1 /*
2 * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc_implementation/shared/adaptiveSizePolicy.hpp"
31 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
32 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
33 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
34 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
36 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
37 #include "gc_implementation/parNew/parNewGeneration.hpp"
38 #include "gc_implementation/shared/collectorCounters.hpp"
39 #include "gc_implementation/shared/gcTimer.hpp"
40 #include "gc_implementation/shared/gcTrace.hpp"
41 #include "gc_implementation/shared/gcTraceTime.hpp"
42 #include "gc_implementation/shared/isGCActiveMark.hpp"
43 #include "gc_interface/collectedHeap.inline.hpp"
44 #include "memory/allocation.hpp"
45 #include "memory/cardGeneration.inline.hpp"
46 #include "memory/cardTableRS.hpp"
47 #include "memory/collectorPolicy.hpp"
48 #include "memory/gcLocker.inline.hpp"
49 #include "memory/genCollectedHeap.hpp"
50 #include "memory/genMarkSweep.hpp"
51 #include "memory/genOopClosures.inline.hpp"
52 #include "memory/iterator.inline.hpp"
53 #include "memory/padded.hpp"
54 #include "memory/referencePolicy.hpp"
55 #include "memory/resourceArea.hpp"
56 #include "memory/strongRootsScope.hpp"
57 #include "memory/tenuredGeneration.hpp"
58 #include "oops/oop.inline.hpp"
59 #include "prims/jvmtiExport.hpp"
60 #include "runtime/atomic.inline.hpp"
61 #include "runtime/globals_extension.hpp"
62 #include "runtime/handles.inline.hpp"
63 #include "runtime/java.hpp"
64 #include "runtime/orderAccess.inline.hpp"
65 #include "runtime/vmThread.hpp"
66 #include "services/memoryService.hpp"
67 #include "services/runtimeService.hpp"
68 #include "utilities/stack.inline.hpp"
69 #include "utilities/taskqueue.inline.hpp"
70
71 // statics
72 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
73 bool CMSCollector::_full_gc_requested = false;
74 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
75
76 //////////////////////////////////////////////////////////////////
77 // In support of CMS/VM thread synchronization
78 //////////////////////////////////////////////////////////////////
79 // We split use of the CGC_lock into 2 "levels".
80 // The low-level locking is of the usual CGC_lock monitor. We introduce
81 // a higher level "token" (hereafter "CMS token") built on top of the
82 // low level monitor (hereafter "CGC lock").
83 // The token-passing protocol gives priority to the VM thread. The
84 // CMS-lock doesn't provide any fairness guarantees, but clients
85 // should ensure that it is only held for very short, bounded
86 // durations.
87 //
88 // When either of the CMS thread or the VM thread is involved in
89 // collection operations during which it does not want the other
90 // thread to interfere, it obtains the CMS token.
91 //
92 // If either thread tries to get the token while the other has
93 // it, that thread waits. However, if the VM thread and CMS thread
94 // both want the token, then the VM thread gets priority while the
95 // CMS thread waits. This ensures, for instance, that the "concurrent"
96 // phases of the CMS thread's work do not block out the VM thread
97 // for long periods of time as the CMS thread continues to hog
98 // the token. (See bug 4616232).
99 //
100 // The baton-passing functions are, however, controlled by the
101 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
102 // and here the low-level CMS lock, not the high level token,
103 // ensures mutual exclusion.
104 //
105 // Two important conditions that we have to satisfy:
106 // 1. if a thread does a low-level wait on the CMS lock, then it
107 // relinquishes the CMS token if it were holding that token
108 // when it acquired the low-level CMS lock.
109 // 2. any low-level notifications on the low-level lock
110 // should only be sent when a thread has relinquished the token.
111 //
112 // In the absence of either property, we'd have potential deadlock.
113 //
114 // We protect each of the CMS (concurrent and sequential) phases
115 // with the CMS _token_, not the CMS _lock_.
116 //
117 // The only code protected by CMS lock is the token acquisition code
118 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
119 // baton-passing code.
120 //
121 // Unfortunately, i couldn't come up with a good abstraction to factor and
122 // hide the naked CGC_lock manipulation in the baton-passing code
123 // further below. That's something we should try to do. Also, the proof
124 // of correctness of this 2-level locking scheme is far from obvious,
125 // and potentially quite slippery. We have an uneasy suspicion, for instance,
126 // that there may be a theoretical possibility of delay/starvation in the
127 // low-level lock/wait/notify scheme used for the baton-passing because of
128 // potential interference with the priority scheme embodied in the
129 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
130 // invocation further below and marked with "XXX 20011219YSR".
131 // Indeed, as we note elsewhere, this may become yet more slippery
132 // in the presence of multiple CMS and/or multiple VM threads. XXX
133
134 class CMSTokenSync: public StackObj {
135 private:
136 bool _is_cms_thread;
137 public:
138 CMSTokenSync(bool is_cms_thread):
139 _is_cms_thread(is_cms_thread) {
140 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
141 "Incorrect argument to constructor");
142 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
143 }
144
145 ~CMSTokenSync() {
146 assert(_is_cms_thread ?
147 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
148 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
149 "Incorrect state");
150 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
151 }
152 };
153
154 // Convenience class that does a CMSTokenSync, and then acquires
155 // upto three locks.
156 class CMSTokenSyncWithLocks: public CMSTokenSync {
157 private:
158 // Note: locks are acquired in textual declaration order
159 // and released in the opposite order
160 MutexLockerEx _locker1, _locker2, _locker3;
161 public:
162 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
163 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
164 CMSTokenSync(is_cms_thread),
165 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
166 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
167 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
168 { }
169 };
170
171
172 //////////////////////////////////////////////////////////////////
173 // Concurrent Mark-Sweep Generation /////////////////////////////
174 //////////////////////////////////////////////////////////////////
175
176 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
177
178 // This struct contains per-thread things necessary to support parallel
179 // young-gen collection.
180 class CMSParGCThreadState: public CHeapObj<mtGC> {
181 public:
182 CFLS_LAB lab;
183 PromotionInfo promo;
184
185 // Constructor.
186 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
187 promo.setSpace(cfls);
188 }
189 };
190
191 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
192 ReservedSpace rs, size_t initial_byte_size,
193 CardTableRS* ct, bool use_adaptive_freelists,
194 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
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 use_adaptive_freelists,
212 dictionaryChoice);
213 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
214 _cmsSpace->_gen = this;
215
216 _gc_stats = new CMSGCStats();
217
218 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
219 // offsets match. The ability to tell free chunks from objects
220 // depends on this property.
221 debug_only(
222 FreeChunk* junk = NULL;
223 assert(UseCompressedClassPointers ||
224 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
225 "Offset of FreeChunk::_prev within FreeChunk must match"
226 " that of OopDesc::_klass within OopDesc");
227 )
228
229 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
230 for (uint i = 0; i < ParallelGCThreads; i++) {
231 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
232 }
233
234 _incremental_collection_failed = false;
235 // The "dilatation_factor" is the expansion that can occur on
236 // account of the fact that the minimum object size in the CMS
237 // generation may be larger than that in, say, a contiguous young
238 // generation.
239 // Ideally, in the calculation below, we'd compute the dilatation
240 // factor as: MinChunkSize/(promoting_gen's min object size)
241 // Since we do not have such a general query interface for the
242 // promoting generation, we'll instead just use the minimum
243 // object size (which today is a header's worth of space);
244 // note that all arithmetic is in units of HeapWords.
245 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
246 assert(_dilatation_factor >= 1.0, "from previous assert");
247 }
248
249
250 // The field "_initiating_occupancy" represents the occupancy percentage
251 // at which we trigger a new collection cycle. Unless explicitly specified
252 // via CMSInitiatingOccupancyFraction (argument "io" below), it
253 // is calculated by:
254 //
255 // Let "f" be MinHeapFreeRatio in
256 //
257 // _initiating_occupancy = 100-f +
258 // f * (CMSTriggerRatio/100)
259 // where CMSTriggerRatio is the argument "tr" below.
260 //
261 // That is, if we assume the heap is at its desired maximum occupancy at the
262 // end of a collection, we let CMSTriggerRatio of the (purported) free
263 // space be allocated before initiating a new collection cycle.
264 //
265 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
266 assert(io <= 100 && tr <= 100, "Check the arguments");
267 if (io >= 0) {
268 _initiating_occupancy = (double)io / 100.0;
269 } else {
270 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
271 (double)(tr * MinHeapFreeRatio) / 100.0)
272 / 100.0;
273 }
274 }
275
276 void ConcurrentMarkSweepGeneration::ref_processor_init() {
277 assert(collector() != NULL, "no collector");
278 collector()->ref_processor_init();
279 }
280
281 void CMSCollector::ref_processor_init() {
282 if (_ref_processor == NULL) {
283 // Allocate and initialize a reference processor
284 _ref_processor =
285 new ReferenceProcessor(_span, // span
286 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
287 (int) ParallelGCThreads, // mt processing degree
288 _cmsGen->refs_discovery_is_mt(), // mt discovery
289 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
290 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
291 &_is_alive_closure); // closure for liveness info
292 // Initialize the _ref_processor field of CMSGen
293 _cmsGen->set_ref_processor(_ref_processor);
294
295 }
296 }
297
298 AdaptiveSizePolicy* CMSCollector::size_policy() {
299 GenCollectedHeap* gch = GenCollectedHeap::heap();
300 return gch->gen_policy()->size_policy();
301 }
302
303 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
304
305 const char* gen_name = "old";
306 GenCollectorPolicy* gcp = (GenCollectorPolicy*) GenCollectedHeap::heap()->collector_policy();
307
308 // Generation Counters - generation 1, 1 subspace
309 _gen_counters = new GenerationCounters(gen_name, 1, 1,
310 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
311
312 _space_counters = new GSpaceCounters(gen_name, 0,
313 _virtual_space.reserved_size(),
314 this, _gen_counters);
315 }
316
317 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
318 _cms_gen(cms_gen)
319 {
320 assert(alpha <= 100, "bad value");
321 _saved_alpha = alpha;
322
323 // Initialize the alphas to the bootstrap value of 100.
324 _gc0_alpha = _cms_alpha = 100;
325
326 _cms_begin_time.update();
327 _cms_end_time.update();
328
329 _gc0_duration = 0.0;
330 _gc0_period = 0.0;
331 _gc0_promoted = 0;
332
333 _cms_duration = 0.0;
334 _cms_period = 0.0;
335 _cms_allocated = 0;
336
337 _cms_used_at_gc0_begin = 0;
338 _cms_used_at_gc0_end = 0;
339 _allow_duty_cycle_reduction = false;
340 _valid_bits = 0;
341 }
342
343 double CMSStats::cms_free_adjustment_factor(size_t free) const {
344 // TBD: CR 6909490
345 return 1.0;
346 }
347
348 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
349 }
350
351 // If promotion failure handling is on use
352 // the padded average size of the promotion for each
353 // young generation collection.
354 double CMSStats::time_until_cms_gen_full() const {
355 size_t cms_free = _cms_gen->cmsSpace()->free();
356 GenCollectedHeap* gch = GenCollectedHeap::heap();
357 size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
358 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
359 if (cms_free > expected_promotion) {
360 // Start a cms collection if there isn't enough space to promote
361 // for the next minor collection. Use the padded average as
362 // a safety factor.
363 cms_free -= expected_promotion;
364
365 // Adjust by the safety factor.
366 double cms_free_dbl = (double)cms_free;
367 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
368 // Apply a further correction factor which tries to adjust
369 // for recent occurance of concurrent mode failures.
370 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
371 cms_free_dbl = cms_free_dbl * cms_adjustment;
372
373 if (PrintGCDetails && Verbose) {
374 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
375 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
376 cms_free, expected_promotion);
377 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
378 cms_free_dbl, cms_consumption_rate() + 1.0);
379 }
380 // Add 1 in case the consumption rate goes to zero.
381 return cms_free_dbl / (cms_consumption_rate() + 1.0);
382 }
383 return 0.0;
384 }
385
386 // Compare the duration of the cms collection to the
387 // time remaining before the cms generation is empty.
388 // Note that the time from the start of the cms collection
389 // to the start of the cms sweep (less than the total
390 // duration of the cms collection) can be used. This
391 // has been tried and some applications experienced
392 // promotion failures early in execution. This was
393 // possibly because the averages were not accurate
394 // enough at the beginning.
395 double CMSStats::time_until_cms_start() const {
396 // We add "gc0_period" to the "work" calculation
397 // below because this query is done (mostly) at the
398 // end of a scavenge, so we need to conservatively
399 // account for that much possible delay
400 // in the query so as to avoid concurrent mode failures
401 // due to starting the collection just a wee bit too
402 // late.
403 double work = cms_duration() + gc0_period();
404 double deadline = time_until_cms_gen_full();
405 // If a concurrent mode failure occurred recently, we want to be
406 // more conservative and halve our expected time_until_cms_gen_full()
407 if (work > deadline) {
408 if (Verbose && PrintGCDetails) {
409 gclog_or_tty->print(
410 " CMSCollector: collect because of anticipated promotion "
411 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
412 gc0_period(), time_until_cms_gen_full());
413 }
414 return 0.0;
415 }
416 return work - deadline;
417 }
418
419 #ifndef PRODUCT
420 void CMSStats::print_on(outputStream *st) const {
421 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
422 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
423 gc0_duration(), gc0_period(), gc0_promoted());
424 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
425 cms_duration(), cms_period(), cms_allocated());
426 st->print(",cms_since_beg=%g,cms_since_end=%g",
427 cms_time_since_begin(), cms_time_since_end());
428 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
429 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
430
431 if (valid()) {
432 st->print(",promo_rate=%g,cms_alloc_rate=%g",
433 promotion_rate(), cms_allocation_rate());
434 st->print(",cms_consumption_rate=%g,time_until_full=%g",
435 cms_consumption_rate(), time_until_cms_gen_full());
436 }
437 st->print(" ");
438 }
439 #endif // #ifndef PRODUCT
440
441 CMSCollector::CollectorState CMSCollector::_collectorState =
442 CMSCollector::Idling;
443 bool CMSCollector::_foregroundGCIsActive = false;
444 bool CMSCollector::_foregroundGCShouldWait = false;
445
446 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
447 CardTableRS* ct,
448 ConcurrentMarkSweepPolicy* cp):
449 _cmsGen(cmsGen),
450 _ct(ct),
451 _ref_processor(NULL), // will be set later
452 _conc_workers(NULL), // may be set later
453 _abort_preclean(false),
454 _start_sampling(false),
455 _between_prologue_and_epilogue(false),
456 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
457 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
458 -1 /* lock-free */, "No_lock" /* dummy */),
459 _modUnionClosurePar(&_modUnionTable),
460 // Adjust my span to cover old (cms) gen
461 _span(cmsGen->reserved()),
462 // Construct the is_alive_closure with _span & markBitMap
463 _is_alive_closure(_span, &_markBitMap),
464 _restart_addr(NULL),
465 _overflow_list(NULL),
466 _stats(cmsGen),
467 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
468 //verify that this lock should be acquired with safepoint check.
469 Monitor::_safepoint_check_sometimes)),
470 _eden_chunk_array(NULL), // may be set in ctor body
471 _eden_chunk_capacity(0), // -- ditto --
472 _eden_chunk_index(0), // -- ditto --
473 _survivor_plab_array(NULL), // -- ditto --
474 _survivor_chunk_array(NULL), // -- ditto --
475 _survivor_chunk_capacity(0), // -- ditto --
476 _survivor_chunk_index(0), // -- ditto --
477 _ser_pmc_preclean_ovflw(0),
478 _ser_kac_preclean_ovflw(0),
479 _ser_pmc_remark_ovflw(0),
480 _par_pmc_remark_ovflw(0),
481 _ser_kac_ovflw(0),
482 _par_kac_ovflw(0),
483 #ifndef PRODUCT
484 _num_par_pushes(0),
485 #endif
486 _collection_count_start(0),
487 _verifying(false),
488 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
489 _completed_initialization(false),
490 _collector_policy(cp),
491 _should_unload_classes(CMSClassUnloadingEnabled),
492 _concurrent_cycles_since_last_unload(0),
493 _roots_scanning_options(GenCollectedHeap::SO_None),
494 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
495 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
496 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
497 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
498 _cms_start_registered(false)
499 {
500 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
501 ExplicitGCInvokesConcurrent = true;
502 }
503 // Now expand the span and allocate the collection support structures
504 // (MUT, marking bit map etc.) to cover both generations subject to
505 // collection.
506
507 // For use by dirty card to oop closures.
508 _cmsGen->cmsSpace()->set_collector(this);
509
510 // Allocate MUT and marking bit map
511 {
512 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
513 if (!_markBitMap.allocate(_span)) {
514 warning("Failed to allocate CMS Bit Map");
515 return;
516 }
517 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
518 }
519 {
520 _modUnionTable.allocate(_span);
521 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
522 }
523
524 if (!_markStack.allocate(MarkStackSize)) {
525 warning("Failed to allocate CMS Marking Stack");
526 return;
527 }
528
529 // Support for multi-threaded concurrent phases
530 if (CMSConcurrentMTEnabled) {
531 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
532 // just for now
533 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
534 }
535 if (ConcGCThreads > 1) {
536 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
537 ConcGCThreads, true);
538 if (_conc_workers == NULL) {
539 warning("GC/CMS: _conc_workers allocation failure: "
540 "forcing -CMSConcurrentMTEnabled");
541 CMSConcurrentMTEnabled = false;
542 } else {
543 _conc_workers->initialize_workers();
544 }
545 } else {
546 CMSConcurrentMTEnabled = false;
547 }
548 }
549 if (!CMSConcurrentMTEnabled) {
550 ConcGCThreads = 0;
551 } else {
552 // Turn off CMSCleanOnEnter optimization temporarily for
553 // the MT case where it's not fixed yet; see 6178663.
554 CMSCleanOnEnter = false;
555 }
556 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
557 "Inconsistency");
558
559 // Parallel task queues; these are shared for the
560 // concurrent and stop-world phases of CMS, but
561 // are not shared with parallel scavenge (ParNew).
562 {
563 uint i;
564 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
565
566 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
567 || ParallelRefProcEnabled)
568 && num_queues > 0) {
569 _task_queues = new OopTaskQueueSet(num_queues);
570 if (_task_queues == NULL) {
571 warning("task_queues allocation failure.");
572 return;
573 }
574 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
575 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
576 for (i = 0; i < num_queues; i++) {
577 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
578 if (q == NULL) {
579 warning("work_queue allocation failure.");
580 return;
581 }
582 _task_queues->register_queue(i, q);
583 }
584 for (i = 0; i < num_queues; i++) {
585 _task_queues->queue(i)->initialize();
586 _hash_seed[i] = 17; // copied from ParNew
587 }
588 }
589 }
590
591 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
592
593 // Clip CMSBootstrapOccupancy between 0 and 100.
594 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
595
596 // Now tell CMS generations the identity of their collector
597 ConcurrentMarkSweepGeneration::set_collector(this);
598
599 // Create & start a CMS thread for this CMS collector
600 _cmsThread = ConcurrentMarkSweepThread::start(this);
601 assert(cmsThread() != NULL, "CMS Thread should have been created");
602 assert(cmsThread()->collector() == this,
603 "CMS Thread should refer to this gen");
604 assert(CGC_lock != NULL, "Where's the CGC_lock?");
605
606 // Support for parallelizing young gen rescan
607 GenCollectedHeap* gch = GenCollectedHeap::heap();
608 assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
609 _young_gen = (ParNewGeneration*)gch->young_gen();
610 if (gch->supports_inline_contig_alloc()) {
611 _top_addr = gch->top_addr();
612 _end_addr = gch->end_addr();
613 assert(_young_gen != NULL, "no _young_gen");
614 _eden_chunk_index = 0;
615 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
616 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
617 }
618
619 // Support for parallelizing survivor space rescan
620 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
621 const size_t max_plab_samples =
622 ((DefNewGeneration*)_young_gen)->max_survivor_size() / plab_sample_minimum_size();
623
624 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
625 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
626 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
627 _survivor_chunk_capacity = 2*max_plab_samples;
628 for (uint i = 0; i < ParallelGCThreads; i++) {
629 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
630 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
631 assert(cur->end() == 0, "Should be 0");
632 assert(cur->array() == vec, "Should be vec");
633 assert(cur->capacity() == max_plab_samples, "Error");
634 }
635 }
636
637 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
638 _gc_counters = new CollectorCounters("CMS", 1);
639 _completed_initialization = true;
640 _inter_sweep_timer.start(); // start of time
641 }
642
643 size_t CMSCollector::plab_sample_minimum_size() {
644 // The default value of MinTLABSize is 2k, but there is
645 // no way to get the default value if the flag has been overridden.
646 return MAX2(ThreadLocalAllocBuffer::min_size() * HeapWordSize, 2 * K);
647 }
648
649 const char* ConcurrentMarkSweepGeneration::name() const {
650 return "concurrent mark-sweep generation";
651 }
652 void ConcurrentMarkSweepGeneration::update_counters() {
653 if (UsePerfData) {
654 _space_counters->update_all();
655 _gen_counters->update_all();
656 }
657 }
658
659 // this is an optimized version of update_counters(). it takes the
660 // used value as a parameter rather than computing it.
661 //
662 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
663 if (UsePerfData) {
664 _space_counters->update_used(used);
665 _space_counters->update_capacity();
666 _gen_counters->update_all();
667 }
668 }
669
670 void ConcurrentMarkSweepGeneration::print() const {
671 Generation::print();
672 cmsSpace()->print();
673 }
674
675 #ifndef PRODUCT
676 void ConcurrentMarkSweepGeneration::print_statistics() {
677 cmsSpace()->printFLCensus(0);
678 }
679 #endif
680
681 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
682 GenCollectedHeap* gch = GenCollectedHeap::heap();
683 if (PrintGCDetails) {
684 // I didn't want to change the logging when removing the level concept,
685 // but I guess this logging could say "old" or something instead of "1".
686 assert(this == gch->old_gen(),
687 "The CMS generation should be the old generation");
688 uint level = 1;
689 if (Verbose) {
690 gclog_or_tty->print("[%u %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
691 level, short_name(), s, used(), capacity());
692 } else {
693 gclog_or_tty->print("[%u %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
694 level, short_name(), s, used() / K, capacity() / K);
695 }
696 }
697 if (Verbose) {
698 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
699 gch->used(), gch->capacity());
700 } else {
701 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
702 gch->used() / K, gch->capacity() / K);
703 }
704 }
705
706 size_t
707 ConcurrentMarkSweepGeneration::contiguous_available() const {
708 // dld proposes an improvement in precision here. If the committed
709 // part of the space ends in a free block we should add that to
710 // uncommitted size in the calculation below. Will make this
711 // change later, staying with the approximation below for the
712 // time being. -- ysr.
713 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
714 }
715
716 size_t
717 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
718 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
719 }
720
721 size_t ConcurrentMarkSweepGeneration::max_available() const {
722 return free() + _virtual_space.uncommitted_size();
723 }
724
725 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
726 size_t available = max_available();
727 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
728 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
729 if (Verbose && PrintGCDetails) {
730 gclog_or_tty->print_cr(
731 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
732 "max_promo("SIZE_FORMAT")",
733 res? "":" not", available, res? ">=":"<",
734 av_promo, max_promotion_in_bytes);
735 }
736 return res;
737 }
738
739 // At a promotion failure dump information on block layout in heap
740 // (cms old generation).
741 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
742 if (CMSDumpAtPromotionFailure) {
743 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
744 }
745 }
746
747 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
748 // Clear the promotion information. These pointers can be adjusted
749 // along with all the other pointers into the heap but
750 // compaction is expected to be a rare event with
751 // a heap using cms so don't do it without seeing the need.
752 for (uint i = 0; i < ParallelGCThreads; i++) {
753 _par_gc_thread_states[i]->promo.reset();
754 }
755 }
756
757 void ConcurrentMarkSweepGeneration::compute_new_size() {
758 assert_locked_or_safepoint(Heap_lock);
759
760 // If incremental collection failed, we just want to expand
761 // to the limit.
762 if (incremental_collection_failed()) {
763 clear_incremental_collection_failed();
764 grow_to_reserved();
765 return;
766 }
767
768 // The heap has been compacted but not reset yet.
769 // Any metric such as free() or used() will be incorrect.
770
771 CardGeneration::compute_new_size();
772
773 // Reset again after a possible resizing
774 if (did_compact()) {
775 cmsSpace()->reset_after_compaction();
776 }
777 }
778
779 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
780 assert_locked_or_safepoint(Heap_lock);
781
782 // If incremental collection failed, we just want to expand
783 // to the limit.
784 if (incremental_collection_failed()) {
785 clear_incremental_collection_failed();
786 grow_to_reserved();
787 return;
788 }
789
790 double free_percentage = ((double) free()) / capacity();
791 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
792 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
793
794 // compute expansion delta needed for reaching desired free percentage
795 if (free_percentage < desired_free_percentage) {
796 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
797 assert(desired_capacity >= capacity(), "invalid expansion size");
798 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
799 if (PrintGCDetails && Verbose) {
800 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
801 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
802 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
803 gclog_or_tty->print_cr(" Desired free fraction %f", desired_free_percentage);
804 gclog_or_tty->print_cr(" Maximum free fraction %f", maximum_free_percentage);
805 gclog_or_tty->print_cr(" Capacity "SIZE_FORMAT, capacity() / 1000);
806 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT, desired_capacity / 1000);
807 GenCollectedHeap* gch = GenCollectedHeap::heap();
808 assert(this == gch->_old_gen, "The CMS generation should always be the old generation");
809 size_t young_size = gch->_young_gen->capacity();
810 gclog_or_tty->print_cr(" Young gen size "SIZE_FORMAT, young_size / 1000);
811 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
812 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT, contiguous_available() / 1000);
813 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)", expand_bytes);
814 }
815 // safe if expansion fails
816 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
817 if (PrintGCDetails && Verbose) {
818 gclog_or_tty->print_cr(" Expanded free fraction %f",
819 ((double) free()) / capacity());
820 }
821 } else {
822 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
823 assert(desired_capacity <= capacity(), "invalid expansion size");
824 size_t shrink_bytes = capacity() - desired_capacity;
825 // Don't shrink unless the delta is greater than the minimum shrink we want
826 if (shrink_bytes >= MinHeapDeltaBytes) {
827 shrink_free_list_by(shrink_bytes);
828 }
829 }
830 }
831
832 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
833 return cmsSpace()->freelistLock();
834 }
835
836 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
837 bool tlab) {
838 CMSSynchronousYieldRequest yr;
839 MutexLockerEx x(freelistLock(),
840 Mutex::_no_safepoint_check_flag);
841 return have_lock_and_allocate(size, tlab);
842 }
843
844 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
845 bool tlab /* ignored */) {
846 assert_lock_strong(freelistLock());
847 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
848 HeapWord* res = cmsSpace()->allocate(adjustedSize);
849 // Allocate the object live (grey) if the background collector has
850 // started marking. This is necessary because the marker may
851 // have passed this address and consequently this object will
852 // not otherwise be greyed and would be incorrectly swept up.
853 // Note that if this object contains references, the writing
854 // of those references will dirty the card containing this object
855 // allowing the object to be blackened (and its references scanned)
856 // either during a preclean phase or at the final checkpoint.
857 if (res != NULL) {
858 // We may block here with an uninitialized object with
859 // its mark-bit or P-bits not yet set. Such objects need
860 // to be safely navigable by block_start().
861 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
862 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
863 collector()->direct_allocated(res, adjustedSize);
864 _direct_allocated_words += adjustedSize;
865 // allocation counters
866 NOT_PRODUCT(
867 _numObjectsAllocated++;
868 _numWordsAllocated += (int)adjustedSize;
869 )
870 }
871 return res;
872 }
873
874 // In the case of direct allocation by mutators in a generation that
875 // is being concurrently collected, the object must be allocated
876 // live (grey) if the background collector has started marking.
877 // This is necessary because the marker may
878 // have passed this address and consequently this object will
879 // not otherwise be greyed and would be incorrectly swept up.
880 // Note that if this object contains references, the writing
881 // of those references will dirty the card containing this object
882 // allowing the object to be blackened (and its references scanned)
883 // either during a preclean phase or at the final checkpoint.
884 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
885 assert(_markBitMap.covers(start, size), "Out of bounds");
886 if (_collectorState >= Marking) {
887 MutexLockerEx y(_markBitMap.lock(),
888 Mutex::_no_safepoint_check_flag);
889 // [see comments preceding SweepClosure::do_blk() below for details]
890 //
891 // Can the P-bits be deleted now? JJJ
892 //
893 // 1. need to mark the object as live so it isn't collected
894 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
895 // 3. need to mark the end of the object so marking, precleaning or sweeping
896 // can skip over uninitialized or unparsable objects. An allocated
897 // object is considered uninitialized for our purposes as long as
898 // its klass word is NULL. All old gen objects are parsable
899 // as soon as they are initialized.)
900 _markBitMap.mark(start); // object is live
901 _markBitMap.mark(start + 1); // object is potentially uninitialized?
902 _markBitMap.mark(start + size - 1);
903 // mark end of object
904 }
905 // check that oop looks uninitialized
906 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
907 }
908
909 void CMSCollector::promoted(bool par, HeapWord* start,
910 bool is_obj_array, size_t obj_size) {
911 assert(_markBitMap.covers(start), "Out of bounds");
912 // See comment in direct_allocated() about when objects should
913 // be allocated live.
914 if (_collectorState >= Marking) {
915 // we already hold the marking bit map lock, taken in
916 // the prologue
917 if (par) {
918 _markBitMap.par_mark(start);
919 } else {
920 _markBitMap.mark(start);
921 }
922 // We don't need to mark the object as uninitialized (as
923 // in direct_allocated above) because this is being done with the
924 // world stopped and the object will be initialized by the
925 // time the marking, precleaning or sweeping get to look at it.
926 // But see the code for copying objects into the CMS generation,
927 // where we need to ensure that concurrent readers of the
928 // block offset table are able to safely navigate a block that
929 // is in flux from being free to being allocated (and in
930 // transition while being copied into) and subsequently
931 // becoming a bona-fide object when the copy/promotion is complete.
932 assert(SafepointSynchronize::is_at_safepoint(),
933 "expect promotion only at safepoints");
934
935 if (_collectorState < Sweeping) {
936 // Mark the appropriate cards in the modUnionTable, so that
937 // this object gets scanned before the sweep. If this is
938 // not done, CMS generation references in the object might
939 // not get marked.
940 // For the case of arrays, which are otherwise precisely
941 // marked, we need to dirty the entire array, not just its head.
942 if (is_obj_array) {
943 // The [par_]mark_range() method expects mr.end() below to
944 // be aligned to the granularity of a bit's representation
945 // in the heap. In the case of the MUT below, that's a
946 // card size.
947 MemRegion mr(start,
948 (HeapWord*)round_to((intptr_t)(start + obj_size),
949 CardTableModRefBS::card_size /* bytes */));
950 if (par) {
951 _modUnionTable.par_mark_range(mr);
952 } else {
953 _modUnionTable.mark_range(mr);
954 }
955 } else { // not an obj array; we can just mark the head
956 if (par) {
957 _modUnionTable.par_mark(start);
958 } else {
959 _modUnionTable.mark(start);
960 }
961 }
962 }
963 }
964 }
965
966 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
967 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
968 // allocate, copy and if necessary update promoinfo --
969 // delegate to underlying space.
970 assert_lock_strong(freelistLock());
971
972 #ifndef PRODUCT
973 if (GenCollectedHeap::heap()->promotion_should_fail()) {
974 return NULL;
975 }
976 #endif // #ifndef PRODUCT
977
978 oop res = _cmsSpace->promote(obj, obj_size);
979 if (res == NULL) {
980 // expand and retry
981 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
982 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
983 // Since this is the old generation, we don't try to promote
984 // into a more senior generation.
985 res = _cmsSpace->promote(obj, obj_size);
986 }
987 if (res != NULL) {
988 // See comment in allocate() about when objects should
989 // be allocated live.
990 assert(obj->is_oop(), "Will dereference klass pointer below");
991 collector()->promoted(false, // Not parallel
992 (HeapWord*)res, obj->is_objArray(), obj_size);
993 // promotion counters
994 NOT_PRODUCT(
995 _numObjectsPromoted++;
996 _numWordsPromoted +=
997 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
998 )
999 }
1000 return res;
1001 }
1002
1003
1004 // IMPORTANT: Notes on object size recognition in CMS.
1005 // ---------------------------------------------------
1006 // A block of storage in the CMS generation is always in
1007 // one of three states. A free block (FREE), an allocated
1008 // object (OBJECT) whose size() method reports the correct size,
1009 // and an intermediate state (TRANSIENT) in which its size cannot
1010 // be accurately determined.
1011 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1012 // -----------------------------------------------------
1013 // FREE: klass_word & 1 == 1; mark_word holds block size
1014 //
1015 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1016 // obj->size() computes correct size
1017 //
1018 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1019 //
1020 // STATE IDENTIFICATION: (64 bit+COOPS)
1021 // ------------------------------------
1022 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1023 //
1024 // OBJECT: klass_word installed; klass_word != 0;
1025 // obj->size() computes correct size
1026 //
1027 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1028 //
1029 //
1030 // STATE TRANSITION DIAGRAM
1031 //
1032 // mut / parnew mut / parnew
1033 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1034 // ^ |
1035 // |------------------------ DEAD <------------------------------------|
1036 // sweep mut
1037 //
1038 // While a block is in TRANSIENT state its size cannot be determined
1039 // so readers will either need to come back later or stall until
1040 // the size can be determined. Note that for the case of direct
1041 // allocation, P-bits, when available, may be used to determine the
1042 // size of an object that may not yet have been initialized.
1043
1044 // Things to support parallel young-gen collection.
1045 oop
1046 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1047 oop old, markOop m,
1048 size_t word_sz) {
1049 #ifndef PRODUCT
1050 if (GenCollectedHeap::heap()->promotion_should_fail()) {
1051 return NULL;
1052 }
1053 #endif // #ifndef PRODUCT
1054
1055 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1056 PromotionInfo* promoInfo = &ps->promo;
1057 // if we are tracking promotions, then first ensure space for
1058 // promotion (including spooling space for saving header if necessary).
1059 // then allocate and copy, then track promoted info if needed.
1060 // When tracking (see PromotionInfo::track()), the mark word may
1061 // be displaced and in this case restoration of the mark word
1062 // occurs in the (oop_since_save_marks_)iterate phase.
1063 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1064 // Out of space for allocating spooling buffers;
1065 // try expanding and allocating spooling buffers.
1066 if (!expand_and_ensure_spooling_space(promoInfo)) {
1067 return NULL;
1068 }
1069 }
1070 assert(promoInfo->has_spooling_space(), "Control point invariant");
1071 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1072 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1073 if (obj_ptr == NULL) {
1074 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1075 if (obj_ptr == NULL) {
1076 return NULL;
1077 }
1078 }
1079 oop obj = oop(obj_ptr);
1080 OrderAccess::storestore();
1081 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1082 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1083 // IMPORTANT: See note on object initialization for CMS above.
1084 // Otherwise, copy the object. Here we must be careful to insert the
1085 // klass pointer last, since this marks the block as an allocated object.
1086 // Except with compressed oops it's the mark word.
1087 HeapWord* old_ptr = (HeapWord*)old;
1088 // Restore the mark word copied above.
1089 obj->set_mark(m);
1090 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1091 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1092 OrderAccess::storestore();
1093
1094 if (UseCompressedClassPointers) {
1095 // Copy gap missed by (aligned) header size calculation below
1096 obj->set_klass_gap(old->klass_gap());
1097 }
1098 if (word_sz > (size_t)oopDesc::header_size()) {
1099 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1100 obj_ptr + oopDesc::header_size(),
1101 word_sz - oopDesc::header_size());
1102 }
1103
1104 // Now we can track the promoted object, if necessary. We take care
1105 // to delay the transition from uninitialized to full object
1106 // (i.e., insertion of klass pointer) until after, so that it
1107 // atomically becomes a promoted object.
1108 if (promoInfo->tracking()) {
1109 promoInfo->track((PromotedObject*)obj, old->klass());
1110 }
1111 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1112 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1113 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1114
1115 // Finally, install the klass pointer (this should be volatile).
