1 /*
2 * Copyright (c) 2001, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/symbolTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc_implementation/concurrentMarkSweep/cmsAdaptiveSizePolicy.hpp"
31 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
32 #include "gc_implementation/concurrentMarkSweep/cmsGCAdaptivePolicyCounters.hpp"
33 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
34 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
36 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
37 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
38 #include "gc_implementation/parNew/parNewGeneration.hpp"
39 #include "gc_implementation/shared/collectorCounters.hpp"
40 #include "gc_implementation/shared/gcTimer.hpp"
41 #include "gc_implementation/shared/gcTrace.hpp"
42 #include "gc_implementation/shared/gcTraceTime.hpp"
43 #include "gc_implementation/shared/isGCActiveMark.hpp"
44 #include "gc_interface/collectedHeap.inline.hpp"
45 #include "memory/allocation.hpp"
46 #include "memory/cardTableRS.hpp"
47 #include "memory/collectorPolicy.hpp"
48 #include "memory/gcLocker.inline.hpp"
49 #include "memory/genCollectedHeap.hpp"
50 #include "memory/genMarkSweep.hpp"
51 #include "memory/genOopClosures.inline.hpp"
52 #include "memory/iterator.hpp"
53 #include "memory/padded.hpp"
54 #include "memory/referencePolicy.hpp"
55 #include "memory/resourceArea.hpp"
56 #include "memory/tenuredGeneration.hpp"
57 #include "oops/oop.inline.hpp"
58 #include "prims/jvmtiExport.hpp"
59 #include "runtime/globals_extension.hpp"
60 #include "runtime/handles.inline.hpp"
61 #include "runtime/java.hpp"
62 #include "runtime/vmThread.hpp"
63 #include "services/memoryService.hpp"
64 #include "services/runtimeService.hpp"
65
66 // statics
67 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
68 bool CMSCollector::_full_gc_requested = false;
69 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
70
71 //////////////////////////////////////////////////////////////////
72 // In support of CMS/VM thread synchronization
73 //////////////////////////////////////////////////////////////////
74 // We split use of the CGC_lock into 2 "levels".
75 // The low-level locking is of the usual CGC_lock monitor. We introduce
76 // a higher level "token" (hereafter "CMS token") built on top of the
77 // low level monitor (hereafter "CGC lock").
78 // The token-passing protocol gives priority to the VM thread. The
79 // CMS-lock doesn't provide any fairness guarantees, but clients
80 // should ensure that it is only held for very short, bounded
81 // durations.
82 //
83 // When either of the CMS thread or the VM thread is involved in
84 // collection operations during which it does not want the other
85 // thread to interfere, it obtains the CMS token.
86 //
87 // If either thread tries to get the token while the other has
88 // it, that thread waits. However, if the VM thread and CMS thread
89 // both want the token, then the VM thread gets priority while the
90 // CMS thread waits. This ensures, for instance, that the "concurrent"
91 // phases of the CMS thread's work do not block out the VM thread
92 // for long periods of time as the CMS thread continues to hog
93 // the token. (See bug 4616232).
94 //
95 // The baton-passing functions are, however, controlled by the
96 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
97 // and here the low-level CMS lock, not the high level token,
98 // ensures mutual exclusion.
99 //
100 // Two important conditions that we have to satisfy:
101 // 1. if a thread does a low-level wait on the CMS lock, then it
102 // relinquishes the CMS token if it were holding that token
103 // when it acquired the low-level CMS lock.
104 // 2. any low-level notifications on the low-level lock
105 // should only be sent when a thread has relinquished the token.
106 //
107 // In the absence of either property, we'd have potential deadlock.
108 //
109 // We protect each of the CMS (concurrent and sequential) phases
110 // with the CMS _token_, not the CMS _lock_.
111 //
112 // The only code protected by CMS lock is the token acquisition code
113 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
114 // baton-passing code.
115 //
116 // Unfortunately, i couldn't come up with a good abstraction to factor and
117 // hide the naked CGC_lock manipulation in the baton-passing code
118 // further below. That's something we should try to do. Also, the proof
119 // of correctness of this 2-level locking scheme is far from obvious,
120 // and potentially quite slippery. We have an uneasy suspicion, for instance,
121 // that there may be a theoretical possibility of delay/starvation in the
122 // low-level lock/wait/notify scheme used for the baton-passing because of
123 // potential interference with the priority scheme embodied in the
124 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
125 // invocation further below and marked with "XXX 20011219YSR".
126 // Indeed, as we note elsewhere, this may become yet more slippery
127 // in the presence of multiple CMS and/or multiple VM threads. XXX
128
129 class CMSTokenSync: public StackObj {
130 private:
131 bool _is_cms_thread;
132 public:
133 CMSTokenSync(bool is_cms_thread):
134 _is_cms_thread(is_cms_thread) {
135 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
136 "Incorrect argument to constructor");
137 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
138 }
139
140 ~CMSTokenSync() {
141 assert(_is_cms_thread ?
142 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
143 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
144 "Incorrect state");
145 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
146 }
147 };
148
149 // Convenience class that does a CMSTokenSync, and then acquires
150 // upto three locks.
151 class CMSTokenSyncWithLocks: public CMSTokenSync {
152 private:
153 // Note: locks are acquired in textual declaration order
154 // and released in the opposite order
155 MutexLockerEx _locker1, _locker2, _locker3;
156 public:
157 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
158 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
159 CMSTokenSync(is_cms_thread),
160 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
161 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
162 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
163 { }
164 };
165
166
167 // Wrapper class to temporarily disable icms during a foreground cms collection.
168 class ICMSDisabler: public StackObj {
169 public:
170 // The ctor disables icms and wakes up the thread so it notices the change;
171 // the dtor re-enables icms. Note that the CMSCollector methods will check
172 // CMSIncrementalMode.
173 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
174 ~ICMSDisabler() { CMSCollector::enable_icms(); }
175 };
176
177 //////////////////////////////////////////////////////////////////
178 // Concurrent Mark-Sweep Generation /////////////////////////////
179 //////////////////////////////////////////////////////////////////
180
181 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
182
183 // This struct contains per-thread things necessary to support parallel
184 // young-gen collection.
185 class CMSParGCThreadState: public CHeapObj<mtGC> {
186 public:
187 CFLS_LAB lab;
188 PromotionInfo promo;
189
190 // Constructor.
191 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
192 promo.setSpace(cfls);
193 }
194 };
195
196 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
197 ReservedSpace rs, size_t initial_byte_size, int level,
198 CardTableRS* ct, bool use_adaptive_freelists,
199 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
200 CardGeneration(rs, initial_byte_size, level, ct),
201 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
202 _debug_collection_type(Concurrent_collection_type),
203 _did_compact(false)
204 {
205 HeapWord* bottom = (HeapWord*) _virtual_space.low();
206 HeapWord* end = (HeapWord*) _virtual_space.high();
207
208 _direct_allocated_words = 0;
209 NOT_PRODUCT(
210 _numObjectsPromoted = 0;
211 _numWordsPromoted = 0;
212 _numObjectsAllocated = 0;
213 _numWordsAllocated = 0;
214 )
215
216 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
217 use_adaptive_freelists,
218 dictionaryChoice);
219 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
220 if (_cmsSpace == NULL) {
221 vm_exit_during_initialization(
222 "CompactibleFreeListSpace allocation failure");
223 }
224 _cmsSpace->_gen = this;
225
226 _gc_stats = new CMSGCStats();
227
228 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
229 // offsets match. The ability to tell free chunks from objects
230 // depends on this property.
231 debug_only(
232 FreeChunk* junk = NULL;
233 assert(UseCompressedClassPointers ||
234 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
235 "Offset of FreeChunk::_prev within FreeChunk must match"
236 " that of OopDesc::_klass within OopDesc");
237 )
238 if (CollectedHeap::use_parallel_gc_threads()) {
239 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
240 _par_gc_thread_states =
241 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
242 if (_par_gc_thread_states == NULL) {
243 vm_exit_during_initialization("Could not allocate par gc structs");
244 }
245 for (uint i = 0; i < ParallelGCThreads; i++) {
246 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
247 if (_par_gc_thread_states[i] == NULL) {
248 vm_exit_during_initialization("Could not allocate par gc structs");
249 }
250 }
251 } else {
252 _par_gc_thread_states = NULL;
253 }
254 _incremental_collection_failed = false;
255 // The "dilatation_factor" is the expansion that can occur on
256 // account of the fact that the minimum object size in the CMS
257 // generation may be larger than that in, say, a contiguous young
258 // generation.
259 // Ideally, in the calculation below, we'd compute the dilatation
260 // factor as: MinChunkSize/(promoting_gen's min object size)
261 // Since we do not have such a general query interface for the
262 // promoting generation, we'll instead just use the minimum
263 // object size (which today is a header's worth of space);
264 // note that all arithmetic is in units of HeapWords.
265 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
266 assert(_dilatation_factor >= 1.0, "from previous assert");
267 }
268
269
270 // The field "_initiating_occupancy" represents the occupancy percentage
271 // at which we trigger a new collection cycle. Unless explicitly specified
272 // via CMSInitiatingOccupancyFraction (argument "io" below), it
273 // is calculated by:
274 //
275 // Let "f" be MinHeapFreeRatio in
276 //
277 // _initiating_occupancy = 100-f +
278 // f * (CMSTriggerRatio/100)
279 // where CMSTriggerRatio is the argument "tr" below.
280 //
281 // That is, if we assume the heap is at its desired maximum occupancy at the
282 // end of a collection, we let CMSTriggerRatio of the (purported) free
283 // space be allocated before initiating a new collection cycle.
284 //
285 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
286 assert(io <= 100 && tr <= 100, "Check the arguments");
287 if (io >= 0) {
288 _initiating_occupancy = (double)io / 100.0;
289 } else {
290 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
291 (double)(tr * MinHeapFreeRatio) / 100.0)
292 / 100.0;
293 }
294 }
295
296 void ConcurrentMarkSweepGeneration::ref_processor_init() {
297 assert(collector() != NULL, "no collector");
298 collector()->ref_processor_init();
299 }
300
301 void CMSCollector::ref_processor_init() {
302 if (_ref_processor == NULL) {
303 // Allocate and initialize a reference processor
304 _ref_processor =
305 new ReferenceProcessor(_span, // span
306 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
307 (int) ParallelGCThreads, // mt processing degree
308 _cmsGen->refs_discovery_is_mt(), // mt discovery
309 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
310 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
311 &_is_alive_closure, // closure for liveness info
312 false); // next field updates do not need write barrier
313 // Initialize the _ref_processor field of CMSGen
314 _cmsGen->set_ref_processor(_ref_processor);
315
316 }
317 }
318
319 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
320 GenCollectedHeap* gch = GenCollectedHeap::heap();
321 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
322 "Wrong type of heap");
323 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
324 gch->gen_policy()->size_policy();
325 assert(sp->is_gc_cms_adaptive_size_policy(),
326 "Wrong type of size policy");
327 return sp;
328 }
329
330 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
331 CMSGCAdaptivePolicyCounters* results =
332 (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
333 assert(
334 results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
335 "Wrong gc policy counter kind");
336 return results;
337 }
338
339
340 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
341
342 const char* gen_name = "old";
343
344 // Generation Counters - generation 1, 1 subspace
345 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
346
347 _space_counters = new GSpaceCounters(gen_name, 0,
348 _virtual_space.reserved_size(),
349 this, _gen_counters);
350 }
351
352 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
353 _cms_gen(cms_gen)
354 {
355 assert(alpha <= 100, "bad value");
356 _saved_alpha = alpha;
357
358 // Initialize the alphas to the bootstrap value of 100.
359 _gc0_alpha = _cms_alpha = 100;
360
361 _cms_begin_time.update();
362 _cms_end_time.update();
363
364 _gc0_duration = 0.0;
365 _gc0_period = 0.0;
366 _gc0_promoted = 0;
367
368 _cms_duration = 0.0;
369 _cms_period = 0.0;
370 _cms_allocated = 0;
371
372 _cms_used_at_gc0_begin = 0;
373 _cms_used_at_gc0_end = 0;
374 _allow_duty_cycle_reduction = false;
375 _valid_bits = 0;
376 _icms_duty_cycle = CMSIncrementalDutyCycle;
377 }
378
379 double CMSStats::cms_free_adjustment_factor(size_t free) const {
380 // TBD: CR 6909490
381 return 1.0;
382 }
383
384 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
385 }
386
387 // If promotion failure handling is on use
388 // the padded average size of the promotion for each
389 // young generation collection.
390 double CMSStats::time_until_cms_gen_full() const {
391 size_t cms_free = _cms_gen->cmsSpace()->free();
392 GenCollectedHeap* gch = GenCollectedHeap::heap();
393 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
394 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
395 if (cms_free > expected_promotion) {
396 // Start a cms collection if there isn't enough space to promote
397 // for the next minor collection. Use the padded average as
398 // a safety factor.
399 cms_free -= expected_promotion;
400
401 // Adjust by the safety factor.
402 double cms_free_dbl = (double)cms_free;
403 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
404 // Apply a further correction factor which tries to adjust
405 // for recent occurance of concurrent mode failures.
406 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
407 cms_free_dbl = cms_free_dbl * cms_adjustment;
408
409 if (PrintGCDetails && Verbose) {
410 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
411 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
412 cms_free, expected_promotion);
413 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
414 cms_free_dbl, cms_consumption_rate() + 1.0);
415 }
416 // Add 1 in case the consumption rate goes to zero.
417 return cms_free_dbl / (cms_consumption_rate() + 1.0);
418 }
419 return 0.0;
420 }
421
422 // Compare the duration of the cms collection to the
423 // time remaining before the cms generation is empty.
424 // Note that the time from the start of the cms collection
425 // to the start of the cms sweep (less than the total
426 // duration of the cms collection) can be used. This
427 // has been tried and some applications experienced
428 // promotion failures early in execution. This was
429 // possibly because the averages were not accurate
430 // enough at the beginning.
431 double CMSStats::time_until_cms_start() const {
432 // We add "gc0_period" to the "work" calculation
433 // below because this query is done (mostly) at the
434 // end of a scavenge, so we need to conservatively
435 // account for that much possible delay
436 // in the query so as to avoid concurrent mode failures
437 // due to starting the collection just a wee bit too
438 // late.
439 double work = cms_duration() + gc0_period();
440 double deadline = time_until_cms_gen_full();
441 // If a concurrent mode failure occurred recently, we want to be
442 // more conservative and halve our expected time_until_cms_gen_full()
443 if (work > deadline) {
444 if (Verbose && PrintGCDetails) {
445 gclog_or_tty->print(
446 " CMSCollector: collect because of anticipated promotion "
447 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
448 gc0_period(), time_until_cms_gen_full());
449 }
450 return 0.0;
451 }
452 return work - deadline;
453 }
454
455 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
456 // amount of change to prevent wild oscillation.
457 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
458 unsigned int new_duty_cycle) {
459 assert(old_duty_cycle <= 100, "bad input value");
460 assert(new_duty_cycle <= 100, "bad input value");
461
462 // Note: use subtraction with caution since it may underflow (values are
463 // unsigned). Addition is safe since we're in the range 0-100.
464 unsigned int damped_duty_cycle = new_duty_cycle;
465 if (new_duty_cycle < old_duty_cycle) {
466 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
467 if (new_duty_cycle + largest_delta < old_duty_cycle) {
468 damped_duty_cycle = old_duty_cycle - largest_delta;
469 }
470 } else if (new_duty_cycle > old_duty_cycle) {
471 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
472 if (new_duty_cycle > old_duty_cycle + largest_delta) {
473 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
474 }
475 }
476 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
477
478 if (CMSTraceIncrementalPacing) {
479 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
480 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
481 }
482 return damped_duty_cycle;
483 }
484
485 unsigned int CMSStats::icms_update_duty_cycle_impl() {
486 assert(CMSIncrementalPacing && valid(),
487 "should be handled in icms_update_duty_cycle()");
488
489 double cms_time_so_far = cms_timer().seconds();
490 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
491 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
492
493 // Avoid division by 0.
494 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
495 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
496
497 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
498 if (new_duty_cycle > _icms_duty_cycle) {
499 // Avoid very small duty cycles (1 or 2); 0 is allowed.
500 if (new_duty_cycle > 2) {
501 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
502 new_duty_cycle);
503 }
504 } else if (_allow_duty_cycle_reduction) {
505 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
506 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
507 // Respect the minimum duty cycle.
508 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
509 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
510 }
511
512 if (PrintGCDetails || CMSTraceIncrementalPacing) {
513 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
514 }
515
516 _allow_duty_cycle_reduction = false;
517 return _icms_duty_cycle;
518 }
519
520 #ifndef PRODUCT
521 void CMSStats::print_on(outputStream *st) const {
522 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
523 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
524 gc0_duration(), gc0_period(), gc0_promoted());
525 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
526 cms_duration(), cms_duration_per_mb(),
527 cms_period(), cms_allocated());
528 st->print(",cms_since_beg=%g,cms_since_end=%g",
529 cms_time_since_begin(), cms_time_since_end());
530 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
531 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
532 if (CMSIncrementalMode) {
533 st->print(",dc=%d", icms_duty_cycle());
534 }
535
536 if (valid()) {
537 st->print(",promo_rate=%g,cms_alloc_rate=%g",
538 promotion_rate(), cms_allocation_rate());
539 st->print(",cms_consumption_rate=%g,time_until_full=%g",
540 cms_consumption_rate(), time_until_cms_gen_full());
541 }
542 st->print(" ");
543 }
544 #endif // #ifndef PRODUCT
545
546 CMSCollector::CollectorState CMSCollector::_collectorState =
547 CMSCollector::Idling;
548 bool CMSCollector::_foregroundGCIsActive = false;
549 bool CMSCollector::_foregroundGCShouldWait = false;
550
551 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
552 CardTableRS* ct,
553 ConcurrentMarkSweepPolicy* cp):
554 _cmsGen(cmsGen),
555 _ct(ct),
556 _ref_processor(NULL), // will be set later
557 _conc_workers(NULL), // may be set later
558 _abort_preclean(false),
559 _start_sampling(false),
560 _between_prologue_and_epilogue(false),
561 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
562 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
563 -1 /* lock-free */, "No_lock" /* dummy */),
564 _modUnionClosure(&_modUnionTable),
565 _modUnionClosurePar(&_modUnionTable),
566 // Adjust my span to cover old (cms) gen
567 _span(cmsGen->reserved()),
568 // Construct the is_alive_closure with _span & markBitMap
569 _is_alive_closure(_span, &_markBitMap),
570 _restart_addr(NULL),
571 _overflow_list(NULL),
572 _stats(cmsGen),
573 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true)),
574 _eden_chunk_array(NULL), // may be set in ctor body
575 _eden_chunk_capacity(0), // -- ditto --
576 _eden_chunk_index(0), // -- ditto --
577 _survivor_plab_array(NULL), // -- ditto --
578 _survivor_chunk_array(NULL), // -- ditto --
579 _survivor_chunk_capacity(0), // -- ditto --
580 _survivor_chunk_index(0), // -- ditto --
581 _ser_pmc_preclean_ovflw(0),
582 _ser_kac_preclean_ovflw(0),
583 _ser_pmc_remark_ovflw(0),
584 _par_pmc_remark_ovflw(0),
585 _ser_kac_ovflw(0),
586 _par_kac_ovflw(0),
587 #ifndef PRODUCT
588 _num_par_pushes(0),
589 #endif
590 _collection_count_start(0),
591 _verifying(false),
592 _icms_start_limit(NULL),
593 _icms_stop_limit(NULL),
594 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
595 _completed_initialization(false),
596 _collector_policy(cp),
597 _should_unload_classes(CMSClassUnloadingEnabled),
598 _concurrent_cycles_since_last_unload(0),
599 _roots_scanning_options(SharedHeap::SO_None),
600 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
601 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
602 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
603 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
604 _cms_start_registered(false)
605 {
606 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
607 ExplicitGCInvokesConcurrent = true;
608 }
609 // Now expand the span and allocate the collection support structures
610 // (MUT, marking bit map etc.) to cover both generations subject to
611 // collection.
612
613 // For use by dirty card to oop closures.
614 _cmsGen->cmsSpace()->set_collector(this);
615
616 // Allocate MUT and marking bit map
617 {
618 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
619 if (!_markBitMap.allocate(_span)) {
620 warning("Failed to allocate CMS Bit Map");
621 return;
622 }
623 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
624 }
625 {
626 _modUnionTable.allocate(_span);
627 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
628 }
629
630 if (!_markStack.allocate(MarkStackSize)) {
631 warning("Failed to allocate CMS Marking Stack");
632 return;
633 }
634
635 // Support for multi-threaded concurrent phases
636 if (CMSConcurrentMTEnabled) {
637 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
638 // just for now
639 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
640 }
641 if (ConcGCThreads > 1) {
642 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
643 ConcGCThreads, true);
644 if (_conc_workers == NULL) {
645 warning("GC/CMS: _conc_workers allocation failure: "
646 "forcing -CMSConcurrentMTEnabled");
647 CMSConcurrentMTEnabled = false;
648 } else {
649 _conc_workers->initialize_workers();
650 }
651 } else {
652 CMSConcurrentMTEnabled = false;
653 }
654 }
655 if (!CMSConcurrentMTEnabled) {
656 ConcGCThreads = 0;
657 } else {
658 // Turn off CMSCleanOnEnter optimization temporarily for
659 // the MT case where it's not fixed yet; see 6178663.
660 CMSCleanOnEnter = false;
661 }
662 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
663 "Inconsistency");
664
665 // Parallel task queues; these are shared for the
666 // concurrent and stop-world phases of CMS, but
667 // are not shared with parallel scavenge (ParNew).
668 {
669 uint i;
670 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
671
672 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
673 || ParallelRefProcEnabled)
674 && num_queues > 0) {
675 _task_queues = new OopTaskQueueSet(num_queues);
676 if (_task_queues == NULL) {
677 warning("task_queues allocation failure.");
678 return;
679 }
680 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
681 if (_hash_seed == NULL) {
682 warning("_hash_seed array allocation failure");
683 return;
684 }
685
686 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
687 for (i = 0; i < num_queues; i++) {
688 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
689 if (q == NULL) {
690 warning("work_queue allocation failure.");
691 return;
692 }
693 _task_queues->register_queue(i, q);
694 }
695 for (i = 0; i < num_queues; i++) {
696 _task_queues->queue(i)->initialize();
697 _hash_seed[i] = 17; // copied from ParNew
698 }
699 }
700 }
701
702 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
703
704 // Clip CMSBootstrapOccupancy between 0 and 100.
705 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
706
707 _full_gcs_since_conc_gc = 0;
708
709 // Now tell CMS generations the identity of their collector
710 ConcurrentMarkSweepGeneration::set_collector(this);
711
712 // Create & start a CMS thread for this CMS collector
713 _cmsThread = ConcurrentMarkSweepThread::start(this);
714 assert(cmsThread() != NULL, "CMS Thread should have been created");
715 assert(cmsThread()->collector() == this,
716 "CMS Thread should refer to this gen");
717 assert(CGC_lock != NULL, "Where's the CGC_lock?");
718
719 // Support for parallelizing young gen rescan
720 GenCollectedHeap* gch = GenCollectedHeap::heap();
721 _young_gen = gch->prev_gen(_cmsGen);
722 if (gch->supports_inline_contig_alloc()) {
723 _top_addr = gch->top_addr();
724 _end_addr = gch->end_addr();
725 assert(_young_gen != NULL, "no _young_gen");
726 _eden_chunk_index = 0;
727 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
728 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
729 if (_eden_chunk_array == NULL) {
730 _eden_chunk_capacity = 0;
731 warning("GC/CMS: _eden_chunk_array allocation failure");
732 }
733 }
734 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
735
736 // Support for parallelizing survivor space rescan
737 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
738 const size_t max_plab_samples =
739 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
740
741 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
742 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
743 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
744 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
745 || _cursor == NULL) {
746 warning("Failed to allocate survivor plab/chunk array");
747 if (_survivor_plab_array != NULL) {
748 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
749 _survivor_plab_array = NULL;
750 }
751 if (_survivor_chunk_array != NULL) {
752 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
753 _survivor_chunk_array = NULL;
754 }
755 if (_cursor != NULL) {
756 FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
757 _cursor = NULL;
758 }
759 } else {
760 _survivor_chunk_capacity = 2*max_plab_samples;
761 for (uint i = 0; i < ParallelGCThreads; i++) {
762 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
763 if (vec == NULL) {
764 warning("Failed to allocate survivor plab array");
765 for (int j = i; j > 0; j--) {
766 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
767 }
768 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
769 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
770 _survivor_plab_array = NULL;
771 _survivor_chunk_array = NULL;
772 _survivor_chunk_capacity = 0;
773 break;
774 } else {
775 ChunkArray* cur =
776 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
777 max_plab_samples);
778 assert(cur->end() == 0, "Should be 0");
779 assert(cur->array() == vec, "Should be vec");
780 assert(cur->capacity() == max_plab_samples, "Error");
781 }
782 }
783 }
784 }
785 assert( ( _survivor_plab_array != NULL
786 && _survivor_chunk_array != NULL)
787 || ( _survivor_chunk_capacity == 0
788 && _survivor_chunk_index == 0),
789 "Error");
790
791 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
792 _gc_counters = new CollectorCounters("CMS", 1);
793 _completed_initialization = true;
794 _inter_sweep_timer.start(); // start of time
795 }
796
797 const char* ConcurrentMarkSweepGeneration::name() const {
798 return "concurrent mark-sweep generation";
799 }
800 void ConcurrentMarkSweepGeneration::update_counters() {
801 if (UsePerfData) {
802 _space_counters->update_all();
803 _gen_counters->update_all();
804 }
805 }
806
807 // this is an optimized version of update_counters(). it takes the
808 // used value as a parameter rather than computing it.
809 //
810 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
811 if (UsePerfData) {
812 _space_counters->update_used(used);
813 _space_counters->update_capacity();
814 _gen_counters->update_all();
815 }
816 }
817
818 void ConcurrentMarkSweepGeneration::print() const {
819 Generation::print();
820 cmsSpace()->print();
821 }
822
823 #ifndef PRODUCT
824 void ConcurrentMarkSweepGeneration::print_statistics() {
825 cmsSpace()->printFLCensus(0);
826 }
827 #endif
828
829 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
830 GenCollectedHeap* gch = GenCollectedHeap::heap();
831 if (PrintGCDetails) {
832 if (Verbose) {
833 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
834 level(), short_name(), s, used(), capacity());
835 } else {
836 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
837 level(), short_name(), s, used() / K, capacity() / K);
838 }
839 }
840 if (Verbose) {
841 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
842 gch->used(), gch->capacity());
843 } else {
844 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
845 gch->used() / K, gch->capacity() / K);
846 }
847 }
848
849 size_t
850 ConcurrentMarkSweepGeneration::contiguous_available() const {
851 // dld proposes an improvement in precision here. If the committed
852 // part of the space ends in a free block we should add that to
853 // uncommitted size in the calculation below. Will make this
854 // change later, staying with the approximation below for the
855 // time being. -- ysr.
856 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
857 }
858
859 size_t
860 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
861 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
862 }
863
864 size_t ConcurrentMarkSweepGeneration::max_available() const {
865 return free() + _virtual_space.uncommitted_size();
866 }
867
868 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
869 size_t available = max_available();
870 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
871 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
872 if (Verbose && PrintGCDetails) {
873 gclog_or_tty->print_cr(
874 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
875 "max_promo("SIZE_FORMAT")",
876 res? "":" not", available, res? ">=":"<",
877 av_promo, max_promotion_in_bytes);
878 }
879 return res;
880 }
881
882 // At a promotion failure dump information on block layout in heap
883 // (cms old generation).
884 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
885 if (CMSDumpAtPromotionFailure) {
886 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
887 }
888 }
889
890 CompactibleSpace*
891 ConcurrentMarkSweepGeneration::first_compaction_space() const {
892 return _cmsSpace;
893 }
894
895 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
896 // Clear the promotion information. These pointers can be adjusted
897 // along with all the other pointers into the heap but
898 // compaction is expected to be a rare event with
899 // a heap using cms so don't do it without seeing the need.
900 if (CollectedHeap::use_parallel_gc_threads()) {
901 for (uint i = 0; i < ParallelGCThreads; i++) {
902 _par_gc_thread_states[i]->promo.reset();
903 }
904 }
905 }
906
907 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
908 blk->do_space(_cmsSpace);
909 }
910
911 void ConcurrentMarkSweepGeneration::compute_new_size() {
912 assert_locked_or_safepoint(Heap_lock);
913
914 // If incremental collection failed, we just want to expand
915 // to the limit.
916 if (incremental_collection_failed()) {
917 clear_incremental_collection_failed();
918 grow_to_reserved();
919 return;
920 }
921
922 // The heap has been compacted but not reset yet.
923 // Any metric such as free() or used() will be incorrect.
924
925 CardGeneration::compute_new_size();
926
927 // Reset again after a possible resizing
928 if (did_compact()) {
929 cmsSpace()->reset_after_compaction();
930 }
931 }
932
933 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
934 assert_locked_or_safepoint(Heap_lock);
935
936 // If incremental collection failed, we just want to expand
937 // to the limit.
938 if (incremental_collection_failed()) {
939 clear_incremental_collection_failed();
940 grow_to_reserved();
941 return;
942 }
943
944 double free_percentage = ((double) free()) / capacity();
945 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
946 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
947
948 // compute expansion delta needed for reaching desired free percentage
949 if (free_percentage < desired_free_percentage) {
950 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
951 assert(desired_capacity >= capacity(), "invalid expansion size");
952 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
953 if (PrintGCDetails && Verbose) {
954 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
955 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
956 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
957 gclog_or_tty->print_cr(" Desired free fraction %f",
958 desired_free_percentage);
959 gclog_or_tty->print_cr(" Maximum free fraction %f",
960 maximum_free_percentage);
961 gclog_or_tty->print_cr(" Capacity "SIZE_FORMAT, capacity()/1000);
962 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
963 desired_capacity/1000);
964 int prev_level = level() - 1;
965 if (prev_level >= 0) {
966 size_t prev_size = 0;
967 GenCollectedHeap* gch = GenCollectedHeap::heap();
968 Generation* prev_gen = gch->_gens[prev_level];
969 prev_size = prev_gen->capacity();
970 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
971 prev_size/1000);
972 }
973 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
974 unsafe_max_alloc_nogc()/1000);
975 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
976 contiguous_available()/1000);
977 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
978 expand_bytes);
979 }
980 // safe if expansion fails
981 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
982 if (PrintGCDetails && Verbose) {
983 gclog_or_tty->print_cr(" Expanded free fraction %f",
984 ((double) free()) / capacity());
985 }
986 } else {
987 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
988 assert(desired_capacity <= capacity(), "invalid expansion size");
989 size_t shrink_bytes = capacity() - desired_capacity;
990 // Don't shrink unless the delta is greater than the minimum shrink we want
991 if (shrink_bytes >= MinHeapDeltaBytes) {
992 shrink_free_list_by(shrink_bytes);
993 }
994 }
995 }
996
997 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
998 return cmsSpace()->freelistLock();
999 }
1000
1001 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
1002 bool tlab) {
1003 CMSSynchronousYieldRequest yr;
1004 MutexLockerEx x(freelistLock(),
1005 Mutex::_no_safepoint_check_flag);
1006 return have_lock_and_allocate(size, tlab);
1007 }
1008
1009 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
1010 bool tlab /* ignored */) {
1011 assert_lock_strong(freelistLock());
1012 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1013 HeapWord* res = cmsSpace()->allocate(adjustedSize);
1014 // Allocate the object live (grey) if the background collector has
1015 // started marking. This is necessary because the marker may
1016 // have passed this address and consequently this object will
1017 // not otherwise be greyed and would be incorrectly swept up.
1018 // Note that if this object contains references, the writing
1019 // of those references will dirty the card containing this object
1020 // allowing the object to be blackened (and its references scanned)
1021 // either during a preclean phase or at the final checkpoint.
1022 if (res != NULL) {
1023 // We may block here with an uninitialized object with
1024 // its mark-bit or P-bits not yet set. Such objects need
1025 // to be safely navigable by block_start().
1026 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1027 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1028 collector()->direct_allocated(res, adjustedSize);
1029 _direct_allocated_words += adjustedSize;
1030 // allocation counters
1031 NOT_PRODUCT(
1032 _numObjectsAllocated++;
1033 _numWordsAllocated += (int)adjustedSize;
1034 )
1035 }
1036 return res;
1037 }
1038
1039 // In the case of direct allocation by mutators in a generation that
1040 // is being concurrently collected, the object must be allocated
1041 // live (grey) if the background collector has started marking.
1042 // This is necessary because the marker may
1043 // have passed this address and consequently this object will
1044 // not otherwise be greyed and would be incorrectly swept up.
1045 // Note that if this object contains references, the writing
1046 // of those references will dirty the card containing this object
1047 // allowing the object to be blackened (and its references scanned)
1048 // either during a preclean phase or at the final checkpoint.
1049 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1050 assert(_markBitMap.covers(start, size), "Out of bounds");
1051 if (_collectorState >= Marking) {
1052 MutexLockerEx y(_markBitMap.lock(),
1053 Mutex::_no_safepoint_check_flag);
1054 // [see comments preceding SweepClosure::do_blk() below for details]
1055 //
1056 // Can the P-bits be deleted now? JJJ
1057 //
1058 // 1. need to mark the object as live so it isn't collected
1059 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1060 // 3. need to mark the end of the object so marking, precleaning or sweeping
1061 // can skip over uninitialized or unparsable objects. An allocated
1062 // object is considered uninitialized for our purposes as long as
1063 // its klass word is NULL. All old gen objects are parsable
1064 // as soon as they are initialized.)
1065 _markBitMap.mark(start); // object is live
1066 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1067 _markBitMap.mark(start + size - 1);
1068 // mark end of object
1069 }
1070 // check that oop looks uninitialized
1071 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1072 }
1073
1074 void CMSCollector::promoted(bool par, HeapWord* start,
1075 bool is_obj_array, size_t obj_size) {
1076 assert(_markBitMap.covers(start), "Out of bounds");
1077 // See comment in direct_allocated() about when objects should
1078 // be allocated live.
1079 if (_collectorState >= Marking) {
1080 // we already hold the marking bit map lock, taken in
1081 // the prologue
1082 if (par) {
1083 _markBitMap.par_mark(start);
1084 } else {
1085 _markBitMap.mark(start);
1086 }
1087 // We don't need to mark the object as uninitialized (as
1088 // in direct_allocated above) because this is being done with the
1089 // world stopped and the object will be initialized by the
1090 // time the marking, precleaning or sweeping get to look at it.
1091 // But see the code for copying objects into the CMS generation,
1092 // where we need to ensure that concurrent readers of the
1093 // block offset table are able to safely navigate a block that
1094 // is in flux from being free to being allocated (and in
1095 // transition while being copied into) and subsequently
1096 // becoming a bona-fide object when the copy/promotion is complete.
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 // IMPORTANT: Notes on object size recognition in CMS.
1313 // ---------------------------------------------------
1314 // A block of storage in the CMS generation is always in
1315 // one of three states. A free block (FREE), an allocated
1316 // object (OBJECT) whose size() method reports the correct size,
1317 // and an intermediate state (TRANSIENT) in which its size cannot
1318 // be accurately determined.
1319 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1320 // -----------------------------------------------------
1321 // FREE: klass_word & 1 == 1; mark_word holds block size
1322 //
1323 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1324 // obj->size() computes correct size
1325 //
1326 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1327 //
1328 // STATE IDENTIFICATION: (64 bit+COOPS)
1329 // ------------------------------------
1330 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1331 //
1332 // OBJECT: klass_word installed; klass_word != 0;
1333 // obj->size() computes correct size
1334 //
1335 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1336 //
1337 //
1338 // STATE TRANSITION DIAGRAM
1339 //
1340 // mut / parnew mut / parnew
1341 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1342 // ^ |
1343 // |------------------------ DEAD <------------------------------------|
1344 // sweep mut
1345 //
1346 // While a block is in TRANSIENT state its size cannot be determined
1347 // so readers will either need to come back later or stall until
1348 // the size can be determined. Note that for the case of direct
1349 // allocation, P-bits, when available, may be used to determine the
1350 // size of an object that may not yet have been initialized.
1351
1352 // Things to support parallel young-gen collection.
1353 oop
1354 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1355 oop old, markOop m,
1356 size_t word_sz) {
1357 #ifndef PRODUCT
1358 if (Universe::heap()->promotion_should_fail()) {
1359 return NULL;
1360 }
1361 #endif // #ifndef PRODUCT
1362
1363 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1364 PromotionInfo* promoInfo = &ps->promo;
1365 // if we are tracking promotions, then first ensure space for
1366 // promotion (including spooling space for saving header if necessary).
1367 // then allocate and copy, then track promoted info if needed.
1368 // When tracking (see PromotionInfo::track()), the mark word may
1369 // be displaced and in this case restoration of the mark word
1370 // occurs in the (oop_since_save_marks_)iterate phase.
1371 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1372 // Out of space for allocating spooling buffers;
1373 // try expanding and allocating spooling buffers.
1374 if (!expand_and_ensure_spooling_space(promoInfo)) {
1375 return NULL;
1376 }
1377 }
1378 assert(promoInfo->has_spooling_space(), "Control point invariant");
1379 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1380 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1381 if (obj_ptr == NULL) {
1382 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1383 if (obj_ptr == NULL) {
1384 return NULL;
1385 }
1386 }
1387 oop obj = oop(obj_ptr);
1388 OrderAccess::storestore();
1389 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1390 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1391 // IMPORTANT: See note on object initialization for CMS above.
1392 // Otherwise, copy the object. Here we must be careful to insert the
1393 // klass pointer last, since this marks the block as an allocated object.
1394 // Except with compressed oops it's the mark word.
1395 HeapWord* old_ptr = (HeapWord*)old;
1396 // Restore the mark word copied above.
1397 obj->set_mark(m);
1398 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1399 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1400 OrderAccess::storestore();
1401
1402 if (UseCompressedClassPointers) {
1403 // Copy gap missed by (aligned) header size calculation below
1404 obj->set_klass_gap(old->klass_gap());
1405 }
1406 if (word_sz > (size_t)oopDesc::header_size()) {
1407 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1408 obj_ptr + oopDesc::header_size(),
1409 word_sz - oopDesc::header_size());
1410 }
1411
1412 // Now we can track the promoted object, if necessary. We take care
1413 // to delay the transition from uninitialized to full object
1414 // (i.e., insertion of klass pointer) until after, so that it
1415 // atomically becomes a promoted object.
1416 if (promoInfo->tracking()) {
1417 promoInfo->track((PromotedObject*)obj, old->klass());
1418 }
1419 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1420 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1421 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1422
1423 // Finally, install the klass pointer (this should be volatile).
1424 OrderAccess::storestore();
1425 obj->set_klass(old->klass());
1426 // We should now be able to calculate the right size for this object
1427 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1428
1429 collector()->promoted(true, // parallel
1430 obj_ptr, old->is_objArray(), word_sz);
1431
1432 NOT_PRODUCT(
1433 Atomic::inc_ptr(&_numObjectsPromoted);
1434 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1435 )
1436
1437 return obj;
1438 }
1439
1440 void
1441 ConcurrentMarkSweepGeneration::
1442 par_promote_alloc_undo(int thread_num,
1443 HeapWord* obj, size_t word_sz) {
1444 // CMS does not support promotion undo.
1445 ShouldNotReachHere();
1446 }
1447
1448 void
1449 ConcurrentMarkSweepGeneration::
1450 par_promote_alloc_done(int thread_num) {
1451 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1452 ps->lab.retire(thread_num);
1453 }
1454
1455 void
1456 ConcurrentMarkSweepGeneration::
1457 par_oop_since_save_marks_iterate_done(int thread_num) {
1458 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1459 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1460 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1461 }
1462
1463 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1464 size_t size,
1465 bool tlab)
1466 {
1467 // We allow a STW collection only if a full
1468 // collection was requested.
1469 return full || should_allocate(size, tlab); // FIX ME !!!
1470 // This and promotion failure handling are connected at the
1471 // hip and should be fixed by untying them.
1472 }
1473
1474 bool CMSCollector::shouldConcurrentCollect() {
1475 if (_full_gc_requested) {
1476 if (Verbose && PrintGCDetails) {
1477 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1478 " gc request (or gc_locker)");
1479 }
1480 return true;
1481 }
1482
1483 // For debugging purposes, change the type of collection.
