1 /*
2 * Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc_implementation/shared/adaptiveSizePolicy.hpp"
31 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
32 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
33 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
34 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
36 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
37 #include "gc_implementation/parNew/parNewGeneration.hpp"
38 #include "gc_implementation/shared/collectorCounters.hpp"
39 #include "gc_implementation/shared/gcTimer.hpp"
40 #include "gc_implementation/shared/gcTrace.hpp"
41 #include "gc_implementation/shared/gcTraceTime.hpp"
42 #include "gc_implementation/shared/isGCActiveMark.hpp"
43 #include "gc_interface/collectedHeap.inline.hpp"
44 #include "memory/allocation.hpp"
45 #include "memory/cardTableRS.hpp"
46 #include "memory/collectorPolicy.hpp"
47 #include "memory/gcLocker.inline.hpp"
48 #include "memory/genCollectedHeap.hpp"
49 #include "memory/genMarkSweep.hpp"
50 #include "memory/genOopClosures.inline.hpp"
51 #include "memory/iterator.inline.hpp"
52 #include "memory/padded.hpp"
53 #include "memory/referencePolicy.hpp"
54 #include "memory/resourceArea.hpp"
55 #include "memory/tenuredGeneration.hpp"
56 #include "oops/oop.inline.hpp"
57 #include "prims/jvmtiExport.hpp"
58 #include "runtime/atomic.inline.hpp"
59 #include "runtime/globals_extension.hpp"
60 #include "runtime/handles.inline.hpp"
61 #include "runtime/java.hpp"
62 #include "runtime/orderAccess.inline.hpp"
63 #include "runtime/vmThread.hpp"
64 #include "services/memoryService.hpp"
65 #include "services/runtimeService.hpp"
66
67 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
68
69 // statics
70 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
71 bool CMSCollector::_full_gc_requested = false;
72 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
73
74 //////////////////////////////////////////////////////////////////
75 // In support of CMS/VM thread synchronization
76 //////////////////////////////////////////////////////////////////
77 // We split use of the CGC_lock into 2 "levels".
78 // The low-level locking is of the usual CGC_lock monitor. We introduce
79 // a higher level "token" (hereafter "CMS token") built on top of the
80 // low level monitor (hereafter "CGC lock").
81 // The token-passing protocol gives priority to the VM thread. The
82 // CMS-lock doesn't provide any fairness guarantees, but clients
83 // should ensure that it is only held for very short, bounded
84 // durations.
85 //
86 // When either of the CMS thread or the VM thread is involved in
87 // collection operations during which it does not want the other
88 // thread to interfere, it obtains the CMS token.
89 //
90 // If either thread tries to get the token while the other has
91 // it, that thread waits. However, if the VM thread and CMS thread
92 // both want the token, then the VM thread gets priority while the
93 // CMS thread waits. This ensures, for instance, that the "concurrent"
94 // phases of the CMS thread's work do not block out the VM thread
95 // for long periods of time as the CMS thread continues to hog
96 // the token. (See bug 4616232).
97 //
98 // The baton-passing functions are, however, controlled by the
99 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
100 // and here the low-level CMS lock, not the high level token,
101 // ensures mutual exclusion.
102 //
103 // Two important conditions that we have to satisfy:
104 // 1. if a thread does a low-level wait on the CMS lock, then it
105 // relinquishes the CMS token if it were holding that token
106 // when it acquired the low-level CMS lock.
107 // 2. any low-level notifications on the low-level lock
108 // should only be sent when a thread has relinquished the token.
109 //
110 // In the absence of either property, we'd have potential deadlock.
111 //
112 // We protect each of the CMS (concurrent and sequential) phases
113 // with the CMS _token_, not the CMS _lock_.
114 //
115 // The only code protected by CMS lock is the token acquisition code
116 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
117 // baton-passing code.
118 //
119 // Unfortunately, i couldn't come up with a good abstraction to factor and
120 // hide the naked CGC_lock manipulation in the baton-passing code
121 // further below. That's something we should try to do. Also, the proof
122 // of correctness of this 2-level locking scheme is far from obvious,
123 // and potentially quite slippery. We have an uneasy suspicion, for instance,
124 // that there may be a theoretical possibility of delay/starvation in the
125 // low-level lock/wait/notify scheme used for the baton-passing because of
126 // potential interference with the priority scheme embodied in the
127 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
128 // invocation further below and marked with "XXX 20011219YSR".
129 // Indeed, as we note elsewhere, this may become yet more slippery
130 // in the presence of multiple CMS and/or multiple VM threads. XXX
131
132 class CMSTokenSync: public StackObj {
133 private:
134 bool _is_cms_thread;
135 public:
136 CMSTokenSync(bool is_cms_thread):
137 _is_cms_thread(is_cms_thread) {
138 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
139 "Incorrect argument to constructor");
140 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
141 }
142
143 ~CMSTokenSync() {
144 assert(_is_cms_thread ?
145 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
146 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
147 "Incorrect state");
148 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
149 }
150 };
151
152 // Convenience class that does a CMSTokenSync, and then acquires
153 // upto three locks.
154 class CMSTokenSyncWithLocks: public CMSTokenSync {
155 private:
156 // Note: locks are acquired in textual declaration order
157 // and released in the opposite order
158 MutexLockerEx _locker1, _locker2, _locker3;
159 public:
160 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
161 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
162 CMSTokenSync(is_cms_thread),
163 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
164 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
165 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
166 { }
167 };
168
169
170 // Wrapper class to temporarily disable icms during a foreground cms collection.
171 class ICMSDisabler: public StackObj {
172 public:
173 // The ctor disables icms and wakes up the thread so it notices the change;
174 // the dtor re-enables icms. Note that the CMSCollector methods will check
175 // CMSIncrementalMode.
176 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
177 ~ICMSDisabler() { CMSCollector::enable_icms(); }
178 };
179
180 //////////////////////////////////////////////////////////////////
181 // Concurrent Mark-Sweep Generation /////////////////////////////
182 //////////////////////////////////////////////////////////////////
183
184 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
185
186 // This struct contains per-thread things necessary to support parallel
187 // young-gen collection.
188 class CMSParGCThreadState: public CHeapObj<mtGC> {
189 public:
190 CFLS_LAB lab;
191 PromotionInfo promo;
192
193 // Constructor.
194 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
195 promo.setSpace(cfls);
196 }
197 };
198
199 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
200 ReservedSpace rs, size_t initial_byte_size, int level,
201 CardTableRS* ct, bool use_adaptive_freelists,
202 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
203 CardGeneration(rs, initial_byte_size, level, ct),
204 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
205 _debug_collection_type(Concurrent_collection_type),
206 _did_compact(false)
207 {
208 HeapWord* bottom = (HeapWord*) _virtual_space.low();
209 HeapWord* end = (HeapWord*) _virtual_space.high();
210
211 _direct_allocated_words = 0;
212 NOT_PRODUCT(
213 _numObjectsPromoted = 0;
214 _numWordsPromoted = 0;
215 _numObjectsAllocated = 0;
216 _numWordsAllocated = 0;
217 )
218
219 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
220 use_adaptive_freelists,
221 dictionaryChoice);
222 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
223 if (_cmsSpace == NULL) {
224 vm_exit_during_initialization(
225 "CompactibleFreeListSpace allocation failure");
226 }
227 _cmsSpace->_gen = this;
228
229 _gc_stats = new CMSGCStats();
230
231 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
232 // offsets match. The ability to tell free chunks from objects
233 // depends on this property.
234 debug_only(
235 FreeChunk* junk = NULL;
236 assert(UseCompressedClassPointers ||
237 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
238 "Offset of FreeChunk::_prev within FreeChunk must match"
239 " that of OopDesc::_klass within OopDesc");
240 )
241 if (CollectedHeap::use_parallel_gc_threads()) {
242 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
243 _par_gc_thread_states =
244 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
245 if (_par_gc_thread_states == NULL) {
246 vm_exit_during_initialization("Could not allocate par gc structs");
247 }
248 for (uint i = 0; i < ParallelGCThreads; i++) {
249 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
250 if (_par_gc_thread_states[i] == NULL) {
251 vm_exit_during_initialization("Could not allocate par gc structs");
252 }
253 }
254 } else {
255 _par_gc_thread_states = NULL;
256 }
257 _incremental_collection_failed = false;
258 // The "dilatation_factor" is the expansion that can occur on
259 // account of the fact that the minimum object size in the CMS
260 // generation may be larger than that in, say, a contiguous young
261 // generation.
262 // Ideally, in the calculation below, we'd compute the dilatation
263 // factor as: MinChunkSize/(promoting_gen's min object size)
264 // Since we do not have such a general query interface for the
265 // promoting generation, we'll instead just use the minimum
266 // object size (which today is a header's worth of space);
267 // note that all arithmetic is in units of HeapWords.
268 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
269 assert(_dilatation_factor >= 1.0, "from previous assert");
270 }
271
272
273 // The field "_initiating_occupancy" represents the occupancy percentage
274 // at which we trigger a new collection cycle. Unless explicitly specified
275 // via CMSInitiatingOccupancyFraction (argument "io" below), it
276 // is calculated by:
277 //
278 // Let "f" be MinHeapFreeRatio in
279 //
280 // _initiating_occupancy = 100-f +
281 // f * (CMSTriggerRatio/100)
282 // where CMSTriggerRatio is the argument "tr" below.
283 //
284 // That is, if we assume the heap is at its desired maximum occupancy at the
285 // end of a collection, we let CMSTriggerRatio of the (purported) free
286 // space be allocated before initiating a new collection cycle.
287 //
288 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
289 assert(io <= 100 && tr <= 100, "Check the arguments");
290 if (io >= 0) {
291 _initiating_occupancy = (double)io / 100.0;
292 } else {
293 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
294 (double)(tr * MinHeapFreeRatio) / 100.0)
295 / 100.0;
296 }
297 }
298
299 void ConcurrentMarkSweepGeneration::ref_processor_init() {
300 assert(collector() != NULL, "no collector");
301 collector()->ref_processor_init();
302 }
303
304 void CMSCollector::ref_processor_init() {
305 if (_ref_processor == NULL) {
306 // Allocate and initialize a reference processor
307 _ref_processor =
308 new ReferenceProcessor(_span, // span
309 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
310 (int) ParallelGCThreads, // mt processing degree
311 _cmsGen->refs_discovery_is_mt(), // mt discovery
312 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
313 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
314 &_is_alive_closure); // closure for liveness info
315 // Initialize the _ref_processor field of CMSGen
316 _cmsGen->set_ref_processor(_ref_processor);
317
318 }
319 }
320
321 AdaptiveSizePolicy* CMSCollector::size_policy() {
322 GenCollectedHeap* gch = GenCollectedHeap::heap();
323 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
324 "Wrong type of heap");
325 return gch->gen_policy()->size_policy();
326 }
327
328 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
329
330 const char* gen_name = "old";
331 GenCollectorPolicy* gcp = (GenCollectorPolicy*) GenCollectedHeap::heap()->collector_policy();
332
333 // Generation Counters - generation 1, 1 subspace
334 _gen_counters = new GenerationCounters(gen_name, 1, 1,
335 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
336
337 _space_counters = new GSpaceCounters(gen_name, 0,
338 _virtual_space.reserved_size(),
339 this, _gen_counters);
340 }
341
342 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
343 _cms_gen(cms_gen)
344 {
345 assert(alpha <= 100, "bad value");
346 _saved_alpha = alpha;
347
348 // Initialize the alphas to the bootstrap value of 100.
349 _gc0_alpha = _cms_alpha = 100;
350
351 _cms_begin_time.update();
352 _cms_end_time.update();
353
354 _gc0_duration = 0.0;
355 _gc0_period = 0.0;
356 _gc0_promoted = 0;
357
358 _cms_duration = 0.0;
359 _cms_period = 0.0;
360 _cms_allocated = 0;
361
362 _cms_used_at_gc0_begin = 0;
363 _cms_used_at_gc0_end = 0;
364 _allow_duty_cycle_reduction = false;
365 _valid_bits = 0;
366 _icms_duty_cycle = CMSIncrementalDutyCycle;
367 }
368
369 double CMSStats::cms_free_adjustment_factor(size_t free) const {
370 // TBD: CR 6909490
371 return 1.0;
372 }
373
374 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
375 }
376
377 // If promotion failure handling is on use
378 // the padded average size of the promotion for each
379 // young generation collection.
380 double CMSStats::time_until_cms_gen_full() const {
381 size_t cms_free = _cms_gen->cmsSpace()->free();
382 GenCollectedHeap* gch = GenCollectedHeap::heap();
383 size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
384 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
385 if (cms_free > expected_promotion) {
386 // Start a cms collection if there isn't enough space to promote
387 // for the next minor collection. Use the padded average as
388 // a safety factor.
389 cms_free -= expected_promotion;
390
391 // Adjust by the safety factor.
392 double cms_free_dbl = (double)cms_free;
393 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
394 // Apply a further correction factor which tries to adjust
395 // for recent occurance of concurrent mode failures.
396 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
397 cms_free_dbl = cms_free_dbl * cms_adjustment;
398
399 if (PrintGCDetails && Verbose) {
400 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
401 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
402 cms_free, expected_promotion);
403 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
404 cms_free_dbl, cms_consumption_rate() + 1.0);
405 }
406 // Add 1 in case the consumption rate goes to zero.
407 return cms_free_dbl / (cms_consumption_rate() + 1.0);
408 }
409 return 0.0;
410 }
411
412 // Compare the duration of the cms collection to the
413 // time remaining before the cms generation is empty.
414 // Note that the time from the start of the cms collection
415 // to the start of the cms sweep (less than the total
416 // duration of the cms collection) can be used. This
417 // has been tried and some applications experienced
418 // promotion failures early in execution. This was
419 // possibly because the averages were not accurate
420 // enough at the beginning.
421 double CMSStats::time_until_cms_start() const {
422 // We add "gc0_period" to the "work" calculation
423 // below because this query is done (mostly) at the
424 // end of a scavenge, so we need to conservatively
425 // account for that much possible delay
426 // in the query so as to avoid concurrent mode failures
427 // due to starting the collection just a wee bit too
428 // late.
429 double work = cms_duration() + gc0_period();
430 double deadline = time_until_cms_gen_full();
431 // If a concurrent mode failure occurred recently, we want to be
432 // more conservative and halve our expected time_until_cms_gen_full()
433 if (work > deadline) {
434 if (Verbose && PrintGCDetails) {
435 gclog_or_tty->print(
436 " CMSCollector: collect because of anticipated promotion "
437 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
438 gc0_period(), time_until_cms_gen_full());
439 }
440 return 0.0;
441 }
442 return work - deadline;
443 }
444
445 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
446 // amount of change to prevent wild oscillation.
447 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
448 unsigned int new_duty_cycle) {
449 assert(old_duty_cycle <= 100, "bad input value");
450 assert(new_duty_cycle <= 100, "bad input value");
451
452 // Note: use subtraction with caution since it may underflow (values are
453 // unsigned). Addition is safe since we're in the range 0-100.
454 unsigned int damped_duty_cycle = new_duty_cycle;
455 if (new_duty_cycle < old_duty_cycle) {
456 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
457 if (new_duty_cycle + largest_delta < old_duty_cycle) {
458 damped_duty_cycle = old_duty_cycle - largest_delta;
459 }
460 } else if (new_duty_cycle > old_duty_cycle) {
461 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
462 if (new_duty_cycle > old_duty_cycle + largest_delta) {
463 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
464 }
465 }
466 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
467
468 if (CMSTraceIncrementalPacing) {
469 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
470 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
471 }
472 return damped_duty_cycle;
473 }
474
475 unsigned int CMSStats::icms_update_duty_cycle_impl() {
476 assert(CMSIncrementalPacing && valid(),
477 "should be handled in icms_update_duty_cycle()");
478
479 double cms_time_so_far = cms_timer().seconds();
480 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
481 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
482
483 // Avoid division by 0.
484 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
485 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
486
487 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
488 if (new_duty_cycle > _icms_duty_cycle) {
489 // Avoid very small duty cycles (1 or 2); 0 is allowed.
490 if (new_duty_cycle > 2) {
491 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
492 new_duty_cycle);
493 }
494 } else if (_allow_duty_cycle_reduction) {
495 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
496 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
497 // Respect the minimum duty cycle.
498 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
499 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
500 }
501
502 if (PrintGCDetails || CMSTraceIncrementalPacing) {
503 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
504 }
505
506 _allow_duty_cycle_reduction = false;
507 return _icms_duty_cycle;
508 }
509
510 #ifndef PRODUCT
511 void CMSStats::print_on(outputStream *st) const {
512 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
513 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
514 gc0_duration(), gc0_period(), gc0_promoted());
515 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
516 cms_duration(), cms_duration_per_mb(),
517 cms_period(), cms_allocated());
518 st->print(",cms_since_beg=%g,cms_since_end=%g",
519 cms_time_since_begin(), cms_time_since_end());
520 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
521 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
522 if (CMSIncrementalMode) {
523 st->print(",dc=%d", icms_duty_cycle());
524 }
525
526 if (valid()) {
527 st->print(",promo_rate=%g,cms_alloc_rate=%g",
528 promotion_rate(), cms_allocation_rate());
529 st->print(",cms_consumption_rate=%g,time_until_full=%g",
530 cms_consumption_rate(), time_until_cms_gen_full());
531 }
532 st->print(" ");
533 }
534 #endif // #ifndef PRODUCT
535
536 CMSCollector::CollectorState CMSCollector::_collectorState =
537 CMSCollector::Idling;
538 bool CMSCollector::_foregroundGCIsActive = false;
539 bool CMSCollector::_foregroundGCShouldWait = false;
540
541 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
542 CardTableRS* ct,
543 ConcurrentMarkSweepPolicy* cp):
544 _cmsGen(cmsGen),
545 _ct(ct),
546 _ref_processor(NULL), // will be set later
547 _conc_workers(NULL), // may be set later
548 _abort_preclean(false),
549 _start_sampling(false),
550 _between_prologue_and_epilogue(false),
551 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
552 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
553 -1 /* lock-free */, "No_lock" /* dummy */),
554 _modUnionClosure(&_modUnionTable),
555 _modUnionClosurePar(&_modUnionTable),
556 // Adjust my span to cover old (cms) gen
557 _span(cmsGen->reserved()),
558 // Construct the is_alive_closure with _span & markBitMap
559 _is_alive_closure(_span, &_markBitMap),
560 _restart_addr(NULL),
561 _overflow_list(NULL),
562 _stats(cmsGen),
563 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true)),
564 _eden_chunk_array(NULL), // may be set in ctor body
565 _eden_chunk_capacity(0), // -- ditto --
566 _eden_chunk_index(0), // -- ditto --
567 _survivor_plab_array(NULL), // -- ditto --
568 _survivor_chunk_array(NULL), // -- ditto --
569 _survivor_chunk_capacity(0), // -- ditto --
570 _survivor_chunk_index(0), // -- ditto --
571 _ser_pmc_preclean_ovflw(0),
572 _ser_kac_preclean_ovflw(0),
573 _ser_pmc_remark_ovflw(0),
574 _par_pmc_remark_ovflw(0),
575 _ser_kac_ovflw(0),
576 _par_kac_ovflw(0),
577 #ifndef PRODUCT
578 _num_par_pushes(0),
579 #endif
580 _collection_count_start(0),
581 _verifying(false),
582 _icms_start_limit(NULL),
583 _icms_stop_limit(NULL),
584 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
585 _completed_initialization(false),
586 _collector_policy(cp),
587 _should_unload_classes(CMSClassUnloadingEnabled),
588 _concurrent_cycles_since_last_unload(0),
589 _roots_scanning_options(SharedHeap::SO_None),
590 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
591 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
592 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
593 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
594 _cms_start_registered(false)
595 {
596 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
597 ExplicitGCInvokesConcurrent = true;
598 }
599 // Now expand the span and allocate the collection support structures
600 // (MUT, marking bit map etc.) to cover both generations subject to
601 // collection.
602
603 // For use by dirty card to oop closures.
604 _cmsGen->cmsSpace()->set_collector(this);
605
606 // Allocate MUT and marking bit map
607 {
608 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
609 if (!_markBitMap.allocate(_span)) {
610 warning("Failed to allocate CMS Bit Map");
611 return;
612 }
613 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
614 }
615 {
616 _modUnionTable.allocate(_span);
617 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
618 }
619
620 if (!_markStack.allocate(MarkStackSize)) {
621 warning("Failed to allocate CMS Marking Stack");
622 return;
623 }
624
625 // Support for multi-threaded concurrent phases
626 if (CMSConcurrentMTEnabled) {
627 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
628 // just for now
629 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
630 }
631 if (ConcGCThreads > 1) {
632 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
633 ConcGCThreads, true);
634 if (_conc_workers == NULL) {
635 warning("GC/CMS: _conc_workers allocation failure: "
636 "forcing -CMSConcurrentMTEnabled");
637 CMSConcurrentMTEnabled = false;
638 } else {
639 _conc_workers->initialize_workers();
640 }
641 } else {
642 CMSConcurrentMTEnabled = false;
643 }
644 }
645 if (!CMSConcurrentMTEnabled) {
646 ConcGCThreads = 0;
647 } else {
648 // Turn off CMSCleanOnEnter optimization temporarily for
649 // the MT case where it's not fixed yet; see 6178663.
