1 #ifdef USE_PRAGMA_IDENT_SRC
2 #pragma ident "@(#)concurrentMarkSweepGeneration.cpp 1.293 08/10/30 20:45:16 JVM"
3 #endif
4 /*
5 * Copyright 2001-2008 Sun Microsystems, Inc. All Rights Reserved.
6 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
7 *
8 * This code is free software; you can redistribute it and/or modify it
9 * under the terms of the GNU General Public License version 2 only, as
10 * published by the Free Software Foundation.
11 *
12 * This code is distributed in the hope that it will be useful, but WITHOUT
13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
15 * version 2 for more details (a copy is included in the LICENSE file that
16 * accompanied this code).
17 *
18 * You should have received a copy of the GNU General Public License version
19 * 2 along with this work; if not, write to the Free Software Foundation,
20 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
21 *
22 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
23 * CA 95054 USA or visit www.sun.com if you need additional information or
24 * have any questions.
25 *
26 */
27
28 # include "incls/_precompiled.incl"
29 # include "incls/_concurrentMarkSweepGeneration.cpp.incl"
30
31 // statics
32 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
33 bool CMSCollector::_full_gc_requested = false;
34
35 //////////////////////////////////////////////////////////////////
36 // In support of CMS/VM thread synchronization
37 //////////////////////////////////////////////////////////////////
38 // We split use of the CGC_lock into 2 "levels".
39 // The low-level locking is of the usual CGC_lock monitor. We introduce
40 // a higher level "token" (hereafter "CMS token") built on top of the
41 // low level monitor (hereafter "CGC lock").
42 // The token-passing protocol gives priority to the VM thread. The
43 // CMS-lock doesn't provide any fairness guarantees, but clients
44 // should ensure that it is only held for very short, bounded
45 // durations.
46 //
47 // When either of the CMS thread or the VM thread is involved in
48 // collection operations during which it does not want the other
49 // thread to interfere, it obtains the CMS token.
50 //
51 // If either thread tries to get the token while the other has
52 // it, that thread waits. However, if the VM thread and CMS thread
53 // both want the token, then the VM thread gets priority while the
54 // CMS thread waits. This ensures, for instance, that the "concurrent"
55 // phases of the CMS thread's work do not block out the VM thread
56 // for long periods of time as the CMS thread continues to hog
57 // the token. (See bug 4616232).
58 //
59 // The baton-passing functions are, however, controlled by the
60 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
61 // and here the low-level CMS lock, not the high level token,
62 // ensures mutual exclusion.
63 //
64 // Two important conditions that we have to satisfy:
65 // 1. if a thread does a low-level wait on the CMS lock, then it
66 // relinquishes the CMS token if it were holding that token
67 // when it acquired the low-level CMS lock.
68 // 2. any low-level notifications on the low-level lock
69 // should only be sent when a thread has relinquished the token.
70 //
71 // In the absence of either property, we'd have potential deadlock.
72 //
73 // We protect each of the CMS (concurrent and sequential) phases
74 // with the CMS _token_, not the CMS _lock_.
75 //
76 // The only code protected by CMS lock is the token acquisition code
77 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
78 // baton-passing code.
79 //
80 // Unfortunately, i couldn't come up with a good abstraction to factor and
81 // hide the naked CGC_lock manipulation in the baton-passing code
82 // further below. That's something we should try to do. Also, the proof
83 // of correctness of this 2-level locking scheme is far from obvious,
84 // and potentially quite slippery. We have an uneasy supsicion, for instance,
85 // that there may be a theoretical possibility of delay/starvation in the
86 // low-level lock/wait/notify scheme used for the baton-passing because of
87 // potential intereference with the priority scheme embodied in the
88 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
89 // invocation further below and marked with "XXX 20011219YSR".
90 // Indeed, as we note elsewhere, this may become yet more slippery
91 // in the presence of multiple CMS and/or multiple VM threads. XXX
92
93 class CMSTokenSync: public StackObj {
94 private:
95 bool _is_cms_thread;
96 public:
97 CMSTokenSync(bool is_cms_thread):
98 _is_cms_thread(is_cms_thread) {
99 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
100 "Incorrect argument to constructor");
101 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
102 }
103
104 ~CMSTokenSync() {
105 assert(_is_cms_thread ?
106 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
107 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
108 "Incorrect state");
109 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
110 }
111 };
112
113 // Convenience class that does a CMSTokenSync, and then acquires
114 // upto three locks.
115 class CMSTokenSyncWithLocks: public CMSTokenSync {
116 private:
117 // Note: locks are acquired in textual declaration order
118 // and released in the opposite order
119 MutexLockerEx _locker1, _locker2, _locker3;
120 public:
121 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
122 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
123 CMSTokenSync(is_cms_thread),
124 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
125 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
126 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
127 { }
128 };
129
130
131 // Wrapper class to temporarily disable icms during a foreground cms collection.
132 class ICMSDisabler: public StackObj {
133 public:
134 // The ctor disables icms and wakes up the thread so it notices the change;
135 // the dtor re-enables icms. Note that the CMSCollector methods will check
136 // CMSIncrementalMode.
137 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
138 ~ICMSDisabler() { CMSCollector::enable_icms(); }
139 };
140
141 //////////////////////////////////////////////////////////////////
142 // Concurrent Mark-Sweep Generation /////////////////////////////
143 //////////////////////////////////////////////////////////////////
144
145 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
146
147 // This struct contains per-thread things necessary to support parallel
148 // young-gen collection.
149 class CMSParGCThreadState: public CHeapObj {
150 public:
151 CFLS_LAB lab;
152 PromotionInfo promo;
153
154 // Constructor.
155 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
156 promo.setSpace(cfls);
157 }
158 };
159
160 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
161 ReservedSpace rs, size_t initial_byte_size, int level,
162 CardTableRS* ct, bool use_adaptive_freelists,
163 FreeBlockDictionary::DictionaryChoice dictionaryChoice) :
164 CardGeneration(rs, initial_byte_size, level, ct),
165 _dilatation_factor(((double)MinChunkSize)/((double)(oopDesc::header_size()))),
166 _debug_collection_type(Concurrent_collection_type)
167 {
168 HeapWord* bottom = (HeapWord*) _virtual_space.low();
169 HeapWord* end = (HeapWord*) _virtual_space.high();
170
171 _direct_allocated_words = 0;
172 NOT_PRODUCT(
173 _numObjectsPromoted = 0;
174 _numWordsPromoted = 0;
175 _numObjectsAllocated = 0;
176 _numWordsAllocated = 0;
177 )
178
179 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
180 use_adaptive_freelists,
181 dictionaryChoice);
182 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
183 if (_cmsSpace == NULL) {
184 vm_exit_during_initialization(
185 "CompactibleFreeListSpace allocation failure");
186 }
187 _cmsSpace->_gen = this;
188
189 _gc_stats = new CMSGCStats();
190
191 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
192 // offsets match. The ability to tell free chunks from objects
193 // depends on this property.
194 debug_only(
195 FreeChunk* junk = NULL;
196 assert(junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
197 "Offset of FreeChunk::_prev within FreeChunk must match"
198 " that of OopDesc::_klass within OopDesc");
199 )
200 if (ParallelGCThreads > 0) {
201 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
202 _par_gc_thread_states =
203 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads);
204 if (_par_gc_thread_states == NULL) {
205 vm_exit_during_initialization("Could not allocate par gc structs");
206 }
207 for (uint i = 0; i < ParallelGCThreads; i++) {
208 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
209 if (_par_gc_thread_states[i] == NULL) {
210 vm_exit_during_initialization("Could not allocate par gc structs");
211 }
212 }
213 } else {
214 _par_gc_thread_states = NULL;
215 }
216 _incremental_collection_failed = false;
217 // The "dilatation_factor" is the expansion that can occur on
218 // account of the fact that the minimum object size in the CMS
219 // generation may be larger than that in, say, a contiguous young
220 // generation.
221 // Ideally, in the calculation below, we'd compute the dilatation
222 // factor as: MinChunkSize/(promoting_gen's min object size)
223 // Since we do not have such a general query interface for the
224 // promoting generation, we'll instead just use the mimimum
225 // object size (which today is a header's worth of space);
226 // note that all arithmetic is in units of HeapWords.
227 assert(MinChunkSize >= oopDesc::header_size(), "just checking");
228 assert(_dilatation_factor >= 1.0, "from previous assert");
229 }
230
231 void ConcurrentMarkSweepGeneration::ref_processor_init() {
232 assert(collector() != NULL, "no collector");
233 collector()->ref_processor_init();
234 }
235
236 void CMSCollector::ref_processor_init() {
237 if (_ref_processor == NULL) {
238 // Allocate and initialize a reference processor
239 _ref_processor = ReferenceProcessor::create_ref_processor(
240 _span, // span
241 _cmsGen->refs_discovery_is_atomic(), // atomic_discovery
242 _cmsGen->refs_discovery_is_mt(), // mt_discovery
243 &_is_alive_closure,
244 ParallelGCThreads,
245 ParallelRefProcEnabled);
246 // Initialize the _ref_processor field of CMSGen
247 _cmsGen->set_ref_processor(_ref_processor);
248
249 // Allocate a dummy ref processor for perm gen.
250 ReferenceProcessor* rp2 = new ReferenceProcessor();
251 if (rp2 == NULL) {
252 vm_exit_during_initialization("Could not allocate ReferenceProcessor object");
253 }
254 _permGen->set_ref_processor(rp2);
255 }
256 }
257
258 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
259 GenCollectedHeap* gch = GenCollectedHeap::heap();
260 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
261 "Wrong type of heap");
262 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
263 gch->gen_policy()->size_policy();
264 assert(sp->is_gc_cms_adaptive_size_policy(),
265 "Wrong type of size policy");
266 return sp;
267 }
268
269 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
270 CMSGCAdaptivePolicyCounters* results =
271 (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
272 assert(
273 results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
274 "Wrong gc policy counter kind");
275 return results;
276 }
277
278
279 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
280
281 const char* gen_name = "old";
282
283 // Generation Counters - generation 1, 1 subspace
284 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
285
286 _space_counters = new GSpaceCounters(gen_name, 0,
287 _virtual_space.reserved_size(),
288 this, _gen_counters);
289 }
290
291 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
292 _cms_gen(cms_gen)
293 {
294 assert(alpha <= 100, "bad value");
295 _saved_alpha = alpha;
296
297 // Initialize the alphas to the bootstrap value of 100.
298 _gc0_alpha = _cms_alpha = 100;
299
300 _cms_begin_time.update();
301 _cms_end_time.update();
302
303 _gc0_duration = 0.0;
304 _gc0_period = 0.0;
305 _gc0_promoted = 0;
306
307 _cms_duration = 0.0;
308 _cms_period = 0.0;
309 _cms_allocated = 0;
310
311 _cms_used_at_gc0_begin = 0;
312 _cms_used_at_gc0_end = 0;
313 _allow_duty_cycle_reduction = false;
314 _valid_bits = 0;
315 _icms_duty_cycle = CMSIncrementalDutyCycle;
316 }
317
318 // If promotion failure handling is on use
319 // the padded average size of the promotion for each
320 // young generation collection.
321 double CMSStats::time_until_cms_gen_full() const {
322 size_t cms_free = _cms_gen->cmsSpace()->free();
323 GenCollectedHeap* gch = GenCollectedHeap::heap();
324 size_t expected_promotion = gch->get_gen(0)->capacity();
325 if (HandlePromotionFailure) {
326 expected_promotion = MIN2(
327 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average(),
328 expected_promotion);
329 }
330 if (cms_free > expected_promotion) {
331 // Start a cms collection if there isn't enough space to promote
332 // for the next minor collection. Use the padded average as
333 // a safety factor.
334 cms_free -= expected_promotion;
335
336 // Adjust by the safety factor.
337 double cms_free_dbl = (double)cms_free;
338 cms_free_dbl = cms_free_dbl * (100.0 - CMSIncrementalSafetyFactor) / 100.0;
339
340 if (PrintGCDetails && Verbose) {
341 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
342 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
343 cms_free, expected_promotion);
344 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
345 cms_free_dbl, cms_consumption_rate() + 1.0);
346 }
347 // Add 1 in case the consumption rate goes to zero.
348 return cms_free_dbl / (cms_consumption_rate() + 1.0);
349 }
350 return 0.0;
351 }
352
353 // Compare the duration of the cms collection to the
354 // time remaining before the cms generation is empty.
355 // Note that the time from the start of the cms collection
356 // to the start of the cms sweep (less than the total
357 // duration of the cms collection) can be used. This
358 // has been tried and some applications experienced
359 // promotion failures early in execution. This was
360 // possibly because the averages were not accurate
361 // enough at the beginning.
362 double CMSStats::time_until_cms_start() const {
363 // We add "gc0_period" to the "work" calculation
364 // below because this query is done (mostly) at the
365 // end of a scavenge, so we need to conservatively
366 // account for that much possible delay
367 // in the query so as to avoid concurrent mode failures
368 // due to starting the collection just a wee bit too
369 // late.
370 double work = cms_duration() + gc0_period();
371 double deadline = time_until_cms_gen_full();
372 if (work > deadline) {
373 if (Verbose && PrintGCDetails) {
374 gclog_or_tty->print(
375 " CMSCollector: collect because of anticipated promotion "
376 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
377 gc0_period(), time_until_cms_gen_full());
378 }
379 return 0.0;
380 }
381 return work - deadline;
382 }
383
384 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
385 // amount of change to prevent wild oscillation.
386 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
387 unsigned int new_duty_cycle) {
388 assert(old_duty_cycle <= 100, "bad input value");
389 assert(new_duty_cycle <= 100, "bad input value");
390
391 // Note: use subtraction with caution since it may underflow (values are
392 // unsigned). Addition is safe since we're in the range 0-100.
393 unsigned int damped_duty_cycle = new_duty_cycle;
394 if (new_duty_cycle < old_duty_cycle) {
395 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
396 if (new_duty_cycle + largest_delta < old_duty_cycle) {
397 damped_duty_cycle = old_duty_cycle - largest_delta;
398 }
399 } else if (new_duty_cycle > old_duty_cycle) {
400 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
401 if (new_duty_cycle > old_duty_cycle + largest_delta) {
402 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
403 }
404 }
405 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
406
407 if (CMSTraceIncrementalPacing) {
408 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
409 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
410 }
411 return damped_duty_cycle;
412 }
413
414 unsigned int CMSStats::icms_update_duty_cycle_impl() {
415 assert(CMSIncrementalPacing && valid(),
416 "should be handled in icms_update_duty_cycle()");
417
418 double cms_time_so_far = cms_timer().seconds();
419 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
420 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
421
422 // Avoid division by 0.
423 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
424 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
425
426 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
427 if (new_duty_cycle > _icms_duty_cycle) {
428 // Avoid very small duty cycles (1 or 2); 0 is allowed.
429 if (new_duty_cycle > 2) {
430 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
431 new_duty_cycle);
432 }
433 } else if (_allow_duty_cycle_reduction) {
434 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
435 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
436 // Respect the minimum duty cycle.
437 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
438 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
439 }
440
441 if (PrintGCDetails || CMSTraceIncrementalPacing) {
442 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
443 }
444
445 _allow_duty_cycle_reduction = false;
446 return _icms_duty_cycle;
447 }
448
449 #ifndef PRODUCT
450 void CMSStats::print_on(outputStream *st) const {
451 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
452 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
453 gc0_duration(), gc0_period(), gc0_promoted());
454 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
455 cms_duration(), cms_duration_per_mb(),
456 cms_period(), cms_allocated());
457 st->print(",cms_since_beg=%g,cms_since_end=%g",
458 cms_time_since_begin(), cms_time_since_end());
459 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
460 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
461 if (CMSIncrementalMode) {
462 st->print(",dc=%d", icms_duty_cycle());
463 }
464
465 if (valid()) {
466 st->print(",promo_rate=%g,cms_alloc_rate=%g",
467 promotion_rate(), cms_allocation_rate());
468 st->print(",cms_consumption_rate=%g,time_until_full=%g",
469 cms_consumption_rate(), time_until_cms_gen_full());
470 }
471 st->print(" ");
472 }
473 #endif // #ifndef PRODUCT
474
475 CMSCollector::CollectorState CMSCollector::_collectorState =
476 CMSCollector::Idling;
477 bool CMSCollector::_foregroundGCIsActive = false;
478 bool CMSCollector::_foregroundGCShouldWait = false;
479
480 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
481 ConcurrentMarkSweepGeneration* permGen,
482 CardTableRS* ct,
483 ConcurrentMarkSweepPolicy* cp):
484 _cmsGen(cmsGen),
485 _permGen(permGen),
486 _ct(ct),
487 _ref_processor(NULL), // will be set later
488 _conc_workers(NULL), // may be set later
489 _abort_preclean(false),
490 _start_sampling(false),
491 _between_prologue_and_epilogue(false),
492 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
493 _perm_gen_verify_bit_map(0, -1 /* no mutex */, "No_lock"),
494 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
495 -1 /* lock-free */, "No_lock" /* dummy */),
496 _modUnionClosure(&_modUnionTable),
497 _modUnionClosurePar(&_modUnionTable),
498 // Adjust my span to cover old (cms) gen and perm gen
499 _span(cmsGen->reserved()._union(permGen->reserved())),
500 // Construct the is_alive_closure with _span & markBitMap
501 _is_alive_closure(_span, &_markBitMap),
502 _restart_addr(NULL),
503 _overflow_list(NULL),
504 _preserved_oop_stack(NULL),
505 _preserved_mark_stack(NULL),
506 _stats(cmsGen),
507 _eden_chunk_array(NULL), // may be set in ctor body
508 _eden_chunk_capacity(0), // -- ditto --
509 _eden_chunk_index(0), // -- ditto --
510 _survivor_plab_array(NULL), // -- ditto --
511 _survivor_chunk_array(NULL), // -- ditto --
512 _survivor_chunk_capacity(0), // -- ditto --
513 _survivor_chunk_index(0), // -- ditto --
514 _ser_pmc_preclean_ovflw(0),
515 _ser_pmc_remark_ovflw(0),
516 _par_pmc_remark_ovflw(0),
517 _ser_kac_ovflw(0),
518 _par_kac_ovflw(0),
519 #ifndef PRODUCT
520 _num_par_pushes(0),
521 #endif
522 _collection_count_start(0),
523 _verifying(false),
524 _icms_start_limit(NULL),
525 _icms_stop_limit(NULL),
526 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
527 _completed_initialization(false),
528 _collector_policy(cp),
529 _unload_classes(false),
530 _unloaded_classes_last_cycle(false),
531 _sweep_estimate(CMS_SweepWeight, CMS_SweepPadding)
532 {
533 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
534 ExplicitGCInvokesConcurrent = true;
535 }
536 // Now expand the span and allocate the collection support structures
537 // (MUT, marking bit map etc.) to cover both generations subject to
538 // collection.
539
540 // First check that _permGen is adjacent to _cmsGen and above it.
541 assert( _cmsGen->reserved().word_size() > 0
542 && _permGen->reserved().word_size() > 0,
543 "generations should not be of zero size");
544 assert(_cmsGen->reserved().intersection(_permGen->reserved()).is_empty(),
545 "_cmsGen and _permGen should not overlap");
546 assert(_cmsGen->reserved().end() == _permGen->reserved().start(),
547 "_cmsGen->end() different from _permGen->start()");
548
549 // For use by dirty card to oop closures.
550 _cmsGen->cmsSpace()->set_collector(this);
551 _permGen->cmsSpace()->set_collector(this);
552
553 // Allocate MUT and marking bit map
554 {
555 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
556 if (!_markBitMap.allocate(_span)) {
557 warning("Failed to allocate CMS Bit Map");
558 return;
559 }
560 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
561 }
562 {
563 _modUnionTable.allocate(_span);
564 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
565 }
566
567 if (!_markStack.allocate(CMSMarkStackSize)) {
568 warning("Failed to allocate CMS Marking Stack");
569 return;
570 }
571 if (!_revisitStack.allocate(CMSRevisitStackSize)) {
572 warning("Failed to allocate CMS Revisit Stack");
573 return;
574 }
575
576 // Support for multi-threaded concurrent phases
577 if (ParallelGCThreads > 0 && CMSConcurrentMTEnabled) {
578 if (FLAG_IS_DEFAULT(ParallelCMSThreads)) {
579 // just for now
580 FLAG_SET_DEFAULT(ParallelCMSThreads, (ParallelGCThreads + 3)/4);
581 }
582 if (ParallelCMSThreads > 1) {
583 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
584 ParallelCMSThreads, true);
585 if (_conc_workers == NULL) {
586 warning("GC/CMS: _conc_workers allocation failure: "
587 "forcing -CMSConcurrentMTEnabled");
588 CMSConcurrentMTEnabled = false;
589 }
590 } else {
591 CMSConcurrentMTEnabled = false;
592 }
593 }
594 if (!CMSConcurrentMTEnabled) {
595 ParallelCMSThreads = 0;
596 } else {
597 // Turn off CMSCleanOnEnter optimization temporarily for
598 // the MT case where it's not fixed yet; see 6178663.
599 CMSCleanOnEnter = false;
600 }
601 assert((_conc_workers != NULL) == (ParallelCMSThreads > 1),
602 "Inconsistency");
603
604 // Parallel task queues; these are shared for the
605 // concurrent and stop-world phases of CMS, but
606 // are not shared with parallel scavenge (ParNew).
607 {
608 uint i;
609 uint num_queues = (uint) MAX2(ParallelGCThreads, ParallelCMSThreads);
610
611 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
612 || ParallelRefProcEnabled)
613 && num_queues > 0) {
614 _task_queues = new OopTaskQueueSet(num_queues);
615 if (_task_queues == NULL) {
616 warning("task_queues allocation failure.");
617 return;
618 }
619 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues);
620 if (_hash_seed == NULL) {
621 warning("_hash_seed array allocation failure");
622 return;
623 }
624
625 // XXX use a global constant instead of 64!
626 typedef struct OopTaskQueuePadded {
627 OopTaskQueue work_queue;
628 char pad[64 - sizeof(OopTaskQueue)]; // prevent false sharing
629 } OopTaskQueuePadded;
630
631 for (i = 0; i < num_queues; i++) {
632 OopTaskQueuePadded *q_padded = new OopTaskQueuePadded();
633 if (q_padded == NULL) {
634 warning("work_queue allocation failure.");
635 return;
636 }
637 _task_queues->register_queue(i, &q_padded->work_queue);
638 }
639 for (i = 0; i < num_queues; i++) {
640 _task_queues->queue(i)->initialize();
641 _hash_seed[i] = 17; // copied from ParNew
642 }
643 }
644 }
645
646 // "initiatingOccupancy" is the occupancy ratio at which we trigger
647 // a new collection cycle. Unless explicitly specified via
648 // CMSTriggerRatio, it is calculated by:
649 // Let "f" be MinHeapFreeRatio in
650 //
651 // intiatingOccupancy = 100-f +
652 // f * (CMSTriggerRatio/100)
653 // That is, if we assume the heap is at its desired maximum occupancy at the
654 // end of a collection, we let CMSTriggerRatio of the (purported) free
655 // space be allocated before initiating a new collection cycle.
656 if (CMSInitiatingOccupancyFraction > 0) {
657 _initiatingOccupancy = (double)CMSInitiatingOccupancyFraction / 100.0;
658 } else {
659 _initiatingOccupancy = ((100 - MinHeapFreeRatio) +
660 (double)(CMSTriggerRatio *
661 MinHeapFreeRatio) / 100.0)
662 / 100.0;
663 }
664 // Clip CMSBootstrapOccupancy between 0 and 100.
665 _bootstrap_occupancy = ((double)MIN2((intx)100, MAX2((intx)0, CMSBootstrapOccupancy)))
666 /(double)100;
667
668 _full_gcs_since_conc_gc = 0;
669
670 // Now tell CMS generations the identity of their collector
671 ConcurrentMarkSweepGeneration::set_collector(this);
672
673 // Create & start a CMS thread for this CMS collector
674 _cmsThread = ConcurrentMarkSweepThread::start(this);
675 assert(cmsThread() != NULL, "CMS Thread should have been created");
676 assert(cmsThread()->collector() == this,
677 "CMS Thread should refer to this gen");
678 assert(CGC_lock != NULL, "Where's the CGC_lock?");
679
680 // Support for parallelizing young gen rescan
681 GenCollectedHeap* gch = GenCollectedHeap::heap();
682 _young_gen = gch->prev_gen(_cmsGen);
683 if (gch->supports_inline_contig_alloc()) {
684 _top_addr = gch->top_addr();
685 _end_addr = gch->end_addr();
686 assert(_young_gen != NULL, "no _young_gen");
687 _eden_chunk_index = 0;
688 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
689 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity);
690 if (_eden_chunk_array == NULL) {
691 _eden_chunk_capacity = 0;
692 warning("GC/CMS: _eden_chunk_array allocation failure");
693 }
694 }
695 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
696
697 // Support for parallelizing survivor space rescan
698 if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) {
699 size_t max_plab_samples = MaxNewSize/((SurvivorRatio+2)*MinTLABSize);
700 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads);
701 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples);
702 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads);
703 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
704 || _cursor == NULL) {
705 warning("Failed to allocate survivor plab/chunk array");
706 if (_survivor_plab_array != NULL) {
707 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
708 _survivor_plab_array = NULL;
709 }
710 if (_survivor_chunk_array != NULL) {
711 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
712 _survivor_chunk_array = NULL;
713 }
714 if (_cursor != NULL) {
715 FREE_C_HEAP_ARRAY(size_t, _cursor);
716 _cursor = NULL;
717 }
718 } else {
719 _survivor_chunk_capacity = 2*max_plab_samples;
720 for (uint i = 0; i < ParallelGCThreads; i++) {
721 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples);
722 if (vec == NULL) {
723 warning("Failed to allocate survivor plab array");
724 for (int j = i; j > 0; j--) {
725 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array());
726 }
727 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
728 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
729 _survivor_plab_array = NULL;
730 _survivor_chunk_array = NULL;
731 _survivor_chunk_capacity = 0;
732 break;
733 } else {
734 ChunkArray* cur =
735 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
736 max_plab_samples);
737 assert(cur->end() == 0, "Should be 0");
738 assert(cur->array() == vec, "Should be vec");
739 assert(cur->capacity() == max_plab_samples, "Error");
740 }
741 }
742 }
743 }
744 assert( ( _survivor_plab_array != NULL
745 && _survivor_chunk_array != NULL)
746 || ( _survivor_chunk_capacity == 0
747 && _survivor_chunk_index == 0),
748 "Error");
749
750 // Choose what strong roots should be scanned depending on verification options
751 // and perm gen collection mode.
752 if (!CMSClassUnloadingEnabled) {
753 // If class unloading is disabled we want to include all classes into the root set.
754 add_root_scanning_option(SharedHeap::SO_AllClasses);
755 } else {
756 add_root_scanning_option(SharedHeap::SO_SystemClasses);
757 }
758
759 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
760 _gc_counters = new CollectorCounters("CMS", 1);
761 _completed_initialization = true;
762 _sweep_timer.start(); // start of time
763 }
764
765 const char* ConcurrentMarkSweepGeneration::name() const {
766 return "concurrent mark-sweep generation";
767 }
768 void ConcurrentMarkSweepGeneration::update_counters() {
769 if (UsePerfData) {
770 _space_counters->update_all();
771 _gen_counters->update_all();
772 }
773 }
774
775 // this is an optimized version of update_counters(). it takes the
776 // used value as a parameter rather than computing it.
777 //
778 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
779 if (UsePerfData) {
780 _space_counters->update_used(used);
781 _space_counters->update_capacity();
782 _gen_counters->update_all();
783 }
784 }
785
786 void ConcurrentMarkSweepGeneration::print() const {
787 Generation::print();
788 cmsSpace()->print();
789 }
790
791 #ifndef PRODUCT
792 void ConcurrentMarkSweepGeneration::print_statistics() {
793 cmsSpace()->printFLCensus(0);
794 }
795 #endif
796
797 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
798 GenCollectedHeap* gch = GenCollectedHeap::heap();
799 if (PrintGCDetails) {
800 if (Verbose) {
801 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
802 level(), short_name(), s, used(), capacity());
803 } else {
804 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
805 level(), short_name(), s, used() / K, capacity() / K);
806 }
807 }
808 if (Verbose) {
809 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
810 gch->used(), gch->capacity());
811 } else {
812 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
813 gch->used() / K, gch->capacity() / K);
814 }
815 }
816
817 size_t
818 ConcurrentMarkSweepGeneration::contiguous_available() const {
819 // dld proposes an improvement in precision here. If the committed
820 // part of the space ends in a free block we should add that to
821 // uncommitted size in the calculation below. Will make this
822 // change later, staying with the approximation below for the
823 // time being. -- ysr.
824 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
825 }
826
827 size_t
828 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
829 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
830 }
831
832 size_t ConcurrentMarkSweepGeneration::max_available() const {
833 return free() + _virtual_space.uncommitted_size();
834 }
835
836 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(
837 size_t max_promotion_in_bytes,
838 bool younger_handles_promotion_failure) const {
839
840 // This is the most conservative test. Full promotion is
841 // guaranteed if this is used. The multiplicative factor is to
842 // account for the worst case "dilatation".
843 double adjusted_max_promo_bytes = _dilatation_factor * max_promotion_in_bytes;
844 if (adjusted_max_promo_bytes > (double)max_uintx) { // larger than size_t
845 adjusted_max_promo_bytes = (double)max_uintx;
846 }
847 bool result = (max_contiguous_available() >= (size_t)adjusted_max_promo_bytes);
848
849 if (younger_handles_promotion_failure && !result) {
850 // Full promotion is not guaranteed because fragmentation
851 // of the cms generation can prevent the full promotion.
852 result = (max_available() >= (size_t)adjusted_max_promo_bytes);
853
854 if (!result) {
855 // With promotion failure handling the test for the ability
856 // to support the promotion does not have to be guaranteed.
857 // Use an average of the amount promoted.
858 result = max_available() >= (size_t)
859 gc_stats()->avg_promoted()->padded_average();
860 if (PrintGC && Verbose && result) {
861 gclog_or_tty->print_cr(
862 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
863 " max_available: " SIZE_FORMAT
864 " avg_promoted: " SIZE_FORMAT,
865 max_available(), (size_t)
866 gc_stats()->avg_promoted()->padded_average());
867 }
868 } else {
869 if (PrintGC && Verbose) {
870 gclog_or_tty->print_cr(
871 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
872 " max_available: " SIZE_FORMAT
873 " adj_max_promo_bytes: " SIZE_FORMAT,
874 max_available(), (size_t)adjusted_max_promo_bytes);
875 }
876 }
877 } else {
878 if (PrintGC && Verbose) {
879 gclog_or_tty->print_cr(
880 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
881 " contiguous_available: " SIZE_FORMAT
882 " adj_max_promo_bytes: " SIZE_FORMAT,
883 max_contiguous_available(), (size_t)adjusted_max_promo_bytes);
884 }
885 }
886 return result;
887 }
888
889 CompactibleSpace*
890 ConcurrentMarkSweepGeneration::first_compaction_space() const {
891 return _cmsSpace;
892 }
893
894 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
895 // Clear the promotion information. These pointers can be adjusted
896 // along with all the other pointers into the heap but
897 // compaction is expected to be a rare event with
898 // a heap using cms so don't do it without seeing the need.
899 if (ParallelGCThreads > 0) {
900 for (uint i = 0; i < ParallelGCThreads; i++) {
901 _par_gc_thread_states[i]->promo.reset();
902 }
903 }
904 }
905
906 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
907 blk->do_space(_cmsSpace);
908 }
909
910 void ConcurrentMarkSweepGeneration::compute_new_size() {
911 assert_locked_or_safepoint(Heap_lock);
912
913 // If incremental collection failed, we just want to expand
914 // to the limit.
915 if (incremental_collection_failed()) {
916 clear_incremental_collection_failed();
917 grow_to_reserved();
918 return;
919 }
920
921 size_t expand_bytes = 0;
922 double free_percentage = ((double) free()) / capacity();
923 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
924 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
925
926 // compute expansion delta needed for reaching desired free percentage
927 if (free_percentage < desired_free_percentage) {
928 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
929 assert(desired_capacity >= capacity(), "invalid expansion size");
930 expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
931 }
932 if (expand_bytes > 0) {
933 if (PrintGCDetails && Verbose) {
934 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
935 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
936 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
937 gclog_or_tty->print_cr(" Desired free fraction %f",
938 desired_free_percentage);
939 gclog_or_tty->print_cr(" Maximum free fraction %f",
940 maximum_free_percentage);
941 gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000);
942 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
943 desired_capacity/1000);
944 int prev_level = level() - 1;
945 if (prev_level >= 0) {
946 size_t prev_size = 0;
947 GenCollectedHeap* gch = GenCollectedHeap::heap();
948 Generation* prev_gen = gch->_gens[prev_level];
949 prev_size = prev_gen->capacity();
950 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
951 prev_size/1000);
952 }
953 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
954 unsafe_max_alloc_nogc()/1000);
955 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
956 contiguous_available()/1000);
957 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
958 expand_bytes);
959 }
960 // safe if expansion fails
961 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
962 if (PrintGCDetails && Verbose) {
963 gclog_or_tty->print_cr(" Expanded free fraction %f",
964 ((double) free()) / capacity());
965 }
966 }
967 }
968
969 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
970 return cmsSpace()->freelistLock();
971 }
972
973 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
974 bool tlab) {
975 CMSSynchronousYieldRequest yr;
976 MutexLockerEx x(freelistLock(),
977 Mutex::_no_safepoint_check_flag);
978 return have_lock_and_allocate(size, tlab);
979 }
980
981 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
982 bool tlab) {
983 assert_lock_strong(freelistLock());
984 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
985 HeapWord* res = cmsSpace()->allocate(adjustedSize);
986 // Allocate the object live (grey) if the background collector has
987 // started marking. This is necessary because the marker may
988 // have passed this address and consequently this object will
989 // not otherwise be greyed and would be incorrectly swept up.
990 // Note that if this object contains references, the writing
991 // of those references will dirty the card containing this object
992 // allowing the object to be blackened (and its references scanned)
993 // either during a preclean phase or at the final checkpoint.
994 if (res != NULL) {
995 collector()->direct_allocated(res, adjustedSize);
996 _direct_allocated_words += adjustedSize;
997 // allocation counters
998 NOT_PRODUCT(
999 _numObjectsAllocated++;
1000 _numWordsAllocated += (int)adjustedSize;
1001 )
1002 }
1003 return res;
1004 }
1005
1006 // In the case of direct allocation by mutators in a generation that
1007 // is being concurrently collected, the object must be allocated
1008 // live (grey) if the background collector has started marking.
1009 // This is necessary because the marker may
1010 // have passed this address and consequently this object will
1011 // not otherwise be greyed and would be incorrectly swept up.
1012 // Note that if this object contains references, the writing
1013 // of those references will dirty the card containing this object
1014 // allowing the object to be blackened (and its references scanned)
1015 // either during a preclean phase or at the final checkpoint.
1016 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1017 assert(_markBitMap.covers(start, size), "Out of bounds");
1018 if (_collectorState >= Marking) {
1019 MutexLockerEx y(_markBitMap.lock(),
1020 Mutex::_no_safepoint_check_flag);
1021 // [see comments preceding SweepClosure::do_blk() below for details]
1022 // 1. need to mark the object as live so it isn't collected
1023 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1024 // 3. need to mark the end of the object so sweeper can skip over it
1025 // if it's uninitialized when the sweeper reaches it.
1026 _markBitMap.mark(start); // object is live
1027 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1028 _markBitMap.mark(start + size - 1);
1029 // mark end of object
1030 }
1031 // check that oop looks uninitialized
1032 assert(oop(start)->klass() == NULL, "_klass should be NULL");
1033 }
1034
1035 void CMSCollector::promoted(bool par, HeapWord* start,
1036 bool is_obj_array, size_t obj_size) {
1037 assert(_markBitMap.covers(start), "Out of bounds");
1038 // See comment in direct_allocated() about when objects should
1039 // be allocated live.
1040 if (_collectorState >= Marking) {
1041 // we already hold the marking bit map lock, taken in
1042 // the prologue
1043 if (par) {
1044 _markBitMap.par_mark(start);
1045 } else {
1046 _markBitMap.mark(start);
1047 }
1048 // We don't need to mark the object as uninitialized (as
1049 // in direct_allocated above) because this is being done with the
1050 // world stopped and the object will be initialized by the
1051 // time the sweeper gets to look at it.
1052 assert(SafepointSynchronize::is_at_safepoint(),
1053 "expect promotion only at safepoints");
1054
1055 if (_collectorState < Sweeping) {
1056 // Mark the appropriate cards in the modUnionTable, so that
1057 // this object gets scanned before the sweep. If this is
1058 // not done, CMS generation references in the object might
1059 // not get marked.
1060 // For the case of arrays, which are otherwise precisely
1061 // marked, we need to dirty the entire array, not just its head.
1062 if (is_obj_array) {
1063 // The [par_]mark_range() method expects mr.end() below to
1064 // be aligned to the granularity of a bit's representation
1065 // in the heap. In the case of the MUT below, that's a
1066 // card size.
1067 MemRegion mr(start,
1068 (HeapWord*)round_to((intptr_t)(start + obj_size),
1069 CardTableModRefBS::card_size /* bytes */));
1070 if (par) {
1071 _modUnionTable.par_mark_range(mr);
1072 } else {
1073 _modUnionTable.mark_range(mr);
1074 }
1075 } else { // not an obj array; we can just mark the head
1076 if (par) {
1077 _modUnionTable.par_mark(start);
1078 } else {
1079 _modUnionTable.mark(start);
1080 }
1081 }
1082 }
1083 }
1084 }
1085
1086 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1087 {
1088 size_t delta = pointer_delta(addr, space->bottom());
1089 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1090 }
1091
1092 void CMSCollector::icms_update_allocation_limits()
1093 {
1094 Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1095 EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1096
1097 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1098 if (CMSTraceIncrementalPacing) {
1099 stats().print();
1100 }
1101
1102 assert(duty_cycle <= 100, "invalid duty cycle");
1103 if (duty_cycle != 0) {
1104 // The duty_cycle is a percentage between 0 and 100; convert to words and
1105 // then compute the offset from the endpoints of the space.
1106 size_t free_words = eden->free() / HeapWordSize;
1107 double free_words_dbl = (double)free_words;
1108 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1109 size_t offset_words = (free_words - duty_cycle_words) / 2;
1110
1111 _icms_start_limit = eden->top() + offset_words;
1112 _icms_stop_limit = eden->end() - offset_words;
1113
1114 // The limits may be adjusted (shifted to the right) by
1115 // CMSIncrementalOffset, to allow the application more mutator time after a
1116 // young gen gc (when all mutators were stopped) and before CMS starts and
1117 // takes away one or more cpus.
1118 if (CMSIncrementalOffset != 0) {
1119 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1120 size_t adjustment = (size_t)adjustment_dbl;
1121 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1122 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1123 _icms_start_limit += adjustment;
1124 _icms_stop_limit = tmp_stop;
1125 }
1126 }
1127 }
1128 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1129 _icms_start_limit = _icms_stop_limit = eden->end();
1130 }
1131
1132 // Install the new start limit.
1133 eden->set_soft_end(_icms_start_limit);
1134
1135 if (CMSTraceIncrementalMode) {
1136 gclog_or_tty->print(" icms alloc limits: "
1137 PTR_FORMAT "," PTR_FORMAT
1138 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1139 _icms_start_limit, _icms_stop_limit,
1140 percent_of_space(eden, _icms_start_limit),
1141 percent_of_space(eden, _icms_stop_limit));
1142 if (Verbose) {
1143 gclog_or_tty->print("eden: ");
1144 eden->print_on(gclog_or_tty);
1145 }
1146 }
1147 }
1148
1149 // Any changes here should try to maintain the invariant
1150 // that if this method is called with _icms_start_limit
1151 // and _icms_stop_limit both NULL, then it should return NULL
1152 // and not notify the icms thread.
1153 HeapWord*
1154 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1155 size_t word_size)
1156 {
1157 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1158 // nop.