1484 // If the rotation is not on the concurrent collection
1485 // type, don't start a concurrent collection.
1486 NOT_PRODUCT(
1487 if (RotateCMSCollectionTypes &&
1488 (_cmsGen->debug_collection_type() !=
1489 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1490 assert(_cmsGen->debug_collection_type() !=
1491 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1492 "Bad cms collection type");
1493 return false;
1494 }
1495 )
1496
1497 FreelistLocker x(this);
1498 // ------------------------------------------------------------------
1499 // Print out lots of information which affects the initiation of
1500 // a collection.
1501 if (PrintCMSInitiationStatistics && stats().valid()) {
1502 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1503 gclog_or_tty->stamp();
1504 gclog_or_tty->print_cr("");
1505 stats().print_on(gclog_or_tty);
1506 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1507 stats().time_until_cms_gen_full());
1508 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1509 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1510 _cmsGen->contiguous_available());
1511 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1512 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1513 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1514 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1515 gclog_or_tty->print_cr("metadata initialized %d",
1516 MetaspaceGC::should_concurrent_collect());
1517 }
1518 // ------------------------------------------------------------------
1519
1520 // If the estimated time to complete a cms collection (cms_duration())
1521 // is less than the estimated time remaining until the cms generation
1522 // is full, start a collection.
1523 if (!UseCMSInitiatingOccupancyOnly) {
1524 if (stats().valid()) {
1525 if (stats().time_until_cms_start() == 0.0) {
1526 return true;
1527 }
1528 } else {
1529 // We want to conservatively collect somewhat early in order
1530 // to try and "bootstrap" our CMS/promotion statistics;
1531 // this branch will not fire after the first successful CMS
1532 // collection because the stats should then be valid.
1533 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1534 if (Verbose && PrintGCDetails) {
1535 gclog_or_tty->print_cr(
1536 " CMSCollector: collect for bootstrapping statistics:"
1537 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1538 _bootstrap_occupancy);
1539 }
1540 return true;
1541 }
1542 }
1543 }
1544
1545 // Otherwise, we start a collection cycle if
1546 // old gen want a collection cycle started. Each may use
1547 // an appropriate criterion for making this decision.
1548 // XXX We need to make sure that the gen expansion
1549 // criterion dovetails well with this. XXX NEED TO FIX THIS
1550 if (_cmsGen->should_concurrent_collect()) {
1551 if (Verbose && PrintGCDetails) {
1552 gclog_or_tty->print_cr("CMS old gen initiated");
1553 }
1554 return true;
1555 }
1556
1557 // We start a collection if we believe an incremental collection may fail;
1558 // this is not likely to be productive in practice because it's probably too
1559 // late anyway.
1560 GenCollectedHeap* gch = GenCollectedHeap::heap();
1561 assert(gch->collector_policy()->is_two_generation_policy(),
1562 "You may want to check the correctness of the following");
1563 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1564 if (Verbose && PrintGCDetails) {
1565 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1566 }
1567 return true;
1568 }
1569
1570 if (MetaspaceGC::should_concurrent_collect()) {
1571 if (Verbose && PrintGCDetails) {
1572 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1573 }
1574 return true;
1575 }
1576
1577 return false;
1578 }
1579
1580 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1581
1582 // Clear _expansion_cause fields of constituent generations
1583 void CMSCollector::clear_expansion_cause() {
1584 _cmsGen->clear_expansion_cause();
1585 }
1586
1587 // We should be conservative in starting a collection cycle. To
1588 // start too eagerly runs the risk of collecting too often in the
1589 // extreme. To collect too rarely falls back on full collections,
1590 // which works, even if not optimum in terms of concurrent work.
1591 // As a work around for too eagerly collecting, use the flag
1592 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1593 // giving the user an easily understandable way of controlling the
1594 // collections.
1595 // We want to start a new collection cycle if any of the following
1596 // conditions hold:
1597 // . our current occupancy exceeds the configured initiating occupancy
1598 // for this generation, or
1599 // . we recently needed to expand this space and have not, since that
1600 // expansion, done a collection of this generation, or
1601 // . the underlying space believes that it may be a good idea to initiate
1602 // a concurrent collection (this may be based on criteria such as the
1603 // following: the space uses linear allocation and linear allocation is
1604 // going to fail, or there is believed to be excessive fragmentation in
1605 // the generation, etc... or ...
1606 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1607 // the case of the old generation; see CR 6543076):
1608 // we may be approaching a point at which allocation requests may fail because
1609 // we will be out of sufficient free space given allocation rate estimates.]
1610 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1611
1612 assert_lock_strong(freelistLock());
1613 if (occupancy() > initiating_occupancy()) {
1614 if (PrintGCDetails && Verbose) {
1615 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1616 short_name(), occupancy(), initiating_occupancy());
1617 }
1618 return true;
1619 }
1620 if (UseCMSInitiatingOccupancyOnly) {
1621 return false;
1622 }
1623 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1624 if (PrintGCDetails && Verbose) {
1625 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1626 short_name());
1627 }
1628 return true;
1629 }
1630 if (_cmsSpace->should_concurrent_collect()) {
1631 if (PrintGCDetails && Verbose) {
1632 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1633 short_name());
1634 }
1635 return true;
1636 }
1637 return false;
1638 }
1639
1640 void ConcurrentMarkSweepGeneration::collect(bool full,
1641 bool clear_all_soft_refs,
1642 size_t size,
1643 bool tlab)
1644 {
1645 collector()->collect(full, clear_all_soft_refs, size, tlab);
1646 }
1647
1648 void CMSCollector::collect(bool full,
1649 bool clear_all_soft_refs,
1650 size_t size,
1651 bool tlab)
1652 {
1653 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1654 // For debugging purposes skip the collection if the state
1655 // is not currently idle
1656 if (TraceCMSState) {
1657 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1658 Thread::current(), full, _collectorState);
1659 }
1660 return;
1661 }
1662
1663 // The following "if" branch is present for defensive reasons.
1664 // In the current uses of this interface, it can be replaced with:
1665 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1666 // But I am not placing that assert here to allow future
1667 // generality in invoking this interface.
1668 if (GC_locker::is_active()) {
1669 // A consistency test for GC_locker
1670 assert(GC_locker::needs_gc(), "Should have been set already");
1671 // Skip this foreground collection, instead
1672 // expanding the heap if necessary.
1673 // Need the free list locks for the call to free() in compute_new_size()
1674 compute_new_size();
1675 return;
1676 }
1677 acquire_control_and_collect(full, clear_all_soft_refs);
1678 _full_gcs_since_conc_gc++;
1679 }
1680
1681 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1682 GenCollectedHeap* gch = GenCollectedHeap::heap();
1683 unsigned int gc_count = gch->total_full_collections();
1684 if (gc_count == full_gc_count) {
1685 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1686 _full_gc_requested = true;
1687 _full_gc_cause = cause;
1688 CGC_lock->notify(); // nudge CMS thread
1689 } else {
1690 assert(gc_count > full_gc_count, "Error: causal loop");
1691 }
1692 }
1693
1694 bool CMSCollector::is_external_interruption() {
1695 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1696 return GCCause::is_user_requested_gc(cause) ||
1697 GCCause::is_serviceability_requested_gc(cause);
1698 }
1699
1700 void CMSCollector::report_concurrent_mode_interruption() {
1701 if (is_external_interruption()) {
1702 if (PrintGCDetails) {
1703 gclog_or_tty->print(" (concurrent mode interrupted)");
1704 }
1705 } else {
1706 if (PrintGCDetails) {
1707 gclog_or_tty->print(" (concurrent mode failure)");
1708 }
1709 _gc_tracer_cm->report_concurrent_mode_failure();
1710 }
1711 }
1712
1713
1714 // The foreground and background collectors need to coordinate in order
1715 // to make sure that they do not mutually interfere with CMS collections.
1716 // When a background collection is active,
1717 // the foreground collector may need to take over (preempt) and
1718 // synchronously complete an ongoing collection. Depending on the
1719 // frequency of the background collections and the heap usage
1720 // of the application, this preemption can be seldom or frequent.
1721 // There are only certain
1722 // points in the background collection that the "collection-baton"
1723 // can be passed to the foreground collector.
1724 //
1725 // The foreground collector will wait for the baton before
1726 // starting any part of the collection. The foreground collector
1727 // will only wait at one location.
1728 //
1729 // The background collector will yield the baton before starting a new
1730 // phase of the collection (e.g., before initial marking, marking from roots,
1731 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1732 // of the loop which switches the phases. The background collector does some
1733 // of the phases (initial mark, final re-mark) with the world stopped.
1734 // Because of locking involved in stopping the world,
1735 // the foreground collector should not block waiting for the background
1736 // collector when it is doing a stop-the-world phase. The background
1737 // collector will yield the baton at an additional point just before
1738 // it enters a stop-the-world phase. Once the world is stopped, the
1739 // background collector checks the phase of the collection. If the
1740 // phase has not changed, it proceeds with the collection. If the
1741 // phase has changed, it skips that phase of the collection. See
1742 // the comments on the use of the Heap_lock in collect_in_background().
1743 //
1744 // Variable used in baton passing.
1745 // _foregroundGCIsActive - Set to true by the foreground collector when
1746 // it wants the baton. The foreground clears it when it has finished
1747 // the collection.
1748 // _foregroundGCShouldWait - Set to true by the background collector
1749 // when it is running. The foreground collector waits while
1750 // _foregroundGCShouldWait is true.
1751 // CGC_lock - monitor used to protect access to the above variables
1752 // and to notify the foreground and background collectors.
1753 // _collectorState - current state of the CMS collection.
1754 //
1755 // The foreground collector
1756 // acquires the CGC_lock
1757 // sets _foregroundGCIsActive
1758 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1759 // various locks acquired in preparation for the collection
1760 // are released so as not to block the background collector
1761 // that is in the midst of a collection
1762 // proceeds with the collection
1763 // clears _foregroundGCIsActive
1764 // returns
1765 //
1766 // The background collector in a loop iterating on the phases of the
1767 // collection
1768 // acquires the CGC_lock
1769 // sets _foregroundGCShouldWait
1770 // if _foregroundGCIsActive is set
1771 // clears _foregroundGCShouldWait, notifies _CGC_lock
1772 // waits on _CGC_lock for _foregroundGCIsActive to become false
1773 // and exits the loop.
1774 // otherwise
1775 // proceed with that phase of the collection
1776 // if the phase is a stop-the-world phase,
1777 // yield the baton once more just before enqueueing
1778 // the stop-world CMS operation (executed by the VM thread).
1779 // returns after all phases of the collection are done
1780 //
1781
1782 void CMSCollector::acquire_control_and_collect(bool full,
1783 bool clear_all_soft_refs) {
1784 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1785 assert(!Thread::current()->is_ConcurrentGC_thread(),
1786 "shouldn't try to acquire control from self!");
1787
1788 // Start the protocol for acquiring control of the
1789 // collection from the background collector (aka CMS thread).
1790 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1791 "VM thread should have CMS token");
1792 // Remember the possibly interrupted state of an ongoing
1793 // concurrent collection
1794 CollectorState first_state = _collectorState;
1795
1796 // Signal to a possibly ongoing concurrent collection that
1797 // we want to do a foreground collection.
1798 _foregroundGCIsActive = true;
1799
1800 // Disable incremental mode during a foreground collection.
1801 ICMSDisabler icms_disabler;
1802
1803 // release locks and wait for a notify from the background collector
1804 // releasing the locks in only necessary for phases which
1805 // do yields to improve the granularity of the collection.
1806 assert_lock_strong(bitMapLock());
1807 // We need to lock the Free list lock for the space that we are
1808 // currently collecting.
1809 assert(haveFreelistLocks(), "Must be holding free list locks");
1810 bitMapLock()->unlock();
1811 releaseFreelistLocks();
1812 {
1813 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1814 if (_foregroundGCShouldWait) {
1815 // We are going to be waiting for action for the CMS thread;
1816 // it had better not be gone (for instance at shutdown)!
1817 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1818 "CMS thread must be running");
1819 // Wait here until the background collector gives us the go-ahead
1820 ConcurrentMarkSweepThread::clear_CMS_flag(
1821 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1822 // Get a possibly blocked CMS thread going:
1823 // Note that we set _foregroundGCIsActive true above,
1824 // without protection of the CGC_lock.
1825 CGC_lock->notify();
1826 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1827 "Possible deadlock");
1828 while (_foregroundGCShouldWait) {
1829 // wait for notification
1830 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1831 // Possibility of delay/starvation here, since CMS token does
1832 // not know to give priority to VM thread? Actually, i think
1833 // there wouldn't be any delay/starvation, but the proof of
1834 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1835 }
1836 ConcurrentMarkSweepThread::set_CMS_flag(
1837 ConcurrentMarkSweepThread::CMS_vm_has_token);
1838 }
1839 }
1840 // The CMS_token is already held. Get back the other locks.
1841 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1842 "VM thread should have CMS token");
1843 getFreelistLocks();
1844 bitMapLock()->lock_without_safepoint_check();
1845 if (TraceCMSState) {
1846 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1847 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1848 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1849 }
1850
1851 // Check if we need to do a compaction, or if not, whether
1852 // we need to start the mark-sweep from scratch.
1853 bool should_compact = false;
1854 bool should_start_over = false;
1855 decide_foreground_collection_type(clear_all_soft_refs,
1856 &should_compact, &should_start_over);
1857
1858 NOT_PRODUCT(
1859 if (RotateCMSCollectionTypes) {
1860 if (_cmsGen->debug_collection_type() ==
1861 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1862 should_compact = true;
1863 } else if (_cmsGen->debug_collection_type() ==
1864 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1865 should_compact = false;
1866 }
1867 }
1868 )
1869
1870 if (first_state > Idling) {
1871 report_concurrent_mode_interruption();
1872 }
1873
1874 set_did_compact(should_compact);
1875 if (should_compact) {
1876 // If the collection is being acquired from the background
1877 // collector, there may be references on the discovered
1878 // references lists that have NULL referents (being those
1879 // that were concurrently cleared by a mutator) or
1880 // that are no longer active (having been enqueued concurrently
1881 // by the mutator).
1882 // Scrub the list of those references because Mark-Sweep-Compact
1883 // code assumes referents are not NULL and that all discovered
1884 // Reference objects are active.
1885 ref_processor()->clean_up_discovered_references();
1886
1887 if (first_state > Idling) {
1888 save_heap_summary();
1889 }
1890
1891 do_compaction_work(clear_all_soft_refs);
1892
1893 // Has the GC time limit been exceeded?
1894 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1895 size_t max_eden_size = young_gen->max_capacity() -
1896 young_gen->to()->capacity() -
1897 young_gen->from()->capacity();
1898 GenCollectedHeap* gch = GenCollectedHeap::heap();
1899 GCCause::Cause gc_cause = gch->gc_cause();
1900 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1901 young_gen->eden()->used(),
1902 _cmsGen->max_capacity(),
1903 max_eden_size,
1904 full,
1905 gc_cause,
1906 gch->collector_policy());
1907 } else {
1908 do_mark_sweep_work(clear_all_soft_refs, first_state,
1909 should_start_over);
1910 }
1911 // Reset the expansion cause, now that we just completed
1912 // a collection cycle.
1913 clear_expansion_cause();
1914 _foregroundGCIsActive = false;
1915 return;
1916 }
1917
1918 // Resize the tenured generation
1919 // after obtaining the free list locks for the
1920 // two generations.
1921 void CMSCollector::compute_new_size() {
1922 assert_locked_or_safepoint(Heap_lock);
1923 FreelistLocker z(this);
1924 MetaspaceGC::compute_new_size();
1925 _cmsGen->compute_new_size_free_list();
1926 }
1927
1928 // A work method used by foreground collection to determine
1929 // what type of collection (compacting or not, continuing or fresh)
1930 // it should do.
1931 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1932 // and CMSCompactWhenClearAllSoftRefs the default in the future
1933 // and do away with the flags after a suitable period.
1934 void CMSCollector::decide_foreground_collection_type(
1935 bool clear_all_soft_refs, bool* should_compact,
1936 bool* should_start_over) {
1937 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1938 // flag is set, and we have either requested a System.gc() or
1939 // the number of full gc's since the last concurrent cycle
1940 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1941 // or if an incremental collection has failed
1942 GenCollectedHeap* gch = GenCollectedHeap::heap();
1943 assert(gch->collector_policy()->is_two_generation_policy(),
1944 "You may want to check the correctness of the following");
1945 // Inform cms gen if this was due to partial collection failing.
1946 // The CMS gen may use this fact to determine its expansion policy.
1947 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1948 assert(!_cmsGen->incremental_collection_failed(),
1949 "Should have been noticed, reacted to and cleared");
1950 _cmsGen->set_incremental_collection_failed();
1951 }
1952 *should_compact =
1953 UseCMSCompactAtFullCollection &&
1954 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1955 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1956 gch->incremental_collection_will_fail(true /* consult_young */));
1957 *should_start_over = false;
1958 if (clear_all_soft_refs && !*should_compact) {
1959 // We are about to do a last ditch collection attempt
1960 // so it would normally make sense to do a compaction
1961 // to reclaim as much space as possible.
1962 if (CMSCompactWhenClearAllSoftRefs) {
1963 // Default: The rationale is that in this case either
1964 // we are past the final marking phase, in which case
1965 // we'd have to start over, or so little has been done
1966 // that there's little point in saving that work. Compaction
1967 // appears to be the sensible choice in either case.
1968 *should_compact = true;
1969 } else {
1970 // We have been asked to clear all soft refs, but not to
1971 // compact. Make sure that we aren't past the final checkpoint
1972 // phase, for that is where we process soft refs. If we are already
1973 // past that phase, we'll need to redo the refs discovery phase and
1974 // if necessary clear soft refs that weren't previously
1975 // cleared. We do so by remembering the phase in which
1976 // we came in, and if we are past the refs processing
1977 // phase, we'll choose to just redo the mark-sweep
1978 // collection from scratch.
1979 if (_collectorState > FinalMarking) {
1980 // We are past the refs processing phase;
1981 // start over and do a fresh synchronous CMS cycle
1982 _collectorState = Resetting; // skip to reset to start new cycle
1983 reset(false /* == !asynch */);
1984 *should_start_over = true;
1985 } // else we can continue a possibly ongoing current cycle
1986 }
1987 }
1988 }
1989
1990 // A work method used by the foreground collector to do
1991 // a mark-sweep-compact.
1992 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1993 GenCollectedHeap* gch = GenCollectedHeap::heap();
1994
1995 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1996 gc_timer->register_gc_start();
1997
1998 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1999 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
2000
2001 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL);
2002 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
2003 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
2004 "collections passed to foreground collector", _full_gcs_since_conc_gc);
2005 }
2006
2007 // Sample collection interval time and reset for collection pause.
2008 if (UseAdaptiveSizePolicy) {
2009 size_policy()->msc_collection_begin();
2010 }
2011
2012 // Temporarily widen the span of the weak reference processing to
2013 // the entire heap.
2014 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
2015 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
2016 // Temporarily, clear the "is_alive_non_header" field of the
2017 // reference processor.
2018 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
2019 // Temporarily make reference _processing_ single threaded (non-MT).
2020 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
2021 // Temporarily make refs discovery atomic
2022 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
2023 // Temporarily make reference _discovery_ single threaded (non-MT)
2024 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
2025
2026 ref_processor()->set_enqueuing_is_done(false);
2027 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
2028 ref_processor()->setup_policy(clear_all_soft_refs);
2029 // If an asynchronous collection finishes, the _modUnionTable is
2030 // all clear. If we are assuming the collection from an asynchronous
2031 // collection, clear the _modUnionTable.
2032 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
2033 "_modUnionTable should be clear if the baton was not passed");
2034 _modUnionTable.clear_all();
2035 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
2036 "mod union for klasses should be clear if the baton was passed");
2037 _ct->klass_rem_set()->clear_mod_union();
2038
2039 // We must adjust the allocation statistics being maintained
2040 // in the free list space. We do so by reading and clearing
2041 // the sweep timer and updating the block flux rate estimates below.
2042 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
2043 if (_inter_sweep_timer.is_active()) {
2044 _inter_sweep_timer.stop();
2045 // Note that we do not use this sample to update the _inter_sweep_estimate.
2046 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
2047 _inter_sweep_estimate.padded_average(),
2048 _intra_sweep_estimate.padded_average());
2049 }
2050
2051 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2052 ref_processor(), clear_all_soft_refs);
2053 #ifdef ASSERT
2054 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2055 size_t free_size = cms_space->free();
2056 assert(free_size ==
2057 pointer_delta(cms_space->end(), cms_space->compaction_top())
2058 * HeapWordSize,
2059 "All the free space should be compacted into one chunk at top");
2060 assert(cms_space->dictionary()->total_chunk_size(
2061 debug_only(cms_space->freelistLock())) == 0 ||
2062 cms_space->totalSizeInIndexedFreeLists() == 0,
2063 "All the free space should be in a single chunk");
2064 size_t num = cms_space->totalCount();
2065 assert((free_size == 0 && num == 0) ||
2066 (free_size > 0 && (num == 1 || num == 2)),
2067 "There should be at most 2 free chunks after compaction");
2068 #endif // ASSERT
2069 _collectorState = Resetting;
2070 assert(_restart_addr == NULL,
2071 "Should have been NULL'd before baton was passed");
2072 reset(false /* == !asynch */);
2073 _cmsGen->reset_after_compaction();
2074 _concurrent_cycles_since_last_unload = 0;
2075
2076 // Clear any data recorded in the PLAB chunk arrays.
2077 if (_survivor_plab_array != NULL) {
2078 reset_survivor_plab_arrays();
2079 }
2080
2081 // Adjust the per-size allocation stats for the next epoch.
2082 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2083 // Restart the "inter sweep timer" for the next epoch.
2084 _inter_sweep_timer.reset();
2085 _inter_sweep_timer.start();
2086
2087 // Sample collection pause time and reset for collection interval.
2088 if (UseAdaptiveSizePolicy) {
2089 size_policy()->msc_collection_end(gch->gc_cause());
2090 }
2091
2092 gc_timer->register_gc_end();
2093
2094 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
2095
2096 // For a mark-sweep-compact, compute_new_size() will be called
2097 // in the heap's do_collection() method.
2098 }
2099
2100 // A work method used by the foreground collector to do
2101 // a mark-sweep, after taking over from a possibly on-going
2102 // concurrent mark-sweep collection.
2103 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2104 CollectorState first_state, bool should_start_over) {
2105 if (PrintGC && Verbose) {
2106 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2107 "collector with count %d",
2108 _full_gcs_since_conc_gc);
2109 }
2110 switch (_collectorState) {
2111 case Idling:
2112 if (first_state == Idling || should_start_over) {
2113 // The background GC was not active, or should
2114 // restarted from scratch; start the cycle.
2115 _collectorState = InitialMarking;
2116 }
2117 // If first_state was not Idling, then a background GC
2118 // was in progress and has now finished. No need to do it
2119 // again. Leave the state as Idling.
2120 break;
2121 case Precleaning:
2122 // In the foreground case don't do the precleaning since
2123 // it is not done concurrently and there is extra work
2124 // required.
2125 _collectorState = FinalMarking;
2126 }
2127 collect_in_foreground(clear_all_soft_refs, GenCollectedHeap::heap()->gc_cause());
2128
2129 // For a mark-sweep, compute_new_size() will be called
2130 // in the heap's do_collection() method.
2131 }
2132
2133
2134 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
2135 DefNewGeneration* dng = _young_gen->as_DefNewGeneration();
2136 EdenSpace* eden_space = dng->eden();
2137 ContiguousSpace* from_space = dng->from();
2138 ContiguousSpace* to_space = dng->to();
2139 // Eden
2140 if (_eden_chunk_array != NULL) {
2141 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2142 eden_space->bottom(), eden_space->top(),
2143 eden_space->end(), eden_space->capacity());
2144 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
2145 "_eden_chunk_capacity=" SIZE_FORMAT,
2146 _eden_chunk_index, _eden_chunk_capacity);
2147 for (size_t i = 0; i < _eden_chunk_index; i++) {
2148 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2149 i, _eden_chunk_array[i]);
2150 }
2151 }
2152 // Survivor
2153 if (_survivor_chunk_array != NULL) {
2154 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2155 from_space->bottom(), from_space->top(),
2156 from_space->end(), from_space->capacity());
2157 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
2158 "_survivor_chunk_capacity=" SIZE_FORMAT,
2159 _survivor_chunk_index, _survivor_chunk_capacity);
2160 for (size_t i = 0; i < _survivor_chunk_index; i++) {
2161 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2162 i, _survivor_chunk_array[i]);
2163 }
2164 }
2165 }
2166
2167 void CMSCollector::getFreelistLocks() const {
2168 // Get locks for all free lists in all generations that this
2169 // collector is responsible for
2170 _cmsGen->freelistLock()->lock_without_safepoint_check();
2171 }
2172
2173 void CMSCollector::releaseFreelistLocks() const {
2174 // Release locks for all free lists in all generations that this
2175 // collector is responsible for
2176 _cmsGen->freelistLock()->unlock();
2177 }
2178
2179 bool CMSCollector::haveFreelistLocks() const {
2180 // Check locks for all free lists in all generations that this
2181 // collector is responsible for
2182 assert_lock_strong(_cmsGen->freelistLock());
2183 PRODUCT_ONLY(ShouldNotReachHere());
2184 return true;
2185 }
2186
2187 // A utility class that is used by the CMS collector to
2188 // temporarily "release" the foreground collector from its
2189 // usual obligation to wait for the background collector to
2190 // complete an ongoing phase before proceeding.
2191 class ReleaseForegroundGC: public StackObj {
2192 private:
2193 CMSCollector* _c;
2194 public:
2195 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2196 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2197 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2198 // allow a potentially blocked foreground collector to proceed
2199 _c->_foregroundGCShouldWait = false;
2200 if (_c->_foregroundGCIsActive) {
2201 CGC_lock->notify();
2202 }
2203 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2204 "Possible deadlock");
2205 }
2206
2207 ~ReleaseForegroundGC() {
2208 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2209 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2210 _c->_foregroundGCShouldWait = true;
2211 }
2212 };
2213
2214 // There are separate collect_in_background and collect_in_foreground because of
2215 // the different locking requirements of the background collector and the
2216 // foreground collector. There was originally an attempt to share
2217 // one "collect" method between the background collector and the foreground
2218 // collector but the if-then-else required made it cleaner to have
2219 // separate methods.
2220 void CMSCollector::collect_in_background(bool clear_all_soft_refs, GCCause::Cause cause) {
2221 assert(Thread::current()->is_ConcurrentGC_thread(),
2222 "A CMS asynchronous collection is only allowed on a CMS thread.");
2223
2224 GenCollectedHeap* gch = GenCollectedHeap::heap();
2225 {
2226 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2227 MutexLockerEx hl(Heap_lock, safepoint_check);
2228 FreelistLocker fll(this);
2229 MutexLockerEx x(CGC_lock, safepoint_check);
2230 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2231 // The foreground collector is active or we're
2232 // not using asynchronous collections. Skip this
2233 // background collection.
2234 assert(!_foregroundGCShouldWait, "Should be clear");
2235 return;
2236 } else {
2237 assert(_collectorState == Idling, "Should be idling before start.");
2238 _collectorState = InitialMarking;
2239 register_gc_start(cause);
2240 // Reset the expansion cause, now that we are about to begin
2241 // a new cycle.
2242 clear_expansion_cause();
2243
2244 // Clear the MetaspaceGC flag since a concurrent collection
2245 // is starting but also clear it after the collection.
2246 MetaspaceGC::set_should_concurrent_collect(false);
2247 }
2248 // Decide if we want to enable class unloading as part of the
2249 // ensuing concurrent GC cycle.
2250 update_should_unload_classes();
2251 _full_gc_requested = false; // acks all outstanding full gc requests
2252 _full_gc_cause = GCCause::_no_gc;
2253 // Signal that we are about to start a collection
2254 gch->increment_total_full_collections(); // ... starting a collection cycle
2255 _collection_count_start = gch->total_full_collections();
2256 }
2257
2258 // Used for PrintGC
2259 size_t prev_used;
2260 if (PrintGC && Verbose) {
2261 prev_used = _cmsGen->used(); // XXXPERM
2262 }
2263
2264 // The change of the collection state is normally done at this level;
2265 // the exceptions are phases that are executed while the world is
2266 // stopped. For those phases the change of state is done while the
2267 // world is stopped. For baton passing purposes this allows the
2268 // background collector to finish the phase and change state atomically.
2269 // The foreground collector cannot wait on a phase that is done
2270 // while the world is stopped because the foreground collector already
2271 // has the world stopped and would deadlock.
2272 while (_collectorState != Idling) {
2273 if (TraceCMSState) {
2274 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2275 Thread::current(), _collectorState);
2276 }
2277 // The foreground collector
2278 // holds the Heap_lock throughout its collection.
2279 // holds the CMS token (but not the lock)
2280 // except while it is waiting for the background collector to yield.
2281 //
2282 // The foreground collector should be blocked (not for long)
2283 // if the background collector is about to start a phase
2284 // executed with world stopped. If the background
2285 // collector has already started such a phase, the
2286 // foreground collector is blocked waiting for the
2287 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2288 // are executed in the VM thread.
2289 //
2290 // The locking order is
2291 // PendingListLock (PLL) -- if applicable (FinalMarking)
2292 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2293 // CMS token (claimed in
2294 // stop_world_and_do() -->
2295 // safepoint_synchronize() -->
2296 // CMSThread::synchronize())
2297
2298 {
2299 // Check if the FG collector wants us to yield.
2300 CMSTokenSync x(true); // is cms thread
2301 if (waitForForegroundGC()) {
2302 // We yielded to a foreground GC, nothing more to be
2303 // done this round.
2304 assert(_foregroundGCShouldWait == false, "We set it to false in "
2305 "waitForForegroundGC()");
2306 if (TraceCMSState) {
2307 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2308 " exiting collection CMS state %d",
2309 Thread::current(), _collectorState);
2310 }
2311 return;
2312 } else {
2313 // The background collector can run but check to see if the
2314 // foreground collector has done a collection while the
2315 // background collector was waiting to get the CGC_lock
2316 // above. If yes, break so that _foregroundGCShouldWait
2317 // is cleared before returning.
2318 if (_collectorState == Idling) {
2319 break;
2320 }
2321 }
2322 }
2323
2324 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2325 "should be waiting");
2326
2327 switch (_collectorState) {
2328 case InitialMarking:
2329 {
2330 ReleaseForegroundGC x(this);
2331 stats().record_cms_begin();
2332 VM_CMS_Initial_Mark initial_mark_op(this);
2333 VMThread::execute(&initial_mark_op);
2334 }
2335 // The collector state may be any legal state at this point
2336 // since the background collector may have yielded to the
2337 // foreground collector.
2338 break;
2339 case Marking:
2340 // initial marking in checkpointRootsInitialWork has been completed
2341 if (markFromRoots(true)) { // we were successful
2342 assert(_collectorState == Precleaning, "Collector state should "
2343 "have changed");
2344 } else {
2345 assert(_foregroundGCIsActive, "Internal state inconsistency");
2346 }
2347 break;
2348 case Precleaning:
2349 if (UseAdaptiveSizePolicy) {
2350 size_policy()->concurrent_precleaning_begin();
2351 }
2352 // marking from roots in markFromRoots has been completed
2353 preclean();
2354 if (UseAdaptiveSizePolicy) {
2355 size_policy()->concurrent_precleaning_end();
2356 }
2357 assert(_collectorState == AbortablePreclean ||
2358 _collectorState == FinalMarking,
2359 "Collector state should have changed");
2360 break;
2361 case AbortablePreclean:
2362 if (UseAdaptiveSizePolicy) {
2363 size_policy()->concurrent_phases_resume();
2364 }
2365 abortable_preclean();
2366 if (UseAdaptiveSizePolicy) {
2367 size_policy()->concurrent_precleaning_end();
2368 }
2369 assert(_collectorState == FinalMarking, "Collector state should "
2370 "have changed");
2371 break;
2372 case FinalMarking:
2373 {
2374 ReleaseForegroundGC x(this);
2375
2376 VM_CMS_Final_Remark final_remark_op(this);
2377 VMThread::execute(&final_remark_op);
2378 }
2379 assert(_foregroundGCShouldWait, "block post-condition");
2380 break;
2381 case Sweeping:
2382 if (UseAdaptiveSizePolicy) {
2383 size_policy()->concurrent_sweeping_begin();
2384 }
2385 // final marking in checkpointRootsFinal has been completed
2386 sweep(true);
2387 assert(_collectorState == Resizing, "Collector state change "
2388 "to Resizing must be done under the free_list_lock");
2389 _full_gcs_since_conc_gc = 0;
2390
2391 // Stop the timers for adaptive size policy for the concurrent phases
2392 if (UseAdaptiveSizePolicy) {
2393 size_policy()->concurrent_sweeping_end();
2394 size_policy()->concurrent_phases_end(gch->gc_cause(),
2395 gch->prev_gen(_cmsGen)->capacity(),
2396 _cmsGen->free());
2397 }
2398
2399 case Resizing: {
2400 // Sweeping has been completed...
2401 // At this point the background collection has completed.
2402 // Don't move the call to compute_new_size() down
2403 // into code that might be executed if the background
2404 // collection was preempted.
2405 {
2406 ReleaseForegroundGC x(this); // unblock FG collection
2407 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2408 CMSTokenSync z(true); // not strictly needed.
2409 if (_collectorState == Resizing) {
2410 compute_new_size();
2411 save_heap_summary();
2412 _collectorState = Resetting;
2413 } else {
2414 assert(_collectorState == Idling, "The state should only change"
2415 " because the foreground collector has finished the collection");
2416 }
2417 }
2418 break;
2419 }
2420 case Resetting:
2421 // CMS heap resizing has been completed
2422 reset(true);
2423 assert(_collectorState == Idling, "Collector state should "
2424 "have changed");
2425
2426 MetaspaceGC::set_should_concurrent_collect(false);
2427
2428 stats().record_cms_end();
2429 // Don't move the concurrent_phases_end() and compute_new_size()
2430 // calls to here because a preempted background collection
2431 // has it's state set to "Resetting".
2432 break;
2433 case Idling:
2434 default:
2435 ShouldNotReachHere();
2436 break;
2437 }
2438 if (TraceCMSState) {
2439 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2440 Thread::current(), _collectorState);
2441 }
2442 assert(_foregroundGCShouldWait, "block post-condition");
2443 }
2444
2445 // Should this be in gc_epilogue?
2446 collector_policy()->counters()->update_counters();
2447
2448 {
2449 // Clear _foregroundGCShouldWait and, in the event that the
2450 // foreground collector is waiting, notify it, before
2451 // returning.
2452 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2453 _foregroundGCShouldWait = false;
2454 if (_foregroundGCIsActive) {
2455 CGC_lock->notify();
2456 }
2457 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2458 "Possible deadlock");
2459 }
2460 if (TraceCMSState) {
2461 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2462 " exiting collection CMS state %d",
2463 Thread::current(), _collectorState);
2464 }
2465 if (PrintGC && Verbose) {
2466 _cmsGen->print_heap_change(prev_used);
2467 }
2468 }
2469
2470 void CMSCollector::register_foreground_gc_start(GCCause::Cause cause) {
2471 if (!_cms_start_registered) {
2472 register_gc_start(cause);
2473 }
2474 }
2475
2476 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2477 _cms_start_registered = true;
2478 _gc_timer_cm->register_gc_start();
2479 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2480 }
2481
2482 void CMSCollector::register_gc_end() {
2483 if (_cms_start_registered) {
2484 report_heap_summary(GCWhen::AfterGC);
2485
2486 _gc_timer_cm->register_gc_end();
2487 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2488 _cms_start_registered = false;
2489 }
2490 }
2491
2492 void CMSCollector::save_heap_summary() {
2493 GenCollectedHeap* gch = GenCollectedHeap::heap();
2494 _last_heap_summary = gch->create_heap_summary();
2495 _last_metaspace_summary = gch->create_metaspace_summary();
2496 }
2497
2498 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2499 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2500 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2501 }
2502
2503 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs, GCCause::Cause cause) {
2504 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2505 "Foreground collector should be waiting, not executing");
2506 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2507 "may only be done by the VM Thread with the world stopped");
2508 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2509 "VM thread should have CMS token");
2510
2511 NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2512 true, NULL);)
2513 if (UseAdaptiveSizePolicy) {
2514 size_policy()->ms_collection_begin();
2515 }
2516 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2517
2518 HandleMark hm; // Discard invalid handles created during verification
2519
2520 if (VerifyBeforeGC &&
2521 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2522 Universe::verify();
2523 }
2524
2525 // Snapshot the soft reference policy to be used in this collection cycle.
2526 ref_processor()->setup_policy(clear_all_soft_refs);
2527
2528 // Decide if class unloading should be done
2529 update_should_unload_classes();
2530
2531 bool init_mark_was_synchronous = false; // until proven otherwise
2532 while (_collectorState != Idling) {
2533 if (TraceCMSState) {
2534 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2535 Thread::current(), _collectorState);
2536 }
2537 switch (_collectorState) {
2538 case InitialMarking:
2539 register_foreground_gc_start(cause);
2540 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2541 checkpointRootsInitial(false);
2542 assert(_collectorState == Marking, "Collector state should have changed"
2543 " within checkpointRootsInitial()");
2544 break;
2545 case Marking:
2546 // initial marking in checkpointRootsInitialWork has been completed
2547 if (VerifyDuringGC &&
2548 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2549 Universe::verify("Verify before initial mark: ");
2550 }
2551 {
2552 bool res = markFromRoots(false);
2553 assert(res && _collectorState == FinalMarking, "Collector state should "
2554 "have changed");
2555 break;
2556 }
2557 case FinalMarking:
2558 if (VerifyDuringGC &&
2559 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2560 Universe::verify("Verify before re-mark: ");
2561 }
2562 checkpointRootsFinal(false, clear_all_soft_refs,
2563 init_mark_was_synchronous);
2564 assert(_collectorState == Sweeping, "Collector state should not "
2565 "have changed within checkpointRootsFinal()");
2566 break;
2567 case Sweeping:
2568 // final marking in checkpointRootsFinal has been completed
2569 if (VerifyDuringGC &&
2570 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2571 Universe::verify("Verify before sweep: ");
2572 }
2573 sweep(false);
2574 assert(_collectorState == Resizing, "Incorrect state");
2575 break;
2576 case Resizing: {
2577 // Sweeping has been completed; the actual resize in this case
2578 // is done separately; nothing to be done in this state.
2579 _collectorState = Resetting;
2580 break;
2581 }
2582 case Resetting:
2583 // The heap has been resized.
2584 if (VerifyDuringGC &&
2585 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2586 Universe::verify("Verify before reset: ");
2587 }
2588 save_heap_summary();
2589 reset(false);
2590 assert(_collectorState == Idling, "Collector state should "
2591 "have changed");
2592 break;
2593 case Precleaning:
2594 case AbortablePreclean:
2595 // Elide the preclean phase
2596 _collectorState = FinalMarking;
2597 break;
2598 default:
2599 ShouldNotReachHere();
2600 }
2601 if (TraceCMSState) {
2602 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2603 Thread::current(), _collectorState);
2604 }
2605 }
2606
2607 if (UseAdaptiveSizePolicy) {
2608 GenCollectedHeap* gch = GenCollectedHeap::heap();
2609 size_policy()->ms_collection_end(gch->gc_cause());
2610 }
2611
2612 if (VerifyAfterGC &&
2613 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2614 Universe::verify();
2615 }
2616 if (TraceCMSState) {
2617 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2618 " exiting collection CMS state %d",
2619 Thread::current(), _collectorState);
2620 }
2621 }
2622
2623 bool CMSCollector::waitForForegroundGC() {
2624 bool res = false;
2625 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2626 "CMS thread should have CMS token");
2627 // Block the foreground collector until the
2628 // background collectors decides whether to
2629 // yield.
2630 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2631 _foregroundGCShouldWait = true;
2632 if (_foregroundGCIsActive) {
2633 // The background collector yields to the
2634 // foreground collector and returns a value
2635 // indicating that it has yielded. The foreground
2636 // collector can proceed.
