1 /*
2 * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc/cms/cmsCollectorPolicy.hpp"
31 #include "gc/cms/cmsOopClosures.inline.hpp"
32 #include "gc/cms/compactibleFreeListSpace.hpp"
33 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
34 #include "gc/cms/concurrentMarkSweepThread.hpp"
35 #include "gc/cms/parNewGeneration.hpp"
36 #include "gc/cms/vmCMSOperations.hpp"
37 #include "gc/serial/genMarkSweep.hpp"
38 #include "gc/serial/tenuredGeneration.hpp"
39 #include "gc/shared/adaptiveSizePolicy.hpp"
40 #include "gc/shared/cardGeneration.inline.hpp"
41 #include "gc/shared/cardTableRS.hpp"
42 #include "gc/shared/collectedHeap.inline.hpp"
43 #include "gc/shared/collectorCounters.hpp"
44 #include "gc/shared/collectorPolicy.hpp"
45 #include "gc/shared/gcLocker.inline.hpp"
46 #include "gc/shared/gcPolicyCounters.hpp"
47 #include "gc/shared/gcTimer.hpp"
48 #include "gc/shared/gcTrace.hpp"
49 #include "gc/shared/gcTraceTime.hpp"
50 #include "gc/shared/genCollectedHeap.hpp"
51 #include "gc/shared/genOopClosures.inline.hpp"
52 #include "gc/shared/isGCActiveMark.hpp"
53 #include "gc/shared/referencePolicy.hpp"
54 #include "gc/shared/strongRootsScope.hpp"
55 #include "gc/shared/taskqueue.inline.hpp"
56 #include "memory/allocation.hpp"
57 #include "memory/iterator.inline.hpp"
58 #include "memory/padded.hpp"
59 #include "memory/resourceArea.hpp"
60 #include "oops/oop.inline.hpp"
61 #include "prims/jvmtiExport.hpp"
62 #include "runtime/atomic.inline.hpp"
63 #include "runtime/globals_extension.hpp"
64 #include "runtime/handles.inline.hpp"
65 #include "runtime/java.hpp"
66 #include "runtime/orderAccess.inline.hpp"
67 #include "runtime/vmThread.hpp"
68 #include "services/memoryService.hpp"
69 #include "services/runtimeService.hpp"
70 #include "utilities/stack.inline.hpp"
71
72 // statics
73 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
74 bool CMSCollector::_full_gc_requested = false;
75 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
76
77 //////////////////////////////////////////////////////////////////
78 // In support of CMS/VM thread synchronization
79 //////////////////////////////////////////////////////////////////
80 // We split use of the CGC_lock into 2 "levels".
81 // The low-level locking is of the usual CGC_lock monitor. We introduce
82 // a higher level "token" (hereafter "CMS token") built on top of the
83 // low level monitor (hereafter "CGC lock").
84 // The token-passing protocol gives priority to the VM thread. The
85 // CMS-lock doesn't provide any fairness guarantees, but clients
86 // should ensure that it is only held for very short, bounded
87 // durations.
88 //
89 // When either of the CMS thread or the VM thread is involved in
90 // collection operations during which it does not want the other
91 // thread to interfere, it obtains the CMS token.
92 //
93 // If either thread tries to get the token while the other has
94 // it, that thread waits. However, if the VM thread and CMS thread
95 // both want the token, then the VM thread gets priority while the
96 // CMS thread waits. This ensures, for instance, that the "concurrent"
97 // phases of the CMS thread's work do not block out the VM thread
98 // for long periods of time as the CMS thread continues to hog
99 // the token. (See bug 4616232).
100 //
101 // The baton-passing functions are, however, controlled by the
102 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
103 // and here the low-level CMS lock, not the high level token,
104 // ensures mutual exclusion.
105 //
106 // Two important conditions that we have to satisfy:
107 // 1. if a thread does a low-level wait on the CMS lock, then it
108 // relinquishes the CMS token if it were holding that token
109 // when it acquired the low-level CMS lock.
110 // 2. any low-level notifications on the low-level lock
111 // should only be sent when a thread has relinquished the token.
112 //
113 // In the absence of either property, we'd have potential deadlock.
114 //
115 // We protect each of the CMS (concurrent and sequential) phases
116 // with the CMS _token_, not the CMS _lock_.
117 //
118 // The only code protected by CMS lock is the token acquisition code
119 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
120 // baton-passing code.
121 //
122 // Unfortunately, i couldn't come up with a good abstraction to factor and
123 // hide the naked CGC_lock manipulation in the baton-passing code
124 // further below. That's something we should try to do. Also, the proof
125 // of correctness of this 2-level locking scheme is far from obvious,
126 // and potentially quite slippery. We have an uneasy suspicion, for instance,
127 // that there may be a theoretical possibility of delay/starvation in the
128 // low-level lock/wait/notify scheme used for the baton-passing because of
129 // potential interference with the priority scheme embodied in the
130 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
131 // invocation further below and marked with "XXX 20011219YSR".
132 // Indeed, as we note elsewhere, this may become yet more slippery
133 // in the presence of multiple CMS and/or multiple VM threads. XXX
134
135 class CMSTokenSync: public StackObj {
136 private:
137 bool _is_cms_thread;
138 public:
139 CMSTokenSync(bool is_cms_thread):
140 _is_cms_thread(is_cms_thread) {
141 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
142 "Incorrect argument to constructor");
143 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
144 }
145
146 ~CMSTokenSync() {
147 assert(_is_cms_thread ?
148 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
149 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
150 "Incorrect state");
151 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
152 }
153 };
154
155 // Convenience class that does a CMSTokenSync, and then acquires
156 // upto three locks.
157 class CMSTokenSyncWithLocks: public CMSTokenSync {
158 private:
159 // Note: locks are acquired in textual declaration order
160 // and released in the opposite order
161 MutexLockerEx _locker1, _locker2, _locker3;
162 public:
163 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
164 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
165 CMSTokenSync(is_cms_thread),
166 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
167 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
168 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
169 { }
170 };
171
172
173 //////////////////////////////////////////////////////////////////
174 // Concurrent Mark-Sweep Generation /////////////////////////////
175 //////////////////////////////////////////////////////////////////
176
177 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
178
179 // This struct contains per-thread things necessary to support parallel
180 // young-gen collection.
181 class CMSParGCThreadState: public CHeapObj<mtGC> {
182 public:
183 CFLS_LAB lab;
184 PromotionInfo promo;
185
186 // Constructor.
187 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
188 promo.setSpace(cfls);
189 }
190 };
191
192 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
193 ReservedSpace rs, size_t initial_byte_size,
194 CardTableRS* ct, bool use_adaptive_freelists,
195 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
196 CardGeneration(rs, initial_byte_size, ct),
197 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
198 _did_compact(false)
199 {
200 HeapWord* bottom = (HeapWord*) _virtual_space.low();
201 HeapWord* end = (HeapWord*) _virtual_space.high();
202
203 _direct_allocated_words = 0;
204 NOT_PRODUCT(
205 _numObjectsPromoted = 0;
206 _numWordsPromoted = 0;
207 _numObjectsAllocated = 0;
208 _numWordsAllocated = 0;
209 )
210
211 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
212 use_adaptive_freelists,
213 dictionaryChoice);
214 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
215 _cmsSpace->_old_gen = this;
216
217 _gc_stats = new CMSGCStats();
218
219 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
220 // offsets match. The ability to tell free chunks from objects
221 // depends on this property.
222 debug_only(
223 FreeChunk* junk = NULL;
224 assert(UseCompressedClassPointers ||
225 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
226 "Offset of FreeChunk::_prev within FreeChunk must match"
227 " that of OopDesc::_klass within OopDesc");
228 )
229
230 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
231 for (uint i = 0; i < ParallelGCThreads; i++) {
232 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
233 }
234
235 _incremental_collection_failed = false;
236 // The "dilatation_factor" is the expansion that can occur on
237 // account of the fact that the minimum object size in the CMS
238 // generation may be larger than that in, say, a contiguous young
239 // generation.
240 // Ideally, in the calculation below, we'd compute the dilatation
241 // factor as: MinChunkSize/(promoting_gen's min object size)
242 // Since we do not have such a general query interface for the
243 // promoting generation, we'll instead just use the minimum
244 // object size (which today is a header's worth of space);
245 // note that all arithmetic is in units of HeapWords.
246 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
247 assert(_dilatation_factor >= 1.0, "from previous assert");
248 }
249
250
251 // The field "_initiating_occupancy" represents the occupancy percentage
252 // at which we trigger a new collection cycle. Unless explicitly specified
253 // via CMSInitiatingOccupancyFraction (argument "io" below), it
254 // is calculated by:
255 //
256 // Let "f" be MinHeapFreeRatio in
257 //
258 // _initiating_occupancy = 100-f +
259 // f * (CMSTriggerRatio/100)
260 // where CMSTriggerRatio is the argument "tr" below.
261 //
262 // That is, if we assume the heap is at its desired maximum occupancy at the
263 // end of a collection, we let CMSTriggerRatio of the (purported) free
264 // space be allocated before initiating a new collection cycle.
265 //
266 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
267 assert(io <= 100 && tr <= 100, "Check the arguments");
268 if (io >= 0) {
269 _initiating_occupancy = (double)io / 100.0;
270 } else {
271 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
272 (double)(tr * MinHeapFreeRatio) / 100.0)
273 / 100.0;
274 }
275 }
276
277 void ConcurrentMarkSweepGeneration::ref_processor_init() {
278 assert(collector() != NULL, "no collector");
279 collector()->ref_processor_init();
280 }
281
282 void CMSCollector::ref_processor_init() {
283 if (_ref_processor == NULL) {
284 // Allocate and initialize a reference processor
285 _ref_processor =
286 new ReferenceProcessor(_span, // span
287 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
288 ParallelGCThreads, // mt processing degree
289 _cmsGen->refs_discovery_is_mt(), // mt discovery
290 MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
291 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
292 &_is_alive_closure); // closure for liveness info
293 // Initialize the _ref_processor field of CMSGen
294 _cmsGen->set_ref_processor(_ref_processor);
295
296 }
297 }
298
299 AdaptiveSizePolicy* CMSCollector::size_policy() {
300 GenCollectedHeap* gch = GenCollectedHeap::heap();
301 return gch->gen_policy()->size_policy();
302 }
303
304 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
305
306 const char* gen_name = "old";
307 GenCollectorPolicy* gcp = GenCollectedHeap::heap()->gen_policy();
308 // Generation Counters - generation 1, 1 subspace
309 _gen_counters = new GenerationCounters(gen_name, 1, 1,
310 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
311
312 _space_counters = new GSpaceCounters(gen_name, 0,
313 _virtual_space.reserved_size(),
314 this, _gen_counters);
315 }
316
317 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
318 _cms_gen(cms_gen)
319 {
320 assert(alpha <= 100, "bad value");
321 _saved_alpha = alpha;
322
323 // Initialize the alphas to the bootstrap value of 100.
324 _gc0_alpha = _cms_alpha = 100;
325
326 _cms_begin_time.update();
327 _cms_end_time.update();
328
329 _gc0_duration = 0.0;
330 _gc0_period = 0.0;
331 _gc0_promoted = 0;
332
333 _cms_duration = 0.0;
334 _cms_period = 0.0;
335 _cms_allocated = 0;
336
337 _cms_used_at_gc0_begin = 0;
338 _cms_used_at_gc0_end = 0;
339 _allow_duty_cycle_reduction = false;
340 _valid_bits = 0;
341 }
342
343 double CMSStats::cms_free_adjustment_factor(size_t free) const {
344 // TBD: CR 6909490
345 return 1.0;
346 }
347
348 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
349 }
350
351 // If promotion failure handling is on use
352 // the padded average size of the promotion for each
353 // young generation collection.
354 double CMSStats::time_until_cms_gen_full() const {
355 size_t cms_free = _cms_gen->cmsSpace()->free();
356 GenCollectedHeap* gch = GenCollectedHeap::heap();
357 size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
358 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
359 if (cms_free > expected_promotion) {
360 // Start a cms collection if there isn't enough space to promote
361 // for the next young collection. Use the padded average as
362 // a safety factor.
363 cms_free -= expected_promotion;
364
365 // Adjust by the safety factor.
366 double cms_free_dbl = (double)cms_free;
367 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
368 // Apply a further correction factor which tries to adjust
369 // for recent occurance of concurrent mode failures.
370 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
371 cms_free_dbl = cms_free_dbl * cms_adjustment;
372
373 if (PrintGCDetails && Verbose) {
374 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
375 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
376 cms_free, expected_promotion);
377 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
378 cms_free_dbl, cms_consumption_rate() + 1.0);
379 }
380 // Add 1 in case the consumption rate goes to zero.
381 return cms_free_dbl / (cms_consumption_rate() + 1.0);
382 }
383 return 0.0;
384 }
385
386 // Compare the duration of the cms collection to the
387 // time remaining before the cms generation is empty.
388 // Note that the time from the start of the cms collection
389 // to the start of the cms sweep (less than the total
390 // duration of the cms collection) can be used. This
391 // has been tried and some applications experienced
392 // promotion failures early in execution. This was
393 // possibly because the averages were not accurate
394 // enough at the beginning.
395 double CMSStats::time_until_cms_start() const {
396 // We add "gc0_period" to the "work" calculation
397 // below because this query is done (mostly) at the
398 // end of a scavenge, so we need to conservatively
399 // account for that much possible delay
400 // in the query so as to avoid concurrent mode failures
401 // due to starting the collection just a wee bit too
402 // late.
403 double work = cms_duration() + gc0_period();
404 double deadline = time_until_cms_gen_full();
405 // If a concurrent mode failure occurred recently, we want to be
406 // more conservative and halve our expected time_until_cms_gen_full()
407 if (work > deadline) {
408 if (Verbose && PrintGCDetails) {
409 gclog_or_tty->print(
410 " CMSCollector: collect because of anticipated promotion "
411 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
412 gc0_period(), time_until_cms_gen_full());
413 }
414 return 0.0;
415 }
416 return work - deadline;
417 }
418
419 #ifndef PRODUCT
420 void CMSStats::print_on(outputStream *st) const {
421 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
422 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
423 gc0_duration(), gc0_period(), gc0_promoted());
424 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
425 cms_duration(), cms_period(), cms_allocated());
426 st->print(",cms_since_beg=%g,cms_since_end=%g",
427 cms_time_since_begin(), cms_time_since_end());
428 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
429 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
430
431 if (valid()) {
432 st->print(",promo_rate=%g,cms_alloc_rate=%g",
433 promotion_rate(), cms_allocation_rate());
434 st->print(",cms_consumption_rate=%g,time_until_full=%g",
435 cms_consumption_rate(), time_until_cms_gen_full());
436 }
437 st->print(" ");
438 }
439 #endif // #ifndef PRODUCT
440
441 CMSCollector::CollectorState CMSCollector::_collectorState =
442 CMSCollector::Idling;
443 bool CMSCollector::_foregroundGCIsActive = false;
444 bool CMSCollector::_foregroundGCShouldWait = false;
445
446 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
447 CardTableRS* ct,
448 ConcurrentMarkSweepPolicy* cp):
449 _cmsGen(cmsGen),
450 _ct(ct),
451 _ref_processor(NULL), // will be set later
452 _conc_workers(NULL), // may be set later
453 _abort_preclean(false),
454 _start_sampling(false),
455 _between_prologue_and_epilogue(false),
456 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
457 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
458 -1 /* lock-free */, "No_lock" /* dummy */),
459 _modUnionClosurePar(&_modUnionTable),
460 // Adjust my span to cover old (cms) gen
461 _span(cmsGen->reserved()),
462 // Construct the is_alive_closure with _span & markBitMap
463 _is_alive_closure(_span, &_markBitMap),
464 _restart_addr(NULL),
465 _overflow_list(NULL),
466 _stats(cmsGen),
467 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
468 //verify that this lock should be acquired with safepoint check.
469 Monitor::_safepoint_check_sometimes)),
470 _eden_chunk_array(NULL), // may be set in ctor body
471 _eden_chunk_capacity(0), // -- ditto --
472 _eden_chunk_index(0), // -- ditto --
473 _survivor_plab_array(NULL), // -- ditto --
474 _survivor_chunk_array(NULL), // -- ditto --
475 _survivor_chunk_capacity(0), // -- ditto --
476 _survivor_chunk_index(0), // -- ditto --
477 _ser_pmc_preclean_ovflw(0),
478 _ser_kac_preclean_ovflw(0),
479 _ser_pmc_remark_ovflw(0),
480 _par_pmc_remark_ovflw(0),
481 _ser_kac_ovflw(0),
482 _par_kac_ovflw(0),
483 #ifndef PRODUCT
484 _num_par_pushes(0),
485 #endif
486 _collection_count_start(0),
487 _verifying(false),
488 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
489 _completed_initialization(false),
490 _collector_policy(cp),
491 _should_unload_classes(CMSClassUnloadingEnabled),
492 _concurrent_cycles_since_last_unload(0),
493 _roots_scanning_options(GenCollectedHeap::SO_None),
494 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
495 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
496 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
497 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
498 _cms_start_registered(false)
499 {
500 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
501 ExplicitGCInvokesConcurrent = true;
502 }
503 // Now expand the span and allocate the collection support structures
504 // (MUT, marking bit map etc.) to cover both generations subject to
505 // collection.
506
507 // For use by dirty card to oop closures.
508 _cmsGen->cmsSpace()->set_collector(this);
509
510 // Allocate MUT and marking bit map
511 {
512 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
513 if (!_markBitMap.allocate(_span)) {
514 warning("Failed to allocate CMS Bit Map");
515 return;
516 }
517 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
518 }
519 {
520 _modUnionTable.allocate(_span);
521 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
522 }
523
524 if (!_markStack.allocate(MarkStackSize)) {
525 warning("Failed to allocate CMS Marking Stack");
526 return;
527 }
528
529 // Support for multi-threaded concurrent phases
530 if (CMSConcurrentMTEnabled) {
531 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
532 // just for now
533 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
534 }
535 if (ConcGCThreads > 1) {
536 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
537 ConcGCThreads, true);
538 if (_conc_workers == NULL) {
539 warning("GC/CMS: _conc_workers allocation failure: "
540 "forcing -CMSConcurrentMTEnabled");
541 CMSConcurrentMTEnabled = false;
542 } else {
543 _conc_workers->initialize_workers();
544 }
545 } else {
546 CMSConcurrentMTEnabled = false;
547 }
548 }
549 if (!CMSConcurrentMTEnabled) {
550 ConcGCThreads = 0;
551 } else {
552 // Turn off CMSCleanOnEnter optimization temporarily for
553 // the MT case where it's not fixed yet; see 6178663.
554 CMSCleanOnEnter = false;
555 }
556 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
557 "Inconsistency");
558
559 // Parallel task queues; these are shared for the
560 // concurrent and stop-world phases of CMS, but
561 // are not shared with parallel scavenge (ParNew).
562 {
563 uint i;
564 uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
565
566 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
567 || ParallelRefProcEnabled)
568 && num_queues > 0) {
569 _task_queues = new OopTaskQueueSet(num_queues);
570 if (_task_queues == NULL) {
571 warning("task_queues allocation failure.");
572 return;
573 }
574 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
575 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
576 for (i = 0; i < num_queues; i++) {
577 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
578 if (q == NULL) {
579 warning("work_queue allocation failure.");
580 return;
581 }
582 _task_queues->register_queue(i, q);
583 }
584 for (i = 0; i < num_queues; i++) {
585 _task_queues->queue(i)->initialize();
586 _hash_seed[i] = 17; // copied from ParNew
587 }
588 }
589 }
590
591 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
592
593 // Clip CMSBootstrapOccupancy between 0 and 100.
594 _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
595
596 // Now tell CMS generations the identity of their collector
597 ConcurrentMarkSweepGeneration::set_collector(this);
598
599 // Create & start a CMS thread for this CMS collector
600 _cmsThread = ConcurrentMarkSweepThread::start(this);
601 assert(cmsThread() != NULL, "CMS Thread should have been created");
602 assert(cmsThread()->collector() == this,
603 "CMS Thread should refer to this gen");
604 assert(CGC_lock != NULL, "Where's the CGC_lock?");
605
606 // Support for parallelizing young gen rescan
607 GenCollectedHeap* gch = GenCollectedHeap::heap();
608 assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
609 _young_gen = (ParNewGeneration*)gch->young_gen();
610 if (gch->supports_inline_contig_alloc()) {
611 _top_addr = gch->top_addr();
612 _end_addr = gch->end_addr();
613 assert(_young_gen != NULL, "no _young_gen");
614 _eden_chunk_index = 0;
615 _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
616 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
617 }
618
619 // Support for parallelizing survivor space rescan
620 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
621 const size_t max_plab_samples =
622 _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
623
624 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
625 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
626 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
627 _survivor_chunk_capacity = max_plab_samples;
628 for (uint i = 0; i < ParallelGCThreads; i++) {
629 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
630 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
631 assert(cur->end() == 0, "Should be 0");
632 assert(cur->array() == vec, "Should be vec");
633 assert(cur->capacity() == max_plab_samples, "Error");
634 }
635 }
636
637 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
638 _gc_counters = new CollectorCounters("CMS", 1);
639 _completed_initialization = true;
640 _inter_sweep_timer.start(); // start of time
641 }
642
643 const char* ConcurrentMarkSweepGeneration::name() const {
644 return "concurrent mark-sweep generation";
645 }
646 void ConcurrentMarkSweepGeneration::update_counters() {
647 if (UsePerfData) {
648 _space_counters->update_all();
649 _gen_counters->update_all();
650 }
651 }
652
653 // this is an optimized version of update_counters(). it takes the
654 // used value as a parameter rather than computing it.
655 //
656 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
657 if (UsePerfData) {
658 _space_counters->update_used(used);
659 _space_counters->update_capacity();
660 _gen_counters->update_all();
661 }
662 }
663
664 void ConcurrentMarkSweepGeneration::print() const {
665 Generation::print();
666 cmsSpace()->print();
667 }
668
669 #ifndef PRODUCT
670 void ConcurrentMarkSweepGeneration::print_statistics() {
671 cmsSpace()->printFLCensus(0);
672 }
673 #endif
674
675 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
676 GenCollectedHeap* gch = GenCollectedHeap::heap();
677 if (PrintGCDetails) {
678 // I didn't want to change the logging when removing the level concept,
679 // but I guess this logging could say "old" or something instead of "1".
680 assert(gch->is_old_gen(this),
681 "The CMS generation should be the old generation");
682 uint level = 1;
683 if (Verbose) {
684 gclog_or_tty->print("[%u %s-%s: " SIZE_FORMAT "(" SIZE_FORMAT ")]",
685 level, short_name(), s, used(), capacity());
686 } else {
687 gclog_or_tty->print("[%u %s-%s: " SIZE_FORMAT "K(" SIZE_FORMAT "K)]",
688 level, short_name(), s, used() / K, capacity() / K);
689 }
690 }
691 if (Verbose) {
692 gclog_or_tty->print(" " SIZE_FORMAT "(" SIZE_FORMAT ")",
693 gch->used(), gch->capacity());
694 } else {
695 gclog_or_tty->print(" " SIZE_FORMAT "K(" SIZE_FORMAT "K)",
696 gch->used() / K, gch->capacity() / K);
697 }
698 }
699
700 size_t
701 ConcurrentMarkSweepGeneration::contiguous_available() const {
702 // dld proposes an improvement in precision here. If the committed
703 // part of the space ends in a free block we should add that to
704 // uncommitted size in the calculation below. Will make this
705 // change later, staying with the approximation below for the
706 // time being. -- ysr.
707 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
708 }
709
710 size_t
711 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
712 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
713 }
714
715 size_t ConcurrentMarkSweepGeneration::max_available() const {
716 return free() + _virtual_space.uncommitted_size();
717 }
718
719 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
720 size_t available = max_available();
721 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
722 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
723 if (Verbose && PrintGCDetails) {
724 gclog_or_tty->print_cr(
725 "CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "),"
726 "max_promo(" SIZE_FORMAT ")",
727 res? "":" not", available, res? ">=":"<",
728 av_promo, max_promotion_in_bytes);
729 }
730 return res;
731 }
732
733 // At a promotion failure dump information on block layout in heap
734 // (cms old generation).
735 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
736 if (CMSDumpAtPromotionFailure) {
737 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
738 }
739 }
740
741 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
742 // Clear the promotion information. These pointers can be adjusted
743 // along with all the other pointers into the heap but
744 // compaction is expected to be a rare event with
745 // a heap using cms so don't do it without seeing the need.
746 for (uint i = 0; i < ParallelGCThreads; i++) {
747 _par_gc_thread_states[i]->promo.reset();
748 }
749 }
750
751 void ConcurrentMarkSweepGeneration::compute_new_size() {
752 assert_locked_or_safepoint(Heap_lock);
753
754 // If incremental collection failed, we just want to expand
755 // to the limit.
756 if (incremental_collection_failed()) {
757 clear_incremental_collection_failed();
758 grow_to_reserved();
759 return;
760 }
761
762 // The heap has been compacted but not reset yet.
763 // Any metric such as free() or used() will be incorrect.
764
765 CardGeneration::compute_new_size();
766
767 // Reset again after a possible resizing
768 if (did_compact()) {
769 cmsSpace()->reset_after_compaction();
770 }
771 }
772
773 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
774 assert_locked_or_safepoint(Heap_lock);
775
776 // If incremental collection failed, we just want to expand
777 // to the limit.
778 if (incremental_collection_failed()) {
779 clear_incremental_collection_failed();
780 grow_to_reserved();
781 return;
782 }
783
784 double free_percentage = ((double) free()) / capacity();
785 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
786 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
787
788 // compute expansion delta needed for reaching desired free percentage
789 if (free_percentage < desired_free_percentage) {
790 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
791 assert(desired_capacity >= capacity(), "invalid expansion size");
792 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
793 if (PrintGCDetails && Verbose) {
794 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
795 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
796 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
797 gclog_or_tty->print_cr(" Desired free fraction %f", desired_free_percentage);
798 gclog_or_tty->print_cr(" Maximum free fraction %f", maximum_free_percentage);
799 gclog_or_tty->print_cr(" Capacity " SIZE_FORMAT, capacity() / 1000);
800 gclog_or_tty->print_cr(" Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
801 GenCollectedHeap* gch = GenCollectedHeap::heap();
802 assert(gch->is_old_gen(this), "The CMS generation should always be the old generation");
803 size_t young_size = gch->young_gen()->capacity();
804 gclog_or_tty->print_cr(" Young gen size " SIZE_FORMAT, young_size / 1000);
805 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
806 gclog_or_tty->print_cr(" contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
807 gclog_or_tty->print_cr(" Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
808 }
809 // safe if expansion fails
810 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
811 if (PrintGCDetails && Verbose) {
812 gclog_or_tty->print_cr(" Expanded free fraction %f", ((double) free()) / capacity());
813 }
814 } else {
815 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
816 assert(desired_capacity <= capacity(), "invalid expansion size");
817 size_t shrink_bytes = capacity() - desired_capacity;
818 // Don't shrink unless the delta is greater than the minimum shrink we want
819 if (shrink_bytes >= MinHeapDeltaBytes) {
820 shrink_free_list_by(shrink_bytes);
821 }
822 }
823 }
824
825 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
826 return cmsSpace()->freelistLock();
827 }
828
829 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
830 CMSSynchronousYieldRequest yr;
831 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
832 return have_lock_and_allocate(size, tlab);
833 }
834
835 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
836 bool tlab /* ignored */) {
837 assert_lock_strong(freelistLock());
838 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
839 HeapWord* res = cmsSpace()->allocate(adjustedSize);
840 // Allocate the object live (grey) if the background collector has
841 // started marking. This is necessary because the marker may
842 // have passed this address and consequently this object will
843 // not otherwise be greyed and would be incorrectly swept up.
844 // Note that if this object contains references, the writing
845 // of those references will dirty the card containing this object
846 // allowing the object to be blackened (and its references scanned)
847 // either during a preclean phase or at the final checkpoint.
848 if (res != NULL) {
849 // We may block here with an uninitialized object with
850 // its mark-bit or P-bits not yet set. Such objects need
851 // to be safely navigable by block_start().
852 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
853 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
854 collector()->direct_allocated(res, adjustedSize);
855 _direct_allocated_words += adjustedSize;
856 // allocation counters
857 NOT_PRODUCT(
858 _numObjectsAllocated++;
859 _numWordsAllocated += (int)adjustedSize;
860 )
861 }
862 return res;
863 }
864
865 // In the case of direct allocation by mutators in a generation that
866 // is being concurrently collected, the object must be allocated
867 // live (grey) if the background collector has started marking.
868 // This is necessary because the marker may
869 // have passed this address and consequently this object will
870 // not otherwise be greyed and would be incorrectly swept up.
871 // Note that if this object contains references, the writing
872 // of those references will dirty the card containing this object
873 // allowing the object to be blackened (and its references scanned)
874 // either during a preclean phase or at the final checkpoint.
875 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
876 assert(_markBitMap.covers(start, size), "Out of bounds");
877 if (_collectorState >= Marking) {
878 MutexLockerEx y(_markBitMap.lock(),
879 Mutex::_no_safepoint_check_flag);
880 // [see comments preceding SweepClosure::do_blk() below for details]
881 //
882 // Can the P-bits be deleted now? JJJ
883 //
884 // 1. need to mark the object as live so it isn't collected
885 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
886 // 3. need to mark the end of the object so marking, precleaning or sweeping
887 // can skip over uninitialized or unparsable objects. An allocated
888 // object is considered uninitialized for our purposes as long as
889 // its klass word is NULL. All old gen objects are parsable
890 // as soon as they are initialized.)
891 _markBitMap.mark(start); // object is live
892 _markBitMap.mark(start + 1); // object is potentially uninitialized?
893 _markBitMap.mark(start + size - 1);
894 // mark end of object
895 }
896 // check that oop looks uninitialized
897 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
898 }
899
900 void CMSCollector::promoted(bool par, HeapWord* start,
901 bool is_obj_array, size_t obj_size) {
902 assert(_markBitMap.covers(start), "Out of bounds");
903 // See comment in direct_allocated() about when objects should
904 // be allocated live.
905 if (_collectorState >= Marking) {
906 // we already hold the marking bit map lock, taken in
907 // the prologue
908 if (par) {
909 _markBitMap.par_mark(start);
910 } else {
911 _markBitMap.mark(start);
912 }
913 // We don't need to mark the object as uninitialized (as
914 // in direct_allocated above) because this is being done with the
915 // world stopped and the object will be initialized by the
916 // time the marking, precleaning or sweeping get to look at it.
917 // But see the code for copying objects into the CMS generation,
918 // where we need to ensure that concurrent readers of the
919 // block offset table are able to safely navigate a block that
920 // is in flux from being free to being allocated (and in
921 // transition while being copied into) and subsequently
922 // becoming a bona-fide object when the copy/promotion is complete.
923 assert(SafepointSynchronize::is_at_safepoint(),
924 "expect promotion only at safepoints");
925
926 if (_collectorState < Sweeping) {
927 // Mark the appropriate cards in the modUnionTable, so that
928 // this object gets scanned before the sweep. If this is
929 // not done, CMS generation references in the object might
930 // not get marked.
931 // For the case of arrays, which are otherwise precisely
932 // marked, we need to dirty the entire array, not just its head.
933 if (is_obj_array) {
934 // The [par_]mark_range() method expects mr.end() below to
935 // be aligned to the granularity of a bit's representation
936 // in the heap. In the case of the MUT below, that's a
937 // card size.
938 MemRegion mr(start,
939 (HeapWord*)round_to((intptr_t)(start + obj_size),
940 CardTableModRefBS::card_size /* bytes */));
941 if (par) {
942 _modUnionTable.par_mark_range(mr);
943 } else {
944 _modUnionTable.mark_range(mr);
945 }
946 } else { // not an obj array; we can just mark the head
947 if (par) {
948 _modUnionTable.par_mark(start);
949 } else {
950 _modUnionTable.mark(start);
951 }
952 }
953 }
954 }
955 }
956
957 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
958 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
959 // allocate, copy and if necessary update promoinfo --
960 // delegate to underlying space.
961 assert_lock_strong(freelistLock());
962
963 #ifndef PRODUCT
964 if (GenCollectedHeap::heap()->promotion_should_fail()) {
965 return NULL;
966 }
967 #endif // #ifndef PRODUCT
968
969 oop res = _cmsSpace->promote(obj, obj_size);
970 if (res == NULL) {
971 // expand and retry
972 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
973 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
974 // Since this is the old generation, we don't try to promote
975 // into a more senior generation.
976 res = _cmsSpace->promote(obj, obj_size);
977 }
978 if (res != NULL) {
979 // See comment in allocate() about when objects should
980 // be allocated live.
981 assert(obj->is_oop(), "Will dereference klass pointer below");
982 collector()->promoted(false, // Not parallel
983 (HeapWord*)res, obj->is_objArray(), obj_size);
984 // promotion counters
985 NOT_PRODUCT(
986 _numObjectsPromoted++;
987 _numWordsPromoted +=
988 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
989 )
990 }
991 return res;
992 }
993
994
995 // IMPORTANT: Notes on object size recognition in CMS.
996 // ---------------------------------------------------
997 // A block of storage in the CMS generation is always in
998 // one of three states. A free block (FREE), an allocated
999 // object (OBJECT) whose size() method reports the correct size,
1000 // and an intermediate state (TRANSIENT) in which its size cannot
1001 // be accurately determined.
1002 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1003 // -----------------------------------------------------
1004 // FREE: klass_word & 1 == 1; mark_word holds block size
1005 //
1006 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1007 // obj->size() computes correct size
1008 //
1009 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1010 //
1011 // STATE IDENTIFICATION: (64 bit+COOPS)
1012 // ------------------------------------
1013 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1014 //
1015 // OBJECT: klass_word installed; klass_word != 0;
1016 // obj->size() computes correct size
1017 //
1018 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1019 //
1020 //
1021 // STATE TRANSITION DIAGRAM
1022 //
1023 // mut / parnew mut / parnew
1024 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1025 // ^ |
1026 // |------------------------ DEAD <------------------------------------|
1027 // sweep mut
1028 //
1029 // While a block is in TRANSIENT state its size cannot be determined
1030 // so readers will either need to come back later or stall until
1031 // the size can be determined. Note that for the case of direct
1032 // allocation, P-bits, when available, may be used to determine the
1033 // size of an object that may not yet have been initialized.
1034
1035 // Things to support parallel young-gen collection.
1036 oop
1037 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1038 oop old, markOop m,
1039 size_t word_sz) {
1040 #ifndef PRODUCT
1041 if (GenCollectedHeap::heap()->promotion_should_fail()) {
1042 return NULL;
1043 }
1044 #endif // #ifndef PRODUCT
1045
1046 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1047 PromotionInfo* promoInfo = &ps->promo;
1048 // if we are tracking promotions, then first ensure space for
1049 // promotion (including spooling space for saving header if necessary).
1050 // then allocate and copy, then track promoted info if needed.
1051 // When tracking (see PromotionInfo::track()), the mark word may
1052 // be displaced and in this case restoration of the mark word
1053 // occurs in the (oop_since_save_marks_)iterate phase.
1054 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1055 // Out of space for allocating spooling buffers;
1056 // try expanding and allocating spooling buffers.
1057 if (!expand_and_ensure_spooling_space(promoInfo)) {
1058 return NULL;
1059 }
1060 }
1061 assert(promoInfo->has_spooling_space(), "Control point invariant");
1062 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1063 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1064 if (obj_ptr == NULL) {
1065 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1066 if (obj_ptr == NULL) {
1067 return NULL;
1068 }
1069 }
1070 oop obj = oop(obj_ptr);
1071 OrderAccess::storestore();
1072 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1073 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1074 // IMPORTANT: See note on object initialization for CMS above.
1075 // Otherwise, copy the object. Here we must be careful to insert the
1076 // klass pointer last, since this marks the block as an allocated object.
1077 // Except with compressed oops it's the mark word.
1078 HeapWord* old_ptr = (HeapWord*)old;
1079 // Restore the mark word copied above.
1080 obj->set_mark(m);
1081 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1082 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1083 OrderAccess::storestore();
1084
1085 if (UseCompressedClassPointers) {
1086 // Copy gap missed by (aligned) header size calculation below
1087 obj->set_klass_gap(old->klass_gap());
1088 }
1089 if (word_sz > (size_t)oopDesc::header_size()) {
1090 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1091 obj_ptr + oopDesc::header_size(),
1092 word_sz - oopDesc::header_size());
1093 }
1094
1095 // Now we can track the promoted object, if necessary. We take care
1096 // to delay the transition from uninitialized to full object
1097 // (i.e., insertion of klass pointer) until after, so that it
1098 // atomically becomes a promoted object.