1159 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1160 if (top <= _icms_start_limit) {
1161 if (CMSTraceIncrementalMode) {
1162 space->print_on(gclog_or_tty);
1163 gclog_or_tty->stamp();
1164 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1165 ", new limit=" PTR_FORMAT
1166 " (" SIZE_FORMAT "%%)",
1167 top, _icms_stop_limit,
1168 percent_of_space(space, _icms_stop_limit));
1169 }
1170 ConcurrentMarkSweepThread::start_icms();
1171 assert(top < _icms_stop_limit, "Tautology");
1172 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1173 return _icms_stop_limit;
1174 }
1175
1176 // The allocation will cross both the _start and _stop limits, so do the
1177 // stop notification also and return end().
1178 if (CMSTraceIncrementalMode) {
1179 space->print_on(gclog_or_tty);
1180 gclog_or_tty->stamp();
1181 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1182 ", new limit=" PTR_FORMAT
1183 " (" SIZE_FORMAT "%%)",
1184 top, space->end(),
1185 percent_of_space(space, space->end()));
1186 }
1187 ConcurrentMarkSweepThread::stop_icms();
1188 return space->end();
1189 }
1190
1191 if (top <= _icms_stop_limit) {
1192 if (CMSTraceIncrementalMode) {
1193 space->print_on(gclog_or_tty);
1194 gclog_or_tty->stamp();
1195 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1196 ", new limit=" PTR_FORMAT
1197 " (" SIZE_FORMAT "%%)",
1198 top, space->end(),
1199 percent_of_space(space, space->end()));
1200 }
1201 ConcurrentMarkSweepThread::stop_icms();
1202 return space->end();
1203 }
1204
1205 if (CMSTraceIncrementalMode) {
1206 space->print_on(gclog_or_tty);
1207 gclog_or_tty->stamp();
1208 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1209 ", new limit=" PTR_FORMAT,
1210 top, NULL);
1211 }
1212 }
1213
1214 return NULL;
1215 }
1216
1217 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size, oop* ref) {
1218 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1219 // allocate, copy and if necessary update promoinfo --
1220 // delegate to underlying space.
1221 assert_lock_strong(freelistLock());
1222
1223 #ifndef PRODUCT
1224 if (Universe::heap()->promotion_should_fail()) {
1225 return NULL;
1226 }
1227 #endif // #ifndef PRODUCT
1228
1229 oop res = _cmsSpace->promote(obj, obj_size, ref);
1230 if (res == NULL) {
1231 // expand and retry
1232 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1233 expand(s*HeapWordSize, MinHeapDeltaBytes,
1234 CMSExpansionCause::_satisfy_promotion);
1235 // Since there's currently no next generation, we don't try to promote
1236 // into a more senior generation.
1237 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1238 "is made to pass on a possibly failing "
1239 "promotion to next generation");
1240 res = _cmsSpace->promote(obj, obj_size, ref);
1241 }
1242 if (res != NULL) {
1243 // See comment in allocate() about when objects should
1244 // be allocated live.
1245 assert(obj->is_oop(), "Will dereference klass pointer below");
1246 collector()->promoted(false, // Not parallel
1247 (HeapWord*)res, obj->is_objArray(), obj_size);
1248 // promotion counters
1249 NOT_PRODUCT(
1250 _numObjectsPromoted++;
1251 _numWordsPromoted +=
1252 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1253 )
1254 }
1255 return res;
1256 }
1257
1258
1259 HeapWord*
1260 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1261 HeapWord* top,
1262 size_t word_sz)
1263 {
1264 return collector()->allocation_limit_reached(space, top, word_sz);
1265 }
1266
1267 // Things to support parallel young-gen collection.
1268 oop
1269 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1270 oop old, markOop m,
1271 size_t word_sz) {
1272 #ifndef PRODUCT
1273 if (Universe::heap()->promotion_should_fail()) {
1274 return NULL;
1275 }
1276 #endif // #ifndef PRODUCT
1277
1278 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1279 PromotionInfo* promoInfo = &ps->promo;
1280 // if we are tracking promotions, then first ensure space for
1281 // promotion (including spooling space for saving header if necessary).
1282 // then allocate and copy, then track promoted info if needed.
1283 // When tracking (see PromotionInfo::track()), the mark word may
1284 // be displaced and in this case restoration of the mark word
1285 // occurs in the (oop_since_save_marks_)iterate phase.
1286 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1287 // Out of space for allocating spooling buffers;
1288 // try expanding and allocating spooling buffers.
1289 if (!expand_and_ensure_spooling_space(promoInfo)) {
1290 return NULL;
1291 }
1292 }
1293 assert(promoInfo->has_spooling_space(), "Control point invariant");
1294 HeapWord* obj_ptr = ps->lab.alloc(word_sz);
1295 if (obj_ptr == NULL) {
1296 obj_ptr = expand_and_par_lab_allocate(ps, word_sz);
1297 if (obj_ptr == NULL) {
1298 return NULL;
1299 }
1300 }
1301 oop obj = oop(obj_ptr);
1302 assert(obj->klass() == NULL, "Object should be uninitialized here.");
1303 // Otherwise, copy the object. Here we must be careful to insert the
1304 // klass pointer last, since this marks the block as an allocated object.
1305 HeapWord* old_ptr = (HeapWord*)old;
1306 if (word_sz > (size_t)oopDesc::header_size()) {
1307 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1308 obj_ptr + oopDesc::header_size(),
1309 word_sz - oopDesc::header_size());
1310 }
1311 // Restore the mark word copied above.
1312 obj->set_mark(m);
1313 // Now we can track the promoted object, if necessary. We take care
1314 // To delay the transition from uninitialized to full object
1315 // (i.e., insertion of klass pointer) until after, so that it
1316 // atomically becomes a promoted object.
1317 if (promoInfo->tracking()) {
1318 promoInfo->track((PromotedObject*)obj, old->klass());
1319 }
1320 // Finally, install the klass pointer.
1321 obj->set_klass(old->klass());
1322
1323 assert(old->is_oop(), "Will dereference klass ptr below");
1324 collector()->promoted(true, // parallel
1325 obj_ptr, old->is_objArray(), word_sz);
1326
1327 NOT_PRODUCT(
1328 Atomic::inc(&_numObjectsPromoted);
1329 Atomic::add((jint)CompactibleFreeListSpace::adjustObjectSize(obj->size()),
1330 &_numWordsPromoted);
1331 )
1332
1333 return obj;
1334 }
1335
1336 void
1337 ConcurrentMarkSweepGeneration::
1338 par_promote_alloc_undo(int thread_num,
1339 HeapWord* obj, size_t word_sz) {
1340 // CMS does not support promotion undo.
1341 ShouldNotReachHere();
1342 }
1343
1344 void
1345 ConcurrentMarkSweepGeneration::
1346 par_promote_alloc_done(int thread_num) {
1347 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1348 ps->lab.retire();
1349 #if CFLS_LAB_REFILL_STATS
1350 if (thread_num == 0) {
1351 _cmsSpace->print_par_alloc_stats();
1352 }
1353 #endif
1354 }
1355
1356 void
1357 ConcurrentMarkSweepGeneration::
1358 par_oop_since_save_marks_iterate_done(int thread_num) {
1359 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1360 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1361 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1362 }
1363
1364 // XXXPERM
1365 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1366 size_t size,
1367 bool tlab)
1368 {
1369 // We allow a STW collection only if a full
1370 // collection was requested.
1371 return full || should_allocate(size, tlab); // FIX ME !!!
1372 // This and promotion failure handling are connected at the
1373 // hip and should be fixed by untying them.
1374 }
1375
1376 bool CMSCollector::shouldConcurrentCollect() {
1377 if (_full_gc_requested) {
1378 assert(ExplicitGCInvokesConcurrent, "Unexpected state");
1379 if (Verbose && PrintGCDetails) {
1380 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1381 " gc request");
1382 }
1383 return true;
1384 }
1385
1386 // For debugging purposes, change the type of collection.
1387 // If the rotation is not on the concurrent collection
1388 // type, don't start a concurrent collection.
1389 NOT_PRODUCT(
1390 if (RotateCMSCollectionTypes &&
1391 (_cmsGen->debug_collection_type() !=
1392 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1393 assert(_cmsGen->debug_collection_type() !=
1394 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1395 "Bad cms collection type");
1396 return false;
1397 }
1398 )
1399
1400 FreelistLocker x(this);
1401 // ------------------------------------------------------------------
1402 // Print out lots of information which affects the initiation of
1403 // a collection.
1404 if (PrintCMSInitiationStatistics && stats().valid()) {
1405 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1406 gclog_or_tty->stamp();
1407 gclog_or_tty->print_cr("");
1408 stats().print_on(gclog_or_tty);
1409 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1410 stats().time_until_cms_gen_full());
1411 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1412 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1413 _cmsGen->contiguous_available());
1414 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1415 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1416 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1417 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", initiatingOccupancy());
1418 }
1419 // ------------------------------------------------------------------
1420
1421 // If the estimated time to complete a cms collection (cms_duration())
1422 // is less than the estimated time remaining until the cms generation
1423 // is full, start a collection.
1424 if (!UseCMSInitiatingOccupancyOnly) {
1425 if (stats().valid()) {
1426 if (stats().time_until_cms_start() == 0.0) {
1427 return true;
1428 }
1429 } else {
1430 // We want to conservatively collect somewhat early in order
1431 // to try and "bootstrap" our CMS/promotion statistics;
1432 // this branch will not fire after the first successful CMS
1433 // collection because the stats should then be valid.
1434 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1435 if (Verbose && PrintGCDetails) {
1436 gclog_or_tty->print_cr(
1437 " CMSCollector: collect for bootstrapping statistics:"
1438 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1439 _bootstrap_occupancy);
1440 }
1441 return true;
1442 }
1443 }
1444 }
1445
1446 // Otherwise, we start a collection cycle if either the perm gen or
1447 // old gen want a collection cycle started. Each may use
1448 // an appropriate criterion for making this decision.
1449 // XXX We need to make sure that the gen expansion
1450 // criterion dovetails well with this.
1451 if (_cmsGen->shouldConcurrentCollect(initiatingOccupancy())) {
1452 if (Verbose && PrintGCDetails) {
1453 gclog_or_tty->print_cr("CMS old gen initiated");
1454 }
1455 return true;
1456 }
1457
1458 if (cms_should_unload_classes() &&
1459 _permGen->shouldConcurrentCollect(initiatingOccupancy())) {
1460 if (Verbose && PrintGCDetails) {
1461 gclog_or_tty->print_cr("CMS perm gen initiated");
1462 }
1463 return true;
1464 }
1465
1466 return false;
1467 }
1468
1469 // Clear _expansion_cause fields of constituent generations
1470 void CMSCollector::clear_expansion_cause() {
1471 _cmsGen->clear_expansion_cause();
1472 _permGen->clear_expansion_cause();
1473 }
1474
1475 bool ConcurrentMarkSweepGeneration::shouldConcurrentCollect(
1476 double initiatingOccupancy) {
1477 // We should be conservative in starting a collection cycle. To
1478 // start too eagerly runs the risk of collecting too often in the
1479 // extreme. To collect too rarely falls back on full collections,
1480 // which works, even if not optimum in terms of concurrent work.
1481 // As a work around for too eagerly collecting, use the flag
1482 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1483 // giving the user an easily understandable way of controlling the
1484 // collections.
1485 // We want to start a new collection cycle if any of the following
1486 // conditions hold:
1487 // . our current occupancy exceeds the initiating occupancy, or
1488 // . we recently needed to expand and have not since that expansion,
1489 // collected, or
1490 // . we are not using adaptive free lists and linear allocation is
1491 // going to fail, or
1492 // . (for old gen) incremental collection has already failed or
1493 // may soon fail in the near future as we may not be able to absorb
1494 // promotions.
1495 assert_lock_strong(freelistLock());
1496
1497 if (occupancy() > initiatingOccupancy) {
1498 if (PrintGCDetails && Verbose) {
1499 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1500 short_name(), occupancy(), initiatingOccupancy);
1501 }
1502 return true;
1503 }
1504 if (UseCMSInitiatingOccupancyOnly) {
1505 return false;
1506 }
1507 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1508 if (PrintGCDetails && Verbose) {
1509 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1510 short_name());
1511 }
1512 return true;
1513 }
1514 GenCollectedHeap* gch = GenCollectedHeap::heap();
1515 assert(gch->collector_policy()->is_two_generation_policy(),
1516 "You may want to check the correctness of the following");
1517 if (gch->incremental_collection_will_fail()) {
1518 if (PrintGCDetails && Verbose) {
1519 gclog_or_tty->print(" %s: collect because incremental collection will fail ",
1520 short_name());
1521 }
1522 return true;
1523 }
1524 if (!_cmsSpace->adaptive_freelists() &&
1525 _cmsSpace->linearAllocationWouldFail()) {
1526 if (PrintGCDetails && Verbose) {
1527 gclog_or_tty->print(" %s: collect because of linAB ",
1528 short_name());
1529 }
1530 return true;
1531 }
1532 return false;
1533 }
1534
1535 void ConcurrentMarkSweepGeneration::collect(bool full,
1536 bool clear_all_soft_refs,
1537 size_t size,
1538 bool tlab)
1539 {
1540 collector()->collect(full, clear_all_soft_refs, size, tlab);
1541 }
1542
1543 void CMSCollector::collect(bool full,
1544 bool clear_all_soft_refs,
1545 size_t size,
1546 bool tlab)
1547 {
1548 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1549 // For debugging purposes skip the collection if the state
1550 // is not currently idle
1551 if (TraceCMSState) {
1552 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1553 Thread::current(), full, _collectorState);
1554 }
1555 return;
1556 }
1557
1558 // The following "if" branch is present for defensive reasons.
1559 // In the current uses of this interface, it can be replaced with:
1560 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1561 // But I am not placing that assert here to allow future
1562 // generality in invoking this interface.
1563 if (GC_locker::is_active()) {
1564 // A consistency test for GC_locker
1565 assert(GC_locker::needs_gc(), "Should have been set already");
1566 // Skip this foreground collection, instead
1567 // expanding the heap if necessary.
1568 // Need the free list locks for the call to free() in compute_new_size()
1569 compute_new_size();
1570 return;
1571 }
1572 acquire_control_and_collect(full, clear_all_soft_refs);
1573 _full_gcs_since_conc_gc++;
1574
1575 }
1576
1577 void CMSCollector::request_full_gc(unsigned int full_gc_count) {
1578 GenCollectedHeap* gch = GenCollectedHeap::heap();
1579 unsigned int gc_count = gch->total_full_collections();
1580 if (gc_count == full_gc_count) {
1581 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1582 _full_gc_requested = true;
1583 CGC_lock->notify(); // nudge CMS thread
1584 }
1585 }
1586
1587
1588 // The foreground and background collectors need to coordinate in order
1589 // to make sure that they do not mutually interfere with CMS collections.
1590 // When a background collection is active,
1591 // the foreground collector may need to take over (preempt) and
1592 // synchronously complete an ongoing collection. Depending on the
1593 // frequency of the background collections and the heap usage
1594 // of the application, this preemption can be seldom or frequent.
1595 // There are only certain
1596 // points in the background collection that the "collection-baton"
1597 // can be passed to the foreground collector.
1598 //
1599 // The foreground collector will wait for the baton before
1600 // starting any part of the collection. The foreground collector
1601 // will only wait at one location.
1602 //
1603 // The background collector will yield the baton before starting a new
1604 // phase of the collection (e.g., before initial marking, marking from roots,
1605 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1606 // of the loop which switches the phases. The background collector does some
1607 // of the phases (initial mark, final re-mark) with the world stopped.
1608 // Because of locking involved in stopping the world,
1609 // the foreground collector should not block waiting for the background
1610 // collector when it is doing a stop-the-world phase. The background
1611 // collector will yield the baton at an additional point just before
1612 // it enters a stop-the-world phase. Once the world is stopped, the
1613 // background collector checks the phase of the collection. If the
1614 // phase has not changed, it proceeds with the collection. If the
1615 // phase has changed, it skips that phase of the collection. See
1616 // the comments on the use of the Heap_lock in collect_in_background().
1617 //
1618 // Variable used in baton passing.
1619 // _foregroundGCIsActive - Set to true by the foreground collector when
1620 // it wants the baton. The foreground clears it when it has finished
1621 // the collection.
1622 // _foregroundGCShouldWait - Set to true by the background collector
1623 // when it is running. The foreground collector waits while
1624 // _foregroundGCShouldWait is true.
1625 // CGC_lock - monitor used to protect access to the above variables
1626 // and to notify the foreground and background collectors.
1627 // _collectorState - current state of the CMS collection.
1628 //
1629 // The foreground collector
1630 // acquires the CGC_lock
1631 // sets _foregroundGCIsActive
1632 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1633 // various locks acquired in preparation for the collection
1634 // are released so as not to block the background collector
1635 // that is in the midst of a collection
1636 // proceeds with the collection
1637 // clears _foregroundGCIsActive
1638 // returns
1639 //
1640 // The background collector in a loop iterating on the phases of the
1641 // collection
1642 // acquires the CGC_lock
1643 // sets _foregroundGCShouldWait
1644 // if _foregroundGCIsActive is set
1645 // clears _foregroundGCShouldWait, notifies _CGC_lock
1646 // waits on _CGC_lock for _foregroundGCIsActive to become false
1647 // and exits the loop.
1648 // otherwise
1649 // proceed with that phase of the collection
1650 // if the phase is a stop-the-world phase,
1651 // yield the baton once more just before enqueueing
1652 // the stop-world CMS operation (executed by the VM thread).
1653 // returns after all phases of the collection are done
1654 //
1655
1656 void CMSCollector::acquire_control_and_collect(bool full,
1657 bool clear_all_soft_refs) {
1658 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1659 assert(!Thread::current()->is_ConcurrentGC_thread(),
1660 "shouldn't try to acquire control from self!");
1661
1662 // Start the protocol for acquiring control of the
1663 // collection from the background collector (aka CMS thread).
1664 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1665 "VM thread should have CMS token");
1666 // Remember the possibly interrupted state of an ongoing
1667 // concurrent collection
1668 CollectorState first_state = _collectorState;
1669
1670 // Signal to a possibly ongoing concurrent collection that
1671 // we want to do a foreground collection.
1672 _foregroundGCIsActive = true;
1673
1674 // Disable incremental mode during a foreground collection.
1675 ICMSDisabler icms_disabler;
1676
1677 // release locks and wait for a notify from the background collector
1678 // releasing the locks in only necessary for phases which
1679 // do yields to improve the granularity of the collection.
1680 assert_lock_strong(bitMapLock());
1681 // We need to lock the Free list lock for the space that we are
1682 // currently collecting.
1683 assert(haveFreelistLocks(), "Must be holding free list locks");
1684 bitMapLock()->unlock();
1685 releaseFreelistLocks();
1686 {
1687 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1688 if (_foregroundGCShouldWait) {
1689 // We are going to be waiting for action for the CMS thread;
1690 // it had better not be gone (for instance at shutdown)!
1691 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1692 "CMS thread must be running");
1693 // Wait here until the background collector gives us the go-ahead
1694 ConcurrentMarkSweepThread::clear_CMS_flag(
1695 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1696 // Get a possibly blocked CMS thread going:
1697 // Note that we set _foregroundGCIsActive true above,
1698 // without protection of the CGC_lock.
1699 CGC_lock->notify();
1700 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1701 "Possible deadlock");
1702 while (_foregroundGCShouldWait) {
1703 // wait for notification
1704 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1705 // Possibility of delay/starvation here, since CMS token does
1706 // not know to give priority to VM thread? Actually, i think
1707 // there wouldn't be any delay/starvation, but the proof of
1708 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1709 }
1710 ConcurrentMarkSweepThread::set_CMS_flag(
1711 ConcurrentMarkSweepThread::CMS_vm_has_token);
1712 }
1713 }
1714 // The CMS_token is already held. Get back the other locks.
1715 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1716 "VM thread should have CMS token");
1717 getFreelistLocks();
1718 bitMapLock()->lock_without_safepoint_check();
1719 if (TraceCMSState) {
1720 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1721 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1722 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1723 }
1724
1725 // Check if we need to do a compaction, or if not, whether
1726 // we need to start the mark-sweep from scratch.
1727 bool should_compact = false;
1728 bool should_start_over = false;
1729 decide_foreground_collection_type(clear_all_soft_refs,
1730 &should_compact, &should_start_over);
1731
1732 NOT_PRODUCT(
1733 if (RotateCMSCollectionTypes) {
1734 if (_cmsGen->debug_collection_type() ==
1735 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1736 should_compact = true;
1737 } else if (_cmsGen->debug_collection_type() ==
1738 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1739 should_compact = false;
1740 }
1741 }
1742 )
1743
1744 if (PrintGCDetails && first_state > Idling) {
1745 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1746 if (GCCause::is_user_requested_gc(cause) ||
1747 GCCause::is_serviceability_requested_gc(cause)) {
1748 gclog_or_tty->print(" (concurrent mode interrupted)");
1749 } else {
1750 gclog_or_tty->print(" (concurrent mode failure)");
1751 }
1752 }
1753
1754 if (should_compact) {
1755 // If the collection is being acquired from the background
1756 // collector, there may be references on the discovered
1757 // references lists that have NULL referents (being those
1758 // that were concurrently cleared by a mutator) or
1759 // that are no longer active (having been enqueued concurrently
1760 // by the mutator).
1761 // Scrub the list of those references because Mark-Sweep-Compact
1762 // code assumes referents are not NULL and that all discovered
1763 // Reference objects are active.
1764 ref_processor()->clean_up_discovered_references();
1765
1766 do_compaction_work(clear_all_soft_refs);
1767
1768 // Has the GC time limit been exceeded?
1769 check_gc_time_limit();
1770
1771 } else {
1772 do_mark_sweep_work(clear_all_soft_refs, first_state,
1773 should_start_over);
1774 }
1775 // Reset the expansion cause, now that we just completed
1776 // a collection cycle.
1777 clear_expansion_cause();
1778 _foregroundGCIsActive = false;
1779 return;
1780 }
1781
1782 void CMSCollector::check_gc_time_limit() {
1783
1784 // Ignore explicit GC's. Exiting here does not set the flag and
1785 // does not reset the count. Updating of the averages for system
1786 // GC's is still controlled by UseAdaptiveSizePolicyWithSystemGC.
1787 GCCause::Cause gc_cause = GenCollectedHeap::heap()->gc_cause();
1788 if (GCCause::is_user_requested_gc(gc_cause) ||
1789 GCCause::is_serviceability_requested_gc(gc_cause)) {
1790 return;
1791 }
1792
1793 // Calculate the fraction of the CMS generation was freed during
1794 // the last collection.
1795 // Only consider the STW compacting cost for now.
1796 //
1797 // Note that the gc time limit test only works for the collections
1798 // of the young gen + tenured gen and not for collections of the
1799 // permanent gen. That is because the calculation of the space
1800 // freed by the collection is the free space in the young gen +
1801 // tenured gen.
1802
1803 double fraction_free =
1804 ((double)_cmsGen->free())/((double)_cmsGen->max_capacity());
1805 if ((100.0 * size_policy()->compacting_gc_cost()) >
1806 ((double) GCTimeLimit) &&
1807 ((fraction_free * 100) < GCHeapFreeLimit)) {
1808 size_policy()->inc_gc_time_limit_count();
1809 if (UseGCOverheadLimit &&
1810 (size_policy()->gc_time_limit_count() >
1811 AdaptiveSizePolicyGCTimeLimitThreshold)) {
1812 size_policy()->set_gc_time_limit_exceeded(true);
1813 // Avoid consecutive OOM due to the gc time limit by resetting
1814 // the counter.
1815 size_policy()->reset_gc_time_limit_count();
1816 if (PrintGCDetails) {
1817 gclog_or_tty->print_cr(" GC is exceeding overhead limit "
1818 "of %d%%", GCTimeLimit);
1819 }
1820 } else {
1821 if (PrintGCDetails) {
1822 gclog_or_tty->print_cr(" GC would exceed overhead limit "
1823 "of %d%%", GCTimeLimit);
1824 }
1825 }
1826 } else {
1827 size_policy()->reset_gc_time_limit_count();
1828 }
1829 }
1830
1831 // Resize the perm generation and the tenured generation
1832 // after obtaining the free list locks for the
1833 // two generations.
1834 void CMSCollector::compute_new_size() {
1835 assert_locked_or_safepoint(Heap_lock);
1836 FreelistLocker z(this);
1837 _permGen->compute_new_size();
1838 _cmsGen->compute_new_size();
1839 }
1840
1841 // A work method used by foreground collection to determine
1842 // what type of collection (compacting or not, continuing or fresh)
1843 // it should do.
1844 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1845 // and CMSCompactWhenClearAllSoftRefs the default in the future
1846 // and do away with the flags after a suitable period.
1847 void CMSCollector::decide_foreground_collection_type(
1848 bool clear_all_soft_refs, bool* should_compact,
1849 bool* should_start_over) {
1850 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1851 // flag is set, and we have either requested a System.gc() or
1852 // the number of full gc's since the last concurrent cycle
1853 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1854 // or if an incremental collection has failed
1855 GenCollectedHeap* gch = GenCollectedHeap::heap();
1856 assert(gch->collector_policy()->is_two_generation_policy(),
1857 "You may want to check the correctness of the following");
1858 // Inform cms gen if this was due to partial collection failing.
1859 // The CMS gen may use this fact to determine its expansion policy.
1860 if (gch->incremental_collection_will_fail()) {
1861 assert(!_cmsGen->incremental_collection_failed(),
1862 "Should have been noticed, reacted to and cleared");
1863 _cmsGen->set_incremental_collection_failed();
1864 }
1865 *should_compact =
1866 UseCMSCompactAtFullCollection &&
1867 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1868 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1869 gch->incremental_collection_will_fail());
1870 *should_start_over = false;
1871 if (clear_all_soft_refs && !*should_compact) {
1872 // We are about to do a last ditch collection attempt
1873 // so it would normally make sense to do a compaction
1874 // to reclaim as much space as possible.
1875 if (CMSCompactWhenClearAllSoftRefs) {
1876 // Default: The rationale is that in this case either
1877 // we are past the final marking phase, in which case
1878 // we'd have to start over, or so little has been done
1879 // that there's little point in saving that work. Compaction
1880 // appears to be the sensible choice in either case.
1881 *should_compact = true;
1882 } else {
1883 // We have been asked to clear all soft refs, but not to
1884 // compact. Make sure that we aren't past the final checkpoint
1885 // phase, for that is where we process soft refs. If we are already
1886 // past that phase, we'll need to redo the refs discovery phase and
1887 // if necessary clear soft refs that weren't previously
1888 // cleared. We do so by remembering the phase in which
1889 // we came in, and if we are past the refs processing
1890 // phase, we'll choose to just redo the mark-sweep
1891 // collection from scratch.
1892 if (_collectorState > FinalMarking) {
1893 // We are past the refs processing phase;
1894 // start over and do a fresh synchronous CMS cycle
1895 _collectorState = Resetting; // skip to reset to start new cycle
1896 reset(false /* == !asynch */);
1897 *should_start_over = true;
1898 } // else we can continue a possibly ongoing current cycle
1899 }
1900 }
1901 }
1902
1903 // A work method used by the foreground collector to do
1904 // a mark-sweep-compact.
1905 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1906 GenCollectedHeap* gch = GenCollectedHeap::heap();
1907 TraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, gclog_or_tty);
1908 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
1909 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
1910 "collections passed to foreground collector", _full_gcs_since_conc_gc);
1911 }
1912
1913 // Sample collection interval time and reset for collection pause.
1914 if (UseAdaptiveSizePolicy) {
1915 size_policy()->msc_collection_begin();
1916 }
1917
1918 // Temporarily widen the span of the weak reference processing to
1919 // the entire heap.
1920 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1921 ReferenceProcessorSpanMutator x(ref_processor(), new_span);
1922
1923 // Temporarily, clear the "is_alive_non_header" field of the
1924 // reference processor.
1925 ReferenceProcessorIsAliveMutator y(ref_processor(), NULL);
1926
1927 // Temporarily make reference _processing_ single threaded (non-MT).
1928 ReferenceProcessorMTProcMutator z(ref_processor(), false);
1929
1930 // Temporarily make refs discovery atomic
1931 ReferenceProcessorAtomicMutator w(ref_processor(), true);
1932
1933 ref_processor()->set_enqueuing_is_done(false);
1934 ref_processor()->enable_discovery();
1935 // If an asynchronous collection finishes, the _modUnionTable is
1936 // all clear. If we are assuming the collection from an asynchronous
1937 // collection, clear the _modUnionTable.
1938 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1939 "_modUnionTable should be clear if the baton was not passed");
1940 _modUnionTable.clear_all();
1941
1942 // We must adjust the allocation statistics being maintained
1943 // in the free list space. We do so by reading and clearing
1944 // the sweep timer and updating the block flux rate estimates below.
1945 assert(_sweep_timer.is_active(), "We should never see the timer inactive");
1946 _sweep_timer.stop();
1947 // Note that we do not use this sample to update the _sweep_estimate.
1948 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_sweep_timer.seconds()),
1949 _sweep_estimate.padded_average());
1950
1951 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1952 ref_processor(), clear_all_soft_refs);
1953 #ifdef ASSERT
1954 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1955 size_t free_size = cms_space->free();
1956 assert(free_size ==
1957 pointer_delta(cms_space->end(), cms_space->compaction_top())
1958 * HeapWordSize,
1959 "All the free space should be compacted into one chunk at top");
1960 assert(cms_space->dictionary()->totalChunkSize(
1961 debug_only(cms_space->freelistLock())) == 0 ||
1962 cms_space->totalSizeInIndexedFreeLists() == 0,
1963 "All the free space should be in a single chunk");
1964 size_t num = cms_space->totalCount();
1965 assert((free_size == 0 && num == 0) ||
1966 (free_size > 0 && (num == 1 || num == 2)),
1967 "There should be at most 2 free chunks after compaction");
1968 #endif // ASSERT
1969 _collectorState = Resetting;
1970 assert(_restart_addr == NULL,
1971 "Should have been NULL'd before baton was passed");
1972 reset(false /* == !asynch */);
1973 _cmsGen->reset_after_compaction();
1974
1975 if (verifying() && !cms_should_unload_classes()) {
1976 perm_gen_verify_bit_map()->clear_all();
1977 }
1978
1979 // Clear any data recorded in the PLAB chunk arrays.
1980 if (_survivor_plab_array != NULL) {
1981 reset_survivor_plab_arrays();
1982 }
1983
1984 // Adjust the per-size allocation stats for the next epoch.
1985 _cmsGen->cmsSpace()->endSweepFLCensus(sweepCount() /* fake */);
1986 // Restart the "sweep timer" for next epoch.
1987 _sweep_timer.reset();
1988 _sweep_timer.start();
1989
1990 // Sample collection pause time and reset for collection interval.
1991 if (UseAdaptiveSizePolicy) {
1992 size_policy()->msc_collection_end(gch->gc_cause());
1993 }
1994
1995 // For a mark-sweep-compact, compute_new_size() will be called
1996 // in the heap's do_collection() method.
1997 }
1998
1999 // A work method used by the foreground collector to do
2000 // a mark-sweep, after taking over from a possibly on-going
2001 // concurrent mark-sweep collection.
2002 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2003 CollectorState first_state, bool should_start_over) {
2004 if (PrintGC && Verbose) {
2005 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2006 "collector with count %d",
2007 _full_gcs_since_conc_gc);
2008 }
2009 switch (_collectorState) {
2010 case Idling:
2011 if (first_state == Idling || should_start_over) {
2012 // The background GC was not active, or should
2013 // restarted from scratch; start the cycle.
2014 _collectorState = InitialMarking;
2015 }
2016 // If first_state was not Idling, then a background GC
2017 // was in progress and has now finished. No need to do it
2018 // again. Leave the state as Idling.
2019 break;
2020 case Precleaning:
2021 // In the foreground case don't do the precleaning since
2022 // it is not done concurrently and there is extra work
2023 // required.
2024 _collectorState = FinalMarking;
2025 }
2026 if (PrintGCDetails &&
2027 (_collectorState > Idling ||
2028 !GCCause::is_user_requested_gc(GenCollectedHeap::heap()->gc_cause()))) {
2029 gclog_or_tty->print(" (concurrent mode failure)");
2030 }
2031 collect_in_foreground(clear_all_soft_refs);
2032
2033 // For a mark-sweep, compute_new_size() will be called
2034 // in the heap's do_collection() method.
2035 }
2036
2037
2038 void CMSCollector::getFreelistLocks() const {
2039 // Get locks for all free lists in all generations that this
2040 // collector is responsible for
2041 _cmsGen->freelistLock()->lock_without_safepoint_check();
2042 _permGen->freelistLock()->lock_without_safepoint_check();
2043 }
2044
2045 void CMSCollector::releaseFreelistLocks() const {
2046 // Release locks for all free lists in all generations that this
2047 // collector is responsible for
2048 _cmsGen->freelistLock()->unlock();
2049 _permGen->freelistLock()->unlock();
2050 }
2051
2052 bool CMSCollector::haveFreelistLocks() const {
2053 // Check locks for all free lists in all generations that this
2054 // collector is responsible for
2055 assert_lock_strong(_cmsGen->freelistLock());
2056 assert_lock_strong(_permGen->freelistLock());
2057 PRODUCT_ONLY(ShouldNotReachHere());
2058 return true;
2059 }
2060
2061 // A utility class that is used by the CMS collector to
2062 // temporarily "release" the foreground collector from its
2063 // usual obligation to wait for the background collector to
2064 // complete an ongoing phase before proceeding.
2065 class ReleaseForegroundGC: public StackObj {
2066 private:
2067 CMSCollector* _c;
2068 public:
2069 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2070 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2071 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2072 // allow a potentially blocked foreground collector to proceed
2073 _c->_foregroundGCShouldWait = false;
2074 if (_c->_foregroundGCIsActive) {
2075 CGC_lock->notify();
2076 }
2077 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2078 "Possible deadlock");
2079 }
2080
2081 ~ReleaseForegroundGC() {
2082 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2083 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2084 _c->_foregroundGCShouldWait = true;
2085 }
2086 };
2087
2088 // There are separate collect_in_background and collect_in_foreground because of
2089 // the different locking requirements of the background collector and the
2090 // foreground collector. There was originally an attempt to share
2091 // one "collect" method between the background collector and the foreground
2092 // collector but the if-then-else required made it cleaner to have
2093 // separate methods.
2094 void CMSCollector::collect_in_background(bool clear_all_soft_refs) {
2095 assert(Thread::current()->is_ConcurrentGC_thread(),
2096 "A CMS asynchronous collection is only allowed on a CMS thread.");
2097
2098 GenCollectedHeap* gch = GenCollectedHeap::heap();
2099 {
2100 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2101 MutexLockerEx hl(Heap_lock, safepoint_check);
2102 MutexLockerEx x(CGC_lock, safepoint_check);
2103 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2104 // The foreground collector is active or we're
2105 // not using asynchronous collections. Skip this
2106 // background collection.
2107 assert(!_foregroundGCShouldWait, "Should be clear");
2108 return;
2109 } else {
2110 assert(_collectorState == Idling, "Should be idling before start.");
2111 _collectorState = InitialMarking;
2112 // Reset the expansion cause, now that we are about to begin
2113 // a new cycle.
2114 clear_expansion_cause();
2115 }
2116 _unloaded_classes_last_cycle = cms_should_unload_classes(); // ... from last cycle
2117 // This controls class unloading in response to an explicit gc request.
2118 // If ExplicitGCInvokesConcurrentAndUnloadsClasses is set, then
2119 // we will unload classes even if CMSClassUnloadingEnabled is not set.
2120 // See CR 6541037 and related CRs.
2121 _unload_classes = _full_gc_requested // ... for this cycle
2122 && ExplicitGCInvokesConcurrentAndUnloadsClasses;
2123 _full_gc_requested = false; // acks all outstanding full gc requests
2124 // Signal that we are about to start a collection
2125 gch->increment_total_full_collections(); // ... starting a collection cycle
2126 _collection_count_start = gch->total_full_collections();
2127 }
2128
2129 // Used for PrintGC
2130 size_t prev_used;
2131 if (PrintGC && Verbose) {
2132 prev_used = _cmsGen->used(); // XXXPERM
2133 }
2134
2135 // The change of the collection state is normally done at this level;
2136 // the exceptions are phases that are executed while the world is
2137 // stopped. For those phases the change of state is done while the
2138 // world is stopped. For baton passing purposes this allows the
2139 // background collector to finish the phase and change state atomically.
2140 // The foreground collector cannot wait on a phase that is done
2141 // while the world is stopped because the foreground collector already
2142 // has the world stopped and would deadlock.
2143 while (_collectorState != Idling) {
2144 if (TraceCMSState) {
2145 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2146 Thread::current(), _collectorState);
2147 }
2148 // The foreground collector
2149 // holds the Heap_lock throughout its collection.
2150 // holds the CMS token (but not the lock)
2151 // except while it is waiting for the background collector to yield.
2152 //
2153 // The foreground collector should be blocked (not for long)
2154 // if the background collector is about to start a phase
2155 // executed with world stopped. If the background
2156 // collector has already started such a phase, the
2157 // foreground collector is blocked waiting for the
2158 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2159 // are executed in the VM thread.
2160 //
2161 // The locking order is
2162 // PendingListLock (PLL) -- if applicable (FinalMarking)
2163 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2164 // CMS token (claimed in
2165 // stop_world_and_do() -->
2166 // safepoint_synchronize() -->
2167 // CMSThread::synchronize())
2168
2169 {
2170 // Check if the FG collector wants us to yield.
2171 CMSTokenSync x(true); // is cms thread
2172 if (waitForForegroundGC()) {
2173 // We yielded to a foreground GC, nothing more to be
2174 // done this round.
2175 assert(_foregroundGCShouldWait == false, "We set it to false in "
2176 "waitForForegroundGC()");
2177 if (TraceCMSState) {
2178 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2179 " exiting collection CMS state %d",
2180 Thread::current(), _collectorState);
2181 }
2182 return;
2183 } else {
2184 // The background collector can run but check to see if the
2185 // foreground collector has done a collection while the
2186 // background collector was waiting to get the CGC_lock
2187 // above. If yes, break so that _foregroundGCShouldWait
2188 // is cleared before returning.
2189 if (_collectorState == Idling) {
2190 break;
2191 }
2192 }
2193 }
2194
2195 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2196 "should be waiting");
2197
2198 switch (_collectorState) {
2199 case InitialMarking:
2200 {
2201 ReleaseForegroundGC x(this);
2202 stats().record_cms_begin();
2203
2204 VM_CMS_Initial_Mark initial_mark_op(this);
2205 VMThread::execute(&initial_mark_op);
2206 }
2207 // The collector state may be any legal state at this point
2208 // since the background collector may have yielded to the
2209 // foreground collector.
2210 break;
2211 case Marking:
2212 // initial marking in checkpointRootsInitialWork has been completed
2213 if (markFromRoots(true)) { // we were successful
2214 assert(_collectorState == Precleaning, "Collector state should "
2215 "have changed");
2216 } else {
2217 assert(_foregroundGCIsActive, "Internal state inconsistency");
2218 }
2219 break;
2220 case Precleaning:
2221 if (UseAdaptiveSizePolicy) {
2222 size_policy()->concurrent_precleaning_begin();
2223 }
2224 // marking from roots in markFromRoots has been completed
2225 preclean();
2226 if (UseAdaptiveSizePolicy) {
2227 size_policy()->concurrent_precleaning_end();
2228 }
2229 assert(_collectorState == AbortablePreclean ||
2230 _collectorState == FinalMarking,
2231 "Collector state should have changed");
2232 break;
2233 case AbortablePreclean:
2234 if (UseAdaptiveSizePolicy) {
2235 size_policy()->concurrent_phases_resume();
2236 }
2237 abortable_preclean();
2238 if (UseAdaptiveSizePolicy) {
2239 size_policy()->concurrent_precleaning_end();
2240 }
2241 assert(_collectorState == FinalMarking, "Collector state should "
2242 "have changed");
2243 break;
2244 case FinalMarking:
2245 {
2246 ReleaseForegroundGC x(this);
2247
2248 VM_CMS_Final_Remark final_remark_op(this);
2249 VMThread::execute(&final_remark_op);
2250 }
2251 assert(_foregroundGCShouldWait, "block post-condition");
2252 break;
2253 case Sweeping:
2254 if (UseAdaptiveSizePolicy) {
2255 size_policy()->concurrent_sweeping_begin();
2256 }
2257 // final marking in checkpointRootsFinal has been completed
2258 sweep(true);
2259 assert(_collectorState == Resizing, "Collector state change "
2260 "to Resizing must be done under the free_list_lock");
2261 _full_gcs_since_conc_gc = 0;
2262
2263 // Stop the timers for adaptive size policy for the concurrent phases
2264 if (UseAdaptiveSizePolicy) {
2265 size_policy()->concurrent_sweeping_end();
2266 size_policy()->concurrent_phases_end(gch->gc_cause(),
2267 gch->prev_gen(_cmsGen)->capacity(),
2268 _cmsGen->free());
2269 }
2270
2271 case Resizing: {
2272 // Sweeping has been completed...
