1 /*
2 * Copyright (c) 2001, 2010, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
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23 */
24
25 # include "incls/_precompiled.incl"
26 # include "incls/_concurrentMarkSweepGeneration.cpp.incl"
27
28 // statics
29 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
30 bool CMSCollector::_full_gc_requested = false;
31
32 //////////////////////////////////////////////////////////////////
33 // In support of CMS/VM thread synchronization
34 //////////////////////////////////////////////////////////////////
35 // We split use of the CGC_lock into 2 "levels".
36 // The low-level locking is of the usual CGC_lock monitor. We introduce
37 // a higher level "token" (hereafter "CMS token") built on top of the
38 // low level monitor (hereafter "CGC lock").
39 // The token-passing protocol gives priority to the VM thread. The
40 // CMS-lock doesn't provide any fairness guarantees, but clients
41 // should ensure that it is only held for very short, bounded
42 // durations.
43 //
44 // When either of the CMS thread or the VM thread is involved in
45 // collection operations during which it does not want the other
46 // thread to interfere, it obtains the CMS token.
47 //
48 // If either thread tries to get the token while the other has
49 // it, that thread waits. However, if the VM thread and CMS thread
50 // both want the token, then the VM thread gets priority while the
51 // CMS thread waits. This ensures, for instance, that the "concurrent"
52 // phases of the CMS thread's work do not block out the VM thread
53 // for long periods of time as the CMS thread continues to hog
54 // the token. (See bug 4616232).
55 //
56 // The baton-passing functions are, however, controlled by the
57 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
58 // and here the low-level CMS lock, not the high level token,
59 // ensures mutual exclusion.
60 //
61 // Two important conditions that we have to satisfy:
62 // 1. if a thread does a low-level wait on the CMS lock, then it
63 // relinquishes the CMS token if it were holding that token
64 // when it acquired the low-level CMS lock.
65 // 2. any low-level notifications on the low-level lock
66 // should only be sent when a thread has relinquished the token.
67 //
68 // In the absence of either property, we'd have potential deadlock.
69 //
70 // We protect each of the CMS (concurrent and sequential) phases
71 // with the CMS _token_, not the CMS _lock_.
72 //
73 // The only code protected by CMS lock is the token acquisition code
74 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
75 // baton-passing code.
76 //
77 // Unfortunately, i couldn't come up with a good abstraction to factor and
78 // hide the naked CGC_lock manipulation in the baton-passing code
79 // further below. That's something we should try to do. Also, the proof
80 // of correctness of this 2-level locking scheme is far from obvious,
81 // and potentially quite slippery. We have an uneasy supsicion, for instance,
82 // that there may be a theoretical possibility of delay/starvation in the
83 // low-level lock/wait/notify scheme used for the baton-passing because of
84 // potential intereference with the priority scheme embodied in the
85 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
86 // invocation further below and marked with "XXX 20011219YSR".
87 // Indeed, as we note elsewhere, this may become yet more slippery
88 // in the presence of multiple CMS and/or multiple VM threads. XXX
89
90 class CMSTokenSync: public StackObj {
91 private:
92 bool _is_cms_thread;
93 public:
94 CMSTokenSync(bool is_cms_thread):
95 _is_cms_thread(is_cms_thread) {
96 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
97 "Incorrect argument to constructor");
98 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
99 }
100
101 ~CMSTokenSync() {
102 assert(_is_cms_thread ?
103 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
104 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
105 "Incorrect state");
106 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
107 }
108 };
109
110 // Convenience class that does a CMSTokenSync, and then acquires
111 // upto three locks.
112 class CMSTokenSyncWithLocks: public CMSTokenSync {
113 private:
114 // Note: locks are acquired in textual declaration order
115 // and released in the opposite order
116 MutexLockerEx _locker1, _locker2, _locker3;
117 public:
118 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
119 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
120 CMSTokenSync(is_cms_thread),
121 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
122 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
123 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
124 { }
125 };
126
127
128 // Wrapper class to temporarily disable icms during a foreground cms collection.
129 class ICMSDisabler: public StackObj {
130 public:
131 // The ctor disables icms and wakes up the thread so it notices the change;
132 // the dtor re-enables icms. Note that the CMSCollector methods will check
133 // CMSIncrementalMode.
134 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
135 ~ICMSDisabler() { CMSCollector::enable_icms(); }
136 };
137
138 //////////////////////////////////////////////////////////////////
139 // Concurrent Mark-Sweep Generation /////////////////////////////
140 //////////////////////////////////////////////////////////////////
141
142 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
143
144 // This struct contains per-thread things necessary to support parallel
145 // young-gen collection.
146 class CMSParGCThreadState: public CHeapObj {
147 public:
148 CFLS_LAB lab;
149 PromotionInfo promo;
150
151 // Constructor.
152 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
153 promo.setSpace(cfls);
154 }
155 };
156
157 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
158 ReservedSpace rs, size_t initial_byte_size, int level,
159 CardTableRS* ct, bool use_adaptive_freelists,
160 FreeBlockDictionary::DictionaryChoice dictionaryChoice) :
161 CardGeneration(rs, initial_byte_size, level, ct),
162 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
163 _debug_collection_type(Concurrent_collection_type)
164 {
165 HeapWord* bottom = (HeapWord*) _virtual_space.low();
166 HeapWord* end = (HeapWord*) _virtual_space.high();
167
168 _direct_allocated_words = 0;
169 NOT_PRODUCT(
170 _numObjectsPromoted = 0;
171 _numWordsPromoted = 0;
172 _numObjectsAllocated = 0;
173 _numWordsAllocated = 0;
174 )
175
176 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
177 use_adaptive_freelists,
178 dictionaryChoice);
179 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
180 if (_cmsSpace == NULL) {
181 vm_exit_during_initialization(
182 "CompactibleFreeListSpace allocation failure");
183 }
184 _cmsSpace->_gen = this;
185
186 _gc_stats = new CMSGCStats();
187
188 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
189 // offsets match. The ability to tell free chunks from objects
190 // depends on this property.
191 debug_only(
192 FreeChunk* junk = NULL;
193 assert(UseCompressedOops ||
194 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
195 "Offset of FreeChunk::_prev within FreeChunk must match"
196 " that of OopDesc::_klass within OopDesc");
197 )
198 if (ParallelGCThreads > 0) {
199 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
200 _par_gc_thread_states =
201 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads);
202 if (_par_gc_thread_states == NULL) {
203 vm_exit_during_initialization("Could not allocate par gc structs");
204 }
205 for (uint i = 0; i < ParallelGCThreads; i++) {
206 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
207 if (_par_gc_thread_states[i] == NULL) {
208 vm_exit_during_initialization("Could not allocate par gc structs");
209 }
210 }
211 } else {
212 _par_gc_thread_states = NULL;
213 }
214 _incremental_collection_failed = false;
215 // The "dilatation_factor" is the expansion that can occur on
216 // account of the fact that the minimum object size in the CMS
217 // generation may be larger than that in, say, a contiguous young
218 // generation.
219 // Ideally, in the calculation below, we'd compute the dilatation
220 // factor as: MinChunkSize/(promoting_gen's min object size)
221 // Since we do not have such a general query interface for the
222 // promoting generation, we'll instead just use the mimimum
223 // object size (which today is a header's worth of space);
224 // note that all arithmetic is in units of HeapWords.
225 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
226 assert(_dilatation_factor >= 1.0, "from previous assert");
227 }
228
229
230 // The field "_initiating_occupancy" represents the occupancy percentage
231 // at which we trigger a new collection cycle. Unless explicitly specified
232 // via CMSInitiating[Perm]OccupancyFraction (argument "io" below), it
233 // is calculated by:
234 //
235 // Let "f" be MinHeapFreeRatio in
236 //
237 // _intiating_occupancy = 100-f +
238 // f * (CMSTrigger[Perm]Ratio/100)
239 // where CMSTrigger[Perm]Ratio is the argument "tr" below.
240 //
241 // That is, if we assume the heap is at its desired maximum occupancy at the
242 // end of a collection, we let CMSTrigger[Perm]Ratio of the (purported) free
243 // space be allocated before initiating a new collection cycle.
244 //
245 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, intx tr) {
246 assert(io <= 100 && tr >= 0 && tr <= 100, "Check the arguments");
247 if (io >= 0) {
248 _initiating_occupancy = (double)io / 100.0;
249 } else {
250 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
251 (double)(tr * MinHeapFreeRatio) / 100.0)
252 / 100.0;
253 }
254 }
255
256 void ConcurrentMarkSweepGeneration::ref_processor_init() {
257 assert(collector() != NULL, "no collector");
258 collector()->ref_processor_init();
259 }
260
261 void CMSCollector::ref_processor_init() {
262 if (_ref_processor == NULL) {
263 // Allocate and initialize a reference processor
264 _ref_processor = ReferenceProcessor::create_ref_processor(
265 _span, // span
266 _cmsGen->refs_discovery_is_atomic(), // atomic_discovery
267 _cmsGen->refs_discovery_is_mt(), // mt_discovery
268 &_is_alive_closure,
269 ParallelGCThreads,
270 ParallelRefProcEnabled);
271 // Initialize the _ref_processor field of CMSGen
272 _cmsGen->set_ref_processor(_ref_processor);
273
274 // Allocate a dummy ref processor for perm gen.
275 ReferenceProcessor* rp2 = new ReferenceProcessor();
276 if (rp2 == NULL) {
277 vm_exit_during_initialization("Could not allocate ReferenceProcessor object");
278 }
279 _permGen->set_ref_processor(rp2);
280 }
281 }
282
283 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
284 GenCollectedHeap* gch = GenCollectedHeap::heap();
285 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
286 "Wrong type of heap");
287 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
288 gch->gen_policy()->size_policy();
289 assert(sp->is_gc_cms_adaptive_size_policy(),
290 "Wrong type of size policy");
291 return sp;
292 }
293
294 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
295 CMSGCAdaptivePolicyCounters* results =
296 (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
297 assert(
298 results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
299 "Wrong gc policy counter kind");
300 return results;
301 }
302
303
304 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
305
306 const char* gen_name = "old";
307
308 // Generation Counters - generation 1, 1 subspace
309 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
310
311 _space_counters = new GSpaceCounters(gen_name, 0,
312 _virtual_space.reserved_size(),
313 this, _gen_counters);
314 }
315
316 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
317 _cms_gen(cms_gen)
318 {
319 assert(alpha <= 100, "bad value");
320 _saved_alpha = alpha;
321
322 // Initialize the alphas to the bootstrap value of 100.
323 _gc0_alpha = _cms_alpha = 100;
324
325 _cms_begin_time.update();
326 _cms_end_time.update();
327
328 _gc0_duration = 0.0;
329 _gc0_period = 0.0;
330 _gc0_promoted = 0;
331
332 _cms_duration = 0.0;
333 _cms_period = 0.0;
334 _cms_allocated = 0;
335
336 _cms_used_at_gc0_begin = 0;
337 _cms_used_at_gc0_end = 0;
338 _allow_duty_cycle_reduction = false;
339 _valid_bits = 0;
340 _icms_duty_cycle = CMSIncrementalDutyCycle;
341 }
342
343 double CMSStats::cms_free_adjustment_factor(size_t free) const {
344 // TBD: CR 6909490
345 return 1.0;
346 }
347
348 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
349 }
350
351 // If promotion failure handling is on use
352 // the padded average size of the promotion for each
353 // young generation collection.
354 double CMSStats::time_until_cms_gen_full() const {
355 size_t cms_free = _cms_gen->cmsSpace()->free();
356 GenCollectedHeap* gch = GenCollectedHeap::heap();
357 size_t expected_promotion = gch->get_gen(0)->capacity();
358 if (HandlePromotionFailure) {
359 expected_promotion = MIN2(
360 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average(),
361 expected_promotion);
362 }
363 if (cms_free > expected_promotion) {
364 // Start a cms collection if there isn't enough space to promote
365 // for the next minor collection. Use the padded average as
366 // a safety factor.
367 cms_free -= expected_promotion;
368
369 // Adjust by the safety factor.
370 double cms_free_dbl = (double)cms_free;
371 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
372 // Apply a further correction factor which tries to adjust
373 // for recent occurance of concurrent mode failures.
374 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
375 cms_free_dbl = cms_free_dbl * cms_adjustment;
376
377 if (PrintGCDetails && Verbose) {
378 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
379 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
380 cms_free, expected_promotion);
381 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
382 cms_free_dbl, cms_consumption_rate() + 1.0);
383 }
384 // Add 1 in case the consumption rate goes to zero.
385 return cms_free_dbl / (cms_consumption_rate() + 1.0);
386 }
387 return 0.0;
388 }
389
390 // Compare the duration of the cms collection to the
391 // time remaining before the cms generation is empty.
392 // Note that the time from the start of the cms collection
393 // to the start of the cms sweep (less than the total
394 // duration of the cms collection) can be used. This
395 // has been tried and some applications experienced
396 // promotion failures early in execution. This was
397 // possibly because the averages were not accurate
398 // enough at the beginning.
399 double CMSStats::time_until_cms_start() const {
400 // We add "gc0_period" to the "work" calculation
401 // below because this query is done (mostly) at the
402 // end of a scavenge, so we need to conservatively
403 // account for that much possible delay
404 // in the query so as to avoid concurrent mode failures
405 // due to starting the collection just a wee bit too
406 // late.
407 double work = cms_duration() + gc0_period();
408 double deadline = time_until_cms_gen_full();
409 // If a concurrent mode failure occurred recently, we want to be
410 // more conservative and halve our expected time_until_cms_gen_full()
411 if (work > deadline) {
412 if (Verbose && PrintGCDetails) {
413 gclog_or_tty->print(
414 " CMSCollector: collect because of anticipated promotion "
415 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
416 gc0_period(), time_until_cms_gen_full());
417 }
418 return 0.0;
419 }
420 return work - deadline;
421 }
422
423 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
424 // amount of change to prevent wild oscillation.
425 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
426 unsigned int new_duty_cycle) {
427 assert(old_duty_cycle <= 100, "bad input value");
428 assert(new_duty_cycle <= 100, "bad input value");
429
430 // Note: use subtraction with caution since it may underflow (values are
431 // unsigned). Addition is safe since we're in the range 0-100.
432 unsigned int damped_duty_cycle = new_duty_cycle;
433 if (new_duty_cycle < old_duty_cycle) {
434 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
435 if (new_duty_cycle + largest_delta < old_duty_cycle) {
436 damped_duty_cycle = old_duty_cycle - largest_delta;
437 }
438 } else if (new_duty_cycle > old_duty_cycle) {
439 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
440 if (new_duty_cycle > old_duty_cycle + largest_delta) {
441 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
442 }
443 }
444 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
445
446 if (CMSTraceIncrementalPacing) {
447 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
448 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
449 }
450 return damped_duty_cycle;
451 }
452
453 unsigned int CMSStats::icms_update_duty_cycle_impl() {
454 assert(CMSIncrementalPacing && valid(),
455 "should be handled in icms_update_duty_cycle()");
456
457 double cms_time_so_far = cms_timer().seconds();
458 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
459 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
460
461 // Avoid division by 0.
462 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
463 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
464
465 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
466 if (new_duty_cycle > _icms_duty_cycle) {
467 // Avoid very small duty cycles (1 or 2); 0 is allowed.
468 if (new_duty_cycle > 2) {
469 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
470 new_duty_cycle);
471 }
472 } else if (_allow_duty_cycle_reduction) {
473 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
474 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
475 // Respect the minimum duty cycle.
476 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
477 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
478 }
479
480 if (PrintGCDetails || CMSTraceIncrementalPacing) {
481 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
482 }
483
484 _allow_duty_cycle_reduction = false;
485 return _icms_duty_cycle;
486 }
487
488 #ifndef PRODUCT
489 void CMSStats::print_on(outputStream *st) const {
490 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
491 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
492 gc0_duration(), gc0_period(), gc0_promoted());
493 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
494 cms_duration(), cms_duration_per_mb(),
495 cms_period(), cms_allocated());
496 st->print(",cms_since_beg=%g,cms_since_end=%g",
497 cms_time_since_begin(), cms_time_since_end());
498 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
499 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
500 if (CMSIncrementalMode) {
501 st->print(",dc=%d", icms_duty_cycle());
502 }
503
504 if (valid()) {
505 st->print(",promo_rate=%g,cms_alloc_rate=%g",
506 promotion_rate(), cms_allocation_rate());
507 st->print(",cms_consumption_rate=%g,time_until_full=%g",
508 cms_consumption_rate(), time_until_cms_gen_full());
509 }
510 st->print(" ");
511 }
512 #endif // #ifndef PRODUCT
513
514 CMSCollector::CollectorState CMSCollector::_collectorState =
515 CMSCollector::Idling;
516 bool CMSCollector::_foregroundGCIsActive = false;
517 bool CMSCollector::_foregroundGCShouldWait = false;
518
519 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
520 ConcurrentMarkSweepGeneration* permGen,
521 CardTableRS* ct,
522 ConcurrentMarkSweepPolicy* cp):
523 _cmsGen(cmsGen),
524 _permGen(permGen),
525 _ct(ct),
526 _ref_processor(NULL), // will be set later
527 _conc_workers(NULL), // may be set later
528 _abort_preclean(false),
529 _start_sampling(false),
530 _between_prologue_and_epilogue(false),
531 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
532 _perm_gen_verify_bit_map(0, -1 /* no mutex */, "No_lock"),
533 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
534 -1 /* lock-free */, "No_lock" /* dummy */),
535 _modUnionClosure(&_modUnionTable),
536 _modUnionClosurePar(&_modUnionTable),
537 // Adjust my span to cover old (cms) gen and perm gen
538 _span(cmsGen->reserved()._union(permGen->reserved())),
539 // Construct the is_alive_closure with _span & markBitMap
540 _is_alive_closure(_span, &_markBitMap),
541 _restart_addr(NULL),
542 _overflow_list(NULL),
543 _preserved_oop_stack(NULL),
544 _preserved_mark_stack(NULL),
545 _stats(cmsGen),
546 _eden_chunk_array(NULL), // may be set in ctor body
547 _eden_chunk_capacity(0), // -- ditto --
548 _eden_chunk_index(0), // -- ditto --
549 _survivor_plab_array(NULL), // -- ditto --
550 _survivor_chunk_array(NULL), // -- ditto --
551 _survivor_chunk_capacity(0), // -- ditto --
552 _survivor_chunk_index(0), // -- ditto --
553 _ser_pmc_preclean_ovflw(0),
554 _ser_kac_preclean_ovflw(0),
555 _ser_pmc_remark_ovflw(0),
556 _par_pmc_remark_ovflw(0),
557 _ser_kac_ovflw(0),
558 _par_kac_ovflw(0),
559 #ifndef PRODUCT
560 _num_par_pushes(0),
561 #endif
562 _collection_count_start(0),
563 _verifying(false),
564 _icms_start_limit(NULL),
565 _icms_stop_limit(NULL),
566 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
567 _completed_initialization(false),
568 _collector_policy(cp),
569 _should_unload_classes(false),
570 _concurrent_cycles_since_last_unload(0),
571 _roots_scanning_options(0),
572 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
573 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding)
574 {
575 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
576 ExplicitGCInvokesConcurrent = true;
577 }
578 // Now expand the span and allocate the collection support structures
579 // (MUT, marking bit map etc.) to cover both generations subject to
580 // collection.
581
582 // First check that _permGen is adjacent to _cmsGen and above it.
583 assert( _cmsGen->reserved().word_size() > 0
584 && _permGen->reserved().word_size() > 0,
585 "generations should not be of zero size");
586 assert(_cmsGen->reserved().intersection(_permGen->reserved()).is_empty(),
587 "_cmsGen and _permGen should not overlap");
588 assert(_cmsGen->reserved().end() == _permGen->reserved().start(),
589 "_cmsGen->end() different from _permGen->start()");
590
591 // For use by dirty card to oop closures.
592 _cmsGen->cmsSpace()->set_collector(this);
593 _permGen->cmsSpace()->set_collector(this);
594
595 // Allocate MUT and marking bit map
596 {
597 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
598 if (!_markBitMap.allocate(_span)) {
599 warning("Failed to allocate CMS Bit Map");
600 return;
601 }
602 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
603 }
604 {
605 _modUnionTable.allocate(_span);
606 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
607 }
608
609 if (!_markStack.allocate(MarkStackSize)) {
610 warning("Failed to allocate CMS Marking Stack");
611 return;
612 }
613 if (!_revisitStack.allocate(CMSRevisitStackSize)) {
614 warning("Failed to allocate CMS Revisit Stack");
615 return;
616 }
617
618 // Support for multi-threaded concurrent phases
619 if (ParallelGCThreads > 0 && CMSConcurrentMTEnabled) {
620 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
621 // just for now
622 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
623 }
624 if (ConcGCThreads > 1) {
625 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
626 ConcGCThreads, true);
627 if (_conc_workers == NULL) {
628 warning("GC/CMS: _conc_workers allocation failure: "
629 "forcing -CMSConcurrentMTEnabled");
630 CMSConcurrentMTEnabled = false;
631 }
632 } else {
633 CMSConcurrentMTEnabled = false;
634 }
635 }
636 if (!CMSConcurrentMTEnabled) {
637 ConcGCThreads = 0;
638 } else {
639 // Turn off CMSCleanOnEnter optimization temporarily for
640 // the MT case where it's not fixed yet; see 6178663.
641 CMSCleanOnEnter = false;
642 }
643 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
644 "Inconsistency");
645
646 // Parallel task queues; these are shared for the
647 // concurrent and stop-world phases of CMS, but
648 // are not shared with parallel scavenge (ParNew).
649 {
650 uint i;
651 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
652
653 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
654 || ParallelRefProcEnabled)
655 && num_queues > 0) {
656 _task_queues = new OopTaskQueueSet(num_queues);
657 if (_task_queues == NULL) {
658 warning("task_queues allocation failure.");
659 return;
660 }
661 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues);
662 if (_hash_seed == NULL) {
663 warning("_hash_seed array allocation failure");
664 return;
665 }
666
667 // XXX use a global constant instead of 64!
668 typedef struct OopTaskQueuePadded {
669 OopTaskQueue work_queue;
670 char pad[64 - sizeof(OopTaskQueue)]; // prevent false sharing
671 } OopTaskQueuePadded;
672
673 for (i = 0; i < num_queues; i++) {
674 OopTaskQueuePadded *q_padded = new OopTaskQueuePadded();
675 if (q_padded == NULL) {
676 warning("work_queue allocation failure.");
677 return;
678 }
679 _task_queues->register_queue(i, &q_padded->work_queue);
680 }
681 for (i = 0; i < num_queues; i++) {
682 _task_queues->queue(i)->initialize();
683 _hash_seed[i] = 17; // copied from ParNew
684 }
685 }
686 }
687
688 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
689 _permGen->init_initiating_occupancy(CMSInitiatingPermOccupancyFraction, CMSTriggerPermRatio);
690
691 // Clip CMSBootstrapOccupancy between 0 and 100.
692 _bootstrap_occupancy = ((double)MIN2((uintx)100, MAX2((uintx)0, CMSBootstrapOccupancy)))
693 /(double)100;
694
695 _full_gcs_since_conc_gc = 0;
696
697 // Now tell CMS generations the identity of their collector
698 ConcurrentMarkSweepGeneration::set_collector(this);
699
700 // Create & start a CMS thread for this CMS collector
701 _cmsThread = ConcurrentMarkSweepThread::start(this);
702 assert(cmsThread() != NULL, "CMS Thread should have been created");
703 assert(cmsThread()->collector() == this,
704 "CMS Thread should refer to this gen");
705 assert(CGC_lock != NULL, "Where's the CGC_lock?");
706
707 // Support for parallelizing young gen rescan
708 GenCollectedHeap* gch = GenCollectedHeap::heap();
709 _young_gen = gch->prev_gen(_cmsGen);
710 if (gch->supports_inline_contig_alloc()) {
711 _top_addr = gch->top_addr();
712 _end_addr = gch->end_addr();
713 assert(_young_gen != NULL, "no _young_gen");
714 _eden_chunk_index = 0;
715 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
716 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity);
717 if (_eden_chunk_array == NULL) {
718 _eden_chunk_capacity = 0;
719 warning("GC/CMS: _eden_chunk_array allocation failure");
720 }
721 }
722 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
723
724 // Support for parallelizing survivor space rescan
725 if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) {
726 const size_t max_plab_samples =
727 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
728
729 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads);
730 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples);
731 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads);
732 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
733 || _cursor == NULL) {
734 warning("Failed to allocate survivor plab/chunk array");
735 if (_survivor_plab_array != NULL) {
736 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
737 _survivor_plab_array = NULL;
738 }
739 if (_survivor_chunk_array != NULL) {
740 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
741 _survivor_chunk_array = NULL;
742 }
743 if (_cursor != NULL) {
744 FREE_C_HEAP_ARRAY(size_t, _cursor);
745 _cursor = NULL;
746 }
747 } else {
748 _survivor_chunk_capacity = 2*max_plab_samples;
749 for (uint i = 0; i < ParallelGCThreads; i++) {
750 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples);
751 if (vec == NULL) {
752 warning("Failed to allocate survivor plab array");
753 for (int j = i; j > 0; j--) {
754 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array());
755 }
756 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
757 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
758 _survivor_plab_array = NULL;
759 _survivor_chunk_array = NULL;
760 _survivor_chunk_capacity = 0;
761 break;
762 } else {
763 ChunkArray* cur =
764 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
765 max_plab_samples);
766 assert(cur->end() == 0, "Should be 0");
767 assert(cur->array() == vec, "Should be vec");
768 assert(cur->capacity() == max_plab_samples, "Error");
769 }
770 }
771 }
772 }
773 assert( ( _survivor_plab_array != NULL
774 && _survivor_chunk_array != NULL)
775 || ( _survivor_chunk_capacity == 0
776 && _survivor_chunk_index == 0),
777 "Error");
778
779 // Choose what strong roots should be scanned depending on verification options
780 // and perm gen collection mode.
781 if (!CMSClassUnloadingEnabled) {
782 // If class unloading is disabled we want to include all classes into the root set.
783 add_root_scanning_option(SharedHeap::SO_AllClasses);
784 } else {
785 add_root_scanning_option(SharedHeap::SO_SystemClasses);
786 }
787
788 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
789 _gc_counters = new CollectorCounters("CMS", 1);
790 _completed_initialization = true;
791 _inter_sweep_timer.start(); // start of time
792 #ifdef SPARC
793 // Issue a stern warning, but allow use for experimentation and debugging.
794 if (VM_Version::is_sun4v() && UseMemSetInBOT) {
795 assert(!FLAG_IS_DEFAULT(UseMemSetInBOT), "Error");
796 warning("Experimental flag -XX:+UseMemSetInBOT is known to cause instability"
797 " on sun4v; please understand that you are using at your own risk!");
798 }
799 #endif
800 }
801
802 const char* ConcurrentMarkSweepGeneration::name() const {
803 return "concurrent mark-sweep generation";
804 }
805 void ConcurrentMarkSweepGeneration::update_counters() {
806 if (UsePerfData) {
807 _space_counters->update_all();
808 _gen_counters->update_all();
809 }
810 }
811
812 // this is an optimized version of update_counters(). it takes the
813 // used value as a parameter rather than computing it.
814 //
815 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
816 if (UsePerfData) {
817 _space_counters->update_used(used);
818 _space_counters->update_capacity();
819 _gen_counters->update_all();
820 }
821 }
822
823 void ConcurrentMarkSweepGeneration::print() const {
824 Generation::print();
825 cmsSpace()->print();
826 }
827
828 #ifndef PRODUCT
829 void ConcurrentMarkSweepGeneration::print_statistics() {
830 cmsSpace()->printFLCensus(0);
831 }
832 #endif
833
834 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
835 GenCollectedHeap* gch = GenCollectedHeap::heap();
836 if (PrintGCDetails) {
837 if (Verbose) {
838 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
839 level(), short_name(), s, used(), capacity());
840 } else {
841 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
842 level(), short_name(), s, used() / K, capacity() / K);
843 }
844 }
845 if (Verbose) {
846 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
847 gch->used(), gch->capacity());
848 } else {
849 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
850 gch->used() / K, gch->capacity() / K);
851 }
852 }
853
854 size_t
855 ConcurrentMarkSweepGeneration::contiguous_available() const {
856 // dld proposes an improvement in precision here. If the committed
857 // part of the space ends in a free block we should add that to
858 // uncommitted size in the calculation below. Will make this
859 // change later, staying with the approximation below for the
860 // time being. -- ysr.
861 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
862 }
863
864 size_t
865 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
866 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
867 }
868
869 size_t ConcurrentMarkSweepGeneration::max_available() const {
870 return free() + _virtual_space.uncommitted_size();
871 }
872
873 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(
874 size_t max_promotion_in_bytes,
875 bool younger_handles_promotion_failure) const {
876
877 // This is the most conservative test. Full promotion is
878 // guaranteed if this is used. The multiplicative factor is to
879 // account for the worst case "dilatation".
880 double adjusted_max_promo_bytes = _dilatation_factor * max_promotion_in_bytes;
881 if (adjusted_max_promo_bytes > (double)max_uintx) { // larger than size_t
882 adjusted_max_promo_bytes = (double)max_uintx;
883 }
884 bool result = (max_contiguous_available() >= (size_t)adjusted_max_promo_bytes);
885
886 if (younger_handles_promotion_failure && !result) {
887 // Full promotion is not guaranteed because fragmentation
888 // of the cms generation can prevent the full promotion.
889 result = (max_available() >= (size_t)adjusted_max_promo_bytes);
890
891 if (!result) {
892 // With promotion failure handling the test for the ability
893 // to support the promotion does not have to be guaranteed.
894 // Use an average of the amount promoted.
895 result = max_available() >= (size_t)
896 gc_stats()->avg_promoted()->padded_average();
897 if (PrintGC && Verbose && result) {
898 gclog_or_tty->print_cr(
899 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
900 " max_available: " SIZE_FORMAT
901 " avg_promoted: " SIZE_FORMAT,
902 max_available(), (size_t)
903 gc_stats()->avg_promoted()->padded_average());
904 }
905 } else {
906 if (PrintGC && Verbose) {
907 gclog_or_tty->print_cr(
908 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
909 " max_available: " SIZE_FORMAT
910 " adj_max_promo_bytes: " SIZE_FORMAT,
911 max_available(), (size_t)adjusted_max_promo_bytes);
912 }
913 }
914 } else {
915 if (PrintGC && Verbose) {
916 gclog_or_tty->print_cr(
917 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
918 " contiguous_available: " SIZE_FORMAT
919 " adj_max_promo_bytes: " SIZE_FORMAT,
920 max_contiguous_available(), (size_t)adjusted_max_promo_bytes);
921 }
922 }
923 return result;
924 }
925
926 // At a promotion failure dump information on block layout in heap
927 // (cms old generation).
928 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
929 if (CMSDumpAtPromotionFailure) {
930 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
931 }
932 }
933
934 CompactibleSpace*
935 ConcurrentMarkSweepGeneration::first_compaction_space() const {
936 return _cmsSpace;
937 }
938
939 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
940 // Clear the promotion information. These pointers can be adjusted
941 // along with all the other pointers into the heap but
942 // compaction is expected to be a rare event with
943 // a heap using cms so don't do it without seeing the need.
944 if (ParallelGCThreads > 0) {
945 for (uint i = 0; i < ParallelGCThreads; i++) {
946 _par_gc_thread_states[i]->promo.reset();
947 }
948 }
949 }
950
951 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
952 blk->do_space(_cmsSpace);
953 }
954
955 void ConcurrentMarkSweepGeneration::compute_new_size() {
956 assert_locked_or_safepoint(Heap_lock);
957
958 // If incremental collection failed, we just want to expand
959 // to the limit.
960 if (incremental_collection_failed()) {
961 clear_incremental_collection_failed();
962 grow_to_reserved();
963 return;
964 }
965
966 size_t expand_bytes = 0;
967 double free_percentage = ((double) free()) / capacity();
968 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
969 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
970
971 // compute expansion delta needed for reaching desired free percentage
972 if (free_percentage < desired_free_percentage) {
973 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
974 assert(desired_capacity >= capacity(), "invalid expansion size");
975 expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
976 }
977 if (expand_bytes > 0) {
978 if (PrintGCDetails && Verbose) {
979 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
980 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
981 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
982 gclog_or_tty->print_cr(" Desired free fraction %f",
983 desired_free_percentage);
984 gclog_or_tty->print_cr(" Maximum free fraction %f",
985 maximum_free_percentage);
986 gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000);
987 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
988 desired_capacity/1000);
989 int prev_level = level() - 1;
990 if (prev_level >= 0) {
991 size_t prev_size = 0;
992 GenCollectedHeap* gch = GenCollectedHeap::heap();
993 Generation* prev_gen = gch->_gens[prev_level];
994 prev_size = prev_gen->capacity();
995 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
996 prev_size/1000);
997 }
998 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
999 unsafe_max_alloc_nogc()/1000);
1000 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
1001 contiguous_available()/1000);
1002 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
1003 expand_bytes);
1004 }
1005 // safe if expansion fails
1006 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
1007 if (PrintGCDetails && Verbose) {
1008 gclog_or_tty->print_cr(" Expanded free fraction %f",
1009 ((double) free()) / capacity());
1010 }
1011 }
1012 }
1013
1014 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
1015 return cmsSpace()->freelistLock();
1016 }
1017
1018 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
1019 bool tlab) {
1020 CMSSynchronousYieldRequest yr;
1021 MutexLockerEx x(freelistLock(),
1022 Mutex::_no_safepoint_check_flag);
1023 return have_lock_and_allocate(size, tlab);
1024 }
1025
1026 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
1027 bool tlab) {
1028 assert_lock_strong(freelistLock());
1029 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1030 HeapWord* res = cmsSpace()->allocate(adjustedSize);
1031 // Allocate the object live (grey) if the background collector has
1032 // started marking. This is necessary because the marker may
1033 // have passed this address and consequently this object will
1034 // not otherwise be greyed and would be incorrectly swept up.
1035 // Note that if this object contains references, the writing
1036 // of those references will dirty the card containing this object
1037 // allowing the object to be blackened (and its references scanned)
1038 // either during a preclean phase or at the final checkpoint.
1039 if (res != NULL) {
1040 collector()->direct_allocated(res, adjustedSize);
1041 _direct_allocated_words += adjustedSize;
1042 // allocation counters
1043 NOT_PRODUCT(
1044 _numObjectsAllocated++;
1045 _numWordsAllocated += (int)adjustedSize;
1046 )
1047 }
1048 return res;
1049 }
1050
1051 // In the case of direct allocation by mutators in a generation that
1052 // is being concurrently collected, the object must be allocated
1053 // live (grey) if the background collector has started marking.
1054 // This is necessary because the marker may
1055 // have passed this address and consequently this object will
1056 // not otherwise be greyed and would be incorrectly swept up.
1057 // Note that if this object contains references, the writing
1058 // of those references will dirty the card containing this object
1059 // allowing the object to be blackened (and its references scanned)
1060 // either during a preclean phase or at the final checkpoint.
1061 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1062 assert(_markBitMap.covers(start, size), "Out of bounds");
1063 if (_collectorState >= Marking) {
1064 MutexLockerEx y(_markBitMap.lock(),
1065 Mutex::_no_safepoint_check_flag);
1066 // [see comments preceding SweepClosure::do_blk() below for details]
1067 // 1. need to mark the object as live so it isn't collected
1068 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1069 // 3. need to mark the end of the object so sweeper can skip over it
1070 // if it's uninitialized when the sweeper reaches it.
1071 _markBitMap.mark(start); // object is live
1072 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1073 _markBitMap.mark(start + size - 1);
1074 // mark end of object
1075 }
1076 // check that oop looks uninitialized
1077 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1078 }
1079
1080 void CMSCollector::promoted(bool par, HeapWord* start,
1081 bool is_obj_array, size_t obj_size) {
1082 assert(_markBitMap.covers(start), "Out of bounds");
1083 // See comment in direct_allocated() about when objects should
1084 // be allocated live.
1085 if (_collectorState >= Marking) {
1086 // we already hold the marking bit map lock, taken in
1087 // the prologue
1088 if (par) {
1089 _markBitMap.par_mark(start);
1090 } else {
1091 _markBitMap.mark(start);
1092 }
1093 // We don't need to mark the object as uninitialized (as
1094 // in direct_allocated above) because this is being done with the
1095 // world stopped and the object will be initialized by the
1096 // time the sweeper gets to look at it.
1097 assert(SafepointSynchronize::is_at_safepoint(),
1098 "expect promotion only at safepoints");
1099
1100 if (_collectorState < Sweeping) {
1101 // Mark the appropriate cards in the modUnionTable, so that
1102 // this object gets scanned before the sweep. If this is
1103 // not done, CMS generation references in the object might
1104 // not get marked.
1105 // For the case of arrays, which are otherwise precisely
1106 // marked, we need to dirty the entire array, not just its head.
1107 if (is_obj_array) {
1108 // The [par_]mark_range() method expects mr.end() below to
1109 // be aligned to the granularity of a bit's representation
1110 // in the heap. In the case of the MUT below, that's a
1111 // card size.
1112 MemRegion mr(start,
1113 (HeapWord*)round_to((intptr_t)(start + obj_size),
1114 CardTableModRefBS::card_size /* bytes */));
1115 if (par) {
1116 _modUnionTable.par_mark_range(mr);
1117 } else {
1118 _modUnionTable.mark_range(mr);
1119 }
1120 } else { // not an obj array; we can just mark the head
1121 if (par) {
1122 _modUnionTable.par_mark(start);
1123 } else {
1124 _modUnionTable.mark(start);
1125 }
1126 }
1127 }
1128 }
1129 }
1130
1131 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1132 {
1133 size_t delta = pointer_delta(addr, space->bottom());
1134 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1135 }
1136
1137 void CMSCollector::icms_update_allocation_limits()
1138 {
1139 Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1140 EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1141
1142 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1143 if (CMSTraceIncrementalPacing) {
1144 stats().print();
1145 }
1146
1147 assert(duty_cycle <= 100, "invalid duty cycle");
1148 if (duty_cycle != 0) {
1149 // The duty_cycle is a percentage between 0 and 100; convert to words and
1150 // then compute the offset from the endpoints of the space.
1151 size_t free_words = eden->free() / HeapWordSize;
1152 double free_words_dbl = (double)free_words;
1153 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1154 size_t offset_words = (free_words - duty_cycle_words) / 2;
1155
1156 _icms_start_limit = eden->top() + offset_words;
1157 _icms_stop_limit = eden->end() - offset_words;
1158
1159 // The limits may be adjusted (shifted to the right) by
1160 // CMSIncrementalOffset, to allow the application more mutator time after a
1161 // young gen gc (when all mutators were stopped) and before CMS starts and
1162 // takes away one or more cpus.
1163 if (CMSIncrementalOffset != 0) {
1164 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1165 size_t adjustment = (size_t)adjustment_dbl;
1166 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1167 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1168 _icms_start_limit += adjustment;
1169 _icms_stop_limit = tmp_stop;
1170 }
1171 }
1172 }
1173 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1174 _icms_start_limit = _icms_stop_limit = eden->end();
1175 }
1176
1177 // Install the new start limit.
1178 eden->set_soft_end(_icms_start_limit);
1179
1180 if (CMSTraceIncrementalMode) {
1181 gclog_or_tty->print(" icms alloc limits: "
1182 PTR_FORMAT "," PTR_FORMAT
1183 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1184 _icms_start_limit, _icms_stop_limit,
1185 percent_of_space(eden, _icms_start_limit),
1186 percent_of_space(eden, _icms_stop_limit));
1187 if (Verbose) {
1188 gclog_or_tty->print("eden: ");
1189 eden->print_on(gclog_or_tty);
1190 }
1191 }
1192 }
1193
1194 // Any changes here should try to maintain the invariant
1195 // that if this method is called with _icms_start_limit
1196 // and _icms_stop_limit both NULL, then it should return NULL
1197 // and not notify the icms thread.
1198 HeapWord*
1199 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1200 size_t word_size)
1201 {
1202 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1203 // nop.
1204 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1205 if (top <= _icms_start_limit) {
1206 if (CMSTraceIncrementalMode) {
1207 space->print_on(gclog_or_tty);
1208 gclog_or_tty->stamp();
1209 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1210 ", new limit=" PTR_FORMAT
1211 " (" SIZE_FORMAT "%%)",
1212 top, _icms_stop_limit,
1213 percent_of_space(space, _icms_stop_limit));
1214 }
1215 ConcurrentMarkSweepThread::start_icms();
1216 assert(top < _icms_stop_limit, "Tautology");
1217 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1218 return _icms_stop_limit;
1219 }
1220
1221 // The allocation will cross both the _start and _stop limits, so do the
1222 // stop notification also and return end().
