of workers. Just
4914 // pass ParallelGCThreads so this behavior is unchanged.
4915 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4916 work_q,
4917 ParallelGCThreads)) {
4918 // found something in global overflow list;
4919 // not yet ready to go stealing work from others.
4920 // We'd like to assert(work_q->size() != 0, ...)
4921 // because we just took work from the overflow list,
4922 // but of course we can't since all of that could have
4923 // been already stolen from us.
4924 // "He giveth and He taketh away."
4925 continue;
4926 }
4927 // Verify that we have no work before we resort to stealing
4928 assert(work_q->size() == 0, "Have work, shouldn't steal");
4929 // Try to steal from other queues that have work
4930 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4931 NOT_PRODUCT(num_steals++;)
4932 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4933 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4934 // Do scanning work
4935 obj_to_scan->oop_iterate(cl);
4936 // Loop around, finish this work, and try to steal some more
4937 } else if (terminator()->offer_termination()) {
4938 break; // nirvana from the infinite cycle
4939 }
4940 }
4941 NOT_PRODUCT(
4942 if (PrintCMSStatistics != 0) {
4943 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
4944 }
4945 )
4946 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4947 "Else our work is not yet done");
4948 }
4949
4950 // Record object boundaries in _eden_chunk_array by sampling the eden
4951 // top in the slow-path eden object allocation code path and record
4952 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4953 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4954 // sampling in sample_eden() that activates during the part of the
4955 // preclean phase.
4956 void CMSCollector::sample_eden_chunk() {
4957 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4958 if (_eden_chunk_lock->try_lock()) {
4959 // Record a sample. This is the critical section. The contents
4960 // of the _eden_chunk_array have to be non-decreasing in the
4961 // address order.
4962 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4963 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4964 "Unexpected state of Eden");
4965 if (_eden_chunk_index == 0 ||
4966 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4967 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4968 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4969 _eden_chunk_index++; // commit sample
4970 }
4971 _eden_chunk_lock->unlock();
4972 }
4973 }
4974 }
4975
4976 // Return a thread-local PLAB recording array, as appropriate.
4977 void* CMSCollector::get_data_recorder(int thr_num) {
4978 if (_survivor_plab_array != NULL &&
4979 (CMSPLABRecordAlways ||
4980 (_collectorState > Marking && _collectorState < FinalMarking))) {
4981 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4982 ChunkArray* ca = &_survivor_plab_array[thr_num];
4983 ca->reset(); // clear it so that fresh data is recorded
4984 return (void*) ca;
4985 } else {
4986 return NULL;
4987 }
4988 }
4989
4990 // Reset all the thread-local PLAB recording arrays
4991 void CMSCollector::reset_survivor_plab_arrays() {
4992 for (uint i = 0; i < ParallelGCThreads; i++) {
4993 _survivor_plab_array[i].reset();
4994 }
4995 }
4996
4997 // Merge the per-thread plab arrays into the global survivor chunk
4998 // array which will provide the partitioning of the survivor space
4999 // for CMS initial scan and rescan.
5000 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5001 int no_of_gc_threads) {
5002 assert(_survivor_plab_array != NULL, "Error");
5003 assert(_survivor_chunk_array != NULL, "Error");
5004 assert(_collectorState == FinalMarking ||
5005 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
5006 for (int j = 0; j < no_of_gc_threads; j++) {
5007 _cursor[j] = 0;
5008 }
5009 HeapWord* top = surv->top();
5010 size_t i;
5011 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5012 HeapWord* min_val = top; // Higher than any PLAB address
5013 uint min_tid = 0; // position of min_val this round
5014 for (int j = 0; j < no_of_gc_threads; j++) {
5015 ChunkArray* cur_sca = &_survivor_plab_array[j];
5016 if (_cursor[j] == cur_sca->end()) {
5017 continue;
5018 }
5019 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5020 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5021 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5022 if (cur_val < min_val) {
5023 min_tid = j;
5024 min_val = cur_val;
5025 } else {
5026 assert(cur_val < top, "All recorded addresses should be less");
5027 }
5028 }
5029 // At this point min_val and min_tid are respectively
5030 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5031 // and the thread (j) that witnesses that address.
5032 // We record this address in the _survivor_chunk_array[i]
5033 // and increment _cursor[min_tid] prior to the next round i.
5034 if (min_val == top) {
5035 break;
5036 }
5037 _survivor_chunk_array[i] = min_val;
5038 _cursor[min_tid]++;
5039 }
5040 // We are all done; record the size of the _survivor_chunk_array
5041 _survivor_chunk_index = i; // exclusive: [0, i)
5042 if (PrintCMSStatistics > 0) {
5043 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5044 }
5045 // Verify that we used up all the recorded entries
5046 #ifdef ASSERT
5047 size_t total = 0;
5048 for (int j = 0; j < no_of_gc_threads; j++) {
5049 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5050 total += _cursor[j];
5051 }
5052 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5053 // Check that the merged array is in sorted order
5054 if (total > 0) {
5055 for (size_t i = 0; i < total - 1; i++) {
5056 if (PrintCMSStatistics > 0) {
5057 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5058 i, p2i(_survivor_chunk_array[i]));
5059 }
5060 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5061 "Not sorted");
5062 }
5063 }
5064 #endif // ASSERT
5065 }
5066
5067 // Set up the space's par_seq_tasks structure for work claiming
5068 // for parallel initial scan and rescan of young gen.
5069 // See ParRescanTask where this is currently used.
5070 void
5071 CMSCollector::
5072 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5073 assert(n_threads > 0, "Unexpected n_threads argument");
5074
5075 // Eden space
5076 if (!_young_gen->eden()->is_empty()) {
5077 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
5078 assert(!pst->valid(), "Clobbering existing data?");
5079 // Each valid entry in [0, _eden_chunk_index) represents a task.
5080 size_t n_tasks = _eden_chunk_index + 1;
5081 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5082 // Sets the condition for completion of the subtask (how many threads
5083 // need to finish in order to be done).
5084 pst->set_n_threads(n_threads);
5085 pst->set_n_tasks((int)n_tasks);
5086 }
5087
5088 // Merge the survivor plab arrays into _survivor_chunk_array
5089 if (_survivor_plab_array != NULL) {
5090 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5091 } else {
5092 assert(_survivor_chunk_index == 0, "Error");
5093 }
5094
5095 // To space
5096 {
5097 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5098 assert(!pst->valid(), "Clobbering existing data?");
5099 // Sets the condition for completion of the subtask (how many threads
5100 // need to finish in order to be done).
5101 pst->set_n_threads(n_threads);
5102 pst->set_n_tasks(1);
5103 assert(pst->valid(), "Error");
5104 }
5105
5106 // From space
5107 {
5108 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5109 assert(!pst->valid(), "Clobbering existing data?");
5110 size_t n_tasks = _survivor_chunk_index + 1;
5111 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5112 // Sets the condition for completion of the subtask (how many threads
5113 // need to finish in order to be done).
5114 pst->set_n_threads(n_threads);
5115 pst->set_n_tasks((int)n_tasks);
5116 assert(pst->valid(), "Error");
5117 }
5118 }
5119
5120 // Parallel version of remark
5121 void CMSCollector::do_remark_parallel() {
5122 GenCollectedHeap* gch = GenCollectedHeap::heap();
5123 FlexibleWorkGang* workers = gch->workers();
5124 assert(workers != NULL, "Need parallel worker threads.");
5125 // Choose to use the number of GC workers most recently set
5126 // into "active_workers". If active_workers is not set, set it
5127 // to ParallelGCThreads.
5128 int n_workers = workers->active_workers();
5129 if (n_workers == 0) {
5130 assert(n_workers > 0, "Should have been set during scavenge");
5131 n_workers = ParallelGCThreads;
5132 workers->set_active_workers(n_workers);
5133 }
5134 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5135
5136 CMSParRemarkTask tsk(this,
5137 cms_space,
5138 n_workers, workers, task_queues());
5139
5140 // Set up for parallel process_roots work.
5141 gch->set_par_threads(n_workers);
5142 // We won't be iterating over the cards in the card table updating
5143 // the younger_gen cards, so we shouldn't call the following else
5144 // the verification code as well as subsequent younger_refs_iterate
5145 // code would get confused. XXX
5146 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5147
5148 // The young gen rescan work will not be done as part of
5149 // process_roots (which currently doesn't know how to
5150 // parallelize such a scan), but rather will be broken up into
5151 // a set of parallel tasks (via the sampling that the [abortable]
5152 // preclean phase did of eden, plus the [two] tasks of
5153 // scanning the [two] survivor spaces. Further fine-grain
5154 // parallelization of the scanning of the survivor spaces
5155 // themselves, and of precleaning of the younger gen itself
5156 // is deferred to the future.
5157 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5158
5159 // The dirty card rescan work is broken up into a "sequence"
5160 // of parallel tasks (per constituent space) that are dynamically
5161 // claimed by the parallel threads.
5162 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5163
5164 // It turns out that even when we're using 1 thread, doing the work in a
5165 // separate thread causes wide variance in run times. We can't help this
5166 // in the multi-threaded case, but we special-case n=1 here to get
5167 // repeatable measurements of the 1-thread overhead of the parallel code.
5168 if (n_workers > 1) {
5169 // Make refs discovery MT-safe, if it isn't already: it may not
5170 // necessarily be so, since it's possible that we are doing
5171 // ST marking.
5172 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5173 StrongRootsScope srs;
5174 workers->run_task(&tsk);
5175 } else {
5176 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5177 StrongRootsScope srs;
5178 tsk.work(0);
5179 }
5180
5181 gch->set_par_threads(0); // 0 ==> non-parallel.
5182 // restore, single-threaded for now, any preserved marks
5183 // as a result of work_q overflow
5184 restore_preserved_marks_if_any();
5185 }
5186
5187 // Non-parallel version of remark
5188 void CMSCollector::do_remark_non_parallel() {
5189 ResourceMark rm;
5190 HandleMark hm;
5191 GenCollectedHeap* gch = GenCollectedHeap::heap();
5192 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5193
5194 MarkRefsIntoAndScanClosure
5195 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5196 &_markStack, this,
5197 false /* should_yield */, false /* not precleaning */);
5198 MarkFromDirtyCardsClosure
5199 markFromDirtyCardsClosure(this, _span,
5200 NULL, // space is set further below
5201 &_markBitMap, &_markStack, &mrias_cl);
5202 {
5203 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5204 // Iterate over the dirty cards, setting the corresponding bits in the
5205 // mod union table.
5206 {
5207 ModUnionClosure modUnionClosure(&_modUnionTable);
5208 _ct->ct_bs()->dirty_card_iterate(
5209 _cmsGen->used_region(),
5210 &modUnionClosure);
5211 }
5212 // Having transferred these marks into the modUnionTable, we just need
5213 // to rescan the marked objects on the dirty cards in the modUnionTable.
5214 // The initial marking may have been done during an asynchronous
5215 // collection so there may be dirty bits in the mod-union table.
5216 const int alignment =
5217 CardTableModRefBS::card_size * BitsPerWord;
5218 {
5219 // ... First handle dirty cards in CMS gen
5220 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5221 MemRegion ur = _cmsGen->used_region();
5222 HeapWord* lb = ur.start();
5223 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5224 MemRegion cms_span(lb, ub);
5225 _modUnionTable.dirty_range_iterate_clear(cms_span,
5226 &markFromDirtyCardsClosure);
5227 verify_work_stacks_empty();
5228 if (PrintCMSStatistics != 0) {
5229 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5230 markFromDirtyCardsClosure.num_dirty_cards());
5231 }
5232 }
5233 }
5234 if (VerifyDuringGC &&
5235 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5236 HandleMark hm; // Discard invalid handles created during verification
5237 Universe::verify();
5238 }
5239 {
5240 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5241
5242 verify_work_stacks_empty();
5243
5244 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5245 StrongRootsScope srs;
5246
5247 gch->gen_process_roots(_cmsGen->level(),
5248 true, // younger gens as roots
5249 false, // use the local StrongRootsScope
5250 GenCollectedHeap::ScanningOption(roots_scanning_options()),
5251 should_unload_classes(),
5252 &mrias_cl,
5253 NULL,
5254 NULL); // The dirty klasses will be handled below
5255
5256 assert(should_unload_classes()
5257 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5258 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5259 }
5260
5261 {
5262 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5263
5264 verify_work_stacks_empty();
5265
5266 // Scan all class loader data objects that might have been introduced
5267 // during concurrent marking.
5268 ResourceMark rm;
5269 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5270 for (int i = 0; i < array->length(); i++) {
5271 mrias_cl.do_class_loader_data(array->at(i));
5272 }
5273
5274 // We don't need to keep track of new CLDs anymore.
5275 ClassLoaderDataGraph::remember_new_clds(false);
5276
5277 verify_work_stacks_empty();
5278 }
5279
5280 {
5281 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5282
5283 verify_work_stacks_empty();
5284
5285 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5286 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5287
5288 verify_work_stacks_empty();
5289 }
5290
5291 // We might have added oops to ClassLoaderData::_handles during the
5292 // concurrent marking phase. These oops point to newly allocated objects
5293 // that are guaranteed to be kept alive. Either by the direct allocation
5294 // code, or when the young collector processes the roots. Hence,
5295 // we don't have to revisit the _handles block during the remark phase.
5296
5297 verify_work_stacks_empty();
5298 // Restore evacuated mark words, if any, used for overflow list links
5299 if (!CMSOverflowEarlyRestoration) {
5300 restore_preserved_marks_if_any();
5301 }
5302 verify_overflow_empty();
5303 }
5304
5305 ////////////////////////////////////////////////////////
5306 // Parallel Reference Processing Task Proxy Class
5307 ////////////////////////////////////////////////////////
5308 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5309 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5310 CMSCollector* _collector;
5311 CMSBitMap* _mark_bit_map;
5312 const MemRegion _span;
5313 ProcessTask& _task;
5314
5315 public:
5316 CMSRefProcTaskProxy(ProcessTask& task,
5317 CMSCollector* collector,
5318 const MemRegion& span,
5319 CMSBitMap* mark_bit_map,
5320 AbstractWorkGang* workers,
5321 OopTaskQueueSet* task_queues):
5322 // XXX Should superclass AGTWOQ also know about AWG since it knows
5323 // about the task_queues used by the AWG? Then it could initialize
5324 // the terminator() object. See 6984287. The set_for_termination()
5325 // below is a temporary band-aid for the regression in 6984287.
5326 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5327 task_queues),
5328 _task(task),
5329 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5330 {
5331 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5332 "Inconsistency in _span");
5333 set_for_termination(workers->active_workers());
5334 }
5335
5336 OopTaskQueueSet* task_queues() { return queues(); }
5337
5338 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5339
5340 void do_work_steal(int i,
5341 CMSParDrainMarkingStackClosure* drain,
5342 CMSParKeepAliveClosure* keep_alive,
5343 int* seed);
5344
5345 virtual void work(uint worker_id);
5346 };
5347
5348 void CMSRefProcTaskProxy::work(uint worker_id) {
5349 ResourceMark rm;
5350 HandleMark hm;
5351 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5352 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5353 _mark_bit_map,
5354 work_queue(worker_id));
5355 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5356 _mark_bit_map,
5357 work_queue(worker_id));
5358 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5359 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5360 if (_task.marks_oops_alive()) {
5361 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5362 _collector->hash_seed(worker_id));
5363 }
5364 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5365 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5366 }
5367
5368 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5369 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5370 EnqueueTask& _task;
5371
5372 public:
5373 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5374 : AbstractGangTask("Enqueue reference objects in parallel"),
5375 _task(task)
5376 { }
5377
5378 virtual void work(uint worker_id)
5379 {
5380 _task.work(worker_id);
5381 }
5382 };
5383
5384 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5385 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5386 _span(span),
5387 _bit_map(bit_map),
5388 _work_queue(work_queue),
5389 _mark_and_push(collector, span, bit_map, work_queue),
5390 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5391 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5392 { }
5393
5394 // . see if we can share work_queues with ParNew? XXX
5395 void CMSRefProcTaskProxy::do_work_steal(int i,
5396 CMSParDrainMarkingStackClosure* drain,
5397 CMSParKeepAliveClosure* keep_alive,
5398 int* seed) {
5399 OopTaskQueue* work_q = work_queue(i);
5400 NOT_PRODUCT(int num_steals = 0;)
5401 oop obj_to_scan;
5402
5403 while (true) {
5404 // Completely finish any left over work from (an) earlier round(s)
5405 drain->trim_queue(0);
5406 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5407 (size_t)ParGCDesiredObjsFromOverflowList);
5408 // Now check if there's any work in the overflow list
5409 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5410 // only affects the number of attempts made to get work from the
5411 // overflow list and does not affect the number of workers. Just
5412 // pass ParallelGCThreads so this behavior is unchanged.