1099 if (promoInfo->tracking()) {
1100 promoInfo->track((PromotedObject*)obj, old->klass());
1101 }
1102 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1103 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1104 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1105
1106 // Finally, install the klass pointer (this should be volatile).
1107 OrderAccess::storestore();
1108 obj->set_klass(old->klass());
1109 // We should now be able to calculate the right size for this object
1110 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1111
1112 collector()->promoted(true, // parallel
1113 obj_ptr, old->is_objArray(), word_sz);
1114
1115 NOT_PRODUCT(
1116 Atomic::inc_ptr(&_numObjectsPromoted);
1117 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1118 )
1119
1120 return obj;
1121 }
1122
1123 void
1124 ConcurrentMarkSweepGeneration::
1125 par_promote_alloc_done(int thread_num) {
1126 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1127 ps->lab.retire(thread_num);
1128 }
1129
1130 void
1131 ConcurrentMarkSweepGeneration::
1132 par_oop_since_save_marks_iterate_done(int thread_num) {
1133 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1134 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1135 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1136 }
1137
1138 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1139 size_t size,
1140 bool tlab)
1141 {
1142 // We allow a STW collection only if a full
1143 // collection was requested.
1144 return full || should_allocate(size, tlab); // FIX ME !!!
1145 // This and promotion failure handling are connected at the
1146 // hip and should be fixed by untying them.
1147 }
1148
1149 bool CMSCollector::shouldConcurrentCollect() {
1150 if (_full_gc_requested) {
1151 if (Verbose && PrintGCDetails) {
1152 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1153 " gc request (or gc_locker)");
1154 }
1155 return true;
1156 }
1157
1158 FreelistLocker x(this);
1159 // ------------------------------------------------------------------
1160 // Print out lots of information which affects the initiation of
1161 // a collection.
1162 if (PrintCMSInitiationStatistics && stats().valid()) {
1163 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1164 gclog_or_tty->stamp();
1165 gclog_or_tty->cr();
1166 stats().print_on(gclog_or_tty);
1167 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1168 stats().time_until_cms_gen_full());
1169 gclog_or_tty->print_cr("free=" SIZE_FORMAT, _cmsGen->free());
1170 gclog_or_tty->print_cr("contiguous_available=" SIZE_FORMAT,
1171 _cmsGen->contiguous_available());
1172 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1173 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1174 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1175 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1176 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1177 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1178 gclog_or_tty->print_cr("metadata initialized %d",
1179 MetaspaceGC::should_concurrent_collect());
1180 }
1181 // ------------------------------------------------------------------
1182
1183 // If the estimated time to complete a cms collection (cms_duration())
1184 // is less than the estimated time remaining until the cms generation
1185 // is full, start a collection.
1186 if (!UseCMSInitiatingOccupancyOnly) {
1187 if (stats().valid()) {
1188 if (stats().time_until_cms_start() == 0.0) {
1189 return true;
1190 }
1191 } else {
1192 // We want to conservatively collect somewhat early in order
1193 // to try and "bootstrap" our CMS/promotion statistics;
1194 // this branch will not fire after the first successful CMS
1195 // collection because the stats should then be valid.
1196 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1197 if (Verbose && PrintGCDetails) {
1198 gclog_or_tty->print_cr(
1199 " CMSCollector: collect for bootstrapping statistics:"
1200 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1201 _bootstrap_occupancy);
1202 }
1203 return true;
1204 }
1205 }
1206 }
1207
1208 // Otherwise, we start a collection cycle if
1209 // old gen want a collection cycle started. Each may use
1210 // an appropriate criterion for making this decision.
1211 // XXX We need to make sure that the gen expansion
1212 // criterion dovetails well with this. XXX NEED TO FIX THIS
1213 if (_cmsGen->should_concurrent_collect()) {
1214 if (Verbose && PrintGCDetails) {
1215 gclog_or_tty->print_cr("CMS old gen initiated");
1216 }
1217 return true;
1218 }
1219
1220 // We start a collection if we believe an incremental collection may fail;
1221 // this is not likely to be productive in practice because it's probably too
1222 // late anyway.
1223 GenCollectedHeap* gch = GenCollectedHeap::heap();
1224 assert(gch->collector_policy()->is_generation_policy(),
1225 "You may want to check the correctness of the following");
1226 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1227 if (Verbose && PrintGCDetails) {
1228 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1229 }
1230 return true;
1231 }
1232
1233 if (MetaspaceGC::should_concurrent_collect()) {
1234 if (Verbose && PrintGCDetails) {
1235 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1236 }
1237 return true;
1238 }
1239
1240 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1241 if (CMSTriggerInterval >= 0) {
1242 if (CMSTriggerInterval == 0) {
1243 // Trigger always
1244 return true;
1245 }
1246
1247 // Check the CMS time since begin (we do not check the stats validity
1248 // as we want to be able to trigger the first CMS cycle as well)
1249 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1250 if (Verbose && PrintGCDetails) {
1251 if (stats().valid()) {
1252 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1253 stats().cms_time_since_begin());
1254 } else {
1255 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1256 }
1257 }
1258 return true;
1259 }
1260 }
1261
1262 return false;
1263 }
1264
1265 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1266
1267 // Clear _expansion_cause fields of constituent generations
1268 void CMSCollector::clear_expansion_cause() {
1269 _cmsGen->clear_expansion_cause();
1270 }
1271
1272 // We should be conservative in starting a collection cycle. To
1273 // start too eagerly runs the risk of collecting too often in the
1274 // extreme. To collect too rarely falls back on full collections,
1275 // which works, even if not optimum in terms of concurrent work.
1276 // As a work around for too eagerly collecting, use the flag
1277 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1278 // giving the user an easily understandable way of controlling the
1279 // collections.
1280 // We want to start a new collection cycle if any of the following
1281 // conditions hold:
1282 // . our current occupancy exceeds the configured initiating occupancy
1283 // for this generation, or
1284 // . we recently needed to expand this space and have not, since that
1285 // expansion, done a collection of this generation, or
1286 // . the underlying space believes that it may be a good idea to initiate
1287 // a concurrent collection (this may be based on criteria such as the
1288 // following: the space uses linear allocation and linear allocation is
1289 // going to fail, or there is believed to be excessive fragmentation in
1290 // the generation, etc... or ...
1291 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1292 // the case of the old generation; see CR 6543076):
1293 // we may be approaching a point at which allocation requests may fail because
1294 // we will be out of sufficient free space given allocation rate estimates.]
1295 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1296
1297 assert_lock_strong(freelistLock());
1298 if (occupancy() > initiating_occupancy()) {
1299 if (PrintGCDetails && Verbose) {
1300 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1301 short_name(), occupancy(), initiating_occupancy());
1302 }
1303 return true;
1304 }
1305 if (UseCMSInitiatingOccupancyOnly) {
1306 return false;
1307 }
1308 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1309 if (PrintGCDetails && Verbose) {
1310 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1311 short_name());
1312 }
1313 return true;
1314 }
1315 if (_cmsSpace->should_concurrent_collect()) {
1316 if (PrintGCDetails && Verbose) {
1317 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1318 short_name());
1319 }
1320 return true;
1321 }
1322 return false;
1323 }
1324
1325 void ConcurrentMarkSweepGeneration::collect(bool full,
1326 bool clear_all_soft_refs,
1327 size_t size,
1328 bool tlab)
1329 {
1330 collector()->collect(full, clear_all_soft_refs, size, tlab);
1331 }
1332
1333 void CMSCollector::collect(bool full,
1334 bool clear_all_soft_refs,
1335 size_t size,
1336 bool tlab)
1337 {
1338 // The following "if" branch is present for defensive reasons.
1339 // In the current uses of this interface, it can be replaced with:
1340 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1341 // But I am not placing that assert here to allow future
1342 // generality in invoking this interface.
1343 if (GC_locker::is_active()) {
1344 // A consistency test for GC_locker
1345 assert(GC_locker::needs_gc(), "Should have been set already");
1346 // Skip this foreground collection, instead
1347 // expanding the heap if necessary.
1348 // Need the free list locks for the call to free() in compute_new_size()
1349 compute_new_size();
1350 return;
1351 }
1352 acquire_control_and_collect(full, clear_all_soft_refs);
1353 }
1354
1355 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1356 GenCollectedHeap* gch = GenCollectedHeap::heap();
1357 unsigned int gc_count = gch->total_full_collections();
1358 if (gc_count == full_gc_count) {
1359 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1360 _full_gc_requested = true;
1361 _full_gc_cause = cause;
1362 CGC_lock->notify(); // nudge CMS thread
1363 } else {
1364 assert(gc_count > full_gc_count, "Error: causal loop");
1365 }
1366 }
1367
1368 bool CMSCollector::is_external_interruption() {
1369 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1370 return GCCause::is_user_requested_gc(cause) ||
1371 GCCause::is_serviceability_requested_gc(cause);
1372 }
1373
1374 void CMSCollector::report_concurrent_mode_interruption() {
1375 if (is_external_interruption()) {
1376 if (PrintGCDetails) {
1377 gclog_or_tty->print(" (concurrent mode interrupted)");
1378 }
1379 } else {
1380 if (PrintGCDetails) {
1381 gclog_or_tty->print(" (concurrent mode failure)");
1382 }
1383 _gc_tracer_cm->report_concurrent_mode_failure();
1384 }
1385 }
1386
1387
1388 // The foreground and background collectors need to coordinate in order
1389 // to make sure that they do not mutually interfere with CMS collections.
1390 // When a background collection is active,
1391 // the foreground collector may need to take over (preempt) and
1392 // synchronously complete an ongoing collection. Depending on the
1393 // frequency of the background collections and the heap usage
1394 // of the application, this preemption can be seldom or frequent.
1395 // There are only certain
1396 // points in the background collection that the "collection-baton"
1397 // can be passed to the foreground collector.
1398 //
1399 // The foreground collector will wait for the baton before
1400 // starting any part of the collection. The foreground collector
1401 // will only wait at one location.
1402 //
1403 // The background collector will yield the baton before starting a new
1404 // phase of the collection (e.g., before initial marking, marking from roots,
1405 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1406 // of the loop which switches the phases. The background collector does some
1407 // of the phases (initial mark, final re-mark) with the world stopped.
1408 // Because of locking involved in stopping the world,
1409 // the foreground collector should not block waiting for the background
1410 // collector when it is doing a stop-the-world phase. The background
1411 // collector will yield the baton at an additional point just before
1412 // it enters a stop-the-world phase. Once the world is stopped, the
1413 // background collector checks the phase of the collection. If the
1414 // phase has not changed, it proceeds with the collection. If the
1415 // phase has changed, it skips that phase of the collection. See
1416 // the comments on the use of the Heap_lock in collect_in_background().
1417 //
1418 // Variable used in baton passing.
1419 // _foregroundGCIsActive - Set to true by the foreground collector when
1420 // it wants the baton. The foreground clears it when it has finished
1421 // the collection.
1422 // _foregroundGCShouldWait - Set to true by the background collector
1423 // when it is running. The foreground collector waits while
1424 // _foregroundGCShouldWait is true.
1425 // CGC_lock - monitor used to protect access to the above variables
1426 // and to notify the foreground and background collectors.
1427 // _collectorState - current state of the CMS collection.
1428 //
1429 // The foreground collector
1430 // acquires the CGC_lock
1431 // sets _foregroundGCIsActive
1432 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1433 // various locks acquired in preparation for the collection
1434 // are released so as not to block the background collector
1435 // that is in the midst of a collection
1436 // proceeds with the collection
1437 // clears _foregroundGCIsActive
1438 // returns
1439 //
1440 // The background collector in a loop iterating on the phases of the
1441 // collection
1442 // acquires the CGC_lock
1443 // sets _foregroundGCShouldWait
1444 // if _foregroundGCIsActive is set
1445 // clears _foregroundGCShouldWait, notifies _CGC_lock
1446 // waits on _CGC_lock for _foregroundGCIsActive to become false
1447 // and exits the loop.
1448 // otherwise
1449 // proceed with that phase of the collection
1450 // if the phase is a stop-the-world phase,
1451 // yield the baton once more just before enqueueing
1452 // the stop-world CMS operation (executed by the VM thread).
1453 // returns after all phases of the collection are done
1454 //
1455
1456 void CMSCollector::acquire_control_and_collect(bool full,
1457 bool clear_all_soft_refs) {
1458 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1459 assert(!Thread::current()->is_ConcurrentGC_thread(),
1460 "shouldn't try to acquire control from self!");
1461
1462 // Start the protocol for acquiring control of the
1463 // collection from the background collector (aka CMS thread).
1464 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1465 "VM thread should have CMS token");
1466 // Remember the possibly interrupted state of an ongoing
1467 // concurrent collection
1468 CollectorState first_state = _collectorState;
1469
1470 // Signal to a possibly ongoing concurrent collection that
1471 // we want to do a foreground collection.
1472 _foregroundGCIsActive = true;
1473
1474 // release locks and wait for a notify from the background collector
1475 // releasing the locks in only necessary for phases which
1476 // do yields to improve the granularity of the collection.
1477 assert_lock_strong(bitMapLock());
1478 // We need to lock the Free list lock for the space that we are
1479 // currently collecting.
1480 assert(haveFreelistLocks(), "Must be holding free list locks");
1481 bitMapLock()->unlock();
1482 releaseFreelistLocks();
1483 {
1484 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1485 if (_foregroundGCShouldWait) {
1486 // We are going to be waiting for action for the CMS thread;
1487 // it had better not be gone (for instance at shutdown)!
1488 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1489 "CMS thread must be running");
1490 // Wait here until the background collector gives us the go-ahead
1491 ConcurrentMarkSweepThread::clear_CMS_flag(
1492 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1493 // Get a possibly blocked CMS thread going:
1494 // Note that we set _foregroundGCIsActive true above,
1495 // without protection of the CGC_lock.
1496 CGC_lock->notify();
1497 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1498 "Possible deadlock");
1499 while (_foregroundGCShouldWait) {
1500 // wait for notification
1501 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1502 // Possibility of delay/starvation here, since CMS token does
1503 // not know to give priority to VM thread? Actually, i think
1504 // there wouldn't be any delay/starvation, but the proof of
1505 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1506 }
1507 ConcurrentMarkSweepThread::set_CMS_flag(
1508 ConcurrentMarkSweepThread::CMS_vm_has_token);
1509 }
1510 }
1511 // The CMS_token is already held. Get back the other locks.
1512 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1513 "VM thread should have CMS token");
1514 getFreelistLocks();
1515 bitMapLock()->lock_without_safepoint_check();
1516 if (TraceCMSState) {
1517 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1518 INTPTR_FORMAT " with first state %d", p2i(Thread::current()), first_state);
1519 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1520 }
1521
1522 // Inform cms gen if this was due to partial collection failing.
1523 // The CMS gen may use this fact to determine its expansion policy.
1524 GenCollectedHeap* gch = GenCollectedHeap::heap();
1525 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1526 assert(!_cmsGen->incremental_collection_failed(),
1527 "Should have been noticed, reacted to and cleared");
1528 _cmsGen->set_incremental_collection_failed();
1529 }
1530
1531 if (first_state > Idling) {
1532 report_concurrent_mode_interruption();
1533 }
1534
1535 set_did_compact(true);
1536
1537 // If the collection is being acquired from the background
1538 // collector, there may be references on the discovered
1539 // references lists. Abandon those references, since some
1540 // of them may have become unreachable after concurrent
1541 // discovery; the STW compacting collector will redo discovery
1542 // more precisely, without being subject to floating garbage.
1543 // Leaving otherwise unreachable references in the discovered
1544 // lists would require special handling.
1545 ref_processor()->disable_discovery();
1546 ref_processor()->abandon_partial_discovery();
1547 ref_processor()->verify_no_references_recorded();
1548
1549 if (first_state > Idling) {
1550 save_heap_summary();
1551 }
1552
1553 do_compaction_work(clear_all_soft_refs);
1554
1555 // Has the GC time limit been exceeded?
1556 size_t max_eden_size = _young_gen->max_capacity() -
1557 _young_gen->to()->capacity() -
1558 _young_gen->from()->capacity();
1559 GCCause::Cause gc_cause = gch->gc_cause();
1560 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1561 _young_gen->eden()->used(),
1562 _cmsGen->max_capacity(),
1563 max_eden_size,
1564 full,
1565 gc_cause,
1566 gch->collector_policy());
1567
1568 // Reset the expansion cause, now that we just completed
1569 // a collection cycle.
1570 clear_expansion_cause();
1571 _foregroundGCIsActive = false;
1572 return;
1573 }
1574
1575 // Resize the tenured generation
1576 // after obtaining the free list locks for the
1577 // two generations.
1578 void CMSCollector::compute_new_size() {
1579 assert_locked_or_safepoint(Heap_lock);
1580 FreelistLocker z(this);
1581 MetaspaceGC::compute_new_size();
1582 _cmsGen->compute_new_size_free_list();
1583 }
1584
1585 // A work method used by the foreground collector to do
1586 // a mark-sweep-compact.
1587 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1588 GenCollectedHeap* gch = GenCollectedHeap::heap();
1589
1590 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1591 gc_timer->register_gc_start();
1592
1593 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1594 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1595
1596 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL);
1597
1598 // Temporarily widen the span of the weak reference processing to
1599 // the entire heap.
1600 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1601 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1602 // Temporarily, clear the "is_alive_non_header" field of the
1603 // reference processor.
1604 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1605 // Temporarily make reference _processing_ single threaded (non-MT).
1606 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1607 // Temporarily make refs discovery atomic
1608 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1609 // Temporarily make reference _discovery_ single threaded (non-MT)
1610 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1611
1612 ref_processor()->set_enqueuing_is_done(false);
1613 ref_processor()->enable_discovery();
1614 ref_processor()->setup_policy(clear_all_soft_refs);
1615 // If an asynchronous collection finishes, the _modUnionTable is
1616 // all clear. If we are assuming the collection from an asynchronous
1617 // collection, clear the _modUnionTable.
1618 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1619 "_modUnionTable should be clear if the baton was not passed");
1620 _modUnionTable.clear_all();
1621 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1622 "mod union for klasses should be clear if the baton was passed");
1623 _ct->klass_rem_set()->clear_mod_union();
1624
1625 // We must adjust the allocation statistics being maintained
1626 // in the free list space. We do so by reading and clearing
1627 // the sweep timer and updating the block flux rate estimates below.
1628 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1629 if (_inter_sweep_timer.is_active()) {
1630 _inter_sweep_timer.stop();
1631 // Note that we do not use this sample to update the _inter_sweep_estimate.
1632 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1633 _inter_sweep_estimate.padded_average(),
1634 _intra_sweep_estimate.padded_average());
1635 }
1636
1637 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1638 #ifdef ASSERT
1639 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1640 size_t free_size = cms_space->free();
1641 assert(free_size ==
1642 pointer_delta(cms_space->end(), cms_space->compaction_top())
1643 * HeapWordSize,
1644 "All the free space should be compacted into one chunk at top");
1645 assert(cms_space->dictionary()->total_chunk_size(
1646 debug_only(cms_space->freelistLock())) == 0 ||
1647 cms_space->totalSizeInIndexedFreeLists() == 0,
1648 "All the free space should be in a single chunk");
1649 size_t num = cms_space->totalCount();
1650 assert((free_size == 0 && num == 0) ||
1651 (free_size > 0 && (num == 1 || num == 2)),
1652 "There should be at most 2 free chunks after compaction");
1653 #endif // ASSERT
1654 _collectorState = Resetting;
1655 assert(_restart_addr == NULL,
1656 "Should have been NULL'd before baton was passed");
1657 reset(false /* == !concurrent */);
1658 _cmsGen->reset_after_compaction();
1659 _concurrent_cycles_since_last_unload = 0;
1660
1661 // Clear any data recorded in the PLAB chunk arrays.
1662 if (_survivor_plab_array != NULL) {
1663 reset_survivor_plab_arrays();
1664 }
1665
1666 // Adjust the per-size allocation stats for the next epoch.
1667 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1668 // Restart the "inter sweep timer" for the next epoch.
1669 _inter_sweep_timer.reset();
1670 _inter_sweep_timer.start();
1671
1672 gc_timer->register_gc_end();
1673
1674 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1675
1676 // For a mark-sweep-compact, compute_new_size() will be called
1677 // in the heap's do_collection() method.
1678 }
1679
1680 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1681 ContiguousSpace* eden_space = _young_gen->eden();
1682 ContiguousSpace* from_space = _young_gen->from();
1683 ContiguousSpace* to_space = _young_gen->to();
1684 // Eden
1685 if (_eden_chunk_array != NULL) {
1686 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1687 p2i(eden_space->bottom()), p2i(eden_space->top()),
1688 p2i(eden_space->end()), eden_space->capacity());
1689 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1690 "_eden_chunk_capacity=" SIZE_FORMAT,
1691 _eden_chunk_index, _eden_chunk_capacity);
1692 for (size_t i = 0; i < _eden_chunk_index; i++) {
1693 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1694 i, p2i(_eden_chunk_array[i]));
1695 }
1696 }
1697 // Survivor
1698 if (_survivor_chunk_array != NULL) {
1699 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1700 p2i(from_space->bottom()), p2i(from_space->top()),
1701 p2i(from_space->end()), from_space->capacity());
1702 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1703 "_survivor_chunk_capacity=" SIZE_FORMAT,
1704 _survivor_chunk_index, _survivor_chunk_capacity);
1705 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1706 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1707 i, p2i(_survivor_chunk_array[i]));
1708 }
1709 }
1710 }
1711
1712 void CMSCollector::getFreelistLocks() const {
1713 // Get locks for all free lists in all generations that this
1714 // collector is responsible for
1715 _cmsGen->freelistLock()->lock_without_safepoint_check();
1716 }
1717
1718 void CMSCollector::releaseFreelistLocks() const {
1719 // Release locks for all free lists in all generations that this
1720 // collector is responsible for
1721 _cmsGen->freelistLock()->unlock();
1722 }
1723
1724 bool CMSCollector::haveFreelistLocks() const {
1725 // Check locks for all free lists in all generations that this
1726 // collector is responsible for
1727 assert_lock_strong(_cmsGen->freelistLock());
1728 PRODUCT_ONLY(ShouldNotReachHere());
1729 return true;
1730 }
1731
1732 // A utility class that is used by the CMS collector to
1733 // temporarily "release" the foreground collector from its
1734 // usual obligation to wait for the background collector to
1735 // complete an ongoing phase before proceeding.
1736 class ReleaseForegroundGC: public StackObj {
1737 private:
1738 CMSCollector* _c;
1739 public:
1740 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1741 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1742 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1743 // allow a potentially blocked foreground collector to proceed
1744 _c->_foregroundGCShouldWait = false;
1745 if (_c->_foregroundGCIsActive) {
1746 CGC_lock->notify();
1747 }
1748 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1749 "Possible deadlock");
1750 }
1751
1752 ~ReleaseForegroundGC() {
1753 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1754 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1755 _c->_foregroundGCShouldWait = true;
1756 }
1757 };
1758
1759 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1760 assert(Thread::current()->is_ConcurrentGC_thread(),
1761 "A CMS asynchronous collection is only allowed on a CMS thread.");
1762
1763 GenCollectedHeap* gch = GenCollectedHeap::heap();
1764 {
1765 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1766 MutexLockerEx hl(Heap_lock, safepoint_check);
1767 FreelistLocker fll(this);
1768 MutexLockerEx x(CGC_lock, safepoint_check);
1769 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
1770 // The foreground collector is active or we're
1771 // not using asynchronous collections. Skip this
1772 // background collection.
1773 assert(!_foregroundGCShouldWait, "Should be clear");
1774 return;
1775 } else {
1776 assert(_collectorState == Idling, "Should be idling before start.");
1777 _collectorState = InitialMarking;
1778 register_gc_start(cause);
1779 // Reset the expansion cause, now that we are about to begin
1780 // a new cycle.
1781 clear_expansion_cause();
1782
1783 // Clear the MetaspaceGC flag since a concurrent collection
1784 // is starting but also clear it after the collection.
1785 MetaspaceGC::set_should_concurrent_collect(false);
1786 }
1787 // Decide if we want to enable class unloading as part of the
1788 // ensuing concurrent GC cycle.
1789 update_should_unload_classes();
1790 _full_gc_requested = false; // acks all outstanding full gc requests
1791 _full_gc_cause = GCCause::_no_gc;
1792 // Signal that we are about to start a collection
1793 gch->increment_total_full_collections(); // ... starting a collection cycle
1794 _collection_count_start = gch->total_full_collections();
1795 }
1796
1797 // Used for PrintGC
1798 size_t prev_used;
1799 if (PrintGC && Verbose) {
1800 prev_used = _cmsGen->used();
1801 }
1802
1803 // The change of the collection state is normally done at this level;
1804 // the exceptions are phases that are executed while the world is
1805 // stopped. For those phases the change of state is done while the
1806 // world is stopped. For baton passing purposes this allows the
1807 // background collector to finish the phase and change state atomically.
1808 // The foreground collector cannot wait on a phase that is done
1809 // while the world is stopped because the foreground collector already
1810 // has the world stopped and would deadlock.
1811 while (_collectorState != Idling) {
1812 if (TraceCMSState) {
1813 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
1814 p2i(Thread::current()), _collectorState);
1815 }
1816 // The foreground collector
1817 // holds the Heap_lock throughout its collection.
1818 // holds the CMS token (but not the lock)
1819 // except while it is waiting for the background collector to yield.
1820 //
1821 // The foreground collector should be blocked (not for long)
1822 // if the background collector is about to start a phase
1823 // executed with world stopped. If the background
1824 // collector has already started such a phase, the
1825 // foreground collector is blocked waiting for the
1826 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1827 // are executed in the VM thread.
1828 //
1829 // The locking order is
1830 // PendingListLock (PLL) -- if applicable (FinalMarking)
1831 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1832 // CMS token (claimed in
1833 // stop_world_and_do() -->
1834 // safepoint_synchronize() -->
1835 // CMSThread::synchronize())
1836
1837 {
1838 // Check if the FG collector wants us to yield.
1839 CMSTokenSync x(true); // is cms thread
1840 if (waitForForegroundGC()) {
1841 // We yielded to a foreground GC, nothing more to be
1842 // done this round.
1843 assert(_foregroundGCShouldWait == false, "We set it to false in "
1844 "waitForForegroundGC()");
1845 if (TraceCMSState) {
1846 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1847 " exiting collection CMS state %d",
1848 p2i(Thread::current()), _collectorState);
1849 }
1850 return;
1851 } else {
1852 // The background collector can run but check to see if the
1853 // foreground collector has done a collection while the
1854 // background collector was waiting to get the CGC_lock
1855 // above. If yes, break so that _foregroundGCShouldWait
1856 // is cleared before returning.
1857 if (_collectorState == Idling) {
1858 break;
1859 }
1860 }
1861 }
1862
1863 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1864 "should be waiting");
1865
1866 switch (_collectorState) {
1867 case InitialMarking:
1868 {
1869 ReleaseForegroundGC x(this);
1870 stats().record_cms_begin();
1871 VM_CMS_Initial_Mark initial_mark_op(this);
1872 VMThread::execute(&initial_mark_op);
1873 }
1874 // The collector state may be any legal state at this point
1875 // since the background collector may have yielded to the
1876 // foreground collector.
1877 break;
1878 case Marking:
1879 // initial marking in checkpointRootsInitialWork has been completed
1880 if (markFromRoots()) { // we were successful
1881 assert(_collectorState == Precleaning, "Collector state should "
1882 "have changed");
1883 } else {
1884 assert(_foregroundGCIsActive, "Internal state inconsistency");
1885 }
1886 break;
1887 case Precleaning:
1888 // marking from roots in markFromRoots has been completed
1889 preclean();
1890 assert(_collectorState == AbortablePreclean ||
1891 _collectorState == FinalMarking,
1892 "Collector state should have changed");
1893 break;
1894 case AbortablePreclean:
1895 abortable_preclean();
1896 assert(_collectorState == FinalMarking, "Collector state should "
1897 "have changed");
1898 break;
1899 case FinalMarking:
1900 {
1901 ReleaseForegroundGC x(this);
1902
1903 VM_CMS_Final_Remark final_remark_op(this);
1904 VMThread::execute(&final_remark_op);
1905 }
1906 assert(_foregroundGCShouldWait, "block post-condition");
1907 break;
1908 case Sweeping:
1909 // final marking in checkpointRootsFinal has been completed
1910 sweep();
1911 assert(_collectorState == Resizing, "Collector state change "
1912 "to Resizing must be done under the free_list_lock");
1913
1914 case Resizing: {
1915 // Sweeping has been completed...
1916 // At this point the background collection has completed.
1917 // Don't move the call to compute_new_size() down
1918 // into code that might be executed if the background
1919 // collection was preempted.
1920 {
1921 ReleaseForegroundGC x(this); // unblock FG collection
1922 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1923 CMSTokenSync z(true); // not strictly needed.
1924 if (_collectorState == Resizing) {
1925 compute_new_size();
1926 save_heap_summary();
1927 _collectorState = Resetting;
1928 } else {
1929 assert(_collectorState == Idling, "The state should only change"
1930 " because the foreground collector has finished the collection");
1931 }
1932 }
1933 break;
1934 }
1935 case Resetting:
1936 // CMS heap resizing has been completed
1937 reset(true);
1938 assert(_collectorState == Idling, "Collector state should "
1939 "have changed");
1940
1941 MetaspaceGC::set_should_concurrent_collect(false);
1942
1943 stats().record_cms_end();
1944 // Don't move the concurrent_phases_end() and compute_new_size()
1945 // calls to here because a preempted background collection
1946 // has it's state set to "Resetting".
1947 break;
1948 case Idling:
1949 default:
1950 ShouldNotReachHere();
1951 break;
1952 }
1953 if (TraceCMSState) {
1954 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1955 p2i(Thread::current()), _collectorState);
1956 }
1957 assert(_foregroundGCShouldWait, "block post-condition");
1958 }
1959
1960 // Should this be in gc_epilogue?
1961 collector_policy()->counters()->update_counters();
1962
1963 {
1964 // Clear _foregroundGCShouldWait and, in the event that the
1965 // foreground collector is waiting, notify it, before
1966 // returning.
1967 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1968 _foregroundGCShouldWait = false;
1969 if (_foregroundGCIsActive) {
1970 CGC_lock->notify();
1971 }
1972 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1973 "Possible deadlock");
1974 }
1975 if (TraceCMSState) {
1976 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1977 " exiting collection CMS state %d",
1978 p2i(Thread::current()), _collectorState);
1979 }
1980 if (PrintGC && Verbose) {
1981 _cmsGen->print_heap_change(prev_used);
1982 }
1983 }
1984
1985 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1986 _cms_start_registered = true;
1987 _gc_timer_cm->register_gc_start();
1988 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1989 }
1990
1991 void CMSCollector::register_gc_end() {
1992 if (_cms_start_registered) {
1993 report_heap_summary(GCWhen::AfterGC);
1994
1995 _gc_timer_cm->register_gc_end();
1996 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1997 _cms_start_registered = false;
1998 }
1999 }
2000
2001 void CMSCollector::save_heap_summary() {
2002 GenCollectedHeap* gch = GenCollectedHeap::heap();
2003 _last_heap_summary = gch->create_heap_summary();
2004 _last_metaspace_summary = gch->create_metaspace_summary();
2005 }
2006
2007 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2008 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2009 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2010 }
2011
2012 bool CMSCollector::waitForForegroundGC() {
2013 bool res = false;
2014 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2015 "CMS thread should have CMS token");
2016 // Block the foreground collector until the
2017 // background collectors decides whether to
2018 // yield.
2019 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2020 _foregroundGCShouldWait = true;
2021 if (_foregroundGCIsActive) {
2022 // The background collector yields to the
2023 // foreground collector and returns a value
2024 // indicating that it has yielded. The foreground
2025 // collector can proceed.
2026 res = true;
2027 _foregroundGCShouldWait = false;
2028 ConcurrentMarkSweepThread::clear_CMS_flag(
2029 ConcurrentMarkSweepThread::CMS_cms_has_token);
2030 ConcurrentMarkSweepThread::set_CMS_flag(
2031 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2032 // Get a possibly blocked foreground thread going
2033 CGC_lock->notify();
2034 if (TraceCMSState) {
2035 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2036 p2i(Thread::current()), _collectorState);
2037 }
2038 while (_foregroundGCIsActive) {
2039 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2040 }
2041 ConcurrentMarkSweepThread::set_CMS_flag(
2042 ConcurrentMarkSweepThread::CMS_cms_has_token);
2043 ConcurrentMarkSweepThread::clear_CMS_flag(
2044 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2045 }
2046 if (TraceCMSState) {
2047 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2048 p2i(Thread::current()), _collectorState);
2049 }
2050 return res;
2051 }
2052
2053 // Because of the need to lock the free lists and other structures in
2054 // the collector, common to all the generations that the collector is
2055 // collecting, we need the gc_prologues of individual CMS generations
2056 // delegate to their collector. It may have been simpler had the
2057 // current infrastructure allowed one to call a prologue on a
2058 // collector. In the absence of that we have the generation's
2059 // prologue delegate to the collector, which delegates back
2060 // some "local" work to a worker method in the individual generations
2061 // that it's responsible for collecting, while itself doing any
2062 // work common to all generations it's responsible for. A similar
2063 // comment applies to the gc_epilogue()'s.
2064 // The role of the variable _between_prologue_and_epilogue is to
2065 // enforce the invocation protocol.
2066 void CMSCollector::gc_prologue(bool full) {
2067 // Call gc_prologue_work() for the CMSGen
2068 // we are responsible for.
2069
2070 // The following locking discipline assumes that we are only called
2071 // when the world is stopped.
2072 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2073
2074 // The CMSCollector prologue must call the gc_prologues for the
2075 // "generations" that it's responsible
2076 // for.
2077
2078 assert( Thread::current()->is_VM_thread()
2079 || ( CMSScavengeBeforeRemark
2080 && Thread::current()->is_ConcurrentGC_thread()),
2081 "Incorrect thread type for prologue execution");
2082
2083 if (_between_prologue_and_epilogue) {
2084 // We have already been invoked; this is a gc_prologue delegation
2085 // from yet another CMS generation that we are responsible for, just
2086 // ignore it since all relevant work has already been done.
2087 return;
2088 }
2089
2090 // set a bit saying prologue has been called; cleared in epilogue
2091 _between_prologue_and_epilogue = true;
2092 // Claim locks for common data structures, then call gc_prologue_work()
2093 // for each CMSGen.
2094
2095 getFreelistLocks(); // gets free list locks on constituent spaces
2096 bitMapLock()->lock_without_safepoint_check();
2097
2098 // Should call gc_prologue_work() for all cms gens we are responsible for
2099 bool duringMarking = _collectorState >= Marking
2100 && _collectorState < Sweeping;
2101
2102 // The young collections clear the modified oops state, which tells if
2103 // there are any modified oops in the class. The remark phase also needs
2104 // that information. Tell the young collection to save the union of all
2105 // modified klasses.
2106 if (duringMarking) {
2107 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2108 }
2109
2110 bool registerClosure = duringMarking;
2111
2112 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2113
2114 if (!full) {
2115 stats().record_gc0_begin();
2116 }
2117 }
2118
2119 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2120
2121 _capacity_at_prologue = capacity();
2122 _used_at_prologue = used();
2123
2124 // Delegate to CMScollector which knows how to coordinate between
2125 // this and any other CMS generations that it is responsible for
2126 // collecting.
2127 collector()->gc_prologue(full);
2128 }
2129
2130 // This is a "private" interface for use by this generation's CMSCollector.
2131 // Not to be called directly by any other entity (for instance,
2132 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2133 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2134 bool registerClosure, ModUnionClosure* modUnionClosure) {
2135 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2136 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2137 "Should be NULL");
2138 if (registerClosure) {
2139 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2140 }
2141 cmsSpace()->gc_prologue();
2142 // Clear stat counters
2143 NOT_PRODUCT(
2144 assert(_numObjectsPromoted == 0, "check");
2145 assert(_numWordsPromoted == 0, "check");
2146 if (Verbose && PrintGC) {
2147 gclog_or_tty->print("Allocated " SIZE_FORMAT " objects, "
2148 SIZE_FORMAT " bytes concurrently",
2149 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2150 }
2151 _numObjectsAllocated = 0;
2152 _numWordsAllocated = 0;
2153 )
2154 }
2155
2156 void CMSCollector::gc_epilogue(bool full) {
2157 // The following locking discipline assumes that we are only called
2158 // when the world is stopped.
2159 assert(SafepointSynchronize::is_at_safepoint(),
2160 "world is stopped assumption");
2161
2162 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2163 // if linear allocation blocks need to be appropriately marked to allow the
2164 // the blocks to be parsable. We also check here whether we need to nudge the
2165 // CMS collector thread to start a new cycle (if it's not already active).
