1 /*
2 * Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc_implementation/shared/adaptiveSizePolicy.hpp"
31 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
32 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
33 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
34 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
36 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
37 #include "gc_implementation/parNew/parNewGeneration.hpp"
38 #include "gc_implementation/shared/collectorCounters.hpp"
39 #include "gc_implementation/shared/gcTimer.hpp"
40 #include "gc_implementation/shared/gcTrace.hpp"
41 #include "gc_implementation/shared/gcTraceTime.hpp"
42 #include "gc_implementation/shared/isGCActiveMark.hpp"
43 #include "gc_interface/collectedHeap.inline.hpp"
44 #include "memory/allocation.hpp"
45 #include "memory/cardTableRS.hpp"
46 #include "memory/collectorPolicy.hpp"
47 #include "memory/gcLocker.inline.hpp"
48 #include "memory/genCollectedHeap.hpp"
49 #include "memory/genMarkSweep.hpp"
50 #include "memory/genOopClosures.inline.hpp"
51 #include "memory/iterator.inline.hpp"
52 #include "memory/padded.hpp"
53 #include "memory/referencePolicy.hpp"
54 #include "memory/resourceArea.hpp"
55 #include "memory/tenuredGeneration.hpp"
56 #include "oops/oop.inline.hpp"
57 #include "prims/jvmtiExport.hpp"
58 #include "runtime/atomic.inline.hpp"
59 #include "runtime/globals_extension.hpp"
60 #include "runtime/handles.inline.hpp"
61 #include "runtime/java.hpp"
62 #include "runtime/orderAccess.inline.hpp"
63 #include "runtime/vmThread.hpp"
64 #include "services/memoryService.hpp"
65 #include "services/runtimeService.hpp"
66
67 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
68
69 // statics
70 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
71 bool CMSCollector::_full_gc_requested = false;
72 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
73
74 //////////////////////////////////////////////////////////////////
75 // In support of CMS/VM thread synchronization
76 //////////////////////////////////////////////////////////////////
77 // We split use of the CGC_lock into 2 "levels".
78 // The low-level locking is of the usual CGC_lock monitor. We introduce
79 // a higher level "token" (hereafter "CMS token") built on top of the
80 // low level monitor (hereafter "CGC lock").
81 // The token-passing protocol gives priority to the VM thread. The
82 // CMS-lock doesn't provide any fairness guarantees, but clients
83 // should ensure that it is only held for very short, bounded
84 // durations.
85 //
86 // When either of the CMS thread or the VM thread is involved in
87 // collection operations during which it does not want the other
88 // thread to interfere, it obtains the CMS token.
89 //
90 // If either thread tries to get the token while the other has
91 // it, that thread waits. However, if the VM thread and CMS thread
92 // both want the token, then the VM thread gets priority while the
93 // CMS thread waits. This ensures, for instance, that the "concurrent"
94 // phases of the CMS thread's work do not block out the VM thread
95 // for long periods of time as the CMS thread continues to hog
96 // the token. (See bug 4616232).
97 //
98 // The baton-passing functions are, however, controlled by the
99 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
100 // and here the low-level CMS lock, not the high level token,
101 // ensures mutual exclusion.
102 //
103 // Two important conditions that we have to satisfy:
104 // 1. if a thread does a low-level wait on the CMS lock, then it
105 // relinquishes the CMS token if it were holding that token
106 // when it acquired the low-level CMS lock.
107 // 2. any low-level notifications on the low-level lock
108 // should only be sent when a thread has relinquished the token.
109 //
110 // In the absence of either property, we'd have potential deadlock.
111 //
112 // We protect each of the CMS (concurrent and sequential) phases
113 // with the CMS _token_, not the CMS _lock_.
114 //
115 // The only code protected by CMS lock is the token acquisition code
116 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
117 // baton-passing code.
118 //
119 // Unfortunately, i couldn't come up with a good abstraction to factor and
120 // hide the naked CGC_lock manipulation in the baton-passing code
121 // further below. That's something we should try to do. Also, the proof
122 // of correctness of this 2-level locking scheme is far from obvious,
123 // and potentially quite slippery. We have an uneasy suspicion, for instance,
124 // that there may be a theoretical possibility of delay/starvation in the
125 // low-level lock/wait/notify scheme used for the baton-passing because of
126 // potential interference with the priority scheme embodied in the
127 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
128 // invocation further below and marked with "XXX 20011219YSR".
129 // Indeed, as we note elsewhere, this may become yet more slippery
130 // in the presence of multiple CMS and/or multiple VM threads. XXX
131
132 class CMSTokenSync: public StackObj {
133 private:
134 bool _is_cms_thread;
135 public:
136 CMSTokenSync(bool is_cms_thread):
137 _is_cms_thread(is_cms_thread) {
138 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
139 "Incorrect argument to constructor");
140 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
141 }
142
143 ~CMSTokenSync() {
144 assert(_is_cms_thread ?
145 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
146 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
147 "Incorrect state");
148 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
149 }
150 };
151
152 // Convenience class that does a CMSTokenSync, and then acquires
153 // upto three locks.
154 class CMSTokenSyncWithLocks: public CMSTokenSync {
155 private:
156 // Note: locks are acquired in textual declaration order
157 // and released in the opposite order
158 MutexLockerEx _locker1, _locker2, _locker3;
159 public:
160 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
161 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
162 CMSTokenSync(is_cms_thread),
163 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
164 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
165 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
166 { }
167 };
168
169
170 //////////////////////////////////////////////////////////////////
171 // Concurrent Mark-Sweep Generation /////////////////////////////
172 //////////////////////////////////////////////////////////////////
173
174 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
175
176 // This struct contains per-thread things necessary to support parallel
177 // young-gen collection.
178 class CMSParGCThreadState: public CHeapObj<mtGC> {
179 public:
180 CFLS_LAB lab;
181 PromotionInfo promo;
182
183 // Constructor.
184 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
185 promo.setSpace(cfls);
186 }
187 };
188
189 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
190 ReservedSpace rs, size_t initial_byte_size, int level,
191 CardTableRS* ct, bool use_adaptive_freelists,
192 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
193 CardGeneration(rs, initial_byte_size, level, ct),
194 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
195 _debug_collection_type(Concurrent_collection_type),
196 _did_compact(false)
197 {
198 HeapWord* bottom = (HeapWord*) _virtual_space.low();
199 HeapWord* end = (HeapWord*) _virtual_space.high();
200
201 _direct_allocated_words = 0;
202 NOT_PRODUCT(
203 _numObjectsPromoted = 0;
204 _numWordsPromoted = 0;
205 _numObjectsAllocated = 0;
206 _numWordsAllocated = 0;
207 )
208
209 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
210 use_adaptive_freelists,
211 dictionaryChoice);
212 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
213 if (_cmsSpace == NULL) {
214 vm_exit_during_initialization(
215 "CompactibleFreeListSpace allocation failure");
216 }
217 _cmsSpace->_gen = this;
218
219 _gc_stats = new CMSGCStats();
220
221 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
222 // offsets match. The ability to tell free chunks from objects
223 // depends on this property.
224 debug_only(
225 FreeChunk* junk = NULL;
226 assert(UseCompressedClassPointers ||
227 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
228 "Offset of FreeChunk::_prev within FreeChunk must match"
229 " that of OopDesc::_klass within OopDesc");
230 )
231 if (CollectedHeap::use_parallel_gc_threads()) {
232 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
233 _par_gc_thread_states =
234 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
235 if (_par_gc_thread_states == NULL) {
236 vm_exit_during_initialization("Could not allocate par gc structs");
237 }
238 for (uint i = 0; i < ParallelGCThreads; i++) {
239 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
240 if (_par_gc_thread_states[i] == NULL) {
241 vm_exit_during_initialization("Could not allocate par gc structs");
242 }
243 }
244 } else {
245 _par_gc_thread_states = NULL;
246 }
247 _incremental_collection_failed = false;
248 // The "dilatation_factor" is the expansion that can occur on
249 // account of the fact that the minimum object size in the CMS
250 // generation may be larger than that in, say, a contiguous young
251 // generation.
252 // Ideally, in the calculation below, we'd compute the dilatation
253 // factor as: MinChunkSize/(promoting_gen's min object size)
254 // Since we do not have such a general query interface for the
255 // promoting generation, we'll instead just use the minimum
256 // object size (which today is a header's worth of space);
257 // note that all arithmetic is in units of HeapWords.
258 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
259 assert(_dilatation_factor >= 1.0, "from previous assert");
260 }
261
262
263 // The field "_initiating_occupancy" represents the occupancy percentage
264 // at which we trigger a new collection cycle. Unless explicitly specified
265 // via CMSInitiatingOccupancyFraction (argument "io" below), it
266 // is calculated by:
267 //
268 // Let "f" be MinHeapFreeRatio in
269 //
270 // _initiating_occupancy = 100-f +
271 // f * (CMSTriggerRatio/100)
272 // where CMSTriggerRatio is the argument "tr" below.
273 //
274 // That is, if we assume the heap is at its desired maximum occupancy at the
275 // end of a collection, we let CMSTriggerRatio of the (purported) free
276 // space be allocated before initiating a new collection cycle.
277 //
278 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
279 assert(io <= 100 && tr <= 100, "Check the arguments");
280 if (io >= 0) {
281 _initiating_occupancy = (double)io / 100.0;
282 } else {
283 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
284 (double)(tr * MinHeapFreeRatio) / 100.0)
285 / 100.0;
286 }
287 }
288
289 void ConcurrentMarkSweepGeneration::ref_processor_init() {
290 assert(collector() != NULL, "no collector");
291 collector()->ref_processor_init();
292 }
293
294 void CMSCollector::ref_processor_init() {
295 if (_ref_processor == NULL) {
296 // Allocate and initialize a reference processor
297 _ref_processor =
298 new ReferenceProcessor(_span, // span
299 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
300 (int) ParallelGCThreads, // mt processing degree
301 _cmsGen->refs_discovery_is_mt(), // mt discovery
302 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
303 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
304 &_is_alive_closure); // closure for liveness info
305 // Initialize the _ref_processor field of CMSGen
306 _cmsGen->set_ref_processor(_ref_processor);
307
308 }
309 }
310
311 AdaptiveSizePolicy* CMSCollector::size_policy() {
312 GenCollectedHeap* gch = GenCollectedHeap::heap();
313 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
314 "Wrong type of heap");
315 return gch->gen_policy()->size_policy();
316 }
317
318 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
319
320 const char* gen_name = "old";
321 GenCollectorPolicy* gcp = (GenCollectorPolicy*) GenCollectedHeap::heap()->collector_policy();
322
323 // Generation Counters - generation 1, 1 subspace
324 _gen_counters = new GenerationCounters(gen_name, 1, 1,
325 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
326
327 _space_counters = new GSpaceCounters(gen_name, 0,
328 _virtual_space.reserved_size(),
329 this, _gen_counters);
330 }
331
332 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
333 _cms_gen(cms_gen)
334 {
335 assert(alpha <= 100, "bad value");
336 _saved_alpha = alpha;
337
338 // Initialize the alphas to the bootstrap value of 100.
339 _gc0_alpha = _cms_alpha = 100;
340
341 _cms_begin_time.update();
342 _cms_end_time.update();
343
344 _gc0_duration = 0.0;
345 _gc0_period = 0.0;
346 _gc0_promoted = 0;
347
348 _cms_duration = 0.0;
349 _cms_period = 0.0;
350 _cms_allocated = 0;
351
352 _cms_used_at_gc0_begin = 0;
353 _cms_used_at_gc0_end = 0;
354 _allow_duty_cycle_reduction = false;
355 _valid_bits = 0;
356 }
357
358 double CMSStats::cms_free_adjustment_factor(size_t free) const {
359 // TBD: CR 6909490
360 return 1.0;
361 }
362
363 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
364 }
365
366 // If promotion failure handling is on use
367 // the padded average size of the promotion for each
368 // young generation collection.
369 double CMSStats::time_until_cms_gen_full() const {
370 size_t cms_free = _cms_gen->cmsSpace()->free();
371 GenCollectedHeap* gch = GenCollectedHeap::heap();
372 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
373 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
374 if (cms_free > expected_promotion) {
375 // Start a cms collection if there isn't enough space to promote
376 // for the next minor collection. Use the padded average as
377 // a safety factor.
378 cms_free -= expected_promotion;
379
380 // Adjust by the safety factor.
381 double cms_free_dbl = (double)cms_free;
382 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
383 // Apply a further correction factor which tries to adjust
384 // for recent occurance of concurrent mode failures.
385 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
386 cms_free_dbl = cms_free_dbl * cms_adjustment;
387
388 if (PrintGCDetails && Verbose) {
389 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
390 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
391 cms_free, expected_promotion);
392 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
393 cms_free_dbl, cms_consumption_rate() + 1.0);
394 }
395 // Add 1 in case the consumption rate goes to zero.
396 return cms_free_dbl / (cms_consumption_rate() + 1.0);
397 }
398 return 0.0;
399 }
400
401 // Compare the duration of the cms collection to the
402 // time remaining before the cms generation is empty.
403 // Note that the time from the start of the cms collection
404 // to the start of the cms sweep (less than the total
405 // duration of the cms collection) can be used. This
406 // has been tried and some applications experienced
407 // promotion failures early in execution. This was
408 // possibly because the averages were not accurate
409 // enough at the beginning.
410 double CMSStats::time_until_cms_start() const {
411 // We add "gc0_period" to the "work" calculation
412 // below because this query is done (mostly) at the
413 // end of a scavenge, so we need to conservatively
414 // account for that much possible delay
415 // in the query so as to avoid concurrent mode failures
416 // due to starting the collection just a wee bit too
417 // late.
418 double work = cms_duration() + gc0_period();
419 double deadline = time_until_cms_gen_full();
420 // If a concurrent mode failure occurred recently, we want to be
421 // more conservative and halve our expected time_until_cms_gen_full()
422 if (work > deadline) {
423 if (Verbose && PrintGCDetails) {
424 gclog_or_tty->print(
425 " CMSCollector: collect because of anticipated promotion "
426 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
427 gc0_period(), time_until_cms_gen_full());
428 }
429 return 0.0;
430 }
431 return work - deadline;
432 }
433
434 #ifndef PRODUCT
435 void CMSStats::print_on(outputStream *st) const {
436 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
437 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
438 gc0_duration(), gc0_period(), gc0_promoted());
439 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
440 cms_duration(), cms_period(), cms_allocated());
441 st->print(",cms_since_beg=%g,cms_since_end=%g",
442 cms_time_since_begin(), cms_time_since_end());
443 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
444 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
445
446 if (valid()) {
447 st->print(",promo_rate=%g,cms_alloc_rate=%g",
448 promotion_rate(), cms_allocation_rate());
449 st->print(",cms_consumption_rate=%g,time_until_full=%g",
450 cms_consumption_rate(), time_until_cms_gen_full());
451 }
452 st->print(" ");
453 }
454 #endif // #ifndef PRODUCT
455
456 CMSCollector::CollectorState CMSCollector::_collectorState =
457 CMSCollector::Idling;
458 bool CMSCollector::_foregroundGCIsActive = false;
459 bool CMSCollector::_foregroundGCShouldWait = false;
460
461 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
462 CardTableRS* ct,
463 ConcurrentMarkSweepPolicy* cp):
464 _cmsGen(cmsGen),
465 _ct(ct),
466 _ref_processor(NULL), // will be set later
467 _conc_workers(NULL), // may be set later
468 _abort_preclean(false),
469 _start_sampling(false),
470 _between_prologue_and_epilogue(false),
471 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
472 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
473 -1 /* lock-free */, "No_lock" /* dummy */),
474 _modUnionClosure(&_modUnionTable),
475 _modUnionClosurePar(&_modUnionTable),
476 // Adjust my span to cover old (cms) gen
477 _span(cmsGen->reserved()),
478 // Construct the is_alive_closure with _span & markBitMap
479 _is_alive_closure(_span, &_markBitMap),
480 _restart_addr(NULL),
481 _overflow_list(NULL),
482 _stats(cmsGen),
483 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true)),
484 _eden_chunk_array(NULL), // may be set in ctor body
485 _eden_chunk_capacity(0), // -- ditto --
486 _eden_chunk_index(0), // -- ditto --
487 _survivor_plab_array(NULL), // -- ditto --
488 _survivor_chunk_array(NULL), // -- ditto --
489 _survivor_chunk_capacity(0), // -- ditto --
490 _survivor_chunk_index(0), // -- ditto --
491 _ser_pmc_preclean_ovflw(0),
492 _ser_kac_preclean_ovflw(0),
493 _ser_pmc_remark_ovflw(0),
494 _par_pmc_remark_ovflw(0),
495 _ser_kac_ovflw(0),
496 _par_kac_ovflw(0),
497 #ifndef PRODUCT
498 _num_par_pushes(0),
499 #endif
500 _collection_count_start(0),
501 _verifying(false),
502 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
503 _completed_initialization(false),
504 _collector_policy(cp),
505 _should_unload_classes(CMSClassUnloadingEnabled),
506 _concurrent_cycles_since_last_unload(0),
507 _roots_scanning_options(SharedHeap::SO_None),
508 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
509 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
510 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
511 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
512 _cms_start_registered(false)
513 {
514 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
515 ExplicitGCInvokesConcurrent = true;
516 }
517 // Now expand the span and allocate the collection support structures
518 // (MUT, marking bit map etc.) to cover both generations subject to
519 // collection.
520
521 // For use by dirty card to oop closures.
522 _cmsGen->cmsSpace()->set_collector(this);
523
524 // Allocate MUT and marking bit map
525 {
526 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
527 if (!_markBitMap.allocate(_span)) {
528 warning("Failed to allocate CMS Bit Map");
529 return;
530 }
531 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
532 }
533 {
534 _modUnionTable.allocate(_span);
535 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
536 }
537
538 if (!_markStack.allocate(MarkStackSize)) {
539 warning("Failed to allocate CMS Marking Stack");
540 return;
541 }
542
543 // Support for multi-threaded concurrent phases
544 if (CMSConcurrentMTEnabled) {
545 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
546 // just for now
547 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
548 }
549 if (ConcGCThreads > 1) {
550 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
551 ConcGCThreads, true);
552 if (_conc_workers == NULL) {
553 warning("GC/CMS: _conc_workers allocation failure: "
554 "forcing -CMSConcurrentMTEnabled");
555 CMSConcurrentMTEnabled = false;
556 } else {
557 _conc_workers->initialize_workers();
558 }
559 } else {
560 CMSConcurrentMTEnabled = false;
561 }
562 }
563 if (!CMSConcurrentMTEnabled) {
564 ConcGCThreads = 0;
565 } else {
566 // Turn off CMSCleanOnEnter optimization temporarily for
567 // the MT case where it's not fixed yet; see 6178663.
568 CMSCleanOnEnter = false;
569 }
570 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
571 "Inconsistency");
572
573 // Parallel task queues; these are shared for the
574 // concurrent and stop-world phases of CMS, but
575 // are not shared with parallel scavenge (ParNew).
576 {
577 uint i;
578 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
579
580 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
581 || ParallelRefProcEnabled)
582 && num_queues > 0) {
583 _task_queues = new OopTaskQueueSet(num_queues);
584 if (_task_queues == NULL) {
585 warning("task_queues allocation failure.");
586 return;
587 }
588 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
589 if (_hash_seed == NULL) {
590 warning("_hash_seed array allocation failure");
591 return;
592 }
593
594 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
595 for (i = 0; i < num_queues; i++) {
596 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
597 if (q == NULL) {
598 warning("work_queue allocation failure.");
599 return;
600 }
601 _task_queues->register_queue(i, q);
602 }
603 for (i = 0; i < num_queues; i++) {
604 _task_queues->queue(i)->initialize();
605 _hash_seed[i] = 17; // copied from ParNew
606 }
607 }
608 }
609
610 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
611
612 // Clip CMSBootstrapOccupancy between 0 and 100.
613 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
614
615 _full_gcs_since_conc_gc = 0;
616
617 // Now tell CMS generations the identity of their collector
618 ConcurrentMarkSweepGeneration::set_collector(this);
619
620 // Create & start a CMS thread for this CMS collector
621 _cmsThread = ConcurrentMarkSweepThread::start(this);
622 assert(cmsThread() != NULL, "CMS Thread should have been created");
623 assert(cmsThread()->collector() == this,
624 "CMS Thread should refer to this gen");
625 assert(CGC_lock != NULL, "Where's the CGC_lock?");
626
627 // Support for parallelizing young gen rescan
628 GenCollectedHeap* gch = GenCollectedHeap::heap();
629 _young_gen = gch->prev_gen(_cmsGen);
630 if (gch->supports_inline_contig_alloc()) {
631 _top_addr = gch->top_addr();
632 _end_addr = gch->end_addr();
633 assert(_young_gen != NULL, "no _young_gen");
634 _eden_chunk_index = 0;
635 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
636 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
637 if (_eden_chunk_array == NULL) {
638 _eden_chunk_capacity = 0;
639 warning("GC/CMS: _eden_chunk_array allocation failure");
640 }
641 }
642 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
643
644 // Support for parallelizing survivor space rescan
645 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
646 const size_t max_plab_samples =
647 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
648
649 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
650 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
651 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
652 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
653 || _cursor == NULL) {
654 warning("Failed to allocate survivor plab/chunk array");
655 if (_survivor_plab_array != NULL) {
656 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
657 _survivor_plab_array = NULL;
658 }
659 if (_survivor_chunk_array != NULL) {
660 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
661 _survivor_chunk_array = NULL;
662 }
663 if (_cursor != NULL) {
664 FREE_C_HEAP_ARRAY(size_t, _cursor);
665 _cursor = NULL;
666 }
667 } else {
668 _survivor_chunk_capacity = 2*max_plab_samples;
669 for (uint i = 0; i < ParallelGCThreads; i++) {
670 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
671 if (vec == NULL) {
672 warning("Failed to allocate survivor plab array");
673 for (int j = i; j > 0; j--) {
674 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array());
675 }
676 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
677 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
678 _survivor_plab_array = NULL;
679 _survivor_chunk_array = NULL;
680 _survivor_chunk_capacity = 0;
681 break;
682 } else {
683 ChunkArray* cur =
684 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
685 max_plab_samples);
686 assert(cur->end() == 0, "Should be 0");
687 assert(cur->array() == vec, "Should be vec");
688 assert(cur->capacity() == max_plab_samples, "Error");
689 }
690 }
691 }
692 }
693 assert( ( _survivor_plab_array != NULL
694 && _survivor_chunk_array != NULL)
695 || ( _survivor_chunk_capacity == 0
696 && _survivor_chunk_index == 0),
697 "Error");
698
699 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
700 _gc_counters = new CollectorCounters("CMS", 1);
701 _completed_initialization = true;
702 _inter_sweep_timer.start(); // start of time
703 }
704
705 const char* ConcurrentMarkSweepGeneration::name() const {
706 return "concurrent mark-sweep generation";
707 }
708 void ConcurrentMarkSweepGeneration::update_counters() {
709 if (UsePerfData) {
710 _space_counters->update_all();
711 _gen_counters->update_all();
712 }
713 }
714
715 // this is an optimized version of update_counters(). it takes the
716 // used value as a parameter rather than computing it.
717 //
718 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
719 if (UsePerfData) {
720 _space_counters->update_used(used);
721 _space_counters->update_capacity();
722 _gen_counters->update_all();
723 }
724 }
725
726 void ConcurrentMarkSweepGeneration::print() const {
727 Generation::print();
728 cmsSpace()->print();
729 }
730
731 #ifndef PRODUCT
732 void ConcurrentMarkSweepGeneration::print_statistics() {
733 cmsSpace()->printFLCensus(0);
734 }
735 #endif
736
737 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
738 GenCollectedHeap* gch = GenCollectedHeap::heap();
739 if (PrintGCDetails) {
740 if (Verbose) {
741 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
742 level(), short_name(), s, used(), capacity());
743 } else {
744 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
745 level(), short_name(), s, used() / K, capacity() / K);
746 }
747 }
748 if (Verbose) {
749 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
750 gch->used(), gch->capacity());
751 } else {
752 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
753 gch->used() / K, gch->capacity() / K);
754 }
755 }
756
757 size_t
758 ConcurrentMarkSweepGeneration::contiguous_available() const {
759 // dld proposes an improvement in precision here. If the committed
760 // part of the space ends in a free block we should add that to
761 // uncommitted size in the calculation below. Will make this
762 // change later, staying with the approximation below for the
763 // time being. -- ysr.
764 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
765 }
766
767 size_t
768 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
769 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
770 }
771
772 size_t ConcurrentMarkSweepGeneration::max_available() const {
773 return free() + _virtual_space.uncommitted_size();
774 }
775
776 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
777 size_t available = max_available();
778 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
779 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
780 if (Verbose && PrintGCDetails) {
781 gclog_or_tty->print_cr(
782 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
783 "max_promo("SIZE_FORMAT")",
784 res? "":" not", available, res? ">=":"<",
785 av_promo, max_promotion_in_bytes);
786 }
787 return res;
788 }
789
790 // At a promotion failure dump information on block layout in heap
791 // (cms old generation).
792 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
793 if (CMSDumpAtPromotionFailure) {
794 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
795 }
796 }
797
798 CompactibleSpace*
799 ConcurrentMarkSweepGeneration::first_compaction_space() const {
800 return _cmsSpace;
801 }
802
803 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
804 // Clear the promotion information. These pointers can be adjusted
805 // along with all the other pointers into the heap but
806 // compaction is expected to be a rare event with
807 // a heap using cms so don't do it without seeing the need.
808 for (uint i = 0; i < ParallelGCThreads; i++) {
809 _par_gc_thread_states[i]->promo.reset();
810 }
811 }
812
813 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
814 blk->do_space(_cmsSpace);
815 }
816
817 void ConcurrentMarkSweepGeneration::compute_new_size() {
818 assert_locked_or_safepoint(Heap_lock);
819
820 // If incremental collection failed, we just want to expand
821 // to the limit.
822 if (incremental_collection_failed()) {
823 clear_incremental_collection_failed();
824 grow_to_reserved();
825 return;
826 }
827
828 // The heap has been compacted but not reset yet.
829 // Any metric such as free() or used() will be incorrect.
830
831 CardGeneration::compute_new_size();
832
833 // Reset again after a possible resizing
834 if (did_compact()) {
835 cmsSpace()->reset_after_compaction();
836 }
837 }
838
839 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
840 assert_locked_or_safepoint(Heap_lock);
841
842 // If incremental collection failed, we just want to expand
843 // to the limit.
844 if (incremental_collection_failed()) {
845 clear_incremental_collection_failed();
846 grow_to_reserved();
847 return;
848 }
849
850 double free_percentage = ((double) free()) / capacity();
851 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
852 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
853
854 // compute expansion delta needed for reaching desired free percentage
855 if (free_percentage < desired_free_percentage) {
856 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
857 assert(desired_capacity >= capacity(), "invalid expansion size");
858 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
859 if (PrintGCDetails && Verbose) {
860 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
861 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
862 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
863 gclog_or_tty->print_cr(" Desired free fraction %f",
864 desired_free_percentage);
865 gclog_or_tty->print_cr(" Maximum free fraction %f",
866 maximum_free_percentage);
867 gclog_or_tty->print_cr(" Capacity "SIZE_FORMAT, capacity()/1000);
868 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
869 desired_capacity/1000);
870 int prev_level = level() - 1;
871 if (prev_level >= 0) {
872 size_t prev_size = 0;
873 GenCollectedHeap* gch = GenCollectedHeap::heap();
874 Generation* prev_gen = gch->_gens[prev_level];
875 prev_size = prev_gen->capacity();
876 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
877 prev_size/1000);
878 }
879 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
880 unsafe_max_alloc_nogc()/1000);
881 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
882 contiguous_available()/1000);
883 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
884 expand_bytes);
885 }
886 // safe if expansion fails
887 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
888 if (PrintGCDetails && Verbose) {
889 gclog_or_tty->print_cr(" Expanded free fraction %f",
890 ((double) free()) / capacity());
891 }
892 } else {
893 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
894 assert(desired_capacity <= capacity(), "invalid expansion size");
895 size_t shrink_bytes = capacity() - desired_capacity;
896 // Don't shrink unless the delta is greater than the minimum shrink we want
897 if (shrink_bytes >= MinHeapDeltaBytes) {
898 shrink_free_list_by(shrink_bytes);
899 }
900 }
901 }
902
903 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
904 return cmsSpace()->freelistLock();
905 }
906
907 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
908 bool tlab) {
909 CMSSynchronousYieldRequest yr;
910 MutexLockerEx x(freelistLock(),
911 Mutex::_no_safepoint_check_flag);
912 return have_lock_and_allocate(size, tlab);
913 }
914
915 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
916 bool tlab /* ignored */) {
917 assert_lock_strong(freelistLock());
918 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
919 HeapWord* res = cmsSpace()->allocate(adjustedSize);
920 // Allocate the object live (grey) if the background collector has
921 // started marking. This is necessary because the marker may
922 // have passed this address and consequently this object will
923 // not otherwise be greyed and would be incorrectly swept up.
924 // Note that if this object contains references, the writing
925 // of those references will dirty the card containing this object
926 // allowing the object to be blackened (and its references scanned)
927 // either during a preclean phase or at the final checkpoint.
928 if (res != NULL) {
929 // We may block here with an uninitialized object with
930 // its mark-bit or P-bits not yet set. Such objects need
931 // to be safely navigable by block_start().
932 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
933 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
934 collector()->direct_allocated(res, adjustedSize);
935 _direct_allocated_words += adjustedSize;
936 // allocation counters
937 NOT_PRODUCT(
938 _numObjectsAllocated++;
939 _numWordsAllocated += (int)adjustedSize;
940 )
941 }
942 return res;
943 }
944
945 // In the case of direct allocation by mutators in a generation that
946 // is being concurrently collected, the object must be allocated
947 // live (grey) if the background collector has started marking.
948 // This is necessary because the marker may
949 // have passed this address and consequently this object will
950 // not otherwise be greyed and would be incorrectly swept up.
951 // Note that if this object contains references, the writing
952 // of those references will dirty the card containing this object
953 // allowing the object to be blackened (and its references scanned)
954 // either during a preclean phase or at the final checkpoint.
955 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
956 assert(_markBitMap.covers(start, size), "Out of bounds");
957 if (_collectorState >= Marking) {
958 MutexLockerEx y(_markBitMap.lock(),
959 Mutex::_no_safepoint_check_flag);
960 // [see comments preceding SweepClosure::do_blk() below for details]
961 //
962 // Can the P-bits be deleted now? JJJ
963 //
964 // 1. need to mark the object as live so it isn't collected
965 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
966 // 3. need to mark the end of the object so marking, precleaning or sweeping
967 // can skip over uninitialized or unparsable objects. An allocated
968 // object is considered uninitialized for our purposes as long as
969 // its klass word is NULL. All old gen objects are parsable
970 // as soon as they are initialized.)
971 _markBitMap.mark(start); // object is live
972 _markBitMap.mark(start + 1); // object is potentially uninitialized?
973 _markBitMap.mark(start + size - 1);
974 // mark end of object
975 }
976 // check that oop looks uninitialized
977 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
978 }
979
980 void CMSCollector::promoted(bool par, HeapWord* start,
981 bool is_obj_array, size_t obj_size) {
982 assert(_markBitMap.covers(start), "Out of bounds");
983 // See comment in direct_allocated() about when objects should
984 // be allocated live.
985 if (_collectorState >= Marking) {
986 // we already hold the marking bit map lock, taken in
987 // the prologue
988 if (par) {
989 _markBitMap.par_mark(start);
990 } else {
991 _markBitMap.mark(start);
992 }
993 // We don't need to mark the object as uninitialized (as
994 // in direct_allocated above) because this is being done with the
995 // world stopped and the object will be initialized by the
996 // time the marking, precleaning or sweeping get to look at it.
997 // But see the code for copying objects into the CMS generation,
998 // where we need to ensure that concurrent readers of the
999 // block offset table are able to safely navigate a block that
1000 // is in flux from being free to being allocated (and in
1001 // transition while being copied into) and subsequently
1002 // becoming a bona-fide object when the copy/promotion is complete.
1003 assert(SafepointSynchronize::is_at_safepoint(),
1004 "expect promotion only at safepoints");
1005
1006 if (_collectorState < Sweeping) {
1007 // Mark the appropriate cards in the modUnionTable, so that
1008 // this object gets scanned before the sweep. If this is
1009 // not done, CMS generation references in the object might
1010 // not get marked.
1011 // For the case of arrays, which are otherwise precisely
1012 // marked, we need to dirty the entire array, not just its head.
1013 if (is_obj_array) {
1014 // The [par_]mark_range() method expects mr.end() below to
1015 // be aligned to the granularity of a bit's representation
1016 // in the heap. In the case of the MUT below, that's a
1017 // card size.
1018 MemRegion mr(start,
1019 (HeapWord*)round_to((intptr_t)(start + obj_size),
1020 CardTableModRefBS::card_size /* bytes */));
1021 if (par) {
1022 _modUnionTable.par_mark_range(mr);
1023 } else {
1024 _modUnionTable.mark_range(mr);
1025 }
1026 } else { // not an obj array; we can just mark the head
1027 if (par) {
1028 _modUnionTable.par_mark(start);
1029 } else {
1030 _modUnionTable.mark(start);
1031 }
1032 }
1033 }
1034 }
1035 }
1036
1037 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1038 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1039 // allocate, copy and if necessary update promoinfo --
1040 // delegate to underlying space.
1041 assert_lock_strong(freelistLock());
1042
1043 #ifndef PRODUCT
1044 if (Universe::heap()->promotion_should_fail()) {
1045 return NULL;
1046 }
1047 #endif // #ifndef PRODUCT
1048
1049 oop res = _cmsSpace->promote(obj, obj_size);
1050 if (res == NULL) {
1051 // expand and retry
1052 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1053 expand(s*HeapWordSize, MinHeapDeltaBytes,
1054 CMSExpansionCause::_satisfy_promotion);
1055 // Since there's currently no next generation, we don't try to promote
1056 // into a more senior generation.
1057 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1058 "is made to pass on a possibly failing "
1059 "promotion to next generation");
1060 res = _cmsSpace->promote(obj, obj_size);
1061 }
1062 if (res != NULL) {
1063 // See comment in allocate() about when objects should
1064 // be allocated live.
1065 assert(obj->is_oop(), "Will dereference klass pointer below");
1066 collector()->promoted(false, // Not parallel
1067 (HeapWord*)res, obj->is_objArray(), obj_size);
1068 // promotion counters
1069 NOT_PRODUCT(
1070 _numObjectsPromoted++;
1071 _numWordsPromoted +=
1072 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1073 )
1074 }
1075 return res;
1076 }
1077
1078
1079 // IMPORTANT: Notes on object size recognition in CMS.
1080 // ---------------------------------------------------
1081 // A block of storage in the CMS generation is always in
1082 // one of three states. A free block (FREE), an allocated
1083 // object (OBJECT) whose size() method reports the correct size,
1084 // and an intermediate state (TRANSIENT) in which its size cannot
1085 // be accurately determined.
1086 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1087 // -----------------------------------------------------
1088 // FREE: klass_word & 1 == 1; mark_word holds block size
1089 //
1090 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1091 // obj->size() computes correct size
1092 //
1093 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1094 //
1095 // STATE IDENTIFICATION: (64 bit+COOPS)
1096 // ------------------------------------
1097 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1098 //
1099 // OBJECT: klass_word installed; klass_word != 0;
1100 // obj->size() computes correct size
1101 //
1102 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1103 //
1104 //
1105 // STATE TRANSITION DIAGRAM
1106 //
1107 // mut / parnew mut / parnew
1108 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1109 // ^ |
1110 // |------------------------ DEAD <------------------------------------|
1111 // sweep mut
1112 //
1113 // While a block is in TRANSIENT state its size cannot be determined
1114 // so readers will either need to come back later or stall until
1115 // the size can be determined. Note that for the case of direct
1116 // allocation, P-bits, when available, may be used to determine the
1117 // size of an object that may not yet have been initialized.
1118
1119 // Things to support parallel young-gen collection.
1120 oop
1121 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1122 oop old, markOop m,
1123 size_t word_sz) {
1124 #ifndef PRODUCT
1125 if (Universe::heap()->promotion_should_fail()) {
1126 return NULL;
1127 }
1128 #endif // #ifndef PRODUCT
1129
1130 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1131 PromotionInfo* promoInfo = &ps->promo;
1132 // if we are tracking promotions, then first ensure space for
1133 // promotion (including spooling space for saving header if necessary).
1134 // then allocate and copy, then track promoted info if needed.
1135 // When tracking (see PromotionInfo::track()), the mark word may
1136 // be displaced and in this case restoration of the mark word
1137 // occurs in the (oop_since_save_marks_)iterate phase.
1138 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1139 // Out of space for allocating spooling buffers;
1140 // try expanding and allocating spooling buffers.
1141 if (!expand_and_ensure_spooling_space(promoInfo)) {
1142 return NULL;
1143 }
1144 }
1145 assert(promoInfo->has_spooling_space(), "Control point invariant");
1146 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1147 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1148 if (obj_ptr == NULL) {
1149 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1150 if (obj_ptr == NULL) {
1151 return NULL;
1152 }
1153 }
1154 oop obj = oop(obj_ptr);
1155 OrderAccess::storestore();
1156 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1157 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1158 // IMPORTANT: See note on object initialization for CMS above.
1159 // Otherwise, copy the object. Here we must be careful to insert the
1160 // klass pointer last, since this marks the block as an allocated object.
1161 // Except with compressed oops it's the mark word.
1162 HeapWord* old_ptr = (HeapWord*)old;
1163 // Restore the mark word copied above.
1164 obj->set_mark(m);
1165 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1166 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1167 OrderAccess::storestore();
1168
1169 if (UseCompressedClassPointers) {
1170 // Copy gap missed by (aligned) header size calculation below
1171 obj->set_klass_gap(old->klass_gap());
1172 }
1173 if (word_sz > (size_t)oopDesc::header_size()) {
1174 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1175 obj_ptr + oopDesc::header_size(),
1176 word_sz - oopDesc::header_size());
1177 }
1178
1179 // Now we can track the promoted object, if necessary. We take care
1180 // to delay the transition from uninitialized to full object
1181 // (i.e., insertion of klass pointer) until after, so that it
1182 // atomically becomes a promoted object.
1183 if (promoInfo->tracking()) {
1184 promoInfo->track((PromotedObject*)obj, old->klass());
1185 }
1186 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1187 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1188 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1189
1190 // Finally, install the klass pointer (this should be volatile).
