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/symbolTable.hpp"
29 #include "classfile/systemDictionary.hpp"
30 #include "code/codeCache.hpp"
31 #include "gc/cms/cmsCollectorPolicy.hpp"
32 #include "gc/cms/cmsOopClosures.inline.hpp"
33 #include "gc/cms/compactibleFreeListSpace.hpp"
34 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
35 #include "gc/cms/concurrentMarkSweepThread.hpp"
36 #include "gc/cms/parNewGeneration.hpp"
37 #include "gc/cms/vmCMSOperations.hpp"
38 #include "gc/serial/genMarkSweep.hpp"
39 #include "gc/serial/tenuredGeneration.hpp"
40 #include "gc/shared/adaptiveSizePolicy.hpp"
41 #include "gc/shared/cardGeneration.inline.hpp"
42 #include "gc/shared/cardTableRS.hpp"
43 #include "gc/shared/collectedHeap.inline.hpp"
44 #include "gc/shared/collectorCounters.hpp"
45 #include "gc/shared/collectorPolicy.hpp"
46 #include "gc/shared/gcLocker.inline.hpp"
47 #include "gc/shared/gcPolicyCounters.hpp"
48 #include "gc/shared/gcTimer.hpp"
49 #include "gc/shared/gcTrace.hpp"
50 #include "gc/shared/gcTraceTime.hpp"
51 #include "gc/shared/genCollectedHeap.hpp"
52 #include "gc/shared/genOopClosures.inline.hpp"
53 #include "gc/shared/isGCActiveMark.hpp"
54 #include "gc/shared/referencePolicy.hpp"
55 #include "gc/shared/strongRootsScope.hpp"
56 #include "gc/shared/taskqueue.inline.hpp"
57 #include "memory/allocation.hpp"
58 #include "memory/iterator.inline.hpp"
59 #include "memory/padded.hpp"
60 #include "memory/resourceArea.hpp"
61 #include "oops/oop.inline.hpp"
62 #include "prims/jvmtiExport.hpp"
63 #include "runtime/atomic.inline.hpp"
64 #include "runtime/globals_extension.hpp"
65 #include "runtime/handles.inline.hpp"
66 #include "runtime/java.hpp"
67 #include "runtime/orderAccess.inline.hpp"
68 #include "runtime/vmThread.hpp"
69 #include "services/memoryService.hpp"
70 #include "services/runtimeService.hpp"
71 #include "utilities/stack.inline.hpp"
72
73 // statics
74 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
75 bool CMSCollector::_full_gc_requested = false;
76 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
77
78 //////////////////////////////////////////////////////////////////
79 // In support of CMS/VM thread synchronization
80 //////////////////////////////////////////////////////////////////
81 // We split use of the CGC_lock into 2 "levels".
82 // The low-level locking is of the usual CGC_lock monitor. We introduce
83 // a higher level "token" (hereafter "CMS token") built on top of the
84 // low level monitor (hereafter "CGC lock").
85 // The token-passing protocol gives priority to the VM thread. The
86 // CMS-lock doesn't provide any fairness guarantees, but clients
87 // should ensure that it is only held for very short, bounded
88 // durations.
89 //
90 // When either of the CMS thread or the VM thread is involved in
91 // collection operations during which it does not want the other
92 // thread to interfere, it obtains the CMS token.
93 //
94 // If either thread tries to get the token while the other has
95 // it, that thread waits. However, if the VM thread and CMS thread
96 // both want the token, then the VM thread gets priority while the
97 // CMS thread waits. This ensures, for instance, that the "concurrent"
98 // phases of the CMS thread's work do not block out the VM thread
99 // for long periods of time as the CMS thread continues to hog
100 // the token. (See bug 4616232).
101 //
102 // The baton-passing functions are, however, controlled by the
103 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
104 // and here the low-level CMS lock, not the high level token,
105 // ensures mutual exclusion.
106 //
107 // Two important conditions that we have to satisfy:
108 // 1. if a thread does a low-level wait on the CMS lock, then it
109 // relinquishes the CMS token if it were holding that token
110 // when it acquired the low-level CMS lock.
111 // 2. any low-level notifications on the low-level lock
112 // should only be sent when a thread has relinquished the token.
113 //
114 // In the absence of either property, we'd have potential deadlock.
115 //
116 // We protect each of the CMS (concurrent and sequential) phases
117 // with the CMS _token_, not the CMS _lock_.
118 //
119 // The only code protected by CMS lock is the token acquisition code
120 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
121 // baton-passing code.
122 //
123 // Unfortunately, i couldn't come up with a good abstraction to factor and
124 // hide the naked CGC_lock manipulation in the baton-passing code
125 // further below. That's something we should try to do. Also, the proof
126 // of correctness of this 2-level locking scheme is far from obvious,
127 // and potentially quite slippery. We have an uneasy suspicion, for instance,
128 // that there may be a theoretical possibility of delay/starvation in the
129 // low-level lock/wait/notify scheme used for the baton-passing because of
130 // potential interference with the priority scheme embodied in the
131 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
132 // invocation further below and marked with "XXX 20011219YSR".
133 // Indeed, as we note elsewhere, this may become yet more slippery
134 // in the presence of multiple CMS and/or multiple VM threads. XXX
135
136 class CMSTokenSync: public StackObj {
137 private:
138 bool _is_cms_thread;
139 public:
140 CMSTokenSync(bool is_cms_thread):
141 _is_cms_thread(is_cms_thread) {
142 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
143 "Incorrect argument to constructor");
144 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
145 }
146
147 ~CMSTokenSync() {
148 assert(_is_cms_thread ?
149 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
150 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
151 "Incorrect state");
152 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
153 }
154 };
155
156 // Convenience class that does a CMSTokenSync, and then acquires
157 // upto three locks.
158 class CMSTokenSyncWithLocks: public CMSTokenSync {
159 private:
160 // Note: locks are acquired in textual declaration order
161 // and released in the opposite order
162 MutexLockerEx _locker1, _locker2, _locker3;
163 public:
164 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
165 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
166 CMSTokenSync(is_cms_thread),
167 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
168 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
169 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
170 { }
171 };
172
173
174 //////////////////////////////////////////////////////////////////
175 // Concurrent Mark-Sweep Generation /////////////////////////////
176 //////////////////////////////////////////////////////////////////
177
178 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
179
180 // This struct contains per-thread things necessary to support parallel
181 // young-gen collection.
182 class CMSParGCThreadState: public CHeapObj<mtGC> {
183 public:
184 CFLS_LAB lab;
185 PromotionInfo promo;
186
187 // Constructor.
188 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
189 promo.setSpace(cfls);
190 }
191 };
192
193 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
194 ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct) :
195 CardGeneration(rs, initial_byte_size, ct),
196 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
197 _did_compact(false)
198 {
199 HeapWord* bottom = (HeapWord*) _virtual_space.low();
200 HeapWord* end = (HeapWord*) _virtual_space.high();
201
202 _direct_allocated_words = 0;
203 NOT_PRODUCT(
204 _numObjectsPromoted = 0;
205 _numWordsPromoted = 0;
206 _numObjectsAllocated = 0;
207 _numWordsAllocated = 0;
208 )
209
210 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end));
211 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
212 _cmsSpace->_old_gen = this;
213
214 _gc_stats = new CMSGCStats();
215
216 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
217 // offsets match. The ability to tell free chunks from objects
218 // depends on this property.
219 debug_only(
220 FreeChunk* junk = NULL;
221 assert(UseCompressedClassPointers ||
222 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
223 "Offset of FreeChunk::_prev within FreeChunk must match"
224 " that of OopDesc::_klass within OopDesc");
225 )
226
227 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
228 for (uint i = 0; i < ParallelGCThreads; i++) {
229 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
230 }
231
232 _incremental_collection_failed = false;
233 // The "dilatation_factor" is the expansion that can occur on
234 // account of the fact that the minimum object size in the CMS
235 // generation may be larger than that in, say, a contiguous young
236 // generation.
237 // Ideally, in the calculation below, we'd compute the dilatation
238 // factor as: MinChunkSize/(promoting_gen's min object size)
239 // Since we do not have such a general query interface for the
240 // promoting generation, we'll instead just use the minimum
241 // object size (which today is a header's worth of space);
242 // note that all arithmetic is in units of HeapWords.
243 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
244 assert(_dilatation_factor >= 1.0, "from previous assert");
245 }
246
247
248 // The field "_initiating_occupancy" represents the occupancy percentage
249 // at which we trigger a new collection cycle. Unless explicitly specified
250 // via CMSInitiatingOccupancyFraction (argument "io" below), it
251 // is calculated by:
252 //
253 // Let "f" be MinHeapFreeRatio in
254 //
255 // _initiating_occupancy = 100-f +
256 // f * (CMSTriggerRatio/100)
257 // where CMSTriggerRatio is the argument "tr" below.
258 //
259 // That is, if we assume the heap is at its desired maximum occupancy at the
260 // end of a collection, we let CMSTriggerRatio of the (purported) free
261 // space be allocated before initiating a new collection cycle.
262 //
263 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
264 assert(io <= 100 && tr <= 100, "Check the arguments");
265 if (io >= 0) {
266 _initiating_occupancy = (double)io / 100.0;
267 } else {
268 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
269 (double)(tr * MinHeapFreeRatio) / 100.0)
270 / 100.0;
271 }
272 }
273
274 void ConcurrentMarkSweepGeneration::ref_processor_init() {
275 assert(collector() != NULL, "no collector");
276 collector()->ref_processor_init();
277 }
278
279 void CMSCollector::ref_processor_init() {
280 if (_ref_processor == NULL) {
281 // Allocate and initialize a reference processor
282 _ref_processor =
283 new ReferenceProcessor(_span, // span
284 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
285 ParallelGCThreads, // mt processing degree
286 _cmsGen->refs_discovery_is_mt(), // mt discovery
287 MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
288 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
289 &_is_alive_closure); // closure for liveness info
290 // Initialize the _ref_processor field of CMSGen
291 _cmsGen->set_ref_processor(_ref_processor);
292
293 }
294 }
295
296 AdaptiveSizePolicy* CMSCollector::size_policy() {
297 GenCollectedHeap* gch = GenCollectedHeap::heap();
298 return gch->gen_policy()->size_policy();
299 }
300
301 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
302
303 const char* gen_name = "old";
304 GenCollectorPolicy* gcp = GenCollectedHeap::heap()->gen_policy();
305 // Generation Counters - generation 1, 1 subspace
306 _gen_counters = new GenerationCounters(gen_name, 1, 1,
307 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
308
309 _space_counters = new GSpaceCounters(gen_name, 0,
310 _virtual_space.reserved_size(),
311 this, _gen_counters);
312 }
313
314 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
315 _cms_gen(cms_gen)
316 {
317 assert(alpha <= 100, "bad value");
318 _saved_alpha = alpha;
319
320 // Initialize the alphas to the bootstrap value of 100.
321 _gc0_alpha = _cms_alpha = 100;
322
323 _cms_begin_time.update();
324 _cms_end_time.update();
325
326 _gc0_duration = 0.0;
327 _gc0_period = 0.0;
328 _gc0_promoted = 0;
329
330 _cms_duration = 0.0;
331 _cms_period = 0.0;
332 _cms_allocated = 0;
333
334 _cms_used_at_gc0_begin = 0;
335 _cms_used_at_gc0_end = 0;
336 _allow_duty_cycle_reduction = false;
337 _valid_bits = 0;
338 }
339
340 double CMSStats::cms_free_adjustment_factor(size_t free) const {
341 // TBD: CR 6909490
342 return 1.0;
343 }
344
345 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
346 }
347
348 // If promotion failure handling is on use
349 // the padded average size of the promotion for each
350 // young generation collection.
351 double CMSStats::time_until_cms_gen_full() const {
352 size_t cms_free = _cms_gen->cmsSpace()->free();
353 GenCollectedHeap* gch = GenCollectedHeap::heap();
354 size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
355 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
356 if (cms_free > expected_promotion) {
357 // Start a cms collection if there isn't enough space to promote
358 // for the next young collection. Use the padded average as
359 // a safety factor.
360 cms_free -= expected_promotion;
361
362 // Adjust by the safety factor.
363 double cms_free_dbl = (double)cms_free;
364 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
365 // Apply a further correction factor which tries to adjust
366 // for recent occurance of concurrent mode failures.
367 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
368 cms_free_dbl = cms_free_dbl * cms_adjustment;
369
370 if (PrintGCDetails && Verbose) {
371 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
372 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
373 cms_free, expected_promotion);
374 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
375 cms_free_dbl, cms_consumption_rate() + 1.0);
376 }
377 // Add 1 in case the consumption rate goes to zero.
378 return cms_free_dbl / (cms_consumption_rate() + 1.0);
379 }
380 return 0.0;
381 }
382
383 // Compare the duration of the cms collection to the
384 // time remaining before the cms generation is empty.
385 // Note that the time from the start of the cms collection
386 // to the start of the cms sweep (less than the total
387 // duration of the cms collection) can be used. This
388 // has been tried and some applications experienced
389 // promotion failures early in execution. This was
390 // possibly because the averages were not accurate
391 // enough at the beginning.
392 double CMSStats::time_until_cms_start() const {
393 // We add "gc0_period" to the "work" calculation
394 // below because this query is done (mostly) at the
395 // end of a scavenge, so we need to conservatively
396 // account for that much possible delay
397 // in the query so as to avoid concurrent mode failures
398 // due to starting the collection just a wee bit too
399 // late.
400 double work = cms_duration() + gc0_period();
401 double deadline = time_until_cms_gen_full();
402 // If a concurrent mode failure occurred recently, we want to be
403 // more conservative and halve our expected time_until_cms_gen_full()
404 if (work > deadline) {
405 if (Verbose && PrintGCDetails) {
406 gclog_or_tty->print(
407 " CMSCollector: collect because of anticipated promotion "
408 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
409 gc0_period(), time_until_cms_gen_full());
410 }
411 return 0.0;
412 }
413 return work - deadline;
414 }
415
416 #ifndef PRODUCT
417 void CMSStats::print_on(outputStream *st) const {
418 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
419 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
420 gc0_duration(), gc0_period(), gc0_promoted());
421 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
422 cms_duration(), cms_period(), cms_allocated());
423 st->print(",cms_since_beg=%g,cms_since_end=%g",
424 cms_time_since_begin(), cms_time_since_end());
425 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
426 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
427
428 if (valid()) {
429 st->print(",promo_rate=%g,cms_alloc_rate=%g",
430 promotion_rate(), cms_allocation_rate());
431 st->print(",cms_consumption_rate=%g,time_until_full=%g",
432 cms_consumption_rate(), time_until_cms_gen_full());
433 }
434 st->print(" ");
435 }
436 #endif // #ifndef PRODUCT
437
438 CMSCollector::CollectorState CMSCollector::_collectorState =
439 CMSCollector::Idling;
440 bool CMSCollector::_foregroundGCIsActive = false;
441 bool CMSCollector::_foregroundGCShouldWait = false;
442
443 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
444 CardTableRS* ct,
445 ConcurrentMarkSweepPolicy* cp):
446 _cmsGen(cmsGen),
447 _ct(ct),
448 _ref_processor(NULL), // will be set later
449 _conc_workers(NULL), // may be set later
450 _abort_preclean(false),
451 _start_sampling(false),
452 _between_prologue_and_epilogue(false),
453 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
454 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
455 -1 /* lock-free */, "No_lock" /* dummy */),
456 _modUnionClosurePar(&_modUnionTable),
457 // Adjust my span to cover old (cms) gen
458 _span(cmsGen->reserved()),
459 // Construct the is_alive_closure with _span & markBitMap
460 _is_alive_closure(_span, &_markBitMap),
461 _restart_addr(NULL),
462 _overflow_list(NULL),
463 _stats(cmsGen),
464 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
465 //verify that this lock should be acquired with safepoint check.
466 Monitor::_safepoint_check_sometimes)),
467 _eden_chunk_array(NULL), // may be set in ctor body
468 _eden_chunk_capacity(0), // -- ditto --
469 _eden_chunk_index(0), // -- ditto --
470 _survivor_plab_array(NULL), // -- ditto --
471 _survivor_chunk_array(NULL), // -- ditto --
472 _survivor_chunk_capacity(0), // -- ditto --
473 _survivor_chunk_index(0), // -- ditto --
474 _ser_pmc_preclean_ovflw(0),
475 _ser_kac_preclean_ovflw(0),
476 _ser_pmc_remark_ovflw(0),
477 _par_pmc_remark_ovflw(0),
478 _ser_kac_ovflw(0),
479 _par_kac_ovflw(0),
480 #ifndef PRODUCT
481 _num_par_pushes(0),
482 #endif
483 _collection_count_start(0),
484 _verifying(false),
485 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
486 _completed_initialization(false),
487 _collector_policy(cp),
488 _should_unload_classes(CMSClassUnloadingEnabled),
489 _concurrent_cycles_since_last_unload(0),
490 _roots_scanning_options(GenCollectedHeap::SO_None),
491 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
492 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
493 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
494 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
495 _cms_start_registered(false)
496 {
497 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
498 ExplicitGCInvokesConcurrent = true;
499 }
500 // Now expand the span and allocate the collection support structures
501 // (MUT, marking bit map etc.) to cover both generations subject to
502 // collection.
503
504 // For use by dirty card to oop closures.
505 _cmsGen->cmsSpace()->set_collector(this);
506
507 // Allocate MUT and marking bit map
508 {
509 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
510 if (!_markBitMap.allocate(_span)) {
511 warning("Failed to allocate CMS Bit Map");
512 return;
513 }
514 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
515 }
516 {
517 _modUnionTable.allocate(_span);
518 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
519 }
520
521 if (!_markStack.allocate(MarkStackSize)) {
522 warning("Failed to allocate CMS Marking Stack");
523 return;
524 }
525
526 // Support for multi-threaded concurrent phases
527 if (CMSConcurrentMTEnabled) {
528 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
529 // just for now
530 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
531 }
532 if (ConcGCThreads > 1) {
533 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
534 ConcGCThreads, true);
535 if (_conc_workers == NULL) {
536 warning("GC/CMS: _conc_workers allocation failure: "
537 "forcing -CMSConcurrentMTEnabled");
538 CMSConcurrentMTEnabled = false;
539 } else {
540 _conc_workers->initialize_workers();
541 }
542 } else {
543 CMSConcurrentMTEnabled = false;
544 }
545 }
546 if (!CMSConcurrentMTEnabled) {
547 ConcGCThreads = 0;
548 } else {
549 // Turn off CMSCleanOnEnter optimization temporarily for
550 // the MT case where it's not fixed yet; see 6178663.
551 CMSCleanOnEnter = false;
552 }
553 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
554 "Inconsistency");
555
556 // Parallel task queues; these are shared for the
557 // concurrent and stop-world phases of CMS, but
558 // are not shared with parallel scavenge (ParNew).
559 {
560 uint i;
561 uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
562
563 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
564 || ParallelRefProcEnabled)
565 && num_queues > 0) {
566 _task_queues = new OopTaskQueueSet(num_queues);
567 if (_task_queues == NULL) {
568 warning("task_queues allocation failure.");
569 return;
570 }
571 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
572 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
573 for (i = 0; i < num_queues; i++) {
574 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
575 if (q == NULL) {
576 warning("work_queue allocation failure.");
577 return;
578 }
579 _task_queues->register_queue(i, q);
580 }
581 for (i = 0; i < num_queues; i++) {
582 _task_queues->queue(i)->initialize();
583 _hash_seed[i] = 17; // copied from ParNew
584 }
585 }
586 }
587
588 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
589
590 // Clip CMSBootstrapOccupancy between 0 and 100.
591 _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
592
593 // Now tell CMS generations the identity of their collector
594 ConcurrentMarkSweepGeneration::set_collector(this);
595
596 // Create & start a CMS thread for this CMS collector
597 _cmsThread = ConcurrentMarkSweepThread::start(this);
598 assert(cmsThread() != NULL, "CMS Thread should have been created");
599 assert(cmsThread()->collector() == this,
600 "CMS Thread should refer to this gen");
601 assert(CGC_lock != NULL, "Where's the CGC_lock?");
602
603 // Support for parallelizing young gen rescan
604 GenCollectedHeap* gch = GenCollectedHeap::heap();
605 assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
606 _young_gen = (ParNewGeneration*)gch->young_gen();
607 if (gch->supports_inline_contig_alloc()) {
608 _top_addr = gch->top_addr();
609 _end_addr = gch->end_addr();
610 assert(_young_gen != NULL, "no _young_gen");
611 _eden_chunk_index = 0;
612 _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
613 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
614 }
615
616 // Support for parallelizing survivor space rescan
617 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
618 const size_t max_plab_samples =
619 _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
620
621 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
622 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
623 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
624 _survivor_chunk_capacity = max_plab_samples;
625 for (uint i = 0; i < ParallelGCThreads; i++) {
626 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
627 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
628 assert(cur->end() == 0, "Should be 0");
629 assert(cur->array() == vec, "Should be vec");
630 assert(cur->capacity() == max_plab_samples, "Error");
631 }
632 }
633
634 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
635 _gc_counters = new CollectorCounters("CMS", 1);
636 _completed_initialization = true;
637 _inter_sweep_timer.start(); // start of time
638 }
639
640 const char* ConcurrentMarkSweepGeneration::name() const {
641 return "concurrent mark-sweep generation";
642 }
643 void ConcurrentMarkSweepGeneration::update_counters() {
644 if (UsePerfData) {
645 _space_counters->update_all();
646 _gen_counters->update_all();
647 }
648 }
649
650 // this is an optimized version of update_counters(). it takes the
651 // used value as a parameter rather than computing it.
652 //
653 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
654 if (UsePerfData) {
655 _space_counters->update_used(used);
656 _space_counters->update_capacity();
657 _gen_counters->update_all();
658 }
659 }
660
661 void ConcurrentMarkSweepGeneration::print() const {
662 Generation::print();
663 cmsSpace()->print();
664 }
665
666 #ifndef PRODUCT
667 void ConcurrentMarkSweepGeneration::print_statistics() {
668 cmsSpace()->printFLCensus(0);
669 }
670 #endif
671
672 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
673 GenCollectedHeap* gch = GenCollectedHeap::heap();
674 if (PrintGCDetails) {
675 // I didn't want to change the logging when removing the level concept,
676 // but I guess this logging could say "old" or something instead of "1".
677 assert(gch->is_old_gen(this),
678 "The CMS generation should be the old generation");
679 uint level = 1;
680 if (Verbose) {
681 gclog_or_tty->print("[%u %s-%s: " SIZE_FORMAT "(" SIZE_FORMAT ")]",
682 level, short_name(), s, used(), capacity());
683 } else {
684 gclog_or_tty->print("[%u %s-%s: " SIZE_FORMAT "K(" SIZE_FORMAT "K)]",
685 level, short_name(), s, used() / K, capacity() / K);
686 }
687 }
688 if (Verbose) {
689 gclog_or_tty->print(" " SIZE_FORMAT "(" SIZE_FORMAT ")",
690 gch->used(), gch->capacity());
691 } else {
692 gclog_or_tty->print(" " SIZE_FORMAT "K(" SIZE_FORMAT "K)",
693 gch->used() / K, gch->capacity() / K);
694 }
695 }
696
697 size_t
698 ConcurrentMarkSweepGeneration::contiguous_available() const {
699 // dld proposes an improvement in precision here. If the committed
700 // part of the space ends in a free block we should add that to
701 // uncommitted size in the calculation below. Will make this
702 // change later, staying with the approximation below for the
703 // time being. -- ysr.
704 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
705 }
706
707 size_t
708 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
709 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
710 }
711
712 size_t ConcurrentMarkSweepGeneration::max_available() const {
713 return free() + _virtual_space.uncommitted_size();
714 }
715
716 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
717 size_t available = max_available();
718 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
719 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
720 if (Verbose && PrintGCDetails) {
721 gclog_or_tty->print_cr(
722 "CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "),"
723 "max_promo(" SIZE_FORMAT ")",
724 res? "":" not", available, res? ">=":"<",
725 av_promo, max_promotion_in_bytes);
726 }
727 return res;
728 }
729
730 // At a promotion failure dump information on block layout in heap
731 // (cms old generation).
732 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
733 if (CMSDumpAtPromotionFailure) {
734 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
735 }
736 }
737
738 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
739 // Clear the promotion information. These pointers can be adjusted
740 // along with all the other pointers into the heap but
741 // compaction is expected to be a rare event with
742 // a heap using cms so don't do it without seeing the need.
743 for (uint i = 0; i < ParallelGCThreads; i++) {
744 _par_gc_thread_states[i]->promo.reset();
745 }
746 }
747
748 void ConcurrentMarkSweepGeneration::compute_new_size() {
749 assert_locked_or_safepoint(Heap_lock);
750
751 // If incremental collection failed, we just want to expand
752 // to the limit.
753 if (incremental_collection_failed()) {
754 clear_incremental_collection_failed();
755 grow_to_reserved();
756 return;
757 }
758
759 // The heap has been compacted but not reset yet.
760 // Any metric such as free() or used() will be incorrect.
761
762 CardGeneration::compute_new_size();
763
764 // Reset again after a possible resizing
765 if (did_compact()) {
766 cmsSpace()->reset_after_compaction();
767 }
768 }
769
770 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
771 assert_locked_or_safepoint(Heap_lock);
772
773 // If incremental collection failed, we just want to expand
774 // to the limit.
775 if (incremental_collection_failed()) {
776 clear_incremental_collection_failed();
777 grow_to_reserved();
778 return;
779 }
780
781 double free_percentage = ((double) free()) / capacity();
782 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
783 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
784
785 // compute expansion delta needed for reaching desired free percentage
786 if (free_percentage < desired_free_percentage) {
787 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
788 assert(desired_capacity >= capacity(), "invalid expansion size");
789 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
790 if (PrintGCDetails && Verbose) {
791 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
792 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
793 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
794 gclog_or_tty->print_cr(" Desired free fraction %f", desired_free_percentage);
795 gclog_or_tty->print_cr(" Maximum free fraction %f", maximum_free_percentage);
796 gclog_or_tty->print_cr(" Capacity " SIZE_FORMAT, capacity() / 1000);
797 gclog_or_tty->print_cr(" Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
798 GenCollectedHeap* gch = GenCollectedHeap::heap();
799 assert(gch->is_old_gen(this), "The CMS generation should always be the old generation");
800 size_t young_size = gch->young_gen()->capacity();
801 gclog_or_tty->print_cr(" Young gen size " SIZE_FORMAT, young_size / 1000);
802 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
803 gclog_or_tty->print_cr(" contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
804 gclog_or_tty->print_cr(" Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
805 }
806 // safe if expansion fails
807 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
808 if (PrintGCDetails && Verbose) {
809 gclog_or_tty->print_cr(" Expanded free fraction %f", ((double) free()) / capacity());
810 }
811 } else {
812 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
813 assert(desired_capacity <= capacity(), "invalid expansion size");
814 size_t shrink_bytes = capacity() - desired_capacity;
815 // Don't shrink unless the delta is greater than the minimum shrink we want
816 if (shrink_bytes >= MinHeapDeltaBytes) {
817 shrink_free_list_by(shrink_bytes);
818 }
819 }
820 }
821
822 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
823 return cmsSpace()->freelistLock();
824 }
825
826 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
827 CMSSynchronousYieldRequest yr;
828 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
829 return have_lock_and_allocate(size, tlab);
830 }
831
832 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
833 bool tlab /* ignored */) {
834 assert_lock_strong(freelistLock());
835 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
836 HeapWord* res = cmsSpace()->allocate(adjustedSize);
837 // Allocate the object live (grey) if the background collector has
838 // started marking. This is necessary because the marker may
839 // have passed this address and consequently this object will
840 // not otherwise be greyed and would be incorrectly swept up.
841 // Note that if this object contains references, the writing
842 // of those references will dirty the card containing this object
843 // allowing the object to be blackened (and its references scanned)
844 // either during a preclean phase or at the final checkpoint.
845 if (res != NULL) {
846 // We may block here with an uninitialized object with
847 // its mark-bit or P-bits not yet set. Such objects need
848 // to be safely navigable by block_start().
849 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
850 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
851 collector()->direct_allocated(res, adjustedSize);
852 _direct_allocated_words += adjustedSize;
853 // allocation counters
854 NOT_PRODUCT(
855 _numObjectsAllocated++;
856 _numWordsAllocated += (int)adjustedSize;
857 )
858 }
859 return res;
860 }
861
862 // In the case of direct allocation by mutators in a generation that
863 // is being concurrently collected, the object must be allocated
864 // live (grey) if the background collector has started marking.
865 // This is necessary because the marker may
866 // have passed this address and consequently this object will
867 // not otherwise be greyed and would be incorrectly swept up.
868 // Note that if this object contains references, the writing
869 // of those references will dirty the card containing this object
870 // allowing the object to be blackened (and its references scanned)
871 // either during a preclean phase or at the final checkpoint.
872 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
873 assert(_markBitMap.covers(start, size), "Out of bounds");
874 if (_collectorState >= Marking) {
875 MutexLockerEx y(_markBitMap.lock(),
876 Mutex::_no_safepoint_check_flag);
877 // [see comments preceding SweepClosure::do_blk() below for details]
878 //
879 // Can the P-bits be deleted now? JJJ
880 //
881 // 1. need to mark the object as live so it isn't collected
882 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
883 // 3. need to mark the end of the object so marking, precleaning or sweeping
884 // can skip over uninitialized or unparsable objects. An allocated
885 // object is considered uninitialized for our purposes as long as
886 // its klass word is NULL. All old gen objects are parsable
887 // as soon as they are initialized.)
888 _markBitMap.mark(start); // object is live
889 _markBitMap.mark(start + 1); // object is potentially uninitialized?
890 _markBitMap.mark(start + size - 1);
891 // mark end of object
892 }
893 // check that oop looks uninitialized
894 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
895 }
896
897 void CMSCollector::promoted(bool par, HeapWord* start,
898 bool is_obj_array, size_t obj_size) {
899 assert(_markBitMap.covers(start), "Out of bounds");
900 // See comment in direct_allocated() about when objects should
901 // be allocated live.
902 if (_collectorState >= Marking) {
903 // we already hold the marking bit map lock, taken in
904 // the prologue
905 if (par) {
906 _markBitMap.par_mark(start);
907 } else {
908 _markBitMap.mark(start);
909 }
910 // We don't need to mark the object as uninitialized (as
911 // in direct_allocated above) because this is being done with the
912 // world stopped and the object will be initialized by the
913 // time the marking, precleaning or sweeping get to look at it.
914 // But see the code for copying objects into the CMS generation,
915 // where we need to ensure that concurrent readers of the
916 // block offset table are able to safely navigate a block that
917 // is in flux from being free to being allocated (and in
918 // transition while being copied into) and subsequently
919 // becoming a bona-fide object when the copy/promotion is complete.
920 assert(SafepointSynchronize::is_at_safepoint(),
921 "expect promotion only at safepoints");
922
923 if (_collectorState < Sweeping) {
924 // Mark the appropriate cards in the modUnionTable, so that
925 // this object gets scanned before the sweep. If this is
926 // not done, CMS generation references in the object might
927 // not get marked.
928 // For the case of arrays, which are otherwise precisely
929 // marked, we need to dirty the entire array, not just its head.
930 if (is_obj_array) {
931 // The [par_]mark_range() method expects mr.end() below to
932 // be aligned to the granularity of a bit's representation
933 // in the heap. In the case of the MUT below, that's a
934 // card size.
935 MemRegion mr(start,
936 (HeapWord*)round_to((intptr_t)(start + obj_size),
937 CardTableModRefBS::card_size /* bytes */));
938 if (par) {
939 _modUnionTable.par_mark_range(mr);
940 } else {
941 _modUnionTable.mark_range(mr);
942 }
943 } else { // not an obj array; we can just mark the head
944 if (par) {
945 _modUnionTable.par_mark(start);
946 } else {
947 _modUnionTable.mark(start);
948 }
949 }
950 }
951 }
952 }
953
954 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
955 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
956 // allocate, copy and if necessary update promoinfo --
957 // delegate to underlying space.
958 assert_lock_strong(freelistLock());
959
960 #ifndef PRODUCT
961 if (GenCollectedHeap::heap()->promotion_should_fail()) {
962 return NULL;
963 }
964 #endif // #ifndef PRODUCT
965
966 oop res = _cmsSpace->promote(obj, obj_size);
967 if (res == NULL) {
968 // expand and retry
969 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
970 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
971 // Since this is the old generation, we don't try to promote
972 // into a more senior generation.
973 res = _cmsSpace->promote(obj, obj_size);
974 }
975 if (res != NULL) {
976 // See comment in allocate() about when objects should
977 // be allocated live.
978 assert(obj->is_oop(), "Will dereference klass pointer below");
979 collector()->promoted(false, // Not parallel
980 (HeapWord*)res, obj->is_objArray(), obj_size);
981 // promotion counters
982 NOT_PRODUCT(
983 _numObjectsPromoted++;
984 _numWordsPromoted +=
985 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
986 )
987 }
988 return res;
989 }
990
991
992 // IMPORTANT: Notes on object size recognition in CMS.
993 // ---------------------------------------------------
994 // A block of storage in the CMS generation is always in
995 // one of three states. A free block (FREE), an allocated
996 // object (OBJECT) whose size() method reports the correct size,
997 // and an intermediate state (TRANSIENT) in which its size cannot
998 // be accurately determined.
999 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1000 // -----------------------------------------------------
1001 // FREE: klass_word & 1 == 1; mark_word holds block size
1002 //
1003 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1004 // obj->size() computes correct size
1005 //
1006 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1007 //
1008 // STATE IDENTIFICATION: (64 bit+COOPS)
1009 // ------------------------------------
1010 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1011 //
1012 // OBJECT: klass_word installed; klass_word != 0;
1013 // obj->size() computes correct size
1014 //
1015 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1016 //
1017 //
1018 // STATE TRANSITION DIAGRAM
1019 //
1020 // mut / parnew mut / parnew
1021 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1022 // ^ |
1023 // |------------------------ DEAD <------------------------------------|
1024 // sweep mut
1025 //
1026 // While a block is in TRANSIENT state its size cannot be determined
1027 // so readers will either need to come back later or stall until
1028 // the size can be determined. Note that for the case of direct
1029 // allocation, P-bits, when available, may be used to determine the
1030 // size of an object that may not yet have been initialized.
1031
1032 // Things to support parallel young-gen collection.
1033 oop
1034 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1035 oop old, markOop m,
1036 size_t word_sz) {
1037 #ifndef PRODUCT
1038 if (GenCollectedHeap::heap()->promotion_should_fail()) {
1039 return NULL;
1040 }
1041 #endif // #ifndef PRODUCT
1042
1043 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1044 PromotionInfo* promoInfo = &ps->promo;
1045 // if we are tracking promotions, then first ensure space for
1046 // promotion (including spooling space for saving header if necessary).
1047 // then allocate and copy, then track promoted info if needed.
1048 // When tracking (see PromotionInfo::track()), the mark word may
1049 // be displaced and in this case restoration of the mark word
1050 // occurs in the (oop_since_save_marks_)iterate phase.
1051 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1052 // Out of space for allocating spooling buffers;
1053 // try expanding and allocating spooling buffers.
1054 if (!expand_and_ensure_spooling_space(promoInfo)) {
1055 return NULL;
1056 }
1057 }
1058 assert(promoInfo->has_spooling_space(), "Control point invariant");
1059 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1060 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1061 if (obj_ptr == NULL) {
1062 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1063 if (obj_ptr == NULL) {
1064 return NULL;
1065 }
1066 }
1067 oop obj = oop(obj_ptr);
1068 OrderAccess::storestore();
1069 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1070 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1071 // IMPORTANT: See note on object initialization for CMS above.
1072 // Otherwise, copy the object. Here we must be careful to insert the
1073 // klass pointer last, since this marks the block as an allocated object.
1074 // Except with compressed oops it's the mark word.
1075 HeapWord* old_ptr = (HeapWord*)old;
1076 // Restore the mark word copied above.
1077 obj->set_mark(m);
1078 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1079 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1080 OrderAccess::storestore();
1081
1082 if (UseCompressedClassPointers) {
1083 // Copy gap missed by (aligned) header size calculation below
1084 obj->set_klass_gap(old->klass_gap());
1085 }
1086 if (word_sz > (size_t)oopDesc::header_size()) {
1087 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1088 obj_ptr + oopDesc::header_size(),
1089 word_sz - oopDesc::header_size());
1090 }
1091
1092 // Now we can track the promoted object, if necessary. We take care
1093 // to delay the transition from uninitialized to full object
1094 // (i.e., insertion of klass pointer) until after, so that it
1095 // atomically becomes a promoted object.