1116 OrderAccess::storestore();
1117 obj->set_klass(old->klass());
1118 // We should now be able to calculate the right size for this object
1119 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1120
1121 collector()->promoted(true, // parallel
1122 obj_ptr, old->is_objArray(), word_sz);
1123
1124 NOT_PRODUCT(
1125 Atomic::inc_ptr(&_numObjectsPromoted);
1126 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1127 )
1128
1129 return obj;
1130 }
1131
1132 void
1133 ConcurrentMarkSweepGeneration::
1134 par_promote_alloc_done(int thread_num) {
1135 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1136 ps->lab.retire(thread_num);
1137 }
1138
1139 void
1140 ConcurrentMarkSweepGeneration::
1141 par_oop_since_save_marks_iterate_done(int thread_num) {
1142 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1143 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1144 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1145 }
1146
1147 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1148 size_t size,
1149 bool tlab)
1150 {
1151 // We allow a STW collection only if a full
1152 // collection was requested.
1153 return full || should_allocate(size, tlab); // FIX ME !!!
1154 // This and promotion failure handling are connected at the
1155 // hip and should be fixed by untying them.
1156 }
1157
1158 bool CMSCollector::shouldConcurrentCollect() {
1159 if (_full_gc_requested) {
1160 if (Verbose && PrintGCDetails) {
1161 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1162 " gc request (or gc_locker)");
1163 }
1164 return true;
1165 }
1166
1167 FreelistLocker x(this);
1168 // ------------------------------------------------------------------
1169 // Print out lots of information which affects the initiation of
1170 // a collection.
1171 if (PrintCMSInitiationStatistics && stats().valid()) {
1172 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1173 gclog_or_tty->stamp();
1174 gclog_or_tty->cr();
1175 stats().print_on(gclog_or_tty);
1176 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1177 stats().time_until_cms_gen_full());
1178 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1179 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1180 _cmsGen->contiguous_available());
1181 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1182 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1183 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1184 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1185 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1186 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1187 gclog_or_tty->print_cr("metadata initialized %d",
1188 MetaspaceGC::should_concurrent_collect());
1189 }
1190 // ------------------------------------------------------------------
1191
1192 // If the estimated time to complete a cms collection (cms_duration())
1193 // is less than the estimated time remaining until the cms generation
1194 // is full, start a collection.
1195 if (!UseCMSInitiatingOccupancyOnly) {
1196 if (stats().valid()) {
1197 if (stats().time_until_cms_start() == 0.0) {
1198 return true;
1199 }
1200 } else {
1201 // We want to conservatively collect somewhat early in order
1202 // to try and "bootstrap" our CMS/promotion statistics;
1203 // this branch will not fire after the first successful CMS
1204 // collection because the stats should then be valid.
1205 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1206 if (Verbose && PrintGCDetails) {
1207 gclog_or_tty->print_cr(
1208 " CMSCollector: collect for bootstrapping statistics:"
1209 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1210 _bootstrap_occupancy);
1211 }
1212 return true;
1213 }
1214 }
1215 }
1216
1217 // Otherwise, we start a collection cycle if
1218 // old gen want a collection cycle started. Each may use
1219 // an appropriate criterion for making this decision.
1220 // XXX We need to make sure that the gen expansion
1221 // criterion dovetails well with this. XXX NEED TO FIX THIS
1222 if (_cmsGen->should_concurrent_collect()) {
1223 if (Verbose && PrintGCDetails) {
1224 gclog_or_tty->print_cr("CMS old gen initiated");
1225 }
1226 return true;
1227 }
1228
1229 // We start a collection if we believe an incremental collection may fail;
1230 // this is not likely to be productive in practice because it's probably too
1231 // late anyway.
1232 GenCollectedHeap* gch = GenCollectedHeap::heap();
1233 assert(gch->collector_policy()->is_generation_policy(),
1234 "You may want to check the correctness of the following");
1235 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1236 if (Verbose && PrintGCDetails) {
1237 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1238 }
1239 return true;
1240 }
1241
1242 if (MetaspaceGC::should_concurrent_collect()) {
1243 if (Verbose && PrintGCDetails) {
1244 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1245 }
1246 return true;
1247 }
1248
1249 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1250 if (CMSTriggerInterval >= 0) {
1251 if (CMSTriggerInterval == 0) {
1252 // Trigger always
1253 return true;
1254 }
1255
1256 // Check the CMS time since begin (we do not check the stats validity
1257 // as we want to be able to trigger the first CMS cycle as well)
1258 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1259 if (Verbose && PrintGCDetails) {
1260 if (stats().valid()) {
1261 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1262 stats().cms_time_since_begin());
1263 } else {
1264 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1265 }
1266 }
1267 return true;
1268 }
1269 }
1270
1271 return false;
1272 }
1273
1274 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1275
1276 // Clear _expansion_cause fields of constituent generations
1277 void CMSCollector::clear_expansion_cause() {
1278 _cmsGen->clear_expansion_cause();
1279 }
1280
1281 // We should be conservative in starting a collection cycle. To
1282 // start too eagerly runs the risk of collecting too often in the
1283 // extreme. To collect too rarely falls back on full collections,
1284 // which works, even if not optimum in terms of concurrent work.
1285 // As a work around for too eagerly collecting, use the flag
1286 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1287 // giving the user an easily understandable way of controlling the
1288 // collections.
1289 // We want to start a new collection cycle if any of the following
1290 // conditions hold:
1291 // . our current occupancy exceeds the configured initiating occupancy
1292 // for this generation, or
1293 // . we recently needed to expand this space and have not, since that
1294 // expansion, done a collection of this generation, or
1295 // . the underlying space believes that it may be a good idea to initiate
1296 // a concurrent collection (this may be based on criteria such as the
1297 // following: the space uses linear allocation and linear allocation is
1298 // going to fail, or there is believed to be excessive fragmentation in
1299 // the generation, etc... or ...
1300 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1301 // the case of the old generation; see CR 6543076):
1302 // we may be approaching a point at which allocation requests may fail because
1303 // we will be out of sufficient free space given allocation rate estimates.]
1304 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1305
1306 assert_lock_strong(freelistLock());
1307 if (occupancy() > initiating_occupancy()) {
1308 if (PrintGCDetails && Verbose) {
1309 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1310 short_name(), occupancy(), initiating_occupancy());
1311 }
1312 return true;
1313 }
1314 if (UseCMSInitiatingOccupancyOnly) {
1315 return false;
1316 }
1317 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1318 if (PrintGCDetails && Verbose) {
1319 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1320 short_name());
1321 }
1322 return true;
1323 }
1324 if (_cmsSpace->should_concurrent_collect()) {
1325 if (PrintGCDetails && Verbose) {
1326 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1327 short_name());
1328 }
1329 return true;
1330 }
1331 return false;
1332 }
1333
1334 void ConcurrentMarkSweepGeneration::collect(bool full,
1335 bool clear_all_soft_refs,
1336 size_t size,
1337 bool tlab)
1338 {
1339 collector()->collect(full, clear_all_soft_refs, size, tlab);
1340 }
1341
1342 void CMSCollector::collect(bool full,
1343 bool clear_all_soft_refs,
1344 size_t size,
1345 bool tlab)
1346 {
1347 // The following "if" branch is present for defensive reasons.
1348 // In the current uses of this interface, it can be replaced with:
1349 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1350 // But I am not placing that assert here to allow future
1351 // generality in invoking this interface.
1352 if (GC_locker::is_active()) {
1353 // A consistency test for GC_locker
1354 assert(GC_locker::needs_gc(), "Should have been set already");
1355 // Skip this foreground collection, instead
1356 // expanding the heap if necessary.
1357 // Need the free list locks for the call to free() in compute_new_size()
1358 compute_new_size();
1359 return;
1360 }
1361 acquire_control_and_collect(full, clear_all_soft_refs);
1362 }
1363
1364 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1365 GenCollectedHeap* gch = GenCollectedHeap::heap();
1366 unsigned int gc_count = gch->total_full_collections();
1367 if (gc_count == full_gc_count) {
1368 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1369 _full_gc_requested = true;
1370 _full_gc_cause = cause;
1371 CGC_lock->notify(); // nudge CMS thread
1372 } else {
1373 assert(gc_count > full_gc_count, "Error: causal loop");
1374 }
1375 }
1376
1377 bool CMSCollector::is_external_interruption() {
1378 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1379 return GCCause::is_user_requested_gc(cause) ||
1380 GCCause::is_serviceability_requested_gc(cause);
1381 }
1382
1383 void CMSCollector::report_concurrent_mode_interruption() {
1384 if (is_external_interruption()) {
1385 if (PrintGCDetails) {
1386 gclog_or_tty->print(" (concurrent mode interrupted)");
1387 }
1388 } else {
1389 if (PrintGCDetails) {
1390 gclog_or_tty->print(" (concurrent mode failure)");
1391 }
1392 _gc_tracer_cm->report_concurrent_mode_failure();
1393 }
1394 }
1395
1396
1397 // The foreground and background collectors need to coordinate in order
1398 // to make sure that they do not mutually interfere with CMS collections.
1399 // When a background collection is active,
1400 // the foreground collector may need to take over (preempt) and
1401 // synchronously complete an ongoing collection. Depending on the
1402 // frequency of the background collections and the heap usage
1403 // of the application, this preemption can be seldom or frequent.
1404 // There are only certain
1405 // points in the background collection that the "collection-baton"
1406 // can be passed to the foreground collector.
1407 //
1408 // The foreground collector will wait for the baton before
1409 // starting any part of the collection. The foreground collector
1410 // will only wait at one location.
1411 //
1412 // The background collector will yield the baton before starting a new
1413 // phase of the collection (e.g., before initial marking, marking from roots,
1414 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1415 // of the loop which switches the phases. The background collector does some
1416 // of the phases (initial mark, final re-mark) with the world stopped.
1417 // Because of locking involved in stopping the world,
1418 // the foreground collector should not block waiting for the background
1419 // collector when it is doing a stop-the-world phase. The background
1420 // collector will yield the baton at an additional point just before
1421 // it enters a stop-the-world phase. Once the world is stopped, the
1422 // background collector checks the phase of the collection. If the
1423 // phase has not changed, it proceeds with the collection. If the
1424 // phase has changed, it skips that phase of the collection. See
1425 // the comments on the use of the Heap_lock in collect_in_background().
1426 //
1427 // Variable used in baton passing.
1428 // _foregroundGCIsActive - Set to true by the foreground collector when
1429 // it wants the baton. The foreground clears it when it has finished
1430 // the collection.
1431 // _foregroundGCShouldWait - Set to true by the background collector
1432 // when it is running. The foreground collector waits while
1433 // _foregroundGCShouldWait is true.
1434 // CGC_lock - monitor used to protect access to the above variables
1435 // and to notify the foreground and background collectors.
1436 // _collectorState - current state of the CMS collection.
1437 //
1438 // The foreground collector
1439 // acquires the CGC_lock
1440 // sets _foregroundGCIsActive
1441 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1442 // various locks acquired in preparation for the collection
1443 // are released so as not to block the background collector
1444 // that is in the midst of a collection
1445 // proceeds with the collection
1446 // clears _foregroundGCIsActive
1447 // returns
1448 //
1449 // The background collector in a loop iterating on the phases of the
1450 // collection
1451 // acquires the CGC_lock
1452 // sets _foregroundGCShouldWait
1453 // if _foregroundGCIsActive is set
1454 // clears _foregroundGCShouldWait, notifies _CGC_lock
1455 // waits on _CGC_lock for _foregroundGCIsActive to become false
1456 // and exits the loop.
1457 // otherwise
1458 // proceed with that phase of the collection
1459 // if the phase is a stop-the-world phase,
1460 // yield the baton once more just before enqueueing
1461 // the stop-world CMS operation (executed by the VM thread).
1462 // returns after all phases of the collection are done
1463 //
1464
1465 void CMSCollector::acquire_control_and_collect(bool full,
1466 bool clear_all_soft_refs) {
1467 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1468 assert(!Thread::current()->is_ConcurrentGC_thread(),
1469 "shouldn't try to acquire control from self!");
1470
1471 // Start the protocol for acquiring control of the
1472 // collection from the background collector (aka CMS thread).
1473 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1474 "VM thread should have CMS token");
1475 // Remember the possibly interrupted state of an ongoing
1476 // concurrent collection
1477 CollectorState first_state = _collectorState;
1478
1479 // Signal to a possibly ongoing concurrent collection that
1480 // we want to do a foreground collection.
1481 _foregroundGCIsActive = true;
1482
1483 // release locks and wait for a notify from the background collector
1484 // releasing the locks in only necessary for phases which
1485 // do yields to improve the granularity of the collection.
1486 assert_lock_strong(bitMapLock());
1487 // We need to lock the Free list lock for the space that we are
1488 // currently collecting.
1489 assert(haveFreelistLocks(), "Must be holding free list locks");
1490 bitMapLock()->unlock();
1491 releaseFreelistLocks();
1492 {
1493 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1494 if (_foregroundGCShouldWait) {
1495 // We are going to be waiting for action for the CMS thread;
1496 // it had better not be gone (for instance at shutdown)!
1497 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1498 "CMS thread must be running");
1499 // Wait here until the background collector gives us the go-ahead
1500 ConcurrentMarkSweepThread::clear_CMS_flag(
1501 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1502 // Get a possibly blocked CMS thread going:
1503 // Note that we set _foregroundGCIsActive true above,
1504 // without protection of the CGC_lock.
1505 CGC_lock->notify();
1506 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1507 "Possible deadlock");
1508 while (_foregroundGCShouldWait) {
1509 // wait for notification
1510 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1511 // Possibility of delay/starvation here, since CMS token does
1512 // not know to give priority to VM thread? Actually, i think
1513 // there wouldn't be any delay/starvation, but the proof of
1514 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1515 }
1516 ConcurrentMarkSweepThread::set_CMS_flag(
1517 ConcurrentMarkSweepThread::CMS_vm_has_token);
1518 }
1519 }
1520 // The CMS_token is already held. Get back the other locks.
1521 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1522 "VM thread should have CMS token");
1523 getFreelistLocks();
1524 bitMapLock()->lock_without_safepoint_check();
1525 if (TraceCMSState) {
1526 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1527 INTPTR_FORMAT " with first state %d", p2i(Thread::current()), first_state);
1528 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1529 }
1530
1531 // Inform cms gen if this was due to partial collection failing.
1532 // The CMS gen may use this fact to determine its expansion policy.
1533 GenCollectedHeap* gch = GenCollectedHeap::heap();
1534 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1535 assert(!_cmsGen->incremental_collection_failed(),
1536 "Should have been noticed, reacted to and cleared");
1537 _cmsGen->set_incremental_collection_failed();
1538 }
1539
1540 if (first_state > Idling) {
1541 report_concurrent_mode_interruption();
1542 }
1543
1544 set_did_compact(true);
1545
1546 // If the collection is being acquired from the background
1547 // collector, there may be references on the discovered
1548 // references lists. Abandon those references, since some
1549 // of them may have become unreachable after concurrent
1550 // discovery; the STW compacting collector will redo discovery
1551 // more precisely, without being subject to floating garbage.
1552 // Leaving otherwise unreachable references in the discovered
1553 // lists would require special handling.
1554 ref_processor()->disable_discovery();
1555 ref_processor()->abandon_partial_discovery();
1556 ref_processor()->verify_no_references_recorded();
1557
1558 if (first_state > Idling) {
1559 save_heap_summary();
1560 }
1561
1562 do_compaction_work(clear_all_soft_refs);
1563
1564 // Has the GC time limit been exceeded?
1565 size_t max_eden_size = _young_gen->max_capacity() -
1566 _young_gen->to()->capacity() -
1567 _young_gen->from()->capacity();
1568 GCCause::Cause gc_cause = gch->gc_cause();
1569 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1570 _young_gen->eden()->used(),
1571 _cmsGen->max_capacity(),
1572 max_eden_size,
1573 full,
1574 gc_cause,
1575 gch->collector_policy());
1576
1577 // Reset the expansion cause, now that we just completed
1578 // a collection cycle.
1579 clear_expansion_cause();
1580 _foregroundGCIsActive = false;
1581 return;
1582 }
1583
1584 // Resize the tenured generation
1585 // after obtaining the free list locks for the
1586 // two generations.
1587 void CMSCollector::compute_new_size() {
1588 assert_locked_or_safepoint(Heap_lock);
1589 FreelistLocker z(this);
1590 MetaspaceGC::compute_new_size();
1591 _cmsGen->compute_new_size_free_list();
1592 }
1593
1594 // A work method used by the foreground collector to do
1595 // a mark-sweep-compact.
1596 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1597 GenCollectedHeap* gch = GenCollectedHeap::heap();
1598
1599 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1600 gc_timer->register_gc_start();
1601
1602 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1603 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1604
1605 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
1606
1607 // Temporarily widen the span of the weak reference processing to
1608 // the entire heap.
1609 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1610 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1611 // Temporarily, clear the "is_alive_non_header" field of the
1612 // reference processor.
1613 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1614 // Temporarily make reference _processing_ single threaded (non-MT).
1615 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1616 // Temporarily make refs discovery atomic
1617 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1618 // Temporarily make reference _discovery_ single threaded (non-MT)
1619 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1620
1621 ref_processor()->set_enqueuing_is_done(false);
1622 ref_processor()->enable_discovery();
1623 ref_processor()->setup_policy(clear_all_soft_refs);
1624 // If an asynchronous collection finishes, the _modUnionTable is
1625 // all clear. If we are assuming the collection from an asynchronous
1626 // collection, clear the _modUnionTable.
1627 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1628 "_modUnionTable should be clear if the baton was not passed");
1629 _modUnionTable.clear_all();
1630 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1631 "mod union for klasses should be clear if the baton was passed");
1632 _ct->klass_rem_set()->clear_mod_union();
1633
1634 // We must adjust the allocation statistics being maintained
1635 // in the free list space. We do so by reading and clearing
1636 // the sweep timer and updating the block flux rate estimates below.
1637 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1638 if (_inter_sweep_timer.is_active()) {
1639 _inter_sweep_timer.stop();
1640 // Note that we do not use this sample to update the _inter_sweep_estimate.
1641 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1642 _inter_sweep_estimate.padded_average(),
1643 _intra_sweep_estimate.padded_average());
1644 }
1645
1646 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1647 #ifdef ASSERT
1648 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1649 size_t free_size = cms_space->free();
1650 assert(free_size ==
1651 pointer_delta(cms_space->end(), cms_space->compaction_top())
1652 * HeapWordSize,
1653 "All the free space should be compacted into one chunk at top");
1654 assert(cms_space->dictionary()->total_chunk_size(
1655 debug_only(cms_space->freelistLock())) == 0 ||
1656 cms_space->totalSizeInIndexedFreeLists() == 0,
1657 "All the free space should be in a single chunk");
1658 size_t num = cms_space->totalCount();
1659 assert((free_size == 0 && num == 0) ||
1660 (free_size > 0 && (num == 1 || num == 2)),
1661 "There should be at most 2 free chunks after compaction");
1662 #endif // ASSERT
1663 _collectorState = Resetting;
1664 assert(_restart_addr == NULL,
1665 "Should have been NULL'd before baton was passed");
1666 reset(false /* == !concurrent */);
1667 _cmsGen->reset_after_compaction();
1668 _concurrent_cycles_since_last_unload = 0;
1669
1670 // Clear any data recorded in the PLAB chunk arrays.
1671 if (_survivor_plab_array != NULL) {
1672 reset_survivor_plab_arrays();
1673 }
1674
1675 // Adjust the per-size allocation stats for the next epoch.
1676 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1677 // Restart the "inter sweep timer" for the next epoch.
1678 _inter_sweep_timer.reset();
1679 _inter_sweep_timer.start();
1680
1681 gc_timer->register_gc_end();
1682
1683 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1684
1685 // For a mark-sweep-compact, compute_new_size() will be called
1686 // in the heap's do_collection() method.
1687 }
1688
1689 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1690 ContiguousSpace* eden_space = _young_gen->eden();
1691 ContiguousSpace* from_space = _young_gen->from();
1692 ContiguousSpace* to_space = _young_gen->to();
1693 // Eden
1694 if (_eden_chunk_array != NULL) {
1695 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1696 p2i(eden_space->bottom()), p2i(eden_space->top()),
1697 p2i(eden_space->end()), eden_space->capacity());
1698 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1699 "_eden_chunk_capacity=" SIZE_FORMAT,
1700 _eden_chunk_index, _eden_chunk_capacity);
1701 for (size_t i = 0; i < _eden_chunk_index; i++) {
1702 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1703 i, p2i(_eden_chunk_array[i]));
1704 }
1705 }
1706 // Survivor
1707 if (_survivor_chunk_array != NULL) {
1708 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1709 p2i(from_space->bottom()), p2i(from_space->top()),
1710 p2i(from_space->end()), from_space->capacity());
1711 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1712 "_survivor_chunk_capacity=" SIZE_FORMAT,
1713 _survivor_chunk_index, _survivor_chunk_capacity);
1714 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1715 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1716 i, p2i(_survivor_chunk_array[i]));
1717 }
1718 }
1719 }
1720
1721 void CMSCollector::getFreelistLocks() const {
1722 // Get locks for all free lists in all generations that this
1723 // collector is responsible for
1724 _cmsGen->freelistLock()->lock_without_safepoint_check();
1725 }
1726
1727 void CMSCollector::releaseFreelistLocks() const {
1728 // Release locks for all free lists in all generations that this
1729 // collector is responsible for
1730 _cmsGen->freelistLock()->unlock();
1731 }
1732
1733 bool CMSCollector::haveFreelistLocks() const {
1734 // Check locks for all free lists in all generations that this
1735 // collector is responsible for
1736 assert_lock_strong(_cmsGen->freelistLock());
1737 PRODUCT_ONLY(ShouldNotReachHere());
1738 return true;
1739 }
1740
1741 // A utility class that is used by the CMS collector to
1742 // temporarily "release" the foreground collector from its
1743 // usual obligation to wait for the background collector to
1744 // complete an ongoing phase before proceeding.
1745 class ReleaseForegroundGC: public StackObj {
1746 private:
1747 CMSCollector* _c;
1748 public:
1749 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1750 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1751 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1752 // allow a potentially blocked foreground collector to proceed
1753 _c->_foregroundGCShouldWait = false;
1754 if (_c->_foregroundGCIsActive) {
1755 CGC_lock->notify();
1756 }
1757 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1758 "Possible deadlock");
1759 }
1760
1761 ~ReleaseForegroundGC() {
1762 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1763 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1764 _c->_foregroundGCShouldWait = true;
1765 }
1766 };
1767
1768 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1769 assert(Thread::current()->is_ConcurrentGC_thread(),
1770 "A CMS asynchronous collection is only allowed on a CMS thread.");
1771
1772 GenCollectedHeap* gch = GenCollectedHeap::heap();
1773 {
1774 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1775 MutexLockerEx hl(Heap_lock, safepoint_check);
1776 FreelistLocker fll(this);
1777 MutexLockerEx x(CGC_lock, safepoint_check);
1778 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
1779 // The foreground collector is active or we're
1780 // not using asynchronous collections. Skip this
1781 // background collection.
1782 assert(!_foregroundGCShouldWait, "Should be clear");
1783 return;
1784 } else {
1785 assert(_collectorState == Idling, "Should be idling before start.");
1786 _collectorState = InitialMarking;
1787 register_gc_start(cause);
1788 // Reset the expansion cause, now that we are about to begin
1789 // a new cycle.
1790 clear_expansion_cause();
1791
1792 // Clear the MetaspaceGC flag since a concurrent collection
1793 // is starting but also clear it after the collection.
1794 MetaspaceGC::set_should_concurrent_collect(false);
1795 }
1796 // Decide if we want to enable class unloading as part of the
1797 // ensuing concurrent GC cycle.
1798 update_should_unload_classes();
1799 _full_gc_requested = false; // acks all outstanding full gc requests
1800 _full_gc_cause = GCCause::_no_gc;
1801 // Signal that we are about to start a collection
1802 gch->increment_total_full_collections(); // ... starting a collection cycle
1803 _collection_count_start = gch->total_full_collections();
1804 }
1805
1806 // Used for PrintGC
1807 size_t prev_used;
1808 if (PrintGC && Verbose) {
1809 prev_used = _cmsGen->used();
1810 }
1811
1812 // The change of the collection state is normally done at this level;
1813 // the exceptions are phases that are executed while the world is
1814 // stopped. For those phases the change of state is done while the
1815 // world is stopped. For baton passing purposes this allows the
1816 // background collector to finish the phase and change state atomically.
1817 // The foreground collector cannot wait on a phase that is done
1818 // while the world is stopped because the foreground collector already
1819 // has the world stopped and would deadlock.
1820 while (_collectorState != Idling) {
1821 if (TraceCMSState) {
1822 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
1823 p2i(Thread::current()), _collectorState);
1824 }
1825 // The foreground collector
1826 // holds the Heap_lock throughout its collection.
1827 // holds the CMS token (but not the lock)
1828 // except while it is waiting for the background collector to yield.
1829 //
1830 // The foreground collector should be blocked (not for long)
1831 // if the background collector is about to start a phase
1832 // executed with world stopped. If the background
1833 // collector has already started such a phase, the
1834 // foreground collector is blocked waiting for the
1835 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1836 // are executed in the VM thread.
1837 //
1838 // The locking order is
1839 // PendingListLock (PLL) -- if applicable (FinalMarking)
1840 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1841 // CMS token (claimed in
1842 // stop_world_and_do() -->
1843 // safepoint_synchronize() -->
1844 // CMSThread::synchronize())
1845
1846 {
1847 // Check if the FG collector wants us to yield.
1848 CMSTokenSync x(true); // is cms thread
1849 if (waitForForegroundGC()) {
1850 // We yielded to a foreground GC, nothing more to be
1851 // done this round.
1852 assert(_foregroundGCShouldWait == false, "We set it to false in "
1853 "waitForForegroundGC()");
1854 if (TraceCMSState) {
1855 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1856 " exiting collection CMS state %d",
1857 p2i(Thread::current()), _collectorState);
1858 }
1859 return;
1860 } else {
1861 // The background collector can run but check to see if the
1862 // foreground collector has done a collection while the
1863 // background collector was waiting to get the CGC_lock
1864 // above. If yes, break so that _foregroundGCShouldWait
1865 // is cleared before returning.
1866 if (_collectorState == Idling) {
1867 break;
1868 }
1869 }
1870 }
1871
1872 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1873 "should be waiting");
1874
1875 switch (_collectorState) {
1876 case InitialMarking:
1877 {
1878 ReleaseForegroundGC x(this);
1879 stats().record_cms_begin();
1880 VM_CMS_Initial_Mark initial_mark_op(this);
1881 VMThread::execute(&initial_mark_op);
1882 }
1883 // The collector state may be any legal state at this point
1884 // since the background collector may have yielded to the
1885 // foreground collector.
1886 break;
1887 case Marking:
1888 // initial marking in checkpointRootsInitialWork has been completed
1889 if (markFromRoots()) { // we were successful
1890 assert(_collectorState == Precleaning, "Collector state should "
1891 "have changed");
1892 } else {
1893 assert(_foregroundGCIsActive, "Internal state inconsistency");
1894 }
1895 break;
1896 case Precleaning:
1897 // marking from roots in markFromRoots has been completed
1898 preclean();
1899 assert(_collectorState == AbortablePreclean ||
1900 _collectorState == FinalMarking,
1901 "Collector state should have changed");
1902 break;
1903 case AbortablePreclean:
1904 abortable_preclean();
1905 assert(_collectorState == FinalMarking, "Collector state should "
1906 "have changed");
1907 break;
1908 case FinalMarking:
1909 {
1910 ReleaseForegroundGC x(this);
1911
1912 VM_CMS_Final_Remark final_remark_op(this);
1913 VMThread::execute(&final_remark_op);
1914 }
1915 assert(_foregroundGCShouldWait, "block post-condition");
1916 break;
1917 case Sweeping:
1918 // final marking in checkpointRootsFinal has been completed
1919 sweep();
1920 assert(_collectorState == Resizing, "Collector state change "
1921 "to Resizing must be done under the free_list_lock");
1922
1923 case Resizing: {
1924 // Sweeping has been completed...
1925 // At this point the background collection has completed.
1926 // Don't move the call to compute_new_size() down
1927 // into code that might be executed if the background
1928 // collection was preempted.
1929 {
1930 ReleaseForegroundGC x(this); // unblock FG collection
1931 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1932 CMSTokenSync z(true); // not strictly needed.
1933 if (_collectorState == Resizing) {
1934 compute_new_size();
1935 save_heap_summary();
1936 _collectorState = Resetting;
1937 } else {
1938 assert(_collectorState == Idling, "The state should only change"
1939 " because the foreground collector has finished the collection");
1940 }
1941 }
1942 break;
1943 }
1944 case Resetting:
1945 // CMS heap resizing has been completed
1946 reset(true);
1947 assert(_collectorState == Idling, "Collector state should "
1948 "have changed");
1949
1950 MetaspaceGC::set_should_concurrent_collect(false);
1951
1952 stats().record_cms_end();
1953 // Don't move the concurrent_phases_end() and compute_new_size()
1954 // calls to here because a preempted background collection
1955 // has it's state set to "Resetting".
1956 break;
1957 case Idling:
1958 default:
1959 ShouldNotReachHere();
1960 break;
1961 }
1962 if (TraceCMSState) {
1963 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1964 p2i(Thread::current()), _collectorState);
1965 }
1966 assert(_foregroundGCShouldWait, "block post-condition");
1967 }
1968
1969 // Should this be in gc_epilogue?
1970 collector_policy()->counters()->update_counters();
1971
1972 {
1973 // Clear _foregroundGCShouldWait and, in the event that the
1974 // foreground collector is waiting, notify it, before
1975 // returning.
1976 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1977 _foregroundGCShouldWait = false;
1978 if (_foregroundGCIsActive) {
1979 CGC_lock->notify();
1980 }
1981 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1982 "Possible deadlock");
1983 }
1984 if (TraceCMSState) {
1985 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1986 " exiting collection CMS state %d",
1987 p2i(Thread::current()), _collectorState);
1988 }
1989 if (PrintGC && Verbose) {
1990 _cmsGen->print_heap_change(prev_used);
1991 }
1992 }
1993
1994 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1995 _cms_start_registered = true;
1996 _gc_timer_cm->register_gc_start();
1997 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1998 }
1999
2000 void CMSCollector::register_gc_end() {
2001 if (_cms_start_registered) {
2002 report_heap_summary(GCWhen::AfterGC);
2003
2004 _gc_timer_cm->register_gc_end();
2005 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2006 _cms_start_registered = false;
2007 }
2008 }
2009
2010 void CMSCollector::save_heap_summary() {
2011 GenCollectedHeap* gch = GenCollectedHeap::heap();
2012 _last_heap_summary = gch->create_heap_summary();
2013 _last_metaspace_summary = gch->create_metaspace_summary();
2014 }
2015
2016 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2017 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2018 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2019 }
2020
2021 bool CMSCollector::waitForForegroundGC() {
2022 bool res = false;
2023 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2024 "CMS thread should have CMS token");
2025 // Block the foreground collector until the
2026 // background collectors decides whether to
2027 // yield.
2028 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2029 _foregroundGCShouldWait = true;
2030 if (_foregroundGCIsActive) {
2031 // The background collector yields to the
2032 // foreground collector and returns a value
2033 // indicating that it has yielded. The foreground
2034 // collector can proceed.
2035 res = true;
2036 _foregroundGCShouldWait = false;
2037 ConcurrentMarkSweepThread::clear_CMS_flag(
2038 ConcurrentMarkSweepThread::CMS_cms_has_token);
2039 ConcurrentMarkSweepThread::set_CMS_flag(
2040 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2041 // Get a possibly blocked foreground thread going
2042 CGC_lock->notify();
2043 if (TraceCMSState) {
2044 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2045 p2i(Thread::current()), _collectorState);
2046 }
2047 while (_foregroundGCIsActive) {
2048 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2049 }
2050 ConcurrentMarkSweepThread::set_CMS_flag(
2051 ConcurrentMarkSweepThread::CMS_cms_has_token);
2052 ConcurrentMarkSweepThread::clear_CMS_flag(
2053 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2054 }
2055 if (TraceCMSState) {
2056 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2057 p2i(Thread::current()), _collectorState);
2058 }
2059 return res;
2060 }
2061
2062 // Because of the need to lock the free lists and other structures in
2063 // the collector, common to all the generations that the collector is
2064 // collecting, we need the gc_prologues of individual CMS generations
2065 // delegate to their collector. It may have been simpler had the
2066 // current infrastructure allowed one to call a prologue on a
2067 // collector. In the absence of that we have the generation's
2068 // prologue delegate to the collector, which delegates back
2069 // some "local" work to a worker method in the individual generations
2070 // that it's responsible for collecting, while itself doing any
2071 // work common to all generations it's responsible for. A similar
2072 // comment applies to the gc_epilogue()'s.
2073 // The role of the variable _between_prologue_and_epilogue is to
2074 // enforce the invocation protocol.
2075 void CMSCollector::gc_prologue(bool full) {
2076 // Call gc_prologue_work() for the CMSGen
2077 // we are responsible for.
2078
2079 // The following locking discipline assumes that we are only called
2080 // when the world is stopped.
2081 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2082
2083 // The CMSCollector prologue must call the gc_prologues for the
2084 // "generations" that it's responsible
2085 // for.
2086
2087 assert( Thread::current()->is_VM_thread()
2088 || ( CMSScavengeBeforeRemark
2089 && Thread::current()->is_ConcurrentGC_thread()),
2090 "Incorrect thread type for prologue execution");
2091
2092 if (_between_prologue_and_epilogue) {
2093 // We have already been invoked; this is a gc_prologue delegation
2094 // from yet another CMS generation that we are responsible for, just
2095 // ignore it since all relevant work has already been done.
2096 return;
2097 }
2098
2099 // set a bit saying prologue has been called; cleared in epilogue
2100 _between_prologue_and_epilogue = true;
2101 // Claim locks for common data structures, then call gc_prologue_work()
2102 // for each CMSGen.
2103
2104 getFreelistLocks(); // gets free list locks on constituent spaces
2105 bitMapLock()->lock_without_safepoint_check();
2106
2107 // Should call gc_prologue_work() for all cms gens we are responsible for
2108 bool duringMarking = _collectorState >= Marking
2109 && _collectorState < Sweeping;
2110
2111 // The young collections clear the modified oops state, which tells if
2112 // there are any modified oops in the class. The remark phase also needs
2113 // that information. Tell the young collection to save the union of all
2114 // modified klasses.
2115 if (duringMarking) {
2116 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2117 }
2118
2119 bool registerClosure = duringMarking;
2120
2121 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2122
2123 if (!full) {
2124 stats().record_gc0_begin();
2125 }
2126 }
2127
2128 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2129
2130 _capacity_at_prologue = capacity();
2131 _used_at_prologue = used();
2132
2133 // Delegate to CMScollector which knows how to coordinate between
2134 // this and any other CMS generations that it is responsible for
2135 // collecting.
2136 collector()->gc_prologue(full);
2137 }
2138
2139 // This is a "private" interface for use by this generation's CMSCollector.
2140 // Not to be called directly by any other entity (for instance,
2141 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2142 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2143 bool registerClosure, ModUnionClosure* modUnionClosure) {
2144 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2145 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2146 "Should be NULL");
2147 if (registerClosure) {
2148 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2149 }
2150 cmsSpace()->gc_prologue();
2151 // Clear stat counters
2152 NOT_PRODUCT(
2153 assert(_numObjectsPromoted == 0, "check");
2154 assert(_numWordsPromoted == 0, "check");
2155 if (Verbose && PrintGC) {
2156 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2157 SIZE_FORMAT" bytes concurrently",
2158 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2159 }
2160 _numObjectsAllocated = 0;
2161 _numWordsAllocated = 0;
2162 )
2163 }
2164
2165 void CMSCollector::gc_epilogue(bool full) {
2166 // The following locking discipline assumes that we are only called
2167 // when the world is stopped.
2168 assert(SafepointSynchronize::is_at_safepoint(),
2169 "world is stopped assumption");
2170
2171 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2172 // if linear allocation blocks need to be appropriately marked to allow the
2173 // the blocks to be parsable. We also check here whether we need to nudge the
2174 // CMS collector thread to start a new cycle (if it's not already active).
2175 assert( Thread::current()->is_VM_thread()
2176 || ( CMSScavengeBeforeRemark
2177 && Thread::current()->is_ConcurrentGC_thread()),
2178 "Incorrect thread type for epilogue execution");
2179
2180 if (!_between_prologue_and_epilogue) {
2181 // We have already been invoked; this is a gc_epilogue delegation
2182 // from yet another CMS generation that we are responsible for, just
2183 // ignore it since all relevant work has already been done.
