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