1096 if (promoInfo->tracking()) {
1097 promoInfo->track((PromotedObject*)obj, old->klass());
1098 }
1099 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1100 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1101 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1102
1103 // Finally, install the klass pointer (this should be volatile).
1104 OrderAccess::storestore();
1105 obj->set_klass(old->klass());
1106 // We should now be able to calculate the right size for this object
1107 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1108
1109 collector()->promoted(true, // parallel
1110 obj_ptr, old->is_objArray(), word_sz);
1111
1112 NOT_PRODUCT(
1113 Atomic::inc_ptr(&_numObjectsPromoted);
1114 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1115 )
1116
1117 return obj;
1118 }
1119
1120 void
1121 ConcurrentMarkSweepGeneration::
1122 par_promote_alloc_done(int thread_num) {
1123 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1124 ps->lab.retire(thread_num);
1125 }
1126
1127 void
1128 ConcurrentMarkSweepGeneration::
1129 par_oop_since_save_marks_iterate_done(int thread_num) {
1130 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1131 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1132 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1133 }
1134
1135 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1136 size_t size,
1137 bool tlab)
1138 {
1139 // We allow a STW collection only if a full
1140 // collection was requested.
1141 return full || should_allocate(size, tlab); // FIX ME !!!
1142 // This and promotion failure handling are connected at the
1143 // hip and should be fixed by untying them.
1144 }
1145
1146 bool CMSCollector::shouldConcurrentCollect() {
1147 if (_full_gc_requested) {
1148 if (Verbose && PrintGCDetails) {
1149 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1150 " gc request (or gc_locker)");
1151 }
1152 return true;
1153 }
1154
1155 FreelistLocker x(this);
1156 // ------------------------------------------------------------------
1157 // Print out lots of information which affects the initiation of
1158 // a collection.
1159 if (PrintCMSInitiationStatistics && stats().valid()) {
1160 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1161 gclog_or_tty->stamp();
1162 gclog_or_tty->cr();
1163 stats().print_on(gclog_or_tty);
1164 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1165 stats().time_until_cms_gen_full());
1166 gclog_or_tty->print_cr("free=" SIZE_FORMAT, _cmsGen->free());
1167 gclog_or_tty->print_cr("contiguous_available=" SIZE_FORMAT,
1168 _cmsGen->contiguous_available());
1169 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1170 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1171 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1172 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1173 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1174 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1175 gclog_or_tty->print_cr("metadata initialized %d",
1176 MetaspaceGC::should_concurrent_collect());
1177 }
1178 // ------------------------------------------------------------------
1179
1180 // If the estimated time to complete a cms collection (cms_duration())
1181 // is less than the estimated time remaining until the cms generation
1182 // is full, start a collection.
1183 if (!UseCMSInitiatingOccupancyOnly) {
1184 if (stats().valid()) {
1185 if (stats().time_until_cms_start() == 0.0) {
1186 return true;
1187 }
1188 } else {
1189 // We want to conservatively collect somewhat early in order
1190 // to try and "bootstrap" our CMS/promotion statistics;
1191 // this branch will not fire after the first successful CMS
1192 // collection because the stats should then be valid.
1193 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1194 if (Verbose && PrintGCDetails) {
1195 gclog_or_tty->print_cr(
1196 " CMSCollector: collect for bootstrapping statistics:"
1197 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1198 _bootstrap_occupancy);
1199 }
1200 return true;
1201 }
1202 }
1203 }
1204
1205 // Otherwise, we start a collection cycle if
1206 // old gen want a collection cycle started. Each may use
1207 // an appropriate criterion for making this decision.
1208 // XXX We need to make sure that the gen expansion
1209 // criterion dovetails well with this. XXX NEED TO FIX THIS
1210 if (_cmsGen->should_concurrent_collect()) {
1211 if (Verbose && PrintGCDetails) {
1212 gclog_or_tty->print_cr("CMS old gen initiated");
1213 }
1214 return true;
1215 }
1216
1217 // We start a collection if we believe an incremental collection may fail;
1218 // this is not likely to be productive in practice because it's probably too
1219 // late anyway.
1220 GenCollectedHeap* gch = GenCollectedHeap::heap();
1221 assert(gch->collector_policy()->is_generation_policy(),
1222 "You may want to check the correctness of the following");
1223 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1224 if (Verbose && PrintGCDetails) {
1225 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1226 }
1227 return true;
1228 }
1229
1230 if (MetaspaceGC::should_concurrent_collect()) {
1231 if (Verbose && PrintGCDetails) {
1232 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1233 }
1234 return true;
1235 }
1236
1237 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1238 if (CMSTriggerInterval >= 0) {
1239 if (CMSTriggerInterval == 0) {
1240 // Trigger always
1241 return true;
1242 }
1243
1244 // Check the CMS time since begin (we do not check the stats validity
1245 // as we want to be able to trigger the first CMS cycle as well)
1246 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1247 if (Verbose && PrintGCDetails) {
1248 if (stats().valid()) {
1249 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1250 stats().cms_time_since_begin());
1251 } else {
1252 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1253 }
1254 }
1255 return true;
1256 }
1257 }
1258
1259 return false;
1260 }
1261
1262 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1263
1264 // Clear _expansion_cause fields of constituent generations
1265 void CMSCollector::clear_expansion_cause() {
1266 _cmsGen->clear_expansion_cause();
1267 }
1268
1269 // We should be conservative in starting a collection cycle. To
1270 // start too eagerly runs the risk of collecting too often in the
1271 // extreme. To collect too rarely falls back on full collections,
1272 // which works, even if not optimum in terms of concurrent work.
1273 // As a work around for too eagerly collecting, use the flag
1274 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1275 // giving the user an easily understandable way of controlling the
1276 // collections.
1277 // We want to start a new collection cycle if any of the following
1278 // conditions hold:
1279 // . our current occupancy exceeds the configured initiating occupancy
1280 // for this generation, or
1281 // . we recently needed to expand this space and have not, since that
1282 // expansion, done a collection of this generation, or
1283 // . the underlying space believes that it may be a good idea to initiate
1284 // a concurrent collection (this may be based on criteria such as the
1285 // following: the space uses linear allocation and linear allocation is
1286 // going to fail, or there is believed to be excessive fragmentation in
1287 // the generation, etc... or ...
1288 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1289 // the case of the old generation; see CR 6543076):
1290 // we may be approaching a point at which allocation requests may fail because
1291 // we will be out of sufficient free space given allocation rate estimates.]
1292 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1293
1294 assert_lock_strong(freelistLock());
1295 if (occupancy() > initiating_occupancy()) {
1296 if (PrintGCDetails && Verbose) {
1297 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1298 short_name(), occupancy(), initiating_occupancy());
1299 }
1300 return true;
1301 }
1302 if (UseCMSInitiatingOccupancyOnly) {
1303 return false;
1304 }
1305 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1306 if (PrintGCDetails && Verbose) {
1307 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1308 short_name());
1309 }
1310 return true;
1311 }
1312 return false;
1313 }
1314
1315 void ConcurrentMarkSweepGeneration::collect(bool full,
1316 bool clear_all_soft_refs,
1317 size_t size,
1318 bool tlab)
1319 {
1320 collector()->collect(full, clear_all_soft_refs, size, tlab);
1321 }
1322
1323 void CMSCollector::collect(bool full,
1324 bool clear_all_soft_refs,
1325 size_t size,
1326 bool tlab)
1327 {
1328 // The following "if" branch is present for defensive reasons.
1329 // In the current uses of this interface, it can be replaced with:
1330 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1331 // But I am not placing that assert here to allow future
1332 // generality in invoking this interface.
1333 if (GC_locker::is_active()) {
1334 // A consistency test for GC_locker
1335 assert(GC_locker::needs_gc(), "Should have been set already");
1336 // Skip this foreground collection, instead
1337 // expanding the heap if necessary.
1338 // Need the free list locks for the call to free() in compute_new_size()
1339 compute_new_size();
1340 return;
1341 }
1342 acquire_control_and_collect(full, clear_all_soft_refs);
1343 }
1344
1345 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1346 GenCollectedHeap* gch = GenCollectedHeap::heap();
1347 unsigned int gc_count = gch->total_full_collections();
1348 if (gc_count == full_gc_count) {
1349 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1350 _full_gc_requested = true;
1351 _full_gc_cause = cause;
1352 CGC_lock->notify(); // nudge CMS thread
1353 } else {
1354 assert(gc_count > full_gc_count, "Error: causal loop");
1355 }
1356 }
1357
1358 bool CMSCollector::is_external_interruption() {
1359 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1360 return GCCause::is_user_requested_gc(cause) ||
1361 GCCause::is_serviceability_requested_gc(cause);
1362 }
1363
1364 void CMSCollector::report_concurrent_mode_interruption() {
1365 if (is_external_interruption()) {
1366 if (PrintGCDetails) {
1367 gclog_or_tty->print(" (concurrent mode interrupted)");
1368 }
1369 } else {
1370 if (PrintGCDetails) {
1371 gclog_or_tty->print(" (concurrent mode failure)");
1372 }
1373 _gc_tracer_cm->report_concurrent_mode_failure();
1374 }
1375 }
1376
1377
1378 // The foreground and background collectors need to coordinate in order
1379 // to make sure that they do not mutually interfere with CMS collections.
1380 // When a background collection is active,
1381 // the foreground collector may need to take over (preempt) and
1382 // synchronously complete an ongoing collection. Depending on the
1383 // frequency of the background collections and the heap usage
1384 // of the application, this preemption can be seldom or frequent.
1385 // There are only certain
1386 // points in the background collection that the "collection-baton"
1387 // can be passed to the foreground collector.
1388 //
1389 // The foreground collector will wait for the baton before
1390 // starting any part of the collection. The foreground collector
1391 // will only wait at one location.
1392 //
1393 // The background collector will yield the baton before starting a new
1394 // phase of the collection (e.g., before initial marking, marking from roots,
1395 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1396 // of the loop which switches the phases. The background collector does some
1397 // of the phases (initial mark, final re-mark) with the world stopped.
1398 // Because of locking involved in stopping the world,
1399 // the foreground collector should not block waiting for the background
1400 // collector when it is doing a stop-the-world phase. The background
1401 // collector will yield the baton at an additional point just before
1402 // it enters a stop-the-world phase. Once the world is stopped, the
1403 // background collector checks the phase of the collection. If the
1404 // phase has not changed, it proceeds with the collection. If the
1405 // phase has changed, it skips that phase of the collection. See
1406 // the comments on the use of the Heap_lock in collect_in_background().
1407 //
1408 // Variable used in baton passing.
1409 // _foregroundGCIsActive - Set to true by the foreground collector when
1410 // it wants the baton. The foreground clears it when it has finished
1411 // the collection.
1412 // _foregroundGCShouldWait - Set to true by the background collector
1413 // when it is running. The foreground collector waits while
1414 // _foregroundGCShouldWait is true.
1415 // CGC_lock - monitor used to protect access to the above variables
1416 // and to notify the foreground and background collectors.
1417 // _collectorState - current state of the CMS collection.
1418 //
1419 // The foreground collector
1420 // acquires the CGC_lock
1421 // sets _foregroundGCIsActive
1422 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1423 // various locks acquired in preparation for the collection
1424 // are released so as not to block the background collector
1425 // that is in the midst of a collection
1426 // proceeds with the collection
1427 // clears _foregroundGCIsActive
1428 // returns
1429 //
1430 // The background collector in a loop iterating on the phases of the
1431 // collection
1432 // acquires the CGC_lock
1433 // sets _foregroundGCShouldWait
1434 // if _foregroundGCIsActive is set
1435 // clears _foregroundGCShouldWait, notifies _CGC_lock
1436 // waits on _CGC_lock for _foregroundGCIsActive to become false
1437 // and exits the loop.
1438 // otherwise
1439 // proceed with that phase of the collection
1440 // if the phase is a stop-the-world phase,
1441 // yield the baton once more just before enqueueing
1442 // the stop-world CMS operation (executed by the VM thread).
1443 // returns after all phases of the collection are done
1444 //
1445
1446 void CMSCollector::acquire_control_and_collect(bool full,
1447 bool clear_all_soft_refs) {
1448 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1449 assert(!Thread::current()->is_ConcurrentGC_thread(),
1450 "shouldn't try to acquire control from self!");
1451
1452 // Start the protocol for acquiring control of the
1453 // collection from the background collector (aka CMS thread).
1454 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1455 "VM thread should have CMS token");
1456 // Remember the possibly interrupted state of an ongoing
1457 // concurrent collection
1458 CollectorState first_state = _collectorState;
1459
1460 // Signal to a possibly ongoing concurrent collection that
1461 // we want to do a foreground collection.
1462 _foregroundGCIsActive = true;
1463
1464 // release locks and wait for a notify from the background collector
1465 // releasing the locks in only necessary for phases which
1466 // do yields to improve the granularity of the collection.
1467 assert_lock_strong(bitMapLock());
1468 // We need to lock the Free list lock for the space that we are
1469 // currently collecting.
1470 assert(haveFreelistLocks(), "Must be holding free list locks");
1471 bitMapLock()->unlock();
1472 releaseFreelistLocks();
1473 {
1474 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1475 if (_foregroundGCShouldWait) {
1476 // We are going to be waiting for action for the CMS thread;
1477 // it had better not be gone (for instance at shutdown)!
1478 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1479 "CMS thread must be running");
1480 // Wait here until the background collector gives us the go-ahead
1481 ConcurrentMarkSweepThread::clear_CMS_flag(
1482 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1483 // Get a possibly blocked CMS thread going:
1484 // Note that we set _foregroundGCIsActive true above,
1485 // without protection of the CGC_lock.
1486 CGC_lock->notify();
1487 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1488 "Possible deadlock");
1489 while (_foregroundGCShouldWait) {
1490 // wait for notification
1491 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1492 // Possibility of delay/starvation here, since CMS token does
1493 // not know to give priority to VM thread? Actually, i think
1494 // there wouldn't be any delay/starvation, but the proof of
1495 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1496 }
1497 ConcurrentMarkSweepThread::set_CMS_flag(
1498 ConcurrentMarkSweepThread::CMS_vm_has_token);
1499 }
1500 }
1501 // The CMS_token is already held. Get back the other locks.
1502 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1503 "VM thread should have CMS token");
1504 getFreelistLocks();
1505 bitMapLock()->lock_without_safepoint_check();
1506 if (TraceCMSState) {
1507 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1508 INTPTR_FORMAT " with first state %d", p2i(Thread::current()), first_state);
1509 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1510 }
1511
1512 // Inform cms gen if this was due to partial collection failing.
1513 // The CMS gen may use this fact to determine its expansion policy.
1514 GenCollectedHeap* gch = GenCollectedHeap::heap();
1515 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1516 assert(!_cmsGen->incremental_collection_failed(),
1517 "Should have been noticed, reacted to and cleared");
1518 _cmsGen->set_incremental_collection_failed();
1519 }
1520
1521 if (first_state > Idling) {
1522 report_concurrent_mode_interruption();
1523 }
1524
1525 set_did_compact(true);
1526
1527 // If the collection is being acquired from the background
1528 // collector, there may be references on the discovered
1529 // references lists. Abandon those references, since some
1530 // of them may have become unreachable after concurrent
1531 // discovery; the STW compacting collector will redo discovery
1532 // more precisely, without being subject to floating garbage.
1533 // Leaving otherwise unreachable references in the discovered
1534 // lists would require special handling.
1535 ref_processor()->disable_discovery();
1536 ref_processor()->abandon_partial_discovery();
1537 ref_processor()->verify_no_references_recorded();
1538
1539 if (first_state > Idling) {
1540 save_heap_summary();
1541 }
1542
1543 do_compaction_work(clear_all_soft_refs);
1544
1545 // Has the GC time limit been exceeded?
1546 size_t max_eden_size = _young_gen->max_eden_size();
1547 GCCause::Cause gc_cause = gch->gc_cause();
1548 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1549 _young_gen->eden()->used(),
1550 _cmsGen->max_capacity(),
1551 max_eden_size,
1552 full,
1553 gc_cause,
1554 gch->collector_policy());
1555
1556 // Reset the expansion cause, now that we just completed
1557 // a collection cycle.
1558 clear_expansion_cause();
1559 _foregroundGCIsActive = false;
1560 return;
1561 }
1562
1563 // Resize the tenured generation
1564 // after obtaining the free list locks for the
1565 // two generations.
1566 void CMSCollector::compute_new_size() {
1567 assert_locked_or_safepoint(Heap_lock);
1568 FreelistLocker z(this);
1569 MetaspaceGC::compute_new_size();
1570 _cmsGen->compute_new_size_free_list();
1571 }
1572
1573 // A work method used by the foreground collector to do
1574 // a mark-sweep-compact.
1575 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1576 GenCollectedHeap* gch = GenCollectedHeap::heap();
1577
1578 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1579 gc_timer->register_gc_start();
1580
1581 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1582 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1583
1584 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL);
1585
1586 // Temporarily widen the span of the weak reference processing to
1587 // the entire heap.
1588 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1589 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1590 // Temporarily, clear the "is_alive_non_header" field of the
1591 // reference processor.
1592 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1593 // Temporarily make reference _processing_ single threaded (non-MT).
1594 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1595 // Temporarily make refs discovery atomic
1596 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1597 // Temporarily make reference _discovery_ single threaded (non-MT)
1598 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1599
1600 ref_processor()->set_enqueuing_is_done(false);
1601 ref_processor()->enable_discovery();
1602 ref_processor()->setup_policy(clear_all_soft_refs);
1603 // If an asynchronous collection finishes, the _modUnionTable is
1604 // all clear. If we are assuming the collection from an asynchronous
1605 // collection, clear the _modUnionTable.
1606 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1607 "_modUnionTable should be clear if the baton was not passed");
1608 _modUnionTable.clear_all();
1609 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1610 "mod union for klasses should be clear if the baton was passed");
1611 _ct->klass_rem_set()->clear_mod_union();
1612
1613 // We must adjust the allocation statistics being maintained
1614 // in the free list space. We do so by reading and clearing
1615 // the sweep timer and updating the block flux rate estimates below.
1616 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1617 if (_inter_sweep_timer.is_active()) {
1618 _inter_sweep_timer.stop();
1619 // Note that we do not use this sample to update the _inter_sweep_estimate.
1620 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1621 _inter_sweep_estimate.padded_average(),
1622 _intra_sweep_estimate.padded_average());
1623 }
1624
1625 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1626 #ifdef ASSERT
1627 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1628 size_t free_size = cms_space->free();
1629 assert(free_size ==
1630 pointer_delta(cms_space->end(), cms_space->compaction_top())
1631 * HeapWordSize,
1632 "All the free space should be compacted into one chunk at top");
1633 assert(cms_space->dictionary()->total_chunk_size(
1634 debug_only(cms_space->freelistLock())) == 0 ||
1635 cms_space->totalSizeInIndexedFreeLists() == 0,
1636 "All the free space should be in a single chunk");
1637 size_t num = cms_space->totalCount();
1638 assert((free_size == 0 && num == 0) ||
1639 (free_size > 0 && (num == 1 || num == 2)),
1640 "There should be at most 2 free chunks after compaction");
1641 #endif // ASSERT
1642 _collectorState = Resetting;
1643 assert(_restart_addr == NULL,
1644 "Should have been NULL'd before baton was passed");
1645 reset_stw();
1646 _cmsGen->reset_after_compaction();
1647 _concurrent_cycles_since_last_unload = 0;
1648
1649 // Clear any data recorded in the PLAB chunk arrays.
1650 if (_survivor_plab_array != NULL) {
1651 reset_survivor_plab_arrays();
1652 }
1653
1654 // Adjust the per-size allocation stats for the next epoch.
1655 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1656 // Restart the "inter sweep timer" for the next epoch.
1657 _inter_sweep_timer.reset();
1658 _inter_sweep_timer.start();
1659
1660 gc_timer->register_gc_end();
1661
1662 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1663
1664 // For a mark-sweep-compact, compute_new_size() will be called
1665 // in the heap's do_collection() method.
1666 }
1667
1668 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1669 ContiguousSpace* eden_space = _young_gen->eden();
1670 ContiguousSpace* from_space = _young_gen->from();
1671 ContiguousSpace* to_space = _young_gen->to();
1672 // Eden
1673 if (_eden_chunk_array != NULL) {
1674 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1675 p2i(eden_space->bottom()), p2i(eden_space->top()),
1676 p2i(eden_space->end()), eden_space->capacity());
1677 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1678 "_eden_chunk_capacity=" SIZE_FORMAT,
1679 _eden_chunk_index, _eden_chunk_capacity);
1680 for (size_t i = 0; i < _eden_chunk_index; i++) {
1681 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1682 i, p2i(_eden_chunk_array[i]));
1683 }
1684 }
1685 // Survivor
1686 if (_survivor_chunk_array != NULL) {
1687 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1688 p2i(from_space->bottom()), p2i(from_space->top()),
1689 p2i(from_space->end()), from_space->capacity());
1690 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1691 "_survivor_chunk_capacity=" SIZE_FORMAT,
1692 _survivor_chunk_index, _survivor_chunk_capacity);
1693 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1694 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1695 i, p2i(_survivor_chunk_array[i]));
1696 }
1697 }
1698 }
1699
1700 void CMSCollector::getFreelistLocks() const {
1701 // Get locks for all free lists in all generations that this
1702 // collector is responsible for
1703 _cmsGen->freelistLock()->lock_without_safepoint_check();
1704 }
1705
1706 void CMSCollector::releaseFreelistLocks() const {
1707 // Release locks for all free lists in all generations that this
1708 // collector is responsible for
1709 _cmsGen->freelistLock()->unlock();
1710 }
1711
1712 bool CMSCollector::haveFreelistLocks() const {
1713 // Check locks for all free lists in all generations that this
1714 // collector is responsible for
1715 assert_lock_strong(_cmsGen->freelistLock());
1716 PRODUCT_ONLY(ShouldNotReachHere());
1717 return true;
1718 }
1719
1720 // A utility class that is used by the CMS collector to
1721 // temporarily "release" the foreground collector from its
1722 // usual obligation to wait for the background collector to
1723 // complete an ongoing phase before proceeding.
1724 class ReleaseForegroundGC: public StackObj {
1725 private:
1726 CMSCollector* _c;
1727 public:
1728 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1729 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1730 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1731 // allow a potentially blocked foreground collector to proceed
1732 _c->_foregroundGCShouldWait = false;
1733 if (_c->_foregroundGCIsActive) {
1734 CGC_lock->notify();
1735 }
1736 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1737 "Possible deadlock");
1738 }
1739
1740 ~ReleaseForegroundGC() {
1741 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1742 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1743 _c->_foregroundGCShouldWait = true;
1744 }
1745 };
1746
1747 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1748 assert(Thread::current()->is_ConcurrentGC_thread(),
1749 "A CMS asynchronous collection is only allowed on a CMS thread.");
1750
1751 GenCollectedHeap* gch = GenCollectedHeap::heap();
1752 {
1753 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1754 MutexLockerEx hl(Heap_lock, safepoint_check);
1755 FreelistLocker fll(this);
1756 MutexLockerEx x(CGC_lock, safepoint_check);
1757 if (_foregroundGCIsActive) {
1758 // The foreground collector is. Skip this
1759 // background collection.
1760 assert(!_foregroundGCShouldWait, "Should be clear");
1761 return;
1762 } else {
1763 assert(_collectorState == Idling, "Should be idling before start.");
1764 _collectorState = InitialMarking;
1765 register_gc_start(cause);
1766 // Reset the expansion cause, now that we are about to begin
1767 // a new cycle.
1768 clear_expansion_cause();
1769
1770 // Clear the MetaspaceGC flag since a concurrent collection
1771 // is starting but also clear it after the collection.
1772 MetaspaceGC::set_should_concurrent_collect(false);
1773 }
1774 // Decide if we want to enable class unloading as part of the
1775 // ensuing concurrent GC cycle.
1776 update_should_unload_classes();
1777 _full_gc_requested = false; // acks all outstanding full gc requests
1778 _full_gc_cause = GCCause::_no_gc;
1779 // Signal that we are about to start a collection
1780 gch->increment_total_full_collections(); // ... starting a collection cycle
1781 _collection_count_start = gch->total_full_collections();
1782 }
1783
1784 // Used for PrintGC
1785 size_t prev_used = 0;
1786 if (PrintGC && Verbose) {
1787 prev_used = _cmsGen->used();
1788 }
1789
1790 // The change of the collection state is normally done at this level;
1791 // the exceptions are phases that are executed while the world is
1792 // stopped. For those phases the change of state is done while the
1793 // world is stopped. For baton passing purposes this allows the
1794 // background collector to finish the phase and change state atomically.
1795 // The foreground collector cannot wait on a phase that is done
1796 // while the world is stopped because the foreground collector already
1797 // has the world stopped and would deadlock.
1798 while (_collectorState != Idling) {
1799 if (TraceCMSState) {
1800 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
1801 p2i(Thread::current()), _collectorState);
1802 }
1803 // The foreground collector
1804 // holds the Heap_lock throughout its collection.
1805 // holds the CMS token (but not the lock)
1806 // except while it is waiting for the background collector to yield.
1807 //
1808 // The foreground collector should be blocked (not for long)
1809 // if the background collector is about to start a phase
1810 // executed with world stopped. If the background
1811 // collector has already started such a phase, the
1812 // foreground collector is blocked waiting for the
1813 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1814 // are executed in the VM thread.
1815 //
1816 // The locking order is
1817 // PendingListLock (PLL) -- if applicable (FinalMarking)
1818 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1819 // CMS token (claimed in
1820 // stop_world_and_do() -->
1821 // safepoint_synchronize() -->
1822 // CMSThread::synchronize())
1823
1824 {
1825 // Check if the FG collector wants us to yield.
1826 CMSTokenSync x(true); // is cms thread
1827 if (waitForForegroundGC()) {
1828 // We yielded to a foreground GC, nothing more to be
1829 // done this round.
1830 assert(_foregroundGCShouldWait == false, "We set it to false in "
1831 "waitForForegroundGC()");
1832 if (TraceCMSState) {
1833 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1834 " exiting collection CMS state %d",
1835 p2i(Thread::current()), _collectorState);
1836 }
1837 return;
1838 } else {
1839 // The background collector can run but check to see if the
1840 // foreground collector has done a collection while the
1841 // background collector was waiting to get the CGC_lock
1842 // above. If yes, break so that _foregroundGCShouldWait
1843 // is cleared before returning.
1844 if (_collectorState == Idling) {
1845 break;
1846 }
1847 }
1848 }
1849
1850 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1851 "should be waiting");
1852
1853 switch (_collectorState) {
1854 case InitialMarking:
1855 {
1856 ReleaseForegroundGC x(this);
1857 stats().record_cms_begin();
1858 VM_CMS_Initial_Mark initial_mark_op(this);
1859 VMThread::execute(&initial_mark_op);
1860 }
1861 // The collector state may be any legal state at this point
1862 // since the background collector may have yielded to the
1863 // foreground collector.
1864 break;
1865 case Marking:
1866 // initial marking in checkpointRootsInitialWork has been completed
1867 if (markFromRoots()) { // we were successful
1868 assert(_collectorState == Precleaning, "Collector state should "
1869 "have changed");
1870 } else {
1871 assert(_foregroundGCIsActive, "Internal state inconsistency");
1872 }
1873 break;
1874 case Precleaning:
1875 // marking from roots in markFromRoots has been completed
1876 preclean();
1877 assert(_collectorState == AbortablePreclean ||
1878 _collectorState == FinalMarking,
1879 "Collector state should have changed");
1880 break;
1881 case AbortablePreclean:
1882 abortable_preclean();
1883 assert(_collectorState == FinalMarking, "Collector state should "
1884 "have changed");
1885 break;
1886 case FinalMarking:
1887 {
1888 ReleaseForegroundGC x(this);
1889
1890 VM_CMS_Final_Remark final_remark_op(this);
1891 VMThread::execute(&final_remark_op);
1892 }
1893 assert(_foregroundGCShouldWait, "block post-condition");
1894 break;
1895 case Sweeping:
1896 // final marking in checkpointRootsFinal has been completed
1897 sweep();
1898 assert(_collectorState == Resizing, "Collector state change "
1899 "to Resizing must be done under the free_list_lock");
1900
1901 case Resizing: {
1902 // Sweeping has been completed...
1903 // At this point the background collection has completed.
1904 // Don't move the call to compute_new_size() down
1905 // into code that might be executed if the background
1906 // collection was preempted.
1907 {
1908 ReleaseForegroundGC x(this); // unblock FG collection
1909 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1910 CMSTokenSync z(true); // not strictly needed.
1911 if (_collectorState == Resizing) {
1912 compute_new_size();
1913 save_heap_summary();
1914 _collectorState = Resetting;
1915 } else {
1916 assert(_collectorState == Idling, "The state should only change"
1917 " because the foreground collector has finished the collection");
1918 }
1919 }
1920 break;
1921 }
1922 case Resetting:
1923 // CMS heap resizing has been completed
1924 reset_concurrent();
1925 assert(_collectorState == Idling, "Collector state should "
1926 "have changed");
1927
1928 MetaspaceGC::set_should_concurrent_collect(false);
1929
1930 stats().record_cms_end();
1931 // Don't move the concurrent_phases_end() and compute_new_size()
1932 // calls to here because a preempted background collection
1933 // has it's state set to "Resetting".
1934 break;
1935 case Idling:
1936 default:
1937 ShouldNotReachHere();
1938 break;
1939 }
1940 if (TraceCMSState) {
1941 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1942 p2i(Thread::current()), _collectorState);
1943 }
1944 assert(_foregroundGCShouldWait, "block post-condition");
1945 }
1946
1947 // Should this be in gc_epilogue?
1948 collector_policy()->counters()->update_counters();
1949
1950 {
1951 // Clear _foregroundGCShouldWait and, in the event that the
1952 // foreground collector is waiting, notify it, before
1953 // returning.
1954 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1955 _foregroundGCShouldWait = false;
1956 if (_foregroundGCIsActive) {
1957 CGC_lock->notify();
1958 }
1959 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1960 "Possible deadlock");
1961 }
1962 if (TraceCMSState) {
1963 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1964 " exiting collection CMS state %d",
1965 p2i(Thread::current()), _collectorState);
1966 }
1967 if (PrintGC && Verbose) {
1968 _cmsGen->print_heap_change(prev_used);
1969 }
1970 }
1971
1972 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1973 _cms_start_registered = true;
1974 _gc_timer_cm->register_gc_start();
1975 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1976 }
1977
1978 void CMSCollector::register_gc_end() {
1979 if (_cms_start_registered) {
1980 report_heap_summary(GCWhen::AfterGC);
1981
1982 _gc_timer_cm->register_gc_end();
1983 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1984 _cms_start_registered = false;
1985 }
1986 }
1987
1988 void CMSCollector::save_heap_summary() {
1989 GenCollectedHeap* gch = GenCollectedHeap::heap();
1990 _last_heap_summary = gch->create_heap_summary();
1991 _last_metaspace_summary = gch->create_metaspace_summary();
1992 }
1993
1994 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1995 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1996 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1997 }
1998
1999 bool CMSCollector::waitForForegroundGC() {
2000 bool res = false;
2001 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2002 "CMS thread should have CMS token");
2003 // Block the foreground collector until the
2004 // background collectors decides whether to
2005 // yield.
2006 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2007 _foregroundGCShouldWait = true;
2008 if (_foregroundGCIsActive) {
2009 // The background collector yields to the
2010 // foreground collector and returns a value
2011 // indicating that it has yielded. The foreground
2012 // collector can proceed.
2013 res = true;
2014 _foregroundGCShouldWait = false;
2015 ConcurrentMarkSweepThread::clear_CMS_flag(
2016 ConcurrentMarkSweepThread::CMS_cms_has_token);
2017 ConcurrentMarkSweepThread::set_CMS_flag(
2018 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2019 // Get a possibly blocked foreground thread going
2020 CGC_lock->notify();
2021 if (TraceCMSState) {
2022 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2023 p2i(Thread::current()), _collectorState);
2024 }
2025 while (_foregroundGCIsActive) {
2026 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2027 }
2028 ConcurrentMarkSweepThread::set_CMS_flag(
2029 ConcurrentMarkSweepThread::CMS_cms_has_token);
2030 ConcurrentMarkSweepThread::clear_CMS_flag(
2031 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2032 }
2033 if (TraceCMSState) {
2034 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2035 p2i(Thread::current()), _collectorState);
2036 }
2037 return res;
2038 }
2039
2040 // Because of the need to lock the free lists and other structures in
2041 // the collector, common to all the generations that the collector is
2042 // collecting, we need the gc_prologues of individual CMS generations
2043 // delegate to their collector. It may have been simpler had the
2044 // current infrastructure allowed one to call a prologue on a
2045 // collector. In the absence of that we have the generation's
2046 // prologue delegate to the collector, which delegates back
2047 // some "local" work to a worker method in the individual generations
2048 // that it's responsible for collecting, while itself doing any
2049 // work common to all generations it's responsible for. A similar
2050 // comment applies to the gc_epilogue()'s.
2051 // The role of the variable _between_prologue_and_epilogue is to
2052 // enforce the invocation protocol.
2053 void CMSCollector::gc_prologue(bool full) {
2054 // Call gc_prologue_work() for the CMSGen
2055 // we are responsible for.
2056
2057 // The following locking discipline assumes that we are only called
2058 // when the world is stopped.
2059 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2060
2061 // The CMSCollector prologue must call the gc_prologues for the
2062 // "generations" that it's responsible
2063 // for.
2064
2065 assert( Thread::current()->is_VM_thread()
2066 || ( CMSScavengeBeforeRemark
2067 && Thread::current()->is_ConcurrentGC_thread()),
2068 "Incorrect thread type for prologue execution");
2069
2070 if (_between_prologue_and_epilogue) {
2071 // We have already been invoked; this is a gc_prologue delegation
2072 // from yet another CMS generation that we are responsible for, just
2073 // ignore it since all relevant work has already been done.
2074 return;
2075 }
2076
2077 // set a bit saying prologue has been called; cleared in epilogue
2078 _between_prologue_and_epilogue = true;
2079 // Claim locks for common data structures, then call gc_prologue_work()
2080 // for each CMSGen.
2081
2082 getFreelistLocks(); // gets free list locks on constituent spaces
2083 bitMapLock()->lock_without_safepoint_check();
2084
2085 // Should call gc_prologue_work() for all cms gens we are responsible for
2086 bool duringMarking = _collectorState >= Marking
2087 && _collectorState < Sweeping;
2088
2089 // The young collections clear the modified oops state, which tells if
2090 // there are any modified oops in the class. The remark phase also needs
2091 // that information. Tell the young collection to save the union of all
2092 // modified klasses.
2093 if (duringMarking) {
2094 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2095 }
2096
2097 bool registerClosure = duringMarking;
2098
2099 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2100
2101 if (!full) {
2102 stats().record_gc0_begin();
2103 }
2104 }
2105
2106 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2107
2108 _capacity_at_prologue = capacity();
2109 _used_at_prologue = used();
2110
2111 // Delegate to CMScollector which knows how to coordinate between
2112 // this and any other CMS generations that it is responsible for
2113 // collecting.
2114 collector()->gc_prologue(full);
2115 }
2116
2117 // This is a "private" interface for use by this generation's CMSCollector.
2118 // Not to be called directly by any other entity (for instance,
2119 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2120 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2121 bool registerClosure, ModUnionClosure* modUnionClosure) {
2122 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2123 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2124 "Should be NULL");
2125 if (registerClosure) {
2126 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2127 }
2128 cmsSpace()->gc_prologue();
2129 // Clear stat counters
2130 NOT_PRODUCT(
2131 assert(_numObjectsPromoted == 0, "check");
2132 assert(_numWordsPromoted == 0, "check");
2133 if (Verbose && PrintGC) {
2134 gclog_or_tty->print("Allocated " SIZE_FORMAT " objects, "
2135 SIZE_FORMAT " bytes concurrently",
2136 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2137 }
2138 _numObjectsAllocated = 0;
2139 _numWordsAllocated = 0;
2140 )
2141 }
2142
2143 void CMSCollector::gc_epilogue(bool full) {
2144 // The following locking discipline assumes that we are only called
2145 // when the world is stopped.
