1 /*
2 * Copyright (c) 2001, 2014, 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/cardTableRS.hpp"
46 #include "memory/collectorPolicy.hpp"
47 #include "memory/gcLocker.inline.hpp"
48 #include "memory/genCollectedHeap.hpp"
49 #include "memory/genMarkSweep.hpp"
50 #include "memory/genOopClosures.inline.hpp"
51 #include "memory/iterator.inline.hpp"
52 #include "memory/padded.hpp"
53 #include "memory/referencePolicy.hpp"
54 #include "memory/resourceArea.hpp"
55 #include "memory/tenuredGeneration.hpp"
56 #include "oops/oop.inline.hpp"
57 #include "prims/jvmtiExport.hpp"
58 #include "runtime/atomic.inline.hpp"
59 #include "runtime/globals_extension.hpp"
60 #include "runtime/handles.inline.hpp"
61 #include "runtime/java.hpp"
62 #include "runtime/orderAccess.inline.hpp"
63 #include "runtime/vmThread.hpp"
64 #include "services/memoryService.hpp"
65 #include "services/runtimeService.hpp"
66
67 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
68
69 // statics
70 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
71 bool CMSCollector::_full_gc_requested = false;
72 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
73
74 //////////////////////////////////////////////////////////////////
75 // In support of CMS/VM thread synchronization
76 //////////////////////////////////////////////////////////////////
77 // We split use of the CGC_lock into 2 "levels".
78 // The low-level locking is of the usual CGC_lock monitor. We introduce
79 // a higher level "token" (hereafter "CMS token") built on top of the
80 // low level monitor (hereafter "CGC lock").
81 // The token-passing protocol gives priority to the VM thread. The
82 // CMS-lock doesn't provide any fairness guarantees, but clients
83 // should ensure that it is only held for very short, bounded
84 // durations.
85 //
86 // When either of the CMS thread or the VM thread is involved in
87 // collection operations during which it does not want the other
88 // thread to interfere, it obtains the CMS token.
89 //
90 // If either thread tries to get the token while the other has
91 // it, that thread waits. However, if the VM thread and CMS thread
92 // both want the token, then the VM thread gets priority while the
93 // CMS thread waits. This ensures, for instance, that the "concurrent"
94 // phases of the CMS thread's work do not block out the VM thread
95 // for long periods of time as the CMS thread continues to hog
96 // the token. (See bug 4616232).
97 //
98 // The baton-passing functions are, however, controlled by the
99 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
100 // and here the low-level CMS lock, not the high level token,
101 // ensures mutual exclusion.
102 //
103 // Two important conditions that we have to satisfy:
104 // 1. if a thread does a low-level wait on the CMS lock, then it
105 // relinquishes the CMS token if it were holding that token
106 // when it acquired the low-level CMS lock.
107 // 2. any low-level notifications on the low-level lock
108 // should only be sent when a thread has relinquished the token.
109 //
110 // In the absence of either property, we'd have potential deadlock.
111 //
112 // We protect each of the CMS (concurrent and sequential) phases
113 // with the CMS _token_, not the CMS _lock_.
114 //
115 // The only code protected by CMS lock is the token acquisition code
116 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
117 // baton-passing code.
118 //
119 // Unfortunately, i couldn't come up with a good abstraction to factor and
120 // hide the naked CGC_lock manipulation in the baton-passing code
121 // further below. That's something we should try to do. Also, the proof
122 // of correctness of this 2-level locking scheme is far from obvious,
123 // and potentially quite slippery. We have an uneasy suspicion, for instance,
124 // that there may be a theoretical possibility of delay/starvation in the
125 // low-level lock/wait/notify scheme used for the baton-passing because of
126 // potential interference with the priority scheme embodied in the
127 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
128 // invocation further below and marked with "XXX 20011219YSR".
129 // Indeed, as we note elsewhere, this may become yet more slippery
130 // in the presence of multiple CMS and/or multiple VM threads. XXX
131
132 class CMSTokenSync: public StackObj {
133 private:
134 bool _is_cms_thread;
135 public:
136 CMSTokenSync(bool is_cms_thread):
137 _is_cms_thread(is_cms_thread) {
138 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
139 "Incorrect argument to constructor");
140 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
141 }
142
143 ~CMSTokenSync() {
144 assert(_is_cms_thread ?
145 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
146 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
147 "Incorrect state");
148 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
149 }
150 };
151
152 // Convenience class that does a CMSTokenSync, and then acquires
153 // upto three locks.
154 class CMSTokenSyncWithLocks: public CMSTokenSync {
155 private:
156 // Note: locks are acquired in textual declaration order
157 // and released in the opposite order
158 MutexLockerEx _locker1, _locker2, _locker3;
159 public:
160 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
161 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
162 CMSTokenSync(is_cms_thread),
163 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
164 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
165 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
166 { }
167 };
168
169
170 //////////////////////////////////////////////////////////////////
171 // Concurrent Mark-Sweep Generation /////////////////////////////
172 //////////////////////////////////////////////////////////////////
173
174 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
175
176 // This struct contains per-thread things necessary to support parallel
177 // young-gen collection.
178 class CMSParGCThreadState: public CHeapObj<mtGC> {
179 public:
180 CFLS_LAB lab;
181 PromotionInfo promo;
182
183 // Constructor.
184 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
185 promo.setSpace(cfls);
186 }
187 };
188
189 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
190 ReservedSpace rs, size_t initial_byte_size, int level,
191 CardTableRS* ct, bool use_adaptive_freelists,
192 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
193 CardGeneration(rs, initial_byte_size, level, ct),
194 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
195 _debug_collection_type(Concurrent_collection_type),
196 _did_compact(false)
197 {
198 HeapWord* bottom = (HeapWord*) _virtual_space.low();
199 HeapWord* end = (HeapWord*) _virtual_space.high();
200
201 _direct_allocated_words = 0;
202 NOT_PRODUCT(
203 _numObjectsPromoted = 0;
204 _numWordsPromoted = 0;
205 _numObjectsAllocated = 0;
206 _numWordsAllocated = 0;
207 )
208
209 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
210 use_adaptive_freelists,
211 dictionaryChoice);
212 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
213 if (_cmsSpace == NULL) {
214 vm_exit_during_initialization(
215 "CompactibleFreeListSpace allocation failure");
216 }
217 _cmsSpace->_gen = this;
218
219 _gc_stats = new CMSGCStats();
220
221 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
222 // offsets match. The ability to tell free chunks from objects
223 // depends on this property.
224 debug_only(
225 FreeChunk* junk = NULL;
226 assert(UseCompressedClassPointers ||
227 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
228 "Offset of FreeChunk::_prev within FreeChunk must match"
229 " that of OopDesc::_klass within OopDesc");
230 )
231 if (CollectedHeap::use_parallel_gc_threads()) {
232 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
233 _par_gc_thread_states =
234 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
235 if (_par_gc_thread_states == NULL) {
236 vm_exit_during_initialization("Could not allocate par gc structs");
237 }
238 for (uint i = 0; i < ParallelGCThreads; i++) {
239 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
240 if (_par_gc_thread_states[i] == NULL) {
241 vm_exit_during_initialization("Could not allocate par gc structs");
242 }
243 }
244 } else {
245 _par_gc_thread_states = NULL;
246 }
247 _incremental_collection_failed = false;
248 // The "dilatation_factor" is the expansion that can occur on
249 // account of the fact that the minimum object size in the CMS
250 // generation may be larger than that in, say, a contiguous young
251 // generation.
252 // Ideally, in the calculation below, we'd compute the dilatation
253 // factor as: MinChunkSize/(promoting_gen's min object size)
254 // Since we do not have such a general query interface for the
255 // promoting generation, we'll instead just use the minimum
256 // object size (which today is a header's worth of space);
257 // note that all arithmetic is in units of HeapWords.
258 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
259 assert(_dilatation_factor >= 1.0, "from previous assert");
260 }
261
262
263 // The field "_initiating_occupancy" represents the occupancy percentage
264 // at which we trigger a new collection cycle. Unless explicitly specified
265 // via CMSInitiatingOccupancyFraction (argument "io" below), it
266 // is calculated by:
267 //
268 // Let "f" be MinHeapFreeRatio in
269 //
270 // _initiating_occupancy = 100-f +
271 // f * (CMSTriggerRatio/100)
272 // where CMSTriggerRatio is the argument "tr" below.
273 //
274 // That is, if we assume the heap is at its desired maximum occupancy at the
275 // end of a collection, we let CMSTriggerRatio of the (purported) free
276 // space be allocated before initiating a new collection cycle.
277 //
278 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
279 assert(io <= 100 && tr <= 100, "Check the arguments");
280 if (io >= 0) {
281 _initiating_occupancy = (double)io / 100.0;
282 } else {
283 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
284 (double)(tr * MinHeapFreeRatio) / 100.0)
285 / 100.0;
286 }
287 }
288
289 void ConcurrentMarkSweepGeneration::ref_processor_init() {
290 assert(collector() != NULL, "no collector");
291 collector()->ref_processor_init();
292 }
293
294 void CMSCollector::ref_processor_init() {
295 if (_ref_processor == NULL) {
296 // Allocate and initialize a reference processor
297 _ref_processor =
298 new ReferenceProcessor(_span, // span
299 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
300 (int) ParallelGCThreads, // mt processing degree
301 _cmsGen->refs_discovery_is_mt(), // mt discovery
302 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
303 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
304 &_is_alive_closure); // closure for liveness info
305 // Initialize the _ref_processor field of CMSGen
306 _cmsGen->set_ref_processor(_ref_processor);
307
308 }
309 }
310
311 AdaptiveSizePolicy* CMSCollector::size_policy() {
312 GenCollectedHeap* gch = GenCollectedHeap::heap();
313 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
314 "Wrong type of heap");
315 return gch->gen_policy()->size_policy();
316 }
317
318 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
319
320 const char* gen_name = "old";
321 GenCollectorPolicy* gcp = (GenCollectorPolicy*) GenCollectedHeap::heap()->collector_policy();
322
323 // Generation Counters - generation 1, 1 subspace
324 _gen_counters = new GenerationCounters(gen_name, 1, 1,
325 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
326
327 _space_counters = new GSpaceCounters(gen_name, 0,
328 _virtual_space.reserved_size(),
329 this, _gen_counters);
330 }
331
332 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
333 _cms_gen(cms_gen)
334 {
335 assert(alpha <= 100, "bad value");
336 _saved_alpha = alpha;
337
338 // Initialize the alphas to the bootstrap value of 100.
339 _gc0_alpha = _cms_alpha = 100;
340
341 _cms_begin_time.update();
342 _cms_end_time.update();
343
344 _gc0_duration = 0.0;
345 _gc0_period = 0.0;
346 _gc0_promoted = 0;
347
348 _cms_duration = 0.0;
349 _cms_period = 0.0;
350 _cms_allocated = 0;
351
352 _cms_used_at_gc0_begin = 0;
353 _cms_used_at_gc0_end = 0;
354 _allow_duty_cycle_reduction = false;
355 _valid_bits = 0;
356 }
357
358 double CMSStats::cms_free_adjustment_factor(size_t free) const {
359 // TBD: CR 6909490
360 return 1.0;
361 }
362
363 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
364 }
365
366 // If promotion failure handling is on use
367 // the padded average size of the promotion for each
368 // young generation collection.
369 double CMSStats::time_until_cms_gen_full() const {
370 size_t cms_free = _cms_gen->cmsSpace()->free();
371 GenCollectedHeap* gch = GenCollectedHeap::heap();
372 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
373 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
374 if (cms_free > expected_promotion) {
375 // Start a cms collection if there isn't enough space to promote
376 // for the next minor collection. Use the padded average as
377 // a safety factor.
378 cms_free -= expected_promotion;
379
380 // Adjust by the safety factor.
381 double cms_free_dbl = (double)cms_free;
382 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
383 // Apply a further correction factor which tries to adjust
384 // for recent occurance of concurrent mode failures.
385 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
386 cms_free_dbl = cms_free_dbl * cms_adjustment;
387
388 if (PrintGCDetails && Verbose) {
389 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
390 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
391 cms_free, expected_promotion);
392 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
393 cms_free_dbl, cms_consumption_rate() + 1.0);
394 }
395 // Add 1 in case the consumption rate goes to zero.
396 return cms_free_dbl / (cms_consumption_rate() + 1.0);
397 }
398 return 0.0;
399 }
400
401 // Compare the duration of the cms collection to the
402 // time remaining before the cms generation is empty.
403 // Note that the time from the start of the cms collection
404 // to the start of the cms sweep (less than the total
405 // duration of the cms collection) can be used. This
406 // has been tried and some applications experienced
407 // promotion failures early in execution. This was
408 // possibly because the averages were not accurate
409 // enough at the beginning.
410 double CMSStats::time_until_cms_start() const {
411 // We add "gc0_period" to the "work" calculation
412 // below because this query is done (mostly) at the
413 // end of a scavenge, so we need to conservatively
414 // account for that much possible delay
415 // in the query so as to avoid concurrent mode failures
416 // due to starting the collection just a wee bit too
417 // late.
418 double work = cms_duration() + gc0_period();
419 double deadline = time_until_cms_gen_full();
420 // If a concurrent mode failure occurred recently, we want to be
421 // more conservative and halve our expected time_until_cms_gen_full()
422 if (work > deadline) {
423 if (Verbose && PrintGCDetails) {
424 gclog_or_tty->print(
425 " CMSCollector: collect because of anticipated promotion "
426 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
427 gc0_period(), time_until_cms_gen_full());
428 }
429 return 0.0;
430 }
431 return work - deadline;
432 }
433
434 #ifndef PRODUCT
435 void CMSStats::print_on(outputStream *st) const {
436 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
437 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
438 gc0_duration(), gc0_period(), gc0_promoted());
439 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
440 cms_duration(), cms_duration_per_mb(),
441 cms_period(), cms_allocated());
442 st->print(",cms_since_beg=%g,cms_since_end=%g",
443 cms_time_since_begin(), cms_time_since_end());
444 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
445 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
446
447 if (valid()) {
448 st->print(",promo_rate=%g,cms_alloc_rate=%g",
449 promotion_rate(), cms_allocation_rate());
450 st->print(",cms_consumption_rate=%g,time_until_full=%g",
451 cms_consumption_rate(), time_until_cms_gen_full());
452 }
453 st->print(" ");
454 }
455 #endif // #ifndef PRODUCT
456
457 CMSCollector::CollectorState CMSCollector::_collectorState =
458 CMSCollector::Idling;
459 bool CMSCollector::_foregroundGCIsActive = false;
460 bool CMSCollector::_foregroundGCShouldWait = false;
461
462 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
463 CardTableRS* ct,
464 ConcurrentMarkSweepPolicy* cp):
465 _cmsGen(cmsGen),
466 _ct(ct),
467 _ref_processor(NULL), // will be set later
468 _conc_workers(NULL), // may be set later
469 _abort_preclean(false),
470 _start_sampling(false),
471 _between_prologue_and_epilogue(false),
472 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
473 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
474 -1 /* lock-free */, "No_lock" /* dummy */),
475 _modUnionClosure(&_modUnionTable),
476 _modUnionClosurePar(&_modUnionTable),
477 // Adjust my span to cover old (cms) gen
478 _span(cmsGen->reserved()),
479 // Construct the is_alive_closure with _span & markBitMap
480 _is_alive_closure(_span, &_markBitMap),
481 _restart_addr(NULL),
482 _overflow_list(NULL),
483 _stats(cmsGen),
484 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true)),
485 _eden_chunk_array(NULL), // may be set in ctor body
486 _eden_chunk_capacity(0), // -- ditto --
487 _eden_chunk_index(0), // -- ditto --
488 _survivor_plab_array(NULL), // -- ditto --
489 _survivor_chunk_array(NULL), // -- ditto --
490 _survivor_chunk_capacity(0), // -- ditto --
491 _survivor_chunk_index(0), // -- ditto --
492 _ser_pmc_preclean_ovflw(0),
493 _ser_kac_preclean_ovflw(0),
494 _ser_pmc_remark_ovflw(0),
495 _par_pmc_remark_ovflw(0),
496 _ser_kac_ovflw(0),
497 _par_kac_ovflw(0),
498 #ifndef PRODUCT
499 _num_par_pushes(0),
500 #endif
501 _collection_count_start(0),
502 _verifying(false),
503 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
504 _completed_initialization(false),
505 _collector_policy(cp),
506 _should_unload_classes(CMSClassUnloadingEnabled),
507 _concurrent_cycles_since_last_unload(0),
508 _roots_scanning_options(SharedHeap::SO_None),
509 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
510 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
511 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
512 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
513 _cms_start_registered(false)
514 {
515 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
516 ExplicitGCInvokesConcurrent = true;
517 }
518 // Now expand the span and allocate the collection support structures
519 // (MUT, marking bit map etc.) to cover both generations subject to
520 // collection.
521
522 // For use by dirty card to oop closures.
523 _cmsGen->cmsSpace()->set_collector(this);
524
525 // Allocate MUT and marking bit map
526 {
527 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
528 if (!_markBitMap.allocate(_span)) {
529 warning("Failed to allocate CMS Bit Map");
530 return;
531 }
532 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
533 }
534 {
535 _modUnionTable.allocate(_span);
536 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
537 }
538
539 if (!_markStack.allocate(MarkStackSize)) {
540 warning("Failed to allocate CMS Marking Stack");
541 return;
542 }
543
544 // Support for multi-threaded concurrent phases
545 if (CMSConcurrentMTEnabled) {
546 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
547 // just for now
548 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
549 }
550 if (ConcGCThreads > 1) {
551 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
552 ConcGCThreads, true);
553 if (_conc_workers == NULL) {
554 warning("GC/CMS: _conc_workers allocation failure: "
555 "forcing -CMSConcurrentMTEnabled");
556 CMSConcurrentMTEnabled = false;
557 } else {
558 _conc_workers->initialize_workers();
559 }
560 } else {
561 CMSConcurrentMTEnabled = false;
562 }
563 }
564 if (!CMSConcurrentMTEnabled) {
565 ConcGCThreads = 0;
566 } else {
567 // Turn off CMSCleanOnEnter optimization temporarily for
568 // the MT case where it's not fixed yet; see 6178663.
569 CMSCleanOnEnter = false;
570 }
571 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
572 "Inconsistency");
573
574 // Parallel task queues; these are shared for the
575 // concurrent and stop-world phases of CMS, but
576 // are not shared with parallel scavenge (ParNew).
577 {
578 uint i;
579 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
580
581 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
582 || ParallelRefProcEnabled)
583 && num_queues > 0) {
584 _task_queues = new OopTaskQueueSet(num_queues);
585 if (_task_queues == NULL) {
586 warning("task_queues allocation failure.");
587 return;
588 }
589 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
590 if (_hash_seed == NULL) {
591 warning("_hash_seed array allocation failure");
592 return;
593 }
594
595 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
596 for (i = 0; i < num_queues; i++) {
597 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
598 if (q == NULL) {
599 warning("work_queue allocation failure.");
600 return;
601 }
602 _task_queues->register_queue(i, q);
603 }
604 for (i = 0; i < num_queues; i++) {
605 _task_queues->queue(i)->initialize();
606 _hash_seed[i] = 17; // copied from ParNew
607 }
608 }
609 }
610
611 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
612
613 // Clip CMSBootstrapOccupancy between 0 and 100.
614 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
615
616 _full_gcs_since_conc_gc = 0;
617
618 // Now tell CMS generations the identity of their collector
619 ConcurrentMarkSweepGeneration::set_collector(this);
620
621 // Create & start a CMS thread for this CMS collector
622 _cmsThread = ConcurrentMarkSweepThread::start(this);
623 assert(cmsThread() != NULL, "CMS Thread should have been created");
624 assert(cmsThread()->collector() == this,
625 "CMS Thread should refer to this gen");
626 assert(CGC_lock != NULL, "Where's the CGC_lock?");
627
628 // Support for parallelizing young gen rescan
629 GenCollectedHeap* gch = GenCollectedHeap::heap();
630 _young_gen = gch->prev_gen(_cmsGen);
631 if (gch->supports_inline_contig_alloc()) {
632 _top_addr = gch->top_addr();
633 _end_addr = gch->end_addr();
634 assert(_young_gen != NULL, "no _young_gen");
635 _eden_chunk_index = 0;
636 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
637 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
638 if (_eden_chunk_array == NULL) {
639 _eden_chunk_capacity = 0;
640 warning("GC/CMS: _eden_chunk_array allocation failure");
641 }
642 }
643 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
644
645 // Support for parallelizing survivor space rescan
646 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
647 const size_t max_plab_samples =
648 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
649
650 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
651 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
652 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
653 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
654 || _cursor == NULL) {
655 warning("Failed to allocate survivor plab/chunk array");
656 if (_survivor_plab_array != NULL) {
657 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
658 _survivor_plab_array = NULL;
659 }
660 if (_survivor_chunk_array != NULL) {
661 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
662 _survivor_chunk_array = NULL;
663 }
664 if (_cursor != NULL) {
665 FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
666 _cursor = NULL;
667 }
668 } else {
669 _survivor_chunk_capacity = 2*max_plab_samples;
670 for (uint i = 0; i < ParallelGCThreads; i++) {
671 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
672 if (vec == NULL) {
673 warning("Failed to allocate survivor plab array");
674 for (int j = i; j > 0; j--) {
675 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
676 }
677 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
678 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
679 _survivor_plab_array = NULL;
680 _survivor_chunk_array = NULL;
681 _survivor_chunk_capacity = 0;
682 break;
683 } else {
684 ChunkArray* cur =
685 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
686 max_plab_samples);
687 assert(cur->end() == 0, "Should be 0");
688 assert(cur->array() == vec, "Should be vec");
689 assert(cur->capacity() == max_plab_samples, "Error");
690 }
691 }
692 }
693 }
694 assert( ( _survivor_plab_array != NULL
695 && _survivor_chunk_array != NULL)
696 || ( _survivor_chunk_capacity == 0
697 && _survivor_chunk_index == 0),
698 "Error");
699
700 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
701 _gc_counters = new CollectorCounters("CMS", 1);
702 _completed_initialization = true;
703 _inter_sweep_timer.start(); // start of time
704 }
705
706 const char* ConcurrentMarkSweepGeneration::name() const {
707 return "concurrent mark-sweep generation";
708 }
709 void ConcurrentMarkSweepGeneration::update_counters() {
710 if (UsePerfData) {
711 _space_counters->update_all();
712 _gen_counters->update_all();
713 }
714 }
715
716 // this is an optimized version of update_counters(). it takes the
717 // used value as a parameter rather than computing it.
718 //
719 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
720 if (UsePerfData) {
721 _space_counters->update_used(used);
722 _space_counters->update_capacity();
723 _gen_counters->update_all();
724 }
725 }
726
727 void ConcurrentMarkSweepGeneration::print() const {
728 Generation::print();
729 cmsSpace()->print();
730 }
731
732 #ifndef PRODUCT
733 void ConcurrentMarkSweepGeneration::print_statistics() {
734 cmsSpace()->printFLCensus(0);
735 }
736 #endif
737
738 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
739 GenCollectedHeap* gch = GenCollectedHeap::heap();
740 if (PrintGCDetails) {
741 if (Verbose) {
742 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
743 level(), short_name(), s, used(), capacity());
744 } else {
745 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
746 level(), short_name(), s, used() / K, capacity() / K);
747 }
748 }
749 if (Verbose) {
750 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
751 gch->used(), gch->capacity());
752 } else {
753 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
754 gch->used() / K, gch->capacity() / K);
755 }
756 }
757
758 size_t
759 ConcurrentMarkSweepGeneration::contiguous_available() const {
760 // dld proposes an improvement in precision here. If the committed
761 // part of the space ends in a free block we should add that to
762 // uncommitted size in the calculation below. Will make this
763 // change later, staying with the approximation below for the
764 // time being. -- ysr.
765 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
766 }
767
768 size_t
769 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
770 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
771 }
772
773 size_t ConcurrentMarkSweepGeneration::max_available() const {
774 return free() + _virtual_space.uncommitted_size();
775 }
776
777 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
778 size_t available = max_available();
779 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
780 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
781 if (Verbose && PrintGCDetails) {
782 gclog_or_tty->print_cr(
783 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
784 "max_promo("SIZE_FORMAT")",
785 res? "":" not", available, res? ">=":"<",
786 av_promo, max_promotion_in_bytes);
787 }
788 return res;
789 }
790
791 // At a promotion failure dump information on block layout in heap
792 // (cms old generation).
793 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
794 if (CMSDumpAtPromotionFailure) {
795 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
796 }
797 }
798
799 CompactibleSpace*
800 ConcurrentMarkSweepGeneration::first_compaction_space() const {
801 return _cmsSpace;
802 }
803
804 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
805 // Clear the promotion information. These pointers can be adjusted
806 // along with all the other pointers into the heap but
807 // compaction is expected to be a rare event with
808 // a heap using cms so don't do it without seeing the need.
809 if (CollectedHeap::use_parallel_gc_threads()) {
810 for (uint i = 0; i < ParallelGCThreads; i++) {
811 _par_gc_thread_states[i]->promo.reset();
812 }
813 }
814 }
815
816 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
817 blk->do_space(_cmsSpace);
818 }
819
820 void ConcurrentMarkSweepGeneration::compute_new_size() {
821 assert_locked_or_safepoint(Heap_lock);
822
823 // If incremental collection failed, we just want to expand
824 // to the limit.
825 if (incremental_collection_failed()) {
826 clear_incremental_collection_failed();
827 grow_to_reserved();
828 return;
829 }
830
831 // The heap has been compacted but not reset yet.
832 // Any metric such as free() or used() will be incorrect.
833
834 CardGeneration::compute_new_size();
835
836 // Reset again after a possible resizing
837 if (did_compact()) {
838 cmsSpace()->reset_after_compaction();
839 }
840 }
841
842 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
843 assert_locked_or_safepoint(Heap_lock);
844
845 // If incremental collection failed, we just want to expand
846 // to the limit.
847 if (incremental_collection_failed()) {
848 clear_incremental_collection_failed();
849 grow_to_reserved();
850 return;
851 }
852
853 double free_percentage = ((double) free()) / capacity();
854 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
855 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
856
857 // compute expansion delta needed for reaching desired free percentage
858 if (free_percentage < desired_free_percentage) {
859 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
860 assert(desired_capacity >= capacity(), "invalid expansion size");
861 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
862 if (PrintGCDetails && Verbose) {
863 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
864 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
865 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
866 gclog_or_tty->print_cr(" Desired free fraction %f",
867 desired_free_percentage);
868 gclog_or_tty->print_cr(" Maximum free fraction %f",
869 maximum_free_percentage);
870 gclog_or_tty->print_cr(" Capacity "SIZE_FORMAT, capacity()/1000);
871 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
872 desired_capacity/1000);
873 int prev_level = level() - 1;
874 if (prev_level >= 0) {
875 size_t prev_size = 0;
876 GenCollectedHeap* gch = GenCollectedHeap::heap();
877 Generation* prev_gen = gch->_gens[prev_level];
878 prev_size = prev_gen->capacity();
879 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
880 prev_size/1000);
881 }
882 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
883 unsafe_max_alloc_nogc()/1000);
884 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
885 contiguous_available()/1000);
886 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
887 expand_bytes);
888 }
889 // safe if expansion fails
890 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
891 if (PrintGCDetails && Verbose) {
892 gclog_or_tty->print_cr(" Expanded free fraction %f",
893 ((double) free()) / capacity());
894 }
895 } else {
896 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
897 assert(desired_capacity <= capacity(), "invalid expansion size");
898 size_t shrink_bytes = capacity() - desired_capacity;
899 // Don't shrink unless the delta is greater than the minimum shrink we want
900 if (shrink_bytes >= MinHeapDeltaBytes) {
901 shrink_free_list_by(shrink_bytes);
902 }
903 }
904 }
905
906 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
907 return cmsSpace()->freelistLock();
908 }
909
910 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
911 bool tlab) {
912 CMSSynchronousYieldRequest yr;
913 MutexLockerEx x(freelistLock(),
914 Mutex::_no_safepoint_check_flag);
915 return have_lock_and_allocate(size, tlab);
916 }
917
918 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
919 bool tlab /* ignored */) {
920 assert_lock_strong(freelistLock());
921 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
922 HeapWord* res = cmsSpace()->allocate(adjustedSize);
923 // Allocate the object live (grey) if the background collector has
924 // started marking. This is necessary because the marker may
925 // have passed this address and consequently this object will
926 // not otherwise be greyed and would be incorrectly swept up.
927 // Note that if this object contains references, the writing
928 // of those references will dirty the card containing this object
929 // allowing the object to be blackened (and its references scanned)
930 // either during a preclean phase or at the final checkpoint.
931 if (res != NULL) {
932 // We may block here with an uninitialized object with
933 // its mark-bit or P-bits not yet set. Such objects need
934 // to be safely navigable by block_start().
935 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
936 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
937 collector()->direct_allocated(res, adjustedSize);
938 _direct_allocated_words += adjustedSize;
939 // allocation counters
940 NOT_PRODUCT(
941 _numObjectsAllocated++;
942 _numWordsAllocated += (int)adjustedSize;
943 )
944 }
945 return res;
946 }
947
948 // In the case of direct allocation by mutators in a generation that
949 // is being concurrently collected, the object must be allocated
950 // live (grey) if the background collector has started marking.
951 // This is necessary because the marker may
952 // have passed this address and consequently this object will
953 // not otherwise be greyed and would be incorrectly swept up.
954 // Note that if this object contains references, the writing
955 // of those references will dirty the card containing this object
956 // allowing the object to be blackened (and its references scanned)
957 // either during a preclean phase or at the final checkpoint.
958 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
959 assert(_markBitMap.covers(start, size), "Out of bounds");
960 if (_collectorState >= Marking) {
961 MutexLockerEx y(_markBitMap.lock(),
962 Mutex::_no_safepoint_check_flag);
963 // [see comments preceding SweepClosure::do_blk() below for details]
964 //
965 // Can the P-bits be deleted now? JJJ
966 //
967 // 1. need to mark the object as live so it isn't collected
968 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
969 // 3. need to mark the end of the object so marking, precleaning or sweeping
970 // can skip over uninitialized or unparsable objects. An allocated
971 // object is considered uninitialized for our purposes as long as
972 // its klass word is NULL. All old gen objects are parsable
973 // as soon as they are initialized.)
974 _markBitMap.mark(start); // object is live
975 _markBitMap.mark(start + 1); // object is potentially uninitialized?
976 _markBitMap.mark(start + size - 1);
977 // mark end of object
978 }
979 // check that oop looks uninitialized
980 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
981 }
982
983 void CMSCollector::promoted(bool par, HeapWord* start,
984 bool is_obj_array, size_t obj_size) {
985 assert(_markBitMap.covers(start), "Out of bounds");
986 // See comment in direct_allocated() about when objects should
987 // be allocated live.
988 if (_collectorState >= Marking) {
989 // we already hold the marking bit map lock, taken in
990 // the prologue
991 if (par) {
992 _markBitMap.par_mark(start);
993 } else {
994 _markBitMap.mark(start);
995 }
996 // We don't need to mark the object as uninitialized (as
997 // in direct_allocated above) because this is being done with the
998 // world stopped and the object will be initialized by the
999 // time the marking, precleaning or sweeping get to look at it.
1000 // But see the code for copying objects into the CMS generation,
1001 // where we need to ensure that concurrent readers of the
1002 // block offset table are able to safely navigate a block that
1003 // is in flux from being free to being allocated (and in
1004 // transition while being copied into) and subsequently
1005 // becoming a bona-fide object when the copy/promotion is complete.
1006 assert(SafepointSynchronize::is_at_safepoint(),
1007 "expect promotion only at safepoints");
1008
1009 if (_collectorState < Sweeping) {
1010 // Mark the appropriate cards in the modUnionTable, so that
1011 // this object gets scanned before the sweep. If this is
1012 // not done, CMS generation references in the object might
1013 // not get marked.
1014 // For the case of arrays, which are otherwise precisely
1015 // marked, we need to dirty the entire array, not just its head.
1016 if (is_obj_array) {
1017 // The [par_]mark_range() method expects mr.end() below to
1018 // be aligned to the granularity of a bit's representation
1019 // in the heap. In the case of the MUT below, that's a
1020 // card size.
1021 MemRegion mr(start,
1022 (HeapWord*)round_to((intptr_t)(start + obj_size),
1023 CardTableModRefBS::card_size /* bytes */));
1024 if (par) {
1025 _modUnionTable.par_mark_range(mr);
1026 } else {
1027 _modUnionTable.mark_range(mr);
1028 }
1029 } else { // not an obj array; we can just mark the head
1030 if (par) {
1031 _modUnionTable.par_mark(start);
1032 } else {
1033 _modUnionTable.mark(start);
1034 }
1035 }
1036 }
1037 }
1038 }
1039
1040 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1041 {
1042 size_t delta = pointer_delta(addr, space->bottom());
1043 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1044 }
1045
1046 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1047 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1048 // allocate, copy and if necessary update promoinfo --
1049 // delegate to underlying space.
1050 assert_lock_strong(freelistLock());
1051
1052 #ifndef PRODUCT
1053 if (Universe::heap()->promotion_should_fail()) {
1054 return NULL;
1055 }
1056 #endif // #ifndef PRODUCT
1057
1058 oop res = _cmsSpace->promote(obj, obj_size);
1059 if (res == NULL) {
1060 // expand and retry
1061 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1062 expand(s*HeapWordSize, MinHeapDeltaBytes,
1063 CMSExpansionCause::_satisfy_promotion);
1064 // Since there's currently no next generation, we don't try to promote
1065 // into a more senior generation.
1066 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1067 "is made to pass on a possibly failing "
1068 "promotion to next generation");
1069 res = _cmsSpace->promote(obj, obj_size);
1070 }
1071 if (res != NULL) {
1072 // See comment in allocate() about when objects should
1073 // be allocated live.
1074 assert(obj->is_oop(), "Will dereference klass pointer below");
1075 collector()->promoted(false, // Not parallel
1076 (HeapWord*)res, obj->is_objArray(), obj_size);
1077 // promotion counters
1078 NOT_PRODUCT(
1079 _numObjectsPromoted++;
1080 _numWordsPromoted +=
1081 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1082 )
1083 }
1084 return res;
1085 }
1086
1087
1088 // IMPORTANT: Notes on object size recognition in CMS.
1089 // ---------------------------------------------------
1090 // A block of storage in the CMS generation is always in
1091 // one of three states. A free block (FREE), an allocated
1092 // object (OBJECT) whose size() method reports the correct size,
1093 // and an intermediate state (TRANSIENT) in which its size cannot
1094 // be accurately determined.
1095 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1096 // -----------------------------------------------------
1097 // FREE: klass_word & 1 == 1; mark_word holds block size
1098 //
1099 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1100 // obj->size() computes correct size
1101 //
1102 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1103 //
1104 // STATE IDENTIFICATION: (64 bit+COOPS)
1105 // ------------------------------------
1106 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1107 //
1108 // OBJECT: klass_word installed; klass_word != 0;
1109 // obj->size() computes correct size
1110 //
1111 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1112 //
1113 //
1114 // STATE TRANSITION DIAGRAM
1115 //
1116 // mut / parnew mut / parnew
1117 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1118 // ^ |
1119 // |------------------------ DEAD <------------------------------------|
1120 // sweep mut
1121 //
1122 // While a block is in TRANSIENT state its size cannot be determined
1123 // so readers will either need to come back later or stall until
1124 // the size can be determined. Note that for the case of direct
1125 // allocation, P-bits, when available, may be used to determine the
1126 // size of an object that may not yet have been initialized.
1127
1128 // Things to support parallel young-gen collection.
1129 oop
1130 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1131 oop old, markOop m,
1132 size_t word_sz) {
1133 #ifndef PRODUCT
1134 if (Universe::heap()->promotion_should_fail()) {
1135 return NULL;
1136 }
1137 #endif // #ifndef PRODUCT
1138
1139 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1140 PromotionInfo* promoInfo = &ps->promo;
1141 // if we are tracking promotions, then first ensure space for
1142 // promotion (including spooling space for saving header if necessary).
1143 // then allocate and copy, then track promoted info if needed.
1144 // When tracking (see PromotionInfo::track()), the mark word may
1145 // be displaced and in this case restoration of the mark word
1146 // occurs in the (oop_since_save_marks_)iterate phase.
1147 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1148 // Out of space for allocating spooling buffers;
1149 // try expanding and allocating spooling buffers.
1150 if (!expand_and_ensure_spooling_space(promoInfo)) {
1151 return NULL;
1152 }
1153 }
1154 assert(promoInfo->has_spooling_space(), "Control point invariant");
1155 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1156 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1157 if (obj_ptr == NULL) {
1158 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1159 if (obj_ptr == NULL) {
1160 return NULL;
1161 }
1162 }
1163 oop obj = oop(obj_ptr);
1164 OrderAccess::storestore();
1165 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1166 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1167 // IMPORTANT: See note on object initialization for CMS above.
1168 // Otherwise, copy the object. Here we must be careful to insert the
1169 // klass pointer last, since this marks the block as an allocated object.
1170 // Except with compressed oops it's the mark word.
1171 HeapWord* old_ptr = (HeapWord*)old;
1172 // Restore the mark word copied above.
1173 obj->set_mark(m);
1174 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1175 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1176 OrderAccess::storestore();
1177
1178 if (UseCompressedClassPointers) {
1179 // Copy gap missed by (aligned) header size calculation below
1180 obj->set_klass_gap(old->klass_gap());
1181 }
1182 if (word_sz > (size_t)oopDesc::header_size()) {
1183 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1184 obj_ptr + oopDesc::header_size(),
1185 word_sz - oopDesc::header_size());
1186 }
1187
1188 // Now we can track the promoted object, if necessary. We take care
1189 // to delay the transition from uninitialized to full object
1190 // (i.e., insertion of klass pointer) until after, so that it
1191 // atomically becomes a promoted object.
1192 if (promoInfo->tracking()) {
1193 promoInfo->track((PromotedObject*)obj, old->klass());
1194 }
1195 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1196 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1197 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1198
1199 // Finally, install the klass pointer (this should be volatile).
1200 OrderAccess::storestore();
1201 obj->set_klass(old->klass());
1202 // We should now be able to calculate the right size for this object
1203 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1204
1205 collector()->promoted(true, // parallel
1206 obj_ptr, old->is_objArray(), word_sz);
1207
1208 NOT_PRODUCT(
1209 Atomic::inc_ptr(&_numObjectsPromoted);
1210 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1211 )
1212
1213 return obj;
1214 }
1215
1216 void
1217 ConcurrentMarkSweepGeneration::
1218 par_promote_alloc_undo(int thread_num,
1219 HeapWord* obj, size_t word_sz) {
1220 // CMS does not support promotion undo.