2166 assert( Thread::current()->is_VM_thread()
2167 || ( CMSScavengeBeforeRemark
2168 && Thread::current()->is_ConcurrentGC_thread()),
2169 "Incorrect thread type for epilogue execution");
2170
2171 if (!_between_prologue_and_epilogue) {
2172 // We have already been invoked; this is a gc_epilogue delegation
2173 // from yet another CMS generation that we are responsible for, just
2174 // ignore it since all relevant work has already been done.
2175 return;
2176 }
2177 assert(haveFreelistLocks(), "must have freelist locks");
2178 assert_lock_strong(bitMapLock());
2179
2180 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2181
2182 _cmsGen->gc_epilogue_work(full);
2183
2184 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2185 // in case sampling was not already enabled, enable it
2186 _start_sampling = true;
2187 }
2188 // reset _eden_chunk_array so sampling starts afresh
2189 _eden_chunk_index = 0;
2190
2191 size_t cms_used = _cmsGen->cmsSpace()->used();
2192
2193 // update performance counters - this uses a special version of
2194 // update_counters() that allows the utilization to be passed as a
2195 // parameter, avoiding multiple calls to used().
2196 //
2197 _cmsGen->update_counters(cms_used);
2198
2199 bitMapLock()->unlock();
2200 releaseFreelistLocks();
2201
2202 if (!CleanChunkPoolAsync) {
2203 Chunk::clean_chunk_pool();
2204 }
2205
2206 set_did_compact(false);
2207 _between_prologue_and_epilogue = false; // ready for next cycle
2208 }
2209
2210 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2211 collector()->gc_epilogue(full);
2212
2213 // Also reset promotion tracking in par gc thread states.
2214 for (uint i = 0; i < ParallelGCThreads; i++) {
2215 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2216 }
2217 }
2218
2219 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2220 assert(!incremental_collection_failed(), "Should have been cleared");
2221 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2222 cmsSpace()->gc_epilogue();
2223 // Print stat counters
2224 NOT_PRODUCT(
2225 assert(_numObjectsAllocated == 0, "check");
2226 assert(_numWordsAllocated == 0, "check");
2227 if (Verbose && PrintGC) {
2228 gclog_or_tty->print("Promoted " SIZE_FORMAT " objects, "
2229 SIZE_FORMAT " bytes",
2230 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2231 }
2232 _numObjectsPromoted = 0;
2233 _numWordsPromoted = 0;
2234 )
2235
2236 if (PrintGC && Verbose) {
2237 // Call down the chain in contiguous_available needs the freelistLock
2238 // so print this out before releasing the freeListLock.
2239 gclog_or_tty->print(" Contiguous available " SIZE_FORMAT " bytes ",
2240 contiguous_available());
2241 }
2242 }
2243
2244 #ifndef PRODUCT
2245 bool CMSCollector::have_cms_token() {
2246 Thread* thr = Thread::current();
2247 if (thr->is_VM_thread()) {
2248 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2249 } else if (thr->is_ConcurrentGC_thread()) {
2250 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2251 } else if (thr->is_GC_task_thread()) {
2252 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2253 ParGCRareEvent_lock->owned_by_self();
2254 }
2255 return false;
2256 }
2257 #endif
2258
2259 // Check reachability of the given heap address in CMS generation,
2260 // treating all other generations as roots.
2261 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2262 // We could "guarantee" below, rather than assert, but I'll
2263 // leave these as "asserts" so that an adventurous debugger
2264 // could try this in the product build provided some subset of
2265 // the conditions were met, provided they were interested in the
2266 // results and knew that the computation below wouldn't interfere
2267 // with other concurrent computations mutating the structures
2268 // being read or written.
2269 assert(SafepointSynchronize::is_at_safepoint(),
2270 "Else mutations in object graph will make answer suspect");
2271 assert(have_cms_token(), "Should hold cms token");
2272 assert(haveFreelistLocks(), "must hold free list locks");
2273 assert_lock_strong(bitMapLock());
2274
2275 // Clear the marking bit map array before starting, but, just
2276 // for kicks, first report if the given address is already marked
2277 gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2278 _markBitMap.isMarked(addr) ? "" : " not");
2279
2280 if (verify_after_remark()) {
2281 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2282 bool result = verification_mark_bm()->isMarked(addr);
2283 gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2284 result ? "IS" : "is NOT");
2285 return result;
2286 } else {
2287 gclog_or_tty->print_cr("Could not compute result");
2288 return false;
2289 }
2290 }
2291
2292
2293 void
2294 CMSCollector::print_on_error(outputStream* st) {
2295 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2296 if (collector != NULL) {
2297 CMSBitMap* bitmap = &collector->_markBitMap;
2298 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2299 bitmap->print_on_error(st, " Bits: ");
2300
2301 st->cr();
2302
2303 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2304 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2305 mut_bitmap->print_on_error(st, " Bits: ");
2306 }
2307 }
2308
2309 ////////////////////////////////////////////////////////
2310 // CMS Verification Support
2311 ////////////////////////////////////////////////////////
2312 // Following the remark phase, the following invariant
2313 // should hold -- each object in the CMS heap which is
2314 // marked in markBitMap() should be marked in the verification_mark_bm().
2315
2316 class VerifyMarkedClosure: public BitMapClosure {
2317 CMSBitMap* _marks;
2318 bool _failed;
2319
2320 public:
2321 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2322
2323 bool do_bit(size_t offset) {
2324 HeapWord* addr = _marks->offsetToHeapWord(offset);
2325 if (!_marks->isMarked(addr)) {
2326 oop(addr)->print_on(gclog_or_tty);
2327 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2328 _failed = true;
2329 }
2330 return true;
2331 }
2332
2333 bool failed() { return _failed; }
2334 };
2335
2336 bool CMSCollector::verify_after_remark(bool silent) {
2337 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2338 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2339 static bool init = false;
2340
2341 assert(SafepointSynchronize::is_at_safepoint(),
2342 "Else mutations in object graph will make answer suspect");
2343 assert(have_cms_token(),
2344 "Else there may be mutual interference in use of "
2345 " verification data structures");
2346 assert(_collectorState > Marking && _collectorState <= Sweeping,
2347 "Else marking info checked here may be obsolete");
2348 assert(haveFreelistLocks(), "must hold free list locks");
2349 assert_lock_strong(bitMapLock());
2350
2351
2352 // Allocate marking bit map if not already allocated
2353 if (!init) { // first time
2354 if (!verification_mark_bm()->allocate(_span)) {
2355 return false;
2356 }
2357 init = true;
2358 }
2359
2360 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2361
2362 // Turn off refs discovery -- so we will be tracing through refs.
2363 // This is as intended, because by this time
2364 // GC must already have cleared any refs that need to be cleared,
2365 // and traced those that need to be marked; moreover,
2366 // the marking done here is not going to interfere in any
2367 // way with the marking information used by GC.
2368 NoRefDiscovery no_discovery(ref_processor());
2369
2370 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2371
2372 // Clear any marks from a previous round
2373 verification_mark_bm()->clear_all();
2374 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2375 verify_work_stacks_empty();
2376
2377 GenCollectedHeap* gch = GenCollectedHeap::heap();
2378 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2379 // Update the saved marks which may affect the root scans.
2380 gch->save_marks();
2381
2382 if (CMSRemarkVerifyVariant == 1) {
2383 // In this first variant of verification, we complete
2384 // all marking, then check if the new marks-vector is
2385 // a subset of the CMS marks-vector.
2386 verify_after_remark_work_1();
2387 } else if (CMSRemarkVerifyVariant == 2) {
2388 // In this second variant of verification, we flag an error
2389 // (i.e. an object reachable in the new marks-vector not reachable
2390 // in the CMS marks-vector) immediately, also indicating the
2391 // identify of an object (A) that references the unmarked object (B) --
2392 // presumably, a mutation to A failed to be picked up by preclean/remark?
2393 verify_after_remark_work_2();
2394 } else {
2395 warning("Unrecognized value " UINTX_FORMAT " for CMSRemarkVerifyVariant",
2396 CMSRemarkVerifyVariant);
2397 }
2398 if (!silent) gclog_or_tty->print(" done] ");
2399 return true;
2400 }
2401
2402 void CMSCollector::verify_after_remark_work_1() {
2403 ResourceMark rm;
2404 HandleMark hm;
2405 GenCollectedHeap* gch = GenCollectedHeap::heap();
2406
2407 // Get a clear set of claim bits for the roots processing to work with.
2408 ClassLoaderDataGraph::clear_claimed_marks();
2409
2410 // Mark from roots one level into CMS
2411 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2412 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2413
2414 {
2415 StrongRootsScope srs(1);
2416
2417 gch->old_process_roots(&srs,
2418 true, // young gen as roots
2419 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2420 should_unload_classes(),
2421 ¬Older,
2422 NULL);
2423 }
2424
2425 // Now mark from the roots
2426 MarkFromRootsClosure markFromRootsClosure(this, _span,
2427 verification_mark_bm(), verification_mark_stack(),
2428 false /* don't yield */, true /* verifying */);
2429 assert(_restart_addr == NULL, "Expected pre-condition");
2430 verification_mark_bm()->iterate(&markFromRootsClosure);
2431 while (_restart_addr != NULL) {
2432 // Deal with stack overflow: by restarting at the indicated
2433 // address.
2434 HeapWord* ra = _restart_addr;
2435 markFromRootsClosure.reset(ra);
2436 _restart_addr = NULL;
2437 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2438 }
2439 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2440 verify_work_stacks_empty();
2441
2442 // Marking completed -- now verify that each bit marked in
2443 // verification_mark_bm() is also marked in markBitMap(); flag all
2444 // errors by printing corresponding objects.
2445 VerifyMarkedClosure vcl(markBitMap());
2446 verification_mark_bm()->iterate(&vcl);
2447 if (vcl.failed()) {
2448 gclog_or_tty->print("Verification failed");
2449 gch->print_on(gclog_or_tty);
2450 fatal("CMS: failed marking verification after remark");
2451 }
2452 }
2453
2454 class VerifyKlassOopsKlassClosure : public KlassClosure {
2455 class VerifyKlassOopsClosure : public OopClosure {
2456 CMSBitMap* _bitmap;
2457 public:
2458 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2459 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2460 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2461 } _oop_closure;
2462 public:
2463 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2464 void do_klass(Klass* k) {
2465 k->oops_do(&_oop_closure);
2466 }
2467 };
2468
2469 void CMSCollector::verify_after_remark_work_2() {
2470 ResourceMark rm;
2471 HandleMark hm;
2472 GenCollectedHeap* gch = GenCollectedHeap::heap();
2473
2474 // Get a clear set of claim bits for the roots processing to work with.
2475 ClassLoaderDataGraph::clear_claimed_marks();
2476
2477 // Mark from roots one level into CMS
2478 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2479 markBitMap());
2480 CLDToOopClosure cld_closure(¬Older, true);
2481
2482 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2483
2484 {
2485 StrongRootsScope srs(1);
2486
2487 gch->old_process_roots(&srs,
2488 true, // young gen as roots
2489 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2490 should_unload_classes(),
2491 ¬Older,
2492 &cld_closure);
2493 }
2494
2495 // Now mark from the roots
2496 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2497 verification_mark_bm(), markBitMap(), verification_mark_stack());
2498 assert(_restart_addr == NULL, "Expected pre-condition");
2499 verification_mark_bm()->iterate(&markFromRootsClosure);
2500 while (_restart_addr != NULL) {
2501 // Deal with stack overflow: by restarting at the indicated
2502 // address.
2503 HeapWord* ra = _restart_addr;
2504 markFromRootsClosure.reset(ra);
2505 _restart_addr = NULL;
2506 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2507 }
2508 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2509 verify_work_stacks_empty();
2510
2511 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2512 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2513
2514 // Marking completed -- now verify that each bit marked in
2515 // verification_mark_bm() is also marked in markBitMap(); flag all
2516 // errors by printing corresponding objects.
2517 VerifyMarkedClosure vcl(markBitMap());
2518 verification_mark_bm()->iterate(&vcl);
2519 assert(!vcl.failed(), "Else verification above should not have succeeded");
2520 }
2521
2522 void ConcurrentMarkSweepGeneration::save_marks() {
2523 // delegate to CMS space
2524 cmsSpace()->save_marks();
2525 for (uint i = 0; i < ParallelGCThreads; i++) {
2526 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2527 }
2528 }
2529
2530 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2531 return cmsSpace()->no_allocs_since_save_marks();
2532 }
2533
2534 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2535 \
2536 void ConcurrentMarkSweepGeneration:: \
2537 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2538 cl->assert_generation(this); \
2539 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2540 save_marks(); \
2541 }
2542
2543 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2544
2545 void
2546 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2547 if (freelistLock()->owned_by_self()) {
2548 Generation::oop_iterate(cl);
2549 } else {
2550 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2551 Generation::oop_iterate(cl);
2552 }
2553 }
2554
2555 void
2556 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2557 if (freelistLock()->owned_by_self()) {
2558 Generation::object_iterate(cl);
2559 } else {
2560 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2561 Generation::object_iterate(cl);
2562 }
2563 }
2564
2565 void
2566 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2567 if (freelistLock()->owned_by_self()) {
2568 Generation::safe_object_iterate(cl);
2569 } else {
2570 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2571 Generation::safe_object_iterate(cl);
2572 }
2573 }
2574
2575 void
2576 ConcurrentMarkSweepGeneration::post_compact() {
2577 }
2578
2579 void
2580 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2581 // Fix the linear allocation blocks to look like free blocks.
2582
2583 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2584 // are not called when the heap is verified during universe initialization and
2585 // at vm shutdown.
2586 if (freelistLock()->owned_by_self()) {
2587 cmsSpace()->prepare_for_verify();
2588 } else {
2589 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2590 cmsSpace()->prepare_for_verify();
2591 }
2592 }
2593
2594 void
2595 ConcurrentMarkSweepGeneration::verify() {
2596 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2597 // are not called when the heap is verified during universe initialization and
2598 // at vm shutdown.
2599 if (freelistLock()->owned_by_self()) {
2600 cmsSpace()->verify();
2601 } else {
2602 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2603 cmsSpace()->verify();
2604 }
2605 }
2606
2607 void CMSCollector::verify() {
2608 _cmsGen->verify();
2609 }
2610
2611 #ifndef PRODUCT
2612 bool CMSCollector::overflow_list_is_empty() const {
2613 assert(_num_par_pushes >= 0, "Inconsistency");
2614 if (_overflow_list == NULL) {
2615 assert(_num_par_pushes == 0, "Inconsistency");
2616 }
2617 return _overflow_list == NULL;
2618 }
2619
2620 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2621 // merely consolidate assertion checks that appear to occur together frequently.
2622 void CMSCollector::verify_work_stacks_empty() const {
2623 assert(_markStack.isEmpty(), "Marking stack should be empty");
2624 assert(overflow_list_is_empty(), "Overflow list should be empty");
2625 }
2626
2627 void CMSCollector::verify_overflow_empty() const {
2628 assert(overflow_list_is_empty(), "Overflow list should be empty");
2629 assert(no_preserved_marks(), "No preserved marks");
2630 }
2631 #endif // PRODUCT
2632
2633 // Decide if we want to enable class unloading as part of the
2634 // ensuing concurrent GC cycle. We will collect and
2635 // unload classes if it's the case that:
2636 // (1) an explicit gc request has been made and the flag
2637 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2638 // (2) (a) class unloading is enabled at the command line, and
2639 // (b) old gen is getting really full
2640 // NOTE: Provided there is no change in the state of the heap between
2641 // calls to this method, it should have idempotent results. Moreover,
2642 // its results should be monotonically increasing (i.e. going from 0 to 1,
2643 // but not 1 to 0) between successive calls between which the heap was
2644 // not collected. For the implementation below, it must thus rely on
2645 // the property that concurrent_cycles_since_last_unload()
2646 // will not decrease unless a collection cycle happened and that
2647 // _cmsGen->is_too_full() are
2648 // themselves also monotonic in that sense. See check_monotonicity()
2649 // below.
2650 void CMSCollector::update_should_unload_classes() {
2651 _should_unload_classes = false;
2652 // Condition 1 above
2653 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2654 _should_unload_classes = true;
2655 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2656 // Disjuncts 2.b.(i,ii,iii) above
2657 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2658 CMSClassUnloadingMaxInterval)
2659 || _cmsGen->is_too_full();
2660 }
2661 }
2662
2663 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2664 bool res = should_concurrent_collect();
2665 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2666 return res;
2667 }
2668
2669 void CMSCollector::setup_cms_unloading_and_verification_state() {
2670 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2671 || VerifyBeforeExit;
2672 const int rso = GenCollectedHeap::SO_AllCodeCache;
2673
2674 // We set the proper root for this CMS cycle here.
2675 if (should_unload_classes()) { // Should unload classes this cycle
2676 remove_root_scanning_option(rso); // Shrink the root set appropriately
2677 set_verifying(should_verify); // Set verification state for this cycle
2678 return; // Nothing else needs to be done at this time
2679 }
2680
2681 // Not unloading classes this cycle
2682 assert(!should_unload_classes(), "Inconsistency!");
2683
2684 // If we are not unloading classes then add SO_AllCodeCache to root
2685 // scanning options.
2686 add_root_scanning_option(rso);
2687
2688 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2689 set_verifying(true);
2690 } else if (verifying() && !should_verify) {
2691 // We were verifying, but some verification flags got disabled.
2692 set_verifying(false);
2693 // Exclude symbols, strings and code cache elements from root scanning to
2694 // reduce IM and RM pauses.
2695 remove_root_scanning_option(rso);
2696 }
2697 }
2698
2699
2700 #ifndef PRODUCT
2701 HeapWord* CMSCollector::block_start(const void* p) const {
2702 const HeapWord* addr = (HeapWord*)p;
2703 if (_span.contains(p)) {
2704 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2705 return _cmsGen->cmsSpace()->block_start(p);
2706 }
2707 }
2708 return NULL;
2709 }
2710 #endif
2711
2712 HeapWord*
2713 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2714 bool tlab,
2715 bool parallel) {
2716 CMSSynchronousYieldRequest yr;
2717 assert(!tlab, "Can't deal with TLAB allocation");
2718 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2719 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2720 if (GCExpandToAllocateDelayMillis > 0) {
2721 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2722 }
2723 return have_lock_and_allocate(word_size, tlab);
2724 }
2725
2726 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2727 size_t bytes,
2728 size_t expand_bytes,
2729 CMSExpansionCause::Cause cause)
2730 {
2731
2732 bool success = expand(bytes, expand_bytes);
2733
2734 // remember why we expanded; this information is used
2735 // by shouldConcurrentCollect() when making decisions on whether to start
2736 // a new CMS cycle.
2737 if (success) {
2738 set_expansion_cause(cause);
2739 if (PrintGCDetails && Verbose) {
2740 gclog_or_tty->print_cr("Expanded CMS gen for %s",
2741 CMSExpansionCause::to_string(cause));
2742 }
2743 }
2744 }
2745
2746 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2747 HeapWord* res = NULL;
2748 MutexLocker x(ParGCRareEvent_lock);
2749 while (true) {
2750 // Expansion by some other thread might make alloc OK now:
2751 res = ps->lab.alloc(word_sz);
2752 if (res != NULL) return res;
2753 // If there's not enough expansion space available, give up.
2754 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2755 return NULL;
2756 }
2757 // Otherwise, we try expansion.
2758 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2759 // Now go around the loop and try alloc again;
2760 // A competing par_promote might beat us to the expansion space,
2761 // so we may go around the loop again if promotion fails again.
2762 if (GCExpandToAllocateDelayMillis > 0) {
2763 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2764 }
2765 }
2766 }
2767
2768
2769 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2770 PromotionInfo* promo) {
2771 MutexLocker x(ParGCRareEvent_lock);
2772 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2773 while (true) {
2774 // Expansion by some other thread might make alloc OK now:
2775 if (promo->ensure_spooling_space()) {
2776 assert(promo->has_spooling_space(),
2777 "Post-condition of successful ensure_spooling_space()");
2778 return true;
2779 }
2780 // If there's not enough expansion space available, give up.
2781 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2782 return false;
2783 }
2784 // Otherwise, we try expansion.
2785 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2786 // Now go around the loop and try alloc again;
2787 // A competing allocation might beat us to the expansion space,
2788 // so we may go around the loop again if allocation fails again.
2789 if (GCExpandToAllocateDelayMillis > 0) {
2790 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2791 }
2792 }
2793 }
2794
2795 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2796 // Only shrink if a compaction was done so that all the free space
2797 // in the generation is in a contiguous block at the end.
2798 if (did_compact()) {
2799 CardGeneration::shrink(bytes);
2800 }
2801 }
2802
2803 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2804 assert_locked_or_safepoint(Heap_lock);
2805 }
2806
2807 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2808 assert_locked_or_safepoint(Heap_lock);
2809 assert_lock_strong(freelistLock());
2810 if (PrintGCDetails && Verbose) {
2811 warning("Shrinking of CMS not yet implemented");
2812 }
2813 return;
2814 }
2815
2816
2817 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2818 // phases.
2819 class CMSPhaseAccounting: public StackObj {
2820 public:
2821 CMSPhaseAccounting(CMSCollector *collector,
2822 const char *phase,
2823 bool print_cr = true);
2824 ~CMSPhaseAccounting();
2825
2826 private:
2827 CMSCollector *_collector;
2828 const char *_phase;
2829 elapsedTimer _wallclock;
2830 bool _print_cr;
2831
2832 public:
2833 // Not MT-safe; so do not pass around these StackObj's
2834 // where they may be accessed by other threads.
2835 jlong wallclock_millis() {
2836 assert(_wallclock.is_active(), "Wall clock should not stop");
2837 _wallclock.stop(); // to record time
2838 jlong ret = _wallclock.milliseconds();
2839 _wallclock.start(); // restart
2840 return ret;
2841 }
2842 };
2843
2844 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2845 const char *phase,
2846 bool print_cr) :
2847 _collector(collector), _phase(phase), _print_cr(print_cr) {
2848
2849 if (PrintCMSStatistics != 0) {
2850 _collector->resetYields();
2851 }
2852 if (PrintGCDetails) {
2853 gclog_or_tty->gclog_stamp();
2854 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
2855 _collector->cmsGen()->short_name(), _phase);
2856 }
2857 _collector->resetTimer();
2858 _wallclock.start();
2859 _collector->startTimer();
2860 }
2861
2862 CMSPhaseAccounting::~CMSPhaseAccounting() {
2863 assert(_wallclock.is_active(), "Wall clock should not have stopped");
2864 _collector->stopTimer();
2865 _wallclock.stop();
2866 if (PrintGCDetails) {
2867 gclog_or_tty->gclog_stamp();
2868 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
2869 _collector->cmsGen()->short_name(),
2870 _phase, _collector->timerValue(), _wallclock.seconds());
2871 if (_print_cr) {
2872 gclog_or_tty->cr();
2873 }
2874 if (PrintCMSStatistics != 0) {
2875 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
2876 _collector->yields());
2877 }
2878 }
2879 }
2880
2881 // CMS work
2882
2883 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2884 class CMSParMarkTask : public AbstractGangTask {
2885 protected:
2886 CMSCollector* _collector;
2887 uint _n_workers;
2888 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2889 AbstractGangTask(name),
2890 _collector(collector),
2891 _n_workers(n_workers) {}
2892 // Work method in support of parallel rescan ... of young gen spaces
2893 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2894 ContiguousSpace* space,
2895 HeapWord** chunk_array, size_t chunk_top);
2896 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2897 };
2898
2899 // Parallel initial mark task
2900 class CMSParInitialMarkTask: public CMSParMarkTask {
2901 StrongRootsScope* _strong_roots_scope;
2902 public:
2903 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2904 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2905 _strong_roots_scope(strong_roots_scope) {}
2906 void work(uint worker_id);
2907 };
2908
2909 // Checkpoint the roots into this generation from outside
2910 // this generation. [Note this initial checkpoint need only
2911 // be approximate -- we'll do a catch up phase subsequently.]
2912 void CMSCollector::checkpointRootsInitial() {
2913 assert(_collectorState == InitialMarking, "Wrong collector state");
2914 check_correct_thread_executing();
2915 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2916
2917 save_heap_summary();
2918 report_heap_summary(GCWhen::BeforeGC);
2919
2920 ReferenceProcessor* rp = ref_processor();
2921 assert(_restart_addr == NULL, "Control point invariant");
2922 {
2923 // acquire locks for subsequent manipulations
2924 MutexLockerEx x(bitMapLock(),
2925 Mutex::_no_safepoint_check_flag);
2926 checkpointRootsInitialWork();
2927 // enable ("weak") refs discovery
2928 rp->enable_discovery();
2929 _collectorState = Marking;
2930 }
2931 }
2932
2933 void CMSCollector::checkpointRootsInitialWork() {
2934 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2935 assert(_collectorState == InitialMarking, "just checking");
2936
2937 // Already have locks.
2938 assert_lock_strong(bitMapLock());
2939 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2940
2941 // Setup the verification and class unloading state for this
2942 // CMS collection cycle.
2943 setup_cms_unloading_and_verification_state();
2944
2945 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
2946 PrintGCDetails && Verbose, true, _gc_timer_cm);)
2947
2948 // Reset all the PLAB chunk arrays if necessary.
2949 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2950 reset_survivor_plab_arrays();
2951 }
2952
2953 ResourceMark rm;
2954 HandleMark hm;
2955
2956 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2957 GenCollectedHeap* gch = GenCollectedHeap::heap();
2958
2959 verify_work_stacks_empty();
2960 verify_overflow_empty();
2961
2962 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2963 // Update the saved marks which may affect the root scans.
2964 gch->save_marks();
2965
2966 // weak reference processing has not started yet.
2967 ref_processor()->set_enqueuing_is_done(false);
2968
2969 // Need to remember all newly created CLDs,
2970 // so that we can guarantee that the remark finds them.
2971 ClassLoaderDataGraph::remember_new_clds(true);
2972
2973 // Whenever a CLD is found, it will be claimed before proceeding to mark
2974 // the klasses. The claimed marks need to be cleared before marking starts.
2975 ClassLoaderDataGraph::clear_claimed_marks();
2976
2977 if (CMSPrintEdenSurvivorChunks) {
2978 print_eden_and_survivor_chunk_arrays();
2979 }
2980
2981 {
2982 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2983 if (CMSParallelInitialMarkEnabled) {
2984 // The parallel version.
2985 WorkGang* workers = gch->workers();
2986 assert(workers != NULL, "Need parallel worker threads.");
2987 uint n_workers = workers->active_workers();
2988
2989 StrongRootsScope srs(n_workers);
2990
2991 CMSParInitialMarkTask tsk(this, &srs, n_workers);
2992 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2993 if (n_workers > 1) {
2994 workers->run_task(&tsk);
2995 } else {
2996 tsk.work(0);
2997 }
2998 } else {
2999 // The serial version.
3000 CLDToOopClosure cld_closure(¬Older, true);
3001 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3002
3003 StrongRootsScope srs(1);
3004
3005 gch->old_process_roots(&srs,
3006 true, // young gen as roots
3007 GenCollectedHeap::ScanningOption(roots_scanning_options()),
3008 should_unload_classes(),
3009 ¬Older,
3010 &cld_closure);
3011 }
3012 }
3013
3014 // Clear mod-union table; it will be dirtied in the prologue of
3015 // CMS generation per each young generation collection.
3016
3017 assert(_modUnionTable.isAllClear(),
3018 "Was cleared in most recent final checkpoint phase"
3019 " or no bits are set in the gc_prologue before the start of the next "
3020 "subsequent marking phase.");
3021
3022 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3023
3024 // Save the end of the used_region of the constituent generations
3025 // to be used to limit the extent of sweep in each generation.
3026 save_sweep_limits();
3027 verify_overflow_empty();
3028 }
3029
3030 bool CMSCollector::markFromRoots() {
3031 // we might be tempted to assert that:
3032 // assert(!SafepointSynchronize::is_at_safepoint(),
3033 // "inconsistent argument?");
3034 // However that wouldn't be right, because it's possible that
3035 // a safepoint is indeed in progress as a young generation
3036 // stop-the-world GC happens even as we mark in this generation.
3037 assert(_collectorState == Marking, "inconsistent state?");
3038 check_correct_thread_executing();
3039 verify_overflow_empty();
3040
3041 // Weak ref discovery note: We may be discovering weak
3042 // refs in this generation concurrent (but interleaved) with
3043 // weak ref discovery by the young generation collector.
3044
3045 CMSTokenSyncWithLocks ts(true, bitMapLock());
3046 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3047 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3048 bool res = markFromRootsWork();
3049 if (res) {
3050 _collectorState = Precleaning;
3051 } else { // We failed and a foreground collection wants to take over
3052 assert(_foregroundGCIsActive, "internal state inconsistency");
3053 assert(_restart_addr == NULL, "foreground will restart from scratch");
3054 if (PrintGCDetails) {
3055 gclog_or_tty->print_cr("bailing out to foreground collection");
3056 }
3057 }
3058 verify_overflow_empty();
3059 return res;
3060 }
3061
3062 bool CMSCollector::markFromRootsWork() {
3063 // iterate over marked bits in bit map, doing a full scan and mark
3064 // from these roots using the following algorithm:
3065 // . if oop is to the right of the current scan pointer,
3066 // mark corresponding bit (we'll process it later)
3067 // . else (oop is to left of current scan pointer)
3068 // push oop on marking stack
3069 // . drain the marking stack
3070
3071 // Note that when we do a marking step we need to hold the
3072 // bit map lock -- recall that direct allocation (by mutators)
3073 // and promotion (by the young generation collector) is also
3074 // marking the bit map. [the so-called allocate live policy.]
3075 // Because the implementation of bit map marking is not
3076 // robust wrt simultaneous marking of bits in the same word,
3077 // we need to make sure that there is no such interference
3078 // between concurrent such updates.
3079
3080 // already have locks
3081 assert_lock_strong(bitMapLock());
3082
3083 verify_work_stacks_empty();
3084 verify_overflow_empty();
3085 bool result = false;
3086 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3087 result = do_marking_mt();
3088 } else {
3089 result = do_marking_st();
3090 }
3091 return result;
3092 }
3093
3094 // Forward decl
3095 class CMSConcMarkingTask;
3096
3097 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3098 CMSCollector* _collector;
3099 CMSConcMarkingTask* _task;
3100 public:
3101 virtual void yield();
3102
3103 // "n_threads" is the number of threads to be terminated.
3104 // "queue_set" is a set of work queues of other threads.
3105 // "collector" is the CMS collector associated with this task terminator.
3106 // "yield" indicates whether we need the gang as a whole to yield.
3107 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3108 ParallelTaskTerminator(n_threads, queue_set),
3109 _collector(collector) { }
3110
3111 void set_task(CMSConcMarkingTask* task) {
3112 _task = task;
3113 }
3114 };
3115
3116 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3117 CMSConcMarkingTask* _task;
3118 public:
3119 bool should_exit_termination();
3120 void set_task(CMSConcMarkingTask* task) {
3121 _task = task;
3122 }
3123 };
3124
3125 // MT Concurrent Marking Task
3126 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3127 CMSCollector* _collector;
3128 uint _n_workers; // requested/desired # workers
3129 bool _result;
3130 CompactibleFreeListSpace* _cms_space;
3131 char _pad_front[64]; // padding to ...
3132 HeapWord* _global_finger; // ... avoid sharing cache line
3133 char _pad_back[64];
3134 HeapWord* _restart_addr;
3135
3136 // Exposed here for yielding support
3137 Mutex* const _bit_map_lock;
3138
3139 // The per thread work queues, available here for stealing
3140 OopTaskQueueSet* _task_queues;
3141
3142 // Termination (and yielding) support
3143 CMSConcMarkingTerminator _term;
3144 CMSConcMarkingTerminatorTerminator _term_term;
3145
3146 public:
3147 CMSConcMarkingTask(CMSCollector* collector,
3148 CompactibleFreeListSpace* cms_space,
3149 YieldingFlexibleWorkGang* workers,
3150 OopTaskQueueSet* task_queues):
3151 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3152 _collector(collector),
3153 _cms_space(cms_space),
3154 _n_workers(0), _result(true),
3155 _task_queues(task_queues),
3156 _term(_n_workers, task_queues, _collector),
3157 _bit_map_lock(collector->bitMapLock())
3158 {
3159 _requested_size = _n_workers;
3160 _term.set_task(this);
3161 _term_term.set_task(this);
3162 _restart_addr = _global_finger = _cms_space->bottom();
3163 }
3164
3165
3166 OopTaskQueueSet* task_queues() { return _task_queues; }
3167
3168 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3169
3170 HeapWord** global_finger_addr() { return &_global_finger; }
3171
3172 CMSConcMarkingTerminator* terminator() { return &_term; }
3173
3174 virtual void set_for_termination(uint active_workers) {
3175 terminator()->reset_for_reuse(active_workers);
3176 }
3177
3178 void work(uint worker_id);
3179 bool should_yield() {
3180 return ConcurrentMarkSweepThread::should_yield()
3181 && !_collector->foregroundGCIsActive();
3182 }
3183
3184 virtual void coordinator_yield(); // stuff done by coordinator
3185 bool result() { return _result; }
3186
3187 void reset(HeapWord* ra) {
3188 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3189 _restart_addr = _global_finger = ra;
3190 _term.reset_for_reuse();
3191 }
3192
3193 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3194 OopTaskQueue* work_q);
3195
3196 private:
3197 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3198 void do_work_steal(int i);
3199 void bump_global_finger(HeapWord* f);
3200 };
3201
3202 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3203 assert(_task != NULL, "Error");
3204 return _task->yielding();
3205 // Note that we do not need the disjunct || _task->should_yield() above
3206 // because we want terminating threads to yield only if the task
3207 // is already in the midst of yielding, which happens only after at least one
3208 // thread has yielded.
3209 }
3210
3211 void CMSConcMarkingTerminator::yield() {
3212 if (_task->should_yield()) {
3213 _task->yield();
3214 } else {
3215 ParallelTaskTerminator::yield();
3216 }
3217 }
3218
3219 ////////////////////////////////////////////////////////////////
3220 // Concurrent Marking Algorithm Sketch
3221 ////////////////////////////////////////////////////////////////
3222 // Until all tasks exhausted (both spaces):
3223 // -- claim next available chunk
3224 // -- bump global finger via CAS
3225 // -- find first object that starts in this chunk
3226 // and start scanning bitmap from that position
3227 // -- scan marked objects for oops
3228 // -- CAS-mark target, and if successful:
3229 // . if target oop is above global finger (volatile read)
3230 // nothing to do
3231 // . if target oop is in chunk and above local finger
3232 // then nothing to do
3233 // . else push on work-queue
3234 // -- Deal with possible overflow issues:
3235 // . local work-queue overflow causes stuff to be pushed on
3236 // global (common) overflow queue
3237 // . always first empty local work queue
3238 // . then get a batch of oops from global work queue if any
3239 // . then do work stealing
3240 // -- When all tasks claimed (both spaces)
3241 // and local work queue empty,
3242 // then in a loop do:
3243 // . check global overflow stack; steal a batch of oops and trace
3244 // . try to steal from other threads oif GOS is empty
3245 // . if neither is available, offer termination
3246 // -- Terminate and return result
3247 //
3248 void CMSConcMarkingTask::work(uint worker_id) {
3249 elapsedTimer _timer;
3250 ResourceMark rm;
3251 HandleMark hm;
3252
3253 DEBUG_ONLY(_collector->verify_overflow_empty();)
3254
3255 // Before we begin work, our work queue should be empty
3256 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3257 // Scan the bitmap covering _cms_space, tracing through grey objects.
3258 _timer.start();
3259 do_scan_and_mark(worker_id, _cms_space);
3260 _timer.stop();
3261 if (PrintCMSStatistics != 0) {
3262 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3263 worker_id, _timer.seconds());
3264 // XXX: need xxx/xxx type of notation, two timers
3265 }
3266
3267 // ... do work stealing
3268 _timer.reset();
3269 _timer.start();
3270 do_work_steal(worker_id);
3271 _timer.stop();
3272 if (PrintCMSStatistics != 0) {
3273 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3274 worker_id, _timer.seconds());
3275 // XXX: need xxx/xxx type of notation, two timers
3276 }
3277 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3278 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3279 // Note that under the current task protocol, the
3280 // following assertion is true even of the spaces
3281 // expanded since the completion of the concurrent
3282 // marking. XXX This will likely change under a strict
3283 // ABORT semantics.
3284 // After perm removal the comparison was changed to
3285 // greater than or equal to from strictly greater than.
3286 // Before perm removal the highest address sweep would
3287 // have been at the end of perm gen but now is at the
3288 // end of the tenured gen.
