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->gen_process_roots(&srs,
2418 GenCollectedHeap::OldGen,
2419 true, // young gen as roots
2420 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2421 should_unload_classes(),
2422 ¬Older,
2423 NULL,
2424 NULL);
2425 }
2426
2427 // Now mark from the roots
2428 MarkFromRootsClosure markFromRootsClosure(this, _span,
2429 verification_mark_bm(), verification_mark_stack(),
2430 false /* don't yield */, true /* verifying */);
2431 assert(_restart_addr == NULL, "Expected pre-condition");
2432 verification_mark_bm()->iterate(&markFromRootsClosure);
2433 while (_restart_addr != NULL) {
2434 // Deal with stack overflow: by restarting at the indicated
2435 // address.
2436 HeapWord* ra = _restart_addr;
2437 markFromRootsClosure.reset(ra);
2438 _restart_addr = NULL;
2439 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2440 }
2441 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2442 verify_work_stacks_empty();
2443
2444 // Marking completed -- now verify that each bit marked in
2445 // verification_mark_bm() is also marked in markBitMap(); flag all
2446 // errors by printing corresponding objects.
2447 VerifyMarkedClosure vcl(markBitMap());
2448 verification_mark_bm()->iterate(&vcl);
2449 if (vcl.failed()) {
2450 gclog_or_tty->print("Verification failed");
2451 gch->print_on(gclog_or_tty);
2452 fatal("CMS: failed marking verification after remark");
2453 }
2454 }
2455
2456 class VerifyKlassOopsKlassClosure : public KlassClosure {
2457 class VerifyKlassOopsClosure : public OopClosure {
2458 CMSBitMap* _bitmap;
2459 public:
2460 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2461 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2462 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2463 } _oop_closure;
2464 public:
2465 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2466 void do_klass(Klass* k) {
2467 k->oops_do(&_oop_closure);
2468 }
2469 };
2470
2471 void CMSCollector::verify_after_remark_work_2() {
2472 ResourceMark rm;
2473 HandleMark hm;
2474 GenCollectedHeap* gch = GenCollectedHeap::heap();
2475
2476 // Get a clear set of claim bits for the roots processing to work with.
2477 ClassLoaderDataGraph::clear_claimed_marks();
2478
2479 // Mark from roots one level into CMS
2480 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2481 markBitMap());
2482 CLDToOopClosure cld_closure(¬Older, true);
2483
2484 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2485
2486 {
2487 StrongRootsScope srs(1);
2488
2489 gch->gen_process_roots(&srs,
2490 GenCollectedHeap::OldGen,
2491 true, // young gen as roots
2492 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2493 should_unload_classes(),
2494 ¬Older,
2495 NULL,
2496 &cld_closure);
2497 }
2498
2499 // Now mark from the roots
2500 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2501 verification_mark_bm(), markBitMap(), verification_mark_stack());
2502 assert(_restart_addr == NULL, "Expected pre-condition");
2503 verification_mark_bm()->iterate(&markFromRootsClosure);
2504 while (_restart_addr != NULL) {
2505 // Deal with stack overflow: by restarting at the indicated
2506 // address.
2507 HeapWord* ra = _restart_addr;
2508 markFromRootsClosure.reset(ra);
2509 _restart_addr = NULL;
2510 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2511 }
2512 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2513 verify_work_stacks_empty();
2514
2515 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2516 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2517
2518 // Marking completed -- now verify that each bit marked in
2519 // verification_mark_bm() is also marked in markBitMap(); flag all
2520 // errors by printing corresponding objects.
2521 VerifyMarkedClosure vcl(markBitMap());
2522 verification_mark_bm()->iterate(&vcl);
2523 assert(!vcl.failed(), "Else verification above should not have succeeded");
2524 }
2525
2526 void ConcurrentMarkSweepGeneration::save_marks() {
2527 // delegate to CMS space
2528 cmsSpace()->save_marks();
2529 for (uint i = 0; i < ParallelGCThreads; i++) {
2530 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2531 }
2532 }
2533
2534 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2535 return cmsSpace()->no_allocs_since_save_marks();
2536 }
2537
2538 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2539 \
2540 void ConcurrentMarkSweepGeneration:: \
2541 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2542 cl->set_generation(this); \
2543 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2544 cl->reset_generation(); \
2545 save_marks(); \
2546 }
2547
2548 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2549
2550 void
2551 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2552 if (freelistLock()->owned_by_self()) {
2553 Generation::oop_iterate(cl);
2554 } else {
2555 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2556 Generation::oop_iterate(cl);
2557 }
2558 }
2559
2560 void
2561 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2562 if (freelistLock()->owned_by_self()) {
2563 Generation::object_iterate(cl);
2564 } else {
2565 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2566 Generation::object_iterate(cl);
2567 }
2568 }
2569
2570 void
2571 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2572 if (freelistLock()->owned_by_self()) {
2573 Generation::safe_object_iterate(cl);
2574 } else {
2575 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2576 Generation::safe_object_iterate(cl);
2577 }
2578 }
2579
2580 void
2581 ConcurrentMarkSweepGeneration::post_compact() {
2582 }
2583
2584 void
2585 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2586 // Fix the linear allocation blocks to look like free blocks.
2587
2588 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2589 // are not called when the heap is verified during universe initialization and
2590 // at vm shutdown.
2591 if (freelistLock()->owned_by_self()) {
2592 cmsSpace()->prepare_for_verify();
2593 } else {
2594 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2595 cmsSpace()->prepare_for_verify();
2596 }
2597 }
2598
2599 void
2600 ConcurrentMarkSweepGeneration::verify() {
2601 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2602 // are not called when the heap is verified during universe initialization and
2603 // at vm shutdown.
2604 if (freelistLock()->owned_by_self()) {
2605 cmsSpace()->verify();
2606 } else {
2607 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2608 cmsSpace()->verify();
2609 }
2610 }
2611
2612 void CMSCollector::verify() {
2613 _cmsGen->verify();
2614 }
2615
2616 #ifndef PRODUCT
2617 bool CMSCollector::overflow_list_is_empty() const {
2618 assert(_num_par_pushes >= 0, "Inconsistency");
2619 if (_overflow_list == NULL) {
2620 assert(_num_par_pushes == 0, "Inconsistency");
2621 }
2622 return _overflow_list == NULL;
2623 }
2624
2625 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2626 // merely consolidate assertion checks that appear to occur together frequently.
2627 void CMSCollector::verify_work_stacks_empty() const {
2628 assert(_markStack.isEmpty(), "Marking stack should be empty");
2629 assert(overflow_list_is_empty(), "Overflow list should be empty");
2630 }
2631
2632 void CMSCollector::verify_overflow_empty() const {
2633 assert(overflow_list_is_empty(), "Overflow list should be empty");
2634 assert(no_preserved_marks(), "No preserved marks");
2635 }
2636 #endif // PRODUCT
2637
2638 // Decide if we want to enable class unloading as part of the
2639 // ensuing concurrent GC cycle. We will collect and
2640 // unload classes if it's the case that:
2641 // (1) an explicit gc request has been made and the flag
2642 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2643 // (2) (a) class unloading is enabled at the command line, and
2644 // (b) old gen is getting really full
2645 // NOTE: Provided there is no change in the state of the heap between
2646 // calls to this method, it should have idempotent results. Moreover,
2647 // its results should be monotonically increasing (i.e. going from 0 to 1,
2648 // but not 1 to 0) between successive calls between which the heap was
2649 // not collected. For the implementation below, it must thus rely on
2650 // the property that concurrent_cycles_since_last_unload()
2651 // will not decrease unless a collection cycle happened and that
2652 // _cmsGen->is_too_full() are
2653 // themselves also monotonic in that sense. See check_monotonicity()
2654 // below.
2655 void CMSCollector::update_should_unload_classes() {
2656 _should_unload_classes = false;
2657 // Condition 1 above
2658 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2659 _should_unload_classes = true;
2660 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2661 // Disjuncts 2.b.(i,ii,iii) above
2662 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2663 CMSClassUnloadingMaxInterval)
2664 || _cmsGen->is_too_full();
2665 }
2666 }
2667
2668 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2669 bool res = should_concurrent_collect();
2670 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2671 return res;
2672 }
2673
2674 void CMSCollector::setup_cms_unloading_and_verification_state() {
2675 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2676 || VerifyBeforeExit;
2677 const int rso = GenCollectedHeap::SO_AllCodeCache;
2678
2679 // We set the proper root for this CMS cycle here.
2680 if (should_unload_classes()) { // Should unload classes this cycle
2681 remove_root_scanning_option(rso); // Shrink the root set appropriately
2682 set_verifying(should_verify); // Set verification state for this cycle
2683 return; // Nothing else needs to be done at this time
2684 }
2685
2686 // Not unloading classes this cycle
2687 assert(!should_unload_classes(), "Inconsistency!");
2688
2689 // If we are not unloading classes then add SO_AllCodeCache to root
2690 // scanning options.
2691 add_root_scanning_option(rso);
2692
2693 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2694 set_verifying(true);
2695 } else if (verifying() && !should_verify) {
2696 // We were verifying, but some verification flags got disabled.
2697 set_verifying(false);
2698 // Exclude symbols, strings and code cache elements from root scanning to
2699 // reduce IM and RM pauses.
2700 remove_root_scanning_option(rso);
2701 }
2702 }
2703
2704
2705 #ifndef PRODUCT
2706 HeapWord* CMSCollector::block_start(const void* p) const {
2707 const HeapWord* addr = (HeapWord*)p;
2708 if (_span.contains(p)) {
2709 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2710 return _cmsGen->cmsSpace()->block_start(p);
2711 }
2712 }
2713 return NULL;
2714 }
2715 #endif
2716
2717 HeapWord*
2718 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2719 bool tlab,
2720 bool parallel) {
2721 CMSSynchronousYieldRequest yr;
2722 assert(!tlab, "Can't deal with TLAB allocation");
2723 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2724 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2725 if (GCExpandToAllocateDelayMillis > 0) {
2726 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2727 }
2728 return have_lock_and_allocate(word_size, tlab);
2729 }
2730
2731 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2732 size_t bytes,
2733 size_t expand_bytes,
2734 CMSExpansionCause::Cause cause)
2735 {
2736
2737 bool success = expand(bytes, expand_bytes);
2738
2739 // remember why we expanded; this information is used
2740 // by shouldConcurrentCollect() when making decisions on whether to start
2741 // a new CMS cycle.
2742 if (success) {
2743 set_expansion_cause(cause);
2744 if (PrintGCDetails && Verbose) {
2745 gclog_or_tty->print_cr("Expanded CMS gen for %s",
2746 CMSExpansionCause::to_string(cause));
2747 }
2748 }
2749 }
2750
2751 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2752 HeapWord* res = NULL;
2753 MutexLocker x(ParGCRareEvent_lock);
2754 while (true) {
2755 // Expansion by some other thread might make alloc OK now:
2756 res = ps->lab.alloc(word_sz);
2757 if (res != NULL) return res;
2758 // If there's not enough expansion space available, give up.
2759 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2760 return NULL;
2761 }
2762 // Otherwise, we try expansion.
2763 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2764 // Now go around the loop and try alloc again;
2765 // A competing par_promote might beat us to the expansion space,
2766 // so we may go around the loop again if promotion fails again.
2767 if (GCExpandToAllocateDelayMillis > 0) {
2768 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2769 }
2770 }
2771 }
2772
2773
2774 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2775 PromotionInfo* promo) {
2776 MutexLocker x(ParGCRareEvent_lock);
2777 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2778 while (true) {
2779 // Expansion by some other thread might make alloc OK now:
2780 if (promo->ensure_spooling_space()) {
2781 assert(promo->has_spooling_space(),
2782 "Post-condition of successful ensure_spooling_space()");
2783 return true;
2784 }
2785 // If there's not enough expansion space available, give up.
2786 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2787 return false;
2788 }
2789 // Otherwise, we try expansion.
2790 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2791 // Now go around the loop and try alloc again;
2792 // A competing allocation might beat us to the expansion space,
2793 // so we may go around the loop again if allocation fails again.
2794 if (GCExpandToAllocateDelayMillis > 0) {
2795 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2796 }
2797 }
2798 }
2799
2800 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2801 // Only shrink if a compaction was done so that all the free space
2802 // in the generation is in a contiguous block at the end.
2803 if (did_compact()) {
2804 CardGeneration::shrink(bytes);
2805 }
2806 }
2807
2808 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2809 assert_locked_or_safepoint(Heap_lock);
2810 }
2811
2812 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2813 assert_locked_or_safepoint(Heap_lock);
2814 assert_lock_strong(freelistLock());
2815 if (PrintGCDetails && Verbose) {
2816 warning("Shrinking of CMS not yet implemented");
2817 }
2818 return;
2819 }
2820
2821
2822 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2823 // phases.
2824 class CMSPhaseAccounting: public StackObj {
2825 public:
2826 CMSPhaseAccounting(CMSCollector *collector,
2827 const char *phase,
2828 bool print_cr = true);
2829 ~CMSPhaseAccounting();
2830
2831 private:
2832 CMSCollector *_collector;
2833 const char *_phase;
2834 elapsedTimer _wallclock;
2835 bool _print_cr;
2836
2837 public:
2838 // Not MT-safe; so do not pass around these StackObj's
2839 // where they may be accessed by other threads.
2840 jlong wallclock_millis() {
2841 assert(_wallclock.is_active(), "Wall clock should not stop");
2842 _wallclock.stop(); // to record time
2843 jlong ret = _wallclock.milliseconds();
2844 _wallclock.start(); // restart
2845 return ret;
2846 }
2847 };
2848
2849 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2850 const char *phase,
2851 bool print_cr) :
2852 _collector(collector), _phase(phase), _print_cr(print_cr) {
2853
2854 if (PrintCMSStatistics != 0) {
2855 _collector->resetYields();
2856 }
2857 if (PrintGCDetails) {
2858 gclog_or_tty->gclog_stamp();
2859 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
2860 _collector->cmsGen()->short_name(), _phase);
2861 }
2862 _collector->resetTimer();
2863 _wallclock.start();
2864 _collector->startTimer();
2865 }
2866
2867 CMSPhaseAccounting::~CMSPhaseAccounting() {
2868 assert(_wallclock.is_active(), "Wall clock should not have stopped");
2869 _collector->stopTimer();
2870 _wallclock.stop();
2871 if (PrintGCDetails) {
2872 gclog_or_tty->gclog_stamp();
2873 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
2874 _collector->cmsGen()->short_name(),
2875 _phase, _collector->timerValue(), _wallclock.seconds());
2876 if (_print_cr) {
2877 gclog_or_tty->cr();
2878 }
2879 if (PrintCMSStatistics != 0) {
2880 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
2881 _collector->yields());
2882 }
2883 }
2884 }
2885
2886 // CMS work
2887
2888 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2889 class CMSParMarkTask : public AbstractGangTask {
2890 protected:
2891 CMSCollector* _collector;
2892 uint _n_workers;
2893 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2894 AbstractGangTask(name),
2895 _collector(collector),
2896 _n_workers(n_workers) {}
2897 // Work method in support of parallel rescan ... of young gen spaces
2898 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2899 ContiguousSpace* space,
2900 HeapWord** chunk_array, size_t chunk_top);
2901 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2902 };
2903
2904 // Parallel initial mark task
2905 class CMSParInitialMarkTask: public CMSParMarkTask {
2906 StrongRootsScope* _strong_roots_scope;
2907 public:
2908 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2909 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2910 _strong_roots_scope(strong_roots_scope) {}
2911 void work(uint worker_id);
2912 };
2913
2914 // Checkpoint the roots into this generation from outside
2915 // this generation. [Note this initial checkpoint need only
2916 // be approximate -- we'll do a catch up phase subsequently.]
2917 void CMSCollector::checkpointRootsInitial() {
2918 assert(_collectorState == InitialMarking, "Wrong collector state");
2919 check_correct_thread_executing();
2920 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2921
2922 save_heap_summary();
2923 report_heap_summary(GCWhen::BeforeGC);
2924
2925 ReferenceProcessor* rp = ref_processor();
2926 assert(_restart_addr == NULL, "Control point invariant");
2927 {
2928 // acquire locks for subsequent manipulations
2929 MutexLockerEx x(bitMapLock(),
2930 Mutex::_no_safepoint_check_flag);
2931 checkpointRootsInitialWork();
2932 // enable ("weak") refs discovery
2933 rp->enable_discovery();
2934 _collectorState = Marking;
2935 }
2936 }
2937
2938 void CMSCollector::checkpointRootsInitialWork() {
2939 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2940 assert(_collectorState == InitialMarking, "just checking");
2941
2942 // Already have locks.
2943 assert_lock_strong(bitMapLock());
2944 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2945
2946 // Setup the verification and class unloading state for this
2947 // CMS collection cycle.
2948 setup_cms_unloading_and_verification_state();
2949
2950 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
2951 PrintGCDetails && Verbose, true, _gc_timer_cm);)
2952
2953 // Reset all the PLAB chunk arrays if necessary.
2954 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2955 reset_survivor_plab_arrays();
2956 }
2957
2958 ResourceMark rm;
2959 HandleMark hm;
2960
2961 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2962 GenCollectedHeap* gch = GenCollectedHeap::heap();
2963
2964 verify_work_stacks_empty();
2965 verify_overflow_empty();
2966
2967 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2968 // Update the saved marks which may affect the root scans.
2969 gch->save_marks();
2970
2971 // weak reference processing has not started yet.
2972 ref_processor()->set_enqueuing_is_done(false);
2973
2974 // Need to remember all newly created CLDs,
2975 // so that we can guarantee that the remark finds them.
2976 ClassLoaderDataGraph::remember_new_clds(true);
2977
2978 // Whenever a CLD is found, it will be claimed before proceeding to mark
2979 // the klasses. The claimed marks need to be cleared before marking starts.
2980 ClassLoaderDataGraph::clear_claimed_marks();
2981
2982 if (CMSPrintEdenSurvivorChunks) {
2983 print_eden_and_survivor_chunk_arrays();
2984 }
2985
2986 {
2987 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2988 if (CMSParallelInitialMarkEnabled) {
2989 // The parallel version.
2990 WorkGang* workers = gch->workers();
2991 assert(workers != NULL, "Need parallel worker threads.");
2992 uint n_workers = workers->active_workers();
2993
2994 StrongRootsScope srs(n_workers);
2995
2996 CMSParInitialMarkTask tsk(this, &srs, n_workers);
2997 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2998 if (n_workers > 1) {
2999 workers->run_task(&tsk);
3000 } else {
3001 tsk.work(0);
3002 }
3003 } else {
3004 // The serial version.
3005 CLDToOopClosure cld_closure(¬Older, true);
3006 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3007
3008 StrongRootsScope srs(1);
3009
3010 gch->gen_process_roots(&srs,
3011 GenCollectedHeap::OldGen,
3012 true, // young gen as roots
3013 GenCollectedHeap::ScanningOption(roots_scanning_options()),
3014 should_unload_classes(),
3015 ¬Older,
3016 NULL,
3017 &cld_closure);
3018 }
3019 }
3020
3021 // Clear mod-union table; it will be dirtied in the prologue of
3022 // CMS generation per each young generation collection.
3023
3024 assert(_modUnionTable.isAllClear(),
3025 "Was cleared in most recent final checkpoint phase"
3026 " or no bits are set in the gc_prologue before the start of the next "
3027 "subsequent marking phase.");
3028
3029 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3030
3031 // Save the end of the used_region of the constituent generations
3032 // to be used to limit the extent of sweep in each generation.
3033 save_sweep_limits();
3034 verify_overflow_empty();
3035 }
3036
3037 bool CMSCollector::markFromRoots() {
3038 // we might be tempted to assert that:
3039 // assert(!SafepointSynchronize::is_at_safepoint(),
3040 // "inconsistent argument?");
3041 // However that wouldn't be right, because it's possible that
3042 // a safepoint is indeed in progress as a young generation
3043 // stop-the-world GC happens even as we mark in this generation.
3044 assert(_collectorState == Marking, "inconsistent state?");
3045 check_correct_thread_executing();
3046 verify_overflow_empty();
3047
3048 // Weak ref discovery note: We may be discovering weak
3049 // refs in this generation concurrent (but interleaved) with
3050 // weak ref discovery by the young generation collector.
3051
3052 CMSTokenSyncWithLocks ts(true, bitMapLock());
3053 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3054 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3055 bool res = markFromRootsWork();
3056 if (res) {
3057 _collectorState = Precleaning;
3058 } else { // We failed and a foreground collection wants to take over
3059 assert(_foregroundGCIsActive, "internal state inconsistency");
3060 assert(_restart_addr == NULL, "foreground will restart from scratch");
3061 if (PrintGCDetails) {
3062 gclog_or_tty->print_cr("bailing out to foreground collection");
3063 }
3064 }
3065 verify_overflow_empty();
3066 return res;
3067 }
3068
3069 bool CMSCollector::markFromRootsWork() {
3070 // iterate over marked bits in bit map, doing a full scan and mark
3071 // from these roots using the following algorithm:
3072 // . if oop is to the right of the current scan pointer,
3073 // mark corresponding bit (we'll process it later)
3074 // . else (oop is to left of current scan pointer)
3075 // push oop on marking stack
3076 // . drain the marking stack
3077
3078 // Note that when we do a marking step we need to hold the
3079 // bit map lock -- recall that direct allocation (by mutators)
3080 // and promotion (by the young generation collector) is also
3081 // marking the bit map. [the so-called allocate live policy.]
3082 // Because the implementation of bit map marking is not
3083 // robust wrt simultaneous marking of bits in the same word,
3084 // we need to make sure that there is no such interference
3085 // between concurrent such updates.
3086
3087 // already have locks
3088 assert_lock_strong(bitMapLock());
3089
3090 verify_work_stacks_empty();
3091 verify_overflow_empty();
3092 bool result = false;
3093 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3094 result = do_marking_mt();
3095 } else {
3096 result = do_marking_st();
3097 }
3098 return result;
3099 }
3100
3101 // Forward decl
3102 class CMSConcMarkingTask;
3103
3104 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3105 CMSCollector* _collector;
3106 CMSConcMarkingTask* _task;
3107 public:
3108 virtual void yield();
3109
3110 // "n_threads" is the number of threads to be terminated.
3111 // "queue_set" is a set of work queues of other threads.
3112 // "collector" is the CMS collector associated with this task terminator.
3113 // "yield" indicates whether we need the gang as a whole to yield.
3114 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3115 ParallelTaskTerminator(n_threads, queue_set),
3116 _collector(collector) { }
3117
3118 void set_task(CMSConcMarkingTask* task) {
3119 _task = task;
3120 }
3121 };
3122
3123 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3124 CMSConcMarkingTask* _task;
3125 public:
3126 bool should_exit_termination();
3127 void set_task(CMSConcMarkingTask* task) {
3128 _task = task;
3129 }
3130 };
3131
3132 // MT Concurrent Marking Task
3133 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3134 CMSCollector* _collector;
3135 uint _n_workers; // requested/desired # workers
3136 bool _result;
3137 CompactibleFreeListSpace* _cms_space;
3138 char _pad_front[64]; // padding to ...
3139 HeapWord* _global_finger; // ... avoid sharing cache line
3140 char _pad_back[64];
3141 HeapWord* _restart_addr;
3142
3143 // Exposed here for yielding support
3144 Mutex* const _bit_map_lock;
3145
3146 // The per thread work queues, available here for stealing
3147 OopTaskQueueSet* _task_queues;
3148
3149 // Termination (and yielding) support
3150 CMSConcMarkingTerminator _term;
3151 CMSConcMarkingTerminatorTerminator _term_term;
3152
3153 public:
3154 CMSConcMarkingTask(CMSCollector* collector,
3155 CompactibleFreeListSpace* cms_space,
3156 YieldingFlexibleWorkGang* workers,
3157 OopTaskQueueSet* task_queues):
3158 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3159 _collector(collector),
3160 _cms_space(cms_space),
3161 _n_workers(0), _result(true),
3162 _task_queues(task_queues),
3163 _term(_n_workers, task_queues, _collector),
3164 _bit_map_lock(collector->bitMapLock())
3165 {
3166 _requested_size = _n_workers;
3167 _term.set_task(this);
3168 _term_term.set_task(this);
3169 _restart_addr = _global_finger = _cms_space->bottom();
3170 }
3171
3172
3173 OopTaskQueueSet* task_queues() { return _task_queues; }
3174
3175 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3176
3177 HeapWord** global_finger_addr() { return &_global_finger; }
3178
3179 CMSConcMarkingTerminator* terminator() { return &_term; }
3180
3181 virtual void set_for_termination(uint active_workers) {
3182 terminator()->reset_for_reuse(active_workers);
3183 }
3184
3185 void work(uint worker_id);
3186 bool should_yield() {
3187 return ConcurrentMarkSweepThread::should_yield()
3188 && !_collector->foregroundGCIsActive();
3189 }
3190
3191 virtual void coordinator_yield(); // stuff done by coordinator
3192 bool result() { return _result; }
3193
3194 void reset(HeapWord* ra) {
3195 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3196 _restart_addr = _global_finger = ra;
3197 _term.reset_for_reuse();
3198 }
3199
3200 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3201 OopTaskQueue* work_q);
3202
3203 private:
3204 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3205 void do_work_steal(int i);
3206 void bump_global_finger(HeapWord* f);
3207 };
3208
3209 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3210 assert(_task != NULL, "Error");
3211 return _task->yielding();
3212 // Note that we do not need the disjunct || _task->should_yield() above
3213 // because we want terminating threads to yield only if the task
3214 // is already in the midst of yielding, which happens only after at least one
3215 // thread has yielded.
3216 }
3217
3218 void CMSConcMarkingTerminator::yield() {
3219 if (_task->should_yield()) {
3220 _task->yield();
3221 } else {
3222 ParallelTaskTerminator::yield();
3223 }
3224 }
3225
3226 ////////////////////////////////////////////////////////////////
3227 // Concurrent Marking Algorithm Sketch
3228 ////////////////////////////////////////////////////////////////
3229 // Until all tasks exhausted (both spaces):
3230 // -- claim next available chunk
3231 // -- bump global finger via CAS
3232 // -- find first object that starts in this chunk
3233 // and start scanning bitmap from that position
3234 // -- scan marked objects for oops
3235 // -- CAS-mark target, and if successful:
3236 // . if target oop is above global finger (volatile read)
3237 // nothing to do
3238 // . if target oop is in chunk and above local finger
3239 // then nothing to do
3240 // . else push on work-queue
3241 // -- Deal with possible overflow issues:
3242 // . local work-queue overflow causes stuff to be pushed on
3243 // global (common) overflow queue
3244 // . always first empty local work queue
3245 // . then get a batch of oops from global work queue if any
3246 // . then do work stealing
3247 // -- When all tasks claimed (both spaces)
3248 // and local work queue empty,
3249 // then in a loop do:
3250 // . check global overflow stack; steal a batch of oops and trace
3251 // . try to steal from other threads oif GOS is empty
3252 // . if neither is available, offer termination
3253 // -- Terminate and return result
3254 //
3255 void CMSConcMarkingTask::work(uint worker_id) {
3256 elapsedTimer _timer;
3257 ResourceMark rm;
3258 HandleMark hm;
3259
3260 DEBUG_ONLY(_collector->verify_overflow_empty();)
3261
3262 // Before we begin work, our work queue should be empty
3263 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3264 // Scan the bitmap covering _cms_space, tracing through grey objects.