2273 // At this point the background collection has completed.
2274 // Don't move the call to compute_new_size() down
2275 // into code that might be executed if the background
2276 // collection was preempted.
2277 {
2278 ReleaseForegroundGC x(this); // unblock FG collection
2279 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2280 CMSTokenSync z(true); // not strictly needed.
2281 if (_collectorState == Resizing) {
2282 compute_new_size();
2283 _collectorState = Resetting;
2284 } else {
2285 assert(_collectorState == Idling, "The state should only change"
2286 " because the foreground collector has finished the collection");
2287 }
2288 }
2289 break;
2290 }
2291 case Resetting:
2292 // CMS heap resizing has been completed
2293 reset(true);
2294 assert(_collectorState == Idling, "Collector state should "
2295 "have changed");
2296 stats().record_cms_end();
2297 // Don't move the concurrent_phases_end() and compute_new_size()
2298 // calls to here because a preempted background collection
2299 // has it's state set to "Resetting".
2300 break;
2301 case Idling:
2302 default:
2303 ShouldNotReachHere();
2304 break;
2305 }
2306 if (TraceCMSState) {
2307 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2308 Thread::current(), _collectorState);
2309 }
2310 assert(_foregroundGCShouldWait, "block post-condition");
2311 }
2312
2313 // Should this be in gc_epilogue?
2314 collector_policy()->counters()->update_counters();
2315
2316 {
2317 // Clear _foregroundGCShouldWait and, in the event that the
2318 // foreground collector is waiting, notify it, before
2319 // returning.
2320 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2321 _foregroundGCShouldWait = false;
2322 if (_foregroundGCIsActive) {
2323 CGC_lock->notify();
2324 }
2325 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2326 "Possible deadlock");
2327 }
2328 if (TraceCMSState) {
2329 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2330 " exiting collection CMS state %d",
2331 Thread::current(), _collectorState);
2332 }
2333 if (PrintGC && Verbose) {
2334 _cmsGen->print_heap_change(prev_used);
2335 }
2336 }
2337
2338 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs) {
2339 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2340 "Foreground collector should be waiting, not executing");
2341 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2342 "may only be done by the VM Thread with the world stopped");
2343 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2344 "VM thread should have CMS token");
2345
2346 NOT_PRODUCT(TraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2347 true, gclog_or_tty);)
2348 if (UseAdaptiveSizePolicy) {
2349 size_policy()->ms_collection_begin();
2350 }
2351 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2352
2353 HandleMark hm; // Discard invalid handles created during verification
2354
2355 if (VerifyBeforeGC &&
2356 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2357 Universe::verify(true);
2358 }
2359
2360 bool init_mark_was_synchronous = false; // until proven otherwise
2361 while (_collectorState != Idling) {
2362 if (TraceCMSState) {
2363 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2364 Thread::current(), _collectorState);
2365 }
2366 switch (_collectorState) {
2367 case InitialMarking:
2368 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2369 checkpointRootsInitial(false);
2370 assert(_collectorState == Marking, "Collector state should have changed"
2371 " within checkpointRootsInitial()");
2372 break;
2373 case Marking:
2374 // initial marking in checkpointRootsInitialWork has been completed
2375 if (VerifyDuringGC &&
2376 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2377 gclog_or_tty->print("Verify before initial mark: ");
2378 Universe::verify(true);
2379 }
2380 {
2381 bool res = markFromRoots(false);
2382 assert(res && _collectorState == FinalMarking, "Collector state should "
2383 "have changed");
2384 break;
2385 }
2386 case FinalMarking:
2387 if (VerifyDuringGC &&
2388 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2389 gclog_or_tty->print("Verify before re-mark: ");
2390 Universe::verify(true);
2391 }
2392 checkpointRootsFinal(false, clear_all_soft_refs,
2393 init_mark_was_synchronous);
2394 assert(_collectorState == Sweeping, "Collector state should not "
2395 "have changed within checkpointRootsFinal()");
2396 break;
2397 case Sweeping:
2398 // final marking in checkpointRootsFinal has been completed
2399 if (VerifyDuringGC &&
2400 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2401 gclog_or_tty->print("Verify before sweep: ");
2402 Universe::verify(true);
2403 }
2404 sweep(false);
2405 assert(_collectorState == Resizing, "Incorrect state");
2406 break;
2407 case Resizing: {
2408 // Sweeping has been completed; the actual resize in this case
2409 // is done separately; nothing to be done in this state.
2410 _collectorState = Resetting;
2411 break;
2412 }
2413 case Resetting:
2414 // The heap has been resized.
2415 if (VerifyDuringGC &&
2416 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2417 gclog_or_tty->print("Verify before reset: ");
2418 Universe::verify(true);
2419 }
2420 reset(false);
2421 assert(_collectorState == Idling, "Collector state should "
2422 "have changed");
2423 break;
2424 case Precleaning:
2425 case AbortablePreclean:
2426 // Elide the preclean phase
2427 _collectorState = FinalMarking;
2428 break;
2429 default:
2430 ShouldNotReachHere();
2431 }
2432 if (TraceCMSState) {
2433 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2434 Thread::current(), _collectorState);
2435 }
2436 }
2437
2438 if (UseAdaptiveSizePolicy) {
2439 GenCollectedHeap* gch = GenCollectedHeap::heap();
2440 size_policy()->ms_collection_end(gch->gc_cause());
2441 }
2442
2443 if (VerifyAfterGC &&
2444 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2445 Universe::verify(true);
2446 }
2447 if (TraceCMSState) {
2448 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2449 " exiting collection CMS state %d",
2450 Thread::current(), _collectorState);
2451 }
2452 }
2453
2454 bool CMSCollector::waitForForegroundGC() {
2455 bool res = false;
2456 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2457 "CMS thread should have CMS token");
2458 // Block the foreground collector until the
2459 // background collectors decides whether to
2460 // yield.
2461 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2462 _foregroundGCShouldWait = true;
2463 if (_foregroundGCIsActive) {
2464 // The background collector yields to the
2465 // foreground collector and returns a value
2466 // indicating that it has yielded. The foreground
2467 // collector can proceed.
2468 res = true;
2469 _foregroundGCShouldWait = false;
2470 ConcurrentMarkSweepThread::clear_CMS_flag(
2471 ConcurrentMarkSweepThread::CMS_cms_has_token);
2472 ConcurrentMarkSweepThread::set_CMS_flag(
2473 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2474 // Get a possibly blocked foreground thread going
2475 CGC_lock->notify();
2476 if (TraceCMSState) {
2477 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2478 Thread::current(), _collectorState);
2479 }
2480 while (_foregroundGCIsActive) {
2481 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2482 }
2483 ConcurrentMarkSweepThread::set_CMS_flag(
2484 ConcurrentMarkSweepThread::CMS_cms_has_token);
2485 ConcurrentMarkSweepThread::clear_CMS_flag(
2486 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2487 }
2488 if (TraceCMSState) {
2489 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2490 Thread::current(), _collectorState);
2491 }
2492 return res;
2493 }
2494
2495 // Because of the need to lock the free lists and other structures in
2496 // the collector, common to all the generations that the collector is
2497 // collecting, we need the gc_prologues of individual CMS generations
2498 // delegate to their collector. It may have been simpler had the
2499 // current infrastructure allowed one to call a prologue on a
2500 // collector. In the absence of that we have the generation's
2501 // prologue delegate to the collector, which delegates back
2502 // some "local" work to a worker method in the individual generations
2503 // that it's responsible for collecting, while itself doing any
2504 // work common to all generations it's responsible for. A similar
2505 // comment applies to the gc_epilogue()'s.
2506 // The role of the varaible _between_prologue_and_epilogue is to
2507 // enforce the invocation protocol.
2508 void CMSCollector::gc_prologue(bool full) {
2509 // Call gc_prologue_work() for each CMSGen and PermGen that
2510 // we are responsible for.
2511
2512 // The following locking discipline assumes that we are only called
2513 // when the world is stopped.
2514 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2515
2516 // The CMSCollector prologue must call the gc_prologues for the
2517 // "generations" (including PermGen if any) that it's responsible
2518 // for.
2519
2520 assert( Thread::current()->is_VM_thread()
2521 || ( CMSScavengeBeforeRemark
2522 && Thread::current()->is_ConcurrentGC_thread()),
2523 "Incorrect thread type for prologue execution");
2524
2525 if (_between_prologue_and_epilogue) {
2526 // We have already been invoked; this is a gc_prologue delegation
2527 // from yet another CMS generation that we are responsible for, just
2528 // ignore it since all relevant work has already been done.
2529 return;
2530 }
2531
2532 // set a bit saying prologue has been called; cleared in epilogue
2533 _between_prologue_and_epilogue = true;
2534 // Claim locks for common data structures, then call gc_prologue_work()
2535 // for each CMSGen and PermGen that we are responsible for.
2536
2537 getFreelistLocks(); // gets free list locks on constituent spaces
2538 bitMapLock()->lock_without_safepoint_check();
2539
2540 // Should call gc_prologue_work() for all cms gens we are responsible for
2541 bool registerClosure = _collectorState >= Marking
2542 && _collectorState < Sweeping;
2543 ModUnionClosure* muc = ParallelGCThreads > 0 ? &_modUnionClosurePar
2544 : &_modUnionClosure;
2545 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2546 _permGen->gc_prologue_work(full, registerClosure, muc);
2547
2548 if (!full) {
2549 stats().record_gc0_begin();
2550 }
2551 }
2552
2553 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2554 // Delegate to CMScollector which knows how to coordinate between
2555 // this and any other CMS generations that it is responsible for
2556 // collecting.
2557 collector()->gc_prologue(full);
2558 }
2559
2560 // This is a "private" interface for use by this generation's CMSCollector.
2561 // Not to be called directly by any other entity (for instance,
2562 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2563 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2564 bool registerClosure, ModUnionClosure* modUnionClosure) {
2565 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2566 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2567 "Should be NULL");
2568 if (registerClosure) {
2569 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2570 }
2571 cmsSpace()->gc_prologue();
2572 // Clear stat counters
2573 NOT_PRODUCT(
2574 assert(_numObjectsPromoted == 0, "check");
2575 assert(_numWordsPromoted == 0, "check");
2576 if (Verbose && PrintGC) {
2577 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2578 SIZE_FORMAT" bytes concurrently",
2579 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2580 }
2581 _numObjectsAllocated = 0;
2582 _numWordsAllocated = 0;
2583 )
2584 }
2585
2586 void CMSCollector::gc_epilogue(bool full) {
2587 // The following locking discipline assumes that we are only called
2588 // when the world is stopped.
2589 assert(SafepointSynchronize::is_at_safepoint(),
2590 "world is stopped assumption");
2591
2592 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2593 // if linear allocation blocks need to be appropriately marked to allow the
2594 // the blocks to be parsable. We also check here whether we need to nudge the
2595 // CMS collector thread to start a new cycle (if it's not already active).
2596 assert( Thread::current()->is_VM_thread()
2597 || ( CMSScavengeBeforeRemark
2598 && Thread::current()->is_ConcurrentGC_thread()),
2599 "Incorrect thread type for epilogue execution");
2600
2601 if (!_between_prologue_and_epilogue) {
2602 // We have already been invoked; this is a gc_epilogue delegation
2603 // from yet another CMS generation that we are responsible for, just
2604 // ignore it since all relevant work has already been done.
2605 return;
2606 }
2607 assert(haveFreelistLocks(), "must have freelist locks");
2608 assert_lock_strong(bitMapLock());
2609
2610 _cmsGen->gc_epilogue_work(full);
2611 _permGen->gc_epilogue_work(full);
2612
2613 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2614 // in case sampling was not already enabled, enable it
2615 _start_sampling = true;
2616 }
2617 // reset _eden_chunk_array so sampling starts afresh
2618 _eden_chunk_index = 0;
2619
2620 size_t cms_used = _cmsGen->cmsSpace()->used();
2621 size_t perm_used = _permGen->cmsSpace()->used();
2622
2623 // update performance counters - this uses a special version of
2624 // update_counters() that allows the utilization to be passed as a
2625 // parameter, avoiding multiple calls to used().
2626 //
2627 _cmsGen->update_counters(cms_used);
2628 _permGen->update_counters(perm_used);
2629
2630 if (CMSIncrementalMode) {
2631 icms_update_allocation_limits();
2632 }
2633
2634 bitMapLock()->unlock();
2635 releaseFreelistLocks();
2636
2637 _between_prologue_and_epilogue = false; // ready for next cycle
2638 }
2639
2640 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2641 collector()->gc_epilogue(full);
2642
2643 // Also reset promotion tracking in par gc thread states.
2644 if (ParallelGCThreads > 0) {
2645 for (uint i = 0; i < ParallelGCThreads; i++) {
2646 _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2647 }
2648 }
2649 }
2650
2651 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2652 assert(!incremental_collection_failed(), "Should have been cleared");
2653 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2654 cmsSpace()->gc_epilogue();
2655 // Print stat counters
2656 NOT_PRODUCT(
2657 assert(_numObjectsAllocated == 0, "check");
2658 assert(_numWordsAllocated == 0, "check");
2659 if (Verbose && PrintGC) {
2660 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2661 SIZE_FORMAT" bytes",
2662 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2663 }
2664 _numObjectsPromoted = 0;
2665 _numWordsPromoted = 0;
2666 )
2667
2668 if (PrintGC && Verbose) {
2669 // Call down the chain in contiguous_available needs the freelistLock
2670 // so print this out before releasing the freeListLock.
2671 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2672 contiguous_available());
2673 }
2674 }
2675
2676 #ifndef PRODUCT
2677 bool CMSCollector::have_cms_token() {
2678 Thread* thr = Thread::current();
2679 if (thr->is_VM_thread()) {
2680 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2681 } else if (thr->is_ConcurrentGC_thread()) {
2682 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2683 } else if (thr->is_GC_task_thread()) {
2684 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2685 ParGCRareEvent_lock->owned_by_self();
2686 }
2687 return false;
2688 }
2689 #endif
2690
2691 // Check reachability of the given heap address in CMS generation,
2692 // treating all other generations as roots.
2693 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2694 // We could "guarantee" below, rather than assert, but i'll
2695 // leave these as "asserts" so that an adventurous debugger
2696 // could try this in the product build provided some subset of
2697 // the conditions were met, provided they were intersted in the
2698 // results and knew that the computation below wouldn't interfere
2699 // with other concurrent computations mutating the structures
2700 // being read or written.
2701 assert(SafepointSynchronize::is_at_safepoint(),
2702 "Else mutations in object graph will make answer suspect");
2703 assert(have_cms_token(), "Should hold cms token");
2704 assert(haveFreelistLocks(), "must hold free list locks");
2705 assert_lock_strong(bitMapLock());
2706
2707 // Clear the marking bit map array before starting, but, just
2708 // for kicks, first report if the given address is already marked
2709 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2710 _markBitMap.isMarked(addr) ? "" : " not");
2711
2712 if (verify_after_remark()) {
2713 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2714 bool result = verification_mark_bm()->isMarked(addr);
2715 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2716 result ? "IS" : "is NOT");
2717 return result;
2718 } else {
2719 gclog_or_tty->print_cr("Could not compute result");
2720 return false;
2721 }
2722 }
2723
2724 ////////////////////////////////////////////////////////
2725 // CMS Verification Support
2726 ////////////////////////////////////////////////////////
2727 // Following the remark phase, the following invariant
2728 // should hold -- each object in the CMS heap which is
2729 // marked in markBitMap() should be marked in the verification_mark_bm().
2730
2731 class VerifyMarkedClosure: public BitMapClosure {
2732 CMSBitMap* _marks;
2733 bool _failed;
2734
2735 public:
2736 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2737
2738 void do_bit(size_t offset) {
2739 HeapWord* addr = _marks->offsetToHeapWord(offset);
2740 if (!_marks->isMarked(addr)) {
2741 oop(addr)->print();
2742 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2743 _failed = true;
2744 }
2745 }
2746
2747 bool failed() { return _failed; }
2748 };
2749
2750 bool CMSCollector::verify_after_remark() {
2751 gclog_or_tty->print(" [Verifying CMS Marking... ");
2752 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2753 static bool init = false;
2754
2755 assert(SafepointSynchronize::is_at_safepoint(),
2756 "Else mutations in object graph will make answer suspect");
2757 assert(have_cms_token(),
2758 "Else there may be mutual interference in use of "
2759 " verification data structures");
2760 assert(_collectorState > Marking && _collectorState <= Sweeping,
2761 "Else marking info checked here may be obsolete");
2762 assert(haveFreelistLocks(), "must hold free list locks");
2763 assert_lock_strong(bitMapLock());
2764
2765
2766 // Allocate marking bit map if not already allocated
2767 if (!init) { // first time
2768 if (!verification_mark_bm()->allocate(_span)) {
2769 return false;
2770 }
2771 init = true;
2772 }
2773
2774 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2775
2776 // Turn off refs discovery -- so we will be tracing through refs.
2777 // This is as intended, because by this time
2778 // GC must already have cleared any refs that need to be cleared,
2779 // and traced those that need to be marked; moreover,
2780 // the marking done here is not going to intefere in any
2781 // way with the marking information used by GC.
2782 NoRefDiscovery no_discovery(ref_processor());
2783
2784 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2785
2786 // Clear any marks from a previous round
2787 verification_mark_bm()->clear_all();
2788 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2789 assert(overflow_list_is_empty(), "overflow list should be empty");
2790
2791 GenCollectedHeap* gch = GenCollectedHeap::heap();
2792 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2793 // Update the saved marks which may affect the root scans.
2794 gch->save_marks();
2795
2796 if (CMSRemarkVerifyVariant == 1) {
2797 // In this first variant of verification, we complete
2798 // all marking, then check if the new marks-verctor is
2799 // a subset of the CMS marks-vector.
2800 verify_after_remark_work_1();
2801 } else if (CMSRemarkVerifyVariant == 2) {
2802 // In this second variant of verification, we flag an error
2803 // (i.e. an object reachable in the new marks-vector not reachable
2804 // in the CMS marks-vector) immediately, also indicating the
2805 // identify of an object (A) that references the unmarked object (B) --
2806 // presumably, a mutation to A failed to be picked up by preclean/remark?
2807 verify_after_remark_work_2();
2808 } else {
2809 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2810 CMSRemarkVerifyVariant);
2811 }
2812 gclog_or_tty->print(" done] ");
2813 return true;
2814 }
2815
2816 void CMSCollector::verify_after_remark_work_1() {
2817 ResourceMark rm;
2818 HandleMark hm;
2819 GenCollectedHeap* gch = GenCollectedHeap::heap();
2820
2821 // Mark from roots one level into CMS
2822 MarkRefsIntoClosure notOlder(_span, verification_mark_bm(), true /* nmethods */);
2823 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2824
2825 gch->gen_process_strong_roots(_cmsGen->level(),
2826 true, // younger gens are roots
2827 true, // collecting perm gen
2828 SharedHeap::ScanningOption(roots_scanning_options()),
2829 NULL, ¬Older);
2830
2831 // Now mark from the roots
2832 assert(_revisitStack.isEmpty(), "Should be empty");
2833 MarkFromRootsClosure markFromRootsClosure(this, _span,
2834 verification_mark_bm(), verification_mark_stack(), &_revisitStack,
2835 false /* don't yield */, true /* verifying */);
2836 assert(_restart_addr == NULL, "Expected pre-condition");
2837 verification_mark_bm()->iterate(&markFromRootsClosure);
2838 while (_restart_addr != NULL) {
2839 // Deal with stack overflow: by restarting at the indicated
2840 // address.
2841 HeapWord* ra = _restart_addr;
2842 markFromRootsClosure.reset(ra);
2843 _restart_addr = NULL;
2844 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2845 }
2846 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2847 verify_work_stacks_empty();
2848 // Should reset the revisit stack above, since no class tree
2849 // surgery is forthcoming.
2850 _revisitStack.reset(); // throwing away all contents
2851
2852 // Marking completed -- now verify that each bit marked in
2853 // verification_mark_bm() is also marked in markBitMap(); flag all
2854 // errors by printing corresponding objects.
2855 VerifyMarkedClosure vcl(markBitMap());
2856 verification_mark_bm()->iterate(&vcl);
2857 if (vcl.failed()) {
2858 gclog_or_tty->print("Verification failed");
2859 Universe::heap()->print();
2860 fatal(" ... aborting");
2861 }
2862 }
2863
2864 void CMSCollector::verify_after_remark_work_2() {
2865 ResourceMark rm;
2866 HandleMark hm;
2867 GenCollectedHeap* gch = GenCollectedHeap::heap();
2868
2869 // Mark from roots one level into CMS
2870 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2871 markBitMap(), true /* nmethods */);
2872 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2873 gch->gen_process_strong_roots(_cmsGen->level(),
2874 true, // younger gens are roots
2875 true, // collecting perm gen
2876 SharedHeap::ScanningOption(roots_scanning_options()),
2877 NULL, ¬Older);
2878
2879 // Now mark from the roots
2880 assert(_revisitStack.isEmpty(), "Should be empty");
2881 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2882 verification_mark_bm(), markBitMap(), verification_mark_stack());
2883 assert(_restart_addr == NULL, "Expected pre-condition");
2884 verification_mark_bm()->iterate(&markFromRootsClosure);
2885 while (_restart_addr != NULL) {
2886 // Deal with stack overflow: by restarting at the indicated
2887 // address.
2888 HeapWord* ra = _restart_addr;
2889 markFromRootsClosure.reset(ra);
2890 _restart_addr = NULL;
2891 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2892 }
2893 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2894 verify_work_stacks_empty();
2895 // Should reset the revisit stack above, since no class tree
2896 // surgery is forthcoming.
2897 _revisitStack.reset(); // throwing away all contents
2898
2899 // Marking completed -- now verify that each bit marked in
2900 // verification_mark_bm() is also marked in markBitMap(); flag all
2901 // errors by printing corresponding objects.
2902 VerifyMarkedClosure vcl(markBitMap());
2903 verification_mark_bm()->iterate(&vcl);
2904 assert(!vcl.failed(), "Else verification above should not have succeeded");
2905 }
2906
2907 void ConcurrentMarkSweepGeneration::save_marks() {
2908 // delegate to CMS space
2909 cmsSpace()->save_marks();
2910 for (uint i = 0; i < ParallelGCThreads; i++) {
2911 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2912 }
2913 }
2914
2915 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2916 return cmsSpace()->no_allocs_since_save_marks();
2917 }
2918
2919 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2920 \
2921 void ConcurrentMarkSweepGeneration:: \
2922 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2923 cl->set_generation(this); \
2924 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2925 cl->reset_generation(); \
2926 save_marks(); \
2927 }
2928
2929 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2930
2931 void
2932 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
2933 {
2934 // Not currently implemented; need to do the following. -- ysr.
2935 // dld -- I think that is used for some sort of allocation profiler. So it
2936 // really means the objects allocated by the mutator since the last
2937 // GC. We could potentially implement this cheaply by recording only
2938 // the direct allocations in a side data structure.
2939 //
2940 // I think we probably ought not to be required to support these
2941 // iterations at any arbitrary point; I think there ought to be some
2942 // call to enable/disable allocation profiling in a generation/space,
2943 // and the iterator ought to return the objects allocated in the
2944 // gen/space since the enable call, or the last iterator call (which
2945 // will probably be at a GC.) That way, for gens like CM&S that would
2946 // require some extra data structure to support this, we only pay the
2947 // cost when it's in use...
2948 cmsSpace()->object_iterate_since_last_GC(blk);
2949 }
2950
2951 void
2952 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
2953 cl->set_generation(this);
2954 younger_refs_in_space_iterate(_cmsSpace, cl);
2955 cl->reset_generation();
2956 }
2957
2958 void
2959 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, OopClosure* cl) {
2960 if (freelistLock()->owned_by_self()) {
2961 Generation::oop_iterate(mr, cl);
2962 } else {
2963 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2964 Generation::oop_iterate(mr, cl);
2965 }
2966 }
2967
2968 void
2969 ConcurrentMarkSweepGeneration::oop_iterate(OopClosure* cl) {
2970 if (freelistLock()->owned_by_self()) {
2971 Generation::oop_iterate(cl);
2972 } else {
2973 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2974 Generation::oop_iterate(cl);
2975 }
2976 }
2977
2978 void
2979 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2980 if (freelistLock()->owned_by_self()) {
2981 Generation::object_iterate(cl);
2982 } else {
2983 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2984 Generation::object_iterate(cl);
2985 }
2986 }
2987
2988 void
2989 ConcurrentMarkSweepGeneration::pre_adjust_pointers() {
2990 }
2991
2992 void
2993 ConcurrentMarkSweepGeneration::post_compact() {
2994 }
2995
2996 void
2997 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2998 // Fix the linear allocation blocks to look like free blocks.
2999
3000 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3001 // are not called when the heap is verified during universe initialization and
3002 // at vm shutdown.
3003 if (freelistLock()->owned_by_self()) {
3004 cmsSpace()->prepare_for_verify();
3005 } else {
3006 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3007 cmsSpace()->prepare_for_verify();
3008 }
3009 }
3010
3011 void
3012 ConcurrentMarkSweepGeneration::verify(bool allow_dirty /* ignored */) {
3013 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3014 // are not called when the heap is verified during universe initialization and
3015 // at vm shutdown.
3016 if (freelistLock()->owned_by_self()) {
3017 cmsSpace()->verify(false /* ignored */);
3018 } else {
3019 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3020 cmsSpace()->verify(false /* ignored */);
3021 }
3022 }
3023
3024 void CMSCollector::verify(bool allow_dirty /* ignored */) {
3025 _cmsGen->verify(allow_dirty);
3026 _permGen->verify(allow_dirty);
3027 }
3028
3029 #ifndef PRODUCT
3030 bool CMSCollector::overflow_list_is_empty() const {
3031 assert(_num_par_pushes >= 0, "Inconsistency");
3032 if (_overflow_list == NULL) {
3033 assert(_num_par_pushes == 0, "Inconsistency");
3034 }
3035 return _overflow_list == NULL;
3036 }
3037
3038 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3039 // merely consolidate assertion checks that appear to occur together frequently.
3040 void CMSCollector::verify_work_stacks_empty() const {
3041 assert(_markStack.isEmpty(), "Marking stack should be empty");
3042 assert(overflow_list_is_empty(), "Overflow list should be empty");
3043 }
3044
3045 void CMSCollector::verify_overflow_empty() const {
3046 assert(overflow_list_is_empty(), "Overflow list should be empty");
3047 assert(no_preserved_marks(), "No preserved marks");
3048 }
3049 #endif // PRODUCT
3050
3051 void CMSCollector::setup_cms_unloading_and_verification_state() {
3052 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3053 || VerifyBeforeExit;
3054 const int rso = SharedHeap::SO_Symbols | SharedHeap::SO_Strings
3055 | SharedHeap::SO_CodeCache;
3056
3057 if (cms_should_unload_classes()) { // Should unload classes this cycle
3058 remove_root_scanning_option(rso); // Shrink the root set appropriately
3059 set_verifying(should_verify); // Set verification state for this cycle
3060 return; // Nothing else needs to be done at this time
3061 }
3062
3063 // Not unloading classes this cycle
3064 assert(!cms_should_unload_classes(), "Inconsitency!");
3065 if ((!verifying() || cms_unloaded_classes_last_cycle()) && should_verify) {
3066 // We were not verifying, or we _were_ unloading classes in the last cycle,
3067 // AND some verification options are enabled this cycle; in this case,
3068 // we must make sure that the deadness map is allocated if not already so,
3069 // and cleared (if already allocated previously --
3070 // CMSBitMap::sizeInBits() is used to determine if it's allocated).
3071 if (perm_gen_verify_bit_map()->sizeInBits() == 0) {
3072 if (!perm_gen_verify_bit_map()->allocate(_permGen->reserved())) {
3073 warning("Failed to allocate permanent generation verification CMS Bit Map;\n"
3074 "permanent generation verification disabled");
3075 return; // Note that we leave verification disabled, so we'll retry this
3076 // allocation next cycle. We _could_ remember this failure
3077 // and skip further attempts and permanently disable verification
3078 // attempts if that is considered more desirable.
3079 }
3080 assert(perm_gen_verify_bit_map()->covers(_permGen->reserved()),
3081 "_perm_gen_ver_bit_map inconsistency?");
3082 } else {
3083 perm_gen_verify_bit_map()->clear_all();
3084 }
3085 // Include symbols, strings and code cache elements to prevent their resurrection.
3086 add_root_scanning_option(rso);
3087 set_verifying(true);
3088 } else if (verifying() && !should_verify) {
3089 // We were verifying, but some verification flags got disabled.
3090 set_verifying(false);
3091 // Exclude symbols, strings and code cache elements from root scanning to
3092 // reduce IM and RM pauses.
3093 remove_root_scanning_option(rso);
3094 }
3095 }
3096
3097
3098 #ifndef PRODUCT
3099 HeapWord* CMSCollector::block_start(const void* p) const {
3100 const HeapWord* addr = (HeapWord*)p;
3101 if (_span.contains(p)) {
3102 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3103 return _cmsGen->cmsSpace()->block_start(p);
3104 } else {
3105 assert(_permGen->cmsSpace()->is_in_reserved(addr),
3106 "Inconsistent _span?");
3107 return _permGen->cmsSpace()->block_start(p);
3108 }
3109 }
3110 return NULL;
3111 }
3112 #endif
3113
3114 HeapWord*
3115 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3116 bool tlab,
3117 bool parallel) {
3118 assert(!tlab, "Can't deal with TLAB allocation");
3119 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3120 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3121 CMSExpansionCause::_satisfy_allocation);
3122 if (GCExpandToAllocateDelayMillis > 0) {
3123 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3124 }
3125 return have_lock_and_allocate(word_size, tlab);
3126 }
3127
3128 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3129 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3130 // to CardGeneration and share it...
3131 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3132 CMSExpansionCause::Cause cause)
3133 {
3134 assert_locked_or_safepoint(Heap_lock);
3135
3136 size_t aligned_bytes = ReservedSpace::page_align_size_up(bytes);
3137 size_t aligned_expand_bytes = ReservedSpace::page_align_size_up(expand_bytes);
3138 bool success = false;
3139 if (aligned_expand_bytes > aligned_bytes) {
3140 success = grow_by(aligned_expand_bytes);
3141 }
3142 if (!success) {
3143 success = grow_by(aligned_bytes);
3144 }
3145 if (!success) {
3146 size_t remaining_bytes = _virtual_space.uncommitted_size();
3147 if (remaining_bytes > 0) {
3148 success = grow_by(remaining_bytes);
3149 }
3150 }
3151 if (GC_locker::is_active()) {
3152 if (PrintGC && Verbose) {
3153 gclog_or_tty->print_cr("Garbage collection disabled, expanded heap instead");
3154 }
3155 }
3156 // remember why we expanded; this information is used
3157 // by shouldConcurrentCollect() when making decisions on whether to start
3158 // a new CMS cycle.
3159 if (success) {
3160 set_expansion_cause(cause);
3161 if (PrintGCDetails && Verbose) {
3162 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3163 CMSExpansionCause::to_string(cause));
3164 }
3165 }
3166 }
3167
3168 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3169 HeapWord* res = NULL;
3170 MutexLocker x(ParGCRareEvent_lock);
3171 while (true) {
3172 // Expansion by some other thread might make alloc OK now:
3173 res = ps->lab.alloc(word_sz);
3174 if (res != NULL) return res;
3175 // If there's not enough expansion space available, give up.
3176 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3177 return NULL;
3178 }
3179 // Otherwise, we try expansion.
3180 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3181 CMSExpansionCause::_allocate_par_lab);
3182 // Now go around the loop and try alloc again;
3183 // A competing par_promote might beat us to the expansion space,
3184 // so we may go around the loop again if promotion fails agaion.
3185 if (GCExpandToAllocateDelayMillis > 0) {
3186 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3187 }
3188 }
3189 }
3190
3191
3192 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3193 PromotionInfo* promo) {
3194 MutexLocker x(ParGCRareEvent_lock);
3195 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3196 while (true) {
3197 // Expansion by some other thread might make alloc OK now:
3198 if (promo->ensure_spooling_space()) {
3199 assert(promo->has_spooling_space(),
3200 "Post-condition of successful ensure_spooling_space()");
3201 return true;
3202 }
3203 // If there's not enough expansion space available, give up.
3204 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3205 return false;
3206 }
3207 // Otherwise, we try expansion.
3208 expand(refill_size_bytes, MinHeapDeltaBytes,
3209 CMSExpansionCause::_allocate_par_spooling_space);
3210 // Now go around the loop and try alloc again;
3211 // A competing allocation might beat us to the expansion space,
3212 // so we may go around the loop again if allocation fails again.
3213 if (GCExpandToAllocateDelayMillis > 0) {
3214 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3215 }
3216 }
3217 }
3218
3219
3220
3221 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3222 assert_locked_or_safepoint(Heap_lock);
3223 size_t size = ReservedSpace::page_align_size_down(bytes);
3224 if (size > 0) {
3225 shrink_by(size);
3226 }
3227 }
3228
3229 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3230 assert_locked_or_safepoint(Heap_lock);
3231 bool result = _virtual_space.expand_by(bytes);
3232 if (result) {
3233 HeapWord* old_end = _cmsSpace->end();
3234 size_t new_word_size =
3235 heap_word_size(_virtual_space.committed_size());
3236 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3237 _bts->resize(new_word_size); // resize the block offset shared array
3238 Universe::heap()->barrier_set()->resize_covered_region(mr);
3239 // Hmmmm... why doesn't CFLS::set_end verify locking?
3240 // This is quite ugly; FIX ME XXX
3241 _cmsSpace->assert_locked();
3242 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3243
3244 // update the space and generation capacity counters
3245 if (UsePerfData) {
3246 _space_counters->update_capacity();
3247 _gen_counters->update_all();
3248 }
3249
3250 if (Verbose && PrintGC) {
3251 size_t new_mem_size = _virtual_space.committed_size();
3252 size_t old_mem_size = new_mem_size - bytes;
3253 gclog_or_tty->print_cr("Expanding %s from %ldK by %ldK to %ldK",
3254 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3255 }
3256 }
3257 return result;
3258 }
3259
3260 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3261 assert_locked_or_safepoint(Heap_lock);
3262 bool success = true;
3263 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3264 if (remaining_bytes > 0) {
3265 success = grow_by(remaining_bytes);
3266 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3267 }
3268 return success;
3269 }
3270
3271 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3272 assert_locked_or_safepoint(Heap_lock);
3273 assert_lock_strong(freelistLock());
3274 // XXX Fix when compaction is implemented.
3275 warning("Shrinking of CMS not yet implemented");
3276 return;
3277 }
3278
3279
3280 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3281 // phases.
3282 class CMSPhaseAccounting: public StackObj {
3283 public:
3284 CMSPhaseAccounting(CMSCollector *collector,
3285 const char *phase,
3286 bool print_cr = true);
3287 ~CMSPhaseAccounting();
3288
3289 private:
3290 CMSCollector *_collector;
3291 const char *_phase;
3292 elapsedTimer _wallclock;
3293 bool _print_cr;
3294
3295 public:
3296 // Not MT-safe; so do not pass around these StackObj's
3297 // where they may be accessed by other threads.
3298 jlong wallclock_millis() {
3299 assert(_wallclock.is_active(), "Wall clock should not stop");
3300 _wallclock.stop(); // to record time
3301 jlong ret = _wallclock.milliseconds();
3302 _wallclock.start(); // restart
3303 return ret;
3304 }
3305 };
3306
3307 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3308 const char *phase,
3309 bool print_cr) :
3310 _collector(collector), _phase(phase), _print_cr(print_cr) {
3311
3312 if (PrintCMSStatistics != 0) {
3313 _collector->resetYields();
3314 }
3315 if (PrintGCDetails && PrintGCTimeStamps) {
3316 gclog_or_tty->date_stamp(PrintGCDateStamps);
3317 gclog_or_tty->stamp();
3318 gclog_or_tty->print_cr(": [%s-concurrent-%s-start]",
3319 _collector->cmsGen()->short_name(), _phase);
3320 }
3321 _collector->resetTimer();
3322 _wallclock.start();
3323 _collector->startTimer();
3324 }
3325
3326 CMSPhaseAccounting::~CMSPhaseAccounting() {
3327 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3328 _collector->stopTimer();
3329 _wallclock.stop();
3330 if (PrintGCDetails) {
3331 gclog_or_tty->date_stamp(PrintGCDateStamps);
3332 if (PrintGCTimeStamps) {
3333 gclog_or_tty->stamp();
3334 gclog_or_tty->print(": ");
3335 }
3336 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3337 _collector->cmsGen()->short_name(),
3338 _phase, _collector->timerValue(), _wallclock.seconds());
3339 if (_print_cr) {
3340 gclog_or_tty->print_cr("");
3341 }
3342 if (PrintCMSStatistics != 0) {
3343 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3344 _collector->yields());
3345 }
3346 }
3347 }
3348
3349 // CMS work
3350
3351 // Checkpoint the roots into this generation from outside
3352 // this generation. [Note this initial checkpoint need only
3353 // be approximate -- we'll do a catch up phase subsequently.]
3354 void CMSCollector::checkpointRootsInitial(bool asynch) {
3355 assert(_collectorState == InitialMarking, "Wrong collector state");
3356 check_correct_thread_executing();
3357 ReferenceProcessor* rp = ref_processor();
3358 SpecializationStats::clear();
3359 assert(_restart_addr == NULL, "Control point invariant");
3360 if (asynch) {
3361 // acquire locks for subsequent manipulations
3362 MutexLockerEx x(bitMapLock(),
3363 Mutex::_no_safepoint_check_flag);
3364 checkpointRootsInitialWork(asynch);
3365 rp->verify_no_references_recorded();
3366 rp->enable_discovery(); // enable ("weak") refs discovery
3367 _collectorState = Marking;
3368 } else {
3369 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3370 // which recognizes if we are a CMS generation, and doesn't try to turn on
3371 // discovery; verify that they aren't meddling.
3372 assert(!rp->discovery_is_atomic(),
3373 "incorrect setting of discovery predicate");
3374 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3375 "ref discovery for this generation kind");
3376 // already have locks
3377 checkpointRootsInitialWork(asynch);
3378 rp->enable_discovery(); // now enable ("weak") refs discovery
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(TraceTime t("\ncheckpointRootsInitialWork",
3402 PrintGCDetails && Verbose, true, gclog_or_tty);)
3403 if (UseAdaptiveSizePolicy) {
3404 size_policy()->checkpoint_roots_initial_begin();
3405 }
3406
3407 // Reset all the PLAB chunk arrays if necessary.
3408 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3409 reset_survivor_plab_arrays();
3410 }
3411
3412 ResourceMark rm;
3413 HandleMark hm;
3414
3415 FalseClosure falseClosure;
3416 // In the case of a synchronous collection, we will elide the
3417 // remark step, so it's important to catch all the nmethod oops
3418 // in this step; hence the last argument to the constrcutor below.
3419 MarkRefsIntoClosure notOlder(_span, &_markBitMap, !asynch /* nmethods */);
3420 GenCollectedHeap* gch = GenCollectedHeap::heap();
3421
3422 verify_work_stacks_empty();
3423 verify_overflow_empty();
3424
3425 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3426 // Update the saved marks which may affect the root scans.
3427 gch->save_marks();
3428
3429 // weak reference processing has not started yet.
3430 ref_processor()->set_enqueuing_is_done(false);
3431
3432 {
3433 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3434 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3435 gch->gen_process_strong_roots(_cmsGen->level(),
3436 true, // younger gens are roots
3437 true, // collecting perm gen
3438 SharedHeap::ScanningOption(roots_scanning_options()),
3439 NULL, ¬Older);
3440 }
3441
3442 // Clear mod-union table; it will be dirtied in the prologue of
3443 // CMS generation per each younger generation collection.