2637 res = true;
2638 _foregroundGCShouldWait = false;
2639 ConcurrentMarkSweepThread::clear_CMS_flag(
2640 ConcurrentMarkSweepThread::CMS_cms_has_token);
2641 ConcurrentMarkSweepThread::set_CMS_flag(
2642 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2643 // Get a possibly blocked foreground thread going
2644 CGC_lock->notify();
2645 if (TraceCMSState) {
2646 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2647 Thread::current(), _collectorState);
2648 }
2649 while (_foregroundGCIsActive) {
2650 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2651 }
2652 ConcurrentMarkSweepThread::set_CMS_flag(
2653 ConcurrentMarkSweepThread::CMS_cms_has_token);
2654 ConcurrentMarkSweepThread::clear_CMS_flag(
2655 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2656 }
2657 if (TraceCMSState) {
2658 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2659 Thread::current(), _collectorState);
2660 }
2661 return res;
2662 }
2663
2664 // Because of the need to lock the free lists and other structures in
2665 // the collector, common to all the generations that the collector is
2666 // collecting, we need the gc_prologues of individual CMS generations
2667 // delegate to their collector. It may have been simpler had the
2668 // current infrastructure allowed one to call a prologue on a
2669 // collector. In the absence of that we have the generation's
2670 // prologue delegate to the collector, which delegates back
2671 // some "local" work to a worker method in the individual generations
2672 // that it's responsible for collecting, while itself doing any
2673 // work common to all generations it's responsible for. A similar
2674 // comment applies to the gc_epilogue()'s.
2675 // The role of the variable _between_prologue_and_epilogue is to
2676 // enforce the invocation protocol.
2677 void CMSCollector::gc_prologue(bool full) {
2678 // Call gc_prologue_work() for the CMSGen
2679 // we are responsible for.
2680
2681 // The following locking discipline assumes that we are only called
2682 // when the world is stopped.
2683 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2684
2685 // The CMSCollector prologue must call the gc_prologues for the
2686 // "generations" that it's responsible
2687 // for.
2688
2689 assert( Thread::current()->is_VM_thread()
2690 || ( CMSScavengeBeforeRemark
2691 && Thread::current()->is_ConcurrentGC_thread()),
2692 "Incorrect thread type for prologue execution");
2693
2694 if (_between_prologue_and_epilogue) {
2695 // We have already been invoked; this is a gc_prologue delegation
2696 // from yet another CMS generation that we are responsible for, just
2697 // ignore it since all relevant work has already been done.
2698 return;
2699 }
2700
2701 // set a bit saying prologue has been called; cleared in epilogue
2702 _between_prologue_and_epilogue = true;
2703 // Claim locks for common data structures, then call gc_prologue_work()
2704 // for each CMSGen.
2705
2706 getFreelistLocks(); // gets free list locks on constituent spaces
2707 bitMapLock()->lock_without_safepoint_check();
2708
2709 // Should call gc_prologue_work() for all cms gens we are responsible for
2710 bool duringMarking = _collectorState >= Marking
2711 && _collectorState < Sweeping;
2712
2713 // The young collections clear the modified oops state, which tells if
2714 // there are any modified oops in the class. The remark phase also needs
2715 // that information. Tell the young collection to save the union of all
2716 // modified klasses.
2717 if (duringMarking) {
2718 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2719 }
2720
2721 bool registerClosure = duringMarking;
2722
2723 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2724 &_modUnionClosurePar
2725 : &_modUnionClosure;
2726 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2727
2728 if (!full) {
2729 stats().record_gc0_begin();
2730 }
2731 }
2732
2733 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2734
2735 _capacity_at_prologue = capacity();
2736 _used_at_prologue = used();
2737
2738 // Delegate to CMScollector which knows how to coordinate between
2739 // this and any other CMS generations that it is responsible for
2740 // collecting.
2741 collector()->gc_prologue(full);
2742 }
2743
2744 // This is a "private" interface for use by this generation's CMSCollector.
2745 // Not to be called directly by any other entity (for instance,
2746 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2747 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2748 bool registerClosure, ModUnionClosure* modUnionClosure) {
2749 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2750 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2751 "Should be NULL");
2752 if (registerClosure) {
2753 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2754 }
2755 cmsSpace()->gc_prologue();
2756 // Clear stat counters
2757 NOT_PRODUCT(
2758 assert(_numObjectsPromoted == 0, "check");
2759 assert(_numWordsPromoted == 0, "check");
2760 if (Verbose && PrintGC) {
2761 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2762 SIZE_FORMAT" bytes concurrently",
2763 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2764 }
2765 _numObjectsAllocated = 0;
2766 _numWordsAllocated = 0;
2767 )
2768 }
2769
2770 void CMSCollector::gc_epilogue(bool full) {
2771 // The following locking discipline assumes that we are only called
2772 // when the world is stopped.
2773 assert(SafepointSynchronize::is_at_safepoint(),
2774 "world is stopped assumption");
2775
2776 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2777 // if linear allocation blocks need to be appropriately marked to allow the
2778 // the blocks to be parsable. We also check here whether we need to nudge the
2779 // CMS collector thread to start a new cycle (if it's not already active).
2780 assert( Thread::current()->is_VM_thread()
2781 || ( CMSScavengeBeforeRemark
2782 && Thread::current()->is_ConcurrentGC_thread()),
2783 "Incorrect thread type for epilogue execution");
2784
2785 if (!_between_prologue_and_epilogue) {
2786 // We have already been invoked; this is a gc_epilogue delegation
2787 // from yet another CMS generation that we are responsible for, just
2788 // ignore it since all relevant work has already been done.
2789 return;
2790 }
2791 assert(haveFreelistLocks(), "must have freelist locks");
2792 assert_lock_strong(bitMapLock());
2793
2794 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2795
2796 _cmsGen->gc_epilogue_work(full);
2797
2798 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2799 // in case sampling was not already enabled, enable it
2800 _start_sampling = true;
2801 }
2802 // reset _eden_chunk_array so sampling starts afresh
2803 _eden_chunk_index = 0;
2804
2805 size_t cms_used = _cmsGen->cmsSpace()->used();
2806
2807 // update performance counters - this uses a special version of
2808 // update_counters() that allows the utilization to be passed as a
2809 // parameter, avoiding multiple calls to used().
2810 //
2811 _cmsGen->update_counters(cms_used);
2812
2813 if (CMSIncrementalMode) {
2814 icms_update_allocation_limits();
2815 }
2816
2817 bitMapLock()->unlock();
2818 releaseFreelistLocks();
2819
2820 if (!CleanChunkPoolAsync) {
2821 Chunk::clean_chunk_pool();
2822 }
2823
2824 set_did_compact(false);
2825 _between_prologue_and_epilogue = false; // ready for next cycle
2826 }
2827
2828 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2829 collector()->gc_epilogue(full);
2830
2831 // Also reset promotion tracking in par gc thread states.
2832 if (CollectedHeap::use_parallel_gc_threads()) {
2833 for (uint i = 0; i < ParallelGCThreads; i++) {
2834 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2835 }
2836 }
2837 }
2838
2839 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2840 assert(!incremental_collection_failed(), "Should have been cleared");
2841 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2842 cmsSpace()->gc_epilogue();
2843 // Print stat counters
2844 NOT_PRODUCT(
2845 assert(_numObjectsAllocated == 0, "check");
2846 assert(_numWordsAllocated == 0, "check");
2847 if (Verbose && PrintGC) {
2848 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2849 SIZE_FORMAT" bytes",
2850 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2851 }
2852 _numObjectsPromoted = 0;
2853 _numWordsPromoted = 0;
2854 )
2855
2856 if (PrintGC && Verbose) {
2857 // Call down the chain in contiguous_available needs the freelistLock
2858 // so print this out before releasing the freeListLock.
2859 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2860 contiguous_available());
2861 }
2862 }
2863
2864 #ifndef PRODUCT
2865 bool CMSCollector::have_cms_token() {
2866 Thread* thr = Thread::current();
2867 if (thr->is_VM_thread()) {
2868 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2869 } else if (thr->is_ConcurrentGC_thread()) {
2870 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2871 } else if (thr->is_GC_task_thread()) {
2872 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2873 ParGCRareEvent_lock->owned_by_self();
2874 }
2875 return false;
2876 }
2877 #endif
2878
2879 // Check reachability of the given heap address in CMS generation,
2880 // treating all other generations as roots.
2881 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2882 // We could "guarantee" below, rather than assert, but I'll
2883 // leave these as "asserts" so that an adventurous debugger
2884 // could try this in the product build provided some subset of
2885 // the conditions were met, provided they were interested in the
2886 // results and knew that the computation below wouldn't interfere
2887 // with other concurrent computations mutating the structures
2888 // being read or written.
2889 assert(SafepointSynchronize::is_at_safepoint(),
2890 "Else mutations in object graph will make answer suspect");
2891 assert(have_cms_token(), "Should hold cms token");
2892 assert(haveFreelistLocks(), "must hold free list locks");
2893 assert_lock_strong(bitMapLock());
2894
2895 // Clear the marking bit map array before starting, but, just
2896 // for kicks, first report if the given address is already marked
2897 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2898 _markBitMap.isMarked(addr) ? "" : " not");
2899
2900 if (verify_after_remark()) {
2901 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2902 bool result = verification_mark_bm()->isMarked(addr);
2903 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2904 result ? "IS" : "is NOT");
2905 return result;
2906 } else {
2907 gclog_or_tty->print_cr("Could not compute result");
2908 return false;
2909 }
2910 }
2911
2912
2913 void
2914 CMSCollector::print_on_error(outputStream* st) {
2915 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2916 if (collector != NULL) {
2917 CMSBitMap* bitmap = &collector->_markBitMap;
2918 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, bitmap);
2919 bitmap->print_on_error(st, " Bits: ");
2920
2921 st->cr();
2922
2923 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2924 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, mut_bitmap);
2925 mut_bitmap->print_on_error(st, " Bits: ");
2926 }
2927 }
2928
2929 ////////////////////////////////////////////////////////
2930 // CMS Verification Support
2931 ////////////////////////////////////////////////////////
2932 // Following the remark phase, the following invariant
2933 // should hold -- each object in the CMS heap which is
2934 // marked in markBitMap() should be marked in the verification_mark_bm().
2935
2936 class VerifyMarkedClosure: public BitMapClosure {
2937 CMSBitMap* _marks;
2938 bool _failed;
2939
2940 public:
2941 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2942
2943 bool do_bit(size_t offset) {
2944 HeapWord* addr = _marks->offsetToHeapWord(offset);
2945 if (!_marks->isMarked(addr)) {
2946 oop(addr)->print_on(gclog_or_tty);
2947 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2948 _failed = true;
2949 }
2950 return true;
2951 }
2952
2953 bool failed() { return _failed; }
2954 };
2955
2956 bool CMSCollector::verify_after_remark(bool silent) {
2957 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2958 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2959 static bool init = false;
2960
2961 assert(SafepointSynchronize::is_at_safepoint(),
2962 "Else mutations in object graph will make answer suspect");
2963 assert(have_cms_token(),
2964 "Else there may be mutual interference in use of "
2965 " verification data structures");
2966 assert(_collectorState > Marking && _collectorState <= Sweeping,
2967 "Else marking info checked here may be obsolete");
2968 assert(haveFreelistLocks(), "must hold free list locks");
2969 assert_lock_strong(bitMapLock());
2970
2971
2972 // Allocate marking bit map if not already allocated
2973 if (!init) { // first time
2974 if (!verification_mark_bm()->allocate(_span)) {
2975 return false;
2976 }
2977 init = true;
2978 }
2979
2980 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2981
2982 // Turn off refs discovery -- so we will be tracing through refs.
2983 // This is as intended, because by this time
2984 // GC must already have cleared any refs that need to be cleared,
2985 // and traced those that need to be marked; moreover,
2986 // the marking done here is not going to interfere in any
2987 // way with the marking information used by GC.
2988 NoRefDiscovery no_discovery(ref_processor());
2989
2990 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2991
2992 // Clear any marks from a previous round
2993 verification_mark_bm()->clear_all();
2994 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2995 verify_work_stacks_empty();
2996
2997 GenCollectedHeap* gch = GenCollectedHeap::heap();
2998 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2999 // Update the saved marks which may affect the root scans.
3000 gch->save_marks();
3001
3002 if (CMSRemarkVerifyVariant == 1) {
3003 // In this first variant of verification, we complete
3004 // all marking, then check if the new marks-vector is
3005 // a subset of the CMS marks-vector.
3006 verify_after_remark_work_1();
3007 } else if (CMSRemarkVerifyVariant == 2) {
3008 // In this second variant of verification, we flag an error
3009 // (i.e. an object reachable in the new marks-vector not reachable
3010 // in the CMS marks-vector) immediately, also indicating the
3011 // identify of an object (A) that references the unmarked object (B) --
3012 // presumably, a mutation to A failed to be picked up by preclean/remark?
3013 verify_after_remark_work_2();
3014 } else {
3015 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
3016 CMSRemarkVerifyVariant);
3017 }
3018 if (!silent) gclog_or_tty->print(" done] ");
3019 return true;
3020 }
3021
3022 void CMSCollector::verify_after_remark_work_1() {
3023 ResourceMark rm;
3024 HandleMark hm;
3025 GenCollectedHeap* gch = GenCollectedHeap::heap();
3026
3027 // Get a clear set of claim bits for the strong roots processing to work with.
3028 ClassLoaderDataGraph::clear_claimed_marks();
3029
3030 // Mark from roots one level into CMS
3031 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
3032 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3033
3034 gch->gen_process_strong_roots(_cmsGen->level(),
3035 true, // younger gens are roots
3036 true, // activate StrongRootsScope
3037 SharedHeap::ScanningOption(roots_scanning_options()),
3038 ¬Older,
3039 NULL,
3040 NULL); // SSS: Provide correct closure
3041
3042 // Now mark from the roots
3043 MarkFromRootsClosure markFromRootsClosure(this, _span,
3044 verification_mark_bm(), verification_mark_stack(),
3045 false /* don't yield */, true /* verifying */);
3046 assert(_restart_addr == NULL, "Expected pre-condition");
3047 verification_mark_bm()->iterate(&markFromRootsClosure);
3048 while (_restart_addr != NULL) {
3049 // Deal with stack overflow: by restarting at the indicated
3050 // address.
3051 HeapWord* ra = _restart_addr;
3052 markFromRootsClosure.reset(ra);
3053 _restart_addr = NULL;
3054 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3055 }
3056 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3057 verify_work_stacks_empty();
3058
3059 // Marking completed -- now verify that each bit marked in
3060 // verification_mark_bm() is also marked in markBitMap(); flag all
3061 // errors by printing corresponding objects.
3062 VerifyMarkedClosure vcl(markBitMap());
3063 verification_mark_bm()->iterate(&vcl);
3064 if (vcl.failed()) {
3065 gclog_or_tty->print("Verification failed");
3066 Universe::heap()->print_on(gclog_or_tty);
3067 fatal("CMS: failed marking verification after remark");
3068 }
3069 }
3070
3071 class VerifyKlassOopsKlassClosure : public KlassClosure {
3072 class VerifyKlassOopsClosure : public OopClosure {
3073 CMSBitMap* _bitmap;
3074 public:
3075 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
3076 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
3077 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
3078 } _oop_closure;
3079 public:
3080 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
3081 void do_klass(Klass* k) {
3082 k->oops_do(&_oop_closure);
3083 }
3084 };
3085
3086 void CMSCollector::verify_after_remark_work_2() {
3087 ResourceMark rm;
3088 HandleMark hm;
3089 GenCollectedHeap* gch = GenCollectedHeap::heap();
3090
3091 // Get a clear set of claim bits for the strong roots processing to work with.
3092 ClassLoaderDataGraph::clear_claimed_marks();
3093
3094 // Mark from roots one level into CMS
3095 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
3096 markBitMap());
3097 CMKlassClosure klass_closure(¬Older);
3098
3099 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3100 gch->gen_process_strong_roots(_cmsGen->level(),
3101 true, // younger gens are roots
3102 true, // activate StrongRootsScope
3103 SharedHeap::ScanningOption(roots_scanning_options()),
3104 ¬Older,
3105 NULL,
3106 &klass_closure);
3107
3108 // Now mark from the roots
3109 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
3110 verification_mark_bm(), markBitMap(), verification_mark_stack());
3111 assert(_restart_addr == NULL, "Expected pre-condition");
3112 verification_mark_bm()->iterate(&markFromRootsClosure);
3113 while (_restart_addr != NULL) {
3114 // Deal with stack overflow: by restarting at the indicated
3115 // address.
3116 HeapWord* ra = _restart_addr;
3117 markFromRootsClosure.reset(ra);
3118 _restart_addr = NULL;
3119 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3120 }
3121 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3122 verify_work_stacks_empty();
3123
3124 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
3125 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
3126
3127 // Marking completed -- now verify that each bit marked in
3128 // verification_mark_bm() is also marked in markBitMap(); flag all
3129 // errors by printing corresponding objects.
3130 VerifyMarkedClosure vcl(markBitMap());
3131 verification_mark_bm()->iterate(&vcl);
3132 assert(!vcl.failed(), "Else verification above should not have succeeded");
3133 }
3134
3135 void ConcurrentMarkSweepGeneration::save_marks() {
3136 // delegate to CMS space
3137 cmsSpace()->save_marks();
3138 for (uint i = 0; i < ParallelGCThreads; i++) {
3139 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3140 }
3141 }
3142
3143 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3144 return cmsSpace()->no_allocs_since_save_marks();
3145 }
3146
3147 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3148 \
3149 void ConcurrentMarkSweepGeneration:: \
3150 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3151 cl->set_generation(this); \
3152 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3153 cl->reset_generation(); \
3154 save_marks(); \
3155 }
3156
3157 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3158
3159 void
3160 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3161 cl->set_generation(this);
3162 younger_refs_in_space_iterate(_cmsSpace, cl);
3163 cl->reset_generation();
3164 }
3165
3166 void
3167 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, ExtendedOopClosure* cl) {
3168 if (freelistLock()->owned_by_self()) {
3169 Generation::oop_iterate(mr, cl);
3170 } else {
3171 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3172 Generation::oop_iterate(mr, cl);
3173 }
3174 }
3175
3176 void
3177 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
3178 if (freelistLock()->owned_by_self()) {
3179 Generation::oop_iterate(cl);
3180 } else {
3181 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3182 Generation::oop_iterate(cl);
3183 }
3184 }
3185
3186 void
3187 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3188 if (freelistLock()->owned_by_self()) {
3189 Generation::object_iterate(cl);
3190 } else {
3191 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3192 Generation::object_iterate(cl);
3193 }
3194 }
3195
3196 void
3197 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3198 if (freelistLock()->owned_by_self()) {
3199 Generation::safe_object_iterate(cl);
3200 } else {
3201 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3202 Generation::safe_object_iterate(cl);
3203 }
3204 }
3205
3206 void
3207 ConcurrentMarkSweepGeneration::post_compact() {
3208 }
3209
3210 void
3211 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3212 // Fix the linear allocation blocks to look like free blocks.
3213
3214 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3215 // are not called when the heap is verified during universe initialization and
3216 // at vm shutdown.
3217 if (freelistLock()->owned_by_self()) {
3218 cmsSpace()->prepare_for_verify();
3219 } else {
3220 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3221 cmsSpace()->prepare_for_verify();
3222 }
3223 }
3224
3225 void
3226 ConcurrentMarkSweepGeneration::verify() {
3227 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3228 // are not called when the heap is verified during universe initialization and
3229 // at vm shutdown.
3230 if (freelistLock()->owned_by_self()) {
3231 cmsSpace()->verify();
3232 } else {
3233 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3234 cmsSpace()->verify();
3235 }
3236 }
3237
3238 void CMSCollector::verify() {
3239 _cmsGen->verify();
3240 }
3241
3242 #ifndef PRODUCT
3243 bool CMSCollector::overflow_list_is_empty() const {
3244 assert(_num_par_pushes >= 0, "Inconsistency");
3245 if (_overflow_list == NULL) {
3246 assert(_num_par_pushes == 0, "Inconsistency");
3247 }
3248 return _overflow_list == NULL;
3249 }
3250
3251 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3252 // merely consolidate assertion checks that appear to occur together frequently.
3253 void CMSCollector::verify_work_stacks_empty() const {
3254 assert(_markStack.isEmpty(), "Marking stack should be empty");
3255 assert(overflow_list_is_empty(), "Overflow list should be empty");
3256 }
3257
3258 void CMSCollector::verify_overflow_empty() const {
3259 assert(overflow_list_is_empty(), "Overflow list should be empty");
3260 assert(no_preserved_marks(), "No preserved marks");
3261 }
3262 #endif // PRODUCT
3263
3264 // Decide if we want to enable class unloading as part of the
3265 // ensuing concurrent GC cycle. We will collect and
3266 // unload classes if it's the case that:
3267 // (1) an explicit gc request has been made and the flag
3268 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3269 // (2) (a) class unloading is enabled at the command line, and
3270 // (b) old gen is getting really full
3271 // NOTE: Provided there is no change in the state of the heap between
3272 // calls to this method, it should have idempotent results. Moreover,
3273 // its results should be monotonically increasing (i.e. going from 0 to 1,
3274 // but not 1 to 0) between successive calls between which the heap was
3275 // not collected. For the implementation below, it must thus rely on
3276 // the property that concurrent_cycles_since_last_unload()
3277 // will not decrease unless a collection cycle happened and that
3278 // _cmsGen->is_too_full() are
3279 // themselves also monotonic in that sense. See check_monotonicity()
3280 // below.
3281 void CMSCollector::update_should_unload_classes() {
3282 _should_unload_classes = false;
3283 // Condition 1 above
3284 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3285 _should_unload_classes = true;
3286 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3287 // Disjuncts 2.b.(i,ii,iii) above
3288 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3289 CMSClassUnloadingMaxInterval)
3290 || _cmsGen->is_too_full();
3291 }
3292 }
3293
3294 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3295 bool res = should_concurrent_collect();
3296 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3297 return res;
3298 }
3299
3300 void CMSCollector::setup_cms_unloading_and_verification_state() {
3301 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3302 || VerifyBeforeExit;
3303 const int rso = SharedHeap::SO_Strings | SharedHeap::SO_AllCodeCache;
3304
3305 // We set the proper root for this CMS cycle here.
3306 if (should_unload_classes()) { // Should unload classes this cycle
3307 remove_root_scanning_option(SharedHeap::SO_AllClasses);
3308 add_root_scanning_option(SharedHeap::SO_SystemClasses);
3309 remove_root_scanning_option(rso); // Shrink the root set appropriately
3310 set_verifying(should_verify); // Set verification state for this cycle
3311 return; // Nothing else needs to be done at this time
3312 }
3313
3314 // Not unloading classes this cycle
3315 assert(!should_unload_classes(), "Inconsistency!");
3316 remove_root_scanning_option(SharedHeap::SO_SystemClasses);
3317 add_root_scanning_option(SharedHeap::SO_AllClasses);
3318
3319 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3320 // Include symbols, strings and code cache elements to prevent their resurrection.
3321 add_root_scanning_option(rso);
3322 set_verifying(true);
3323 } else if (verifying() && !should_verify) {
3324 // We were verifying, but some verification flags got disabled.
3325 set_verifying(false);
3326 // Exclude symbols, strings and code cache elements from root scanning to
3327 // reduce IM and RM pauses.
3328 remove_root_scanning_option(rso);
3329 }
3330 }
3331
3332
3333 #ifndef PRODUCT
3334 HeapWord* CMSCollector::block_start(const void* p) const {
3335 const HeapWord* addr = (HeapWord*)p;
3336 if (_span.contains(p)) {
3337 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3338 return _cmsGen->cmsSpace()->block_start(p);
3339 }
3340 }
3341 return NULL;
3342 }
3343 #endif
3344
3345 HeapWord*
3346 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3347 bool tlab,
3348 bool parallel) {
3349 CMSSynchronousYieldRequest yr;
3350 assert(!tlab, "Can't deal with TLAB allocation");
3351 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3352 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3353 CMSExpansionCause::_satisfy_allocation);
3354 if (GCExpandToAllocateDelayMillis > 0) {
3355 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3356 }
3357 return have_lock_and_allocate(word_size, tlab);
3358 }
3359
3360 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3361 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3362 // to CardGeneration and share it...
3363 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3364 return CardGeneration::expand(bytes, expand_bytes);
3365 }
3366
3367 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3368 CMSExpansionCause::Cause cause)
3369 {
3370
3371 bool success = expand(bytes, expand_bytes);
3372
3373 // remember why we expanded; this information is used
3374 // by shouldConcurrentCollect() when making decisions on whether to start
3375 // a new CMS cycle.
3376 if (success) {
3377 set_expansion_cause(cause);
3378 if (PrintGCDetails && Verbose) {
3379 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3380 CMSExpansionCause::to_string(cause));
3381 }
3382 }
3383 }
3384
3385 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3386 HeapWord* res = NULL;
3387 MutexLocker x(ParGCRareEvent_lock);
3388 while (true) {
3389 // Expansion by some other thread might make alloc OK now:
3390 res = ps->lab.alloc(word_sz);
3391 if (res != NULL) return res;
3392 // If there's not enough expansion space available, give up.
3393 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3394 return NULL;
3395 }
3396 // Otherwise, we try expansion.
3397 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3398 CMSExpansionCause::_allocate_par_lab);
3399 // Now go around the loop and try alloc again;
3400 // A competing par_promote might beat us to the expansion space,
3401 // so we may go around the loop again if promotion fails again.
3402 if (GCExpandToAllocateDelayMillis > 0) {
3403 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3404 }
3405 }
3406 }
3407
3408
3409 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3410 PromotionInfo* promo) {
3411 MutexLocker x(ParGCRareEvent_lock);
3412 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3413 while (true) {
3414 // Expansion by some other thread might make alloc OK now:
3415 if (promo->ensure_spooling_space()) {
3416 assert(promo->has_spooling_space(),
3417 "Post-condition of successful ensure_spooling_space()");
3418 return true;
3419 }
3420 // If there's not enough expansion space available, give up.
3421 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3422 return false;
3423 }
3424 // Otherwise, we try expansion.
3425 expand(refill_size_bytes, MinHeapDeltaBytes,
3426 CMSExpansionCause::_allocate_par_spooling_space);
3427 // Now go around the loop and try alloc again;
3428 // A competing allocation might beat us to the expansion space,
3429 // so we may go around the loop again if allocation fails again.
3430 if (GCExpandToAllocateDelayMillis > 0) {
3431 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3432 }
3433 }
3434 }
3435
3436
3437 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3438 assert_locked_or_safepoint(ExpandHeap_lock);
3439 // Shrink committed space
3440 _virtual_space.shrink_by(bytes);
3441 // Shrink space; this also shrinks the space's BOT
3442 _cmsSpace->set_end((HeapWord*) _virtual_space.high());
3443 size_t new_word_size = heap_word_size(_cmsSpace->capacity());
3444 // Shrink the shared block offset array
3445 _bts->resize(new_word_size);
3446 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3447 // Shrink the card table
3448 Universe::heap()->barrier_set()->resize_covered_region(mr);
3449
3450 if (Verbose && PrintGC) {
3451 size_t new_mem_size = _virtual_space.committed_size();
3452 size_t old_mem_size = new_mem_size + bytes;
3453 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3454 name(), old_mem_size/K, new_mem_size/K);
3455 }
3456 }
3457
3458 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3459 assert_locked_or_safepoint(Heap_lock);
3460 size_t size = ReservedSpace::page_align_size_down(bytes);
3461 // Only shrink if a compaction was done so that all the free space
3462 // in the generation is in a contiguous block at the end.
3463 if (size > 0 && did_compact()) {
3464 shrink_by(size);
3465 }
3466 }
3467
3468 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3469 assert_locked_or_safepoint(Heap_lock);
3470 bool result = _virtual_space.expand_by(bytes);
3471 if (result) {
3472 size_t new_word_size =
3473 heap_word_size(_virtual_space.committed_size());
3474 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3475 _bts->resize(new_word_size); // resize the block offset shared array
3476 Universe::heap()->barrier_set()->resize_covered_region(mr);
3477 // Hmmmm... why doesn't CFLS::set_end verify locking?
3478 // This is quite ugly; FIX ME XXX
3479 _cmsSpace->assert_locked(freelistLock());
3480 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3481
3482 // update the space and generation capacity counters
3483 if (UsePerfData) {
3484 _space_counters->update_capacity();
3485 _gen_counters->update_all();
3486 }
3487
3488 if (Verbose && PrintGC) {
3489 size_t new_mem_size = _virtual_space.committed_size();
3490 size_t old_mem_size = new_mem_size - bytes;
3491 gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3492 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3493 }
3494 }
3495 return result;
3496 }
3497
3498 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3499 assert_locked_or_safepoint(Heap_lock);
3500 bool success = true;
3501 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3502 if (remaining_bytes > 0) {
3503 success = grow_by(remaining_bytes);
3504 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3505 }
3506 return success;
3507 }
3508
3509 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
3510 assert_locked_or_safepoint(Heap_lock);
3511 assert_lock_strong(freelistLock());
3512 if (PrintGCDetails && Verbose) {
3513 warning("Shrinking of CMS not yet implemented");
3514 }
3515 return;
3516 }
3517
3518
3519 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3520 // phases.
3521 class CMSPhaseAccounting: public StackObj {
3522 public:
3523 CMSPhaseAccounting(CMSCollector *collector,
3524 const char *phase,
3525 bool print_cr = true);
3526 ~CMSPhaseAccounting();
3527
3528 private:
3529 CMSCollector *_collector;
3530 const char *_phase;
3531 elapsedTimer _wallclock;
3532 bool _print_cr;
3533
3534 public:
3535 // Not MT-safe; so do not pass around these StackObj's
3536 // where they may be accessed by other threads.
3537 jlong wallclock_millis() {
3538 assert(_wallclock.is_active(), "Wall clock should not stop");
3539 _wallclock.stop(); // to record time
3540 jlong ret = _wallclock.milliseconds();
3541 _wallclock.start(); // restart
3542 return ret;
3543 }
3544 };
3545
3546 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3547 const char *phase,
3548 bool print_cr) :
3549 _collector(collector), _phase(phase), _print_cr(print_cr) {
3550
3551 if (PrintCMSStatistics != 0) {
3552 _collector->resetYields();
3553 }
3554 if (PrintGCDetails) {
3555 gclog_or_tty->date_stamp(PrintGCDateStamps);
3556 gclog_or_tty->stamp(PrintGCTimeStamps);
3557 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
3558 _collector->cmsGen()->short_name(), _phase);
3559 }
3560 _collector->resetTimer();
3561 _wallclock.start();
3562 _collector->startTimer();
3563 }
3564
3565 CMSPhaseAccounting::~CMSPhaseAccounting() {
3566 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3567 _collector->stopTimer();
3568 _wallclock.stop();
3569 if (PrintGCDetails) {
3570 gclog_or_tty->date_stamp(PrintGCDateStamps);
3571 gclog_or_tty->stamp(PrintGCTimeStamps);
3572 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3573 _collector->cmsGen()->short_name(),
3574 _phase, _collector->timerValue(), _wallclock.seconds());
3575 if (_print_cr) {
3576 gclog_or_tty->print_cr("");
3577 }
3578 if (PrintCMSStatistics != 0) {
3579 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3580 _collector->yields());
3581 }
3582 }
3583 }
3584
3585 // CMS work
3586
3587 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
3588 class CMSParMarkTask : public AbstractGangTask {
3589 protected:
3590 CMSCollector* _collector;
3591 int _n_workers;
3592 CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
3593 AbstractGangTask(name),
3594 _collector(collector),
3595 _n_workers(n_workers) {}
3596 // Work method in support of parallel rescan ... of young gen spaces
3597 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
3598 ContiguousSpace* space,
3599 HeapWord** chunk_array, size_t chunk_top);
3600 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
3601 };
3602
3603 // Parallel initial mark task
3604 class CMSParInitialMarkTask: public CMSParMarkTask {
3605 public:
3606 CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
3607 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
3608 collector, n_workers) {}
3609 void work(uint worker_id);
3610 };
3611
3612 // Checkpoint the roots into this generation from outside
3613 // this generation. [Note this initial checkpoint need only
3614 // be approximate -- we'll do a catch up phase subsequently.]
3615 void CMSCollector::checkpointRootsInitial(bool asynch) {
3616 assert(_collectorState == InitialMarking, "Wrong collector state");
3617 check_correct_thread_executing();
3618 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3619
3620 save_heap_summary();
3621 report_heap_summary(GCWhen::BeforeGC);
3622
3623 ReferenceProcessor* rp = ref_processor();
3624 SpecializationStats::clear();
3625 assert(_restart_addr == NULL, "Control point invariant");
3626 if (asynch) {
3627 // acquire locks for subsequent manipulations
3628 MutexLockerEx x(bitMapLock(),
3629 Mutex::_no_safepoint_check_flag);
3630 checkpointRootsInitialWork(asynch);
3631 // enable ("weak") refs discovery
3632 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3633 _collectorState = Marking;
3634 } else {
3635 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3636 // which recognizes if we are a CMS generation, and doesn't try to turn on
3637 // discovery; verify that they aren't meddling.
3638 assert(!rp->discovery_is_atomic(),
3639 "incorrect setting of discovery predicate");
3640 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3641 "ref discovery for this generation kind");
3642 // already have locks
3643 checkpointRootsInitialWork(asynch);
3644 // now enable ("weak") refs discovery
3645 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3646 _collectorState = Marking;
3647 }
3648 SpecializationStats::print();
3649 }
3650
3651 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3652 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3653 assert(_collectorState == InitialMarking, "just checking");
3654
3655 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3656 // precede our marking with a collection of all
3657 // younger generations to keep floating garbage to a minimum.
3658 // XXX: we won't do this for now -- it's an optimization to be done later.
3659
3660 // already have locks
3661 assert_lock_strong(bitMapLock());
3662 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3663
3664 // Setup the verification and class unloading state for this
3665 // CMS collection cycle.
3666 setup_cms_unloading_and_verification_state();
3667
3668 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3669 PrintGCDetails && Verbose, true, _gc_timer_cm);)
3670 if (UseAdaptiveSizePolicy) {
3671 size_policy()->checkpoint_roots_initial_begin();
3672 }
3673
3674 // Reset all the PLAB chunk arrays if necessary.
3675 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3676 reset_survivor_plab_arrays();
3677 }
3678
3679 ResourceMark rm;
3680 HandleMark hm;
3681
3682 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3683 GenCollectedHeap* gch = GenCollectedHeap::heap();
3684
3685 verify_work_stacks_empty();
3686 verify_overflow_empty();
3687
3688 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3689 // Update the saved marks which may affect the root scans.
3690 gch->save_marks();
3691
3692 // weak reference processing has not started yet.
3693 ref_processor()->set_enqueuing_is_done(false);
3694
3695 // Need to remember all newly created CLDs,
3696 // so that we can guarantee that the remark finds them.
3697 ClassLoaderDataGraph::remember_new_clds(true);
3698
3699 // Whenever a CLD is found, it will be claimed before proceeding to mark
3700 // the klasses. The claimed marks need to be cleared before marking starts.
3701 ClassLoaderDataGraph::clear_claimed_marks();
3702
3703 if (CMSPrintEdenSurvivorChunks) {
3704 print_eden_and_survivor_chunk_arrays();
3705 }
3706
3707 {
3708 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3709 if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3710 // The parallel version.
3711 FlexibleWorkGang* workers = gch->workers();
3712 assert(workers != NULL, "Need parallel worker threads.");
3713 int n_workers = workers->active_workers();
3714 CMSParInitialMarkTask tsk(this, n_workers);
3715 gch->set_par_threads(n_workers);
3716 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3717 if (n_workers > 1) {
3718 GenCollectedHeap::StrongRootsScope srs(gch);
3719 workers->run_task(&tsk);
3720 } else {
3721 GenCollectedHeap::StrongRootsScope srs(gch);
3722 tsk.work(0);
3723 }
3724 gch->set_par_threads(0);
3725 } else {
3726 // The serial version.
3727 CMKlassClosure klass_closure(¬Older);
3728 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3729 gch->gen_process_strong_roots(_cmsGen->level(),
3730 true, // younger gens are roots
3731 true, // activate StrongRootsScope
3732 SharedHeap::ScanningOption(roots_scanning_options()),
3733 ¬Older,
3734 NULL,
3735 &klass_closure);
3736 }
3737 }
3738
3739 // Clear mod-union table; it will be dirtied in the prologue of
3740 // CMS generation per each younger generation collection.
3741
3742 assert(_modUnionTable.isAllClear(),
3743 "Was cleared in most recent final checkpoint phase"
3744 " or no bits are set in the gc_prologue before the start of the next "
3745 "subsequent marking phase.");
3746
3747 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3748
3749 // Save the end of the used_region of the constituent generations
3750 // to be used to limit the extent of sweep in each generation.
3751 save_sweep_limits();
3752 if (UseAdaptiveSizePolicy) {
3753 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3754 }
3755 verify_overflow_empty();
3756 }
3757
3758 bool CMSCollector::markFromRoots(bool asynch) {
3759 // we might be tempted to assert that:
3760 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3761 // "inconsistent argument?");
3762 // However that wouldn't be right, because it's possible that
3763 // a safepoint is indeed in progress as a younger generation
3764 // stop-the-world GC happens even as we mark in this generation.
3765 assert(_collectorState == Marking, "inconsistent state?");
3766 check_correct_thread_executing();
3767 verify_overflow_empty();
3768
3769 bool res;
3770 if (asynch) {
3771
3772 // Start the timers for adaptive size policy for the concurrent phases
3773 // Do it here so that the foreground MS can use the concurrent
3774 // timer since a foreground MS might has the sweep done concurrently
3775 // or STW.
3776 if (UseAdaptiveSizePolicy) {
3777 size_policy()->concurrent_marking_begin();
3778 }
3779
3780 // Weak ref discovery note: We may be discovering weak
3781 // refs in this generation concurrent (but interleaved) with
3782 // weak ref discovery by a younger generation collector.
3783
3784 CMSTokenSyncWithLocks ts(true, bitMapLock());
3785 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3786 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3787 res = markFromRootsWork(asynch);
3788 if (res) {
3789 _collectorState = Precleaning;
3790 } else { // We failed and a foreground collection wants to take over
3791 assert(_foregroundGCIsActive, "internal state inconsistency");
3792 assert(_restart_addr == NULL, "foreground will restart from scratch");
3793 if (PrintGCDetails) {
3794 gclog_or_tty->print_cr("bailing out to foreground collection");
3795 }
3796 }
3797 if (UseAdaptiveSizePolicy) {
3798 size_policy()->concurrent_marking_end();
3799 }
3800 } else {
3801 assert(SafepointSynchronize::is_at_safepoint(),
3802 "inconsistent with asynch == false");
3803 if (UseAdaptiveSizePolicy) {
3804 size_policy()->ms_collection_marking_begin();
3805 }
3806 // already have locks
3807 res = markFromRootsWork(asynch);
3808 _collectorState = FinalMarking;
3809 if (UseAdaptiveSizePolicy) {
3810 GenCollectedHeap* gch = GenCollectedHeap::heap();
3811 size_policy()->ms_collection_marking_end(gch->gc_cause());
3812 }
3813 }
3814 verify_overflow_empty();
3815 return res;
3816 }
3817
3818 bool CMSCollector::markFromRootsWork(bool asynch) {
3819 // iterate over marked bits in bit map, doing a full scan and mark
3820 // from these roots using the following algorithm:
3821 // . if oop is to the right of the current scan pointer,
3822 // mark corresponding bit (we'll process it later)
3823 // . else (oop is to left of current scan pointer)
3824 // push oop on marking stack
3825 // . drain the marking stack
3826
3827 // Note that when we do a marking step we need to hold the
3828 // bit map lock -- recall that direct allocation (by mutators)
3829 // and promotion (by younger generation collectors) is also
3830 // marking the bit map. [the so-called allocate live policy.]
3831 // Because the implementation of bit map marking is not
3832 // robust wrt simultaneous marking of bits in the same word,
3833 // we need to make sure that there is no such interference
3834 // between concurrent such updates.