3265 _timer.start();
3266 do_scan_and_mark(worker_id, _cms_space);
3267 _timer.stop();
3268 if (PrintCMSStatistics != 0) {
3269 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3270 worker_id, _timer.seconds());
3271 // XXX: need xxx/xxx type of notation, two timers
3272 }
3273
3274 // ... do work stealing
3275 _timer.reset();
3276 _timer.start();
3277 do_work_steal(worker_id);
3278 _timer.stop();
3279 if (PrintCMSStatistics != 0) {
3280 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3281 worker_id, _timer.seconds());
3282 // XXX: need xxx/xxx type of notation, two timers
3283 }
3284 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3285 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3286 // Note that under the current task protocol, the
3287 // following assertion is true even of the spaces
3288 // expanded since the completion of the concurrent
3289 // marking. XXX This will likely change under a strict
3290 // ABORT semantics.
3291 // After perm removal the comparison was changed to
3292 // greater than or equal to from strictly greater than.
3293 // Before perm removal the highest address sweep would
3294 // have been at the end of perm gen but now is at the
3295 // end of the tenured gen.
3296 assert(_global_finger >= _cms_space->end(),
3297 "All tasks have been completed");
3298 DEBUG_ONLY(_collector->verify_overflow_empty();)
3299 }
3300
3301 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3302 HeapWord* read = _global_finger;
3303 HeapWord* cur = read;
3304 while (f > read) {
3305 cur = read;
3306 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3307 if (cur == read) {
3308 // our cas succeeded
3309 assert(_global_finger >= f, "protocol consistency");
3310 break;
3311 }
3312 }
3313 }
3314
3315 // This is really inefficient, and should be redone by
3316 // using (not yet available) block-read and -write interfaces to the
3317 // stack and the work_queue. XXX FIX ME !!!
3318 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3319 OopTaskQueue* work_q) {
3320 // Fast lock-free check
3321 if (ovflw_stk->length() == 0) {
3322 return false;
3323 }
3324 assert(work_q->size() == 0, "Shouldn't steal");
3325 MutexLockerEx ml(ovflw_stk->par_lock(),
3326 Mutex::_no_safepoint_check_flag);
3327 // Grab up to 1/4 the size of the work queue
3328 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3329 (size_t)ParGCDesiredObjsFromOverflowList);
3330 num = MIN2(num, ovflw_stk->length());
3331 for (int i = (int) num; i > 0; i--) {
3332 oop cur = ovflw_stk->pop();
3333 assert(cur != NULL, "Counted wrong?");
3334 work_q->push(cur);
3335 }
3336 return num > 0;
3337 }
3338
3339 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3340 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3341 int n_tasks = pst->n_tasks();
3342 // We allow that there may be no tasks to do here because
3343 // we are restarting after a stack overflow.
3344 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3345 uint nth_task = 0;
3346
3347 HeapWord* aligned_start = sp->bottom();
3348 if (sp->used_region().contains(_restart_addr)) {
3349 // Align down to a card boundary for the start of 0th task
3350 // for this space.
3351 aligned_start =
3352 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3353 CardTableModRefBS::card_size);
3354 }
3355
3356 size_t chunk_size = sp->marking_task_size();
3357 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3358 // Having claimed the nth task in this space,
3359 // compute the chunk that it corresponds to:
3360 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3361 aligned_start + (nth_task+1)*chunk_size);
3362 // Try and bump the global finger via a CAS;
3363 // note that we need to do the global finger bump
3364 // _before_ taking the intersection below, because
3365 // the task corresponding to that region will be
3366 // deemed done even if the used_region() expands
3367 // because of allocation -- as it almost certainly will
3368 // during start-up while the threads yield in the
3369 // closure below.
3370 HeapWord* finger = span.end();
3371 bump_global_finger(finger); // atomically
3372 // There are null tasks here corresponding to chunks
3373 // beyond the "top" address of the space.
3374 span = span.intersection(sp->used_region());
3375 if (!span.is_empty()) { // Non-null task
3376 HeapWord* prev_obj;
3377 assert(!span.contains(_restart_addr) || nth_task == 0,
3378 "Inconsistency");
3379 if (nth_task == 0) {
3380 // For the 0th task, we'll not need to compute a block_start.
3381 if (span.contains(_restart_addr)) {
3382 // In the case of a restart because of stack overflow,
3383 // we might additionally skip a chunk prefix.
3384 prev_obj = _restart_addr;
3385 } else {
3386 prev_obj = span.start();
3387 }
3388 } else {
3389 // We want to skip the first object because
3390 // the protocol is to scan any object in its entirety
3391 // that _starts_ in this span; a fortiori, any
3392 // object starting in an earlier span is scanned
3393 // as part of an earlier claimed task.
3394 // Below we use the "careful" version of block_start
3395 // so we do not try to navigate uninitialized objects.
3396 prev_obj = sp->block_start_careful(span.start());
3397 // Below we use a variant of block_size that uses the
3398 // Printezis bits to avoid waiting for allocated
3399 // objects to become initialized/parsable.
3400 while (prev_obj < span.start()) {
3401 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3402 if (sz > 0) {
3403 prev_obj += sz;
3404 } else {
3405 // In this case we may end up doing a bit of redundant
3406 // scanning, but that appears unavoidable, short of
3407 // locking the free list locks; see bug 6324141.
3408 break;
3409 }
3410 }
3411 }
3412 if (prev_obj < span.end()) {
3413 MemRegion my_span = MemRegion(prev_obj, span.end());
3414 // Do the marking work within a non-empty span --
3415 // the last argument to the constructor indicates whether the
3416 // iteration should be incremental with periodic yields.
3417 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3418 &_collector->_markBitMap,
3419 work_queue(i),
3420 &_collector->_markStack);
3421 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3422 } // else nothing to do for this task
3423 } // else nothing to do for this task
3424 }
3425 // We'd be tempted to assert here that since there are no
3426 // more tasks left to claim in this space, the global_finger
3427 // must exceed space->top() and a fortiori space->end(). However,
3428 // that would not quite be correct because the bumping of
3429 // global_finger occurs strictly after the claiming of a task,
3430 // so by the time we reach here the global finger may not yet
3431 // have been bumped up by the thread that claimed the last
3432 // task.
3433 pst->all_tasks_completed();
3434 }
3435
3436 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3437 private:
3438 CMSCollector* _collector;
3439 CMSConcMarkingTask* _task;
3440 MemRegion _span;
3441 CMSBitMap* _bit_map;
3442 CMSMarkStack* _overflow_stack;
3443 OopTaskQueue* _work_queue;
3444 protected:
3445 DO_OOP_WORK_DEFN
3446 public:
3447 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3448 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3449 MetadataAwareOopClosure(collector->ref_processor()),
3450 _collector(collector),
3451 _task(task),
3452 _span(collector->_span),
3453 _work_queue(work_queue),
3454 _bit_map(bit_map),
3455 _overflow_stack(overflow_stack)
3456 { }
3457 virtual void do_oop(oop* p);
3458 virtual void do_oop(narrowOop* p);
3459
3460 void trim_queue(size_t max);
3461 void handle_stack_overflow(HeapWord* lost);
3462 void do_yield_check() {
3463 if (_task->should_yield()) {
3464 _task->yield();
3465 }
3466 }
3467 };
3468
3469 // Grey object scanning during work stealing phase --
3470 // the salient assumption here is that any references
3471 // that are in these stolen objects being scanned must
3472 // already have been initialized (else they would not have
3473 // been published), so we do not need to check for
3474 // uninitialized objects before pushing here.
3475 void Par_ConcMarkingClosure::do_oop(oop obj) {
3476 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3477 HeapWord* addr = (HeapWord*)obj;
3478 // Check if oop points into the CMS generation
3479 // and is not marked
3480 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3481 // a white object ...
3482 // If we manage to "claim" the object, by being the
3483 // first thread to mark it, then we push it on our
3484 // marking stack
3485 if (_bit_map->par_mark(addr)) { // ... now grey
3486 // push on work queue (grey set)
3487 bool simulate_overflow = false;
3488 NOT_PRODUCT(
3489 if (CMSMarkStackOverflowALot &&
3490 _collector->simulate_overflow()) {
3491 // simulate a stack overflow
3492 simulate_overflow = true;
3493 }
3494 )
3495 if (simulate_overflow ||
3496 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3497 // stack overflow
3498 if (PrintCMSStatistics != 0) {
3499 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3500 SIZE_FORMAT, _overflow_stack->capacity());
3501 }
3502 // We cannot assert that the overflow stack is full because
3503 // it may have been emptied since.
3504 assert(simulate_overflow ||
3505 _work_queue->size() == _work_queue->max_elems(),
3506 "Else push should have succeeded");
3507 handle_stack_overflow(addr);
3508 }
3509 } // Else, some other thread got there first
3510 do_yield_check();
3511 }
3512 }
3513
3514 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3515 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3516
3517 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3518 while (_work_queue->size() > max) {
3519 oop new_oop;
3520 if (_work_queue->pop_local(new_oop)) {
3521 assert(new_oop->is_oop(), "Should be an oop");
3522 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3523 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3524 new_oop->oop_iterate(this); // do_oop() above
3525 do_yield_check();
3526 }
3527 }
3528 }
3529
3530 // Upon stack overflow, we discard (part of) the stack,
3531 // remembering the least address amongst those discarded
3532 // in CMSCollector's _restart_address.
3533 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3534 // We need to do this under a mutex to prevent other
3535 // workers from interfering with the work done below.
3536 MutexLockerEx ml(_overflow_stack->par_lock(),
3537 Mutex::_no_safepoint_check_flag);
3538 // Remember the least grey address discarded
3539 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3540 _collector->lower_restart_addr(ra);
3541 _overflow_stack->reset(); // discard stack contents
3542 _overflow_stack->expand(); // expand the stack if possible
3543 }
3544
3545
3546 void CMSConcMarkingTask::do_work_steal(int i) {
3547 OopTaskQueue* work_q = work_queue(i);
3548 oop obj_to_scan;
3549 CMSBitMap* bm = &(_collector->_markBitMap);
3550 CMSMarkStack* ovflw = &(_collector->_markStack);
3551 int* seed = _collector->hash_seed(i);
3552 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3553 while (true) {
3554 cl.trim_queue(0);
3555 assert(work_q->size() == 0, "Should have been emptied above");
3556 if (get_work_from_overflow_stack(ovflw, work_q)) {
3557 // Can't assert below because the work obtained from the
3558 // overflow stack may already have been stolen from us.
3559 // assert(work_q->size() > 0, "Work from overflow stack");
3560 continue;
3561 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3562 assert(obj_to_scan->is_oop(), "Should be an oop");
3563 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3564 obj_to_scan->oop_iterate(&cl);
3565 } else if (terminator()->offer_termination(&_term_term)) {
3566 assert(work_q->size() == 0, "Impossible!");
3567 break;
3568 } else if (yielding() || should_yield()) {
3569 yield();
3570 }
3571 }
3572 }
3573
3574 // This is run by the CMS (coordinator) thread.
3575 void CMSConcMarkingTask::coordinator_yield() {
3576 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3577 "CMS thread should hold CMS token");
3578 // First give up the locks, then yield, then re-lock
3579 // We should probably use a constructor/destructor idiom to
3580 // do this unlock/lock or modify the MutexUnlocker class to
3581 // serve our purpose. XXX
3582 assert_lock_strong(_bit_map_lock);
3583 _bit_map_lock->unlock();
3584 ConcurrentMarkSweepThread::desynchronize(true);
3585 _collector->stopTimer();
3586 if (PrintCMSStatistics != 0) {
3587 _collector->incrementYields();
3588 }
3589
3590 // It is possible for whichever thread initiated the yield request
3591 // not to get a chance to wake up and take the bitmap lock between
3592 // this thread releasing it and reacquiring it. So, while the
3593 // should_yield() flag is on, let's sleep for a bit to give the
3594 // other thread a chance to wake up. The limit imposed on the number
3595 // of iterations is defensive, to avoid any unforseen circumstances
3596 // putting us into an infinite loop. Since it's always been this
3597 // (coordinator_yield()) method that was observed to cause the
3598 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3599 // which is by default non-zero. For the other seven methods that
3600 // also perform the yield operation, as are using a different
3601 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3602 // can enable the sleeping for those methods too, if necessary.
3603 // See 6442774.
3604 //
3605 // We really need to reconsider the synchronization between the GC
3606 // thread and the yield-requesting threads in the future and we
3607 // should really use wait/notify, which is the recommended
3608 // way of doing this type of interaction. Additionally, we should
3609 // consolidate the eight methods that do the yield operation and they
3610 // are almost identical into one for better maintainability and
3611 // readability. See 6445193.
3612 //
3613 // Tony 2006.06.29
3614 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3615 ConcurrentMarkSweepThread::should_yield() &&
3616 !CMSCollector::foregroundGCIsActive(); ++i) {
3617 os::sleep(Thread::current(), 1, false);
3618 }
3619
3620 ConcurrentMarkSweepThread::synchronize(true);
3621 _bit_map_lock->lock_without_safepoint_check();
3622 _collector->startTimer();
3623 }
3624
3625 bool CMSCollector::do_marking_mt() {
3626 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3627 uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3628 conc_workers()->active_workers(),
3629 Threads::number_of_non_daemon_threads());
3630 conc_workers()->set_active_workers(num_workers);
3631
3632 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3633
3634 CMSConcMarkingTask tsk(this,
3635 cms_space,
3636 conc_workers(),
3637 task_queues());
3638
3639 // Since the actual number of workers we get may be different
3640 // from the number we requested above, do we need to do anything different
3641 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3642 // class?? XXX
3643 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3644
3645 // Refs discovery is already non-atomic.
3646 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3647 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3648 conc_workers()->start_task(&tsk);
3649 while (tsk.yielded()) {
3650 tsk.coordinator_yield();
3651 conc_workers()->continue_task(&tsk);
3652 }
3653 // If the task was aborted, _restart_addr will be non-NULL
3654 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3655 while (_restart_addr != NULL) {
3656 // XXX For now we do not make use of ABORTED state and have not
3657 // yet implemented the right abort semantics (even in the original
3658 // single-threaded CMS case). That needs some more investigation
3659 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3660 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3661 // If _restart_addr is non-NULL, a marking stack overflow
3662 // occurred; we need to do a fresh marking iteration from the
3663 // indicated restart address.
3664 if (_foregroundGCIsActive) {
3665 // We may be running into repeated stack overflows, having
3666 // reached the limit of the stack size, while making very
3667 // slow forward progress. It may be best to bail out and
3668 // let the foreground collector do its job.
3669 // Clear _restart_addr, so that foreground GC
3670 // works from scratch. This avoids the headache of
3671 // a "rescan" which would otherwise be needed because
3672 // of the dirty mod union table & card table.
3673 _restart_addr = NULL;
3674 return false;
3675 }
3676 // Adjust the task to restart from _restart_addr
3677 tsk.reset(_restart_addr);
3678 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3679 _restart_addr);
3680 _restart_addr = NULL;
3681 // Get the workers going again
3682 conc_workers()->start_task(&tsk);
3683 while (tsk.yielded()) {
3684 tsk.coordinator_yield();
3685 conc_workers()->continue_task(&tsk);
3686 }
3687 }
3688 assert(tsk.completed(), "Inconsistency");
3689 assert(tsk.result() == true, "Inconsistency");
3690 return true;
3691 }
3692
3693 bool CMSCollector::do_marking_st() {
3694 ResourceMark rm;
3695 HandleMark hm;
3696
3697 // Temporarily make refs discovery single threaded (non-MT)
3698 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3699 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3700 &_markStack, CMSYield);
3701 // the last argument to iterate indicates whether the iteration
3702 // should be incremental with periodic yields.
3703 _markBitMap.iterate(&markFromRootsClosure);
3704 // If _restart_addr is non-NULL, a marking stack overflow
3705 // occurred; we need to do a fresh iteration from the
3706 // indicated restart address.
3707 while (_restart_addr != NULL) {
3708 if (_foregroundGCIsActive) {
3709 // We may be running into repeated stack overflows, having
3710 // reached the limit of the stack size, while making very
3711 // slow forward progress. It may be best to bail out and
3712 // let the foreground collector do its job.
3713 // Clear _restart_addr, so that foreground GC
3714 // works from scratch. This avoids the headache of
3715 // a "rescan" which would otherwise be needed because
3716 // of the dirty mod union table & card table.
3717 _restart_addr = NULL;
3718 return false; // indicating failure to complete marking
3719 }
3720 // Deal with stack overflow:
3721 // we restart marking from _restart_addr
3722 HeapWord* ra = _restart_addr;
3723 markFromRootsClosure.reset(ra);
3724 _restart_addr = NULL;
3725 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3726 }
3727 return true;
3728 }
3729
3730 void CMSCollector::preclean() {
3731 check_correct_thread_executing();
3732 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3733 verify_work_stacks_empty();
3734 verify_overflow_empty();
3735 _abort_preclean = false;
3736 if (CMSPrecleaningEnabled) {
3737 if (!CMSEdenChunksRecordAlways) {
3738 _eden_chunk_index = 0;
3739 }
3740 size_t used = get_eden_used();
3741 size_t capacity = get_eden_capacity();
3742 // Don't start sampling unless we will get sufficiently
3743 // many samples.
3744 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3745 * CMSScheduleRemarkEdenPenetration)) {
3746 _start_sampling = true;
3747 } else {
3748 _start_sampling = false;
3749 }
3750 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3751 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
3752 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3753 }
3754 CMSTokenSync x(true); // is cms thread
3755 if (CMSPrecleaningEnabled) {
3756 sample_eden();
3757 _collectorState = AbortablePreclean;
3758 } else {
3759 _collectorState = FinalMarking;
3760 }
3761 verify_work_stacks_empty();
3762 verify_overflow_empty();
3763 }
3764
3765 // Try and schedule the remark such that young gen
3766 // occupancy is CMSScheduleRemarkEdenPenetration %.
3767 void CMSCollector::abortable_preclean() {
3768 check_correct_thread_executing();
3769 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3770 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3771
3772 // If Eden's current occupancy is below this threshold,
3773 // immediately schedule the remark; else preclean
3774 // past the next scavenge in an effort to
3775 // schedule the pause as described above. By choosing
3776 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3777 // we will never do an actual abortable preclean cycle.
3778 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3779 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3780 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
3781 // We need more smarts in the abortable preclean
3782 // loop below to deal with cases where allocation
3783 // in young gen is very very slow, and our precleaning
3784 // is running a losing race against a horde of
3785 // mutators intent on flooding us with CMS updates
3786 // (dirty cards).
3787 // One, admittedly dumb, strategy is to give up
3788 // after a certain number of abortable precleaning loops
3789 // or after a certain maximum time. We want to make
3790 // this smarter in the next iteration.
3791 // XXX FIX ME!!! YSR
3792 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3793 while (!(should_abort_preclean() ||
3794 ConcurrentMarkSweepThread::should_terminate())) {
3795 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3796 cumworkdone += workdone;
3797 loops++;
3798 // Voluntarily terminate abortable preclean phase if we have
3799 // been at it for too long.
3800 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3801 loops >= CMSMaxAbortablePrecleanLoops) {
3802 if (PrintGCDetails) {
3803 gclog_or_tty->print(" CMS: abort preclean due to loops ");
3804 }
3805 break;
3806 }
3807 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3808 if (PrintGCDetails) {
3809 gclog_or_tty->print(" CMS: abort preclean due to time ");
3810 }
3811 break;
3812 }
3813 // If we are doing little work each iteration, we should
3814 // take a short break.
3815 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3816 // Sleep for some time, waiting for work to accumulate
3817 stopTimer();
3818 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3819 startTimer();
3820 waited++;
3821 }
3822 }
3823 if (PrintCMSStatistics > 0) {
3824 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3825 loops, waited, cumworkdone);
3826 }
3827 }
3828 CMSTokenSync x(true); // is cms thread
3829 if (_collectorState != Idling) {
3830 assert(_collectorState == AbortablePreclean,
3831 "Spontaneous state transition?");
3832 _collectorState = FinalMarking;
3833 } // Else, a foreground collection completed this CMS cycle.
3834 return;
3835 }
3836
3837 // Respond to an Eden sampling opportunity
3838 void CMSCollector::sample_eden() {
3839 // Make sure a young gc cannot sneak in between our
3840 // reading and recording of a sample.
3841 assert(Thread::current()->is_ConcurrentGC_thread(),
3842 "Only the cms thread may collect Eden samples");
3843 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3844 "Should collect samples while holding CMS token");
3845 if (!_start_sampling) {
3846 return;
3847 }
3848 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3849 // is populated by the young generation.
3850 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3851 if (_eden_chunk_index < _eden_chunk_capacity) {
3852 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3853 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3854 "Unexpected state of Eden");
3855 // We'd like to check that what we just sampled is an oop-start address;
3856 // however, we cannot do that here since the object may not yet have been
3857 // initialized. So we'll instead do the check when we _use_ this sample
3858 // later.
3859 if (_eden_chunk_index == 0 ||
3860 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3861 _eden_chunk_array[_eden_chunk_index-1])
3862 >= CMSSamplingGrain)) {
3863 _eden_chunk_index++; // commit sample
3864 }
3865 }
3866 }
3867 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3868 size_t used = get_eden_used();
3869 size_t capacity = get_eden_capacity();
3870 assert(used <= capacity, "Unexpected state of Eden");
3871 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3872 _abort_preclean = true;
3873 }
3874 }
3875 }
3876
3877
3878 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3879 assert(_collectorState == Precleaning ||
3880 _collectorState == AbortablePreclean, "incorrect state");
3881 ResourceMark rm;
3882 HandleMark hm;
3883
3884 // Precleaning is currently not MT but the reference processor
3885 // may be set for MT. Disable it temporarily here.
3886 ReferenceProcessor* rp = ref_processor();
3887 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3888
3889 // Do one pass of scrubbing the discovered reference lists
3890 // to remove any reference objects with strongly-reachable
3891 // referents.
3892 if (clean_refs) {
3893 CMSPrecleanRefsYieldClosure yield_cl(this);
3894 assert(rp->span().equals(_span), "Spans should be equal");
3895 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3896 &_markStack, true /* preclean */);
3897 CMSDrainMarkingStackClosure complete_trace(this,
3898 _span, &_markBitMap, &_markStack,
3899 &keep_alive, true /* preclean */);
3900
3901 // We don't want this step to interfere with a young
3902 // collection because we don't want to take CPU
3903 // or memory bandwidth away from the young GC threads
3904 // (which may be as many as there are CPUs).
3905 // Note that we don't need to protect ourselves from
3906 // interference with mutators because they can't
3907 // manipulate the discovered reference lists nor affect
3908 // the computed reachability of the referents, the
3909 // only properties manipulated by the precleaning
3910 // of these reference lists.
3911 stopTimer();
3912 CMSTokenSyncWithLocks x(true /* is cms thread */,
3913 bitMapLock());
3914 startTimer();
3915 sample_eden();
3916
3917 // The following will yield to allow foreground
3918 // collection to proceed promptly. XXX YSR:
3919 // The code in this method may need further
3920 // tweaking for better performance and some restructuring
3921 // for cleaner interfaces.
3922 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3923 rp->preclean_discovered_references(
3924 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3925 gc_timer);
3926 }
3927
3928 if (clean_survivor) { // preclean the active survivor space(s)
3929 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3930 &_markBitMap, &_modUnionTable,
3931 &_markStack, true /* precleaning phase */);
3932 stopTimer();
3933 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3934 bitMapLock());
3935 startTimer();
3936 unsigned int before_count =
3937 GenCollectedHeap::heap()->total_collections();
3938 SurvivorSpacePrecleanClosure
3939 sss_cl(this, _span, &_markBitMap, &_markStack,
3940 &pam_cl, before_count, CMSYield);
3941 _young_gen->from()->object_iterate_careful(&sss_cl);
3942 _young_gen->to()->object_iterate_careful(&sss_cl);
3943 }
3944 MarkRefsIntoAndScanClosure
3945 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3946 &_markStack, this, CMSYield,
3947 true /* precleaning phase */);
3948 // CAUTION: The following closure has persistent state that may need to
3949 // be reset upon a decrease in the sequence of addresses it
3950 // processes.
3951 ScanMarkedObjectsAgainCarefullyClosure
3952 smoac_cl(this, _span,
3953 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3954
3955 // Preclean dirty cards in ModUnionTable and CardTable using
3956 // appropriate convergence criterion;
3957 // repeat CMSPrecleanIter times unless we find that
3958 // we are losing.
3959 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3960 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3961 "Bad convergence multiplier");
3962 assert(CMSPrecleanThreshold >= 100,
3963 "Unreasonably low CMSPrecleanThreshold");
3964
3965 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3966 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3967 numIter < CMSPrecleanIter;
3968 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3969 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3970 if (Verbose && PrintGCDetails) {
3971 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3972 }
3973 // Either there are very few dirty cards, so re-mark
3974 // pause will be small anyway, or our pre-cleaning isn't
3975 // that much faster than the rate at which cards are being
3976 // dirtied, so we might as well stop and re-mark since
3977 // precleaning won't improve our re-mark time by much.
3978 if (curNumCards <= CMSPrecleanThreshold ||
3979 (numIter > 0 &&
3980 (curNumCards * CMSPrecleanDenominator >
3981 lastNumCards * CMSPrecleanNumerator))) {
3982 numIter++;
3983 cumNumCards += curNumCards;
3984 break;
3985 }
3986 }
3987
3988 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
3989
3990 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3991 cumNumCards += curNumCards;
3992 if (PrintGCDetails && PrintCMSStatistics != 0) {
3993 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3994 curNumCards, cumNumCards, numIter);
3995 }
3996 return cumNumCards; // as a measure of useful work done
3997 }
3998
3999 // PRECLEANING NOTES:
4000 // Precleaning involves:
4001 // . reading the bits of the modUnionTable and clearing the set bits.