5413 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5414 work_q,
5415 ParallelGCThreads)) {
5416 // Found something in global overflow list;
5417 // not yet ready to go stealing work from others.
5418 // We'd like to assert(work_q->size() != 0, ...)
5419 // because we just took work from the overflow list,
5420 // but of course we can't, since all of that might have
5421 // been already stolen from us.
5422 continue;
5423 }
5424 // Verify that we have no work before we resort to stealing
5425 assert(work_q->size() == 0, "Have work, shouldn't steal");
5426 // Try to steal from other queues that have work
5427 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5428 NOT_PRODUCT(num_steals++;)
5429 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5430 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5431 // Do scanning work
5432 obj_to_scan->oop_iterate(keep_alive);
5433 // Loop around, finish this work, and try to steal some more
5434 } else if (terminator()->offer_termination()) {
5435 break; // nirvana from the infinite cycle
5436 }
5437 }
5438 NOT_PRODUCT(
5439 if (PrintCMSStatistics != 0) {
5440 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5441 }
5442 )
5443 }
5444
5445 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5446 {
5447 GenCollectedHeap* gch = GenCollectedHeap::heap();
5448 FlexibleWorkGang* workers = gch->workers();
5449 assert(workers != NULL, "Need parallel worker threads.");
5450 CMSRefProcTaskProxy rp_task(task, &_collector,
5451 _collector.ref_processor()->span(),
5452 _collector.markBitMap(),
5453 workers, _collector.task_queues());
5454 workers->run_task(&rp_task);
5455 }
5456
5457 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5458 {
5459
5460 GenCollectedHeap* gch = GenCollectedHeap::heap();
5461 FlexibleWorkGang* workers = gch->workers();
5462 assert(workers != NULL, "Need parallel worker threads.");
5463 CMSRefEnqueueTaskProxy enq_task(task);
5464 workers->run_task(&enq_task);
5465 }
5466
5467 void CMSCollector::refProcessingWork() {
5468 ResourceMark rm;
5469 HandleMark hm;
5470
5471 ReferenceProcessor* rp = ref_processor();
5472 assert(rp->span().equals(_span), "Spans should be equal");
5473 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5474 // Process weak references.
5475 rp->setup_policy(false);
5476 verify_work_stacks_empty();
5477
5478 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5479 &_markStack, false /* !preclean */);
5480 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5481 _span, &_markBitMap, &_markStack,
5482 &cmsKeepAliveClosure, false /* !preclean */);
5483 {
5484 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5485
5486 ReferenceProcessorStats stats;
5487 if (rp->processing_is_mt()) {
5488 // Set the degree of MT here. If the discovery is done MT, there
5489 // may have been a different number of threads doing the discovery
5490 // and a different number of discovered lists may have Ref objects.
5491 // That is OK as long as the Reference lists are balanced (see
5492 // balance_all_queues() and balance_queues()).
5493 GenCollectedHeap* gch = GenCollectedHeap::heap();
5494 int active_workers = ParallelGCThreads;
5495 FlexibleWorkGang* workers = gch->workers();
5496 if (workers != NULL) {
5497 active_workers = workers->active_workers();
5498 // The expectation is that active_workers will have already
5499 // been set to a reasonable value. If it has not been set,
5500 // investigate.
5501 assert(active_workers > 0, "Should have been set during scavenge");
5502 }
5503 rp->set_active_mt_degree(active_workers);
5504 CMSRefProcTaskExecutor task_executor(*this);
5505 stats = rp->process_discovered_references(&_is_alive_closure,
5506 &cmsKeepAliveClosure,
5507 &cmsDrainMarkingStackClosure,
5508 &task_executor,
5509 _gc_timer_cm,
5510 _gc_tracer_cm->gc_id());
5511 } else {
5512 stats = rp->process_discovered_references(&_is_alive_closure,
5513 &cmsKeepAliveClosure,
5514 &cmsDrainMarkingStackClosure,
5515 NULL,
5516 _gc_timer_cm,
5517 _gc_tracer_cm->gc_id());
5518 }
5519 _gc_tracer_cm->report_gc_reference_stats(stats);
5520
5521 }
5522
5523 // This is the point where the entire marking should have completed.
5524 verify_work_stacks_empty();
5525
5526 if (should_unload_classes()) {
5527 {
5528 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5529
5530 // Unload classes and purge the SystemDictionary.
5531 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5532
5533 // Unload nmethods.
5534 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5535
5536 // Prune dead klasses from subklass/sibling/implementor lists.
5537 Klass::clean_weak_klass_links(&_is_alive_closure);
5538 }
5539
5540 {
5541 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5542 // Clean up unreferenced symbols in symbol table.
5543 SymbolTable::unlink();
5544 }
5545
5546 {
5547 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5548 // Delete entries for dead interned strings.
5549 StringTable::unlink(&_is_alive_closure);
5550 }
5551 }
5552
5553
5554 // Restore any preserved marks as a result of mark stack or
5555 // work queue overflow
5556 restore_preserved_marks_if_any(); // done single-threaded for now
5557
5558 rp->set_enqueuing_is_done(true);
5559 if (rp->processing_is_mt()) {
5560 rp->balance_all_queues();
5561 CMSRefProcTaskExecutor task_executor(*this);
5562 rp->enqueue_discovered_references(&task_executor);
5563 } else {
5564 rp->enqueue_discovered_references(NULL);
5565 }
5566 rp->verify_no_references_recorded();
5567 assert(!rp->discovery_enabled(), "should have been disabled");
5568 }
5569
5570 #ifndef PRODUCT
5571 void CMSCollector::check_correct_thread_executing() {
5572 Thread* t = Thread::current();
5573 // Only the VM thread or the CMS thread should be here.
5574 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5575 "Unexpected thread type");
5576 // If this is the vm thread, the foreground process
5577 // should not be waiting. Note that _foregroundGCIsActive is
5578 // true while the foreground collector is waiting.
5579 if (_foregroundGCShouldWait) {
5580 // We cannot be the VM thread
5581 assert(t->is_ConcurrentGC_thread(),
5582 "Should be CMS thread");
5583 } else {
5584 // We can be the CMS thread only if we are in a stop-world
5585 // phase of CMS collection.
5586 if (t->is_ConcurrentGC_thread()) {
5587 assert(_collectorState == InitialMarking ||
5588 _collectorState == FinalMarking,
5589 "Should be a stop-world phase");
5590 // The CMS thread should be holding the CMS_token.
5591 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5592 "Potential interference with concurrently "
5593 "executing VM thread");
5594 }
5595 }
5596 }
5597 #endif
5598
5599 void CMSCollector::sweep() {
5600 assert(_collectorState == Sweeping, "just checking");
5601 check_correct_thread_executing();
5602 verify_work_stacks_empty();
5603 verify_overflow_empty();
5604 increment_sweep_count();
5605 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5606
5607 _inter_sweep_timer.stop();
5608 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5609
5610 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5611 _intra_sweep_timer.reset();
5612 _intra_sweep_timer.start();
5613 {
5614 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5615 CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5616 // First sweep the old gen
5617 {
5618 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5619 bitMapLock());
5620 sweepWork(_cmsGen);
5621 }
5622
5623 // Update Universe::_heap_*_at_gc figures.
5624 // We need all the free list locks to make the abstract state
5625 // transition from Sweeping to Resetting. See detailed note
5626 // further below.
5627 {
5628 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5629 // Update heap occupancy information which is used as
5630 // input to soft ref clearing policy at the next gc.
5631 Universe::update_heap_info_at_gc();
5632 _collectorState = Resizing;
5633 }
5634 }
5635 verify_work_stacks_empty();
5636 verify_overflow_empty();
5637
5638 if (should_unload_classes()) {
5639 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5640 // requires that the virtual spaces are stable and not deleted.
5641 ClassLoaderDataGraph::set_should_purge(true);
5642 }
5643
5644 _intra_sweep_timer.stop();
5645 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5646
5647 _inter_sweep_timer.reset();
5648 _inter_sweep_timer.start();
5649
5650 // We need to use a monotonically non-decreasing time in ms
5651 // or we will see time-warp warnings and os::javaTimeMillis()
5652 // does not guarantee monotonicity.
5653 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5654 update_time_of_last_gc(now);
5655
5656 // NOTE on abstract state transitions:
5657 // Mutators allocate-live and/or mark the mod-union table dirty
5658 // based on the state of the collection. The former is done in
5659 // the interval [Marking, Sweeping] and the latter in the interval
5660 // [Marking, Sweeping). Thus the transitions into the Marking state
5661 // and out of the Sweeping state must be synchronously visible
5662 // globally to the mutators.
5663 // The transition into the Marking state happens with the world
5664 // stopped so the mutators will globally see it. Sweeping is
5665 // done asynchronously by the background collector so the transition
5666 // from the Sweeping state to the Resizing state must be done
5667 // under the freelistLock (as is the check for whether to
5668 // allocate-live and whether to dirty the mod-union table).
5669 assert(_collectorState == Resizing, "Change of collector state to"
5670 " Resizing must be done under the freelistLocks (plural)");
5671
5672 // Now that sweeping has been completed, we clear
5673 // the incremental_collection_failed flag,
5674 // thus inviting a younger gen collection to promote into
5675 // this generation. If such a promotion may still fail,
5676 // the flag will be set again when a young collection is
5677 // attempted.
5678 GenCollectedHeap* gch = GenCollectedHeap::heap();
5679 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5680 gch->update_full_collections_completed(_collection_count_start);
5681 }
5682
5683 // FIX ME!!! Looks like this belongs in CFLSpace, with
5684 // CMSGen merely delegating to it.
5685 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5686 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5687 HeapWord* minAddr = _cmsSpace->bottom();
5688 HeapWord* largestAddr =
5689 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5690 if (largestAddr == NULL) {
5691 // The dictionary appears to be empty. In this case
5692 // try to coalesce at the end of the heap.
5693 largestAddr = _cmsSpace->end();
5694 }
5695 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5696 size_t nearLargestOffset =
5697 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5698 if (PrintFLSStatistics != 0) {
5699 gclog_or_tty->print_cr(
5700 "CMS: Large Block: " PTR_FORMAT ";"
5701 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5702 p2i(largestAddr),
5703 p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5704 }
5705 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5706 }
5707
5708 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5709 return addr >= _cmsSpace->nearLargestChunk();
5710 }
5711
5712 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5713 return _cmsSpace->find_chunk_at_end();
5714 }
5715
5716 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
5717 bool full) {
5718 // The next lower level has been collected. Gather any statistics
5719 // that are of interest at this point.
5720 if (!full && (current_level + 1) == level()) {
5721 // Gather statistics on the young generation collection.
5722 collector()->stats().record_gc0_end(used());
5723 }
5724 }
5725
5726 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen) {
5727 // We iterate over the space(s) underlying this generation,
5728 // checking the mark bit map to see if the bits corresponding
5729 // to specific blocks are marked or not. Blocks that are
5730 // marked are live and are not swept up. All remaining blocks
5731 // are swept up, with coalescing on-the-fly as we sweep up
5732 // contiguous free and/or garbage blocks:
5733 // We need to ensure that the sweeper synchronizes with allocators
5734 // and stop-the-world collectors. In particular, the following
5735 // locks are used:
5736 // . CMS token: if this is held, a stop the world collection cannot occur
5737 // . freelistLock: if this is held no allocation can occur from this
5738 // generation by another thread
5739 // . bitMapLock: if this is held, no other thread can access or update
5740 //
5741
5742 // Note that we need to hold the freelistLock if we use
5743 // block iterate below; else the iterator might go awry if
5744 // a mutator (or promotion) causes block contents to change
5745 // (for instance if the allocator divvies up a block).
5746 // If we hold the free list lock, for all practical purposes
5747 // young generation GC's can't occur (they'll usually need to
5748 // promote), so we might as well prevent all young generation
5749 // GC's while we do a sweeping step. For the same reason, we might
5750 // as well take the bit map lock for the entire duration
5751
5752 // check that we hold the requisite locks
5753 assert(have_cms_token(), "Should hold cms token");
5754 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5755 assert_lock_strong(gen->freelistLock());
5756 assert_lock_strong(bitMapLock());
5757
5758 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5759 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5760 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5761 _inter_sweep_estimate.padded_average(),
5762 _intra_sweep_estimate.padded_average());
5763 gen->setNearLargestChunk();
5764
5765 {
5766 SweepClosure sweepClosure(this, gen, &_markBitMap, CMSYield);
5767 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5768 // We need to free-up/coalesce garbage/blocks from a
5769 // co-terminal free run. This is done in the SweepClosure
5770 // destructor; so, do not remove this scope, else the
5771 // end-of-sweep-census below will be off by a little bit.
5772 }
5773 gen->cmsSpace()->sweep_completed();
5774 gen->cmsSpace()->endSweepFLCensus(sweep_count());
5775 if (should_unload_classes()) { // unloaded classes this cycle,
5776 _concurrent_cycles_since_last_unload = 0; // ... reset count
5777 } else { // did not unload classes,
5778 _concurrent_cycles_since_last_unload++; // ... increment count
5779 }
5780 }
5781
5782 // Reset CMS data structures (for now just the marking bit map)
5783 // preparatory for the next cycle.
5784 void CMSCollector::reset(bool concurrent) {
5785 if (concurrent) {
5786 CMSTokenSyncWithLocks ts(true, bitMapLock());
5787
5788 // If the state is not "Resetting", the foreground thread
5789 // has done a collection and the resetting.
5790 if (_collectorState != Resetting) {
5791 assert(_collectorState == Idling, "The state should only change"
5792 " because the foreground collector has finished the collection");
5793 return;
5794 }
5795
5796 // Clear the mark bitmap (no grey objects to start with)
5797 // for the next cycle.
5798 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5799 CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5800
5801 HeapWord* curAddr = _markBitMap.startWord();
5802 while (curAddr < _markBitMap.endWord()) {
5803 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5804 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5805 _markBitMap.clear_large_range(chunk);
5806 if (ConcurrentMarkSweepThread::should_yield() &&
5807 !foregroundGCIsActive() &&
5808 CMSYield) {
5809 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5810 "CMS thread should hold CMS token");
5811 assert_lock_strong(bitMapLock());
5812 bitMapLock()->unlock();
5813 ConcurrentMarkSweepThread::desynchronize(true);
5814 stopTimer();
5815 if (PrintCMSStatistics != 0) {
5816 incrementYields();
5817 }
5818
5819 // See the comment in coordinator_yield()
5820 for (unsigned i = 0; i < CMSYieldSleepCount &&
5821 ConcurrentMarkSweepThread::should_yield() &&
5822 !CMSCollector::foregroundGCIsActive(); ++i) {
5823 os::sleep(Thread::current(), 1, false);
5824 }
5825
5826 ConcurrentMarkSweepThread::synchronize(true);
5827 bitMapLock()->lock_without_safepoint_check();
5828 startTimer();
5829 }
5830 curAddr = chunk.end();
5831 }
5832 // A successful mostly concurrent collection has been done.
5833 // Because only the full (i.e., concurrent mode failure) collections
5834 // are being measured for gc overhead limits, clean the "near" flag
5835 // and count.
5836 size_policy()->reset_gc_overhead_limit_count();
5837 _collectorState = Idling;
5838 } else {
5839 // already have the lock
5840 assert(_collectorState == Resetting, "just checking");
5841 assert_lock_strong(bitMapLock());
5842 _markBitMap.clear_all();
5843 _collectorState = Idling;
5844 }
5845
5846 register_gc_end();
5847 }
5848
5849 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5850 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5851 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
5852 TraceCollectorStats tcs(counters());
5853
5854 switch (op) {
5855 case CMS_op_checkpointRootsInitial: {
5856 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5857 checkpointRootsInitial();
5858 if (PrintGC) {
5859 _cmsGen->printOccupancy("initial-mark");
5860 }
5861 break;
5862 }
5863 case CMS_op_checkpointRootsFinal: {
5864 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5865 checkpointRootsFinal();
5866 if (PrintGC) {
5867 _cmsGen->printOccupancy("remark");
5868 }
5869 break;
5870 }
5871 default:
5872 fatal("No such CMS_op");
5873 }
5874 }
5875
5876 #ifndef PRODUCT
5877 size_t const CMSCollector::skip_header_HeapWords() {
5878 return FreeChunk::header_size();
5879 }
5880
5881 // Try and collect here conditions that should hold when
5882 // CMS thread is exiting. The idea is that the foreground GC
5883 // thread should not be blocked if it wants to terminate
5884 // the CMS thread and yet continue to run the VM for a while
5885 // after that.