2184 return;
2185 }
2186 assert(haveFreelistLocks(), "must have freelist locks");
2187 assert_lock_strong(bitMapLock());
2188
2189 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2190
2191 _cmsGen->gc_epilogue_work(full);
2192
2193 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2194 // in case sampling was not already enabled, enable it
2195 _start_sampling = true;
2196 }
2197 // reset _eden_chunk_array so sampling starts afresh
2198 _eden_chunk_index = 0;
2199
2200 size_t cms_used = _cmsGen->cmsSpace()->used();
2201
2202 // update performance counters - this uses a special version of
2203 // update_counters() that allows the utilization to be passed as a
2204 // parameter, avoiding multiple calls to used().
2205 //
2206 _cmsGen->update_counters(cms_used);
2207
2208 bitMapLock()->unlock();
2209 releaseFreelistLocks();
2210
2211 if (!CleanChunkPoolAsync) {
2212 Chunk::clean_chunk_pool();
2213 }
2214
2215 set_did_compact(false);
2216 _between_prologue_and_epilogue = false; // ready for next cycle
2217 }
2218
2219 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2220 collector()->gc_epilogue(full);
2221
2222 // Also reset promotion tracking in par gc thread states.
2223 for (uint i = 0; i < ParallelGCThreads; i++) {
2224 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2225 }
2226 }
2227
2228 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2229 assert(!incremental_collection_failed(), "Should have been cleared");
2230 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2231 cmsSpace()->gc_epilogue();
2232 // Print stat counters
2233 NOT_PRODUCT(
2234 assert(_numObjectsAllocated == 0, "check");
2235 assert(_numWordsAllocated == 0, "check");
2236 if (Verbose && PrintGC) {
2237 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2238 SIZE_FORMAT" bytes",
2239 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2240 }
2241 _numObjectsPromoted = 0;
2242 _numWordsPromoted = 0;
2243 )
2244
2245 if (PrintGC && Verbose) {
2246 // Call down the chain in contiguous_available needs the freelistLock
2247 // so print this out before releasing the freeListLock.
2248 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2249 contiguous_available());
2250 }
2251 }
2252
2253 #ifndef PRODUCT
2254 bool CMSCollector::have_cms_token() {
2255 Thread* thr = Thread::current();
2256 if (thr->is_VM_thread()) {
2257 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2258 } else if (thr->is_ConcurrentGC_thread()) {
2259 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2260 } else if (thr->is_GC_task_thread()) {
2261 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2262 ParGCRareEvent_lock->owned_by_self();
2263 }
2264 return false;
2265 }
2266 #endif
2267
2268 // Check reachability of the given heap address in CMS generation,
2269 // treating all other generations as roots.
2270 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2271 // We could "guarantee" below, rather than assert, but I'll
2272 // leave these as "asserts" so that an adventurous debugger
2273 // could try this in the product build provided some subset of
2274 // the conditions were met, provided they were interested in the
2275 // results and knew that the computation below wouldn't interfere
2276 // with other concurrent computations mutating the structures
2277 // being read or written.
2278 assert(SafepointSynchronize::is_at_safepoint(),
2279 "Else mutations in object graph will make answer suspect");
2280 assert(have_cms_token(), "Should hold cms token");
2281 assert(haveFreelistLocks(), "must hold free list locks");
2282 assert_lock_strong(bitMapLock());
2283
2284 // Clear the marking bit map array before starting, but, just
2285 // for kicks, first report if the given address is already marked
2286 gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2287 _markBitMap.isMarked(addr) ? "" : " not");
2288
2289 if (verify_after_remark()) {
2290 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2291 bool result = verification_mark_bm()->isMarked(addr);
2292 gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2293 result ? "IS" : "is NOT");
2294 return result;
2295 } else {
2296 gclog_or_tty->print_cr("Could not compute result");
2297 return false;
2298 }
2299 }
2300
2301
2302 void
2303 CMSCollector::print_on_error(outputStream* st) {
2304 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2305 if (collector != NULL) {
2306 CMSBitMap* bitmap = &collector->_markBitMap;
2307 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2308 bitmap->print_on_error(st, " Bits: ");
2309
2310 st->cr();
2311
2312 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2313 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2314 mut_bitmap->print_on_error(st, " Bits: ");
2315 }
2316 }
2317
2318 ////////////////////////////////////////////////////////
2319 // CMS Verification Support
2320 ////////////////////////////////////////////////////////
2321 // Following the remark phase, the following invariant
2322 // should hold -- each object in the CMS heap which is
2323 // marked in markBitMap() should be marked in the verification_mark_bm().
2324
2325 class VerifyMarkedClosure: public BitMapClosure {
2326 CMSBitMap* _marks;
2327 bool _failed;
2328
2329 public:
2330 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2331
2332 bool do_bit(size_t offset) {
2333 HeapWord* addr = _marks->offsetToHeapWord(offset);
2334 if (!_marks->isMarked(addr)) {
2335 oop(addr)->print_on(gclog_or_tty);
2336 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", p2i(addr));
2337 _failed = true;
2338 }
2339 return true;
2340 }
2341
2342 bool failed() { return _failed; }
2343 };
2344
2345 bool CMSCollector::verify_after_remark(bool silent) {
2346 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2347 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2348 static bool init = false;
2349
2350 assert(SafepointSynchronize::is_at_safepoint(),
2351 "Else mutations in object graph will make answer suspect");
2352 assert(have_cms_token(),
2353 "Else there may be mutual interference in use of "
2354 " verification data structures");
2355 assert(_collectorState > Marking && _collectorState <= Sweeping,
2356 "Else marking info checked here may be obsolete");
2357 assert(haveFreelistLocks(), "must hold free list locks");
2358 assert_lock_strong(bitMapLock());
2359
2360
2361 // Allocate marking bit map if not already allocated
2362 if (!init) { // first time
2363 if (!verification_mark_bm()->allocate(_span)) {
2364 return false;
2365 }
2366 init = true;
2367 }
2368
2369 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2370
2371 // Turn off refs discovery -- so we will be tracing through refs.
2372 // This is as intended, because by this time
2373 // GC must already have cleared any refs that need to be cleared,
2374 // and traced those that need to be marked; moreover,
2375 // the marking done here is not going to interfere in any
2376 // way with the marking information used by GC.
2377 NoRefDiscovery no_discovery(ref_processor());
2378
2379 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2380
2381 // Clear any marks from a previous round
2382 verification_mark_bm()->clear_all();
2383 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2384 verify_work_stacks_empty();
2385
2386 GenCollectedHeap* gch = GenCollectedHeap::heap();
2387 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2388 // Update the saved marks which may affect the root scans.
2389 gch->save_marks();
2390
2391 if (CMSRemarkVerifyVariant == 1) {
2392 // In this first variant of verification, we complete
2393 // all marking, then check if the new marks-vector is
2394 // a subset of the CMS marks-vector.
2395 verify_after_remark_work_1();
2396 } else if (CMSRemarkVerifyVariant == 2) {
2397 // In this second variant of verification, we flag an error
2398 // (i.e. an object reachable in the new marks-vector not reachable
2399 // in the CMS marks-vector) immediately, also indicating the
2400 // identify of an object (A) that references the unmarked object (B) --
2401 // presumably, a mutation to A failed to be picked up by preclean/remark?
2402 verify_after_remark_work_2();
2403 } else {
2404 warning("Unrecognized value " UINTX_FORMAT " for CMSRemarkVerifyVariant",
2405 CMSRemarkVerifyVariant);
2406 }
2407 if (!silent) gclog_or_tty->print(" done] ");
2408 return true;
2409 }
2410
2411 void CMSCollector::verify_after_remark_work_1() {
2412 ResourceMark rm;
2413 HandleMark hm;
2414 GenCollectedHeap* gch = GenCollectedHeap::heap();
2415
2416 // Get a clear set of claim bits for the roots processing to work with.
2417 ClassLoaderDataGraph::clear_claimed_marks();
2418
2419 // Mark from roots one level into CMS
2420 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2421 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2422
2423 gch->gen_process_roots(Generation::Old,
2424 true, // younger gens are roots
2425 true, // activate StrongRootsScope
2426 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2427 should_unload_classes(),
2428 ¬Older,
2429 NULL,
2430 NULL); // SSS: Provide correct closure
2431
2432 // Now mark from the roots
2433 MarkFromRootsClosure markFromRootsClosure(this, _span,
2434 verification_mark_bm(), verification_mark_stack(),
2435 false /* don't yield */, true /* verifying */);
2436 assert(_restart_addr == NULL, "Expected pre-condition");
2437 verification_mark_bm()->iterate(&markFromRootsClosure);
2438 while (_restart_addr != NULL) {
2439 // Deal with stack overflow: by restarting at the indicated
2440 // address.
2441 HeapWord* ra = _restart_addr;
2442 markFromRootsClosure.reset(ra);
2443 _restart_addr = NULL;
2444 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2445 }
2446 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2447 verify_work_stacks_empty();
2448
2449 // Marking completed -- now verify that each bit marked in
2450 // verification_mark_bm() is also marked in markBitMap(); flag all
2451 // errors by printing corresponding objects.
2452 VerifyMarkedClosure vcl(markBitMap());
2453 verification_mark_bm()->iterate(&vcl);
2454 if (vcl.failed()) {
2455 gclog_or_tty->print("Verification failed");
2456 gch->print_on(gclog_or_tty);
2457 fatal("CMS: failed marking verification after remark");
2458 }
2459 }
2460
2461 class VerifyKlassOopsKlassClosure : public KlassClosure {
2462 class VerifyKlassOopsClosure : public OopClosure {
2463 CMSBitMap* _bitmap;
2464 public:
2465 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2466 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2467 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2468 } _oop_closure;
2469 public:
2470 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2471 void do_klass(Klass* k) {
2472 k->oops_do(&_oop_closure);
2473 }
2474 };
2475
2476 void CMSCollector::verify_after_remark_work_2() {
2477 ResourceMark rm;
2478 HandleMark hm;
2479 GenCollectedHeap* gch = GenCollectedHeap::heap();
2480
2481 // Get a clear set of claim bits for the roots processing to work with.
2482 ClassLoaderDataGraph::clear_claimed_marks();
2483
2484 // Mark from roots one level into CMS
2485 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2486 markBitMap());
2487 CLDToOopClosure cld_closure(¬Older, true);
2488
2489 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2490
2491 gch->gen_process_roots(Generation::Old,
2492 true, // younger gens are roots
2493 true, // activate StrongRootsScope
2494 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2495 should_unload_classes(),
2496 ¬Older,
2497 NULL,
2498 &cld_closure);
2499
2500 // Now mark from the roots
2501 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2502 verification_mark_bm(), markBitMap(), verification_mark_stack());
2503 assert(_restart_addr == NULL, "Expected pre-condition");
2504 verification_mark_bm()->iterate(&markFromRootsClosure);
2505 while (_restart_addr != NULL) {
2506 // Deal with stack overflow: by restarting at the indicated
2507 // address.
2508 HeapWord* ra = _restart_addr;
2509 markFromRootsClosure.reset(ra);
2510 _restart_addr = NULL;
2511 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2512 }
2513 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2514 verify_work_stacks_empty();
2515
2516 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2517 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2518
2519 // Marking completed -- now verify that each bit marked in
2520 // verification_mark_bm() is also marked in markBitMap(); flag all
2521 // errors by printing corresponding objects.
2522 VerifyMarkedClosure vcl(markBitMap());
2523 verification_mark_bm()->iterate(&vcl);
2524 assert(!vcl.failed(), "Else verification above should not have succeeded");
2525 }
2526
2527 void ConcurrentMarkSweepGeneration::save_marks() {
2528 // delegate to CMS space
2529 cmsSpace()->save_marks();
2530 for (uint i = 0; i < ParallelGCThreads; i++) {
2531 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2532 }
2533 }
2534
2535 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2536 return cmsSpace()->no_allocs_since_save_marks();
2537 }
2538
2539 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2540 \
2541 void ConcurrentMarkSweepGeneration:: \
2542 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2543 cl->set_generation(this); \
2544 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2545 cl->reset_generation(); \
2546 save_marks(); \
2547 }
2548
2549 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2550
2551 void
2552 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2553 if (freelistLock()->owned_by_self()) {
2554 Generation::oop_iterate(cl);
2555 } else {
2556 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2557 Generation::oop_iterate(cl);
2558 }
2559 }
2560
2561 void
2562 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2563 if (freelistLock()->owned_by_self()) {
2564 Generation::object_iterate(cl);
2565 } else {
2566 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2567 Generation::object_iterate(cl);
2568 }
2569 }
2570
2571 void
2572 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2573 if (freelistLock()->owned_by_self()) {
2574 Generation::safe_object_iterate(cl);
2575 } else {
2576 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2577 Generation::safe_object_iterate(cl);
2578 }
2579 }
2580
2581 void
2582 ConcurrentMarkSweepGeneration::post_compact() {
2583 }
2584
2585 void
2586 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2587 // Fix the linear allocation blocks to look like free blocks.
2588
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()->prepare_for_verify();
2594 } else {
2595 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2596 cmsSpace()->prepare_for_verify();
2597 }
2598 }
2599
2600 void
2601 ConcurrentMarkSweepGeneration::verify() {
2602 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2603 // are not called when the heap is verified during universe initialization and
2604 // at vm shutdown.
2605 if (freelistLock()->owned_by_self()) {
2606 cmsSpace()->verify();
2607 } else {
2608 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2609 cmsSpace()->verify();
2610 }
2611 }
2612
2613 void CMSCollector::verify() {
2614 _cmsGen->verify();
2615 }
2616
2617 #ifndef PRODUCT
2618 bool CMSCollector::overflow_list_is_empty() const {
2619 assert(_num_par_pushes >= 0, "Inconsistency");
2620 if (_overflow_list == NULL) {
2621 assert(_num_par_pushes == 0, "Inconsistency");
2622 }
2623 return _overflow_list == NULL;
2624 }
2625
2626 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2627 // merely consolidate assertion checks that appear to occur together frequently.
2628 void CMSCollector::verify_work_stacks_empty() const {
2629 assert(_markStack.isEmpty(), "Marking stack should be empty");
2630 assert(overflow_list_is_empty(), "Overflow list should be empty");
2631 }
2632
2633 void CMSCollector::verify_overflow_empty() const {
2634 assert(overflow_list_is_empty(), "Overflow list should be empty");
2635 assert(no_preserved_marks(), "No preserved marks");
2636 }
2637 #endif // PRODUCT
2638
2639 // Decide if we want to enable class unloading as part of the
2640 // ensuing concurrent GC cycle. We will collect and
2641 // unload classes if it's the case that:
2642 // (1) an explicit gc request has been made and the flag
2643 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2644 // (2) (a) class unloading is enabled at the command line, and
2645 // (b) old gen is getting really full
2646 // NOTE: Provided there is no change in the state of the heap between
2647 // calls to this method, it should have idempotent results. Moreover,
2648 // its results should be monotonically increasing (i.e. going from 0 to 1,
2649 // but not 1 to 0) between successive calls between which the heap was
2650 // not collected. For the implementation below, it must thus rely on
2651 // the property that concurrent_cycles_since_last_unload()
2652 // will not decrease unless a collection cycle happened and that
2653 // _cmsGen->is_too_full() are
2654 // themselves also monotonic in that sense. See check_monotonicity()
2655 // below.
2656 void CMSCollector::update_should_unload_classes() {
2657 _should_unload_classes = false;
2658 // Condition 1 above
2659 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2660 _should_unload_classes = true;
2661 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2662 // Disjuncts 2.b.(i,ii,iii) above
2663 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2664 CMSClassUnloadingMaxInterval)
2665 || _cmsGen->is_too_full();
2666 }
2667 }
2668
2669 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2670 bool res = should_concurrent_collect();
2671 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2672 return res;
2673 }
2674
2675 void CMSCollector::setup_cms_unloading_and_verification_state() {
2676 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2677 || VerifyBeforeExit;
2678 const int rso = GenCollectedHeap::SO_AllCodeCache;
2679
2680 // We set the proper root for this CMS cycle here.
2681 if (should_unload_classes()) { // Should unload classes this cycle
2682 remove_root_scanning_option(rso); // Shrink the root set appropriately
2683 set_verifying(should_verify); // Set verification state for this cycle
2684 return; // Nothing else needs to be done at this time
2685 }
2686
2687 // Not unloading classes this cycle
2688 assert(!should_unload_classes(), "Inconsistency!");
2689
2690 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2691 // Include symbols, strings and code cache elements to prevent their resurrection.
2692 add_root_scanning_option(rso);
2693 set_verifying(true);
2694 } else if (verifying() && !should_verify) {
2695 // We were verifying, but some verification flags got disabled.
2696 set_verifying(false);
2697 // Exclude symbols, strings and code cache elements from root scanning to
2698 // reduce IM and RM pauses.
2699 remove_root_scanning_option(rso);
2700 }
2701 }
2702
2703
2704 #ifndef PRODUCT
2705 HeapWord* CMSCollector::block_start(const void* p) const {
2706 const HeapWord* addr = (HeapWord*)p;
2707 if (_span.contains(p)) {
2708 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2709 return _cmsGen->cmsSpace()->block_start(p);
2710 }
2711 }
2712 return NULL;
2713 }
2714 #endif
2715
2716 HeapWord*
2717 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2718 bool tlab,
2719 bool parallel) {
2720 CMSSynchronousYieldRequest yr;
2721 assert(!tlab, "Can't deal with TLAB allocation");
2722 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2723 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2724 if (GCExpandToAllocateDelayMillis > 0) {
2725 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2726 }
2727 return have_lock_and_allocate(word_size, tlab);
2728 }
2729
2730 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2731 size_t bytes,
2732 size_t expand_bytes,
2733 CMSExpansionCause::Cause cause)
2734 {
2735
2736 bool success = expand(bytes, expand_bytes);
2737
2738 // remember why we expanded; this information is used
2739 // by shouldConcurrentCollect() when making decisions on whether to start
2740 // a new CMS cycle.
2741 if (success) {
2742 set_expansion_cause(cause);
2743 if (PrintGCDetails && Verbose) {
2744 gclog_or_tty->print_cr("Expanded CMS gen for %s",
2745 CMSExpansionCause::to_string(cause));
2746 }
2747 }
2748 }
2749
2750 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2751 HeapWord* res = NULL;
2752 MutexLocker x(ParGCRareEvent_lock);
2753 while (true) {
2754 // Expansion by some other thread might make alloc OK now:
2755 res = ps->lab.alloc(word_sz);
2756 if (res != NULL) return res;
2757 // If there's not enough expansion space available, give up.
2758 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2759 return NULL;
2760 }
2761 // Otherwise, we try expansion.
2762 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2763 // Now go around the loop and try alloc again;
2764 // A competing par_promote might beat us to the expansion space,
2765 // so we may go around the loop again if promotion fails again.
2766 if (GCExpandToAllocateDelayMillis > 0) {
2767 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2768 }
2769 }
2770 }
2771
2772
2773 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2774 PromotionInfo* promo) {
2775 MutexLocker x(ParGCRareEvent_lock);
2776 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2777 while (true) {
2778 // Expansion by some other thread might make alloc OK now:
2779 if (promo->ensure_spooling_space()) {
2780 assert(promo->has_spooling_space(),
2781 "Post-condition of successful ensure_spooling_space()");
2782 return true;
2783 }
2784 // If there's not enough expansion space available, give up.
2785 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2786 return false;
2787 }
2788 // Otherwise, we try expansion.
2789 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2790 // Now go around the loop and try alloc again;
2791 // A competing allocation might beat us to the expansion space,
2792 // so we may go around the loop again if allocation fails again.
2793 if (GCExpandToAllocateDelayMillis > 0) {
2794 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2795 }
2796 }
2797 }
2798
2799 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2800 // Only shrink if a compaction was done so that all the free space
2801 // in the generation is in a contiguous block at the end.
2802 if (did_compact()) {
2803 CardGeneration::shrink(bytes);
2804 }
2805 }
2806
2807 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2808 assert_locked_or_safepoint(Heap_lock);
2809 }
2810
2811 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2812 assert_locked_or_safepoint(Heap_lock);
2813 assert_lock_strong(freelistLock());
2814 if (PrintGCDetails && Verbose) {
2815 warning("Shrinking of CMS not yet implemented");
2816 }
2817 return;
2818 }
2819
2820
2821 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2822 // phases.
2823 class CMSPhaseAccounting: public StackObj {
2824 public:
2825 CMSPhaseAccounting(CMSCollector *collector,
2826 const char *phase,
2827 const GCId gc_id,
2828 bool print_cr = true);
2829 ~CMSPhaseAccounting();
2830
2831 private:
2832 CMSCollector *_collector;
2833 const char *_phase;
2834 elapsedTimer _wallclock;
2835 bool _print_cr;
2836 const GCId _gc_id;
2837
2838 public:
2839 // Not MT-safe; so do not pass around these StackObj's
2840 // where they may be accessed by other threads.
2841 jlong wallclock_millis() {
2842 assert(_wallclock.is_active(), "Wall clock should not stop");
2843 _wallclock.stop(); // to record time
2844 jlong ret = _wallclock.milliseconds();
2845 _wallclock.start(); // restart
2846 return ret;
2847 }
2848 };
2849
2850 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2851 const char *phase,
2852 const GCId gc_id,
2853 bool print_cr) :
2854 _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
2855
2856 if (PrintCMSStatistics != 0) {
2857 _collector->resetYields();
2858 }
2859 if (PrintGCDetails) {
2860 gclog_or_tty->gclog_stamp(_gc_id);
2861 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
2862 _collector->cmsGen()->short_name(), _phase);
2863 }
2864 _collector->resetTimer();
2865 _wallclock.start();
2866 _collector->startTimer();
2867 }
2868
2869 CMSPhaseAccounting::~CMSPhaseAccounting() {
2870 assert(_wallclock.is_active(), "Wall clock should not have stopped");
2871 _collector->stopTimer();
2872 _wallclock.stop();
2873 if (PrintGCDetails) {
2874 gclog_or_tty->gclog_stamp(_gc_id);
2875 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
2876 _collector->cmsGen()->short_name(),
2877 _phase, _collector->timerValue(), _wallclock.seconds());
2878 if (_print_cr) {
2879 gclog_or_tty->cr();
2880 }
2881 if (PrintCMSStatistics != 0) {
2882 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
2883 _collector->yields());
2884 }
2885 }
2886 }
2887
2888 // CMS work
2889
2890 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2891 class CMSParMarkTask : public AbstractGangTask {
2892 protected:
2893 CMSCollector* _collector;
2894 uint _n_workers;
2895 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2896 AbstractGangTask(name),
2897 _collector(collector),
2898 _n_workers(n_workers) {}
2899 // Work method in support of parallel rescan ... of young gen spaces
2900 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2901 ContiguousSpace* space,
2902 HeapWord** chunk_array, size_t chunk_top);
2903 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2904 };
2905
2906 // Parallel initial mark task
2907 class CMSParInitialMarkTask: public CMSParMarkTask {
2908 public:
2909 CMSParInitialMarkTask(CMSCollector* collector, uint n_workers) :
2910 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
2911 collector, n_workers) {}
2912 void work(uint worker_id);
2913 };
2914
2915 // Checkpoint the roots into this generation from outside
2916 // this generation. [Note this initial checkpoint need only
2917 // be approximate -- we'll do a catch up phase subsequently.]
2918 void CMSCollector::checkpointRootsInitial() {
2919 assert(_collectorState == InitialMarking, "Wrong collector state");
2920 check_correct_thread_executing();
2921 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2922
2923 save_heap_summary();
2924 report_heap_summary(GCWhen::BeforeGC);
2925
2926 ReferenceProcessor* rp = ref_processor();
2927 assert(_restart_addr == NULL, "Control point invariant");
2928 {
2929 // acquire locks for subsequent manipulations
2930 MutexLockerEx x(bitMapLock(),
2931 Mutex::_no_safepoint_check_flag);
2932 checkpointRootsInitialWork();
2933 // enable ("weak") refs discovery
2934 rp->enable_discovery();
2935 _collectorState = Marking;
2936 }
2937 }
2938
2939 void CMSCollector::checkpointRootsInitialWork() {
2940 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2941 assert(_collectorState == InitialMarking, "just checking");
2942
2943 // If there has not been a GC[n-1] since last GC[n] cycle completed,
2944 // precede our marking with a collection of all
2945 // younger generations to keep floating garbage to a minimum.
2946 // XXX: we won't do this for now -- it's an optimization to be done later.
2947
2948 // already have locks
2949 assert_lock_strong(bitMapLock());
2950 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2951
2952 // Setup the verification and class unloading state for this
2953 // CMS collection cycle.
2954 setup_cms_unloading_and_verification_state();
2955
2956 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
2957 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
2958
2959 // Reset all the PLAB chunk arrays if necessary.
2960 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2961 reset_survivor_plab_arrays();
2962 }
2963
2964 ResourceMark rm;
2965 HandleMark hm;
2966
2967 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2968 GenCollectedHeap* gch = GenCollectedHeap::heap();
2969
2970 verify_work_stacks_empty();
2971 verify_overflow_empty();
2972
2973 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2974 // Update the saved marks which may affect the root scans.
2975 gch->save_marks();
2976
2977 // weak reference processing has not started yet.
2978 ref_processor()->set_enqueuing_is_done(false);
2979
2980 // Need to remember all newly created CLDs,
2981 // so that we can guarantee that the remark finds them.
2982 ClassLoaderDataGraph::remember_new_clds(true);
2983
2984 // Whenever a CLD is found, it will be claimed before proceeding to mark
2985 // the klasses. The claimed marks need to be cleared before marking starts.
2986 ClassLoaderDataGraph::clear_claimed_marks();
2987
2988 if (CMSPrintEdenSurvivorChunks) {
2989 print_eden_and_survivor_chunk_arrays();
2990 }
2991
2992 {
2993 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2994 if (CMSParallelInitialMarkEnabled) {
2995 // The parallel version.
2996 FlexibleWorkGang* workers = gch->workers();
2997 assert(workers != NULL, "Need parallel worker threads.");
2998 uint n_workers = workers->active_workers();
2999 CMSParInitialMarkTask tsk(this, n_workers);
3000 gch->set_par_threads(n_workers);
3001 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3002 if (n_workers > 1) {
3003 StrongRootsScope srs;
3004 workers->run_task(&tsk);
3005 } else {
3006 StrongRootsScope srs;
3007 tsk.work(0);
3008 }
3009 gch->set_par_threads(0);
3010 } else {
3011 // The serial version.
3012 CLDToOopClosure cld_closure(¬Older, true);
3013 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3014 gch->gen_process_roots(Generation::Old,
3015 true, // younger gens are roots
3016 true, // activate StrongRootsScope
3017 GenCollectedHeap::ScanningOption(roots_scanning_options()),
3018 should_unload_classes(),
3019 ¬Older,
3020 NULL,
3021 &cld_closure);
3022 }
3023 }
3024
3025 // Clear mod-union table; it will be dirtied in the prologue of
3026 // CMS generation per each younger generation collection.
3027
3028 assert(_modUnionTable.isAllClear(),
3029 "Was cleared in most recent final checkpoint phase"
3030 " or no bits are set in the gc_prologue before the start of the next "
3031 "subsequent marking phase.");
3032
3033 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3034
3035 // Save the end of the used_region of the constituent generations
3036 // to be used to limit the extent of sweep in each generation.
3037 save_sweep_limits();
3038 verify_overflow_empty();
3039 }
3040
3041 bool CMSCollector::markFromRoots() {
3042 // we might be tempted to assert that:
3043 // assert(!SafepointSynchronize::is_at_safepoint(),
3044 // "inconsistent argument?");
3045 // However that wouldn't be right, because it's possible that
3046 // a safepoint is indeed in progress as a younger generation
3047 // stop-the-world GC happens even as we mark in this generation.
3048 assert(_collectorState == Marking, "inconsistent state?");
3049 check_correct_thread_executing();
3050 verify_overflow_empty();
3051
3052 // Weak ref discovery note: We may be discovering weak
3053 // refs in this generation concurrent (but interleaved) with
3054 // weak ref discovery by a younger generation collector.
3055
3056 CMSTokenSyncWithLocks ts(true, bitMapLock());
3057 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3058 CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3059 bool res = markFromRootsWork();
3060 if (res) {
3061 _collectorState = Precleaning;
3062 } else { // We failed and a foreground collection wants to take over
3063 assert(_foregroundGCIsActive, "internal state inconsistency");
3064 assert(_restart_addr == NULL, "foreground will restart from scratch");
3065 if (PrintGCDetails) {
3066 gclog_or_tty->print_cr("bailing out to foreground collection");
3067 }
3068 }
3069 verify_overflow_empty();
3070 return res;
3071 }
3072
3073 bool CMSCollector::markFromRootsWork() {
3074 // iterate over marked bits in bit map, doing a full scan and mark
3075 // from these roots using the following algorithm:
3076 // . if oop is to the right of the current scan pointer,
3077 // mark corresponding bit (we'll process it later)
3078 // . else (oop is to left of current scan pointer)
3079 // push oop on marking stack
3080 // . drain the marking stack
3081
3082 // Note that when we do a marking step we need to hold the
3083 // bit map lock -- recall that direct allocation (by mutators)
3084 // and promotion (by younger generation collectors) is also
3085 // marking the bit map. [the so-called allocate live policy.]
3086 // Because the implementation of bit map marking is not
3087 // robust wrt simultaneous marking of bits in the same word,
3088 // we need to make sure that there is no such interference
3089 // between concurrent such updates.
3090
3091 // already have locks
3092 assert_lock_strong(bitMapLock());
3093
3094 verify_work_stacks_empty();
3095 verify_overflow_empty();
3096 bool result = false;
3097 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3098 result = do_marking_mt();
3099 } else {
3100 result = do_marking_st();
3101 }
3102 return result;
3103 }
3104
3105 // Forward decl
3106 class CMSConcMarkingTask;
3107
3108 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3109 CMSCollector* _collector;
3110 CMSConcMarkingTask* _task;
3111 public:
3112 virtual void yield();
3113
3114 // "n_threads" is the number of threads to be terminated.
3115 // "queue_set" is a set of work queues of other threads.
3116 // "collector" is the CMS collector associated with this task terminator.
3117 // "yield" indicates whether we need the gang as a whole to yield.
3118 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3119 ParallelTaskTerminator(n_threads, queue_set),
3120 _collector(collector) { }
3121
3122 void set_task(CMSConcMarkingTask* task) {
3123 _task = task;
3124 }
3125 };
3126
3127 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3128 CMSConcMarkingTask* _task;
3129 public:
3130 bool should_exit_termination();
3131 void set_task(CMSConcMarkingTask* task) {
3132 _task = task;
3133 }
3134 };
3135
3136 // MT Concurrent Marking Task
3137 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3138 CMSCollector* _collector;
3139 uint _n_workers; // requested/desired # workers
3140 bool _result;
3141 CompactibleFreeListSpace* _cms_space;
3142 char _pad_front[64]; // padding to ...
3143 HeapWord* _global_finger; // ... avoid sharing cache line
3144 char _pad_back[64];
3145 HeapWord* _restart_addr;
3146
3147 // Exposed here for yielding support
3148 Mutex* const _bit_map_lock;
3149
3150 // The per thread work queues, available here for stealing
3151 OopTaskQueueSet* _task_queues;
3152
3153 // Termination (and yielding) support
3154 CMSConcMarkingTerminator _term;
3155 CMSConcMarkingTerminatorTerminator _term_term;
3156
3157 public:
3158 CMSConcMarkingTask(CMSCollector* collector,
3159 CompactibleFreeListSpace* cms_space,
3160 YieldingFlexibleWorkGang* workers,
3161 OopTaskQueueSet* task_queues):
3162 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3163 _collector(collector),
3164 _cms_space(cms_space),
3165 _n_workers(0), _result(true),
3166 _task_queues(task_queues),
3167 _term(_n_workers, task_queues, _collector),
3168 _bit_map_lock(collector->bitMapLock())
3169 {
3170 _requested_size = _n_workers;
3171 _term.set_task(this);
3172 _term_term.set_task(this);
3173 _restart_addr = _global_finger = _cms_space->bottom();
3174 }
3175
3176
3177 OopTaskQueueSet* task_queues() { return _task_queues; }
3178
3179 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3180
3181 HeapWord** global_finger_addr() { return &_global_finger; }
3182
3183 CMSConcMarkingTerminator* terminator() { return &_term; }
3184
3185 virtual void set_for_termination(uint active_workers) {
3186 terminator()->reset_for_reuse(active_workers);
3187 }
3188
3189 void work(uint worker_id);
3190 bool should_yield() {
3191 return ConcurrentMarkSweepThread::should_yield()
3192 && !_collector->foregroundGCIsActive();
3193 }
3194
3195 virtual void coordinator_yield(); // stuff done by coordinator
3196 bool result() { return _result; }
3197
3198 void reset(HeapWord* ra) {
3199 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3200 _restart_addr = _global_finger = ra;
3201 _term.reset_for_reuse();
3202 }
3203
3204 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3205 OopTaskQueue* work_q);
3206
3207 private:
3208 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3209 void do_work_steal(int i);
3210 void bump_global_finger(HeapWord* f);
3211 };
3212
3213 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3214 assert(_task != NULL, "Error");
3215 return _task->yielding();
3216 // Note that we do not need the disjunct || _task->should_yield() above
3217 // because we want terminating threads to yield only if the task
3218 // is already in the midst of yielding, which happens only after at least one
3219 // thread has yielded.
3220 }
3221
3222 void CMSConcMarkingTerminator::yield() {
3223 if (_task->should_yield()) {
3224 _task->yield();
3225 } else {
3226 ParallelTaskTerminator::yield();
3227 }
3228 }
3229
3230 ////////////////////////////////////////////////////////////////
3231 // Concurrent Marking Algorithm Sketch
3232 ////////////////////////////////////////////////////////////////
3233 // Until all tasks exhausted (both spaces):
3234 // -- claim next available chunk
3235 // -- bump global finger via CAS
3236 // -- find first object that starts in this chunk
3237 // and start scanning bitmap from that position
3238 // -- scan marked objects for oops
3239 // -- CAS-mark target, and if successful:
3240 // . if target oop is above global finger (volatile read)
3241 // nothing to do
3242 // . if target oop is in chunk and above local finger
3243 // then nothing to do
3244 // . else push on work-queue
3245 // -- Deal with possible overflow issues:
3246 // . local work-queue overflow causes stuff to be pushed on
3247 // global (common) overflow queue
3248 // . always first empty local work queue
3249 // . then get a batch of oops from global work queue if any
3250 // . then do work stealing
3251 // -- When all tasks claimed (both spaces)
3252 // and local work queue empty,
3253 // then in a loop do:
3254 // . check global overflow stack; steal a batch of oops and trace
3255 // . try to steal from other threads oif GOS is empty
3256 // . if neither is available, offer termination
3257 // -- Terminate and return result
3258 //
3259 void CMSConcMarkingTask::work(uint worker_id) {
3260 elapsedTimer _timer;
3261 ResourceMark rm;
3262 HandleMark hm;
3263
3264 DEBUG_ONLY(_collector->verify_overflow_empty();)
3265
3266 // Before we begin work, our work queue should be empty
3267 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3268 // Scan the bitmap covering _cms_space, tracing through grey objects.
3269 _timer.start();
3270 do_scan_and_mark(worker_id, _cms_space);
3271 _timer.stop();
3272 if (PrintCMSStatistics != 0) {
3273 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3274 worker_id, _timer.seconds());
3275 // XXX: need xxx/xxx type of notation, two timers
3276 }
3277
3278 // ... do work stealing
3279 _timer.reset();
3280 _timer.start();
3281 do_work_steal(worker_id);
3282 _timer.stop();
3283 if (PrintCMSStatistics != 0) {
3284 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3285 worker_id, _timer.seconds());
3286 // XXX: need xxx/xxx type of notation, two timers
3287 }
3288 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3289 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3290 // Note that under the current task protocol, the
3291 // following assertion is true even of the spaces
3292 // expanded since the completion of the concurrent
3293 // marking. XXX This will likely change under a strict
3294 // ABORT semantics.
3295 // After perm removal the comparison was changed to
3296 // greater than or equal to from strictly greater than.
3297 // Before perm removal the highest address sweep would
3298 // have been at the end of perm gen but now is at the
3299 // end of the tenured gen.
3300 assert(_global_finger >= _cms_space->end(),
3301 "All tasks have been completed");
3302 DEBUG_ONLY(_collector->verify_overflow_empty();)
3303 }
3304
3305 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3306 HeapWord* read = _global_finger;
3307 HeapWord* cur = read;
3308 while (f > read) {
3309 cur = read;
3310 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3311 if (cur == read) {
3312 // our cas succeeded
3313 assert(_global_finger >= f, "protocol consistency");
3314 break;
3315 }
3316 }
3317 }
3318
3319 // This is really inefficient, and should be redone by
3320 // using (not yet available) block-read and -write interfaces to the
3321 // stack and the work_queue. XXX FIX ME !!!