3444
3445 assert(_modUnionTable.isAllClear(),
3446 "Was cleared in most recent final checkpoint phase"
3447 " or no bits are set in the gc_prologue before the start of the next "
3448 "subsequent marking phase.");
3449
3450 // Temporarily disabled, since pre/post-consumption closures don't
3451 // care about precleaned cards
3452 #if 0
3453 {
3454 MemRegion mr = MemRegion((HeapWord*)_virtual_space.low(),
3455 (HeapWord*)_virtual_space.high());
3456 _ct->ct_bs()->preclean_dirty_cards(mr);
3457 }
3458 #endif
3459
3460 // Save the end of the used_region of the constituent generations
3461 // to be used to limit the extent of sweep in each generation.
3462 save_sweep_limits();
3463 if (UseAdaptiveSizePolicy) {
3464 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3465 }
3466 verify_overflow_empty();
3467 }
3468
3469 bool CMSCollector::markFromRoots(bool asynch) {
3470 // we might be tempted to assert that:
3471 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3472 // "inconsistent argument?");
3473 // However that wouldn't be right, because it's possible that
3474 // a safepoint is indeed in progress as a younger generation
3475 // stop-the-world GC happens even as we mark in this generation.
3476 assert(_collectorState == Marking, "inconsistent state?");
3477 check_correct_thread_executing();
3478 verify_overflow_empty();
3479
3480 bool res;
3481 if (asynch) {
3482
3483 // Start the timers for adaptive size policy for the concurrent phases
3484 // Do it here so that the foreground MS can use the concurrent
3485 // timer since a foreground MS might has the sweep done concurrently
3486 // or STW.
3487 if (UseAdaptiveSizePolicy) {
3488 size_policy()->concurrent_marking_begin();
3489 }
3490
3491 // Weak ref discovery note: We may be discovering weak
3492 // refs in this generation concurrent (but interleaved) with
3493 // weak ref discovery by a younger generation collector.
3494
3495 CMSTokenSyncWithLocks ts(true, bitMapLock());
3496 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3497 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3498 res = markFromRootsWork(asynch);
3499 if (res) {
3500 _collectorState = Precleaning;
3501 } else { // We failed and a foreground collection wants to take over
3502 assert(_foregroundGCIsActive, "internal state inconsistency");
3503 assert(_restart_addr == NULL, "foreground will restart from scratch");
3504 if (PrintGCDetails) {
3505 gclog_or_tty->print_cr("bailing out to foreground collection");
3506 }
3507 }
3508 if (UseAdaptiveSizePolicy) {
3509 size_policy()->concurrent_marking_end();
3510 }
3511 } else {
3512 assert(SafepointSynchronize::is_at_safepoint(),
3513 "inconsistent with asynch == false");
3514 if (UseAdaptiveSizePolicy) {
3515 size_policy()->ms_collection_marking_begin();
3516 }
3517 // already have locks
3518 res = markFromRootsWork(asynch);
3519 _collectorState = FinalMarking;
3520 if (UseAdaptiveSizePolicy) {
3521 GenCollectedHeap* gch = GenCollectedHeap::heap();
3522 size_policy()->ms_collection_marking_end(gch->gc_cause());
3523 }
3524 }
3525 verify_overflow_empty();
3526 return res;
3527 }
3528
3529 bool CMSCollector::markFromRootsWork(bool asynch) {
3530 // iterate over marked bits in bit map, doing a full scan and mark
3531 // from these roots using the following algorithm:
3532 // . if oop is to the right of the current scan pointer,
3533 // mark corresponding bit (we'll process it later)
3534 // . else (oop is to left of current scan pointer)
3535 // push oop on marking stack
3536 // . drain the marking stack
3537
3538 // Note that when we do a marking step we need to hold the
3539 // bit map lock -- recall that direct allocation (by mutators)
3540 // and promotion (by younger generation collectors) is also
3541 // marking the bit map. [the so-called allocate live policy.]
3542 // Because the implementation of bit map marking is not
3543 // robust wrt simultaneous marking of bits in the same word,
3544 // we need to make sure that there is no such interference
3545 // between concurrent such updates.
3546
3547 // already have locks
3548 assert_lock_strong(bitMapLock());
3549
3550 // Clear the revisit stack, just in case there are any
3551 // obsolete contents from a short-circuited previous CMS cycle.
3552 _revisitStack.reset();
3553 verify_work_stacks_empty();
3554 verify_overflow_empty();
3555 assert(_revisitStack.isEmpty(), "tabula rasa");
3556
3557 bool result = false;
3558 if (CMSConcurrentMTEnabled && ParallelCMSThreads > 0) {
3559 result = do_marking_mt(asynch);
3560 } else {
3561 result = do_marking_st(asynch);
3562 }
3563 return result;
3564 }
3565
3566 // Forward decl
3567 class CMSConcMarkingTask;
3568
3569 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3570 CMSCollector* _collector;
3571 CMSConcMarkingTask* _task;
3572 bool _yield;
3573 protected:
3574 virtual void yield();
3575 public:
3576 // "n_threads" is the number of threads to be terminated.
3577 // "queue_set" is a set of work queues of other threads.
3578 // "collector" is the CMS collector associated with this task terminator.
3579 // "yield" indicates whether we need the gang as a whole to yield.
3580 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set,
3581 CMSCollector* collector, bool yield) :
3582 ParallelTaskTerminator(n_threads, queue_set),
3583 _collector(collector),
3584 _yield(yield) { }
3585
3586 void set_task(CMSConcMarkingTask* task) {
3587 _task = task;
3588 }
3589 };
3590
3591 // MT Concurrent Marking Task
3592 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3593 CMSCollector* _collector;
3594 YieldingFlexibleWorkGang* _workers; // the whole gang
3595 int _n_workers; // requested/desired # workers
3596 bool _asynch;
3597 bool _result;
3598 CompactibleFreeListSpace* _cms_space;
3599 CompactibleFreeListSpace* _perm_space;
3600 HeapWord* _global_finger;
3601 HeapWord* _restart_addr;
3602
3603 // Exposed here for yielding support
3604 Mutex* const _bit_map_lock;
3605
3606 // The per thread work queues, available here for stealing
3607 OopTaskQueueSet* _task_queues;
3608 CMSConcMarkingTerminator _term;
3609
3610 public:
3611 CMSConcMarkingTask(CMSCollector* collector,
3612 CompactibleFreeListSpace* cms_space,
3613 CompactibleFreeListSpace* perm_space,
3614 bool asynch, int n_workers,
3615 YieldingFlexibleWorkGang* workers,
3616 OopTaskQueueSet* task_queues):
3617 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3618 _collector(collector),
3619 _cms_space(cms_space),
3620 _perm_space(perm_space),
3621 _asynch(asynch), _n_workers(n_workers), _result(true),
3622 _workers(workers), _task_queues(task_queues),
3623 _term(n_workers, task_queues, _collector, asynch),
3624 _bit_map_lock(collector->bitMapLock())
3625 {
3626 assert(n_workers <= workers->total_workers(),
3627 "Else termination won't work correctly today"); // XXX FIX ME!
3628 _requested_size = n_workers;
3629 _term.set_task(this);
3630 assert(_cms_space->bottom() < _perm_space->bottom(),
3631 "Finger incorrectly initialized below");
3632 _restart_addr = _global_finger = _cms_space->bottom();
3633 }
3634
3635
3636 OopTaskQueueSet* task_queues() { return _task_queues; }
3637
3638 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3639
3640 HeapWord** global_finger_addr() { return &_global_finger; }
3641
3642 CMSConcMarkingTerminator* terminator() { return &_term; }
3643
3644 void work(int i);
3645
3646 virtual void coordinator_yield(); // stuff done by coordinator
3647 bool result() { return _result; }
3648
3649 void reset(HeapWord* ra) {
3650 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3651 assert(_global_finger >= _perm_space->end(), "Postcondition of ::work(i)");
3652 assert(ra < _perm_space->end(), "ra too large");
3653 _restart_addr = _global_finger = ra;
3654 _term.reset_for_reuse();
3655 }
3656
3657 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3658 OopTaskQueue* work_q);
3659
3660 private:
3661 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3662 void do_work_steal(int i);
3663 void bump_global_finger(HeapWord* f);
3664 };
3665
3666 void CMSConcMarkingTerminator::yield() {
3667 if (ConcurrentMarkSweepThread::should_yield() &&
3668 !_collector->foregroundGCIsActive() &&
3669 _yield) {
3670 _task->yield();
3671 } else {
3672 ParallelTaskTerminator::yield();
3673 }
3674 }
3675
3676 ////////////////////////////////////////////////////////////////
3677 // Concurrent Marking Algorithm Sketch
3678 ////////////////////////////////////////////////////////////////
3679 // Until all tasks exhausted (both spaces):
3680 // -- claim next available chunk
3681 // -- bump global finger via CAS
3682 // -- find first object that starts in this chunk
3683 // and start scanning bitmap from that position
3684 // -- scan marked objects for oops
3685 // -- CAS-mark target, and if successful:
3686 // . if target oop is above global finger (volatile read)
3687 // nothing to do
3688 // . if target oop is in chunk and above local finger
3689 // then nothing to do
3690 // . else push on work-queue
3691 // -- Deal with possible overflow issues:
3692 // . local work-queue overflow causes stuff to be pushed on
3693 // global (common) overflow queue
3694 // . always first empty local work queue
3695 // . then get a batch of oops from global work queue if any
3696 // . then do work stealing
3697 // -- When all tasks claimed (both spaces)
3698 // and local work queue empty,
3699 // then in a loop do:
3700 // . check global overflow stack; steal a batch of oops and trace
3701 // . try to steal from other threads oif GOS is empty
3702 // . if neither is available, offer termination
3703 // -- Terminate and return result
3704 //
3705 void CMSConcMarkingTask::work(int i) {
3706 elapsedTimer _timer;
3707 ResourceMark rm;
3708 HandleMark hm;
3709
3710 DEBUG_ONLY(_collector->verify_overflow_empty();)
3711
3712 // Before we begin work, our work queue should be empty
3713 assert(work_queue(i)->size() == 0, "Expected to be empty");
3714 // Scan the bitmap covering _cms_space, tracing through grey objects.
3715 _timer.start();
3716 do_scan_and_mark(i, _cms_space);
3717 _timer.stop();
3718 if (PrintCMSStatistics != 0) {
3719 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3720 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3721 }
3722
3723 // ... do the same for the _perm_space
3724 _timer.reset();
3725 _timer.start();
3726 do_scan_and_mark(i, _perm_space);
3727 _timer.stop();
3728 if (PrintCMSStatistics != 0) {
3729 gclog_or_tty->print_cr("Finished perm space scanning in %dth thread: %3.3f sec",
3730 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3731 }
3732
3733 // ... do work stealing
3734 _timer.reset();
3735 _timer.start();
3736 do_work_steal(i);
3737 _timer.stop();
3738 if (PrintCMSStatistics != 0) {
3739 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3740 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3741 }
3742 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3743 assert(work_queue(i)->size() == 0, "Should have been emptied");
3744 // Note that under the current task protocol, the
3745 // following assertion is true even of the spaces
3746 // expanded since the completion of the concurrent
3747 // marking. XXX This will likely change under a strict
3748 // ABORT semantics.
3749 assert(_global_finger > _cms_space->end() &&
3750 _global_finger >= _perm_space->end(),
3751 "All tasks have been completed");
3752 DEBUG_ONLY(_collector->verify_overflow_empty();)
3753 }
3754
3755 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3756 HeapWord* read = _global_finger;
3757 HeapWord* cur = read;
3758 while (f > read) {
3759 cur = read;
3760 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3761 if (cur == read) {
3762 // our cas succeeded
3763 assert(_global_finger >= f, "protocol consistency");
3764 break;
3765 }
3766 }
3767 }
3768
3769 // This is really inefficient, and should be redone by
3770 // using (not yet available) block-read and -write interfaces to the
3771 // stack and the work_queue. XXX FIX ME !!!
3772 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3773 OopTaskQueue* work_q) {
3774 // Fast lock-free check
3775 if (ovflw_stk->length() == 0) {
3776 return false;
3777 }
3778 assert(work_q->size() == 0, "Shouldn't steal");
3779 MutexLockerEx ml(ovflw_stk->par_lock(),
3780 Mutex::_no_safepoint_check_flag);
3781 // Grab up to 1/4 the size of the work queue
3782 size_t num = MIN2((size_t)work_q->max_elems()/4,
3783 (size_t)ParGCDesiredObjsFromOverflowList);
3784 num = MIN2(num, ovflw_stk->length());
3785 for (int i = (int) num; i > 0; i--) {
3786 oop cur = ovflw_stk->pop();
3787 assert(cur != NULL, "Counted wrong?");
3788 work_q->push(cur);
3789 }
3790 return num > 0;
3791 }
3792
3793 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3794 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3795 int n_tasks = pst->n_tasks();
3796 // We allow that there may be no tasks to do here because
3797 // we are restarting after a stack overflow.
3798 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3799 int nth_task = 0;
3800
3801 HeapWord* aligned_start = sp->bottom();
3802 if (sp->used_region().contains(_restart_addr)) {
3803 // Align down to a card boundary for the start of 0th task
3804 // for this space.
3805 aligned_start =
3806 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3807 CardTableModRefBS::card_size);
3808 }
3809
3810 size_t chunk_size = sp->marking_task_size();
3811 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3812 // Having claimed the nth task in this space,
3813 // compute the chunk that it corresponds to:
3814 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3815 aligned_start + (nth_task+1)*chunk_size);
3816 // Try and bump the global finger via a CAS;
3817 // note that we need to do the global finger bump
3818 // _before_ taking the intersection below, because
3819 // the task corresponding to that region will be
3820 // deemed done even if the used_region() expands
3821 // because of allocation -- as it almost certainly will
3822 // during start-up while the threads yield in the
3823 // closure below.
3824 HeapWord* finger = span.end();
3825 bump_global_finger(finger); // atomically
3826 // There are null tasks here corresponding to chunks
3827 // beyond the "top" address of the space.
3828 span = span.intersection(sp->used_region());
3829 if (!span.is_empty()) { // Non-null task
3830 HeapWord* prev_obj;
3831 assert(!span.contains(_restart_addr) || nth_task == 0,
3832 "Inconsistency");
3833 if (nth_task == 0) {
3834 // For the 0th task, we'll not need to compute a block_start.
3835 if (span.contains(_restart_addr)) {
3836 // In the case of a restart because of stack overflow,
3837 // we might additionally skip a chunk prefix.
3838 prev_obj = _restart_addr;
3839 } else {
3840 prev_obj = span.start();
3841 }
3842 } else {
3843 // We want to skip the first object because
3844 // the protocol is to scan any object in its entirety
3845 // that _starts_ in this span; a fortiori, any
3846 // object starting in an earlier span is scanned
3847 // as part of an earlier claimed task.
3848 // Below we use the "careful" version of block_start
3849 // so we do not try to navigate uninitialized objects.
3850 prev_obj = sp->block_start_careful(span.start());
3851 // Below we use a variant of block_size that uses the
3852 // Printezis bits to avoid waiting for allocated
3853 // objects to become initialized/parsable.
3854 while (prev_obj < span.start()) {
3855 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3856 if (sz > 0) {
3857 prev_obj += sz;
3858 } else {
3859 // In this case we may end up doing a bit of redundant
3860 // scanning, but that appears unavoidable, short of
3861 // locking the free list locks; see bug 6324141.
3862 break;
3863 }
3864 }
3865 }
3866 if (prev_obj < span.end()) {
3867 MemRegion my_span = MemRegion(prev_obj, span.end());
3868 // Do the marking work within a non-empty span --
3869 // the last argument to the constructor indicates whether the
3870 // iteration should be incremental with periodic yields.
3871 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3872 &_collector->_markBitMap,
3873 work_queue(i),
3874 &_collector->_markStack,
3875 &_collector->_revisitStack,
3876 _asynch);
3877 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3878 } // else nothing to do for this task
3879 } // else nothing to do for this task
3880 }
3881 // We'd be tempted to assert here that since there are no
3882 // more tasks left to claim in this space, the global_finger
3883 // must exceed space->top() and a fortiori space->end(). However,
3884 // that would not quite be correct because the bumping of
3885 // global_finger occurs strictly after the claiming of a task,
3886 // so by the time we reach here the global finger may not yet
3887 // have been bumped up by the thread that claimed the last
3888 // task.
3889 pst->all_tasks_completed();
3890 }
3891
3892 class Par_ConcMarkingClosure: public OopClosure {
3893 CMSCollector* _collector;
3894 MemRegion _span;
3895 CMSBitMap* _bit_map;
3896 CMSMarkStack* _overflow_stack;
3897 CMSMarkStack* _revisit_stack; // XXXXXX Check proper use
3898 OopTaskQueue* _work_queue;
3899
3900 public:
3901 Par_ConcMarkingClosure(CMSCollector* collector, OopTaskQueue* work_queue,
3902 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3903 _collector(collector),
3904 _span(_collector->_span),
3905 _work_queue(work_queue),
3906 _bit_map(bit_map),
3907 _overflow_stack(overflow_stack) { } // need to initialize revisit stack etc.
3908
3909 void do_oop(oop* p);
3910 void trim_queue(size_t max);
3911 void handle_stack_overflow(HeapWord* lost);
3912 };
3913
3914 // Grey object scanning during work stealing phase --
3915 // the salient assumption here is that any references
3916 // that are in these stolen objects being scanned must
3917 // already have been initialized (else they would not have
3918 // been published), so we do not need to check for
3919 // uninitialized objects before pushing here.
3920 void Par_ConcMarkingClosure::do_oop(oop* p) {
3921 oop this_oop = *p;
3922 assert(this_oop->is_oop_or_null(true),
3923 "expected an oop or NULL");
3924 HeapWord* addr = (HeapWord*)this_oop;
3925 // Check if oop points into the CMS generation
3926 // and is not marked
3927 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3928 // a white object ...
3929 // If we manage to "claim" the object, by being the
3930 // first thread to mark it, then we push it on our
3931 // marking stack
3932 if (_bit_map->par_mark(addr)) { // ... now grey
3933 // push on work queue (grey set)
3934 bool simulate_overflow = false;
3935 NOT_PRODUCT(
3936 if (CMSMarkStackOverflowALot &&
3937 _collector->simulate_overflow()) {
3938 // simulate a stack overflow
3939 simulate_overflow = true;
3940 }
3941 )
3942 if (simulate_overflow ||
3943 !(_work_queue->push(this_oop) || _overflow_stack->par_push(this_oop))) {
3944 // stack overflow
3945 if (PrintCMSStatistics != 0) {
3946 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3947 SIZE_FORMAT, _overflow_stack->capacity());
3948 }
3949 // We cannot assert that the overflow stack is full because
3950 // it may have been emptied since.
3951 assert(simulate_overflow ||
3952 _work_queue->size() == _work_queue->max_elems(),
3953 "Else push should have succeeded");
3954 handle_stack_overflow(addr);
3955 }
3956 } // Else, some other thread got there first
3957 }
3958 }
3959
3960 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3961 while (_work_queue->size() > max) {
3962 oop new_oop;
3963 if (_work_queue->pop_local(new_oop)) {
3964 assert(new_oop->is_oop(), "Should be an oop");
3965 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3966 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3967 assert(new_oop->is_parsable(), "Should be parsable");
3968 new_oop->oop_iterate(this); // do_oop() above
3969 }
3970 }
3971 }
3972
3973 // Upon stack overflow, we discard (part of) the stack,
3974 // remembering the least address amongst those discarded
3975 // in CMSCollector's _restart_address.
3976 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3977 // We need to do this under a mutex to prevent other
3978 // workers from interfering with the work done below.
3979 MutexLockerEx ml(_overflow_stack->par_lock(),
3980 Mutex::_no_safepoint_check_flag);
3981 // Remember the least grey address discarded
3982 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3983 _collector->lower_restart_addr(ra);
3984 _overflow_stack->reset(); // discard stack contents
3985 _overflow_stack->expand(); // expand the stack if possible
3986 }
3987
3988
3989 void CMSConcMarkingTask::do_work_steal(int i) {
3990 OopTaskQueue* work_q = work_queue(i);
3991 oop obj_to_scan;
3992 CMSBitMap* bm = &(_collector->_markBitMap);
3993 CMSMarkStack* ovflw = &(_collector->_markStack);
3994 int* seed = _collector->hash_seed(i);
3995 Par_ConcMarkingClosure cl(_collector, work_q, bm, ovflw);
3996 while (true) {
3997 cl.trim_queue(0);
3998 assert(work_q->size() == 0, "Should have been emptied above");
3999 if (get_work_from_overflow_stack(ovflw, work_q)) {
4000 // Can't assert below because the work obtained from the
4001 // overflow stack may already have been stolen from us.
4002 // assert(work_q->size() > 0, "Work from overflow stack");
4003 continue;
4004 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4005 assert(obj_to_scan->is_oop(), "Should be an oop");
4006 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4007 obj_to_scan->oop_iterate(&cl);
4008 } else if (terminator()->offer_termination()) {
4009 assert(work_q->size() == 0, "Impossible!");
4010 break;
4011 }
4012 }
4013 }
4014
4015 // This is run by the CMS (coordinator) thread.
4016 void CMSConcMarkingTask::coordinator_yield() {
4017 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4018 "CMS thread should hold CMS token");
4019
4020 // First give up the locks, then yield, then re-lock
4021 // We should probably use a constructor/destructor idiom to
4022 // do this unlock/lock or modify the MutexUnlocker class to
4023 // serve our purpose. XXX
4024 assert_lock_strong(_bit_map_lock);
4025 _bit_map_lock->unlock();
4026 ConcurrentMarkSweepThread::desynchronize(true);
4027 ConcurrentMarkSweepThread::acknowledge_yield_request();
4028 _collector->stopTimer();
4029 if (PrintCMSStatistics != 0) {
4030 _collector->incrementYields();
4031 }
4032 _collector->icms_wait();
4033
4034 // It is possible for whichever thread initiated the yield request
4035 // not to get a chance to wake up and take the bitmap lock between
4036 // this thread releasing it and reacquiring it. So, while the
4037 // should_yield() flag is on, let's sleep for a bit to give the
4038 // other thread a chance to wake up. The limit imposed on the number
4039 // of iterations is defensive, to avoid any unforseen circumstances
4040 // putting us into an infinite loop. Since it's always been this
4041 // (coordinator_yield()) method that was observed to cause the
4042 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4043 // which is by default non-zero. For the other seven methods that
4044 // also perform the yield operation, as are using a different
4045 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4046 // can enable the sleeping for those methods too, if necessary.
4047 // See 6442774.
4048 //
4049 // We really need to reconsider the synchronization between the GC
4050 // thread and the yield-requesting threads in the future and we
4051 // should really use wait/notify, which is the recommended
4052 // way of doing this type of interaction. Additionally, we should
4053 // consolidate the eight methods that do the yield operation and they
4054 // are almost identical into one for better maintenability and
4055 // readability. See 6445193.
4056 //
4057 // Tony 2006.06.29
4058 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4059 ConcurrentMarkSweepThread::should_yield() &&
4060 !CMSCollector::foregroundGCIsActive(); ++i) {
4061 os::sleep(Thread::current(), 1, false);
4062 ConcurrentMarkSweepThread::acknowledge_yield_request();
4063 }
4064
4065 ConcurrentMarkSweepThread::synchronize(true);
4066 _bit_map_lock->lock_without_safepoint_check();
4067 _collector->startTimer();
4068 }
4069
4070 bool CMSCollector::do_marking_mt(bool asynch) {
4071 assert(ParallelCMSThreads > 0 && conc_workers() != NULL, "precondition");
4072 // In the future this would be determined ergonomically, based
4073 // on #cpu's, # active mutator threads (and load), and mutation rate.
4074 int num_workers = ParallelCMSThreads;
4075
4076 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4077 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
4078
4079 CMSConcMarkingTask tsk(this, cms_space, perm_space,
4080 asynch, num_workers /* number requested XXX */,
4081 conc_workers(), task_queues());
4082
4083 // Since the actual number of workers we get may be different
4084 // from the number we requested above, do we need to do anything different
4085 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4086 // class?? XXX
4087 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4088 perm_space->initialize_sequential_subtasks_for_marking(num_workers);
4089
4090 // Refs discovery is already non-atomic.
4091 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4092 // Mutate the Refs discovery so it is MT during the
4093 // multi-threaded marking phase.
4094 ReferenceProcessorMTMutator mt(ref_processor(), num_workers > 1);
4095
4096 conc_workers()->start_task(&tsk);
4097 while (tsk.yielded()) {
4098 tsk.coordinator_yield();
4099 conc_workers()->continue_task(&tsk);
4100 }
4101 // If the task was aborted, _restart_addr will be non-NULL
4102 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4103 while (_restart_addr != NULL) {
4104 // XXX For now we do not make use of ABORTED state and have not
4105 // yet implemented the right abort semantics (even in the original
4106 // single-threaded CMS case). That needs some more investigation
4107 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4108 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4109 // If _restart_addr is non-NULL, a marking stack overflow
4110 // occured; we need to do a fresh marking iteration from the
4111 // indicated restart address.
4112 if (_foregroundGCIsActive && asynch) {
4113 // We may be running into repeated stack overflows, having
4114 // reached the limit of the stack size, while making very
4115 // slow forward progress. It may be best to bail out and
4116 // let the foreground collector do its job.
4117 // Clear _restart_addr, so that foreground GC
4118 // works from scratch. This avoids the headache of
4119 // a "rescan" which would otherwise be needed because
4120 // of the dirty mod union table & card table.
4121 _restart_addr = NULL;
4122 return false;
4123 }
4124 // Adjust the task to restart from _restart_addr
4125 tsk.reset(_restart_addr);
4126 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4127 _restart_addr);
4128 perm_space->initialize_sequential_subtasks_for_marking(num_workers,
4129 _restart_addr);
4130 _restart_addr = NULL;
4131 // Get the workers going again
4132 conc_workers()->start_task(&tsk);
4133 while (tsk.yielded()) {
4134 tsk.coordinator_yield();
4135 conc_workers()->continue_task(&tsk);
4136 }
4137 }
4138 assert(tsk.completed(), "Inconsistency");
4139 assert(tsk.result() == true, "Inconsistency");
4140 return true;
4141 }
4142
4143 bool CMSCollector::do_marking_st(bool asynch) {
4144 ResourceMark rm;
4145 HandleMark hm;
4146
4147 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4148 &_markStack, &_revisitStack, CMSYield && asynch);
4149 // the last argument to iterate indicates whether the iteration
4150 // should be incremental with periodic yields.
4151 _markBitMap.iterate(&markFromRootsClosure);
4152 // If _restart_addr is non-NULL, a marking stack overflow
4153 // occured; we need to do a fresh iteration from the
4154 // indicated restart address.
4155 while (_restart_addr != NULL) {
4156 if (_foregroundGCIsActive && asynch) {
4157 // We may be running into repeated stack overflows, having
4158 // reached the limit of the stack size, while making very
4159 // slow forward progress. It may be best to bail out and
4160 // let the foreground collector do its job.
4161 // Clear _restart_addr, so that foreground GC
4162 // works from scratch. This avoids the headache of
4163 // a "rescan" which would otherwise be needed because
4164 // of the dirty mod union table & card table.
4165 _restart_addr = NULL;
4166 return false; // indicating failure to complete marking
4167 }
4168 // Deal with stack overflow:
4169 // we restart marking from _restart_addr
4170 HeapWord* ra = _restart_addr;
4171 markFromRootsClosure.reset(ra);
4172 _restart_addr = NULL;
4173 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4174 }
4175 return true;
4176 }
4177
4178 void CMSCollector::preclean() {
4179 check_correct_thread_executing();
4180 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4181 verify_work_stacks_empty();
4182 verify_overflow_empty();
4183 _abort_preclean = false;
4184 if (CMSPrecleaningEnabled) {
4185 _eden_chunk_index = 0;
4186 size_t used = get_eden_used();
4187 size_t capacity = get_eden_capacity();
4188 // Don't start sampling unless we will get sufficiently
4189 // many samples.
4190 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4191 * CMSScheduleRemarkEdenPenetration)) {
4192 _start_sampling = true;
4193 } else {
4194 _start_sampling = false;
4195 }
4196 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4197 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4198 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4199 }
4200 CMSTokenSync x(true); // is cms thread
4201 if (CMSPrecleaningEnabled) {
4202 sample_eden();
4203 _collectorState = AbortablePreclean;
4204 } else {
4205 _collectorState = FinalMarking;
4206 }
4207 verify_work_stacks_empty();
4208 verify_overflow_empty();
4209 }
4210
4211 // Try and schedule the remark such that young gen
4212 // occupancy is CMSScheduleRemarkEdenPenetration %.
4213 void CMSCollector::abortable_preclean() {
4214 check_correct_thread_executing();
4215 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4216 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4217
4218 // If Eden's current occupancy is below this threshold,
4219 // immediately schedule the remark; else preclean
4220 // past the next scavenge in an effort to
4221 // schedule the pause as described avove. By choosing
4222 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4223 // we will never do an actual abortable preclean cycle.
4224 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4225 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4226 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4227 // We need more smarts in the abortable preclean
4228 // loop below to deal with cases where allocation
4229 // in young gen is very very slow, and our precleaning
4230 // is running a losing race against a horde of
4231 // mutators intent on flooding us with CMS updates
4232 // (dirty cards).
4233 // One, admittedly dumb, strategy is to give up
4234 // after a certain number of abortable precleaning loops
4235 // or after a certain maximum time. We want to make
4236 // this smarter in the next iteration.
4237 // XXX FIX ME!!! YSR
4238 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4239 while (!(should_abort_preclean() ||
4240 ConcurrentMarkSweepThread::should_terminate())) {
4241 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4242 cumworkdone += workdone;
4243 loops++;
4244 // Voluntarily terminate abortable preclean phase if we have
4245 // been at it for too long.
4246 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4247 loops >= CMSMaxAbortablePrecleanLoops) {
4248 if (PrintGCDetails) {
4249 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4250 }
4251 break;
4252 }
4253 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4254 if (PrintGCDetails) {
4255 gclog_or_tty->print(" CMS: abort preclean due to time ");
4256 }
4257 break;
4258 }
4259 // If we are doing little work each iteration, we should
4260 // take a short break.
4261 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4262 // Sleep for some time, waiting for work to accumulate
4263 stopTimer();
4264 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4265 startTimer();
4266 waited++;
4267 }
4268 }
4269 if (PrintCMSStatistics > 0) {
4270 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4271 loops, waited, cumworkdone);
4272 }
4273 }
4274 CMSTokenSync x(true); // is cms thread
4275 if (_collectorState != Idling) {
4276 assert(_collectorState == AbortablePreclean,
4277 "Spontaneous state transition?");
4278 _collectorState = FinalMarking;
4279 } // Else, a foreground collection completed this CMS cycle.
4280 return;
4281 }
4282
4283 // Respond to an Eden sampling opportunity
4284 void CMSCollector::sample_eden() {
4285 // Make sure a young gc cannot sneak in between our
4286 // reading and recording of a sample.
4287 assert(Thread::current()->is_ConcurrentGC_thread(),
4288 "Only the cms thread may collect Eden samples");
4289 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4290 "Should collect samples while holding CMS token");
4291 if (!_start_sampling) {
4292 return;
4293 }
4294 if (_eden_chunk_array) {
4295 if (_eden_chunk_index < _eden_chunk_capacity) {
4296 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4297 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4298 "Unexpected state of Eden");
4299 // We'd like to check that what we just sampled is an oop-start address;
4300 // however, we cannot do that here since the object may not yet have been
4301 // initialized. So we'll instead do the check when we _use_ this sample
4302 // later.
4303 if (_eden_chunk_index == 0 ||
4304 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4305 _eden_chunk_array[_eden_chunk_index-1])
4306 >= CMSSamplingGrain)) {
4307 _eden_chunk_index++; // commit sample
4308 }
4309 }
4310 }
4311 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4312 size_t used = get_eden_used();
4313 size_t capacity = get_eden_capacity();
4314 assert(used <= capacity, "Unexpected state of Eden");
4315 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4316 _abort_preclean = true;
4317 }
4318 }
4319 }
4320
4321
4322 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4323 assert(_collectorState == Precleaning ||
4324 _collectorState == AbortablePreclean, "incorrect state");
4325 ResourceMark rm;
4326 HandleMark hm;
4327 // Do one pass of scrubbing the discovered reference lists
4328 // to remove any reference objects with strongly-reachable
4329 // referents.
4330 if (clean_refs) {
4331 ReferenceProcessor* rp = ref_processor();
4332 CMSPrecleanRefsYieldClosure yield_cl(this);
4333 assert(rp->span().equals(_span), "Spans should be equal");
4334 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4335 &_markStack);
4336 CMSDrainMarkingStackClosure complete_trace(this,
4337 _span, &_markBitMap, &_markStack,
4338 &keep_alive);
4339
4340 // We don't want this step to interfere with a young
4341 // collection because we don't want to take CPU
4342 // or memory bandwidth away from the young GC threads
4343 // (which may be as many as there are CPUs).
4344 // Note that we don't need to protect ourselves from
4345 // interference with mutators because they can't
4346 // manipulate the discovered reference lists nor affect
4347 // the computed reachability of the referents, the
4348 // only properties manipulated by the precleaning
4349 // of these reference lists.
4350 stopTimer();
4351 CMSTokenSyncWithLocks x(true /* is cms thread */,
4352 bitMapLock());
4353 startTimer();
4354 sample_eden();
4355 // The following will yield to allow foreground
4356 // collection to proceed promptly. XXX YSR:
4357 // The code in this method may need further
4358 // tweaking for better performance and some restructuring
4359 // for cleaner interfaces.
4360 rp->preclean_discovered_references(
4361 rp->is_alive_non_header(), &keep_alive, &complete_trace,
4362 &yield_cl);
4363 }
4364
4365 if (clean_survivor) { // preclean the active survivor space(s)
4366 assert(_young_gen->kind() == Generation::DefNew ||
4367 _young_gen->kind() == Generation::ParNew ||
4368 _young_gen->kind() == Generation::ASParNew,
4369 "incorrect type for cast");
4370 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4371 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4372 &_markBitMap, &_modUnionTable,
4373 &_markStack, &_revisitStack,
4374 true /* precleaning phase */);
4375 stopTimer();
4376 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4377 bitMapLock());
4378 startTimer();
4379 unsigned int before_count =
4380 GenCollectedHeap::heap()->total_collections();
4381 SurvivorSpacePrecleanClosure
4382 sss_cl(this, _span, &_markBitMap, &_markStack,
4383 &pam_cl, before_count, CMSYield);
4384 dng->from()->object_iterate_careful(&sss_cl);
4385 dng->to()->object_iterate_careful(&sss_cl);
4386 }
4387 MarkRefsIntoAndScanClosure
4388 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4389 &_markStack, &_revisitStack, this, CMSYield,
4390 true /* precleaning phase */);
4391 // CAUTION: The following closure has persistent state that may need to
4392 // be reset upon a decrease in the sequence of addresses it
4393 // processes.
4394 ScanMarkedObjectsAgainCarefullyClosure
4395 smoac_cl(this, _span,
4396 &_markBitMap, &_markStack, &_revisitStack, &mrias_cl, CMSYield);
4397
4398 // Preclean dirty cards in ModUnionTable and CardTable using
4399 // appropriate convergence criterion;
4400 // repeat CMSPrecleanIter times unless we find that
4401 // we are losing.
4402 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4403 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4404 "Bad convergence multiplier");
4405 assert(CMSPrecleanThreshold >= 100,
4406 "Unreasonably low CMSPrecleanThreshold");
4407
4408 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4409 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4410 numIter < CMSPrecleanIter;
4411 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4412 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4413 if (CMSPermGenPrecleaningEnabled) {
4414 curNumCards += preclean_mod_union_table(_permGen, &smoac_cl);
4415 }
4416 if (Verbose && PrintGCDetails) {
4417 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4418 }
4419 // Either there are very few dirty cards, so re-mark
4420 // pause will be small anyway, or our pre-cleaning isn't
4421 // that much faster than the rate at which cards are being
4422 // dirtied, so we might as well stop and re-mark since
4423 // precleaning won't improve our re-mark time by much.
4424 if (curNumCards <= CMSPrecleanThreshold ||
4425 (numIter > 0 &&
4426 (curNumCards * CMSPrecleanDenominator >
4427 lastNumCards * CMSPrecleanNumerator))) {
4428 numIter++;
4429 cumNumCards += curNumCards;
4430 break;
4431 }
4432 }
4433 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4434 if (CMSPermGenPrecleaningEnabled) {
4435 curNumCards += preclean_card_table(_permGen, &smoac_cl);
4436 }
4437 cumNumCards += curNumCards;
4438 if (PrintGCDetails && PrintCMSStatistics != 0) {
4439 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4440 curNumCards, cumNumCards, numIter);
4441 }
4442 return cumNumCards; // as a measure of useful work done
4443 }
4444
4445 // PRECLEANING NOTES:
4446 // Precleaning involves:
4447 // . reading the bits of the modUnionTable and clearing the set bits.
4448 // . For the cards corresponding to the set bits, we scan the
4449 // objects on those cards. This means we need the free_list_lock
4450 // so that we can safely iterate over the CMS space when scanning
4451 // for oops.
4452 // . When we scan the objects, we'll be both reading and setting
4453 // marks in the marking bit map, so we'll need the marking bit map.
4454 // . For protecting _collector_state transitions, we take the CGC_lock.
4455 // Note that any races in the reading of of card table entries by the
4456 // CMS thread on the one hand and the clearing of those entries by the
4457 // VM thread or the setting of those entries by the mutator threads on the
4458 // other are quite benign. However, for efficiency it makes sense to keep
4459 // the VM thread from racing with the CMS thread while the latter is
4460 // dirty card info to the modUnionTable. We therefore also use the
4461 // CGC_lock to protect the reading of the card table and the mod union
4462 // table by the CM thread.
4463 // . We run concurrently with mutator updates, so scanning
4464 // needs to be done carefully -- we should not try to scan
4465 // potentially uninitialized objects.
4466 //
4467 // Locking strategy: While holding the CGC_lock, we scan over and
4468 // reset a maximal dirty range of the mod union / card tables, then lock
4469 // the free_list_lock and bitmap lock to do a full marking, then
4470 // release these locks; and repeat the cycle. This allows for a
4471 // certain amount of fairness in the sharing of these locks between
4472 // the CMS collector on the one hand, and the VM thread and the
4473 // mutators on the other.
4474
4475 // NOTE: preclean_mod_union_table() and preclean_card_table()
4476 // further below are largely identical; if you need to modify
4477 // one of these methods, please check the other method too.
4478
4479 size_t CMSCollector::preclean_mod_union_table(
4480 ConcurrentMarkSweepGeneration* gen,
4481 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4482 verify_work_stacks_empty();
4483 verify_overflow_empty();
4484
4485 // strategy: starting with the first card, accumulate contiguous
4486 // ranges of dirty cards; clear these cards, then scan the region
4487 // covered by these cards.
4488
4489 // Since all of the MUT is committed ahead, we can just use
4490 // that, in case the generations expand while we are precleaning.
4491 // It might also be fine to just use the committed part of the
4492 // generation, but we might potentially miss cards when the
4493 // generation is rapidly expanding while we are in the midst
4494 // of precleaning.
4495 HeapWord* startAddr = gen->reserved().start();
4496 HeapWord* endAddr = gen->reserved().end();
4497
4498 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4499
4500 size_t numDirtyCards, cumNumDirtyCards;
4501 HeapWord *nextAddr, *lastAddr;
4502 for (cumNumDirtyCards = numDirtyCards = 0,
4503 nextAddr = lastAddr = startAddr;
4504 nextAddr < endAddr;
4505 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4506
4507 ResourceMark rm;
4508 HandleMark hm;
4509
4510 MemRegion dirtyRegion;
4511 {
4512 stopTimer();
4513 CMSTokenSync ts(true);
4514 startTimer();
4515 sample_eden();
4516 // Get dirty region starting at nextOffset (inclusive),
4517 // simultaneously clearing it.
4518 dirtyRegion =
4519 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4520 assert(dirtyRegion.start() >= nextAddr,
4521 "returned region inconsistent?");
4522 }
4523 // Remember where the next search should begin.