4002 // . For the cards corresponding to the set bits, we scan the
4003 // objects on those cards. This means we need the free_list_lock
4004 // so that we can safely iterate over the CMS space when scanning
4005 // for oops.
4006 // . When we scan the objects, we'll be both reading and setting
4007 // marks in the marking bit map, so we'll need the marking bit map.
4008 // . For protecting _collector_state transitions, we take the CGC_lock.
4009 // Note that any races in the reading of of card table entries by the
4010 // CMS thread on the one hand and the clearing of those entries by the
4011 // VM thread or the setting of those entries by the mutator threads on the
4012 // other are quite benign. However, for efficiency it makes sense to keep
4013 // the VM thread from racing with the CMS thread while the latter is
4014 // dirty card info to the modUnionTable. We therefore also use the
4015 // CGC_lock to protect the reading of the card table and the mod union
4016 // table by the CM thread.
4017 // . We run concurrently with mutator updates, so scanning
4018 // needs to be done carefully -- we should not try to scan
4019 // potentially uninitialized objects.
4020 //
4021 // Locking strategy: While holding the CGC_lock, we scan over and
4022 // reset a maximal dirty range of the mod union / card tables, then lock
4023 // the free_list_lock and bitmap lock to do a full marking, then
4024 // release these locks; and repeat the cycle. This allows for a
4025 // certain amount of fairness in the sharing of these locks between
4026 // the CMS collector on the one hand, and the VM thread and the
4027 // mutators on the other.
4028
4029 // NOTE: preclean_mod_union_table() and preclean_card_table()
4030 // further below are largely identical; if you need to modify
4031 // one of these methods, please check the other method too.
4032
4033 size_t CMSCollector::preclean_mod_union_table(
4034 ConcurrentMarkSweepGeneration* old_gen,
4035 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4036 verify_work_stacks_empty();
4037 verify_overflow_empty();
4038
4039 // strategy: starting with the first card, accumulate contiguous
4040 // ranges of dirty cards; clear these cards, then scan the region
4041 // covered by these cards.
4042
4043 // Since all of the MUT is committed ahead, we can just use
4044 // that, in case the generations expand while we are precleaning.
4045 // It might also be fine to just use the committed part of the
4046 // generation, but we might potentially miss cards when the
4047 // generation is rapidly expanding while we are in the midst
4048 // of precleaning.
4049 HeapWord* startAddr = old_gen->reserved().start();
4050 HeapWord* endAddr = old_gen->reserved().end();
4051
4052 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4053
4054 size_t numDirtyCards, cumNumDirtyCards;
4055 HeapWord *nextAddr, *lastAddr;
4056 for (cumNumDirtyCards = numDirtyCards = 0,
4057 nextAddr = lastAddr = startAddr;
4058 nextAddr < endAddr;
4059 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4060
4061 ResourceMark rm;
4062 HandleMark hm;
4063
4064 MemRegion dirtyRegion;
4065 {
4066 stopTimer();
4067 // Potential yield point
4068 CMSTokenSync ts(true);
4069 startTimer();
4070 sample_eden();
4071 // Get dirty region starting at nextOffset (inclusive),
4072 // simultaneously clearing it.
4073 dirtyRegion =
4074 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4075 assert(dirtyRegion.start() >= nextAddr,
4076 "returned region inconsistent?");
4077 }
4078 // Remember where the next search should begin.
4079 // The returned region (if non-empty) is a right open interval,
4080 // so lastOffset is obtained from the right end of that
4081 // interval.
4082 lastAddr = dirtyRegion.end();
4083 // Should do something more transparent and less hacky XXX
4084 numDirtyCards =
4085 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4086
4087 // We'll scan the cards in the dirty region (with periodic
4088 // yields for foreground GC as needed).
4089 if (!dirtyRegion.is_empty()) {
4090 assert(numDirtyCards > 0, "consistency check");
4091 HeapWord* stop_point = NULL;
4092 stopTimer();
4093 // Potential yield point
4094 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
4095 bitMapLock());
4096 startTimer();
4097 {
4098 verify_work_stacks_empty();
4099 verify_overflow_empty();
4100 sample_eden();
4101 stop_point =
4102 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4103 }
4104 if (stop_point != NULL) {
4105 // The careful iteration stopped early either because it found an
4106 // uninitialized object, or because we were in the midst of an
4107 // "abortable preclean", which should now be aborted. Redirty
4108 // the bits corresponding to the partially-scanned or unscanned
4109 // cards. We'll either restart at the next block boundary or
4110 // abort the preclean.
4111 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4112 "Should only be AbortablePreclean.");
4113 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4114 if (should_abort_preclean()) {
4115 break; // out of preclean loop
4116 } else {
4117 // Compute the next address at which preclean should pick up;
4118 // might need bitMapLock in order to read P-bits.
4119 lastAddr = next_card_start_after_block(stop_point);
4120 }
4121 }
4122 } else {
4123 assert(lastAddr == endAddr, "consistency check");
4124 assert(numDirtyCards == 0, "consistency check");
4125 break;
4126 }
4127 }
4128 verify_work_stacks_empty();
4129 verify_overflow_empty();
4130 return cumNumDirtyCards;
4131 }
4132
4133 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4134 // below are largely identical; if you need to modify
4135 // one of these methods, please check the other method too.
4136
4137 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
4138 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4139 // strategy: it's similar to precleamModUnionTable above, in that
4140 // we accumulate contiguous ranges of dirty cards, mark these cards
4141 // precleaned, then scan the region covered by these cards.
4142 HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high());
4143 HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4144
4145 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4146
4147 size_t numDirtyCards, cumNumDirtyCards;
4148 HeapWord *lastAddr, *nextAddr;
4149
4150 for (cumNumDirtyCards = numDirtyCards = 0,
4151 nextAddr = lastAddr = startAddr;
4152 nextAddr < endAddr;
4153 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4154
4155 ResourceMark rm;
4156 HandleMark hm;
4157
4158 MemRegion dirtyRegion;
4159 {
4160 // See comments in "Precleaning notes" above on why we
4161 // do this locking. XXX Could the locking overheads be
4162 // too high when dirty cards are sparse? [I don't think so.]
4163 stopTimer();
4164 CMSTokenSync x(true); // is cms thread
4165 startTimer();
4166 sample_eden();
4167 // Get and clear dirty region from card table
4168 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4169 MemRegion(nextAddr, endAddr),
4170 true,
4171 CardTableModRefBS::precleaned_card_val());
4172
4173 assert(dirtyRegion.start() >= nextAddr,
4174 "returned region inconsistent?");
4175 }
4176 lastAddr = dirtyRegion.end();
4177 numDirtyCards =
4178 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4179
4180 if (!dirtyRegion.is_empty()) {
4181 stopTimer();
4182 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4183 startTimer();
4184 sample_eden();
4185 verify_work_stacks_empty();
4186 verify_overflow_empty();
4187 HeapWord* stop_point =
4188 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4189 if (stop_point != NULL) {
4190 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4191 "Should only be AbortablePreclean.");
4192 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4193 if (should_abort_preclean()) {
4194 break; // out of preclean loop
4195 } else {
4196 // Compute the next address at which preclean should pick up.
4197 lastAddr = next_card_start_after_block(stop_point);
4198 }
4199 }
4200 } else {
4201 break;
4202 }
4203 }
4204 verify_work_stacks_empty();
4205 verify_overflow_empty();
4206 return cumNumDirtyCards;
4207 }
4208
4209 class PrecleanKlassClosure : public KlassClosure {
4210 KlassToOopClosure _cm_klass_closure;
4211 public:
4212 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4213 void do_klass(Klass* k) {
4214 if (k->has_accumulated_modified_oops()) {
4215 k->clear_accumulated_modified_oops();
4216
4217 _cm_klass_closure.do_klass(k);
4218 }
4219 }
4220 };
4221
4222 // The freelist lock is needed to prevent asserts, is it really needed?
4223 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4224
4225 cl->set_freelistLock(freelistLock);
4226
4227 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4228
4229 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4230 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4231 PrecleanKlassClosure preclean_klass_closure(cl);
4232 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4233
4234 verify_work_stacks_empty();
4235 verify_overflow_empty();
4236 }
4237
4238 void CMSCollector::checkpointRootsFinal() {
4239 assert(_collectorState == FinalMarking, "incorrect state transition?");
4240 check_correct_thread_executing();
4241 // world is stopped at this checkpoint
4242 assert(SafepointSynchronize::is_at_safepoint(),
4243 "world should be stopped");
4244 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4245
4246 verify_work_stacks_empty();
4247 verify_overflow_empty();
4248
4249 if (PrintGCDetails) {
4250 gclog_or_tty->print("[YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)]",
4251 _young_gen->used() / K,
4252 _young_gen->capacity() / K);
4253 }
4254 {
4255 if (CMSScavengeBeforeRemark) {
4256 GenCollectedHeap* gch = GenCollectedHeap::heap();
4257 // Temporarily set flag to false, GCH->do_collection will
4258 // expect it to be false and set to true
4259 FlagSetting fl(gch->_is_gc_active, false);
4260 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4261 PrintGCDetails && Verbose, true, _gc_timer_cm);)
4262 gch->do_collection(true, // full (i.e. force, see below)
4263 false, // !clear_all_soft_refs
4264 0, // size
4265 false, // is_tlab
4266 GenCollectedHeap::YoungGen // type
4267 );
4268 }
4269 FreelistLocker x(this);
4270 MutexLockerEx y(bitMapLock(),
4271 Mutex::_no_safepoint_check_flag);
4272 checkpointRootsFinalWork();
4273 }
4274 verify_work_stacks_empty();
4275 verify_overflow_empty();
4276 }
4277
4278 void CMSCollector::checkpointRootsFinalWork() {
4279 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm);)
4280
4281 assert(haveFreelistLocks(), "must have free list locks");
4282 assert_lock_strong(bitMapLock());
4283
4284 ResourceMark rm;
4285 HandleMark hm;
4286
4287 GenCollectedHeap* gch = GenCollectedHeap::heap();
4288
4289 if (should_unload_classes()) {
4290 CodeCache::gc_prologue();
4291 }
4292 assert(haveFreelistLocks(), "must have free list locks");
4293 assert_lock_strong(bitMapLock());
4294
4295 // We might assume that we need not fill TLAB's when
4296 // CMSScavengeBeforeRemark is set, because we may have just done
4297 // a scavenge which would have filled all TLAB's -- and besides
4298 // Eden would be empty. This however may not always be the case --
4299 // for instance although we asked for a scavenge, it may not have
4300 // happened because of a JNI critical section. We probably need
4301 // a policy for deciding whether we can in that case wait until
4302 // the critical section releases and then do the remark following
4303 // the scavenge, and skip it here. In the absence of that policy,
4304 // or of an indication of whether the scavenge did indeed occur,
4305 // we cannot rely on TLAB's having been filled and must do
4306 // so here just in case a scavenge did not happen.
4307 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4308 // Update the saved marks which may affect the root scans.
4309 gch->save_marks();
4310
4311 if (CMSPrintEdenSurvivorChunks) {
4312 print_eden_and_survivor_chunk_arrays();
4313 }
4314
4315 {
4316 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4317
4318 // Note on the role of the mod union table:
4319 // Since the marker in "markFromRoots" marks concurrently with
4320 // mutators, it is possible for some reachable objects not to have been
4321 // scanned. For instance, an only reference to an object A was
4322 // placed in object B after the marker scanned B. Unless B is rescanned,
4323 // A would be collected. Such updates to references in marked objects
4324 // are detected via the mod union table which is the set of all cards
4325 // dirtied since the first checkpoint in this GC cycle and prior to
4326 // the most recent young generation GC, minus those cleaned up by the
4327 // concurrent precleaning.
4328 if (CMSParallelRemarkEnabled) {
4329 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm);
4330 do_remark_parallel();
4331 } else {
4332 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false, _gc_timer_cm);
4333 do_remark_non_parallel();
4334 }
4335 }
4336 verify_work_stacks_empty();
4337 verify_overflow_empty();
4338
4339 {
4340 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm);)
4341 refProcessingWork();
4342 }
4343 verify_work_stacks_empty();
4344 verify_overflow_empty();
4345
4346 if (should_unload_classes()) {
4347 CodeCache::gc_epilogue();
4348 }
4349 JvmtiExport::gc_epilogue();
4350
4351 // If we encountered any (marking stack / work queue) overflow
4352 // events during the current CMS cycle, take appropriate
4353 // remedial measures, where possible, so as to try and avoid
4354 // recurrence of that condition.
4355 assert(_markStack.isEmpty(), "No grey objects");
4356 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4357 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4358 if (ser_ovflw > 0) {
4359 if (PrintCMSStatistics != 0) {
4360 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4361 "(pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT
4362 ", kac_preclean=" SIZE_FORMAT ")",
4363 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4364 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4365 }
4366 _markStack.expand();
4367 _ser_pmc_remark_ovflw = 0;
4368 _ser_pmc_preclean_ovflw = 0;
4369 _ser_kac_preclean_ovflw = 0;
4370 _ser_kac_ovflw = 0;
4371 }
4372 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4373 if (PrintCMSStatistics != 0) {
4374 gclog_or_tty->print_cr("Work queue overflow (benign) "
4375 "(pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4376 _par_pmc_remark_ovflw, _par_kac_ovflw);
4377 }
4378 _par_pmc_remark_ovflw = 0;
4379 _par_kac_ovflw = 0;
4380 }
4381 if (PrintCMSStatistics != 0) {
4382 if (_markStack._hit_limit > 0) {
4383 gclog_or_tty->print_cr(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4384 _markStack._hit_limit);
4385 }
4386 if (_markStack._failed_double > 0) {
4387 gclog_or_tty->print_cr(" (benign) Failed stack doubling (" SIZE_FORMAT "),"
4388 " current capacity " SIZE_FORMAT,
4389 _markStack._failed_double,
4390 _markStack.capacity());
4391 }
4392 }
4393 _markStack._hit_limit = 0;
4394 _markStack._failed_double = 0;
4395
4396 if ((VerifyAfterGC || VerifyDuringGC) &&
4397 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4398 verify_after_remark();
4399 }
4400
4401 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4402
4403 // Change under the freelistLocks.
4404 _collectorState = Sweeping;
4405 // Call isAllClear() under bitMapLock
4406 assert(_modUnionTable.isAllClear(),
4407 "Should be clear by end of the final marking");
4408 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4409 "Should be clear by end of the final marking");
4410 }
4411
4412 void CMSParInitialMarkTask::work(uint worker_id) {
4413 elapsedTimer _timer;
4414 ResourceMark rm;
4415 HandleMark hm;
4416
4417 // ---------- scan from roots --------------
4418 _timer.start();
4419 GenCollectedHeap* gch = GenCollectedHeap::heap();
4420 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4421
4422 // ---------- young gen roots --------------
4423 {
4424 work_on_young_gen_roots(worker_id, &par_mri_cl);
4425 _timer.stop();
4426 if (PrintCMSStatistics != 0) {
4427 gclog_or_tty->print_cr(
4428 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4429 worker_id, _timer.seconds());
4430 }
4431 }
4432
4433 // ---------- remaining roots --------------
4434 _timer.reset();
4435 _timer.start();
4436
4437 CLDToOopClosure cld_closure(&par_mri_cl, true);
4438
4439 gch->gen_process_roots(_strong_roots_scope,
4440 GenCollectedHeap::OldGen,
4441 false, // yg was scanned above
4442 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4443 _collector->should_unload_classes(),
4444 &par_mri_cl,
4445 NULL,
4446 &cld_closure);
4447 assert(_collector->should_unload_classes()
4448 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4449 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4450 _timer.stop();
4451 if (PrintCMSStatistics != 0) {
4452 gclog_or_tty->print_cr(
4453 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4454 worker_id, _timer.seconds());
4455 }
4456 }
4457
4458 // Parallel remark task
4459 class CMSParRemarkTask: public CMSParMarkTask {
4460 CompactibleFreeListSpace* _cms_space;
4461
4462 // The per-thread work queues, available here for stealing.
4463 OopTaskQueueSet* _task_queues;
4464 ParallelTaskTerminator _term;
4465 StrongRootsScope* _strong_roots_scope;
4466
4467 public:
4468 // A value of 0 passed to n_workers will cause the number of
4469 // workers to be taken from the active workers in the work gang.
4470 CMSParRemarkTask(CMSCollector* collector,
4471 CompactibleFreeListSpace* cms_space,
4472 uint n_workers, WorkGang* workers,
4473 OopTaskQueueSet* task_queues,
4474 StrongRootsScope* strong_roots_scope):
4475 CMSParMarkTask("Rescan roots and grey objects in parallel",
4476 collector, n_workers),
4477 _cms_space(cms_space),
4478 _task_queues(task_queues),
4479 _term(n_workers, task_queues),
4480 _strong_roots_scope(strong_roots_scope) { }
4481
4482 OopTaskQueueSet* task_queues() { return _task_queues; }
4483
4484 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4485
4486 ParallelTaskTerminator* terminator() { return &_term; }
4487 uint n_workers() { return _n_workers; }
4488
4489 void work(uint worker_id);
4490
4491 private:
4492 // ... of dirty cards in old space
4493 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4494 Par_MarkRefsIntoAndScanClosure* cl);
4495
4496 // ... work stealing for the above
4497 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4498 };
4499
4500 class RemarkKlassClosure : public KlassClosure {
4501 KlassToOopClosure _cm_klass_closure;
4502 public:
4503 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4504 void do_klass(Klass* k) {
4505 // Check if we have modified any oops in the Klass during the concurrent marking.
4506 if (k->has_accumulated_modified_oops()) {
4507 k->clear_accumulated_modified_oops();
4508
4509 // We could have transfered the current modified marks to the accumulated marks,
4510 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4511 } else if (k->has_modified_oops()) {
4512 // Don't clear anything, this info is needed by the next young collection.
4513 } else {
4514 // No modified oops in the Klass.
4515 return;
4516 }
4517
4518 // The klass has modified fields, need to scan the klass.
4519 _cm_klass_closure.do_klass(k);
4520 }
4521 };
4522
4523 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4524 ParNewGeneration* young_gen = _collector->_young_gen;
4525 ContiguousSpace* eden_space = young_gen->eden();
4526 ContiguousSpace* from_space = young_gen->from();
4527 ContiguousSpace* to_space = young_gen->to();
4528
4529 HeapWord** eca = _collector->_eden_chunk_array;
4530 size_t ect = _collector->_eden_chunk_index;
4531 HeapWord** sca = _collector->_survivor_chunk_array;
4532 size_t sct = _collector->_survivor_chunk_index;
4533
4534 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4535 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4536
4537 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4538 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4539 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4540 }
4541
4542 // work_queue(i) is passed to the closure
4543 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
4544 // also is passed to do_dirty_card_rescan_tasks() and to
4545 // do_work_steal() to select the i-th task_queue.
4546
4547 void CMSParRemarkTask::work(uint worker_id) {
4548 elapsedTimer _timer;
4549 ResourceMark rm;
4550 HandleMark hm;
4551
4552 // ---------- rescan from roots --------------
4553 _timer.start();
4554 GenCollectedHeap* gch = GenCollectedHeap::heap();
4555 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4556 _collector->_span, _collector->ref_processor(),
4557 &(_collector->_markBitMap),
4558 work_queue(worker_id));
4559
4560 // Rescan young gen roots first since these are likely
4561 // coarsely partitioned and may, on that account, constitute
4562 // the critical path; thus, it's best to start off that
4563 // work first.
4564 // ---------- young gen roots --------------
4565 {
4566 work_on_young_gen_roots(worker_id, &par_mrias_cl);
4567 _timer.stop();
4568 if (PrintCMSStatistics != 0) {
4569 gclog_or_tty->print_cr(
4570 "Finished young gen rescan work in %dth thread: %3.3f sec",
4571 worker_id, _timer.seconds());
4572 }
4573 }
4574
4575 // ---------- remaining roots --------------
4576 _timer.reset();
4577 _timer.start();
4578 gch->gen_process_roots(_strong_roots_scope,
4579 GenCollectedHeap::OldGen,
4580 false, // yg was scanned above
4581 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4582 _collector->should_unload_classes(),
4583 &par_mrias_cl,
4584 NULL,
4585 NULL); // The dirty klasses will be handled below
4586
4587 assert(_collector->should_unload_classes()
4588 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4589 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4590 _timer.stop();
4591 if (PrintCMSStatistics != 0) {
4592 gclog_or_tty->print_cr(
4593 "Finished remaining root rescan work in %dth thread: %3.3f sec",
4594 worker_id, _timer.seconds());
4595 }
4596
4597 // ---------- unhandled CLD scanning ----------
4598 if (worker_id == 0) { // Single threaded at the moment.
4599 _timer.reset();
4600 _timer.start();
4601
4602 // Scan all new class loader data objects and new dependencies that were
4603 // introduced during concurrent marking.
4604 ResourceMark rm;
4605 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4606 for (int i = 0; i < array->length(); i++) {
4607 par_mrias_cl.do_cld_nv(array->at(i));
4608 }
4609
4610 // We don't need to keep track of new CLDs anymore.
4611 ClassLoaderDataGraph::remember_new_clds(false);
4612
4613 _timer.stop();
4614 if (PrintCMSStatistics != 0) {
4615 gclog_or_tty->print_cr(
4616 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4617 worker_id, _timer.seconds());
4618 }
4619 }
4620
4621 // ---------- dirty klass scanning ----------
4622 if (worker_id == 0) { // Single threaded at the moment.
4623 _timer.reset();
4624 _timer.start();
4625
4626 // Scan all classes that was dirtied during the concurrent marking phase.
4627 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4628 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4629
4630 _timer.stop();
4631 if (PrintCMSStatistics != 0) {
4632 gclog_or_tty->print_cr(
4633 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4634 worker_id, _timer.seconds());
4635 }
4636 }
4637
4638 // We might have added oops to ClassLoaderData::_handles during the
4639 // concurrent marking phase. These oops point to newly allocated objects
4640 // that are guaranteed to be kept alive. Either by the direct allocation
4641 // code, or when the young collector processes the roots. Hence,
4642 // we don't have to revisit the _handles block during the remark phase.
4643
4644 // ---------- rescan dirty cards ------------
4645 _timer.reset();
4646 _timer.start();
4647
4648 // Do the rescan tasks for each of the two spaces
4649 // (cms_space) in turn.
4650 // "worker_id" is passed to select the task_queue for "worker_id"
4651 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4652 _timer.stop();
4653 if (PrintCMSStatistics != 0) {
4654 gclog_or_tty->print_cr(
4655 "Finished dirty card rescan work in %dth thread: %3.3f sec",
4656 worker_id, _timer.seconds());
4657 }
4658
4659 // ---------- steal work from other threads ...
4660 // ---------- ... and drain overflow list.
4661 _timer.reset();
4662 _timer.start();
4663 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4664 _timer.stop();
4665 if (PrintCMSStatistics != 0) {
4666 gclog_or_tty->print_cr(
4667 "Finished work stealing in %dth thread: %3.3f sec",
4668 worker_id, _timer.seconds());
4669 }
4670 }
4671
4672 // Note that parameter "i" is not used.
4673 void
4674 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4675 OopsInGenClosure* cl, ContiguousSpace* space,
4676 HeapWord** chunk_array, size_t chunk_top) {
4677 // Until all tasks completed:
4678 // . claim an unclaimed task
4679 // . compute region boundaries corresponding to task claimed
4680 // using chunk_array
4681 // . par_oop_iterate(cl) over that region
4682
4683 ResourceMark rm;
4684 HandleMark hm;
4685
4686 SequentialSubTasksDone* pst = space->par_seq_tasks();
4687
4688 uint nth_task = 0;
4689 uint n_tasks = pst->n_tasks();
4690
4691 if (n_tasks > 0) {
4692 assert(pst->valid(), "Uninitialized use?");
4693 HeapWord *start, *end;
4694 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4695 // We claimed task # nth_task; compute its boundaries.
4696 if (chunk_top == 0) { // no samples were taken
4697 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4698 start = space->bottom();
4699 end = space->top();
4700 } else if (nth_task == 0) {
4701 start = space->bottom();
4702 end = chunk_array[nth_task];
4703 } else if (nth_task < (uint)chunk_top) {
4704 assert(nth_task >= 1, "Control point invariant");
4705 start = chunk_array[nth_task - 1];
4706 end = chunk_array[nth_task];
4707 } else {
4708 assert(nth_task == (uint)chunk_top, "Control point invariant");
4709 start = chunk_array[chunk_top - 1];
4710 end = space->top();
4711 }
4712 MemRegion mr(start, end);
4713 // Verify that mr is in space
4714 assert(mr.is_empty() || space->used_region().contains(mr),
4715 "Should be in space");
4716 // Verify that "start" is an object boundary
4717 assert(mr.is_empty() || oop(mr.start())->is_oop(),
4718 "Should be an oop");
4719 space->par_oop_iterate(mr, cl);
4720 }
4721 pst->all_tasks_completed();
4722 }
4723 }
4724
4725 void
4726 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4727 CompactibleFreeListSpace* sp, int i,
4728 Par_MarkRefsIntoAndScanClosure* cl) {
4729 // Until all tasks completed:
4730 // . claim an unclaimed task
4731 // . compute region boundaries corresponding to task claimed
4732 // . transfer dirty bits ct->mut for that region
4733 // . apply rescanclosure to dirty mut bits for that region
4734
4735 ResourceMark rm;
4736 HandleMark hm;
4737
4738 OopTaskQueue* work_q = work_queue(i);
4739 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4740 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4741 // CAUTION: This closure has state that persists across calls to
4742 // the work method dirty_range_iterate_clear() in that it has
4743 // embedded in it a (subtype of) UpwardsObjectClosure. The
4744 // use of that state in the embedded UpwardsObjectClosure instance
4745 // assumes that the cards are always iterated (even if in parallel
4746 // by several threads) in monotonically increasing order per each
4747 // thread. This is true of the implementation below which picks
4748 // card ranges (chunks) in monotonically increasing order globally
4749 // and, a-fortiori, in monotonically increasing order per thread
4750 // (the latter order being a subsequence of the former).