3322 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3323 OopTaskQueue* work_q) {
3324 // Fast lock-free check
3325 if (ovflw_stk->length() == 0) {
3326 return false;
3327 }
3328 assert(work_q->size() == 0, "Shouldn't steal");
3329 MutexLockerEx ml(ovflw_stk->par_lock(),
3330 Mutex::_no_safepoint_check_flag);
3331 // Grab up to 1/4 the size of the work queue
3332 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3333 (size_t)ParGCDesiredObjsFromOverflowList);
3334 num = MIN2(num, ovflw_stk->length());
3335 for (int i = (int) num; i > 0; i--) {
3336 oop cur = ovflw_stk->pop();
3337 assert(cur != NULL, "Counted wrong?");
3338 work_q->push(cur);
3339 }
3340 return num > 0;
3341 }
3342
3343 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3344 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3345 int n_tasks = pst->n_tasks();
3346 // We allow that there may be no tasks to do here because
3347 // we are restarting after a stack overflow.
3348 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3349 uint nth_task = 0;
3350
3351 HeapWord* aligned_start = sp->bottom();
3352 if (sp->used_region().contains(_restart_addr)) {
3353 // Align down to a card boundary for the start of 0th task
3354 // for this space.
3355 aligned_start =
3356 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3357 CardTableModRefBS::card_size);
3358 }
3359
3360 size_t chunk_size = sp->marking_task_size();
3361 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3362 // Having claimed the nth task in this space,
3363 // compute the chunk that it corresponds to:
3364 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3365 aligned_start + (nth_task+1)*chunk_size);
3366 // Try and bump the global finger via a CAS;
3367 // note that we need to do the global finger bump
3368 // _before_ taking the intersection below, because
3369 // the task corresponding to that region will be
3370 // deemed done even if the used_region() expands
3371 // because of allocation -- as it almost certainly will
3372 // during start-up while the threads yield in the
3373 // closure below.
3374 HeapWord* finger = span.end();
3375 bump_global_finger(finger); // atomically
3376 // There are null tasks here corresponding to chunks
3377 // beyond the "top" address of the space.
3378 span = span.intersection(sp->used_region());
3379 if (!span.is_empty()) { // Non-null task
3380 HeapWord* prev_obj;
3381 assert(!span.contains(_restart_addr) || nth_task == 0,
3382 "Inconsistency");
3383 if (nth_task == 0) {
3384 // For the 0th task, we'll not need to compute a block_start.
3385 if (span.contains(_restart_addr)) {
3386 // In the case of a restart because of stack overflow,
3387 // we might additionally skip a chunk prefix.
3388 prev_obj = _restart_addr;
3389 } else {
3390 prev_obj = span.start();
3391 }
3392 } else {
3393 // We want to skip the first object because
3394 // the protocol is to scan any object in its entirety
3395 // that _starts_ in this span; a fortiori, any
3396 // object starting in an earlier span is scanned
3397 // as part of an earlier claimed task.
3398 // Below we use the "careful" version of block_start
3399 // so we do not try to navigate uninitialized objects.
3400 prev_obj = sp->block_start_careful(span.start());
3401 // Below we use a variant of block_size that uses the
3402 // Printezis bits to avoid waiting for allocated
3403 // objects to become initialized/parsable.
3404 while (prev_obj < span.start()) {
3405 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3406 if (sz > 0) {
3407 prev_obj += sz;
3408 } else {
3409 // In this case we may end up doing a bit of redundant
3410 // scanning, but that appears unavoidable, short of
3411 // locking the free list locks; see bug 6324141.
3412 break;
3413 }
3414 }
3415 }
3416 if (prev_obj < span.end()) {
3417 MemRegion my_span = MemRegion(prev_obj, span.end());
3418 // Do the marking work within a non-empty span --
3419 // the last argument to the constructor indicates whether the
3420 // iteration should be incremental with periodic yields.
3421 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3422 &_collector->_markBitMap,
3423 work_queue(i),
3424 &_collector->_markStack);
3425 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3426 } // else nothing to do for this task
3427 } // else nothing to do for this task
3428 }
3429 // We'd be tempted to assert here that since there are no
3430 // more tasks left to claim in this space, the global_finger
3431 // must exceed space->top() and a fortiori space->end(). However,
3432 // that would not quite be correct because the bumping of
3433 // global_finger occurs strictly after the claiming of a task,
3434 // so by the time we reach here the global finger may not yet
3435 // have been bumped up by the thread that claimed the last
3436 // task.
3437 pst->all_tasks_completed();
3438 }
3439
3440 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3441 private:
3442 CMSCollector* _collector;
3443 CMSConcMarkingTask* _task;
3444 MemRegion _span;
3445 CMSBitMap* _bit_map;
3446 CMSMarkStack* _overflow_stack;
3447 OopTaskQueue* _work_queue;
3448 protected:
3449 DO_OOP_WORK_DEFN
3450 public:
3451 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3452 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3453 MetadataAwareOopClosure(collector->ref_processor()),
3454 _collector(collector),
3455 _task(task),
3456 _span(collector->_span),
3457 _work_queue(work_queue),
3458 _bit_map(bit_map),
3459 _overflow_stack(overflow_stack)
3460 { }
3461 virtual void do_oop(oop* p);
3462 virtual void do_oop(narrowOop* p);
3463
3464 void trim_queue(size_t max);
3465 void handle_stack_overflow(HeapWord* lost);
3466 void do_yield_check() {
3467 if (_task->should_yield()) {
3468 _task->yield();
3469 }
3470 }
3471 };
3472
3473 // Grey object scanning during work stealing phase --
3474 // the salient assumption here is that any references
3475 // that are in these stolen objects being scanned must
3476 // already have been initialized (else they would not have
3477 // been published), so we do not need to check for
3478 // uninitialized objects before pushing here.
3479 void Par_ConcMarkingClosure::do_oop(oop obj) {
3480 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
3481 HeapWord* addr = (HeapWord*)obj;
3482 // Check if oop points into the CMS generation
3483 // and is not marked
3484 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3485 // a white object ...
3486 // If we manage to "claim" the object, by being the
3487 // first thread to mark it, then we push it on our
3488 // marking stack
3489 if (_bit_map->par_mark(addr)) { // ... now grey
3490 // push on work queue (grey set)
3491 bool simulate_overflow = false;
3492 NOT_PRODUCT(
3493 if (CMSMarkStackOverflowALot &&
3494 _collector->simulate_overflow()) {
3495 // simulate a stack overflow
3496 simulate_overflow = true;
3497 }
3498 )
3499 if (simulate_overflow ||
3500 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3501 // stack overflow
3502 if (PrintCMSStatistics != 0) {
3503 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3504 SIZE_FORMAT, _overflow_stack->capacity());
3505 }
3506 // We cannot assert that the overflow stack is full because
3507 // it may have been emptied since.
3508 assert(simulate_overflow ||
3509 _work_queue->size() == _work_queue->max_elems(),
3510 "Else push should have succeeded");
3511 handle_stack_overflow(addr);
3512 }
3513 } // Else, some other thread got there first
3514 do_yield_check();
3515 }
3516 }
3517
3518 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3519 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3520
3521 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3522 while (_work_queue->size() > max) {
3523 oop new_oop;
3524 if (_work_queue->pop_local(new_oop)) {
3525 assert(new_oop->is_oop(), "Should be an oop");
3526 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3527 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3528 new_oop->oop_iterate(this); // do_oop() above
3529 do_yield_check();
3530 }
3531 }
3532 }
3533
3534 // Upon stack overflow, we discard (part of) the stack,
3535 // remembering the least address amongst those discarded
3536 // in CMSCollector's _restart_address.
3537 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3538 // We need to do this under a mutex to prevent other
3539 // workers from interfering with the work done below.
3540 MutexLockerEx ml(_overflow_stack->par_lock(),
3541 Mutex::_no_safepoint_check_flag);
3542 // Remember the least grey address discarded
3543 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3544 _collector->lower_restart_addr(ra);
3545 _overflow_stack->reset(); // discard stack contents
3546 _overflow_stack->expand(); // expand the stack if possible
3547 }
3548
3549
3550 void CMSConcMarkingTask::do_work_steal(int i) {
3551 OopTaskQueue* work_q = work_queue(i);
3552 oop obj_to_scan;
3553 CMSBitMap* bm = &(_collector->_markBitMap);
3554 CMSMarkStack* ovflw = &(_collector->_markStack);
3555 int* seed = _collector->hash_seed(i);
3556 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3557 while (true) {
3558 cl.trim_queue(0);
3559 assert(work_q->size() == 0, "Should have been emptied above");
3560 if (get_work_from_overflow_stack(ovflw, work_q)) {
3561 // Can't assert below because the work obtained from the
3562 // overflow stack may already have been stolen from us.
3563 // assert(work_q->size() > 0, "Work from overflow stack");
3564 continue;
3565 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3566 assert(obj_to_scan->is_oop(), "Should be an oop");
3567 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3568 obj_to_scan->oop_iterate(&cl);
3569 } else if (terminator()->offer_termination(&_term_term)) {
3570 assert(work_q->size() == 0, "Impossible!");
3571 break;
3572 } else if (yielding() || should_yield()) {
3573 yield();
3574 }
3575 }
3576 }
3577
3578 // This is run by the CMS (coordinator) thread.
3579 void CMSConcMarkingTask::coordinator_yield() {
3580 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3581 "CMS thread should hold CMS token");
3582 // First give up the locks, then yield, then re-lock
3583 // We should probably use a constructor/destructor idiom to
3584 // do this unlock/lock or modify the MutexUnlocker class to
3585 // serve our purpose. XXX
3586 assert_lock_strong(_bit_map_lock);
3587 _bit_map_lock->unlock();
3588 ConcurrentMarkSweepThread::desynchronize(true);
3589 _collector->stopTimer();
3590 if (PrintCMSStatistics != 0) {
3591 _collector->incrementYields();
3592 }
3593
3594 // It is possible for whichever thread initiated the yield request
3595 // not to get a chance to wake up and take the bitmap lock between
3596 // this thread releasing it and reacquiring it. So, while the
3597 // should_yield() flag is on, let's sleep for a bit to give the
3598 // other thread a chance to wake up. The limit imposed on the number
3599 // of iterations is defensive, to avoid any unforseen circumstances
3600 // putting us into an infinite loop. Since it's always been this
3601 // (coordinator_yield()) method that was observed to cause the
3602 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3603 // which is by default non-zero. For the other seven methods that
3604 // also perform the yield operation, as are using a different
3605 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3606 // can enable the sleeping for those methods too, if necessary.
3607 // See 6442774.
3608 //
3609 // We really need to reconsider the synchronization between the GC
3610 // thread and the yield-requesting threads in the future and we
3611 // should really use wait/notify, which is the recommended
3612 // way of doing this type of interaction. Additionally, we should
3613 // consolidate the eight methods that do the yield operation and they
3614 // are almost identical into one for better maintainability and
3615 // readability. See 6445193.
3616 //
3617 // Tony 2006.06.29
3618 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3619 ConcurrentMarkSweepThread::should_yield() &&
3620 !CMSCollector::foregroundGCIsActive(); ++i) {
3621 os::sleep(Thread::current(), 1, false);
3622 }
3623
3624 ConcurrentMarkSweepThread::synchronize(true);
3625 _bit_map_lock->lock_without_safepoint_check();
3626 _collector->startTimer();
3627 }
3628
3629 bool CMSCollector::do_marking_mt() {
3630 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3631 uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3632 conc_workers()->active_workers(),
3633 Threads::number_of_non_daemon_threads());
3634 conc_workers()->set_active_workers(num_workers);
3635
3636 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3637
3638 CMSConcMarkingTask tsk(this,
3639 cms_space,
3640 conc_workers(),
3641 task_queues());
3642
3643 // Since the actual number of workers we get may be different
3644 // from the number we requested above, do we need to do anything different
3645 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3646 // class?? XXX
3647 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3648
3649 // Refs discovery is already non-atomic.
3650 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3651 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3652 conc_workers()->start_task(&tsk);
3653 while (tsk.yielded()) {
3654 tsk.coordinator_yield();
3655 conc_workers()->continue_task(&tsk);
3656 }
3657 // If the task was aborted, _restart_addr will be non-NULL
3658 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3659 while (_restart_addr != NULL) {
3660 // XXX For now we do not make use of ABORTED state and have not
3661 // yet implemented the right abort semantics (even in the original
3662 // single-threaded CMS case). That needs some more investigation
3663 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3664 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3665 // If _restart_addr is non-NULL, a marking stack overflow
3666 // occurred; we need to do a fresh marking iteration from the
3667 // indicated restart address.
3668 if (_foregroundGCIsActive) {
3669 // We may be running into repeated stack overflows, having
3670 // reached the limit of the stack size, while making very
3671 // slow forward progress. It may be best to bail out and
3672 // let the foreground collector do its job.
3673 // Clear _restart_addr, so that foreground GC
3674 // works from scratch. This avoids the headache of
3675 // a "rescan" which would otherwise be needed because
3676 // of the dirty mod union table & card table.
3677 _restart_addr = NULL;
3678 return false;
3679 }
3680 // Adjust the task to restart from _restart_addr
3681 tsk.reset(_restart_addr);
3682 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3683 _restart_addr);
3684 _restart_addr = NULL;
3685 // Get the workers going again
3686 conc_workers()->start_task(&tsk);
3687 while (tsk.yielded()) {
3688 tsk.coordinator_yield();
3689 conc_workers()->continue_task(&tsk);
3690 }
3691 }
3692 assert(tsk.completed(), "Inconsistency");
3693 assert(tsk.result() == true, "Inconsistency");
3694 return true;
3695 }
3696
3697 bool CMSCollector::do_marking_st() {
3698 ResourceMark rm;
3699 HandleMark hm;
3700
3701 // Temporarily make refs discovery single threaded (non-MT)
3702 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3703 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3704 &_markStack, CMSYield);
3705 // the last argument to iterate indicates whether the iteration
3706 // should be incremental with periodic yields.
3707 _markBitMap.iterate(&markFromRootsClosure);
3708 // If _restart_addr is non-NULL, a marking stack overflow
3709 // occurred; we need to do a fresh iteration from the
3710 // indicated restart address.
3711 while (_restart_addr != NULL) {
3712 if (_foregroundGCIsActive) {
3713 // We may be running into repeated stack overflows, having
3714 // reached the limit of the stack size, while making very
3715 // slow forward progress. It may be best to bail out and
3716 // let the foreground collector do its job.
3717 // Clear _restart_addr, so that foreground GC
3718 // works from scratch. This avoids the headache of
3719 // a "rescan" which would otherwise be needed because
3720 // of the dirty mod union table & card table.
3721 _restart_addr = NULL;
3722 return false; // indicating failure to complete marking
3723 }
3724 // Deal with stack overflow:
3725 // we restart marking from _restart_addr
3726 HeapWord* ra = _restart_addr;
3727 markFromRootsClosure.reset(ra);
3728 _restart_addr = NULL;
3729 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3730 }
3731 return true;
3732 }
3733
3734 void CMSCollector::preclean() {
3735 check_correct_thread_executing();
3736 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3737 verify_work_stacks_empty();
3738 verify_overflow_empty();
3739 _abort_preclean = false;
3740 if (CMSPrecleaningEnabled) {
3741 if (!CMSEdenChunksRecordAlways) {
3742 _eden_chunk_index = 0;
3743 }
3744 size_t used = get_eden_used();
3745 size_t capacity = get_eden_capacity();
3746 // Don't start sampling unless we will get sufficiently
3747 // many samples.
3748 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3749 * CMSScheduleRemarkEdenPenetration)) {
3750 _start_sampling = true;
3751 } else {
3752 _start_sampling = false;
3753 }
3754 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3755 CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3756 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3757 }
3758 CMSTokenSync x(true); // is cms thread
3759 if (CMSPrecleaningEnabled) {
3760 sample_eden();
3761 _collectorState = AbortablePreclean;
3762 } else {
3763 _collectorState = FinalMarking;
3764 }
3765 verify_work_stacks_empty();
3766 verify_overflow_empty();
3767 }
3768
3769 // Try and schedule the remark such that young gen
3770 // occupancy is CMSScheduleRemarkEdenPenetration %.
3771 void CMSCollector::abortable_preclean() {
3772 check_correct_thread_executing();
3773 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3774 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3775
3776 // If Eden's current occupancy is below this threshold,
3777 // immediately schedule the remark; else preclean
3778 // past the next scavenge in an effort to
3779 // schedule the pause as described above. By choosing
3780 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3781 // we will never do an actual abortable preclean cycle.
3782 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3783 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3784 CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3785 // We need more smarts in the abortable preclean
3786 // loop below to deal with cases where allocation
3787 // in young gen is very very slow, and our precleaning
3788 // is running a losing race against a horde of
3789 // mutators intent on flooding us with CMS updates
3790 // (dirty cards).
3791 // One, admittedly dumb, strategy is to give up
3792 // after a certain number of abortable precleaning loops
3793 // or after a certain maximum time. We want to make
3794 // this smarter in the next iteration.
3795 // XXX FIX ME!!! YSR
3796 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3797 while (!(should_abort_preclean() ||
3798 ConcurrentMarkSweepThread::should_terminate())) {
3799 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3800 cumworkdone += workdone;
3801 loops++;
3802 // Voluntarily terminate abortable preclean phase if we have
3803 // been at it for too long.
3804 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3805 loops >= CMSMaxAbortablePrecleanLoops) {
3806 if (PrintGCDetails) {
3807 gclog_or_tty->print(" CMS: abort preclean due to loops ");
3808 }
3809 break;
3810 }
3811 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3812 if (PrintGCDetails) {
3813 gclog_or_tty->print(" CMS: abort preclean due to time ");
3814 }
3815 break;
3816 }
3817 // If we are doing little work each iteration, we should
3818 // take a short break.
3819 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3820 // Sleep for some time, waiting for work to accumulate
3821 stopTimer();
3822 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3823 startTimer();
3824 waited++;
3825 }
3826 }
3827 if (PrintCMSStatistics > 0) {
3828 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3829 loops, waited, cumworkdone);
3830 }
3831 }
3832 CMSTokenSync x(true); // is cms thread
3833 if (_collectorState != Idling) {
3834 assert(_collectorState == AbortablePreclean,
3835 "Spontaneous state transition?");
3836 _collectorState = FinalMarking;
3837 } // Else, a foreground collection completed this CMS cycle.
3838 return;
3839 }
3840
3841 // Respond to an Eden sampling opportunity
3842 void CMSCollector::sample_eden() {
3843 // Make sure a young gc cannot sneak in between our
3844 // reading and recording of a sample.
3845 assert(Thread::current()->is_ConcurrentGC_thread(),
3846 "Only the cms thread may collect Eden samples");
3847 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3848 "Should collect samples while holding CMS token");
3849 if (!_start_sampling) {
3850 return;
3851 }
3852 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3853 // is populated by the young generation.
3854 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3855 if (_eden_chunk_index < _eden_chunk_capacity) {
3856 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3857 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3858 "Unexpected state of Eden");
3859 // We'd like to check that what we just sampled is an oop-start address;
3860 // however, we cannot do that here since the object may not yet have been
3861 // initialized. So we'll instead do the check when we _use_ this sample
3862 // later.
3863 if (_eden_chunk_index == 0 ||
3864 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3865 _eden_chunk_array[_eden_chunk_index-1])
3866 >= CMSSamplingGrain)) {
3867 _eden_chunk_index++; // commit sample
3868 }
3869 }
3870 }
3871 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3872 size_t used = get_eden_used();
3873 size_t capacity = get_eden_capacity();
3874 assert(used <= capacity, "Unexpected state of Eden");
3875 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3876 _abort_preclean = true;
3877 }
3878 }
3879 }
3880
3881
3882 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3883 assert(_collectorState == Precleaning ||
3884 _collectorState == AbortablePreclean, "incorrect state");
3885 ResourceMark rm;
3886 HandleMark hm;
3887
3888 // Precleaning is currently not MT but the reference processor
3889 // may be set for MT. Disable it temporarily here.
3890 ReferenceProcessor* rp = ref_processor();
3891 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3892
3893 // Do one pass of scrubbing the discovered reference lists
3894 // to remove any reference objects with strongly-reachable
3895 // referents.
3896 if (clean_refs) {
3897 CMSPrecleanRefsYieldClosure yield_cl(this);
3898 assert(rp->span().equals(_span), "Spans should be equal");
3899 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3900 &_markStack, true /* preclean */);
3901 CMSDrainMarkingStackClosure complete_trace(this,
3902 _span, &_markBitMap, &_markStack,
3903 &keep_alive, true /* preclean */);
3904
3905 // We don't want this step to interfere with a young
3906 // collection because we don't want to take CPU
3907 // or memory bandwidth away from the young GC threads
3908 // (which may be as many as there are CPUs).
3909 // Note that we don't need to protect ourselves from
3910 // interference with mutators because they can't
3911 // manipulate the discovered reference lists nor affect
3912 // the computed reachability of the referents, the
3913 // only properties manipulated by the precleaning
3914 // of these reference lists.
3915 stopTimer();
3916 CMSTokenSyncWithLocks x(true /* is cms thread */,
3917 bitMapLock());
3918 startTimer();
3919 sample_eden();
3920
3921 // The following will yield to allow foreground
3922 // collection to proceed promptly. XXX YSR:
3923 // The code in this method may need further
3924 // tweaking for better performance and some restructuring
3925 // for cleaner interfaces.
3926 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3927 rp->preclean_discovered_references(
3928 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3929 gc_timer, _gc_tracer_cm->gc_id());
3930 }
3931
3932 if (clean_survivor) { // preclean the active survivor space(s)
3933 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3934 &_markBitMap, &_modUnionTable,
3935 &_markStack, true /* precleaning phase */);
3936 stopTimer();
3937 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3938 bitMapLock());
3939 startTimer();
3940 unsigned int before_count =
3941 GenCollectedHeap::heap()->total_collections();
3942 SurvivorSpacePrecleanClosure
3943 sss_cl(this, _span, &_markBitMap, &_markStack,
3944 &pam_cl, before_count, CMSYield);
3945 _young_gen->from()->object_iterate_careful(&sss_cl);
3946 _young_gen->to()->object_iterate_careful(&sss_cl);
3947 }
3948 MarkRefsIntoAndScanClosure
3949 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3950 &_markStack, this, CMSYield,
3951 true /* precleaning phase */);
3952 // CAUTION: The following closure has persistent state that may need to
3953 // be reset upon a decrease in the sequence of addresses it
3954 // processes.
3955 ScanMarkedObjectsAgainCarefullyClosure
3956 smoac_cl(this, _span,
3957 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3958
3959 // Preclean dirty cards in ModUnionTable and CardTable using
3960 // appropriate convergence criterion;
3961 // repeat CMSPrecleanIter times unless we find that
3962 // we are losing.
3963 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3964 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3965 "Bad convergence multiplier");
3966 assert(CMSPrecleanThreshold >= 100,
3967 "Unreasonably low CMSPrecleanThreshold");
3968
3969 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3970 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3971 numIter < CMSPrecleanIter;
3972 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3973 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3974 if (Verbose && PrintGCDetails) {
3975 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3976 }
3977 // Either there are very few dirty cards, so re-mark
3978 // pause will be small anyway, or our pre-cleaning isn't
3979 // that much faster than the rate at which cards are being
3980 // dirtied, so we might as well stop and re-mark since
3981 // precleaning won't improve our re-mark time by much.
3982 if (curNumCards <= CMSPrecleanThreshold ||
3983 (numIter > 0 &&
3984 (curNumCards * CMSPrecleanDenominator >
3985 lastNumCards * CMSPrecleanNumerator))) {
3986 numIter++;
3987 cumNumCards += curNumCards;
3988 break;
3989 }
3990 }
3991
3992 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
3993
3994 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3995 cumNumCards += curNumCards;
3996 if (PrintGCDetails && PrintCMSStatistics != 0) {
3997 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3998 curNumCards, cumNumCards, numIter);
3999 }
4000 return cumNumCards; // as a measure of useful work done
4001 }
4002
4003 // PRECLEANING NOTES:
4004 // Precleaning involves:
4005 // . reading the bits of the modUnionTable and clearing the set bits.
4006 // . For the cards corresponding to the set bits, we scan the
4007 // objects on those cards. This means we need the free_list_lock
4008 // so that we can safely iterate over the CMS space when scanning
4009 // for oops.
4010 // . When we scan the objects, we'll be both reading and setting
4011 // marks in the marking bit map, so we'll need the marking bit map.
4012 // . For protecting _collector_state transitions, we take the CGC_lock.
4013 // Note that any races in the reading of of card table entries by the
4014 // CMS thread on the one hand and the clearing of those entries by the
4015 // VM thread or the setting of those entries by the mutator threads on the
4016 // other are quite benign. However, for efficiency it makes sense to keep
4017 // the VM thread from racing with the CMS thread while the latter is
4018 // dirty card info to the modUnionTable. We therefore also use the
4019 // CGC_lock to protect the reading of the card table and the mod union
4020 // table by the CM thread.
4021 // . We run concurrently with mutator updates, so scanning
4022 // needs to be done carefully -- we should not try to scan
4023 // potentially uninitialized objects.
4024 //
4025 // Locking strategy: While holding the CGC_lock, we scan over and
4026 // reset a maximal dirty range of the mod union / card tables, then lock
4027 // the free_list_lock and bitmap lock to do a full marking, then
4028 // release these locks; and repeat the cycle. This allows for a
4029 // certain amount of fairness in the sharing of these locks between
4030 // the CMS collector on the one hand, and the VM thread and the
4031 // mutators on the other.
4032
4033 // NOTE: preclean_mod_union_table() and preclean_card_table()
4034 // further below are largely identical; if you need to modify
4035 // one of these methods, please check the other method too.
4036
4037 size_t CMSCollector::preclean_mod_union_table(
4038 ConcurrentMarkSweepGeneration* gen,
4039 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4040 verify_work_stacks_empty();
4041 verify_overflow_empty();
4042
4043 // strategy: starting with the first card, accumulate contiguous
4044 // ranges of dirty cards; clear these cards, then scan the region
4045 // covered by these cards.
4046
4047 // Since all of the MUT is committed ahead, we can just use
4048 // that, in case the generations expand while we are precleaning.
4049 // It might also be fine to just use the committed part of the
4050 // generation, but we might potentially miss cards when the
4051 // generation is rapidly expanding while we are in the midst
4052 // of precleaning.
4053 HeapWord* startAddr = gen->reserved().start();
4054 HeapWord* endAddr = gen->reserved().end();
4055
4056 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4057
4058 size_t numDirtyCards, cumNumDirtyCards;
4059 HeapWord *nextAddr, *lastAddr;
4060 for (cumNumDirtyCards = numDirtyCards = 0,
4061 nextAddr = lastAddr = startAddr;
4062 nextAddr < endAddr;
4063 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4064
4065 ResourceMark rm;
4066 HandleMark hm;
4067
4068 MemRegion dirtyRegion;
4069 {
4070 stopTimer();
4071 // Potential yield point
4072 CMSTokenSync ts(true);
4073 startTimer();
4074 sample_eden();
4075 // Get dirty region starting at nextOffset (inclusive),
4076 // simultaneously clearing it.
4077 dirtyRegion =
4078 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4079 assert(dirtyRegion.start() >= nextAddr,
4080 "returned region inconsistent?");
4081 }
4082 // Remember where the next search should begin.
4083 // The returned region (if non-empty) is a right open interval,
4084 // so lastOffset is obtained from the right end of that
4085 // interval.
4086 lastAddr = dirtyRegion.end();
4087 // Should do something more transparent and less hacky XXX
4088 numDirtyCards =
4089 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4090
4091 // We'll scan the cards in the dirty region (with periodic
4092 // yields for foreground GC as needed).
4093 if (!dirtyRegion.is_empty()) {
4094 assert(numDirtyCards > 0, "consistency check");
4095 HeapWord* stop_point = NULL;
4096 stopTimer();
4097 // Potential yield point
4098 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4099 bitMapLock());
4100 startTimer();
4101 {
4102 verify_work_stacks_empty();
4103 verify_overflow_empty();
4104 sample_eden();
4105 stop_point =
4106 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4107 }
4108 if (stop_point != NULL) {
4109 // The careful iteration stopped early either because it found an
4110 // uninitialized object, or because we were in the midst of an
4111 // "abortable preclean", which should now be aborted. Redirty
4112 // the bits corresponding to the partially-scanned or unscanned
4113 // cards. We'll either restart at the next block boundary or
4114 // abort the preclean.
4115 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4116 "Should only be AbortablePreclean.");
4117 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4118 if (should_abort_preclean()) {
4119 break; // out of preclean loop
4120 } else {
4121 // Compute the next address at which preclean should pick up;
4122 // might need bitMapLock in order to read P-bits.
4123 lastAddr = next_card_start_after_block(stop_point);
4124 }
4125 }
4126 } else {
4127 assert(lastAddr == endAddr, "consistency check");
4128 assert(numDirtyCards == 0, "consistency check");
4129 break;
4130 }
4131 }
4132 verify_work_stacks_empty();
4133 verify_overflow_empty();
4134 return cumNumDirtyCards;
4135 }
4136
4137 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4138 // below are largely identical; if you need to modify
4139 // one of these methods, please check the other method too.
4140
4141 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4142 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4143 // strategy: it's similar to precleamModUnionTable above, in that
4144 // we accumulate contiguous ranges of dirty cards, mark these cards
4145 // precleaned, then scan the region covered by these cards.
4146 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4147 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4148
4149 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4150
4151 size_t numDirtyCards, cumNumDirtyCards;
4152 HeapWord *lastAddr, *nextAddr;
4153
4154 for (cumNumDirtyCards = numDirtyCards = 0,
4155 nextAddr = lastAddr = startAddr;
4156 nextAddr < endAddr;
4157 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4158
4159 ResourceMark rm;
4160 HandleMark hm;
4161
4162 MemRegion dirtyRegion;
4163 {
4164 // See comments in "Precleaning notes" above on why we
4165 // do this locking. XXX Could the locking overheads be
4166 // too high when dirty cards are sparse? [I don't think so.]
4167 stopTimer();
4168 CMSTokenSync x(true); // is cms thread
4169 startTimer();
4170 sample_eden();
4171 // Get and clear dirty region from card table
4172 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4173 MemRegion(nextAddr, endAddr),
4174 true,
4175 CardTableModRefBS::precleaned_card_val());
4176
4177 assert(dirtyRegion.start() >= nextAddr,
4178 "returned region inconsistent?");
4179 }
4180 lastAddr = dirtyRegion.end();
4181 numDirtyCards =
4182 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4183
4184 if (!dirtyRegion.is_empty()) {
4185 stopTimer();
4186 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4187 startTimer();
4188 sample_eden();
4189 verify_work_stacks_empty();
4190 verify_overflow_empty();
4191 HeapWord* stop_point =
4192 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4193 if (stop_point != NULL) {
4194 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4195 "Should only be AbortablePreclean.");
4196 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4197 if (should_abort_preclean()) {
4198 break; // out of preclean loop
4199 } else {
4200 // Compute the next address at which preclean should pick up.
4201 lastAddr = next_card_start_after_block(stop_point);
4202 }
4203 }
4204 } else {
4205 break;
4206 }
4207 }
4208 verify_work_stacks_empty();
4209 verify_overflow_empty();
4210 return cumNumDirtyCards;
4211 }
4212
4213 class PrecleanKlassClosure : public KlassClosure {
4214 KlassToOopClosure _cm_klass_closure;
4215 public:
4216 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4217 void do_klass(Klass* k) {
4218 if (k->has_accumulated_modified_oops()) {
4219 k->clear_accumulated_modified_oops();
4220
4221 _cm_klass_closure.do_klass(k);
4222 }
4223 }
4224 };
4225
4226 // The freelist lock is needed to prevent asserts, is it really needed?
4227 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4228
4229 cl->set_freelistLock(freelistLock);
4230
4231 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4232
4233 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4234 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4235 PrecleanKlassClosure preclean_klass_closure(cl);
4236 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4237
4238 verify_work_stacks_empty();
4239 verify_overflow_empty();
4240 }
4241
4242 void CMSCollector::checkpointRootsFinal() {
4243 assert(_collectorState == FinalMarking, "incorrect state transition?");
4244 check_correct_thread_executing();
4245 // world is stopped at this checkpoint
4246 assert(SafepointSynchronize::is_at_safepoint(),
4247 "world should be stopped");
4248 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4249
4250 verify_work_stacks_empty();
4251 verify_overflow_empty();
4252
4253 if (PrintGCDetails) {
4254 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4255 _young_gen->used() / K,
4256 _young_gen->capacity() / K);
4257 }
4258 {
4259 if (CMSScavengeBeforeRemark) {
4260 GenCollectedHeap* gch = GenCollectedHeap::heap();
4261 // Temporarily set flag to false, GCH->do_collection will
4262 // expect it to be false and set to true
4263 FlagSetting fl(gch->_is_gc_active, false);
4264 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4265 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4266 gch->do_collection(true, // full (i.e. force, see below)
4267 false, // !clear_all_soft_refs
4268 0, // size
4269 false, // is_tlab
4270 Generation::Young // type
4271 );
4272 }
4273 FreelistLocker x(this);
4274 MutexLockerEx y(bitMapLock(),
4275 Mutex::_no_safepoint_check_flag);
4276 checkpointRootsFinalWork();
4277 }
4278 verify_work_stacks_empty();
4279 verify_overflow_empty();
4280 }
4281
4282 void CMSCollector::checkpointRootsFinalWork() {
4283 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4284
4285 assert(haveFreelistLocks(), "must have free list locks");
4286 assert_lock_strong(bitMapLock());
4287
4288 ResourceMark rm;
4289 HandleMark hm;
4290
4291 GenCollectedHeap* gch = GenCollectedHeap::heap();
4292
4293 if (should_unload_classes()) {
4294 CodeCache::gc_prologue();
4295 }
4296 assert(haveFreelistLocks(), "must have free list locks");
4297 assert_lock_strong(bitMapLock());
4298
4299 // We might assume that we need not fill TLAB's when
4300 // CMSScavengeBeforeRemark is set, because we may have just done
4301 // a scavenge which would have filled all TLAB's -- and besides
4302 // Eden would be empty. This however may not always be the case --
4303 // for instance although we asked for a scavenge, it may not have
4304 // happened because of a JNI critical section. We probably need
4305 // a policy for deciding whether we can in that case wait until
4306 // the critical section releases and then do the remark following
4307 // the scavenge, and skip it here. In the absence of that policy,
4308 // or of an indication of whether the scavenge did indeed occur,
4309 // we cannot rely on TLAB's having been filled and must do
4310 // so here just in case a scavenge did not happen.
4311 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4312 // Update the saved marks which may affect the root scans.
4313 gch->save_marks();
4314
4315 if (CMSPrintEdenSurvivorChunks) {
4316 print_eden_and_survivor_chunk_arrays();
4317 }
4318
4319 {
4320 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4321
4322 // Note on the role of the mod union table:
4323 // Since the marker in "markFromRoots" marks concurrently with
4324 // mutators, it is possible for some reachable objects not to have been
4325 // scanned. For instance, an only reference to an object A was
4326 // placed in object B after the marker scanned B. Unless B is rescanned,
4327 // A would be collected. Such updates to references in marked objects
4328 // are detected via the mod union table which is the set of all cards
4329 // dirtied since the first checkpoint in this GC cycle and prior to
4330 // the most recent young generation GC, minus those cleaned up by the
4331 // concurrent precleaning.
4332 if (CMSParallelRemarkEnabled) {
4333 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
4334 do_remark_parallel();
4335 } else {
4336 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4337 _gc_timer_cm, _gc_tracer_cm->gc_id());
4338 do_remark_non_parallel();
4339 }
4340 }
4341 verify_work_stacks_empty();
4342 verify_overflow_empty();
4343
4344 {
4345 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4346 refProcessingWork();
4347 }
4348 verify_work_stacks_empty();
4349 verify_overflow_empty();
4350
4351 if (should_unload_classes()) {
4352 CodeCache::gc_epilogue();
4353 }
4354 JvmtiExport::gc_epilogue();
4355
4356 // If we encountered any (marking stack / work queue) overflow
4357 // events during the current CMS cycle, take appropriate
4358 // remedial measures, where possible, so as to try and avoid
4359 // recurrence of that condition.