3835
3836 // already have locks
3837 assert_lock_strong(bitMapLock());
3838
3839 verify_work_stacks_empty();
3840 verify_overflow_empty();
3841 bool result = false;
3842 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3843 result = do_marking_mt(asynch);
3844 } else {
3845 result = do_marking_st(asynch);
3846 }
3847 return result;
3848 }
3849
3850 // Forward decl
3851 class CMSConcMarkingTask;
3852
3853 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3854 CMSCollector* _collector;
3855 CMSConcMarkingTask* _task;
3856 public:
3857 virtual void yield();
3858
3859 // "n_threads" is the number of threads to be terminated.
3860 // "queue_set" is a set of work queues of other threads.
3861 // "collector" is the CMS collector associated with this task terminator.
3862 // "yield" indicates whether we need the gang as a whole to yield.
3863 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3864 ParallelTaskTerminator(n_threads, queue_set),
3865 _collector(collector) { }
3866
3867 void set_task(CMSConcMarkingTask* task) {
3868 _task = task;
3869 }
3870 };
3871
3872 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3873 CMSConcMarkingTask* _task;
3874 public:
3875 bool should_exit_termination();
3876 void set_task(CMSConcMarkingTask* task) {
3877 _task = task;
3878 }
3879 };
3880
3881 // MT Concurrent Marking Task
3882 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3883 CMSCollector* _collector;
3884 int _n_workers; // requested/desired # workers
3885 bool _asynch;
3886 bool _result;
3887 CompactibleFreeListSpace* _cms_space;
3888 char _pad_front[64]; // padding to ...
3889 HeapWord* _global_finger; // ... avoid sharing cache line
3890 char _pad_back[64];
3891 HeapWord* _restart_addr;
3892
3893 // Exposed here for yielding support
3894 Mutex* const _bit_map_lock;
3895
3896 // The per thread work queues, available here for stealing
3897 OopTaskQueueSet* _task_queues;
3898
3899 // Termination (and yielding) support
3900 CMSConcMarkingTerminator _term;
3901 CMSConcMarkingTerminatorTerminator _term_term;
3902
3903 public:
3904 CMSConcMarkingTask(CMSCollector* collector,
3905 CompactibleFreeListSpace* cms_space,
3906 bool asynch,
3907 YieldingFlexibleWorkGang* workers,
3908 OopTaskQueueSet* task_queues):
3909 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3910 _collector(collector),
3911 _cms_space(cms_space),
3912 _asynch(asynch), _n_workers(0), _result(true),
3913 _task_queues(task_queues),
3914 _term(_n_workers, task_queues, _collector),
3915 _bit_map_lock(collector->bitMapLock())
3916 {
3917 _requested_size = _n_workers;
3918 _term.set_task(this);
3919 _term_term.set_task(this);
3920 _restart_addr = _global_finger = _cms_space->bottom();
3921 }
3922
3923
3924 OopTaskQueueSet* task_queues() { return _task_queues; }
3925
3926 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3927
3928 HeapWord** global_finger_addr() { return &_global_finger; }
3929
3930 CMSConcMarkingTerminator* terminator() { return &_term; }
3931
3932 virtual void set_for_termination(int active_workers) {
3933 terminator()->reset_for_reuse(active_workers);
3934 }
3935
3936 void work(uint worker_id);
3937 bool should_yield() {
3938 return ConcurrentMarkSweepThread::should_yield()
3939 && !_collector->foregroundGCIsActive()
3940 && _asynch;
3941 }
3942
3943 virtual void coordinator_yield(); // stuff done by coordinator
3944 bool result() { return _result; }
3945
3946 void reset(HeapWord* ra) {
3947 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3948 _restart_addr = _global_finger = ra;
3949 _term.reset_for_reuse();
3950 }
3951
3952 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3953 OopTaskQueue* work_q);
3954
3955 private:
3956 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3957 void do_work_steal(int i);
3958 void bump_global_finger(HeapWord* f);
3959 };
3960
3961 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3962 assert(_task != NULL, "Error");
3963 return _task->yielding();
3964 // Note that we do not need the disjunct || _task->should_yield() above
3965 // because we want terminating threads to yield only if the task
3966 // is already in the midst of yielding, which happens only after at least one
3967 // thread has yielded.
3968 }
3969
3970 void CMSConcMarkingTerminator::yield() {
3971 if (_task->should_yield()) {
3972 _task->yield();
3973 } else {
3974 ParallelTaskTerminator::yield();
3975 }
3976 }
3977
3978 ////////////////////////////////////////////////////////////////
3979 // Concurrent Marking Algorithm Sketch
3980 ////////////////////////////////////////////////////////////////
3981 // Until all tasks exhausted (both spaces):
3982 // -- claim next available chunk
3983 // -- bump global finger via CAS
3984 // -- find first object that starts in this chunk
3985 // and start scanning bitmap from that position
3986 // -- scan marked objects for oops
3987 // -- CAS-mark target, and if successful:
3988 // . if target oop is above global finger (volatile read)
3989 // nothing to do
3990 // . if target oop is in chunk and above local finger
3991 // then nothing to do
3992 // . else push on work-queue
3993 // -- Deal with possible overflow issues:
3994 // . local work-queue overflow causes stuff to be pushed on
3995 // global (common) overflow queue
3996 // . always first empty local work queue
3997 // . then get a batch of oops from global work queue if any
3998 // . then do work stealing
3999 // -- When all tasks claimed (both spaces)
4000 // and local work queue empty,
4001 // then in a loop do:
4002 // . check global overflow stack; steal a batch of oops and trace
4003 // . try to steal from other threads oif GOS is empty
4004 // . if neither is available, offer termination
4005 // -- Terminate and return result
4006 //
4007 void CMSConcMarkingTask::work(uint worker_id) {
4008 elapsedTimer _timer;
4009 ResourceMark rm;
4010 HandleMark hm;
4011
4012 DEBUG_ONLY(_collector->verify_overflow_empty();)
4013
4014 // Before we begin work, our work queue should be empty
4015 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
4016 // Scan the bitmap covering _cms_space, tracing through grey objects.
4017 _timer.start();
4018 do_scan_and_mark(worker_id, _cms_space);
4019 _timer.stop();
4020 if (PrintCMSStatistics != 0) {
4021 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
4022 worker_id, _timer.seconds());
4023 // XXX: need xxx/xxx type of notation, two timers
4024 }
4025
4026 // ... do work stealing
4027 _timer.reset();
4028 _timer.start();
4029 do_work_steal(worker_id);
4030 _timer.stop();
4031 if (PrintCMSStatistics != 0) {
4032 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
4033 worker_id, _timer.seconds());
4034 // XXX: need xxx/xxx type of notation, two timers
4035 }
4036 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
4037 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
4038 // Note that under the current task protocol, the
4039 // following assertion is true even of the spaces
4040 // expanded since the completion of the concurrent
4041 // marking. XXX This will likely change under a strict
4042 // ABORT semantics.
4043 // After perm removal the comparison was changed to
4044 // greater than or equal to from strictly greater than.
4045 // Before perm removal the highest address sweep would
4046 // have been at the end of perm gen but now is at the
4047 // end of the tenured gen.
4048 assert(_global_finger >= _cms_space->end(),
4049 "All tasks have been completed");
4050 DEBUG_ONLY(_collector->verify_overflow_empty();)
4051 }
4052
4053 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
4054 HeapWord* read = _global_finger;
4055 HeapWord* cur = read;
4056 while (f > read) {
4057 cur = read;
4058 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
4059 if (cur == read) {
4060 // our cas succeeded
4061 assert(_global_finger >= f, "protocol consistency");
4062 break;
4063 }
4064 }
4065 }
4066
4067 // This is really inefficient, and should be redone by
4068 // using (not yet available) block-read and -write interfaces to the
4069 // stack and the work_queue. XXX FIX ME !!!
4070 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
4071 OopTaskQueue* work_q) {
4072 // Fast lock-free check
4073 if (ovflw_stk->length() == 0) {
4074 return false;
4075 }
4076 assert(work_q->size() == 0, "Shouldn't steal");
4077 MutexLockerEx ml(ovflw_stk->par_lock(),
4078 Mutex::_no_safepoint_check_flag);
4079 // Grab up to 1/4 the size of the work queue
4080 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4081 (size_t)ParGCDesiredObjsFromOverflowList);
4082 num = MIN2(num, ovflw_stk->length());
4083 for (int i = (int) num; i > 0; i--) {
4084 oop cur = ovflw_stk->pop();
4085 assert(cur != NULL, "Counted wrong?");
4086 work_q->push(cur);
4087 }
4088 return num > 0;
4089 }
4090
4091 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
4092 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4093 int n_tasks = pst->n_tasks();
4094 // We allow that there may be no tasks to do here because
4095 // we are restarting after a stack overflow.
4096 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
4097 uint nth_task = 0;
4098
4099 HeapWord* aligned_start = sp->bottom();
4100 if (sp->used_region().contains(_restart_addr)) {
4101 // Align down to a card boundary for the start of 0th task
4102 // for this space.
4103 aligned_start =
4104 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
4105 CardTableModRefBS::card_size);
4106 }
4107
4108 size_t chunk_size = sp->marking_task_size();
4109 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4110 // Having claimed the nth task in this space,
4111 // compute the chunk that it corresponds to:
4112 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
4113 aligned_start + (nth_task+1)*chunk_size);
4114 // Try and bump the global finger via a CAS;
4115 // note that we need to do the global finger bump
4116 // _before_ taking the intersection below, because
4117 // the task corresponding to that region will be
4118 // deemed done even if the used_region() expands
4119 // because of allocation -- as it almost certainly will
4120 // during start-up while the threads yield in the
4121 // closure below.
4122 HeapWord* finger = span.end();
4123 bump_global_finger(finger); // atomically
4124 // There are null tasks here corresponding to chunks
4125 // beyond the "top" address of the space.
4126 span = span.intersection(sp->used_region());
4127 if (!span.is_empty()) { // Non-null task
4128 HeapWord* prev_obj;
4129 assert(!span.contains(_restart_addr) || nth_task == 0,
4130 "Inconsistency");
4131 if (nth_task == 0) {
4132 // For the 0th task, we'll not need to compute a block_start.
4133 if (span.contains(_restart_addr)) {
4134 // In the case of a restart because of stack overflow,
4135 // we might additionally skip a chunk prefix.
4136 prev_obj = _restart_addr;
4137 } else {
4138 prev_obj = span.start();
4139 }
4140 } else {
4141 // We want to skip the first object because
4142 // the protocol is to scan any object in its entirety
4143 // that _starts_ in this span; a fortiori, any
4144 // object starting in an earlier span is scanned
4145 // as part of an earlier claimed task.
4146 // Below we use the "careful" version of block_start
4147 // so we do not try to navigate uninitialized objects.
4148 prev_obj = sp->block_start_careful(span.start());
4149 // Below we use a variant of block_size that uses the
4150 // Printezis bits to avoid waiting for allocated
4151 // objects to become initialized/parsable.
4152 while (prev_obj < span.start()) {
4153 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4154 if (sz > 0) {
4155 prev_obj += sz;
4156 } else {
4157 // In this case we may end up doing a bit of redundant
4158 // scanning, but that appears unavoidable, short of
4159 // locking the free list locks; see bug 6324141.
4160 break;
4161 }
4162 }
4163 }
4164 if (prev_obj < span.end()) {
4165 MemRegion my_span = MemRegion(prev_obj, span.end());
4166 // Do the marking work within a non-empty span --
4167 // the last argument to the constructor indicates whether the
4168 // iteration should be incremental with periodic yields.
4169 Par_MarkFromRootsClosure cl(this, _collector, my_span,
4170 &_collector->_markBitMap,
4171 work_queue(i),
4172 &_collector->_markStack,
4173 _asynch);
4174 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4175 } // else nothing to do for this task
4176 } // else nothing to do for this task
4177 }
4178 // We'd be tempted to assert here that since there are no
4179 // more tasks left to claim in this space, the global_finger
4180 // must exceed space->top() and a fortiori space->end(). However,
4181 // that would not quite be correct because the bumping of
4182 // global_finger occurs strictly after the claiming of a task,
4183 // so by the time we reach here the global finger may not yet
4184 // have been bumped up by the thread that claimed the last
4185 // task.
4186 pst->all_tasks_completed();
4187 }
4188
4189 class Par_ConcMarkingClosure: public CMSOopClosure {
4190 private:
4191 CMSCollector* _collector;
4192 CMSConcMarkingTask* _task;
4193 MemRegion _span;
4194 CMSBitMap* _bit_map;
4195 CMSMarkStack* _overflow_stack;
4196 OopTaskQueue* _work_queue;
4197 protected:
4198 DO_OOP_WORK_DEFN
4199 public:
4200 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4201 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
4202 CMSOopClosure(collector->ref_processor()),
4203 _collector(collector),
4204 _task(task),
4205 _span(collector->_span),
4206 _work_queue(work_queue),
4207 _bit_map(bit_map),
4208 _overflow_stack(overflow_stack)
4209 { }
4210 virtual void do_oop(oop* p);
4211 virtual void do_oop(narrowOop* p);
4212
4213 void trim_queue(size_t max);
4214 void handle_stack_overflow(HeapWord* lost);
4215 void do_yield_check() {
4216 if (_task->should_yield()) {
4217 _task->yield();
4218 }
4219 }
4220 };
4221
4222 // Grey object scanning during work stealing phase --
4223 // the salient assumption here is that any references
4224 // that are in these stolen objects being scanned must
4225 // already have been initialized (else they would not have
4226 // been published), so we do not need to check for
4227 // uninitialized objects before pushing here.
4228 void Par_ConcMarkingClosure::do_oop(oop obj) {
4229 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4230 HeapWord* addr = (HeapWord*)obj;
4231 // Check if oop points into the CMS generation
4232 // and is not marked
4233 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4234 // a white object ...
4235 // If we manage to "claim" the object, by being the
4236 // first thread to mark it, then we push it on our
4237 // marking stack
4238 if (_bit_map->par_mark(addr)) { // ... now grey
4239 // push on work queue (grey set)
4240 bool simulate_overflow = false;
4241 NOT_PRODUCT(
4242 if (CMSMarkStackOverflowALot &&
4243 _collector->simulate_overflow()) {
4244 // simulate a stack overflow
4245 simulate_overflow = true;
4246 }
4247 )
4248 if (simulate_overflow ||
4249 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4250 // stack overflow
4251 if (PrintCMSStatistics != 0) {
4252 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4253 SIZE_FORMAT, _overflow_stack->capacity());
4254 }
4255 // We cannot assert that the overflow stack is full because
4256 // it may have been emptied since.
4257 assert(simulate_overflow ||
4258 _work_queue->size() == _work_queue->max_elems(),
4259 "Else push should have succeeded");
4260 handle_stack_overflow(addr);
4261 }
4262 } // Else, some other thread got there first
4263 do_yield_check();
4264 }
4265 }
4266
4267 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4268 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4269
4270 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4271 while (_work_queue->size() > max) {
4272 oop new_oop;
4273 if (_work_queue->pop_local(new_oop)) {
4274 assert(new_oop->is_oop(), "Should be an oop");
4275 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4276 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4277 new_oop->oop_iterate(this); // do_oop() above
4278 do_yield_check();
4279 }
4280 }
4281 }
4282
4283 // Upon stack overflow, we discard (part of) the stack,
4284 // remembering the least address amongst those discarded
4285 // in CMSCollector's _restart_address.
4286 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4287 // We need to do this under a mutex to prevent other
4288 // workers from interfering with the work done below.
4289 MutexLockerEx ml(_overflow_stack->par_lock(),
4290 Mutex::_no_safepoint_check_flag);
4291 // Remember the least grey address discarded
4292 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4293 _collector->lower_restart_addr(ra);
4294 _overflow_stack->reset(); // discard stack contents
4295 _overflow_stack->expand(); // expand the stack if possible
4296 }
4297
4298
4299 void CMSConcMarkingTask::do_work_steal(int i) {
4300 OopTaskQueue* work_q = work_queue(i);
4301 oop obj_to_scan;
4302 CMSBitMap* bm = &(_collector->_markBitMap);
4303 CMSMarkStack* ovflw = &(_collector->_markStack);
4304 int* seed = _collector->hash_seed(i);
4305 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4306 while (true) {
4307 cl.trim_queue(0);
4308 assert(work_q->size() == 0, "Should have been emptied above");
4309 if (get_work_from_overflow_stack(ovflw, work_q)) {
4310 // Can't assert below because the work obtained from the
4311 // overflow stack may already have been stolen from us.
4312 // assert(work_q->size() > 0, "Work from overflow stack");
4313 continue;
4314 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4315 assert(obj_to_scan->is_oop(), "Should be an oop");
4316 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4317 obj_to_scan->oop_iterate(&cl);
4318 } else if (terminator()->offer_termination(&_term_term)) {
4319 assert(work_q->size() == 0, "Impossible!");
4320 break;
4321 } else if (yielding() || should_yield()) {
4322 yield();
4323 }
4324 }
4325 }
4326
4327 // This is run by the CMS (coordinator) thread.
4328 void CMSConcMarkingTask::coordinator_yield() {
4329 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4330 "CMS thread should hold CMS token");
4331 // First give up the locks, then yield, then re-lock
4332 // We should probably use a constructor/destructor idiom to
4333 // do this unlock/lock or modify the MutexUnlocker class to
4334 // serve our purpose. XXX
4335 assert_lock_strong(_bit_map_lock);
4336 _bit_map_lock->unlock();
4337 ConcurrentMarkSweepThread::desynchronize(true);
4338 ConcurrentMarkSweepThread::acknowledge_yield_request();
4339 _collector->stopTimer();
4340 if (PrintCMSStatistics != 0) {
4341 _collector->incrementYields();
4342 }
4343 _collector->icms_wait();
4344
4345 // It is possible for whichever thread initiated the yield request
4346 // not to get a chance to wake up and take the bitmap lock between
4347 // this thread releasing it and reacquiring it. So, while the
4348 // should_yield() flag is on, let's sleep for a bit to give the
4349 // other thread a chance to wake up. The limit imposed on the number
4350 // of iterations is defensive, to avoid any unforseen circumstances
4351 // putting us into an infinite loop. Since it's always been this
4352 // (coordinator_yield()) method that was observed to cause the
4353 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4354 // which is by default non-zero. For the other seven methods that
4355 // also perform the yield operation, as are using a different
4356 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4357 // can enable the sleeping for those methods too, if necessary.
4358 // See 6442774.
4359 //
4360 // We really need to reconsider the synchronization between the GC
4361 // thread and the yield-requesting threads in the future and we
4362 // should really use wait/notify, which is the recommended
4363 // way of doing this type of interaction. Additionally, we should
4364 // consolidate the eight methods that do the yield operation and they
4365 // are almost identical into one for better maintainability and
4366 // readability. See 6445193.
4367 //
4368 // Tony 2006.06.29
4369 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4370 ConcurrentMarkSweepThread::should_yield() &&
4371 !CMSCollector::foregroundGCIsActive(); ++i) {
4372 os::sleep(Thread::current(), 1, false);
4373 ConcurrentMarkSweepThread::acknowledge_yield_request();
4374 }
4375
4376 ConcurrentMarkSweepThread::synchronize(true);
4377 _bit_map_lock->lock_without_safepoint_check();
4378 _collector->startTimer();
4379 }
4380
4381 bool CMSCollector::do_marking_mt(bool asynch) {
4382 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4383 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4384 conc_workers()->total_workers(),
4385 conc_workers()->active_workers(),
4386 Threads::number_of_non_daemon_threads());
4387 conc_workers()->set_active_workers(num_workers);
4388
4389 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4390
4391 CMSConcMarkingTask tsk(this,
4392 cms_space,
4393 asynch,
4394 conc_workers(),
4395 task_queues());
4396
4397 // Since the actual number of workers we get may be different
4398 // from the number we requested above, do we need to do anything different
4399 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4400 // class?? XXX
4401 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4402
4403 // Refs discovery is already non-atomic.
4404 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4405 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4406 conc_workers()->start_task(&tsk);
4407 while (tsk.yielded()) {
4408 tsk.coordinator_yield();
4409 conc_workers()->continue_task(&tsk);
4410 }
4411 // If the task was aborted, _restart_addr will be non-NULL
4412 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4413 while (_restart_addr != NULL) {
4414 // XXX For now we do not make use of ABORTED state and have not
4415 // yet implemented the right abort semantics (even in the original
4416 // single-threaded CMS case). That needs some more investigation
4417 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4418 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4419 // If _restart_addr is non-NULL, a marking stack overflow
4420 // occurred; we need to do a fresh marking iteration from the
4421 // indicated restart address.
4422 if (_foregroundGCIsActive && asynch) {
4423 // We may be running into repeated stack overflows, having
4424 // reached the limit of the stack size, while making very
4425 // slow forward progress. It may be best to bail out and
4426 // let the foreground collector do its job.
4427 // Clear _restart_addr, so that foreground GC
4428 // works from scratch. This avoids the headache of
4429 // a "rescan" which would otherwise be needed because
4430 // of the dirty mod union table & card table.
4431 _restart_addr = NULL;
4432 return false;
4433 }
4434 // Adjust the task to restart from _restart_addr
4435 tsk.reset(_restart_addr);
4436 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4437 _restart_addr);
4438 _restart_addr = NULL;
4439 // Get the workers going again
4440 conc_workers()->start_task(&tsk);
4441 while (tsk.yielded()) {
4442 tsk.coordinator_yield();
4443 conc_workers()->continue_task(&tsk);
4444 }
4445 }
4446 assert(tsk.completed(), "Inconsistency");
4447 assert(tsk.result() == true, "Inconsistency");
4448 return true;
4449 }
4450
4451 bool CMSCollector::do_marking_st(bool asynch) {
4452 ResourceMark rm;
4453 HandleMark hm;
4454
4455 // Temporarily make refs discovery single threaded (non-MT)
4456 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4457 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4458 &_markStack, CMSYield && asynch);
4459 // the last argument to iterate indicates whether the iteration
4460 // should be incremental with periodic yields.
4461 _markBitMap.iterate(&markFromRootsClosure);
4462 // If _restart_addr is non-NULL, a marking stack overflow
4463 // occurred; we need to do a fresh iteration from the
4464 // indicated restart address.
4465 while (_restart_addr != NULL) {
4466 if (_foregroundGCIsActive && asynch) {
4467 // We may be running into repeated stack overflows, having
4468 // reached the limit of the stack size, while making very
4469 // slow forward progress. It may be best to bail out and
4470 // let the foreground collector do its job.
4471 // Clear _restart_addr, so that foreground GC
4472 // works from scratch. This avoids the headache of
4473 // a "rescan" which would otherwise be needed because
4474 // of the dirty mod union table & card table.
4475 _restart_addr = NULL;
4476 return false; // indicating failure to complete marking
4477 }
4478 // Deal with stack overflow:
4479 // we restart marking from _restart_addr
4480 HeapWord* ra = _restart_addr;
4481 markFromRootsClosure.reset(ra);
4482 _restart_addr = NULL;
4483 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4484 }
4485 return true;
4486 }
4487
4488 void CMSCollector::preclean() {
4489 check_correct_thread_executing();
4490 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4491 verify_work_stacks_empty();
4492 verify_overflow_empty();
4493 _abort_preclean = false;
4494 if (CMSPrecleaningEnabled) {
4495 if (!CMSEdenChunksRecordAlways) {
4496 _eden_chunk_index = 0;
4497 }
4498 size_t used = get_eden_used();
4499 size_t capacity = get_eden_capacity();
4500 // Don't start sampling unless we will get sufficiently
4501 // many samples.
4502 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4503 * CMSScheduleRemarkEdenPenetration)) {
4504 _start_sampling = true;
4505 } else {
4506 _start_sampling = false;
4507 }
4508 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4509 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4510 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4511 }
4512 CMSTokenSync x(true); // is cms thread
4513 if (CMSPrecleaningEnabled) {
4514 sample_eden();
4515 _collectorState = AbortablePreclean;
4516 } else {
4517 _collectorState = FinalMarking;
4518 }
4519 verify_work_stacks_empty();
4520 verify_overflow_empty();
4521 }
4522
4523 // Try and schedule the remark such that young gen
4524 // occupancy is CMSScheduleRemarkEdenPenetration %.
4525 void CMSCollector::abortable_preclean() {
4526 check_correct_thread_executing();
4527 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4528 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4529
4530 // If Eden's current occupancy is below this threshold,
4531 // immediately schedule the remark; else preclean
4532 // past the next scavenge in an effort to
4533 // schedule the pause as described above. By choosing
4534 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4535 // we will never do an actual abortable preclean cycle.
4536 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4537 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4538 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4539 // We need more smarts in the abortable preclean
4540 // loop below to deal with cases where allocation
4541 // in young gen is very very slow, and our precleaning
4542 // is running a losing race against a horde of
4543 // mutators intent on flooding us with CMS updates
4544 // (dirty cards).
4545 // One, admittedly dumb, strategy is to give up
4546 // after a certain number of abortable precleaning loops
4547 // or after a certain maximum time. We want to make
4548 // this smarter in the next iteration.
4549 // XXX FIX ME!!! YSR
4550 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4551 while (!(should_abort_preclean() ||
4552 ConcurrentMarkSweepThread::should_terminate())) {
4553 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4554 cumworkdone += workdone;
4555 loops++;
4556 // Voluntarily terminate abortable preclean phase if we have
4557 // been at it for too long.
4558 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4559 loops >= CMSMaxAbortablePrecleanLoops) {
4560 if (PrintGCDetails) {
4561 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4562 }
4563 break;
4564 }
4565 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4566 if (PrintGCDetails) {
4567 gclog_or_tty->print(" CMS: abort preclean due to time ");
4568 }
4569 break;
4570 }
4571 // If we are doing little work each iteration, we should
4572 // take a short break.
4573 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4574 // Sleep for some time, waiting for work to accumulate
4575 stopTimer();
4576 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4577 startTimer();
4578 waited++;
4579 }
4580 }
4581 if (PrintCMSStatistics > 0) {
4582 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4583 loops, waited, cumworkdone);
4584 }
4585 }
4586 CMSTokenSync x(true); // is cms thread
4587 if (_collectorState != Idling) {
4588 assert(_collectorState == AbortablePreclean,
4589 "Spontaneous state transition?");
4590 _collectorState = FinalMarking;
4591 } // Else, a foreground collection completed this CMS cycle.
4592 return;
4593 }
4594
4595 // Respond to an Eden sampling opportunity
4596 void CMSCollector::sample_eden() {
4597 // Make sure a young gc cannot sneak in between our
4598 // reading and recording of a sample.
4599 assert(Thread::current()->is_ConcurrentGC_thread(),
4600 "Only the cms thread may collect Eden samples");
4601 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4602 "Should collect samples while holding CMS token");
4603 if (!_start_sampling) {
4604 return;
4605 }
4606 // When CMSEdenChunksRecordAlways is true, the eden chunk array
4607 // is populated by the young generation.
4608 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
4609 if (_eden_chunk_index < _eden_chunk_capacity) {
4610 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4611 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4612 "Unexpected state of Eden");
4613 // We'd like to check that what we just sampled is an oop-start address;
4614 // however, we cannot do that here since the object may not yet have been
4615 // initialized. So we'll instead do the check when we _use_ this sample
4616 // later.
4617 if (_eden_chunk_index == 0 ||
4618 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4619 _eden_chunk_array[_eden_chunk_index-1])
4620 >= CMSSamplingGrain)) {
4621 _eden_chunk_index++; // commit sample
4622 }
4623 }
4624 }
4625 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4626 size_t used = get_eden_used();
4627 size_t capacity = get_eden_capacity();
4628 assert(used <= capacity, "Unexpected state of Eden");
4629 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4630 _abort_preclean = true;
4631 }
4632 }
4633 }
4634
4635
4636 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4637 assert(_collectorState == Precleaning ||
4638 _collectorState == AbortablePreclean, "incorrect state");
4639 ResourceMark rm;
4640 HandleMark hm;
4641
4642 // Precleaning is currently not MT but the reference processor
4643 // may be set for MT. Disable it temporarily here.
4644 ReferenceProcessor* rp = ref_processor();
4645 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4646
4647 // Do one pass of scrubbing the discovered reference lists
4648 // to remove any reference objects with strongly-reachable
4649 // referents.
4650 if (clean_refs) {
4651 CMSPrecleanRefsYieldClosure yield_cl(this);
4652 assert(rp->span().equals(_span), "Spans should be equal");
4653 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4654 &_markStack, true /* preclean */);
4655 CMSDrainMarkingStackClosure complete_trace(this,
4656 _span, &_markBitMap, &_markStack,
4657 &keep_alive, true /* preclean */);
4658
4659 // We don't want this step to interfere with a young
4660 // collection because we don't want to take CPU
4661 // or memory bandwidth away from the young GC threads
4662 // (which may be as many as there are CPUs).
4663 // Note that we don't need to protect ourselves from
4664 // interference with mutators because they can't
4665 // manipulate the discovered reference lists nor affect
4666 // the computed reachability of the referents, the
4667 // only properties manipulated by the precleaning
4668 // of these reference lists.
4669 stopTimer();
4670 CMSTokenSyncWithLocks x(true /* is cms thread */,
4671 bitMapLock());
4672 startTimer();
4673 sample_eden();
4674
4675 // The following will yield to allow foreground
4676 // collection to proceed promptly. XXX YSR:
4677 // The code in this method may need further
4678 // tweaking for better performance and some restructuring
4679 // for cleaner interfaces.
4680 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4681 rp->preclean_discovered_references(
4682 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
4683 gc_timer);
4684 }
4685
4686 if (clean_survivor) { // preclean the active survivor space(s)
4687 assert(_young_gen->kind() == Generation::DefNew ||
4688 _young_gen->kind() == Generation::ParNew ||
4689 _young_gen->kind() == Generation::ASParNew,
4690 "incorrect type for cast");
4691 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4692 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4693 &_markBitMap, &_modUnionTable,
4694 &_markStack, true /* precleaning phase */);
4695 stopTimer();
4696 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4697 bitMapLock());
4698 startTimer();
4699 unsigned int before_count =
4700 GenCollectedHeap::heap()->total_collections();
4701 SurvivorSpacePrecleanClosure
4702 sss_cl(this, _span, &_markBitMap, &_markStack,
4703 &pam_cl, before_count, CMSYield);
4704 dng->from()->object_iterate_careful(&sss_cl);
4705 dng->to()->object_iterate_careful(&sss_cl);
4706 }
4707 MarkRefsIntoAndScanClosure
4708 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4709 &_markStack, this, CMSYield,
4710 true /* precleaning phase */);
4711 // CAUTION: The following closure has persistent state that may need to
4712 // be reset upon a decrease in the sequence of addresses it
4713 // processes.
4714 ScanMarkedObjectsAgainCarefullyClosure
4715 smoac_cl(this, _span,
4716 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4717
4718 // Preclean dirty cards in ModUnionTable and CardTable using
4719 // appropriate convergence criterion;
4720 // repeat CMSPrecleanIter times unless we find that
4721 // we are losing.
4722 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4723 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4724 "Bad convergence multiplier");
4725 assert(CMSPrecleanThreshold >= 100,
4726 "Unreasonably low CMSPrecleanThreshold");
4727
4728 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4729 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4730 numIter < CMSPrecleanIter;
4731 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4732 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4733 if (Verbose && PrintGCDetails) {
4734 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4735 }
4736 // Either there are very few dirty cards, so re-mark
4737 // pause will be small anyway, or our pre-cleaning isn't
4738 // that much faster than the rate at which cards are being
4739 // dirtied, so we might as well stop and re-mark since
4740 // precleaning won't improve our re-mark time by much.
4741 if (curNumCards <= CMSPrecleanThreshold ||
4742 (numIter > 0 &&
4743 (curNumCards * CMSPrecleanDenominator >
4744 lastNumCards * CMSPrecleanNumerator))) {
4745 numIter++;
4746 cumNumCards += curNumCards;
4747 break;
4748 }
4749 }
4750
4751 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4752
4753 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4754 cumNumCards += curNumCards;
4755 if (PrintGCDetails && PrintCMSStatistics != 0) {
4756 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4757 curNumCards, cumNumCards, numIter);
4758 }
4759 return cumNumCards; // as a measure of useful work done
4760 }
4761
4762 // PRECLEANING NOTES:
4763 // Precleaning involves:
4764 // . reading the bits of the modUnionTable and clearing the set bits.
4765 // . For the cards corresponding to the set bits, we scan the
4766 // objects on those cards. This means we need the free_list_lock
4767 // so that we can safely iterate over the CMS space when scanning
4768 // for oops.
4769 // . When we scan the objects, we'll be both reading and setting
4770 // marks in the marking bit map, so we'll need the marking bit map.
4771 // . For protecting _collector_state transitions, we take the CGC_lock.
4772 // Note that any races in the reading of of card table entries by the
4773 // CMS thread on the one hand and the clearing of those entries by the
4774 // VM thread or the setting of those entries by the mutator threads on the
4775 // other are quite benign. However, for efficiency it makes sense to keep
4776 // the VM thread from racing with the CMS thread while the latter is
4777 // dirty card info to the modUnionTable. We therefore also use the
4778 // CGC_lock to protect the reading of the card table and the mod union
4779 // table by the CM thread.
4780 // . We run concurrently with mutator updates, so scanning
4781 // needs to be done carefully -- we should not try to scan
4782 // potentially uninitialized objects.
4783 //
4784 // Locking strategy: While holding the CGC_lock, we scan over and
4785 // reset a maximal dirty range of the mod union / card tables, then lock
4786 // the free_list_lock and bitmap lock to do a full marking, then
4787 // release these locks; and repeat the cycle. This allows for a
4788 // certain amount of fairness in the sharing of these locks between
4789 // the CMS collector on the one hand, and the VM thread and the
4790 // mutators on the other.
4791
4792 // NOTE: preclean_mod_union_table() and preclean_card_table()
4793 // further below are largely identical; if you need to modify
4794 // one of these methods, please check the other method too.
4795
4796 size_t CMSCollector::preclean_mod_union_table(
4797 ConcurrentMarkSweepGeneration* gen,
4798 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4799 verify_work_stacks_empty();
4800 verify_overflow_empty();
4801
4802 // strategy: starting with the first card, accumulate contiguous
4803 // ranges of dirty cards; clear these cards, then scan the region
4804 // covered by these cards.
4805
4806 // Since all of the MUT is committed ahead, we can just use
4807 // that, in case the generations expand while we are precleaning.
4808 // It might also be fine to just use the committed part of the
4809 // generation, but we might potentially miss cards when the
4810 // generation is rapidly expanding while we are in the midst
4811 // of precleaning.
4812 HeapWord* startAddr = gen->reserved().start();
4813 HeapWord* endAddr = gen->reserved().end();
4814
4815 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4816
4817 size_t numDirtyCards, cumNumDirtyCards;
4818 HeapWord *nextAddr, *lastAddr;
4819 for (cumNumDirtyCards = numDirtyCards = 0,
4820 nextAddr = lastAddr = startAddr;
4821 nextAddr < endAddr;
4822 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4823
4824 ResourceMark rm;
4825 HandleMark hm;
4826
4827 MemRegion dirtyRegion;
4828 {
4829 stopTimer();
4830 // Potential yield point
4831 CMSTokenSync ts(true);
4832 startTimer();
4833 sample_eden();
4834 // Get dirty region starting at nextOffset (inclusive),
4835 // simultaneously clearing it.
4836 dirtyRegion =
4837 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4838 assert(dirtyRegion.start() >= nextAddr,
4839 "returned region inconsistent?");
4840 }
4841 // Remember where the next search should begin.
4842 // The returned region (if non-empty) is a right open interval,
4843 // so lastOffset is obtained from the right end of that
4844 // interval.
4845 lastAddr = dirtyRegion.end();
4846 // Should do something more transparent and less hacky XXX
4847 numDirtyCards =
4848 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4849
4850 // We'll scan the cards in the dirty region (with periodic
4851 // yields for foreground GC as needed).
4852 if (!dirtyRegion.is_empty()) {
4853 assert(numDirtyCards > 0, "consistency check");
4854 HeapWord* stop_point = NULL;
4855 stopTimer();
4856 // Potential yield point
4857 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4858 bitMapLock());
4859 startTimer();
4860 {
4861 verify_work_stacks_empty();
4862 verify_overflow_empty();
4863 sample_eden();
4864 stop_point =
4865 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4866 }
4867 if (stop_point != NULL) {
4868 // The careful iteration stopped early either because it found an
4869 // uninitialized object, or because we were in the midst of an
4870 // "abortable preclean", which should now be aborted. Redirty
4871 // the bits corresponding to the partially-scanned or unscanned
4872 // cards. We'll either restart at the next block boundary or
4873 // abort the preclean.
4874 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4875 "Should only be AbortablePreclean.");
4876 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4877 if (should_abort_preclean()) {
4878 break; // out of preclean loop
4879 } else {
4880 // Compute the next address at which preclean should pick up;
4881 // might need bitMapLock in order to read P-bits.
4882 lastAddr = next_card_start_after_block(stop_point);
4883 }
4884 }
4885 } else {
4886 assert(lastAddr == endAddr, "consistency check");
4887 assert(numDirtyCards == 0, "consistency check");
4888 break;
4889 }
4890 }
4891 verify_work_stacks_empty();
4892 verify_overflow_empty();
4893 return cumNumDirtyCards;
4894 }
4895
4896 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4897 // below are largely identical; if you need to modify
4898 // one of these methods, please check the other method too.
4899
4900 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4901 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4902 // strategy: it's similar to precleamModUnionTable above, in that
4903 // we accumulate contiguous ranges of dirty cards, mark these cards
4904 // precleaned, then scan the region covered by these cards.
4905 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4906 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4907
4908 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4909
4910 size_t numDirtyCards, cumNumDirtyCards;
4911 HeapWord *lastAddr, *nextAddr;
4912
4913 for (cumNumDirtyCards = numDirtyCards = 0,
4914 nextAddr = lastAddr = startAddr;
4915 nextAddr < endAddr;
4916 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4917
4918 ResourceMark rm;
4919 HandleMark hm;
4920
4921 MemRegion dirtyRegion;
4922 {
4923 // See comments in "Precleaning notes" above on why we
4924 // do this locking. XXX Could the locking overheads be
4925 // too high when dirty cards are sparse? [I don't think so.]
4926 stopTimer();
4927 CMSTokenSync x(true); // is cms thread
4928 startTimer();
4929 sample_eden();
4930 // Get and clear dirty region from card table
4931 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4932 MemRegion(nextAddr, endAddr),
4933 true,
4934 CardTableModRefBS::precleaned_card_val());
4935
4936 assert(dirtyRegion.start() >= nextAddr,
4937 "returned region inconsistent?");
4938 }
4939 lastAddr = dirtyRegion.end();
4940 numDirtyCards =
4941 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4942
4943 if (!dirtyRegion.is_empty()) {
4944 stopTimer();
4945 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4946 startTimer();
4947 sample_eden();
4948 verify_work_stacks_empty();
4949 verify_overflow_empty();
4950 HeapWord* stop_point =
4951 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4952 if (stop_point != NULL) {
4953 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4954 "Should only be AbortablePreclean.");
4955 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4956 if (should_abort_preclean()) {
4957 break; // out of preclean loop
4958 } else {
4959 // Compute the next address at which preclean should pick up.
4960 lastAddr = next_card_start_after_block(stop_point);
4961 }
4962 }
4963 } else {
4964 break;
4965 }
4966 }
4967 verify_work_stacks_empty();
4968 verify_overflow_empty();
4969 return cumNumDirtyCards;
4970 }
4971
4972 class PrecleanKlassClosure : public KlassClosure {
4973 CMKlassClosure _cm_klass_closure;
4974 public:
4975 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4976 void do_klass(Klass* k) {
4977 if (k->has_accumulated_modified_oops()) {
4978 k->clear_accumulated_modified_oops();
4979
4980 _cm_klass_closure.do_klass(k);
4981 }
4982 }
4983 };
4984
4985 // The freelist lock is needed to prevent asserts, is it really needed?