650 CMSCleanOnEnter = false;
651 }
652 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
653 "Inconsistency");
654
655 // Parallel task queues; these are shared for the
656 // concurrent and stop-world phases of CMS, but
657 // are not shared with parallel scavenge (ParNew).
658 {
659 uint i;
660 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
661
662 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
663 || ParallelRefProcEnabled)
664 && num_queues > 0) {
665 _task_queues = new OopTaskQueueSet(num_queues);
666 if (_task_queues == NULL) {
667 warning("task_queues allocation failure.");
668 return;
669 }
670 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
671 if (_hash_seed == NULL) {
672 warning("_hash_seed array allocation failure");
673 return;
674 }
675
676 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
677 for (i = 0; i < num_queues; i++) {
678 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
679 if (q == NULL) {
680 warning("work_queue allocation failure.");
681 return;
682 }
683 _task_queues->register_queue(i, q);
684 }
685 for (i = 0; i < num_queues; i++) {
686 _task_queues->queue(i)->initialize();
687 _hash_seed[i] = 17; // copied from ParNew
688 }
689 }
690 }
691
692 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
693
694 // Clip CMSBootstrapOccupancy between 0 and 100.
695 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
696
697 _full_gcs_since_conc_gc = 0;
698
699 // Now tell CMS generations the identity of their collector
700 ConcurrentMarkSweepGeneration::set_collector(this);
701
702 // Create & start a CMS thread for this CMS collector
703 _cmsThread = ConcurrentMarkSweepThread::start(this);
704 assert(cmsThread() != NULL, "CMS Thread should have been created");
705 assert(cmsThread()->collector() == this,
706 "CMS Thread should refer to this gen");
707 assert(CGC_lock != NULL, "Where's the CGC_lock?");
708
709 // Support for parallelizing young gen rescan
710 GenCollectedHeap* gch = GenCollectedHeap::heap();
711 _young_gen = gch->young_gen();
712 if (gch->supports_inline_contig_alloc()) {
713 _top_addr = gch->top_addr();
714 _end_addr = gch->end_addr();
715 assert(_young_gen != NULL, "no _young_gen");
716 _eden_chunk_index = 0;
717 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
718 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
719 if (_eden_chunk_array == NULL) {
720 _eden_chunk_capacity = 0;
721 warning("GC/CMS: _eden_chunk_array allocation failure");
722 }
723 }
724 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
725
726 // Support for parallelizing survivor space rescan
727 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
728 const size_t max_plab_samples =
729 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
730
731 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
732 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
733 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
734 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
735 || _cursor == NULL) {
736 warning("Failed to allocate survivor plab/chunk array");
737 if (_survivor_plab_array != NULL) {
738 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
739 _survivor_plab_array = NULL;
740 }
741 if (_survivor_chunk_array != NULL) {
742 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
743 _survivor_chunk_array = NULL;
744 }
745 if (_cursor != NULL) {
746 FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
747 _cursor = NULL;
748 }
749 } else {
750 _survivor_chunk_capacity = 2*max_plab_samples;
751 for (uint i = 0; i < ParallelGCThreads; i++) {
752 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
753 if (vec == NULL) {
754 warning("Failed to allocate survivor plab array");
755 for (int j = i; j > 0; j--) {
756 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
757 }
758 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
759 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
760 _survivor_plab_array = NULL;
761 _survivor_chunk_array = NULL;
762 _survivor_chunk_capacity = 0;
763 break;
764 } else {
765 ChunkArray* cur =
766 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
767 max_plab_samples);
768 assert(cur->end() == 0, "Should be 0");
769 assert(cur->array() == vec, "Should be vec");
770 assert(cur->capacity() == max_plab_samples, "Error");
771 }
772 }
773 }
774 }
775 assert( ( _survivor_plab_array != NULL
776 && _survivor_chunk_array != NULL)
777 || ( _survivor_chunk_capacity == 0
778 && _survivor_chunk_index == 0),
779 "Error");
780
781 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
782 _gc_counters = new CollectorCounters("CMS", 1);
783 _completed_initialization = true;
784 _inter_sweep_timer.start(); // start of time
785 }
786
787 const char* ConcurrentMarkSweepGeneration::name() const {
788 return "concurrent mark-sweep generation";
789 }
790 void ConcurrentMarkSweepGeneration::update_counters() {
791 if (UsePerfData) {
792 _space_counters->update_all();
793 _gen_counters->update_all();
794 }
795 }
796
797 // this is an optimized version of update_counters(). it takes the
798 // used value as a parameter rather than computing it.
799 //
800 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
801 if (UsePerfData) {
802 _space_counters->update_used(used);
803 _space_counters->update_capacity();
804 _gen_counters->update_all();
805 }
806 }
807
808 void ConcurrentMarkSweepGeneration::print() const {
809 Generation::print();
810 cmsSpace()->print();
811 }
812
813 #ifndef PRODUCT
814 void ConcurrentMarkSweepGeneration::print_statistics() {
815 cmsSpace()->printFLCensus(0);
816 }
817 #endif
818
819 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
820 GenCollectedHeap* gch = GenCollectedHeap::heap();
821 if (PrintGCDetails) {
822 if (Verbose) {
823 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
824 level(), short_name(), s, used(), capacity());
825 } else {
826 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
827 level(), short_name(), s, used() / K, capacity() / K);
828 }
829 }
830 if (Verbose) {
831 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
832 gch->used(), gch->capacity());
833 } else {
834 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
835 gch->used() / K, gch->capacity() / K);
836 }
837 }
838
839 size_t
840 ConcurrentMarkSweepGeneration::contiguous_available() const {
841 // dld proposes an improvement in precision here. If the committed
842 // part of the space ends in a free block we should add that to
843 // uncommitted size in the calculation below. Will make this
844 // change later, staying with the approximation below for the
845 // time being. -- ysr.
846 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
847 }
848
849 size_t
850 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
851 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
852 }
853
854 size_t ConcurrentMarkSweepGeneration::max_available() const {
855 return free() + _virtual_space.uncommitted_size();
856 }
857
858 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
859 size_t available = max_available();
860 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
861 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
862 if (Verbose && PrintGCDetails) {
863 gclog_or_tty->print_cr(
864 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
865 "max_promo("SIZE_FORMAT")",
866 res? "":" not", available, res? ">=":"<",
867 av_promo, max_promotion_in_bytes);
868 }
869 return res;
870 }
871
872 // At a promotion failure dump information on block layout in heap
873 // (cms old generation).
874 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
875 if (CMSDumpAtPromotionFailure) {
876 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
877 }
878 }
879
880 CompactibleSpace*
881 ConcurrentMarkSweepGeneration::first_compaction_space() const {
882 return _cmsSpace;
883 }
884
885 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
886 // Clear the promotion information. These pointers can be adjusted
887 // along with all the other pointers into the heap but
888 // compaction is expected to be a rare event with
889 // a heap using cms so don't do it without seeing the need.
890 if (CollectedHeap::use_parallel_gc_threads()) {
891 for (uint i = 0; i < ParallelGCThreads; i++) {
892 _par_gc_thread_states[i]->promo.reset();
893 }
894 }
895 }
896
897 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
898 blk->do_space(_cmsSpace);
899 }
900
901 void ConcurrentMarkSweepGeneration::compute_new_size() {
902 assert_locked_or_safepoint(Heap_lock);
903
904 // If incremental collection failed, we just want to expand
905 // to the limit.
906 if (incremental_collection_failed()) {
907 clear_incremental_collection_failed();
908 grow_to_reserved();
909 return;
910 }
911
912 // The heap has been compacted but not reset yet.
913 // Any metric such as free() or used() will be incorrect.
914
915 CardGeneration::compute_new_size();
916
917 // Reset again after a possible resizing
918 if (did_compact()) {
919 cmsSpace()->reset_after_compaction();
920 }
921 }
922
923 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
924 assert_locked_or_safepoint(Heap_lock);
925
926 // If incremental collection failed, we just want to expand
927 // to the limit.
928 if (incremental_collection_failed()) {
929 clear_incremental_collection_failed();
930 grow_to_reserved();
931 return;
932 }
933
934 double free_percentage = ((double) free()) / capacity();
935 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
936 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
937
938 // compute expansion delta needed for reaching desired free percentage
939 if (free_percentage < desired_free_percentage) {
940 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
941 assert(desired_capacity >= capacity(), "invalid expansion size");
942 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
943 if (PrintGCDetails && Verbose) {
944 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
945 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
946 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
947 gclog_or_tty->print_cr(" Desired free fraction %f",
948 desired_free_percentage);
949 gclog_or_tty->print_cr(" Maximum free fraction %f",
950 maximum_free_percentage);
951 gclog_or_tty->print_cr(" Capacity "SIZE_FORMAT, capacity()/1000);
952 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
953 desired_capacity/1000);
954 int prev_level = level() - 1;
955 if (prev_level >= 0) {
956 size_t prev_size = 0;
957 GenCollectedHeap* gch = GenCollectedHeap::heap();
958 Generation* prev_gen = gch->young_gen();
959 prev_size = prev_gen->capacity();
960 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
961 prev_size/1000);
962 }
963 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
964 unsafe_max_alloc_nogc()/1000);
965 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
966 contiguous_available()/1000);
967 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
968 expand_bytes);
969 }
970 // safe if expansion fails
971 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
972 if (PrintGCDetails && Verbose) {
973 gclog_or_tty->print_cr(" Expanded free fraction %f",
974 ((double) free()) / capacity());
975 }
976 } else {
977 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
978 assert(desired_capacity <= capacity(), "invalid expansion size");
979 size_t shrink_bytes = capacity() - desired_capacity;
980 // Don't shrink unless the delta is greater than the minimum shrink we want
981 if (shrink_bytes >= MinHeapDeltaBytes) {
982 shrink_free_list_by(shrink_bytes);
983 }
984 }
985 }
986
987 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
988 return cmsSpace()->freelistLock();
989 }
990
991 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
992 bool tlab) {
993 CMSSynchronousYieldRequest yr;
994 MutexLockerEx x(freelistLock(),
995 Mutex::_no_safepoint_check_flag);
996 return have_lock_and_allocate(size, tlab);
997 }
998
999 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
1000 bool tlab /* ignored */) {
1001 assert_lock_strong(freelistLock());
1002 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1003 HeapWord* res = cmsSpace()->allocate(adjustedSize);
1004 // Allocate the object live (grey) if the background collector has
1005 // started marking. This is necessary because the marker may
1006 // have passed this address and consequently this object will
1007 // not otherwise be greyed and would be incorrectly swept up.
1008 // Note that if this object contains references, the writing
1009 // of those references will dirty the card containing this object
1010 // allowing the object to be blackened (and its references scanned)
1011 // either during a preclean phase or at the final checkpoint.
1012 if (res != NULL) {
1013 // We may block here with an uninitialized object with
1014 // its mark-bit or P-bits not yet set. Such objects need
1015 // to be safely navigable by block_start().
1016 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1017 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1018 collector()->direct_allocated(res, adjustedSize);
1019 _direct_allocated_words += adjustedSize;
1020 // allocation counters
1021 NOT_PRODUCT(
1022 _numObjectsAllocated++;
1023 _numWordsAllocated += (int)adjustedSize;
1024 )
1025 }
1026 return res;
1027 }
1028
1029 // In the case of direct allocation by mutators in a generation that
1030 // is being concurrently collected, the object must be allocated
1031 // live (grey) if the background collector has started marking.
1032 // This is necessary because the marker may
1033 // have passed this address and consequently this object will
1034 // not otherwise be greyed and would be incorrectly swept up.
1035 // Note that if this object contains references, the writing
1036 // of those references will dirty the card containing this object
1037 // allowing the object to be blackened (and its references scanned)
1038 // either during a preclean phase or at the final checkpoint.
1039 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1040 assert(_markBitMap.covers(start, size), "Out of bounds");
1041 if (_collectorState >= Marking) {
1042 MutexLockerEx y(_markBitMap.lock(),
1043 Mutex::_no_safepoint_check_flag);
1044 // [see comments preceding SweepClosure::do_blk() below for details]
1045 //
1046 // Can the P-bits be deleted now? JJJ
1047 //
1048 // 1. need to mark the object as live so it isn't collected
1049 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1050 // 3. need to mark the end of the object so marking, precleaning or sweeping
1051 // can skip over uninitialized or unparsable objects. An allocated
1052 // object is considered uninitialized for our purposes as long as
1053 // its klass word is NULL. All old gen objects are parsable
1054 // as soon as they are initialized.)
1055 _markBitMap.mark(start); // object is live
1056 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1057 _markBitMap.mark(start + size - 1);
1058 // mark end of object
1059 }
1060 // check that oop looks uninitialized
1061 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1062 }
1063
1064 void CMSCollector::promoted(bool par, HeapWord* start,
1065 bool is_obj_array, size_t obj_size) {
1066 assert(_markBitMap.covers(start), "Out of bounds");
1067 // See comment in direct_allocated() about when objects should
1068 // be allocated live.
1069 if (_collectorState >= Marking) {
1070 // we already hold the marking bit map lock, taken in
1071 // the prologue
1072 if (par) {
1073 _markBitMap.par_mark(start);
1074 } else {
1075 _markBitMap.mark(start);
1076 }
1077 // We don't need to mark the object as uninitialized (as
1078 // in direct_allocated above) because this is being done with the
1079 // world stopped and the object will be initialized by the
1080 // time the marking, precleaning or sweeping get to look at it.
1081 // But see the code for copying objects into the CMS generation,
1082 // where we need to ensure that concurrent readers of the
1083 // block offset table are able to safely navigate a block that
1084 // is in flux from being free to being allocated (and in
1085 // transition while being copied into) and subsequently
1086 // becoming a bona-fide object when the copy/promotion is complete.
1087 assert(SafepointSynchronize::is_at_safepoint(),
1088 "expect promotion only at safepoints");
1089
1090 if (_collectorState < Sweeping) {
1091 // Mark the appropriate cards in the modUnionTable, so that
1092 // this object gets scanned before the sweep. If this is
1093 // not done, CMS generation references in the object might
1094 // not get marked.
1095 // For the case of arrays, which are otherwise precisely
1096 // marked, we need to dirty the entire array, not just its head.
1097 if (is_obj_array) {
1098 // The [par_]mark_range() method expects mr.end() below to
1099 // be aligned to the granularity of a bit's representation
1100 // in the heap. In the case of the MUT below, that's a
1101 // card size.
1102 MemRegion mr(start,
1103 (HeapWord*)round_to((intptr_t)(start + obj_size),
1104 CardTableModRefBS::card_size /* bytes */));
1105 if (par) {
1106 _modUnionTable.par_mark_range(mr);
1107 } else {
1108 _modUnionTable.mark_range(mr);
1109 }
1110 } else { // not an obj array; we can just mark the head
1111 if (par) {
1112 _modUnionTable.par_mark(start);
1113 } else {
1114 _modUnionTable.mark(start);
1115 }
1116 }
1117 }
1118 }
1119 }
1120
1121 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1122 {
1123 size_t delta = pointer_delta(addr, space->bottom());
1124 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1125 }
1126
1127 void CMSCollector::icms_update_allocation_limits()
1128 {
1129 Generation* young = GenCollectedHeap::heap()->young_gen();
1130 EdenSpace* eden = young->as_DefNewGeneration()->eden();
1131
1132 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1133 if (CMSTraceIncrementalPacing) {
1134 stats().print();
1135 }
1136
1137 assert(duty_cycle <= 100, "invalid duty cycle");
1138 if (duty_cycle != 0) {
1139 // The duty_cycle is a percentage between 0 and 100; convert to words and
1140 // then compute the offset from the endpoints of the space.
1141 size_t free_words = eden->free() / HeapWordSize;
1142 double free_words_dbl = (double)free_words;
1143 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1144 size_t offset_words = (free_words - duty_cycle_words) / 2;
1145
1146 _icms_start_limit = eden->top() + offset_words;
1147 _icms_stop_limit = eden->end() - offset_words;
1148
1149 // The limits may be adjusted (shifted to the right) by
1150 // CMSIncrementalOffset, to allow the application more mutator time after a
1151 // young gen gc (when all mutators were stopped) and before CMS starts and
1152 // takes away one or more cpus.
1153 if (CMSIncrementalOffset != 0) {
1154 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1155 size_t adjustment = (size_t)adjustment_dbl;
1156 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1157 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1158 _icms_start_limit += adjustment;
1159 _icms_stop_limit = tmp_stop;
1160 }
1161 }
1162 }
1163 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1164 _icms_start_limit = _icms_stop_limit = eden->end();
1165 }
1166
1167 // Install the new start limit.
1168 eden->set_soft_end(_icms_start_limit);
1169
1170 if (CMSTraceIncrementalMode) {
1171 gclog_or_tty->print(" icms alloc limits: "
1172 PTR_FORMAT "," PTR_FORMAT
1173 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1174 p2i(_icms_start_limit), p2i(_icms_stop_limit),
1175 percent_of_space(eden, _icms_start_limit),
1176 percent_of_space(eden, _icms_stop_limit));
1177 if (Verbose) {
1178 gclog_or_tty->print("eden: ");
1179 eden->print_on(gclog_or_tty);
1180 }
1181 }
1182 }
1183
1184 // Any changes here should try to maintain the invariant
1185 // that if this method is called with _icms_start_limit
1186 // and _icms_stop_limit both NULL, then it should return NULL
1187 // and not notify the icms thread.
1188 HeapWord*
1189 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1190 size_t word_size)
1191 {
1192 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1193 // nop.
1194 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1195 if (top <= _icms_start_limit) {
1196 if (CMSTraceIncrementalMode) {
1197 space->print_on(gclog_or_tty);
1198 gclog_or_tty->stamp();
1199 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1200 ", new limit=" PTR_FORMAT
1201 " (" SIZE_FORMAT "%%)",
1202 p2i(top), p2i(_icms_stop_limit),
1203 percent_of_space(space, _icms_stop_limit));
1204 }
1205 ConcurrentMarkSweepThread::start_icms();
1206 assert(top < _icms_stop_limit, "Tautology");
1207 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1208 return _icms_stop_limit;
1209 }
1210
1211 // The allocation will cross both the _start and _stop limits, so do the
1212 // stop notification also and return end().
1213 if (CMSTraceIncrementalMode) {
1214 space->print_on(gclog_or_tty);
1215 gclog_or_tty->stamp();
1216 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1217 ", new limit=" PTR_FORMAT
1218 " (" SIZE_FORMAT "%%)",
1219 p2i(top), p2i(space->end()),
1220 percent_of_space(space, space->end()));
1221 }
1222 ConcurrentMarkSweepThread::stop_icms();
1223 return space->end();
1224 }
1225
1226 if (top <= _icms_stop_limit) {
1227 if (CMSTraceIncrementalMode) {
1228 space->print_on(gclog_or_tty);
1229 gclog_or_tty->stamp();
1230 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1231 ", new limit=" PTR_FORMAT
1232 " (" SIZE_FORMAT "%%)",
1233 top, space->end(),
1234 percent_of_space(space, space->end()));
1235 }
1236 ConcurrentMarkSweepThread::stop_icms();
1237 return space->end();
1238 }
1239
1240 if (CMSTraceIncrementalMode) {
1241 space->print_on(gclog_or_tty);
1242 gclog_or_tty->stamp();
1243 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1244 ", new limit=" PTR_FORMAT,
1245 top, NULL);
1246 }
1247 }
1248
1249 return NULL;
1250 }
1251
1252 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1253 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1254 // allocate, copy and if necessary update promoinfo --
1255 // delegate to underlying space.
1256 assert_lock_strong(freelistLock());
1257
1258 #ifndef PRODUCT
1259 if (Universe::heap()->promotion_should_fail()) {
1260 return NULL;
1261 }
1262 #endif // #ifndef PRODUCT
1263
1264 oop res = _cmsSpace->promote(obj, obj_size);
1265 if (res == NULL) {
1266 // expand and retry
1267 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1268 expand(s*HeapWordSize, MinHeapDeltaBytes,
1269 CMSExpansionCause::_satisfy_promotion);
1270 // Since this is the old generation, we don't try to promote
1271 // into a more senior generation.
1272 res = _cmsSpace->promote(obj, obj_size);
1273 }
1274 if (res != NULL) {
1275 // See comment in allocate() about when objects should
1276 // be allocated live.
1277 assert(obj->is_oop(), "Will dereference klass pointer below");
1278 collector()->promoted(false, // Not parallel
1279 (HeapWord*)res, obj->is_objArray(), obj_size);
1280 // promotion counters
1281 NOT_PRODUCT(
1282 _numObjectsPromoted++;
1283 _numWordsPromoted +=
1284 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1285 )
1286 }
1287 return res;
1288 }
1289
1290
1291 HeapWord*
1292 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1293 HeapWord* top,
1294 size_t word_sz)
1295 {
1296 return collector()->allocation_limit_reached(space, top, word_sz);
1297 }
1298
1299 // IMPORTANT: Notes on object size recognition in CMS.