4524 // The returned region (if non-empty) is a right open interval,
4525 // so lastOffset is obtained from the right end of that
4526 // interval.
4527 lastAddr = dirtyRegion.end();
4528 // Should do something more transparent and less hacky XXX
4529 numDirtyCards =
4530 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4531
4532 // We'll scan the cards in the dirty region (with periodic
4533 // yields for foreground GC as needed).
4534 if (!dirtyRegion.is_empty()) {
4535 assert(numDirtyCards > 0, "consistency check");
4536 HeapWord* stop_point = NULL;
4537 {
4538 stopTimer();
4539 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4540 bitMapLock());
4541 startTimer();
4542 verify_work_stacks_empty();
4543 verify_overflow_empty();
4544 sample_eden();
4545 stop_point =
4546 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4547 }
4548 if (stop_point != NULL) {
4549 // The careful iteration stopped early either because it found an
4550 // uninitialized object, or because we were in the midst of an
4551 // "abortable preclean", which should now be aborted. Redirty
4552 // the bits corresponding to the partially-scanned or unscanned
4553 // cards. We'll either restart at the next block boundary or
4554 // abort the preclean.
4555 assert((CMSPermGenPrecleaningEnabled && (gen == _permGen)) ||
4556 (_collectorState == AbortablePreclean && should_abort_preclean()),
4557 "Unparsable objects should only be in perm gen.");
4558
4559 stopTimer();
4560 CMSTokenSyncWithLocks ts(true, bitMapLock());
4561 startTimer();
4562 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4563 if (should_abort_preclean()) {
4564 break; // out of preclean loop
4565 } else {
4566 // Compute the next address at which preclean should pick up;
4567 // might need bitMapLock in order to read P-bits.
4568 lastAddr = next_card_start_after_block(stop_point);
4569 }
4570 }
4571 } else {
4572 assert(lastAddr == endAddr, "consistency check");
4573 assert(numDirtyCards == 0, "consistency check");
4574 break;
4575 }
4576 }
4577 verify_work_stacks_empty();
4578 verify_overflow_empty();
4579 return cumNumDirtyCards;
4580 }
4581
4582 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4583 // below are largely identical; if you need to modify
4584 // one of these methods, please check the other method too.
4585
4586 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4587 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4588 // strategy: it's similar to precleamModUnionTable above, in that
4589 // we accumulate contiguous ranges of dirty cards, mark these cards
4590 // precleaned, then scan the region covered by these cards.
4591 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4592 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4593
4594 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4595
4596 size_t numDirtyCards, cumNumDirtyCards;
4597 HeapWord *lastAddr, *nextAddr;
4598
4599 for (cumNumDirtyCards = numDirtyCards = 0,
4600 nextAddr = lastAddr = startAddr;
4601 nextAddr < endAddr;
4602 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4603
4604 ResourceMark rm;
4605 HandleMark hm;
4606
4607 MemRegion dirtyRegion;
4608 {
4609 // See comments in "Precleaning notes" above on why we
4610 // do this locking. XXX Could the locking overheads be
4611 // too high when dirty cards are sparse? [I don't think so.]
4612 stopTimer();
4613 CMSTokenSync x(true); // is cms thread
4614 startTimer();
4615 sample_eden();
4616 // Get and clear dirty region from card table
4617 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_preclean(
4618 MemRegion(nextAddr, endAddr));
4619 assert(dirtyRegion.start() >= nextAddr,
4620 "returned region inconsistent?");
4621 }
4622 lastAddr = dirtyRegion.end();
4623 numDirtyCards =
4624 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4625
4626 if (!dirtyRegion.is_empty()) {
4627 stopTimer();
4628 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4629 startTimer();
4630 sample_eden();
4631 verify_work_stacks_empty();
4632 verify_overflow_empty();
4633 HeapWord* stop_point =
4634 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4635 if (stop_point != NULL) {
4636 // The careful iteration stopped early because it found an
4637 // uninitialized object. Redirty the bits corresponding to the
4638 // partially-scanned or unscanned cards, and start again at the
4639 // next block boundary.
4640 assert(CMSPermGenPrecleaningEnabled ||
4641 (_collectorState == AbortablePreclean && should_abort_preclean()),
4642 "Unparsable objects should only be in perm gen.");
4643 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4644 if (should_abort_preclean()) {
4645 break; // out of preclean loop
4646 } else {
4647 // Compute the next address at which preclean should pick up.
4648 lastAddr = next_card_start_after_block(stop_point);
4649 }
4650 }
4651 } else {
4652 break;
4653 }
4654 }
4655 verify_work_stacks_empty();
4656 verify_overflow_empty();
4657 return cumNumDirtyCards;
4658 }
4659
4660 void CMSCollector::checkpointRootsFinal(bool asynch,
4661 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4662 assert(_collectorState == FinalMarking, "incorrect state transition?");
4663 check_correct_thread_executing();
4664 // world is stopped at this checkpoint
4665 assert(SafepointSynchronize::is_at_safepoint(),
4666 "world should be stopped");
4667 verify_work_stacks_empty();
4668 verify_overflow_empty();
4669
4670 SpecializationStats::clear();
4671 if (PrintGCDetails) {
4672 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4673 _young_gen->used() / K,
4674 _young_gen->capacity() / K);
4675 }
4676 if (asynch) {
4677 if (CMSScavengeBeforeRemark) {
4678 GenCollectedHeap* gch = GenCollectedHeap::heap();
4679 // Temporarily set flag to false, GCH->do_collection will
4680 // expect it to be false and set to true
4681 FlagSetting fl(gch->_is_gc_active, false);
4682 NOT_PRODUCT(TraceTime t("Scavenge-Before-Remark",
4683 PrintGCDetails && Verbose, true, gclog_or_tty);)
4684 int level = _cmsGen->level() - 1;
4685 if (level >= 0) {
4686 gch->do_collection(true, // full (i.e. force, see below)
4687 false, // !clear_all_soft_refs
4688 0, // size
4689 false, // is_tlab
4690 level // max_level
4691 );
4692 }
4693 }
4694 FreelistLocker x(this);
4695 MutexLockerEx y(bitMapLock(),
4696 Mutex::_no_safepoint_check_flag);
4697 assert(!init_mark_was_synchronous, "but that's impossible!");
4698 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4699 } else {
4700 // already have all the locks
4701 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4702 init_mark_was_synchronous);
4703 }
4704 verify_work_stacks_empty();
4705 verify_overflow_empty();
4706 SpecializationStats::print();
4707 }
4708
4709 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4710 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4711
4712 NOT_PRODUCT(TraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, gclog_or_tty);)
4713
4714 assert(haveFreelistLocks(), "must have free list locks");
4715 assert_lock_strong(bitMapLock());
4716
4717 if (UseAdaptiveSizePolicy) {
4718 size_policy()->checkpoint_roots_final_begin();
4719 }
4720
4721 ResourceMark rm;
4722 HandleMark hm;
4723
4724 GenCollectedHeap* gch = GenCollectedHeap::heap();
4725
4726 if (cms_should_unload_classes()) {
4727 CodeCache::gc_prologue();
4728 }
4729 assert(haveFreelistLocks(), "must have free list locks");
4730 assert_lock_strong(bitMapLock());
4731
4732 if (!init_mark_was_synchronous) {
4733 // We might assume that we need not fill TLAB's when
4734 // CMSScavengeBeforeRemark is set, because we may have just done
4735 // a scavenge which would have filled all TLAB's -- and besides
4736 // Eden would be empty. This however may not always be the case --
4737 // for instance although we asked for a scavenge, it may not have
4738 // happened because of a JNI critical section. We probably need
4739 // a policy for deciding whether we can in that case wait until
4740 // the critical section releases and then do the remark following
4741 // the scavenge, and skip it here. In the absence of that policy,
4742 // or of an indication of whether the scavenge did indeed occur,
4743 // we cannot rely on TLAB's having been filled and must do
4744 // so here just in case a scavenge did not happen.
4745 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4746 // Update the saved marks which may affect the root scans.
4747 gch->save_marks();
4748
4749 {
4750 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4751
4752 // Note on the role of the mod union table:
4753 // Since the marker in "markFromRoots" marks concurrently with
4754 // mutators, it is possible for some reachable objects not to have been
4755 // scanned. For instance, an only reference to an object A was
4756 // placed in object B after the marker scanned B. Unless B is rescanned,
4757 // A would be collected. Such updates to references in marked objects
4758 // are detected via the mod union table which is the set of all cards
4759 // dirtied since the first checkpoint in this GC cycle and prior to
4760 // the most recent young generation GC, minus those cleaned up by the
4761 // concurrent precleaning.
4762 if (CMSParallelRemarkEnabled && ParallelGCThreads > 0) {
4763 TraceTime t("Rescan (parallel) ", PrintGCDetails, false, gclog_or_tty);
4764 do_remark_parallel();
4765 } else {
4766 TraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4767 gclog_or_tty);
4768 do_remark_non_parallel();
4769 }
4770 }
4771 } else {
4772 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
4773 // The initial mark was stop-world, so there's no rescanning to
4774 // do; go straight on to the next step below.
4775 }
4776 verify_work_stacks_empty();
4777 verify_overflow_empty();
4778
4779 {
4780 NOT_PRODUCT(TraceTime ts("refProcessingWork", PrintGCDetails, false, gclog_or_tty);)
4781 refProcessingWork(asynch, clear_all_soft_refs);
4782 }
4783 verify_work_stacks_empty();
4784 verify_overflow_empty();
4785
4786 if (cms_should_unload_classes()) {
4787 CodeCache::gc_epilogue();
4788 }
4789
4790 // If we encountered any (marking stack / work queue) overflow
4791 // events during the current CMS cycle, take appropriate
4792 // remedial measures, where possible, so as to try and avoid
4793 // recurrence of that condition.
4794 assert(_markStack.isEmpty(), "No grey objects");
4795 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4796 _ser_kac_ovflw;
4797 if (ser_ovflw > 0) {
4798 if (PrintCMSStatistics != 0) {
4799 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4800 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4801 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4802 _ser_kac_ovflw);
4803 }
4804 _markStack.expand();
4805 _ser_pmc_remark_ovflw = 0;
4806 _ser_pmc_preclean_ovflw = 0;
4807 _ser_kac_ovflw = 0;
4808 }
4809 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4810 if (PrintCMSStatistics != 0) {
4811 gclog_or_tty->print_cr("Work queue overflow (benign) "
4812 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4813 _par_pmc_remark_ovflw, _par_kac_ovflw);
4814 }
4815 _par_pmc_remark_ovflw = 0;
4816 _par_kac_ovflw = 0;
4817 }
4818 if (PrintCMSStatistics != 0) {
4819 if (_markStack._hit_limit > 0) {
4820 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4821 _markStack._hit_limit);
4822 }
4823 if (_markStack._failed_double > 0) {
4824 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4825 " current capacity "SIZE_FORMAT,
4826 _markStack._failed_double,
4827 _markStack.capacity());
4828 }
4829 }
4830 _markStack._hit_limit = 0;
4831 _markStack._failed_double = 0;
4832
4833 if ((VerifyAfterGC || VerifyDuringGC) &&
4834 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4835 verify_after_remark();
4836 }
4837
4838 // Change under the freelistLocks.
4839 _collectorState = Sweeping;
4840 // Call isAllClear() under bitMapLock
4841 assert(_modUnionTable.isAllClear(), "Should be clear by end of the"
4842 " final marking");
4843 if (UseAdaptiveSizePolicy) {
4844 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
4845 }
4846 }
4847
4848 // Parallel remark task
4849 class CMSParRemarkTask: public AbstractGangTask {
4850 CMSCollector* _collector;
4851 WorkGang* _workers;
4852 int _n_workers;
4853 CompactibleFreeListSpace* _cms_space;
4854 CompactibleFreeListSpace* _perm_space;
4855
4856 // The per-thread work queues, available here for stealing.
4857 OopTaskQueueSet* _task_queues;
4858 ParallelTaskTerminator _term;
4859
4860 public:
4861 CMSParRemarkTask(CMSCollector* collector,
4862 CompactibleFreeListSpace* cms_space,
4863 CompactibleFreeListSpace* perm_space,
4864 int n_workers, WorkGang* workers,
4865 OopTaskQueueSet* task_queues):
4866 AbstractGangTask("Rescan roots and grey objects in parallel"),
4867 _collector(collector),
4868 _cms_space(cms_space), _perm_space(perm_space),
4869 _n_workers(n_workers),
4870 _workers(workers),
4871 _task_queues(task_queues),
4872 _term(workers->total_workers(), task_queues) { }
4873
4874 OopTaskQueueSet* task_queues() { return _task_queues; }
4875
4876 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4877
4878 ParallelTaskTerminator* terminator() { return &_term; }
4879
4880 void work(int i);
4881
4882 private:
4883 // Work method in support of parallel rescan ... of young gen spaces
4884 void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
4885 ContiguousSpace* space,
4886 HeapWord** chunk_array, size_t chunk_top);
4887
4888 // ... of dirty cards in old space
4889 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4890 Par_MarkRefsIntoAndScanClosure* cl);
4891
4892 // ... work stealing for the above
4893 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4894 };
4895
4896 void CMSParRemarkTask::work(int i) {
4897 elapsedTimer _timer;
4898 ResourceMark rm;
4899 HandleMark hm;
4900
4901 // ---------- rescan from roots --------------
4902 _timer.start();
4903 GenCollectedHeap* gch = GenCollectedHeap::heap();
4904 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4905 _collector->_span, _collector->ref_processor(),
4906 &(_collector->_markBitMap),
4907 work_queue(i), &(_collector->_revisitStack));
4908
4909 // Rescan young gen roots first since these are likely
4910 // coarsely partitioned and may, on that account, constitute
4911 // the critical path; thus, it's best to start off that
4912 // work first.
4913 // ---------- young gen roots --------------
4914 {
4915 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
4916 EdenSpace* eden_space = dng->eden();
4917 ContiguousSpace* from_space = dng->from();
4918 ContiguousSpace* to_space = dng->to();
4919
4920 HeapWord** eca = _collector->_eden_chunk_array;
4921 size_t ect = _collector->_eden_chunk_index;
4922 HeapWord** sca = _collector->_survivor_chunk_array;
4923 size_t sct = _collector->_survivor_chunk_index;
4924
4925 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4926 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4927
4928 do_young_space_rescan(i, &par_mrias_cl, to_space, NULL, 0);
4929 do_young_space_rescan(i, &par_mrias_cl, from_space, sca, sct);
4930 do_young_space_rescan(i, &par_mrias_cl, eden_space, eca, ect);
4931
4932 _timer.stop();
4933 if (PrintCMSStatistics != 0) {
4934 gclog_or_tty->print_cr(
4935 "Finished young gen rescan work in %dth thread: %3.3f sec",
4936 i, _timer.seconds());
4937 }
4938 }
4939
4940 // ---------- remaining roots --------------
4941 _timer.reset();
4942 _timer.start();
4943 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
4944 false, // yg was scanned above
4945 true, // collecting perm gen
4946 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4947 NULL, &par_mrias_cl);
4948 _timer.stop();
4949 if (PrintCMSStatistics != 0) {
4950 gclog_or_tty->print_cr(
4951 "Finished remaining root rescan work in %dth thread: %3.3f sec",
4952 i, _timer.seconds());
4953 }
4954
4955 // ---------- rescan dirty cards ------------
4956 _timer.reset();
4957 _timer.start();
4958
4959 // Do the rescan tasks for each of the two spaces
4960 // (cms_space and perm_space) in turn.
4961 do_dirty_card_rescan_tasks(_cms_space, i, &par_mrias_cl);
4962 do_dirty_card_rescan_tasks(_perm_space, i, &par_mrias_cl);
4963 _timer.stop();
4964 if (PrintCMSStatistics != 0) {
4965 gclog_or_tty->print_cr(
4966 "Finished dirty card rescan work in %dth thread: %3.3f sec",
4967 i, _timer.seconds());
4968 }
4969
4970 // ---------- steal work from other threads ...
4971 // ---------- ... and drain overflow list.
4972 _timer.reset();
4973 _timer.start();
4974 do_work_steal(i, &par_mrias_cl, _collector->hash_seed(i));
4975 _timer.stop();
4976 if (PrintCMSStatistics != 0) {
4977 gclog_or_tty->print_cr(
4978 "Finished work stealing in %dth thread: %3.3f sec",
4979 i, _timer.seconds());
4980 }
4981 }
4982
4983 void
4984 CMSParRemarkTask::do_young_space_rescan(int i,
4985 Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
4986 HeapWord** chunk_array, size_t chunk_top) {
4987 // Until all tasks completed:
4988 // . claim an unclaimed task
4989 // . compute region boundaries corresponding to task claimed
4990 // using chunk_array
4991 // . par_oop_iterate(cl) over that region
4992
4993 ResourceMark rm;
4994 HandleMark hm;
4995
4996 SequentialSubTasksDone* pst = space->par_seq_tasks();
4997 assert(pst->valid(), "Uninitialized use?");
4998
4999 int nth_task = 0;
5000 int n_tasks = pst->n_tasks();
5001
5002 HeapWord *start, *end;
5003 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5004 // We claimed task # nth_task; compute its boundaries.
5005 if (chunk_top == 0) { // no samples were taken
5006 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5007 start = space->bottom();
5008 end = space->top();
5009 } else if (nth_task == 0) {
5010 start = space->bottom();
5011 end = chunk_array[nth_task];
5012 } else if (nth_task < (jint)chunk_top) {
5013 assert(nth_task >= 1, "Control point invariant");
5014 start = chunk_array[nth_task - 1];
5015 end = chunk_array[nth_task];
5016 } else {
5017 assert(nth_task == (jint)chunk_top, "Control point invariant");
5018 start = chunk_array[chunk_top - 1];
5019 end = space->top();
5020 }
5021 MemRegion mr(start, end);
5022 // Verify that mr is in space
5023 assert(mr.is_empty() || space->used_region().contains(mr),
5024 "Should be in space");
5025 // Verify that "start" is an object boundary
5026 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5027 "Should be an oop");
5028 space->par_oop_iterate(mr, cl);
5029 }
5030 pst->all_tasks_completed();
5031 }
5032
5033 void
5034 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5035 CompactibleFreeListSpace* sp, int i,
5036 Par_MarkRefsIntoAndScanClosure* cl) {
5037 // Until all tasks completed:
5038 // . claim an unclaimed task
5039 // . compute region boundaries corresponding to task claimed
5040 // . transfer dirty bits ct->mut for that region
5041 // . apply rescanclosure to dirty mut bits for that region
5042
5043 ResourceMark rm;
5044 HandleMark hm;
5045
5046 OopTaskQueue* work_q = work_queue(i);
5047 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5048 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5049 // CAUTION: This closure has state that persists across calls to
5050 // the work method dirty_range_iterate_clear() in that it has
5051 // imbedded in it a (subtype of) UpwardsObjectClosure. The
5052 // use of that state in the imbedded UpwardsObjectClosure instance
5053 // assumes that the cards are always iterated (even if in parallel
5054 // by several threads) in monotonically increasing order per each
5055 // thread. This is true of the implementation below which picks
5056 // card ranges (chunks) in monotonically increasing order globally
5057 // and, a-fortiori, in monotonically increasing order per thread
5058 // (the latter order being a subsequence of the former).
5059 // If the work code below is ever reorganized into a more chaotic
5060 // work-partitioning form than the current "sequential tasks"
5061 // paradigm, the use of that persistent state will have to be
5062 // revisited and modified appropriately. See also related
5063 // bug 4756801 work on which should examine this code to make
5064 // sure that the changes there do not run counter to the
5065 // assumptions made here and necessary for correctness and
5066 // efficiency. Note also that this code might yield inefficient
5067 // behaviour in the case of very large objects that span one or
5068 // more work chunks. Such objects would potentially be scanned
5069 // several times redundantly. Work on 4756801 should try and
5070 // address that performance anomaly if at all possible. XXX
5071 MemRegion full_span = _collector->_span;
5072 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5073 CMSMarkStack* rs = &(_collector->_revisitStack); // shared
5074 MarkFromDirtyCardsClosure
5075 greyRescanClosure(_collector, full_span, // entire span of interest
5076 sp, bm, work_q, rs, cl);
5077
5078 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5079 assert(pst->valid(), "Uninitialized use?");
5080 int nth_task = 0;
5081 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5082 MemRegion span = sp->used_region();
5083 HeapWord* start_addr = span.start();
5084 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5085 alignment);
5086 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5087 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5088 start_addr, "Check alignment");
5089 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5090 chunk_size, "Check alignment");
5091
5092 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5093 // Having claimed the nth_task, compute corresponding mem-region,
5094 // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5095 // The alignment restriction ensures that we do not need any
5096 // synchronization with other gang-workers while setting or
5097 // clearing bits in thus chunk of the MUT.
5098 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5099 start_addr + (nth_task+1)*chunk_size);
5100 // The last chunk's end might be way beyond end of the
5101 // used region. In that case pull back appropriately.
5102 if (this_span.end() > end_addr) {
5103 this_span.set_end(end_addr);
5104 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5105 }
5106 // Iterate over the dirty cards covering this chunk, marking them
5107 // precleaned, and setting the corresponding bits in the mod union
5108 // table. Since we have been careful to partition at Card and MUT-word
5109 // boundaries no synchronization is needed between parallel threads.
5110 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5111 &modUnionClosure);
5112
5113 // Having transferred these marks into the modUnionTable,
5114 // rescan the marked objects on the dirty cards in the modUnionTable.
5115 // Even if this is at a synchronous collection, the initial marking
5116 // may have been done during an asynchronous collection so there
5117 // may be dirty bits in the mod-union table.
5118 _collector->_modUnionTable.dirty_range_iterate_clear(
5119 this_span, &greyRescanClosure);
5120 _collector->_modUnionTable.verifyNoOneBitsInRange(
5121 this_span.start(),
5122 this_span.end());
5123 }
5124 pst->all_tasks_completed(); // declare that i am done
5125 }
5126
5127 // . see if we can share work_queues with ParNew? XXX
5128 void
5129 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5130 int* seed) {
5131 OopTaskQueue* work_q = work_queue(i);
5132 NOT_PRODUCT(int num_steals = 0;)
5133 oop obj_to_scan;
5134 CMSBitMap* bm = &(_collector->_markBitMap);
5135 size_t num_from_overflow_list =
5136 MIN2((size_t)work_q->max_elems()/4,
5137 (size_t)ParGCDesiredObjsFromOverflowList);
5138
5139 while (true) {
5140 // Completely finish any left over work from (an) earlier round(s)
5141 cl->trim_queue(0);
5142 // Now check if there's any work in the overflow list
5143 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5144 work_q)) {
5145 // found something in global overflow list;
5146 // not yet ready to go stealing work from others.
5147 // We'd like to assert(work_q->size() != 0, ...)
5148 // because we just took work from the overflow list,
5149 // but of course we can't since all of that could have
5150 // been already stolen from us.
5151 // "He giveth and He taketh away."
5152 continue;
5153 }
5154 // Verify that we have no work before we resort to stealing
5155 assert(work_q->size() == 0, "Have work, shouldn't steal");
5156 // Try to steal from other queues that have work
5157 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5158 NOT_PRODUCT(num_steals++;)
5159 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5160 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5161 // Do scanning work
5162 obj_to_scan->oop_iterate(cl);
5163 // Loop around, finish this work, and try to steal some more
5164 } else if (terminator()->offer_termination()) {
5165 break; // nirvana from the infinite cycle
5166 }
5167 }
5168 NOT_PRODUCT(
5169 if (PrintCMSStatistics != 0) {
5170 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5171 }
5172 )
5173 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5174 "Else our work is not yet done");
5175 }
5176
5177 // Return a thread-local PLAB recording array, as appropriate.
5178 void* CMSCollector::get_data_recorder(int thr_num) {
5179 if (_survivor_plab_array != NULL &&
5180 (CMSPLABRecordAlways ||
5181 (_collectorState > Marking && _collectorState < FinalMarking))) {
5182 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5183 ChunkArray* ca = &_survivor_plab_array[thr_num];
5184 ca->reset(); // clear it so that fresh data is recorded
5185 return (void*) ca;
5186 } else {
5187 return NULL;
5188 }
5189 }
5190
5191 // Reset all the thread-local PLAB recording arrays
5192 void CMSCollector::reset_survivor_plab_arrays() {
5193 for (uint i = 0; i < ParallelGCThreads; i++) {
5194 _survivor_plab_array[i].reset();
5195 }
5196 }
5197
5198 // Merge the per-thread plab arrays into the global survivor chunk
5199 // array which will provide the partitioning of the survivor space
5200 // for CMS rescan.
5201 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv) {
5202 assert(_survivor_plab_array != NULL, "Error");
5203 assert(_survivor_chunk_array != NULL, "Error");
5204 assert(_collectorState == FinalMarking, "Error");
5205 for (uint j = 0; j < ParallelGCThreads; j++) {
5206 _cursor[j] = 0;
5207 }
5208 HeapWord* top = surv->top();
5209 size_t i;
5210 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5211 HeapWord* min_val = top; // Higher than any PLAB address
5212 uint min_tid = 0; // position of min_val this round
5213 for (uint j = 0; j < ParallelGCThreads; j++) {
5214 ChunkArray* cur_sca = &_survivor_plab_array[j];
5215 if (_cursor[j] == cur_sca->end()) {
5216 continue;
5217 }
5218 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5219 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5220 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5221 if (cur_val < min_val) {
5222 min_tid = j;
5223 min_val = cur_val;
5224 } else {
5225 assert(cur_val < top, "All recorded addresses should be less");
5226 }
5227 }
5228 // At this point min_val and min_tid are respectively
5229 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5230 // and the thread (j) that witnesses that address.
5231 // We record this address in the _survivor_chunk_array[i]
5232 // and increment _cursor[min_tid] prior to the next round i.
5233 if (min_val == top) {
5234 break;
5235 }
5236 _survivor_chunk_array[i] = min_val;
5237 _cursor[min_tid]++;
5238 }
5239 // We are all done; record the size of the _survivor_chunk_array
5240 _survivor_chunk_index = i; // exclusive: [0, i)
5241 if (PrintCMSStatistics > 0) {
5242 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5243 }
5244 // Verify that we used up all the recorded entries
5245 #ifdef ASSERT
5246 size_t total = 0;
5247 for (uint j = 0; j < ParallelGCThreads; j++) {
5248 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5249 total += _cursor[j];
5250 }
5251 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5252 // Check that the merged array is in sorted order
5253 if (total > 0) {
5254 for (size_t i = 0; i < total - 1; i++) {
5255 if (PrintCMSStatistics > 0) {
5256 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5257 i, _survivor_chunk_array[i]);
5258 }
5259 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5260 "Not sorted");
5261 }
5262 }
5263 #endif // ASSERT
5264 }
5265
5266 // Set up the space's par_seq_tasks structure for work claiming
5267 // for parallel rescan of young gen.
5268 // See ParRescanTask where this is currently used.
5269 void
5270 CMSCollector::
5271 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5272 assert(n_threads > 0, "Unexpected n_threads argument");
5273 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5274
5275 // Eden space
5276 {
5277 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5278 assert(!pst->valid(), "Clobbering existing data?");
5279 // Each valid entry in [0, _eden_chunk_index) represents a task.
5280 size_t n_tasks = _eden_chunk_index + 1;
5281 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5282 pst->set_par_threads(n_threads);
5283 pst->set_n_tasks((int)n_tasks);
5284 }
5285
5286 // Merge the survivor plab arrays into _survivor_chunk_array
5287 if (_survivor_plab_array != NULL) {
5288 merge_survivor_plab_arrays(dng->from());
5289 } else {
5290 assert(_survivor_chunk_index == 0, "Error");
5291 }
5292
5293 // To space
5294 {
5295 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5296 assert(!pst->valid(), "Clobbering existing data?");
5297 pst->set_par_threads(n_threads);
5298 pst->set_n_tasks(1);
5299 assert(pst->valid(), "Error");
5300 }
5301
5302 // From space
5303 {
5304 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5305 assert(!pst->valid(), "Clobbering existing data?");
5306 size_t n_tasks = _survivor_chunk_index + 1;
5307 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5308 pst->set_par_threads(n_threads);
5309 pst->set_n_tasks((int)n_tasks);
5310 assert(pst->valid(), "Error");
5311 }
5312 }
5313
5314 // Parallel version of remark
5315 void CMSCollector::do_remark_parallel() {
5316 GenCollectedHeap* gch = GenCollectedHeap::heap();
5317 WorkGang* workers = gch->workers();
5318 assert(workers != NULL, "Need parallel worker threads.");
5319 int n_workers = workers->total_workers();
5320 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5321 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
5322
5323 CMSParRemarkTask tsk(this,
5324 cms_space, perm_space,
5325 n_workers, workers, task_queues());
5326
5327 // Set up for parallel process_strong_roots work.
5328 gch->set_par_threads(n_workers);
5329 gch->change_strong_roots_parity();
5330 // We won't be iterating over the cards in the card table updating
5331 // the younger_gen cards, so we shouldn't call the following else
5332 // the verification code as well as subsequent younger_refs_iterate
5333 // code would get confused. XXX
5334 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5335
5336 // The young gen rescan work will not be done as part of
5337 // process_strong_roots (which currently doesn't knw how to
5338 // parallelize such a scan), but rather will be broken up into
5339 // a set of parallel tasks (via the sampling that the [abortable]
5340 // preclean phase did of EdenSpace, plus the [two] tasks of
5341 // scanning the [two] survivor spaces. Further fine-grain
5342 // parallelization of the scanning of the survivor spaces
5343 // themselves, and of precleaning of the younger gen itself
5344 // is deferred to the future.
5345 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5346
5347 // The dirty card rescan work is broken up into a "sequence"
5348 // of parallel tasks (per constituent space) that are dynamically
5349 // claimed by the parallel threads.
5350 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5351 perm_space->initialize_sequential_subtasks_for_rescan(n_workers);
5352
5353 // It turns out that even when we're using 1 thread, doing the work in a
5354 // separate thread causes wide variance in run times. We can't help this
5355 // in the multi-threaded case, but we special-case n=1 here to get
5356 // repeatable measurements of the 1-thread overhead of the parallel code.
5357 if (n_workers > 1) {
5358 // Make refs discovery MT-safe
5359 ReferenceProcessorMTMutator mt(ref_processor(), true);
5360 workers->run_task(&tsk);
5361 } else {
5362 tsk.work(0);
5363 }
5364 gch->set_par_threads(0); // 0 ==> non-parallel.
5365 // restore, single-threaded for now, any preserved marks
5366 // as a result of work_q overflow
5367 restore_preserved_marks_if_any();
5368 }
5369
5370 // Non-parallel version of remark
5371 void CMSCollector::do_remark_non_parallel() {
5372 ResourceMark rm;
5373 HandleMark hm;
5374 GenCollectedHeap* gch = GenCollectedHeap::heap();
5375 MarkRefsIntoAndScanClosure
5376 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
5377 &_markStack, &_revisitStack, this,
5378 false /* should_yield */, false /* not precleaning */);
5379 MarkFromDirtyCardsClosure
5380 markFromDirtyCardsClosure(this, _span,
5381 NULL, // space is set further below
5382 &_markBitMap, &_markStack, &_revisitStack,
5383 &mrias_cl);
5384 {
5385 TraceTime t("grey object rescan", PrintGCDetails, false, gclog_or_tty);
5386 // Iterate over the dirty cards, marking them precleaned, and
5387 // setting the corresponding bits in the mod union table.
5388 {
5389 ModUnionClosure modUnionClosure(&_modUnionTable);
5390 _ct->ct_bs()->dirty_card_iterate(
5391 _cmsGen->used_region(),
5392 &modUnionClosure);
5393 _ct->ct_bs()->dirty_card_iterate(
5394 _permGen->used_region(),
5395 &modUnionClosure);
5396 }
5397 // Having transferred these marks into the modUnionTable, we just need
5398 // to rescan the marked objects on the dirty cards in the modUnionTable.
5399 // The initial marking may have been done during an asynchronous
5400 // collection so there may be dirty bits in the mod-union table.
5401 const int alignment =
5402 CardTableModRefBS::card_size * BitsPerWord;
5403 {
5404 // ... First handle dirty cards in CMS gen
5405 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5406 MemRegion ur = _cmsGen->used_region();
5407 HeapWord* lb = ur.start();
5408 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5409 MemRegion cms_span(lb, ub);
5410 _modUnionTable.dirty_range_iterate_clear(cms_span,
5411 &markFromDirtyCardsClosure);
5412 verify_work_stacks_empty();
5413 if (PrintCMSStatistics != 0) {
5414 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5415 markFromDirtyCardsClosure.num_dirty_cards());
5416 }
5417 }
5418 {
5419 // .. and then repeat for dirty cards in perm gen
5420 markFromDirtyCardsClosure.set_space(_permGen->cmsSpace());
5421 MemRegion ur = _permGen->used_region();
5422 HeapWord* lb = ur.start();
5423 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5424 MemRegion perm_span(lb, ub);
5425 _modUnionTable.dirty_range_iterate_clear(perm_span,
5426 &markFromDirtyCardsClosure);
5427 verify_work_stacks_empty();
5428 if (PrintCMSStatistics != 0) {
5429 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in perm gen) ",
5430 markFromDirtyCardsClosure.num_dirty_cards());
5431 }
5432 }
5433 }
5434 if (VerifyDuringGC &&
5435 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5436 HandleMark hm; // Discard invalid handles created during verification
5437 Universe::verify(true);
5438 }
5439 {
5440 TraceTime t("root rescan", PrintGCDetails, false, gclog_or_tty);
5441
5442 verify_work_stacks_empty();
5443
5444 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5445 gch->gen_process_strong_roots(_cmsGen->level(),
5446 true, // younger gens as roots
5447 true, // collecting perm gen
5448 SharedHeap::ScanningOption(roots_scanning_options()),
5449 NULL, &mrias_cl);
5450 }
5451 verify_work_stacks_empty();
5452 // Restore evacuated mark words, if any, used for overflow list links
5453 if (!CMSOverflowEarlyRestoration) {
5454 restore_preserved_marks_if_any();
5455 }
5456 verify_overflow_empty();
5457 }
5458
5459 ////////////////////////////////////////////////////////
5460 // Parallel Reference Processing Task Proxy Class
5461 ////////////////////////////////////////////////////////
5462 class CMSRefProcTaskProxy: public AbstractGangTask {
5463 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5464 CMSCollector* _collector;
5465 CMSBitMap* _mark_bit_map;
5466 const MemRegion _span;
5467 OopTaskQueueSet* _task_queues;
5468 ParallelTaskTerminator _term;
5469 ProcessTask& _task;
5470
5471 public:
5472 CMSRefProcTaskProxy(ProcessTask& task,
5473 CMSCollector* collector,
5474 const MemRegion& span,
5475 CMSBitMap* mark_bit_map,
5476 int total_workers,
5477 OopTaskQueueSet* task_queues):
5478 AbstractGangTask("Process referents by policy in parallel"),
5479 _task(task),
5480 _collector(collector), _span(span), _mark_bit_map(mark_bit_map),
5481 _task_queues(task_queues),
5482 _term(total_workers, task_queues)
5483 {
5484 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5485 "Inconsistency in _span");
5486 }
5487 OopTaskQueueSet* task_queues() { return _task_queues; }
5488
5489 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5490
5491 ParallelTaskTerminator* terminator() { return &_term; }
5492
5493 void do_work_steal(int i,
5494 CMSParDrainMarkingStackClosure* drain,
5495 CMSParKeepAliveClosure* keep_alive,
5496 int* seed);
5497
5498 virtual void work(int i);
5499 };
5500
5501 void CMSRefProcTaskProxy::work(int i) {
5502 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5503 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5504 _mark_bit_map, work_queue(i));
5505 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5506 _mark_bit_map, work_queue(i));
5507 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5508 _task.work(i, is_alive_closure, par_keep_alive, par_drain_stack);
5509 if (_task.marks_oops_alive()) {
5510 do_work_steal(i, &par_drain_stack, &par_keep_alive,
5511 _collector->hash_seed(i));
5512 }
5513 assert(work_queue(i)->size() == 0, "work_queue should be empty");
5514 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5515 }
5516
5517 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5518 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5519 EnqueueTask& _task;
5520
5521 public:
5522 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5523 : AbstractGangTask("Enqueue reference objects in parallel"),
5524 _task(task)
5525 { }
5526
5527 virtual void work(int i)
5528 {
5529 _task.work(i);
5530 }
5531 };
5532
5533 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5534 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5535 _collector(collector),
5536 _span(span),
5537 _bit_map(bit_map),
5538 _work_queue(work_queue),
5539 _mark_and_push(collector, span, bit_map, work_queue),
5540 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5541 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5542 { }
5543
5544 // . see if we can share work_queues with ParNew? XXX
5545 void CMSRefProcTaskProxy::do_work_steal(int i,
5546 CMSParDrainMarkingStackClosure* drain,
5547 CMSParKeepAliveClosure* keep_alive,
5548 int* seed) {
5549 OopTaskQueue* work_q = work_queue(i);
5550 NOT_PRODUCT(int num_steals = 0;)
5551 oop obj_to_scan;
5552 size_t num_from_overflow_list =
5553 MIN2((size_t)work_q->max_elems()/4,
5554 (size_t)ParGCDesiredObjsFromOverflowList);
5555
5556 while (true) {
5557 // Completely finish any left over work from (an) earlier round(s)
5558 drain->trim_queue(0);
5559 // Now check if there's any work in the overflow list
5560 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5561 work_q)) {
5562 // Found something in global overflow list;
5563 // not yet ready to go stealing work from others.
5564 // We'd like to assert(work_q->size() != 0, ...)
5565 // because we just took work from the overflow list,
5566 // but of course we can't, since all of that might have
5567 // been already stolen from us.
5568 continue;
5569 }
5570 // Verify that we have no work before we resort to stealing
5571 assert(work_q->size() == 0, "Have work, shouldn't steal");
5572 // Try to steal from other queues that have work
5573 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5574 NOT_PRODUCT(num_steals++;)
5575 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5576 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5577 // Do scanning work
5578 obj_to_scan->oop_iterate(keep_alive);
5579 // Loop around, finish this work, and try to steal some more
5580 } else if (terminator()->offer_termination()) {
5581 break; // nirvana from the infinite cycle
5582 }
5583 }
5584 NOT_PRODUCT(
5585 if (PrintCMSStatistics != 0) {
5586 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5587 }
5588 )
5589 }
5590
5591 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5592 {
5593 GenCollectedHeap* gch = GenCollectedHeap::heap();
5594 WorkGang* workers = gch->workers();
5595 assert(workers != NULL, "Need parallel worker threads.");
5596 int n_workers = workers->total_workers();
5597 CMSRefProcTaskProxy rp_task(task, &_collector,
5598 _collector.ref_processor()->span(),
5599 _collector.markBitMap(),
5600 n_workers, _collector.task_queues());
5601 workers->run_task(&rp_task);
5602 }
5603
5604 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5605 {
5606
5607 GenCollectedHeap* gch = GenCollectedHeap::heap();
5608 WorkGang* workers = gch->workers();
5609 assert(workers != NULL, "Need parallel worker threads.");
5610 CMSRefEnqueueTaskProxy enq_task(task);
5611 workers->run_task(&enq_task);
5612 }
5613
5614 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5615
5616 ResourceMark rm;
5617 HandleMark hm;
5618 ReferencePolicy* soft_ref_policy;
5619
5620 assert(!ref_processor()->enqueuing_is_done(), "Enqueuing should not be complete");
5621 // Process weak references.