1191 OrderAccess::storestore();
1192 obj->set_klass(old->klass());
1193 // We should now be able to calculate the right size for this object
1194 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1195
1196 collector()->promoted(true, // parallel
1197 obj_ptr, old->is_objArray(), word_sz);
1198
1199 NOT_PRODUCT(
1200 Atomic::inc_ptr(&_numObjectsPromoted);
1201 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1202 )
1203
1204 return obj;
1205 }
1206
1207 void
1208 ConcurrentMarkSweepGeneration::
1209 par_promote_alloc_undo(int thread_num,
1210 HeapWord* obj, size_t word_sz) {
1211 // CMS does not support promotion undo.
1212 ShouldNotReachHere();
1213 }
1214
1215 void
1216 ConcurrentMarkSweepGeneration::
1217 par_promote_alloc_done(int thread_num) {
1218 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1219 ps->lab.retire(thread_num);
1220 }
1221
1222 void
1223 ConcurrentMarkSweepGeneration::
1224 par_oop_since_save_marks_iterate_done(int thread_num) {
1225 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1226 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1227 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1228 }
1229
1230 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1231 size_t size,
1232 bool tlab)
1233 {
1234 // We allow a STW collection only if a full
1235 // collection was requested.
1236 return full || should_allocate(size, tlab); // FIX ME !!!
1237 // This and promotion failure handling are connected at the
1238 // hip and should be fixed by untying them.
1239 }
1240
1241 bool CMSCollector::shouldConcurrentCollect() {
1242 if (_full_gc_requested) {
1243 if (Verbose && PrintGCDetails) {
1244 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1245 " gc request (or gc_locker)");
1246 }
1247 return true;
1248 }
1249
1250 // For debugging purposes, change the type of collection.
1251 // If the rotation is not on the concurrent collection
1252 // type, don't start a concurrent collection.
1253 NOT_PRODUCT(
1254 if (RotateCMSCollectionTypes &&
1255 (_cmsGen->debug_collection_type() !=
1256 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1257 assert(_cmsGen->debug_collection_type() !=
1258 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1259 "Bad cms collection type");
1260 return false;
1261 }
1262 )
1263
1264 FreelistLocker x(this);
1265 // ------------------------------------------------------------------
1266 // Print out lots of information which affects the initiation of
1267 // a collection.
1268 if (PrintCMSInitiationStatistics && stats().valid()) {
1269 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1270 gclog_or_tty->stamp();
1271 gclog_or_tty->cr();
1272 stats().print_on(gclog_or_tty);
1273 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1274 stats().time_until_cms_gen_full());
1275 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1276 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1277 _cmsGen->contiguous_available());
1278 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1279 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1280 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1281 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1282 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1283 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1284 gclog_or_tty->print_cr("metadata initialized %d",
1285 MetaspaceGC::should_concurrent_collect());
1286 }
1287 // ------------------------------------------------------------------
1288
1289 // If the estimated time to complete a cms collection (cms_duration())
1290 // is less than the estimated time remaining until the cms generation
1291 // is full, start a collection.
1292 if (!UseCMSInitiatingOccupancyOnly) {
1293 if (stats().valid()) {
1294 if (stats().time_until_cms_start() == 0.0) {
1295 return true;
1296 }
1297 } else {
1298 // We want to conservatively collect somewhat early in order
1299 // to try and "bootstrap" our CMS/promotion statistics;
1300 // this branch will not fire after the first successful CMS
1301 // collection because the stats should then be valid.
1302 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1303 if (Verbose && PrintGCDetails) {
1304 gclog_or_tty->print_cr(
1305 " CMSCollector: collect for bootstrapping statistics:"
1306 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1307 _bootstrap_occupancy);
1308 }
1309 return true;
1310 }
1311 }
1312 }
1313
1314 // Otherwise, we start a collection cycle if
1315 // old gen want a collection cycle started. Each may use
1316 // an appropriate criterion for making this decision.
1317 // XXX We need to make sure that the gen expansion
1318 // criterion dovetails well with this. XXX NEED TO FIX THIS
1319 if (_cmsGen->should_concurrent_collect()) {
1320 if (Verbose && PrintGCDetails) {
1321 gclog_or_tty->print_cr("CMS old gen initiated");
1322 }
1323 return true;
1324 }
1325
1326 // We start a collection if we believe an incremental collection may fail;
1327 // this is not likely to be productive in practice because it's probably too
1328 // late anyway.
1329 GenCollectedHeap* gch = GenCollectedHeap::heap();
1330 assert(gch->collector_policy()->is_generation_policy(),
1331 "You may want to check the correctness of the following");
1332 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1333 if (Verbose && PrintGCDetails) {
1334 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1335 }
1336 return true;
1337 }
1338
1339 if (MetaspaceGC::should_concurrent_collect()) {
1340 if (Verbose && PrintGCDetails) {
1341 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1342 }
1343 return true;
1344 }
1345
1346 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1347 if (CMSTriggerInterval >= 0) {
1348 if (CMSTriggerInterval == 0) {
1349 // Trigger always
1350 return true;
1351 }
1352
1353 // Check the CMS time since begin (we do not check the stats validity
1354 // as we want to be able to trigger the first CMS cycle as well)
1355 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1356 if (Verbose && PrintGCDetails) {
1357 if (stats().valid()) {
1358 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1359 stats().cms_time_since_begin());
1360 } else {
1361 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1362 }
1363 }
1364 return true;
1365 }
1366 }
1367
1368 return false;
1369 }
1370
1371 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1372
1373 // Clear _expansion_cause fields of constituent generations
1374 void CMSCollector::clear_expansion_cause() {
1375 _cmsGen->clear_expansion_cause();
1376 }
1377
1378 // We should be conservative in starting a collection cycle. To
1379 // start too eagerly runs the risk of collecting too often in the
1380 // extreme. To collect too rarely falls back on full collections,
1381 // which works, even if not optimum in terms of concurrent work.
1382 // As a work around for too eagerly collecting, use the flag
1383 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1384 // giving the user an easily understandable way of controlling the
1385 // collections.
1386 // We want to start a new collection cycle if any of the following
1387 // conditions hold:
1388 // . our current occupancy exceeds the configured initiating occupancy
1389 // for this generation, or
1390 // . we recently needed to expand this space and have not, since that
1391 // expansion, done a collection of this generation, or
1392 // . the underlying space believes that it may be a good idea to initiate
1393 // a concurrent collection (this may be based on criteria such as the
1394 // following: the space uses linear allocation and linear allocation is
1395 // going to fail, or there is believed to be excessive fragmentation in
1396 // the generation, etc... or ...
1397 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1398 // the case of the old generation; see CR 6543076):
1399 // we may be approaching a point at which allocation requests may fail because
1400 // we will be out of sufficient free space given allocation rate estimates.]
1401 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1402
1403 assert_lock_strong(freelistLock());
1404 if (occupancy() > initiating_occupancy()) {
1405 if (PrintGCDetails && Verbose) {
1406 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1407 short_name(), occupancy(), initiating_occupancy());
1408 }
1409 return true;
1410 }
1411 if (UseCMSInitiatingOccupancyOnly) {
1412 return false;
1413 }
1414 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1415 if (PrintGCDetails && Verbose) {
1416 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1417 short_name());
1418 }
1419 return true;
1420 }
1421 if (_cmsSpace->should_concurrent_collect()) {
1422 if (PrintGCDetails && Verbose) {
1423 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1424 short_name());
1425 }
1426 return true;
1427 }
1428 return false;
1429 }
1430
1431 void ConcurrentMarkSweepGeneration::collect(bool full,
1432 bool clear_all_soft_refs,
1433 size_t size,
1434 bool tlab)
1435 {
1436 collector()->collect(full, clear_all_soft_refs, size, tlab);
1437 }
1438
1439 void CMSCollector::collect(bool full,
1440 bool clear_all_soft_refs,
1441 size_t size,
1442 bool tlab)
1443 {
1444 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1445 // For debugging purposes skip the collection if the state
1446 // is not currently idle
1447 if (TraceCMSState) {
1448 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1449 Thread::current(), full, _collectorState);
1450 }
1451 return;
1452 }
1453
1454 // The following "if" branch is present for defensive reasons.
1455 // In the current uses of this interface, it can be replaced with:
1456 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1457 // But I am not placing that assert here to allow future
1458 // generality in invoking this interface.
1459 if (GC_locker::is_active()) {
1460 // A consistency test for GC_locker
1461 assert(GC_locker::needs_gc(), "Should have been set already");
1462 // Skip this foreground collection, instead
1463 // expanding the heap if necessary.
1464 // Need the free list locks for the call to free() in compute_new_size()
1465 compute_new_size();
1466 return;
1467 }
1468 acquire_control_and_collect(full, clear_all_soft_refs);
1469 _full_gcs_since_conc_gc++;
1470 }
1471
1472 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1473 GenCollectedHeap* gch = GenCollectedHeap::heap();
1474 unsigned int gc_count = gch->total_full_collections();
1475 if (gc_count == full_gc_count) {
1476 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1477 _full_gc_requested = true;
1478 _full_gc_cause = cause;
1479 CGC_lock->notify(); // nudge CMS thread
1480 } else {
1481 assert(gc_count > full_gc_count, "Error: causal loop");
1482 }
1483 }
1484
1485 bool CMSCollector::is_external_interruption() {
1486 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1487 return GCCause::is_user_requested_gc(cause) ||
1488 GCCause::is_serviceability_requested_gc(cause);
1489 }
1490
1491 void CMSCollector::report_concurrent_mode_interruption() {
1492 if (is_external_interruption()) {
1493 if (PrintGCDetails) {
1494 gclog_or_tty->print(" (concurrent mode interrupted)");
1495 }
1496 } else {
1497 if (PrintGCDetails) {
1498 gclog_or_tty->print(" (concurrent mode failure)");
1499 }
1500 _gc_tracer_cm->report_concurrent_mode_failure();
1501 }
1502 }
1503
1504
1505 // The foreground and background collectors need to coordinate in order
1506 // to make sure that they do not mutually interfere with CMS collections.
1507 // When a background collection is active,
1508 // the foreground collector may need to take over (preempt) and
1509 // synchronously complete an ongoing collection. Depending on the
1510 // frequency of the background collections and the heap usage
1511 // of the application, this preemption can be seldom or frequent.
1512 // There are only certain
1513 // points in the background collection that the "collection-baton"
1514 // can be passed to the foreground collector.
1515 //
1516 // The foreground collector will wait for the baton before
1517 // starting any part of the collection. The foreground collector
1518 // will only wait at one location.
1519 //
1520 // The background collector will yield the baton before starting a new
1521 // phase of the collection (e.g., before initial marking, marking from roots,
1522 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1523 // of the loop which switches the phases. The background collector does some
1524 // of the phases (initial mark, final re-mark) with the world stopped.
1525 // Because of locking involved in stopping the world,
1526 // the foreground collector should not block waiting for the background
1527 // collector when it is doing a stop-the-world phase. The background
1528 // collector will yield the baton at an additional point just before
1529 // it enters a stop-the-world phase. Once the world is stopped, the
1530 // background collector checks the phase of the collection. If the
1531 // phase has not changed, it proceeds with the collection. If the
1532 // phase has changed, it skips that phase of the collection. See
1533 // the comments on the use of the Heap_lock in collect_in_background().
1534 //
1535 // Variable used in baton passing.
1536 // _foregroundGCIsActive - Set to true by the foreground collector when
1537 // it wants the baton. The foreground clears it when it has finished
1538 // the collection.
1539 // _foregroundGCShouldWait - Set to true by the background collector
1540 // when it is running. The foreground collector waits while
1541 // _foregroundGCShouldWait is true.
1542 // CGC_lock - monitor used to protect access to the above variables
1543 // and to notify the foreground and background collectors.
1544 // _collectorState - current state of the CMS collection.
1545 //
1546 // The foreground collector
1547 // acquires the CGC_lock
1548 // sets _foregroundGCIsActive
1549 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1550 // various locks acquired in preparation for the collection
1551 // are released so as not to block the background collector
1552 // that is in the midst of a collection
1553 // proceeds with the collection
1554 // clears _foregroundGCIsActive
1555 // returns
1556 //
1557 // The background collector in a loop iterating on the phases of the
1558 // collection
1559 // acquires the CGC_lock
1560 // sets _foregroundGCShouldWait
1561 // if _foregroundGCIsActive is set
1562 // clears _foregroundGCShouldWait, notifies _CGC_lock
1563 // waits on _CGC_lock for _foregroundGCIsActive to become false
1564 // and exits the loop.
1565 // otherwise
1566 // proceed with that phase of the collection
1567 // if the phase is a stop-the-world phase,
1568 // yield the baton once more just before enqueueing
1569 // the stop-world CMS operation (executed by the VM thread).
1570 // returns after all phases of the collection are done
1571 //
1572
1573 void CMSCollector::acquire_control_and_collect(bool full,
1574 bool clear_all_soft_refs) {
1575 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1576 assert(!Thread::current()->is_ConcurrentGC_thread(),
1577 "shouldn't try to acquire control from self!");
1578
1579 // Start the protocol for acquiring control of the
1580 // collection from the background collector (aka CMS thread).
1581 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1582 "VM thread should have CMS token");
1583 // Remember the possibly interrupted state of an ongoing
1584 // concurrent collection
1585 CollectorState first_state = _collectorState;
1586
1587 // Signal to a possibly ongoing concurrent collection that
1588 // we want to do a foreground collection.
1589 _foregroundGCIsActive = true;
1590
1591 // release locks and wait for a notify from the background collector
1592 // releasing the locks in only necessary for phases which
1593 // do yields to improve the granularity of the collection.
1594 assert_lock_strong(bitMapLock());
1595 // We need to lock the Free list lock for the space that we are
1596 // currently collecting.
1597 assert(haveFreelistLocks(), "Must be holding free list locks");
1598 bitMapLock()->unlock();
1599 releaseFreelistLocks();
1600 {
1601 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1602 if (_foregroundGCShouldWait) {
1603 // We are going to be waiting for action for the CMS thread;
1604 // it had better not be gone (for instance at shutdown)!
1605 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1606 "CMS thread must be running");
1607 // Wait here until the background collector gives us the go-ahead
1608 ConcurrentMarkSweepThread::clear_CMS_flag(
1609 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1610 // Get a possibly blocked CMS thread going:
1611 // Note that we set _foregroundGCIsActive true above,
1612 // without protection of the CGC_lock.
1613 CGC_lock->notify();
1614 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1615 "Possible deadlock");
1616 while (_foregroundGCShouldWait) {
1617 // wait for notification
1618 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1619 // Possibility of delay/starvation here, since CMS token does
1620 // not know to give priority to VM thread? Actually, i think
1621 // there wouldn't be any delay/starvation, but the proof of
1622 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1623 }
1624 ConcurrentMarkSweepThread::set_CMS_flag(
1625 ConcurrentMarkSweepThread::CMS_vm_has_token);
1626 }
1627 }
1628 // The CMS_token is already held. Get back the other locks.
1629 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1630 "VM thread should have CMS token");
1631 getFreelistLocks();
1632 bitMapLock()->lock_without_safepoint_check();
1633 if (TraceCMSState) {
1634 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1635 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1636 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1637 }
1638
1639 // Check if we need to do a compaction, or if not, whether
1640 // we need to start the mark-sweep from scratch.
1641 bool should_compact = false;
1642 bool should_start_over = false;
1643 decide_foreground_collection_type(clear_all_soft_refs,
1644 &should_compact, &should_start_over);
1645
1646 NOT_PRODUCT(
1647 if (RotateCMSCollectionTypes) {
1648 if (_cmsGen->debug_collection_type() ==
1649 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1650 should_compact = true;
1651 } else if (_cmsGen->debug_collection_type() ==
1652 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1653 should_compact = false;
1654 }
1655 }
1656 )
1657
1658 if (first_state > Idling) {
1659 report_concurrent_mode_interruption();
1660 }
1661
1662 set_did_compact(should_compact);
1663 if (should_compact) {
1664 // If the collection is being acquired from the background
1665 // collector, there may be references on the discovered
1666 // references lists that have NULL referents (being those
1667 // that were concurrently cleared by a mutator) or
1668 // that are no longer active (having been enqueued concurrently
1669 // by the mutator).
1670 // Scrub the list of those references because Mark-Sweep-Compact
1671 // code assumes referents are not NULL and that all discovered
1672 // Reference objects are active.
1673 ref_processor()->clean_up_discovered_references();
1674
1675 if (first_state > Idling) {
1676 save_heap_summary();
1677 }
1678
1679 do_compaction_work(clear_all_soft_refs);
1680
1681 // Has the GC time limit been exceeded?
1682 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1683 size_t max_eden_size = young_gen->max_capacity() -
1684 young_gen->to()->capacity() -
1685 young_gen->from()->capacity();
1686 GenCollectedHeap* gch = GenCollectedHeap::heap();
1687 GCCause::Cause gc_cause = gch->gc_cause();
1688 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1689 young_gen->eden()->used(),
1690 _cmsGen->max_capacity(),
1691 max_eden_size,
1692 full,
1693 gc_cause,
1694 gch->collector_policy());
1695 } else {
1696 do_mark_sweep_work(clear_all_soft_refs, first_state,
1697 should_start_over);
1698 }
1699 // Reset the expansion cause, now that we just completed
1700 // a collection cycle.
1701 clear_expansion_cause();
1702 _foregroundGCIsActive = false;
1703 return;
1704 }
1705
1706 // Resize the tenured generation
1707 // after obtaining the free list locks for the
1708 // two generations.
1709 void CMSCollector::compute_new_size() {
1710 assert_locked_or_safepoint(Heap_lock);
1711 FreelistLocker z(this);
1712 MetaspaceGC::compute_new_size();
1713 _cmsGen->compute_new_size_free_list();
1714 }
1715
1716 // A work method used by foreground collection to determine
1717 // what type of collection (compacting or not, continuing or fresh)
1718 // it should do.
1719 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1720 // and CMSCompactWhenClearAllSoftRefs the default in the future
1721 // and do away with the flags after a suitable period.
1722 void CMSCollector::decide_foreground_collection_type(
1723 bool clear_all_soft_refs, bool* should_compact,
1724 bool* should_start_over) {
1725 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1726 // flag is set, and we have either requested a System.gc() or
1727 // the number of full gc's since the last concurrent cycle
1728 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1729 // or if an incremental collection has failed
1730 GenCollectedHeap* gch = GenCollectedHeap::heap();
1731 assert(gch->collector_policy()->is_generation_policy(),
1732 "You may want to check the correctness of the following");
1733 // Inform cms gen if this was due to partial collection failing.
1734 // The CMS gen may use this fact to determine its expansion policy.
1735 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1736 assert(!_cmsGen->incremental_collection_failed(),
1737 "Should have been noticed, reacted to and cleared");
1738 _cmsGen->set_incremental_collection_failed();
1739 }
1740 *should_compact =
1741 UseCMSCompactAtFullCollection &&
1742 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1743 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1744 gch->incremental_collection_will_fail(true /* consult_young */));
1745 *should_start_over = false;
1746 if (clear_all_soft_refs && !*should_compact) {
1747 // We are about to do a last ditch collection attempt
1748 // so it would normally make sense to do a compaction
1749 // to reclaim as much space as possible.
1750 if (CMSCompactWhenClearAllSoftRefs) {
1751 // Default: The rationale is that in this case either
1752 // we are past the final marking phase, in which case
1753 // we'd have to start over, or so little has been done
1754 // that there's little point in saving that work. Compaction
1755 // appears to be the sensible choice in either case.
1756 *should_compact = true;
1757 } else {
1758 // We have been asked to clear all soft refs, but not to
1759 // compact. Make sure that we aren't past the final checkpoint
1760 // phase, for that is where we process soft refs. If we are already
1761 // past that phase, we'll need to redo the refs discovery phase and
1762 // if necessary clear soft refs that weren't previously
1763 // cleared. We do so by remembering the phase in which
1764 // we came in, and if we are past the refs processing
1765 // phase, we'll choose to just redo the mark-sweep
1766 // collection from scratch.
1767 if (_collectorState > FinalMarking) {
1768 // We are past the refs processing phase;
1769 // start over and do a fresh synchronous CMS cycle
1770 _collectorState = Resetting; // skip to reset to start new cycle
1771 reset(false /* == !asynch */);
1772 *should_start_over = true;
1773 } // else we can continue a possibly ongoing current cycle
1774 }
1775 }
1776 }
1777
1778 // A work method used by the foreground collector to do
1779 // a mark-sweep-compact.
1780 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1781 GenCollectedHeap* gch = GenCollectedHeap::heap();
1782
1783 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1784 gc_timer->register_gc_start();
1785
1786 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1787 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1788
1789 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
1790 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
1791 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
1792 "collections passed to foreground collector", _full_gcs_since_conc_gc);
1793 }
1794
1795 // Temporarily widen the span of the weak reference processing to
1796 // the entire heap.
1797 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1798 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1799 // Temporarily, clear the "is_alive_non_header" field of the
1800 // reference processor.
1801 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1802 // Temporarily make reference _processing_ single threaded (non-MT).
1803 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1804 // Temporarily make refs discovery atomic
1805 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1806 // Temporarily make reference _discovery_ single threaded (non-MT)
1807 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1808
1809 ref_processor()->set_enqueuing_is_done(false);
1810 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
1811 ref_processor()->setup_policy(clear_all_soft_refs);
1812 // If an asynchronous collection finishes, the _modUnionTable is
1813 // all clear. If we are assuming the collection from an asynchronous
1814 // collection, clear the _modUnionTable.
1815 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1816 "_modUnionTable should be clear if the baton was not passed");
1817 _modUnionTable.clear_all();
1818 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1819 "mod union for klasses should be clear if the baton was passed");
1820 _ct->klass_rem_set()->clear_mod_union();
1821
1822 // We must adjust the allocation statistics being maintained
1823 // in the free list space. We do so by reading and clearing
1824 // the sweep timer and updating the block flux rate estimates below.
1825 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1826 if (_inter_sweep_timer.is_active()) {
1827 _inter_sweep_timer.stop();
1828 // Note that we do not use this sample to update the _inter_sweep_estimate.
1829 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1830 _inter_sweep_estimate.padded_average(),
1831 _intra_sweep_estimate.padded_average());
1832 }
1833
1834 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1835 ref_processor(), clear_all_soft_refs);
1836 #ifdef ASSERT
1837 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1838 size_t free_size = cms_space->free();
1839 assert(free_size ==
1840 pointer_delta(cms_space->end(), cms_space->compaction_top())
1841 * HeapWordSize,
1842 "All the free space should be compacted into one chunk at top");
1843 assert(cms_space->dictionary()->total_chunk_size(
1844 debug_only(cms_space->freelistLock())) == 0 ||
1845 cms_space->totalSizeInIndexedFreeLists() == 0,
1846 "All the free space should be in a single chunk");
1847 size_t num = cms_space->totalCount();
1848 assert((free_size == 0 && num == 0) ||
1849 (free_size > 0 && (num == 1 || num == 2)),
1850 "There should be at most 2 free chunks after compaction");
1851 #endif // ASSERT
1852 _collectorState = Resetting;
1853 assert(_restart_addr == NULL,
1854 "Should have been NULL'd before baton was passed");
1855 reset(false /* == !asynch */);
1856 _cmsGen->reset_after_compaction();
1857 _concurrent_cycles_since_last_unload = 0;
1858
1859 // Clear any data recorded in the PLAB chunk arrays.
1860 if (_survivor_plab_array != NULL) {
1861 reset_survivor_plab_arrays();
1862 }
1863
1864 // Adjust the per-size allocation stats for the next epoch.
1865 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1866 // Restart the "inter sweep timer" for the next epoch.
1867 _inter_sweep_timer.reset();
1868 _inter_sweep_timer.start();
1869
1870 gc_timer->register_gc_end();
1871
1872 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1873
1874 // For a mark-sweep-compact, compute_new_size() will be called
1875 // in the heap's do_collection() method.
1876 }
1877
1878 // A work method used by the foreground collector to do
1879 // a mark-sweep, after taking over from a possibly on-going
1880 // concurrent mark-sweep collection.
1881 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
1882 CollectorState first_state, bool should_start_over) {
1883 if (PrintGC && Verbose) {
1884 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
1885 "collector with count %d",
1886 _full_gcs_since_conc_gc);
1887 }
1888 switch (_collectorState) {
1889 case Idling:
1890 if (first_state == Idling || should_start_over) {
1891 // The background GC was not active, or should
1892 // restarted from scratch; start the cycle.
1893 _collectorState = InitialMarking;
1894 }
1895 // If first_state was not Idling, then a background GC
1896 // was in progress and has now finished. No need to do it
1897 // again. Leave the state as Idling.
1898 break;
1899 case Precleaning:
1900 // In the foreground case don't do the precleaning since
1901 // it is not done concurrently and there is extra work
1902 // required.
1903 _collectorState = FinalMarking;
1904 }
1905 collect_in_foreground(clear_all_soft_refs, GenCollectedHeap::heap()->gc_cause());
1906
1907 // For a mark-sweep, compute_new_size() will be called
1908 // in the heap's do_collection() method.
1909 }
1910
1911
1912 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1913 DefNewGeneration* dng = _young_gen->as_DefNewGeneration();
1914 ContiguousSpace* eden_space = dng->eden();
1915 ContiguousSpace* from_space = dng->from();
1916 ContiguousSpace* to_space = dng->to();
1917 // Eden
1918 if (_eden_chunk_array != NULL) {
1919 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1920 eden_space->bottom(), eden_space->top(),
1921 eden_space->end(), eden_space->capacity());
1922 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1923 "_eden_chunk_capacity=" SIZE_FORMAT,
1924 _eden_chunk_index, _eden_chunk_capacity);
1925 for (size_t i = 0; i < _eden_chunk_index; i++) {
1926 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1927 i, _eden_chunk_array[i]);
1928 }
1929 }
1930 // Survivor
1931 if (_survivor_chunk_array != NULL) {
1932 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1933 from_space->bottom(), from_space->top(),
1934 from_space->end(), from_space->capacity());
1935 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1936 "_survivor_chunk_capacity=" SIZE_FORMAT,
1937 _survivor_chunk_index, _survivor_chunk_capacity);
1938 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1939 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1940 i, _survivor_chunk_array[i]);
1941 }
1942 }
1943 }
1944
1945 void CMSCollector::getFreelistLocks() const {
1946 // Get locks for all free lists in all generations that this
1947 // collector is responsible for
1948 _cmsGen->freelistLock()->lock_without_safepoint_check();
1949 }
1950
1951 void CMSCollector::releaseFreelistLocks() const {
1952 // Release locks for all free lists in all generations that this
1953 // collector is responsible for
1954 _cmsGen->freelistLock()->unlock();
1955 }
1956
1957 bool CMSCollector::haveFreelistLocks() const {
1958 // Check locks for all free lists in all generations that this
1959 // collector is responsible for
1960 assert_lock_strong(_cmsGen->freelistLock());
1961 PRODUCT_ONLY(ShouldNotReachHere());
1962 return true;
1963 }
1964
1965 // A utility class that is used by the CMS collector to
1966 // temporarily "release" the foreground collector from its
1967 // usual obligation to wait for the background collector to
1968 // complete an ongoing phase before proceeding.
1969 class ReleaseForegroundGC: public StackObj {
1970 private:
1971 CMSCollector* _c;
1972 public:
1973 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1974 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1975 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1976 // allow a potentially blocked foreground collector to proceed
1977 _c->_foregroundGCShouldWait = false;
1978 if (_c->_foregroundGCIsActive) {
1979 CGC_lock->notify();
1980 }
1981 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1982 "Possible deadlock");
1983 }
1984
1985 ~ReleaseForegroundGC() {
1986 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1987 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1988 _c->_foregroundGCShouldWait = true;
1989 }
1990 };
1991
1992 // There are separate collect_in_background and collect_in_foreground because of
1993 // the different locking requirements of the background collector and the
1994 // foreground collector. There was originally an attempt to share
1995 // one "collect" method between the background collector and the foreground
1996 // collector but the if-then-else required made it cleaner to have
1997 // separate methods.
1998 void CMSCollector::collect_in_background(bool clear_all_soft_refs, GCCause::Cause cause) {
1999 assert(Thread::current()->is_ConcurrentGC_thread(),
2000 "A CMS asynchronous collection is only allowed on a CMS thread.");
2001
2002 GenCollectedHeap* gch = GenCollectedHeap::heap();
2003 {
2004 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2005 MutexLockerEx hl(Heap_lock, safepoint_check);
2006 FreelistLocker fll(this);
2007 MutexLockerEx x(CGC_lock, safepoint_check);
2008 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2009 // The foreground collector is active or we're
2010 // not using asynchronous collections. Skip this
2011 // background collection.
2012 assert(!_foregroundGCShouldWait, "Should be clear");
2013 return;
2014 } else {
2015 assert(_collectorState == Idling, "Should be idling before start.");
2016 _collectorState = InitialMarking;
2017 register_gc_start(cause);
2018 // Reset the expansion cause, now that we are about to begin
2019 // a new cycle.
2020 clear_expansion_cause();
2021
2022 // Clear the MetaspaceGC flag since a concurrent collection
2023 // is starting but also clear it after the collection.
2024 MetaspaceGC::set_should_concurrent_collect(false);
2025 }
2026 // Decide if we want to enable class unloading as part of the
2027 // ensuing concurrent GC cycle.
2028 update_should_unload_classes();
2029 _full_gc_requested = false; // acks all outstanding full gc requests
2030 _full_gc_cause = GCCause::_no_gc;
2031 // Signal that we are about to start a collection
2032 gch->increment_total_full_collections(); // ... starting a collection cycle
2033 _collection_count_start = gch->total_full_collections();
2034 }
2035
2036 // Used for PrintGC
2037 size_t prev_used;
2038 if (PrintGC && Verbose) {
2039 prev_used = _cmsGen->used(); // XXXPERM
2040 }
2041
2042 // The change of the collection state is normally done at this level;
2043 // the exceptions are phases that are executed while the world is
2044 // stopped. For those phases the change of state is done while the
2045 // world is stopped. For baton passing purposes this allows the
2046 // background collector to finish the phase and change state atomically.
2047 // The foreground collector cannot wait on a phase that is done
2048 // while the world is stopped because the foreground collector already
2049 // has the world stopped and would deadlock.
2050 while (_collectorState != Idling) {
2051 if (TraceCMSState) {
2052 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2053 Thread::current(), _collectorState);
2054 }
2055 // The foreground collector
2056 // holds the Heap_lock throughout its collection.
2057 // holds the CMS token (but not the lock)
2058 // except while it is waiting for the background collector to yield.
2059 //
2060 // The foreground collector should be blocked (not for long)
2061 // if the background collector is about to start a phase
2062 // executed with world stopped. If the background
2063 // collector has already started such a phase, the
2064 // foreground collector is blocked waiting for the
2065 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2066 // are executed in the VM thread.
2067 //
2068 // The locking order is
2069 // PendingListLock (PLL) -- if applicable (FinalMarking)
2070 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2071 // CMS token (claimed in
2072 // stop_world_and_do() -->
2073 // safepoint_synchronize() -->
2074 // CMSThread::synchronize())
2075
2076 {
2077 // Check if the FG collector wants us to yield.
2078 CMSTokenSync x(true); // is cms thread
2079 if (waitForForegroundGC()) {
2080 // We yielded to a foreground GC, nothing more to be
2081 // done this round.
2082 assert(_foregroundGCShouldWait == false, "We set it to false in "
2083 "waitForForegroundGC()");
2084 if (TraceCMSState) {
2085 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2086 " exiting collection CMS state %d",
2087 Thread::current(), _collectorState);
2088 }
2089 return;
2090 } else {
2091 // The background collector can run but check to see if the
2092 // foreground collector has done a collection while the
2093 // background collector was waiting to get the CGC_lock
2094 // above. If yes, break so that _foregroundGCShouldWait
2095 // is cleared before returning.
2096 if (_collectorState == Idling) {
2097 break;
2098 }
2099 }
2100 }
2101
2102 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2103 "should be waiting");
2104
2105 switch (_collectorState) {
2106 case InitialMarking:
2107 {
2108 ReleaseForegroundGC x(this);
2109 stats().record_cms_begin();
2110 VM_CMS_Initial_Mark initial_mark_op(this);
2111 VMThread::execute(&initial_mark_op);
2112 }
2113 // The collector state may be any legal state at this point
2114 // since the background collector may have yielded to the
2115 // foreground collector.
2116 break;
2117 case Marking:
2118 // initial marking in checkpointRootsInitialWork has been completed
2119 if (markFromRoots(true)) { // we were successful
2120 assert(_collectorState == Precleaning, "Collector state should "
2121 "have changed");
2122 } else {
2123 assert(_foregroundGCIsActive, "Internal state inconsistency");
2124 }
2125 break;
2126 case Precleaning:
2127 // marking from roots in markFromRoots has been completed
2128 preclean();
2129 assert(_collectorState == AbortablePreclean ||
2130 _collectorState == FinalMarking,
2131 "Collector state should have changed");
2132 break;
2133 case AbortablePreclean:
2134 abortable_preclean();
2135 assert(_collectorState == FinalMarking, "Collector state should "
2136 "have changed");
2137 break;
2138 case FinalMarking:
2139 {
2140 ReleaseForegroundGC x(this);
2141
2142 VM_CMS_Final_Remark final_remark_op(this);
2143 VMThread::execute(&final_remark_op);
2144 }
2145 assert(_foregroundGCShouldWait, "block post-condition");
2146 break;
2147 case Sweeping:
2148 // final marking in checkpointRootsFinal has been completed
2149 sweep(true);
2150 assert(_collectorState == Resizing, "Collector state change "
2151 "to Resizing must be done under the free_list_lock");
2152 _full_gcs_since_conc_gc = 0;
2153
2154 case Resizing: {
2155 // Sweeping has been completed...
2156 // At this point the background collection has completed.
2157 // Don't move the call to compute_new_size() down
2158 // into code that might be executed if the background
2159 // collection was preempted.
2160 {
2161 ReleaseForegroundGC x(this); // unblock FG collection
2162 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2163 CMSTokenSync z(true); // not strictly needed.
2164 if (_collectorState == Resizing) {
2165 compute_new_size();
2166 save_heap_summary();
2167 _collectorState = Resetting;
2168 } else {
2169 assert(_collectorState == Idling, "The state should only change"
2170 " because the foreground collector has finished the collection");
2171 }
2172 }
2173 break;
2174 }
2175 case Resetting:
2176 // CMS heap resizing has been completed
2177 reset(true);
2178 assert(_collectorState == Idling, "Collector state should "
2179 "have changed");
2180
2181 MetaspaceGC::set_should_concurrent_collect(false);
2182
2183 stats().record_cms_end();
2184 // Don't move the concurrent_phases_end() and compute_new_size()
2185 // calls to here because a preempted background collection
2186 // has it's state set to "Resetting".
2187 break;
2188 case Idling:
2189 default:
2190 ShouldNotReachHere();
2191 break;
2192 }
2193 if (TraceCMSState) {
2194 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2195 Thread::current(), _collectorState);
2196 }
2197 assert(_foregroundGCShouldWait, "block post-condition");
2198 }
2199
2200 // Should this be in gc_epilogue?
2201 collector_policy()->counters()->update_counters();
2202
2203 {
2204 // Clear _foregroundGCShouldWait and, in the event that the
2205 // foreground collector is waiting, notify it, before
2206 // returning.
2207 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2208 _foregroundGCShouldWait = false;
2209 if (_foregroundGCIsActive) {
2210 CGC_lock->notify();
2211 }
2212 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2213 "Possible deadlock");
2214 }
2215 if (TraceCMSState) {
2216 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2217 " exiting collection CMS state %d",
2218 Thread::current(), _collectorState);
2219 }
2220 if (PrintGC && Verbose) {
2221 _cmsGen->print_heap_change(prev_used);
2222 }
2223 }
2224
2225 void CMSCollector::register_foreground_gc_start(GCCause::Cause cause) {
2226 if (!_cms_start_registered) {
2227 register_gc_start(cause);
2228 }
2229 }
2230
2231 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2232 _cms_start_registered = true;
2233 _gc_timer_cm->register_gc_start();
2234 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2235 }
2236
2237 void CMSCollector::register_gc_end() {
2238 if (_cms_start_registered) {
2239 report_heap_summary(GCWhen::AfterGC);
2240
2241 _gc_timer_cm->register_gc_end();
2242 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2243 _cms_start_registered = false;
2244 }
2245 }
2246
2247 void CMSCollector::save_heap_summary() {
2248 GenCollectedHeap* gch = GenCollectedHeap::heap();
2249 _last_heap_summary = gch->create_heap_summary();
2250 _last_metaspace_summary = gch->create_metaspace_summary();
2251 }
2252
2253 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2254 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2255 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2256 }
2257
2258 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs, GCCause::Cause cause) {
2259 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2260 "Foreground collector should be waiting, not executing");
2261 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2262 "may only be done by the VM Thread with the world stopped");
2263 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2264 "VM thread should have CMS token");
2265
2266 // The gc id is created in register_foreground_gc_start if this collection is synchronous
2267 const GCId gc_id = _collectorState == InitialMarking ? GCId::peek() : _gc_tracer_cm->gc_id();
2268 NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2269 true, NULL, gc_id);)
2270 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2271
2272 HandleMark hm; // Discard invalid handles created during verification
2273
2274 if (VerifyBeforeGC &&
2275 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2276 Universe::verify();
2277 }
2278
2279 // Snapshot the soft reference policy to be used in this collection cycle.
2280 ref_processor()->setup_policy(clear_all_soft_refs);
2281
2282 // Decide if class unloading should be done
2283 update_should_unload_classes();
2284
2285 bool init_mark_was_synchronous = false; // until proven otherwise
2286 while (_collectorState != Idling) {
2287 if (TraceCMSState) {
2288 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2289 Thread::current(), _collectorState);
2290 }
2291 switch (_collectorState) {
2292 case InitialMarking:
2293 register_foreground_gc_start(cause);
2294 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2295 checkpointRootsInitial(false);
2296 assert(_collectorState == Marking, "Collector state should have changed"
2297 " within checkpointRootsInitial()");
2298 break;
2299 case Marking:
2300 // initial marking in checkpointRootsInitialWork has been completed
2301 if (VerifyDuringGC &&
2302 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2303 Universe::verify("Verify before initial mark: ");
2304 }
2305 {
2306 bool res = markFromRoots(false);
2307 assert(res && _collectorState == FinalMarking, "Collector state should "
2308 "have changed");
2309 break;
2310 }
2311 case FinalMarking:
2312 if (VerifyDuringGC &&
2313 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2314 Universe::verify("Verify before re-mark: ");
2315 }
2316 checkpointRootsFinal(false, clear_all_soft_refs,
2317 init_mark_was_synchronous);
2318 assert(_collectorState == Sweeping, "Collector state should not "
2319 "have changed within checkpointRootsFinal()");
2320 break;
2321 case Sweeping:
2322 // final marking in checkpointRootsFinal has been completed
2323 if (VerifyDuringGC &&
2324 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2325 Universe::verify("Verify before sweep: ");
2326 }
2327 sweep(false);
2328 assert(_collectorState == Resizing, "Incorrect state");
2329 break;
2330 case Resizing: {
2331 // Sweeping has been completed; the actual resize in this case
2332 // is done separately; nothing to be done in this state.