4986 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4987
4988 cl->set_freelistLock(freelistLock);
4989
4990 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4991
4992 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4993 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4994 PrecleanKlassClosure preclean_klass_closure(cl);
4995 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4996
4997 verify_work_stacks_empty();
4998 verify_overflow_empty();
4999 }
5000
5001 void CMSCollector::checkpointRootsFinal(bool asynch,
5002 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
5003 assert(_collectorState == FinalMarking, "incorrect state transition?");
5004 check_correct_thread_executing();
5005 // world is stopped at this checkpoint
5006 assert(SafepointSynchronize::is_at_safepoint(),
5007 "world should be stopped");
5008 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5009
5010 verify_work_stacks_empty();
5011 verify_overflow_empty();
5012
5013 SpecializationStats::clear();
5014 if (PrintGCDetails) {
5015 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
5016 _young_gen->used() / K,
5017 _young_gen->capacity() / K);
5018 }
5019 if (asynch) {
5020 if (CMSScavengeBeforeRemark) {
5021 GenCollectedHeap* gch = GenCollectedHeap::heap();
5022 // Temporarily set flag to false, GCH->do_collection will
5023 // expect it to be false and set to true
5024 FlagSetting fl(gch->_is_gc_active, false);
5025 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
5026 PrintGCDetails && Verbose, true, _gc_timer_cm);)
5027 int level = _cmsGen->level() - 1;
5028 if (level >= 0) {
5029 gch->do_collection(true, // full (i.e. force, see below)
5030 false, // !clear_all_soft_refs
5031 0, // size
5032 false, // is_tlab
5033 level // max_level
5034 );
5035 }
5036 }
5037 FreelistLocker x(this);
5038 MutexLockerEx y(bitMapLock(),
5039 Mutex::_no_safepoint_check_flag);
5040 assert(!init_mark_was_synchronous, "but that's impossible!");
5041 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
5042 } else {
5043 // already have all the locks
5044 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
5045 init_mark_was_synchronous);
5046 }
5047 verify_work_stacks_empty();
5048 verify_overflow_empty();
5049 SpecializationStats::print();
5050 }
5051
5052 void CMSCollector::checkpointRootsFinalWork(bool asynch,
5053 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
5054
5055 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm);)
5056
5057 assert(haveFreelistLocks(), "must have free list locks");
5058 assert_lock_strong(bitMapLock());
5059
5060 if (UseAdaptiveSizePolicy) {
5061 size_policy()->checkpoint_roots_final_begin();
5062 }
5063
5064 ResourceMark rm;
5065 HandleMark hm;
5066
5067 GenCollectedHeap* gch = GenCollectedHeap::heap();
5068
5069 if (should_unload_classes()) {
5070 CodeCache::gc_prologue();
5071 }
5072 assert(haveFreelistLocks(), "must have free list locks");
5073 assert_lock_strong(bitMapLock());
5074
5075 if (!init_mark_was_synchronous) {
5076 // We might assume that we need not fill TLAB's when
5077 // CMSScavengeBeforeRemark is set, because we may have just done
5078 // a scavenge which would have filled all TLAB's -- and besides
5079 // Eden would be empty. This however may not always be the case --
5080 // for instance although we asked for a scavenge, it may not have
5081 // happened because of a JNI critical section. We probably need
5082 // a policy for deciding whether we can in that case wait until
5083 // the critical section releases and then do the remark following
5084 // the scavenge, and skip it here. In the absence of that policy,
5085 // or of an indication of whether the scavenge did indeed occur,
5086 // we cannot rely on TLAB's having been filled and must do
5087 // so here just in case a scavenge did not happen.
5088 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
5089 // Update the saved marks which may affect the root scans.
5090 gch->save_marks();
5091
5092 if (CMSPrintEdenSurvivorChunks) {
5093 print_eden_and_survivor_chunk_arrays();
5094 }
5095
5096 {
5097 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
5098
5099 // Note on the role of the mod union table:
5100 // Since the marker in "markFromRoots" marks concurrently with
5101 // mutators, it is possible for some reachable objects not to have been
5102 // scanned. For instance, an only reference to an object A was
5103 // placed in object B after the marker scanned B. Unless B is rescanned,
5104 // A would be collected. Such updates to references in marked objects
5105 // are detected via the mod union table which is the set of all cards
5106 // dirtied since the first checkpoint in this GC cycle and prior to
5107 // the most recent young generation GC, minus those cleaned up by the
5108 // concurrent precleaning.
5109 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
5110 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm);
5111 do_remark_parallel();
5112 } else {
5113 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
5114 _gc_timer_cm);
5115 do_remark_non_parallel();
5116 }
5117 }
5118 } else {
5119 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
5120 // The initial mark was stop-world, so there's no rescanning to
5121 // do; go straight on to the next step below.
5122 }
5123 verify_work_stacks_empty();
5124 verify_overflow_empty();
5125
5126 {
5127 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm);)
5128 refProcessingWork(asynch, clear_all_soft_refs);
5129 }
5130 verify_work_stacks_empty();
5131 verify_overflow_empty();
5132
5133 if (should_unload_classes()) {
5134 CodeCache::gc_epilogue();
5135 }
5136 JvmtiExport::gc_epilogue();
5137
5138 // If we encountered any (marking stack / work queue) overflow
5139 // events during the current CMS cycle, take appropriate
5140 // remedial measures, where possible, so as to try and avoid
5141 // recurrence of that condition.
5142 assert(_markStack.isEmpty(), "No grey objects");
5143 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5144 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
5145 if (ser_ovflw > 0) {
5146 if (PrintCMSStatistics != 0) {
5147 gclog_or_tty->print_cr("Marking stack overflow (benign) "
5148 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5149 ", kac_preclean="SIZE_FORMAT")",
5150 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5151 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5152 }
5153 _markStack.expand();
5154 _ser_pmc_remark_ovflw = 0;
5155 _ser_pmc_preclean_ovflw = 0;
5156 _ser_kac_preclean_ovflw = 0;
5157 _ser_kac_ovflw = 0;
5158 }
5159 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5160 if (PrintCMSStatistics != 0) {
5161 gclog_or_tty->print_cr("Work queue overflow (benign) "
5162 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5163 _par_pmc_remark_ovflw, _par_kac_ovflw);
5164 }
5165 _par_pmc_remark_ovflw = 0;
5166 _par_kac_ovflw = 0;
5167 }
5168 if (PrintCMSStatistics != 0) {
5169 if (_markStack._hit_limit > 0) {
5170 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5171 _markStack._hit_limit);
5172 }
5173 if (_markStack._failed_double > 0) {
5174 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5175 " current capacity "SIZE_FORMAT,
5176 _markStack._failed_double,
5177 _markStack.capacity());
5178 }
5179 }
5180 _markStack._hit_limit = 0;
5181 _markStack._failed_double = 0;
5182
5183 if ((VerifyAfterGC || VerifyDuringGC) &&
5184 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5185 verify_after_remark();
5186 }
5187
5188 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
5189
5190 // Change under the freelistLocks.
5191 _collectorState = Sweeping;
5192 // Call isAllClear() under bitMapLock
5193 assert(_modUnionTable.isAllClear(),
5194 "Should be clear by end of the final marking");
5195 assert(_ct->klass_rem_set()->mod_union_is_clear(),
5196 "Should be clear by end of the final marking");
5197 if (UseAdaptiveSizePolicy) {
5198 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
5199 }
5200 }
5201
5202 void CMSParInitialMarkTask::work(uint worker_id) {
5203 elapsedTimer _timer;
5204 ResourceMark rm;
5205 HandleMark hm;
5206
5207 // ---------- scan from roots --------------
5208 _timer.start();
5209 GenCollectedHeap* gch = GenCollectedHeap::heap();
5210 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
5211 CMKlassClosure klass_closure(&par_mri_cl);
5212
5213 // ---------- young gen roots --------------
5214 {
5215 work_on_young_gen_roots(worker_id, &par_mri_cl);
5216 _timer.stop();
5217 if (PrintCMSStatistics != 0) {
5218 gclog_or_tty->print_cr(
5219 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
5220 worker_id, _timer.seconds());
5221 }
5222 }
5223
5224 // ---------- remaining roots --------------
5225 _timer.reset();
5226 _timer.start();
5227 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5228 false, // yg was scanned above
5229 false, // this is parallel code
5230 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5231 &par_mri_cl,
5232 NULL,
5233 &klass_closure);
5234 assert(_collector->should_unload_classes()
5235 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5236 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5237 _timer.stop();
5238 if (PrintCMSStatistics != 0) {
5239 gclog_or_tty->print_cr(
5240 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
5241 worker_id, _timer.seconds());
5242 }
5243 }
5244
5245 // Parallel remark task
5246 class CMSParRemarkTask: public CMSParMarkTask {
5247 CompactibleFreeListSpace* _cms_space;
5248
5249 // The per-thread work queues, available here for stealing.
5250 OopTaskQueueSet* _task_queues;
5251 ParallelTaskTerminator _term;
5252
5253 public:
5254 // A value of 0 passed to n_workers will cause the number of
5255 // workers to be taken from the active workers in the work gang.
5256 CMSParRemarkTask(CMSCollector* collector,
5257 CompactibleFreeListSpace* cms_space,
5258 int n_workers, FlexibleWorkGang* workers,
5259 OopTaskQueueSet* task_queues):
5260 CMSParMarkTask("Rescan roots and grey objects in parallel",
5261 collector, n_workers),
5262 _cms_space(cms_space),
5263 _task_queues(task_queues),
5264 _term(n_workers, task_queues) { }
5265
5266 OopTaskQueueSet* task_queues() { return _task_queues; }
5267
5268 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5269
5270 ParallelTaskTerminator* terminator() { return &_term; }
5271 int n_workers() { return _n_workers; }
5272
5273 void work(uint worker_id);
5274
5275 private:
5276 // ... of dirty cards in old space
5277 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5278 Par_MarkRefsIntoAndScanClosure* cl);
5279
5280 // ... work stealing for the above
5281 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5282 };
5283
5284 class RemarkKlassClosure : public KlassClosure {
5285 CMKlassClosure _cm_klass_closure;
5286 public:
5287 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
5288 void do_klass(Klass* k) {
5289 // Check if we have modified any oops in the Klass during the concurrent marking.
5290 if (k->has_accumulated_modified_oops()) {
5291 k->clear_accumulated_modified_oops();
5292
5293 // We could have transfered the current modified marks to the accumulated marks,
5294 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
5295 } else if (k->has_modified_oops()) {
5296 // Don't clear anything, this info is needed by the next young collection.
5297 } else {
5298 // No modified oops in the Klass.
5299 return;
5300 }
5301
5302 // The klass has modified fields, need to scan the klass.
5303 _cm_klass_closure.do_klass(k);
5304 }
5305 };
5306
5307 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
5308 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5309 EdenSpace* eden_space = dng->eden();
5310 ContiguousSpace* from_space = dng->from();
5311 ContiguousSpace* to_space = dng->to();
5312
5313 HeapWord** eca = _collector->_eden_chunk_array;
5314 size_t ect = _collector->_eden_chunk_index;
5315 HeapWord** sca = _collector->_survivor_chunk_array;
5316 size_t sct = _collector->_survivor_chunk_index;
5317
5318 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5319 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5320
5321 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
5322 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
5323 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
5324 }
5325
5326 // work_queue(i) is passed to the closure
5327 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5328 // also is passed to do_dirty_card_rescan_tasks() and to
5329 // do_work_steal() to select the i-th task_queue.
5330
5331 void CMSParRemarkTask::work(uint worker_id) {
5332 elapsedTimer _timer;
5333 ResourceMark rm;
5334 HandleMark hm;
5335
5336 // ---------- rescan from roots --------------
5337 _timer.start();
5338 GenCollectedHeap* gch = GenCollectedHeap::heap();
5339 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5340 _collector->_span, _collector->ref_processor(),
5341 &(_collector->_markBitMap),
5342 work_queue(worker_id));
5343
5344 // Rescan young gen roots first since these are likely
5345 // coarsely partitioned and may, on that account, constitute
5346 // the critical path; thus, it's best to start off that
5347 // work first.
5348 // ---------- young gen roots --------------
5349 {
5350 work_on_young_gen_roots(worker_id, &par_mrias_cl);
5351 _timer.stop();
5352 if (PrintCMSStatistics != 0) {
5353 gclog_or_tty->print_cr(
5354 "Finished young gen rescan work in %dth thread: %3.3f sec",
5355 worker_id, _timer.seconds());
5356 }
5357 }
5358
5359 // ---------- remaining roots --------------
5360 _timer.reset();
5361 _timer.start();
5362 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5363 false, // yg was scanned above
5364 false, // this is parallel code
5365 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5366 &par_mrias_cl,
5367 NULL,
5368 NULL); // The dirty klasses will be handled below
5369 assert(_collector->should_unload_classes()
5370 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5371 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5372 _timer.stop();
5373 if (PrintCMSStatistics != 0) {
5374 gclog_or_tty->print_cr(
5375 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5376 worker_id, _timer.seconds());
5377 }
5378
5379 // ---------- unhandled CLD scanning ----------
5380 if (worker_id == 0) { // Single threaded at the moment.
5381 _timer.reset();
5382 _timer.start();
5383
5384 // Scan all new class loader data objects and new dependencies that were
5385 // introduced during concurrent marking.
5386 ResourceMark rm;
5387 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5388 for (int i = 0; i < array->length(); i++) {
5389 par_mrias_cl.do_class_loader_data(array->at(i));
5390 }
5391
5392 // We don't need to keep track of new CLDs anymore.
5393 ClassLoaderDataGraph::remember_new_clds(false);
5394
5395 _timer.stop();
5396 if (PrintCMSStatistics != 0) {
5397 gclog_or_tty->print_cr(
5398 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
5399 worker_id, _timer.seconds());
5400 }
5401 }
5402
5403 // ---------- dirty klass scanning ----------
5404 if (worker_id == 0) { // Single threaded at the moment.
5405 _timer.reset();
5406 _timer.start();
5407
5408 // Scan all classes that was dirtied during the concurrent marking phase.
5409 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
5410 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5411
5412 _timer.stop();
5413 if (PrintCMSStatistics != 0) {
5414 gclog_or_tty->print_cr(
5415 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
5416 worker_id, _timer.seconds());
5417 }
5418 }
5419
5420 // We might have added oops to ClassLoaderData::_handles during the
5421 // concurrent marking phase. These oops point to newly allocated objects
5422 // that are guaranteed to be kept alive. Either by the direct allocation
5423 // code, or when the young collector processes the strong roots. Hence,
5424 // we don't have to revisit the _handles block during the remark phase.
5425
5426 // ---------- rescan dirty cards ------------
5427 _timer.reset();
5428 _timer.start();
5429
5430 // Do the rescan tasks for each of the two spaces
5431 // (cms_space) in turn.
5432 // "worker_id" is passed to select the task_queue for "worker_id"
5433 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5434 _timer.stop();
5435 if (PrintCMSStatistics != 0) {
5436 gclog_or_tty->print_cr(
5437 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5438 worker_id, _timer.seconds());
5439 }
5440
5441 // ---------- steal work from other threads ...
5442 // ---------- ... and drain overflow list.
5443 _timer.reset();
5444 _timer.start();
5445 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5446 _timer.stop();
5447 if (PrintCMSStatistics != 0) {
5448 gclog_or_tty->print_cr(
5449 "Finished work stealing in %dth thread: %3.3f sec",
5450 worker_id, _timer.seconds());
5451 }
5452 }
5453
5454 // Note that parameter "i" is not used.
5455 void
5456 CMSParMarkTask::do_young_space_rescan(uint worker_id,
5457 OopsInGenClosure* cl, ContiguousSpace* space,
5458 HeapWord** chunk_array, size_t chunk_top) {
5459 // Until all tasks completed:
5460 // . claim an unclaimed task
5461 // . compute region boundaries corresponding to task claimed
5462 // using chunk_array
5463 // . par_oop_iterate(cl) over that region
5464
5465 ResourceMark rm;
5466 HandleMark hm;
5467
5468 SequentialSubTasksDone* pst = space->par_seq_tasks();
5469
5470 uint nth_task = 0;
5471 uint n_tasks = pst->n_tasks();
5472
5473 if (n_tasks > 0) {
5474 assert(pst->valid(), "Uninitialized use?");
5475 HeapWord *start, *end;
5476 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5477 // We claimed task # nth_task; compute its boundaries.
5478 if (chunk_top == 0) { // no samples were taken
5479 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5480 start = space->bottom();
5481 end = space->top();
5482 } else if (nth_task == 0) {
5483 start = space->bottom();
5484 end = chunk_array[nth_task];
5485 } else if (nth_task < (uint)chunk_top) {
5486 assert(nth_task >= 1, "Control point invariant");
5487 start = chunk_array[nth_task - 1];
5488 end = chunk_array[nth_task];
5489 } else {
5490 assert(nth_task == (uint)chunk_top, "Control point invariant");
5491 start = chunk_array[chunk_top - 1];
5492 end = space->top();
5493 }
5494 MemRegion mr(start, end);
5495 // Verify that mr is in space
5496 assert(mr.is_empty() || space->used_region().contains(mr),
5497 "Should be in space");
5498 // Verify that "start" is an object boundary
5499 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5500 "Should be an oop");
5501 space->par_oop_iterate(mr, cl);
5502 }
5503 pst->all_tasks_completed();
5504 }
5505 }
5506
5507 void
5508 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5509 CompactibleFreeListSpace* sp, int i,
5510 Par_MarkRefsIntoAndScanClosure* cl) {
5511 // Until all tasks completed:
5512 // . claim an unclaimed task
5513 // . compute region boundaries corresponding to task claimed
5514 // . transfer dirty bits ct->mut for that region
5515 // . apply rescanclosure to dirty mut bits for that region
5516
5517 ResourceMark rm;
5518 HandleMark hm;
5519
5520 OopTaskQueue* work_q = work_queue(i);
5521 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5522 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5523 // CAUTION: This closure has state that persists across calls to
5524 // the work method dirty_range_iterate_clear() in that it has
5525 // embedded in it a (subtype of) UpwardsObjectClosure. The
5526 // use of that state in the embedded UpwardsObjectClosure instance
5527 // assumes that the cards are always iterated (even if in parallel
5528 // by several threads) in monotonically increasing order per each
5529 // thread. This is true of the implementation below which picks
5530 // card ranges (chunks) in monotonically increasing order globally
5531 // and, a-fortiori, in monotonically increasing order per thread
5532 // (the latter order being a subsequence of the former).
5533 // If the work code below is ever reorganized into a more chaotic
5534 // work-partitioning form than the current "sequential tasks"
5535 // paradigm, the use of that persistent state will have to be
5536 // revisited and modified appropriately. See also related
5537 // bug 4756801 work on which should examine this code to make
5538 // sure that the changes there do not run counter to the
5539 // assumptions made here and necessary for correctness and
5540 // efficiency. Note also that this code might yield inefficient
5541 // behavior in the case of very large objects that span one or
5542 // more work chunks. Such objects would potentially be scanned
5543 // several times redundantly. Work on 4756801 should try and
5544 // address that performance anomaly if at all possible. XXX
5545 MemRegion full_span = _collector->_span;
5546 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5547 MarkFromDirtyCardsClosure
5548 greyRescanClosure(_collector, full_span, // entire span of interest
5549 sp, bm, work_q, cl);
5550
5551 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5552 assert(pst->valid(), "Uninitialized use?");
5553 uint nth_task = 0;
5554 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5555 MemRegion span = sp->used_region();
5556 HeapWord* start_addr = span.start();
5557 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5558 alignment);
5559 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5560 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5561 start_addr, "Check alignment");
5562 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5563 chunk_size, "Check alignment");
5564
5565 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5566 // Having claimed the nth_task, compute corresponding mem-region,
5567 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
5568 // The alignment restriction ensures that we do not need any
5569 // synchronization with other gang-workers while setting or
5570 // clearing bits in thus chunk of the MUT.
5571 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5572 start_addr + (nth_task+1)*chunk_size);
5573 // The last chunk's end might be way beyond end of the
5574 // used region. In that case pull back appropriately.
5575 if (this_span.end() > end_addr) {
5576 this_span.set_end(end_addr);
5577 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5578 }
5579 // Iterate over the dirty cards covering this chunk, marking them
5580 // precleaned, and setting the corresponding bits in the mod union
5581 // table. Since we have been careful to partition at Card and MUT-word
5582 // boundaries no synchronization is needed between parallel threads.
5583 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5584 &modUnionClosure);
5585
5586 // Having transferred these marks into the modUnionTable,
5587 // rescan the marked objects on the dirty cards in the modUnionTable.
5588 // Even if this is at a synchronous collection, the initial marking
5589 // may have been done during an asynchronous collection so there
5590 // may be dirty bits in the mod-union table.
5591 _collector->_modUnionTable.dirty_range_iterate_clear(
5592 this_span, &greyRescanClosure);
5593 _collector->_modUnionTable.verifyNoOneBitsInRange(
5594 this_span.start(),
5595 this_span.end());
5596 }
5597 pst->all_tasks_completed(); // declare that i am done
5598 }
5599
5600 // . see if we can share work_queues with ParNew? XXX
5601 void
5602 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5603 int* seed) {
5604 OopTaskQueue* work_q = work_queue(i);
5605 NOT_PRODUCT(int num_steals = 0;)
5606 oop obj_to_scan;
5607 CMSBitMap* bm = &(_collector->_markBitMap);
5608
5609 while (true) {
5610 // Completely finish any left over work from (an) earlier round(s)
5611 cl->trim_queue(0);
5612 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5613 (size_t)ParGCDesiredObjsFromOverflowList);
5614 // Now check if there's any work in the overflow list
5615 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5616 // only affects the number of attempts made to get work from the
5617 // overflow list and does not affect the number of workers. Just
5618 // pass ParallelGCThreads so this behavior is unchanged.
5619 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5620 work_q,
5621 ParallelGCThreads)) {
5622 // found something in global overflow list;
5623 // not yet ready to go stealing work from others.
5624 // We'd like to assert(work_q->size() != 0, ...)
5625 // because we just took work from the overflow list,
5626 // but of course we can't since all of that could have
5627 // been already stolen from us.
5628 // "He giveth and He taketh away."
5629 continue;
5630 }
5631 // Verify that we have no work before we resort to stealing
5632 assert(work_q->size() == 0, "Have work, shouldn't steal");
5633 // Try to steal from other queues that have work
5634 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5635 NOT_PRODUCT(num_steals++;)
5636 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5637 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5638 // Do scanning work
5639 obj_to_scan->oop_iterate(cl);
5640 // Loop around, finish this work, and try to steal some more
5641 } else if (terminator()->offer_termination()) {
5642 break; // nirvana from the infinite cycle
5643 }
5644 }
5645 NOT_PRODUCT(
5646 if (PrintCMSStatistics != 0) {
5647 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5648 }
5649 )
5650 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5651 "Else our work is not yet done");
5652 }
5653
5654 // Record object boundaries in _eden_chunk_array by sampling the eden
5655 // top in the slow-path eden object allocation code path and record
5656 // the boundaries, if CMSEdenChunksRecordAlways is true. If
5657 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
5658 // sampling in sample_eden() that activates during the part of the
5659 // preclean phase.
5660 void CMSCollector::sample_eden_chunk() {
5661 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
5662 if (_eden_chunk_lock->try_lock()) {
5663 // Record a sample. This is the critical section. The contents
5664 // of the _eden_chunk_array have to be non-decreasing in the
5665 // address order.
5666 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
5667 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
5668 "Unexpected state of Eden");
5669 if (_eden_chunk_index == 0 ||
5670 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
5671 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
5672 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
5673 _eden_chunk_index++; // commit sample
5674 }
5675 _eden_chunk_lock->unlock();
5676 }
5677 }
5678 }
5679
5680 // Return a thread-local PLAB recording array, as appropriate.
5681 void* CMSCollector::get_data_recorder(int thr_num) {
5682 if (_survivor_plab_array != NULL &&
5683 (CMSPLABRecordAlways ||
5684 (_collectorState > Marking && _collectorState < FinalMarking))) {
5685 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5686 ChunkArray* ca = &_survivor_plab_array[thr_num];
5687 ca->reset(); // clear it so that fresh data is recorded
5688 return (void*) ca;
5689 } else {
5690 return NULL;
5691 }
5692 }
5693
5694 // Reset all the thread-local PLAB recording arrays
5695 void CMSCollector::reset_survivor_plab_arrays() {
5696 for (uint i = 0; i < ParallelGCThreads; i++) {
5697 _survivor_plab_array[i].reset();
5698 }
5699 }
5700
5701 // Merge the per-thread plab arrays into the global survivor chunk
5702 // array which will provide the partitioning of the survivor space
5703 // for CMS initial scan and rescan.
5704 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5705 int no_of_gc_threads) {
5706 assert(_survivor_plab_array != NULL, "Error");
5707 assert(_survivor_chunk_array != NULL, "Error");
5708 assert(_collectorState == FinalMarking ||
5709 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
5710 for (int j = 0; j < no_of_gc_threads; j++) {
5711 _cursor[j] = 0;
5712 }
5713 HeapWord* top = surv->top();
5714 size_t i;
5715 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5716 HeapWord* min_val = top; // Higher than any PLAB address
5717 uint min_tid = 0; // position of min_val this round
5718 for (int j = 0; j < no_of_gc_threads; j++) {
5719 ChunkArray* cur_sca = &_survivor_plab_array[j];
5720 if (_cursor[j] == cur_sca->end()) {
5721 continue;
5722 }
5723 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5724 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5725 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5726 if (cur_val < min_val) {
5727 min_tid = j;
5728 min_val = cur_val;
5729 } else {
5730 assert(cur_val < top, "All recorded addresses should be less");
5731 }
5732 }
5733 // At this point min_val and min_tid are respectively
5734 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5735 // and the thread (j) that witnesses that address.
5736 // We record this address in the _survivor_chunk_array[i]
5737 // and increment _cursor[min_tid] prior to the next round i.
5738 if (min_val == top) {
5739 break;
5740 }
5741 _survivor_chunk_array[i] = min_val;
5742 _cursor[min_tid]++;
5743 }
5744 // We are all done; record the size of the _survivor_chunk_array
5745 _survivor_chunk_index = i; // exclusive: [0, i)
5746 if (PrintCMSStatistics > 0) {
5747 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5748 }
5749 // Verify that we used up all the recorded entries
5750 #ifdef ASSERT
5751 size_t total = 0;
5752 for (int j = 0; j < no_of_gc_threads; j++) {
5753 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5754 total += _cursor[j];
5755 }
5756 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5757 // Check that the merged array is in sorted order
5758 if (total > 0) {
5759 for (size_t i = 0; i < total - 1; i++) {
5760 if (PrintCMSStatistics > 0) {
5761 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5762 i, _survivor_chunk_array[i]);
5763 }
5764 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5765 "Not sorted");
5766 }
5767 }
5768 #endif // ASSERT
5769 }
5770
5771 // Set up the space's par_seq_tasks structure for work claiming
5772 // for parallel initial scan and rescan of young gen.
5773 // See ParRescanTask where this is currently used.
5774 void
5775 CMSCollector::
5776 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5777 assert(n_threads > 0, "Unexpected n_threads argument");
5778 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5779
5780 // Eden space
5781 if (!dng->eden()->is_empty()) {
5782 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5783 assert(!pst->valid(), "Clobbering existing data?");
5784 // Each valid entry in [0, _eden_chunk_index) represents a task.
5785 size_t n_tasks = _eden_chunk_index + 1;
5786 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5787 // Sets the condition for completion of the subtask (how many threads
5788 // need to finish in order to be done).
5789 pst->set_n_threads(n_threads);
5790 pst->set_n_tasks((int)n_tasks);
5791 }
5792
5793 // Merge the survivor plab arrays into _survivor_chunk_array
5794 if (_survivor_plab_array != NULL) {
5795 merge_survivor_plab_arrays(dng->from(), n_threads);
5796 } else {
5797 assert(_survivor_chunk_index == 0, "Error");
5798 }
5799
5800 // To space
5801 {
5802 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5803 assert(!pst->valid(), "Clobbering existing data?");
5804 // Sets the condition for completion of the subtask (how many threads
5805 // need to finish in order to be done).
5806 pst->set_n_threads(n_threads);
5807 pst->set_n_tasks(1);
5808 assert(pst->valid(), "Error");
5809 }
5810
5811 // From space
5812 {
5813 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5814 assert(!pst->valid(), "Clobbering existing data?");
5815 size_t n_tasks = _survivor_chunk_index + 1;
5816 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5817 // Sets the condition for completion of the subtask (how many threads
5818 // need to finish in order to be done).
5819 pst->set_n_threads(n_threads);
5820 pst->set_n_tasks((int)n_tasks);
5821 assert(pst->valid(), "Error");
5822 }
5823 }
5824
5825 // Parallel version of remark
5826 void CMSCollector::do_remark_parallel() {
5827 GenCollectedHeap* gch = GenCollectedHeap::heap();
5828 FlexibleWorkGang* workers = gch->workers();
5829 assert(workers != NULL, "Need parallel worker threads.");
5830 // Choose to use the number of GC workers most recently set
5831 // into "active_workers". If active_workers is not set, set it
5832 // to ParallelGCThreads.
5833 int n_workers = workers->active_workers();
5834 if (n_workers == 0) {
5835 assert(n_workers > 0, "Should have been set during scavenge");
5836 n_workers = ParallelGCThreads;
5837 workers->set_active_workers(n_workers);
5838 }
5839 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5840
5841 CMSParRemarkTask tsk(this,
5842 cms_space,
5843 n_workers, workers, task_queues());
5844
5845 // Set up for parallel process_strong_roots work.
5846 gch->set_par_threads(n_workers);
5847 // We won't be iterating over the cards in the card table updating
5848 // the younger_gen cards, so we shouldn't call the following else
5849 // the verification code as well as subsequent younger_refs_iterate
5850 // code would get confused. XXX
5851 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5852
5853 // The young gen rescan work will not be done as part of
5854 // process_strong_roots (which currently doesn't knw how to
5855 // parallelize such a scan), but rather will be broken up into
5856 // a set of parallel tasks (via the sampling that the [abortable]
5857 // preclean phase did of EdenSpace, plus the [two] tasks of
5858 // scanning the [two] survivor spaces. Further fine-grain
5859 // parallelization of the scanning of the survivor spaces
5860 // themselves, and of precleaning of the younger gen itself
5861 // is deferred to the future.
5862 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5863
5864 // The dirty card rescan work is broken up into a "sequence"
5865 // of parallel tasks (per constituent space) that are dynamically
5866 // claimed by the parallel threads.
5867 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5868
5869 // It turns out that even when we're using 1 thread, doing the work in a
5870 // separate thread causes wide variance in run times. We can't help this
5871 // in the multi-threaded case, but we special-case n=1 here to get
5872 // repeatable measurements of the 1-thread overhead of the parallel code.
5873 if (n_workers > 1) {
5874 // Make refs discovery MT-safe, if it isn't already: it may not
5875 // necessarily be so, since it's possible that we are doing
5876 // ST marking.
5877 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5878 GenCollectedHeap::StrongRootsScope srs(gch);
5879 workers->run_task(&tsk);
5880 } else {
5881 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5882 GenCollectedHeap::StrongRootsScope srs(gch);
5883 tsk.work(0);
5884 }
5885
5886 gch->set_par_threads(0); // 0 ==> non-parallel.
5887 // restore, single-threaded for now, any preserved marks
5888 // as a result of work_q overflow
5889 restore_preserved_marks_if_any();
5890 }
5891
5892 // Non-parallel version of remark
5893 void CMSCollector::do_remark_non_parallel() {
5894 ResourceMark rm;
5895 HandleMark hm;
5896 GenCollectedHeap* gch = GenCollectedHeap::heap();
5897 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5898
5899 MarkRefsIntoAndScanClosure
5900 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5901 &_markStack, this,
5902 false /* should_yield */, false /* not precleaning */);
5903 MarkFromDirtyCardsClosure
5904 markFromDirtyCardsClosure(this, _span,
5905 NULL, // space is set further below
5906 &_markBitMap, &_markStack, &mrias_cl);
5907 {
5908 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm);
5909 // Iterate over the dirty cards, setting the corresponding bits in the
5910 // mod union table.
5911 {
5912 ModUnionClosure modUnionClosure(&_modUnionTable);
5913 _ct->ct_bs()->dirty_card_iterate(
5914 _cmsGen->used_region(),
5915 &modUnionClosure);
5916 }
5917 // Having transferred these marks into the modUnionTable, we just need
5918 // to rescan the marked objects on the dirty cards in the modUnionTable.
5919 // The initial marking may have been done during an asynchronous
5920 // collection so there may be dirty bits in the mod-union table.
5921 const int alignment =
5922 CardTableModRefBS::card_size * BitsPerWord;
5923 {
5924 // ... First handle dirty cards in CMS gen
5925 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5926 MemRegion ur = _cmsGen->used_region();
5927 HeapWord* lb = ur.start();
5928 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5929 MemRegion cms_span(lb, ub);
5930 _modUnionTable.dirty_range_iterate_clear(cms_span,
5931 &markFromDirtyCardsClosure);
5932 verify_work_stacks_empty();
5933 if (PrintCMSStatistics != 0) {
5934 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5935 markFromDirtyCardsClosure.num_dirty_cards());
5936 }
5937 }
5938 }
5939 if (VerifyDuringGC &&
5940 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5941 HandleMark hm; // Discard invalid handles created during verification
5942 Universe::verify();
5943 }
5944 {
5945 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm);
5946
5947 verify_work_stacks_empty();
5948
5949 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5950 GenCollectedHeap::StrongRootsScope srs(gch);
5951 gch->gen_process_strong_roots(_cmsGen->level(),
5952 true, // younger gens as roots
5953 false, // use the local StrongRootsScope
5954 SharedHeap::ScanningOption(roots_scanning_options()),
5955 &mrias_cl,
5956 NULL,
5957 NULL); // The dirty klasses will be handled below
5958
5959 assert(should_unload_classes()
5960 || (roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5961 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5962 }
5963
5964 {
5965 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm);
5966
5967 verify_work_stacks_empty();
5968
5969 // Scan all class loader data objects that might have been introduced
5970 // during concurrent marking.
5971 ResourceMark rm;
5972 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5973 for (int i = 0; i < array->length(); i++) {
5974 mrias_cl.do_class_loader_data(array->at(i));
5975 }
5976
5977 // We don't need to keep track of new CLDs anymore.
5978 ClassLoaderDataGraph::remember_new_clds(false);
5979
5980 verify_work_stacks_empty();
5981 }
5982
5983 {
5984 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm);
5985
5986 verify_work_stacks_empty();
5987
5988 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5989 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5990
5991 verify_work_stacks_empty();
5992 }
5993
5994 // We might have added oops to ClassLoaderData::_handles during the
5995 // concurrent marking phase. These oops point to newly allocated objects
5996 // that are guaranteed to be kept alive. Either by the direct allocation
5997 // code, or when the young collector processes the strong roots. Hence,
5998 // we don't have to revisit the _handles block during the remark phase.
5999
6000 verify_work_stacks_empty();
6001 // Restore evacuated mark words, if any, used for overflow list links
6002 if (!CMSOverflowEarlyRestoration) {
6003 restore_preserved_marks_if_any();
6004 }
6005 verify_overflow_empty();
6006 }
6007
6008 ////////////////////////////////////////////////////////
6009 // Parallel Reference Processing Task Proxy Class
6010 ////////////////////////////////////////////////////////
6011 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
6012 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
6013 CMSCollector* _collector;
6014 CMSBitMap* _mark_bit_map;
6015 const MemRegion _span;
6016 ProcessTask& _task;
6017
6018 public:
6019 CMSRefProcTaskProxy(ProcessTask& task,
6020 CMSCollector* collector,
6021 const MemRegion& span,
6022 CMSBitMap* mark_bit_map,
6023 AbstractWorkGang* workers,
6024 OopTaskQueueSet* task_queues):
6025 // XXX Should superclass AGTWOQ also know about AWG since it knows
6026 // about the task_queues used by the AWG? Then it could initialize
6027 // the terminator() object. See 6984287. The set_for_termination()
6028 // below is a temporary band-aid for the regression in 6984287.
6029 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
6030 task_queues),
6031 _task(task),
6032 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
6033 {
6034 assert(_collector->_span.equals(_span) && !_span.is_empty(),
6035 "Inconsistency in _span");
6036 set_for_termination(workers->active_workers());
6037 }
6038
6039 OopTaskQueueSet* task_queues() { return queues(); }
6040
6041 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
6042
6043 void do_work_steal(int i,
6044 CMSParDrainMarkingStackClosure* drain,
6045 CMSParKeepAliveClosure* keep_alive,
6046 int* seed);
6047
6048 virtual void work(uint worker_id);
6049 };
6050
6051 void CMSRefProcTaskProxy::work(uint worker_id) {
6052 assert(_collector->_span.equals(_span), "Inconsistency in _span");
6053 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
6054 _mark_bit_map,
6055 work_queue(worker_id));
6056 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
6057 _mark_bit_map,
6058 work_queue(worker_id));
6059 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
6060 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
6061 if (_task.marks_oops_alive()) {
6062 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
6063 _collector->hash_seed(worker_id));
6064 }
6065 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
6066 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
6067 }
6068
6069 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
6070 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
6071 EnqueueTask& _task;
6072
6073 public:
6074 CMSRefEnqueueTaskProxy(EnqueueTask& task)
6075 : AbstractGangTask("Enqueue reference objects in parallel"),
6076 _task(task)
6077 { }
6078
6079 virtual void work(uint worker_id)
6080 {
6081 _task.work(worker_id);
6082 }
6083 };
6084
6085 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
6086 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
6087 _span(span),
6088 _bit_map(bit_map),
6089 _work_queue(work_queue),
6090 _mark_and_push(collector, span, bit_map, work_queue),
6091 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6092 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
6093 { }
6094
6095 // . see if we can share work_queues with ParNew? XXX
6096 void CMSRefProcTaskProxy::do_work_steal(int i,
6097 CMSParDrainMarkingStackClosure* drain,
6098 CMSParKeepAliveClosure* keep_alive,
6099 int* seed) {
6100 OopTaskQueue* work_q = work_queue(i);
6101 NOT_PRODUCT(int num_steals = 0;)
6102 oop obj_to_scan;
6103
6104 while (true) {
6105 // Completely finish any left over work from (an) earlier round(s)
6106 drain->trim_queue(0);
6107 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
6108 (size_t)ParGCDesiredObjsFromOverflowList);
6109 // Now check if there's any work in the overflow list
6110 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
6111 // only affects the number of attempts made to get work from the
6112 // overflow list and does not affect the number of workers. Just
6113 // pass ParallelGCThreads so this behavior is unchanged.
6114 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
6115 work_q,
6116 ParallelGCThreads)) {
6117 // Found something in global overflow list;
6118 // not yet ready to go stealing work from others.
6119 // We'd like to assert(work_q->size() != 0, ...)
6120 // because we just took work from the overflow list,
6121 // but of course we can't, since all of that might have
6122 // been already stolen from us.
6123 continue;
6124 }
6125 // Verify that we have no work before we resort to stealing
6126 assert(work_q->size() == 0, "Have work, shouldn't steal");
6127 // Try to steal from other queues that have work
6128 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
6129 NOT_PRODUCT(num_steals++;)
6130 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
6131 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
6132 // Do scanning work
6133 obj_to_scan->oop_iterate(keep_alive);
6134 // Loop around, finish this work, and try to steal some more
6135 } else if (terminator()->offer_termination()) {
6136 break; // nirvana from the infinite cycle
6137 }
6138 }
6139 NOT_PRODUCT(
6140 if (PrintCMSStatistics != 0) {
6141 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
6142 }
6143 )
6144 }
6145
6146 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
6147 {
6148 GenCollectedHeap* gch = GenCollectedHeap::heap();
6149 FlexibleWorkGang* workers = gch->workers();
6150 assert(workers != NULL, "Need parallel worker threads.");
6151 CMSRefProcTaskProxy rp_task(task, &_collector,
6152 _collector.ref_processor()->span(),
6153 _collector.markBitMap(),
6154 workers, _collector.task_queues());
6155 workers->run_task(&rp_task);
6156 }
6157
6158 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
6159 {
6160
6161 GenCollectedHeap* gch = GenCollectedHeap::heap();
6162 FlexibleWorkGang* workers = gch->workers();
6163 assert(workers != NULL, "Need parallel worker threads.");
6164 CMSRefEnqueueTaskProxy enq_task(task);
6165 workers->run_task(&enq_task);
6166 }
6167
6168 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
6169
6170 ResourceMark rm;
6171 HandleMark hm;
6172
6173 ReferenceProcessor* rp = ref_processor();
6174 assert(rp->span().equals(_span), "Spans should be equal");
6175 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
6176 // Process weak references.