2146 assert(SafepointSynchronize::is_at_safepoint(),
2147 "world is stopped assumption");
2148
2149 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2150 // if linear allocation blocks need to be appropriately marked to allow the
2151 // the blocks to be parsable. We also check here whether we need to nudge the
2152 // CMS collector thread to start a new cycle (if it's not already active).
2153 assert( Thread::current()->is_VM_thread()
2154 || ( CMSScavengeBeforeRemark
2155 && Thread::current()->is_ConcurrentGC_thread()),
2156 "Incorrect thread type for epilogue execution");
2157
2158 if (!_between_prologue_and_epilogue) {
2159 // We have already been invoked; this is a gc_epilogue delegation
2160 // from yet another CMS generation that we are responsible for, just
2161 // ignore it since all relevant work has already been done.
2162 return;
2163 }
2164 assert(haveFreelistLocks(), "must have freelist locks");
2165 assert_lock_strong(bitMapLock());
2166
2167 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2168
2169 _cmsGen->gc_epilogue_work(full);
2170
2171 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2172 // in case sampling was not already enabled, enable it
2173 _start_sampling = true;
2174 }
2175 // reset _eden_chunk_array so sampling starts afresh
2176 _eden_chunk_index = 0;
2177
2178 size_t cms_used = _cmsGen->cmsSpace()->used();
2179
2180 // update performance counters - this uses a special version of
2181 // update_counters() that allows the utilization to be passed as a
2182 // parameter, avoiding multiple calls to used().
2183 //
2184 _cmsGen->update_counters(cms_used);
2185
2186 bitMapLock()->unlock();
2187 releaseFreelistLocks();
2188
2189 if (!CleanChunkPoolAsync) {
2190 Chunk::clean_chunk_pool();
2191 }
2192
2193 set_did_compact(false);
2194 _between_prologue_and_epilogue = false; // ready for next cycle
2195 }
2196
2197 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2198 collector()->gc_epilogue(full);
2199
2200 // Also reset promotion tracking in par gc thread states.
2201 for (uint i = 0; i < ParallelGCThreads; i++) {
2202 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2203 }
2204 }
2205
2206 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2207 assert(!incremental_collection_failed(), "Should have been cleared");
2208 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2209 cmsSpace()->gc_epilogue();
2210 // Print stat counters
2211 NOT_PRODUCT(
2212 assert(_numObjectsAllocated == 0, "check");
2213 assert(_numWordsAllocated == 0, "check");
2214 if (Verbose && PrintGC) {
2215 gclog_or_tty->print("Promoted " SIZE_FORMAT " objects, "
2216 SIZE_FORMAT " bytes",
2217 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2218 }
2219 _numObjectsPromoted = 0;
2220 _numWordsPromoted = 0;
2221 )
2222
2223 if (PrintGC && Verbose) {
2224 // Call down the chain in contiguous_available needs the freelistLock
2225 // so print this out before releasing the freeListLock.
2226 gclog_or_tty->print(" Contiguous available " SIZE_FORMAT " bytes ",
2227 contiguous_available());
2228 }
2229 }
2230
2231 #ifndef PRODUCT
2232 bool CMSCollector::have_cms_token() {
2233 Thread* thr = Thread::current();
2234 if (thr->is_VM_thread()) {
2235 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2236 } else if (thr->is_ConcurrentGC_thread()) {
2237 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2238 } else if (thr->is_GC_task_thread()) {
2239 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2240 ParGCRareEvent_lock->owned_by_self();
2241 }
2242 return false;
2243 }
2244
2245 // Check reachability of the given heap address in CMS generation,
2246 // treating all other generations as roots.
2247 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2248 // We could "guarantee" below, rather than assert, but I'll
2249 // leave these as "asserts" so that an adventurous debugger
2250 // could try this in the product build provided some subset of
2251 // the conditions were met, provided they were interested in the
2252 // results and knew that the computation below wouldn't interfere
2253 // with other concurrent computations mutating the structures
2254 // being read or written.
2255 assert(SafepointSynchronize::is_at_safepoint(),
2256 "Else mutations in object graph will make answer suspect");
2257 assert(have_cms_token(), "Should hold cms token");
2258 assert(haveFreelistLocks(), "must hold free list locks");
2259 assert_lock_strong(bitMapLock());
2260
2261 // Clear the marking bit map array before starting, but, just
2262 // for kicks, first report if the given address is already marked
2263 tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2264 _markBitMap.isMarked(addr) ? "" : " not");
2265
2266 if (verify_after_remark()) {
2267 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2268 bool result = verification_mark_bm()->isMarked(addr);
2269 tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2270 result ? "IS" : "is NOT");
2271 return result;
2272 } else {
2273 tty->print_cr("Could not compute result");
2274 return false;
2275 }
2276 }
2277 #endif
2278
2279 void
2280 CMSCollector::print_on_error(outputStream* st) {
2281 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2282 if (collector != NULL) {
2283 CMSBitMap* bitmap = &collector->_markBitMap;
2284 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2285 bitmap->print_on_error(st, " Bits: ");
2286
2287 st->cr();
2288
2289 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2290 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2291 mut_bitmap->print_on_error(st, " Bits: ");
2292 }
2293 }
2294
2295 ////////////////////////////////////////////////////////
2296 // CMS Verification Support
2297 ////////////////////////////////////////////////////////
2298 // Following the remark phase, the following invariant
2299 // should hold -- each object in the CMS heap which is
2300 // marked in markBitMap() should be marked in the verification_mark_bm().
2301
2302 class VerifyMarkedClosure: public BitMapClosure {
2303 CMSBitMap* _marks;
2304 bool _failed;
2305
2306 public:
2307 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2308
2309 bool do_bit(size_t offset) {
2310 HeapWord* addr = _marks->offsetToHeapWord(offset);
2311 if (!_marks->isMarked(addr)) {
2312 oop(addr)->print_on(gclog_or_tty);
2313 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2314 _failed = true;
2315 }
2316 return true;
2317 }
2318
2319 bool failed() { return _failed; }
2320 };
2321
2322 bool CMSCollector::verify_after_remark(bool silent) {
2323 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2324 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2325 static bool init = false;
2326
2327 assert(SafepointSynchronize::is_at_safepoint(),
2328 "Else mutations in object graph will make answer suspect");
2329 assert(have_cms_token(),
2330 "Else there may be mutual interference in use of "
2331 " verification data structures");
2332 assert(_collectorState > Marking && _collectorState <= Sweeping,
2333 "Else marking info checked here may be obsolete");
2334 assert(haveFreelistLocks(), "must hold free list locks");
2335 assert_lock_strong(bitMapLock());
2336
2337
2338 // Allocate marking bit map if not already allocated
2339 if (!init) { // first time
2340 if (!verification_mark_bm()->allocate(_span)) {
2341 return false;
2342 }
2343 init = true;
2344 }
2345
2346 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2347
2348 // Turn off refs discovery -- so we will be tracing through refs.
2349 // This is as intended, because by this time
2350 // GC must already have cleared any refs that need to be cleared,
2351 // and traced those that need to be marked; moreover,
2352 // the marking done here is not going to interfere in any
2353 // way with the marking information used by GC.
2354 NoRefDiscovery no_discovery(ref_processor());
2355
2356 #if defined(COMPILER2) || INCLUDE_JVMCI
2357 DerivedPointerTableDeactivate dpt_deact;
2358 #endif
2359
2360 // Clear any marks from a previous round
2361 verification_mark_bm()->clear_all();
2362 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2363 verify_work_stacks_empty();
2364
2365 GenCollectedHeap* gch = GenCollectedHeap::heap();
2366 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2367 // Update the saved marks which may affect the root scans.
2368 gch->save_marks();
2369
2370 if (CMSRemarkVerifyVariant == 1) {
2371 // In this first variant of verification, we complete
2372 // all marking, then check if the new marks-vector is
2373 // a subset of the CMS marks-vector.
2374 verify_after_remark_work_1();
2375 } else if (CMSRemarkVerifyVariant == 2) {
2376 // In this second variant of verification, we flag an error
2377 // (i.e. an object reachable in the new marks-vector not reachable
2378 // in the CMS marks-vector) immediately, also indicating the
2379 // identify of an object (A) that references the unmarked object (B) --
2380 // presumably, a mutation to A failed to be picked up by preclean/remark?
2381 verify_after_remark_work_2();
2382 } else {
2383 warning("Unrecognized value " UINTX_FORMAT " for CMSRemarkVerifyVariant",
2384 CMSRemarkVerifyVariant);
2385 }
2386 if (!silent) gclog_or_tty->print(" done] ");
2387 return true;
2388 }
2389
2390 void CMSCollector::verify_after_remark_work_1() {
2391 ResourceMark rm;
2392 HandleMark hm;
2393 GenCollectedHeap* gch = GenCollectedHeap::heap();
2394
2395 // Get a clear set of claim bits for the roots processing to work with.
2396 ClassLoaderDataGraph::clear_claimed_marks();
2397
2398 // Mark from roots one level into CMS
2399 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2400 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2401
2402 {
2403 StrongRootsScope srs(1);
2404
2405 gch->gen_process_roots(&srs,
2406 GenCollectedHeap::OldGen,
2407 true, // young gen as roots
2408 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2409 should_unload_classes(),
2410 ¬Older,
2411 NULL,
2412 NULL);
2413 }
2414
2415 // Now mark from the roots
2416 MarkFromRootsClosure markFromRootsClosure(this, _span,
2417 verification_mark_bm(), verification_mark_stack(),
2418 false /* don't yield */, true /* verifying */);
2419 assert(_restart_addr == NULL, "Expected pre-condition");
2420 verification_mark_bm()->iterate(&markFromRootsClosure);
2421 while (_restart_addr != NULL) {
2422 // Deal with stack overflow: by restarting at the indicated
2423 // address.
2424 HeapWord* ra = _restart_addr;
2425 markFromRootsClosure.reset(ra);
2426 _restart_addr = NULL;
2427 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2428 }
2429 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2430 verify_work_stacks_empty();
2431
2432 // Marking completed -- now verify that each bit marked in
2433 // verification_mark_bm() is also marked in markBitMap(); flag all
2434 // errors by printing corresponding objects.
2435 VerifyMarkedClosure vcl(markBitMap());
2436 verification_mark_bm()->iterate(&vcl);
2437 if (vcl.failed()) {
2438 gclog_or_tty->print("Verification failed");
2439 gch->print_on(gclog_or_tty);
2440 fatal("CMS: failed marking verification after remark");
2441 }
2442 }
2443
2444 class VerifyKlassOopsKlassClosure : public KlassClosure {
2445 class VerifyKlassOopsClosure : public OopClosure {
2446 CMSBitMap* _bitmap;
2447 public:
2448 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2449 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2450 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2451 } _oop_closure;
2452 public:
2453 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2454 void do_klass(Klass* k) {
2455 k->oops_do(&_oop_closure);
2456 }
2457 };
2458
2459 void CMSCollector::verify_after_remark_work_2() {
2460 ResourceMark rm;
2461 HandleMark hm;
2462 GenCollectedHeap* gch = GenCollectedHeap::heap();
2463
2464 // Get a clear set of claim bits for the roots processing to work with.
2465 ClassLoaderDataGraph::clear_claimed_marks();
2466
2467 // Mark from roots one level into CMS
2468 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2469 markBitMap());
2470 CLDToOopClosure cld_closure(¬Older, true);
2471
2472 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2473
2474 {
2475 StrongRootsScope srs(1);
2476
2477 gch->gen_process_roots(&srs,
2478 GenCollectedHeap::OldGen,
2479 true, // young gen as roots
2480 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2481 should_unload_classes(),
2482 ¬Older,
2483 NULL,
2484 &cld_closure);
2485 }
2486
2487 // Now mark from the roots
2488 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2489 verification_mark_bm(), markBitMap(), verification_mark_stack());
2490 assert(_restart_addr == NULL, "Expected pre-condition");
2491 verification_mark_bm()->iterate(&markFromRootsClosure);
2492 while (_restart_addr != NULL) {
2493 // Deal with stack overflow: by restarting at the indicated
2494 // address.
2495 HeapWord* ra = _restart_addr;
2496 markFromRootsClosure.reset(ra);
2497 _restart_addr = NULL;
2498 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2499 }
2500 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2501 verify_work_stacks_empty();
2502
2503 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2504 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2505
2506 // Marking completed -- now verify that each bit marked in
2507 // verification_mark_bm() is also marked in markBitMap(); flag all
2508 // errors by printing corresponding objects.
2509 VerifyMarkedClosure vcl(markBitMap());
2510 verification_mark_bm()->iterate(&vcl);
2511 assert(!vcl.failed(), "Else verification above should not have succeeded");
2512 }
2513
2514 void ConcurrentMarkSweepGeneration::save_marks() {
2515 // delegate to CMS space
2516 cmsSpace()->save_marks();
2517 for (uint i = 0; i < ParallelGCThreads; i++) {
2518 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2519 }
2520 }
2521
2522 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2523 return cmsSpace()->no_allocs_since_save_marks();
2524 }
2525
2526 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2527 \
2528 void ConcurrentMarkSweepGeneration:: \
2529 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2530 cl->set_generation(this); \
2531 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2532 cl->reset_generation(); \
2533 save_marks(); \
2534 }
2535
2536 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2537
2538 void
2539 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2540 if (freelistLock()->owned_by_self()) {
2541 Generation::oop_iterate(cl);
2542 } else {
2543 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2544 Generation::oop_iterate(cl);
2545 }
2546 }
2547
2548 void
2549 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2550 if (freelistLock()->owned_by_self()) {
2551 Generation::object_iterate(cl);
2552 } else {
2553 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2554 Generation::object_iterate(cl);
2555 }
2556 }
2557
2558 void
2559 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2560 if (freelistLock()->owned_by_self()) {
2561 Generation::safe_object_iterate(cl);
2562 } else {
2563 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2564 Generation::safe_object_iterate(cl);
2565 }
2566 }
2567
2568 void
2569 ConcurrentMarkSweepGeneration::post_compact() {
2570 }
2571
2572 void
2573 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2574 // Fix the linear allocation blocks to look like free blocks.
2575
2576 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2577 // are not called when the heap is verified during universe initialization and
2578 // at vm shutdown.
2579 if (freelistLock()->owned_by_self()) {
2580 cmsSpace()->prepare_for_verify();
2581 } else {
2582 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2583 cmsSpace()->prepare_for_verify();
2584 }
2585 }
2586
2587 void
2588 ConcurrentMarkSweepGeneration::verify() {
2589 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2590 // are not called when the heap is verified during universe initialization and
2591 // at vm shutdown.
2592 if (freelistLock()->owned_by_self()) {
2593 cmsSpace()->verify();
2594 } else {
2595 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2596 cmsSpace()->verify();
2597 }
2598 }
2599
2600 void CMSCollector::verify() {
2601 _cmsGen->verify();
2602 }
2603
2604 #ifndef PRODUCT
2605 bool CMSCollector::overflow_list_is_empty() const {
2606 assert(_num_par_pushes >= 0, "Inconsistency");
2607 if (_overflow_list == NULL) {
2608 assert(_num_par_pushes == 0, "Inconsistency");
2609 }
2610 return _overflow_list == NULL;
2611 }
2612
2613 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2614 // merely consolidate assertion checks that appear to occur together frequently.
2615 void CMSCollector::verify_work_stacks_empty() const {
2616 assert(_markStack.isEmpty(), "Marking stack should be empty");
2617 assert(overflow_list_is_empty(), "Overflow list should be empty");
2618 }
2619
2620 void CMSCollector::verify_overflow_empty() const {
2621 assert(overflow_list_is_empty(), "Overflow list should be empty");
2622 assert(no_preserved_marks(), "No preserved marks");
2623 }
2624 #endif // PRODUCT
2625
2626 // Decide if we want to enable class unloading as part of the
2627 // ensuing concurrent GC cycle. We will collect and
2628 // unload classes if it's the case that:
2629 // (1) an explicit gc request has been made and the flag
2630 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2631 // (2) (a) class unloading is enabled at the command line, and
2632 // (b) old gen is getting really full
2633 // NOTE: Provided there is no change in the state of the heap between
2634 // calls to this method, it should have idempotent results. Moreover,
2635 // its results should be monotonically increasing (i.e. going from 0 to 1,
2636 // but not 1 to 0) between successive calls between which the heap was
2637 // not collected. For the implementation below, it must thus rely on
2638 // the property that concurrent_cycles_since_last_unload()
2639 // will not decrease unless a collection cycle happened and that
2640 // _cmsGen->is_too_full() are
2641 // themselves also monotonic in that sense. See check_monotonicity()
2642 // below.
2643 void CMSCollector::update_should_unload_classes() {
2644 _should_unload_classes = false;
2645 // Condition 1 above
2646 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2647 _should_unload_classes = true;
2648 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2649 // Disjuncts 2.b.(i,ii,iii) above
2650 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2651 CMSClassUnloadingMaxInterval)
2652 || _cmsGen->is_too_full();
2653 }
2654 }
2655
2656 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2657 bool res = should_concurrent_collect();
2658 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2659 return res;
2660 }
2661
2662 void CMSCollector::setup_cms_unloading_and_verification_state() {
2663 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2664 || VerifyBeforeExit;
2665 const int rso = GenCollectedHeap::SO_AllCodeCache;
2666
2667 // We set the proper root for this CMS cycle here.
2668 if (should_unload_classes()) { // Should unload classes this cycle
2669 remove_root_scanning_option(rso); // Shrink the root set appropriately
2670 set_verifying(should_verify); // Set verification state for this cycle
2671 return; // Nothing else needs to be done at this time
2672 }
2673
2674 // Not unloading classes this cycle
2675 assert(!should_unload_classes(), "Inconsistency!");
2676
2677 // If we are not unloading classes then add SO_AllCodeCache to root
2678 // scanning options.
2679 add_root_scanning_option(rso);
2680
2681 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2682 set_verifying(true);
2683 } else if (verifying() && !should_verify) {
2684 // We were verifying, but some verification flags got disabled.
2685 set_verifying(false);
2686 // Exclude symbols, strings and code cache elements from root scanning to
2687 // reduce IM and RM pauses.
2688 remove_root_scanning_option(rso);
2689 }
2690 }
2691
2692
2693 #ifndef PRODUCT
2694 HeapWord* CMSCollector::block_start(const void* p) const {
2695 const HeapWord* addr = (HeapWord*)p;
2696 if (_span.contains(p)) {
2697 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2698 return _cmsGen->cmsSpace()->block_start(p);
2699 }
2700 }
2701 return NULL;
2702 }
2703 #endif
2704
2705 HeapWord*
2706 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2707 bool tlab,
2708 bool parallel) {
2709 CMSSynchronousYieldRequest yr;
2710 assert(!tlab, "Can't deal with TLAB allocation");
2711 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2712 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2713 if (GCExpandToAllocateDelayMillis > 0) {
2714 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2715 }
2716 return have_lock_and_allocate(word_size, tlab);
2717 }
2718
2719 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2720 size_t bytes,
2721 size_t expand_bytes,
2722 CMSExpansionCause::Cause cause)
2723 {
2724
2725 bool success = expand(bytes, expand_bytes);
2726
2727 // remember why we expanded; this information is used
2728 // by shouldConcurrentCollect() when making decisions on whether to start
2729 // a new CMS cycle.
2730 if (success) {
2731 set_expansion_cause(cause);
2732 if (PrintGCDetails && Verbose) {
2733 gclog_or_tty->print_cr("Expanded CMS gen for %s",
2734 CMSExpansionCause::to_string(cause));
2735 }
2736 }
2737 }
2738
2739 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2740 HeapWord* res = NULL;
2741 MutexLocker x(ParGCRareEvent_lock);
2742 while (true) {
2743 // Expansion by some other thread might make alloc OK now:
2744 res = ps->lab.alloc(word_sz);
2745 if (res != NULL) return res;
2746 // If there's not enough expansion space available, give up.
2747 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2748 return NULL;
2749 }
2750 // Otherwise, we try expansion.
2751 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2752 // Now go around the loop and try alloc again;
2753 // A competing par_promote might beat us to the expansion space,
2754 // so we may go around the loop again if promotion fails again.
2755 if (GCExpandToAllocateDelayMillis > 0) {
2756 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2757 }
2758 }
2759 }
2760
2761
2762 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2763 PromotionInfo* promo) {
2764 MutexLocker x(ParGCRareEvent_lock);
2765 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2766 while (true) {
2767 // Expansion by some other thread might make alloc OK now:
2768 if (promo->ensure_spooling_space()) {
2769 assert(promo->has_spooling_space(),
2770 "Post-condition of successful ensure_spooling_space()");
2771 return true;
2772 }
2773 // If there's not enough expansion space available, give up.
2774 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2775 return false;
2776 }
2777 // Otherwise, we try expansion.
2778 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2779 // Now go around the loop and try alloc again;
2780 // A competing allocation might beat us to the expansion space,
2781 // so we may go around the loop again if allocation fails again.
2782 if (GCExpandToAllocateDelayMillis > 0) {
2783 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2784 }
2785 }
2786 }
2787
2788 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2789 // Only shrink if a compaction was done so that all the free space
2790 // in the generation is in a contiguous block at the end.
2791 if (did_compact()) {
2792 CardGeneration::shrink(bytes);
2793 }
2794 }
2795
2796 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2797 assert_locked_or_safepoint(Heap_lock);
2798 }
2799
2800 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2801 assert_locked_or_safepoint(Heap_lock);
2802 assert_lock_strong(freelistLock());
2803 if (PrintGCDetails && Verbose) {
2804 warning("Shrinking of CMS not yet implemented");
2805 }
2806 return;
2807 }
2808
2809
2810 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2811 // phases.
2812 class CMSPhaseAccounting: public StackObj {
2813 public:
2814 CMSPhaseAccounting(CMSCollector *collector,
2815 const char *phase,
2816 bool print_cr = true);
2817 ~CMSPhaseAccounting();
2818
2819 private:
2820 CMSCollector *_collector;
2821 const char *_phase;
2822 elapsedTimer _wallclock;
2823 bool _print_cr;
2824
2825 public:
2826 // Not MT-safe; so do not pass around these StackObj's
2827 // where they may be accessed by other threads.
2828 jlong wallclock_millis() {
2829 assert(_wallclock.is_active(), "Wall clock should not stop");
2830 _wallclock.stop(); // to record time
2831 jlong ret = _wallclock.milliseconds();
2832 _wallclock.start(); // restart
2833 return ret;
2834 }
2835 };
2836
2837 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2838 const char *phase,
2839 bool print_cr) :
2840 _collector(collector), _phase(phase), _print_cr(print_cr) {
2841
2842 if (PrintCMSStatistics != 0) {
2843 _collector->resetYields();
2844 }
2845 if (PrintGCDetails) {
2846 gclog_or_tty->gclog_stamp();
2847 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
2848 _collector->cmsGen()->short_name(), _phase);
2849 }
2850 _collector->resetTimer();
2851 _wallclock.start();
2852 _collector->startTimer();
2853 }
2854
2855 CMSPhaseAccounting::~CMSPhaseAccounting() {
2856 assert(_wallclock.is_active(), "Wall clock should not have stopped");
2857 _collector->stopTimer();
2858 _wallclock.stop();
2859 if (PrintGCDetails) {
2860 gclog_or_tty->gclog_stamp();
2861 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
2862 _collector->cmsGen()->short_name(),
2863 _phase, _collector->timerValue(), _wallclock.seconds());
2864 if (_print_cr) {
2865 gclog_or_tty->cr();
2866 }
2867 if (PrintCMSStatistics != 0) {
2868 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
2869 _collector->yields());
2870 }
2871 }
2872 }
2873
2874 // CMS work
2875
2876 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2877 class CMSParMarkTask : public AbstractGangTask {
2878 protected:
2879 CMSCollector* _collector;
2880 uint _n_workers;
2881 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2882 AbstractGangTask(name),
2883 _collector(collector),
2884 _n_workers(n_workers) {}
2885 // Work method in support of parallel rescan ... of young gen spaces
2886 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2887 ContiguousSpace* space,
2888 HeapWord** chunk_array, size_t chunk_top);
2889 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2890 };
2891
2892 // Parallel initial mark task
2893 class CMSParInitialMarkTask: public CMSParMarkTask {
2894 StrongRootsScope* _strong_roots_scope;
2895 public:
2896 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2897 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2898 _strong_roots_scope(strong_roots_scope) {}
2899 void work(uint worker_id);
2900 };
2901
2902 // Checkpoint the roots into this generation from outside
2903 // this generation. [Note this initial checkpoint need only
2904 // be approximate -- we'll do a catch up phase subsequently.]
2905 void CMSCollector::checkpointRootsInitial() {
2906 assert(_collectorState == InitialMarking, "Wrong collector state");
2907 check_correct_thread_executing();
2908 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2909
2910 save_heap_summary();
2911 report_heap_summary(GCWhen::BeforeGC);
2912
2913 ReferenceProcessor* rp = ref_processor();
2914 assert(_restart_addr == NULL, "Control point invariant");
2915 {
2916 // acquire locks for subsequent manipulations
2917 MutexLockerEx x(bitMapLock(),
2918 Mutex::_no_safepoint_check_flag);
2919 checkpointRootsInitialWork();
2920 // enable ("weak") refs discovery
2921 rp->enable_discovery();
2922 _collectorState = Marking;
2923 }
2924 }
2925
2926 void CMSCollector::checkpointRootsInitialWork() {
2927 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2928 assert(_collectorState == InitialMarking, "just checking");
2929
2930 // Already have locks.
2931 assert_lock_strong(bitMapLock());
2932 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2933
2934 // Setup the verification and class unloading state for this
2935 // CMS collection cycle.
2936 setup_cms_unloading_and_verification_state();
2937
2938 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
2939 PrintGCDetails && Verbose, true, _gc_timer_cm);)
2940
2941 // Reset all the PLAB chunk arrays if necessary.
2942 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2943 reset_survivor_plab_arrays();
2944 }
2945
2946 ResourceMark rm;
2947 HandleMark hm;
2948
2949 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2950 GenCollectedHeap* gch = GenCollectedHeap::heap();
2951
2952 verify_work_stacks_empty();
2953 verify_overflow_empty();
2954
2955 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2956 // Update the saved marks which may affect the root scans.
2957 gch->save_marks();
2958
2959 // weak reference processing has not started yet.
2960 ref_processor()->set_enqueuing_is_done(false);
2961
2962 // Need to remember all newly created CLDs,
2963 // so that we can guarantee that the remark finds them.
2964 ClassLoaderDataGraph::remember_new_clds(true);
2965
2966 // Whenever a CLD is found, it will be claimed before proceeding to mark
2967 // the klasses. The claimed marks need to be cleared before marking starts.
2968 ClassLoaderDataGraph::clear_claimed_marks();
2969
2970 if (CMSPrintEdenSurvivorChunks) {
2971 print_eden_and_survivor_chunk_arrays();
2972 }
2973
2974 {
2975 #if defined(COMPILER2) || INCLUDE_JVMCI
2976 DerivedPointerTableDeactivate dpt_deact;
2977 #endif
2978 if (CMSParallelInitialMarkEnabled) {
2979 // The parallel version.
2980 WorkGang* workers = gch->workers();
2981 assert(workers != NULL, "Need parallel worker threads.");
2982 uint n_workers = workers->active_workers();
2983
2984 StrongRootsScope srs(n_workers);
2985
2986 CMSParInitialMarkTask tsk(this, &srs, n_workers);
2987 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2988 if (n_workers > 1) {
2989 workers->run_task(&tsk);
2990 } else {
2991 tsk.work(0);
2992 }
2993 } else {
2994 // The serial version.
2995 CLDToOopClosure cld_closure(¬Older, true);
2996 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2997
2998 StrongRootsScope srs(1);
2999
3000 gch->gen_process_roots(&srs,
3001 GenCollectedHeap::OldGen,
3002 true, // young gen as roots
3003 GenCollectedHeap::ScanningOption(roots_scanning_options()),
3004 should_unload_classes(),
3005 ¬Older,
3006 NULL,
3007 &cld_closure);
3008 }
3009 }
3010
3011 // Clear mod-union table; it will be dirtied in the prologue of
3012 // CMS generation per each young generation collection.
3013
3014 assert(_modUnionTable.isAllClear(),
3015 "Was cleared in most recent final checkpoint phase"
3016 " or no bits are set in the gc_prologue before the start of the next "
3017 "subsequent marking phase.");
3018
3019 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3020
3021 // Save the end of the used_region of the constituent generations
3022 // to be used to limit the extent of sweep in each generation.
3023 save_sweep_limits();
3024 verify_overflow_empty();
3025 }
3026
3027 bool CMSCollector::markFromRoots() {
3028 // we might be tempted to assert that:
3029 // assert(!SafepointSynchronize::is_at_safepoint(),
3030 // "inconsistent argument?");
3031 // However that wouldn't be right, because it's possible that
3032 // a safepoint is indeed in progress as a young generation
3033 // stop-the-world GC happens even as we mark in this generation.
3034 assert(_collectorState == Marking, "inconsistent state?");
3035 check_correct_thread_executing();
3036 verify_overflow_empty();
3037
3038 // Weak ref discovery note: We may be discovering weak
3039 // refs in this generation concurrent (but interleaved) with
3040 // weak ref discovery by the young generation collector.
3041
3042 CMSTokenSyncWithLocks ts(true, bitMapLock());
3043 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3044 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3045 bool res = markFromRootsWork();
3046 if (res) {
3047 _collectorState = Precleaning;
3048 } else { // We failed and a foreground collection wants to take over
3049 assert(_foregroundGCIsActive, "internal state inconsistency");
3050 assert(_restart_addr == NULL, "foreground will restart from scratch");
3051 if (PrintGCDetails) {
3052 gclog_or_tty->print_cr("bailing out to foreground collection");
3053 }
3054 }
3055 verify_overflow_empty();
3056 return res;
3057 }
3058
3059 bool CMSCollector::markFromRootsWork() {
3060 // iterate over marked bits in bit map, doing a full scan and mark
3061 // from these roots using the following algorithm:
3062 // . if oop is to the right of the current scan pointer,
3063 // mark corresponding bit (we'll process it later)
3064 // . else (oop is to left of current scan pointer)
3065 // push oop on marking stack
3066 // . drain the marking stack
3067
3068 // Note that when we do a marking step we need to hold the
3069 // bit map lock -- recall that direct allocation (by mutators)
3070 // and promotion (by the young generation collector) is also
3071 // marking the bit map. [the so-called allocate live policy.]
3072 // Because the implementation of bit map marking is not
3073 // robust wrt simultaneous marking of bits in the same word,
3074 // we need to make sure that there is no such interference
3075 // between concurrent such updates.
3076
3077 // already have locks
3078 assert_lock_strong(bitMapLock());
3079
3080 verify_work_stacks_empty();
3081 verify_overflow_empty();
3082 bool result = false;
3083 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3084 result = do_marking_mt();
3085 } else {
3086 result = do_marking_st();
3087 }
3088 return result;
3089 }
3090
3091 // Forward decl
3092 class CMSConcMarkingTask;
3093
3094 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3095 CMSCollector* _collector;
3096 CMSConcMarkingTask* _task;
3097 public:
3098 virtual void yield();
3099
3100 // "n_threads" is the number of threads to be terminated.
3101 // "queue_set" is a set of work queues of other threads.
3102 // "collector" is the CMS collector associated with this task terminator.
3103 // "yield" indicates whether we need the gang as a whole to yield.
3104 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3105 ParallelTaskTerminator(n_threads, queue_set),
3106 _collector(collector) { }
3107
3108 void set_task(CMSConcMarkingTask* task) {
3109 _task = task;
3110 }
3111 };
3112
3113 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3114 CMSConcMarkingTask* _task;
3115 public:
3116 bool should_exit_termination();
3117 void set_task(CMSConcMarkingTask* task) {
3118 _task = task;
3119 }
3120 };
3121
3122 // MT Concurrent Marking Task
3123 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3124 CMSCollector* _collector;
3125 uint _n_workers; // requested/desired # workers
3126 bool _result;
3127 CompactibleFreeListSpace* _cms_space;
3128 char _pad_front[64]; // padding to ...
3129 HeapWord* _global_finger; // ... avoid sharing cache line
3130 char _pad_back[64];
3131 HeapWord* _restart_addr;
3132
3133 // Exposed here for yielding support
3134 Mutex* const _bit_map_lock;
3135
3136 // The per thread work queues, available here for stealing
3137 OopTaskQueueSet* _task_queues;
3138
3139 // Termination (and yielding) support
3140 CMSConcMarkingTerminator _term;
3141 CMSConcMarkingTerminatorTerminator _term_term;
3142
3143 public:
3144 CMSConcMarkingTask(CMSCollector* collector,
3145 CompactibleFreeListSpace* cms_space,
3146 YieldingFlexibleWorkGang* workers,
3147 OopTaskQueueSet* task_queues):
3148 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3149 _collector(collector),
3150 _cms_space(cms_space),
3151 _n_workers(0), _result(true),
3152 _task_queues(task_queues),
3153 _term(_n_workers, task_queues, _collector),
3154 _bit_map_lock(collector->bitMapLock())
3155 {
3156 _requested_size = _n_workers;
3157 _term.set_task(this);
3158 _term_term.set_task(this);
3159 _restart_addr = _global_finger = _cms_space->bottom();
3160 }
3161
3162
3163 OopTaskQueueSet* task_queues() { return _task_queues; }
3164
3165 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3166
3167 HeapWord** global_finger_addr() { return &_global_finger; }
3168
3169 CMSConcMarkingTerminator* terminator() { return &_term; }
3170
3171 virtual void set_for_termination(uint active_workers) {
3172 terminator()->reset_for_reuse(active_workers);
3173 }
3174
3175 void work(uint worker_id);
3176 bool should_yield() {
3177 return ConcurrentMarkSweepThread::should_yield()
3178 && !_collector->foregroundGCIsActive();
3179 }
3180
3181 virtual void coordinator_yield(); // stuff done by coordinator
3182 bool result() { return _result; }
3183
3184 void reset(HeapWord* ra) {
3185 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3186 _restart_addr = _global_finger = ra;
3187 _term.reset_for_reuse();
3188 }
3189
3190 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3191 OopTaskQueue* work_q);
3192
3193 private:
3194 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3195 void do_work_steal(int i);
3196 void bump_global_finger(HeapWord* f);
3197 };
3198
3199 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3200 assert(_task != NULL, "Error");
3201 return _task->yielding();
3202 // Note that we do not need the disjunct || _task->should_yield() above
3203 // because we want terminating threads to yield only if the task
3204 // is already in the midst of yielding, which happens only after at least one
3205 // thread has yielded.
3206 }
3207
3208 void CMSConcMarkingTerminator::yield() {
3209 if (_task->should_yield()) {
3210 _task->yield();
3211 } else {
3212 ParallelTaskTerminator::yield();
3213 }
3214 }
3215
3216 ////////////////////////////////////////////////////////////////
3217 // Concurrent Marking Algorithm Sketch
3218 ////////////////////////////////////////////////////////////////
3219 // Until all tasks exhausted (both spaces):
3220 // -- claim next available chunk
3221 // -- bump global finger via CAS
3222 // -- find first object that starts in this chunk
3223 // and start scanning bitmap from that position
3224 // -- scan marked objects for oops
3225 // -- CAS-mark target, and if successful:
3226 // . if target oop is above global finger (volatile read)
3227 // nothing to do
3228 // . if target oop is in chunk and above local finger
3229 // then nothing to do
3230 // . else push on work-queue
3231 // -- Deal with possible overflow issues:
3232 // . local work-queue overflow causes stuff to be pushed on
3233 // global (common) overflow queue
3234 // . always first empty local work queue
3235 // . then get a batch of oops from global work queue if any
3236 // . then do work stealing
3237 // -- When all tasks claimed (both spaces)
3238 // and local work queue empty,
3239 // then in a loop do:
3240 // . check global overflow stack; steal a batch of oops and trace
3241 // . try to steal from other threads oif GOS is empty
3242 // . if neither is available, offer termination
3243 // -- Terminate and return result
3244 //
3245 void CMSConcMarkingTask::work(uint worker_id) {
3246 elapsedTimer _timer;
3247 ResourceMark rm;
3248 HandleMark hm;
3249
3250 DEBUG_ONLY(_collector->verify_overflow_empty();)
3251
3252 // Before we begin work, our work queue should be empty
3253 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3254 // Scan the bitmap covering _cms_space, tracing through grey objects.