1300 // ---------------------------------------------------
1301 // A block of storage in the CMS generation is always in
1302 // one of three states. A free block (FREE), an allocated
1303 // object (OBJECT) whose size() method reports the correct size,
1304 // and an intermediate state (TRANSIENT) in which its size cannot
1305 // be accurately determined.
1306 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1307 // -----------------------------------------------------
1308 // FREE: klass_word & 1 == 1; mark_word holds block size
1309 //
1310 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1311 // obj->size() computes correct size
1312 //
1313 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1314 //
1315 // STATE IDENTIFICATION: (64 bit+COOPS)
1316 // ------------------------------------
1317 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1318 //
1319 // OBJECT: klass_word installed; klass_word != 0;
1320 // obj->size() computes correct size
1321 //
1322 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1323 //
1324 //
1325 // STATE TRANSITION DIAGRAM
1326 //
1327 // mut / parnew mut / parnew
1328 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1329 // ^ |
1330 // |------------------------ DEAD <------------------------------------|
1331 // sweep mut
1332 //
1333 // While a block is in TRANSIENT state its size cannot be determined
1334 // so readers will either need to come back later or stall until
1335 // the size can be determined. Note that for the case of direct
1336 // allocation, P-bits, when available, may be used to determine the
1337 // size of an object that may not yet have been initialized.
1338
1339 // Things to support parallel young-gen collection.
1340 oop
1341 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1342 oop old, markOop m,
1343 size_t word_sz) {
1344 #ifndef PRODUCT
1345 if (Universe::heap()->promotion_should_fail()) {
1346 return NULL;
1347 }
1348 #endif // #ifndef PRODUCT
1349
1350 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1351 PromotionInfo* promoInfo = &ps->promo;
1352 // if we are tracking promotions, then first ensure space for
1353 // promotion (including spooling space for saving header if necessary).
1354 // then allocate and copy, then track promoted info if needed.
1355 // When tracking (see PromotionInfo::track()), the mark word may
1356 // be displaced and in this case restoration of the mark word
1357 // occurs in the (oop_since_save_marks_)iterate phase.
1358 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1359 // Out of space for allocating spooling buffers;
1360 // try expanding and allocating spooling buffers.
1361 if (!expand_and_ensure_spooling_space(promoInfo)) {
1362 return NULL;
1363 }
1364 }
1365 assert(promoInfo->has_spooling_space(), "Control point invariant");
1366 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1367 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1368 if (obj_ptr == NULL) {
1369 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1370 if (obj_ptr == NULL) {
1371 return NULL;
1372 }
1373 }
1374 oop obj = oop(obj_ptr);
1375 OrderAccess::storestore();
1376 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1377 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1378 // IMPORTANT: See note on object initialization for CMS above.
1379 // Otherwise, copy the object. Here we must be careful to insert the
1380 // klass pointer last, since this marks the block as an allocated object.
1381 // Except with compressed oops it's the mark word.
1382 HeapWord* old_ptr = (HeapWord*)old;
1383 // Restore the mark word copied above.
1384 obj->set_mark(m);
1385 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1386 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1387 OrderAccess::storestore();
1388
1389 if (UseCompressedClassPointers) {
1390 // Copy gap missed by (aligned) header size calculation below
1391 obj->set_klass_gap(old->klass_gap());
1392 }
1393 if (word_sz > (size_t)oopDesc::header_size()) {
1394 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1395 obj_ptr + oopDesc::header_size(),
1396 word_sz - oopDesc::header_size());
1397 }
1398
1399 // Now we can track the promoted object, if necessary. We take care
1400 // to delay the transition from uninitialized to full object
1401 // (i.e., insertion of klass pointer) until after, so that it
1402 // atomically becomes a promoted object.
1403 if (promoInfo->tracking()) {
1404 promoInfo->track((PromotedObject*)obj, old->klass());
1405 }
1406 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1407 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1408 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1409
1410 // Finally, install the klass pointer (this should be volatile).
1411 OrderAccess::storestore();
1412 obj->set_klass(old->klass());
1413 // We should now be able to calculate the right size for this object
1414 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1415
1416 collector()->promoted(true, // parallel
1417 obj_ptr, old->is_objArray(), word_sz);
1418
1419 NOT_PRODUCT(
1420 Atomic::inc_ptr(&_numObjectsPromoted);
1421 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1422 )
1423
1424 return obj;
1425 }
1426
1427 void
1428 ConcurrentMarkSweepGeneration::
1429 par_promote_alloc_undo(int thread_num,
1430 HeapWord* obj, size_t word_sz) {
1431 // CMS does not support promotion undo.
1432 ShouldNotReachHere();
1433 }
1434
1435 void
1436 ConcurrentMarkSweepGeneration::
1437 par_promote_alloc_done(int thread_num) {
1438 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1439 ps->lab.retire(thread_num);
1440 }
1441
1442 void
1443 ConcurrentMarkSweepGeneration::
1444 par_oop_since_save_marks_iterate_done(int thread_num) {
1445 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1446 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1447 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1448 }
1449
1450 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1451 size_t size,
1452 bool tlab)
1453 {
1454 // We allow a STW collection only if a full
1455 // collection was requested.
1456 return full || should_allocate(size, tlab); // FIX ME !!!
1457 // This and promotion failure handling are connected at the
1458 // hip and should be fixed by untying them.
1459 }
1460
1461 bool CMSCollector::shouldConcurrentCollect() {
1462 if (_full_gc_requested) {
1463 if (Verbose && PrintGCDetails) {
1464 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1465 " gc request (or gc_locker)");
1466 }
1467 return true;
1468 }
1469
1470 // For debugging purposes, change the type of collection.
1471 // If the rotation is not on the concurrent collection
1472 // type, don't start a concurrent collection.
1473 NOT_PRODUCT(
1474 if (RotateCMSCollectionTypes &&
1475 (_cmsGen->debug_collection_type() !=
1476 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1477 assert(_cmsGen->debug_collection_type() !=
1478 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1479 "Bad cms collection type");
1480 return false;
1481 }
1482 )
1483
1484 FreelistLocker x(this);
1485 // ------------------------------------------------------------------
1486 // Print out lots of information which affects the initiation of
1487 // a collection.
1488 if (PrintCMSInitiationStatistics && stats().valid()) {
1489 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1490 gclog_or_tty->stamp();
1491 gclog_or_tty->cr();
1492 stats().print_on(gclog_or_tty);
1493 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1494 stats().time_until_cms_gen_full());
1495 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1496 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1497 _cmsGen->contiguous_available());
1498 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1499 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1500 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1501 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1502 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1503 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1504 gclog_or_tty->print_cr("metadata initialized %d",
1505 MetaspaceGC::should_concurrent_collect());
1506 }
1507 // ------------------------------------------------------------------
1508
1509 // If the estimated time to complete a cms collection (cms_duration())
1510 // is less than the estimated time remaining until the cms generation
1511 // is full, start a collection.
1512 if (!UseCMSInitiatingOccupancyOnly) {
1513 if (stats().valid()) {
1514 if (stats().time_until_cms_start() == 0.0) {
1515 return true;
1516 }
1517 } else {
1518 // We want to conservatively collect somewhat early in order
1519 // to try and "bootstrap" our CMS/promotion statistics;
1520 // this branch will not fire after the first successful CMS
1521 // collection because the stats should then be valid.
1522 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1523 if (Verbose && PrintGCDetails) {
1524 gclog_or_tty->print_cr(
1525 " CMSCollector: collect for bootstrapping statistics:"
1526 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1527 _bootstrap_occupancy);
1528 }
1529 return true;
1530 }
1531 }
1532 }
1533
1534 // Otherwise, we start a collection cycle if
1535 // old gen want a collection cycle started. Each may use
1536 // an appropriate criterion for making this decision.
1537 // XXX We need to make sure that the gen expansion
1538 // criterion dovetails well with this. XXX NEED TO FIX THIS
1539 if (_cmsGen->should_concurrent_collect()) {
1540 if (Verbose && PrintGCDetails) {
1541 gclog_or_tty->print_cr("CMS old gen initiated");
1542 }
1543 return true;
1544 }
1545
1546 // We start a collection if we believe an incremental collection may fail;
1547 // this is not likely to be productive in practice because it's probably too
1548 // late anyway.
1549 GenCollectedHeap* gch = GenCollectedHeap::heap();
1550 assert(gch->collector_policy()->is_generation_policy(),
1551 "You may want to check the correctness of the following");
1552 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1553 if (Verbose && PrintGCDetails) {
1554 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1555 }
1556 return true;
1557 }
1558
1559 if (MetaspaceGC::should_concurrent_collect()) {
1560 if (Verbose && PrintGCDetails) {
1561 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1562 }
1563 return true;
1564 }
1565
1566 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1567 if (CMSTriggerInterval >= 0) {
1568 if (CMSTriggerInterval == 0) {
1569 // Trigger always
1570 return true;
1571 }
1572
1573 // Check the CMS time since begin (we do not check the stats validity
1574 // as we want to be able to trigger the first CMS cycle as well)
1575 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1576 if (Verbose && PrintGCDetails) {
1577 if (stats().valid()) {
1578 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1579 stats().cms_time_since_begin());
1580 } else {
1581 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1582 }
1583 }
1584 return true;
1585 }
1586 }
1587
1588 return false;
1589 }
1590
1591 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1592
1593 // Clear _expansion_cause fields of constituent generations
1594 void CMSCollector::clear_expansion_cause() {
1595 _cmsGen->clear_expansion_cause();
1596 }
1597
1598 // We should be conservative in starting a collection cycle. To
1599 // start too eagerly runs the risk of collecting too often in the
1600 // extreme. To collect too rarely falls back on full collections,
1601 // which works, even if not optimum in terms of concurrent work.
1602 // As a work around for too eagerly collecting, use the flag
1603 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1604 // giving the user an easily understandable way of controlling the
1605 // collections.
1606 // We want to start a new collection cycle if any of the following
1607 // conditions hold:
1608 // . our current occupancy exceeds the configured initiating occupancy
1609 // for this generation, or
1610 // . we recently needed to expand this space and have not, since that
1611 // expansion, done a collection of this generation, or
1612 // . the underlying space believes that it may be a good idea to initiate
1613 // a concurrent collection (this may be based on criteria such as the
1614 // following: the space uses linear allocation and linear allocation is
1615 // going to fail, or there is believed to be excessive fragmentation in
1616 // the generation, etc... or ...
1617 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1618 // the case of the old generation; see CR 6543076):
1619 // we may be approaching a point at which allocation requests may fail because
1620 // we will be out of sufficient free space given allocation rate estimates.]
1621 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1622
1623 assert_lock_strong(freelistLock());
1624 if (occupancy() > initiating_occupancy()) {
1625 if (PrintGCDetails && Verbose) {
1626 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1627 short_name(), occupancy(), initiating_occupancy());
1628 }
1629 return true;
1630 }
1631 if (UseCMSInitiatingOccupancyOnly) {
1632 return false;
1633 }
1634 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1635 if (PrintGCDetails && Verbose) {
1636 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1637 short_name());
1638 }
1639 return true;
1640 }
1641 if (_cmsSpace->should_concurrent_collect()) {
1642 if (PrintGCDetails && Verbose) {
1643 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1644 short_name());
1645 }
1646 return true;
1647 }
1648 return false;
1649 }
1650
1651 void ConcurrentMarkSweepGeneration::collect(bool full,
1652 bool clear_all_soft_refs,
1653 size_t size,
1654 bool tlab)
1655 {
1656 collector()->collect(full, clear_all_soft_refs, size, tlab);
1657 }
1658
1659 void CMSCollector::collect(bool full,
1660 bool clear_all_soft_refs,
1661 size_t size,
1662 bool tlab)
1663 {
1664 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1665 // For debugging purposes skip the collection if the state
1666 // is not currently idle
1667 if (TraceCMSState) {
1668 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1669 Thread::current(), full, _collectorState);
1670 }
1671 return;
1672 }
1673
1674 // The following "if" branch is present for defensive reasons.
1675 // In the current uses of this interface, it can be replaced with:
1676 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1677 // But I am not placing that assert here to allow future
1678 // generality in invoking this interface.
1679 if (GC_locker::is_active()) {
1680 // A consistency test for GC_locker
1681 assert(GC_locker::needs_gc(), "Should have been set already");
1682 // Skip this foreground collection, instead
1683 // expanding the heap if necessary.
1684 // Need the free list locks for the call to free() in compute_new_size()
1685 compute_new_size();
1686 return;
1687 }
1688 acquire_control_and_collect(full, clear_all_soft_refs);
1689 _full_gcs_since_conc_gc++;
1690 }
1691
1692 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1693 GenCollectedHeap* gch = GenCollectedHeap::heap();
1694 unsigned int gc_count = gch->total_full_collections();
1695 if (gc_count == full_gc_count) {
1696 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1697 _full_gc_requested = true;
1698 _full_gc_cause = cause;
1699 CGC_lock->notify(); // nudge CMS thread
1700 } else {
1701 assert(gc_count > full_gc_count, "Error: causal loop");
1702 }
1703 }
1704
1705 bool CMSCollector::is_external_interruption() {
1706 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1707 return GCCause::is_user_requested_gc(cause) ||
1708 GCCause::is_serviceability_requested_gc(cause);
1709 }
1710
1711 void CMSCollector::report_concurrent_mode_interruption() {
1712 if (is_external_interruption()) {
1713 if (PrintGCDetails) {
1714 gclog_or_tty->print(" (concurrent mode interrupted)");
1715 }
1716 } else {
1717 if (PrintGCDetails) {
1718 gclog_or_tty->print(" (concurrent mode failure)");
1719 }
1720 _gc_tracer_cm->report_concurrent_mode_failure();
1721 }
1722 }
1723
1724
1725 // The foreground and background collectors need to coordinate in order
1726 // to make sure that they do not mutually interfere with CMS collections.
1727 // When a background collection is active,
1728 // the foreground collector may need to take over (preempt) and
1729 // synchronously complete an ongoing collection. Depending on the
1730 // frequency of the background collections and the heap usage
1731 // of the application, this preemption can be seldom or frequent.
1732 // There are only certain
1733 // points in the background collection that the "collection-baton"
1734 // can be passed to the foreground collector.
1735 //
1736 // The foreground collector will wait for the baton before
1737 // starting any part of the collection. The foreground collector
1738 // will only wait at one location.
1739 //
1740 // The background collector will yield the baton before starting a new
1741 // phase of the collection (e.g., before initial marking, marking from roots,
1742 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1743 // of the loop which switches the phases. The background collector does some
1744 // of the phases (initial mark, final re-mark) with the world stopped.
1745 // Because of locking involved in stopping the world,
1746 // the foreground collector should not block waiting for the background
1747 // collector when it is doing a stop-the-world phase. The background
1748 // collector will yield the baton at an additional point just before
1749 // it enters a stop-the-world phase. Once the world is stopped, the
1750 // background collector checks the phase of the collection. If the
1751 // phase has not changed, it proceeds with the collection. If the
1752 // phase has changed, it skips that phase of the collection. See
1753 // the comments on the use of the Heap_lock in collect_in_background().
1754 //
1755 // Variable used in baton passing.
1756 // _foregroundGCIsActive - Set to true by the foreground collector when
1757 // it wants the baton. The foreground clears it when it has finished
1758 // the collection.
1759 // _foregroundGCShouldWait - Set to true by the background collector
1760 // when it is running. The foreground collector waits while
1761 // _foregroundGCShouldWait is true.
1762 // CGC_lock - monitor used to protect access to the above variables
1763 // and to notify the foreground and background collectors.
1764 // _collectorState - current state of the CMS collection.
1765 //
1766 // The foreground collector
1767 // acquires the CGC_lock
1768 // sets _foregroundGCIsActive
1769 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1770 // various locks acquired in preparation for the collection
1771 // are released so as not to block the background collector
1772 // that is in the midst of a collection
1773 // proceeds with the collection
1774 // clears _foregroundGCIsActive
1775 // returns
1776 //
1777 // The background collector in a loop iterating on the phases of the
1778 // collection
1779 // acquires the CGC_lock
1780 // sets _foregroundGCShouldWait
1781 // if _foregroundGCIsActive is set
1782 // clears _foregroundGCShouldWait, notifies _CGC_lock
1783 // waits on _CGC_lock for _foregroundGCIsActive to become false
1784 // and exits the loop.
1785 // otherwise
1786 // proceed with that phase of the collection
1787 // if the phase is a stop-the-world phase,
1788 // yield the baton once more just before enqueueing
1789 // the stop-world CMS operation (executed by the VM thread).
1790 // returns after all phases of the collection are done
1791 //
1792
1793 void CMSCollector::acquire_control_and_collect(bool full,
1794 bool clear_all_soft_refs) {
1795 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1796 assert(!Thread::current()->is_ConcurrentGC_thread(),
1797 "shouldn't try to acquire control from self!");
1798
1799 // Start the protocol for acquiring control of the
1800 // collection from the background collector (aka CMS thread).
1801 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1802 "VM thread should have CMS token");
1803 // Remember the possibly interrupted state of an ongoing
1804 // concurrent collection
1805 CollectorState first_state = _collectorState;
1806
1807 // Signal to a possibly ongoing concurrent collection that
1808 // we want to do a foreground collection.
1809 _foregroundGCIsActive = true;
1810
1811 // Disable incremental mode during a foreground collection.
1812 ICMSDisabler icms_disabler;
1813
1814 // release locks and wait for a notify from the background collector
1815 // releasing the locks in only necessary for phases which
1816 // do yields to improve the granularity of the collection.
1817 assert_lock_strong(bitMapLock());
1818 // We need to lock the Free list lock for the space that we are
1819 // currently collecting.
1820 assert(haveFreelistLocks(), "Must be holding free list locks");
1821 bitMapLock()->unlock();
1822 releaseFreelistLocks();
1823 {
1824 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1825 if (_foregroundGCShouldWait) {
1826 // We are going to be waiting for action for the CMS thread;
1827 // it had better not be gone (for instance at shutdown)!
1828 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1829 "CMS thread must be running");
1830 // Wait here until the background collector gives us the go-ahead
1831 ConcurrentMarkSweepThread::clear_CMS_flag(
1832 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1833 // Get a possibly blocked CMS thread going:
1834 // Note that we set _foregroundGCIsActive true above,
1835 // without protection of the CGC_lock.
1836 CGC_lock->notify();
1837 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1838 "Possible deadlock");
1839 while (_foregroundGCShouldWait) {
1840 // wait for notification
1841 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1842 // Possibility of delay/starvation here, since CMS token does
1843 // not know to give priority to VM thread? Actually, i think
1844 // there wouldn't be any delay/starvation, but the proof of
1845 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1846 }
1847 ConcurrentMarkSweepThread::set_CMS_flag(
1848 ConcurrentMarkSweepThread::CMS_vm_has_token);
1849 }
1850 }
1851 // The CMS_token is already held. Get back the other locks.
1852 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1853 "VM thread should have CMS token");
1854 getFreelistLocks();
1855 bitMapLock()->lock_without_safepoint_check();
1856 if (TraceCMSState) {
1857 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1858 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1859 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1860 }
1861
1862 // Check if we need to do a compaction, or if not, whether
1863 // we need to start the mark-sweep from scratch.
1864 bool should_compact = false;
1865 bool should_start_over = false;
1866 decide_foreground_collection_type(clear_all_soft_refs,
1867 &should_compact, &should_start_over);
1868
1869 NOT_PRODUCT(
1870 if (RotateCMSCollectionTypes) {
1871 if (_cmsGen->debug_collection_type() ==
1872 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1873 should_compact = true;
1874 } else if (_cmsGen->debug_collection_type() ==
1875 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1876 should_compact = false;
1877 }
1878 }
1879 )
1880
1881 if (first_state > Idling) {
1882 report_concurrent_mode_interruption();
1883 }
1884
1885 set_did_compact(should_compact);
1886 if (should_compact) {
1887 // If the collection is being acquired from the background
1888 // collector, there may be references on the discovered
1889 // references lists that have NULL referents (being those
1890 // that were concurrently cleared by a mutator) or
1891 // that are no longer active (having been enqueued concurrently
1892 // by the mutator).
1893 // Scrub the list of those references because Mark-Sweep-Compact
1894 // code assumes referents are not NULL and that all discovered
1895 // Reference objects are active.
1896 ref_processor()->clean_up_discovered_references();
1897
1898 if (first_state > Idling) {
1899 save_heap_summary();
1900 }
1901
1902 do_compaction_work(clear_all_soft_refs);
1903
1904 // Has the GC time limit been exceeded?
1905 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1906 size_t max_eden_size = young_gen->max_capacity() -
1907 young_gen->to()->capacity() -
1908 young_gen->from()->capacity();
1909 GenCollectedHeap* gch = GenCollectedHeap::heap();
1910 GCCause::Cause gc_cause = gch->gc_cause();
1911 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1912 young_gen->eden()->used(),
1913 _cmsGen->max_capacity(),
1914 max_eden_size,
1915 full,
1916 gc_cause,
1917 gch->collector_policy());
1918 } else {
1919 do_mark_sweep_work(clear_all_soft_refs, first_state,
1920 should_start_over);
1921 }
1922 // Reset the expansion cause, now that we just completed
1923 // a collection cycle.
1924 clear_expansion_cause();
1925 _foregroundGCIsActive = false;
1926 return;
1927 }
1928
1929 // Resize the tenured generation
1930 // after obtaining the free list locks for the
1931 // two generations.