6177 rp->setup_policy(clear_all_soft_refs);
6178 verify_work_stacks_empty();
6179
6180 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
6181 &_markStack, false /* !preclean */);
6182 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
6183 _span, &_markBitMap, &_markStack,
6184 &cmsKeepAliveClosure, false /* !preclean */);
6185 {
6186 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm);
6187
6188 ReferenceProcessorStats stats;
6189 if (rp->processing_is_mt()) {
6190 // Set the degree of MT here. If the discovery is done MT, there
6191 // may have been a different number of threads doing the discovery
6192 // and a different number of discovered lists may have Ref objects.
6193 // That is OK as long as the Reference lists are balanced (see
6194 // balance_all_queues() and balance_queues()).
6195 GenCollectedHeap* gch = GenCollectedHeap::heap();
6196 int active_workers = ParallelGCThreads;
6197 FlexibleWorkGang* workers = gch->workers();
6198 if (workers != NULL) {
6199 active_workers = workers->active_workers();
6200 // The expectation is that active_workers will have already
6201 // been set to a reasonable value. If it has not been set,
6202 // investigate.
6203 assert(active_workers > 0, "Should have been set during scavenge");
6204 }
6205 rp->set_active_mt_degree(active_workers);
6206 CMSRefProcTaskExecutor task_executor(*this);
6207 stats = rp->process_discovered_references(&_is_alive_closure,
6208 &cmsKeepAliveClosure,
6209 &cmsDrainMarkingStackClosure,
6210 &task_executor,
6211 _gc_timer_cm);
6212 } else {
6213 stats = rp->process_discovered_references(&_is_alive_closure,
6214 &cmsKeepAliveClosure,
6215 &cmsDrainMarkingStackClosure,
6216 NULL,
6217 _gc_timer_cm);
6218 }
6219 _gc_tracer_cm->report_gc_reference_stats(stats);
6220
6221 }
6222
6223 // This is the point where the entire marking should have completed.
6224 verify_work_stacks_empty();
6225
6226 if (should_unload_classes()) {
6227 {
6228 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm);
6229
6230 // Unload classes and purge the SystemDictionary.
6231 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
6232
6233 // Unload nmethods.
6234 CodeCache::do_unloading(&_is_alive_closure, purged_class);
6235
6236 // Prune dead klasses from subklass/sibling/implementor lists.
6237 Klass::clean_weak_klass_links(&_is_alive_closure);
6238 }
6239
6240 {
6241 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm);
6242 // Clean up unreferenced symbols in symbol table.
6243 SymbolTable::unlink();
6244 }
6245 }
6246
6247 // CMS doesn't use the StringTable as hard roots when class unloading is turned off.
6248 // Need to check if we really scanned the StringTable.
6249 if ((roots_scanning_options() & SharedHeap::SO_Strings) == 0) {
6250 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm);
6251 // Delete entries for dead interned strings.
6252 StringTable::unlink(&_is_alive_closure);
6253 }
6254
6255 // Restore any preserved marks as a result of mark stack or
6256 // work queue overflow
6257 restore_preserved_marks_if_any(); // done single-threaded for now
6258
6259 rp->set_enqueuing_is_done(true);
6260 if (rp->processing_is_mt()) {
6261 rp->balance_all_queues();
6262 CMSRefProcTaskExecutor task_executor(*this);
6263 rp->enqueue_discovered_references(&task_executor);
6264 } else {
6265 rp->enqueue_discovered_references(NULL);
6266 }
6267 rp->verify_no_references_recorded();
6268 assert(!rp->discovery_enabled(), "should have been disabled");
6269 }
6270
6271 #ifndef PRODUCT
6272 void CMSCollector::check_correct_thread_executing() {
6273 Thread* t = Thread::current();
6274 // Only the VM thread or the CMS thread should be here.
6275 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6276 "Unexpected thread type");
6277 // If this is the vm thread, the foreground process
6278 // should not be waiting. Note that _foregroundGCIsActive is
6279 // true while the foreground collector is waiting.
6280 if (_foregroundGCShouldWait) {
6281 // We cannot be the VM thread
6282 assert(t->is_ConcurrentGC_thread(),
6283 "Should be CMS thread");
6284 } else {
6285 // We can be the CMS thread only if we are in a stop-world
6286 // phase of CMS collection.
6287 if (t->is_ConcurrentGC_thread()) {
6288 assert(_collectorState == InitialMarking ||
6289 _collectorState == FinalMarking,
6290 "Should be a stop-world phase");
6291 // The CMS thread should be holding the CMS_token.
6292 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6293 "Potential interference with concurrently "
6294 "executing VM thread");
6295 }
6296 }
6297 }
6298 #endif
6299
6300 void CMSCollector::sweep(bool asynch) {
6301 assert(_collectorState == Sweeping, "just checking");
6302 check_correct_thread_executing();
6303 verify_work_stacks_empty();
6304 verify_overflow_empty();
6305 increment_sweep_count();
6306 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6307
6308 _inter_sweep_timer.stop();
6309 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6310 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
6311
6312 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6313 _intra_sweep_timer.reset();
6314 _intra_sweep_timer.start();
6315 if (asynch) {
6316 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6317 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
6318 // First sweep the old gen
6319 {
6320 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6321 bitMapLock());
6322 sweepWork(_cmsGen, asynch);
6323 }
6324
6325 // Update Universe::_heap_*_at_gc figures.
6326 // We need all the free list locks to make the abstract state
6327 // transition from Sweeping to Resetting. See detailed note
6328 // further below.
6329 {
6330 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6331 // Update heap occupancy information which is used as
6332 // input to soft ref clearing policy at the next gc.
6333 Universe::update_heap_info_at_gc();
6334 _collectorState = Resizing;
6335 }
6336 } else {
6337 // already have needed locks
6338 sweepWork(_cmsGen, asynch);
6339 // Update heap occupancy information which is used as
6340 // input to soft ref clearing policy at the next gc.
6341 Universe::update_heap_info_at_gc();
6342 _collectorState = Resizing;
6343 }
6344 verify_work_stacks_empty();
6345 verify_overflow_empty();
6346
6347 if (should_unload_classes()) {
6348 ClassLoaderDataGraph::purge();
6349 }
6350
6351 _intra_sweep_timer.stop();
6352 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6353
6354 _inter_sweep_timer.reset();
6355 _inter_sweep_timer.start();
6356
6357 // We need to use a monotonically non-decreasing time in ms
6358 // or we will see time-warp warnings and os::javaTimeMillis()
6359 // does not guarantee monotonicity.
6360 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6361 update_time_of_last_gc(now);
6362
6363 // NOTE on abstract state transitions:
6364 // Mutators allocate-live and/or mark the mod-union table dirty
6365 // based on the state of the collection. The former is done in
6366 // the interval [Marking, Sweeping] and the latter in the interval
6367 // [Marking, Sweeping). Thus the transitions into the Marking state
6368 // and out of the Sweeping state must be synchronously visible
6369 // globally to the mutators.
6370 // The transition into the Marking state happens with the world
6371 // stopped so the mutators will globally see it. Sweeping is
6372 // done asynchronously by the background collector so the transition
6373 // from the Sweeping state to the Resizing state must be done
6374 // under the freelistLock (as is the check for whether to
6375 // allocate-live and whether to dirty the mod-union table).
6376 assert(_collectorState == Resizing, "Change of collector state to"
6377 " Resizing must be done under the freelistLocks (plural)");
6378
6379 // Now that sweeping has been completed, we clear
6380 // the incremental_collection_failed flag,
6381 // thus inviting a younger gen collection to promote into
6382 // this generation. If such a promotion may still fail,
6383 // the flag will be set again when a young collection is
6384 // attempted.
6385 GenCollectedHeap* gch = GenCollectedHeap::heap();
6386 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6387 gch->update_full_collections_completed(_collection_count_start);
6388 }
6389
6390 // FIX ME!!! Looks like this belongs in CFLSpace, with
6391 // CMSGen merely delegating to it.
6392 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6393 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6394 HeapWord* minAddr = _cmsSpace->bottom();
6395 HeapWord* largestAddr =
6396 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6397 if (largestAddr == NULL) {
6398 // The dictionary appears to be empty. In this case
6399 // try to coalesce at the end of the heap.
6400 largestAddr = _cmsSpace->end();
6401 }
6402 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6403 size_t nearLargestOffset =
6404 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6405 if (PrintFLSStatistics != 0) {
6406 gclog_or_tty->print_cr(
6407 "CMS: Large Block: " PTR_FORMAT ";"
6408 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6409 largestAddr,
6410 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6411 }
6412 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6413 }
6414
6415 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6416 return addr >= _cmsSpace->nearLargestChunk();
6417 }
6418
6419 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6420 return _cmsSpace->find_chunk_at_end();
6421 }
6422
6423 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6424 bool full) {
6425 // The next lower level has been collected. Gather any statistics
6426 // that are of interest at this point.
6427 if (!full && (current_level + 1) == level()) {
6428 // Gather statistics on the young generation collection.
6429 collector()->stats().record_gc0_end(used());
6430 }
6431 }
6432
6433 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6434 GenCollectedHeap* gch = GenCollectedHeap::heap();
6435 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6436 "Wrong type of heap");
6437 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6438 gch->gen_policy()->size_policy();
6439 assert(sp->is_gc_cms_adaptive_size_policy(),
6440 "Wrong type of size policy");
6441 return sp;
6442 }
6443
6444 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6445 if (PrintGCDetails && Verbose) {
6446 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6447 }
6448 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6449 _debug_collection_type =
6450 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6451 if (PrintGCDetails && Verbose) {
6452 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6453 }
6454 }
6455
6456 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6457 bool asynch) {
6458 // We iterate over the space(s) underlying this generation,
6459 // checking the mark bit map to see if the bits corresponding
6460 // to specific blocks are marked or not. Blocks that are
6461 // marked are live and are not swept up. All remaining blocks
6462 // are swept up, with coalescing on-the-fly as we sweep up
6463 // contiguous free and/or garbage blocks:
6464 // We need to ensure that the sweeper synchronizes with allocators
6465 // and stop-the-world collectors. In particular, the following
6466 // locks are used:
6467 // . CMS token: if this is held, a stop the world collection cannot occur
6468 // . freelistLock: if this is held no allocation can occur from this
6469 // generation by another thread
6470 // . bitMapLock: if this is held, no other thread can access or update
6471 //
6472
6473 // Note that we need to hold the freelistLock if we use
6474 // block iterate below; else the iterator might go awry if
6475 // a mutator (or promotion) causes block contents to change
6476 // (for instance if the allocator divvies up a block).
6477 // If we hold the free list lock, for all practical purposes
6478 // young generation GC's can't occur (they'll usually need to
6479 // promote), so we might as well prevent all young generation
6480 // GC's while we do a sweeping step. For the same reason, we might
6481 // as well take the bit map lock for the entire duration
6482
6483 // check that we hold the requisite locks
6484 assert(have_cms_token(), "Should hold cms token");
6485 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6486 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6487 "Should possess CMS token to sweep");
6488 assert_lock_strong(gen->freelistLock());
6489 assert_lock_strong(bitMapLock());
6490
6491 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6492 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6493 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6494 _inter_sweep_estimate.padded_average(),
6495 _intra_sweep_estimate.padded_average());
6496 gen->setNearLargestChunk();
6497
6498 {
6499 SweepClosure sweepClosure(this, gen, &_markBitMap,
6500 CMSYield && asynch);
6501 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6502 // We need to free-up/coalesce garbage/blocks from a
6503 // co-terminal free run. This is done in the SweepClosure
6504 // destructor; so, do not remove this scope, else the
6505 // end-of-sweep-census below will be off by a little bit.
6506 }
6507 gen->cmsSpace()->sweep_completed();
6508 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6509 if (should_unload_classes()) { // unloaded classes this cycle,
6510 _concurrent_cycles_since_last_unload = 0; // ... reset count
6511 } else { // did not unload classes,
6512 _concurrent_cycles_since_last_unload++; // ... increment count
6513 }
6514 }
6515
6516 // Reset CMS data structures (for now just the marking bit map)
6517 // preparatory for the next cycle.
6518 void CMSCollector::reset(bool asynch) {
6519 GenCollectedHeap* gch = GenCollectedHeap::heap();
6520 CMSAdaptiveSizePolicy* sp = size_policy();
6521 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6522 if (asynch) {
6523 CMSTokenSyncWithLocks ts(true, bitMapLock());
6524
6525 // If the state is not "Resetting", the foreground thread
6526 // has done a collection and the resetting.
6527 if (_collectorState != Resetting) {
6528 assert(_collectorState == Idling, "The state should only change"
6529 " because the foreground collector has finished the collection");
6530 return;
6531 }
6532
6533 // Clear the mark bitmap (no grey objects to start with)
6534 // for the next cycle.
6535 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6536 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6537
6538 HeapWord* curAddr = _markBitMap.startWord();
6539 while (curAddr < _markBitMap.endWord()) {
6540 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6541 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6542 _markBitMap.clear_large_range(chunk);
6543 if (ConcurrentMarkSweepThread::should_yield() &&
6544 !foregroundGCIsActive() &&
6545 CMSYield) {
6546 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6547 "CMS thread should hold CMS token");
6548 assert_lock_strong(bitMapLock());
6549 bitMapLock()->unlock();
6550 ConcurrentMarkSweepThread::desynchronize(true);
6551 ConcurrentMarkSweepThread::acknowledge_yield_request();
6552 stopTimer();
6553 if (PrintCMSStatistics != 0) {
6554 incrementYields();
6555 }
6556 icms_wait();
6557
6558 // See the comment in coordinator_yield()
6559 for (unsigned i = 0; i < CMSYieldSleepCount &&
6560 ConcurrentMarkSweepThread::should_yield() &&
6561 !CMSCollector::foregroundGCIsActive(); ++i) {
6562 os::sleep(Thread::current(), 1, false);
6563 ConcurrentMarkSweepThread::acknowledge_yield_request();
6564 }
6565
6566 ConcurrentMarkSweepThread::synchronize(true);
6567 bitMapLock()->lock_without_safepoint_check();
6568 startTimer();
6569 }
6570 curAddr = chunk.end();
6571 }
6572 // A successful mostly concurrent collection has been done.
6573 // Because only the full (i.e., concurrent mode failure) collections
6574 // are being measured for gc overhead limits, clean the "near" flag
6575 // and count.
6576 sp->reset_gc_overhead_limit_count();
6577 _collectorState = Idling;
6578 } else {
6579 // already have the lock
6580 assert(_collectorState == Resetting, "just checking");
6581 assert_lock_strong(bitMapLock());
6582 _markBitMap.clear_all();
6583 _collectorState = Idling;
6584 }
6585
6586 // Stop incremental mode after a cycle completes, so that any future cycles
6587 // are triggered by allocation.
6588 stop_icms();
6589
6590 NOT_PRODUCT(
6591 if (RotateCMSCollectionTypes) {
6592 _cmsGen->rotate_debug_collection_type();
6593 }
6594 )
6595
6596 register_gc_end();
6597 }
6598
6599 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6600 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6601 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6602 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL);
6603 TraceCollectorStats tcs(counters());
6604
6605 switch (op) {
6606 case CMS_op_checkpointRootsInitial: {
6607 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6608 checkpointRootsInitial(true); // asynch
6609 if (PrintGC) {
6610 _cmsGen->printOccupancy("initial-mark");
6611 }
6612 break;
6613 }
6614 case CMS_op_checkpointRootsFinal: {
6615 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6616 checkpointRootsFinal(true, // asynch
6617 false, // !clear_all_soft_refs
6618 false); // !init_mark_was_synchronous
6619 if (PrintGC) {
6620 _cmsGen->printOccupancy("remark");
6621 }
6622 break;
6623 }
6624 default:
6625 fatal("No such CMS_op");
6626 }
6627 }
6628
6629 #ifndef PRODUCT
6630 size_t const CMSCollector::skip_header_HeapWords() {
6631 return FreeChunk::header_size();
6632 }
6633
6634 // Try and collect here conditions that should hold when
6635 // CMS thread is exiting. The idea is that the foreground GC
6636 // thread should not be blocked if it wants to terminate
6637 // the CMS thread and yet continue to run the VM for a while
6638 // after that.
6639 void CMSCollector::verify_ok_to_terminate() const {
6640 assert(Thread::current()->is_ConcurrentGC_thread(),
6641 "should be called by CMS thread");
6642 assert(!_foregroundGCShouldWait, "should be false");
6643 // We could check here that all the various low-level locks
6644 // are not held by the CMS thread, but that is overkill; see
6645 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6646 // is checked.
6647 }
6648 #endif
6649
6650 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6651 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6652 "missing Printezis mark?");
6653 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6654 size_t size = pointer_delta(nextOneAddr + 1, addr);
6655 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6656 "alignment problem");
6657 assert(size >= 3, "Necessary for Printezis marks to work");
6658 return size;
6659 }
6660
6661 // A variant of the above (block_size_using_printezis_bits()) except
6662 // that we return 0 if the P-bits are not yet set.
6663 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6664 if (_markBitMap.isMarked(addr + 1)) {
6665 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6666 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6667 size_t size = pointer_delta(nextOneAddr + 1, addr);
6668 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6669 "alignment problem");
6670 assert(size >= 3, "Necessary for Printezis marks to work");
6671 return size;
6672 }
6673 return 0;
6674 }
6675
6676 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6677 size_t sz = 0;
6678 oop p = (oop)addr;
6679 if (p->klass_or_null() != NULL) {
6680 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6681 } else {
6682 sz = block_size_using_printezis_bits(addr);
6683 }
6684 assert(sz > 0, "size must be nonzero");
6685 HeapWord* next_block = addr + sz;
6686 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6687 CardTableModRefBS::card_size);
6688 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6689 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6690 "must be different cards");
6691 return next_card;
6692 }
6693
6694
6695 // CMS Bit Map Wrapper /////////////////////////////////////////
6696
6697 // Construct a CMS bit map infrastructure, but don't create the
6698 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6699 // further below.
6700 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6701 _bm(),
6702 _shifter(shifter),
6703 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6704 {
6705 _bmStartWord = 0;
6706 _bmWordSize = 0;
6707 }
6708
6709 bool CMSBitMap::allocate(MemRegion mr) {
6710 _bmStartWord = mr.start();
6711 _bmWordSize = mr.word_size();
6712 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6713 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6714 if (!brs.is_reserved()) {
6715 warning("CMS bit map allocation failure");
6716 return false;
6717 }
6718 // For now we'll just commit all of the bit map up front.
6719 // Later on we'll try to be more parsimonious with swap.
6720 if (!_virtual_space.initialize(brs, brs.size())) {
6721 warning("CMS bit map backing store failure");
6722 return false;
6723 }
6724 assert(_virtual_space.committed_size() == brs.size(),
6725 "didn't reserve backing store for all of CMS bit map?");
6726 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6727 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6728 _bmWordSize, "inconsistency in bit map sizing");
6729 _bm.set_size(_bmWordSize >> _shifter);
6730
6731 // bm.clear(); // can we rely on getting zero'd memory? verify below
6732 assert(isAllClear(),
6733 "Expected zero'd memory from ReservedSpace constructor");
6734 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6735 "consistency check");
6736 return true;
6737 }
6738
6739 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6740 HeapWord *next_addr, *end_addr, *last_addr;
6741 assert_locked();
6742 assert(covers(mr), "out-of-range error");
6743 // XXX assert that start and end are appropriately aligned
6744 for (next_addr = mr.start(), end_addr = mr.end();
6745 next_addr < end_addr; next_addr = last_addr) {
6746 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6747 last_addr = dirty_region.end();
6748 if (!dirty_region.is_empty()) {
6749 cl->do_MemRegion(dirty_region);
6750 } else {
6751 assert(last_addr == end_addr, "program logic");
6752 return;
6753 }
6754 }
6755 }
6756
6757 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6758 _bm.print_on_error(st, prefix);
6759 }
6760
6761 #ifndef PRODUCT
6762 void CMSBitMap::assert_locked() const {
6763 CMSLockVerifier::assert_locked(lock());
6764 }
6765
6766 bool CMSBitMap::covers(MemRegion mr) const {
6767 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6768 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6769 "size inconsistency");
6770 return (mr.start() >= _bmStartWord) &&
6771 (mr.end() <= endWord());
6772 }
6773
6774 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6775 return (start >= _bmStartWord && (start + size) <= endWord());
6776 }
6777
6778 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6779 // verify that there are no 1 bits in the interval [left, right)
6780 FalseBitMapClosure falseBitMapClosure;
6781 iterate(&falseBitMapClosure, left, right);
6782 }
6783
6784 void CMSBitMap::region_invariant(MemRegion mr)
6785 {
6786 assert_locked();
6787 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6788 assert(!mr.is_empty(), "unexpected empty region");
6789 assert(covers(mr), "mr should be covered by bit map");
6790 // convert address range into offset range
6791 size_t start_ofs = heapWordToOffset(mr.start());
6792 // Make sure that end() is appropriately aligned
6793 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6794 (1 << (_shifter+LogHeapWordSize))),
6795 "Misaligned mr.end()");
6796 size_t end_ofs = heapWordToOffset(mr.end());
6797 assert(end_ofs > start_ofs, "Should mark at least one bit");
6798 }
6799
6800 #endif
6801
6802 bool CMSMarkStack::allocate(size_t size) {
6803 // allocate a stack of the requisite depth
6804 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6805 size * sizeof(oop)));
6806 if (!rs.is_reserved()) {
6807 warning("CMSMarkStack allocation failure");
6808 return false;
6809 }
6810 if (!_virtual_space.initialize(rs, rs.size())) {
6811 warning("CMSMarkStack backing store failure");
6812 return false;
6813 }
6814 assert(_virtual_space.committed_size() == rs.size(),
6815 "didn't reserve backing store for all of CMS stack?");
6816 _base = (oop*)(_virtual_space.low());
6817 _index = 0;
6818 _capacity = size;
6819 NOT_PRODUCT(_max_depth = 0);
6820 return true;
6821 }
6822
6823 // XXX FIX ME !!! In the MT case we come in here holding a
6824 // leaf lock. For printing we need to take a further lock
6825 // which has lower rank. We need to recalibrate the two
6826 // lock-ranks involved in order to be able to print the
6827 // messages below. (Or defer the printing to the caller.
6828 // For now we take the expedient path of just disabling the
6829 // messages for the problematic case.)
6830 void CMSMarkStack::expand() {
6831 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6832 if (_capacity == MarkStackSizeMax) {
6833 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6834 // We print a warning message only once per CMS cycle.
6835 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6836 }
6837 return;
6838 }
6839 // Double capacity if possible
6840 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6841 // Do not give up existing stack until we have managed to
6842 // get the double capacity that we desired.
6843 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6844 new_capacity * sizeof(oop)));
6845 if (rs.is_reserved()) {
6846 // Release the backing store associated with old stack
6847 _virtual_space.release();
6848 // Reinitialize virtual space for new stack
6849 if (!_virtual_space.initialize(rs, rs.size())) {
6850 fatal("Not enough swap for expanded marking stack");
6851 }
6852 _base = (oop*)(_virtual_space.low());
6853 _index = 0;
6854 _capacity = new_capacity;
6855 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6856 // Failed to double capacity, continue;
6857 // we print a detail message only once per CMS cycle.
6858 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6859 SIZE_FORMAT"K",
6860 _capacity / K, new_capacity / K);
6861 }
6862 }
6863
6864
6865 // Closures
6866 // XXX: there seems to be a lot of code duplication here;
6867 // should refactor and consolidate common code.
6868
6869 // This closure is used to mark refs into the CMS generation in
6870 // the CMS bit map. Called at the first checkpoint. This closure
6871 // assumes that we do not need to re-mark dirty cards; if the CMS
6872 // generation on which this is used is not an oldest
6873 // generation then this will lose younger_gen cards!
6874
6875 MarkRefsIntoClosure::MarkRefsIntoClosure(
6876 MemRegion span, CMSBitMap* bitMap):
6877 _span(span),
6878 _bitMap(bitMap)
6879 {
6880 assert(_ref_processor == NULL, "deliberately left NULL");
6881 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6882 }
6883
6884 void MarkRefsIntoClosure::do_oop(oop obj) {
6885 // if p points into _span, then mark corresponding bit in _markBitMap
6886 assert(obj->is_oop(), "expected an oop");
6887 HeapWord* addr = (HeapWord*)obj;
6888 if (_span.contains(addr)) {
6889 // this should be made more efficient
6890 _bitMap->mark(addr);
6891 }
6892 }
6893
6894 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6895 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6896
6897 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6898 MemRegion span, CMSBitMap* bitMap):
6899 _span(span),
6900 _bitMap(bitMap)
6901 {
6902 assert(_ref_processor == NULL, "deliberately left NULL");
6903 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6904 }
6905
6906 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6907 // if p points into _span, then mark corresponding bit in _markBitMap
6908 assert(obj->is_oop(), "expected an oop");
6909 HeapWord* addr = (HeapWord*)obj;
6910 if (_span.contains(addr)) {
6911 // this should be made more efficient
6912 _bitMap->par_mark(addr);
6913 }
6914 }
6915
6916 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6917 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6918
6919 // A variant of the above, used for CMS marking verification.
6920 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6921 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6922 _span(span),
6923 _verification_bm(verification_bm),
6924 _cms_bm(cms_bm)
6925 {
6926 assert(_ref_processor == NULL, "deliberately left NULL");
6927 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6928 }
6929
6930 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6931 // if p points into _span, then mark corresponding bit in _markBitMap
6932 assert(obj->is_oop(), "expected an oop");
6933 HeapWord* addr = (HeapWord*)obj;
6934 if (_span.contains(addr)) {
6935 _verification_bm->mark(addr);
6936 if (!_cms_bm->isMarked(addr)) {
6937 oop(addr)->print();
6938 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6939 fatal("... aborting");
6940 }
6941 }
6942 }
6943
6944 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6945 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6946
6947 //////////////////////////////////////////////////
6948 // MarkRefsIntoAndScanClosure
6949 //////////////////////////////////////////////////
6950
6951 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6952 ReferenceProcessor* rp,
6953 CMSBitMap* bit_map,
6954 CMSBitMap* mod_union_table,
6955 CMSMarkStack* mark_stack,
6956 CMSCollector* collector,
6957 bool should_yield,
6958 bool concurrent_precleaning):
6959 _collector(collector),
6960 _span(span),
6961 _bit_map(bit_map),
6962 _mark_stack(mark_stack),
6963 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6964 mark_stack, concurrent_precleaning),
6965 _yield(should_yield),
6966 _concurrent_precleaning(concurrent_precleaning),
6967 _freelistLock(NULL)
6968 {
6969 _ref_processor = rp;
6970 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6971 }
6972
6973 // This closure is used to mark refs into the CMS generation at the
6974 // second (final) checkpoint, and to scan and transitively follow
6975 // the unmarked oops. It is also used during the concurrent precleaning
6976 // phase while scanning objects on dirty cards in the CMS generation.
6977 // The marks are made in the marking bit map and the marking stack is
6978 // used for keeping the (newly) grey objects during the scan.
6979 // The parallel version (Par_...) appears further below.
6980 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6981 if (obj != NULL) {
6982 assert(obj->is_oop(), "expected an oop");
6983 HeapWord* addr = (HeapWord*)obj;
6984 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6985 assert(_collector->overflow_list_is_empty(),
6986 "overflow list should be empty");
6987 if (_span.contains(addr) &&
6988 !_bit_map->isMarked(addr)) {
6989 // mark bit map (object is now grey)
6990 _bit_map->mark(addr);
6991 // push on marking stack (stack should be empty), and drain the
6992 // stack by applying this closure to the oops in the oops popped
6993 // from the stack (i.e. blacken the grey objects)
6994 bool res = _mark_stack->push(obj);
6995 assert(res, "Should have space to push on empty stack");
6996 do {
6997 oop new_oop = _mark_stack->pop();
6998 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6999 assert(_bit_map->isMarked((HeapWord*)new_oop),
7000 "only grey objects on this stack");
7001 // iterate over the oops in this oop, marking and pushing
7002 // the ones in CMS heap (i.e. in _span).
7003 new_oop->oop_iterate(&_pushAndMarkClosure);
7004 // check if it's time to yield
7005 do_yield_check();
7006 } while (!_mark_stack->isEmpty() ||
7007 (!_concurrent_precleaning && take_from_overflow_list()));
7008 // if marking stack is empty, and we are not doing this
7009 // during precleaning, then check the overflow list
7010 }
7011 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7012 assert(_collector->overflow_list_is_empty(),
7013 "overflow list was drained above");
7014 // We could restore evacuated mark words, if any, used for
7015 // overflow list links here because the overflow list is
7016 // provably empty here. That would reduce the maximum
7017 // size requirements for preserved_{oop,mark}_stack.
7018 // But we'll just postpone it until we are all done
7019 // so we can just stream through.
7020 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
7021 _collector->restore_preserved_marks_if_any();
7022 assert(_collector->no_preserved_marks(), "No preserved marks");
7023 }
7024 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
7025 "All preserved marks should have been restored above");
7026 }
7027 }
7028
7029 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
7030 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
7031
7032 void MarkRefsIntoAndScanClosure::do_yield_work() {
7033 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7034 "CMS thread should hold CMS token");
7035 assert_lock_strong(_freelistLock);
7036 assert_lock_strong(_bit_map->lock());
7037 // relinquish the free_list_lock and bitMaplock()
7038 _bit_map->lock()->unlock();
7039 _freelistLock->unlock();
7040 ConcurrentMarkSweepThread::desynchronize(true);
7041 ConcurrentMarkSweepThread::acknowledge_yield_request();
7042 _collector->stopTimer();
7043 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7044 if (PrintCMSStatistics != 0) {
7045 _collector->incrementYields();
7046 }
7047 _collector->icms_wait();
7048
7049 // See the comment in coordinator_yield()
7050 for (unsigned i = 0;
7051 i < CMSYieldSleepCount &&
7052 ConcurrentMarkSweepThread::should_yield() &&
7053 !CMSCollector::foregroundGCIsActive();
7054 ++i) {
7055 os::sleep(Thread::current(), 1, false);
7056 ConcurrentMarkSweepThread::acknowledge_yield_request();
7057 }
7058
7059 ConcurrentMarkSweepThread::synchronize(true);
7060 _freelistLock->lock_without_safepoint_check();
7061 _bit_map->lock()->lock_without_safepoint_check();
7062 _collector->startTimer();
7063 }
7064
7065 ///////////////////////////////////////////////////////////
7066 // Par_MarkRefsIntoAndScanClosure: a parallel version of
7067 // MarkRefsIntoAndScanClosure
7068 ///////////////////////////////////////////////////////////
7069 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
7070 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
7071 CMSBitMap* bit_map, OopTaskQueue* work_queue):
7072 _span(span),
7073 _bit_map(bit_map),
7074 _work_queue(work_queue),
7075 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
7076 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
7077 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
7078 {
7079 _ref_processor = rp;
7080 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7081 }
7082
7083 // This closure is used to mark refs into the CMS generation at the
7084 // second (final) checkpoint, and to scan and transitively follow
7085 // the unmarked oops. The marks are made in the marking bit map and
7086 // the work_queue is used for keeping the (newly) grey objects during
7087 // the scan phase whence they are also available for stealing by parallel
7088 // threads. Since the marking bit map is shared, updates are
7089 // synchronized (via CAS).
7090 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
7091 if (obj != NULL) {
7092 // Ignore mark word because this could be an already marked oop
7093 // that may be chained at the end of the overflow list.
7094 assert(obj->is_oop(true), "expected an oop");
7095 HeapWord* addr = (HeapWord*)obj;
7096 if (_span.contains(addr) &&
7097 !_bit_map->isMarked(addr)) {
7098 // mark bit map (object will become grey):
7099 // It is possible for several threads to be
7100 // trying to "claim" this object concurrently;
7101 // the unique thread that succeeds in marking the
7102 // object first will do the subsequent push on
7103 // to the work queue (or overflow list).
7104 if (_bit_map->par_mark(addr)) {
7105 // push on work_queue (which may not be empty), and trim the
7106 // queue to an appropriate length by applying this closure to
7107 // the oops in the oops popped from the stack (i.e. blacken the
7108 // grey objects)
7109 bool res = _work_queue->push(obj);
7110 assert(res, "Low water mark should be less than capacity?");
7111 trim_queue(_low_water_mark);
7112 } // Else, another thread claimed the object
7113 }
7114 }
7115 }
7116
7117 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7118 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7119
7120 // This closure is used to rescan the marked objects on the dirty cards
7121 // in the mod union table and the card table proper.
7122 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
7123 oop p, MemRegion mr) {
7124
7125 size_t size = 0;
7126 HeapWord* addr = (HeapWord*)p;
7127 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7128 assert(_span.contains(addr), "we are scanning the CMS generation");
7129 // check if it's time to yield
7130 if (do_yield_check()) {
7131 // We yielded for some foreground stop-world work,
7132 // and we have been asked to abort this ongoing preclean cycle.
7133 return 0;
7134 }
7135 if (_bitMap->isMarked(addr)) {
7136 // it's marked; is it potentially uninitialized?
7137 if (p->klass_or_null() != NULL) {
7138 // an initialized object; ignore mark word in verification below
7139 // since we are running concurrent with mutators
7140 assert(p->is_oop(true), "should be an oop");
7141 if (p->is_objArray()) {
7142 // objArrays are precisely marked; restrict scanning
7143 // to dirty cards only.
7144 size = CompactibleFreeListSpace::adjustObjectSize(
7145 p->oop_iterate(_scanningClosure, mr));
7146 } else {
7147 // A non-array may have been imprecisely marked; we need
7148 // to scan object in its entirety.
7149 size = CompactibleFreeListSpace::adjustObjectSize(
7150 p->oop_iterate(_scanningClosure));
7151 }
7152 #ifdef ASSERT
7153 size_t direct_size =
7154 CompactibleFreeListSpace::adjustObjectSize(p->size());
7155 assert(size == direct_size, "Inconsistency in size");
7156 assert(size >= 3, "Necessary for Printezis marks to work");
7157 if (!_bitMap->isMarked(addr+1)) {
7158 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
7159 } else {
7160 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
7161 assert(_bitMap->isMarked(addr+size-1),
7162 "inconsistent Printezis mark");
7163 }
7164 #endif // ASSERT
7165 } else {
7166 // An uninitialized object.
7167 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
7168 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7169 size = pointer_delta(nextOneAddr + 1, addr);
7170 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7171 "alignment problem");
7172 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
7173 // will dirty the card when the klass pointer is installed in the
7174 // object (signaling the completion of initialization).
7175 }
7176 } else {
7177 // Either a not yet marked object or an uninitialized object
7178 if (p->klass_or_null() == NULL) {
7179 // An uninitialized object, skip to the next card, since
7180 // we may not be able to read its P-bits yet.
7181 assert(size == 0, "Initial value");
7182 } else {
7183 // An object not (yet) reached by marking: we merely need to
7184 // compute its size so as to go look at the next block.
7185 assert(p->is_oop(true), "should be an oop");
7186 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
7187 }
7188 }
7189 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7190 return size;
7191 }
7192
7193 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
7194 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7195 "CMS thread should hold CMS token");
7196 assert_lock_strong(_freelistLock);
7197 assert_lock_strong(_bitMap->lock());
7198 // relinquish the free_list_lock and bitMaplock()
7199 _bitMap->lock()->unlock();
7200 _freelistLock->unlock();
7201 ConcurrentMarkSweepThread::desynchronize(true);
7202 ConcurrentMarkSweepThread::acknowledge_yield_request();
7203 _collector->stopTimer();
7204 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7205 if (PrintCMSStatistics != 0) {
7206 _collector->incrementYields();
7207 }
7208 _collector->icms_wait();
7209
7210 // See the comment in coordinator_yield()
7211 for (unsigned i = 0; i < CMSYieldSleepCount &&
7212 ConcurrentMarkSweepThread::should_yield() &&
7213 !CMSCollector::foregroundGCIsActive(); ++i) {
7214 os::sleep(Thread::current(), 1, false);
7215 ConcurrentMarkSweepThread::acknowledge_yield_request();
7216 }
7217
7218 ConcurrentMarkSweepThread::synchronize(true);
7219 _freelistLock->lock_without_safepoint_check();
7220 _bitMap->lock()->lock_without_safepoint_check();
7221 _collector->startTimer();
7222 }
7223
7224
7225 //////////////////////////////////////////////////////////////////
7226 // SurvivorSpacePrecleanClosure
7227 //////////////////////////////////////////////////////////////////
7228 // This (single-threaded) closure is used to preclean the oops in
7229 // the survivor spaces.
7230 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
7231
7232 HeapWord* addr = (HeapWord*)p;
7233 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7234 assert(!_span.contains(addr), "we are scanning the survivor spaces");
7235 assert(p->klass_or_null() != NULL, "object should be initialized");
7236 // an initialized object; ignore mark word in verification below
7237 // since we are running concurrent with mutators
7238 assert(p->is_oop(true), "should be an oop");
7239 // Note that we do not yield while we iterate over
7240 // the interior oops of p, pushing the relevant ones
7241 // on our marking stack.
7242 size_t size = p->oop_iterate(_scanning_closure);
7243 do_yield_check();
7244 // Observe that below, we do not abandon the preclean
7245 // phase as soon as we should; rather we empty the
7246 // marking stack before returning. This is to satisfy
7247 // some existing assertions. In general, it may be a
7248 // good idea to abort immediately and complete the marking
7249 // from the grey objects at a later time.
7250 while (!_mark_stack->isEmpty()) {
7251 oop new_oop = _mark_stack->pop();
7252 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7253 assert(_bit_map->isMarked((HeapWord*)new_oop),
7254 "only grey objects on this stack");
7255 // iterate over the oops in this oop, marking and pushing
7256 // the ones in CMS heap (i.e. in _span).
7257 new_oop->oop_iterate(_scanning_closure);
7258 // check if it's time to yield
7259 do_yield_check();
7260 }
7261 unsigned int after_count =
7262 GenCollectedHeap::heap()->total_collections();
7263 bool abort = (_before_count != after_count) ||
7264 _collector->should_abort_preclean();
7265 return abort ? 0 : size;
7266 }
7267
7268 void SurvivorSpacePrecleanClosure::do_yield_work() {
7269 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7270 "CMS thread should hold CMS token");
7271 assert_lock_strong(_bit_map->lock());
7272 // Relinquish the bit map lock
7273 _bit_map->lock()->unlock();
7274 ConcurrentMarkSweepThread::desynchronize(true);
7275 ConcurrentMarkSweepThread::acknowledge_yield_request();
7276 _collector->stopTimer();
7277 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7278 if (PrintCMSStatistics != 0) {
7279 _collector->incrementYields();
7280 }
7281 _collector->icms_wait();
7282
7283 // See the comment in coordinator_yield()
7284 for (unsigned i = 0; i < CMSYieldSleepCount &&
7285 ConcurrentMarkSweepThread::should_yield() &&
7286 !CMSCollector::foregroundGCIsActive(); ++i) {
7287 os::sleep(Thread::current(), 1, false);
7288 ConcurrentMarkSweepThread::acknowledge_yield_request();
7289 }
7290
7291 ConcurrentMarkSweepThread::synchronize(true);
7292 _bit_map->lock()->lock_without_safepoint_check();
7293 _collector->startTimer();
7294 }
7295
7296 // This closure is used to rescan the marked objects on the dirty cards
7297 // in the mod union table and the card table proper. In the parallel
7298 // case, although the bitMap is shared, we do a single read so the
7299 // isMarked() query is "safe".
7300 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7301 // Ignore mark word because we are running concurrent with mutators
7302 assert(p->is_oop_or_null(true), "expected an oop or null");
7303 HeapWord* addr = (HeapWord*)p;
7304 assert(_span.contains(addr), "we are scanning the CMS generation");
7305 bool is_obj_array = false;
7306 #ifdef ASSERT
7307 if (!_parallel) {
7308 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7309 assert(_collector->overflow_list_is_empty(),
7310 "overflow list should be empty");
7311
7312 }
7313 #endif // ASSERT
7314 if (_bit_map->isMarked(addr)) {
7315 // Obj arrays are precisely marked, non-arrays are not;
7316 // so we scan objArrays precisely and non-arrays in their
7317 // entirety.