5622 if (clear_all_soft_refs) {
5623 soft_ref_policy = new AlwaysClearPolicy();
5624 } else {
5625 #ifdef COMPILER2
5626 soft_ref_policy = new LRUMaxHeapPolicy();
5627 #else
5628 soft_ref_policy = new LRUCurrentHeapPolicy();
5629 #endif // COMPILER2
5630 }
5631 verify_work_stacks_empty();
5632
5633 ReferenceProcessor* rp = ref_processor();
5634 assert(rp->span().equals(_span), "Spans should be equal");
5635 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5636 &_markStack);
5637 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5638 _span, &_markBitMap, &_markStack,
5639 &cmsKeepAliveClosure);
5640 {
5641 TraceTime t("weak refs processing", PrintGCDetails, false, gclog_or_tty);
5642 if (rp->processing_is_mt()) {
5643 CMSRefProcTaskExecutor task_executor(*this);
5644 rp->process_discovered_references(soft_ref_policy,
5645 &_is_alive_closure,
5646 &cmsKeepAliveClosure,
5647 &cmsDrainMarkingStackClosure,
5648 &task_executor);
5649 } else {
5650 rp->process_discovered_references(soft_ref_policy,
5651 &_is_alive_closure,
5652 &cmsKeepAliveClosure,
5653 &cmsDrainMarkingStackClosure,
5654 NULL);
5655 }
5656 verify_work_stacks_empty();
5657 }
5658
5659 if (cms_should_unload_classes()) {
5660 {
5661 TraceTime t("class unloading", PrintGCDetails, false, gclog_or_tty);
5662
5663 // Follow SystemDictionary roots and unload classes
5664 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5665
5666 // Follow CodeCache roots and unload any methods marked for unloading
5667 CodeCache::do_unloading(&_is_alive_closure,
5668 &cmsKeepAliveClosure,
5669 purged_class);
5670
5671 cmsDrainMarkingStackClosure.do_void();
5672 verify_work_stacks_empty();
5673
5674 // Update subklass/sibling/implementor links in KlassKlass descendants
5675 assert(!_revisitStack.isEmpty(), "revisit stack should not be empty");
5676 oop k;
5677 while ((k = _revisitStack.pop()) != NULL) {
5678 ((Klass*)(oopDesc*)k)->follow_weak_klass_links(
5679 &_is_alive_closure,
5680 &cmsKeepAliveClosure);
5681 }
5682 assert(!ClassUnloading ||
5683 (_markStack.isEmpty() && overflow_list_is_empty()),
5684 "Should not have found new reachable objects");
5685 assert(_revisitStack.isEmpty(), "revisit stack should have been drained");
5686 cmsDrainMarkingStackClosure.do_void();
5687 verify_work_stacks_empty();
5688 }
5689
5690 {
5691 TraceTime t("scrub symbol & string tables", PrintGCDetails, false, gclog_or_tty);
5692 // Now clean up stale oops in SymbolTable and StringTable
5693 SymbolTable::unlink(&_is_alive_closure);
5694 StringTable::unlink(&_is_alive_closure);
5695 }
5696 }
5697
5698 verify_work_stacks_empty();
5699 // Restore any preserved marks as a result of mark stack or
5700 // work queue overflow
5701 restore_preserved_marks_if_any(); // done single-threaded for now
5702
5703 rp->set_enqueuing_is_done(true);
5704 if (rp->processing_is_mt()) {
5705 CMSRefProcTaskExecutor task_executor(*this);
5706 rp->enqueue_discovered_references(&task_executor);
5707 } else {
5708 rp->enqueue_discovered_references(NULL);
5709 }
5710 rp->verify_no_references_recorded();
5711 assert(!rp->discovery_enabled(), "should have been disabled");
5712
5713 // JVMTI object tagging is based on JNI weak refs. If any of these
5714 // refs were cleared then JVMTI needs to update its maps and
5715 // maybe post ObjectFrees to agents.
5716 JvmtiExport::cms_ref_processing_epilogue();
5717 }
5718
5719 #ifndef PRODUCT
5720 void CMSCollector::check_correct_thread_executing() {
5721 Thread* t = Thread::current();
5722 // Only the VM thread or the CMS thread should be here.
5723 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5724 "Unexpected thread type");
5725 // If this is the vm thread, the foreground process
5726 // should not be waiting. Note that _foregroundGCIsActive is
5727 // true while the foreground collector is waiting.
5728 if (_foregroundGCShouldWait) {
5729 // We cannot be the VM thread
5730 assert(t->is_ConcurrentGC_thread(),
5731 "Should be CMS thread");
5732 } else {
5733 // We can be the CMS thread only if we are in a stop-world
5734 // phase of CMS collection.
5735 if (t->is_ConcurrentGC_thread()) {
5736 assert(_collectorState == InitialMarking ||
5737 _collectorState == FinalMarking,
5738 "Should be a stop-world phase");
5739 // The CMS thread should be holding the CMS_token.
5740 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5741 "Potential interference with concurrently "
5742 "executing VM thread");
5743 }
5744 }
5745 }
5746 #endif
5747
5748 void CMSCollector::sweep(bool asynch) {
5749 assert(_collectorState == Sweeping, "just checking");
5750 check_correct_thread_executing();
5751 verify_work_stacks_empty();
5752 verify_overflow_empty();
5753 incrementSweepCount();
5754 _sweep_timer.stop();
5755 _sweep_estimate.sample(_sweep_timer.seconds());
5756 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
5757
5758 // PermGen verification support: If perm gen sweeping is disabled in
5759 // this cycle, we preserve the perm gen object "deadness" information
5760 // in the perm_gen_verify_bit_map. In order to do that we traverse
5761 // all blocks in perm gen and mark all dead objects.
5762 if (verifying() && !cms_should_unload_classes()) {
5763 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
5764 bitMapLock());
5765 assert(perm_gen_verify_bit_map()->sizeInBits() != 0,
5766 "Should have already been allocated");
5767 MarkDeadObjectsClosure mdo(this, _permGen->cmsSpace(),
5768 markBitMap(), perm_gen_verify_bit_map());
5769 _permGen->cmsSpace()->blk_iterate(&mdo);
5770 }
5771
5772 if (asynch) {
5773 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5774 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
5775 // First sweep the old gen then the perm gen
5776 {
5777 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5778 bitMapLock());
5779 sweepWork(_cmsGen, asynch);
5780 }
5781
5782 // Now repeat for perm gen
5783 if (cms_should_unload_classes()) {
5784 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
5785 bitMapLock());
5786 sweepWork(_permGen, asynch);
5787 }
5788
5789 // Update Universe::_heap_*_at_gc figures.
5790 // We need all the free list locks to make the abstract state
5791 // transition from Sweeping to Resetting. See detailed note
5792 // further below.
5793 {
5794 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5795 _permGen->freelistLock());
5796 // Update heap occupancy information which is used as
5797 // input to soft ref clearing policy at the next gc.
5798 Universe::update_heap_info_at_gc();
5799 _collectorState = Resizing;
5800 }
5801 } else {
5802 // already have needed locks
5803 sweepWork(_cmsGen, asynch);
5804
5805 if (cms_should_unload_classes()) {
5806 sweepWork(_permGen, asynch);
5807 }
5808 // Update heap occupancy information which is used as
5809 // input to soft ref clearing policy at the next gc.
5810 Universe::update_heap_info_at_gc();
5811 _collectorState = Resizing;
5812 }
5813 verify_work_stacks_empty();
5814 verify_overflow_empty();
5815
5816 _sweep_timer.reset();
5817 _sweep_timer.start();
5818
5819 update_time_of_last_gc(os::javaTimeMillis());
5820
5821 // NOTE on abstract state transitions:
5822 // Mutators allocate-live and/or mark the mod-union table dirty
5823 // based on the state of the collection. The former is done in
5824 // the interval [Marking, Sweeping] and the latter in the interval
5825 // [Marking, Sweeping). Thus the transitions into the Marking state
5826 // and out of the Sweeping state must be synchronously visible
5827 // globally to the mutators.
5828 // The transition into the Marking state happens with the world
5829 // stopped so the mutators will globally see it. Sweeping is
5830 // done asynchronously by the background collector so the transition
5831 // from the Sweeping state to the Resizing state must be done
5832 // under the freelistLock (as is the check for whether to
5833 // allocate-live and whether to dirty the mod-union table).
5834 assert(_collectorState == Resizing, "Change of collector state to"
5835 " Resizing must be done under the freelistLocks (plural)");
5836
5837 // Now that sweeping has been completed, if the GCH's
5838 // incremental_collection_will_fail flag is set, clear it,
5839 // thus inviting a younger gen collection to promote into
5840 // this generation. If such a promotion may still fail,
5841 // the flag will be set again when a young collection is
5842 // attempted.
5843 // I think the incremental_collection_will_fail flag's use
5844 // is specific to a 2 generation collection policy, so i'll
5845 // assert that that's the configuration we are operating within.
5846 // The use of the flag can and should be generalized appropriately
5847 // in the future to deal with a general n-generation system.
5848
5849 GenCollectedHeap* gch = GenCollectedHeap::heap();
5850 assert(gch->collector_policy()->is_two_generation_policy(),
5851 "Resetting of incremental_collection_will_fail flag"
5852 " may be incorrect otherwise");
5853 gch->clear_incremental_collection_will_fail();
5854 gch->update_full_collections_completed(_collection_count_start);
5855 }
5856
5857 // FIX ME!!! Looks like this belongs in CFLSpace, with
5858 // CMSGen merely delegating to it.
5859 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5860 double nearLargestPercent = 0.999;
5861 HeapWord* minAddr = _cmsSpace->bottom();
5862 HeapWord* largestAddr =
5863 (HeapWord*) _cmsSpace->dictionary()->findLargestDict();
5864 if (largestAddr == 0) {
5865 // The dictionary appears to be empty. In this case
5866 // try to coalesce at the end of the heap.
5867 largestAddr = _cmsSpace->end();
5868 }
5869 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5870 size_t nearLargestOffset =
5871 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5872 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5873 }
5874
5875 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5876 return addr >= _cmsSpace->nearLargestChunk();
5877 }
5878
5879 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5880 return _cmsSpace->find_chunk_at_end();
5881 }
5882
5883 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
5884 bool full) {
5885 // The next lower level has been collected. Gather any statistics
5886 // that are of interest at this point.
5887 if (!full && (current_level + 1) == level()) {
5888 // Gather statistics on the young generation collection.
5889 collector()->stats().record_gc0_end(used());
5890 }
5891 }
5892
5893 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
5894 GenCollectedHeap* gch = GenCollectedHeap::heap();
5895 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
5896 "Wrong type of heap");
5897 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
5898 gch->gen_policy()->size_policy();
5899 assert(sp->is_gc_cms_adaptive_size_policy(),
5900 "Wrong type of size policy");
5901 return sp;
5902 }
5903
5904 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
5905 if (PrintGCDetails && Verbose) {
5906 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
5907 }
5908 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
5909 _debug_collection_type =
5910 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
5911 if (PrintGCDetails && Verbose) {
5912 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
5913 }
5914 }
5915
5916 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
5917 bool asynch) {
5918 // We iterate over the space(s) underlying this generation,
5919 // checking the mark bit map to see if the bits corresponding
5920 // to specific blocks are marked or not. Blocks that are
5921 // marked are live and are not swept up. All remaining blocks
5922 // are swept up, with coalescing on-the-fly as we sweep up
5923 // contiguous free and/or garbage blocks:
5924 // We need to ensure that the sweeper synchronizes with allocators
5925 // and stop-the-world collectors. In particular, the following
5926 // locks are used:
5927 // . CMS token: if this is held, a stop the world collection cannot occur
5928 // . freelistLock: if this is held no allocation can occur from this
5929 // generation by another thread
5930 // . bitMapLock: if this is held, no other thread can access or update
5931 //
5932
5933 // Note that we need to hold the freelistLock if we use
5934 // block iterate below; else the iterator might go awry if
5935 // a mutator (or promotion) causes block contents to change
5936 // (for instance if the allocator divvies up a block).
5937 // If we hold the free list lock, for all practical purposes
5938 // young generation GC's can't occur (they'll usually need to
5939 // promote), so we might as well prevent all young generation
5940 // GC's while we do a sweeping step. For the same reason, we might
5941 // as well take the bit map lock for the entire duration
5942
5943 // check that we hold the requisite locks
5944 assert(have_cms_token(), "Should hold cms token");
5945 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
5946 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
5947 "Should possess CMS token to sweep");
5948 assert_lock_strong(gen->freelistLock());
5949 assert_lock_strong(bitMapLock());
5950
5951 assert(!_sweep_timer.is_active(), "Was switched off in an outer context");
5952 gen->cmsSpace()->beginSweepFLCensus((float)(_sweep_timer.seconds()),
5953 _sweep_estimate.padded_average());
5954 gen->setNearLargestChunk();
5955
5956 {
5957 SweepClosure sweepClosure(this, gen, &_markBitMap,
5958 CMSYield && asynch);
5959 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5960 // We need to free-up/coalesce garbage/blocks from a
5961 // co-terminal free run. This is done in the SweepClosure
5962 // destructor; so, do not remove this scope, else the
5963 // end-of-sweep-census below will be off by a little bit.
5964 }
5965 gen->cmsSpace()->sweep_completed();
5966 gen->cmsSpace()->endSweepFLCensus(sweepCount());
5967 }
5968
5969 // Reset CMS data structures (for now just the marking bit map)
5970 // preparatory for the next cycle.
5971 void CMSCollector::reset(bool asynch) {
5972 GenCollectedHeap* gch = GenCollectedHeap::heap();
5973 CMSAdaptiveSizePolicy* sp = size_policy();
5974 AdaptiveSizePolicyOutput(sp, gch->total_collections());
5975 if (asynch) {
5976 CMSTokenSyncWithLocks ts(true, bitMapLock());
5977
5978 // If the state is not "Resetting", the foreground thread
5979 // has done a collection and the resetting.
5980 if (_collectorState != Resetting) {
5981 assert(_collectorState == Idling, "The state should only change"
5982 " because the foreground collector has finished the collection");
5983 return;
5984 }
5985
5986 // Clear the mark bitmap (no grey objects to start with)
5987 // for the next cycle.
5988 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5989 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
5990
5991 HeapWord* curAddr = _markBitMap.startWord();
5992 while (curAddr < _markBitMap.endWord()) {
5993 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5994 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5995 _markBitMap.clear_large_range(chunk);
5996 if (ConcurrentMarkSweepThread::should_yield() &&
5997 !foregroundGCIsActive() &&
5998 CMSYield) {
5999 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6000 "CMS thread should hold CMS token");
6001 assert_lock_strong(bitMapLock());
6002 bitMapLock()->unlock();
6003 ConcurrentMarkSweepThread::desynchronize(true);
6004 ConcurrentMarkSweepThread::acknowledge_yield_request();
6005 stopTimer();
6006 if (PrintCMSStatistics != 0) {
6007 incrementYields();
6008 }
6009 icms_wait();
6010
6011 // See the comment in coordinator_yield()
6012 for (unsigned i = 0; i < CMSYieldSleepCount &&
6013 ConcurrentMarkSweepThread::should_yield() &&
6014 !CMSCollector::foregroundGCIsActive(); ++i) {
6015 os::sleep(Thread::current(), 1, false);
6016 ConcurrentMarkSweepThread::acknowledge_yield_request();
6017 }
6018
6019 ConcurrentMarkSweepThread::synchronize(true);
6020 bitMapLock()->lock_without_safepoint_check();
6021 startTimer();
6022 }
6023 curAddr = chunk.end();
6024 }
6025 _collectorState = Idling;
6026 } else {
6027 // already have the lock
6028 assert(_collectorState == Resetting, "just checking");
6029 assert_lock_strong(bitMapLock());
6030 _markBitMap.clear_all();
6031 _collectorState = Idling;
6032 }
6033
6034 // Stop incremental mode after a cycle completes, so that any future cycles
6035 // are triggered by allocation.
6036 stop_icms();
6037
6038 NOT_PRODUCT(
6039 if (RotateCMSCollectionTypes) {
6040 _cmsGen->rotate_debug_collection_type();
6041 }
6042 )
6043 }
6044
6045 void CMSCollector::do_CMS_operation(CMS_op_type op) {
6046 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6047 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6048 TraceTime t("GC", PrintGC, !PrintGCDetails, gclog_or_tty);
6049 TraceCollectorStats tcs(counters());
6050
6051 switch (op) {
6052 case CMS_op_checkpointRootsInitial: {
6053 checkpointRootsInitial(true); // asynch
6054 if (PrintGC) {
6055 _cmsGen->printOccupancy("initial-mark");
6056 }
6057 break;
6058 }
6059 case CMS_op_checkpointRootsFinal: {
6060 checkpointRootsFinal(true, // asynch
6061 false, // !clear_all_soft_refs
6062 false); // !init_mark_was_synchronous
6063 if (PrintGC) {
6064 _cmsGen->printOccupancy("remark");
6065 }
6066 break;
6067 }
6068 default:
6069 fatal("No such CMS_op");
6070 }
6071 }
6072
6073 #ifndef PRODUCT
6074 size_t const CMSCollector::skip_header_HeapWords() {
6075 return FreeChunk::header_size();
6076 }
6077
6078 // Try and collect here conditions that should hold when
6079 // CMS thread is exiting. The idea is that the foreground GC
6080 // thread should not be blocked if it wants to terminate
6081 // the CMS thread and yet continue to run the VM for a while
6082 // after that.
6083 void CMSCollector::verify_ok_to_terminate() const {
6084 assert(Thread::current()->is_ConcurrentGC_thread(),
6085 "should be called by CMS thread");
6086 assert(!_foregroundGCShouldWait, "should be false");
6087 // We could check here that all the various low-level locks
6088 // are not held by the CMS thread, but that is overkill; see
6089 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6090 // is checked.
6091 }
6092 #endif
6093
6094 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6095 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6096 "missing Printezis mark?");
6097 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6098 size_t size = pointer_delta(nextOneAddr + 1, addr);
6099 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6100 "alignment problem");
6101 assert(size >= 3, "Necessary for Printezis marks to work");
6102 return size;
6103 }
6104
6105 // A variant of the above (block_size_using_printezis_bits()) except
6106 // that we return 0 if the P-bits are not yet set.
6107 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6108 if (_markBitMap.isMarked(addr)) {
6109 assert(_markBitMap.isMarked(addr + 1), "Missing Printezis bit?");
6110 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6111 size_t size = pointer_delta(nextOneAddr + 1, addr);
6112 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6113 "alignment problem");
6114 assert(size >= 3, "Necessary for Printezis marks to work");
6115 return size;
6116 } else {
6117 assert(!_markBitMap.isMarked(addr + 1), "Bit map inconsistency?");
6118 return 0;
6119 }
6120 }
6121
6122 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6123 size_t sz = 0;
6124 oop p = (oop)addr;
6125 if (p->klass() != NULL && p->is_parsable()) {
6126 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6127 } else {
6128 sz = block_size_using_printezis_bits(addr);
6129 }
6130 assert(sz > 0, "size must be nonzero");
6131 HeapWord* next_block = addr + sz;
6132 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6133 CardTableModRefBS::card_size);
6134 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6135 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6136 "must be different cards");
6137 return next_card;
6138 }
6139
6140
6141 // CMS Bit Map Wrapper /////////////////////////////////////////
6142
6143 // Construct a CMS bit map infrastructure, but don't create the
6144 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6145 // further below.
6146 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6147 _bm(NULL,0),
6148 _shifter(shifter),
6149 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6150 {
6151 _bmStartWord = 0;
6152 _bmWordSize = 0;
6153 }
6154
6155 bool CMSBitMap::allocate(MemRegion mr) {
6156 _bmStartWord = mr.start();
6157 _bmWordSize = mr.word_size();
6158 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6159 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6160 if (!brs.is_reserved()) {
6161 warning("CMS bit map allocation failure");
6162 return false;
6163 }
6164 // For now we'll just commit all of the bit map up fromt.
6165 // Later on we'll try to be more parsimonious with swap.
6166 if (!_virtual_space.initialize(brs, brs.size())) {
6167 warning("CMS bit map backing store failure");
6168 return false;
6169 }
6170 assert(_virtual_space.committed_size() == brs.size(),
6171 "didn't reserve backing store for all of CMS bit map?");
6172 _bm.set_map((uintptr_t*)_virtual_space.low());
6173 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6174 _bmWordSize, "inconsistency in bit map sizing");
6175 _bm.set_size(_bmWordSize >> _shifter);
6176
6177 // bm.clear(); // can we rely on getting zero'd memory? verify below
6178 assert(isAllClear(),
6179 "Expected zero'd memory from ReservedSpace constructor");
6180 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6181 "consistency check");
6182 return true;
6183 }
6184
6185 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6186 HeapWord *next_addr, *end_addr, *last_addr;
6187 assert_locked();
6188 assert(covers(mr), "out-of-range error");
6189 // XXX assert that start and end are appropriately aligned
6190 for (next_addr = mr.start(), end_addr = mr.end();
6191 next_addr < end_addr; next_addr = last_addr) {
6192 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6193 last_addr = dirty_region.end();
6194 if (!dirty_region.is_empty()) {
6195 cl->do_MemRegion(dirty_region);
6196 } else {
6197 assert(last_addr == end_addr, "program logic");
6198 return;
6199 }
6200 }
6201 }
6202
6203 #ifndef PRODUCT
6204 void CMSBitMap::assert_locked() const {
6205 CMSLockVerifier::assert_locked(lock());
6206 }
6207
6208 bool CMSBitMap::covers(MemRegion mr) const {
6209 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6210 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6211 "size inconsistency");
6212 return (mr.start() >= _bmStartWord) &&
6213 (mr.end() <= endWord());
6214 }
6215
6216 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6217 return (start >= _bmStartWord && (start + size) <= endWord());
6218 }
6219
6220 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6221 // verify that there are no 1 bits in the interval [left, right)
6222 FalseBitMapClosure falseBitMapClosure;
6223 iterate(&falseBitMapClosure, left, right);
6224 }
6225
6226 void CMSBitMap::region_invariant(MemRegion mr)
6227 {
6228 assert_locked();
6229 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6230 assert(!mr.is_empty(), "unexpected empty region");
6231 assert(covers(mr), "mr should be covered by bit map");
6232 // convert address range into offset range
6233 size_t start_ofs = heapWordToOffset(mr.start());
6234 // Make sure that end() is appropriately aligned
6235 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6236 (1 << (_shifter+LogHeapWordSize))),
6237 "Misaligned mr.end()");
6238 size_t end_ofs = heapWordToOffset(mr.end());
6239 assert(end_ofs > start_ofs, "Should mark at least one bit");
6240 }
6241
6242 #endif
6243
6244 bool CMSMarkStack::allocate(size_t size) {
6245 // allocate a stack of the requisite depth
6246 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6247 size * sizeof(oop)));
6248 if (!rs.is_reserved()) {
6249 warning("CMSMarkStack allocation failure");
6250 return false;
6251 }
6252 if (!_virtual_space.initialize(rs, rs.size())) {
6253 warning("CMSMarkStack backing store failure");
6254 return false;
6255 }
6256 assert(_virtual_space.committed_size() == rs.size(),
6257 "didn't reserve backing store for all of CMS stack?");
6258 _base = (oop*)(_virtual_space.low());
6259 _index = 0;
6260 _capacity = size;
6261 NOT_PRODUCT(_max_depth = 0);
6262 return true;
6263 }
6264
6265 // XXX FIX ME !!! In the MT case we come in here holding a
6266 // leaf lock. For printing we need to take a further lock
6267 // which has lower rank. We need to recallibrate the two
6268 // lock-ranks involved in order to be able to rpint the
6269 // messages below. (Or defer the printing to the caller.
6270 // For now we take the expedient path of just disabling the
6271 // messages for the problematic case.)
6272 void CMSMarkStack::expand() {
6273 assert(_capacity <= CMSMarkStackSizeMax, "stack bigger than permitted");
6274 if (_capacity == CMSMarkStackSizeMax) {
6275 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6276 // We print a warning message only once per CMS cycle.
6277 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6278 }
6279 return;
6280 }
6281 // Double capacity if possible
6282 size_t new_capacity = MIN2(_capacity*2, CMSMarkStackSizeMax);
6283 // Do not give up existing stack until we have managed to
6284 // get the double capacity that we desired.
6285 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6286 new_capacity * sizeof(oop)));
6287 if (rs.is_reserved()) {
6288 // Release the backing store associated with old stack
6289 _virtual_space.release();
6290 // Reinitialize virtual space for new stack
6291 if (!_virtual_space.initialize(rs, rs.size())) {
6292 fatal("Not enough swap for expanded marking stack");
6293 }
6294 _base = (oop*)(_virtual_space.low());
6295 _index = 0;
6296 _capacity = new_capacity;
6297 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6298 // Failed to double capacity, continue;
6299 // we print a detail message only once per CMS cycle.
6300 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6301 SIZE_FORMAT"K",
6302 _capacity / K, new_capacity / K);
6303 }
6304 }
6305
6306
6307 // Closures
6308 // XXX: there seems to be a lot of code duplication here;
6309 // should refactor and consolidate common code.
6310
6311 // This closure is used to mark refs into the CMS generation in
6312 // the CMS bit map. Called at the first checkpoint. This closure
6313 // assumes that we do not need to re-mark dirty cards; if the CMS
6314 // generation on which this is used is not an oldest (modulo perm gen)
6315 // generation then this will lose younger_gen cards!
6316
6317 MarkRefsIntoClosure::MarkRefsIntoClosure(
6318 MemRegion span, CMSBitMap* bitMap, bool should_do_nmethods):
6319 _span(span),
6320 _bitMap(bitMap),
6321 _should_do_nmethods(should_do_nmethods)
6322 {
6323 assert(_ref_processor == NULL, "deliberately left NULL");
6324 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6325 }
6326
6327 void MarkRefsIntoClosure::do_oop(oop* p) {
6328 // if p points into _span, then mark corresponding bit in _markBitMap
6329 oop thisOop = *p;
6330 if (thisOop != NULL) {
6331 assert(thisOop->is_oop(), "expected an oop");
6332 HeapWord* addr = (HeapWord*)thisOop;
6333 if (_span.contains(addr)) {
6334 // this should be made more efficient
6335 _bitMap->mark(addr);
6336 }
6337 }
6338 }
6339
6340 // A variant of the above, used for CMS marking verification.
6341 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6342 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6343 bool should_do_nmethods):
6344 _span(span),
6345 _verification_bm(verification_bm),
6346 _cms_bm(cms_bm),
6347 _should_do_nmethods(should_do_nmethods) {
6348 assert(_ref_processor == NULL, "deliberately left NULL");
6349 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6350 }
6351
6352 void MarkRefsIntoVerifyClosure::do_oop(oop* p) {
6353 // if p points into _span, then mark corresponding bit in _markBitMap
6354 oop this_oop = *p;
6355 if (this_oop != NULL) {
6356 assert(this_oop->is_oop(), "expected an oop");
6357 HeapWord* addr = (HeapWord*)this_oop;
6358 if (_span.contains(addr)) {
6359 _verification_bm->mark(addr);
6360 if (!_cms_bm->isMarked(addr)) {
6361 oop(addr)->print();
6362 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
6363 fatal("... aborting");
6364 }
6365 }
6366 }
6367 }
6368
6369 //////////////////////////////////////////////////
6370 // MarkRefsIntoAndScanClosure
6371 //////////////////////////////////////////////////
6372
6373 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6374 ReferenceProcessor* rp,
6375 CMSBitMap* bit_map,
6376 CMSBitMap* mod_union_table,
6377 CMSMarkStack* mark_stack,
6378 CMSMarkStack* revisit_stack,
6379 CMSCollector* collector,
6380 bool should_yield,
6381 bool concurrent_precleaning):
6382 _collector(collector),
6383 _span(span),
6384 _bit_map(bit_map),
6385 _mark_stack(mark_stack),
6386 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6387 mark_stack, revisit_stack, concurrent_precleaning),
6388 _yield(should_yield),
6389 _concurrent_precleaning(concurrent_precleaning),
6390 _freelistLock(NULL)
6391 {
6392 _ref_processor = rp;
6393 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6394 }
6395
6396 // This closure is used to mark refs into the CMS generation at the
6397 // second (final) checkpoint, and to scan and transitively follow
6398 // the unmarked oops. It is also used during the concurrent precleaning
6399 // phase while scanning objects on dirty cards in the CMS generation.
6400 // The marks are made in the marking bit map and the marking stack is
6401 // used for keeping the (newly) grey objects during the scan.
6402 // The parallel version (Par_...) appears further below.
6403 void MarkRefsIntoAndScanClosure::do_oop(oop* p) {
6404 oop this_oop = *p;
6405 if (this_oop != NULL) {
6406 assert(this_oop->is_oop(), "expected an oop");
6407 HeapWord* addr = (HeapWord*)this_oop;
6408 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6409 assert(_collector->overflow_list_is_empty(), "should be empty");
6410 if (_span.contains(addr) &&
6411 !_bit_map->isMarked(addr)) {
6412 // mark bit map (object is now grey)
6413 _bit_map->mark(addr);
6414 // push on marking stack (stack should be empty), and drain the
6415 // stack by applying this closure to the oops in the oops popped
6416 // from the stack (i.e. blacken the grey objects)
6417 bool res = _mark_stack->push(this_oop);
6418 assert(res, "Should have space to push on empty stack");
6419 do {
6420 oop new_oop = _mark_stack->pop();
6421 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6422 assert(new_oop->is_parsable(), "Found unparsable oop");
6423 assert(_bit_map->isMarked((HeapWord*)new_oop),
6424 "only grey objects on this stack");
6425 // iterate over the oops in this oop, marking and pushing
6426 // the ones in CMS heap (i.e. in _span).
6427 new_oop->oop_iterate(&_pushAndMarkClosure);
6428 // check if it's time to yield
6429 do_yield_check();
6430 } while (!_mark_stack->isEmpty() ||
6431 (!_concurrent_precleaning && take_from_overflow_list()));
6432 // if marking stack is empty, and we are not doing this
6433 // during precleaning, then check the overflow list
6434 }
6435 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6436 assert(_collector->overflow_list_is_empty(),
6437 "overflow list was drained above");
6438 // We could restore evacuated mark words, if any, used for
6439 // overflow list links here because the overflow list is
6440 // provably empty here. That would reduce the maximum
6441 // size requirements for preserved_{oop,mark}_stack.
6442 // But we'll just postpone it until we are all done
6443 // so we can just stream through.
6444 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6445 _collector->restore_preserved_marks_if_any();
6446 assert(_collector->no_preserved_marks(), "No preserved marks");
6447 }
6448 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6449 "All preserved marks should have been restored above");
6450 }
6451 }
6452
6453 void MarkRefsIntoAndScanClosure::do_yield_work() {
6454 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6455 "CMS thread should hold CMS token");
6456 assert_lock_strong(_freelistLock);
6457 assert_lock_strong(_bit_map->lock());
6458 // relinquish the free_list_lock and bitMaplock()
6459 _bit_map->lock()->unlock();
6460 _freelistLock->unlock();
6461 ConcurrentMarkSweepThread::desynchronize(true);
6462 ConcurrentMarkSweepThread::acknowledge_yield_request();
6463 _collector->stopTimer();
6464 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6465 if (PrintCMSStatistics != 0) {
6466 _collector->incrementYields();
6467 }
6468 _collector->icms_wait();
6469
6470 // See the comment in coordinator_yield()
6471 for (unsigned i = 0; i < CMSYieldSleepCount &&
6472 ConcurrentMarkSweepThread::should_yield() &&
6473 !CMSCollector::foregroundGCIsActive(); ++i) {
6474 os::sleep(Thread::current(), 1, false);
6475 ConcurrentMarkSweepThread::acknowledge_yield_request();
6476 }
6477
6478 ConcurrentMarkSweepThread::synchronize(true);
6479 _freelistLock->lock_without_safepoint_check();
6480 _bit_map->lock()->lock_without_safepoint_check();
6481 _collector->startTimer();
6482 }
6483
6484 ///////////////////////////////////////////////////////////
6485 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6486 // MarkRefsIntoAndScanClosure
6487 ///////////////////////////////////////////////////////////
6488 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6489 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6490 CMSBitMap* bit_map, OopTaskQueue* work_queue, CMSMarkStack* revisit_stack):
6491 _span(span),
6492 _bit_map(bit_map),
6493 _work_queue(work_queue),
6494 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6495 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6496 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue,
6497 revisit_stack)
6498 {
6499 _ref_processor = rp;
6500 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6501 }
6502
6503 // This closure is used to mark refs into the CMS generation at the
6504 // second (final) checkpoint, and to scan and transitively follow
6505 // the unmarked oops. The marks are made in the marking bit map and
6506 // the work_queue is used for keeping the (newly) grey objects during
6507 // the scan phase whence they are also available for stealing by parallel
6508 // threads. Since the marking bit map is shared, updates are
6509 // synchronized (via CAS).
6510 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) {
6511 oop this_oop = *p;
6512 if (this_oop != NULL) {
6513 // Ignore mark word because this could be an already marked oop
6514 // that may be chained at the end of the overflow list.
6515 assert(this_oop->is_oop(true /* ignore mark word */), "expected an oop");
6516 HeapWord* addr = (HeapWord*)this_oop;
6517 if (_span.contains(addr) &&
6518 !_bit_map->isMarked(addr)) {
6519 // mark bit map (object will become grey):
6520 // It is possible for several threads to be
6521 // trying to "claim" this object concurrently;
6522 // the unique thread that succeeds in marking the
6523 // object first will do the subsequent push on
6524 // to the work queue (or overflow list).
6525 if (_bit_map->par_mark(addr)) {
6526 // push on work_queue (which may not be empty), and trim the
6527 // queue to an appropriate length by applying this closure to
6528 // the oops in the oops popped from the stack (i.e. blacken the
6529 // grey objects)
6530 bool res = _work_queue->push(this_oop);
6531 assert(res, "Low water mark should be less than capacity?");
6532 trim_queue(_low_water_mark);
6533 } // Else, another thread claimed the object
6534 }
6535 }
6536 }
6537
6538 // This closure is used to rescan the marked objects on the dirty cards
6539 // in the mod union table and the card table proper.
6540 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6541 oop p, MemRegion mr) {
6542
6543 size_t size = 0;
6544 HeapWord* addr = (HeapWord*)p;
6545 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6546 assert(_span.contains(addr), "we are scanning the CMS generation");
6547 // check if it's time to yield
6548 if (do_yield_check()) {
6549 // We yielded for some foreground stop-world work,
6550 // and we have been asked to abort this ongoing preclean cycle.
6551 return 0;
6552 }
6553 if (_bitMap->isMarked(addr)) {
6554 // it's marked; is it potentially uninitialized?
6555 if (p->klass() != NULL) {
6556 if (CMSPermGenPrecleaningEnabled && !p->is_parsable()) {
6557 // Signal precleaning to redirty the card since
6558 // the klass pointer is already installed.
6559 assert(size == 0, "Initial value");
6560 } else {
6561 assert(p->is_parsable(), "must be parsable.");
6562 // an initialized object; ignore mark word in verification below
6563 // since we are running concurrent with mutators
6564 assert(p->is_oop(true), "should be an oop");
6565 if (p->is_objArray()) {
6566 // objArrays are precisely marked; restrict scanning
6567 // to dirty cards only.
6568 size = p->oop_iterate(_scanningClosure, mr);
6569 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6570 "adjustObjectSize should be the identity for array sizes, "
6571 "which are necessarily larger than minimum object size of "
6572 "two heap words");
6573 } else {
6574 // A non-array may have been imprecisely marked; we need
6575 // to scan object in its entirety.
6576 size = CompactibleFreeListSpace::adjustObjectSize(
6577 p->oop_iterate(_scanningClosure));
6578 }
6579 #ifdef DEBUG
6580 size_t direct_size =
6581 CompactibleFreeListSpace::adjustObjectSize(p->size());
6582 assert(size == direct_size, "Inconsistency in size");
6583 assert(size >= 3, "Necessary for Printezis marks to work");
6584 if (!_bitMap->isMarked(addr+1)) {
6585 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6586 } else {
6587 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6588 assert(_bitMap->isMarked(addr+size-1),
6589 "inconsistent Printezis mark");
6590 }
6591 #endif // DEBUG
6592 }
6593 } else {
6594 // an unitialized object
6595 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6596 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6597 size = pointer_delta(nextOneAddr + 1, addr);
6598 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6599 "alignment problem");
6600 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6601 // will dirty the card when the klass pointer is installed in the
6602 // object (signalling the completion of initialization).
6603 }
6604 } else {
6605 // Either a not yet marked object or an uninitialized object
6606 if (p->klass() == NULL || !p->is_parsable()) {
6607 // An uninitialized object, skip to the next card, since
6608 // we may not be able to read its P-bits yet.
6609 assert(size == 0, "Initial value");
6610 } else {
6611 // An object not (yet) reached by marking: we merely need to
6612 // compute its size so as to go look at the next block.
6613 assert(p->is_oop(true), "should be an oop");
6614 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6615 }
6616 }
6617 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6618 return size;
6619 }
6620
6621 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6622 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6623 "CMS thread should hold CMS token");
6624 assert_lock_strong(_freelistLock);
6625 assert_lock_strong(_bitMap->lock());
6626 // relinquish the free_list_lock and bitMaplock()
6627 _bitMap->lock()->unlock();
6628 _freelistLock->unlock();
6629 ConcurrentMarkSweepThread::desynchronize(true);
6630 ConcurrentMarkSweepThread::acknowledge_yield_request();
6631 _collector->stopTimer();
6632 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6633 if (PrintCMSStatistics != 0) {
6634 _collector->incrementYields();
6635 }
6636 _collector->icms_wait();
6637
6638 // See the comment in coordinator_yield()
6639 for (unsigned i = 0; i < CMSYieldSleepCount &&
6640 ConcurrentMarkSweepThread::should_yield() &&
6641 !CMSCollector::foregroundGCIsActive(); ++i) {
6642 os::sleep(Thread::current(), 1, false);
6643 ConcurrentMarkSweepThread::acknowledge_yield_request();
6644 }
6645
6646 ConcurrentMarkSweepThread::synchronize(true);
6647 _freelistLock->lock_without_safepoint_check();
6648 _bitMap->lock()->lock_without_safepoint_check();
6649 _collector->startTimer();
6650 }
6651
6652
6653 //////////////////////////////////////////////////////////////////
6654 // SurvivorSpacePrecleanClosure
6655 //////////////////////////////////////////////////////////////////
6656 // This (single-threaded) closure is used to preclean the oops in
6657 // the survivor spaces.
6658 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6659
6660 HeapWord* addr = (HeapWord*)p;
6661 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6662 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6663 assert(p->klass() != NULL, "object should be initializd");
6664 assert(p->is_parsable(), "must be parsable.");
6665 // an initialized object; ignore mark word in verification below
6666 // since we are running concurrent with mutators
6667 assert(p->is_oop(true), "should be an oop");
6668 // Note that we do not yield while we iterate over
6669 // the interior oops of p, pushing the relevant ones
6670 // on our marking stack.
6671 size_t size = p->oop_iterate(_scanning_closure);
6672 do_yield_check();
6673 // Observe that below, we do not abandon the preclean
6674 // phase as soon as we should; rather we empty the
6675 // marking stack before returning. This is to satisfy
6676 // some existing assertions. In general, it may be a
6677 // good idea to abort immediately and complete the marking
6678 // from the grey objects at a later time.
6679 while (!_mark_stack->isEmpty()) {
6680 oop new_oop = _mark_stack->pop();
6681 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6682 assert(new_oop->is_parsable(), "Found unparsable oop");
6683 assert(_bit_map->isMarked((HeapWord*)new_oop),
6684 "only grey objects on this stack");
6685 // iterate over the oops in this oop, marking and pushing
6686 // the ones in CMS heap (i.e. in _span).
6687 new_oop->oop_iterate(_scanning_closure);
6688 // check if it's time to yield
6689 do_yield_check();
6690 }
6691 unsigned int after_count =
6692 GenCollectedHeap::heap()->total_collections();
6693 bool abort = (_before_count != after_count) ||
6694 _collector->should_abort_preclean();
6695 return abort ? 0 : size;
6696 }
6697
6698 void SurvivorSpacePrecleanClosure::do_yield_work() {
6699 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6700 "CMS thread should hold CMS token");
6701 assert_lock_strong(_bit_map->lock());
6702 // Relinquish the bit map lock
6703 _bit_map->lock()->unlock();
6704 ConcurrentMarkSweepThread::desynchronize(true);
6705 ConcurrentMarkSweepThread::acknowledge_yield_request();
6706 _collector->stopTimer();
6707 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6708 if (PrintCMSStatistics != 0) {
6709 _collector->incrementYields();
6710 }
6711 _collector->icms_wait();
6712
6713 // See the comment in coordinator_yield()
6714 for (unsigned i = 0; i < CMSYieldSleepCount &&
6715 ConcurrentMarkSweepThread::should_yield() &&
6716 !CMSCollector::foregroundGCIsActive(); ++i) {
6717 os::sleep(Thread::current(), 1, false);
6718 ConcurrentMarkSweepThread::acknowledge_yield_request();
6719 }
6720
6721 ConcurrentMarkSweepThread::synchronize(true);
6722 _bit_map->lock()->lock_without_safepoint_check();
6723 _collector->startTimer();
6724 }
6725
6726 // This closure is used to rescan the marked objects on the dirty cards
6727 // in the mod union table and the card table proper. In the parallel
6728 // case, although the bitMap is shared, we do a single read so the
6729 // isMarked() query is "safe".