2333 _collectorState = Resetting;
2334 break;
2335 }
2336 case Resetting:
2337 // The heap has been resized.
2338 if (VerifyDuringGC &&
2339 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2340 Universe::verify("Verify before reset: ");
2341 }
2342 save_heap_summary();
2343 reset(false);
2344 assert(_collectorState == Idling, "Collector state should "
2345 "have changed");
2346 break;
2347 case Precleaning:
2348 case AbortablePreclean:
2349 // Elide the preclean phase
2350 _collectorState = FinalMarking;
2351 break;
2352 default:
2353 ShouldNotReachHere();
2354 }
2355 if (TraceCMSState) {
2356 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2357 Thread::current(), _collectorState);
2358 }
2359 }
2360
2361 if (VerifyAfterGC &&
2362 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2363 Universe::verify();
2364 }
2365 if (TraceCMSState) {
2366 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2367 " exiting collection CMS state %d",
2368 Thread::current(), _collectorState);
2369 }
2370 }
2371
2372 bool CMSCollector::waitForForegroundGC() {
2373 bool res = false;
2374 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2375 "CMS thread should have CMS token");
2376 // Block the foreground collector until the
2377 // background collectors decides whether to
2378 // yield.
2379 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2380 _foregroundGCShouldWait = true;
2381 if (_foregroundGCIsActive) {
2382 // The background collector yields to the
2383 // foreground collector and returns a value
2384 // indicating that it has yielded. The foreground
2385 // collector can proceed.
2386 res = true;
2387 _foregroundGCShouldWait = false;
2388 ConcurrentMarkSweepThread::clear_CMS_flag(
2389 ConcurrentMarkSweepThread::CMS_cms_has_token);
2390 ConcurrentMarkSweepThread::set_CMS_flag(
2391 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2392 // Get a possibly blocked foreground thread going
2393 CGC_lock->notify();
2394 if (TraceCMSState) {
2395 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2396 Thread::current(), _collectorState);
2397 }
2398 while (_foregroundGCIsActive) {
2399 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2400 }
2401 ConcurrentMarkSweepThread::set_CMS_flag(
2402 ConcurrentMarkSweepThread::CMS_cms_has_token);
2403 ConcurrentMarkSweepThread::clear_CMS_flag(
2404 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2405 }
2406 if (TraceCMSState) {
2407 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2408 Thread::current(), _collectorState);
2409 }
2410 return res;
2411 }
2412
2413 // Because of the need to lock the free lists and other structures in
2414 // the collector, common to all the generations that the collector is
2415 // collecting, we need the gc_prologues of individual CMS generations
2416 // delegate to their collector. It may have been simpler had the
2417 // current infrastructure allowed one to call a prologue on a
2418 // collector. In the absence of that we have the generation's
2419 // prologue delegate to the collector, which delegates back
2420 // some "local" work to a worker method in the individual generations
2421 // that it's responsible for collecting, while itself doing any
2422 // work common to all generations it's responsible for. A similar
2423 // comment applies to the gc_epilogue()'s.
2424 // The role of the variable _between_prologue_and_epilogue is to
2425 // enforce the invocation protocol.
2426 void CMSCollector::gc_prologue(bool full) {
2427 // Call gc_prologue_work() for the CMSGen
2428 // we are responsible for.
2429
2430 // The following locking discipline assumes that we are only called
2431 // when the world is stopped.
2432 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2433
2434 // The CMSCollector prologue must call the gc_prologues for the
2435 // "generations" that it's responsible
2436 // for.
2437
2438 assert( Thread::current()->is_VM_thread()
2439 || ( CMSScavengeBeforeRemark
2440 && Thread::current()->is_ConcurrentGC_thread()),
2441 "Incorrect thread type for prologue execution");
2442
2443 if (_between_prologue_and_epilogue) {
2444 // We have already been invoked; this is a gc_prologue delegation
2445 // from yet another CMS generation that we are responsible for, just
2446 // ignore it since all relevant work has already been done.
2447 return;
2448 }
2449
2450 // set a bit saying prologue has been called; cleared in epilogue
2451 _between_prologue_and_epilogue = true;
2452 // Claim locks for common data structures, then call gc_prologue_work()
2453 // for each CMSGen.
2454
2455 getFreelistLocks(); // gets free list locks on constituent spaces
2456 bitMapLock()->lock_without_safepoint_check();
2457
2458 // Should call gc_prologue_work() for all cms gens we are responsible for
2459 bool duringMarking = _collectorState >= Marking
2460 && _collectorState < Sweeping;
2461
2462 // The young collections clear the modified oops state, which tells if
2463 // there are any modified oops in the class. The remark phase also needs
2464 // that information. Tell the young collection to save the union of all
2465 // modified klasses.
2466 if (duringMarking) {
2467 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2468 }
2469
2470 bool registerClosure = duringMarking;
2471
2472 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2473 &_modUnionClosurePar
2474 : &_modUnionClosure;
2475 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2476
2477 if (!full) {
2478 stats().record_gc0_begin();
2479 }
2480 }
2481
2482 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2483
2484 _capacity_at_prologue = capacity();
2485 _used_at_prologue = used();
2486
2487 // Delegate to CMScollector which knows how to coordinate between
2488 // this and any other CMS generations that it is responsible for
2489 // collecting.
2490 collector()->gc_prologue(full);
2491 }
2492
2493 // This is a "private" interface for use by this generation's CMSCollector.
2494 // Not to be called directly by any other entity (for instance,
2495 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2496 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2497 bool registerClosure, ModUnionClosure* modUnionClosure) {
2498 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2499 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2500 "Should be NULL");
2501 if (registerClosure) {
2502 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2503 }
2504 cmsSpace()->gc_prologue();
2505 // Clear stat counters
2506 NOT_PRODUCT(
2507 assert(_numObjectsPromoted == 0, "check");
2508 assert(_numWordsPromoted == 0, "check");
2509 if (Verbose && PrintGC) {
2510 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2511 SIZE_FORMAT" bytes concurrently",
2512 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2513 }
2514 _numObjectsAllocated = 0;
2515 _numWordsAllocated = 0;
2516 )
2517 }
2518
2519 void CMSCollector::gc_epilogue(bool full) {
2520 // The following locking discipline assumes that we are only called
2521 // when the world is stopped.
2522 assert(SafepointSynchronize::is_at_safepoint(),
2523 "world is stopped assumption");
2524
2525 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2526 // if linear allocation blocks need to be appropriately marked to allow the
2527 // the blocks to be parsable. We also check here whether we need to nudge the
2528 // CMS collector thread to start a new cycle (if it's not already active).
2529 assert( Thread::current()->is_VM_thread()
2530 || ( CMSScavengeBeforeRemark
2531 && Thread::current()->is_ConcurrentGC_thread()),
2532 "Incorrect thread type for epilogue execution");
2533
2534 if (!_between_prologue_and_epilogue) {
2535 // We have already been invoked; this is a gc_epilogue delegation
2536 // from yet another CMS generation that we are responsible for, just
2537 // ignore it since all relevant work has already been done.
2538 return;
2539 }
2540 assert(haveFreelistLocks(), "must have freelist locks");
2541 assert_lock_strong(bitMapLock());
2542
2543 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2544
2545 _cmsGen->gc_epilogue_work(full);
2546
2547 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2548 // in case sampling was not already enabled, enable it
2549 _start_sampling = true;
2550 }
2551 // reset _eden_chunk_array so sampling starts afresh
2552 _eden_chunk_index = 0;
2553
2554 size_t cms_used = _cmsGen->cmsSpace()->used();
2555
2556 // update performance counters - this uses a special version of
2557 // update_counters() that allows the utilization to be passed as a
2558 // parameter, avoiding multiple calls to used().
2559 //
2560 _cmsGen->update_counters(cms_used);
2561
2562 bitMapLock()->unlock();
2563 releaseFreelistLocks();
2564
2565 if (!CleanChunkPoolAsync) {
2566 Chunk::clean_chunk_pool();
2567 }
2568
2569 set_did_compact(false);
2570 _between_prologue_and_epilogue = false; // ready for next cycle
2571 }
2572
2573 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2574 collector()->gc_epilogue(full);
2575
2576 // Also reset promotion tracking in par gc thread states.
2577 for (uint i = 0; i < ParallelGCThreads; i++) {
2578 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2579 }
2580 }
2581
2582 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2583 assert(!incremental_collection_failed(), "Should have been cleared");
2584 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2585 cmsSpace()->gc_epilogue();
2586 // Print stat counters
2587 NOT_PRODUCT(
2588 assert(_numObjectsAllocated == 0, "check");
2589 assert(_numWordsAllocated == 0, "check");
2590 if (Verbose && PrintGC) {
2591 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2592 SIZE_FORMAT" bytes",
2593 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2594 }
2595 _numObjectsPromoted = 0;
2596 _numWordsPromoted = 0;
2597 )
2598
2599 if (PrintGC && Verbose) {
2600 // Call down the chain in contiguous_available needs the freelistLock
2601 // so print this out before releasing the freeListLock.
2602 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2603 contiguous_available());
2604 }
2605 }
2606
2607 #ifndef PRODUCT
2608 bool CMSCollector::have_cms_token() {
2609 Thread* thr = Thread::current();
2610 if (thr->is_VM_thread()) {
2611 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2612 } else if (thr->is_ConcurrentGC_thread()) {
2613 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2614 } else if (thr->is_GC_task_thread()) {
2615 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2616 ParGCRareEvent_lock->owned_by_self();
2617 }
2618 return false;
2619 }
2620 #endif
2621
2622 // Check reachability of the given heap address in CMS generation,
2623 // treating all other generations as roots.
2624 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2625 // We could "guarantee" below, rather than assert, but I'll
2626 // leave these as "asserts" so that an adventurous debugger
2627 // could try this in the product build provided some subset of
2628 // the conditions were met, provided they were interested in the
2629 // results and knew that the computation below wouldn't interfere
2630 // with other concurrent computations mutating the structures
2631 // being read or written.
2632 assert(SafepointSynchronize::is_at_safepoint(),
2633 "Else mutations in object graph will make answer suspect");
2634 assert(have_cms_token(), "Should hold cms token");
2635 assert(haveFreelistLocks(), "must hold free list locks");
2636 assert_lock_strong(bitMapLock());
2637
2638 // Clear the marking bit map array before starting, but, just
2639 // for kicks, first report if the given address is already marked
2640 gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", addr,
2641 _markBitMap.isMarked(addr) ? "" : " not");
2642
2643 if (verify_after_remark()) {
2644 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2645 bool result = verification_mark_bm()->isMarked(addr);
2646 gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", addr,
2647 result ? "IS" : "is NOT");
2648 return result;
2649 } else {
2650 gclog_or_tty->print_cr("Could not compute result");
2651 return false;
2652 }
2653 }
2654
2655
2656 void
2657 CMSCollector::print_on_error(outputStream* st) {
2658 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2659 if (collector != NULL) {
2660 CMSBitMap* bitmap = &collector->_markBitMap;
2661 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, bitmap);
2662 bitmap->print_on_error(st, " Bits: ");
2663
2664 st->cr();
2665
2666 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2667 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, mut_bitmap);
2668 mut_bitmap->print_on_error(st, " Bits: ");
2669 }
2670 }
2671
2672 ////////////////////////////////////////////////////////
2673 // CMS Verification Support
2674 ////////////////////////////////////////////////////////
2675 // Following the remark phase, the following invariant
2676 // should hold -- each object in the CMS heap which is
2677 // marked in markBitMap() should be marked in the verification_mark_bm().
2678
2679 class VerifyMarkedClosure: public BitMapClosure {
2680 CMSBitMap* _marks;
2681 bool _failed;
2682
2683 public:
2684 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2685
2686 bool do_bit(size_t offset) {
2687 HeapWord* addr = _marks->offsetToHeapWord(offset);
2688 if (!_marks->isMarked(addr)) {
2689 oop(addr)->print_on(gclog_or_tty);
2690 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2691 _failed = true;
2692 }
2693 return true;
2694 }
2695
2696 bool failed() { return _failed; }
2697 };
2698
2699 bool CMSCollector::verify_after_remark(bool silent) {
2700 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2701 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2702 static bool init = false;
2703
2704 assert(SafepointSynchronize::is_at_safepoint(),
2705 "Else mutations in object graph will make answer suspect");
2706 assert(have_cms_token(),
2707 "Else there may be mutual interference in use of "
2708 " verification data structures");
2709 assert(_collectorState > Marking && _collectorState <= Sweeping,
2710 "Else marking info checked here may be obsolete");
2711 assert(haveFreelistLocks(), "must hold free list locks");
2712 assert_lock_strong(bitMapLock());
2713
2714
2715 // Allocate marking bit map if not already allocated
2716 if (!init) { // first time
2717 if (!verification_mark_bm()->allocate(_span)) {
2718 return false;
2719 }
2720 init = true;
2721 }
2722
2723 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2724
2725 // Turn off refs discovery -- so we will be tracing through refs.
2726 // This is as intended, because by this time
2727 // GC must already have cleared any refs that need to be cleared,
2728 // and traced those that need to be marked; moreover,
2729 // the marking done here is not going to interfere in any
2730 // way with the marking information used by GC.
2731 NoRefDiscovery no_discovery(ref_processor());
2732
2733 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2734
2735 // Clear any marks from a previous round
2736 verification_mark_bm()->clear_all();
2737 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2738 verify_work_stacks_empty();
2739
2740 GenCollectedHeap* gch = GenCollectedHeap::heap();
2741 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2742 // Update the saved marks which may affect the root scans.
2743 gch->save_marks();
2744
2745 if (CMSRemarkVerifyVariant == 1) {
2746 // In this first variant of verification, we complete
2747 // all marking, then check if the new marks-vector is
2748 // a subset of the CMS marks-vector.
2749 verify_after_remark_work_1();
2750 } else if (CMSRemarkVerifyVariant == 2) {
2751 // In this second variant of verification, we flag an error
2752 // (i.e. an object reachable in the new marks-vector not reachable
2753 // in the CMS marks-vector) immediately, also indicating the
2754 // identify of an object (A) that references the unmarked object (B) --
2755 // presumably, a mutation to A failed to be picked up by preclean/remark?
2756 verify_after_remark_work_2();
2757 } else {
2758 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2759 CMSRemarkVerifyVariant);
2760 }
2761 if (!silent) gclog_or_tty->print(" done] ");
2762 return true;
2763 }
2764
2765 void CMSCollector::verify_after_remark_work_1() {
2766 ResourceMark rm;
2767 HandleMark hm;
2768 GenCollectedHeap* gch = GenCollectedHeap::heap();
2769
2770 // Get a clear set of claim bits for the roots processing to work with.
2771 ClassLoaderDataGraph::clear_claimed_marks();
2772
2773 // Mark from roots one level into CMS
2774 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2775 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2776
2777 gch->gen_process_roots(_cmsGen->level(),
2778 true, // younger gens are roots
2779 true, // activate StrongRootsScope
2780 SharedHeap::ScanningOption(roots_scanning_options()),
2781 should_unload_classes(),
2782 ¬Older,
2783 NULL,
2784 NULL); // SSS: Provide correct closure
2785
2786 // Now mark from the roots
2787 MarkFromRootsClosure markFromRootsClosure(this, _span,
2788 verification_mark_bm(), verification_mark_stack(),
2789 false /* don't yield */, true /* verifying */);
2790 assert(_restart_addr == NULL, "Expected pre-condition");
2791 verification_mark_bm()->iterate(&markFromRootsClosure);
2792 while (_restart_addr != NULL) {
2793 // Deal with stack overflow: by restarting at the indicated
2794 // address.
2795 HeapWord* ra = _restart_addr;
2796 markFromRootsClosure.reset(ra);
2797 _restart_addr = NULL;
2798 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2799 }
2800 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2801 verify_work_stacks_empty();
2802
2803 // Marking completed -- now verify that each bit marked in
2804 // verification_mark_bm() is also marked in markBitMap(); flag all
2805 // errors by printing corresponding objects.
2806 VerifyMarkedClosure vcl(markBitMap());
2807 verification_mark_bm()->iterate(&vcl);
2808 if (vcl.failed()) {
2809 gclog_or_tty->print("Verification failed");
2810 Universe::heap()->print_on(gclog_or_tty);
2811 fatal("CMS: failed marking verification after remark");
2812 }
2813 }
2814
2815 class VerifyKlassOopsKlassClosure : public KlassClosure {
2816 class VerifyKlassOopsClosure : public OopClosure {
2817 CMSBitMap* _bitmap;
2818 public:
2819 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2820 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2821 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2822 } _oop_closure;
2823 public:
2824 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2825 void do_klass(Klass* k) {
2826 k->oops_do(&_oop_closure);
2827 }
2828 };
2829
2830 void CMSCollector::verify_after_remark_work_2() {
2831 ResourceMark rm;
2832 HandleMark hm;
2833 GenCollectedHeap* gch = GenCollectedHeap::heap();
2834
2835 // Get a clear set of claim bits for the roots processing to work with.
2836 ClassLoaderDataGraph::clear_claimed_marks();
2837
2838 // Mark from roots one level into CMS
2839 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2840 markBitMap());
2841 CLDToOopClosure cld_closure(¬Older, true);
2842
2843 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2844
2845 gch->gen_process_roots(_cmsGen->level(),
2846 true, // younger gens are roots
2847 true, // activate StrongRootsScope
2848 SharedHeap::ScanningOption(roots_scanning_options()),
2849 should_unload_classes(),
2850 ¬Older,
2851 NULL,
2852 &cld_closure);
2853
2854 // Now mark from the roots
2855 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2856 verification_mark_bm(), markBitMap(), verification_mark_stack());
2857 assert(_restart_addr == NULL, "Expected pre-condition");
2858 verification_mark_bm()->iterate(&markFromRootsClosure);
2859 while (_restart_addr != NULL) {
2860 // Deal with stack overflow: by restarting at the indicated
2861 // address.
2862 HeapWord* ra = _restart_addr;
2863 markFromRootsClosure.reset(ra);
2864 _restart_addr = NULL;
2865 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2866 }
2867 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2868 verify_work_stacks_empty();
2869
2870 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2871 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2872
2873 // Marking completed -- now verify that each bit marked in
2874 // verification_mark_bm() is also marked in markBitMap(); flag all
2875 // errors by printing corresponding objects.
2876 VerifyMarkedClosure vcl(markBitMap());
2877 verification_mark_bm()->iterate(&vcl);
2878 assert(!vcl.failed(), "Else verification above should not have succeeded");
2879 }
2880
2881 void ConcurrentMarkSweepGeneration::save_marks() {
2882 // delegate to CMS space
2883 cmsSpace()->save_marks();
2884 for (uint i = 0; i < ParallelGCThreads; i++) {
2885 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2886 }
2887 }
2888
2889 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2890 return cmsSpace()->no_allocs_since_save_marks();
2891 }
2892
2893 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2894 \
2895 void ConcurrentMarkSweepGeneration:: \
2896 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2897 cl->set_generation(this); \
2898 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2899 cl->reset_generation(); \
2900 save_marks(); \
2901 }
2902
2903 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2904
2905 void
2906 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
2907 cl->set_generation(this);
2908 younger_refs_in_space_iterate(_cmsSpace, cl);
2909 cl->reset_generation();
2910 }
2911
2912 void
2913 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2914 if (freelistLock()->owned_by_self()) {
2915 Generation::oop_iterate(cl);
2916 } else {
2917 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2918 Generation::oop_iterate(cl);
2919 }
2920 }
2921
2922 void
2923 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2924 if (freelistLock()->owned_by_self()) {
2925 Generation::object_iterate(cl);
2926 } else {
2927 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2928 Generation::object_iterate(cl);
2929 }
2930 }
2931
2932 void
2933 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2934 if (freelistLock()->owned_by_self()) {
2935 Generation::safe_object_iterate(cl);
2936 } else {
2937 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2938 Generation::safe_object_iterate(cl);
2939 }
2940 }
2941
2942 void
2943 ConcurrentMarkSweepGeneration::post_compact() {
2944 }
2945
2946 void
2947 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2948 // Fix the linear allocation blocks to look like free blocks.
2949
2950 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2951 // are not called when the heap is verified during universe initialization and
2952 // at vm shutdown.
2953 if (freelistLock()->owned_by_self()) {
2954 cmsSpace()->prepare_for_verify();
2955 } else {
2956 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2957 cmsSpace()->prepare_for_verify();
2958 }
2959 }
2960
2961 void
2962 ConcurrentMarkSweepGeneration::verify() {
2963 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2964 // are not called when the heap is verified during universe initialization and
2965 // at vm shutdown.
2966 if (freelistLock()->owned_by_self()) {
2967 cmsSpace()->verify();
2968 } else {
2969 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2970 cmsSpace()->verify();
2971 }
2972 }
2973
2974 void CMSCollector::verify() {
2975 _cmsGen->verify();
2976 }
2977
2978 #ifndef PRODUCT
2979 bool CMSCollector::overflow_list_is_empty() const {
2980 assert(_num_par_pushes >= 0, "Inconsistency");
2981 if (_overflow_list == NULL) {
2982 assert(_num_par_pushes == 0, "Inconsistency");
2983 }
2984 return _overflow_list == NULL;
2985 }
2986
2987 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2988 // merely consolidate assertion checks that appear to occur together frequently.
2989 void CMSCollector::verify_work_stacks_empty() const {
2990 assert(_markStack.isEmpty(), "Marking stack should be empty");
2991 assert(overflow_list_is_empty(), "Overflow list should be empty");
2992 }
2993
2994 void CMSCollector::verify_overflow_empty() const {
2995 assert(overflow_list_is_empty(), "Overflow list should be empty");
2996 assert(no_preserved_marks(), "No preserved marks");
2997 }
2998 #endif // PRODUCT
2999
3000 // Decide if we want to enable class unloading as part of the
3001 // ensuing concurrent GC cycle. We will collect and
3002 // unload classes if it's the case that:
3003 // (1) an explicit gc request has been made and the flag
3004 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3005 // (2) (a) class unloading is enabled at the command line, and
3006 // (b) old gen is getting really full
3007 // NOTE: Provided there is no change in the state of the heap between
3008 // calls to this method, it should have idempotent results. Moreover,
3009 // its results should be monotonically increasing (i.e. going from 0 to 1,
3010 // but not 1 to 0) between successive calls between which the heap was
3011 // not collected. For the implementation below, it must thus rely on
3012 // the property that concurrent_cycles_since_last_unload()
3013 // will not decrease unless a collection cycle happened and that
3014 // _cmsGen->is_too_full() are
3015 // themselves also monotonic in that sense. See check_monotonicity()
3016 // below.
3017 void CMSCollector::update_should_unload_classes() {
3018 _should_unload_classes = false;
3019 // Condition 1 above
3020 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3021 _should_unload_classes = true;
3022 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3023 // Disjuncts 2.b.(i,ii,iii) above
3024 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3025 CMSClassUnloadingMaxInterval)
3026 || _cmsGen->is_too_full();
3027 }
3028 }
3029
3030 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3031 bool res = should_concurrent_collect();
3032 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3033 return res;
3034 }
3035
3036 void CMSCollector::setup_cms_unloading_and_verification_state() {
3037 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3038 || VerifyBeforeExit;
3039 const int rso = SharedHeap::SO_AllCodeCache;
3040
3041 // We set the proper root for this CMS cycle here.
3042 if (should_unload_classes()) { // Should unload classes this cycle
3043 remove_root_scanning_option(rso); // Shrink the root set appropriately
3044 set_verifying(should_verify); // Set verification state for this cycle
3045 return; // Nothing else needs to be done at this time
3046 }
3047
3048 // Not unloading classes this cycle
3049 assert(!should_unload_classes(), "Inconsistency!");
3050
3051 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3052 // Include symbols, strings and code cache elements to prevent their resurrection.
3053 add_root_scanning_option(rso);
3054 set_verifying(true);
3055 } else if (verifying() && !should_verify) {
3056 // We were verifying, but some verification flags got disabled.
3057 set_verifying(false);
3058 // Exclude symbols, strings and code cache elements from root scanning to
3059 // reduce IM and RM pauses.
3060 remove_root_scanning_option(rso);
3061 }
3062 }
3063
3064
3065 #ifndef PRODUCT
3066 HeapWord* CMSCollector::block_start(const void* p) const {
3067 const HeapWord* addr = (HeapWord*)p;
3068 if (_span.contains(p)) {
3069 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3070 return _cmsGen->cmsSpace()->block_start(p);
3071 }
3072 }
3073 return NULL;
3074 }
3075 #endif
3076
3077 HeapWord*
3078 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3079 bool tlab,
3080 bool parallel) {
3081 CMSSynchronousYieldRequest yr;
3082 assert(!tlab, "Can't deal with TLAB allocation");
3083 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3084 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3085 CMSExpansionCause::_satisfy_allocation);
3086 if (GCExpandToAllocateDelayMillis > 0) {
3087 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3088 }
3089 return have_lock_and_allocate(word_size, tlab);
3090 }
3091
3092 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3093 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3094 // to CardGeneration and share it...
3095 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3096 return CardGeneration::expand(bytes, expand_bytes);
3097 }
3098
3099 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3100 CMSExpansionCause::Cause cause)
3101 {
3102
3103 bool success = expand(bytes, expand_bytes);
3104
3105 // remember why we expanded; this information is used
3106 // by shouldConcurrentCollect() when making decisions on whether to start
3107 // a new CMS cycle.
3108 if (success) {
3109 set_expansion_cause(cause);
3110 if (PrintGCDetails && Verbose) {
3111 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3112 CMSExpansionCause::to_string(cause));
3113 }
3114 }
3115 }
3116
3117 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3118 HeapWord* res = NULL;
3119 MutexLocker x(ParGCRareEvent_lock);
3120 while (true) {
3121 // Expansion by some other thread might make alloc OK now:
3122 res = ps->lab.alloc(word_sz);
3123 if (res != NULL) return res;
3124 // If there's not enough expansion space available, give up.
3125 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3126 return NULL;
3127 }
3128 // Otherwise, we try expansion.
3129 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3130 CMSExpansionCause::_allocate_par_lab);
3131 // Now go around the loop and try alloc again;
3132 // A competing par_promote might beat us to the expansion space,
3133 // so we may go around the loop again if promotion fails again.
3134 if (GCExpandToAllocateDelayMillis > 0) {
3135 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3136 }
3137 }
3138 }
3139
3140
3141 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3142 PromotionInfo* promo) {
3143 MutexLocker x(ParGCRareEvent_lock);
3144 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3145 while (true) {
3146 // Expansion by some other thread might make alloc OK now:
3147 if (promo->ensure_spooling_space()) {
3148 assert(promo->has_spooling_space(),
3149 "Post-condition of successful ensure_spooling_space()");
3150 return true;
3151 }
3152 // If there's not enough expansion space available, give up.
3153 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3154 return false;
3155 }
3156 // Otherwise, we try expansion.
3157 expand(refill_size_bytes, MinHeapDeltaBytes,
3158 CMSExpansionCause::_allocate_par_spooling_space);
3159 // Now go around the loop and try alloc again;
3160 // A competing allocation might beat us to the expansion space,
3161 // so we may go around the loop again if allocation fails again.
3162 if (GCExpandToAllocateDelayMillis > 0) {
3163 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3164 }
3165 }
3166 }
3167
3168
3169 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3170 assert_locked_or_safepoint(ExpandHeap_lock);
3171 // Shrink committed space
3172 _virtual_space.shrink_by(bytes);
3173 // Shrink space; this also shrinks the space's BOT
3174 _cmsSpace->set_end((HeapWord*) _virtual_space.high());
3175 size_t new_word_size = heap_word_size(_cmsSpace->capacity());
3176 // Shrink the shared block offset array
3177 _bts->resize(new_word_size);
3178 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3179 // Shrink the card table
3180 Universe::heap()->barrier_set()->resize_covered_region(mr);
3181
3182 if (Verbose && PrintGC) {
3183 size_t new_mem_size = _virtual_space.committed_size();
3184 size_t old_mem_size = new_mem_size + bytes;
3185 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3186 name(), old_mem_size/K, new_mem_size/K);
3187 }
3188 }
3189
3190 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3191 assert_locked_or_safepoint(Heap_lock);
3192 size_t size = ReservedSpace::page_align_size_down(bytes);
3193 // Only shrink if a compaction was done so that all the free space
3194 // in the generation is in a contiguous block at the end.
3195 if (size > 0 && did_compact()) {
3196 shrink_by(size);
3197 }
3198 }
3199
3200 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3201 assert_locked_or_safepoint(Heap_lock);
3202 bool result = _virtual_space.expand_by(bytes);
3203 if (result) {
3204 size_t new_word_size =
3205 heap_word_size(_virtual_space.committed_size());
3206 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3207 _bts->resize(new_word_size); // resize the block offset shared array
3208 Universe::heap()->barrier_set()->resize_covered_region(mr);
3209 // Hmmmm... why doesn't CFLS::set_end verify locking?
3210 // This is quite ugly; FIX ME XXX
3211 _cmsSpace->assert_locked(freelistLock());
3212 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3213
3214 // update the space and generation capacity counters
3215 if (UsePerfData) {
3216 _space_counters->update_capacity();
3217 _gen_counters->update_all();
3218 }
3219
3220 if (Verbose && PrintGC) {
3221 size_t new_mem_size = _virtual_space.committed_size();
3222 size_t old_mem_size = new_mem_size - bytes;
3223 gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3224 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3225 }
3226 }
3227 return result;
3228 }
3229
3230 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3231 assert_locked_or_safepoint(Heap_lock);
3232 bool success = true;
3233 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3234 if (remaining_bytes > 0) {
3235 success = grow_by(remaining_bytes);
3236 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3237 }
3238 return success;
3239 }
3240
3241 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
3242 assert_locked_or_safepoint(Heap_lock);
3243 assert_lock_strong(freelistLock());
3244 if (PrintGCDetails && Verbose) {
3245 warning("Shrinking of CMS not yet implemented");
3246 }
3247 return;
3248 }
3249
3250
3251 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3252 // phases.
3253 class CMSPhaseAccounting: public StackObj {
3254 public:
3255 CMSPhaseAccounting(CMSCollector *collector,
3256 const char *phase,
3257 const GCId gc_id,
3258 bool print_cr = true);
3259 ~CMSPhaseAccounting();
3260
3261 private:
3262 CMSCollector *_collector;
3263 const char *_phase;
3264 elapsedTimer _wallclock;
3265 bool _print_cr;
3266 const GCId _gc_id;
3267
3268 public:
3269 // Not MT-safe; so do not pass around these StackObj's
3270 // where they may be accessed by other threads.
3271 jlong wallclock_millis() {
3272 assert(_wallclock.is_active(), "Wall clock should not stop");
3273 _wallclock.stop(); // to record time
3274 jlong ret = _wallclock.milliseconds();
3275 _wallclock.start(); // restart
3276 return ret;
3277 }
3278 };
3279
3280 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3281 const char *phase,
3282 const GCId gc_id,
3283 bool print_cr) :
3284 _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
3285
3286 if (PrintCMSStatistics != 0) {
3287 _collector->resetYields();
3288 }
3289 if (PrintGCDetails) {
3290 gclog_or_tty->gclog_stamp(_gc_id);
3291 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
3292 _collector->cmsGen()->short_name(), _phase);
3293 }
3294 _collector->resetTimer();
3295 _wallclock.start();
3296 _collector->startTimer();
3297 }
3298
3299 CMSPhaseAccounting::~CMSPhaseAccounting() {
3300 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3301 _collector->stopTimer();
3302 _wallclock.stop();
3303 if (PrintGCDetails) {
3304 gclog_or_tty->gclog_stamp(_gc_id);
3305 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3306 _collector->cmsGen()->short_name(),
3307 _phase, _collector->timerValue(), _wallclock.seconds());
3308 if (_print_cr) {
3309 gclog_or_tty->cr();
3310 }
3311 if (PrintCMSStatistics != 0) {
3312 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3313 _collector->yields());
3314 }
3315 }
3316 }
3317
3318 // CMS work
3319
3320 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
3321 class CMSParMarkTask : public AbstractGangTask {
3322 protected:
3323 CMSCollector* _collector;
3324 int _n_workers;
3325 CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
3326 AbstractGangTask(name),
3327 _collector(collector),
3328 _n_workers(n_workers) {}
3329 // Work method in support of parallel rescan ... of young gen spaces
3330 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
3331 ContiguousSpace* space,
3332 HeapWord** chunk_array, size_t chunk_top);
3333 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
3334 };
3335
3336 // Parallel initial mark task
3337 class CMSParInitialMarkTask: public CMSParMarkTask {
3338 public:
3339 CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
3340 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
3341 collector, n_workers) {}
3342 void work(uint worker_id);
3343 };
3344
3345 // Checkpoint the roots into this generation from outside
3346 // this generation. [Note this initial checkpoint need only
3347 // be approximate -- we'll do a catch up phase subsequently.]
3348 void CMSCollector::checkpointRootsInitial(bool asynch) {
3349 assert(_collectorState == InitialMarking, "Wrong collector state");
3350 check_correct_thread_executing();
3351 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3352
3353 save_heap_summary();
3354 report_heap_summary(GCWhen::BeforeGC);
3355
3356 ReferenceProcessor* rp = ref_processor();
3357 SpecializationStats::clear();
3358 assert(_restart_addr == NULL, "Control point invariant");
3359 if (asynch) {
3360 // acquire locks for subsequent manipulations
3361 MutexLockerEx x(bitMapLock(),
3362 Mutex::_no_safepoint_check_flag);
3363 checkpointRootsInitialWork(asynch);
3364 // enable ("weak") refs discovery
3365 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3366 _collectorState = Marking;
3367 } else {
3368 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3369 // which recognizes if we are a CMS generation, and doesn't try to turn on
3370 // discovery; verify that they aren't meddling.
3371 assert(!rp->discovery_is_atomic(),
3372 "incorrect setting of discovery predicate");
3373 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3374 "ref discovery for this generation kind");
3375 // already have locks
3376 checkpointRootsInitialWork(asynch);
3377 // now enable ("weak") refs discovery
3378 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3379 _collectorState = Marking;
3380 }
3381 SpecializationStats::print();
3382 }
3383
3384 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3385 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3386 assert(_collectorState == InitialMarking, "just checking");
3387
3388 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3389 // precede our marking with a collection of all
3390 // younger generations to keep floating garbage to a minimum.
3391 // XXX: we won't do this for now -- it's an optimization to be done later.
3392
3393 // already have locks
3394 assert_lock_strong(bitMapLock());
3395 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3396
3397 // Setup the verification and class unloading state for this
3398 // CMS collection cycle.
3399 setup_cms_unloading_and_verification_state();
3400
3401 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3402 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
3403
3404 // Reset all the PLAB chunk arrays if necessary.
3405 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3406 reset_survivor_plab_arrays();
3407 }
3408
3409 ResourceMark rm;
3410 HandleMark hm;
3411
3412 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3413 GenCollectedHeap* gch = GenCollectedHeap::heap();
3414
3415 verify_work_stacks_empty();
3416 verify_overflow_empty();
3417
3418 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3419 // Update the saved marks which may affect the root scans.
3420 gch->save_marks();
3421
3422 // weak reference processing has not started yet.
3423 ref_processor()->set_enqueuing_is_done(false);
3424
3425 // Need to remember all newly created CLDs,
3426 // so that we can guarantee that the remark finds them.
3427 ClassLoaderDataGraph::remember_new_clds(true);
3428
3429 // Whenever a CLD is found, it will be claimed before proceeding to mark
3430 // the klasses. The claimed marks need to be cleared before marking starts.
3431 ClassLoaderDataGraph::clear_claimed_marks();
3432
3433 if (CMSPrintEdenSurvivorChunks) {
3434 print_eden_and_survivor_chunk_arrays();
3435 }
3436
3437 {
3438 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3439 if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3440 // The parallel version.
3441 FlexibleWorkGang* workers = gch->workers();
3442 assert(workers != NULL, "Need parallel worker threads.");
3443 int n_workers = workers->active_workers();
3444 CMSParInitialMarkTask tsk(this, n_workers);
3445 gch->set_par_threads(n_workers);
3446 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3447 if (n_workers > 1) {
3448 GenCollectedHeap::StrongRootsScope srs(gch);
3449 workers->run_task(&tsk);
3450 } else {
3451 GenCollectedHeap::StrongRootsScope srs(gch);
3452 tsk.work(0);
3453 }
3454 gch->set_par_threads(0);
3455 } else {
3456 // The serial version.
3457 CLDToOopClosure cld_closure(¬Older, true);
3458 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3459 gch->gen_process_roots(_cmsGen->level(),
3460 true, // younger gens are roots
3461 true, // activate StrongRootsScope
3462 SharedHeap::ScanningOption(roots_scanning_options()),
3463 should_unload_classes(),
3464 ¬Older,
3465 NULL,
3466 &cld_closure);
3467 }
3468 }
3469
3470 // Clear mod-union table; it will be dirtied in the prologue of
3471 // CMS generation per each younger generation collection.
3472
3473 assert(_modUnionTable.isAllClear(),
3474 "Was cleared in most recent final checkpoint phase"
3475 " or no bits are set in the gc_prologue before the start of the next "
3476 "subsequent marking phase.");
3477
3478 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3479
3480 // Save the end of the used_region of the constituent generations
3481 // to be used to limit the extent of sweep in each generation.
3482 save_sweep_limits();
3483 verify_overflow_empty();
3484 }
3485
3486 bool CMSCollector::markFromRoots(bool asynch) {
3487 // we might be tempted to assert that:
3488 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3489 // "inconsistent argument?");
3490 // However that wouldn't be right, because it's possible that
3491 // a safepoint is indeed in progress as a younger generation
3492 // stop-the-world GC happens even as we mark in this generation.
3493 assert(_collectorState == Marking, "inconsistent state?");
3494 check_correct_thread_executing();
3495 verify_overflow_empty();
3496
3497 bool res;
3498 if (asynch) {
3499 // Weak ref discovery note: We may be discovering weak
3500 // refs in this generation concurrent (but interleaved) with
3501 // weak ref discovery by a younger generation collector.