1932 void CMSCollector::compute_new_size() {
1933 assert_locked_or_safepoint(Heap_lock);
1934 FreelistLocker z(this);
1935 MetaspaceGC::compute_new_size();
1936 _cmsGen->compute_new_size_free_list();
1937 }
1938
1939 // A work method used by foreground collection to determine
1940 // what type of collection (compacting or not, continuing or fresh)
1941 // it should do.
1942 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1943 // and CMSCompactWhenClearAllSoftRefs the default in the future
1944 // and do away with the flags after a suitable period.
1945 void CMSCollector::decide_foreground_collection_type(
1946 bool clear_all_soft_refs, bool* should_compact,
1947 bool* should_start_over) {
1948 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1949 // flag is set, and we have either requested a System.gc() or
1950 // the number of full gc's since the last concurrent cycle
1951 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1952 // or if an incremental collection has failed
1953 GenCollectedHeap* gch = GenCollectedHeap::heap();
1954 assert(gch->collector_policy()->is_generation_policy(),
1955 "You may want to check the correctness of the following");
1956 // Inform cms gen if this was due to partial collection failing.
1957 // The CMS gen may use this fact to determine its expansion policy.
1958 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1959 assert(!_cmsGen->incremental_collection_failed(),
1960 "Should have been noticed, reacted to and cleared");
1961 _cmsGen->set_incremental_collection_failed();
1962 }
1963 *should_compact =
1964 UseCMSCompactAtFullCollection &&
1965 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1966 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1967 gch->incremental_collection_will_fail(true /* consult_young */));
1968 *should_start_over = false;
1969 if (clear_all_soft_refs && !*should_compact) {
1970 // We are about to do a last ditch collection attempt
1971 // so it would normally make sense to do a compaction
1972 // to reclaim as much space as possible.
1973 if (CMSCompactWhenClearAllSoftRefs) {
1974 // Default: The rationale is that in this case either
1975 // we are past the final marking phase, in which case
1976 // we'd have to start over, or so little has been done
1977 // that there's little point in saving that work. Compaction
1978 // appears to be the sensible choice in either case.
1979 *should_compact = true;
1980 } else {
1981 // We have been asked to clear all soft refs, but not to
1982 // compact. Make sure that we aren't past the final checkpoint
1983 // phase, for that is where we process soft refs. If we are already
1984 // past that phase, we'll need to redo the refs discovery phase and
1985 // if necessary clear soft refs that weren't previously
1986 // cleared. We do so by remembering the phase in which
1987 // we came in, and if we are past the refs processing
1988 // phase, we'll choose to just redo the mark-sweep
1989 // collection from scratch.
1990 if (_collectorState > FinalMarking) {
1991 // We are past the refs processing phase;
1992 // start over and do a fresh synchronous CMS cycle
1993 _collectorState = Resetting; // skip to reset to start new cycle
1994 reset(false /* == !asynch */);
1995 *should_start_over = true;
1996 } // else we can continue a possibly ongoing current cycle
1997 }
1998 }
1999 }
2000
2001 // A work method used by the foreground collector to do
2002 // a mark-sweep-compact.
2003 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
2004 GenCollectedHeap* gch = GenCollectedHeap::heap();
2005
2006 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
2007 gc_timer->register_gc_start();
2008
2009 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
2010 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
2011
2012 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
2013 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
2014 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
2015 "collections passed to foreground collector", _full_gcs_since_conc_gc);
2016 }
2017
2018 // Temporarily widen the span of the weak reference processing to
2019 // the entire heap.
2020 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
2021 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
2022 // Temporarily, clear the "is_alive_non_header" field of the
2023 // reference processor.
2024 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
2025 // Temporarily make reference _processing_ single threaded (non-MT).
2026 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
2027 // Temporarily make refs discovery atomic
2028 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
2029 // Temporarily make reference _discovery_ single threaded (non-MT)
2030 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
2031
2032 ref_processor()->set_enqueuing_is_done(false);
2033 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
2034 ref_processor()->setup_policy(clear_all_soft_refs);
2035 // If an asynchronous collection finishes, the _modUnionTable is
2036 // all clear. If we are assuming the collection from an asynchronous
2037 // collection, clear the _modUnionTable.
2038 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
2039 "_modUnionTable should be clear if the baton was not passed");
2040 _modUnionTable.clear_all();
2041 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
2042 "mod union for klasses should be clear if the baton was passed");
2043 _ct->klass_rem_set()->clear_mod_union();
2044
2045 // We must adjust the allocation statistics being maintained
2046 // in the free list space. We do so by reading and clearing
2047 // the sweep timer and updating the block flux rate estimates below.
2048 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
2049 if (_inter_sweep_timer.is_active()) {
2050 _inter_sweep_timer.stop();
2051 // Note that we do not use this sample to update the _inter_sweep_estimate.
2052 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
2053 _inter_sweep_estimate.padded_average(),
2054 _intra_sweep_estimate.padded_average());
2055 }
2056
2057 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2058 ref_processor(), clear_all_soft_refs);
2059 #ifdef ASSERT
2060 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2061 size_t free_size = cms_space->free();
2062 assert(free_size ==
2063 pointer_delta(cms_space->end(), cms_space->compaction_top())
2064 * HeapWordSize,
2065 "All the free space should be compacted into one chunk at top");
2066 assert(cms_space->dictionary()->total_chunk_size(
2067 debug_only(cms_space->freelistLock())) == 0 ||
2068 cms_space->totalSizeInIndexedFreeLists() == 0,
2069 "All the free space should be in a single chunk");
2070 size_t num = cms_space->totalCount();
2071 assert((free_size == 0 && num == 0) ||
2072 (free_size > 0 && (num == 1 || num == 2)),
2073 "There should be at most 2 free chunks after compaction");
2074 #endif // ASSERT
2075 _collectorState = Resetting;
2076 assert(_restart_addr == NULL,
2077 "Should have been NULL'd before baton was passed");
2078 reset(false /* == !asynch */);
2079 _cmsGen->reset_after_compaction();
2080 _concurrent_cycles_since_last_unload = 0;
2081
2082 // Clear any data recorded in the PLAB chunk arrays.
2083 if (_survivor_plab_array != NULL) {
2084 reset_survivor_plab_arrays();
2085 }
2086
2087 // Adjust the per-size allocation stats for the next epoch.
2088 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2089 // Restart the "inter sweep timer" for the next epoch.
2090 _inter_sweep_timer.reset();
2091 _inter_sweep_timer.start();
2092
2093 gc_timer->register_gc_end();
2094
2095 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
2096
2097 // For a mark-sweep-compact, compute_new_size() will be called
2098 // in the heap's do_collection() method.
2099 }
2100
2101 // A work method used by the foreground collector to do
2102 // a mark-sweep, after taking over from a possibly on-going
2103 // concurrent mark-sweep collection.
2104 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2105 CollectorState first_state, bool should_start_over) {
2106 if (PrintGC && Verbose) {
2107 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2108 "collector with count %d",
2109 _full_gcs_since_conc_gc);
2110 }
2111 switch (_collectorState) {
2112 case Idling:
2113 if (first_state == Idling || should_start_over) {
2114 // The background GC was not active, or should
2115 // restarted from scratch; start the cycle.
2116 _collectorState = InitialMarking;
2117 }
2118 // If first_state was not Idling, then a background GC
2119 // was in progress and has now finished. No need to do it
2120 // again. Leave the state as Idling.
2121 break;
2122 case Precleaning:
2123 // In the foreground case don't do the precleaning since
2124 // it is not done concurrently and there is extra work
2125 // required.
2126 _collectorState = FinalMarking;
2127 }
2128 collect_in_foreground(clear_all_soft_refs, GenCollectedHeap::heap()->gc_cause());
2129
2130 // For a mark-sweep, compute_new_size() will be called
2131 // in the heap's do_collection() method.
2132 }
2133
2134
2135 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
2136 DefNewGeneration* dng = _young_gen->as_DefNewGeneration();
2137 EdenSpace* eden_space = dng->eden();
2138 ContiguousSpace* from_space = dng->from();
2139 ContiguousSpace* to_space = dng->to();
2140 // Eden
2141 if (_eden_chunk_array != NULL) {
2142 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2143 eden_space->bottom(), eden_space->top(),
2144 eden_space->end(), eden_space->capacity());
2145 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
2146 "_eden_chunk_capacity=" SIZE_FORMAT,
2147 _eden_chunk_index, _eden_chunk_capacity);
2148 for (size_t i = 0; i < _eden_chunk_index; i++) {
2149 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2150 i, _eden_chunk_array[i]);
2151 }
2152 }
2153 // Survivor
2154 if (_survivor_chunk_array != NULL) {
2155 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2156 from_space->bottom(), from_space->top(),
2157 from_space->end(), from_space->capacity());
2158 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
2159 "_survivor_chunk_capacity=" SIZE_FORMAT,
2160 _survivor_chunk_index, _survivor_chunk_capacity);
2161 for (size_t i = 0; i < _survivor_chunk_index; i++) {
2162 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2163 i, _survivor_chunk_array[i]);
2164 }
2165 }
2166 }
2167
2168 void CMSCollector::getFreelistLocks() const {
2169 // Get locks for all free lists in all generations that this
2170 // collector is responsible for
2171 _cmsGen->freelistLock()->lock_without_safepoint_check();
2172 }
2173
2174 void CMSCollector::releaseFreelistLocks() const {
2175 // Release locks for all free lists in all generations that this
2176 // collector is responsible for
2177 _cmsGen->freelistLock()->unlock();
2178 }
2179
2180 bool CMSCollector::haveFreelistLocks() const {
2181 // Check locks for all free lists in all generations that this
2182 // collector is responsible for
2183 assert_lock_strong(_cmsGen->freelistLock());
2184 PRODUCT_ONLY(ShouldNotReachHere());
2185 return true;
2186 }
2187
2188 // A utility class that is used by the CMS collector to
2189 // temporarily "release" the foreground collector from its
2190 // usual obligation to wait for the background collector to
2191 // complete an ongoing phase before proceeding.
2192 class ReleaseForegroundGC: public StackObj {
2193 private:
2194 CMSCollector* _c;
2195 public:
2196 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2197 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2198 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2199 // allow a potentially blocked foreground collector to proceed
2200 _c->_foregroundGCShouldWait = false;
2201 if (_c->_foregroundGCIsActive) {
2202 CGC_lock->notify();
2203 }
2204 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2205 "Possible deadlock");
2206 }
2207
2208 ~ReleaseForegroundGC() {
2209 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2210 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2211 _c->_foregroundGCShouldWait = true;
2212 }
2213 };
2214
2215 // There are separate collect_in_background and collect_in_foreground because of
2216 // the different locking requirements of the background collector and the
2217 // foreground collector. There was originally an attempt to share
2218 // one "collect" method between the background collector and the foreground
2219 // collector but the if-then-else required made it cleaner to have
2220 // separate methods.
2221 void CMSCollector::collect_in_background(bool clear_all_soft_refs, GCCause::Cause cause) {
2222 assert(Thread::current()->is_ConcurrentGC_thread(),
2223 "A CMS asynchronous collection is only allowed on a CMS thread.");
2224
2225 GenCollectedHeap* gch = GenCollectedHeap::heap();
2226 {
2227 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2228 MutexLockerEx hl(Heap_lock, safepoint_check);
2229 FreelistLocker fll(this);
2230 MutexLockerEx x(CGC_lock, safepoint_check);
2231 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2232 // The foreground collector is active or we're
2233 // not using asynchronous collections. Skip this
2234 // background collection.
2235 assert(!_foregroundGCShouldWait, "Should be clear");
2236 return;
2237 } else {
2238 assert(_collectorState == Idling, "Should be idling before start.");
2239 _collectorState = InitialMarking;
2240 register_gc_start(cause);
2241 // Reset the expansion cause, now that we are about to begin
2242 // a new cycle.
2243 clear_expansion_cause();
2244
2245 // Clear the MetaspaceGC flag since a concurrent collection
2246 // is starting but also clear it after the collection.
2247 MetaspaceGC::set_should_concurrent_collect(false);
2248 }
2249 // Decide if we want to enable class unloading as part of the
2250 // ensuing concurrent GC cycle.
2251 update_should_unload_classes();
2252 _full_gc_requested = false; // acks all outstanding full gc requests
2253 _full_gc_cause = GCCause::_no_gc;
2254 // Signal that we are about to start a collection
2255 gch->increment_total_full_collections(); // ... starting a collection cycle
2256 _collection_count_start = gch->total_full_collections();
2257 }
2258
2259 // Used for PrintGC
2260 size_t prev_used;
2261 if (PrintGC && Verbose) {
2262 prev_used = _cmsGen->used(); // XXXPERM
2263 }
2264
2265 // The change of the collection state is normally done at this level;
2266 // the exceptions are phases that are executed while the world is
2267 // stopped. For those phases the change of state is done while the
2268 // world is stopped. For baton passing purposes this allows the
2269 // background collector to finish the phase and change state atomically.
2270 // The foreground collector cannot wait on a phase that is done
2271 // while the world is stopped because the foreground collector already
2272 // has the world stopped and would deadlock.
2273 while (_collectorState != Idling) {
2274 if (TraceCMSState) {
2275 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2276 Thread::current(), _collectorState);
2277 }
2278 // The foreground collector
2279 // holds the Heap_lock throughout its collection.
2280 // holds the CMS token (but not the lock)
2281 // except while it is waiting for the background collector to yield.
2282 //
2283 // The foreground collector should be blocked (not for long)
2284 // if the background collector is about to start a phase
2285 // executed with world stopped. If the background
2286 // collector has already started such a phase, the
2287 // foreground collector is blocked waiting for the
2288 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2289 // are executed in the VM thread.
2290 //
2291 // The locking order is
2292 // PendingListLock (PLL) -- if applicable (FinalMarking)
2293 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2294 // CMS token (claimed in
2295 // stop_world_and_do() -->
2296 // safepoint_synchronize() -->
2297 // CMSThread::synchronize())
2298
2299 {
2300 // Check if the FG collector wants us to yield.
2301 CMSTokenSync x(true); // is cms thread
2302 if (waitForForegroundGC()) {
2303 // We yielded to a foreground GC, nothing more to be
2304 // done this round.
2305 assert(_foregroundGCShouldWait == false, "We set it to false in "
2306 "waitForForegroundGC()");
2307 if (TraceCMSState) {
2308 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2309 " exiting collection CMS state %d",
2310 Thread::current(), _collectorState);
2311 }
2312 return;
2313 } else {
2314 // The background collector can run but check to see if the
2315 // foreground collector has done a collection while the
2316 // background collector was waiting to get the CGC_lock
2317 // above. If yes, break so that _foregroundGCShouldWait
2318 // is cleared before returning.
2319 if (_collectorState == Idling) {
2320 break;
2321 }
2322 }
2323 }
2324
2325 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2326 "should be waiting");
2327
2328 switch (_collectorState) {
2329 case InitialMarking:
2330 {
2331 ReleaseForegroundGC x(this);
2332 stats().record_cms_begin();
2333 VM_CMS_Initial_Mark initial_mark_op(this);
2334 VMThread::execute(&initial_mark_op);
2335 }
2336 // The collector state may be any legal state at this point
2337 // since the background collector may have yielded to the
2338 // foreground collector.
2339 break;
2340 case Marking:
2341 // initial marking in checkpointRootsInitialWork has been completed
2342 if (markFromRoots(true)) { // we were successful
2343 assert(_collectorState == Precleaning, "Collector state should "
2344 "have changed");
2345 } else {
2346 assert(_foregroundGCIsActive, "Internal state inconsistency");
2347 }
2348 break;
2349 case Precleaning:
2350 // marking from roots in markFromRoots has been completed
2351 preclean();
2352 assert(_collectorState == AbortablePreclean ||
2353 _collectorState == FinalMarking,
2354 "Collector state should have changed");
2355 break;
2356 case AbortablePreclean:
2357 abortable_preclean();
2358 assert(_collectorState == FinalMarking, "Collector state should "
2359 "have changed");
2360 break;
2361 case FinalMarking:
2362 {
2363 ReleaseForegroundGC x(this);
2364
2365 VM_CMS_Final_Remark final_remark_op(this);
2366 VMThread::execute(&final_remark_op);
2367 }
2368 assert(_foregroundGCShouldWait, "block post-condition");
2369 break;
2370 case Sweeping:
2371 // final marking in checkpointRootsFinal has been completed
2372 sweep(true);
2373 assert(_collectorState == Resizing, "Collector state change "
2374 "to Resizing must be done under the free_list_lock");
2375 _full_gcs_since_conc_gc = 0;
2376
2377 case Resizing: {
2378 // Sweeping has been completed...
2379 // At this point the background collection has completed.
2380 // Don't move the call to compute_new_size() down
2381 // into code that might be executed if the background
2382 // collection was preempted.
2383 {
2384 ReleaseForegroundGC x(this); // unblock FG collection
2385 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2386 CMSTokenSync z(true); // not strictly needed.
2387 if (_collectorState == Resizing) {
2388 compute_new_size();
2389 save_heap_summary();
2390 _collectorState = Resetting;
2391 } else {
2392 assert(_collectorState == Idling, "The state should only change"
2393 " because the foreground collector has finished the collection");
2394 }
2395 }
2396 break;
2397 }
2398 case Resetting:
2399 // CMS heap resizing has been completed
2400 reset(true);
2401 assert(_collectorState == Idling, "Collector state should "
2402 "have changed");
2403
2404 MetaspaceGC::set_should_concurrent_collect(false);
2405
2406 stats().record_cms_end();
2407 // Don't move the concurrent_phases_end() and compute_new_size()
2408 // calls to here because a preempted background collection
2409 // has it's state set to "Resetting".
2410 break;
2411 case Idling:
2412 default:
2413 ShouldNotReachHere();
2414 break;
2415 }
2416 if (TraceCMSState) {
2417 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2418 Thread::current(), _collectorState);
2419 }
2420 assert(_foregroundGCShouldWait, "block post-condition");
2421 }
2422
2423 // Should this be in gc_epilogue?
2424 collector_policy()->counters()->update_counters();
2425
2426 {
2427 // Clear _foregroundGCShouldWait and, in the event that the
2428 // foreground collector is waiting, notify it, before
2429 // returning.
2430 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2431 _foregroundGCShouldWait = false;
2432 if (_foregroundGCIsActive) {
2433 CGC_lock->notify();
2434 }
2435 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2436 "Possible deadlock");
2437 }
2438 if (TraceCMSState) {
2439 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2440 " exiting collection CMS state %d",
2441 Thread::current(), _collectorState);
2442 }
2443 if (PrintGC && Verbose) {
2444 _cmsGen->print_heap_change(prev_used);
2445 }
2446 }
2447
2448 void CMSCollector::register_foreground_gc_start(GCCause::Cause cause) {
2449 if (!_cms_start_registered) {
2450 register_gc_start(cause);
2451 }
2452 }
2453
2454 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2455 _cms_start_registered = true;
2456 _gc_timer_cm->register_gc_start();
2457 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2458 }
2459
2460 void CMSCollector::register_gc_end() {
2461 if (_cms_start_registered) {
2462 report_heap_summary(GCWhen::AfterGC);
2463
2464 _gc_timer_cm->register_gc_end();
2465 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2466 _cms_start_registered = false;
2467 }
2468 }
2469
2470 void CMSCollector::save_heap_summary() {
2471 GenCollectedHeap* gch = GenCollectedHeap::heap();
2472 _last_heap_summary = gch->create_heap_summary();
2473 _last_metaspace_summary = gch->create_metaspace_summary();
2474 }
2475
2476 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2477 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2478 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2479 }
2480
2481 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs, GCCause::Cause cause) {
2482 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2483 "Foreground collector should be waiting, not executing");
2484 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2485 "may only be done by the VM Thread with the world stopped");
2486 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2487 "VM thread should have CMS token");
2488
2489 // The gc id is created in register_foreground_gc_start if this collection is synchronous
2490 const GCId gc_id = _collectorState == InitialMarking ? GCId::peek() : _gc_tracer_cm->gc_id();
2491 NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2492 true, NULL, gc_id);)
2493 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2494
2495 HandleMark hm; // Discard invalid handles created during verification
2496
2497 if (VerifyBeforeGC &&
2498 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2499 Universe::verify();
2500 }
2501
2502 // Snapshot the soft reference policy to be used in this collection cycle.