5886 void CMSCollector::verify_ok_to_terminate() const {
5887 assert(Thread::current()->is_ConcurrentGC_thread(),
5888 "should be called by CMS thread");
5889 assert(!_foregroundGCShouldWait, "should be false");
5890 // We could check here that all the various low-level locks
5891 // are not held by the CMS thread, but that is overkill; see
5892 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5893 // is checked.
5894 }
5895 #endif
5896
5897 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5898 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5899 "missing Printezis mark?");
5900 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5901 size_t size = pointer_delta(nextOneAddr + 1, addr);
5902 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5903 "alignment problem");
5904 assert(size >= 3, "Necessary for Printezis marks to work");
5905 return size;
5906 }
5907
5908 // A variant of the above (block_size_using_printezis_bits()) except
5909 // that we return 0 if the P-bits are not yet set.
5910 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5911 if (_markBitMap.isMarked(addr + 1)) {
5912 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5913 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5914 size_t size = pointer_delta(nextOneAddr + 1, addr);
5915 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5916 "alignment problem");
5917 assert(size >= 3, "Necessary for Printezis marks to work");
5918 return size;
5919 }
5920 return 0;
5921 }
5922
5923 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5924 size_t sz = 0;
5925 oop p = (oop)addr;
5926 if (p->klass_or_null() != NULL) {
5927 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5928 } else {
5929 sz = block_size_using_printezis_bits(addr);
5930 }
5931 assert(sz > 0, "size must be nonzero");
5932 HeapWord* next_block = addr + sz;
5933 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
5934 CardTableModRefBS::card_size);
5935 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
5936 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5937 "must be different cards");
5938 return next_card;
5939 }
5940
5941
5942 // CMS Bit Map Wrapper /////////////////////////////////////////
5943
5944 // Construct a CMS bit map infrastructure, but don't create the
5945 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5946 // further below.
5947 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5948 _bm(),
5949 _shifter(shifter),
5950 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5951 Monitor::_safepoint_check_sometimes) : NULL)
5952 {
5953 _bmStartWord = 0;
5954 _bmWordSize = 0;
5955 }
5956
5957 bool CMSBitMap::allocate(MemRegion mr) {
5958 _bmStartWord = mr.start();
5959 _bmWordSize = mr.word_size();
5960 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5961 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5962 if (!brs.is_reserved()) {
5963 warning("CMS bit map allocation failure");
5964 return false;
5965 }
5966 // For now we'll just commit all of the bit map up front.
5967 // Later on we'll try to be more parsimonious with swap.
5968 if (!_virtual_space.initialize(brs, brs.size())) {
5969 warning("CMS bit map backing store failure");
5970 return false;
5971 }
5972 assert(_virtual_space.committed_size() == brs.size(),
5973 "didn't reserve backing store for all of CMS bit map?");
5974 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5975 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5976 _bmWordSize, "inconsistency in bit map sizing");
5977 _bm.set_size(_bmWordSize >> _shifter);
5978
5979 // bm.clear(); // can we rely on getting zero'd memory? verify below
5980 assert(isAllClear(),
5981 "Expected zero'd memory from ReservedSpace constructor");
5982 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5983 "consistency check");
5984 return true;
5985 }
5986
5987 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5988 HeapWord *next_addr, *end_addr, *last_addr;
5989 assert_locked();
5990 assert(covers(mr), "out-of-range error");
5991 // XXX assert that start and end are appropriately aligned
5992 for (next_addr = mr.start(), end_addr = mr.end();
5993 next_addr < end_addr; next_addr = last_addr) {
5994 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5995 last_addr = dirty_region.end();
5996 if (!dirty_region.is_empty()) {
5997 cl->do_MemRegion(dirty_region);
5998 } else {
5999 assert(last_addr == end_addr, "program logic");
6000 return;
6001 }
6002 }
6003 }
6004
6005 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6006 _bm.print_on_error(st, prefix);
6007 }
6008
6009 #ifndef PRODUCT
6010 void CMSBitMap::assert_locked() const {
6011 CMSLockVerifier::assert_locked(lock());
6012 }
6013
6014 bool CMSBitMap::covers(MemRegion mr) const {
6015 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6016 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6017 "size inconsistency");
6018 return (mr.start() >= _bmStartWord) &&
6019 (mr.end() <= endWord());
6020 }
6021
6022 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6023 return (start >= _bmStartWord && (start + size) <= endWord());
6024 }
6025
6026 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6027 // verify that there are no 1 bits in the interval [left, right)
6028 FalseBitMapClosure falseBitMapClosure;
6029 iterate(&falseBitMapClosure, left, right);
6030 }
6031
6032 void CMSBitMap::region_invariant(MemRegion mr)
6033 {
6034 assert_locked();
6035 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6036 assert(!mr.is_empty(), "unexpected empty region");
6037 assert(covers(mr), "mr should be covered by bit map");
6038 // convert address range into offset range
6039 size_t start_ofs = heapWordToOffset(mr.start());
6040 // Make sure that end() is appropriately aligned
6041 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6042 (1 << (_shifter+LogHeapWordSize))),
6043 "Misaligned mr.end()");
6044 size_t end_ofs = heapWordToOffset(mr.end());
6045 assert(end_ofs > start_ofs, "Should mark at least one bit");
6046 }
6047
6048 #endif
6049
6050 bool CMSMarkStack::allocate(size_t size) {
6051 // allocate a stack of the requisite depth
6052 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6053 size * sizeof(oop)));
6054 if (!rs.is_reserved()) {
6055 warning("CMSMarkStack allocation failure");
6056 return false;
6057 }
6058 if (!_virtual_space.initialize(rs, rs.size())) {
6059 warning("CMSMarkStack backing store failure");
6060 return false;
6061 }
6062 assert(_virtual_space.committed_size() == rs.size(),
6063 "didn't reserve backing store for all of CMS stack?");
6064 _base = (oop*)(_virtual_space.low());
6065 _index = 0;
6066 _capacity = size;
6067 NOT_PRODUCT(_max_depth = 0);
6068 return true;
6069 }
6070
6071 // XXX FIX ME !!! In the MT case we come in here holding a
6072 // leaf lock. For printing we need to take a further lock
6073 // which has lower rank. We need to recalibrate the two
6074 // lock-ranks involved in order to be able to print the
6075 // messages below. (Or defer the printing to the caller.
6076 // For now we take the expedient path of just disabling the
6077 // messages for the problematic case.)
6078 void CMSMarkStack::expand() {
6079 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6080 if (_capacity == MarkStackSizeMax) {
6081 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6082 // We print a warning message only once per CMS cycle.
6083 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6084 }
6085 return;
6086 }
6087 // Double capacity if possible
6088 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6089 // Do not give up existing stack until we have managed to
6090 // get the double capacity that we desired.
6091 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6092 new_capacity * sizeof(oop)));
6093 if (rs.is_reserved()) {
6094 // Release the backing store associated with old stack
6095 _virtual_space.release();
6096 // Reinitialize virtual space for new stack
6097 if (!_virtual_space.initialize(rs, rs.size())) {
6098 fatal("Not enough swap for expanded marking stack");
6099 }
6100 _base = (oop*)(_virtual_space.low());
6101 _index = 0;
6102 _capacity = new_capacity;
6103 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6104 // Failed to double capacity, continue;
6105 // we print a detail message only once per CMS cycle.
6106 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6107 SIZE_FORMAT"K",
6108 _capacity / K, new_capacity / K);
6109 }
6110 }
6111
6112
6113 // Closures
6114 // XXX: there seems to be a lot of code duplication here;
6115 // should refactor and consolidate common code.
6116
6117 // This closure is used to mark refs into the CMS generation in
6118 // the CMS bit map. Called at the first checkpoint. This closure
6119 // assumes that we do not need to re-mark dirty cards; if the CMS
6120 // generation on which this is used is not an oldest
6121 // generation then this will lose younger_gen cards!
6122
6123 MarkRefsIntoClosure::MarkRefsIntoClosure(
6124 MemRegion span, CMSBitMap* bitMap):
6125 _span(span),
6126 _bitMap(bitMap)
6127 {
6128 assert(_ref_processor == NULL, "deliberately left NULL");
6129 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6130 }
6131
6132 void MarkRefsIntoClosure::do_oop(oop obj) {
6133 // if p points into _span, then mark corresponding bit in _markBitMap
6134 assert(obj->is_oop(), "expected an oop");
6135 HeapWord* addr = (HeapWord*)obj;
6136 if (_span.contains(addr)) {
6137 // this should be made more efficient
6138 _bitMap->mark(addr);
6139 }
6140 }
6141
6142 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6143 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6144
6145 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6146 MemRegion span, CMSBitMap* bitMap):
6147 _span(span),
6148 _bitMap(bitMap)
6149 {
6150 assert(_ref_processor == NULL, "deliberately left NULL");
6151 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6152 }
6153
6154 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6155 // if p points into _span, then mark corresponding bit in _markBitMap
6156 assert(obj->is_oop(), "expected an oop");
6157 HeapWord* addr = (HeapWord*)obj;
6158 if (_span.contains(addr)) {
6159 // this should be made more efficient
6160 _bitMap->par_mark(addr);
6161 }
6162 }
6163
6164 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6165 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6166
6167 // A variant of the above, used for CMS marking verification.
6168 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6169 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6170 _span(span),
6171 _verification_bm(verification_bm),
6172 _cms_bm(cms_bm)
6173 {
6174 assert(_ref_processor == NULL, "deliberately left NULL");
6175 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6176 }
6177
6178 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6179 // if p points into _span, then mark corresponding bit in _markBitMap
6180 assert(obj->is_oop(), "expected an oop");
6181 HeapWord* addr = (HeapWord*)obj;
6182 if (_span.contains(addr)) {
6183 _verification_bm->mark(addr);
6184 if (!_cms_bm->isMarked(addr)) {
6185 oop(addr)->print();
6186 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6187 fatal("... aborting");
6188 }
6189 }
6190 }
6191
6192 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6193 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6194
6195 //////////////////////////////////////////////////
6196 // MarkRefsIntoAndScanClosure
6197 //////////////////////////////////////////////////
6198
6199 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6200 ReferenceProcessor* rp,
6201 CMSBitMap* bit_map,
6202 CMSBitMap* mod_union_table,
6203 CMSMarkStack* mark_stack,
6204 CMSCollector* collector,
6205 bool should_yield,
6206 bool concurrent_precleaning):
6207 _collector(collector),
6208 _span(span),
6209 _bit_map(bit_map),
6210 _mark_stack(mark_stack),
6211 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6212 mark_stack, concurrent_precleaning),
6213 _yield(should_yield),
6214 _concurrent_precleaning(concurrent_precleaning),
6215 _freelistLock(NULL)
6216 {
6217 _ref_processor = rp;
6218 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6219 }
6220
6221 // This closure is used to mark refs into the CMS generation at the
6222 // second (final) checkpoint, and to scan and transitively follow
6223 // the unmarked oops. It is also used during the concurrent precleaning
6224 // phase while scanning objects on dirty cards in the CMS generation.
6225 // The marks are made in the marking bit map and the marking stack is
6226 // used for keeping the (newly) grey objects during the scan.
6227 // The parallel version (Par_...) appears further below.
6228 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6229 if (obj != NULL) {
6230 assert(obj->is_oop(), "expected an oop");
6231 HeapWord* addr = (HeapWord*)obj;
6232 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6233 assert(_collector->overflow_list_is_empty(),
6234 "overflow list should be empty");
6235 if (_span.contains(addr) &&
6236 !_bit_map->isMarked(addr)) {
6237 // mark bit map (object is now grey)
6238 _bit_map->mark(addr);
6239 // push on marking stack (stack should be empty), and drain the
6240 // stack by applying this closure to the oops in the oops popped
6241 // from the stack (i.e. blacken the grey objects)
6242 bool res = _mark_stack->push(obj);
6243 assert(res, "Should have space to push on empty stack");
6244 do {
6245 oop new_oop = _mark_stack->pop();
6246 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6247 assert(_bit_map->isMarked((HeapWord*)new_oop),
6248 "only grey objects on this stack");
6249 // iterate over the oops in this oop, marking and pushing
6250 // the ones in CMS heap (i.e. in _span).
6251 new_oop->oop_iterate(&_pushAndMarkClosure);
6252 // check if it's time to yield
6253 do_yield_check();
6254 } while (!_mark_stack->isEmpty() ||
6255 (!_concurrent_precleaning && take_from_overflow_list()));
6256 // if marking stack is empty, and we are not doing this
6257 // during precleaning, then check the overflow list
6258 }
6259 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6260 assert(_collector->overflow_list_is_empty(),
6261 "overflow list was drained above");
6262 // We could restore evacuated mark words, if any, used for
6263 // overflow list links here because the overflow list is
6264 // provably empty here. That would reduce the maximum
6265 // size requirements for preserved_{oop,mark}_stack.
6266 // But we'll just postpone it until we are all done
6267 // so we can just stream through.
6268 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6269 _collector->restore_preserved_marks_if_any();
6270 assert(_collector->no_preserved_marks(), "No preserved marks");
6271 }
6272 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6273 "All preserved marks should have been restored above");
6274 }
6275 }
6276
6277 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6278 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6279
6280 void MarkRefsIntoAndScanClosure::do_yield_work() {
6281 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6282 "CMS thread should hold CMS token");
6283 assert_lock_strong(_freelistLock);
6284 assert_lock_strong(_bit_map->lock());
6285 // relinquish the free_list_lock and bitMaplock()
6286 _bit_map->lock()->unlock();
6287 _freelistLock->unlock();
6288 ConcurrentMarkSweepThread::desynchronize(true);
6289 _collector->stopTimer();
6290 if (PrintCMSStatistics != 0) {
6291 _collector->incrementYields();
6292 }
6293
6294 // See the comment in coordinator_yield()
6295 for (unsigned i = 0;
6296 i < CMSYieldSleepCount &&
6297 ConcurrentMarkSweepThread::should_yield() &&
6298 !CMSCollector::foregroundGCIsActive();
6299 ++i) {
6300 os::sleep(Thread::current(), 1, false);
6301 }
6302
6303 ConcurrentMarkSweepThread::synchronize(true);
6304 _freelistLock->lock_without_safepoint_check();
6305 _bit_map->lock()->lock_without_safepoint_check();
6306 _collector->startTimer();
6307 }
6308
6309 ///////////////////////////////////////////////////////////
6310 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6311 // MarkRefsIntoAndScanClosure
6312 ///////////////////////////////////////////////////////////
6313 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6314 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6315 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6316 _span(span),
6317 _bit_map(bit_map),
6318 _work_queue(work_queue),
6319 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6320 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6321 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6322 {
6323 _ref_processor = rp;
6324 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6325 }
6326
6327 // This closure is used to mark refs into the CMS generation at the
6328 // second (final) checkpoint, and to scan and transitively follow
6329 // the unmarked oops. The marks are made in the marking bit map and
6330 // the work_queue is used for keeping the (newly) grey objects during
6331 // the scan phase whence they are also available for stealing by parallel
6332 // threads. Since the marking bit map is shared, updates are
6333 // synchronized (via CAS).
6334 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6335 if (obj != NULL) {
6336 // Ignore mark word because this could be an already marked oop
6337 // that may be chained at the end of the overflow list.
6338 assert(obj->is_oop(true), "expected an oop");
6339 HeapWord* addr = (HeapWord*)obj;
6340 if (_span.contains(addr) &&
6341 !_bit_map->isMarked(addr)) {
6342 // mark bit map (object will become grey):
6343 // It is possible for several threads to be
6344 // trying to "claim" this object concurrently;
6345 // the unique thread that succeeds in marking the
6346 // object first will do the subsequent push on
6347 // to the work queue (or overflow list).
6348 if (_bit_map->par_mark(addr)) {
6349 // push on work_queue (which may not be empty), and trim the
6350 // queue to an appropriate length by applying this closure to
6351 // the oops in the oops popped from the stack (i.e. blacken the
6352 // grey objects)
6353 bool res = _work_queue->push(obj);
6354 assert(res, "Low water mark should be less than capacity?");
6355 trim_queue(_low_water_mark);
6356 } // Else, another thread claimed the object
6357 }
6358 }
6359 }
6360
6361 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6362 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6363
6364 // This closure is used to rescan the marked objects on the dirty cards
6365 // in the mod union table and the card table proper.