4360 assert(_markStack.isEmpty(), "No grey objects");
4361 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4362 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4363 if (ser_ovflw > 0) {
4364 if (PrintCMSStatistics != 0) {
4365 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4366 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4367 ", kac_preclean="SIZE_FORMAT")",
4368 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4369 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4370 }
4371 _markStack.expand();
4372 _ser_pmc_remark_ovflw = 0;
4373 _ser_pmc_preclean_ovflw = 0;
4374 _ser_kac_preclean_ovflw = 0;
4375 _ser_kac_ovflw = 0;
4376 }
4377 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4378 if (PrintCMSStatistics != 0) {
4379 gclog_or_tty->print_cr("Work queue overflow (benign) "
4380 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4381 _par_pmc_remark_ovflw, _par_kac_ovflw);
4382 }
4383 _par_pmc_remark_ovflw = 0;
4384 _par_kac_ovflw = 0;
4385 }
4386 if (PrintCMSStatistics != 0) {
4387 if (_markStack._hit_limit > 0) {
4388 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4389 _markStack._hit_limit);
4390 }
4391 if (_markStack._failed_double > 0) {
4392 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4393 " current capacity "SIZE_FORMAT,
4394 _markStack._failed_double,
4395 _markStack.capacity());
4396 }
4397 }
4398 _markStack._hit_limit = 0;
4399 _markStack._failed_double = 0;
4400
4401 if ((VerifyAfterGC || VerifyDuringGC) &&
4402 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4403 verify_after_remark();
4404 }
4405
4406 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4407
4408 // Change under the freelistLocks.
4409 _collectorState = Sweeping;
4410 // Call isAllClear() under bitMapLock
4411 assert(_modUnionTable.isAllClear(),
4412 "Should be clear by end of the final marking");
4413 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4414 "Should be clear by end of the final marking");
4415 }
4416
4417 void CMSParInitialMarkTask::work(uint worker_id) {
4418 elapsedTimer _timer;
4419 ResourceMark rm;
4420 HandleMark hm;
4421
4422 // ---------- scan from roots --------------
4423 _timer.start();
4424 GenCollectedHeap* gch = GenCollectedHeap::heap();
4425 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4426
4427 // ---------- young gen roots --------------
4428 {
4429 work_on_young_gen_roots(worker_id, &par_mri_cl);
4430 _timer.stop();
4431 if (PrintCMSStatistics != 0) {
4432 gclog_or_tty->print_cr(
4433 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4434 worker_id, _timer.seconds());
4435 }
4436 }
4437
4438 // ---------- remaining roots --------------
4439 _timer.reset();
4440 _timer.start();
4441
4442 CLDToOopClosure cld_closure(&par_mri_cl, true);
4443
4444 gch->gen_process_roots(Generation::Old,
4445 false, // yg was scanned above
4446 false, // this is parallel code
4447 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4448 _collector->should_unload_classes(),
4449 &par_mri_cl,
4450 NULL,
4451 &cld_closure);
4452 assert(_collector->should_unload_classes()
4453 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4454 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4455 _timer.stop();
4456 if (PrintCMSStatistics != 0) {
4457 gclog_or_tty->print_cr(
4458 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4459 worker_id, _timer.seconds());
4460 }
4461 }
4462
4463 // Parallel remark task
4464 class CMSParRemarkTask: public CMSParMarkTask {
4465 CompactibleFreeListSpace* _cms_space;
4466
4467 // The per-thread work queues, available here for stealing.
4468 OopTaskQueueSet* _task_queues;
4469 ParallelTaskTerminator _term;
4470
4471 public:
4472 // A value of 0 passed to n_workers will cause the number of
4473 // workers to be taken from the active workers in the work gang.
4474 CMSParRemarkTask(CMSCollector* collector,
4475 CompactibleFreeListSpace* cms_space,
4476 uint n_workers, FlexibleWorkGang* workers,
4477 OopTaskQueueSet* task_queues):
4478 CMSParMarkTask("Rescan roots and grey objects in parallel",
4479 collector, n_workers),
4480 _cms_space(cms_space),
4481 _task_queues(task_queues),
4482 _term(n_workers, task_queues) { }
4483
4484 OopTaskQueueSet* task_queues() { return _task_queues; }
4485
4486 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4487
4488 ParallelTaskTerminator* terminator() { return &_term; }
4489 uint n_workers() { return _n_workers; }
4490
4491 void work(uint worker_id);
4492
4493 private:
4494 // ... of dirty cards in old space
4495 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4496 Par_MarkRefsIntoAndScanClosure* cl);
4497
4498 // ... work stealing for the above
4499 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4500 };
4501
4502 class RemarkKlassClosure : public KlassClosure {
4503 KlassToOopClosure _cm_klass_closure;
4504 public:
4505 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4506 void do_klass(Klass* k) {
4507 // Check if we have modified any oops in the Klass during the concurrent marking.
4508 if (k->has_accumulated_modified_oops()) {
4509 k->clear_accumulated_modified_oops();
4510
4511 // We could have transfered the current modified marks to the accumulated marks,
4512 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4513 } else if (k->has_modified_oops()) {
4514 // Don't clear anything, this info is needed by the next young collection.
4515 } else {
4516 // No modified oops in the Klass.
4517 return;
4518 }
4519
4520 // The klass has modified fields, need to scan the klass.
4521 _cm_klass_closure.do_klass(k);
4522 }
4523 };
4524
4525 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4526 ParNewGeneration* young_gen = _collector->_young_gen;
4527 ContiguousSpace* eden_space = young_gen->eden();
4528 ContiguousSpace* from_space = young_gen->from();
4529 ContiguousSpace* to_space = young_gen->to();
4530
4531 HeapWord** eca = _collector->_eden_chunk_array;
4532 size_t ect = _collector->_eden_chunk_index;
4533 HeapWord** sca = _collector->_survivor_chunk_array;
4534 size_t sct = _collector->_survivor_chunk_index;
4535
4536 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4537 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4538
4539 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4540 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4541 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4542 }
4543
4544 // work_queue(i) is passed to the closure
4545 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
4546 // also is passed to do_dirty_card_rescan_tasks() and to
4547 // do_work_steal() to select the i-th task_queue.
4548
4549 void CMSParRemarkTask::work(uint worker_id) {
4550 elapsedTimer _timer;
4551 ResourceMark rm;
4552 HandleMark hm;
4553
4554 // ---------- rescan from roots --------------
4555 _timer.start();
4556 GenCollectedHeap* gch = GenCollectedHeap::heap();
4557 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4558 _collector->_span, _collector->ref_processor(),
4559 &(_collector->_markBitMap),
4560 work_queue(worker_id));
4561
4562 // Rescan young gen roots first since these are likely
4563 // coarsely partitioned and may, on that account, constitute
4564 // the critical path; thus, it's best to start off that
4565 // work first.
4566 // ---------- young gen roots --------------
4567 {
4568 work_on_young_gen_roots(worker_id, &par_mrias_cl);
4569 _timer.stop();
4570 if (PrintCMSStatistics != 0) {
4571 gclog_or_tty->print_cr(
4572 "Finished young gen rescan work in %dth thread: %3.3f sec",
4573 worker_id, _timer.seconds());
4574 }
4575 }
4576
4577 // ---------- remaining roots --------------
4578 _timer.reset();
4579 _timer.start();
4580 gch->gen_process_roots(Generation::Old,
4581 false, // yg was scanned above
4582 false, // this is parallel code
4583 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4584 _collector->should_unload_classes(),
4585 &par_mrias_cl,
4586 NULL,
4587 NULL); // The dirty klasses will be handled below
4588
4589 assert(_collector->should_unload_classes()
4590 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4591 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4592 _timer.stop();
4593 if (PrintCMSStatistics != 0) {
4594 gclog_or_tty->print_cr(
4595 "Finished remaining root rescan work in %dth thread: %3.3f sec",
4596 worker_id, _timer.seconds());
4597 }
4598
4599 // ---------- unhandled CLD scanning ----------
4600 if (worker_id == 0) { // Single threaded at the moment.
4601 _timer.reset();
4602 _timer.start();
4603
4604 // Scan all new class loader data objects and new dependencies that were
4605 // introduced during concurrent marking.
4606 ResourceMark rm;
4607 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4608 for (int i = 0; i < array->length(); i++) {
4609 par_mrias_cl.do_class_loader_data(array->at(i));
4610 }
4611
4612 // We don't need to keep track of new CLDs anymore.
4613 ClassLoaderDataGraph::remember_new_clds(false);
4614
4615 _timer.stop();
4616 if (PrintCMSStatistics != 0) {
4617 gclog_or_tty->print_cr(
4618 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4619 worker_id, _timer.seconds());
4620 }
4621 }
4622
4623 // ---------- dirty klass scanning ----------
4624 if (worker_id == 0) { // Single threaded at the moment.
4625 _timer.reset();
4626 _timer.start();
4627
4628 // Scan all classes that was dirtied during the concurrent marking phase.
4629 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4630 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4631
4632 _timer.stop();
4633 if (PrintCMSStatistics != 0) {
4634 gclog_or_tty->print_cr(
4635 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4636 worker_id, _timer.seconds());
4637 }
4638 }
4639
4640 // We might have added oops to ClassLoaderData::_handles during the
4641 // concurrent marking phase. These oops point to newly allocated objects
4642 // that are guaranteed to be kept alive. Either by the direct allocation
4643 // code, or when the young collector processes the roots. Hence,
4644 // we don't have to revisit the _handles block during the remark phase.
4645
4646 // ---------- rescan dirty cards ------------
4647 _timer.reset();
4648 _timer.start();
4649
4650 // Do the rescan tasks for each of the two spaces
4651 // (cms_space) in turn.
4652 // "worker_id" is passed to select the task_queue for "worker_id"
4653 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4654 _timer.stop();
4655 if (PrintCMSStatistics != 0) {
4656 gclog_or_tty->print_cr(
4657 "Finished dirty card rescan work in %dth thread: %3.3f sec",
4658 worker_id, _timer.seconds());
4659 }
4660
4661 // ---------- steal work from other threads ...
4662 // ---------- ... and drain overflow list.
4663 _timer.reset();
4664 _timer.start();
4665 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4666 _timer.stop();
4667 if (PrintCMSStatistics != 0) {
4668 gclog_or_tty->print_cr(
4669 "Finished work stealing in %dth thread: %3.3f sec",
4670 worker_id, _timer.seconds());
4671 }
4672 }
4673
4674 // Note that parameter "i" is not used.
4675 void
4676 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4677 OopsInGenClosure* cl, ContiguousSpace* space,
4678 HeapWord** chunk_array, size_t chunk_top) {
4679 // Until all tasks completed:
4680 // . claim an unclaimed task
4681 // . compute region boundaries corresponding to task claimed
4682 // using chunk_array
4683 // . par_oop_iterate(cl) over that region
4684
4685 ResourceMark rm;
4686 HandleMark hm;
4687
4688 SequentialSubTasksDone* pst = space->par_seq_tasks();
4689
4690 uint nth_task = 0;
4691 uint n_tasks = pst->n_tasks();
4692
4693 if (n_tasks > 0) {
4694 assert(pst->valid(), "Uninitialized use?");
4695 HeapWord *start, *end;
4696 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4697 // We claimed task # nth_task; compute its boundaries.
4698 if (chunk_top == 0) { // no samples were taken
4699 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4700 start = space->bottom();
4701 end = space->top();
4702 } else if (nth_task == 0) {
4703 start = space->bottom();
4704 end = chunk_array[nth_task];
4705 } else if (nth_task < (uint)chunk_top) {
4706 assert(nth_task >= 1, "Control point invariant");
4707 start = chunk_array[nth_task - 1];
4708 end = chunk_array[nth_task];
4709 } else {
4710 assert(nth_task == (uint)chunk_top, "Control point invariant");
4711 start = chunk_array[chunk_top - 1];
4712 end = space->top();
4713 }
4714 MemRegion mr(start, end);
4715 // Verify that mr is in space
4716 assert(mr.is_empty() || space->used_region().contains(mr),
4717 "Should be in space");
4718 // Verify that "start" is an object boundary
4719 assert(mr.is_empty() || oop(mr.start())->is_oop(),
4720 "Should be an oop");
4721 space->par_oop_iterate(mr, cl);
4722 }
4723 pst->all_tasks_completed();
4724 }
4725 }
4726
4727 void
4728 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4729 CompactibleFreeListSpace* sp, int i,
4730 Par_MarkRefsIntoAndScanClosure* cl) {
4731 // Until all tasks completed:
4732 // . claim an unclaimed task
4733 // . compute region boundaries corresponding to task claimed
4734 // . transfer dirty bits ct->mut for that region
4735 // . apply rescanclosure to dirty mut bits for that region
4736
4737 ResourceMark rm;
4738 HandleMark hm;
4739
4740 OopTaskQueue* work_q = work_queue(i);
4741 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4742 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4743 // CAUTION: This closure has state that persists across calls to
4744 // the work method dirty_range_iterate_clear() in that it has
4745 // embedded in it a (subtype of) UpwardsObjectClosure. The
4746 // use of that state in the embedded UpwardsObjectClosure instance
4747 // assumes that the cards are always iterated (even if in parallel
4748 // by several threads) in monotonically increasing order per each
4749 // thread. This is true of the implementation below which picks
4750 // card ranges (chunks) in monotonically increasing order globally
4751 // and, a-fortiori, in monotonically increasing order per thread
4752 // (the latter order being a subsequence of the former).
4753 // If the work code below is ever reorganized into a more chaotic
4754 // work-partitioning form than the current "sequential tasks"
4755 // paradigm, the use of that persistent state will have to be
4756 // revisited and modified appropriately. See also related
4757 // bug 4756801 work on which should examine this code to make
4758 // sure that the changes there do not run counter to the
4759 // assumptions made here and necessary for correctness and
4760 // efficiency. Note also that this code might yield inefficient
4761 // behavior in the case of very large objects that span one or
4762 // more work chunks. Such objects would potentially be scanned
4763 // several times redundantly. Work on 4756801 should try and
4764 // address that performance anomaly if at all possible. XXX
4765 MemRegion full_span = _collector->_span;
4766 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4767 MarkFromDirtyCardsClosure
4768 greyRescanClosure(_collector, full_span, // entire span of interest
4769 sp, bm, work_q, cl);
4770
4771 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4772 assert(pst->valid(), "Uninitialized use?");
4773 uint nth_task = 0;
4774 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4775 MemRegion span = sp->used_region();
4776 HeapWord* start_addr = span.start();
4777 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4778 alignment);
4779 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4780 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4781 start_addr, "Check alignment");
4782 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4783 chunk_size, "Check alignment");
4784
4785 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4786 // Having claimed the nth_task, compute corresponding mem-region,
4787 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4788 // The alignment restriction ensures that we do not need any
4789 // synchronization with other gang-workers while setting or
4790 // clearing bits in thus chunk of the MUT.
4791 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4792 start_addr + (nth_task+1)*chunk_size);
4793 // The last chunk's end might be way beyond end of the
4794 // used region. In that case pull back appropriately.
4795 if (this_span.end() > end_addr) {
4796 this_span.set_end(end_addr);
4797 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4798 }
4799 // Iterate over the dirty cards covering this chunk, marking them
4800 // precleaned, and setting the corresponding bits in the mod union
4801 // table. Since we have been careful to partition at Card and MUT-word
4802 // boundaries no synchronization is needed between parallel threads.
4803 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4804 &modUnionClosure);
4805
4806 // Having transferred these marks into the modUnionTable,
4807 // rescan the marked objects on the dirty cards in the modUnionTable.
4808 // Even if this is at a synchronous collection, the initial marking
4809 // may have been done during an asynchronous collection so there
4810 // may be dirty bits in the mod-union table.
4811 _collector->_modUnionTable.dirty_range_iterate_clear(
4812 this_span, &greyRescanClosure);
4813 _collector->_modUnionTable.verifyNoOneBitsInRange(
4814 this_span.start(),
4815 this_span.end());
4816 }
4817 pst->all_tasks_completed(); // declare that i am done
4818 }
4819
4820 // . see if we can share work_queues with ParNew? XXX
4821 void
4822 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4823 int* seed) {
4824 OopTaskQueue* work_q = work_queue(i);
4825 NOT_PRODUCT(int num_steals = 0;)
4826 oop obj_to_scan;
4827 CMSBitMap* bm = &(_collector->_markBitMap);
4828
4829 while (true) {
4830 // Completely finish any left over work from (an) earlier round(s)
4831 cl->trim_queue(0);
4832 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4833 (size_t)ParGCDesiredObjsFromOverflowList);
4834 // Now check if there's any work in the overflow list
4835 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4836 // only affects the number of attempts made to get work from the
4837 // overflow list and does not affect the number of workers. Just
4838 // pass ParallelGCThreads so this behavior is unchanged.
4839 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4840 work_q,
4841 ParallelGCThreads)) {
4842 // found something in global overflow list;
4843 // not yet ready to go stealing work from others.
4844 // We'd like to assert(work_q->size() != 0, ...)
4845 // because we just took work from the overflow list,
4846 // but of course we can't since all of that could have
4847 // been already stolen from us.
4848 // "He giveth and He taketh away."
4849 continue;
4850 }
4851 // Verify that we have no work before we resort to stealing
4852 assert(work_q->size() == 0, "Have work, shouldn't steal");
4853 // Try to steal from other queues that have work
4854 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4855 NOT_PRODUCT(num_steals++;)
4856 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4857 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4858 // Do scanning work
4859 obj_to_scan->oop_iterate(cl);
4860 // Loop around, finish this work, and try to steal some more
4861 } else if (terminator()->offer_termination()) {
4862 break; // nirvana from the infinite cycle
4863 }
4864 }
4865 NOT_PRODUCT(
4866 if (PrintCMSStatistics != 0) {
4867 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
4868 }
4869 )
4870 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4871 "Else our work is not yet done");
4872 }
4873
4874 // Record object boundaries in _eden_chunk_array by sampling the eden
4875 // top in the slow-path eden object allocation code path and record
4876 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4877 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4878 // sampling in sample_eden() that activates during the part of the
4879 // preclean phase.
4880 void CMSCollector::sample_eden_chunk() {
4881 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4882 if (_eden_chunk_lock->try_lock()) {
4883 // Record a sample. This is the critical section. The contents
4884 // of the _eden_chunk_array have to be non-decreasing in the
4885 // address order.
4886 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4887 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4888 "Unexpected state of Eden");
4889 if (_eden_chunk_index == 0 ||
4890 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4891 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4892 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4893 _eden_chunk_index++; // commit sample
4894 }
4895 _eden_chunk_lock->unlock();
4896 }
4897 }
4898 }
4899
4900 // Return a thread-local PLAB recording array, as appropriate.
4901 void* CMSCollector::get_data_recorder(int thr_num) {
4902 if (_survivor_plab_array != NULL &&
4903 (CMSPLABRecordAlways ||
4904 (_collectorState > Marking && _collectorState < FinalMarking))) {
4905 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4906 ChunkArray* ca = &_survivor_plab_array[thr_num];
4907 ca->reset(); // clear it so that fresh data is recorded
4908 return (void*) ca;
4909 } else {
4910 return NULL;
4911 }
4912 }
4913
4914 // Reset all the thread-local PLAB recording arrays
4915 void CMSCollector::reset_survivor_plab_arrays() {
4916 for (uint i = 0; i < ParallelGCThreads; i++) {
4917 _survivor_plab_array[i].reset();
4918 }
4919 }
4920
4921 // Merge the per-thread plab arrays into the global survivor chunk
4922 // array which will provide the partitioning of the survivor space
4923 // for CMS initial scan and rescan.
4924 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4925 int no_of_gc_threads) {
4926 assert(_survivor_plab_array != NULL, "Error");
4927 assert(_survivor_chunk_array != NULL, "Error");
4928 assert(_collectorState == FinalMarking ||
4929 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4930 for (int j = 0; j < no_of_gc_threads; j++) {
4931 _cursor[j] = 0;
4932 }
4933 HeapWord* top = surv->top();
4934 size_t i;
4935 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4936 HeapWord* min_val = top; // Higher than any PLAB address
4937 uint min_tid = 0; // position of min_val this round
4938 for (int j = 0; j < no_of_gc_threads; j++) {
4939 ChunkArray* cur_sca = &_survivor_plab_array[j];
4940 if (_cursor[j] == cur_sca->end()) {
4941 continue;
4942 }
4943 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4944 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4945 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4946 if (cur_val < min_val) {
4947 min_tid = j;
4948 min_val = cur_val;
4949 } else {
4950 assert(cur_val < top, "All recorded addresses should be less");
4951 }
4952 }
4953 // At this point min_val and min_tid are respectively
4954 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4955 // and the thread (j) that witnesses that address.
4956 // We record this address in the _survivor_chunk_array[i]
4957 // and increment _cursor[min_tid] prior to the next round i.
4958 if (min_val == top) {
4959 break;
4960 }
4961 _survivor_chunk_array[i] = min_val;
4962 _cursor[min_tid]++;
4963 }
4964 // We are all done; record the size of the _survivor_chunk_array
4965 _survivor_chunk_index = i; // exclusive: [0, i)
4966 if (PrintCMSStatistics > 0) {
4967 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4968 }
4969 // Verify that we used up all the recorded entries
4970 #ifdef ASSERT
4971 size_t total = 0;
4972 for (int j = 0; j < no_of_gc_threads; j++) {
4973 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4974 total += _cursor[j];
4975 }
4976 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4977 // Check that the merged array is in sorted order
4978 if (total > 0) {
4979 for (size_t i = 0; i < total - 1; i++) {
4980 if (PrintCMSStatistics > 0) {
4981 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4982 i, p2i(_survivor_chunk_array[i]));
4983 }
4984 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4985 "Not sorted");
4986 }
4987 }
4988 #endif // ASSERT
4989 }
4990
4991 // Set up the space's par_seq_tasks structure for work claiming
4992 // for parallel initial scan and rescan of young gen.
4993 // See ParRescanTask where this is currently used.
4994 void
4995 CMSCollector::
4996 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4997 assert(n_threads > 0, "Unexpected n_threads argument");
4998
4999 // Eden space
5000 if (!_young_gen->eden()->is_empty()) {
5001 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
5002 assert(!pst->valid(), "Clobbering existing data?");
5003 // Each valid entry in [0, _eden_chunk_index) represents a task.
5004 size_t n_tasks = _eden_chunk_index + 1;
5005 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5006 // Sets the condition for completion of the subtask (how many threads
5007 // need to finish in order to be done).
5008 pst->set_n_threads(n_threads);
5009 pst->set_n_tasks((int)n_tasks);
5010 }
5011
5012 // Merge the survivor plab arrays into _survivor_chunk_array
5013 if (_survivor_plab_array != NULL) {
5014 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5015 } else {
5016 assert(_survivor_chunk_index == 0, "Error");
5017 }
5018
5019 // To space
5020 {
5021 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5022 assert(!pst->valid(), "Clobbering existing data?");
5023 // Sets the condition for completion of the subtask (how many threads
5024 // need to finish in order to be done).
5025 pst->set_n_threads(n_threads);
5026 pst->set_n_tasks(1);
5027 assert(pst->valid(), "Error");
5028 }
5029
5030 // From space
5031 {
5032 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5033 assert(!pst->valid(), "Clobbering existing data?");
5034 size_t n_tasks = _survivor_chunk_index + 1;
5035 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5036 // Sets the condition for completion of the subtask (how many threads
5037 // need to finish in order to be done).
5038 pst->set_n_threads(n_threads);
5039 pst->set_n_tasks((int)n_tasks);
5040 assert(pst->valid(), "Error");
5041 }
5042 }
5043
5044 // Parallel version of remark
5045 void CMSCollector::do_remark_parallel() {
5046 GenCollectedHeap* gch = GenCollectedHeap::heap();
5047 FlexibleWorkGang* workers = gch->workers();
5048 assert(workers != NULL, "Need parallel worker threads.");
5049 // Choose to use the number of GC workers most recently set
5050 // into "active_workers". If active_workers is not set, set it
5051 // to ParallelGCThreads.
5052 uint n_workers = workers->active_workers();
5053 if (n_workers == 0) {
5054 assert(n_workers > 0, "Should have been set during scavenge");
5055 n_workers = ParallelGCThreads;
5056 workers->set_active_workers(n_workers);
5057 }
5058 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5059
5060 CMSParRemarkTask tsk(this,
5061 cms_space,
5062 n_workers, workers, task_queues());
5063
5064 // Set up for parallel process_roots work.
5065 gch->set_par_threads(n_workers);
5066 // We won't be iterating over the cards in the card table updating
5067 // the younger_gen cards, so we shouldn't call the following else
5068 // the verification code as well as subsequent younger_refs_iterate
5069 // code would get confused. XXX
5070 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5071
5072 // The young gen rescan work will not be done as part of
5073 // process_roots (which currently doesn't know how to
5074 // parallelize such a scan), but rather will be broken up into
5075 // a set of parallel tasks (via the sampling that the [abortable]
5076 // preclean phase did of eden, plus the [two] tasks of
5077 // scanning the [two] survivor spaces. Further fine-grain
5078 // parallelization of the scanning of the survivor spaces
5079 // themselves, and of precleaning of the younger gen itself
5080 // is deferred to the future.
5081 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5082
5083 // The dirty card rescan work is broken up into a "sequence"
5084 // of parallel tasks (per constituent space) that are dynamically
5085 // claimed by the parallel threads.
5086 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5087
5088 // It turns out that even when we're using 1 thread, doing the work in a
5089 // separate thread causes wide variance in run times. We can't help this
5090 // in the multi-threaded case, but we special-case n=1 here to get
5091 // repeatable measurements of the 1-thread overhead of the parallel code.
5092 if (n_workers > 1) {
5093 // Make refs discovery MT-safe, if it isn't already: it may not
5094 // necessarily be so, since it's possible that we are doing
5095 // ST marking.
5096 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5097 StrongRootsScope srs;
5098 workers->run_task(&tsk);
5099 } else {
5100 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5101 StrongRootsScope srs;
5102 tsk.work(0);
5103 }
5104
5105 gch->set_par_threads(0); // 0 ==> non-parallel.
5106 // restore, single-threaded for now, any preserved marks
5107 // as a result of work_q overflow
5108 restore_preserved_marks_if_any();
5109 }
5110
5111 // Non-parallel version of remark
5112 void CMSCollector::do_remark_non_parallel() {
5113 ResourceMark rm;
5114 HandleMark hm;
5115 GenCollectedHeap* gch = GenCollectedHeap::heap();
5116 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5117
5118 MarkRefsIntoAndScanClosure
5119 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5120 &_markStack, this,
5121 false /* should_yield */, false /* not precleaning */);
5122 MarkFromDirtyCardsClosure
5123 markFromDirtyCardsClosure(this, _span,
5124 NULL, // space is set further below
5125 &_markBitMap, &_markStack, &mrias_cl);
5126 {
5127 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5128 // Iterate over the dirty cards, setting the corresponding bits in the
5129 // mod union table.
5130 {
5131 ModUnionClosure modUnionClosure(&_modUnionTable);
5132 _ct->ct_bs()->dirty_card_iterate(
5133 _cmsGen->used_region(),
5134 &modUnionClosure);
5135 }
5136 // Having transferred these marks into the modUnionTable, we just need
5137 // to rescan the marked objects on the dirty cards in the modUnionTable.
5138 // The initial marking may have been done during an asynchronous
5139 // collection so there may be dirty bits in the mod-union table.
5140 const int alignment =
5141 CardTableModRefBS::card_size * BitsPerWord;
5142 {
5143 // ... First handle dirty cards in CMS gen
5144 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5145 MemRegion ur = _cmsGen->used_region();
5146 HeapWord* lb = ur.start();
5147 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5148 MemRegion cms_span(lb, ub);
5149 _modUnionTable.dirty_range_iterate_clear(cms_span,
5150 &markFromDirtyCardsClosure);
5151 verify_work_stacks_empty();
5152 if (PrintCMSStatistics != 0) {
5153 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5154 markFromDirtyCardsClosure.num_dirty_cards());
5155 }
5156 }
5157 }
5158 if (VerifyDuringGC &&
5159 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5160 HandleMark hm; // Discard invalid handles created during verification
5161 Universe::verify();
5162 }
5163 {
5164 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5165
5166 verify_work_stacks_empty();
5167
5168 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5169 StrongRootsScope srs;
5170
5171 gch->gen_process_roots(Generation::Old,
5172 true, // younger gens as roots
5173 false, // use the local StrongRootsScope
5174 GenCollectedHeap::ScanningOption(roots_scanning_options()),
5175 should_unload_classes(),
5176 &mrias_cl,
5177 NULL,
5178 NULL); // The dirty klasses will be handled below
5179
5180 assert(should_unload_classes()
5181 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5182 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5183 }
5184
5185 {
5186 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5187
5188 verify_work_stacks_empty();
5189
5190 // Scan all class loader data objects that might have been introduced
5191 // during concurrent marking.
5192 ResourceMark rm;
5193 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5194 for (int i = 0; i < array->length(); i++) {
5195 mrias_cl.do_class_loader_data(array->at(i));
5196 }
5197
5198 // We don't need to keep track of new CLDs anymore.
5199 ClassLoaderDataGraph::remember_new_clds(false);
5200
5201 verify_work_stacks_empty();
5202 }
5203
5204 {
5205 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5206
5207 verify_work_stacks_empty();
5208
5209 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5210 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5211
5212 verify_work_stacks_empty();
5213 }
5214
5215 // We might have added oops to ClassLoaderData::_handles during the
5216 // concurrent marking phase. These oops point to newly allocated objects
5217 // that are guaranteed to be kept alive. Either by the direct allocation
5218 // code, or when the young collector processes the roots. Hence,
5219 // we don't have to revisit the _handles block during the remark phase.
5220
5221 verify_work_stacks_empty();
5222 // Restore evacuated mark words, if any, used for overflow list links
5223 if (!CMSOverflowEarlyRestoration) {
5224 restore_preserved_marks_if_any();
5225 }
5226 verify_overflow_empty();
5227 }
5228
5229 ////////////////////////////////////////////////////////
5230 // Parallel Reference Processing Task Proxy Class
5231 ////////////////////////////////////////////////////////
5232 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5233 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5234 CMSCollector* _collector;
5235 CMSBitMap* _mark_bit_map;
5236 const MemRegion _span;
5237 ProcessTask& _task;
5238
5239 public:
5240 CMSRefProcTaskProxy(ProcessTask& task,
5241 CMSCollector* collector,
5242 const MemRegion& span,
5243 CMSBitMap* mark_bit_map,
5244 AbstractWorkGang* workers,
5245 OopTaskQueueSet* task_queues):
5246 // XXX Should superclass AGTWOQ also know about AWG since it knows
5247 // about the task_queues used by the AWG? Then it could initialize
5248 // the terminator() object. See 6984287. The set_for_termination()
5249 // below is a temporary band-aid for the regression in 6984287.
5250 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5251 task_queues),
5252 _task(task),
5253 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5254 {
5255 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5256 "Inconsistency in _span");
5257 set_for_termination(workers->active_workers());
5258 }
5259
5260 OopTaskQueueSet* task_queues() { return queues(); }
5261
5262 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5263
5264 void do_work_steal(int i,
5265 CMSParDrainMarkingStackClosure* drain,
5266 CMSParKeepAliveClosure* keep_alive,
5267 int* seed);
5268
5269 virtual void work(uint worker_id);
5270 };
5271
5272 void CMSRefProcTaskProxy::work(uint worker_id) {
5273 ResourceMark rm;
5274 HandleMark hm;
5275 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5276 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5277 _mark_bit_map,
5278 work_queue(worker_id));
5279 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5280 _mark_bit_map,
5281 work_queue(worker_id));
5282 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5283 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5284 if (_task.marks_oops_alive()) {
5285 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5286 _collector->hash_seed(worker_id));
5287 }
5288 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5289 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5290 }
5291
5292 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5293 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5294 EnqueueTask& _task;
5295
5296 public:
5297 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5298 : AbstractGangTask("Enqueue reference objects in parallel"),
5299 _task(task)
5300 { }
5301
5302 virtual void work(uint worker_id)
5303 {
5304 _task.work(worker_id);
5305 }
5306 };
5307
5308 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5309 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5310 _span(span),
5311 _bit_map(bit_map),
5312 _work_queue(work_queue),
5313 _mark_and_push(collector, span, bit_map, work_queue),
5314 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5315 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5316 { }
5317
5318 // . see if we can share work_queues with ParNew? XXX
5319 void CMSRefProcTaskProxy::do_work_steal(int i,
5320 CMSParDrainMarkingStackClosure* drain,
5321 CMSParKeepAliveClosure* keep_alive,
5322 int* seed) {
5323 OopTaskQueue* work_q = work_queue(i);
5324 NOT_PRODUCT(int num_steals = 0;)
5325 oop obj_to_scan;
5326
5327 while (true) {
5328 // Completely finish any left over work from (an) earlier round(s)
5329 drain->trim_queue(0);
5330 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5331 (size_t)ParGCDesiredObjsFromOverflowList);
5332 // Now check if there's any work in the overflow list
5333 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5334 // only affects the number of attempts made to get work from the
5335 // overflow list and does not affect the number of workers. Just
5336 // pass ParallelGCThreads so this behavior is unchanged.
5337 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5338 work_q,
5339 ParallelGCThreads)) {
5340 // Found something in global overflow list;
5341 // not yet ready to go stealing work from others.
5342 // We'd like to assert(work_q->size() != 0, ...)
5343 // because we just took work from the overflow list,
5344 // but of course we can't, since all of that might have
5345 // been already stolen from us.
5346 continue;
5347 }
5348 // Verify that we have no work before we resort to stealing
5349 assert(work_q->size() == 0, "Have work, shouldn't steal");
5350 // Try to steal from other queues that have work
5351 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5352 NOT_PRODUCT(num_steals++;)
5353 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5354 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5355 // Do scanning work
5356 obj_to_scan->oop_iterate(keep_alive);
5357 // Loop around, finish this work, and try to steal some more
5358 } else if (terminator()->offer_termination()) {
5359 break; // nirvana from the infinite cycle
5360 }
5361 }
5362 NOT_PRODUCT(
5363 if (PrintCMSStatistics != 0) {
5364 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5365 }
5366 )
5367 }
5368
5369 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5370 {
5371 GenCollectedHeap* gch = GenCollectedHeap::heap();
5372 FlexibleWorkGang* workers = gch->workers();
5373 assert(workers != NULL, "Need parallel worker threads.");
5374 CMSRefProcTaskProxy rp_task(task, &_collector,
5375 _collector.ref_processor()->span(),
5376 _collector.markBitMap(),
5377 workers, _collector.task_queues());
5378 workers->run_task(&rp_task);
5379 }
5380
5381 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5382 {
5383
5384 GenCollectedHeap* gch = GenCollectedHeap::heap();
5385 FlexibleWorkGang* workers = gch->workers();
5386 assert(workers != NULL, "Need parallel worker threads.");
5387 CMSRefEnqueueTaskProxy enq_task(task);
5388 workers->run_task(&enq_task);
5389 }
5390
5391 void CMSCollector::refProcessingWork() {
5392 ResourceMark rm;
5393 HandleMark hm;
5394
5395 ReferenceProcessor* rp = ref_processor();
5396 assert(rp->span().equals(_span), "Spans should be equal");
5397 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5398 // Process weak references.
5399 rp->setup_policy(false);
5400 verify_work_stacks_empty();
5401
5402 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5403 &_markStack, false /* !preclean */);
5404 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5405 _span, &_markBitMap, &_markStack,
5406 &cmsKeepAliveClosure, false /* !preclean */);
5407 {
5408 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5409
5410 ReferenceProcessorStats stats;
5411 if (rp->processing_is_mt()) {
5412 // Set the degree of MT here. If the discovery is done MT, there
5413 // may have been a different number of threads doing the discovery
5414 // and a different number of discovered lists may have Ref objects.
5415 // That is OK as long as the Reference lists are balanced (see
5416 // balance_all_queues() and balance_queues()).
5417 GenCollectedHeap* gch = GenCollectedHeap::heap();
5418 uint active_workers = ParallelGCThreads;
5419 FlexibleWorkGang* workers = gch->workers();
5420 if (workers != NULL) {
5421 active_workers = workers->active_workers();
5422 // The expectation is that active_workers will have already
5423 // been set to a reasonable value. If it has not been set,
5424 // investigate.
5425 assert(active_workers > 0, "Should have been set during scavenge");
5426 }
5427 rp->set_active_mt_degree(active_workers);
5428 CMSRefProcTaskExecutor task_executor(*this);
5429 stats = rp->process_discovered_references(&_is_alive_closure,
5430 &cmsKeepAliveClosure,
5431 &cmsDrainMarkingStackClosure,
5432 &task_executor,
5433 _gc_timer_cm,
5434 _gc_tracer_cm->gc_id());
5435 } else {
5436 stats = rp->process_discovered_references(&_is_alive_closure,
5437 &cmsKeepAliveClosure,
5438 &cmsDrainMarkingStackClosure,
5439 NULL,
5440 _gc_timer_cm,
5441 _gc_tracer_cm->gc_id());
5442 }
5443 _gc_tracer_cm->report_gc_reference_stats(stats);
5444
5445 }
5446
5447 // This is the point where the entire marking should have completed.