3289 assert(_global_finger >= _cms_space->end(),
3290 "All tasks have been completed");
3291 DEBUG_ONLY(_collector->verify_overflow_empty();)
3292 }
3293
3294 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3295 HeapWord* read = _global_finger;
3296 HeapWord* cur = read;
3297 while (f > read) {
3298 cur = read;
3299 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3300 if (cur == read) {
3301 // our cas succeeded
3302 assert(_global_finger >= f, "protocol consistency");
3303 break;
3304 }
3305 }
3306 }
3307
3308 // This is really inefficient, and should be redone by
3309 // using (not yet available) block-read and -write interfaces to the
3310 // stack and the work_queue. XXX FIX ME !!!
3311 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3312 OopTaskQueue* work_q) {
3313 // Fast lock-free check
3314 if (ovflw_stk->length() == 0) {
3315 return false;
3316 }
3317 assert(work_q->size() == 0, "Shouldn't steal");
3318 MutexLockerEx ml(ovflw_stk->par_lock(),
3319 Mutex::_no_safepoint_check_flag);
3320 // Grab up to 1/4 the size of the work queue
3321 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3322 (size_t)ParGCDesiredObjsFromOverflowList);
3323 num = MIN2(num, ovflw_stk->length());
3324 for (int i = (int) num; i > 0; i--) {
3325 oop cur = ovflw_stk->pop();
3326 assert(cur != NULL, "Counted wrong?");
3327 work_q->push(cur);
3328 }
3329 return num > 0;
3330 }
3331
3332 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3333 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3334 int n_tasks = pst->n_tasks();
3335 // We allow that there may be no tasks to do here because
3336 // we are restarting after a stack overflow.
3337 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3338 uint nth_task = 0;
3339
3340 HeapWord* aligned_start = sp->bottom();
3341 if (sp->used_region().contains(_restart_addr)) {
3342 // Align down to a card boundary for the start of 0th task
3343 // for this space.
3344 aligned_start =
3345 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3346 CardTableModRefBS::card_size);
3347 }
3348
3349 size_t chunk_size = sp->marking_task_size();
3350 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3351 // Having claimed the nth task in this space,
3352 // compute the chunk that it corresponds to:
3353 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3354 aligned_start + (nth_task+1)*chunk_size);
3355 // Try and bump the global finger via a CAS;
3356 // note that we need to do the global finger bump
3357 // _before_ taking the intersection below, because
3358 // the task corresponding to that region will be
3359 // deemed done even if the used_region() expands
3360 // because of allocation -- as it almost certainly will
3361 // during start-up while the threads yield in the
3362 // closure below.
3363 HeapWord* finger = span.end();
3364 bump_global_finger(finger); // atomically
3365 // There are null tasks here corresponding to chunks
3366 // beyond the "top" address of the space.
3367 span = span.intersection(sp->used_region());
3368 if (!span.is_empty()) { // Non-null task
3369 HeapWord* prev_obj;
3370 assert(!span.contains(_restart_addr) || nth_task == 0,
3371 "Inconsistency");
3372 if (nth_task == 0) {
3373 // For the 0th task, we'll not need to compute a block_start.
3374 if (span.contains(_restart_addr)) {
3375 // In the case of a restart because of stack overflow,
3376 // we might additionally skip a chunk prefix.
3377 prev_obj = _restart_addr;
3378 } else {
3379 prev_obj = span.start();
3380 }
3381 } else {
3382 // We want to skip the first object because
3383 // the protocol is to scan any object in its entirety
3384 // that _starts_ in this span; a fortiori, any
3385 // object starting in an earlier span is scanned
3386 // as part of an earlier claimed task.
3387 // Below we use the "careful" version of block_start
3388 // so we do not try to navigate uninitialized objects.
3389 prev_obj = sp->block_start_careful(span.start());
3390 // Below we use a variant of block_size that uses the
3391 // Printezis bits to avoid waiting for allocated
3392 // objects to become initialized/parsable.
3393 while (prev_obj < span.start()) {
3394 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3395 if (sz > 0) {
3396 prev_obj += sz;
3397 } else {
3398 // In this case we may end up doing a bit of redundant
3399 // scanning, but that appears unavoidable, short of
3400 // locking the free list locks; see bug 6324141.
3401 break;
3402 }
3403 }
3404 }
3405 if (prev_obj < span.end()) {
3406 MemRegion my_span = MemRegion(prev_obj, span.end());
3407 // Do the marking work within a non-empty span --
3408 // the last argument to the constructor indicates whether the
3409 // iteration should be incremental with periodic yields.
3410 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3411 &_collector->_markBitMap,
3412 work_queue(i),
3413 &_collector->_markStack);
3414 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3415 } // else nothing to do for this task
3416 } // else nothing to do for this task
3417 }
3418 // We'd be tempted to assert here that since there are no
3419 // more tasks left to claim in this space, the global_finger
3420 // must exceed space->top() and a fortiori space->end(). However,
3421 // that would not quite be correct because the bumping of
3422 // global_finger occurs strictly after the claiming of a task,
3423 // so by the time we reach here the global finger may not yet
3424 // have been bumped up by the thread that claimed the last
3425 // task.
3426 pst->all_tasks_completed();
3427 }
3428
3429 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3430 private:
3431 CMSCollector* _collector;
3432 CMSConcMarkingTask* _task;
3433 MemRegion _span;
3434 CMSBitMap* _bit_map;
3435 CMSMarkStack* _overflow_stack;
3436 OopTaskQueue* _work_queue;
3437 protected:
3438 DO_OOP_WORK_DEFN
3439 public:
3440 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3441 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3442 MetadataAwareOopClosure(collector->ref_processor()),
3443 _collector(collector),
3444 _task(task),
3445 _span(collector->_span),
3446 _work_queue(work_queue),
3447 _bit_map(bit_map),
3448 _overflow_stack(overflow_stack)
3449 { }
3450 virtual void do_oop(oop* p);
3451 virtual void do_oop(narrowOop* p);
3452
3453 void trim_queue(size_t max);
3454 void handle_stack_overflow(HeapWord* lost);
3455 void do_yield_check() {
3456 if (_task->should_yield()) {
3457 _task->yield();
3458 }
3459 }
3460 };
3461
3462 // Grey object scanning during work stealing phase --
3463 // the salient assumption here is that any references
3464 // that are in these stolen objects being scanned must
3465 // already have been initialized (else they would not have
3466 // been published), so we do not need to check for
3467 // uninitialized objects before pushing here.
3468 void Par_ConcMarkingClosure::do_oop(oop obj) {
3469 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3470 HeapWord* addr = (HeapWord*)obj;
3471 // Check if oop points into the CMS generation
3472 // and is not marked
3473 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3474 // a white object ...
3475 // If we manage to "claim" the object, by being the
3476 // first thread to mark it, then we push it on our
3477 // marking stack
3478 if (_bit_map->par_mark(addr)) { // ... now grey
3479 // push on work queue (grey set)
3480 bool simulate_overflow = false;
3481 NOT_PRODUCT(
3482 if (CMSMarkStackOverflowALot &&
3483 _collector->simulate_overflow()) {
3484 // simulate a stack overflow
3485 simulate_overflow = true;
3486 }
3487 )
3488 if (simulate_overflow ||
3489 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3490 // stack overflow
3491 if (PrintCMSStatistics != 0) {
3492 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3493 SIZE_FORMAT, _overflow_stack->capacity());
3494 }
3495 // We cannot assert that the overflow stack is full because
3496 // it may have been emptied since.
3497 assert(simulate_overflow ||
3498 _work_queue->size() == _work_queue->max_elems(),
3499 "Else push should have succeeded");
3500 handle_stack_overflow(addr);
3501 }
3502 } // Else, some other thread got there first
3503 do_yield_check();
3504 }
3505 }
3506
3507 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3508 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3509
3510 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3511 while (_work_queue->size() > max) {
3512 oop new_oop;
3513 if (_work_queue->pop_local(new_oop)) {
3514 assert(new_oop->is_oop(), "Should be an oop");
3515 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3516 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3517 new_oop->oop_iterate(this); // do_oop() above
3518 do_yield_check();
3519 }
3520 }
3521 }
3522
3523 // Upon stack overflow, we discard (part of) the stack,
3524 // remembering the least address amongst those discarded
3525 // in CMSCollector's _restart_address.
3526 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3527 // We need to do this under a mutex to prevent other
3528 // workers from interfering with the work done below.
3529 MutexLockerEx ml(_overflow_stack->par_lock(),
3530 Mutex::_no_safepoint_check_flag);
3531 // Remember the least grey address discarded
3532 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3533 _collector->lower_restart_addr(ra);
3534 _overflow_stack->reset(); // discard stack contents
3535 _overflow_stack->expand(); // expand the stack if possible
3536 }
3537
3538
3539 void CMSConcMarkingTask::do_work_steal(int i) {
3540 OopTaskQueue* work_q = work_queue(i);
3541 oop obj_to_scan;
3542 CMSBitMap* bm = &(_collector->_markBitMap);
3543 CMSMarkStack* ovflw = &(_collector->_markStack);
3544 int* seed = _collector->hash_seed(i);
3545 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3546 while (true) {
3547 cl.trim_queue(0);
3548 assert(work_q->size() == 0, "Should have been emptied above");
3549 if (get_work_from_overflow_stack(ovflw, work_q)) {
3550 // Can't assert below because the work obtained from the
3551 // overflow stack may already have been stolen from us.
3552 // assert(work_q->size() > 0, "Work from overflow stack");
3553 continue;
3554 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3555 assert(obj_to_scan->is_oop(), "Should be an oop");
3556 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3557 obj_to_scan->oop_iterate(&cl);
3558 } else if (terminator()->offer_termination(&_term_term)) {
3559 assert(work_q->size() == 0, "Impossible!");
3560 break;
3561 } else if (yielding() || should_yield()) {
3562 yield();
3563 }
3564 }
3565 }
3566
3567 // This is run by the CMS (coordinator) thread.
3568 void CMSConcMarkingTask::coordinator_yield() {
3569 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3570 "CMS thread should hold CMS token");
3571 // First give up the locks, then yield, then re-lock
3572 // We should probably use a constructor/destructor idiom to
3573 // do this unlock/lock or modify the MutexUnlocker class to
3574 // serve our purpose. XXX
3575 assert_lock_strong(_bit_map_lock);
3576 _bit_map_lock->unlock();
3577 ConcurrentMarkSweepThread::desynchronize(true);
3578 _collector->stopTimer();
3579 if (PrintCMSStatistics != 0) {
3580 _collector->incrementYields();
3581 }
3582
3583 // It is possible for whichever thread initiated the yield request
3584 // not to get a chance to wake up and take the bitmap lock between
3585 // this thread releasing it and reacquiring it. So, while the
3586 // should_yield() flag is on, let's sleep for a bit to give the
3587 // other thread a chance to wake up. The limit imposed on the number
3588 // of iterations is defensive, to avoid any unforseen circumstances
3589 // putting us into an infinite loop. Since it's always been this
3590 // (coordinator_yield()) method that was observed to cause the
3591 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3592 // which is by default non-zero. For the other seven methods that
3593 // also perform the yield operation, as are using a different
3594 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3595 // can enable the sleeping for those methods too, if necessary.
3596 // See 6442774.
3597 //
3598 // We really need to reconsider the synchronization between the GC
3599 // thread and the yield-requesting threads in the future and we
3600 // should really use wait/notify, which is the recommended
3601 // way of doing this type of interaction. Additionally, we should
3602 // consolidate the eight methods that do the yield operation and they
3603 // are almost identical into one for better maintainability and
3604 // readability. See 6445193.
3605 //
3606 // Tony 2006.06.29
3607 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3608 ConcurrentMarkSweepThread::should_yield() &&
3609 !CMSCollector::foregroundGCIsActive(); ++i) {
3610 os::sleep(Thread::current(), 1, false);
3611 }
3612
3613 ConcurrentMarkSweepThread::synchronize(true);
3614 _bit_map_lock->lock_without_safepoint_check();
3615 _collector->startTimer();
3616 }
3617
3618 bool CMSCollector::do_marking_mt() {
3619 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3620 uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3621 conc_workers()->active_workers(),
3622 Threads::number_of_non_daemon_threads());
3623 conc_workers()->set_active_workers(num_workers);
3624
3625 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3626
3627 CMSConcMarkingTask tsk(this,
3628 cms_space,
3629 conc_workers(),
3630 task_queues());
3631
3632 // Since the actual number of workers we get may be different
3633 // from the number we requested above, do we need to do anything different
3634 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3635 // class?? XXX
3636 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3637
3638 // Refs discovery is already non-atomic.
3639 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3640 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3641 conc_workers()->start_task(&tsk);
3642 while (tsk.yielded()) {
3643 tsk.coordinator_yield();
3644 conc_workers()->continue_task(&tsk);
3645 }
3646 // If the task was aborted, _restart_addr will be non-NULL
3647 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3648 while (_restart_addr != NULL) {
3649 // XXX For now we do not make use of ABORTED state and have not
3650 // yet implemented the right abort semantics (even in the original
3651 // single-threaded CMS case). That needs some more investigation
3652 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3653 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3654 // If _restart_addr is non-NULL, a marking stack overflow
3655 // occurred; we need to do a fresh marking iteration from the
3656 // indicated restart address.
3657 if (_foregroundGCIsActive) {
3658 // We may be running into repeated stack overflows, having
3659 // reached the limit of the stack size, while making very
3660 // slow forward progress. It may be best to bail out and
3661 // let the foreground collector do its job.
3662 // Clear _restart_addr, so that foreground GC
3663 // works from scratch. This avoids the headache of
3664 // a "rescan" which would otherwise be needed because
3665 // of the dirty mod union table & card table.
3666 _restart_addr = NULL;
3667 return false;
3668 }
3669 // Adjust the task to restart from _restart_addr
3670 tsk.reset(_restart_addr);
3671 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3672 _restart_addr);
3673 _restart_addr = NULL;
3674 // Get the workers going again
3675 conc_workers()->start_task(&tsk);
3676 while (tsk.yielded()) {
3677 tsk.coordinator_yield();
3678 conc_workers()->continue_task(&tsk);
3679 }
3680 }
3681 assert(tsk.completed(), "Inconsistency");
3682 assert(tsk.result() == true, "Inconsistency");
3683 return true;
3684 }
3685
3686 bool CMSCollector::do_marking_st() {
3687 ResourceMark rm;
3688 HandleMark hm;
3689
3690 // Temporarily make refs discovery single threaded (non-MT)
3691 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3692 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3693 &_markStack, CMSYield);
3694 // the last argument to iterate indicates whether the iteration
3695 // should be incremental with periodic yields.
3696 _markBitMap.iterate(&markFromRootsClosure);
3697 // If _restart_addr is non-NULL, a marking stack overflow
3698 // occurred; we need to do a fresh iteration from the
3699 // indicated restart address.
3700 while (_restart_addr != NULL) {
3701 if (_foregroundGCIsActive) {
3702 // We may be running into repeated stack overflows, having
3703 // reached the limit of the stack size, while making very
3704 // slow forward progress. It may be best to bail out and
3705 // let the foreground collector do its job.
3706 // Clear _restart_addr, so that foreground GC
3707 // works from scratch. This avoids the headache of
3708 // a "rescan" which would otherwise be needed because
3709 // of the dirty mod union table & card table.
3710 _restart_addr = NULL;
3711 return false; // indicating failure to complete marking
3712 }
3713 // Deal with stack overflow:
3714 // we restart marking from _restart_addr
3715 HeapWord* ra = _restart_addr;
3716 markFromRootsClosure.reset(ra);
3717 _restart_addr = NULL;
3718 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3719 }
3720 return true;
3721 }
3722
3723 void CMSCollector::preclean() {
3724 check_correct_thread_executing();
3725 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3726 verify_work_stacks_empty();
3727 verify_overflow_empty();
3728 _abort_preclean = false;
3729 if (CMSPrecleaningEnabled) {
3730 if (!CMSEdenChunksRecordAlways) {
3731 _eden_chunk_index = 0;
3732 }
3733 size_t used = get_eden_used();
3734 size_t capacity = get_eden_capacity();
3735 // Don't start sampling unless we will get sufficiently
3736 // many samples.
3737 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3738 * CMSScheduleRemarkEdenPenetration)) {
3739 _start_sampling = true;
3740 } else {
3741 _start_sampling = false;
3742 }
3743 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3744 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
3745 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3746 }
3747 CMSTokenSync x(true); // is cms thread
3748 if (CMSPrecleaningEnabled) {
3749 sample_eden();
3750 _collectorState = AbortablePreclean;
3751 } else {
3752 _collectorState = FinalMarking;
3753 }
3754 verify_work_stacks_empty();
3755 verify_overflow_empty();
3756 }
3757
3758 // Try and schedule the remark such that young gen
3759 // occupancy is CMSScheduleRemarkEdenPenetration %.
3760 void CMSCollector::abortable_preclean() {
3761 check_correct_thread_executing();
3762 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3763 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3764
3765 // If Eden's current occupancy is below this threshold,
3766 // immediately schedule the remark; else preclean
3767 // past the next scavenge in an effort to
3768 // schedule the pause as described above. By choosing
3769 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3770 // we will never do an actual abortable preclean cycle.
3771 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3772 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3773 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
3774 // We need more smarts in the abortable preclean
3775 // loop below to deal with cases where allocation
3776 // in young gen is very very slow, and our precleaning
3777 // is running a losing race against a horde of
3778 // mutators intent on flooding us with CMS updates
3779 // (dirty cards).
3780 // One, admittedly dumb, strategy is to give up
3781 // after a certain number of abortable precleaning loops
3782 // or after a certain maximum time. We want to make
3783 // this smarter in the next iteration.
3784 // XXX FIX ME!!! YSR
3785 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3786 while (!(should_abort_preclean() ||
3787 ConcurrentMarkSweepThread::should_terminate())) {
3788 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3789 cumworkdone += workdone;
3790 loops++;
3791 // Voluntarily terminate abortable preclean phase if we have
3792 // been at it for too long.
3793 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3794 loops >= CMSMaxAbortablePrecleanLoops) {
3795 if (PrintGCDetails) {
3796 gclog_or_tty->print(" CMS: abort preclean due to loops ");
3797 }
3798 break;
3799 }
3800 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3801 if (PrintGCDetails) {
3802 gclog_or_tty->print(" CMS: abort preclean due to time ");
3803 }
3804 break;
3805 }
3806 // If we are doing little work each iteration, we should
3807 // take a short break.
3808 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3809 // Sleep for some time, waiting for work to accumulate
3810 stopTimer();
3811 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3812 startTimer();
3813 waited++;
3814 }
3815 }
3816 if (PrintCMSStatistics > 0) {
3817 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3818 loops, waited, cumworkdone);
3819 }
3820 }
3821 CMSTokenSync x(true); // is cms thread
3822 if (_collectorState != Idling) {
3823 assert(_collectorState == AbortablePreclean,
3824 "Spontaneous state transition?");
3825 _collectorState = FinalMarking;
3826 } // Else, a foreground collection completed this CMS cycle.
3827 return;
3828 }
3829
3830 // Respond to an Eden sampling opportunity
3831 void CMSCollector::sample_eden() {
3832 // Make sure a young gc cannot sneak in between our
3833 // reading and recording of a sample.
3834 assert(Thread::current()->is_ConcurrentGC_thread(),
3835 "Only the cms thread may collect Eden samples");
3836 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3837 "Should collect samples while holding CMS token");
3838 if (!_start_sampling) {
3839 return;
3840 }
3841 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3842 // is populated by the young generation.
3843 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3844 if (_eden_chunk_index < _eden_chunk_capacity) {
3845 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3846 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3847 "Unexpected state of Eden");
3848 // We'd like to check that what we just sampled is an oop-start address;
3849 // however, we cannot do that here since the object may not yet have been
3850 // initialized. So we'll instead do the check when we _use_ this sample
3851 // later.
3852 if (_eden_chunk_index == 0 ||
3853 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3854 _eden_chunk_array[_eden_chunk_index-1])
3855 >= CMSSamplingGrain)) {
3856 _eden_chunk_index++; // commit sample
3857 }
3858 }
3859 }
3860 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3861 size_t used = get_eden_used();
3862 size_t capacity = get_eden_capacity();
3863 assert(used <= capacity, "Unexpected state of Eden");
3864 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3865 _abort_preclean = true;
3866 }
3867 }
3868 }
3869
3870
3871 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3872 assert(_collectorState == Precleaning ||
3873 _collectorState == AbortablePreclean, "incorrect state");
3874 ResourceMark rm;
3875 HandleMark hm;
3876
3877 // Precleaning is currently not MT but the reference processor
3878 // may be set for MT. Disable it temporarily here.
3879 ReferenceProcessor* rp = ref_processor();
3880 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3881
3882 // Do one pass of scrubbing the discovered reference lists
3883 // to remove any reference objects with strongly-reachable
3884 // referents.
3885 if (clean_refs) {
3886 CMSPrecleanRefsYieldClosure yield_cl(this);
3887 assert(rp->span().equals(_span), "Spans should be equal");
3888 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3889 &_markStack, true /* preclean */);
3890 CMSDrainMarkingStackClosure complete_trace(this,
3891 _span, &_markBitMap, &_markStack,
3892 &keep_alive, true /* preclean */);
3893
3894 // We don't want this step to interfere with a young
3895 // collection because we don't want to take CPU
3896 // or memory bandwidth away from the young GC threads
3897 // (which may be as many as there are CPUs).
3898 // Note that we don't need to protect ourselves from
3899 // interference with mutators because they can't
3900 // manipulate the discovered reference lists nor affect
3901 // the computed reachability of the referents, the
3902 // only properties manipulated by the precleaning
3903 // of these reference lists.
3904 stopTimer();
3905 CMSTokenSyncWithLocks x(true /* is cms thread */,
3906 bitMapLock());
3907 startTimer();
3908 sample_eden();
3909
3910 // The following will yield to allow foreground
3911 // collection to proceed promptly. XXX YSR:
3912 // The code in this method may need further
3913 // tweaking for better performance and some restructuring
3914 // for cleaner interfaces.
3915 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3916 rp->preclean_discovered_references(
3917 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3918 gc_timer);
3919 }
3920
3921 if (clean_survivor) { // preclean the active survivor space(s)
3922 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3923 &_markBitMap, &_modUnionTable,
3924 &_markStack, true /* precleaning phase */);
3925 stopTimer();
3926 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3927 bitMapLock());
3928 startTimer();
3929 unsigned int before_count =
3930 GenCollectedHeap::heap()->total_collections();
3931 SurvivorSpacePrecleanClosure
3932 sss_cl(this, _span, &_markBitMap, &_markStack,
3933 &pam_cl, before_count, CMSYield);
3934 _young_gen->from()->object_iterate_careful(&sss_cl);
3935 _young_gen->to()->object_iterate_careful(&sss_cl);
3936 }
3937 MarkRefsIntoAndScanClosure
3938 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3939 &_markStack, this, CMSYield,
3940 true /* precleaning phase */);
3941 // CAUTION: The following closure has persistent state that may need to
3942 // be reset upon a decrease in the sequence of addresses it
3943 // processes.
3944 ScanMarkedObjectsAgainCarefullyClosure
3945 smoac_cl(this, _span,
3946 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3947
3948 // Preclean dirty cards in ModUnionTable and CardTable using
3949 // appropriate convergence criterion;
3950 // repeat CMSPrecleanIter times unless we find that
3951 // we are losing.
3952 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3953 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3954 "Bad convergence multiplier");
3955 assert(CMSPrecleanThreshold >= 100,
3956 "Unreasonably low CMSPrecleanThreshold");
3957
3958 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3959 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3960 numIter < CMSPrecleanIter;
3961 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3962 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3963 if (Verbose && PrintGCDetails) {
3964 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3965 }
3966 // Either there are very few dirty cards, so re-mark
3967 // pause will be small anyway, or our pre-cleaning isn't
3968 // that much faster than the rate at which cards are being
3969 // dirtied, so we might as well stop and re-mark since
3970 // precleaning won't improve our re-mark time by much.
3971 if (curNumCards <= CMSPrecleanThreshold ||
3972 (numIter > 0 &&
3973 (curNumCards * CMSPrecleanDenominator >
3974 lastNumCards * CMSPrecleanNumerator))) {
3975 numIter++;
3976 cumNumCards += curNumCards;
3977 break;
3978 }
3979 }
3980
3981 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
3982
3983 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3984 cumNumCards += curNumCards;
3985 if (PrintGCDetails && PrintCMSStatistics != 0) {
3986 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3987 curNumCards, cumNumCards, numIter);
3988 }
3989 return cumNumCards; // as a measure of useful work done
3990 }
3991
3992 // PRECLEANING NOTES:
3993 // Precleaning involves:
3994 // . reading the bits of the modUnionTable and clearing the set bits.
3995 // . For the cards corresponding to the set bits, we scan the
3996 // objects on those cards. This means we need the free_list_lock
3997 // so that we can safely iterate over the CMS space when scanning
3998 // for oops.
3999 // . When we scan the objects, we'll be both reading and setting
4000 // marks in the marking bit map, so we'll need the marking bit map.
4001 // . For protecting _collector_state transitions, we take the CGC_lock.
4002 // Note that any races in the reading of of card table entries by the
4003 // CMS thread on the one hand and the clearing of those entries by the
4004 // VM thread or the setting of those entries by the mutator threads on the
4005 // other are quite benign. However, for efficiency it makes sense to keep
4006 // the VM thread from racing with the CMS thread while the latter is
4007 // dirty card info to the modUnionTable. We therefore also use the
4008 // CGC_lock to protect the reading of the card table and the mod union
4009 // table by the CM thread.
4010 // . We run concurrently with mutator updates, so scanning
4011 // needs to be done carefully -- we should not try to scan
4012 // potentially uninitialized objects.
4013 //
4014 // Locking strategy: While holding the CGC_lock, we scan over and
4015 // reset a maximal dirty range of the mod union / card tables, then lock
4016 // the free_list_lock and bitmap lock to do a full marking, then
4017 // release these locks; and repeat the cycle. This allows for a
4018 // certain amount of fairness in the sharing of these locks between
4019 // the CMS collector on the one hand, and the VM thread and the
4020 // mutators on the other.
4021
4022 // NOTE: preclean_mod_union_table() and preclean_card_table()
4023 // further below are largely identical; if you need to modify
4024 // one of these methods, please check the other method too.
4025
4026 size_t CMSCollector::preclean_mod_union_table(
4027 ConcurrentMarkSweepGeneration* old_gen,
4028 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4029 verify_work_stacks_empty();
4030 verify_overflow_empty();
4031
4032 // strategy: starting with the first card, accumulate contiguous
4033 // ranges of dirty cards; clear these cards, then scan the region
4034 // covered by these cards.
4035
4036 // Since all of the MUT is committed ahead, we can just use
4037 // that, in case the generations expand while we are precleaning.
4038 // It might also be fine to just use the committed part of the
4039 // generation, but we might potentially miss cards when the
4040 // generation is rapidly expanding while we are in the midst
4041 // of precleaning.
4042 HeapWord* startAddr = old_gen->reserved().start();
4043 HeapWord* endAddr = old_gen->reserved().end();
4044
4045 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4046
4047 size_t numDirtyCards, cumNumDirtyCards;
4048 HeapWord *nextAddr, *lastAddr;
4049 for (cumNumDirtyCards = numDirtyCards = 0,
4050 nextAddr = lastAddr = startAddr;
4051 nextAddr < endAddr;
4052 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4053
4054 ResourceMark rm;
4055 HandleMark hm;
4056
4057 MemRegion dirtyRegion;
4058 {
4059 stopTimer();
4060 // Potential yield point
4061 CMSTokenSync ts(true);
4062 startTimer();
4063 sample_eden();
4064 // Get dirty region starting at nextOffset (inclusive),
4065 // simultaneously clearing it.
4066 dirtyRegion =
4067 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4068 assert(dirtyRegion.start() >= nextAddr,
4069 "returned region inconsistent?");
4070 }
4071 // Remember where the next search should begin.
4072 // The returned region (if non-empty) is a right open interval,
4073 // so lastOffset is obtained from the right end of that
4074 // interval.
4075 lastAddr = dirtyRegion.end();
4076 // Should do something more transparent and less hacky XXX
4077 numDirtyCards =
4078 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4079
4080 // We'll scan the cards in the dirty region (with periodic
4081 // yields for foreground GC as needed).
4082 if (!dirtyRegion.is_empty()) {
4083 assert(numDirtyCards > 0, "consistency check");
4084 HeapWord* stop_point = NULL;
4085 stopTimer();
4086 // Potential yield point
4087 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
4088 bitMapLock());
4089 startTimer();
4090 {
4091 verify_work_stacks_empty();
4092 verify_overflow_empty();
4093 sample_eden();
4094 stop_point =
4095 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4096 }
4097 if (stop_point != NULL) {
4098 // The careful iteration stopped early either because it found an
4099 // uninitialized object, or because we were in the midst of an
4100 // "abortable preclean", which should now be aborted. Redirty
4101 // the bits corresponding to the partially-scanned or unscanned
4102 // cards. We'll either restart at the next block boundary or
4103 // abort the preclean.
4104 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4105 "Should only be AbortablePreclean.");
4106 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4107 if (should_abort_preclean()) {
4108 break; // out of preclean loop
4109 } else {
4110 // Compute the next address at which preclean should pick up;
4111 // might need bitMapLock in order to read P-bits.
4112 lastAddr = next_card_start_after_block(stop_point);
4113 }
4114 }
4115 } else {
4116 assert(lastAddr == endAddr, "consistency check");
4117 assert(numDirtyCards == 0, "consistency check");
4118 break;
4119 }
4120 }
4121 verify_work_stacks_empty();
4122 verify_overflow_empty();
4123 return cumNumDirtyCards;
4124 }
4125
4126 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4127 // below are largely identical; if you need to modify
4128 // one of these methods, please check the other method too.
4129
4130 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
4131 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4132 // strategy: it's similar to precleamModUnionTable above, in that
4133 // we accumulate contiguous ranges of dirty cards, mark these cards
4134 // precleaned, then scan the region covered by these cards.
4135 HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high());
4136 HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4137
4138 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4139
4140 size_t numDirtyCards, cumNumDirtyCards;
4141 HeapWord *lastAddr, *nextAddr;
4142
4143 for (cumNumDirtyCards = numDirtyCards = 0,
4144 nextAddr = lastAddr = startAddr;
4145 nextAddr < endAddr;
4146 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4147
4148 ResourceMark rm;
4149 HandleMark hm;
4150
4151 MemRegion dirtyRegion;
4152 {
4153 // See comments in "Precleaning notes" above on why we
4154 // do this locking. XXX Could the locking overheads be
4155 // too high when dirty cards are sparse? [I don't think so.]
4156 stopTimer();
4157 CMSTokenSync x(true); // is cms thread
4158 startTimer();
4159 sample_eden();
4160 // Get and clear dirty region from card table
4161 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4162 MemRegion(nextAddr, endAddr),
4163 true,
4164 CardTableModRefBS::precleaned_card_val());
4165
4166 assert(dirtyRegion.start() >= nextAddr,
4167 "returned region inconsistent?");
4168 }
4169 lastAddr = dirtyRegion.end();
4170 numDirtyCards =
4171 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4172
4173 if (!dirtyRegion.is_empty()) {
4174 stopTimer();
4175 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4176 startTimer();
4177 sample_eden();
4178 verify_work_stacks_empty();
4179 verify_overflow_empty();
4180 HeapWord* stop_point =
4181 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4182 if (stop_point != NULL) {
4183 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4184 "Should only be AbortablePreclean.");
4185 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4186 if (should_abort_preclean()) {
4187 break; // out of preclean loop
4188 } else {
4189 // Compute the next address at which preclean should pick up.
4190 lastAddr = next_card_start_after_block(stop_point);
4191 }
4192 }
4193 } else {
4194 break;
4195 }
4196 }
4197 verify_work_stacks_empty();
4198 verify_overflow_empty();
4199 return cumNumDirtyCards;
4200 }
4201
4202 class PrecleanKlassClosure : public KlassClosure {
4203 KlassToOopClosure _cm_klass_closure;
4204 public:
4205 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4206 void do_klass(Klass* k) {
4207 if (k->has_accumulated_modified_oops()) {
4208 k->clear_accumulated_modified_oops();
4209
4210 _cm_klass_closure.do_klass(k);
4211 }
4212 }
4213 };
4214
4215 // The freelist lock is needed to prevent asserts, is it really needed?
4216 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4217
4218 cl->set_freelistLock(freelistLock);
4219
4220 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4221
4222 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4223 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4224 PrecleanKlassClosure preclean_klass_closure(cl);
4225 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4226
4227 verify_work_stacks_empty();
4228 verify_overflow_empty();
4229 }
4230
4231 void CMSCollector::checkpointRootsFinal() {
4232 assert(_collectorState == FinalMarking, "incorrect state transition?");
4233 check_correct_thread_executing();
4234 // world is stopped at this checkpoint
4235 assert(SafepointSynchronize::is_at_safepoint(),
4236 "world should be stopped");
4237 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4238
4239 verify_work_stacks_empty();
4240 verify_overflow_empty();
4241
4242 if (PrintGCDetails) {
4243 gclog_or_tty->print("[YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)]",
4244 _young_gen->used() / K,
4245 _young_gen->capacity() / K);
4246 }
4247 {
4248 if (CMSScavengeBeforeRemark) {
4249 GenCollectedHeap* gch = GenCollectedHeap::heap();
4250 // Temporarily set flag to false, GCH->do_collection will
4251 // expect it to be false and set to true
4252 FlagSetting fl(gch->_is_gc_active, false);
4253 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4254 PrintGCDetails && Verbose, true, _gc_timer_cm);)
4255 gch->do_collection(true, // full (i.e. force, see below)
4256 false, // !clear_all_soft_refs
4257 0, // size
4258 false, // is_tlab
4259 GenCollectedHeap::YoungGen // type
4260 );
4261 }
4262 FreelistLocker x(this);
4263 MutexLockerEx y(bitMapLock(),
4264 Mutex::_no_safepoint_check_flag);
4265 checkpointRootsFinalWork();
4266 }
4267 verify_work_stacks_empty();
4268 verify_overflow_empty();
4269 }
4270
4271 void CMSCollector::checkpointRootsFinalWork() {
4272 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm);)
4273
4274 assert(haveFreelistLocks(), "must have free list locks");
4275 assert_lock_strong(bitMapLock());
4276
4277 ResourceMark rm;
4278 HandleMark hm;
4279
4280 GenCollectedHeap* gch = GenCollectedHeap::heap();
4281
4282 if (should_unload_classes()) {
4283 CodeCache::gc_prologue();
4284 }
4285 assert(haveFreelistLocks(), "must have free list locks");
4286 assert_lock_strong(bitMapLock());
4287
4288 // We might assume that we need not fill TLAB's when
4289 // CMSScavengeBeforeRemark is set, because we may have just done
4290 // a scavenge which would have filled all TLAB's -- and besides
4291 // Eden would be empty. This however may not always be the case --
4292 // for instance although we asked for a scavenge, it may not have
4293 // happened because of a JNI critical section. We probably need
4294 // a policy for deciding whether we can in that case wait until
4295 // the critical section releases and then do the remark following
4296 // the scavenge, and skip it here. In the absence of that policy,
4297 // or of an indication of whether the scavenge did indeed occur,
4298 // we cannot rely on TLAB's having been filled and must do
4299 // so here just in case a scavenge did not happen.
4300 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4301 // Update the saved marks which may affect the root scans.
4302 gch->save_marks();
4303
4304 if (CMSPrintEdenSurvivorChunks) {
4305 print_eden_and_survivor_chunk_arrays();
4306 }
4307
4308 {
4309 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4310
4311 // Note on the role of the mod union table:
4312 // Since the marker in "markFromRoots" marks concurrently with
4313 // mutators, it is possible for some reachable objects not to have been
4314 // scanned. For instance, an only reference to an object A was
4315 // placed in object B after the marker scanned B. Unless B is rescanned,
4316 // A would be collected. Such updates to references in marked objects
4317 // are detected via the mod union table which is the set of all cards
4318 // dirtied since the first checkpoint in this GC cycle and prior to
4319 // the most recent young generation GC, minus those cleaned up by the
4320 // concurrent precleaning.
4321 if (CMSParallelRemarkEnabled) {
4322 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm);
4323 do_remark_parallel();
4324 } else {
4325 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false, _gc_timer_cm);
4326 do_remark_non_parallel();
4327 }
4328 }
4329 verify_work_stacks_empty();
4330 verify_overflow_empty();
4331
4332 {
4333 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm);)
4334 refProcessingWork();
4335 }
4336 verify_work_stacks_empty();
4337 verify_overflow_empty();
4338
4339 if (should_unload_classes()) {
4340 CodeCache::gc_epilogue();
4341 }
4342 JvmtiExport::gc_epilogue();
4343
4344 // If we encountered any (marking stack / work queue) overflow
4345 // events during the current CMS cycle, take appropriate
4346 // remedial measures, where possible, so as to try and avoid
4347 // recurrence of that condition.