3255 _timer.start();
3256 do_scan_and_mark(worker_id, _cms_space);
3257 _timer.stop();
3258 if (PrintCMSStatistics != 0) {
3259 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3260 worker_id, _timer.seconds());
3261 // XXX: need xxx/xxx type of notation, two timers
3262 }
3263
3264 // ... do work stealing
3265 _timer.reset();
3266 _timer.start();
3267 do_work_steal(worker_id);
3268 _timer.stop();
3269 if (PrintCMSStatistics != 0) {
3270 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3271 worker_id, _timer.seconds());
3272 // XXX: need xxx/xxx type of notation, two timers
3273 }
3274 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3275 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3276 // Note that under the current task protocol, the
3277 // following assertion is true even of the spaces
3278 // expanded since the completion of the concurrent
3279 // marking. XXX This will likely change under a strict
3280 // ABORT semantics.
3281 // After perm removal the comparison was changed to
3282 // greater than or equal to from strictly greater than.
3283 // Before perm removal the highest address sweep would
3284 // have been at the end of perm gen but now is at the
3285 // end of the tenured gen.
3286 assert(_global_finger >= _cms_space->end(),
3287 "All tasks have been completed");
3288 DEBUG_ONLY(_collector->verify_overflow_empty();)
3289 }
3290
3291 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3292 HeapWord* read = _global_finger;
3293 HeapWord* cur = read;
3294 while (f > read) {
3295 cur = read;
3296 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3297 if (cur == read) {
3298 // our cas succeeded
3299 assert(_global_finger >= f, "protocol consistency");
3300 break;
3301 }
3302 }
3303 }
3304
3305 // This is really inefficient, and should be redone by
3306 // using (not yet available) block-read and -write interfaces to the
3307 // stack and the work_queue. XXX FIX ME !!!
3308 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3309 OopTaskQueue* work_q) {
3310 // Fast lock-free check
3311 if (ovflw_stk->length() == 0) {
3312 return false;
3313 }
3314 assert(work_q->size() == 0, "Shouldn't steal");
3315 MutexLockerEx ml(ovflw_stk->par_lock(),
3316 Mutex::_no_safepoint_check_flag);
3317 // Grab up to 1/4 the size of the work queue
3318 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3319 (size_t)ParGCDesiredObjsFromOverflowList);
3320 num = MIN2(num, ovflw_stk->length());
3321 for (int i = (int) num; i > 0; i--) {
3322 oop cur = ovflw_stk->pop();
3323 assert(cur != NULL, "Counted wrong?");
3324 work_q->push(cur);
3325 }
3326 return num > 0;
3327 }
3328
3329 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3330 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3331 int n_tasks = pst->n_tasks();
3332 // We allow that there may be no tasks to do here because
3333 // we are restarting after a stack overflow.
3334 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3335 uint nth_task = 0;
3336
3337 HeapWord* aligned_start = sp->bottom();
3338 if (sp->used_region().contains(_restart_addr)) {
3339 // Align down to a card boundary for the start of 0th task
3340 // for this space.
3341 aligned_start =
3342 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3343 CardTableModRefBS::card_size);
3344 }
3345
3346 size_t chunk_size = sp->marking_task_size();
3347 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3348 // Having claimed the nth task in this space,
3349 // compute the chunk that it corresponds to:
3350 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3351 aligned_start + (nth_task+1)*chunk_size);
3352 // Try and bump the global finger via a CAS;
3353 // note that we need to do the global finger bump
3354 // _before_ taking the intersection below, because
3355 // the task corresponding to that region will be
3356 // deemed done even if the used_region() expands
3357 // because of allocation -- as it almost certainly will
3358 // during start-up while the threads yield in the
3359 // closure below.
3360 HeapWord* finger = span.end();
3361 bump_global_finger(finger); // atomically
3362 // There are null tasks here corresponding to chunks
3363 // beyond the "top" address of the space.
3364 span = span.intersection(sp->used_region());
3365 if (!span.is_empty()) { // Non-null task
3366 HeapWord* prev_obj;
3367 assert(!span.contains(_restart_addr) || nth_task == 0,
3368 "Inconsistency");
3369 if (nth_task == 0) {
3370 // For the 0th task, we'll not need to compute a block_start.
3371 if (span.contains(_restart_addr)) {
3372 // In the case of a restart because of stack overflow,
3373 // we might additionally skip a chunk prefix.
3374 prev_obj = _restart_addr;
3375 } else {
3376 prev_obj = span.start();
3377 }
3378 } else {
3379 // We want to skip the first object because
3380 // the protocol is to scan any object in its entirety
3381 // that _starts_ in this span; a fortiori, any
3382 // object starting in an earlier span is scanned
3383 // as part of an earlier claimed task.
3384 // Below we use the "careful" version of block_start
3385 // so we do not try to navigate uninitialized objects.
3386 prev_obj = sp->block_start_careful(span.start());
3387 // Below we use a variant of block_size that uses the
3388 // Printezis bits to avoid waiting for allocated
3389 // objects to become initialized/parsable.
3390 while (prev_obj < span.start()) {
3391 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3392 if (sz > 0) {
3393 prev_obj += sz;
3394 } else {
3395 // In this case we may end up doing a bit of redundant
3396 // scanning, but that appears unavoidable, short of
3397 // locking the free list locks; see bug 6324141.
3398 break;
3399 }
3400 }
3401 }
3402 if (prev_obj < span.end()) {
3403 MemRegion my_span = MemRegion(prev_obj, span.end());
3404 // Do the marking work within a non-empty span --
3405 // the last argument to the constructor indicates whether the
3406 // iteration should be incremental with periodic yields.
3407 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3408 &_collector->_markBitMap,
3409 work_queue(i),
3410 &_collector->_markStack);
3411 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3412 } // else nothing to do for this task
3413 } // else nothing to do for this task
3414 }
3415 // We'd be tempted to assert here that since there are no
3416 // more tasks left to claim in this space, the global_finger
3417 // must exceed space->top() and a fortiori space->end(). However,
3418 // that would not quite be correct because the bumping of
3419 // global_finger occurs strictly after the claiming of a task,
3420 // so by the time we reach here the global finger may not yet
3421 // have been bumped up by the thread that claimed the last
3422 // task.
3423 pst->all_tasks_completed();
3424 }
3425
3426 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3427 private:
3428 CMSCollector* _collector;
3429 CMSConcMarkingTask* _task;
3430 MemRegion _span;
3431 CMSBitMap* _bit_map;
3432 CMSMarkStack* _overflow_stack;
3433 OopTaskQueue* _work_queue;
3434 protected:
3435 DO_OOP_WORK_DEFN
3436 public:
3437 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3438 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3439 MetadataAwareOopClosure(collector->ref_processor()),
3440 _collector(collector),
3441 _task(task),
3442 _span(collector->_span),
3443 _work_queue(work_queue),
3444 _bit_map(bit_map),
3445 _overflow_stack(overflow_stack)
3446 { }
3447 virtual void do_oop(oop* p);
3448 virtual void do_oop(narrowOop* p);
3449
3450 void trim_queue(size_t max);
3451 void handle_stack_overflow(HeapWord* lost);
3452 void do_yield_check() {
3453 if (_task->should_yield()) {
3454 _task->yield();
3455 }
3456 }
3457 };
3458
3459 // Grey object scanning during work stealing phase --
3460 // the salient assumption here is that any references
3461 // that are in these stolen objects being scanned must
3462 // already have been initialized (else they would not have
3463 // been published), so we do not need to check for
3464 // uninitialized objects before pushing here.
3465 void Par_ConcMarkingClosure::do_oop(oop obj) {
3466 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3467 HeapWord* addr = (HeapWord*)obj;
3468 // Check if oop points into the CMS generation
3469 // and is not marked
3470 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3471 // a white object ...
3472 // If we manage to "claim" the object, by being the
3473 // first thread to mark it, then we push it on our
3474 // marking stack
3475 if (_bit_map->par_mark(addr)) { // ... now grey
3476 // push on work queue (grey set)
3477 bool simulate_overflow = false;
3478 NOT_PRODUCT(
3479 if (CMSMarkStackOverflowALot &&
3480 _collector->simulate_overflow()) {
3481 // simulate a stack overflow
3482 simulate_overflow = true;
3483 }
3484 )
3485 if (simulate_overflow ||
3486 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3487 // stack overflow
3488 if (PrintCMSStatistics != 0) {
3489 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3490 SIZE_FORMAT, _overflow_stack->capacity());
3491 }
3492 // We cannot assert that the overflow stack is full because
3493 // it may have been emptied since.
3494 assert(simulate_overflow ||
3495 _work_queue->size() == _work_queue->max_elems(),
3496 "Else push should have succeeded");
3497 handle_stack_overflow(addr);
3498 }
3499 } // Else, some other thread got there first
3500 do_yield_check();
3501 }
3502 }
3503
3504 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3505 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3506
3507 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3508 while (_work_queue->size() > max) {
3509 oop new_oop;
3510 if (_work_queue->pop_local(new_oop)) {
3511 assert(new_oop->is_oop(), "Should be an oop");
3512 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3513 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3514 new_oop->oop_iterate(this); // do_oop() above
3515 do_yield_check();
3516 }
3517 }
3518 }
3519
3520 // Upon stack overflow, we discard (part of) the stack,
3521 // remembering the least address amongst those discarded
3522 // in CMSCollector's _restart_address.
3523 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3524 // We need to do this under a mutex to prevent other
3525 // workers from interfering with the work done below.
3526 MutexLockerEx ml(_overflow_stack->par_lock(),
3527 Mutex::_no_safepoint_check_flag);
3528 // Remember the least grey address discarded
3529 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3530 _collector->lower_restart_addr(ra);
3531 _overflow_stack->reset(); // discard stack contents
3532 _overflow_stack->expand(); // expand the stack if possible
3533 }
3534
3535
3536 void CMSConcMarkingTask::do_work_steal(int i) {
3537 OopTaskQueue* work_q = work_queue(i);
3538 oop obj_to_scan;
3539 CMSBitMap* bm = &(_collector->_markBitMap);
3540 CMSMarkStack* ovflw = &(_collector->_markStack);
3541 int* seed = _collector->hash_seed(i);
3542 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3543 while (true) {
3544 cl.trim_queue(0);
3545 assert(work_q->size() == 0, "Should have been emptied above");
3546 if (get_work_from_overflow_stack(ovflw, work_q)) {
3547 // Can't assert below because the work obtained from the
3548 // overflow stack may already have been stolen from us.
3549 // assert(work_q->size() > 0, "Work from overflow stack");
3550 continue;
3551 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3552 assert(obj_to_scan->is_oop(), "Should be an oop");
3553 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3554 obj_to_scan->oop_iterate(&cl);
3555 } else if (terminator()->offer_termination(&_term_term)) {
3556 assert(work_q->size() == 0, "Impossible!");
3557 break;
3558 } else if (yielding() || should_yield()) {
3559 yield();
3560 }
3561 }
3562 }
3563
3564 // This is run by the CMS (coordinator) thread.
3565 void CMSConcMarkingTask::coordinator_yield() {
3566 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3567 "CMS thread should hold CMS token");
3568 // First give up the locks, then yield, then re-lock
3569 // We should probably use a constructor/destructor idiom to
3570 // do this unlock/lock or modify the MutexUnlocker class to
3571 // serve our purpose. XXX
3572 assert_lock_strong(_bit_map_lock);
3573 _bit_map_lock->unlock();
3574 ConcurrentMarkSweepThread::desynchronize(true);
3575 _collector->stopTimer();
3576 if (PrintCMSStatistics != 0) {
3577 _collector->incrementYields();
3578 }
3579
3580 // It is possible for whichever thread initiated the yield request
3581 // not to get a chance to wake up and take the bitmap lock between
3582 // this thread releasing it and reacquiring it. So, while the
3583 // should_yield() flag is on, let's sleep for a bit to give the
3584 // other thread a chance to wake up. The limit imposed on the number
3585 // of iterations is defensive, to avoid any unforseen circumstances
3586 // putting us into an infinite loop. Since it's always been this
3587 // (coordinator_yield()) method that was observed to cause the
3588 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3589 // which is by default non-zero. For the other seven methods that
3590 // also perform the yield operation, as are using a different
3591 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3592 // can enable the sleeping for those methods too, if necessary.
3593 // See 6442774.
3594 //
3595 // We really need to reconsider the synchronization between the GC
3596 // thread and the yield-requesting threads in the future and we
3597 // should really use wait/notify, which is the recommended
3598 // way of doing this type of interaction. Additionally, we should
3599 // consolidate the eight methods that do the yield operation and they
3600 // are almost identical into one for better maintainability and
3601 // readability. See 6445193.
3602 //
3603 // Tony 2006.06.29
3604 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3605 ConcurrentMarkSweepThread::should_yield() &&
3606 !CMSCollector::foregroundGCIsActive(); ++i) {
3607 os::sleep(Thread::current(), 1, false);
3608 }
3609
3610 ConcurrentMarkSweepThread::synchronize(true);
3611 _bit_map_lock->lock_without_safepoint_check();
3612 _collector->startTimer();
3613 }
3614
3615 bool CMSCollector::do_marking_mt() {
3616 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3617 uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3618 conc_workers()->active_workers(),
3619 Threads::number_of_non_daemon_threads());
3620 conc_workers()->set_active_workers(num_workers);
3621
3622 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3623
3624 CMSConcMarkingTask tsk(this,
3625 cms_space,
3626 conc_workers(),
3627 task_queues());
3628
3629 // Since the actual number of workers we get may be different
3630 // from the number we requested above, do we need to do anything different
3631 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3632 // class?? XXX
3633 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3634
3635 // Refs discovery is already non-atomic.
3636 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3637 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3638 conc_workers()->start_task(&tsk);
3639 while (tsk.yielded()) {
3640 tsk.coordinator_yield();
3641 conc_workers()->continue_task(&tsk);
3642 }
3643 // If the task was aborted, _restart_addr will be non-NULL
3644 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3645 while (_restart_addr != NULL) {
3646 // XXX For now we do not make use of ABORTED state and have not
3647 // yet implemented the right abort semantics (even in the original
3648 // single-threaded CMS case). That needs some more investigation
3649 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3650 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3651 // If _restart_addr is non-NULL, a marking stack overflow
3652 // occurred; we need to do a fresh marking iteration from the
3653 // indicated restart address.
3654 if (_foregroundGCIsActive) {
3655 // We may be running into repeated stack overflows, having
3656 // reached the limit of the stack size, while making very
3657 // slow forward progress. It may be best to bail out and
3658 // let the foreground collector do its job.
3659 // Clear _restart_addr, so that foreground GC
3660 // works from scratch. This avoids the headache of
3661 // a "rescan" which would otherwise be needed because
3662 // of the dirty mod union table & card table.
3663 _restart_addr = NULL;
3664 return false;
3665 }
3666 // Adjust the task to restart from _restart_addr
3667 tsk.reset(_restart_addr);
3668 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3669 _restart_addr);
3670 _restart_addr = NULL;
3671 // Get the workers going again
3672 conc_workers()->start_task(&tsk);
3673 while (tsk.yielded()) {
3674 tsk.coordinator_yield();
3675 conc_workers()->continue_task(&tsk);
3676 }
3677 }
3678 assert(tsk.completed(), "Inconsistency");
3679 assert(tsk.result() == true, "Inconsistency");
3680 return true;
3681 }
3682
3683 bool CMSCollector::do_marking_st() {
3684 ResourceMark rm;
3685 HandleMark hm;
3686
3687 // Temporarily make refs discovery single threaded (non-MT)
3688 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3689 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3690 &_markStack, CMSYield);
3691 // the last argument to iterate indicates whether the iteration
3692 // should be incremental with periodic yields.
3693 _markBitMap.iterate(&markFromRootsClosure);
3694 // If _restart_addr is non-NULL, a marking stack overflow
3695 // occurred; we need to do a fresh iteration from the
3696 // indicated restart address.
3697 while (_restart_addr != NULL) {
3698 if (_foregroundGCIsActive) {
3699 // We may be running into repeated stack overflows, having
3700 // reached the limit of the stack size, while making very
3701 // slow forward progress. It may be best to bail out and
3702 // let the foreground collector do its job.
3703 // Clear _restart_addr, so that foreground GC
3704 // works from scratch. This avoids the headache of
3705 // a "rescan" which would otherwise be needed because
3706 // of the dirty mod union table & card table.
3707 _restart_addr = NULL;
3708 return false; // indicating failure to complete marking
3709 }
3710 // Deal with stack overflow:
3711 // we restart marking from _restart_addr
3712 HeapWord* ra = _restart_addr;
3713 markFromRootsClosure.reset(ra);
3714 _restart_addr = NULL;
3715 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3716 }
3717 return true;
3718 }
3719
3720 void CMSCollector::preclean() {
3721 check_correct_thread_executing();
3722 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3723 verify_work_stacks_empty();
3724 verify_overflow_empty();
3725 _abort_preclean = false;
3726 if (CMSPrecleaningEnabled) {
3727 if (!CMSEdenChunksRecordAlways) {
3728 _eden_chunk_index = 0;
3729 }
3730 size_t used = get_eden_used();
3731 size_t capacity = get_eden_capacity();
3732 // Don't start sampling unless we will get sufficiently
3733 // many samples.
3734 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3735 * CMSScheduleRemarkEdenPenetration)) {
3736 _start_sampling = true;
3737 } else {
3738 _start_sampling = false;
3739 }
3740 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3741 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
3742 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3743 }
3744 CMSTokenSync x(true); // is cms thread
3745 if (CMSPrecleaningEnabled) {
3746 sample_eden();
3747 _collectorState = AbortablePreclean;
3748 } else {
3749 _collectorState = FinalMarking;
3750 }
3751 verify_work_stacks_empty();
3752 verify_overflow_empty();
3753 }
3754
3755 // Try and schedule the remark such that young gen
3756 // occupancy is CMSScheduleRemarkEdenPenetration %.
3757 void CMSCollector::abortable_preclean() {
3758 check_correct_thread_executing();
3759 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3760 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3761
3762 // If Eden's current occupancy is below this threshold,
3763 // immediately schedule the remark; else preclean
3764 // past the next scavenge in an effort to
3765 // schedule the pause as described above. By choosing
3766 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3767 // we will never do an actual abortable preclean cycle.
3768 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3769 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3770 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
3771 // We need more smarts in the abortable preclean
3772 // loop below to deal with cases where allocation
3773 // in young gen is very very slow, and our precleaning
3774 // is running a losing race against a horde of
3775 // mutators intent on flooding us with CMS updates
3776 // (dirty cards).
3777 // One, admittedly dumb, strategy is to give up
3778 // after a certain number of abortable precleaning loops
3779 // or after a certain maximum time. We want to make
3780 // this smarter in the next iteration.
3781 // XXX FIX ME!!! YSR
3782 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3783 while (!(should_abort_preclean() ||
3784 ConcurrentMarkSweepThread::should_terminate())) {
3785 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3786 cumworkdone += workdone;
3787 loops++;
3788 // Voluntarily terminate abortable preclean phase if we have
3789 // been at it for too long.
3790 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3791 loops >= CMSMaxAbortablePrecleanLoops) {
3792 if (PrintGCDetails) {
3793 gclog_or_tty->print(" CMS: abort preclean due to loops ");
3794 }
3795 break;
3796 }
3797 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3798 if (PrintGCDetails) {
3799 gclog_or_tty->print(" CMS: abort preclean due to time ");
3800 }
3801 break;
3802 }
3803 // If we are doing little work each iteration, we should
3804 // take a short break.
3805 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3806 // Sleep for some time, waiting for work to accumulate
3807 stopTimer();
3808 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3809 startTimer();
3810 waited++;
3811 }
3812 }
3813 if (PrintCMSStatistics > 0) {
3814 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3815 loops, waited, cumworkdone);
3816 }
3817 }
3818 CMSTokenSync x(true); // is cms thread
3819 if (_collectorState != Idling) {
3820 assert(_collectorState == AbortablePreclean,
3821 "Spontaneous state transition?");
3822 _collectorState = FinalMarking;
3823 } // Else, a foreground collection completed this CMS cycle.
3824 return;
3825 }
3826
3827 // Respond to an Eden sampling opportunity
3828 void CMSCollector::sample_eden() {
3829 // Make sure a young gc cannot sneak in between our
3830 // reading and recording of a sample.
3831 assert(Thread::current()->is_ConcurrentGC_thread(),
3832 "Only the cms thread may collect Eden samples");
3833 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3834 "Should collect samples while holding CMS token");
3835 if (!_start_sampling) {
3836 return;
3837 }
3838 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3839 // is populated by the young generation.
3840 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3841 if (_eden_chunk_index < _eden_chunk_capacity) {
3842 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3843 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3844 "Unexpected state of Eden");
3845 // We'd like to check that what we just sampled is an oop-start address;
3846 // however, we cannot do that here since the object may not yet have been
3847 // initialized. So we'll instead do the check when we _use_ this sample
3848 // later.
3849 if (_eden_chunk_index == 0 ||
3850 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3851 _eden_chunk_array[_eden_chunk_index-1])
3852 >= CMSSamplingGrain)) {
3853 _eden_chunk_index++; // commit sample
3854 }
3855 }
3856 }
3857 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3858 size_t used = get_eden_used();
3859 size_t capacity = get_eden_capacity();
3860 assert(used <= capacity, "Unexpected state of Eden");
3861 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3862 _abort_preclean = true;
3863 }
3864 }
3865 }
3866
3867
3868 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3869 assert(_collectorState == Precleaning ||
3870 _collectorState == AbortablePreclean, "incorrect state");
3871 ResourceMark rm;
3872 HandleMark hm;
3873
3874 // Precleaning is currently not MT but the reference processor
3875 // may be set for MT. Disable it temporarily here.
3876 ReferenceProcessor* rp = ref_processor();
3877 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3878
3879 // Do one pass of scrubbing the discovered reference lists
3880 // to remove any reference objects with strongly-reachable
3881 // referents.
3882 if (clean_refs) {
3883 CMSPrecleanRefsYieldClosure yield_cl(this);
3884 assert(rp->span().equals(_span), "Spans should be equal");
3885 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3886 &_markStack, true /* preclean */);
3887 CMSDrainMarkingStackClosure complete_trace(this,
3888 _span, &_markBitMap, &_markStack,
3889 &keep_alive, true /* preclean */);
3890
3891 // We don't want this step to interfere with a young
3892 // collection because we don't want to take CPU
3893 // or memory bandwidth away from the young GC threads
3894 // (which may be as many as there are CPUs).
3895 // Note that we don't need to protect ourselves from
3896 // interference with mutators because they can't
3897 // manipulate the discovered reference lists nor affect
3898 // the computed reachability of the referents, the
3899 // only properties manipulated by the precleaning
3900 // of these reference lists.
3901 stopTimer();
3902 CMSTokenSyncWithLocks x(true /* is cms thread */,
3903 bitMapLock());
3904 startTimer();
3905 sample_eden();
3906
3907 // The following will yield to allow foreground
3908 // collection to proceed promptly. XXX YSR:
3909 // The code in this method may need further
3910 // tweaking for better performance and some restructuring
3911 // for cleaner interfaces.
3912 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3913 rp->preclean_discovered_references(
3914 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3915 gc_timer);
3916 }
3917
3918 if (clean_survivor) { // preclean the active survivor space(s)
3919 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3920 &_markBitMap, &_modUnionTable,
3921 &_markStack, true /* precleaning phase */);
3922 stopTimer();
3923 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3924 bitMapLock());
3925 startTimer();
3926 unsigned int before_count =
3927 GenCollectedHeap::heap()->total_collections();
3928 SurvivorSpacePrecleanClosure
3929 sss_cl(this, _span, &_markBitMap, &_markStack,
3930 &pam_cl, before_count, CMSYield);
3931 _young_gen->from()->object_iterate_careful(&sss_cl);
3932 _young_gen->to()->object_iterate_careful(&sss_cl);
3933 }
3934 MarkRefsIntoAndScanClosure
3935 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3936 &_markStack, this, CMSYield,
3937 true /* precleaning phase */);
3938 // CAUTION: The following closure has persistent state that may need to
3939 // be reset upon a decrease in the sequence of addresses it
3940 // processes.
3941 ScanMarkedObjectsAgainCarefullyClosure
3942 smoac_cl(this, _span,
3943 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3944
3945 // Preclean dirty cards in ModUnionTable and CardTable using
3946 // appropriate convergence criterion;
3947 // repeat CMSPrecleanIter times unless we find that
3948 // we are losing.
3949 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3950 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3951 "Bad convergence multiplier");
3952 assert(CMSPrecleanThreshold >= 100,
3953 "Unreasonably low CMSPrecleanThreshold");
3954
3955 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3956 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3957 numIter < CMSPrecleanIter;
3958 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3959 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3960 if (Verbose && PrintGCDetails) {
3961 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3962 }
3963 // Either there are very few dirty cards, so re-mark
3964 // pause will be small anyway, or our pre-cleaning isn't
3965 // that much faster than the rate at which cards are being
3966 // dirtied, so we might as well stop and re-mark since
3967 // precleaning won't improve our re-mark time by much.
3968 if (curNumCards <= CMSPrecleanThreshold ||
3969 (numIter > 0 &&
3970 (curNumCards * CMSPrecleanDenominator >
3971 lastNumCards * CMSPrecleanNumerator))) {
3972 numIter++;
3973 cumNumCards += curNumCards;
3974 break;
3975 }
3976 }
3977
3978 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
3979
3980 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3981 cumNumCards += curNumCards;
3982 if (PrintGCDetails && PrintCMSStatistics != 0) {
3983 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3984 curNumCards, cumNumCards, numIter);
3985 }
3986 return cumNumCards; // as a measure of useful work done
3987 }
3988
3989 // PRECLEANING NOTES:
3990 // Precleaning involves:
3991 // . reading the bits of the modUnionTable and clearing the set bits.
3992 // . For the cards corresponding to the set bits, we scan the
3993 // objects on those cards. This means we need the free_list_lock
3994 // so that we can safely iterate over the CMS space when scanning
3995 // for oops.
3996 // . When we scan the objects, we'll be both reading and setting
3997 // marks in the marking bit map, so we'll need the marking bit map.
3998 // . For protecting _collector_state transitions, we take the CGC_lock.
3999 // Note that any races in the reading of of card table entries by the
4000 // CMS thread on the one hand and the clearing of those entries by the
4001 // VM thread or the setting of those entries by the mutator threads on the
4002 // other are quite benign. However, for efficiency it makes sense to keep
4003 // the VM thread from racing with the CMS thread while the latter is
4004 // dirty card info to the modUnionTable. We therefore also use the
4005 // CGC_lock to protect the reading of the card table and the mod union
4006 // table by the CM thread.
4007 // . We run concurrently with mutator updates, so scanning
4008 // needs to be done carefully -- we should not try to scan
4009 // potentially uninitialized objects.
4010 //
4011 // Locking strategy: While holding the CGC_lock, we scan over and
4012 // reset a maximal dirty range of the mod union / card tables, then lock
4013 // the free_list_lock and bitmap lock to do a full marking, then
4014 // release these locks; and repeat the cycle. This allows for a
4015 // certain amount of fairness in the sharing of these locks between
4016 // the CMS collector on the one hand, and the VM thread and the
4017 // mutators on the other.
4018
4019 // NOTE: preclean_mod_union_table() and preclean_card_table()
4020 // further below are largely identical; if you need to modify
4021 // one of these methods, please check the other method too.
4022
4023 size_t CMSCollector::preclean_mod_union_table(
4024 ConcurrentMarkSweepGeneration* old_gen,
4025 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4026 verify_work_stacks_empty();
4027 verify_overflow_empty();
4028
4029 // strategy: starting with the first card, accumulate contiguous
4030 // ranges of dirty cards; clear these cards, then scan the region
4031 // covered by these cards.
4032
4033 // Since all of the MUT is committed ahead, we can just use
4034 // that, in case the generations expand while we are precleaning.
4035 // It might also be fine to just use the committed part of the
4036 // generation, but we might potentially miss cards when the
4037 // generation is rapidly expanding while we are in the midst
4038 // of precleaning.
4039 HeapWord* startAddr = old_gen->reserved().start();
4040 HeapWord* endAddr = old_gen->reserved().end();
4041
4042 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4043
4044 size_t numDirtyCards, cumNumDirtyCards;
4045 HeapWord *nextAddr, *lastAddr;
4046 for (cumNumDirtyCards = numDirtyCards = 0,
4047 nextAddr = lastAddr = startAddr;
4048 nextAddr < endAddr;
4049 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4050
4051 ResourceMark rm;
4052 HandleMark hm;
4053
4054 MemRegion dirtyRegion;
4055 {
4056 stopTimer();
4057 // Potential yield point
4058 CMSTokenSync ts(true);
4059 startTimer();
4060 sample_eden();
4061 // Get dirty region starting at nextOffset (inclusive),
4062 // simultaneously clearing it.
4063 dirtyRegion =
4064 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4065 assert(dirtyRegion.start() >= nextAddr,
4066 "returned region inconsistent?");
4067 }
4068 // Remember where the next search should begin.
4069 // The returned region (if non-empty) is a right open interval,
4070 // so lastOffset is obtained from the right end of that
4071 // interval.
4072 lastAddr = dirtyRegion.end();
4073 // Should do something more transparent and less hacky XXX
4074 numDirtyCards =
4075 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4076
4077 // We'll scan the cards in the dirty region (with periodic
4078 // yields for foreground GC as needed).
4079 if (!dirtyRegion.is_empty()) {
4080 assert(numDirtyCards > 0, "consistency check");
4081 HeapWord* stop_point = NULL;
4082 stopTimer();
4083 // Potential yield point
4084 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
4085 bitMapLock());
4086 startTimer();
4087 {
4088 verify_work_stacks_empty();
4089 verify_overflow_empty();
4090 sample_eden();
4091 stop_point =
4092 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4093 }
4094 if (stop_point != NULL) {
4095 // The careful iteration stopped early either because it found an
4096 // uninitialized object, or because we were in the midst of an
4097 // "abortable preclean", which should now be aborted. Redirty
4098 // the bits corresponding to the partially-scanned or unscanned
4099 // cards. We'll either restart at the next block boundary or
4100 // abort the preclean.
4101 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4102 "Should only be AbortablePreclean.");
4103 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4104 if (should_abort_preclean()) {
4105 break; // out of preclean loop
4106 } else {
4107 // Compute the next address at which preclean should pick up;
4108 // might need bitMapLock in order to read P-bits.
4109 lastAddr = next_card_start_after_block(stop_point);
4110 }
4111 }
4112 } else {
4113 assert(lastAddr == endAddr, "consistency check");
4114 assert(numDirtyCards == 0, "consistency check");
4115 break;
4116 }
4117 }
4118 verify_work_stacks_empty();
4119 verify_overflow_empty();
4120 return cumNumDirtyCards;
4121 }
4122
4123 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4124 // below are largely identical; if you need to modify
4125 // one of these methods, please check the other method too.
4126
4127 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
4128 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4129 // strategy: it's similar to precleamModUnionTable above, in that
4130 // we accumulate contiguous ranges of dirty cards, mark these cards
4131 // precleaned, then scan the region covered by these cards.
4132 HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high());
4133 HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4134
4135 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4136
4137 size_t numDirtyCards, cumNumDirtyCards;
4138 HeapWord *lastAddr, *nextAddr;
4139
4140 for (cumNumDirtyCards = numDirtyCards = 0,
4141 nextAddr = lastAddr = startAddr;
4142 nextAddr < endAddr;
4143 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4144
4145 ResourceMark rm;
4146 HandleMark hm;
4147
4148 MemRegion dirtyRegion;
4149 {
4150 // See comments in "Precleaning notes" above on why we
4151 // do this locking. XXX Could the locking overheads be
4152 // too high when dirty cards are sparse? [I don't think so.]
4153 stopTimer();
4154 CMSTokenSync x(true); // is cms thread
4155 startTimer();
4156 sample_eden();
4157 // Get and clear dirty region from card table
4158 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4159 MemRegion(nextAddr, endAddr),
4160 true,
4161 CardTableModRefBS::precleaned_card_val());
4162
4163 assert(dirtyRegion.start() >= nextAddr,
4164 "returned region inconsistent?");
4165 }
4166 lastAddr = dirtyRegion.end();
4167 numDirtyCards =
4168 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4169
4170 if (!dirtyRegion.is_empty()) {
4171 stopTimer();
4172 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4173 startTimer();
4174 sample_eden();
4175 verify_work_stacks_empty();
4176 verify_overflow_empty();
4177 HeapWord* stop_point =
4178 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4179 if (stop_point != NULL) {
4180 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4181 "Should only be AbortablePreclean.");
4182 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4183 if (should_abort_preclean()) {
4184 break; // out of preclean loop
4185 } else {
4186 // Compute the next address at which preclean should pick up.
4187 lastAddr = next_card_start_after_block(stop_point);
4188 }
4189 }
4190 } else {
4191 break;
4192 }
4193 }
4194 verify_work_stacks_empty();
4195 verify_overflow_empty();
4196 return cumNumDirtyCards;
4197 }
4198
4199 class PrecleanKlassClosure : public KlassClosure {
4200 KlassToOopClosure _cm_klass_closure;
4201 public:
4202 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4203 void do_klass(Klass* k) {
4204 if (k->has_accumulated_modified_oops()) {
4205 k->clear_accumulated_modified_oops();
4206
4207 _cm_klass_closure.do_klass(k);
4208 }
4209 }
4210 };
4211
4212 // The freelist lock is needed to prevent asserts, is it really needed?
4213 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4214
4215 cl->set_freelistLock(freelistLock);
4216
4217 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4218
4219 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4220 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4221 PrecleanKlassClosure preclean_klass_closure(cl);
4222 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4223
4224 verify_work_stacks_empty();
4225 verify_overflow_empty();
4226 }
4227
4228 void CMSCollector::checkpointRootsFinal() {
4229 assert(_collectorState == FinalMarking, "incorrect state transition?");
4230 check_correct_thread_executing();
4231 // world is stopped at this checkpoint
4232 assert(SafepointSynchronize::is_at_safepoint(),
4233 "world should be stopped");
4234 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4235
4236 verify_work_stacks_empty();
4237 verify_overflow_empty();
4238
4239 if (PrintGCDetails) {
4240 gclog_or_tty->print("[YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)]",
4241 _young_gen->used() / K,
4242 _young_gen->capacity() / K);
4243 }
4244 {
4245 if (CMSScavengeBeforeRemark) {
4246 GenCollectedHeap* gch = GenCollectedHeap::heap();
4247 // Temporarily set flag to false, GCH->do_collection will
4248 // expect it to be false and set to true
4249 FlagSetting fl(gch->_is_gc_active, false);
4250 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4251 PrintGCDetails && Verbose, true, _gc_timer_cm);)
4252 gch->do_collection(true, // full (i.e. force, see below)
4253 false, // !clear_all_soft_refs
4254 0, // size
4255 false, // is_tlab
4256 GenCollectedHeap::YoungGen // type
4257 );
4258 }
4259 FreelistLocker x(this);
4260 MutexLockerEx y(bitMapLock(),
4261 Mutex::_no_safepoint_check_flag);
4262 checkpointRootsFinalWork();
4263 }
4264 verify_work_stacks_empty();
4265 verify_overflow_empty();
4266 }
4267
4268 void CMSCollector::checkpointRootsFinalWork() {
4269 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm);)
4270
4271 assert(haveFreelistLocks(), "must have free list locks");
4272 assert_lock_strong(bitMapLock());
4273
4274 ResourceMark rm;
4275 HandleMark hm;
4276
4277 GenCollectedHeap* gch = GenCollectedHeap::heap();
4278
4279 if (should_unload_classes()) {
4280 CodeCache::gc_prologue();
4281 }
4282 assert(haveFreelistLocks(), "must have free list locks");
4283 assert_lock_strong(bitMapLock());
4284
4285 // We might assume that we need not fill TLAB's when
4286 // CMSScavengeBeforeRemark is set, because we may have just done
4287 // a scavenge which would have filled all TLAB's -- and besides
4288 // Eden would be empty. This however may not always be the case --
4289 // for instance although we asked for a scavenge, it may not have
4290 // happened because of a JNI critical section. We probably need
4291 // a policy for deciding whether we can in that case wait until
4292 // the critical section releases and then do the remark following
4293 // the scavenge, and skip it here. In the absence of that policy,
4294 // or of an indication of whether the scavenge did indeed occur,
4295 // we cannot rely on TLAB's having been filled and must do
4296 // so here just in case a scavenge did not happen.
4297 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4298 // Update the saved marks which may affect the root scans.