6366 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6367 oop p, MemRegion mr) {
6368
6369 size_t size = 0;
6370 HeapWord* addr = (HeapWord*)p;
6371 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6372 assert(_span.contains(addr), "we are scanning the CMS generation");
6373 // check if it's time to yield
6374 if (do_yield_check()) {
6375 // We yielded for some foreground stop-world work,
6376 // and we have been asked to abort this ongoing preclean cycle.
6377 return 0;
6378 }
6379 if (_bitMap->isMarked(addr)) {
6380 // it's marked; is it potentially uninitialized?
6381 if (p->klass_or_null() != NULL) {
6382 // an initialized object; ignore mark word in verification below
6383 // since we are running concurrent with mutators
6384 assert(p->is_oop(true), "should be an oop");
6385 if (p->is_objArray()) {
6386 // objArrays are precisely marked; restrict scanning
6387 // to dirty cards only.
6388 size = CompactibleFreeListSpace::adjustObjectSize(
6389 p->oop_iterate(_scanningClosure, mr));
6390 } else {
6391 // A non-array may have been imprecisely marked; we need
6392 // to scan object in its entirety.
6393 size = CompactibleFreeListSpace::adjustObjectSize(
6394 p->oop_iterate(_scanningClosure));
6395 }
6396 #ifdef ASSERT
6397 size_t direct_size =
6398 CompactibleFreeListSpace::adjustObjectSize(p->size());
6399 assert(size == direct_size, "Inconsistency in size");
6400 assert(size >= 3, "Necessary for Printezis marks to work");
6401 if (!_bitMap->isMarked(addr+1)) {
6402 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6403 } else {
6404 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6405 assert(_bitMap->isMarked(addr+size-1),
6406 "inconsistent Printezis mark");
6407 }
6408 #endif // ASSERT
6409 } else {
6410 // An uninitialized object.
6411 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6412 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6413 size = pointer_delta(nextOneAddr + 1, addr);
6414 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6415 "alignment problem");
6416 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6417 // will dirty the card when the klass pointer is installed in the
6418 // object (signaling the completion of initialization).
6419 }
6420 } else {
6421 // Either a not yet marked object or an uninitialized object
6422 if (p->klass_or_null() == NULL) {
6423 // An uninitialized object, skip to the next card, since
6424 // we may not be able to read its P-bits yet.
6425 assert(size == 0, "Initial value");
6426 } else {
6427 // An object not (yet) reached by marking: we merely need to
6428 // compute its size so as to go look at the next block.
6429 assert(p->is_oop(true), "should be an oop");
6430 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6431 }
6432 }
6433 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6434 return size;
6435 }
6436
6437 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6438 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6439 "CMS thread should hold CMS token");
6440 assert_lock_strong(_freelistLock);
6441 assert_lock_strong(_bitMap->lock());
6442 // relinquish the free_list_lock and bitMaplock()
6443 _bitMap->lock()->unlock();
6444 _freelistLock->unlock();
6445 ConcurrentMarkSweepThread::desynchronize(true);
6446 _collector->stopTimer();
6447 if (PrintCMSStatistics != 0) {
6448 _collector->incrementYields();
6449 }
6450
6451 // See the comment in coordinator_yield()
6452 for (unsigned i = 0; i < CMSYieldSleepCount &&
6453 ConcurrentMarkSweepThread::should_yield() &&
6454 !CMSCollector::foregroundGCIsActive(); ++i) {
6455 os::sleep(Thread::current(), 1, false);
6456 }
6457
6458 ConcurrentMarkSweepThread::synchronize(true);
6459 _freelistLock->lock_without_safepoint_check();
6460 _bitMap->lock()->lock_without_safepoint_check();
6461 _collector->startTimer();
6462 }
6463
6464
6465 //////////////////////////////////////////////////////////////////
6466 // SurvivorSpacePrecleanClosure
6467 //////////////////////////////////////////////////////////////////
6468 // This (single-threaded) closure is used to preclean the oops in
6469 // the survivor spaces.
6470 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6471
6472 HeapWord* addr = (HeapWord*)p;
6473 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6474 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6475 assert(p->klass_or_null() != NULL, "object should be initialized");
6476 // an initialized object; ignore mark word in verification below
6477 // since we are running concurrent with mutators
6478 assert(p->is_oop(true), "should be an oop");
6479 // Note that we do not yield while we iterate over
6480 // the interior oops of p, pushing the relevant ones
6481 // on our marking stack.
6482 size_t size = p->oop_iterate(_scanning_closure);
6483 do_yield_check();
6484 // Observe that below, we do not abandon the preclean
6485 // phase as soon as we should; rather we empty the
6486 // marking stack before returning. This is to satisfy
6487 // some existing assertions. In general, it may be a
6488 // good idea to abort immediately and complete the marking
6489 // from the grey objects at a later time.
6490 while (!_mark_stack->isEmpty()) {
6491 oop new_oop = _mark_stack->pop();
6492 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6493 assert(_bit_map->isMarked((HeapWord*)new_oop),
6494 "only grey objects on this stack");
6495 // iterate over the oops in this oop, marking and pushing
6496 // the ones in CMS heap (i.e. in _span).
6497 new_oop->oop_iterate(_scanning_closure);
6498 // check if it's time to yield
6499 do_yield_check();
6500 }
6501 unsigned int after_count =
6502 GenCollectedHeap::heap()->total_collections();
6503 bool abort = (_before_count != after_count) ||
6504 _collector->should_abort_preclean();
6505 return abort ? 0 : size;
6506 }
6507
6508 void SurvivorSpacePrecleanClosure::do_yield_work() {
6509 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6510 "CMS thread should hold CMS token");
6511 assert_lock_strong(_bit_map->lock());
6512 // Relinquish the bit map lock
6513 _bit_map->lock()->unlock();
6514 ConcurrentMarkSweepThread::desynchronize(true);
6515 _collector->stopTimer();
6516 if (PrintCMSStatistics != 0) {
6517 _collector->incrementYields();
6518 }
6519
6520 // See the comment in coordinator_yield()
6521 for (unsigned i = 0; i < CMSYieldSleepCount &&
6522 ConcurrentMarkSweepThread::should_yield() &&
6523 !CMSCollector::foregroundGCIsActive(); ++i) {
6524 os::sleep(Thread::current(), 1, false);
6525 }
6526
6527 ConcurrentMarkSweepThread::synchronize(true);
6528 _bit_map->lock()->lock_without_safepoint_check();
6529 _collector->startTimer();
6530 }
6531
6532 // This closure is used to rescan the marked objects on the dirty cards
6533 // in the mod union table and the card table proper. In the parallel
6534 // case, although the bitMap is shared, we do a single read so the
6535 // isMarked() query is "safe".
6536 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6537 // Ignore mark word because we are running concurrent with mutators
6538 assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
6539 HeapWord* addr = (HeapWord*)p;
6540 assert(_span.contains(addr), "we are scanning the CMS generation");
6541 bool is_obj_array = false;
6542 #ifdef ASSERT
6543 if (!_parallel) {
6544 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6545 assert(_collector->overflow_list_is_empty(),
6546 "overflow list should be empty");
6547
6548 }
6549 #endif // ASSERT
6550 if (_bit_map->isMarked(addr)) {
6551 // Obj arrays are precisely marked, non-arrays are not;
6552 // so we scan objArrays precisely and non-arrays in their
6553 // entirety.
6554 if (p->is_objArray()) {
6555 is_obj_array = true;
6556 if (_parallel) {
6557 p->oop_iterate(_par_scan_closure, mr);
6558 } else {
6559 p->oop_iterate(_scan_closure, mr);
6560 }
6561 } else {
6562 if (_parallel) {
6563 p->oop_iterate(_par_scan_closure);
6564 } else {
6565 p->oop_iterate(_scan_closure);
6566 }
6567 }
6568 }
6569 #ifdef ASSERT
6570 if (!_parallel) {
6571 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6572 assert(_collector->overflow_list_is_empty(),
6573 "overflow list should be empty");
6574
6575 }
6576 #endif // ASSERT
6577 return is_obj_array;
6578 }
6579
6580 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6581 MemRegion span,
6582 CMSBitMap* bitMap, CMSMarkStack* markStack,
6583 bool should_yield, bool verifying):
6584 _collector(collector),
6585 _span(span),
6586 _bitMap(bitMap),
6587 _mut(&collector->_modUnionTable),
6588 _markStack(markStack),
6589 _yield(should_yield),
6590 _skipBits(0)
6591 {
6592 assert(_markStack->isEmpty(), "stack should be empty");
6593 _finger = _bitMap->startWord();
6594 _threshold = _finger;
6595 assert(_collector->_restart_addr == NULL, "Sanity check");
6596 assert(_span.contains(_finger), "Out of bounds _finger?");
6597 DEBUG_ONLY(_verifying = verifying;)
6598 }
6599
6600 void MarkFromRootsClosure::reset(HeapWord* addr) {
6601 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6602 assert(_span.contains(addr), "Out of bounds _finger?");
6603 _finger = addr;
6604 _threshold = (HeapWord*)round_to(
6605 (intptr_t)_finger, CardTableModRefBS::card_size);
6606 }
6607
6608 // Should revisit to see if this should be restructured for
6609 // greater efficiency.
6610 bool MarkFromRootsClosure::do_bit(size_t offset) {
6611 if (_skipBits > 0) {
6612 _skipBits--;
6613 return true;
6614 }
6615 // convert offset into a HeapWord*
6616 HeapWord* addr = _bitMap->startWord() + offset;
6617 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6618 "address out of range");
6619 assert(_bitMap->isMarked(addr), "tautology");
6620 if (_bitMap->isMarked(addr+1)) {
6621 // this is an allocated but not yet initialized object
6622 assert(_skipBits == 0, "tautology");
6623 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6624 oop p = oop(addr);
6625 if (p->klass_or_null() == NULL) {
6626 DEBUG_ONLY(if (!_verifying) {)
6627 // We re-dirty the cards on which this object lies and increase
6628 // the _threshold so that we'll come back to scan this object
6629 // during the preclean or remark phase. (CMSCleanOnEnter)
6630 if (CMSCleanOnEnter) {
6631 size_t sz = _collector->block_size_using_printezis_bits(addr);
6632 HeapWord* end_card_addr = (HeapWord*)round_to(
6633 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6634 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6635 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6636 // Bump _threshold to end_card_addr; note that
6637 // _threshold cannot possibly exceed end_card_addr, anyhow.
6638 // This prevents future clearing of the card as the scan proceeds
6639 // to the right.
6640 assert(_threshold <= end_card_addr,
6641 "Because we are just scanning into this object");
6642 if (_threshold < end_card_addr) {
6643 _threshold = end_card_addr;
6644 }
6645 if (p->klass_or_null() != NULL) {
6646 // Redirty the range of cards...
6647 _mut->mark_range(redirty_range);
6648 } // ...else the setting of klass will dirty the card anyway.
6649 }
6650 DEBUG_ONLY(})
6651 return true;
6652 }
6653 }
6654 scanOopsInOop(addr);
6655 return true;
6656 }
6657
6658 // We take a break if we've been at this for a while,
6659 // so as to avoid monopolizing the locks involved.
6660 void MarkFromRootsClosure::do_yield_work() {
6661 // First give up the locks, then yield, then re-lock
6662 // We should probably use a constructor/destructor idiom to
6663 // do this unlock/lock or modify the MutexUnlocker class to
6664 // serve our purpose. XXX
6665 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6666 "CMS thread should hold CMS token");
6667 assert_lock_strong(_bitMap->lock());
6668 _bitMap->lock()->unlock();
6669 ConcurrentMarkSweepThread::desynchronize(true);
6670 _collector->stopTimer();
6671 if (PrintCMSStatistics != 0) {
6672 _collector->incrementYields();
6673 }
6674
6675 // See the comment in coordinator_yield()
6676 for (unsigned i = 0; i < CMSYieldSleepCount &&
6677 ConcurrentMarkSweepThread::should_yield() &&
6678 !CMSCollector::foregroundGCIsActive(); ++i) {
6679 os::sleep(Thread::current(), 1, false);
6680 }
6681
6682 ConcurrentMarkSweepThread::synchronize(true);
6683 _bitMap->lock()->lock_without_safepoint_check();
6684 _collector->startTimer();
6685 }
6686
6687 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6688 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6689 assert(_markStack->isEmpty(),
6690 "should drain stack to limit stack usage");
6691 // convert ptr to an oop preparatory to scanning
6692 oop obj = oop(ptr);
6693 // Ignore mark word in verification below, since we
6694 // may be running concurrent with mutators.
6695 assert(obj->is_oop(true), "should be an oop");
6696 assert(_finger <= ptr, "_finger runneth ahead");
6697 // advance the finger to right end of this object
6698 _finger = ptr + obj->size();
6699 assert(_finger > ptr, "we just incremented it above");
6700 // On large heaps, it may take us some time to get through
6701 // the marking phase. During
6702 // this time it's possible that a lot of mutations have
6703 // accumulated in the card table and the mod union table --
6704 // these mutation records are redundant until we have
6705 // actually traced into the corresponding card.
6706 // Here, we check whether advancing the finger would make
6707 // us cross into a new card, and if so clear corresponding
6708 // cards in the MUT (preclean them in the card-table in the
6709 // future).
6710
6711 DEBUG_ONLY(if (!_verifying) {)
6712 // The clean-on-enter optimization is disabled by default,
6713 // until we fix 6178663.
6714 if (CMSCleanOnEnter && (_finger > _threshold)) {
6715 // [_threshold, _finger) represents the interval
6716 // of cards to be cleared in MUT (or precleaned in card table).
6717 // The set of cards to be cleared is all those that overlap
6718 // with the interval [_threshold, _finger); note that
6719 // _threshold is always kept card-aligned but _finger isn't
6720 // always card-aligned.
6721 HeapWord* old_threshold = _threshold;
6722 assert(old_threshold == (HeapWord*)round_to(
6723 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6724 "_threshold should always be card-aligned");
6725 _threshold = (HeapWord*)round_to(
6726 (intptr_t)_finger, CardTableModRefBS::card_size);
6727 MemRegion mr(old_threshold, _threshold);
6728 assert(!mr.is_empty(), "Control point invariant");
6729 assert(_span.contains(mr), "Should clear within span");
6730 _mut->clear_range(mr);
6731 }
6732 DEBUG_ONLY(})
6733 // Note: the finger doesn't advance while we drain
6734 // the stack below.
6735 PushOrMarkClosure pushOrMarkClosure(_collector,
6736 _span, _bitMap, _markStack,
6737 _finger, this);
6738 bool res = _markStack->push(obj);
6739 assert(res, "Empty non-zero size stack should have space for single push");
6740 while (!_markStack->isEmpty()) {
6741 oop new_oop = _markStack->pop();
6742 // Skip verifying header mark word below because we are
6743 // running concurrent with mutators.
6744 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6745 // now scan this oop's oops
6746 new_oop->oop_iterate(&pushOrMarkClosure);
6747 do_yield_check();
6748 }
6749 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6750 }
6751
6752 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6753 CMSCollector* collector, MemRegion span,
6754 CMSBitMap* bit_map,
6755 OopTaskQueue* work_queue,
6756 CMSMarkStack* overflow_stack):
6757 _collector(collector),
6758 _whole_span(collector->_span),
6759 _span(span),
6760 _bit_map(bit_map),
6761 _mut(&collector->_modUnionTable),
6762 _work_queue(work_queue),
6763 _overflow_stack(overflow_stack),
6764 _skip_bits(0),
6765 _task(task)
6766 {
6767 assert(_work_queue->size() == 0, "work_queue should be empty");
6768 _finger = span.start();
6769 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6770 assert(_span.contains(_finger), "Out of bounds _finger?");
6771 }
6772
6773 // Should revisit to see if this should be restructured for
6774 // greater efficiency.
6775 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6776 if (_skip_bits > 0) {
6777 _skip_bits--;
6778 return true;
6779 }
6780 // convert offset into a HeapWord*
6781 HeapWord* addr = _bit_map->startWord() + offset;
6782 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6783 "address out of range");
6784 assert(_bit_map->isMarked(addr), "tautology");
6785 if (_bit_map->isMarked(addr+1)) {
6786 // this is an allocated object that might not yet be initialized
6787 assert(_skip_bits == 0, "tautology");
6788 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6789 oop p = oop(addr);
6790 if (p->klass_or_null() == NULL) {
6791 // in the case of Clean-on-Enter optimization, redirty card
6792 // and avoid clearing card by increasing the threshold.