3502
3503 CMSTokenSyncWithLocks ts(true, bitMapLock());
3504 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3505 CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3506 res = markFromRootsWork(asynch);
3507 if (res) {
3508 _collectorState = Precleaning;
3509 } else { // We failed and a foreground collection wants to take over
3510 assert(_foregroundGCIsActive, "internal state inconsistency");
3511 assert(_restart_addr == NULL, "foreground will restart from scratch");
3512 if (PrintGCDetails) {
3513 gclog_or_tty->print_cr("bailing out to foreground collection");
3514 }
3515 }
3516 } else {
3517 assert(SafepointSynchronize::is_at_safepoint(),
3518 "inconsistent with asynch == false");
3519 // already have locks
3520 res = markFromRootsWork(asynch);
3521 _collectorState = FinalMarking;
3522 }
3523 verify_overflow_empty();
3524 return res;
3525 }
3526
3527 bool CMSCollector::markFromRootsWork(bool asynch) {
3528 // iterate over marked bits in bit map, doing a full scan and mark
3529 // from these roots using the following algorithm:
3530 // . if oop is to the right of the current scan pointer,
3531 // mark corresponding bit (we'll process it later)
3532 // . else (oop is to left of current scan pointer)
3533 // push oop on marking stack
3534 // . drain the marking stack
3535
3536 // Note that when we do a marking step we need to hold the
3537 // bit map lock -- recall that direct allocation (by mutators)
3538 // and promotion (by younger generation collectors) is also
3539 // marking the bit map. [the so-called allocate live policy.]
3540 // Because the implementation of bit map marking is not
3541 // robust wrt simultaneous marking of bits in the same word,
3542 // we need to make sure that there is no such interference
3543 // between concurrent such updates.
3544
3545 // already have locks
3546 assert_lock_strong(bitMapLock());
3547
3548 verify_work_stacks_empty();
3549 verify_overflow_empty();
3550 bool result = false;
3551 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3552 result = do_marking_mt(asynch);
3553 } else {
3554 result = do_marking_st(asynch);
3555 }
3556 return result;
3557 }
3558
3559 // Forward decl
3560 class CMSConcMarkingTask;
3561
3562 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3563 CMSCollector* _collector;
3564 CMSConcMarkingTask* _task;
3565 public:
3566 virtual void yield();
3567
3568 // "n_threads" is the number of threads to be terminated.
3569 // "queue_set" is a set of work queues of other threads.
3570 // "collector" is the CMS collector associated with this task terminator.
3571 // "yield" indicates whether we need the gang as a whole to yield.
3572 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3573 ParallelTaskTerminator(n_threads, queue_set),
3574 _collector(collector) { }
3575
3576 void set_task(CMSConcMarkingTask* task) {
3577 _task = task;
3578 }
3579 };
3580
3581 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3582 CMSConcMarkingTask* _task;
3583 public:
3584 bool should_exit_termination();
3585 void set_task(CMSConcMarkingTask* task) {
3586 _task = task;
3587 }
3588 };
3589
3590 // MT Concurrent Marking Task
3591 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3592 CMSCollector* _collector;
3593 int _n_workers; // requested/desired # workers
3594 bool _asynch;
3595 bool _result;
3596 CompactibleFreeListSpace* _cms_space;
3597 char _pad_front[64]; // padding to ...
3598 HeapWord* _global_finger; // ... avoid sharing cache line
3599 char _pad_back[64];
3600 HeapWord* _restart_addr;
3601
3602 // Exposed here for yielding support
3603 Mutex* const _bit_map_lock;
3604
3605 // The per thread work queues, available here for stealing
3606 OopTaskQueueSet* _task_queues;
3607
3608 // Termination (and yielding) support
3609 CMSConcMarkingTerminator _term;
3610 CMSConcMarkingTerminatorTerminator _term_term;
3611
3612 public:
3613 CMSConcMarkingTask(CMSCollector* collector,
3614 CompactibleFreeListSpace* cms_space,
3615 bool asynch,
3616 YieldingFlexibleWorkGang* workers,
3617 OopTaskQueueSet* task_queues):
3618 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3619 _collector(collector),
3620 _cms_space(cms_space),
3621 _asynch(asynch), _n_workers(0), _result(true),
3622 _task_queues(task_queues),
3623 _term(_n_workers, task_queues, _collector),
3624 _bit_map_lock(collector->bitMapLock())
3625 {
3626 _requested_size = _n_workers;
3627 _term.set_task(this);
3628 _term_term.set_task(this);
3629 _restart_addr = _global_finger = _cms_space->bottom();
3630 }
3631
3632
3633 OopTaskQueueSet* task_queues() { return _task_queues; }
3634
3635 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3636
3637 HeapWord** global_finger_addr() { return &_global_finger; }
3638
3639 CMSConcMarkingTerminator* terminator() { return &_term; }
3640
3641 virtual void set_for_termination(int active_workers) {
3642 terminator()->reset_for_reuse(active_workers);
3643 }
3644
3645 void work(uint worker_id);
3646 bool should_yield() {
3647 return ConcurrentMarkSweepThread::should_yield()
3648 && !_collector->foregroundGCIsActive()
3649 && _asynch;
3650 }
3651
3652 virtual void coordinator_yield(); // stuff done by coordinator
3653 bool result() { return _result; }
3654
3655 void reset(HeapWord* ra) {
3656 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3657 _restart_addr = _global_finger = ra;
3658 _term.reset_for_reuse();
3659 }
3660
3661 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3662 OopTaskQueue* work_q);
3663
3664 private:
3665 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3666 void do_work_steal(int i);
3667 void bump_global_finger(HeapWord* f);
3668 };
3669
3670 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3671 assert(_task != NULL, "Error");
3672 return _task->yielding();
3673 // Note that we do not need the disjunct || _task->should_yield() above
3674 // because we want terminating threads to yield only if the task
3675 // is already in the midst of yielding, which happens only after at least one
3676 // thread has yielded.
3677 }
3678
3679 void CMSConcMarkingTerminator::yield() {
3680 if (_task->should_yield()) {
3681 _task->yield();
3682 } else {
3683 ParallelTaskTerminator::yield();
3684 }
3685 }
3686
3687 ////////////////////////////////////////////////////////////////
3688 // Concurrent Marking Algorithm Sketch
3689 ////////////////////////////////////////////////////////////////
3690 // Until all tasks exhausted (both spaces):
3691 // -- claim next available chunk
3692 // -- bump global finger via CAS
3693 // -- find first object that starts in this chunk
3694 // and start scanning bitmap from that position
3695 // -- scan marked objects for oops
3696 // -- CAS-mark target, and if successful:
3697 // . if target oop is above global finger (volatile read)
3698 // nothing to do
3699 // . if target oop is in chunk and above local finger
3700 // then nothing to do
3701 // . else push on work-queue
3702 // -- Deal with possible overflow issues:
3703 // . local work-queue overflow causes stuff to be pushed on
3704 // global (common) overflow queue
3705 // . always first empty local work queue
3706 // . then get a batch of oops from global work queue if any
3707 // . then do work stealing
3708 // -- When all tasks claimed (both spaces)
3709 // and local work queue empty,
3710 // then in a loop do:
3711 // . check global overflow stack; steal a batch of oops and trace
3712 // . try to steal from other threads oif GOS is empty
3713 // . if neither is available, offer termination
3714 // -- Terminate and return result
3715 //
3716 void CMSConcMarkingTask::work(uint worker_id) {
3717 elapsedTimer _timer;
3718 ResourceMark rm;
3719 HandleMark hm;
3720
3721 DEBUG_ONLY(_collector->verify_overflow_empty();)
3722
3723 // Before we begin work, our work queue should be empty
3724 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3725 // Scan the bitmap covering _cms_space, tracing through grey objects.
3726 _timer.start();
3727 do_scan_and_mark(worker_id, _cms_space);
3728 _timer.stop();
3729 if (PrintCMSStatistics != 0) {
3730 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3731 worker_id, _timer.seconds());
3732 // XXX: need xxx/xxx type of notation, two timers
3733 }
3734
3735 // ... do work stealing
3736 _timer.reset();
3737 _timer.start();
3738 do_work_steal(worker_id);
3739 _timer.stop();
3740 if (PrintCMSStatistics != 0) {
3741 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3742 worker_id, _timer.seconds());
3743 // XXX: need xxx/xxx type of notation, two timers
3744 }
3745 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3746 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3747 // Note that under the current task protocol, the
3748 // following assertion is true even of the spaces
3749 // expanded since the completion of the concurrent
3750 // marking. XXX This will likely change under a strict
3751 // ABORT semantics.
3752 // After perm removal the comparison was changed to
3753 // greater than or equal to from strictly greater than.
3754 // Before perm removal the highest address sweep would
3755 // have been at the end of perm gen but now is at the
3756 // end of the tenured gen.
3757 assert(_global_finger >= _cms_space->end(),
3758 "All tasks have been completed");
3759 DEBUG_ONLY(_collector->verify_overflow_empty();)
3760 }
3761
3762 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3763 HeapWord* read = _global_finger;
3764 HeapWord* cur = read;
3765 while (f > read) {
3766 cur = read;
3767 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3768 if (cur == read) {
3769 // our cas succeeded
3770 assert(_global_finger >= f, "protocol consistency");
3771 break;
3772 }
3773 }
3774 }
3775
3776 // This is really inefficient, and should be redone by
3777 // using (not yet available) block-read and -write interfaces to the
3778 // stack and the work_queue. XXX FIX ME !!!
3779 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3780 OopTaskQueue* work_q) {
3781 // Fast lock-free check
3782 if (ovflw_stk->length() == 0) {
3783 return false;
3784 }
3785 assert(work_q->size() == 0, "Shouldn't steal");
3786 MutexLockerEx ml(ovflw_stk->par_lock(),
3787 Mutex::_no_safepoint_check_flag);
3788 // Grab up to 1/4 the size of the work queue
3789 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3790 (size_t)ParGCDesiredObjsFromOverflowList);
3791 num = MIN2(num, ovflw_stk->length());
3792 for (int i = (int) num; i > 0; i--) {
3793 oop cur = ovflw_stk->pop();
3794 assert(cur != NULL, "Counted wrong?");
3795 work_q->push(cur);
3796 }
3797 return num > 0;
3798 }
3799
3800 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3801 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3802 int n_tasks = pst->n_tasks();
3803 // We allow that there may be no tasks to do here because
3804 // we are restarting after a stack overflow.
3805 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3806 uint nth_task = 0;
3807
3808 HeapWord* aligned_start = sp->bottom();
3809 if (sp->used_region().contains(_restart_addr)) {
3810 // Align down to a card boundary for the start of 0th task
3811 // for this space.
3812 aligned_start =
3813 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3814 CardTableModRefBS::card_size);
3815 }
3816
3817 size_t chunk_size = sp->marking_task_size();
3818 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3819 // Having claimed the nth task in this space,
3820 // compute the chunk that it corresponds to:
3821 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3822 aligned_start + (nth_task+1)*chunk_size);
3823 // Try and bump the global finger via a CAS;
3824 // note that we need to do the global finger bump
3825 // _before_ taking the intersection below, because
3826 // the task corresponding to that region will be
3827 // deemed done even if the used_region() expands
3828 // because of allocation -- as it almost certainly will
3829 // during start-up while the threads yield in the
3830 // closure below.
3831 HeapWord* finger = span.end();
3832 bump_global_finger(finger); // atomically
3833 // There are null tasks here corresponding to chunks
3834 // beyond the "top" address of the space.
3835 span = span.intersection(sp->used_region());
3836 if (!span.is_empty()) { // Non-null task
3837 HeapWord* prev_obj;
3838 assert(!span.contains(_restart_addr) || nth_task == 0,
3839 "Inconsistency");
3840 if (nth_task == 0) {
3841 // For the 0th task, we'll not need to compute a block_start.
3842 if (span.contains(_restart_addr)) {
3843 // In the case of a restart because of stack overflow,
3844 // we might additionally skip a chunk prefix.
3845 prev_obj = _restart_addr;
3846 } else {
3847 prev_obj = span.start();
3848 }
3849 } else {
3850 // We want to skip the first object because
3851 // the protocol is to scan any object in its entirety
3852 // that _starts_ in this span; a fortiori, any
3853 // object starting in an earlier span is scanned
3854 // as part of an earlier claimed task.
3855 // Below we use the "careful" version of block_start
3856 // so we do not try to navigate uninitialized objects.
3857 prev_obj = sp->block_start_careful(span.start());
3858 // Below we use a variant of block_size that uses the
3859 // Printezis bits to avoid waiting for allocated
3860 // objects to become initialized/parsable.
3861 while (prev_obj < span.start()) {
3862 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3863 if (sz > 0) {
3864 prev_obj += sz;
3865 } else {
3866 // In this case we may end up doing a bit of redundant
3867 // scanning, but that appears unavoidable, short of
3868 // locking the free list locks; see bug 6324141.
3869 break;
3870 }
3871 }
3872 }
3873 if (prev_obj < span.end()) {
3874 MemRegion my_span = MemRegion(prev_obj, span.end());
3875 // Do the marking work within a non-empty span --
3876 // the last argument to the constructor indicates whether the
3877 // iteration should be incremental with periodic yields.
3878 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3879 &_collector->_markBitMap,
3880 work_queue(i),
3881 &_collector->_markStack,
3882 _asynch);
3883 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3884 } // else nothing to do for this task
3885 } // else nothing to do for this task
3886 }
3887 // We'd be tempted to assert here that since there are no
3888 // more tasks left to claim in this space, the global_finger
3889 // must exceed space->top() and a fortiori space->end(). However,
3890 // that would not quite be correct because the bumping of
3891 // global_finger occurs strictly after the claiming of a task,
3892 // so by the time we reach here the global finger may not yet
3893 // have been bumped up by the thread that claimed the last
3894 // task.
3895 pst->all_tasks_completed();
3896 }
3897
3898 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3899 private:
3900 CMSCollector* _collector;
3901 CMSConcMarkingTask* _task;
3902 MemRegion _span;
3903 CMSBitMap* _bit_map;
3904 CMSMarkStack* _overflow_stack;
3905 OopTaskQueue* _work_queue;
3906 protected:
3907 DO_OOP_WORK_DEFN
3908 public:
3909 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3910 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3911 MetadataAwareOopClosure(collector->ref_processor()),
3912 _collector(collector),
3913 _task(task),
3914 _span(collector->_span),
3915 _work_queue(work_queue),
3916 _bit_map(bit_map),
3917 _overflow_stack(overflow_stack)
3918 { }
3919 virtual void do_oop(oop* p);
3920 virtual void do_oop(narrowOop* p);
3921
3922 void trim_queue(size_t max);
3923 void handle_stack_overflow(HeapWord* lost);
3924 void do_yield_check() {
3925 if (_task->should_yield()) {
3926 _task->yield();
3927 }
3928 }
3929 };
3930
3931 // Grey object scanning during work stealing phase --
3932 // the salient assumption here is that any references
3933 // that are in these stolen objects being scanned must
3934 // already have been initialized (else they would not have
3935 // been published), so we do not need to check for
3936 // uninitialized objects before pushing here.
3937 void Par_ConcMarkingClosure::do_oop(oop obj) {
3938 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
3939 HeapWord* addr = (HeapWord*)obj;
3940 // Check if oop points into the CMS generation
3941 // and is not marked
3942 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3943 // a white object ...
3944 // If we manage to "claim" the object, by being the
3945 // first thread to mark it, then we push it on our
3946 // marking stack
3947 if (_bit_map->par_mark(addr)) { // ... now grey
3948 // push on work queue (grey set)
3949 bool simulate_overflow = false;
3950 NOT_PRODUCT(
3951 if (CMSMarkStackOverflowALot &&
3952 _collector->simulate_overflow()) {
3953 // simulate a stack overflow
3954 simulate_overflow = true;
3955 }
3956 )
3957 if (simulate_overflow ||
3958 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3959 // stack overflow
3960 if (PrintCMSStatistics != 0) {
3961 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3962 SIZE_FORMAT, _overflow_stack->capacity());
3963 }
3964 // We cannot assert that the overflow stack is full because
3965 // it may have been emptied since.
3966 assert(simulate_overflow ||
3967 _work_queue->size() == _work_queue->max_elems(),
3968 "Else push should have succeeded");
3969 handle_stack_overflow(addr);
3970 }
3971 } // Else, some other thread got there first
3972 do_yield_check();
3973 }
3974 }
3975
3976 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3977 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3978
3979 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3980 while (_work_queue->size() > max) {
3981 oop new_oop;
3982 if (_work_queue->pop_local(new_oop)) {
3983 assert(new_oop->is_oop(), "Should be an oop");
3984 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3985 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3986 new_oop->oop_iterate(this); // do_oop() above
3987 do_yield_check();
3988 }
3989 }
3990 }
3991
3992 // Upon stack overflow, we discard (part of) the stack,
3993 // remembering the least address amongst those discarded
3994 // in CMSCollector's _restart_address.
3995 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3996 // We need to do this under a mutex to prevent other
3997 // workers from interfering with the work done below.
3998 MutexLockerEx ml(_overflow_stack->par_lock(),
3999 Mutex::_no_safepoint_check_flag);
4000 // Remember the least grey address discarded
4001 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4002 _collector->lower_restart_addr(ra);
4003 _overflow_stack->reset(); // discard stack contents
4004 _overflow_stack->expand(); // expand the stack if possible
4005 }
4006
4007
4008 void CMSConcMarkingTask::do_work_steal(int i) {
4009 OopTaskQueue* work_q = work_queue(i);
4010 oop obj_to_scan;
4011 CMSBitMap* bm = &(_collector->_markBitMap);
4012 CMSMarkStack* ovflw = &(_collector->_markStack);
4013 int* seed = _collector->hash_seed(i);
4014 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4015 while (true) {
4016 cl.trim_queue(0);
4017 assert(work_q->size() == 0, "Should have been emptied above");
4018 if (get_work_from_overflow_stack(ovflw, work_q)) {
4019 // Can't assert below because the work obtained from the
4020 // overflow stack may already have been stolen from us.
4021 // assert(work_q->size() > 0, "Work from overflow stack");
4022 continue;
4023 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4024 assert(obj_to_scan->is_oop(), "Should be an oop");
4025 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4026 obj_to_scan->oop_iterate(&cl);
4027 } else if (terminator()->offer_termination(&_term_term)) {
4028 assert(work_q->size() == 0, "Impossible!");
4029 break;
4030 } else if (yielding() || should_yield()) {
4031 yield();
4032 }
4033 }
4034 }
4035
4036 // This is run by the CMS (coordinator) thread.
4037 void CMSConcMarkingTask::coordinator_yield() {
4038 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4039 "CMS thread should hold CMS token");
4040 // First give up the locks, then yield, then re-lock
4041 // We should probably use a constructor/destructor idiom to
4042 // do this unlock/lock or modify the MutexUnlocker class to
4043 // serve our purpose. XXX
4044 assert_lock_strong(_bit_map_lock);
4045 _bit_map_lock->unlock();
4046 ConcurrentMarkSweepThread::desynchronize(true);
4047 _collector->stopTimer();
4048 if (PrintCMSStatistics != 0) {
4049 _collector->incrementYields();
4050 }
4051
4052 // It is possible for whichever thread initiated the yield request
4053 // not to get a chance to wake up and take the bitmap lock between
4054 // this thread releasing it and reacquiring it. So, while the
4055 // should_yield() flag is on, let's sleep for a bit to give the
4056 // other thread a chance to wake up. The limit imposed on the number
4057 // of iterations is defensive, to avoid any unforseen circumstances
4058 // putting us into an infinite loop. Since it's always been this
4059 // (coordinator_yield()) method that was observed to cause the
4060 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4061 // which is by default non-zero. For the other seven methods that
4062 // also perform the yield operation, as are using a different
4063 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4064 // can enable the sleeping for those methods too, if necessary.
4065 // See 6442774.
4066 //
4067 // We really need to reconsider the synchronization between the GC
4068 // thread and the yield-requesting threads in the future and we
4069 // should really use wait/notify, which is the recommended
4070 // way of doing this type of interaction. Additionally, we should
4071 // consolidate the eight methods that do the yield operation and they
4072 // are almost identical into one for better maintainability and
4073 // readability. See 6445193.
4074 //
4075 // Tony 2006.06.29
4076 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4077 ConcurrentMarkSweepThread::should_yield() &&
4078 !CMSCollector::foregroundGCIsActive(); ++i) {
4079 os::sleep(Thread::current(), 1, false);
4080 }
4081
4082 ConcurrentMarkSweepThread::synchronize(true);
4083 _bit_map_lock->lock_without_safepoint_check();
4084 _collector->startTimer();
4085 }
4086
4087 bool CMSCollector::do_marking_mt(bool asynch) {
4088 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4089 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4090 conc_workers()->total_workers(),
4091 conc_workers()->active_workers(),
4092 Threads::number_of_non_daemon_threads());
4093 conc_workers()->set_active_workers(num_workers);
4094
4095 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4096
4097 CMSConcMarkingTask tsk(this,
4098 cms_space,
4099 asynch,
4100 conc_workers(),
4101 task_queues());
4102
4103 // Since the actual number of workers we get may be different
4104 // from the number we requested above, do we need to do anything different
4105 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4106 // class?? XXX
4107 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4108
4109 // Refs discovery is already non-atomic.
4110 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4111 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4112 conc_workers()->start_task(&tsk);
4113 while (tsk.yielded()) {
4114 tsk.coordinator_yield();
4115 conc_workers()->continue_task(&tsk);
4116 }
4117 // If the task was aborted, _restart_addr will be non-NULL
4118 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4119 while (_restart_addr != NULL) {
4120 // XXX For now we do not make use of ABORTED state and have not
4121 // yet implemented the right abort semantics (even in the original
4122 // single-threaded CMS case). That needs some more investigation
4123 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4124 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4125 // If _restart_addr is non-NULL, a marking stack overflow
4126 // occurred; we need to do a fresh marking iteration from the
4127 // indicated restart address.
4128 if (_foregroundGCIsActive && asynch) {
4129 // We may be running into repeated stack overflows, having
4130 // reached the limit of the stack size, while making very
4131 // slow forward progress. It may be best to bail out and
4132 // let the foreground collector do its job.
4133 // Clear _restart_addr, so that foreground GC
4134 // works from scratch. This avoids the headache of
4135 // a "rescan" which would otherwise be needed because
4136 // of the dirty mod union table & card table.
4137 _restart_addr = NULL;
4138 return false;
4139 }
4140 // Adjust the task to restart from _restart_addr
4141 tsk.reset(_restart_addr);
4142 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4143 _restart_addr);
4144 _restart_addr = NULL;
4145 // Get the workers going again
4146 conc_workers()->start_task(&tsk);
4147 while (tsk.yielded()) {
4148 tsk.coordinator_yield();
4149 conc_workers()->continue_task(&tsk);
4150 }
4151 }
4152 assert(tsk.completed(), "Inconsistency");
4153 assert(tsk.result() == true, "Inconsistency");
4154 return true;
4155 }
4156
4157 bool CMSCollector::do_marking_st(bool asynch) {
4158 ResourceMark rm;
4159 HandleMark hm;
4160
4161 // Temporarily make refs discovery single threaded (non-MT)
4162 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4163 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4164 &_markStack, CMSYield && asynch);
4165 // the last argument to iterate indicates whether the iteration
4166 // should be incremental with periodic yields.
4167 _markBitMap.iterate(&markFromRootsClosure);
4168 // If _restart_addr is non-NULL, a marking stack overflow
4169 // occurred; we need to do a fresh iteration from the
4170 // indicated restart address.
4171 while (_restart_addr != NULL) {
4172 if (_foregroundGCIsActive && asynch) {
4173 // We may be running into repeated stack overflows, having
4174 // reached the limit of the stack size, while making very
4175 // slow forward progress. It may be best to bail out and
4176 // let the foreground collector do its job.
4177 // Clear _restart_addr, so that foreground GC
4178 // works from scratch. This avoids the headache of
4179 // a "rescan" which would otherwise be needed because
4180 // of the dirty mod union table & card table.
4181 _restart_addr = NULL;
4182 return false; // indicating failure to complete marking
4183 }
4184 // Deal with stack overflow:
4185 // we restart marking from _restart_addr
4186 HeapWord* ra = _restart_addr;
4187 markFromRootsClosure.reset(ra);
4188 _restart_addr = NULL;
4189 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4190 }
4191 return true;
4192 }
4193
4194 void CMSCollector::preclean() {
4195 check_correct_thread_executing();
4196 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4197 verify_work_stacks_empty();
4198 verify_overflow_empty();
4199 _abort_preclean = false;
4200 if (CMSPrecleaningEnabled) {
4201 if (!CMSEdenChunksRecordAlways) {
4202 _eden_chunk_index = 0;
4203 }
4204 size_t used = get_eden_used();
4205 size_t capacity = get_eden_capacity();
4206 // Don't start sampling unless we will get sufficiently
4207 // many samples.
4208 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4209 * CMSScheduleRemarkEdenPenetration)) {
4210 _start_sampling = true;
4211 } else {
4212 _start_sampling = false;
4213 }
4214 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4215 CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
4216 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4217 }
4218 CMSTokenSync x(true); // is cms thread
4219 if (CMSPrecleaningEnabled) {
4220 sample_eden();
4221 _collectorState = AbortablePreclean;
4222 } else {
4223 _collectorState = FinalMarking;
4224 }
4225 verify_work_stacks_empty();
4226 verify_overflow_empty();
4227 }
4228
4229 // Try and schedule the remark such that young gen
4230 // occupancy is CMSScheduleRemarkEdenPenetration %.
4231 void CMSCollector::abortable_preclean() {
4232 check_correct_thread_executing();
4233 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4234 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4235
4236 // If Eden's current occupancy is below this threshold,
4237 // immediately schedule the remark; else preclean
4238 // past the next scavenge in an effort to
4239 // schedule the pause as described above. By choosing
4240 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4241 // we will never do an actual abortable preclean cycle.
4242 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4243 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4244 CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
4245 // We need more smarts in the abortable preclean
4246 // loop below to deal with cases where allocation
4247 // in young gen is very very slow, and our precleaning
4248 // is running a losing race against a horde of
4249 // mutators intent on flooding us with CMS updates
4250 // (dirty cards).
4251 // One, admittedly dumb, strategy is to give up
4252 // after a certain number of abortable precleaning loops
4253 // or after a certain maximum time. We want to make
4254 // this smarter in the next iteration.
4255 // XXX FIX ME!!! YSR
4256 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4257 while (!(should_abort_preclean() ||
4258 ConcurrentMarkSweepThread::should_terminate())) {
4259 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4260 cumworkdone += workdone;
4261 loops++;
4262 // Voluntarily terminate abortable preclean phase if we have
4263 // been at it for too long.
4264 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4265 loops >= CMSMaxAbortablePrecleanLoops) {
4266 if (PrintGCDetails) {
4267 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4268 }
4269 break;
4270 }
4271 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4272 if (PrintGCDetails) {
4273 gclog_or_tty->print(" CMS: abort preclean due to time ");
4274 }
4275 break;
4276 }
4277 // If we are doing little work each iteration, we should
4278 // take a short break.
4279 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4280 // Sleep for some time, waiting for work to accumulate
4281 stopTimer();
4282 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4283 startTimer();
4284 waited++;
4285 }
4286 }
4287 if (PrintCMSStatistics > 0) {
4288 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
4289 loops, waited, cumworkdone);
4290 }
4291 }
4292 CMSTokenSync x(true); // is cms thread
4293 if (_collectorState != Idling) {
4294 assert(_collectorState == AbortablePreclean,
4295 "Spontaneous state transition?");
4296 _collectorState = FinalMarking;
4297 } // Else, a foreground collection completed this CMS cycle.
4298 return;
4299 }
4300
4301 // Respond to an Eden sampling opportunity
4302 void CMSCollector::sample_eden() {
4303 // Make sure a young gc cannot sneak in between our
4304 // reading and recording of a sample.
4305 assert(Thread::current()->is_ConcurrentGC_thread(),
4306 "Only the cms thread may collect Eden samples");
4307 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4308 "Should collect samples while holding CMS token");
4309 if (!_start_sampling) {
4310 return;
4311 }
4312 // When CMSEdenChunksRecordAlways is true, the eden chunk array
4313 // is populated by the young generation.
4314 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
4315 if (_eden_chunk_index < _eden_chunk_capacity) {
4316 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4317 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4318 "Unexpected state of Eden");
4319 // We'd like to check that what we just sampled is an oop-start address;
4320 // however, we cannot do that here since the object may not yet have been
4321 // initialized. So we'll instead do the check when we _use_ this sample
4322 // later.
4323 if (_eden_chunk_index == 0 ||
4324 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4325 _eden_chunk_array[_eden_chunk_index-1])
4326 >= CMSSamplingGrain)) {
4327 _eden_chunk_index++; // commit sample
4328 }
4329 }
4330 }
4331 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4332 size_t used = get_eden_used();
4333 size_t capacity = get_eden_capacity();
4334 assert(used <= capacity, "Unexpected state of Eden");
4335 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4336 _abort_preclean = true;
4337 }
4338 }
4339 }
4340
4341
4342 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4343 assert(_collectorState == Precleaning ||
4344 _collectorState == AbortablePreclean, "incorrect state");
4345 ResourceMark rm;
4346 HandleMark hm;
4347
4348 // Precleaning is currently not MT but the reference processor
4349 // may be set for MT. Disable it temporarily here.
4350 ReferenceProcessor* rp = ref_processor();
4351 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4352
4353 // Do one pass of scrubbing the discovered reference lists
4354 // to remove any reference objects with strongly-reachable
4355 // referents.
4356 if (clean_refs) {
4357 CMSPrecleanRefsYieldClosure yield_cl(this);
4358 assert(rp->span().equals(_span), "Spans should be equal");
4359 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4360 &_markStack, true /* preclean */);
4361 CMSDrainMarkingStackClosure complete_trace(this,
4362 _span, &_markBitMap, &_markStack,
4363 &keep_alive, true /* preclean */);
4364
4365 // We don't want this step to interfere with a young
4366 // collection because we don't want to take CPU
4367 // or memory bandwidth away from the young GC threads
4368 // (which may be as many as there are CPUs).
4369 // Note that we don't need to protect ourselves from
4370 // interference with mutators because they can't
4371 // manipulate the discovered reference lists nor affect
4372 // the computed reachability of the referents, the
4373 // only properties manipulated by the precleaning
4374 // of these reference lists.
4375 stopTimer();
4376 CMSTokenSyncWithLocks x(true /* is cms thread */,
4377 bitMapLock());
4378 startTimer();
4379 sample_eden();
4380
4381 // The following will yield to allow foreground
4382 // collection to proceed promptly. XXX YSR:
4383 // The code in this method may need further
4384 // tweaking for better performance and some restructuring
4385 // for cleaner interfaces.
4386 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4387 rp->preclean_discovered_references(
4388 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
4389 gc_timer, _gc_tracer_cm->gc_id());
4390 }
4391
4392 if (clean_survivor) { // preclean the active survivor space(s)
4393 assert(_young_gen->kind() == Generation::DefNew ||
4394 _young_gen->kind() == Generation::ParNew,
4395 "incorrect type for cast");
4396 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4397 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4398 &_markBitMap, &_modUnionTable,
4399 &_markStack, true /* precleaning phase */);
4400 stopTimer();
4401 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4402 bitMapLock());
4403 startTimer();
4404 unsigned int before_count =
4405 GenCollectedHeap::heap()->total_collections();
4406 SurvivorSpacePrecleanClosure
4407 sss_cl(this, _span, &_markBitMap, &_markStack,
4408 &pam_cl, before_count, CMSYield);
4409 dng->from()->object_iterate_careful(&sss_cl);
4410 dng->to()->object_iterate_careful(&sss_cl);
4411 }
4412 MarkRefsIntoAndScanClosure
4413 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4414 &_markStack, this, CMSYield,
4415 true /* precleaning phase */);
4416 // CAUTION: The following closure has persistent state that may need to
4417 // be reset upon a decrease in the sequence of addresses it
4418 // processes.
4419 ScanMarkedObjectsAgainCarefullyClosure
4420 smoac_cl(this, _span,
4421 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4422
4423 // Preclean dirty cards in ModUnionTable and CardTable using
4424 // appropriate convergence criterion;
4425 // repeat CMSPrecleanIter times unless we find that
4426 // we are losing.
4427 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4428 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4429 "Bad convergence multiplier");
4430 assert(CMSPrecleanThreshold >= 100,
4431 "Unreasonably low CMSPrecleanThreshold");
4432
4433 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4434 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4435 numIter < CMSPrecleanIter;
4436 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4437 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4438 if (Verbose && PrintGCDetails) {
4439 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
4440 }
4441 // Either there are very few dirty cards, so re-mark
4442 // pause will be small anyway, or our pre-cleaning isn't
4443 // that much faster than the rate at which cards are being
4444 // dirtied, so we might as well stop and re-mark since
4445 // precleaning won't improve our re-mark time by much.
4446 if (curNumCards <= CMSPrecleanThreshold ||
4447 (numIter > 0 &&
4448 (curNumCards * CMSPrecleanDenominator >
4449 lastNumCards * CMSPrecleanNumerator))) {
4450 numIter++;
4451 cumNumCards += curNumCards;
4452 break;
4453 }
4454 }
4455
4456 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4457
4458 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4459 cumNumCards += curNumCards;
4460 if (PrintGCDetails && PrintCMSStatistics != 0) {
4461 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4462 curNumCards, cumNumCards, numIter);
4463 }
4464 return cumNumCards; // as a measure of useful work done
4465 }
4466
4467 // PRECLEANING NOTES:
4468 // Precleaning involves:
4469 // . reading the bits of the modUnionTable and clearing the set bits.
4470 // . For the cards corresponding to the set bits, we scan the
4471 // objects on those cards. This means we need the free_list_lock
4472 // so that we can safely iterate over the CMS space when scanning
4473 // for oops.
4474 // . When we scan the objects, we'll be both reading and setting
4475 // marks in the marking bit map, so we'll need the marking bit map.
4476 // . For protecting _collector_state transitions, we take the CGC_lock.
4477 // Note that any races in the reading of of card table entries by the
4478 // CMS thread on the one hand and the clearing of those entries by the
4479 // VM thread or the setting of those entries by the mutator threads on the
4480 // other are quite benign. However, for efficiency it makes sense to keep
4481 // the VM thread from racing with the CMS thread while the latter is
4482 // dirty card info to the modUnionTable. We therefore also use the
4483 // CGC_lock to protect the reading of the card table and the mod union
4484 // table by the CM thread.
4485 // . We run concurrently with mutator updates, so scanning
4486 // needs to be done carefully -- we should not try to scan
4487 // potentially uninitialized objects.
4488 //
4489 // Locking strategy: While holding the CGC_lock, we scan over and
4490 // reset a maximal dirty range of the mod union / card tables, then lock
4491 // the free_list_lock and bitmap lock to do a full marking, then
4492 // release these locks; and repeat the cycle. This allows for a
4493 // certain amount of fairness in the sharing of these locks between
4494 // the CMS collector on the one hand, and the VM thread and the
4495 // mutators on the other.
4496
4497 // NOTE: preclean_mod_union_table() and preclean_card_table()
4498 // further below are largely identical; if you need to modify
4499 // one of these methods, please check the other method too.
4500
4501 size_t CMSCollector::preclean_mod_union_table(
4502 ConcurrentMarkSweepGeneration* gen,
4503 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4504 verify_work_stacks_empty();
4505 verify_overflow_empty();
4506
4507 // strategy: starting with the first card, accumulate contiguous
4508 // ranges of dirty cards; clear these cards, then scan the region
4509 // covered by these cards.
4510
4511 // Since all of the MUT is committed ahead, we can just use
4512 // that, in case the generations expand while we are precleaning.
4513 // It might also be fine to just use the committed part of the
4514 // generation, but we might potentially miss cards when the
4515 // generation is rapidly expanding while we are in the midst
4516 // of precleaning.
4517 HeapWord* startAddr = gen->reserved().start();
4518 HeapWord* endAddr = gen->reserved().end();
4519
4520 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4521
4522 size_t numDirtyCards, cumNumDirtyCards;
4523 HeapWord *nextAddr, *lastAddr;
4524 for (cumNumDirtyCards = numDirtyCards = 0,
4525 nextAddr = lastAddr = startAddr;
4526 nextAddr < endAddr;
4527 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4528
4529 ResourceMark rm;
4530 HandleMark hm;
4531
4532 MemRegion dirtyRegion;
4533 {
4534 stopTimer();
4535 // Potential yield point
4536 CMSTokenSync ts(true);
4537 startTimer();
4538 sample_eden();
4539 // Get dirty region starting at nextOffset (inclusive),
4540 // simultaneously clearing it.
4541 dirtyRegion =
4542 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4543 assert(dirtyRegion.start() >= nextAddr,
4544 "returned region inconsistent?");
4545 }
4546 // Remember where the next search should begin.
4547 // The returned region (if non-empty) is a right open interval,
4548 // so lastOffset is obtained from the right end of that
4549 // interval.
4550 lastAddr = dirtyRegion.end();
4551 // Should do something more transparent and less hacky XXX
4552 numDirtyCards =
4553 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4554
4555 // We'll scan the cards in the dirty region (with periodic
4556 // yields for foreground GC as needed).
4557 if (!dirtyRegion.is_empty()) {
4558 assert(numDirtyCards > 0, "consistency check");
4559 HeapWord* stop_point = NULL;
4560 stopTimer();
4561 // Potential yield point
4562 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4563 bitMapLock());
4564 startTimer();
4565 {
4566 verify_work_stacks_empty();
4567 verify_overflow_empty();
4568 sample_eden();
4569 stop_point =
4570 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4571 }
4572 if (stop_point != NULL) {
4573 // The careful iteration stopped early either because it found an
4574 // uninitialized object, or because we were in the midst of an
4575 // "abortable preclean", which should now be aborted. Redirty
4576 // the bits corresponding to the partially-scanned or unscanned
4577 // cards. We'll either restart at the next block boundary or
4578 // abort the preclean.
4579 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4580 "Should only be AbortablePreclean.");
4581 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4582 if (should_abort_preclean()) {
4583 break; // out of preclean loop
4584 } else {
4585 // Compute the next address at which preclean should pick up;
4586 // might need bitMapLock in order to read P-bits.
4587 lastAddr = next_card_start_after_block(stop_point);
4588 }
4589 }
4590 } else {
4591 assert(lastAddr == endAddr, "consistency check");
4592 assert(numDirtyCards == 0, "consistency check");
4593 break;
4594 }
4595 }
4596 verify_work_stacks_empty();
4597 verify_overflow_empty();
4598 return cumNumDirtyCards;
4599 }
4600
4601 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4602 // below are largely identical; if you need to modify
4603 // one of these methods, please check the other method too.
4604
4605 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4606 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4607 // strategy: it's similar to precleamModUnionTable above, in that
4608 // we accumulate contiguous ranges of dirty cards, mark these cards
4609 // precleaned, then scan the region covered by these cards.