4299 gch->save_marks();
4300
4301 if (CMSPrintEdenSurvivorChunks) {
4302 print_eden_and_survivor_chunk_arrays();
4303 }
4304
4305 {
4306 #if defined(COMPILER2) || INCLUDE_JVMCI
4307 DerivedPointerTableDeactivate dpt_deact;
4308 #endif
4309
4310 // Note on the role of the mod union table:
4311 // Since the marker in "markFromRoots" marks concurrently with
4312 // mutators, it is possible for some reachable objects not to have been
4313 // scanned. For instance, an only reference to an object A was
4314 // placed in object B after the marker scanned B. Unless B is rescanned,
4315 // A would be collected. Such updates to references in marked objects
4316 // are detected via the mod union table which is the set of all cards
4317 // dirtied since the first checkpoint in this GC cycle and prior to
4318 // the most recent young generation GC, minus those cleaned up by the
4319 // concurrent precleaning.
4320 if (CMSParallelRemarkEnabled) {
4321 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm);
4322 do_remark_parallel();
4323 } else {
4324 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false, _gc_timer_cm);
4325 do_remark_non_parallel();
4326 }
4327 }
4328 verify_work_stacks_empty();
4329 verify_overflow_empty();
4330
4331 {
4332 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm);)
4333 refProcessingWork();
4334 }
4335 verify_work_stacks_empty();
4336 verify_overflow_empty();
4337
4338 if (should_unload_classes()) {
4339 CodeCache::gc_epilogue();
4340 }
4341 JvmtiExport::gc_epilogue();
4342
4343 // If we encountered any (marking stack / work queue) overflow
4344 // events during the current CMS cycle, take appropriate
4345 // remedial measures, where possible, so as to try and avoid
4346 // recurrence of that condition.
4347 assert(_markStack.isEmpty(), "No grey objects");
4348 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4349 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4350 if (ser_ovflw > 0) {
4351 if (PrintCMSStatistics != 0) {
4352 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4353 "(pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT
4354 ", kac_preclean=" SIZE_FORMAT ")",
4355 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4356 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4357 }
4358 _markStack.expand();
4359 _ser_pmc_remark_ovflw = 0;
4360 _ser_pmc_preclean_ovflw = 0;
4361 _ser_kac_preclean_ovflw = 0;
4362 _ser_kac_ovflw = 0;
4363 }
4364 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4365 if (PrintCMSStatistics != 0) {
4366 gclog_or_tty->print_cr("Work queue overflow (benign) "
4367 "(pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4368 _par_pmc_remark_ovflw, _par_kac_ovflw);
4369 }
4370 _par_pmc_remark_ovflw = 0;
4371 _par_kac_ovflw = 0;
4372 }
4373 if (PrintCMSStatistics != 0) {
4374 if (_markStack._hit_limit > 0) {
4375 gclog_or_tty->print_cr(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4376 _markStack._hit_limit);
4377 }
4378 if (_markStack._failed_double > 0) {
4379 gclog_or_tty->print_cr(" (benign) Failed stack doubling (" SIZE_FORMAT "),"
4380 " current capacity " SIZE_FORMAT,
4381 _markStack._failed_double,
4382 _markStack.capacity());
4383 }
4384 }
4385 _markStack._hit_limit = 0;
4386 _markStack._failed_double = 0;
4387
4388 if ((VerifyAfterGC || VerifyDuringGC) &&
4389 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4390 verify_after_remark();
4391 }
4392
4393 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4394
4395 // Change under the freelistLocks.
4396 _collectorState = Sweeping;
4397 // Call isAllClear() under bitMapLock
4398 assert(_modUnionTable.isAllClear(),
4399 "Should be clear by end of the final marking");
4400 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4401 "Should be clear by end of the final marking");
4402 }
4403
4404 void CMSParInitialMarkTask::work(uint worker_id) {
4405 elapsedTimer _timer;
4406 ResourceMark rm;
4407 HandleMark hm;
4408
4409 // ---------- scan from roots --------------
4410 _timer.start();
4411 GenCollectedHeap* gch = GenCollectedHeap::heap();
4412 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4413
4414 // ---------- young gen roots --------------
4415 {
4416 work_on_young_gen_roots(worker_id, &par_mri_cl);
4417 _timer.stop();
4418 if (PrintCMSStatistics != 0) {
4419 gclog_or_tty->print_cr(
4420 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4421 worker_id, _timer.seconds());
4422 }
4423 }
4424
4425 // ---------- remaining roots --------------
4426 _timer.reset();
4427 _timer.start();
4428
4429 CLDToOopClosure cld_closure(&par_mri_cl, true);
4430
4431 gch->gen_process_roots(_strong_roots_scope,
4432 GenCollectedHeap::OldGen,
4433 false, // yg was scanned above
4434 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4435 _collector->should_unload_classes(),
4436 &par_mri_cl,
4437 NULL,
4438 &cld_closure);
4439 assert(_collector->should_unload_classes()
4440 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4441 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4442 _timer.stop();
4443 if (PrintCMSStatistics != 0) {
4444 gclog_or_tty->print_cr(
4445 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4446 worker_id, _timer.seconds());
4447 }
4448 }
4449
4450 // Parallel remark task
4451 class CMSParRemarkTask: public CMSParMarkTask {
4452 CompactibleFreeListSpace* _cms_space;
4453
4454 // The per-thread work queues, available here for stealing.
4455 OopTaskQueueSet* _task_queues;
4456 ParallelTaskTerminator _term;
4457 StrongRootsScope* _strong_roots_scope;
4458
4459 public:
4460 // A value of 0 passed to n_workers will cause the number of
4461 // workers to be taken from the active workers in the work gang.
4462 CMSParRemarkTask(CMSCollector* collector,
4463 CompactibleFreeListSpace* cms_space,
4464 uint n_workers, WorkGang* workers,
4465 OopTaskQueueSet* task_queues,
4466 StrongRootsScope* strong_roots_scope):
4467 CMSParMarkTask("Rescan roots and grey objects in parallel",
4468 collector, n_workers),
4469 _cms_space(cms_space),
4470 _task_queues(task_queues),
4471 _term(n_workers, task_queues),
4472 _strong_roots_scope(strong_roots_scope) { }
4473
4474 OopTaskQueueSet* task_queues() { return _task_queues; }
4475
4476 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4477
4478 ParallelTaskTerminator* terminator() { return &_term; }
4479 uint n_workers() { return _n_workers; }
4480
4481 void work(uint worker_id);
4482
4483 private:
4484 // ... of dirty cards in old space
4485 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4486 Par_MarkRefsIntoAndScanClosure* cl);
4487
4488 // ... work stealing for the above
4489 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4490 };
4491
4492 class RemarkKlassClosure : public KlassClosure {
4493 KlassToOopClosure _cm_klass_closure;
4494 public:
4495 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4496 void do_klass(Klass* k) {
4497 // Check if we have modified any oops in the Klass during the concurrent marking.
4498 if (k->has_accumulated_modified_oops()) {
4499 k->clear_accumulated_modified_oops();
4500
4501 // We could have transfered the current modified marks to the accumulated marks,
4502 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4503 } else if (k->has_modified_oops()) {
4504 // Don't clear anything, this info is needed by the next young collection.
4505 } else {
4506 // No modified oops in the Klass.
4507 return;
4508 }
4509
4510 // The klass has modified fields, need to scan the klass.
4511 _cm_klass_closure.do_klass(k);
4512 }
4513 };
4514
4515 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4516 ParNewGeneration* young_gen = _collector->_young_gen;
4517 ContiguousSpace* eden_space = young_gen->eden();
4518 ContiguousSpace* from_space = young_gen->from();
4519 ContiguousSpace* to_space = young_gen->to();
4520
4521 HeapWord** eca = _collector->_eden_chunk_array;
4522 size_t ect = _collector->_eden_chunk_index;
4523 HeapWord** sca = _collector->_survivor_chunk_array;
4524 size_t sct = _collector->_survivor_chunk_index;
4525
4526 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4527 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4528
4529 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4530 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4531 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4532 }
4533
4534 // work_queue(i) is passed to the closure
4535 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
4536 // also is passed to do_dirty_card_rescan_tasks() and to
4537 // do_work_steal() to select the i-th task_queue.
4538
4539 void CMSParRemarkTask::work(uint worker_id) {
4540 elapsedTimer _timer;
4541 ResourceMark rm;
4542 HandleMark hm;
4543
4544 // ---------- rescan from roots --------------
4545 _timer.start();
4546 GenCollectedHeap* gch = GenCollectedHeap::heap();
4547 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4548 _collector->_span, _collector->ref_processor(),
4549 &(_collector->_markBitMap),
4550 work_queue(worker_id));
4551
4552 // Rescan young gen roots first since these are likely
4553 // coarsely partitioned and may, on that account, constitute
4554 // the critical path; thus, it's best to start off that
4555 // work first.
4556 // ---------- young gen roots --------------
4557 {
4558 work_on_young_gen_roots(worker_id, &par_mrias_cl);
4559 _timer.stop();
4560 if (PrintCMSStatistics != 0) {
4561 gclog_or_tty->print_cr(
4562 "Finished young gen rescan work in %dth thread: %3.3f sec",
4563 worker_id, _timer.seconds());
4564 }
4565 }
4566
4567 // ---------- remaining roots --------------
4568 _timer.reset();
4569 _timer.start();
4570 gch->gen_process_roots(_strong_roots_scope,
4571 GenCollectedHeap::OldGen,
4572 false, // yg was scanned above
4573 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4574 _collector->should_unload_classes(),
4575 &par_mrias_cl,
4576 NULL,
4577 NULL); // The dirty klasses will be handled below
4578
4579 assert(_collector->should_unload_classes()
4580 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4581 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4582 _timer.stop();
4583 if (PrintCMSStatistics != 0) {
4584 gclog_or_tty->print_cr(
4585 "Finished remaining root rescan work in %dth thread: %3.3f sec",
4586 worker_id, _timer.seconds());
4587 }
4588
4589 // ---------- unhandled CLD scanning ----------
4590 if (worker_id == 0) { // Single threaded at the moment.
4591 _timer.reset();
4592 _timer.start();
4593
4594 // Scan all new class loader data objects and new dependencies that were
4595 // introduced during concurrent marking.
4596 ResourceMark rm;
4597 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4598 for (int i = 0; i < array->length(); i++) {
4599 par_mrias_cl.do_cld_nv(array->at(i));
4600 }
4601
4602 // We don't need to keep track of new CLDs anymore.
4603 ClassLoaderDataGraph::remember_new_clds(false);
4604
4605 _timer.stop();
4606 if (PrintCMSStatistics != 0) {
4607 gclog_or_tty->print_cr(
4608 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4609 worker_id, _timer.seconds());
4610 }
4611 }
4612
4613 // ---------- dirty klass scanning ----------
4614 if (worker_id == 0) { // Single threaded at the moment.
4615 _timer.reset();
4616 _timer.start();
4617
4618 // Scan all classes that was dirtied during the concurrent marking phase.
4619 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4620 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4621
4622 _timer.stop();
4623 if (PrintCMSStatistics != 0) {
4624 gclog_or_tty->print_cr(
4625 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4626 worker_id, _timer.seconds());
4627 }
4628 }
4629
4630 // We might have added oops to ClassLoaderData::_handles during the
4631 // concurrent marking phase. These oops point to newly allocated objects
4632 // that are guaranteed to be kept alive. Either by the direct allocation
4633 // code, or when the young collector processes the roots. Hence,
4634 // we don't have to revisit the _handles block during the remark phase.
4635
4636 // ---------- rescan dirty cards ------------
4637 _timer.reset();
4638 _timer.start();
4639
4640 // Do the rescan tasks for each of the two spaces
4641 // (cms_space) in turn.
4642 // "worker_id" is passed to select the task_queue for "worker_id"
4643 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4644 _timer.stop();
4645 if (PrintCMSStatistics != 0) {
4646 gclog_or_tty->print_cr(
4647 "Finished dirty card rescan work in %dth thread: %3.3f sec",
4648 worker_id, _timer.seconds());
4649 }
4650
4651 // ---------- steal work from other threads ...
4652 // ---------- ... and drain overflow list.
4653 _timer.reset();
4654 _timer.start();
4655 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4656 _timer.stop();
4657 if (PrintCMSStatistics != 0) {
4658 gclog_or_tty->print_cr(
4659 "Finished work stealing in %dth thread: %3.3f sec",
4660 worker_id, _timer.seconds());
4661 }
4662 }
4663
4664 // Note that parameter "i" is not used.
4665 void
4666 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4667 OopsInGenClosure* cl, ContiguousSpace* space,
4668 HeapWord** chunk_array, size_t chunk_top) {
4669 // Until all tasks completed:
4670 // . claim an unclaimed task
4671 // . compute region boundaries corresponding to task claimed
4672 // using chunk_array
4673 // . par_oop_iterate(cl) over that region
4674
4675 ResourceMark rm;
4676 HandleMark hm;
4677
4678 SequentialSubTasksDone* pst = space->par_seq_tasks();
4679
4680 uint nth_task = 0;
4681 uint n_tasks = pst->n_tasks();
4682
4683 if (n_tasks > 0) {
4684 assert(pst->valid(), "Uninitialized use?");
4685 HeapWord *start, *end;
4686 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4687 // We claimed task # nth_task; compute its boundaries.
4688 if (chunk_top == 0) { // no samples were taken
4689 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4690 start = space->bottom();
4691 end = space->top();
4692 } else if (nth_task == 0) {
4693 start = space->bottom();
4694 end = chunk_array[nth_task];
4695 } else if (nth_task < (uint)chunk_top) {
4696 assert(nth_task >= 1, "Control point invariant");
4697 start = chunk_array[nth_task - 1];
4698 end = chunk_array[nth_task];
4699 } else {
4700 assert(nth_task == (uint)chunk_top, "Control point invariant");
4701 start = chunk_array[chunk_top - 1];
4702 end = space->top();
4703 }
4704 MemRegion mr(start, end);
4705 // Verify that mr is in space
4706 assert(mr.is_empty() || space->used_region().contains(mr),
4707 "Should be in space");
4708 // Verify that "start" is an object boundary
4709 assert(mr.is_empty() || oop(mr.start())->is_oop(),
4710 "Should be an oop");
4711 space->par_oop_iterate(mr, cl);
4712 }
4713 pst->all_tasks_completed();
4714 }
4715 }
4716
4717 void
4718 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4719 CompactibleFreeListSpace* sp, int i,
4720 Par_MarkRefsIntoAndScanClosure* cl) {
4721 // Until all tasks completed:
4722 // . claim an unclaimed task
4723 // . compute region boundaries corresponding to task claimed
4724 // . transfer dirty bits ct->mut for that region
4725 // . apply rescanclosure to dirty mut bits for that region
4726
4727 ResourceMark rm;
4728 HandleMark hm;
4729
4730 OopTaskQueue* work_q = work_queue(i);
4731 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4732 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4733 // CAUTION: This closure has state that persists across calls to
4734 // the work method dirty_range_iterate_clear() in that it has
4735 // embedded in it a (subtype of) UpwardsObjectClosure. The
4736 // use of that state in the embedded UpwardsObjectClosure instance
4737 // assumes that the cards are always iterated (even if in parallel
4738 // by several threads) in monotonically increasing order per each
4739 // thread. This is true of the implementation below which picks
4740 // card ranges (chunks) in monotonically increasing order globally
4741 // and, a-fortiori, in monotonically increasing order per thread
4742 // (the latter order being a subsequence of the former).
4743 // If the work code below is ever reorganized into a more chaotic
4744 // work-partitioning form than the current "sequential tasks"
4745 // paradigm, the use of that persistent state will have to be
4746 // revisited and modified appropriately. See also related
4747 // bug 4756801 work on which should examine this code to make
4748 // sure that the changes there do not run counter to the
4749 // assumptions made here and necessary for correctness and
4750 // efficiency. Note also that this code might yield inefficient
4751 // behavior in the case of very large objects that span one or
4752 // more work chunks. Such objects would potentially be scanned
4753 // several times redundantly. Work on 4756801 should try and
4754 // address that performance anomaly if at all possible. XXX
4755 MemRegion full_span = _collector->_span;
4756 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4757 MarkFromDirtyCardsClosure
4758 greyRescanClosure(_collector, full_span, // entire span of interest
4759 sp, bm, work_q, cl);
4760
4761 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4762 assert(pst->valid(), "Uninitialized use?");
4763 uint nth_task = 0;
4764 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4765 MemRegion span = sp->used_region();
4766 HeapWord* start_addr = span.start();
4767 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4768 alignment);
4769 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4770 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4771 start_addr, "Check alignment");
4772 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4773 chunk_size, "Check alignment");
4774
4775 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4776 // Having claimed the nth_task, compute corresponding mem-region,
4777 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4778 // The alignment restriction ensures that we do not need any
4779 // synchronization with other gang-workers while setting or
4780 // clearing bits in thus chunk of the MUT.
4781 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4782 start_addr + (nth_task+1)*chunk_size);
4783 // The last chunk's end might be way beyond end of the
4784 // used region. In that case pull back appropriately.
4785 if (this_span.end() > end_addr) {
4786 this_span.set_end(end_addr);
4787 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4788 }
4789 // Iterate over the dirty cards covering this chunk, marking them
4790 // precleaned, and setting the corresponding bits in the mod union
4791 // table. Since we have been careful to partition at Card and MUT-word
4792 // boundaries no synchronization is needed between parallel threads.
4793 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4794 &modUnionClosure);
4795
4796 // Having transferred these marks into the modUnionTable,
4797 // rescan the marked objects on the dirty cards in the modUnionTable.
4798 // Even if this is at a synchronous collection, the initial marking
4799 // may have been done during an asynchronous collection so there
4800 // may be dirty bits in the mod-union table.
4801 _collector->_modUnionTable.dirty_range_iterate_clear(
4802 this_span, &greyRescanClosure);
4803 _collector->_modUnionTable.verifyNoOneBitsInRange(
4804 this_span.start(),
4805 this_span.end());
4806 }
4807 pst->all_tasks_completed(); // declare that i am done
4808 }
4809
4810 // . see if we can share work_queues with ParNew? XXX
4811 void
4812 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4813 int* seed) {
4814 OopTaskQueue* work_q = work_queue(i);
4815 NOT_PRODUCT(int num_steals = 0;)
4816 oop obj_to_scan;
4817 CMSBitMap* bm = &(_collector->_markBitMap);
4818
4819 while (true) {
4820 // Completely finish any left over work from (an) earlier round(s)
4821 cl->trim_queue(0);
4822 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4823 (size_t)ParGCDesiredObjsFromOverflowList);
4824 // Now check if there's any work in the overflow list
4825 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4826 // only affects the number of attempts made to get work from the
4827 // overflow list and does not affect the number of workers. Just
4828 // pass ParallelGCThreads so this behavior is unchanged.
4829 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4830 work_q,
4831 ParallelGCThreads)) {
4832 // found something in global overflow list;
4833 // not yet ready to go stealing work from others.
4834 // We'd like to assert(work_q->size() != 0, ...)
4835 // because we just took work from the overflow list,
4836 // but of course we can't since all of that could have
4837 // been already stolen from us.
4838 // "He giveth and He taketh away."
4839 continue;
4840 }
4841 // Verify that we have no work before we resort to stealing
4842 assert(work_q->size() == 0, "Have work, shouldn't steal");
4843 // Try to steal from other queues that have work
4844 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4845 NOT_PRODUCT(num_steals++;)
4846 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4847 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4848 // Do scanning work
4849 obj_to_scan->oop_iterate(cl);
4850 // Loop around, finish this work, and try to steal some more
4851 } else if (terminator()->offer_termination()) {
4852 break; // nirvana from the infinite cycle
4853 }
4854 }
4855 NOT_PRODUCT(
4856 if (PrintCMSStatistics != 0) {
4857 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
4858 }
4859 )
4860 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4861 "Else our work is not yet done");
4862 }
4863
4864 // Record object boundaries in _eden_chunk_array by sampling the eden
4865 // top in the slow-path eden object allocation code path and record
4866 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4867 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4868 // sampling in sample_eden() that activates during the part of the
4869 // preclean phase.
4870 void CMSCollector::sample_eden_chunk() {
4871 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4872 if (_eden_chunk_lock->try_lock()) {
4873 // Record a sample. This is the critical section. The contents
4874 // of the _eden_chunk_array have to be non-decreasing in the
4875 // address order.
4876 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4877 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4878 "Unexpected state of Eden");
4879 if (_eden_chunk_index == 0 ||
4880 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4881 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4882 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4883 _eden_chunk_index++; // commit sample
4884 }
4885 _eden_chunk_lock->unlock();
4886 }
4887 }
4888 }
4889
4890 // Return a thread-local PLAB recording array, as appropriate.
4891 void* CMSCollector::get_data_recorder(int thr_num) {
4892 if (_survivor_plab_array != NULL &&
4893 (CMSPLABRecordAlways ||
4894 (_collectorState > Marking && _collectorState < FinalMarking))) {
4895 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4896 ChunkArray* ca = &_survivor_plab_array[thr_num];
4897 ca->reset(); // clear it so that fresh data is recorded
4898 return (void*) ca;
4899 } else {
4900 return NULL;
4901 }
4902 }
4903
4904 // Reset all the thread-local PLAB recording arrays
4905 void CMSCollector::reset_survivor_plab_arrays() {
4906 for (uint i = 0; i < ParallelGCThreads; i++) {
4907 _survivor_plab_array[i].reset();
4908 }
4909 }
4910
4911 // Merge the per-thread plab arrays into the global survivor chunk
4912 // array which will provide the partitioning of the survivor space
4913 // for CMS initial scan and rescan.
4914 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4915 int no_of_gc_threads) {
4916 assert(_survivor_plab_array != NULL, "Error");
4917 assert(_survivor_chunk_array != NULL, "Error");
4918 assert(_collectorState == FinalMarking ||
4919 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4920 for (int j = 0; j < no_of_gc_threads; j++) {
4921 _cursor[j] = 0;
4922 }
4923 HeapWord* top = surv->top();
4924 size_t i;
4925 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4926 HeapWord* min_val = top; // Higher than any PLAB address
4927 uint min_tid = 0; // position of min_val this round
4928 for (int j = 0; j < no_of_gc_threads; j++) {
4929 ChunkArray* cur_sca = &_survivor_plab_array[j];
4930 if (_cursor[j] == cur_sca->end()) {
4931 continue;
4932 }
4933 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4934 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4935 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4936 if (cur_val < min_val) {
4937 min_tid = j;
4938 min_val = cur_val;
4939 } else {
4940 assert(cur_val < top, "All recorded addresses should be less");
4941 }
4942 }
4943 // At this point min_val and min_tid are respectively
4944 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4945 // and the thread (j) that witnesses that address.
4946 // We record this address in the _survivor_chunk_array[i]
4947 // and increment _cursor[min_tid] prior to the next round i.
4948 if (min_val == top) {
4949 break;
4950 }
4951 _survivor_chunk_array[i] = min_val;
4952 _cursor[min_tid]++;
4953 }
4954 // We are all done; record the size of the _survivor_chunk_array
4955 _survivor_chunk_index = i; // exclusive: [0, i)
4956 if (PrintCMSStatistics > 0) {
4957 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4958 }
4959 // Verify that we used up all the recorded entries
4960 #ifdef ASSERT
4961 size_t total = 0;
4962 for (int j = 0; j < no_of_gc_threads; j++) {
4963 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4964 total += _cursor[j];
4965 }
4966 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4967 // Check that the merged array is in sorted order
4968 if (total > 0) {
4969 for (size_t i = 0; i < total - 1; i++) {
4970 if (PrintCMSStatistics > 0) {
4971 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4972 i, p2i(_survivor_chunk_array[i]));
4973 }
4974 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4975 "Not sorted");
4976 }
4977 }
4978 #endif // ASSERT
4979 }
4980
4981 // Set up the space's par_seq_tasks structure for work claiming
4982 // for parallel initial scan and rescan of young gen.
4983 // See ParRescanTask where this is currently used.
4984 void
4985 CMSCollector::
4986 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4987 assert(n_threads > 0, "Unexpected n_threads argument");
4988
4989 // Eden space
4990 if (!_young_gen->eden()->is_empty()) {
4991 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4992 assert(!pst->valid(), "Clobbering existing data?");
4993 // Each valid entry in [0, _eden_chunk_index) represents a task.
4994 size_t n_tasks = _eden_chunk_index + 1;
4995 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4996 // Sets the condition for completion of the subtask (how many threads
4997 // need to finish in order to be done).
4998 pst->set_n_threads(n_threads);
4999 pst->set_n_tasks((int)n_tasks);
5000 }
5001
5002 // Merge the survivor plab arrays into _survivor_chunk_array
5003 if (_survivor_plab_array != NULL) {
5004 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5005 } else {
5006 assert(_survivor_chunk_index == 0, "Error");
5007 }
5008
5009 // To space
5010 {
5011 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5012 assert(!pst->valid(), "Clobbering existing data?");
5013 // Sets the condition for completion of the subtask (how many threads
5014 // need to finish in order to be done).
5015 pst->set_n_threads(n_threads);
5016 pst->set_n_tasks(1);
5017 assert(pst->valid(), "Error");
5018 }
5019
5020 // From space
5021 {
5022 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5023 assert(!pst->valid(), "Clobbering existing data?");
5024 size_t n_tasks = _survivor_chunk_index + 1;
5025 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5026 // Sets the condition for completion of the subtask (how many threads
5027 // need to finish in order to be done).
5028 pst->set_n_threads(n_threads);
5029 pst->set_n_tasks((int)n_tasks);
5030 assert(pst->valid(), "Error");
5031 }
5032 }
5033
5034 // Parallel version of remark
5035 void CMSCollector::do_remark_parallel() {
5036 GenCollectedHeap* gch = GenCollectedHeap::heap();
5037 WorkGang* workers = gch->workers();
5038 assert(workers != NULL, "Need parallel worker threads.");
5039 // Choose to use the number of GC workers most recently set
5040 // into "active_workers".
5041 uint n_workers = workers->active_workers();
5042
5043 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5044
5045 StrongRootsScope srs(n_workers);
5046
5047 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
5048
5049 // We won't be iterating over the cards in the card table updating
5050 // the younger_gen cards, so we shouldn't call the following else
5051 // the verification code as well as subsequent younger_refs_iterate
5052 // code would get confused. XXX
5053 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5054
5055 // The young gen rescan work will not be done as part of
5056 // process_roots (which currently doesn't know how to
5057 // parallelize such a scan), but rather will be broken up into
5058 // a set of parallel tasks (via the sampling that the [abortable]
5059 // preclean phase did of eden, plus the [two] tasks of
5060 // scanning the [two] survivor spaces. Further fine-grain
5061 // parallelization of the scanning of the survivor spaces
5062 // themselves, and of precleaning of the young gen itself
5063 // is deferred to the future.
5064 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5065
5066 // The dirty card rescan work is broken up into a "sequence"
5067 // of parallel tasks (per constituent space) that are dynamically
5068 // claimed by the parallel threads.
5069 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5070
5071 // It turns out that even when we're using 1 thread, doing the work in a
5072 // separate thread causes wide variance in run times. We can't help this
5073 // in the multi-threaded case, but we special-case n=1 here to get
5074 // repeatable measurements of the 1-thread overhead of the parallel code.
5075 if (n_workers > 1) {
5076 // Make refs discovery MT-safe, if it isn't already: it may not
5077 // necessarily be so, since it's possible that we are doing
5078 // ST marking.
5079 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5080 workers->run_task(&tsk);
5081 } else {
5082 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5083 tsk.work(0);
5084 }
5085
5086 // restore, single-threaded for now, any preserved marks
5087 // as a result of work_q overflow
5088 restore_preserved_marks_if_any();
5089 }
5090
5091 // Non-parallel version of remark
5092 void CMSCollector::do_remark_non_parallel() {
5093 ResourceMark rm;
5094 HandleMark hm;
5095 GenCollectedHeap* gch = GenCollectedHeap::heap();
5096 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5097
5098 MarkRefsIntoAndScanClosure
5099 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5100 &_markStack, this,
5101 false /* should_yield */, false /* not precleaning */);
5102 MarkFromDirtyCardsClosure
5103 markFromDirtyCardsClosure(this, _span,
5104 NULL, // space is set further below
5105 &_markBitMap, &_markStack, &mrias_cl);
5106 {
5107 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm);
5108 // Iterate over the dirty cards, setting the corresponding bits in the
5109 // mod union table.
5110 {
5111 ModUnionClosure modUnionClosure(&_modUnionTable);
5112 _ct->ct_bs()->dirty_card_iterate(
5113 _cmsGen->used_region(),
5114 &modUnionClosure);
5115 }
5116 // Having transferred these marks into the modUnionTable, we just need
5117 // to rescan the marked objects on the dirty cards in the modUnionTable.
5118 // The initial marking may have been done during an asynchronous
5119 // collection so there may be dirty bits in the mod-union table.
5120 const int alignment =
5121 CardTableModRefBS::card_size * BitsPerWord;
5122 {
5123 // ... First handle dirty cards in CMS gen
5124 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5125 MemRegion ur = _cmsGen->used_region();
5126 HeapWord* lb = ur.start();
5127 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5128 MemRegion cms_span(lb, ub);
5129 _modUnionTable.dirty_range_iterate_clear(cms_span,
5130 &markFromDirtyCardsClosure);
5131 verify_work_stacks_empty();
5132 if (PrintCMSStatistics != 0) {
5133 gclog_or_tty->print(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ",
5134 markFromDirtyCardsClosure.num_dirty_cards());
5135 }
5136 }
5137 }
5138 if (VerifyDuringGC &&
5139 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5140 HandleMark hm; // Discard invalid handles created during verification
5141 Universe::verify();
5142 }
5143 {
5144 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm);
5145
5146 verify_work_stacks_empty();
5147
5148 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5149 StrongRootsScope srs(1);
5150
5151 gch->gen_process_roots(&srs,
5152 GenCollectedHeap::OldGen,
5153 true, // young gen as roots
5154 GenCollectedHeap::ScanningOption(roots_scanning_options()),
5155 should_unload_classes(),
5156 &mrias_cl,
5157 NULL,
5158 NULL); // The dirty klasses will be handled below
5159
5160 assert(should_unload_classes()
5161 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5162 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5163 }
5164
5165 {
5166 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm);
5167
5168 verify_work_stacks_empty();
5169
5170 // Scan all class loader data objects that might have been introduced
5171 // during concurrent marking.
5172 ResourceMark rm;
5173 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5174 for (int i = 0; i < array->length(); i++) {
5175 mrias_cl.do_cld_nv(array->at(i));
5176 }
5177
5178 // We don't need to keep track of new CLDs anymore.
5179 ClassLoaderDataGraph::remember_new_clds(false);
5180
5181 verify_work_stacks_empty();
5182 }
5183
5184 {
5185 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm);
5186
5187 verify_work_stacks_empty();
5188
5189 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5190 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5191
5192 verify_work_stacks_empty();
5193 }
5194
5195 // We might have added oops to ClassLoaderData::_handles during the
5196 // concurrent marking phase. These oops point to newly allocated objects
5197 // that are guaranteed to be kept alive. Either by the direct allocation
5198 // code, or when the young collector processes the roots. Hence,
5199 // we don't have to revisit the _handles block during the remark phase.
5200
5201 verify_work_stacks_empty();
5202 // Restore evacuated mark words, if any, used for overflow list links
5203 restore_preserved_marks_if_any();
5204
5205 verify_overflow_empty();
5206 }
5207
5208 ////////////////////////////////////////////////////////
5209 // Parallel Reference Processing Task Proxy Class
5210 ////////////////////////////////////////////////////////
5211 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5212 OopTaskQueueSet* _queues;
5213 ParallelTaskTerminator _terminator;
5214 public:
5215 AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5216 AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5217 ParallelTaskTerminator* terminator() { return &_terminator; }
5218 OopTaskQueueSet* queues() { return _queues; }
5219 };
5220
5221 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5222 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5223 CMSCollector* _collector;
5224 CMSBitMap* _mark_bit_map;
5225 const MemRegion _span;
5226 ProcessTask& _task;
5227
5228 public:
5229 CMSRefProcTaskProxy(ProcessTask& task,
5230 CMSCollector* collector,
5231 const MemRegion& span,
5232 CMSBitMap* mark_bit_map,
5233 AbstractWorkGang* workers,
5234 OopTaskQueueSet* task_queues):
5235 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5236 task_queues,
5237 workers->active_workers()),
5238 _task(task),
5239 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5240 {
5241 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5242 "Inconsistency in _span");
5243 }
5244
5245 OopTaskQueueSet* task_queues() { return queues(); }
5246
5247 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5248
5249 void do_work_steal(int i,
5250 CMSParDrainMarkingStackClosure* drain,
5251 CMSParKeepAliveClosure* keep_alive,
5252 int* seed);
5253
5254 virtual void work(uint worker_id);
5255 };
5256
5257 void CMSRefProcTaskProxy::work(uint worker_id) {
5258 ResourceMark rm;
5259 HandleMark hm;
5260 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5261 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5262 _mark_bit_map,
5263 work_queue(worker_id));
5264 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5265 _mark_bit_map,
5266 work_queue(worker_id));
5267 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5268 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5269 if (_task.marks_oops_alive()) {
5270 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5271 _collector->hash_seed(worker_id));
5272 }
5273 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5274 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5275 }
5276
5277 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5278 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5279 EnqueueTask& _task;
5280
5281 public:
5282 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5283 : AbstractGangTask("Enqueue reference objects in parallel"),
5284 _task(task)
5285 { }
5286
5287 virtual void work(uint worker_id)
5288 {
5289 _task.work(worker_id);
5290 }
5291 };
5292
5293 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5294 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5295 _span(span),
5296 _bit_map(bit_map),
5297 _work_queue(work_queue),
5298 _mark_and_push(collector, span, bit_map, work_queue),
5299 _low_water_mark(MIN2((work_queue->max_elems()/4),
5300 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5301 { }
5302
5303 // . see if we can share work_queues with ParNew? XXX
5304 void CMSRefProcTaskProxy::do_work_steal(int i,
5305 CMSParDrainMarkingStackClosure* drain,
5306 CMSParKeepAliveClosure* keep_alive,
5307 int* seed) {
5308 OopTaskQueue* work_q = work_queue(i);
5309 NOT_PRODUCT(int num_steals = 0;)
5310 oop obj_to_scan;
5311
5312 while (true) {
5313 // Completely finish any left over work from (an) earlier round(s)
5314 drain->trim_queue(0);
5315 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5316 (size_t)ParGCDesiredObjsFromOverflowList);
5317 // Now check if there's any work in the overflow list
5318 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5319 // only affects the number of attempts made to get work from the
5320 // overflow list and does not affect the number of workers. Just
5321 // pass ParallelGCThreads so this behavior is unchanged.
5322 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5323 work_q,
5324 ParallelGCThreads)) {
5325 // Found something in global overflow list;
5326 // not yet ready to go stealing work from others.
5327 // We'd like to assert(work_q->size() != 0, ...)
5328 // because we just took work from the overflow list,
5329 // but of course we can't, since all of that might have
5330 // been already stolen from us.
5331 continue;
5332 }
5333 // Verify that we have no work before we resort to stealing
5334 assert(work_q->size() == 0, "Have work, shouldn't steal");
5335 // Try to steal from other queues that have work
5336 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5337 NOT_PRODUCT(num_steals++;)
5338 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5339 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5340 // Do scanning work
5341 obj_to_scan->oop_iterate(keep_alive);
5342 // Loop around, finish this work, and try to steal some more
5343 } else if (terminator()->offer_termination()) {
5344 break; // nirvana from the infinite cycle
5345 }
5346 }
5347 NOT_PRODUCT(
5348 if (PrintCMSStatistics != 0) {
5349 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5350 }
5351 )
5352 }
5353
5354 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5355 {
5356 GenCollectedHeap* gch = GenCollectedHeap::heap();
5357 WorkGang* workers = gch->workers();
5358 assert(workers != NULL, "Need parallel worker threads.");
5359 CMSRefProcTaskProxy rp_task(task, &_collector,
5360 _collector.ref_processor()->span(),
5361 _collector.markBitMap(),
5362 workers, _collector.task_queues());
5363 workers->run_task(&rp_task);
5364 }
5365
5366 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5367 {
5368
5369 GenCollectedHeap* gch = GenCollectedHeap::heap();
5370 WorkGang* workers = gch->workers();
5371 assert(workers != NULL, "Need parallel worker threads.");
5372 CMSRefEnqueueTaskProxy enq_task(task);
5373 workers->run_task(&enq_task);
5374 }
5375
5376 void CMSCollector::refProcessingWork() {
5377 ResourceMark rm;
5378 HandleMark hm;
5379
5380 ReferenceProcessor* rp = ref_processor();
5381 assert(rp->span().equals(_span), "Spans should be equal");
5382 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5383 // Process weak references.