1221 ShouldNotReachHere();
1222 }
1223
1224 void
1225 ConcurrentMarkSweepGeneration::
1226 par_promote_alloc_done(int thread_num) {
1227 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1228 ps->lab.retire(thread_num);
1229 }
1230
1231 void
1232 ConcurrentMarkSweepGeneration::
1233 par_oop_since_save_marks_iterate_done(int thread_num) {
1234 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1235 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1236 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1237 }
1238
1239 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1240 size_t size,
1241 bool tlab)
1242 {
1243 // We allow a STW collection only if a full
1244 // collection was requested.
1245 return full || should_allocate(size, tlab); // FIX ME !!!
1246 // This and promotion failure handling are connected at the
1247 // hip and should be fixed by untying them.
1248 }
1249
1250 bool CMSCollector::shouldConcurrentCollect() {
1251 if (_full_gc_requested) {
1252 if (Verbose && PrintGCDetails) {
1253 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1254 " gc request (or gc_locker)");
1255 }
1256 return true;
1257 }
1258
1259 // For debugging purposes, change the type of collection.
1260 // If the rotation is not on the concurrent collection
1261 // type, don't start a concurrent collection.
1262 NOT_PRODUCT(
1263 if (RotateCMSCollectionTypes &&
1264 (_cmsGen->debug_collection_type() !=
1265 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1266 assert(_cmsGen->debug_collection_type() !=
1267 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1268 "Bad cms collection type");
1269 return false;
1270 }
1271 )
1272
1273 FreelistLocker x(this);
1274 // ------------------------------------------------------------------
1275 // Print out lots of information which affects the initiation of
1276 // a collection.
1277 if (PrintCMSInitiationStatistics && stats().valid()) {
1278 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1279 gclog_or_tty->stamp();
1280 gclog_or_tty->cr();
1281 stats().print_on(gclog_or_tty);
1282 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1283 stats().time_until_cms_gen_full());
1284 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1285 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1286 _cmsGen->contiguous_available());
1287 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1288 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1289 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1290 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1291 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1292 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1293 gclog_or_tty->print_cr("metadata initialized %d",
1294 MetaspaceGC::should_concurrent_collect());
1295 }
1296 // ------------------------------------------------------------------
1297
1298 // If the estimated time to complete a cms collection (cms_duration())
1299 // is less than the estimated time remaining until the cms generation
1300 // is full, start a collection.
1301 if (!UseCMSInitiatingOccupancyOnly) {
1302 if (stats().valid()) {
1303 if (stats().time_until_cms_start() == 0.0) {
1304 return true;
1305 }
1306 } else {
1307 // We want to conservatively collect somewhat early in order
1308 // to try and "bootstrap" our CMS/promotion statistics;
1309 // this branch will not fire after the first successful CMS
1310 // collection because the stats should then be valid.
1311 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1312 if (Verbose && PrintGCDetails) {
1313 gclog_or_tty->print_cr(
1314 " CMSCollector: collect for bootstrapping statistics:"
1315 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1316 _bootstrap_occupancy);
1317 }
1318 return true;
1319 }
1320 }
1321 }
1322
1323 // Otherwise, we start a collection cycle if
1324 // old gen want a collection cycle started. Each may use
1325 // an appropriate criterion for making this decision.
1326 // XXX We need to make sure that the gen expansion
1327 // criterion dovetails well with this. XXX NEED TO FIX THIS
1328 if (_cmsGen->should_concurrent_collect()) {
1329 if (Verbose && PrintGCDetails) {
1330 gclog_or_tty->print_cr("CMS old gen initiated");
1331 }
1332 return true;
1333 }
1334
1335 // We start a collection if we believe an incremental collection may fail;
1336 // this is not likely to be productive in practice because it's probably too
1337 // late anyway.
1338 GenCollectedHeap* gch = GenCollectedHeap::heap();
1339 assert(gch->collector_policy()->is_generation_policy(),
1340 "You may want to check the correctness of the following");
1341 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1342 if (Verbose && PrintGCDetails) {
1343 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1344 }
1345 return true;
1346 }
1347
1348 if (MetaspaceGC::should_concurrent_collect()) {
1349 if (Verbose && PrintGCDetails) {
1350 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1351 }
1352 return true;
1353 }
1354
1355 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1356 if (CMSTriggerInterval >= 0) {
1357 if (CMSTriggerInterval == 0) {
1358 // Trigger always
1359 return true;
1360 }
1361
1362 // Check the CMS time since begin (we do not check the stats validity
1363 // as we want to be able to trigger the first CMS cycle as well)
1364 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1365 if (Verbose && PrintGCDetails) {
1366 if (stats().valid()) {
1367 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1368 stats().cms_time_since_begin());
1369 } else {
1370 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1371 }
1372 }
1373 return true;
1374 }
1375 }
1376
1377 return false;
1378 }
1379
1380 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1381
1382 // Clear _expansion_cause fields of constituent generations
1383 void CMSCollector::clear_expansion_cause() {
1384 _cmsGen->clear_expansion_cause();
1385 }
1386
1387 // We should be conservative in starting a collection cycle. To
1388 // start too eagerly runs the risk of collecting too often in the
1389 // extreme. To collect too rarely falls back on full collections,
1390 // which works, even if not optimum in terms of concurrent work.
1391 // As a work around for too eagerly collecting, use the flag
1392 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1393 // giving the user an easily understandable way of controlling the
1394 // collections.
1395 // We want to start a new collection cycle if any of the following
1396 // conditions hold:
1397 // . our current occupancy exceeds the configured initiating occupancy
1398 // for this generation, or
1399 // . we recently needed to expand this space and have not, since that
1400 // expansion, done a collection of this generation, or
1401 // . the underlying space believes that it may be a good idea to initiate
1402 // a concurrent collection (this may be based on criteria such as the
1403 // following: the space uses linear allocation and linear allocation is
1404 // going to fail, or there is believed to be excessive fragmentation in
1405 // the generation, etc... or ...
1406 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1407 // the case of the old generation; see CR 6543076):
1408 // we may be approaching a point at which allocation requests may fail because
1409 // we will be out of sufficient free space given allocation rate estimates.]
1410 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1411
1412 assert_lock_strong(freelistLock());
1413 if (occupancy() > initiating_occupancy()) {
1414 if (PrintGCDetails && Verbose) {
1415 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1416 short_name(), occupancy(), initiating_occupancy());
1417 }
1418 return true;
1419 }
1420 if (UseCMSInitiatingOccupancyOnly) {
1421 return false;
1422 }
1423 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1424 if (PrintGCDetails && Verbose) {
1425 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1426 short_name());
1427 }
1428 return true;
1429 }
1430 if (_cmsSpace->should_concurrent_collect()) {
1431 if (PrintGCDetails && Verbose) {
1432 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1433 short_name());
1434 }
1435 return true;
1436 }
1437 return false;
1438 }
1439
1440 void ConcurrentMarkSweepGeneration::collect(bool full,
1441 bool clear_all_soft_refs,
1442 size_t size,
1443 bool tlab)
1444 {
1445 collector()->collect(full, clear_all_soft_refs, size, tlab);
1446 }
1447
1448 void CMSCollector::collect(bool full,
1449 bool clear_all_soft_refs,
1450 size_t size,
1451 bool tlab)
1452 {
1453 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1454 // For debugging purposes skip the collection if the state
1455 // is not currently idle
1456 if (TraceCMSState) {
1457 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1458 Thread::current(), full, _collectorState);
1459 }
1460 return;
1461 }
1462
1463 // The following "if" branch is present for defensive reasons.
1464 // In the current uses of this interface, it can be replaced with:
1465 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1466 // But I am not placing that assert here to allow future
1467 // generality in invoking this interface.
1468 if (GC_locker::is_active()) {
1469 // A consistency test for GC_locker
1470 assert(GC_locker::needs_gc(), "Should have been set already");
1471 // Skip this foreground collection, instead
1472 // expanding the heap if necessary.
1473 // Need the free list locks for the call to free() in compute_new_size()
1474 compute_new_size();
1475 return;
1476 }
1477 acquire_control_and_collect(full, clear_all_soft_refs);
1478 _full_gcs_since_conc_gc++;
1479 }
1480
1481 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1482 GenCollectedHeap* gch = GenCollectedHeap::heap();
1483 unsigned int gc_count = gch->total_full_collections();
1484 if (gc_count == full_gc_count) {
1485 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1486 _full_gc_requested = true;
1487 _full_gc_cause = cause;
1488 CGC_lock->notify(); // nudge CMS thread
1489 } else {
1490 assert(gc_count > full_gc_count, "Error: causal loop");
1491 }
1492 }
1493
1494 bool CMSCollector::is_external_interruption() {
1495 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1496 return GCCause::is_user_requested_gc(cause) ||
1497 GCCause::is_serviceability_requested_gc(cause);
1498 }
1499
1500 void CMSCollector::report_concurrent_mode_interruption() {
1501 if (is_external_interruption()) {
1502 if (PrintGCDetails) {
1503 gclog_or_tty->print(" (concurrent mode interrupted)");
1504 }
1505 } else {
1506 if (PrintGCDetails) {
1507 gclog_or_tty->print(" (concurrent mode failure)");
1508 }
1509 _gc_tracer_cm->report_concurrent_mode_failure();
1510 }
1511 }
1512
1513
1514 // The foreground and background collectors need to coordinate in order
1515 // to make sure that they do not mutually interfere with CMS collections.
1516 // When a background collection is active,
1517 // the foreground collector may need to take over (preempt) and
1518 // synchronously complete an ongoing collection. Depending on the
1519 // frequency of the background collections and the heap usage
1520 // of the application, this preemption can be seldom or frequent.
1521 // There are only certain
1522 // points in the background collection that the "collection-baton"
1523 // can be passed to the foreground collector.
1524 //
1525 // The foreground collector will wait for the baton before
1526 // starting any part of the collection. The foreground collector
1527 // will only wait at one location.
1528 //
1529 // The background collector will yield the baton before starting a new
1530 // phase of the collection (e.g., before initial marking, marking from roots,
1531 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1532 // of the loop which switches the phases. The background collector does some
1533 // of the phases (initial mark, final re-mark) with the world stopped.
1534 // Because of locking involved in stopping the world,
1535 // the foreground collector should not block waiting for the background
1536 // collector when it is doing a stop-the-world phase. The background
1537 // collector will yield the baton at an additional point just before
1538 // it enters a stop-the-world phase. Once the world is stopped, the
1539 // background collector checks the phase of the collection. If the
1540 // phase has not changed, it proceeds with the collection. If the
1541 // phase has changed, it skips that phase of the collection. See
1542 // the comments on the use of the Heap_lock in collect_in_background().
1543 //
1544 // Variable used in baton passing.
1545 // _foregroundGCIsActive - Set to true by the foreground collector when
1546 // it wants the baton. The foreground clears it when it has finished
1547 // the collection.
1548 // _foregroundGCShouldWait - Set to true by the background collector
1549 // when it is running. The foreground collector waits while
1550 // _foregroundGCShouldWait is true.
1551 // CGC_lock - monitor used to protect access to the above variables
1552 // and to notify the foreground and background collectors.
1553 // _collectorState - current state of the CMS collection.
1554 //
1555 // The foreground collector
1556 // acquires the CGC_lock
1557 // sets _foregroundGCIsActive
1558 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1559 // various locks acquired in preparation for the collection
1560 // are released so as not to block the background collector
1561 // that is in the midst of a collection
1562 // proceeds with the collection
1563 // clears _foregroundGCIsActive
1564 // returns
1565 //
1566 // The background collector in a loop iterating on the phases of the
1567 // collection
1568 // acquires the CGC_lock
1569 // sets _foregroundGCShouldWait
1570 // if _foregroundGCIsActive is set
1571 // clears _foregroundGCShouldWait, notifies _CGC_lock
1572 // waits on _CGC_lock for _foregroundGCIsActive to become false
1573 // and exits the loop.
1574 // otherwise
1575 // proceed with that phase of the collection
1576 // if the phase is a stop-the-world phase,
1577 // yield the baton once more just before enqueueing
1578 // the stop-world CMS operation (executed by the VM thread).
1579 // returns after all phases of the collection are done
1580 //
1581
1582 void CMSCollector::acquire_control_and_collect(bool full,
1583 bool clear_all_soft_refs) {
1584 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1585 assert(!Thread::current()->is_ConcurrentGC_thread(),
1586 "shouldn't try to acquire control from self!");
1587
1588 // Start the protocol for acquiring control of the
1589 // collection from the background collector (aka CMS thread).
1590 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1591 "VM thread should have CMS token");
1592 // Remember the possibly interrupted state of an ongoing
1593 // concurrent collection
1594 CollectorState first_state = _collectorState;
1595
1596 // Signal to a possibly ongoing concurrent collection that
1597 // we want to do a foreground collection.
1598 _foregroundGCIsActive = true;
1599
1600 // release locks and wait for a notify from the background collector
1601 // releasing the locks in only necessary for phases which
1602 // do yields to improve the granularity of the collection.
1603 assert_lock_strong(bitMapLock());
1604 // We need to lock the Free list lock for the space that we are
1605 // currently collecting.
1606 assert(haveFreelistLocks(), "Must be holding free list locks");
1607 bitMapLock()->unlock();
1608 releaseFreelistLocks();
1609 {
1610 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1611 if (_foregroundGCShouldWait) {
1612 // We are going to be waiting for action for the CMS thread;
1613 // it had better not be gone (for instance at shutdown)!
1614 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1615 "CMS thread must be running");
1616 // Wait here until the background collector gives us the go-ahead
1617 ConcurrentMarkSweepThread::clear_CMS_flag(
1618 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1619 // Get a possibly blocked CMS thread going:
1620 // Note that we set _foregroundGCIsActive true above,
1621 // without protection of the CGC_lock.
1622 CGC_lock->notify();
1623 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1624 "Possible deadlock");
1625 while (_foregroundGCShouldWait) {
1626 // wait for notification
1627 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1628 // Possibility of delay/starvation here, since CMS token does
1629 // not know to give priority to VM thread? Actually, i think
1630 // there wouldn't be any delay/starvation, but the proof of
1631 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1632 }
1633 ConcurrentMarkSweepThread::set_CMS_flag(
1634 ConcurrentMarkSweepThread::CMS_vm_has_token);
1635 }
1636 }
1637 // The CMS_token is already held. Get back the other locks.
1638 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1639 "VM thread should have CMS token");
1640 getFreelistLocks();
1641 bitMapLock()->lock_without_safepoint_check();
1642 if (TraceCMSState) {
1643 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1644 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1645 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1646 }
1647
1648 // Check if we need to do a compaction, or if not, whether
1649 // we need to start the mark-sweep from scratch.
1650 bool should_compact = false;
1651 bool should_start_over = false;
1652 decide_foreground_collection_type(clear_all_soft_refs,
1653 &should_compact, &should_start_over);
1654
1655 NOT_PRODUCT(
1656 if (RotateCMSCollectionTypes) {
1657 if (_cmsGen->debug_collection_type() ==
1658 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1659 should_compact = true;
1660 } else if (_cmsGen->debug_collection_type() ==
1661 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1662 should_compact = false;
1663 }
1664 }
1665 )
1666
1667 if (first_state > Idling) {
1668 report_concurrent_mode_interruption();
1669 }
1670
1671 set_did_compact(should_compact);
1672 if (should_compact) {
1673 // If the collection is being acquired from the background
1674 // collector, there may be references on the discovered
1675 // references lists that have NULL referents (being those
1676 // that were concurrently cleared by a mutator) or
1677 // that are no longer active (having been enqueued concurrently
1678 // by the mutator).
1679 // Scrub the list of those references because Mark-Sweep-Compact
1680 // code assumes referents are not NULL and that all discovered
1681 // Reference objects are active.
1682 ref_processor()->clean_up_discovered_references();
1683
1684 if (first_state > Idling) {
1685 save_heap_summary();
1686 }
1687
1688 do_compaction_work(clear_all_soft_refs);
1689
1690 // Has the GC time limit been exceeded?
1691 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1692 size_t max_eden_size = young_gen->max_capacity() -
1693 young_gen->to()->capacity() -
1694 young_gen->from()->capacity();
1695 GenCollectedHeap* gch = GenCollectedHeap::heap();
1696 GCCause::Cause gc_cause = gch->gc_cause();
1697 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1698 young_gen->eden()->used(),
1699 _cmsGen->max_capacity(),
1700 max_eden_size,
1701 full,
1702 gc_cause,
1703 gch->collector_policy());
1704 } else {
1705 do_mark_sweep_work(clear_all_soft_refs, first_state,
1706 should_start_over);
1707 }
1708 // Reset the expansion cause, now that we just completed
1709 // a collection cycle.
1710 clear_expansion_cause();
1711 _foregroundGCIsActive = false;
1712 return;
1713 }
1714
1715 // Resize the tenured generation
1716 // after obtaining the free list locks for the
1717 // two generations.
1718 void CMSCollector::compute_new_size() {
1719 assert_locked_or_safepoint(Heap_lock);
1720 FreelistLocker z(this);
1721 MetaspaceGC::compute_new_size();
1722 _cmsGen->compute_new_size_free_list();
1723 }
1724
1725 // A work method used by foreground collection to determine
1726 // what type of collection (compacting or not, continuing or fresh)
1727 // it should do.
1728 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1729 // and CMSCompactWhenClearAllSoftRefs the default in the future
1730 // and do away with the flags after a suitable period.
1731 void CMSCollector::decide_foreground_collection_type(
1732 bool clear_all_soft_refs, bool* should_compact,
1733 bool* should_start_over) {
1734 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1735 // flag is set, and we have either requested a System.gc() or
1736 // the number of full gc's since the last concurrent cycle
1737 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1738 // or if an incremental collection has failed
1739 GenCollectedHeap* gch = GenCollectedHeap::heap();
1740 assert(gch->collector_policy()->is_generation_policy(),
1741 "You may want to check the correctness of the following");
1742 // Inform cms gen if this was due to partial collection failing.
1743 // The CMS gen may use this fact to determine its expansion policy.
1744 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1745 assert(!_cmsGen->incremental_collection_failed(),
1746 "Should have been noticed, reacted to and cleared");
1747 _cmsGen->set_incremental_collection_failed();
1748 }
1749 *should_compact =
1750 UseCMSCompactAtFullCollection &&
1751 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1752 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1753 gch->incremental_collection_will_fail(true /* consult_young */));
1754 *should_start_over = false;
1755 if (clear_all_soft_refs && !*should_compact) {
1756 // We are about to do a last ditch collection attempt
1757 // so it would normally make sense to do a compaction
1758 // to reclaim as much space as possible.
1759 if (CMSCompactWhenClearAllSoftRefs) {
1760 // Default: The rationale is that in this case either
1761 // we are past the final marking phase, in which case
1762 // we'd have to start over, or so little has been done
1763 // that there's little point in saving that work. Compaction
1764 // appears to be the sensible choice in either case.
1765 *should_compact = true;
1766 } else {
1767 // We have been asked to clear all soft refs, but not to
1768 // compact. Make sure that we aren't past the final checkpoint
1769 // phase, for that is where we process soft refs. If we are already
1770 // past that phase, we'll need to redo the refs discovery phase and
1771 // if necessary clear soft refs that weren't previously
1772 // cleared. We do so by remembering the phase in which
1773 // we came in, and if we are past the refs processing
1774 // phase, we'll choose to just redo the mark-sweep
1775 // collection from scratch.
1776 if (_collectorState > FinalMarking) {
1777 // We are past the refs processing phase;
1778 // start over and do a fresh synchronous CMS cycle
1779 _collectorState = Resetting; // skip to reset to start new cycle
1780 reset(false /* == !asynch */);
1781 *should_start_over = true;
1782 } // else we can continue a possibly ongoing current cycle
1783 }
1784 }
1785 }
1786
1787 // A work method used by the foreground collector to do
1788 // a mark-sweep-compact.
1789 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1790 GenCollectedHeap* gch = GenCollectedHeap::heap();
1791
1792 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1793 gc_timer->register_gc_start();
1794
1795 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1796 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1797
1798 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
1799 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
1800 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
1801 "collections passed to foreground collector", _full_gcs_since_conc_gc);
1802 }
1803
1804 // Temporarily widen the span of the weak reference processing to
1805 // the entire heap.
1806 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1807 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1808 // Temporarily, clear the "is_alive_non_header" field of the
1809 // reference processor.
1810 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1811 // Temporarily make reference _processing_ single threaded (non-MT).
1812 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1813 // Temporarily make refs discovery atomic
1814 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1815 // Temporarily make reference _discovery_ single threaded (non-MT)
1816 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1817
1818 ref_processor()->set_enqueuing_is_done(false);
1819 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
1820 ref_processor()->setup_policy(clear_all_soft_refs);
1821 // If an asynchronous collection finishes, the _modUnionTable is
1822 // all clear. If we are assuming the collection from an asynchronous
1823 // collection, clear the _modUnionTable.
1824 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1825 "_modUnionTable should be clear if the baton was not passed");
1826 _modUnionTable.clear_all();
1827 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1828 "mod union for klasses should be clear if the baton was passed");
1829 _ct->klass_rem_set()->clear_mod_union();
1830
1831 // We must adjust the allocation statistics being maintained
1832 // in the free list space. We do so by reading and clearing
1833 // the sweep timer and updating the block flux rate estimates below.
1834 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1835 if (_inter_sweep_timer.is_active()) {
1836 _inter_sweep_timer.stop();
1837 // Note that we do not use this sample to update the _inter_sweep_estimate.
1838 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1839 _inter_sweep_estimate.padded_average(),
1840 _intra_sweep_estimate.padded_average());
1841 }
1842
1843 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1844 ref_processor(), clear_all_soft_refs);
1845 #ifdef ASSERT
1846 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1847 size_t free_size = cms_space->free();
1848 assert(free_size ==
1849 pointer_delta(cms_space->end(), cms_space->compaction_top())
1850 * HeapWordSize,
1851 "All the free space should be compacted into one chunk at top");
1852 assert(cms_space->dictionary()->total_chunk_size(
1853 debug_only(cms_space->freelistLock())) == 0 ||
1854 cms_space->totalSizeInIndexedFreeLists() == 0,
1855 "All the free space should be in a single chunk");
1856 size_t num = cms_space->totalCount();
1857 assert((free_size == 0 && num == 0) ||
1858 (free_size > 0 && (num == 1 || num == 2)),
1859 "There should be at most 2 free chunks after compaction");
1860 #endif // ASSERT
1861 _collectorState = Resetting;
1862 assert(_restart_addr == NULL,
1863 "Should have been NULL'd before baton was passed");
1864 reset(false /* == !asynch */);
1865 _cmsGen->reset_after_compaction();
1866 _concurrent_cycles_since_last_unload = 0;
1867
1868 // Clear any data recorded in the PLAB chunk arrays.
1869 if (_survivor_plab_array != NULL) {
1870 reset_survivor_plab_arrays();
1871 }
1872
1873 // Adjust the per-size allocation stats for the next epoch.
1874 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1875 // Restart the "inter sweep timer" for the next epoch.
1876 _inter_sweep_timer.reset();
1877 _inter_sweep_timer.start();
1878
1879 gc_timer->register_gc_end();
1880
1881 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1882
1883 // For a mark-sweep-compact, compute_new_size() will be called
1884 // in the heap's do_collection() method.
1885 }
1886
1887 // A work method used by the foreground collector to do
1888 // a mark-sweep, after taking over from a possibly on-going
1889 // concurrent mark-sweep collection.
1890 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
1891 CollectorState first_state, bool should_start_over) {
1892 if (PrintGC && Verbose) {
1893 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
1894 "collector with count %d",
1895 _full_gcs_since_conc_gc);
1896 }
1897 switch (_collectorState) {
1898 case Idling:
1899 if (first_state == Idling || should_start_over) {
1900 // The background GC was not active, or should
1901 // restarted from scratch; start the cycle.
1902 _collectorState = InitialMarking;
1903 }
1904 // If first_state was not Idling, then a background GC
1905 // was in progress and has now finished. No need to do it
1906 // again. Leave the state as Idling.
1907 break;
1908 case Precleaning:
1909 // In the foreground case don't do the precleaning since
1910 // it is not done concurrently and there is extra work
1911 // required.
1912 _collectorState = FinalMarking;
1913 }
1914 collect_in_foreground(clear_all_soft_refs, GenCollectedHeap::heap()->gc_cause());
1915
1916 // For a mark-sweep, compute_new_size() will be called
1917 // in the heap's do_collection() method.
1918 }
1919
1920
1921 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1922 DefNewGeneration* dng = _young_gen->as_DefNewGeneration();
1923 ContiguousSpace* eden_space = dng->eden();
1924 ContiguousSpace* from_space = dng->from();
1925 ContiguousSpace* to_space = dng->to();
1926 // Eden
1927 if (_eden_chunk_array != NULL) {
1928 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1929 eden_space->bottom(), eden_space->top(),
1930 eden_space->end(), eden_space->capacity());
1931 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1932 "_eden_chunk_capacity=" SIZE_FORMAT,
1933 _eden_chunk_index, _eden_chunk_capacity);
1934 for (size_t i = 0; i < _eden_chunk_index; i++) {
1935 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1936 i, _eden_chunk_array[i]);
1937 }
1938 }
1939 // Survivor
1940 if (_survivor_chunk_array != NULL) {
1941 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1942 from_space->bottom(), from_space->top(),
1943 from_space->end(), from_space->capacity());
1944 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1945 "_survivor_chunk_capacity=" SIZE_FORMAT,
1946 _survivor_chunk_index, _survivor_chunk_capacity);
1947 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1948 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1949 i, _survivor_chunk_array[i]);
1950 }
1951 }
1952 }
1953
1954 void CMSCollector::getFreelistLocks() const {
1955 // Get locks for all free lists in all generations that this
1956 // collector is responsible for
1957 _cmsGen->freelistLock()->lock_without_safepoint_check();
1958 }
1959
1960 void CMSCollector::releaseFreelistLocks() const {
1961 // Release locks for all free lists in all generations that this
1962 // collector is responsible for
1963 _cmsGen->freelistLock()->unlock();
1964 }
1965
1966 bool CMSCollector::haveFreelistLocks() const {
1967 // Check locks for all free lists in all generations that this
1968 // collector is responsible for
1969 assert_lock_strong(_cmsGen->freelistLock());
1970 PRODUCT_ONLY(ShouldNotReachHere());
1971 return true;
1972 }
1973
1974 // A utility class that is used by the CMS collector to
1975 // temporarily "release" the foreground collector from its
1976 // usual obligation to wait for the background collector to
1977 // complete an ongoing phase before proceeding.
1978 class ReleaseForegroundGC: public StackObj {
1979 private:
1980 CMSCollector* _c;
1981 public:
1982 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1983 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1984 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1985 // allow a potentially blocked foreground collector to proceed
1986 _c->_foregroundGCShouldWait = false;
1987 if (_c->_foregroundGCIsActive) {
1988 CGC_lock->notify();
1989 }
1990 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1991 "Possible deadlock");
1992 }
1993
1994 ~ReleaseForegroundGC() {
1995 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1996 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1997 _c->_foregroundGCShouldWait = true;
1998 }
1999 };
2000
2001 // There are separate collect_in_background and collect_in_foreground because of
2002 // the different locking requirements of the background collector and the
2003 // foreground collector. There was originally an attempt to share
2004 // one "collect" method between the background collector and the foreground
2005 // collector but the if-then-else required made it cleaner to have
2006 // separate methods.
2007 void CMSCollector::collect_in_background(bool clear_all_soft_refs, GCCause::Cause cause) {
2008 assert(Thread::current()->is_ConcurrentGC_thread(),
2009 "A CMS asynchronous collection is only allowed on a CMS thread.");
2010
2011 GenCollectedHeap* gch = GenCollectedHeap::heap();
2012 {
2013 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2014 MutexLockerEx hl(Heap_lock, safepoint_check);
2015 FreelistLocker fll(this);
2016 MutexLockerEx x(CGC_lock, safepoint_check);
2017 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2018 // The foreground collector is active or we're
2019 // not using asynchronous collections. Skip this
2020 // background collection.
2021 assert(!_foregroundGCShouldWait, "Should be clear");
2022 return;
2023 } else {
2024 assert(_collectorState == Idling, "Should be idling before start.");
2025 _collectorState = InitialMarking;
2026 register_gc_start(cause);
2027 // Reset the expansion cause, now that we are about to begin
2028 // a new cycle.
2029 clear_expansion_cause();
2030
2031 // Clear the MetaspaceGC flag since a concurrent collection
2032 // is starting but also clear it after the collection.
2033 MetaspaceGC::set_should_concurrent_collect(false);
2034 }
2035 // Decide if we want to enable class unloading as part of the
2036 // ensuing concurrent GC cycle.
2037 update_should_unload_classes();
2038 _full_gc_requested = false; // acks all outstanding full gc requests
2039 _full_gc_cause = GCCause::_no_gc;
2040 // Signal that we are about to start a collection
2041 gch->increment_total_full_collections(); // ... starting a collection cycle
2042 _collection_count_start = gch->total_full_collections();
2043 }
2044
2045 // Used for PrintGC
2046 size_t prev_used;
2047 if (PrintGC && Verbose) {
2048 prev_used = _cmsGen->used(); // XXXPERM
2049 }
2050
2051 // The change of the collection state is normally done at this level;
2052 // the exceptions are phases that are executed while the world is
2053 // stopped. For those phases the change of state is done while the
2054 // world is stopped. For baton passing purposes this allows the
2055 // background collector to finish the phase and change state atomically.
2056 // The foreground collector cannot wait on a phase that is done
2057 // while the world is stopped because the foreground collector already
2058 // has the world stopped and would deadlock.
2059 while (_collectorState != Idling) {
2060 if (TraceCMSState) {
2061 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2062 Thread::current(), _collectorState);
2063 }
2064 // The foreground collector
2065 // holds the Heap_lock throughout its collection.
2066 // holds the CMS token (but not the lock)
2067 // except while it is waiting for the background collector to yield.
2068 //
2069 // The foreground collector should be blocked (not for long)
2070 // if the background collector is about to start a phase
2071 // executed with world stopped. If the background
2072 // collector has already started such a phase, the
2073 // foreground collector is blocked waiting for the
2074 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2075 // are executed in the VM thread.
2076 //
2077 // The locking order is
2078 // PendingListLock (PLL) -- if applicable (FinalMarking)
2079 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2080 // CMS token (claimed in
2081 // stop_world_and_do() -->
2082 // safepoint_synchronize() -->
2083 // CMSThread::synchronize())
2084
2085 {
2086 // Check if the FG collector wants us to yield.
2087 CMSTokenSync x(true); // is cms thread
2088 if (waitForForegroundGC()) {
2089 // We yielded to a foreground GC, nothing more to be
2090 // done this round.
2091 assert(_foregroundGCShouldWait == false, "We set it to false in "
2092 "waitForForegroundGC()");
2093 if (TraceCMSState) {
2094 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2095 " exiting collection CMS state %d",
2096 Thread::current(), _collectorState);
2097 }
2098 return;
2099 } else {
2100 // The background collector can run but check to see if the
2101 // foreground collector has done a collection while the
2102 // background collector was waiting to get the CGC_lock
2103 // above. If yes, break so that _foregroundGCShouldWait
2104 // is cleared before returning.
2105 if (_collectorState == Idling) {
2106 break;
2107 }
2108 }
2109 }
2110
2111 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2112 "should be waiting");
2113
2114 switch (_collectorState) {
2115 case InitialMarking:
2116 {
2117 ReleaseForegroundGC x(this);
2118 stats().record_cms_begin();
2119 VM_CMS_Initial_Mark initial_mark_op(this);
2120 VMThread::execute(&initial_mark_op);
2121 }
2122 // The collector state may be any legal state at this point
2123 // since the background collector may have yielded to the
2124 // foreground collector.
2125 break;
2126 case Marking:
2127 // initial marking in checkpointRootsInitialWork has been completed
2128 if (markFromRoots(true)) { // we were successful
2129 assert(_collectorState == Precleaning, "Collector state should "
2130 "have changed");
2131 } else {
2132 assert(_foregroundGCIsActive, "Internal state inconsistency");
2133 }
2134 break;
2135 case Precleaning:
2136 // marking from roots in markFromRoots has been completed
2137 preclean();
2138 assert(_collectorState == AbortablePreclean ||
2139 _collectorState == FinalMarking,
2140 "Collector state should have changed");
2141 break;
2142 case AbortablePreclean:
2143 abortable_preclean();
2144 assert(_collectorState == FinalMarking, "Collector state should "
2145 "have changed");
2146 break;
2147 case FinalMarking:
2148 {
2149 ReleaseForegroundGC x(this);
2150
2151 VM_CMS_Final_Remark final_remark_op(this);
2152 VMThread::execute(&final_remark_op);
2153 }
2154 assert(_foregroundGCShouldWait, "block post-condition");
2155 break;
2156 case Sweeping:
2157 // final marking in checkpointRootsFinal has been completed
2158 sweep(true);
2159 assert(_collectorState == Resizing, "Collector state change "
2160 "to Resizing must be done under the free_list_lock");
2161 _full_gcs_since_conc_gc = 0;
2162
2163 case Resizing: {
2164 // Sweeping has been completed...
2165 // At this point the background collection has completed.
2166 // Don't move the call to compute_new_size() down
2167 // into code that might be executed if the background
2168 // collection was preempted.
2169 {
2170 ReleaseForegroundGC x(this); // unblock FG collection
2171 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2172 CMSTokenSync z(true); // not strictly needed.
2173 if (_collectorState == Resizing) {
2174 compute_new_size();
2175 save_heap_summary();
2176 _collectorState = Resetting;
2177 } else {
2178 assert(_collectorState == Idling, "The state should only change"
2179 " because the foreground collector has finished the collection");
2180 }
2181 }
2182 break;
2183 }
2184 case Resetting:
2185 // CMS heap resizing has been completed
2186 reset(true);
2187 assert(_collectorState == Idling, "Collector state should "
2188 "have changed");
2189
2190 MetaspaceGC::set_should_concurrent_collect(false);
2191
2192 stats().record_cms_end();
2193 // Don't move the concurrent_phases_end() and compute_new_size()
2194 // calls to here because a preempted background collection
2195 // has it's state set to "Resetting".
2196 break;
2197 case Idling:
2198 default:
2199 ShouldNotReachHere();
2200 break;
2201 }
2202 if (TraceCMSState) {
2203 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2204 Thread::current(), _collectorState);
2205 }
2206 assert(_foregroundGCShouldWait, "block post-condition");
2207 }
2208
2209 // Should this be in gc_epilogue?
2210 collector_policy()->counters()->update_counters();
2211
2212 {
2213 // Clear _foregroundGCShouldWait and, in the event that the
2214 // foreground collector is waiting, notify it, before
2215 // returning.
2216 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2217 _foregroundGCShouldWait = false;
2218 if (_foregroundGCIsActive) {
2219 CGC_lock->notify();
2220 }
2221 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2222 "Possible deadlock");
2223 }
2224 if (TraceCMSState) {
2225 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2226 " exiting collection CMS state %d",
2227 Thread::current(), _collectorState);
2228 }
2229 if (PrintGC && Verbose) {
2230 _cmsGen->print_heap_change(prev_used);
2231 }
2232 }
2233
2234 void CMSCollector::register_foreground_gc_start(GCCause::Cause cause) {
2235 if (!_cms_start_registered) {
2236 register_gc_start(cause);
2237 }
2238 }
2239
2240 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2241 _cms_start_registered = true;
2242 _gc_timer_cm->register_gc_start();
2243 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2244 }
2245
2246 void CMSCollector::register_gc_end() {
2247 if (_cms_start_registered) {
2248 report_heap_summary(GCWhen::AfterGC);
2249
2250 _gc_timer_cm->register_gc_end();
2251 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2252 _cms_start_registered = false;
2253 }
2254 }
2255
2256 void CMSCollector::save_heap_summary() {
2257 GenCollectedHeap* gch = GenCollectedHeap::heap();
2258 _last_heap_summary = gch->create_heap_summary();
2259 _last_metaspace_summary = gch->create_metaspace_summary();
2260 }
2261
2262 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2263 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2264 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2265 }
2266
2267 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs, GCCause::Cause cause) {
2268 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2269 "Foreground collector should be waiting, not executing");
2270 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2271 "may only be done by the VM Thread with the world stopped");
2272 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2273 "VM thread should have CMS token");
2274
2275 // The gc id is created in register_foreground_gc_start if this collection is synchronous
2276 const GCId gc_id = _collectorState == InitialMarking ? GCId::peek() : _gc_tracer_cm->gc_id();
2277 NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2278 true, NULL, gc_id);)
2279 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2280
2281 HandleMark hm; // Discard invalid handles created during verification
2282
2283 if (VerifyBeforeGC &&
2284 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2285 Universe::verify();
2286 }
2287
2288 // Snapshot the soft reference policy to be used in this collection cycle.
2289 ref_processor()->setup_policy(clear_all_soft_refs);
2290
2291 // Decide if class unloading should be done
2292 update_should_unload_classes();
2293
2294 bool init_mark_was_synchronous = false; // until proven otherwise
2295 while (_collectorState != Idling) {
2296 if (TraceCMSState) {
2297 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2298 Thread::current(), _collectorState);
2299 }
2300 switch (_collectorState) {
2301 case InitialMarking:
2302 register_foreground_gc_start(cause);
2303 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2304 checkpointRootsInitial(false);
2305 assert(_collectorState == Marking, "Collector state should have changed"
2306 " within checkpointRootsInitial()");
2307 break;
2308 case Marking:
2309 // initial marking in checkpointRootsInitialWork has been completed
2310 if (VerifyDuringGC &&
2311 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2312 Universe::verify("Verify before initial mark: ");
2313 }
2314 {
2315 bool res = markFromRoots(false);
2316 assert(res && _collectorState == FinalMarking, "Collector state should "
2317 "have changed");
2318 break;
2319 }
2320 case FinalMarking:
2321 if (VerifyDuringGC &&
2322 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2323 Universe::verify("Verify before re-mark: ");
2324 }
2325 checkpointRootsFinal(false, clear_all_soft_refs,
2326 init_mark_was_synchronous);
2327 assert(_collectorState == Sweeping, "Collector state should not "
2328 "have changed within checkpointRootsFinal()");
2329 break;
2330 case Sweeping:
2331 // final marking in checkpointRootsFinal has been completed
2332 if (VerifyDuringGC &&
2333 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2334 Universe::verify("Verify before sweep: ");
2335 }
2336 sweep(false);
2337 assert(_collectorState == Resizing, "Incorrect state");
2338 break;
2339 case Resizing: {
2340 // Sweeping has been completed; the actual resize in this case
2341 // is done separately; nothing to be done in this state.