1223 if (CMSTraceIncrementalMode) {
1224 space->print_on(gclog_or_tty);
1225 gclog_or_tty->stamp();
1226 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1227 ", new limit=" PTR_FORMAT
1228 " (" SIZE_FORMAT "%%)",
1229 top, space->end(),
1230 percent_of_space(space, space->end()));
1231 }
1232 ConcurrentMarkSweepThread::stop_icms();
1233 return space->end();
1234 }
1235
1236 if (top <= _icms_stop_limit) {
1237 if (CMSTraceIncrementalMode) {
1238 space->print_on(gclog_or_tty);
1239 gclog_or_tty->stamp();
1240 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1241 ", new limit=" PTR_FORMAT
1242 " (" SIZE_FORMAT "%%)",
1243 top, space->end(),
1244 percent_of_space(space, space->end()));
1245 }
1246 ConcurrentMarkSweepThread::stop_icms();
1247 return space->end();
1248 }
1249
1250 if (CMSTraceIncrementalMode) {
1251 space->print_on(gclog_or_tty);
1252 gclog_or_tty->stamp();
1253 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1254 ", new limit=" PTR_FORMAT,
1255 top, NULL);
1256 }
1257 }
1258
1259 return NULL;
1260 }
1261
1262 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1263 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1264 // allocate, copy and if necessary update promoinfo --
1265 // delegate to underlying space.
1266 assert_lock_strong(freelistLock());
1267
1268 #ifndef PRODUCT
1269 if (Universe::heap()->promotion_should_fail()) {
1270 return NULL;
1271 }
1272 #endif // #ifndef PRODUCT
1273
1274 oop res = _cmsSpace->promote(obj, obj_size);
1275 if (res == NULL) {
1276 // expand and retry
1277 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1278 expand(s*HeapWordSize, MinHeapDeltaBytes,
1279 CMSExpansionCause::_satisfy_promotion);
1280 // Since there's currently no next generation, we don't try to promote
1281 // into a more senior generation.
1282 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1283 "is made to pass on a possibly failing "
1284 "promotion to next generation");
1285 res = _cmsSpace->promote(obj, obj_size);
1286 }
1287 if (res != NULL) {
1288 // See comment in allocate() about when objects should
1289 // be allocated live.
1290 assert(obj->is_oop(), "Will dereference klass pointer below");
1291 collector()->promoted(false, // Not parallel
1292 (HeapWord*)res, obj->is_objArray(), obj_size);
1293 // promotion counters
1294 NOT_PRODUCT(
1295 _numObjectsPromoted++;
1296 _numWordsPromoted +=
1297 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1298 )
1299 }
1300 return res;
1301 }
1302
1303
1304 HeapWord*
1305 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1306 HeapWord* top,
1307 size_t word_sz)
1308 {
1309 return collector()->allocation_limit_reached(space, top, word_sz);
1310 }
1311
1312 // Things to support parallel young-gen collection.
1313 oop
1314 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1315 oop old, markOop m,
1316 size_t word_sz) {
1317 #ifndef PRODUCT
1318 if (Universe::heap()->promotion_should_fail()) {
1319 return NULL;
1320 }
1321 #endif // #ifndef PRODUCT
1322
1323 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1324 PromotionInfo* promoInfo = &ps->promo;
1325 // if we are tracking promotions, then first ensure space for
1326 // promotion (including spooling space for saving header if necessary).
1327 // then allocate and copy, then track promoted info if needed.
1328 // When tracking (see PromotionInfo::track()), the mark word may
1329 // be displaced and in this case restoration of the mark word
1330 // occurs in the (oop_since_save_marks_)iterate phase.
1331 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1332 // Out of space for allocating spooling buffers;
1333 // try expanding and allocating spooling buffers.
1334 if (!expand_and_ensure_spooling_space(promoInfo)) {
1335 return NULL;
1336 }
1337 }
1338 assert(promoInfo->has_spooling_space(), "Control point invariant");
1339 HeapWord* obj_ptr = ps->lab.alloc(word_sz);
1340 if (obj_ptr == NULL) {
1341 obj_ptr = expand_and_par_lab_allocate(ps, word_sz);
1342 if (obj_ptr == NULL) {
1343 return NULL;
1344 }
1345 }
1346 oop obj = oop(obj_ptr);
1347 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1348 // Otherwise, copy the object. Here we must be careful to insert the
1349 // klass pointer last, since this marks the block as an allocated object.
1350 // Except with compressed oops it's the mark word.
1351 HeapWord* old_ptr = (HeapWord*)old;
1352 if (word_sz > (size_t)oopDesc::header_size()) {
1353 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1354 obj_ptr + oopDesc::header_size(),
1355 word_sz - oopDesc::header_size());
1356 }
1357
1358 if (UseCompressedOops) {
1359 // Copy gap missed by (aligned) header size calculation above
1360 obj->set_klass_gap(old->klass_gap());
1361 }
1362
1363 // Restore the mark word copied above.
1364 obj->set_mark(m);
1365
1366 // Now we can track the promoted object, if necessary. We take care
1367 // to delay the transition from uninitialized to full object
1368 // (i.e., insertion of klass pointer) until after, so that it
1369 // atomically becomes a promoted object.
1370 if (promoInfo->tracking()) {
1371 promoInfo->track((PromotedObject*)obj, old->klass());
1372 }
1373
1374 // Finally, install the klass pointer (this should be volatile).
1375 obj->set_klass(old->klass());
1376
1377 assert(old->is_oop(), "Will dereference klass ptr below");
1378 collector()->promoted(true, // parallel
1379 obj_ptr, old->is_objArray(), word_sz);
1380
1381 NOT_PRODUCT(
1382 Atomic::inc(&_numObjectsPromoted);
1383 Atomic::add((jint)CompactibleFreeListSpace::adjustObjectSize(obj->size()),
1384 &_numWordsPromoted);
1385 )
1386
1387 return obj;
1388 }
1389
1390 void
1391 ConcurrentMarkSweepGeneration::
1392 par_promote_alloc_undo(int thread_num,
1393 HeapWord* obj, size_t word_sz) {
1394 // CMS does not support promotion undo.
1395 ShouldNotReachHere();
1396 }
1397
1398 void
1399 ConcurrentMarkSweepGeneration::
1400 par_promote_alloc_done(int thread_num) {
1401 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1402 ps->lab.retire(thread_num);
1403 }
1404
1405 void
1406 ConcurrentMarkSweepGeneration::
1407 par_oop_since_save_marks_iterate_done(int thread_num) {
1408 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1409 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1410 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1411 }
1412
1413 // XXXPERM
1414 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1415 size_t size,
1416 bool tlab)
1417 {
1418 // We allow a STW collection only if a full
1419 // collection was requested.
1420 return full || should_allocate(size, tlab); // FIX ME !!!
1421 // This and promotion failure handling are connected at the
1422 // hip and should be fixed by untying them.
1423 }
1424
1425 bool CMSCollector::shouldConcurrentCollect() {
1426 if (_full_gc_requested) {
1427 if (Verbose && PrintGCDetails) {
1428 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1429 " gc request (or gc_locker)");
1430 }
1431 return true;
1432 }
1433
1434 // For debugging purposes, change the type of collection.
1435 // If the rotation is not on the concurrent collection
1436 // type, don't start a concurrent collection.
1437 NOT_PRODUCT(
1438 if (RotateCMSCollectionTypes &&
1439 (_cmsGen->debug_collection_type() !=
1440 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1441 assert(_cmsGen->debug_collection_type() !=
1442 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1443 "Bad cms collection type");
1444 return false;
1445 }
1446 )
1447
1448 FreelistLocker x(this);
1449 // ------------------------------------------------------------------
1450 // Print out lots of information which affects the initiation of
1451 // a collection.
1452 if (PrintCMSInitiationStatistics && stats().valid()) {
1453 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1454 gclog_or_tty->stamp();
1455 gclog_or_tty->print_cr("");
1456 stats().print_on(gclog_or_tty);
1457 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1458 stats().time_until_cms_gen_full());
1459 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1460 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1461 _cmsGen->contiguous_available());
1462 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1463 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1464 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1465 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1466 gclog_or_tty->print_cr("initiatingPermOccupancy=%3.7f", _permGen->initiating_occupancy());
1467 }
1468 // ------------------------------------------------------------------
1469
1470 // If the estimated time to complete a cms collection (cms_duration())
1471 // is less than the estimated time remaining until the cms generation
1472 // is full, start a collection.
1473 if (!UseCMSInitiatingOccupancyOnly) {
1474 if (stats().valid()) {
1475 if (stats().time_until_cms_start() == 0.0) {
1476 return true;
1477 }
1478 } else {
1479 // We want to conservatively collect somewhat early in order
1480 // to try and "bootstrap" our CMS/promotion statistics;
1481 // this branch will not fire after the first successful CMS
1482 // collection because the stats should then be valid.
1483 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1484 if (Verbose && PrintGCDetails) {
1485 gclog_or_tty->print_cr(
1486 " CMSCollector: collect for bootstrapping statistics:"
1487 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1488 _bootstrap_occupancy);
1489 }
1490 return true;
1491 }
1492 }
1493 }
1494
1495 // Otherwise, we start a collection cycle if either the perm gen or
1496 // old gen want a collection cycle started. Each may use
1497 // an appropriate criterion for making this decision.
1498 // XXX We need to make sure that the gen expansion
1499 // criterion dovetails well with this. XXX NEED TO FIX THIS
1500 if (_cmsGen->should_concurrent_collect()) {
1501 if (Verbose && PrintGCDetails) {
1502 gclog_or_tty->print_cr("CMS old gen initiated");
1503 }
1504 return true;
1505 }
1506
1507 // We start a collection if we believe an incremental collection may fail;
1508 // this is not likely to be productive in practice because it's probably too
1509 // late anyway.
1510 GenCollectedHeap* gch = GenCollectedHeap::heap();
1511 assert(gch->collector_policy()->is_two_generation_policy(),
1512 "You may want to check the correctness of the following");
1513 if (gch->incremental_collection_will_fail()) {
1514 if (PrintGCDetails && Verbose) {
1515 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1516 }
1517 return true;
1518 }
1519
1520 if (CMSClassUnloadingEnabled && _permGen->should_concurrent_collect()) {
1521 bool res = update_should_unload_classes();
1522 if (res) {
1523 if (Verbose && PrintGCDetails) {
1524 gclog_or_tty->print_cr("CMS perm gen initiated");
1525 }
1526 return true;
1527 }
1528 }
1529 return false;
1530 }
1531
1532 // Clear _expansion_cause fields of constituent generations
1533 void CMSCollector::clear_expansion_cause() {
1534 _cmsGen->clear_expansion_cause();
1535 _permGen->clear_expansion_cause();
1536 }
1537
1538 // We should be conservative in starting a collection cycle. To
1539 // start too eagerly runs the risk of collecting too often in the
1540 // extreme. To collect too rarely falls back on full collections,
1541 // which works, even if not optimum in terms of concurrent work.
1542 // As a work around for too eagerly collecting, use the flag
1543 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1544 // giving the user an easily understandable way of controlling the
1545 // collections.
1546 // We want to start a new collection cycle if any of the following
1547 // conditions hold:
1548 // . our current occupancy exceeds the configured initiating occupancy
1549 // for this generation, or
1550 // . we recently needed to expand this space and have not, since that
1551 // expansion, done a collection of this generation, or
1552 // . the underlying space believes that it may be a good idea to initiate
1553 // a concurrent collection (this may be based on criteria such as the
1554 // following: the space uses linear allocation and linear allocation is
1555 // going to fail, or there is believed to be excessive fragmentation in
1556 // the generation, etc... or ...
1557 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1558 // the case of the old generation, not the perm generation; see CR 6543076):
1559 // we may be approaching a point at which allocation requests may fail because
1560 // we will be out of sufficient free space given allocation rate estimates.]
1561 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1562
1563 assert_lock_strong(freelistLock());
1564 if (occupancy() > initiating_occupancy()) {
1565 if (PrintGCDetails && Verbose) {
1566 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1567 short_name(), occupancy(), initiating_occupancy());
1568 }
1569 return true;
1570 }
1571 if (UseCMSInitiatingOccupancyOnly) {
1572 return false;
1573 }
1574 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1575 if (PrintGCDetails && Verbose) {
1576 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1577 short_name());
1578 }
1579 return true;
1580 }
1581 if (_cmsSpace->should_concurrent_collect()) {
1582 if (PrintGCDetails && Verbose) {
1583 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1584 short_name());
1585 }
1586 return true;
1587 }
1588 return false;
1589 }
1590
1591 void ConcurrentMarkSweepGeneration::collect(bool full,
1592 bool clear_all_soft_refs,
1593 size_t size,
1594 bool tlab)
1595 {
1596 collector()->collect(full, clear_all_soft_refs, size, tlab);
1597 }
1598
1599 void CMSCollector::collect(bool full,
1600 bool clear_all_soft_refs,
1601 size_t size,
1602 bool tlab)
1603 {
1604 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1605 // For debugging purposes skip the collection if the state
1606 // is not currently idle
1607 if (TraceCMSState) {
1608 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1609 Thread::current(), full, _collectorState);
1610 }
1611 return;
1612 }
1613
1614 // The following "if" branch is present for defensive reasons.
1615 // In the current uses of this interface, it can be replaced with:
1616 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1617 // But I am not placing that assert here to allow future
1618 // generality in invoking this interface.
1619 if (GC_locker::is_active()) {
1620 // A consistency test for GC_locker
1621 assert(GC_locker::needs_gc(), "Should have been set already");
1622 // Skip this foreground collection, instead
1623 // expanding the heap if necessary.
1624 // Need the free list locks for the call to free() in compute_new_size()
1625 compute_new_size();
1626 return;
1627 }
1628 acquire_control_and_collect(full, clear_all_soft_refs);
1629 _full_gcs_since_conc_gc++;
1630
1631 }
1632
1633 void CMSCollector::request_full_gc(unsigned int full_gc_count) {
1634 GenCollectedHeap* gch = GenCollectedHeap::heap();
1635 unsigned int gc_count = gch->total_full_collections();
1636 if (gc_count == full_gc_count) {
1637 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1638 _full_gc_requested = true;
1639 CGC_lock->notify(); // nudge CMS thread
1640 }
1641 }
1642
1643
1644 // The foreground and background collectors need to coordinate in order
1645 // to make sure that they do not mutually interfere with CMS collections.
1646 // When a background collection is active,
1647 // the foreground collector may need to take over (preempt) and
1648 // synchronously complete an ongoing collection. Depending on the
1649 // frequency of the background collections and the heap usage
1650 // of the application, this preemption can be seldom or frequent.
1651 // There are only certain
1652 // points in the background collection that the "collection-baton"
1653 // can be passed to the foreground collector.
1654 //
1655 // The foreground collector will wait for the baton before
1656 // starting any part of the collection. The foreground collector
1657 // will only wait at one location.
1658 //
1659 // The background collector will yield the baton before starting a new
1660 // phase of the collection (e.g., before initial marking, marking from roots,
1661 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1662 // of the loop which switches the phases. The background collector does some
1663 // of the phases (initial mark, final re-mark) with the world stopped.
1664 // Because of locking involved in stopping the world,
1665 // the foreground collector should not block waiting for the background
1666 // collector when it is doing a stop-the-world phase. The background
1667 // collector will yield the baton at an additional point just before
1668 // it enters a stop-the-world phase. Once the world is stopped, the
1669 // background collector checks the phase of the collection. If the
1670 // phase has not changed, it proceeds with the collection. If the
1671 // phase has changed, it skips that phase of the collection. See
1672 // the comments on the use of the Heap_lock in collect_in_background().
1673 //
1674 // Variable used in baton passing.
1675 // _foregroundGCIsActive - Set to true by the foreground collector when
1676 // it wants the baton. The foreground clears it when it has finished
1677 // the collection.
1678 // _foregroundGCShouldWait - Set to true by the background collector
1679 // when it is running. The foreground collector waits while
1680 // _foregroundGCShouldWait is true.
1681 // CGC_lock - monitor used to protect access to the above variables
1682 // and to notify the foreground and background collectors.
1683 // _collectorState - current state of the CMS collection.
1684 //
1685 // The foreground collector
1686 // acquires the CGC_lock
1687 // sets _foregroundGCIsActive
1688 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1689 // various locks acquired in preparation for the collection
1690 // are released so as not to block the background collector
1691 // that is in the midst of a collection
1692 // proceeds with the collection
1693 // clears _foregroundGCIsActive
1694 // returns
1695 //
1696 // The background collector in a loop iterating on the phases of the
1697 // collection
1698 // acquires the CGC_lock
1699 // sets _foregroundGCShouldWait
1700 // if _foregroundGCIsActive is set
1701 // clears _foregroundGCShouldWait, notifies _CGC_lock
1702 // waits on _CGC_lock for _foregroundGCIsActive to become false
1703 // and exits the loop.
1704 // otherwise
1705 // proceed with that phase of the collection
1706 // if the phase is a stop-the-world phase,
1707 // yield the baton once more just before enqueueing
1708 // the stop-world CMS operation (executed by the VM thread).
1709 // returns after all phases of the collection are done
1710 //
1711
1712 void CMSCollector::acquire_control_and_collect(bool full,
1713 bool clear_all_soft_refs) {
1714 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1715 assert(!Thread::current()->is_ConcurrentGC_thread(),
1716 "shouldn't try to acquire control from self!");
1717
1718 // Start the protocol for acquiring control of the
1719 // collection from the background collector (aka CMS thread).
1720 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1721 "VM thread should have CMS token");
1722 // Remember the possibly interrupted state of an ongoing
1723 // concurrent collection
1724 CollectorState first_state = _collectorState;
1725
1726 // Signal to a possibly ongoing concurrent collection that
1727 // we want to do a foreground collection.
1728 _foregroundGCIsActive = true;
1729
1730 // Disable incremental mode during a foreground collection.
1731 ICMSDisabler icms_disabler;
1732
1733 // release locks and wait for a notify from the background collector
1734 // releasing the locks in only necessary for phases which
1735 // do yields to improve the granularity of the collection.
1736 assert_lock_strong(bitMapLock());
1737 // We need to lock the Free list lock for the space that we are
1738 // currently collecting.
1739 assert(haveFreelistLocks(), "Must be holding free list locks");
1740 bitMapLock()->unlock();
1741 releaseFreelistLocks();
1742 {
1743 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1744 if (_foregroundGCShouldWait) {
1745 // We are going to be waiting for action for the CMS thread;
1746 // it had better not be gone (for instance at shutdown)!
1747 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1748 "CMS thread must be running");
1749 // Wait here until the background collector gives us the go-ahead
1750 ConcurrentMarkSweepThread::clear_CMS_flag(
1751 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1752 // Get a possibly blocked CMS thread going:
1753 // Note that we set _foregroundGCIsActive true above,
1754 // without protection of the CGC_lock.
1755 CGC_lock->notify();
1756 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1757 "Possible deadlock");
1758 while (_foregroundGCShouldWait) {
1759 // wait for notification
1760 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1761 // Possibility of delay/starvation here, since CMS token does
1762 // not know to give priority to VM thread? Actually, i think
1763 // there wouldn't be any delay/starvation, but the proof of
1764 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1765 }
1766 ConcurrentMarkSweepThread::set_CMS_flag(
1767 ConcurrentMarkSweepThread::CMS_vm_has_token);
1768 }
1769 }
1770 // The CMS_token is already held. Get back the other locks.
1771 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1772 "VM thread should have CMS token");
1773 getFreelistLocks();
1774 bitMapLock()->lock_without_safepoint_check();
1775 if (TraceCMSState) {
1776 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1777 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1778 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1779 }
1780
1781 // Check if we need to do a compaction, or if not, whether
1782 // we need to start the mark-sweep from scratch.
1783 bool should_compact = false;
1784 bool should_start_over = false;
1785 decide_foreground_collection_type(clear_all_soft_refs,
1786 &should_compact, &should_start_over);
1787
1788 NOT_PRODUCT(
1789 if (RotateCMSCollectionTypes) {
1790 if (_cmsGen->debug_collection_type() ==
1791 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1792 should_compact = true;
1793 } else if (_cmsGen->debug_collection_type() ==
1794 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1795 should_compact = false;
1796 }
1797 }
1798 )
1799
1800 if (PrintGCDetails && first_state > Idling) {
1801 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1802 if (GCCause::is_user_requested_gc(cause) ||
1803 GCCause::is_serviceability_requested_gc(cause)) {
1804 gclog_or_tty->print(" (concurrent mode interrupted)");
1805 } else {
1806 gclog_or_tty->print(" (concurrent mode failure)");
1807 }
1808 }
1809
1810 if (should_compact) {
1811 // If the collection is being acquired from the background
1812 // collector, there may be references on the discovered
1813 // references lists that have NULL referents (being those
1814 // that were concurrently cleared by a mutator) or
1815 // that are no longer active (having been enqueued concurrently
1816 // by the mutator).
1817 // Scrub the list of those references because Mark-Sweep-Compact
1818 // code assumes referents are not NULL and that all discovered
1819 // Reference objects are active.
1820 ref_processor()->clean_up_discovered_references();
1821
1822 do_compaction_work(clear_all_soft_refs);
1823
1824 // Has the GC time limit been exceeded?
1825 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1826 size_t max_eden_size = young_gen->max_capacity() -
1827 young_gen->to()->capacity() -
1828 young_gen->from()->capacity();
1829 GenCollectedHeap* gch = GenCollectedHeap::heap();
1830 GCCause::Cause gc_cause = gch->gc_cause();
1831 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1832 young_gen->eden()->used(),
1833 _cmsGen->max_capacity(),
1834 max_eden_size,
1835 full,
1836 gc_cause,
1837 gch->collector_policy());
1838 } else {
1839 do_mark_sweep_work(clear_all_soft_refs, first_state,
1840 should_start_over);
1841 }
1842 // Reset the expansion cause, now that we just completed
1843 // a collection cycle.
1844 clear_expansion_cause();
1845 _foregroundGCIsActive = false;
1846 return;
1847 }
1848
1849 // Resize the perm generation and the tenured generation
1850 // after obtaining the free list locks for the
1851 // two generations.
1852 void CMSCollector::compute_new_size() {
1853 assert_locked_or_safepoint(Heap_lock);
1854 FreelistLocker z(this);
1855 _permGen->compute_new_size();
1856 _cmsGen->compute_new_size();
1857 }
1858
1859 // A work method used by foreground collection to determine
1860 // what type of collection (compacting or not, continuing or fresh)
1861 // it should do.
1862 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1863 // and CMSCompactWhenClearAllSoftRefs the default in the future
1864 // and do away with the flags after a suitable period.
1865 void CMSCollector::decide_foreground_collection_type(
1866 bool clear_all_soft_refs, bool* should_compact,
1867 bool* should_start_over) {
1868 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1869 // flag is set, and we have either requested a System.gc() or
1870 // the number of full gc's since the last concurrent cycle
1871 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1872 // or if an incremental collection has failed
1873 GenCollectedHeap* gch = GenCollectedHeap::heap();
1874 assert(gch->collector_policy()->is_two_generation_policy(),
1875 "You may want to check the correctness of the following");
1876 // Inform cms gen if this was due to partial collection failing.
1877 // The CMS gen may use this fact to determine its expansion policy.
1878 if (gch->incremental_collection_will_fail()) {
1879 assert(!_cmsGen->incremental_collection_failed(),
1880 "Should have been noticed, reacted to and cleared");
1881 _cmsGen->set_incremental_collection_failed();
1882 }
1883 *should_compact =
1884 UseCMSCompactAtFullCollection &&
1885 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1886 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1887 gch->incremental_collection_will_fail());
1888 *should_start_over = false;
1889 if (clear_all_soft_refs && !*should_compact) {
1890 // We are about to do a last ditch collection attempt
1891 // so it would normally make sense to do a compaction
1892 // to reclaim as much space as possible.
1893 if (CMSCompactWhenClearAllSoftRefs) {
1894 // Default: The rationale is that in this case either
1895 // we are past the final marking phase, in which case
1896 // we'd have to start over, or so little has been done
1897 // that there's little point in saving that work. Compaction
1898 // appears to be the sensible choice in either case.
1899 *should_compact = true;
1900 } else {
1901 // We have been asked to clear all soft refs, but not to
1902 // compact. Make sure that we aren't past the final checkpoint
1903 // phase, for that is where we process soft refs. If we are already
1904 // past that phase, we'll need to redo the refs discovery phase and
1905 // if necessary clear soft refs that weren't previously
1906 // cleared. We do so by remembering the phase in which
1907 // we came in, and if we are past the refs processing
1908 // phase, we'll choose to just redo the mark-sweep
1909 // collection from scratch.
1910 if (_collectorState > FinalMarking) {
1911 // We are past the refs processing phase;
1912 // start over and do a fresh synchronous CMS cycle
1913 _collectorState = Resetting; // skip to reset to start new cycle
1914 reset(false /* == !asynch */);
1915 *should_start_over = true;
1916 } // else we can continue a possibly ongoing current cycle
1917 }
1918 }
1919 }
1920
1921 // A work method used by the foreground collector to do
1922 // a mark-sweep-compact.
1923 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1924 GenCollectedHeap* gch = GenCollectedHeap::heap();
1925 TraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, gclog_or_tty);
1926 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
1927 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
1928 "collections passed to foreground collector", _full_gcs_since_conc_gc);
1929 }
1930
1931 // Sample collection interval time and reset for collection pause.
1932 if (UseAdaptiveSizePolicy) {
1933 size_policy()->msc_collection_begin();
1934 }
1935
1936 // Temporarily widen the span of the weak reference processing to
1937 // the entire heap.
1938 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1939 ReferenceProcessorSpanMutator x(ref_processor(), new_span);
1940
1941 // Temporarily, clear the "is_alive_non_header" field of the
1942 // reference processor.
1943 ReferenceProcessorIsAliveMutator y(ref_processor(), NULL);
1944
1945 // Temporarily make reference _processing_ single threaded (non-MT).
1946 ReferenceProcessorMTProcMutator z(ref_processor(), false);
1947
1948 // Temporarily make refs discovery atomic
1949 ReferenceProcessorAtomicMutator w(ref_processor(), true);
1950
1951 ref_processor()->set_enqueuing_is_done(false);
1952 ref_processor()->enable_discovery();
1953 ref_processor()->setup_policy(clear_all_soft_refs);
1954 // If an asynchronous collection finishes, the _modUnionTable is
1955 // all clear. If we are assuming the collection from an asynchronous
1956 // collection, clear the _modUnionTable.
1957 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1958 "_modUnionTable should be clear if the baton was not passed");
1959 _modUnionTable.clear_all();
1960
1961 // We must adjust the allocation statistics being maintained
1962 // in the free list space. We do so by reading and clearing
1963 // the sweep timer and updating the block flux rate estimates below.
1964 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1965 if (_inter_sweep_timer.is_active()) {
1966 _inter_sweep_timer.stop();
1967 // Note that we do not use this sample to update the _inter_sweep_estimate.
1968 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1969 _inter_sweep_estimate.padded_average(),
1970 _intra_sweep_estimate.padded_average());
1971 }
1972
1973 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1974 ref_processor(), clear_all_soft_refs);
1975 #ifdef ASSERT
1976 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1977 size_t free_size = cms_space->free();
1978 assert(free_size ==
1979 pointer_delta(cms_space->end(), cms_space->compaction_top())
1980 * HeapWordSize,
1981 "All the free space should be compacted into one chunk at top");
1982 assert(cms_space->dictionary()->totalChunkSize(
1983 debug_only(cms_space->freelistLock())) == 0 ||
1984 cms_space->totalSizeInIndexedFreeLists() == 0,
1985 "All the free space should be in a single chunk");
1986 size_t num = cms_space->totalCount();
1987 assert((free_size == 0 && num == 0) ||
1988 (free_size > 0 && (num == 1 || num == 2)),
1989 "There should be at most 2 free chunks after compaction");
1990 #endif // ASSERT
1991 _collectorState = Resetting;
1992 assert(_restart_addr == NULL,
1993 "Should have been NULL'd before baton was passed");
1994 reset(false /* == !asynch */);
1995 _cmsGen->reset_after_compaction();
1996 _concurrent_cycles_since_last_unload = 0;
1997
1998 if (verifying() && !should_unload_classes()) {
1999 perm_gen_verify_bit_map()->clear_all();
2000 }
2001
2002 // Clear any data recorded in the PLAB chunk arrays.
2003 if (_survivor_plab_array != NULL) {
2004 reset_survivor_plab_arrays();
2005 }
2006
2007 // Adjust the per-size allocation stats for the next epoch.
2008 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2009 // Restart the "inter sweep timer" for the next epoch.
2010 _inter_sweep_timer.reset();
2011 _inter_sweep_timer.start();
2012
2013 // Sample collection pause time and reset for collection interval.
2014 if (UseAdaptiveSizePolicy) {
2015 size_policy()->msc_collection_end(gch->gc_cause());
2016 }
2017
2018 // For a mark-sweep-compact, compute_new_size() will be called
2019 // in the heap's do_collection() method.
2020 }
2021
2022 // A work method used by the foreground collector to do
2023 // a mark-sweep, after taking over from a possibly on-going
2024 // concurrent mark-sweep collection.
2025 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2026 CollectorState first_state, bool should_start_over) {
2027 if (PrintGC && Verbose) {
2028 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2029 "collector with count %d",
2030 _full_gcs_since_conc_gc);
2031 }
2032 switch (_collectorState) {
2033 case Idling:
2034 if (first_state == Idling || should_start_over) {
2035 // The background GC was not active, or should
2036 // restarted from scratch; start the cycle.
2037 _collectorState = InitialMarking;
2038 }
2039 // If first_state was not Idling, then a background GC
2040 // was in progress and has now finished. No need to do it
2041 // again. Leave the state as Idling.
2042 break;
2043 case Precleaning:
2044 // In the foreground case don't do the precleaning since
2045 // it is not done concurrently and there is extra work
2046 // required.
2047 _collectorState = FinalMarking;
2048 }
2049 if (PrintGCDetails &&
2050 (_collectorState > Idling ||
2051 !GCCause::is_user_requested_gc(GenCollectedHeap::heap()->gc_cause()))) {
2052 gclog_or_tty->print(" (concurrent mode failure)");
2053 }
2054 collect_in_foreground(clear_all_soft_refs);
2055
2056 // For a mark-sweep, compute_new_size() will be called
2057 // in the heap's do_collection() method.
2058 }
2059
2060
2061 void CMSCollector::getFreelistLocks() const {
2062 // Get locks for all free lists in all generations that this
2063 // collector is responsible for
2064 _cmsGen->freelistLock()->lock_without_safepoint_check();
2065 _permGen->freelistLock()->lock_without_safepoint_check();
2066 }
2067
2068 void CMSCollector::releaseFreelistLocks() const {
2069 // Release locks for all free lists in all generations that this
2070 // collector is responsible for
2071 _cmsGen->freelistLock()->unlock();
2072 _permGen->freelistLock()->unlock();
2073 }
2074
2075 bool CMSCollector::haveFreelistLocks() const {
2076 // Check locks for all free lists in all generations that this
2077 // collector is responsible for
2078 assert_lock_strong(_cmsGen->freelistLock());
2079 assert_lock_strong(_permGen->freelistLock());
2080 PRODUCT_ONLY(ShouldNotReachHere());
2081 return true;
2082 }
2083
2084 // A utility class that is used by the CMS collector to
2085 // temporarily "release" the foreground collector from its
2086 // usual obligation to wait for the background collector to
2087 // complete an ongoing phase before proceeding.
2088 class ReleaseForegroundGC: public StackObj {
2089 private:
2090 CMSCollector* _c;
2091 public:
2092 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2093 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2094 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2095 // allow a potentially blocked foreground collector to proceed
2096 _c->_foregroundGCShouldWait = false;
2097 if (_c->_foregroundGCIsActive) {
2098 CGC_lock->notify();
2099 }
2100 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2101 "Possible deadlock");
2102 }
2103
2104 ~ReleaseForegroundGC() {
2105 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2106 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2107 _c->_foregroundGCShouldWait = true;
2108 }
2109 };
2110
2111 // There are separate collect_in_background and collect_in_foreground because of
2112 // the different locking requirements of the background collector and the
2113 // foreground collector. There was originally an attempt to share
2114 // one "collect" method between the background collector and the foreground
2115 // collector but the if-then-else required made it cleaner to have
2116 // separate methods.
2117 void CMSCollector::collect_in_background(bool clear_all_soft_refs) {
2118 assert(Thread::current()->is_ConcurrentGC_thread(),
2119 "A CMS asynchronous collection is only allowed on a CMS thread.");
2120
2121 GenCollectedHeap* gch = GenCollectedHeap::heap();
2122 {
2123 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2124 MutexLockerEx hl(Heap_lock, safepoint_check);
2125 FreelistLocker fll(this);
2126 MutexLockerEx x(CGC_lock, safepoint_check);
2127 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2128 // The foreground collector is active or we're
2129 // not using asynchronous collections. Skip this
2130 // background collection.
2131 assert(!_foregroundGCShouldWait, "Should be clear");
2132 return;
2133 } else {
2134 assert(_collectorState == Idling, "Should be idling before start.");
2135 _collectorState = InitialMarking;
2136 // Reset the expansion cause, now that we are about to begin
2137 // a new cycle.
2138 clear_expansion_cause();
2139 }
2140 // Decide if we want to enable class unloading as part of the
2141 // ensuing concurrent GC cycle.
2142 update_should_unload_classes();
2143 _full_gc_requested = false; // acks all outstanding full gc requests
2144 // Signal that we are about to start a collection
2145 gch->increment_total_full_collections(); // ... starting a collection cycle
2146 _collection_count_start = gch->total_full_collections();
2147 }
2148
2149 // Used for PrintGC
2150 size_t prev_used;
2151 if (PrintGC && Verbose) {
2152 prev_used = _cmsGen->used(); // XXXPERM
2153 }
2154
2155 // The change of the collection state is normally done at this level;
2156 // the exceptions are phases that are executed while the world is
2157 // stopped. For those phases the change of state is done while the
2158 // world is stopped. For baton passing purposes this allows the
2159 // background collector to finish the phase and change state atomically.
2160 // The foreground collector cannot wait on a phase that is done
2161 // while the world is stopped because the foreground collector already
2162 // has the world stopped and would deadlock.
2163 while (_collectorState != Idling) {
2164 if (TraceCMSState) {
2165 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2166 Thread::current(), _collectorState);
2167 }
2168 // The foreground collector
2169 // holds the Heap_lock throughout its collection.
2170 // holds the CMS token (but not the lock)
2171 // except while it is waiting for the background collector to yield.
2172 //
2173 // The foreground collector should be blocked (not for long)
2174 // if the background collector is about to start a phase
2175 // executed with world stopped. If the background
2176 // collector has already started such a phase, the
2177 // foreground collector is blocked waiting for the
2178 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2179 // are executed in the VM thread.
2180 //
2181 // The locking order is
2182 // PendingListLock (PLL) -- if applicable (FinalMarking)
2183 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2184 // CMS token (claimed in
2185 // stop_world_and_do() -->
2186 // safepoint_synchronize() -->
2187 // CMSThread::synchronize())
2188
2189 {
2190 // Check if the FG collector wants us to yield.
2191 CMSTokenSync x(true); // is cms thread
2192 if (waitForForegroundGC()) {
2193 // We yielded to a foreground GC, nothing more to be
2194 // done this round.
2195 assert(_foregroundGCShouldWait == false, "We set it to false in "
2196 "waitForForegroundGC()");
2197 if (TraceCMSState) {
2198 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2199 " exiting collection CMS state %d",
2200 Thread::current(), _collectorState);
2201 }
2202 return;
2203 } else {
2204 // The background collector can run but check to see if the
2205 // foreground collector has done a collection while the
2206 // background collector was waiting to get the CGC_lock
2207 // above. If yes, break so that _foregroundGCShouldWait
2208 // is cleared before returning.
2209 if (_collectorState == Idling) {
2210 break;
2211 }
2212 }
2213 }
2214
2215 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2216 "should be waiting");
2217
2218 switch (_collectorState) {
2219 case InitialMarking:
2220 {
2221 ReleaseForegroundGC x(this);
2222 stats().record_cms_begin();
2223
2224 VM_CMS_Initial_Mark initial_mark_op(this);
2225 VMThread::execute(&initial_mark_op);
2226 }
2227 // The collector state may be any legal state at this point
2228 // since the background collector may have yielded to the
2229 // foreground collector.
2230 break;
2231 case Marking:
2232 // initial marking in checkpointRootsInitialWork has been completed
2233 if (markFromRoots(true)) { // we were successful
2234 assert(_collectorState == Precleaning, "Collector state should "
2235 "have changed");
2236 } else {
2237 assert(_foregroundGCIsActive, "Internal state inconsistency");
2238 }
2239 break;
2240 case Precleaning:
2241 if (UseAdaptiveSizePolicy) {
2242 size_policy()->concurrent_precleaning_begin();
2243 }
2244 // marking from roots in markFromRoots has been completed
2245 preclean();
2246 if (UseAdaptiveSizePolicy) {
2247 size_policy()->concurrent_precleaning_end();
2248 }
2249 assert(_collectorState == AbortablePreclean ||
2250 _collectorState == FinalMarking,
2251 "Collector state should have changed");
2252 break;
2253 case AbortablePreclean:
2254 if (UseAdaptiveSizePolicy) {
2255 size_policy()->concurrent_phases_resume();
2256 }
2257 abortable_preclean();
2258 if (UseAdaptiveSizePolicy) {
2259 size_policy()->concurrent_precleaning_end();
2260 }
2261 assert(_collectorState == FinalMarking, "Collector state should "
2262 "have changed");
2263 break;
2264 case FinalMarking:
2265 {
2266 ReleaseForegroundGC x(this);
2267
2268 VM_CMS_Final_Remark final_remark_op(this);
2269 VMThread::execute(&final_remark_op);
2270 }
2271 assert(_foregroundGCShouldWait, "block post-condition");
2272 break;
2273 case Sweeping:
2274 if (UseAdaptiveSizePolicy) {
2275 size_policy()->concurrent_sweeping_begin();
2276 }
2277 // final marking in checkpointRootsFinal has been completed
2278 sweep(true);
2279 assert(_collectorState == Resizing, "Collector state change "
2280 "to Resizing must be done under the free_list_lock");
2281 _full_gcs_since_conc_gc = 0;
2282
2283 // Stop the timers for adaptive size policy for the concurrent phases
2284 if (UseAdaptiveSizePolicy) {
2285 size_policy()->concurrent_sweeping_end();
2286 size_policy()->concurrent_phases_end(gch->gc_cause(),
2287 gch->prev_gen(_cmsGen)->capacity(),
2288 _cmsGen->free());
2289 }
2290
2291 case Resizing: {
2292 // Sweeping has been completed...
2293 // At this point the background collection has completed.
2294 // Don't move the call to compute_new_size() down
2295 // into code that might be executed if the background
2296 // collection was preempted.
2297 {
2298 ReleaseForegroundGC x(this); // unblock FG collection
2299 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2300 CMSTokenSync z(true); // not strictly needed.
2301 if (_collectorState == Resizing) {
2302 compute_new_size();
2303 _collectorState = Resetting;
2304 } else {
2305 assert(_collectorState == Idling, "The state should only change"
2306 " because the foreground collector has finished the collection");
2307 }
2308 }
2309 break;
2310 }
2311 case Resetting:
2312 // CMS heap resizing has been completed
2313 reset(true);
2314 assert(_collectorState == Idling, "Collector state should "
2315 "have changed");
2316 stats().record_cms_end();
2317 // Don't move the concurrent_phases_end() and compute_new_size()
2318 // calls to here because a preempted background collection
2319 // has it's state set to "Resetting".
2320 break;
2321 case Idling:
2322 default:
2323 ShouldNotReachHere();
2324 break;
2325 }
2326 if (TraceCMSState) {
2327 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2328 Thread::current(), _collectorState);
2329 }
2330 assert(_foregroundGCShouldWait, "block post-condition");
2331 }
2332
2333 // Should this be in gc_epilogue?
2334 collector_policy()->counters()->update_counters();
2335
2336 {
2337 // Clear _foregroundGCShouldWait and, in the event that the
2338 // foreground collector is waiting, notify it, before
2339 // returning.
2340 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2341 _foregroundGCShouldWait = false;
2342 if (_foregroundGCIsActive) {
2343 CGC_lock->notify();
2344 }
2345 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2346 "Possible deadlock");
2347 }
2348 if (TraceCMSState) {
2349 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2350 " exiting collection CMS state %d",
2351 Thread::current(), _collectorState);
2352 }
2353 if (PrintGC && Verbose) {
2354 _cmsGen->print_heap_change(prev_used);
2355 }
2356 }
2357
2358 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs) {
2359 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2360 "Foreground collector should be waiting, not executing");
2361 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2362 "may only be done by the VM Thread with the world stopped");
2363 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2364 "VM thread should have CMS token");
2365
2366 NOT_PRODUCT(TraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2367 true, gclog_or_tty);)
2368 if (UseAdaptiveSizePolicy) {
2369 size_policy()->ms_collection_begin();
2370 }
2371 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2372
2373 HandleMark hm; // Discard invalid handles created during verification
2374
2375 if (VerifyBeforeGC &&
2376 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2377 Universe::verify(true);
2378 }
2379
2380 // Snapshot the soft reference policy to be used in this collection cycle.