5384 rp->setup_policy(false);
5385 verify_work_stacks_empty();
5386
5387 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5388 &_markStack, false /* !preclean */);
5389 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5390 _span, &_markBitMap, &_markStack,
5391 &cmsKeepAliveClosure, false /* !preclean */);
5392 {
5393 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm);
5394
5395 ReferenceProcessorStats stats;
5396 if (rp->processing_is_mt()) {
5397 // Set the degree of MT here. If the discovery is done MT, there
5398 // may have been a different number of threads doing the discovery
5399 // and a different number of discovered lists may have Ref objects.
5400 // That is OK as long as the Reference lists are balanced (see
5401 // balance_all_queues() and balance_queues()).
5402 GenCollectedHeap* gch = GenCollectedHeap::heap();
5403 uint active_workers = ParallelGCThreads;
5404 WorkGang* workers = gch->workers();
5405 if (workers != NULL) {
5406 active_workers = workers->active_workers();
5407 // The expectation is that active_workers will have already
5408 // been set to a reasonable value. If it has not been set,
5409 // investigate.
5410 assert(active_workers > 0, "Should have been set during scavenge");
5411 }
5412 rp->set_active_mt_degree(active_workers);
5413 CMSRefProcTaskExecutor task_executor(*this);
5414 stats = rp->process_discovered_references(&_is_alive_closure,
5415 &cmsKeepAliveClosure,
5416 &cmsDrainMarkingStackClosure,
5417 &task_executor,
5418 _gc_timer_cm);
5419 } else {
5420 stats = rp->process_discovered_references(&_is_alive_closure,
5421 &cmsKeepAliveClosure,
5422 &cmsDrainMarkingStackClosure,
5423 NULL,
5424 _gc_timer_cm);
5425 }
5426 _gc_tracer_cm->report_gc_reference_stats(stats);
5427
5428 }
5429
5430 // This is the point where the entire marking should have completed.
5431 verify_work_stacks_empty();
5432
5433 if (should_unload_classes()) {
5434 {
5435 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm);
5436
5437 // Unload classes and purge the SystemDictionary.
5438 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5439
5440 // Unload nmethods.
5441 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5442
5443 // Prune dead klasses from subklass/sibling/implementor lists.
5444 Klass::clean_weak_klass_links(&_is_alive_closure);
5445 }
5446
5447 {
5448 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm);
5449 // Clean up unreferenced symbols in symbol table.
5450 SymbolTable::unlink();
5451 }
5452
5453 {
5454 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm);
5455 // Delete entries for dead interned strings.
5456 StringTable::unlink(&_is_alive_closure);
5457 }
5458 }
5459
5460
5461 // Restore any preserved marks as a result of mark stack or
5462 // work queue overflow
5463 restore_preserved_marks_if_any(); // done single-threaded for now
5464
5465 rp->set_enqueuing_is_done(true);
5466 if (rp->processing_is_mt()) {
5467 rp->balance_all_queues();
5468 CMSRefProcTaskExecutor task_executor(*this);
5469 rp->enqueue_discovered_references(&task_executor);
5470 } else {
5471 rp->enqueue_discovered_references(NULL);
5472 }
5473 rp->verify_no_references_recorded();
5474 assert(!rp->discovery_enabled(), "should have been disabled");
5475 }
5476
5477 #ifndef PRODUCT
5478 void CMSCollector::check_correct_thread_executing() {
5479 Thread* t = Thread::current();
5480 // Only the VM thread or the CMS thread should be here.
5481 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5482 "Unexpected thread type");
5483 // If this is the vm thread, the foreground process
5484 // should not be waiting. Note that _foregroundGCIsActive is
5485 // true while the foreground collector is waiting.
5486 if (_foregroundGCShouldWait) {
5487 // We cannot be the VM thread
5488 assert(t->is_ConcurrentGC_thread(),
5489 "Should be CMS thread");
5490 } else {
5491 // We can be the CMS thread only if we are in a stop-world
5492 // phase of CMS collection.
5493 if (t->is_ConcurrentGC_thread()) {
5494 assert(_collectorState == InitialMarking ||
5495 _collectorState == FinalMarking,
5496 "Should be a stop-world phase");
5497 // The CMS thread should be holding the CMS_token.
5498 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5499 "Potential interference with concurrently "
5500 "executing VM thread");
5501 }
5502 }
5503 }
5504 #endif
5505
5506 void CMSCollector::sweep() {
5507 assert(_collectorState == Sweeping, "just checking");
5508 check_correct_thread_executing();
5509 verify_work_stacks_empty();
5510 verify_overflow_empty();
5511 increment_sweep_count();
5512 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5513
5514 _inter_sweep_timer.stop();
5515 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5516
5517 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5518 _intra_sweep_timer.reset();
5519 _intra_sweep_timer.start();
5520 {
5521 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5522 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
5523 // First sweep the old gen
5524 {
5525 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5526 bitMapLock());
5527 sweepWork(_cmsGen);
5528 }
5529
5530 // Update Universe::_heap_*_at_gc figures.
5531 // We need all the free list locks to make the abstract state
5532 // transition from Sweeping to Resetting. See detailed note
5533 // further below.
5534 {
5535 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5536 // Update heap occupancy information which is used as
5537 // input to soft ref clearing policy at the next gc.
5538 Universe::update_heap_info_at_gc();
5539 _collectorState = Resizing;
5540 }
5541 }
5542 verify_work_stacks_empty();
5543 verify_overflow_empty();
5544
5545 if (should_unload_classes()) {
5546 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5547 // requires that the virtual spaces are stable and not deleted.
5548 ClassLoaderDataGraph::set_should_purge(true);
5549 }
5550
5551 _intra_sweep_timer.stop();
5552 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5553
5554 _inter_sweep_timer.reset();
5555 _inter_sweep_timer.start();
5556
5557 // We need to use a monotonically non-decreasing time in ms
5558 // or we will see time-warp warnings and os::javaTimeMillis()
5559 // does not guarantee monotonicity.
5560 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5561 update_time_of_last_gc(now);
5562
5563 // NOTE on abstract state transitions:
5564 // Mutators allocate-live and/or mark the mod-union table dirty
5565 // based on the state of the collection. The former is done in
5566 // the interval [Marking, Sweeping] and the latter in the interval
5567 // [Marking, Sweeping). Thus the transitions into the Marking state
5568 // and out of the Sweeping state must be synchronously visible
5569 // globally to the mutators.
5570 // The transition into the Marking state happens with the world
5571 // stopped so the mutators will globally see it. Sweeping is
5572 // done asynchronously by the background collector so the transition
5573 // from the Sweeping state to the Resizing state must be done
5574 // under the freelistLock (as is the check for whether to
5575 // allocate-live and whether to dirty the mod-union table).
5576 assert(_collectorState == Resizing, "Change of collector state to"
5577 " Resizing must be done under the freelistLocks (plural)");
5578
5579 // Now that sweeping has been completed, we clear
5580 // the incremental_collection_failed flag,
5581 // thus inviting a younger gen collection to promote into
5582 // this generation. If such a promotion may still fail,
5583 // the flag will be set again when a young collection is
5584 // attempted.
5585 GenCollectedHeap* gch = GenCollectedHeap::heap();
5586 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5587 gch->update_full_collections_completed(_collection_count_start);
5588 }
5589
5590 // FIX ME!!! Looks like this belongs in CFLSpace, with
5591 // CMSGen merely delegating to it.
5592 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5593 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5594 HeapWord* minAddr = _cmsSpace->bottom();
5595 HeapWord* largestAddr =
5596 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5597 if (largestAddr == NULL) {
5598 // The dictionary appears to be empty. In this case
5599 // try to coalesce at the end of the heap.
5600 largestAddr = _cmsSpace->end();
5601 }
5602 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5603 size_t nearLargestOffset =
5604 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5605 if (PrintFLSStatistics != 0) {
5606 gclog_or_tty->print_cr(
5607 "CMS: Large Block: " PTR_FORMAT ";"
5608 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5609 p2i(largestAddr),
5610 p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5611 }
5612 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5613 }
5614
5615 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5616 return addr >= _cmsSpace->nearLargestChunk();
5617 }
5618
5619 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5620 return _cmsSpace->find_chunk_at_end();
5621 }
5622
5623 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5624 bool full) {
5625 // If the young generation has been collected, gather any statistics
5626 // that are of interest at this point.
5627 bool current_is_young = GenCollectedHeap::heap()->is_young_gen(current_generation);
5628 if (!full && current_is_young) {
5629 // Gather statistics on the young generation collection.
5630 collector()->stats().record_gc0_end(used());
5631 }
5632 }
5633
5634 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5635 // We iterate over the space(s) underlying this generation,
5636 // checking the mark bit map to see if the bits corresponding
5637 // to specific blocks are marked or not. Blocks that are
5638 // marked are live and are not swept up. All remaining blocks
5639 // are swept up, with coalescing on-the-fly as we sweep up
5640 // contiguous free and/or garbage blocks:
5641 // We need to ensure that the sweeper synchronizes with allocators
5642 // and stop-the-world collectors. In particular, the following
5643 // locks are used:
5644 // . CMS token: if this is held, a stop the world collection cannot occur
5645 // . freelistLock: if this is held no allocation can occur from this
5646 // generation by another thread
5647 // . bitMapLock: if this is held, no other thread can access or update
5648 //
5649
5650 // Note that we need to hold the freelistLock if we use
5651 // block iterate below; else the iterator might go awry if
5652 // a mutator (or promotion) causes block contents to change
5653 // (for instance if the allocator divvies up a block).
5654 // If we hold the free list lock, for all practical purposes
5655 // young generation GC's can't occur (they'll usually need to
5656 // promote), so we might as well prevent all young generation
5657 // GC's while we do a sweeping step. For the same reason, we might
5658 // as well take the bit map lock for the entire duration
5659
5660 // check that we hold the requisite locks
5661 assert(have_cms_token(), "Should hold cms token");
5662 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5663 assert_lock_strong(old_gen->freelistLock());
5664 assert_lock_strong(bitMapLock());
5665
5666 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5667 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5668 old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5669 _inter_sweep_estimate.padded_average(),
5670 _intra_sweep_estimate.padded_average());
5671 old_gen->setNearLargestChunk();
5672
5673 {
5674 SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5675 old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5676 // We need to free-up/coalesce garbage/blocks from a
5677 // co-terminal free run. This is done in the SweepClosure
5678 // destructor; so, do not remove this scope, else the
5679 // end-of-sweep-census below will be off by a little bit.
5680 }
5681 old_gen->cmsSpace()->sweep_completed();
5682 old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5683 if (should_unload_classes()) { // unloaded classes this cycle,
5684 _concurrent_cycles_since_last_unload = 0; // ... reset count
5685 } else { // did not unload classes,
5686 _concurrent_cycles_since_last_unload++; // ... increment count
5687 }
5688 }
5689
5690 // Reset CMS data structures (for now just the marking bit map)
5691 // preparatory for the next cycle.
5692 void CMSCollector::reset_concurrent() {
5693 CMSTokenSyncWithLocks ts(true, bitMapLock());
5694
5695 // If the state is not "Resetting", the foreground thread
5696 // has done a collection and the resetting.
5697 if (_collectorState != Resetting) {
5698 assert(_collectorState == Idling, "The state should only change"
5699 " because the foreground collector has finished the collection");
5700 return;
5701 }
5702
5703 // Clear the mark bitmap (no grey objects to start with)
5704 // for the next cycle.
5705 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5706 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
5707
5708 HeapWord* curAddr = _markBitMap.startWord();
5709 while (curAddr < _markBitMap.endWord()) {
5710 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5711 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5712 _markBitMap.clear_large_range(chunk);
5713 if (ConcurrentMarkSweepThread::should_yield() &&
5714 !foregroundGCIsActive() &&
5715 CMSYield) {
5716 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5717 "CMS thread should hold CMS token");
5718 assert_lock_strong(bitMapLock());
5719 bitMapLock()->unlock();
5720 ConcurrentMarkSweepThread::desynchronize(true);
5721 stopTimer();
5722 if (PrintCMSStatistics != 0) {
5723 incrementYields();
5724 }
5725
5726 // See the comment in coordinator_yield()
5727 for (unsigned i = 0; i < CMSYieldSleepCount &&
5728 ConcurrentMarkSweepThread::should_yield() &&
5729 !CMSCollector::foregroundGCIsActive(); ++i) {
5730 os::sleep(Thread::current(), 1, false);
5731 }
5732
5733 ConcurrentMarkSweepThread::synchronize(true);
5734 bitMapLock()->lock_without_safepoint_check();
5735 startTimer();
5736 }
5737 curAddr = chunk.end();
5738 }
5739 // A successful mostly concurrent collection has been done.
5740 // Because only the full (i.e., concurrent mode failure) collections
5741 // are being measured for gc overhead limits, clean the "near" flag
5742 // and count.
5743 size_policy()->reset_gc_overhead_limit_count();
5744 _collectorState = Idling;
5745
5746 register_gc_end();
5747 }
5748
5749 // Same as above but for STW paths
5750 void CMSCollector::reset_stw() {
5751 // already have the lock
5752 assert(_collectorState == Resetting, "just checking");
5753 assert_lock_strong(bitMapLock());
5754 GCIdMarkAndRestore gc_id_mark(_cmsThread->gc_id());
5755 _markBitMap.clear_all();
5756 _collectorState = Idling;
5757 register_gc_end();
5758 }
5759
5760 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5761 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5762 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL);
5763 TraceCollectorStats tcs(counters());
5764
5765 switch (op) {
5766 case CMS_op_checkpointRootsInitial: {
5767 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5768 checkpointRootsInitial();
5769 if (PrintGC) {
5770 _cmsGen->printOccupancy("initial-mark");
5771 }
5772 break;
5773 }
5774 case CMS_op_checkpointRootsFinal: {
5775 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5776 checkpointRootsFinal();
5777 if (PrintGC) {
5778 _cmsGen->printOccupancy("remark");
5779 }
5780 break;
5781 }
5782 default:
5783 fatal("No such CMS_op");
5784 }
5785 }
5786
5787 #ifndef PRODUCT
5788 size_t const CMSCollector::skip_header_HeapWords() {
5789 return FreeChunk::header_size();
5790 }
5791
5792 // Try and collect here conditions that should hold when
5793 // CMS thread is exiting. The idea is that the foreground GC
5794 // thread should not be blocked if it wants to terminate
5795 // the CMS thread and yet continue to run the VM for a while
5796 // after that.
5797 void CMSCollector::verify_ok_to_terminate() const {
5798 assert(Thread::current()->is_ConcurrentGC_thread(),
5799 "should be called by CMS thread");
5800 assert(!_foregroundGCShouldWait, "should be false");
5801 // We could check here that all the various low-level locks
5802 // are not held by the CMS thread, but that is overkill; see
5803 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5804 // is checked.
5805 }
5806 #endif
5807
5808 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5809 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5810 "missing Printezis mark?");
5811 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5812 size_t size = pointer_delta(nextOneAddr + 1, addr);
5813 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5814 "alignment problem");
5815 assert(size >= 3, "Necessary for Printezis marks to work");
5816 return size;
5817 }
5818
5819 // A variant of the above (block_size_using_printezis_bits()) except
5820 // that we return 0 if the P-bits are not yet set.
5821 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5822 if (_markBitMap.isMarked(addr + 1)) {
5823 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5824 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5825 size_t size = pointer_delta(nextOneAddr + 1, addr);
5826 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5827 "alignment problem");
5828 assert(size >= 3, "Necessary for Printezis marks to work");
5829 return size;
5830 }
5831 return 0;
5832 }
5833
5834 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5835 size_t sz = 0;
5836 oop p = (oop)addr;
5837 if (p->klass_or_null() != NULL) {
5838 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5839 } else {
5840 sz = block_size_using_printezis_bits(addr);
5841 }
5842 assert(sz > 0, "size must be nonzero");
5843 HeapWord* next_block = addr + sz;
5844 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
5845 CardTableModRefBS::card_size);
5846 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
5847 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5848 "must be different cards");
5849 return next_card;
5850 }
5851
5852
5853 // CMS Bit Map Wrapper /////////////////////////////////////////
5854
5855 // Construct a CMS bit map infrastructure, but don't create the
5856 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5857 // further below.
5858 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5859 _bm(),
5860 _shifter(shifter),
5861 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5862 Monitor::_safepoint_check_sometimes) : NULL)
5863 {
5864 _bmStartWord = 0;
5865 _bmWordSize = 0;
5866 }
5867
5868 bool CMSBitMap::allocate(MemRegion mr) {
5869 _bmStartWord = mr.start();
5870 _bmWordSize = mr.word_size();
5871 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5872 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5873 if (!brs.is_reserved()) {
5874 warning("CMS bit map allocation failure");
5875 return false;
5876 }
5877 // For now we'll just commit all of the bit map up front.
5878 // Later on we'll try to be more parsimonious with swap.
5879 if (!_virtual_space.initialize(brs, brs.size())) {
5880 warning("CMS bit map backing store failure");
5881 return false;
5882 }
5883 assert(_virtual_space.committed_size() == brs.size(),
5884 "didn't reserve backing store for all of CMS bit map?");
5885 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5886 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5887 _bmWordSize, "inconsistency in bit map sizing");
5888 _bm.set_size(_bmWordSize >> _shifter);
5889
5890 // bm.clear(); // can we rely on getting zero'd memory? verify below
5891 assert(isAllClear(),
5892 "Expected zero'd memory from ReservedSpace constructor");
5893 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5894 "consistency check");
5895 return true;
5896 }
5897
5898 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5899 HeapWord *next_addr, *end_addr, *last_addr;
5900 assert_locked();
5901 assert(covers(mr), "out-of-range error");
5902 // XXX assert that start and end are appropriately aligned
5903 for (next_addr = mr.start(), end_addr = mr.end();
5904 next_addr < end_addr; next_addr = last_addr) {
5905 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5906 last_addr = dirty_region.end();
5907 if (!dirty_region.is_empty()) {
5908 cl->do_MemRegion(dirty_region);
5909 } else {
5910 assert(last_addr == end_addr, "program logic");
5911 return;
5912 }
5913 }
5914 }
5915
5916 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5917 _bm.print_on_error(st, prefix);
5918 }
5919
5920 #ifndef PRODUCT
5921 void CMSBitMap::assert_locked() const {
5922 CMSLockVerifier::assert_locked(lock());
5923 }
5924
5925 bool CMSBitMap::covers(MemRegion mr) const {
5926 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5927 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5928 "size inconsistency");
5929 return (mr.start() >= _bmStartWord) &&
5930 (mr.end() <= endWord());
5931 }
5932
5933 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5934 return (start >= _bmStartWord && (start + size) <= endWord());
5935 }
5936
5937 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5938 // verify that there are no 1 bits in the interval [left, right)
5939 FalseBitMapClosure falseBitMapClosure;
5940 iterate(&falseBitMapClosure, left, right);
5941 }
5942
5943 void CMSBitMap::region_invariant(MemRegion mr)
5944 {
5945 assert_locked();
5946 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5947 assert(!mr.is_empty(), "unexpected empty region");
5948 assert(covers(mr), "mr should be covered by bit map");
5949 // convert address range into offset range
5950 size_t start_ofs = heapWordToOffset(mr.start());
5951 // Make sure that end() is appropriately aligned
5952 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5953 (1 << (_shifter+LogHeapWordSize))),
5954 "Misaligned mr.end()");
5955 size_t end_ofs = heapWordToOffset(mr.end());
5956 assert(end_ofs > start_ofs, "Should mark at least one bit");
5957 }
5958
5959 #endif
5960
5961 bool CMSMarkStack::allocate(size_t size) {
5962 // allocate a stack of the requisite depth
5963 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5964 size * sizeof(oop)));
5965 if (!rs.is_reserved()) {
5966 warning("CMSMarkStack allocation failure");
5967 return false;
5968 }
5969 if (!_virtual_space.initialize(rs, rs.size())) {
5970 warning("CMSMarkStack backing store failure");
5971 return false;
5972 }
5973 assert(_virtual_space.committed_size() == rs.size(),
5974 "didn't reserve backing store for all of CMS stack?");
5975 _base = (oop*)(_virtual_space.low());
5976 _index = 0;
5977 _capacity = size;
5978 NOT_PRODUCT(_max_depth = 0);
5979 return true;
5980 }
5981
5982 // XXX FIX ME !!! In the MT case we come in here holding a
5983 // leaf lock. For printing we need to take a further lock
5984 // which has lower rank. We need to recalibrate the two
5985 // lock-ranks involved in order to be able to print the
5986 // messages below. (Or defer the printing to the caller.
5987 // For now we take the expedient path of just disabling the
5988 // messages for the problematic case.)
5989 void CMSMarkStack::expand() {
5990 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5991 if (_capacity == MarkStackSizeMax) {
5992 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
5993 // We print a warning message only once per CMS cycle.
5994 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
5995 }
5996 return;
5997 }
5998 // Double capacity if possible
5999 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6000 // Do not give up existing stack until we have managed to
6001 // get the double capacity that we desired.
6002 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6003 new_capacity * sizeof(oop)));
6004 if (rs.is_reserved()) {
6005 // Release the backing store associated with old stack
6006 _virtual_space.release();
6007 // Reinitialize virtual space for new stack
6008 if (!_virtual_space.initialize(rs, rs.size())) {
6009 fatal("Not enough swap for expanded marking stack");
6010 }
6011 _base = (oop*)(_virtual_space.low());
6012 _index = 0;
6013 _capacity = new_capacity;
6014 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6015 // Failed to double capacity, continue;
6016 // we print a detail message only once per CMS cycle.
6017 gclog_or_tty->print(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to "
6018 SIZE_FORMAT "K",
6019 _capacity / K, new_capacity / K);
6020 }
6021 }
6022
6023
6024 // Closures
6025 // XXX: there seems to be a lot of code duplication here;
6026 // should refactor and consolidate common code.
6027
6028 // This closure is used to mark refs into the CMS generation in
6029 // the CMS bit map. Called at the first checkpoint. This closure
6030 // assumes that we do not need to re-mark dirty cards; if the CMS
6031 // generation on which this is used is not an oldest
6032 // generation then this will lose younger_gen cards!
6033
6034 MarkRefsIntoClosure::MarkRefsIntoClosure(
6035 MemRegion span, CMSBitMap* bitMap):
6036 _span(span),
6037 _bitMap(bitMap)
6038 {
6039 assert(ref_processor() == NULL, "deliberately left NULL");
6040 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6041 }
6042
6043 void MarkRefsIntoClosure::do_oop(oop obj) {
6044 // if p points into _span, then mark corresponding bit in _markBitMap
6045 assert(obj->is_oop(), "expected an oop");
6046 HeapWord* addr = (HeapWord*)obj;
6047 if (_span.contains(addr)) {
6048 // this should be made more efficient
6049 _bitMap->mark(addr);
6050 }
6051 }
6052
6053 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6054 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6055
6056 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6057 MemRegion span, CMSBitMap* bitMap):
6058 _span(span),
6059 _bitMap(bitMap)
6060 {
6061 assert(ref_processor() == NULL, "deliberately left NULL");
6062 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6063 }
6064
6065 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6066 // if p points into _span, then mark corresponding bit in _markBitMap
6067 assert(obj->is_oop(), "expected an oop");
6068 HeapWord* addr = (HeapWord*)obj;
6069 if (_span.contains(addr)) {
6070 // this should be made more efficient
6071 _bitMap->par_mark(addr);
6072 }
6073 }
6074
6075 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6076 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6077
6078 // A variant of the above, used for CMS marking verification.
6079 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6080 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6081 _span(span),
6082 _verification_bm(verification_bm),
6083 _cms_bm(cms_bm)
6084 {
6085 assert(ref_processor() == NULL, "deliberately left NULL");
6086 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6087 }
6088
6089 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6090 // if p points into _span, then mark corresponding bit in _markBitMap
6091 assert(obj->is_oop(), "expected an oop");
6092 HeapWord* addr = (HeapWord*)obj;
6093 if (_span.contains(addr)) {
6094 _verification_bm->mark(addr);
6095 if (!_cms_bm->isMarked(addr)) {
6096 oop(addr)->print();
6097 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6098 fatal("... aborting");
6099 }
6100 }
6101 }
6102
6103 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6104 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6105
6106 //////////////////////////////////////////////////
6107 // MarkRefsIntoAndScanClosure
6108 //////////////////////////////////////////////////
6109
6110 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6111 ReferenceProcessor* rp,
6112 CMSBitMap* bit_map,
6113 CMSBitMap* mod_union_table,
6114 CMSMarkStack* mark_stack,
6115 CMSCollector* collector,
6116 bool should_yield,
6117 bool concurrent_precleaning):
6118 _collector(collector),
6119 _span(span),
6120 _bit_map(bit_map),
6121 _mark_stack(mark_stack),
6122 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6123 mark_stack, concurrent_precleaning),
6124 _yield(should_yield),
6125 _concurrent_precleaning(concurrent_precleaning),
6126 _freelistLock(NULL)
6127 {
6128 // FIXME: Should initialize in base class constructor.
6129 assert(rp != NULL, "ref_processor shouldn't be NULL");
6130 set_ref_processor_internal(rp);
6131 }
6132
6133 // This closure is used to mark refs into the CMS generation at the
6134 // second (final) checkpoint, and to scan and transitively follow
6135 // the unmarked oops. It is also used during the concurrent precleaning
6136 // phase while scanning objects on dirty cards in the CMS generation.
6137 // The marks are made in the marking bit map and the marking stack is
6138 // used for keeping the (newly) grey objects during the scan.
6139 // The parallel version (Par_...) appears further below.
6140 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6141 if (obj != NULL) {
6142 assert(obj->is_oop(), "expected an oop");
6143 HeapWord* addr = (HeapWord*)obj;
6144 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6145 assert(_collector->overflow_list_is_empty(),
6146 "overflow list should be empty");
6147 if (_span.contains(addr) &&
6148 !_bit_map->isMarked(addr)) {
6149 // mark bit map (object is now grey)
6150 _bit_map->mark(addr);
6151 // push on marking stack (stack should be empty), and drain the
6152 // stack by applying this closure to the oops in the oops popped
6153 // from the stack (i.e. blacken the grey objects)
6154 bool res = _mark_stack->push(obj);
6155 assert(res, "Should have space to push on empty stack");
6156 do {
6157 oop new_oop = _mark_stack->pop();
6158 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6159 assert(_bit_map->isMarked((HeapWord*)new_oop),
6160 "only grey objects on this stack");
6161 // iterate over the oops in this oop, marking and pushing
6162 // the ones in CMS heap (i.e. in _span).
6163 new_oop->oop_iterate(&_pushAndMarkClosure);
6164 // check if it's time to yield
6165 do_yield_check();
6166 } while (!_mark_stack->isEmpty() ||
6167 (!_concurrent_precleaning && take_from_overflow_list()));
6168 // if marking stack is empty, and we are not doing this
6169 // during precleaning, then check the overflow list
6170 }
6171 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6172 assert(_collector->overflow_list_is_empty(),
6173 "overflow list was drained above");
6174
6175 assert(_collector->no_preserved_marks(),
6176 "All preserved marks should have been restored above");
6177 }
6178 }
6179
6180 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6181 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6182
6183 void MarkRefsIntoAndScanClosure::do_yield_work() {
6184 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6185 "CMS thread should hold CMS token");
6186 assert_lock_strong(_freelistLock);
6187 assert_lock_strong(_bit_map->lock());
6188 // relinquish the free_list_lock and bitMaplock()
6189 _bit_map->lock()->unlock();
6190 _freelistLock->unlock();
6191 ConcurrentMarkSweepThread::desynchronize(true);
6192 _collector->stopTimer();
6193 if (PrintCMSStatistics != 0) {
6194 _collector->incrementYields();
6195 }
6196
6197 // See the comment in coordinator_yield()
6198 for (unsigned i = 0;
6199 i < CMSYieldSleepCount &&
6200 ConcurrentMarkSweepThread::should_yield() &&
6201 !CMSCollector::foregroundGCIsActive();
6202 ++i) {
6203 os::sleep(Thread::current(), 1, false);
6204 }
6205
6206 ConcurrentMarkSweepThread::synchronize(true);
6207 _freelistLock->lock_without_safepoint_check();
6208 _bit_map->lock()->lock_without_safepoint_check();
6209 _collector->startTimer();
6210 }
6211
6212 ///////////////////////////////////////////////////////////
6213 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6214 // MarkRefsIntoAndScanClosure
6215 ///////////////////////////////////////////////////////////
6216 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6217 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6218 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6219 _span(span),
6220 _bit_map(bit_map),
6221 _work_queue(work_queue),
6222 _low_water_mark(MIN2((work_queue->max_elems()/4),
6223 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6224 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6225 {
6226 // FIXME: Should initialize in base class constructor.
6227 assert(rp != NULL, "ref_processor shouldn't be NULL");
6228 set_ref_processor_internal(rp);
6229 }
6230
6231 // This closure is used to mark refs into the CMS generation at the
6232 // second (final) checkpoint, and to scan and transitively follow
6233 // the unmarked oops. The marks are made in the marking bit map and
6234 // the work_queue is used for keeping the (newly) grey objects during
6235 // the scan phase whence they are also available for stealing by parallel
6236 // threads. Since the marking bit map is shared, updates are
6237 // synchronized (via CAS).
6238 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6239 if (obj != NULL) {
6240 // Ignore mark word because this could be an already marked oop
6241 // that may be chained at the end of the overflow list.
6242 assert(obj->is_oop(true), "expected an oop");
6243 HeapWord* addr = (HeapWord*)obj;
6244 if (_span.contains(addr) &&
6245 !_bit_map->isMarked(addr)) {
6246 // mark bit map (object will become grey):
6247 // It is possible for several threads to be
6248 // trying to "claim" this object concurrently;
6249 // the unique thread that succeeds in marking the
6250 // object first will do the subsequent push on
6251 // to the work queue (or overflow list).
6252 if (_bit_map->par_mark(addr)) {
6253 // push on work_queue (which may not be empty), and trim the
6254 // queue to an appropriate length by applying this closure to
6255 // the oops in the oops popped from the stack (i.e. blacken the
6256 // grey objects)
6257 bool res = _work_queue->push(obj);
6258 assert(res, "Low water mark should be less than capacity?");
6259 trim_queue(_low_water_mark);
6260 } // Else, another thread claimed the object
6261 }
6262 }
6263 }
6264
6265 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6266 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6267
6268 // This closure is used to rescan the marked objects on the dirty cards
6269 // in the mod union table and the card table proper.
6270 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6271 oop p, MemRegion mr) {
6272
6273 size_t size = 0;
6274 HeapWord* addr = (HeapWord*)p;
6275 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6276 assert(_span.contains(addr), "we are scanning the CMS generation");
6277 // check if it's time to yield
6278 if (do_yield_check()) {
6279 // We yielded for some foreground stop-world work,
6280 // and we have been asked to abort this ongoing preclean cycle.
6281 return 0;
6282 }
6283 if (_bitMap->isMarked(addr)) {
6284 // it's marked; is it potentially uninitialized?
6285 if (p->klass_or_null() != NULL) {
6286 // an initialized object; ignore mark word in verification below
6287 // since we are running concurrent with mutators
6288 assert(p->is_oop(true), "should be an oop");
6289 if (p->is_objArray()) {
6290 // objArrays are precisely marked; restrict scanning
6291 // to dirty cards only.
6292 size = CompactibleFreeListSpace::adjustObjectSize(
6293 p->oop_iterate_size(_scanningClosure, mr));
6294 } else {
6295 // A non-array may have been imprecisely marked; we need
6296 // to scan object in its entirety.
6297 size = CompactibleFreeListSpace::adjustObjectSize(
6298 p->oop_iterate_size(_scanningClosure));
6299 }
6300 #ifdef ASSERT
6301 size_t direct_size =
6302 CompactibleFreeListSpace::adjustObjectSize(p->size());
6303 assert(size == direct_size, "Inconsistency in size");
6304 assert(size >= 3, "Necessary for Printezis marks to work");
6305 if (!_bitMap->isMarked(addr+1)) {
6306 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6307 } else {
6308 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6309 assert(_bitMap->isMarked(addr+size-1),
6310 "inconsistent Printezis mark");
6311 }
6312 #endif // ASSERT
6313 } else {
6314 // An uninitialized object.
6315 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6316 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6317 size = pointer_delta(nextOneAddr + 1, addr);
6318 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6319 "alignment problem");
6320 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6321 // will dirty the card when the klass pointer is installed in the
6322 // object (signaling the completion of initialization).
6323 }
6324 } else {
6325 // Either a not yet marked object or an uninitialized object
6326 if (p->klass_or_null() == NULL) {
6327 // An uninitialized object, skip to the next card, since
6328 // we may not be able to read its P-bits yet.
6329 assert(size == 0, "Initial value");
6330 } else {
6331 // An object not (yet) reached by marking: we merely need to
6332 // compute its size so as to go look at the next block.
6333 assert(p->is_oop(true), "should be an oop");
6334 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6335 }
6336 }
6337 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6338 return size;
6339 }
6340
6341 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6342 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6343 "CMS thread should hold CMS token");
6344 assert_lock_strong(_freelistLock);
6345 assert_lock_strong(_bitMap->lock());
6346 // relinquish the free_list_lock and bitMaplock()
6347 _bitMap->lock()->unlock();
6348 _freelistLock->unlock();
6349 ConcurrentMarkSweepThread::desynchronize(true);
6350 _collector->stopTimer();
6351 if (PrintCMSStatistics != 0) {
6352 _collector->incrementYields();
6353 }
6354
6355 // See the comment in coordinator_yield()
6356 for (unsigned i = 0; i < CMSYieldSleepCount &&
6357 ConcurrentMarkSweepThread::should_yield() &&
6358 !CMSCollector::foregroundGCIsActive(); ++i) {
6359 os::sleep(Thread::current(), 1, false);
6360 }
6361
6362 ConcurrentMarkSweepThread::synchronize(true);
6363 _freelistLock->lock_without_safepoint_check();
6364 _bitMap->lock()->lock_without_safepoint_check();
6365 _collector->startTimer();
6366 }
6367
6368
6369 //////////////////////////////////////////////////////////////////
6370 // SurvivorSpacePrecleanClosure
6371 //////////////////////////////////////////////////////////////////
6372 // This (single-threaded) closure is used to preclean the oops in
6373 // the survivor spaces.
6374 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6375
6376 HeapWord* addr = (HeapWord*)p;
6377 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6378 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6379 assert(p->klass_or_null() != NULL, "object should be initialized");
6380 // an initialized object; ignore mark word in verification below
6381 // since we are running concurrent with mutators
6382 assert(p->is_oop(true), "should be an oop");
6383 // Note that we do not yield while we iterate over
6384 // the interior oops of p, pushing the relevant ones
6385 // on our marking stack.
6386 size_t size = p->oop_iterate_size(_scanning_closure);
6387 do_yield_check();
6388 // Observe that below, we do not abandon the preclean
6389 // phase as soon as we should; rather we empty the
6390 // marking stack before returning. This is to satisfy
6391 // some existing assertions. In general, it may be a
6392 // good idea to abort immediately and complete the marking
6393 // from the grey objects at a later time.
6394 while (!_mark_stack->isEmpty()) {
6395 oop new_oop = _mark_stack->pop();
6396 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6397 assert(_bit_map->isMarked((HeapWord*)new_oop),
6398 "only grey objects on this stack");
6399 // iterate over the oops in this oop, marking and pushing
6400 // the ones in CMS heap (i.e. in _span).