2342 _collectorState = Resetting;
2343 break;
2344 }
2345 case Resetting:
2346 // The heap has been resized.
2347 if (VerifyDuringGC &&
2348 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2349 Universe::verify("Verify before reset: ");
2350 }
2351 save_heap_summary();
2352 reset(false);
2353 assert(_collectorState == Idling, "Collector state should "
2354 "have changed");
2355 break;
2356 case Precleaning:
2357 case AbortablePreclean:
2358 // Elide the preclean phase
2359 _collectorState = FinalMarking;
2360 break;
2361 default:
2362 ShouldNotReachHere();
2363 }
2364 if (TraceCMSState) {
2365 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2366 Thread::current(), _collectorState);
2367 }
2368 }
2369
2370 if (VerifyAfterGC &&
2371 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2372 Universe::verify();
2373 }
2374 if (TraceCMSState) {
2375 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2376 " exiting collection CMS state %d",
2377 Thread::current(), _collectorState);
2378 }
2379 }
2380
2381 bool CMSCollector::waitForForegroundGC() {
2382 bool res = false;
2383 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2384 "CMS thread should have CMS token");
2385 // Block the foreground collector until the
2386 // background collectors decides whether to
2387 // yield.
2388 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2389 _foregroundGCShouldWait = true;
2390 if (_foregroundGCIsActive) {
2391 // The background collector yields to the
2392 // foreground collector and returns a value
2393 // indicating that it has yielded. The foreground
2394 // collector can proceed.
2395 res = true;
2396 _foregroundGCShouldWait = false;
2397 ConcurrentMarkSweepThread::clear_CMS_flag(
2398 ConcurrentMarkSweepThread::CMS_cms_has_token);
2399 ConcurrentMarkSweepThread::set_CMS_flag(
2400 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2401 // Get a possibly blocked foreground thread going
2402 CGC_lock->notify();
2403 if (TraceCMSState) {
2404 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2405 Thread::current(), _collectorState);
2406 }
2407 while (_foregroundGCIsActive) {
2408 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2409 }
2410 ConcurrentMarkSweepThread::set_CMS_flag(
2411 ConcurrentMarkSweepThread::CMS_cms_has_token);
2412 ConcurrentMarkSweepThread::clear_CMS_flag(
2413 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2414 }
2415 if (TraceCMSState) {
2416 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2417 Thread::current(), _collectorState);
2418 }
2419 return res;
2420 }
2421
2422 // Because of the need to lock the free lists and other structures in
2423 // the collector, common to all the generations that the collector is
2424 // collecting, we need the gc_prologues of individual CMS generations
2425 // delegate to their collector. It may have been simpler had the
2426 // current infrastructure allowed one to call a prologue on a
2427 // collector. In the absence of that we have the generation's
2428 // prologue delegate to the collector, which delegates back
2429 // some "local" work to a worker method in the individual generations
2430 // that it's responsible for collecting, while itself doing any
2431 // work common to all generations it's responsible for. A similar
2432 // comment applies to the gc_epilogue()'s.
2433 // The role of the variable _between_prologue_and_epilogue is to
2434 // enforce the invocation protocol.
2435 void CMSCollector::gc_prologue(bool full) {
2436 // Call gc_prologue_work() for the CMSGen
2437 // we are responsible for.
2438
2439 // The following locking discipline assumes that we are only called
2440 // when the world is stopped.
2441 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2442
2443 // The CMSCollector prologue must call the gc_prologues for the
2444 // "generations" that it's responsible
2445 // for.
2446
2447 assert( Thread::current()->is_VM_thread()
2448 || ( CMSScavengeBeforeRemark
2449 && Thread::current()->is_ConcurrentGC_thread()),
2450 "Incorrect thread type for prologue execution");
2451
2452 if (_between_prologue_and_epilogue) {
2453 // We have already been invoked; this is a gc_prologue delegation
2454 // from yet another CMS generation that we are responsible for, just
2455 // ignore it since all relevant work has already been done.
2456 return;
2457 }
2458
2459 // set a bit saying prologue has been called; cleared in epilogue
2460 _between_prologue_and_epilogue = true;
2461 // Claim locks for common data structures, then call gc_prologue_work()
2462 // for each CMSGen.
2463
2464 getFreelistLocks(); // gets free list locks on constituent spaces
2465 bitMapLock()->lock_without_safepoint_check();
2466
2467 // Should call gc_prologue_work() for all cms gens we are responsible for
2468 bool duringMarking = _collectorState >= Marking
2469 && _collectorState < Sweeping;
2470
2471 // The young collections clear the modified oops state, which tells if
2472 // there are any modified oops in the class. The remark phase also needs
2473 // that information. Tell the young collection to save the union of all
2474 // modified klasses.
2475 if (duringMarking) {
2476 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2477 }
2478
2479 bool registerClosure = duringMarking;
2480
2481 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2482 &_modUnionClosurePar
2483 : &_modUnionClosure;
2484 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2485
2486 if (!full) {
2487 stats().record_gc0_begin();
2488 }
2489 }
2490
2491 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2492
2493 _capacity_at_prologue = capacity();
2494 _used_at_prologue = used();
2495
2496 // Delegate to CMScollector which knows how to coordinate between
2497 // this and any other CMS generations that it is responsible for
2498 // collecting.
2499 collector()->gc_prologue(full);
2500 }
2501
2502 // This is a "private" interface for use by this generation's CMSCollector.
2503 // Not to be called directly by any other entity (for instance,
2504 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2505 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2506 bool registerClosure, ModUnionClosure* modUnionClosure) {
2507 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2508 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2509 "Should be NULL");
2510 if (registerClosure) {
2511 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2512 }
2513 cmsSpace()->gc_prologue();
2514 // Clear stat counters
2515 NOT_PRODUCT(
2516 assert(_numObjectsPromoted == 0, "check");
2517 assert(_numWordsPromoted == 0, "check");
2518 if (Verbose && PrintGC) {
2519 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2520 SIZE_FORMAT" bytes concurrently",
2521 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2522 }
2523 _numObjectsAllocated = 0;
2524 _numWordsAllocated = 0;
2525 )
2526 }
2527
2528 void CMSCollector::gc_epilogue(bool full) {
2529 // The following locking discipline assumes that we are only called
2530 // when the world is stopped.
2531 assert(SafepointSynchronize::is_at_safepoint(),
2532 "world is stopped assumption");
2533
2534 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2535 // if linear allocation blocks need to be appropriately marked to allow the
2536 // the blocks to be parsable. We also check here whether we need to nudge the
2537 // CMS collector thread to start a new cycle (if it's not already active).
2538 assert( Thread::current()->is_VM_thread()
2539 || ( CMSScavengeBeforeRemark
2540 && Thread::current()->is_ConcurrentGC_thread()),
2541 "Incorrect thread type for epilogue execution");
2542
2543 if (!_between_prologue_and_epilogue) {
2544 // We have already been invoked; this is a gc_epilogue delegation
2545 // from yet another CMS generation that we are responsible for, just
2546 // ignore it since all relevant work has already been done.
2547 return;
2548 }
2549 assert(haveFreelistLocks(), "must have freelist locks");
2550 assert_lock_strong(bitMapLock());
2551
2552 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2553
2554 _cmsGen->gc_epilogue_work(full);
2555
2556 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2557 // in case sampling was not already enabled, enable it
2558 _start_sampling = true;
2559 }
2560 // reset _eden_chunk_array so sampling starts afresh
2561 _eden_chunk_index = 0;
2562
2563 size_t cms_used = _cmsGen->cmsSpace()->used();
2564
2565 // update performance counters - this uses a special version of
2566 // update_counters() that allows the utilization to be passed as a
2567 // parameter, avoiding multiple calls to used().
2568 //
2569 _cmsGen->update_counters(cms_used);
2570
2571 bitMapLock()->unlock();
2572 releaseFreelistLocks();
2573
2574 if (!CleanChunkPoolAsync) {
2575 Chunk::clean_chunk_pool();
2576 }
2577
2578 set_did_compact(false);
2579 _between_prologue_and_epilogue = false; // ready for next cycle
2580 }
2581
2582 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2583 collector()->gc_epilogue(full);
2584
2585 // Also reset promotion tracking in par gc thread states.
2586 if (CollectedHeap::use_parallel_gc_threads()) {
2587 for (uint i = 0; i < ParallelGCThreads; i++) {
2588 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2589 }
2590 }
2591 }
2592
2593 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2594 assert(!incremental_collection_failed(), "Should have been cleared");
2595 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2596 cmsSpace()->gc_epilogue();
2597 // Print stat counters
2598 NOT_PRODUCT(
2599 assert(_numObjectsAllocated == 0, "check");
2600 assert(_numWordsAllocated == 0, "check");
2601 if (Verbose && PrintGC) {
2602 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2603 SIZE_FORMAT" bytes",
2604 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2605 }
2606 _numObjectsPromoted = 0;
2607 _numWordsPromoted = 0;
2608 )
2609
2610 if (PrintGC && Verbose) {
2611 // Call down the chain in contiguous_available needs the freelistLock
2612 // so print this out before releasing the freeListLock.
2613 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2614 contiguous_available());
2615 }
2616 }
2617
2618 #ifndef PRODUCT
2619 bool CMSCollector::have_cms_token() {
2620 Thread* thr = Thread::current();
2621 if (thr->is_VM_thread()) {
2622 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2623 } else if (thr->is_ConcurrentGC_thread()) {
2624 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2625 } else if (thr->is_GC_task_thread()) {
2626 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2627 ParGCRareEvent_lock->owned_by_self();
2628 }
2629 return false;
2630 }
2631 #endif
2632
2633 // Check reachability of the given heap address in CMS generation,
2634 // treating all other generations as roots.
2635 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2636 // We could "guarantee" below, rather than assert, but I'll
2637 // leave these as "asserts" so that an adventurous debugger
2638 // could try this in the product build provided some subset of
2639 // the conditions were met, provided they were interested in the
2640 // results and knew that the computation below wouldn't interfere
2641 // with other concurrent computations mutating the structures
2642 // being read or written.
2643 assert(SafepointSynchronize::is_at_safepoint(),
2644 "Else mutations in object graph will make answer suspect");
2645 assert(have_cms_token(), "Should hold cms token");
2646 assert(haveFreelistLocks(), "must hold free list locks");
2647 assert_lock_strong(bitMapLock());
2648
2649 // Clear the marking bit map array before starting, but, just
2650 // for kicks, first report if the given address is already marked
2651 gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", addr,
2652 _markBitMap.isMarked(addr) ? "" : " not");
2653
2654 if (verify_after_remark()) {
2655 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2656 bool result = verification_mark_bm()->isMarked(addr);
2657 gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", addr,
2658 result ? "IS" : "is NOT");
2659 return result;
2660 } else {
2661 gclog_or_tty->print_cr("Could not compute result");
2662 return false;
2663 }
2664 }
2665
2666
2667 void
2668 CMSCollector::print_on_error(outputStream* st) {
2669 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2670 if (collector != NULL) {
2671 CMSBitMap* bitmap = &collector->_markBitMap;
2672 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, bitmap);
2673 bitmap->print_on_error(st, " Bits: ");
2674
2675 st->cr();
2676
2677 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2678 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, mut_bitmap);
2679 mut_bitmap->print_on_error(st, " Bits: ");
2680 }
2681 }
2682
2683 ////////////////////////////////////////////////////////
2684 // CMS Verification Support
2685 ////////////////////////////////////////////////////////
2686 // Following the remark phase, the following invariant
2687 // should hold -- each object in the CMS heap which is
2688 // marked in markBitMap() should be marked in the verification_mark_bm().
2689
2690 class VerifyMarkedClosure: public BitMapClosure {
2691 CMSBitMap* _marks;
2692 bool _failed;
2693
2694 public:
2695 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2696
2697 bool do_bit(size_t offset) {
2698 HeapWord* addr = _marks->offsetToHeapWord(offset);
2699 if (!_marks->isMarked(addr)) {
2700 oop(addr)->print_on(gclog_or_tty);
2701 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2702 _failed = true;
2703 }
2704 return true;
2705 }
2706
2707 bool failed() { return _failed; }
2708 };
2709
2710 bool CMSCollector::verify_after_remark(bool silent) {
2711 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2712 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2713 static bool init = false;
2714
2715 assert(SafepointSynchronize::is_at_safepoint(),
2716 "Else mutations in object graph will make answer suspect");
2717 assert(have_cms_token(),
2718 "Else there may be mutual interference in use of "
2719 " verification data structures");
2720 assert(_collectorState > Marking && _collectorState <= Sweeping,
2721 "Else marking info checked here may be obsolete");
2722 assert(haveFreelistLocks(), "must hold free list locks");
2723 assert_lock_strong(bitMapLock());
2724
2725
2726 // Allocate marking bit map if not already allocated
2727 if (!init) { // first time
2728 if (!verification_mark_bm()->allocate(_span)) {
2729 return false;
2730 }
2731 init = true;
2732 }
2733
2734 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2735
2736 // Turn off refs discovery -- so we will be tracing through refs.
2737 // This is as intended, because by this time
2738 // GC must already have cleared any refs that need to be cleared,
2739 // and traced those that need to be marked; moreover,
2740 // the marking done here is not going to interfere in any
2741 // way with the marking information used by GC.
2742 NoRefDiscovery no_discovery(ref_processor());
2743
2744 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2745
2746 // Clear any marks from a previous round
2747 verification_mark_bm()->clear_all();
2748 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2749 verify_work_stacks_empty();
2750
2751 GenCollectedHeap* gch = GenCollectedHeap::heap();
2752 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2753 // Update the saved marks which may affect the root scans.
2754 gch->save_marks();
2755
2756 if (CMSRemarkVerifyVariant == 1) {
2757 // In this first variant of verification, we complete
2758 // all marking, then check if the new marks-vector is
2759 // a subset of the CMS marks-vector.
2760 verify_after_remark_work_1();
2761 } else if (CMSRemarkVerifyVariant == 2) {
2762 // In this second variant of verification, we flag an error
2763 // (i.e. an object reachable in the new marks-vector not reachable
2764 // in the CMS marks-vector) immediately, also indicating the
2765 // identify of an object (A) that references the unmarked object (B) --
2766 // presumably, a mutation to A failed to be picked up by preclean/remark?
2767 verify_after_remark_work_2();
2768 } else {
2769 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2770 CMSRemarkVerifyVariant);
2771 }
2772 if (!silent) gclog_or_tty->print(" done] ");
2773 return true;
2774 }
2775
2776 void CMSCollector::verify_after_remark_work_1() {
2777 ResourceMark rm;
2778 HandleMark hm;
2779 GenCollectedHeap* gch = GenCollectedHeap::heap();
2780
2781 // Get a clear set of claim bits for the roots processing to work with.
2782 ClassLoaderDataGraph::clear_claimed_marks();
2783
2784 // Mark from roots one level into CMS
2785 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2786 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2787
2788 gch->gen_process_roots(_cmsGen->level(),
2789 true, // younger gens are roots
2790 true, // activate StrongRootsScope
2791 SharedHeap::ScanningOption(roots_scanning_options()),
2792 should_unload_classes(),
2793 ¬Older,
2794 NULL,
2795 NULL); // SSS: Provide correct closure
2796
2797 // Now mark from the roots
2798 MarkFromRootsClosure markFromRootsClosure(this, _span,
2799 verification_mark_bm(), verification_mark_stack(),
2800 false /* don't yield */, true /* verifying */);
2801 assert(_restart_addr == NULL, "Expected pre-condition");
2802 verification_mark_bm()->iterate(&markFromRootsClosure);
2803 while (_restart_addr != NULL) {
2804 // Deal with stack overflow: by restarting at the indicated
2805 // address.
2806 HeapWord* ra = _restart_addr;
2807 markFromRootsClosure.reset(ra);
2808 _restart_addr = NULL;
2809 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2810 }
2811 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2812 verify_work_stacks_empty();
2813
2814 // Marking completed -- now verify that each bit marked in
2815 // verification_mark_bm() is also marked in markBitMap(); flag all
2816 // errors by printing corresponding objects.
2817 VerifyMarkedClosure vcl(markBitMap());
2818 verification_mark_bm()->iterate(&vcl);
2819 if (vcl.failed()) {
2820 gclog_or_tty->print("Verification failed");
2821 Universe::heap()->print_on(gclog_or_tty);
2822 fatal("CMS: failed marking verification after remark");
2823 }
2824 }
2825
2826 class VerifyKlassOopsKlassClosure : public KlassClosure {
2827 class VerifyKlassOopsClosure : public OopClosure {
2828 CMSBitMap* _bitmap;
2829 public:
2830 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2831 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2832 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2833 } _oop_closure;
2834 public:
2835 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2836 void do_klass(Klass* k) {
2837 k->oops_do(&_oop_closure);
2838 }
2839 };
2840
2841 void CMSCollector::verify_after_remark_work_2() {
2842 ResourceMark rm;
2843 HandleMark hm;
2844 GenCollectedHeap* gch = GenCollectedHeap::heap();
2845
2846 // Get a clear set of claim bits for the roots processing to work with.
2847 ClassLoaderDataGraph::clear_claimed_marks();
2848
2849 // Mark from roots one level into CMS
2850 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2851 markBitMap());
2852 CLDToOopClosure cld_closure(¬Older, true);
2853
2854 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2855
2856 gch->gen_process_roots(_cmsGen->level(),
2857 true, // younger gens are roots
2858 true, // activate StrongRootsScope
2859 SharedHeap::ScanningOption(roots_scanning_options()),
2860 should_unload_classes(),
2861 ¬Older,
2862 NULL,
2863 &cld_closure);
2864
2865 // Now mark from the roots
2866 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2867 verification_mark_bm(), markBitMap(), verification_mark_stack());
2868 assert(_restart_addr == NULL, "Expected pre-condition");
2869 verification_mark_bm()->iterate(&markFromRootsClosure);
2870 while (_restart_addr != NULL) {
2871 // Deal with stack overflow: by restarting at the indicated
2872 // address.
2873 HeapWord* ra = _restart_addr;
2874 markFromRootsClosure.reset(ra);
2875 _restart_addr = NULL;
2876 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2877 }
2878 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2879 verify_work_stacks_empty();
2880
2881 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2882 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2883
2884 // Marking completed -- now verify that each bit marked in
2885 // verification_mark_bm() is also marked in markBitMap(); flag all
2886 // errors by printing corresponding objects.
2887 VerifyMarkedClosure vcl(markBitMap());
2888 verification_mark_bm()->iterate(&vcl);
2889 assert(!vcl.failed(), "Else verification above should not have succeeded");
2890 }
2891
2892 void ConcurrentMarkSweepGeneration::save_marks() {
2893 // delegate to CMS space
2894 cmsSpace()->save_marks();
2895 for (uint i = 0; i < ParallelGCThreads; i++) {
2896 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2897 }
2898 }
2899
2900 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2901 return cmsSpace()->no_allocs_since_save_marks();
2902 }
2903
2904 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2905 \
2906 void ConcurrentMarkSweepGeneration:: \
2907 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2908 cl->set_generation(this); \
2909 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2910 cl->reset_generation(); \
2911 save_marks(); \
2912 }
2913
2914 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2915
2916 void
2917 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
2918 cl->set_generation(this);
2919 younger_refs_in_space_iterate(_cmsSpace, cl);
2920 cl->reset_generation();
2921 }
2922
2923 void
2924 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2925 if (freelistLock()->owned_by_self()) {
2926 Generation::oop_iterate(cl);
2927 } else {
2928 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2929 Generation::oop_iterate(cl);
2930 }
2931 }
2932
2933 void
2934 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2935 if (freelistLock()->owned_by_self()) {
2936 Generation::object_iterate(cl);
2937 } else {
2938 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2939 Generation::object_iterate(cl);
2940 }
2941 }
2942
2943 void
2944 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2945 if (freelistLock()->owned_by_self()) {
2946 Generation::safe_object_iterate(cl);
2947 } else {
2948 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2949 Generation::safe_object_iterate(cl);
2950 }
2951 }
2952
2953 void
2954 ConcurrentMarkSweepGeneration::post_compact() {
2955 }
2956
2957 void
2958 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2959 // Fix the linear allocation blocks to look like free blocks.
2960
2961 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2962 // are not called when the heap is verified during universe initialization and
2963 // at vm shutdown.
2964 if (freelistLock()->owned_by_self()) {
2965 cmsSpace()->prepare_for_verify();
2966 } else {
2967 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2968 cmsSpace()->prepare_for_verify();
2969 }
2970 }
2971
2972 void
2973 ConcurrentMarkSweepGeneration::verify() {
2974 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2975 // are not called when the heap is verified during universe initialization and
2976 // at vm shutdown.
2977 if (freelistLock()->owned_by_self()) {
2978 cmsSpace()->verify();
2979 } else {
2980 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2981 cmsSpace()->verify();
2982 }
2983 }
2984
2985 void CMSCollector::verify() {
2986 _cmsGen->verify();
2987 }
2988
2989 #ifndef PRODUCT
2990 bool CMSCollector::overflow_list_is_empty() const {
2991 assert(_num_par_pushes >= 0, "Inconsistency");
2992 if (_overflow_list == NULL) {
2993 assert(_num_par_pushes == 0, "Inconsistency");
2994 }
2995 return _overflow_list == NULL;
2996 }
2997
2998 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2999 // merely consolidate assertion checks that appear to occur together frequently.
3000 void CMSCollector::verify_work_stacks_empty() const {
3001 assert(_markStack.isEmpty(), "Marking stack should be empty");
3002 assert(overflow_list_is_empty(), "Overflow list should be empty");
3003 }
3004
3005 void CMSCollector::verify_overflow_empty() const {
3006 assert(overflow_list_is_empty(), "Overflow list should be empty");
3007 assert(no_preserved_marks(), "No preserved marks");
3008 }
3009 #endif // PRODUCT
3010
3011 // Decide if we want to enable class unloading as part of the
3012 // ensuing concurrent GC cycle. We will collect and
3013 // unload classes if it's the case that:
3014 // (1) an explicit gc request has been made and the flag
3015 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3016 // (2) (a) class unloading is enabled at the command line, and
3017 // (b) old gen is getting really full
3018 // NOTE: Provided there is no change in the state of the heap between
3019 // calls to this method, it should have idempotent results. Moreover,
3020 // its results should be monotonically increasing (i.e. going from 0 to 1,
3021 // but not 1 to 0) between successive calls between which the heap was
3022 // not collected. For the implementation below, it must thus rely on
3023 // the property that concurrent_cycles_since_last_unload()
3024 // will not decrease unless a collection cycle happened and that
3025 // _cmsGen->is_too_full() are
3026 // themselves also monotonic in that sense. See check_monotonicity()
3027 // below.
3028 void CMSCollector::update_should_unload_classes() {
3029 _should_unload_classes = false;
3030 // Condition 1 above
3031 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3032 _should_unload_classes = true;
3033 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3034 // Disjuncts 2.b.(i,ii,iii) above
3035 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3036 CMSClassUnloadingMaxInterval)
3037 || _cmsGen->is_too_full();
3038 }
3039 }
3040
3041 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3042 bool res = should_concurrent_collect();
3043 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3044 return res;
3045 }
3046
3047 void CMSCollector::setup_cms_unloading_and_verification_state() {
3048 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3049 || VerifyBeforeExit;
3050 const int rso = SharedHeap::SO_AllCodeCache;
3051
3052 // We set the proper root for this CMS cycle here.
3053 if (should_unload_classes()) { // Should unload classes this cycle
3054 remove_root_scanning_option(rso); // Shrink the root set appropriately
3055 set_verifying(should_verify); // Set verification state for this cycle
3056 return; // Nothing else needs to be done at this time
3057 }
3058
3059 // Not unloading classes this cycle
3060 assert(!should_unload_classes(), "Inconsistency!");
3061
3062 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3063 // Include symbols, strings and code cache elements to prevent their resurrection.
3064 add_root_scanning_option(rso);
3065 set_verifying(true);
3066 } else if (verifying() && !should_verify) {
3067 // We were verifying, but some verification flags got disabled.
3068 set_verifying(false);
3069 // Exclude symbols, strings and code cache elements from root scanning to
3070 // reduce IM and RM pauses.
3071 remove_root_scanning_option(rso);
3072 }
3073 }
3074
3075
3076 #ifndef PRODUCT
3077 HeapWord* CMSCollector::block_start(const void* p) const {
3078 const HeapWord* addr = (HeapWord*)p;
3079 if (_span.contains(p)) {
3080 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3081 return _cmsGen->cmsSpace()->block_start(p);
3082 }
3083 }
3084 return NULL;
3085 }
3086 #endif
3087
3088 HeapWord*
3089 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3090 bool tlab,
3091 bool parallel) {
3092 CMSSynchronousYieldRequest yr;
3093 assert(!tlab, "Can't deal with TLAB allocation");
3094 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3095 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3096 CMSExpansionCause::_satisfy_allocation);
3097 if (GCExpandToAllocateDelayMillis > 0) {
3098 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3099 }
3100 return have_lock_and_allocate(word_size, tlab);
3101 }
3102
3103 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3104 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3105 // to CardGeneration and share it...
3106 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3107 return CardGeneration::expand(bytes, expand_bytes);
3108 }
3109
3110 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3111 CMSExpansionCause::Cause cause)
3112 {
3113
3114 bool success = expand(bytes, expand_bytes);
3115
3116 // remember why we expanded; this information is used
3117 // by shouldConcurrentCollect() when making decisions on whether to start
3118 // a new CMS cycle.
3119 if (success) {
3120 set_expansion_cause(cause);
3121 if (PrintGCDetails && Verbose) {
3122 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3123 CMSExpansionCause::to_string(cause));
3124 }
3125 }
3126 }
3127
3128 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3129 HeapWord* res = NULL;
3130 MutexLocker x(ParGCRareEvent_lock);
3131 while (true) {
3132 // Expansion by some other thread might make alloc OK now:
3133 res = ps->lab.alloc(word_sz);
3134 if (res != NULL) return res;
3135 // If there's not enough expansion space available, give up.
3136 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3137 return NULL;
3138 }
3139 // Otherwise, we try expansion.
3140 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3141 CMSExpansionCause::_allocate_par_lab);
3142 // Now go around the loop and try alloc again;
3143 // A competing par_promote might beat us to the expansion space,
3144 // so we may go around the loop again if promotion fails again.
3145 if (GCExpandToAllocateDelayMillis > 0) {
3146 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3147 }
3148 }
3149 }
3150
3151
3152 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3153 PromotionInfo* promo) {
3154 MutexLocker x(ParGCRareEvent_lock);
3155 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3156 while (true) {
3157 // Expansion by some other thread might make alloc OK now:
3158 if (promo->ensure_spooling_space()) {
3159 assert(promo->has_spooling_space(),
3160 "Post-condition of successful ensure_spooling_space()");
3161 return true;
3162 }
3163 // If there's not enough expansion space available, give up.
3164 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3165 return false;
3166 }
3167 // Otherwise, we try expansion.
3168 expand(refill_size_bytes, MinHeapDeltaBytes,
3169 CMSExpansionCause::_allocate_par_spooling_space);
3170 // Now go around the loop and try alloc again;
3171 // A competing allocation might beat us to the expansion space,
3172 // so we may go around the loop again if allocation fails again.
3173 if (GCExpandToAllocateDelayMillis > 0) {
3174 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3175 }
3176 }
3177 }
3178
3179
3180 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3181 assert_locked_or_safepoint(ExpandHeap_lock);
3182 // Shrink committed space
3183 _virtual_space.shrink_by(bytes);
3184 // Shrink space; this also shrinks the space's BOT
3185 _cmsSpace->set_end((HeapWord*) _virtual_space.high());
3186 size_t new_word_size = heap_word_size(_cmsSpace->capacity());
3187 // Shrink the shared block offset array
3188 _bts->resize(new_word_size);
3189 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3190 // Shrink the card table
3191 Universe::heap()->barrier_set()->resize_covered_region(mr);
3192
3193 if (Verbose && PrintGC) {
3194 size_t new_mem_size = _virtual_space.committed_size();
3195 size_t old_mem_size = new_mem_size + bytes;
3196 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3197 name(), old_mem_size/K, new_mem_size/K);
3198 }
3199 }
3200
3201 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3202 assert_locked_or_safepoint(Heap_lock);
3203 size_t size = ReservedSpace::page_align_size_down(bytes);
3204 // Only shrink if a compaction was done so that all the free space
3205 // in the generation is in a contiguous block at the end.
3206 if (size > 0 && did_compact()) {
3207 shrink_by(size);
3208 }
3209 }
3210
3211 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3212 assert_locked_or_safepoint(Heap_lock);
3213 bool result = _virtual_space.expand_by(bytes);
3214 if (result) {
3215 size_t new_word_size =
3216 heap_word_size(_virtual_space.committed_size());
3217 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3218 _bts->resize(new_word_size); // resize the block offset shared array
3219 Universe::heap()->barrier_set()->resize_covered_region(mr);
3220 // Hmmmm... why doesn't CFLS::set_end verify locking?
3221 // This is quite ugly; FIX ME XXX
3222 _cmsSpace->assert_locked(freelistLock());
3223 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3224
3225 // update the space and generation capacity counters
3226 if (UsePerfData) {
3227 _space_counters->update_capacity();
3228 _gen_counters->update_all();
3229 }
3230
3231 if (Verbose && PrintGC) {
3232 size_t new_mem_size = _virtual_space.committed_size();
3233 size_t old_mem_size = new_mem_size - bytes;
3234 gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3235 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3236 }
3237 }
3238 return result;
3239 }
3240
3241 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3242 assert_locked_or_safepoint(Heap_lock);
3243 bool success = true;
3244 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3245 if (remaining_bytes > 0) {
3246 success = grow_by(remaining_bytes);
3247 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3248 }
3249 return success;
3250 }
3251
3252 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
3253 assert_locked_or_safepoint(Heap_lock);
3254 assert_lock_strong(freelistLock());
3255 if (PrintGCDetails && Verbose) {
3256 warning("Shrinking of CMS not yet implemented");
3257 }
3258 return;
3259 }
3260
3261
3262 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3263 // phases.
3264 class CMSPhaseAccounting: public StackObj {
3265 public:
3266 CMSPhaseAccounting(CMSCollector *collector,
3267 const char *phase,
3268 const GCId gc_id,
3269 bool print_cr = true);
3270 ~CMSPhaseAccounting();
3271
3272 private:
3273 CMSCollector *_collector;
3274 const char *_phase;
3275 elapsedTimer _wallclock;
3276 bool _print_cr;
3277 const GCId _gc_id;
3278
3279 public:
3280 // Not MT-safe; so do not pass around these StackObj's
3281 // where they may be accessed by other threads.
3282 jlong wallclock_millis() {
3283 assert(_wallclock.is_active(), "Wall clock should not stop");
3284 _wallclock.stop(); // to record time
3285 jlong ret = _wallclock.milliseconds();
3286 _wallclock.start(); // restart
3287 return ret;
3288 }
3289 };
3290
3291 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3292 const char *phase,
3293 const GCId gc_id,
3294 bool print_cr) :
3295 _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
3296
3297 if (PrintCMSStatistics != 0) {
3298 _collector->resetYields();
3299 }
3300 if (PrintGCDetails) {
3301 gclog_or_tty->gclog_stamp(_gc_id);
3302 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
3303 _collector->cmsGen()->short_name(), _phase);
3304 }
3305 _collector->resetTimer();
3306 _wallclock.start();
3307 _collector->startTimer();
3308 }
3309
3310 CMSPhaseAccounting::~CMSPhaseAccounting() {
3311 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3312 _collector->stopTimer();
3313 _wallclock.stop();
3314 if (PrintGCDetails) {
3315 gclog_or_tty->gclog_stamp(_gc_id);
3316 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3317 _collector->cmsGen()->short_name(),
3318 _phase, _collector->timerValue(), _wallclock.seconds());
3319 if (_print_cr) {
3320 gclog_or_tty->cr();
3321 }
3322 if (PrintCMSStatistics != 0) {
3323 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3324 _collector->yields());
3325 }
3326 }
3327 }
3328
3329 // CMS work
3330
3331 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
3332 class CMSParMarkTask : public AbstractGangTask {
3333 protected:
3334 CMSCollector* _collector;
3335 int _n_workers;
3336 CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
3337 AbstractGangTask(name),
3338 _collector(collector),
3339 _n_workers(n_workers) {}
3340 // Work method in support of parallel rescan ... of young gen spaces
3341 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
3342 ContiguousSpace* space,
3343 HeapWord** chunk_array, size_t chunk_top);
3344 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
3345 };
3346
3347 // Parallel initial mark task
3348 class CMSParInitialMarkTask: public CMSParMarkTask {
3349 public:
3350 CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
3351 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
3352 collector, n_workers) {}
3353 void work(uint worker_id);
3354 };
3355
3356 // Checkpoint the roots into this generation from outside
3357 // this generation. [Note this initial checkpoint need only
3358 // be approximate -- we'll do a catch up phase subsequently.]
3359 void CMSCollector::checkpointRootsInitial(bool asynch) {
3360 assert(_collectorState == InitialMarking, "Wrong collector state");
3361 check_correct_thread_executing();
3362 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3363
3364 save_heap_summary();
3365 report_heap_summary(GCWhen::BeforeGC);
3366
3367 ReferenceProcessor* rp = ref_processor();
3368 SpecializationStats::clear();
3369 assert(_restart_addr == NULL, "Control point invariant");
3370 if (asynch) {
3371 // acquire locks for subsequent manipulations
3372 MutexLockerEx x(bitMapLock(),
3373 Mutex::_no_safepoint_check_flag);
3374 checkpointRootsInitialWork(asynch);
3375 // enable ("weak") refs discovery
3376 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3377 _collectorState = Marking;
3378 } else {
3379 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3380 // which recognizes if we are a CMS generation, and doesn't try to turn on
3381 // discovery; verify that they aren't meddling.
3382 assert(!rp->discovery_is_atomic(),
3383 "incorrect setting of discovery predicate");
3384 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3385 "ref discovery for this generation kind");
3386 // already have locks
3387 checkpointRootsInitialWork(asynch);
3388 // now enable ("weak") refs discovery
3389 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3390 _collectorState = Marking;
3391 }
3392 SpecializationStats::print();
3393 }
3394
3395 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3396 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3397 assert(_collectorState == InitialMarking, "just checking");
3398
3399 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3400 // precede our marking with a collection of all
3401 // younger generations to keep floating garbage to a minimum.
3402 // XXX: we won't do this for now -- it's an optimization to be done later.
3403
3404 // already have locks
3405 assert_lock_strong(bitMapLock());
3406 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3407
3408 // Setup the verification and class unloading state for this
3409 // CMS collection cycle.
3410 setup_cms_unloading_and_verification_state();
3411
3412 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3413 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
3414
3415 // Reset all the PLAB chunk arrays if necessary.
3416 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3417 reset_survivor_plab_arrays();
3418 }
3419
3420 ResourceMark rm;
3421 HandleMark hm;
3422
3423 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3424 GenCollectedHeap* gch = GenCollectedHeap::heap();
3425
3426 verify_work_stacks_empty();
3427 verify_overflow_empty();
3428
3429 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3430 // Update the saved marks which may affect the root scans.
3431 gch->save_marks();
3432
3433 // weak reference processing has not started yet.
3434 ref_processor()->set_enqueuing_is_done(false);
3435
3436 // Need to remember all newly created CLDs,
3437 // so that we can guarantee that the remark finds them.
3438 ClassLoaderDataGraph::remember_new_clds(true);
3439
3440 // Whenever a CLD is found, it will be claimed before proceeding to mark
3441 // the klasses. The claimed marks need to be cleared before marking starts.
3442 ClassLoaderDataGraph::clear_claimed_marks();
3443
3444 if (CMSPrintEdenSurvivorChunks) {
3445 print_eden_and_survivor_chunk_arrays();
3446 }
3447
3448 {
3449 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3450 if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3451 // The parallel version.
3452 FlexibleWorkGang* workers = gch->workers();
3453 assert(workers != NULL, "Need parallel worker threads.");
3454 int n_workers = workers->active_workers();
3455 CMSParInitialMarkTask tsk(this, n_workers);
3456 gch->set_par_threads(n_workers);
3457 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3458 if (n_workers > 1) {
3459 GenCollectedHeap::StrongRootsScope srs(gch);
3460 workers->run_task(&tsk);
3461 } else {
3462 GenCollectedHeap::StrongRootsScope srs(gch);
3463 tsk.work(0);
3464 }
3465 gch->set_par_threads(0);
3466 } else {
3467 // The serial version.
3468 CLDToOopClosure cld_closure(¬Older, true);
3469 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3470 gch->gen_process_roots(_cmsGen->level(),
3471 true, // younger gens are roots
3472 true, // activate StrongRootsScope
3473 SharedHeap::ScanningOption(roots_scanning_options()),
3474 should_unload_classes(),
3475 ¬Older,
3476 NULL,
3477 &cld_closure);
3478 }
3479 }
3480
3481 // Clear mod-union table; it will be dirtied in the prologue of
3482 // CMS generation per each younger generation collection.
3483
3484 assert(_modUnionTable.isAllClear(),
3485 "Was cleared in most recent final checkpoint phase"
3486 " or no bits are set in the gc_prologue before the start of the next "
3487 "subsequent marking phase.");
3488
3489 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3490
3491 // Save the end of the used_region of the constituent generations
3492 // to be used to limit the extent of sweep in each generation.
3493 save_sweep_limits();
3494 verify_overflow_empty();
3495 }
3496
3497 bool CMSCollector::markFromRoots(bool asynch) {
3498 // we might be tempted to assert that:
3499 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3500 // "inconsistent argument?");
3501 // However that wouldn't be right, because it's possible that
3502 // a safepoint is indeed in progress as a younger generation
3503 // stop-the-world GC happens even as we mark in this generation.
3504 assert(_collectorState == Marking, "inconsistent state?");
3505 check_correct_thread_executing();
3506 verify_overflow_empty();
3507
3508 bool res;
3509 if (asynch) {
3510 // Weak ref discovery note: We may be discovering weak
3511 // refs in this generation concurrent (but interleaved) with
3512 // weak ref discovery by a younger generation collector.