4610 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4611 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4612
4613 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4614
4615 size_t numDirtyCards, cumNumDirtyCards;
4616 HeapWord *lastAddr, *nextAddr;
4617
4618 for (cumNumDirtyCards = numDirtyCards = 0,
4619 nextAddr = lastAddr = startAddr;
4620 nextAddr < endAddr;
4621 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4622
4623 ResourceMark rm;
4624 HandleMark hm;
4625
4626 MemRegion dirtyRegion;
4627 {
4628 // See comments in "Precleaning notes" above on why we
4629 // do this locking. XXX Could the locking overheads be
4630 // too high when dirty cards are sparse? [I don't think so.]
4631 stopTimer();
4632 CMSTokenSync x(true); // is cms thread
4633 startTimer();
4634 sample_eden();
4635 // Get and clear dirty region from card table
4636 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4637 MemRegion(nextAddr, endAddr),
4638 true,
4639 CardTableModRefBS::precleaned_card_val());
4640
4641 assert(dirtyRegion.start() >= nextAddr,
4642 "returned region inconsistent?");
4643 }
4644 lastAddr = dirtyRegion.end();
4645 numDirtyCards =
4646 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4647
4648 if (!dirtyRegion.is_empty()) {
4649 stopTimer();
4650 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4651 startTimer();
4652 sample_eden();
4653 verify_work_stacks_empty();
4654 verify_overflow_empty();
4655 HeapWord* stop_point =
4656 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4657 if (stop_point != NULL) {
4658 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4659 "Should only be AbortablePreclean.");
4660 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4661 if (should_abort_preclean()) {
4662 break; // out of preclean loop
4663 } else {
4664 // Compute the next address at which preclean should pick up.
4665 lastAddr = next_card_start_after_block(stop_point);
4666 }
4667 }
4668 } else {
4669 break;
4670 }
4671 }
4672 verify_work_stacks_empty();
4673 verify_overflow_empty();
4674 return cumNumDirtyCards;
4675 }
4676
4677 class PrecleanKlassClosure : public KlassClosure {
4678 KlassToOopClosure _cm_klass_closure;
4679 public:
4680 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4681 void do_klass(Klass* k) {
4682 if (k->has_accumulated_modified_oops()) {
4683 k->clear_accumulated_modified_oops();
4684
4685 _cm_klass_closure.do_klass(k);
4686 }
4687 }
4688 };
4689
4690 // The freelist lock is needed to prevent asserts, is it really needed?
4691 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4692
4693 cl->set_freelistLock(freelistLock);
4694
4695 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4696
4697 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4698 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4699 PrecleanKlassClosure preclean_klass_closure(cl);
4700 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4701
4702 verify_work_stacks_empty();
4703 verify_overflow_empty();
4704 }
4705
4706 void CMSCollector::checkpointRootsFinal(bool asynch,
4707 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4708 assert(_collectorState == FinalMarking, "incorrect state transition?");
4709 check_correct_thread_executing();
4710 // world is stopped at this checkpoint
4711 assert(SafepointSynchronize::is_at_safepoint(),
4712 "world should be stopped");
4713 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4714
4715 verify_work_stacks_empty();
4716 verify_overflow_empty();
4717
4718 SpecializationStats::clear();
4719 if (PrintGCDetails) {
4720 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4721 _young_gen->used() / K,
4722 _young_gen->capacity() / K);
4723 }
4724 if (asynch) {
4725 if (CMSScavengeBeforeRemark) {
4726 GenCollectedHeap* gch = GenCollectedHeap::heap();
4727 // Temporarily set flag to false, GCH->do_collection will
4728 // expect it to be false and set to true
4729 FlagSetting fl(gch->_is_gc_active, false);
4730 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4731 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4732 int level = _cmsGen->level() - 1;
4733 if (level >= 0) {
4734 gch->do_collection(true, // full (i.e. force, see below)
4735 false, // !clear_all_soft_refs
4736 0, // size
4737 false, // is_tlab
4738 level // max_level
4739 );
4740 }
4741 }
4742 FreelistLocker x(this);
4743 MutexLockerEx y(bitMapLock(),
4744 Mutex::_no_safepoint_check_flag);
4745 assert(!init_mark_was_synchronous, "but that's impossible!");
4746 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4747 } else {
4748 // already have all the locks
4749 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4750 init_mark_was_synchronous);
4751 }
4752 verify_work_stacks_empty();
4753 verify_overflow_empty();
4754 SpecializationStats::print();
4755 }
4756
4757 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4758 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4759
4760 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4761
4762 assert(haveFreelistLocks(), "must have free list locks");
4763 assert_lock_strong(bitMapLock());
4764
4765 ResourceMark rm;
4766 HandleMark hm;
4767
4768 GenCollectedHeap* gch = GenCollectedHeap::heap();
4769
4770 if (should_unload_classes()) {
4771 CodeCache::gc_prologue();
4772 }
4773 assert(haveFreelistLocks(), "must have free list locks");
4774 assert_lock_strong(bitMapLock());
4775
4776 if (!init_mark_was_synchronous) {
4777 // We might assume that we need not fill TLAB's when
4778 // CMSScavengeBeforeRemark is set, because we may have just done
4779 // a scavenge which would have filled all TLAB's -- and besides
4780 // Eden would be empty. This however may not always be the case --
4781 // for instance although we asked for a scavenge, it may not have
4782 // happened because of a JNI critical section. We probably need
4783 // a policy for deciding whether we can in that case wait until
4784 // the critical section releases and then do the remark following
4785 // the scavenge, and skip it here. In the absence of that policy,
4786 // or of an indication of whether the scavenge did indeed occur,
4787 // we cannot rely on TLAB's having been filled and must do
4788 // so here just in case a scavenge did not happen.
4789 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4790 // Update the saved marks which may affect the root scans.
4791 gch->save_marks();
4792
4793 if (CMSPrintEdenSurvivorChunks) {
4794 print_eden_and_survivor_chunk_arrays();
4795 }
4796
4797 {
4798 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4799
4800 // Note on the role of the mod union table:
4801 // Since the marker in "markFromRoots" marks concurrently with
4802 // mutators, it is possible for some reachable objects not to have been
4803 // scanned. For instance, an only reference to an object A was
4804 // placed in object B after the marker scanned B. Unless B is rescanned,
4805 // A would be collected. Such updates to references in marked objects
4806 // are detected via the mod union table which is the set of all cards
4807 // dirtied since the first checkpoint in this GC cycle and prior to
4808 // the most recent young generation GC, minus those cleaned up by the
4809 // concurrent precleaning.
4810 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
4811 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
4812 do_remark_parallel();
4813 } else {
4814 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4815 _gc_timer_cm, _gc_tracer_cm->gc_id());
4816 do_remark_non_parallel();
4817 }
4818 }
4819 } else {
4820 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
4821 // The initial mark was stop-world, so there's no rescanning to
4822 // do; go straight on to the next step below.
4823 }
4824 verify_work_stacks_empty();
4825 verify_overflow_empty();
4826
4827 {
4828 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4829 refProcessingWork(asynch, clear_all_soft_refs);
4830 }
4831 verify_work_stacks_empty();
4832 verify_overflow_empty();
4833
4834 if (should_unload_classes()) {
4835 CodeCache::gc_epilogue();
4836 }
4837 JvmtiExport::gc_epilogue();
4838
4839 // If we encountered any (marking stack / work queue) overflow
4840 // events during the current CMS cycle, take appropriate
4841 // remedial measures, where possible, so as to try and avoid
4842 // recurrence of that condition.
4843 assert(_markStack.isEmpty(), "No grey objects");
4844 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4845 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4846 if (ser_ovflw > 0) {
4847 if (PrintCMSStatistics != 0) {
4848 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4849 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4850 ", kac_preclean="SIZE_FORMAT")",
4851 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4852 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4853 }
4854 _markStack.expand();
4855 _ser_pmc_remark_ovflw = 0;
4856 _ser_pmc_preclean_ovflw = 0;
4857 _ser_kac_preclean_ovflw = 0;
4858 _ser_kac_ovflw = 0;
4859 }
4860 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4861 if (PrintCMSStatistics != 0) {
4862 gclog_or_tty->print_cr("Work queue overflow (benign) "
4863 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4864 _par_pmc_remark_ovflw, _par_kac_ovflw);
4865 }
4866 _par_pmc_remark_ovflw = 0;
4867 _par_kac_ovflw = 0;
4868 }
4869 if (PrintCMSStatistics != 0) {
4870 if (_markStack._hit_limit > 0) {
4871 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4872 _markStack._hit_limit);
4873 }
4874 if (_markStack._failed_double > 0) {
4875 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4876 " current capacity "SIZE_FORMAT,
4877 _markStack._failed_double,
4878 _markStack.capacity());
4879 }
4880 }
4881 _markStack._hit_limit = 0;
4882 _markStack._failed_double = 0;
4883
4884 if ((VerifyAfterGC || VerifyDuringGC) &&
4885 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4886 verify_after_remark();
4887 }
4888
4889 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4890
4891 // Change under the freelistLocks.
4892 _collectorState = Sweeping;
4893 // Call isAllClear() under bitMapLock
4894 assert(_modUnionTable.isAllClear(),
4895 "Should be clear by end of the final marking");
4896 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4897 "Should be clear by end of the final marking");
4898 }
4899
4900 void CMSParInitialMarkTask::work(uint worker_id) {
4901 elapsedTimer _timer;
4902 ResourceMark rm;
4903 HandleMark hm;
4904
4905 // ---------- scan from roots --------------
4906 _timer.start();
4907 GenCollectedHeap* gch = GenCollectedHeap::heap();
4908 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4909
4910 // ---------- young gen roots --------------
4911 {
4912 work_on_young_gen_roots(worker_id, &par_mri_cl);
4913 _timer.stop();
4914 if (PrintCMSStatistics != 0) {
4915 gclog_or_tty->print_cr(
4916 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4917 worker_id, _timer.seconds());
4918 }
4919 }
4920
4921 // ---------- remaining roots --------------
4922 _timer.reset();
4923 _timer.start();
4924
4925 CLDToOopClosure cld_closure(&par_mri_cl, true);
4926
4927 gch->gen_process_roots(_collector->_cmsGen->level(),
4928 false, // yg was scanned above
4929 false, // this is parallel code
4930 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4931 _collector->should_unload_classes(),
4932 &par_mri_cl,
4933 NULL,
4934 &cld_closure);
4935 assert(_collector->should_unload_classes()
4936 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
4937 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4938 _timer.stop();
4939 if (PrintCMSStatistics != 0) {
4940 gclog_or_tty->print_cr(
4941 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4942 worker_id, _timer.seconds());
4943 }
4944 }
4945
4946 // Parallel remark task
4947 class CMSParRemarkTask: public CMSParMarkTask {
4948 CompactibleFreeListSpace* _cms_space;
4949
4950 // The per-thread work queues, available here for stealing.
4951 OopTaskQueueSet* _task_queues;
4952 ParallelTaskTerminator _term;
4953
4954 public:
4955 // A value of 0 passed to n_workers will cause the number of
4956 // workers to be taken from the active workers in the work gang.
4957 CMSParRemarkTask(CMSCollector* collector,
4958 CompactibleFreeListSpace* cms_space,
4959 int n_workers, FlexibleWorkGang* workers,
4960 OopTaskQueueSet* task_queues):
4961 CMSParMarkTask("Rescan roots and grey objects in parallel",
4962 collector, n_workers),
4963 _cms_space(cms_space),
4964 _task_queues(task_queues),
4965 _term(n_workers, task_queues) { }
4966
4967 OopTaskQueueSet* task_queues() { return _task_queues; }
4968
4969 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4970
4971 ParallelTaskTerminator* terminator() { return &_term; }
4972 int n_workers() { return _n_workers; }
4973
4974 void work(uint worker_id);
4975
4976 private:
4977 // ... of dirty cards in old space
4978 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4979 Par_MarkRefsIntoAndScanClosure* cl);
4980
4981 // ... work stealing for the above
4982 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4983 };
4984
4985 class RemarkKlassClosure : public KlassClosure {
4986 KlassToOopClosure _cm_klass_closure;
4987 public:
4988 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4989 void do_klass(Klass* k) {
4990 // Check if we have modified any oops in the Klass during the concurrent marking.
4991 if (k->has_accumulated_modified_oops()) {
4992 k->clear_accumulated_modified_oops();
4993
4994 // We could have transfered the current modified marks to the accumulated marks,
4995 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4996 } else if (k->has_modified_oops()) {
4997 // Don't clear anything, this info is needed by the next young collection.
4998 } else {
4999 // No modified oops in the Klass.
5000 return;
5001 }
5002
5003 // The klass has modified fields, need to scan the klass.
5004 _cm_klass_closure.do_klass(k);
5005 }
5006 };
5007
5008 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
5009 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5010 ContiguousSpace* eden_space = dng->eden();
5011 ContiguousSpace* from_space = dng->from();
5012 ContiguousSpace* to_space = dng->to();
5013
5014 HeapWord** eca = _collector->_eden_chunk_array;
5015 size_t ect = _collector->_eden_chunk_index;
5016 HeapWord** sca = _collector->_survivor_chunk_array;
5017 size_t sct = _collector->_survivor_chunk_index;
5018
5019 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5020 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5021
5022 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
5023 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
5024 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
5025 }
5026
5027 // work_queue(i) is passed to the closure
5028 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5029 // also is passed to do_dirty_card_rescan_tasks() and to
5030 // do_work_steal() to select the i-th task_queue.
5031
5032 void CMSParRemarkTask::work(uint worker_id) {
5033 elapsedTimer _timer;
5034 ResourceMark rm;
5035 HandleMark hm;
5036
5037 // ---------- rescan from roots --------------
5038 _timer.start();
5039 GenCollectedHeap* gch = GenCollectedHeap::heap();
5040 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5041 _collector->_span, _collector->ref_processor(),
5042 &(_collector->_markBitMap),
5043 work_queue(worker_id));
5044
5045 // Rescan young gen roots first since these are likely
5046 // coarsely partitioned and may, on that account, constitute
5047 // the critical path; thus, it's best to start off that
5048 // work first.
5049 // ---------- young gen roots --------------
5050 {
5051 work_on_young_gen_roots(worker_id, &par_mrias_cl);
5052 _timer.stop();
5053 if (PrintCMSStatistics != 0) {
5054 gclog_or_tty->print_cr(
5055 "Finished young gen rescan work in %dth thread: %3.3f sec",
5056 worker_id, _timer.seconds());
5057 }
5058 }
5059
5060 // ---------- remaining roots --------------
5061 _timer.reset();
5062 _timer.start();
5063 gch->gen_process_roots(_collector->_cmsGen->level(),
5064 false, // yg was scanned above
5065 false, // this is parallel code
5066 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5067 _collector->should_unload_classes(),
5068 &par_mrias_cl,
5069 NULL,
5070 NULL); // The dirty klasses will be handled below
5071
5072 assert(_collector->should_unload_classes()
5073 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5074 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5075 _timer.stop();
5076 if (PrintCMSStatistics != 0) {
5077 gclog_or_tty->print_cr(
5078 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5079 worker_id, _timer.seconds());
5080 }
5081
5082 // ---------- unhandled CLD scanning ----------
5083 if (worker_id == 0) { // Single threaded at the moment.
5084 _timer.reset();
5085 _timer.start();
5086
5087 // Scan all new class loader data objects and new dependencies that were
5088 // introduced during concurrent marking.
5089 ResourceMark rm;
5090 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5091 for (int i = 0; i < array->length(); i++) {
5092 par_mrias_cl.do_class_loader_data(array->at(i));
5093 }
5094
5095 // We don't need to keep track of new CLDs anymore.
5096 ClassLoaderDataGraph::remember_new_clds(false);
5097
5098 _timer.stop();
5099 if (PrintCMSStatistics != 0) {
5100 gclog_or_tty->print_cr(
5101 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
5102 worker_id, _timer.seconds());
5103 }
5104 }
5105
5106 // ---------- dirty klass scanning ----------
5107 if (worker_id == 0) { // Single threaded at the moment.
5108 _timer.reset();
5109 _timer.start();
5110
5111 // Scan all classes that was dirtied during the concurrent marking phase.
5112 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
5113 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5114
5115 _timer.stop();
5116 if (PrintCMSStatistics != 0) {
5117 gclog_or_tty->print_cr(
5118 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
5119 worker_id, _timer.seconds());
5120 }
5121 }
5122
5123 // We might have added oops to ClassLoaderData::_handles during the
5124 // concurrent marking phase. These oops point to newly allocated objects
5125 // that are guaranteed to be kept alive. Either by the direct allocation
5126 // code, or when the young collector processes the roots. Hence,
5127 // we don't have to revisit the _handles block during the remark phase.
5128
5129 // ---------- rescan dirty cards ------------
5130 _timer.reset();
5131 _timer.start();
5132
5133 // Do the rescan tasks for each of the two spaces
5134 // (cms_space) in turn.
5135 // "worker_id" is passed to select the task_queue for "worker_id"
5136 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5137 _timer.stop();
5138 if (PrintCMSStatistics != 0) {
5139 gclog_or_tty->print_cr(
5140 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5141 worker_id, _timer.seconds());
5142 }
5143
5144 // ---------- steal work from other threads ...
5145 // ---------- ... and drain overflow list.
5146 _timer.reset();
5147 _timer.start();
5148 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5149 _timer.stop();
5150 if (PrintCMSStatistics != 0) {
5151 gclog_or_tty->print_cr(
5152 "Finished work stealing in %dth thread: %3.3f sec",
5153 worker_id, _timer.seconds());
5154 }
5155 }
5156
5157 // Note that parameter "i" is not used.
5158 void
5159 CMSParMarkTask::do_young_space_rescan(uint worker_id,
5160 OopsInGenClosure* cl, ContiguousSpace* space,
5161 HeapWord** chunk_array, size_t chunk_top) {
5162 // Until all tasks completed:
5163 // . claim an unclaimed task
5164 // . compute region boundaries corresponding to task claimed
5165 // using chunk_array
5166 // . par_oop_iterate(cl) over that region
5167
5168 ResourceMark rm;
5169 HandleMark hm;
5170
5171 SequentialSubTasksDone* pst = space->par_seq_tasks();
5172
5173 uint nth_task = 0;
5174 uint n_tasks = pst->n_tasks();
5175
5176 if (n_tasks > 0) {
5177 assert(pst->valid(), "Uninitialized use?");
5178 HeapWord *start, *end;
5179 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5180 // We claimed task # nth_task; compute its boundaries.
5181 if (chunk_top == 0) { // no samples were taken
5182 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
5183 start = space->bottom();
5184 end = space->top();
5185 } else if (nth_task == 0) {
5186 start = space->bottom();
5187 end = chunk_array[nth_task];
5188 } else if (nth_task < (uint)chunk_top) {
5189 assert(nth_task >= 1, "Control point invariant");
5190 start = chunk_array[nth_task - 1];
5191 end = chunk_array[nth_task];
5192 } else {
5193 assert(nth_task == (uint)chunk_top, "Control point invariant");
5194 start = chunk_array[chunk_top - 1];
5195 end = space->top();
5196 }
5197 MemRegion mr(start, end);
5198 // Verify that mr is in space
5199 assert(mr.is_empty() || space->used_region().contains(mr),
5200 "Should be in space");
5201 // Verify that "start" is an object boundary
5202 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5203 "Should be an oop");
5204 space->par_oop_iterate(mr, cl);
5205 }
5206 pst->all_tasks_completed();
5207 }
5208 }
5209
5210 void
5211 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5212 CompactibleFreeListSpace* sp, int i,
5213 Par_MarkRefsIntoAndScanClosure* cl) {
5214 // Until all tasks completed:
5215 // . claim an unclaimed task
5216 // . compute region boundaries corresponding to task claimed
5217 // . transfer dirty bits ct->mut for that region
5218 // . apply rescanclosure to dirty mut bits for that region
5219
5220 ResourceMark rm;
5221 HandleMark hm;
5222
5223 OopTaskQueue* work_q = work_queue(i);
5224 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5225 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5226 // CAUTION: This closure has state that persists across calls to
5227 // the work method dirty_range_iterate_clear() in that it has
5228 // embedded in it a (subtype of) UpwardsObjectClosure. The
5229 // use of that state in the embedded UpwardsObjectClosure instance
5230 // assumes that the cards are always iterated (even if in parallel
5231 // by several threads) in monotonically increasing order per each
5232 // thread. This is true of the implementation below which picks
5233 // card ranges (chunks) in monotonically increasing order globally
5234 // and, a-fortiori, in monotonically increasing order per thread
5235 // (the latter order being a subsequence of the former).
5236 // If the work code below is ever reorganized into a more chaotic
5237 // work-partitioning form than the current "sequential tasks"
5238 // paradigm, the use of that persistent state will have to be
5239 // revisited and modified appropriately. See also related
5240 // bug 4756801 work on which should examine this code to make
5241 // sure that the changes there do not run counter to the
5242 // assumptions made here and necessary for correctness and
5243 // efficiency. Note also that this code might yield inefficient
5244 // behavior in the case of very large objects that span one or
5245 // more work chunks. Such objects would potentially be scanned
5246 // several times redundantly. Work on 4756801 should try and
5247 // address that performance anomaly if at all possible. XXX
5248 MemRegion full_span = _collector->_span;
5249 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5250 MarkFromDirtyCardsClosure
5251 greyRescanClosure(_collector, full_span, // entire span of interest
5252 sp, bm, work_q, cl);
5253
5254 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5255 assert(pst->valid(), "Uninitialized use?");
5256 uint nth_task = 0;
5257 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5258 MemRegion span = sp->used_region();
5259 HeapWord* start_addr = span.start();
5260 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5261 alignment);
5262 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5263 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5264 start_addr, "Check alignment");
5265 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5266 chunk_size, "Check alignment");
5267
5268 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5269 // Having claimed the nth_task, compute corresponding mem-region,
5270 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
5271 // The alignment restriction ensures that we do not need any
5272 // synchronization with other gang-workers while setting or
5273 // clearing bits in thus chunk of the MUT.
5274 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5275 start_addr + (nth_task+1)*chunk_size);
5276 // The last chunk's end might be way beyond end of the
5277 // used region. In that case pull back appropriately.
5278 if (this_span.end() > end_addr) {
5279 this_span.set_end(end_addr);
5280 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5281 }
5282 // Iterate over the dirty cards covering this chunk, marking them
5283 // precleaned, and setting the corresponding bits in the mod union
5284 // table. Since we have been careful to partition at Card and MUT-word
5285 // boundaries no synchronization is needed between parallel threads.
5286 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5287 &modUnionClosure);
5288
5289 // Having transferred these marks into the modUnionTable,
5290 // rescan the marked objects on the dirty cards in the modUnionTable.
5291 // Even if this is at a synchronous collection, the initial marking
5292 // may have been done during an asynchronous collection so there
5293 // may be dirty bits in the mod-union table.
5294 _collector->_modUnionTable.dirty_range_iterate_clear(
5295 this_span, &greyRescanClosure);
5296 _collector->_modUnionTable.verifyNoOneBitsInRange(
5297 this_span.start(),
5298 this_span.end());
5299 }
5300 pst->all_tasks_completed(); // declare that i am done
5301 }
5302
5303 // . see if we can share work_queues with ParNew? XXX
5304 void
5305 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5306 int* seed) {
5307 OopTaskQueue* work_q = work_queue(i);
5308 NOT_PRODUCT(int num_steals = 0;)
5309 oop obj_to_scan;
5310 CMSBitMap* bm = &(_collector->_markBitMap);
5311
5312 while (true) {
5313 // Completely finish any left over work from (an) earlier round(s)
5314 cl->trim_queue(0);
5315 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5316 (size_t)ParGCDesiredObjsFromOverflowList);
5317 // Now check if there's any work in the overflow list
5318 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5319 // only affects the number of attempts made to get work from the
5320 // overflow list and does not affect the number of workers. Just
5321 // pass ParallelGCThreads so this behavior is unchanged.
5322 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5323 work_q,
5324 ParallelGCThreads)) {
5325 // found something in global overflow list;
5326 // not yet ready to go stealing work from others.
5327 // We'd like to assert(work_q->size() != 0, ...)
5328 // because we just took work from the overflow list,
5329 // but of course we can't since all of that could have
5330 // been already stolen from us.
5331 // "He giveth and He taketh away."
5332 continue;
5333 }
5334 // Verify that we have no work before we resort to stealing
5335 assert(work_q->size() == 0, "Have work, shouldn't steal");
5336 // Try to steal from other queues that have work
5337 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5338 NOT_PRODUCT(num_steals++;)
5339 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5340 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5341 // Do scanning work
5342 obj_to_scan->oop_iterate(cl);
5343 // Loop around, finish this work, and try to steal some more
5344 } else if (terminator()->offer_termination()) {
5345 break; // nirvana from the infinite cycle
5346 }
5347 }
5348 NOT_PRODUCT(
5349 if (PrintCMSStatistics != 0) {
5350 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5351 }
5352 )
5353 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5354 "Else our work is not yet done");
5355 }
5356
5357 // Record object boundaries in _eden_chunk_array by sampling the eden
5358 // top in the slow-path eden object allocation code path and record
5359 // the boundaries, if CMSEdenChunksRecordAlways is true. If
5360 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
5361 // sampling in sample_eden() that activates during the part of the
5362 // preclean phase.
5363 void CMSCollector::sample_eden_chunk() {
5364 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
5365 if (_eden_chunk_lock->try_lock()) {
5366 // Record a sample. This is the critical section. The contents
5367 // of the _eden_chunk_array have to be non-decreasing in the
5368 // address order.
5369 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
5370 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
5371 "Unexpected state of Eden");
5372 if (_eden_chunk_index == 0 ||
5373 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
5374 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
5375 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
5376 _eden_chunk_index++; // commit sample
5377 }
5378 _eden_chunk_lock->unlock();
5379 }
5380 }
5381 }
5382
5383 // Return a thread-local PLAB recording array, as appropriate.
5384 void* CMSCollector::get_data_recorder(int thr_num) {
5385 if (_survivor_plab_array != NULL &&
5386 (CMSPLABRecordAlways ||
5387 (_collectorState > Marking && _collectorState < FinalMarking))) {
5388 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5389 ChunkArray* ca = &_survivor_plab_array[thr_num];
5390 ca->reset(); // clear it so that fresh data is recorded
5391 return (void*) ca;
5392 } else {
5393 return NULL;
5394 }
5395 }
5396
5397 // Reset all the thread-local PLAB recording arrays
5398 void CMSCollector::reset_survivor_plab_arrays() {
5399 for (uint i = 0; i < ParallelGCThreads; i++) {
5400 _survivor_plab_array[i].reset();
5401 }
5402 }
5403
5404 // Merge the per-thread plab arrays into the global survivor chunk
5405 // array which will provide the partitioning of the survivor space
5406 // for CMS initial scan and rescan.
5407 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5408 int no_of_gc_threads) {
5409 assert(_survivor_plab_array != NULL, "Error");
5410 assert(_survivor_chunk_array != NULL, "Error");
5411 assert(_collectorState == FinalMarking ||
5412 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
5413 for (int j = 0; j < no_of_gc_threads; j++) {
5414 _cursor[j] = 0;
5415 }
5416 HeapWord* top = surv->top();
5417 size_t i;
5418 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5419 HeapWord* min_val = top; // Higher than any PLAB address
5420 uint min_tid = 0; // position of min_val this round
5421 for (int j = 0; j < no_of_gc_threads; j++) {
5422 ChunkArray* cur_sca = &_survivor_plab_array[j];
5423 if (_cursor[j] == cur_sca->end()) {
5424 continue;
5425 }
5426 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5427 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5428 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5429 if (cur_val < min_val) {
5430 min_tid = j;
5431 min_val = cur_val;
5432 } else {
5433 assert(cur_val < top, "All recorded addresses should be less");
5434 }
5435 }
5436 // At this point min_val and min_tid are respectively
5437 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5438 // and the thread (j) that witnesses that address.
5439 // We record this address in the _survivor_chunk_array[i]
5440 // and increment _cursor[min_tid] prior to the next round i.
5441 if (min_val == top) {
5442 break;
5443 }
5444 _survivor_chunk_array[i] = min_val;
5445 _cursor[min_tid]++;
5446 }
5447 // We are all done; record the size of the _survivor_chunk_array
5448 _survivor_chunk_index = i; // exclusive: [0, i)
5449 if (PrintCMSStatistics > 0) {
5450 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5451 }
5452 // Verify that we used up all the recorded entries
5453 #ifdef ASSERT
5454 size_t total = 0;
5455 for (int j = 0; j < no_of_gc_threads; j++) {
5456 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5457 total += _cursor[j];
5458 }
5459 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5460 // Check that the merged array is in sorted order
5461 if (total > 0) {
5462 for (size_t i = 0; i < total - 1; i++) {
5463 if (PrintCMSStatistics > 0) {
5464 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5465 i, _survivor_chunk_array[i]);
5466 }
5467 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5468 "Not sorted");
5469 }
5470 }
5471 #endif // ASSERT
5472 }
5473
5474 // Set up the space's par_seq_tasks structure for work claiming
5475 // for parallel initial scan and rescan of young gen.
5476 // See ParRescanTask where this is currently used.
5477 void
5478 CMSCollector::
5479 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5480 assert(n_threads > 0, "Unexpected n_threads argument");
5481 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5482
5483 // Eden space
5484 if (!dng->eden()->is_empty()) {
5485 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5486 assert(!pst->valid(), "Clobbering existing data?");
5487 // Each valid entry in [0, _eden_chunk_index) represents a task.
5488 size_t n_tasks = _eden_chunk_index + 1;
5489 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5490 // Sets the condition for completion of the subtask (how many threads
5491 // need to finish in order to be done).
5492 pst->set_n_threads(n_threads);
5493 pst->set_n_tasks((int)n_tasks);
5494 }
5495
5496 // Merge the survivor plab arrays into _survivor_chunk_array
5497 if (_survivor_plab_array != NULL) {
5498 merge_survivor_plab_arrays(dng->from(), n_threads);
5499 } else {
5500 assert(_survivor_chunk_index == 0, "Error");
5501 }
5502
5503 // To space
5504 {
5505 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5506 assert(!pst->valid(), "Clobbering existing data?");
5507 // Sets the condition for completion of the subtask (how many threads
5508 // need to finish in order to be done).
5509 pst->set_n_threads(n_threads);
5510 pst->set_n_tasks(1);
5511 assert(pst->valid(), "Error");
5512 }
5513
5514 // From space
5515 {
5516 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5517 assert(!pst->valid(), "Clobbering existing data?");
5518 size_t n_tasks = _survivor_chunk_index + 1;
5519 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5520 // Sets the condition for completion of the subtask (how many threads
5521 // need to finish in order to be done).
5522 pst->set_n_threads(n_threads);
5523 pst->set_n_tasks((int)n_tasks);
5524 assert(pst->valid(), "Error");
5525 }
5526 }
5527
5528 // Parallel version of remark
5529 void CMSCollector::do_remark_parallel() {
5530 GenCollectedHeap* gch = GenCollectedHeap::heap();
5531 FlexibleWorkGang* workers = gch->workers();
5532 assert(workers != NULL, "Need parallel worker threads.");
5533 // Choose to use the number of GC workers most recently set
5534 // into "active_workers". If active_workers is not set, set it
5535 // to ParallelGCThreads.
5536 int n_workers = workers->active_workers();
5537 if (n_workers == 0) {
5538 assert(n_workers > 0, "Should have been set during scavenge");
5539 n_workers = ParallelGCThreads;
5540 workers->set_active_workers(n_workers);
5541 }
5542 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5543
5544 CMSParRemarkTask tsk(this,
5545 cms_space,
5546 n_workers, workers, task_queues());
5547
5548 // Set up for parallel process_roots work.
5549 gch->set_par_threads(n_workers);
5550 // We won't be iterating over the cards in the card table updating
5551 // the younger_gen cards, so we shouldn't call the following else
5552 // the verification code as well as subsequent younger_refs_iterate
5553 // code would get confused. XXX
5554 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5555
5556 // The young gen rescan work will not be done as part of
5557 // process_roots (which currently doesn't know how to
5558 // parallelize such a scan), but rather will be broken up into
5559 // a set of parallel tasks (via the sampling that the [abortable]
5560 // preclean phase did of eden, plus the [two] tasks of
5561 // scanning the [two] survivor spaces. Further fine-grain
5562 // parallelization of the scanning of the survivor spaces
5563 // themselves, and of precleaning of the younger gen itself
5564 // is deferred to the future.
5565 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5566
5567 // The dirty card rescan work is broken up into a "sequence"
5568 // of parallel tasks (per constituent space) that are dynamically
5569 // claimed by the parallel threads.
5570 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5571
5572 // It turns out that even when we're using 1 thread, doing the work in a
5573 // separate thread causes wide variance in run times. We can't help this
5574 // in the multi-threaded case, but we special-case n=1 here to get
5575 // repeatable measurements of the 1-thread overhead of the parallel code.
5576 if (n_workers > 1) {
5577 // Make refs discovery MT-safe, if it isn't already: it may not
5578 // necessarily be so, since it's possible that we are doing
5579 // ST marking.
5580 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5581 GenCollectedHeap::StrongRootsScope srs(gch);
5582 workers->run_task(&tsk);
5583 } else {
5584 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5585 GenCollectedHeap::StrongRootsScope srs(gch);
5586 tsk.work(0);
5587 }
5588
5589 gch->set_par_threads(0); // 0 ==> non-parallel.
5590 // restore, single-threaded for now, any preserved marks
5591 // as a result of work_q overflow
5592 restore_preserved_marks_if_any();
5593 }
5594
5595 // Non-parallel version of remark
5596 void CMSCollector::do_remark_non_parallel() {
5597 ResourceMark rm;
5598 HandleMark hm;
5599 GenCollectedHeap* gch = GenCollectedHeap::heap();
5600 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5601
5602 MarkRefsIntoAndScanClosure
5603 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5604 &_markStack, this,
5605 false /* should_yield */, false /* not precleaning */);
5606 MarkFromDirtyCardsClosure
5607 markFromDirtyCardsClosure(this, _span,
5608 NULL, // space is set further below
5609 &_markBitMap, &_markStack, &mrias_cl);
5610 {
5611 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5612 // Iterate over the dirty cards, setting the corresponding bits in the
5613 // mod union table.
5614 {
5615 ModUnionClosure modUnionClosure(&_modUnionTable);
5616 _ct->ct_bs()->dirty_card_iterate(
5617 _cmsGen->used_region(),
5618 &modUnionClosure);
5619 }
5620 // Having transferred these marks into the modUnionTable, we just need
5621 // to rescan the marked objects on the dirty cards in the modUnionTable.
5622 // The initial marking may have been done during an asynchronous
5623 // collection so there may be dirty bits in the mod-union table.
5624 const int alignment =
5625 CardTableModRefBS::card_size * BitsPerWord;
5626 {
5627 // ... First handle dirty cards in CMS gen
5628 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5629 MemRegion ur = _cmsGen->used_region();
5630 HeapWord* lb = ur.start();
5631 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5632 MemRegion cms_span(lb, ub);
5633 _modUnionTable.dirty_range_iterate_clear(cms_span,
5634 &markFromDirtyCardsClosure);
5635 verify_work_stacks_empty();
5636 if (PrintCMSStatistics != 0) {
5637 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5638 markFromDirtyCardsClosure.num_dirty_cards());
5639 }
5640 }
5641 }
5642 if (VerifyDuringGC &&
5643 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5644 HandleMark hm; // Discard invalid handles created during verification
5645 Universe::verify();
5646 }
5647 {
5648 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5649
5650 verify_work_stacks_empty();
5651
5652 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5653 GenCollectedHeap::StrongRootsScope srs(gch);
5654
5655 gch->gen_process_roots(_cmsGen->level(),
5656 true, // younger gens as roots
5657 false, // use the local StrongRootsScope
5658 SharedHeap::ScanningOption(roots_scanning_options()),
5659 should_unload_classes(),
5660 &mrias_cl,
5661 NULL,
5662 NULL); // The dirty klasses will be handled below
5663
5664 assert(should_unload_classes()
5665 || (roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5666 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5667 }
5668
5669 {
5670 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5671
5672 verify_work_stacks_empty();
5673
5674 // Scan all class loader data objects that might have been introduced
5675 // during concurrent marking.
5676 ResourceMark rm;
5677 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5678 for (int i = 0; i < array->length(); i++) {
5679 mrias_cl.do_class_loader_data(array->at(i));
5680 }
5681
5682 // We don't need to keep track of new CLDs anymore.
5683 ClassLoaderDataGraph::remember_new_clds(false);
5684
5685 verify_work_stacks_empty();
5686 }
5687
5688 {
5689 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5690
5691 verify_work_stacks_empty();
5692
5693 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5694 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5695
5696 verify_work_stacks_empty();
5697 }
5698
5699 // We might have added oops to ClassLoaderData::_handles during the
5700 // concurrent marking phase. These oops point to newly allocated objects
5701 // that are guaranteed to be kept alive. Either by the direct allocation
5702 // code, or when the young collector processes the roots. Hence,
5703 // we don't have to revisit the _handles block during the remark phase.
5704
5705 verify_work_stacks_empty();
5706 // Restore evacuated mark words, if any, used for overflow list links
5707 if (!CMSOverflowEarlyRestoration) {
5708 restore_preserved_marks_if_any();
5709 }
5710 verify_overflow_empty();
5711 }
5712
5713 ////////////////////////////////////////////////////////
5714 // Parallel Reference Processing Task Proxy Class
5715 ////////////////////////////////////////////////////////
5716 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5717 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5718 CMSCollector* _collector;
5719 CMSBitMap* _mark_bit_map;
5720 const MemRegion _span;
5721 ProcessTask& _task;
5722
5723 public:
5724 CMSRefProcTaskProxy(ProcessTask& task,
5725 CMSCollector* collector,
5726 const MemRegion& span,
5727 CMSBitMap* mark_bit_map,
5728 AbstractWorkGang* workers,
5729 OopTaskQueueSet* task_queues):
5730 // XXX Should superclass AGTWOQ also know about AWG since it knows
5731 // about the task_queues used by the AWG? Then it could initialize
5732 // the terminator() object. See 6984287. The set_for_termination()
5733 // below is a temporary band-aid for the regression in 6984287.