2503 ref_processor()->setup_policy(clear_all_soft_refs);
2504
2505 // Decide if class unloading should be done
2506 update_should_unload_classes();
2507
2508 bool init_mark_was_synchronous = false; // until proven otherwise
2509 while (_collectorState != Idling) {
2510 if (TraceCMSState) {
2511 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2512 Thread::current(), _collectorState);
2513 }
2514 switch (_collectorState) {
2515 case InitialMarking:
2516 register_foreground_gc_start(cause);
2517 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2518 checkpointRootsInitial(false);
2519 assert(_collectorState == Marking, "Collector state should have changed"
2520 " within checkpointRootsInitial()");
2521 break;
2522 case Marking:
2523 // initial marking in checkpointRootsInitialWork has been completed
2524 if (VerifyDuringGC &&
2525 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2526 Universe::verify("Verify before initial mark: ");
2527 }
2528 {
2529 bool res = markFromRoots(false);
2530 assert(res && _collectorState == FinalMarking, "Collector state should "
2531 "have changed");
2532 break;
2533 }
2534 case FinalMarking:
2535 if (VerifyDuringGC &&
2536 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2537 Universe::verify("Verify before re-mark: ");
2538 }
2539 checkpointRootsFinal(false, clear_all_soft_refs,
2540 init_mark_was_synchronous);
2541 assert(_collectorState == Sweeping, "Collector state should not "
2542 "have changed within checkpointRootsFinal()");
2543 break;
2544 case Sweeping:
2545 // final marking in checkpointRootsFinal has been completed
2546 if (VerifyDuringGC &&
2547 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2548 Universe::verify("Verify before sweep: ");
2549 }
2550 sweep(false);
2551 assert(_collectorState == Resizing, "Incorrect state");
2552 break;
2553 case Resizing: {
2554 // Sweeping has been completed; the actual resize in this case
2555 // is done separately; nothing to be done in this state.
2556 _collectorState = Resetting;
2557 break;
2558 }
2559 case Resetting:
2560 // The heap has been resized.
2561 if (VerifyDuringGC &&
2562 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2563 Universe::verify("Verify before reset: ");
2564 }
2565 save_heap_summary();
2566 reset(false);
2567 assert(_collectorState == Idling, "Collector state should "
2568 "have changed");
2569 break;
2570 case Precleaning:
2571 case AbortablePreclean:
2572 // Elide the preclean phase
2573 _collectorState = FinalMarking;
2574 break;
2575 default:
2576 ShouldNotReachHere();
2577 }
2578 if (TraceCMSState) {
2579 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2580 Thread::current(), _collectorState);
2581 }
2582 }
2583
2584 if (VerifyAfterGC &&
2585 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2586 Universe::verify();
2587 }
2588 if (TraceCMSState) {
2589 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2590 " exiting collection CMS state %d",
2591 Thread::current(), _collectorState);
2592 }
2593 }
2594
2595 bool CMSCollector::waitForForegroundGC() {
2596 bool res = false;
2597 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2598 "CMS thread should have CMS token");
2599 // Block the foreground collector until the
2600 // background collectors decides whether to
2601 // yield.
2602 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2603 _foregroundGCShouldWait = true;
2604 if (_foregroundGCIsActive) {
2605 // The background collector yields to the
2606 // foreground collector and returns a value
2607 // indicating that it has yielded. The foreground
2608 // collector can proceed.
2609 res = true;
2610 _foregroundGCShouldWait = false;
2611 ConcurrentMarkSweepThread::clear_CMS_flag(
2612 ConcurrentMarkSweepThread::CMS_cms_has_token);
2613 ConcurrentMarkSweepThread::set_CMS_flag(
2614 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2615 // Get a possibly blocked foreground thread going
2616 CGC_lock->notify();
2617 if (TraceCMSState) {
2618 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2619 Thread::current(), _collectorState);
2620 }
2621 while (_foregroundGCIsActive) {
2622 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2623 }
2624 ConcurrentMarkSweepThread::set_CMS_flag(
2625 ConcurrentMarkSweepThread::CMS_cms_has_token);
2626 ConcurrentMarkSweepThread::clear_CMS_flag(
2627 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2628 }
2629 if (TraceCMSState) {
2630 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2631 Thread::current(), _collectorState);
2632 }
2633 return res;
2634 }
2635
2636 // Because of the need to lock the free lists and other structures in
2637 // the collector, common to all the generations that the collector is
2638 // collecting, we need the gc_prologues of individual CMS generations
2639 // delegate to their collector. It may have been simpler had the
2640 // current infrastructure allowed one to call a prologue on a
2641 // collector. In the absence of that we have the generation's
2642 // prologue delegate to the collector, which delegates back
2643 // some "local" work to a worker method in the individual generations
2644 // that it's responsible for collecting, while itself doing any
2645 // work common to all generations it's responsible for. A similar
2646 // comment applies to the gc_epilogue()'s.
2647 // The role of the variable _between_prologue_and_epilogue is to
2648 // enforce the invocation protocol.
2649 void CMSCollector::gc_prologue(bool full) {
2650 // Call gc_prologue_work() for the CMSGen
2651 // we are responsible for.
2652
2653 // The following locking discipline assumes that we are only called
2654 // when the world is stopped.
2655 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2656
2657 // The CMSCollector prologue must call the gc_prologues for the
2658 // "generations" that it's responsible
2659 // for.
2660
2661 assert( Thread::current()->is_VM_thread()
2662 || ( CMSScavengeBeforeRemark
2663 && Thread::current()->is_ConcurrentGC_thread()),
2664 "Incorrect thread type for prologue execution");
2665
2666 if (_between_prologue_and_epilogue) {
2667 // We have already been invoked; this is a gc_prologue delegation
2668 // from yet another CMS generation that we are responsible for, just
2669 // ignore it since all relevant work has already been done.
2670 return;
2671 }
2672
2673 // set a bit saying prologue has been called; cleared in epilogue
2674 _between_prologue_and_epilogue = true;
2675 // Claim locks for common data structures, then call gc_prologue_work()
2676 // for each CMSGen.
2677
2678 getFreelistLocks(); // gets free list locks on constituent spaces
2679 bitMapLock()->lock_without_safepoint_check();
2680
2681 // Should call gc_prologue_work() for all cms gens we are responsible for
2682 bool duringMarking = _collectorState >= Marking
2683 && _collectorState < Sweeping;
2684
2685 // The young collections clear the modified oops state, which tells if
2686 // there are any modified oops in the class. The remark phase also needs
2687 // that information. Tell the young collection to save the union of all
2688 // modified klasses.
2689 if (duringMarking) {
2690 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2691 }
2692
2693 bool registerClosure = duringMarking;
2694
2695 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2696 &_modUnionClosurePar
2697 : &_modUnionClosure;
2698 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2699
2700 if (!full) {
2701 stats().record_gc0_begin();
2702 }
2703 }
2704
2705 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2706
2707 _capacity_at_prologue = capacity();
2708 _used_at_prologue = used();
2709
2710 // Delegate to CMScollector which knows how to coordinate between
2711 // this and any other CMS generations that it is responsible for
2712 // collecting.
2713 collector()->gc_prologue(full);
2714 }
2715
2716 // This is a "private" interface for use by this generation's CMSCollector.
2717 // Not to be called directly by any other entity (for instance,
2718 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2719 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2720 bool registerClosure, ModUnionClosure* modUnionClosure) {
2721 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2722 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2723 "Should be NULL");
2724 if (registerClosure) {
2725 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2726 }
2727 cmsSpace()->gc_prologue();
2728 // Clear stat counters
2729 NOT_PRODUCT(
2730 assert(_numObjectsPromoted == 0, "check");
2731 assert(_numWordsPromoted == 0, "check");
2732 if (Verbose && PrintGC) {
2733 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2734 SIZE_FORMAT" bytes concurrently",
2735 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2736 }
2737 _numObjectsAllocated = 0;
2738 _numWordsAllocated = 0;
2739 )
2740 }
2741
2742 void CMSCollector::gc_epilogue(bool full) {
2743 // The following locking discipline assumes that we are only called
2744 // when the world is stopped.
2745 assert(SafepointSynchronize::is_at_safepoint(),
2746 "world is stopped assumption");
2747
2748 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2749 // if linear allocation blocks need to be appropriately marked to allow the
2750 // the blocks to be parsable. We also check here whether we need to nudge the
2751 // CMS collector thread to start a new cycle (if it's not already active).
2752 assert( Thread::current()->is_VM_thread()
2753 || ( CMSScavengeBeforeRemark
2754 && Thread::current()->is_ConcurrentGC_thread()),
2755 "Incorrect thread type for epilogue execution");
2756
2757 if (!_between_prologue_and_epilogue) {
2758 // We have already been invoked; this is a gc_epilogue delegation
2759 // from yet another CMS generation that we are responsible for, just
2760 // ignore it since all relevant work has already been done.
2761 return;
2762 }
2763 assert(haveFreelistLocks(), "must have freelist locks");
2764 assert_lock_strong(bitMapLock());
2765
2766 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2767
2768 _cmsGen->gc_epilogue_work(full);
2769
2770 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2771 // in case sampling was not already enabled, enable it
2772 _start_sampling = true;
2773 }
2774 // reset _eden_chunk_array so sampling starts afresh
2775 _eden_chunk_index = 0;
2776
2777 size_t cms_used = _cmsGen->cmsSpace()->used();
2778
2779 // update performance counters - this uses a special version of
2780 // update_counters() that allows the utilization to be passed as a
2781 // parameter, avoiding multiple calls to used().
2782 //
2783 _cmsGen->update_counters(cms_used);
2784
2785 if (CMSIncrementalMode) {
2786 icms_update_allocation_limits();
2787 }
2788
2789 bitMapLock()->unlock();
2790 releaseFreelistLocks();
2791
2792 if (!CleanChunkPoolAsync) {
2793 Chunk::clean_chunk_pool();
2794 }
2795
2796 set_did_compact(false);
2797 _between_prologue_and_epilogue = false; // ready for next cycle
2798 }
2799
2800 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2801 collector()->gc_epilogue(full);
2802
2803 // Also reset promotion tracking in par gc thread states.
2804 if (CollectedHeap::use_parallel_gc_threads()) {
2805 for (uint i = 0; i < ParallelGCThreads; i++) {
2806 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2807 }
2808 }
2809 }
2810
2811 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2812 assert(!incremental_collection_failed(), "Should have been cleared");
2813 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2814 cmsSpace()->gc_epilogue();
2815 // Print stat counters
2816 NOT_PRODUCT(
2817 assert(_numObjectsAllocated == 0, "check");
2818 assert(_numWordsAllocated == 0, "check");
2819 if (Verbose && PrintGC) {
2820 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2821 SIZE_FORMAT" bytes",
2822 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2823 }
2824 _numObjectsPromoted = 0;
2825 _numWordsPromoted = 0;
2826 )
2827
2828 if (PrintGC && Verbose) {
2829 // Call down the chain in contiguous_available needs the freelistLock
2830 // so print this out before releasing the freeListLock.
2831 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2832 contiguous_available());
2833 }
2834 }
2835
2836 #ifndef PRODUCT
2837 bool CMSCollector::have_cms_token() {
2838 Thread* thr = Thread::current();
2839 if (thr->is_VM_thread()) {
2840 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2841 } else if (thr->is_ConcurrentGC_thread()) {
2842 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2843 } else if (thr->is_GC_task_thread()) {
2844 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2845 ParGCRareEvent_lock->owned_by_self();
2846 }
2847 return false;
2848 }
2849 #endif
2850
2851 // Check reachability of the given heap address in CMS generation,
2852 // treating all other generations as roots.
2853 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2854 // We could "guarantee" below, rather than assert, but I'll
2855 // leave these as "asserts" so that an adventurous debugger
2856 // could try this in the product build provided some subset of
2857 // the conditions were met, provided they were interested in the
2858 // results and knew that the computation below wouldn't interfere
2859 // with other concurrent computations mutating the structures
2860 // being read or written.
2861 assert(SafepointSynchronize::is_at_safepoint(),
2862 "Else mutations in object graph will make answer suspect");
2863 assert(have_cms_token(), "Should hold cms token");
2864 assert(haveFreelistLocks(), "must hold free list locks");
2865 assert_lock_strong(bitMapLock());
2866
2867 // Clear the marking bit map array before starting, but, just
2868 // for kicks, first report if the given address is already marked
2869 gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", addr,
2870 _markBitMap.isMarked(addr) ? "" : " not");
2871
2872 if (verify_after_remark()) {
2873 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2874 bool result = verification_mark_bm()->isMarked(addr);
2875 gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", addr,
2876 result ? "IS" : "is NOT");
2877 return result;
2878 } else {
2879 gclog_or_tty->print_cr("Could not compute result");
2880 return false;
2881 }
2882 }
2883
2884
2885 void
2886 CMSCollector::print_on_error(outputStream* st) {
2887 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2888 if (collector != NULL) {
2889 CMSBitMap* bitmap = &collector->_markBitMap;
2890 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, bitmap);
2891 bitmap->print_on_error(st, " Bits: ");
2892
2893 st->cr();
2894
2895 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2896 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, mut_bitmap);
2897 mut_bitmap->print_on_error(st, " Bits: ");
2898 }
2899 }
2900
2901 ////////////////////////////////////////////////////////
2902 // CMS Verification Support
2903 ////////////////////////////////////////////////////////
2904 // Following the remark phase, the following invariant
2905 // should hold -- each object in the CMS heap which is
2906 // marked in markBitMap() should be marked in the verification_mark_bm().
2907
2908 class VerifyMarkedClosure: public BitMapClosure {
2909 CMSBitMap* _marks;
2910 bool _failed;
2911
2912 public:
2913 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2914
2915 bool do_bit(size_t offset) {
2916 HeapWord* addr = _marks->offsetToHeapWord(offset);
2917 if (!_marks->isMarked(addr)) {
2918 oop(addr)->print_on(gclog_or_tty);
2919 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2920 _failed = true;
2921 }
2922 return true;
2923 }
2924
2925 bool failed() { return _failed; }
2926 };
2927
2928 bool CMSCollector::verify_after_remark(bool silent) {
2929 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2930 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2931 static bool init = false;
2932
2933 assert(SafepointSynchronize::is_at_safepoint(),
2934 "Else mutations in object graph will make answer suspect");
2935 assert(have_cms_token(),
2936 "Else there may be mutual interference in use of "
2937 " verification data structures");
2938 assert(_collectorState > Marking && _collectorState <= Sweeping,
2939 "Else marking info checked here may be obsolete");
2940 assert(haveFreelistLocks(), "must hold free list locks");
2941 assert_lock_strong(bitMapLock());
2942
2943
2944 // Allocate marking bit map if not already allocated
2945 if (!init) { // first time
2946 if (!verification_mark_bm()->allocate(_span)) {
2947 return false;
2948 }
2949 init = true;
2950 }
2951
2952 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2953
2954 // Turn off refs discovery -- so we will be tracing through refs.
2955 // This is as intended, because by this time
2956 // GC must already have cleared any refs that need to be cleared,
2957 // and traced those that need to be marked; moreover,
2958 // the marking done here is not going to interfere in any
2959 // way with the marking information used by GC.
2960 NoRefDiscovery no_discovery(ref_processor());
2961
2962 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2963
2964 // Clear any marks from a previous round
2965 verification_mark_bm()->clear_all();
2966 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2967 verify_work_stacks_empty();
2968
2969 GenCollectedHeap* gch = GenCollectedHeap::heap();
2970 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2971 // Update the saved marks which may affect the root scans.
2972 gch->save_marks();
2973
2974 if (CMSRemarkVerifyVariant == 1) {
2975 // In this first variant of verification, we complete
2976 // all marking, then check if the new marks-vector is
2977 // a subset of the CMS marks-vector.
2978 verify_after_remark_work_1();
2979 } else if (CMSRemarkVerifyVariant == 2) {
2980 // In this second variant of verification, we flag an error
2981 // (i.e. an object reachable in the new marks-vector not reachable
2982 // in the CMS marks-vector) immediately, also indicating the
2983 // identify of an object (A) that references the unmarked object (B) --
2984 // presumably, a mutation to A failed to be picked up by preclean/remark?
2985 verify_after_remark_work_2();
2986 } else {
2987 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2988 CMSRemarkVerifyVariant);
2989 }
2990 if (!silent) gclog_or_tty->print(" done] ");
2991 return true;
2992 }
2993
2994 void CMSCollector::verify_after_remark_work_1() {
2995 ResourceMark rm;
2996 HandleMark hm;
2997 GenCollectedHeap* gch = GenCollectedHeap::heap();
2998
2999 // Get a clear set of claim bits for the roots processing to work with.
3000 ClassLoaderDataGraph::clear_claimed_marks();
3001
3002 // Mark from roots one level into CMS
3003 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
3004 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3005
3006 gch->gen_process_roots(_cmsGen->level(),
3007 true, // younger gens are roots
3008 true, // activate StrongRootsScope
3009 SharedHeap::ScanningOption(roots_scanning_options()),
3010 should_unload_classes(),
3011 ¬Older,
3012 NULL,
3013 NULL); // SSS: Provide correct closure
3014
3015 // Now mark from the roots
3016 MarkFromRootsClosure markFromRootsClosure(this, _span,
3017 verification_mark_bm(), verification_mark_stack(),
3018 false /* don't yield */, true /* verifying */);
3019 assert(_restart_addr == NULL, "Expected pre-condition");
3020 verification_mark_bm()->iterate(&markFromRootsClosure);
3021 while (_restart_addr != NULL) {
3022 // Deal with stack overflow: by restarting at the indicated
3023 // address.
3024 HeapWord* ra = _restart_addr;
3025 markFromRootsClosure.reset(ra);
3026 _restart_addr = NULL;
3027 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3028 }
3029 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3030 verify_work_stacks_empty();
3031
3032 // Marking completed -- now verify that each bit marked in
3033 // verification_mark_bm() is also marked in markBitMap(); flag all
3034 // errors by printing corresponding objects.
3035 VerifyMarkedClosure vcl(markBitMap());
3036 verification_mark_bm()->iterate(&vcl);
3037 if (vcl.failed()) {
3038 gclog_or_tty->print("Verification failed");
3039 Universe::heap()->print_on(gclog_or_tty);
3040 fatal("CMS: failed marking verification after remark");
3041 }
3042 }
3043
3044 class VerifyKlassOopsKlassClosure : public KlassClosure {
3045 class VerifyKlassOopsClosure : public OopClosure {
3046 CMSBitMap* _bitmap;
3047 public:
3048 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
3049 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
3050 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
3051 } _oop_closure;
3052 public:
3053 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
3054 void do_klass(Klass* k) {
3055 k->oops_do(&_oop_closure);
3056 }
3057 };
3058
3059 void CMSCollector::verify_after_remark_work_2() {
3060 ResourceMark rm;
3061 HandleMark hm;
3062 GenCollectedHeap* gch = GenCollectedHeap::heap();
3063
3064 // Get a clear set of claim bits for the roots processing to work with.
3065 ClassLoaderDataGraph::clear_claimed_marks();
3066
3067 // Mark from roots one level into CMS
3068 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
3069 markBitMap());
3070 CLDToOopClosure cld_closure(¬Older, true);
3071
3072 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3073
3074 gch->gen_process_roots(_cmsGen->level(),
3075 true, // younger gens are roots
3076 true, // activate StrongRootsScope
3077 SharedHeap::ScanningOption(roots_scanning_options()),
3078 should_unload_classes(),
3079 ¬Older,
3080 NULL,
3081 &cld_closure);
3082
3083 // Now mark from the roots
3084 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
3085 verification_mark_bm(), markBitMap(), verification_mark_stack());
3086 assert(_restart_addr == NULL, "Expected pre-condition");
3087 verification_mark_bm()->iterate(&markFromRootsClosure);
3088 while (_restart_addr != NULL) {
3089 // Deal with stack overflow: by restarting at the indicated
3090 // address.
3091 HeapWord* ra = _restart_addr;
3092 markFromRootsClosure.reset(ra);
3093 _restart_addr = NULL;
3094 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3095 }
3096 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3097 verify_work_stacks_empty();
3098
3099 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
3100 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
3101
3102 // Marking completed -- now verify that each bit marked in
3103 // verification_mark_bm() is also marked in markBitMap(); flag all
3104 // errors by printing corresponding objects.
3105 VerifyMarkedClosure vcl(markBitMap());
3106 verification_mark_bm()->iterate(&vcl);
3107 assert(!vcl.failed(), "Else verification above should not have succeeded");
3108 }
3109
3110 void ConcurrentMarkSweepGeneration::save_marks() {
3111 // delegate to CMS space
3112 cmsSpace()->save_marks();
3113 for (uint i = 0; i < ParallelGCThreads; i++) {
3114 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3115 }
3116 }
3117
3118 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3119 return cmsSpace()->no_allocs_since_save_marks();
3120 }
3121
3122 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3123 \
3124 void ConcurrentMarkSweepGeneration:: \
3125 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3126 cl->set_generation(this); \
3127 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3128 cl->reset_generation(); \
3129 save_marks(); \
3130 }
3131
3132 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3133
3134 void
3135 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3136 cl->set_generation(this);
3137 younger_refs_in_space_iterate(_cmsSpace, cl);
3138 cl->reset_generation();
3139 }
3140
3141 void
3142 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
3143 if (freelistLock()->owned_by_self()) {
3144 Generation::oop_iterate(cl);
3145 } else {
3146 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3147 Generation::oop_iterate(cl);
3148 }
3149 }
3150
3151 void
3152 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3153 if (freelistLock()->owned_by_self()) {
3154 Generation::object_iterate(cl);
3155 } else {
3156 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3157 Generation::object_iterate(cl);
3158 }
3159 }
3160
3161 void
3162 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3163 if (freelistLock()->owned_by_self()) {
3164 Generation::safe_object_iterate(cl);
3165 } else {
3166 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3167 Generation::safe_object_iterate(cl);
3168 }
3169 }
3170
3171 void
3172 ConcurrentMarkSweepGeneration::post_compact() {
3173 }
3174
3175 void
3176 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3177 // Fix the linear allocation blocks to look like free blocks.