6401 new_oop->oop_iterate(_scanning_closure);
6402 // check if it's time to yield
6403 do_yield_check();
6404 }
6405 unsigned int after_count =
6406 GenCollectedHeap::heap()->total_collections();
6407 bool abort = (_before_count != after_count) ||
6408 _collector->should_abort_preclean();
6409 return abort ? 0 : size;
6410 }
6411
6412 void SurvivorSpacePrecleanClosure::do_yield_work() {
6413 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6414 "CMS thread should hold CMS token");
6415 assert_lock_strong(_bit_map->lock());
6416 // Relinquish the bit map lock
6417 _bit_map->lock()->unlock();
6418 ConcurrentMarkSweepThread::desynchronize(true);
6419 _collector->stopTimer();
6420 if (PrintCMSStatistics != 0) {
6421 _collector->incrementYields();
6422 }
6423
6424 // See the comment in coordinator_yield()
6425 for (unsigned i = 0; i < CMSYieldSleepCount &&
6426 ConcurrentMarkSweepThread::should_yield() &&
6427 !CMSCollector::foregroundGCIsActive(); ++i) {
6428 os::sleep(Thread::current(), 1, false);
6429 }
6430
6431 ConcurrentMarkSweepThread::synchronize(true);
6432 _bit_map->lock()->lock_without_safepoint_check();
6433 _collector->startTimer();
6434 }
6435
6436 // This closure is used to rescan the marked objects on the dirty cards
6437 // in the mod union table and the card table proper. In the parallel
6438 // case, although the bitMap is shared, we do a single read so the
6439 // isMarked() query is "safe".
6440 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6441 // Ignore mark word because we are running concurrent with mutators
6442 assert(p->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6443 HeapWord* addr = (HeapWord*)p;
6444 assert(_span.contains(addr), "we are scanning the CMS generation");
6445 bool is_obj_array = false;
6446 #ifdef ASSERT
6447 if (!_parallel) {
6448 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6449 assert(_collector->overflow_list_is_empty(),
6450 "overflow list should be empty");
6451
6452 }
6453 #endif // ASSERT
6454 if (_bit_map->isMarked(addr)) {
6455 // Obj arrays are precisely marked, non-arrays are not;
6456 // so we scan objArrays precisely and non-arrays in their
6457 // entirety.
6458 if (p->is_objArray()) {
6459 is_obj_array = true;
6460 if (_parallel) {
6461 p->oop_iterate(_par_scan_closure, mr);
6462 } else {
6463 p->oop_iterate(_scan_closure, mr);
6464 }
6465 } else {
6466 if (_parallel) {
6467 p->oop_iterate(_par_scan_closure);
6468 } else {
6469 p->oop_iterate(_scan_closure);
6470 }
6471 }
6472 }
6473 #ifdef ASSERT
6474 if (!_parallel) {
6475 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6476 assert(_collector->overflow_list_is_empty(),
6477 "overflow list should be empty");
6478
6479 }
6480 #endif // ASSERT
6481 return is_obj_array;
6482 }
6483
6484 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6485 MemRegion span,
6486 CMSBitMap* bitMap, CMSMarkStack* markStack,
6487 bool should_yield, bool verifying):
6488 _collector(collector),
6489 _span(span),
6490 _bitMap(bitMap),
6491 _mut(&collector->_modUnionTable),
6492 _markStack(markStack),
6493 _yield(should_yield),
6494 _skipBits(0)
6495 {
6496 assert(_markStack->isEmpty(), "stack should be empty");
6497 _finger = _bitMap->startWord();
6498 _threshold = _finger;
6499 assert(_collector->_restart_addr == NULL, "Sanity check");
6500 assert(_span.contains(_finger), "Out of bounds _finger?");
6501 DEBUG_ONLY(_verifying = verifying;)
6502 }
6503
6504 void MarkFromRootsClosure::reset(HeapWord* addr) {
6505 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6506 assert(_span.contains(addr), "Out of bounds _finger?");
6507 _finger = addr;
6508 _threshold = (HeapWord*)round_to(
6509 (intptr_t)_finger, CardTableModRefBS::card_size);
6510 }
6511
6512 // Should revisit to see if this should be restructured for
6513 // greater efficiency.
6514 bool MarkFromRootsClosure::do_bit(size_t offset) {
6515 if (_skipBits > 0) {
6516 _skipBits--;
6517 return true;
6518 }
6519 // convert offset into a HeapWord*
6520 HeapWord* addr = _bitMap->startWord() + offset;
6521 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6522 "address out of range");
6523 assert(_bitMap->isMarked(addr), "tautology");
6524 if (_bitMap->isMarked(addr+1)) {
6525 // this is an allocated but not yet initialized object
6526 assert(_skipBits == 0, "tautology");
6527 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6528 oop p = oop(addr);
6529 if (p->klass_or_null() == NULL) {
6530 DEBUG_ONLY(if (!_verifying) {)
6531 // We re-dirty the cards on which this object lies and increase
6532 // the _threshold so that we'll come back to scan this object
6533 // during the preclean or remark phase. (CMSCleanOnEnter)
6534 if (CMSCleanOnEnter) {
6535 size_t sz = _collector->block_size_using_printezis_bits(addr);
6536 HeapWord* end_card_addr = (HeapWord*)round_to(
6537 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6538 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6539 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6540 // Bump _threshold to end_card_addr; note that
6541 // _threshold cannot possibly exceed end_card_addr, anyhow.
6542 // This prevents future clearing of the card as the scan proceeds
6543 // to the right.
6544 assert(_threshold <= end_card_addr,
6545 "Because we are just scanning into this object");
6546 if (_threshold < end_card_addr) {
6547 _threshold = end_card_addr;
6548 }
6549 if (p->klass_or_null() != NULL) {
6550 // Redirty the range of cards...
6551 _mut->mark_range(redirty_range);
6552 } // ...else the setting of klass will dirty the card anyway.
6553 }
6554 DEBUG_ONLY(})
6555 return true;
6556 }
6557 }
6558 scanOopsInOop(addr);
6559 return true;
6560 }
6561
6562 // We take a break if we've been at this for a while,
6563 // so as to avoid monopolizing the locks involved.
6564 void MarkFromRootsClosure::do_yield_work() {
6565 // First give up the locks, then yield, then re-lock
6566 // We should probably use a constructor/destructor idiom to
6567 // do this unlock/lock or modify the MutexUnlocker class to
6568 // serve our purpose. XXX
6569 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6570 "CMS thread should hold CMS token");
6571 assert_lock_strong(_bitMap->lock());
6572 _bitMap->lock()->unlock();
6573 ConcurrentMarkSweepThread::desynchronize(true);
6574 _collector->stopTimer();
6575 if (PrintCMSStatistics != 0) {
6576 _collector->incrementYields();
6577 }
6578
6579 // See the comment in coordinator_yield()
6580 for (unsigned i = 0; i < CMSYieldSleepCount &&
6581 ConcurrentMarkSweepThread::should_yield() &&
6582 !CMSCollector::foregroundGCIsActive(); ++i) {
6583 os::sleep(Thread::current(), 1, false);
6584 }
6585
6586 ConcurrentMarkSweepThread::synchronize(true);
6587 _bitMap->lock()->lock_without_safepoint_check();
6588 _collector->startTimer();
6589 }
6590
6591 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6592 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6593 assert(_markStack->isEmpty(),
6594 "should drain stack to limit stack usage");
6595 // convert ptr to an oop preparatory to scanning
6596 oop obj = oop(ptr);
6597 // Ignore mark word in verification below, since we
6598 // may be running concurrent with mutators.
6599 assert(obj->is_oop(true), "should be an oop");
6600 assert(_finger <= ptr, "_finger runneth ahead");
6601 // advance the finger to right end of this object
6602 _finger = ptr + obj->size();
6603 assert(_finger > ptr, "we just incremented it above");
6604 // On large heaps, it may take us some time to get through
6605 // the marking phase. During
6606 // this time it's possible that a lot of mutations have
6607 // accumulated in the card table and the mod union table --
6608 // these mutation records are redundant until we have
6609 // actually traced into the corresponding card.
6610 // Here, we check whether advancing the finger would make
6611 // us cross into a new card, and if so clear corresponding
6612 // cards in the MUT (preclean them in the card-table in the
6613 // future).
6614
6615 DEBUG_ONLY(if (!_verifying) {)
6616 // The clean-on-enter optimization is disabled by default,
6617 // until we fix 6178663.
6618 if (CMSCleanOnEnter && (_finger > _threshold)) {
6619 // [_threshold, _finger) represents the interval
6620 // of cards to be cleared in MUT (or precleaned in card table).
6621 // The set of cards to be cleared is all those that overlap
6622 // with the interval [_threshold, _finger); note that
6623 // _threshold is always kept card-aligned but _finger isn't
6624 // always card-aligned.
6625 HeapWord* old_threshold = _threshold;
6626 assert(old_threshold == (HeapWord*)round_to(
6627 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6628 "_threshold should always be card-aligned");
6629 _threshold = (HeapWord*)round_to(
6630 (intptr_t)_finger, CardTableModRefBS::card_size);
6631 MemRegion mr(old_threshold, _threshold);
6632 assert(!mr.is_empty(), "Control point invariant");
6633 assert(_span.contains(mr), "Should clear within span");
6634 _mut->clear_range(mr);
6635 }
6636 DEBUG_ONLY(})
6637 // Note: the finger doesn't advance while we drain
6638 // the stack below.
6639 PushOrMarkClosure pushOrMarkClosure(_collector,
6640 _span, _bitMap, _markStack,
6641 _finger, this);
6642 bool res = _markStack->push(obj);
6643 assert(res, "Empty non-zero size stack should have space for single push");
6644 while (!_markStack->isEmpty()) {
6645 oop new_oop = _markStack->pop();
6646 // Skip verifying header mark word below because we are
6647 // running concurrent with mutators.
6648 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6649 // now scan this oop's oops
6650 new_oop->oop_iterate(&pushOrMarkClosure);
6651 do_yield_check();
6652 }
6653 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6654 }
6655
6656 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6657 CMSCollector* collector, MemRegion span,
6658 CMSBitMap* bit_map,
6659 OopTaskQueue* work_queue,
6660 CMSMarkStack* overflow_stack):
6661 _collector(collector),
6662 _whole_span(collector->_span),
6663 _span(span),
6664 _bit_map(bit_map),
6665 _mut(&collector->_modUnionTable),
6666 _work_queue(work_queue),
6667 _overflow_stack(overflow_stack),
6668 _skip_bits(0),
6669 _task(task)
6670 {
6671 assert(_work_queue->size() == 0, "work_queue should be empty");
6672 _finger = span.start();
6673 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6674 assert(_span.contains(_finger), "Out of bounds _finger?");
6675 }
6676
6677 // Should revisit to see if this should be restructured for
6678 // greater efficiency.
6679 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6680 if (_skip_bits > 0) {
6681 _skip_bits--;
6682 return true;
6683 }
6684 // convert offset into a HeapWord*
6685 HeapWord* addr = _bit_map->startWord() + offset;
6686 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6687 "address out of range");
6688 assert(_bit_map->isMarked(addr), "tautology");
6689 if (_bit_map->isMarked(addr+1)) {
6690 // this is an allocated object that might not yet be initialized
6691 assert(_skip_bits == 0, "tautology");
6692 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6693 oop p = oop(addr);
6694 if (p->klass_or_null() == NULL) {
6695 // in the case of Clean-on-Enter optimization, redirty card
6696 // and avoid clearing card by increasing the threshold.
6697 return true;
6698 }
6699 }
6700 scan_oops_in_oop(addr);
6701 return true;
6702 }
6703
6704 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6705 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6706 // Should we assert that our work queue is empty or
6707 // below some drain limit?
6708 assert(_work_queue->size() == 0,
6709 "should drain stack to limit stack usage");
6710 // convert ptr to an oop preparatory to scanning
6711 oop obj = oop(ptr);
6712 // Ignore mark word in verification below, since we
6713 // may be running concurrent with mutators.
6714 assert(obj->is_oop(true), "should be an oop");
6715 assert(_finger <= ptr, "_finger runneth ahead");
6716 // advance the finger to right end of this object
6717 _finger = ptr + obj->size();
6718 assert(_finger > ptr, "we just incremented it above");
6719 // On large heaps, it may take us some time to get through
6720 // the marking phase. During
6721 // this time it's possible that a lot of mutations have
6722 // accumulated in the card table and the mod union table --
6723 // these mutation records are redundant until we have
6724 // actually traced into the corresponding card.
6725 // Here, we check whether advancing the finger would make
6726 // us cross into a new card, and if so clear corresponding
6727 // cards in the MUT (preclean them in the card-table in the
6728 // future).
6729
6730 // The clean-on-enter optimization is disabled by default,
6731 // until we fix 6178663.
6732 if (CMSCleanOnEnter && (_finger > _threshold)) {
6733 // [_threshold, _finger) represents the interval
6734 // of cards to be cleared in MUT (or precleaned in card table).
6735 // The set of cards to be cleared is all those that overlap
6736 // with the interval [_threshold, _finger); note that
6737 // _threshold is always kept card-aligned but _finger isn't
6738 // always card-aligned.
6739 HeapWord* old_threshold = _threshold;
6740 assert(old_threshold == (HeapWord*)round_to(
6741 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6742 "_threshold should always be card-aligned");
6743 _threshold = (HeapWord*)round_to(
6744 (intptr_t)_finger, CardTableModRefBS::card_size);
6745 MemRegion mr(old_threshold, _threshold);
6746 assert(!mr.is_empty(), "Control point invariant");
6747 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6748 _mut->clear_range(mr);
6749 }
6750
6751 // Note: the local finger doesn't advance while we drain
6752 // the stack below, but the global finger sure can and will.
6753 HeapWord** gfa = _task->global_finger_addr();
6754 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6755 _span, _bit_map,
6756 _work_queue,
6757 _overflow_stack,
6758 _finger,
6759 gfa, this);
6760 bool res = _work_queue->push(obj); // overflow could occur here
6761 assert(res, "Will hold once we use workqueues");
6762 while (true) {
6763 oop new_oop;
6764 if (!_work_queue->pop_local(new_oop)) {
6765 // We emptied our work_queue; check if there's stuff that can
6766 // be gotten from the overflow stack.
6767 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6768 _overflow_stack, _work_queue)) {
6769 do_yield_check();
6770 continue;
6771 } else { // done
6772 break;
6773 }
6774 }
6775 // Skip verifying header mark word below because we are
6776 // running concurrent with mutators.
6777 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6778 // now scan this oop's oops
6779 new_oop->oop_iterate(&pushOrMarkClosure);
6780 do_yield_check();
6781 }
6782 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6783 }
6784
6785 // Yield in response to a request from VM Thread or
6786 // from mutators.
6787 void Par_MarkFromRootsClosure::do_yield_work() {
6788 assert(_task != NULL, "sanity");
6789 _task->yield();
6790 }
6791
6792 // A variant of the above used for verifying CMS marking work.
6793 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6794 MemRegion span,
6795 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6796 CMSMarkStack* mark_stack):
6797 _collector(collector),
6798 _span(span),
6799 _verification_bm(verification_bm),
6800 _cms_bm(cms_bm),
6801 _mark_stack(mark_stack),
6802 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6803 mark_stack)
6804 {
6805 assert(_mark_stack->isEmpty(), "stack should be empty");
6806 _finger = _verification_bm->startWord();
6807 assert(_collector->_restart_addr == NULL, "Sanity check");
6808 assert(_span.contains(_finger), "Out of bounds _finger?");
6809 }
6810
6811 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6812 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6813 assert(_span.contains(addr), "Out of bounds _finger?");
6814 _finger = addr;
6815 }
6816
6817 // Should revisit to see if this should be restructured for
6818 // greater efficiency.
6819 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6820 // convert offset into a HeapWord*
6821 HeapWord* addr = _verification_bm->startWord() + offset;
6822 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6823 "address out of range");
6824 assert(_verification_bm->isMarked(addr), "tautology");
6825 assert(_cms_bm->isMarked(addr), "tautology");
6826
6827 assert(_mark_stack->isEmpty(),
6828 "should drain stack to limit stack usage");
6829 // convert addr to an oop preparatory to scanning
6830 oop obj = oop(addr);
6831 assert(obj->is_oop(), "should be an oop");
6832 assert(_finger <= addr, "_finger runneth ahead");
6833 // advance the finger to right end of this object
6834 _finger = addr + obj->size();
6835 assert(_finger > addr, "we just incremented it above");
6836 // Note: the finger doesn't advance while we drain
6837 // the stack below.
6838 bool res = _mark_stack->push(obj);
6839 assert(res, "Empty non-zero size stack should have space for single push");
6840 while (!_mark_stack->isEmpty()) {
6841 oop new_oop = _mark_stack->pop();
6842 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6843 // now scan this oop's oops
6844 new_oop->oop_iterate(&_pam_verify_closure);
6845 }
6846 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6847 return true;
6848 }
6849
6850 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6851 CMSCollector* collector, MemRegion span,
6852 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6853 CMSMarkStack* mark_stack):
6854 MetadataAwareOopClosure(collector->ref_processor()),
6855 _collector(collector),
6856 _span(span),
6857 _verification_bm(verification_bm),
6858 _cms_bm(cms_bm),
6859 _mark_stack(mark_stack)
6860 { }
6861
6862 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6863 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6864
6865 // Upon stack overflow, we discard (part of) the stack,
6866 // remembering the least address amongst those discarded
6867 // in CMSCollector's _restart_address.
6868 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6869 // Remember the least grey address discarded
6870 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6871 _collector->lower_restart_addr(ra);
6872 _mark_stack->reset(); // discard stack contents
6873 _mark_stack->expand(); // expand the stack if possible
6874 }
6875
6876 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6877 assert(obj->is_oop_or_null(), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6878 HeapWord* addr = (HeapWord*)obj;
6879 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6880 // Oop lies in _span and isn't yet grey or black
6881 _verification_bm->mark(addr); // now grey
6882 if (!_cms_bm->isMarked(addr)) {
6883 oop(addr)->print();
6884 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
6885 p2i(addr));
6886 fatal("... aborting");
6887 }
6888
6889 if (!_mark_stack->push(obj)) { // stack overflow
6890 if (PrintCMSStatistics != 0) {
6891 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6892 SIZE_FORMAT, _mark_stack->capacity());
6893 }
6894 assert(_mark_stack->isFull(), "Else push should have succeeded");
6895 handle_stack_overflow(addr);
6896 }
6897 // anything including and to the right of _finger
6898 // will be scanned as we iterate over the remainder of the
6899 // bit map
6900 }
6901 }
6902
6903 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6904 MemRegion span,
6905 CMSBitMap* bitMap, CMSMarkStack* markStack,
6906 HeapWord* finger, MarkFromRootsClosure* parent) :
6907 MetadataAwareOopClosure(collector->ref_processor()),
6908 _collector(collector),
6909 _span(span),
6910 _bitMap(bitMap),
6911 _markStack(markStack),
6912 _finger(finger),
6913 _parent(parent)
6914 { }
6915
6916 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
6917 MemRegion span,
6918 CMSBitMap* bit_map,
6919 OopTaskQueue* work_queue,
6920 CMSMarkStack* overflow_stack,
6921 HeapWord* finger,
6922 HeapWord** global_finger_addr,
6923 Par_MarkFromRootsClosure* parent) :
6924 MetadataAwareOopClosure(collector->ref_processor()),
6925 _collector(collector),
6926 _whole_span(collector->_span),
6927 _span(span),
6928 _bit_map(bit_map),
6929 _work_queue(work_queue),
6930 _overflow_stack(overflow_stack),
6931 _finger(finger),
6932 _global_finger_addr(global_finger_addr),
6933 _parent(parent)
6934 { }
6935
6936 // Assumes thread-safe access by callers, who are
6937 // responsible for mutual exclusion.
6938 void CMSCollector::lower_restart_addr(HeapWord* low) {
6939 assert(_span.contains(low), "Out of bounds addr");
6940 if (_restart_addr == NULL) {
6941 _restart_addr = low;
6942 } else {
6943 _restart_addr = MIN2(_restart_addr, low);
6944 }
6945 }
6946
6947 // Upon stack overflow, we discard (part of) the stack,
6948 // remembering the least address amongst those discarded
6949 // in CMSCollector's _restart_address.
6950 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6951 // Remember the least grey address discarded
6952 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6953 _collector->lower_restart_addr(ra);
6954 _markStack->reset(); // discard stack contents
6955 _markStack->expand(); // expand the stack if possible
6956 }
6957
6958 // Upon stack overflow, we discard (part of) the stack,
6959 // remembering the least address amongst those discarded
6960 // in CMSCollector's _restart_address.
6961 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6962 // We need to do this under a mutex to prevent other
6963 // workers from interfering with the work done below.
6964 MutexLockerEx ml(_overflow_stack->par_lock(),
6965 Mutex::_no_safepoint_check_flag);
6966 // Remember the least grey address discarded
6967 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6968 _collector->lower_restart_addr(ra);
6969 _overflow_stack->reset(); // discard stack contents
6970 _overflow_stack->expand(); // expand the stack if possible
6971 }
6972
6973 void PushOrMarkClosure::do_oop(oop obj) {
6974 // Ignore mark word because we are running concurrent with mutators.
6975 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6976 HeapWord* addr = (HeapWord*)obj;
6977 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6978 // Oop lies in _span and isn't yet grey or black
6979 _bitMap->mark(addr); // now grey
6980 if (addr < _finger) {
6981 // the bit map iteration has already either passed, or
6982 // sampled, this bit in the bit map; we'll need to
6983 // use the marking stack to scan this oop's oops.
6984 bool simulate_overflow = false;
6985 NOT_PRODUCT(
6986 if (CMSMarkStackOverflowALot &&
6987 _collector->simulate_overflow()) {
6988 // simulate a stack overflow
6989 simulate_overflow = true;
6990 }
6991 )
6992 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6993 if (PrintCMSStatistics != 0) {
6994 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6995 SIZE_FORMAT, _markStack->capacity());
6996 }
6997 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6998 handle_stack_overflow(addr);
6999 }
7000 }
7001 // anything including and to the right of _finger
7002 // will be scanned as we iterate over the remainder of the
7003 // bit map
7004 do_yield_check();
7005 }
7006 }
7007
7008 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7009 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7010
7011 void Par_PushOrMarkClosure::do_oop(oop obj) {
7012 // Ignore mark word because we are running concurrent with mutators.
7013 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
7014 HeapWord* addr = (HeapWord*)obj;
7015 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7016 // Oop lies in _span and isn't yet grey or black
7017 // We read the global_finger (volatile read) strictly after marking oop
7018 bool res = _bit_map->par_mark(addr); // now grey
7019 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7020 // Should we push this marked oop on our stack?
7021 // -- if someone else marked it, nothing to do
7022 // -- if target oop is above global finger nothing to do
7023 // -- if target oop is in chunk and above local finger
7024 // then nothing to do
7025 // -- else push on work queue
7026 if ( !res // someone else marked it, they will deal with it
7027 || (addr >= *gfa) // will be scanned in a later task
7028 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7029 return;
7030 }
7031 // the bit map iteration has already either passed, or
7032 // sampled, this bit in the bit map; we'll need to
7033 // use the marking stack to scan this oop's oops.
7034 bool simulate_overflow = false;
7035 NOT_PRODUCT(
7036 if (CMSMarkStackOverflowALot &&
7037 _collector->simulate_overflow()) {
7038 // simulate a stack overflow
7039 simulate_overflow = true;
7040 }
7041 )
7042 if (simulate_overflow ||
7043 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7044 // stack overflow
7045 if (PrintCMSStatistics != 0) {
7046 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7047 SIZE_FORMAT, _overflow_stack->capacity());
7048 }
7049 // We cannot assert that the overflow stack is full because
7050 // it may have been emptied since.
7051 assert(simulate_overflow ||
7052 _work_queue->size() == _work_queue->max_elems(),
7053 "Else push should have succeeded");
7054 handle_stack_overflow(addr);
7055 }
7056 do_yield_check();
7057 }
7058 }
7059
7060 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7061 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7062
7063 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7064 MemRegion span,
7065 ReferenceProcessor* rp,
7066 CMSBitMap* bit_map,
7067 CMSBitMap* mod_union_table,
7068 CMSMarkStack* mark_stack,
7069 bool concurrent_precleaning):
7070 MetadataAwareOopClosure(rp),
7071 _collector(collector),
7072 _span(span),
7073 _bit_map(bit_map),
7074 _mod_union_table(mod_union_table),
7075 _mark_stack(mark_stack),
7076 _concurrent_precleaning(concurrent_precleaning)
7077 {
7078 assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
7079 }
7080
7081 // Grey object rescan during pre-cleaning and second checkpoint phases --
7082 // the non-parallel version (the parallel version appears further below.)
7083 void PushAndMarkClosure::do_oop(oop obj) {
7084 // Ignore mark word verification. If during concurrent precleaning,
7085 // the object monitor may be locked. If during the checkpoint
7086 // phases, the object may already have been reached by a different
7087 // path and may be at the end of the global overflow list (so
7088 // the mark word may be NULL).
7089 assert(obj->is_oop_or_null(true /* ignore mark word */),
7090 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
7091 HeapWord* addr = (HeapWord*)obj;
7092 // Check if oop points into the CMS generation
7093 // and is not marked
7094 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7095 // a white object ...
7096 _bit_map->mark(addr); // ... now grey
7097 // push on the marking stack (grey set)
7098 bool simulate_overflow = false;
7099 NOT_PRODUCT(
7100 if (CMSMarkStackOverflowALot &&
7101 _collector->simulate_overflow()) {
7102 // simulate a stack overflow
7103 simulate_overflow = true;
7104 }
7105 )
7106 if (simulate_overflow || !_mark_stack->push(obj)) {
7107 if (_concurrent_precleaning) {
7108 // During precleaning we can just dirty the appropriate card(s)
7109 // in the mod union table, thus ensuring that the object remains
7110 // in the grey set and continue. In the case of object arrays
7111 // we need to dirty all of the cards that the object spans,
7112 // since the rescan of object arrays will be limited to the
7113 // dirty cards.
7114 // Note that no one can be interfering with us in this action
7115 // of dirtying the mod union table, so no locking or atomics
7116 // are required.
7117 if (obj->is_objArray()) {
7118 size_t sz = obj->size();
7119 HeapWord* end_card_addr = (HeapWord*)round_to(
7120 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7121 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7122 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7123 _mod_union_table->mark_range(redirty_range);
7124 } else {
7125 _mod_union_table->mark(addr);
7126 }
7127 _collector->_ser_pmc_preclean_ovflw++;
7128 } else {
7129 // During the remark phase, we need to remember this oop
7130 // in the overflow list.
7131 _collector->push_on_overflow_list(obj);
7132 _collector->_ser_pmc_remark_ovflw++;
7133 }
7134 }
7135 }
7136 }
7137
7138 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7139 MemRegion span,
7140 ReferenceProcessor* rp,
7141 CMSBitMap* bit_map,
7142 OopTaskQueue* work_queue):
7143 MetadataAwareOopClosure(rp),
7144 _collector(collector),
7145 _span(span),
7146 _bit_map(bit_map),
7147 _work_queue(work_queue)
7148 {
7149 assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
7150 }
7151
7152 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7153 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7154
7155 // Grey object rescan during second checkpoint phase --
7156 // the parallel version.
7157 void Par_PushAndMarkClosure::do_oop(oop obj) {
7158 // In the assert below, we ignore the mark word because
7159 // this oop may point to an already visited object that is
7160 // on the overflow stack (in which case the mark word has
7161 // been hijacked for chaining into the overflow stack --
7162 // if this is the last object in the overflow stack then
7163 // its mark word will be NULL). Because this object may
7164 // have been subsequently popped off the global overflow
7165 // stack, and the mark word possibly restored to the prototypical
7166 // value, by the time we get to examined this failing assert in
7167 // the debugger, is_oop_or_null(false) may subsequently start
7168 // to hold.
7169 assert(obj->is_oop_or_null(true),
7170 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
7171 HeapWord* addr = (HeapWord*)obj;
7172 // Check if oop points into the CMS generation
7173 // and is not marked
7174 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7175 // a white object ...
7176 // If we manage to "claim" the object, by being the
7177 // first thread to mark it, then we push it on our
7178 // marking stack
7179 if (_bit_map->par_mark(addr)) { // ... now grey
7180 // push on work queue (grey set)
7181 bool simulate_overflow = false;
7182 NOT_PRODUCT(
7183 if (CMSMarkStackOverflowALot &&
7184 _collector->par_simulate_overflow()) {
7185 // simulate a stack overflow
7186 simulate_overflow = true;
7187 }
7188 )
7189 if (simulate_overflow || !_work_queue->push(obj)) {
7190 _collector->par_push_on_overflow_list(obj);
7191 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7192 }
7193 } // Else, some other thread got there first
7194 }
7195 }
7196
7197 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7198 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7199
7200 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7201 Mutex* bml = _collector->bitMapLock();
7202 assert_lock_strong(bml);
7203 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7204 "CMS thread should hold CMS token");
7205
7206 bml->unlock();
7207 ConcurrentMarkSweepThread::desynchronize(true);
7208
7209 _collector->stopTimer();
7210 if (PrintCMSStatistics != 0) {
7211 _collector->incrementYields();
7212 }
7213
7214 // See the comment in coordinator_yield()
7215 for (unsigned i = 0; i < CMSYieldSleepCount &&
7216 ConcurrentMarkSweepThread::should_yield() &&
7217 !CMSCollector::foregroundGCIsActive(); ++i) {
7218 os::sleep(Thread::current(), 1, false);
7219 }
7220
7221 ConcurrentMarkSweepThread::synchronize(true);
7222 bml->lock();
7223
7224 _collector->startTimer();
7225 }
7226
7227 bool CMSPrecleanRefsYieldClosure::should_return() {
7228 if (ConcurrentMarkSweepThread::should_yield()) {
7229 do_yield_work();
7230 }
7231 return _collector->foregroundGCIsActive();
7232 }
7233
7234 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7235 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7236 "mr should be aligned to start at a card boundary");
7237 // We'd like to assert:
7238 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7239 // "mr should be a range of cards");
7240 // However, that would be too strong in one case -- the last
7241 // partition ends at _unallocated_block which, in general, can be
7242 // an arbitrary boundary, not necessarily card aligned.
7243 if (PrintCMSStatistics != 0) {
7244 _num_dirty_cards +=
7245 mr.word_size()/CardTableModRefBS::card_size_in_words;
7246 }
7247 _space->object_iterate_mem(mr, &_scan_cl);
7248 }
7249
7250 SweepClosure::SweepClosure(CMSCollector* collector,
7251 ConcurrentMarkSweepGeneration* g,
7252 CMSBitMap* bitMap, bool should_yield) :
7253 _collector(collector),
7254 _g(g),
7255 _sp(g->cmsSpace()),
7256 _limit(_sp->sweep_limit()),
7257 _freelistLock(_sp->freelistLock()),
7258 _bitMap(bitMap),
7259 _yield(should_yield),
7260 _inFreeRange(false), // No free range at beginning of sweep
7261 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7262 _lastFreeRangeCoalesced(false),
7263 _freeFinger(g->used_region().start())
7264 {
7265 NOT_PRODUCT(
7266 _numObjectsFreed = 0;
7267 _numWordsFreed = 0;
7268 _numObjectsLive = 0;
7269 _numWordsLive = 0;
7270 _numObjectsAlreadyFree = 0;
7271 _numWordsAlreadyFree = 0;
7272 _last_fc = NULL;
7273
7274 _sp->initializeIndexedFreeListArrayReturnedBytes();
7275 _sp->dictionary()->initialize_dict_returned_bytes();
7276 )
7277 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7278 "sweep _limit out of bounds");
7279 if (CMSTraceSweeper) {
7280 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7281 p2i(_limit));
7282 }
7283 }
7284
7285 void SweepClosure::print_on(outputStream* st) const {
7286 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7287 p2i(_sp->bottom()), p2i(_sp->end()));
7288 tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7289 tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7290 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7291 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7292 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7293 }
7294
7295 #ifndef PRODUCT
7296 // Assertion checking only: no useful work in product mode --
7297 // however, if any of the flags below become product flags,
7298 // you may need to review this code to see if it needs to be
7299 // enabled in product mode.
7300 SweepClosure::~SweepClosure() {
7301 assert_lock_strong(_freelistLock);
7302 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7303 "sweep _limit out of bounds");
7304 if (inFreeRange()) {
7305 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7306 print();
7307 ShouldNotReachHere();
7308 }
7309 if (Verbose && PrintGC) {
7310 gclog_or_tty->print("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7311 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7312 gclog_or_tty->print_cr("\nLive " SIZE_FORMAT " objects, "
7313 SIZE_FORMAT " bytes "
7314 "Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7315 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7316 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7317 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7318 * sizeof(HeapWord);
7319 gclog_or_tty->print_cr("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7320
7321 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7322 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7323 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7324 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7325 gclog_or_tty->print("Returned " SIZE_FORMAT " bytes", returned_bytes);
7326 gclog_or_tty->print(" Indexed List Returned " SIZE_FORMAT " bytes",
7327 indexListReturnedBytes);
7328 gclog_or_tty->print_cr(" Dictionary Returned " SIZE_FORMAT " bytes",
7329 dict_returned_bytes);
7330 }
7331 }
7332 if (CMSTraceSweeper) {
7333 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7334 p2i(_limit));
7335 }
7336 }
7337 #endif // PRODUCT
7338
7339 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7340 bool freeRangeInFreeLists) {
7341 if (CMSTraceSweeper) {
7342 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7343 p2i(freeFinger), freeRangeInFreeLists);
7344 }
7345 assert(!inFreeRange(), "Trampling existing free range");
7346 set_inFreeRange(true);
7347 set_lastFreeRangeCoalesced(false);
7348
7349 set_freeFinger(freeFinger);
7350 set_freeRangeInFreeLists(freeRangeInFreeLists);
7351 if (CMSTestInFreeList) {
7352 if (freeRangeInFreeLists) {
7353 FreeChunk* fc = (FreeChunk*) freeFinger;
7354 assert(fc->is_free(), "A chunk on the free list should be free.");
7355 assert(fc->size() > 0, "Free range should have a size");
7356 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7357 }
7358 }
7359 }
7360
7361 // Note that the sweeper runs concurrently with mutators. Thus,
7362 // it is possible for direct allocation in this generation to happen
7363 // in the middle of the sweep. Note that the sweeper also coalesces
7364 // contiguous free blocks. Thus, unless the sweeper and the allocator
7365 // synchronize appropriately freshly allocated blocks may get swept up.
7366 // This is accomplished by the sweeper locking the free lists while
7367 // it is sweeping. Thus blocks that are determined to be free are
7368 // indeed free. There is however one additional complication:
7369 // blocks that have been allocated since the final checkpoint and
7370 // mark, will not have been marked and so would be treated as
7371 // unreachable and swept up. To prevent this, the allocator marks
7372 // the bit map when allocating during the sweep phase. This leads,
7373 // however, to a further complication -- objects may have been allocated
7374 // but not yet initialized -- in the sense that the header isn't yet
7375 // installed. The sweeper can not then determine the size of the block
7376 // in order to skip over it. To deal with this case, we use a technique
7377 // (due to Printezis) to encode such uninitialized block sizes in the
7378 // bit map. Since the bit map uses a bit per every HeapWord, but the
7379 // CMS generation has a minimum object size of 3 HeapWords, it follows
7380 // that "normal marks" won't be adjacent in the bit map (there will
7381 // always be at least two 0 bits between successive 1 bits). We make use
7382 // of these "unused" bits to represent uninitialized blocks -- the bit
7383 // corresponding to the start of the uninitialized object and the next
7384 // bit are both set. Finally, a 1 bit marks the end of the object that
7385 // started with the two consecutive 1 bits to indicate its potentially
7386 // uninitialized state.
7387
7388 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7389 FreeChunk* fc = (FreeChunk*)addr;
7390 size_t res;
7391
7392 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7393 // than "addr == _limit" because although _limit was a block boundary when
7394 // we started the sweep, it may no longer be one because heap expansion
7395 // may have caused us to coalesce the block ending at the address _limit
7396 // with a newly expanded chunk (this happens when _limit was set to the
7397 // previous _end of the space), so we may have stepped past _limit:
7398 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7399 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7400 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7401 "sweep _limit out of bounds");
7402 assert(addr < _sp->end(), "addr out of bounds");
7403 // Flush any free range we might be holding as a single
7404 // coalesced chunk to the appropriate free list.