2381 ref_processor()->setup_policy(clear_all_soft_refs);
2382
2383 bool init_mark_was_synchronous = false; // until proven otherwise
2384 while (_collectorState != Idling) {
2385 if (TraceCMSState) {
2386 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2387 Thread::current(), _collectorState);
2388 }
2389 switch (_collectorState) {
2390 case InitialMarking:
2391 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2392 checkpointRootsInitial(false);
2393 assert(_collectorState == Marking, "Collector state should have changed"
2394 " within checkpointRootsInitial()");
2395 break;
2396 case Marking:
2397 // initial marking in checkpointRootsInitialWork has been completed
2398 if (VerifyDuringGC &&
2399 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2400 gclog_or_tty->print("Verify before initial mark: ");
2401 Universe::verify(true);
2402 }
2403 {
2404 bool res = markFromRoots(false);
2405 assert(res && _collectorState == FinalMarking, "Collector state should "
2406 "have changed");
2407 break;
2408 }
2409 case FinalMarking:
2410 if (VerifyDuringGC &&
2411 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2412 gclog_or_tty->print("Verify before re-mark: ");
2413 Universe::verify(true);
2414 }
2415 checkpointRootsFinal(false, clear_all_soft_refs,
2416 init_mark_was_synchronous);
2417 assert(_collectorState == Sweeping, "Collector state should not "
2418 "have changed within checkpointRootsFinal()");
2419 break;
2420 case Sweeping:
2421 // final marking in checkpointRootsFinal has been completed
2422 if (VerifyDuringGC &&
2423 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2424 gclog_or_tty->print("Verify before sweep: ");
2425 Universe::verify(true);
2426 }
2427 sweep(false);
2428 assert(_collectorState == Resizing, "Incorrect state");
2429 break;
2430 case Resizing: {
2431 // Sweeping has been completed; the actual resize in this case
2432 // is done separately; nothing to be done in this state.
2433 _collectorState = Resetting;
2434 break;
2435 }
2436 case Resetting:
2437 // The heap has been resized.
2438 if (VerifyDuringGC &&
2439 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2440 gclog_or_tty->print("Verify before reset: ");
2441 Universe::verify(true);
2442 }
2443 reset(false);
2444 assert(_collectorState == Idling, "Collector state should "
2445 "have changed");
2446 break;
2447 case Precleaning:
2448 case AbortablePreclean:
2449 // Elide the preclean phase
2450 _collectorState = FinalMarking;
2451 break;
2452 default:
2453 ShouldNotReachHere();
2454 }
2455 if (TraceCMSState) {
2456 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2457 Thread::current(), _collectorState);
2458 }
2459 }
2460
2461 if (UseAdaptiveSizePolicy) {
2462 GenCollectedHeap* gch = GenCollectedHeap::heap();
2463 size_policy()->ms_collection_end(gch->gc_cause());
2464 }
2465
2466 if (VerifyAfterGC &&
2467 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2468 Universe::verify(true);
2469 }
2470 if (TraceCMSState) {
2471 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2472 " exiting collection CMS state %d",
2473 Thread::current(), _collectorState);
2474 }
2475 }
2476
2477 bool CMSCollector::waitForForegroundGC() {
2478 bool res = false;
2479 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2480 "CMS thread should have CMS token");
2481 // Block the foreground collector until the
2482 // background collectors decides whether to
2483 // yield.
2484 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2485 _foregroundGCShouldWait = true;
2486 if (_foregroundGCIsActive) {
2487 // The background collector yields to the
2488 // foreground collector and returns a value
2489 // indicating that it has yielded. The foreground
2490 // collector can proceed.
2491 res = true;
2492 _foregroundGCShouldWait = false;
2493 ConcurrentMarkSweepThread::clear_CMS_flag(
2494 ConcurrentMarkSweepThread::CMS_cms_has_token);
2495 ConcurrentMarkSweepThread::set_CMS_flag(
2496 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2497 // Get a possibly blocked foreground thread going
2498 CGC_lock->notify();
2499 if (TraceCMSState) {
2500 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2501 Thread::current(), _collectorState);
2502 }
2503 while (_foregroundGCIsActive) {
2504 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2505 }
2506 ConcurrentMarkSweepThread::set_CMS_flag(
2507 ConcurrentMarkSweepThread::CMS_cms_has_token);
2508 ConcurrentMarkSweepThread::clear_CMS_flag(
2509 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2510 }
2511 if (TraceCMSState) {
2512 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2513 Thread::current(), _collectorState);
2514 }
2515 return res;
2516 }
2517
2518 // Because of the need to lock the free lists and other structures in
2519 // the collector, common to all the generations that the collector is
2520 // collecting, we need the gc_prologues of individual CMS generations
2521 // delegate to their collector. It may have been simpler had the
2522 // current infrastructure allowed one to call a prologue on a
2523 // collector. In the absence of that we have the generation's
2524 // prologue delegate to the collector, which delegates back
2525 // some "local" work to a worker method in the individual generations
2526 // that it's responsible for collecting, while itself doing any
2527 // work common to all generations it's responsible for. A similar
2528 // comment applies to the gc_epilogue()'s.
2529 // The role of the varaible _between_prologue_and_epilogue is to
2530 // enforce the invocation protocol.
2531 void CMSCollector::gc_prologue(bool full) {
2532 // Call gc_prologue_work() for each CMSGen and PermGen that
2533 // we are responsible for.
2534
2535 // The following locking discipline assumes that we are only called
2536 // when the world is stopped.
2537 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2538
2539 // The CMSCollector prologue must call the gc_prologues for the
2540 // "generations" (including PermGen if any) that it's responsible
2541 // for.
2542
2543 assert( Thread::current()->is_VM_thread()
2544 || ( CMSScavengeBeforeRemark
2545 && Thread::current()->is_ConcurrentGC_thread()),
2546 "Incorrect thread type for prologue execution");
2547
2548 if (_between_prologue_and_epilogue) {
2549 // We have already been invoked; this is a gc_prologue delegation
2550 // from yet another CMS generation that we are responsible for, just
2551 // ignore it since all relevant work has already been done.
2552 return;
2553 }
2554
2555 // set a bit saying prologue has been called; cleared in epilogue
2556 _between_prologue_and_epilogue = true;
2557 // Claim locks for common data structures, then call gc_prologue_work()
2558 // for each CMSGen and PermGen that we are responsible for.
2559
2560 getFreelistLocks(); // gets free list locks on constituent spaces
2561 bitMapLock()->lock_without_safepoint_check();
2562
2563 // Should call gc_prologue_work() for all cms gens we are responsible for
2564 bool registerClosure = _collectorState >= Marking
2565 && _collectorState < Sweeping;
2566 ModUnionClosure* muc = ParallelGCThreads > 0 ? &_modUnionClosurePar
2567 : &_modUnionClosure;
2568 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2569 _permGen->gc_prologue_work(full, registerClosure, muc);
2570
2571 if (!full) {
2572 stats().record_gc0_begin();
2573 }
2574 }
2575
2576 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2577 // Delegate to CMScollector which knows how to coordinate between
2578 // this and any other CMS generations that it is responsible for
2579 // collecting.
2580 collector()->gc_prologue(full);
2581 }
2582
2583 // This is a "private" interface for use by this generation's CMSCollector.
2584 // Not to be called directly by any other entity (for instance,
2585 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2586 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2587 bool registerClosure, ModUnionClosure* modUnionClosure) {
2588 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2589 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2590 "Should be NULL");
2591 if (registerClosure) {
2592 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2593 }
2594 cmsSpace()->gc_prologue();
2595 // Clear stat counters
2596 NOT_PRODUCT(
2597 assert(_numObjectsPromoted == 0, "check");
2598 assert(_numWordsPromoted == 0, "check");
2599 if (Verbose && PrintGC) {
2600 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2601 SIZE_FORMAT" bytes concurrently",
2602 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2603 }
2604 _numObjectsAllocated = 0;
2605 _numWordsAllocated = 0;
2606 )
2607 }
2608
2609 void CMSCollector::gc_epilogue(bool full) {
2610 // The following locking discipline assumes that we are only called
2611 // when the world is stopped.
2612 assert(SafepointSynchronize::is_at_safepoint(),
2613 "world is stopped assumption");
2614
2615 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2616 // if linear allocation blocks need to be appropriately marked to allow the
2617 // the blocks to be parsable. We also check here whether we need to nudge the
2618 // CMS collector thread to start a new cycle (if it's not already active).
2619 assert( Thread::current()->is_VM_thread()
2620 || ( CMSScavengeBeforeRemark
2621 && Thread::current()->is_ConcurrentGC_thread()),
2622 "Incorrect thread type for epilogue execution");
2623
2624 if (!_between_prologue_and_epilogue) {
2625 // We have already been invoked; this is a gc_epilogue delegation
2626 // from yet another CMS generation that we are responsible for, just
2627 // ignore it since all relevant work has already been done.
2628 return;
2629 }
2630 assert(haveFreelistLocks(), "must have freelist locks");
2631 assert_lock_strong(bitMapLock());
2632
2633 _cmsGen->gc_epilogue_work(full);
2634 _permGen->gc_epilogue_work(full);
2635
2636 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2637 // in case sampling was not already enabled, enable it
2638 _start_sampling = true;
2639 }
2640 // reset _eden_chunk_array so sampling starts afresh
2641 _eden_chunk_index = 0;
2642
2643 size_t cms_used = _cmsGen->cmsSpace()->used();
2644 size_t perm_used = _permGen->cmsSpace()->used();
2645
2646 // update performance counters - this uses a special version of
2647 // update_counters() that allows the utilization to be passed as a
2648 // parameter, avoiding multiple calls to used().
2649 //
2650 _cmsGen->update_counters(cms_used);
2651 _permGen->update_counters(perm_used);
2652
2653 if (CMSIncrementalMode) {
2654 icms_update_allocation_limits();
2655 }
2656
2657 bitMapLock()->unlock();
2658 releaseFreelistLocks();
2659
2660 _between_prologue_and_epilogue = false; // ready for next cycle
2661 }
2662
2663 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2664 collector()->gc_epilogue(full);
2665
2666 // Also reset promotion tracking in par gc thread states.
2667 if (ParallelGCThreads > 0) {
2668 for (uint i = 0; i < ParallelGCThreads; i++) {
2669 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2670 }
2671 }
2672 }
2673
2674 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2675 assert(!incremental_collection_failed(), "Should have been cleared");
2676 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2677 cmsSpace()->gc_epilogue();
2678 // Print stat counters
2679 NOT_PRODUCT(
2680 assert(_numObjectsAllocated == 0, "check");
2681 assert(_numWordsAllocated == 0, "check");
2682 if (Verbose && PrintGC) {
2683 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2684 SIZE_FORMAT" bytes",
2685 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2686 }
2687 _numObjectsPromoted = 0;
2688 _numWordsPromoted = 0;
2689 )
2690
2691 if (PrintGC && Verbose) {
2692 // Call down the chain in contiguous_available needs the freelistLock
2693 // so print this out before releasing the freeListLock.
2694 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2695 contiguous_available());
2696 }
2697 }
2698
2699 #ifndef PRODUCT
2700 bool CMSCollector::have_cms_token() {
2701 Thread* thr = Thread::current();
2702 if (thr->is_VM_thread()) {
2703 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2704 } else if (thr->is_ConcurrentGC_thread()) {
2705 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2706 } else if (thr->is_GC_task_thread()) {
2707 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2708 ParGCRareEvent_lock->owned_by_self();
2709 }
2710 return false;
2711 }
2712 #endif
2713
2714 // Check reachability of the given heap address in CMS generation,
2715 // treating all other generations as roots.
2716 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2717 // We could "guarantee" below, rather than assert, but i'll
2718 // leave these as "asserts" so that an adventurous debugger
2719 // could try this in the product build provided some subset of
2720 // the conditions were met, provided they were intersted in the
2721 // results and knew that the computation below wouldn't interfere
2722 // with other concurrent computations mutating the structures
2723 // being read or written.
2724 assert(SafepointSynchronize::is_at_safepoint(),
2725 "Else mutations in object graph will make answer suspect");
2726 assert(have_cms_token(), "Should hold cms token");
2727 assert(haveFreelistLocks(), "must hold free list locks");
2728 assert_lock_strong(bitMapLock());
2729
2730 // Clear the marking bit map array before starting, but, just
2731 // for kicks, first report if the given address is already marked
2732 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2733 _markBitMap.isMarked(addr) ? "" : " not");
2734
2735 if (verify_after_remark()) {
2736 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2737 bool result = verification_mark_bm()->isMarked(addr);
2738 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2739 result ? "IS" : "is NOT");
2740 return result;
2741 } else {
2742 gclog_or_tty->print_cr("Could not compute result");
2743 return false;
2744 }
2745 }
2746
2747 ////////////////////////////////////////////////////////
2748 // CMS Verification Support
2749 ////////////////////////////////////////////////////////
2750 // Following the remark phase, the following invariant
2751 // should hold -- each object in the CMS heap which is
2752 // marked in markBitMap() should be marked in the verification_mark_bm().
2753
2754 class VerifyMarkedClosure: public BitMapClosure {
2755 CMSBitMap* _marks;
2756 bool _failed;
2757
2758 public:
2759 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2760
2761 bool do_bit(size_t offset) {
2762 HeapWord* addr = _marks->offsetToHeapWord(offset);
2763 if (!_marks->isMarked(addr)) {
2764 oop(addr)->print_on(gclog_or_tty);
2765 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2766 _failed = true;
2767 }
2768 return true;
2769 }
2770
2771 bool failed() { return _failed; }
2772 };
2773
2774 bool CMSCollector::verify_after_remark() {
2775 gclog_or_tty->print(" [Verifying CMS Marking... ");
2776 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2777 static bool init = false;
2778
2779 assert(SafepointSynchronize::is_at_safepoint(),
2780 "Else mutations in object graph will make answer suspect");
2781 assert(have_cms_token(),
2782 "Else there may be mutual interference in use of "
2783 " verification data structures");
2784 assert(_collectorState > Marking && _collectorState <= Sweeping,
2785 "Else marking info checked here may be obsolete");
2786 assert(haveFreelistLocks(), "must hold free list locks");
2787 assert_lock_strong(bitMapLock());
2788
2789
2790 // Allocate marking bit map if not already allocated
2791 if (!init) { // first time
2792 if (!verification_mark_bm()->allocate(_span)) {
2793 return false;
2794 }
2795 init = true;
2796 }
2797
2798 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2799
2800 // Turn off refs discovery -- so we will be tracing through refs.
2801 // This is as intended, because by this time
2802 // GC must already have cleared any refs that need to be cleared,
2803 // and traced those that need to be marked; moreover,
2804 // the marking done here is not going to intefere in any
2805 // way with the marking information used by GC.
2806 NoRefDiscovery no_discovery(ref_processor());
2807
2808 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2809
2810 // Clear any marks from a previous round
2811 verification_mark_bm()->clear_all();
2812 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2813 verify_work_stacks_empty();
2814
2815 GenCollectedHeap* gch = GenCollectedHeap::heap();
2816 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2817 // Update the saved marks which may affect the root scans.
2818 gch->save_marks();
2819
2820 if (CMSRemarkVerifyVariant == 1) {
2821 // In this first variant of verification, we complete
2822 // all marking, then check if the new marks-verctor is
2823 // a subset of the CMS marks-vector.
2824 verify_after_remark_work_1();
2825 } else if (CMSRemarkVerifyVariant == 2) {
2826 // In this second variant of verification, we flag an error
2827 // (i.e. an object reachable in the new marks-vector not reachable
2828 // in the CMS marks-vector) immediately, also indicating the
2829 // identify of an object (A) that references the unmarked object (B) --
2830 // presumably, a mutation to A failed to be picked up by preclean/remark?
2831 verify_after_remark_work_2();
2832 } else {
2833 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2834 CMSRemarkVerifyVariant);
2835 }
2836 gclog_or_tty->print(" done] ");
2837 return true;
2838 }
2839
2840 void CMSCollector::verify_after_remark_work_1() {
2841 ResourceMark rm;
2842 HandleMark hm;
2843 GenCollectedHeap* gch = GenCollectedHeap::heap();
2844
2845 // Mark from roots one level into CMS
2846 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2847 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2848
2849 gch->gen_process_strong_roots(_cmsGen->level(),
2850 true, // younger gens are roots
2851 true, // activate StrongRootsScope
2852 true, // collecting perm gen
2853 SharedHeap::ScanningOption(roots_scanning_options()),
2854 ¬Older,
2855 true, // walk code active on stacks
2856 NULL);
2857
2858 // Now mark from the roots
2859 assert(_revisitStack.isEmpty(), "Should be empty");
2860 MarkFromRootsClosure markFromRootsClosure(this, _span,
2861 verification_mark_bm(), verification_mark_stack(), &_revisitStack,
2862 false /* don't yield */, true /* verifying */);
2863 assert(_restart_addr == NULL, "Expected pre-condition");
2864 verification_mark_bm()->iterate(&markFromRootsClosure);
2865 while (_restart_addr != NULL) {
2866 // Deal with stack overflow: by restarting at the indicated
2867 // address.
2868 HeapWord* ra = _restart_addr;
2869 markFromRootsClosure.reset(ra);
2870 _restart_addr = NULL;
2871 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2872 }
2873 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2874 verify_work_stacks_empty();
2875 // Should reset the revisit stack above, since no class tree
2876 // surgery is forthcoming.
2877 _revisitStack.reset(); // throwing away all contents
2878
2879 // Marking completed -- now verify that each bit marked in
2880 // verification_mark_bm() is also marked in markBitMap(); flag all
2881 // errors by printing corresponding objects.
2882 VerifyMarkedClosure vcl(markBitMap());
2883 verification_mark_bm()->iterate(&vcl);
2884 if (vcl.failed()) {
2885 gclog_or_tty->print("Verification failed");
2886 Universe::heap()->print_on(gclog_or_tty);
2887 fatal("CMS: failed marking verification after remark");
2888 }
2889 }
2890
2891 void CMSCollector::verify_after_remark_work_2() {
2892 ResourceMark rm;
2893 HandleMark hm;
2894 GenCollectedHeap* gch = GenCollectedHeap::heap();
2895
2896 // Mark from roots one level into CMS
2897 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2898 markBitMap());
2899 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2900 gch->gen_process_strong_roots(_cmsGen->level(),
2901 true, // younger gens are roots
2902 true, // activate StrongRootsScope
2903 true, // collecting perm gen
2904 SharedHeap::ScanningOption(roots_scanning_options()),
2905 ¬Older,
2906 true, // walk code active on stacks
2907 NULL);
2908
2909 // Now mark from the roots
2910 assert(_revisitStack.isEmpty(), "Should be empty");
2911 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2912 verification_mark_bm(), markBitMap(), verification_mark_stack());
2913 assert(_restart_addr == NULL, "Expected pre-condition");
2914 verification_mark_bm()->iterate(&markFromRootsClosure);
2915 while (_restart_addr != NULL) {
2916 // Deal with stack overflow: by restarting at the indicated
2917 // address.
2918 HeapWord* ra = _restart_addr;
2919 markFromRootsClosure.reset(ra);
2920 _restart_addr = NULL;
2921 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2922 }
2923 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2924 verify_work_stacks_empty();
2925 // Should reset the revisit stack above, since no class tree
2926 // surgery is forthcoming.
2927 _revisitStack.reset(); // throwing away all contents
2928
2929 // Marking completed -- now verify that each bit marked in
2930 // verification_mark_bm() is also marked in markBitMap(); flag all
2931 // errors by printing corresponding objects.
2932 VerifyMarkedClosure vcl(markBitMap());
2933 verification_mark_bm()->iterate(&vcl);
2934 assert(!vcl.failed(), "Else verification above should not have succeeded");
2935 }
2936
2937 void ConcurrentMarkSweepGeneration::save_marks() {
2938 // delegate to CMS space
2939 cmsSpace()->save_marks();
2940 for (uint i = 0; i < ParallelGCThreads; i++) {
2941 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2942 }
2943 }
2944
2945 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2946 return cmsSpace()->no_allocs_since_save_marks();
2947 }
2948
2949 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2950 \
2951 void ConcurrentMarkSweepGeneration:: \
2952 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2953 cl->set_generation(this); \
2954 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2955 cl->reset_generation(); \
2956 save_marks(); \
2957 }
2958
2959 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2960
2961 void
2962 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
2963 {
2964 // Not currently implemented; need to do the following. -- ysr.
2965 // dld -- I think that is used for some sort of allocation profiler. So it
2966 // really means the objects allocated by the mutator since the last
2967 // GC. We could potentially implement this cheaply by recording only
2968 // the direct allocations in a side data structure.
2969 //
2970 // I think we probably ought not to be required to support these
2971 // iterations at any arbitrary point; I think there ought to be some
2972 // call to enable/disable allocation profiling in a generation/space,
2973 // and the iterator ought to return the objects allocated in the
2974 // gen/space since the enable call, or the last iterator call (which
2975 // will probably be at a GC.) That way, for gens like CM&S that would
2976 // require some extra data structure to support this, we only pay the
2977 // cost when it's in use...
2978 cmsSpace()->object_iterate_since_last_GC(blk);
2979 }
2980
2981 void
2982 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
2983 cl->set_generation(this);
2984 younger_refs_in_space_iterate(_cmsSpace, cl);
2985 cl->reset_generation();
2986 }
2987
2988 void
2989 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, OopClosure* cl) {
2990 if (freelistLock()->owned_by_self()) {
2991 Generation::oop_iterate(mr, cl);
2992 } else {
2993 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2994 Generation::oop_iterate(mr, cl);
2995 }
2996 }
2997
2998 void
2999 ConcurrentMarkSweepGeneration::oop_iterate(OopClosure* cl) {
3000 if (freelistLock()->owned_by_self()) {
3001 Generation::oop_iterate(cl);
3002 } else {
3003 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3004 Generation::oop_iterate(cl);
3005 }
3006 }
3007
3008 void
3009 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3010 if (freelistLock()->owned_by_self()) {
3011 Generation::object_iterate(cl);
3012 } else {
3013 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3014 Generation::object_iterate(cl);
3015 }
3016 }
3017
3018 void
3019 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3020 if (freelistLock()->owned_by_self()) {
3021 Generation::safe_object_iterate(cl);
3022 } else {
3023 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3024 Generation::safe_object_iterate(cl);
3025 }
3026 }
3027
3028 void
3029 ConcurrentMarkSweepGeneration::pre_adjust_pointers() {
3030 }
3031
3032 void
3033 ConcurrentMarkSweepGeneration::post_compact() {
3034 }
3035
3036 void
3037 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3038 // Fix the linear allocation blocks to look like free blocks.
3039
3040 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3041 // are not called when the heap is verified during universe initialization and
3042 // at vm shutdown.
3043 if (freelistLock()->owned_by_self()) {
3044 cmsSpace()->prepare_for_verify();
3045 } else {
3046 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3047 cmsSpace()->prepare_for_verify();
3048 }
3049 }
3050
3051 void
3052 ConcurrentMarkSweepGeneration::verify(bool allow_dirty /* ignored */) {
3053 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3054 // are not called when the heap is verified during universe initialization and
3055 // at vm shutdown.
3056 if (freelistLock()->owned_by_self()) {
3057 cmsSpace()->verify(false /* ignored */);
3058 } else {
3059 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3060 cmsSpace()->verify(false /* ignored */);
3061 }
3062 }
3063
3064 void CMSCollector::verify(bool allow_dirty /* ignored */) {
3065 _cmsGen->verify(allow_dirty);
3066 _permGen->verify(allow_dirty);
3067 }
3068
3069 #ifndef PRODUCT
3070 bool CMSCollector::overflow_list_is_empty() const {
3071 assert(_num_par_pushes >= 0, "Inconsistency");
3072 if (_overflow_list == NULL) {
3073 assert(_num_par_pushes == 0, "Inconsistency");
3074 }
3075 return _overflow_list == NULL;
3076 }
3077
3078 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3079 // merely consolidate assertion checks that appear to occur together frequently.
3080 void CMSCollector::verify_work_stacks_empty() const {
3081 assert(_markStack.isEmpty(), "Marking stack should be empty");
3082 assert(overflow_list_is_empty(), "Overflow list should be empty");
3083 }
3084
3085 void CMSCollector::verify_overflow_empty() const {
3086 assert(overflow_list_is_empty(), "Overflow list should be empty");
3087 assert(no_preserved_marks(), "No preserved marks");
3088 }
3089 #endif // PRODUCT
3090
3091 // Decide if we want to enable class unloading as part of the
3092 // ensuing concurrent GC cycle. We will collect the perm gen and
3093 // unload classes if it's the case that:
3094 // (1) an explicit gc request has been made and the flag
3095 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3096 // (2) (a) class unloading is enabled at the command line, and
3097 // (b) (i) perm gen threshold has been crossed, or
3098 // (ii) old gen is getting really full, or
3099 // (iii) the previous N CMS collections did not collect the
3100 // perm gen
3101 // NOTE: Provided there is no change in the state of the heap between
3102 // calls to this method, it should have idempotent results. Moreover,
3103 // its results should be monotonically increasing (i.e. going from 0 to 1,
3104 // but not 1 to 0) between successive calls between which the heap was
3105 // not collected. For the implementation below, it must thus rely on
3106 // the property that concurrent_cycles_since_last_unload()
3107 // will not decrease unless a collection cycle happened and that
3108 // _permGen->should_concurrent_collect() and _cmsGen->is_too_full() are
3109 // themselves also monotonic in that sense. See check_monotonicity()
3110 // below.
3111 bool CMSCollector::update_should_unload_classes() {
3112 _should_unload_classes = false;
3113 // Condition 1 above
3114 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3115 _should_unload_classes = true;
3116 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3117 // Disjuncts 2.b.(i,ii,iii) above
3118 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3119 CMSClassUnloadingMaxInterval)
3120 || _permGen->should_concurrent_collect()
3121 || _cmsGen->is_too_full();
3122 }
3123 return _should_unload_classes;
3124 }
3125
3126 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3127 bool res = should_concurrent_collect();
3128 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3129 return res;
3130 }
3131
3132 void CMSCollector::setup_cms_unloading_and_verification_state() {
3133 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3134 || VerifyBeforeExit;
3135 const int rso = SharedHeap::SO_Symbols | SharedHeap::SO_Strings
3136 | SharedHeap::SO_CodeCache;
3137
3138 if (should_unload_classes()) { // Should unload classes this cycle
3139 remove_root_scanning_option(rso); // Shrink the root set appropriately
3140 set_verifying(should_verify); // Set verification state for this cycle
3141 return; // Nothing else needs to be done at this time
3142 }
3143
3144 // Not unloading classes this cycle
3145 assert(!should_unload_classes(), "Inconsitency!");
3146 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3147 // We were not verifying, or we _were_ unloading classes in the last cycle,
3148 // AND some verification options are enabled this cycle; in this case,
3149 // we must make sure that the deadness map is allocated if not already so,
3150 // and cleared (if already allocated previously --
3151 // CMSBitMap::sizeInBits() is used to determine if it's allocated).
3152 if (perm_gen_verify_bit_map()->sizeInBits() == 0) {
3153 if (!perm_gen_verify_bit_map()->allocate(_permGen->reserved())) {
3154 warning("Failed to allocate permanent generation verification CMS Bit Map;\n"
3155 "permanent generation verification disabled");
3156 return; // Note that we leave verification disabled, so we'll retry this
3157 // allocation next cycle. We _could_ remember this failure
3158 // and skip further attempts and permanently disable verification
3159 // attempts if that is considered more desirable.
3160 }
3161 assert(perm_gen_verify_bit_map()->covers(_permGen->reserved()),
3162 "_perm_gen_ver_bit_map inconsistency?");
3163 } else {
3164 perm_gen_verify_bit_map()->clear_all();
3165 }
3166 // Include symbols, strings and code cache elements to prevent their resurrection.
3167 add_root_scanning_option(rso);
3168 set_verifying(true);
3169 } else if (verifying() && !should_verify) {
3170 // We were verifying, but some verification flags got disabled.
3171 set_verifying(false);
3172 // Exclude symbols, strings and code cache elements from root scanning to
3173 // reduce IM and RM pauses.
3174 remove_root_scanning_option(rso);
3175 }
3176 }
3177
3178
3179 #ifndef PRODUCT
3180 HeapWord* CMSCollector::block_start(const void* p) const {
3181 const HeapWord* addr = (HeapWord*)p;
3182 if (_span.contains(p)) {
3183 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3184 return _cmsGen->cmsSpace()->block_start(p);
3185 } else {
3186 assert(_permGen->cmsSpace()->is_in_reserved(addr),
3187 "Inconsistent _span?");
3188 return _permGen->cmsSpace()->block_start(p);
3189 }
3190 }
3191 return NULL;
3192 }
3193 #endif
3194
3195 HeapWord*
3196 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3197 bool tlab,
3198 bool parallel) {
3199 assert(!tlab, "Can't deal with TLAB allocation");
3200 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3201 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3202 CMSExpansionCause::_satisfy_allocation);
3203 if (GCExpandToAllocateDelayMillis > 0) {
3204 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3205 }
3206 return have_lock_and_allocate(word_size, tlab);
3207 }
3208
3209 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3210 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3211 // to CardGeneration and share it...
3212 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3213 return CardGeneration::expand(bytes, expand_bytes);
3214 }
3215
3216 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3217 CMSExpansionCause::Cause cause)
3218 {
3219
3220 bool success = expand(bytes, expand_bytes);
3221
3222 // remember why we expanded; this information is used
3223 // by shouldConcurrentCollect() when making decisions on whether to start
3224 // a new CMS cycle.
3225 if (success) {
3226 set_expansion_cause(cause);
3227 if (PrintGCDetails && Verbose) {
3228 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3229 CMSExpansionCause::to_string(cause));
3230 }
3231 }
3232 }
3233
3234 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3235 HeapWord* res = NULL;
3236 MutexLocker x(ParGCRareEvent_lock);
3237 while (true) {
3238 // Expansion by some other thread might make alloc OK now:
3239 res = ps->lab.alloc(word_sz);
3240 if (res != NULL) return res;
3241 // If there's not enough expansion space available, give up.
3242 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3243 return NULL;
3244 }
3245 // Otherwise, we try expansion.
3246 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3247 CMSExpansionCause::_allocate_par_lab);
3248 // Now go around the loop and try alloc again;
3249 // A competing par_promote might beat us to the expansion space,
3250 // so we may go around the loop again if promotion fails agaion.
3251 if (GCExpandToAllocateDelayMillis > 0) {
3252 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3253 }
3254 }
3255 }
3256
3257
3258 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3259 PromotionInfo* promo) {
3260 MutexLocker x(ParGCRareEvent_lock);
3261 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3262 while (true) {
3263 // Expansion by some other thread might make alloc OK now:
3264 if (promo->ensure_spooling_space()) {
3265 assert(promo->has_spooling_space(),
3266 "Post-condition of successful ensure_spooling_space()");
3267 return true;
3268 }
3269 // If there's not enough expansion space available, give up.
3270 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3271 return false;
3272 }
3273 // Otherwise, we try expansion.
3274 expand(refill_size_bytes, MinHeapDeltaBytes,
3275 CMSExpansionCause::_allocate_par_spooling_space);
3276 // Now go around the loop and try alloc again;
3277 // A competing allocation might beat us to the expansion space,
3278 // so we may go around the loop again if allocation fails again.
3279 if (GCExpandToAllocateDelayMillis > 0) {
3280 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3281 }
3282 }
3283 }
3284
3285
3286
3287 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3288 assert_locked_or_safepoint(Heap_lock);
3289 size_t size = ReservedSpace::page_align_size_down(bytes);
3290 if (size > 0) {
3291 shrink_by(size);
3292 }
3293 }
3294
3295 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3296 assert_locked_or_safepoint(Heap_lock);
3297 bool result = _virtual_space.expand_by(bytes);
3298 if (result) {
3299 HeapWord* old_end = _cmsSpace->end();
3300 size_t new_word_size =
3301 heap_word_size(_virtual_space.committed_size());
3302 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3303 _bts->resize(new_word_size); // resize the block offset shared array
3304 Universe::heap()->barrier_set()->resize_covered_region(mr);
3305 // Hmmmm... why doesn't CFLS::set_end verify locking?
3306 // This is quite ugly; FIX ME XXX
3307 _cmsSpace->assert_locked(freelistLock());
3308 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3309
3310 // update the space and generation capacity counters
3311 if (UsePerfData) {
3312 _space_counters->update_capacity();
3313 _gen_counters->update_all();
3314 }
3315
3316 if (Verbose && PrintGC) {
3317 size_t new_mem_size = _virtual_space.committed_size();
3318 size_t old_mem_size = new_mem_size - bytes;
3319 gclog_or_tty->print_cr("Expanding %s from %ldK by %ldK to %ldK",
3320 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3321 }
3322 }
3323 return result;
3324 }
3325
3326 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3327 assert_locked_or_safepoint(Heap_lock);
3328 bool success = true;
3329 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3330 if (remaining_bytes > 0) {
3331 success = grow_by(remaining_bytes);
3332 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3333 }
3334 return success;
3335 }
3336
3337 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3338 assert_locked_or_safepoint(Heap_lock);
3339 assert_lock_strong(freelistLock());
3340 // XXX Fix when compaction is implemented.
3341 warning("Shrinking of CMS not yet implemented");
3342 return;
3343 }
3344
3345
3346 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3347 // phases.
3348 class CMSPhaseAccounting: public StackObj {
3349 public:
3350 CMSPhaseAccounting(CMSCollector *collector,
3351 const char *phase,
3352 bool print_cr = true);
3353 ~CMSPhaseAccounting();
3354
3355 private:
3356 CMSCollector *_collector;
3357 const char *_phase;
3358 elapsedTimer _wallclock;
3359 bool _print_cr;
3360
3361 public:
3362 // Not MT-safe; so do not pass around these StackObj's
3363 // where they may be accessed by other threads.
3364 jlong wallclock_millis() {
3365 assert(_wallclock.is_active(), "Wall clock should not stop");
3366 _wallclock.stop(); // to record time
3367 jlong ret = _wallclock.milliseconds();
3368 _wallclock.start(); // restart
3369 return ret;
3370 }
3371 };
3372
3373 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3374 const char *phase,
3375 bool print_cr) :
3376 _collector(collector), _phase(phase), _print_cr(print_cr) {
3377
3378 if (PrintCMSStatistics != 0) {
3379 _collector->resetYields();
3380 }
3381 if (PrintGCDetails && PrintGCTimeStamps) {
3382 gclog_or_tty->date_stamp(PrintGCDateStamps);
3383 gclog_or_tty->stamp();
3384 gclog_or_tty->print_cr(": [%s-concurrent-%s-start]",
3385 _collector->cmsGen()->short_name(), _phase);
3386 }
3387 _collector->resetTimer();
3388 _wallclock.start();
3389 _collector->startTimer();
3390 }
3391
3392 CMSPhaseAccounting::~CMSPhaseAccounting() {
3393 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3394 _collector->stopTimer();
3395 _wallclock.stop();
3396 if (PrintGCDetails) {
3397 gclog_or_tty->date_stamp(PrintGCDateStamps);
3398 if (PrintGCTimeStamps) {
3399 gclog_or_tty->stamp();
3400 gclog_or_tty->print(": ");
3401 }
3402 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3403 _collector->cmsGen()->short_name(),
3404 _phase, _collector->timerValue(), _wallclock.seconds());
3405 if (_print_cr) {
3406 gclog_or_tty->print_cr("");
3407 }
3408 if (PrintCMSStatistics != 0) {
3409 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3410 _collector->yields());
3411 }
3412 }
3413 }
3414
3415 // CMS work
3416
3417 // Checkpoint the roots into this generation from outside
3418 // this generation. [Note this initial checkpoint need only
3419 // be approximate -- we'll do a catch up phase subsequently.]
3420 void CMSCollector::checkpointRootsInitial(bool asynch) {
3421 assert(_collectorState == InitialMarking, "Wrong collector state");
3422 check_correct_thread_executing();
3423 ReferenceProcessor* rp = ref_processor();
3424 SpecializationStats::clear();
3425 assert(_restart_addr == NULL, "Control point invariant");
3426 if (asynch) {
3427 // acquire locks for subsequent manipulations
3428 MutexLockerEx x(bitMapLock(),
3429 Mutex::_no_safepoint_check_flag);
3430 checkpointRootsInitialWork(asynch);
3431 rp->verify_no_references_recorded();
3432 rp->enable_discovery(); // enable ("weak") refs discovery
3433 _collectorState = Marking;
3434 } else {
3435 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3436 // which recognizes if we are a CMS generation, and doesn't try to turn on
3437 // discovery; verify that they aren't meddling.
3438 assert(!rp->discovery_is_atomic(),
3439 "incorrect setting of discovery predicate");
3440 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3441 "ref discovery for this generation kind");
3442 // already have locks
3443 checkpointRootsInitialWork(asynch);
3444 rp->enable_discovery(); // now enable ("weak") refs discovery
3445 _collectorState = Marking;
3446 }
3447 SpecializationStats::print();
3448 }
3449
3450 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3451 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3452 assert(_collectorState == InitialMarking, "just checking");
3453
3454 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3455 // precede our marking with a collection of all
3456 // younger generations to keep floating garbage to a minimum.
3457 // XXX: we won't do this for now -- it's an optimization to be done later.
3458
3459 // already have locks
3460 assert_lock_strong(bitMapLock());
3461 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3462
3463 // Setup the verification and class unloading state for this
3464 // CMS collection cycle.
3465 setup_cms_unloading_and_verification_state();
3466
3467 NOT_PRODUCT(TraceTime t("\ncheckpointRootsInitialWork",
3468 PrintGCDetails && Verbose, true, gclog_or_tty);)
3469 if (UseAdaptiveSizePolicy) {
3470 size_policy()->checkpoint_roots_initial_begin();
3471 }
3472
3473 // Reset all the PLAB chunk arrays if necessary.
3474 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3475 reset_survivor_plab_arrays();
3476 }
3477
3478 ResourceMark rm;
3479 HandleMark hm;
3480
3481 FalseClosure falseClosure;
3482 // In the case of a synchronous collection, we will elide the
3483 // remark step, so it's important to catch all the nmethod oops
3484 // in this step.
3485 // The final 'true' flag to gen_process_strong_roots will ensure this.
3486 // If 'async' is true, we can relax the nmethod tracing.
3487 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3488 GenCollectedHeap* gch = GenCollectedHeap::heap();
3489
3490 verify_work_stacks_empty();
3491 verify_overflow_empty();
3492
3493 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3494 // Update the saved marks which may affect the root scans.
3495 gch->save_marks();
3496
3497 // weak reference processing has not started yet.
3498 ref_processor()->set_enqueuing_is_done(false);
3499
3500 {
3501 // This is not needed. DEBUG_ONLY(RememberKlassesChecker imx(true);)
3502 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3503 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3504 gch->gen_process_strong_roots(_cmsGen->level(),
3505 true, // younger gens are roots
3506 true, // activate StrongRootsScope
3507 true, // collecting perm gen
3508 SharedHeap::ScanningOption(roots_scanning_options()),
3509 ¬Older,
3510 true, // walk all of code cache if (so & SO_CodeCache)
3511 NULL);
3512 }
3513
3514 // Clear mod-union table; it will be dirtied in the prologue of
3515 // CMS generation per each younger generation collection.
3516
3517 assert(_modUnionTable.isAllClear(),
3518 "Was cleared in most recent final checkpoint phase"
3519 " or no bits are set in the gc_prologue before the start of the next "
3520 "subsequent marking phase.");
3521
3522 // Temporarily disabled, since pre/post-consumption closures don't
3523 // care about precleaned cards
3524 #if 0
3525 {
3526 MemRegion mr = MemRegion((HeapWord*)_virtual_space.low(),
3527 (HeapWord*)_virtual_space.high());
3528 _ct->ct_bs()->preclean_dirty_cards(mr);
3529 }
3530 #endif
3531
3532 // Save the end of the used_region of the constituent generations
3533 // to be used to limit the extent of sweep in each generation.
3534 save_sweep_limits();
3535 if (UseAdaptiveSizePolicy) {
3536 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3537 }
3538 verify_overflow_empty();
3539 }
3540
3541 bool CMSCollector::markFromRoots(bool asynch) {
3542 // we might be tempted to assert that:
3543 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3544 // "inconsistent argument?");
3545 // However that wouldn't be right, because it's possible that
3546 // a safepoint is indeed in progress as a younger generation
3547 // stop-the-world GC happens even as we mark in this generation.
3548 assert(_collectorState == Marking, "inconsistent state?");
3549 check_correct_thread_executing();
3550 verify_overflow_empty();
3551
3552 bool res;
3553 if (asynch) {
3554
3555 // Start the timers for adaptive size policy for the concurrent phases
3556 // Do it here so that the foreground MS can use the concurrent
3557 // timer since a foreground MS might has the sweep done concurrently
3558 // or STW.
3559 if (UseAdaptiveSizePolicy) {
3560 size_policy()->concurrent_marking_begin();
3561 }
3562
3563 // Weak ref discovery note: We may be discovering weak
3564 // refs in this generation concurrent (but interleaved) with
3565 // weak ref discovery by a younger generation collector.