3178
3179 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3180 // are not called when the heap is verified during universe initialization and
3181 // at vm shutdown.
3182 if (freelistLock()->owned_by_self()) {
3183 cmsSpace()->prepare_for_verify();
3184 } else {
3185 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3186 cmsSpace()->prepare_for_verify();
3187 }
3188 }
3189
3190 void
3191 ConcurrentMarkSweepGeneration::verify() {
3192 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3193 // are not called when the heap is verified during universe initialization and
3194 // at vm shutdown.
3195 if (freelistLock()->owned_by_self()) {
3196 cmsSpace()->verify();
3197 } else {
3198 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3199 cmsSpace()->verify();
3200 }
3201 }
3202
3203 void CMSCollector::verify() {
3204 _cmsGen->verify();
3205 }
3206
3207 #ifndef PRODUCT
3208 bool CMSCollector::overflow_list_is_empty() const {
3209 assert(_num_par_pushes >= 0, "Inconsistency");
3210 if (_overflow_list == NULL) {
3211 assert(_num_par_pushes == 0, "Inconsistency");
3212 }
3213 return _overflow_list == NULL;
3214 }
3215
3216 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3217 // merely consolidate assertion checks that appear to occur together frequently.
3218 void CMSCollector::verify_work_stacks_empty() const {
3219 assert(_markStack.isEmpty(), "Marking stack should be empty");
3220 assert(overflow_list_is_empty(), "Overflow list should be empty");
3221 }
3222
3223 void CMSCollector::verify_overflow_empty() const {
3224 assert(overflow_list_is_empty(), "Overflow list should be empty");
3225 assert(no_preserved_marks(), "No preserved marks");
3226 }
3227 #endif // PRODUCT
3228
3229 // Decide if we want to enable class unloading as part of the
3230 // ensuing concurrent GC cycle. We will collect and
3231 // unload classes if it's the case that:
3232 // (1) an explicit gc request has been made and the flag
3233 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3234 // (2) (a) class unloading is enabled at the command line, and
3235 // (b) old gen is getting really full
3236 // NOTE: Provided there is no change in the state of the heap between
3237 // calls to this method, it should have idempotent results. Moreover,
3238 // its results should be monotonically increasing (i.e. going from 0 to 1,
3239 // but not 1 to 0) between successive calls between which the heap was
3240 // not collected. For the implementation below, it must thus rely on
3241 // the property that concurrent_cycles_since_last_unload()
3242 // will not decrease unless a collection cycle happened and that
3243 // _cmsGen->is_too_full() are
3244 // themselves also monotonic in that sense. See check_monotonicity()
3245 // below.
3246 void CMSCollector::update_should_unload_classes() {
3247 _should_unload_classes = false;
3248 // Condition 1 above
3249 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3250 _should_unload_classes = true;
3251 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3252 // Disjuncts 2.b.(i,ii,iii) above
3253 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3254 CMSClassUnloadingMaxInterval)
3255 || _cmsGen->is_too_full();
3256 }
3257 }
3258
3259 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3260 bool res = should_concurrent_collect();
3261 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3262 return res;
3263 }
3264
3265 void CMSCollector::setup_cms_unloading_and_verification_state() {
3266 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3267 || VerifyBeforeExit;
3268 const int rso = SharedHeap::SO_AllCodeCache;
3269
3270 // We set the proper root for this CMS cycle here.
3271 if (should_unload_classes()) { // Should unload classes this cycle
3272 remove_root_scanning_option(rso); // Shrink the root set appropriately
3273 set_verifying(should_verify); // Set verification state for this cycle
3274 return; // Nothing else needs to be done at this time
3275 }
3276
3277 // Not unloading classes this cycle
3278 assert(!should_unload_classes(), "Inconsistency!");
3279
3280 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3281 // Include symbols, strings and code cache elements to prevent their resurrection.
3282 add_root_scanning_option(rso);
3283 set_verifying(true);
3284 } else if (verifying() && !should_verify) {
3285 // We were verifying, but some verification flags got disabled.
3286 set_verifying(false);
3287 // Exclude symbols, strings and code cache elements from root scanning to
3288 // reduce IM and RM pauses.
3289 remove_root_scanning_option(rso);
3290 }
3291 }
3292
3293
3294 #ifndef PRODUCT
3295 HeapWord* CMSCollector::block_start(const void* p) const {
3296 const HeapWord* addr = (HeapWord*)p;
3297 if (_span.contains(p)) {
3298 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3299 return _cmsGen->cmsSpace()->block_start(p);
3300 }
3301 }
3302 return NULL;
3303 }
3304 #endif
3305
3306 HeapWord*
3307 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3308 bool tlab,
3309 bool parallel) {
3310 CMSSynchronousYieldRequest yr;
3311 assert(!tlab, "Can't deal with TLAB allocation");
3312 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3313 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3314 CMSExpansionCause::_satisfy_allocation);
3315 if (GCExpandToAllocateDelayMillis > 0) {
3316 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3317 }
3318 return have_lock_and_allocate(word_size, tlab);
3319 }
3320
3321 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3322 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3323 // to CardGeneration and share it...
3324 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3325 return CardGeneration::expand(bytes, expand_bytes);
3326 }
3327
3328 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3329 CMSExpansionCause::Cause cause)
3330 {
3331
3332 bool success = expand(bytes, expand_bytes);
3333
3334 // remember why we expanded; this information is used
3335 // by shouldConcurrentCollect() when making decisions on whether to start
3336 // a new CMS cycle.
3337 if (success) {
3338 set_expansion_cause(cause);
3339 if (PrintGCDetails && Verbose) {
3340 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3341 CMSExpansionCause::to_string(cause));
3342 }
3343 }
3344 }
3345
3346 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3347 HeapWord* res = NULL;
3348 MutexLocker x(ParGCRareEvent_lock);
3349 while (true) {
3350 // Expansion by some other thread might make alloc OK now:
3351 res = ps->lab.alloc(word_sz);
3352 if (res != NULL) return res;
3353 // If there's not enough expansion space available, give up.
3354 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3355 return NULL;
3356 }
3357 // Otherwise, we try expansion.
3358 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3359 CMSExpansionCause::_allocate_par_lab);
3360 // Now go around the loop and try alloc again;
3361 // A competing par_promote might beat us to the expansion space,
3362 // so we may go around the loop again if promotion fails again.
3363 if (GCExpandToAllocateDelayMillis > 0) {
3364 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3365 }
3366 }
3367 }
3368
3369
3370 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3371 PromotionInfo* promo) {
3372 MutexLocker x(ParGCRareEvent_lock);
3373 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3374 while (true) {
3375 // Expansion by some other thread might make alloc OK now:
3376 if (promo->ensure_spooling_space()) {
3377 assert(promo->has_spooling_space(),
3378 "Post-condition of successful ensure_spooling_space()");
3379 return true;
3380 }
3381 // If there's not enough expansion space available, give up.
3382 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3383 return false;
3384 }
3385 // Otherwise, we try expansion.
3386 expand(refill_size_bytes, MinHeapDeltaBytes,
3387 CMSExpansionCause::_allocate_par_spooling_space);
3388 // Now go around the loop and try alloc again;
3389 // A competing allocation might beat us to the expansion space,
3390 // so we may go around the loop again if allocation fails again.
3391 if (GCExpandToAllocateDelayMillis > 0) {
3392 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3393 }
3394 }
3395 }
3396
3397
3398 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3399 assert_locked_or_safepoint(ExpandHeap_lock);
3400 // Shrink committed space
3401 _virtual_space.shrink_by(bytes);
3402 // Shrink space; this also shrinks the space's BOT
3403 _cmsSpace->set_end((HeapWord*) _virtual_space.high());
3404 size_t new_word_size = heap_word_size(_cmsSpace->capacity());
3405 // Shrink the shared block offset array
3406 _bts->resize(new_word_size);
3407 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3408 // Shrink the card table
3409 Universe::heap()->barrier_set()->resize_covered_region(mr);
3410
3411 if (Verbose && PrintGC) {
3412 size_t new_mem_size = _virtual_space.committed_size();
3413 size_t old_mem_size = new_mem_size + bytes;
3414 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3415 name(), old_mem_size/K, new_mem_size/K);
3416 }
3417 }
3418
3419 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3420 assert_locked_or_safepoint(Heap_lock);
3421 size_t size = ReservedSpace::page_align_size_down(bytes);
3422 // Only shrink if a compaction was done so that all the free space
3423 // in the generation is in a contiguous block at the end.
3424 if (size > 0 && did_compact()) {
3425 shrink_by(size);
3426 }
3427 }
3428
3429 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3430 assert_locked_or_safepoint(Heap_lock);
3431 bool result = _virtual_space.expand_by(bytes);
3432 if (result) {
3433 size_t new_word_size =
3434 heap_word_size(_virtual_space.committed_size());
3435 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3436 _bts->resize(new_word_size); // resize the block offset shared array
3437 Universe::heap()->barrier_set()->resize_covered_region(mr);
3438 // Hmmmm... why doesn't CFLS::set_end verify locking?
3439 // This is quite ugly; FIX ME XXX
3440 _cmsSpace->assert_locked(freelistLock());
3441 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3442
3443 // update the space and generation capacity counters
3444 if (UsePerfData) {
3445 _space_counters->update_capacity();
3446 _gen_counters->update_all();
3447 }
3448
3449 if (Verbose && PrintGC) {
3450 size_t new_mem_size = _virtual_space.committed_size();
3451 size_t old_mem_size = new_mem_size - bytes;
3452 gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3453 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3454 }
3455 }
3456 return result;
3457 }
3458
3459 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3460 assert_locked_or_safepoint(Heap_lock);
3461 bool success = true;
3462 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3463 if (remaining_bytes > 0) {
3464 success = grow_by(remaining_bytes);
3465 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3466 }
3467 return success;
3468 }
3469
3470 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
3471 assert_locked_or_safepoint(Heap_lock);
3472 assert_lock_strong(freelistLock());
3473 if (PrintGCDetails && Verbose) {
3474 warning("Shrinking of CMS not yet implemented");
3475 }
3476 return;
3477 }
3478
3479
3480 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3481 // phases.
3482 class CMSPhaseAccounting: public StackObj {
3483 public:
3484 CMSPhaseAccounting(CMSCollector *collector,
3485 const char *phase,
3486 const GCId gc_id,
3487 bool print_cr = true);
3488 ~CMSPhaseAccounting();
3489
3490 private:
3491 CMSCollector *_collector;
3492 const char *_phase;
3493 elapsedTimer _wallclock;
3494 bool _print_cr;
3495 const GCId _gc_id;
3496
3497 public:
3498 // Not MT-safe; so do not pass around these StackObj's
3499 // where they may be accessed by other threads.
3500 jlong wallclock_millis() {
3501 assert(_wallclock.is_active(), "Wall clock should not stop");
3502 _wallclock.stop(); // to record time
3503 jlong ret = _wallclock.milliseconds();
3504 _wallclock.start(); // restart
3505 return ret;
3506 }
3507 };
3508
3509 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3510 const char *phase,
3511 const GCId gc_id,
3512 bool print_cr) :
3513 _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
3514
3515 if (PrintCMSStatistics != 0) {
3516 _collector->resetYields();
3517 }
3518 if (PrintGCDetails) {
3519 gclog_or_tty->gclog_stamp(_gc_id);
3520 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
3521 _collector->cmsGen()->short_name(), _phase);
3522 }
3523 _collector->resetTimer();
3524 _wallclock.start();
3525 _collector->startTimer();
3526 }
3527
3528 CMSPhaseAccounting::~CMSPhaseAccounting() {
3529 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3530 _collector->stopTimer();
3531 _wallclock.stop();
3532 if (PrintGCDetails) {
3533 gclog_or_tty->gclog_stamp(_gc_id);
3534 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3535 _collector->cmsGen()->short_name(),
3536 _phase, _collector->timerValue(), _wallclock.seconds());
3537 if (_print_cr) {
3538 gclog_or_tty->cr();
3539 }
3540 if (PrintCMSStatistics != 0) {
3541 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3542 _collector->yields());
3543 }
3544 }
3545 }
3546
3547 // CMS work
3548
3549 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
3550 class CMSParMarkTask : public AbstractGangTask {
3551 protected:
3552 CMSCollector* _collector;
3553 int _n_workers;
3554 CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
3555 AbstractGangTask(name),
3556 _collector(collector),
3557 _n_workers(n_workers) {}
3558 // Work method in support of parallel rescan ... of young gen spaces
3559 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
3560 ContiguousSpace* space,
3561 HeapWord** chunk_array, size_t chunk_top);
3562 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
3563 };
3564
3565 // Parallel initial mark task
3566 class CMSParInitialMarkTask: public CMSParMarkTask {
3567 public:
3568 CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
3569 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
3570 collector, n_workers) {}
3571 void work(uint worker_id);
3572 };
3573
3574 // Checkpoint the roots into this generation from outside
3575 // this generation. [Note this initial checkpoint need only
3576 // be approximate -- we'll do a catch up phase subsequently.]
3577 void CMSCollector::checkpointRootsInitial(bool asynch) {
3578 assert(_collectorState == InitialMarking, "Wrong collector state");
3579 check_correct_thread_executing();
3580 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3581
3582 save_heap_summary();
3583 report_heap_summary(GCWhen::BeforeGC);
3584
3585 ReferenceProcessor* rp = ref_processor();
3586 SpecializationStats::clear();
3587 assert(_restart_addr == NULL, "Control point invariant");
3588 if (asynch) {
3589 // acquire locks for subsequent manipulations
3590 MutexLockerEx x(bitMapLock(),
3591 Mutex::_no_safepoint_check_flag);
3592 checkpointRootsInitialWork(asynch);
3593 // enable ("weak") refs discovery
3594 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3595 _collectorState = Marking;
3596 } else {
3597 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3598 // which recognizes if we are a CMS generation, and doesn't try to turn on
3599 // discovery; verify that they aren't meddling.
3600 assert(!rp->discovery_is_atomic(),
3601 "incorrect setting of discovery predicate");
3602 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3603 "ref discovery for this generation kind");
3604 // already have locks
3605 checkpointRootsInitialWork(asynch);
3606 // now enable ("weak") refs discovery
3607 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3608 _collectorState = Marking;
3609 }
3610 SpecializationStats::print();
3611 }
3612
3613 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3614 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3615 assert(_collectorState == InitialMarking, "just checking");
3616
3617 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3618 // precede our marking with a collection of all
3619 // younger generations to keep floating garbage to a minimum.
3620 // XXX: we won't do this for now -- it's an optimization to be done later.
3621
3622 // already have locks
3623 assert_lock_strong(bitMapLock());
3624 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3625
3626 // Setup the verification and class unloading state for this
3627 // CMS collection cycle.
3628 setup_cms_unloading_and_verification_state();
3629
3630 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3631 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
3632
3633 // Reset all the PLAB chunk arrays if necessary.
3634 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3635 reset_survivor_plab_arrays();
3636 }
3637
3638 ResourceMark rm;
3639 HandleMark hm;
3640
3641 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3642 GenCollectedHeap* gch = GenCollectedHeap::heap();
3643
3644 verify_work_stacks_empty();
3645 verify_overflow_empty();
3646
3647 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3648 // Update the saved marks which may affect the root scans.
3649 gch->save_marks();
3650
3651 // weak reference processing has not started yet.
3652 ref_processor()->set_enqueuing_is_done(false);
3653
3654 // Need to remember all newly created CLDs,
3655 // so that we can guarantee that the remark finds them.
3656 ClassLoaderDataGraph::remember_new_clds(true);
3657
3658 // Whenever a CLD is found, it will be claimed before proceeding to mark
3659 // the klasses. The claimed marks need to be cleared before marking starts.
3660 ClassLoaderDataGraph::clear_claimed_marks();
3661
3662 if (CMSPrintEdenSurvivorChunks) {
3663 print_eden_and_survivor_chunk_arrays();
3664 }
3665
3666 {
3667 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3668 if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3669 // The parallel version.
3670 FlexibleWorkGang* workers = gch->workers();
3671 assert(workers != NULL, "Need parallel worker threads.");
3672 int n_workers = workers->active_workers();
3673 CMSParInitialMarkTask tsk(this, n_workers);
3674 gch->set_par_threads(n_workers);
3675 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3676 if (n_workers > 1) {
3677 GenCollectedHeap::StrongRootsScope srs(gch);
3678 workers->run_task(&tsk);
3679 } else {
3680 GenCollectedHeap::StrongRootsScope srs(gch);
3681 tsk.work(0);
3682 }
3683 gch->set_par_threads(0);
3684 } else {
3685 // The serial version.
3686 CLDToOopClosure cld_closure(¬Older, true);
3687 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3688 gch->gen_process_roots(_cmsGen->level(),
3689 true, // younger gens are roots
3690 true, // activate StrongRootsScope
3691 SharedHeap::ScanningOption(roots_scanning_options()),
3692 should_unload_classes(),
3693 ¬Older,
3694 NULL,
3695 &cld_closure);
3696 }
3697 }
3698
3699 // Clear mod-union table; it will be dirtied in the prologue of
3700 // CMS generation per each younger generation collection.
3701
3702 assert(_modUnionTable.isAllClear(),
3703 "Was cleared in most recent final checkpoint phase"
3704 " or no bits are set in the gc_prologue before the start of the next "
3705 "subsequent marking phase.");
3706
3707 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3708
3709 // Save the end of the used_region of the constituent generations
3710 // to be used to limit the extent of sweep in each generation.
3711 save_sweep_limits();
3712 verify_overflow_empty();
3713 }
3714
3715 bool CMSCollector::markFromRoots(bool asynch) {
3716 // we might be tempted to assert that:
3717 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3718 // "inconsistent argument?");
3719 // However that wouldn't be right, because it's possible that
3720 // a safepoint is indeed in progress as a younger generation
3721 // stop-the-world GC happens even as we mark in this generation.
3722 assert(_collectorState == Marking, "inconsistent state?");
3723 check_correct_thread_executing();
3724 verify_overflow_empty();
3725
3726 bool res;
3727 if (asynch) {
3728 // Weak ref discovery note: We may be discovering weak
3729 // refs in this generation concurrent (but interleaved) with
3730 // weak ref discovery by a younger generation collector.
3731
3732 CMSTokenSyncWithLocks ts(true, bitMapLock());
3733 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3734 CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3735 res = markFromRootsWork(asynch);
3736 if (res) {
3737 _collectorState = Precleaning;
3738 } else { // We failed and a foreground collection wants to take over
3739 assert(_foregroundGCIsActive, "internal state inconsistency");
3740 assert(_restart_addr == NULL, "foreground will restart from scratch");
3741 if (PrintGCDetails) {
3742 gclog_or_tty->print_cr("bailing out to foreground collection");
3743 }
3744 }
3745 } else {
3746 assert(SafepointSynchronize::is_at_safepoint(),
3747 "inconsistent with asynch == false");
3748 // already have locks
3749 res = markFromRootsWork(asynch);
3750 _collectorState = FinalMarking;
3751 }
3752 verify_overflow_empty();
3753 return res;
3754 }
3755
3756 bool CMSCollector::markFromRootsWork(bool asynch) {
3757 // iterate over marked bits in bit map, doing a full scan and mark
3758 // from these roots using the following algorithm:
3759 // . if oop is to the right of the current scan pointer,
3760 // mark corresponding bit (we'll process it later)
3761 // . else (oop is to left of current scan pointer)
3762 // push oop on marking stack
3763 // . drain the marking stack
3764
3765 // Note that when we do a marking step we need to hold the
3766 // bit map lock -- recall that direct allocation (by mutators)
3767 // and promotion (by younger generation collectors) is also
3768 // marking the bit map. [the so-called allocate live policy.]
3769 // Because the implementation of bit map marking is not
3770 // robust wrt simultaneous marking of bits in the same word,
3771 // we need to make sure that there is no such interference
3772 // between concurrent such updates.
3773
3774 // already have locks
3775 assert_lock_strong(bitMapLock());
3776
3777 verify_work_stacks_empty();
3778 verify_overflow_empty();
3779 bool result = false;
3780 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3781 result = do_marking_mt(asynch);
3782 } else {
3783 result = do_marking_st(asynch);
3784 }
3785 return result;
3786 }
3787
3788 // Forward decl
3789 class CMSConcMarkingTask;
3790
3791 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3792 CMSCollector* _collector;
3793 CMSConcMarkingTask* _task;
3794 public:
3795 virtual void yield();
3796
3797 // "n_threads" is the number of threads to be terminated.
3798 // "queue_set" is a set of work queues of other threads.
3799 // "collector" is the CMS collector associated with this task terminator.
3800 // "yield" indicates whether we need the gang as a whole to yield.
3801 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3802 ParallelTaskTerminator(n_threads, queue_set),
3803 _collector(collector) { }
3804
3805 void set_task(CMSConcMarkingTask* task) {
3806 _task = task;
3807 }
3808 };
3809
3810 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3811 CMSConcMarkingTask* _task;
3812 public:
3813 bool should_exit_termination();
3814 void set_task(CMSConcMarkingTask* task) {
3815 _task = task;
3816 }
3817 };
3818
3819 // MT Concurrent Marking Task
3820 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3821 CMSCollector* _collector;
3822 int _n_workers; // requested/desired # workers
3823 bool _asynch;
3824 bool _result;
3825 CompactibleFreeListSpace* _cms_space;
3826 char _pad_front[64]; // padding to ...