6793 return true;
6794 }
6795 }
6796 scan_oops_in_oop(addr);
6797 return true;
6798 }
6799
6800 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6801 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6802 // Should we assert that our work queue is empty or
6803 // below some drain limit?
6804 assert(_work_queue->size() == 0,
6805 "should drain stack to limit stack usage");
6806 // convert ptr to an oop preparatory to scanning
6807 oop obj = oop(ptr);
6808 // Ignore mark word in verification below, since we
6809 // may be running concurrent with mutators.
6810 assert(obj->is_oop(true), "should be an oop");
6811 assert(_finger <= ptr, "_finger runneth ahead");
6812 // advance the finger to right end of this object
6813 _finger = ptr + obj->size();
6814 assert(_finger > ptr, "we just incremented it above");
6815 // On large heaps, it may take us some time to get through
6816 // the marking phase. During
6817 // this time it's possible that a lot of mutations have
6818 // accumulated in the card table and the mod union table --
6819 // these mutation records are redundant until we have
6820 // actually traced into the corresponding card.
6821 // Here, we check whether advancing the finger would make
6822 // us cross into a new card, and if so clear corresponding
6823 // cards in the MUT (preclean them in the card-table in the
6824 // future).
6825
6826 // The clean-on-enter optimization is disabled by default,
6827 // until we fix 6178663.
6828 if (CMSCleanOnEnter && (_finger > _threshold)) {
6829 // [_threshold, _finger) represents the interval
6830 // of cards to be cleared in MUT (or precleaned in card table).
6831 // The set of cards to be cleared is all those that overlap
6832 // with the interval [_threshold, _finger); note that
6833 // _threshold is always kept card-aligned but _finger isn't
6834 // always card-aligned.
6835 HeapWord* old_threshold = _threshold;
6836 assert(old_threshold == (HeapWord*)round_to(
6837 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6838 "_threshold should always be card-aligned");
6839 _threshold = (HeapWord*)round_to(
6840 (intptr_t)_finger, CardTableModRefBS::card_size);
6841 MemRegion mr(old_threshold, _threshold);
6842 assert(!mr.is_empty(), "Control point invariant");
6843 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6844 _mut->clear_range(mr);
6845 }
6846
6847 // Note: the local finger doesn't advance while we drain
6848 // the stack below, but the global finger sure can and will.
6849 HeapWord** gfa = _task->global_finger_addr();
6850 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6851 _span, _bit_map,
6852 _work_queue,
6853 _overflow_stack,
6854 _finger,
6855 gfa, this);
6856 bool res = _work_queue->push(obj); // overflow could occur here
6857 assert(res, "Will hold once we use workqueues");
6858 while (true) {
6859 oop new_oop;
6860 if (!_work_queue->pop_local(new_oop)) {
6861 // We emptied our work_queue; check if there's stuff that can
6862 // be gotten from the overflow stack.
6863 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6864 _overflow_stack, _work_queue)) {
6865 do_yield_check();
6866 continue;
6867 } else { // done
6868 break;
6869 }
6870 }
6871 // Skip verifying header mark word below because we are
6872 // running concurrent with mutators.
6873 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6874 // now scan this oop's oops
6875 new_oop->oop_iterate(&pushOrMarkClosure);
6876 do_yield_check();
6877 }
6878 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6879 }
6880
6881 // Yield in response to a request from VM Thread or
6882 // from mutators.
6883 void Par_MarkFromRootsClosure::do_yield_work() {
6884 assert(_task != NULL, "sanity");
6885 _task->yield();
6886 }
6887
6888 // A variant of the above used for verifying CMS marking work.
6889 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6890 MemRegion span,
6891 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6892 CMSMarkStack* mark_stack):
6893 _collector(collector),
6894 _span(span),
6895 _verification_bm(verification_bm),
6896 _cms_bm(cms_bm),
6897 _mark_stack(mark_stack),
6898 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6899 mark_stack)
6900 {
6901 assert(_mark_stack->isEmpty(), "stack should be empty");
6902 _finger = _verification_bm->startWord();
6903 assert(_collector->_restart_addr == NULL, "Sanity check");
6904 assert(_span.contains(_finger), "Out of bounds _finger?");
6905 }
6906
6907 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6908 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6909 assert(_span.contains(addr), "Out of bounds _finger?");
6910 _finger = addr;
6911 }
6912
6913 // Should revisit to see if this should be restructured for
6914 // greater efficiency.
6915 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6916 // convert offset into a HeapWord*
6917 HeapWord* addr = _verification_bm->startWord() + offset;
6918 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6919 "address out of range");
6920 assert(_verification_bm->isMarked(addr), "tautology");
6921 assert(_cms_bm->isMarked(addr), "tautology");
6922
6923 assert(_mark_stack->isEmpty(),
6924 "should drain stack to limit stack usage");
6925 // convert addr to an oop preparatory to scanning
6926 oop obj = oop(addr);
6927 assert(obj->is_oop(), "should be an oop");
6928 assert(_finger <= addr, "_finger runneth ahead");
6929 // advance the finger to right end of this object
6930 _finger = addr + obj->size();
6931 assert(_finger > addr, "we just incremented it above");
6932 // Note: the finger doesn't advance while we drain
6933 // the stack below.
6934 bool res = _mark_stack->push(obj);
6935 assert(res, "Empty non-zero size stack should have space for single push");
6936 while (!_mark_stack->isEmpty()) {
6937 oop new_oop = _mark_stack->pop();
6938 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6939 // now scan this oop's oops
6940 new_oop->oop_iterate(&_pam_verify_closure);
6941 }
6942 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6943 return true;
6944 }
6945
6946 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6947 CMSCollector* collector, MemRegion span,
6948 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6949 CMSMarkStack* mark_stack):
6950 MetadataAwareOopClosure(collector->ref_processor()),
6951 _collector(collector),
6952 _span(span),
6953 _verification_bm(verification_bm),
6954 _cms_bm(cms_bm),
6955 _mark_stack(mark_stack)
6956 { }
6957
6958 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6959 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6960
6961 // Upon stack overflow, we discard (part of) the stack,
6962 // remembering the least address amongst those discarded
6963 // in CMSCollector's _restart_address.
6964 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6965 // Remember the least grey address discarded
6966 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6967 _collector->lower_restart_addr(ra);
6968 _mark_stack->reset(); // discard stack contents
6969 _mark_stack->expand(); // expand the stack if possible
6970 }
6971
6972 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6973 assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
6974 HeapWord* addr = (HeapWord*)obj;
6975 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6976 // Oop lies in _span and isn't yet grey or black
6977 _verification_bm->mark(addr); // now grey
6978 if (!_cms_bm->isMarked(addr)) {
6979 oop(addr)->print();
6980 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
6981 p2i(addr));
6982 fatal("... aborting");
6983 }
6984
6985 if (!_mark_stack->push(obj)) { // stack overflow
6986 if (PrintCMSStatistics != 0) {
6987 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6988 SIZE_FORMAT, _mark_stack->capacity());
6989 }
6990 assert(_mark_stack->isFull(), "Else push should have succeeded");
6991 handle_stack_overflow(addr);
6992 }
6993 // anything including and to the right of _finger
6994 // will be scanned as we iterate over the remainder of the
6995 // bit map
6996 }
6997 }
6998
6999 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7000 MemRegion span,
7001 CMSBitMap* bitMap, CMSMarkStack* markStack,
7002 HeapWord* finger, MarkFromRootsClosure* parent) :
7003 MetadataAwareOopClosure(collector->ref_processor()),
7004 _collector(collector),
7005 _span(span),
7006 _bitMap(bitMap),
7007 _markStack(markStack),
7008 _finger(finger),
7009 _parent(parent)
7010 { }
7011
7012 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7013 MemRegion span,
7014 CMSBitMap* bit_map,
7015 OopTaskQueue* work_queue,
7016 CMSMarkStack* overflow_stack,
7017 HeapWord* finger,
7018 HeapWord** global_finger_addr,
7019 Par_MarkFromRootsClosure* parent) :
7020 MetadataAwareOopClosure(collector->ref_processor()),
7021 _collector(collector),
7022 _whole_span(collector->_span),
7023 _span(span),
7024 _bit_map(bit_map),
7025 _work_queue(work_queue),
7026 _overflow_stack(overflow_stack),
7027 _finger(finger),
7028 _global_finger_addr(global_finger_addr),
7029 _parent(parent)
7030 { }
7031
7032 // Assumes thread-safe access by callers, who are
7033 // responsible for mutual exclusion.
7034 void CMSCollector::lower_restart_addr(HeapWord* low) {
7035 assert(_span.contains(low), "Out of bounds addr");
7036 if (_restart_addr == NULL) {
7037 _restart_addr = low;
7038 } else {
7039 _restart_addr = MIN2(_restart_addr, low);
7040 }
7041 }
7042
7043 // Upon stack overflow, we discard (part of) the stack,
7044 // remembering the least address amongst those discarded
7045 // in CMSCollector's _restart_address.
7046 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7047 // Remember the least grey address discarded
7048 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7049 _collector->lower_restart_addr(ra);
7050 _markStack->reset(); // discard stack contents
7051 _markStack->expand(); // expand the stack if possible
7052 }
7053
7054 // Upon stack overflow, we discard (part of) the stack,
7055 // remembering the least address amongst those discarded
7056 // in CMSCollector's _restart_address.
7057 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7058 // We need to do this under a mutex to prevent other
7059 // workers from interfering with the work done below.
7060 MutexLockerEx ml(_overflow_stack->par_lock(),
7061 Mutex::_no_safepoint_check_flag);
7062 // Remember the least grey address discarded
7063 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7064 _collector->lower_restart_addr(ra);
7065 _overflow_stack->reset(); // discard stack contents
7066 _overflow_stack->expand(); // expand the stack if possible
7067 }
7068
7069 void PushOrMarkClosure::do_oop(oop obj) {
7070 // Ignore mark word because we are running concurrent with mutators.
7071 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7072 HeapWord* addr = (HeapWord*)obj;
7073 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7074 // Oop lies in _span and isn't yet grey or black
7075 _bitMap->mark(addr); // now grey
7076 if (addr < _finger) {
7077 // the bit map iteration has already either passed, or
7078 // sampled, this bit in the bit map; we'll need to
7079 // use the marking stack to scan this oop's oops.
7080 bool simulate_overflow = false;
7081 NOT_PRODUCT(
7082 if (CMSMarkStackOverflowALot &&
7083 _collector->simulate_overflow()) {
7084 // simulate a stack overflow
7085 simulate_overflow = true;
7086 }
7087 )
7088 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7089 if (PrintCMSStatistics != 0) {
7090 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7091 SIZE_FORMAT, _markStack->capacity());
7092 }
7093 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7094 handle_stack_overflow(addr);
7095 }
7096 }
7097 // anything including and to the right of _finger
7098 // will be scanned as we iterate over the remainder of the
7099 // bit map
7100 do_yield_check();
7101 }
7102 }
7103
7104 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7105 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7106
7107 void Par_PushOrMarkClosure::do_oop(oop obj) {
7108 // Ignore mark word because we are running concurrent with mutators.
7109 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7110 HeapWord* addr = (HeapWord*)obj;
7111 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7112 // Oop lies in _span and isn't yet grey or black
7113 // We read the global_finger (volatile read) strictly after marking oop
7114 bool res = _bit_map->par_mark(addr); // now grey
7115 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7116 // Should we push this marked oop on our stack?
7117 // -- if someone else marked it, nothing to do
7118 // -- if target oop is above global finger nothing to do
7119 // -- if target oop is in chunk and above local finger
7120 // then nothing to do
7121 // -- else push on work queue
7122 if ( !res // someone else marked it, they will deal with it
7123 || (addr >= *gfa) // will be scanned in a later task
7124 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7125 return;
7126 }
7127 // the bit map iteration has already either passed, or
7128 // sampled, this bit in the bit map; we'll need to
7129 // use the marking stack to scan this oop's oops.
7130 bool simulate_overflow = false;
7131 NOT_PRODUCT(
7132 if (CMSMarkStackOverflowALot &&
7133 _collector->simulate_overflow()) {
7134 // simulate a stack overflow
7135 simulate_overflow = true;
7136 }
7137 )
7138 if (simulate_overflow ||
7139 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7140 // stack overflow
7141 if (PrintCMSStatistics != 0) {
7142 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7143 SIZE_FORMAT, _overflow_stack->capacity());
7144 }
7145 // We cannot assert that the overflow stack is full because
7146 // it may have been emptied since.
7147 assert(simulate_overflow ||
7148 _work_queue->size() == _work_queue->max_elems(),
7149 "Else push should have succeeded");
7150 handle_stack_overflow(addr);
7151 }
7152 do_yield_check();
7153 }
7154 }
7155
7156 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7157 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7158
7159 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7160 MemRegion span,
7161 ReferenceProcessor* rp,
7162 CMSBitMap* bit_map,
7163 CMSBitMap* mod_union_table,
7164 CMSMarkStack* mark_stack,
7165 bool concurrent_precleaning):
7166 MetadataAwareOopClosure(rp),
7167 _collector(collector),
7168 _span(span),
7169 _bit_map(bit_map),
7170 _mod_union_table(mod_union_table),
7171 _mark_stack(mark_stack),
7172 _concurrent_precleaning(concurrent_precleaning)
7173 {
7174 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7175 }
7176
7177 // Grey object rescan during pre-cleaning and second checkpoint phases --
7178 // the non-parallel version (the parallel version appears further below.)
7179 void PushAndMarkClosure::do_oop(oop obj) {
7180 // Ignore mark word verification. If during concurrent precleaning,
7181 // the object monitor may be locked. If during the checkpoint
7182 // phases, the object may already have been reached by a different
7183 // path and may be at the end of the global overflow list (so
7184 // the mark word may be NULL).
7185 assert(obj->is_oop_or_null(true /* ignore mark word */),
7186 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7187 HeapWord* addr = (HeapWord*)obj;
7188 // Check if oop points into the CMS generation
7189 // and is not marked
7190 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7191 // a white object ...
7192 _bit_map->mark(addr); // ... now grey
7193 // push on the marking stack (grey set)
7194 bool simulate_overflow = false;
7195 NOT_PRODUCT(
7196 if (CMSMarkStackOverflowALot &&
7197 _collector->simulate_overflow()) {
7198 // simulate a stack overflow
7199 simulate_overflow = true;
7200 }
7201 )
7202 if (simulate_overflow || !_mark_stack->push(obj)) {
7203 if (_concurrent_precleaning) {
7204 // During precleaning we can just dirty the appropriate card(s)
7205 // in the mod union table, thus ensuring that the object remains
7206 // in the grey set and continue. In the case of object arrays
7207 // we need to dirty all of the cards that the object spans,
7208 // since the rescan of object arrays will be limited to the
7209 // dirty cards.
7210 // Note that no one can be interfering with us in this action
7211 // of dirtying the mod union table, so no locking or atomics
7212 // are required.
7213 if (obj->is_objArray()) {
7214 size_t sz = obj->size();
7215 HeapWord* end_card_addr = (HeapWord*)round_to(
7216 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7217 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7218 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7219 _mod_union_table->mark_range(redirty_range);
7220 } else {
7221 _mod_union_table->mark(addr);
7222 }
7223 _collector->_ser_pmc_preclean_ovflw++;
7224 } else {
7225 // During the remark phase, we need to remember this oop
7226 // in the overflow list.
7227 _collector->push_on_overflow_list(obj);
7228 _collector->_ser_pmc_remark_ovflw++;
7229 }
7230 }
7231 }
7232 }
7233
7234 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7235 MemRegion span,
7236 ReferenceProcessor* rp,
7237 CMSBitMap* bit_map,
7238 OopTaskQueue* work_queue):
7239 MetadataAwareOopClosure(rp),
7240 _collector(collector),
7241 _span(span),
7242 _bit_map(bit_map),
7243 _work_queue(work_queue)
7244 {
7245 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7246 }
7247
7248 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7249 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7250
7251 // Grey object rescan during second checkpoint phase --
7252 // the parallel version.