4751 // If the work code below is ever reorganized into a more chaotic
4752 // work-partitioning form than the current "sequential tasks"
4753 // paradigm, the use of that persistent state will have to be
4754 // revisited and modified appropriately. See also related
4755 // bug 4756801 work on which should examine this code to make
4756 // sure that the changes there do not run counter to the
4757 // assumptions made here and necessary for correctness and
4758 // efficiency. Note also that this code might yield inefficient
4759 // behavior in the case of very large objects that span one or
4760 // more work chunks. Such objects would potentially be scanned
4761 // several times redundantly. Work on 4756801 should try and
4762 // address that performance anomaly if at all possible. XXX
4763 MemRegion full_span = _collector->_span;
4764 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4765 MarkFromDirtyCardsClosure
4766 greyRescanClosure(_collector, full_span, // entire span of interest
4767 sp, bm, work_q, cl);
4768
4769 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4770 assert(pst->valid(), "Uninitialized use?");
4771 uint nth_task = 0;
4772 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4773 MemRegion span = sp->used_region();
4774 HeapWord* start_addr = span.start();
4775 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4776 alignment);
4777 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4778 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4779 start_addr, "Check alignment");
4780 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4781 chunk_size, "Check alignment");
4782
4783 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4784 // Having claimed the nth_task, compute corresponding mem-region,
4785 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4786 // The alignment restriction ensures that we do not need any
4787 // synchronization with other gang-workers while setting or
4788 // clearing bits in thus chunk of the MUT.
4789 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4790 start_addr + (nth_task+1)*chunk_size);
4791 // The last chunk's end might be way beyond end of the
4792 // used region. In that case pull back appropriately.
4793 if (this_span.end() > end_addr) {
4794 this_span.set_end(end_addr);
4795 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4796 }
4797 // Iterate over the dirty cards covering this chunk, marking them
4798 // precleaned, and setting the corresponding bits in the mod union
4799 // table. Since we have been careful to partition at Card and MUT-word
4800 // boundaries no synchronization is needed between parallel threads.
4801 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4802 &modUnionClosure);
4803
4804 // Having transferred these marks into the modUnionTable,
4805 // rescan the marked objects on the dirty cards in the modUnionTable.
4806 // Even if this is at a synchronous collection, the initial marking
4807 // may have been done during an asynchronous collection so there
4808 // may be dirty bits in the mod-union table.
4809 _collector->_modUnionTable.dirty_range_iterate_clear(
4810 this_span, &greyRescanClosure);
4811 _collector->_modUnionTable.verifyNoOneBitsInRange(
4812 this_span.start(),
4813 this_span.end());
4814 }
4815 pst->all_tasks_completed(); // declare that i am done
4816 }
4817
4818 // . see if we can share work_queues with ParNew? XXX
4819 void
4820 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4821 int* seed) {
4822 OopTaskQueue* work_q = work_queue(i);
4823 NOT_PRODUCT(int num_steals = 0;)
4824 oop obj_to_scan;
4825 CMSBitMap* bm = &(_collector->_markBitMap);
4826
4827 while (true) {
4828 // Completely finish any left over work from (an) earlier round(s)
4829 cl->trim_queue(0);
4830 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4831 (size_t)ParGCDesiredObjsFromOverflowList);
4832 // Now check if there's any work in the overflow list
4833 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4834 // only affects the number of attempts made to get work from the
4835 // overflow list and does not affect the number of workers. Just
4836 // pass ParallelGCThreads so this behavior is unchanged.
4837 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4838 work_q,
4839 ParallelGCThreads)) {
4840 // found something in global overflow list;
4841 // not yet ready to go stealing work from others.
4842 // We'd like to assert(work_q->size() != 0, ...)
4843 // because we just took work from the overflow list,
4844 // but of course we can't since all of that could have
4845 // been already stolen from us.
4846 // "He giveth and He taketh away."
4847 continue;
4848 }
4849 // Verify that we have no work before we resort to stealing
4850 assert(work_q->size() == 0, "Have work, shouldn't steal");
4851 // Try to steal from other queues that have work
4852 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4853 NOT_PRODUCT(num_steals++;)
4854 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4855 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4856 // Do scanning work
4857 obj_to_scan->oop_iterate(cl);
4858 // Loop around, finish this work, and try to steal some more
4859 } else if (terminator()->offer_termination()) {
4860 break; // nirvana from the infinite cycle
4861 }
4862 }
4863 NOT_PRODUCT(
4864 if (PrintCMSStatistics != 0) {
4865 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
4866 }
4867 )
4868 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4869 "Else our work is not yet done");
4870 }
4871
4872 // Record object boundaries in _eden_chunk_array by sampling the eden
4873 // top in the slow-path eden object allocation code path and record
4874 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4875 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4876 // sampling in sample_eden() that activates during the part of the
4877 // preclean phase.
4878 void CMSCollector::sample_eden_chunk() {
4879 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4880 if (_eden_chunk_lock->try_lock()) {
4881 // Record a sample. This is the critical section. The contents
4882 // of the _eden_chunk_array have to be non-decreasing in the
4883 // address order.
4884 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4885 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4886 "Unexpected state of Eden");
4887 if (_eden_chunk_index == 0 ||
4888 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4889 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4890 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4891 _eden_chunk_index++; // commit sample
4892 }
4893 _eden_chunk_lock->unlock();
4894 }
4895 }
4896 }
4897
4898 // Return a thread-local PLAB recording array, as appropriate.
4899 void* CMSCollector::get_data_recorder(int thr_num) {
4900 if (_survivor_plab_array != NULL &&
4901 (CMSPLABRecordAlways ||
4902 (_collectorState > Marking && _collectorState < FinalMarking))) {
4903 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4904 ChunkArray* ca = &_survivor_plab_array[thr_num];
4905 ca->reset(); // clear it so that fresh data is recorded
4906 return (void*) ca;
4907 } else {
4908 return NULL;
4909 }
4910 }
4911
4912 // Reset all the thread-local PLAB recording arrays
4913 void CMSCollector::reset_survivor_plab_arrays() {
4914 for (uint i = 0; i < ParallelGCThreads; i++) {
4915 _survivor_plab_array[i].reset();
4916 }
4917 }
4918
4919 // Merge the per-thread plab arrays into the global survivor chunk
4920 // array which will provide the partitioning of the survivor space
4921 // for CMS initial scan and rescan.
4922 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4923 int no_of_gc_threads) {
4924 assert(_survivor_plab_array != NULL, "Error");
4925 assert(_survivor_chunk_array != NULL, "Error");
4926 assert(_collectorState == FinalMarking ||
4927 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4928 for (int j = 0; j < no_of_gc_threads; j++) {
4929 _cursor[j] = 0;
4930 }
4931 HeapWord* top = surv->top();
4932 size_t i;
4933 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4934 HeapWord* min_val = top; // Higher than any PLAB address
4935 uint min_tid = 0; // position of min_val this round
4936 for (int j = 0; j < no_of_gc_threads; j++) {
4937 ChunkArray* cur_sca = &_survivor_plab_array[j];
4938 if (_cursor[j] == cur_sca->end()) {
4939 continue;
4940 }
4941 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4942 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4943 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4944 if (cur_val < min_val) {
4945 min_tid = j;
4946 min_val = cur_val;
4947 } else {
4948 assert(cur_val < top, "All recorded addresses should be less");
4949 }
4950 }
4951 // At this point min_val and min_tid are respectively
4952 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4953 // and the thread (j) that witnesses that address.
4954 // We record this address in the _survivor_chunk_array[i]
4955 // and increment _cursor[min_tid] prior to the next round i.
4956 if (min_val == top) {
4957 break;
4958 }
4959 _survivor_chunk_array[i] = min_val;
4960 _cursor[min_tid]++;
4961 }
4962 // We are all done; record the size of the _survivor_chunk_array
4963 _survivor_chunk_index = i; // exclusive: [0, i)
4964 if (PrintCMSStatistics > 0) {
4965 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4966 }
4967 // Verify that we used up all the recorded entries
4968 #ifdef ASSERT
4969 size_t total = 0;
4970 for (int j = 0; j < no_of_gc_threads; j++) {
4971 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4972 total += _cursor[j];
4973 }
4974 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4975 // Check that the merged array is in sorted order
4976 if (total > 0) {
4977 for (size_t i = 0; i < total - 1; i++) {
4978 if (PrintCMSStatistics > 0) {
4979 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4980 i, p2i(_survivor_chunk_array[i]));
4981 }
4982 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4983 "Not sorted");
4984 }
4985 }
4986 #endif // ASSERT
4987 }
4988
4989 // Set up the space's par_seq_tasks structure for work claiming
4990 // for parallel initial scan and rescan of young gen.
4991 // See ParRescanTask where this is currently used.
4992 void
4993 CMSCollector::
4994 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4995 assert(n_threads > 0, "Unexpected n_threads argument");
4996
4997 // Eden space
4998 if (!_young_gen->eden()->is_empty()) {
4999 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
5000 assert(!pst->valid(), "Clobbering existing data?");
5001 // Each valid entry in [0, _eden_chunk_index) represents a task.
5002 size_t n_tasks = _eden_chunk_index + 1;
5003 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5004 // Sets the condition for completion of the subtask (how many threads
5005 // need to finish in order to be done).
5006 pst->set_n_threads(n_threads);
5007 pst->set_n_tasks((int)n_tasks);
5008 }
5009
5010 // Merge the survivor plab arrays into _survivor_chunk_array
5011 if (_survivor_plab_array != NULL) {
5012 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5013 } else {
5014 assert(_survivor_chunk_index == 0, "Error");
5015 }
5016
5017 // To space
5018 {
5019 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5020 assert(!pst->valid(), "Clobbering existing data?");
5021 // Sets the condition for completion of the subtask (how many threads
5022 // need to finish in order to be done).
5023 pst->set_n_threads(n_threads);
5024 pst->set_n_tasks(1);
5025 assert(pst->valid(), "Error");
5026 }
5027
5028 // From space
5029 {
5030 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5031 assert(!pst->valid(), "Clobbering existing data?");
5032 size_t n_tasks = _survivor_chunk_index + 1;
5033 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5034 // Sets the condition for completion of the subtask (how many threads
5035 // need to finish in order to be done).
5036 pst->set_n_threads(n_threads);
5037 pst->set_n_tasks((int)n_tasks);
5038 assert(pst->valid(), "Error");
5039 }
5040 }
5041
5042 // Parallel version of remark
5043 void CMSCollector::do_remark_parallel() {
5044 GenCollectedHeap* gch = GenCollectedHeap::heap();
5045 WorkGang* workers = gch->workers();
5046 assert(workers != NULL, "Need parallel worker threads.");
5047 // Choose to use the number of GC workers most recently set
5048 // into "active_workers".
5049 uint n_workers = workers->active_workers();
5050
5051 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5052
5053 StrongRootsScope srs(n_workers);
5054
5055 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
5056
5057 // We won't be iterating over the cards in the card table updating
5058 // the younger_gen cards, so we shouldn't call the following else
5059 // the verification code as well as subsequent younger_refs_iterate
5060 // code would get confused. XXX
5061 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5062
5063 // The young gen rescan work will not be done as part of
5064 // process_roots (which currently doesn't know how to
5065 // parallelize such a scan), but rather will be broken up into
5066 // a set of parallel tasks (via the sampling that the [abortable]
5067 // preclean phase did of eden, plus the [two] tasks of
5068 // scanning the [two] survivor spaces. Further fine-grain
5069 // parallelization of the scanning of the survivor spaces
5070 // themselves, and of precleaning of the young gen itself
5071 // is deferred to the future.
5072 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5073
5074 // The dirty card rescan work is broken up into a "sequence"
5075 // of parallel tasks (per constituent space) that are dynamically
5076 // claimed by the parallel threads.
5077 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5078
5079 // It turns out that even when we're using 1 thread, doing the work in a
5080 // separate thread causes wide variance in run times. We can't help this
5081 // in the multi-threaded case, but we special-case n=1 here to get
5082 // repeatable measurements of the 1-thread overhead of the parallel code.
5083 if (n_workers > 1) {
5084 // Make refs discovery MT-safe, if it isn't already: it may not
5085 // necessarily be so, since it's possible that we are doing
5086 // ST marking.
5087 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5088 workers->run_task(&tsk);
5089 } else {
5090 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5091 tsk.work(0);
5092 }
5093
5094 // restore, single-threaded for now, any preserved marks
5095 // as a result of work_q overflow
5096 restore_preserved_marks_if_any();
5097 }
5098
5099 // Non-parallel version of remark
5100 void CMSCollector::do_remark_non_parallel() {
5101 ResourceMark rm;
5102 HandleMark hm;
5103 GenCollectedHeap* gch = GenCollectedHeap::heap();
5104 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5105
5106 MarkRefsIntoAndScanClosure
5107 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5108 &_markStack, this,
5109 false /* should_yield */, false /* not precleaning */);
5110 MarkFromDirtyCardsClosure
5111 markFromDirtyCardsClosure(this, _span,
5112 NULL, // space is set further below
5113 &_markBitMap, &_markStack, &mrias_cl);
5114 {
5115 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm);
5116 // Iterate over the dirty cards, setting the corresponding bits in the
5117 // mod union table.
5118 {
5119 ModUnionClosure modUnionClosure(&_modUnionTable);
5120 _ct->ct_bs()->dirty_card_iterate(
5121 _cmsGen->used_region(),
5122 &modUnionClosure);
5123 }
5124 // Having transferred these marks into the modUnionTable, we just need
5125 // to rescan the marked objects on the dirty cards in the modUnionTable.
5126 // The initial marking may have been done during an asynchronous
5127 // collection so there may be dirty bits in the mod-union table.
5128 const int alignment =
5129 CardTableModRefBS::card_size * BitsPerWord;
5130 {
5131 // ... First handle dirty cards in CMS gen
5132 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5133 MemRegion ur = _cmsGen->used_region();
5134 HeapWord* lb = ur.start();
5135 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5136 MemRegion cms_span(lb, ub);
5137 _modUnionTable.dirty_range_iterate_clear(cms_span,
5138 &markFromDirtyCardsClosure);
5139 verify_work_stacks_empty();
5140 if (PrintCMSStatistics != 0) {
5141 gclog_or_tty->print(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ",
5142 markFromDirtyCardsClosure.num_dirty_cards());
5143 }
5144 }
5145 }
5146 if (VerifyDuringGC &&
5147 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5148 HandleMark hm; // Discard invalid handles created during verification
5149 Universe::verify();
5150 }
5151 {
5152 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm);
5153
5154 verify_work_stacks_empty();
5155
5156 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5157 StrongRootsScope srs(1);
5158
5159 gch->gen_process_roots(&srs,
5160 GenCollectedHeap::OldGen,
5161 true, // young gen as roots
5162 GenCollectedHeap::ScanningOption(roots_scanning_options()),
5163 should_unload_classes(),
5164 &mrias_cl,
5165 NULL,
5166 NULL); // The dirty klasses will be handled below
5167
5168 assert(should_unload_classes()
5169 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5170 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5171 }
5172
5173 {
5174 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm);
5175
5176 verify_work_stacks_empty();
5177
5178 // Scan all class loader data objects that might have been introduced
5179 // during concurrent marking.
5180 ResourceMark rm;
5181 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5182 for (int i = 0; i < array->length(); i++) {
5183 mrias_cl.do_cld_nv(array->at(i));
5184 }
5185
5186 // We don't need to keep track of new CLDs anymore.
5187 ClassLoaderDataGraph::remember_new_clds(false);
5188
5189 verify_work_stacks_empty();
5190 }
5191
5192 {
5193 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm);
5194
5195 verify_work_stacks_empty();
5196
5197 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5198 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5199
5200 verify_work_stacks_empty();
5201 }
5202
5203 // We might have added oops to ClassLoaderData::_handles during the
5204 // concurrent marking phase. These oops point to newly allocated objects
5205 // that are guaranteed to be kept alive. Either by the direct allocation
5206 // code, or when the young collector processes the roots. Hence,
5207 // we don't have to revisit the _handles block during the remark phase.
5208
5209 verify_work_stacks_empty();
5210 // Restore evacuated mark words, if any, used for overflow list links
5211 if (!CMSOverflowEarlyRestoration) {
5212 restore_preserved_marks_if_any();
5213 }
5214 verify_overflow_empty();
5215 }
5216
5217 ////////////////////////////////////////////////////////
5218 // Parallel Reference Processing Task Proxy Class
5219 ////////////////////////////////////////////////////////
5220 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5221 OopTaskQueueSet* _queues;
5222 ParallelTaskTerminator _terminator;
5223 public:
5224 AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5225 AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5226 ParallelTaskTerminator* terminator() { return &_terminator; }
5227 OopTaskQueueSet* queues() { return _queues; }
5228 };
5229
5230 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5231 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5232 CMSCollector* _collector;
5233 CMSBitMap* _mark_bit_map;
5234 const MemRegion _span;
5235 ProcessTask& _task;
5236
5237 public:
5238 CMSRefProcTaskProxy(ProcessTask& task,
5239 CMSCollector* collector,
5240 const MemRegion& span,
5241 CMSBitMap* mark_bit_map,
5242 AbstractWorkGang* workers,
5243 OopTaskQueueSet* task_queues):
5244 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5245 task_queues,
5246 workers->active_workers()),
5247 _task(task),
5248 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5249 {
5250 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5251 "Inconsistency in _span");
5252 }
5253
5254 OopTaskQueueSet* task_queues() { return queues(); }
5255
5256 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5257
5258 void do_work_steal(int i,
5259 CMSParDrainMarkingStackClosure* drain,
5260 CMSParKeepAliveClosure* keep_alive,
5261 int* seed);
5262
5263 virtual void work(uint worker_id);
5264 };
5265
5266 void CMSRefProcTaskProxy::work(uint worker_id) {
5267 ResourceMark rm;
5268 HandleMark hm;
5269 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5270 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5271 _mark_bit_map,
5272 work_queue(worker_id));
5273 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5274 _mark_bit_map,
5275 work_queue(worker_id));
5276 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5277 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5278 if (_task.marks_oops_alive()) {
5279 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5280 _collector->hash_seed(worker_id));
5281 }
5282 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5283 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5284 }
5285
5286 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5287 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5288 EnqueueTask& _task;
5289
5290 public:
5291 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5292 : AbstractGangTask("Enqueue reference objects in parallel"),
5293 _task(task)
5294 { }
5295
5296 virtual void work(uint worker_id)
5297 {
5298 _task.work(worker_id);
5299 }
5300 };
5301
5302 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5303 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5304 _span(span),
5305 _bit_map(bit_map),
5306 _work_queue(work_queue),
5307 _mark_and_push(collector, span, bit_map, work_queue),
5308 _low_water_mark(MIN2((work_queue->max_elems()/4),
5309 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5310 { }
5311
5312 // . see if we can share work_queues with ParNew? XXX
5313 void CMSRefProcTaskProxy::do_work_steal(int i,
5314 CMSParDrainMarkingStackClosure* drain,
5315 CMSParKeepAliveClosure* keep_alive,
5316 int* seed) {
5317 OopTaskQueue* work_q = work_queue(i);
5318 NOT_PRODUCT(int num_steals = 0;)
5319 oop obj_to_scan;
5320
5321 while (true) {
5322 // Completely finish any left over work from (an) earlier round(s)
5323 drain->trim_queue(0);
5324 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5325 (size_t)ParGCDesiredObjsFromOverflowList);
5326 // Now check if there's any work in the overflow list
5327 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5328 // only affects the number of attempts made to get work from the
5329 // overflow list and does not affect the number of workers. Just
5330 // pass ParallelGCThreads so this behavior is unchanged.
5331 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5332 work_q,
5333 ParallelGCThreads)) {
5334 // Found something in global overflow list;
5335 // not yet ready to go stealing work from others.
5336 // We'd like to assert(work_q->size() != 0, ...)
5337 // because we just took work from the overflow list,
5338 // but of course we can't, since all of that might have
5339 // been already stolen from us.
5340 continue;
5341 }
5342 // Verify that we have no work before we resort to stealing
5343 assert(work_q->size() == 0, "Have work, shouldn't steal");
5344 // Try to steal from other queues that have work
5345 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5346 NOT_PRODUCT(num_steals++;)
5347 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5348 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5349 // Do scanning work
5350 obj_to_scan->oop_iterate(keep_alive);
5351 // Loop around, finish this work, and try to steal some more
5352 } else if (terminator()->offer_termination()) {
5353 break; // nirvana from the infinite cycle
5354 }
5355 }
5356 NOT_PRODUCT(
5357 if (PrintCMSStatistics != 0) {
5358 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5359 }
5360 )
5361 }
5362
5363 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5364 {
5365 GenCollectedHeap* gch = GenCollectedHeap::heap();
5366 WorkGang* workers = gch->workers();
5367 assert(workers != NULL, "Need parallel worker threads.");
5368 CMSRefProcTaskProxy rp_task(task, &_collector,
5369 _collector.ref_processor()->span(),
5370 _collector.markBitMap(),
5371 workers, _collector.task_queues());
5372 workers->run_task(&rp_task);
5373 }
5374
5375 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5376 {
5377
5378 GenCollectedHeap* gch = GenCollectedHeap::heap();
5379 WorkGang* workers = gch->workers();
5380 assert(workers != NULL, "Need parallel worker threads.");
5381 CMSRefEnqueueTaskProxy enq_task(task);
5382 workers->run_task(&enq_task);
5383 }
5384
5385 void CMSCollector::refProcessingWork() {
5386 ResourceMark rm;
5387 HandleMark hm;
5388
5389 ReferenceProcessor* rp = ref_processor();
5390 assert(rp->span().equals(_span), "Spans should be equal");
5391 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5392 // Process weak references.
5393 rp->setup_policy(false);
5394 verify_work_stacks_empty();
5395
5396 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5397 &_markStack, false /* !preclean */);
5398 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5399 _span, &_markBitMap, &_markStack,
5400 &cmsKeepAliveClosure, false /* !preclean */);
5401 {
5402 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm);
5403
5404 ReferenceProcessorStats stats;
5405 if (rp->processing_is_mt()) {
5406 // Set the degree of MT here. If the discovery is done MT, there
5407 // may have been a different number of threads doing the discovery
5408 // and a different number of discovered lists may have Ref objects.
5409 // That is OK as long as the Reference lists are balanced (see
5410 // balance_all_queues() and balance_queues()).
5411 GenCollectedHeap* gch = GenCollectedHeap::heap();
5412 uint active_workers = ParallelGCThreads;
5413 WorkGang* workers = gch->workers();
5414 if (workers != NULL) {
5415 active_workers = workers->active_workers();
5416 // The expectation is that active_workers will have already
5417 // been set to a reasonable value. If it has not been set,
5418 // investigate.
5419 assert(active_workers > 0, "Should have been set during scavenge");
5420 }
5421 rp->set_active_mt_degree(active_workers);
5422 CMSRefProcTaskExecutor task_executor(*this);
5423 stats = rp->process_discovered_references(&_is_alive_closure,
5424 &cmsKeepAliveClosure,
5425 &cmsDrainMarkingStackClosure,
5426 &task_executor,
5427 _gc_timer_cm);
5428 } else {
5429 stats = rp->process_discovered_references(&_is_alive_closure,
5430 &cmsKeepAliveClosure,
5431 &cmsDrainMarkingStackClosure,
5432 NULL,
5433 _gc_timer_cm);
5434 }
5435 _gc_tracer_cm->report_gc_reference_stats(stats);
5436
5437 }
5438
5439 // This is the point where the entire marking should have completed.
5440 verify_work_stacks_empty();
5441
5442 if (should_unload_classes()) {
5443 {
5444 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm);
5445
5446 // Unload classes and purge the SystemDictionary.
5447 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5448
5449 // Unload nmethods.
5450 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5451
5452 // Prune dead klasses from subklass/sibling/implementor lists.
5453 Klass::clean_weak_klass_links(&_is_alive_closure);
5454 }
5455
5456 {
5457 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm);
5458 // Clean up unreferenced symbols in symbol table.
5459 SymbolTable::unlink();
5460 }
5461
5462 {
5463 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm);
5464 // Delete entries for dead interned strings.
5465 StringTable::unlink(&_is_alive_closure);
5466 }
5467 }
5468
5469
5470 // Restore any preserved marks as a result of mark stack or
5471 // work queue overflow
5472 restore_preserved_marks_if_any(); // done single-threaded for now
5473
5474 rp->set_enqueuing_is_done(true);
5475 if (rp->processing_is_mt()) {
5476 rp->balance_all_queues();
5477 CMSRefProcTaskExecutor task_executor(*this);
5478 rp->enqueue_discovered_references(&task_executor);
5479 } else {
5480 rp->enqueue_discovered_references(NULL);
5481 }
5482 rp->verify_no_references_recorded();
5483 assert(!rp->discovery_enabled(), "should have been disabled");
5484 }
5485
5486 #ifndef PRODUCT
5487 void CMSCollector::check_correct_thread_executing() {
5488 Thread* t = Thread::current();
5489 // Only the VM thread or the CMS thread should be here.
5490 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5491 "Unexpected thread type");
5492 // If this is the vm thread, the foreground process
5493 // should not be waiting. Note that _foregroundGCIsActive is
5494 // true while the foreground collector is waiting.
5495 if (_foregroundGCShouldWait) {
5496 // We cannot be the VM thread
5497 assert(t->is_ConcurrentGC_thread(),
5498 "Should be CMS thread");
5499 } else {
5500 // We can be the CMS thread only if we are in a stop-world
5501 // phase of CMS collection.
5502 if (t->is_ConcurrentGC_thread()) {
5503 assert(_collectorState == InitialMarking ||
5504 _collectorState == FinalMarking,
5505 "Should be a stop-world phase");
5506 // The CMS thread should be holding the CMS_token.
5507 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5508 "Potential interference with concurrently "
5509 "executing VM thread");
5510 }
5511 }
5512 }
5513 #endif
5514
5515 void CMSCollector::sweep() {
5516 assert(_collectorState == Sweeping, "just checking");
5517 check_correct_thread_executing();
5518 verify_work_stacks_empty();
5519 verify_overflow_empty();
5520 increment_sweep_count();
5521 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5522
5523 _inter_sweep_timer.stop();
5524 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5525
5526 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5527 _intra_sweep_timer.reset();
5528 _intra_sweep_timer.start();
5529 {
5530 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5531 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
5532 // First sweep the old gen
5533 {
5534 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5535 bitMapLock());
5536 sweepWork(_cmsGen);
5537 }
5538
5539 // Update Universe::_heap_*_at_gc figures.
5540 // We need all the free list locks to make the abstract state
5541 // transition from Sweeping to Resetting. See detailed note
5542 // further below.
5543 {
5544 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5545 // Update heap occupancy information which is used as
5546 // input to soft ref clearing policy at the next gc.
5547 Universe::update_heap_info_at_gc();
5548 _collectorState = Resizing;
5549 }
5550 }
5551 verify_work_stacks_empty();
5552 verify_overflow_empty();
5553
5554 if (should_unload_classes()) {
5555 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5556 // requires that the virtual spaces are stable and not deleted.
5557 ClassLoaderDataGraph::set_should_purge(true);
5558 }
5559
5560 _intra_sweep_timer.stop();
5561 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5562
5563 _inter_sweep_timer.reset();
5564 _inter_sweep_timer.start();
5565
5566 // We need to use a monotonically non-decreasing time in ms
5567 // or we will see time-warp warnings and os::javaTimeMillis()
5568 // does not guarantee monotonicity.