4348 assert(_markStack.isEmpty(), "No grey objects");
4349 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4350 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4351 if (ser_ovflw > 0) {
4352 if (PrintCMSStatistics != 0) {
4353 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4354 "(pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT
4355 ", kac_preclean=" SIZE_FORMAT ")",
4356 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4357 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4358 }
4359 _markStack.expand();
4360 _ser_pmc_remark_ovflw = 0;
4361 _ser_pmc_preclean_ovflw = 0;
4362 _ser_kac_preclean_ovflw = 0;
4363 _ser_kac_ovflw = 0;
4364 }
4365 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4366 if (PrintCMSStatistics != 0) {
4367 gclog_or_tty->print_cr("Work queue overflow (benign) "
4368 "(pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4369 _par_pmc_remark_ovflw, _par_kac_ovflw);
4370 }
4371 _par_pmc_remark_ovflw = 0;
4372 _par_kac_ovflw = 0;
4373 }
4374 if (PrintCMSStatistics != 0) {
4375 if (_markStack._hit_limit > 0) {
4376 gclog_or_tty->print_cr(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4377 _markStack._hit_limit);
4378 }
4379 if (_markStack._failed_double > 0) {
4380 gclog_or_tty->print_cr(" (benign) Failed stack doubling (" SIZE_FORMAT "),"
4381 " current capacity " SIZE_FORMAT,
4382 _markStack._failed_double,
4383 _markStack.capacity());
4384 }
4385 }
4386 _markStack._hit_limit = 0;
4387 _markStack._failed_double = 0;
4388
4389 if ((VerifyAfterGC || VerifyDuringGC) &&
4390 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4391 verify_after_remark();
4392 }
4393
4394 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4395
4396 // Change under the freelistLocks.
4397 _collectorState = Sweeping;
4398 // Call isAllClear() under bitMapLock
4399 assert(_modUnionTable.isAllClear(),
4400 "Should be clear by end of the final marking");
4401 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4402 "Should be clear by end of the final marking");
4403 }
4404
4405 void CMSParInitialMarkTask::work(uint worker_id) {
4406 elapsedTimer _timer;
4407 ResourceMark rm;
4408 HandleMark hm;
4409
4410 // ---------- scan from roots --------------
4411 _timer.start();
4412 GenCollectedHeap* gch = GenCollectedHeap::heap();
4413 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4414
4415 // ---------- young gen roots --------------
4416 {
4417 work_on_young_gen_roots(worker_id, &par_mri_cl);
4418 _timer.stop();
4419 if (PrintCMSStatistics != 0) {
4420 gclog_or_tty->print_cr(
4421 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4422 worker_id, _timer.seconds());
4423 }
4424 }
4425
4426 // ---------- remaining roots --------------
4427 _timer.reset();
4428 _timer.start();
4429
4430 CLDToOopClosure cld_closure(&par_mri_cl, true);
4431
4432 gch->old_process_roots(_strong_roots_scope,
4433 false, // yg was scanned above
4434 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4435 _collector->should_unload_classes(),
4436 &par_mri_cl,
4437 &cld_closure);
4438 assert(_collector->should_unload_classes()
4439 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4440 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4441 _timer.stop();
4442 if (PrintCMSStatistics != 0) {
4443 gclog_or_tty->print_cr(
4444 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4445 worker_id, _timer.seconds());
4446 }
4447 }
4448
4449 // Parallel remark task
4450 class CMSParRemarkTask: public CMSParMarkTask {
4451 CompactibleFreeListSpace* _cms_space;
4452
4453 // The per-thread work queues, available here for stealing.
4454 OopTaskQueueSet* _task_queues;
4455 ParallelTaskTerminator _term;
4456 StrongRootsScope* _strong_roots_scope;
4457
4458 public:
4459 // A value of 0 passed to n_workers will cause the number of
4460 // workers to be taken from the active workers in the work gang.
4461 CMSParRemarkTask(CMSCollector* collector,
4462 CompactibleFreeListSpace* cms_space,
4463 uint n_workers, WorkGang* workers,
4464 OopTaskQueueSet* task_queues,
4465 StrongRootsScope* strong_roots_scope):
4466 CMSParMarkTask("Rescan roots and grey objects in parallel",
4467 collector, n_workers),
4468 _cms_space(cms_space),
4469 _task_queues(task_queues),
4470 _term(n_workers, task_queues),
4471 _strong_roots_scope(strong_roots_scope) { }
4472
4473 OopTaskQueueSet* task_queues() { return _task_queues; }
4474
4475 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4476
4477 ParallelTaskTerminator* terminator() { return &_term; }
4478 uint n_workers() { return _n_workers; }
4479
4480 void work(uint worker_id);
4481
4482 private:
4483 // ... of dirty cards in old space
4484 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4485 Par_MarkRefsIntoAndScanClosure* cl);
4486
4487 // ... work stealing for the above
4488 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4489 };
4490
4491 class RemarkKlassClosure : public KlassClosure {
4492 KlassToOopClosure _cm_klass_closure;
4493 public:
4494 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4495 void do_klass(Klass* k) {
4496 // Check if we have modified any oops in the Klass during the concurrent marking.
4497 if (k->has_accumulated_modified_oops()) {
4498 k->clear_accumulated_modified_oops();
4499
4500 // We could have transfered the current modified marks to the accumulated marks,
4501 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4502 } else if (k->has_modified_oops()) {
4503 // Don't clear anything, this info is needed by the next young collection.
4504 } else {
4505 // No modified oops in the Klass.
4506 return;
4507 }
4508
4509 // The klass has modified fields, need to scan the klass.
4510 _cm_klass_closure.do_klass(k);
4511 }
4512 };
4513
4514 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4515 ParNewGeneration* young_gen = _collector->_young_gen;
4516 ContiguousSpace* eden_space = young_gen->eden();
4517 ContiguousSpace* from_space = young_gen->from();
4518 ContiguousSpace* to_space = young_gen->to();
4519
4520 HeapWord** eca = _collector->_eden_chunk_array;
4521 size_t ect = _collector->_eden_chunk_index;
4522 HeapWord** sca = _collector->_survivor_chunk_array;
4523 size_t sct = _collector->_survivor_chunk_index;
4524
4525 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4526 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4527
4528 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4529 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4530 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4531 }
4532
4533 // work_queue(i) is passed to the closure
4534 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
4535 // also is passed to do_dirty_card_rescan_tasks() and to
4536 // do_work_steal() to select the i-th task_queue.
4537
4538 void CMSParRemarkTask::work(uint worker_id) {
4539 elapsedTimer _timer;
4540 ResourceMark rm;
4541 HandleMark hm;
4542
4543 // ---------- rescan from roots --------------
4544 _timer.start();
4545 GenCollectedHeap* gch = GenCollectedHeap::heap();
4546 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4547 _collector->_span, _collector->ref_processor(),
4548 &(_collector->_markBitMap),
4549 work_queue(worker_id));
4550
4551 // Rescan young gen roots first since these are likely
4552 // coarsely partitioned and may, on that account, constitute
4553 // the critical path; thus, it's best to start off that
4554 // work first.
4555 // ---------- young gen roots --------------
4556 {
4557 work_on_young_gen_roots(worker_id, &par_mrias_cl);
4558 _timer.stop();
4559 if (PrintCMSStatistics != 0) {
4560 gclog_or_tty->print_cr(
4561 "Finished young gen rescan work in %dth thread: %3.3f sec",
4562 worker_id, _timer.seconds());
4563 }
4564 }
4565
4566 // ---------- remaining roots --------------
4567 _timer.reset();
4568 _timer.start();
4569 gch->old_process_roots(_strong_roots_scope,
4570 false, // yg was scanned above
4571 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4572 _collector->should_unload_classes(),
4573 &par_mrias_cl,
4574 NULL); // The dirty klasses will be handled below
4575
4576 assert(_collector->should_unload_classes()
4577 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4578 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4579 _timer.stop();
4580 if (PrintCMSStatistics != 0) {
4581 gclog_or_tty->print_cr(
4582 "Finished remaining root rescan work in %dth thread: %3.3f sec",
4583 worker_id, _timer.seconds());
4584 }
4585
4586 // ---------- unhandled CLD scanning ----------
4587 if (worker_id == 0) { // Single threaded at the moment.
4588 _timer.reset();
4589 _timer.start();
4590
4591 // Scan all new class loader data objects and new dependencies that were
4592 // introduced during concurrent marking.
4593 ResourceMark rm;
4594 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4595 for (int i = 0; i < array->length(); i++) {
4596 par_mrias_cl.do_cld_nv(array->at(i));
4597 }
4598
4599 // We don't need to keep track of new CLDs anymore.
4600 ClassLoaderDataGraph::remember_new_clds(false);
4601
4602 _timer.stop();
4603 if (PrintCMSStatistics != 0) {
4604 gclog_or_tty->print_cr(
4605 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4606 worker_id, _timer.seconds());
4607 }
4608 }
4609
4610 // ---------- dirty klass scanning ----------
4611 if (worker_id == 0) { // Single threaded at the moment.
4612 _timer.reset();
4613 _timer.start();
4614
4615 // Scan all classes that was dirtied during the concurrent marking phase.
4616 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4617 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4618
4619 _timer.stop();
4620 if (PrintCMSStatistics != 0) {
4621 gclog_or_tty->print_cr(
4622 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4623 worker_id, _timer.seconds());
4624 }
4625 }
4626
4627 // We might have added oops to ClassLoaderData::_handles during the
4628 // concurrent marking phase. These oops point to newly allocated objects
4629 // that are guaranteed to be kept alive. Either by the direct allocation
4630 // code, or when the young collector processes the roots. Hence,
4631 // we don't have to revisit the _handles block during the remark phase.
4632
4633 // ---------- rescan dirty cards ------------
4634 _timer.reset();
4635 _timer.start();
4636
4637 // Do the rescan tasks for each of the two spaces
4638 // (cms_space) in turn.
4639 // "worker_id" is passed to select the task_queue for "worker_id"
4640 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4641 _timer.stop();
4642 if (PrintCMSStatistics != 0) {
4643 gclog_or_tty->print_cr(
4644 "Finished dirty card rescan work in %dth thread: %3.3f sec",
4645 worker_id, _timer.seconds());
4646 }
4647
4648 // ---------- steal work from other threads ...
4649 // ---------- ... and drain overflow list.
4650 _timer.reset();
4651 _timer.start();
4652 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4653 _timer.stop();
4654 if (PrintCMSStatistics != 0) {
4655 gclog_or_tty->print_cr(
4656 "Finished work stealing in %dth thread: %3.3f sec",
4657 worker_id, _timer.seconds());
4658 }
4659 }
4660
4661 // Note that parameter "i" is not used.
4662 void
4663 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4664 OopsInGenClosure* cl, ContiguousSpace* space,
4665 HeapWord** chunk_array, size_t chunk_top) {
4666 // Until all tasks completed:
4667 // . claim an unclaimed task
4668 // . compute region boundaries corresponding to task claimed
4669 // using chunk_array
4670 // . par_oop_iterate(cl) over that region
4671
4672 ResourceMark rm;
4673 HandleMark hm;
4674
4675 SequentialSubTasksDone* pst = space->par_seq_tasks();
4676
4677 uint nth_task = 0;
4678 uint n_tasks = pst->n_tasks();
4679
4680 if (n_tasks > 0) {
4681 assert(pst->valid(), "Uninitialized use?");
4682 HeapWord *start, *end;
4683 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4684 // We claimed task # nth_task; compute its boundaries.
4685 if (chunk_top == 0) { // no samples were taken
4686 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4687 start = space->bottom();
4688 end = space->top();
4689 } else if (nth_task == 0) {
4690 start = space->bottom();
4691 end = chunk_array[nth_task];
4692 } else if (nth_task < (uint)chunk_top) {
4693 assert(nth_task >= 1, "Control point invariant");
4694 start = chunk_array[nth_task - 1];
4695 end = chunk_array[nth_task];
4696 } else {
4697 assert(nth_task == (uint)chunk_top, "Control point invariant");
4698 start = chunk_array[chunk_top - 1];
4699 end = space->top();
4700 }
4701 MemRegion mr(start, end);
4702 // Verify that mr is in space
4703 assert(mr.is_empty() || space->used_region().contains(mr),
4704 "Should be in space");
4705 // Verify that "start" is an object boundary
4706 assert(mr.is_empty() || oop(mr.start())->is_oop(),
4707 "Should be an oop");
4708 space->par_oop_iterate(mr, cl);
4709 }
4710 pst->all_tasks_completed();
4711 }
4712 }
4713
4714 void
4715 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4716 CompactibleFreeListSpace* sp, int i,
4717 Par_MarkRefsIntoAndScanClosure* cl) {
4718 // Until all tasks completed:
4719 // . claim an unclaimed task
4720 // . compute region boundaries corresponding to task claimed
4721 // . transfer dirty bits ct->mut for that region
4722 // . apply rescanclosure to dirty mut bits for that region
4723
4724 ResourceMark rm;
4725 HandleMark hm;
4726
4727 OopTaskQueue* work_q = work_queue(i);
4728 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4729 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4730 // CAUTION: This closure has state that persists across calls to
4731 // the work method dirty_range_iterate_clear() in that it has
4732 // embedded in it a (subtype of) UpwardsObjectClosure. The
4733 // use of that state in the embedded UpwardsObjectClosure instance
4734 // assumes that the cards are always iterated (even if in parallel
4735 // by several threads) in monotonically increasing order per each
4736 // thread. This is true of the implementation below which picks
4737 // card ranges (chunks) in monotonically increasing order globally
4738 // and, a-fortiori, in monotonically increasing order per thread
4739 // (the latter order being a subsequence of the former).
4740 // If the work code below is ever reorganized into a more chaotic
4741 // work-partitioning form than the current "sequential tasks"
4742 // paradigm, the use of that persistent state will have to be
4743 // revisited and modified appropriately. See also related
4744 // bug 4756801 work on which should examine this code to make
4745 // sure that the changes there do not run counter to the
4746 // assumptions made here and necessary for correctness and
4747 // efficiency. Note also that this code might yield inefficient
4748 // behavior in the case of very large objects that span one or
4749 // more work chunks. Such objects would potentially be scanned
4750 // several times redundantly. Work on 4756801 should try and
4751 // address that performance anomaly if at all possible. XXX
4752 MemRegion full_span = _collector->_span;
4753 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4754 MarkFromDirtyCardsClosure
4755 greyRescanClosure(_collector, full_span, // entire span of interest
4756 sp, bm, work_q, cl);
4757
4758 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4759 assert(pst->valid(), "Uninitialized use?");
4760 uint nth_task = 0;
4761 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4762 MemRegion span = sp->used_region();
4763 HeapWord* start_addr = span.start();
4764 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4765 alignment);
4766 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4767 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4768 start_addr, "Check alignment");
4769 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4770 chunk_size, "Check alignment");
4771
4772 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4773 // Having claimed the nth_task, compute corresponding mem-region,
4774 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4775 // The alignment restriction ensures that we do not need any
4776 // synchronization with other gang-workers while setting or
4777 // clearing bits in thus chunk of the MUT.
4778 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4779 start_addr + (nth_task+1)*chunk_size);
4780 // The last chunk's end might be way beyond end of the
4781 // used region. In that case pull back appropriately.
4782 if (this_span.end() > end_addr) {
4783 this_span.set_end(end_addr);
4784 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4785 }
4786 // Iterate over the dirty cards covering this chunk, marking them
4787 // precleaned, and setting the corresponding bits in the mod union
4788 // table. Since we have been careful to partition at Card and MUT-word
4789 // boundaries no synchronization is needed between parallel threads.
4790 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4791 &modUnionClosure);
4792
4793 // Having transferred these marks into the modUnionTable,
4794 // rescan the marked objects on the dirty cards in the modUnionTable.
4795 // Even if this is at a synchronous collection, the initial marking
4796 // may have been done during an asynchronous collection so there
4797 // may be dirty bits in the mod-union table.
4798 _collector->_modUnionTable.dirty_range_iterate_clear(
4799 this_span, &greyRescanClosure);
4800 _collector->_modUnionTable.verifyNoOneBitsInRange(
4801 this_span.start(),
4802 this_span.end());
4803 }
4804 pst->all_tasks_completed(); // declare that i am done
4805 }
4806
4807 // . see if we can share work_queues with ParNew? XXX
4808 void
4809 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4810 int* seed) {
4811 OopTaskQueue* work_q = work_queue(i);
4812 NOT_PRODUCT(int num_steals = 0;)
4813 oop obj_to_scan;
4814 CMSBitMap* bm = &(_collector->_markBitMap);
4815
4816 while (true) {
4817 // Completely finish any left over work from (an) earlier round(s)
4818 cl->trim_queue(0);
4819 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4820 (size_t)ParGCDesiredObjsFromOverflowList);
4821 // Now check if there's any work in the overflow list
4822 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4823 // only affects the number of attempts made to get work from the
4824 // overflow list and does not affect the number of workers. Just
4825 // pass ParallelGCThreads so this behavior is unchanged.
4826 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4827 work_q,
4828 ParallelGCThreads)) {
4829 // found something in global overflow list;
4830 // not yet ready to go stealing work from others.
4831 // We'd like to assert(work_q->size() != 0, ...)
4832 // because we just took work from the overflow list,
4833 // but of course we can't since all of that could have
4834 // been already stolen from us.
4835 // "He giveth and He taketh away."
4836 continue;
4837 }
4838 // Verify that we have no work before we resort to stealing
4839 assert(work_q->size() == 0, "Have work, shouldn't steal");
4840 // Try to steal from other queues that have work
4841 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4842 NOT_PRODUCT(num_steals++;)
4843 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4844 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4845 // Do scanning work
4846 obj_to_scan->oop_iterate(cl);
4847 // Loop around, finish this work, and try to steal some more
4848 } else if (terminator()->offer_termination()) {
4849 break; // nirvana from the infinite cycle
4850 }
4851 }
4852 NOT_PRODUCT(
4853 if (PrintCMSStatistics != 0) {
4854 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
4855 }
4856 )
4857 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4858 "Else our work is not yet done");
4859 }
4860
4861 // Record object boundaries in _eden_chunk_array by sampling the eden
4862 // top in the slow-path eden object allocation code path and record
4863 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4864 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4865 // sampling in sample_eden() that activates during the part of the
4866 // preclean phase.
4867 void CMSCollector::sample_eden_chunk() {
4868 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4869 if (_eden_chunk_lock->try_lock()) {
4870 // Record a sample. This is the critical section. The contents
4871 // of the _eden_chunk_array have to be non-decreasing in the
4872 // address order.
4873 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4874 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4875 "Unexpected state of Eden");
4876 if (_eden_chunk_index == 0 ||
4877 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4878 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4879 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4880 _eden_chunk_index++; // commit sample
4881 }
4882 _eden_chunk_lock->unlock();
4883 }
4884 }
4885 }
4886
4887 // Return a thread-local PLAB recording array, as appropriate.
4888 void* CMSCollector::get_data_recorder(int thr_num) {
4889 if (_survivor_plab_array != NULL &&
4890 (CMSPLABRecordAlways ||
4891 (_collectorState > Marking && _collectorState < FinalMarking))) {
4892 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4893 ChunkArray* ca = &_survivor_plab_array[thr_num];
4894 ca->reset(); // clear it so that fresh data is recorded
4895 return (void*) ca;
4896 } else {
4897 return NULL;
4898 }
4899 }
4900
4901 // Reset all the thread-local PLAB recording arrays
4902 void CMSCollector::reset_survivor_plab_arrays() {
4903 for (uint i = 0; i < ParallelGCThreads; i++) {
4904 _survivor_plab_array[i].reset();
4905 }
4906 }
4907
4908 // Merge the per-thread plab arrays into the global survivor chunk
4909 // array which will provide the partitioning of the survivor space
4910 // for CMS initial scan and rescan.
4911 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4912 int no_of_gc_threads) {
4913 assert(_survivor_plab_array != NULL, "Error");
4914 assert(_survivor_chunk_array != NULL, "Error");
4915 assert(_collectorState == FinalMarking ||
4916 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4917 for (int j = 0; j < no_of_gc_threads; j++) {
4918 _cursor[j] = 0;
4919 }
4920 HeapWord* top = surv->top();
4921 size_t i;
4922 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4923 HeapWord* min_val = top; // Higher than any PLAB address
4924 uint min_tid = 0; // position of min_val this round
4925 for (int j = 0; j < no_of_gc_threads; j++) {
4926 ChunkArray* cur_sca = &_survivor_plab_array[j];
4927 if (_cursor[j] == cur_sca->end()) {
4928 continue;
4929 }
4930 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4931 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4932 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4933 if (cur_val < min_val) {
4934 min_tid = j;
4935 min_val = cur_val;
4936 } else {
4937 assert(cur_val < top, "All recorded addresses should be less");
4938 }
4939 }
4940 // At this point min_val and min_tid are respectively
4941 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4942 // and the thread (j) that witnesses that address.
4943 // We record this address in the _survivor_chunk_array[i]
4944 // and increment _cursor[min_tid] prior to the next round i.
4945 if (min_val == top) {
4946 break;
4947 }
4948 _survivor_chunk_array[i] = min_val;
4949 _cursor[min_tid]++;
4950 }
4951 // We are all done; record the size of the _survivor_chunk_array
4952 _survivor_chunk_index = i; // exclusive: [0, i)
4953 if (PrintCMSStatistics > 0) {
4954 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4955 }
4956 // Verify that we used up all the recorded entries
4957 #ifdef ASSERT
4958 size_t total = 0;
4959 for (int j = 0; j < no_of_gc_threads; j++) {
4960 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4961 total += _cursor[j];
4962 }
4963 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4964 // Check that the merged array is in sorted order
4965 if (total > 0) {
4966 for (size_t i = 0; i < total - 1; i++) {
4967 if (PrintCMSStatistics > 0) {
4968 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4969 i, p2i(_survivor_chunk_array[i]));
4970 }
4971 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4972 "Not sorted");
4973 }
4974 }
4975 #endif // ASSERT
4976 }
4977
4978 // Set up the space's par_seq_tasks structure for work claiming
4979 // for parallel initial scan and rescan of young gen.
4980 // See ParRescanTask where this is currently used.
4981 void
4982 CMSCollector::
4983 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4984 assert(n_threads > 0, "Unexpected n_threads argument");
4985
4986 // Eden space
4987 if (!_young_gen->eden()->is_empty()) {
4988 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4989 assert(!pst->valid(), "Clobbering existing data?");
4990 // Each valid entry in [0, _eden_chunk_index) represents a task.
4991 size_t n_tasks = _eden_chunk_index + 1;
4992 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4993 // Sets the condition for completion of the subtask (how many threads
4994 // need to finish in order to be done).
4995 pst->set_n_threads(n_threads);
4996 pst->set_n_tasks((int)n_tasks);
4997 }
4998
4999 // Merge the survivor plab arrays into _survivor_chunk_array
5000 if (_survivor_plab_array != NULL) {
5001 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5002 } else {
5003 assert(_survivor_chunk_index == 0, "Error");
5004 }
5005
5006 // To space
5007 {
5008 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5009 assert(!pst->valid(), "Clobbering existing data?");
5010 // Sets the condition for completion of the subtask (how many threads
5011 // need to finish in order to be done).
5012 pst->set_n_threads(n_threads);
5013 pst->set_n_tasks(1);
5014 assert(pst->valid(), "Error");
5015 }
5016
5017 // From space
5018 {
5019 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5020 assert(!pst->valid(), "Clobbering existing data?");
5021 size_t n_tasks = _survivor_chunk_index + 1;
5022 assert(n_tasks == 1 || _survivor_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 assert(pst->valid(), "Error");
5028 }
5029 }
5030
5031 // Parallel version of remark
5032 void CMSCollector::do_remark_parallel() {
5033 GenCollectedHeap* gch = GenCollectedHeap::heap();
5034 WorkGang* workers = gch->workers();
5035 assert(workers != NULL, "Need parallel worker threads.");
5036 // Choose to use the number of GC workers most recently set
5037 // into "active_workers".
5038 uint n_workers = workers->active_workers();
5039
5040 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5041
5042 StrongRootsScope srs(n_workers);
5043
5044 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
5045
5046 // We won't be iterating over the cards in the card table updating
5047 // the younger_gen cards, so we shouldn't call the following else
5048 // the verification code as well as subsequent younger_refs_iterate
5049 // code would get confused. XXX
5050 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5051
5052 // The young gen rescan work will not be done as part of
5053 // process_roots (which currently doesn't know how to
5054 // parallelize such a scan), but rather will be broken up into
5055 // a set of parallel tasks (via the sampling that the [abortable]
5056 // preclean phase did of eden, plus the [two] tasks of
5057 // scanning the [two] survivor spaces. Further fine-grain
5058 // parallelization of the scanning of the survivor spaces
5059 // themselves, and of precleaning of the young gen itself
5060 // is deferred to the future.
5061 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5062
5063 // The dirty card rescan work is broken up into a "sequence"
5064 // of parallel tasks (per constituent space) that are dynamically
5065 // claimed by the parallel threads.
5066 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5067
5068 // It turns out that even when we're using 1 thread, doing the work in a
5069 // separate thread causes wide variance in run times. We can't help this
5070 // in the multi-threaded case, but we special-case n=1 here to get
5071 // repeatable measurements of the 1-thread overhead of the parallel code.
5072 if (n_workers > 1) {
5073 // Make refs discovery MT-safe, if it isn't already: it may not
5074 // necessarily be so, since it's possible that we are doing
5075 // ST marking.
5076 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5077 workers->run_task(&tsk);
5078 } else {
5079 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5080 tsk.work(0);
5081 }
5082
5083 // restore, single-threaded for now, any preserved marks
5084 // as a result of work_q overflow
5085 restore_preserved_marks_if_any();
5086 }
5087
5088 // Non-parallel version of remark
5089 void CMSCollector::do_remark_non_parallel() {
5090 ResourceMark rm;
5091 HandleMark hm;
5092 GenCollectedHeap* gch = GenCollectedHeap::heap();
5093 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5094
5095 MarkRefsIntoAndScanClosure
5096 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5097 &_markStack, this,
5098 false /* should_yield */, false /* not precleaning */);
5099 MarkFromDirtyCardsClosure
5100 markFromDirtyCardsClosure(this, _span,
5101 NULL, // space is set further below
5102 &_markBitMap, &_markStack, &mrias_cl);
5103 {
5104 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm);
5105 // Iterate over the dirty cards, setting the corresponding bits in the
5106 // mod union table.
5107 {
5108 ModUnionClosure modUnionClosure(&_modUnionTable);
5109 _ct->ct_bs()->dirty_card_iterate(
5110 _cmsGen->used_region(),
5111 &modUnionClosure);
5112 }
5113 // Having transferred these marks into the modUnionTable, we just need
5114 // to rescan the marked objects on the dirty cards in the modUnionTable.
5115 // The initial marking may have been done during an asynchronous
5116 // collection so there may be dirty bits in the mod-union table.
5117 const int alignment =
5118 CardTableModRefBS::card_size * BitsPerWord;
5119 {
5120 // ... First handle dirty cards in CMS gen
5121 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5122 MemRegion ur = _cmsGen->used_region();
5123 HeapWord* lb = ur.start();
5124 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5125 MemRegion cms_span(lb, ub);
5126 _modUnionTable.dirty_range_iterate_clear(cms_span,
5127 &markFromDirtyCardsClosure);
5128 verify_work_stacks_empty();
5129 if (PrintCMSStatistics != 0) {
5130 gclog_or_tty->print(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ",
5131 markFromDirtyCardsClosure.num_dirty_cards());
5132 }
5133 }
5134 }
5135 if (VerifyDuringGC &&
5136 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5137 HandleMark hm; // Discard invalid handles created during verification
5138 Universe::verify();
5139 }
5140 {
5141 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm);
5142
5143 verify_work_stacks_empty();
5144
5145 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5146 StrongRootsScope srs(1);
5147
5148 gch->old_process_roots(&srs,
5149 true, // young gen as roots
5150 GenCollectedHeap::ScanningOption(roots_scanning_options()),
5151 should_unload_classes(),
5152 &mrias_cl,
5153 NULL); // The dirty klasses will be handled below
5154
5155 assert(should_unload_classes()
5156 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5157 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5158 }
5159
5160 {
5161 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm);
5162
5163 verify_work_stacks_empty();
5164
5165 // Scan all class loader data objects that might have been introduced
5166 // during concurrent marking.
5167 ResourceMark rm;
5168 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5169 for (int i = 0; i < array->length(); i++) {
5170 mrias_cl.do_cld_nv(array->at(i));
5171 }
5172
5173 // We don't need to keep track of new CLDs anymore.
5174 ClassLoaderDataGraph::remember_new_clds(false);
5175
5176 verify_work_stacks_empty();
5177 }
5178
5179 {
5180 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm);
5181
5182 verify_work_stacks_empty();
5183
5184 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5185 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5186
5187 verify_work_stacks_empty();
5188 }
5189
5190 // We might have added oops to ClassLoaderData::_handles during the
5191 // concurrent marking phase. These oops point to newly allocated objects
5192 // that are guaranteed to be kept alive. Either by the direct allocation
5193 // code, or when the young collector processes the roots. Hence,
5194 // we don't have to revisit the _handles block during the remark phase.
5195
5196 verify_work_stacks_empty();
5197 // Restore evacuated mark words, if any, used for overflow list links
5198 if (!CMSOverflowEarlyRestoration) {
5199 restore_preserved_marks_if_any();
5200 }
5201 verify_overflow_empty();
5202 }
5203
5204 ////////////////////////////////////////////////////////
5205 // Parallel Reference Processing Task Proxy Class
5206 ////////////////////////////////////////////////////////
5207 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5208 OopTaskQueueSet* _queues;
5209 ParallelTaskTerminator _terminator;
5210 public:
5211 AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5212 AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5213 ParallelTaskTerminator* terminator() { return &_terminator; }
5214 OopTaskQueueSet* queues() { return _queues; }
5215 };
5216
5217 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5218 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5219 CMSCollector* _collector;
5220 CMSBitMap* _mark_bit_map;
5221 const MemRegion _span;
5222 ProcessTask& _task;
5223
5224 public:
5225 CMSRefProcTaskProxy(ProcessTask& task,
5226 CMSCollector* collector,
5227 const MemRegion& span,
5228 CMSBitMap* mark_bit_map,
5229 AbstractWorkGang* workers,
5230 OopTaskQueueSet* task_queues):
5231 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5232 task_queues,
5233 workers->active_workers()),
5234 _task(task),
5235 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5236 {
5237 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5238 "Inconsistency in _span");
5239 }
5240
5241 OopTaskQueueSet* task_queues() { return queues(); }
5242
5243 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5244
5245 void do_work_steal(int i,
5246 CMSParDrainMarkingStackClosure* drain,
5247 CMSParKeepAliveClosure* keep_alive,
5248 int* seed);
5249
5250 virtual void work(uint worker_id);
5251 };
5252
5253 void CMSRefProcTaskProxy::work(uint worker_id) {
5254 ResourceMark rm;
5255 HandleMark hm;
5256 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5257 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5258 _mark_bit_map,
5259 work_queue(worker_id));
5260 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5261 _mark_bit_map,
5262 work_queue(worker_id));
5263 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5264 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5265 if (_task.marks_oops_alive()) {
5266 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5267 _collector->hash_seed(worker_id));
5268 }
5269 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5270 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5271 }
5272
5273 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5274 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5275 EnqueueTask& _task;
5276
5277 public:
5278 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5279 : AbstractGangTask("Enqueue reference objects in parallel"),
5280 _task(task)
5281 { }
5282
5283 virtual void work(uint worker_id)
5284 {
5285 _task.work(worker_id);
5286 }
5287 };
5288
5289 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5290 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5291 _span(span),
5292 _bit_map(bit_map),
5293 _work_queue(work_queue),
5294 _mark_and_push(collector, span, bit_map, work_queue),
5295 _low_water_mark(MIN2((work_queue->max_elems()/4),
5296 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5297 { }
5298
5299 // . see if we can share work_queues with ParNew? XXX
5300 void CMSRefProcTaskProxy::do_work_steal(int i,
5301 CMSParDrainMarkingStackClosure* drain,
5302 CMSParKeepAliveClosure* keep_alive,
5303 int* seed) {
5304 OopTaskQueue* work_q = work_queue(i);
5305 NOT_PRODUCT(int num_steals = 0;)
5306 oop obj_to_scan;
5307
5308 while (true) {
5309 // Completely finish any left over work from (an) earlier round(s)
5310 drain->trim_queue(0);
5311 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5312 (size_t)ParGCDesiredObjsFromOverflowList);
5313 // Now check if there's any work in the overflow list
5314 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5315 // only affects the number of attempts made to get work from the
5316 // overflow list and does not affect the number of workers. Just
5317 // pass ParallelGCThreads so this behavior is unchanged.
5318 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5319 work_q,
5320 ParallelGCThreads)) {
5321 // Found something in global overflow list;
5322 // not yet ready to go stealing work from others.
5323 // We'd like to assert(work_q->size() != 0, ...)
5324 // because we just took work from the overflow list,
5325 // but of course we can't, since all of that might have
5326 // been already stolen from us.
5327 continue;
5328 }
5329 // Verify that we have no work before we resort to stealing
5330 assert(work_q->size() == 0, "Have work, shouldn't steal");
5331 // Try to steal from other queues that have work
5332 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5333 NOT_PRODUCT(num_steals++;)
5334 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5335 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5336 // Do scanning work
5337 obj_to_scan->oop_iterate(keep_alive);
5338 // Loop around, finish this work, and try to steal some more
5339 } else if (terminator()->offer_termination()) {
5340 break; // nirvana from the infinite cycle
5341 }
5342 }
5343 NOT_PRODUCT(
5344 if (PrintCMSStatistics != 0) {
5345 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5346 }
5347 )
5348 }
5349
5350 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5351 {
5352 GenCollectedHeap* gch = GenCollectedHeap::heap();
5353 WorkGang* workers = gch->workers();
5354 assert(workers != NULL, "Need parallel worker threads.");
5355 CMSRefProcTaskProxy rp_task(task, &_collector,
5356 _collector.ref_processor()->span(),
5357 _collector.markBitMap(),
5358 workers, _collector.task_queues());
5359 workers->run_task(&rp_task);
5360 }
5361
5362 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5363 {
5364
5365 GenCollectedHeap* gch = GenCollectedHeap::heap();
5366 WorkGang* workers = gch->workers();
5367 assert(workers != NULL, "Need parallel worker threads.");
5368 CMSRefEnqueueTaskProxy enq_task(task);
5369 workers->run_task(&enq_task);
5370 }
5371
5372 void CMSCollector::refProcessingWork() {
5373 ResourceMark rm;
5374 HandleMark hm;
5375
5376 ReferenceProcessor* rp = ref_processor();
5377 assert(rp->span().equals(_span), "Spans should be equal");
5378 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5379 // Process weak references.
5380 rp->setup_policy(false);
5381 verify_work_stacks_empty();
5382
5383 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5384 &_markStack, false /* !preclean */);
5385 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5386 _span, &_markBitMap, &_markStack,
5387 &cmsKeepAliveClosure, false /* !preclean */);
5388 {
5389 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm);
5390
5391 ReferenceProcessorStats stats;
5392 if (rp->processing_is_mt()) {
5393 // Set the degree of MT here. If the discovery is done MT, there
5394 // may have been a different number of threads doing the discovery
5395 // and a different number of discovered lists may have Ref objects.
5396 // That is OK as long as the Reference lists are balanced (see
5397 // balance_all_queues() and balance_queues()).
5398 GenCollectedHeap* gch = GenCollectedHeap::heap();
5399 uint active_workers = ParallelGCThreads;
5400 WorkGang* workers = gch->workers();
5401 if (workers != NULL) {
5402 active_workers = workers->active_workers();
5403 // The expectation is that active_workers will have already
5404 // been set to a reasonable value. If it has not been set,
5405 // investigate.
5406 assert(active_workers > 0, "Should have been set during scavenge");
5407 }
5408 rp->set_active_mt_degree(active_workers);
5409 CMSRefProcTaskExecutor task_executor(*this);
5410 stats = rp->process_discovered_references(&_is_alive_closure,
5411 &cmsKeepAliveClosure,
5412 &cmsDrainMarkingStackClosure,
5413 &task_executor,
5414 _gc_timer_cm);
5415 } else {
5416 stats = rp->process_discovered_references(&_is_alive_closure,
5417 &cmsKeepAliveClosure,
5418 &cmsDrainMarkingStackClosure,
5419 NULL,
5420 _gc_timer_cm);
5421 }
5422 _gc_tracer_cm->report_gc_reference_stats(stats);
5423
5424 }
5425
5426 // This is the point where the entire marking should have completed.