5734 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5735 task_queues),
5736 _task(task),
5737 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5738 {
5739 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5740 "Inconsistency in _span");
5741 set_for_termination(workers->active_workers());
5742 }
5743
5744 OopTaskQueueSet* task_queues() { return queues(); }
5745
5746 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5747
5748 void do_work_steal(int i,
5749 CMSParDrainMarkingStackClosure* drain,
5750 CMSParKeepAliveClosure* keep_alive,
5751 int* seed);
5752
5753 virtual void work(uint worker_id);
5754 };
5755
5756 void CMSRefProcTaskProxy::work(uint worker_id) {
5757 ResourceMark rm;
5758 HandleMark hm;
5759 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5760 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5761 _mark_bit_map,
5762 work_queue(worker_id));
5763 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5764 _mark_bit_map,
5765 work_queue(worker_id));
5766 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5767 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5768 if (_task.marks_oops_alive()) {
5769 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5770 _collector->hash_seed(worker_id));
5771 }
5772 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5773 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5774 }
5775
5776 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5777 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5778 EnqueueTask& _task;
5779
5780 public:
5781 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5782 : AbstractGangTask("Enqueue reference objects in parallel"),
5783 _task(task)
5784 { }
5785
5786 virtual void work(uint worker_id)
5787 {
5788 _task.work(worker_id);
5789 }
5790 };
5791
5792 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5793 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5794 _span(span),
5795 _bit_map(bit_map),
5796 _work_queue(work_queue),
5797 _mark_and_push(collector, span, bit_map, work_queue),
5798 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5799 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5800 { }
5801
5802 // . see if we can share work_queues with ParNew? XXX
5803 void CMSRefProcTaskProxy::do_work_steal(int i,
5804 CMSParDrainMarkingStackClosure* drain,
5805 CMSParKeepAliveClosure* keep_alive,
5806 int* seed) {
5807 OopTaskQueue* work_q = work_queue(i);
5808 NOT_PRODUCT(int num_steals = 0;)
5809 oop obj_to_scan;
5810
5811 while (true) {
5812 // Completely finish any left over work from (an) earlier round(s)
5813 drain->trim_queue(0);
5814 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5815 (size_t)ParGCDesiredObjsFromOverflowList);
5816 // Now check if there's any work in the overflow list
5817 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5818 // only affects the number of attempts made to get work from the
5819 // overflow list and does not affect the number of workers. Just
5820 // pass ParallelGCThreads so this behavior is unchanged.
5821 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5822 work_q,
5823 ParallelGCThreads)) {
5824 // Found something in global overflow list;
5825 // not yet ready to go stealing work from others.
5826 // We'd like to assert(work_q->size() != 0, ...)
5827 // because we just took work from the overflow list,
5828 // but of course we can't, since all of that might have
5829 // been already stolen from us.
5830 continue;
5831 }
5832 // Verify that we have no work before we resort to stealing
5833 assert(work_q->size() == 0, "Have work, shouldn't steal");
5834 // Try to steal from other queues that have work
5835 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5836 NOT_PRODUCT(num_steals++;)
5837 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5838 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5839 // Do scanning work
5840 obj_to_scan->oop_iterate(keep_alive);
5841 // Loop around, finish this work, and try to steal some more
5842 } else if (terminator()->offer_termination()) {
5843 break; // nirvana from the infinite cycle
5844 }
5845 }
5846 NOT_PRODUCT(
5847 if (PrintCMSStatistics != 0) {
5848 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5849 }
5850 )
5851 }
5852
5853 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5854 {
5855 GenCollectedHeap* gch = GenCollectedHeap::heap();
5856 FlexibleWorkGang* workers = gch->workers();
5857 assert(workers != NULL, "Need parallel worker threads.");
5858 CMSRefProcTaskProxy rp_task(task, &_collector,
5859 _collector.ref_processor()->span(),
5860 _collector.markBitMap(),
5861 workers, _collector.task_queues());
5862 workers->run_task(&rp_task);
5863 }
5864
5865 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5866 {
5867
5868 GenCollectedHeap* gch = GenCollectedHeap::heap();
5869 FlexibleWorkGang* workers = gch->workers();
5870 assert(workers != NULL, "Need parallel worker threads.");
5871 CMSRefEnqueueTaskProxy enq_task(task);
5872 workers->run_task(&enq_task);
5873 }
5874
5875 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5876
5877 ResourceMark rm;
5878 HandleMark hm;
5879
5880 ReferenceProcessor* rp = ref_processor();
5881 assert(rp->span().equals(_span), "Spans should be equal");
5882 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5883 // Process weak references.
5884 rp->setup_policy(clear_all_soft_refs);
5885 verify_work_stacks_empty();
5886
5887 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5888 &_markStack, false /* !preclean */);
5889 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5890 _span, &_markBitMap, &_markStack,
5891 &cmsKeepAliveClosure, false /* !preclean */);
5892 {
5893 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5894
5895 ReferenceProcessorStats stats;
5896 if (rp->processing_is_mt()) {
5897 // Set the degree of MT here. If the discovery is done MT, there
5898 // may have been a different number of threads doing the discovery
5899 // and a different number of discovered lists may have Ref objects.
5900 // That is OK as long as the Reference lists are balanced (see
5901 // balance_all_queues() and balance_queues()).
5902 GenCollectedHeap* gch = GenCollectedHeap::heap();
5903 int active_workers = ParallelGCThreads;
5904 FlexibleWorkGang* workers = gch->workers();
5905 if (workers != NULL) {
5906 active_workers = workers->active_workers();
5907 // The expectation is that active_workers will have already
5908 // been set to a reasonable value. If it has not been set,
5909 // investigate.
5910 assert(active_workers > 0, "Should have been set during scavenge");
5911 }
5912 rp->set_active_mt_degree(active_workers);
5913 CMSRefProcTaskExecutor task_executor(*this);
5914 stats = rp->process_discovered_references(&_is_alive_closure,
5915 &cmsKeepAliveClosure,
5916 &cmsDrainMarkingStackClosure,
5917 &task_executor,
5918 _gc_timer_cm,
5919 _gc_tracer_cm->gc_id());
5920 } else {
5921 stats = rp->process_discovered_references(&_is_alive_closure,
5922 &cmsKeepAliveClosure,
5923 &cmsDrainMarkingStackClosure,
5924 NULL,
5925 _gc_timer_cm,
5926 _gc_tracer_cm->gc_id());
5927 }
5928 _gc_tracer_cm->report_gc_reference_stats(stats);
5929
5930 }
5931
5932 // This is the point where the entire marking should have completed.
5933 verify_work_stacks_empty();
5934
5935 if (should_unload_classes()) {
5936 {
5937 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5938
5939 // Unload classes and purge the SystemDictionary.
5940 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5941
5942 // Unload nmethods.
5943 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5944
5945 // Prune dead klasses from subklass/sibling/implementor lists.
5946 Klass::clean_weak_klass_links(&_is_alive_closure);
5947 }
5948
5949 {
5950 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5951 // Clean up unreferenced symbols in symbol table.
5952 SymbolTable::unlink();
5953 }
5954
5955 {
5956 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5957 // Delete entries for dead interned strings.
5958 StringTable::unlink(&_is_alive_closure);
5959 }
5960 }
5961
5962
5963 // Restore any preserved marks as a result of mark stack or
5964 // work queue overflow
5965 restore_preserved_marks_if_any(); // done single-threaded for now
5966
5967 rp->set_enqueuing_is_done(true);
5968 if (rp->processing_is_mt()) {
5969 rp->balance_all_queues();
5970 CMSRefProcTaskExecutor task_executor(*this);
5971 rp->enqueue_discovered_references(&task_executor);
5972 } else {
5973 rp->enqueue_discovered_references(NULL);
5974 }
5975 rp->verify_no_references_recorded();
5976 assert(!rp->discovery_enabled(), "should have been disabled");
5977 }
5978
5979 #ifndef PRODUCT
5980 void CMSCollector::check_correct_thread_executing() {
5981 Thread* t = Thread::current();
5982 // Only the VM thread or the CMS thread should be here.
5983 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5984 "Unexpected thread type");
5985 // If this is the vm thread, the foreground process
5986 // should not be waiting. Note that _foregroundGCIsActive is
5987 // true while the foreground collector is waiting.
5988 if (_foregroundGCShouldWait) {
5989 // We cannot be the VM thread
5990 assert(t->is_ConcurrentGC_thread(),
5991 "Should be CMS thread");
5992 } else {
5993 // We can be the CMS thread only if we are in a stop-world
5994 // phase of CMS collection.
5995 if (t->is_ConcurrentGC_thread()) {
5996 assert(_collectorState == InitialMarking ||
5997 _collectorState == FinalMarking,
5998 "Should be a stop-world phase");
5999 // The CMS thread should be holding the CMS_token.
6000 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6001 "Potential interference with concurrently "
6002 "executing VM thread");
6003 }
6004 }
6005 }
6006 #endif
6007
6008 void CMSCollector::sweep(bool asynch) {
6009 assert(_collectorState == Sweeping, "just checking");
6010 check_correct_thread_executing();
6011 verify_work_stacks_empty();
6012 verify_overflow_empty();
6013 increment_sweep_count();
6014 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6015
6016 _inter_sweep_timer.stop();
6017 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6018
6019 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6020 _intra_sweep_timer.reset();
6021 _intra_sweep_timer.start();
6022 if (asynch) {
6023 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6024 CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
6025 // First sweep the old gen
6026 {
6027 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6028 bitMapLock());
6029 sweepWork(_cmsGen, asynch);
6030 }
6031
6032 // Update Universe::_heap_*_at_gc figures.
6033 // We need all the free list locks to make the abstract state
6034 // transition from Sweeping to Resetting. See detailed note
6035 // further below.
6036 {
6037 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6038 // Update heap occupancy information which is used as
6039 // input to soft ref clearing policy at the next gc.
6040 Universe::update_heap_info_at_gc();
6041 _collectorState = Resizing;
6042 }
6043 } else {
6044 // already have needed locks
6045 sweepWork(_cmsGen, asynch);
6046 // Update heap occupancy information which is used as
6047 // input to soft ref clearing policy at the next gc.
6048 Universe::update_heap_info_at_gc();
6049 _collectorState = Resizing;
6050 }
6051 verify_work_stacks_empty();
6052 verify_overflow_empty();
6053
6054 if (should_unload_classes()) {
6055 // Delay purge to the beginning of the next safepoint. Metaspace::contains
6056 // requires that the virtual spaces are stable and not deleted.
6057 ClassLoaderDataGraph::set_should_purge(true);
6058 }
6059
6060 _intra_sweep_timer.stop();
6061 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6062
6063 _inter_sweep_timer.reset();
6064 _inter_sweep_timer.start();
6065
6066 // We need to use a monotonically non-decreasing time in ms
6067 // or we will see time-warp warnings and os::javaTimeMillis()
6068 // does not guarantee monotonicity.
6069 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6070 update_time_of_last_gc(now);
6071
6072 // NOTE on abstract state transitions:
6073 // Mutators allocate-live and/or mark the mod-union table dirty
6074 // based on the state of the collection. The former is done in
6075 // the interval [Marking, Sweeping] and the latter in the interval
6076 // [Marking, Sweeping). Thus the transitions into the Marking state
6077 // and out of the Sweeping state must be synchronously visible
6078 // globally to the mutators.
6079 // The transition into the Marking state happens with the world
6080 // stopped so the mutators will globally see it. Sweeping is
6081 // done asynchronously by the background collector so the transition
6082 // from the Sweeping state to the Resizing state must be done
6083 // under the freelistLock (as is the check for whether to
6084 // allocate-live and whether to dirty the mod-union table).
6085 assert(_collectorState == Resizing, "Change of collector state to"
6086 " Resizing must be done under the freelistLocks (plural)");
6087
6088 // Now that sweeping has been completed, we clear
6089 // the incremental_collection_failed flag,
6090 // thus inviting a younger gen collection to promote into
6091 // this generation. If such a promotion may still fail,
6092 // the flag will be set again when a young collection is
6093 // attempted.
6094 GenCollectedHeap* gch = GenCollectedHeap::heap();
6095 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6096 gch->update_full_collections_completed(_collection_count_start);
6097 }
6098
6099 // FIX ME!!! Looks like this belongs in CFLSpace, with
6100 // CMSGen merely delegating to it.
6101 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6102 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6103 HeapWord* minAddr = _cmsSpace->bottom();
6104 HeapWord* largestAddr =
6105 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6106 if (largestAddr == NULL) {
6107 // The dictionary appears to be empty. In this case
6108 // try to coalesce at the end of the heap.
6109 largestAddr = _cmsSpace->end();
6110 }
6111 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6112 size_t nearLargestOffset =
6113 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6114 if (PrintFLSStatistics != 0) {
6115 gclog_or_tty->print_cr(
6116 "CMS: Large Block: " PTR_FORMAT ";"
6117 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6118 largestAddr,
6119 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6120 }
6121 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6122 }
6123
6124 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6125 return addr >= _cmsSpace->nearLargestChunk();
6126 }
6127
6128 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6129 return _cmsSpace->find_chunk_at_end();
6130 }
6131
6132 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6133 bool full) {
6134 // The next lower level has been collected. Gather any statistics
6135 // that are of interest at this point.
6136 if (!full && (current_level + 1) == level()) {
6137 // Gather statistics on the young generation collection.
6138 collector()->stats().record_gc0_end(used());
6139 }
6140 }
6141
6142 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6143 if (PrintGCDetails && Verbose) {
6144 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6145 }
6146 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6147 _debug_collection_type =
6148 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6149 if (PrintGCDetails && Verbose) {
6150 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6151 }
6152 }
6153
6154 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6155 bool asynch) {
6156 // We iterate over the space(s) underlying this generation,
6157 // checking the mark bit map to see if the bits corresponding
6158 // to specific blocks are marked or not. Blocks that are
6159 // marked are live and are not swept up. All remaining blocks
6160 // are swept up, with coalescing on-the-fly as we sweep up
6161 // contiguous free and/or garbage blocks:
6162 // We need to ensure that the sweeper synchronizes with allocators
6163 // and stop-the-world collectors. In particular, the following
6164 // locks are used:
6165 // . CMS token: if this is held, a stop the world collection cannot occur
6166 // . freelistLock: if this is held no allocation can occur from this
6167 // generation by another thread
6168 // . bitMapLock: if this is held, no other thread can access or update
6169 //
6170
6171 // Note that we need to hold the freelistLock if we use
6172 // block iterate below; else the iterator might go awry if
6173 // a mutator (or promotion) causes block contents to change
6174 // (for instance if the allocator divvies up a block).
6175 // If we hold the free list lock, for all practical purposes
6176 // young generation GC's can't occur (they'll usually need to
6177 // promote), so we might as well prevent all young generation
6178 // GC's while we do a sweeping step. For the same reason, we might
6179 // as well take the bit map lock for the entire duration
6180
6181 // check that we hold the requisite locks
6182 assert(have_cms_token(), "Should hold cms token");
6183 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6184 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6185 "Should possess CMS token to sweep");
6186 assert_lock_strong(gen->freelistLock());
6187 assert_lock_strong(bitMapLock());
6188
6189 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6190 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6191 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6192 _inter_sweep_estimate.padded_average(),
6193 _intra_sweep_estimate.padded_average());
6194 gen->setNearLargestChunk();
6195
6196 {
6197 SweepClosure sweepClosure(this, gen, &_markBitMap,
6198 CMSYield && asynch);
6199 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6200 // We need to free-up/coalesce garbage/blocks from a
6201 // co-terminal free run. This is done in the SweepClosure
6202 // destructor; so, do not remove this scope, else the
6203 // end-of-sweep-census below will be off by a little bit.
6204 }
6205 gen->cmsSpace()->sweep_completed();
6206 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6207 if (should_unload_classes()) { // unloaded classes this cycle,
6208 _concurrent_cycles_since_last_unload = 0; // ... reset count
6209 } else { // did not unload classes,
6210 _concurrent_cycles_since_last_unload++; // ... increment count
6211 }
6212 }
6213
6214 // Reset CMS data structures (for now just the marking bit map)
6215 // preparatory for the next cycle.
6216 void CMSCollector::reset(bool asynch) {
6217 if (asynch) {
6218 CMSTokenSyncWithLocks ts(true, bitMapLock());
6219
6220 // If the state is not "Resetting", the foreground thread
6221 // has done a collection and the resetting.
6222 if (_collectorState != Resetting) {
6223 assert(_collectorState == Idling, "The state should only change"
6224 " because the foreground collector has finished the collection");
6225 return;
6226 }
6227
6228 // Clear the mark bitmap (no grey objects to start with)
6229 // for the next cycle.
6230 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6231 CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
6232
6233 HeapWord* curAddr = _markBitMap.startWord();
6234 while (curAddr < _markBitMap.endWord()) {
6235 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6236 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6237 _markBitMap.clear_large_range(chunk);
6238 if (ConcurrentMarkSweepThread::should_yield() &&
6239 !foregroundGCIsActive() &&
6240 CMSYield) {
6241 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6242 "CMS thread should hold CMS token");
6243 assert_lock_strong(bitMapLock());
6244 bitMapLock()->unlock();
6245 ConcurrentMarkSweepThread::desynchronize(true);
6246 stopTimer();
6247 if (PrintCMSStatistics != 0) {
6248 incrementYields();
6249 }
6250
6251 // See the comment in coordinator_yield()
6252 for (unsigned i = 0; i < CMSYieldSleepCount &&
6253 ConcurrentMarkSweepThread::should_yield() &&
6254 !CMSCollector::foregroundGCIsActive(); ++i) {
6255 os::sleep(Thread::current(), 1, false);
6256 }
6257
6258 ConcurrentMarkSweepThread::synchronize(true);
6259 bitMapLock()->lock_without_safepoint_check();
6260 startTimer();
6261 }
6262 curAddr = chunk.end();
6263 }
6264 // A successful mostly concurrent collection has been done.
6265 // Because only the full (i.e., concurrent mode failure) collections
6266 // are being measured for gc overhead limits, clean the "near" flag
6267 // and count.
6268 size_policy()->reset_gc_overhead_limit_count();
6269 _collectorState = Idling;
6270 } else {
6271 // already have the lock
6272 assert(_collectorState == Resetting, "just checking");
6273 assert_lock_strong(bitMapLock());
6274 _markBitMap.clear_all();
6275 _collectorState = Idling;
6276 }
6277
6278 NOT_PRODUCT(
6279 if (RotateCMSCollectionTypes) {
6280 _cmsGen->rotate_debug_collection_type();
6281 }
6282 )
6283
6284 register_gc_end();
6285 }
6286
6287 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6288 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6289 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6290 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
6291 TraceCollectorStats tcs(counters());
6292
6293 switch (op) {
6294 case CMS_op_checkpointRootsInitial: {
6295 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6296 checkpointRootsInitial(true); // asynch
6297 if (PrintGC) {
6298 _cmsGen->printOccupancy("initial-mark");
6299 }
6300 break;
6301 }
6302 case CMS_op_checkpointRootsFinal: {
6303 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6304 checkpointRootsFinal(true, // asynch
6305 false, // !clear_all_soft_refs
6306 false); // !init_mark_was_synchronous
6307 if (PrintGC) {
6308 _cmsGen->printOccupancy("remark");
6309 }
6310 break;
6311 }
6312 default:
6313 fatal("No such CMS_op");
6314 }
6315 }
6316
6317 #ifndef PRODUCT
6318 size_t const CMSCollector::skip_header_HeapWords() {
6319 return FreeChunk::header_size();
6320 }
6321
6322 // Try and collect here conditions that should hold when
6323 // CMS thread is exiting. The idea is that the foreground GC
6324 // thread should not be blocked if it wants to terminate
6325 // the CMS thread and yet continue to run the VM for a while
6326 // after that.
6327 void CMSCollector::verify_ok_to_terminate() const {
6328 assert(Thread::current()->is_ConcurrentGC_thread(),
6329 "should be called by CMS thread");
6330 assert(!_foregroundGCShouldWait, "should be false");
6331 // We could check here that all the various low-level locks
6332 // are not held by the CMS thread, but that is overkill; see
6333 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6334 // is checked.
6335 }
6336 #endif
6337
6338 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6339 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6340 "missing Printezis mark?");
6341 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6342 size_t size = pointer_delta(nextOneAddr + 1, addr);
6343 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6344 "alignment problem");
6345 assert(size >= 3, "Necessary for Printezis marks to work");
6346 return size;
6347 }
6348
6349 // A variant of the above (block_size_using_printezis_bits()) except
6350 // that we return 0 if the P-bits are not yet set.
6351 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6352 if (_markBitMap.isMarked(addr + 1)) {
6353 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6354 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6355 size_t size = pointer_delta(nextOneAddr + 1, addr);
6356 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6357 "alignment problem");
6358 assert(size >= 3, "Necessary for Printezis marks to work");
6359 return size;
6360 }
6361 return 0;
6362 }
6363
6364 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6365 size_t sz = 0;
6366 oop p = (oop)addr;
6367 if (p->klass_or_null() != NULL) {
6368 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6369 } else {
6370 sz = block_size_using_printezis_bits(addr);
6371 }
6372 assert(sz > 0, "size must be nonzero");
6373 HeapWord* next_block = addr + sz;
6374 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6375 CardTableModRefBS::card_size);
6376 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6377 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6378 "must be different cards");
6379 return next_card;
6380 }
6381
6382
6383 // CMS Bit Map Wrapper /////////////////////////////////////////
6384
6385 // Construct a CMS bit map infrastructure, but don't create the
6386 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6387 // further below.
6388 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6389 _bm(),
6390 _shifter(shifter),
6391 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true ,
6392 Monitor::_safepoint_check_sometimes) : NULL)
6393 {
6394 _bmStartWord = 0;
6395 _bmWordSize = 0;
6396 }
6397
6398 bool CMSBitMap::allocate(MemRegion mr) {
6399 _bmStartWord = mr.start();
6400 _bmWordSize = mr.word_size();
6401 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6402 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6403 if (!brs.is_reserved()) {
6404 warning("CMS bit map allocation failure");
6405 return false;
6406 }
6407 // For now we'll just commit all of the bit map up front.
6408 // Later on we'll try to be more parsimonious with swap.
6409 if (!_virtual_space.initialize(brs, brs.size())) {
6410 warning("CMS bit map backing store failure");
6411 return false;
6412 }
6413 assert(_virtual_space.committed_size() == brs.size(),
6414 "didn't reserve backing store for all of CMS bit map?");
6415 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6416 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6417 _bmWordSize, "inconsistency in bit map sizing");
6418 _bm.set_size(_bmWordSize >> _shifter);
6419
6420 // bm.clear(); // can we rely on getting zero'd memory? verify below
6421 assert(isAllClear(),
6422 "Expected zero'd memory from ReservedSpace constructor");
6423 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6424 "consistency check");
6425 return true;
6426 }
6427
6428 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6429 HeapWord *next_addr, *end_addr, *last_addr;
6430 assert_locked();
6431 assert(covers(mr), "out-of-range error");
6432 // XXX assert that start and end are appropriately aligned
6433 for (next_addr = mr.start(), end_addr = mr.end();
6434 next_addr < end_addr; next_addr = last_addr) {
6435 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6436 last_addr = dirty_region.end();
6437 if (!dirty_region.is_empty()) {
6438 cl->do_MemRegion(dirty_region);
6439 } else {
6440 assert(last_addr == end_addr, "program logic");
6441 return;
6442 }
6443 }
6444 }
6445
6446 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6447 _bm.print_on_error(st, prefix);
6448 }
6449
6450 #ifndef PRODUCT
6451 void CMSBitMap::assert_locked() const {
6452 CMSLockVerifier::assert_locked(lock());
6453 }
6454
6455 bool CMSBitMap::covers(MemRegion mr) const {
6456 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6457 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6458 "size inconsistency");
6459 return (mr.start() >= _bmStartWord) &&
6460 (mr.end() <= endWord());
6461 }
6462
6463 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6464 return (start >= _bmStartWord && (start + size) <= endWord());
6465 }
6466
6467 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6468 // verify that there are no 1 bits in the interval [left, right)
6469 FalseBitMapClosure falseBitMapClosure;
6470 iterate(&falseBitMapClosure, left, right);
6471 }
6472
6473 void CMSBitMap::region_invariant(MemRegion mr)
6474 {
6475 assert_locked();
6476 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6477 assert(!mr.is_empty(), "unexpected empty region");
6478 assert(covers(mr), "mr should be covered by bit map");
6479 // convert address range into offset range
6480 size_t start_ofs = heapWordToOffset(mr.start());
6481 // Make sure that end() is appropriately aligned
6482 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6483 (1 << (_shifter+LogHeapWordSize))),
6484 "Misaligned mr.end()");
6485 size_t end_ofs = heapWordToOffset(mr.end());
6486 assert(end_ofs > start_ofs, "Should mark at least one bit");
6487 }
6488
6489 #endif
6490
6491 bool CMSMarkStack::allocate(size_t size) {
6492 // allocate a stack of the requisite depth
6493 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6494 size * sizeof(oop)));
6495 if (!rs.is_reserved()) {
6496 warning("CMSMarkStack allocation failure");
6497 return false;
6498 }
6499 if (!_virtual_space.initialize(rs, rs.size())) {
6500 warning("CMSMarkStack backing store failure");
6501 return false;
6502 }
6503 assert(_virtual_space.committed_size() == rs.size(),
6504 "didn't reserve backing store for all of CMS stack?");
6505 _base = (oop*)(_virtual_space.low());
6506 _index = 0;
6507 _capacity = size;
6508 NOT_PRODUCT(_max_depth = 0);
6509 return true;
6510 }
6511
6512 // XXX FIX ME !!! In the MT case we come in here holding a
6513 // leaf lock. For printing we need to take a further lock
6514 // which has lower rank. We need to recalibrate the two
6515 // lock-ranks involved in order to be able to print the
6516 // messages below. (Or defer the printing to the caller.
6517 // For now we take the expedient path of just disabling the
6518 // messages for the problematic case.)
6519 void CMSMarkStack::expand() {
6520 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6521 if (_capacity == MarkStackSizeMax) {
6522 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6523 // We print a warning message only once per CMS cycle.
6524 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6525 }
6526 return;
6527 }
6528 // Double capacity if possible
6529 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6530 // Do not give up existing stack until we have managed to
6531 // get the double capacity that we desired.
6532 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6533 new_capacity * sizeof(oop)));
6534 if (rs.is_reserved()) {
6535 // Release the backing store associated with old stack
6536 _virtual_space.release();
6537 // Reinitialize virtual space for new stack
6538 if (!_virtual_space.initialize(rs, rs.size())) {
6539 fatal("Not enough swap for expanded marking stack");
6540 }
6541 _base = (oop*)(_virtual_space.low());
6542 _index = 0;
6543 _capacity = new_capacity;
6544 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6545 // Failed to double capacity, continue;
6546 // we print a detail message only once per CMS cycle.
6547 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6548 SIZE_FORMAT"K",
6549 _capacity / K, new_capacity / K);
6550 }
6551 }
6552
6553
6554 // Closures
6555 // XXX: there seems to be a lot of code duplication here;
6556 // should refactor and consolidate common code.
6557
6558 // This closure is used to mark refs into the CMS generation in
6559 // the CMS bit map. Called at the first checkpoint. This closure
6560 // assumes that we do not need to re-mark dirty cards; if the CMS
6561 // generation on which this is used is not an oldest
6562 // generation then this will lose younger_gen cards!
6563
6564 MarkRefsIntoClosure::MarkRefsIntoClosure(
6565 MemRegion span, CMSBitMap* bitMap):
6566 _span(span),
6567 _bitMap(bitMap)
6568 {
6569 assert(_ref_processor == NULL, "deliberately left NULL");
6570 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6571 }
6572
6573 void MarkRefsIntoClosure::do_oop(oop obj) {
6574 // if p points into _span, then mark corresponding bit in _markBitMap
6575 assert(obj->is_oop(), "expected an oop");
6576 HeapWord* addr = (HeapWord*)obj;
6577 if (_span.contains(addr)) {
6578 // this should be made more efficient
6579 _bitMap->mark(addr);
6580 }
6581 }
6582
6583 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6584 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6585
6586 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6587 MemRegion span, CMSBitMap* bitMap):
6588 _span(span),
6589 _bitMap(bitMap)
6590 {
6591 assert(_ref_processor == NULL, "deliberately left NULL");
6592 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6593 }
6594
6595 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6596 // if p points into _span, then mark corresponding bit in _markBitMap
6597 assert(obj->is_oop(), "expected an oop");
6598 HeapWord* addr = (HeapWord*)obj;
6599 if (_span.contains(addr)) {
6600 // this should be made more efficient
6601 _bitMap->par_mark(addr);
6602 }
6603 }
6604
6605 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6606 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6607
6608 // A variant of the above, used for CMS marking verification.
6609 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6610 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6611 _span(span),
6612 _verification_bm(verification_bm),
6613 _cms_bm(cms_bm)
6614 {
6615 assert(_ref_processor == NULL, "deliberately left NULL");
6616 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6617 }
6618
6619 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6620 // if p points into _span, then mark corresponding bit in _markBitMap
6621 assert(obj->is_oop(), "expected an oop");
6622 HeapWord* addr = (HeapWord*)obj;
6623 if (_span.contains(addr)) {
6624 _verification_bm->mark(addr);
6625 if (!_cms_bm->isMarked(addr)) {
6626 oop(addr)->print();
6627 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6628 fatal("... aborting");
6629 }
6630 }
6631 }
6632
6633 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6634 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6635
6636 //////////////////////////////////////////////////
6637 // MarkRefsIntoAndScanClosure
6638 //////////////////////////////////////////////////
6639
6640 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6641 ReferenceProcessor* rp,
6642 CMSBitMap* bit_map,
6643 CMSBitMap* mod_union_table,
6644 CMSMarkStack* mark_stack,
6645 CMSCollector* collector,
6646 bool should_yield,
6647 bool concurrent_precleaning):
6648 _collector(collector),
6649 _span(span),
6650 _bit_map(bit_map),
6651 _mark_stack(mark_stack),
6652 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6653 mark_stack, concurrent_precleaning),
6654 _yield(should_yield),
6655 _concurrent_precleaning(concurrent_precleaning),
6656 _freelistLock(NULL)
6657 {
6658 _ref_processor = rp;
6659 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6660 }
6661
6662 // This closure is used to mark refs into the CMS generation at the
6663 // second (final) checkpoint, and to scan and transitively follow
6664 // the unmarked oops. It is also used during the concurrent precleaning
6665 // phase while scanning objects on dirty cards in the CMS generation.
6666 // The marks are made in the marking bit map and the marking stack is
6667 // used for keeping the (newly) grey objects during the scan.
6668 // The parallel version (Par_...) appears further below.
6669 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6670 if (obj != NULL) {
6671 assert(obj->is_oop(), "expected an oop");
6672 HeapWord* addr = (HeapWord*)obj;
6673 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6674 assert(_collector->overflow_list_is_empty(),
6675 "overflow list should be empty");
6676 if (_span.contains(addr) &&
6677 !_bit_map->isMarked(addr)) {
6678 // mark bit map (object is now grey)
6679 _bit_map->mark(addr);
6680 // push on marking stack (stack should be empty), and drain the
6681 // stack by applying this closure to the oops in the oops popped
6682 // from the stack (i.e. blacken the grey objects)
6683 bool res = _mark_stack->push(obj);
6684 assert(res, "Should have space to push on empty stack");
6685 do {
6686 oop new_oop = _mark_stack->pop();
6687 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6688 assert(_bit_map->isMarked((HeapWord*)new_oop),
6689 "only grey objects on this stack");
6690 // iterate over the oops in this oop, marking and pushing
6691 // the ones in CMS heap (i.e. in _span).
6692 new_oop->oop_iterate(&_pushAndMarkClosure);
6693 // check if it's time to yield
6694 do_yield_check();
6695 } while (!_mark_stack->isEmpty() ||
6696 (!_concurrent_precleaning && take_from_overflow_list()));
6697 // if marking stack is empty, and we are not doing this
6698 // during precleaning, then check the overflow list
6699 }
6700 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6701 assert(_collector->overflow_list_is_empty(),
6702 "overflow list was drained above");
6703 // We could restore evacuated mark words, if any, used for
6704 // overflow list links here because the overflow list is
6705 // provably empty here. That would reduce the maximum
6706 // size requirements for preserved_{oop,mark}_stack.
6707 // But we'll just postpone it until we are all done
6708 // so we can just stream through.
6709 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6710 _collector->restore_preserved_marks_if_any();
6711 assert(_collector->no_preserved_marks(), "No preserved marks");
6712 }
6713 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6714 "All preserved marks should have been restored above");
6715 }
6716 }
6717
6718 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6719 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6720
6721 void MarkRefsIntoAndScanClosure::do_yield_work() {
6722 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6723 "CMS thread should hold CMS token");
6724 assert_lock_strong(_freelistLock);
6725 assert_lock_strong(_bit_map->lock());
6726 // relinquish the free_list_lock and bitMaplock()
6727 _bit_map->lock()->unlock();
6728 _freelistLock->unlock();
6729 ConcurrentMarkSweepThread::desynchronize(true);
6730 _collector->stopTimer();
6731 if (PrintCMSStatistics != 0) {
6732 _collector->incrementYields();
6733 }
6734
6735 // See the comment in coordinator_yield()
6736 for (unsigned i = 0;
6737 i < CMSYieldSleepCount &&
6738 ConcurrentMarkSweepThread::should_yield() &&
6739 !CMSCollector::foregroundGCIsActive();
6740 ++i) {
6741 os::sleep(Thread::current(), 1, false);
6742 }
6743
6744 ConcurrentMarkSweepThread::synchronize(true);
6745 _freelistLock->lock_without_safepoint_check();
6746 _bit_map->lock()->lock_without_safepoint_check();
6747 _collector->startTimer();
6748 }
6749
6750 ///////////////////////////////////////////////////////////
6751 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6752 // MarkRefsIntoAndScanClosure
6753 ///////////////////////////////////////////////////////////
6754 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6755 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6756 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6757 _span(span),
6758 _bit_map(bit_map),
6759 _work_queue(work_queue),
6760 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6761 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6762 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6763 {
6764 _ref_processor = rp;
6765 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6766 }
6767
6768 // This closure is used to mark refs into the CMS generation at the
6769 // second (final) checkpoint, and to scan and transitively follow
6770 // the unmarked oops. The marks are made in the marking bit map and
6771 // the work_queue is used for keeping the (newly) grey objects during
6772 // the scan phase whence they are also available for stealing by parallel
6773 // threads. Since the marking bit map is shared, updates are
6774 // synchronized (via CAS).
6775 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6776 if (obj != NULL) {
6777 // Ignore mark word because this could be an already marked oop
6778 // that may be chained at the end of the overflow list.
6779 assert(obj->is_oop(true), "expected an oop");
6780 HeapWord* addr = (HeapWord*)obj;
6781 if (_span.contains(addr) &&
6782 !_bit_map->isMarked(addr)) {
6783 // mark bit map (object will become grey):
6784 // It is possible for several threads to be
6785 // trying to "claim" this object concurrently;
6786 // the unique thread that succeeds in marking the
6787 // object first will do the subsequent push on
6788 // to the work queue (or overflow list).
6789 if (_bit_map->par_mark(addr)) {
6790 // push on work_queue (which may not be empty), and trim the
6791 // queue to an appropriate length by applying this closure to
6792 // the oops in the oops popped from the stack (i.e. blacken the
6793 // grey objects)
6794 bool res = _work_queue->push(obj);
6795 assert(res, "Low water mark should be less than capacity?");
6796 trim_queue(_low_water_mark);
6797 } // Else, another thread claimed the object
6798 }
6799 }
6800 }
6801
6802 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6803 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6804
6805 // This closure is used to rescan the marked objects on the dirty cards
6806 // in the mod union table and the card table proper.
6807 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6808 oop p, MemRegion mr) {
6809
6810 size_t size = 0;
6811 HeapWord* addr = (HeapWord*)p;
6812 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6813 assert(_span.contains(addr), "we are scanning the CMS generation");
6814 // check if it's time to yield
6815 if (do_yield_check()) {
6816 // We yielded for some foreground stop-world work,
6817 // and we have been asked to abort this ongoing preclean cycle.
6818 return 0;
6819 }
6820 if (_bitMap->isMarked(addr)) {
6821 // it's marked; is it potentially uninitialized?
6822 if (p->klass_or_null() != NULL) {
6823 // an initialized object; ignore mark word in verification below
6824 // since we are running concurrent with mutators
6825 assert(p->is_oop(true), "should be an oop");
6826 if (p->is_objArray()) {
6827 // objArrays are precisely marked; restrict scanning
6828 // to dirty cards only.
6829 size = CompactibleFreeListSpace::adjustObjectSize(
6830 p->oop_iterate(_scanningClosure, mr));
6831 } else {
6832 // A non-array may have been imprecisely marked; we need
6833 // to scan object in its entirety.
6834 size = CompactibleFreeListSpace::adjustObjectSize(
6835 p->oop_iterate(_scanningClosure));
6836 }
6837 #ifdef ASSERT
6838 size_t direct_size =
6839 CompactibleFreeListSpace::adjustObjectSize(p->size());
6840 assert(size == direct_size, "Inconsistency in size");
6841 assert(size >= 3, "Necessary for Printezis marks to work");
6842 if (!_bitMap->isMarked(addr+1)) {
6843 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6844 } else {
6845 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6846 assert(_bitMap->isMarked(addr+size-1),
6847 "inconsistent Printezis mark");
6848 }
6849 #endif // ASSERT
6850 } else {
6851 // An uninitialized object.
6852 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6853 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6854 size = pointer_delta(nextOneAddr + 1, addr);
6855 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6856 "alignment problem");
6857 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6858 // will dirty the card when the klass pointer is installed in the
6859 // object (signaling the completion of initialization).
6860 }
6861 } else {
6862 // Either a not yet marked object or an uninitialized object
6863 if (p->klass_or_null() == NULL) {
6864 // An uninitialized object, skip to the next card, since
6865 // we may not be able to read its P-bits yet.
6866 assert(size == 0, "Initial value");
6867 } else {
6868 // An object not (yet) reached by marking: we merely need to
6869 // compute its size so as to go look at the next block.
6870 assert(p->is_oop(true), "should be an oop");
6871 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6872 }
6873 }
6874 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6875 return size;
6876 }
6877
6878 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6879 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6880 "CMS thread should hold CMS token");
6881 assert_lock_strong(_freelistLock);
6882 assert_lock_strong(_bitMap->lock());
6883 // relinquish the free_list_lock and bitMaplock()
6884 _bitMap->lock()->unlock();
6885 _freelistLock->unlock();
6886 ConcurrentMarkSweepThread::desynchronize(true);
6887 _collector->stopTimer();
6888 if (PrintCMSStatistics != 0) {
6889 _collector->incrementYields();
6890 }
6891
6892 // See the comment in coordinator_yield()
6893 for (unsigned i = 0; i < CMSYieldSleepCount &&
6894 ConcurrentMarkSweepThread::should_yield() &&
6895 !CMSCollector::foregroundGCIsActive(); ++i) {
6896 os::sleep(Thread::current(), 1, false);
6897 }
6898
6899 ConcurrentMarkSweepThread::synchronize(true);
6900 _freelistLock->lock_without_safepoint_check();
6901 _bitMap->lock()->lock_without_safepoint_check();
6902 _collector->startTimer();
6903 }
6904
6905
6906 //////////////////////////////////////////////////////////////////
6907 // SurvivorSpacePrecleanClosure
6908 //////////////////////////////////////////////////////////////////
6909 // This (single-threaded) closure is used to preclean the oops in
6910 // the survivor spaces.