5448 verify_work_stacks_empty();
5449
5450 if (should_unload_classes()) {
5451 {
5452 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5453
5454 // Unload classes and purge the SystemDictionary.
5455 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5456
5457 // Unload nmethods.
5458 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5459
5460 // Prune dead klasses from subklass/sibling/implementor lists.
5461 Klass::clean_weak_klass_links(&_is_alive_closure);
5462 }
5463
5464 {
5465 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5466 // Clean up unreferenced symbols in symbol table.
5467 SymbolTable::unlink();
5468 }
5469
5470 {
5471 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5472 // Delete entries for dead interned strings.
5473 StringTable::unlink(&_is_alive_closure);
5474 }
5475 }
5476
5477
5478 // Restore any preserved marks as a result of mark stack or
5479 // work queue overflow
5480 restore_preserved_marks_if_any(); // done single-threaded for now
5481
5482 rp->set_enqueuing_is_done(true);
5483 if (rp->processing_is_mt()) {
5484 rp->balance_all_queues();
5485 CMSRefProcTaskExecutor task_executor(*this);
5486 rp->enqueue_discovered_references(&task_executor);
5487 } else {
5488 rp->enqueue_discovered_references(NULL);
5489 }
5490 rp->verify_no_references_recorded();
5491 assert(!rp->discovery_enabled(), "should have been disabled");
5492 }
5493
5494 #ifndef PRODUCT
5495 void CMSCollector::check_correct_thread_executing() {
5496 Thread* t = Thread::current();
5497 // Only the VM thread or the CMS thread should be here.
5498 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5499 "Unexpected thread type");
5500 // If this is the vm thread, the foreground process
5501 // should not be waiting. Note that _foregroundGCIsActive is
5502 // true while the foreground collector is waiting.
5503 if (_foregroundGCShouldWait) {
5504 // We cannot be the VM thread
5505 assert(t->is_ConcurrentGC_thread(),
5506 "Should be CMS thread");
5507 } else {
5508 // We can be the CMS thread only if we are in a stop-world
5509 // phase of CMS collection.
5510 if (t->is_ConcurrentGC_thread()) {
5511 assert(_collectorState == InitialMarking ||
5512 _collectorState == FinalMarking,
5513 "Should be a stop-world phase");
5514 // The CMS thread should be holding the CMS_token.
5515 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5516 "Potential interference with concurrently "
5517 "executing VM thread");
5518 }
5519 }
5520 }
5521 #endif
5522
5523 void CMSCollector::sweep() {
5524 assert(_collectorState == Sweeping, "just checking");
5525 check_correct_thread_executing();
5526 verify_work_stacks_empty();
5527 verify_overflow_empty();
5528 increment_sweep_count();
5529 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5530
5531 _inter_sweep_timer.stop();
5532 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5533
5534 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5535 _intra_sweep_timer.reset();
5536 _intra_sweep_timer.start();
5537 {
5538 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5539 CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5540 // First sweep the old gen
5541 {
5542 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5543 bitMapLock());
5544 sweepWork(_cmsGen);
5545 }
5546
5547 // Update Universe::_heap_*_at_gc figures.
5548 // We need all the free list locks to make the abstract state
5549 // transition from Sweeping to Resetting. See detailed note
5550 // further below.
5551 {
5552 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5553 // Update heap occupancy information which is used as
5554 // input to soft ref clearing policy at the next gc.
5555 Universe::update_heap_info_at_gc();
5556 _collectorState = Resizing;
5557 }
5558 }
5559 verify_work_stacks_empty();
5560 verify_overflow_empty();
5561
5562 if (should_unload_classes()) {
5563 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5564 // requires that the virtual spaces are stable and not deleted.
5565 ClassLoaderDataGraph::set_should_purge(true);
5566 }
5567
5568 _intra_sweep_timer.stop();
5569 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5570
5571 _inter_sweep_timer.reset();
5572 _inter_sweep_timer.start();
5573
5574 // We need to use a monotonically non-decreasing time in ms
5575 // or we will see time-warp warnings and os::javaTimeMillis()
5576 // does not guarantee monotonicity.
5577 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5578 update_time_of_last_gc(now);
5579
5580 // NOTE on abstract state transitions:
5581 // Mutators allocate-live and/or mark the mod-union table dirty
5582 // based on the state of the collection. The former is done in
5583 // the interval [Marking, Sweeping] and the latter in the interval
5584 // [Marking, Sweeping). Thus the transitions into the Marking state
5585 // and out of the Sweeping state must be synchronously visible
5586 // globally to the mutators.
5587 // The transition into the Marking state happens with the world
5588 // stopped so the mutators will globally see it. Sweeping is
5589 // done asynchronously by the background collector so the transition
5590 // from the Sweeping state to the Resizing state must be done
5591 // under the freelistLock (as is the check for whether to
5592 // allocate-live and whether to dirty the mod-union table).
5593 assert(_collectorState == Resizing, "Change of collector state to"
5594 " Resizing must be done under the freelistLocks (plural)");
5595
5596 // Now that sweeping has been completed, we clear
5597 // the incremental_collection_failed flag,
5598 // thus inviting a younger gen collection to promote into
5599 // this generation. If such a promotion may still fail,
5600 // the flag will be set again when a young collection is
5601 // attempted.
5602 GenCollectedHeap* gch = GenCollectedHeap::heap();
5603 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5604 gch->update_full_collections_completed(_collection_count_start);
5605 }
5606
5607 // FIX ME!!! Looks like this belongs in CFLSpace, with
5608 // CMSGen merely delegating to it.
5609 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5610 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5611 HeapWord* minAddr = _cmsSpace->bottom();
5612 HeapWord* largestAddr =
5613 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5614 if (largestAddr == NULL) {
5615 // The dictionary appears to be empty. In this case
5616 // try to coalesce at the end of the heap.
5617 largestAddr = _cmsSpace->end();
5618 }
5619 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5620 size_t nearLargestOffset =
5621 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5622 if (PrintFLSStatistics != 0) {
5623 gclog_or_tty->print_cr(
5624 "CMS: Large Block: " PTR_FORMAT ";"
5625 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5626 p2i(largestAddr),
5627 p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5628 }
5629 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5630 }
5631
5632 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5633 return addr >= _cmsSpace->nearLargestChunk();
5634 }
5635
5636 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5637 return _cmsSpace->find_chunk_at_end();
5638 }
5639
5640 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5641 bool full) {
5642 // If the young generation has been collected, gather any statistics
5643 // that are of interest at this point.
5644 bool current_is_young = (current_generation == GenCollectedHeap::heap()->young_gen());
5645 if (!full && current_is_young) {
5646 // Gather statistics on the young generation collection.
5647 collector()->stats().record_gc0_end(used());
5648 }
5649 }
5650
5651 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen) {
5652 // We iterate over the space(s) underlying this generation,
5653 // checking the mark bit map to see if the bits corresponding
5654 // to specific blocks are marked or not. Blocks that are
5655 // marked are live and are not swept up. All remaining blocks
5656 // are swept up, with coalescing on-the-fly as we sweep up
5657 // contiguous free and/or garbage blocks:
5658 // We need to ensure that the sweeper synchronizes with allocators
5659 // and stop-the-world collectors. In particular, the following
5660 // locks are used:
5661 // . CMS token: if this is held, a stop the world collection cannot occur
5662 // . freelistLock: if this is held no allocation can occur from this
5663 // generation by another thread
5664 // . bitMapLock: if this is held, no other thread can access or update
5665 //
5666
5667 // Note that we need to hold the freelistLock if we use
5668 // block iterate below; else the iterator might go awry if
5669 // a mutator (or promotion) causes block contents to change
5670 // (for instance if the allocator divvies up a block).
5671 // If we hold the free list lock, for all practical purposes
5672 // young generation GC's can't occur (they'll usually need to
5673 // promote), so we might as well prevent all young generation
5674 // GC's while we do a sweeping step. For the same reason, we might
5675 // as well take the bit map lock for the entire duration
5676
5677 // check that we hold the requisite locks
5678 assert(have_cms_token(), "Should hold cms token");
5679 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5680 assert_lock_strong(gen->freelistLock());
5681 assert_lock_strong(bitMapLock());
5682
5683 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5684 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5685 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5686 _inter_sweep_estimate.padded_average(),
5687 _intra_sweep_estimate.padded_average());
5688 gen->setNearLargestChunk();
5689
5690 {
5691 SweepClosure sweepClosure(this, gen, &_markBitMap, CMSYield);
5692 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5693 // We need to free-up/coalesce garbage/blocks from a
5694 // co-terminal free run. This is done in the SweepClosure
5695 // destructor; so, do not remove this scope, else the
5696 // end-of-sweep-census below will be off by a little bit.
5697 }
5698 gen->cmsSpace()->sweep_completed();
5699 gen->cmsSpace()->endSweepFLCensus(sweep_count());
5700 if (should_unload_classes()) { // unloaded classes this cycle,
5701 _concurrent_cycles_since_last_unload = 0; // ... reset count
5702 } else { // did not unload classes,
5703 _concurrent_cycles_since_last_unload++; // ... increment count
5704 }
5705 }
5706
5707 // Reset CMS data structures (for now just the marking bit map)
5708 // preparatory for the next cycle.
5709 void CMSCollector::reset(bool concurrent) {
5710 if (concurrent) {
5711 CMSTokenSyncWithLocks ts(true, bitMapLock());
5712
5713 // If the state is not "Resetting", the foreground thread
5714 // has done a collection and the resetting.
5715 if (_collectorState != Resetting) {
5716 assert(_collectorState == Idling, "The state should only change"
5717 " because the foreground collector has finished the collection");
5718 return;
5719 }
5720
5721 // Clear the mark bitmap (no grey objects to start with)
5722 // for the next cycle.
5723 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5724 CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5725
5726 HeapWord* curAddr = _markBitMap.startWord();
5727 while (curAddr < _markBitMap.endWord()) {
5728 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5729 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5730 _markBitMap.clear_large_range(chunk);
5731 if (ConcurrentMarkSweepThread::should_yield() &&
5732 !foregroundGCIsActive() &&
5733 CMSYield) {
5734 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5735 "CMS thread should hold CMS token");
5736 assert_lock_strong(bitMapLock());
5737 bitMapLock()->unlock();
5738 ConcurrentMarkSweepThread::desynchronize(true);
5739 stopTimer();
5740 if (PrintCMSStatistics != 0) {
5741 incrementYields();
5742 }
5743
5744 // See the comment in coordinator_yield()
5745 for (unsigned i = 0; i < CMSYieldSleepCount &&
5746 ConcurrentMarkSweepThread::should_yield() &&
5747 !CMSCollector::foregroundGCIsActive(); ++i) {
5748 os::sleep(Thread::current(), 1, false);
5749 }
5750
5751 ConcurrentMarkSweepThread::synchronize(true);
5752 bitMapLock()->lock_without_safepoint_check();
5753 startTimer();
5754 }
5755 curAddr = chunk.end();
5756 }
5757 // A successful mostly concurrent collection has been done.
5758 // Because only the full (i.e., concurrent mode failure) collections
5759 // are being measured for gc overhead limits, clean the "near" flag
5760 // and count.
5761 size_policy()->reset_gc_overhead_limit_count();
5762 _collectorState = Idling;
5763 } else {
5764 // already have the lock
5765 assert(_collectorState == Resetting, "just checking");
5766 assert_lock_strong(bitMapLock());
5767 _markBitMap.clear_all();
5768 _collectorState = Idling;
5769 }
5770
5771 register_gc_end();
5772 }
5773
5774 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5775 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5776 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
5777 TraceCollectorStats tcs(counters());
5778
5779 switch (op) {
5780 case CMS_op_checkpointRootsInitial: {
5781 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5782 checkpointRootsInitial();
5783 if (PrintGC) {
5784 _cmsGen->printOccupancy("initial-mark");
5785 }
5786 break;
5787 }
5788 case CMS_op_checkpointRootsFinal: {
5789 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5790 checkpointRootsFinal();
5791 if (PrintGC) {
5792 _cmsGen->printOccupancy("remark");
5793 }
5794 break;
5795 }
5796 default:
5797 fatal("No such CMS_op");
5798 }
5799 }
5800
5801 #ifndef PRODUCT
5802 size_t const CMSCollector::skip_header_HeapWords() {
5803 return FreeChunk::header_size();
5804 }
5805
5806 // Try and collect here conditions that should hold when
5807 // CMS thread is exiting. The idea is that the foreground GC
5808 // thread should not be blocked if it wants to terminate
5809 // the CMS thread and yet continue to run the VM for a while
5810 // after that.
5811 void CMSCollector::verify_ok_to_terminate() const {
5812 assert(Thread::current()->is_ConcurrentGC_thread(),
5813 "should be called by CMS thread");
5814 assert(!_foregroundGCShouldWait, "should be false");
5815 // We could check here that all the various low-level locks
5816 // are not held by the CMS thread, but that is overkill; see
5817 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5818 // is checked.
5819 }
5820 #endif
5821
5822 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5823 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5824 "missing Printezis mark?");
5825 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5826 size_t size = pointer_delta(nextOneAddr + 1, addr);
5827 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5828 "alignment problem");
5829 assert(size >= 3, "Necessary for Printezis marks to work");
5830 return size;
5831 }
5832
5833 // A variant of the above (block_size_using_printezis_bits()) except
5834 // that we return 0 if the P-bits are not yet set.
5835 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5836 if (_markBitMap.isMarked(addr + 1)) {
5837 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5838 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5839 size_t size = pointer_delta(nextOneAddr + 1, addr);
5840 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5841 "alignment problem");
5842 assert(size >= 3, "Necessary for Printezis marks to work");
5843 return size;
5844 }
5845 return 0;
5846 }
5847
5848 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5849 size_t sz = 0;
5850 oop p = (oop)addr;
5851 if (p->klass_or_null() != NULL) {
5852 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5853 } else {
5854 sz = block_size_using_printezis_bits(addr);
5855 }
5856 assert(sz > 0, "size must be nonzero");
5857 HeapWord* next_block = addr + sz;
5858 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
5859 CardTableModRefBS::card_size);
5860 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
5861 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5862 "must be different cards");
5863 return next_card;
5864 }
5865
5866
5867 // CMS Bit Map Wrapper /////////////////////////////////////////
5868
5869 // Construct a CMS bit map infrastructure, but don't create the
5870 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5871 // further below.
5872 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5873 _bm(),
5874 _shifter(shifter),
5875 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5876 Monitor::_safepoint_check_sometimes) : NULL)
5877 {
5878 _bmStartWord = 0;
5879 _bmWordSize = 0;
5880 }
5881
5882 bool CMSBitMap::allocate(MemRegion mr) {
5883 _bmStartWord = mr.start();
5884 _bmWordSize = mr.word_size();
5885 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5886 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5887 if (!brs.is_reserved()) {
5888 warning("CMS bit map allocation failure");
5889 return false;
5890 }
5891 // For now we'll just commit all of the bit map up front.
5892 // Later on we'll try to be more parsimonious with swap.
5893 if (!_virtual_space.initialize(brs, brs.size())) {
5894 warning("CMS bit map backing store failure");
5895 return false;
5896 }
5897 assert(_virtual_space.committed_size() == brs.size(),
5898 "didn't reserve backing store for all of CMS bit map?");
5899 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5900 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5901 _bmWordSize, "inconsistency in bit map sizing");
5902 _bm.set_size(_bmWordSize >> _shifter);
5903
5904 // bm.clear(); // can we rely on getting zero'd memory? verify below
5905 assert(isAllClear(),
5906 "Expected zero'd memory from ReservedSpace constructor");
5907 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5908 "consistency check");
5909 return true;
5910 }
5911
5912 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5913 HeapWord *next_addr, *end_addr, *last_addr;
5914 assert_locked();
5915 assert(covers(mr), "out-of-range error");
5916 // XXX assert that start and end are appropriately aligned
5917 for (next_addr = mr.start(), end_addr = mr.end();
5918 next_addr < end_addr; next_addr = last_addr) {
5919 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5920 last_addr = dirty_region.end();
5921 if (!dirty_region.is_empty()) {
5922 cl->do_MemRegion(dirty_region);
5923 } else {
5924 assert(last_addr == end_addr, "program logic");
5925 return;
5926 }
5927 }
5928 }
5929
5930 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5931 _bm.print_on_error(st, prefix);
5932 }
5933
5934 #ifndef PRODUCT
5935 void CMSBitMap::assert_locked() const {
5936 CMSLockVerifier::assert_locked(lock());
5937 }
5938
5939 bool CMSBitMap::covers(MemRegion mr) const {
5940 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5941 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5942 "size inconsistency");
5943 return (mr.start() >= _bmStartWord) &&
5944 (mr.end() <= endWord());
5945 }
5946
5947 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5948 return (start >= _bmStartWord && (start + size) <= endWord());
5949 }
5950
5951 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5952 // verify that there are no 1 bits in the interval [left, right)
5953 FalseBitMapClosure falseBitMapClosure;
5954 iterate(&falseBitMapClosure, left, right);
5955 }
5956
5957 void CMSBitMap::region_invariant(MemRegion mr)
5958 {
5959 assert_locked();
5960 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5961 assert(!mr.is_empty(), "unexpected empty region");
5962 assert(covers(mr), "mr should be covered by bit map");
5963 // convert address range into offset range
5964 size_t start_ofs = heapWordToOffset(mr.start());
5965 // Make sure that end() is appropriately aligned
5966 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5967 (1 << (_shifter+LogHeapWordSize))),
5968 "Misaligned mr.end()");
5969 size_t end_ofs = heapWordToOffset(mr.end());
5970 assert(end_ofs > start_ofs, "Should mark at least one bit");
5971 }
5972
5973 #endif
5974
5975 bool CMSMarkStack::allocate(size_t size) {
5976 // allocate a stack of the requisite depth
5977 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5978 size * sizeof(oop)));
5979 if (!rs.is_reserved()) {
5980 warning("CMSMarkStack allocation failure");
5981 return false;
5982 }
5983 if (!_virtual_space.initialize(rs, rs.size())) {
5984 warning("CMSMarkStack backing store failure");
5985 return false;
5986 }
5987 assert(_virtual_space.committed_size() == rs.size(),
5988 "didn't reserve backing store for all of CMS stack?");
5989 _base = (oop*)(_virtual_space.low());
5990 _index = 0;
5991 _capacity = size;
5992 NOT_PRODUCT(_max_depth = 0);
5993 return true;
5994 }
5995
5996 // XXX FIX ME !!! In the MT case we come in here holding a
5997 // leaf lock. For printing we need to take a further lock
5998 // which has lower rank. We need to recalibrate the two
5999 // lock-ranks involved in order to be able to print the
6000 // messages below. (Or defer the printing to the caller.
6001 // For now we take the expedient path of just disabling the
6002 // messages for the problematic case.)
6003 void CMSMarkStack::expand() {
6004 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6005 if (_capacity == MarkStackSizeMax) {
6006 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6007 // We print a warning message only once per CMS cycle.
6008 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6009 }
6010 return;
6011 }
6012 // Double capacity if possible
6013 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6014 // Do not give up existing stack until we have managed to
6015 // get the double capacity that we desired.
6016 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6017 new_capacity * sizeof(oop)));
6018 if (rs.is_reserved()) {
6019 // Release the backing store associated with old stack
6020 _virtual_space.release();
6021 // Reinitialize virtual space for new stack
6022 if (!_virtual_space.initialize(rs, rs.size())) {
6023 fatal("Not enough swap for expanded marking stack");
6024 }
6025 _base = (oop*)(_virtual_space.low());
6026 _index = 0;
6027 _capacity = new_capacity;
6028 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6029 // Failed to double capacity, continue;
6030 // we print a detail message only once per CMS cycle.
6031 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6032 SIZE_FORMAT"K",
6033 _capacity / K, new_capacity / K);
6034 }
6035 }
6036
6037
6038 // Closures
6039 // XXX: there seems to be a lot of code duplication here;
6040 // should refactor and consolidate common code.
6041
6042 // This closure is used to mark refs into the CMS generation in
6043 // the CMS bit map. Called at the first checkpoint. This closure
6044 // assumes that we do not need to re-mark dirty cards; if the CMS
6045 // generation on which this is used is not an oldest
6046 // generation then this will lose younger_gen cards!
6047
6048 MarkRefsIntoClosure::MarkRefsIntoClosure(
6049 MemRegion span, CMSBitMap* bitMap):
6050 _span(span),
6051 _bitMap(bitMap)
6052 {
6053 assert(_ref_processor == NULL, "deliberately left NULL");
6054 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6055 }
6056
6057 void MarkRefsIntoClosure::do_oop(oop obj) {
6058 // if p points into _span, then mark corresponding bit in _markBitMap
6059 assert(obj->is_oop(), "expected an oop");
6060 HeapWord* addr = (HeapWord*)obj;
6061 if (_span.contains(addr)) {
6062 // this should be made more efficient
6063 _bitMap->mark(addr);
6064 }
6065 }
6066
6067 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6068 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6069
6070 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6071 MemRegion span, CMSBitMap* bitMap):
6072 _span(span),
6073 _bitMap(bitMap)
6074 {
6075 assert(_ref_processor == NULL, "deliberately left NULL");
6076 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6077 }
6078
6079 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6080 // if p points into _span, then mark corresponding bit in _markBitMap
6081 assert(obj->is_oop(), "expected an oop");
6082 HeapWord* addr = (HeapWord*)obj;
6083 if (_span.contains(addr)) {
6084 // this should be made more efficient
6085 _bitMap->par_mark(addr);
6086 }
6087 }
6088
6089 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6090 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6091
6092 // A variant of the above, used for CMS marking verification.
6093 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6094 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6095 _span(span),
6096 _verification_bm(verification_bm),
6097 _cms_bm(cms_bm)
6098 {
6099 assert(_ref_processor == NULL, "deliberately left NULL");
6100 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6101 }
6102
6103 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6104 // if p points into _span, then mark corresponding bit in _markBitMap
6105 assert(obj->is_oop(), "expected an oop");
6106 HeapWord* addr = (HeapWord*)obj;
6107 if (_span.contains(addr)) {
6108 _verification_bm->mark(addr);
6109 if (!_cms_bm->isMarked(addr)) {
6110 oop(addr)->print();
6111 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6112 fatal("... aborting");
6113 }
6114 }
6115 }
6116
6117 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6118 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6119
6120 //////////////////////////////////////////////////
6121 // MarkRefsIntoAndScanClosure
6122 //////////////////////////////////////////////////
6123
6124 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6125 ReferenceProcessor* rp,
6126 CMSBitMap* bit_map,
6127 CMSBitMap* mod_union_table,
6128 CMSMarkStack* mark_stack,
6129 CMSCollector* collector,
6130 bool should_yield,
6131 bool concurrent_precleaning):
6132 _collector(collector),
6133 _span(span),
6134 _bit_map(bit_map),
6135 _mark_stack(mark_stack),
6136 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6137 mark_stack, concurrent_precleaning),
6138 _yield(should_yield),
6139 _concurrent_precleaning(concurrent_precleaning),
6140 _freelistLock(NULL)
6141 {
6142 _ref_processor = rp;
6143 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6144 }
6145
6146 // This closure is used to mark refs into the CMS generation at the
6147 // second (final) checkpoint, and to scan and transitively follow
6148 // the unmarked oops. It is also used during the concurrent precleaning
6149 // phase while scanning objects on dirty cards in the CMS generation.
6150 // The marks are made in the marking bit map and the marking stack is
6151 // used for keeping the (newly) grey objects during the scan.
6152 // The parallel version (Par_...) appears further below.
6153 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6154 if (obj != NULL) {
6155 assert(obj->is_oop(), "expected an oop");
6156 HeapWord* addr = (HeapWord*)obj;
6157 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6158 assert(_collector->overflow_list_is_empty(),
6159 "overflow list should be empty");
6160 if (_span.contains(addr) &&
6161 !_bit_map->isMarked(addr)) {
6162 // mark bit map (object is now grey)
6163 _bit_map->mark(addr);
6164 // push on marking stack (stack should be empty), and drain the
6165 // stack by applying this closure to the oops in the oops popped
6166 // from the stack (i.e. blacken the grey objects)
6167 bool res = _mark_stack->push(obj);
6168 assert(res, "Should have space to push on empty stack");
6169 do {
6170 oop new_oop = _mark_stack->pop();
6171 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6172 assert(_bit_map->isMarked((HeapWord*)new_oop),
6173 "only grey objects on this stack");
6174 // iterate over the oops in this oop, marking and pushing
6175 // the ones in CMS heap (i.e. in _span).
6176 new_oop->oop_iterate(&_pushAndMarkClosure);
6177 // check if it's time to yield
6178 do_yield_check();
6179 } while (!_mark_stack->isEmpty() ||
6180 (!_concurrent_precleaning && take_from_overflow_list()));
6181 // if marking stack is empty, and we are not doing this
6182 // during precleaning, then check the overflow list
6183 }
6184 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6185 assert(_collector->overflow_list_is_empty(),
6186 "overflow list was drained above");
6187 // We could restore evacuated mark words, if any, used for
6188 // overflow list links here because the overflow list is
6189 // provably empty here. That would reduce the maximum
6190 // size requirements for preserved_{oop,mark}_stack.
6191 // But we'll just postpone it until we are all done
6192 // so we can just stream through.
6193 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6194 _collector->restore_preserved_marks_if_any();
6195 assert(_collector->no_preserved_marks(), "No preserved marks");
6196 }
6197 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6198 "All preserved marks should have been restored above");
6199 }
6200 }
6201
6202 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6203 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6204
6205 void MarkRefsIntoAndScanClosure::do_yield_work() {
6206 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6207 "CMS thread should hold CMS token");
6208 assert_lock_strong(_freelistLock);
6209 assert_lock_strong(_bit_map->lock());
6210 // relinquish the free_list_lock and bitMaplock()
6211 _bit_map->lock()->unlock();
6212 _freelistLock->unlock();
6213 ConcurrentMarkSweepThread::desynchronize(true);
6214 _collector->stopTimer();
6215 if (PrintCMSStatistics != 0) {
6216 _collector->incrementYields();
6217 }
6218
6219 // See the comment in coordinator_yield()
6220 for (unsigned i = 0;
6221 i < CMSYieldSleepCount &&
6222 ConcurrentMarkSweepThread::should_yield() &&
6223 !CMSCollector::foregroundGCIsActive();
6224 ++i) {
6225 os::sleep(Thread::current(), 1, false);
6226 }
6227
6228 ConcurrentMarkSweepThread::synchronize(true);
6229 _freelistLock->lock_without_safepoint_check();
6230 _bit_map->lock()->lock_without_safepoint_check();
6231 _collector->startTimer();
6232 }
6233
6234 ///////////////////////////////////////////////////////////
6235 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6236 // MarkRefsIntoAndScanClosure
6237 ///////////////////////////////////////////////////////////
6238 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6239 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6240 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6241 _span(span),
6242 _bit_map(bit_map),
6243 _work_queue(work_queue),
6244 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6245 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6246 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6247 {
6248 _ref_processor = rp;
6249 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6250 }
6251
6252 // This closure is used to mark refs into the CMS generation at the
6253 // second (final) checkpoint, and to scan and transitively follow
6254 // the unmarked oops. The marks are made in the marking bit map and
6255 // the work_queue is used for keeping the (newly) grey objects during
6256 // the scan phase whence they are also available for stealing by parallel
6257 // threads. Since the marking bit map is shared, updates are
6258 // synchronized (via CAS).
6259 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6260 if (obj != NULL) {
6261 // Ignore mark word because this could be an already marked oop
6262 // that may be chained at the end of the overflow list.
6263 assert(obj->is_oop(true), "expected an oop");
6264 HeapWord* addr = (HeapWord*)obj;
6265 if (_span.contains(addr) &&
6266 !_bit_map->isMarked(addr)) {
6267 // mark bit map (object will become grey):
6268 // It is possible for several threads to be
6269 // trying to "claim" this object concurrently;
6270 // the unique thread that succeeds in marking the
6271 // object first will do the subsequent push on
6272 // to the work queue (or overflow list).
6273 if (_bit_map->par_mark(addr)) {
6274 // push on work_queue (which may not be empty), and trim the
6275 // queue to an appropriate length by applying this closure to
6276 // the oops in the oops popped from the stack (i.e. blacken the
6277 // grey objects)
6278 bool res = _work_queue->push(obj);
6279 assert(res, "Low water mark should be less than capacity?");
6280 trim_queue(_low_water_mark);
6281 } // Else, another thread claimed the object
6282 }
6283 }
6284 }
6285
6286 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6287 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6288
6289 // This closure is used to rescan the marked objects on the dirty cards
6290 // in the mod union table and the card table proper.
6291 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6292 oop p, MemRegion mr) {
6293
6294 size_t size = 0;
6295 HeapWord* addr = (HeapWord*)p;
6296 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6297 assert(_span.contains(addr), "we are scanning the CMS generation");
6298 // check if it's time to yield
6299 if (do_yield_check()) {
6300 // We yielded for some foreground stop-world work,
6301 // and we have been asked to abort this ongoing preclean cycle.
6302 return 0;
6303 }
6304 if (_bitMap->isMarked(addr)) {
6305 // it's marked; is it potentially uninitialized?
6306 if (p->klass_or_null() != NULL) {
6307 // an initialized object; ignore mark word in verification below
6308 // since we are running concurrent with mutators
6309 assert(p->is_oop(true), "should be an oop");
6310 if (p->is_objArray()) {
6311 // objArrays are precisely marked; restrict scanning
6312 // to dirty cards only.
6313 size = CompactibleFreeListSpace::adjustObjectSize(
6314 p->oop_iterate(_scanningClosure, mr));
6315 } else {
6316 // A non-array may have been imprecisely marked; we need
6317 // to scan object in its entirety.
6318 size = CompactibleFreeListSpace::adjustObjectSize(
6319 p->oop_iterate(_scanningClosure));
6320 }
6321 #ifdef ASSERT
6322 size_t direct_size =
6323 CompactibleFreeListSpace::adjustObjectSize(p->size());
6324 assert(size == direct_size, "Inconsistency in size");
6325 assert(size >= 3, "Necessary for Printezis marks to work");
6326 if (!_bitMap->isMarked(addr+1)) {
6327 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6328 } else {
6329 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6330 assert(_bitMap->isMarked(addr+size-1),
6331 "inconsistent Printezis mark");
6332 }
6333 #endif // ASSERT
6334 } else {
6335 // An uninitialized object.
6336 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6337 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6338 size = pointer_delta(nextOneAddr + 1, addr);
6339 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6340 "alignment problem");
6341 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6342 // will dirty the card when the klass pointer is installed in the
6343 // object (signaling the completion of initialization).
6344 }
6345 } else {
6346 // Either a not yet marked object or an uninitialized object
6347 if (p->klass_or_null() == NULL) {
6348 // An uninitialized object, skip to the next card, since
6349 // we may not be able to read its P-bits yet.
6350 assert(size == 0, "Initial value");
6351 } else {
6352 // An object not (yet) reached by marking: we merely need to
6353 // compute its size so as to go look at the next block.
6354 assert(p->is_oop(true), "should be an oop");
6355 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6356 }
6357 }
6358 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6359 return size;
6360 }
6361
6362 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6363 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6364 "CMS thread should hold CMS token");
6365 assert_lock_strong(_freelistLock);
6366 assert_lock_strong(_bitMap->lock());
6367 // relinquish the free_list_lock and bitMaplock()
6368 _bitMap->lock()->unlock();
6369 _freelistLock->unlock();
6370 ConcurrentMarkSweepThread::desynchronize(true);
6371 _collector->stopTimer();
6372 if (PrintCMSStatistics != 0) {
6373 _collector->incrementYields();
6374 }
6375
6376 // See the comment in coordinator_yield()
6377 for (unsigned i = 0; i < CMSYieldSleepCount &&
6378 ConcurrentMarkSweepThread::should_yield() &&
6379 !CMSCollector::foregroundGCIsActive(); ++i) {
6380 os::sleep(Thread::current(), 1, false);
6381 }
6382
6383 ConcurrentMarkSweepThread::synchronize(true);
6384 _freelistLock->lock_without_safepoint_check();
6385 _bitMap->lock()->lock_without_safepoint_check();
6386 _collector->startTimer();
6387 }
6388
6389
6390 //////////////////////////////////////////////////////////////////
6391 // SurvivorSpacePrecleanClosure
6392 //////////////////////////////////////////////////////////////////
6393 // This (single-threaded) closure is used to preclean the oops in
6394 // the survivor spaces.
6395 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6396
6397 HeapWord* addr = (HeapWord*)p;
6398 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6399 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6400 assert(p->klass_or_null() != NULL, "object should be initialized");
6401 // an initialized object; ignore mark word in verification below
6402 // since we are running concurrent with mutators
6403 assert(p->is_oop(true), "should be an oop");
6404 // Note that we do not yield while we iterate over
6405 // the interior oops of p, pushing the relevant ones
6406 // on our marking stack.
6407 size_t size = p->oop_iterate(_scanning_closure);
6408 do_yield_check();
6409 // Observe that below, we do not abandon the preclean
6410 // phase as soon as we should; rather we empty the
6411 // marking stack before returning. This is to satisfy
6412 // some existing assertions. In general, it may be a
6413 // good idea to abort immediately and complete the marking
6414 // from the grey objects at a later time.
6415 while (!_mark_stack->isEmpty()) {
6416 oop new_oop = _mark_stack->pop();
6417 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6418 assert(_bit_map->isMarked((HeapWord*)new_oop),
6419 "only grey objects on this stack");
6420 // iterate over the oops in this oop, marking and pushing
6421 // the ones in CMS heap (i.e. in _span).
6422 new_oop->oop_iterate(_scanning_closure);
6423 // check if it's time to yield
6424 do_yield_check();
6425 }
6426 unsigned int after_count =
6427 GenCollectedHeap::heap()->total_collections();
6428 bool abort = (_before_count != after_count) ||
6429 _collector->should_abort_preclean();
6430 return abort ? 0 : size;
6431 }
6432
6433 void SurvivorSpacePrecleanClosure::do_yield_work() {
6434 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6435 "CMS thread should hold CMS token");
6436 assert_lock_strong(_bit_map->lock());
6437 // Relinquish the bit map lock
6438 _bit_map->lock()->unlock();
6439 ConcurrentMarkSweepThread::desynchronize(true);
6440 _collector->stopTimer();
6441 if (PrintCMSStatistics != 0) {
6442 _collector->incrementYields();
6443 }
6444
6445 // See the comment in coordinator_yield()
6446 for (unsigned i = 0; i < CMSYieldSleepCount &&
6447 ConcurrentMarkSweepThread::should_yield() &&
6448 !CMSCollector::foregroundGCIsActive(); ++i) {
6449 os::sleep(Thread::current(), 1, false);
6450 }
6451
6452 ConcurrentMarkSweepThread::synchronize(true);
6453 _bit_map->lock()->lock_without_safepoint_check();
6454 _collector->startTimer();
6455 }
6456
6457 // This closure is used to rescan the marked objects on the dirty cards
6458 // in the mod union table and the card table proper. In the parallel
6459 // case, although the bitMap is shared, we do a single read so the
6460 // isMarked() query is "safe".
6461 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6462 // Ignore mark word because we are running concurrent with mutators
6463 assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
6464 HeapWord* addr = (HeapWord*)p;
6465 assert(_span.contains(addr), "we are scanning the CMS generation");
6466 bool is_obj_array = false;
6467 #ifdef ASSERT
6468 if (!_parallel) {
6469 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6470 assert(_collector->overflow_list_is_empty(),
6471 "overflow list should be empty");
6472
6473 }
6474 #endif // ASSERT
6475 if (_bit_map->isMarked(addr)) {
6476 // Obj arrays are precisely marked, non-arrays are not;
6477 // so we scan objArrays precisely and non-arrays in their
6478 // entirety.