3513
3514 CMSTokenSyncWithLocks ts(true, bitMapLock());
3515 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3516 CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3517 res = markFromRootsWork(asynch);
3518 if (res) {
3519 _collectorState = Precleaning;
3520 } else { // We failed and a foreground collection wants to take over
3521 assert(_foregroundGCIsActive, "internal state inconsistency");
3522 assert(_restart_addr == NULL, "foreground will restart from scratch");
3523 if (PrintGCDetails) {
3524 gclog_or_tty->print_cr("bailing out to foreground collection");
3525 }
3526 }
3527 } else {
3528 assert(SafepointSynchronize::is_at_safepoint(),
3529 "inconsistent with asynch == false");
3530 // already have locks
3531 res = markFromRootsWork(asynch);
3532 _collectorState = FinalMarking;
3533 }
3534 verify_overflow_empty();
3535 return res;
3536 }
3537
3538 bool CMSCollector::markFromRootsWork(bool asynch) {
3539 // iterate over marked bits in bit map, doing a full scan and mark
3540 // from these roots using the following algorithm:
3541 // . if oop is to the right of the current scan pointer,
3542 // mark corresponding bit (we'll process it later)
3543 // . else (oop is to left of current scan pointer)
3544 // push oop on marking stack
3545 // . drain the marking stack
3546
3547 // Note that when we do a marking step we need to hold the
3548 // bit map lock -- recall that direct allocation (by mutators)
3549 // and promotion (by younger generation collectors) is also
3550 // marking the bit map. [the so-called allocate live policy.]
3551 // Because the implementation of bit map marking is not
3552 // robust wrt simultaneous marking of bits in the same word,
3553 // we need to make sure that there is no such interference
3554 // between concurrent such updates.
3555
3556 // already have locks
3557 assert_lock_strong(bitMapLock());
3558
3559 verify_work_stacks_empty();
3560 verify_overflow_empty();
3561 bool result = false;
3562 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3563 result = do_marking_mt(asynch);
3564 } else {
3565 result = do_marking_st(asynch);
3566 }
3567 return result;
3568 }
3569
3570 // Forward decl
3571 class CMSConcMarkingTask;
3572
3573 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3574 CMSCollector* _collector;
3575 CMSConcMarkingTask* _task;
3576 public:
3577 virtual void yield();
3578
3579 // "n_threads" is the number of threads to be terminated.
3580 // "queue_set" is a set of work queues of other threads.
3581 // "collector" is the CMS collector associated with this task terminator.
3582 // "yield" indicates whether we need the gang as a whole to yield.
3583 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3584 ParallelTaskTerminator(n_threads, queue_set),
3585 _collector(collector) { }
3586
3587 void set_task(CMSConcMarkingTask* task) {
3588 _task = task;
3589 }
3590 };
3591
3592 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3593 CMSConcMarkingTask* _task;
3594 public:
3595 bool should_exit_termination();
3596 void set_task(CMSConcMarkingTask* task) {
3597 _task = task;
3598 }
3599 };
3600
3601 // MT Concurrent Marking Task
3602 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3603 CMSCollector* _collector;
3604 int _n_workers; // requested/desired # workers
3605 bool _asynch;
3606 bool _result;
3607 CompactibleFreeListSpace* _cms_space;
3608 char _pad_front[64]; // padding to ...
3609 HeapWord* _global_finger; // ... avoid sharing cache line
3610 char _pad_back[64];
3611 HeapWord* _restart_addr;
3612
3613 // Exposed here for yielding support
3614 Mutex* const _bit_map_lock;
3615
3616 // The per thread work queues, available here for stealing
3617 OopTaskQueueSet* _task_queues;
3618
3619 // Termination (and yielding) support
3620 CMSConcMarkingTerminator _term;
3621 CMSConcMarkingTerminatorTerminator _term_term;
3622
3623 public:
3624 CMSConcMarkingTask(CMSCollector* collector,
3625 CompactibleFreeListSpace* cms_space,
3626 bool asynch,
3627 YieldingFlexibleWorkGang* workers,
3628 OopTaskQueueSet* task_queues):
3629 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3630 _collector(collector),
3631 _cms_space(cms_space),
3632 _asynch(asynch), _n_workers(0), _result(true),
3633 _task_queues(task_queues),
3634 _term(_n_workers, task_queues, _collector),
3635 _bit_map_lock(collector->bitMapLock())
3636 {
3637 _requested_size = _n_workers;
3638 _term.set_task(this);
3639 _term_term.set_task(this);
3640 _restart_addr = _global_finger = _cms_space->bottom();
3641 }
3642
3643
3644 OopTaskQueueSet* task_queues() { return _task_queues; }
3645
3646 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3647
3648 HeapWord** global_finger_addr() { return &_global_finger; }
3649
3650 CMSConcMarkingTerminator* terminator() { return &_term; }
3651
3652 virtual void set_for_termination(int active_workers) {
3653 terminator()->reset_for_reuse(active_workers);
3654 }
3655
3656 void work(uint worker_id);
3657 bool should_yield() {
3658 return ConcurrentMarkSweepThread::should_yield()
3659 && !_collector->foregroundGCIsActive()
3660 && _asynch;
3661 }
3662
3663 virtual void coordinator_yield(); // stuff done by coordinator
3664 bool result() { return _result; }
3665
3666 void reset(HeapWord* ra) {
3667 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3668 _restart_addr = _global_finger = ra;
3669 _term.reset_for_reuse();
3670 }
3671
3672 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3673 OopTaskQueue* work_q);
3674
3675 private:
3676 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3677 void do_work_steal(int i);
3678 void bump_global_finger(HeapWord* f);
3679 };
3680
3681 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3682 assert(_task != NULL, "Error");
3683 return _task->yielding();
3684 // Note that we do not need the disjunct || _task->should_yield() above
3685 // because we want terminating threads to yield only if the task
3686 // is already in the midst of yielding, which happens only after at least one
3687 // thread has yielded.
3688 }
3689
3690 void CMSConcMarkingTerminator::yield() {
3691 if (_task->should_yield()) {
3692 _task->yield();
3693 } else {
3694 ParallelTaskTerminator::yield();
3695 }
3696 }
3697
3698 ////////////////////////////////////////////////////////////////
3699 // Concurrent Marking Algorithm Sketch
3700 ////////////////////////////////////////////////////////////////
3701 // Until all tasks exhausted (both spaces):
3702 // -- claim next available chunk
3703 // -- bump global finger via CAS
3704 // -- find first object that starts in this chunk
3705 // and start scanning bitmap from that position
3706 // -- scan marked objects for oops
3707 // -- CAS-mark target, and if successful:
3708 // . if target oop is above global finger (volatile read)
3709 // nothing to do
3710 // . if target oop is in chunk and above local finger
3711 // then nothing to do
3712 // . else push on work-queue
3713 // -- Deal with possible overflow issues:
3714 // . local work-queue overflow causes stuff to be pushed on
3715 // global (common) overflow queue
3716 // . always first empty local work queue
3717 // . then get a batch of oops from global work queue if any
3718 // . then do work stealing
3719 // -- When all tasks claimed (both spaces)
3720 // and local work queue empty,
3721 // then in a loop do:
3722 // . check global overflow stack; steal a batch of oops and trace
3723 // . try to steal from other threads oif GOS is empty
3724 // . if neither is available, offer termination
3725 // -- Terminate and return result
3726 //
3727 void CMSConcMarkingTask::work(uint worker_id) {
3728 elapsedTimer _timer;
3729 ResourceMark rm;
3730 HandleMark hm;
3731
3732 DEBUG_ONLY(_collector->verify_overflow_empty();)
3733
3734 // Before we begin work, our work queue should be empty
3735 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3736 // Scan the bitmap covering _cms_space, tracing through grey objects.
3737 _timer.start();
3738 do_scan_and_mark(worker_id, _cms_space);
3739 _timer.stop();
3740 if (PrintCMSStatistics != 0) {
3741 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3742 worker_id, _timer.seconds());
3743 // XXX: need xxx/xxx type of notation, two timers
3744 }
3745
3746 // ... do work stealing
3747 _timer.reset();
3748 _timer.start();
3749 do_work_steal(worker_id);
3750 _timer.stop();
3751 if (PrintCMSStatistics != 0) {
3752 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3753 worker_id, _timer.seconds());
3754 // XXX: need xxx/xxx type of notation, two timers
3755 }
3756 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3757 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3758 // Note that under the current task protocol, the
3759 // following assertion is true even of the spaces
3760 // expanded since the completion of the concurrent
3761 // marking. XXX This will likely change under a strict
3762 // ABORT semantics.
3763 // After perm removal the comparison was changed to
3764 // greater than or equal to from strictly greater than.
3765 // Before perm removal the highest address sweep would
3766 // have been at the end of perm gen but now is at the
3767 // end of the tenured gen.
3768 assert(_global_finger >= _cms_space->end(),
3769 "All tasks have been completed");
3770 DEBUG_ONLY(_collector->verify_overflow_empty();)
3771 }
3772
3773 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3774 HeapWord* read = _global_finger;
3775 HeapWord* cur = read;
3776 while (f > read) {
3777 cur = read;
3778 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3779 if (cur == read) {
3780 // our cas succeeded
3781 assert(_global_finger >= f, "protocol consistency");
3782 break;
3783 }
3784 }
3785 }
3786
3787 // This is really inefficient, and should be redone by
3788 // using (not yet available) block-read and -write interfaces to the
3789 // stack and the work_queue. XXX FIX ME !!!
3790 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3791 OopTaskQueue* work_q) {
3792 // Fast lock-free check
3793 if (ovflw_stk->length() == 0) {
3794 return false;
3795 }
3796 assert(work_q->size() == 0, "Shouldn't steal");
3797 MutexLockerEx ml(ovflw_stk->par_lock(),
3798 Mutex::_no_safepoint_check_flag);
3799 // Grab up to 1/4 the size of the work queue
3800 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3801 (size_t)ParGCDesiredObjsFromOverflowList);
3802 num = MIN2(num, ovflw_stk->length());
3803 for (int i = (int) num; i > 0; i--) {
3804 oop cur = ovflw_stk->pop();
3805 assert(cur != NULL, "Counted wrong?");
3806 work_q->push(cur);
3807 }
3808 return num > 0;
3809 }
3810
3811 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3812 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3813 int n_tasks = pst->n_tasks();
3814 // We allow that there may be no tasks to do here because
3815 // we are restarting after a stack overflow.
3816 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3817 uint nth_task = 0;
3818
3819 HeapWord* aligned_start = sp->bottom();
3820 if (sp->used_region().contains(_restart_addr)) {
3821 // Align down to a card boundary for the start of 0th task
3822 // for this space.
3823 aligned_start =
3824 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3825 CardTableModRefBS::card_size);
3826 }
3827
3828 size_t chunk_size = sp->marking_task_size();
3829 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3830 // Having claimed the nth task in this space,
3831 // compute the chunk that it corresponds to:
3832 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3833 aligned_start + (nth_task+1)*chunk_size);
3834 // Try and bump the global finger via a CAS;
3835 // note that we need to do the global finger bump
3836 // _before_ taking the intersection below, because
3837 // the task corresponding to that region will be
3838 // deemed done even if the used_region() expands
3839 // because of allocation -- as it almost certainly will
3840 // during start-up while the threads yield in the
3841 // closure below.
3842 HeapWord* finger = span.end();
3843 bump_global_finger(finger); // atomically
3844 // There are null tasks here corresponding to chunks
3845 // beyond the "top" address of the space.
3846 span = span.intersection(sp->used_region());
3847 if (!span.is_empty()) { // Non-null task
3848 HeapWord* prev_obj;
3849 assert(!span.contains(_restart_addr) || nth_task == 0,
3850 "Inconsistency");
3851 if (nth_task == 0) {
3852 // For the 0th task, we'll not need to compute a block_start.
3853 if (span.contains(_restart_addr)) {
3854 // In the case of a restart because of stack overflow,
3855 // we might additionally skip a chunk prefix.
3856 prev_obj = _restart_addr;
3857 } else {
3858 prev_obj = span.start();
3859 }
3860 } else {
3861 // We want to skip the first object because
3862 // the protocol is to scan any object in its entirety
3863 // that _starts_ in this span; a fortiori, any
3864 // object starting in an earlier span is scanned
3865 // as part of an earlier claimed task.
3866 // Below we use the "careful" version of block_start
3867 // so we do not try to navigate uninitialized objects.
3868 prev_obj = sp->block_start_careful(span.start());
3869 // Below we use a variant of block_size that uses the
3870 // Printezis bits to avoid waiting for allocated
3871 // objects to become initialized/parsable.
3872 while (prev_obj < span.start()) {
3873 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3874 if (sz > 0) {
3875 prev_obj += sz;
3876 } else {
3877 // In this case we may end up doing a bit of redundant
3878 // scanning, but that appears unavoidable, short of
3879 // locking the free list locks; see bug 6324141.
3880 break;
3881 }
3882 }
3883 }
3884 if (prev_obj < span.end()) {
3885 MemRegion my_span = MemRegion(prev_obj, span.end());
3886 // Do the marking work within a non-empty span --
3887 // the last argument to the constructor indicates whether the
3888 // iteration should be incremental with periodic yields.
3889 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3890 &_collector->_markBitMap,
3891 work_queue(i),
3892 &_collector->_markStack,
3893 _asynch);
3894 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3895 } // else nothing to do for this task
3896 } // else nothing to do for this task
3897 }
3898 // We'd be tempted to assert here that since there are no
3899 // more tasks left to claim in this space, the global_finger
3900 // must exceed space->top() and a fortiori space->end(). However,
3901 // that would not quite be correct because the bumping of
3902 // global_finger occurs strictly after the claiming of a task,
3903 // so by the time we reach here the global finger may not yet
3904 // have been bumped up by the thread that claimed the last
3905 // task.
3906 pst->all_tasks_completed();
3907 }
3908
3909 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3910 private:
3911 CMSCollector* _collector;
3912 CMSConcMarkingTask* _task;
3913 MemRegion _span;
3914 CMSBitMap* _bit_map;
3915 CMSMarkStack* _overflow_stack;
3916 OopTaskQueue* _work_queue;
3917 protected:
3918 DO_OOP_WORK_DEFN
3919 public:
3920 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3921 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3922 MetadataAwareOopClosure(collector->ref_processor()),
3923 _collector(collector),
3924 _task(task),
3925 _span(collector->_span),
3926 _work_queue(work_queue),
3927 _bit_map(bit_map),
3928 _overflow_stack(overflow_stack)
3929 { }
3930 virtual void do_oop(oop* p);
3931 virtual void do_oop(narrowOop* p);
3932
3933 void trim_queue(size_t max);
3934 void handle_stack_overflow(HeapWord* lost);
3935 void do_yield_check() {
3936 if (_task->should_yield()) {
3937 _task->yield();
3938 }
3939 }
3940 };
3941
3942 // Grey object scanning during work stealing phase --
3943 // the salient assumption here is that any references
3944 // that are in these stolen objects being scanned must
3945 // already have been initialized (else they would not have
3946 // been published), so we do not need to check for
3947 // uninitialized objects before pushing here.
3948 void Par_ConcMarkingClosure::do_oop(oop obj) {
3949 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
3950 HeapWord* addr = (HeapWord*)obj;
3951 // Check if oop points into the CMS generation
3952 // and is not marked
3953 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3954 // a white object ...
3955 // If we manage to "claim" the object, by being the
3956 // first thread to mark it, then we push it on our
3957 // marking stack
3958 if (_bit_map->par_mark(addr)) { // ... now grey
3959 // push on work queue (grey set)
3960 bool simulate_overflow = false;
3961 NOT_PRODUCT(
3962 if (CMSMarkStackOverflowALot &&
3963 _collector->simulate_overflow()) {
3964 // simulate a stack overflow
3965 simulate_overflow = true;
3966 }
3967 )
3968 if (simulate_overflow ||
3969 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3970 // stack overflow
3971 if (PrintCMSStatistics != 0) {
3972 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3973 SIZE_FORMAT, _overflow_stack->capacity());
3974 }
3975 // We cannot assert that the overflow stack is full because
3976 // it may have been emptied since.
3977 assert(simulate_overflow ||
3978 _work_queue->size() == _work_queue->max_elems(),
3979 "Else push should have succeeded");
3980 handle_stack_overflow(addr);
3981 }
3982 } // Else, some other thread got there first
3983 do_yield_check();
3984 }
3985 }
3986
3987 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3988 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3989
3990 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3991 while (_work_queue->size() > max) {
3992 oop new_oop;
3993 if (_work_queue->pop_local(new_oop)) {
3994 assert(new_oop->is_oop(), "Should be an oop");
3995 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3996 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3997 new_oop->oop_iterate(this); // do_oop() above
3998 do_yield_check();
3999 }
4000 }
4001 }
4002
4003 // Upon stack overflow, we discard (part of) the stack,
4004 // remembering the least address amongst those discarded
4005 // in CMSCollector's _restart_address.
4006 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4007 // We need to do this under a mutex to prevent other
4008 // workers from interfering with the work done below.
4009 MutexLockerEx ml(_overflow_stack->par_lock(),
4010 Mutex::_no_safepoint_check_flag);
4011 // Remember the least grey address discarded
4012 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4013 _collector->lower_restart_addr(ra);
4014 _overflow_stack->reset(); // discard stack contents
4015 _overflow_stack->expand(); // expand the stack if possible
4016 }
4017
4018
4019 void CMSConcMarkingTask::do_work_steal(int i) {
4020 OopTaskQueue* work_q = work_queue(i);
4021 oop obj_to_scan;
4022 CMSBitMap* bm = &(_collector->_markBitMap);
4023 CMSMarkStack* ovflw = &(_collector->_markStack);
4024 int* seed = _collector->hash_seed(i);
4025 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4026 while (true) {
4027 cl.trim_queue(0);
4028 assert(work_q->size() == 0, "Should have been emptied above");
4029 if (get_work_from_overflow_stack(ovflw, work_q)) {
4030 // Can't assert below because the work obtained from the
4031 // overflow stack may already have been stolen from us.
4032 // assert(work_q->size() > 0, "Work from overflow stack");
4033 continue;
4034 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4035 assert(obj_to_scan->is_oop(), "Should be an oop");
4036 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4037 obj_to_scan->oop_iterate(&cl);
4038 } else if (terminator()->offer_termination(&_term_term)) {
4039 assert(work_q->size() == 0, "Impossible!");
4040 break;
4041 } else if (yielding() || should_yield()) {
4042 yield();
4043 }
4044 }
4045 }
4046
4047 // This is run by the CMS (coordinator) thread.
4048 void CMSConcMarkingTask::coordinator_yield() {
4049 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4050 "CMS thread should hold CMS token");
4051 // First give up the locks, then yield, then re-lock
4052 // We should probably use a constructor/destructor idiom to
4053 // do this unlock/lock or modify the MutexUnlocker class to
4054 // serve our purpose. XXX
4055 assert_lock_strong(_bit_map_lock);
4056 _bit_map_lock->unlock();
4057 ConcurrentMarkSweepThread::desynchronize(true);
4058 _collector->stopTimer();
4059 if (PrintCMSStatistics != 0) {
4060 _collector->incrementYields();
4061 }
4062
4063 // It is possible for whichever thread initiated the yield request
4064 // not to get a chance to wake up and take the bitmap lock between
4065 // this thread releasing it and reacquiring it. So, while the
4066 // should_yield() flag is on, let's sleep for a bit to give the
4067 // other thread a chance to wake up. The limit imposed on the number
4068 // of iterations is defensive, to avoid any unforseen circumstances
4069 // putting us into an infinite loop. Since it's always been this
4070 // (coordinator_yield()) method that was observed to cause the
4071 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4072 // which is by default non-zero. For the other seven methods that
4073 // also perform the yield operation, as are using a different
4074 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4075 // can enable the sleeping for those methods too, if necessary.
4076 // See 6442774.
4077 //
4078 // We really need to reconsider the synchronization between the GC
4079 // thread and the yield-requesting threads in the future and we
4080 // should really use wait/notify, which is the recommended
4081 // way of doing this type of interaction. Additionally, we should
4082 // consolidate the eight methods that do the yield operation and they
4083 // are almost identical into one for better maintainability and
4084 // readability. See 6445193.
4085 //
4086 // Tony 2006.06.29
4087 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4088 ConcurrentMarkSweepThread::should_yield() &&
4089 !CMSCollector::foregroundGCIsActive(); ++i) {
4090 os::sleep(Thread::current(), 1, false);
4091 }
4092
4093 ConcurrentMarkSweepThread::synchronize(true);
4094 _bit_map_lock->lock_without_safepoint_check();
4095 _collector->startTimer();
4096 }
4097
4098 bool CMSCollector::do_marking_mt(bool asynch) {
4099 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4100 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4101 conc_workers()->total_workers(),
4102 conc_workers()->active_workers(),
4103 Threads::number_of_non_daemon_threads());
4104 conc_workers()->set_active_workers(num_workers);
4105
4106 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4107
4108 CMSConcMarkingTask tsk(this,
4109 cms_space,
4110 asynch,
4111 conc_workers(),
4112 task_queues());
4113
4114 // Since the actual number of workers we get may be different
4115 // from the number we requested above, do we need to do anything different
4116 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4117 // class?? XXX
4118 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4119
4120 // Refs discovery is already non-atomic.
4121 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4122 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4123 conc_workers()->start_task(&tsk);
4124 while (tsk.yielded()) {
4125 tsk.coordinator_yield();
4126 conc_workers()->continue_task(&tsk);
4127 }
4128 // If the task was aborted, _restart_addr will be non-NULL
4129 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4130 while (_restart_addr != NULL) {
4131 // XXX For now we do not make use of ABORTED state and have not
4132 // yet implemented the right abort semantics (even in the original
4133 // single-threaded CMS case). That needs some more investigation
4134 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4135 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4136 // If _restart_addr is non-NULL, a marking stack overflow
4137 // occurred; we need to do a fresh marking iteration from the
4138 // indicated restart address.
4139 if (_foregroundGCIsActive && asynch) {
4140 // We may be running into repeated stack overflows, having
4141 // reached the limit of the stack size, while making very
4142 // slow forward progress. It may be best to bail out and
4143 // let the foreground collector do its job.
4144 // Clear _restart_addr, so that foreground GC
4145 // works from scratch. This avoids the headache of
4146 // a "rescan" which would otherwise be needed because
4147 // of the dirty mod union table & card table.
4148 _restart_addr = NULL;
4149 return false;
4150 }
4151 // Adjust the task to restart from _restart_addr
4152 tsk.reset(_restart_addr);
4153 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4154 _restart_addr);
4155 _restart_addr = NULL;
4156 // Get the workers going again
4157 conc_workers()->start_task(&tsk);
4158 while (tsk.yielded()) {
4159 tsk.coordinator_yield();
4160 conc_workers()->continue_task(&tsk);
4161 }
4162 }
4163 assert(tsk.completed(), "Inconsistency");
4164 assert(tsk.result() == true, "Inconsistency");
4165 return true;
4166 }
4167
4168 bool CMSCollector::do_marking_st(bool asynch) {
4169 ResourceMark rm;
4170 HandleMark hm;
4171
4172 // Temporarily make refs discovery single threaded (non-MT)
4173 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4174 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4175 &_markStack, CMSYield && asynch);
4176 // the last argument to iterate indicates whether the iteration
4177 // should be incremental with periodic yields.
4178 _markBitMap.iterate(&markFromRootsClosure);
4179 // If _restart_addr is non-NULL, a marking stack overflow
4180 // occurred; we need to do a fresh iteration from the
4181 // indicated restart address.
4182 while (_restart_addr != NULL) {
4183 if (_foregroundGCIsActive && asynch) {
4184 // We may be running into repeated stack overflows, having
4185 // reached the limit of the stack size, while making very
4186 // slow forward progress. It may be best to bail out and
4187 // let the foreground collector do its job.
4188 // Clear _restart_addr, so that foreground GC
4189 // works from scratch. This avoids the headache of
4190 // a "rescan" which would otherwise be needed because
4191 // of the dirty mod union table & card table.
4192 _restart_addr = NULL;
4193 return false; // indicating failure to complete marking
4194 }
4195 // Deal with stack overflow:
4196 // we restart marking from _restart_addr
4197 HeapWord* ra = _restart_addr;
4198 markFromRootsClosure.reset(ra);
4199 _restart_addr = NULL;
4200 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4201 }
4202 return true;
4203 }
4204
4205 void CMSCollector::preclean() {
4206 check_correct_thread_executing();
4207 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4208 verify_work_stacks_empty();
4209 verify_overflow_empty();
4210 _abort_preclean = false;
4211 if (CMSPrecleaningEnabled) {
4212 if (!CMSEdenChunksRecordAlways) {
4213 _eden_chunk_index = 0;
4214 }
4215 size_t used = get_eden_used();
4216 size_t capacity = get_eden_capacity();
4217 // Don't start sampling unless we will get sufficiently
4218 // many samples.
4219 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4220 * CMSScheduleRemarkEdenPenetration)) {
4221 _start_sampling = true;
4222 } else {
4223 _start_sampling = false;
4224 }
4225 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4226 CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
4227 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4228 }
4229 CMSTokenSync x(true); // is cms thread
4230 if (CMSPrecleaningEnabled) {
4231 sample_eden();
4232 _collectorState = AbortablePreclean;
4233 } else {
4234 _collectorState = FinalMarking;
4235 }
4236 verify_work_stacks_empty();
4237 verify_overflow_empty();
4238 }
4239
4240 // Try and schedule the remark such that young gen
4241 // occupancy is CMSScheduleRemarkEdenPenetration %.
4242 void CMSCollector::abortable_preclean() {
4243 check_correct_thread_executing();
4244 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4245 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4246
4247 // If Eden's current occupancy is below this threshold,
4248 // immediately schedule the remark; else preclean
4249 // past the next scavenge in an effort to
4250 // schedule the pause as described above. By choosing
4251 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4252 // we will never do an actual abortable preclean cycle.
4253 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4254 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4255 CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
4256 // We need more smarts in the abortable preclean
4257 // loop below to deal with cases where allocation
4258 // in young gen is very very slow, and our precleaning
4259 // is running a losing race against a horde of
4260 // mutators intent on flooding us with CMS updates
4261 // (dirty cards).
4262 // One, admittedly dumb, strategy is to give up
4263 // after a certain number of abortable precleaning loops
4264 // or after a certain maximum time. We want to make
4265 // this smarter in the next iteration.
4266 // XXX FIX ME!!! YSR
4267 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4268 while (!(should_abort_preclean() ||
4269 ConcurrentMarkSweepThread::should_terminate())) {
4270 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4271 cumworkdone += workdone;
4272 loops++;
4273 // Voluntarily terminate abortable preclean phase if we have
4274 // been at it for too long.
4275 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4276 loops >= CMSMaxAbortablePrecleanLoops) {
4277 if (PrintGCDetails) {
4278 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4279 }
4280 break;
4281 }
4282 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4283 if (PrintGCDetails) {
4284 gclog_or_tty->print(" CMS: abort preclean due to time ");
4285 }
4286 break;
4287 }
4288 // If we are doing little work each iteration, we should
4289 // take a short break.
4290 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4291 // Sleep for some time, waiting for work to accumulate
4292 stopTimer();
4293 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4294 startTimer();
4295 waited++;
4296 }
4297 }
4298 if (PrintCMSStatistics > 0) {
4299 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
4300 loops, waited, cumworkdone);
4301 }
4302 }
4303 CMSTokenSync x(true); // is cms thread
4304 if (_collectorState != Idling) {
4305 assert(_collectorState == AbortablePreclean,
4306 "Spontaneous state transition?");
4307 _collectorState = FinalMarking;
4308 } // Else, a foreground collection completed this CMS cycle.
4309 return;
4310 }
4311
4312 // Respond to an Eden sampling opportunity
4313 void CMSCollector::sample_eden() {
4314 // Make sure a young gc cannot sneak in between our
4315 // reading and recording of a sample.
4316 assert(Thread::current()->is_ConcurrentGC_thread(),
4317 "Only the cms thread may collect Eden samples");
4318 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4319 "Should collect samples while holding CMS token");
4320 if (!_start_sampling) {
4321 return;
4322 }
4323 // When CMSEdenChunksRecordAlways is true, the eden chunk array
4324 // is populated by the young generation.
4325 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
4326 if (_eden_chunk_index < _eden_chunk_capacity) {
4327 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4328 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4329 "Unexpected state of Eden");
4330 // We'd like to check that what we just sampled is an oop-start address;
4331 // however, we cannot do that here since the object may not yet have been
4332 // initialized. So we'll instead do the check when we _use_ this sample
4333 // later.
4334 if (_eden_chunk_index == 0 ||
4335 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4336 _eden_chunk_array[_eden_chunk_index-1])
4337 >= CMSSamplingGrain)) {
4338 _eden_chunk_index++; // commit sample
4339 }
4340 }
4341 }
4342 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4343 size_t used = get_eden_used();
4344 size_t capacity = get_eden_capacity();
4345 assert(used <= capacity, "Unexpected state of Eden");
4346 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4347 _abort_preclean = true;
4348 }
4349 }
4350 }
4351
4352
4353 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4354 assert(_collectorState == Precleaning ||
4355 _collectorState == AbortablePreclean, "incorrect state");
4356 ResourceMark rm;
4357 HandleMark hm;
4358
4359 // Precleaning is currently not MT but the reference processor
4360 // may be set for MT. Disable it temporarily here.
4361 ReferenceProcessor* rp = ref_processor();
4362 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4363
4364 // Do one pass of scrubbing the discovered reference lists
4365 // to remove any reference objects with strongly-reachable
4366 // referents.
4367 if (clean_refs) {
4368 CMSPrecleanRefsYieldClosure yield_cl(this);
4369 assert(rp->span().equals(_span), "Spans should be equal");
4370 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4371 &_markStack, true /* preclean */);
4372 CMSDrainMarkingStackClosure complete_trace(this,
4373 _span, &_markBitMap, &_markStack,
4374 &keep_alive, true /* preclean */);
4375
4376 // We don't want this step to interfere with a young
4377 // collection because we don't want to take CPU
4378 // or memory bandwidth away from the young GC threads
4379 // (which may be as many as there are CPUs).
4380 // Note that we don't need to protect ourselves from
4381 // interference with mutators because they can't
4382 // manipulate the discovered reference lists nor affect
4383 // the computed reachability of the referents, the
4384 // only properties manipulated by the precleaning
4385 // of these reference lists.
4386 stopTimer();
4387 CMSTokenSyncWithLocks x(true /* is cms thread */,
4388 bitMapLock());
4389 startTimer();
4390 sample_eden();
4391
4392 // The following will yield to allow foreground
4393 // collection to proceed promptly. XXX YSR:
4394 // The code in this method may need further
4395 // tweaking for better performance and some restructuring
4396 // for cleaner interfaces.
4397 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4398 rp->preclean_discovered_references(
4399 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
4400 gc_timer, _gc_tracer_cm->gc_id());
4401 }
4402
4403 if (clean_survivor) { // preclean the active survivor space(s)
4404 assert(_young_gen->kind() == Generation::DefNew ||
4405 _young_gen->kind() == Generation::ParNew,
4406 "incorrect type for cast");
4407 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4408 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4409 &_markBitMap, &_modUnionTable,
4410 &_markStack, true /* precleaning phase */);
4411 stopTimer();
4412 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4413 bitMapLock());
4414 startTimer();
4415 unsigned int before_count =
4416 GenCollectedHeap::heap()->total_collections();
4417 SurvivorSpacePrecleanClosure
4418 sss_cl(this, _span, &_markBitMap, &_markStack,
4419 &pam_cl, before_count, CMSYield);
4420 dng->from()->object_iterate_careful(&sss_cl);
4421 dng->to()->object_iterate_careful(&sss_cl);
4422 }
4423 MarkRefsIntoAndScanClosure
4424 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4425 &_markStack, this, CMSYield,
4426 true /* precleaning phase */);
4427 // CAUTION: The following closure has persistent state that may need to
4428 // be reset upon a decrease in the sequence of addresses it
4429 // processes.
4430 ScanMarkedObjectsAgainCarefullyClosure
4431 smoac_cl(this, _span,
4432 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4433
4434 // Preclean dirty cards in ModUnionTable and CardTable using
4435 // appropriate convergence criterion;
4436 // repeat CMSPrecleanIter times unless we find that
4437 // we are losing.
4438 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4439 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4440 "Bad convergence multiplier");
4441 assert(CMSPrecleanThreshold >= 100,
4442 "Unreasonably low CMSPrecleanThreshold");
4443
4444 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4445 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4446 numIter < CMSPrecleanIter;
4447 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4448 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4449 if (Verbose && PrintGCDetails) {
4450 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
4451 }
4452 // Either there are very few dirty cards, so re-mark
4453 // pause will be small anyway, or our pre-cleaning isn't
4454 // that much faster than the rate at which cards are being
4455 // dirtied, so we might as well stop and re-mark since
4456 // precleaning won't improve our re-mark time by much.
4457 if (curNumCards <= CMSPrecleanThreshold ||
4458 (numIter > 0 &&
4459 (curNumCards * CMSPrecleanDenominator >
4460 lastNumCards * CMSPrecleanNumerator))) {
4461 numIter++;
4462 cumNumCards += curNumCards;
4463 break;
4464 }
4465 }
4466
4467 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4468
4469 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4470 cumNumCards += curNumCards;
4471 if (PrintGCDetails && PrintCMSStatistics != 0) {
4472 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4473 curNumCards, cumNumCards, numIter);
4474 }
4475 return cumNumCards; // as a measure of useful work done
4476 }
4477
4478 // PRECLEANING NOTES:
4479 // Precleaning involves:
4480 // . reading the bits of the modUnionTable and clearing the set bits.
4481 // . For the cards corresponding to the set bits, we scan the
4482 // objects on those cards. This means we need the free_list_lock
4483 // so that we can safely iterate over the CMS space when scanning
4484 // for oops.
4485 // . When we scan the objects, we'll be both reading and setting
4486 // marks in the marking bit map, so we'll need the marking bit map.
4487 // . For protecting _collector_state transitions, we take the CGC_lock.
4488 // Note that any races in the reading of of card table entries by the
4489 // CMS thread on the one hand and the clearing of those entries by the
4490 // VM thread or the setting of those entries by the mutator threads on the
4491 // other are quite benign. However, for efficiency it makes sense to keep
4492 // the VM thread from racing with the CMS thread while the latter is
4493 // dirty card info to the modUnionTable. We therefore also use the
4494 // CGC_lock to protect the reading of the card table and the mod union
4495 // table by the CM thread.
4496 // . We run concurrently with mutator updates, so scanning
4497 // needs to be done carefully -- we should not try to scan
4498 // potentially uninitialized objects.
4499 //
4500 // Locking strategy: While holding the CGC_lock, we scan over and
4501 // reset a maximal dirty range of the mod union / card tables, then lock
4502 // the free_list_lock and bitmap lock to do a full marking, then
4503 // release these locks; and repeat the cycle. This allows for a
4504 // certain amount of fairness in the sharing of these locks between
4505 // the CMS collector on the one hand, and the VM thread and the
4506 // mutators on the other.
4507
4508 // NOTE: preclean_mod_union_table() and preclean_card_table()
4509 // further below are largely identical; if you need to modify
4510 // one of these methods, please check the other method too.
4511
4512 size_t CMSCollector::preclean_mod_union_table(
4513 ConcurrentMarkSweepGeneration* gen,
4514 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4515 verify_work_stacks_empty();
4516 verify_overflow_empty();
4517
4518 // strategy: starting with the first card, accumulate contiguous
4519 // ranges of dirty cards; clear these cards, then scan the region
4520 // covered by these cards.
4521
4522 // Since all of the MUT is committed ahead, we can just use
4523 // that, in case the generations expand while we are precleaning.
4524 // It might also be fine to just use the committed part of the
4525 // generation, but we might potentially miss cards when the
4526 // generation is rapidly expanding while we are in the midst
4527 // of precleaning.
4528 HeapWord* startAddr = gen->reserved().start();
4529 HeapWord* endAddr = gen->reserved().end();
4530
4531 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4532
4533 size_t numDirtyCards, cumNumDirtyCards;
4534 HeapWord *nextAddr, *lastAddr;
4535 for (cumNumDirtyCards = numDirtyCards = 0,
4536 nextAddr = lastAddr = startAddr;
4537 nextAddr < endAddr;
4538 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4539
4540 ResourceMark rm;
4541 HandleMark hm;
4542
4543 MemRegion dirtyRegion;
4544 {
4545 stopTimer();
4546 // Potential yield point
4547 CMSTokenSync ts(true);
4548 startTimer();
4549 sample_eden();
4550 // Get dirty region starting at nextOffset (inclusive),
4551 // simultaneously clearing it.
4552 dirtyRegion =
4553 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4554 assert(dirtyRegion.start() >= nextAddr,
4555 "returned region inconsistent?");
4556 }
4557 // Remember where the next search should begin.
4558 // The returned region (if non-empty) is a right open interval,
4559 // so lastOffset is obtained from the right end of that
4560 // interval.
4561 lastAddr = dirtyRegion.end();
4562 // Should do something more transparent and less hacky XXX
4563 numDirtyCards =
4564 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4565
4566 // We'll scan the cards in the dirty region (with periodic
4567 // yields for foreground GC as needed).
4568 if (!dirtyRegion.is_empty()) {
4569 assert(numDirtyCards > 0, "consistency check");
4570 HeapWord* stop_point = NULL;
4571 stopTimer();
4572 // Potential yield point
4573 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4574 bitMapLock());
4575 startTimer();
4576 {
4577 verify_work_stacks_empty();
4578 verify_overflow_empty();
4579 sample_eden();
4580 stop_point =
4581 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4582 }
4583 if (stop_point != NULL) {
4584 // The careful iteration stopped early either because it found an
4585 // uninitialized object, or because we were in the midst of an
4586 // "abortable preclean", which should now be aborted. Redirty
4587 // the bits corresponding to the partially-scanned or unscanned
4588 // cards. We'll either restart at the next block boundary or
4589 // abort the preclean.
4590 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4591 "Should only be AbortablePreclean.");
4592 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4593 if (should_abort_preclean()) {
4594 break; // out of preclean loop
4595 } else {
4596 // Compute the next address at which preclean should pick up;
4597 // might need bitMapLock in order to read P-bits.
4598 lastAddr = next_card_start_after_block(stop_point);
4599 }
4600 }
4601 } else {
4602 assert(lastAddr == endAddr, "consistency check");
4603 assert(numDirtyCards == 0, "consistency check");
4604 break;
4605 }
4606 }
4607 verify_work_stacks_empty();
4608 verify_overflow_empty();
4609 return cumNumDirtyCards;
4610 }
4611
4612 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4613 // below are largely identical; if you need to modify
4614 // one of these methods, please check the other method too.
4615
4616 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4617 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4618 // strategy: it's similar to precleamModUnionTable above, in that
4619 // we accumulate contiguous ranges of dirty cards, mark these cards
4620 // precleaned, then scan the region covered by these cards.
4621 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4622 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4623
4624 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4625
4626 size_t numDirtyCards, cumNumDirtyCards;
4627 HeapWord *lastAddr, *nextAddr;
4628
4629 for (cumNumDirtyCards = numDirtyCards = 0,
4630 nextAddr = lastAddr = startAddr;
4631 nextAddr < endAddr;
4632 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4633
4634 ResourceMark rm;
4635 HandleMark hm;
4636
4637 MemRegion dirtyRegion;
4638 {
4639 // See comments in "Precleaning notes" above on why we
4640 // do this locking. XXX Could the locking overheads be
4641 // too high when dirty cards are sparse? [I don't think so.]