3566
3567 CMSTokenSyncWithLocks ts(true, bitMapLock());
3568 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3569 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3570 res = markFromRootsWork(asynch);
3571 if (res) {
3572 _collectorState = Precleaning;
3573 } else { // We failed and a foreground collection wants to take over
3574 assert(_foregroundGCIsActive, "internal state inconsistency");
3575 assert(_restart_addr == NULL, "foreground will restart from scratch");
3576 if (PrintGCDetails) {
3577 gclog_or_tty->print_cr("bailing out to foreground collection");
3578 }
3579 }
3580 if (UseAdaptiveSizePolicy) {
3581 size_policy()->concurrent_marking_end();
3582 }
3583 } else {
3584 assert(SafepointSynchronize::is_at_safepoint(),
3585 "inconsistent with asynch == false");
3586 if (UseAdaptiveSizePolicy) {
3587 size_policy()->ms_collection_marking_begin();
3588 }
3589 // already have locks
3590 res = markFromRootsWork(asynch);
3591 _collectorState = FinalMarking;
3592 if (UseAdaptiveSizePolicy) {
3593 GenCollectedHeap* gch = GenCollectedHeap::heap();
3594 size_policy()->ms_collection_marking_end(gch->gc_cause());
3595 }
3596 }
3597 verify_overflow_empty();
3598 return res;
3599 }
3600
3601 bool CMSCollector::markFromRootsWork(bool asynch) {
3602 // iterate over marked bits in bit map, doing a full scan and mark
3603 // from these roots using the following algorithm:
3604 // . if oop is to the right of the current scan pointer,
3605 // mark corresponding bit (we'll process it later)
3606 // . else (oop is to left of current scan pointer)
3607 // push oop on marking stack
3608 // . drain the marking stack
3609
3610 // Note that when we do a marking step we need to hold the
3611 // bit map lock -- recall that direct allocation (by mutators)
3612 // and promotion (by younger generation collectors) is also
3613 // marking the bit map. [the so-called allocate live policy.]
3614 // Because the implementation of bit map marking is not
3615 // robust wrt simultaneous marking of bits in the same word,
3616 // we need to make sure that there is no such interference
3617 // between concurrent such updates.
3618
3619 // already have locks
3620 assert_lock_strong(bitMapLock());
3621
3622 // Clear the revisit stack, just in case there are any
3623 // obsolete contents from a short-circuited previous CMS cycle.
3624 _revisitStack.reset();
3625 verify_work_stacks_empty();
3626 verify_overflow_empty();
3627 assert(_revisitStack.isEmpty(), "tabula rasa");
3628 DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());)
3629 bool result = false;
3630 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3631 result = do_marking_mt(asynch);
3632 } else {
3633 result = do_marking_st(asynch);
3634 }
3635 return result;
3636 }
3637
3638 // Forward decl
3639 class CMSConcMarkingTask;
3640
3641 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3642 CMSCollector* _collector;
3643 CMSConcMarkingTask* _task;
3644 bool _yield;
3645 protected:
3646 virtual void yield();
3647 public:
3648 // "n_threads" is the number of threads to be terminated.
3649 // "queue_set" is a set of work queues of other threads.
3650 // "collector" is the CMS collector associated with this task terminator.
3651 // "yield" indicates whether we need the gang as a whole to yield.
3652 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set,
3653 CMSCollector* collector, bool yield) :
3654 ParallelTaskTerminator(n_threads, queue_set),
3655 _collector(collector),
3656 _yield(yield) { }
3657
3658 void set_task(CMSConcMarkingTask* task) {
3659 _task = task;
3660 }
3661 };
3662
3663 // MT Concurrent Marking Task
3664 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3665 CMSCollector* _collector;
3666 YieldingFlexibleWorkGang* _workers; // the whole gang
3667 int _n_workers; // requested/desired # workers
3668 bool _asynch;
3669 bool _result;
3670 CompactibleFreeListSpace* _cms_space;
3671 CompactibleFreeListSpace* _perm_space;
3672 HeapWord* _global_finger;
3673 HeapWord* _restart_addr;
3674
3675 // Exposed here for yielding support
3676 Mutex* const _bit_map_lock;
3677
3678 // The per thread work queues, available here for stealing
3679 OopTaskQueueSet* _task_queues;
3680 CMSConcMarkingTerminator _term;
3681
3682 public:
3683 CMSConcMarkingTask(CMSCollector* collector,
3684 CompactibleFreeListSpace* cms_space,
3685 CompactibleFreeListSpace* perm_space,
3686 bool asynch, int n_workers,
3687 YieldingFlexibleWorkGang* workers,
3688 OopTaskQueueSet* task_queues):
3689 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3690 _collector(collector),
3691 _cms_space(cms_space),
3692 _perm_space(perm_space),
3693 _asynch(asynch), _n_workers(n_workers), _result(true),
3694 _workers(workers), _task_queues(task_queues),
3695 _term(n_workers, task_queues, _collector, asynch),
3696 _bit_map_lock(collector->bitMapLock())
3697 {
3698 assert(n_workers <= workers->total_workers(),
3699 "Else termination won't work correctly today"); // XXX FIX ME!
3700 _requested_size = n_workers;
3701 _term.set_task(this);
3702 assert(_cms_space->bottom() < _perm_space->bottom(),
3703 "Finger incorrectly initialized below");
3704 _restart_addr = _global_finger = _cms_space->bottom();
3705 }
3706
3707
3708 OopTaskQueueSet* task_queues() { return _task_queues; }
3709
3710 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3711
3712 HeapWord** global_finger_addr() { return &_global_finger; }
3713
3714 CMSConcMarkingTerminator* terminator() { return &_term; }
3715
3716 void work(int i);
3717
3718 virtual void coordinator_yield(); // stuff done by coordinator
3719 bool result() { return _result; }
3720
3721 void reset(HeapWord* ra) {
3722 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3723 assert(_global_finger >= _perm_space->end(), "Postcondition of ::work(i)");
3724 assert(ra < _perm_space->end(), "ra too large");
3725 _restart_addr = _global_finger = ra;
3726 _term.reset_for_reuse();
3727 }
3728
3729 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3730 OopTaskQueue* work_q);
3731
3732 private:
3733 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3734 void do_work_steal(int i);
3735 void bump_global_finger(HeapWord* f);
3736 };
3737
3738 void CMSConcMarkingTerminator::yield() {
3739 if (ConcurrentMarkSweepThread::should_yield() &&
3740 !_collector->foregroundGCIsActive() &&
3741 _yield) {
3742 _task->yield();
3743 } else {
3744 ParallelTaskTerminator::yield();
3745 }
3746 }
3747
3748 ////////////////////////////////////////////////////////////////
3749 // Concurrent Marking Algorithm Sketch
3750 ////////////////////////////////////////////////////////////////
3751 // Until all tasks exhausted (both spaces):
3752 // -- claim next available chunk
3753 // -- bump global finger via CAS
3754 // -- find first object that starts in this chunk
3755 // and start scanning bitmap from that position
3756 // -- scan marked objects for oops
3757 // -- CAS-mark target, and if successful:
3758 // . if target oop is above global finger (volatile read)
3759 // nothing to do
3760 // . if target oop is in chunk and above local finger
3761 // then nothing to do
3762 // . else push on work-queue
3763 // -- Deal with possible overflow issues:
3764 // . local work-queue overflow causes stuff to be pushed on
3765 // global (common) overflow queue
3766 // . always first empty local work queue
3767 // . then get a batch of oops from global work queue if any
3768 // . then do work stealing
3769 // -- When all tasks claimed (both spaces)
3770 // and local work queue empty,
3771 // then in a loop do:
3772 // . check global overflow stack; steal a batch of oops and trace
3773 // . try to steal from other threads oif GOS is empty
3774 // . if neither is available, offer termination
3775 // -- Terminate and return result
3776 //
3777 void CMSConcMarkingTask::work(int i) {
3778 elapsedTimer _timer;
3779 ResourceMark rm;
3780 HandleMark hm;
3781
3782 DEBUG_ONLY(_collector->verify_overflow_empty();)
3783
3784 // Before we begin work, our work queue should be empty
3785 assert(work_queue(i)->size() == 0, "Expected to be empty");
3786 // Scan the bitmap covering _cms_space, tracing through grey objects.
3787 _timer.start();
3788 do_scan_and_mark(i, _cms_space);
3789 _timer.stop();
3790 if (PrintCMSStatistics != 0) {
3791 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3792 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3793 }
3794
3795 // ... do the same for the _perm_space
3796 _timer.reset();
3797 _timer.start();
3798 do_scan_and_mark(i, _perm_space);
3799 _timer.stop();
3800 if (PrintCMSStatistics != 0) {
3801 gclog_or_tty->print_cr("Finished perm space scanning in %dth thread: %3.3f sec",
3802 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3803 }
3804
3805 // ... do work stealing
3806 _timer.reset();
3807 _timer.start();
3808 do_work_steal(i);
3809 _timer.stop();
3810 if (PrintCMSStatistics != 0) {
3811 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3812 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3813 }
3814 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3815 assert(work_queue(i)->size() == 0, "Should have been emptied");
3816 // Note that under the current task protocol, the
3817 // following assertion is true even of the spaces
3818 // expanded since the completion of the concurrent
3819 // marking. XXX This will likely change under a strict
3820 // ABORT semantics.
3821 assert(_global_finger > _cms_space->end() &&
3822 _global_finger >= _perm_space->end(),
3823 "All tasks have been completed");
3824 DEBUG_ONLY(_collector->verify_overflow_empty();)
3825 }
3826
3827 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3828 HeapWord* read = _global_finger;
3829 HeapWord* cur = read;
3830 while (f > read) {
3831 cur = read;
3832 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3833 if (cur == read) {
3834 // our cas succeeded
3835 assert(_global_finger >= f, "protocol consistency");
3836 break;
3837 }
3838 }
3839 }
3840
3841 // This is really inefficient, and should be redone by
3842 // using (not yet available) block-read and -write interfaces to the
3843 // stack and the work_queue. XXX FIX ME !!!
3844 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3845 OopTaskQueue* work_q) {
3846 // Fast lock-free check
3847 if (ovflw_stk->length() == 0) {
3848 return false;
3849 }
3850 assert(work_q->size() == 0, "Shouldn't steal");
3851 MutexLockerEx ml(ovflw_stk->par_lock(),
3852 Mutex::_no_safepoint_check_flag);
3853 // Grab up to 1/4 the size of the work queue
3854 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3855 (size_t)ParGCDesiredObjsFromOverflowList);
3856 num = MIN2(num, ovflw_stk->length());
3857 for (int i = (int) num; i > 0; i--) {
3858 oop cur = ovflw_stk->pop();
3859 assert(cur != NULL, "Counted wrong?");
3860 work_q->push(cur);
3861 }
3862 return num > 0;
3863 }
3864
3865 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3866 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3867 int n_tasks = pst->n_tasks();
3868 // We allow that there may be no tasks to do here because
3869 // we are restarting after a stack overflow.
3870 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3871 int nth_task = 0;
3872
3873 HeapWord* aligned_start = sp->bottom();
3874 if (sp->used_region().contains(_restart_addr)) {
3875 // Align down to a card boundary for the start of 0th task
3876 // for this space.
3877 aligned_start =
3878 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3879 CardTableModRefBS::card_size);
3880 }
3881
3882 size_t chunk_size = sp->marking_task_size();
3883 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3884 // Having claimed the nth task in this space,
3885 // compute the chunk that it corresponds to:
3886 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3887 aligned_start + (nth_task+1)*chunk_size);
3888 // Try and bump the global finger via a CAS;
3889 // note that we need to do the global finger bump
3890 // _before_ taking the intersection below, because
3891 // the task corresponding to that region will be
3892 // deemed done even if the used_region() expands
3893 // because of allocation -- as it almost certainly will
3894 // during start-up while the threads yield in the
3895 // closure below.
3896 HeapWord* finger = span.end();
3897 bump_global_finger(finger); // atomically
3898 // There are null tasks here corresponding to chunks
3899 // beyond the "top" address of the space.
3900 span = span.intersection(sp->used_region());
3901 if (!span.is_empty()) { // Non-null task
3902 HeapWord* prev_obj;
3903 assert(!span.contains(_restart_addr) || nth_task == 0,
3904 "Inconsistency");
3905 if (nth_task == 0) {
3906 // For the 0th task, we'll not need to compute a block_start.
3907 if (span.contains(_restart_addr)) {
3908 // In the case of a restart because of stack overflow,
3909 // we might additionally skip a chunk prefix.
3910 prev_obj = _restart_addr;
3911 } else {
3912 prev_obj = span.start();
3913 }
3914 } else {
3915 // We want to skip the first object because
3916 // the protocol is to scan any object in its entirety
3917 // that _starts_ in this span; a fortiori, any
3918 // object starting in an earlier span is scanned
3919 // as part of an earlier claimed task.
3920 // Below we use the "careful" version of block_start
3921 // so we do not try to navigate uninitialized objects.
3922 prev_obj = sp->block_start_careful(span.start());
3923 // Below we use a variant of block_size that uses the
3924 // Printezis bits to avoid waiting for allocated
3925 // objects to become initialized/parsable.
3926 while (prev_obj < span.start()) {
3927 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3928 if (sz > 0) {
3929 prev_obj += sz;
3930 } else {
3931 // In this case we may end up doing a bit of redundant
3932 // scanning, but that appears unavoidable, short of
3933 // locking the free list locks; see bug 6324141.
3934 break;
3935 }
3936 }
3937 }
3938 if (prev_obj < span.end()) {
3939 MemRegion my_span = MemRegion(prev_obj, span.end());
3940 // Do the marking work within a non-empty span --
3941 // the last argument to the constructor indicates whether the
3942 // iteration should be incremental with periodic yields.
3943 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3944 &_collector->_markBitMap,
3945 work_queue(i),
3946 &_collector->_markStack,
3947 &_collector->_revisitStack,
3948 _asynch);
3949 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3950 } // else nothing to do for this task
3951 } // else nothing to do for this task
3952 }
3953 // We'd be tempted to assert here that since there are no
3954 // more tasks left to claim in this space, the global_finger
3955 // must exceed space->top() and a fortiori space->end(). However,
3956 // that would not quite be correct because the bumping of
3957 // global_finger occurs strictly after the claiming of a task,
3958 // so by the time we reach here the global finger may not yet
3959 // have been bumped up by the thread that claimed the last
3960 // task.
3961 pst->all_tasks_completed();
3962 }
3963
3964 class Par_ConcMarkingClosure: public Par_KlassRememberingOopClosure {
3965 private:
3966 MemRegion _span;
3967 CMSBitMap* _bit_map;
3968 CMSMarkStack* _overflow_stack;
3969 OopTaskQueue* _work_queue;
3970 protected:
3971 DO_OOP_WORK_DEFN
3972 public:
3973 Par_ConcMarkingClosure(CMSCollector* collector, OopTaskQueue* work_queue,
3974 CMSBitMap* bit_map, CMSMarkStack* overflow_stack,
3975 CMSMarkStack* revisit_stack):
3976 Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
3977 _span(_collector->_span),
3978 _work_queue(work_queue),
3979 _bit_map(bit_map),
3980 _overflow_stack(overflow_stack)
3981 { }
3982 virtual void do_oop(oop* p);
3983 virtual void do_oop(narrowOop* p);
3984 void trim_queue(size_t max);
3985 void handle_stack_overflow(HeapWord* lost);
3986 };
3987
3988 // Grey object scanning during work stealing phase --
3989 // the salient assumption here is that any references
3990 // that are in these stolen objects being scanned must
3991 // already have been initialized (else they would not have
3992 // been published), so we do not need to check for
3993 // uninitialized objects before pushing here.
3994 void Par_ConcMarkingClosure::do_oop(oop obj) {
3995 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
3996 HeapWord* addr = (HeapWord*)obj;
3997 // Check if oop points into the CMS generation
3998 // and is not marked
3999 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4000 // a white object ...
4001 // If we manage to "claim" the object, by being the
4002 // first thread to mark it, then we push it on our
4003 // marking stack
4004 if (_bit_map->par_mark(addr)) { // ... now grey
4005 // push on work queue (grey set)
4006 bool simulate_overflow = false;
4007 NOT_PRODUCT(
4008 if (CMSMarkStackOverflowALot &&
4009 _collector->simulate_overflow()) {
4010 // simulate a stack overflow
4011 simulate_overflow = true;
4012 }
4013 )
4014 if (simulate_overflow ||
4015 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4016 // stack overflow
4017 if (PrintCMSStatistics != 0) {
4018 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4019 SIZE_FORMAT, _overflow_stack->capacity());
4020 }
4021 // We cannot assert that the overflow stack is full because
4022 // it may have been emptied since.
4023 assert(simulate_overflow ||
4024 _work_queue->size() == _work_queue->max_elems(),
4025 "Else push should have succeeded");
4026 handle_stack_overflow(addr);
4027 }
4028 } // Else, some other thread got there first
4029 }
4030 }
4031
4032 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4033 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4034
4035 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4036 while (_work_queue->size() > max) {
4037 oop new_oop;
4038 if (_work_queue->pop_local(new_oop)) {
4039 assert(new_oop->is_oop(), "Should be an oop");
4040 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4041 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4042 assert(new_oop->is_parsable(), "Should be parsable");
4043 new_oop->oop_iterate(this); // do_oop() above
4044 }
4045 }
4046 }
4047
4048 // Upon stack overflow, we discard (part of) the stack,
4049 // remembering the least address amongst those discarded
4050 // in CMSCollector's _restart_address.
4051 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4052 // We need to do this under a mutex to prevent other
4053 // workers from interfering with the work done below.
4054 MutexLockerEx ml(_overflow_stack->par_lock(),
4055 Mutex::_no_safepoint_check_flag);
4056 // Remember the least grey address discarded
4057 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4058 _collector->lower_restart_addr(ra);
4059 _overflow_stack->reset(); // discard stack contents
4060 _overflow_stack->expand(); // expand the stack if possible
4061 }
4062
4063
4064 void CMSConcMarkingTask::do_work_steal(int i) {
4065 OopTaskQueue* work_q = work_queue(i);
4066 oop obj_to_scan;
4067 CMSBitMap* bm = &(_collector->_markBitMap);
4068 CMSMarkStack* ovflw = &(_collector->_markStack);
4069 CMSMarkStack* revisit = &(_collector->_revisitStack);
4070 int* seed = _collector->hash_seed(i);
4071 Par_ConcMarkingClosure cl(_collector, work_q, bm, ovflw, revisit);
4072 while (true) {
4073 cl.trim_queue(0);
4074 assert(work_q->size() == 0, "Should have been emptied above");
4075 if (get_work_from_overflow_stack(ovflw, work_q)) {
4076 // Can't assert below because the work obtained from the
4077 // overflow stack may already have been stolen from us.
4078 // assert(work_q->size() > 0, "Work from overflow stack");
4079 continue;
4080 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4081 assert(obj_to_scan->is_oop(), "Should be an oop");
4082 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4083 obj_to_scan->oop_iterate(&cl);
4084 } else if (terminator()->offer_termination()) {
4085 assert(work_q->size() == 0, "Impossible!");
4086 break;
4087 }
4088 }
4089 }
4090
4091 // This is run by the CMS (coordinator) thread.
4092 void CMSConcMarkingTask::coordinator_yield() {
4093 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4094 "CMS thread should hold CMS token");
4095 DEBUG_ONLY(RememberKlassesChecker mux(false);)
4096 // First give up the locks, then yield, then re-lock
4097 // We should probably use a constructor/destructor idiom to
4098 // do this unlock/lock or modify the MutexUnlocker class to
4099 // serve our purpose. XXX
4100 assert_lock_strong(_bit_map_lock);
4101 _bit_map_lock->unlock();
4102 ConcurrentMarkSweepThread::desynchronize(true);
4103 ConcurrentMarkSweepThread::acknowledge_yield_request();
4104 _collector->stopTimer();
4105 if (PrintCMSStatistics != 0) {
4106 _collector->incrementYields();
4107 }
4108 _collector->icms_wait();
4109
4110 // It is possible for whichever thread initiated the yield request
4111 // not to get a chance to wake up and take the bitmap lock between
4112 // this thread releasing it and reacquiring it. So, while the
4113 // should_yield() flag is on, let's sleep for a bit to give the
4114 // other thread a chance to wake up. The limit imposed on the number
4115 // of iterations is defensive, to avoid any unforseen circumstances
4116 // putting us into an infinite loop. Since it's always been this
4117 // (coordinator_yield()) method that was observed to cause the
4118 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4119 // which is by default non-zero. For the other seven methods that
4120 // also perform the yield operation, as are using a different
4121 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4122 // can enable the sleeping for those methods too, if necessary.
4123 // See 6442774.
4124 //
4125 // We really need to reconsider the synchronization between the GC
4126 // thread and the yield-requesting threads in the future and we
4127 // should really use wait/notify, which is the recommended
4128 // way of doing this type of interaction. Additionally, we should
4129 // consolidate the eight methods that do the yield operation and they
4130 // are almost identical into one for better maintenability and
4131 // readability. See 6445193.
4132 //
4133 // Tony 2006.06.29
4134 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4135 ConcurrentMarkSweepThread::should_yield() &&
4136 !CMSCollector::foregroundGCIsActive(); ++i) {
4137 os::sleep(Thread::current(), 1, false);
4138 ConcurrentMarkSweepThread::acknowledge_yield_request();
4139 }
4140
4141 ConcurrentMarkSweepThread::synchronize(true);
4142 _bit_map_lock->lock_without_safepoint_check();
4143 _collector->startTimer();
4144 }
4145
4146 bool CMSCollector::do_marking_mt(bool asynch) {
4147 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4148 // In the future this would be determined ergonomically, based
4149 // on #cpu's, # active mutator threads (and load), and mutation rate.
4150 int num_workers = ConcGCThreads;
4151
4152 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4153 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
4154
4155 CMSConcMarkingTask tsk(this, cms_space, perm_space,
4156 asynch, num_workers /* number requested XXX */,
4157 conc_workers(), task_queues());
4158
4159 // Since the actual number of workers we get may be different
4160 // from the number we requested above, do we need to do anything different
4161 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4162 // class?? XXX
4163 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4164 perm_space->initialize_sequential_subtasks_for_marking(num_workers);
4165
4166 // Refs discovery is already non-atomic.
4167 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4168 // Mutate the Refs discovery so it is MT during the
4169 // multi-threaded marking phase.
4170 ReferenceProcessorMTMutator mt(ref_processor(), num_workers > 1);
4171 DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());)
4172 conc_workers()->start_task(&tsk);
4173 while (tsk.yielded()) {
4174 tsk.coordinator_yield();
4175 conc_workers()->continue_task(&tsk);
4176 }
4177 // If the task was aborted, _restart_addr will be non-NULL
4178 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4179 while (_restart_addr != NULL) {
4180 // XXX For now we do not make use of ABORTED state and have not
4181 // yet implemented the right abort semantics (even in the original
4182 // single-threaded CMS case). That needs some more investigation
4183 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4184 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4185 // If _restart_addr is non-NULL, a marking stack overflow
4186 // occurred; we need to do a fresh marking iteration from the
4187 // indicated restart address.
4188 if (_foregroundGCIsActive && asynch) {
4189 // We may be running into repeated stack overflows, having
4190 // reached the limit of the stack size, while making very
4191 // slow forward progress. It may be best to bail out and
4192 // let the foreground collector do its job.
4193 // Clear _restart_addr, so that foreground GC
4194 // works from scratch. This avoids the headache of
4195 // a "rescan" which would otherwise be needed because
4196 // of the dirty mod union table & card table.
4197 _restart_addr = NULL;
4198 return false;
4199 }
4200 // Adjust the task to restart from _restart_addr
4201 tsk.reset(_restart_addr);
4202 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4203 _restart_addr);
4204 perm_space->initialize_sequential_subtasks_for_marking(num_workers,
4205 _restart_addr);
4206 _restart_addr = NULL;
4207 // Get the workers going again
4208 conc_workers()->start_task(&tsk);
4209 while (tsk.yielded()) {
4210 tsk.coordinator_yield();
4211 conc_workers()->continue_task(&tsk);
4212 }
4213 }
4214 assert(tsk.completed(), "Inconsistency");
4215 assert(tsk.result() == true, "Inconsistency");
4216 return true;
4217 }
4218
4219 bool CMSCollector::do_marking_st(bool asynch) {
4220 ResourceMark rm;
4221 HandleMark hm;
4222
4223 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4224 &_markStack, &_revisitStack, CMSYield && asynch);
4225 // the last argument to iterate indicates whether the iteration
4226 // should be incremental with periodic yields.
4227 _markBitMap.iterate(&markFromRootsClosure);
4228 // If _restart_addr is non-NULL, a marking stack overflow
4229 // occurred; we need to do a fresh iteration from the
4230 // indicated restart address.
4231 while (_restart_addr != NULL) {
4232 if (_foregroundGCIsActive && asynch) {
4233 // We may be running into repeated stack overflows, having
4234 // reached the limit of the stack size, while making very
4235 // slow forward progress. It may be best to bail out and
4236 // let the foreground collector do its job.
4237 // Clear _restart_addr, so that foreground GC
4238 // works from scratch. This avoids the headache of
4239 // a "rescan" which would otherwise be needed because
4240 // of the dirty mod union table & card table.
4241 _restart_addr = NULL;
4242 return false; // indicating failure to complete marking
4243 }
4244 // Deal with stack overflow:
4245 // we restart marking from _restart_addr
4246 HeapWord* ra = _restart_addr;
4247 markFromRootsClosure.reset(ra);
4248 _restart_addr = NULL;
4249 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4250 }
4251 return true;
4252 }
4253
4254 void CMSCollector::preclean() {
4255 check_correct_thread_executing();
4256 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4257 verify_work_stacks_empty();
4258 verify_overflow_empty();
4259 _abort_preclean = false;
4260 if (CMSPrecleaningEnabled) {
4261 _eden_chunk_index = 0;
4262 size_t used = get_eden_used();
4263 size_t capacity = get_eden_capacity();
4264 // Don't start sampling unless we will get sufficiently
4265 // many samples.
4266 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4267 * CMSScheduleRemarkEdenPenetration)) {
4268 _start_sampling = true;
4269 } else {
4270 _start_sampling = false;
4271 }
4272 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4273 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4274 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4275 }
4276 CMSTokenSync x(true); // is cms thread
4277 if (CMSPrecleaningEnabled) {
4278 sample_eden();
4279 _collectorState = AbortablePreclean;
4280 } else {
4281 _collectorState = FinalMarking;
4282 }
4283 verify_work_stacks_empty();
4284 verify_overflow_empty();
4285 }
4286
4287 // Try and schedule the remark such that young gen
4288 // occupancy is CMSScheduleRemarkEdenPenetration %.
4289 void CMSCollector::abortable_preclean() {
4290 check_correct_thread_executing();
4291 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4292 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4293
4294 // If Eden's current occupancy is below this threshold,
4295 // immediately schedule the remark; else preclean
4296 // past the next scavenge in an effort to
4297 // schedule the pause as described avove. By choosing
4298 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4299 // we will never do an actual abortable preclean cycle.
4300 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4301 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4302 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4303 // We need more smarts in the abortable preclean
4304 // loop below to deal with cases where allocation
4305 // in young gen is very very slow, and our precleaning
4306 // is running a losing race against a horde of
4307 // mutators intent on flooding us with CMS updates
4308 // (dirty cards).
4309 // One, admittedly dumb, strategy is to give up
4310 // after a certain number of abortable precleaning loops
4311 // or after a certain maximum time. We want to make
4312 // this smarter in the next iteration.
4313 // XXX FIX ME!!! YSR
4314 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4315 while (!(should_abort_preclean() ||
4316 ConcurrentMarkSweepThread::should_terminate())) {
4317 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4318 cumworkdone += workdone;
4319 loops++;
4320 // Voluntarily terminate abortable preclean phase if we have
4321 // been at it for too long.
4322 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4323 loops >= CMSMaxAbortablePrecleanLoops) {
4324 if (PrintGCDetails) {
4325 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4326 }
4327 break;
4328 }
4329 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4330 if (PrintGCDetails) {
4331 gclog_or_tty->print(" CMS: abort preclean due to time ");
4332 }
4333 break;
4334 }
4335 // If we are doing little work each iteration, we should
4336 // take a short break.
4337 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4338 // Sleep for some time, waiting for work to accumulate
4339 stopTimer();
4340 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4341 startTimer();
4342 waited++;
4343 }
4344 }
4345 if (PrintCMSStatistics > 0) {
4346 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4347 loops, waited, cumworkdone);
4348 }
4349 }
4350 CMSTokenSync x(true); // is cms thread
4351 if (_collectorState != Idling) {
4352 assert(_collectorState == AbortablePreclean,
4353 "Spontaneous state transition?");
4354 _collectorState = FinalMarking;
4355 } // Else, a foreground collection completed this CMS cycle.
4356 return;
4357 }
4358
4359 // Respond to an Eden sampling opportunity
4360 void CMSCollector::sample_eden() {
4361 // Make sure a young gc cannot sneak in between our
4362 // reading and recording of a sample.
4363 assert(Thread::current()->is_ConcurrentGC_thread(),
4364 "Only the cms thread may collect Eden samples");
4365 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4366 "Should collect samples while holding CMS token");
4367 if (!_start_sampling) {
4368 return;
4369 }
4370 if (_eden_chunk_array) {
4371 if (_eden_chunk_index < _eden_chunk_capacity) {
4372 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4373 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4374 "Unexpected state of Eden");
4375 // We'd like to check that what we just sampled is an oop-start address;
4376 // however, we cannot do that here since the object may not yet have been
4377 // initialized. So we'll instead do the check when we _use_ this sample
4378 // later.
4379 if (_eden_chunk_index == 0 ||
4380 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4381 _eden_chunk_array[_eden_chunk_index-1])
4382 >= CMSSamplingGrain)) {
4383 _eden_chunk_index++; // commit sample
4384 }
4385 }
4386 }
4387 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4388 size_t used = get_eden_used();
4389 size_t capacity = get_eden_capacity();
4390 assert(used <= capacity, "Unexpected state of Eden");
4391 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4392 _abort_preclean = true;
4393 }
4394 }
4395 }
4396
4397
4398 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4399 assert(_collectorState == Precleaning ||
4400 _collectorState == AbortablePreclean, "incorrect state");
4401 ResourceMark rm;
4402 HandleMark hm;
4403 // Do one pass of scrubbing the discovered reference lists
4404 // to remove any reference objects with strongly-reachable
4405 // referents.
4406 if (clean_refs) {
4407 ReferenceProcessor* rp = ref_processor();
4408 CMSPrecleanRefsYieldClosure yield_cl(this);
4409 assert(rp->span().equals(_span), "Spans should be equal");
4410 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4411 &_markStack, &_revisitStack,
4412 true /* preclean */);
4413 CMSDrainMarkingStackClosure complete_trace(this,
4414 _span, &_markBitMap, &_markStack,
4415 &keep_alive, true /* preclean */);
4416
4417 // We don't want this step to interfere with a young
4418 // collection because we don't want to take CPU
4419 // or memory bandwidth away from the young GC threads
4420 // (which may be as many as there are CPUs).
4421 // Note that we don't need to protect ourselves from
4422 // interference with mutators because they can't
4423 // manipulate the discovered reference lists nor affect
4424 // the computed reachability of the referents, the
4425 // only properties manipulated by the precleaning
4426 // of these reference lists.
4427 stopTimer();
4428 CMSTokenSyncWithLocks x(true /* is cms thread */,
4429 bitMapLock());
4430 startTimer();
4431 sample_eden();
4432
4433 // The following will yield to allow foreground
4434 // collection to proceed promptly. XXX YSR:
4435 // The code in this method may need further
4436 // tweaking for better performance and some restructuring
4437 // for cleaner interfaces.
4438 rp->preclean_discovered_references(
4439 rp->is_alive_non_header(), &keep_alive, &complete_trace,
4440 &yield_cl, should_unload_classes());
4441 }
4442
4443 if (clean_survivor) { // preclean the active survivor space(s)
4444 assert(_young_gen->kind() == Generation::DefNew ||
4445 _young_gen->kind() == Generation::ParNew ||
4446 _young_gen->kind() == Generation::ASParNew,
4447 "incorrect type for cast");
4448 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4449 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4450 &_markBitMap, &_modUnionTable,
4451 &_markStack, &_revisitStack,
4452 true /* precleaning phase */);
4453 stopTimer();
4454 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4455 bitMapLock());
4456 startTimer();
4457 unsigned int before_count =
4458 GenCollectedHeap::heap()->total_collections();
4459 SurvivorSpacePrecleanClosure
4460 sss_cl(this, _span, &_markBitMap, &_markStack,
4461 &pam_cl, before_count, CMSYield);
4462 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4463 dng->from()->object_iterate_careful(&sss_cl);
4464 dng->to()->object_iterate_careful(&sss_cl);
4465 }
4466 MarkRefsIntoAndScanClosure
4467 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4468 &_markStack, &_revisitStack, this, CMSYield,
4469 true /* precleaning phase */);
4470 // CAUTION: The following closure has persistent state that may need to
4471 // be reset upon a decrease in the sequence of addresses it
4472 // processes.
4473 ScanMarkedObjectsAgainCarefullyClosure
4474 smoac_cl(this, _span,
4475 &_markBitMap, &_markStack, &_revisitStack, &mrias_cl, CMSYield);
4476
4477 // Preclean dirty cards in ModUnionTable and CardTable using
4478 // appropriate convergence criterion;
4479 // repeat CMSPrecleanIter times unless we find that
4480 // we are losing.
4481 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4482 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4483 "Bad convergence multiplier");
4484 assert(CMSPrecleanThreshold >= 100,
4485 "Unreasonably low CMSPrecleanThreshold");
4486
4487 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4488 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4489 numIter < CMSPrecleanIter;
4490 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4491 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4492 if (CMSPermGenPrecleaningEnabled) {
4493 curNumCards += preclean_mod_union_table(_permGen, &smoac_cl);
4494 }
4495 if (Verbose && PrintGCDetails) {
4496 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4497 }
4498 // Either there are very few dirty cards, so re-mark
4499 // pause will be small anyway, or our pre-cleaning isn't
4500 // that much faster than the rate at which cards are being
4501 // dirtied, so we might as well stop and re-mark since
4502 // precleaning won't improve our re-mark time by much.
4503 if (curNumCards <= CMSPrecleanThreshold ||
4504 (numIter > 0 &&
4505 (curNumCards * CMSPrecleanDenominator >
4506 lastNumCards * CMSPrecleanNumerator))) {
4507 numIter++;
4508 cumNumCards += curNumCards;
4509 break;
4510 }
4511 }
4512 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4513 if (CMSPermGenPrecleaningEnabled) {
4514 curNumCards += preclean_card_table(_permGen, &smoac_cl);
4515 }
4516 cumNumCards += curNumCards;
4517 if (PrintGCDetails && PrintCMSStatistics != 0) {
4518 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4519 curNumCards, cumNumCards, numIter);
4520 }
4521 return cumNumCards; // as a measure of useful work done
4522 }
4523
4524 // PRECLEANING NOTES:
4525 // Precleaning involves:
4526 // . reading the bits of the modUnionTable and clearing the set bits.
4527 // . For the cards corresponding to the set bits, we scan the
4528 // objects on those cards. This means we need the free_list_lock
4529 // so that we can safely iterate over the CMS space when scanning
4530 // for oops.
4531 // . When we scan the objects, we'll be both reading and setting
4532 // marks in the marking bit map, so we'll need the marking bit map.
4533 // . For protecting _collector_state transitions, we take the CGC_lock.
4534 // Note that any races in the reading of of card table entries by the
4535 // CMS thread on the one hand and the clearing of those entries by the
4536 // VM thread or the setting of those entries by the mutator threads on the
4537 // other are quite benign. However, for efficiency it makes sense to keep
4538 // the VM thread from racing with the CMS thread while the latter is
4539 // dirty card info to the modUnionTable. We therefore also use the
4540 // CGC_lock to protect the reading of the card table and the mod union
4541 // table by the CM thread.
4542 // . We run concurrently with mutator updates, so scanning
4543 // needs to be done carefully -- we should not try to scan
4544 // potentially uninitialized objects.
4545 //
4546 // Locking strategy: While holding the CGC_lock, we scan over and
4547 // reset a maximal dirty range of the mod union / card tables, then lock
4548 // the free_list_lock and bitmap lock to do a full marking, then
4549 // release these locks; and repeat the cycle. This allows for a
4550 // certain amount of fairness in the sharing of these locks between
4551 // the CMS collector on the one hand, and the VM thread and the
4552 // mutators on the other.
4553
4554 // NOTE: preclean_mod_union_table() and preclean_card_table()
4555 // further below are largely identical; if you need to modify
4556 // one of these methods, please check the other method too.
4557
4558 size_t CMSCollector::preclean_mod_union_table(
4559 ConcurrentMarkSweepGeneration* gen,
4560 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4561 verify_work_stacks_empty();
4562 verify_overflow_empty();
4563
4564 // Turn off checking for this method but turn it back on
4565 // selectively. There are yield points in this method
4566 // but it is difficult to turn the checking off just around
4567 // the yield points. It is simpler to selectively turn
4568 // it on.
4569 DEBUG_ONLY(RememberKlassesChecker mux(false);)
4570
4571 // strategy: starting with the first card, accumulate contiguous
4572 // ranges of dirty cards; clear these cards, then scan the region
4573 // covered by these cards.
4574
4575 // Since all of the MUT is committed ahead, we can just use
4576 // that, in case the generations expand while we are precleaning.
4577 // It might also be fine to just use the committed part of the
4578 // generation, but we might potentially miss cards when the
4579 // generation is rapidly expanding while we are in the midst
4580 // of precleaning.
4581 HeapWord* startAddr = gen->reserved().start();
4582 HeapWord* endAddr = gen->reserved().end();
4583
4584 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4585
4586 size_t numDirtyCards, cumNumDirtyCards;
4587 HeapWord *nextAddr, *lastAddr;
4588 for (cumNumDirtyCards = numDirtyCards = 0,
4589 nextAddr = lastAddr = startAddr;
4590 nextAddr < endAddr;
4591 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4592
4593 ResourceMark rm;
4594 HandleMark hm;
4595
4596 MemRegion dirtyRegion;
4597 {
4598 stopTimer();
4599 // Potential yield point
4600 CMSTokenSync ts(true);
4601 startTimer();
4602 sample_eden();
4603 // Get dirty region starting at nextOffset (inclusive),
4604 // simultaneously clearing it.
4605 dirtyRegion =
4606 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4607 assert(dirtyRegion.start() >= nextAddr,
4608 "returned region inconsistent?");
4609 }
4610 // Remember where the next search should begin.
4611 // The returned region (if non-empty) is a right open interval,
4612 // so lastOffset is obtained from the right end of that
4613 // interval.
4614 lastAddr = dirtyRegion.end();
4615 // Should do something more transparent and less hacky XXX
4616 numDirtyCards =
4617 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4618
4619 // We'll scan the cards in the dirty region (with periodic
4620 // yields for foreground GC as needed).
4621 if (!dirtyRegion.is_empty()) {
4622 assert(numDirtyCards > 0, "consistency check");
4623 HeapWord* stop_point = NULL;
4624 stopTimer();
4625 // Potential yield point
4626 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4627 bitMapLock());
4628 startTimer();
4629 {
4630 verify_work_stacks_empty();
4631 verify_overflow_empty();
4632 sample_eden();
4633 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4634 stop_point =
4635 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4636 }
4637 if (stop_point != NULL) {
4638 // The careful iteration stopped early either because it found an
4639 // uninitialized object, or because we were in the midst of an
4640 // "abortable preclean", which should now be aborted. Redirty
4641 // the bits corresponding to the partially-scanned or unscanned
4642 // cards. We'll either restart at the next block boundary or
4643 // abort the preclean.
4644 assert((CMSPermGenPrecleaningEnabled && (gen == _permGen)) ||
4645 (_collectorState == AbortablePreclean && should_abort_preclean()),
4646 "Unparsable objects should only be in perm gen.");
4647 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4648 if (should_abort_preclean()) {
4649 break; // out of preclean loop
4650 } else {
4651 // Compute the next address at which preclean should pick up;
4652 // might need bitMapLock in order to read P-bits.
4653 lastAddr = next_card_start_after_block(stop_point);
4654 }
4655 }
4656 } else {
4657 assert(lastAddr == endAddr, "consistency check");
4658 assert(numDirtyCards == 0, "consistency check");
4659 break;
4660 }
4661 }
4662 verify_work_stacks_empty();
4663 verify_overflow_empty();
4664 return cumNumDirtyCards;
4665 }
4666
4667 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4668 // below are largely identical; if you need to modify
4669 // one of these methods, please check the other method too.
4670
4671 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4672 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4673 // strategy: it's similar to precleamModUnionTable above, in that
4674 // we accumulate contiguous ranges of dirty cards, mark these cards
4675 // precleaned, then scan the region covered by these cards.