5569 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5570 update_time_of_last_gc(now);
5571
5572 // NOTE on abstract state transitions:
5573 // Mutators allocate-live and/or mark the mod-union table dirty
5574 // based on the state of the collection. The former is done in
5575 // the interval [Marking, Sweeping] and the latter in the interval
5576 // [Marking, Sweeping). Thus the transitions into the Marking state
5577 // and out of the Sweeping state must be synchronously visible
5578 // globally to the mutators.
5579 // The transition into the Marking state happens with the world
5580 // stopped so the mutators will globally see it. Sweeping is
5581 // done asynchronously by the background collector so the transition
5582 // from the Sweeping state to the Resizing state must be done
5583 // under the freelistLock (as is the check for whether to
5584 // allocate-live and whether to dirty the mod-union table).
5585 assert(_collectorState == Resizing, "Change of collector state to"
5586 " Resizing must be done under the freelistLocks (plural)");
5587
5588 // Now that sweeping has been completed, we clear
5589 // the incremental_collection_failed flag,
5590 // thus inviting a younger gen collection to promote into
5591 // this generation. If such a promotion may still fail,
5592 // the flag will be set again when a young collection is
5593 // attempted.
5594 GenCollectedHeap* gch = GenCollectedHeap::heap();
5595 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5596 gch->update_full_collections_completed(_collection_count_start);
5597 }
5598
5599 // FIX ME!!! Looks like this belongs in CFLSpace, with
5600 // CMSGen merely delegating to it.
5601 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5602 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5603 HeapWord* minAddr = _cmsSpace->bottom();
5604 HeapWord* largestAddr =
5605 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5606 if (largestAddr == NULL) {
5607 // The dictionary appears to be empty. In this case
5608 // try to coalesce at the end of the heap.
5609 largestAddr = _cmsSpace->end();
5610 }
5611 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5612 size_t nearLargestOffset =
5613 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5614 if (PrintFLSStatistics != 0) {
5615 gclog_or_tty->print_cr(
5616 "CMS: Large Block: " PTR_FORMAT ";"
5617 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5618 p2i(largestAddr),
5619 p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5620 }
5621 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5622 }
5623
5624 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5625 return addr >= _cmsSpace->nearLargestChunk();
5626 }
5627
5628 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5629 return _cmsSpace->find_chunk_at_end();
5630 }
5631
5632 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5633 bool full) {
5634 // If the young generation has been collected, gather any statistics
5635 // that are of interest at this point.
5636 bool current_is_young = GenCollectedHeap::heap()->is_young_gen(current_generation);
5637 if (!full && current_is_young) {
5638 // Gather statistics on the young generation collection.
5639 collector()->stats().record_gc0_end(used());
5640 }
5641 }
5642
5643 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5644 // We iterate over the space(s) underlying this generation,
5645 // checking the mark bit map to see if the bits corresponding
5646 // to specific blocks are marked or not. Blocks that are
5647 // marked are live and are not swept up. All remaining blocks
5648 // are swept up, with coalescing on-the-fly as we sweep up
5649 // contiguous free and/or garbage blocks:
5650 // We need to ensure that the sweeper synchronizes with allocators
5651 // and stop-the-world collectors. In particular, the following
5652 // locks are used:
5653 // . CMS token: if this is held, a stop the world collection cannot occur
5654 // . freelistLock: if this is held no allocation can occur from this
5655 // generation by another thread
5656 // . bitMapLock: if this is held, no other thread can access or update
5657 //
5658
5659 // Note that we need to hold the freelistLock if we use
5660 // block iterate below; else the iterator might go awry if
5661 // a mutator (or promotion) causes block contents to change
5662 // (for instance if the allocator divvies up a block).
5663 // If we hold the free list lock, for all practical purposes
5664 // young generation GC's can't occur (they'll usually need to
5665 // promote), so we might as well prevent all young generation
5666 // GC's while we do a sweeping step. For the same reason, we might
5667 // as well take the bit map lock for the entire duration
5668
5669 // check that we hold the requisite locks
5670 assert(have_cms_token(), "Should hold cms token");
5671 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5672 assert_lock_strong(old_gen->freelistLock());
5673 assert_lock_strong(bitMapLock());
5674
5675 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5676 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5677 old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5678 _inter_sweep_estimate.padded_average(),
5679 _intra_sweep_estimate.padded_average());
5680 old_gen->setNearLargestChunk();
5681
5682 {
5683 SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5684 old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5685 // We need to free-up/coalesce garbage/blocks from a
5686 // co-terminal free run. This is done in the SweepClosure
5687 // destructor; so, do not remove this scope, else the
5688 // end-of-sweep-census below will be off by a little bit.
5689 }
5690 old_gen->cmsSpace()->sweep_completed();
5691 old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5692 if (should_unload_classes()) { // unloaded classes this cycle,
5693 _concurrent_cycles_since_last_unload = 0; // ... reset count
5694 } else { // did not unload classes,
5695 _concurrent_cycles_since_last_unload++; // ... increment count
5696 }
5697 }
5698
5699 // Reset CMS data structures (for now just the marking bit map)
5700 // preparatory for the next cycle.
5701 void CMSCollector::reset(bool concurrent) {
5702 if (concurrent) {
5703 CMSTokenSyncWithLocks ts(true, bitMapLock());
5704
5705 // If the state is not "Resetting", the foreground thread
5706 // has done a collection and the resetting.
5707 if (_collectorState != Resetting) {
5708 assert(_collectorState == Idling, "The state should only change"
5709 " because the foreground collector has finished the collection");
5710 return;
5711 }
5712
5713 // Clear the mark bitmap (no grey objects to start with)
5714 // for the next cycle.
5715 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5716 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
5717
5718 HeapWord* curAddr = _markBitMap.startWord();
5719 while (curAddr < _markBitMap.endWord()) {
5720 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5721 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5722 _markBitMap.clear_large_range(chunk);
5723 if (ConcurrentMarkSweepThread::should_yield() &&
5724 !foregroundGCIsActive() &&
5725 CMSYield) {
5726 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5727 "CMS thread should hold CMS token");
5728 assert_lock_strong(bitMapLock());
5729 bitMapLock()->unlock();
5730 ConcurrentMarkSweepThread::desynchronize(true);
5731 stopTimer();
5732 if (PrintCMSStatistics != 0) {
5733 incrementYields();
5734 }
5735
5736 // See the comment in coordinator_yield()
5737 for (unsigned i = 0; i < CMSYieldSleepCount &&
5738 ConcurrentMarkSweepThread::should_yield() &&
5739 !CMSCollector::foregroundGCIsActive(); ++i) {
5740 os::sleep(Thread::current(), 1, false);
5741 }
5742
5743 ConcurrentMarkSweepThread::synchronize(true);
5744 bitMapLock()->lock_without_safepoint_check();
5745 startTimer();
5746 }
5747 curAddr = chunk.end();
5748 }
5749 // A successful mostly concurrent collection has been done.
5750 // Because only the full (i.e., concurrent mode failure) collections
5751 // are being measured for gc overhead limits, clean the "near" flag
5752 // and count.
5753 size_policy()->reset_gc_overhead_limit_count();
5754 _collectorState = Idling;
5755 } else {
5756 // already have the lock
5757 assert(_collectorState == Resetting, "just checking");
5758 assert_lock_strong(bitMapLock());
5759 _markBitMap.clear_all();
5760 _collectorState = Idling;
5761 }
5762
5763 register_gc_end();
5764 }
5765
5766 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5767 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5768 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL);
5769 TraceCollectorStats tcs(counters());
5770
5771 switch (op) {
5772 case CMS_op_checkpointRootsInitial: {
5773 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5774 checkpointRootsInitial();
5775 if (PrintGC) {
5776 _cmsGen->printOccupancy("initial-mark");
5777 }
5778 break;
5779 }
5780 case CMS_op_checkpointRootsFinal: {
5781 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5782 checkpointRootsFinal();
5783 if (PrintGC) {
5784 _cmsGen->printOccupancy("remark");
5785 }
5786 break;
5787 }
5788 default:
5789 fatal("No such CMS_op");
5790 }
5791 }
5792
5793 #ifndef PRODUCT
5794 size_t const CMSCollector::skip_header_HeapWords() {
5795 return FreeChunk::header_size();
5796 }
5797
5798 // Try and collect here conditions that should hold when
5799 // CMS thread is exiting. The idea is that the foreground GC
5800 // thread should not be blocked if it wants to terminate
5801 // the CMS thread and yet continue to run the VM for a while
5802 // after that.
5803 void CMSCollector::verify_ok_to_terminate() const {
5804 assert(Thread::current()->is_ConcurrentGC_thread(),
5805 "should be called by CMS thread");
5806 assert(!_foregroundGCShouldWait, "should be false");
5807 // We could check here that all the various low-level locks
5808 // are not held by the CMS thread, but that is overkill; see
5809 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5810 // is checked.
5811 }
5812 #endif
5813
5814 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5815 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5816 "missing Printezis mark?");
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
5825 // A variant of the above (block_size_using_printezis_bits()) except
5826 // that we return 0 if the P-bits are not yet set.
5827 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5828 if (_markBitMap.isMarked(addr + 1)) {
5829 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5830 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5831 size_t size = pointer_delta(nextOneAddr + 1, addr);
5832 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5833 "alignment problem");
5834 assert(size >= 3, "Necessary for Printezis marks to work");
5835 return size;
5836 }
5837 return 0;
5838 }
5839
5840 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5841 size_t sz = 0;
5842 oop p = (oop)addr;
5843 if (p->klass_or_null() != NULL) {
5844 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5845 } else {
5846 sz = block_size_using_printezis_bits(addr);
5847 }
5848 assert(sz > 0, "size must be nonzero");
5849 HeapWord* next_block = addr + sz;
5850 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
5851 CardTableModRefBS::card_size);
5852 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
5853 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5854 "must be different cards");
5855 return next_card;
5856 }
5857
5858
5859 // CMS Bit Map Wrapper /////////////////////////////////////////
5860
5861 // Construct a CMS bit map infrastructure, but don't create the
5862 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5863 // further below.
5864 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5865 _bm(),
5866 _shifter(shifter),
5867 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5868 Monitor::_safepoint_check_sometimes) : NULL)
5869 {
5870 _bmStartWord = 0;
5871 _bmWordSize = 0;
5872 }
5873
5874 bool CMSBitMap::allocate(MemRegion mr) {
5875 _bmStartWord = mr.start();
5876 _bmWordSize = mr.word_size();
5877 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5878 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5879 if (!brs.is_reserved()) {
5880 warning("CMS bit map allocation failure");
5881 return false;
5882 }
5883 // For now we'll just commit all of the bit map up front.
5884 // Later on we'll try to be more parsimonious with swap.
5885 if (!_virtual_space.initialize(brs, brs.size())) {
5886 warning("CMS bit map backing store failure");
5887 return false;
5888 }
5889 assert(_virtual_space.committed_size() == brs.size(),
5890 "didn't reserve backing store for all of CMS bit map?");
5891 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5892 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5893 _bmWordSize, "inconsistency in bit map sizing");
5894 _bm.set_size(_bmWordSize >> _shifter);
5895
5896 // bm.clear(); // can we rely on getting zero'd memory? verify below
5897 assert(isAllClear(),
5898 "Expected zero'd memory from ReservedSpace constructor");
5899 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5900 "consistency check");
5901 return true;
5902 }
5903
5904 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5905 HeapWord *next_addr, *end_addr, *last_addr;
5906 assert_locked();
5907 assert(covers(mr), "out-of-range error");
5908 // XXX assert that start and end are appropriately aligned
5909 for (next_addr = mr.start(), end_addr = mr.end();
5910 next_addr < end_addr; next_addr = last_addr) {
5911 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5912 last_addr = dirty_region.end();
5913 if (!dirty_region.is_empty()) {
5914 cl->do_MemRegion(dirty_region);
5915 } else {
5916 assert(last_addr == end_addr, "program logic");
5917 return;
5918 }
5919 }
5920 }
5921
5922 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5923 _bm.print_on_error(st, prefix);
5924 }
5925
5926 #ifndef PRODUCT
5927 void CMSBitMap::assert_locked() const {
5928 CMSLockVerifier::assert_locked(lock());
5929 }
5930
5931 bool CMSBitMap::covers(MemRegion mr) const {
5932 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5933 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5934 "size inconsistency");
5935 return (mr.start() >= _bmStartWord) &&
5936 (mr.end() <= endWord());
5937 }
5938
5939 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5940 return (start >= _bmStartWord && (start + size) <= endWord());
5941 }
5942
5943 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5944 // verify that there are no 1 bits in the interval [left, right)
5945 FalseBitMapClosure falseBitMapClosure;
5946 iterate(&falseBitMapClosure, left, right);
5947 }
5948
5949 void CMSBitMap::region_invariant(MemRegion mr)
5950 {
5951 assert_locked();
5952 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5953 assert(!mr.is_empty(), "unexpected empty region");
5954 assert(covers(mr), "mr should be covered by bit map");
5955 // convert address range into offset range
5956 size_t start_ofs = heapWordToOffset(mr.start());
5957 // Make sure that end() is appropriately aligned
5958 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5959 (1 << (_shifter+LogHeapWordSize))),
5960 "Misaligned mr.end()");
5961 size_t end_ofs = heapWordToOffset(mr.end());
5962 assert(end_ofs > start_ofs, "Should mark at least one bit");
5963 }
5964
5965 #endif
5966
5967 bool CMSMarkStack::allocate(size_t size) {
5968 // allocate a stack of the requisite depth
5969 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5970 size * sizeof(oop)));
5971 if (!rs.is_reserved()) {
5972 warning("CMSMarkStack allocation failure");
5973 return false;
5974 }
5975 if (!_virtual_space.initialize(rs, rs.size())) {
5976 warning("CMSMarkStack backing store failure");
5977 return false;
5978 }
5979 assert(_virtual_space.committed_size() == rs.size(),
5980 "didn't reserve backing store for all of CMS stack?");
5981 _base = (oop*)(_virtual_space.low());
5982 _index = 0;
5983 _capacity = size;
5984 NOT_PRODUCT(_max_depth = 0);
5985 return true;
5986 }
5987
5988 // XXX FIX ME !!! In the MT case we come in here holding a
5989 // leaf lock. For printing we need to take a further lock
5990 // which has lower rank. We need to recalibrate the two
5991 // lock-ranks involved in order to be able to print the
5992 // messages below. (Or defer the printing to the caller.
5993 // For now we take the expedient path of just disabling the
5994 // messages for the problematic case.)
5995 void CMSMarkStack::expand() {
5996 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5997 if (_capacity == MarkStackSizeMax) {
5998 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
5999 // We print a warning message only once per CMS cycle.
6000 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6001 }
6002 return;
6003 }
6004 // Double capacity if possible
6005 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6006 // Do not give up existing stack until we have managed to
6007 // get the double capacity that we desired.
6008 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6009 new_capacity * sizeof(oop)));
6010 if (rs.is_reserved()) {
6011 // Release the backing store associated with old stack
6012 _virtual_space.release();
6013 // Reinitialize virtual space for new stack
6014 if (!_virtual_space.initialize(rs, rs.size())) {
6015 fatal("Not enough swap for expanded marking stack");
6016 }
6017 _base = (oop*)(_virtual_space.low());
6018 _index = 0;
6019 _capacity = new_capacity;
6020 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6021 // Failed to double capacity, continue;
6022 // we print a detail message only once per CMS cycle.
6023 gclog_or_tty->print(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to "
6024 SIZE_FORMAT "K",
6025 _capacity / K, new_capacity / K);
6026 }
6027 }
6028
6029
6030 // Closures
6031 // XXX: there seems to be a lot of code duplication here;
6032 // should refactor and consolidate common code.
6033
6034 // This closure is used to mark refs into the CMS generation in
6035 // the CMS bit map. Called at the first checkpoint. This closure
6036 // assumes that we do not need to re-mark dirty cards; if the CMS
6037 // generation on which this is used is not an oldest
6038 // generation then this will lose younger_gen cards!
6039
6040 MarkRefsIntoClosure::MarkRefsIntoClosure(
6041 MemRegion span, CMSBitMap* bitMap):
6042 _span(span),
6043 _bitMap(bitMap)
6044 {
6045 assert(_ref_processor == NULL, "deliberately left NULL");
6046 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6047 }
6048
6049 void MarkRefsIntoClosure::do_oop(oop obj) {
6050 // if p points into _span, then mark corresponding bit in _markBitMap
6051 assert(obj->is_oop(), "expected an oop");
6052 HeapWord* addr = (HeapWord*)obj;
6053 if (_span.contains(addr)) {
6054 // this should be made more efficient
6055 _bitMap->mark(addr);
6056 }
6057 }
6058
6059 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6060 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6061
6062 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6063 MemRegion span, CMSBitMap* bitMap):
6064 _span(span),
6065 _bitMap(bitMap)
6066 {
6067 assert(_ref_processor == NULL, "deliberately left NULL");
6068 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6069 }
6070
6071 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6072 // if p points into _span, then mark corresponding bit in _markBitMap
6073 assert(obj->is_oop(), "expected an oop");
6074 HeapWord* addr = (HeapWord*)obj;
6075 if (_span.contains(addr)) {
6076 // this should be made more efficient
6077 _bitMap->par_mark(addr);
6078 }
6079 }
6080
6081 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6082 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6083
6084 // A variant of the above, used for CMS marking verification.
6085 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6086 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6087 _span(span),
6088 _verification_bm(verification_bm),
6089 _cms_bm(cms_bm)
6090 {
6091 assert(_ref_processor == NULL, "deliberately left NULL");
6092 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6093 }
6094
6095 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6096 // if p points into _span, then mark corresponding bit in _markBitMap
6097 assert(obj->is_oop(), "expected an oop");
6098 HeapWord* addr = (HeapWord*)obj;
6099 if (_span.contains(addr)) {
6100 _verification_bm->mark(addr);
6101 if (!_cms_bm->isMarked(addr)) {
6102 oop(addr)->print();
6103 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6104 fatal("... aborting");
6105 }
6106 }
6107 }
6108
6109 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6110 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6111
6112 //////////////////////////////////////////////////
6113 // MarkRefsIntoAndScanClosure
6114 //////////////////////////////////////////////////
6115
6116 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6117 ReferenceProcessor* rp,
6118 CMSBitMap* bit_map,
6119 CMSBitMap* mod_union_table,
6120 CMSMarkStack* mark_stack,
6121 CMSCollector* collector,
6122 bool should_yield,
6123 bool concurrent_precleaning):
6124 _collector(collector),
6125 _span(span),
6126 _bit_map(bit_map),
6127 _mark_stack(mark_stack),
6128 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6129 mark_stack, concurrent_precleaning),
6130 _yield(should_yield),
6131 _concurrent_precleaning(concurrent_precleaning),
6132 _freelistLock(NULL)
6133 {
6134 _ref_processor = rp;
6135 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6136 }
6137
6138 // This closure is used to mark refs into the CMS generation at the
6139 // second (final) checkpoint, and to scan and transitively follow
6140 // the unmarked oops. It is also used during the concurrent precleaning
6141 // phase while scanning objects on dirty cards in the CMS generation.
6142 // The marks are made in the marking bit map and the marking stack is
6143 // used for keeping the (newly) grey objects during the scan.
6144 // The parallel version (Par_...) appears further below.
6145 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6146 if (obj != NULL) {
6147 assert(obj->is_oop(), "expected an oop");
6148 HeapWord* addr = (HeapWord*)obj;
6149 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6150 assert(_collector->overflow_list_is_empty(),
6151 "overflow list should be empty");
6152 if (_span.contains(addr) &&
6153 !_bit_map->isMarked(addr)) {
6154 // mark bit map (object is now grey)
6155 _bit_map->mark(addr);
6156 // push on marking stack (stack should be empty), and drain the
6157 // stack by applying this closure to the oops in the oops popped
6158 // from the stack (i.e. blacken the grey objects)
6159 bool res = _mark_stack->push(obj);
6160 assert(res, "Should have space to push on empty stack");
6161 do {
6162 oop new_oop = _mark_stack->pop();
6163 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6164 assert(_bit_map->isMarked((HeapWord*)new_oop),
6165 "only grey objects on this stack");
6166 // iterate over the oops in this oop, marking and pushing
6167 // the ones in CMS heap (i.e. in _span).
6168 new_oop->oop_iterate(&_pushAndMarkClosure);
6169 // check if it's time to yield
6170 do_yield_check();
6171 } while (!_mark_stack->isEmpty() ||
6172 (!_concurrent_precleaning && take_from_overflow_list()));
6173 // if marking stack is empty, and we are not doing this
6174 // during precleaning, then check the overflow list
6175 }
6176 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6177 assert(_collector->overflow_list_is_empty(),
6178 "overflow list was drained above");
6179 // We could restore evacuated mark words, if any, used for
6180 // overflow list links here because the overflow list is
6181 // provably empty here. That would reduce the maximum
6182 // size requirements for preserved_{oop,mark}_stack.
6183 // But we'll just postpone it until we are all done
6184 // so we can just stream through.
6185 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6186 _collector->restore_preserved_marks_if_any();
6187 assert(_collector->no_preserved_marks(), "No preserved marks");
6188 }
6189 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6190 "All preserved marks should have been restored above");
6191 }
6192 }
6193
6194 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6195 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6196
6197 void MarkRefsIntoAndScanClosure::do_yield_work() {
6198 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6199 "CMS thread should hold CMS token");
6200 assert_lock_strong(_freelistLock);
6201 assert_lock_strong(_bit_map->lock());
6202 // relinquish the free_list_lock and bitMaplock()
6203 _bit_map->lock()->unlock();
6204 _freelistLock->unlock();
6205 ConcurrentMarkSweepThread::desynchronize(true);
6206 _collector->stopTimer();
6207 if (PrintCMSStatistics != 0) {
6208 _collector->incrementYields();
6209 }
6210
6211 // See the comment in coordinator_yield()
6212 for (unsigned i = 0;
6213 i < CMSYieldSleepCount &&
6214 ConcurrentMarkSweepThread::should_yield() &&
6215 !CMSCollector::foregroundGCIsActive();
6216 ++i) {
6217 os::sleep(Thread::current(), 1, false);
6218 }
6219
6220 ConcurrentMarkSweepThread::synchronize(true);
6221 _freelistLock->lock_without_safepoint_check();
6222 _bit_map->lock()->lock_without_safepoint_check();
6223 _collector->startTimer();
6224 }
6225
6226 ///////////////////////////////////////////////////////////
6227 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6228 // MarkRefsIntoAndScanClosure
6229 ///////////////////////////////////////////////////////////
6230 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6231 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6232 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6233 _span(span),
6234 _bit_map(bit_map),
6235 _work_queue(work_queue),
6236 _low_water_mark(MIN2((work_queue->max_elems()/4),
6237 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6238 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6239 {
6240 _ref_processor = rp;
6241 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6242 }
6243
6244 // This closure is used to mark refs into the CMS generation at the
6245 // second (final) checkpoint, and to scan and transitively follow
6246 // the unmarked oops. The marks are made in the marking bit map and
6247 // the work_queue is used for keeping the (newly) grey objects during
6248 // the scan phase whence they are also available for stealing by parallel
6249 // threads. Since the marking bit map is shared, updates are
6250 // synchronized (via CAS).
6251 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6252 if (obj != NULL) {
6253 // Ignore mark word because this could be an already marked oop
6254 // that may be chained at the end of the overflow list.
6255 assert(obj->is_oop(true), "expected an oop");
6256 HeapWord* addr = (HeapWord*)obj;
6257 if (_span.contains(addr) &&
6258 !_bit_map->isMarked(addr)) {
6259 // mark bit map (object will become grey):
6260 // It is possible for several threads to be
6261 // trying to "claim" this object concurrently;
6262 // the unique thread that succeeds in marking the
6263 // object first will do the subsequent push on
6264 // to the work queue (or overflow list).
6265 if (_bit_map->par_mark(addr)) {
6266 // push on work_queue (which may not be empty), and trim the
6267 // queue to an appropriate length by applying this closure to
6268 // the oops in the oops popped from the stack (i.e. blacken the
6269 // grey objects)
6270 bool res = _work_queue->push(obj);
6271 assert(res, "Low water mark should be less than capacity?");
6272 trim_queue(_low_water_mark);
6273 } // Else, another thread claimed the object
6274 }
6275 }
6276 }
6277
6278 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6279 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6280
6281 // This closure is used to rescan the marked objects on the dirty cards
6282 // in the mod union table and the card table proper.
6283 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6284 oop p, MemRegion mr) {
6285
6286 size_t size = 0;
6287 HeapWord* addr = (HeapWord*)p;
6288 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6289 assert(_span.contains(addr), "we are scanning the CMS generation");
6290 // check if it's time to yield
6291 if (do_yield_check()) {
6292 // We yielded for some foreground stop-world work,
6293 // and we have been asked to abort this ongoing preclean cycle.
6294 return 0;
6295 }
6296 if (_bitMap->isMarked(addr)) {
6297 // it's marked; is it potentially uninitialized?
6298 if (p->klass_or_null() != NULL) {
6299 // an initialized object; ignore mark word in verification below
6300 // since we are running concurrent with mutators
6301 assert(p->is_oop(true), "should be an oop");
6302 if (p->is_objArray()) {
6303 // objArrays are precisely marked; restrict scanning
6304 // to dirty cards only.
6305 size = CompactibleFreeListSpace::adjustObjectSize(
6306 p->oop_iterate_size(_scanningClosure, mr));
6307 } else {
6308 // A non-array may have been imprecisely marked; we need
6309 // to scan object in its entirety.
6310 size = CompactibleFreeListSpace::adjustObjectSize(
6311 p->oop_iterate_size(_scanningClosure));
6312 }
6313 #ifdef ASSERT
6314 size_t direct_size =
6315 CompactibleFreeListSpace::adjustObjectSize(p->size());
6316 assert(size == direct_size, "Inconsistency in size");
6317 assert(size >= 3, "Necessary for Printezis marks to work");
6318 if (!_bitMap->isMarked(addr+1)) {
6319 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6320 } else {
6321 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6322 assert(_bitMap->isMarked(addr+size-1),
6323 "inconsistent Printezis mark");
6324 }
6325 #endif // ASSERT
6326 } else {
6327 // An uninitialized object.
6328 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6329 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6330 size = pointer_delta(nextOneAddr + 1, addr);
6331 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6332 "alignment problem");
6333 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6334 // will dirty the card when the klass pointer is installed in the
6335 // object (signaling the completion of initialization).