6730 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6731 // Ignore mark word because we are running concurrent with mutators
6732 assert(p->is_oop_or_null(true), "expected an oop or null");
6733 HeapWord* addr = (HeapWord*)p;
6734 assert(_span.contains(addr), "we are scanning the CMS generation");
6735 bool is_obj_array = false;
6736 #ifdef DEBUG
6737 if (!_parallel) {
6738 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6739 assert(_collector->overflow_list_is_empty(),
6740 "overflow list should be empty");
6741
6742 }
6743 #endif // DEBUG
6744 if (_bit_map->isMarked(addr)) {
6745 // Obj arrays are precisely marked, non-arrays are not;
6746 // so we scan objArrays precisely and non-arrays in their
6747 // entirety.
6748 if (p->is_objArray()) {
6749 is_obj_array = true;
6750 if (_parallel) {
6751 p->oop_iterate(_par_scan_closure, mr);
6752 } else {
6753 p->oop_iterate(_scan_closure, mr);
6754 }
6755 } else {
6756 if (_parallel) {
6757 p->oop_iterate(_par_scan_closure);
6758 } else {
6759 p->oop_iterate(_scan_closure);
6760 }
6761 }
6762 }
6763 #ifdef DEBUG
6764 if (!_parallel) {
6765 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6766 assert(_collector->overflow_list_is_empty(),
6767 "overflow list should be empty");
6768
6769 }
6770 #endif // DEBUG
6771 return is_obj_array;
6772 }
6773
6774 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6775 MemRegion span,
6776 CMSBitMap* bitMap, CMSMarkStack* markStack,
6777 CMSMarkStack* revisitStack,
6778 bool should_yield, bool verifying):
6779 _collector(collector),
6780 _span(span),
6781 _bitMap(bitMap),
6782 _mut(&collector->_modUnionTable),
6783 _markStack(markStack),
6784 _revisitStack(revisitStack),
6785 _yield(should_yield),
6786 _skipBits(0)
6787 {
6788 assert(_markStack->isEmpty(), "stack should be empty");
6789 _finger = _bitMap->startWord();
6790 _threshold = _finger;
6791 assert(_collector->_restart_addr == NULL, "Sanity check");
6792 assert(_span.contains(_finger), "Out of bounds _finger?");
6793 DEBUG_ONLY(_verifying = verifying;)
6794 }
6795
6796 void MarkFromRootsClosure::reset(HeapWord* addr) {
6797 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6798 assert(_span.contains(addr), "Out of bounds _finger?");
6799 _finger = addr;
6800 _threshold = (HeapWord*)round_to(
6801 (intptr_t)_finger, CardTableModRefBS::card_size);
6802 }
6803
6804 // Should revisit to see if this should be restructured for
6805 // greater efficiency.
6806 void MarkFromRootsClosure::do_bit(size_t offset) {
6807 if (_skipBits > 0) {
6808 _skipBits--;
6809 return;
6810 }
6811 // convert offset into a HeapWord*
6812 HeapWord* addr = _bitMap->startWord() + offset;
6813 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6814 "address out of range");
6815 assert(_bitMap->isMarked(addr), "tautology");
6816 if (_bitMap->isMarked(addr+1)) {
6817 // this is an allocated but not yet initialized object
6818 assert(_skipBits == 0, "tautology");
6819 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6820 oop p = oop(addr);
6821 if (p->klass() == NULL || !p->is_parsable()) {
6822 DEBUG_ONLY(if (!_verifying) {)
6823 // We re-dirty the cards on which this object lies and increase
6824 // the _threshold so that we'll come back to scan this object
6825 // during the preclean or remark phase. (CMSCleanOnEnter)
6826 if (CMSCleanOnEnter) {
6827 size_t sz = _collector->block_size_using_printezis_bits(addr);
6828 HeapWord* end_card_addr = (HeapWord*)round_to(
6829 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6830 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6831 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6832 // Bump _threshold to end_card_addr; note that
6833 // _threshold cannot possibly exceed end_card_addr, anyhow.
6834 // This prevents future clearing of the card as the scan proceeds
6835 // to the right.
6836 assert(_threshold <= end_card_addr,
6837 "Because we are just scanning into this object");
6838 if (_threshold < end_card_addr) {
6839 _threshold = end_card_addr;
6840 }
6841 if (p->klass() != NULL) {
6842 // Redirty the range of cards...
6843 _mut->mark_range(redirty_range);
6844 } // ...else the setting of klass will dirty the card anyway.
6845 }
6846 DEBUG_ONLY(})
6847 return;
6848 }
6849 }
6850 scanOopsInOop(addr);
6851 }
6852
6853 // We take a break if we've been at this for a while,
6854 // so as to avoid monopolizing the locks involved.
6855 void MarkFromRootsClosure::do_yield_work() {
6856 // First give up the locks, then yield, then re-lock
6857 // We should probably use a constructor/destructor idiom to
6858 // do this unlock/lock or modify the MutexUnlocker class to
6859 // serve our purpose. XXX
6860 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6861 "CMS thread should hold CMS token");
6862 assert_lock_strong(_bitMap->lock());
6863 _bitMap->lock()->unlock();
6864 ConcurrentMarkSweepThread::desynchronize(true);
6865 ConcurrentMarkSweepThread::acknowledge_yield_request();
6866 _collector->stopTimer();
6867 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6868 if (PrintCMSStatistics != 0) {
6869 _collector->incrementYields();
6870 }
6871 _collector->icms_wait();
6872
6873 // See the comment in coordinator_yield()
6874 for (unsigned i = 0; i < CMSYieldSleepCount &&
6875 ConcurrentMarkSweepThread::should_yield() &&
6876 !CMSCollector::foregroundGCIsActive(); ++i) {
6877 os::sleep(Thread::current(), 1, false);
6878 ConcurrentMarkSweepThread::acknowledge_yield_request();
6879 }
6880
6881 ConcurrentMarkSweepThread::synchronize(true);
6882 _bitMap->lock()->lock_without_safepoint_check();
6883 _collector->startTimer();
6884 }
6885
6886 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6887 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6888 assert(_markStack->isEmpty(),
6889 "should drain stack to limit stack usage");
6890 // convert ptr to an oop preparatory to scanning
6891 oop this_oop = oop(ptr);
6892 // Ignore mark word in verification below, since we
6893 // may be running concurrent with mutators.
6894 assert(this_oop->is_oop(true), "should be an oop");
6895 assert(_finger <= ptr, "_finger runneth ahead");
6896 // advance the finger to right end of this object
6897 _finger = ptr + this_oop->size();
6898 assert(_finger > ptr, "we just incremented it above");
6899 // On large heaps, it may take us some time to get through
6900 // the marking phase (especially if running iCMS). During
6901 // this time it's possible that a lot of mutations have
6902 // accumulated in the card table and the mod union table --
6903 // these mutation records are redundant until we have
6904 // actually traced into the corresponding card.
6905 // Here, we check whether advancing the finger would make
6906 // us cross into a new card, and if so clear corresponding
6907 // cards in the MUT (preclean them in the card-table in the
6908 // future).
6909
6910 DEBUG_ONLY(if (!_verifying) {)
6911 // The clean-on-enter optimization is disabled by default,
6912 // until we fix 6178663.
6913 if (CMSCleanOnEnter && (_finger > _threshold)) {
6914 // [_threshold, _finger) represents the interval
6915 // of cards to be cleared in MUT (or precleaned in card table).
6916 // The set of cards to be cleared is all those that overlap
6917 // with the interval [_threshold, _finger); note that
6918 // _threshold is always kept card-aligned but _finger isn't
6919 // always card-aligned.
6920 HeapWord* old_threshold = _threshold;
6921 assert(old_threshold == (HeapWord*)round_to(
6922 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6923 "_threshold should always be card-aligned");
6924 _threshold = (HeapWord*)round_to(
6925 (intptr_t)_finger, CardTableModRefBS::card_size);
6926 MemRegion mr(old_threshold, _threshold);
6927 assert(!mr.is_empty(), "Control point invariant");
6928 assert(_span.contains(mr), "Should clear within span");
6929 // XXX When _finger crosses from old gen into perm gen
6930 // we may be doing unnecessary cleaning; do better in the
6931 // future by detecting that condition and clearing fewer
6932 // MUT/CT entries.
6933 _mut->clear_range(mr);
6934 }
6935 DEBUG_ONLY(})
6936
6937 // Note: the finger doesn't advance while we drain
6938 // the stack below.
6939 PushOrMarkClosure pushOrMarkClosure(_collector,
6940 _span, _bitMap, _markStack,
6941 _revisitStack,
6942 _finger, this);
6943 bool res = _markStack->push(this_oop);
6944 assert(res, "Empty non-zero size stack should have space for single push");
6945 while (!_markStack->isEmpty()) {
6946 oop new_oop = _markStack->pop();
6947 // Skip verifying header mark word below because we are
6948 // running concurrent with mutators.
6949 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6950 // now scan this oop's oops
6951 new_oop->oop_iterate(&pushOrMarkClosure);
6952 do_yield_check();
6953 }
6954 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6955 }
6956
6957 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6958 CMSCollector* collector, MemRegion span,
6959 CMSBitMap* bit_map,
6960 OopTaskQueue* work_queue,
6961 CMSMarkStack* overflow_stack,
6962 CMSMarkStack* revisit_stack,
6963 bool should_yield):
6964 _collector(collector),
6965 _whole_span(collector->_span),
6966 _span(span),
6967 _bit_map(bit_map),
6968 _mut(&collector->_modUnionTable),
6969 _work_queue(work_queue),
6970 _overflow_stack(overflow_stack),
6971 _revisit_stack(revisit_stack),
6972 _yield(should_yield),
6973 _skip_bits(0),
6974 _task(task)
6975 {
6976 assert(_work_queue->size() == 0, "work_queue should be empty");
6977 _finger = span.start();
6978 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6979 assert(_span.contains(_finger), "Out of bounds _finger?");
6980 }
6981
6982 // Should revisit to see if this should be restructured for
6983 // greater efficiency.
6984 void Par_MarkFromRootsClosure::do_bit(size_t offset) {
6985 if (_skip_bits > 0) {
6986 _skip_bits--;
6987 return;
6988 }
6989 // convert offset into a HeapWord*
6990 HeapWord* addr = _bit_map->startWord() + offset;
6991 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6992 "address out of range");
6993 assert(_bit_map->isMarked(addr), "tautology");
6994 if (_bit_map->isMarked(addr+1)) {
6995 // this is an allocated object that might not yet be initialized
6996 assert(_skip_bits == 0, "tautology");
6997 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6998 oop p = oop(addr);
6999 if (p->klass() == NULL || !p->is_parsable()) {
7000 // in the case of Clean-on-Enter optimization, redirty card
7001 // and avoid clearing card by increasing the threshold.
7002 return;
7003 }
7004 }
7005 scan_oops_in_oop(addr);
7006 }
7007
7008 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7009 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7010 // Should we assert that our work queue is empty or
7011 // below some drain limit?
7012 assert(_work_queue->size() == 0,
7013 "should drain stack to limit stack usage");
7014 // convert ptr to an oop preparatory to scanning
7015 oop this_oop = oop(ptr);
7016 // Ignore mark word in verification below, since we
7017 // may be running concurrent with mutators.
7018 assert(this_oop->is_oop(true), "should be an oop");
7019 assert(_finger <= ptr, "_finger runneth ahead");
7020 // advance the finger to right end of this object
7021 _finger = ptr + this_oop->size();
7022 assert(_finger > ptr, "we just incremented it above");
7023 // On large heaps, it may take us some time to get through
7024 // the marking phase (especially if running iCMS). During
7025 // this time it's possible that a lot of mutations have
7026 // accumulated in the card table and the mod union table --
7027 // these mutation records are redundant until we have
7028 // actually traced into the corresponding card.
7029 // Here, we check whether advancing the finger would make
7030 // us cross into a new card, and if so clear corresponding
7031 // cards in the MUT (preclean them in the card-table in the
7032 // future).
7033
7034 // The clean-on-enter optimization is disabled by default,
7035 // until we fix 6178663.
7036 if (CMSCleanOnEnter && (_finger > _threshold)) {
7037 // [_threshold, _finger) represents the interval
7038 // of cards to be cleared in MUT (or precleaned in card table).
7039 // The set of cards to be cleared is all those that overlap
7040 // with the interval [_threshold, _finger); note that
7041 // _threshold is always kept card-aligned but _finger isn't
7042 // always card-aligned.
7043 HeapWord* old_threshold = _threshold;
7044 assert(old_threshold == (HeapWord*)round_to(
7045 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7046 "_threshold should always be card-aligned");
7047 _threshold = (HeapWord*)round_to(
7048 (intptr_t)_finger, CardTableModRefBS::card_size);
7049 MemRegion mr(old_threshold, _threshold);
7050 assert(!mr.is_empty(), "Control point invariant");
7051 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7052 // XXX When _finger crosses from old gen into perm gen
7053 // we may be doing unnecessary cleaning; do better in the
7054 // future by detecting that condition and clearing fewer
7055 // MUT/CT entries.
7056 _mut->clear_range(mr);
7057 }
7058
7059 // Note: the local finger doesn't advance while we drain
7060 // the stack below, but the global finger sure can and will.
7061 HeapWord** gfa = _task->global_finger_addr();
7062 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7063 _span, _bit_map,
7064 _work_queue,
7065 _overflow_stack,
7066 _revisit_stack,
7067 _finger,
7068 gfa, this);
7069 bool res = _work_queue->push(this_oop); // overflow could occur here
7070 assert(res, "Will hold once we use workqueues");
7071 while (true) {
7072 oop new_oop;
7073 if (!_work_queue->pop_local(new_oop)) {
7074 // We emptied our work_queue; check if there's stuff that can
7075 // be gotten from the overflow stack.
7076 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7077 _overflow_stack, _work_queue)) {
7078 do_yield_check();
7079 continue;
7080 } else { // done
7081 break;
7082 }
7083 }
7084 // Skip verifying header mark word below because we are
7085 // running concurrent with mutators.
7086 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7087 // now scan this oop's oops
7088 new_oop->oop_iterate(&pushOrMarkClosure);
7089 do_yield_check();
7090 }
7091 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7092 }
7093
7094 // Yield in response to a request from VM Thread or
7095 // from mutators.
7096 void Par_MarkFromRootsClosure::do_yield_work() {
7097 assert(_task != NULL, "sanity");
7098 _task->yield();
7099 }
7100
7101 // A variant of the above used for verifying CMS marking work.
7102 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7103 MemRegion span,
7104 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7105 CMSMarkStack* mark_stack):
7106 _collector(collector),
7107 _span(span),
7108 _verification_bm(verification_bm),
7109 _cms_bm(cms_bm),
7110 _mark_stack(mark_stack),
7111 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7112 mark_stack)
7113 {
7114 assert(_mark_stack->isEmpty(), "stack should be empty");
7115 _finger = _verification_bm->startWord();
7116 assert(_collector->_restart_addr == NULL, "Sanity check");
7117 assert(_span.contains(_finger), "Out of bounds _finger?");
7118 }
7119
7120 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7121 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7122 assert(_span.contains(addr), "Out of bounds _finger?");
7123 _finger = addr;
7124 }
7125
7126 // Should revisit to see if this should be restructured for
7127 // greater efficiency.
7128 void MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7129 // convert offset into a HeapWord*
7130 HeapWord* addr = _verification_bm->startWord() + offset;
7131 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7132 "address out of range");
7133 assert(_verification_bm->isMarked(addr), "tautology");
7134 assert(_cms_bm->isMarked(addr), "tautology");
7135
7136 assert(_mark_stack->isEmpty(),
7137 "should drain stack to limit stack usage");
7138 // convert addr to an oop preparatory to scanning
7139 oop this_oop = oop(addr);
7140 assert(this_oop->is_oop(), "should be an oop");
7141 assert(_finger <= addr, "_finger runneth ahead");
7142 // advance the finger to right end of this object
7143 _finger = addr + this_oop->size();
7144 assert(_finger > addr, "we just incremented it above");
7145 // Note: the finger doesn't advance while we drain
7146 // the stack below.
7147 bool res = _mark_stack->push(this_oop);
7148 assert(res, "Empty non-zero size stack should have space for single push");
7149 while (!_mark_stack->isEmpty()) {
7150 oop new_oop = _mark_stack->pop();
7151 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7152 // now scan this oop's oops
7153 new_oop->oop_iterate(&_pam_verify_closure);
7154 }
7155 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7156 }
7157
7158 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7159 CMSCollector* collector, MemRegion span,
7160 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7161 CMSMarkStack* mark_stack):
7162 OopClosure(collector->ref_processor()),
7163 _collector(collector),
7164 _span(span),
7165 _verification_bm(verification_bm),
7166 _cms_bm(cms_bm),
7167 _mark_stack(mark_stack)
7168 { }
7169
7170
7171 // Upon stack overflow, we discard (part of) the stack,
7172 // remembering the least address amongst those discarded
7173 // in CMSCollector's _restart_address.
7174 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7175 // Remember the least grey address discarded
7176 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7177 _collector->lower_restart_addr(ra);
7178 _mark_stack->reset(); // discard stack contents
7179 _mark_stack->expand(); // expand the stack if possible
7180 }
7181
7182 void PushAndMarkVerifyClosure::do_oop(oop* p) {
7183 oop this_oop = *p;
7184 assert(this_oop->is_oop_or_null(), "expected an oop or NULL");
7185 HeapWord* addr = (HeapWord*)this_oop;
7186 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7187 // Oop lies in _span and isn't yet grey or black
7188 _verification_bm->mark(addr); // now grey
7189 if (!_cms_bm->isMarked(addr)) {
7190 oop(addr)->print();
7191 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
7192 fatal("... aborting");
7193 }
7194
7195 if (!_mark_stack->push(this_oop)) { // stack overflow
7196 if (PrintCMSStatistics != 0) {
7197 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7198 SIZE_FORMAT, _mark_stack->capacity());
7199 }
7200 assert(_mark_stack->isFull(), "Else push should have succeeded");
7201 handle_stack_overflow(addr);
7202 }
7203 // anything including and to the right of _finger
7204 // will be scanned as we iterate over the remainder of the
7205 // bit map
7206 }
7207 }
7208
7209 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7210 MemRegion span,
7211 CMSBitMap* bitMap, CMSMarkStack* markStack,
7212 CMSMarkStack* revisitStack,
7213 HeapWord* finger, MarkFromRootsClosure* parent) :
7214 OopClosure(collector->ref_processor()),
7215 _collector(collector),
7216 _span(span),
7217 _bitMap(bitMap),
7218 _markStack(markStack),
7219 _revisitStack(revisitStack),
7220 _finger(finger),
7221 _parent(parent),
7222 _should_remember_klasses(collector->cms_should_unload_classes())
7223 { }
7224
7225 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7226 MemRegion span,
7227 CMSBitMap* bit_map,
7228 OopTaskQueue* work_queue,
7229 CMSMarkStack* overflow_stack,
7230 CMSMarkStack* revisit_stack,
7231 HeapWord* finger,
7232 HeapWord** global_finger_addr,
7233 Par_MarkFromRootsClosure* parent) :
7234 OopClosure(collector->ref_processor()),
7235 _collector(collector),
7236 _whole_span(collector->_span),
7237 _span(span),
7238 _bit_map(bit_map),
7239 _work_queue(work_queue),
7240 _overflow_stack(overflow_stack),
7241 _revisit_stack(revisit_stack),
7242 _finger(finger),
7243 _global_finger_addr(global_finger_addr),
7244 _parent(parent),
7245 _should_remember_klasses(collector->cms_should_unload_classes())
7246 { }
7247
7248 // Assumes thread-safe access by callers, who are
7249 // responsible for mutual exclusion.
7250 void CMSCollector::lower_restart_addr(HeapWord* low) {
7251 assert(_span.contains(low), "Out of bounds addr");
7252 if (_restart_addr == NULL) {
7253 _restart_addr = low;
7254 } else {
7255 _restart_addr = MIN2(_restart_addr, low);
7256 }
7257 }
7258
7259 // Upon stack overflow, we discard (part of) the stack,
7260 // remembering the least address amongst those discarded
7261 // in CMSCollector's _restart_address.
7262 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7263 // Remember the least grey address discarded
7264 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7265 _collector->lower_restart_addr(ra);
7266 _markStack->reset(); // discard stack contents
7267 _markStack->expand(); // expand the stack if possible
7268 }
7269
7270 // Upon stack overflow, we discard (part of) the stack,
7271 // remembering the least address amongst those discarded
7272 // in CMSCollector's _restart_address.
7273 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7274 // We need to do this under a mutex to prevent other
7275 // workers from interfering with the work done below.
7276 MutexLockerEx ml(_overflow_stack->par_lock(),
7277 Mutex::_no_safepoint_check_flag);
7278 // Remember the least grey address discarded
7279 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7280 _collector->lower_restart_addr(ra);
7281 _overflow_stack->reset(); // discard stack contents
7282 _overflow_stack->expand(); // expand the stack if possible
7283 }
7284
7285
7286 void PushOrMarkClosure::do_oop(oop* p) {
7287 oop thisOop = *p;
7288 // Ignore mark word because we are running concurrent with mutators.
7289 assert(thisOop->is_oop_or_null(true), "expected an oop or NULL");
7290 HeapWord* addr = (HeapWord*)thisOop;
7291 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7292 // Oop lies in _span and isn't yet grey or black
7293 _bitMap->mark(addr); // now grey
7294 if (addr < _finger) {
7295 // the bit map iteration has already either passed, or
7296 // sampled, this bit in the bit map; we'll need to
7297 // use the marking stack to scan this oop's oops.
7298 bool simulate_overflow = false;
7299 NOT_PRODUCT(
7300 if (CMSMarkStackOverflowALot &&
7301 _collector->simulate_overflow()) {
7302 // simulate a stack overflow
7303 simulate_overflow = true;
7304 }
7305 )
7306 if (simulate_overflow || !_markStack->push(thisOop)) { // stack overflow
7307 if (PrintCMSStatistics != 0) {
7308 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7309 SIZE_FORMAT, _markStack->capacity());
7310 }
7311 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7312 handle_stack_overflow(addr);
7313 }
7314 }
7315 // anything including and to the right of _finger
7316 // will be scanned as we iterate over the remainder of the
7317 // bit map
7318 do_yield_check();
7319 }
7320 }
7321
7322 void Par_PushOrMarkClosure::do_oop(oop* p) {
7323 oop this_oop = *p;
7324 // Ignore mark word because we are running concurrent with mutators.
7325 assert(this_oop->is_oop_or_null(true), "expected an oop or NULL");
7326 HeapWord* addr = (HeapWord*)this_oop;
7327 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7328 // Oop lies in _span and isn't yet grey or black
7329 // We read the global_finger (volatile read) strictly after marking oop
7330 bool res = _bit_map->par_mark(addr); // now grey
7331 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7332 // Should we push this marked oop on our stack?
7333 // -- if someone else marked it, nothing to do
7334 // -- if target oop is above global finger nothing to do
7335 // -- if target oop is in chunk and above local finger
7336 // then nothing to do
7337 // -- else push on work queue
7338 if ( !res // someone else marked it, they will deal with it
7339 || (addr >= *gfa) // will be scanned in a later task
7340 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7341 return;
7342 }
7343 // the bit map iteration has already either passed, or
7344 // sampled, this bit in the bit map; we'll need to
7345 // use the marking stack to scan this oop's oops.
7346 bool simulate_overflow = false;
7347 NOT_PRODUCT(
7348 if (CMSMarkStackOverflowALot &&
7349 _collector->simulate_overflow()) {
7350 // simulate a stack overflow
7351 simulate_overflow = true;
7352 }
7353 )
7354 if (simulate_overflow ||
7355 !(_work_queue->push(this_oop) || _overflow_stack->par_push(this_oop))) {
7356 // stack overflow
7357 if (PrintCMSStatistics != 0) {
7358 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7359 SIZE_FORMAT, _overflow_stack->capacity());
7360 }
7361 // We cannot assert that the overflow stack is full because
7362 // it may have been emptied since.
7363 assert(simulate_overflow ||
7364 _work_queue->size() == _work_queue->max_elems(),
7365 "Else push should have succeeded");
7366 handle_stack_overflow(addr);
7367 }
7368 do_yield_check();
7369 }
7370 }
7371
7372
7373 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7374 MemRegion span,
7375 ReferenceProcessor* rp,
7376 CMSBitMap* bit_map,
7377 CMSBitMap* mod_union_table,
7378 CMSMarkStack* mark_stack,
7379 CMSMarkStack* revisit_stack,
7380 bool concurrent_precleaning):
7381 OopClosure(rp),
7382 _collector(collector),
7383 _span(span),
7384 _bit_map(bit_map),
7385 _mod_union_table(mod_union_table),
7386 _mark_stack(mark_stack),
7387 _revisit_stack(revisit_stack),
7388 _concurrent_precleaning(concurrent_precleaning),
7389 _should_remember_klasses(collector->cms_should_unload_classes())
7390 {
7391 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7392 }
7393
7394 // Grey object rescan during pre-cleaning and second checkpoint phases --
7395 // the non-parallel version (the parallel version appears further below.)
7396 void PushAndMarkClosure::do_oop(oop* p) {
7397 oop this_oop = *p;
7398 // Ignore mark word verification. If during concurrent precleaning
7399 // the object monitor may be locked. If during the checkpoint
7400 // phases, the object may already have been reached by a different
7401 // path and may be at the end of the global overflow list (so
7402 // the mark word may be NULL).
7403 assert(this_oop->is_oop_or_null(true/* ignore mark word */),
7404 "expected an oop or NULL");
7405 HeapWord* addr = (HeapWord*)this_oop;
7406 // Check if oop points into the CMS generation
7407 // and is not marked
7408 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7409 // a white object ...
7410 _bit_map->mark(addr); // ... now grey
7411 // push on the marking stack (grey set)
7412 bool simulate_overflow = false;
7413 NOT_PRODUCT(
7414 if (CMSMarkStackOverflowALot &&
7415 _collector->simulate_overflow()) {
7416 // simulate a stack overflow
7417 simulate_overflow = true;
7418 }
7419 )
7420 if (simulate_overflow || !_mark_stack->push(this_oop)) {
7421 if (_concurrent_precleaning) {
7422 // During precleaning we can just dirty the appropriate card(s)
7423 // in the mod union table, thus ensuring that the object remains
7424 // in the grey set and continue. In the case of object arrays
7425 // we need to dirty all of the cards that the object spans,
7426 // since the rescan of object arrays will be limited to the
7427 // dirty cards.
7428 // Note that no one can be intefering with us in this action
7429 // of dirtying the mod union table, so no locking or atomics
7430 // are required.
7431 if (this_oop->is_objArray()) {
7432 size_t sz = this_oop->size();
7433 HeapWord* end_card_addr = (HeapWord*)round_to(
7434 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7435 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7436 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7437 _mod_union_table->mark_range(redirty_range);
7438 } else {
7439 _mod_union_table->mark(addr);
7440 }
7441 _collector->_ser_pmc_preclean_ovflw++;
7442 } else {
7443 // During the remark phase, we need to remember this oop
7444 // in the overflow list.
7445 _collector->push_on_overflow_list(this_oop);
7446 _collector->_ser_pmc_remark_ovflw++;
7447 }
7448 }
7449 }
7450 }
7451
7452 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7453 MemRegion span,
7454 ReferenceProcessor* rp,
7455 CMSBitMap* bit_map,
7456 OopTaskQueue* work_queue,
7457 CMSMarkStack* revisit_stack):
7458 OopClosure(rp),
7459 _collector(collector),
7460 _span(span),
7461 _bit_map(bit_map),
7462 _work_queue(work_queue),
7463 _revisit_stack(revisit_stack),
7464 _should_remember_klasses(collector->cms_should_unload_classes())
7465 {
7466 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7467 }
7468
7469 // Grey object rescan during second checkpoint phase --
7470 // the parallel version.
7471 void Par_PushAndMarkClosure::do_oop(oop* p) {
7472 oop this_oop = *p;
7473 // In the assert below, we ignore the mark word because
7474 // this oop may point to an already visited object that is
7475 // on the overflow stack (in which case the mark word has
7476 // been hijacked for chaining into the overflow stack --
7477 // if this is the last object in the overflow stack then
7478 // its mark word will be NULL). Because this object may
7479 // have been subsequently popped off the global overflow
7480 // stack, and the mark word possibly restored to the prototypical
7481 // value, by the time we get to examined this failing assert in
7482 // the debugger, is_oop_or_null(false) may subsequently start
7483 // to hold.
7484 assert(this_oop->is_oop_or_null(true),
7485 "expected an oop or NULL");
7486 HeapWord* addr = (HeapWord*)this_oop;
7487 // Check if oop points into the CMS generation
7488 // and is not marked
7489 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7490 // a white object ...
7491 // If we manage to "claim" the object, by being the
7492 // first thread to mark it, then we push it on our
7493 // marking stack
7494 if (_bit_map->par_mark(addr)) { // ... now grey
7495 // push on work queue (grey set)
7496 bool simulate_overflow = false;
7497 NOT_PRODUCT(
7498 if (CMSMarkStackOverflowALot &&
7499 _collector->par_simulate_overflow()) {
7500 // simulate a stack overflow
7501 simulate_overflow = true;
7502 }
7503 )
7504 if (simulate_overflow || !_work_queue->push(this_oop)) {
7505 _collector->par_push_on_overflow_list(this_oop);
7506 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7507 }
7508 } // Else, some other thread got there first
7509 }
7510 }
7511
7512 void PushAndMarkClosure::remember_klass(Klass* k) {
7513 if (!_revisit_stack->push(oop(k))) {
7514 fatal("Revisit stack overflowed in PushAndMarkClosure");
7515 }
7516 }
7517
7518 void Par_PushAndMarkClosure::remember_klass(Klass* k) {
7519 if (!_revisit_stack->par_push(oop(k))) {
7520 fatal("Revist stack overflowed in Par_PushAndMarkClosure");
7521 }
7522 }
7523
7524 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7525 Mutex* bml = _collector->bitMapLock();
7526 assert_lock_strong(bml);
7527 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7528 "CMS thread should hold CMS token");
7529
7530 bml->unlock();
7531 ConcurrentMarkSweepThread::desynchronize(true);
7532
7533 ConcurrentMarkSweepThread::acknowledge_yield_request();
7534
7535 _collector->stopTimer();
7536 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7537 if (PrintCMSStatistics != 0) {
7538 _collector->incrementYields();
7539 }
7540 _collector->icms_wait();
7541
7542 // See the comment in coordinator_yield()
7543 for (unsigned i = 0; i < CMSYieldSleepCount &&
7544 ConcurrentMarkSweepThread::should_yield() &&
7545 !CMSCollector::foregroundGCIsActive(); ++i) {
7546 os::sleep(Thread::current(), 1, false);
7547 ConcurrentMarkSweepThread::acknowledge_yield_request();
7548 }
7549
7550 ConcurrentMarkSweepThread::synchronize(true);
7551 bml->lock();
7552
7553 _collector->startTimer();
7554 }
7555
7556 bool CMSPrecleanRefsYieldClosure::should_return() {
7557 if (ConcurrentMarkSweepThread::should_yield()) {
7558 do_yield_work();
7559 }
7560 return _collector->foregroundGCIsActive();
7561 }
7562
7563 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7564 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7565 "mr should be aligned to start at a card boundary");
7566 // We'd like to assert:
7567 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7568 // "mr should be a range of cards");
7569 // However, that would be too strong in one case -- the last
7570 // partition ends at _unallocated_block which, in general, can be
7571 // an arbitrary boundary, not necessarily card aligned.
7572 if (PrintCMSStatistics != 0) {
7573 _num_dirty_cards +=
7574 mr.word_size()/CardTableModRefBS::card_size_in_words;
7575 }
7576 _space->object_iterate_mem(mr, &_scan_cl);
7577 }
7578
7579 SweepClosure::SweepClosure(CMSCollector* collector,
7580 ConcurrentMarkSweepGeneration* g,
7581 CMSBitMap* bitMap, bool should_yield) :
7582 _collector(collector),
7583 _g(g),
7584 _sp(g->cmsSpace()),
7585 _limit(_sp->sweep_limit()),
7586 _freelistLock(_sp->freelistLock()),
7587 _bitMap(bitMap),
7588 _yield(should_yield),
7589 _inFreeRange(false), // No free range at beginning of sweep
7590 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7591 _lastFreeRangeCoalesced(false),
7592 _freeFinger(g->used_region().start())
7593 {
7594 NOT_PRODUCT(
7595 _numObjectsFreed = 0;
7596 _numWordsFreed = 0;
7597 _numObjectsLive = 0;
7598 _numWordsLive = 0;
7599 _numObjectsAlreadyFree = 0;
7600 _numWordsAlreadyFree = 0;
7601 _last_fc = NULL;
7602
7603 _sp->initializeIndexedFreeListArrayReturnedBytes();
7604 _sp->dictionary()->initializeDictReturnedBytes();
7605 )
7606 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7607 "sweep _limit out of bounds");
7608 if (CMSTraceSweeper) {
7609 gclog_or_tty->print("\n====================\nStarting new sweep\n");
7610 }
7611 }
7612
7613 // We need this destructor to reclaim any space at the end
7614 // of the space, which do_blk below may not have added back to
7615 // the free lists. [basically dealing with the "fringe effect"]
7616 SweepClosure::~SweepClosure() {
7617 assert_lock_strong(_freelistLock);
7618 // this should be treated as the end of a free run if any
7619 // The current free range should be returned to the free lists
7620 // as one coalesced chunk.
7621 if (inFreeRange()) {
7622 flushCurFreeChunk(freeFinger(),
7623 pointer_delta(_limit, freeFinger()));
7624 assert(freeFinger() < _limit, "the finger pointeth off base");
7625 if (CMSTraceSweeper) {
7626 gclog_or_tty->print("destructor:");
7627 gclog_or_tty->print("Sweep:put_free_blk 0x%x ("SIZE_FORMAT") "
7628 "[coalesced:"SIZE_FORMAT"]\n",
7629 freeFinger(), pointer_delta(_limit, freeFinger()),
7630 lastFreeRangeCoalesced());
7631 }
7632 }
7633 NOT_PRODUCT(
7634 if (Verbose && PrintGC) {
7635 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, "
7636 SIZE_FORMAT " bytes",
7637 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7638 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7639 SIZE_FORMAT" bytes "
7640 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7641 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7642 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7643 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) *
7644 sizeof(HeapWord);
7645 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7646
7647 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7648 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7649 size_t dictReturnedBytes = _sp->dictionary()->sumDictReturnedBytes();
7650 size_t returnedBytes = indexListReturnedBytes + dictReturnedBytes;
7651 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returnedBytes);
7652 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7653 indexListReturnedBytes);
7654 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7655 dictReturnedBytes);
7656 }
7657 }
7658 )
7659 // Now, in debug mode, just null out the sweep_limit
7660 NOT_PRODUCT(_sp->clear_sweep_limit();)
7661 if (CMSTraceSweeper) {
7662 gclog_or_tty->print("end of sweep\n================\n");
7663 }
7664 }
7665
7666 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7667 bool freeRangeInFreeLists) {
7668 if (CMSTraceSweeper) {
7669 gclog_or_tty->print("---- Start free range 0x%x with free block [%d] (%d)\n",
7670 freeFinger, _sp->block_size(freeFinger),
7671 freeRangeInFreeLists);
7672 }
7673 assert(!inFreeRange(), "Trampling existing free range");
7674 set_inFreeRange(true);
7675 set_lastFreeRangeCoalesced(false);
7676
7677 set_freeFinger(freeFinger);
7678 set_freeRangeInFreeLists(freeRangeInFreeLists);
7679 if (CMSTestInFreeList) {
7680 if (freeRangeInFreeLists) {
7681 FreeChunk* fc = (FreeChunk*) freeFinger;
7682 assert(fc->isFree(), "A chunk on the free list should be free.");
7683 assert(fc->size() > 0, "Free range should have a size");
7684 assert(_sp->verifyChunkInFreeLists(fc), "Chunk is not in free lists");
7685 }
7686 }
7687 }
7688
7689 // Note that the sweeper runs concurrently with mutators. Thus,
7690 // it is possible for direct allocation in this generation to happen
7691 // in the middle of the sweep. Note that the sweeper also coalesces
7692 // contiguous free blocks. Thus, unless the sweeper and the allocator
7693 // synchronize appropriately freshly allocated blocks may get swept up.
7694 // This is accomplished by the sweeper locking the free lists while
7695 // it is sweeping. Thus blocks that are determined to be free are
7696 // indeed free. There is however one additional complication:
7697 // blocks that have been allocated since the final checkpoint and
7698 // mark, will not have been marked and so would be treated as
7699 // unreachable and swept up. To prevent this, the allocator marks
7700 // the bit map when allocating during the sweep phase. This leads,
7701 // however, to a further complication -- objects may have been allocated
7702 // but not yet initialized -- in the sense that the header isn't yet
7703 // installed. The sweeper can not then determine the size of the block
7704 // in order to skip over it. To deal with this case, we use a technique
7705 // (due to Printezis) to encode such uninitialized block sizes in the
7706 // bit map. Since the bit map uses a bit per every HeapWord, but the
7707 // CMS generation has a minimum object size of 3 HeapWords, it follows
7708 // that "normal marks" won't be adjacent in the bit map (there will
7709 // always be at least two 0 bits between successive 1 bits). We make use
7710 // of these "unused" bits to represent uninitialized blocks -- the bit
7711 // corresponding to the start of the uninitialized object and the next
7712 // bit are both set. Finally, a 1 bit marks the end of the object that
7713 // started with the two consecutive 1 bits to indicate its potentially
7714 // uninitialized state.
7715
7716 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7717 FreeChunk* fc = (FreeChunk*)addr;
7718 size_t res;
7719
7720 // check if we are done sweepinrg
7721 if (addr == _limit) { // we have swept up to the limit, do nothing more
7722 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7723 "sweep _limit out of bounds");
7724 // help the closure application finish
7725 return pointer_delta(_sp->end(), _limit);
7726 }
7727 assert(addr <= _limit, "sweep invariant");
7728
7729 // check if we should yield
7730 do_yield_check(addr);
7731 if (fc->isFree()) {
7732 // Chunk that is already free
7733 res = fc->size();
7734 doAlreadyFreeChunk(fc);
7735 debug_only(_sp->verifyFreeLists());
7736 assert(res == fc->size(), "Don't expect the size to change");
7737 NOT_PRODUCT(
7738 _numObjectsAlreadyFree++;
7739 _numWordsAlreadyFree += res;
7740 )
7741 NOT_PRODUCT(_last_fc = fc;)
7742 } else if (!_bitMap->isMarked(addr)) {
7743 // Chunk is fresh garbage
7744 res = doGarbageChunk(fc);
7745 debug_only(_sp->verifyFreeLists());
7746 NOT_PRODUCT(
7747 _numObjectsFreed++;
7748 _numWordsFreed += res;
7749 )
7750 } else {
7751 // Chunk that is alive.
7752 res = doLiveChunk(fc);
7753 debug_only(_sp->verifyFreeLists());
7754 NOT_PRODUCT(
7755 _numObjectsLive++;
7756 _numWordsLive += res;
7757 )
7758 }
7759 return res;
7760 }
7761
7762 // For the smart allocation, record following
7763 // split deaths - a free chunk is removed from its free list because
7764 // it is being split into two or more chunks.
7765 // split birth - a free chunk is being added to its free list because
7766 // a larger free chunk has been split and resulted in this free chunk.
7767 // coal death - a free chunk is being removed from its free list because
7768 // it is being coalesced into a large free chunk.
7769 // coal birth - a free chunk is being added to its free list because
7770 // it was created when two or more free chunks where coalesced into
7771 // this free chunk.