3827 HeapWord* _global_finger; // ... avoid sharing cache line
3828 char _pad_back[64];
3829 HeapWord* _restart_addr;
3830
3831 // Exposed here for yielding support
3832 Mutex* const _bit_map_lock;
3833
3834 // The per thread work queues, available here for stealing
3835 OopTaskQueueSet* _task_queues;
3836
3837 // Termination (and yielding) support
3838 CMSConcMarkingTerminator _term;
3839 CMSConcMarkingTerminatorTerminator _term_term;
3840
3841 public:
3842 CMSConcMarkingTask(CMSCollector* collector,
3843 CompactibleFreeListSpace* cms_space,
3844 bool asynch,
3845 YieldingFlexibleWorkGang* workers,
3846 OopTaskQueueSet* task_queues):
3847 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3848 _collector(collector),
3849 _cms_space(cms_space),
3850 _asynch(asynch), _n_workers(0), _result(true),
3851 _task_queues(task_queues),
3852 _term(_n_workers, task_queues, _collector),
3853 _bit_map_lock(collector->bitMapLock())
3854 {
3855 _requested_size = _n_workers;
3856 _term.set_task(this);
3857 _term_term.set_task(this);
3858 _restart_addr = _global_finger = _cms_space->bottom();
3859 }
3860
3861
3862 OopTaskQueueSet* task_queues() { return _task_queues; }
3863
3864 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3865
3866 HeapWord** global_finger_addr() { return &_global_finger; }
3867
3868 CMSConcMarkingTerminator* terminator() { return &_term; }
3869
3870 virtual void set_for_termination(int active_workers) {
3871 terminator()->reset_for_reuse(active_workers);
3872 }
3873
3874 void work(uint worker_id);
3875 bool should_yield() {
3876 return ConcurrentMarkSweepThread::should_yield()
3877 && !_collector->foregroundGCIsActive()
3878 && _asynch;
3879 }
3880
3881 virtual void coordinator_yield(); // stuff done by coordinator
3882 bool result() { return _result; }
3883
3884 void reset(HeapWord* ra) {
3885 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3886 _restart_addr = _global_finger = ra;
3887 _term.reset_for_reuse();
3888 }
3889
3890 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3891 OopTaskQueue* work_q);
3892
3893 private:
3894 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3895 void do_work_steal(int i);
3896 void bump_global_finger(HeapWord* f);
3897 };
3898
3899 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3900 assert(_task != NULL, "Error");
3901 return _task->yielding();
3902 // Note that we do not need the disjunct || _task->should_yield() above
3903 // because we want terminating threads to yield only if the task
3904 // is already in the midst of yielding, which happens only after at least one
3905 // thread has yielded.
3906 }
3907
3908 void CMSConcMarkingTerminator::yield() {
3909 if (_task->should_yield()) {
3910 _task->yield();
3911 } else {
3912 ParallelTaskTerminator::yield();
3913 }
3914 }
3915
3916 ////////////////////////////////////////////////////////////////
3917 // Concurrent Marking Algorithm Sketch
3918 ////////////////////////////////////////////////////////////////
3919 // Until all tasks exhausted (both spaces):
3920 // -- claim next available chunk
3921 // -- bump global finger via CAS
3922 // -- find first object that starts in this chunk
3923 // and start scanning bitmap from that position
3924 // -- scan marked objects for oops
3925 // -- CAS-mark target, and if successful:
3926 // . if target oop is above global finger (volatile read)
3927 // nothing to do
3928 // . if target oop is in chunk and above local finger
3929 // then nothing to do
3930 // . else push on work-queue
3931 // -- Deal with possible overflow issues:
3932 // . local work-queue overflow causes stuff to be pushed on
3933 // global (common) overflow queue
3934 // . always first empty local work queue
3935 // . then get a batch of oops from global work queue if any
3936 // . then do work stealing
3937 // -- When all tasks claimed (both spaces)
3938 // and local work queue empty,
3939 // then in a loop do:
3940 // . check global overflow stack; steal a batch of oops and trace
3941 // . try to steal from other threads oif GOS is empty
3942 // . if neither is available, offer termination
3943 // -- Terminate and return result
3944 //
3945 void CMSConcMarkingTask::work(uint worker_id) {
3946 elapsedTimer _timer;
3947 ResourceMark rm;
3948 HandleMark hm;
3949
3950 DEBUG_ONLY(_collector->verify_overflow_empty();)
3951
3952 // Before we begin work, our work queue should be empty
3953 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3954 // Scan the bitmap covering _cms_space, tracing through grey objects.
3955 _timer.start();
3956 do_scan_and_mark(worker_id, _cms_space);
3957 _timer.stop();
3958 if (PrintCMSStatistics != 0) {
3959 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3960 worker_id, _timer.seconds());
3961 // XXX: need xxx/xxx type of notation, two timers
3962 }
3963
3964 // ... do work stealing
3965 _timer.reset();
3966 _timer.start();
3967 do_work_steal(worker_id);
3968 _timer.stop();
3969 if (PrintCMSStatistics != 0) {
3970 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3971 worker_id, _timer.seconds());
3972 // XXX: need xxx/xxx type of notation, two timers
3973 }
3974 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3975 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3976 // Note that under the current task protocol, the
3977 // following assertion is true even of the spaces
3978 // expanded since the completion of the concurrent
3979 // marking. XXX This will likely change under a strict
3980 // ABORT semantics.
3981 // After perm removal the comparison was changed to
3982 // greater than or equal to from strictly greater than.
3983 // Before perm removal the highest address sweep would
3984 // have been at the end of perm gen but now is at the
3985 // end of the tenured gen.
3986 assert(_global_finger >= _cms_space->end(),
3987 "All tasks have been completed");
3988 DEBUG_ONLY(_collector->verify_overflow_empty();)
3989 }
3990
3991 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3992 HeapWord* read = _global_finger;
3993 HeapWord* cur = read;
3994 while (f > read) {
3995 cur = read;
3996 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3997 if (cur == read) {
3998 // our cas succeeded
3999 assert(_global_finger >= f, "protocol consistency");
4000 break;
4001 }
4002 }
4003 }
4004
4005 // This is really inefficient, and should be redone by
4006 // using (not yet available) block-read and -write interfaces to the
4007 // stack and the work_queue. XXX FIX ME !!!
4008 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
4009 OopTaskQueue* work_q) {
4010 // Fast lock-free check
4011 if (ovflw_stk->length() == 0) {
4012 return false;
4013 }
4014 assert(work_q->size() == 0, "Shouldn't steal");
4015 MutexLockerEx ml(ovflw_stk->par_lock(),
4016 Mutex::_no_safepoint_check_flag);
4017 // Grab up to 1/4 the size of the work queue
4018 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4019 (size_t)ParGCDesiredObjsFromOverflowList);
4020 num = MIN2(num, ovflw_stk->length());
4021 for (int i = (int) num; i > 0; i--) {
4022 oop cur = ovflw_stk->pop();
4023 assert(cur != NULL, "Counted wrong?");
4024 work_q->push(cur);
4025 }
4026 return num > 0;
4027 }
4028
4029 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
4030 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4031 int n_tasks = pst->n_tasks();
4032 // We allow that there may be no tasks to do here because
4033 // we are restarting after a stack overflow.
4034 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
4035 uint nth_task = 0;
4036
4037 HeapWord* aligned_start = sp->bottom();
4038 if (sp->used_region().contains(_restart_addr)) {
4039 // Align down to a card boundary for the start of 0th task
4040 // for this space.
4041 aligned_start =
4042 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
4043 CardTableModRefBS::card_size);
4044 }
4045
4046 size_t chunk_size = sp->marking_task_size();
4047 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4048 // Having claimed the nth task in this space,
4049 // compute the chunk that it corresponds to:
4050 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
4051 aligned_start + (nth_task+1)*chunk_size);
4052 // Try and bump the global finger via a CAS;
4053 // note that we need to do the global finger bump
4054 // _before_ taking the intersection below, because
4055 // the task corresponding to that region will be
4056 // deemed done even if the used_region() expands
4057 // because of allocation -- as it almost certainly will
4058 // during start-up while the threads yield in the
4059 // closure below.
4060 HeapWord* finger = span.end();
4061 bump_global_finger(finger); // atomically
4062 // There are null tasks here corresponding to chunks
4063 // beyond the "top" address of the space.
4064 span = span.intersection(sp->used_region());
4065 if (!span.is_empty()) { // Non-null task
4066 HeapWord* prev_obj;
4067 assert(!span.contains(_restart_addr) || nth_task == 0,
4068 "Inconsistency");
4069 if (nth_task == 0) {
4070 // For the 0th task, we'll not need to compute a block_start.
4071 if (span.contains(_restart_addr)) {
4072 // In the case of a restart because of stack overflow,
4073 // we might additionally skip a chunk prefix.
4074 prev_obj = _restart_addr;
4075 } else {
4076 prev_obj = span.start();
4077 }
4078 } else {
4079 // We want to skip the first object because
4080 // the protocol is to scan any object in its entirety
4081 // that _starts_ in this span; a fortiori, any
4082 // object starting in an earlier span is scanned
4083 // as part of an earlier claimed task.
4084 // Below we use the "careful" version of block_start
4085 // so we do not try to navigate uninitialized objects.
4086 prev_obj = sp->block_start_careful(span.start());
4087 // Below we use a variant of block_size that uses the
4088 // Printezis bits to avoid waiting for allocated
4089 // objects to become initialized/parsable.
4090 while (prev_obj < span.start()) {
4091 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4092 if (sz > 0) {
4093 prev_obj += sz;
4094 } else {
4095 // In this case we may end up doing a bit of redundant
4096 // scanning, but that appears unavoidable, short of
4097 // locking the free list locks; see bug 6324141.
4098 break;
4099 }
4100 }
4101 }
4102 if (prev_obj < span.end()) {
4103 MemRegion my_span = MemRegion(prev_obj, span.end());
4104 // Do the marking work within a non-empty span --
4105 // the last argument to the constructor indicates whether the
4106 // iteration should be incremental with periodic yields.
4107 Par_MarkFromRootsClosure cl(this, _collector, my_span,
4108 &_collector->_markBitMap,
4109 work_queue(i),
4110 &_collector->_markStack,
4111 _asynch);
4112 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4113 } // else nothing to do for this task
4114 } // else nothing to do for this task
4115 }
4116 // We'd be tempted to assert here that since there are no
4117 // more tasks left to claim in this space, the global_finger
4118 // must exceed space->top() and a fortiori space->end(). However,
4119 // that would not quite be correct because the bumping of
4120 // global_finger occurs strictly after the claiming of a task,
4121 // so by the time we reach here the global finger may not yet
4122 // have been bumped up by the thread that claimed the last
4123 // task.
4124 pst->all_tasks_completed();
4125 }
4126
4127 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
4128 private:
4129 CMSCollector* _collector;
4130 CMSConcMarkingTask* _task;
4131 MemRegion _span;
4132 CMSBitMap* _bit_map;
4133 CMSMarkStack* _overflow_stack;
4134 OopTaskQueue* _work_queue;
4135 protected:
4136 DO_OOP_WORK_DEFN
4137 public:
4138 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4139 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
4140 MetadataAwareOopClosure(collector->ref_processor()),
4141 _collector(collector),
4142 _task(task),
4143 _span(collector->_span),
4144 _work_queue(work_queue),
4145 _bit_map(bit_map),
4146 _overflow_stack(overflow_stack)
4147 { }
4148 virtual void do_oop(oop* p);
4149 virtual void do_oop(narrowOop* p);
4150
4151 void trim_queue(size_t max);
4152 void handle_stack_overflow(HeapWord* lost);
4153 void do_yield_check() {
4154 if (_task->should_yield()) {
4155 _task->yield();
4156 }
4157 }
4158 };
4159
4160 // Grey object scanning during work stealing phase --
4161 // the salient assumption here is that any references
4162 // that are in these stolen objects being scanned must
4163 // already have been initialized (else they would not have
4164 // been published), so we do not need to check for
4165 // uninitialized objects before pushing here.
4166 void Par_ConcMarkingClosure::do_oop(oop obj) {
4167 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
4168 HeapWord* addr = (HeapWord*)obj;
4169 // Check if oop points into the CMS generation
4170 // and is not marked
4171 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4172 // a white object ...
4173 // If we manage to "claim" the object, by being the
4174 // first thread to mark it, then we push it on our
4175 // marking stack
4176 if (_bit_map->par_mark(addr)) { // ... now grey
4177 // push on work queue (grey set)
4178 bool simulate_overflow = false;
4179 NOT_PRODUCT(
4180 if (CMSMarkStackOverflowALot &&
4181 _collector->simulate_overflow()) {
4182 // simulate a stack overflow
4183 simulate_overflow = true;
4184 }
4185 )
4186 if (simulate_overflow ||
4187 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4188 // stack overflow
4189 if (PrintCMSStatistics != 0) {
4190 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4191 SIZE_FORMAT, _overflow_stack->capacity());
4192 }
4193 // We cannot assert that the overflow stack is full because
4194 // it may have been emptied since.
4195 assert(simulate_overflow ||
4196 _work_queue->size() == _work_queue->max_elems(),
4197 "Else push should have succeeded");
4198 handle_stack_overflow(addr);
4199 }
4200 } // Else, some other thread got there first
4201 do_yield_check();
4202 }
4203 }
4204
4205 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4206 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4207
4208 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4209 while (_work_queue->size() > max) {
4210 oop new_oop;
4211 if (_work_queue->pop_local(new_oop)) {
4212 assert(new_oop->is_oop(), "Should be an oop");
4213 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4214 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4215 new_oop->oop_iterate(this); // do_oop() above
4216 do_yield_check();
4217 }
4218 }
4219 }
4220
4221 // Upon stack overflow, we discard (part of) the stack,
4222 // remembering the least address amongst those discarded
4223 // in CMSCollector's _restart_address.
4224 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4225 // We need to do this under a mutex to prevent other
4226 // workers from interfering with the work done below.
4227 MutexLockerEx ml(_overflow_stack->par_lock(),
4228 Mutex::_no_safepoint_check_flag);
4229 // Remember the least grey address discarded
4230 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4231 _collector->lower_restart_addr(ra);
4232 _overflow_stack->reset(); // discard stack contents
4233 _overflow_stack->expand(); // expand the stack if possible
4234 }
4235
4236
4237 void CMSConcMarkingTask::do_work_steal(int i) {
4238 OopTaskQueue* work_q = work_queue(i);
4239 oop obj_to_scan;
4240 CMSBitMap* bm = &(_collector->_markBitMap);
4241 CMSMarkStack* ovflw = &(_collector->_markStack);
4242 int* seed = _collector->hash_seed(i);
4243 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4244 while (true) {
4245 cl.trim_queue(0);
4246 assert(work_q->size() == 0, "Should have been emptied above");
4247 if (get_work_from_overflow_stack(ovflw, work_q)) {
4248 // Can't assert below because the work obtained from the
4249 // overflow stack may already have been stolen from us.
4250 // assert(work_q->size() > 0, "Work from overflow stack");
4251 continue;
4252 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4253 assert(obj_to_scan->is_oop(), "Should be an oop");
4254 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4255 obj_to_scan->oop_iterate(&cl);
4256 } else if (terminator()->offer_termination(&_term_term)) {
4257 assert(work_q->size() == 0, "Impossible!");
4258 break;
4259 } else if (yielding() || should_yield()) {
4260 yield();
4261 }
4262 }
4263 }
4264
4265 // This is run by the CMS (coordinator) thread.
4266 void CMSConcMarkingTask::coordinator_yield() {
4267 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4268 "CMS thread should hold CMS token");
4269 // First give up the locks, then yield, then re-lock
4270 // We should probably use a constructor/destructor idiom to
4271 // do this unlock/lock or modify the MutexUnlocker class to
4272 // serve our purpose. XXX
4273 assert_lock_strong(_bit_map_lock);
4274 _bit_map_lock->unlock();
4275 ConcurrentMarkSweepThread::desynchronize(true);
4276 ConcurrentMarkSweepThread::acknowledge_yield_request();
4277 _collector->stopTimer();
4278 if (PrintCMSStatistics != 0) {
4279 _collector->incrementYields();
4280 }
4281 _collector->icms_wait();
4282
4283 // It is possible for whichever thread initiated the yield request
4284 // not to get a chance to wake up and take the bitmap lock between
4285 // this thread releasing it and reacquiring it. So, while the
4286 // should_yield() flag is on, let's sleep for a bit to give the
4287 // other thread a chance to wake up. The limit imposed on the number
4288 // of iterations is defensive, to avoid any unforseen circumstances
4289 // putting us into an infinite loop. Since it's always been this
4290 // (coordinator_yield()) method that was observed to cause the
4291 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4292 // which is by default non-zero. For the other seven methods that
4293 // also perform the yield operation, as are using a different
4294 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4295 // can enable the sleeping for those methods too, if necessary.
4296 // See 6442774.
4297 //
4298 // We really need to reconsider the synchronization between the GC
4299 // thread and the yield-requesting threads in the future and we
4300 // should really use wait/notify, which is the recommended
4301 // way of doing this type of interaction. Additionally, we should
4302 // consolidate the eight methods that do the yield operation and they
4303 // are almost identical into one for better maintainability and
4304 // readability. See 6445193.
4305 //
4306 // Tony 2006.06.29
4307 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4308 ConcurrentMarkSweepThread::should_yield() &&
4309 !CMSCollector::foregroundGCIsActive(); ++i) {
4310 os::sleep(Thread::current(), 1, false);
4311 ConcurrentMarkSweepThread::acknowledge_yield_request();
4312 }
4313
4314 ConcurrentMarkSweepThread::synchronize(true);
4315 _bit_map_lock->lock_without_safepoint_check();
4316 _collector->startTimer();
4317 }
4318
4319 bool CMSCollector::do_marking_mt(bool asynch) {
4320 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4321 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4322 conc_workers()->total_workers(),
4323 conc_workers()->active_workers(),
4324 Threads::number_of_non_daemon_threads());
4325 conc_workers()->set_active_workers(num_workers);
4326
4327 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4328
4329 CMSConcMarkingTask tsk(this,
4330 cms_space,
4331 asynch,
4332 conc_workers(),
4333 task_queues());
4334
4335 // Since the actual number of workers we get may be different
4336 // from the number we requested above, do we need to do anything different
4337 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4338 // class?? XXX
4339 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4340
4341 // Refs discovery is already non-atomic.
4342 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4343 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4344 conc_workers()->start_task(&tsk);
4345 while (tsk.yielded()) {
4346 tsk.coordinator_yield();
4347 conc_workers()->continue_task(&tsk);
4348 }
4349 // If the task was aborted, _restart_addr will be non-NULL
4350 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4351 while (_restart_addr != NULL) {
4352 // XXX For now we do not make use of ABORTED state and have not
4353 // yet implemented the right abort semantics (even in the original
4354 // single-threaded CMS case). That needs some more investigation
4355 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4356 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4357 // If _restart_addr is non-NULL, a marking stack overflow
4358 // occurred; we need to do a fresh marking iteration from the
4359 // indicated restart address.
4360 if (_foregroundGCIsActive && asynch) {
4361 // We may be running into repeated stack overflows, having
4362 // reached the limit of the stack size, while making very
4363 // slow forward progress. It may be best to bail out and
4364 // let the foreground collector do its job.
4365 // Clear _restart_addr, so that foreground GC
4366 // works from scratch. This avoids the headache of
4367 // a "rescan" which would otherwise be needed because
4368 // of the dirty mod union table & card table.
4369 _restart_addr = NULL;
4370 return false;
4371 }
4372 // Adjust the task to restart from _restart_addr
4373 tsk.reset(_restart_addr);
4374 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4375 _restart_addr);
4376 _restart_addr = NULL;
4377 // Get the workers going again
4378 conc_workers()->start_task(&tsk);
4379 while (tsk.yielded()) {
4380 tsk.coordinator_yield();
4381 conc_workers()->continue_task(&tsk);
4382 }
4383 }
4384 assert(tsk.completed(), "Inconsistency");
4385 assert(tsk.result() == true, "Inconsistency");
4386 return true;
4387 }
4388
4389 bool CMSCollector::do_marking_st(bool asynch) {
4390 ResourceMark rm;
4391 HandleMark hm;
4392
4393 // Temporarily make refs discovery single threaded (non-MT)
4394 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4395 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4396 &_markStack, CMSYield && asynch);
4397 // the last argument to iterate indicates whether the iteration
4398 // should be incremental with periodic yields.
4399 _markBitMap.iterate(&markFromRootsClosure);
4400 // If _restart_addr is non-NULL, a marking stack overflow
4401 // occurred; we need to do a fresh iteration from the
4402 // indicated restart address.
4403 while (_restart_addr != NULL) {
4404 if (_foregroundGCIsActive && asynch) {
4405 // We may be running into repeated stack overflows, having
4406 // reached the limit of the stack size, while making very
4407 // slow forward progress. It may be best to bail out and
4408 // let the foreground collector do its job.