6479 if (p->is_objArray()) {
6480 is_obj_array = true;
6481 if (_parallel) {
6482 p->oop_iterate(_par_scan_closure, mr);
6483 } else {
6484 p->oop_iterate(_scan_closure, mr);
6485 }
6486 } else {
6487 if (_parallel) {
6488 p->oop_iterate(_par_scan_closure);
6489 } else {
6490 p->oop_iterate(_scan_closure);
6491 }
6492 }
6493 }
6494 #ifdef ASSERT
6495 if (!_parallel) {
6496 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6497 assert(_collector->overflow_list_is_empty(),
6498 "overflow list should be empty");
6499
6500 }
6501 #endif // ASSERT
6502 return is_obj_array;
6503 }
6504
6505 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6506 MemRegion span,
6507 CMSBitMap* bitMap, CMSMarkStack* markStack,
6508 bool should_yield, bool verifying):
6509 _collector(collector),
6510 _span(span),
6511 _bitMap(bitMap),
6512 _mut(&collector->_modUnionTable),
6513 _markStack(markStack),
6514 _yield(should_yield),
6515 _skipBits(0)
6516 {
6517 assert(_markStack->isEmpty(), "stack should be empty");
6518 _finger = _bitMap->startWord();
6519 _threshold = _finger;
6520 assert(_collector->_restart_addr == NULL, "Sanity check");
6521 assert(_span.contains(_finger), "Out of bounds _finger?");
6522 DEBUG_ONLY(_verifying = verifying;)
6523 }
6524
6525 void MarkFromRootsClosure::reset(HeapWord* addr) {
6526 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6527 assert(_span.contains(addr), "Out of bounds _finger?");
6528 _finger = addr;
6529 _threshold = (HeapWord*)round_to(
6530 (intptr_t)_finger, CardTableModRefBS::card_size);
6531 }
6532
6533 // Should revisit to see if this should be restructured for
6534 // greater efficiency.
6535 bool MarkFromRootsClosure::do_bit(size_t offset) {
6536 if (_skipBits > 0) {
6537 _skipBits--;
6538 return true;
6539 }
6540 // convert offset into a HeapWord*
6541 HeapWord* addr = _bitMap->startWord() + offset;
6542 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6543 "address out of range");
6544 assert(_bitMap->isMarked(addr), "tautology");
6545 if (_bitMap->isMarked(addr+1)) {
6546 // this is an allocated but not yet initialized object
6547 assert(_skipBits == 0, "tautology");
6548 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6549 oop p = oop(addr);
6550 if (p->klass_or_null() == NULL) {
6551 DEBUG_ONLY(if (!_verifying) {)
6552 // We re-dirty the cards on which this object lies and increase
6553 // the _threshold so that we'll come back to scan this object
6554 // during the preclean or remark phase. (CMSCleanOnEnter)
6555 if (CMSCleanOnEnter) {
6556 size_t sz = _collector->block_size_using_printezis_bits(addr);
6557 HeapWord* end_card_addr = (HeapWord*)round_to(
6558 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6559 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6560 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6561 // Bump _threshold to end_card_addr; note that
6562 // _threshold cannot possibly exceed end_card_addr, anyhow.
6563 // This prevents future clearing of the card as the scan proceeds
6564 // to the right.
6565 assert(_threshold <= end_card_addr,
6566 "Because we are just scanning into this object");
6567 if (_threshold < end_card_addr) {
6568 _threshold = end_card_addr;
6569 }
6570 if (p->klass_or_null() != NULL) {
6571 // Redirty the range of cards...
6572 _mut->mark_range(redirty_range);
6573 } // ...else the setting of klass will dirty the card anyway.
6574 }
6575 DEBUG_ONLY(})
6576 return true;
6577 }
6578 }
6579 scanOopsInOop(addr);
6580 return true;
6581 }
6582
6583 // We take a break if we've been at this for a while,
6584 // so as to avoid monopolizing the locks involved.
6585 void MarkFromRootsClosure::do_yield_work() {
6586 // First give up the locks, then yield, then re-lock
6587 // We should probably use a constructor/destructor idiom to
6588 // do this unlock/lock or modify the MutexUnlocker class to
6589 // serve our purpose. XXX
6590 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6591 "CMS thread should hold CMS token");
6592 assert_lock_strong(_bitMap->lock());
6593 _bitMap->lock()->unlock();
6594 ConcurrentMarkSweepThread::desynchronize(true);
6595 _collector->stopTimer();
6596 if (PrintCMSStatistics != 0) {
6597 _collector->incrementYields();
6598 }
6599
6600 // See the comment in coordinator_yield()
6601 for (unsigned i = 0; i < CMSYieldSleepCount &&
6602 ConcurrentMarkSweepThread::should_yield() &&
6603 !CMSCollector::foregroundGCIsActive(); ++i) {
6604 os::sleep(Thread::current(), 1, false);
6605 }
6606
6607 ConcurrentMarkSweepThread::synchronize(true);
6608 _bitMap->lock()->lock_without_safepoint_check();
6609 _collector->startTimer();
6610 }
6611
6612 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6613 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6614 assert(_markStack->isEmpty(),
6615 "should drain stack to limit stack usage");
6616 // convert ptr to an oop preparatory to scanning
6617 oop obj = oop(ptr);
6618 // Ignore mark word in verification below, since we
6619 // may be running concurrent with mutators.
6620 assert(obj->is_oop(true), "should be an oop");
6621 assert(_finger <= ptr, "_finger runneth ahead");
6622 // advance the finger to right end of this object
6623 _finger = ptr + obj->size();
6624 assert(_finger > ptr, "we just incremented it above");
6625 // On large heaps, it may take us some time to get through
6626 // the marking phase. During
6627 // this time it's possible that a lot of mutations have
6628 // accumulated in the card table and the mod union table --
6629 // these mutation records are redundant until we have
6630 // actually traced into the corresponding card.
6631 // Here, we check whether advancing the finger would make
6632 // us cross into a new card, and if so clear corresponding
6633 // cards in the MUT (preclean them in the card-table in the
6634 // future).
6635
6636 DEBUG_ONLY(if (!_verifying) {)
6637 // The clean-on-enter optimization is disabled by default,
6638 // until we fix 6178663.
6639 if (CMSCleanOnEnter && (_finger > _threshold)) {
6640 // [_threshold, _finger) represents the interval
6641 // of cards to be cleared in MUT (or precleaned in card table).
6642 // The set of cards to be cleared is all those that overlap
6643 // with the interval [_threshold, _finger); note that
6644 // _threshold is always kept card-aligned but _finger isn't
6645 // always card-aligned.
6646 HeapWord* old_threshold = _threshold;
6647 assert(old_threshold == (HeapWord*)round_to(
6648 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6649 "_threshold should always be card-aligned");
6650 _threshold = (HeapWord*)round_to(
6651 (intptr_t)_finger, CardTableModRefBS::card_size);
6652 MemRegion mr(old_threshold, _threshold);
6653 assert(!mr.is_empty(), "Control point invariant");
6654 assert(_span.contains(mr), "Should clear within span");
6655 _mut->clear_range(mr);
6656 }
6657 DEBUG_ONLY(})
6658 // Note: the finger doesn't advance while we drain
6659 // the stack below.
6660 PushOrMarkClosure pushOrMarkClosure(_collector,
6661 _span, _bitMap, _markStack,
6662 _finger, this);
6663 bool res = _markStack->push(obj);
6664 assert(res, "Empty non-zero size stack should have space for single push");
6665 while (!_markStack->isEmpty()) {
6666 oop new_oop = _markStack->pop();
6667 // Skip verifying header mark word below because we are
6668 // running concurrent with mutators.
6669 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6670 // now scan this oop's oops
6671 new_oop->oop_iterate(&pushOrMarkClosure);
6672 do_yield_check();
6673 }
6674 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6675 }
6676
6677 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6678 CMSCollector* collector, MemRegion span,
6679 CMSBitMap* bit_map,
6680 OopTaskQueue* work_queue,
6681 CMSMarkStack* overflow_stack):
6682 _collector(collector),
6683 _whole_span(collector->_span),
6684 _span(span),
6685 _bit_map(bit_map),
6686 _mut(&collector->_modUnionTable),
6687 _work_queue(work_queue),
6688 _overflow_stack(overflow_stack),
6689 _skip_bits(0),
6690 _task(task)
6691 {
6692 assert(_work_queue->size() == 0, "work_queue should be empty");
6693 _finger = span.start();
6694 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6695 assert(_span.contains(_finger), "Out of bounds _finger?");
6696 }
6697
6698 // Should revisit to see if this should be restructured for
6699 // greater efficiency.
6700 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6701 if (_skip_bits > 0) {
6702 _skip_bits--;
6703 return true;
6704 }
6705 // convert offset into a HeapWord*
6706 HeapWord* addr = _bit_map->startWord() + offset;
6707 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6708 "address out of range");
6709 assert(_bit_map->isMarked(addr), "tautology");
6710 if (_bit_map->isMarked(addr+1)) {
6711 // this is an allocated object that might not yet be initialized
6712 assert(_skip_bits == 0, "tautology");
6713 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6714 oop p = oop(addr);
6715 if (p->klass_or_null() == NULL) {
6716 // in the case of Clean-on-Enter optimization, redirty card
6717 // and avoid clearing card by increasing the threshold.
6718 return true;
6719 }
6720 }
6721 scan_oops_in_oop(addr);
6722 return true;
6723 }
6724
6725 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6726 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6727 // Should we assert that our work queue is empty or
6728 // below some drain limit?
6729 assert(_work_queue->size() == 0,
6730 "should drain stack to limit stack usage");
6731 // convert ptr to an oop preparatory to scanning
6732 oop obj = oop(ptr);
6733 // Ignore mark word in verification below, since we
6734 // may be running concurrent with mutators.
6735 assert(obj->is_oop(true), "should be an oop");
6736 assert(_finger <= ptr, "_finger runneth ahead");
6737 // advance the finger to right end of this object
6738 _finger = ptr + obj->size();
6739 assert(_finger > ptr, "we just incremented it above");
6740 // On large heaps, it may take us some time to get through
6741 // the marking phase. During
6742 // this time it's possible that a lot of mutations have
6743 // accumulated in the card table and the mod union table --
6744 // these mutation records are redundant until we have
6745 // actually traced into the corresponding card.
6746 // Here, we check whether advancing the finger would make
6747 // us cross into a new card, and if so clear corresponding
6748 // cards in the MUT (preclean them in the card-table in the
6749 // future).
6750
6751 // The clean-on-enter optimization is disabled by default,
6752 // until we fix 6178663.
6753 if (CMSCleanOnEnter && (_finger > _threshold)) {
6754 // [_threshold, _finger) represents the interval
6755 // of cards to be cleared in MUT (or precleaned in card table).
6756 // The set of cards to be cleared is all those that overlap
6757 // with the interval [_threshold, _finger); note that
6758 // _threshold is always kept card-aligned but _finger isn't
6759 // always card-aligned.
6760 HeapWord* old_threshold = _threshold;
6761 assert(old_threshold == (HeapWord*)round_to(
6762 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6763 "_threshold should always be card-aligned");
6764 _threshold = (HeapWord*)round_to(
6765 (intptr_t)_finger, CardTableModRefBS::card_size);
6766 MemRegion mr(old_threshold, _threshold);
6767 assert(!mr.is_empty(), "Control point invariant");
6768 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6769 _mut->clear_range(mr);
6770 }
6771
6772 // Note: the local finger doesn't advance while we drain
6773 // the stack below, but the global finger sure can and will.
6774 HeapWord** gfa = _task->global_finger_addr();
6775 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6776 _span, _bit_map,
6777 _work_queue,
6778 _overflow_stack,
6779 _finger,
6780 gfa, this);
6781 bool res = _work_queue->push(obj); // overflow could occur here
6782 assert(res, "Will hold once we use workqueues");
6783 while (true) {
6784 oop new_oop;
6785 if (!_work_queue->pop_local(new_oop)) {
6786 // We emptied our work_queue; check if there's stuff that can
6787 // be gotten from the overflow stack.
6788 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6789 _overflow_stack, _work_queue)) {
6790 do_yield_check();
6791 continue;
6792 } else { // done
6793 break;
6794 }
6795 }
6796 // Skip verifying header mark word below because we are
6797 // running concurrent with mutators.
6798 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6799 // now scan this oop's oops
6800 new_oop->oop_iterate(&pushOrMarkClosure);
6801 do_yield_check();
6802 }
6803 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6804 }
6805
6806 // Yield in response to a request from VM Thread or
6807 // from mutators.
6808 void Par_MarkFromRootsClosure::do_yield_work() {
6809 assert(_task != NULL, "sanity");
6810 _task->yield();
6811 }
6812
6813 // A variant of the above used for verifying CMS marking work.
6814 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6815 MemRegion span,
6816 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6817 CMSMarkStack* mark_stack):
6818 _collector(collector),
6819 _span(span),
6820 _verification_bm(verification_bm),
6821 _cms_bm(cms_bm),
6822 _mark_stack(mark_stack),
6823 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6824 mark_stack)
6825 {
6826 assert(_mark_stack->isEmpty(), "stack should be empty");
6827 _finger = _verification_bm->startWord();
6828 assert(_collector->_restart_addr == NULL, "Sanity check");
6829 assert(_span.contains(_finger), "Out of bounds _finger?");
6830 }
6831
6832 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6833 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6834 assert(_span.contains(addr), "Out of bounds _finger?");
6835 _finger = addr;
6836 }
6837
6838 // Should revisit to see if this should be restructured for
6839 // greater efficiency.
6840 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6841 // convert offset into a HeapWord*
6842 HeapWord* addr = _verification_bm->startWord() + offset;
6843 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6844 "address out of range");
6845 assert(_verification_bm->isMarked(addr), "tautology");
6846 assert(_cms_bm->isMarked(addr), "tautology");
6847
6848 assert(_mark_stack->isEmpty(),
6849 "should drain stack to limit stack usage");
6850 // convert addr to an oop preparatory to scanning
6851 oop obj = oop(addr);
6852 assert(obj->is_oop(), "should be an oop");
6853 assert(_finger <= addr, "_finger runneth ahead");
6854 // advance the finger to right end of this object
6855 _finger = addr + obj->size();
6856 assert(_finger > addr, "we just incremented it above");
6857 // Note: the finger doesn't advance while we drain
6858 // the stack below.
6859 bool res = _mark_stack->push(obj);
6860 assert(res, "Empty non-zero size stack should have space for single push");
6861 while (!_mark_stack->isEmpty()) {
6862 oop new_oop = _mark_stack->pop();
6863 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6864 // now scan this oop's oops
6865 new_oop->oop_iterate(&_pam_verify_closure);
6866 }
6867 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6868 return true;
6869 }
6870
6871 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6872 CMSCollector* collector, MemRegion span,
6873 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6874 CMSMarkStack* mark_stack):
6875 MetadataAwareOopClosure(collector->ref_processor()),
6876 _collector(collector),
6877 _span(span),
6878 _verification_bm(verification_bm),
6879 _cms_bm(cms_bm),
6880 _mark_stack(mark_stack)
6881 { }
6882
6883 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6884 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6885
6886 // Upon stack overflow, we discard (part of) the stack,
6887 // remembering the least address amongst those discarded
6888 // in CMSCollector's _restart_address.
6889 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6890 // Remember the least grey address discarded
6891 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6892 _collector->lower_restart_addr(ra);
6893 _mark_stack->reset(); // discard stack contents
6894 _mark_stack->expand(); // expand the stack if possible
6895 }
6896
6897 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6898 assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
6899 HeapWord* addr = (HeapWord*)obj;
6900 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6901 // Oop lies in _span and isn't yet grey or black
6902 _verification_bm->mark(addr); // now grey
6903 if (!_cms_bm->isMarked(addr)) {
6904 oop(addr)->print();
6905 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
6906 p2i(addr));
6907 fatal("... aborting");
6908 }
6909
6910 if (!_mark_stack->push(obj)) { // stack overflow
6911 if (PrintCMSStatistics != 0) {
6912 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6913 SIZE_FORMAT, _mark_stack->capacity());
6914 }
6915 assert(_mark_stack->isFull(), "Else push should have succeeded");
6916 handle_stack_overflow(addr);
6917 }
6918 // anything including and to the right of _finger
6919 // will be scanned as we iterate over the remainder of the
6920 // bit map
6921 }
6922 }
6923
6924 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6925 MemRegion span,
6926 CMSBitMap* bitMap, CMSMarkStack* markStack,
6927 HeapWord* finger, MarkFromRootsClosure* parent) :
6928 MetadataAwareOopClosure(collector->ref_processor()),
6929 _collector(collector),
6930 _span(span),
6931 _bitMap(bitMap),
6932 _markStack(markStack),
6933 _finger(finger),
6934 _parent(parent)
6935 { }
6936
6937 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
6938 MemRegion span,
6939 CMSBitMap* bit_map,
6940 OopTaskQueue* work_queue,
6941 CMSMarkStack* overflow_stack,
6942 HeapWord* finger,
6943 HeapWord** global_finger_addr,
6944 Par_MarkFromRootsClosure* parent) :
6945 MetadataAwareOopClosure(collector->ref_processor()),
6946 _collector(collector),
6947 _whole_span(collector->_span),
6948 _span(span),
6949 _bit_map(bit_map),
6950 _work_queue(work_queue),
6951 _overflow_stack(overflow_stack),
6952 _finger(finger),
6953 _global_finger_addr(global_finger_addr),
6954 _parent(parent)
6955 { }
6956
6957 // Assumes thread-safe access by callers, who are
6958 // responsible for mutual exclusion.
6959 void CMSCollector::lower_restart_addr(HeapWord* low) {
6960 assert(_span.contains(low), "Out of bounds addr");
6961 if (_restart_addr == NULL) {
6962 _restart_addr = low;
6963 } else {
6964 _restart_addr = MIN2(_restart_addr, low);
6965 }
6966 }
6967
6968 // Upon stack overflow, we discard (part of) the stack,
6969 // remembering the least address amongst those discarded
6970 // in CMSCollector's _restart_address.
6971 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6972 // Remember the least grey address discarded
6973 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6974 _collector->lower_restart_addr(ra);
6975 _markStack->reset(); // discard stack contents
6976 _markStack->expand(); // expand the stack if possible
6977 }
6978
6979 // Upon stack overflow, we discard (part of) the stack,
6980 // remembering the least address amongst those discarded
6981 // in CMSCollector's _restart_address.
6982 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6983 // We need to do this under a mutex to prevent other
6984 // workers from interfering with the work done below.
6985 MutexLockerEx ml(_overflow_stack->par_lock(),
6986 Mutex::_no_safepoint_check_flag);
6987 // Remember the least grey address discarded
6988 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6989 _collector->lower_restart_addr(ra);
6990 _overflow_stack->reset(); // discard stack contents
6991 _overflow_stack->expand(); // expand the stack if possible
6992 }
6993
6994 void PushOrMarkClosure::do_oop(oop obj) {
6995 // Ignore mark word because we are running concurrent with mutators.
6996 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
6997 HeapWord* addr = (HeapWord*)obj;
6998 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6999 // Oop lies in _span and isn't yet grey or black
7000 _bitMap->mark(addr); // now grey
7001 if (addr < _finger) {
7002 // the bit map iteration has already either passed, or
7003 // sampled, this bit in the bit map; we'll need to
7004 // use the marking stack to scan this oop's oops.
7005 bool simulate_overflow = false;
7006 NOT_PRODUCT(
7007 if (CMSMarkStackOverflowALot &&
7008 _collector->simulate_overflow()) {
7009 // simulate a stack overflow
7010 simulate_overflow = true;
7011 }
7012 )
7013 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7014 if (PrintCMSStatistics != 0) {
7015 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7016 SIZE_FORMAT, _markStack->capacity());
7017 }
7018 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7019 handle_stack_overflow(addr);
7020 }
7021 }
7022 // anything including and to the right of _finger
7023 // will be scanned as we iterate over the remainder of the
7024 // bit map
7025 do_yield_check();
7026 }
7027 }
7028
7029 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7030 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7031
7032 void Par_PushOrMarkClosure::do_oop(oop obj) {
7033 // Ignore mark word because we are running concurrent with mutators.
7034 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7035 HeapWord* addr = (HeapWord*)obj;
7036 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7037 // Oop lies in _span and isn't yet grey or black
7038 // We read the global_finger (volatile read) strictly after marking oop
7039 bool res = _bit_map->par_mark(addr); // now grey
7040 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7041 // Should we push this marked oop on our stack?
7042 // -- if someone else marked it, nothing to do
7043 // -- if target oop is above global finger nothing to do
7044 // -- if target oop is in chunk and above local finger
7045 // then nothing to do
7046 // -- else push on work queue
7047 if ( !res // someone else marked it, they will deal with it
7048 || (addr >= *gfa) // will be scanned in a later task
7049 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7050 return;
7051 }
7052 // the bit map iteration has already either passed, or
7053 // sampled, this bit in the bit map; we'll need to
7054 // use the marking stack to scan this oop's oops.
7055 bool simulate_overflow = false;
7056 NOT_PRODUCT(
7057 if (CMSMarkStackOverflowALot &&
7058 _collector->simulate_overflow()) {
7059 // simulate a stack overflow
7060 simulate_overflow = true;
7061 }
7062 )
7063 if (simulate_overflow ||
7064 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7065 // stack overflow
7066 if (PrintCMSStatistics != 0) {
7067 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7068 SIZE_FORMAT, _overflow_stack->capacity());
7069 }
7070 // We cannot assert that the overflow stack is full because
7071 // it may have been emptied since.
7072 assert(simulate_overflow ||
7073 _work_queue->size() == _work_queue->max_elems(),
7074 "Else push should have succeeded");
7075 handle_stack_overflow(addr);
7076 }
7077 do_yield_check();
7078 }
7079 }
7080
7081 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7082 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7083
7084 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7085 MemRegion span,
7086 ReferenceProcessor* rp,
7087 CMSBitMap* bit_map,
7088 CMSBitMap* mod_union_table,
7089 CMSMarkStack* mark_stack,
7090 bool concurrent_precleaning):
7091 MetadataAwareOopClosure(rp),
7092 _collector(collector),
7093 _span(span),
7094 _bit_map(bit_map),
7095 _mod_union_table(mod_union_table),
7096 _mark_stack(mark_stack),
7097 _concurrent_precleaning(concurrent_precleaning)
7098 {
7099 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7100 }
7101
7102 // Grey object rescan during pre-cleaning and second checkpoint phases --
7103 // the non-parallel version (the parallel version appears further below.)
7104 void PushAndMarkClosure::do_oop(oop obj) {
7105 // Ignore mark word verification. If during concurrent precleaning,
7106 // the object monitor may be locked. If during the checkpoint
7107 // phases, the object may already have been reached by a different
7108 // path and may be at the end of the global overflow list (so
7109 // the mark word may be NULL).
7110 assert(obj->is_oop_or_null(true /* ignore mark word */),
7111 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7112 HeapWord* addr = (HeapWord*)obj;
7113 // Check if oop points into the CMS generation
7114 // and is not marked
7115 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7116 // a white object ...
7117 _bit_map->mark(addr); // ... now grey
7118 // push on the marking stack (grey set)
7119 bool simulate_overflow = false;
7120 NOT_PRODUCT(
7121 if (CMSMarkStackOverflowALot &&
7122 _collector->simulate_overflow()) {
7123 // simulate a stack overflow
7124 simulate_overflow = true;
7125 }
7126 )
7127 if (simulate_overflow || !_mark_stack->push(obj)) {
7128 if (_concurrent_precleaning) {
7129 // During precleaning we can just dirty the appropriate card(s)
7130 // in the mod union table, thus ensuring that the object remains
7131 // in the grey set and continue. In the case of object arrays
7132 // we need to dirty all of the cards that the object spans,
7133 // since the rescan of object arrays will be limited to the
7134 // dirty cards.
7135 // Note that no one can be interfering with us in this action
7136 // of dirtying the mod union table, so no locking or atomics
7137 // are required.
7138 if (obj->is_objArray()) {
7139 size_t sz = obj->size();
7140 HeapWord* end_card_addr = (HeapWord*)round_to(
7141 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7142 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7143 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7144 _mod_union_table->mark_range(redirty_range);
7145 } else {
7146 _mod_union_table->mark(addr);
7147 }
7148 _collector->_ser_pmc_preclean_ovflw++;
7149 } else {
7150 // During the remark phase, we need to remember this oop
7151 // in the overflow list.
7152 _collector->push_on_overflow_list(obj);
7153 _collector->_ser_pmc_remark_ovflw++;
7154 }
7155 }
7156 }
7157 }
7158
7159 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7160 MemRegion span,
7161 ReferenceProcessor* rp,
7162 CMSBitMap* bit_map,
7163 OopTaskQueue* work_queue):
7164 MetadataAwareOopClosure(rp),
7165 _collector(collector),
7166 _span(span),
7167 _bit_map(bit_map),
7168 _work_queue(work_queue)
7169 {
7170 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7171 }
7172
7173 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7174 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7175
7176 // Grey object rescan during second checkpoint phase --
7177 // the parallel version.
7178 void Par_PushAndMarkClosure::do_oop(oop obj) {
7179 // In the assert below, we ignore the mark word because
7180 // this oop may point to an already visited object that is
7181 // on the overflow stack (in which case the mark word has
7182 // been hijacked for chaining into the overflow stack --
7183 // if this is the last object in the overflow stack then
7184 // its mark word will be NULL). Because this object may
7185 // have been subsequently popped off the global overflow
7186 // stack, and the mark word possibly restored to the prototypical
7187 // value, by the time we get to examined this failing assert in
7188 // the debugger, is_oop_or_null(false) may subsequently start
7189 // to hold.
7190 assert(obj->is_oop_or_null(true),
7191 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7192 HeapWord* addr = (HeapWord*)obj;
7193 // Check if oop points into the CMS generation
7194 // and is not marked
7195 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7196 // a white object ...
7197 // If we manage to "claim" the object, by being the
7198 // first thread to mark it, then we push it on our
7199 // marking stack
7200 if (_bit_map->par_mark(addr)) { // ... now grey
7201 // push on work queue (grey set)
7202 bool simulate_overflow = false;
7203 NOT_PRODUCT(
7204 if (CMSMarkStackOverflowALot &&
7205 _collector->par_simulate_overflow()) {
7206 // simulate a stack overflow
7207 simulate_overflow = true;
7208 }
7209 )
7210 if (simulate_overflow || !_work_queue->push(obj)) {
7211 _collector->par_push_on_overflow_list(obj);
7212 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7213 }
7214 } // Else, some other thread got there first
7215 }
7216 }
7217
7218 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7219 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7220
7221 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7222 Mutex* bml = _collector->bitMapLock();
7223 assert_lock_strong(bml);
7224 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7225 "CMS thread should hold CMS token");
7226
7227 bml->unlock();
7228 ConcurrentMarkSweepThread::desynchronize(true);
7229
7230 _collector->stopTimer();
7231 if (PrintCMSStatistics != 0) {
7232 _collector->incrementYields();
7233 }
7234
7235 // See the comment in coordinator_yield()
7236 for (unsigned i = 0; i < CMSYieldSleepCount &&
7237 ConcurrentMarkSweepThread::should_yield() &&
7238 !CMSCollector::foregroundGCIsActive(); ++i) {
7239 os::sleep(Thread::current(), 1, false);
7240 }
7241
7242 ConcurrentMarkSweepThread::synchronize(true);
7243 bml->lock();
7244
7245 _collector->startTimer();
7246 }
7247
7248 bool CMSPrecleanRefsYieldClosure::should_return() {
7249 if (ConcurrentMarkSweepThread::should_yield()) {
7250 do_yield_work();
7251 }
7252 return _collector->foregroundGCIsActive();
7253 }
7254
7255 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7256 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7257 "mr should be aligned to start at a card boundary");
7258 // We'd like to assert:
7259 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7260 // "mr should be a range of cards");
7261 // However, that would be too strong in one case -- the last
7262 // partition ends at _unallocated_block which, in general, can be
7263 // an arbitrary boundary, not necessarily card aligned.
7264 if (PrintCMSStatistics != 0) {
7265 _num_dirty_cards +=
7266 mr.word_size()/CardTableModRefBS::card_size_in_words;
7267 }
7268 _space->object_iterate_mem(mr, &_scan_cl);
7269 }
7270
7271 SweepClosure::SweepClosure(CMSCollector* collector,
7272 ConcurrentMarkSweepGeneration* g,
7273 CMSBitMap* bitMap, bool should_yield) :
7274 _collector(collector),
7275 _g(g),
7276 _sp(g->cmsSpace()),
7277 _limit(_sp->sweep_limit()),
7278 _freelistLock(_sp->freelistLock()),
7279 _bitMap(bitMap),
7280 _yield(should_yield),
7281 _inFreeRange(false), // No free range at beginning of sweep
7282 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7283 _lastFreeRangeCoalesced(false),
7284 _freeFinger(g->used_region().start())
7285 {
7286 NOT_PRODUCT(
7287 _numObjectsFreed = 0;
7288 _numWordsFreed = 0;
7289 _numObjectsLive = 0;
7290 _numWordsLive = 0;
7291 _numObjectsAlreadyFree = 0;
7292 _numWordsAlreadyFree = 0;
7293 _last_fc = NULL;
7294
7295 _sp->initializeIndexedFreeListArrayReturnedBytes();
7296 _sp->dictionary()->initialize_dict_returned_bytes();
7297 )
7298 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7299 "sweep _limit out of bounds");
7300 if (CMSTraceSweeper) {
7301 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7302 p2i(_limit));
7303 }
7304 }
7305
7306 void SweepClosure::print_on(outputStream* st) const {
7307 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7308 p2i(_sp->bottom()), p2i(_sp->end()));
7309 tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7310 tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7311 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7312 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7313 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7314 }
7315
7316 #ifndef PRODUCT
7317 // Assertion checking only: no useful work in product mode --
7318 // however, if any of the flags below become product flags,
7319 // you may need to review this code to see if it needs to be
7320 // enabled in product mode.
7321 SweepClosure::~SweepClosure() {
7322 assert_lock_strong(_freelistLock);
7323 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7324 "sweep _limit out of bounds");
7325 if (inFreeRange()) {
7326 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7327 print();
7328 ShouldNotReachHere();
7329 }
7330 if (Verbose && PrintGC) {
7331 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7332 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7333 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7334 SIZE_FORMAT" bytes "
7335 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7336 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7337 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7338 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7339 * sizeof(HeapWord);
7340 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7341
7342 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7343 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7344 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7345 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7346 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7347 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7348 indexListReturnedBytes);
7349 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7350 dict_returned_bytes);
7351 }
7352 }
7353 if (CMSTraceSweeper) {
7354 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7355 p2i(_limit));
7356 }
7357 }
7358 #endif // PRODUCT
7359
7360 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7361 bool freeRangeInFreeLists) {
7362 if (CMSTraceSweeper) {
7363 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7364 p2i(freeFinger), freeRangeInFreeLists);
7365 }
7366 assert(!inFreeRange(), "Trampling existing free range");
7367 set_inFreeRange(true);
7368 set_lastFreeRangeCoalesced(false);
7369
7370 set_freeFinger(freeFinger);
7371 set_freeRangeInFreeLists(freeRangeInFreeLists);
7372 if (CMSTestInFreeList) {
7373 if (freeRangeInFreeLists) {
7374 FreeChunk* fc = (FreeChunk*) freeFinger;
7375 assert(fc->is_free(), "A chunk on the free list should be free.");
7376 assert(fc->size() > 0, "Free range should have a size");
7377 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7378 }
7379 }
7380 }
7381
7382 // Note that the sweeper runs concurrently with mutators. Thus,
7383 // it is possible for direct allocation in this generation to happen
7384 // in the middle of the sweep. Note that the sweeper also coalesces
7385 // contiguous free blocks. Thus, unless the sweeper and the allocator
7386 // synchronize appropriately freshly allocated blocks may get swept up.
7387 // This is accomplished by the sweeper locking the free lists while
7388 // it is sweeping. Thus blocks that are determined to be free are
7389 // indeed free. There is however one additional complication:
7390 // blocks that have been allocated since the final checkpoint and
7391 // mark, will not have been marked and so would be treated as
7392 // unreachable and swept up. To prevent this, the allocator marks
7393 // the bit map when allocating during the sweep phase. This leads,
7394 // however, to a further complication -- objects may have been allocated
7395 // but not yet initialized -- in the sense that the header isn't yet
7396 // installed. The sweeper can not then determine the size of the block
7397 // in order to skip over it. To deal with this case, we use a technique
7398 // (due to Printezis) to encode such uninitialized block sizes in the
7399 // bit map. Since the bit map uses a bit per every HeapWord, but the
7400 // CMS generation has a minimum object size of 3 HeapWords, it follows
7401 // that "normal marks" won't be adjacent in the bit map (there will
7402 // always be at least two 0 bits between successive 1 bits). We make use
7403 // of these "unused" bits to represent uninitialized blocks -- the bit
7404 // corresponding to the start of the uninitialized object and the next
7405 // bit are both set. Finally, a 1 bit marks the end of the object that
7406 // started with the two consecutive 1 bits to indicate its potentially
7407 // uninitialized state.
7408
7409 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7410 FreeChunk* fc = (FreeChunk*)addr;
7411 size_t res;
7412
7413 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7414 // than "addr == _limit" because although _limit was a block boundary when
7415 // we started the sweep, it may no longer be one because heap expansion
7416 // may have caused us to coalesce the block ending at the address _limit
7417 // with a newly expanded chunk (this happens when _limit was set to the
7418 // previous _end of the space), so we may have stepped past _limit:
7419 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7420 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7421 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7422 "sweep _limit out of bounds");
7423 assert(addr < _sp->end(), "addr out of bounds");
7424 // Flush any free range we might be holding as a single
7425 // coalesced chunk to the appropriate free list.
7426 if (inFreeRange()) {
7427 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7428 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", p2i(freeFinger())));
7429 flush_cur_free_chunk(freeFinger(),
7430 pointer_delta(addr, freeFinger()));
7431 if (CMSTraceSweeper) {
7432 gclog_or_tty->print("Sweep: last chunk: ");
7433 gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
7434 "[coalesced:%d]\n",
7435 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7436 lastFreeRangeCoalesced() ? 1 : 0);
7437 }
7438 }
7439
7440 // help the iterator loop finish
7441 return pointer_delta(_sp->end(), addr);
7442 }
7443
7444 assert(addr < _limit, "sweep invariant");
7445 // check if we should yield
7446 do_yield_check(addr);
7447 if (fc->is_free()) {
7448 // Chunk that is already free
7449 res = fc->size();
7450 do_already_free_chunk(fc);
7451 debug_only(_sp->verifyFreeLists());
7452 // If we flush the chunk at hand in lookahead_and_flush()
7453 // and it's coalesced with a preceding chunk, then the
7454 // process of "mangling" the payload of the coalesced block
7455 // will cause erasure of the size information from the
7456 // (erstwhile) header of all the coalesced blocks but the
7457 // first, so the first disjunct in the assert will not hold
7458 // in that specific case (in which case the second disjunct
7459 // will hold).
7460 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7461 "Otherwise the size info doesn't change at this step");
7462 NOT_PRODUCT(
7463 _numObjectsAlreadyFree++;
7464 _numWordsAlreadyFree += res;
7465 )
7466 NOT_PRODUCT(_last_fc = fc;)
7467 } else if (!_bitMap->isMarked(addr)) {
7468 // Chunk is fresh garbage
7469 res = do_garbage_chunk(fc);
7470 debug_only(_sp->verifyFreeLists());
7471 NOT_PRODUCT(
7472 _numObjectsFreed++;
7473 _numWordsFreed += res;
7474 )
7475 } else {
7476 // Chunk that is alive.
7477 res = do_live_chunk(fc);
7478 debug_only(_sp->verifyFreeLists());
7479 NOT_PRODUCT(
7480 _numObjectsLive++;
7481 _numWordsLive += res;
7482 )
7483 }
7484 return res;
7485 }
7486
7487 // For the smart allocation, record following
7488 // split deaths - a free chunk is removed from its free list because
7489 // it is being split into two or more chunks.
7490 // split birth - a free chunk is being added to its free list because
7491 // a larger free chunk has been split and resulted in this free chunk.
7492 // coal death - a free chunk is being removed from its free list because
7493 // it is being coalesced into a large free chunk.
7494 // coal birth - a free chunk is being added to its free list because
7495 // it was created when two or more free chunks where coalesced into
7496 // this free chunk.
7497 //
7498 // These statistics are used to determine the desired number of free
7499 // chunks of a given size. The desired number is chosen to be relative
7500 // to the end of a CMS sweep. The desired number at the end of a sweep
7501 // is the
7502 // count-at-end-of-previous-sweep (an amount that was enough)
7503 // - count-at-beginning-of-current-sweep (the excess)
7504 // + split-births (gains in this size during interval)
7505 // - split-deaths (demands on this size during interval)
7506 // where the interval is from the end of one sweep to the end of the
7507 // next.
7508 //
7509 // When sweeping the sweeper maintains an accumulated chunk which is
7510 // the chunk that is made up of chunks that have been coalesced. That
7511 // will be termed the left-hand chunk. A new chunk of garbage that
7512 // is being considered for coalescing will be referred to as the
7513 // right-hand chunk.