7772 //
7773 // These statistics are used to determine the desired number of free
7774 // chunks of a given size. The desired number is chosen to be relative
7775 // to the end of a CMS sweep. The desired number at the end of a sweep
7776 // is the
7777 // count-at-end-of-previous-sweep (an amount that was enough)
7778 // - count-at-beginning-of-current-sweep (the excess)
7779 // + split-births (gains in this size during interval)
7780 // - split-deaths (demands on this size during interval)
7781 // where the interval is from the end of one sweep to the end of the
7782 // next.
7783 //
7784 // When sweeping the sweeper maintains an accumulated chunk which is
7785 // the chunk that is made up of chunks that have been coalesced. That
7786 // will be termed the left-hand chunk. A new chunk of garbage that
7787 // is being considered for coalescing will be referred to as the
7788 // right-hand chunk.
7789 //
7790 // When making a decision on whether to coalesce a right-hand chunk with
7791 // the current left-hand chunk, the current count vs. the desired count
7792 // of the left-hand chunk is considered. Also if the right-hand chunk
7793 // is near the large chunk at the end of the heap (see
7794 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7795 // left-hand chunk is coalesced.
7796 //
7797 // When making a decision about whether to split a chunk, the desired count
7798 // vs. the current count of the candidate to be split is also considered.
7799 // If the candidate is underpopulated (currently fewer chunks than desired)
7800 // a chunk of an overpopulated (currently more chunks than desired) size may
7801 // be chosen. The "hint" associated with a free list, if non-null, points
7802 // to a free list which may be overpopulated.
7803 //
7804
7805 void SweepClosure::doAlreadyFreeChunk(FreeChunk* fc) {
7806 size_t size = fc->size();
7807 // Chunks that cannot be coalesced are not in the
7808 // free lists.
7809 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7810 assert(_sp->verifyChunkInFreeLists(fc),
7811 "free chunk should be in free lists");
7812 }
7813 // a chunk that is already free, should not have been
7814 // marked in the bit map
7815 HeapWord* addr = (HeapWord*) fc;
7816 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7817 // Verify that the bit map has no bits marked between
7818 // addr and purported end of this block.
7819 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7820
7821 // Some chunks cannot be coalesced in under any circumstances.
7822 // See the definition of cantCoalesce().
7823 if (!fc->cantCoalesce()) {
7824 // This chunk can potentially be coalesced.
7825 if (_sp->adaptive_freelists()) {
7826 // All the work is done in
7827 doPostIsFreeOrGarbageChunk(fc, size);
7828 } else { // Not adaptive free lists
7829 // this is a free chunk that can potentially be coalesced by the sweeper;
7830 if (!inFreeRange()) {
7831 // if the next chunk is a free block that can't be coalesced
7832 // it doesn't make sense to remove this chunk from the free lists
7833 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7834 assert((HeapWord*)nextChunk <= _limit, "sweep invariant");
7835 if ((HeapWord*)nextChunk < _limit && // there's a next chunk...
7836 nextChunk->isFree() && // which is free...
7837 nextChunk->cantCoalesce()) { // ... but cant be coalesced
7838 // nothing to do
7839 } else {
7840 // Potentially the start of a new free range:
7841 // Don't eagerly remove it from the free lists.
7842 // No need to remove it if it will just be put
7843 // back again. (Also from a pragmatic point of view
7844 // if it is a free block in a region that is beyond
7845 // any allocated blocks, an assertion will fail)
7846 // Remember the start of a free run.
7847 initialize_free_range(addr, true);
7848 // end - can coalesce with next chunk
7849 }
7850 } else {
7851 // the midst of a free range, we are coalescing
7852 debug_only(record_free_block_coalesced(fc);)
7853 if (CMSTraceSweeper) {
7854 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
7855 }
7856 // remove it from the free lists
7857 _sp->removeFreeChunkFromFreeLists(fc);
7858 set_lastFreeRangeCoalesced(true);
7859 // If the chunk is being coalesced and the current free range is
7860 // in the free lists, remove the current free range so that it
7861 // will be returned to the free lists in its entirety - all
7862 // the coalesced pieces included.
7863 if (freeRangeInFreeLists()) {
7864 FreeChunk* ffc = (FreeChunk*) freeFinger();
7865 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7866 "Size of free range is inconsistent with chunk size.");
7867 if (CMSTestInFreeList) {
7868 assert(_sp->verifyChunkInFreeLists(ffc),
7869 "free range is not in free lists");
7870 }
7871 _sp->removeFreeChunkFromFreeLists(ffc);
7872 set_freeRangeInFreeLists(false);
7873 }
7874 }
7875 }
7876 } else {
7877 // Code path common to both original and adaptive free lists.
7878
7879 // cant coalesce with previous block; this should be treated
7880 // as the end of a free run if any
7881 if (inFreeRange()) {
7882 // we kicked some butt; time to pick up the garbage
7883 assert(freeFinger() < addr, "the finger pointeth off base");
7884 flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger()));
7885 }
7886 // else, nothing to do, just continue
7887 }
7888 }
7889
7890 size_t SweepClosure::doGarbageChunk(FreeChunk* fc) {
7891 // This is a chunk of garbage. It is not in any free list.
7892 // Add it to a free list or let it possibly be coalesced into
7893 // a larger chunk.
7894 HeapWord* addr = (HeapWord*) fc;
7895 size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7896
7897 if (_sp->adaptive_freelists()) {
7898 // Verify that the bit map has no bits marked between
7899 // addr and purported end of just dead object.
7900 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7901
7902 doPostIsFreeOrGarbageChunk(fc, size);
7903 } else {
7904 if (!inFreeRange()) {
7905 // start of a new free range
7906 assert(size > 0, "A free range should have a size");
7907 initialize_free_range(addr, false);
7908
7909 } else {
7910 // this will be swept up when we hit the end of the
7911 // free range
7912 if (CMSTraceSweeper) {
7913 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
7914 }
7915 // If the chunk is being coalesced and the current free range is
7916 // in the free lists, remove the current free range so that it
7917 // will be returned to the free lists in its entirety - all
7918 // the coalesced pieces included.
7919 if (freeRangeInFreeLists()) {
7920 FreeChunk* ffc = (FreeChunk*)freeFinger();
7921 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7922 "Size of free range is inconsistent with chunk size.");
7923 if (CMSTestInFreeList) {
7924 assert(_sp->verifyChunkInFreeLists(ffc),
7925 "free range is not in free lists");
7926 }
7927 _sp->removeFreeChunkFromFreeLists(ffc);
7928 set_freeRangeInFreeLists(false);
7929 }
7930 set_lastFreeRangeCoalesced(true);
7931 }
7932 // this will be swept up when we hit the end of the free range
7933
7934 // Verify that the bit map has no bits marked between
7935 // addr and purported end of just dead object.
7936 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7937 }
7938 return size;
7939 }
7940
7941 size_t SweepClosure::doLiveChunk(FreeChunk* fc) {
7942 HeapWord* addr = (HeapWord*) fc;
7943 // The sweeper has just found a live object. Return any accumulated
7944 // left hand chunk to the free lists.
7945 if (inFreeRange()) {
7946 if (_sp->adaptive_freelists()) {
7947 flushCurFreeChunk(freeFinger(),
7948 pointer_delta(addr, freeFinger()));
7949 } else { // not adaptive freelists
7950 set_inFreeRange(false);
7951 // Add the free range back to the free list if it is not already
7952 // there.
7953 if (!freeRangeInFreeLists()) {
7954 assert(freeFinger() < addr, "the finger pointeth off base");
7955 if (CMSTraceSweeper) {
7956 gclog_or_tty->print("Sweep:put_free_blk 0x%x (%d) "
7957 "[coalesced:%d]\n",
7958 freeFinger(), pointer_delta(addr, freeFinger()),
7959 lastFreeRangeCoalesced());
7960 }
7961 _sp->addChunkAndRepairOffsetTable(freeFinger(),
7962 pointer_delta(addr, freeFinger()), lastFreeRangeCoalesced());
7963 }
7964 }
7965 }
7966
7967 // Common code path for original and adaptive free lists.
7968
7969 // this object is live: we'd normally expect this to be
7970 // an oop, and like to assert the following:
7971 // assert(oop(addr)->is_oop(), "live block should be an oop");
7972 // However, as we commented above, this may be an object whose
7973 // header hasn't yet been initialized.
7974 size_t size;
7975 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7976 if (_bitMap->isMarked(addr + 1)) {
7977 // Determine the size from the bit map, rather than trying to
7978 // compute it from the object header.
7979 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7980 size = pointer_delta(nextOneAddr + 1, addr);
7981 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7982 "alignment problem");
7983
7984 #ifdef DEBUG
7985 if (oop(addr)->klass() != NULL &&
7986 ( !_collector->cms_should_unload_classes()
7987 || oop(addr)->is_parsable())) {
7988 // Ignore mark word because we are running concurrent with mutators
7989 assert(oop(addr)->is_oop(true), "live block should be an oop");
7990 assert(size ==
7991 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7992 "P-mark and computed size do not agree");
7993 }
7994 #endif
7995
7996 } else {
7997 // This should be an initialized object that's alive.
7998 assert(oop(addr)->klass() != NULL &&
7999 (!_collector->cms_should_unload_classes()
8000 || oop(addr)->is_parsable()),
8001 "Should be an initialized object");
8002 // Ignore mark word because we are running concurrent with mutators
8003 assert(oop(addr)->is_oop(true), "live block should be an oop");
8004 // Verify that the bit map has no bits marked between
8005 // addr and purported end of this block.
8006 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8007 assert(size >= 3, "Necessary for Printezis marks to work");
8008 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8009 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8010 }
8011 return size;
8012 }
8013
8014 void SweepClosure::doPostIsFreeOrGarbageChunk(FreeChunk* fc,
8015 size_t chunkSize) {
8016 // doPostIsFreeOrGarbageChunk() should only be called in the smart allocation
8017 // scheme.
8018 bool fcInFreeLists = fc->isFree();
8019 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8020 assert((HeapWord*)fc <= _limit, "sweep invariant");
8021 if (CMSTestInFreeList && fcInFreeLists) {
8022 assert(_sp->verifyChunkInFreeLists(fc),
8023 "free chunk is not in free lists");
8024 }
8025
8026
8027 if (CMSTraceSweeper) {
8028 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8029 }
8030
8031 HeapWord* addr = (HeapWord*) fc;
8032
8033 bool coalesce;
8034 size_t left = pointer_delta(addr, freeFinger());
8035 size_t right = chunkSize;
8036 switch (FLSCoalescePolicy) {
8037 // numeric value forms a coalition aggressiveness metric
8038 case 0: { // never coalesce
8039 coalesce = false;
8040 break;
8041 }
8042 case 1: { // coalesce if left & right chunks on overpopulated lists
8043 coalesce = _sp->coalOverPopulated(left) &&
8044 _sp->coalOverPopulated(right);
8045 break;
8046 }
8047 case 2: { // coalesce if left chunk on overpopulated list (default)
8048 coalesce = _sp->coalOverPopulated(left);
8049 break;
8050 }
8051 case 3: { // coalesce if left OR right chunk on overpopulated list
8052 coalesce = _sp->coalOverPopulated(left) ||
8053 _sp->coalOverPopulated(right);
8054 break;
8055 }
8056 case 4: { // always coalesce
8057 coalesce = true;
8058 break;
8059 }
8060 default:
8061 ShouldNotReachHere();
8062 }
8063
8064 // Should the current free range be coalesced?
8065 // If the chunk is in a free range and either we decided to coalesce above
8066 // or the chunk is near the large block at the end of the heap
8067 // (isNearLargestChunk() returns true), then coalesce this chunk.
8068 bool doCoalesce = inFreeRange() &&
8069 (coalesce || _g->isNearLargestChunk((HeapWord*)fc));
8070 if (doCoalesce) {
8071 // Coalesce the current free range on the left with the new
8072 // chunk on the right. If either is on a free list,
8073 // it must be removed from the list and stashed in the closure.
8074 if (freeRangeInFreeLists()) {
8075 FreeChunk* ffc = (FreeChunk*)freeFinger();
8076 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8077 "Size of free range is inconsistent with chunk size.");
8078 if (CMSTestInFreeList) {
8079 assert(_sp->verifyChunkInFreeLists(ffc),
8080 "Chunk is not in free lists");
8081 }
8082 _sp->coalDeath(ffc->size());
8083 _sp->removeFreeChunkFromFreeLists(ffc);
8084 set_freeRangeInFreeLists(false);
8085 }
8086 if (fcInFreeLists) {
8087 _sp->coalDeath(chunkSize);
8088 assert(fc->size() == chunkSize,
8089 "The chunk has the wrong size or is not in the free lists");
8090 _sp->removeFreeChunkFromFreeLists(fc);
8091 }
8092 set_lastFreeRangeCoalesced(true);
8093 } else { // not in a free range and/or should not coalesce
8094 // Return the current free range and start a new one.
8095 if (inFreeRange()) {
8096 // In a free range but cannot coalesce with the right hand chunk.
8097 // Put the current free range into the free lists.
8098 flushCurFreeChunk(freeFinger(),
8099 pointer_delta(addr, freeFinger()));
8100 }
8101 // Set up for new free range. Pass along whether the right hand
8102 // chunk is in the free lists.
8103 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8104 }
8105 }
8106 void SweepClosure::flushCurFreeChunk(HeapWord* chunk, size_t size) {
8107 assert(inFreeRange(), "Should only be called if currently in a free range.");
8108 assert(size > 0,
8109 "A zero sized chunk cannot be added to the free lists.");
8110 if (!freeRangeInFreeLists()) {
8111 if(CMSTestInFreeList) {
8112 FreeChunk* fc = (FreeChunk*) chunk;
8113 fc->setSize(size);
8114 assert(!_sp->verifyChunkInFreeLists(fc),
8115 "chunk should not be in free lists yet");
8116 }
8117 if (CMSTraceSweeper) {
8118 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8119 chunk, size);
8120 }
8121 // A new free range is going to be starting. The current
8122 // free range has not been added to the free lists yet or
8123 // was removed so add it back.
8124 // If the current free range was coalesced, then the death
8125 // of the free range was recorded. Record a birth now.
8126 if (lastFreeRangeCoalesced()) {
8127 _sp->coalBirth(size);
8128 }
8129 _sp->addChunkAndRepairOffsetTable(chunk, size,
8130 lastFreeRangeCoalesced());
8131 }
8132 set_inFreeRange(false);
8133 set_freeRangeInFreeLists(false);
8134 }
8135
8136 // We take a break if we've been at this for a while,
8137 // so as to avoid monopolizing the locks involved.
8138 void SweepClosure::do_yield_work(HeapWord* addr) {
8139 // Return current free chunk being used for coalescing (if any)
8140 // to the appropriate freelist. After yielding, the next
8141 // free block encountered will start a coalescing range of
8142 // free blocks. If the next free block is adjacent to the
8143 // chunk just flushed, they will need to wait for the next
8144 // sweep to be coalesced.
8145 if (inFreeRange()) {
8146 flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger()));
8147 }
8148
8149 // First give up the locks, then yield, then re-lock.
8150 // We should probably use a constructor/destructor idiom to
8151 // do this unlock/lock or modify the MutexUnlocker class to
8152 // serve our purpose. XXX
8153 assert_lock_strong(_bitMap->lock());
8154 assert_lock_strong(_freelistLock);
8155 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8156 "CMS thread should hold CMS token");
8157 _bitMap->lock()->unlock();
8158 _freelistLock->unlock();
8159 ConcurrentMarkSweepThread::desynchronize(true);
8160 ConcurrentMarkSweepThread::acknowledge_yield_request();
8161 _collector->stopTimer();
8162 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8163 if (PrintCMSStatistics != 0) {
8164 _collector->incrementYields();
8165 }
8166 _collector->icms_wait();
8167
8168 // See the comment in coordinator_yield()
8169 for (unsigned i = 0; i < CMSYieldSleepCount &&
8170 ConcurrentMarkSweepThread::should_yield() &&
8171 !CMSCollector::foregroundGCIsActive(); ++i) {
8172 os::sleep(Thread::current(), 1, false);
8173 ConcurrentMarkSweepThread::acknowledge_yield_request();
8174 }
8175
8176 ConcurrentMarkSweepThread::synchronize(true);
8177 _freelistLock->lock();
8178 _bitMap->lock()->lock_without_safepoint_check();
8179 _collector->startTimer();
8180 }
8181
8182 #ifndef PRODUCT
8183 // This is actually very useful in a product build if it can
8184 // be called from the debugger. Compile it into the product
8185 // as needed.
8186 bool debug_verifyChunkInFreeLists(FreeChunk* fc) {
8187 return debug_cms_space->verifyChunkInFreeLists(fc);
8188 }
8189
8190 void SweepClosure::record_free_block_coalesced(FreeChunk* fc) const {
8191 if (CMSTraceSweeper) {
8192 gclog_or_tty->print("Sweep:coal_free_blk 0x%x (%d)\n", fc, fc->size());
8193 }
8194 }
8195 #endif
8196
8197 // CMSIsAliveClosure
8198 bool CMSIsAliveClosure::do_object_b(oop obj) {
8199 HeapWord* addr = (HeapWord*)obj;
8200 return addr != NULL &&
8201 (!_span.contains(addr) || _bit_map->isMarked(addr));
8202 }
8203
8204 // CMSKeepAliveClosure: the serial version
8205 void CMSKeepAliveClosure::do_oop(oop* p) {
8206 oop this_oop = *p;
8207 HeapWord* addr = (HeapWord*)this_oop;
8208 if (_span.contains(addr) &&
8209 !_bit_map->isMarked(addr)) {
8210 _bit_map->mark(addr);
8211 bool simulate_overflow = false;
8212 NOT_PRODUCT(
8213 if (CMSMarkStackOverflowALot &&
8214 _collector->simulate_overflow()) {
8215 // simulate a stack overflow
8216 simulate_overflow = true;
8217 }
8218 )
8219 if (simulate_overflow || !_mark_stack->push(this_oop)) {
8220 _collector->push_on_overflow_list(this_oop);
8221 _collector->_ser_kac_ovflw++;
8222 }
8223 }
8224 }
8225
8226 // CMSParKeepAliveClosure: a parallel version of the above.
8227 // The work queues are private to each closure (thread),
8228 // but (may be) available for stealing by other threads.
8229 void CMSParKeepAliveClosure::do_oop(oop* p) {
8230 oop this_oop = *p;
8231 HeapWord* addr = (HeapWord*)this_oop;
8232 if (_span.contains(addr) &&
8233 !_bit_map->isMarked(addr)) {
8234 // In general, during recursive tracing, several threads
8235 // may be concurrently getting here; the first one to
8236 // "tag" it, claims it.
8237 if (_bit_map->par_mark(addr)) {
8238 bool res = _work_queue->push(this_oop);
8239 assert(res, "Low water mark should be much less than capacity");
8240 // Do a recursive trim in the hope that this will keep
8241 // stack usage lower, but leave some oops for potential stealers
8242 trim_queue(_low_water_mark);
8243 } // Else, another thread got there first
8244 }
8245 }
8246
8247 void CMSParKeepAliveClosure::trim_queue(uint max) {
8248 while (_work_queue->size() > max) {
8249 oop new_oop;
8250 if (_work_queue->pop_local(new_oop)) {
8251 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8252 assert(_bit_map->isMarked((HeapWord*)new_oop),
8253 "no white objects on this stack!");
8254 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8255 // iterate over the oops in this oop, marking and pushing
8256 // the ones in CMS heap (i.e. in _span).
8257 new_oop->oop_iterate(&_mark_and_push);
8258 }
8259 }
8260 }
8261
8262 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) {
8263 oop this_oop = *p;
8264 HeapWord* addr = (HeapWord*)this_oop;
8265 if (_span.contains(addr) &&
8266 !_bit_map->isMarked(addr)) {
8267 if (_bit_map->par_mark(addr)) {
8268 bool simulate_overflow = false;
8269 NOT_PRODUCT(
8270 if (CMSMarkStackOverflowALot &&
8271 _collector->par_simulate_overflow()) {
8272 // simulate a stack overflow
8273 simulate_overflow = true;
8274 }
8275 )
8276 if (simulate_overflow || !_work_queue->push(this_oop)) {
8277 _collector->par_push_on_overflow_list(this_oop);
8278 _collector->_par_kac_ovflw++;
8279 }
8280 } // Else another thread got there already
8281 }
8282 }
8283
8284 //////////////////////////////////////////////////////////////////
8285 // CMSExpansionCause /////////////////////////////
8286 //////////////////////////////////////////////////////////////////
8287 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8288 switch (cause) {
8289 case _no_expansion:
8290 return "No expansion";
8291 case _satisfy_free_ratio:
8292 return "Free ratio";
8293 case _satisfy_promotion:
8294 return "Satisfy promotion";
8295 case _satisfy_allocation:
8296 return "allocation";
8297 case _allocate_par_lab:
8298 return "Par LAB";
8299 case _allocate_par_spooling_space:
8300 return "Par Spooling Space";
8301 case _adaptive_size_policy:
8302 return "Ergonomics";
8303 default:
8304 return "unknown";
8305 }
8306 }
8307
8308 void CMSDrainMarkingStackClosure::do_void() {
8309 // the max number to take from overflow list at a time
8310 const size_t num = _mark_stack->capacity()/4;
8311 while (!_mark_stack->isEmpty() ||
8312 // if stack is empty, check the overflow list
8313 _collector->take_from_overflow_list(num, _mark_stack)) {
8314 oop this_oop = _mark_stack->pop();
8315 HeapWord* addr = (HeapWord*)this_oop;
8316 assert(_span.contains(addr), "Should be within span");
8317 assert(_bit_map->isMarked(addr), "Should be marked");
8318 assert(this_oop->is_oop(), "Should be an oop");
8319 this_oop->oop_iterate(_keep_alive);
8320 }
8321 }
8322
8323 void CMSParDrainMarkingStackClosure::do_void() {
8324 // drain queue
8325 trim_queue(0);
8326 }
8327
8328 // Trim our work_queue so its length is below max at return
8329 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8330 while (_work_queue->size() > max) {
8331 oop new_oop;
8332 if (_work_queue->pop_local(new_oop)) {
8333 assert(new_oop->is_oop(), "Expected an oop");
8334 assert(_bit_map->isMarked((HeapWord*)new_oop),
8335 "no white objects on this stack!");
8336 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8337 // iterate over the oops in this oop, marking and pushing
8338 // the ones in CMS heap (i.e. in _span).
8339 new_oop->oop_iterate(&_mark_and_push);
8340 }
8341 }
8342 }
8343
8344 ////////////////////////////////////////////////////////////////////
8345 // Support for Marking Stack Overflow list handling and related code
8346 ////////////////////////////////////////////////////////////////////
8347 // Much of the following code is similar in shape and spirit to the
8348 // code used in ParNewGC. We should try and share that code
8349 // as much as possible in the future.
8350
8351 #ifndef PRODUCT
8352 // Debugging support for CMSStackOverflowALot
8353
8354 // It's OK to call this multi-threaded; the worst thing
8355 // that can happen is that we'll get a bunch of closely
8356 // spaced simulated oveflows, but that's OK, in fact
8357 // probably good as it would exercise the overflow code
8358 // under contention.
8359 bool CMSCollector::simulate_overflow() {
8360 if (_overflow_counter-- <= 0) { // just being defensive
8361 _overflow_counter = CMSMarkStackOverflowInterval;
8362 return true;
8363 } else {
8364 return false;
8365 }
8366 }
8367
8368 bool CMSCollector::par_simulate_overflow() {
8369 return simulate_overflow();
8370 }
8371 #endif
8372
8373 // Single-threaded
8374 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8375 assert(stack->isEmpty(), "Expected precondition");
8376 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8377 size_t i = num;
8378 oop cur = _overflow_list;
8379 const markOop proto = markOopDesc::prototype();
8380 NOT_PRODUCT(size_t n = 0;)
8381 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8382 next = oop(cur->mark());
8383 cur->set_mark(proto); // until proven otherwise
8384 assert(cur->is_oop(), "Should be an oop");
8385 bool res = stack->push(cur);
8386 assert(res, "Bit off more than can chew?");
8387 NOT_PRODUCT(n++;)
8388 }
8389 _overflow_list = cur;
8390 #ifndef PRODUCT
8391 assert(_num_par_pushes >= n, "Too many pops?");
8392 _num_par_pushes -=n;
8393 #endif
8394 return !stack->isEmpty();
8395 }
8396
8397 // Multi-threaded; use CAS to break off a prefix
8398 bool CMSCollector::par_take_from_overflow_list(size_t num,
8399 OopTaskQueue* work_q) {
8400 assert(work_q->size() == 0, "That's the current policy");
8401 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8402 if (_overflow_list == NULL) {
8403 return false;
8404 }
8405 // Grab the entire list; we'll put back a suffix
8406 oop prefix = (oop)Atomic::xchg_ptr(NULL, &_overflow_list);
8407 if (prefix == NULL) { // someone grabbed it before we did ...
8408 // ... we could spin for a short while, but for now we don't
8409 return false;
8410 }
8411 size_t i = num;
8412 oop cur = prefix;
8413 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8414 if (cur->mark() != NULL) {
8415 oop suffix_head = cur->mark(); // suffix will be put back on global list
8416 cur->set_mark(NULL); // break off suffix
8417 // Find tail of suffix so we can prepend suffix to global list
8418 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8419 oop suffix_tail = cur;
8420 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8421 "Tautology");
8422 oop observed_overflow_list = _overflow_list;
8423 do {
8424 cur = observed_overflow_list;
8425 suffix_tail->set_mark(markOop(cur));
8426 observed_overflow_list =
8427 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur);
8428 } while (cur != observed_overflow_list);
8429 }
8430
8431 // Push the prefix elements on work_q
8432 assert(prefix != NULL, "control point invariant");
8433 const markOop proto = markOopDesc::prototype();
8434 oop next;
8435 NOT_PRODUCT(size_t n = 0;)
8436 for (cur = prefix; cur != NULL; cur = next) {
8437 next = oop(cur->mark());
8438 cur->set_mark(proto); // until proven otherwise
8439 assert(cur->is_oop(), "Should be an oop");
8440 bool res = work_q->push(cur);
8441 assert(res, "Bit off more than we can chew?");
8442 NOT_PRODUCT(n++;)
8443 }
8444 #ifndef PRODUCT
8445 assert(_num_par_pushes >= n, "Too many pops?");
8446 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8447 #endif
8448 return true;
8449 }
8450
8451 // Single-threaded
8452 void CMSCollector::push_on_overflow_list(oop p) {
8453 NOT_PRODUCT(_num_par_pushes++;)
8454 assert(p->is_oop(), "Not an oop");
8455 preserve_mark_if_necessary(p);
8456 p->set_mark((markOop)_overflow_list);
8457 _overflow_list = p;
8458 }
8459
8460 // Multi-threaded; use CAS to prepend to overflow list
8461 void CMSCollector::par_push_on_overflow_list(oop p) {
8462 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8463 assert(p->is_oop(), "Not an oop");
8464 par_preserve_mark_if_necessary(p);
8465 oop observed_overflow_list = _overflow_list;
8466 oop cur_overflow_list;
8467 do {
8468 cur_overflow_list = observed_overflow_list;
8469 p->set_mark(markOop(cur_overflow_list));
8470 observed_overflow_list =
8471 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8472 } while (cur_overflow_list != observed_overflow_list);
8473 }
8474
8475 // Single threaded
8476 // General Note on GrowableArray: pushes may silently fail
8477 // because we are (temporarily) out of C-heap for expanding
8478 // the stack. The problem is quite ubiquitous and affects
8479 // a lot of code in the JVM. The prudent thing for GrowableArray
8480 // to do (for now) is to exit with an error. However, that may
8481 // be too draconian in some cases because the caller may be
8482 // able to recover without much harm. For suych cases, we
8483 // should probably introduce a "soft_push" method which returns
8484 // an indication of success or failure with the assumption that
8485 // the caller may be able to recover from a failure; code in
8486 // the VM can then be changed, incrementally, to deal with such
8487 // failures where possible, thus, incrementally hardening the VM
8488 // in such low resource situations.
8489 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8490 int PreserveMarkStackSize = 128;
8491
8492 if (_preserved_oop_stack == NULL) {
8493 assert(_preserved_mark_stack == NULL,
8494 "bijection with preserved_oop_stack");
8495 // Allocate the stacks
8496 _preserved_oop_stack = new (ResourceObj::C_HEAP)
8497 GrowableArray<oop>(PreserveMarkStackSize, true);
8498 _preserved_mark_stack = new (ResourceObj::C_HEAP)
8499 GrowableArray<markOop>(PreserveMarkStackSize, true);
8500 if (_preserved_oop_stack == NULL || _preserved_mark_stack == NULL) {
8501 vm_exit_out_of_memory(2* PreserveMarkStackSize * sizeof(oop) /* punt */,
8502 "Preserved Mark/Oop Stack for CMS (C-heap)");
8503 }
8504 }
8505 _preserved_oop_stack->push(p);
8506 _preserved_mark_stack->push(m);
8507 assert(m == p->mark(), "Mark word changed");
8508 assert(_preserved_oop_stack->length() == _preserved_mark_stack->length(),
8509 "bijection");
8510 }
8511
8512 // Single threaded
8513 void CMSCollector::preserve_mark_if_necessary(oop p) {
8514 markOop m = p->mark();
8515 if (m->must_be_preserved(p)) {
8516 preserve_mark_work(p, m);
8517 }
8518 }
8519
8520 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8521 markOop m = p->mark();
8522 if (m->must_be_preserved(p)) {
8523 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8524 // Even though we read the mark word without holding
8525 // the lock, we are assured that it will not change
8526 // because we "own" this oop, so no other thread can
8527 // be trying to push it on the overflow list; see
8528 // the assertion in preserve_mark_work() that checks
8529 // that m == p->mark().
8530 preserve_mark_work(p, m);
8531 }
8532 }
8533
8534 // We should be able to do this multi-threaded,
8535 // a chunk of stack being a task (this is
8536 // correct because each oop only ever appears
8537 // once in the overflow list. However, it's
8538 // not very easy to completely overlap this with
8539 // other operations, so will generally not be done
8540 // until all work's been completed. Because we
8541 // expect the preserved oop stack (set) to be small,
8542 // it's probably fine to do this single-threaded.
8543 // We can explore cleverer concurrent/overlapped/parallel
8544 // processing of preserved marks if we feel the
8545 // need for this in the future. Stack overflow should
8546 // be so rare in practice and, when it happens, its
8547 // effect on performance so great that this will
8548 // likely just be in the noise anyway.
8549 void CMSCollector::restore_preserved_marks_if_any() {
8550 if (_preserved_oop_stack == NULL) {
8551 assert(_preserved_mark_stack == NULL,
8552 "bijection with preserved_oop_stack");
8553 return;
8554 }
8555
8556 assert(SafepointSynchronize::is_at_safepoint(),
8557 "world should be stopped");
8558 assert(Thread::current()->is_ConcurrentGC_thread() ||
8559 Thread::current()->is_VM_thread(),
8560 "should be single-threaded");
8561
8562 int length = _preserved_oop_stack->length();
8563 assert(_preserved_mark_stack->length() == length, "bijection");
8564 for (int i = 0; i < length; i++) {
8565 oop p = _preserved_oop_stack->at(i);
8566 assert(p->is_oop(), "Should be an oop");
8567 assert(_span.contains(p), "oop should be in _span");
8568 assert(p->mark() == markOopDesc::prototype(),
8569 "Set when taken from overflow list");
8570 markOop m = _preserved_mark_stack->at(i);
8571 p->set_mark(m);
8572 }
8573 _preserved_mark_stack->clear();
8574 _preserved_oop_stack->clear();
8575 assert(_preserved_mark_stack->is_empty() &&
8576 _preserved_oop_stack->is_empty(),
8577 "stacks were cleared above");
8578 }
8579
8580 #ifndef PRODUCT
8581 bool CMSCollector::no_preserved_marks() const {
8582 return ( ( _preserved_mark_stack == NULL
8583 && _preserved_oop_stack == NULL)
8584 || ( _preserved_mark_stack->is_empty()
8585 && _preserved_oop_stack->is_empty()));
8586 }
8587 #endif
8588
8589 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
8590 {
8591 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
8592 CMSAdaptiveSizePolicy* size_policy =
8593 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
8594 assert(size_policy->is_gc_cms_adaptive_size_policy(),
8595 "Wrong type for size policy");
8596 return size_policy;
8597 }
8598
8599 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
8600 size_t desired_promo_size) {
8601 if (cur_promo_size < desired_promo_size) {
8602 size_t expand_bytes = desired_promo_size - cur_promo_size;
8603 if (PrintAdaptiveSizePolicy && Verbose) {
8604 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
8605 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
8606 expand_bytes);
8607 }
8608 expand(expand_bytes,
8609 MinHeapDeltaBytes,
8610 CMSExpansionCause::_adaptive_size_policy);
8611 } else if (desired_promo_size < cur_promo_size) {
8612 size_t shrink_bytes = cur_promo_size - desired_promo_size;
8613 if (PrintAdaptiveSizePolicy && Verbose) {
8614 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
8615 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
8616 shrink_bytes);
8617 }
8618 shrink(shrink_bytes);
8619 }
8620 }
8621
8622 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
8623 GenCollectedHeap* gch = GenCollectedHeap::heap();
8624 CMSGCAdaptivePolicyCounters* counters =
8625 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
8626 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
8627 "Wrong kind of counters");
8628 return counters;
8629 }
8630
8631
8632 void ASConcurrentMarkSweepGeneration::update_counters() {
8633 if (UsePerfData) {
8634 _space_counters->update_all();
8635 _gen_counters->update_all();
8636 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8637 GenCollectedHeap* gch = GenCollectedHeap::heap();
8638 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
8639 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
8640 "Wrong gc statistics type");
8641 counters->update_counters(gc_stats_l);
8642 }
8643 }
8644
8645 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
8646 if (UsePerfData) {
8647 _space_counters->update_used(used);
8648 _space_counters->update_capacity();
8649 _gen_counters->update_all();
8650
8651 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8652 GenCollectedHeap* gch = GenCollectedHeap::heap();
8653 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
8654 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
8655 "Wrong gc statistics type");
8656 counters->update_counters(gc_stats_l);
8657 }
8658 }
8659
8660 // The desired expansion delta is computed so that:
8661 // . desired free percentage or greater is used
8662 void ASConcurrentMarkSweepGeneration::compute_new_size() {
8663 assert_locked_or_safepoint(Heap_lock);
8664
8665 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
8666
8667 // If incremental collection failed, we just want to expand
8668 // to the limit.
8669 if (incremental_collection_failed()) {
8670 clear_incremental_collection_failed();
8671 grow_to_reserved();
8672 return;
8673 }
8674
8675 assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing");
8676
8677 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
8678 "Wrong type of heap");
8679 int prev_level = level() - 1;
8680 assert(prev_level >= 0, "The cms generation is the lowest generation");
8681 Generation* prev_gen = gch->get_gen(prev_level);
8682 assert(prev_gen->kind() == Generation::ASParNew,
8683 "Wrong type of young generation");
8684 ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen;
8685 size_t cur_eden = younger_gen->eden()->capacity();
8686 CMSAdaptiveSizePolicy* size_policy = cms_size_policy();
8687 size_t cur_promo = free();
8688 size_policy->compute_tenured_generation_free_space(cur_promo,
8689 max_available(),
8690 cur_eden);
8691 resize(cur_promo, size_policy->promo_size());
8692
8693 // Record the new size of the space in the cms generation
8694 // that is available for promotions. This is temporary.
8695 // It should be the desired promo size.
8696 size_policy->avg_cms_promo()->sample(free());
8697 size_policy->avg_old_live()->sample(used());
8698
8699 if (UsePerfData) {
8700 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8701 counters->update_cms_capacity_counter(capacity());
8702 }
8703 }
8704
8705 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
8706 assert_locked_or_safepoint(Heap_lock);
8707 assert_lock_strong(freelistLock());
8708 HeapWord* old_end = _cmsSpace->end();
8709 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
8710 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
8711 FreeChunk* chunk_at_end = find_chunk_at_end();
8712 if (chunk_at_end == NULL) {
8713 // No room to shrink
8714 if (PrintGCDetails && Verbose) {
8715 gclog_or_tty->print_cr("No room to shrink: old_end "
8716 PTR_FORMAT " unallocated_start " PTR_FORMAT
8717 " chunk_at_end " PTR_FORMAT,
8718 old_end, unallocated_start, chunk_at_end);
8719 }
8720 return;
8721 } else {
8722
8723 // Find the chunk at the end of the space and determine
8724 // how much it can be shrunk.
8725 size_t shrinkable_size_in_bytes = chunk_at_end->size();
8726 size_t aligned_shrinkable_size_in_bytes =
8727 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
8728 assert(unallocated_start <= chunk_at_end->end(),
8729 "Inconsistent chunk at end of space");
8730 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
8731 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
8732
8733 // Shrink the underlying space
8734 _virtual_space.shrink_by(bytes);
8735 if (PrintGCDetails && Verbose) {
8736 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
8737 " desired_bytes " SIZE_FORMAT
8738 " shrinkable_size_in_bytes " SIZE_FORMAT
8739 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
8740 " bytes " SIZE_FORMAT,
8741 desired_bytes, shrinkable_size_in_bytes,
8742 aligned_shrinkable_size_in_bytes, bytes);
8743 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
8744 " unallocated_start " SIZE_FORMAT,
8745 old_end, unallocated_start);
8746 }
8747
8748 // If the space did shrink (shrinking is not guaranteed),
8749 // shrink the chunk at the end by the appropriate amount.
8750 if (((HeapWord*)_virtual_space.high()) < old_end) {
8751 size_t new_word_size =
8752 heap_word_size(_virtual_space.committed_size());
8753
8754 // Have to remove the chunk from the dictionary because it is changing
8755 // size and might be someplace elsewhere in the dictionary.
8756
8757 // Get the chunk at end, shrink it, and put it
8758 // back.
8759 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
8760 size_t word_size_change = word_size_before - new_word_size;
8761 size_t chunk_at_end_old_size = chunk_at_end->size();
8762 assert(chunk_at_end_old_size >= word_size_change,
8763 "Shrink is too large");
8764 chunk_at_end->setSize(chunk_at_end_old_size -
8765 word_size_change);
8766 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
8767 word_size_change);
8768
8769 _cmsSpace->returnChunkToDictionary(chunk_at_end);
8770
8771 MemRegion mr(_cmsSpace->bottom(), new_word_size);
8772 _bts->resize(new_word_size); // resize the block offset shared array
8773 Universe::heap()->barrier_set()->resize_covered_region(mr);
8774 _cmsSpace->assert_locked();
8775 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
8776
8777 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
8778
8779 // update the space and generation capacity counters
8780 if (UsePerfData) {
8781 _space_counters->update_capacity();
8782 _gen_counters->update_all();
8783 }
8784
8785 if (Verbose && PrintGCDetails) {
8786 size_t new_mem_size = _virtual_space.committed_size();
8787 size_t old_mem_size = new_mem_size + bytes;
8788 gclog_or_tty->print_cr("Shrinking %s from %ldK by %ldK to %ldK",
8789 name(), old_mem_size/K, bytes/K, new_mem_size/K);
8790 }
8791 }
8792
8793 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
8794 "Inconsistency at end of space");
8795 assert(chunk_at_end->end() == _cmsSpace->end(),
8796 "Shrinking is inconsistent");
8797 return;
8798 }
8799 }
8800
8801 // Transfer some number of overflown objects to usual marking
8802 // stack. Return true if some objects were transferred.
8803 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8804 size_t num = MIN2((size_t)_mark_stack->capacity()/4,
8805 (size_t)ParGCDesiredObjsFromOverflowList);
8806
8807 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8808 assert(_collector->overflow_list_is_empty() || res,
8809 "If list is not empty, we should have taken something");
8810 assert(!res || !_mark_stack->isEmpty(),
8811 "If we took something, it should now be on our stack");
8812 return res;
8813 }
8814
8815 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8816 size_t res = _sp->block_size_no_stall(addr, _collector);
8817 assert(res != 0, "Should always be able to compute a size");
8818 if (_sp->block_is_obj(addr)) {
8819 if (_live_bit_map->isMarked(addr)) {
8820 // It can't have been dead in a previous cycle
8821 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8822 } else {
8823 _dead_bit_map->mark(addr); // mark the dead object
8824 }
8825 }
8826 return res;
8827 }