6911 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6912
6913 HeapWord* addr = (HeapWord*)p;
6914 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6915 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6916 assert(p->klass_or_null() != NULL, "object should be initialized");
6917 // an initialized object; ignore mark word in verification below
6918 // since we are running concurrent with mutators
6919 assert(p->is_oop(true), "should be an oop");
6920 // Note that we do not yield while we iterate over
6921 // the interior oops of p, pushing the relevant ones
6922 // on our marking stack.
6923 size_t size = p->oop_iterate(_scanning_closure);
6924 do_yield_check();
6925 // Observe that below, we do not abandon the preclean
6926 // phase as soon as we should; rather we empty the
6927 // marking stack before returning. This is to satisfy
6928 // some existing assertions. In general, it may be a
6929 // good idea to abort immediately and complete the marking
6930 // from the grey objects at a later time.
6931 while (!_mark_stack->isEmpty()) {
6932 oop new_oop = _mark_stack->pop();
6933 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6934 assert(_bit_map->isMarked((HeapWord*)new_oop),
6935 "only grey objects on this stack");
6936 // iterate over the oops in this oop, marking and pushing
6937 // the ones in CMS heap (i.e. in _span).
6938 new_oop->oop_iterate(_scanning_closure);
6939 // check if it's time to yield
6940 do_yield_check();
6941 }
6942 unsigned int after_count =
6943 GenCollectedHeap::heap()->total_collections();
6944 bool abort = (_before_count != after_count) ||
6945 _collector->should_abort_preclean();
6946 return abort ? 0 : size;
6947 }
6948
6949 void SurvivorSpacePrecleanClosure::do_yield_work() {
6950 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6951 "CMS thread should hold CMS token");
6952 assert_lock_strong(_bit_map->lock());
6953 // Relinquish the bit map lock
6954 _bit_map->lock()->unlock();
6955 ConcurrentMarkSweepThread::desynchronize(true);
6956 _collector->stopTimer();
6957 if (PrintCMSStatistics != 0) {
6958 _collector->incrementYields();
6959 }
6960
6961 // See the comment in coordinator_yield()
6962 for (unsigned i = 0; i < CMSYieldSleepCount &&
6963 ConcurrentMarkSweepThread::should_yield() &&
6964 !CMSCollector::foregroundGCIsActive(); ++i) {
6965 os::sleep(Thread::current(), 1, false);
6966 }
6967
6968 ConcurrentMarkSweepThread::synchronize(true);
6969 _bit_map->lock()->lock_without_safepoint_check();
6970 _collector->startTimer();
6971 }
6972
6973 // This closure is used to rescan the marked objects on the dirty cards
6974 // in the mod union table and the card table proper. In the parallel
6975 // case, although the bitMap is shared, we do a single read so the
6976 // isMarked() query is "safe".
6977 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6978 // Ignore mark word because we are running concurrent with mutators
6979 assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
6980 HeapWord* addr = (HeapWord*)p;
6981 assert(_span.contains(addr), "we are scanning the CMS generation");
6982 bool is_obj_array = false;
6983 #ifdef ASSERT
6984 if (!_parallel) {
6985 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6986 assert(_collector->overflow_list_is_empty(),
6987 "overflow list should be empty");
6988
6989 }
6990 #endif // ASSERT
6991 if (_bit_map->isMarked(addr)) {
6992 // Obj arrays are precisely marked, non-arrays are not;
6993 // so we scan objArrays precisely and non-arrays in their
6994 // entirety.
6995 if (p->is_objArray()) {
6996 is_obj_array = true;
6997 if (_parallel) {
6998 p->oop_iterate(_par_scan_closure, mr);
6999 } else {
7000 p->oop_iterate(_scan_closure, mr);
7001 }
7002 } else {
7003 if (_parallel) {
7004 p->oop_iterate(_par_scan_closure);
7005 } else {
7006 p->oop_iterate(_scan_closure);
7007 }
7008 }
7009 }
7010 #ifdef ASSERT
7011 if (!_parallel) {
7012 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7013 assert(_collector->overflow_list_is_empty(),
7014 "overflow list should be empty");
7015
7016 }
7017 #endif // ASSERT
7018 return is_obj_array;
7019 }
7020
7021 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7022 MemRegion span,
7023 CMSBitMap* bitMap, CMSMarkStack* markStack,
7024 bool should_yield, bool verifying):
7025 _collector(collector),
7026 _span(span),
7027 _bitMap(bitMap),
7028 _mut(&collector->_modUnionTable),
7029 _markStack(markStack),
7030 _yield(should_yield),
7031 _skipBits(0)
7032 {
7033 assert(_markStack->isEmpty(), "stack should be empty");
7034 _finger = _bitMap->startWord();
7035 _threshold = _finger;
7036 assert(_collector->_restart_addr == NULL, "Sanity check");
7037 assert(_span.contains(_finger), "Out of bounds _finger?");
7038 DEBUG_ONLY(_verifying = verifying;)
7039 }
7040
7041 void MarkFromRootsClosure::reset(HeapWord* addr) {
7042 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7043 assert(_span.contains(addr), "Out of bounds _finger?");
7044 _finger = addr;
7045 _threshold = (HeapWord*)round_to(
7046 (intptr_t)_finger, CardTableModRefBS::card_size);
7047 }
7048
7049 // Should revisit to see if this should be restructured for
7050 // greater efficiency.
7051 bool MarkFromRootsClosure::do_bit(size_t offset) {
7052 if (_skipBits > 0) {
7053 _skipBits--;
7054 return true;
7055 }
7056 // convert offset into a HeapWord*
7057 HeapWord* addr = _bitMap->startWord() + offset;
7058 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7059 "address out of range");
7060 assert(_bitMap->isMarked(addr), "tautology");
7061 if (_bitMap->isMarked(addr+1)) {
7062 // this is an allocated but not yet initialized object
7063 assert(_skipBits == 0, "tautology");
7064 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7065 oop p = oop(addr);
7066 if (p->klass_or_null() == NULL) {
7067 DEBUG_ONLY(if (!_verifying) {)
7068 // We re-dirty the cards on which this object lies and increase
7069 // the _threshold so that we'll come back to scan this object
7070 // during the preclean or remark phase. (CMSCleanOnEnter)
7071 if (CMSCleanOnEnter) {
7072 size_t sz = _collector->block_size_using_printezis_bits(addr);
7073 HeapWord* end_card_addr = (HeapWord*)round_to(
7074 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7075 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7076 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7077 // Bump _threshold to end_card_addr; note that
7078 // _threshold cannot possibly exceed end_card_addr, anyhow.
7079 // This prevents future clearing of the card as the scan proceeds
7080 // to the right.
7081 assert(_threshold <= end_card_addr,
7082 "Because we are just scanning into this object");
7083 if (_threshold < end_card_addr) {
7084 _threshold = end_card_addr;
7085 }
7086 if (p->klass_or_null() != NULL) {
7087 // Redirty the range of cards...
7088 _mut->mark_range(redirty_range);
7089 } // ...else the setting of klass will dirty the card anyway.
7090 }
7091 DEBUG_ONLY(})
7092 return true;
7093 }
7094 }
7095 scanOopsInOop(addr);
7096 return true;
7097 }
7098
7099 // We take a break if we've been at this for a while,
7100 // so as to avoid monopolizing the locks involved.
7101 void MarkFromRootsClosure::do_yield_work() {
7102 // First give up the locks, then yield, then re-lock
7103 // We should probably use a constructor/destructor idiom to
7104 // do this unlock/lock or modify the MutexUnlocker class to
7105 // serve our purpose. XXX
7106 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7107 "CMS thread should hold CMS token");
7108 assert_lock_strong(_bitMap->lock());
7109 _bitMap->lock()->unlock();
7110 ConcurrentMarkSweepThread::desynchronize(true);
7111 _collector->stopTimer();
7112 if (PrintCMSStatistics != 0) {
7113 _collector->incrementYields();
7114 }
7115
7116 // See the comment in coordinator_yield()
7117 for (unsigned i = 0; i < CMSYieldSleepCount &&
7118 ConcurrentMarkSweepThread::should_yield() &&
7119 !CMSCollector::foregroundGCIsActive(); ++i) {
7120 os::sleep(Thread::current(), 1, false);
7121 }
7122
7123 ConcurrentMarkSweepThread::synchronize(true);
7124 _bitMap->lock()->lock_without_safepoint_check();
7125 _collector->startTimer();
7126 }
7127
7128 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7129 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7130 assert(_markStack->isEmpty(),
7131 "should drain stack to limit stack usage");
7132 // convert ptr to an oop preparatory to scanning
7133 oop obj = oop(ptr);
7134 // Ignore mark word in verification below, since we
7135 // may be running concurrent with mutators.
7136 assert(obj->is_oop(true), "should be an oop");
7137 assert(_finger <= ptr, "_finger runneth ahead");
7138 // advance the finger to right end of this object
7139 _finger = ptr + obj->size();
7140 assert(_finger > ptr, "we just incremented it above");
7141 // On large heaps, it may take us some time to get through
7142 // the marking phase. During
7143 // this time it's possible that a lot of mutations have
7144 // accumulated in the card table and the mod union table --
7145 // these mutation records are redundant until we have
7146 // actually traced into the corresponding card.
7147 // Here, we check whether advancing the finger would make
7148 // us cross into a new card, and if so clear corresponding
7149 // cards in the MUT (preclean them in the card-table in the
7150 // future).
7151
7152 DEBUG_ONLY(if (!_verifying) {)
7153 // The clean-on-enter optimization is disabled by default,
7154 // until we fix 6178663.
7155 if (CMSCleanOnEnter && (_finger > _threshold)) {
7156 // [_threshold, _finger) represents the interval
7157 // of cards to be cleared in MUT (or precleaned in card table).
7158 // The set of cards to be cleared is all those that overlap
7159 // with the interval [_threshold, _finger); note that
7160 // _threshold is always kept card-aligned but _finger isn't
7161 // always card-aligned.
7162 HeapWord* old_threshold = _threshold;
7163 assert(old_threshold == (HeapWord*)round_to(
7164 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7165 "_threshold should always be card-aligned");
7166 _threshold = (HeapWord*)round_to(
7167 (intptr_t)_finger, CardTableModRefBS::card_size);
7168 MemRegion mr(old_threshold, _threshold);
7169 assert(!mr.is_empty(), "Control point invariant");
7170 assert(_span.contains(mr), "Should clear within span");
7171 _mut->clear_range(mr);
7172 }
7173 DEBUG_ONLY(})
7174 // Note: the finger doesn't advance while we drain
7175 // the stack below.
7176 PushOrMarkClosure pushOrMarkClosure(_collector,
7177 _span, _bitMap, _markStack,
7178 _finger, this);
7179 bool res = _markStack->push(obj);
7180 assert(res, "Empty non-zero size stack should have space for single push");
7181 while (!_markStack->isEmpty()) {
7182 oop new_oop = _markStack->pop();
7183 // Skip verifying header mark word below because we are
7184 // running concurrent with mutators.
7185 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7186 // now scan this oop's oops
7187 new_oop->oop_iterate(&pushOrMarkClosure);
7188 do_yield_check();
7189 }
7190 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7191 }
7192
7193 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7194 CMSCollector* collector, MemRegion span,
7195 CMSBitMap* bit_map,
7196 OopTaskQueue* work_queue,
7197 CMSMarkStack* overflow_stack,
7198 bool should_yield):
7199 _collector(collector),
7200 _whole_span(collector->_span),
7201 _span(span),
7202 _bit_map(bit_map),
7203 _mut(&collector->_modUnionTable),
7204 _work_queue(work_queue),
7205 _overflow_stack(overflow_stack),
7206 _yield(should_yield),
7207 _skip_bits(0),
7208 _task(task)
7209 {
7210 assert(_work_queue->size() == 0, "work_queue should be empty");
7211 _finger = span.start();
7212 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7213 assert(_span.contains(_finger), "Out of bounds _finger?");
7214 }
7215
7216 // Should revisit to see if this should be restructured for
7217 // greater efficiency.
7218 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7219 if (_skip_bits > 0) {
7220 _skip_bits--;
7221 return true;
7222 }
7223 // convert offset into a HeapWord*
7224 HeapWord* addr = _bit_map->startWord() + offset;
7225 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7226 "address out of range");
7227 assert(_bit_map->isMarked(addr), "tautology");
7228 if (_bit_map->isMarked(addr+1)) {
7229 // this is an allocated object that might not yet be initialized
7230 assert(_skip_bits == 0, "tautology");
7231 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7232 oop p = oop(addr);
7233 if (p->klass_or_null() == NULL) {
7234 // in the case of Clean-on-Enter optimization, redirty card
7235 // and avoid clearing card by increasing the threshold.
7236 return true;
7237 }
7238 }
7239 scan_oops_in_oop(addr);
7240 return true;
7241 }
7242
7243 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7244 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7245 // Should we assert that our work queue is empty or
7246 // below some drain limit?
7247 assert(_work_queue->size() == 0,
7248 "should drain stack to limit stack usage");
7249 // convert ptr to an oop preparatory to scanning
7250 oop obj = oop(ptr);
7251 // Ignore mark word in verification below, since we
7252 // may be running concurrent with mutators.
7253 assert(obj->is_oop(true), "should be an oop");
7254 assert(_finger <= ptr, "_finger runneth ahead");
7255 // advance the finger to right end of this object
7256 _finger = ptr + obj->size();
7257 assert(_finger > ptr, "we just incremented it above");
7258 // On large heaps, it may take us some time to get through
7259 // the marking phase. During
7260 // this time it's possible that a lot of mutations have
7261 // accumulated in the card table and the mod union table --
7262 // these mutation records are redundant until we have
7263 // actually traced into the corresponding card.
7264 // Here, we check whether advancing the finger would make
7265 // us cross into a new card, and if so clear corresponding
7266 // cards in the MUT (preclean them in the card-table in the
7267 // future).
7268
7269 // The clean-on-enter optimization is disabled by default,
7270 // until we fix 6178663.
7271 if (CMSCleanOnEnter && (_finger > _threshold)) {
7272 // [_threshold, _finger) represents the interval
7273 // of cards to be cleared in MUT (or precleaned in card table).
7274 // The set of cards to be cleared is all those that overlap
7275 // with the interval [_threshold, _finger); note that
7276 // _threshold is always kept card-aligned but _finger isn't
7277 // always card-aligned.
7278 HeapWord* old_threshold = _threshold;
7279 assert(old_threshold == (HeapWord*)round_to(
7280 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7281 "_threshold should always be card-aligned");
7282 _threshold = (HeapWord*)round_to(
7283 (intptr_t)_finger, CardTableModRefBS::card_size);
7284 MemRegion mr(old_threshold, _threshold);
7285 assert(!mr.is_empty(), "Control point invariant");
7286 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7287 _mut->clear_range(mr);
7288 }
7289
7290 // Note: the local finger doesn't advance while we drain
7291 // the stack below, but the global finger sure can and will.
7292 HeapWord** gfa = _task->global_finger_addr();
7293 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7294 _span, _bit_map,
7295 _work_queue,
7296 _overflow_stack,
7297 _finger,
7298 gfa, this);
7299 bool res = _work_queue->push(obj); // overflow could occur here
7300 assert(res, "Will hold once we use workqueues");
7301 while (true) {
7302 oop new_oop;
7303 if (!_work_queue->pop_local(new_oop)) {
7304 // We emptied our work_queue; check if there's stuff that can
7305 // be gotten from the overflow stack.
7306 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7307 _overflow_stack, _work_queue)) {
7308 do_yield_check();
7309 continue;
7310 } else { // done
7311 break;
7312 }
7313 }
7314 // Skip verifying header mark word below because we are
7315 // running concurrent with mutators.
7316 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7317 // now scan this oop's oops
7318 new_oop->oop_iterate(&pushOrMarkClosure);
7319 do_yield_check();
7320 }
7321 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7322 }
7323
7324 // Yield in response to a request from VM Thread or
7325 // from mutators.
7326 void Par_MarkFromRootsClosure::do_yield_work() {
7327 assert(_task != NULL, "sanity");
7328 _task->yield();
7329 }
7330
7331 // A variant of the above used for verifying CMS marking work.
7332 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7333 MemRegion span,
7334 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7335 CMSMarkStack* mark_stack):
7336 _collector(collector),
7337 _span(span),
7338 _verification_bm(verification_bm),
7339 _cms_bm(cms_bm),
7340 _mark_stack(mark_stack),
7341 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7342 mark_stack)
7343 {
7344 assert(_mark_stack->isEmpty(), "stack should be empty");
7345 _finger = _verification_bm->startWord();
7346 assert(_collector->_restart_addr == NULL, "Sanity check");
7347 assert(_span.contains(_finger), "Out of bounds _finger?");
7348 }
7349
7350 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7351 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7352 assert(_span.contains(addr), "Out of bounds _finger?");
7353 _finger = addr;
7354 }
7355
7356 // Should revisit to see if this should be restructured for
7357 // greater efficiency.
7358 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7359 // convert offset into a HeapWord*
7360 HeapWord* addr = _verification_bm->startWord() + offset;
7361 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7362 "address out of range");
7363 assert(_verification_bm->isMarked(addr), "tautology");
7364 assert(_cms_bm->isMarked(addr), "tautology");
7365
7366 assert(_mark_stack->isEmpty(),
7367 "should drain stack to limit stack usage");
7368 // convert addr to an oop preparatory to scanning
7369 oop obj = oop(addr);
7370 assert(obj->is_oop(), "should be an oop");
7371 assert(_finger <= addr, "_finger runneth ahead");
7372 // advance the finger to right end of this object
7373 _finger = addr + obj->size();
7374 assert(_finger > addr, "we just incremented it above");
7375 // Note: the finger doesn't advance while we drain
7376 // the stack below.
7377 bool res = _mark_stack->push(obj);
7378 assert(res, "Empty non-zero size stack should have space for single push");
7379 while (!_mark_stack->isEmpty()) {
7380 oop new_oop = _mark_stack->pop();
7381 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7382 // now scan this oop's oops
7383 new_oop->oop_iterate(&_pam_verify_closure);
7384 }
7385 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7386 return true;
7387 }
7388
7389 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7390 CMSCollector* collector, MemRegion span,
7391 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7392 CMSMarkStack* mark_stack):
7393 MetadataAwareOopClosure(collector->ref_processor()),
7394 _collector(collector),
7395 _span(span),
7396 _verification_bm(verification_bm),
7397 _cms_bm(cms_bm),
7398 _mark_stack(mark_stack)
7399 { }
7400
7401 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7402 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7403
7404 // Upon stack overflow, we discard (part of) the stack,
7405 // remembering the least address amongst those discarded
7406 // in CMSCollector's _restart_address.
7407 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7408 // Remember the least grey address discarded
7409 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7410 _collector->lower_restart_addr(ra);
7411 _mark_stack->reset(); // discard stack contents
7412 _mark_stack->expand(); // expand the stack if possible
7413 }
7414
7415 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7416 assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7417 HeapWord* addr = (HeapWord*)obj;
7418 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7419 // Oop lies in _span and isn't yet grey or black
7420 _verification_bm->mark(addr); // now grey
7421 if (!_cms_bm->isMarked(addr)) {
7422 oop(addr)->print();
7423 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7424 addr);
7425 fatal("... aborting");
7426 }
7427
7428 if (!_mark_stack->push(obj)) { // stack overflow
7429 if (PrintCMSStatistics != 0) {
7430 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7431 SIZE_FORMAT, _mark_stack->capacity());
7432 }
7433 assert(_mark_stack->isFull(), "Else push should have succeeded");
7434 handle_stack_overflow(addr);
7435 }
7436 // anything including and to the right of _finger
7437 // will be scanned as we iterate over the remainder of the
7438 // bit map
7439 }
7440 }
7441
7442 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7443 MemRegion span,
7444 CMSBitMap* bitMap, CMSMarkStack* markStack,
7445 HeapWord* finger, MarkFromRootsClosure* parent) :
7446 MetadataAwareOopClosure(collector->ref_processor()),
7447 _collector(collector),
7448 _span(span),
7449 _bitMap(bitMap),
7450 _markStack(markStack),
7451 _finger(finger),
7452 _parent(parent)
7453 { }
7454
7455 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7456 MemRegion span,
7457 CMSBitMap* bit_map,
7458 OopTaskQueue* work_queue,
7459 CMSMarkStack* overflow_stack,
7460 HeapWord* finger,
7461 HeapWord** global_finger_addr,
7462 Par_MarkFromRootsClosure* parent) :
7463 MetadataAwareOopClosure(collector->ref_processor()),
7464 _collector(collector),
7465 _whole_span(collector->_span),
7466 _span(span),
7467 _bit_map(bit_map),
7468 _work_queue(work_queue),
7469 _overflow_stack(overflow_stack),
7470 _finger(finger),
7471 _global_finger_addr(global_finger_addr),
7472 _parent(parent)
7473 { }
7474
7475 // Assumes thread-safe access by callers, who are
7476 // responsible for mutual exclusion.
7477 void CMSCollector::lower_restart_addr(HeapWord* low) {
7478 assert(_span.contains(low), "Out of bounds addr");
7479 if (_restart_addr == NULL) {
7480 _restart_addr = low;
7481 } else {
7482 _restart_addr = MIN2(_restart_addr, low);
7483 }
7484 }
7485
7486 // Upon stack overflow, we discard (part of) the stack,
7487 // remembering the least address amongst those discarded
7488 // in CMSCollector's _restart_address.
7489 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7490 // Remember the least grey address discarded
7491 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7492 _collector->lower_restart_addr(ra);
7493 _markStack->reset(); // discard stack contents
7494 _markStack->expand(); // expand the stack if possible
7495 }
7496
7497 // Upon stack overflow, we discard (part of) the stack,
7498 // remembering the least address amongst those discarded
7499 // in CMSCollector's _restart_address.
7500 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7501 // We need to do this under a mutex to prevent other
7502 // workers from interfering with the work done below.
7503 MutexLockerEx ml(_overflow_stack->par_lock(),
7504 Mutex::_no_safepoint_check_flag);
7505 // Remember the least grey address discarded
7506 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7507 _collector->lower_restart_addr(ra);
7508 _overflow_stack->reset(); // discard stack contents
7509 _overflow_stack->expand(); // expand the stack if possible
7510 }
7511
7512 void PushOrMarkClosure::do_oop(oop obj) {
7513 // Ignore mark word because we are running concurrent with mutators.
7514 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7515 HeapWord* addr = (HeapWord*)obj;
7516 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7517 // Oop lies in _span and isn't yet grey or black
7518 _bitMap->mark(addr); // now grey
7519 if (addr < _finger) {
7520 // the bit map iteration has already either passed, or
7521 // sampled, this bit in the bit map; we'll need to
7522 // use the marking stack to scan this oop's oops.
7523 bool simulate_overflow = false;
7524 NOT_PRODUCT(
7525 if (CMSMarkStackOverflowALot &&
7526 _collector->simulate_overflow()) {
7527 // simulate a stack overflow
7528 simulate_overflow = true;
7529 }
7530 )
7531 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7532 if (PrintCMSStatistics != 0) {
7533 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7534 SIZE_FORMAT, _markStack->capacity());
7535 }
7536 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7537 handle_stack_overflow(addr);
7538 }
7539 }
7540 // anything including and to the right of _finger
7541 // will be scanned as we iterate over the remainder of the
7542 // bit map
7543 do_yield_check();
7544 }
7545 }
7546
7547 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7548 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7549
7550 void Par_PushOrMarkClosure::do_oop(oop obj) {
7551 // Ignore mark word because we are running concurrent with mutators.
7552 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7553 HeapWord* addr = (HeapWord*)obj;
7554 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7555 // Oop lies in _span and isn't yet grey or black
7556 // We read the global_finger (volatile read) strictly after marking oop
7557 bool res = _bit_map->par_mark(addr); // now grey
7558 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7559 // Should we push this marked oop on our stack?
7560 // -- if someone else marked it, nothing to do
7561 // -- if target oop is above global finger nothing to do
7562 // -- if target oop is in chunk and above local finger
7563 // then nothing to do
7564 // -- else push on work queue
7565 if ( !res // someone else marked it, they will deal with it
7566 || (addr >= *gfa) // will be scanned in a later task
7567 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7568 return;
7569 }
7570 // the bit map iteration has already either passed, or
7571 // sampled, this bit in the bit map; we'll need to
7572 // use the marking stack to scan this oop's oops.
7573 bool simulate_overflow = false;
7574 NOT_PRODUCT(
7575 if (CMSMarkStackOverflowALot &&
7576 _collector->simulate_overflow()) {
7577 // simulate a stack overflow
7578 simulate_overflow = true;
7579 }
7580 )
7581 if (simulate_overflow ||
7582 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7583 // stack overflow
7584 if (PrintCMSStatistics != 0) {
7585 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7586 SIZE_FORMAT, _overflow_stack->capacity());
7587 }
7588 // We cannot assert that the overflow stack is full because
7589 // it may have been emptied since.
7590 assert(simulate_overflow ||
7591 _work_queue->size() == _work_queue->max_elems(),
7592 "Else push should have succeeded");
7593 handle_stack_overflow(addr);
7594 }
7595 do_yield_check();
7596 }
7597 }
7598
7599 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7600 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7601
7602 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7603 MemRegion span,
7604 ReferenceProcessor* rp,
7605 CMSBitMap* bit_map,
7606 CMSBitMap* mod_union_table,
7607 CMSMarkStack* mark_stack,
7608 bool concurrent_precleaning):
7609 MetadataAwareOopClosure(rp),
7610 _collector(collector),
7611 _span(span),
7612 _bit_map(bit_map),
7613 _mod_union_table(mod_union_table),
7614 _mark_stack(mark_stack),
7615 _concurrent_precleaning(concurrent_precleaning)
7616 {
7617 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7618 }
7619
7620 // Grey object rescan during pre-cleaning and second checkpoint phases --
7621 // the non-parallel version (the parallel version appears further below.)
7622 void PushAndMarkClosure::do_oop(oop obj) {
7623 // Ignore mark word verification. If during concurrent precleaning,
7624 // the object monitor may be locked. If during the checkpoint
7625 // phases, the object may already have been reached by a different
7626 // path and may be at the end of the global overflow list (so
7627 // the mark word may be NULL).
7628 assert(obj->is_oop_or_null(true /* ignore mark word */),
7629 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7630 HeapWord* addr = (HeapWord*)obj;
7631 // Check if oop points into the CMS generation
7632 // and is not marked
7633 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7634 // a white object ...
7635 _bit_map->mark(addr); // ... now grey
7636 // push on the marking stack (grey set)
7637 bool simulate_overflow = false;
7638 NOT_PRODUCT(
7639 if (CMSMarkStackOverflowALot &&
7640 _collector->simulate_overflow()) {
7641 // simulate a stack overflow
7642 simulate_overflow = true;
7643 }
7644 )
7645 if (simulate_overflow || !_mark_stack->push(obj)) {
7646 if (_concurrent_precleaning) {
7647 // During precleaning we can just dirty the appropriate card(s)
7648 // in the mod union table, thus ensuring that the object remains
7649 // in the grey set and continue. In the case of object arrays
7650 // we need to dirty all of the cards that the object spans,
7651 // since the rescan of object arrays will be limited to the
7652 // dirty cards.
7653 // Note that no one can be interfering with us in this action
7654 // of dirtying the mod union table, so no locking or atomics
7655 // are required.
7656 if (obj->is_objArray()) {
7657 size_t sz = obj->size();
7658 HeapWord* end_card_addr = (HeapWord*)round_to(
7659 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7660 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7661 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7662 _mod_union_table->mark_range(redirty_range);
7663 } else {
7664 _mod_union_table->mark(addr);
7665 }
7666 _collector->_ser_pmc_preclean_ovflw++;
7667 } else {
7668 // During the remark phase, we need to remember this oop
7669 // in the overflow list.
7670 _collector->push_on_overflow_list(obj);
7671 _collector->_ser_pmc_remark_ovflw++;
7672 }
7673 }
7674 }
7675 }
7676
7677 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7678 MemRegion span,
7679 ReferenceProcessor* rp,
7680 CMSBitMap* bit_map,
7681 OopTaskQueue* work_queue):
7682 MetadataAwareOopClosure(rp),
7683 _collector(collector),
7684 _span(span),
7685 _bit_map(bit_map),
7686 _work_queue(work_queue)
7687 {
7688 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7689 }
7690
7691 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7692 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7693
7694 // Grey object rescan during second checkpoint phase --
7695 // the parallel version.
7696 void Par_PushAndMarkClosure::do_oop(oop obj) {
7697 // In the assert below, we ignore the mark word because
7698 // this oop may point to an already visited object that is
7699 // on the overflow stack (in which case the mark word has
7700 // been hijacked for chaining into the overflow stack --
7701 // if this is the last object in the overflow stack then
7702 // its mark word will be NULL). Because this object may
7703 // have been subsequently popped off the global overflow
7704 // stack, and the mark word possibly restored to the prototypical
7705 // value, by the time we get to examined this failing assert in
7706 // the debugger, is_oop_or_null(false) may subsequently start
7707 // to hold.
7708 assert(obj->is_oop_or_null(true),
7709 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7710 HeapWord* addr = (HeapWord*)obj;
7711 // Check if oop points into the CMS generation
7712 // and is not marked
7713 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7714 // a white object ...
7715 // If we manage to "claim" the object, by being the
7716 // first thread to mark it, then we push it on our
7717 // marking stack
7718 if (_bit_map->par_mark(addr)) { // ... now grey
7719 // push on work queue (grey set)
7720 bool simulate_overflow = false;
7721 NOT_PRODUCT(
7722 if (CMSMarkStackOverflowALot &&
7723 _collector->par_simulate_overflow()) {
7724 // simulate a stack overflow
7725 simulate_overflow = true;
7726 }
7727 )
7728 if (simulate_overflow || !_work_queue->push(obj)) {
7729 _collector->par_push_on_overflow_list(obj);
7730 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7731 }
7732 } // Else, some other thread got there first
7733 }
7734 }
7735
7736 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7737 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7738
7739 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7740 Mutex* bml = _collector->bitMapLock();
7741 assert_lock_strong(bml);
7742 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7743 "CMS thread should hold CMS token");
7744
7745 bml->unlock();
7746 ConcurrentMarkSweepThread::desynchronize(true);
7747
7748 _collector->stopTimer();
7749 if (PrintCMSStatistics != 0) {
7750 _collector->incrementYields();
7751 }
7752
7753 // See the comment in coordinator_yield()
7754 for (unsigned i = 0; i < CMSYieldSleepCount &&
7755 ConcurrentMarkSweepThread::should_yield() &&
7756 !CMSCollector::foregroundGCIsActive(); ++i) {
7757 os::sleep(Thread::current(), 1, false);
7758 }
7759
7760 ConcurrentMarkSweepThread::synchronize(true);
7761 bml->lock();
7762
7763 _collector->startTimer();
7764 }
7765
7766 bool CMSPrecleanRefsYieldClosure::should_return() {
7767 if (ConcurrentMarkSweepThread::should_yield()) {
7768 do_yield_work();
7769 }
7770 return _collector->foregroundGCIsActive();
7771 }
7772
7773 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7774 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7775 "mr should be aligned to start at a card boundary");
7776 // We'd like to assert:
7777 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7778 // "mr should be a range of cards");
7779 // However, that would be too strong in one case -- the last
7780 // partition ends at _unallocated_block which, in general, can be
7781 // an arbitrary boundary, not necessarily card aligned.
7782 if (PrintCMSStatistics != 0) {
7783 _num_dirty_cards +=
7784 mr.word_size()/CardTableModRefBS::card_size_in_words;
7785 }
7786 _space->object_iterate_mem(mr, &_scan_cl);
7787 }
7788
7789 SweepClosure::SweepClosure(CMSCollector* collector,
7790 ConcurrentMarkSweepGeneration* g,
7791 CMSBitMap* bitMap, bool should_yield) :
7792 _collector(collector),
7793 _g(g),
7794 _sp(g->cmsSpace()),
7795 _limit(_sp->sweep_limit()),
7796 _freelistLock(_sp->freelistLock()),
7797 _bitMap(bitMap),
7798 _yield(should_yield),
7799 _inFreeRange(false), // No free range at beginning of sweep
7800 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7801 _lastFreeRangeCoalesced(false),
7802 _freeFinger(g->used_region().start())
7803 {
7804 NOT_PRODUCT(
7805 _numObjectsFreed = 0;
7806 _numWordsFreed = 0;
7807 _numObjectsLive = 0;
7808 _numWordsLive = 0;
7809 _numObjectsAlreadyFree = 0;
7810 _numWordsAlreadyFree = 0;
7811 _last_fc = NULL;
7812
7813 _sp->initializeIndexedFreeListArrayReturnedBytes();
7814 _sp->dictionary()->initialize_dict_returned_bytes();
7815 )
7816 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7817 "sweep _limit out of bounds");
7818 if (CMSTraceSweeper) {
7819 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7820 _limit);
7821 }
7822 }
7823
7824 void SweepClosure::print_on(outputStream* st) const {
7825 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7826 _sp->bottom(), _sp->end());
7827 tty->print_cr("_limit = " PTR_FORMAT, _limit);
7828 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
7829 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
7830 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7831 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7832 }
7833
7834 #ifndef PRODUCT
7835 // Assertion checking only: no useful work in product mode --
7836 // however, if any of the flags below become product flags,
7837 // you may need to review this code to see if it needs to be
7838 // enabled in product mode.
7839 SweepClosure::~SweepClosure() {
7840 assert_lock_strong(_freelistLock);
7841 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7842 "sweep _limit out of bounds");
7843 if (inFreeRange()) {
7844 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7845 print();
7846 ShouldNotReachHere();
7847 }
7848 if (Verbose && PrintGC) {
7849 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7850 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7851 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7852 SIZE_FORMAT" bytes "
7853 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7854 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7855 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7856 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7857 * sizeof(HeapWord);
7858 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7859
7860 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7861 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7862 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7863 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7864 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7865 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7866 indexListReturnedBytes);
7867 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7868 dict_returned_bytes);
7869 }
7870 }
7871 if (CMSTraceSweeper) {
7872 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7873 _limit);
7874 }
7875 }
7876 #endif // PRODUCT
7877
7878 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7879 bool freeRangeInFreeLists) {
7880 if (CMSTraceSweeper) {
7881 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7882 freeFinger, freeRangeInFreeLists);
7883 }
7884 assert(!inFreeRange(), "Trampling existing free range");
7885 set_inFreeRange(true);
7886 set_lastFreeRangeCoalesced(false);
7887
7888 set_freeFinger(freeFinger);
7889 set_freeRangeInFreeLists(freeRangeInFreeLists);
7890 if (CMSTestInFreeList) {
7891 if (freeRangeInFreeLists) {
7892 FreeChunk* fc = (FreeChunk*) freeFinger;
7893 assert(fc->is_free(), "A chunk on the free list should be free.");
7894 assert(fc->size() > 0, "Free range should have a size");
7895 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7896 }
7897 }
7898 }
7899
7900 // Note that the sweeper runs concurrently with mutators. Thus,
7901 // it is possible for direct allocation in this generation to happen
7902 // in the middle of the sweep. Note that the sweeper also coalesces
7903 // contiguous free blocks. Thus, unless the sweeper and the allocator
7904 // synchronize appropriately freshly allocated blocks may get swept up.
7905 // This is accomplished by the sweeper locking the free lists while
7906 // it is sweeping. Thus blocks that are determined to be free are
7907 // indeed free. There is however one additional complication:
7908 // blocks that have been allocated since the final checkpoint and
7909 // mark, will not have been marked and so would be treated as
7910 // unreachable and swept up. To prevent this, the allocator marks
7911 // the bit map when allocating during the sweep phase. This leads,
7912 // however, to a further complication -- objects may have been allocated
7913 // but not yet initialized -- in the sense that the header isn't yet
7914 // installed. The sweeper can not then determine the size of the block
7915 // in order to skip over it. To deal with this case, we use a technique
7916 // (due to Printezis) to encode such uninitialized block sizes in the
7917 // bit map. Since the bit map uses a bit per every HeapWord, but the
7918 // CMS generation has a minimum object size of 3 HeapWords, it follows
7919 // that "normal marks" won't be adjacent in the bit map (there will
7920 // always be at least two 0 bits between successive 1 bits). We make use
7921 // of these "unused" bits to represent uninitialized blocks -- the bit
7922 // corresponding to the start of the uninitialized object and the next
7923 // bit are both set. Finally, a 1 bit marks the end of the object that
7924 // started with the two consecutive 1 bits to indicate its potentially
7925 // uninitialized state.
7926
7927 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7928 FreeChunk* fc = (FreeChunk*)addr;
7929 size_t res;
7930
7931 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7932 // than "addr == _limit" because although _limit was a block boundary when
7933 // we started the sweep, it may no longer be one because heap expansion
7934 // may have caused us to coalesce the block ending at the address _limit
7935 // with a newly expanded chunk (this happens when _limit was set to the
7936 // previous _end of the space), so we may have stepped past _limit:
7937 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7938 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7939 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7940 "sweep _limit out of bounds");
7941 assert(addr < _sp->end(), "addr out of bounds");
7942 // Flush any free range we might be holding as a single
7943 // coalesced chunk to the appropriate free list.
7944 if (inFreeRange()) {
7945 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7946 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
7947 flush_cur_free_chunk(freeFinger(),
7948 pointer_delta(addr, freeFinger()));
7949 if (CMSTraceSweeper) {
7950 gclog_or_tty->print("Sweep: last chunk: ");
7951 gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
7952 "[coalesced:%d]\n",
7953 freeFinger(), pointer_delta(addr, freeFinger()),
7954 lastFreeRangeCoalesced() ? 1 : 0);
7955 }
7956 }
7957
7958 // help the iterator loop finish
7959 return pointer_delta(_sp->end(), addr);
7960 }
7961
7962 assert(addr < _limit, "sweep invariant");
7963 // check if we should yield
7964 do_yield_check(addr);
7965 if (fc->is_free()) {
7966 // Chunk that is already free
7967 res = fc->size();
7968 do_already_free_chunk(fc);
7969 debug_only(_sp->verifyFreeLists());
7970 // If we flush the chunk at hand in lookahead_and_flush()
7971 // and it's coalesced with a preceding chunk, then the
7972 // process of "mangling" the payload of the coalesced block
7973 // will cause erasure of the size information from the
7974 // (erstwhile) header of all the coalesced blocks but the
7975 // first, so the first disjunct in the assert will not hold
7976 // in that specific case (in which case the second disjunct
7977 // will hold).