6336 }
6337 } else {
6338 // Either a not yet marked object or an uninitialized object
6339 if (p->klass_or_null() == NULL) {
6340 // An uninitialized object, skip to the next card, since
6341 // we may not be able to read its P-bits yet.
6342 assert(size == 0, "Initial value");
6343 } else {
6344 // An object not (yet) reached by marking: we merely need to
6345 // compute its size so as to go look at the next block.
6346 assert(p->is_oop(true), "should be an oop");
6347 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6348 }
6349 }
6350 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6351 return size;
6352 }
6353
6354 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6355 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6356 "CMS thread should hold CMS token");
6357 assert_lock_strong(_freelistLock);
6358 assert_lock_strong(_bitMap->lock());
6359 // relinquish the free_list_lock and bitMaplock()
6360 _bitMap->lock()->unlock();
6361 _freelistLock->unlock();
6362 ConcurrentMarkSweepThread::desynchronize(true);
6363 _collector->stopTimer();
6364 if (PrintCMSStatistics != 0) {
6365 _collector->incrementYields();
6366 }
6367
6368 // See the comment in coordinator_yield()
6369 for (unsigned i = 0; i < CMSYieldSleepCount &&
6370 ConcurrentMarkSweepThread::should_yield() &&
6371 !CMSCollector::foregroundGCIsActive(); ++i) {
6372 os::sleep(Thread::current(), 1, false);
6373 }
6374
6375 ConcurrentMarkSweepThread::synchronize(true);
6376 _freelistLock->lock_without_safepoint_check();
6377 _bitMap->lock()->lock_without_safepoint_check();
6378 _collector->startTimer();
6379 }
6380
6381
6382 //////////////////////////////////////////////////////////////////
6383 // SurvivorSpacePrecleanClosure
6384 //////////////////////////////////////////////////////////////////
6385 // This (single-threaded) closure is used to preclean the oops in
6386 // the survivor spaces.
6387 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6388
6389 HeapWord* addr = (HeapWord*)p;
6390 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6391 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6392 assert(p->klass_or_null() != NULL, "object should be initialized");
6393 // an initialized object; ignore mark word in verification below
6394 // since we are running concurrent with mutators
6395 assert(p->is_oop(true), "should be an oop");
6396 // Note that we do not yield while we iterate over
6397 // the interior oops of p, pushing the relevant ones
6398 // on our marking stack.
6399 size_t size = p->oop_iterate_size(_scanning_closure);
6400 do_yield_check();
6401 // Observe that below, we do not abandon the preclean
6402 // phase as soon as we should; rather we empty the
6403 // marking stack before returning. This is to satisfy
6404 // some existing assertions. In general, it may be a
6405 // good idea to abort immediately and complete the marking
6406 // from the grey objects at a later time.
6407 while (!_mark_stack->isEmpty()) {
6408 oop new_oop = _mark_stack->pop();
6409 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6410 assert(_bit_map->isMarked((HeapWord*)new_oop),
6411 "only grey objects on this stack");
6412 // iterate over the oops in this oop, marking and pushing
6413 // the ones in CMS heap (i.e. in _span).
6414 new_oop->oop_iterate(_scanning_closure);
6415 // check if it's time to yield
6416 do_yield_check();
6417 }
6418 unsigned int after_count =
6419 GenCollectedHeap::heap()->total_collections();
6420 bool abort = (_before_count != after_count) ||
6421 _collector->should_abort_preclean();
6422 return abort ? 0 : size;
6423 }
6424
6425 void SurvivorSpacePrecleanClosure::do_yield_work() {
6426 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6427 "CMS thread should hold CMS token");
6428 assert_lock_strong(_bit_map->lock());
6429 // Relinquish the bit map lock
6430 _bit_map->lock()->unlock();
6431 ConcurrentMarkSweepThread::desynchronize(true);
6432 _collector->stopTimer();
6433 if (PrintCMSStatistics != 0) {
6434 _collector->incrementYields();
6435 }
6436
6437 // See the comment in coordinator_yield()
6438 for (unsigned i = 0; i < CMSYieldSleepCount &&
6439 ConcurrentMarkSweepThread::should_yield() &&
6440 !CMSCollector::foregroundGCIsActive(); ++i) {
6441 os::sleep(Thread::current(), 1, false);
6442 }
6443
6444 ConcurrentMarkSweepThread::synchronize(true);
6445 _bit_map->lock()->lock_without_safepoint_check();
6446 _collector->startTimer();
6447 }
6448
6449 // This closure is used to rescan the marked objects on the dirty cards
6450 // in the mod union table and the card table proper. In the parallel
6451 // case, although the bitMap is shared, we do a single read so the
6452 // isMarked() query is "safe".
6453 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6454 // Ignore mark word because we are running concurrent with mutators
6455 assert(p->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6456 HeapWord* addr = (HeapWord*)p;
6457 assert(_span.contains(addr), "we are scanning the CMS generation");
6458 bool is_obj_array = false;
6459 #ifdef ASSERT
6460 if (!_parallel) {
6461 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6462 assert(_collector->overflow_list_is_empty(),
6463 "overflow list should be empty");
6464
6465 }
6466 #endif // ASSERT
6467 if (_bit_map->isMarked(addr)) {
6468 // Obj arrays are precisely marked, non-arrays are not;
6469 // so we scan objArrays precisely and non-arrays in their
6470 // entirety.
6471 if (p->is_objArray()) {
6472 is_obj_array = true;
6473 if (_parallel) {
6474 p->oop_iterate(_par_scan_closure, mr);
6475 } else {
6476 p->oop_iterate(_scan_closure, mr);
6477 }
6478 } else {
6479 if (_parallel) {
6480 p->oop_iterate(_par_scan_closure);
6481 } else {
6482 p->oop_iterate(_scan_closure);
6483 }
6484 }
6485 }
6486 #ifdef ASSERT
6487 if (!_parallel) {
6488 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6489 assert(_collector->overflow_list_is_empty(),
6490 "overflow list should be empty");
6491
6492 }
6493 #endif // ASSERT
6494 return is_obj_array;
6495 }
6496
6497 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6498 MemRegion span,
6499 CMSBitMap* bitMap, CMSMarkStack* markStack,
6500 bool should_yield, bool verifying):
6501 _collector(collector),
6502 _span(span),
6503 _bitMap(bitMap),
6504 _mut(&collector->_modUnionTable),
6505 _markStack(markStack),
6506 _yield(should_yield),
6507 _skipBits(0)
6508 {
6509 assert(_markStack->isEmpty(), "stack should be empty");
6510 _finger = _bitMap->startWord();
6511 _threshold = _finger;
6512 assert(_collector->_restart_addr == NULL, "Sanity check");
6513 assert(_span.contains(_finger), "Out of bounds _finger?");
6514 DEBUG_ONLY(_verifying = verifying;)
6515 }
6516
6517 void MarkFromRootsClosure::reset(HeapWord* addr) {
6518 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6519 assert(_span.contains(addr), "Out of bounds _finger?");
6520 _finger = addr;
6521 _threshold = (HeapWord*)round_to(
6522 (intptr_t)_finger, CardTableModRefBS::card_size);
6523 }
6524
6525 // Should revisit to see if this should be restructured for
6526 // greater efficiency.
6527 bool MarkFromRootsClosure::do_bit(size_t offset) {
6528 if (_skipBits > 0) {
6529 _skipBits--;
6530 return true;
6531 }
6532 // convert offset into a HeapWord*
6533 HeapWord* addr = _bitMap->startWord() + offset;
6534 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6535 "address out of range");
6536 assert(_bitMap->isMarked(addr), "tautology");
6537 if (_bitMap->isMarked(addr+1)) {
6538 // this is an allocated but not yet initialized object
6539 assert(_skipBits == 0, "tautology");
6540 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6541 oop p = oop(addr);
6542 if (p->klass_or_null() == NULL) {
6543 DEBUG_ONLY(if (!_verifying) {)
6544 // We re-dirty the cards on which this object lies and increase
6545 // the _threshold so that we'll come back to scan this object
6546 // during the preclean or remark phase. (CMSCleanOnEnter)
6547 if (CMSCleanOnEnter) {
6548 size_t sz = _collector->block_size_using_printezis_bits(addr);
6549 HeapWord* end_card_addr = (HeapWord*)round_to(
6550 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6551 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6552 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6553 // Bump _threshold to end_card_addr; note that
6554 // _threshold cannot possibly exceed end_card_addr, anyhow.
6555 // This prevents future clearing of the card as the scan proceeds
6556 // to the right.
6557 assert(_threshold <= end_card_addr,
6558 "Because we are just scanning into this object");
6559 if (_threshold < end_card_addr) {
6560 _threshold = end_card_addr;
6561 }
6562 if (p->klass_or_null() != NULL) {
6563 // Redirty the range of cards...
6564 _mut->mark_range(redirty_range);
6565 } // ...else the setting of klass will dirty the card anyway.
6566 }
6567 DEBUG_ONLY(})
6568 return true;
6569 }
6570 }
6571 scanOopsInOop(addr);
6572 return true;
6573 }
6574
6575 // We take a break if we've been at this for a while,
6576 // so as to avoid monopolizing the locks involved.
6577 void MarkFromRootsClosure::do_yield_work() {
6578 // First give up the locks, then yield, then re-lock
6579 // We should probably use a constructor/destructor idiom to
6580 // do this unlock/lock or modify the MutexUnlocker class to
6581 // serve our purpose. XXX
6582 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6583 "CMS thread should hold CMS token");
6584 assert_lock_strong(_bitMap->lock());
6585 _bitMap->lock()->unlock();
6586 ConcurrentMarkSweepThread::desynchronize(true);
6587 _collector->stopTimer();
6588 if (PrintCMSStatistics != 0) {
6589 _collector->incrementYields();
6590 }
6591
6592 // See the comment in coordinator_yield()
6593 for (unsigned i = 0; i < CMSYieldSleepCount &&
6594 ConcurrentMarkSweepThread::should_yield() &&
6595 !CMSCollector::foregroundGCIsActive(); ++i) {
6596 os::sleep(Thread::current(), 1, false);
6597 }
6598
6599 ConcurrentMarkSweepThread::synchronize(true);
6600 _bitMap->lock()->lock_without_safepoint_check();
6601 _collector->startTimer();
6602 }
6603
6604 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6605 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6606 assert(_markStack->isEmpty(),
6607 "should drain stack to limit stack usage");
6608 // convert ptr to an oop preparatory to scanning
6609 oop obj = oop(ptr);
6610 // Ignore mark word in verification below, since we
6611 // may be running concurrent with mutators.
6612 assert(obj->is_oop(true), "should be an oop");
6613 assert(_finger <= ptr, "_finger runneth ahead");
6614 // advance the finger to right end of this object
6615 _finger = ptr + obj->size();
6616 assert(_finger > ptr, "we just incremented it above");
6617 // On large heaps, it may take us some time to get through
6618 // the marking phase. During
6619 // this time it's possible that a lot of mutations have
6620 // accumulated in the card table and the mod union table --
6621 // these mutation records are redundant until we have
6622 // actually traced into the corresponding card.
6623 // Here, we check whether advancing the finger would make
6624 // us cross into a new card, and if so clear corresponding
6625 // cards in the MUT (preclean them in the card-table in the
6626 // future).
6627
6628 DEBUG_ONLY(if (!_verifying) {)
6629 // The clean-on-enter optimization is disabled by default,
6630 // until we fix 6178663.
6631 if (CMSCleanOnEnter && (_finger > _threshold)) {
6632 // [_threshold, _finger) represents the interval
6633 // of cards to be cleared in MUT (or precleaned in card table).
6634 // The set of cards to be cleared is all those that overlap
6635 // with the interval [_threshold, _finger); note that
6636 // _threshold is always kept card-aligned but _finger isn't
6637 // always card-aligned.
6638 HeapWord* old_threshold = _threshold;
6639 assert(old_threshold == (HeapWord*)round_to(
6640 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6641 "_threshold should always be card-aligned");
6642 _threshold = (HeapWord*)round_to(
6643 (intptr_t)_finger, CardTableModRefBS::card_size);
6644 MemRegion mr(old_threshold, _threshold);
6645 assert(!mr.is_empty(), "Control point invariant");
6646 assert(_span.contains(mr), "Should clear within span");
6647 _mut->clear_range(mr);
6648 }
6649 DEBUG_ONLY(})
6650 // Note: the finger doesn't advance while we drain
6651 // the stack below.
6652 PushOrMarkClosure pushOrMarkClosure(_collector,
6653 _span, _bitMap, _markStack,
6654 _finger, this);
6655 bool res = _markStack->push(obj);
6656 assert(res, "Empty non-zero size stack should have space for single push");
6657 while (!_markStack->isEmpty()) {
6658 oop new_oop = _markStack->pop();
6659 // Skip verifying header mark word below because we are
6660 // running concurrent with mutators.
6661 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6662 // now scan this oop's oops
6663 new_oop->oop_iterate(&pushOrMarkClosure);
6664 do_yield_check();
6665 }
6666 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6667 }
6668
6669 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6670 CMSCollector* collector, MemRegion span,
6671 CMSBitMap* bit_map,
6672 OopTaskQueue* work_queue,
6673 CMSMarkStack* overflow_stack):
6674 _collector(collector),
6675 _whole_span(collector->_span),
6676 _span(span),
6677 _bit_map(bit_map),
6678 _mut(&collector->_modUnionTable),
6679 _work_queue(work_queue),
6680 _overflow_stack(overflow_stack),
6681 _skip_bits(0),
6682 _task(task)
6683 {
6684 assert(_work_queue->size() == 0, "work_queue should be empty");
6685 _finger = span.start();
6686 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6687 assert(_span.contains(_finger), "Out of bounds _finger?");
6688 }
6689
6690 // Should revisit to see if this should be restructured for
6691 // greater efficiency.
6692 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6693 if (_skip_bits > 0) {
6694 _skip_bits--;
6695 return true;
6696 }
6697 // convert offset into a HeapWord*
6698 HeapWord* addr = _bit_map->startWord() + offset;
6699 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6700 "address out of range");
6701 assert(_bit_map->isMarked(addr), "tautology");
6702 if (_bit_map->isMarked(addr+1)) {
6703 // this is an allocated object that might not yet be initialized
6704 assert(_skip_bits == 0, "tautology");
6705 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6706 oop p = oop(addr);
6707 if (p->klass_or_null() == NULL) {
6708 // in the case of Clean-on-Enter optimization, redirty card
6709 // and avoid clearing card by increasing the threshold.
6710 return true;
6711 }
6712 }
6713 scan_oops_in_oop(addr);
6714 return true;
6715 }
6716
6717 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6718 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6719 // Should we assert that our work queue is empty or
6720 // below some drain limit?
6721 assert(_work_queue->size() == 0,
6722 "should drain stack to limit stack usage");
6723 // convert ptr to an oop preparatory to scanning
6724 oop obj = oop(ptr);
6725 // Ignore mark word in verification below, since we
6726 // may be running concurrent with mutators.
6727 assert(obj->is_oop(true), "should be an oop");
6728 assert(_finger <= ptr, "_finger runneth ahead");
6729 // advance the finger to right end of this object
6730 _finger = ptr + obj->size();
6731 assert(_finger > ptr, "we just incremented it above");
6732 // On large heaps, it may take us some time to get through
6733 // the marking phase. During
6734 // this time it's possible that a lot of mutations have
6735 // accumulated in the card table and the mod union table --
6736 // these mutation records are redundant until we have
6737 // actually traced into the corresponding card.
6738 // Here, we check whether advancing the finger would make
6739 // us cross into a new card, and if so clear corresponding
6740 // cards in the MUT (preclean them in the card-table in the
6741 // future).
6742
6743 // The clean-on-enter optimization is disabled by default,
6744 // until we fix 6178663.
6745 if (CMSCleanOnEnter && (_finger > _threshold)) {
6746 // [_threshold, _finger) represents the interval
6747 // of cards to be cleared in MUT (or precleaned in card table).
6748 // The set of cards to be cleared is all those that overlap
6749 // with the interval [_threshold, _finger); note that
6750 // _threshold is always kept card-aligned but _finger isn't
6751 // always card-aligned.
6752 HeapWord* old_threshold = _threshold;
6753 assert(old_threshold == (HeapWord*)round_to(
6754 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6755 "_threshold should always be card-aligned");
6756 _threshold = (HeapWord*)round_to(
6757 (intptr_t)_finger, CardTableModRefBS::card_size);
6758 MemRegion mr(old_threshold, _threshold);
6759 assert(!mr.is_empty(), "Control point invariant");
6760 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6761 _mut->clear_range(mr);
6762 }
6763
6764 // Note: the local finger doesn't advance while we drain
6765 // the stack below, but the global finger sure can and will.
6766 HeapWord** gfa = _task->global_finger_addr();
6767 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6768 _span, _bit_map,
6769 _work_queue,
6770 _overflow_stack,
6771 _finger,
6772 gfa, this);
6773 bool res = _work_queue->push(obj); // overflow could occur here
6774 assert(res, "Will hold once we use workqueues");
6775 while (true) {
6776 oop new_oop;
6777 if (!_work_queue->pop_local(new_oop)) {
6778 // We emptied our work_queue; check if there's stuff that can
6779 // be gotten from the overflow stack.
6780 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6781 _overflow_stack, _work_queue)) {
6782 do_yield_check();
6783 continue;
6784 } else { // done
6785 break;
6786 }
6787 }
6788 // Skip verifying header mark word below because we are
6789 // running concurrent with mutators.
6790 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6791 // now scan this oop's oops
6792 new_oop->oop_iterate(&pushOrMarkClosure);
6793 do_yield_check();
6794 }
6795 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6796 }
6797
6798 // Yield in response to a request from VM Thread or
6799 // from mutators.
6800 void Par_MarkFromRootsClosure::do_yield_work() {
6801 assert(_task != NULL, "sanity");
6802 _task->yield();
6803 }
6804
6805 // A variant of the above used for verifying CMS marking work.
6806 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6807 MemRegion span,
6808 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6809 CMSMarkStack* mark_stack):
6810 _collector(collector),
6811 _span(span),
6812 _verification_bm(verification_bm),
6813 _cms_bm(cms_bm),
6814 _mark_stack(mark_stack),
6815 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6816 mark_stack)
6817 {
6818 assert(_mark_stack->isEmpty(), "stack should be empty");
6819 _finger = _verification_bm->startWord();
6820 assert(_collector->_restart_addr == NULL, "Sanity check");
6821 assert(_span.contains(_finger), "Out of bounds _finger?");
6822 }
6823
6824 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6825 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6826 assert(_span.contains(addr), "Out of bounds _finger?");
6827 _finger = addr;
6828 }
6829
6830 // Should revisit to see if this should be restructured for
6831 // greater efficiency.
6832 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6833 // convert offset into a HeapWord*
6834 HeapWord* addr = _verification_bm->startWord() + offset;
6835 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6836 "address out of range");
6837 assert(_verification_bm->isMarked(addr), "tautology");
6838 assert(_cms_bm->isMarked(addr), "tautology");
6839
6840 assert(_mark_stack->isEmpty(),
6841 "should drain stack to limit stack usage");
6842 // convert addr to an oop preparatory to scanning
6843 oop obj = oop(addr);
6844 assert(obj->is_oop(), "should be an oop");
6845 assert(_finger <= addr, "_finger runneth ahead");
6846 // advance the finger to right end of this object
6847 _finger = addr + obj->size();
6848 assert(_finger > addr, "we just incremented it above");
6849 // Note: the finger doesn't advance while we drain
6850 // the stack below.
6851 bool res = _mark_stack->push(obj);
6852 assert(res, "Empty non-zero size stack should have space for single push");
6853 while (!_mark_stack->isEmpty()) {
6854 oop new_oop = _mark_stack->pop();
6855 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6856 // now scan this oop's oops
6857 new_oop->oop_iterate(&_pam_verify_closure);
6858 }
6859 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6860 return true;
6861 }
6862
6863 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6864 CMSCollector* collector, MemRegion span,
6865 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6866 CMSMarkStack* mark_stack):
6867 MetadataAwareOopClosure(collector->ref_processor()),
6868 _collector(collector),
6869 _span(span),
6870 _verification_bm(verification_bm),
6871 _cms_bm(cms_bm),
6872 _mark_stack(mark_stack)
6873 { }
6874
6875 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6876 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6877
6878 // Upon stack overflow, we discard (part of) the stack,
6879 // remembering the least address amongst those discarded
6880 // in CMSCollector's _restart_address.
6881 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6882 // Remember the least grey address discarded
6883 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6884 _collector->lower_restart_addr(ra);
6885 _mark_stack->reset(); // discard stack contents
6886 _mark_stack->expand(); // expand the stack if possible
6887 }
6888
6889 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6890 assert(obj->is_oop_or_null(), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6891 HeapWord* addr = (HeapWord*)obj;
6892 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6893 // Oop lies in _span and isn't yet grey or black
6894 _verification_bm->mark(addr); // now grey
6895 if (!_cms_bm->isMarked(addr)) {
6896 oop(addr)->print();
6897 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
6898 p2i(addr));
6899 fatal("... aborting");
6900 }
6901
6902 if (!_mark_stack->push(obj)) { // stack overflow
6903 if (PrintCMSStatistics != 0) {
6904 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6905 SIZE_FORMAT, _mark_stack->capacity());
6906 }
6907 assert(_mark_stack->isFull(), "Else push should have succeeded");
6908 handle_stack_overflow(addr);
6909 }
6910 // anything including and to the right of _finger
6911 // will be scanned as we iterate over the remainder of the
6912 // bit map
6913 }
6914 }
6915
6916 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6917 MemRegion span,
6918 CMSBitMap* bitMap, CMSMarkStack* markStack,
6919 HeapWord* finger, MarkFromRootsClosure* parent) :
6920 MetadataAwareOopClosure(collector->ref_processor()),
6921 _collector(collector),
6922 _span(span),
6923 _bitMap(bitMap),
6924 _markStack(markStack),
6925 _finger(finger),
6926 _parent(parent)
6927 { }
6928
6929 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
6930 MemRegion span,
6931 CMSBitMap* bit_map,
6932 OopTaskQueue* work_queue,
6933 CMSMarkStack* overflow_stack,
6934 HeapWord* finger,
6935 HeapWord** global_finger_addr,
6936 Par_MarkFromRootsClosure* parent) :
6937 MetadataAwareOopClosure(collector->ref_processor()),
6938 _collector(collector),
6939 _whole_span(collector->_span),
6940 _span(span),
6941 _bit_map(bit_map),
6942 _work_queue(work_queue),
6943 _overflow_stack(overflow_stack),
6944 _finger(finger),
6945 _global_finger_addr(global_finger_addr),
6946 _parent(parent)
6947 { }
6948
6949 // Assumes thread-safe access by callers, who are
6950 // responsible for mutual exclusion.
6951 void CMSCollector::lower_restart_addr(HeapWord* low) {
6952 assert(_span.contains(low), "Out of bounds addr");
6953 if (_restart_addr == NULL) {
6954 _restart_addr = low;
6955 } else {
6956 _restart_addr = MIN2(_restart_addr, low);
6957 }
6958 }
6959
6960 // Upon stack overflow, we discard (part of) the stack,
6961 // remembering the least address amongst those discarded
6962 // in CMSCollector's _restart_address.
6963 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6964 // Remember the least grey address discarded
6965 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6966 _collector->lower_restart_addr(ra);
6967 _markStack->reset(); // discard stack contents
6968 _markStack->expand(); // expand the stack if possible
6969 }
6970
6971 // Upon stack overflow, we discard (part of) the stack,
6972 // remembering the least address amongst those discarded
6973 // in CMSCollector's _restart_address.
6974 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6975 // We need to do this under a mutex to prevent other
6976 // workers from interfering with the work done below.
6977 MutexLockerEx ml(_overflow_stack->par_lock(),
6978 Mutex::_no_safepoint_check_flag);
6979 // Remember the least grey address discarded
6980 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6981 _collector->lower_restart_addr(ra);
6982 _overflow_stack->reset(); // discard stack contents
6983 _overflow_stack->expand(); // expand the stack if possible
6984 }
6985
6986 void PushOrMarkClosure::do_oop(oop obj) {
6987 // Ignore mark word because we are running concurrent with mutators.
6988 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6989 HeapWord* addr = (HeapWord*)obj;
6990 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6991 // Oop lies in _span and isn't yet grey or black
6992 _bitMap->mark(addr); // now grey
6993 if (addr < _finger) {
6994 // the bit map iteration has already either passed, or
6995 // sampled, this bit in the bit map; we'll need to
6996 // use the marking stack to scan this oop's oops.
6997 bool simulate_overflow = false;
6998 NOT_PRODUCT(
6999 if (CMSMarkStackOverflowALot &&
7000 _collector->simulate_overflow()) {
7001 // simulate a stack overflow
7002 simulate_overflow = true;
7003 }
7004 )
7005 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7006 if (PrintCMSStatistics != 0) {
7007 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7008 SIZE_FORMAT, _markStack->capacity());
7009 }
7010 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7011 handle_stack_overflow(addr);
7012 }
7013 }
7014 // anything including and to the right of _finger
7015 // will be scanned as we iterate over the remainder of the
7016 // bit map
7017 do_yield_check();
7018 }
7019 }
7020
7021 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7022 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7023
7024 void Par_PushOrMarkClosure::do_oop(oop obj) {
7025 // Ignore mark word because we are running concurrent with mutators.
7026 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
7027 HeapWord* addr = (HeapWord*)obj;
7028 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7029 // Oop lies in _span and isn't yet grey or black
7030 // We read the global_finger (volatile read) strictly after marking oop
7031 bool res = _bit_map->par_mark(addr); // now grey
7032 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7033 // Should we push this marked oop on our stack?
7034 // -- if someone else marked it, nothing to do
7035 // -- if target oop is above global finger nothing to do
7036 // -- if target oop is in chunk and above local finger
7037 // then nothing to do
7038 // -- else push on work queue
7039 if ( !res // someone else marked it, they will deal with it
7040 || (addr >= *gfa) // will be scanned in a later task
7041 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7042 return;
7043 }
7044 // the bit map iteration has already either passed, or
7045 // sampled, this bit in the bit map; we'll need to
7046 // use the marking stack to scan this oop's oops.
7047 bool simulate_overflow = false;
7048 NOT_PRODUCT(
7049 if (CMSMarkStackOverflowALot &&
7050 _collector->simulate_overflow()) {
7051 // simulate a stack overflow
7052 simulate_overflow = true;
7053 }
7054 )
7055 if (simulate_overflow ||
7056 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7057 // stack overflow
7058 if (PrintCMSStatistics != 0) {
7059 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7060 SIZE_FORMAT, _overflow_stack->capacity());
7061 }
7062 // We cannot assert that the overflow stack is full because
7063 // it may have been emptied since.