4676 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4677 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4678
4679 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4680
4681 size_t numDirtyCards, cumNumDirtyCards;
4682 HeapWord *lastAddr, *nextAddr;
4683
4684 for (cumNumDirtyCards = numDirtyCards = 0,
4685 nextAddr = lastAddr = startAddr;
4686 nextAddr < endAddr;
4687 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4688
4689 ResourceMark rm;
4690 HandleMark hm;
4691
4692 MemRegion dirtyRegion;
4693 {
4694 // See comments in "Precleaning notes" above on why we
4695 // do this locking. XXX Could the locking overheads be
4696 // too high when dirty cards are sparse? [I don't think so.]
4697 stopTimer();
4698 CMSTokenSync x(true); // is cms thread
4699 startTimer();
4700 sample_eden();
4701 // Get and clear dirty region from card table
4702 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4703 MemRegion(nextAddr, endAddr),
4704 true,
4705 CardTableModRefBS::precleaned_card_val());
4706
4707 assert(dirtyRegion.start() >= nextAddr,
4708 "returned region inconsistent?");
4709 }
4710 lastAddr = dirtyRegion.end();
4711 numDirtyCards =
4712 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4713
4714 if (!dirtyRegion.is_empty()) {
4715 stopTimer();
4716 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4717 startTimer();
4718 sample_eden();
4719 verify_work_stacks_empty();
4720 verify_overflow_empty();
4721 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4722 HeapWord* stop_point =
4723 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4724 if (stop_point != NULL) {
4725 // The careful iteration stopped early because it found an
4726 // uninitialized object. Redirty the bits corresponding to the
4727 // partially-scanned or unscanned cards, and start again at the
4728 // next block boundary.
4729 assert(CMSPermGenPrecleaningEnabled ||
4730 (_collectorState == AbortablePreclean && should_abort_preclean()),
4731 "Unparsable objects should only be in perm gen.");
4732 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4733 if (should_abort_preclean()) {
4734 break; // out of preclean loop
4735 } else {
4736 // Compute the next address at which preclean should pick up.
4737 lastAddr = next_card_start_after_block(stop_point);
4738 }
4739 }
4740 } else {
4741 break;
4742 }
4743 }
4744 verify_work_stacks_empty();
4745 verify_overflow_empty();
4746 return cumNumDirtyCards;
4747 }
4748
4749 void CMSCollector::checkpointRootsFinal(bool asynch,
4750 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4751 assert(_collectorState == FinalMarking, "incorrect state transition?");
4752 check_correct_thread_executing();
4753 // world is stopped at this checkpoint
4754 assert(SafepointSynchronize::is_at_safepoint(),
4755 "world should be stopped");
4756 verify_work_stacks_empty();
4757 verify_overflow_empty();
4758
4759 SpecializationStats::clear();
4760 if (PrintGCDetails) {
4761 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4762 _young_gen->used() / K,
4763 _young_gen->capacity() / K);
4764 }
4765 if (asynch) {
4766 if (CMSScavengeBeforeRemark) {
4767 GenCollectedHeap* gch = GenCollectedHeap::heap();
4768 // Temporarily set flag to false, GCH->do_collection will
4769 // expect it to be false and set to true
4770 FlagSetting fl(gch->_is_gc_active, false);
4771 NOT_PRODUCT(TraceTime t("Scavenge-Before-Remark",
4772 PrintGCDetails && Verbose, true, gclog_or_tty);)
4773 int level = _cmsGen->level() - 1;
4774 if (level >= 0) {
4775 gch->do_collection(true, // full (i.e. force, see below)
4776 false, // !clear_all_soft_refs
4777 0, // size
4778 false, // is_tlab
4779 level // max_level
4780 );
4781 }
4782 }
4783 FreelistLocker x(this);
4784 MutexLockerEx y(bitMapLock(),
4785 Mutex::_no_safepoint_check_flag);
4786 assert(!init_mark_was_synchronous, "but that's impossible!");
4787 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4788 } else {
4789 // already have all the locks
4790 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4791 init_mark_was_synchronous);
4792 }
4793 verify_work_stacks_empty();
4794 verify_overflow_empty();
4795 SpecializationStats::print();
4796 }
4797
4798 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4799 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4800
4801 NOT_PRODUCT(TraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, gclog_or_tty);)
4802
4803 assert(haveFreelistLocks(), "must have free list locks");
4804 assert_lock_strong(bitMapLock());
4805
4806 if (UseAdaptiveSizePolicy) {
4807 size_policy()->checkpoint_roots_final_begin();
4808 }
4809
4810 ResourceMark rm;
4811 HandleMark hm;
4812
4813 GenCollectedHeap* gch = GenCollectedHeap::heap();
4814
4815 if (should_unload_classes()) {
4816 CodeCache::gc_prologue();
4817 }
4818 assert(haveFreelistLocks(), "must have free list locks");
4819 assert_lock_strong(bitMapLock());
4820
4821 DEBUG_ONLY(RememberKlassesChecker fmx(should_unload_classes());)
4822 if (!init_mark_was_synchronous) {
4823 // We might assume that we need not fill TLAB's when
4824 // CMSScavengeBeforeRemark is set, because we may have just done
4825 // a scavenge which would have filled all TLAB's -- and besides
4826 // Eden would be empty. This however may not always be the case --
4827 // for instance although we asked for a scavenge, it may not have
4828 // happened because of a JNI critical section. We probably need
4829 // a policy for deciding whether we can in that case wait until
4830 // the critical section releases and then do the remark following
4831 // the scavenge, and skip it here. In the absence of that policy,
4832 // or of an indication of whether the scavenge did indeed occur,
4833 // we cannot rely on TLAB's having been filled and must do
4834 // so here just in case a scavenge did not happen.
4835 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4836 // Update the saved marks which may affect the root scans.
4837 gch->save_marks();
4838
4839 {
4840 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4841
4842 // Note on the role of the mod union table:
4843 // Since the marker in "markFromRoots" marks concurrently with
4844 // mutators, it is possible for some reachable objects not to have been
4845 // scanned. For instance, an only reference to an object A was
4846 // placed in object B after the marker scanned B. Unless B is rescanned,
4847 // A would be collected. Such updates to references in marked objects
4848 // are detected via the mod union table which is the set of all cards
4849 // dirtied since the first checkpoint in this GC cycle and prior to
4850 // the most recent young generation GC, minus those cleaned up by the
4851 // concurrent precleaning.
4852 if (CMSParallelRemarkEnabled && ParallelGCThreads > 0) {
4853 TraceTime t("Rescan (parallel) ", PrintGCDetails, false, gclog_or_tty);
4854 do_remark_parallel();
4855 } else {
4856 TraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4857 gclog_or_tty);
4858 do_remark_non_parallel();
4859 }
4860 }
4861 } else {
4862 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
4863 // The initial mark was stop-world, so there's no rescanning to
4864 // do; go straight on to the next step below.
4865 }
4866 verify_work_stacks_empty();
4867 verify_overflow_empty();
4868
4869 {
4870 NOT_PRODUCT(TraceTime ts("refProcessingWork", PrintGCDetails, false, gclog_or_tty);)
4871 refProcessingWork(asynch, clear_all_soft_refs);
4872 }
4873 verify_work_stacks_empty();
4874 verify_overflow_empty();
4875
4876 if (should_unload_classes()) {
4877 CodeCache::gc_epilogue();
4878 }
4879
4880 // If we encountered any (marking stack / work queue) overflow
4881 // events during the current CMS cycle, take appropriate
4882 // remedial measures, where possible, so as to try and avoid
4883 // recurrence of that condition.
4884 assert(_markStack.isEmpty(), "No grey objects");
4885 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4886 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4887 if (ser_ovflw > 0) {
4888 if (PrintCMSStatistics != 0) {
4889 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4890 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4891 ", kac_preclean="SIZE_FORMAT")",
4892 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4893 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4894 }
4895 _markStack.expand();
4896 _ser_pmc_remark_ovflw = 0;
4897 _ser_pmc_preclean_ovflw = 0;
4898 _ser_kac_preclean_ovflw = 0;
4899 _ser_kac_ovflw = 0;
4900 }
4901 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4902 if (PrintCMSStatistics != 0) {
4903 gclog_or_tty->print_cr("Work queue overflow (benign) "
4904 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4905 _par_pmc_remark_ovflw, _par_kac_ovflw);
4906 }
4907 _par_pmc_remark_ovflw = 0;
4908 _par_kac_ovflw = 0;
4909 }
4910 if (PrintCMSStatistics != 0) {
4911 if (_markStack._hit_limit > 0) {
4912 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4913 _markStack._hit_limit);
4914 }
4915 if (_markStack._failed_double > 0) {
4916 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4917 " current capacity "SIZE_FORMAT,
4918 _markStack._failed_double,
4919 _markStack.capacity());
4920 }
4921 }
4922 _markStack._hit_limit = 0;
4923 _markStack._failed_double = 0;
4924
4925 // Check that all the klasses have been checked
4926 assert(_revisitStack.isEmpty(), "Not all klasses revisited");
4927
4928 if ((VerifyAfterGC || VerifyDuringGC) &&
4929 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4930 verify_after_remark();
4931 }
4932
4933 // Change under the freelistLocks.
4934 _collectorState = Sweeping;
4935 // Call isAllClear() under bitMapLock
4936 assert(_modUnionTable.isAllClear(), "Should be clear by end of the"
4937 " final marking");
4938 if (UseAdaptiveSizePolicy) {
4939 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
4940 }
4941 }
4942
4943 // Parallel remark task
4944 class CMSParRemarkTask: public AbstractGangTask {
4945 CMSCollector* _collector;
4946 WorkGang* _workers;
4947 int _n_workers;
4948 CompactibleFreeListSpace* _cms_space;
4949 CompactibleFreeListSpace* _perm_space;
4950
4951 // The per-thread work queues, available here for stealing.
4952 OopTaskQueueSet* _task_queues;
4953 ParallelTaskTerminator _term;
4954
4955 public:
4956 CMSParRemarkTask(CMSCollector* collector,
4957 CompactibleFreeListSpace* cms_space,
4958 CompactibleFreeListSpace* perm_space,
4959 int n_workers, WorkGang* workers,
4960 OopTaskQueueSet* task_queues):
4961 AbstractGangTask("Rescan roots and grey objects in parallel"),
4962 _collector(collector),
4963 _cms_space(cms_space), _perm_space(perm_space),
4964 _n_workers(n_workers),
4965 _workers(workers),
4966 _task_queues(task_queues),
4967 _term(workers->total_workers(), task_queues) { }
4968
4969 OopTaskQueueSet* task_queues() { return _task_queues; }
4970
4971 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4972
4973 ParallelTaskTerminator* terminator() { return &_term; }
4974
4975 void work(int i);
4976
4977 private:
4978 // Work method in support of parallel rescan ... of young gen spaces
4979 void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
4980 ContiguousSpace* space,
4981 HeapWord** chunk_array, size_t chunk_top);
4982
4983 // ... of dirty cards in old space
4984 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4985 Par_MarkRefsIntoAndScanClosure* cl);
4986
4987 // ... work stealing for the above
4988 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4989 };
4990
4991 void CMSParRemarkTask::work(int i) {
4992 elapsedTimer _timer;
4993 ResourceMark rm;
4994 HandleMark hm;
4995
4996 // ---------- rescan from roots --------------
4997 _timer.start();
4998 GenCollectedHeap* gch = GenCollectedHeap::heap();
4999 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5000 _collector->_span, _collector->ref_processor(),
5001 &(_collector->_markBitMap),
5002 work_queue(i), &(_collector->_revisitStack));
5003
5004 // Rescan young gen roots first since these are likely
5005 // coarsely partitioned and may, on that account, constitute
5006 // the critical path; thus, it's best to start off that
5007 // work first.
5008 // ---------- young gen roots --------------
5009 {
5010 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5011 EdenSpace* eden_space = dng->eden();
5012 ContiguousSpace* from_space = dng->from();
5013 ContiguousSpace* to_space = dng->to();
5014
5015 HeapWord** eca = _collector->_eden_chunk_array;
5016 size_t ect = _collector->_eden_chunk_index;
5017 HeapWord** sca = _collector->_survivor_chunk_array;
5018 size_t sct = _collector->_survivor_chunk_index;
5019
5020 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5021 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5022
5023 do_young_space_rescan(i, &par_mrias_cl, to_space, NULL, 0);
5024 do_young_space_rescan(i, &par_mrias_cl, from_space, sca, sct);
5025 do_young_space_rescan(i, &par_mrias_cl, eden_space, eca, ect);
5026
5027 _timer.stop();
5028 if (PrintCMSStatistics != 0) {
5029 gclog_or_tty->print_cr(
5030 "Finished young gen rescan work in %dth thread: %3.3f sec",
5031 i, _timer.seconds());
5032 }
5033 }
5034
5035 // ---------- remaining roots --------------
5036 _timer.reset();
5037 _timer.start();
5038 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5039 false, // yg was scanned above
5040 false, // this is parallel code
5041 true, // collecting perm gen
5042 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5043 &par_mrias_cl,
5044 true, // walk all of code cache if (so & SO_CodeCache)
5045 NULL);
5046 assert(_collector->should_unload_classes()
5047 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache),
5048 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5049 _timer.stop();
5050 if (PrintCMSStatistics != 0) {
5051 gclog_or_tty->print_cr(
5052 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5053 i, _timer.seconds());
5054 }
5055
5056 // ---------- rescan dirty cards ------------
5057 _timer.reset();
5058 _timer.start();
5059
5060 // Do the rescan tasks for each of the two spaces
5061 // (cms_space and perm_space) in turn.
5062 do_dirty_card_rescan_tasks(_cms_space, i, &par_mrias_cl);
5063 do_dirty_card_rescan_tasks(_perm_space, i, &par_mrias_cl);
5064 _timer.stop();
5065 if (PrintCMSStatistics != 0) {
5066 gclog_or_tty->print_cr(
5067 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5068 i, _timer.seconds());
5069 }
5070
5071 // ---------- steal work from other threads ...
5072 // ---------- ... and drain overflow list.
5073 _timer.reset();
5074 _timer.start();
5075 do_work_steal(i, &par_mrias_cl, _collector->hash_seed(i));
5076 _timer.stop();
5077 if (PrintCMSStatistics != 0) {
5078 gclog_or_tty->print_cr(
5079 "Finished work stealing in %dth thread: %3.3f sec",
5080 i, _timer.seconds());
5081 }
5082 }
5083
5084 void
5085 CMSParRemarkTask::do_young_space_rescan(int i,
5086 Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
5087 HeapWord** chunk_array, size_t chunk_top) {
5088 // Until all tasks completed:
5089 // . claim an unclaimed task
5090 // . compute region boundaries corresponding to task claimed
5091 // using chunk_array
5092 // . par_oop_iterate(cl) over that region
5093
5094 ResourceMark rm;
5095 HandleMark hm;
5096
5097 SequentialSubTasksDone* pst = space->par_seq_tasks();
5098 assert(pst->valid(), "Uninitialized use?");
5099
5100 int nth_task = 0;
5101 int n_tasks = pst->n_tasks();
5102
5103 HeapWord *start, *end;
5104 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5105 // We claimed task # nth_task; compute its boundaries.
5106 if (chunk_top == 0) { // no samples were taken
5107 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5108 start = space->bottom();
5109 end = space->top();
5110 } else if (nth_task == 0) {
5111 start = space->bottom();
5112 end = chunk_array[nth_task];
5113 } else if (nth_task < (jint)chunk_top) {
5114 assert(nth_task >= 1, "Control point invariant");
5115 start = chunk_array[nth_task - 1];
5116 end = chunk_array[nth_task];
5117 } else {
5118 assert(nth_task == (jint)chunk_top, "Control point invariant");
5119 start = chunk_array[chunk_top - 1];
5120 end = space->top();
5121 }
5122 MemRegion mr(start, end);
5123 // Verify that mr is in space
5124 assert(mr.is_empty() || space->used_region().contains(mr),
5125 "Should be in space");
5126 // Verify that "start" is an object boundary
5127 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5128 "Should be an oop");
5129 space->par_oop_iterate(mr, cl);
5130 }
5131 pst->all_tasks_completed();
5132 }
5133
5134 void
5135 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5136 CompactibleFreeListSpace* sp, int i,
5137 Par_MarkRefsIntoAndScanClosure* cl) {
5138 // Until all tasks completed:
5139 // . claim an unclaimed task
5140 // . compute region boundaries corresponding to task claimed
5141 // . transfer dirty bits ct->mut for that region
5142 // . apply rescanclosure to dirty mut bits for that region
5143
5144 ResourceMark rm;
5145 HandleMark hm;
5146
5147 OopTaskQueue* work_q = work_queue(i);
5148 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5149 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5150 // CAUTION: This closure has state that persists across calls to
5151 // the work method dirty_range_iterate_clear() in that it has
5152 // imbedded in it a (subtype of) UpwardsObjectClosure. The
5153 // use of that state in the imbedded UpwardsObjectClosure instance
5154 // assumes that the cards are always iterated (even if in parallel
5155 // by several threads) in monotonically increasing order per each
5156 // thread. This is true of the implementation below which picks
5157 // card ranges (chunks) in monotonically increasing order globally
5158 // and, a-fortiori, in monotonically increasing order per thread
5159 // (the latter order being a subsequence of the former).
5160 // If the work code below is ever reorganized into a more chaotic
5161 // work-partitioning form than the current "sequential tasks"
5162 // paradigm, the use of that persistent state will have to be
5163 // revisited and modified appropriately. See also related
5164 // bug 4756801 work on which should examine this code to make
5165 // sure that the changes there do not run counter to the
5166 // assumptions made here and necessary for correctness and
5167 // efficiency. Note also that this code might yield inefficient
5168 // behaviour in the case of very large objects that span one or
5169 // more work chunks. Such objects would potentially be scanned
5170 // several times redundantly. Work on 4756801 should try and
5171 // address that performance anomaly if at all possible. XXX
5172 MemRegion full_span = _collector->_span;
5173 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5174 CMSMarkStack* rs = &(_collector->_revisitStack); // shared
5175 MarkFromDirtyCardsClosure
5176 greyRescanClosure(_collector, full_span, // entire span of interest
5177 sp, bm, work_q, rs, cl);
5178
5179 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5180 assert(pst->valid(), "Uninitialized use?");
5181 int nth_task = 0;
5182 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5183 MemRegion span = sp->used_region();
5184 HeapWord* start_addr = span.start();
5185 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5186 alignment);
5187 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5188 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5189 start_addr, "Check alignment");
5190 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5191 chunk_size, "Check alignment");
5192
5193 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5194 // Having claimed the nth_task, compute corresponding mem-region,
5195 // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5196 // The alignment restriction ensures that we do not need any
5197 // synchronization with other gang-workers while setting or
5198 // clearing bits in thus chunk of the MUT.
5199 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5200 start_addr + (nth_task+1)*chunk_size);
5201 // The last chunk's end might be way beyond end of the
5202 // used region. In that case pull back appropriately.
5203 if (this_span.end() > end_addr) {
5204 this_span.set_end(end_addr);
5205 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5206 }
5207 // Iterate over the dirty cards covering this chunk, marking them
5208 // precleaned, and setting the corresponding bits in the mod union
5209 // table. Since we have been careful to partition at Card and MUT-word
5210 // boundaries no synchronization is needed between parallel threads.
5211 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5212 &modUnionClosure);
5213
5214 // Having transferred these marks into the modUnionTable,
5215 // rescan the marked objects on the dirty cards in the modUnionTable.
5216 // Even if this is at a synchronous collection, the initial marking
5217 // may have been done during an asynchronous collection so there
5218 // may be dirty bits in the mod-union table.
5219 _collector->_modUnionTable.dirty_range_iterate_clear(
5220 this_span, &greyRescanClosure);
5221 _collector->_modUnionTable.verifyNoOneBitsInRange(
5222 this_span.start(),
5223 this_span.end());
5224 }
5225 pst->all_tasks_completed(); // declare that i am done
5226 }
5227
5228 // . see if we can share work_queues with ParNew? XXX
5229 void
5230 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5231 int* seed) {
5232 OopTaskQueue* work_q = work_queue(i);
5233 NOT_PRODUCT(int num_steals = 0;)
5234 oop obj_to_scan;
5235 CMSBitMap* bm = &(_collector->_markBitMap);
5236
5237 while (true) {
5238 // Completely finish any left over work from (an) earlier round(s)
5239 cl->trim_queue(0);
5240 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5241 (size_t)ParGCDesiredObjsFromOverflowList);
5242 // Now check if there's any work in the overflow list
5243 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5244 work_q)) {
5245 // found something in global overflow list;
5246 // not yet ready to go stealing work from others.
5247 // We'd like to assert(work_q->size() != 0, ...)
5248 // because we just took work from the overflow list,
5249 // but of course we can't since all of that could have
5250 // been already stolen from us.
5251 // "He giveth and He taketh away."
5252 continue;
5253 }
5254 // Verify that we have no work before we resort to stealing
5255 assert(work_q->size() == 0, "Have work, shouldn't steal");
5256 // Try to steal from other queues that have work
5257 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5258 NOT_PRODUCT(num_steals++;)
5259 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5260 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5261 // Do scanning work
5262 obj_to_scan->oop_iterate(cl);
5263 // Loop around, finish this work, and try to steal some more
5264 } else if (terminator()->offer_termination()) {
5265 break; // nirvana from the infinite cycle
5266 }
5267 }
5268 NOT_PRODUCT(
5269 if (PrintCMSStatistics != 0) {
5270 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5271 }
5272 )
5273 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5274 "Else our work is not yet done");
5275 }
5276
5277 // Return a thread-local PLAB recording array, as appropriate.
5278 void* CMSCollector::get_data_recorder(int thr_num) {
5279 if (_survivor_plab_array != NULL &&
5280 (CMSPLABRecordAlways ||
5281 (_collectorState > Marking && _collectorState < FinalMarking))) {
5282 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5283 ChunkArray* ca = &_survivor_plab_array[thr_num];
5284 ca->reset(); // clear it so that fresh data is recorded
5285 return (void*) ca;
5286 } else {
5287 return NULL;
5288 }
5289 }
5290
5291 // Reset all the thread-local PLAB recording arrays
5292 void CMSCollector::reset_survivor_plab_arrays() {
5293 for (uint i = 0; i < ParallelGCThreads; i++) {
5294 _survivor_plab_array[i].reset();
5295 }
5296 }
5297
5298 // Merge the per-thread plab arrays into the global survivor chunk
5299 // array which will provide the partitioning of the survivor space
5300 // for CMS rescan.
5301 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv) {
5302 assert(_survivor_plab_array != NULL, "Error");
5303 assert(_survivor_chunk_array != NULL, "Error");
5304 assert(_collectorState == FinalMarking, "Error");
5305 for (uint j = 0; j < ParallelGCThreads; j++) {
5306 _cursor[j] = 0;
5307 }
5308 HeapWord* top = surv->top();
5309 size_t i;
5310 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5311 HeapWord* min_val = top; // Higher than any PLAB address
5312 uint min_tid = 0; // position of min_val this round
5313 for (uint j = 0; j < ParallelGCThreads; j++) {
5314 ChunkArray* cur_sca = &_survivor_plab_array[j];
5315 if (_cursor[j] == cur_sca->end()) {
5316 continue;
5317 }
5318 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5319 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5320 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5321 if (cur_val < min_val) {
5322 min_tid = j;
5323 min_val = cur_val;
5324 } else {
5325 assert(cur_val < top, "All recorded addresses should be less");
5326 }
5327 }
5328 // At this point min_val and min_tid are respectively
5329 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5330 // and the thread (j) that witnesses that address.
5331 // We record this address in the _survivor_chunk_array[i]
5332 // and increment _cursor[min_tid] prior to the next round i.
5333 if (min_val == top) {
5334 break;
5335 }
5336 _survivor_chunk_array[i] = min_val;
5337 _cursor[min_tid]++;
5338 }
5339 // We are all done; record the size of the _survivor_chunk_array
5340 _survivor_chunk_index = i; // exclusive: [0, i)
5341 if (PrintCMSStatistics > 0) {
5342 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5343 }
5344 // Verify that we used up all the recorded entries
5345 #ifdef ASSERT
5346 size_t total = 0;
5347 for (uint j = 0; j < ParallelGCThreads; j++) {
5348 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5349 total += _cursor[j];
5350 }
5351 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5352 // Check that the merged array is in sorted order
5353 if (total > 0) {
5354 for (size_t i = 0; i < total - 1; i++) {
5355 if (PrintCMSStatistics > 0) {
5356 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5357 i, _survivor_chunk_array[i]);
5358 }
5359 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5360 "Not sorted");
5361 }
5362 }
5363 #endif // ASSERT
5364 }
5365
5366 // Set up the space's par_seq_tasks structure for work claiming
5367 // for parallel rescan of young gen.
5368 // See ParRescanTask where this is currently used.
5369 void
5370 CMSCollector::
5371 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5372 assert(n_threads > 0, "Unexpected n_threads argument");
5373 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5374
5375 // Eden space
5376 {
5377 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5378 assert(!pst->valid(), "Clobbering existing data?");
5379 // Each valid entry in [0, _eden_chunk_index) represents a task.
5380 size_t n_tasks = _eden_chunk_index + 1;
5381 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5382 pst->set_par_threads(n_threads);
5383 pst->set_n_tasks((int)n_tasks);
5384 }
5385
5386 // Merge the survivor plab arrays into _survivor_chunk_array
5387 if (_survivor_plab_array != NULL) {
5388 merge_survivor_plab_arrays(dng->from());
5389 } else {
5390 assert(_survivor_chunk_index == 0, "Error");
5391 }
5392
5393 // To space
5394 {
5395 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5396 assert(!pst->valid(), "Clobbering existing data?");
5397 pst->set_par_threads(n_threads);
5398 pst->set_n_tasks(1);
5399 assert(pst->valid(), "Error");
5400 }
5401
5402 // From space
5403 {
5404 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5405 assert(!pst->valid(), "Clobbering existing data?");
5406 size_t n_tasks = _survivor_chunk_index + 1;
5407 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5408 pst->set_par_threads(n_threads);
5409 pst->set_n_tasks((int)n_tasks);
5410 assert(pst->valid(), "Error");
5411 }
5412 }
5413
5414 // Parallel version of remark
5415 void CMSCollector::do_remark_parallel() {
5416 GenCollectedHeap* gch = GenCollectedHeap::heap();
5417 WorkGang* workers = gch->workers();
5418 assert(workers != NULL, "Need parallel worker threads.");
5419 int n_workers = workers->total_workers();
5420 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5421 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
5422
5423 CMSParRemarkTask tsk(this,
5424 cms_space, perm_space,
5425 n_workers, workers, task_queues());
5426
5427 // Set up for parallel process_strong_roots work.
5428 gch->set_par_threads(n_workers);
5429 // We won't be iterating over the cards in the card table updating
5430 // the younger_gen cards, so we shouldn't call the following else
5431 // the verification code as well as subsequent younger_refs_iterate
5432 // code would get confused. XXX
5433 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5434
5435 // The young gen rescan work will not be done as part of
5436 // process_strong_roots (which currently doesn't knw how to
5437 // parallelize such a scan), but rather will be broken up into
5438 // a set of parallel tasks (via the sampling that the [abortable]
5439 // preclean phase did of EdenSpace, plus the [two] tasks of
5440 // scanning the [two] survivor spaces. Further fine-grain
5441 // parallelization of the scanning of the survivor spaces
5442 // themselves, and of precleaning of the younger gen itself
5443 // is deferred to the future.
5444 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5445
5446 // The dirty card rescan work is broken up into a "sequence"
5447 // of parallel tasks (per constituent space) that are dynamically
5448 // claimed by the parallel threads.
5449 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5450 perm_space->initialize_sequential_subtasks_for_rescan(n_workers);
5451
5452 // It turns out that even when we're using 1 thread, doing the work in a
5453 // separate thread causes wide variance in run times. We can't help this
5454 // in the multi-threaded case, but we special-case n=1 here to get
5455 // repeatable measurements of the 1-thread overhead of the parallel code.
5456 if (n_workers > 1) {
5457 // Make refs discovery MT-safe
5458 ReferenceProcessorMTMutator mt(ref_processor(), true);
5459 GenCollectedHeap::StrongRootsScope srs(gch);
5460 workers->run_task(&tsk);
5461 } else {
5462 GenCollectedHeap::StrongRootsScope srs(gch);
5463 tsk.work(0);
5464 }
5465 gch->set_par_threads(0); // 0 ==> non-parallel.
5466 // restore, single-threaded for now, any preserved marks
5467 // as a result of work_q overflow
5468 restore_preserved_marks_if_any();
5469 }
5470
5471 // Non-parallel version of remark
5472 void CMSCollector::do_remark_non_parallel() {
5473 ResourceMark rm;
5474 HandleMark hm;
5475 GenCollectedHeap* gch = GenCollectedHeap::heap();
5476 MarkRefsIntoAndScanClosure
5477 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
5478 &_markStack, &_revisitStack, this,
5479 false /* should_yield */, false /* not precleaning */);
5480 MarkFromDirtyCardsClosure
5481 markFromDirtyCardsClosure(this, _span,
5482 NULL, // space is set further below
5483 &_markBitMap, &_markStack, &_revisitStack,
5484 &mrias_cl);
5485 {
5486 TraceTime t("grey object rescan", PrintGCDetails, false, gclog_or_tty);
5487 // Iterate over the dirty cards, setting the corresponding bits in the
5488 // mod union table.
5489 {
5490 ModUnionClosure modUnionClosure(&_modUnionTable);
5491 _ct->ct_bs()->dirty_card_iterate(
5492 _cmsGen->used_region(),
5493 &modUnionClosure);
5494 _ct->ct_bs()->dirty_card_iterate(
5495 _permGen->used_region(),
5496 &modUnionClosure);
5497 }
5498 // Having transferred these marks into the modUnionTable, we just need
5499 // to rescan the marked objects on the dirty cards in the modUnionTable.
5500 // The initial marking may have been done during an asynchronous
5501 // collection so there may be dirty bits in the mod-union table.
5502 const int alignment =
5503 CardTableModRefBS::card_size * BitsPerWord;
5504 {
5505 // ... First handle dirty cards in CMS gen
5506 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5507 MemRegion ur = _cmsGen->used_region();
5508 HeapWord* lb = ur.start();
5509 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5510 MemRegion cms_span(lb, ub);
5511 _modUnionTable.dirty_range_iterate_clear(cms_span,
5512 &markFromDirtyCardsClosure);
5513 verify_work_stacks_empty();
5514 if (PrintCMSStatistics != 0) {
5515 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5516 markFromDirtyCardsClosure.num_dirty_cards());
5517 }
5518 }
5519 {
5520 // .. and then repeat for dirty cards in perm gen
5521 markFromDirtyCardsClosure.set_space(_permGen->cmsSpace());
5522 MemRegion ur = _permGen->used_region();
5523 HeapWord* lb = ur.start();
5524 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5525 MemRegion perm_span(lb, ub);
5526 _modUnionTable.dirty_range_iterate_clear(perm_span,
5527 &markFromDirtyCardsClosure);
5528 verify_work_stacks_empty();
5529 if (PrintCMSStatistics != 0) {
5530 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in perm gen) ",
5531 markFromDirtyCardsClosure.num_dirty_cards());
5532 }
5533 }
5534 }
5535 if (VerifyDuringGC &&
5536 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5537 HandleMark hm; // Discard invalid handles created during verification
5538 Universe::verify(true);
5539 }
5540 {
5541 TraceTime t("root rescan", PrintGCDetails, false, gclog_or_tty);
5542
5543 verify_work_stacks_empty();
5544
5545 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5546 GenCollectedHeap::StrongRootsScope srs(gch);
5547 gch->gen_process_strong_roots(_cmsGen->level(),
5548 true, // younger gens as roots
5549 false, // use the local StrongRootsScope
5550 true, // collecting perm gen
5551 SharedHeap::ScanningOption(roots_scanning_options()),
5552 &mrias_cl,
5553 true, // walk code active on stacks
5554 NULL);
5555 assert(should_unload_classes()
5556 || (roots_scanning_options() & SharedHeap::SO_CodeCache),
5557 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5558 }
5559 verify_work_stacks_empty();
5560 // Restore evacuated mark words, if any, used for overflow list links
5561 if (!CMSOverflowEarlyRestoration) {
5562 restore_preserved_marks_if_any();
5563 }
5564 verify_overflow_empty();
5565 }
5566
5567 ////////////////////////////////////////////////////////
5568 // Parallel Reference Processing Task Proxy Class
5569 ////////////////////////////////////////////////////////
5570 class CMSRefProcTaskProxy: public AbstractGangTask {
5571 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5572 CMSCollector* _collector;
5573 CMSBitMap* _mark_bit_map;
5574 const MemRegion _span;
5575 OopTaskQueueSet* _task_queues;
5576 ParallelTaskTerminator _term;
5577 ProcessTask& _task;
5578
5579 public:
5580 CMSRefProcTaskProxy(ProcessTask& task,
5581 CMSCollector* collector,
5582 const MemRegion& span,
5583 CMSBitMap* mark_bit_map,
5584 int total_workers,
5585 OopTaskQueueSet* task_queues):
5586 AbstractGangTask("Process referents by policy in parallel"),
5587 _task(task),
5588 _collector(collector), _span(span), _mark_bit_map(mark_bit_map),
5589 _task_queues(task_queues),
5590 _term(total_workers, task_queues)
5591 {
5592 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5593 "Inconsistency in _span");
5594 }
5595
5596 OopTaskQueueSet* task_queues() { return _task_queues; }
5597
5598 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5599
5600 ParallelTaskTerminator* terminator() { return &_term; }
5601
5602 void do_work_steal(int i,
5603 CMSParDrainMarkingStackClosure* drain,
5604 CMSParKeepAliveClosure* keep_alive,
5605 int* seed);
5606
5607 virtual void work(int i);
5608 };
5609
5610 void CMSRefProcTaskProxy::work(int i) {
5611 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5612 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5613 _mark_bit_map,
5614 &_collector->_revisitStack,
5615 work_queue(i));
5616 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5617 _mark_bit_map,
5618 &_collector->_revisitStack,
5619 work_queue(i));
5620 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5621 _task.work(i, is_alive_closure, par_keep_alive, par_drain_stack);
5622 if (_task.marks_oops_alive()) {
5623 do_work_steal(i, &par_drain_stack, &par_keep_alive,
5624 _collector->hash_seed(i));
5625 }
5626 assert(work_queue(i)->size() == 0, "work_queue should be empty");
5627 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5628 }
5629
5630 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5631 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5632 EnqueueTask& _task;
5633
5634 public:
5635 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5636 : AbstractGangTask("Enqueue reference objects in parallel"),
5637 _task(task)
5638 { }
5639
5640 virtual void work(int i)
5641 {
5642 _task.work(i);
5643 }
5644 };
5645
5646 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5647 MemRegion span, CMSBitMap* bit_map, CMSMarkStack* revisit_stack,
5648 OopTaskQueue* work_queue):
5649 Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
5650 _span(span),
5651 _bit_map(bit_map),
5652 _work_queue(work_queue),
5653 _mark_and_push(collector, span, bit_map, revisit_stack, work_queue),
5654 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5655 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5656 { }
5657
5658 // . see if we can share work_queues with ParNew? XXX
5659 void CMSRefProcTaskProxy::do_work_steal(int i,
5660 CMSParDrainMarkingStackClosure* drain,
5661 CMSParKeepAliveClosure* keep_alive,
5662 int* seed) {
5663 OopTaskQueue* work_q = work_queue(i);
5664 NOT_PRODUCT(int num_steals = 0;)
5665 oop obj_to_scan;
5666
5667 while (true) {
5668 // Completely finish any left over work from (an) earlier round(s)
5669 drain->trim_queue(0);
5670 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5671 (size_t)ParGCDesiredObjsFromOverflowList);
5672 // Now check if there's any work in the overflow list
5673 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5674 work_q)) {
5675 // Found something in global overflow list;
5676 // not yet ready to go stealing work from others.
5677 // We'd like to assert(work_q->size() != 0, ...)
5678 // because we just took work from the overflow list,
5679 // but of course we can't, since all of that might have
5680 // been already stolen from us.
5681 continue;
5682 }
5683 // Verify that we have no work before we resort to stealing
5684 assert(work_q->size() == 0, "Have work, shouldn't steal");
5685 // Try to steal from other queues that have work
5686 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5687 NOT_PRODUCT(num_steals++;)
5688 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5689 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5690 // Do scanning work
5691 obj_to_scan->oop_iterate(keep_alive);
5692 // Loop around, finish this work, and try to steal some more
5693 } else if (terminator()->offer_termination()) {
5694 break; // nirvana from the infinite cycle
5695 }
5696 }
5697 NOT_PRODUCT(
5698 if (PrintCMSStatistics != 0) {
5699 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5700 }
5701 )
5702 }
5703
5704 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5705 {
5706 GenCollectedHeap* gch = GenCollectedHeap::heap();
5707 WorkGang* workers = gch->workers();
5708 assert(workers != NULL, "Need parallel worker threads.");
5709 int n_workers = workers->total_workers();
5710 CMSRefProcTaskProxy rp_task(task, &_collector,
5711 _collector.ref_processor()->span(),
5712 _collector.markBitMap(),
5713 n_workers, _collector.task_queues());
5714 workers->run_task(&rp_task);
5715 }
5716
5717 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5718 {
5719
5720 GenCollectedHeap* gch = GenCollectedHeap::heap();
5721 WorkGang* workers = gch->workers();
5722 assert(workers != NULL, "Need parallel worker threads.");
5723 CMSRefEnqueueTaskProxy enq_task(task);
5724 workers->run_task(&enq_task);
5725 }
5726
5727 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5728
5729 ResourceMark rm;
5730 HandleMark hm;
5731
5732 ReferenceProcessor* rp = ref_processor();
5733 assert(rp->span().equals(_span), "Spans should be equal");
5734 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5735 // Process weak references.
5736 rp->setup_policy(clear_all_soft_refs);
5737 verify_work_stacks_empty();
5738
5739 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5740 &_markStack, &_revisitStack,
5741 false /* !preclean */);
5742 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5743 _span, &_markBitMap, &_markStack,
5744 &cmsKeepAliveClosure, false /* !preclean */);
5745 {
5746 TraceTime t("weak refs processing", PrintGCDetails, false, gclog_or_tty);
5747 if (rp->processing_is_mt()) {
5748 CMSRefProcTaskExecutor task_executor(*this);
5749 rp->process_discovered_references(&_is_alive_closure,
5750 &cmsKeepAliveClosure,
5751 &cmsDrainMarkingStackClosure,
5752 &task_executor);
5753 } else {
5754 rp->process_discovered_references(&_is_alive_closure,
5755 &cmsKeepAliveClosure,
5756 &cmsDrainMarkingStackClosure,
5757 NULL);
5758 }
5759 verify_work_stacks_empty();
5760 }
5761
5762 if (should_unload_classes()) {
5763 {
5764 TraceTime t("class unloading", PrintGCDetails, false, gclog_or_tty);
5765
5766 // Follow SystemDictionary roots and unload classes
5767 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5768
5769 // Follow CodeCache roots and unload any methods marked for unloading
5770 CodeCache::do_unloading(&_is_alive_closure,
5771 &cmsKeepAliveClosure,
5772 purged_class);
5773
5774 cmsDrainMarkingStackClosure.do_void();
5775 verify_work_stacks_empty();
5776
5777 // Update subklass/sibling/implementor links in KlassKlass descendants
5778 assert(!_revisitStack.isEmpty(), "revisit stack should not be empty");
5779 oop k;
5780 while ((k = _revisitStack.pop()) != NULL) {
5781 ((Klass*)(oopDesc*)k)->follow_weak_klass_links(
5782 &_is_alive_closure,
5783 &cmsKeepAliveClosure);
5784 }
5785 assert(!ClassUnloading ||
5786 (_markStack.isEmpty() && overflow_list_is_empty()),
5787 "Should not have found new reachable objects");
5788 assert(_revisitStack.isEmpty(), "revisit stack should have been drained");
5789 cmsDrainMarkingStackClosure.do_void();
5790 verify_work_stacks_empty();
5791 }
5792
5793 {
5794 TraceTime t("scrub symbol & string tables", PrintGCDetails, false, gclog_or_tty);
5795 // Now clean up stale oops in SymbolTable and StringTable
5796 SymbolTable::unlink(&_is_alive_closure);
5797 StringTable::unlink(&_is_alive_closure);
5798 }
5799 }
5800
5801 verify_work_stacks_empty();
5802 // Restore any preserved marks as a result of mark stack or
5803 // work queue overflow
5804 restore_preserved_marks_if_any(); // done single-threaded for now
5805
5806 rp->set_enqueuing_is_done(true);
5807 if (rp->processing_is_mt()) {
5808 CMSRefProcTaskExecutor task_executor(*this);
5809 rp->enqueue_discovered_references(&task_executor);
5810 } else {
5811 rp->enqueue_discovered_references(NULL);
5812 }
5813 rp->verify_no_references_recorded();
5814 assert(!rp->discovery_enabled(), "should have been disabled");
5815
5816 // JVMTI object tagging is based on JNI weak refs. If any of these
5817 // refs were cleared then JVMTI needs to update its maps and
5818 // maybe post ObjectFrees to agents.