7253 void Par_PushAndMarkClosure::do_oop(oop obj) {
7254 // In the assert below, we ignore the mark word because
7255 // this oop may point to an already visited object that is
7256 // on the overflow stack (in which case the mark word has
7257 // been hijacked for chaining into the overflow stack --
7258 // if this is the last object in the overflow stack then
7259 // its mark word will be NULL). Because this object may
7260 // have been subsequently popped off the global overflow
7261 // stack, and the mark word possibly restored to the prototypical
7262 // value, by the time we get to examined this failing assert in
7263 // the debugger, is_oop_or_null(false) may subsequently start
7264 // to hold.
7265 assert(obj->is_oop_or_null(true),
7266 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7267 HeapWord* addr = (HeapWord*)obj;
7268 // Check if oop points into the CMS generation
7269 // and is not marked
7270 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7271 // a white object ...
7272 // If we manage to "claim" the object, by being the
7273 // first thread to mark it, then we push it on our
7274 // marking stack
7275 if (_bit_map->par_mark(addr)) { // ... now grey
7276 // push on work queue (grey set)
7277 bool simulate_overflow = false;
7278 NOT_PRODUCT(
7279 if (CMSMarkStackOverflowALot &&
7280 _collector->par_simulate_overflow()) {
7281 // simulate a stack overflow
7282 simulate_overflow = true;
7283 }
7284 )
7285 if (simulate_overflow || !_work_queue->push(obj)) {
7286 _collector->par_push_on_overflow_list(obj);
7287 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7288 }
7289 } // Else, some other thread got there first
7290 }
7291 }
7292
7293 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7294 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7295
7296 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7297 Mutex* bml = _collector->bitMapLock();
7298 assert_lock_strong(bml);
7299 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7300 "CMS thread should hold CMS token");
7301
7302 bml->unlock();
7303 ConcurrentMarkSweepThread::desynchronize(true);
7304
7305 _collector->stopTimer();
7306 if (PrintCMSStatistics != 0) {
7307 _collector->incrementYields();
7308 }
7309
7310 // See the comment in coordinator_yield()
7311 for (unsigned i = 0; i < CMSYieldSleepCount &&
7312 ConcurrentMarkSweepThread::should_yield() &&
7313 !CMSCollector::foregroundGCIsActive(); ++i) {
7314 os::sleep(Thread::current(), 1, false);
7315 }
7316
7317 ConcurrentMarkSweepThread::synchronize(true);
7318 bml->lock();
7319
7320 _collector->startTimer();
7321 }
7322
7323 bool CMSPrecleanRefsYieldClosure::should_return() {
7324 if (ConcurrentMarkSweepThread::should_yield()) {
7325 do_yield_work();
7326 }
7327 return _collector->foregroundGCIsActive();
7328 }
7329
7330 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7331 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7332 "mr should be aligned to start at a card boundary");
7333 // We'd like to assert:
7334 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7335 // "mr should be a range of cards");
7336 // However, that would be too strong in one case -- the last
7337 // partition ends at _unallocated_block which, in general, can be
7338 // an arbitrary boundary, not necessarily card aligned.
7339 if (PrintCMSStatistics != 0) {
7340 _num_dirty_cards +=
7341 mr.word_size()/CardTableModRefBS::card_size_in_words;
7342 }
7343 _space->object_iterate_mem(mr, &_scan_cl);
7344 }
7345
7346 SweepClosure::SweepClosure(CMSCollector* collector,
7347 ConcurrentMarkSweepGeneration* g,
7348 CMSBitMap* bitMap, bool should_yield) :
7349 _collector(collector),
7350 _g(g),
7351 _sp(g->cmsSpace()),
7352 _limit(_sp->sweep_limit()),
7353 _freelistLock(_sp->freelistLock()),
7354 _bitMap(bitMap),
7355 _yield(should_yield),
7356 _inFreeRange(false), // No free range at beginning of sweep
7357 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7358 _lastFreeRangeCoalesced(false),
7359 _freeFinger(g->used_region().start())
7360 {
7361 NOT_PRODUCT(
7362 _numObjectsFreed = 0;
7363 _numWordsFreed = 0;
7364 _numObjectsLive = 0;
7365 _numWordsLive = 0;
7366 _numObjectsAlreadyFree = 0;
7367 _numWordsAlreadyFree = 0;
7368 _last_fc = NULL;
7369
7370 _sp->initializeIndexedFreeListArrayReturnedBytes();
7371 _sp->dictionary()->initialize_dict_returned_bytes();
7372 )
7373 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7374 "sweep _limit out of bounds");
7375 if (CMSTraceSweeper) {
7376 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7377 p2i(_limit));
7378 }
7379 }
7380
7381 void SweepClosure::print_on(outputStream* st) const {
7382 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7383 p2i(_sp->bottom()), p2i(_sp->end()));
7384 tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7385 tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7386 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7387 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7388 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7389 }
7390
7391 #ifndef PRODUCT
7392 // Assertion checking only: no useful work in product mode --
7393 // however, if any of the flags below become product flags,
7394 // you may need to review this code to see if it needs to be
7395 // enabled in product mode.
7396 SweepClosure::~SweepClosure() {
7397 assert_lock_strong(_freelistLock);
7398 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7399 "sweep _limit out of bounds");
7400 if (inFreeRange()) {
7401 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7402 print();
7403 ShouldNotReachHere();
7404 }
7405 if (Verbose && PrintGC) {
7406 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7407 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7408 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7409 SIZE_FORMAT" bytes "
7410 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7411 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7412 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7413 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7414 * sizeof(HeapWord);
7415 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7416
7417 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7418 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7419 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7420 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7421 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7422 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7423 indexListReturnedBytes);
7424 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7425 dict_returned_bytes);
7426 }
7427 }
7428 if (CMSTraceSweeper) {
7429 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7430 p2i(_limit));
7431 }
7432 }
7433 #endif // PRODUCT
7434
7435 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7436 bool freeRangeInFreeLists) {
7437 if (CMSTraceSweeper) {
7438 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7439 p2i(freeFinger), freeRangeInFreeLists);
7440 }
7441 assert(!inFreeRange(), "Trampling existing free range");
7442 set_inFreeRange(true);
7443 set_lastFreeRangeCoalesced(false);
7444
7445 set_freeFinger(freeFinger);
7446 set_freeRangeInFreeLists(freeRangeInFreeLists);
7447 if (CMSTestInFreeList) {
7448 if (freeRangeInFreeLists) {
7449 FreeChunk* fc = (FreeChunk*) freeFinger;
7450 assert(fc->is_free(), "A chunk on the free list should be free.");
7451 assert(fc->size() > 0, "Free range should have a size");
7452 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7453 }
7454 }
7455 }
7456
7457 // Note that the sweeper runs concurrently with mutators. Thus,
7458 // it is possible for direct allocation in this generation to happen
7459 // in the middle of the sweep. Note that the sweeper also coalesces
7460 // contiguous free blocks. Thus, unless the sweeper and the allocator
7461 // synchronize appropriately freshly allocated blocks may get swept up.
7462 // This is accomplished by the sweeper locking the free lists while
7463 // it is sweeping. Thus blocks that are determined to be free are
7464 // indeed free. There is however one additional complication:
7465 // blocks that have been allocated since the final checkpoint and
7466 // mark, will not have been marked and so would be treated as
7467 // unreachable and swept up. To prevent this, the allocator marks
7468 // the bit map when allocating during the sweep phase. This leads,
7469 // however, to a further complication -- objects may have been allocated
7470 // but not yet initialized -- in the sense that the header isn't yet
7471 // installed. The sweeper can not then determine the size of the block
7472 // in order to skip over it. To deal with this case, we use a technique
7473 // (due to Printezis) to encode such uninitialized block sizes in the
7474 // bit map. Since the bit map uses a bit per every HeapWord, but the
7475 // CMS generation has a minimum object size of 3 HeapWords, it follows
7476 // that "normal marks" won't be adjacent in the bit map (there will
7477 // always be at least two 0 bits between successive 1 bits). We make use
7478 // of these "unused" bits to represent uninitialized blocks -- the bit
7479 // corresponding to the start of the uninitialized object and the next
7480 // bit are both set. Finally, a 1 bit marks the end of the object that
7481 // started with the two consecutive 1 bits to indicate its potentially
7482 // uninitialized state.
7483
7484 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7485 FreeChunk* fc = (FreeChunk*)addr;
7486 size_t res;
7487
7488 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7489 // than "addr == _limit" because although _limit was a block boundary when
7490 // we started the sweep, it may no longer be one because heap expansion
7491 // may have caused us to coalesce the block ending at the address _limit
7492 // with a newly expanded chunk (this happens when _limit was set to the
7493 // previous _end of the space), so we may have stepped past _limit:
7494 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7495 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7496 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7497 "sweep _limit out of bounds");
7498 assert(addr < _sp->end(), "addr out of bounds");
7499 // Flush any free range we might be holding as a single
7500 // coalesced chunk to the appropriate free list.
7501 if (inFreeRange()) {
7502 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7503 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", p2i(freeFinger())));
7504 flush_cur_free_chunk(freeFinger(),
7505 pointer_delta(addr, freeFinger()));
7506 if (CMSTraceSweeper) {
7507 gclog_or_tty->print("Sweep: last chunk: ");
7508 gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
7509 "[coalesced:%d]\n",
7510 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7511 lastFreeRangeCoalesced() ? 1 : 0);
7512 }
7513 }
7514
7515 // help the iterator loop finish
7516 return pointer_delta(_sp->end(), addr);
7517 }
7518
7519 assert(addr < _limit, "sweep invariant");
7520 // check if we should yield
7521 do_yield_check(addr);
7522 if (fc->is_free()) {
7523 // Chunk that is already free
7524 res = fc->size();
7525 do_already_free_chunk(fc);
7526 debug_only(_sp->verifyFreeLists());
7527 // If we flush the chunk at hand in lookahead_and_flush()
7528 // and it's coalesced with a preceding chunk, then the
7529 // process of "mangling" the payload of the coalesced block
7530 // will cause erasure of the size information from the
7531 // (erstwhile) header of all the coalesced blocks but the
7532 // first, so the first disjunct in the assert will not hold
7533 // in that specific case (in which case the second disjunct
7534 // will hold).
7535 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7536 "Otherwise the size info doesn't change at this step");
7537 NOT_PRODUCT(
7538 _numObjectsAlreadyFree++;
7539 _numWordsAlreadyFree += res;
7540 )
7541 NOT_PRODUCT(_last_fc = fc;)
7542 } else if (!_bitMap->isMarked(addr)) {
7543 // Chunk is fresh garbage
7544 res = do_garbage_chunk(fc);
7545 debug_only(_sp->verifyFreeLists());
7546 NOT_PRODUCT(
7547 _numObjectsFreed++;
7548 _numWordsFreed += res;
7549 )
7550 } else {
7551 // Chunk that is alive.
7552 res = do_live_chunk(fc);
7553 debug_only(_sp->verifyFreeLists());
7554 NOT_PRODUCT(
7555 _numObjectsLive++;
7556 _numWordsLive += res;
7557 )
7558 }
7559 return res;
7560 }
7561
7562 // For the smart allocation, record following
7563 // split deaths - a free chunk is removed from its free list because
7564 // it is being split into two or more chunks.
7565 // split birth - a free chunk is being added to its free list because
7566 // a larger free chunk has been split and resulted in this free chunk.
7567 // coal death - a free chunk is being removed from its free list because
7568 // it is being coalesced into a large free chunk.
7569 // coal birth - a free chunk is being added to its free list because
7570 // it was created when two or more free chunks where coalesced into
7571 // this free chunk.
7572 //
7573 // These statistics are used to determine the desired number of free
7574 // chunks of a given size. The desired number is chosen to be relative
7575 // to the end of a CMS sweep. The desired number at the end of a sweep
7576 // is the
7577 // count-at-end-of-previous-sweep (an amount that was enough)
7578 // - count-at-beginning-of-current-sweep (the excess)
7579 // + split-births (gains in this size during interval)
7580 // - split-deaths (demands on this size during interval)
7581 // where the interval is from the end of one sweep to the end of the
7582 // next.
7583 //
7584 // When sweeping the sweeper maintains an accumulated chunk which is
7585 // the chunk that is made up of chunks that have been coalesced. That
7586 // will be termed the left-hand chunk. A new chunk of garbage that
7587 // is being considered for coalescing will be referred to as the
7588 // right-hand chunk.
7589 //
7590 // When making a decision on whether to coalesce a right-hand chunk with
7591 // the current left-hand chunk, the current count vs. the desired count
7592 // of the left-hand chunk is considered. Also if the right-hand chunk
7593 // is near the large chunk at the end of the heap (see
7594 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7595 // left-hand chunk is coalesced.
7596 //
7597 // When making a decision about whether to split a chunk, the desired count
7598 // vs. the current count of the candidate to be split is also considered.
7599 // If the candidate is underpopulated (currently fewer chunks than desired)
7600 // a chunk of an overpopulated (currently more chunks than desired) size may
7601 // be chosen. The "hint" associated with a free list, if non-null, points
7602 // to a free list which may be overpopulated.
7603 //
7604
7605 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7606 const size_t size = fc->size();
7607 // Chunks that cannot be coalesced are not in the
7608 // free lists.
7609 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7610 assert(_sp->verify_chunk_in_free_list(fc),
7611 "free chunk should be in free lists");
7612 }
7613 // a chunk that is already free, should not have been
7614 // marked in the bit map
7615 HeapWord* const addr = (HeapWord*) fc;
7616 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7617 // Verify that the bit map has no bits marked between
7618 // addr and purported end of this block.
7619 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7620
7621 // Some chunks cannot be coalesced under any circumstances.
7622 // See the definition of cantCoalesce().
7623 if (!fc->cantCoalesce()) {
7624 // This chunk can potentially be coalesced.
7625 if (_sp->adaptive_freelists()) {
7626 // All the work is done in
7627 do_post_free_or_garbage_chunk(fc, size);
7628 } else { // Not adaptive free lists
7629 // this is a free chunk that can potentially be coalesced by the sweeper;
7630 if (!inFreeRange()) {
7631 // if the next chunk is a free block that can't be coalesced
7632 // it doesn't make sense to remove this chunk from the free lists
7633 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7634 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
7635 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
7636 nextChunk->is_free() && // ... which is free...
7637 nextChunk->cantCoalesce()) { // ... but can't be coalesced
7638 // nothing to do
7639 } else {
7640 // Potentially the start of a new free range:
7641 // Don't eagerly remove it from the free lists.
7642 // No need to remove it if it will just be put
7643 // back again. (Also from a pragmatic point of view
7644 // if it is a free block in a region that is beyond
7645 // any allocated blocks, an assertion will fail)
7646 // Remember the start of a free run.
7647 initialize_free_range(addr, true);
7648 // end - can coalesce with next chunk
7649 }
7650 } else {
7651 // the midst of a free range, we are coalescing
7652 print_free_block_coalesced(fc);
7653 if (CMSTraceSweeper) {
7654 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7655 }
7656 // remove it from the free lists
7657 _sp->removeFreeChunkFromFreeLists(fc);
7658 set_lastFreeRangeCoalesced(true);
7659 // If the chunk is being coalesced and the current free range is
7660 // in the free lists, remove the current free range so that it
7661 // will be returned to the free lists in its entirety - all
7662 // the coalesced pieces included.
7663 if (freeRangeInFreeLists()) {
7664 FreeChunk* ffc = (FreeChunk*) freeFinger();
7665 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7666 "Size of free range is inconsistent with chunk size.");
7667 if (CMSTestInFreeList) {
7668 assert(_sp->verify_chunk_in_free_list(ffc),
7669 "free range is not in free lists");
7670 }
7671 _sp->removeFreeChunkFromFreeLists(ffc);
7672 set_freeRangeInFreeLists(false);
7673 }
7674 }
7675 }
7676 // Note that if the chunk is not coalescable (the else arm
7677 // below), we unconditionally flush, without needing to do
7678 // a "lookahead," as we do below.
7679 if (inFreeRange()) lookahead_and_flush(fc, size);
7680 } else {
7681 // Code path common to both original and adaptive free lists.
7682
7683 // cant coalesce with previous block; this should be treated
7684 // as the end of a free run if any
7685 if (inFreeRange()) {
7686 // we kicked some butt; time to pick up the garbage
7687 assert(freeFinger() < addr, "freeFinger points too high");
7688 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7689 }
7690 // else, nothing to do, just continue
7691 }
7692 }
7693
7694 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7695 // This is a chunk of garbage. It is not in any free list.
7696 // Add it to a free list or let it possibly be coalesced into
7697 // a larger chunk.