7064 assert(simulate_overflow ||
7065 _work_queue->size() == _work_queue->max_elems(),
7066 "Else push should have succeeded");
7067 handle_stack_overflow(addr);
7068 }
7069 do_yield_check();
7070 }
7071 }
7072
7073 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7074 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7075
7076 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7077 MemRegion span,
7078 ReferenceProcessor* rp,
7079 CMSBitMap* bit_map,
7080 CMSBitMap* mod_union_table,
7081 CMSMarkStack* mark_stack,
7082 bool concurrent_precleaning):
7083 MetadataAwareOopClosure(rp),
7084 _collector(collector),
7085 _span(span),
7086 _bit_map(bit_map),
7087 _mod_union_table(mod_union_table),
7088 _mark_stack(mark_stack),
7089 _concurrent_precleaning(concurrent_precleaning)
7090 {
7091 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7092 }
7093
7094 // Grey object rescan during pre-cleaning and second checkpoint phases --
7095 // the non-parallel version (the parallel version appears further below.)
7096 void PushAndMarkClosure::do_oop(oop obj) {
7097 // Ignore mark word verification. If during concurrent precleaning,
7098 // the object monitor may be locked. If during the checkpoint
7099 // phases, the object may already have been reached by a different
7100 // path and may be at the end of the global overflow list (so
7101 // the mark word may be NULL).
7102 assert(obj->is_oop_or_null(true /* ignore mark word */),
7103 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
7104 HeapWord* addr = (HeapWord*)obj;
7105 // Check if oop points into the CMS generation
7106 // and is not marked
7107 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7108 // a white object ...
7109 _bit_map->mark(addr); // ... now grey
7110 // push on the marking stack (grey set)
7111 bool simulate_overflow = false;
7112 NOT_PRODUCT(
7113 if (CMSMarkStackOverflowALot &&
7114 _collector->simulate_overflow()) {
7115 // simulate a stack overflow
7116 simulate_overflow = true;
7117 }
7118 )
7119 if (simulate_overflow || !_mark_stack->push(obj)) {
7120 if (_concurrent_precleaning) {
7121 // During precleaning we can just dirty the appropriate card(s)
7122 // in the mod union table, thus ensuring that the object remains
7123 // in the grey set and continue. In the case of object arrays
7124 // we need to dirty all of the cards that the object spans,
7125 // since the rescan of object arrays will be limited to the
7126 // dirty cards.
7127 // Note that no one can be interfering with us in this action
7128 // of dirtying the mod union table, so no locking or atomics
7129 // are required.
7130 if (obj->is_objArray()) {
7131 size_t sz = obj->size();
7132 HeapWord* end_card_addr = (HeapWord*)round_to(
7133 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7134 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7135 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7136 _mod_union_table->mark_range(redirty_range);
7137 } else {
7138 _mod_union_table->mark(addr);
7139 }
7140 _collector->_ser_pmc_preclean_ovflw++;
7141 } else {
7142 // During the remark phase, we need to remember this oop
7143 // in the overflow list.
7144 _collector->push_on_overflow_list(obj);
7145 _collector->_ser_pmc_remark_ovflw++;
7146 }
7147 }
7148 }
7149 }
7150
7151 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7152 MemRegion span,
7153 ReferenceProcessor* rp,
7154 CMSBitMap* bit_map,
7155 OopTaskQueue* work_queue):
7156 MetadataAwareOopClosure(rp),
7157 _collector(collector),
7158 _span(span),
7159 _bit_map(bit_map),
7160 _work_queue(work_queue)
7161 {
7162 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7163 }
7164
7165 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7166 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7167
7168 // Grey object rescan during second checkpoint phase --
7169 // the parallel version.
7170 void Par_PushAndMarkClosure::do_oop(oop obj) {
7171 // In the assert below, we ignore the mark word because
7172 // this oop may point to an already visited object that is
7173 // on the overflow stack (in which case the mark word has
7174 // been hijacked for chaining into the overflow stack --
7175 // if this is the last object in the overflow stack then
7176 // its mark word will be NULL). Because this object may
7177 // have been subsequently popped off the global overflow
7178 // stack, and the mark word possibly restored to the prototypical
7179 // value, by the time we get to examined this failing assert in
7180 // the debugger, is_oop_or_null(false) may subsequently start
7181 // to hold.
7182 assert(obj->is_oop_or_null(true),
7183 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
7184 HeapWord* addr = (HeapWord*)obj;
7185 // Check if oop points into the CMS generation
7186 // and is not marked
7187 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7188 // a white object ...
7189 // If we manage to "claim" the object, by being the
7190 // first thread to mark it, then we push it on our
7191 // marking stack
7192 if (_bit_map->par_mark(addr)) { // ... now grey
7193 // push on work queue (grey set)
7194 bool simulate_overflow = false;
7195 NOT_PRODUCT(
7196 if (CMSMarkStackOverflowALot &&
7197 _collector->par_simulate_overflow()) {
7198 // simulate a stack overflow
7199 simulate_overflow = true;
7200 }
7201 )
7202 if (simulate_overflow || !_work_queue->push(obj)) {
7203 _collector->par_push_on_overflow_list(obj);
7204 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7205 }
7206 } // Else, some other thread got there first
7207 }
7208 }
7209
7210 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7211 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7212
7213 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7214 Mutex* bml = _collector->bitMapLock();
7215 assert_lock_strong(bml);
7216 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7217 "CMS thread should hold CMS token");
7218
7219 bml->unlock();
7220 ConcurrentMarkSweepThread::desynchronize(true);
7221
7222 _collector->stopTimer();
7223 if (PrintCMSStatistics != 0) {
7224 _collector->incrementYields();
7225 }
7226
7227 // See the comment in coordinator_yield()
7228 for (unsigned i = 0; i < CMSYieldSleepCount &&
7229 ConcurrentMarkSweepThread::should_yield() &&
7230 !CMSCollector::foregroundGCIsActive(); ++i) {
7231 os::sleep(Thread::current(), 1, false);
7232 }
7233
7234 ConcurrentMarkSweepThread::synchronize(true);
7235 bml->lock();
7236
7237 _collector->startTimer();
7238 }
7239
7240 bool CMSPrecleanRefsYieldClosure::should_return() {
7241 if (ConcurrentMarkSweepThread::should_yield()) {
7242 do_yield_work();
7243 }
7244 return _collector->foregroundGCIsActive();
7245 }
7246
7247 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7248 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7249 "mr should be aligned to start at a card boundary");
7250 // We'd like to assert:
7251 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7252 // "mr should be a range of cards");
7253 // However, that would be too strong in one case -- the last
7254 // partition ends at _unallocated_block which, in general, can be
7255 // an arbitrary boundary, not necessarily card aligned.
7256 if (PrintCMSStatistics != 0) {
7257 _num_dirty_cards +=
7258 mr.word_size()/CardTableModRefBS::card_size_in_words;
7259 }
7260 _space->object_iterate_mem(mr, &_scan_cl);
7261 }
7262
7263 SweepClosure::SweepClosure(CMSCollector* collector,
7264 ConcurrentMarkSweepGeneration* g,
7265 CMSBitMap* bitMap, bool should_yield) :
7266 _collector(collector),
7267 _g(g),
7268 _sp(g->cmsSpace()),
7269 _limit(_sp->sweep_limit()),
7270 _freelistLock(_sp->freelistLock()),
7271 _bitMap(bitMap),
7272 _yield(should_yield),
7273 _inFreeRange(false), // No free range at beginning of sweep
7274 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7275 _lastFreeRangeCoalesced(false),
7276 _freeFinger(g->used_region().start())
7277 {
7278 NOT_PRODUCT(
7279 _numObjectsFreed = 0;
7280 _numWordsFreed = 0;
7281 _numObjectsLive = 0;
7282 _numWordsLive = 0;
7283 _numObjectsAlreadyFree = 0;
7284 _numWordsAlreadyFree = 0;
7285 _last_fc = NULL;
7286
7287 _sp->initializeIndexedFreeListArrayReturnedBytes();
7288 _sp->dictionary()->initialize_dict_returned_bytes();
7289 )
7290 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7291 "sweep _limit out of bounds");
7292 if (CMSTraceSweeper) {
7293 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7294 p2i(_limit));
7295 }
7296 }
7297
7298 void SweepClosure::print_on(outputStream* st) const {
7299 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7300 p2i(_sp->bottom()), p2i(_sp->end()));
7301 tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7302 tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7303 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7304 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7305 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7306 }
7307
7308 #ifndef PRODUCT
7309 // Assertion checking only: no useful work in product mode --
7310 // however, if any of the flags below become product flags,
7311 // you may need to review this code to see if it needs to be
7312 // enabled in product mode.
7313 SweepClosure::~SweepClosure() {
7314 assert_lock_strong(_freelistLock);
7315 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7316 "sweep _limit out of bounds");
7317 if (inFreeRange()) {
7318 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7319 print();
7320 ShouldNotReachHere();
7321 }
7322 if (Verbose && PrintGC) {
7323 gclog_or_tty->print("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7324 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7325 gclog_or_tty->print_cr("\nLive " SIZE_FORMAT " objects, "
7326 SIZE_FORMAT " bytes "
7327 "Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7328 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7329 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7330 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7331 * sizeof(HeapWord);
7332 gclog_or_tty->print_cr("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7333
7334 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7335 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7336 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7337 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7338 gclog_or_tty->print("Returned " SIZE_FORMAT " bytes", returned_bytes);
7339 gclog_or_tty->print(" Indexed List Returned " SIZE_FORMAT " bytes",
7340 indexListReturnedBytes);
7341 gclog_or_tty->print_cr(" Dictionary Returned " SIZE_FORMAT " bytes",
7342 dict_returned_bytes);
7343 }
7344 }
7345 if (CMSTraceSweeper) {
7346 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7347 p2i(_limit));
7348 }
7349 }
7350 #endif // PRODUCT
7351
7352 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7353 bool freeRangeInFreeLists) {
7354 if (CMSTraceSweeper) {
7355 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7356 p2i(freeFinger), freeRangeInFreeLists);
7357 }
7358 assert(!inFreeRange(), "Trampling existing free range");
7359 set_inFreeRange(true);
7360 set_lastFreeRangeCoalesced(false);
7361
7362 set_freeFinger(freeFinger);
7363 set_freeRangeInFreeLists(freeRangeInFreeLists);
7364 if (CMSTestInFreeList) {
7365 if (freeRangeInFreeLists) {
7366 FreeChunk* fc = (FreeChunk*) freeFinger;
7367 assert(fc->is_free(), "A chunk on the free list should be free.");
7368 assert(fc->size() > 0, "Free range should have a size");
7369 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7370 }
7371 }
7372 }
7373
7374 // Note that the sweeper runs concurrently with mutators. Thus,
7375 // it is possible for direct allocation in this generation to happen
7376 // in the middle of the sweep. Note that the sweeper also coalesces
7377 // contiguous free blocks. Thus, unless the sweeper and the allocator
7378 // synchronize appropriately freshly allocated blocks may get swept up.
7379 // This is accomplished by the sweeper locking the free lists while
7380 // it is sweeping. Thus blocks that are determined to be free are
7381 // indeed free. There is however one additional complication:
7382 // blocks that have been allocated since the final checkpoint and
7383 // mark, will not have been marked and so would be treated as
7384 // unreachable and swept up. To prevent this, the allocator marks
7385 // the bit map when allocating during the sweep phase. This leads,
7386 // however, to a further complication -- objects may have been allocated
7387 // but not yet initialized -- in the sense that the header isn't yet
7388 // installed. The sweeper can not then determine the size of the block
7389 // in order to skip over it. To deal with this case, we use a technique
7390 // (due to Printezis) to encode such uninitialized block sizes in the
7391 // bit map. Since the bit map uses a bit per every HeapWord, but the
7392 // CMS generation has a minimum object size of 3 HeapWords, it follows
7393 // that "normal marks" won't be adjacent in the bit map (there will
7394 // always be at least two 0 bits between successive 1 bits). We make use
7395 // of these "unused" bits to represent uninitialized blocks -- the bit
7396 // corresponding to the start of the uninitialized object and the next
7397 // bit are both set. Finally, a 1 bit marks the end of the object that
7398 // started with the two consecutive 1 bits to indicate its potentially
7399 // uninitialized state.
7400
7401 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7402 FreeChunk* fc = (FreeChunk*)addr;
7403 size_t res;
7404
7405 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7406 // than "addr == _limit" because although _limit was a block boundary when
7407 // we started the sweep, it may no longer be one because heap expansion
7408 // may have caused us to coalesce the block ending at the address _limit
7409 // with a newly expanded chunk (this happens when _limit was set to the
7410 // previous _end of the space), so we may have stepped past _limit:
7411 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7412 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7413 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7414 "sweep _limit out of bounds");
7415 assert(addr < _sp->end(), "addr out of bounds");
7416 // Flush any free range we might be holding as a single
7417 // coalesced chunk to the appropriate free list.
7418 if (inFreeRange()) {
7419 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7420 "freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger()));
7421 flush_cur_free_chunk(freeFinger(),
7422 pointer_delta(addr, freeFinger()));
7423 if (CMSTraceSweeper) {
7424 gclog_or_tty->print("Sweep: last chunk: ");
7425 gclog_or_tty->print("put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") "
7426 "[coalesced:%d]\n",
7427 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7428 lastFreeRangeCoalesced() ? 1 : 0);
7429 }
7430 }
7431
7432 // help the iterator loop finish
7433 return pointer_delta(_sp->end(), addr);
7434 }
7435
7436 assert(addr < _limit, "sweep invariant");
7437 // check if we should yield
7438 do_yield_check(addr);
7439 if (fc->is_free()) {
7440 // Chunk that is already free
7441 res = fc->size();
7442 do_already_free_chunk(fc);
7443 debug_only(_sp->verifyFreeLists());
7444 // If we flush the chunk at hand in lookahead_and_flush()
7445 // and it's coalesced with a preceding chunk, then the
7446 // process of "mangling" the payload of the coalesced block
7447 // will cause erasure of the size information from the
7448 // (erstwhile) header of all the coalesced blocks but the
7449 // first, so the first disjunct in the assert will not hold
7450 // in that specific case (in which case the second disjunct
7451 // will hold).
7452 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7453 "Otherwise the size info doesn't change at this step");
7454 NOT_PRODUCT(
7455 _numObjectsAlreadyFree++;
7456 _numWordsAlreadyFree += res;
7457 )
7458 NOT_PRODUCT(_last_fc = fc;)
7459 } else if (!_bitMap->isMarked(addr)) {
7460 // Chunk is fresh garbage
7461 res = do_garbage_chunk(fc);
7462 debug_only(_sp->verifyFreeLists());
7463 NOT_PRODUCT(
7464 _numObjectsFreed++;
7465 _numWordsFreed += res;
7466 )
7467 } else {
7468 // Chunk that is alive.
7469 res = do_live_chunk(fc);
7470 debug_only(_sp->verifyFreeLists());
7471 NOT_PRODUCT(
7472 _numObjectsLive++;
7473 _numWordsLive += res;
7474 )
7475 }
7476 return res;
7477 }
7478
7479 // For the smart allocation, record following
7480 // split deaths - a free chunk is removed from its free list because
7481 // it is being split into two or more chunks.
7482 // split birth - a free chunk is being added to its free list because
7483 // a larger free chunk has been split and resulted in this free chunk.
7484 // coal death - a free chunk is being removed from its free list because
7485 // it is being coalesced into a large free chunk.
7486 // coal birth - a free chunk is being added to its free list because
7487 // it was created when two or more free chunks where coalesced into
7488 // this free chunk.
7489 //
7490 // These statistics are used to determine the desired number of free
7491 // chunks of a given size. The desired number is chosen to be relative
7492 // to the end of a CMS sweep. The desired number at the end of a sweep
7493 // is the
7494 // count-at-end-of-previous-sweep (an amount that was enough)
7495 // - count-at-beginning-of-current-sweep (the excess)
7496 // + split-births (gains in this size during interval)
7497 // - split-deaths (demands on this size during interval)
7498 // where the interval is from the end of one sweep to the end of the
7499 // next.
7500 //
7501 // When sweeping the sweeper maintains an accumulated chunk which is
7502 // the chunk that is made up of chunks that have been coalesced. That
7503 // will be termed the left-hand chunk. A new chunk of garbage that
7504 // is being considered for coalescing will be referred to as the
7505 // right-hand chunk.
7506 //
7507 // When making a decision on whether to coalesce a right-hand chunk with
7508 // the current left-hand chunk, the current count vs. the desired count
7509 // of the left-hand chunk is considered. Also if the right-hand chunk
7510 // is near the large chunk at the end of the heap (see
7511 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7512 // left-hand chunk is coalesced.
7513 //
7514 // When making a decision about whether to split a chunk, the desired count
7515 // vs. the current count of the candidate to be split is also considered.
7516 // If the candidate is underpopulated (currently fewer chunks than desired)
7517 // a chunk of an overpopulated (currently more chunks than desired) size may
7518 // be chosen. The "hint" associated with a free list, if non-null, points
7519 // to a free list which may be overpopulated.
7520 //
7521
7522 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7523 const size_t size = fc->size();
7524 // Chunks that cannot be coalesced are not in the
7525 // free lists.
7526 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7527 assert(_sp->verify_chunk_in_free_list(fc),
7528 "free chunk should be in free lists");
7529 }
7530 // a chunk that is already free, should not have been
7531 // marked in the bit map
7532 HeapWord* const addr = (HeapWord*) fc;
7533 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7534 // Verify that the bit map has no bits marked between
7535 // addr and purported end of this block.
7536 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7537
7538 // Some chunks cannot be coalesced under any circumstances.
7539 // See the definition of cantCoalesce().
7540 if (!fc->cantCoalesce()) {
7541 // This chunk can potentially be coalesced.
7542 if (_sp->adaptive_freelists()) {
7543 // All the work is done in
7544 do_post_free_or_garbage_chunk(fc, size);
7545 } else { // Not adaptive free lists
7546 // this is a free chunk that can potentially be coalesced by the sweeper;
7547 if (!inFreeRange()) {
7548 // if the next chunk is a free block that can't be coalesced
7549 // it doesn't make sense to remove this chunk from the free lists
7550 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7551 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
7552 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
7553 nextChunk->is_free() && // ... which is free...
7554 nextChunk->cantCoalesce()) { // ... but can't be coalesced
7555 // nothing to do
7556 } else {
7557 // Potentially the start of a new free range:
7558 // Don't eagerly remove it from the free lists.
7559 // No need to remove it if it will just be put
7560 // back again. (Also from a pragmatic point of view
7561 // if it is a free block in a region that is beyond
7562 // any allocated blocks, an assertion will fail)
7563 // Remember the start of a free run.
7564 initialize_free_range(addr, true);
7565 // end - can coalesce with next chunk
7566 }
7567 } else {
7568 // the midst of a free range, we are coalescing
7569 print_free_block_coalesced(fc);
7570 if (CMSTraceSweeper) {
7571 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7572 }
7573 // remove it from the free lists
7574 _sp->removeFreeChunkFromFreeLists(fc);
7575 set_lastFreeRangeCoalesced(true);
7576 // If the chunk is being coalesced and the current free range is
7577 // in the free lists, remove the current free range so that it
7578 // will be returned to the free lists in its entirety - all
7579 // the coalesced pieces included.
7580 if (freeRangeInFreeLists()) {
7581 FreeChunk* ffc = (FreeChunk*) freeFinger();
7582 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7583 "Size of free range is inconsistent with chunk size.");
7584 if (CMSTestInFreeList) {
7585 assert(_sp->verify_chunk_in_free_list(ffc),
7586 "free range is not in free lists");
7587 }
7588 _sp->removeFreeChunkFromFreeLists(ffc);
7589 set_freeRangeInFreeLists(false);
7590 }
7591 }
7592 }
7593 // Note that if the chunk is not coalescable (the else arm
7594 // below), we unconditionally flush, without needing to do
7595 // a "lookahead," as we do below.
7596 if (inFreeRange()) lookahead_and_flush(fc, size);
7597 } else {
7598 // Code path common to both original and adaptive free lists.
7599
7600 // cant coalesce with previous block; this should be treated
7601 // as the end of a free run if any
7602 if (inFreeRange()) {
7603 // we kicked some butt; time to pick up the garbage
7604 assert(freeFinger() < addr, "freeFinger points too high");
7605 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7606 }
7607 // else, nothing to do, just continue
7608 }
7609 }
7610
7611 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7612 // This is a chunk of garbage. It is not in any free list.
7613 // Add it to a free list or let it possibly be coalesced into
7614 // a larger chunk.
7615 HeapWord* const addr = (HeapWord*) fc;
7616 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7617
7618 if (_sp->adaptive_freelists()) {
7619 // Verify that the bit map has no bits marked between
7620 // addr and purported end of just dead object.
7621 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7622
7623 do_post_free_or_garbage_chunk(fc, size);
7624 } else {
7625 if (!inFreeRange()) {
7626 // start of a new free range
7627 assert(size > 0, "A free range should have a size");
7628 initialize_free_range(addr, false);
7629 } else {
7630 // this will be swept up when we hit the end of the
7631 // free range
7632 if (CMSTraceSweeper) {
7633 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7634 }
7635 // If the chunk is being coalesced and the current free range is
7636 // in the free lists, remove the current free range so that it
7637 // will be returned to the free lists in its entirety - all
7638 // the coalesced pieces included.
7639 if (freeRangeInFreeLists()) {
7640 FreeChunk* ffc = (FreeChunk*)freeFinger();
7641 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7642 "Size of free range is inconsistent with chunk size.");
7643 if (CMSTestInFreeList) {
7644 assert(_sp->verify_chunk_in_free_list(ffc),
7645 "free range is not in free lists");
7646 }
7647 _sp->removeFreeChunkFromFreeLists(ffc);
7648 set_freeRangeInFreeLists(false);
7649 }
7650 set_lastFreeRangeCoalesced(true);
7651 }
7652 // this will be swept up when we hit the end of the free range
7653
7654 // Verify that the bit map has no bits marked between
7655 // addr and purported end of just dead object.
7656 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7657 }
7658 assert(_limit >= addr + size,
7659 "A freshly garbage chunk can't possibly straddle over _limit");
7660 if (inFreeRange()) lookahead_and_flush(fc, size);
7661 return size;
7662 }
7663
7664 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7665 HeapWord* addr = (HeapWord*) fc;
7666 // The sweeper has just found a live object. Return any accumulated
7667 // left hand chunk to the free lists.
7668 if (inFreeRange()) {
7669 assert(freeFinger() < addr, "freeFinger points too high");
7670 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7671 }
7672
7673 // This object is live: we'd normally expect this to be
7674 // an oop, and like to assert the following:
7675 // assert(oop(addr)->is_oop(), "live block should be an oop");
7676 // However, as we commented above, this may be an object whose
7677 // header hasn't yet been initialized.
7678 size_t size;
7679 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7680 if (_bitMap->isMarked(addr + 1)) {
7681 // Determine the size from the bit map, rather than trying to
7682 // compute it from the object header.
7683 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7684 size = pointer_delta(nextOneAddr + 1, addr);
7685 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7686 "alignment problem");
7687
7688 #ifdef ASSERT
7689 if (oop(addr)->klass_or_null() != NULL) {
7690 // Ignore mark word because we are running concurrent with mutators
7691 assert(oop(addr)->is_oop(true), "live block should be an oop");
7692 assert(size ==
7693 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7694 "P-mark and computed size do not agree");
7695 }
7696 #endif
7697
7698 } else {
7699 // This should be an initialized object that's alive.
7700 assert(oop(addr)->klass_or_null() != NULL,
7701 "Should be an initialized object");
7702 // Ignore mark word because we are running concurrent with mutators
7703 assert(oop(addr)->is_oop(true), "live block should be an oop");
7704 // Verify that the bit map has no bits marked between
7705 // addr and purported end of this block.
7706 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7707 assert(size >= 3, "Necessary for Printezis marks to work");
7708 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7709 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7710 }
7711 return size;
7712 }
7713
7714 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7715 size_t chunkSize) {
7716 // do_post_free_or_garbage_chunk() should only be called in the case
7717 // of the adaptive free list allocator.
7718 const bool fcInFreeLists = fc->is_free();
7719 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
7720 assert((HeapWord*)fc <= _limit, "sweep invariant");
7721 if (CMSTestInFreeList && fcInFreeLists) {
7722 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7723 }
7724
7725 if (CMSTraceSweeper) {
7726 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7727 }
7728
7729 HeapWord* const fc_addr = (HeapWord*) fc;
7730
7731 bool coalesce;
7732 const size_t left = pointer_delta(fc_addr, freeFinger());
7733 const size_t right = chunkSize;
7734 switch (FLSCoalescePolicy) {
7735 // numeric value forms a coalition aggressiveness metric
7736 case 0: { // never coalesce
7737 coalesce = false;
7738 break;
7739 }
7740 case 1: { // coalesce if left & right chunks on overpopulated lists
7741 coalesce = _sp->coalOverPopulated(left) &&
7742 _sp->coalOverPopulated(right);
7743 break;
7744 }
7745 case 2: { // coalesce if left chunk on overpopulated list (default)
7746 coalesce = _sp->coalOverPopulated(left);
7747 break;
7748 }
7749 case 3: { // coalesce if left OR right chunk on overpopulated list
7750 coalesce = _sp->coalOverPopulated(left) ||
7751 _sp->coalOverPopulated(right);
7752 break;
7753 }
7754 case 4: { // always coalesce
7755 coalesce = true;
7756 break;
7757 }
7758 default:
7759 ShouldNotReachHere();
7760 }
7761
7762 // Should the current free range be coalesced?
7763 // If the chunk is in a free range and either we decided to coalesce above
7764 // or the chunk is near the large block at the end of the heap
7765 // (isNearLargestChunk() returns true), then coalesce this chunk.
7766 const bool doCoalesce = inFreeRange()
7767 && (coalesce || _g->isNearLargestChunk(fc_addr));
7768 if (doCoalesce) {
7769 // Coalesce the current free range on the left with the new
7770 // chunk on the right. If either is on a free list,
7771 // it must be removed from the list and stashed in the closure.