5819 JvmtiExport::cms_ref_processing_epilogue();
5820 }
5821
5822 #ifndef PRODUCT
5823 void CMSCollector::check_correct_thread_executing() {
5824 Thread* t = Thread::current();
5825 // Only the VM thread or the CMS thread should be here.
5826 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5827 "Unexpected thread type");
5828 // If this is the vm thread, the foreground process
5829 // should not be waiting. Note that _foregroundGCIsActive is
5830 // true while the foreground collector is waiting.
5831 if (_foregroundGCShouldWait) {
5832 // We cannot be the VM thread
5833 assert(t->is_ConcurrentGC_thread(),
5834 "Should be CMS thread");
5835 } else {
5836 // We can be the CMS thread only if we are in a stop-world
5837 // phase of CMS collection.
5838 if (t->is_ConcurrentGC_thread()) {
5839 assert(_collectorState == InitialMarking ||
5840 _collectorState == FinalMarking,
5841 "Should be a stop-world phase");
5842 // The CMS thread should be holding the CMS_token.
5843 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5844 "Potential interference with concurrently "
5845 "executing VM thread");
5846 }
5847 }
5848 }
5849 #endif
5850
5851 void CMSCollector::sweep(bool asynch) {
5852 assert(_collectorState == Sweeping, "just checking");
5853 check_correct_thread_executing();
5854 verify_work_stacks_empty();
5855 verify_overflow_empty();
5856 increment_sweep_count();
5857 _inter_sweep_timer.stop();
5858 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5859 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
5860
5861 // PermGen verification support: If perm gen sweeping is disabled in
5862 // this cycle, we preserve the perm gen object "deadness" information
5863 // in the perm_gen_verify_bit_map. In order to do that we traverse
5864 // all blocks in perm gen and mark all dead objects.
5865 if (verifying() && !should_unload_classes()) {
5866 assert(perm_gen_verify_bit_map()->sizeInBits() != 0,
5867 "Should have already been allocated");
5868 MarkDeadObjectsClosure mdo(this, _permGen->cmsSpace(),
5869 markBitMap(), perm_gen_verify_bit_map());
5870 if (asynch) {
5871 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
5872 bitMapLock());
5873 _permGen->cmsSpace()->blk_iterate(&mdo);
5874 } else {
5875 // In the case of synchronous sweep, we already have
5876 // the requisite locks/tokens.
5877 _permGen->cmsSpace()->blk_iterate(&mdo);
5878 }
5879 }
5880
5881 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5882 _intra_sweep_timer.reset();
5883 _intra_sweep_timer.start();
5884 if (asynch) {
5885 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5886 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
5887 // First sweep the old gen then the perm gen
5888 {
5889 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5890 bitMapLock());
5891 sweepWork(_cmsGen, asynch);
5892 }
5893
5894 // Now repeat for perm gen
5895 if (should_unload_classes()) {
5896 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
5897 bitMapLock());
5898 sweepWork(_permGen, asynch);
5899 }
5900
5901 // Update Universe::_heap_*_at_gc figures.
5902 // We need all the free list locks to make the abstract state
5903 // transition from Sweeping to Resetting. See detailed note
5904 // further below.
5905 {
5906 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5907 _permGen->freelistLock());
5908 // Update heap occupancy information which is used as
5909 // input to soft ref clearing policy at the next gc.
5910 Universe::update_heap_info_at_gc();
5911 _collectorState = Resizing;
5912 }
5913 } else {
5914 // already have needed locks
5915 sweepWork(_cmsGen, asynch);
5916
5917 if (should_unload_classes()) {
5918 sweepWork(_permGen, asynch);
5919 }
5920 // Update heap occupancy information which is used as
5921 // input to soft ref clearing policy at the next gc.
5922 Universe::update_heap_info_at_gc();
5923 _collectorState = Resizing;
5924 }
5925 verify_work_stacks_empty();
5926 verify_overflow_empty();
5927
5928 _intra_sweep_timer.stop();
5929 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5930
5931 _inter_sweep_timer.reset();
5932 _inter_sweep_timer.start();
5933
5934 update_time_of_last_gc(os::javaTimeMillis());
5935
5936 // NOTE on abstract state transitions:
5937 // Mutators allocate-live and/or mark the mod-union table dirty
5938 // based on the state of the collection. The former is done in
5939 // the interval [Marking, Sweeping] and the latter in the interval
5940 // [Marking, Sweeping). Thus the transitions into the Marking state
5941 // and out of the Sweeping state must be synchronously visible
5942 // globally to the mutators.
5943 // The transition into the Marking state happens with the world
5944 // stopped so the mutators will globally see it. Sweeping is
5945 // done asynchronously by the background collector so the transition
5946 // from the Sweeping state to the Resizing state must be done
5947 // under the freelistLock (as is the check for whether to
5948 // allocate-live and whether to dirty the mod-union table).
5949 assert(_collectorState == Resizing, "Change of collector state to"
5950 " Resizing must be done under the freelistLocks (plural)");
5951
5952 // Now that sweeping has been completed, if the GCH's
5953 // incremental_collection_will_fail flag is set, clear it,
5954 // thus inviting a younger gen collection to promote into
5955 // this generation. If such a promotion may still fail,
5956 // the flag will be set again when a young collection is
5957 // attempted.
5958 // I think the incremental_collection_will_fail flag's use
5959 // is specific to a 2 generation collection policy, so i'll
5960 // assert that that's the configuration we are operating within.
5961 // The use of the flag can and should be generalized appropriately
5962 // in the future to deal with a general n-generation system.
5963
5964 GenCollectedHeap* gch = GenCollectedHeap::heap();
5965 assert(gch->collector_policy()->is_two_generation_policy(),
5966 "Resetting of incremental_collection_will_fail flag"
5967 " may be incorrect otherwise");
5968 gch->clear_incremental_collection_will_fail();
5969 gch->update_full_collections_completed(_collection_count_start);
5970 }
5971
5972 // FIX ME!!! Looks like this belongs in CFLSpace, with
5973 // CMSGen merely delegating to it.
5974 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5975 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5976 HeapWord* minAddr = _cmsSpace->bottom();
5977 HeapWord* largestAddr =
5978 (HeapWord*) _cmsSpace->dictionary()->findLargestDict();
5979 if (largestAddr == NULL) {
5980 // The dictionary appears to be empty. In this case
5981 // try to coalesce at the end of the heap.
5982 largestAddr = _cmsSpace->end();
5983 }
5984 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5985 size_t nearLargestOffset =
5986 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5987 if (PrintFLSStatistics != 0) {
5988 gclog_or_tty->print_cr(
5989 "CMS: Large Block: " PTR_FORMAT ";"
5990 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5991 largestAddr,
5992 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
5993 }
5994 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5995 }
5996
5997 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5998 return addr >= _cmsSpace->nearLargestChunk();
5999 }
6000
6001 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6002 return _cmsSpace->find_chunk_at_end();
6003 }
6004
6005 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6006 bool full) {
6007 // The next lower level has been collected. Gather any statistics
6008 // that are of interest at this point.
6009 if (!full && (current_level + 1) == level()) {
6010 // Gather statistics on the young generation collection.
6011 collector()->stats().record_gc0_end(used());
6012 }
6013 }
6014
6015 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6016 GenCollectedHeap* gch = GenCollectedHeap::heap();
6017 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6018 "Wrong type of heap");
6019 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6020 gch->gen_policy()->size_policy();
6021 assert(sp->is_gc_cms_adaptive_size_policy(),
6022 "Wrong type of size policy");
6023 return sp;
6024 }
6025
6026 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6027 if (PrintGCDetails && Verbose) {
6028 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6029 }
6030 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6031 _debug_collection_type =
6032 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6033 if (PrintGCDetails && Verbose) {
6034 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6035 }
6036 }
6037
6038 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6039 bool asynch) {
6040 // We iterate over the space(s) underlying this generation,
6041 // checking the mark bit map to see if the bits corresponding
6042 // to specific blocks are marked or not. Blocks that are
6043 // marked are live and are not swept up. All remaining blocks
6044 // are swept up, with coalescing on-the-fly as we sweep up
6045 // contiguous free and/or garbage blocks:
6046 // We need to ensure that the sweeper synchronizes with allocators
6047 // and stop-the-world collectors. In particular, the following
6048 // locks are used:
6049 // . CMS token: if this is held, a stop the world collection cannot occur
6050 // . freelistLock: if this is held no allocation can occur from this
6051 // generation by another thread
6052 // . bitMapLock: if this is held, no other thread can access or update
6053 //
6054
6055 // Note that we need to hold the freelistLock if we use
6056 // block iterate below; else the iterator might go awry if
6057 // a mutator (or promotion) causes block contents to change
6058 // (for instance if the allocator divvies up a block).
6059 // If we hold the free list lock, for all practical purposes
6060 // young generation GC's can't occur (they'll usually need to
6061 // promote), so we might as well prevent all young generation
6062 // GC's while we do a sweeping step. For the same reason, we might
6063 // as well take the bit map lock for the entire duration
6064
6065 // check that we hold the requisite locks
6066 assert(have_cms_token(), "Should hold cms token");
6067 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6068 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6069 "Should possess CMS token to sweep");
6070 assert_lock_strong(gen->freelistLock());
6071 assert_lock_strong(bitMapLock());
6072
6073 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6074 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6075 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6076 _inter_sweep_estimate.padded_average(),
6077 _intra_sweep_estimate.padded_average());
6078 gen->setNearLargestChunk();
6079
6080 {
6081 SweepClosure sweepClosure(this, gen, &_markBitMap,
6082 CMSYield && asynch);
6083 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6084 // We need to free-up/coalesce garbage/blocks from a
6085 // co-terminal free run. This is done in the SweepClosure
6086 // destructor; so, do not remove this scope, else the
6087 // end-of-sweep-census below will be off by a little bit.
6088 }
6089 gen->cmsSpace()->sweep_completed();
6090 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6091 if (should_unload_classes()) { // unloaded classes this cycle,
6092 _concurrent_cycles_since_last_unload = 0; // ... reset count
6093 } else { // did not unload classes,
6094 _concurrent_cycles_since_last_unload++; // ... increment count
6095 }
6096 }
6097
6098 // Reset CMS data structures (for now just the marking bit map)
6099 // preparatory for the next cycle.
6100 void CMSCollector::reset(bool asynch) {
6101 GenCollectedHeap* gch = GenCollectedHeap::heap();
6102 CMSAdaptiveSizePolicy* sp = size_policy();
6103 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6104 if (asynch) {
6105 CMSTokenSyncWithLocks ts(true, bitMapLock());
6106
6107 // If the state is not "Resetting", the foreground thread
6108 // has done a collection and the resetting.
6109 if (_collectorState != Resetting) {
6110 assert(_collectorState == Idling, "The state should only change"
6111 " because the foreground collector has finished the collection");
6112 return;
6113 }
6114
6115 // Clear the mark bitmap (no grey objects to start with)
6116 // for the next cycle.
6117 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6118 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6119
6120 HeapWord* curAddr = _markBitMap.startWord();
6121 while (curAddr < _markBitMap.endWord()) {
6122 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6123 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6124 _markBitMap.clear_large_range(chunk);
6125 if (ConcurrentMarkSweepThread::should_yield() &&
6126 !foregroundGCIsActive() &&
6127 CMSYield) {
6128 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6129 "CMS thread should hold CMS token");
6130 assert_lock_strong(bitMapLock());
6131 bitMapLock()->unlock();
6132 ConcurrentMarkSweepThread::desynchronize(true);
6133 ConcurrentMarkSweepThread::acknowledge_yield_request();
6134 stopTimer();
6135 if (PrintCMSStatistics != 0) {
6136 incrementYields();
6137 }
6138 icms_wait();
6139
6140 // See the comment in coordinator_yield()
6141 for (unsigned i = 0; i < CMSYieldSleepCount &&
6142 ConcurrentMarkSweepThread::should_yield() &&
6143 !CMSCollector::foregroundGCIsActive(); ++i) {
6144 os::sleep(Thread::current(), 1, false);
6145 ConcurrentMarkSweepThread::acknowledge_yield_request();
6146 }
6147
6148 ConcurrentMarkSweepThread::synchronize(true);
6149 bitMapLock()->lock_without_safepoint_check();
6150 startTimer();
6151 }
6152 curAddr = chunk.end();
6153 }
6154 // A successful mostly concurrent collection has been done.
6155 // Because only the full (i.e., concurrent mode failure) collections
6156 // are being measured for gc overhead limits, clean the "near" flag
6157 // and count.
6158 sp->reset_gc_overhead_limit_count();
6159 _collectorState = Idling;
6160 } else {
6161 // already have the lock
6162 assert(_collectorState == Resetting, "just checking");
6163 assert_lock_strong(bitMapLock());
6164 _markBitMap.clear_all();
6165 _collectorState = Idling;
6166 }
6167
6168 // Stop incremental mode after a cycle completes, so that any future cycles
6169 // are triggered by allocation.
6170 stop_icms();
6171
6172 NOT_PRODUCT(
6173 if (RotateCMSCollectionTypes) {
6174 _cmsGen->rotate_debug_collection_type();
6175 }
6176 )
6177 }
6178
6179 void CMSCollector::do_CMS_operation(CMS_op_type op) {
6180 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6181 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6182 TraceTime t("GC", PrintGC, !PrintGCDetails, gclog_or_tty);
6183 TraceCollectorStats tcs(counters());
6184
6185 switch (op) {
6186 case CMS_op_checkpointRootsInitial: {
6187 checkpointRootsInitial(true); // asynch
6188 if (PrintGC) {
6189 _cmsGen->printOccupancy("initial-mark");
6190 }
6191 break;
6192 }
6193 case CMS_op_checkpointRootsFinal: {
6194 checkpointRootsFinal(true, // asynch
6195 false, // !clear_all_soft_refs
6196 false); // !init_mark_was_synchronous
6197 if (PrintGC) {
6198 _cmsGen->printOccupancy("remark");
6199 }
6200 break;
6201 }
6202 default:
6203 fatal("No such CMS_op");
6204 }
6205 }
6206
6207 #ifndef PRODUCT
6208 size_t const CMSCollector::skip_header_HeapWords() {
6209 return FreeChunk::header_size();
6210 }
6211
6212 // Try and collect here conditions that should hold when
6213 // CMS thread is exiting. The idea is that the foreground GC
6214 // thread should not be blocked if it wants to terminate
6215 // the CMS thread and yet continue to run the VM for a while
6216 // after that.
6217 void CMSCollector::verify_ok_to_terminate() const {
6218 assert(Thread::current()->is_ConcurrentGC_thread(),
6219 "should be called by CMS thread");
6220 assert(!_foregroundGCShouldWait, "should be false");
6221 // We could check here that all the various low-level locks
6222 // are not held by the CMS thread, but that is overkill; see
6223 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6224 // is checked.
6225 }
6226 #endif
6227
6228 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6229 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6230 "missing Printezis mark?");
6231 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6232 size_t size = pointer_delta(nextOneAddr + 1, addr);
6233 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6234 "alignment problem");
6235 assert(size >= 3, "Necessary for Printezis marks to work");
6236 return size;
6237 }
6238
6239 // A variant of the above (block_size_using_printezis_bits()) except
6240 // that we return 0 if the P-bits are not yet set.
6241 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6242 if (_markBitMap.isMarked(addr)) {
6243 assert(_markBitMap.isMarked(addr + 1), "Missing Printezis bit?");
6244 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6245 size_t size = pointer_delta(nextOneAddr + 1, addr);
6246 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6247 "alignment problem");
6248 assert(size >= 3, "Necessary for Printezis marks to work");
6249 return size;
6250 } else {
6251 assert(!_markBitMap.isMarked(addr + 1), "Bit map inconsistency?");
6252 return 0;
6253 }
6254 }
6255
6256 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6257 size_t sz = 0;
6258 oop p = (oop)addr;
6259 if (p->klass_or_null() != NULL && p->is_parsable()) {
6260 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6261 } else {
6262 sz = block_size_using_printezis_bits(addr);
6263 }
6264 assert(sz > 0, "size must be nonzero");
6265 HeapWord* next_block = addr + sz;
6266 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6267 CardTableModRefBS::card_size);
6268 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6269 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6270 "must be different cards");
6271 return next_card;
6272 }
6273
6274
6275 // CMS Bit Map Wrapper /////////////////////////////////////////
6276
6277 // Construct a CMS bit map infrastructure, but don't create the
6278 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6279 // further below.
6280 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6281 _bm(),
6282 _shifter(shifter),
6283 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6284 {
6285 _bmStartWord = 0;
6286 _bmWordSize = 0;
6287 }
6288
6289 bool CMSBitMap::allocate(MemRegion mr) {
6290 _bmStartWord = mr.start();
6291 _bmWordSize = mr.word_size();
6292 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6293 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6294 if (!brs.is_reserved()) {
6295 warning("CMS bit map allocation failure");
6296 return false;
6297 }
6298 // For now we'll just commit all of the bit map up fromt.
6299 // Later on we'll try to be more parsimonious with swap.
6300 if (!_virtual_space.initialize(brs, brs.size())) {
6301 warning("CMS bit map backing store failure");
6302 return false;
6303 }
6304 assert(_virtual_space.committed_size() == brs.size(),
6305 "didn't reserve backing store for all of CMS bit map?");
6306 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6307 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6308 _bmWordSize, "inconsistency in bit map sizing");
6309 _bm.set_size(_bmWordSize >> _shifter);
6310
6311 // bm.clear(); // can we rely on getting zero'd memory? verify below
6312 assert(isAllClear(),
6313 "Expected zero'd memory from ReservedSpace constructor");
6314 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6315 "consistency check");
6316 return true;
6317 }
6318
6319 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6320 HeapWord *next_addr, *end_addr, *last_addr;
6321 assert_locked();
6322 assert(covers(mr), "out-of-range error");
6323 // XXX assert that start and end are appropriately aligned
6324 for (next_addr = mr.start(), end_addr = mr.end();
6325 next_addr < end_addr; next_addr = last_addr) {
6326 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6327 last_addr = dirty_region.end();
6328 if (!dirty_region.is_empty()) {
6329 cl->do_MemRegion(dirty_region);
6330 } else {
6331 assert(last_addr == end_addr, "program logic");
6332 return;
6333 }
6334 }
6335 }
6336
6337 #ifndef PRODUCT
6338 void CMSBitMap::assert_locked() const {
6339 CMSLockVerifier::assert_locked(lock());
6340 }
6341
6342 bool CMSBitMap::covers(MemRegion mr) const {
6343 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6344 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6345 "size inconsistency");
6346 return (mr.start() >= _bmStartWord) &&
6347 (mr.end() <= endWord());
6348 }
6349
6350 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6351 return (start >= _bmStartWord && (start + size) <= endWord());
6352 }
6353
6354 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6355 // verify that there are no 1 bits in the interval [left, right)
6356 FalseBitMapClosure falseBitMapClosure;
6357 iterate(&falseBitMapClosure, left, right);
6358 }
6359
6360 void CMSBitMap::region_invariant(MemRegion mr)
6361 {
6362 assert_locked();
6363 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6364 assert(!mr.is_empty(), "unexpected empty region");
6365 assert(covers(mr), "mr should be covered by bit map");
6366 // convert address range into offset range
6367 size_t start_ofs = heapWordToOffset(mr.start());
6368 // Make sure that end() is appropriately aligned
6369 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6370 (1 << (_shifter+LogHeapWordSize))),
6371 "Misaligned mr.end()");
6372 size_t end_ofs = heapWordToOffset(mr.end());
6373 assert(end_ofs > start_ofs, "Should mark at least one bit");
6374 }
6375
6376 #endif
6377
6378 bool CMSMarkStack::allocate(size_t size) {
6379 // allocate a stack of the requisite depth
6380 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6381 size * sizeof(oop)));
6382 if (!rs.is_reserved()) {
6383 warning("CMSMarkStack allocation failure");
6384 return false;
6385 }
6386 if (!_virtual_space.initialize(rs, rs.size())) {
6387 warning("CMSMarkStack backing store failure");
6388 return false;
6389 }
6390 assert(_virtual_space.committed_size() == rs.size(),
6391 "didn't reserve backing store for all of CMS stack?");
6392 _base = (oop*)(_virtual_space.low());
6393 _index = 0;
6394 _capacity = size;
6395 NOT_PRODUCT(_max_depth = 0);
6396 return true;
6397 }
6398
6399 // XXX FIX ME !!! In the MT case we come in here holding a
6400 // leaf lock. For printing we need to take a further lock
6401 // which has lower rank. We need to recallibrate the two
6402 // lock-ranks involved in order to be able to rpint the
6403 // messages below. (Or defer the printing to the caller.
6404 // For now we take the expedient path of just disabling the
6405 // messages for the problematic case.)
6406 void CMSMarkStack::expand() {
6407 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6408 if (_capacity == MarkStackSizeMax) {
6409 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6410 // We print a warning message only once per CMS cycle.
6411 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6412 }
6413 return;
6414 }
6415 // Double capacity if possible
6416 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6417 // Do not give up existing stack until we have managed to
6418 // get the double capacity that we desired.
6419 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6420 new_capacity * sizeof(oop)));
6421 if (rs.is_reserved()) {
6422 // Release the backing store associated with old stack
6423 _virtual_space.release();
6424 // Reinitialize virtual space for new stack
6425 if (!_virtual_space.initialize(rs, rs.size())) {
6426 fatal("Not enough swap for expanded marking stack");
6427 }
6428 _base = (oop*)(_virtual_space.low());
6429 _index = 0;
6430 _capacity = new_capacity;
6431 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6432 // Failed to double capacity, continue;
6433 // we print a detail message only once per CMS cycle.
6434 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6435 SIZE_FORMAT"K",
6436 _capacity / K, new_capacity / K);
6437 }
6438 }
6439
6440
6441 // Closures
6442 // XXX: there seems to be a lot of code duplication here;
6443 // should refactor and consolidate common code.
6444
6445 // This closure is used to mark refs into the CMS generation in
6446 // the CMS bit map. Called at the first checkpoint. This closure
6447 // assumes that we do not need to re-mark dirty cards; if the CMS
6448 // generation on which this is used is not an oldest (modulo perm gen)
6449 // generation then this will lose younger_gen cards!
6450
6451 MarkRefsIntoClosure::MarkRefsIntoClosure(
6452 MemRegion span, CMSBitMap* bitMap):
6453 _span(span),
6454 _bitMap(bitMap)
6455 {
6456 assert(_ref_processor == NULL, "deliberately left NULL");
6457 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6458 }
6459
6460 void MarkRefsIntoClosure::do_oop(oop obj) {
6461 // if p points into _span, then mark corresponding bit in _markBitMap
6462 assert(obj->is_oop(), "expected an oop");
6463 HeapWord* addr = (HeapWord*)obj;
6464 if (_span.contains(addr)) {
6465 // this should be made more efficient
6466 _bitMap->mark(addr);
6467 }
6468 }
6469
6470 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6471 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6472
6473 // A variant of the above, used for CMS marking verification.
6474 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6475 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6476 _span(span),
6477 _verification_bm(verification_bm),
6478 _cms_bm(cms_bm)
6479 {
6480 assert(_ref_processor == NULL, "deliberately left NULL");
6481 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6482 }
6483
6484 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6485 // if p points into _span, then mark corresponding bit in _markBitMap
6486 assert(obj->is_oop(), "expected an oop");
6487 HeapWord* addr = (HeapWord*)obj;
6488 if (_span.contains(addr)) {
6489 _verification_bm->mark(addr);
6490 if (!_cms_bm->isMarked(addr)) {
6491 oop(addr)->print();
6492 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6493 fatal("... aborting");
6494 }
6495 }
6496 }
6497
6498 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6499 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6500
6501 //////////////////////////////////////////////////
6502 // MarkRefsIntoAndScanClosure
6503 //////////////////////////////////////////////////
6504
6505 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6506 ReferenceProcessor* rp,
6507 CMSBitMap* bit_map,
6508 CMSBitMap* mod_union_table,
6509 CMSMarkStack* mark_stack,
6510 CMSMarkStack* revisit_stack,
6511 CMSCollector* collector,
6512 bool should_yield,
6513 bool concurrent_precleaning):
6514 _collector(collector),
6515 _span(span),
6516 _bit_map(bit_map),
6517 _mark_stack(mark_stack),
6518 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6519 mark_stack, revisit_stack, concurrent_precleaning),
6520 _yield(should_yield),
6521 _concurrent_precleaning(concurrent_precleaning),
6522 _freelistLock(NULL)
6523 {
6524 _ref_processor = rp;
6525 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6526 }
6527
6528 // This closure is used to mark refs into the CMS generation at the
6529 // second (final) checkpoint, and to scan and transitively follow
6530 // the unmarked oops. It is also used during the concurrent precleaning
6531 // phase while scanning objects on dirty cards in the CMS generation.
6532 // The marks are made in the marking bit map and the marking stack is
6533 // used for keeping the (newly) grey objects during the scan.
6534 // The parallel version (Par_...) appears further below.
6535 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6536 if (obj != NULL) {
6537 assert(obj->is_oop(), "expected an oop");
6538 HeapWord* addr = (HeapWord*)obj;
6539 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6540 assert(_collector->overflow_list_is_empty(),
6541 "overflow list should be empty");
6542 if (_span.contains(addr) &&
6543 !_bit_map->isMarked(addr)) {
6544 // mark bit map (object is now grey)
6545 _bit_map->mark(addr);
6546 // push on marking stack (stack should be empty), and drain the
6547 // stack by applying this closure to the oops in the oops popped
6548 // from the stack (i.e. blacken the grey objects)
6549 bool res = _mark_stack->push(obj);
6550 assert(res, "Should have space to push on empty stack");
6551 do {
6552 oop new_oop = _mark_stack->pop();
6553 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6554 assert(new_oop->is_parsable(), "Found unparsable oop");
6555 assert(_bit_map->isMarked((HeapWord*)new_oop),
6556 "only grey objects on this stack");
6557 // iterate over the oops in this oop, marking and pushing
6558 // the ones in CMS heap (i.e. in _span).
6559 new_oop->oop_iterate(&_pushAndMarkClosure);
6560 // check if it's time to yield
6561 do_yield_check();
6562 } while (!_mark_stack->isEmpty() ||
6563 (!_concurrent_precleaning && take_from_overflow_list()));
6564 // if marking stack is empty, and we are not doing this
6565 // during precleaning, then check the overflow list
6566 }
6567 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6568 assert(_collector->overflow_list_is_empty(),
6569 "overflow list was drained above");
6570 // We could restore evacuated mark words, if any, used for
6571 // overflow list links here because the overflow list is
6572 // provably empty here. That would reduce the maximum
6573 // size requirements for preserved_{oop,mark}_stack.
6574 // But we'll just postpone it until we are all done
6575 // so we can just stream through.
6576 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6577 _collector->restore_preserved_marks_if_any();
6578 assert(_collector->no_preserved_marks(), "No preserved marks");
6579 }
6580 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6581 "All preserved marks should have been restored above");
6582 }
6583 }
6584
6585 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6586 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6587
6588 void MarkRefsIntoAndScanClosure::do_yield_work() {
6589 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6590 "CMS thread should hold CMS token");
6591 assert_lock_strong(_freelistLock);
6592 assert_lock_strong(_bit_map->lock());
6593 // relinquish the free_list_lock and bitMaplock()
6594 DEBUG_ONLY(RememberKlassesChecker mux(false);)
6595 _bit_map->lock()->unlock();
6596 _freelistLock->unlock();
6597 ConcurrentMarkSweepThread::desynchronize(true);
6598 ConcurrentMarkSweepThread::acknowledge_yield_request();
6599 _collector->stopTimer();
6600 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6601 if (PrintCMSStatistics != 0) {
6602 _collector->incrementYields();
6603 }
6604 _collector->icms_wait();
6605
6606 // See the comment in coordinator_yield()
6607 for (unsigned i = 0;
6608 i < CMSYieldSleepCount &&
6609 ConcurrentMarkSweepThread::should_yield() &&
6610 !CMSCollector::foregroundGCIsActive();
6611 ++i) {
6612 os::sleep(Thread::current(), 1, false);
6613 ConcurrentMarkSweepThread::acknowledge_yield_request();
6614 }
6615
6616 ConcurrentMarkSweepThread::synchronize(true);
6617 _freelistLock->lock_without_safepoint_check();
6618 _bit_map->lock()->lock_without_safepoint_check();
6619 _collector->startTimer();
6620 }
6621
6622 ///////////////////////////////////////////////////////////
6623 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6624 // MarkRefsIntoAndScanClosure
6625 ///////////////////////////////////////////////////////////
6626 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6627 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6628 CMSBitMap* bit_map, OopTaskQueue* work_queue, CMSMarkStack* revisit_stack):
6629 _span(span),
6630 _bit_map(bit_map),
6631 _work_queue(work_queue),
6632 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6633 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6634 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue,
6635 revisit_stack)
6636 {
6637 _ref_processor = rp;
6638 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6639 }
6640
6641 // This closure is used to mark refs into the CMS generation at the
6642 // second (final) checkpoint, and to scan and transitively follow
6643 // the unmarked oops. The marks are made in the marking bit map and
6644 // the work_queue is used for keeping the (newly) grey objects during
6645 // the scan phase whence they are also available for stealing by parallel
6646 // threads. Since the marking bit map is shared, updates are
6647 // synchronized (via CAS).
6648 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6649 if (obj != NULL) {
6650 // Ignore mark word because this could be an already marked oop
6651 // that may be chained at the end of the overflow list.
6652 assert(obj->is_oop(true), "expected an oop");
6653 HeapWord* addr = (HeapWord*)obj;
6654 if (_span.contains(addr) &&
6655 !_bit_map->isMarked(addr)) {
6656 // mark bit map (object will become grey):
6657 // It is possible for several threads to be
6658 // trying to "claim" this object concurrently;
6659 // the unique thread that succeeds in marking the
6660 // object first will do the subsequent push on
6661 // to the work queue (or overflow list).
6662 if (_bit_map->par_mark(addr)) {
6663 // push on work_queue (which may not be empty), and trim the
6664 // queue to an appropriate length by applying this closure to
6665 // the oops in the oops popped from the stack (i.e. blacken the
6666 // grey objects)
6667 bool res = _work_queue->push(obj);
6668 assert(res, "Low water mark should be less than capacity?");
6669 trim_queue(_low_water_mark);
6670 } // Else, another thread claimed the object
6671 }
6672 }
6673 }
6674
6675 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6676 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6677
6678 // This closure is used to rescan the marked objects on the dirty cards
6679 // in the mod union table and the card table proper.
6680 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6681 oop p, MemRegion mr) {
6682
6683 size_t size = 0;
6684 HeapWord* addr = (HeapWord*)p;
6685 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6686 assert(_span.contains(addr), "we are scanning the CMS generation");
6687 // check if it's time to yield
6688 if (do_yield_check()) {
6689 // We yielded for some foreground stop-world work,
6690 // and we have been asked to abort this ongoing preclean cycle.
6691 return 0;
6692 }
6693 if (_bitMap->isMarked(addr)) {
6694 // it's marked; is it potentially uninitialized?
6695 if (p->klass_or_null() != NULL) {
6696 // If is_conc_safe is false, the object may be undergoing
6697 // change by the VM outside a safepoint. Don't try to
6698 // scan it, but rather leave it for the remark phase.
6699 if (CMSPermGenPrecleaningEnabled &&
6700 (!p->is_conc_safe() || !p->is_parsable())) {
6701 // Signal precleaning to redirty the card since
6702 // the klass pointer is already installed.
6703 assert(size == 0, "Initial value");
6704 } else {
6705 assert(p->is_parsable(), "must be parsable.");
6706 // an initialized object; ignore mark word in verification below
6707 // since we are running concurrent with mutators
6708 assert(p->is_oop(true), "should be an oop");
6709 if (p->is_objArray()) {
6710 // objArrays are precisely marked; restrict scanning
6711 // to dirty cards only.
6712 size = CompactibleFreeListSpace::adjustObjectSize(
6713 p->oop_iterate(_scanningClosure, mr));
6714 } else {
6715 // A non-array may have been imprecisely marked; we need
6716 // to scan object in its entirety.
6717 size = CompactibleFreeListSpace::adjustObjectSize(
6718 p->oop_iterate(_scanningClosure));
6719 }
6720 #ifdef DEBUG
6721 size_t direct_size =
6722 CompactibleFreeListSpace::adjustObjectSize(p->size());
6723 assert(size == direct_size, "Inconsistency in size");
6724 assert(size >= 3, "Necessary for Printezis marks to work");
6725 if (!_bitMap->isMarked(addr+1)) {
6726 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6727 } else {
6728 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6729 assert(_bitMap->isMarked(addr+size-1),
6730 "inconsistent Printezis mark");
6731 }
6732 #endif // DEBUG
6733 }
6734 } else {
6735 // an unitialized object
6736 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6737 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6738 size = pointer_delta(nextOneAddr + 1, addr);
6739 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6740 "alignment problem");
6741 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6742 // will dirty the card when the klass pointer is installed in the
6743 // object (signalling the completion of initialization).
6744 }
6745 } else {
6746 // Either a not yet marked object or an uninitialized object
6747 if (p->klass_or_null() == NULL || !p->is_parsable()) {
6748 // An uninitialized object, skip to the next card, since
6749 // we may not be able to read its P-bits yet.
6750 assert(size == 0, "Initial value");
6751 } else {
6752 // An object not (yet) reached by marking: we merely need to
6753 // compute its size so as to go look at the next block.
6754 assert(p->is_oop(true), "should be an oop");
6755 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6756 }
6757 }
6758 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6759 return size;
6760 }
6761
6762 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6763 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6764 "CMS thread should hold CMS token");
6765 assert_lock_strong(_freelistLock);
6766 assert_lock_strong(_bitMap->lock());
6767 DEBUG_ONLY(RememberKlassesChecker mux(false);)
6768 // relinquish the free_list_lock and bitMaplock()
6769 _bitMap->lock()->unlock();
6770 _freelistLock->unlock();
6771 ConcurrentMarkSweepThread::desynchronize(true);
6772 ConcurrentMarkSweepThread::acknowledge_yield_request();
6773 _collector->stopTimer();
6774 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6775 if (PrintCMSStatistics != 0) {
6776 _collector->incrementYields();
6777 }
6778 _collector->icms_wait();
6779
6780 // See the comment in coordinator_yield()
6781 for (unsigned i = 0; i < CMSYieldSleepCount &&
6782 ConcurrentMarkSweepThread::should_yield() &&
6783 !CMSCollector::foregroundGCIsActive(); ++i) {
6784 os::sleep(Thread::current(), 1, false);
6785 ConcurrentMarkSweepThread::acknowledge_yield_request();
6786 }
6787
6788 ConcurrentMarkSweepThread::synchronize(true);
6789 _freelistLock->lock_without_safepoint_check();
6790 _bitMap->lock()->lock_without_safepoint_check();
6791 _collector->startTimer();
6792 }
6793
6794
6795 //////////////////////////////////////////////////////////////////
6796 // SurvivorSpacePrecleanClosure
6797 //////////////////////////////////////////////////////////////////
6798 // This (single-threaded) closure is used to preclean the oops in
6799 // the survivor spaces.
6800 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6801
6802 HeapWord* addr = (HeapWord*)p;
6803 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6804 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6805 assert(p->klass_or_null() != NULL, "object should be initializd");
6806 assert(p->is_parsable(), "must be parsable.");
6807 // an initialized object; ignore mark word in verification below
6808 // since we are running concurrent with mutators
6809 assert(p->is_oop(true), "should be an oop");
6810 // Note that we do not yield while we iterate over
6811 // the interior oops of p, pushing the relevant ones
6812 // on our marking stack.
6813 size_t size = p->oop_iterate(_scanning_closure);
6814 do_yield_check();
6815 // Observe that below, we do not abandon the preclean
6816 // phase as soon as we should; rather we empty the
6817 // marking stack before returning. This is to satisfy
6818 // some existing assertions. In general, it may be a
6819 // good idea to abort immediately and complete the marking
6820 // from the grey objects at a later time.
6821 while (!_mark_stack->isEmpty()) {
6822 oop new_oop = _mark_stack->pop();
6823 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6824 assert(new_oop->is_parsable(), "Found unparsable oop");
6825 assert(_bit_map->isMarked((HeapWord*)new_oop),
6826 "only grey objects on this stack");
6827 // iterate over the oops in this oop, marking and pushing
6828 // the ones in CMS heap (i.e. in _span).
6829 new_oop->oop_iterate(_scanning_closure);
6830 // check if it's time to yield
6831 do_yield_check();
6832 }
6833 unsigned int after_count =
6834 GenCollectedHeap::heap()->total_collections();
6835 bool abort = (_before_count != after_count) ||
6836 _collector->should_abort_preclean();
6837 return abort ? 0 : size;
6838 }
6839
6840 void SurvivorSpacePrecleanClosure::do_yield_work() {
6841 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6842 "CMS thread should hold CMS token");
6843 assert_lock_strong(_bit_map->lock());
6844 DEBUG_ONLY(RememberKlassesChecker smx(false);)
6845 // Relinquish the bit map lock
6846 _bit_map->lock()->unlock();
6847 ConcurrentMarkSweepThread::desynchronize(true);
6848 ConcurrentMarkSweepThread::acknowledge_yield_request();
6849 _collector->stopTimer();
6850 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6851 if (PrintCMSStatistics != 0) {
6852 _collector->incrementYields();
6853 }
6854 _collector->icms_wait();
6855
6856 // See the comment in coordinator_yield()
6857 for (unsigned i = 0; i < CMSYieldSleepCount &&
6858 ConcurrentMarkSweepThread::should_yield() &&
6859 !CMSCollector::foregroundGCIsActive(); ++i) {
6860 os::sleep(Thread::current(), 1, false);
6861 ConcurrentMarkSweepThread::acknowledge_yield_request();
6862 }
6863
6864 ConcurrentMarkSweepThread::synchronize(true);
6865 _bit_map->lock()->lock_without_safepoint_check();
6866 _collector->startTimer();
6867 }
6868
6869 // This closure is used to rescan the marked objects on the dirty cards
6870 // in the mod union table and the card table proper. In the parallel
6871 // case, although the bitMap is shared, we do a single read so the
6872 // isMarked() query is "safe".
6873 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6874 // Ignore mark word because we are running concurrent with mutators
6875 assert(p->is_oop_or_null(true), "expected an oop or null");
6876 HeapWord* addr = (HeapWord*)p;
6877 assert(_span.contains(addr), "we are scanning the CMS generation");
6878 bool is_obj_array = false;
6879 #ifdef DEBUG
6880 if (!_parallel) {
6881 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6882 assert(_collector->overflow_list_is_empty(),
6883 "overflow list should be empty");
6884
6885 }
6886 #endif // DEBUG
6887 if (_bit_map->isMarked(addr)) {
6888 // Obj arrays are precisely marked, non-arrays are not;
6889 // so we scan objArrays precisely and non-arrays in their
6890 // entirety.
6891 if (p->is_objArray()) {
6892 is_obj_array = true;
6893 if (_parallel) {
6894 p->oop_iterate(_par_scan_closure, mr);
6895 } else {
6896 p->oop_iterate(_scan_closure, mr);
6897 }
6898 } else {
6899 if (_parallel) {
6900 p->oop_iterate(_par_scan_closure);
6901 } else {
6902 p->oop_iterate(_scan_closure);
6903 }
6904 }
6905 }
6906 #ifdef DEBUG
6907 if (!_parallel) {
6908 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6909 assert(_collector->overflow_list_is_empty(),
6910 "overflow list should be empty");
6911
6912 }
6913 #endif // DEBUG
6914 return is_obj_array;
6915 }
6916
6917 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6918 MemRegion span,
6919 CMSBitMap* bitMap, CMSMarkStack* markStack,
6920 CMSMarkStack* revisitStack,
6921 bool should_yield, bool verifying):
6922 _collector(collector),
6923 _span(span),
6924 _bitMap(bitMap),
6925 _mut(&collector->_modUnionTable),
6926 _markStack(markStack),
6927 _revisitStack(revisitStack),
6928 _yield(should_yield),
6929 _skipBits(0)
6930 {
6931 assert(_markStack->isEmpty(), "stack should be empty");
6932 _finger = _bitMap->startWord();
6933 _threshold = _finger;
6934 assert(_collector->_restart_addr == NULL, "Sanity check");
6935 assert(_span.contains(_finger), "Out of bounds _finger?");
6936 DEBUG_ONLY(_verifying = verifying;)
6937 }
6938
6939 void MarkFromRootsClosure::reset(HeapWord* addr) {
6940 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6941 assert(_span.contains(addr), "Out of bounds _finger?");
6942 _finger = addr;
6943 _threshold = (HeapWord*)round_to(
6944 (intptr_t)_finger, CardTableModRefBS::card_size);
6945 }
6946
6947 // Should revisit to see if this should be restructured for
6948 // greater efficiency.