7978 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7979 "Otherwise the size info doesn't change at this step");
7980 NOT_PRODUCT(
7981 _numObjectsAlreadyFree++;
7982 _numWordsAlreadyFree += res;
7983 )
7984 NOT_PRODUCT(_last_fc = fc;)
7985 } else if (!_bitMap->isMarked(addr)) {
7986 // Chunk is fresh garbage
7987 res = do_garbage_chunk(fc);
7988 debug_only(_sp->verifyFreeLists());
7989 NOT_PRODUCT(
7990 _numObjectsFreed++;
7991 _numWordsFreed += res;
7992 )
7993 } else {
7994 // Chunk that is alive.
7995 res = do_live_chunk(fc);
7996 debug_only(_sp->verifyFreeLists());
7997 NOT_PRODUCT(
7998 _numObjectsLive++;
7999 _numWordsLive += res;
8000 )
8001 }
8002 return res;
8003 }
8004
8005 // For the smart allocation, record following
8006 // split deaths - a free chunk is removed from its free list because
8007 // it is being split into two or more chunks.
8008 // split birth - a free chunk is being added to its free list because
8009 // a larger free chunk has been split and resulted in this free chunk.
8010 // coal death - a free chunk is being removed from its free list because
8011 // it is being coalesced into a large free chunk.
8012 // coal birth - a free chunk is being added to its free list because
8013 // it was created when two or more free chunks where coalesced into
8014 // this free chunk.
8015 //
8016 // These statistics are used to determine the desired number of free
8017 // chunks of a given size. The desired number is chosen to be relative
8018 // to the end of a CMS sweep. The desired number at the end of a sweep
8019 // is the
8020 // count-at-end-of-previous-sweep (an amount that was enough)
8021 // - count-at-beginning-of-current-sweep (the excess)
8022 // + split-births (gains in this size during interval)
8023 // - split-deaths (demands on this size during interval)
8024 // where the interval is from the end of one sweep to the end of the
8025 // next.
8026 //
8027 // When sweeping the sweeper maintains an accumulated chunk which is
8028 // the chunk that is made up of chunks that have been coalesced. That
8029 // will be termed the left-hand chunk. A new chunk of garbage that
8030 // is being considered for coalescing will be referred to as the
8031 // right-hand chunk.
8032 //
8033 // When making a decision on whether to coalesce a right-hand chunk with
8034 // the current left-hand chunk, the current count vs. the desired count
8035 // of the left-hand chunk is considered. Also if the right-hand chunk
8036 // is near the large chunk at the end of the heap (see
8037 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8038 // left-hand chunk is coalesced.
8039 //
8040 // When making a decision about whether to split a chunk, the desired count
8041 // vs. the current count of the candidate to be split is also considered.
8042 // If the candidate is underpopulated (currently fewer chunks than desired)
8043 // a chunk of an overpopulated (currently more chunks than desired) size may
8044 // be chosen. The "hint" associated with a free list, if non-null, points
8045 // to a free list which may be overpopulated.
8046 //
8047
8048 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8049 const size_t size = fc->size();
8050 // Chunks that cannot be coalesced are not in the
8051 // free lists.
8052 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8053 assert(_sp->verify_chunk_in_free_list(fc),
8054 "free chunk should be in free lists");
8055 }
8056 // a chunk that is already free, should not have been
8057 // marked in the bit map
8058 HeapWord* const addr = (HeapWord*) fc;
8059 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8060 // Verify that the bit map has no bits marked between
8061 // addr and purported end of this block.
8062 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8063
8064 // Some chunks cannot be coalesced under any circumstances.
8065 // See the definition of cantCoalesce().
8066 if (!fc->cantCoalesce()) {
8067 // This chunk can potentially be coalesced.
8068 if (_sp->adaptive_freelists()) {
8069 // All the work is done in
8070 do_post_free_or_garbage_chunk(fc, size);
8071 } else { // Not adaptive free lists
8072 // this is a free chunk that can potentially be coalesced by the sweeper;
8073 if (!inFreeRange()) {
8074 // if the next chunk is a free block that can't be coalesced
8075 // it doesn't make sense to remove this chunk from the free lists
8076 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8077 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8078 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8079 nextChunk->is_free() && // ... which is free...
8080 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8081 // nothing to do
8082 } else {
8083 // Potentially the start of a new free range:
8084 // Don't eagerly remove it from the free lists.
8085 // No need to remove it if it will just be put
8086 // back again. (Also from a pragmatic point of view
8087 // if it is a free block in a region that is beyond
8088 // any allocated blocks, an assertion will fail)
8089 // Remember the start of a free run.
8090 initialize_free_range(addr, true);
8091 // end - can coalesce with next chunk
8092 }
8093 } else {
8094 // the midst of a free range, we are coalescing
8095 print_free_block_coalesced(fc);
8096 if (CMSTraceSweeper) {
8097 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
8098 }
8099 // remove it from the free lists
8100 _sp->removeFreeChunkFromFreeLists(fc);
8101 set_lastFreeRangeCoalesced(true);
8102 // If the chunk is being coalesced and the current free range is
8103 // in the free lists, remove the current free range so that it
8104 // will be returned to the free lists in its entirety - all
8105 // the coalesced pieces included.
8106 if (freeRangeInFreeLists()) {
8107 FreeChunk* ffc = (FreeChunk*) freeFinger();
8108 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8109 "Size of free range is inconsistent with chunk size.");
8110 if (CMSTestInFreeList) {
8111 assert(_sp->verify_chunk_in_free_list(ffc),
8112 "free range is not in free lists");
8113 }
8114 _sp->removeFreeChunkFromFreeLists(ffc);
8115 set_freeRangeInFreeLists(false);
8116 }
8117 }
8118 }
8119 // Note that if the chunk is not coalescable (the else arm
8120 // below), we unconditionally flush, without needing to do
8121 // a "lookahead," as we do below.
8122 if (inFreeRange()) lookahead_and_flush(fc, size);
8123 } else {
8124 // Code path common to both original and adaptive free lists.
8125
8126 // cant coalesce with previous block; this should be treated
8127 // as the end of a free run if any
8128 if (inFreeRange()) {
8129 // we kicked some butt; time to pick up the garbage
8130 assert(freeFinger() < addr, "freeFinger points too high");
8131 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8132 }
8133 // else, nothing to do, just continue
8134 }
8135 }
8136
8137 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8138 // This is a chunk of garbage. It is not in any free list.
8139 // Add it to a free list or let it possibly be coalesced into
8140 // a larger chunk.
8141 HeapWord* const addr = (HeapWord*) fc;
8142 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8143
8144 if (_sp->adaptive_freelists()) {
8145 // Verify that the bit map has no bits marked between
8146 // addr and purported end of just dead object.
8147 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8148
8149 do_post_free_or_garbage_chunk(fc, size);
8150 } else {
8151 if (!inFreeRange()) {
8152 // start of a new free range
8153 assert(size > 0, "A free range should have a size");
8154 initialize_free_range(addr, false);
8155 } else {
8156 // this will be swept up when we hit the end of the
8157 // free range
8158 if (CMSTraceSweeper) {
8159 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
8160 }
8161 // If the chunk is being coalesced and the current free range is
8162 // in the free lists, remove the current free range so that it
8163 // will be returned to the free lists in its entirety - all
8164 // the coalesced pieces included.
8165 if (freeRangeInFreeLists()) {
8166 FreeChunk* ffc = (FreeChunk*)freeFinger();
8167 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8168 "Size of free range is inconsistent with chunk size.");
8169 if (CMSTestInFreeList) {
8170 assert(_sp->verify_chunk_in_free_list(ffc),
8171 "free range is not in free lists");
8172 }
8173 _sp->removeFreeChunkFromFreeLists(ffc);
8174 set_freeRangeInFreeLists(false);
8175 }
8176 set_lastFreeRangeCoalesced(true);
8177 }
8178 // this will be swept up when we hit the end of the free range
8179
8180 // Verify that the bit map has no bits marked between
8181 // addr and purported end of just dead object.
8182 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8183 }
8184 assert(_limit >= addr + size,
8185 "A freshly garbage chunk can't possibly straddle over _limit");
8186 if (inFreeRange()) lookahead_and_flush(fc, size);
8187 return size;
8188 }
8189
8190 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8191 HeapWord* addr = (HeapWord*) fc;
8192 // The sweeper has just found a live object. Return any accumulated
8193 // left hand chunk to the free lists.
8194 if (inFreeRange()) {
8195 assert(freeFinger() < addr, "freeFinger points too high");
8196 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8197 }
8198
8199 // This object is live: we'd normally expect this to be
8200 // an oop, and like to assert the following:
8201 // assert(oop(addr)->is_oop(), "live block should be an oop");
8202 // However, as we commented above, this may be an object whose
8203 // header hasn't yet been initialized.
8204 size_t size;
8205 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8206 if (_bitMap->isMarked(addr + 1)) {
8207 // Determine the size from the bit map, rather than trying to
8208 // compute it from the object header.
8209 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8210 size = pointer_delta(nextOneAddr + 1, addr);
8211 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8212 "alignment problem");
8213
8214 #ifdef ASSERT
8215 if (oop(addr)->klass_or_null() != NULL) {
8216 // Ignore mark word because we are running concurrent with mutators
8217 assert(oop(addr)->is_oop(true), "live block should be an oop");
8218 assert(size ==
8219 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8220 "P-mark and computed size do not agree");
8221 }
8222 #endif
8223
8224 } else {
8225 // This should be an initialized object that's alive.
8226 assert(oop(addr)->klass_or_null() != NULL,
8227 "Should be an initialized object");
8228 // Ignore mark word because we are running concurrent with mutators
8229 assert(oop(addr)->is_oop(true), "live block should be an oop");
8230 // Verify that the bit map has no bits marked between
8231 // addr and purported end of this block.
8232 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8233 assert(size >= 3, "Necessary for Printezis marks to work");
8234 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8235 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8236 }
8237 return size;
8238 }
8239
8240 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8241 size_t chunkSize) {
8242 // do_post_free_or_garbage_chunk() should only be called in the case
8243 // of the adaptive free list allocator.
8244 const bool fcInFreeLists = fc->is_free();
8245 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8246 assert((HeapWord*)fc <= _limit, "sweep invariant");
8247 if (CMSTestInFreeList && fcInFreeLists) {
8248 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8249 }
8250
8251 if (CMSTraceSweeper) {
8252 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", fc, chunkSize);
8253 }
8254
8255 HeapWord* const fc_addr = (HeapWord*) fc;
8256
8257 bool coalesce;
8258 const size_t left = pointer_delta(fc_addr, freeFinger());
8259 const size_t right = chunkSize;
8260 switch (FLSCoalescePolicy) {
8261 // numeric value forms a coalition aggressiveness metric
8262 case 0: { // never coalesce
8263 coalesce = false;
8264 break;
8265 }
8266 case 1: { // coalesce if left & right chunks on overpopulated lists
8267 coalesce = _sp->coalOverPopulated(left) &&
8268 _sp->coalOverPopulated(right);
8269 break;
8270 }
8271 case 2: { // coalesce if left chunk on overpopulated list (default)
8272 coalesce = _sp->coalOverPopulated(left);
8273 break;
8274 }
8275 case 3: { // coalesce if left OR right chunk on overpopulated list
8276 coalesce = _sp->coalOverPopulated(left) ||
8277 _sp->coalOverPopulated(right);
8278 break;
8279 }
8280 case 4: { // always coalesce
8281 coalesce = true;
8282 break;
8283 }
8284 default:
8285 ShouldNotReachHere();
8286 }
8287
8288 // Should the current free range be coalesced?
8289 // If the chunk is in a free range and either we decided to coalesce above
8290 // or the chunk is near the large block at the end of the heap
8291 // (isNearLargestChunk() returns true), then coalesce this chunk.
8292 const bool doCoalesce = inFreeRange()
8293 && (coalesce || _g->isNearLargestChunk(fc_addr));
8294 if (doCoalesce) {
8295 // Coalesce the current free range on the left with the new
8296 // chunk on the right. If either is on a free list,
8297 // it must be removed from the list and stashed in the closure.
8298 if (freeRangeInFreeLists()) {
8299 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8300 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8301 "Size of free range is inconsistent with chunk size.");
8302 if (CMSTestInFreeList) {
8303 assert(_sp->verify_chunk_in_free_list(ffc),
8304 "Chunk is not in free lists");
8305 }
8306 _sp->coalDeath(ffc->size());
8307 _sp->removeFreeChunkFromFreeLists(ffc);
8308 set_freeRangeInFreeLists(false);
8309 }
8310 if (fcInFreeLists) {
8311 _sp->coalDeath(chunkSize);
8312 assert(fc->size() == chunkSize,
8313 "The chunk has the wrong size or is not in the free lists");
8314 _sp->removeFreeChunkFromFreeLists(fc);
8315 }
8316 set_lastFreeRangeCoalesced(true);
8317 print_free_block_coalesced(fc);
8318 } else { // not in a free range and/or should not coalesce
8319 // Return the current free range and start a new one.
8320 if (inFreeRange()) {
8321 // In a free range but cannot coalesce with the right hand chunk.
8322 // Put the current free range into the free lists.
8323 flush_cur_free_chunk(freeFinger(),
8324 pointer_delta(fc_addr, freeFinger()));
8325 }
8326 // Set up for new free range. Pass along whether the right hand
8327 // chunk is in the free lists.
8328 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8329 }
8330 }
8331
8332 // Lookahead flush:
8333 // If we are tracking a free range, and this is the last chunk that
8334 // we'll look at because its end crosses past _limit, we'll preemptively
8335 // flush it along with any free range we may be holding on to. Note that
8336 // this can be the case only for an already free or freshly garbage
8337 // chunk. If this block is an object, it can never straddle
8338 // over _limit. The "straddling" occurs when _limit is set at
8339 // the previous end of the space when this cycle started, and
8340 // a subsequent heap expansion caused the previously co-terminal
8341 // free block to be coalesced with the newly expanded portion,
8342 // thus rendering _limit a non-block-boundary making it dangerous
8343 // for the sweeper to step over and examine.
8344 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8345 assert(inFreeRange(), "Should only be called if currently in a free range.");
8346 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8347 assert(_sp->used_region().contains(eob - 1),
8348 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
8349 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8350 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8351 eob, eob-1, _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8352 if (eob >= _limit) {
8353 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8354 if (CMSTraceSweeper) {
8355 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8356 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8357 "[" PTR_FORMAT "," PTR_FORMAT ")",
8358 _limit, fc, eob, _sp->bottom(), _sp->end());
8359 }
8360 // Return the storage we are tracking back into the free lists.
8361 if (CMSTraceSweeper) {
8362 gclog_or_tty->print_cr("Flushing ... ");
8363 }
8364 assert(freeFinger() < eob, "Error");
8365 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8366 }
8367 }
8368
8369 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8370 assert(inFreeRange(), "Should only be called if currently in a free range.");
8371 assert(size > 0,
8372 "A zero sized chunk cannot be added to the free lists.");
8373 if (!freeRangeInFreeLists()) {
8374 if (CMSTestInFreeList) {
8375 FreeChunk* fc = (FreeChunk*) chunk;
8376 fc->set_size(size);
8377 assert(!_sp->verify_chunk_in_free_list(fc),
8378 "chunk should not be in free lists yet");
8379 }
8380 if (CMSTraceSweeper) {
8381 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
8382 chunk, size);
8383 }
8384 // A new free range is going to be starting. The current
8385 // free range has not been added to the free lists yet or
8386 // was removed so add it back.
8387 // If the current free range was coalesced, then the death
8388 // of the free range was recorded. Record a birth now.
8389 if (lastFreeRangeCoalesced()) {
8390 _sp->coalBirth(size);
8391 }
8392 _sp->addChunkAndRepairOffsetTable(chunk, size,
8393 lastFreeRangeCoalesced());
8394 } else if (CMSTraceSweeper) {
8395 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8396 }
8397 set_inFreeRange(false);
8398 set_freeRangeInFreeLists(false);
8399 }
8400
8401 // We take a break if we've been at this for a while,
8402 // so as to avoid monopolizing the locks involved.
8403 void SweepClosure::do_yield_work(HeapWord* addr) {
8404 // Return current free chunk being used for coalescing (if any)
8405 // to the appropriate freelist. After yielding, the next
8406 // free block encountered will start a coalescing range of
8407 // free blocks. If the next free block is adjacent to the
8408 // chunk just flushed, they will need to wait for the next
8409 // sweep to be coalesced.
8410 if (inFreeRange()) {
8411 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8412 }
8413
8414 // First give up the locks, then yield, then re-lock.
8415 // We should probably use a constructor/destructor idiom to
8416 // do this unlock/lock or modify the MutexUnlocker class to
8417 // serve our purpose. XXX
8418 assert_lock_strong(_bitMap->lock());
8419 assert_lock_strong(_freelistLock);
8420 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8421 "CMS thread should hold CMS token");
8422 _bitMap->lock()->unlock();
8423 _freelistLock->unlock();
8424 ConcurrentMarkSweepThread::desynchronize(true);
8425 _collector->stopTimer();
8426 if (PrintCMSStatistics != 0) {
8427 _collector->incrementYields();
8428 }
8429
8430 // See the comment in coordinator_yield()
8431 for (unsigned i = 0; i < CMSYieldSleepCount &&
8432 ConcurrentMarkSweepThread::should_yield() &&
8433 !CMSCollector::foregroundGCIsActive(); ++i) {
8434 os::sleep(Thread::current(), 1, false);
8435 }
8436
8437 ConcurrentMarkSweepThread::synchronize(true);
8438 _freelistLock->lock();
8439 _bitMap->lock()->lock_without_safepoint_check();
8440 _collector->startTimer();
8441 }
8442
8443 #ifndef PRODUCT
8444 // This is actually very useful in a product build if it can
8445 // be called from the debugger. Compile it into the product
8446 // as needed.
8447 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8448 return debug_cms_space->verify_chunk_in_free_list(fc);
8449 }
8450 #endif
8451
8452 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8453 if (CMSTraceSweeper) {
8454 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8455 fc, fc->size());
8456 }
8457 }
8458
8459 // CMSIsAliveClosure
8460 bool CMSIsAliveClosure::do_object_b(oop obj) {
8461 HeapWord* addr = (HeapWord*)obj;
8462 return addr != NULL &&
8463 (!_span.contains(addr) || _bit_map->isMarked(addr));
8464 }
8465
8466
8467 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8468 MemRegion span,
8469 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8470 bool cpc):
8471 _collector(collector),
8472 _span(span),
8473 _bit_map(bit_map),
8474 _mark_stack(mark_stack),
8475 _concurrent_precleaning(cpc) {
8476 assert(!_span.is_empty(), "Empty span could spell trouble");
8477 }
8478
8479
8480 // CMSKeepAliveClosure: the serial version
8481 void CMSKeepAliveClosure::do_oop(oop obj) {
8482 HeapWord* addr = (HeapWord*)obj;
8483 if (_span.contains(addr) &&
8484 !_bit_map->isMarked(addr)) {
8485 _bit_map->mark(addr);
8486 bool simulate_overflow = false;
8487 NOT_PRODUCT(
8488 if (CMSMarkStackOverflowALot &&
8489 _collector->simulate_overflow()) {
8490 // simulate a stack overflow
8491 simulate_overflow = true;
8492 }
8493 )
8494 if (simulate_overflow || !_mark_stack->push(obj)) {
8495 if (_concurrent_precleaning) {
8496 // We dirty the overflown object and let the remark
8497 // phase deal with it.
8498 assert(_collector->overflow_list_is_empty(), "Error");
8499 // In the case of object arrays, we need to dirty all of
8500 // the cards that the object spans. No locking or atomics
8501 // are needed since no one else can be mutating the mod union
8502 // table.
8503 if (obj->is_objArray()) {
8504 size_t sz = obj->size();
8505 HeapWord* end_card_addr =
8506 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8507 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8508 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8509 _collector->_modUnionTable.mark_range(redirty_range);
8510 } else {
8511 _collector->_modUnionTable.mark(addr);
8512 }
8513 _collector->_ser_kac_preclean_ovflw++;
8514 } else {
8515 _collector->push_on_overflow_list(obj);
8516 _collector->_ser_kac_ovflw++;
8517 }
8518 }
8519 }
8520 }
8521
8522 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8523 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8524
8525 // CMSParKeepAliveClosure: a parallel version of the above.
8526 // The work queues are private to each closure (thread),
8527 // but (may be) available for stealing by other threads.
8528 void CMSParKeepAliveClosure::do_oop(oop obj) {
8529 HeapWord* addr = (HeapWord*)obj;
8530 if (_span.contains(addr) &&
8531 !_bit_map->isMarked(addr)) {
8532 // In general, during recursive tracing, several threads
8533 // may be concurrently getting here; the first one to
8534 // "tag" it, claims it.
8535 if (_bit_map->par_mark(addr)) {
8536 bool res = _work_queue->push(obj);
8537 assert(res, "Low water mark should be much less than capacity");
8538 // Do a recursive trim in the hope that this will keep
8539 // stack usage lower, but leave some oops for potential stealers
8540 trim_queue(_low_water_mark);
8541 } // Else, another thread got there first
8542 }
8543 }
8544
8545 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8546 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8547
8548 void CMSParKeepAliveClosure::trim_queue(uint max) {
8549 while (_work_queue->size() > max) {
8550 oop new_oop;
8551 if (_work_queue->pop_local(new_oop)) {
8552 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8553 assert(_bit_map->isMarked((HeapWord*)new_oop),
8554 "no white objects on this stack!");
8555 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8556 // iterate over the oops in this oop, marking and pushing
8557 // the ones in CMS heap (i.e. in _span).
8558 new_oop->oop_iterate(&_mark_and_push);
8559 }
8560 }
8561 }
8562
8563 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8564 CMSCollector* collector,
8565 MemRegion span, CMSBitMap* bit_map,
8566 OopTaskQueue* work_queue):
8567 _collector(collector),
8568 _span(span),
8569 _bit_map(bit_map),
8570 _work_queue(work_queue) { }
8571
8572 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8573 HeapWord* addr = (HeapWord*)obj;
8574 if (_span.contains(addr) &&
8575 !_bit_map->isMarked(addr)) {
8576 if (_bit_map->par_mark(addr)) {
8577 bool simulate_overflow = false;
8578 NOT_PRODUCT(
8579 if (CMSMarkStackOverflowALot &&
8580 _collector->par_simulate_overflow()) {
8581 // simulate a stack overflow
8582 simulate_overflow = true;
8583 }
8584 )
8585 if (simulate_overflow || !_work_queue->push(obj)) {
8586 _collector->par_push_on_overflow_list(obj);
8587 _collector->_par_kac_ovflw++;
8588 }
8589 } // Else another thread got there already
8590 }
8591 }
8592
8593 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8594 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8595
8596 //////////////////////////////////////////////////////////////////
8597 // CMSExpansionCause /////////////////////////////
8598 //////////////////////////////////////////////////////////////////
8599 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8600 switch (cause) {
8601 case _no_expansion:
8602 return "No expansion";
8603 case _satisfy_free_ratio:
8604 return "Free ratio";
8605 case _satisfy_promotion:
8606 return "Satisfy promotion";
8607 case _satisfy_allocation:
8608 return "allocation";
8609 case _allocate_par_lab:
8610 return "Par LAB";
8611 case _allocate_par_spooling_space:
8612 return "Par Spooling Space";
8613 case _adaptive_size_policy:
8614 return "Ergonomics";
8615 default:
8616 return "unknown";
8617 }
8618 }
8619
8620 void CMSDrainMarkingStackClosure::do_void() {
8621 // the max number to take from overflow list at a time
8622 const size_t num = _mark_stack->capacity()/4;
8623 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8624 "Overflow list should be NULL during concurrent phases");
8625 while (!_mark_stack->isEmpty() ||
8626 // if stack is empty, check the overflow list
8627 _collector->take_from_overflow_list(num, _mark_stack)) {
8628 oop obj = _mark_stack->pop();
8629 HeapWord* addr = (HeapWord*)obj;
8630 assert(_span.contains(addr), "Should be within span");
8631 assert(_bit_map->isMarked(addr), "Should be marked");
8632 assert(obj->is_oop(), "Should be an oop");
8633 obj->oop_iterate(_keep_alive);
8634 }
8635 }
8636
8637 void CMSParDrainMarkingStackClosure::do_void() {
8638 // drain queue
8639 trim_queue(0);
8640 }
8641
8642 // Trim our work_queue so its length is below max at return
8643 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8644 while (_work_queue->size() > max) {
8645 oop new_oop;
8646 if (_work_queue->pop_local(new_oop)) {
8647 assert(new_oop->is_oop(), "Expected an oop");
8648 assert(_bit_map->isMarked((HeapWord*)new_oop),
8649 "no white objects on this stack!");
8650 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8651 // iterate over the oops in this oop, marking and pushing
8652 // the ones in CMS heap (i.e. in _span).
8653 new_oop->oop_iterate(&_mark_and_push);
8654 }
8655 }
8656 }
8657
8658 ////////////////////////////////////////////////////////////////////
8659 // Support for Marking Stack Overflow list handling and related code
8660 ////////////////////////////////////////////////////////////////////
8661 // Much of the following code is similar in shape and spirit to the
8662 // code used in ParNewGC. We should try and share that code
8663 // as much as possible in the future.
8664
8665 #ifndef PRODUCT
8666 // Debugging support for CMSStackOverflowALot
8667
8668 // It's OK to call this multi-threaded; the worst thing
8669 // that can happen is that we'll get a bunch of closely
8670 // spaced simulated overflows, but that's OK, in fact
8671 // probably good as it would exercise the overflow code
8672 // under contention.
8673 bool CMSCollector::simulate_overflow() {
8674 if (_overflow_counter-- <= 0) { // just being defensive
8675 _overflow_counter = CMSMarkStackOverflowInterval;
8676 return true;
8677 } else {
8678 return false;
8679 }
8680 }
8681
8682 bool CMSCollector::par_simulate_overflow() {
8683 return simulate_overflow();
8684 }
8685 #endif
8686
8687 // Single-threaded
8688 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8689 assert(stack->isEmpty(), "Expected precondition");
8690 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8691 size_t i = num;
8692 oop cur = _overflow_list;
8693 const markOop proto = markOopDesc::prototype();
8694 NOT_PRODUCT(ssize_t n = 0;)
8695 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8696 next = oop(cur->mark());
8697 cur->set_mark(proto); // until proven otherwise
8698 assert(cur->is_oop(), "Should be an oop");
8699 bool res = stack->push(cur);
8700 assert(res, "Bit off more than can chew?");
8701 NOT_PRODUCT(n++;)
8702 }
8703 _overflow_list = cur;
8704 #ifndef PRODUCT
8705 assert(_num_par_pushes >= n, "Too many pops?");
8706 _num_par_pushes -=n;
8707 #endif
8708 return !stack->isEmpty();
8709 }
8710
8711 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8712 // (MT-safe) Get a prefix of at most "num" from the list.
8713 // The overflow list is chained through the mark word of
8714 // each object in the list. We fetch the entire list,
8715 // break off a prefix of the right size and return the
8716 // remainder. If other threads try to take objects from
8717 // the overflow list at that time, they will wait for
8718 // some time to see if data becomes available. If (and
8719 // only if) another thread places one or more object(s)
8720 // on the global list before we have returned the suffix
8721 // to the global list, we will walk down our local list
8722 // to find its end and append the global list to
8723 // our suffix before returning it. This suffix walk can
8724 // prove to be expensive (quadratic in the amount of traffic)
8725 // when there are many objects in the overflow list and
8726 // there is much producer-consumer contention on the list.
8727 // *NOTE*: The overflow list manipulation code here and
8728 // in ParNewGeneration:: are very similar in shape,
8729 // except that in the ParNew case we use the old (from/eden)
8730 // copy of the object to thread the list via its klass word.
8731 // Because of the common code, if you make any changes in
8732 // the code below, please check the ParNew version to see if
8733 // similar changes might be needed.
8734 // CR 6797058 has been filed to consolidate the common code.
8735 bool CMSCollector::par_take_from_overflow_list(size_t num,
8736 OopTaskQueue* work_q,
8737 int no_of_gc_threads) {
8738 assert(work_q->size() == 0, "First empty local work queue");
8739 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8740 if (_overflow_list == NULL) {
8741 return false;
8742 }
8743 // Grab the entire list; we'll put back a suffix
8744 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8745 Thread* tid = Thread::current();
8746 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8747 // set to ParallelGCThreads.
8748 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8749 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8750 // If the list is busy, we spin for a short while,
8751 // sleeping between attempts to get the list.
8752 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8753 os::sleep(tid, sleep_time_millis, false);
8754 if (_overflow_list == NULL) {
8755 // Nothing left to take
8756 return false;
8757 } else if (_overflow_list != BUSY) {
8758 // Try and grab the prefix
8759 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8760 }
8761 }
8762 // If the list was found to be empty, or we spun long
8763 // enough, we give up and return empty-handed. If we leave
8764 // the list in the BUSY state below, it must be the case that
8765 // some other thread holds the overflow list and will set it
8766 // to a non-BUSY state in the future.
8767 if (prefix == NULL || prefix == BUSY) {
8768 // Nothing to take or waited long enough
8769 if (prefix == NULL) {
8770 // Write back the NULL in case we overwrote it with BUSY above
8771 // and it is still the same value.
8772 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8773 }
8774 return false;
8775 }
8776 assert(prefix != NULL && prefix != BUSY, "Error");
8777 size_t i = num;
8778 oop cur = prefix;
8779 // Walk down the first "num" objects, unless we reach the end.
8780 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8781 if (cur->mark() == NULL) {
8782 // We have "num" or fewer elements in the list, so there
8783 // is nothing to return to the global list.
8784 // Write back the NULL in lieu of the BUSY we wrote
8785 // above, if it is still the same value.
8786 if (_overflow_list == BUSY) {
8787 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8788 }
8789 } else {
8790 // Chop off the suffix and return it to the global list.
8791 assert(cur->mark() != BUSY, "Error");
8792 oop suffix_head = cur->mark(); // suffix will be put back on global list
8793 cur->set_mark(NULL); // break off suffix
8794 // It's possible that the list is still in the empty(busy) state
8795 // we left it in a short while ago; in that case we may be
8796 // able to place back the suffix without incurring the cost
8797 // of a walk down the list.
8798 oop observed_overflow_list = _overflow_list;
8799 oop cur_overflow_list = observed_overflow_list;
8800 bool attached = false;
8801 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8802 observed_overflow_list =
8803 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8804 if (cur_overflow_list == observed_overflow_list) {
8805 attached = true;
8806 break;
8807 } else cur_overflow_list = observed_overflow_list;
8808 }
8809 if (!attached) {
8810 // Too bad, someone else sneaked in (at least) an element; we'll need
8811 // to do a splice. Find tail of suffix so we can prepend suffix to global
8812 // list.
8813 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8814 oop suffix_tail = cur;
8815 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8816 "Tautology");
8817 observed_overflow_list = _overflow_list;
8818 do {
8819 cur_overflow_list = observed_overflow_list;
8820 if (cur_overflow_list != BUSY) {
8821 // Do the splice ...
8822 suffix_tail->set_mark(markOop(cur_overflow_list));
8823 } else { // cur_overflow_list == BUSY
8824 suffix_tail->set_mark(NULL);
8825 }
8826 // ... and try to place spliced list back on overflow_list ...
8827 observed_overflow_list =
8828 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8829 } while (cur_overflow_list != observed_overflow_list);
8830 // ... until we have succeeded in doing so.
8831 }
8832 }
8833
8834 // Push the prefix elements on work_q
8835 assert(prefix != NULL, "control point invariant");
8836 const markOop proto = markOopDesc::prototype();
8837 oop next;
8838 NOT_PRODUCT(ssize_t n = 0;)
8839 for (cur = prefix; cur != NULL; cur = next) {
8840 next = oop(cur->mark());
8841 cur->set_mark(proto); // until proven otherwise
8842 assert(cur->is_oop(), "Should be an oop");
8843 bool res = work_q->push(cur);
8844 assert(res, "Bit off more than we can chew?");
8845 NOT_PRODUCT(n++;)
8846 }
8847 #ifndef PRODUCT
8848 assert(_num_par_pushes >= n, "Too many pops?");
8849 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8850 #endif
8851 return true;
8852 }
8853
8854 // Single-threaded
8855 void CMSCollector::push_on_overflow_list(oop p) {
8856 NOT_PRODUCT(_num_par_pushes++;)
8857 assert(p->is_oop(), "Not an oop");
8858 preserve_mark_if_necessary(p);
8859 p->set_mark((markOop)_overflow_list);
8860 _overflow_list = p;
8861 }
8862
8863 // Multi-threaded; use CAS to prepend to overflow list
8864 void CMSCollector::par_push_on_overflow_list(oop p) {
8865 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8866 assert(p->is_oop(), "Not an oop");
8867 par_preserve_mark_if_necessary(p);
8868 oop observed_overflow_list = _overflow_list;
8869 oop cur_overflow_list;
8870 do {
8871 cur_overflow_list = observed_overflow_list;
8872 if (cur_overflow_list != BUSY) {
8873 p->set_mark(markOop(cur_overflow_list));
8874 } else {
8875 p->set_mark(NULL);
8876 }
8877 observed_overflow_list =
8878 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8879 } while (cur_overflow_list != observed_overflow_list);
8880 }
8881 #undef BUSY
8882
8883 // Single threaded
8884 // General Note on GrowableArray: pushes may silently fail
8885 // because we are (temporarily) out of C-heap for expanding
8886 // the stack. The problem is quite ubiquitous and affects
8887 // a lot of code in the JVM. The prudent thing for GrowableArray
8888 // to do (for now) is to exit with an error. However, that may
8889 // be too draconian in some cases because the caller may be
8890 // able to recover without much harm. For such cases, we
8891 // should probably introduce a "soft_push" method which returns
8892 // an indication of success or failure with the assumption that
8893 // the caller may be able to recover from a failure; code in
8894 // the VM can then be changed, incrementally, to deal with such
8895 // failures where possible, thus, incrementally hardening the VM
8896 // in such low resource situations.
8897 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8898 _preserved_oop_stack.push(p);
8899 _preserved_mark_stack.push(m);
8900 assert(m == p->mark(), "Mark word changed");
8901 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8902 "bijection");
8903 }
8904
8905 // Single threaded
8906 void CMSCollector::preserve_mark_if_necessary(oop p) {
8907 markOop m = p->mark();
8908 if (m->must_be_preserved(p)) {
8909 preserve_mark_work(p, m);
8910 }
8911 }
8912
8913 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8914 markOop m = p->mark();
8915 if (m->must_be_preserved(p)) {
8916 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8917 // Even though we read the mark word without holding
8918 // the lock, we are assured that it will not change
8919 // because we "own" this oop, so no other thread can
8920 // be trying to push it on the overflow list; see
8921 // the assertion in preserve_mark_work() that checks
8922 // that m == p->mark().
8923 preserve_mark_work(p, m);
8924 }
8925 }
8926
8927 // We should be able to do this multi-threaded,
8928 // a chunk of stack being a task (this is
8929 // correct because each oop only ever appears
8930 // once in the overflow list. However, it's
8931 // not very easy to completely overlap this with
8932 // other operations, so will generally not be done
8933 // until all work's been completed. Because we
8934 // expect the preserved oop stack (set) to be small,
8935 // it's probably fine to do this single-threaded.
8936 // We can explore cleverer concurrent/overlapped/parallel
8937 // processing of preserved marks if we feel the
8938 // need for this in the future. Stack overflow should
8939 // be so rare in practice and, when it happens, its
8940 // effect on performance so great that this will
8941 // likely just be in the noise anyway.
8942 void CMSCollector::restore_preserved_marks_if_any() {
8943 assert(SafepointSynchronize::is_at_safepoint(),
8944 "world should be stopped");
8945 assert(Thread::current()->is_ConcurrentGC_thread() ||
8946 Thread::current()->is_VM_thread(),
8947 "should be single-threaded");
8948 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8949 "bijection");
8950
8951 while (!_preserved_oop_stack.is_empty()) {
8952 oop p = _preserved_oop_stack.pop();
8953 assert(p->is_oop(), "Should be an oop");
8954 assert(_span.contains(p), "oop should be in _span");
8955 assert(p->mark() == markOopDesc::prototype(),
8956 "Set when taken from overflow list");
8957 markOop m = _preserved_mark_stack.pop();
8958 p->set_mark(m);
8959 }
8960 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8961 "stacks were cleared above");
8962 }
8963
8964 #ifndef PRODUCT
8965 bool CMSCollector::no_preserved_marks() const {
8966 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8967 }
8968 #endif
8969
8970 // Transfer some number of overflown objects to usual marking
8971 // stack. Return true if some objects were transferred.
8972 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8973 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8974 (size_t)ParGCDesiredObjsFromOverflowList);
8975
8976 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8977 assert(_collector->overflow_list_is_empty() || res,
8978 "If list is not empty, we should have taken something");
8979 assert(!res || !_mark_stack->isEmpty(),
8980 "If we took something, it should now be on our stack");
8981 return res;
8982 }
8983
8984 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8985 size_t res = _sp->block_size_no_stall(addr, _collector);
8986 if (_sp->block_is_obj(addr)) {
8987 if (_live_bit_map->isMarked(addr)) {
8988 // It can't have been dead in a previous cycle
8989 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8990 } else {
8991 _dead_bit_map->mark(addr); // mark the dead object
8992 }
8993 }
8994 // Could be 0, if the block size could not be computed without stalling.
8995 return res;
8996 }
8997
8998 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8999
9000 switch (phase) {
9001 case CMSCollector::InitialMarking:
9002 initialize(true /* fullGC */ ,
9003 cause /* cause of the GC */,
9004 true /* recordGCBeginTime */,
9005 true /* recordPreGCUsage */,
9006 false /* recordPeakUsage */,
9007 false /* recordPostGCusage */,
9008 true /* recordAccumulatedGCTime */,
9009 false /* recordGCEndTime */,
9010 false /* countCollection */ );
9011 break;
9012
9013 case CMSCollector::FinalMarking:
9014 initialize(true /* fullGC */ ,
9015 cause /* cause of the GC */,
9016 false /* recordGCBeginTime */,
9017 false /* recordPreGCUsage */,
9018 false /* recordPeakUsage */,
9019 false /* recordPostGCusage */,
9020 true /* recordAccumulatedGCTime */,
9021 false /* recordGCEndTime */,
9022 false /* countCollection */ );
9023 break;
9024
9025 case CMSCollector::Sweeping:
9026 initialize(true /* fullGC */ ,
9027 cause /* cause of the GC */,
9028 false /* recordGCBeginTime */,
9029 false /* recordPreGCUsage */,
9030 true /* recordPeakUsage */,
9031 true /* recordPostGCusage */,
9032 false /* recordAccumulatedGCTime */,
9033 true /* recordGCEndTime */,
9034 true /* countCollection */ );
9035 break;
9036
9037 default:
9038 ShouldNotReachHere();
9039 }
9040 }