4642 stopTimer();
4643 CMSTokenSync x(true); // is cms thread
4644 startTimer();
4645 sample_eden();
4646 // Get and clear dirty region from card table
4647 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4648 MemRegion(nextAddr, endAddr),
4649 true,
4650 CardTableModRefBS::precleaned_card_val());
4651
4652 assert(dirtyRegion.start() >= nextAddr,
4653 "returned region inconsistent?");
4654 }
4655 lastAddr = dirtyRegion.end();
4656 numDirtyCards =
4657 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4658
4659 if (!dirtyRegion.is_empty()) {
4660 stopTimer();
4661 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4662 startTimer();
4663 sample_eden();
4664 verify_work_stacks_empty();
4665 verify_overflow_empty();
4666 HeapWord* stop_point =
4667 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4668 if (stop_point != NULL) {
4669 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4670 "Should only be AbortablePreclean.");
4671 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4672 if (should_abort_preclean()) {
4673 break; // out of preclean loop
4674 } else {
4675 // Compute the next address at which preclean should pick up.
4676 lastAddr = next_card_start_after_block(stop_point);
4677 }
4678 }
4679 } else {
4680 break;
4681 }
4682 }
4683 verify_work_stacks_empty();
4684 verify_overflow_empty();
4685 return cumNumDirtyCards;
4686 }
4687
4688 class PrecleanKlassClosure : public KlassClosure {
4689 KlassToOopClosure _cm_klass_closure;
4690 public:
4691 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4692 void do_klass(Klass* k) {
4693 if (k->has_accumulated_modified_oops()) {
4694 k->clear_accumulated_modified_oops();
4695
4696 _cm_klass_closure.do_klass(k);
4697 }
4698 }
4699 };
4700
4701 // The freelist lock is needed to prevent asserts, is it really needed?
4702 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4703
4704 cl->set_freelistLock(freelistLock);
4705
4706 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4707
4708 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4709 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4710 PrecleanKlassClosure preclean_klass_closure(cl);
4711 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4712
4713 verify_work_stacks_empty();
4714 verify_overflow_empty();
4715 }
4716
4717 void CMSCollector::checkpointRootsFinal(bool asynch,
4718 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4719 assert(_collectorState == FinalMarking, "incorrect state transition?");
4720 check_correct_thread_executing();
4721 // world is stopped at this checkpoint
4722 assert(SafepointSynchronize::is_at_safepoint(),
4723 "world should be stopped");
4724 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4725
4726 verify_work_stacks_empty();
4727 verify_overflow_empty();
4728
4729 SpecializationStats::clear();
4730 if (PrintGCDetails) {
4731 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4732 _young_gen->used() / K,
4733 _young_gen->capacity() / K);
4734 }
4735 if (asynch) {
4736 if (CMSScavengeBeforeRemark) {
4737 GenCollectedHeap* gch = GenCollectedHeap::heap();
4738 // Temporarily set flag to false, GCH->do_collection will
4739 // expect it to be false and set to true
4740 FlagSetting fl(gch->_is_gc_active, false);
4741 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4742 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4743 int level = _cmsGen->level() - 1;
4744 if (level >= 0) {
4745 gch->do_collection(true, // full (i.e. force, see below)
4746 false, // !clear_all_soft_refs
4747 0, // size
4748 false, // is_tlab
4749 level // max_level
4750 );
4751 }
4752 }
4753 FreelistLocker x(this);
4754 MutexLockerEx y(bitMapLock(),
4755 Mutex::_no_safepoint_check_flag);
4756 assert(!init_mark_was_synchronous, "but that's impossible!");
4757 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4758 } else {
4759 // already have all the locks
4760 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4761 init_mark_was_synchronous);
4762 }
4763 verify_work_stacks_empty();
4764 verify_overflow_empty();
4765 SpecializationStats::print();
4766 }
4767
4768 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4769 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4770
4771 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4772
4773 assert(haveFreelistLocks(), "must have free list locks");
4774 assert_lock_strong(bitMapLock());
4775
4776 ResourceMark rm;
4777 HandleMark hm;
4778
4779 GenCollectedHeap* gch = GenCollectedHeap::heap();
4780
4781 if (should_unload_classes()) {
4782 CodeCache::gc_prologue();
4783 }
4784 assert(haveFreelistLocks(), "must have free list locks");
4785 assert_lock_strong(bitMapLock());
4786
4787 if (!init_mark_was_synchronous) {
4788 // We might assume that we need not fill TLAB's when
4789 // CMSScavengeBeforeRemark is set, because we may have just done
4790 // a scavenge which would have filled all TLAB's -- and besides
4791 // Eden would be empty. This however may not always be the case --
4792 // for instance although we asked for a scavenge, it may not have
4793 // happened because of a JNI critical section. We probably need
4794 // a policy for deciding whether we can in that case wait until
4795 // the critical section releases and then do the remark following
4796 // the scavenge, and skip it here. In the absence of that policy,
4797 // or of an indication of whether the scavenge did indeed occur,
4798 // we cannot rely on TLAB's having been filled and must do
4799 // so here just in case a scavenge did not happen.
4800 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4801 // Update the saved marks which may affect the root scans.
4802 gch->save_marks();
4803
4804 if (CMSPrintEdenSurvivorChunks) {
4805 print_eden_and_survivor_chunk_arrays();
4806 }
4807
4808 {
4809 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4810
4811 // Note on the role of the mod union table:
4812 // Since the marker in "markFromRoots" marks concurrently with
4813 // mutators, it is possible for some reachable objects not to have been
4814 // scanned. For instance, an only reference to an object A was
4815 // placed in object B after the marker scanned B. Unless B is rescanned,
4816 // A would be collected. Such updates to references in marked objects
4817 // are detected via the mod union table which is the set of all cards
4818 // dirtied since the first checkpoint in this GC cycle and prior to
4819 // the most recent young generation GC, minus those cleaned up by the
4820 // concurrent precleaning.
4821 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
4822 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
4823 do_remark_parallel();
4824 } else {
4825 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4826 _gc_timer_cm, _gc_tracer_cm->gc_id());
4827 do_remark_non_parallel();
4828 }
4829 }
4830 } else {
4831 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
4832 // The initial mark was stop-world, so there's no rescanning to
4833 // do; go straight on to the next step below.
4834 }
4835 verify_work_stacks_empty();
4836 verify_overflow_empty();
4837
4838 {
4839 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4840 refProcessingWork(asynch, clear_all_soft_refs);
4841 }
4842 verify_work_stacks_empty();
4843 verify_overflow_empty();
4844
4845 if (should_unload_classes()) {
4846 CodeCache::gc_epilogue();
4847 }
4848 JvmtiExport::gc_epilogue();
4849
4850 // If we encountered any (marking stack / work queue) overflow
4851 // events during the current CMS cycle, take appropriate
4852 // remedial measures, where possible, so as to try and avoid
4853 // recurrence of that condition.
4854 assert(_markStack.isEmpty(), "No grey objects");
4855 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4856 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4857 if (ser_ovflw > 0) {
4858 if (PrintCMSStatistics != 0) {
4859 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4860 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4861 ", kac_preclean="SIZE_FORMAT")",
4862 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4863 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4864 }
4865 _markStack.expand();
4866 _ser_pmc_remark_ovflw = 0;
4867 _ser_pmc_preclean_ovflw = 0;
4868 _ser_kac_preclean_ovflw = 0;
4869 _ser_kac_ovflw = 0;
4870 }
4871 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4872 if (PrintCMSStatistics != 0) {
4873 gclog_or_tty->print_cr("Work queue overflow (benign) "
4874 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4875 _par_pmc_remark_ovflw, _par_kac_ovflw);
4876 }
4877 _par_pmc_remark_ovflw = 0;
4878 _par_kac_ovflw = 0;
4879 }
4880 if (PrintCMSStatistics != 0) {
4881 if (_markStack._hit_limit > 0) {
4882 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4883 _markStack._hit_limit);
4884 }
4885 if (_markStack._failed_double > 0) {
4886 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4887 " current capacity "SIZE_FORMAT,
4888 _markStack._failed_double,
4889 _markStack.capacity());
4890 }
4891 }
4892 _markStack._hit_limit = 0;
4893 _markStack._failed_double = 0;
4894
4895 if ((VerifyAfterGC || VerifyDuringGC) &&
4896 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4897 verify_after_remark();
4898 }
4899
4900 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4901
4902 // Change under the freelistLocks.
4903 _collectorState = Sweeping;
4904 // Call isAllClear() under bitMapLock
4905 assert(_modUnionTable.isAllClear(),
4906 "Should be clear by end of the final marking");
4907 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4908 "Should be clear by end of the final marking");
4909 }
4910
4911 void CMSParInitialMarkTask::work(uint worker_id) {
4912 elapsedTimer _timer;
4913 ResourceMark rm;
4914 HandleMark hm;
4915
4916 // ---------- scan from roots --------------
4917 _timer.start();
4918 GenCollectedHeap* gch = GenCollectedHeap::heap();
4919 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4920
4921 // ---------- young gen roots --------------
4922 {
4923 work_on_young_gen_roots(worker_id, &par_mri_cl);
4924 _timer.stop();
4925 if (PrintCMSStatistics != 0) {
4926 gclog_or_tty->print_cr(
4927 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4928 worker_id, _timer.seconds());
4929 }
4930 }
4931
4932 // ---------- remaining roots --------------
4933 _timer.reset();
4934 _timer.start();
4935
4936 CLDToOopClosure cld_closure(&par_mri_cl, true);
4937
4938 gch->gen_process_roots(_collector->_cmsGen->level(),
4939 false, // yg was scanned above
4940 false, // this is parallel code
4941 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4942 _collector->should_unload_classes(),
4943 &par_mri_cl,
4944 NULL,
4945 &cld_closure);
4946 assert(_collector->should_unload_classes()
4947 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
4948 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4949 _timer.stop();
4950 if (PrintCMSStatistics != 0) {
4951 gclog_or_tty->print_cr(
4952 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4953 worker_id, _timer.seconds());
4954 }
4955 }
4956
4957 // Parallel remark task
4958 class CMSParRemarkTask: public CMSParMarkTask {
4959 CompactibleFreeListSpace* _cms_space;
4960
4961 // The per-thread work queues, available here for stealing.
4962 OopTaskQueueSet* _task_queues;
4963 ParallelTaskTerminator _term;
4964
4965 public:
4966 // A value of 0 passed to n_workers will cause the number of
4967 // workers to be taken from the active workers in the work gang.
4968 CMSParRemarkTask(CMSCollector* collector,
4969 CompactibleFreeListSpace* cms_space,
4970 int n_workers, FlexibleWorkGang* workers,
4971 OopTaskQueueSet* task_queues):
4972 CMSParMarkTask("Rescan roots and grey objects in parallel",
4973 collector, n_workers),
4974 _cms_space(cms_space),
4975 _task_queues(task_queues),
4976 _term(n_workers, task_queues) { }
4977
4978 OopTaskQueueSet* task_queues() { return _task_queues; }
4979
4980 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4981
4982 ParallelTaskTerminator* terminator() { return &_term; }
4983 int n_workers() { return _n_workers; }
4984
4985 void work(uint worker_id);
4986
4987 private:
4988 // ... of dirty cards in old space
4989 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4990 Par_MarkRefsIntoAndScanClosure* cl);
4991
4992 // ... work stealing for the above
4993 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4994 };
4995
4996 class RemarkKlassClosure : public KlassClosure {
4997 KlassToOopClosure _cm_klass_closure;
4998 public:
4999 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
5000 void do_klass(Klass* k) {
5001 // Check if we have modified any oops in the Klass during the concurrent marking.
5002 if (k->has_accumulated_modified_oops()) {
5003 k->clear_accumulated_modified_oops();
5004
5005 // We could have transfered the current modified marks to the accumulated marks,
5006 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
5007 } else if (k->has_modified_oops()) {
5008 // Don't clear anything, this info is needed by the next young collection.
5009 } else {
5010 // No modified oops in the Klass.
5011 return;
5012 }
5013
5014 // The klass has modified fields, need to scan the klass.
5015 _cm_klass_closure.do_klass(k);
5016 }
5017 };
5018
5019 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
5020 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5021 ContiguousSpace* eden_space = dng->eden();
5022 ContiguousSpace* from_space = dng->from();
5023 ContiguousSpace* to_space = dng->to();
5024
5025 HeapWord** eca = _collector->_eden_chunk_array;
5026 size_t ect = _collector->_eden_chunk_index;
5027 HeapWord** sca = _collector->_survivor_chunk_array;
5028 size_t sct = _collector->_survivor_chunk_index;
5029
5030 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5031 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5032
5033 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
5034 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
5035 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
5036 }
5037
5038 // work_queue(i) is passed to the closure
5039 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5040 // also is passed to do_dirty_card_rescan_tasks() and to
5041 // do_work_steal() to select the i-th task_queue.
5042
5043 void CMSParRemarkTask::work(uint worker_id) {
5044 elapsedTimer _timer;
5045 ResourceMark rm;
5046 HandleMark hm;
5047
5048 // ---------- rescan from roots --------------
5049 _timer.start();
5050 GenCollectedHeap* gch = GenCollectedHeap::heap();
5051 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5052 _collector->_span, _collector->ref_processor(),
5053 &(_collector->_markBitMap),
5054 work_queue(worker_id));
5055
5056 // Rescan young gen roots first since these are likely
5057 // coarsely partitioned and may, on that account, constitute
5058 // the critical path; thus, it's best to start off that
5059 // work first.
5060 // ---------- young gen roots --------------
5061 {
5062 work_on_young_gen_roots(worker_id, &par_mrias_cl);
5063 _timer.stop();
5064 if (PrintCMSStatistics != 0) {
5065 gclog_or_tty->print_cr(
5066 "Finished young gen rescan work in %dth thread: %3.3f sec",
5067 worker_id, _timer.seconds());
5068 }
5069 }
5070
5071 // ---------- remaining roots --------------
5072 _timer.reset();
5073 _timer.start();
5074 gch->gen_process_roots(_collector->_cmsGen->level(),
5075 false, // yg was scanned above
5076 false, // this is parallel code
5077 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5078 _collector->should_unload_classes(),
5079 &par_mrias_cl,
5080 NULL,
5081 NULL); // The dirty klasses will be handled below
5082
5083 assert(_collector->should_unload_classes()
5084 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5085 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5086 _timer.stop();
5087 if (PrintCMSStatistics != 0) {
5088 gclog_or_tty->print_cr(
5089 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5090 worker_id, _timer.seconds());
5091 }
5092
5093 // ---------- unhandled CLD scanning ----------
5094 if (worker_id == 0) { // Single threaded at the moment.
5095 _timer.reset();
5096 _timer.start();
5097
5098 // Scan all new class loader data objects and new dependencies that were
5099 // introduced during concurrent marking.
5100 ResourceMark rm;
5101 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5102 for (int i = 0; i < array->length(); i++) {
5103 par_mrias_cl.do_class_loader_data(array->at(i));
5104 }
5105
5106 // We don't need to keep track of new CLDs anymore.
5107 ClassLoaderDataGraph::remember_new_clds(false);
5108
5109 _timer.stop();
5110 if (PrintCMSStatistics != 0) {
5111 gclog_or_tty->print_cr(
5112 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
5113 worker_id, _timer.seconds());
5114 }
5115 }
5116
5117 // ---------- dirty klass scanning ----------
5118 if (worker_id == 0) { // Single threaded at the moment.
5119 _timer.reset();
5120 _timer.start();
5121
5122 // Scan all classes that was dirtied during the concurrent marking phase.
5123 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
5124 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5125
5126 _timer.stop();
5127 if (PrintCMSStatistics != 0) {
5128 gclog_or_tty->print_cr(
5129 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
5130 worker_id, _timer.seconds());
5131 }
5132 }
5133
5134 // We might have added oops to ClassLoaderData::_handles during the
5135 // concurrent marking phase. These oops point to newly allocated objects
5136 // that are guaranteed to be kept alive. Either by the direct allocation
5137 // code, or when the young collector processes the roots. Hence,
5138 // we don't have to revisit the _handles block during the remark phase.
5139
5140 // ---------- rescan dirty cards ------------
5141 _timer.reset();
5142 _timer.start();
5143
5144 // Do the rescan tasks for each of the two spaces
5145 // (cms_space) in turn.
5146 // "worker_id" is passed to select the task_queue for "worker_id"
5147 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5148 _timer.stop();
5149 if (PrintCMSStatistics != 0) {
5150 gclog_or_tty->print_cr(
5151 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5152 worker_id, _timer.seconds());
5153 }
5154
5155 // ---------- steal work from other threads ...
5156 // ---------- ... and drain overflow list.
5157 _timer.reset();
5158 _timer.start();
5159 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5160 _timer.stop();
5161 if (PrintCMSStatistics != 0) {
5162 gclog_or_tty->print_cr(
5163 "Finished work stealing in %dth thread: %3.3f sec",
5164 worker_id, _timer.seconds());
5165 }
5166 }
5167
5168 // Note that parameter "i" is not used.
5169 void
5170 CMSParMarkTask::do_young_space_rescan(uint worker_id,
5171 OopsInGenClosure* cl, ContiguousSpace* space,
5172 HeapWord** chunk_array, size_t chunk_top) {
5173 // Until all tasks completed:
5174 // . claim an unclaimed task
5175 // . compute region boundaries corresponding to task claimed
5176 // using chunk_array
5177 // . par_oop_iterate(cl) over that region
5178
5179 ResourceMark rm;
5180 HandleMark hm;
5181
5182 SequentialSubTasksDone* pst = space->par_seq_tasks();
5183
5184 uint nth_task = 0;
5185 uint n_tasks = pst->n_tasks();
5186
5187 if (n_tasks > 0) {
5188 assert(pst->valid(), "Uninitialized use?");
5189 HeapWord *start, *end;
5190 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5191 // We claimed task # nth_task; compute its boundaries.
5192 if (chunk_top == 0) { // no samples were taken
5193 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5194 start = space->bottom();
5195 end = space->top();
5196 } else if (nth_task == 0) {
5197 start = space->bottom();
5198 end = chunk_array[nth_task];
5199 } else if (nth_task < (uint)chunk_top) {
5200 assert(nth_task >= 1, "Control point invariant");
5201 start = chunk_array[nth_task - 1];
5202 end = chunk_array[nth_task];
5203 } else {
5204 assert(nth_task == (uint)chunk_top, "Control point invariant");
5205 start = chunk_array[chunk_top - 1];
5206 end = space->top();
5207 }
5208 MemRegion mr(start, end);
5209 // Verify that mr is in space
5210 assert(mr.is_empty() || space->used_region().contains(mr),
5211 "Should be in space");
5212 // Verify that "start" is an object boundary
5213 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5214 "Should be an oop");
5215 space->par_oop_iterate(mr, cl);
5216 }
5217 pst->all_tasks_completed();
5218 }
5219 }
5220
5221 void
5222 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5223 CompactibleFreeListSpace* sp, int i,
5224 Par_MarkRefsIntoAndScanClosure* cl) {
5225 // Until all tasks completed:
5226 // . claim an unclaimed task
5227 // . compute region boundaries corresponding to task claimed
5228 // . transfer dirty bits ct->mut for that region
5229 // . apply rescanclosure to dirty mut bits for that region
5230
5231 ResourceMark rm;
5232 HandleMark hm;
5233
5234 OopTaskQueue* work_q = work_queue(i);
5235 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5236 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5237 // CAUTION: This closure has state that persists across calls to
5238 // the work method dirty_range_iterate_clear() in that it has
5239 // embedded in it a (subtype of) UpwardsObjectClosure. The
5240 // use of that state in the embedded UpwardsObjectClosure instance
5241 // assumes that the cards are always iterated (even if in parallel
5242 // by several threads) in monotonically increasing order per each
5243 // thread. This is true of the implementation below which picks
5244 // card ranges (chunks) in monotonically increasing order globally
5245 // and, a-fortiori, in monotonically increasing order per thread
5246 // (the latter order being a subsequence of the former).
5247 // If the work code below is ever reorganized into a more chaotic
5248 // work-partitioning form than the current "sequential tasks"
5249 // paradigm, the use of that persistent state will have to be
5250 // revisited and modified appropriately. See also related
5251 // bug 4756801 work on which should examine this code to make
5252 // sure that the changes there do not run counter to the
5253 // assumptions made here and necessary for correctness and
5254 // efficiency. Note also that this code might yield inefficient
5255 // behavior in the case of very large objects that span one or
5256 // more work chunks. Such objects would potentially be scanned
5257 // several times redundantly. Work on 4756801 should try and
5258 // address that performance anomaly if at all possible. XXX
5259 MemRegion full_span = _collector->_span;
5260 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5261 MarkFromDirtyCardsClosure
5262 greyRescanClosure(_collector, full_span, // entire span of interest
5263 sp, bm, work_q, cl);
5264
5265 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5266 assert(pst->valid(), "Uninitialized use?");
5267 uint nth_task = 0;
5268 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5269 MemRegion span = sp->used_region();
5270 HeapWord* start_addr = span.start();
5271 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5272 alignment);
5273 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5274 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5275 start_addr, "Check alignment");
5276 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5277 chunk_size, "Check alignment");
5278
5279 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5280 // Having claimed the nth_task, compute corresponding mem-region,
5281 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
5282 // The alignment restriction ensures that we do not need any
5283 // synchronization with other gang-workers while setting or
5284 // clearing bits in thus chunk of the MUT.
5285 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5286 start_addr + (nth_task+1)*chunk_size);
5287 // The last chunk's end might be way beyond end of the
5288 // used region. In that case pull back appropriately.
5289 if (this_span.end() > end_addr) {
5290 this_span.set_end(end_addr);
5291 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5292 }
5293 // Iterate over the dirty cards covering this chunk, marking them
5294 // precleaned, and setting the corresponding bits in the mod union
5295 // table. Since we have been careful to partition at Card and MUT-word
5296 // boundaries no synchronization is needed between parallel threads.
5297 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5298 &modUnionClosure);
5299
5300 // Having transferred these marks into the modUnionTable,
5301 // rescan the marked objects on the dirty cards in the modUnionTable.
5302 // Even if this is at a synchronous collection, the initial marking
5303 // may have been done during an asynchronous collection so there
5304 // may be dirty bits in the mod-union table.
5305 _collector->_modUnionTable.dirty_range_iterate_clear(
5306 this_span, &greyRescanClosure);
5307 _collector->_modUnionTable.verifyNoOneBitsInRange(
5308 this_span.start(),
5309 this_span.end());
5310 }
5311 pst->all_tasks_completed(); // declare that i am done
5312 }
5313
5314 // . see if we can share work_queues with ParNew? XXX
5315 void
5316 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5317 int* seed) {
5318 OopTaskQueue* work_q = work_queue(i);
5319 NOT_PRODUCT(int num_steals = 0;)
5320 oop obj_to_scan;
5321 CMSBitMap* bm = &(_collector->_markBitMap);
5322
5323 while (true) {
5324 // Completely finish any left over work from (an) earlier round(s)
5325 cl->trim_queue(0);
5326 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5327 (size_t)ParGCDesiredObjsFromOverflowList);
5328 // Now check if there's any work in the overflow list
5329 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5330 // only affects the number of attempts made to get work from the
5331 // overflow list and does not affect the number of workers. Just
5332 // pass ParallelGCThreads so this behavior is unchanged.
5333 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5334 work_q,
5335 ParallelGCThreads)) {
5336 // found something in global overflow list;
5337 // not yet ready to go stealing work from others.
5338 // We'd like to assert(work_q->size() != 0, ...)
5339 // because we just took work from the overflow list,
5340 // but of course we can't since all of that could have
5341 // been already stolen from us.
5342 // "He giveth and He taketh away."
5343 continue;
5344 }
5345 // Verify that we have no work before we resort to stealing
5346 assert(work_q->size() == 0, "Have work, shouldn't steal");
5347 // Try to steal from other queues that have work
5348 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5349 NOT_PRODUCT(num_steals++;)
5350 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5351 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5352 // Do scanning work
5353 obj_to_scan->oop_iterate(cl);
5354 // Loop around, finish this work, and try to steal some more
5355 } else if (terminator()->offer_termination()) {
5356 break; // nirvana from the infinite cycle
5357 }
5358 }
5359 NOT_PRODUCT(
5360 if (PrintCMSStatistics != 0) {
5361 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5362 }
5363 )
5364 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5365 "Else our work is not yet done");
5366 }
5367
5368 // Record object boundaries in _eden_chunk_array by sampling the eden
5369 // top in the slow-path eden object allocation code path and record
5370 // the boundaries, if CMSEdenChunksRecordAlways is true. If
5371 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
5372 // sampling in sample_eden() that activates during the part of the
5373 // preclean phase.
5374 void CMSCollector::sample_eden_chunk() {
5375 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
5376 if (_eden_chunk_lock->try_lock()) {
5377 // Record a sample. This is the critical section. The contents
5378 // of the _eden_chunk_array have to be non-decreasing in the
5379 // address order.
5380 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
5381 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
5382 "Unexpected state of Eden");
5383 if (_eden_chunk_index == 0 ||
5384 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
5385 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
5386 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
5387 _eden_chunk_index++; // commit sample
5388 }
5389 _eden_chunk_lock->unlock();
5390 }
5391 }
5392 }
5393
5394 // Return a thread-local PLAB recording array, as appropriate.
5395 void* CMSCollector::get_data_recorder(int thr_num) {
5396 if (_survivor_plab_array != NULL &&
5397 (CMSPLABRecordAlways ||
5398 (_collectorState > Marking && _collectorState < FinalMarking))) {
5399 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5400 ChunkArray* ca = &_survivor_plab_array[thr_num];
5401 ca->reset(); // clear it so that fresh data is recorded
5402 return (void*) ca;
5403 } else {
5404 return NULL;
5405 }
5406 }
5407
5408 // Reset all the thread-local PLAB recording arrays
5409 void CMSCollector::reset_survivor_plab_arrays() {
5410 for (uint i = 0; i < ParallelGCThreads; i++) {
5411 _survivor_plab_array[i].reset();
5412 }
5413 }
5414
5415 // Merge the per-thread plab arrays into the global survivor chunk
5416 // array which will provide the partitioning of the survivor space
5417 // for CMS initial scan and rescan.
5418 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5419 int no_of_gc_threads) {
5420 assert(_survivor_plab_array != NULL, "Error");
5421 assert(_survivor_chunk_array != NULL, "Error");
5422 assert(_collectorState == FinalMarking ||
5423 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
5424 for (int j = 0; j < no_of_gc_threads; j++) {
5425 _cursor[j] = 0;
5426 }
5427 HeapWord* top = surv->top();
5428 size_t i;
5429 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5430 HeapWord* min_val = top; // Higher than any PLAB address
5431 uint min_tid = 0; // position of min_val this round
5432 for (int j = 0; j < no_of_gc_threads; j++) {
5433 ChunkArray* cur_sca = &_survivor_plab_array[j];
5434 if (_cursor[j] == cur_sca->end()) {
5435 continue;
5436 }
5437 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5438 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5439 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5440 if (cur_val < min_val) {
5441 min_tid = j;
5442 min_val = cur_val;
5443 } else {
5444 assert(cur_val < top, "All recorded addresses should be less");
5445 }
5446 }
5447 // At this point min_val and min_tid are respectively
5448 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5449 // and the thread (j) that witnesses that address.
5450 // We record this address in the _survivor_chunk_array[i]
5451 // and increment _cursor[min_tid] prior to the next round i.
5452 if (min_val == top) {
5453 break;
5454 }
5455 _survivor_chunk_array[i] = min_val;
5456 _cursor[min_tid]++;
5457 }
5458 // We are all done; record the size of the _survivor_chunk_array
5459 _survivor_chunk_index = i; // exclusive: [0, i)
5460 if (PrintCMSStatistics > 0) {
5461 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5462 }
5463 // Verify that we used up all the recorded entries
5464 #ifdef ASSERT
5465 size_t total = 0;
5466 for (int j = 0; j < no_of_gc_threads; j++) {
5467 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5468 total += _cursor[j];
5469 }
5470 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5471 // Check that the merged array is in sorted order
5472 if (total > 0) {
5473 for (size_t i = 0; i < total - 1; i++) {
5474 if (PrintCMSStatistics > 0) {
5475 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5476 i, _survivor_chunk_array[i]);
5477 }
5478 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5479 "Not sorted");
5480 }
5481 }
5482 #endif // ASSERT
5483 }
5484
5485 // Set up the space's par_seq_tasks structure for work claiming
5486 // for parallel initial scan and rescan of young gen.
5487 // See ParRescanTask where this is currently used.
5488 void
5489 CMSCollector::
5490 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5491 assert(n_threads > 0, "Unexpected n_threads argument");
5492 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5493
5494 // Eden space
5495 if (!dng->eden()->is_empty()) {
5496 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5497 assert(!pst->valid(), "Clobbering existing data?");
5498 // Each valid entry in [0, _eden_chunk_index) represents a task.
5499 size_t n_tasks = _eden_chunk_index + 1;
5500 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5501 // Sets the condition for completion of the subtask (how many threads
5502 // need to finish in order to be done).
5503 pst->set_n_threads(n_threads);
5504 pst->set_n_tasks((int)n_tasks);
5505 }
5506
5507 // Merge the survivor plab arrays into _survivor_chunk_array
5508 if (_survivor_plab_array != NULL) {
5509 merge_survivor_plab_arrays(dng->from(), n_threads);
5510 } else {
5511 assert(_survivor_chunk_index == 0, "Error");
5512 }
5513
5514 // To space
5515 {
5516 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5517 assert(!pst->valid(), "Clobbering existing data?");
5518 // Sets the condition for completion of the subtask (how many threads
5519 // need to finish in order to be done).
5520 pst->set_n_threads(n_threads);
5521 pst->set_n_tasks(1);
5522 assert(pst->valid(), "Error");
5523 }
5524
5525 // From space
5526 {
5527 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5528 assert(!pst->valid(), "Clobbering existing data?");
5529 size_t n_tasks = _survivor_chunk_index + 1;
5530 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5531 // Sets the condition for completion of the subtask (how many threads
5532 // need to finish in order to be done).
5533 pst->set_n_threads(n_threads);
5534 pst->set_n_tasks((int)n_tasks);
5535 assert(pst->valid(), "Error");
5536 }
5537 }
5538
5539 // Parallel version of remark
5540 void CMSCollector::do_remark_parallel() {
5541 GenCollectedHeap* gch = GenCollectedHeap::heap();
5542 FlexibleWorkGang* workers = gch->workers();
5543 assert(workers != NULL, "Need parallel worker threads.");
5544 // Choose to use the number of GC workers most recently set
5545 // into "active_workers". If active_workers is not set, set it
5546 // to ParallelGCThreads.
5547 int n_workers = workers->active_workers();
5548 if (n_workers == 0) {
5549 assert(n_workers > 0, "Should have been set during scavenge");
5550 n_workers = ParallelGCThreads;
5551 workers->set_active_workers(n_workers);
5552 }
5553 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5554
5555 CMSParRemarkTask tsk(this,
5556 cms_space,
5557 n_workers, workers, task_queues());
5558
5559 // Set up for parallel process_roots work.
5560 gch->set_par_threads(n_workers);
5561 // We won't be iterating over the cards in the card table updating
5562 // the younger_gen cards, so we shouldn't call the following else
5563 // the verification code as well as subsequent younger_refs_iterate
5564 // code would get confused. XXX
5565 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5566
5567 // The young gen rescan work will not be done as part of
5568 // process_roots (which currently doesn't know how to
5569 // parallelize such a scan), but rather will be broken up into
5570 // a set of parallel tasks (via the sampling that the [abortable]
5571 // preclean phase did of EdenSpace, plus the [two] tasks of
5572 // scanning the [two] survivor spaces. Further fine-grain
5573 // parallelization of the scanning of the survivor spaces
5574 // themselves, and of precleaning of the younger gen itself
5575 // is deferred to the future.
5576 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5577
5578 // The dirty card rescan work is broken up into a "sequence"
5579 // of parallel tasks (per constituent space) that are dynamically
5580 // claimed by the parallel threads.
5581 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5582
5583 // It turns out that even when we're using 1 thread, doing the work in a
5584 // separate thread causes wide variance in run times. We can't help this
5585 // in the multi-threaded case, but we special-case n=1 here to get
5586 // repeatable measurements of the 1-thread overhead of the parallel code.
5587 if (n_workers > 1) {
5588 // Make refs discovery MT-safe, if it isn't already: it may not
5589 // necessarily be so, since it's possible that we are doing
5590 // ST marking.
5591 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5592 GenCollectedHeap::StrongRootsScope srs(gch);
5593 workers->run_task(&tsk);
5594 } else {
5595 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5596 GenCollectedHeap::StrongRootsScope srs(gch);
5597 tsk.work(0);
5598 }
5599
5600 gch->set_par_threads(0); // 0 ==> non-parallel.
5601 // restore, single-threaded for now, any preserved marks
5602 // as a result of work_q overflow
5603 restore_preserved_marks_if_any();
5604 }
5605
5606 // Non-parallel version of remark
5607 void CMSCollector::do_remark_non_parallel() {
5608 ResourceMark rm;
5609 HandleMark hm;
5610 GenCollectedHeap* gch = GenCollectedHeap::heap();
5611 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5612
5613 MarkRefsIntoAndScanClosure
5614 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5615 &_markStack, this,
5616 false /* should_yield */, false /* not precleaning */);
5617 MarkFromDirtyCardsClosure
5618 markFromDirtyCardsClosure(this, _span,
5619 NULL, // space is set further below
5620 &_markBitMap, &_markStack, &mrias_cl);
5621 {
5622 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5623 // Iterate over the dirty cards, setting the corresponding bits in the
5624 // mod union table.
5625 {
5626 ModUnionClosure modUnionClosure(&_modUnionTable);
5627 _ct->ct_bs()->dirty_card_iterate(
5628 _cmsGen->used_region(),
5629 &modUnionClosure);
5630 }
5631 // Having transferred these marks into the modUnionTable, we just need
5632 // to rescan the marked objects on the dirty cards in the modUnionTable.
5633 // The initial marking may have been done during an asynchronous
5634 // collection so there may be dirty bits in the mod-union table.
5635 const int alignment =
5636 CardTableModRefBS::card_size * BitsPerWord;
5637 {
5638 // ... First handle dirty cards in CMS gen
5639 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5640 MemRegion ur = _cmsGen->used_region();
5641 HeapWord* lb = ur.start();
5642 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5643 MemRegion cms_span(lb, ub);
5644 _modUnionTable.dirty_range_iterate_clear(cms_span,
5645 &markFromDirtyCardsClosure);
5646 verify_work_stacks_empty();
5647 if (PrintCMSStatistics != 0) {
5648 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5649 markFromDirtyCardsClosure.num_dirty_cards());
5650 }
5651 }
5652 }
5653 if (VerifyDuringGC &&
5654 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5655 HandleMark hm; // Discard invalid handles created during verification
5656 Universe::verify();
5657 }
5658 {
5659 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5660
5661 verify_work_stacks_empty();
5662
5663 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5664 GenCollectedHeap::StrongRootsScope srs(gch);
5665
5666 gch->gen_process_roots(_cmsGen->level(),
5667 true, // younger gens as roots
5668 false, // use the local StrongRootsScope
5669 SharedHeap::ScanningOption(roots_scanning_options()),
5670 should_unload_classes(),
5671 &mrias_cl,
5672 NULL,
5673 NULL); // The dirty klasses will be handled below
5674
5675 assert(should_unload_classes()
5676 || (roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5677 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5678 }
5679
5680 {
5681 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5682
5683 verify_work_stacks_empty();
5684
5685 // Scan all class loader data objects that might have been introduced
5686 // during concurrent marking.
5687 ResourceMark rm;
5688 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5689 for (int i = 0; i < array->length(); i++) {
5690 mrias_cl.do_class_loader_data(array->at(i));
5691 }
5692
5693 // We don't need to keep track of new CLDs anymore.
5694 ClassLoaderDataGraph::remember_new_clds(false);
5695
5696 verify_work_stacks_empty();
5697 }
5698
5699 {
5700 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5701
5702 verify_work_stacks_empty();
5703
5704 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5705 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5706
5707 verify_work_stacks_empty();
5708 }
5709
5710 // We might have added oops to ClassLoaderData::_handles during the
5711 // concurrent marking phase. These oops point to newly allocated objects
5712 // that are guaranteed to be kept alive. Either by the direct allocation
5713 // code, or when the young collector processes the roots. Hence,
5714 // we don't have to revisit the _handles block during the remark phase.
5715
5716 verify_work_stacks_empty();
5717 // Restore evacuated mark words, if any, used for overflow list links
5718 if (!CMSOverflowEarlyRestoration) {
5719 restore_preserved_marks_if_any();
5720 }
5721 verify_overflow_empty();
5722 }
5723
5724 ////////////////////////////////////////////////////////
5725 // Parallel Reference Processing Task Proxy Class
5726 ////////////////////////////////////////////////////////
5727 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5728 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5729 CMSCollector* _collector;
5730 CMSBitMap* _mark_bit_map;
5731 const MemRegion _span;
5732 ProcessTask& _task;
5733
5734 public:
5735 CMSRefProcTaskProxy(ProcessTask& task,
5736 CMSCollector* collector,
5737 const MemRegion& span,
5738 CMSBitMap* mark_bit_map,
5739 AbstractWorkGang* workers,
5740 OopTaskQueueSet* task_queues):
5741 // XXX Should superclass AGTWOQ also know about AWG since it knows
5742 // about the task_queues used by the AWG? Then it could initialize
5743 // the terminator() object. See 6984287. The set_for_termination()
5744 // below is a temporary band-aid for the regression in 6984287.