7698 HeapWord* const addr = (HeapWord*) fc;
7699 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7700
7701 if (_sp->adaptive_freelists()) {
7702 // Verify that the bit map has no bits marked between
7703 // addr and purported end of just dead object.
7704 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7705
7706 do_post_free_or_garbage_chunk(fc, size);
7707 } else {
7708 if (!inFreeRange()) {
7709 // start of a new free range
7710 assert(size > 0, "A free range should have a size");
7711 initialize_free_range(addr, false);
7712 } else {
7713 // this will be swept up when we hit the end of the
7714 // free range
7715 if (CMSTraceSweeper) {
7716 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7717 }
7718 // If the chunk is being coalesced and the current free range is
7719 // in the free lists, remove the current free range so that it
7720 // will be returned to the free lists in its entirety - all
7721 // the coalesced pieces included.
7722 if (freeRangeInFreeLists()) {
7723 FreeChunk* ffc = (FreeChunk*)freeFinger();
7724 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7725 "Size of free range is inconsistent with chunk size.");
7726 if (CMSTestInFreeList) {
7727 assert(_sp->verify_chunk_in_free_list(ffc),
7728 "free range is not in free lists");
7729 }
7730 _sp->removeFreeChunkFromFreeLists(ffc);
7731 set_freeRangeInFreeLists(false);
7732 }
7733 set_lastFreeRangeCoalesced(true);
7734 }
7735 // this will be swept up when we hit the end of the free range
7736
7737 // Verify that the bit map has no bits marked between
7738 // addr and purported end of just dead object.
7739 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7740 }
7741 assert(_limit >= addr + size,
7742 "A freshly garbage chunk can't possibly straddle over _limit");
7743 if (inFreeRange()) lookahead_and_flush(fc, size);
7744 return size;
7745 }
7746
7747 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7748 HeapWord* addr = (HeapWord*) fc;
7749 // The sweeper has just found a live object. Return any accumulated
7750 // left hand chunk to the free lists.
7751 if (inFreeRange()) {
7752 assert(freeFinger() < addr, "freeFinger points too high");
7753 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7754 }
7755
7756 // This object is live: we'd normally expect this to be
7757 // an oop, and like to assert the following:
7758 // assert(oop(addr)->is_oop(), "live block should be an oop");
7759 // However, as we commented above, this may be an object whose
7760 // header hasn't yet been initialized.
7761 size_t size;
7762 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7763 if (_bitMap->isMarked(addr + 1)) {
7764 // Determine the size from the bit map, rather than trying to
7765 // compute it from the object header.
7766 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7767 size = pointer_delta(nextOneAddr + 1, addr);
7768 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7769 "alignment problem");
7770
7771 #ifdef ASSERT
7772 if (oop(addr)->klass_or_null() != NULL) {
7773 // Ignore mark word because we are running concurrent with mutators
7774 assert(oop(addr)->is_oop(true), "live block should be an oop");
7775 assert(size ==
7776 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7777 "P-mark and computed size do not agree");
7778 }
7779 #endif
7780
7781 } else {
7782 // This should be an initialized object that's alive.
7783 assert(oop(addr)->klass_or_null() != NULL,
7784 "Should be an initialized object");
7785 // Ignore mark word because we are running concurrent with mutators
7786 assert(oop(addr)->is_oop(true), "live block should be an oop");
7787 // Verify that the bit map has no bits marked between
7788 // addr and purported end of this block.
7789 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7790 assert(size >= 3, "Necessary for Printezis marks to work");
7791 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7792 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7793 }
7794 return size;
7795 }
7796
7797 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7798 size_t chunkSize) {
7799 // do_post_free_or_garbage_chunk() should only be called in the case
7800 // of the adaptive free list allocator.
7801 const bool fcInFreeLists = fc->is_free();
7802 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
7803 assert((HeapWord*)fc <= _limit, "sweep invariant");
7804 if (CMSTestInFreeList && fcInFreeLists) {
7805 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7806 }
7807
7808 if (CMSTraceSweeper) {
7809 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7810 }
7811
7812 HeapWord* const fc_addr = (HeapWord*) fc;
7813
7814 bool coalesce;
7815 const size_t left = pointer_delta(fc_addr, freeFinger());
7816 const size_t right = chunkSize;
7817 switch (FLSCoalescePolicy) {
7818 // numeric value forms a coalition aggressiveness metric
7819 case 0: { // never coalesce
7820 coalesce = false;
7821 break;
7822 }
7823 case 1: { // coalesce if left & right chunks on overpopulated lists
7824 coalesce = _sp->coalOverPopulated(left) &&
7825 _sp->coalOverPopulated(right);
7826 break;
7827 }
7828 case 2: { // coalesce if left chunk on overpopulated list (default)
7829 coalesce = _sp->coalOverPopulated(left);
7830 break;
7831 }
7832 case 3: { // coalesce if left OR right chunk on overpopulated list
7833 coalesce = _sp->coalOverPopulated(left) ||
7834 _sp->coalOverPopulated(right);
7835 break;
7836 }
7837 case 4: { // always coalesce
7838 coalesce = true;
7839 break;
7840 }
7841 default:
7842 ShouldNotReachHere();
7843 }
7844
7845 // Should the current free range be coalesced?
7846 // If the chunk is in a free range and either we decided to coalesce above
7847 // or the chunk is near the large block at the end of the heap
7848 // (isNearLargestChunk() returns true), then coalesce this chunk.
7849 const bool doCoalesce = inFreeRange()
7850 && (coalesce || _g->isNearLargestChunk(fc_addr));
7851 if (doCoalesce) {
7852 // Coalesce the current free range on the left with the new
7853 // chunk on the right. If either is on a free list,
7854 // it must be removed from the list and stashed in the closure.
7855 if (freeRangeInFreeLists()) {
7856 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7857 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7858 "Size of free range is inconsistent with chunk size.");
7859 if (CMSTestInFreeList) {
7860 assert(_sp->verify_chunk_in_free_list(ffc),
7861 "Chunk is not in free lists");
7862 }
7863 _sp->coalDeath(ffc->size());
7864 _sp->removeFreeChunkFromFreeLists(ffc);
7865 set_freeRangeInFreeLists(false);
7866 }
7867 if (fcInFreeLists) {
7868 _sp->coalDeath(chunkSize);
7869 assert(fc->size() == chunkSize,
7870 "The chunk has the wrong size or is not in the free lists");
7871 _sp->removeFreeChunkFromFreeLists(fc);
7872 }
7873 set_lastFreeRangeCoalesced(true);
7874 print_free_block_coalesced(fc);
7875 } else { // not in a free range and/or should not coalesce
7876 // Return the current free range and start a new one.
7877 if (inFreeRange()) {
7878 // In a free range but cannot coalesce with the right hand chunk.
7879 // Put the current free range into the free lists.
7880 flush_cur_free_chunk(freeFinger(),
7881 pointer_delta(fc_addr, freeFinger()));
7882 }
7883 // Set up for new free range. Pass along whether the right hand
7884 // chunk is in the free lists.
7885 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7886 }
7887 }
7888
7889 // Lookahead flush:
7890 // If we are tracking a free range, and this is the last chunk that
7891 // we'll look at because its end crosses past _limit, we'll preemptively
7892 // flush it along with any free range we may be holding on to. Note that
7893 // this can be the case only for an already free or freshly garbage
7894 // chunk. If this block is an object, it can never straddle
7895 // over _limit. The "straddling" occurs when _limit is set at
7896 // the previous end of the space when this cycle started, and
7897 // a subsequent heap expansion caused the previously co-terminal
7898 // free block to be coalesced with the newly expanded portion,
7899 // thus rendering _limit a non-block-boundary making it dangerous
7900 // for the sweeper to step over and examine.
7901 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7902 assert(inFreeRange(), "Should only be called if currently in a free range.");
7903 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7904 assert(_sp->used_region().contains(eob - 1),
7905 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7906 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7907 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7908 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size));
7909 if (eob >= _limit) {
7910 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7911 if (CMSTraceSweeper) {
7912 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7913 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7914 "[" PTR_FORMAT "," PTR_FORMAT ")",
7915 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7916 }
7917 // Return the storage we are tracking back into the free lists.
7918 if (CMSTraceSweeper) {
7919 gclog_or_tty->print_cr("Flushing ... ");
7920 }
7921 assert(freeFinger() < eob, "Error");
7922 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7923 }
7924 }
7925
7926 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7927 assert(inFreeRange(), "Should only be called if currently in a free range.");
7928 assert(size > 0,
7929 "A zero sized chunk cannot be added to the free lists.");
7930 if (!freeRangeInFreeLists()) {
7931 if (CMSTestInFreeList) {
7932 FreeChunk* fc = (FreeChunk*) chunk;
7933 fc->set_size(size);
7934 assert(!_sp->verify_chunk_in_free_list(fc),
7935 "chunk should not be in free lists yet");
7936 }
7937 if (CMSTraceSweeper) {
7938 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7939 p2i(chunk), size);
7940 }
7941 // A new free range is going to be starting. The current
7942 // free range has not been added to the free lists yet or
7943 // was removed so add it back.
7944 // If the current free range was coalesced, then the death
7945 // of the free range was recorded. Record a birth now.
7946 if (lastFreeRangeCoalesced()) {
7947 _sp->coalBirth(size);
7948 }
7949 _sp->addChunkAndRepairOffsetTable(chunk, size,
7950 lastFreeRangeCoalesced());
7951 } else if (CMSTraceSweeper) {
7952 gclog_or_tty->print_cr("Already in free list: nothing to flush");
7953 }
7954 set_inFreeRange(false);
7955 set_freeRangeInFreeLists(false);
7956 }
7957
7958 // We take a break if we've been at this for a while,
7959 // so as to avoid monopolizing the locks involved.
7960 void SweepClosure::do_yield_work(HeapWord* addr) {
7961 // Return current free chunk being used for coalescing (if any)
7962 // to the appropriate freelist. After yielding, the next
7963 // free block encountered will start a coalescing range of
7964 // free blocks. If the next free block is adjacent to the
7965 // chunk just flushed, they will need to wait for the next
7966 // sweep to be coalesced.
7967 if (inFreeRange()) {
7968 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7969 }
7970
7971 // First give up the locks, then yield, then re-lock.
7972 // We should probably use a constructor/destructor idiom to
7973 // do this unlock/lock or modify the MutexUnlocker class to
7974 // serve our purpose. XXX
7975 assert_lock_strong(_bitMap->lock());
7976 assert_lock_strong(_freelistLock);
7977 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7978 "CMS thread should hold CMS token");
7979 _bitMap->lock()->unlock();
7980 _freelistLock->unlock();
7981 ConcurrentMarkSweepThread::desynchronize(true);
7982 _collector->stopTimer();
7983 if (PrintCMSStatistics != 0) {
7984 _collector->incrementYields();
7985 }
7986
7987 // See the comment in coordinator_yield()
7988 for (unsigned i = 0; i < CMSYieldSleepCount &&
7989 ConcurrentMarkSweepThread::should_yield() &&
7990 !CMSCollector::foregroundGCIsActive(); ++i) {
7991 os::sleep(Thread::current(), 1, false);
7992 }
7993
7994 ConcurrentMarkSweepThread::synchronize(true);
7995 _freelistLock->lock();
7996 _bitMap->lock()->lock_without_safepoint_check();
7997 _collector->startTimer();
7998 }
7999
8000 #ifndef PRODUCT
8001 // This is actually very useful in a product build if it can
8002 // be called from the debugger. Compile it into the product
8003 // as needed.
8004 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8005 return debug_cms_space->verify_chunk_in_free_list(fc);
8006 }
8007 #endif
8008
8009 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8010 if (CMSTraceSweeper) {
8011 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8012 p2i(fc), fc->size());
8013 }
8014 }
8015
8016 // CMSIsAliveClosure
8017 bool CMSIsAliveClosure::do_object_b(oop obj) {
8018 HeapWord* addr = (HeapWord*)obj;
8019 return addr != NULL &&
8020 (!_span.contains(addr) || _bit_map->isMarked(addr));
8021 }
8022
8023
8024 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8025 MemRegion span,
8026 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8027 bool cpc):
8028 _collector(collector),
8029 _span(span),
8030 _bit_map(bit_map),
8031 _mark_stack(mark_stack),
8032 _concurrent_precleaning(cpc) {
8033 assert(!_span.is_empty(), "Empty span could spell trouble");
8034 }
8035
8036
8037 // CMSKeepAliveClosure: the serial version
8038 void CMSKeepAliveClosure::do_oop(oop obj) {
8039 HeapWord* addr = (HeapWord*)obj;
8040 if (_span.contains(addr) &&
8041 !_bit_map->isMarked(addr)) {
8042 _bit_map->mark(addr);
8043 bool simulate_overflow = false;
8044 NOT_PRODUCT(
8045 if (CMSMarkStackOverflowALot &&
8046 _collector->simulate_overflow()) {
8047 // simulate a stack overflow
8048 simulate_overflow = true;
8049 }
8050 )
8051 if (simulate_overflow || !_mark_stack->push(obj)) {
8052 if (_concurrent_precleaning) {
8053 // We dirty the overflown object and let the remark
8054 // phase deal with it.
8055 assert(_collector->overflow_list_is_empty(), "Error");
8056 // In the case of object arrays, we need to dirty all of
8057 // the cards that the object spans. No locking or atomics
8058 // are needed since no one else can be mutating the mod union
8059 // table.
8060 if (obj->is_objArray()) {
8061 size_t sz = obj->size();
8062 HeapWord* end_card_addr =
8063 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8064 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8065 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8066 _collector->_modUnionTable.mark_range(redirty_range);
8067 } else {
8068 _collector->_modUnionTable.mark(addr);
8069 }
8070 _collector->_ser_kac_preclean_ovflw++;
8071 } else {
8072 _collector->push_on_overflow_list(obj);
8073 _collector->_ser_kac_ovflw++;
8074 }
8075 }
8076 }
8077 }
8078
8079 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8080 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8081
8082 // CMSParKeepAliveClosure: a parallel version of the above.
8083 // The work queues are private to each closure (thread),
8084 // but (may be) available for stealing by other threads.
8085 void CMSParKeepAliveClosure::do_oop(oop obj) {
8086 HeapWord* addr = (HeapWord*)obj;
8087 if (_span.contains(addr) &&
8088 !_bit_map->isMarked(addr)) {
8089 // In general, during recursive tracing, several threads
8090 // may be concurrently getting here; the first one to
8091 // "tag" it, claims it.
8092 if (_bit_map->par_mark(addr)) {
8093 bool res = _work_queue->push(obj);
8094 assert(res, "Low water mark should be much less than capacity");
8095 // Do a recursive trim in the hope that this will keep
8096 // stack usage lower, but leave some oops for potential stealers
8097 trim_queue(_low_water_mark);
8098 } // Else, another thread got there first
8099 }
8100 }
8101
8102 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8103 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8104
8105 void CMSParKeepAliveClosure::trim_queue(uint max) {
8106 while (_work_queue->size() > max) {
8107 oop new_oop;
8108 if (_work_queue->pop_local(new_oop)) {
8109 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8110 assert(_bit_map->isMarked((HeapWord*)new_oop),
8111 "no white objects on this stack!");
8112 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8113 // iterate over the oops in this oop, marking and pushing
8114 // the ones in CMS heap (i.e. in _span).