5427 verify_work_stacks_empty();
5428
5429 if (should_unload_classes()) {
5430 {
5431 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm);
5432
5433 // Unload classes and purge the SystemDictionary.
5434 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5435
5436 // Unload nmethods.
5437 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5438
5439 // Prune dead klasses from subklass/sibling/implementor lists.
5440 Klass::clean_weak_klass_links(&_is_alive_closure);
5441 }
5442
5443 {
5444 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm);
5445 // Clean up unreferenced symbols in symbol table.
5446 SymbolTable::unlink();
5447 }
5448
5449 {
5450 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm);
5451 // Delete entries for dead interned strings.
5452 StringTable::unlink(&_is_alive_closure);
5453 }
5454 }
5455
5456
5457 // Restore any preserved marks as a result of mark stack or
5458 // work queue overflow
5459 restore_preserved_marks_if_any(); // done single-threaded for now
5460
5461 rp->set_enqueuing_is_done(true);
5462 if (rp->processing_is_mt()) {
5463 rp->balance_all_queues();
5464 CMSRefProcTaskExecutor task_executor(*this);
5465 rp->enqueue_discovered_references(&task_executor);
5466 } else {
5467 rp->enqueue_discovered_references(NULL);
5468 }
5469 rp->verify_no_references_recorded();
5470 assert(!rp->discovery_enabled(), "should have been disabled");
5471 }
5472
5473 #ifndef PRODUCT
5474 void CMSCollector::check_correct_thread_executing() {
5475 Thread* t = Thread::current();
5476 // Only the VM thread or the CMS thread should be here.
5477 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5478 "Unexpected thread type");
5479 // If this is the vm thread, the foreground process
5480 // should not be waiting. Note that _foregroundGCIsActive is
5481 // true while the foreground collector is waiting.
5482 if (_foregroundGCShouldWait) {
5483 // We cannot be the VM thread
5484 assert(t->is_ConcurrentGC_thread(),
5485 "Should be CMS thread");
5486 } else {
5487 // We can be the CMS thread only if we are in a stop-world
5488 // phase of CMS collection.
5489 if (t->is_ConcurrentGC_thread()) {
5490 assert(_collectorState == InitialMarking ||
5491 _collectorState == FinalMarking,
5492 "Should be a stop-world phase");
5493 // The CMS thread should be holding the CMS_token.
5494 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5495 "Potential interference with concurrently "
5496 "executing VM thread");
5497 }
5498 }
5499 }
5500 #endif
5501
5502 void CMSCollector::sweep() {
5503 assert(_collectorState == Sweeping, "just checking");
5504 check_correct_thread_executing();
5505 verify_work_stacks_empty();
5506 verify_overflow_empty();
5507 increment_sweep_count();
5508 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5509
5510 _inter_sweep_timer.stop();
5511 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5512
5513 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5514 _intra_sweep_timer.reset();
5515 _intra_sweep_timer.start();
5516 {
5517 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5518 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
5519 // First sweep the old gen
5520 {
5521 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5522 bitMapLock());
5523 sweepWork(_cmsGen);
5524 }
5525
5526 // Update Universe::_heap_*_at_gc figures.
5527 // We need all the free list locks to make the abstract state
5528 // transition from Sweeping to Resetting. See detailed note
5529 // further below.
5530 {
5531 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5532 // Update heap occupancy information which is used as
5533 // input to soft ref clearing policy at the next gc.
5534 Universe::update_heap_info_at_gc();
5535 _collectorState = Resizing;
5536 }
5537 }
5538 verify_work_stacks_empty();
5539 verify_overflow_empty();
5540
5541 if (should_unload_classes()) {
5542 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5543 // requires that the virtual spaces are stable and not deleted.
5544 ClassLoaderDataGraph::set_should_purge(true);
5545 }
5546
5547 _intra_sweep_timer.stop();
5548 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5549
5550 _inter_sweep_timer.reset();
5551 _inter_sweep_timer.start();
5552
5553 // We need to use a monotonically non-decreasing time in ms
5554 // or we will see time-warp warnings and os::javaTimeMillis()
5555 // does not guarantee monotonicity.
5556 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5557 update_time_of_last_gc(now);
5558
5559 // NOTE on abstract state transitions:
5560 // Mutators allocate-live and/or mark the mod-union table dirty
5561 // based on the state of the collection. The former is done in
5562 // the interval [Marking, Sweeping] and the latter in the interval
5563 // [Marking, Sweeping). Thus the transitions into the Marking state
5564 // and out of the Sweeping state must be synchronously visible
5565 // globally to the mutators.
5566 // The transition into the Marking state happens with the world
5567 // stopped so the mutators will globally see it. Sweeping is
5568 // done asynchronously by the background collector so the transition
5569 // from the Sweeping state to the Resizing state must be done
5570 // under the freelistLock (as is the check for whether to
5571 // allocate-live and whether to dirty the mod-union table).
5572 assert(_collectorState == Resizing, "Change of collector state to"
5573 " Resizing must be done under the freelistLocks (plural)");
5574
5575 // Now that sweeping has been completed, we clear
5576 // the incremental_collection_failed flag,
5577 // thus inviting a younger gen collection to promote into
5578 // this generation. If such a promotion may still fail,
5579 // the flag will be set again when a young collection is
5580 // attempted.
5581 GenCollectedHeap* gch = GenCollectedHeap::heap();
5582 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5583 gch->update_full_collections_completed(_collection_count_start);
5584 }
5585
5586 // FIX ME!!! Looks like this belongs in CFLSpace, with
5587 // CMSGen merely delegating to it.
5588 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5589 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5590 HeapWord* minAddr = _cmsSpace->bottom();
5591 HeapWord* largestAddr =
5592 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5593 if (largestAddr == NULL) {
5594 // The dictionary appears to be empty. In this case
5595 // try to coalesce at the end of the heap.
5596 largestAddr = _cmsSpace->end();
5597 }
5598 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5599 size_t nearLargestOffset =
5600 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5601 if (PrintFLSStatistics != 0) {
5602 gclog_or_tty->print_cr(
5603 "CMS: Large Block: " PTR_FORMAT ";"
5604 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5605 p2i(largestAddr),
5606 p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5607 }
5608 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5609 }
5610
5611 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5612 return addr >= _cmsSpace->nearLargestChunk();
5613 }
5614
5615 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5616 return _cmsSpace->find_chunk_at_end();
5617 }
5618
5619 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5620 bool full) {
5621 // If the young generation has been collected, gather any statistics
5622 // that are of interest at this point.
5623 bool current_is_young = GenCollectedHeap::heap()->is_young_gen(current_generation);
5624 if (!full && current_is_young) {
5625 // Gather statistics on the young generation collection.
5626 collector()->stats().record_gc0_end(used());
5627 }
5628 }
5629
5630 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5631 // We iterate over the space(s) underlying this generation,
5632 // checking the mark bit map to see if the bits corresponding
5633 // to specific blocks are marked or not. Blocks that are
5634 // marked are live and are not swept up. All remaining blocks
5635 // are swept up, with coalescing on-the-fly as we sweep up
5636 // contiguous free and/or garbage blocks:
5637 // We need to ensure that the sweeper synchronizes with allocators
5638 // and stop-the-world collectors. In particular, the following
5639 // locks are used:
5640 // . CMS token: if this is held, a stop the world collection cannot occur
5641 // . freelistLock: if this is held no allocation can occur from this
5642 // generation by another thread
5643 // . bitMapLock: if this is held, no other thread can access or update
5644 //
5645
5646 // Note that we need to hold the freelistLock if we use
5647 // block iterate below; else the iterator might go awry if
5648 // a mutator (or promotion) causes block contents to change
5649 // (for instance if the allocator divvies up a block).
5650 // If we hold the free list lock, for all practical purposes
5651 // young generation GC's can't occur (they'll usually need to
5652 // promote), so we might as well prevent all young generation
5653 // GC's while we do a sweeping step. For the same reason, we might
5654 // as well take the bit map lock for the entire duration
5655
5656 // check that we hold the requisite locks
5657 assert(have_cms_token(), "Should hold cms token");
5658 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5659 assert_lock_strong(old_gen->freelistLock());
5660 assert_lock_strong(bitMapLock());
5661
5662 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5663 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5664 old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5665 _inter_sweep_estimate.padded_average(),
5666 _intra_sweep_estimate.padded_average());
5667 old_gen->setNearLargestChunk();
5668
5669 {
5670 SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5671 old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5672 // We need to free-up/coalesce garbage/blocks from a
5673 // co-terminal free run. This is done in the SweepClosure
5674 // destructor; so, do not remove this scope, else the
5675 // end-of-sweep-census below will be off by a little bit.
5676 }
5677 old_gen->cmsSpace()->sweep_completed();
5678 old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5679 if (should_unload_classes()) { // unloaded classes this cycle,
5680 _concurrent_cycles_since_last_unload = 0; // ... reset count
5681 } else { // did not unload classes,
5682 _concurrent_cycles_since_last_unload++; // ... increment count
5683 }
5684 }
5685
5686 // Reset CMS data structures (for now just the marking bit map)
5687 // preparatory for the next cycle.
5688 void CMSCollector::reset(bool concurrent) {
5689 if (concurrent) {
5690 CMSTokenSyncWithLocks ts(true, bitMapLock());
5691
5692 // If the state is not "Resetting", the foreground thread
5693 // has done a collection and the resetting.
5694 if (_collectorState != Resetting) {
5695 assert(_collectorState == Idling, "The state should only change"
5696 " because the foreground collector has finished the collection");
5697 return;
5698 }
5699
5700 // Clear the mark bitmap (no grey objects to start with)
5701 // for the next cycle.
5702 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5703 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
5704
5705 HeapWord* curAddr = _markBitMap.startWord();
5706 while (curAddr < _markBitMap.endWord()) {
5707 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5708 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5709 _markBitMap.clear_large_range(chunk);
5710 if (ConcurrentMarkSweepThread::should_yield() &&
5711 !foregroundGCIsActive() &&
5712 CMSYield) {
5713 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5714 "CMS thread should hold CMS token");
5715 assert_lock_strong(bitMapLock());
5716 bitMapLock()->unlock();
5717 ConcurrentMarkSweepThread::desynchronize(true);
5718 stopTimer();
5719 if (PrintCMSStatistics != 0) {
5720 incrementYields();
5721 }
5722
5723 // See the comment in coordinator_yield()
5724 for (unsigned i = 0; i < CMSYieldSleepCount &&
5725 ConcurrentMarkSweepThread::should_yield() &&
5726 !CMSCollector::foregroundGCIsActive(); ++i) {
5727 os::sleep(Thread::current(), 1, false);
5728 }
5729
5730 ConcurrentMarkSweepThread::synchronize(true);
5731 bitMapLock()->lock_without_safepoint_check();
5732 startTimer();
5733 }
5734 curAddr = chunk.end();
5735 }
5736 // A successful mostly concurrent collection has been done.
5737 // Because only the full (i.e., concurrent mode failure) collections
5738 // are being measured for gc overhead limits, clean the "near" flag
5739 // and count.
5740 size_policy()->reset_gc_overhead_limit_count();
5741 _collectorState = Idling;
5742 } else {
5743 // already have the lock
5744 assert(_collectorState == Resetting, "just checking");
5745 assert_lock_strong(bitMapLock());
5746 _markBitMap.clear_all();
5747 _collectorState = Idling;
5748 }
5749
5750 register_gc_end();
5751 }
5752
5753 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5754 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5755 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL);
5756 TraceCollectorStats tcs(counters());
5757
5758 switch (op) {
5759 case CMS_op_checkpointRootsInitial: {
5760 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5761 checkpointRootsInitial();
5762 if (PrintGC) {
5763 _cmsGen->printOccupancy("initial-mark");
5764 }
5765 break;
5766 }
5767 case CMS_op_checkpointRootsFinal: {
5768 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5769 checkpointRootsFinal();
5770 if (PrintGC) {
5771 _cmsGen->printOccupancy("remark");
5772 }
5773 break;
5774 }
5775 default:
5776 fatal("No such CMS_op");
5777 }
5778 }
5779
5780 #ifndef PRODUCT
5781 size_t const CMSCollector::skip_header_HeapWords() {
5782 return FreeChunk::header_size();
5783 }
5784
5785 // Try and collect here conditions that should hold when
5786 // CMS thread is exiting. The idea is that the foreground GC
5787 // thread should not be blocked if it wants to terminate
5788 // the CMS thread and yet continue to run the VM for a while
5789 // after that.
5790 void CMSCollector::verify_ok_to_terminate() const {
5791 assert(Thread::current()->is_ConcurrentGC_thread(),
5792 "should be called by CMS thread");
5793 assert(!_foregroundGCShouldWait, "should be false");
5794 // We could check here that all the various low-level locks
5795 // are not held by the CMS thread, but that is overkill; see
5796 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5797 // is checked.
5798 }
5799 #endif
5800
5801 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5802 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5803 "missing Printezis mark?");
5804 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5805 size_t size = pointer_delta(nextOneAddr + 1, addr);
5806 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5807 "alignment problem");
5808 assert(size >= 3, "Necessary for Printezis marks to work");
5809 return size;
5810 }
5811
5812 // A variant of the above (block_size_using_printezis_bits()) except
5813 // that we return 0 if the P-bits are not yet set.
5814 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5815 if (_markBitMap.isMarked(addr + 1)) {
5816 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5817 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5818 size_t size = pointer_delta(nextOneAddr + 1, addr);
5819 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5820 "alignment problem");
5821 assert(size >= 3, "Necessary for Printezis marks to work");
5822 return size;
5823 }
5824 return 0;
5825 }
5826
5827 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5828 size_t sz = 0;
5829 oop p = (oop)addr;
5830 if (p->klass_or_null() != NULL) {
5831 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5832 } else {
5833 sz = block_size_using_printezis_bits(addr);
5834 }
5835 assert(sz > 0, "size must be nonzero");
5836 HeapWord* next_block = addr + sz;
5837 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
5838 CardTableModRefBS::card_size);
5839 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
5840 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5841 "must be different cards");
5842 return next_card;
5843 }
5844
5845
5846 // CMS Bit Map Wrapper /////////////////////////////////////////
5847
5848 // Construct a CMS bit map infrastructure, but don't create the
5849 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5850 // further below.
5851 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5852 _bm(),
5853 _shifter(shifter),
5854 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5855 Monitor::_safepoint_check_sometimes) : NULL)
5856 {
5857 _bmStartWord = 0;
5858 _bmWordSize = 0;
5859 }
5860
5861 bool CMSBitMap::allocate(MemRegion mr) {
5862 _bmStartWord = mr.start();
5863 _bmWordSize = mr.word_size();
5864 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5865 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5866 if (!brs.is_reserved()) {
5867 warning("CMS bit map allocation failure");
5868 return false;
5869 }
5870 // For now we'll just commit all of the bit map up front.
5871 // Later on we'll try to be more parsimonious with swap.
5872 if (!_virtual_space.initialize(brs, brs.size())) {
5873 warning("CMS bit map backing store failure");
5874 return false;
5875 }
5876 assert(_virtual_space.committed_size() == brs.size(),
5877 "didn't reserve backing store for all of CMS bit map?");
5878 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5879 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5880 _bmWordSize, "inconsistency in bit map sizing");
5881 _bm.set_size(_bmWordSize >> _shifter);
5882
5883 // bm.clear(); // can we rely on getting zero'd memory? verify below
5884 assert(isAllClear(),
5885 "Expected zero'd memory from ReservedSpace constructor");
5886 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5887 "consistency check");
5888 return true;
5889 }
5890
5891 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5892 HeapWord *next_addr, *end_addr, *last_addr;
5893 assert_locked();
5894 assert(covers(mr), "out-of-range error");
5895 // XXX assert that start and end are appropriately aligned
5896 for (next_addr = mr.start(), end_addr = mr.end();
5897 next_addr < end_addr; next_addr = last_addr) {
5898 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5899 last_addr = dirty_region.end();
5900 if (!dirty_region.is_empty()) {
5901 cl->do_MemRegion(dirty_region);
5902 } else {
5903 assert(last_addr == end_addr, "program logic");
5904 return;
5905 }
5906 }
5907 }
5908
5909 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5910 _bm.print_on_error(st, prefix);
5911 }
5912
5913 #ifndef PRODUCT
5914 void CMSBitMap::assert_locked() const {
5915 CMSLockVerifier::assert_locked(lock());
5916 }
5917
5918 bool CMSBitMap::covers(MemRegion mr) const {
5919 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5920 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5921 "size inconsistency");
5922 return (mr.start() >= _bmStartWord) &&
5923 (mr.end() <= endWord());
5924 }
5925
5926 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5927 return (start >= _bmStartWord && (start + size) <= endWord());
5928 }
5929
5930 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5931 // verify that there are no 1 bits in the interval [left, right)
5932 FalseBitMapClosure falseBitMapClosure;
5933 iterate(&falseBitMapClosure, left, right);
5934 }
5935
5936 void CMSBitMap::region_invariant(MemRegion mr)
5937 {
5938 assert_locked();
5939 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5940 assert(!mr.is_empty(), "unexpected empty region");
5941 assert(covers(mr), "mr should be covered by bit map");
5942 // convert address range into offset range
5943 size_t start_ofs = heapWordToOffset(mr.start());
5944 // Make sure that end() is appropriately aligned
5945 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5946 (1 << (_shifter+LogHeapWordSize))),
5947 "Misaligned mr.end()");
5948 size_t end_ofs = heapWordToOffset(mr.end());
5949 assert(end_ofs > start_ofs, "Should mark at least one bit");
5950 }
5951
5952 #endif
5953
5954 bool CMSMarkStack::allocate(size_t size) {
5955 // allocate a stack of the requisite depth
5956 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5957 size * sizeof(oop)));
5958 if (!rs.is_reserved()) {
5959 warning("CMSMarkStack allocation failure");
5960 return false;
5961 }
5962 if (!_virtual_space.initialize(rs, rs.size())) {
5963 warning("CMSMarkStack backing store failure");
5964 return false;
5965 }
5966 assert(_virtual_space.committed_size() == rs.size(),
5967 "didn't reserve backing store for all of CMS stack?");
5968 _base = (oop*)(_virtual_space.low());
5969 _index = 0;
5970 _capacity = size;
5971 NOT_PRODUCT(_max_depth = 0);
5972 return true;
5973 }
5974
5975 // XXX FIX ME !!! In the MT case we come in here holding a
5976 // leaf lock. For printing we need to take a further lock
5977 // which has lower rank. We need to recalibrate the two
5978 // lock-ranks involved in order to be able to print the
5979 // messages below. (Or defer the printing to the caller.
5980 // For now we take the expedient path of just disabling the
5981 // messages for the problematic case.)
5982 void CMSMarkStack::expand() {
5983 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5984 if (_capacity == MarkStackSizeMax) {
5985 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
5986 // We print a warning message only once per CMS cycle.
5987 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
5988 }
5989 return;
5990 }
5991 // Double capacity if possible
5992 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5993 // Do not give up existing stack until we have managed to
5994 // get the double capacity that we desired.
5995 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5996 new_capacity * sizeof(oop)));
5997 if (rs.is_reserved()) {
5998 // Release the backing store associated with old stack
5999 _virtual_space.release();
6000 // Reinitialize virtual space for new stack
6001 if (!_virtual_space.initialize(rs, rs.size())) {
6002 fatal("Not enough swap for expanded marking stack");
6003 }
6004 _base = (oop*)(_virtual_space.low());
6005 _index = 0;
6006 _capacity = new_capacity;
6007 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6008 // Failed to double capacity, continue;
6009 // we print a detail message only once per CMS cycle.
6010 gclog_or_tty->print(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to "
6011 SIZE_FORMAT "K",
6012 _capacity / K, new_capacity / K);
6013 }
6014 }
6015
6016
6017 // Closures
6018 // XXX: there seems to be a lot of code duplication here;
6019 // should refactor and consolidate common code.
6020
6021 // This closure is used to mark refs into the CMS generation in
6022 // the CMS bit map. Called at the first checkpoint. This closure
6023 // assumes that we do not need to re-mark dirty cards; if the CMS
6024 // generation on which this is used is not an oldest
6025 // generation then this will lose younger_gen cards!
6026
6027 MarkRefsIntoClosure::MarkRefsIntoClosure(
6028 MemRegion span, CMSBitMap* bitMap):
6029 _span(span),
6030 _bitMap(bitMap)
6031 {
6032 assert(_ref_processor == NULL, "deliberately left NULL");
6033 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6034 }
6035
6036 void MarkRefsIntoClosure::do_oop(oop obj) {
6037 // if p points into _span, then mark corresponding bit in _markBitMap
6038 assert(obj->is_oop(), "expected an oop");
6039 HeapWord* addr = (HeapWord*)obj;
6040 if (_span.contains(addr)) {
6041 // this should be made more efficient
6042 _bitMap->mark(addr);
6043 }
6044 }
6045
6046 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6047 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6048
6049 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6050 MemRegion span, CMSBitMap* bitMap):
6051 _span(span),
6052 _bitMap(bitMap)
6053 {
6054 assert(_ref_processor == NULL, "deliberately left NULL");
6055 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6056 }
6057
6058 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6059 // if p points into _span, then mark corresponding bit in _markBitMap
6060 assert(obj->is_oop(), "expected an oop");
6061 HeapWord* addr = (HeapWord*)obj;
6062 if (_span.contains(addr)) {
6063 // this should be made more efficient
6064 _bitMap->par_mark(addr);
6065 }
6066 }
6067
6068 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6069 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6070
6071 // A variant of the above, used for CMS marking verification.
6072 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6073 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6074 _span(span),
6075 _verification_bm(verification_bm),
6076 _cms_bm(cms_bm)
6077 {
6078 assert(_ref_processor == NULL, "deliberately left NULL");
6079 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6080 }
6081
6082 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6083 // if p points into _span, then mark corresponding bit in _markBitMap
6084 assert(obj->is_oop(), "expected an oop");
6085 HeapWord* addr = (HeapWord*)obj;
6086 if (_span.contains(addr)) {
6087 _verification_bm->mark(addr);
6088 if (!_cms_bm->isMarked(addr)) {
6089 oop(addr)->print();
6090 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6091 fatal("... aborting");
6092 }
6093 }
6094 }
6095
6096 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6097 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6098
6099 //////////////////////////////////////////////////
6100 // MarkRefsIntoAndScanClosure
6101 //////////////////////////////////////////////////
6102
6103 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6104 ReferenceProcessor* rp,
6105 CMSBitMap* bit_map,
6106 CMSBitMap* mod_union_table,
6107 CMSMarkStack* mark_stack,
6108 CMSCollector* collector,
6109 bool should_yield,
6110 bool concurrent_precleaning):
6111 _collector(collector),
6112 _span(span),
6113 _bit_map(bit_map),
6114 _mark_stack(mark_stack),
6115 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6116 mark_stack, concurrent_precleaning),
6117 _yield(should_yield),
6118 _concurrent_precleaning(concurrent_precleaning),
6119 _freelistLock(NULL)
6120 {
6121 _ref_processor = rp;
6122 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6123 }
6124
6125 // This closure is used to mark refs into the CMS generation at the
6126 // second (final) checkpoint, and to scan and transitively follow
6127 // the unmarked oops. It is also used during the concurrent precleaning
6128 // phase while scanning objects on dirty cards in the CMS generation.
6129 // The marks are made in the marking bit map and the marking stack is
6130 // used for keeping the (newly) grey objects during the scan.
6131 // The parallel version (Par_...) appears further below.
6132 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6133 if (obj != NULL) {
6134 assert(obj->is_oop(), "expected an oop");
6135 HeapWord* addr = (HeapWord*)obj;
6136 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6137 assert(_collector->overflow_list_is_empty(),
6138 "overflow list should be empty");
6139 if (_span.contains(addr) &&
6140 !_bit_map->isMarked(addr)) {
6141 // mark bit map (object is now grey)
6142 _bit_map->mark(addr);
6143 // push on marking stack (stack should be empty), and drain the
6144 // stack by applying this closure to the oops in the oops popped
6145 // from the stack (i.e. blacken the grey objects)
6146 bool res = _mark_stack->push(obj);
6147 assert(res, "Should have space to push on empty stack");
6148 do {
6149 oop new_oop = _mark_stack->pop();
6150 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6151 assert(_bit_map->isMarked((HeapWord*)new_oop),
6152 "only grey objects on this stack");
6153 // iterate over the oops in this oop, marking and pushing
6154 // the ones in CMS heap (i.e. in _span).
6155 new_oop->oop_iterate(&_pushAndMarkClosure);
6156 // check if it's time to yield
6157 do_yield_check();
6158 } while (!_mark_stack->isEmpty() ||
6159 (!_concurrent_precleaning && take_from_overflow_list()));
6160 // if marking stack is empty, and we are not doing this
6161 // during precleaning, then check the overflow list
6162 }
6163 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6164 assert(_collector->overflow_list_is_empty(),
6165 "overflow list was drained above");
6166 // We could restore evacuated mark words, if any, used for
6167 // overflow list links here because the overflow list is
6168 // provably empty here. That would reduce the maximum
6169 // size requirements for preserved_{oop,mark}_stack.
6170 // But we'll just postpone it until we are all done
6171 // so we can just stream through.
6172 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6173 _collector->restore_preserved_marks_if_any();
6174 assert(_collector->no_preserved_marks(), "No preserved marks");
6175 }
6176 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6177 "All preserved marks should have been restored above");
6178 }
6179 }
6180
6181 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6182 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6183
6184 void MarkRefsIntoAndScanClosure::do_yield_work() {
6185 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6186 "CMS thread should hold CMS token");
6187 assert_lock_strong(_freelistLock);
6188 assert_lock_strong(_bit_map->lock());
6189 // relinquish the free_list_lock and bitMaplock()
6190 _bit_map->lock()->unlock();
6191 _freelistLock->unlock();
6192 ConcurrentMarkSweepThread::desynchronize(true);
6193 _collector->stopTimer();
6194 if (PrintCMSStatistics != 0) {
6195 _collector->incrementYields();
6196 }
6197
6198 // See the comment in coordinator_yield()
6199 for (unsigned i = 0;
6200 i < CMSYieldSleepCount &&
6201 ConcurrentMarkSweepThread::should_yield() &&
6202 !CMSCollector::foregroundGCIsActive();
6203 ++i) {
6204 os::sleep(Thread::current(), 1, false);
6205 }
6206
6207 ConcurrentMarkSweepThread::synchronize(true);
6208 _freelistLock->lock_without_safepoint_check();
6209 _bit_map->lock()->lock_without_safepoint_check();
6210 _collector->startTimer();
6211 }
6212
6213 ///////////////////////////////////////////////////////////
6214 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6215 // MarkRefsIntoAndScanClosure
6216 ///////////////////////////////////////////////////////////
6217 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6218 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6219 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6220 _span(span),
6221 _bit_map(bit_map),
6222 _work_queue(work_queue),
6223 _low_water_mark(MIN2((work_queue->max_elems()/4),
6224 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6225 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6226 {
6227 _ref_processor = rp;
6228 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6229 }
6230
6231 // This closure is used to mark refs into the CMS generation at the
6232 // second (final) checkpoint, and to scan and transitively follow
6233 // the unmarked oops. The marks are made in the marking bit map and
6234 // the work_queue is used for keeping the (newly) grey objects during
6235 // the scan phase whence they are also available for stealing by parallel
6236 // threads. Since the marking bit map is shared, updates are
6237 // synchronized (via CAS).
6238 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6239 if (obj != NULL) {
6240 // Ignore mark word because this could be an already marked oop
6241 // that may be chained at the end of the overflow list.
6242 assert(obj->is_oop(true), "expected an oop");
6243 HeapWord* addr = (HeapWord*)obj;
6244 if (_span.contains(addr) &&
6245 !_bit_map->isMarked(addr)) {
6246 // mark bit map (object will become grey):
6247 // It is possible for several threads to be
6248 // trying to "claim" this object concurrently;
6249 // the unique thread that succeeds in marking the
6250 // object first will do the subsequent push on
6251 // to the work queue (or overflow list).
6252 if (_bit_map->par_mark(addr)) {
6253 // push on work_queue (which may not be empty), and trim the
6254 // queue to an appropriate length by applying this closure to
6255 // the oops in the oops popped from the stack (i.e. blacken the
6256 // grey objects)
6257 bool res = _work_queue->push(obj);
6258 assert(res, "Low water mark should be less than capacity?");
6259 trim_queue(_low_water_mark);
6260 } // Else, another thread claimed the object
6261 }
6262 }
6263 }
6264
6265 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6266 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6267
6268 // This closure is used to rescan the marked objects on the dirty cards
6269 // in the mod union table and the card table proper.
6270 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6271 oop p, MemRegion mr) {
6272
6273 size_t size = 0;
6274 HeapWord* addr = (HeapWord*)p;
6275 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6276 assert(_span.contains(addr), "we are scanning the CMS generation");
6277 // check if it's time to yield
6278 if (do_yield_check()) {
6279 // We yielded for some foreground stop-world work,
6280 // and we have been asked to abort this ongoing preclean cycle.
6281 return 0;
6282 }
6283 if (_bitMap->isMarked(addr)) {
6284 // it's marked; is it potentially uninitialized?
6285 if (p->klass_or_null() != NULL) {
6286 // an initialized object; ignore mark word in verification below
6287 // since we are running concurrent with mutators
6288 assert(p->is_oop(true), "should be an oop");
6289 if (p->is_objArray()) {
6290 // objArrays are precisely marked; restrict scanning
6291 // to dirty cards only.
6292 size = CompactibleFreeListSpace::adjustObjectSize(
6293 p->oop_iterate_size(_scanningClosure, mr));
6294 } else {
6295 // A non-array may have been imprecisely marked; we need
6296 // to scan object in its entirety.
6297 size = CompactibleFreeListSpace::adjustObjectSize(
6298 p->oop_iterate_size(_scanningClosure));
6299 }
6300 #ifdef ASSERT
6301 size_t direct_size =
6302 CompactibleFreeListSpace::adjustObjectSize(p->size());
6303 assert(size == direct_size, "Inconsistency in size");
6304 assert(size >= 3, "Necessary for Printezis marks to work");
6305 if (!_bitMap->isMarked(addr+1)) {
6306 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6307 } else {
6308 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6309 assert(_bitMap->isMarked(addr+size-1),
6310 "inconsistent Printezis mark");
6311 }
6312 #endif // ASSERT
6313 } else {
6314 // An uninitialized object.
6315 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6316 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6317 size = pointer_delta(nextOneAddr + 1, addr);
6318 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6319 "alignment problem");
6320 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6321 // will dirty the card when the klass pointer is installed in the
6322 // object (signaling the completion of initialization).
6323 }
6324 } else {
6325 // Either a not yet marked object or an uninitialized object
6326 if (p->klass_or_null() == NULL) {
6327 // An uninitialized object, skip to the next card, since
6328 // we may not be able to read its P-bits yet.
6329 assert(size == 0, "Initial value");
6330 } else {
6331 // An object not (yet) reached by marking: we merely need to
6332 // compute its size so as to go look at the next block.
6333 assert(p->is_oop(true), "should be an oop");
6334 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6335 }
6336 }
6337 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6338 return size;
6339 }
6340
6341 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6342 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6343 "CMS thread should hold CMS token");
6344 assert_lock_strong(_freelistLock);
6345 assert_lock_strong(_bitMap->lock());
6346 // relinquish the free_list_lock and bitMaplock()
6347 _bitMap->lock()->unlock();
6348 _freelistLock->unlock();
6349 ConcurrentMarkSweepThread::desynchronize(true);
6350 _collector->stopTimer();
6351 if (PrintCMSStatistics != 0) {
6352 _collector->incrementYields();
6353 }
6354
6355 // See the comment in coordinator_yield()
6356 for (unsigned i = 0; i < CMSYieldSleepCount &&
6357 ConcurrentMarkSweepThread::should_yield() &&
6358 !CMSCollector::foregroundGCIsActive(); ++i) {
6359 os::sleep(Thread::current(), 1, false);
6360 }
6361
6362 ConcurrentMarkSweepThread::synchronize(true);
6363 _freelistLock->lock_without_safepoint_check();
6364 _bitMap->lock()->lock_without_safepoint_check();
6365 _collector->startTimer();
6366 }
6367
6368
6369 //////////////////////////////////////////////////////////////////
6370 // SurvivorSpacePrecleanClosure
6371 //////////////////////////////////////////////////////////////////
6372 // This (single-threaded) closure is used to preclean the oops in
6373 // the survivor spaces.
6374 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6375
6376 HeapWord* addr = (HeapWord*)p;
6377 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6378 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6379 assert(p->klass_or_null() != NULL, "object should be initialized");
6380 // an initialized object; ignore mark word in verification below
6381 // since we are running concurrent with mutators
6382 assert(p->is_oop(true), "should be an oop");
6383 // Note that we do not yield while we iterate over
6384 // the interior oops of p, pushing the relevant ones
6385 // on our marking stack.
6386 size_t size = p->oop_iterate_size(_scanning_closure);
6387 do_yield_check();
6388 // Observe that below, we do not abandon the preclean
6389 // phase as soon as we should; rather we empty the
6390 // marking stack before returning. This is to satisfy
6391 // some existing assertions. In general, it may be a
6392 // good idea to abort immediately and complete the marking
6393 // from the grey objects at a later time.
6394 while (!_mark_stack->isEmpty()) {
6395 oop new_oop = _mark_stack->pop();
6396 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6397 assert(_bit_map->isMarked((HeapWord*)new_oop),
6398 "only grey objects on this stack");
6399 // iterate over the oops in this oop, marking and pushing
6400 // the ones in CMS heap (i.e. in _span).
6401 new_oop->oop_iterate(_scanning_closure);
6402 // check if it's time to yield
6403 do_yield_check();
6404 }
6405 unsigned int after_count =
6406 GenCollectedHeap::heap()->total_collections();
6407 bool abort = (_before_count != after_count) ||
6408 _collector->should_abort_preclean();
6409 return abort ? 0 : size;
6410 }
6411
6412 void SurvivorSpacePrecleanClosure::do_yield_work() {
6413 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6414 "CMS thread should hold CMS token");
6415 assert_lock_strong(_bit_map->lock());
6416 // Relinquish the bit map lock
6417 _bit_map->lock()->unlock();
6418 ConcurrentMarkSweepThread::desynchronize(true);
6419 _collector->stopTimer();
6420 if (PrintCMSStatistics != 0) {
6421 _collector->incrementYields();
6422 }
6423
6424 // See the comment in coordinator_yield()
6425 for (unsigned i = 0; i < CMSYieldSleepCount &&
6426 ConcurrentMarkSweepThread::should_yield() &&
6427 !CMSCollector::foregroundGCIsActive(); ++i) {
6428 os::sleep(Thread::current(), 1, false);
6429 }
6430
6431 ConcurrentMarkSweepThread::synchronize(true);
6432 _bit_map->lock()->lock_without_safepoint_check();
6433 _collector->startTimer();
6434 }
6435
6436 // This closure is used to rescan the marked objects on the dirty cards
6437 // in the mod union table and the card table proper. In the parallel
6438 // case, although the bitMap is shared, we do a single read so the
6439 // isMarked() query is "safe".
6440 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6441 // Ignore mark word because we are running concurrent with mutators
6442 assert(p->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6443 HeapWord* addr = (HeapWord*)p;
6444 assert(_span.contains(addr), "we are scanning the CMS generation");
6445 bool is_obj_array = false;
6446 #ifdef ASSERT
6447 if (!_parallel) {
6448 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6449 assert(_collector->overflow_list_is_empty(),
6450 "overflow list should be empty");
6451
6452 }
6453 #endif // ASSERT
6454 if (_bit_map->isMarked(addr)) {
6455 // Obj arrays are precisely marked, non-arrays are not;
6456 // so we scan objArrays precisely and non-arrays in their
6457 // entirety.
6458 if (p->is_objArray()) {
6459 is_obj_array = true;
6460 if (_parallel) {
6461 p->oop_iterate(_par_scan_closure, mr);
6462 } else {
6463 p->oop_iterate(_scan_closure, mr);
6464 }
6465 } else {
6466 if (_parallel) {
6467 p->oop_iterate(_par_scan_closure);
6468 } else {
6469 p->oop_iterate(_scan_closure);
6470 }
6471 }
6472 }
6473 #ifdef ASSERT
6474 if (!_parallel) {
6475 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6476 assert(_collector->overflow_list_is_empty(),
6477 "overflow list should be empty");
6478
6479 }
6480 #endif // ASSERT
6481 return is_obj_array;
6482 }
6483
6484 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6485 MemRegion span,
6486 CMSBitMap* bitMap, CMSMarkStack* markStack,
6487 bool should_yield, bool verifying):
6488 _collector(collector),
6489 _span(span),
6490 _bitMap(bitMap),
6491 _mut(&collector->_modUnionTable),
6492 _markStack(markStack),
6493 _yield(should_yield),
6494 _skipBits(0)
6495 {
6496 assert(_markStack->isEmpty(), "stack should be empty");
6497 _finger = _bitMap->startWord();
6498 _threshold = _finger;
6499 assert(_collector->_restart_addr == NULL, "Sanity check");
6500 assert(_span.contains(_finger), "Out of bounds _finger?");
6501 DEBUG_ONLY(_verifying = verifying;)
6502 }
6503
6504 void MarkFromRootsClosure::reset(HeapWord* addr) {
6505 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6506 assert(_span.contains(addr), "Out of bounds _finger?");
6507 _finger = addr;
6508 _threshold = (HeapWord*)round_to(
6509 (intptr_t)_finger, CardTableModRefBS::card_size);
6510 }
6511
6512 // Should revisit to see if this should be restructured for
6513 // greater efficiency.