7772 if (freeRangeInFreeLists()) {
7773 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7774 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7775 "Size of free range is inconsistent with chunk size.");
7776 if (CMSTestInFreeList) {
7777 assert(_sp->verify_chunk_in_free_list(ffc),
7778 "Chunk is not in free lists");
7779 }
7780 _sp->coalDeath(ffc->size());
7781 _sp->removeFreeChunkFromFreeLists(ffc);
7782 set_freeRangeInFreeLists(false);
7783 }
7784 if (fcInFreeLists) {
7785 _sp->coalDeath(chunkSize);
7786 assert(fc->size() == chunkSize,
7787 "The chunk has the wrong size or is not in the free lists");
7788 _sp->removeFreeChunkFromFreeLists(fc);
7789 }
7790 set_lastFreeRangeCoalesced(true);
7791 print_free_block_coalesced(fc);
7792 } else { // not in a free range and/or should not coalesce
7793 // Return the current free range and start a new one.
7794 if (inFreeRange()) {
7795 // In a free range but cannot coalesce with the right hand chunk.
7796 // Put the current free range into the free lists.
7797 flush_cur_free_chunk(freeFinger(),
7798 pointer_delta(fc_addr, freeFinger()));
7799 }
7800 // Set up for new free range. Pass along whether the right hand
7801 // chunk is in the free lists.
7802 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7803 }
7804 }
7805
7806 // Lookahead flush:
7807 // If we are tracking a free range, and this is the last chunk that
7808 // we'll look at because its end crosses past _limit, we'll preemptively
7809 // flush it along with any free range we may be holding on to. Note that
7810 // this can be the case only for an already free or freshly garbage
7811 // chunk. If this block is an object, it can never straddle
7812 // over _limit. The "straddling" occurs when _limit is set at
7813 // the previous end of the space when this cycle started, and
7814 // a subsequent heap expansion caused the previously co-terminal
7815 // free block to be coalesced with the newly expanded portion,
7816 // thus rendering _limit a non-block-boundary making it dangerous
7817 // for the sweeper to step over and examine.
7818 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7819 assert(inFreeRange(), "Should only be called if currently in a free range.");
7820 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7821 assert(_sp->used_region().contains(eob - 1),
7822 "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7823 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7824 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7825 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7826 if (eob >= _limit) {
7827 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7828 if (CMSTraceSweeper) {
7829 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7830 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7831 "[" PTR_FORMAT "," PTR_FORMAT ")",
7832 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7833 }
7834 // Return the storage we are tracking back into the free lists.
7835 if (CMSTraceSweeper) {
7836 gclog_or_tty->print_cr("Flushing ... ");
7837 }
7838 assert(freeFinger() < eob, "Error");
7839 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7840 }
7841 }
7842
7843 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7844 assert(inFreeRange(), "Should only be called if currently in a free range.");
7845 assert(size > 0,
7846 "A zero sized chunk cannot be added to the free lists.");
7847 if (!freeRangeInFreeLists()) {
7848 if (CMSTestInFreeList) {
7849 FreeChunk* fc = (FreeChunk*) chunk;
7850 fc->set_size(size);
7851 assert(!_sp->verify_chunk_in_free_list(fc),
7852 "chunk should not be in free lists yet");
7853 }
7854 if (CMSTraceSweeper) {
7855 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7856 p2i(chunk), size);
7857 }
7858 // A new free range is going to be starting. The current
7859 // free range has not been added to the free lists yet or
7860 // was removed so add it back.
7861 // If the current free range was coalesced, then the death
7862 // of the free range was recorded. Record a birth now.
7863 if (lastFreeRangeCoalesced()) {
7864 _sp->coalBirth(size);
7865 }
7866 _sp->addChunkAndRepairOffsetTable(chunk, size,
7867 lastFreeRangeCoalesced());
7868 } else if (CMSTraceSweeper) {
7869 gclog_or_tty->print_cr("Already in free list: nothing to flush");
7870 }
7871 set_inFreeRange(false);
7872 set_freeRangeInFreeLists(false);
7873 }
7874
7875 // We take a break if we've been at this for a while,
7876 // so as to avoid monopolizing the locks involved.
7877 void SweepClosure::do_yield_work(HeapWord* addr) {
7878 // Return current free chunk being used for coalescing (if any)
7879 // to the appropriate freelist. After yielding, the next
7880 // free block encountered will start a coalescing range of
7881 // free blocks. If the next free block is adjacent to the
7882 // chunk just flushed, they will need to wait for the next
7883 // sweep to be coalesced.
7884 if (inFreeRange()) {
7885 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7886 }
7887
7888 // First give up the locks, then yield, then re-lock.
7889 // We should probably use a constructor/destructor idiom to
7890 // do this unlock/lock or modify the MutexUnlocker class to
7891 // serve our purpose. XXX
7892 assert_lock_strong(_bitMap->lock());
7893 assert_lock_strong(_freelistLock);
7894 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7895 "CMS thread should hold CMS token");
7896 _bitMap->lock()->unlock();
7897 _freelistLock->unlock();
7898 ConcurrentMarkSweepThread::desynchronize(true);
7899 _collector->stopTimer();
7900 if (PrintCMSStatistics != 0) {
7901 _collector->incrementYields();
7902 }
7903
7904 // See the comment in coordinator_yield()
7905 for (unsigned i = 0; i < CMSYieldSleepCount &&
7906 ConcurrentMarkSweepThread::should_yield() &&
7907 !CMSCollector::foregroundGCIsActive(); ++i) {
7908 os::sleep(Thread::current(), 1, false);
7909 }
7910
7911 ConcurrentMarkSweepThread::synchronize(true);
7912 _freelistLock->lock();
7913 _bitMap->lock()->lock_without_safepoint_check();
7914 _collector->startTimer();
7915 }
7916
7917 #ifndef PRODUCT
7918 // This is actually very useful in a product build if it can
7919 // be called from the debugger. Compile it into the product
7920 // as needed.
7921 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7922 return debug_cms_space->verify_chunk_in_free_list(fc);
7923 }
7924 #endif
7925
7926 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7927 if (CMSTraceSweeper) {
7928 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7929 p2i(fc), fc->size());
7930 }
7931 }
7932
7933 // CMSIsAliveClosure
7934 bool CMSIsAliveClosure::do_object_b(oop obj) {
7935 HeapWord* addr = (HeapWord*)obj;
7936 return addr != NULL &&
7937 (!_span.contains(addr) || _bit_map->isMarked(addr));
7938 }
7939
7940
7941 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7942 MemRegion span,
7943 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7944 bool cpc):
7945 _collector(collector),
7946 _span(span),
7947 _bit_map(bit_map),
7948 _mark_stack(mark_stack),
7949 _concurrent_precleaning(cpc) {
7950 assert(!_span.is_empty(), "Empty span could spell trouble");
7951 }
7952
7953
7954 // CMSKeepAliveClosure: the serial version
7955 void CMSKeepAliveClosure::do_oop(oop obj) {
7956 HeapWord* addr = (HeapWord*)obj;
7957 if (_span.contains(addr) &&
7958 !_bit_map->isMarked(addr)) {
7959 _bit_map->mark(addr);
7960 bool simulate_overflow = false;
7961 NOT_PRODUCT(
7962 if (CMSMarkStackOverflowALot &&
7963 _collector->simulate_overflow()) {
7964 // simulate a stack overflow
7965 simulate_overflow = true;
7966 }
7967 )
7968 if (simulate_overflow || !_mark_stack->push(obj)) {
7969 if (_concurrent_precleaning) {
7970 // We dirty the overflown object and let the remark
7971 // phase deal with it.
7972 assert(_collector->overflow_list_is_empty(), "Error");
7973 // In the case of object arrays, we need to dirty all of
7974 // the cards that the object spans. No locking or atomics
7975 // are needed since no one else can be mutating the mod union
7976 // table.
7977 if (obj->is_objArray()) {
7978 size_t sz = obj->size();
7979 HeapWord* end_card_addr =
7980 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
7981 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7982 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7983 _collector->_modUnionTable.mark_range(redirty_range);
7984 } else {
7985 _collector->_modUnionTable.mark(addr);
7986 }
7987 _collector->_ser_kac_preclean_ovflw++;
7988 } else {
7989 _collector->push_on_overflow_list(obj);
7990 _collector->_ser_kac_ovflw++;
7991 }
7992 }
7993 }
7994 }
7995
7996 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7997 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7998
7999 // CMSParKeepAliveClosure: a parallel version of the above.
8000 // The work queues are private to each closure (thread),
8001 // but (may be) available for stealing by other threads.
8002 void CMSParKeepAliveClosure::do_oop(oop obj) {
8003 HeapWord* addr = (HeapWord*)obj;
8004 if (_span.contains(addr) &&
8005 !_bit_map->isMarked(addr)) {
8006 // In general, during recursive tracing, several threads
8007 // may be concurrently getting here; the first one to
8008 // "tag" it, claims it.
8009 if (_bit_map->par_mark(addr)) {
8010 bool res = _work_queue->push(obj);
8011 assert(res, "Low water mark should be much less than capacity");
8012 // Do a recursive trim in the hope that this will keep
8013 // stack usage lower, but leave some oops for potential stealers
8014 trim_queue(_low_water_mark);
8015 } // Else, another thread got there first
8016 }
8017 }
8018
8019 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8020 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8021
8022 void CMSParKeepAliveClosure::trim_queue(uint max) {
8023 while (_work_queue->size() > max) {
8024 oop new_oop;
8025 if (_work_queue->pop_local(new_oop)) {
8026 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8027 assert(_bit_map->isMarked((HeapWord*)new_oop),
8028 "no white objects on this stack!");
8029 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8030 // iterate over the oops in this oop, marking and pushing
8031 // the ones in CMS heap (i.e. in _span).
8032 new_oop->oop_iterate(&_mark_and_push);
8033 }
8034 }
8035 }
8036
8037 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8038 CMSCollector* collector,
8039 MemRegion span, CMSBitMap* bit_map,
8040 OopTaskQueue* work_queue):
8041 _collector(collector),
8042 _span(span),
8043 _bit_map(bit_map),
8044 _work_queue(work_queue) { }
8045
8046 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8047 HeapWord* addr = (HeapWord*)obj;
8048 if (_span.contains(addr) &&
8049 !_bit_map->isMarked(addr)) {
8050 if (_bit_map->par_mark(addr)) {
8051 bool simulate_overflow = false;
8052 NOT_PRODUCT(
8053 if (CMSMarkStackOverflowALot &&
8054 _collector->par_simulate_overflow()) {
8055 // simulate a stack overflow
8056 simulate_overflow = true;
8057 }
8058 )
8059 if (simulate_overflow || !_work_queue->push(obj)) {
8060 _collector->par_push_on_overflow_list(obj);
8061 _collector->_par_kac_ovflw++;
8062 }
8063 } // Else another thread got there already
8064 }
8065 }
8066
8067 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8068 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8069
8070 //////////////////////////////////////////////////////////////////
8071 // CMSExpansionCause /////////////////////////////
8072 //////////////////////////////////////////////////////////////////
8073 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8074 switch (cause) {
8075 case _no_expansion:
8076 return "No expansion";
8077 case _satisfy_free_ratio:
8078 return "Free ratio";
8079 case _satisfy_promotion:
8080 return "Satisfy promotion";
8081 case _satisfy_allocation:
8082 return "allocation";
8083 case _allocate_par_lab:
8084 return "Par LAB";
8085 case _allocate_par_spooling_space:
8086 return "Par Spooling Space";
8087 case _adaptive_size_policy:
8088 return "Ergonomics";
8089 default:
8090 return "unknown";
8091 }
8092 }
8093
8094 void CMSDrainMarkingStackClosure::do_void() {
8095 // the max number to take from overflow list at a time
8096 const size_t num = _mark_stack->capacity()/4;
8097 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8098 "Overflow list should be NULL during concurrent phases");
8099 while (!_mark_stack->isEmpty() ||
8100 // if stack is empty, check the overflow list
8101 _collector->take_from_overflow_list(num, _mark_stack)) {
8102 oop obj = _mark_stack->pop();
8103 HeapWord* addr = (HeapWord*)obj;
8104 assert(_span.contains(addr), "Should be within span");
8105 assert(_bit_map->isMarked(addr), "Should be marked");
8106 assert(obj->is_oop(), "Should be an oop");
8107 obj->oop_iterate(_keep_alive);
8108 }
8109 }
8110
8111 void CMSParDrainMarkingStackClosure::do_void() {
8112 // drain queue
8113 trim_queue(0);
8114 }
8115
8116 // Trim our work_queue so its length is below max at return
8117 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8118 while (_work_queue->size() > max) {
8119 oop new_oop;
8120 if (_work_queue->pop_local(new_oop)) {
8121 assert(new_oop->is_oop(), "Expected an oop");
8122 assert(_bit_map->isMarked((HeapWord*)new_oop),
8123 "no white objects on this stack!");
8124 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8125 // iterate over the oops in this oop, marking and pushing
8126 // the ones in CMS heap (i.e. in _span).
8127 new_oop->oop_iterate(&_mark_and_push);
8128 }
8129 }
8130 }
8131
8132 ////////////////////////////////////////////////////////////////////
8133 // Support for Marking Stack Overflow list handling and related code
8134 ////////////////////////////////////////////////////////////////////
8135 // Much of the following code is similar in shape and spirit to the
8136 // code used in ParNewGC. We should try and share that code
8137 // as much as possible in the future.
8138
8139 #ifndef PRODUCT
8140 // Debugging support for CMSStackOverflowALot
8141
8142 // It's OK to call this multi-threaded; the worst thing
8143 // that can happen is that we'll get a bunch of closely
8144 // spaced simulated overflows, but that's OK, in fact
8145 // probably good as it would exercise the overflow code
8146 // under contention.
8147 bool CMSCollector::simulate_overflow() {
8148 if (_overflow_counter-- <= 0) { // just being defensive
8149 _overflow_counter = CMSMarkStackOverflowInterval;
8150 return true;
8151 } else {
8152 return false;
8153 }
8154 }
8155
8156 bool CMSCollector::par_simulate_overflow() {
8157 return simulate_overflow();
8158 }
8159 #endif
8160
8161 // Single-threaded
8162 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8163 assert(stack->isEmpty(), "Expected precondition");
8164 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8165 size_t i = num;
8166 oop cur = _overflow_list;
8167 const markOop proto = markOopDesc::prototype();
8168 NOT_PRODUCT(ssize_t n = 0;)
8169 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8170 next = oop(cur->mark());
8171 cur->set_mark(proto); // until proven otherwise
8172 assert(cur->is_oop(), "Should be an oop");
8173 bool res = stack->push(cur);
8174 assert(res, "Bit off more than can chew?");
8175 NOT_PRODUCT(n++;)
8176 }
8177 _overflow_list = cur;
8178 #ifndef PRODUCT
8179 assert(_num_par_pushes >= n, "Too many pops?");
8180 _num_par_pushes -=n;
8181 #endif
8182 return !stack->isEmpty();
8183 }
8184
8185 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8186 // (MT-safe) Get a prefix of at most "num" from the list.
8187 // The overflow list is chained through the mark word of
8188 // each object in the list. We fetch the entire list,
8189 // break off a prefix of the right size and return the
8190 // remainder. If other threads try to take objects from
8191 // the overflow list at that time, they will wait for
8192 // some time to see if data becomes available. If (and
8193 // only if) another thread places one or more object(s)
8194 // on the global list before we have returned the suffix
8195 // to the global list, we will walk down our local list
8196 // to find its end and append the global list to
8197 // our suffix before returning it. This suffix walk can
8198 // prove to be expensive (quadratic in the amount of traffic)
8199 // when there are many objects in the overflow list and
8200 // there is much producer-consumer contention on the list.
8201 // *NOTE*: The overflow list manipulation code here and
8202 // in ParNewGeneration:: are very similar in shape,
8203 // except that in the ParNew case we use the old (from/eden)
8204 // copy of the object to thread the list via its klass word.
8205 // Because of the common code, if you make any changes in
8206 // the code below, please check the ParNew version to see if
8207 // similar changes might be needed.
8208 // CR 6797058 has been filed to consolidate the common code.
8209 bool CMSCollector::par_take_from_overflow_list(size_t num,
8210 OopTaskQueue* work_q,
8211 int no_of_gc_threads) {
8212 assert(work_q->size() == 0, "First empty local work queue");
8213 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8214 if (_overflow_list == NULL) {
8215 return false;
8216 }
8217 // Grab the entire list; we'll put back a suffix
8218 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8219 Thread* tid = Thread::current();
8220 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8221 // set to ParallelGCThreads.
8222 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8223 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8224 // If the list is busy, we spin for a short while,
8225 // sleeping between attempts to get the list.
8226 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8227 os::sleep(tid, sleep_time_millis, false);
8228 if (_overflow_list == NULL) {
8229 // Nothing left to take
8230 return false;
8231 } else if (_overflow_list != BUSY) {
8232 // Try and grab the prefix
8233 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8234 }
8235 }
8236 // If the list was found to be empty, or we spun long
8237 // enough, we give up and return empty-handed. If we leave
8238 // the list in the BUSY state below, it must be the case that
8239 // some other thread holds the overflow list and will set it
8240 // to a non-BUSY state in the future.
8241 if (prefix == NULL || prefix == BUSY) {
8242 // Nothing to take or waited long enough
8243 if (prefix == NULL) {
8244 // Write back the NULL in case we overwrote it with BUSY above
8245 // and it is still the same value.
8246 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8247 }
8248 return false;
8249 }
8250 assert(prefix != NULL && prefix != BUSY, "Error");
8251 size_t i = num;
8252 oop cur = prefix;
8253 // Walk down the first "num" objects, unless we reach the end.
8254 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8255 if (cur->mark() == NULL) {
8256 // We have "num" or fewer elements in the list, so there
8257 // is nothing to return to the global list.
8258 // Write back the NULL in lieu of the BUSY we wrote
8259 // above, if it is still the same value.
8260 if (_overflow_list == BUSY) {
8261 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8262 }
8263 } else {
8264 // Chop off the suffix and return it to the global list.
8265 assert(cur->mark() != BUSY, "Error");
8266 oop suffix_head = cur->mark(); // suffix will be put back on global list
8267 cur->set_mark(NULL); // break off suffix
8268 // It's possible that the list is still in the empty(busy) state
8269 // we left it in a short while ago; in that case we may be
8270 // able to place back the suffix without incurring the cost
8271 // of a walk down the list.
8272 oop observed_overflow_list = _overflow_list;
8273 oop cur_overflow_list = observed_overflow_list;
8274 bool attached = false;
8275 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8276 observed_overflow_list =
8277 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8278 if (cur_overflow_list == observed_overflow_list) {
8279 attached = true;
8280 break;
8281 } else cur_overflow_list = observed_overflow_list;
8282 }
8283 if (!attached) {
8284 // Too bad, someone else sneaked in (at least) an element; we'll need
8285 // to do a splice. Find tail of suffix so we can prepend suffix to global
8286 // list.
8287 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8288 oop suffix_tail = cur;
8289 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8290 "Tautology");
8291 observed_overflow_list = _overflow_list;
8292 do {
8293 cur_overflow_list = observed_overflow_list;
8294 if (cur_overflow_list != BUSY) {
8295 // Do the splice ...
8296 suffix_tail->set_mark(markOop(cur_overflow_list));
8297 } else { // cur_overflow_list == BUSY
8298 suffix_tail->set_mark(NULL);
8299 }
8300 // ... and try to place spliced list back on overflow_list ...
8301 observed_overflow_list =
8302 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8303 } while (cur_overflow_list != observed_overflow_list);
8304 // ... until we have succeeded in doing so.
8305 }
8306 }
8307
8308 // Push the prefix elements on work_q
8309 assert(prefix != NULL, "control point invariant");
8310 const markOop proto = markOopDesc::prototype();
8311 oop next;
8312 NOT_PRODUCT(ssize_t n = 0;)
8313 for (cur = prefix; cur != NULL; cur = next) {
8314 next = oop(cur->mark());
8315 cur->set_mark(proto); // until proven otherwise
8316 assert(cur->is_oop(), "Should be an oop");
8317 bool res = work_q->push(cur);
8318 assert(res, "Bit off more than we can chew?");
8319 NOT_PRODUCT(n++;)
8320 }
8321 #ifndef PRODUCT
8322 assert(_num_par_pushes >= n, "Too many pops?");
8323 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8324 #endif
8325 return true;
8326 }
8327
8328 // Single-threaded
8329 void CMSCollector::push_on_overflow_list(oop p) {
8330 NOT_PRODUCT(_num_par_pushes++;)
8331 assert(p->is_oop(), "Not an oop");
8332 preserve_mark_if_necessary(p);
8333 p->set_mark((markOop)_overflow_list);
8334 _overflow_list = p;
8335 }
8336
8337 // Multi-threaded; use CAS to prepend to overflow list
8338 void CMSCollector::par_push_on_overflow_list(oop p) {
8339 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8340 assert(p->is_oop(), "Not an oop");
8341 par_preserve_mark_if_necessary(p);
8342 oop observed_overflow_list = _overflow_list;
8343 oop cur_overflow_list;
8344 do {
8345 cur_overflow_list = observed_overflow_list;
8346 if (cur_overflow_list != BUSY) {
8347 p->set_mark(markOop(cur_overflow_list));
8348 } else {
8349 p->set_mark(NULL);
8350 }
8351 observed_overflow_list =
8352 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8353 } while (cur_overflow_list != observed_overflow_list);
8354 }
8355 #undef BUSY
8356
8357 // Single threaded
8358 // General Note on GrowableArray: pushes may silently fail
8359 // because we are (temporarily) out of C-heap for expanding
8360 // the stack. The problem is quite ubiquitous and affects
8361 // a lot of code in the JVM. The prudent thing for GrowableArray
8362 // to do (for now) is to exit with an error. However, that may
8363 // be too draconian in some cases because the caller may be
8364 // able to recover without much harm. For such cases, we
8365 // should probably introduce a "soft_push" method which returns
8366 // an indication of success or failure with the assumption that
8367 // the caller may be able to recover from a failure; code in
8368 // the VM can then be changed, incrementally, to deal with such
8369 // failures where possible, thus, incrementally hardening the VM
8370 // in such low resource situations.
8371 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8372 _preserved_oop_stack.push(p);
8373 _preserved_mark_stack.push(m);
8374 assert(m == p->mark(), "Mark word changed");
8375 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8376 "bijection");
8377 }
8378
8379 // Single threaded
8380 void CMSCollector::preserve_mark_if_necessary(oop p) {
8381 markOop m = p->mark();
8382 if (m->must_be_preserved(p)) {
8383 preserve_mark_work(p, m);
8384 }
8385 }
8386
8387 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8388 markOop m = p->mark();
8389 if (m->must_be_preserved(p)) {
8390 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8391 // Even though we read the mark word without holding
8392 // the lock, we are assured that it will not change
8393 // because we "own" this oop, so no other thread can
8394 // be trying to push it on the overflow list; see
8395 // the assertion in preserve_mark_work() that checks
8396 // that m == p->mark().
8397 preserve_mark_work(p, m);
8398 }
8399 }
8400
8401 // We should be able to do this multi-threaded,
8402 // a chunk of stack being a task (this is
8403 // correct because each oop only ever appears
8404 // once in the overflow list. However, it's
8405 // not very easy to completely overlap this with
8406 // other operations, so will generally not be done
8407 // until all work's been completed. Because we
8408 // expect the preserved oop stack (set) to be small,
8409 // it's probably fine to do this single-threaded.
8410 // We can explore cleverer concurrent/overlapped/parallel
8411 // processing of preserved marks if we feel the
8412 // need for this in the future. Stack overflow should
8413 // be so rare in practice and, when it happens, its
8414 // effect on performance so great that this will
8415 // likely just be in the noise anyway.
8416 void CMSCollector::restore_preserved_marks_if_any() {
8417 assert(SafepointSynchronize::is_at_safepoint(),
8418 "world should be stopped");
8419 assert(Thread::current()->is_ConcurrentGC_thread() ||
8420 Thread::current()->is_VM_thread(),
8421 "should be single-threaded");
8422 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8423 "bijection");
8424
8425 while (!_preserved_oop_stack.is_empty()) {
8426 oop p = _preserved_oop_stack.pop();
8427 assert(p->is_oop(), "Should be an oop");
8428 assert(_span.contains(p), "oop should be in _span");
8429 assert(p->mark() == markOopDesc::prototype(),
8430 "Set when taken from overflow list");
8431 markOop m = _preserved_mark_stack.pop();
8432 p->set_mark(m);
8433 }
8434 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8435 "stacks were cleared above");
8436 }
8437
8438 #ifndef PRODUCT
8439 bool CMSCollector::no_preserved_marks() const {
8440 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8441 }
8442 #endif
8443
8444 // Transfer some number of overflown objects to usual marking
8445 // stack. Return true if some objects were transferred.
8446 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8447 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8448 (size_t)ParGCDesiredObjsFromOverflowList);
8449
8450 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8451 assert(_collector->overflow_list_is_empty() || res,
8452 "If list is not empty, we should have taken something");
8453 assert(!res || !_mark_stack->isEmpty(),
8454 "If we took something, it should now be on our stack");
8455 return res;
8456 }
8457
8458 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8459 size_t res = _sp->block_size_no_stall(addr, _collector);
8460 if (_sp->block_is_obj(addr)) {
8461 if (_live_bit_map->isMarked(addr)) {
8462 // It can't have been dead in a previous cycle
8463 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8464 } else {
8465 _dead_bit_map->mark(addr); // mark the dead object
8466 }
8467 }
8468 // Could be 0, if the block size could not be computed without stalling.
8469 return res;
8470 }
8471
8472 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8473
8474 switch (phase) {
8475 case CMSCollector::InitialMarking:
8476 initialize(true /* fullGC */ ,
8477 cause /* cause of the GC */,
8478 true /* recordGCBeginTime */,
8479 true /* recordPreGCUsage */,
8480 false /* recordPeakUsage */,
8481 false /* recordPostGCusage */,
8482 true /* recordAccumulatedGCTime */,
8483 false /* recordGCEndTime */,
8484 false /* countCollection */ );
8485 break;
8486
8487 case CMSCollector::FinalMarking:
8488 initialize(true /* fullGC */ ,
8489 cause /* cause of the GC */,
8490 false /* recordGCBeginTime */,
8491 false /* recordPreGCUsage */,
8492 false /* recordPeakUsage */,
8493 false /* recordPostGCusage */,
8494 true /* recordAccumulatedGCTime */,
8495 false /* recordGCEndTime */,
8496 false /* countCollection */ );
8497 break;
8498
8499 case CMSCollector::Sweeping:
8500 initialize(true /* fullGC */ ,
8501 cause /* cause of the GC */,
8502 false /* recordGCBeginTime */,
8503 false /* recordPreGCUsage */,
8504 true /* recordPeakUsage */,
8505 true /* recordPostGCusage */,
8506 false /* recordAccumulatedGCTime */,
8507 true /* recordGCEndTime */,
8508 true /* countCollection */ );
8509 break;
8510
8511 default:
8512 ShouldNotReachHere();
8513 }
8514 }