7405 if (inFreeRange()) {
7406 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7407 "freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger()));
7408 flush_cur_free_chunk(freeFinger(),
7409 pointer_delta(addr, freeFinger()));
7410 if (CMSTraceSweeper) {
7411 gclog_or_tty->print("Sweep: last chunk: ");
7412 gclog_or_tty->print("put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") "
7413 "[coalesced:%d]\n",
7414 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7415 lastFreeRangeCoalesced() ? 1 : 0);
7416 }
7417 }
7418
7419 // help the iterator loop finish
7420 return pointer_delta(_sp->end(), addr);
7421 }
7422
7423 assert(addr < _limit, "sweep invariant");
7424 // check if we should yield
7425 do_yield_check(addr);
7426 if (fc->is_free()) {
7427 // Chunk that is already free
7428 res = fc->size();
7429 do_already_free_chunk(fc);
7430 debug_only(_sp->verifyFreeLists());
7431 // If we flush the chunk at hand in lookahead_and_flush()
7432 // and it's coalesced with a preceding chunk, then the
7433 // process of "mangling" the payload of the coalesced block
7434 // will cause erasure of the size information from the
7435 // (erstwhile) header of all the coalesced blocks but the
7436 // first, so the first disjunct in the assert will not hold
7437 // in that specific case (in which case the second disjunct
7438 // will hold).
7439 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7440 "Otherwise the size info doesn't change at this step");
7441 NOT_PRODUCT(
7442 _numObjectsAlreadyFree++;
7443 _numWordsAlreadyFree += res;
7444 )
7445 NOT_PRODUCT(_last_fc = fc;)
7446 } else if (!_bitMap->isMarked(addr)) {
7447 // Chunk is fresh garbage
7448 res = do_garbage_chunk(fc);
7449 debug_only(_sp->verifyFreeLists());
7450 NOT_PRODUCT(
7451 _numObjectsFreed++;
7452 _numWordsFreed += res;
7453 )
7454 } else {
7455 // Chunk that is alive.
7456 res = do_live_chunk(fc);
7457 debug_only(_sp->verifyFreeLists());
7458 NOT_PRODUCT(
7459 _numObjectsLive++;
7460 _numWordsLive += res;
7461 )
7462 }
7463 return res;
7464 }
7465
7466 // For the smart allocation, record following
7467 // split deaths - a free chunk is removed from its free list because
7468 // it is being split into two or more chunks.
7469 // split birth - a free chunk is being added to its free list because
7470 // a larger free chunk has been split and resulted in this free chunk.
7471 // coal death - a free chunk is being removed from its free list because
7472 // it is being coalesced into a large free chunk.
7473 // coal birth - a free chunk is being added to its free list because
7474 // it was created when two or more free chunks where coalesced into
7475 // this free chunk.
7476 //
7477 // These statistics are used to determine the desired number of free
7478 // chunks of a given size. The desired number is chosen to be relative
7479 // to the end of a CMS sweep. The desired number at the end of a sweep
7480 // is the
7481 // count-at-end-of-previous-sweep (an amount that was enough)
7482 // - count-at-beginning-of-current-sweep (the excess)
7483 // + split-births (gains in this size during interval)
7484 // - split-deaths (demands on this size during interval)
7485 // where the interval is from the end of one sweep to the end of the
7486 // next.
7487 //
7488 // When sweeping the sweeper maintains an accumulated chunk which is
7489 // the chunk that is made up of chunks that have been coalesced. That
7490 // will be termed the left-hand chunk. A new chunk of garbage that
7491 // is being considered for coalescing will be referred to as the
7492 // right-hand chunk.
7493 //
7494 // When making a decision on whether to coalesce a right-hand chunk with
7495 // the current left-hand chunk, the current count vs. the desired count
7496 // of the left-hand chunk is considered. Also if the right-hand chunk
7497 // is near the large chunk at the end of the heap (see
7498 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7499 // left-hand chunk is coalesced.
7500 //
7501 // When making a decision about whether to split a chunk, the desired count
7502 // vs. the current count of the candidate to be split is also considered.
7503 // If the candidate is underpopulated (currently fewer chunks than desired)
7504 // a chunk of an overpopulated (currently more chunks than desired) size may
7505 // be chosen. The "hint" associated with a free list, if non-null, points
7506 // to a free list which may be overpopulated.
7507 //
7508
7509 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7510 const size_t size = fc->size();
7511 // Chunks that cannot be coalesced are not in the
7512 // free lists.
7513 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7514 assert(_sp->verify_chunk_in_free_list(fc),
7515 "free chunk should be in free lists");
7516 }
7517 // a chunk that is already free, should not have been
7518 // marked in the bit map
7519 HeapWord* const addr = (HeapWord*) fc;
7520 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7521 // Verify that the bit map has no bits marked between
7522 // addr and purported end of this block.
7523 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7524
7525 // Some chunks cannot be coalesced under any circumstances.
7526 // See the definition of cantCoalesce().
7527 if (!fc->cantCoalesce()) {
7528 // This chunk can potentially be coalesced.
7529 // All the work is done in
7530 do_post_free_or_garbage_chunk(fc, size);
7531 // Note that if the chunk is not coalescable (the else arm
7532 // below), we unconditionally flush, without needing to do
7533 // a "lookahead," as we do below.
7534 if (inFreeRange()) lookahead_and_flush(fc, size);
7535 } else {
7536 // Code path common to both original and adaptive free lists.
7537
7538 // cant coalesce with previous block; this should be treated
7539 // as the end of a free run if any
7540 if (inFreeRange()) {
7541 // we kicked some butt; time to pick up the garbage
7542 assert(freeFinger() < addr, "freeFinger points too high");
7543 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7544 }
7545 // else, nothing to do, just continue
7546 }
7547 }
7548
7549 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7550 // This is a chunk of garbage. It is not in any free list.
7551 // Add it to a free list or let it possibly be coalesced into
7552 // a larger chunk.
7553 HeapWord* const addr = (HeapWord*) fc;
7554 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7555
7556 // Verify that the bit map has no bits marked between
7557 // addr and purported end of just dead object.
7558 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7559 do_post_free_or_garbage_chunk(fc, size);
7560
7561 assert(_limit >= addr + size,
7562 "A freshly garbage chunk can't possibly straddle over _limit");
7563 if (inFreeRange()) lookahead_and_flush(fc, size);
7564 return size;
7565 }
7566
7567 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7568 HeapWord* addr = (HeapWord*) fc;
7569 // The sweeper has just found a live object. Return any accumulated
7570 // left hand chunk to the free lists.
7571 if (inFreeRange()) {
7572 assert(freeFinger() < addr, "freeFinger points too high");
7573 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7574 }
7575
7576 // This object is live: we'd normally expect this to be
7577 // an oop, and like to assert the following:
7578 // assert(oop(addr)->is_oop(), "live block should be an oop");
7579 // However, as we commented above, this may be an object whose
7580 // header hasn't yet been initialized.
7581 size_t size;
7582 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7583 if (_bitMap->isMarked(addr + 1)) {
7584 // Determine the size from the bit map, rather than trying to
7585 // compute it from the object header.
7586 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7587 size = pointer_delta(nextOneAddr + 1, addr);
7588 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7589 "alignment problem");
7590
7591 #ifdef ASSERT
7592 if (oop(addr)->klass_or_null() != NULL) {
7593 // Ignore mark word because we are running concurrent with mutators
7594 assert(oop(addr)->is_oop(true), "live block should be an oop");
7595 assert(size ==
7596 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7597 "P-mark and computed size do not agree");
7598 }
7599 #endif
7600
7601 } else {
7602 // This should be an initialized object that's alive.
7603 assert(oop(addr)->klass_or_null() != NULL,
7604 "Should be an initialized object");
7605 // Ignore mark word because we are running concurrent with mutators
7606 assert(oop(addr)->is_oop(true), "live block should be an oop");
7607 // Verify that the bit map has no bits marked between
7608 // addr and purported end of this block.
7609 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7610 assert(size >= 3, "Necessary for Printezis marks to work");
7611 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7612 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7613 }
7614 return size;
7615 }
7616
7617 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7618 size_t chunkSize) {
7619 // do_post_free_or_garbage_chunk() should only be called in the case
7620 // of the adaptive free list allocator.
7621 const bool fcInFreeLists = fc->is_free();
7622 assert((HeapWord*)fc <= _limit, "sweep invariant");
7623 if (CMSTestInFreeList && fcInFreeLists) {
7624 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7625 }
7626
7627 if (CMSTraceSweeper) {
7628 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7629 }
7630
7631 HeapWord* const fc_addr = (HeapWord*) fc;
7632
7633 bool coalesce = false;
7634 const size_t left = pointer_delta(fc_addr, freeFinger());
7635 const size_t right = chunkSize;
7636 switch (FLSCoalescePolicy) {
7637 // numeric value forms a coalition aggressiveness metric
7638 case 0: { // never coalesce
7639 coalesce = false;
7640 break;
7641 }
7642 case 1: { // coalesce if left & right chunks on overpopulated lists
7643 coalesce = _sp->coalOverPopulated(left) &&
7644 _sp->coalOverPopulated(right);
7645 break;
7646 }
7647 case 2: { // coalesce if left chunk on overpopulated list (default)
7648 coalesce = _sp->coalOverPopulated(left);
7649 break;
7650 }
7651 case 3: { // coalesce if left OR right chunk on overpopulated list
7652 coalesce = _sp->coalOverPopulated(left) ||
7653 _sp->coalOverPopulated(right);
7654 break;
7655 }
7656 case 4: { // always coalesce
7657 coalesce = true;
7658 break;
7659 }
7660 default:
7661 ShouldNotReachHere();
7662 }
7663
7664 // Should the current free range be coalesced?
7665 // If the chunk is in a free range and either we decided to coalesce above
7666 // or the chunk is near the large block at the end of the heap
7667 // (isNearLargestChunk() returns true), then coalesce this chunk.
7668 const bool doCoalesce = inFreeRange()
7669 && (coalesce || _g->isNearLargestChunk(fc_addr));
7670 if (doCoalesce) {
7671 // Coalesce the current free range on the left with the new
7672 // chunk on the right. If either is on a free list,
7673 // it must be removed from the list and stashed in the closure.
7674 if (freeRangeInFreeLists()) {
7675 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7676 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7677 "Size of free range is inconsistent with chunk size.");
7678 if (CMSTestInFreeList) {
7679 assert(_sp->verify_chunk_in_free_list(ffc),
7680 "Chunk is not in free lists");
7681 }
7682 _sp->coalDeath(ffc->size());
7683 _sp->removeFreeChunkFromFreeLists(ffc);
7684 set_freeRangeInFreeLists(false);
7685 }
7686 if (fcInFreeLists) {
7687 _sp->coalDeath(chunkSize);
7688 assert(fc->size() == chunkSize,
7689 "The chunk has the wrong size or is not in the free lists");
7690 _sp->removeFreeChunkFromFreeLists(fc);
7691 }
7692 set_lastFreeRangeCoalesced(true);
7693 print_free_block_coalesced(fc);
7694 } else { // not in a free range and/or should not coalesce
7695 // Return the current free range and start a new one.
7696 if (inFreeRange()) {
7697 // In a free range but cannot coalesce with the right hand chunk.
7698 // Put the current free range into the free lists.
7699 flush_cur_free_chunk(freeFinger(),
7700 pointer_delta(fc_addr, freeFinger()));
7701 }
7702 // Set up for new free range. Pass along whether the right hand
7703 // chunk is in the free lists.
7704 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7705 }
7706 }
7707
7708 // Lookahead flush:
7709 // If we are tracking a free range, and this is the last chunk that
7710 // we'll look at because its end crosses past _limit, we'll preemptively
7711 // flush it along with any free range we may be holding on to. Note that
7712 // this can be the case only for an already free or freshly garbage
7713 // chunk. If this block is an object, it can never straddle
7714 // over _limit. The "straddling" occurs when _limit is set at
7715 // the previous end of the space when this cycle started, and
7716 // a subsequent heap expansion caused the previously co-terminal
7717 // free block to be coalesced with the newly expanded portion,
7718 // thus rendering _limit a non-block-boundary making it dangerous
7719 // for the sweeper to step over and examine.
7720 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7721 assert(inFreeRange(), "Should only be called if currently in a free range.");
7722 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7723 assert(_sp->used_region().contains(eob - 1),
7724 "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7725 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7726 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7727 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7728 if (eob >= _limit) {
7729 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7730 if (CMSTraceSweeper) {
7731 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7732 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7733 "[" PTR_FORMAT "," PTR_FORMAT ")",
7734 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7735 }
7736 // Return the storage we are tracking back into the free lists.
7737 if (CMSTraceSweeper) {
7738 gclog_or_tty->print_cr("Flushing ... ");
7739 }
7740 assert(freeFinger() < eob, "Error");
7741 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7742 }
7743 }
7744
7745 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7746 assert(inFreeRange(), "Should only be called if currently in a free range.");
7747 assert(size > 0,
7748 "A zero sized chunk cannot be added to the free lists.");
7749 if (!freeRangeInFreeLists()) {
7750 if (CMSTestInFreeList) {
7751 FreeChunk* fc = (FreeChunk*) chunk;
7752 fc->set_size(size);
7753 assert(!_sp->verify_chunk_in_free_list(fc),
7754 "chunk should not be in free lists yet");
7755 }
7756 if (CMSTraceSweeper) {
7757 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7758 p2i(chunk), size);
7759 }
7760 // A new free range is going to be starting. The current
7761 // free range has not been added to the free lists yet or
7762 // was removed so add it back.
7763 // If the current free range was coalesced, then the death
7764 // of the free range was recorded. Record a birth now.
7765 if (lastFreeRangeCoalesced()) {
7766 _sp->coalBirth(size);
7767 }
7768 _sp->addChunkAndRepairOffsetTable(chunk, size,
7769 lastFreeRangeCoalesced());
7770 } else if (CMSTraceSweeper) {
7771 gclog_or_tty->print_cr("Already in free list: nothing to flush");
7772 }
7773 set_inFreeRange(false);
7774 set_freeRangeInFreeLists(false);
7775 }
7776
7777 // We take a break if we've been at this for a while,
7778 // so as to avoid monopolizing the locks involved.
7779 void SweepClosure::do_yield_work(HeapWord* addr) {
7780 // Return current free chunk being used for coalescing (if any)
7781 // to the appropriate freelist. After yielding, the next
7782 // free block encountered will start a coalescing range of
7783 // free blocks. If the next free block is adjacent to the
7784 // chunk just flushed, they will need to wait for the next
7785 // sweep to be coalesced.
7786 if (inFreeRange()) {
7787 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7788 }
7789
7790 // First give up the locks, then yield, then re-lock.
7791 // We should probably use a constructor/destructor idiom to
7792 // do this unlock/lock or modify the MutexUnlocker class to
7793 // serve our purpose. XXX
7794 assert_lock_strong(_bitMap->lock());
7795 assert_lock_strong(_freelistLock);
7796 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7797 "CMS thread should hold CMS token");
7798 _bitMap->lock()->unlock();
7799 _freelistLock->unlock();
7800 ConcurrentMarkSweepThread::desynchronize(true);
7801 _collector->stopTimer();
7802 if (PrintCMSStatistics != 0) {
7803 _collector->incrementYields();
7804 }
7805
7806 // See the comment in coordinator_yield()
7807 for (unsigned i = 0; i < CMSYieldSleepCount &&
7808 ConcurrentMarkSweepThread::should_yield() &&
7809 !CMSCollector::foregroundGCIsActive(); ++i) {
7810 os::sleep(Thread::current(), 1, false);
7811 }
7812
7813 ConcurrentMarkSweepThread::synchronize(true);
7814 _freelistLock->lock();
7815 _bitMap->lock()->lock_without_safepoint_check();
7816 _collector->startTimer();
7817 }
7818
7819 #ifndef PRODUCT
7820 // This is actually very useful in a product build if it can
7821 // be called from the debugger. Compile it into the product
7822 // as needed.
7823 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7824 return debug_cms_space->verify_chunk_in_free_list(fc);
7825 }
7826 #endif
7827
7828 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7829 if (CMSTraceSweeper) {
7830 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7831 p2i(fc), fc->size());
7832 }
7833 }
7834
7835 // CMSIsAliveClosure
7836 bool CMSIsAliveClosure::do_object_b(oop obj) {
7837 HeapWord* addr = (HeapWord*)obj;
7838 return addr != NULL &&
7839 (!_span.contains(addr) || _bit_map->isMarked(addr));
7840 }
7841
7842
7843 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7844 MemRegion span,
7845 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7846 bool cpc):
7847 _collector(collector),
7848 _span(span),
7849 _bit_map(bit_map),
7850 _mark_stack(mark_stack),
7851 _concurrent_precleaning(cpc) {
7852 assert(!_span.is_empty(), "Empty span could spell trouble");
7853 }
7854
7855
7856 // CMSKeepAliveClosure: the serial version
7857 void CMSKeepAliveClosure::do_oop(oop obj) {
7858 HeapWord* addr = (HeapWord*)obj;
7859 if (_span.contains(addr) &&
7860 !_bit_map->isMarked(addr)) {
7861 _bit_map->mark(addr);
7862 bool simulate_overflow = false;
7863 NOT_PRODUCT(
7864 if (CMSMarkStackOverflowALot &&
7865 _collector->simulate_overflow()) {
7866 // simulate a stack overflow
7867 simulate_overflow = true;
7868 }
7869 )
7870 if (simulate_overflow || !_mark_stack->push(obj)) {
7871 if (_concurrent_precleaning) {
7872 // We dirty the overflown object and let the remark
7873 // phase deal with it.
7874 assert(_collector->overflow_list_is_empty(), "Error");
7875 // In the case of object arrays, we need to dirty all of
7876 // the cards that the object spans. No locking or atomics
7877 // are needed since no one else can be mutating the mod union
7878 // table.
7879 if (obj->is_objArray()) {
7880 size_t sz = obj->size();
7881 HeapWord* end_card_addr =
7882 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
7883 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7884 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7885 _collector->_modUnionTable.mark_range(redirty_range);
7886 } else {
7887 _collector->_modUnionTable.mark(addr);
7888 }
7889 _collector->_ser_kac_preclean_ovflw++;
7890 } else {
7891 _collector->push_on_overflow_list(obj);
7892 _collector->_ser_kac_ovflw++;
7893 }
7894 }
7895 }
7896 }
7897
7898 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7899 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7900
7901 // CMSParKeepAliveClosure: a parallel version of the above.
7902 // The work queues are private to each closure (thread),
7903 // but (may be) available for stealing by other threads.
7904 void CMSParKeepAliveClosure::do_oop(oop obj) {
7905 HeapWord* addr = (HeapWord*)obj;
7906 if (_span.contains(addr) &&
7907 !_bit_map->isMarked(addr)) {
7908 // In general, during recursive tracing, several threads
7909 // may be concurrently getting here; the first one to
7910 // "tag" it, claims it.
7911 if (_bit_map->par_mark(addr)) {
7912 bool res = _work_queue->push(obj);
7913 assert(res, "Low water mark should be much less than capacity");
7914 // Do a recursive trim in the hope that this will keep
7915 // stack usage lower, but leave some oops for potential stealers
7916 trim_queue(_low_water_mark);
7917 } // Else, another thread got there first
7918 }
7919 }
7920
7921 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7922 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7923
7924 void CMSParKeepAliveClosure::trim_queue(uint max) {
7925 while (_work_queue->size() > max) {
7926 oop new_oop;
7927 if (_work_queue->pop_local(new_oop)) {
7928 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7929 assert(_bit_map->isMarked((HeapWord*)new_oop),
7930 "no white objects on this stack!");
7931 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7932 // iterate over the oops in this oop, marking and pushing
7933 // the ones in CMS heap (i.e. in _span).
7934 new_oop->oop_iterate(&_mark_and_push);
7935 }
7936 }
7937 }
7938
7939 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7940 CMSCollector* collector,
7941 MemRegion span, CMSBitMap* bit_map,
7942 OopTaskQueue* work_queue):
7943 _collector(collector),
7944 _span(span),
7945 _bit_map(bit_map),
7946 _work_queue(work_queue) { }
7947
7948 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7949 HeapWord* addr = (HeapWord*)obj;
7950 if (_span.contains(addr) &&
7951 !_bit_map->isMarked(addr)) {
7952 if (_bit_map->par_mark(addr)) {
7953 bool simulate_overflow = false;
7954 NOT_PRODUCT(
7955 if (CMSMarkStackOverflowALot &&
7956 _collector->par_simulate_overflow()) {
7957 // simulate a stack overflow
7958 simulate_overflow = true;
7959 }
7960 )
7961 if (simulate_overflow || !_work_queue->push(obj)) {
7962 _collector->par_push_on_overflow_list(obj);
7963 _collector->_par_kac_ovflw++;
7964 }
7965 } // Else another thread got there already
7966 }
7967 }
7968
7969 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7970 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7971
7972 //////////////////////////////////////////////////////////////////
7973 // CMSExpansionCause /////////////////////////////
7974 //////////////////////////////////////////////////////////////////
7975 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7976 switch (cause) {
7977 case _no_expansion:
7978 return "No expansion";
7979 case _satisfy_free_ratio:
7980 return "Free ratio";
7981 case _satisfy_promotion:
7982 return "Satisfy promotion";
7983 case _satisfy_allocation:
7984 return "allocation";
7985 case _allocate_par_lab:
7986 return "Par LAB";
7987 case _allocate_par_spooling_space:
7988 return "Par Spooling Space";
7989 case _adaptive_size_policy:
7990 return "Ergonomics";
7991 default:
7992 return "unknown";
7993 }
7994 }
7995
7996 void CMSDrainMarkingStackClosure::do_void() {
7997 // the max number to take from overflow list at a time
7998 const size_t num = _mark_stack->capacity()/4;
7999 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8000 "Overflow list should be NULL during concurrent phases");
8001 while (!_mark_stack->isEmpty() ||
8002 // if stack is empty, check the overflow list
8003 _collector->take_from_overflow_list(num, _mark_stack)) {
8004 oop obj = _mark_stack->pop();
8005 HeapWord* addr = (HeapWord*)obj;
8006 assert(_span.contains(addr), "Should be within span");
8007 assert(_bit_map->isMarked(addr), "Should be marked");
8008 assert(obj->is_oop(), "Should be an oop");
8009 obj->oop_iterate(_keep_alive);
8010 }
8011 }
8012
8013 void CMSParDrainMarkingStackClosure::do_void() {
8014 // drain queue
8015 trim_queue(0);
8016 }
8017
8018 // Trim our work_queue so its length is below max at return
8019 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8020 while (_work_queue->size() > max) {
8021 oop new_oop;
8022 if (_work_queue->pop_local(new_oop)) {
8023 assert(new_oop->is_oop(), "Expected an oop");
8024 assert(_bit_map->isMarked((HeapWord*)new_oop),
8025 "no white objects on this stack!");
8026 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8027 // iterate over the oops in this oop, marking and pushing
8028 // the ones in CMS heap (i.e. in _span).
8029 new_oop->oop_iterate(&_mark_and_push);
8030 }
8031 }
8032 }
8033
8034 ////////////////////////////////////////////////////////////////////
8035 // Support for Marking Stack Overflow list handling and related code
8036 ////////////////////////////////////////////////////////////////////
8037 // Much of the following code is similar in shape and spirit to the
8038 // code used in ParNewGC. We should try and share that code
8039 // as much as possible in the future.
8040
8041 #ifndef PRODUCT
8042 // Debugging support for CMSStackOverflowALot
8043
8044 // It's OK to call this multi-threaded; the worst thing
8045 // that can happen is that we'll get a bunch of closely
8046 // spaced simulated overflows, but that's OK, in fact
8047 // probably good as it would exercise the overflow code
8048 // under contention.
8049 bool CMSCollector::simulate_overflow() {
8050 if (_overflow_counter-- <= 0) { // just being defensive
8051 _overflow_counter = CMSMarkStackOverflowInterval;
8052 return true;
8053 } else {
8054 return false;
8055 }
8056 }
8057
8058 bool CMSCollector::par_simulate_overflow() {
8059 return simulate_overflow();
8060 }
8061 #endif
8062
8063 // Single-threaded
8064 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8065 assert(stack->isEmpty(), "Expected precondition");
8066 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8067 size_t i = num;
8068 oop cur = _overflow_list;
8069 const markOop proto = markOopDesc::prototype();
8070 NOT_PRODUCT(ssize_t n = 0;)
8071 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8072 next = oop(cur->mark());
8073 cur->set_mark(proto); // until proven otherwise
8074 assert(cur->is_oop(), "Should be an oop");
8075 bool res = stack->push(cur);
8076 assert(res, "Bit off more than can chew?");
8077 NOT_PRODUCT(n++;)
8078 }
8079 _overflow_list = cur;
8080 #ifndef PRODUCT
8081 assert(_num_par_pushes >= n, "Too many pops?");
8082 _num_par_pushes -=n;
8083 #endif
8084 return !stack->isEmpty();
8085 }
8086
8087 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8088 // (MT-safe) Get a prefix of at most "num" from the list.
8089 // The overflow list is chained through the mark word of
8090 // each object in the list. We fetch the entire list,
8091 // break off a prefix of the right size and return the
8092 // remainder. If other threads try to take objects from
8093 // the overflow list at that time, they will wait for
8094 // some time to see if data becomes available. If (and
8095 // only if) another thread places one or more object(s)
8096 // on the global list before we have returned the suffix
8097 // to the global list, we will walk down our local list
8098 // to find its end and append the global list to
8099 // our suffix before returning it. This suffix walk can
8100 // prove to be expensive (quadratic in the amount of traffic)
8101 // when there are many objects in the overflow list and
8102 // there is much producer-consumer contention on the list.
8103 // *NOTE*: The overflow list manipulation code here and
8104 // in ParNewGeneration:: are very similar in shape,
8105 // except that in the ParNew case we use the old (from/eden)
8106 // copy of the object to thread the list via its klass word.
8107 // Because of the common code, if you make any changes in
8108 // the code below, please check the ParNew version to see if
8109 // similar changes might be needed.
8110 // CR 6797058 has been filed to consolidate the common code.
8111 bool CMSCollector::par_take_from_overflow_list(size_t num,
8112 OopTaskQueue* work_q,
8113 int no_of_gc_threads) {
8114 assert(work_q->size() == 0, "First empty local work queue");
8115 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8116 if (_overflow_list == NULL) {
8117 return false;
8118 }
8119 // Grab the entire list; we'll put back a suffix
8120 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8121 Thread* tid = Thread::current();
8122 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8123 // set to ParallelGCThreads.
8124 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8125 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8126 // If the list is busy, we spin for a short while,
8127 // sleeping between attempts to get the list.
8128 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8129 os::sleep(tid, sleep_time_millis, false);
8130 if (_overflow_list == NULL) {
8131 // Nothing left to take
8132 return false;
8133 } else if (_overflow_list != BUSY) {
8134 // Try and grab the prefix
8135 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8136 }
8137 }
8138 // If the list was found to be empty, or we spun long
8139 // enough, we give up and return empty-handed. If we leave
8140 // the list in the BUSY state below, it must be the case that
8141 // some other thread holds the overflow list and will set it
8142 // to a non-BUSY state in the future.
8143 if (prefix == NULL || prefix == BUSY) {
8144 // Nothing to take or waited long enough
8145 if (prefix == NULL) {
8146 // Write back the NULL in case we overwrote it with BUSY above
8147 // and it is still the same value.
8148 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8149 }
8150 return false;
8151 }
8152 assert(prefix != NULL && prefix != BUSY, "Error");
8153 size_t i = num;
8154 oop cur = prefix;
8155 // Walk down the first "num" objects, unless we reach the end.
8156 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8157 if (cur->mark() == NULL) {
8158 // We have "num" or fewer elements in the list, so there
8159 // is nothing to return to the global list.
8160 // Write back the NULL in lieu of the BUSY we wrote
8161 // above, if it is still the same value.
8162 if (_overflow_list == BUSY) {
8163 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8164 }
8165 } else {
8166 // Chop off the suffix and return it to the global list.
8167 assert(cur->mark() != BUSY, "Error");
8168 oop suffix_head = cur->mark(); // suffix will be put back on global list
8169 cur->set_mark(NULL); // break off suffix
8170 // It's possible that the list is still in the empty(busy) state
8171 // we left it in a short while ago; in that case we may be
8172 // able to place back the suffix without incurring the cost
8173 // of a walk down the list.
8174 oop observed_overflow_list = _overflow_list;
8175 oop cur_overflow_list = observed_overflow_list;
8176 bool attached = false;
8177 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8178 observed_overflow_list =
8179 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8180 if (cur_overflow_list == observed_overflow_list) {
8181 attached = true;
8182 break;
8183 } else cur_overflow_list = observed_overflow_list;
8184 }
8185 if (!attached) {
8186 // Too bad, someone else sneaked in (at least) an element; we'll need
8187 // to do a splice. Find tail of suffix so we can prepend suffix to global
8188 // list.
8189 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8190 oop suffix_tail = cur;
8191 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8192 "Tautology");
8193 observed_overflow_list = _overflow_list;
8194 do {
8195 cur_overflow_list = observed_overflow_list;
8196 if (cur_overflow_list != BUSY) {
8197 // Do the splice ...
8198 suffix_tail->set_mark(markOop(cur_overflow_list));
8199 } else { // cur_overflow_list == BUSY
8200 suffix_tail->set_mark(NULL);
8201 }
8202 // ... and try to place spliced list back on overflow_list ...
8203 observed_overflow_list =
8204 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8205 } while (cur_overflow_list != observed_overflow_list);
8206 // ... until we have succeeded in doing so.
8207 }
8208 }
8209
8210 // Push the prefix elements on work_q
8211 assert(prefix != NULL, "control point invariant");
8212 const markOop proto = markOopDesc::prototype();
8213 oop next;
8214 NOT_PRODUCT(ssize_t n = 0;)
8215 for (cur = prefix; cur != NULL; cur = next) {
8216 next = oop(cur->mark());
8217 cur->set_mark(proto); // until proven otherwise
8218 assert(cur->is_oop(), "Should be an oop");
8219 bool res = work_q->push(cur);
8220 assert(res, "Bit off more than we can chew?");
8221 NOT_PRODUCT(n++;)
8222 }
8223 #ifndef PRODUCT
8224 assert(_num_par_pushes >= n, "Too many pops?");
8225 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8226 #endif
8227 return true;
8228 }
8229
8230 // Single-threaded
8231 void CMSCollector::push_on_overflow_list(oop p) {
8232 NOT_PRODUCT(_num_par_pushes++;)
8233 assert(p->is_oop(), "Not an oop");
8234 preserve_mark_if_necessary(p);
8235 p->set_mark((markOop)_overflow_list);
8236 _overflow_list = p;
8237 }
8238
8239 // Multi-threaded; use CAS to prepend to overflow list
8240 void CMSCollector::par_push_on_overflow_list(oop p) {
8241 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8242 assert(p->is_oop(), "Not an oop");
8243 par_preserve_mark_if_necessary(p);
8244 oop observed_overflow_list = _overflow_list;
8245 oop cur_overflow_list;
8246 do {
8247 cur_overflow_list = observed_overflow_list;
8248 if (cur_overflow_list != BUSY) {
8249 p->set_mark(markOop(cur_overflow_list));
8250 } else {
8251 p->set_mark(NULL);
8252 }
8253 observed_overflow_list =
8254 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8255 } while (cur_overflow_list != observed_overflow_list);
8256 }
8257 #undef BUSY
8258
8259 // Single threaded
8260 // General Note on GrowableArray: pushes may silently fail
8261 // because we are (temporarily) out of C-heap for expanding
8262 // the stack. The problem is quite ubiquitous and affects
8263 // a lot of code in the JVM. The prudent thing for GrowableArray
8264 // to do (for now) is to exit with an error. However, that may
8265 // be too draconian in some cases because the caller may be
8266 // able to recover without much harm. For such cases, we
8267 // should probably introduce a "soft_push" method which returns
8268 // an indication of success or failure with the assumption that
8269 // the caller may be able to recover from a failure; code in
8270 // the VM can then be changed, incrementally, to deal with such
8271 // failures where possible, thus, incrementally hardening the VM
8272 // in such low resource situations.
8273 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8274 _preserved_oop_stack.push(p);
8275 _preserved_mark_stack.push(m);
8276 assert(m == p->mark(), "Mark word changed");
8277 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8278 "bijection");
8279 }
8280
8281 // Single threaded
8282 void CMSCollector::preserve_mark_if_necessary(oop p) {
8283 markOop m = p->mark();
8284 if (m->must_be_preserved(p)) {
8285 preserve_mark_work(p, m);
8286 }
8287 }
8288
8289 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8290 markOop m = p->mark();
8291 if (m->must_be_preserved(p)) {
8292 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8293 // Even though we read the mark word without holding
8294 // the lock, we are assured that it will not change
8295 // because we "own" this oop, so no other thread can
8296 // be trying to push it on the overflow list; see
8297 // the assertion in preserve_mark_work() that checks
8298 // that m == p->mark().
8299 preserve_mark_work(p, m);
8300 }
8301 }
8302
8303 // We should be able to do this multi-threaded,
8304 // a chunk of stack being a task (this is
8305 // correct because each oop only ever appears
8306 // once in the overflow list. However, it's
8307 // not very easy to completely overlap this with
8308 // other operations, so will generally not be done
8309 // until all work's been completed. Because we
8310 // expect the preserved oop stack (set) to be small,
8311 // it's probably fine to do this single-threaded.
8312 // We can explore cleverer concurrent/overlapped/parallel
8313 // processing of preserved marks if we feel the
8314 // need for this in the future. Stack overflow should
8315 // be so rare in practice and, when it happens, its
8316 // effect on performance so great that this will
8317 // likely just be in the noise anyway.
8318 void CMSCollector::restore_preserved_marks_if_any() {
8319 assert(SafepointSynchronize::is_at_safepoint(),
8320 "world should be stopped");
8321 assert(Thread::current()->is_ConcurrentGC_thread() ||
8322 Thread::current()->is_VM_thread(),
8323 "should be single-threaded");
8324 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8325 "bijection");
8326
8327 while (!_preserved_oop_stack.is_empty()) {
8328 oop p = _preserved_oop_stack.pop();
8329 assert(p->is_oop(), "Should be an oop");
8330 assert(_span.contains(p), "oop should be in _span");
8331 assert(p->mark() == markOopDesc::prototype(),
8332 "Set when taken from overflow list");
8333 markOop m = _preserved_mark_stack.pop();
8334 p->set_mark(m);
8335 }
8336 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8337 "stacks were cleared above");
8338 }
8339
8340 #ifndef PRODUCT
8341 bool CMSCollector::no_preserved_marks() const {
8342 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8343 }
8344 #endif
8345
8346 // Transfer some number of overflown objects to usual marking
8347 // stack. Return true if some objects were transferred.
8348 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8349 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8350 (size_t)ParGCDesiredObjsFromOverflowList);
8351
8352 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8353 assert(_collector->overflow_list_is_empty() || res,
8354 "If list is not empty, we should have taken something");
8355 assert(!res || !_mark_stack->isEmpty(),
8356 "If we took something, it should now be on our stack");
8357 return res;
8358 }
8359
8360 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8361 size_t res = _sp->block_size_no_stall(addr, _collector);
8362 if (_sp->block_is_obj(addr)) {
8363 if (_live_bit_map->isMarked(addr)) {
8364 // It can't have been dead in a previous cycle
8365 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8366 } else {
8367 _dead_bit_map->mark(addr); // mark the dead object
8368 }
8369 }
8370 // Could be 0, if the block size could not be computed without stalling.
8371 return res;
8372 }
8373
8374 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8375
8376 switch (phase) {
8377 case CMSCollector::InitialMarking:
8378 initialize(true /* fullGC */ ,
8379 cause /* cause of the GC */,
8380 true /* recordGCBeginTime */,
8381 true /* recordPreGCUsage */,
8382 false /* recordPeakUsage */,
8383 false /* recordPostGCusage */,
8384 true /* recordAccumulatedGCTime */,
8385 false /* recordGCEndTime */,
8386 false /* countCollection */ );
8387 break;
8388
8389 case CMSCollector::FinalMarking:
8390 initialize(true /* fullGC */ ,
8391 cause /* cause of the GC */,
8392 false /* recordGCBeginTime */,
8393 false /* recordPreGCUsage */,
8394 false /* recordPeakUsage */,
8395 false /* recordPostGCusage */,
8396 true /* recordAccumulatedGCTime */,
8397 false /* recordGCEndTime */,
8398 false /* countCollection */ );
8399 break;
8400
8401 case CMSCollector::Sweeping:
8402 initialize(true /* fullGC */ ,
8403 cause /* cause of the GC */,
8404 false /* recordGCBeginTime */,
8405 false /* recordPreGCUsage */,
8406 true /* recordPeakUsage */,
8407 true /* recordPostGCusage */,
8408 false /* recordAccumulatedGCTime */,
8409 true /* recordGCEndTime */,
8410 true /* countCollection */ );
8411 break;
8412
8413 default:
8414 ShouldNotReachHere();
8415 }
8416 }