5745 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5746 task_queues),
5747 _task(task),
5748 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5749 {
5750 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5751 "Inconsistency in _span");
5752 set_for_termination(workers->active_workers());
5753 }
5754
5755 OopTaskQueueSet* task_queues() { return queues(); }
5756
5757 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5758
5759 void do_work_steal(int i,
5760 CMSParDrainMarkingStackClosure* drain,
5761 CMSParKeepAliveClosure* keep_alive,
5762 int* seed);
5763
5764 virtual void work(uint worker_id);
5765 };
5766
5767 void CMSRefProcTaskProxy::work(uint worker_id) {
5768 ResourceMark rm;
5769 HandleMark hm;
5770 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5771 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5772 _mark_bit_map,
5773 work_queue(worker_id));
5774 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5775 _mark_bit_map,
5776 work_queue(worker_id));
5777 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5778 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5779 if (_task.marks_oops_alive()) {
5780 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5781 _collector->hash_seed(worker_id));
5782 }
5783 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5784 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5785 }
5786
5787 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5788 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5789 EnqueueTask& _task;
5790
5791 public:
5792 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5793 : AbstractGangTask("Enqueue reference objects in parallel"),
5794 _task(task)
5795 { }
5796
5797 virtual void work(uint worker_id)
5798 {
5799 _task.work(worker_id);
5800 }
5801 };
5802
5803 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5804 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5805 _span(span),
5806 _bit_map(bit_map),
5807 _work_queue(work_queue),
5808 _mark_and_push(collector, span, bit_map, work_queue),
5809 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5810 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5811 { }
5812
5813 // . see if we can share work_queues with ParNew? XXX
5814 void CMSRefProcTaskProxy::do_work_steal(int i,
5815 CMSParDrainMarkingStackClosure* drain,
5816 CMSParKeepAliveClosure* keep_alive,
5817 int* seed) {
5818 OopTaskQueue* work_q = work_queue(i);
5819 NOT_PRODUCT(int num_steals = 0;)
5820 oop obj_to_scan;
5821
5822 while (true) {
5823 // Completely finish any left over work from (an) earlier round(s)
5824 drain->trim_queue(0);
5825 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5826 (size_t)ParGCDesiredObjsFromOverflowList);
5827 // Now check if there's any work in the overflow list
5828 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5829 // only affects the number of attempts made to get work from the
5830 // overflow list and does not affect the number of workers. Just
5831 // pass ParallelGCThreads so this behavior is unchanged.
5832 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5833 work_q,
5834 ParallelGCThreads)) {
5835 // Found something in global overflow list;
5836 // not yet ready to go stealing work from others.
5837 // We'd like to assert(work_q->size() != 0, ...)
5838 // because we just took work from the overflow list,
5839 // but of course we can't, since all of that might have
5840 // been already stolen from us.
5841 continue;
5842 }
5843 // Verify that we have no work before we resort to stealing
5844 assert(work_q->size() == 0, "Have work, shouldn't steal");
5845 // Try to steal from other queues that have work
5846 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5847 NOT_PRODUCT(num_steals++;)
5848 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5849 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5850 // Do scanning work
5851 obj_to_scan->oop_iterate(keep_alive);
5852 // Loop around, finish this work, and try to steal some more
5853 } else if (terminator()->offer_termination()) {
5854 break; // nirvana from the infinite cycle
5855 }
5856 }
5857 NOT_PRODUCT(
5858 if (PrintCMSStatistics != 0) {
5859 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5860 }
5861 )
5862 }
5863
5864 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5865 {
5866 GenCollectedHeap* gch = GenCollectedHeap::heap();
5867 FlexibleWorkGang* workers = gch->workers();
5868 assert(workers != NULL, "Need parallel worker threads.");
5869 CMSRefProcTaskProxy rp_task(task, &_collector,
5870 _collector.ref_processor()->span(),
5871 _collector.markBitMap(),
5872 workers, _collector.task_queues());
5873 workers->run_task(&rp_task);
5874 }
5875
5876 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5877 {
5878
5879 GenCollectedHeap* gch = GenCollectedHeap::heap();
5880 FlexibleWorkGang* workers = gch->workers();
5881 assert(workers != NULL, "Need parallel worker threads.");
5882 CMSRefEnqueueTaskProxy enq_task(task);
5883 workers->run_task(&enq_task);
5884 }
5885
5886 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5887
5888 ResourceMark rm;
5889 HandleMark hm;
5890
5891 ReferenceProcessor* rp = ref_processor();
5892 assert(rp->span().equals(_span), "Spans should be equal");
5893 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5894 // Process weak references.
5895 rp->setup_policy(clear_all_soft_refs);
5896 verify_work_stacks_empty();
5897
5898 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5899 &_markStack, false /* !preclean */);
5900 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5901 _span, &_markBitMap, &_markStack,
5902 &cmsKeepAliveClosure, false /* !preclean */);
5903 {
5904 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5905
5906 ReferenceProcessorStats stats;
5907 if (rp->processing_is_mt()) {
5908 // Set the degree of MT here. If the discovery is done MT, there
5909 // may have been a different number of threads doing the discovery
5910 // and a different number of discovered lists may have Ref objects.
5911 // That is OK as long as the Reference lists are balanced (see
5912 // balance_all_queues() and balance_queues()).
5913 GenCollectedHeap* gch = GenCollectedHeap::heap();
5914 int active_workers = ParallelGCThreads;
5915 FlexibleWorkGang* workers = gch->workers();
5916 if (workers != NULL) {
5917 active_workers = workers->active_workers();
5918 // The expectation is that active_workers will have already
5919 // been set to a reasonable value. If it has not been set,
5920 // investigate.
5921 assert(active_workers > 0, "Should have been set during scavenge");
5922 }
5923 rp->set_active_mt_degree(active_workers);
5924 CMSRefProcTaskExecutor task_executor(*this);
5925 stats = rp->process_discovered_references(&_is_alive_closure,
5926 &cmsKeepAliveClosure,
5927 &cmsDrainMarkingStackClosure,
5928 &task_executor,
5929 _gc_timer_cm,
5930 _gc_tracer_cm->gc_id());
5931 } else {
5932 stats = rp->process_discovered_references(&_is_alive_closure,
5933 &cmsKeepAliveClosure,
5934 &cmsDrainMarkingStackClosure,
5935 NULL,
5936 _gc_timer_cm,
5937 _gc_tracer_cm->gc_id());
5938 }
5939 _gc_tracer_cm->report_gc_reference_stats(stats);
5940
5941 }
5942
5943 // This is the point where the entire marking should have completed.
5944 verify_work_stacks_empty();
5945
5946 if (should_unload_classes()) {
5947 {
5948 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5949
5950 // Unload classes and purge the SystemDictionary.
5951 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5952
5953 // Unload nmethods.
5954 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5955
5956 // Prune dead klasses from subklass/sibling/implementor lists.
5957 Klass::clean_weak_klass_links(&_is_alive_closure);
5958 }
5959
5960 {
5961 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5962 // Clean up unreferenced symbols in symbol table.
5963 SymbolTable::unlink();
5964 }
5965
5966 {
5967 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5968 // Delete entries for dead interned strings.
5969 StringTable::unlink(&_is_alive_closure);
5970 }
5971 }
5972
5973
5974 // Restore any preserved marks as a result of mark stack or
5975 // work queue overflow
5976 restore_preserved_marks_if_any(); // done single-threaded for now
5977
5978 rp->set_enqueuing_is_done(true);
5979 if (rp->processing_is_mt()) {
5980 rp->balance_all_queues();
5981 CMSRefProcTaskExecutor task_executor(*this);
5982 rp->enqueue_discovered_references(&task_executor);
5983 } else {
5984 rp->enqueue_discovered_references(NULL);
5985 }
5986 rp->verify_no_references_recorded();
5987 assert(!rp->discovery_enabled(), "should have been disabled");
5988 }
5989
5990 #ifndef PRODUCT
5991 void CMSCollector::check_correct_thread_executing() {
5992 Thread* t = Thread::current();
5993 // Only the VM thread or the CMS thread should be here.
5994 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5995 "Unexpected thread type");
5996 // If this is the vm thread, the foreground process
5997 // should not be waiting. Note that _foregroundGCIsActive is
5998 // true while the foreground collector is waiting.
5999 if (_foregroundGCShouldWait) {
6000 // We cannot be the VM thread
6001 assert(t->is_ConcurrentGC_thread(),
6002 "Should be CMS thread");
6003 } else {
6004 // We can be the CMS thread only if we are in a stop-world
6005 // phase of CMS collection.
6006 if (t->is_ConcurrentGC_thread()) {
6007 assert(_collectorState == InitialMarking ||
6008 _collectorState == FinalMarking,
6009 "Should be a stop-world phase");
6010 // The CMS thread should be holding the CMS_token.
6011 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6012 "Potential interference with concurrently "
6013 "executing VM thread");
6014 }
6015 }
6016 }
6017 #endif
6018
6019 void CMSCollector::sweep(bool asynch) {
6020 assert(_collectorState == Sweeping, "just checking");
6021 check_correct_thread_executing();
6022 verify_work_stacks_empty();
6023 verify_overflow_empty();
6024 increment_sweep_count();
6025 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6026
6027 _inter_sweep_timer.stop();
6028 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6029
6030 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6031 _intra_sweep_timer.reset();
6032 _intra_sweep_timer.start();
6033 if (asynch) {
6034 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6035 CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
6036 // First sweep the old gen
6037 {
6038 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6039 bitMapLock());
6040 sweepWork(_cmsGen, asynch);
6041 }
6042
6043 // Update Universe::_heap_*_at_gc figures.
6044 // We need all the free list locks to make the abstract state
6045 // transition from Sweeping to Resetting. See detailed note
6046 // further below.
6047 {
6048 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6049 // Update heap occupancy information which is used as
6050 // input to soft ref clearing policy at the next gc.
6051 Universe::update_heap_info_at_gc();
6052 _collectorState = Resizing;
6053 }
6054 } else {
6055 // already have needed locks
6056 sweepWork(_cmsGen, asynch);
6057 // Update heap occupancy information which is used as
6058 // input to soft ref clearing policy at the next gc.
6059 Universe::update_heap_info_at_gc();
6060 _collectorState = Resizing;
6061 }
6062 verify_work_stacks_empty();
6063 verify_overflow_empty();
6064
6065 if (should_unload_classes()) {
6066 // Delay purge to the beginning of the next safepoint. Metaspace::contains
6067 // requires that the virtual spaces are stable and not deleted.
6068 ClassLoaderDataGraph::set_should_purge(true);
6069 }
6070
6071 _intra_sweep_timer.stop();
6072 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6073
6074 _inter_sweep_timer.reset();
6075 _inter_sweep_timer.start();
6076
6077 // We need to use a monotonically non-decreasing time in ms
6078 // or we will see time-warp warnings and os::javaTimeMillis()
6079 // does not guarantee monotonicity.
6080 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6081 update_time_of_last_gc(now);
6082
6083 // NOTE on abstract state transitions:
6084 // Mutators allocate-live and/or mark the mod-union table dirty
6085 // based on the state of the collection. The former is done in
6086 // the interval [Marking, Sweeping] and the latter in the interval
6087 // [Marking, Sweeping). Thus the transitions into the Marking state
6088 // and out of the Sweeping state must be synchronously visible
6089 // globally to the mutators.
6090 // The transition into the Marking state happens with the world
6091 // stopped so the mutators will globally see it. Sweeping is
6092 // done asynchronously by the background collector so the transition
6093 // from the Sweeping state to the Resizing state must be done
6094 // under the freelistLock (as is the check for whether to
6095 // allocate-live and whether to dirty the mod-union table).
6096 assert(_collectorState == Resizing, "Change of collector state to"
6097 " Resizing must be done under the freelistLocks (plural)");
6098
6099 // Now that sweeping has been completed, we clear
6100 // the incremental_collection_failed flag,
6101 // thus inviting a younger gen collection to promote into
6102 // this generation. If such a promotion may still fail,
6103 // the flag will be set again when a young collection is
6104 // attempted.
6105 GenCollectedHeap* gch = GenCollectedHeap::heap();
6106 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6107 gch->update_full_collections_completed(_collection_count_start);
6108 }
6109
6110 // FIX ME!!! Looks like this belongs in CFLSpace, with
6111 // CMSGen merely delegating to it.
6112 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6113 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6114 HeapWord* minAddr = _cmsSpace->bottom();
6115 HeapWord* largestAddr =
6116 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6117 if (largestAddr == NULL) {
6118 // The dictionary appears to be empty. In this case
6119 // try to coalesce at the end of the heap.
6120 largestAddr = _cmsSpace->end();
6121 }
6122 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6123 size_t nearLargestOffset =
6124 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6125 if (PrintFLSStatistics != 0) {
6126 gclog_or_tty->print_cr(
6127 "CMS: Large Block: " PTR_FORMAT ";"
6128 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6129 largestAddr,
6130 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6131 }
6132 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6133 }
6134
6135 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6136 return addr >= _cmsSpace->nearLargestChunk();
6137 }
6138
6139 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6140 return _cmsSpace->find_chunk_at_end();
6141 }
6142
6143 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6144 bool full) {
6145 // The next lower level has been collected. Gather any statistics
6146 // that are of interest at this point.
6147 if (!full && (current_level + 1) == level()) {
6148 // Gather statistics on the young generation collection.
6149 collector()->stats().record_gc0_end(used());
6150 }
6151 }
6152
6153 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6154 if (PrintGCDetails && Verbose) {
6155 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6156 }
6157 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6158 _debug_collection_type =
6159 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6160 if (PrintGCDetails && Verbose) {
6161 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6162 }
6163 }
6164
6165 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6166 bool asynch) {
6167 // We iterate over the space(s) underlying this generation,
6168 // checking the mark bit map to see if the bits corresponding
6169 // to specific blocks are marked or not. Blocks that are
6170 // marked are live and are not swept up. All remaining blocks
6171 // are swept up, with coalescing on-the-fly as we sweep up
6172 // contiguous free and/or garbage blocks:
6173 // We need to ensure that the sweeper synchronizes with allocators
6174 // and stop-the-world collectors. In particular, the following
6175 // locks are used:
6176 // . CMS token: if this is held, a stop the world collection cannot occur
6177 // . freelistLock: if this is held no allocation can occur from this
6178 // generation by another thread
6179 // . bitMapLock: if this is held, no other thread can access or update
6180 //
6181
6182 // Note that we need to hold the freelistLock if we use
6183 // block iterate below; else the iterator might go awry if
6184 // a mutator (or promotion) causes block contents to change
6185 // (for instance if the allocator divvies up a block).
6186 // If we hold the free list lock, for all practical purposes
6187 // young generation GC's can't occur (they'll usually need to
6188 // promote), so we might as well prevent all young generation
6189 // GC's while we do a sweeping step. For the same reason, we might
6190 // as well take the bit map lock for the entire duration
6191
6192 // check that we hold the requisite locks
6193 assert(have_cms_token(), "Should hold cms token");
6194 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6195 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6196 "Should possess CMS token to sweep");
6197 assert_lock_strong(gen->freelistLock());
6198 assert_lock_strong(bitMapLock());
6199
6200 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6201 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6202 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6203 _inter_sweep_estimate.padded_average(),
6204 _intra_sweep_estimate.padded_average());
6205 gen->setNearLargestChunk();
6206
6207 {
6208 SweepClosure sweepClosure(this, gen, &_markBitMap,
6209 CMSYield && asynch);
6210 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6211 // We need to free-up/coalesce garbage/blocks from a
6212 // co-terminal free run. This is done in the SweepClosure
6213 // destructor; so, do not remove this scope, else the
6214 // end-of-sweep-census below will be off by a little bit.
6215 }
6216 gen->cmsSpace()->sweep_completed();
6217 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6218 if (should_unload_classes()) { // unloaded classes this cycle,
6219 _concurrent_cycles_since_last_unload = 0; // ... reset count
6220 } else { // did not unload classes,
6221 _concurrent_cycles_since_last_unload++; // ... increment count
6222 }
6223 }
6224
6225 // Reset CMS data structures (for now just the marking bit map)
6226 // preparatory for the next cycle.
6227 void CMSCollector::reset(bool asynch) {
6228 if (asynch) {
6229 CMSTokenSyncWithLocks ts(true, bitMapLock());
6230
6231 // If the state is not "Resetting", the foreground thread
6232 // has done a collection and the resetting.
6233 if (_collectorState != Resetting) {
6234 assert(_collectorState == Idling, "The state should only change"
6235 " because the foreground collector has finished the collection");
6236 return;
6237 }
6238
6239 // Clear the mark bitmap (no grey objects to start with)
6240 // for the next cycle.
6241 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6242 CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
6243
6244 HeapWord* curAddr = _markBitMap.startWord();
6245 while (curAddr < _markBitMap.endWord()) {
6246 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6247 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6248 _markBitMap.clear_large_range(chunk);
6249 if (ConcurrentMarkSweepThread::should_yield() &&
6250 !foregroundGCIsActive() &&
6251 CMSYield) {
6252 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6253 "CMS thread should hold CMS token");
6254 assert_lock_strong(bitMapLock());
6255 bitMapLock()->unlock();
6256 ConcurrentMarkSweepThread::desynchronize(true);
6257 stopTimer();
6258 if (PrintCMSStatistics != 0) {
6259 incrementYields();
6260 }
6261
6262 // See the comment in coordinator_yield()
6263 for (unsigned i = 0; i < CMSYieldSleepCount &&
6264 ConcurrentMarkSweepThread::should_yield() &&
6265 !CMSCollector::foregroundGCIsActive(); ++i) {
6266 os::sleep(Thread::current(), 1, false);
6267 }
6268
6269 ConcurrentMarkSweepThread::synchronize(true);
6270 bitMapLock()->lock_without_safepoint_check();
6271 startTimer();
6272 }
6273 curAddr = chunk.end();
6274 }
6275 // A successful mostly concurrent collection has been done.
6276 // Because only the full (i.e., concurrent mode failure) collections
6277 // are being measured for gc overhead limits, clean the "near" flag
6278 // and count.
6279 size_policy()->reset_gc_overhead_limit_count();
6280 _collectorState = Idling;
6281 } else {
6282 // already have the lock
6283 assert(_collectorState == Resetting, "just checking");
6284 assert_lock_strong(bitMapLock());
6285 _markBitMap.clear_all();
6286 _collectorState = Idling;
6287 }
6288
6289 NOT_PRODUCT(
6290 if (RotateCMSCollectionTypes) {
6291 _cmsGen->rotate_debug_collection_type();
6292 }
6293 )
6294
6295 register_gc_end();
6296 }
6297
6298 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6299 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6300 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6301 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
6302 TraceCollectorStats tcs(counters());
6303
6304 switch (op) {
6305 case CMS_op_checkpointRootsInitial: {
6306 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6307 checkpointRootsInitial(true); // asynch
6308 if (PrintGC) {
6309 _cmsGen->printOccupancy("initial-mark");
6310 }
6311 break;
6312 }
6313 case CMS_op_checkpointRootsFinal: {
6314 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6315 checkpointRootsFinal(true, // asynch
6316 false, // !clear_all_soft_refs
6317 false); // !init_mark_was_synchronous
6318 if (PrintGC) {
6319 _cmsGen->printOccupancy("remark");
6320 }
6321 break;
6322 }
6323 default:
6324 fatal("No such CMS_op");
6325 }
6326 }
6327
6328 #ifndef PRODUCT
6329 size_t const CMSCollector::skip_header_HeapWords() {
6330 return FreeChunk::header_size();
6331 }
6332
6333 // Try and collect here conditions that should hold when
6334 // CMS thread is exiting. The idea is that the foreground GC
6335 // thread should not be blocked if it wants to terminate
6336 // the CMS thread and yet continue to run the VM for a while
6337 // after that.
6338 void CMSCollector::verify_ok_to_terminate() const {
6339 assert(Thread::current()->is_ConcurrentGC_thread(),
6340 "should be called by CMS thread");
6341 assert(!_foregroundGCShouldWait, "should be false");
6342 // We could check here that all the various low-level locks
6343 // are not held by the CMS thread, but that is overkill; see
6344 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6345 // is checked.
6346 }
6347 #endif
6348
6349 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6350 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6351 "missing Printezis mark?");
6352 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6353 size_t size = pointer_delta(nextOneAddr + 1, addr);
6354 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6355 "alignment problem");
6356 assert(size >= 3, "Necessary for Printezis marks to work");
6357 return size;
6358 }
6359
6360 // A variant of the above (block_size_using_printezis_bits()) except
6361 // that we return 0 if the P-bits are not yet set.
6362 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6363 if (_markBitMap.isMarked(addr + 1)) {
6364 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6365 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6366 size_t size = pointer_delta(nextOneAddr + 1, addr);
6367 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6368 "alignment problem");
6369 assert(size >= 3, "Necessary for Printezis marks to work");
6370 return size;
6371 }
6372 return 0;
6373 }
6374
6375 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6376 size_t sz = 0;
6377 oop p = (oop)addr;
6378 if (p->klass_or_null() != NULL) {
6379 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6380 } else {
6381 sz = block_size_using_printezis_bits(addr);
6382 }
6383 assert(sz > 0, "size must be nonzero");
6384 HeapWord* next_block = addr + sz;
6385 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6386 CardTableModRefBS::card_size);
6387 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6388 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6389 "must be different cards");
6390 return next_card;
6391 }
6392
6393
6394 // CMS Bit Map Wrapper /////////////////////////////////////////
6395
6396 // Construct a CMS bit map infrastructure, but don't create the
6397 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6398 // further below.
6399 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6400 _bm(),
6401 _shifter(shifter),
6402 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6403 {
6404 _bmStartWord = 0;
6405 _bmWordSize = 0;
6406 }
6407
6408 bool CMSBitMap::allocate(MemRegion mr) {
6409 _bmStartWord = mr.start();
6410 _bmWordSize = mr.word_size();
6411 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6412 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6413 if (!brs.is_reserved()) {
6414 warning("CMS bit map allocation failure");
6415 return false;
6416 }
6417 // For now we'll just commit all of the bit map up front.
6418 // Later on we'll try to be more parsimonious with swap.
6419 if (!_virtual_space.initialize(brs, brs.size())) {
6420 warning("CMS bit map backing store failure");
6421 return false;
6422 }
6423 assert(_virtual_space.committed_size() == brs.size(),
6424 "didn't reserve backing store for all of CMS bit map?");
6425 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6426 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6427 _bmWordSize, "inconsistency in bit map sizing");
6428 _bm.set_size(_bmWordSize >> _shifter);
6429
6430 // bm.clear(); // can we rely on getting zero'd memory? verify below
6431 assert(isAllClear(),
6432 "Expected zero'd memory from ReservedSpace constructor");
6433 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6434 "consistency check");
6435 return true;
6436 }
6437
6438 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6439 HeapWord *next_addr, *end_addr, *last_addr;
6440 assert_locked();
6441 assert(covers(mr), "out-of-range error");
6442 // XXX assert that start and end are appropriately aligned
6443 for (next_addr = mr.start(), end_addr = mr.end();
6444 next_addr < end_addr; next_addr = last_addr) {
6445 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6446 last_addr = dirty_region.end();
6447 if (!dirty_region.is_empty()) {
6448 cl->do_MemRegion(dirty_region);
6449 } else {
6450 assert(last_addr == end_addr, "program logic");
6451 return;
6452 }
6453 }
6454 }
6455
6456 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6457 _bm.print_on_error(st, prefix);
6458 }
6459
6460 #ifndef PRODUCT
6461 void CMSBitMap::assert_locked() const {
6462 CMSLockVerifier::assert_locked(lock());
6463 }
6464
6465 bool CMSBitMap::covers(MemRegion mr) const {
6466 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6467 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6468 "size inconsistency");
6469 return (mr.start() >= _bmStartWord) &&
6470 (mr.end() <= endWord());
6471 }
6472
6473 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6474 return (start >= _bmStartWord && (start + size) <= endWord());
6475 }
6476
6477 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6478 // verify that there are no 1 bits in the interval [left, right)
6479 FalseBitMapClosure falseBitMapClosure;
6480 iterate(&falseBitMapClosure, left, right);
6481 }
6482
6483 void CMSBitMap::region_invariant(MemRegion mr)
6484 {
6485 assert_locked();
6486 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6487 assert(!mr.is_empty(), "unexpected empty region");
6488 assert(covers(mr), "mr should be covered by bit map");
6489 // convert address range into offset range
6490 size_t start_ofs = heapWordToOffset(mr.start());
6491 // Make sure that end() is appropriately aligned
6492 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6493 (1 << (_shifter+LogHeapWordSize))),
6494 "Misaligned mr.end()");
6495 size_t end_ofs = heapWordToOffset(mr.end());
6496 assert(end_ofs > start_ofs, "Should mark at least one bit");
6497 }
6498
6499 #endif
6500
6501 bool CMSMarkStack::allocate(size_t size) {
6502 // allocate a stack of the requisite depth
6503 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6504 size * sizeof(oop)));
6505 if (!rs.is_reserved()) {
6506 warning("CMSMarkStack allocation failure");
6507 return false;
6508 }
6509 if (!_virtual_space.initialize(rs, rs.size())) {
6510 warning("CMSMarkStack backing store failure");
6511 return false;
6512 }
6513 assert(_virtual_space.committed_size() == rs.size(),
6514 "didn't reserve backing store for all of CMS stack?");
6515 _base = (oop*)(_virtual_space.low());
6516 _index = 0;
6517 _capacity = size;
6518 NOT_PRODUCT(_max_depth = 0);
6519 return true;
6520 }
6521
6522 // XXX FIX ME !!! In the MT case we come in here holding a
6523 // leaf lock. For printing we need to take a further lock
6524 // which has lower rank. We need to recalibrate the two
6525 // lock-ranks involved in order to be able to print the
6526 // messages below. (Or defer the printing to the caller.
6527 // For now we take the expedient path of just disabling the
6528 // messages for the problematic case.)
6529 void CMSMarkStack::expand() {
6530 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6531 if (_capacity == MarkStackSizeMax) {
6532 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6533 // We print a warning message only once per CMS cycle.
6534 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6535 }
6536 return;
6537 }
6538 // Double capacity if possible
6539 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6540 // Do not give up existing stack until we have managed to
6541 // get the double capacity that we desired.
6542 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6543 new_capacity * sizeof(oop)));
6544 if (rs.is_reserved()) {
6545 // Release the backing store associated with old stack
6546 _virtual_space.release();
6547 // Reinitialize virtual space for new stack
6548 if (!_virtual_space.initialize(rs, rs.size())) {
6549 fatal("Not enough swap for expanded marking stack");
6550 }
6551 _base = (oop*)(_virtual_space.low());
6552 _index = 0;
6553 _capacity = new_capacity;
6554 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6555 // Failed to double capacity, continue;
6556 // we print a detail message only once per CMS cycle.
6557 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6558 SIZE_FORMAT"K",
6559 _capacity / K, new_capacity / K);
6560 }
6561 }
6562
6563
6564 // Closures
6565 // XXX: there seems to be a lot of code duplication here;
6566 // should refactor and consolidate common code.
6567
6568 // This closure is used to mark refs into the CMS generation in
6569 // the CMS bit map. Called at the first checkpoint. This closure
6570 // assumes that we do not need to re-mark dirty cards; if the CMS
6571 // generation on which this is used is not an oldest
6572 // generation then this will lose younger_gen cards!
6573
6574 MarkRefsIntoClosure::MarkRefsIntoClosure(
6575 MemRegion span, CMSBitMap* bitMap):
6576 _span(span),
6577 _bitMap(bitMap)
6578 {
6579 assert(_ref_processor == NULL, "deliberately left NULL");
6580 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6581 }
6582
6583 void MarkRefsIntoClosure::do_oop(oop obj) {
6584 // if p points into _span, then mark corresponding bit in _markBitMap
6585 assert(obj->is_oop(), "expected an oop");
6586 HeapWord* addr = (HeapWord*)obj;
6587 if (_span.contains(addr)) {
6588 // this should be made more efficient
6589 _bitMap->mark(addr);
6590 }
6591 }
6592
6593 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6594 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6595
6596 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6597 MemRegion span, CMSBitMap* bitMap):
6598 _span(span),
6599 _bitMap(bitMap)
6600 {
6601 assert(_ref_processor == NULL, "deliberately left NULL");
6602 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6603 }
6604
6605 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6606 // if p points into _span, then mark corresponding bit in _markBitMap
6607 assert(obj->is_oop(), "expected an oop");
6608 HeapWord* addr = (HeapWord*)obj;
6609 if (_span.contains(addr)) {
6610 // this should be made more efficient
6611 _bitMap->par_mark(addr);
6612 }
6613 }
6614
6615 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6616 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6617
6618 // A variant of the above, used for CMS marking verification.
6619 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6620 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6621 _span(span),
6622 _verification_bm(verification_bm),
6623 _cms_bm(cms_bm)
6624 {
6625 assert(_ref_processor == NULL, "deliberately left NULL");
6626 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6627 }
6628
6629 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6630 // if p points into _span, then mark corresponding bit in _markBitMap
6631 assert(obj->is_oop(), "expected an oop");
6632 HeapWord* addr = (HeapWord*)obj;
6633 if (_span.contains(addr)) {
6634 _verification_bm->mark(addr);
6635 if (!_cms_bm->isMarked(addr)) {
6636 oop(addr)->print();
6637 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6638 fatal("... aborting");
6639 }
6640 }
6641 }
6642
6643 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6644 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6645
6646 //////////////////////////////////////////////////
6647 // MarkRefsIntoAndScanClosure
6648 //////////////////////////////////////////////////
6649
6650 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6651 ReferenceProcessor* rp,
6652 CMSBitMap* bit_map,
6653 CMSBitMap* mod_union_table,
6654 CMSMarkStack* mark_stack,
6655 CMSCollector* collector,
6656 bool should_yield,
6657 bool concurrent_precleaning):
6658 _collector(collector),
6659 _span(span),
6660 _bit_map(bit_map),
6661 _mark_stack(mark_stack),
6662 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6663 mark_stack, concurrent_precleaning),
6664 _yield(should_yield),
6665 _concurrent_precleaning(concurrent_precleaning),
6666 _freelistLock(NULL)
6667 {
6668 _ref_processor = rp;
6669 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6670 }
6671
6672 // This closure is used to mark refs into the CMS generation at the
6673 // second (final) checkpoint, and to scan and transitively follow
6674 // the unmarked oops. It is also used during the concurrent precleaning
6675 // phase while scanning objects on dirty cards in the CMS generation.
6676 // The marks are made in the marking bit map and the marking stack is
6677 // used for keeping the (newly) grey objects during the scan.
6678 // The parallel version (Par_...) appears further below.
6679 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6680 if (obj != NULL) {
6681 assert(obj->is_oop(), "expected an oop");
6682 HeapWord* addr = (HeapWord*)obj;
6683 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6684 assert(_collector->overflow_list_is_empty(),
6685 "overflow list should be empty");
6686 if (_span.contains(addr) &&
6687 !_bit_map->isMarked(addr)) {
6688 // mark bit map (object is now grey)
6689 _bit_map->mark(addr);
6690 // push on marking stack (stack should be empty), and drain the
6691 // stack by applying this closure to the oops in the oops popped
6692 // from the stack (i.e. blacken the grey objects)
6693 bool res = _mark_stack->push(obj);
6694 assert(res, "Should have space to push on empty stack");
6695 do {
6696 oop new_oop = _mark_stack->pop();
6697 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6698 assert(_bit_map->isMarked((HeapWord*)new_oop),
6699 "only grey objects on this stack");
6700 // iterate over the oops in this oop, marking and pushing
6701 // the ones in CMS heap (i.e. in _span).
6702 new_oop->oop_iterate(&_pushAndMarkClosure);
6703 // check if it's time to yield
6704 do_yield_check();
6705 } while (!_mark_stack->isEmpty() ||
6706 (!_concurrent_precleaning && take_from_overflow_list()));
6707 // if marking stack is empty, and we are not doing this
6708 // during precleaning, then check the overflow list
6709 }
6710 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6711 assert(_collector->overflow_list_is_empty(),
6712 "overflow list was drained above");
6713 // We could restore evacuated mark words, if any, used for
6714 // overflow list links here because the overflow list is
6715 // provably empty here. That would reduce the maximum
6716 // size requirements for preserved_{oop,mark}_stack.
6717 // But we'll just postpone it until we are all done
6718 // so we can just stream through.
6719 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6720 _collector->restore_preserved_marks_if_any();
6721 assert(_collector->no_preserved_marks(), "No preserved marks");
6722 }
6723 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6724 "All preserved marks should have been restored above");
6725 }
6726 }
6727
6728 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6729 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6730
6731 void MarkRefsIntoAndScanClosure::do_yield_work() {
6732 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6733 "CMS thread should hold CMS token");
6734 assert_lock_strong(_freelistLock);
6735 assert_lock_strong(_bit_map->lock());
6736 // relinquish the free_list_lock and bitMaplock()
6737 _bit_map->lock()->unlock();
6738 _freelistLock->unlock();
6739 ConcurrentMarkSweepThread::desynchronize(true);
6740 _collector->stopTimer();
6741 if (PrintCMSStatistics != 0) {
6742 _collector->incrementYields();
6743 }
6744
6745 // See the comment in coordinator_yield()
6746 for (unsigned i = 0;
6747 i < CMSYieldSleepCount &&
6748 ConcurrentMarkSweepThread::should_yield() &&
6749 !CMSCollector::foregroundGCIsActive();
6750 ++i) {
6751 os::sleep(Thread::current(), 1, false);
6752 }
6753
6754 ConcurrentMarkSweepThread::synchronize(true);
6755 _freelistLock->lock_without_safepoint_check();
6756 _bit_map->lock()->lock_without_safepoint_check();
6757 _collector->startTimer();
6758 }
6759
6760 ///////////////////////////////////////////////////////////
6761 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6762 // MarkRefsIntoAndScanClosure
6763 ///////////////////////////////////////////////////////////
6764 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6765 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6766 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6767 _span(span),
6768 _bit_map(bit_map),
6769 _work_queue(work_queue),
6770 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6771 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6772 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6773 {
6774 _ref_processor = rp;
6775 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6776 }
6777
6778 // This closure is used to mark refs into the CMS generation at the
6779 // second (final) checkpoint, and to scan and transitively follow
6780 // the unmarked oops. The marks are made in the marking bit map and
6781 // the work_queue is used for keeping the (newly) grey objects during
6782 // the scan phase whence they are also available for stealing by parallel
6783 // threads. Since the marking bit map is shared, updates are
6784 // synchronized (via CAS).
6785 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6786 if (obj != NULL) {
6787 // Ignore mark word because this could be an already marked oop
6788 // that may be chained at the end of the overflow list.
6789 assert(obj->is_oop(true), "expected an oop");
6790 HeapWord* addr = (HeapWord*)obj;
6791 if (_span.contains(addr) &&
6792 !_bit_map->isMarked(addr)) {
6793 // mark bit map (object will become grey):
6794 // It is possible for several threads to be
6795 // trying to "claim" this object concurrently;
6796 // the unique thread that succeeds in marking the
6797 // object first will do the subsequent push on
6798 // to the work queue (or overflow list).
6799 if (_bit_map->par_mark(addr)) {
6800 // push on work_queue (which may not be empty), and trim the
6801 // queue to an appropriate length by applying this closure to
6802 // the oops in the oops popped from the stack (i.e. blacken the
6803 // grey objects)
6804 bool res = _work_queue->push(obj);
6805 assert(res, "Low water mark should be less than capacity?");
6806 trim_queue(_low_water_mark);
6807 } // Else, another thread claimed the object
6808 }
6809 }
6810 }
6811
6812 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6813 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6814
6815 // This closure is used to rescan the marked objects on the dirty cards
6816 // in the mod union table and the card table proper.
6817 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6818 oop p, MemRegion mr) {
6819
6820 size_t size = 0;
6821 HeapWord* addr = (HeapWord*)p;
6822 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6823 assert(_span.contains(addr), "we are scanning the CMS generation");
6824 // check if it's time to yield
6825 if (do_yield_check()) {
6826 // We yielded for some foreground stop-world work,
6827 // and we have been asked to abort this ongoing preclean cycle.
6828 return 0;
6829 }
6830 if (_bitMap->isMarked(addr)) {
6831 // it's marked; is it potentially uninitialized?
6832 if (p->klass_or_null() != NULL) {
6833 // an initialized object; ignore mark word in verification below
6834 // since we are running concurrent with mutators
6835 assert(p->is_oop(true), "should be an oop");
6836 if (p->is_objArray()) {
6837 // objArrays are precisely marked; restrict scanning
6838 // to dirty cards only.
6839 size = CompactibleFreeListSpace::adjustObjectSize(
6840 p->oop_iterate(_scanningClosure, mr));
6841 } else {
6842 // A non-array may have been imprecisely marked; we need
6843 // to scan object in its entirety.
6844 size = CompactibleFreeListSpace::adjustObjectSize(
6845 p->oop_iterate(_scanningClosure));
6846 }
6847 #ifdef ASSERT
6848 size_t direct_size =
6849 CompactibleFreeListSpace::adjustObjectSize(p->size());
6850 assert(size == direct_size, "Inconsistency in size");
6851 assert(size >= 3, "Necessary for Printezis marks to work");
6852 if (!_bitMap->isMarked(addr+1)) {
6853 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6854 } else {
6855 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6856 assert(_bitMap->isMarked(addr+size-1),
6857 "inconsistent Printezis mark");
6858 }
6859 #endif // ASSERT
6860 } else {
6861 // An uninitialized object.
6862 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6863 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6864 size = pointer_delta(nextOneAddr + 1, addr);
6865 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6866 "alignment problem");
6867 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6868 // will dirty the card when the klass pointer is installed in the
6869 // object (signaling the completion of initialization).
6870 }
6871 } else {
6872 // Either a not yet marked object or an uninitialized object
6873 if (p->klass_or_null() == NULL) {
6874 // An uninitialized object, skip to the next card, since
6875 // we may not be able to read its P-bits yet.
6876 assert(size == 0, "Initial value");
6877 } else {
6878 // An object not (yet) reached by marking: we merely need to
6879 // compute its size so as to go look at the next block.
6880 assert(p->is_oop(true), "should be an oop");
6881 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6882 }
6883 }
6884 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6885 return size;
6886 }
6887
6888 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6889 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6890 "CMS thread should hold CMS token");
6891 assert_lock_strong(_freelistLock);
6892 assert_lock_strong(_bitMap->lock());
6893 // relinquish the free_list_lock and bitMaplock()
6894 _bitMap->lock()->unlock();
6895 _freelistLock->unlock();
6896 ConcurrentMarkSweepThread::desynchronize(true);
6897 _collector->stopTimer();
6898 if (PrintCMSStatistics != 0) {
6899 _collector->incrementYields();
6900 }
6901
6902 // See the comment in coordinator_yield()
6903 for (unsigned i = 0; i < CMSYieldSleepCount &&
6904 ConcurrentMarkSweepThread::should_yield() &&
6905 !CMSCollector::foregroundGCIsActive(); ++i) {
6906 os::sleep(Thread::current(), 1, false);
6907 }
6908
6909 ConcurrentMarkSweepThread::synchronize(true);
6910 _freelistLock->lock_without_safepoint_check();
6911 _bitMap->lock()->lock_without_safepoint_check();
6912 _collector->startTimer();
6913 }
6914
6915
6916 //////////////////////////////////////////////////////////////////
6917 // SurvivorSpacePrecleanClosure
6918 //////////////////////////////////////////////////////////////////
6919 // This (single-threaded) closure is used to preclean the oops in
6920 // the survivor spaces.