6514 bool MarkFromRootsClosure::do_bit(size_t offset) {
6515 if (_skipBits > 0) {
6516 _skipBits--;
6517 return true;
6518 }
6519 // convert offset into a HeapWord*
6520 HeapWord* addr = _bitMap->startWord() + offset;
6521 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6522 "address out of range");
6523 assert(_bitMap->isMarked(addr), "tautology");
6524 if (_bitMap->isMarked(addr+1)) {
6525 // this is an allocated but not yet initialized object
6526 assert(_skipBits == 0, "tautology");
6527 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6528 oop p = oop(addr);
6529 if (p->klass_or_null() == NULL) {
6530 DEBUG_ONLY(if (!_verifying) {)
6531 // We re-dirty the cards on which this object lies and increase
6532 // the _threshold so that we'll come back to scan this object
6533 // during the preclean or remark phase. (CMSCleanOnEnter)
6534 if (CMSCleanOnEnter) {
6535 size_t sz = _collector->block_size_using_printezis_bits(addr);
6536 HeapWord* end_card_addr = (HeapWord*)round_to(
6537 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6538 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6539 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6540 // Bump _threshold to end_card_addr; note that
6541 // _threshold cannot possibly exceed end_card_addr, anyhow.
6542 // This prevents future clearing of the card as the scan proceeds
6543 // to the right.
6544 assert(_threshold <= end_card_addr,
6545 "Because we are just scanning into this object");
6546 if (_threshold < end_card_addr) {
6547 _threshold = end_card_addr;
6548 }
6549 if (p->klass_or_null() != NULL) {
6550 // Redirty the range of cards...
6551 _mut->mark_range(redirty_range);
6552 } // ...else the setting of klass will dirty the card anyway.
6553 }
6554 DEBUG_ONLY(})
6555 return true;
6556 }
6557 }
6558 scanOopsInOop(addr);
6559 return true;
6560 }
6561
6562 // We take a break if we've been at this for a while,
6563 // so as to avoid monopolizing the locks involved.
6564 void MarkFromRootsClosure::do_yield_work() {
6565 // First give up the locks, then yield, then re-lock
6566 // We should probably use a constructor/destructor idiom to
6567 // do this unlock/lock or modify the MutexUnlocker class to
6568 // serve our purpose. XXX
6569 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6570 "CMS thread should hold CMS token");
6571 assert_lock_strong(_bitMap->lock());
6572 _bitMap->lock()->unlock();
6573 ConcurrentMarkSweepThread::desynchronize(true);
6574 _collector->stopTimer();
6575 if (PrintCMSStatistics != 0) {
6576 _collector->incrementYields();
6577 }
6578
6579 // See the comment in coordinator_yield()
6580 for (unsigned i = 0; i < CMSYieldSleepCount &&
6581 ConcurrentMarkSweepThread::should_yield() &&
6582 !CMSCollector::foregroundGCIsActive(); ++i) {
6583 os::sleep(Thread::current(), 1, false);
6584 }
6585
6586 ConcurrentMarkSweepThread::synchronize(true);
6587 _bitMap->lock()->lock_without_safepoint_check();
6588 _collector->startTimer();
6589 }
6590
6591 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6592 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6593 assert(_markStack->isEmpty(),
6594 "should drain stack to limit stack usage");
6595 // convert ptr to an oop preparatory to scanning
6596 oop obj = oop(ptr);
6597 // Ignore mark word in verification below, since we
6598 // may be running concurrent with mutators.
6599 assert(obj->is_oop(true), "should be an oop");
6600 assert(_finger <= ptr, "_finger runneth ahead");
6601 // advance the finger to right end of this object
6602 _finger = ptr + obj->size();
6603 assert(_finger > ptr, "we just incremented it above");
6604 // On large heaps, it may take us some time to get through
6605 // the marking phase. During
6606 // this time it's possible that a lot of mutations have
6607 // accumulated in the card table and the mod union table --
6608 // these mutation records are redundant until we have
6609 // actually traced into the corresponding card.
6610 // Here, we check whether advancing the finger would make
6611 // us cross into a new card, and if so clear corresponding
6612 // cards in the MUT (preclean them in the card-table in the
6613 // future).
6614
6615 DEBUG_ONLY(if (!_verifying) {)
6616 // The clean-on-enter optimization is disabled by default,
6617 // until we fix 6178663.
6618 if (CMSCleanOnEnter && (_finger > _threshold)) {
6619 // [_threshold, _finger) represents the interval
6620 // of cards to be cleared in MUT (or precleaned in card table).
6621 // The set of cards to be cleared is all those that overlap
6622 // with the interval [_threshold, _finger); note that
6623 // _threshold is always kept card-aligned but _finger isn't
6624 // always card-aligned.
6625 HeapWord* old_threshold = _threshold;
6626 assert(old_threshold == (HeapWord*)round_to(
6627 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6628 "_threshold should always be card-aligned");
6629 _threshold = (HeapWord*)round_to(
6630 (intptr_t)_finger, CardTableModRefBS::card_size);
6631 MemRegion mr(old_threshold, _threshold);
6632 assert(!mr.is_empty(), "Control point invariant");
6633 assert(_span.contains(mr), "Should clear within span");
6634 _mut->clear_range(mr);
6635 }
6636 DEBUG_ONLY(})
6637 // Note: the finger doesn't advance while we drain
6638 // the stack below.
6639 PushOrMarkClosure pushOrMarkClosure(_collector,
6640 _span, _bitMap, _markStack,
6641 _finger, this);
6642 bool res = _markStack->push(obj);
6643 assert(res, "Empty non-zero size stack should have space for single push");
6644 while (!_markStack->isEmpty()) {
6645 oop new_oop = _markStack->pop();
6646 // Skip verifying header mark word below because we are
6647 // running concurrent with mutators.
6648 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6649 // now scan this oop's oops
6650 new_oop->oop_iterate(&pushOrMarkClosure);
6651 do_yield_check();
6652 }
6653 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6654 }
6655
6656 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6657 CMSCollector* collector, MemRegion span,
6658 CMSBitMap* bit_map,
6659 OopTaskQueue* work_queue,
6660 CMSMarkStack* overflow_stack):
6661 _collector(collector),
6662 _whole_span(collector->_span),
6663 _span(span),
6664 _bit_map(bit_map),
6665 _mut(&collector->_modUnionTable),
6666 _work_queue(work_queue),
6667 _overflow_stack(overflow_stack),
6668 _skip_bits(0),
6669 _task(task)
6670 {
6671 assert(_work_queue->size() == 0, "work_queue should be empty");
6672 _finger = span.start();
6673 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6674 assert(_span.contains(_finger), "Out of bounds _finger?");
6675 }
6676
6677 // Should revisit to see if this should be restructured for
6678 // greater efficiency.
6679 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6680 if (_skip_bits > 0) {
6681 _skip_bits--;
6682 return true;
6683 }
6684 // convert offset into a HeapWord*
6685 HeapWord* addr = _bit_map->startWord() + offset;
6686 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6687 "address out of range");
6688 assert(_bit_map->isMarked(addr), "tautology");
6689 if (_bit_map->isMarked(addr+1)) {
6690 // this is an allocated object that might not yet be initialized
6691 assert(_skip_bits == 0, "tautology");
6692 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6693 oop p = oop(addr);
6694 if (p->klass_or_null() == NULL) {
6695 // in the case of Clean-on-Enter optimization, redirty card
6696 // and avoid clearing card by increasing the threshold.
6697 return true;
6698 }
6699 }
6700 scan_oops_in_oop(addr);
6701 return true;
6702 }
6703
6704 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6705 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6706 // Should we assert that our work queue is empty or
6707 // below some drain limit?
6708 assert(_work_queue->size() == 0,
6709 "should drain stack to limit stack usage");
6710 // convert ptr to an oop preparatory to scanning
6711 oop obj = oop(ptr);
6712 // Ignore mark word in verification below, since we
6713 // may be running concurrent with mutators.
6714 assert(obj->is_oop(true), "should be an oop");
6715 assert(_finger <= ptr, "_finger runneth ahead");
6716 // advance the finger to right end of this object
6717 _finger = ptr + obj->size();
6718 assert(_finger > ptr, "we just incremented it above");
6719 // On large heaps, it may take us some time to get through
6720 // the marking phase. During
6721 // this time it's possible that a lot of mutations have
6722 // accumulated in the card table and the mod union table --
6723 // these mutation records are redundant until we have
6724 // actually traced into the corresponding card.
6725 // Here, we check whether advancing the finger would make
6726 // us cross into a new card, and if so clear corresponding
6727 // cards in the MUT (preclean them in the card-table in the
6728 // future).
6729
6730 // The clean-on-enter optimization is disabled by default,
6731 // until we fix 6178663.
6732 if (CMSCleanOnEnter && (_finger > _threshold)) {
6733 // [_threshold, _finger) represents the interval
6734 // of cards to be cleared in MUT (or precleaned in card table).
6735 // The set of cards to be cleared is all those that overlap
6736 // with the interval [_threshold, _finger); note that
6737 // _threshold is always kept card-aligned but _finger isn't
6738 // always card-aligned.
6739 HeapWord* old_threshold = _threshold;
6740 assert(old_threshold == (HeapWord*)round_to(
6741 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6742 "_threshold should always be card-aligned");
6743 _threshold = (HeapWord*)round_to(
6744 (intptr_t)_finger, CardTableModRefBS::card_size);
6745 MemRegion mr(old_threshold, _threshold);
6746 assert(!mr.is_empty(), "Control point invariant");
6747 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6748 _mut->clear_range(mr);
6749 }
6750
6751 // Note: the local finger doesn't advance while we drain
6752 // the stack below, but the global finger sure can and will.
6753 HeapWord** gfa = _task->global_finger_addr();
6754 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6755 _span, _bit_map,
6756 _work_queue,
6757 _overflow_stack,
6758 _finger,
6759 gfa, this);
6760 bool res = _work_queue->push(obj); // overflow could occur here
6761 assert(res, "Will hold once we use workqueues");
6762 while (true) {
6763 oop new_oop;
6764 if (!_work_queue->pop_local(new_oop)) {
6765 // We emptied our work_queue; check if there's stuff that can
6766 // be gotten from the overflow stack.
6767 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6768 _overflow_stack, _work_queue)) {
6769 do_yield_check();
6770 continue;
6771 } else { // done
6772 break;
6773 }
6774 }
6775 // Skip verifying header mark word below because we are
6776 // running concurrent with mutators.
6777 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6778 // now scan this oop's oops
6779 new_oop->oop_iterate(&pushOrMarkClosure);
6780 do_yield_check();
6781 }
6782 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6783 }
6784
6785 // Yield in response to a request from VM Thread or
6786 // from mutators.
6787 void Par_MarkFromRootsClosure::do_yield_work() {
6788 assert(_task != NULL, "sanity");
6789 _task->yield();
6790 }
6791
6792 // A variant of the above used for verifying CMS marking work.
6793 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6794 MemRegion span,
6795 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6796 CMSMarkStack* mark_stack):
6797 _collector(collector),
6798 _span(span),
6799 _verification_bm(verification_bm),
6800 _cms_bm(cms_bm),
6801 _mark_stack(mark_stack),
6802 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6803 mark_stack)
6804 {
6805 assert(_mark_stack->isEmpty(), "stack should be empty");
6806 _finger = _verification_bm->startWord();
6807 assert(_collector->_restart_addr == NULL, "Sanity check");
6808 assert(_span.contains(_finger), "Out of bounds _finger?");
6809 }
6810
6811 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6812 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6813 assert(_span.contains(addr), "Out of bounds _finger?");
6814 _finger = addr;
6815 }
6816
6817 // Should revisit to see if this should be restructured for
6818 // greater efficiency.
6819 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6820 // convert offset into a HeapWord*
6821 HeapWord* addr = _verification_bm->startWord() + offset;
6822 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6823 "address out of range");
6824 assert(_verification_bm->isMarked(addr), "tautology");
6825 assert(_cms_bm->isMarked(addr), "tautology");
6826
6827 assert(_mark_stack->isEmpty(),
6828 "should drain stack to limit stack usage");
6829 // convert addr to an oop preparatory to scanning
6830 oop obj = oop(addr);
6831 assert(obj->is_oop(), "should be an oop");
6832 assert(_finger <= addr, "_finger runneth ahead");
6833 // advance the finger to right end of this object
6834 _finger = addr + obj->size();
6835 assert(_finger > addr, "we just incremented it above");
6836 // Note: the finger doesn't advance while we drain
6837 // the stack below.
6838 bool res = _mark_stack->push(obj);
6839 assert(res, "Empty non-zero size stack should have space for single push");
6840 while (!_mark_stack->isEmpty()) {
6841 oop new_oop = _mark_stack->pop();
6842 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6843 // now scan this oop's oops
6844 new_oop->oop_iterate(&_pam_verify_closure);
6845 }
6846 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6847 return true;
6848 }
6849
6850 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6851 CMSCollector* collector, MemRegion span,
6852 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6853 CMSMarkStack* mark_stack):
6854 MetadataAwareOopClosure(collector->ref_processor()),
6855 _collector(collector),
6856 _span(span),
6857 _verification_bm(verification_bm),
6858 _cms_bm(cms_bm),
6859 _mark_stack(mark_stack)
6860 { }
6861
6862 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6863 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6864
6865 // Upon stack overflow, we discard (part of) the stack,
6866 // remembering the least address amongst those discarded
6867 // in CMSCollector's _restart_address.
6868 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6869 // Remember the least grey address discarded
6870 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6871 _collector->lower_restart_addr(ra);
6872 _mark_stack->reset(); // discard stack contents
6873 _mark_stack->expand(); // expand the stack if possible
6874 }
6875
6876 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6877 assert(obj->is_oop_or_null(), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6878 HeapWord* addr = (HeapWord*)obj;
6879 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6880 // Oop lies in _span and isn't yet grey or black
6881 _verification_bm->mark(addr); // now grey
6882 if (!_cms_bm->isMarked(addr)) {
6883 oop(addr)->print();
6884 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
6885 p2i(addr));
6886 fatal("... aborting");
6887 }
6888
6889 if (!_mark_stack->push(obj)) { // stack overflow
6890 if (PrintCMSStatistics != 0) {
6891 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6892 SIZE_FORMAT, _mark_stack->capacity());
6893 }
6894 assert(_mark_stack->isFull(), "Else push should have succeeded");
6895 handle_stack_overflow(addr);
6896 }
6897 // anything including and to the right of _finger
6898 // will be scanned as we iterate over the remainder of the
6899 // bit map
6900 }
6901 }
6902
6903 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6904 MemRegion span,
6905 CMSBitMap* bitMap, CMSMarkStack* markStack,
6906 HeapWord* finger, MarkFromRootsClosure* parent) :
6907 MetadataAwareOopClosure(collector->ref_processor()),
6908 _collector(collector),
6909 _span(span),
6910 _bitMap(bitMap),
6911 _markStack(markStack),
6912 _finger(finger),
6913 _parent(parent)
6914 { }
6915
6916 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
6917 MemRegion span,
6918 CMSBitMap* bit_map,
6919 OopTaskQueue* work_queue,
6920 CMSMarkStack* overflow_stack,
6921 HeapWord* finger,
6922 HeapWord** global_finger_addr,
6923 Par_MarkFromRootsClosure* parent) :
6924 MetadataAwareOopClosure(collector->ref_processor()),
6925 _collector(collector),
6926 _whole_span(collector->_span),
6927 _span(span),
6928 _bit_map(bit_map),
6929 _work_queue(work_queue),
6930 _overflow_stack(overflow_stack),
6931 _finger(finger),
6932 _global_finger_addr(global_finger_addr),
6933 _parent(parent)
6934 { }
6935
6936 // Assumes thread-safe access by callers, who are
6937 // responsible for mutual exclusion.
6938 void CMSCollector::lower_restart_addr(HeapWord* low) {
6939 assert(_span.contains(low), "Out of bounds addr");
6940 if (_restart_addr == NULL) {
6941 _restart_addr = low;
6942 } else {
6943 _restart_addr = MIN2(_restart_addr, low);
6944 }
6945 }
6946
6947 // Upon stack overflow, we discard (part of) the stack,
6948 // remembering the least address amongst those discarded
6949 // in CMSCollector's _restart_address.
6950 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6951 // Remember the least grey address discarded
6952 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6953 _collector->lower_restart_addr(ra);
6954 _markStack->reset(); // discard stack contents
6955 _markStack->expand(); // expand the stack if possible
6956 }
6957
6958 // Upon stack overflow, we discard (part of) the stack,
6959 // remembering the least address amongst those discarded
6960 // in CMSCollector's _restart_address.
6961 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6962 // We need to do this under a mutex to prevent other
6963 // workers from interfering with the work done below.
6964 MutexLockerEx ml(_overflow_stack->par_lock(),
6965 Mutex::_no_safepoint_check_flag);
6966 // Remember the least grey address discarded
6967 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6968 _collector->lower_restart_addr(ra);
6969 _overflow_stack->reset(); // discard stack contents
6970 _overflow_stack->expand(); // expand the stack if possible
6971 }
6972
6973 void PushOrMarkClosure::do_oop(oop obj) {
6974 // Ignore mark word because we are running concurrent with mutators.
6975 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6976 HeapWord* addr = (HeapWord*)obj;
6977 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6978 // Oop lies in _span and isn't yet grey or black
6979 _bitMap->mark(addr); // now grey
6980 if (addr < _finger) {
6981 // the bit map iteration has already either passed, or
6982 // sampled, this bit in the bit map; we'll need to
6983 // use the marking stack to scan this oop's oops.
6984 bool simulate_overflow = false;
6985 NOT_PRODUCT(
6986 if (CMSMarkStackOverflowALot &&
6987 _collector->simulate_overflow()) {
6988 // simulate a stack overflow
6989 simulate_overflow = true;
6990 }
6991 )
6992 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6993 if (PrintCMSStatistics != 0) {
6994 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6995 SIZE_FORMAT, _markStack->capacity());
6996 }
6997 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6998 handle_stack_overflow(addr);
6999 }
7000 }
7001 // anything including and to the right of _finger
7002 // will be scanned as we iterate over the remainder of the
7003 // bit map
7004 do_yield_check();
7005 }
7006 }
7007
7008 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7009 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7010
7011 void Par_PushOrMarkClosure::do_oop(oop obj) {
7012 // Ignore mark word because we are running concurrent with mutators.
7013 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
7014 HeapWord* addr = (HeapWord*)obj;
7015 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7016 // Oop lies in _span and isn't yet grey or black
7017 // We read the global_finger (volatile read) strictly after marking oop
7018 bool res = _bit_map->par_mark(addr); // now grey
7019 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7020 // Should we push this marked oop on our stack?
7021 // -- if someone else marked it, nothing to do
7022 // -- if target oop is above global finger nothing to do
7023 // -- if target oop is in chunk and above local finger
7024 // then nothing to do
7025 // -- else push on work queue
7026 if ( !res // someone else marked it, they will deal with it
7027 || (addr >= *gfa) // will be scanned in a later task
7028 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7029 return;
7030 }
7031 // the bit map iteration has already either passed, or
7032 // sampled, this bit in the bit map; we'll need to
7033 // use the marking stack to scan this oop's oops.
7034 bool simulate_overflow = false;
7035 NOT_PRODUCT(
7036 if (CMSMarkStackOverflowALot &&
7037 _collector->simulate_overflow()) {
7038 // simulate a stack overflow
7039 simulate_overflow = true;
7040 }
7041 )
7042 if (simulate_overflow ||
7043 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7044 // stack overflow
7045 if (PrintCMSStatistics != 0) {
7046 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7047 SIZE_FORMAT, _overflow_stack->capacity());
7048 }
7049 // We cannot assert that the overflow stack is full because
7050 // it may have been emptied since.
7051 assert(simulate_overflow ||
7052 _work_queue->size() == _work_queue->max_elems(),
7053 "Else push should have succeeded");
7054 handle_stack_overflow(addr);
7055 }
7056 do_yield_check();
7057 }
7058 }
7059
7060 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7061 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7062
7063 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7064 MemRegion span,
7065 ReferenceProcessor* rp,
7066 CMSBitMap* bit_map,
7067 CMSBitMap* mod_union_table,
7068 CMSMarkStack* mark_stack,
7069 bool concurrent_precleaning):
7070 MetadataAwareOopClosure(rp),
7071 _collector(collector),
7072 _span(span),
7073 _bit_map(bit_map),
7074 _mod_union_table(mod_union_table),
7075 _mark_stack(mark_stack),
7076 _concurrent_precleaning(concurrent_precleaning)
7077 {
7078 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7079 }
7080
7081 // Grey object rescan during pre-cleaning and second checkpoint phases --
7082 // the non-parallel version (the parallel version appears further below.)
7083 void PushAndMarkClosure::do_oop(oop obj) {
7084 // Ignore mark word verification. If during concurrent precleaning,
7085 // the object monitor may be locked. If during the checkpoint
7086 // phases, the object may already have been reached by a different
7087 // path and may be at the end of the global overflow list (so
7088 // the mark word may be NULL).
7089 assert(obj->is_oop_or_null(true /* ignore mark word */),
7090 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
7091 HeapWord* addr = (HeapWord*)obj;
7092 // Check if oop points into the CMS generation
7093 // and is not marked
7094 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7095 // a white object ...
7096 _bit_map->mark(addr); // ... now grey
7097 // push on the marking stack (grey set)
7098 bool simulate_overflow = false;
7099 NOT_PRODUCT(
7100 if (CMSMarkStackOverflowALot &&
7101 _collector->simulate_overflow()) {
7102 // simulate a stack overflow
7103 simulate_overflow = true;
7104 }
7105 )
7106 if (simulate_overflow || !_mark_stack->push(obj)) {
7107 if (_concurrent_precleaning) {
7108 // During precleaning we can just dirty the appropriate card(s)
7109 // in the mod union table, thus ensuring that the object remains
7110 // in the grey set and continue. In the case of object arrays
7111 // we need to dirty all of the cards that the object spans,
7112 // since the rescan of object arrays will be limited to the
7113 // dirty cards.
7114 // Note that no one can be interfering with us in this action
7115 // of dirtying the mod union table, so no locking or atomics
7116 // are required.
7117 if (obj->is_objArray()) {
7118 size_t sz = obj->size();
7119 HeapWord* end_card_addr = (HeapWord*)round_to(
7120 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7121 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7122 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7123 _mod_union_table->mark_range(redirty_range);
7124 } else {
7125 _mod_union_table->mark(addr);
7126 }
7127 _collector->_ser_pmc_preclean_ovflw++;
7128 } else {
7129 // During the remark phase, we need to remember this oop
7130 // in the overflow list.
7131 _collector->push_on_overflow_list(obj);
7132 _collector->_ser_pmc_remark_ovflw++;
7133 }
7134 }
7135 }
7136 }
7137
7138 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7139 MemRegion span,
7140 ReferenceProcessor* rp,
7141 CMSBitMap* bit_map,
7142 OopTaskQueue* work_queue):
7143 MetadataAwareOopClosure(rp),
7144 _collector(collector),
7145 _span(span),
7146 _bit_map(bit_map),
7147 _work_queue(work_queue)
7148 {
7149 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7150 }
7151
7152 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7153 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7154
7155 // Grey object rescan during second checkpoint phase --
7156 // the parallel version.
7157 void Par_PushAndMarkClosure::do_oop(oop obj) {
7158 // In the assert below, we ignore the mark word because
7159 // this oop may point to an already visited object that is
7160 // on the overflow stack (in which case the mark word has
7161 // been hijacked for chaining into the overflow stack --
7162 // if this is the last object in the overflow stack then
7163 // its mark word will be NULL). Because this object may
7164 // have been subsequently popped off the global overflow
7165 // stack, and the mark word possibly restored to the prototypical
7166 // value, by the time we get to examined this failing assert in
7167 // the debugger, is_oop_or_null(false) may subsequently start
7168 // to hold.
7169 assert(obj->is_oop_or_null(true),
7170 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
7171 HeapWord* addr = (HeapWord*)obj;
7172 // Check if oop points into the CMS generation
7173 // and is not marked
7174 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7175 // a white object ...
7176 // If we manage to "claim" the object, by being the
7177 // first thread to mark it, then we push it on our
7178 // marking stack
7179 if (_bit_map->par_mark(addr)) { // ... now grey
7180 // push on work queue (grey set)
7181 bool simulate_overflow = false;
7182 NOT_PRODUCT(
7183 if (CMSMarkStackOverflowALot &&
7184 _collector->par_simulate_overflow()) {
7185 // simulate a stack overflow
7186 simulate_overflow = true;
7187 }
7188 )
7189 if (simulate_overflow || !_work_queue->push(obj)) {
7190 _collector->par_push_on_overflow_list(obj);
7191 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7192 }
7193 } // Else, some other thread got there first
7194 }
7195 }
7196
7197 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7198 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7199
7200 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7201 Mutex* bml = _collector->bitMapLock();
7202 assert_lock_strong(bml);
7203 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7204 "CMS thread should hold CMS token");
7205
7206 bml->unlock();
7207 ConcurrentMarkSweepThread::desynchronize(true);
7208
7209 _collector->stopTimer();
7210 if (PrintCMSStatistics != 0) {
7211 _collector->incrementYields();
7212 }
7213
7214 // See the comment in coordinator_yield()
7215 for (unsigned i = 0; i < CMSYieldSleepCount &&
7216 ConcurrentMarkSweepThread::should_yield() &&
7217 !CMSCollector::foregroundGCIsActive(); ++i) {
7218 os::sleep(Thread::current(), 1, false);
7219 }
7220
7221 ConcurrentMarkSweepThread::synchronize(true);
7222 bml->lock();
7223
7224 _collector->startTimer();
7225 }
7226
7227 bool CMSPrecleanRefsYieldClosure::should_return() {
7228 if (ConcurrentMarkSweepThread::should_yield()) {
7229 do_yield_work();
7230 }
7231 return _collector->foregroundGCIsActive();
7232 }
7233
7234 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7235 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7236 "mr should be aligned to start at a card boundary");
7237 // We'd like to assert:
7238 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7239 // "mr should be a range of cards");
7240 // However, that would be too strong in one case -- the last
7241 // partition ends at _unallocated_block which, in general, can be
7242 // an arbitrary boundary, not necessarily card aligned.
7243 if (PrintCMSStatistics != 0) {
7244 _num_dirty_cards +=
7245 mr.word_size()/CardTableModRefBS::card_size_in_words;
7246 }
7247 _space->object_iterate_mem(mr, &_scan_cl);
7248 }
7249
7250 SweepClosure::SweepClosure(CMSCollector* collector,
7251 ConcurrentMarkSweepGeneration* g,
7252 CMSBitMap* bitMap, bool should_yield) :
7253 _collector(collector),
7254 _g(g),
7255 _sp(g->cmsSpace()),
7256 _limit(_sp->sweep_limit()),
7257 _freelistLock(_sp->freelistLock()),
7258 _bitMap(bitMap),
7259 _yield(should_yield),
7260 _inFreeRange(false), // No free range at beginning of sweep
7261 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7262 _lastFreeRangeCoalesced(false),
7263 _freeFinger(g->used_region().start())
7264 {
7265 NOT_PRODUCT(
7266 _numObjectsFreed = 0;
7267 _numWordsFreed = 0;
7268 _numObjectsLive = 0;
7269 _numWordsLive = 0;
7270 _numObjectsAlreadyFree = 0;
7271 _numWordsAlreadyFree = 0;
7272 _last_fc = NULL;
7273
7274 _sp->initializeIndexedFreeListArrayReturnedBytes();
7275 _sp->dictionary()->initialize_dict_returned_bytes();
7276 )
7277 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7278 "sweep _limit out of bounds");
7279 if (CMSTraceSweeper) {
7280 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7281 p2i(_limit));
7282 }
7283 }
7284
7285 void SweepClosure::print_on(outputStream* st) const {
7286 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7287 p2i(_sp->bottom()), p2i(_sp->end()));
7288 tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7289 tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7290 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7291 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7292 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7293 }
7294
7295 #ifndef PRODUCT
7296 // Assertion checking only: no useful work in product mode --
7297 // however, if any of the flags below become product flags,
7298 // you may need to review this code to see if it needs to be
7299 // enabled in product mode.
7300 SweepClosure::~SweepClosure() {
7301 assert_lock_strong(_freelistLock);
7302 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7303 "sweep _limit out of bounds");
7304 if (inFreeRange()) {
7305 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7306 print();
7307 ShouldNotReachHere();
7308 }
7309 if (Verbose && PrintGC) {
7310 gclog_or_tty->print("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7311 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7312 gclog_or_tty->print_cr("\nLive " SIZE_FORMAT " objects, "
7313 SIZE_FORMAT " bytes "
7314 "Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7315 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7316 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7317 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7318 * sizeof(HeapWord);
7319 gclog_or_tty->print_cr("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7320
7321 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7322 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7323 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7324 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7325 gclog_or_tty->print("Returned " SIZE_FORMAT " bytes", returned_bytes);
7326 gclog_or_tty->print(" Indexed List Returned " SIZE_FORMAT " bytes",
7327 indexListReturnedBytes);
7328 gclog_or_tty->print_cr(" Dictionary Returned " SIZE_FORMAT " bytes",
7329 dict_returned_bytes);
7330 }
7331 }
7332 if (CMSTraceSweeper) {
7333 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7334 p2i(_limit));
7335 }
7336 }
7337 #endif // PRODUCT
7338
7339 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7340 bool freeRangeInFreeLists) {
7341 if (CMSTraceSweeper) {
7342 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7343 p2i(freeFinger), freeRangeInFreeLists);
7344 }
7345 assert(!inFreeRange(), "Trampling existing free range");
7346 set_inFreeRange(true);
7347 set_lastFreeRangeCoalesced(false);
7348
7349 set_freeFinger(freeFinger);
7350 set_freeRangeInFreeLists(freeRangeInFreeLists);
7351 if (CMSTestInFreeList) {
7352 if (freeRangeInFreeLists) {
7353 FreeChunk* fc = (FreeChunk*) freeFinger;
7354 assert(fc->is_free(), "A chunk on the free list should be free.");
7355 assert(fc->size() > 0, "Free range should have a size");
7356 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7357 }
7358 }
7359 }
7360
7361 // Note that the sweeper runs concurrently with mutators. Thus,
7362 // it is possible for direct allocation in this generation to happen
7363 // in the middle of the sweep. Note that the sweeper also coalesces
7364 // contiguous free blocks. Thus, unless the sweeper and the allocator
7365 // synchronize appropriately freshly allocated blocks may get swept up.
7366 // This is accomplished by the sweeper locking the free lists while
7367 // it is sweeping. Thus blocks that are determined to be free are
7368 // indeed free. There is however one additional complication:
7369 // blocks that have been allocated since the final checkpoint and
7370 // mark, will not have been marked and so would be treated as
7371 // unreachable and swept up. To prevent this, the allocator marks
7372 // the bit map when allocating during the sweep phase. This leads,
7373 // however, to a further complication -- objects may have been allocated
7374 // but not yet initialized -- in the sense that the header isn't yet
7375 // installed. The sweeper can not then determine the size of the block
7376 // in order to skip over it. To deal with this case, we use a technique
7377 // (due to Printezis) to encode such uninitialized block sizes in the
7378 // bit map. Since the bit map uses a bit per every HeapWord, but the
7379 // CMS generation has a minimum object size of 3 HeapWords, it follows
7380 // that "normal marks" won't be adjacent in the bit map (there will
7381 // always be at least two 0 bits between successive 1 bits). We make use
7382 // of these "unused" bits to represent uninitialized blocks -- the bit
7383 // corresponding to the start of the uninitialized object and the next
7384 // bit are both set. Finally, a 1 bit marks the end of the object that
7385 // started with the two consecutive 1 bits to indicate its potentially
7386 // uninitialized state.
7387
7388 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7389 FreeChunk* fc = (FreeChunk*)addr;
7390 size_t res;
7391
7392 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7393 // than "addr == _limit" because although _limit was a block boundary when
7394 // we started the sweep, it may no longer be one because heap expansion
7395 // may have caused us to coalesce the block ending at the address _limit
7396 // with a newly expanded chunk (this happens when _limit was set to the
7397 // previous _end of the space), so we may have stepped past _limit:
7398 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7399 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7400 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7401 "sweep _limit out of bounds");
7402 assert(addr < _sp->end(), "addr out of bounds");
7403 // Flush any free range we might be holding as a single
7404 // coalesced chunk to the appropriate free list.
7405 if (inFreeRange()) {
7406 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7407 "freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger()));
7408 flush_cur_free_chunk(freeFinger(),
7409 pointer_delta(addr, freeFinger()));
7410 if (CMSTraceSweeper) {
7411 gclog_or_tty->print("Sweep: last chunk: ");
7412 gclog_or_tty->print("put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") "
7413 "[coalesced:%d]\n",
7414 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7415 lastFreeRangeCoalesced() ? 1 : 0);
7416 }
7417 }
7418
7419 // help the iterator loop finish
7420 return pointer_delta(_sp->end(), addr);
7421 }
7422
7423 assert(addr < _limit, "sweep invariant");
7424 // check if we should yield
7425 do_yield_check(addr);
7426 if (fc->is_free()) {
7427 // Chunk that is already free
7428 res = fc->size();
7429 do_already_free_chunk(fc);
7430 debug_only(_sp->verifyFreeLists());
7431 // If we flush the chunk at hand in lookahead_and_flush()
7432 // and it's coalesced with a preceding chunk, then the
7433 // process of "mangling" the payload of the coalesced block
7434 // will cause erasure of the size information from the
7435 // (erstwhile) header of all the coalesced blocks but the
7436 // first, so the first disjunct in the assert will not hold
7437 // in that specific case (in which case the second disjunct
7438 // will hold).
7439 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7440 "Otherwise the size info doesn't change at this step");
7441 NOT_PRODUCT(
7442 _numObjectsAlreadyFree++;
7443 _numWordsAlreadyFree += res;
7444 )
7445 NOT_PRODUCT(_last_fc = fc;)
7446 } else if (!_bitMap->isMarked(addr)) {
7447 // Chunk is fresh garbage
7448 res = do_garbage_chunk(fc);
7449 debug_only(_sp->verifyFreeLists());
7450 NOT_PRODUCT(
7451 _numObjectsFreed++;
7452 _numWordsFreed += res;
7453 )
7454 } else {
7455 // Chunk that is alive.
7456 res = do_live_chunk(fc);
7457 debug_only(_sp->verifyFreeLists());
7458 NOT_PRODUCT(
7459 _numObjectsLive++;
7460 _numWordsLive += res;
7461 )
7462 }
7463 return res;
7464 }
7465
7466 // For the smart allocation, record following
7467 // split deaths - a free chunk is removed from its free list because
7468 // it is being split into two or more chunks.
7469 // split birth - a free chunk is being added to its free list because
7470 // a larger free chunk has been split and resulted in this free chunk.
7471 // coal death - a free chunk is being removed from its free list because
7472 // it is being coalesced into a large free chunk.
7473 // coal birth - a free chunk is being added to its free list because
7474 // it was created when two or more free chunks where coalesced into
7475 // this free chunk.
7476 //
7477 // These statistics are used to determine the desired number of free
7478 // chunks of a given size. The desired number is chosen to be relative
7479 // to the end of a CMS sweep. The desired number at the end of a sweep
7480 // is the
7481 // count-at-end-of-previous-sweep (an amount that was enough)
7482 // - count-at-beginning-of-current-sweep (the excess)
7483 // + split-births (gains in this size during interval)
7484 // - split-deaths (demands on this size during interval)
7485 // where the interval is from the end of one sweep to the end of the
7486 // next.
7487 //
7488 // When sweeping the sweeper maintains an accumulated chunk which is
7489 // the chunk that is made up of chunks that have been coalesced. That
7490 // will be termed the left-hand chunk. A new chunk of garbage that
7491 // is being considered for coalescing will be referred to as the
7492 // right-hand chunk.