6949 bool MarkFromRootsClosure::do_bit(size_t offset) {
6950 if (_skipBits > 0) {
6951 _skipBits--;
6952 return true;
6953 }
6954 // convert offset into a HeapWord*
6955 HeapWord* addr = _bitMap->startWord() + offset;
6956 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6957 "address out of range");
6958 assert(_bitMap->isMarked(addr), "tautology");
6959 if (_bitMap->isMarked(addr+1)) {
6960 // this is an allocated but not yet initialized object
6961 assert(_skipBits == 0, "tautology");
6962 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6963 oop p = oop(addr);
6964 if (p->klass_or_null() == NULL || !p->is_parsable()) {
6965 DEBUG_ONLY(if (!_verifying) {)
6966 // We re-dirty the cards on which this object lies and increase
6967 // the _threshold so that we'll come back to scan this object
6968 // during the preclean or remark phase. (CMSCleanOnEnter)
6969 if (CMSCleanOnEnter) {
6970 size_t sz = _collector->block_size_using_printezis_bits(addr);
6971 HeapWord* end_card_addr = (HeapWord*)round_to(
6972 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6973 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6974 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6975 // Bump _threshold to end_card_addr; note that
6976 // _threshold cannot possibly exceed end_card_addr, anyhow.
6977 // This prevents future clearing of the card as the scan proceeds
6978 // to the right.
6979 assert(_threshold <= end_card_addr,
6980 "Because we are just scanning into this object");
6981 if (_threshold < end_card_addr) {
6982 _threshold = end_card_addr;
6983 }
6984 if (p->klass_or_null() != NULL) {
6985 // Redirty the range of cards...
6986 _mut->mark_range(redirty_range);
6987 } // ...else the setting of klass will dirty the card anyway.
6988 }
6989 DEBUG_ONLY(})
6990 return true;
6991 }
6992 }
6993 scanOopsInOop(addr);
6994 return true;
6995 }
6996
6997 // We take a break if we've been at this for a while,
6998 // so as to avoid monopolizing the locks involved.
6999 void MarkFromRootsClosure::do_yield_work() {
7000 // First give up the locks, then yield, then re-lock
7001 // We should probably use a constructor/destructor idiom to
7002 // do this unlock/lock or modify the MutexUnlocker class to
7003 // serve our purpose. XXX
7004 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7005 "CMS thread should hold CMS token");
7006 assert_lock_strong(_bitMap->lock());
7007 DEBUG_ONLY(RememberKlassesChecker mux(false);)
7008 _bitMap->lock()->unlock();
7009 ConcurrentMarkSweepThread::desynchronize(true);
7010 ConcurrentMarkSweepThread::acknowledge_yield_request();
7011 _collector->stopTimer();
7012 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7013 if (PrintCMSStatistics != 0) {
7014 _collector->incrementYields();
7015 }
7016 _collector->icms_wait();
7017
7018 // See the comment in coordinator_yield()
7019 for (unsigned i = 0; i < CMSYieldSleepCount &&
7020 ConcurrentMarkSweepThread::should_yield() &&
7021 !CMSCollector::foregroundGCIsActive(); ++i) {
7022 os::sleep(Thread::current(), 1, false);
7023 ConcurrentMarkSweepThread::acknowledge_yield_request();
7024 }
7025
7026 ConcurrentMarkSweepThread::synchronize(true);
7027 _bitMap->lock()->lock_without_safepoint_check();
7028 _collector->startTimer();
7029 }
7030
7031 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7032 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7033 assert(_markStack->isEmpty(),
7034 "should drain stack to limit stack usage");
7035 // convert ptr to an oop preparatory to scanning
7036 oop obj = oop(ptr);
7037 // Ignore mark word in verification below, since we
7038 // may be running concurrent with mutators.
7039 assert(obj->is_oop(true), "should be an oop");
7040 assert(_finger <= ptr, "_finger runneth ahead");
7041 // advance the finger to right end of this object
7042 _finger = ptr + obj->size();
7043 assert(_finger > ptr, "we just incremented it above");
7044 // On large heaps, it may take us some time to get through
7045 // the marking phase (especially if running iCMS). During
7046 // this time it's possible that a lot of mutations have
7047 // accumulated in the card table and the mod union table --
7048 // these mutation records are redundant until we have
7049 // actually traced into the corresponding card.
7050 // Here, we check whether advancing the finger would make
7051 // us cross into a new card, and if so clear corresponding
7052 // cards in the MUT (preclean them in the card-table in the
7053 // future).
7054
7055 DEBUG_ONLY(if (!_verifying) {)
7056 // The clean-on-enter optimization is disabled by default,
7057 // until we fix 6178663.
7058 if (CMSCleanOnEnter && (_finger > _threshold)) {
7059 // [_threshold, _finger) represents the interval
7060 // of cards to be cleared in MUT (or precleaned in card table).
7061 // The set of cards to be cleared is all those that overlap
7062 // with the interval [_threshold, _finger); note that
7063 // _threshold is always kept card-aligned but _finger isn't
7064 // always card-aligned.
7065 HeapWord* old_threshold = _threshold;
7066 assert(old_threshold == (HeapWord*)round_to(
7067 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7068 "_threshold should always be card-aligned");
7069 _threshold = (HeapWord*)round_to(
7070 (intptr_t)_finger, CardTableModRefBS::card_size);
7071 MemRegion mr(old_threshold, _threshold);
7072 assert(!mr.is_empty(), "Control point invariant");
7073 assert(_span.contains(mr), "Should clear within span");
7074 // XXX When _finger crosses from old gen into perm gen
7075 // we may be doing unnecessary cleaning; do better in the
7076 // future by detecting that condition and clearing fewer
7077 // MUT/CT entries.
7078 _mut->clear_range(mr);
7079 }
7080 DEBUG_ONLY(})
7081 // Note: the finger doesn't advance while we drain
7082 // the stack below.
7083 PushOrMarkClosure pushOrMarkClosure(_collector,
7084 _span, _bitMap, _markStack,
7085 _revisitStack,
7086 _finger, this);
7087 bool res = _markStack->push(obj);
7088 assert(res, "Empty non-zero size stack should have space for single push");
7089 while (!_markStack->isEmpty()) {
7090 oop new_oop = _markStack->pop();
7091 // Skip verifying header mark word below because we are
7092 // running concurrent with mutators.
7093 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7094 // now scan this oop's oops
7095 new_oop->oop_iterate(&pushOrMarkClosure);
7096 do_yield_check();
7097 }
7098 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7099 }
7100
7101 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7102 CMSCollector* collector, MemRegion span,
7103 CMSBitMap* bit_map,
7104 OopTaskQueue* work_queue,
7105 CMSMarkStack* overflow_stack,
7106 CMSMarkStack* revisit_stack,
7107 bool should_yield):
7108 _collector(collector),
7109 _whole_span(collector->_span),
7110 _span(span),
7111 _bit_map(bit_map),
7112 _mut(&collector->_modUnionTable),
7113 _work_queue(work_queue),
7114 _overflow_stack(overflow_stack),
7115 _revisit_stack(revisit_stack),
7116 _yield(should_yield),
7117 _skip_bits(0),
7118 _task(task)
7119 {
7120 assert(_work_queue->size() == 0, "work_queue should be empty");
7121 _finger = span.start();
7122 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7123 assert(_span.contains(_finger), "Out of bounds _finger?");
7124 }
7125
7126 // Should revisit to see if this should be restructured for
7127 // greater efficiency.
7128 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7129 if (_skip_bits > 0) {
7130 _skip_bits--;
7131 return true;
7132 }
7133 // convert offset into a HeapWord*
7134 HeapWord* addr = _bit_map->startWord() + offset;
7135 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7136 "address out of range");
7137 assert(_bit_map->isMarked(addr), "tautology");
7138 if (_bit_map->isMarked(addr+1)) {
7139 // this is an allocated object that might not yet be initialized
7140 assert(_skip_bits == 0, "tautology");
7141 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7142 oop p = oop(addr);
7143 if (p->klass_or_null() == NULL || !p->is_parsable()) {
7144 // in the case of Clean-on-Enter optimization, redirty card
7145 // and avoid clearing card by increasing the threshold.
7146 return true;
7147 }
7148 }
7149 scan_oops_in_oop(addr);
7150 return true;
7151 }
7152
7153 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7154 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7155 // Should we assert that our work queue is empty or
7156 // below some drain limit?
7157 assert(_work_queue->size() == 0,
7158 "should drain stack to limit stack usage");
7159 // convert ptr to an oop preparatory to scanning
7160 oop obj = oop(ptr);
7161 // Ignore mark word in verification below, since we
7162 // may be running concurrent with mutators.
7163 assert(obj->is_oop(true), "should be an oop");
7164 assert(_finger <= ptr, "_finger runneth ahead");
7165 // advance the finger to right end of this object
7166 _finger = ptr + obj->size();
7167 assert(_finger > ptr, "we just incremented it above");
7168 // On large heaps, it may take us some time to get through
7169 // the marking phase (especially if running iCMS). During
7170 // this time it's possible that a lot of mutations have
7171 // accumulated in the card table and the mod union table --
7172 // these mutation records are redundant until we have
7173 // actually traced into the corresponding card.
7174 // Here, we check whether advancing the finger would make
7175 // us cross into a new card, and if so clear corresponding
7176 // cards in the MUT (preclean them in the card-table in the
7177 // future).
7178
7179 // The clean-on-enter optimization is disabled by default,
7180 // until we fix 6178663.
7181 if (CMSCleanOnEnter && (_finger > _threshold)) {
7182 // [_threshold, _finger) represents the interval
7183 // of cards to be cleared in MUT (or precleaned in card table).
7184 // The set of cards to be cleared is all those that overlap
7185 // with the interval [_threshold, _finger); note that
7186 // _threshold is always kept card-aligned but _finger isn't
7187 // always card-aligned.
7188 HeapWord* old_threshold = _threshold;
7189 assert(old_threshold == (HeapWord*)round_to(
7190 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7191 "_threshold should always be card-aligned");
7192 _threshold = (HeapWord*)round_to(
7193 (intptr_t)_finger, CardTableModRefBS::card_size);
7194 MemRegion mr(old_threshold, _threshold);
7195 assert(!mr.is_empty(), "Control point invariant");
7196 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7197 // XXX When _finger crosses from old gen into perm gen
7198 // we may be doing unnecessary cleaning; do better in the
7199 // future by detecting that condition and clearing fewer
7200 // MUT/CT entries.
7201 _mut->clear_range(mr);
7202 }
7203
7204 // Note: the local finger doesn't advance while we drain
7205 // the stack below, but the global finger sure can and will.
7206 HeapWord** gfa = _task->global_finger_addr();
7207 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7208 _span, _bit_map,
7209 _work_queue,
7210 _overflow_stack,
7211 _revisit_stack,
7212 _finger,
7213 gfa, this);
7214 bool res = _work_queue->push(obj); // overflow could occur here
7215 assert(res, "Will hold once we use workqueues");
7216 while (true) {
7217 oop new_oop;
7218 if (!_work_queue->pop_local(new_oop)) {
7219 // We emptied our work_queue; check if there's stuff that can
7220 // be gotten from the overflow stack.
7221 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7222 _overflow_stack, _work_queue)) {
7223 do_yield_check();
7224 continue;
7225 } else { // done
7226 break;
7227 }
7228 }
7229 // Skip verifying header mark word below because we are
7230 // running concurrent with mutators.
7231 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7232 // now scan this oop's oops
7233 new_oop->oop_iterate(&pushOrMarkClosure);
7234 do_yield_check();
7235 }
7236 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7237 }
7238
7239 // Yield in response to a request from VM Thread or
7240 // from mutators.
7241 void Par_MarkFromRootsClosure::do_yield_work() {
7242 assert(_task != NULL, "sanity");
7243 _task->yield();
7244 }
7245
7246 // A variant of the above used for verifying CMS marking work.
7247 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7248 MemRegion span,
7249 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7250 CMSMarkStack* mark_stack):
7251 _collector(collector),
7252 _span(span),
7253 _verification_bm(verification_bm),
7254 _cms_bm(cms_bm),
7255 _mark_stack(mark_stack),
7256 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7257 mark_stack)
7258 {
7259 assert(_mark_stack->isEmpty(), "stack should be empty");
7260 _finger = _verification_bm->startWord();
7261 assert(_collector->_restart_addr == NULL, "Sanity check");
7262 assert(_span.contains(_finger), "Out of bounds _finger?");
7263 }
7264
7265 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7266 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7267 assert(_span.contains(addr), "Out of bounds _finger?");
7268 _finger = addr;
7269 }
7270
7271 // Should revisit to see if this should be restructured for
7272 // greater efficiency.
7273 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7274 // convert offset into a HeapWord*
7275 HeapWord* addr = _verification_bm->startWord() + offset;
7276 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7277 "address out of range");
7278 assert(_verification_bm->isMarked(addr), "tautology");
7279 assert(_cms_bm->isMarked(addr), "tautology");
7280
7281 assert(_mark_stack->isEmpty(),
7282 "should drain stack to limit stack usage");
7283 // convert addr to an oop preparatory to scanning
7284 oop obj = oop(addr);
7285 assert(obj->is_oop(), "should be an oop");
7286 assert(_finger <= addr, "_finger runneth ahead");
7287 // advance the finger to right end of this object
7288 _finger = addr + obj->size();
7289 assert(_finger > addr, "we just incremented it above");
7290 // Note: the finger doesn't advance while we drain
7291 // the stack below.
7292 bool res = _mark_stack->push(obj);
7293 assert(res, "Empty non-zero size stack should have space for single push");
7294 while (!_mark_stack->isEmpty()) {
7295 oop new_oop = _mark_stack->pop();
7296 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7297 // now scan this oop's oops
7298 new_oop->oop_iterate(&_pam_verify_closure);
7299 }
7300 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7301 return true;
7302 }
7303
7304 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7305 CMSCollector* collector, MemRegion span,
7306 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7307 CMSMarkStack* mark_stack):
7308 OopClosure(collector->ref_processor()),
7309 _collector(collector),
7310 _span(span),
7311 _verification_bm(verification_bm),
7312 _cms_bm(cms_bm),
7313 _mark_stack(mark_stack)
7314 { }
7315
7316 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7317 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7318
7319 // Upon stack overflow, we discard (part of) the stack,
7320 // remembering the least address amongst those discarded
7321 // in CMSCollector's _restart_address.
7322 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7323 // Remember the least grey address discarded
7324 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7325 _collector->lower_restart_addr(ra);
7326 _mark_stack->reset(); // discard stack contents
7327 _mark_stack->expand(); // expand the stack if possible
7328 }
7329
7330 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7331 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7332 HeapWord* addr = (HeapWord*)obj;
7333 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7334 // Oop lies in _span and isn't yet grey or black
7335 _verification_bm->mark(addr); // now grey
7336 if (!_cms_bm->isMarked(addr)) {
7337 oop(addr)->print();
7338 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7339 addr);
7340 fatal("... aborting");
7341 }
7342
7343 if (!_mark_stack->push(obj)) { // stack overflow
7344 if (PrintCMSStatistics != 0) {
7345 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7346 SIZE_FORMAT, _mark_stack->capacity());
7347 }
7348 assert(_mark_stack->isFull(), "Else push should have succeeded");
7349 handle_stack_overflow(addr);
7350 }
7351 // anything including and to the right of _finger
7352 // will be scanned as we iterate over the remainder of the
7353 // bit map
7354 }
7355 }
7356
7357 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7358 MemRegion span,
7359 CMSBitMap* bitMap, CMSMarkStack* markStack,
7360 CMSMarkStack* revisitStack,
7361 HeapWord* finger, MarkFromRootsClosure* parent) :
7362 KlassRememberingOopClosure(collector, collector->ref_processor(), revisitStack),
7363 _span(span),
7364 _bitMap(bitMap),
7365 _markStack(markStack),
7366 _finger(finger),
7367 _parent(parent)
7368 { }
7369
7370 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7371 MemRegion span,
7372 CMSBitMap* bit_map,
7373 OopTaskQueue* work_queue,
7374 CMSMarkStack* overflow_stack,
7375 CMSMarkStack* revisit_stack,
7376 HeapWord* finger,
7377 HeapWord** global_finger_addr,
7378 Par_MarkFromRootsClosure* parent) :
7379 Par_KlassRememberingOopClosure(collector,
7380 collector->ref_processor(),
7381 revisit_stack),
7382 _whole_span(collector->_span),
7383 _span(span),
7384 _bit_map(bit_map),
7385 _work_queue(work_queue),
7386 _overflow_stack(overflow_stack),
7387 _finger(finger),
7388 _global_finger_addr(global_finger_addr),
7389 _parent(parent)
7390 { }
7391
7392 // Assumes thread-safe access by callers, who are
7393 // responsible for mutual exclusion.
7394 void CMSCollector::lower_restart_addr(HeapWord* low) {
7395 assert(_span.contains(low), "Out of bounds addr");
7396 if (_restart_addr == NULL) {
7397 _restart_addr = low;
7398 } else {
7399 _restart_addr = MIN2(_restart_addr, low);
7400 }
7401 }
7402
7403 // Upon stack overflow, we discard (part of) the stack,
7404 // remembering the least address amongst those discarded
7405 // in CMSCollector's _restart_address.
7406 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7407 // Remember the least grey address discarded
7408 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7409 _collector->lower_restart_addr(ra);
7410 _markStack->reset(); // discard stack contents
7411 _markStack->expand(); // expand the stack if possible
7412 }
7413
7414 // Upon stack overflow, we discard (part of) the stack,
7415 // remembering the least address amongst those discarded
7416 // in CMSCollector's _restart_address.
7417 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7418 // We need to do this under a mutex to prevent other
7419 // workers from interfering with the work done below.
7420 MutexLockerEx ml(_overflow_stack->par_lock(),
7421 Mutex::_no_safepoint_check_flag);
7422 // Remember the least grey address discarded
7423 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7424 _collector->lower_restart_addr(ra);
7425 _overflow_stack->reset(); // discard stack contents
7426 _overflow_stack->expand(); // expand the stack if possible
7427 }
7428
7429 void PushOrMarkClosure::do_oop(oop obj) {
7430 // Ignore mark word because we are running concurrent with mutators.
7431 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7432 HeapWord* addr = (HeapWord*)obj;
7433 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7434 // Oop lies in _span and isn't yet grey or black
7435 _bitMap->mark(addr); // now grey
7436 if (addr < _finger) {
7437 // the bit map iteration has already either passed, or
7438 // sampled, this bit in the bit map; we'll need to
7439 // use the marking stack to scan this oop's oops.
7440 bool simulate_overflow = false;
7441 NOT_PRODUCT(
7442 if (CMSMarkStackOverflowALot &&
7443 _collector->simulate_overflow()) {
7444 // simulate a stack overflow
7445 simulate_overflow = true;
7446 }
7447 )
7448 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7449 if (PrintCMSStatistics != 0) {
7450 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7451 SIZE_FORMAT, _markStack->capacity());
7452 }
7453 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7454 handle_stack_overflow(addr);
7455 }
7456 }
7457 // anything including and to the right of _finger
7458 // will be scanned as we iterate over the remainder of the
7459 // bit map
7460 do_yield_check();
7461 }
7462 }
7463
7464 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7465 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7466
7467 void Par_PushOrMarkClosure::do_oop(oop obj) {
7468 // Ignore mark word because we are running concurrent with mutators.
7469 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7470 HeapWord* addr = (HeapWord*)obj;
7471 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7472 // Oop lies in _span and isn't yet grey or black
7473 // We read the global_finger (volatile read) strictly after marking oop
7474 bool res = _bit_map->par_mark(addr); // now grey
7475 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7476 // Should we push this marked oop on our stack?
7477 // -- if someone else marked it, nothing to do
7478 // -- if target oop is above global finger nothing to do
7479 // -- if target oop is in chunk and above local finger
7480 // then nothing to do
7481 // -- else push on work queue
7482 if ( !res // someone else marked it, they will deal with it
7483 || (addr >= *gfa) // will be scanned in a later task
7484 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7485 return;
7486 }
7487 // the bit map iteration has already either passed, or
7488 // sampled, this bit in the bit map; we'll need to
7489 // use the marking stack to scan this oop's oops.
7490 bool simulate_overflow = false;
7491 NOT_PRODUCT(
7492 if (CMSMarkStackOverflowALot &&
7493 _collector->simulate_overflow()) {
7494 // simulate a stack overflow
7495 simulate_overflow = true;
7496 }
7497 )
7498 if (simulate_overflow ||
7499 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7500 // stack overflow
7501 if (PrintCMSStatistics != 0) {
7502 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7503 SIZE_FORMAT, _overflow_stack->capacity());
7504 }
7505 // We cannot assert that the overflow stack is full because
7506 // it may have been emptied since.
7507 assert(simulate_overflow ||
7508 _work_queue->size() == _work_queue->max_elems(),
7509 "Else push should have succeeded");
7510 handle_stack_overflow(addr);
7511 }
7512 do_yield_check();
7513 }
7514 }
7515
7516 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7517 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7518
7519 KlassRememberingOopClosure::KlassRememberingOopClosure(CMSCollector* collector,
7520 ReferenceProcessor* rp,
7521 CMSMarkStack* revisit_stack) :
7522 OopClosure(rp),
7523 _collector(collector),
7524 _revisit_stack(revisit_stack),
7525 _should_remember_klasses(collector->should_unload_classes()) {}
7526
7527 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7528 MemRegion span,
7529 ReferenceProcessor* rp,
7530 CMSBitMap* bit_map,
7531 CMSBitMap* mod_union_table,
7532 CMSMarkStack* mark_stack,
7533 CMSMarkStack* revisit_stack,
7534 bool concurrent_precleaning):
7535 KlassRememberingOopClosure(collector, rp, revisit_stack),
7536 _span(span),
7537 _bit_map(bit_map),
7538 _mod_union_table(mod_union_table),
7539 _mark_stack(mark_stack),
7540 _concurrent_precleaning(concurrent_precleaning)
7541 {
7542 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7543 }
7544
7545 // Grey object rescan during pre-cleaning and second checkpoint phases --
7546 // the non-parallel version (the parallel version appears further below.)
7547 void PushAndMarkClosure::do_oop(oop obj) {
7548 // Ignore mark word verification. If during concurrent precleaning,
7549 // the object monitor may be locked. If during the checkpoint
7550 // phases, the object may already have been reached by a different
7551 // path and may be at the end of the global overflow list (so
7552 // the mark word may be NULL).
7553 assert(obj->is_oop_or_null(true /* ignore mark word */),
7554 "expected an oop or NULL");
7555 HeapWord* addr = (HeapWord*)obj;
7556 // Check if oop points into the CMS generation
7557 // and is not marked
7558 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7559 // a white object ...
7560 _bit_map->mark(addr); // ... now grey
7561 // push on the marking stack (grey set)
7562 bool simulate_overflow = false;
7563 NOT_PRODUCT(
7564 if (CMSMarkStackOverflowALot &&
7565 _collector->simulate_overflow()) {
7566 // simulate a stack overflow
7567 simulate_overflow = true;
7568 }
7569 )
7570 if (simulate_overflow || !_mark_stack->push(obj)) {
7571 if (_concurrent_precleaning) {
7572 // During precleaning we can just dirty the appropriate card(s)
7573 // in the mod union table, thus ensuring that the object remains
7574 // in the grey set and continue. In the case of object arrays
7575 // we need to dirty all of the cards that the object spans,
7576 // since the rescan of object arrays will be limited to the
7577 // dirty cards.
7578 // Note that no one can be intefering with us in this action
7579 // of dirtying the mod union table, so no locking or atomics
7580 // are required.
7581 if (obj->is_objArray()) {
7582 size_t sz = obj->size();
7583 HeapWord* end_card_addr = (HeapWord*)round_to(
7584 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7585 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7586 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7587 _mod_union_table->mark_range(redirty_range);
7588 } else {
7589 _mod_union_table->mark(addr);
7590 }
7591 _collector->_ser_pmc_preclean_ovflw++;
7592 } else {
7593 // During the remark phase, we need to remember this oop
7594 // in the overflow list.
7595 _collector->push_on_overflow_list(obj);
7596 _collector->_ser_pmc_remark_ovflw++;
7597 }
7598 }
7599 }
7600 }
7601
7602 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7603 MemRegion span,
7604 ReferenceProcessor* rp,
7605 CMSBitMap* bit_map,
7606 OopTaskQueue* work_queue,
7607 CMSMarkStack* revisit_stack):
7608 Par_KlassRememberingOopClosure(collector, rp, revisit_stack),
7609 _span(span),
7610 _bit_map(bit_map),
7611 _work_queue(work_queue)
7612 {
7613 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7614 }
7615
7616 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7617 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7618
7619 // Grey object rescan during second checkpoint phase --
7620 // the parallel version.
7621 void Par_PushAndMarkClosure::do_oop(oop obj) {
7622 // In the assert below, we ignore the mark word because
7623 // this oop may point to an already visited object that is
7624 // on the overflow stack (in which case the mark word has
7625 // been hijacked for chaining into the overflow stack --
7626 // if this is the last object in the overflow stack then
7627 // its mark word will be NULL). Because this object may
7628 // have been subsequently popped off the global overflow
7629 // stack, and the mark word possibly restored to the prototypical
7630 // value, by the time we get to examined this failing assert in
7631 // the debugger, is_oop_or_null(false) may subsequently start
7632 // to hold.
7633 assert(obj->is_oop_or_null(true),
7634 "expected an oop or NULL");
7635 HeapWord* addr = (HeapWord*)obj;
7636 // Check if oop points into the CMS generation
7637 // and is not marked
7638 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7639 // a white object ...
7640 // If we manage to "claim" the object, by being the
7641 // first thread to mark it, then we push it on our
7642 // marking stack
7643 if (_bit_map->par_mark(addr)) { // ... now grey
7644 // push on work queue (grey set)
7645 bool simulate_overflow = false;
7646 NOT_PRODUCT(
7647 if (CMSMarkStackOverflowALot &&
7648 _collector->par_simulate_overflow()) {
7649 // simulate a stack overflow
7650 simulate_overflow = true;
7651 }
7652 )
7653 if (simulate_overflow || !_work_queue->push(obj)) {
7654 _collector->par_push_on_overflow_list(obj);
7655 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7656 }
7657 } // Else, some other thread got there first
7658 }
7659 }
7660
7661 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7662 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7663
7664 void PushAndMarkClosure::remember_mdo(DataLayout* v) {
7665 // TBD
7666 }
7667
7668 void Par_PushAndMarkClosure::remember_mdo(DataLayout* v) {
7669 // TBD
7670 }
7671
7672 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7673 DEBUG_ONLY(RememberKlassesChecker mux(false);)
7674 Mutex* bml = _collector->bitMapLock();
7675 assert_lock_strong(bml);
7676 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7677 "CMS thread should hold CMS token");
7678
7679 bml->unlock();
7680 ConcurrentMarkSweepThread::desynchronize(true);
7681
7682 ConcurrentMarkSweepThread::acknowledge_yield_request();
7683
7684 _collector->stopTimer();
7685 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7686 if (PrintCMSStatistics != 0) {
7687 _collector->incrementYields();
7688 }
7689 _collector->icms_wait();
7690
7691 // See the comment in coordinator_yield()
7692 for (unsigned i = 0; i < CMSYieldSleepCount &&
7693 ConcurrentMarkSweepThread::should_yield() &&
7694 !CMSCollector::foregroundGCIsActive(); ++i) {
7695 os::sleep(Thread::current(), 1, false);
7696 ConcurrentMarkSweepThread::acknowledge_yield_request();
7697 }
7698
7699 ConcurrentMarkSweepThread::synchronize(true);
7700 bml->lock();
7701
7702 _collector->startTimer();
7703 }
7704
7705 bool CMSPrecleanRefsYieldClosure::should_return() {
7706 if (ConcurrentMarkSweepThread::should_yield()) {
7707 do_yield_work();
7708 }
7709 return _collector->foregroundGCIsActive();
7710 }
7711
7712 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7713 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7714 "mr should be aligned to start at a card boundary");
7715 // We'd like to assert:
7716 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7717 // "mr should be a range of cards");
7718 // However, that would be too strong in one case -- the last
7719 // partition ends at _unallocated_block which, in general, can be
7720 // an arbitrary boundary, not necessarily card aligned.
7721 if (PrintCMSStatistics != 0) {
7722 _num_dirty_cards +=
7723 mr.word_size()/CardTableModRefBS::card_size_in_words;
7724 }
7725 _space->object_iterate_mem(mr, &_scan_cl);
7726 }
7727
7728 SweepClosure::SweepClosure(CMSCollector* collector,
7729 ConcurrentMarkSweepGeneration* g,
7730 CMSBitMap* bitMap, bool should_yield) :
7731 _collector(collector),
7732 _g(g),
7733 _sp(g->cmsSpace()),
7734 _limit(_sp->sweep_limit()),
7735 _freelistLock(_sp->freelistLock()),
7736 _bitMap(bitMap),
7737 _yield(should_yield),
7738 _inFreeRange(false), // No free range at beginning of sweep
7739 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7740 _lastFreeRangeCoalesced(false),
7741 _freeFinger(g->used_region().start())
7742 {
7743 NOT_PRODUCT(
7744 _numObjectsFreed = 0;
7745 _numWordsFreed = 0;
7746 _numObjectsLive = 0;
7747 _numWordsLive = 0;
7748 _numObjectsAlreadyFree = 0;
7749 _numWordsAlreadyFree = 0;
7750 _last_fc = NULL;
7751
7752 _sp->initializeIndexedFreeListArrayReturnedBytes();
7753 _sp->dictionary()->initializeDictReturnedBytes();
7754 )
7755 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7756 "sweep _limit out of bounds");
7757 if (CMSTraceSweeper) {
7758 gclog_or_tty->print("\n====================\nStarting new sweep\n");
7759 }
7760 }
7761
7762 // We need this destructor to reclaim any space at the end
7763 // of the space, which do_blk below may not have added back to
7764 // the free lists. [basically dealing with the "fringe effect"]
7765 SweepClosure::~SweepClosure() {
7766 assert_lock_strong(_freelistLock);
7767 // this should be treated as the end of a free run if any
7768 // The current free range should be returned to the free lists
7769 // as one coalesced chunk.
7770 if (inFreeRange()) {
7771 flushCurFreeChunk(freeFinger(),
7772 pointer_delta(_limit, freeFinger()));
7773 assert(freeFinger() < _limit, "the finger pointeth off base");
7774 if (CMSTraceSweeper) {
7775 gclog_or_tty->print("destructor:");
7776 gclog_or_tty->print("Sweep:put_free_blk 0x%x ("SIZE_FORMAT") "
7777 "[coalesced:"SIZE_FORMAT"]\n",
7778 freeFinger(), pointer_delta(_limit, freeFinger()),
7779 lastFreeRangeCoalesced());
7780 }
7781 }
7782 NOT_PRODUCT(
7783 if (Verbose && PrintGC) {
7784 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, "
7785 SIZE_FORMAT " bytes",
7786 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7787 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7788 SIZE_FORMAT" bytes "
7789 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7790 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7791 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7792 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) *
7793 sizeof(HeapWord);
7794 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7795
7796 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7797 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7798 size_t dictReturnedBytes = _sp->dictionary()->sumDictReturnedBytes();
7799 size_t returnedBytes = indexListReturnedBytes + dictReturnedBytes;
7800 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returnedBytes);
7801 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7802 indexListReturnedBytes);
7803 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7804 dictReturnedBytes);
7805 }
7806 }
7807 )
7808 // Now, in debug mode, just null out the sweep_limit
7809 NOT_PRODUCT(_sp->clear_sweep_limit();)
7810 if (CMSTraceSweeper) {
7811 gclog_or_tty->print("end of sweep\n================\n");
7812 }
7813 }
7814
7815 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7816 bool freeRangeInFreeLists) {
7817 if (CMSTraceSweeper) {
7818 gclog_or_tty->print("---- Start free range 0x%x with free block [%d] (%d)\n",
7819 freeFinger, _sp->block_size(freeFinger),
7820 freeRangeInFreeLists);
7821 }
7822 assert(!inFreeRange(), "Trampling existing free range");
7823 set_inFreeRange(true);
7824 set_lastFreeRangeCoalesced(false);
7825
7826 set_freeFinger(freeFinger);
7827 set_freeRangeInFreeLists(freeRangeInFreeLists);
7828 if (CMSTestInFreeList) {
7829 if (freeRangeInFreeLists) {
7830 FreeChunk* fc = (FreeChunk*) freeFinger;
7831 assert(fc->isFree(), "A chunk on the free list should be free.");
7832 assert(fc->size() > 0, "Free range should have a size");
7833 assert(_sp->verifyChunkInFreeLists(fc), "Chunk is not in free lists");
7834 }
7835 }
7836 }
7837
7838 // Note that the sweeper runs concurrently with mutators. Thus,
7839 // it is possible for direct allocation in this generation to happen
7840 // in the middle of the sweep. Note that the sweeper also coalesces
7841 // contiguous free blocks. Thus, unless the sweeper and the allocator
7842 // synchronize appropriately freshly allocated blocks may get swept up.
7843 // This is accomplished by the sweeper locking the free lists while
7844 // it is sweeping. Thus blocks that are determined to be free are
7845 // indeed free. There is however one additional complication:
7846 // blocks that have been allocated since the final checkpoint and
7847 // mark, will not have been marked and so would be treated as
7848 // unreachable and swept up. To prevent this, the allocator marks
7849 // the bit map when allocating during the sweep phase. This leads,
7850 // however, to a further complication -- objects may have been allocated
7851 // but not yet initialized -- in the sense that the header isn't yet
7852 // installed. The sweeper can not then determine the size of the block
7853 // in order to skip over it. To deal with this case, we use a technique
7854 // (due to Printezis) to encode such uninitialized block sizes in the
7855 // bit map. Since the bit map uses a bit per every HeapWord, but the
7856 // CMS generation has a minimum object size of 3 HeapWords, it follows
7857 // that "normal marks" won't be adjacent in the bit map (there will
7858 // always be at least two 0 bits between successive 1 bits). We make use
7859 // of these "unused" bits to represent uninitialized blocks -- the bit
7860 // corresponding to the start of the uninitialized object and the next
7861 // bit are both set. Finally, a 1 bit marks the end of the object that
7862 // started with the two consecutive 1 bits to indicate its potentially
7863 // uninitialized state.
7864
7865 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7866 FreeChunk* fc = (FreeChunk*)addr;
7867 size_t res;
7868
7869 // check if we are done sweepinrg
7870 if (addr == _limit) { // we have swept up to the limit, do nothing more
7871 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7872 "sweep _limit out of bounds");
7873 // help the closure application finish
7874 return pointer_delta(_sp->end(), _limit);
7875 }
7876 assert(addr <= _limit, "sweep invariant");
7877
7878 // check if we should yield
7879 do_yield_check(addr);
7880 if (fc->isFree()) {
7881 // Chunk that is already free
7882 res = fc->size();
7883 doAlreadyFreeChunk(fc);
7884 debug_only(_sp->verifyFreeLists());
7885 assert(res == fc->size(), "Don't expect the size to change");
7886 NOT_PRODUCT(
7887 _numObjectsAlreadyFree++;
7888 _numWordsAlreadyFree += res;
7889 )
7890 NOT_PRODUCT(_last_fc = fc;)
7891 } else if (!_bitMap->isMarked(addr)) {
7892 // Chunk is fresh garbage
7893 res = doGarbageChunk(fc);
7894 debug_only(_sp->verifyFreeLists());
7895 NOT_PRODUCT(
7896 _numObjectsFreed++;
7897 _numWordsFreed += res;
7898 )
7899 } else {
7900 // Chunk that is alive.
7901 res = doLiveChunk(fc);
7902 debug_only(_sp->verifyFreeLists());
7903 NOT_PRODUCT(
7904 _numObjectsLive++;
7905 _numWordsLive += res;
7906 )
7907 }
7908 return res;
7909 }
7910
7911 // For the smart allocation, record following
7912 // split deaths - a free chunk is removed from its free list because
7913 // it is being split into two or more chunks.
7914 // split birth - a free chunk is being added to its free list because
7915 // a larger free chunk has been split and resulted in this free chunk.
7916 // coal death - a free chunk is being removed from its free list because
7917 // it is being coalesced into a large free chunk.
7918 // coal birth - a free chunk is being added to its free list because
7919 // it was created when two or more free chunks where coalesced into
7920 // this free chunk.
7921 //
7922 // These statistics are used to determine the desired number of free
7923 // chunks of a given size. The desired number is chosen to be relative
7924 // to the end of a CMS sweep. The desired number at the end of a sweep
7925 // is the
7926 // count-at-end-of-previous-sweep (an amount that was enough)
7927 // - count-at-beginning-of-current-sweep (the excess)
7928 // + split-births (gains in this size during interval)
7929 // - split-deaths (demands on this size during interval)
7930 // where the interval is from the end of one sweep to the end of the
7931 // next.
7932 //
7933 // When sweeping the sweeper maintains an accumulated chunk which is
7934 // the chunk that is made up of chunks that have been coalesced. That
7935 // will be termed the left-hand chunk. A new chunk of garbage that
7936 // is being considered for coalescing will be referred to as the
7937 // right-hand chunk.
7938 //
7939 // When making a decision on whether to coalesce a right-hand chunk with
7940 // the current left-hand chunk, the current count vs. the desired count
7941 // of the left-hand chunk is considered. Also if the right-hand chunk
7942 // is near the large chunk at the end of the heap (see
7943 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7944 // left-hand chunk is coalesced.
7945 //
7946 // When making a decision about whether to split a chunk, the desired count
7947 // vs. the current count of the candidate to be split is also considered.
7948 // If the candidate is underpopulated (currently fewer chunks than desired)
7949 // a chunk of an overpopulated (currently more chunks than desired) size may
7950 // be chosen. The "hint" associated with a free list, if non-null, points
7951 // to a free list which may be overpopulated.
7952 //
7953
7954 void SweepClosure::doAlreadyFreeChunk(FreeChunk* fc) {
7955 size_t size = fc->size();
7956 // Chunks that cannot be coalesced are not in the
7957 // free lists.
7958 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7959 assert(_sp->verifyChunkInFreeLists(fc),
7960 "free chunk should be in free lists");
7961 }
7962 // a chunk that is already free, should not have been
7963 // marked in the bit map
7964 HeapWord* addr = (HeapWord*) fc;
7965 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7966 // Verify that the bit map has no bits marked between
7967 // addr and purported end of this block.
7968 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7969
7970 // Some chunks cannot be coalesced in under any circumstances.
7971 // See the definition of cantCoalesce().
7972 if (!fc->cantCoalesce()) {
7973 // This chunk can potentially be coalesced.
7974 if (_sp->adaptive_freelists()) {
7975 // All the work is done in
7976 doPostIsFreeOrGarbageChunk(fc, size);
7977 } else { // Not adaptive free lists
7978 // this is a free chunk that can potentially be coalesced by the sweeper;
7979 if (!inFreeRange()) {
7980 // if the next chunk is a free block that can't be coalesced
7981 // it doesn't make sense to remove this chunk from the free lists
7982 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7983 assert((HeapWord*)nextChunk <= _limit, "sweep invariant");
7984 if ((HeapWord*)nextChunk < _limit && // there's a next chunk...
7985 nextChunk->isFree() && // which is free...
7986 nextChunk->cantCoalesce()) { // ... but cant be coalesced
7987 // nothing to do
7988 } else {
7989 // Potentially the start of a new free range:
7990 // Don't eagerly remove it from the free lists.
7991 // No need to remove it if it will just be put
7992 // back again. (Also from a pragmatic point of view
7993 // if it is a free block in a region that is beyond
7994 // any allocated blocks, an assertion will fail)
7995 // Remember the start of a free run.
7996 initialize_free_range(addr, true);
7997 // end - can coalesce with next chunk
7998 }
7999 } else {
8000 // the midst of a free range, we are coalescing
8001 debug_only(record_free_block_coalesced(fc);)
8002 if (CMSTraceSweeper) {
8003 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
8004 }
8005 // remove it from the free lists
8006 _sp->removeFreeChunkFromFreeLists(fc);
8007 set_lastFreeRangeCoalesced(true);
8008 // If the chunk is being coalesced and the current free range is
8009 // in the free lists, remove the current free range so that it
8010 // will be returned to the free lists in its entirety - all
8011 // the coalesced pieces included.
8012 if (freeRangeInFreeLists()) {
8013 FreeChunk* ffc = (FreeChunk*) freeFinger();
8014 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8015 "Size of free range is inconsistent with chunk size.");
8016 if (CMSTestInFreeList) {
8017 assert(_sp->verifyChunkInFreeLists(ffc),
8018 "free range is not in free lists");
8019 }
8020 _sp->removeFreeChunkFromFreeLists(ffc);
8021 set_freeRangeInFreeLists(false);
8022 }
8023 }
8024 }
8025 } else {
8026 // Code path common to both original and adaptive free lists.
8027
8028 // cant coalesce with previous block; this should be treated
8029 // as the end of a free run if any
8030 if (inFreeRange()) {
8031 // we kicked some butt; time to pick up the garbage
8032 assert(freeFinger() < addr, "the finger pointeth off base");
8033 flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger()));
8034 }
8035 // else, nothing to do, just continue
8036 }
8037 }
8038
8039 size_t SweepClosure::doGarbageChunk(FreeChunk* fc) {
8040 // This is a chunk of garbage. It is not in any free list.