6921 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6922
6923 HeapWord* addr = (HeapWord*)p;
6924 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6925 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6926 assert(p->klass_or_null() != NULL, "object should be initialized");
6927 // an initialized object; ignore mark word in verification below
6928 // since we are running concurrent with mutators
6929 assert(p->is_oop(true), "should be an oop");
6930 // Note that we do not yield while we iterate over
6931 // the interior oops of p, pushing the relevant ones
6932 // on our marking stack.
6933 size_t size = p->oop_iterate(_scanning_closure);
6934 do_yield_check();
6935 // Observe that below, we do not abandon the preclean
6936 // phase as soon as we should; rather we empty the
6937 // marking stack before returning. This is to satisfy
6938 // some existing assertions. In general, it may be a
6939 // good idea to abort immediately and complete the marking
6940 // from the grey objects at a later time.
6941 while (!_mark_stack->isEmpty()) {
6942 oop new_oop = _mark_stack->pop();
6943 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6944 assert(_bit_map->isMarked((HeapWord*)new_oop),
6945 "only grey objects on this stack");
6946 // iterate over the oops in this oop, marking and pushing
6947 // the ones in CMS heap (i.e. in _span).
6948 new_oop->oop_iterate(_scanning_closure);
6949 // check if it's time to yield
6950 do_yield_check();
6951 }
6952 unsigned int after_count =
6953 GenCollectedHeap::heap()->total_collections();
6954 bool abort = (_before_count != after_count) ||
6955 _collector->should_abort_preclean();
6956 return abort ? 0 : size;
6957 }
6958
6959 void SurvivorSpacePrecleanClosure::do_yield_work() {
6960 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6961 "CMS thread should hold CMS token");
6962 assert_lock_strong(_bit_map->lock());
6963 // Relinquish the bit map lock
6964 _bit_map->lock()->unlock();
6965 ConcurrentMarkSweepThread::desynchronize(true);
6966 _collector->stopTimer();
6967 if (PrintCMSStatistics != 0) {
6968 _collector->incrementYields();
6969 }
6970
6971 // See the comment in coordinator_yield()
6972 for (unsigned i = 0; i < CMSYieldSleepCount &&
6973 ConcurrentMarkSweepThread::should_yield() &&
6974 !CMSCollector::foregroundGCIsActive(); ++i) {
6975 os::sleep(Thread::current(), 1, false);
6976 }
6977
6978 ConcurrentMarkSweepThread::synchronize(true);
6979 _bit_map->lock()->lock_without_safepoint_check();
6980 _collector->startTimer();
6981 }
6982
6983 // This closure is used to rescan the marked objects on the dirty cards
6984 // in the mod union table and the card table proper. In the parallel
6985 // case, although the bitMap is shared, we do a single read so the
6986 // isMarked() query is "safe".
6987 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6988 // Ignore mark word because we are running concurrent with mutators
6989 assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
6990 HeapWord* addr = (HeapWord*)p;
6991 assert(_span.contains(addr), "we are scanning the CMS generation");
6992 bool is_obj_array = false;
6993 #ifdef ASSERT
6994 if (!_parallel) {
6995 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6996 assert(_collector->overflow_list_is_empty(),
6997 "overflow list should be empty");
6998
6999 }
7000 #endif // ASSERT
7001 if (_bit_map->isMarked(addr)) {
7002 // Obj arrays are precisely marked, non-arrays are not;
7003 // so we scan objArrays precisely and non-arrays in their
7004 // entirety.
7005 if (p->is_objArray()) {
7006 is_obj_array = true;
7007 if (_parallel) {
7008 p->oop_iterate(_par_scan_closure, mr);
7009 } else {
7010 p->oop_iterate(_scan_closure, mr);
7011 }
7012 } else {
7013 if (_parallel) {
7014 p->oop_iterate(_par_scan_closure);
7015 } else {
7016 p->oop_iterate(_scan_closure);
7017 }
7018 }
7019 }
7020 #ifdef ASSERT
7021 if (!_parallel) {
7022 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7023 assert(_collector->overflow_list_is_empty(),
7024 "overflow list should be empty");
7025
7026 }
7027 #endif // ASSERT
7028 return is_obj_array;
7029 }
7030
7031 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7032 MemRegion span,
7033 CMSBitMap* bitMap, CMSMarkStack* markStack,
7034 bool should_yield, bool verifying):
7035 _collector(collector),
7036 _span(span),
7037 _bitMap(bitMap),
7038 _mut(&collector->_modUnionTable),
7039 _markStack(markStack),
7040 _yield(should_yield),
7041 _skipBits(0)
7042 {
7043 assert(_markStack->isEmpty(), "stack should be empty");
7044 _finger = _bitMap->startWord();
7045 _threshold = _finger;
7046 assert(_collector->_restart_addr == NULL, "Sanity check");
7047 assert(_span.contains(_finger), "Out of bounds _finger?");
7048 DEBUG_ONLY(_verifying = verifying;)
7049 }
7050
7051 void MarkFromRootsClosure::reset(HeapWord* addr) {
7052 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7053 assert(_span.contains(addr), "Out of bounds _finger?");
7054 _finger = addr;
7055 _threshold = (HeapWord*)round_to(
7056 (intptr_t)_finger, CardTableModRefBS::card_size);
7057 }
7058
7059 // Should revisit to see if this should be restructured for
7060 // greater efficiency.
7061 bool MarkFromRootsClosure::do_bit(size_t offset) {
7062 if (_skipBits > 0) {
7063 _skipBits--;
7064 return true;
7065 }
7066 // convert offset into a HeapWord*
7067 HeapWord* addr = _bitMap->startWord() + offset;
7068 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7069 "address out of range");
7070 assert(_bitMap->isMarked(addr), "tautology");
7071 if (_bitMap->isMarked(addr+1)) {
7072 // this is an allocated but not yet initialized object
7073 assert(_skipBits == 0, "tautology");
7074 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7075 oop p = oop(addr);
7076 if (p->klass_or_null() == NULL) {
7077 DEBUG_ONLY(if (!_verifying) {)
7078 // We re-dirty the cards on which this object lies and increase
7079 // the _threshold so that we'll come back to scan this object
7080 // during the preclean or remark phase. (CMSCleanOnEnter)
7081 if (CMSCleanOnEnter) {
7082 size_t sz = _collector->block_size_using_printezis_bits(addr);
7083 HeapWord* end_card_addr = (HeapWord*)round_to(
7084 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7085 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7086 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7087 // Bump _threshold to end_card_addr; note that
7088 // _threshold cannot possibly exceed end_card_addr, anyhow.
7089 // This prevents future clearing of the card as the scan proceeds
7090 // to the right.
7091 assert(_threshold <= end_card_addr,
7092 "Because we are just scanning into this object");
7093 if (_threshold < end_card_addr) {
7094 _threshold = end_card_addr;
7095 }
7096 if (p->klass_or_null() != NULL) {
7097 // Redirty the range of cards...
7098 _mut->mark_range(redirty_range);
7099 } // ...else the setting of klass will dirty the card anyway.
7100 }
7101 DEBUG_ONLY(})
7102 return true;
7103 }
7104 }
7105 scanOopsInOop(addr);
7106 return true;
7107 }
7108
7109 // We take a break if we've been at this for a while,
7110 // so as to avoid monopolizing the locks involved.
7111 void MarkFromRootsClosure::do_yield_work() {
7112 // First give up the locks, then yield, then re-lock
7113 // We should probably use a constructor/destructor idiom to
7114 // do this unlock/lock or modify the MutexUnlocker class to
7115 // serve our purpose. XXX
7116 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7117 "CMS thread should hold CMS token");
7118 assert_lock_strong(_bitMap->lock());
7119 _bitMap->lock()->unlock();
7120 ConcurrentMarkSweepThread::desynchronize(true);
7121 _collector->stopTimer();
7122 if (PrintCMSStatistics != 0) {
7123 _collector->incrementYields();
7124 }
7125
7126 // See the comment in coordinator_yield()
7127 for (unsigned i = 0; i < CMSYieldSleepCount &&
7128 ConcurrentMarkSweepThread::should_yield() &&
7129 !CMSCollector::foregroundGCIsActive(); ++i) {
7130 os::sleep(Thread::current(), 1, false);
7131 }
7132
7133 ConcurrentMarkSweepThread::synchronize(true);
7134 _bitMap->lock()->lock_without_safepoint_check();
7135 _collector->startTimer();
7136 }
7137
7138 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7139 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7140 assert(_markStack->isEmpty(),
7141 "should drain stack to limit stack usage");
7142 // convert ptr to an oop preparatory to scanning
7143 oop obj = oop(ptr);
7144 // Ignore mark word in verification below, since we
7145 // may be running concurrent with mutators.
7146 assert(obj->is_oop(true), "should be an oop");
7147 assert(_finger <= ptr, "_finger runneth ahead");
7148 // advance the finger to right end of this object
7149 _finger = ptr + obj->size();
7150 assert(_finger > ptr, "we just incremented it above");
7151 // On large heaps, it may take us some time to get through
7152 // the marking phase. During
7153 // this time it's possible that a lot of mutations have
7154 // accumulated in the card table and the mod union table --
7155 // these mutation records are redundant until we have
7156 // actually traced into the corresponding card.
7157 // Here, we check whether advancing the finger would make
7158 // us cross into a new card, and if so clear corresponding
7159 // cards in the MUT (preclean them in the card-table in the
7160 // future).
7161
7162 DEBUG_ONLY(if (!_verifying) {)
7163 // The clean-on-enter optimization is disabled by default,
7164 // until we fix 6178663.
7165 if (CMSCleanOnEnter && (_finger > _threshold)) {
7166 // [_threshold, _finger) represents the interval
7167 // of cards to be cleared in MUT (or precleaned in card table).
7168 // The set of cards to be cleared is all those that overlap
7169 // with the interval [_threshold, _finger); note that
7170 // _threshold is always kept card-aligned but _finger isn't
7171 // always card-aligned.
7172 HeapWord* old_threshold = _threshold;
7173 assert(old_threshold == (HeapWord*)round_to(
7174 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7175 "_threshold should always be card-aligned");
7176 _threshold = (HeapWord*)round_to(
7177 (intptr_t)_finger, CardTableModRefBS::card_size);
7178 MemRegion mr(old_threshold, _threshold);
7179 assert(!mr.is_empty(), "Control point invariant");
7180 assert(_span.contains(mr), "Should clear within span");
7181 _mut->clear_range(mr);
7182 }
7183 DEBUG_ONLY(})
7184 // Note: the finger doesn't advance while we drain
7185 // the stack below.
7186 PushOrMarkClosure pushOrMarkClosure(_collector,
7187 _span, _bitMap, _markStack,
7188 _finger, this);
7189 bool res = _markStack->push(obj);
7190 assert(res, "Empty non-zero size stack should have space for single push");
7191 while (!_markStack->isEmpty()) {
7192 oop new_oop = _markStack->pop();
7193 // Skip verifying header mark word below because we are
7194 // running concurrent with mutators.
7195 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7196 // now scan this oop's oops
7197 new_oop->oop_iterate(&pushOrMarkClosure);
7198 do_yield_check();
7199 }
7200 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7201 }
7202
7203 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7204 CMSCollector* collector, MemRegion span,
7205 CMSBitMap* bit_map,
7206 OopTaskQueue* work_queue,
7207 CMSMarkStack* overflow_stack,
7208 bool should_yield):
7209 _collector(collector),
7210 _whole_span(collector->_span),
7211 _span(span),
7212 _bit_map(bit_map),
7213 _mut(&collector->_modUnionTable),
7214 _work_queue(work_queue),
7215 _overflow_stack(overflow_stack),
7216 _yield(should_yield),
7217 _skip_bits(0),
7218 _task(task)
7219 {
7220 assert(_work_queue->size() == 0, "work_queue should be empty");
7221 _finger = span.start();
7222 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7223 assert(_span.contains(_finger), "Out of bounds _finger?");
7224 }
7225
7226 // Should revisit to see if this should be restructured for
7227 // greater efficiency.
7228 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7229 if (_skip_bits > 0) {
7230 _skip_bits--;
7231 return true;
7232 }
7233 // convert offset into a HeapWord*
7234 HeapWord* addr = _bit_map->startWord() + offset;
7235 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7236 "address out of range");
7237 assert(_bit_map->isMarked(addr), "tautology");
7238 if (_bit_map->isMarked(addr+1)) {
7239 // this is an allocated object that might not yet be initialized
7240 assert(_skip_bits == 0, "tautology");
7241 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7242 oop p = oop(addr);
7243 if (p->klass_or_null() == NULL) {
7244 // in the case of Clean-on-Enter optimization, redirty card
7245 // and avoid clearing card by increasing the threshold.
7246 return true;
7247 }
7248 }
7249 scan_oops_in_oop(addr);
7250 return true;
7251 }
7252
7253 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7254 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7255 // Should we assert that our work queue is empty or
7256 // below some drain limit?
7257 assert(_work_queue->size() == 0,
7258 "should drain stack to limit stack usage");
7259 // convert ptr to an oop preparatory to scanning
7260 oop obj = oop(ptr);
7261 // Ignore mark word in verification below, since we
7262 // may be running concurrent with mutators.
7263 assert(obj->is_oop(true), "should be an oop");
7264 assert(_finger <= ptr, "_finger runneth ahead");
7265 // advance the finger to right end of this object
7266 _finger = ptr + obj->size();
7267 assert(_finger > ptr, "we just incremented it above");
7268 // On large heaps, it may take us some time to get through
7269 // the marking phase. During
7270 // this time it's possible that a lot of mutations have
7271 // accumulated in the card table and the mod union table --
7272 // these mutation records are redundant until we have
7273 // actually traced into the corresponding card.
7274 // Here, we check whether advancing the finger would make
7275 // us cross into a new card, and if so clear corresponding
7276 // cards in the MUT (preclean them in the card-table in the
7277 // future).
7278
7279 // The clean-on-enter optimization is disabled by default,
7280 // until we fix 6178663.
7281 if (CMSCleanOnEnter && (_finger > _threshold)) {
7282 // [_threshold, _finger) represents the interval
7283 // of cards to be cleared in MUT (or precleaned in card table).
7284 // The set of cards to be cleared is all those that overlap
7285 // with the interval [_threshold, _finger); note that
7286 // _threshold is always kept card-aligned but _finger isn't
7287 // always card-aligned.
7288 HeapWord* old_threshold = _threshold;
7289 assert(old_threshold == (HeapWord*)round_to(
7290 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7291 "_threshold should always be card-aligned");
7292 _threshold = (HeapWord*)round_to(
7293 (intptr_t)_finger, CardTableModRefBS::card_size);
7294 MemRegion mr(old_threshold, _threshold);
7295 assert(!mr.is_empty(), "Control point invariant");
7296 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7297 _mut->clear_range(mr);
7298 }
7299
7300 // Note: the local finger doesn't advance while we drain
7301 // the stack below, but the global finger sure can and will.
7302 HeapWord** gfa = _task->global_finger_addr();
7303 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7304 _span, _bit_map,
7305 _work_queue,
7306 _overflow_stack,
7307 _finger,
7308 gfa, this);
7309 bool res = _work_queue->push(obj); // overflow could occur here
7310 assert(res, "Will hold once we use workqueues");
7311 while (true) {
7312 oop new_oop;
7313 if (!_work_queue->pop_local(new_oop)) {
7314 // We emptied our work_queue; check if there's stuff that can
7315 // be gotten from the overflow stack.
7316 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7317 _overflow_stack, _work_queue)) {
7318 do_yield_check();
7319 continue;
7320 } else { // done
7321 break;
7322 }
7323 }
7324 // Skip verifying header mark word below because we are
7325 // running concurrent with mutators.
7326 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7327 // now scan this oop's oops
7328 new_oop->oop_iterate(&pushOrMarkClosure);
7329 do_yield_check();
7330 }
7331 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7332 }
7333
7334 // Yield in response to a request from VM Thread or
7335 // from mutators.
7336 void Par_MarkFromRootsClosure::do_yield_work() {
7337 assert(_task != NULL, "sanity");
7338 _task->yield();
7339 }
7340
7341 // A variant of the above used for verifying CMS marking work.
7342 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7343 MemRegion span,
7344 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7345 CMSMarkStack* mark_stack):
7346 _collector(collector),
7347 _span(span),
7348 _verification_bm(verification_bm),
7349 _cms_bm(cms_bm),
7350 _mark_stack(mark_stack),
7351 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7352 mark_stack)
7353 {
7354 assert(_mark_stack->isEmpty(), "stack should be empty");
7355 _finger = _verification_bm->startWord();
7356 assert(_collector->_restart_addr == NULL, "Sanity check");
7357 assert(_span.contains(_finger), "Out of bounds _finger?");
7358 }
7359
7360 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7361 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7362 assert(_span.contains(addr), "Out of bounds _finger?");
7363 _finger = addr;
7364 }
7365
7366 // Should revisit to see if this should be restructured for
7367 // greater efficiency.
7368 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7369 // convert offset into a HeapWord*
7370 HeapWord* addr = _verification_bm->startWord() + offset;
7371 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7372 "address out of range");
7373 assert(_verification_bm->isMarked(addr), "tautology");
7374 assert(_cms_bm->isMarked(addr), "tautology");
7375
7376 assert(_mark_stack->isEmpty(),
7377 "should drain stack to limit stack usage");
7378 // convert addr to an oop preparatory to scanning
7379 oop obj = oop(addr);
7380 assert(obj->is_oop(), "should be an oop");
7381 assert(_finger <= addr, "_finger runneth ahead");
7382 // advance the finger to right end of this object
7383 _finger = addr + obj->size();
7384 assert(_finger > addr, "we just incremented it above");
7385 // Note: the finger doesn't advance while we drain
7386 // the stack below.
7387 bool res = _mark_stack->push(obj);
7388 assert(res, "Empty non-zero size stack should have space for single push");
7389 while (!_mark_stack->isEmpty()) {
7390 oop new_oop = _mark_stack->pop();
7391 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7392 // now scan this oop's oops
7393 new_oop->oop_iterate(&_pam_verify_closure);
7394 }
7395 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7396 return true;
7397 }
7398
7399 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7400 CMSCollector* collector, MemRegion span,
7401 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7402 CMSMarkStack* mark_stack):
7403 MetadataAwareOopClosure(collector->ref_processor()),
7404 _collector(collector),
7405 _span(span),
7406 _verification_bm(verification_bm),
7407 _cms_bm(cms_bm),
7408 _mark_stack(mark_stack)
7409 { }
7410
7411 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7412 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7413
7414 // Upon stack overflow, we discard (part of) the stack,
7415 // remembering the least address amongst those discarded
7416 // in CMSCollector's _restart_address.
7417 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7418 // Remember the least grey address discarded
7419 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7420 _collector->lower_restart_addr(ra);
7421 _mark_stack->reset(); // discard stack contents
7422 _mark_stack->expand(); // expand the stack if possible
7423 }
7424
7425 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7426 assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7427 HeapWord* addr = (HeapWord*)obj;
7428 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7429 // Oop lies in _span and isn't yet grey or black
7430 _verification_bm->mark(addr); // now grey
7431 if (!_cms_bm->isMarked(addr)) {
7432 oop(addr)->print();
7433 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7434 addr);
7435 fatal("... aborting");
7436 }
7437
7438 if (!_mark_stack->push(obj)) { // stack overflow
7439 if (PrintCMSStatistics != 0) {
7440 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7441 SIZE_FORMAT, _mark_stack->capacity());
7442 }
7443 assert(_mark_stack->isFull(), "Else push should have succeeded");
7444 handle_stack_overflow(addr);
7445 }
7446 // anything including and to the right of _finger
7447 // will be scanned as we iterate over the remainder of the
7448 // bit map
7449 }
7450 }
7451
7452 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7453 MemRegion span,
7454 CMSBitMap* bitMap, CMSMarkStack* markStack,
7455 HeapWord* finger, MarkFromRootsClosure* parent) :
7456 MetadataAwareOopClosure(collector->ref_processor()),
7457 _collector(collector),
7458 _span(span),
7459 _bitMap(bitMap),
7460 _markStack(markStack),
7461 _finger(finger),
7462 _parent(parent)
7463 { }
7464
7465 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7466 MemRegion span,
7467 CMSBitMap* bit_map,
7468 OopTaskQueue* work_queue,
7469 CMSMarkStack* overflow_stack,
7470 HeapWord* finger,
7471 HeapWord** global_finger_addr,
7472 Par_MarkFromRootsClosure* parent) :
7473 MetadataAwareOopClosure(collector->ref_processor()),
7474 _collector(collector),
7475 _whole_span(collector->_span),
7476 _span(span),
7477 _bit_map(bit_map),
7478 _work_queue(work_queue),
7479 _overflow_stack(overflow_stack),
7480 _finger(finger),
7481 _global_finger_addr(global_finger_addr),
7482 _parent(parent)
7483 { }
7484
7485 // Assumes thread-safe access by callers, who are
7486 // responsible for mutual exclusion.
7487 void CMSCollector::lower_restart_addr(HeapWord* low) {
7488 assert(_span.contains(low), "Out of bounds addr");
7489 if (_restart_addr == NULL) {
7490 _restart_addr = low;
7491 } else {
7492 _restart_addr = MIN2(_restart_addr, low);
7493 }
7494 }
7495
7496 // Upon stack overflow, we discard (part of) the stack,
7497 // remembering the least address amongst those discarded
7498 // in CMSCollector's _restart_address.
7499 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7500 // Remember the least grey address discarded
7501 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7502 _collector->lower_restart_addr(ra);
7503 _markStack->reset(); // discard stack contents
7504 _markStack->expand(); // expand the stack if possible
7505 }
7506
7507 // Upon stack overflow, we discard (part of) the stack,
7508 // remembering the least address amongst those discarded
7509 // in CMSCollector's _restart_address.
7510 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7511 // We need to do this under a mutex to prevent other
7512 // workers from interfering with the work done below.
7513 MutexLockerEx ml(_overflow_stack->par_lock(),
7514 Mutex::_no_safepoint_check_flag);
7515 // Remember the least grey address discarded
7516 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7517 _collector->lower_restart_addr(ra);
7518 _overflow_stack->reset(); // discard stack contents
7519 _overflow_stack->expand(); // expand the stack if possible
7520 }
7521
7522 void PushOrMarkClosure::do_oop(oop obj) {
7523 // Ignore mark word because we are running concurrent with mutators.
7524 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7525 HeapWord* addr = (HeapWord*)obj;
7526 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7527 // Oop lies in _span and isn't yet grey or black
7528 _bitMap->mark(addr); // now grey
7529 if (addr < _finger) {
7530 // the bit map iteration has already either passed, or
7531 // sampled, this bit in the bit map; we'll need to
7532 // use the marking stack to scan this oop's oops.
7533 bool simulate_overflow = false;
7534 NOT_PRODUCT(
7535 if (CMSMarkStackOverflowALot &&
7536 _collector->simulate_overflow()) {
7537 // simulate a stack overflow
7538 simulate_overflow = true;
7539 }
7540 )
7541 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7542 if (PrintCMSStatistics != 0) {
7543 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7544 SIZE_FORMAT, _markStack->capacity());
7545 }
7546 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7547 handle_stack_overflow(addr);
7548 }
7549 }
7550 // anything including and to the right of _finger
7551 // will be scanned as we iterate over the remainder of the
7552 // bit map
7553 do_yield_check();
7554 }
7555 }
7556
7557 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7558 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7559
7560 void Par_PushOrMarkClosure::do_oop(oop obj) {
7561 // Ignore mark word because we are running concurrent with mutators.
7562 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7563 HeapWord* addr = (HeapWord*)obj;
7564 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7565 // Oop lies in _span and isn't yet grey or black
7566 // We read the global_finger (volatile read) strictly after marking oop
7567 bool res = _bit_map->par_mark(addr); // now grey
7568 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7569 // Should we push this marked oop on our stack?
7570 // -- if someone else marked it, nothing to do
7571 // -- if target oop is above global finger nothing to do
7572 // -- if target oop is in chunk and above local finger
7573 // then nothing to do
7574 // -- else push on work queue
7575 if ( !res // someone else marked it, they will deal with it
7576 || (addr >= *gfa) // will be scanned in a later task
7577 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7578 return;
7579 }
7580 // the bit map iteration has already either passed, or
7581 // sampled, this bit in the bit map; we'll need to
7582 // use the marking stack to scan this oop's oops.
7583 bool simulate_overflow = false;
7584 NOT_PRODUCT(
7585 if (CMSMarkStackOverflowALot &&
7586 _collector->simulate_overflow()) {
7587 // simulate a stack overflow
7588 simulate_overflow = true;
7589 }
7590 )
7591 if (simulate_overflow ||
7592 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7593 // stack overflow
7594 if (PrintCMSStatistics != 0) {
7595 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7596 SIZE_FORMAT, _overflow_stack->capacity());
7597 }
7598 // We cannot assert that the overflow stack is full because
7599 // it may have been emptied since.
7600 assert(simulate_overflow ||
7601 _work_queue->size() == _work_queue->max_elems(),
7602 "Else push should have succeeded");
7603 handle_stack_overflow(addr);
7604 }
7605 do_yield_check();
7606 }
7607 }
7608
7609 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7610 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7611
7612 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7613 MemRegion span,
7614 ReferenceProcessor* rp,
7615 CMSBitMap* bit_map,
7616 CMSBitMap* mod_union_table,
7617 CMSMarkStack* mark_stack,
7618 bool concurrent_precleaning):
7619 MetadataAwareOopClosure(rp),
7620 _collector(collector),
7621 _span(span),
7622 _bit_map(bit_map),
7623 _mod_union_table(mod_union_table),
7624 _mark_stack(mark_stack),
7625 _concurrent_precleaning(concurrent_precleaning)
7626 {
7627 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7628 }
7629
7630 // Grey object rescan during pre-cleaning and second checkpoint phases --
7631 // the non-parallel version (the parallel version appears further below.)
7632 void PushAndMarkClosure::do_oop(oop obj) {
7633 // Ignore mark word verification. If during concurrent precleaning,
7634 // the object monitor may be locked. If during the checkpoint
7635 // phases, the object may already have been reached by a different
7636 // path and may be at the end of the global overflow list (so
7637 // the mark word may be NULL).
7638 assert(obj->is_oop_or_null(true /* ignore mark word */),
7639 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7640 HeapWord* addr = (HeapWord*)obj;
7641 // Check if oop points into the CMS generation
7642 // and is not marked
7643 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7644 // a white object ...
7645 _bit_map->mark(addr); // ... now grey
7646 // push on the marking stack (grey set)
7647 bool simulate_overflow = false;
7648 NOT_PRODUCT(
7649 if (CMSMarkStackOverflowALot &&
7650 _collector->simulate_overflow()) {
7651 // simulate a stack overflow
7652 simulate_overflow = true;
7653 }
7654 )
7655 if (simulate_overflow || !_mark_stack->push(obj)) {
7656 if (_concurrent_precleaning) {
7657 // During precleaning we can just dirty the appropriate card(s)
7658 // in the mod union table, thus ensuring that the object remains
7659 // in the grey set and continue. In the case of object arrays
7660 // we need to dirty all of the cards that the object spans,
7661 // since the rescan of object arrays will be limited to the
7662 // dirty cards.
7663 // Note that no one can be interfering with us in this action
7664 // of dirtying the mod union table, so no locking or atomics
7665 // are required.
7666 if (obj->is_objArray()) {
7667 size_t sz = obj->size();
7668 HeapWord* end_card_addr = (HeapWord*)round_to(
7669 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7670 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7671 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7672 _mod_union_table->mark_range(redirty_range);
7673 } else {
7674 _mod_union_table->mark(addr);
7675 }
7676 _collector->_ser_pmc_preclean_ovflw++;
7677 } else {
7678 // During the remark phase, we need to remember this oop
7679 // in the overflow list.
7680 _collector->push_on_overflow_list(obj);
7681 _collector->_ser_pmc_remark_ovflw++;
7682 }
7683 }
7684 }
7685 }
7686
7687 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7688 MemRegion span,
7689 ReferenceProcessor* rp,
7690 CMSBitMap* bit_map,
7691 OopTaskQueue* work_queue):
7692 MetadataAwareOopClosure(rp),
7693 _collector(collector),
7694 _span(span),
7695 _bit_map(bit_map),
7696 _work_queue(work_queue)
7697 {
7698 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7699 }
7700
7701 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7702 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7703
7704 // Grey object rescan during second checkpoint phase --
7705 // the parallel version.
7706 void Par_PushAndMarkClosure::do_oop(oop obj) {
7707 // In the assert below, we ignore the mark word because
7708 // this oop may point to an already visited object that is
7709 // on the overflow stack (in which case the mark word has
7710 // been hijacked for chaining into the overflow stack --
7711 // if this is the last object in the overflow stack then
7712 // its mark word will be NULL). Because this object may
7713 // have been subsequently popped off the global overflow
7714 // stack, and the mark word possibly restored to the prototypical
7715 // value, by the time we get to examined this failing assert in
7716 // the debugger, is_oop_or_null(false) may subsequently start
7717 // to hold.
7718 assert(obj->is_oop_or_null(true),
7719 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7720 HeapWord* addr = (HeapWord*)obj;
7721 // Check if oop points into the CMS generation
7722 // and is not marked
7723 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7724 // a white object ...
7725 // If we manage to "claim" the object, by being the
7726 // first thread to mark it, then we push it on our
7727 // marking stack
7728 if (_bit_map->par_mark(addr)) { // ... now grey
7729 // push on work queue (grey set)
7730 bool simulate_overflow = false;
7731 NOT_PRODUCT(
7732 if (CMSMarkStackOverflowALot &&
7733 _collector->par_simulate_overflow()) {
7734 // simulate a stack overflow
7735 simulate_overflow = true;
7736 }
7737 )
7738 if (simulate_overflow || !_work_queue->push(obj)) {
7739 _collector->par_push_on_overflow_list(obj);
7740 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7741 }
7742 } // Else, some other thread got there first
7743 }
7744 }
7745
7746 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7747 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7748
7749 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7750 Mutex* bml = _collector->bitMapLock();
7751 assert_lock_strong(bml);
7752 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7753 "CMS thread should hold CMS token");
7754
7755 bml->unlock();
7756 ConcurrentMarkSweepThread::desynchronize(true);
7757
7758 _collector->stopTimer();
7759 if (PrintCMSStatistics != 0) {
7760 _collector->incrementYields();
7761 }
7762
7763 // See the comment in coordinator_yield()
7764 for (unsigned i = 0; i < CMSYieldSleepCount &&
7765 ConcurrentMarkSweepThread::should_yield() &&
7766 !CMSCollector::foregroundGCIsActive(); ++i) {
7767 os::sleep(Thread::current(), 1, false);
7768 }
7769
7770 ConcurrentMarkSweepThread::synchronize(true);
7771 bml->lock();
7772
7773 _collector->startTimer();
7774 }
7775
7776 bool CMSPrecleanRefsYieldClosure::should_return() {
7777 if (ConcurrentMarkSweepThread::should_yield()) {
7778 do_yield_work();
7779 }
7780 return _collector->foregroundGCIsActive();
7781 }
7782
7783 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7784 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7785 "mr should be aligned to start at a card boundary");
7786 // We'd like to assert:
7787 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7788 // "mr should be a range of cards");
7789 // However, that would be too strong in one case -- the last
7790 // partition ends at _unallocated_block which, in general, can be
7791 // an arbitrary boundary, not necessarily card aligned.
7792 if (PrintCMSStatistics != 0) {
7793 _num_dirty_cards +=
7794 mr.word_size()/CardTableModRefBS::card_size_in_words;
7795 }
7796 _space->object_iterate_mem(mr, &_scan_cl);
7797 }
7798
7799 SweepClosure::SweepClosure(CMSCollector* collector,
7800 ConcurrentMarkSweepGeneration* g,
7801 CMSBitMap* bitMap, bool should_yield) :
7802 _collector(collector),
7803 _g(g),
7804 _sp(g->cmsSpace()),
7805 _limit(_sp->sweep_limit()),
7806 _freelistLock(_sp->freelistLock()),
7807 _bitMap(bitMap),
7808 _yield(should_yield),
7809 _inFreeRange(false), // No free range at beginning of sweep
7810 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7811 _lastFreeRangeCoalesced(false),
7812 _freeFinger(g->used_region().start())
7813 {
7814 NOT_PRODUCT(
7815 _numObjectsFreed = 0;
7816 _numWordsFreed = 0;
7817 _numObjectsLive = 0;
7818 _numWordsLive = 0;
7819 _numObjectsAlreadyFree = 0;
7820 _numWordsAlreadyFree = 0;
7821 _last_fc = NULL;
7822
7823 _sp->initializeIndexedFreeListArrayReturnedBytes();
7824 _sp->dictionary()->initialize_dict_returned_bytes();
7825 )
7826 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7827 "sweep _limit out of bounds");
7828 if (CMSTraceSweeper) {
7829 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7830 _limit);
7831 }
7832 }
7833
7834 void SweepClosure::print_on(outputStream* st) const {
7835 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7836 _sp->bottom(), _sp->end());
7837 tty->print_cr("_limit = " PTR_FORMAT, _limit);
7838 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
7839 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
7840 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7841 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7842 }
7843
7844 #ifndef PRODUCT
7845 // Assertion checking only: no useful work in product mode --
7846 // however, if any of the flags below become product flags,
7847 // you may need to review this code to see if it needs to be
7848 // enabled in product mode.
7849 SweepClosure::~SweepClosure() {
7850 assert_lock_strong(_freelistLock);
7851 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7852 "sweep _limit out of bounds");
7853 if (inFreeRange()) {
7854 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7855 print();
7856 ShouldNotReachHere();
7857 }
7858 if (Verbose && PrintGC) {
7859 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7860 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7861 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7862 SIZE_FORMAT" bytes "
7863 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7864 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7865 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7866 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7867 * sizeof(HeapWord);
7868 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7869
7870 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7871 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7872 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7873 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7874 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7875 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7876 indexListReturnedBytes);
7877 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7878 dict_returned_bytes);
7879 }
7880 }
7881 if (CMSTraceSweeper) {
7882 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7883 _limit);
7884 }
7885 }
7886 #endif // PRODUCT
7887
7888 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7889 bool freeRangeInFreeLists) {
7890 if (CMSTraceSweeper) {
7891 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7892 freeFinger, freeRangeInFreeLists);
7893 }
7894 assert(!inFreeRange(), "Trampling existing free range");
7895 set_inFreeRange(true);
7896 set_lastFreeRangeCoalesced(false);
7897
7898 set_freeFinger(freeFinger);
7899 set_freeRangeInFreeLists(freeRangeInFreeLists);
7900 if (CMSTestInFreeList) {
7901 if (freeRangeInFreeLists) {
7902 FreeChunk* fc = (FreeChunk*) freeFinger;
7903 assert(fc->is_free(), "A chunk on the free list should be free.");
7904 assert(fc->size() > 0, "Free range should have a size");
7905 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7906 }
7907 }
7908 }
7909
7910 // Note that the sweeper runs concurrently with mutators. Thus,
7911 // it is possible for direct allocation in this generation to happen
7912 // in the middle of the sweep. Note that the sweeper also coalesces
7913 // contiguous free blocks. Thus, unless the sweeper and the allocator
7914 // synchronize appropriately freshly allocated blocks may get swept up.
7915 // This is accomplished by the sweeper locking the free lists while
7916 // it is sweeping. Thus blocks that are determined to be free are
7917 // indeed free. There is however one additional complication:
7918 // blocks that have been allocated since the final checkpoint and
7919 // mark, will not have been marked and so would be treated as
7920 // unreachable and swept up. To prevent this, the allocator marks
7921 // the bit map when allocating during the sweep phase. This leads,
7922 // however, to a further complication -- objects may have been allocated
7923 // but not yet initialized -- in the sense that the header isn't yet
7924 // installed. The sweeper can not then determine the size of the block
7925 // in order to skip over it. To deal with this case, we use a technique
7926 // (due to Printezis) to encode such uninitialized block sizes in the
7927 // bit map. Since the bit map uses a bit per every HeapWord, but the
7928 // CMS generation has a minimum object size of 3 HeapWords, it follows
7929 // that "normal marks" won't be adjacent in the bit map (there will
7930 // always be at least two 0 bits between successive 1 bits). We make use
7931 // of these "unused" bits to represent uninitialized blocks -- the bit
7932 // corresponding to the start of the uninitialized object and the next
7933 // bit are both set. Finally, a 1 bit marks the end of the object that
7934 // started with the two consecutive 1 bits to indicate its potentially
7935 // uninitialized state.
7936
7937 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7938 FreeChunk* fc = (FreeChunk*)addr;
7939 size_t res;
7940
7941 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7942 // than "addr == _limit" because although _limit was a block boundary when
7943 // we started the sweep, it may no longer be one because heap expansion
7944 // may have caused us to coalesce the block ending at the address _limit
7945 // with a newly expanded chunk (this happens when _limit was set to the
7946 // previous _end of the space), so we may have stepped past _limit:
7947 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7948 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7949 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7950 "sweep _limit out of bounds");
7951 assert(addr < _sp->end(), "addr out of bounds");
7952 // Flush any free range we might be holding as a single
7953 // coalesced chunk to the appropriate free list.
7954 if (inFreeRange()) {
7955 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7956 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
7957 flush_cur_free_chunk(freeFinger(),
7958 pointer_delta(addr, freeFinger()));
7959 if (CMSTraceSweeper) {
7960 gclog_or_tty->print("Sweep: last chunk: ");
7961 gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
7962 "[coalesced:%d]\n",
7963 freeFinger(), pointer_delta(addr, freeFinger()),
7964 lastFreeRangeCoalesced() ? 1 : 0);
7965 }
7966 }
7967
7968 // help the iterator loop finish
7969 return pointer_delta(_sp->end(), addr);
7970 }
7971
7972 assert(addr < _limit, "sweep invariant");
7973 // check if we should yield
7974 do_yield_check(addr);
7975 if (fc->is_free()) {
7976 // Chunk that is already free
7977 res = fc->size();
7978 do_already_free_chunk(fc);
7979 debug_only(_sp->verifyFreeLists());
7980 // If we flush the chunk at hand in lookahead_and_flush()
7981 // and it's coalesced with a preceding chunk, then the
7982 // process of "mangling" the payload of the coalesced block
7983 // will cause erasure of the size information from the
7984 // (erstwhile) header of all the coalesced blocks but the
7985 // first, so the first disjunct in the assert will not hold
7986 // in that specific case (in which case the second disjunct
7987 // will hold).