7318 if (p->is_objArray()) {
7319 is_obj_array = true;
7320 if (_parallel) {
7321 p->oop_iterate(_par_scan_closure, mr);
7322 } else {
7323 p->oop_iterate(_scan_closure, mr);
7324 }
7325 } else {
7326 if (_parallel) {
7327 p->oop_iterate(_par_scan_closure);
7328 } else {
7329 p->oop_iterate(_scan_closure);
7330 }
7331 }
7332 }
7333 #ifdef ASSERT
7334 if (!_parallel) {
7335 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7336 assert(_collector->overflow_list_is_empty(),
7337 "overflow list should be empty");
7338
7339 }
7340 #endif // ASSERT
7341 return is_obj_array;
7342 }
7343
7344 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7345 MemRegion span,
7346 CMSBitMap* bitMap, CMSMarkStack* markStack,
7347 bool should_yield, bool verifying):
7348 _collector(collector),
7349 _span(span),
7350 _bitMap(bitMap),
7351 _mut(&collector->_modUnionTable),
7352 _markStack(markStack),
7353 _yield(should_yield),
7354 _skipBits(0)
7355 {
7356 assert(_markStack->isEmpty(), "stack should be empty");
7357 _finger = _bitMap->startWord();
7358 _threshold = _finger;
7359 assert(_collector->_restart_addr == NULL, "Sanity check");
7360 assert(_span.contains(_finger), "Out of bounds _finger?");
7361 DEBUG_ONLY(_verifying = verifying;)
7362 }
7363
7364 void MarkFromRootsClosure::reset(HeapWord* addr) {
7365 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7366 assert(_span.contains(addr), "Out of bounds _finger?");
7367 _finger = addr;
7368 _threshold = (HeapWord*)round_to(
7369 (intptr_t)_finger, CardTableModRefBS::card_size);
7370 }
7371
7372 // Should revisit to see if this should be restructured for
7373 // greater efficiency.
7374 bool MarkFromRootsClosure::do_bit(size_t offset) {
7375 if (_skipBits > 0) {
7376 _skipBits--;
7377 return true;
7378 }
7379 // convert offset into a HeapWord*
7380 HeapWord* addr = _bitMap->startWord() + offset;
7381 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7382 "address out of range");
7383 assert(_bitMap->isMarked(addr), "tautology");
7384 if (_bitMap->isMarked(addr+1)) {
7385 // this is an allocated but not yet initialized object
7386 assert(_skipBits == 0, "tautology");
7387 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7388 oop p = oop(addr);
7389 if (p->klass_or_null() == NULL) {
7390 DEBUG_ONLY(if (!_verifying) {)
7391 // We re-dirty the cards on which this object lies and increase
7392 // the _threshold so that we'll come back to scan this object
7393 // during the preclean or remark phase. (CMSCleanOnEnter)
7394 if (CMSCleanOnEnter) {
7395 size_t sz = _collector->block_size_using_printezis_bits(addr);
7396 HeapWord* end_card_addr = (HeapWord*)round_to(
7397 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7398 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7399 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7400 // Bump _threshold to end_card_addr; note that
7401 // _threshold cannot possibly exceed end_card_addr, anyhow.
7402 // This prevents future clearing of the card as the scan proceeds
7403 // to the right.
7404 assert(_threshold <= end_card_addr,
7405 "Because we are just scanning into this object");
7406 if (_threshold < end_card_addr) {
7407 _threshold = end_card_addr;
7408 }
7409 if (p->klass_or_null() != NULL) {
7410 // Redirty the range of cards...
7411 _mut->mark_range(redirty_range);
7412 } // ...else the setting of klass will dirty the card anyway.
7413 }
7414 DEBUG_ONLY(})
7415 return true;
7416 }
7417 }
7418 scanOopsInOop(addr);
7419 return true;
7420 }
7421
7422 // We take a break if we've been at this for a while,
7423 // so as to avoid monopolizing the locks involved.
7424 void MarkFromRootsClosure::do_yield_work() {
7425 // First give up the locks, then yield, then re-lock
7426 // We should probably use a constructor/destructor idiom to
7427 // do this unlock/lock or modify the MutexUnlocker class to
7428 // serve our purpose. XXX
7429 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7430 "CMS thread should hold CMS token");
7431 assert_lock_strong(_bitMap->lock());
7432 _bitMap->lock()->unlock();
7433 ConcurrentMarkSweepThread::desynchronize(true);
7434 ConcurrentMarkSweepThread::acknowledge_yield_request();
7435 _collector->stopTimer();
7436 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7437 if (PrintCMSStatistics != 0) {
7438 _collector->incrementYields();
7439 }
7440 _collector->icms_wait();
7441
7442 // See the comment in coordinator_yield()
7443 for (unsigned i = 0; i < CMSYieldSleepCount &&
7444 ConcurrentMarkSweepThread::should_yield() &&
7445 !CMSCollector::foregroundGCIsActive(); ++i) {
7446 os::sleep(Thread::current(), 1, false);
7447 ConcurrentMarkSweepThread::acknowledge_yield_request();
7448 }
7449
7450 ConcurrentMarkSweepThread::synchronize(true);
7451 _bitMap->lock()->lock_without_safepoint_check();
7452 _collector->startTimer();
7453 }
7454
7455 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7456 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7457 assert(_markStack->isEmpty(),
7458 "should drain stack to limit stack usage");
7459 // convert ptr to an oop preparatory to scanning
7460 oop obj = oop(ptr);
7461 // Ignore mark word in verification below, since we
7462 // may be running concurrent with mutators.
7463 assert(obj->is_oop(true), "should be an oop");
7464 assert(_finger <= ptr, "_finger runneth ahead");
7465 // advance the finger to right end of this object
7466 _finger = ptr + obj->size();
7467 assert(_finger > ptr, "we just incremented it above");
7468 // On large heaps, it may take us some time to get through
7469 // the marking phase (especially if running iCMS). During
7470 // this time it's possible that a lot of mutations have
7471 // accumulated in the card table and the mod union table --
7472 // these mutation records are redundant until we have
7473 // actually traced into the corresponding card.
7474 // Here, we check whether advancing the finger would make
7475 // us cross into a new card, and if so clear corresponding
7476 // cards in the MUT (preclean them in the card-table in the
7477 // future).
7478
7479 DEBUG_ONLY(if (!_verifying) {)
7480 // The clean-on-enter optimization is disabled by default,
7481 // until we fix 6178663.
7482 if (CMSCleanOnEnter && (_finger > _threshold)) {
7483 // [_threshold, _finger) represents the interval
7484 // of cards to be cleared in MUT (or precleaned in card table).
7485 // The set of cards to be cleared is all those that overlap
7486 // with the interval [_threshold, _finger); note that
7487 // _threshold is always kept card-aligned but _finger isn't
7488 // always card-aligned.
7489 HeapWord* old_threshold = _threshold;
7490 assert(old_threshold == (HeapWord*)round_to(
7491 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7492 "_threshold should always be card-aligned");
7493 _threshold = (HeapWord*)round_to(
7494 (intptr_t)_finger, CardTableModRefBS::card_size);
7495 MemRegion mr(old_threshold, _threshold);
7496 assert(!mr.is_empty(), "Control point invariant");
7497 assert(_span.contains(mr), "Should clear within span");
7498 _mut->clear_range(mr);
7499 }
7500 DEBUG_ONLY(})
7501 // Note: the finger doesn't advance while we drain
7502 // the stack below.
7503 PushOrMarkClosure pushOrMarkClosure(_collector,
7504 _span, _bitMap, _markStack,
7505 _finger, this);
7506 bool res = _markStack->push(obj);
7507 assert(res, "Empty non-zero size stack should have space for single push");
7508 while (!_markStack->isEmpty()) {
7509 oop new_oop = _markStack->pop();
7510 // Skip verifying header mark word below because we are
7511 // running concurrent with mutators.
7512 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7513 // now scan this oop's oops
7514 new_oop->oop_iterate(&pushOrMarkClosure);
7515 do_yield_check();
7516 }
7517 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7518 }
7519
7520 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7521 CMSCollector* collector, MemRegion span,
7522 CMSBitMap* bit_map,
7523 OopTaskQueue* work_queue,
7524 CMSMarkStack* overflow_stack,
7525 bool should_yield):
7526 _collector(collector),
7527 _whole_span(collector->_span),
7528 _span(span),
7529 _bit_map(bit_map),
7530 _mut(&collector->_modUnionTable),
7531 _work_queue(work_queue),
7532 _overflow_stack(overflow_stack),
7533 _yield(should_yield),
7534 _skip_bits(0),
7535 _task(task)
7536 {
7537 assert(_work_queue->size() == 0, "work_queue should be empty");
7538 _finger = span.start();
7539 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7540 assert(_span.contains(_finger), "Out of bounds _finger?");
7541 }
7542
7543 // Should revisit to see if this should be restructured for
7544 // greater efficiency.
7545 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7546 if (_skip_bits > 0) {
7547 _skip_bits--;
7548 return true;
7549 }
7550 // convert offset into a HeapWord*
7551 HeapWord* addr = _bit_map->startWord() + offset;
7552 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7553 "address out of range");
7554 assert(_bit_map->isMarked(addr), "tautology");
7555 if (_bit_map->isMarked(addr+1)) {
7556 // this is an allocated object that might not yet be initialized
7557 assert(_skip_bits == 0, "tautology");
7558 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7559 oop p = oop(addr);
7560 if (p->klass_or_null() == NULL) {
7561 // in the case of Clean-on-Enter optimization, redirty card
7562 // and avoid clearing card by increasing the threshold.
7563 return true;
7564 }
7565 }
7566 scan_oops_in_oop(addr);
7567 return true;
7568 }
7569
7570 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7571 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7572 // Should we assert that our work queue is empty or
7573 // below some drain limit?
7574 assert(_work_queue->size() == 0,
7575 "should drain stack to limit stack usage");
7576 // convert ptr to an oop preparatory to scanning
7577 oop obj = oop(ptr);
7578 // Ignore mark word in verification below, since we
7579 // may be running concurrent with mutators.
7580 assert(obj->is_oop(true), "should be an oop");
7581 assert(_finger <= ptr, "_finger runneth ahead");
7582 // advance the finger to right end of this object
7583 _finger = ptr + obj->size();
7584 assert(_finger > ptr, "we just incremented it above");
7585 // On large heaps, it may take us some time to get through
7586 // the marking phase (especially if running iCMS). During
7587 // this time it's possible that a lot of mutations have
7588 // accumulated in the card table and the mod union table --
7589 // these mutation records are redundant until we have
7590 // actually traced into the corresponding card.
7591 // Here, we check whether advancing the finger would make
7592 // us cross into a new card, and if so clear corresponding
7593 // cards in the MUT (preclean them in the card-table in the
7594 // future).
7595
7596 // The clean-on-enter optimization is disabled by default,
7597 // until we fix 6178663.
7598 if (CMSCleanOnEnter && (_finger > _threshold)) {
7599 // [_threshold, _finger) represents the interval
7600 // of cards to be cleared in MUT (or precleaned in card table).
7601 // The set of cards to be cleared is all those that overlap
7602 // with the interval [_threshold, _finger); note that
7603 // _threshold is always kept card-aligned but _finger isn't
7604 // always card-aligned.
7605 HeapWord* old_threshold = _threshold;
7606 assert(old_threshold == (HeapWord*)round_to(
7607 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7608 "_threshold should always be card-aligned");
7609 _threshold = (HeapWord*)round_to(
7610 (intptr_t)_finger, CardTableModRefBS::card_size);
7611 MemRegion mr(old_threshold, _threshold);
7612 assert(!mr.is_empty(), "Control point invariant");
7613 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7614 _mut->clear_range(mr);
7615 }
7616
7617 // Note: the local finger doesn't advance while we drain
7618 // the stack below, but the global finger sure can and will.
7619 HeapWord** gfa = _task->global_finger_addr();
7620 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7621 _span, _bit_map,
7622 _work_queue,
7623 _overflow_stack,
7624 _finger,
7625 gfa, this);
7626 bool res = _work_queue->push(obj); // overflow could occur here
7627 assert(res, "Will hold once we use workqueues");
7628 while (true) {
7629 oop new_oop;
7630 if (!_work_queue->pop_local(new_oop)) {
7631 // We emptied our work_queue; check if there's stuff that can
7632 // be gotten from the overflow stack.
7633 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7634 _overflow_stack, _work_queue)) {
7635 do_yield_check();
7636 continue;
7637 } else { // done
7638 break;
7639 }
7640 }
7641 // Skip verifying header mark word below because we are
7642 // running concurrent with mutators.
7643 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7644 // now scan this oop's oops
7645 new_oop->oop_iterate(&pushOrMarkClosure);
7646 do_yield_check();
7647 }
7648 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7649 }
7650
7651 // Yield in response to a request from VM Thread or
7652 // from mutators.
7653 void Par_MarkFromRootsClosure::do_yield_work() {
7654 assert(_task != NULL, "sanity");
7655 _task->yield();
7656 }
7657
7658 // A variant of the above used for verifying CMS marking work.
7659 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7660 MemRegion span,
7661 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7662 CMSMarkStack* mark_stack):
7663 _collector(collector),
7664 _span(span),
7665 _verification_bm(verification_bm),
7666 _cms_bm(cms_bm),
7667 _mark_stack(mark_stack),
7668 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7669 mark_stack)
7670 {
7671 assert(_mark_stack->isEmpty(), "stack should be empty");
7672 _finger = _verification_bm->startWord();
7673 assert(_collector->_restart_addr == NULL, "Sanity check");
7674 assert(_span.contains(_finger), "Out of bounds _finger?");
7675 }
7676
7677 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7678 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7679 assert(_span.contains(addr), "Out of bounds _finger?");
7680 _finger = addr;
7681 }
7682
7683 // Should revisit to see if this should be restructured for
7684 // greater efficiency.
7685 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7686 // convert offset into a HeapWord*
7687 HeapWord* addr = _verification_bm->startWord() + offset;
7688 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7689 "address out of range");
7690 assert(_verification_bm->isMarked(addr), "tautology");
7691 assert(_cms_bm->isMarked(addr), "tautology");
7692
7693 assert(_mark_stack->isEmpty(),
7694 "should drain stack to limit stack usage");
7695 // convert addr to an oop preparatory to scanning
7696 oop obj = oop(addr);
7697 assert(obj->is_oop(), "should be an oop");
7698 assert(_finger <= addr, "_finger runneth ahead");
7699 // advance the finger to right end of this object
7700 _finger = addr + obj->size();
7701 assert(_finger > addr, "we just incremented it above");
7702 // Note: the finger doesn't advance while we drain
7703 // the stack below.
7704 bool res = _mark_stack->push(obj);
7705 assert(res, "Empty non-zero size stack should have space for single push");
7706 while (!_mark_stack->isEmpty()) {
7707 oop new_oop = _mark_stack->pop();
7708 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7709 // now scan this oop's oops
7710 new_oop->oop_iterate(&_pam_verify_closure);
7711 }
7712 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7713 return true;
7714 }
7715
7716 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7717 CMSCollector* collector, MemRegion span,
7718 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7719 CMSMarkStack* mark_stack):
7720 CMSOopClosure(collector->ref_processor()),
7721 _collector(collector),
7722 _span(span),
7723 _verification_bm(verification_bm),
7724 _cms_bm(cms_bm),
7725 _mark_stack(mark_stack)
7726 { }
7727
7728 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7729 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7730
7731 // Upon stack overflow, we discard (part of) the stack,
7732 // remembering the least address amongst those discarded
7733 // in CMSCollector's _restart_address.
7734 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7735 // Remember the least grey address discarded
7736 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7737 _collector->lower_restart_addr(ra);
7738 _mark_stack->reset(); // discard stack contents
7739 _mark_stack->expand(); // expand the stack if possible
7740 }
7741
7742 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7743 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7744 HeapWord* addr = (HeapWord*)obj;
7745 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7746 // Oop lies in _span and isn't yet grey or black
7747 _verification_bm->mark(addr); // now grey
7748 if (!_cms_bm->isMarked(addr)) {
7749 oop(addr)->print();
7750 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7751 addr);
7752 fatal("... aborting");
7753 }
7754
7755 if (!_mark_stack->push(obj)) { // stack overflow
7756 if (PrintCMSStatistics != 0) {
7757 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7758 SIZE_FORMAT, _mark_stack->capacity());
7759 }
7760 assert(_mark_stack->isFull(), "Else push should have succeeded");
7761 handle_stack_overflow(addr);
7762 }
7763 // anything including and to the right of _finger
7764 // will be scanned as we iterate over the remainder of the
7765 // bit map
7766 }
7767 }
7768
7769 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7770 MemRegion span,
7771 CMSBitMap* bitMap, CMSMarkStack* markStack,
7772 HeapWord* finger, MarkFromRootsClosure* parent) :
7773 CMSOopClosure(collector->ref_processor()),
7774 _collector(collector),
7775 _span(span),
7776 _bitMap(bitMap),
7777 _markStack(markStack),
7778 _finger(finger),
7779 _parent(parent)
7780 { }
7781
7782 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7783 MemRegion span,
7784 CMSBitMap* bit_map,
7785 OopTaskQueue* work_queue,
7786 CMSMarkStack* overflow_stack,
7787 HeapWord* finger,
7788 HeapWord** global_finger_addr,
7789 Par_MarkFromRootsClosure* parent) :
7790 CMSOopClosure(collector->ref_processor()),
7791 _collector(collector),
7792 _whole_span(collector->_span),
7793 _span(span),
7794 _bit_map(bit_map),
7795 _work_queue(work_queue),
7796 _overflow_stack(overflow_stack),
7797 _finger(finger),
7798 _global_finger_addr(global_finger_addr),
7799 _parent(parent)
7800 { }
7801
7802 // Assumes thread-safe access by callers, who are
7803 // responsible for mutual exclusion.
7804 void CMSCollector::lower_restart_addr(HeapWord* low) {
7805 assert(_span.contains(low), "Out of bounds addr");
7806 if (_restart_addr == NULL) {
7807 _restart_addr = low;
7808 } else {
7809 _restart_addr = MIN2(_restart_addr, low);
7810 }
7811 }
7812
7813 // Upon stack overflow, we discard (part of) the stack,
7814 // remembering the least address amongst those discarded
7815 // in CMSCollector's _restart_address.
7816 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7817 // Remember the least grey address discarded
7818 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7819 _collector->lower_restart_addr(ra);
7820 _markStack->reset(); // discard stack contents
7821 _markStack->expand(); // expand the stack if possible
7822 }
7823
7824 // Upon stack overflow, we discard (part of) the stack,
7825 // remembering the least address amongst those discarded
7826 // in CMSCollector's _restart_address.
7827 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7828 // We need to do this under a mutex to prevent other
7829 // workers from interfering with the work done below.
7830 MutexLockerEx ml(_overflow_stack->par_lock(),
7831 Mutex::_no_safepoint_check_flag);
7832 // Remember the least grey address discarded
7833 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7834 _collector->lower_restart_addr(ra);
7835 _overflow_stack->reset(); // discard stack contents
7836 _overflow_stack->expand(); // expand the stack if possible
7837 }
7838
7839 void CMKlassClosure::do_klass(Klass* k) {
7840 assert(_oop_closure != NULL, "Not initialized?");
7841 k->oops_do(_oop_closure);
7842 }
7843
7844 void PushOrMarkClosure::do_oop(oop obj) {
7845 // Ignore mark word because we are running concurrent with mutators.
7846 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7847 HeapWord* addr = (HeapWord*)obj;
7848 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7849 // Oop lies in _span and isn't yet grey or black
7850 _bitMap->mark(addr); // now grey
7851 if (addr < _finger) {
7852 // the bit map iteration has already either passed, or
7853 // sampled, this bit in the bit map; we'll need to
7854 // use the marking stack to scan this oop's oops.
7855 bool simulate_overflow = false;
7856 NOT_PRODUCT(
7857 if (CMSMarkStackOverflowALot &&
7858 _collector->simulate_overflow()) {
7859 // simulate a stack overflow
7860 simulate_overflow = true;
7861 }
7862 )
7863 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7864 if (PrintCMSStatistics != 0) {
7865 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7866 SIZE_FORMAT, _markStack->capacity());
7867 }
7868 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7869 handle_stack_overflow(addr);
7870 }
7871 }
7872 // anything including and to the right of _finger
7873 // will be scanned as we iterate over the remainder of the
7874 // bit map
7875 do_yield_check();
7876 }
7877 }
7878
7879 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7880 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7881
7882 void Par_PushOrMarkClosure::do_oop(oop obj) {
7883 // Ignore mark word because we are running concurrent with mutators.
7884 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7885 HeapWord* addr = (HeapWord*)obj;
7886 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7887 // Oop lies in _span and isn't yet grey or black
7888 // We read the global_finger (volatile read) strictly after marking oop
7889 bool res = _bit_map->par_mark(addr); // now grey
7890 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7891 // Should we push this marked oop on our stack?
7892 // -- if someone else marked it, nothing to do
7893 // -- if target oop is above global finger nothing to do
7894 // -- if target oop is in chunk and above local finger
7895 // then nothing to do
7896 // -- else push on work queue
7897 if ( !res // someone else marked it, they will deal with it
7898 || (addr >= *gfa) // will be scanned in a later task
7899 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7900 return;
7901 }
7902 // the bit map iteration has already either passed, or
7903 // sampled, this bit in the bit map; we'll need to
7904 // use the marking stack to scan this oop's oops.
7905 bool simulate_overflow = false;
7906 NOT_PRODUCT(
7907 if (CMSMarkStackOverflowALot &&
7908 _collector->simulate_overflow()) {
7909 // simulate a stack overflow
7910 simulate_overflow = true;
7911 }
7912 )
7913 if (simulate_overflow ||
7914 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7915 // stack overflow
7916 if (PrintCMSStatistics != 0) {
7917 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7918 SIZE_FORMAT, _overflow_stack->capacity());
7919 }
7920 // We cannot assert that the overflow stack is full because
7921 // it may have been emptied since.
7922 assert(simulate_overflow ||
7923 _work_queue->size() == _work_queue->max_elems(),
7924 "Else push should have succeeded");
7925 handle_stack_overflow(addr);
7926 }
7927 do_yield_check();
7928 }
7929 }
7930
7931 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7932 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7933
7934 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7935 MemRegion span,
7936 ReferenceProcessor* rp,
7937 CMSBitMap* bit_map,
7938 CMSBitMap* mod_union_table,
7939 CMSMarkStack* mark_stack,
7940 bool concurrent_precleaning):
7941 CMSOopClosure(rp),
7942 _collector(collector),
7943 _span(span),
7944 _bit_map(bit_map),
7945 _mod_union_table(mod_union_table),
7946 _mark_stack(mark_stack),
7947 _concurrent_precleaning(concurrent_precleaning)
7948 {
7949 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7950 }
7951
7952 // Grey object rescan during pre-cleaning and second checkpoint phases --
7953 // the non-parallel version (the parallel version appears further below.)
7954 void PushAndMarkClosure::do_oop(oop obj) {
7955 // Ignore mark word verification. If during concurrent precleaning,
7956 // the object monitor may be locked. If during the checkpoint
7957 // phases, the object may already have been reached by a different
7958 // path and may be at the end of the global overflow list (so
7959 // the mark word may be NULL).
7960 assert(obj->is_oop_or_null(true /* ignore mark word */),
7961 "expected an oop or NULL");
7962 HeapWord* addr = (HeapWord*)obj;
7963 // Check if oop points into the CMS generation
7964 // and is not marked
7965 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7966 // a white object ...
7967 _bit_map->mark(addr); // ... now grey
7968 // push on the marking stack (grey set)
7969 bool simulate_overflow = false;
7970 NOT_PRODUCT(
7971 if (CMSMarkStackOverflowALot &&
7972 _collector->simulate_overflow()) {
7973 // simulate a stack overflow
7974 simulate_overflow = true;
7975 }
7976 )
7977 if (simulate_overflow || !_mark_stack->push(obj)) {
7978 if (_concurrent_precleaning) {
7979 // During precleaning we can just dirty the appropriate card(s)
7980 // in the mod union table, thus ensuring that the object remains
7981 // in the grey set and continue. In the case of object arrays
7982 // we need to dirty all of the cards that the object spans,
7983 // since the rescan of object arrays will be limited to the
7984 // dirty cards.
7985 // Note that no one can be interfering with us in this action
7986 // of dirtying the mod union table, so no locking or atomics
7987 // are required.
7988 if (obj->is_objArray()) {
7989 size_t sz = obj->size();
7990 HeapWord* end_card_addr = (HeapWord*)round_to(
7991 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7992 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7993 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7994 _mod_union_table->mark_range(redirty_range);
7995 } else {
7996 _mod_union_table->mark(addr);
7997 }
7998 _collector->_ser_pmc_preclean_ovflw++;
7999 } else {
8000 // During the remark phase, we need to remember this oop
8001 // in the overflow list.
8002 _collector->push_on_overflow_list(obj);
8003 _collector->_ser_pmc_remark_ovflw++;
8004 }
8005 }
8006 }
8007 }
8008
8009 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
8010 MemRegion span,
8011 ReferenceProcessor* rp,
8012 CMSBitMap* bit_map,
8013 OopTaskQueue* work_queue):
8014 CMSOopClosure(rp),
8015 _collector(collector),
8016 _span(span),
8017 _bit_map(bit_map),
8018 _work_queue(work_queue)
8019 {
8020 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
8021 }
8022
8023 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
8024 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
8025
8026 // Grey object rescan during second checkpoint phase --
8027 // the parallel version.
8028 void Par_PushAndMarkClosure::do_oop(oop obj) {
8029 // In the assert below, we ignore the mark word because
8030 // this oop may point to an already visited object that is
8031 // on the overflow stack (in which case the mark word has
8032 // been hijacked for chaining into the overflow stack --
8033 // if this is the last object in the overflow stack then
8034 // its mark word will be NULL). Because this object may
8035 // have been subsequently popped off the global overflow
8036 // stack, and the mark word possibly restored to the prototypical
8037 // value, by the time we get to examined this failing assert in
8038 // the debugger, is_oop_or_null(false) may subsequently start
8039 // to hold.
8040 assert(obj->is_oop_or_null(true),
8041 "expected an oop or NULL");
8042 HeapWord* addr = (HeapWord*)obj;
8043 // Check if oop points into the CMS generation
8044 // and is not marked
8045 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
8046 // a white object ...
8047 // If we manage to "claim" the object, by being the
8048 // first thread to mark it, then we push it on our
8049 // marking stack
8050 if (_bit_map->par_mark(addr)) { // ... now grey
8051 // push on work queue (grey set)
8052 bool simulate_overflow = false;
8053 NOT_PRODUCT(
8054 if (CMSMarkStackOverflowALot &&
8055 _collector->par_simulate_overflow()) {
8056 // simulate a stack overflow
8057 simulate_overflow = true;
8058 }
8059 )
8060 if (simulate_overflow || !_work_queue->push(obj)) {
8061 _collector->par_push_on_overflow_list(obj);
8062 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
8063 }
8064 } // Else, some other thread got there first
8065 }
8066 }
8067
8068 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
8069 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
8070
8071 void CMSPrecleanRefsYieldClosure::do_yield_work() {
8072 Mutex* bml = _collector->bitMapLock();
8073 assert_lock_strong(bml);
8074 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8075 "CMS thread should hold CMS token");
8076
8077 bml->unlock();
8078 ConcurrentMarkSweepThread::desynchronize(true);
8079
8080 ConcurrentMarkSweepThread::acknowledge_yield_request();
8081
8082 _collector->stopTimer();
8083 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8084 if (PrintCMSStatistics != 0) {
8085 _collector->incrementYields();
8086 }
8087 _collector->icms_wait();
8088
8089 // See the comment in coordinator_yield()
8090 for (unsigned i = 0; i < CMSYieldSleepCount &&
8091 ConcurrentMarkSweepThread::should_yield() &&
8092 !CMSCollector::foregroundGCIsActive(); ++i) {
8093 os::sleep(Thread::current(), 1, false);
8094 ConcurrentMarkSweepThread::acknowledge_yield_request();
8095 }
8096
8097 ConcurrentMarkSweepThread::synchronize(true);
8098 bml->lock();
8099
8100 _collector->startTimer();
8101 }
8102
8103 bool CMSPrecleanRefsYieldClosure::should_return() {
8104 if (ConcurrentMarkSweepThread::should_yield()) {
8105 do_yield_work();
8106 }
8107 return _collector->foregroundGCIsActive();
8108 }
8109
8110 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
8111 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
8112 "mr should be aligned to start at a card boundary");
8113 // We'd like to assert:
8114 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
8115 // "mr should be a range of cards");
8116 // However, that would be too strong in one case -- the last
8117 // partition ends at _unallocated_block which, in general, can be
8118 // an arbitrary boundary, not necessarily card aligned.
8119 if (PrintCMSStatistics != 0) {
8120 _num_dirty_cards +=
8121 mr.word_size()/CardTableModRefBS::card_size_in_words;
8122 }
8123 _space->object_iterate_mem(mr, &_scan_cl);
8124 }
8125
8126 SweepClosure::SweepClosure(CMSCollector* collector,
8127 ConcurrentMarkSweepGeneration* g,
8128 CMSBitMap* bitMap, bool should_yield) :
8129 _collector(collector),
8130 _g(g),
8131 _sp(g->cmsSpace()),
8132 _limit(_sp->sweep_limit()),
8133 _freelistLock(_sp->freelistLock()),
8134 _bitMap(bitMap),
8135 _yield(should_yield),
8136 _inFreeRange(false), // No free range at beginning of sweep
8137 _freeRangeInFreeLists(false), // No free range at beginning of sweep
8138 _lastFreeRangeCoalesced(false),
8139 _freeFinger(g->used_region().start())
8140 {
8141 NOT_PRODUCT(
8142 _numObjectsFreed = 0;
8143 _numWordsFreed = 0;
8144 _numObjectsLive = 0;
8145 _numWordsLive = 0;
8146 _numObjectsAlreadyFree = 0;
8147 _numWordsAlreadyFree = 0;
8148 _last_fc = NULL;
8149
8150 _sp->initializeIndexedFreeListArrayReturnedBytes();
8151 _sp->dictionary()->initialize_dict_returned_bytes();
8152 )
8153 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8154 "sweep _limit out of bounds");
8155 if (CMSTraceSweeper) {
8156 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
8157 _limit);
8158 }
8159 }
8160
8161 void SweepClosure::print_on(outputStream* st) const {
8162 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
8163 _sp->bottom(), _sp->end());
8164 tty->print_cr("_limit = " PTR_FORMAT, _limit);
8165 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
8166 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
8167 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
8168 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
8169 }
8170
8171 #ifndef PRODUCT
8172 // Assertion checking only: no useful work in product mode --
8173 // however, if any of the flags below become product flags,
8174 // you may need to review this code to see if it needs to be
8175 // enabled in product mode.
8176 SweepClosure::~SweepClosure() {
8177 assert_lock_strong(_freelistLock);
8178 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8179 "sweep _limit out of bounds");
8180 if (inFreeRange()) {
8181 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
8182 print();
8183 ShouldNotReachHere();
8184 }
8185 if (Verbose && PrintGC) {
8186 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
8187 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
8188 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
8189 SIZE_FORMAT" bytes "
8190 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
8191 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
8192 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
8193 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
8194 * sizeof(HeapWord);
8195 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
8196
8197 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
8198 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
8199 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
8200 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
8201 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
8202 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
8203 indexListReturnedBytes);
8204 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
8205 dict_returned_bytes);
8206 }
8207 }
8208 if (CMSTraceSweeper) {
8209 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
8210 _limit);
8211 }
8212 }
8213 #endif // PRODUCT
8214
8215 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
8216 bool freeRangeInFreeLists) {
8217 if (CMSTraceSweeper) {
8218 gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n",
8219 freeFinger, freeRangeInFreeLists);
8220 }
8221 assert(!inFreeRange(), "Trampling existing free range");
8222 set_inFreeRange(true);
8223 set_lastFreeRangeCoalesced(false);
8224
8225 set_freeFinger(freeFinger);
8226 set_freeRangeInFreeLists(freeRangeInFreeLists);
8227 if (CMSTestInFreeList) {
8228 if (freeRangeInFreeLists) {
8229 FreeChunk* fc = (FreeChunk*) freeFinger;
8230 assert(fc->is_free(), "A chunk on the free list should be free.");
8231 assert(fc->size() > 0, "Free range should have a size");
8232 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
8233 }
8234 }
8235 }
8236
8237 // Note that the sweeper runs concurrently with mutators. Thus,
8238 // it is possible for direct allocation in this generation to happen
8239 // in the middle of the sweep. Note that the sweeper also coalesces
8240 // contiguous free blocks. Thus, unless the sweeper and the allocator
8241 // synchronize appropriately freshly allocated blocks may get swept up.
8242 // This is accomplished by the sweeper locking the free lists while
8243 // it is sweeping. Thus blocks that are determined to be free are
8244 // indeed free. There is however one additional complication:
8245 // blocks that have been allocated since the final checkpoint and
8246 // mark, will not have been marked and so would be treated as
8247 // unreachable and swept up. To prevent this, the allocator marks
8248 // the bit map when allocating during the sweep phase. This leads,
8249 // however, to a further complication -- objects may have been allocated
8250 // but not yet initialized -- in the sense that the header isn't yet
8251 // installed. The sweeper can not then determine the size of the block
8252 // in order to skip over it. To deal with this case, we use a technique
8253 // (due to Printezis) to encode such uninitialized block sizes in the
8254 // bit map. Since the bit map uses a bit per every HeapWord, but the
8255 // CMS generation has a minimum object size of 3 HeapWords, it follows
8256 // that "normal marks" won't be adjacent in the bit map (there will
8257 // always be at least two 0 bits between successive 1 bits). We make use
8258 // of these "unused" bits to represent uninitialized blocks -- the bit
8259 // corresponding to the start of the uninitialized object and the next
8260 // bit are both set. Finally, a 1 bit marks the end of the object that
8261 // started with the two consecutive 1 bits to indicate its potentially
8262 // uninitialized state.
8263
8264 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8265 FreeChunk* fc = (FreeChunk*)addr;
8266 size_t res;
8267
8268 // Check if we are done sweeping. Below we check "addr >= _limit" rather
8269 // than "addr == _limit" because although _limit was a block boundary when
8270 // we started the sweep, it may no longer be one because heap expansion
8271 // may have caused us to coalesce the block ending at the address _limit
8272 // with a newly expanded chunk (this happens when _limit was set to the
8273 // previous _end of the space), so we may have stepped past _limit:
8274 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8275 if (addr >= _limit) { // we have swept up to or past the limit: finish up
8276 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8277 "sweep _limit out of bounds");
8278 assert(addr < _sp->end(), "addr out of bounds");
8279 // Flush any free range we might be holding as a single
8280 // coalesced chunk to the appropriate free list.
8281 if (inFreeRange()) {
8282 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8283 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8284 flush_cur_free_chunk(freeFinger(),
8285 pointer_delta(addr, freeFinger()));
8286 if (CMSTraceSweeper) {
8287 gclog_or_tty->print("Sweep: last chunk: ");
8288 gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") "
8289 "[coalesced:"SIZE_FORMAT"]\n",
8290 freeFinger(), pointer_delta(addr, freeFinger()),
8291 lastFreeRangeCoalesced());
8292 }
8293 }
8294
8295 // help the iterator loop finish
8296 return pointer_delta(_sp->end(), addr);
8297 }
8298
8299 assert(addr < _limit, "sweep invariant");
8300 // check if we should yield
8301 do_yield_check(addr);
8302 if (fc->is_free()) {
8303 // Chunk that is already free
8304 res = fc->size();
8305 do_already_free_chunk(fc);
8306 debug_only(_sp->verifyFreeLists());
8307 // If we flush the chunk at hand in lookahead_and_flush()
8308 // and it's coalesced with a preceding chunk, then the
8309 // process of "mangling" the payload of the coalesced block
8310 // will cause erasure of the size information from the
8311 // (erstwhile) header of all the coalesced blocks but the
8312 // first, so the first disjunct in the assert will not hold
8313 // in that specific case (in which case the second disjunct
8314 // will hold).
8315 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8316 "Otherwise the size info doesn't change at this step");
8317 NOT_PRODUCT(
8318 _numObjectsAlreadyFree++;
8319 _numWordsAlreadyFree += res;
8320 )
8321 NOT_PRODUCT(_last_fc = fc;)
8322 } else if (!_bitMap->isMarked(addr)) {
8323 // Chunk is fresh garbage
8324 res = do_garbage_chunk(fc);
8325 debug_only(_sp->verifyFreeLists());
8326 NOT_PRODUCT(
8327 _numObjectsFreed++;
8328 _numWordsFreed += res;
8329 )
8330 } else {
8331 // Chunk that is alive.
8332 res = do_live_chunk(fc);
8333 debug_only(_sp->verifyFreeLists());
8334 NOT_PRODUCT(
8335 _numObjectsLive++;
8336 _numWordsLive += res;
8337 )
8338 }
8339 return res;
8340 }
8341
8342 // For the smart allocation, record following
8343 // split deaths - a free chunk is removed from its free list because
8344 // it is being split into two or more chunks.
8345 // split birth - a free chunk is being added to its free list because
8346 // a larger free chunk has been split and resulted in this free chunk.
8347 // coal death - a free chunk is being removed from its free list because
8348 // it is being coalesced into a large free chunk.
8349 // coal birth - a free chunk is being added to its free list because
8350 // it was created when two or more free chunks where coalesced into
8351 // this free chunk.
8352 //
8353 // These statistics are used to determine the desired number of free
8354 // chunks of a given size. The desired number is chosen to be relative
8355 // to the end of a CMS sweep. The desired number at the end of a sweep
8356 // is the
8357 // count-at-end-of-previous-sweep (an amount that was enough)
8358 // - count-at-beginning-of-current-sweep (the excess)
8359 // + split-births (gains in this size during interval)
8360 // - split-deaths (demands on this size during interval)
8361 // where the interval is from the end of one sweep to the end of the
8362 // next.
8363 //
8364 // When sweeping the sweeper maintains an accumulated chunk which is
8365 // the chunk that is made up of chunks that have been coalesced. That
8366 // will be termed the left-hand chunk. A new chunk of garbage that
8367 // is being considered for coalescing will be referred to as the
8368 // right-hand chunk.
8369 //
8370 // When making a decision on whether to coalesce a right-hand chunk with
8371 // the current left-hand chunk, the current count vs. the desired count
8372 // of the left-hand chunk is considered. Also if the right-hand chunk
8373 // is near the large chunk at the end of the heap (see
8374 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8375 // left-hand chunk is coalesced.
8376 //
8377 // When making a decision about whether to split a chunk, the desired count
8378 // vs. the current count of the candidate to be split is also considered.
8379 // If the candidate is underpopulated (currently fewer chunks than desired)
8380 // a chunk of an overpopulated (currently more chunks than desired) size may
8381 // be chosen. The "hint" associated with a free list, if non-null, points
8382 // to a free list which may be overpopulated.
8383 //
8384
8385 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8386 const size_t size = fc->size();
8387 // Chunks that cannot be coalesced are not in the
8388 // free lists.
8389 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8390 assert(_sp->verify_chunk_in_free_list(fc),
8391 "free chunk should be in free lists");
8392 }
8393 // a chunk that is already free, should not have been
8394 // marked in the bit map
8395 HeapWord* const addr = (HeapWord*) fc;
8396 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8397 // Verify that the bit map has no bits marked between
8398 // addr and purported end of this block.
8399 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8400
8401 // Some chunks cannot be coalesced under any circumstances.
8402 // See the definition of cantCoalesce().
8403 if (!fc->cantCoalesce()) {
8404 // This chunk can potentially be coalesced.
8405 if (_sp->adaptive_freelists()) {
8406 // All the work is done in
8407 do_post_free_or_garbage_chunk(fc, size);
8408 } else { // Not adaptive free lists
8409 // this is a free chunk that can potentially be coalesced by the sweeper;
8410 if (!inFreeRange()) {
8411 // if the next chunk is a free block that can't be coalesced
8412 // it doesn't make sense to remove this chunk from the free lists
8413 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8414 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8415 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8416 nextChunk->is_free() && // ... which is free...
8417 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8418 // nothing to do
8419 } else {
8420 // Potentially the start of a new free range:
8421 // Don't eagerly remove it from the free lists.
8422 // No need to remove it if it will just be put
8423 // back again. (Also from a pragmatic point of view
8424 // if it is a free block in a region that is beyond
8425 // any allocated blocks, an assertion will fail)
8426 // Remember the start of a free run.
