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