7988 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7989 "Otherwise the size info doesn't change at this step");
7990 NOT_PRODUCT(
7991 _numObjectsAlreadyFree++;
7992 _numWordsAlreadyFree += res;
7993 )
7994 NOT_PRODUCT(_last_fc = fc;)
7995 } else if (!_bitMap->isMarked(addr)) {
7996 // Chunk is fresh garbage
7997 res = do_garbage_chunk(fc);
7998 debug_only(_sp->verifyFreeLists());
7999 NOT_PRODUCT(
8000 _numObjectsFreed++;
8001 _numWordsFreed += res;
8002 )
8003 } else {
8004 // Chunk that is alive.
8005 res = do_live_chunk(fc);
8006 debug_only(_sp->verifyFreeLists());
8007 NOT_PRODUCT(
8008 _numObjectsLive++;
8009 _numWordsLive += res;
8010 )
8011 }
8012 return res;
8013 }
8014
8015 // For the smart allocation, record following
8016 // split deaths - a free chunk is removed from its free list because
8017 // it is being split into two or more chunks.
8018 // split birth - a free chunk is being added to its free list because
8019 // a larger free chunk has been split and resulted in this free chunk.
8020 // coal death - a free chunk is being removed from its free list because
8021 // it is being coalesced into a large free chunk.
8022 // coal birth - a free chunk is being added to its free list because
8023 // it was created when two or more free chunks where coalesced into
8024 // this free chunk.
8025 //
8026 // These statistics are used to determine the desired number of free
8027 // chunks of a given size. The desired number is chosen to be relative
8028 // to the end of a CMS sweep. The desired number at the end of a sweep
8029 // is the
8030 // count-at-end-of-previous-sweep (an amount that was enough)
8031 // - count-at-beginning-of-current-sweep (the excess)
8032 // + split-births (gains in this size during interval)
8033 // - split-deaths (demands on this size during interval)
8034 // where the interval is from the end of one sweep to the end of the
8035 // next.
8036 //
8037 // When sweeping the sweeper maintains an accumulated chunk which is
8038 // the chunk that is made up of chunks that have been coalesced. That
8039 // will be termed the left-hand chunk. A new chunk of garbage that
8040 // is being considered for coalescing will be referred to as the
8041 // right-hand chunk.
8042 //
8043 // When making a decision on whether to coalesce a right-hand chunk with
8044 // the current left-hand chunk, the current count vs. the desired count
8045 // of the left-hand chunk is considered. Also if the right-hand chunk
8046 // is near the large chunk at the end of the heap (see
8047 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8048 // left-hand chunk is coalesced.
8049 //
8050 // When making a decision about whether to split a chunk, the desired count
8051 // vs. the current count of the candidate to be split is also considered.
8052 // If the candidate is underpopulated (currently fewer chunks than desired)
8053 // a chunk of an overpopulated (currently more chunks than desired) size may
8054 // be chosen. The "hint" associated with a free list, if non-null, points
8055 // to a free list which may be overpopulated.
8056 //
8057
8058 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8059 const size_t size = fc->size();
8060 // Chunks that cannot be coalesced are not in the
8061 // free lists.
8062 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8063 assert(_sp->verify_chunk_in_free_list(fc),
8064 "free chunk should be in free lists");
8065 }
8066 // a chunk that is already free, should not have been
8067 // marked in the bit map
8068 HeapWord* const addr = (HeapWord*) fc;
8069 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8070 // Verify that the bit map has no bits marked between
8071 // addr and purported end of this block.
8072 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8073
8074 // Some chunks cannot be coalesced under any circumstances.
8075 // See the definition of cantCoalesce().
8076 if (!fc->cantCoalesce()) {
8077 // This chunk can potentially be coalesced.
8078 if (_sp->adaptive_freelists()) {
8079 // All the work is done in
8080 do_post_free_or_garbage_chunk(fc, size);
8081 } else { // Not adaptive free lists
8082 // this is a free chunk that can potentially be coalesced by the sweeper;
8083 if (!inFreeRange()) {
8084 // if the next chunk is a free block that can't be coalesced
8085 // it doesn't make sense to remove this chunk from the free lists
8086 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8087 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8088 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8089 nextChunk->is_free() && // ... which is free...
8090 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8091 // nothing to do
8092 } else {
8093 // Potentially the start of a new free range:
8094 // Don't eagerly remove it from the free lists.
8095 // No need to remove it if it will just be put
8096 // back again. (Also from a pragmatic point of view
8097 // if it is a free block in a region that is beyond
8098 // any allocated blocks, an assertion will fail)
8099 // Remember the start of a free run.
8100 initialize_free_range(addr, true);
8101 // end - can coalesce with next chunk
8102 }
8103 } else {
8104 // the midst of a free range, we are coalescing
8105 print_free_block_coalesced(fc);
8106 if (CMSTraceSweeper) {
8107 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
8108 }
8109 // remove it from the free lists
8110 _sp->removeFreeChunkFromFreeLists(fc);
8111 set_lastFreeRangeCoalesced(true);
8112 // If the chunk is being coalesced and the current free range is
8113 // in the free lists, remove the current free range so that it
8114 // will be returned to the free lists in its entirety - all
8115 // the coalesced pieces included.
8116 if (freeRangeInFreeLists()) {
8117 FreeChunk* ffc = (FreeChunk*) freeFinger();
8118 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8119 "Size of free range is inconsistent with chunk size.");
8120 if (CMSTestInFreeList) {
8121 assert(_sp->verify_chunk_in_free_list(ffc),
8122 "free range is not in free lists");
8123 }
8124 _sp->removeFreeChunkFromFreeLists(ffc);
8125 set_freeRangeInFreeLists(false);
8126 }
8127 }
8128 }
8129 // Note that if the chunk is not coalescable (the else arm
8130 // below), we unconditionally flush, without needing to do
8131 // a "lookahead," as we do below.
8132 if (inFreeRange()) lookahead_and_flush(fc, size);
8133 } else {
8134 // Code path common to both original and adaptive free lists.
8135
8136 // cant coalesce with previous block; this should be treated
8137 // as the end of a free run if any
8138 if (inFreeRange()) {
8139 // we kicked some butt; time to pick up the garbage
8140 assert(freeFinger() < addr, "freeFinger points too high");
8141 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8142 }
8143 // else, nothing to do, just continue
8144 }
8145 }
8146
8147 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8148 // This is a chunk of garbage. It is not in any free list.
8149 // Add it to a free list or let it possibly be coalesced into
8150 // a larger chunk.
8151 HeapWord* const addr = (HeapWord*) fc;
8152 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8153
8154 if (_sp->adaptive_freelists()) {
8155 // Verify that the bit map has no bits marked between
8156 // addr and purported end of just dead object.
8157 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8158
8159 do_post_free_or_garbage_chunk(fc, size);
8160 } else {
8161 if (!inFreeRange()) {
8162 // start of a new free range
8163 assert(size > 0, "A free range should have a size");
8164 initialize_free_range(addr, false);
8165 } else {
8166 // this will be swept up when we hit the end of the
8167 // free range
8168 if (CMSTraceSweeper) {
8169 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
8170 }
8171 // If the chunk is being coalesced and the current free range is
8172 // in the free lists, remove the current free range so that it
8173 // will be returned to the free lists in its entirety - all
8174 // the coalesced pieces included.
8175 if (freeRangeInFreeLists()) {
8176 FreeChunk* ffc = (FreeChunk*)freeFinger();
8177 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8178 "Size of free range is inconsistent with chunk size.");
8179 if (CMSTestInFreeList) {
8180 assert(_sp->verify_chunk_in_free_list(ffc),
8181 "free range is not in free lists");
8182 }
8183 _sp->removeFreeChunkFromFreeLists(ffc);
8184 set_freeRangeInFreeLists(false);
8185 }
8186 set_lastFreeRangeCoalesced(true);
8187 }
8188 // this will be swept up when we hit the end of the free range
8189
8190 // Verify that the bit map has no bits marked between
8191 // addr and purported end of just dead object.
8192 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8193 }
8194 assert(_limit >= addr + size,
8195 "A freshly garbage chunk can't possibly straddle over _limit");
8196 if (inFreeRange()) lookahead_and_flush(fc, size);
8197 return size;
8198 }
8199
8200 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8201 HeapWord* addr = (HeapWord*) fc;
8202 // The sweeper has just found a live object. Return any accumulated
8203 // left hand chunk to the free lists.
8204 if (inFreeRange()) {
8205 assert(freeFinger() < addr, "freeFinger points too high");
8206 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8207 }
8208
8209 // This object is live: we'd normally expect this to be
8210 // an oop, and like to assert the following:
8211 // assert(oop(addr)->is_oop(), "live block should be an oop");
8212 // However, as we commented above, this may be an object whose
8213 // header hasn't yet been initialized.
8214 size_t size;
8215 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8216 if (_bitMap->isMarked(addr + 1)) {
8217 // Determine the size from the bit map, rather than trying to
8218 // compute it from the object header.
8219 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8220 size = pointer_delta(nextOneAddr + 1, addr);
8221 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8222 "alignment problem");
8223
8224 #ifdef ASSERT
8225 if (oop(addr)->klass_or_null() != NULL) {
8226 // Ignore mark word because we are running concurrent with mutators
8227 assert(oop(addr)->is_oop(true), "live block should be an oop");
8228 assert(size ==
8229 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8230 "P-mark and computed size do not agree");
8231 }
8232 #endif
8233
8234 } else {
8235 // This should be an initialized object that's alive.
8236 assert(oop(addr)->klass_or_null() != NULL,
8237 "Should be an initialized object");
8238 // Ignore mark word because we are running concurrent with mutators
8239 assert(oop(addr)->is_oop(true), "live block should be an oop");
8240 // Verify that the bit map has no bits marked between
8241 // addr and purported end of this block.
8242 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8243 assert(size >= 3, "Necessary for Printezis marks to work");
8244 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8245 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8246 }
8247 return size;
8248 }
8249
8250 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8251 size_t chunkSize) {
8252 // do_post_free_or_garbage_chunk() should only be called in the case
8253 // of the adaptive free list allocator.
8254 const bool fcInFreeLists = fc->is_free();
8255 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8256 assert((HeapWord*)fc <= _limit, "sweep invariant");
8257 if (CMSTestInFreeList && fcInFreeLists) {
8258 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8259 }
8260
8261 if (CMSTraceSweeper) {
8262 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", fc, chunkSize);
8263 }
8264
8265 HeapWord* const fc_addr = (HeapWord*) fc;
8266
8267 bool coalesce;
8268 const size_t left = pointer_delta(fc_addr, freeFinger());
8269 const size_t right = chunkSize;
8270 switch (FLSCoalescePolicy) {
8271 // numeric value forms a coalition aggressiveness metric
8272 case 0: { // never coalesce
8273 coalesce = false;
8274 break;
8275 }
8276 case 1: { // coalesce if left & right chunks on overpopulated lists
8277 coalesce = _sp->coalOverPopulated(left) &&
8278 _sp->coalOverPopulated(right);
8279 break;
8280 }
8281 case 2: { // coalesce if left chunk on overpopulated list (default)
8282 coalesce = _sp->coalOverPopulated(left);
8283 break;
8284 }
8285 case 3: { // coalesce if left OR right chunk on overpopulated list
8286 coalesce = _sp->coalOverPopulated(left) ||
8287 _sp->coalOverPopulated(right);
8288 break;
8289 }
8290 case 4: { // always coalesce
8291 coalesce = true;
8292 break;
8293 }
8294 default:
8295 ShouldNotReachHere();
8296 }
8297
8298 // Should the current free range be coalesced?
8299 // If the chunk is in a free range and either we decided to coalesce above
8300 // or the chunk is near the large block at the end of the heap
8301 // (isNearLargestChunk() returns true), then coalesce this chunk.
8302 const bool doCoalesce = inFreeRange()
8303 && (coalesce || _g->isNearLargestChunk(fc_addr));
8304 if (doCoalesce) {
8305 // Coalesce the current free range on the left with the new
8306 // chunk on the right. If either is on a free list,
8307 // it must be removed from the list and stashed in the closure.
8308 if (freeRangeInFreeLists()) {
8309 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8310 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8311 "Size of free range is inconsistent with chunk size.");
8312 if (CMSTestInFreeList) {
8313 assert(_sp->verify_chunk_in_free_list(ffc),
8314 "Chunk is not in free lists");
8315 }
8316 _sp->coalDeath(ffc->size());
8317 _sp->removeFreeChunkFromFreeLists(ffc);
8318 set_freeRangeInFreeLists(false);
8319 }
8320 if (fcInFreeLists) {
8321 _sp->coalDeath(chunkSize);
8322 assert(fc->size() == chunkSize,
8323 "The chunk has the wrong size or is not in the free lists");
8324 _sp->removeFreeChunkFromFreeLists(fc);
8325 }
8326 set_lastFreeRangeCoalesced(true);
8327 print_free_block_coalesced(fc);
8328 } else { // not in a free range and/or should not coalesce
8329 // Return the current free range and start a new one.
8330 if (inFreeRange()) {
8331 // In a free range but cannot coalesce with the right hand chunk.
8332 // Put the current free range into the free lists.
8333 flush_cur_free_chunk(freeFinger(),
8334 pointer_delta(fc_addr, freeFinger()));
8335 }
8336 // Set up for new free range. Pass along whether the right hand
8337 // chunk is in the free lists.
8338 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8339 }
8340 }
8341
8342 // Lookahead flush:
8343 // If we are tracking a free range, and this is the last chunk that
8344 // we'll look at because its end crosses past _limit, we'll preemptively
8345 // flush it along with any free range we may be holding on to. Note that
8346 // this can be the case only for an already free or freshly garbage
8347 // chunk. If this block is an object, it can never straddle
8348 // over _limit. The "straddling" occurs when _limit is set at
8349 // the previous end of the space when this cycle started, and
8350 // a subsequent heap expansion caused the previously co-terminal
8351 // free block to be coalesced with the newly expanded portion,
8352 // thus rendering _limit a non-block-boundary making it dangerous
8353 // for the sweeper to step over and examine.
8354 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8355 assert(inFreeRange(), "Should only be called if currently in a free range.");
8356 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8357 assert(_sp->used_region().contains(eob - 1),
8358 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
8359 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8360 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8361 eob, eob-1, _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8362 if (eob >= _limit) {
8363 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8364 if (CMSTraceSweeper) {
8365 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8366 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8367 "[" PTR_FORMAT "," PTR_FORMAT ")",
8368 _limit, fc, eob, _sp->bottom(), _sp->end());
8369 }
8370 // Return the storage we are tracking back into the free lists.
8371 if (CMSTraceSweeper) {
8372 gclog_or_tty->print_cr("Flushing ... ");
8373 }
8374 assert(freeFinger() < eob, "Error");
8375 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8376 }
8377 }
8378
8379 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8380 assert(inFreeRange(), "Should only be called if currently in a free range.");
8381 assert(size > 0,
8382 "A zero sized chunk cannot be added to the free lists.");
8383 if (!freeRangeInFreeLists()) {
8384 if (CMSTestInFreeList) {
8385 FreeChunk* fc = (FreeChunk*) chunk;
8386 fc->set_size(size);
8387 assert(!_sp->verify_chunk_in_free_list(fc),
8388 "chunk should not be in free lists yet");
8389 }
8390 if (CMSTraceSweeper) {
8391 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
8392 chunk, size);
8393 }
8394 // A new free range is going to be starting. The current
8395 // free range has not been added to the free lists yet or
8396 // was removed so add it back.
8397 // If the current free range was coalesced, then the death
8398 // of the free range was recorded. Record a birth now.
8399 if (lastFreeRangeCoalesced()) {
8400 _sp->coalBirth(size);
8401 }
8402 _sp->addChunkAndRepairOffsetTable(chunk, size,
8403 lastFreeRangeCoalesced());
8404 } else if (CMSTraceSweeper) {
8405 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8406 }
8407 set_inFreeRange(false);
8408 set_freeRangeInFreeLists(false);
8409 }
8410
8411 // We take a break if we've been at this for a while,
8412 // so as to avoid monopolizing the locks involved.
8413 void SweepClosure::do_yield_work(HeapWord* addr) {
8414 // Return current free chunk being used for coalescing (if any)
8415 // to the appropriate freelist. After yielding, the next
8416 // free block encountered will start a coalescing range of
8417 // free blocks. If the next free block is adjacent to the
8418 // chunk just flushed, they will need to wait for the next
8419 // sweep to be coalesced.
8420 if (inFreeRange()) {
8421 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8422 }
8423
8424 // First give up the locks, then yield, then re-lock.
8425 // We should probably use a constructor/destructor idiom to
8426 // do this unlock/lock or modify the MutexUnlocker class to
8427 // serve our purpose. XXX
8428 assert_lock_strong(_bitMap->lock());
8429 assert_lock_strong(_freelistLock);
8430 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8431 "CMS thread should hold CMS token");
8432 _bitMap->lock()->unlock();
8433 _freelistLock->unlock();
8434 ConcurrentMarkSweepThread::desynchronize(true);
8435 _collector->stopTimer();
8436 if (PrintCMSStatistics != 0) {
8437 _collector->incrementYields();
8438 }
8439
8440 // See the comment in coordinator_yield()
8441 for (unsigned i = 0; i < CMSYieldSleepCount &&
8442 ConcurrentMarkSweepThread::should_yield() &&
8443 !CMSCollector::foregroundGCIsActive(); ++i) {
8444 os::sleep(Thread::current(), 1, false);
8445 }
8446
8447 ConcurrentMarkSweepThread::synchronize(true);
8448 _freelistLock->lock();
8449 _bitMap->lock()->lock_without_safepoint_check();
8450 _collector->startTimer();
8451 }
8452
8453 #ifndef PRODUCT
8454 // This is actually very useful in a product build if it can
8455 // be called from the debugger. Compile it into the product
8456 // as needed.
8457 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8458 return debug_cms_space->verify_chunk_in_free_list(fc);
8459 }
8460 #endif
8461
8462 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8463 if (CMSTraceSweeper) {
8464 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8465 fc, fc->size());
8466 }
8467 }
8468
8469 // CMSIsAliveClosure
8470 bool CMSIsAliveClosure::do_object_b(oop obj) {
8471 HeapWord* addr = (HeapWord*)obj;
8472 return addr != NULL &&
8473 (!_span.contains(addr) || _bit_map->isMarked(addr));
8474 }
8475
8476
8477 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8478 MemRegion span,
8479 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8480 bool cpc):
8481 _collector(collector),
8482 _span(span),
8483 _bit_map(bit_map),
8484 _mark_stack(mark_stack),
8485 _concurrent_precleaning(cpc) {
8486 assert(!_span.is_empty(), "Empty span could spell trouble");
8487 }
8488
8489
8490 // CMSKeepAliveClosure: the serial version
8491 void CMSKeepAliveClosure::do_oop(oop obj) {
8492 HeapWord* addr = (HeapWord*)obj;
8493 if (_span.contains(addr) &&
8494 !_bit_map->isMarked(addr)) {
8495 _bit_map->mark(addr);
8496 bool simulate_overflow = false;
8497 NOT_PRODUCT(
8498 if (CMSMarkStackOverflowALot &&
8499 _collector->simulate_overflow()) {
8500 // simulate a stack overflow
8501 simulate_overflow = true;
8502 }
8503 )
8504 if (simulate_overflow || !_mark_stack->push(obj)) {
8505 if (_concurrent_precleaning) {
8506 // We dirty the overflown object and let the remark
8507 // phase deal with it.
8508 assert(_collector->overflow_list_is_empty(), "Error");
8509 // In the case of object arrays, we need to dirty all of
8510 // the cards that the object spans. No locking or atomics
8511 // are needed since no one else can be mutating the mod union
8512 // table.
8513 if (obj->is_objArray()) {
8514 size_t sz = obj->size();
8515 HeapWord* end_card_addr =
8516 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8517 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8518 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8519 _collector->_modUnionTable.mark_range(redirty_range);
8520 } else {
8521 _collector->_modUnionTable.mark(addr);
8522 }
8523 _collector->_ser_kac_preclean_ovflw++;
8524 } else {
8525 _collector->push_on_overflow_list(obj);
8526 _collector->_ser_kac_ovflw++;
8527 }
8528 }
8529 }
8530 }
8531
8532 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8533 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8534
8535 // CMSParKeepAliveClosure: a parallel version of the above.
8536 // The work queues are private to each closure (thread),
8537 // but (may be) available for stealing by other threads.
8538 void CMSParKeepAliveClosure::do_oop(oop obj) {
8539 HeapWord* addr = (HeapWord*)obj;
8540 if (_span.contains(addr) &&
8541 !_bit_map->isMarked(addr)) {
8542 // In general, during recursive tracing, several threads
8543 // may be concurrently getting here; the first one to
8544 // "tag" it, claims it.
8545 if (_bit_map->par_mark(addr)) {
8546 bool res = _work_queue->push(obj);
8547 assert(res, "Low water mark should be much less than capacity");
8548 // Do a recursive trim in the hope that this will keep
8549 // stack usage lower, but leave some oops for potential stealers
8550 trim_queue(_low_water_mark);
8551 } // Else, another thread got there first
8552 }
8553 }
8554
8555 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8556 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8557
8558 void CMSParKeepAliveClosure::trim_queue(uint max) {
8559 while (_work_queue->size() > max) {
8560 oop new_oop;
8561 if (_work_queue->pop_local(new_oop)) {
8562 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8563 assert(_bit_map->isMarked((HeapWord*)new_oop),
8564 "no white objects on this stack!");
8565 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8566 // iterate over the oops in this oop, marking and pushing
8567 // the ones in CMS heap (i.e. in _span).
8568 new_oop->oop_iterate(&_mark_and_push);
8569 }
8570 }
8571 }
8572
8573 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8574 CMSCollector* collector,
8575 MemRegion span, CMSBitMap* bit_map,
8576 OopTaskQueue* work_queue):
8577 _collector(collector),
8578 _span(span),
8579 _bit_map(bit_map),
8580 _work_queue(work_queue) { }
8581
8582 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8583 HeapWord* addr = (HeapWord*)obj;
8584 if (_span.contains(addr) &&
8585 !_bit_map->isMarked(addr)) {
8586 if (_bit_map->par_mark(addr)) {
8587 bool simulate_overflow = false;
8588 NOT_PRODUCT(
8589 if (CMSMarkStackOverflowALot &&
8590 _collector->par_simulate_overflow()) {
8591 // simulate a stack overflow
8592 simulate_overflow = true;
8593 }
8594 )
8595 if (simulate_overflow || !_work_queue->push(obj)) {
8596 _collector->par_push_on_overflow_list(obj);
8597 _collector->_par_kac_ovflw++;
8598 }
8599 } // Else another thread got there already
8600 }
8601 }
8602
8603 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8604 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8605
8606 //////////////////////////////////////////////////////////////////
8607 // CMSExpansionCause /////////////////////////////
8608 //////////////////////////////////////////////////////////////////
8609 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8610 switch (cause) {
8611 case _no_expansion:
8612 return "No expansion";
8613 case _satisfy_free_ratio:
8614 return "Free ratio";
8615 case _satisfy_promotion:
8616 return "Satisfy promotion";
8617 case _satisfy_allocation:
8618 return "allocation";
8619 case _allocate_par_lab:
8620 return "Par LAB";
8621 case _allocate_par_spooling_space:
8622 return "Par Spooling Space";
8623 case _adaptive_size_policy:
8624 return "Ergonomics";
8625 default:
8626 return "unknown";
8627 }
8628 }
8629
8630 void CMSDrainMarkingStackClosure::do_void() {
8631 // the max number to take from overflow list at a time
8632 const size_t num = _mark_stack->capacity()/4;
8633 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8634 "Overflow list should be NULL during concurrent phases");
8635 while (!_mark_stack->isEmpty() ||
8636 // if stack is empty, check the overflow list
8637 _collector->take_from_overflow_list(num, _mark_stack)) {
8638 oop obj = _mark_stack->pop();
8639 HeapWord* addr = (HeapWord*)obj;
8640 assert(_span.contains(addr), "Should be within span");
8641 assert(_bit_map->isMarked(addr), "Should be marked");
8642 assert(obj->is_oop(), "Should be an oop");
8643 obj->oop_iterate(_keep_alive);
8644 }
8645 }
8646
8647 void CMSParDrainMarkingStackClosure::do_void() {
8648 // drain queue
8649 trim_queue(0);
8650 }
8651
8652 // Trim our work_queue so its length is below max at return
8653 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8654 while (_work_queue->size() > max) {
8655 oop new_oop;
8656 if (_work_queue->pop_local(new_oop)) {
8657 assert(new_oop->is_oop(), "Expected an oop");
8658 assert(_bit_map->isMarked((HeapWord*)new_oop),
8659 "no white objects on this stack!");
8660 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8661 // iterate over the oops in this oop, marking and pushing
8662 // the ones in CMS heap (i.e. in _span).
8663 new_oop->oop_iterate(&_mark_and_push);
8664 }
8665 }
8666 }
8667
8668 ////////////////////////////////////////////////////////////////////
8669 // Support for Marking Stack Overflow list handling and related code
8670 ////////////////////////////////////////////////////////////////////
8671 // Much of the following code is similar in shape and spirit to the
8672 // code used in ParNewGC. We should try and share that code
8673 // as much as possible in the future.
8674
8675 #ifndef PRODUCT
8676 // Debugging support for CMSStackOverflowALot
8677
8678 // It's OK to call this multi-threaded; the worst thing
8679 // that can happen is that we'll get a bunch of closely
8680 // spaced simulated overflows, but that's OK, in fact
8681 // probably good as it would exercise the overflow code
8682 // under contention.
8683 bool CMSCollector::simulate_overflow() {
8684 if (_overflow_counter-- <= 0) { // just being defensive
8685 _overflow_counter = CMSMarkStackOverflowInterval;
8686 return true;
8687 } else {
8688 return false;
8689 }
8690 }
8691
8692 bool CMSCollector::par_simulate_overflow() {
8693 return simulate_overflow();
8694 }
8695 #endif
8696
8697 // Single-threaded
8698 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8699 assert(stack->isEmpty(), "Expected precondition");
8700 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8701 size_t i = num;
8702 oop cur = _overflow_list;
8703 const markOop proto = markOopDesc::prototype();
8704 NOT_PRODUCT(ssize_t n = 0;)
8705 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8706 next = oop(cur->mark());
8707 cur->set_mark(proto); // until proven otherwise
8708 assert(cur->is_oop(), "Should be an oop");
8709 bool res = stack->push(cur);
8710 assert(res, "Bit off more than can chew?");
8711 NOT_PRODUCT(n++;)
8712 }
8713 _overflow_list = cur;
8714 #ifndef PRODUCT
8715 assert(_num_par_pushes >= n, "Too many pops?");
8716 _num_par_pushes -=n;
8717 #endif
8718 return !stack->isEmpty();
8719 }
8720
8721 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8722 // (MT-safe) Get a prefix of at most "num" from the list.
8723 // The overflow list is chained through the mark word of
8724 // each object in the list. We fetch the entire list,
8725 // break off a prefix of the right size and return the
8726 // remainder. If other threads try to take objects from
8727 // the overflow list at that time, they will wait for
8728 // some time to see if data becomes available. If (and
8729 // only if) another thread places one or more object(s)
8730 // on the global list before we have returned the suffix
8731 // to the global list, we will walk down our local list
8732 // to find its end and append the global list to
8733 // our suffix before returning it. This suffix walk can
8734 // prove to be expensive (quadratic in the amount of traffic)
8735 // when there are many objects in the overflow list and
8736 // there is much producer-consumer contention on the list.
8737 // *NOTE*: The overflow list manipulation code here and
8738 // in ParNewGeneration:: are very similar in shape,
8739 // except that in the ParNew case we use the old (from/eden)
8740 // copy of the object to thread the list via its klass word.
8741 // Because of the common code, if you make any changes in
8742 // the code below, please check the ParNew version to see if
8743 // similar changes might be needed.
8744 // CR 6797058 has been filed to consolidate the common code.
8745 bool CMSCollector::par_take_from_overflow_list(size_t num,
8746 OopTaskQueue* work_q,
8747 int no_of_gc_threads) {
8748 assert(work_q->size() == 0, "First empty local work queue");
8749 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8750 if (_overflow_list == NULL) {
8751 return false;
8752 }
8753 // Grab the entire list; we'll put back a suffix
8754 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8755 Thread* tid = Thread::current();
8756 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8757 // set to ParallelGCThreads.
8758 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8759 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8760 // If the list is busy, we spin for a short while,
8761 // sleeping between attempts to get the list.
8762 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8763 os::sleep(tid, sleep_time_millis, false);
8764 if (_overflow_list == NULL) {
8765 // Nothing left to take
8766 return false;
8767 } else if (_overflow_list != BUSY) {
8768 // Try and grab the prefix
8769 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8770 }
8771 }
8772 // If the list was found to be empty, or we spun long
8773 // enough, we give up and return empty-handed. If we leave
8774 // the list in the BUSY state below, it must be the case that
8775 // some other thread holds the overflow list and will set it
8776 // to a non-BUSY state in the future.
8777 if (prefix == NULL || prefix == BUSY) {
8778 // Nothing to take or waited long enough
8779 if (prefix == NULL) {
8780 // Write back the NULL in case we overwrote it with BUSY above
8781 // and it is still the same value.
8782 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8783 }
8784 return false;
8785 }
8786 assert(prefix != NULL && prefix != BUSY, "Error");
8787 size_t i = num;
8788 oop cur = prefix;
8789 // Walk down the first "num" objects, unless we reach the end.
8790 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8791 if (cur->mark() == NULL) {
8792 // We have "num" or fewer elements in the list, so there
8793 // is nothing to return to the global list.
8794 // Write back the NULL in lieu of the BUSY we wrote
8795 // above, if it is still the same value.
8796 if (_overflow_list == BUSY) {
8797 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8798 }
8799 } else {
8800 // Chop off the suffix and return it to the global list.
8801 assert(cur->mark() != BUSY, "Error");
8802 oop suffix_head = cur->mark(); // suffix will be put back on global list
8803 cur->set_mark(NULL); // break off suffix
8804 // It's possible that the list is still in the empty(busy) state
8805 // we left it in a short while ago; in that case we may be
8806 // able to place back the suffix without incurring the cost
8807 // of a walk down the list.
8808 oop observed_overflow_list = _overflow_list;
8809 oop cur_overflow_list = observed_overflow_list;
8810 bool attached = false;
8811 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8812 observed_overflow_list =
8813 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8814 if (cur_overflow_list == observed_overflow_list) {
8815 attached = true;
8816 break;
8817 } else cur_overflow_list = observed_overflow_list;
8818 }
8819 if (!attached) {
8820 // Too bad, someone else sneaked in (at least) an element; we'll need
8821 // to do a splice. Find tail of suffix so we can prepend suffix to global
8822 // list.
8823 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8824 oop suffix_tail = cur;
8825 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8826 "Tautology");
8827 observed_overflow_list = _overflow_list;
8828 do {
8829 cur_overflow_list = observed_overflow_list;
8830 if (cur_overflow_list != BUSY) {
8831 // Do the splice ...
8832 suffix_tail->set_mark(markOop(cur_overflow_list));
8833 } else { // cur_overflow_list == BUSY
8834 suffix_tail->set_mark(NULL);
8835 }
8836 // ... and try to place spliced list back on overflow_list ...
8837 observed_overflow_list =
8838 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8839 } while (cur_overflow_list != observed_overflow_list);
8840 // ... until we have succeeded in doing so.
8841 }
8842 }
8843
8844 // Push the prefix elements on work_q
8845 assert(prefix != NULL, "control point invariant");
8846 const markOop proto = markOopDesc::prototype();
8847 oop next;
8848 NOT_PRODUCT(ssize_t n = 0;)
8849 for (cur = prefix; cur != NULL; cur = next) {
8850 next = oop(cur->mark());
8851 cur->set_mark(proto); // until proven otherwise
8852 assert(cur->is_oop(), "Should be an oop");
8853 bool res = work_q->push(cur);
8854 assert(res, "Bit off more than we can chew?");
8855 NOT_PRODUCT(n++;)
8856 }
8857 #ifndef PRODUCT
8858 assert(_num_par_pushes >= n, "Too many pops?");
8859 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8860 #endif
8861 return true;
8862 }
8863
8864 // Single-threaded
8865 void CMSCollector::push_on_overflow_list(oop p) {
8866 NOT_PRODUCT(_num_par_pushes++;)
8867 assert(p->is_oop(), "Not an oop");
8868 preserve_mark_if_necessary(p);
8869 p->set_mark((markOop)_overflow_list);
8870 _overflow_list = p;
8871 }
8872
8873 // Multi-threaded; use CAS to prepend to overflow list
8874 void CMSCollector::par_push_on_overflow_list(oop p) {
8875 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8876 assert(p->is_oop(), "Not an oop");
8877 par_preserve_mark_if_necessary(p);
8878 oop observed_overflow_list = _overflow_list;
8879 oop cur_overflow_list;
8880 do {
8881 cur_overflow_list = observed_overflow_list;
8882 if (cur_overflow_list != BUSY) {
8883 p->set_mark(markOop(cur_overflow_list));
8884 } else {
8885 p->set_mark(NULL);
8886 }
8887 observed_overflow_list =
8888 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8889 } while (cur_overflow_list != observed_overflow_list);
8890 }
8891 #undef BUSY
8892
8893 // Single threaded
8894 // General Note on GrowableArray: pushes may silently fail
8895 // because we are (temporarily) out of C-heap for expanding
8896 // the stack. The problem is quite ubiquitous and affects
8897 // a lot of code in the JVM. The prudent thing for GrowableArray
8898 // to do (for now) is to exit with an error. However, that may
8899 // be too draconian in some cases because the caller may be
8900 // able to recover without much harm. For such cases, we
8901 // should probably introduce a "soft_push" method which returns
8902 // an indication of success or failure with the assumption that
8903 // the caller may be able to recover from a failure; code in
8904 // the VM can then be changed, incrementally, to deal with such
8905 // failures where possible, thus, incrementally hardening the VM
8906 // in such low resource situations.
8907 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8908 _preserved_oop_stack.push(p);
8909 _preserved_mark_stack.push(m);
8910 assert(m == p->mark(), "Mark word changed");
8911 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8912 "bijection");
8913 }
8914
8915 // Single threaded
8916 void CMSCollector::preserve_mark_if_necessary(oop p) {
8917 markOop m = p->mark();
8918 if (m->must_be_preserved(p)) {
8919 preserve_mark_work(p, m);
8920 }
8921 }
8922
8923 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8924 markOop m = p->mark();
8925 if (m->must_be_preserved(p)) {
8926 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8927 // Even though we read the mark word without holding
8928 // the lock, we are assured that it will not change
8929 // because we "own" this oop, so no other thread can
8930 // be trying to push it on the overflow list; see
8931 // the assertion in preserve_mark_work() that checks
8932 // that m == p->mark().
8933 preserve_mark_work(p, m);
8934 }
8935 }
8936
8937 // We should be able to do this multi-threaded,
8938 // a chunk of stack being a task (this is
8939 // correct because each oop only ever appears
8940 // once in the overflow list. However, it's
8941 // not very easy to completely overlap this with
8942 // other operations, so will generally not be done
8943 // until all work's been completed. Because we
8944 // expect the preserved oop stack (set) to be small,
8945 // it's probably fine to do this single-threaded.
8946 // We can explore cleverer concurrent/overlapped/parallel
8947 // processing of preserved marks if we feel the
8948 // need for this in the future. Stack overflow should
8949 // be so rare in practice and, when it happens, its
8950 // effect on performance so great that this will
8951 // likely just be in the noise anyway.
8952 void CMSCollector::restore_preserved_marks_if_any() {
8953 assert(SafepointSynchronize::is_at_safepoint(),
8954 "world should be stopped");
8955 assert(Thread::current()->is_ConcurrentGC_thread() ||
8956 Thread::current()->is_VM_thread(),
8957 "should be single-threaded");
8958 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8959 "bijection");
8960
8961 while (!_preserved_oop_stack.is_empty()) {
8962 oop p = _preserved_oop_stack.pop();
8963 assert(p->is_oop(), "Should be an oop");
8964 assert(_span.contains(p), "oop should be in _span");
8965 assert(p->mark() == markOopDesc::prototype(),
8966 "Set when taken from overflow list");
8967 markOop m = _preserved_mark_stack.pop();
8968 p->set_mark(m);
8969 }
8970 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8971 "stacks were cleared above");
8972 }
8973
8974 #ifndef PRODUCT
8975 bool CMSCollector::no_preserved_marks() const {
8976 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8977 }
8978 #endif
8979
8980 // Transfer some number of overflown objects to usual marking
8981 // stack. Return true if some objects were transferred.
8982 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8983 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8984 (size_t)ParGCDesiredObjsFromOverflowList);
8985
8986 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8987 assert(_collector->overflow_list_is_empty() || res,
8988 "If list is not empty, we should have taken something");
8989 assert(!res || !_mark_stack->isEmpty(),
8990 "If we took something, it should now be on our stack");
8991 return res;
8992 }
8993
8994 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8995 size_t res = _sp->block_size_no_stall(addr, _collector);
8996 if (_sp->block_is_obj(addr)) {
8997 if (_live_bit_map->isMarked(addr)) {
8998 // It can't have been dead in a previous cycle
8999 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9000 } else {
9001 _dead_bit_map->mark(addr); // mark the dead object
9002 }
9003 }
9004 // Could be 0, if the block size could not be computed without stalling.
9005 return res;
9006 }
9007
9008 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9009
9010 switch (phase) {
9011 case CMSCollector::InitialMarking:
9012 initialize(true /* fullGC */ ,
9013 cause /* cause of the GC */,
9014 true /* recordGCBeginTime */,
9015 true /* recordPreGCUsage */,
9016 false /* recordPeakUsage */,
9017 false /* recordPostGCusage */,
9018 true /* recordAccumulatedGCTime */,
9019 false /* recordGCEndTime */,
9020 false /* countCollection */ );
9021 break;
9022
9023 case CMSCollector::FinalMarking:
9024 initialize(true /* fullGC */ ,
9025 cause /* cause of the GC */,
9026 false /* recordGCBeginTime */,
9027 false /* recordPreGCUsage */,
9028 false /* recordPeakUsage */,
9029 false /* recordPostGCusage */,
9030 true /* recordAccumulatedGCTime */,
9031 false /* recordGCEndTime */,
9032 false /* countCollection */ );
9033 break;
9034
9035 case CMSCollector::Sweeping:
9036 initialize(true /* fullGC */ ,
9037 cause /* cause of the GC */,
9038 false /* recordGCBeginTime */,
9039 false /* recordPreGCUsage */,
9040 true /* recordPeakUsage */,
9041 true /* recordPostGCusage */,
9042 false /* recordAccumulatedGCTime */,
9043 true /* recordGCEndTime */,
9044 true /* countCollection */ );
9045 break;
9046
9047 default:
9048 ShouldNotReachHere();
9049 }
9050 }