8427 initialize_free_range(addr, true);
8428 // end - can coalesce with next chunk
8429 }
8430 } else {
8431 // the midst of a free range, we are coalescing
8432 print_free_block_coalesced(fc);
8433 if (CMSTraceSweeper) {
8434 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
8435 }
8436 // remove it from the free lists
8437 _sp->removeFreeChunkFromFreeLists(fc);
8438 set_lastFreeRangeCoalesced(true);
8439 // If the chunk is being coalesced and the current free range is
8440 // in the free lists, remove the current free range so that it
8441 // will be returned to the free lists in its entirety - all
8442 // the coalesced pieces included.
8443 if (freeRangeInFreeLists()) {
8444 FreeChunk* ffc = (FreeChunk*) freeFinger();
8445 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8446 "Size of free range is inconsistent with chunk size.");
8447 if (CMSTestInFreeList) {
8448 assert(_sp->verify_chunk_in_free_list(ffc),
8449 "free range is not in free lists");
8450 }
8451 _sp->removeFreeChunkFromFreeLists(ffc);
8452 set_freeRangeInFreeLists(false);
8453 }
8454 }
8455 }
8456 // Note that if the chunk is not coalescable (the else arm
8457 // below), we unconditionally flush, without needing to do
8458 // a "lookahead," as we do below.
8459 if (inFreeRange()) lookahead_and_flush(fc, size);
8460 } else {
8461 // Code path common to both original and adaptive free lists.
8462
8463 // cant coalesce with previous block; this should be treated
8464 // as the end of a free run if any
8465 if (inFreeRange()) {
8466 // we kicked some butt; time to pick up the garbage
8467 assert(freeFinger() < addr, "freeFinger points too high");
8468 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8469 }
8470 // else, nothing to do, just continue
8471 }
8472 }
8473
8474 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8475 // This is a chunk of garbage. It is not in any free list.
8476 // Add it to a free list or let it possibly be coalesced into
8477 // a larger chunk.
8478 HeapWord* const addr = (HeapWord*) fc;
8479 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8480
8481 if (_sp->adaptive_freelists()) {
8482 // Verify that the bit map has no bits marked between
8483 // addr and purported end of just dead object.
8484 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8485
8486 do_post_free_or_garbage_chunk(fc, size);
8487 } else {
8488 if (!inFreeRange()) {
8489 // start of a new free range
8490 assert(size > 0, "A free range should have a size");
8491 initialize_free_range(addr, false);
8492 } else {
8493 // this will be swept up when we hit the end of the
8494 // free range
8495 if (CMSTraceSweeper) {
8496 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
8497 }
8498 // If the chunk is being coalesced and the current free range is
8499 // in the free lists, remove the current free range so that it
8500 // will be returned to the free lists in its entirety - all
8501 // the coalesced pieces included.
8502 if (freeRangeInFreeLists()) {
8503 FreeChunk* ffc = (FreeChunk*)freeFinger();
8504 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8505 "Size of free range is inconsistent with chunk size.");
8506 if (CMSTestInFreeList) {
8507 assert(_sp->verify_chunk_in_free_list(ffc),
8508 "free range is not in free lists");
8509 }
8510 _sp->removeFreeChunkFromFreeLists(ffc);
8511 set_freeRangeInFreeLists(false);
8512 }
8513 set_lastFreeRangeCoalesced(true);
8514 }
8515 // this will be swept up when we hit the end of the free range
8516
8517 // Verify that the bit map has no bits marked between
8518 // addr and purported end of just dead object.
8519 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8520 }
8521 assert(_limit >= addr + size,
8522 "A freshly garbage chunk can't possibly straddle over _limit");
8523 if (inFreeRange()) lookahead_and_flush(fc, size);
8524 return size;
8525 }
8526
8527 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8528 HeapWord* addr = (HeapWord*) fc;
8529 // The sweeper has just found a live object. Return any accumulated
8530 // left hand chunk to the free lists.
8531 if (inFreeRange()) {
8532 assert(freeFinger() < addr, "freeFinger points too high");
8533 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8534 }
8535
8536 // This object is live: we'd normally expect this to be
8537 // an oop, and like to assert the following:
8538 // assert(oop(addr)->is_oop(), "live block should be an oop");
8539 // However, as we commented above, this may be an object whose
8540 // header hasn't yet been initialized.
8541 size_t size;
8542 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8543 if (_bitMap->isMarked(addr + 1)) {
8544 // Determine the size from the bit map, rather than trying to
8545 // compute it from the object header.
8546 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8547 size = pointer_delta(nextOneAddr + 1, addr);
8548 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8549 "alignment problem");
8550
8551 #ifdef ASSERT
8552 if (oop(addr)->klass_or_null() != NULL) {
8553 // Ignore mark word because we are running concurrent with mutators
8554 assert(oop(addr)->is_oop(true), "live block should be an oop");
8555 assert(size ==
8556 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8557 "P-mark and computed size do not agree");
8558 }
8559 #endif
8560
8561 } else {
8562 // This should be an initialized object that's alive.
8563 assert(oop(addr)->klass_or_null() != NULL,
8564 "Should be an initialized object");
8565 // Ignore mark word because we are running concurrent with mutators
8566 assert(oop(addr)->is_oop(true), "live block should be an oop");
8567 // Verify that the bit map has no bits marked between
8568 // addr and purported end of this block.
8569 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8570 assert(size >= 3, "Necessary for Printezis marks to work");
8571 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8572 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8573 }
8574 return size;
8575 }
8576
8577 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8578 size_t chunkSize) {
8579 // do_post_free_or_garbage_chunk() should only be called in the case
8580 // of the adaptive free list allocator.
8581 const bool fcInFreeLists = fc->is_free();
8582 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8583 assert((HeapWord*)fc <= _limit, "sweep invariant");
8584 if (CMSTestInFreeList && fcInFreeLists) {
8585 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8586 }
8587
8588 if (CMSTraceSweeper) {
8589 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8590 }
8591
8592 HeapWord* const fc_addr = (HeapWord*) fc;
8593
8594 bool coalesce;
8595 const size_t left = pointer_delta(fc_addr, freeFinger());
8596 const size_t right = chunkSize;
8597 switch (FLSCoalescePolicy) {
8598 // numeric value forms a coalition aggressiveness metric
8599 case 0: { // never coalesce
8600 coalesce = false;
8601 break;
8602 }
8603 case 1: { // coalesce if left & right chunks on overpopulated lists
8604 coalesce = _sp->coalOverPopulated(left) &&
8605 _sp->coalOverPopulated(right);
8606 break;
8607 }
8608 case 2: { // coalesce if left chunk on overpopulated list (default)
8609 coalesce = _sp->coalOverPopulated(left);
8610 break;
8611 }
8612 case 3: { // coalesce if left OR right chunk on overpopulated list
8613 coalesce = _sp->coalOverPopulated(left) ||
8614 _sp->coalOverPopulated(right);
8615 break;
8616 }
8617 case 4: { // always coalesce
8618 coalesce = true;
8619 break;
8620 }
8621 default:
8622 ShouldNotReachHere();
8623 }
8624
8625 // Should the current free range be coalesced?
8626 // If the chunk is in a free range and either we decided to coalesce above
8627 // or the chunk is near the large block at the end of the heap
8628 // (isNearLargestChunk() returns true), then coalesce this chunk.
8629 const bool doCoalesce = inFreeRange()
8630 && (coalesce || _g->isNearLargestChunk(fc_addr));
8631 if (doCoalesce) {
8632 // Coalesce the current free range on the left with the new
8633 // chunk on the right. If either is on a free list,
8634 // it must be removed from the list and stashed in the closure.
8635 if (freeRangeInFreeLists()) {
8636 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8637 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8638 "Size of free range is inconsistent with chunk size.");
8639 if (CMSTestInFreeList) {
8640 assert(_sp->verify_chunk_in_free_list(ffc),
8641 "Chunk is not in free lists");
8642 }
8643 _sp->coalDeath(ffc->size());
8644 _sp->removeFreeChunkFromFreeLists(ffc);
8645 set_freeRangeInFreeLists(false);
8646 }
8647 if (fcInFreeLists) {
8648 _sp->coalDeath(chunkSize);
8649 assert(fc->size() == chunkSize,
8650 "The chunk has the wrong size or is not in the free lists");
8651 _sp->removeFreeChunkFromFreeLists(fc);
8652 }
8653 set_lastFreeRangeCoalesced(true);
8654 print_free_block_coalesced(fc);
8655 } else { // not in a free range and/or should not coalesce
8656 // Return the current free range and start a new one.
8657 if (inFreeRange()) {
8658 // In a free range but cannot coalesce with the right hand chunk.
8659 // Put the current free range into the free lists.
8660 flush_cur_free_chunk(freeFinger(),
8661 pointer_delta(fc_addr, freeFinger()));
8662 }
8663 // Set up for new free range. Pass along whether the right hand
8664 // chunk is in the free lists.
8665 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8666 }
8667 }
8668
8669 // Lookahead flush:
8670 // If we are tracking a free range, and this is the last chunk that
8671 // we'll look at because its end crosses past _limit, we'll preemptively
8672 // flush it along with any free range we may be holding on to. Note that
8673 // this can be the case only for an already free or freshly garbage
8674 // chunk. If this block is an object, it can never straddle
8675 // over _limit. The "straddling" occurs when _limit is set at
8676 // the previous end of the space when this cycle started, and
8677 // a subsequent heap expansion caused the previously co-terminal
8678 // free block to be coalesced with the newly expanded portion,
8679 // thus rendering _limit a non-block-boundary making it dangerous
8680 // for the sweeper to step over and examine.
8681 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8682 assert(inFreeRange(), "Should only be called if currently in a free range.");
8683 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8684 assert(_sp->used_region().contains(eob - 1),
8685 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
8686 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8687 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8688 eob, eob-1, _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8689 if (eob >= _limit) {
8690 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8691 if (CMSTraceSweeper) {
8692 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8693 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8694 "[" PTR_FORMAT "," PTR_FORMAT ")",
8695 _limit, fc, eob, _sp->bottom(), _sp->end());
8696 }
8697 // Return the storage we are tracking back into the free lists.
8698 if (CMSTraceSweeper) {
8699 gclog_or_tty->print_cr("Flushing ... ");
8700 }
8701 assert(freeFinger() < eob, "Error");
8702 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8703 }
8704 }
8705
8706 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8707 assert(inFreeRange(), "Should only be called if currently in a free range.");
8708 assert(size > 0,
8709 "A zero sized chunk cannot be added to the free lists.");
8710 if (!freeRangeInFreeLists()) {
8711 if (CMSTestInFreeList) {
8712 FreeChunk* fc = (FreeChunk*) chunk;
8713 fc->set_size(size);
8714 assert(!_sp->verify_chunk_in_free_list(fc),
8715 "chunk should not be in free lists yet");
8716 }
8717 if (CMSTraceSweeper) {
8718 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8719 chunk, size);
8720 }
8721 // A new free range is going to be starting. The current
8722 // free range has not been added to the free lists yet or
8723 // was removed so add it back.
8724 // If the current free range was coalesced, then the death
8725 // of the free range was recorded. Record a birth now.
8726 if (lastFreeRangeCoalesced()) {
8727 _sp->coalBirth(size);
8728 }
8729 _sp->addChunkAndRepairOffsetTable(chunk, size,
8730 lastFreeRangeCoalesced());
8731 } else if (CMSTraceSweeper) {
8732 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8733 }
8734 set_inFreeRange(false);
8735 set_freeRangeInFreeLists(false);
8736 }
8737
8738 // We take a break if we've been at this for a while,
8739 // so as to avoid monopolizing the locks involved.
8740 void SweepClosure::do_yield_work(HeapWord* addr) {
8741 // Return current free chunk being used for coalescing (if any)
8742 // to the appropriate freelist. After yielding, the next
8743 // free block encountered will start a coalescing range of
8744 // free blocks. If the next free block is adjacent to the
8745 // chunk just flushed, they will need to wait for the next
8746 // sweep to be coalesced.
8747 if (inFreeRange()) {
8748 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8749 }
8750
8751 // First give up the locks, then yield, then re-lock.
8752 // We should probably use a constructor/destructor idiom to
8753 // do this unlock/lock or modify the MutexUnlocker class to
8754 // serve our purpose. XXX
8755 assert_lock_strong(_bitMap->lock());
8756 assert_lock_strong(_freelistLock);
8757 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8758 "CMS thread should hold CMS token");
8759 _bitMap->lock()->unlock();
8760 _freelistLock->unlock();
8761 ConcurrentMarkSweepThread::desynchronize(true);
8762 ConcurrentMarkSweepThread::acknowledge_yield_request();
8763 _collector->stopTimer();
8764 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8765 if (PrintCMSStatistics != 0) {
8766 _collector->incrementYields();
8767 }
8768 _collector->icms_wait();
8769
8770 // See the comment in coordinator_yield()
8771 for (unsigned i = 0; i < CMSYieldSleepCount &&
8772 ConcurrentMarkSweepThread::should_yield() &&
8773 !CMSCollector::foregroundGCIsActive(); ++i) {
8774 os::sleep(Thread::current(), 1, false);
8775 ConcurrentMarkSweepThread::acknowledge_yield_request();
8776 }
8777
8778 ConcurrentMarkSweepThread::synchronize(true);
8779 _freelistLock->lock();
8780 _bitMap->lock()->lock_without_safepoint_check();
8781 _collector->startTimer();
8782 }
8783
8784 #ifndef PRODUCT
8785 // This is actually very useful in a product build if it can
8786 // be called from the debugger. Compile it into the product
8787 // as needed.
8788 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8789 return debug_cms_space->verify_chunk_in_free_list(fc);
8790 }
8791 #endif
8792
8793 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8794 if (CMSTraceSweeper) {
8795 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8796 fc, fc->size());
8797 }
8798 }
8799
8800 // CMSIsAliveClosure
8801 bool CMSIsAliveClosure::do_object_b(oop obj) {
8802 HeapWord* addr = (HeapWord*)obj;
8803 return addr != NULL &&
8804 (!_span.contains(addr) || _bit_map->isMarked(addr));
8805 }
8806
8807
8808 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8809 MemRegion span,
8810 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8811 bool cpc):
8812 _collector(collector),
8813 _span(span),
8814 _bit_map(bit_map),
8815 _mark_stack(mark_stack),
8816 _concurrent_precleaning(cpc) {
8817 assert(!_span.is_empty(), "Empty span could spell trouble");
8818 }
8819
8820
8821 // CMSKeepAliveClosure: the serial version
8822 void CMSKeepAliveClosure::do_oop(oop obj) {
8823 HeapWord* addr = (HeapWord*)obj;
8824 if (_span.contains(addr) &&
8825 !_bit_map->isMarked(addr)) {
8826 _bit_map->mark(addr);
8827 bool simulate_overflow = false;
8828 NOT_PRODUCT(
8829 if (CMSMarkStackOverflowALot &&
8830 _collector->simulate_overflow()) {
8831 // simulate a stack overflow
8832 simulate_overflow = true;
8833 }
8834 )
8835 if (simulate_overflow || !_mark_stack->push(obj)) {
8836 if (_concurrent_precleaning) {
8837 // We dirty the overflown object and let the remark
8838 // phase deal with it.
8839 assert(_collector->overflow_list_is_empty(), "Error");
8840 // In the case of object arrays, we need to dirty all of
8841 // the cards that the object spans. No locking or atomics
8842 // are needed since no one else can be mutating the mod union
8843 // table.
8844 if (obj->is_objArray()) {
8845 size_t sz = obj->size();
8846 HeapWord* end_card_addr =
8847 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8848 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8849 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8850 _collector->_modUnionTable.mark_range(redirty_range);
8851 } else {
8852 _collector->_modUnionTable.mark(addr);
8853 }
8854 _collector->_ser_kac_preclean_ovflw++;
8855 } else {
8856 _collector->push_on_overflow_list(obj);
8857 _collector->_ser_kac_ovflw++;
8858 }
8859 }
8860 }
8861 }
8862
8863 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8864 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8865
8866 // CMSParKeepAliveClosure: a parallel version of the above.
8867 // The work queues are private to each closure (thread),
8868 // but (may be) available for stealing by other threads.
8869 void CMSParKeepAliveClosure::do_oop(oop obj) {
8870 HeapWord* addr = (HeapWord*)obj;
8871 if (_span.contains(addr) &&
8872 !_bit_map->isMarked(addr)) {
8873 // In general, during recursive tracing, several threads
8874 // may be concurrently getting here; the first one to
8875 // "tag" it, claims it.
8876 if (_bit_map->par_mark(addr)) {
8877 bool res = _work_queue->push(obj);
8878 assert(res, "Low water mark should be much less than capacity");
8879 // Do a recursive trim in the hope that this will keep
8880 // stack usage lower, but leave some oops for potential stealers
8881 trim_queue(_low_water_mark);
8882 } // Else, another thread got there first
8883 }
8884 }
8885
8886 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8887 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8888
8889 void CMSParKeepAliveClosure::trim_queue(uint max) {
8890 while (_work_queue->size() > max) {
8891 oop new_oop;
8892 if (_work_queue->pop_local(new_oop)) {
8893 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8894 assert(_bit_map->isMarked((HeapWord*)new_oop),
8895 "no white objects on this stack!");
8896 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8897 // iterate over the oops in this oop, marking and pushing
8898 // the ones in CMS heap (i.e. in _span).
8899 new_oop->oop_iterate(&_mark_and_push);
8900 }
8901 }
8902 }
8903
8904 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8905 CMSCollector* collector,
8906 MemRegion span, CMSBitMap* bit_map,
8907 OopTaskQueue* work_queue):
8908 _collector(collector),
8909 _span(span),
8910 _bit_map(bit_map),
8911 _work_queue(work_queue) { }
8912
8913 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8914 HeapWord* addr = (HeapWord*)obj;
8915 if (_span.contains(addr) &&
8916 !_bit_map->isMarked(addr)) {
8917 if (_bit_map->par_mark(addr)) {
8918 bool simulate_overflow = false;
8919 NOT_PRODUCT(
8920 if (CMSMarkStackOverflowALot &&
8921 _collector->par_simulate_overflow()) {
8922 // simulate a stack overflow
8923 simulate_overflow = true;
8924 }
8925 )
8926 if (simulate_overflow || !_work_queue->push(obj)) {
8927 _collector->par_push_on_overflow_list(obj);
8928 _collector->_par_kac_ovflw++;
8929 }
8930 } // Else another thread got there already
8931 }
8932 }
8933
8934 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8935 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8936
8937 //////////////////////////////////////////////////////////////////
8938 // CMSExpansionCause /////////////////////////////
8939 //////////////////////////////////////////////////////////////////
8940 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8941 switch (cause) {
8942 case _no_expansion:
8943 return "No expansion";
8944 case _satisfy_free_ratio:
8945 return "Free ratio";
8946 case _satisfy_promotion:
8947 return "Satisfy promotion";
8948 case _satisfy_allocation:
8949 return "allocation";
8950 case _allocate_par_lab:
8951 return "Par LAB";
8952 case _allocate_par_spooling_space:
8953 return "Par Spooling Space";
8954 case _adaptive_size_policy:
8955 return "Ergonomics";
8956 default:
8957 return "unknown";
8958 }
8959 }
8960
8961 void CMSDrainMarkingStackClosure::do_void() {
8962 // the max number to take from overflow list at a time
8963 const size_t num = _mark_stack->capacity()/4;
8964 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8965 "Overflow list should be NULL during concurrent phases");
8966 while (!_mark_stack->isEmpty() ||
8967 // if stack is empty, check the overflow list
8968 _collector->take_from_overflow_list(num, _mark_stack)) {
8969 oop obj = _mark_stack->pop();
8970 HeapWord* addr = (HeapWord*)obj;
8971 assert(_span.contains(addr), "Should be within span");
8972 assert(_bit_map->isMarked(addr), "Should be marked");
8973 assert(obj->is_oop(), "Should be an oop");
8974 obj->oop_iterate(_keep_alive);
8975 }
8976 }
8977
8978 void CMSParDrainMarkingStackClosure::do_void() {
8979 // drain queue
8980 trim_queue(0);
8981 }
8982
8983 // Trim our work_queue so its length is below max at return
8984 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8985 while (_work_queue->size() > max) {
8986 oop new_oop;
8987 if (_work_queue->pop_local(new_oop)) {
8988 assert(new_oop->is_oop(), "Expected an oop");
8989 assert(_bit_map->isMarked((HeapWord*)new_oop),
8990 "no white objects on this stack!");
8991 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8992 // iterate over the oops in this oop, marking and pushing
8993 // the ones in CMS heap (i.e. in _span).
8994 new_oop->oop_iterate(&_mark_and_push);
8995 }
8996 }
8997 }
8998
8999 ////////////////////////////////////////////////////////////////////
9000 // Support for Marking Stack Overflow list handling and related code
9001 ////////////////////////////////////////////////////////////////////
9002 // Much of the following code is similar in shape and spirit to the
9003 // code used in ParNewGC. We should try and share that code
9004 // as much as possible in the future.
9005
9006 #ifndef PRODUCT
9007 // Debugging support for CMSStackOverflowALot
9008
9009 // It's OK to call this multi-threaded; the worst thing
9010 // that can happen is that we'll get a bunch of closely
9011 // spaced simulated overflows, but that's OK, in fact
9012 // probably good as it would exercise the overflow code
9013 // under contention.
9014 bool CMSCollector::simulate_overflow() {
9015 if (_overflow_counter-- <= 0) { // just being defensive
9016 _overflow_counter = CMSMarkStackOverflowInterval;
9017 return true;
9018 } else {
9019 return false;
9020 }
9021 }
9022
9023 bool CMSCollector::par_simulate_overflow() {
9024 return simulate_overflow();
9025 }
9026 #endif
9027
9028 // Single-threaded
9029 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
9030 assert(stack->isEmpty(), "Expected precondition");
9031 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
9032 size_t i = num;
9033 oop cur = _overflow_list;
9034 const markOop proto = markOopDesc::prototype();
9035 NOT_PRODUCT(ssize_t n = 0;)
9036 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
9037 next = oop(cur->mark());
9038 cur->set_mark(proto); // until proven otherwise
9039 assert(cur->is_oop(), "Should be an oop");
9040 bool res = stack->push(cur);
9041 assert(res, "Bit off more than can chew?");
9042 NOT_PRODUCT(n++;)
9043 }
9044 _overflow_list = cur;
9045 #ifndef PRODUCT
9046 assert(_num_par_pushes >= n, "Too many pops?");
9047 _num_par_pushes -=n;
9048 #endif
9049 return !stack->isEmpty();
9050 }
9051
9052 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
9053 // (MT-safe) Get a prefix of at most "num" from the list.
9054 // The overflow list is chained through the mark word of
9055 // each object in the list. We fetch the entire list,
9056 // break off a prefix of the right size and return the
9057 // remainder. If other threads try to take objects from
9058 // the overflow list at that time, they will wait for
9059 // some time to see if data becomes available. If (and
9060 // only if) another thread places one or more object(s)
9061 // on the global list before we have returned the suffix
9062 // to the global list, we will walk down our local list
9063 // to find its end and append the global list to
9064 // our suffix before returning it. This suffix walk can
9065 // prove to be expensive (quadratic in the amount of traffic)
9066 // when there are many objects in the overflow list and
9067 // there is much producer-consumer contention on the list.
9068 // *NOTE*: The overflow list manipulation code here and
9069 // in ParNewGeneration:: are very similar in shape,
9070 // except that in the ParNew case we use the old (from/eden)
9071 // copy of the object to thread the list via its klass word.
9072 // Because of the common code, if you make any changes in
9073 // the code below, please check the ParNew version to see if
9074 // similar changes might be needed.
9075 // CR 6797058 has been filed to consolidate the common code.
9076 bool CMSCollector::par_take_from_overflow_list(size_t num,
9077 OopTaskQueue* work_q,
9078 int no_of_gc_threads) {
9079 assert(work_q->size() == 0, "First empty local work queue");
9080 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
9081 if (_overflow_list == NULL) {
9082 return false;
9083 }
9084 // Grab the entire list; we'll put back a suffix
9085 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9086 Thread* tid = Thread::current();
9087 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
9088 // set to ParallelGCThreads.
9089 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
9090 size_t sleep_time_millis = MAX2((size_t)1, num/100);
9091 // If the list is busy, we spin for a short while,
9092 // sleeping between attempts to get the list.
9093 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
9094 os::sleep(tid, sleep_time_millis, false);
9095 if (_overflow_list == NULL) {
9096 // Nothing left to take
9097 return false;
9098 } else if (_overflow_list != BUSY) {
9099 // Try and grab the prefix
9100 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9101 }
9102 }
9103 // If the list was found to be empty, or we spun long
9104 // enough, we give up and return empty-handed. If we leave
9105 // the list in the BUSY state below, it must be the case that
9106 // some other thread holds the overflow list and will set it
9107 // to a non-BUSY state in the future.
9108 if (prefix == NULL || prefix == BUSY) {
9109 // Nothing to take or waited long enough
9110 if (prefix == NULL) {
9111 // Write back the NULL in case we overwrote it with BUSY above
9112 // and it is still the same value.
9113 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9114 }
9115 return false;
9116 }
9117 assert(prefix != NULL && prefix != BUSY, "Error");
9118 size_t i = num;
9119 oop cur = prefix;
9120 // Walk down the first "num" objects, unless we reach the end.
9121 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
9122 if (cur->mark() == NULL) {
9123 // We have "num" or fewer elements in the list, so there
9124 // is nothing to return to the global list.
9125 // Write back the NULL in lieu of the BUSY we wrote
9126 // above, if it is still the same value.
9127 if (_overflow_list == BUSY) {
9128 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9129 }
9130 } else {
9131 // Chop off the suffix and return it to the global list.
9132 assert(cur->mark() != BUSY, "Error");
9133 oop suffix_head = cur->mark(); // suffix will be put back on global list
9134 cur->set_mark(NULL); // break off suffix
9135 // It's possible that the list is still in the empty(busy) state
9136 // we left it in a short while ago; in that case we may be
9137 // able to place back the suffix without incurring the cost
9138 // of a walk down the list.
9139 oop observed_overflow_list = _overflow_list;
9140 oop cur_overflow_list = observed_overflow_list;
9141 bool attached = false;
9142 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
9143 observed_overflow_list =
9144 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9145 if (cur_overflow_list == observed_overflow_list) {
9146 attached = true;
9147 break;
9148 } else cur_overflow_list = observed_overflow_list;
9149 }
9150 if (!attached) {
9151 // Too bad, someone else sneaked in (at least) an element; we'll need
9152 // to do a splice. Find tail of suffix so we can prepend suffix to global
9153 // list.
9154 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
9155 oop suffix_tail = cur;
9156 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
9157 "Tautology");
9158 observed_overflow_list = _overflow_list;
9159 do {
9160 cur_overflow_list = observed_overflow_list;
9161 if (cur_overflow_list != BUSY) {
9162 // Do the splice ...
9163 suffix_tail->set_mark(markOop(cur_overflow_list));
9164 } else { // cur_overflow_list == BUSY
9165 suffix_tail->set_mark(NULL);
9166 }
9167 // ... and try to place spliced list back on overflow_list ...
9168 observed_overflow_list =
9169 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9170 } while (cur_overflow_list != observed_overflow_list);
9171 // ... until we have succeeded in doing so.
9172 }
9173 }
9174
9175 // Push the prefix elements on work_q
9176 assert(prefix != NULL, "control point invariant");
9177 const markOop proto = markOopDesc::prototype();
9178 oop next;
9179 NOT_PRODUCT(ssize_t n = 0;)
9180 for (cur = prefix; cur != NULL; cur = next) {
9181 next = oop(cur->mark());
9182 cur->set_mark(proto); // until proven otherwise
9183 assert(cur->is_oop(), "Should be an oop");
9184 bool res = work_q->push(cur);
9185 assert(res, "Bit off more than we can chew?");
9186 NOT_PRODUCT(n++;)
9187 }
9188 #ifndef PRODUCT
9189 assert(_num_par_pushes >= n, "Too many pops?");
9190 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
9191 #endif
9192 return true;
9193 }
9194
9195 // Single-threaded
9196 void CMSCollector::push_on_overflow_list(oop p) {
9197 NOT_PRODUCT(_num_par_pushes++;)
9198 assert(p->is_oop(), "Not an oop");
9199 preserve_mark_if_necessary(p);
9200 p->set_mark((markOop)_overflow_list);
9201 _overflow_list = p;
9202 }
9203
9204 // Multi-threaded; use CAS to prepend to overflow list
9205 void CMSCollector::par_push_on_overflow_list(oop p) {
9206 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
9207 assert(p->is_oop(), "Not an oop");
9208 par_preserve_mark_if_necessary(p);
9209 oop observed_overflow_list = _overflow_list;
9210 oop cur_overflow_list;
9211 do {
9212 cur_overflow_list = observed_overflow_list;
9213 if (cur_overflow_list != BUSY) {
9214 p->set_mark(markOop(cur_overflow_list));
9215 } else {
9216 p->set_mark(NULL);
9217 }
9218 observed_overflow_list =
9219 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
9220 } while (cur_overflow_list != observed_overflow_list);
9221 }
9222 #undef BUSY
9223
9224 // Single threaded
9225 // General Note on GrowableArray: pushes may silently fail
9226 // because we are (temporarily) out of C-heap for expanding
9227 // the stack. The problem is quite ubiquitous and affects
9228 // a lot of code in the JVM. The prudent thing for GrowableArray
9229 // to do (for now) is to exit with an error. However, that may
9230 // be too draconian in some cases because the caller may be
9231 // able to recover without much harm. For such cases, we
9232 // should probably introduce a "soft_push" method which returns
9233 // an indication of success or failure with the assumption that
9234 // the caller may be able to recover from a failure; code in
9235 // the VM can then be changed, incrementally, to deal with such
9236 // failures where possible, thus, incrementally hardening the VM
9237 // in such low resource situations.
9238 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9239 _preserved_oop_stack.push(p);
9240 _preserved_mark_stack.push(m);
9241 assert(m == p->mark(), "Mark word changed");
9242 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9243 "bijection");
9244 }
9245
9246 // Single threaded
9247 void CMSCollector::preserve_mark_if_necessary(oop p) {
9248 markOop m = p->mark();
9249 if (m->must_be_preserved(p)) {
9250 preserve_mark_work(p, m);
9251 }
9252 }
9253
9254 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9255 markOop m = p->mark();
9256 if (m->must_be_preserved(p)) {
9257 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9258 // Even though we read the mark word without holding
9259 // the lock, we are assured that it will not change
9260 // because we "own" this oop, so no other thread can
9261 // be trying to push it on the overflow list; see
9262 // the assertion in preserve_mark_work() that checks
9263 // that m == p->mark().
9264 preserve_mark_work(p, m);
9265 }
9266 }
9267
9268 // We should be able to do this multi-threaded,
9269 // a chunk of stack being a task (this is
9270 // correct because each oop only ever appears
9271 // once in the overflow list. However, it's
9272 // not very easy to completely overlap this with
9273 // other operations, so will generally not be done
9274 // until all work's been completed. Because we
9275 // expect the preserved oop stack (set) to be small,
9276 // it's probably fine to do this single-threaded.
9277 // We can explore cleverer concurrent/overlapped/parallel
9278 // processing of preserved marks if we feel the
9279 // need for this in the future. Stack overflow should
9280 // be so rare in practice and, when it happens, its
9281 // effect on performance so great that this will
9282 // likely just be in the noise anyway.
9283 void CMSCollector::restore_preserved_marks_if_any() {
9284 assert(SafepointSynchronize::is_at_safepoint(),
9285 "world should be stopped");
9286 assert(Thread::current()->is_ConcurrentGC_thread() ||
9287 Thread::current()->is_VM_thread(),
9288 "should be single-threaded");
9289 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9290 "bijection");
9291
9292 while (!_preserved_oop_stack.is_empty()) {
9293 oop p = _preserved_oop_stack.pop();
9294 assert(p->is_oop(), "Should be an oop");
9295 assert(_span.contains(p), "oop should be in _span");
9296 assert(p->mark() == markOopDesc::prototype(),
9297 "Set when taken from overflow list");
9298 markOop m = _preserved_mark_stack.pop();
9299 p->set_mark(m);
9300 }
9301 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9302 "stacks were cleared above");
9303 }
9304
9305 #ifndef PRODUCT
9306 bool CMSCollector::no_preserved_marks() const {
9307 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9308 }
9309 #endif
9310
9311 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
9312 {
9313 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9314 CMSAdaptiveSizePolicy* size_policy =
9315 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
9316 assert(size_policy->is_gc_cms_adaptive_size_policy(),
9317 "Wrong type for size policy");
9318 return size_policy;
9319 }
9320
9321 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
9322 size_t desired_promo_size) {
9323 if (cur_promo_size < desired_promo_size) {
9324 size_t expand_bytes = desired_promo_size - cur_promo_size;
9325 if (PrintAdaptiveSizePolicy && Verbose) {
9326 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9327 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
9328 expand_bytes);
9329 }
9330 expand(expand_bytes,
9331 MinHeapDeltaBytes,
9332 CMSExpansionCause::_adaptive_size_policy);
9333 } else if (desired_promo_size < cur_promo_size) {
9334 size_t shrink_bytes = cur_promo_size - desired_promo_size;
9335 if (PrintAdaptiveSizePolicy && Verbose) {
9336 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9337 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
9338 shrink_bytes);
9339 }
9340 shrink(shrink_bytes);
9341 }
9342 }
9343
9344 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
9345 GenCollectedHeap* gch = GenCollectedHeap::heap();
9346 CMSGCAdaptivePolicyCounters* counters =
9347 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
9348 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
9349 "Wrong kind of counters");
9350 return counters;
9351 }
9352
9353
9354 void ASConcurrentMarkSweepGeneration::update_counters() {
9355 if (UsePerfData) {
9356 _space_counters->update_all();
9357 _gen_counters->update_all();
9358 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9359 GenCollectedHeap* gch = GenCollectedHeap::heap();
9360 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9361 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9362 "Wrong gc statistics type");
9363 counters->update_counters(gc_stats_l);
9364 }
9365 }
9366
9367 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
9368 if (UsePerfData) {
9369 _space_counters->update_used(used);
9370 _space_counters->update_capacity();
9371 _gen_counters->update_all();
9372
9373 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9374 GenCollectedHeap* gch = GenCollectedHeap::heap();
9375 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9376 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9377 "Wrong gc statistics type");
9378 counters->update_counters(gc_stats_l);
9379 }
9380 }
9381
9382 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9383 assert_locked_or_safepoint(Heap_lock);
9384 assert_lock_strong(freelistLock());
9385 HeapWord* old_end = _cmsSpace->end();
9386 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9387 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9388 FreeChunk* chunk_at_end = find_chunk_at_end();
9389 if (chunk_at_end == NULL) {
9390 // No room to shrink
9391 if (PrintGCDetails && Verbose) {
9392 gclog_or_tty->print_cr("No room to shrink: old_end "
9393 PTR_FORMAT " unallocated_start " PTR_FORMAT
9394 " chunk_at_end " PTR_FORMAT,
9395 old_end, unallocated_start, chunk_at_end);
9396 }
9397 return;
9398 } else {
9399
9400 // Find the chunk at the end of the space and determine
9401 // how much it can be shrunk.
9402 size_t shrinkable_size_in_bytes = chunk_at_end->size();
9403 size_t aligned_shrinkable_size_in_bytes =
9404 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9405 assert(unallocated_start <= (HeapWord*) chunk_at_end->end(),
9406 "Inconsistent chunk at end of space");
9407 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9408 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9409
9410 // Shrink the underlying space
9411 _virtual_space.shrink_by(bytes);
9412 if (PrintGCDetails && Verbose) {
9413 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9414 " desired_bytes " SIZE_FORMAT
9415 " shrinkable_size_in_bytes " SIZE_FORMAT
9416 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9417 " bytes " SIZE_FORMAT,
9418 desired_bytes, shrinkable_size_in_bytes,
9419 aligned_shrinkable_size_in_bytes, bytes);
9420 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
9421 " unallocated_start " SIZE_FORMAT,
9422 old_end, unallocated_start);
9423 }
9424
9425 // If the space did shrink (shrinking is not guaranteed),
9426 // shrink the chunk at the end by the appropriate amount.
9427 if (((HeapWord*)_virtual_space.high()) < old_end) {
9428 size_t new_word_size =
9429 heap_word_size(_virtual_space.committed_size());
9430
9431 // Have to remove the chunk from the dictionary because it is changing
9432 // size and might be someplace elsewhere in the dictionary.
9433
9434 // Get the chunk at end, shrink it, and put it
9435 // back.
9436 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9437 size_t word_size_change = word_size_before - new_word_size;
9438 size_t chunk_at_end_old_size = chunk_at_end->size();
9439 assert(chunk_at_end_old_size >= word_size_change,
9440 "Shrink is too large");
9441 chunk_at_end->set_size(chunk_at_end_old_size -
9442 word_size_change);
9443 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9444 word_size_change);
9445
9446 _cmsSpace->returnChunkToDictionary(chunk_at_end);
9447
9448 MemRegion mr(_cmsSpace->bottom(), new_word_size);
9449 _bts->resize(new_word_size); // resize the block offset shared array
9450 Universe::heap()->barrier_set()->resize_covered_region(mr);
9451 _cmsSpace->assert_locked();
9452 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9453
9454 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9455
9456 // update the space and generation capacity counters
9457 if (UsePerfData) {
9458 _space_counters->update_capacity();
9459 _gen_counters->update_all();
9460 }
9461
9462 if (Verbose && PrintGCDetails) {
9463 size_t new_mem_size = _virtual_space.committed_size();
9464 size_t old_mem_size = new_mem_size + bytes;
9465 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
9466 name(), old_mem_size/K, bytes/K, new_mem_size/K);
9467 }
9468 }
9469
9470 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9471 "Inconsistency at end of space");
9472 assert(chunk_at_end->end() == (uintptr_t*) _cmsSpace->end(),
9473 "Shrinking is inconsistent");
9474 return;
9475 }
9476 }
9477 // Transfer some number of overflown objects to usual marking
9478 // stack. Return true if some objects were transferred.
9479 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9480 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9481 (size_t)ParGCDesiredObjsFromOverflowList);
9482
9483 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9484 assert(_collector->overflow_list_is_empty() || res,
9485 "If list is not empty, we should have taken something");
9486 assert(!res || !_mark_stack->isEmpty(),
9487 "If we took something, it should now be on our stack");
9488 return res;
9489 }
9490
9491 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9492 size_t res = _sp->block_size_no_stall(addr, _collector);
9493 if (_sp->block_is_obj(addr)) {
9494 if (_live_bit_map->isMarked(addr)) {
9495 // It can't have been dead in a previous cycle
9496 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9497 } else {
9498 _dead_bit_map->mark(addr); // mark the dead object
9499 }
9500 }
9501 // Could be 0, if the block size could not be computed without stalling.
9502 return res;
9503 }
9504
9505 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9506
9507 switch (phase) {
9508 case CMSCollector::InitialMarking:
9509 initialize(true /* fullGC */ ,
9510 cause /* cause of the GC */,
9511 true /* recordGCBeginTime */,
9512 true /* recordPreGCUsage */,
9513 false /* recordPeakUsage */,
9514 false /* recordPostGCusage */,
9515 true /* recordAccumulatedGCTime */,
9516 false /* recordGCEndTime */,
9517 false /* countCollection */ );
9518 break;
9519
9520 case CMSCollector::FinalMarking:
9521 initialize(true /* fullGC */ ,
9522 cause /* cause of the GC */,
9523 false /* recordGCBeginTime */,
9524 false /* recordPreGCUsage */,
9525 false /* recordPeakUsage */,
9526 false /* recordPostGCusage */,
9527 true /* recordAccumulatedGCTime */,
9528 false /* recordGCEndTime */,
9529 false /* countCollection */ );
9530 break;
9531
9532 case CMSCollector::Sweeping:
9533 initialize(true /* fullGC */ ,
9534 cause /* cause of the GC */,
9535 false /* recordGCBeginTime */,
9536 false /* recordPreGCUsage */,
9537 true /* recordPeakUsage */,
9538 true /* recordPostGCusage */,
9539 false /* recordAccumulatedGCTime */,
9540 true /* recordGCEndTime */,
9541 true /* countCollection */ );
9542 break;
9543
9544 default:
9545 ShouldNotReachHere();
9546 }
9547 }