8041 // Add it to a free list or let it possibly be coalesced into
8042 // a larger chunk.
8043 HeapWord* addr = (HeapWord*) fc;
8044 size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8045
8046 if (_sp->adaptive_freelists()) {
8047 // Verify that the bit map has no bits marked between
8048 // addr and purported end of just dead object.
8049 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8050
8051 doPostIsFreeOrGarbageChunk(fc, size);
8052 } else {
8053 if (!inFreeRange()) {
8054 // start of a new free range
8055 assert(size > 0, "A free range should have a size");
8056 initialize_free_range(addr, false);
8057
8058 } else {
8059 // this will be swept up when we hit the end of the
8060 // free range
8061 if (CMSTraceSweeper) {
8062 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
8063 }
8064 // If the chunk is being coalesced and the current free range is
8065 // in the free lists, remove the current free range so that it
8066 // will be returned to the free lists in its entirety - all
8067 // the coalesced pieces included.
8068 if (freeRangeInFreeLists()) {
8069 FreeChunk* ffc = (FreeChunk*)freeFinger();
8070 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8071 "Size of free range is inconsistent with chunk size.");
8072 if (CMSTestInFreeList) {
8073 assert(_sp->verifyChunkInFreeLists(ffc),
8074 "free range is not in free lists");
8075 }
8076 _sp->removeFreeChunkFromFreeLists(ffc);
8077 set_freeRangeInFreeLists(false);
8078 }
8079 set_lastFreeRangeCoalesced(true);
8080 }
8081 // this will be swept up when we hit the end of the free range
8082
8083 // Verify that the bit map has no bits marked between
8084 // addr and purported end of just dead object.
8085 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8086 }
8087 return size;
8088 }
8089
8090 size_t SweepClosure::doLiveChunk(FreeChunk* fc) {
8091 HeapWord* addr = (HeapWord*) fc;
8092 // The sweeper has just found a live object. Return any accumulated
8093 // left hand chunk to the free lists.
8094 if (inFreeRange()) {
8095 if (_sp->adaptive_freelists()) {
8096 flushCurFreeChunk(freeFinger(),
8097 pointer_delta(addr, freeFinger()));
8098 } else { // not adaptive freelists
8099 set_inFreeRange(false);
8100 // Add the free range back to the free list if it is not already
8101 // there.
8102 if (!freeRangeInFreeLists()) {
8103 assert(freeFinger() < addr, "the finger pointeth off base");
8104 if (CMSTraceSweeper) {
8105 gclog_or_tty->print("Sweep:put_free_blk 0x%x (%d) "
8106 "[coalesced:%d]\n",
8107 freeFinger(), pointer_delta(addr, freeFinger()),
8108 lastFreeRangeCoalesced());
8109 }
8110 _sp->addChunkAndRepairOffsetTable(freeFinger(),
8111 pointer_delta(addr, freeFinger()), lastFreeRangeCoalesced());
8112 }
8113 }
8114 }
8115
8116 // Common code path for original and adaptive free lists.
8117
8118 // this object is live: we'd normally expect this to be
8119 // an oop, and like to assert the following:
8120 // assert(oop(addr)->is_oop(), "live block should be an oop");
8121 // However, as we commented above, this may be an object whose
8122 // header hasn't yet been initialized.
8123 size_t size;
8124 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8125 if (_bitMap->isMarked(addr + 1)) {
8126 // Determine the size from the bit map, rather than trying to
8127 // compute it from the object header.
8128 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8129 size = pointer_delta(nextOneAddr + 1, addr);
8130 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8131 "alignment problem");
8132
8133 #ifdef DEBUG
8134 if (oop(addr)->klass_or_null() != NULL &&
8135 ( !_collector->should_unload_classes()
8136 || (oop(addr)->is_parsable()) &&
8137 oop(addr)->is_conc_safe())) {
8138 // Ignore mark word because we are running concurrent with mutators
8139 assert(oop(addr)->is_oop(true), "live block should be an oop");
8140 // is_conc_safe is checked before performing this assertion
8141 // because an object that is not is_conc_safe may yet have
8142 // the return from size() correct.
8143 assert(size ==
8144 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8145 "P-mark and computed size do not agree");
8146 }
8147 #endif
8148
8149 } else {
8150 // This should be an initialized object that's alive.
8151 assert(oop(addr)->klass_or_null() != NULL &&
8152 (!_collector->should_unload_classes()
8153 || oop(addr)->is_parsable()),
8154 "Should be an initialized object");
8155 // Note that there are objects used during class redefinition
8156 // (e.g., merge_cp in VM_RedefineClasses::merge_cp_and_rewrite()
8157 // which are discarded with their is_conc_safe state still
8158 // false. These object may be floating garbage so may be
8159 // seen here. If they are floating garbage their size
8160 // should be attainable from their klass. Do not that
8161 // is_conc_safe() is true for oop(addr).
8162 // Ignore mark word because we are running concurrent with mutators
8163 assert(oop(addr)->is_oop(true), "live block should be an oop");
8164 // Verify that the bit map has no bits marked between
8165 // addr and purported end of this block.
8166 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8167 assert(size >= 3, "Necessary for Printezis marks to work");
8168 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8169 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8170 }
8171 return size;
8172 }
8173
8174 void SweepClosure::doPostIsFreeOrGarbageChunk(FreeChunk* fc,
8175 size_t chunkSize) {
8176 // doPostIsFreeOrGarbageChunk() should only be called in the smart allocation
8177 // scheme.
8178 bool fcInFreeLists = fc->isFree();
8179 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8180 assert((HeapWord*)fc <= _limit, "sweep invariant");
8181 if (CMSTestInFreeList && fcInFreeLists) {
8182 assert(_sp->verifyChunkInFreeLists(fc),
8183 "free chunk is not in free lists");
8184 }
8185
8186
8187 if (CMSTraceSweeper) {
8188 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8189 }
8190
8191 HeapWord* addr = (HeapWord*) fc;
8192
8193 bool coalesce;
8194 size_t left = pointer_delta(addr, freeFinger());
8195 size_t right = chunkSize;
8196 switch (FLSCoalescePolicy) {
8197 // numeric value forms a coalition aggressiveness metric
8198 case 0: { // never coalesce
8199 coalesce = false;
8200 break;
8201 }
8202 case 1: { // coalesce if left & right chunks on overpopulated lists
8203 coalesce = _sp->coalOverPopulated(left) &&
8204 _sp->coalOverPopulated(right);
8205 break;
8206 }
8207 case 2: { // coalesce if left chunk on overpopulated list (default)
8208 coalesce = _sp->coalOverPopulated(left);
8209 break;
8210 }
8211 case 3: { // coalesce if left OR right chunk on overpopulated list
8212 coalesce = _sp->coalOverPopulated(left) ||
8213 _sp->coalOverPopulated(right);
8214 break;
8215 }
8216 case 4: { // always coalesce
8217 coalesce = true;
8218 break;
8219 }
8220 default:
8221 ShouldNotReachHere();
8222 }
8223
8224 // Should the current free range be coalesced?
8225 // If the chunk is in a free range and either we decided to coalesce above
8226 // or the chunk is near the large block at the end of the heap
8227 // (isNearLargestChunk() returns true), then coalesce this chunk.
8228 bool doCoalesce = inFreeRange() &&
8229 (coalesce || _g->isNearLargestChunk((HeapWord*)fc));
8230 if (doCoalesce) {
8231 // Coalesce the current free range on the left with the new
8232 // chunk on the right. If either is on a free list,
8233 // it must be removed from the list and stashed in the closure.
8234 if (freeRangeInFreeLists()) {
8235 FreeChunk* ffc = (FreeChunk*)freeFinger();
8236 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8237 "Size of free range is inconsistent with chunk size.");
8238 if (CMSTestInFreeList) {
8239 assert(_sp->verifyChunkInFreeLists(ffc),
8240 "Chunk is not in free lists");
8241 }
8242 _sp->coalDeath(ffc->size());
8243 _sp->removeFreeChunkFromFreeLists(ffc);
8244 set_freeRangeInFreeLists(false);
8245 }
8246 if (fcInFreeLists) {
8247 _sp->coalDeath(chunkSize);
8248 assert(fc->size() == chunkSize,
8249 "The chunk has the wrong size or is not in the free lists");
8250 _sp->removeFreeChunkFromFreeLists(fc);
8251 }
8252 set_lastFreeRangeCoalesced(true);
8253 } else { // not in a free range and/or should not coalesce
8254 // Return the current free range and start a new one.
8255 if (inFreeRange()) {
8256 // In a free range but cannot coalesce with the right hand chunk.
8257 // Put the current free range into the free lists.
8258 flushCurFreeChunk(freeFinger(),
8259 pointer_delta(addr, freeFinger()));
8260 }
8261 // Set up for new free range. Pass along whether the right hand
8262 // chunk is in the free lists.
8263 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8264 }
8265 }
8266 void SweepClosure::flushCurFreeChunk(HeapWord* chunk, size_t size) {
8267 assert(inFreeRange(), "Should only be called if currently in a free range.");
8268 assert(size > 0,
8269 "A zero sized chunk cannot be added to the free lists.");
8270 if (!freeRangeInFreeLists()) {
8271 if(CMSTestInFreeList) {
8272 FreeChunk* fc = (FreeChunk*) chunk;
8273 fc->setSize(size);
8274 assert(!_sp->verifyChunkInFreeLists(fc),
8275 "chunk should not be in free lists yet");
8276 }
8277 if (CMSTraceSweeper) {
8278 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8279 chunk, size);
8280 }
8281 // A new free range is going to be starting. The current
8282 // free range has not been added to the free lists yet or
8283 // was removed so add it back.
8284 // If the current free range was coalesced, then the death
8285 // of the free range was recorded. Record a birth now.
8286 if (lastFreeRangeCoalesced()) {
8287 _sp->coalBirth(size);
8288 }
8289 _sp->addChunkAndRepairOffsetTable(chunk, size,
8290 lastFreeRangeCoalesced());
8291 }
8292 set_inFreeRange(false);
8293 set_freeRangeInFreeLists(false);
8294 }
8295
8296 // We take a break if we've been at this for a while,
8297 // so as to avoid monopolizing the locks involved.
8298 void SweepClosure::do_yield_work(HeapWord* addr) {
8299 // Return current free chunk being used for coalescing (if any)
8300 // to the appropriate freelist. After yielding, the next
8301 // free block encountered will start a coalescing range of
8302 // free blocks. If the next free block is adjacent to the
8303 // chunk just flushed, they will need to wait for the next
8304 // sweep to be coalesced.
8305 if (inFreeRange()) {
8306 flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger()));
8307 }
8308
8309 // First give up the locks, then yield, then re-lock.
8310 // We should probably use a constructor/destructor idiom to
8311 // do this unlock/lock or modify the MutexUnlocker class to
8312 // serve our purpose. XXX
8313 assert_lock_strong(_bitMap->lock());
8314 assert_lock_strong(_freelistLock);
8315 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8316 "CMS thread should hold CMS token");
8317 _bitMap->lock()->unlock();
8318 _freelistLock->unlock();
8319 ConcurrentMarkSweepThread::desynchronize(true);
8320 ConcurrentMarkSweepThread::acknowledge_yield_request();
8321 _collector->stopTimer();
8322 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8323 if (PrintCMSStatistics != 0) {
8324 _collector->incrementYields();
8325 }
8326 _collector->icms_wait();
8327
8328 // See the comment in coordinator_yield()
8329 for (unsigned i = 0; i < CMSYieldSleepCount &&
8330 ConcurrentMarkSweepThread::should_yield() &&
8331 !CMSCollector::foregroundGCIsActive(); ++i) {
8332 os::sleep(Thread::current(), 1, false);
8333 ConcurrentMarkSweepThread::acknowledge_yield_request();
8334 }
8335
8336 ConcurrentMarkSweepThread::synchronize(true);
8337 _freelistLock->lock();
8338 _bitMap->lock()->lock_without_safepoint_check();
8339 _collector->startTimer();
8340 }
8341
8342 #ifndef PRODUCT
8343 // This is actually very useful in a product build if it can
8344 // be called from the debugger. Compile it into the product
8345 // as needed.
8346 bool debug_verifyChunkInFreeLists(FreeChunk* fc) {
8347 return debug_cms_space->verifyChunkInFreeLists(fc);
8348 }
8349
8350 void SweepClosure::record_free_block_coalesced(FreeChunk* fc) const {
8351 if (CMSTraceSweeper) {
8352 gclog_or_tty->print("Sweep:coal_free_blk 0x%x (%d)\n", fc, fc->size());
8353 }
8354 }
8355 #endif
8356
8357 // CMSIsAliveClosure
8358 bool CMSIsAliveClosure::do_object_b(oop obj) {
8359 HeapWord* addr = (HeapWord*)obj;
8360 return addr != NULL &&
8361 (!_span.contains(addr) || _bit_map->isMarked(addr));
8362 }
8363
8364 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8365 MemRegion span,
8366 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8367 CMSMarkStack* revisit_stack, bool cpc):
8368 KlassRememberingOopClosure(collector, NULL, revisit_stack),
8369 _span(span),
8370 _bit_map(bit_map),
8371 _mark_stack(mark_stack),
8372 _concurrent_precleaning(cpc) {
8373 assert(!_span.is_empty(), "Empty span could spell trouble");
8374 }
8375
8376
8377 // CMSKeepAliveClosure: the serial version
8378 void CMSKeepAliveClosure::do_oop(oop obj) {
8379 HeapWord* addr = (HeapWord*)obj;
8380 if (_span.contains(addr) &&
8381 !_bit_map->isMarked(addr)) {
8382 _bit_map->mark(addr);
8383 bool simulate_overflow = false;
8384 NOT_PRODUCT(
8385 if (CMSMarkStackOverflowALot &&
8386 _collector->simulate_overflow()) {
8387 // simulate a stack overflow
8388 simulate_overflow = true;
8389 }
8390 )
8391 if (simulate_overflow || !_mark_stack->push(obj)) {
8392 if (_concurrent_precleaning) {
8393 // We dirty the overflown object and let the remark
8394 // phase deal with it.
8395 assert(_collector->overflow_list_is_empty(), "Error");
8396 // In the case of object arrays, we need to dirty all of
8397 // the cards that the object spans. No locking or atomics
8398 // are needed since no one else can be mutating the mod union
8399 // table.
8400 if (obj->is_objArray()) {
8401 size_t sz = obj->size();
8402 HeapWord* end_card_addr =
8403 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8404 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8405 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8406 _collector->_modUnionTable.mark_range(redirty_range);
8407 } else {
8408 _collector->_modUnionTable.mark(addr);
8409 }
8410 _collector->_ser_kac_preclean_ovflw++;
8411 } else {
8412 _collector->push_on_overflow_list(obj);
8413 _collector->_ser_kac_ovflw++;
8414 }
8415 }
8416 }
8417 }
8418
8419 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8420 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8421
8422 // CMSParKeepAliveClosure: a parallel version of the above.
8423 // The work queues are private to each closure (thread),
8424 // but (may be) available for stealing by other threads.
8425 void CMSParKeepAliveClosure::do_oop(oop obj) {
8426 HeapWord* addr = (HeapWord*)obj;
8427 if (_span.contains(addr) &&
8428 !_bit_map->isMarked(addr)) {
8429 // In general, during recursive tracing, several threads
8430 // may be concurrently getting here; the first one to
8431 // "tag" it, claims it.
8432 if (_bit_map->par_mark(addr)) {
8433 bool res = _work_queue->push(obj);
8434 assert(res, "Low water mark should be much less than capacity");
8435 // Do a recursive trim in the hope that this will keep
8436 // stack usage lower, but leave some oops for potential stealers
8437 trim_queue(_low_water_mark);
8438 } // Else, another thread got there first
8439 }
8440 }
8441
8442 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8443 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8444
8445 void CMSParKeepAliveClosure::trim_queue(uint max) {
8446 while (_work_queue->size() > max) {
8447 oop new_oop;
8448 if (_work_queue->pop_local(new_oop)) {
8449 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8450 assert(_bit_map->isMarked((HeapWord*)new_oop),
8451 "no white objects on this stack!");
8452 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8453 // iterate over the oops in this oop, marking and pushing
8454 // the ones in CMS heap (i.e. in _span).
8455 new_oop->oop_iterate(&_mark_and_push);
8456 }
8457 }
8458 }
8459
8460 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8461 CMSCollector* collector,
8462 MemRegion span, CMSBitMap* bit_map,
8463 CMSMarkStack* revisit_stack,
8464 OopTaskQueue* work_queue):
8465 Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
8466 _span(span),
8467 _bit_map(bit_map),
8468 _work_queue(work_queue) { }
8469
8470 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8471 HeapWord* addr = (HeapWord*)obj;
8472 if (_span.contains(addr) &&
8473 !_bit_map->isMarked(addr)) {
8474 if (_bit_map->par_mark(addr)) {
8475 bool simulate_overflow = false;
8476 NOT_PRODUCT(
8477 if (CMSMarkStackOverflowALot &&
8478 _collector->par_simulate_overflow()) {
8479 // simulate a stack overflow
8480 simulate_overflow = true;
8481 }
8482 )
8483 if (simulate_overflow || !_work_queue->push(obj)) {
8484 _collector->par_push_on_overflow_list(obj);
8485 _collector->_par_kac_ovflw++;
8486 }
8487 } // Else another thread got there already
8488 }
8489 }
8490
8491 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8492 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8493
8494 //////////////////////////////////////////////////////////////////
8495 // CMSExpansionCause /////////////////////////////
8496 //////////////////////////////////////////////////////////////////
8497 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8498 switch (cause) {
8499 case _no_expansion:
8500 return "No expansion";
8501 case _satisfy_free_ratio:
8502 return "Free ratio";
8503 case _satisfy_promotion:
8504 return "Satisfy promotion";
8505 case _satisfy_allocation:
8506 return "allocation";
8507 case _allocate_par_lab:
8508 return "Par LAB";
8509 case _allocate_par_spooling_space:
8510 return "Par Spooling Space";
8511 case _adaptive_size_policy:
8512 return "Ergonomics";
8513 default:
8514 return "unknown";
8515 }
8516 }
8517
8518 void CMSDrainMarkingStackClosure::do_void() {
8519 // the max number to take from overflow list at a time
8520 const size_t num = _mark_stack->capacity()/4;
8521 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8522 "Overflow list should be NULL during concurrent phases");
8523 while (!_mark_stack->isEmpty() ||
8524 // if stack is empty, check the overflow list
8525 _collector->take_from_overflow_list(num, _mark_stack)) {
8526 oop obj = _mark_stack->pop();
8527 HeapWord* addr = (HeapWord*)obj;
8528 assert(_span.contains(addr), "Should be within span");
8529 assert(_bit_map->isMarked(addr), "Should be marked");
8530 assert(obj->is_oop(), "Should be an oop");
8531 obj->oop_iterate(_keep_alive);
8532 }
8533 }
8534
8535 void CMSParDrainMarkingStackClosure::do_void() {
8536 // drain queue
8537 trim_queue(0);
8538 }
8539
8540 // Trim our work_queue so its length is below max at return
8541 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8542 while (_work_queue->size() > max) {
8543 oop new_oop;
8544 if (_work_queue->pop_local(new_oop)) {
8545 assert(new_oop->is_oop(), "Expected an oop");
8546 assert(_bit_map->isMarked((HeapWord*)new_oop),
8547 "no white objects on this stack!");
8548 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8549 // iterate over the oops in this oop, marking and pushing
8550 // the ones in CMS heap (i.e. in _span).
8551 new_oop->oop_iterate(&_mark_and_push);
8552 }
8553 }
8554 }
8555
8556 ////////////////////////////////////////////////////////////////////
8557 // Support for Marking Stack Overflow list handling and related code
8558 ////////////////////////////////////////////////////////////////////
8559 // Much of the following code is similar in shape and spirit to the
8560 // code used in ParNewGC. We should try and share that code
8561 // as much as possible in the future.
8562
8563 #ifndef PRODUCT
8564 // Debugging support for CMSStackOverflowALot
8565
8566 // It's OK to call this multi-threaded; the worst thing
8567 // that can happen is that we'll get a bunch of closely
8568 // spaced simulated oveflows, but that's OK, in fact
8569 // probably good as it would exercise the overflow code
8570 // under contention.
8571 bool CMSCollector::simulate_overflow() {
8572 if (_overflow_counter-- <= 0) { // just being defensive
8573 _overflow_counter = CMSMarkStackOverflowInterval;
8574 return true;
8575 } else {
8576 return false;
8577 }
8578 }
8579
8580 bool CMSCollector::par_simulate_overflow() {
8581 return simulate_overflow();
8582 }
8583 #endif
8584
8585 // Single-threaded
8586 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8587 assert(stack->isEmpty(), "Expected precondition");
8588 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8589 size_t i = num;
8590 oop cur = _overflow_list;
8591 const markOop proto = markOopDesc::prototype();
8592 NOT_PRODUCT(ssize_t n = 0;)
8593 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8594 next = oop(cur->mark());
8595 cur->set_mark(proto); // until proven otherwise
8596 assert(cur->is_oop(), "Should be an oop");
8597 bool res = stack->push(cur);
8598 assert(res, "Bit off more than can chew?");
8599 NOT_PRODUCT(n++;)
8600 }
8601 _overflow_list = cur;
8602 #ifndef PRODUCT
8603 assert(_num_par_pushes >= n, "Too many pops?");
8604 _num_par_pushes -=n;
8605 #endif
8606 return !stack->isEmpty();
8607 }
8608
8609 #define BUSY (oop(0x1aff1aff))
8610 // (MT-safe) Get a prefix of at most "num" from the list.
8611 // The overflow list is chained through the mark word of
8612 // each object in the list. We fetch the entire list,
8613 // break off a prefix of the right size and return the
8614 // remainder. If other threads try to take objects from
8615 // the overflow list at that time, they will wait for
8616 // some time to see if data becomes available. If (and
8617 // only if) another thread places one or more object(s)
8618 // on the global list before we have returned the suffix
8619 // to the global list, we will walk down our local list
8620 // to find its end and append the global list to
8621 // our suffix before returning it. This suffix walk can
8622 // prove to be expensive (quadratic in the amount of traffic)
8623 // when there are many objects in the overflow list and
8624 // there is much producer-consumer contention on the list.
8625 // *NOTE*: The overflow list manipulation code here and
8626 // in ParNewGeneration:: are very similar in shape,
8627 // except that in the ParNew case we use the old (from/eden)
8628 // copy of the object to thread the list via its klass word.
8629 // Because of the common code, if you make any changes in
8630 // the code below, please check the ParNew version to see if
8631 // similar changes might be needed.
8632 // CR 6797058 has been filed to consolidate the common code.
8633 bool CMSCollector::par_take_from_overflow_list(size_t num,
8634 OopTaskQueue* work_q) {
8635 assert(work_q->size() == 0, "First empty local work queue");
8636 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8637 if (_overflow_list == NULL) {
8638 return false;
8639 }
8640 // Grab the entire list; we'll put back a suffix
8641 oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8642 Thread* tid = Thread::current();
8643 size_t CMSOverflowSpinCount = (size_t)ParallelGCThreads;
8644 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8645 // If the list is busy, we spin for a short while,
8646 // sleeping between attempts to get the list.
8647 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8648 os::sleep(tid, sleep_time_millis, false);
8649 if (_overflow_list == NULL) {
8650 // Nothing left to take
8651 return false;
8652 } else if (_overflow_list != BUSY) {
8653 // Try and grab the prefix
8654 prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8655 }
8656 }
8657 // If the list was found to be empty, or we spun long
8658 // enough, we give up and return empty-handed. If we leave
8659 // the list in the BUSY state below, it must be the case that
8660 // some other thread holds the overflow list and will set it
8661 // to a non-BUSY state in the future.
8662 if (prefix == NULL || prefix == BUSY) {
8663 // Nothing to take or waited long enough
8664 if (prefix == NULL) {
8665 // Write back the NULL in case we overwrote it with BUSY above
8666 // and it is still the same value.
8667 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8668 }
8669 return false;
8670 }
8671 assert(prefix != NULL && prefix != BUSY, "Error");
8672 size_t i = num;
8673 oop cur = prefix;
8674 // Walk down the first "num" objects, unless we reach the end.
8675 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8676 if (cur->mark() == NULL) {
8677 // We have "num" or fewer elements in the list, so there
8678 // is nothing to return to the global list.
8679 // Write back the NULL in lieu of the BUSY we wrote
8680 // above, if it is still the same value.
8681 if (_overflow_list == BUSY) {
8682 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8683 }
8684 } else {
8685 // Chop off the suffix and rerturn it to the global list.
8686 assert(cur->mark() != BUSY, "Error");
8687 oop suffix_head = cur->mark(); // suffix will be put back on global list
8688 cur->set_mark(NULL); // break off suffix
8689 // It's possible that the list is still in the empty(busy) state
8690 // we left it in a short while ago; in that case we may be
8691 // able to place back the suffix without incurring the cost
8692 // of a walk down the list.
8693 oop observed_overflow_list = _overflow_list;
8694 oop cur_overflow_list = observed_overflow_list;
8695 bool attached = false;
8696 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8697 observed_overflow_list =
8698 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8699 if (cur_overflow_list == observed_overflow_list) {
8700 attached = true;
8701 break;
8702 } else cur_overflow_list = observed_overflow_list;
8703 }
8704 if (!attached) {
8705 // Too bad, someone else sneaked in (at least) an element; we'll need
8706 // to do a splice. Find tail of suffix so we can prepend suffix to global
8707 // list.
8708 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8709 oop suffix_tail = cur;
8710 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8711 "Tautology");
8712 observed_overflow_list = _overflow_list;
8713 do {
8714 cur_overflow_list = observed_overflow_list;
8715 if (cur_overflow_list != BUSY) {
8716 // Do the splice ...
8717 suffix_tail->set_mark(markOop(cur_overflow_list));
8718 } else { // cur_overflow_list == BUSY
8719 suffix_tail->set_mark(NULL);
8720 }
8721 // ... and try to place spliced list back on overflow_list ...
8722 observed_overflow_list =
8723 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8724 } while (cur_overflow_list != observed_overflow_list);
8725 // ... until we have succeeded in doing so.
8726 }
8727 }
8728
8729 // Push the prefix elements on work_q
8730 assert(prefix != NULL, "control point invariant");
8731 const markOop proto = markOopDesc::prototype();
8732 oop next;
8733 NOT_PRODUCT(ssize_t n = 0;)
8734 for (cur = prefix; cur != NULL; cur = next) {
8735 next = oop(cur->mark());
8736 cur->set_mark(proto); // until proven otherwise
8737 assert(cur->is_oop(), "Should be an oop");
8738 bool res = work_q->push(cur);
8739 assert(res, "Bit off more than we can chew?");
8740 NOT_PRODUCT(n++;)
8741 }
8742 #ifndef PRODUCT
8743 assert(_num_par_pushes >= n, "Too many pops?");
8744 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8745 #endif
8746 return true;
8747 }
8748
8749 // Single-threaded
8750 void CMSCollector::push_on_overflow_list(oop p) {
8751 NOT_PRODUCT(_num_par_pushes++;)
8752 assert(p->is_oop(), "Not an oop");
8753 preserve_mark_if_necessary(p);
8754 p->set_mark((markOop)_overflow_list);
8755 _overflow_list = p;
8756 }
8757
8758 // Multi-threaded; use CAS to prepend to overflow list
8759 void CMSCollector::par_push_on_overflow_list(oop p) {
8760 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8761 assert(p->is_oop(), "Not an oop");
8762 par_preserve_mark_if_necessary(p);
8763 oop observed_overflow_list = _overflow_list;
8764 oop cur_overflow_list;
8765 do {
8766 cur_overflow_list = observed_overflow_list;
8767 if (cur_overflow_list != BUSY) {
8768 p->set_mark(markOop(cur_overflow_list));
8769 } else {
8770 p->set_mark(NULL);
8771 }
8772 observed_overflow_list =
8773 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8774 } while (cur_overflow_list != observed_overflow_list);
8775 }
8776 #undef BUSY
8777
8778 // Single threaded
8779 // General Note on GrowableArray: pushes may silently fail
8780 // because we are (temporarily) out of C-heap for expanding
8781 // the stack. The problem is quite ubiquitous and affects
8782 // a lot of code in the JVM. The prudent thing for GrowableArray
8783 // to do (for now) is to exit with an error. However, that may
8784 // be too draconian in some cases because the caller may be
8785 // able to recover without much harm. For such cases, we
8786 // should probably introduce a "soft_push" method which returns
8787 // an indication of success or failure with the assumption that
8788 // the caller may be able to recover from a failure; code in
8789 // the VM can then be changed, incrementally, to deal with such
8790 // failures where possible, thus, incrementally hardening the VM
8791 // in such low resource situations.
8792 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8793 if (_preserved_oop_stack == NULL) {
8794 assert(_preserved_mark_stack == NULL,
8795 "bijection with preserved_oop_stack");
8796 // Allocate the stacks
8797 _preserved_oop_stack = new (ResourceObj::C_HEAP)
8798 GrowableArray<oop>(PreserveMarkStackSize, true);
8799 _preserved_mark_stack = new (ResourceObj::C_HEAP)
8800 GrowableArray<markOop>(PreserveMarkStackSize, true);
8801 if (_preserved_oop_stack == NULL || _preserved_mark_stack == NULL) {
8802 vm_exit_out_of_memory(2* PreserveMarkStackSize * sizeof(oop) /* punt */,
8803 "Preserved Mark/Oop Stack for CMS (C-heap)");
8804 }
8805 }
8806 _preserved_oop_stack->push(p);
8807 _preserved_mark_stack->push(m);
8808 assert(m == p->mark(), "Mark word changed");
8809 assert(_preserved_oop_stack->length() == _preserved_mark_stack->length(),
8810 "bijection");
8811 }
8812
8813 // Single threaded
8814 void CMSCollector::preserve_mark_if_necessary(oop p) {
8815 markOop m = p->mark();
8816 if (m->must_be_preserved(p)) {
8817 preserve_mark_work(p, m);
8818 }
8819 }
8820
8821 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8822 markOop m = p->mark();
8823 if (m->must_be_preserved(p)) {
8824 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8825 // Even though we read the mark word without holding
8826 // the lock, we are assured that it will not change
8827 // because we "own" this oop, so no other thread can
8828 // be trying to push it on the overflow list; see
8829 // the assertion in preserve_mark_work() that checks
8830 // that m == p->mark().
8831 preserve_mark_work(p, m);
8832 }
8833 }
8834
8835 // We should be able to do this multi-threaded,
8836 // a chunk of stack being a task (this is
8837 // correct because each oop only ever appears
8838 // once in the overflow list. However, it's
8839 // not very easy to completely overlap this with
8840 // other operations, so will generally not be done
8841 // until all work's been completed. Because we
8842 // expect the preserved oop stack (set) to be small,
8843 // it's probably fine to do this single-threaded.
8844 // We can explore cleverer concurrent/overlapped/parallel
8845 // processing of preserved marks if we feel the
8846 // need for this in the future. Stack overflow should
8847 // be so rare in practice and, when it happens, its
8848 // effect on performance so great that this will
8849 // likely just be in the noise anyway.
8850 void CMSCollector::restore_preserved_marks_if_any() {
8851 if (_preserved_oop_stack == NULL) {
8852 assert(_preserved_mark_stack == NULL,
8853 "bijection with preserved_oop_stack");
8854 return;
8855 }
8856
8857 assert(SafepointSynchronize::is_at_safepoint(),
8858 "world should be stopped");
8859 assert(Thread::current()->is_ConcurrentGC_thread() ||
8860 Thread::current()->is_VM_thread(),
8861 "should be single-threaded");
8862
8863 int length = _preserved_oop_stack->length();
8864 assert(_preserved_mark_stack->length() == length, "bijection");
8865 for (int i = 0; i < length; i++) {
8866 oop p = _preserved_oop_stack->at(i);
8867 assert(p->is_oop(), "Should be an oop");
8868 assert(_span.contains(p), "oop should be in _span");
8869 assert(p->mark() == markOopDesc::prototype(),
8870 "Set when taken from overflow list");
8871 markOop m = _preserved_mark_stack->at(i);
8872 p->set_mark(m);
8873 }
8874 _preserved_mark_stack->clear();
8875 _preserved_oop_stack->clear();
8876 assert(_preserved_mark_stack->is_empty() &&
8877 _preserved_oop_stack->is_empty(),
8878 "stacks were cleared above");
8879 }
8880
8881 #ifndef PRODUCT
8882 bool CMSCollector::no_preserved_marks() const {
8883 return ( ( _preserved_mark_stack == NULL
8884 && _preserved_oop_stack == NULL)
8885 || ( _preserved_mark_stack->is_empty()
8886 && _preserved_oop_stack->is_empty()));
8887 }
8888 #endif
8889
8890 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
8891 {
8892 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
8893 CMSAdaptiveSizePolicy* size_policy =
8894 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
8895 assert(size_policy->is_gc_cms_adaptive_size_policy(),
8896 "Wrong type for size policy");
8897 return size_policy;
8898 }
8899
8900 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
8901 size_t desired_promo_size) {
8902 if (cur_promo_size < desired_promo_size) {
8903 size_t expand_bytes = desired_promo_size - cur_promo_size;
8904 if (PrintAdaptiveSizePolicy && Verbose) {
8905 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
8906 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
8907 expand_bytes);
8908 }
8909 expand(expand_bytes,
8910 MinHeapDeltaBytes,
8911 CMSExpansionCause::_adaptive_size_policy);
8912 } else if (desired_promo_size < cur_promo_size) {
8913 size_t shrink_bytes = cur_promo_size - desired_promo_size;
8914 if (PrintAdaptiveSizePolicy && Verbose) {
8915 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
8916 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
8917 shrink_bytes);
8918 }
8919 shrink(shrink_bytes);
8920 }
8921 }
8922
8923 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
8924 GenCollectedHeap* gch = GenCollectedHeap::heap();
8925 CMSGCAdaptivePolicyCounters* counters =
8926 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
8927 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
8928 "Wrong kind of counters");
8929 return counters;
8930 }
8931
8932
8933 void ASConcurrentMarkSweepGeneration::update_counters() {
8934 if (UsePerfData) {
8935 _space_counters->update_all();
8936 _gen_counters->update_all();
8937 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8938 GenCollectedHeap* gch = GenCollectedHeap::heap();
8939 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
8940 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
8941 "Wrong gc statistics type");
8942 counters->update_counters(gc_stats_l);
8943 }
8944 }
8945
8946 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
8947 if (UsePerfData) {
8948 _space_counters->update_used(used);
8949 _space_counters->update_capacity();
8950 _gen_counters->update_all();
8951
8952 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8953 GenCollectedHeap* gch = GenCollectedHeap::heap();
8954 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
8955 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
8956 "Wrong gc statistics type");
8957 counters->update_counters(gc_stats_l);
8958 }
8959 }
8960
8961 // The desired expansion delta is computed so that:
8962 // . desired free percentage or greater is used
8963 void ASConcurrentMarkSweepGeneration::compute_new_size() {
8964 assert_locked_or_safepoint(Heap_lock);
8965
8966 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
8967
8968 // If incremental collection failed, we just want to expand
8969 // to the limit.
8970 if (incremental_collection_failed()) {
8971 clear_incremental_collection_failed();
8972 grow_to_reserved();
8973 return;
8974 }
8975
8976 assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing");
8977
8978 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
8979 "Wrong type of heap");
8980 int prev_level = level() - 1;
8981 assert(prev_level >= 0, "The cms generation is the lowest generation");
8982 Generation* prev_gen = gch->get_gen(prev_level);
8983 assert(prev_gen->kind() == Generation::ASParNew,
8984 "Wrong type of young generation");
8985 ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen;
8986 size_t cur_eden = younger_gen->eden()->capacity();
8987 CMSAdaptiveSizePolicy* size_policy = cms_size_policy();
8988 size_t cur_promo = free();
8989 size_policy->compute_tenured_generation_free_space(cur_promo,
8990 max_available(),
8991 cur_eden);
8992 resize(cur_promo, size_policy->promo_size());
8993
8994 // Record the new size of the space in the cms generation
8995 // that is available for promotions. This is temporary.
8996 // It should be the desired promo size.
8997 size_policy->avg_cms_promo()->sample(free());
8998 size_policy->avg_old_live()->sample(used());
8999
9000 if (UsePerfData) {
9001 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9002 counters->update_cms_capacity_counter(capacity());
9003 }
9004 }
9005
9006 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9007 assert_locked_or_safepoint(Heap_lock);
9008 assert_lock_strong(freelistLock());
9009 HeapWord* old_end = _cmsSpace->end();
9010 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9011 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9012 FreeChunk* chunk_at_end = find_chunk_at_end();
9013 if (chunk_at_end == NULL) {
9014 // No room to shrink
9015 if (PrintGCDetails && Verbose) {
9016 gclog_or_tty->print_cr("No room to shrink: old_end "
9017 PTR_FORMAT " unallocated_start " PTR_FORMAT
9018 " chunk_at_end " PTR_FORMAT,
9019 old_end, unallocated_start, chunk_at_end);
9020 }
9021 return;
9022 } else {
9023
9024 // Find the chunk at the end of the space and determine
9025 // how much it can be shrunk.
9026 size_t shrinkable_size_in_bytes = chunk_at_end->size();
9027 size_t aligned_shrinkable_size_in_bytes =
9028 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9029 assert(unallocated_start <= chunk_at_end->end(),
9030 "Inconsistent chunk at end of space");
9031 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9032 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9033
9034 // Shrink the underlying space
9035 _virtual_space.shrink_by(bytes);
9036 if (PrintGCDetails && Verbose) {
9037 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9038 " desired_bytes " SIZE_FORMAT
9039 " shrinkable_size_in_bytes " SIZE_FORMAT
9040 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9041 " bytes " SIZE_FORMAT,
9042 desired_bytes, shrinkable_size_in_bytes,
9043 aligned_shrinkable_size_in_bytes, bytes);
9044 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
9045 " unallocated_start " SIZE_FORMAT,
9046 old_end, unallocated_start);
9047 }
9048
9049 // If the space did shrink (shrinking is not guaranteed),
9050 // shrink the chunk at the end by the appropriate amount.
9051 if (((HeapWord*)_virtual_space.high()) < old_end) {
9052 size_t new_word_size =
9053 heap_word_size(_virtual_space.committed_size());
9054
9055 // Have to remove the chunk from the dictionary because it is changing
9056 // size and might be someplace elsewhere in the dictionary.
9057
9058 // Get the chunk at end, shrink it, and put it
9059 // back.
9060 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9061 size_t word_size_change = word_size_before - new_word_size;
9062 size_t chunk_at_end_old_size = chunk_at_end->size();
9063 assert(chunk_at_end_old_size >= word_size_change,
9064 "Shrink is too large");
9065 chunk_at_end->setSize(chunk_at_end_old_size -
9066 word_size_change);
9067 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9068 word_size_change);
9069
9070 _cmsSpace->returnChunkToDictionary(chunk_at_end);
9071
9072 MemRegion mr(_cmsSpace->bottom(), new_word_size);
9073 _bts->resize(new_word_size); // resize the block offset shared array
9074 Universe::heap()->barrier_set()->resize_covered_region(mr);
9075 _cmsSpace->assert_locked();
9076 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9077
9078 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9079
9080 // update the space and generation capacity counters
9081 if (UsePerfData) {
9082 _space_counters->update_capacity();
9083 _gen_counters->update_all();
9084 }
9085
9086 if (Verbose && PrintGCDetails) {
9087 size_t new_mem_size = _virtual_space.committed_size();
9088 size_t old_mem_size = new_mem_size + bytes;
9089 gclog_or_tty->print_cr("Shrinking %s from %ldK by %ldK to %ldK",
9090 name(), old_mem_size/K, bytes/K, new_mem_size/K);
9091 }
9092 }
9093
9094 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9095 "Inconsistency at end of space");
9096 assert(chunk_at_end->end() == _cmsSpace->end(),
9097 "Shrinking is inconsistent");
9098 return;
9099 }
9100 }
9101
9102 // Transfer some number of overflown objects to usual marking
9103 // stack. Return true if some objects were transferred.
9104 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9105 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9106 (size_t)ParGCDesiredObjsFromOverflowList);
9107
9108 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9109 assert(_collector->overflow_list_is_empty() || res,
9110 "If list is not empty, we should have taken something");
9111 assert(!res || !_mark_stack->isEmpty(),
9112 "If we took something, it should now be on our stack");
9113 return res;
9114 }
9115
9116 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9117 size_t res = _sp->block_size_no_stall(addr, _collector);
9118 assert(res != 0, "Should always be able to compute a size");
9119 if (_sp->block_is_obj(addr)) {
9120 if (_live_bit_map->isMarked(addr)) {
9121 // It can't have been dead in a previous cycle
9122 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9123 } else {
9124 _dead_bit_map->mark(addr); // mark the dead object
9125 }
9126 }
9127 return res;
9128 }