7493 //
7494 // When making a decision on whether to coalesce a right-hand chunk with
7495 // the current left-hand chunk, the current count vs. the desired count
7496 // of the left-hand chunk is considered. Also if the right-hand chunk
7497 // is near the large chunk at the end of the heap (see
7498 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7499 // left-hand chunk is coalesced.
7500 //
7501 // When making a decision about whether to split a chunk, the desired count
7502 // vs. the current count of the candidate to be split is also considered.
7503 // If the candidate is underpopulated (currently fewer chunks than desired)
7504 // a chunk of an overpopulated (currently more chunks than desired) size may
7505 // be chosen. The "hint" associated with a free list, if non-null, points
7506 // to a free list which may be overpopulated.
7507 //
7508
7509 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7510 const size_t size = fc->size();
7511 // Chunks that cannot be coalesced are not in the
7512 // free lists.
7513 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7514 assert(_sp->verify_chunk_in_free_list(fc),
7515 "free chunk should be in free lists");
7516 }
7517 // a chunk that is already free, should not have been
7518 // marked in the bit map
7519 HeapWord* const addr = (HeapWord*) fc;
7520 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7521 // Verify that the bit map has no bits marked between
7522 // addr and purported end of this block.
7523 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7524
7525 // Some chunks cannot be coalesced under any circumstances.
7526 // See the definition of cantCoalesce().
7527 if (!fc->cantCoalesce()) {
7528 // This chunk can potentially be coalesced.
7529 if (_sp->adaptive_freelists()) {
7530 // All the work is done in
7531 do_post_free_or_garbage_chunk(fc, size);
7532 } else { // Not adaptive free lists
7533 // this is a free chunk that can potentially be coalesced by the sweeper;
7534 if (!inFreeRange()) {
7535 // if the next chunk is a free block that can't be coalesced
7536 // it doesn't make sense to remove this chunk from the free lists
7537 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7538 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
7539 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
7540 nextChunk->is_free() && // ... which is free...
7541 nextChunk->cantCoalesce()) { // ... but can't be coalesced
7542 // nothing to do
7543 } else {
7544 // Potentially the start of a new free range:
7545 // Don't eagerly remove it from the free lists.
7546 // No need to remove it if it will just be put
7547 // back again. (Also from a pragmatic point of view
7548 // if it is a free block in a region that is beyond
7549 // any allocated blocks, an assertion will fail)
7550 // Remember the start of a free run.
7551 initialize_free_range(addr, true);
7552 // end - can coalesce with next chunk
7553 }
7554 } else {
7555 // the midst of a free range, we are coalescing
7556 print_free_block_coalesced(fc);
7557 if (CMSTraceSweeper) {
7558 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7559 }
7560 // remove it from the free lists
7561 _sp->removeFreeChunkFromFreeLists(fc);
7562 set_lastFreeRangeCoalesced(true);
7563 // If the chunk is being coalesced and the current free range is
7564 // in the free lists, remove the current free range so that it
7565 // will be returned to the free lists in its entirety - all
7566 // the coalesced pieces included.
7567 if (freeRangeInFreeLists()) {
7568 FreeChunk* ffc = (FreeChunk*) freeFinger();
7569 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7570 "Size of free range is inconsistent with chunk size.");
7571 if (CMSTestInFreeList) {
7572 assert(_sp->verify_chunk_in_free_list(ffc),
7573 "free range is not in free lists");
7574 }
7575 _sp->removeFreeChunkFromFreeLists(ffc);
7576 set_freeRangeInFreeLists(false);
7577 }
7578 }
7579 }
7580 // Note that if the chunk is not coalescable (the else arm
7581 // below), we unconditionally flush, without needing to do
7582 // a "lookahead," as we do below.
7583 if (inFreeRange()) lookahead_and_flush(fc, size);
7584 } else {
7585 // Code path common to both original and adaptive free lists.
7586
7587 // cant coalesce with previous block; this should be treated
7588 // as the end of a free run if any
7589 if (inFreeRange()) {
7590 // we kicked some butt; time to pick up the garbage
7591 assert(freeFinger() < addr, "freeFinger points too high");
7592 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7593 }
7594 // else, nothing to do, just continue
7595 }
7596 }
7597
7598 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7599 // This is a chunk of garbage. It is not in any free list.
7600 // Add it to a free list or let it possibly be coalesced into
7601 // a larger chunk.
7602 HeapWord* const addr = (HeapWord*) fc;
7603 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7604
7605 if (_sp->adaptive_freelists()) {
7606 // Verify that the bit map has no bits marked between
7607 // addr and purported end of just dead object.
7608 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7609
7610 do_post_free_or_garbage_chunk(fc, size);
7611 } else {
7612 if (!inFreeRange()) {
7613 // start of a new free range
7614 assert(size > 0, "A free range should have a size");
7615 initialize_free_range(addr, false);
7616 } else {
7617 // this will be swept up when we hit the end of the
7618 // free range
7619 if (CMSTraceSweeper) {
7620 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7621 }
7622 // If the chunk is being coalesced and the current free range is
7623 // in the free lists, remove the current free range so that it
7624 // will be returned to the free lists in its entirety - all
7625 // the coalesced pieces included.
7626 if (freeRangeInFreeLists()) {
7627 FreeChunk* ffc = (FreeChunk*)freeFinger();
7628 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7629 "Size of free range is inconsistent with chunk size.");
7630 if (CMSTestInFreeList) {
7631 assert(_sp->verify_chunk_in_free_list(ffc),
7632 "free range is not in free lists");
7633 }
7634 _sp->removeFreeChunkFromFreeLists(ffc);
7635 set_freeRangeInFreeLists(false);
7636 }
7637 set_lastFreeRangeCoalesced(true);
7638 }
7639 // this will be swept up when we hit the end of the free range
7640
7641 // Verify that the bit map has no bits marked between
7642 // addr and purported end of just dead object.
7643 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7644 }
7645 assert(_limit >= addr + size,
7646 "A freshly garbage chunk can't possibly straddle over _limit");
7647 if (inFreeRange()) lookahead_and_flush(fc, size);
7648 return size;
7649 }
7650
7651 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7652 HeapWord* addr = (HeapWord*) fc;
7653 // The sweeper has just found a live object. Return any accumulated
7654 // left hand chunk to the free lists.
7655 if (inFreeRange()) {
7656 assert(freeFinger() < addr, "freeFinger points too high");
7657 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7658 }
7659
7660 // This object is live: we'd normally expect this to be
7661 // an oop, and like to assert the following:
7662 // assert(oop(addr)->is_oop(), "live block should be an oop");
7663 // However, as we commented above, this may be an object whose
7664 // header hasn't yet been initialized.
7665 size_t size;
7666 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7667 if (_bitMap->isMarked(addr + 1)) {
7668 // Determine the size from the bit map, rather than trying to
7669 // compute it from the object header.
7670 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7671 size = pointer_delta(nextOneAddr + 1, addr);
7672 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7673 "alignment problem");
7674
7675 #ifdef ASSERT
7676 if (oop(addr)->klass_or_null() != NULL) {
7677 // Ignore mark word because we are running concurrent with mutators
7678 assert(oop(addr)->is_oop(true), "live block should be an oop");
7679 assert(size ==
7680 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7681 "P-mark and computed size do not agree");
7682 }
7683 #endif
7684
7685 } else {
7686 // This should be an initialized object that's alive.
7687 assert(oop(addr)->klass_or_null() != NULL,
7688 "Should be an initialized object");
7689 // Ignore mark word because we are running concurrent with mutators
7690 assert(oop(addr)->is_oop(true), "live block should be an oop");
7691 // Verify that the bit map has no bits marked between
7692 // addr and purported end of this block.
7693 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7694 assert(size >= 3, "Necessary for Printezis marks to work");
7695 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7696 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7697 }
7698 return size;
7699 }
7700
7701 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7702 size_t chunkSize) {
7703 // do_post_free_or_garbage_chunk() should only be called in the case
7704 // of the adaptive free list allocator.
7705 const bool fcInFreeLists = fc->is_free();
7706 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
7707 assert((HeapWord*)fc <= _limit, "sweep invariant");
7708 if (CMSTestInFreeList && fcInFreeLists) {
7709 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7710 }
7711
7712 if (CMSTraceSweeper) {
7713 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7714 }
7715
7716 HeapWord* const fc_addr = (HeapWord*) fc;
7717
7718 bool coalesce;
7719 const size_t left = pointer_delta(fc_addr, freeFinger());
7720 const size_t right = chunkSize;
7721 switch (FLSCoalescePolicy) {
7722 // numeric value forms a coalition aggressiveness metric
7723 case 0: { // never coalesce
7724 coalesce = false;
7725 break;
7726 }
7727 case 1: { // coalesce if left & right chunks on overpopulated lists
7728 coalesce = _sp->coalOverPopulated(left) &&
7729 _sp->coalOverPopulated(right);
7730 break;
7731 }
7732 case 2: { // coalesce if left chunk on overpopulated list (default)
7733 coalesce = _sp->coalOverPopulated(left);
7734 break;
7735 }
7736 case 3: { // coalesce if left OR right chunk on overpopulated list
7737 coalesce = _sp->coalOverPopulated(left) ||
7738 _sp->coalOverPopulated(right);
7739 break;
7740 }
7741 case 4: { // always coalesce
7742 coalesce = true;
7743 break;
7744 }
7745 default:
7746 ShouldNotReachHere();
7747 }
7748
7749 // Should the current free range be coalesced?
7750 // If the chunk is in a free range and either we decided to coalesce above
7751 // or the chunk is near the large block at the end of the heap
7752 // (isNearLargestChunk() returns true), then coalesce this chunk.
7753 const bool doCoalesce = inFreeRange()
7754 && (coalesce || _g->isNearLargestChunk(fc_addr));
7755 if (doCoalesce) {
7756 // Coalesce the current free range on the left with the new
7757 // chunk on the right. If either is on a free list,
7758 // it must be removed from the list and stashed in the closure.
7759 if (freeRangeInFreeLists()) {
7760 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7761 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7762 "Size of free range is inconsistent with chunk size.");
7763 if (CMSTestInFreeList) {
7764 assert(_sp->verify_chunk_in_free_list(ffc),
7765 "Chunk is not in free lists");
7766 }
7767 _sp->coalDeath(ffc->size());
7768 _sp->removeFreeChunkFromFreeLists(ffc);
7769 set_freeRangeInFreeLists(false);
7770 }
7771 if (fcInFreeLists) {
7772 _sp->coalDeath(chunkSize);
7773 assert(fc->size() == chunkSize,
7774 "The chunk has the wrong size or is not in the free lists");
7775 _sp->removeFreeChunkFromFreeLists(fc);
7776 }
7777 set_lastFreeRangeCoalesced(true);
7778 print_free_block_coalesced(fc);
7779 } else { // not in a free range and/or should not coalesce
7780 // Return the current free range and start a new one.
7781 if (inFreeRange()) {
7782 // In a free range but cannot coalesce with the right hand chunk.
7783 // Put the current free range into the free lists.
7784 flush_cur_free_chunk(freeFinger(),
7785 pointer_delta(fc_addr, freeFinger()));
7786 }
7787 // Set up for new free range. Pass along whether the right hand
7788 // chunk is in the free lists.
7789 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7790 }
7791 }
7792
7793 // Lookahead flush:
7794 // If we are tracking a free range, and this is the last chunk that
7795 // we'll look at because its end crosses past _limit, we'll preemptively
7796 // flush it along with any free range we may be holding on to. Note that
7797 // this can be the case only for an already free or freshly garbage
7798 // chunk. If this block is an object, it can never straddle
7799 // over _limit. The "straddling" occurs when _limit is set at
7800 // the previous end of the space when this cycle started, and
7801 // a subsequent heap expansion caused the previously co-terminal
7802 // free block to be coalesced with the newly expanded portion,
7803 // thus rendering _limit a non-block-boundary making it dangerous
7804 // for the sweeper to step over and examine.
7805 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7806 assert(inFreeRange(), "Should only be called if currently in a free range.");
7807 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7808 assert(_sp->used_region().contains(eob - 1),
7809 "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7810 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7811 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7812 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7813 if (eob >= _limit) {
7814 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7815 if (CMSTraceSweeper) {
7816 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7817 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7818 "[" PTR_FORMAT "," PTR_FORMAT ")",
7819 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7820 }
7821 // Return the storage we are tracking back into the free lists.
7822 if (CMSTraceSweeper) {
7823 gclog_or_tty->print_cr("Flushing ... ");
7824 }
7825 assert(freeFinger() < eob, "Error");
7826 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7827 }
7828 }
7829
7830 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7831 assert(inFreeRange(), "Should only be called if currently in a free range.");
7832 assert(size > 0,
7833 "A zero sized chunk cannot be added to the free lists.");
7834 if (!freeRangeInFreeLists()) {
7835 if (CMSTestInFreeList) {
7836 FreeChunk* fc = (FreeChunk*) chunk;
7837 fc->set_size(size);
7838 assert(!_sp->verify_chunk_in_free_list(fc),
7839 "chunk should not be in free lists yet");
7840 }
7841 if (CMSTraceSweeper) {
7842 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7843 p2i(chunk), size);
7844 }
7845 // A new free range is going to be starting. The current
7846 // free range has not been added to the free lists yet or
7847 // was removed so add it back.
7848 // If the current free range was coalesced, then the death
7849 // of the free range was recorded. Record a birth now.
7850 if (lastFreeRangeCoalesced()) {
7851 _sp->coalBirth(size);
7852 }
7853 _sp->addChunkAndRepairOffsetTable(chunk, size,
7854 lastFreeRangeCoalesced());
7855 } else if (CMSTraceSweeper) {
7856 gclog_or_tty->print_cr("Already in free list: nothing to flush");
7857 }
7858 set_inFreeRange(false);
7859 set_freeRangeInFreeLists(false);
7860 }
7861
7862 // We take a break if we've been at this for a while,
7863 // so as to avoid monopolizing the locks involved.
7864 void SweepClosure::do_yield_work(HeapWord* addr) {
7865 // Return current free chunk being used for coalescing (if any)
7866 // to the appropriate freelist. After yielding, the next
7867 // free block encountered will start a coalescing range of
7868 // free blocks. If the next free block is adjacent to the
7869 // chunk just flushed, they will need to wait for the next
7870 // sweep to be coalesced.
7871 if (inFreeRange()) {
7872 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7873 }
7874
7875 // First give up the locks, then yield, then re-lock.
7876 // We should probably use a constructor/destructor idiom to
7877 // do this unlock/lock or modify the MutexUnlocker class to
7878 // serve our purpose. XXX
7879 assert_lock_strong(_bitMap->lock());
7880 assert_lock_strong(_freelistLock);
7881 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7882 "CMS thread should hold CMS token");
7883 _bitMap->lock()->unlock();
7884 _freelistLock->unlock();
7885 ConcurrentMarkSweepThread::desynchronize(true);
7886 _collector->stopTimer();
7887 if (PrintCMSStatistics != 0) {
7888 _collector->incrementYields();
7889 }
7890
7891 // See the comment in coordinator_yield()
7892 for (unsigned i = 0; i < CMSYieldSleepCount &&
7893 ConcurrentMarkSweepThread::should_yield() &&
7894 !CMSCollector::foregroundGCIsActive(); ++i) {
7895 os::sleep(Thread::current(), 1, false);
7896 }
7897
7898 ConcurrentMarkSweepThread::synchronize(true);
7899 _freelistLock->lock();
7900 _bitMap->lock()->lock_without_safepoint_check();
7901 _collector->startTimer();
7902 }
7903
7904 #ifndef PRODUCT
7905 // This is actually very useful in a product build if it can
7906 // be called from the debugger. Compile it into the product
7907 // as needed.
7908 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7909 return debug_cms_space->verify_chunk_in_free_list(fc);
7910 }
7911 #endif
7912
7913 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7914 if (CMSTraceSweeper) {
7915 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7916 p2i(fc), fc->size());
7917 }
7918 }
7919
7920 // CMSIsAliveClosure
7921 bool CMSIsAliveClosure::do_object_b(oop obj) {
7922 HeapWord* addr = (HeapWord*)obj;
7923 return addr != NULL &&
7924 (!_span.contains(addr) || _bit_map->isMarked(addr));
7925 }
7926
7927
7928 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7929 MemRegion span,
7930 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7931 bool cpc):
7932 _collector(collector),
7933 _span(span),
7934 _bit_map(bit_map),
7935 _mark_stack(mark_stack),
7936 _concurrent_precleaning(cpc) {
7937 assert(!_span.is_empty(), "Empty span could spell trouble");
7938 }
7939
7940
7941 // CMSKeepAliveClosure: the serial version
7942 void CMSKeepAliveClosure::do_oop(oop obj) {
7943 HeapWord* addr = (HeapWord*)obj;
7944 if (_span.contains(addr) &&
7945 !_bit_map->isMarked(addr)) {
7946 _bit_map->mark(addr);
7947 bool simulate_overflow = false;
7948 NOT_PRODUCT(
7949 if (CMSMarkStackOverflowALot &&
7950 _collector->simulate_overflow()) {
7951 // simulate a stack overflow
7952 simulate_overflow = true;
7953 }
7954 )
7955 if (simulate_overflow || !_mark_stack->push(obj)) {
7956 if (_concurrent_precleaning) {
7957 // We dirty the overflown object and let the remark
7958 // phase deal with it.
7959 assert(_collector->overflow_list_is_empty(), "Error");
7960 // In the case of object arrays, we need to dirty all of
7961 // the cards that the object spans. No locking or atomics
7962 // are needed since no one else can be mutating the mod union
7963 // table.
7964 if (obj->is_objArray()) {
7965 size_t sz = obj->size();
7966 HeapWord* end_card_addr =
7967 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
7968 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7969 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7970 _collector->_modUnionTable.mark_range(redirty_range);
7971 } else {
7972 _collector->_modUnionTable.mark(addr);
7973 }
7974 _collector->_ser_kac_preclean_ovflw++;
7975 } else {
7976 _collector->push_on_overflow_list(obj);
7977 _collector->_ser_kac_ovflw++;
7978 }
7979 }
7980 }
7981 }
7982
7983 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7984 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7985
7986 // CMSParKeepAliveClosure: a parallel version of the above.
7987 // The work queues are private to each closure (thread),
7988 // but (may be) available for stealing by other threads.
7989 void CMSParKeepAliveClosure::do_oop(oop obj) {
7990 HeapWord* addr = (HeapWord*)obj;
7991 if (_span.contains(addr) &&
7992 !_bit_map->isMarked(addr)) {
7993 // In general, during recursive tracing, several threads
7994 // may be concurrently getting here; the first one to
7995 // "tag" it, claims it.
7996 if (_bit_map->par_mark(addr)) {
7997 bool res = _work_queue->push(obj);
7998 assert(res, "Low water mark should be much less than capacity");
7999 // Do a recursive trim in the hope that this will keep
8000 // stack usage lower, but leave some oops for potential stealers
8001 trim_queue(_low_water_mark);
8002 } // Else, another thread got there first
8003 }
8004 }
8005
8006 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8007 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8008
8009 void CMSParKeepAliveClosure::trim_queue(uint max) {
8010 while (_work_queue->size() > max) {
8011 oop new_oop;
8012 if (_work_queue->pop_local(new_oop)) {
8013 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8014 assert(_bit_map->isMarked((HeapWord*)new_oop),
8015 "no white objects on this stack!");
8016 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8017 // iterate over the oops in this oop, marking and pushing
8018 // the ones in CMS heap (i.e. in _span).
8019 new_oop->oop_iterate(&_mark_and_push);
8020 }
8021 }
8022 }
8023
8024 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8025 CMSCollector* collector,
8026 MemRegion span, CMSBitMap* bit_map,
8027 OopTaskQueue* work_queue):
8028 _collector(collector),
8029 _span(span),
8030 _bit_map(bit_map),
8031 _work_queue(work_queue) { }
8032
8033 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8034 HeapWord* addr = (HeapWord*)obj;
8035 if (_span.contains(addr) &&
8036 !_bit_map->isMarked(addr)) {
8037 if (_bit_map->par_mark(addr)) {
8038 bool simulate_overflow = false;
8039 NOT_PRODUCT(
8040 if (CMSMarkStackOverflowALot &&
8041 _collector->par_simulate_overflow()) {
8042 // simulate a stack overflow
8043 simulate_overflow = true;
8044 }
8045 )
8046 if (simulate_overflow || !_work_queue->push(obj)) {
8047 _collector->par_push_on_overflow_list(obj);
8048 _collector->_par_kac_ovflw++;
8049 }
8050 } // Else another thread got there already
8051 }
8052 }
8053
8054 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8055 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8056
8057 //////////////////////////////////////////////////////////////////
8058 // CMSExpansionCause /////////////////////////////
8059 //////////////////////////////////////////////////////////////////
8060 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8061 switch (cause) {
8062 case _no_expansion:
8063 return "No expansion";
8064 case _satisfy_free_ratio:
8065 return "Free ratio";
8066 case _satisfy_promotion:
8067 return "Satisfy promotion";
8068 case _satisfy_allocation:
8069 return "allocation";
8070 case _allocate_par_lab:
8071 return "Par LAB";
8072 case _allocate_par_spooling_space:
8073 return "Par Spooling Space";
8074 case _adaptive_size_policy:
8075 return "Ergonomics";
8076 default:
8077 return "unknown";
8078 }
8079 }
8080
8081 void CMSDrainMarkingStackClosure::do_void() {
8082 // the max number to take from overflow list at a time
8083 const size_t num = _mark_stack->capacity()/4;
8084 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8085 "Overflow list should be NULL during concurrent phases");
8086 while (!_mark_stack->isEmpty() ||
8087 // if stack is empty, check the overflow list
8088 _collector->take_from_overflow_list(num, _mark_stack)) {
8089 oop obj = _mark_stack->pop();
8090 HeapWord* addr = (HeapWord*)obj;
8091 assert(_span.contains(addr), "Should be within span");
8092 assert(_bit_map->isMarked(addr), "Should be marked");
8093 assert(obj->is_oop(), "Should be an oop");
8094 obj->oop_iterate(_keep_alive);
8095 }
8096 }
8097
8098 void CMSParDrainMarkingStackClosure::do_void() {
8099 // drain queue
8100 trim_queue(0);
8101 }
8102
8103 // Trim our work_queue so its length is below max at return
8104 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8105 while (_work_queue->size() > max) {
8106 oop new_oop;
8107 if (_work_queue->pop_local(new_oop)) {
8108 assert(new_oop->is_oop(), "Expected an oop");
8109 assert(_bit_map->isMarked((HeapWord*)new_oop),
8110 "no white objects on this stack!");
8111 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8112 // iterate over the oops in this oop, marking and pushing
8113 // the ones in CMS heap (i.e. in _span).
8114 new_oop->oop_iterate(&_mark_and_push);
8115 }
8116 }
8117 }
8118
8119 ////////////////////////////////////////////////////////////////////
8120 // Support for Marking Stack Overflow list handling and related code
8121 ////////////////////////////////////////////////////////////////////
8122 // Much of the following code is similar in shape and spirit to the
8123 // code used in ParNewGC. We should try and share that code
8124 // as much as possible in the future.
8125
8126 #ifndef PRODUCT
8127 // Debugging support for CMSStackOverflowALot
8128
8129 // It's OK to call this multi-threaded; the worst thing
8130 // that can happen is that we'll get a bunch of closely
8131 // spaced simulated overflows, but that's OK, in fact
8132 // probably good as it would exercise the overflow code
8133 // under contention.
8134 bool CMSCollector::simulate_overflow() {
8135 if (_overflow_counter-- <= 0) { // just being defensive
8136 _overflow_counter = CMSMarkStackOverflowInterval;
8137 return true;
8138 } else {
8139 return false;
8140 }
8141 }
8142
8143 bool CMSCollector::par_simulate_overflow() {
8144 return simulate_overflow();
8145 }
8146 #endif
8147
8148 // Single-threaded
8149 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8150 assert(stack->isEmpty(), "Expected precondition");
8151 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8152 size_t i = num;
8153 oop cur = _overflow_list;
8154 const markOop proto = markOopDesc::prototype();
8155 NOT_PRODUCT(ssize_t n = 0;)
8156 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8157 next = oop(cur->mark());
8158 cur->set_mark(proto); // until proven otherwise
8159 assert(cur->is_oop(), "Should be an oop");
8160 bool res = stack->push(cur);
8161 assert(res, "Bit off more than can chew?");
8162 NOT_PRODUCT(n++;)
8163 }
8164 _overflow_list = cur;
8165 #ifndef PRODUCT
8166 assert(_num_par_pushes >= n, "Too many pops?");
8167 _num_par_pushes -=n;
8168 #endif
8169 return !stack->isEmpty();
8170 }
8171
8172 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8173 // (MT-safe) Get a prefix of at most "num" from the list.
8174 // The overflow list is chained through the mark word of
8175 // each object in the list. We fetch the entire list,
8176 // break off a prefix of the right size and return the
8177 // remainder. If other threads try to take objects from
8178 // the overflow list at that time, they will wait for
8179 // some time to see if data becomes available. If (and
8180 // only if) another thread places one or more object(s)
8181 // on the global list before we have returned the suffix
8182 // to the global list, we will walk down our local list
8183 // to find its end and append the global list to
8184 // our suffix before returning it. This suffix walk can
8185 // prove to be expensive (quadratic in the amount of traffic)
8186 // when there are many objects in the overflow list and
8187 // there is much producer-consumer contention on the list.
8188 // *NOTE*: The overflow list manipulation code here and
8189 // in ParNewGeneration:: are very similar in shape,
8190 // except that in the ParNew case we use the old (from/eden)
8191 // copy of the object to thread the list via its klass word.
8192 // Because of the common code, if you make any changes in
8193 // the code below, please check the ParNew version to see if
8194 // similar changes might be needed.
8195 // CR 6797058 has been filed to consolidate the common code.
8196 bool CMSCollector::par_take_from_overflow_list(size_t num,
8197 OopTaskQueue* work_q,
8198 int no_of_gc_threads) {
8199 assert(work_q->size() == 0, "First empty local work queue");
8200 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8201 if (_overflow_list == NULL) {
8202 return false;
8203 }
8204 // Grab the entire list; we'll put back a suffix
8205 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8206 Thread* tid = Thread::current();
8207 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8208 // set to ParallelGCThreads.
8209 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8210 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8211 // If the list is busy, we spin for a short while,
8212 // sleeping between attempts to get the list.
8213 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8214 os::sleep(tid, sleep_time_millis, false);
8215 if (_overflow_list == NULL) {
8216 // Nothing left to take
8217 return false;
8218 } else if (_overflow_list != BUSY) {
8219 // Try and grab the prefix
8220 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8221 }
8222 }
8223 // If the list was found to be empty, or we spun long
8224 // enough, we give up and return empty-handed. If we leave
8225 // the list in the BUSY state below, it must be the case that
8226 // some other thread holds the overflow list and will set it
8227 // to a non-BUSY state in the future.
8228 if (prefix == NULL || prefix == BUSY) {
8229 // Nothing to take or waited long enough
8230 if (prefix == NULL) {
8231 // Write back the NULL in case we overwrote it with BUSY above
8232 // and it is still the same value.
8233 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8234 }
8235 return false;
8236 }
8237 assert(prefix != NULL && prefix != BUSY, "Error");
8238 size_t i = num;
8239 oop cur = prefix;
8240 // Walk down the first "num" objects, unless we reach the end.
8241 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8242 if (cur->mark() == NULL) {
8243 // We have "num" or fewer elements in the list, so there
8244 // is nothing to return to the global list.
8245 // Write back the NULL in lieu of the BUSY we wrote
8246 // above, if it is still the same value.
8247 if (_overflow_list == BUSY) {
8248 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8249 }
8250 } else {
8251 // Chop off the suffix and return it to the global list.
8252 assert(cur->mark() != BUSY, "Error");
8253 oop suffix_head = cur->mark(); // suffix will be put back on global list
8254 cur->set_mark(NULL); // break off suffix
8255 // It's possible that the list is still in the empty(busy) state
8256 // we left it in a short while ago; in that case we may be
8257 // able to place back the suffix without incurring the cost
8258 // of a walk down the list.
8259 oop observed_overflow_list = _overflow_list;
8260 oop cur_overflow_list = observed_overflow_list;
8261 bool attached = false;
8262 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8263 observed_overflow_list =
8264 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8265 if (cur_overflow_list == observed_overflow_list) {
8266 attached = true;
8267 break;
8268 } else cur_overflow_list = observed_overflow_list;
8269 }
8270 if (!attached) {
8271 // Too bad, someone else sneaked in (at least) an element; we'll need
8272 // to do a splice. Find tail of suffix so we can prepend suffix to global
8273 // list.
8274 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8275 oop suffix_tail = cur;
8276 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8277 "Tautology");
8278 observed_overflow_list = _overflow_list;
8279 do {
8280 cur_overflow_list = observed_overflow_list;
8281 if (cur_overflow_list != BUSY) {
8282 // Do the splice ...
8283 suffix_tail->set_mark(markOop(cur_overflow_list));
8284 } else { // cur_overflow_list == BUSY
8285 suffix_tail->set_mark(NULL);
8286 }
8287 // ... and try to place spliced list back on overflow_list ...
8288 observed_overflow_list =
8289 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8290 } while (cur_overflow_list != observed_overflow_list);
8291 // ... until we have succeeded in doing so.
8292 }
8293 }
8294
8295 // Push the prefix elements on work_q
8296 assert(prefix != NULL, "control point invariant");
8297 const markOop proto = markOopDesc::prototype();
8298 oop next;
8299 NOT_PRODUCT(ssize_t n = 0;)
8300 for (cur = prefix; cur != NULL; cur = next) {
8301 next = oop(cur->mark());
8302 cur->set_mark(proto); // until proven otherwise
8303 assert(cur->is_oop(), "Should be an oop");
8304 bool res = work_q->push(cur);
8305 assert(res, "Bit off more than we can chew?");
8306 NOT_PRODUCT(n++;)
8307 }
8308 #ifndef PRODUCT
8309 assert(_num_par_pushes >= n, "Too many pops?");
8310 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8311 #endif
8312 return true;
8313 }
8314
8315 // Single-threaded
8316 void CMSCollector::push_on_overflow_list(oop p) {
8317 NOT_PRODUCT(_num_par_pushes++;)
8318 assert(p->is_oop(), "Not an oop");
8319 preserve_mark_if_necessary(p);
8320 p->set_mark((markOop)_overflow_list);
8321 _overflow_list = p;
8322 }
8323
8324 // Multi-threaded; use CAS to prepend to overflow list
8325 void CMSCollector::par_push_on_overflow_list(oop p) {
8326 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8327 assert(p->is_oop(), "Not an oop");
8328 par_preserve_mark_if_necessary(p);
8329 oop observed_overflow_list = _overflow_list;
8330 oop cur_overflow_list;
8331 do {
8332 cur_overflow_list = observed_overflow_list;
8333 if (cur_overflow_list != BUSY) {
8334 p->set_mark(markOop(cur_overflow_list));
8335 } else {
8336 p->set_mark(NULL);
8337 }
8338 observed_overflow_list =
8339 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8340 } while (cur_overflow_list != observed_overflow_list);
8341 }
8342 #undef BUSY
8343
8344 // Single threaded
8345 // General Note on GrowableArray: pushes may silently fail
8346 // because we are (temporarily) out of C-heap for expanding
8347 // the stack. The problem is quite ubiquitous and affects
8348 // a lot of code in the JVM. The prudent thing for GrowableArray
8349 // to do (for now) is to exit with an error. However, that may
8350 // be too draconian in some cases because the caller may be
8351 // able to recover without much harm. For such cases, we
8352 // should probably introduce a "soft_push" method which returns
8353 // an indication of success or failure with the assumption that
8354 // the caller may be able to recover from a failure; code in
8355 // the VM can then be changed, incrementally, to deal with such
8356 // failures where possible, thus, incrementally hardening the VM
8357 // in such low resource situations.
8358 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8359 _preserved_oop_stack.push(p);
8360 _preserved_mark_stack.push(m);
8361 assert(m == p->mark(), "Mark word changed");
8362 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8363 "bijection");
8364 }
8365
8366 // Single threaded
8367 void CMSCollector::preserve_mark_if_necessary(oop p) {
8368 markOop m = p->mark();
8369 if (m->must_be_preserved(p)) {
8370 preserve_mark_work(p, m);
8371 }
8372 }
8373
8374 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8375 markOop m = p->mark();
8376 if (m->must_be_preserved(p)) {
8377 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8378 // Even though we read the mark word without holding
8379 // the lock, we are assured that it will not change
8380 // because we "own" this oop, so no other thread can
8381 // be trying to push it on the overflow list; see
8382 // the assertion in preserve_mark_work() that checks
8383 // that m == p->mark().
8384 preserve_mark_work(p, m);
8385 }
8386 }
8387
8388 // We should be able to do this multi-threaded,
8389 // a chunk of stack being a task (this is
8390 // correct because each oop only ever appears
8391 // once in the overflow list. However, it's
8392 // not very easy to completely overlap this with
8393 // other operations, so will generally not be done
8394 // until all work's been completed. Because we
8395 // expect the preserved oop stack (set) to be small,
8396 // it's probably fine to do this single-threaded.
8397 // We can explore cleverer concurrent/overlapped/parallel
8398 // processing of preserved marks if we feel the
8399 // need for this in the future. Stack overflow should
8400 // be so rare in practice and, when it happens, its
8401 // effect on performance so great that this will
8402 // likely just be in the noise anyway.
8403 void CMSCollector::restore_preserved_marks_if_any() {
8404 assert(SafepointSynchronize::is_at_safepoint(),
8405 "world should be stopped");
8406 assert(Thread::current()->is_ConcurrentGC_thread() ||
8407 Thread::current()->is_VM_thread(),
8408 "should be single-threaded");
8409 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8410 "bijection");
8411
8412 while (!_preserved_oop_stack.is_empty()) {
8413 oop p = _preserved_oop_stack.pop();
8414 assert(p->is_oop(), "Should be an oop");
8415 assert(_span.contains(p), "oop should be in _span");
8416 assert(p->mark() == markOopDesc::prototype(),
8417 "Set when taken from overflow list");
8418 markOop m = _preserved_mark_stack.pop();
8419 p->set_mark(m);
8420 }
8421 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8422 "stacks were cleared above");
8423 }
8424
8425 #ifndef PRODUCT
8426 bool CMSCollector::no_preserved_marks() const {
8427 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8428 }
8429 #endif
8430
8431 // Transfer some number of overflown objects to usual marking
8432 // stack. Return true if some objects were transferred.
8433 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8434 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8435 (size_t)ParGCDesiredObjsFromOverflowList);
8436
8437 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8438 assert(_collector->overflow_list_is_empty() || res,
8439 "If list is not empty, we should have taken something");
8440 assert(!res || !_mark_stack->isEmpty(),
8441 "If we took something, it should now be on our stack");
8442 return res;
8443 }
8444
8445 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8446 size_t res = _sp->block_size_no_stall(addr, _collector);
8447 if (_sp->block_is_obj(addr)) {
8448 if (_live_bit_map->isMarked(addr)) {
8449 // It can't have been dead in a previous cycle
8450 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8451 } else {
8452 _dead_bit_map->mark(addr); // mark the dead object
8453 }
8454 }
8455 // Could be 0, if the block size could not be computed without stalling.
8456 return res;
8457 }
8458
8459 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8460
8461 switch (phase) {
8462 case CMSCollector::InitialMarking:
8463 initialize(true /* fullGC */ ,
8464 cause /* cause of the GC */,
8465 true /* recordGCBeginTime */,
8466 true /* recordPreGCUsage */,
8467 false /* recordPeakUsage */,
8468 false /* recordPostGCusage */,
8469 true /* recordAccumulatedGCTime */,
8470 false /* recordGCEndTime */,
8471 false /* countCollection */ );
8472 break;
8473
8474 case CMSCollector::FinalMarking:
8475 initialize(true /* fullGC */ ,
8476 cause /* cause of the GC */,
8477 false /* recordGCBeginTime */,
8478 false /* recordPreGCUsage */,
8479 false /* recordPeakUsage */,
8480 false /* recordPostGCusage */,
8481 true /* recordAccumulatedGCTime */,
8482 false /* recordGCEndTime */,
8483 false /* countCollection */ );
8484 break;
8485
8486 case CMSCollector::Sweeping:
8487 initialize(true /* fullGC */ ,
8488 cause /* cause of the GC */,
8489 false /* recordGCBeginTime */,
8490 false /* recordPreGCUsage */,
8491 true /* recordPeakUsage */,
8492 true /* recordPostGCusage */,
8493 false /* recordAccumulatedGCTime */,
8494 true /* recordGCEndTime */,
8495 true /* countCollection */ );
8496 break;
8497
8498 default:
8499 ShouldNotReachHere();
8500 }
8501 }