7514 //
7515 // When making a decision on whether to coalesce a right-hand chunk with
7516 // the current left-hand chunk, the current count vs. the desired count
7517 // of the left-hand chunk is considered. Also if the right-hand chunk
7518 // is near the large chunk at the end of the heap (see
7519 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7520 // left-hand chunk is coalesced.
7521 //
7522 // When making a decision about whether to split a chunk, the desired count
7523 // vs. the current count of the candidate to be split is also considered.
7524 // If the candidate is underpopulated (currently fewer chunks than desired)
7525 // a chunk of an overpopulated (currently more chunks than desired) size may
7526 // be chosen. The "hint" associated with a free list, if non-null, points
7527 // to a free list which may be overpopulated.
7528 //
7529
7530 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7531 const size_t size = fc->size();
7532 // Chunks that cannot be coalesced are not in the
7533 // free lists.
7534 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7535 assert(_sp->verify_chunk_in_free_list(fc),
7536 "free chunk should be in free lists");
7537 }
7538 // a chunk that is already free, should not have been
7539 // marked in the bit map
7540 HeapWord* const addr = (HeapWord*) fc;
7541 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7542 // Verify that the bit map has no bits marked between
7543 // addr and purported end of this block.
7544 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7545
7546 // Some chunks cannot be coalesced under any circumstances.
7547 // See the definition of cantCoalesce().
7548 if (!fc->cantCoalesce()) {
7549 // This chunk can potentially be coalesced.
7550 if (_sp->adaptive_freelists()) {
7551 // All the work is done in
7552 do_post_free_or_garbage_chunk(fc, size);
7553 } else { // Not adaptive free lists
7554 // this is a free chunk that can potentially be coalesced by the sweeper;
7555 if (!inFreeRange()) {
7556 // if the next chunk is a free block that can't be coalesced
7557 // it doesn't make sense to remove this chunk from the free lists
7558 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7559 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
7560 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
7561 nextChunk->is_free() && // ... which is free...
7562 nextChunk->cantCoalesce()) { // ... but can't be coalesced
7563 // nothing to do
7564 } else {
7565 // Potentially the start of a new free range:
7566 // Don't eagerly remove it from the free lists.
7567 // No need to remove it if it will just be put
7568 // back again. (Also from a pragmatic point of view
7569 // if it is a free block in a region that is beyond
7570 // any allocated blocks, an assertion will fail)
7571 // Remember the start of a free run.
7572 initialize_free_range(addr, true);
7573 // end - can coalesce with next chunk
7574 }
7575 } else {
7576 // the midst of a free range, we are coalescing
7577 print_free_block_coalesced(fc);
7578 if (CMSTraceSweeper) {
7579 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7580 }
7581 // remove it from the free lists
7582 _sp->removeFreeChunkFromFreeLists(fc);
7583 set_lastFreeRangeCoalesced(true);
7584 // If the chunk is being coalesced and the current free range is
7585 // in the free lists, remove the current free range so that it
7586 // will be returned to the free lists in its entirety - all
7587 // the coalesced pieces included.
7588 if (freeRangeInFreeLists()) {
7589 FreeChunk* ffc = (FreeChunk*) freeFinger();
7590 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7591 "Size of free range is inconsistent with chunk size.");
7592 if (CMSTestInFreeList) {
7593 assert(_sp->verify_chunk_in_free_list(ffc),
7594 "free range is not in free lists");
7595 }
7596 _sp->removeFreeChunkFromFreeLists(ffc);
7597 set_freeRangeInFreeLists(false);
7598 }
7599 }
7600 }
7601 // Note that if the chunk is not coalescable (the else arm
7602 // below), we unconditionally flush, without needing to do
7603 // a "lookahead," as we do below.
7604 if (inFreeRange()) lookahead_and_flush(fc, size);
7605 } else {
7606 // Code path common to both original and adaptive free lists.
7607
7608 // cant coalesce with previous block; this should be treated
7609 // as the end of a free run if any
7610 if (inFreeRange()) {
7611 // we kicked some butt; time to pick up the garbage
7612 assert(freeFinger() < addr, "freeFinger points too high");
7613 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7614 }
7615 // else, nothing to do, just continue
7616 }
7617 }
7618
7619 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7620 // This is a chunk of garbage. It is not in any free list.
7621 // Add it to a free list or let it possibly be coalesced into
7622 // a larger chunk.
7623 HeapWord* const addr = (HeapWord*) fc;
7624 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7625
7626 if (_sp->adaptive_freelists()) {
7627 // Verify that the bit map has no bits marked between
7628 // addr and purported end of just dead object.
7629 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7630
7631 do_post_free_or_garbage_chunk(fc, size);
7632 } else {
7633 if (!inFreeRange()) {
7634 // start of a new free range
7635 assert(size > 0, "A free range should have a size");
7636 initialize_free_range(addr, false);
7637 } else {
7638 // this will be swept up when we hit the end of the
7639 // free range
7640 if (CMSTraceSweeper) {
7641 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7642 }
7643 // If the chunk is being coalesced and the current free range is
7644 // in the free lists, remove the current free range so that it
7645 // will be returned to the free lists in its entirety - all
7646 // the coalesced pieces included.
7647 if (freeRangeInFreeLists()) {
7648 FreeChunk* ffc = (FreeChunk*)freeFinger();
7649 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7650 "Size of free range is inconsistent with chunk size.");
7651 if (CMSTestInFreeList) {
7652 assert(_sp->verify_chunk_in_free_list(ffc),
7653 "free range is not in free lists");
7654 }
7655 _sp->removeFreeChunkFromFreeLists(ffc);
7656 set_freeRangeInFreeLists(false);
7657 }
7658 set_lastFreeRangeCoalesced(true);
7659 }
7660 // this will be swept up when we hit the end of the free range
7661
7662 // Verify that the bit map has no bits marked between
7663 // addr and purported end of just dead object.
7664 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7665 }
7666 assert(_limit >= addr + size,
7667 "A freshly garbage chunk can't possibly straddle over _limit");
7668 if (inFreeRange()) lookahead_and_flush(fc, size);
7669 return size;
7670 }
7671
7672 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7673 HeapWord* addr = (HeapWord*) fc;
7674 // The sweeper has just found a live object. Return any accumulated
7675 // left hand chunk to the free lists.
7676 if (inFreeRange()) {
7677 assert(freeFinger() < addr, "freeFinger points too high");
7678 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7679 }
7680
7681 // This object is live: we'd normally expect this to be
7682 // an oop, and like to assert the following:
7683 // assert(oop(addr)->is_oop(), "live block should be an oop");
7684 // However, as we commented above, this may be an object whose
7685 // header hasn't yet been initialized.
7686 size_t size;
7687 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7688 if (_bitMap->isMarked(addr + 1)) {
7689 // Determine the size from the bit map, rather than trying to
7690 // compute it from the object header.
7691 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7692 size = pointer_delta(nextOneAddr + 1, addr);
7693 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7694 "alignment problem");
7695
7696 #ifdef ASSERT
7697 if (oop(addr)->klass_or_null() != NULL) {
7698 // Ignore mark word because we are running concurrent with mutators
7699 assert(oop(addr)->is_oop(true), "live block should be an oop");
7700 assert(size ==
7701 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7702 "P-mark and computed size do not agree");
7703 }
7704 #endif
7705
7706 } else {
7707 // This should be an initialized object that's alive.
7708 assert(oop(addr)->klass_or_null() != NULL,
7709 "Should be an initialized object");
7710 // Ignore mark word because we are running concurrent with mutators
7711 assert(oop(addr)->is_oop(true), "live block should be an oop");
7712 // Verify that the bit map has no bits marked between
7713 // addr and purported end of this block.
7714 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7715 assert(size >= 3, "Necessary for Printezis marks to work");
7716 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7717 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7718 }
7719 return size;
7720 }
7721
7722 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7723 size_t chunkSize) {
7724 // do_post_free_or_garbage_chunk() should only be called in the case
7725 // of the adaptive free list allocator.
7726 const bool fcInFreeLists = fc->is_free();
7727 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
7728 assert((HeapWord*)fc <= _limit, "sweep invariant");
7729 if (CMSTestInFreeList && fcInFreeLists) {
7730 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7731 }
7732
7733 if (CMSTraceSweeper) {
7734 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7735 }
7736
7737 HeapWord* const fc_addr = (HeapWord*) fc;
7738
7739 bool coalesce;
7740 const size_t left = pointer_delta(fc_addr, freeFinger());
7741 const size_t right = chunkSize;
7742 switch (FLSCoalescePolicy) {
7743 // numeric value forms a coalition aggressiveness metric
7744 case 0: { // never coalesce
7745 coalesce = false;
7746 break;
7747 }
7748 case 1: { // coalesce if left & right chunks on overpopulated lists
7749 coalesce = _sp->coalOverPopulated(left) &&
7750 _sp->coalOverPopulated(right);
7751 break;
7752 }
7753 case 2: { // coalesce if left chunk on overpopulated list (default)
7754 coalesce = _sp->coalOverPopulated(left);
7755 break;
7756 }
7757 case 3: { // coalesce if left OR right chunk on overpopulated list
7758 coalesce = _sp->coalOverPopulated(left) ||
7759 _sp->coalOverPopulated(right);
7760 break;
7761 }
7762 case 4: { // always coalesce
7763 coalesce = true;
7764 break;
7765 }
7766 default:
7767 ShouldNotReachHere();
7768 }
7769
7770 // Should the current free range be coalesced?
7771 // If the chunk is in a free range and either we decided to coalesce above
7772 // or the chunk is near the large block at the end of the heap
7773 // (isNearLargestChunk() returns true), then coalesce this chunk.
7774 const bool doCoalesce = inFreeRange()
7775 && (coalesce || _g->isNearLargestChunk(fc_addr));
7776 if (doCoalesce) {
7777 // Coalesce the current free range on the left with the new
7778 // chunk on the right. If either is on a free list,
7779 // it must be removed from the list and stashed in the closure.
7780 if (freeRangeInFreeLists()) {
7781 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7782 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7783 "Size of free range is inconsistent with chunk size.");
7784 if (CMSTestInFreeList) {
7785 assert(_sp->verify_chunk_in_free_list(ffc),
7786 "Chunk is not in free lists");
7787 }
7788 _sp->coalDeath(ffc->size());
7789 _sp->removeFreeChunkFromFreeLists(ffc);
7790 set_freeRangeInFreeLists(false);
7791 }
7792 if (fcInFreeLists) {
7793 _sp->coalDeath(chunkSize);
7794 assert(fc->size() == chunkSize,
7795 "The chunk has the wrong size or is not in the free lists");
7796 _sp->removeFreeChunkFromFreeLists(fc);
7797 }
7798 set_lastFreeRangeCoalesced(true);
7799 print_free_block_coalesced(fc);
7800 } else { // not in a free range and/or should not coalesce
7801 // Return the current free range and start a new one.
7802 if (inFreeRange()) {
7803 // In a free range but cannot coalesce with the right hand chunk.
7804 // Put the current free range into the free lists.
7805 flush_cur_free_chunk(freeFinger(),
7806 pointer_delta(fc_addr, freeFinger()));
7807 }
7808 // Set up for new free range. Pass along whether the right hand
7809 // chunk is in the free lists.
7810 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7811 }
7812 }
7813
7814 // Lookahead flush:
7815 // If we are tracking a free range, and this is the last chunk that
7816 // we'll look at because its end crosses past _limit, we'll preemptively
7817 // flush it along with any free range we may be holding on to. Note that
7818 // this can be the case only for an already free or freshly garbage
7819 // chunk. If this block is an object, it can never straddle
7820 // over _limit. The "straddling" occurs when _limit is set at
7821 // the previous end of the space when this cycle started, and
7822 // a subsequent heap expansion caused the previously co-terminal
7823 // free block to be coalesced with the newly expanded portion,
7824 // thus rendering _limit a non-block-boundary making it dangerous
7825 // for the sweeper to step over and examine.
7826 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7827 assert(inFreeRange(), "Should only be called if currently in a free range.");
7828 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7829 assert(_sp->used_region().contains(eob - 1),
7830 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7831 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7832 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7833 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size));
7834 if (eob >= _limit) {
7835 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7836 if (CMSTraceSweeper) {
7837 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7838 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7839 "[" PTR_FORMAT "," PTR_FORMAT ")",
7840 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7841 }
7842 // Return the storage we are tracking back into the free lists.
7843 if (CMSTraceSweeper) {
7844 gclog_or_tty->print_cr("Flushing ... ");
7845 }
7846 assert(freeFinger() < eob, "Error");
7847 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7848 }
7849 }
7850
7851 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7852 assert(inFreeRange(), "Should only be called if currently in a free range.");
7853 assert(size > 0,
7854 "A zero sized chunk cannot be added to the free lists.");
7855 if (!freeRangeInFreeLists()) {
7856 if (CMSTestInFreeList) {
7857 FreeChunk* fc = (FreeChunk*) chunk;
7858 fc->set_size(size);
7859 assert(!_sp->verify_chunk_in_free_list(fc),
7860 "chunk should not be in free lists yet");
7861 }
7862 if (CMSTraceSweeper) {
7863 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7864 p2i(chunk), size);
7865 }
7866 // A new free range is going to be starting. The current
7867 // free range has not been added to the free lists yet or
7868 // was removed so add it back.
7869 // If the current free range was coalesced, then the death
7870 // of the free range was recorded. Record a birth now.
7871 if (lastFreeRangeCoalesced()) {
7872 _sp->coalBirth(size);
7873 }
7874 _sp->addChunkAndRepairOffsetTable(chunk, size,
7875 lastFreeRangeCoalesced());
7876 } else if (CMSTraceSweeper) {
7877 gclog_or_tty->print_cr("Already in free list: nothing to flush");
7878 }
7879 set_inFreeRange(false);
7880 set_freeRangeInFreeLists(false);
7881 }
7882
7883 // We take a break if we've been at this for a while,
7884 // so as to avoid monopolizing the locks involved.
7885 void SweepClosure::do_yield_work(HeapWord* addr) {
7886 // Return current free chunk being used for coalescing (if any)
7887 // to the appropriate freelist. After yielding, the next
7888 // free block encountered will start a coalescing range of
7889 // free blocks. If the next free block is adjacent to the
7890 // chunk just flushed, they will need to wait for the next
7891 // sweep to be coalesced.
7892 if (inFreeRange()) {
7893 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7894 }
7895
7896 // First give up the locks, then yield, then re-lock.
7897 // We should probably use a constructor/destructor idiom to
7898 // do this unlock/lock or modify the MutexUnlocker class to
7899 // serve our purpose. XXX
7900 assert_lock_strong(_bitMap->lock());
7901 assert_lock_strong(_freelistLock);
7902 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7903 "CMS thread should hold CMS token");
7904 _bitMap->lock()->unlock();
7905 _freelistLock->unlock();
7906 ConcurrentMarkSweepThread::desynchronize(true);
7907 _collector->stopTimer();
7908 if (PrintCMSStatistics != 0) {
7909 _collector->incrementYields();
7910 }
7911
7912 // See the comment in coordinator_yield()
7913 for (unsigned i = 0; i < CMSYieldSleepCount &&
7914 ConcurrentMarkSweepThread::should_yield() &&
7915 !CMSCollector::foregroundGCIsActive(); ++i) {
7916 os::sleep(Thread::current(), 1, false);
7917 }
7918
7919 ConcurrentMarkSweepThread::synchronize(true);
7920 _freelistLock->lock();
7921 _bitMap->lock()->lock_without_safepoint_check();
7922 _collector->startTimer();
7923 }
7924
7925 #ifndef PRODUCT
7926 // This is actually very useful in a product build if it can
7927 // be called from the debugger. Compile it into the product
7928 // as needed.
7929 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7930 return debug_cms_space->verify_chunk_in_free_list(fc);
7931 }
7932 #endif
7933
7934 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7935 if (CMSTraceSweeper) {
7936 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7937 p2i(fc), fc->size());
7938 }
7939 }
7940
7941 // CMSIsAliveClosure
7942 bool CMSIsAliveClosure::do_object_b(oop obj) {
7943 HeapWord* addr = (HeapWord*)obj;
7944 return addr != NULL &&
7945 (!_span.contains(addr) || _bit_map->isMarked(addr));
7946 }
7947
7948
7949 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7950 MemRegion span,
7951 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7952 bool cpc):
7953 _collector(collector),
7954 _span(span),
7955 _bit_map(bit_map),
7956 _mark_stack(mark_stack),
7957 _concurrent_precleaning(cpc) {
7958 assert(!_span.is_empty(), "Empty span could spell trouble");
7959 }
7960
7961
7962 // CMSKeepAliveClosure: the serial version
7963 void CMSKeepAliveClosure::do_oop(oop obj) {
7964 HeapWord* addr = (HeapWord*)obj;
7965 if (_span.contains(addr) &&
7966 !_bit_map->isMarked(addr)) {
7967 _bit_map->mark(addr);
7968 bool simulate_overflow = false;
7969 NOT_PRODUCT(
7970 if (CMSMarkStackOverflowALot &&
7971 _collector->simulate_overflow()) {
7972 // simulate a stack overflow
7973 simulate_overflow = true;
7974 }
7975 )
7976 if (simulate_overflow || !_mark_stack->push(obj)) {
7977 if (_concurrent_precleaning) {
7978 // We dirty the overflown object and let the remark
7979 // phase deal with it.
7980 assert(_collector->overflow_list_is_empty(), "Error");
7981 // In the case of object arrays, we need to dirty all of
7982 // the cards that the object spans. No locking or atomics
7983 // are needed since no one else can be mutating the mod union
7984 // table.
7985 if (obj->is_objArray()) {
7986 size_t sz = obj->size();
7987 HeapWord* end_card_addr =
7988 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
7989 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7990 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7991 _collector->_modUnionTable.mark_range(redirty_range);
7992 } else {
7993 _collector->_modUnionTable.mark(addr);
7994 }
7995 _collector->_ser_kac_preclean_ovflw++;
7996 } else {
7997 _collector->push_on_overflow_list(obj);
7998 _collector->_ser_kac_ovflw++;
7999 }
8000 }
8001 }
8002 }
8003
8004 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8005 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8006
8007 // CMSParKeepAliveClosure: a parallel version of the above.
8008 // The work queues are private to each closure (thread),
8009 // but (may be) available for stealing by other threads.
8010 void CMSParKeepAliveClosure::do_oop(oop obj) {
8011 HeapWord* addr = (HeapWord*)obj;
8012 if (_span.contains(addr) &&
8013 !_bit_map->isMarked(addr)) {
8014 // In general, during recursive tracing, several threads
8015 // may be concurrently getting here; the first one to
8016 // "tag" it, claims it.
8017 if (_bit_map->par_mark(addr)) {
8018 bool res = _work_queue->push(obj);
8019 assert(res, "Low water mark should be much less than capacity");
8020 // Do a recursive trim in the hope that this will keep
8021 // stack usage lower, but leave some oops for potential stealers
8022 trim_queue(_low_water_mark);
8023 } // Else, another thread got there first
8024 }
8025 }
8026
8027 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8028 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8029
8030 void CMSParKeepAliveClosure::trim_queue(uint max) {
8031 while (_work_queue->size() > max) {
8032 oop new_oop;
8033 if (_work_queue->pop_local(new_oop)) {
8034 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8035 assert(_bit_map->isMarked((HeapWord*)new_oop),
8036 "no white objects on this stack!");
8037 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8038 // iterate over the oops in this oop, marking and pushing
8039 // the ones in CMS heap (i.e. in _span).
8040 new_oop->oop_iterate(&_mark_and_push);
8041 }
8042 }
8043 }
8044
8045 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8046 CMSCollector* collector,
8047 MemRegion span, CMSBitMap* bit_map,
8048 OopTaskQueue* work_queue):
8049 _collector(collector),
8050 _span(span),
8051 _bit_map(bit_map),
8052 _work_queue(work_queue) { }
8053
8054 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8055 HeapWord* addr = (HeapWord*)obj;
8056 if (_span.contains(addr) &&
8057 !_bit_map->isMarked(addr)) {
8058 if (_bit_map->par_mark(addr)) {
8059 bool simulate_overflow = false;
8060 NOT_PRODUCT(
8061 if (CMSMarkStackOverflowALot &&
8062 _collector->par_simulate_overflow()) {
8063 // simulate a stack overflow
8064 simulate_overflow = true;
8065 }
8066 )
8067 if (simulate_overflow || !_work_queue->push(obj)) {
8068 _collector->par_push_on_overflow_list(obj);
8069 _collector->_par_kac_ovflw++;
8070 }
8071 } // Else another thread got there already
8072 }
8073 }
8074
8075 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8076 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8077
8078 //////////////////////////////////////////////////////////////////
8079 // CMSExpansionCause /////////////////////////////
8080 //////////////////////////////////////////////////////////////////
8081 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8082 switch (cause) {
8083 case _no_expansion:
8084 return "No expansion";
8085 case _satisfy_free_ratio:
8086 return "Free ratio";
8087 case _satisfy_promotion:
8088 return "Satisfy promotion";
8089 case _satisfy_allocation:
8090 return "allocation";
8091 case _allocate_par_lab:
8092 return "Par LAB";
8093 case _allocate_par_spooling_space:
8094 return "Par Spooling Space";
8095 case _adaptive_size_policy:
8096 return "Ergonomics";
8097 default:
8098 return "unknown";
8099 }
8100 }
8101
8102 void CMSDrainMarkingStackClosure::do_void() {
8103 // the max number to take from overflow list at a time
8104 const size_t num = _mark_stack->capacity()/4;
8105 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8106 "Overflow list should be NULL during concurrent phases");
8107 while (!_mark_stack->isEmpty() ||
8108 // if stack is empty, check the overflow list
8109 _collector->take_from_overflow_list(num, _mark_stack)) {
8110 oop obj = _mark_stack->pop();
8111 HeapWord* addr = (HeapWord*)obj;
8112 assert(_span.contains(addr), "Should be within span");
8113 assert(_bit_map->isMarked(addr), "Should be marked");
8114 assert(obj->is_oop(), "Should be an oop");
8115 obj->oop_iterate(_keep_alive);
8116 }
8117 }
8118
8119 void CMSParDrainMarkingStackClosure::do_void() {
8120 // drain queue
8121 trim_queue(0);
8122 }
8123
8124 // Trim our work_queue so its length is below max at return
8125 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8126 while (_work_queue->size() > max) {
8127 oop new_oop;
8128 if (_work_queue->pop_local(new_oop)) {
8129 assert(new_oop->is_oop(), "Expected an oop");
8130 assert(_bit_map->isMarked((HeapWord*)new_oop),
8131 "no white objects on this stack!");
8132 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8133 // iterate over the oops in this oop, marking and pushing
8134 // the ones in CMS heap (i.e. in _span).
8135 new_oop->oop_iterate(&_mark_and_push);
8136 }
8137 }
8138 }
8139
8140 ////////////////////////////////////////////////////////////////////
8141 // Support for Marking Stack Overflow list handling and related code
8142 ////////////////////////////////////////////////////////////////////
8143 // Much of the following code is similar in shape and spirit to the
8144 // code used in ParNewGC. We should try and share that code
8145 // as much as possible in the future.
8146
8147 #ifndef PRODUCT
8148 // Debugging support for CMSStackOverflowALot
8149
8150 // It's OK to call this multi-threaded; the worst thing
8151 // that can happen is that we'll get a bunch of closely
8152 // spaced simulated overflows, but that's OK, in fact
8153 // probably good as it would exercise the overflow code
8154 // under contention.
8155 bool CMSCollector::simulate_overflow() {
8156 if (_overflow_counter-- <= 0) { // just being defensive
8157 _overflow_counter = CMSMarkStackOverflowInterval;
8158 return true;
8159 } else {
8160 return false;
8161 }
8162 }
8163
8164 bool CMSCollector::par_simulate_overflow() {
8165 return simulate_overflow();
8166 }
8167 #endif
8168
8169 // Single-threaded
8170 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8171 assert(stack->isEmpty(), "Expected precondition");
8172 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8173 size_t i = num;
8174 oop cur = _overflow_list;
8175 const markOop proto = markOopDesc::prototype();
8176 NOT_PRODUCT(ssize_t n = 0;)
8177 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8178 next = oop(cur->mark());
8179 cur->set_mark(proto); // until proven otherwise
8180 assert(cur->is_oop(), "Should be an oop");
8181 bool res = stack->push(cur);
8182 assert(res, "Bit off more than can chew?");
8183 NOT_PRODUCT(n++;)
8184 }
8185 _overflow_list = cur;
8186 #ifndef PRODUCT
8187 assert(_num_par_pushes >= n, "Too many pops?");
8188 _num_par_pushes -=n;
8189 #endif
8190 return !stack->isEmpty();
8191 }
8192
8193 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8194 // (MT-safe) Get a prefix of at most "num" from the list.
8195 // The overflow list is chained through the mark word of
8196 // each object in the list. We fetch the entire list,
8197 // break off a prefix of the right size and return the
8198 // remainder. If other threads try to take objects from
8199 // the overflow list at that time, they will wait for
8200 // some time to see if data becomes available. If (and
8201 // only if) another thread places one or more object(s)
8202 // on the global list before we have returned the suffix
8203 // to the global list, we will walk down our local list
8204 // to find its end and append the global list to
8205 // our suffix before returning it. This suffix walk can
8206 // prove to be expensive (quadratic in the amount of traffic)
8207 // when there are many objects in the overflow list and
8208 // there is much producer-consumer contention on the list.
8209 // *NOTE*: The overflow list manipulation code here and
8210 // in ParNewGeneration:: are very similar in shape,
8211 // except that in the ParNew case we use the old (from/eden)
8212 // copy of the object to thread the list via its klass word.
8213 // Because of the common code, if you make any changes in
8214 // the code below, please check the ParNew version to see if
8215 // similar changes might be needed.
8216 // CR 6797058 has been filed to consolidate the common code.
8217 bool CMSCollector::par_take_from_overflow_list(size_t num,
8218 OopTaskQueue* work_q,
8219 int no_of_gc_threads) {
8220 assert(work_q->size() == 0, "First empty local work queue");
8221 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8222 if (_overflow_list == NULL) {
8223 return false;
8224 }
8225 // Grab the entire list; we'll put back a suffix
8226 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8227 Thread* tid = Thread::current();
8228 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8229 // set to ParallelGCThreads.
8230 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8231 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8232 // If the list is busy, we spin for a short while,
8233 // sleeping between attempts to get the list.
8234 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8235 os::sleep(tid, sleep_time_millis, false);
8236 if (_overflow_list == NULL) {
8237 // Nothing left to take
8238 return false;
8239 } else if (_overflow_list != BUSY) {
8240 // Try and grab the prefix
8241 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8242 }
8243 }
8244 // If the list was found to be empty, or we spun long
8245 // enough, we give up and return empty-handed. If we leave
8246 // the list in the BUSY state below, it must be the case that
8247 // some other thread holds the overflow list and will set it
8248 // to a non-BUSY state in the future.
8249 if (prefix == NULL || prefix == BUSY) {
8250 // Nothing to take or waited long enough
8251 if (prefix == NULL) {
8252 // Write back the NULL in case we overwrote it with BUSY above
8253 // and it is still the same value.
8254 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8255 }
8256 return false;
8257 }
8258 assert(prefix != NULL && prefix != BUSY, "Error");
8259 size_t i = num;
8260 oop cur = prefix;
8261 // Walk down the first "num" objects, unless we reach the end.
8262 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8263 if (cur->mark() == NULL) {
8264 // We have "num" or fewer elements in the list, so there
8265 // is nothing to return to the global list.
8266 // Write back the NULL in lieu of the BUSY we wrote
8267 // above, if it is still the same value.
8268 if (_overflow_list == BUSY) {
8269 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8270 }
8271 } else {
8272 // Chop off the suffix and return it to the global list.
8273 assert(cur->mark() != BUSY, "Error");
8274 oop suffix_head = cur->mark(); // suffix will be put back on global list
8275 cur->set_mark(NULL); // break off suffix
8276 // It's possible that the list is still in the empty(busy) state
8277 // we left it in a short while ago; in that case we may be
8278 // able to place back the suffix without incurring the cost
8279 // of a walk down the list.
8280 oop observed_overflow_list = _overflow_list;
8281 oop cur_overflow_list = observed_overflow_list;
8282 bool attached = false;
8283 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8284 observed_overflow_list =
8285 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8286 if (cur_overflow_list == observed_overflow_list) {
8287 attached = true;
8288 break;
8289 } else cur_overflow_list = observed_overflow_list;
8290 }
8291 if (!attached) {
8292 // Too bad, someone else sneaked in (at least) an element; we'll need
8293 // to do a splice. Find tail of suffix so we can prepend suffix to global
8294 // list.
8295 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8296 oop suffix_tail = cur;
8297 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8298 "Tautology");
8299 observed_overflow_list = _overflow_list;
8300 do {
8301 cur_overflow_list = observed_overflow_list;
8302 if (cur_overflow_list != BUSY) {
8303 // Do the splice ...
8304 suffix_tail->set_mark(markOop(cur_overflow_list));
8305 } else { // cur_overflow_list == BUSY
8306 suffix_tail->set_mark(NULL);
8307 }
8308 // ... and try to place spliced list back on overflow_list ...
8309 observed_overflow_list =
8310 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8311 } while (cur_overflow_list != observed_overflow_list);
8312 // ... until we have succeeded in doing so.
8313 }
8314 }
8315
8316 // Push the prefix elements on work_q
8317 assert(prefix != NULL, "control point invariant");
8318 const markOop proto = markOopDesc::prototype();
8319 oop next;
8320 NOT_PRODUCT(ssize_t n = 0;)
8321 for (cur = prefix; cur != NULL; cur = next) {
8322 next = oop(cur->mark());
8323 cur->set_mark(proto); // until proven otherwise
8324 assert(cur->is_oop(), "Should be an oop");
8325 bool res = work_q->push(cur);
8326 assert(res, "Bit off more than we can chew?");
8327 NOT_PRODUCT(n++;)
8328 }
8329 #ifndef PRODUCT
8330 assert(_num_par_pushes >= n, "Too many pops?");
8331 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8332 #endif
8333 return true;
8334 }
8335
8336 // Single-threaded
8337 void CMSCollector::push_on_overflow_list(oop p) {
8338 NOT_PRODUCT(_num_par_pushes++;)
8339 assert(p->is_oop(), "Not an oop");
8340 preserve_mark_if_necessary(p);
8341 p->set_mark((markOop)_overflow_list);
8342 _overflow_list = p;
8343 }
8344
8345 // Multi-threaded; use CAS to prepend to overflow list
8346 void CMSCollector::par_push_on_overflow_list(oop p) {
8347 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8348 assert(p->is_oop(), "Not an oop");
8349 par_preserve_mark_if_necessary(p);
8350 oop observed_overflow_list = _overflow_list;
8351 oop cur_overflow_list;
8352 do {
8353 cur_overflow_list = observed_overflow_list;
8354 if (cur_overflow_list != BUSY) {
8355 p->set_mark(markOop(cur_overflow_list));
8356 } else {
8357 p->set_mark(NULL);
8358 }
8359 observed_overflow_list =
8360 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8361 } while (cur_overflow_list != observed_overflow_list);
8362 }
8363 #undef BUSY
8364
8365 // Single threaded
8366 // General Note on GrowableArray: pushes may silently fail
8367 // because we are (temporarily) out of C-heap for expanding
8368 // the stack. The problem is quite ubiquitous and affects
8369 // a lot of code in the JVM. The prudent thing for GrowableArray
8370 // to do (for now) is to exit with an error. However, that may
8371 // be too draconian in some cases because the caller may be
8372 // able to recover without much harm. For such cases, we
8373 // should probably introduce a "soft_push" method which returns
8374 // an indication of success or failure with the assumption that
8375 // the caller may be able to recover from a failure; code in
8376 // the VM can then be changed, incrementally, to deal with such
8377 // failures where possible, thus, incrementally hardening the VM
8378 // in such low resource situations.
8379 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8380 _preserved_oop_stack.push(p);
8381 _preserved_mark_stack.push(m);
8382 assert(m == p->mark(), "Mark word changed");
8383 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8384 "bijection");
8385 }
8386
8387 // Single threaded
8388 void CMSCollector::preserve_mark_if_necessary(oop p) {
8389 markOop m = p->mark();
8390 if (m->must_be_preserved(p)) {
8391 preserve_mark_work(p, m);
8392 }
8393 }
8394
8395 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8396 markOop m = p->mark();
8397 if (m->must_be_preserved(p)) {
8398 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8399 // Even though we read the mark word without holding
8400 // the lock, we are assured that it will not change
8401 // because we "own" this oop, so no other thread can
8402 // be trying to push it on the overflow list; see
8403 // the assertion in preserve_mark_work() that checks
8404 // that m == p->mark().
8405 preserve_mark_work(p, m);
8406 }
8407 }
8408
8409 // We should be able to do this multi-threaded,
8410 // a chunk of stack being a task (this is
8411 // correct because each oop only ever appears
8412 // once in the overflow list. However, it's
8413 // not very easy to completely overlap this with
8414 // other operations, so will generally not be done
8415 // until all work's been completed. Because we
8416 // expect the preserved oop stack (set) to be small,
8417 // it's probably fine to do this single-threaded.
8418 // We can explore cleverer concurrent/overlapped/parallel
8419 // processing of preserved marks if we feel the
8420 // need for this in the future. Stack overflow should
8421 // be so rare in practice and, when it happens, its
8422 // effect on performance so great that this will
8423 // likely just be in the noise anyway.
8424 void CMSCollector::restore_preserved_marks_if_any() {
8425 assert(SafepointSynchronize::is_at_safepoint(),
8426 "world should be stopped");
8427 assert(Thread::current()->is_ConcurrentGC_thread() ||
8428 Thread::current()->is_VM_thread(),
8429 "should be single-threaded");
8430 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8431 "bijection");
8432
8433 while (!_preserved_oop_stack.is_empty()) {
8434 oop p = _preserved_oop_stack.pop();
8435 assert(p->is_oop(), "Should be an oop");
8436 assert(_span.contains(p), "oop should be in _span");
8437 assert(p->mark() == markOopDesc::prototype(),
8438 "Set when taken from overflow list");
8439 markOop m = _preserved_mark_stack.pop();
8440 p->set_mark(m);
8441 }
8442 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8443 "stacks were cleared above");
8444 }
8445
8446 #ifndef PRODUCT
8447 bool CMSCollector::no_preserved_marks() const {
8448 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8449 }
8450 #endif
8451
8452 // Transfer some number of overflown objects to usual marking
8453 // stack. Return true if some objects were transferred.
8454 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8455 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8456 (size_t)ParGCDesiredObjsFromOverflowList);
8457
8458 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8459 assert(_collector->overflow_list_is_empty() || res,
8460 "If list is not empty, we should have taken something");
8461 assert(!res || !_mark_stack->isEmpty(),
8462 "If we took something, it should now be on our stack");
8463 return res;
8464 }
8465
8466 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8467 size_t res = _sp->block_size_no_stall(addr, _collector);
8468 if (_sp->block_is_obj(addr)) {
8469 if (_live_bit_map->isMarked(addr)) {
8470 // It can't have been dead in a previous cycle
8471 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8472 } else {
8473 _dead_bit_map->mark(addr); // mark the dead object
8474 }
8475 }
8476 // Could be 0, if the block size could not be computed without stalling.
8477 return res;
8478 }
8479
8480 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8481
8482 switch (phase) {
8483 case CMSCollector::InitialMarking:
8484 initialize(true /* fullGC */ ,
8485 cause /* cause of the GC */,
8486 true /* recordGCBeginTime */,
8487 true /* recordPreGCUsage */,
8488 false /* recordPeakUsage */,
8489 false /* recordPostGCusage */,
8490 true /* recordAccumulatedGCTime */,
8491 false /* recordGCEndTime */,
8492 false /* countCollection */ );
8493 break;
8494
8495 case CMSCollector::FinalMarking:
8496 initialize(true /* fullGC */ ,
8497 cause /* cause of the GC */,
8498 false /* recordGCBeginTime */,
8499 false /* recordPreGCUsage */,
8500 false /* recordPeakUsage */,
8501 false /* recordPostGCusage */,
8502 true /* recordAccumulatedGCTime */,
8503 false /* recordGCEndTime */,
8504 false /* countCollection */ );
8505 break;
8506
8507 case CMSCollector::Sweeping:
8508 initialize(true /* fullGC */ ,
8509 cause /* cause of the GC */,
8510 false /* recordGCBeginTime */,
8511 false /* recordPreGCUsage */,
8512 true /* recordPeakUsage */,
8513 true /* recordPostGCusage */,
8514 false /* recordAccumulatedGCTime */,
8515 true /* recordGCEndTime */,
8516 true /* countCollection */ );
8517 break;
8518
8519 default:
8520 ShouldNotReachHere();
8521 }
8522 }