8115 new_oop->oop_iterate(&_mark_and_push);
8116 }
8117 }
8118 }
8119
8120 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8121 CMSCollector* collector,
8122 MemRegion span, CMSBitMap* bit_map,
8123 OopTaskQueue* work_queue):
8124 _collector(collector),
8125 _span(span),
8126 _bit_map(bit_map),
8127 _work_queue(work_queue) { }
8128
8129 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8130 HeapWord* addr = (HeapWord*)obj;
8131 if (_span.contains(addr) &&
8132 !_bit_map->isMarked(addr)) {
8133 if (_bit_map->par_mark(addr)) {
8134 bool simulate_overflow = false;
8135 NOT_PRODUCT(
8136 if (CMSMarkStackOverflowALot &&
8137 _collector->par_simulate_overflow()) {
8138 // simulate a stack overflow
8139 simulate_overflow = true;
8140 }
8141 )
8142 if (simulate_overflow || !_work_queue->push(obj)) {
8143 _collector->par_push_on_overflow_list(obj);
8144 _collector->_par_kac_ovflw++;
8145 }
8146 } // Else another thread got there already
8147 }
8148 }
8149
8150 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8151 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8152
8153 //////////////////////////////////////////////////////////////////
8154 // CMSExpansionCause /////////////////////////////
8155 //////////////////////////////////////////////////////////////////
8156 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8157 switch (cause) {
8158 case _no_expansion:
8159 return "No expansion";
8160 case _satisfy_free_ratio:
8161 return "Free ratio";
8162 case _satisfy_promotion:
8163 return "Satisfy promotion";
8164 case _satisfy_allocation:
8165 return "allocation";
8166 case _allocate_par_lab:
8167 return "Par LAB";
8168 case _allocate_par_spooling_space:
8169 return "Par Spooling Space";
8170 case _adaptive_size_policy:
8171 return "Ergonomics";
8172 default:
8173 return "unknown";
8174 }
8175 }
8176
8177 void CMSDrainMarkingStackClosure::do_void() {
8178 // the max number to take from overflow list at a time
8179 const size_t num = _mark_stack->capacity()/4;
8180 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8181 "Overflow list should be NULL during concurrent phases");
8182 while (!_mark_stack->isEmpty() ||
8183 // if stack is empty, check the overflow list
8184 _collector->take_from_overflow_list(num, _mark_stack)) {
8185 oop obj = _mark_stack->pop();
8186 HeapWord* addr = (HeapWord*)obj;
8187 assert(_span.contains(addr), "Should be within span");
8188 assert(_bit_map->isMarked(addr), "Should be marked");
8189 assert(obj->is_oop(), "Should be an oop");
8190 obj->oop_iterate(_keep_alive);
8191 }
8192 }
8193
8194 void CMSParDrainMarkingStackClosure::do_void() {
8195 // drain queue
8196 trim_queue(0);
8197 }
8198
8199 // Trim our work_queue so its length is below max at return
8200 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8201 while (_work_queue->size() > max) {
8202 oop new_oop;
8203 if (_work_queue->pop_local(new_oop)) {
8204 assert(new_oop->is_oop(), "Expected an oop");
8205 assert(_bit_map->isMarked((HeapWord*)new_oop),
8206 "no white objects on this stack!");
8207 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8208 // iterate over the oops in this oop, marking and pushing
8209 // the ones in CMS heap (i.e. in _span).
8210 new_oop->oop_iterate(&_mark_and_push);
8211 }
8212 }
8213 }
8214
8215 ////////////////////////////////////////////////////////////////////
8216 // Support for Marking Stack Overflow list handling and related code
8217 ////////////////////////////////////////////////////////////////////
8218 // Much of the following code is similar in shape and spirit to the
8219 // code used in ParNewGC. We should try and share that code
8220 // as much as possible in the future.
8221
8222 #ifndef PRODUCT
8223 // Debugging support for CMSStackOverflowALot
8224
8225 // It's OK to call this multi-threaded; the worst thing
8226 // that can happen is that we'll get a bunch of closely
8227 // spaced simulated overflows, but that's OK, in fact
8228 // probably good as it would exercise the overflow code
8229 // under contention.
8230 bool CMSCollector::simulate_overflow() {
8231 if (_overflow_counter-- <= 0) { // just being defensive
8232 _overflow_counter = CMSMarkStackOverflowInterval;
8233 return true;
8234 } else {
8235 return false;
8236 }
8237 }
8238
8239 bool CMSCollector::par_simulate_overflow() {
8240 return simulate_overflow();
8241 }
8242 #endif
8243
8244 // Single-threaded
8245 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8246 assert(stack->isEmpty(), "Expected precondition");
8247 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8248 size_t i = num;
8249 oop cur = _overflow_list;
8250 const markOop proto = markOopDesc::prototype();
8251 NOT_PRODUCT(ssize_t n = 0;)
8252 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8253 next = oop(cur->mark());
8254 cur->set_mark(proto); // until proven otherwise
8255 assert(cur->is_oop(), "Should be an oop");
8256 bool res = stack->push(cur);
8257 assert(res, "Bit off more than can chew?");
8258 NOT_PRODUCT(n++;)
8259 }
8260 _overflow_list = cur;
8261 #ifndef PRODUCT
8262 assert(_num_par_pushes >= n, "Too many pops?");
8263 _num_par_pushes -=n;
8264 #endif
8265 return !stack->isEmpty();
8266 }
8267
8268 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8269 // (MT-safe) Get a prefix of at most "num" from the list.
8270 // The overflow list is chained through the mark word of
8271 // each object in the list. We fetch the entire list,
8272 // break off a prefix of the right size and return the
8273 // remainder. If other threads try to take objects from
8274 // the overflow list at that time, they will wait for
8275 // some time to see if data becomes available. If (and
8276 // only if) another thread places one or more object(s)
8277 // on the global list before we have returned the suffix
8278 // to the global list, we will walk down our local list
8279 // to find its end and append the global list to
8280 // our suffix before returning it. This suffix walk can
8281 // prove to be expensive (quadratic in the amount of traffic)
8282 // when there are many objects in the overflow list and
8283 // there is much producer-consumer contention on the list.
8284 // *NOTE*: The overflow list manipulation code here and
8285 // in ParNewGeneration:: are very similar in shape,
8286 // except that in the ParNew case we use the old (from/eden)
8287 // copy of the object to thread the list via its klass word.
8288 // Because of the common code, if you make any changes in
8289 // the code below, please check the ParNew version to see if
8290 // similar changes might be needed.
8291 // CR 6797058 has been filed to consolidate the common code.
8292 bool CMSCollector::par_take_from_overflow_list(size_t num,
8293 OopTaskQueue* work_q,
8294 int no_of_gc_threads) {
8295 assert(work_q->size() == 0, "First empty local work queue");
8296 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8297 if (_overflow_list == NULL) {
8298 return false;
8299 }
8300 // Grab the entire list; we'll put back a suffix
8301 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8302 Thread* tid = Thread::current();
8303 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8304 // set to ParallelGCThreads.
8305 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8306 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8307 // If the list is busy, we spin for a short while,
8308 // sleeping between attempts to get the list.
8309 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8310 os::sleep(tid, sleep_time_millis, false);
8311 if (_overflow_list == NULL) {
8312 // Nothing left to take
8313 return false;
8314 } else if (_overflow_list != BUSY) {
8315 // Try and grab the prefix
8316 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8317 }
8318 }
8319 // If the list was found to be empty, or we spun long
8320 // enough, we give up and return empty-handed. If we leave
8321 // the list in the BUSY state below, it must be the case that
8322 // some other thread holds the overflow list and will set it
8323 // to a non-BUSY state in the future.
8324 if (prefix == NULL || prefix == BUSY) {
8325 // Nothing to take or waited long enough
8326 if (prefix == NULL) {
8327 // Write back the NULL in case we overwrote it with BUSY above
8328 // and it is still the same value.
8329 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8330 }
8331 return false;
8332 }
8333 assert(prefix != NULL && prefix != BUSY, "Error");
8334 size_t i = num;
8335 oop cur = prefix;
8336 // Walk down the first "num" objects, unless we reach the end.
8337 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8338 if (cur->mark() == NULL) {
8339 // We have "num" or fewer elements in the list, so there
8340 // is nothing to return to the global list.
8341 // Write back the NULL in lieu of the BUSY we wrote
8342 // above, if it is still the same value.
8343 if (_overflow_list == BUSY) {
8344 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8345 }
8346 } else {
8347 // Chop off the suffix and return it to the global list.
8348 assert(cur->mark() != BUSY, "Error");
8349 oop suffix_head = cur->mark(); // suffix will be put back on global list
8350 cur->set_mark(NULL); // break off suffix
8351 // It's possible that the list is still in the empty(busy) state
8352 // we left it in a short while ago; in that case we may be
8353 // able to place back the suffix without incurring the cost
8354 // of a walk down the list.
8355 oop observed_overflow_list = _overflow_list;
8356 oop cur_overflow_list = observed_overflow_list;
8357 bool attached = false;
8358 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8359 observed_overflow_list =
8360 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8361 if (cur_overflow_list == observed_overflow_list) {
8362 attached = true;
8363 break;
8364 } else cur_overflow_list = observed_overflow_list;
8365 }
8366 if (!attached) {
8367 // Too bad, someone else sneaked in (at least) an element; we'll need
8368 // to do a splice. Find tail of suffix so we can prepend suffix to global
8369 // list.
8370 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8371 oop suffix_tail = cur;
8372 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8373 "Tautology");
8374 observed_overflow_list = _overflow_list;
8375 do {
8376 cur_overflow_list = observed_overflow_list;
8377 if (cur_overflow_list != BUSY) {
8378 // Do the splice ...
8379 suffix_tail->set_mark(markOop(cur_overflow_list));
8380 } else { // cur_overflow_list == BUSY
8381 suffix_tail->set_mark(NULL);
8382 }
8383 // ... and try to place spliced list back on overflow_list ...
8384 observed_overflow_list =
8385 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8386 } while (cur_overflow_list != observed_overflow_list);
8387 // ... until we have succeeded in doing so.
8388 }
8389 }
8390
8391 // Push the prefix elements on work_q
8392 assert(prefix != NULL, "control point invariant");
8393 const markOop proto = markOopDesc::prototype();
8394 oop next;
8395 NOT_PRODUCT(ssize_t n = 0;)
8396 for (cur = prefix; cur != NULL; cur = next) {
8397 next = oop(cur->mark());
8398 cur->set_mark(proto); // until proven otherwise
8399 assert(cur->is_oop(), "Should be an oop");
8400 bool res = work_q->push(cur);
8401 assert(res, "Bit off more than we can chew?");
8402 NOT_PRODUCT(n++;)
8403 }
8404 #ifndef PRODUCT
8405 assert(_num_par_pushes >= n, "Too many pops?");
8406 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8407 #endif
8408 return true;
8409 }
8410
8411 // Single-threaded
8412 void CMSCollector::push_on_overflow_list(oop p) {
8413 NOT_PRODUCT(_num_par_pushes++;)
8414 assert(p->is_oop(), "Not an oop");
8415 preserve_mark_if_necessary(p);
8416 p->set_mark((markOop)_overflow_list);
8417 _overflow_list = p;
8418 }
8419
8420 // Multi-threaded; use CAS to prepend to overflow list
8421 void CMSCollector::par_push_on_overflow_list(oop p) {
8422 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8423 assert(p->is_oop(), "Not an oop");
8424 par_preserve_mark_if_necessary(p);
8425 oop observed_overflow_list = _overflow_list;
8426 oop cur_overflow_list;
8427 do {
8428 cur_overflow_list = observed_overflow_list;
8429 if (cur_overflow_list != BUSY) {
8430 p->set_mark(markOop(cur_overflow_list));
8431 } else {
8432 p->set_mark(NULL);
8433 }
8434 observed_overflow_list =
8435 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8436 } while (cur_overflow_list != observed_overflow_list);
8437 }
8438 #undef BUSY
8439
8440 // Single threaded
8441 // General Note on GrowableArray: pushes may silently fail
8442 // because we are (temporarily) out of C-heap for expanding
8443 // the stack. The problem is quite ubiquitous and affects
8444 // a lot of code in the JVM. The prudent thing for GrowableArray
8445 // to do (for now) is to exit with an error. However, that may
8446 // be too draconian in some cases because the caller may be
8447 // able to recover without much harm. For such cases, we
8448 // should probably introduce a "soft_push" method which returns
8449 // an indication of success or failure with the assumption that
8450 // the caller may be able to recover from a failure; code in
8451 // the VM can then be changed, incrementally, to deal with such
8452 // failures where possible, thus, incrementally hardening the VM
8453 // in such low resource situations.
8454 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8455 _preserved_oop_stack.push(p);
8456 _preserved_mark_stack.push(m);
8457 assert(m == p->mark(), "Mark word changed");
8458 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8459 "bijection");
8460 }
8461
8462 // Single threaded
8463 void CMSCollector::preserve_mark_if_necessary(oop p) {
8464 markOop m = p->mark();
8465 if (m->must_be_preserved(p)) {
8466 preserve_mark_work(p, m);
8467 }
8468 }
8469
8470 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8471 markOop m = p->mark();
8472 if (m->must_be_preserved(p)) {
8473 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8474 // Even though we read the mark word without holding
8475 // the lock, we are assured that it will not change
8476 // because we "own" this oop, so no other thread can
8477 // be trying to push it on the overflow list; see
8478 // the assertion in preserve_mark_work() that checks
8479 // that m == p->mark().
8480 preserve_mark_work(p, m);
8481 }
8482 }
8483
8484 // We should be able to do this multi-threaded,
8485 // a chunk of stack being a task (this is
8486 // correct because each oop only ever appears
8487 // once in the overflow list. However, it's
8488 // not very easy to completely overlap this with
8489 // other operations, so will generally not be done
8490 // until all work's been completed. Because we
8491 // expect the preserved oop stack (set) to be small,
8492 // it's probably fine to do this single-threaded.
8493 // We can explore cleverer concurrent/overlapped/parallel
8494 // processing of preserved marks if we feel the
8495 // need for this in the future. Stack overflow should
8496 // be so rare in practice and, when it happens, its
8497 // effect on performance so great that this will
8498 // likely just be in the noise anyway.
8499 void CMSCollector::restore_preserved_marks_if_any() {
8500 assert(SafepointSynchronize::is_at_safepoint(),
8501 "world should be stopped");
8502 assert(Thread::current()->is_ConcurrentGC_thread() ||
8503 Thread::current()->is_VM_thread(),
8504 "should be single-threaded");
8505 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8506 "bijection");
8507
8508 while (!_preserved_oop_stack.is_empty()) {
8509 oop p = _preserved_oop_stack.pop();
8510 assert(p->is_oop(), "Should be an oop");
8511 assert(_span.contains(p), "oop should be in _span");
8512 assert(p->mark() == markOopDesc::prototype(),
8513 "Set when taken from overflow list");
8514 markOop m = _preserved_mark_stack.pop();
8515 p->set_mark(m);
8516 }
8517 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8518 "stacks were cleared above");
8519 }
8520
8521 #ifndef PRODUCT
8522 bool CMSCollector::no_preserved_marks() const {
8523 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8524 }
8525 #endif
8526
8527 // Transfer some number of overflown objects to usual marking
8528 // stack. Return true if some objects were transferred.
8529 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8530 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8531 (size_t)ParGCDesiredObjsFromOverflowList);
8532
8533 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8534 assert(_collector->overflow_list_is_empty() || res,
8535 "If list is not empty, we should have taken something");
8536 assert(!res || !_mark_stack->isEmpty(),
8537 "If we took something, it should now be on our stack");
8538 return res;
8539 }
8540
8541 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8542 size_t res = _sp->block_size_no_stall(addr, _collector);
8543 if (_sp->block_is_obj(addr)) {
8544 if (_live_bit_map->isMarked(addr)) {
8545 // It can't have been dead in a previous cycle
8546 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8547 } else {
8548 _dead_bit_map->mark(addr); // mark the dead object
8549 }
8550 }
8551 // Could be 0, if the block size could not be computed without stalling.
8552 return res;
8553 }
8554
8555 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8556
8557 switch (phase) {
8558 case CMSCollector::InitialMarking:
8559 initialize(true /* fullGC */ ,
8560 cause /* cause of the GC */,
8561 true /* recordGCBeginTime */,
8562 true /* recordPreGCUsage */,
8563 false /* recordPeakUsage */,
8564 false /* recordPostGCusage */,
8565 true /* recordAccumulatedGCTime */,
8566 false /* recordGCEndTime */,
8567 false /* countCollection */ );
8568 break;
8569
8570 case CMSCollector::FinalMarking:
8571 initialize(true /* fullGC */ ,
8572 cause /* cause of the GC */,
8573 false /* recordGCBeginTime */,
8574 false /* recordPreGCUsage */,
8575 false /* recordPeakUsage */,
8576 false /* recordPostGCusage */,
8577 true /* recordAccumulatedGCTime */,
8578 false /* recordGCEndTime */,
8579 false /* countCollection */ );
8580 break;
8581
8582 case CMSCollector::Sweeping:
8583 initialize(true /* fullGC */ ,
8584 cause /* cause of the GC */,
8585 false /* recordGCBeginTime */,
8586 false /* recordPreGCUsage */,
8587 true /* recordPeakUsage */,
8588 true /* recordPostGCusage */,
8589 false /* recordAccumulatedGCTime */,
8590 true /* recordGCEndTime */,
8591 true /* countCollection */ );
8592 break;
8593
8594 default:
8595 ShouldNotReachHere();
8596 }
8597 }