4409 // Clear _restart_addr, so that foreground GC
4410 // works from scratch. This avoids the headache of
4411 // a "rescan" which would otherwise be needed because
4412 // of the dirty mod union table & card table.
4413 _restart_addr = NULL;
4414 return false; // indicating failure to complete marking
4415 }
4416 // Deal with stack overflow:
4417 // we restart marking from _restart_addr
4418 HeapWord* ra = _restart_addr;
4419 markFromRootsClosure.reset(ra);
4420 _restart_addr = NULL;
4421 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4422 }
4423 return true;
4424 }
4425
4426 void CMSCollector::preclean() {
4427 check_correct_thread_executing();
4428 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4429 verify_work_stacks_empty();
4430 verify_overflow_empty();
4431 _abort_preclean = false;
4432 if (CMSPrecleaningEnabled) {
4433 if (!CMSEdenChunksRecordAlways) {
4434 _eden_chunk_index = 0;
4435 }
4436 size_t used = get_eden_used();
4437 size_t capacity = get_eden_capacity();
4438 // Don't start sampling unless we will get sufficiently
4439 // many samples.
4440 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4441 * CMSScheduleRemarkEdenPenetration)) {
4442 _start_sampling = true;
4443 } else {
4444 _start_sampling = false;
4445 }
4446 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4447 CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
4448 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4449 }
4450 CMSTokenSync x(true); // is cms thread
4451 if (CMSPrecleaningEnabled) {
4452 sample_eden();
4453 _collectorState = AbortablePreclean;
4454 } else {
4455 _collectorState = FinalMarking;
4456 }
4457 verify_work_stacks_empty();
4458 verify_overflow_empty();
4459 }
4460
4461 // Try and schedule the remark such that young gen
4462 // occupancy is CMSScheduleRemarkEdenPenetration %.
4463 void CMSCollector::abortable_preclean() {
4464 check_correct_thread_executing();
4465 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4466 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4467
4468 // If Eden's current occupancy is below this threshold,
4469 // immediately schedule the remark; else preclean
4470 // past the next scavenge in an effort to
4471 // schedule the pause as described above. By choosing
4472 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4473 // we will never do an actual abortable preclean cycle.
4474 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4475 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4476 CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
4477 // We need more smarts in the abortable preclean
4478 // loop below to deal with cases where allocation
4479 // in young gen is very very slow, and our precleaning
4480 // is running a losing race against a horde of
4481 // mutators intent on flooding us with CMS updates
4482 // (dirty cards).
4483 // One, admittedly dumb, strategy is to give up
4484 // after a certain number of abortable precleaning loops
4485 // or after a certain maximum time. We want to make
4486 // this smarter in the next iteration.
4487 // XXX FIX ME!!! YSR
4488 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4489 while (!(should_abort_preclean() ||
4490 ConcurrentMarkSweepThread::should_terminate())) {
4491 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4492 cumworkdone += workdone;
4493 loops++;
4494 // Voluntarily terminate abortable preclean phase if we have
4495 // been at it for too long.
4496 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4497 loops >= CMSMaxAbortablePrecleanLoops) {
4498 if (PrintGCDetails) {
4499 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4500 }
4501 break;
4502 }
4503 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4504 if (PrintGCDetails) {
4505 gclog_or_tty->print(" CMS: abort preclean due to time ");
4506 }
4507 break;
4508 }
4509 // If we are doing little work each iteration, we should
4510 // take a short break.
4511 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4512 // Sleep for some time, waiting for work to accumulate
4513 stopTimer();
4514 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4515 startTimer();
4516 waited++;
4517 }
4518 }
4519 if (PrintCMSStatistics > 0) {
4520 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
4521 loops, waited, cumworkdone);
4522 }
4523 }
4524 CMSTokenSync x(true); // is cms thread
4525 if (_collectorState != Idling) {
4526 assert(_collectorState == AbortablePreclean,
4527 "Spontaneous state transition?");
4528 _collectorState = FinalMarking;
4529 } // Else, a foreground collection completed this CMS cycle.
4530 return;
4531 }
4532
4533 // Respond to an Eden sampling opportunity
4534 void CMSCollector::sample_eden() {
4535 // Make sure a young gc cannot sneak in between our
4536 // reading and recording of a sample.
4537 assert(Thread::current()->is_ConcurrentGC_thread(),
4538 "Only the cms thread may collect Eden samples");
4539 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4540 "Should collect samples while holding CMS token");
4541 if (!_start_sampling) {
4542 return;
4543 }
4544 // When CMSEdenChunksRecordAlways is true, the eden chunk array
4545 // is populated by the young generation.
4546 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
4547 if (_eden_chunk_index < _eden_chunk_capacity) {
4548 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4549 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4550 "Unexpected state of Eden");
4551 // We'd like to check that what we just sampled is an oop-start address;
4552 // however, we cannot do that here since the object may not yet have been
4553 // initialized. So we'll instead do the check when we _use_ this sample
4554 // later.
4555 if (_eden_chunk_index == 0 ||
4556 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4557 _eden_chunk_array[_eden_chunk_index-1])
4558 >= CMSSamplingGrain)) {
4559 _eden_chunk_index++; // commit sample
4560 }
4561 }
4562 }
4563 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4564 size_t used = get_eden_used();
4565 size_t capacity = get_eden_capacity();
4566 assert(used <= capacity, "Unexpected state of Eden");
4567 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4568 _abort_preclean = true;
4569 }
4570 }
4571 }
4572
4573
4574 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4575 assert(_collectorState == Precleaning ||
4576 _collectorState == AbortablePreclean, "incorrect state");
4577 ResourceMark rm;
4578 HandleMark hm;
4579
4580 // Precleaning is currently not MT but the reference processor
4581 // may be set for MT. Disable it temporarily here.
4582 ReferenceProcessor* rp = ref_processor();
4583 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4584
4585 // Do one pass of scrubbing the discovered reference lists
4586 // to remove any reference objects with strongly-reachable
4587 // referents.
4588 if (clean_refs) {
4589 CMSPrecleanRefsYieldClosure yield_cl(this);
4590 assert(rp->span().equals(_span), "Spans should be equal");
4591 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4592 &_markStack, true /* preclean */);
4593 CMSDrainMarkingStackClosure complete_trace(this,
4594 _span, &_markBitMap, &_markStack,
4595 &keep_alive, true /* preclean */);
4596
4597 // We don't want this step to interfere with a young
4598 // collection because we don't want to take CPU
4599 // or memory bandwidth away from the young GC threads
4600 // (which may be as many as there are CPUs).
4601 // Note that we don't need to protect ourselves from
4602 // interference with mutators because they can't
4603 // manipulate the discovered reference lists nor affect
4604 // the computed reachability of the referents, the
4605 // only properties manipulated by the precleaning
4606 // of these reference lists.
4607 stopTimer();
4608 CMSTokenSyncWithLocks x(true /* is cms thread */,
4609 bitMapLock());
4610 startTimer();
4611 sample_eden();
4612
4613 // The following will yield to allow foreground
4614 // collection to proceed promptly. XXX YSR:
4615 // The code in this method may need further
4616 // tweaking for better performance and some restructuring
4617 // for cleaner interfaces.
4618 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4619 rp->preclean_discovered_references(
4620 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
4621 gc_timer, _gc_tracer_cm->gc_id());
4622 }
4623
4624 if (clean_survivor) { // preclean the active survivor space(s)
4625 assert(_young_gen->kind() == Generation::DefNew ||
4626 _young_gen->kind() == Generation::ParNew,
4627 "incorrect type for cast");
4628 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4629 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4630 &_markBitMap, &_modUnionTable,
4631 &_markStack, true /* precleaning phase */);
4632 stopTimer();
4633 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4634 bitMapLock());
4635 startTimer();
4636 unsigned int before_count =
4637 GenCollectedHeap::heap()->total_collections();
4638 SurvivorSpacePrecleanClosure
4639 sss_cl(this, _span, &_markBitMap, &_markStack,
4640 &pam_cl, before_count, CMSYield);
4641 dng->from()->object_iterate_careful(&sss_cl);
4642 dng->to()->object_iterate_careful(&sss_cl);
4643 }
4644 MarkRefsIntoAndScanClosure
4645 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4646 &_markStack, this, CMSYield,
4647 true /* precleaning phase */);
4648 // CAUTION: The following closure has persistent state that may need to
4649 // be reset upon a decrease in the sequence of addresses it
4650 // processes.
4651 ScanMarkedObjectsAgainCarefullyClosure
4652 smoac_cl(this, _span,
4653 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4654
4655 // Preclean dirty cards in ModUnionTable and CardTable using
4656 // appropriate convergence criterion;
4657 // repeat CMSPrecleanIter times unless we find that
4658 // we are losing.
4659 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4660 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4661 "Bad convergence multiplier");
4662 assert(CMSPrecleanThreshold >= 100,
4663 "Unreasonably low CMSPrecleanThreshold");
4664
4665 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4666 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4667 numIter < CMSPrecleanIter;
4668 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4669 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4670 if (Verbose && PrintGCDetails) {
4671 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
4672 }
4673 // Either there are very few dirty cards, so re-mark
4674 // pause will be small anyway, or our pre-cleaning isn't
4675 // that much faster than the rate at which cards are being
4676 // dirtied, so we might as well stop and re-mark since
4677 // precleaning won't improve our re-mark time by much.
4678 if (curNumCards <= CMSPrecleanThreshold ||
4679 (numIter > 0 &&
4680 (curNumCards * CMSPrecleanDenominator >
4681 lastNumCards * CMSPrecleanNumerator))) {
4682 numIter++;
4683 cumNumCards += curNumCards;
4684 break;
4685 }
4686 }
4687
4688 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4689
4690 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4691 cumNumCards += curNumCards;
4692 if (PrintGCDetails && PrintCMSStatistics != 0) {
4693 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4694 curNumCards, cumNumCards, numIter);
4695 }
4696 return cumNumCards; // as a measure of useful work done
4697 }
4698
4699 // PRECLEANING NOTES:
4700 // Precleaning involves:
4701 // . reading the bits of the modUnionTable and clearing the set bits.
4702 // . For the cards corresponding to the set bits, we scan the
4703 // objects on those cards. This means we need the free_list_lock
4704 // so that we can safely iterate over the CMS space when scanning
4705 // for oops.
4706 // . When we scan the objects, we'll be both reading and setting
4707 // marks in the marking bit map, so we'll need the marking bit map.
4708 // . For protecting _collector_state transitions, we take the CGC_lock.
4709 // Note that any races in the reading of of card table entries by the
4710 // CMS thread on the one hand and the clearing of those entries by the
4711 // VM thread or the setting of those entries by the mutator threads on the
4712 // other are quite benign. However, for efficiency it makes sense to keep
4713 // the VM thread from racing with the CMS thread while the latter is
4714 // dirty card info to the modUnionTable. We therefore also use the
4715 // CGC_lock to protect the reading of the card table and the mod union
4716 // table by the CM thread.
4717 // . We run concurrently with mutator updates, so scanning
4718 // needs to be done carefully -- we should not try to scan
4719 // potentially uninitialized objects.
4720 //
4721 // Locking strategy: While holding the CGC_lock, we scan over and
4722 // reset a maximal dirty range of the mod union / card tables, then lock
4723 // the free_list_lock and bitmap lock to do a full marking, then
4724 // release these locks; and repeat the cycle. This allows for a
4725 // certain amount of fairness in the sharing of these locks between
4726 // the CMS collector on the one hand, and the VM thread and the
4727 // mutators on the other.
4728
4729 // NOTE: preclean_mod_union_table() and preclean_card_table()
4730 // further below are largely identical; if you need to modify
4731 // one of these methods, please check the other method too.
4732
4733 size_t CMSCollector::preclean_mod_union_table(
4734 ConcurrentMarkSweepGeneration* gen,
4735 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4736 verify_work_stacks_empty();
4737 verify_overflow_empty();
4738
4739 // strategy: starting with the first card, accumulate contiguous
4740 // ranges of dirty cards; clear these cards, then scan the region
4741 // covered by these cards.
4742
4743 // Since all of the MUT is committed ahead, we can just use
4744 // that, in case the generations expand while we are precleaning.
4745 // It might also be fine to just use the committed part of the
4746 // generation, but we might potentially miss cards when the
4747 // generation is rapidly expanding while we are in the midst
4748 // of precleaning.
4749 HeapWord* startAddr = gen->reserved().start();
4750 HeapWord* endAddr = gen->reserved().end();
4751
4752 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4753
4754 size_t numDirtyCards, cumNumDirtyCards;
4755 HeapWord *nextAddr, *lastAddr;
4756 for (cumNumDirtyCards = numDirtyCards = 0,
4757 nextAddr = lastAddr = startAddr;
4758 nextAddr < endAddr;
4759 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4760
4761 ResourceMark rm;
4762 HandleMark hm;
4763
4764 MemRegion dirtyRegion;
4765 {
4766 stopTimer();
4767 // Potential yield point
4768 CMSTokenSync ts(true);
4769 startTimer();
4770 sample_eden();
4771 // Get dirty region starting at nextOffset (inclusive),
4772 // simultaneously clearing it.
4773 dirtyRegion =
4774 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4775 assert(dirtyRegion.start() >= nextAddr,
4776 "returned region inconsistent?");
4777 }
4778 // Remember where the next search should begin.
4779 // The returned region (if non-empty) is a right open interval,
4780 // so lastOffset is obtained from the right end of that
4781 // interval.
4782 lastAddr = dirtyRegion.end();
4783 // Should do something more transparent and less hacky XXX
4784 numDirtyCards =
4785 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4786
4787 // We'll scan the cards in the dirty region (with periodic
4788 // yields for foreground GC as needed).
4789 if (!dirtyRegion.is_empty()) {
4790 assert(numDirtyCards > 0, "consistency check");
4791 HeapWord* stop_point = NULL;
4792 stopTimer();
4793 // Potential yield point
4794 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4795 bitMapLock());
4796 startTimer();
4797 {
4798 verify_work_stacks_empty();
4799 verify_overflow_empty();
4800 sample_eden();
4801 stop_point =
4802 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4803 }
4804 if (stop_point != NULL) {
4805 // The careful iteration stopped early either because it found an
4806 // uninitialized object, or because we were in the midst of an
4807 // "abortable preclean", which should now be aborted. Redirty
4808 // the bits corresponding to the partially-scanned or unscanned
4809 // cards. We'll either restart at the next block boundary or
4810 // abort the preclean.
4811 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4812 "Should only be AbortablePreclean.");
4813 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4814 if (should_abort_preclean()) {
4815 break; // out of preclean loop
4816 } else {
4817 // Compute the next address at which preclean should pick up;
4818 // might need bitMapLock in order to read P-bits.
4819 lastAddr = next_card_start_after_block(stop_point);
4820 }
4821 }
4822 } else {
4823 assert(lastAddr == endAddr, "consistency check");
4824 assert(numDirtyCards == 0, "consistency check");
4825 break;
4826 }
4827 }
4828 verify_work_stacks_empty();
4829 verify_overflow_empty();
4830 return cumNumDirtyCards;
4831 }
4832
4833 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4834 // below are largely identical; if you need to modify
4835 // one of these methods, please check the other method too.
4836
4837 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4838 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4839 // strategy: it's similar to precleamModUnionTable above, in that
4840 // we accumulate contiguous ranges of dirty cards, mark these cards
4841 // precleaned, then scan the region covered by these cards.
4842 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4843 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4844
4845 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4846
4847 size_t numDirtyCards, cumNumDirtyCards;
4848 HeapWord *lastAddr, *nextAddr;
4849
4850 for (cumNumDirtyCards = numDirtyCards = 0,
4851 nextAddr = lastAddr = startAddr;
4852 nextAddr < endAddr;
4853 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4854
4855 ResourceMark rm;
4856 HandleMark hm;
4857
4858 MemRegion dirtyRegion;
4859 {
4860 // See comments in "Precleaning notes" above on why we
4861 // do this locking. XXX Could the locking overheads be
4862 // too high when dirty cards are sparse? [I don't think so.]
4863 stopTimer();
4864 CMSTokenSync x(true); // is cms thread
4865 startTimer();
4866 sample_eden();
4867 // Get and clear dirty region from card table
4868 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4869 MemRegion(nextAddr, endAddr),
4870 true,
4871 CardTableModRefBS::precleaned_card_val());
4872
4873 assert(dirtyRegion.start() >= nextAddr,
4874 "returned region inconsistent?");
4875 }
4876 lastAddr = dirtyRegion.end();
4877 numDirtyCards =
4878 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4879
4880 if (!dirtyRegion.is_empty()) {
4881 stopTimer();
4882 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4883 startTimer();
4884 sample_eden();
4885 verify_work_stacks_empty();
4886 verify_overflow_empty();
4887 HeapWord* stop_point =
4888 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4889 if (stop_point != NULL) {
4890 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4891 "Should only be AbortablePreclean.");
4892 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4893 if (should_abort_preclean()) {
4894 break; // out of preclean loop
4895 } else {
4896 // Compute the next address at which preclean should pick up.
4897 lastAddr = next_card_start_after_block(stop_point);
4898 }
4899 }
4900 } else {
4901 break;
4902 }
4903 }
4904 verify_work_stacks_empty();
4905 verify_overflow_empty();
4906 return cumNumDirtyCards;
4907 }
4908
4909 class PrecleanKlassClosure : public KlassClosure {
4910 KlassToOopClosure _cm_klass_closure;
4911 public:
4912 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4913 void do_klass(Klass* k) {
4914 if (k->has_accumulated_modified_oops()) {
4915 k->clear_accumulated_modified_oops();
4916
4917 _cm_klass_closure.do_klass(k);
4918 }
4919 }
4920 };
4921
4922 // The freelist lock is needed to prevent asserts, is it really needed?
4923 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4924
4925 cl->set_freelistLock(freelistLock);
4926
4927 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4928
4929 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4930 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4931 PrecleanKlassClosure preclean_klass_closure(cl);
4932 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4933
4934 verify_work_stacks_empty();
4935 verify_overflow_empty();
4936 }
4937
4938 void CMSCollector::checkpointRootsFinal(bool asynch,
4939 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4940 assert(_collectorState == FinalMarking, "incorrect state transition?");
4941 check_correct_thread_executing();
4942 // world is stopped at this checkpoint
4943 assert(SafepointSynchronize::is_at_safepoint(),
4944 "world should be stopped");
4945 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4946
4947 verify_work_stacks_empty();
4948 verify_overflow_empty();
4949
4950 SpecializationStats::clear();
4951 if (PrintGCDetails) {
4952 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4953 _young_gen->used() / K,
4954 _young_gen->capacity() / K);
4955 }
4956 if (asynch) {
4957 if (CMSScavengeBeforeRemark) {
4958 GenCollectedHeap* gch = GenCollectedHeap::heap();
4959 // Temporarily set flag to false, GCH->do_collection will
4960 // expect it to be false and set to true
4961 FlagSetting fl(gch->_is_gc_active, false);
4962 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4963 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4964 int level = _cmsGen->level() - 1;
4965 if (level >= 0) {
4966 gch->do_collection(true, // full (i.e. force, see below)
4967 false, // !clear_all_soft_refs
4968 0, // size
4969 false, // is_tlab
4970 level // max_level
4971 );
4972 }
4973 }
4974 FreelistLocker x(this);
4975 MutexLockerEx y(bitMapLock(),
4976 Mutex::_no_safepoint_check_flag);
4977 assert(!init_mark_was_synchronous, "but that's impossible!");
4978 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4979 } else {
4980 // already have all the locks
4981 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4982 init_mark_was_synchronous);
4983 }
4984 verify_work_stacks_empty();
4985 verify_overflow_empty();
4986 SpecializationStats::print();
4987 }
4988
4989 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4990 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4991
4992 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4993
4994 assert(haveFreelistLocks(), "must have free list locks");
4995 assert_lock_strong(bitMapLock());
4996
4997 ResourceMark rm;
4998 HandleMark hm;
4999
5000 GenCollectedHeap* gch = GenCollectedHeap::heap();
5001
5002 if (should_unload_classes()) {
5003 CodeCache::gc_prologue();
5004 }
5005 assert(haveFreelistLocks(), "must have free list locks");
5006 assert_lock_strong(bitMapLock());
5007
5008 if (!init_mark_was_synchronous) {
5009 // We might assume that we need not fill TLAB's when
5010 // CMSScavengeBeforeRemark is set, because we may have just done
5011 // a scavenge which would have filled all TLAB's -- and besides
5012 // Eden would be empty. This however may not always be the case --
5013 // for instance although we asked for a scavenge, it may not have
5014 // happened because of a JNI critical section. We probably need
5015 // a policy for deciding whether we can in that case wait until
5016 // the critical section releases and then do the remark following
5017 // the scavenge, and skip it here. In the absence of that policy,
5018 // or of an indication of whether the scavenge did indeed occur,
5019 // we cannot rely on TLAB's having been filled and must do
5020 // so here just in case a scavenge did not happen.
5021 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
5022 // Update the saved marks which may affect the root scans.
5023 gch->save_marks();
5024
5025 if (CMSPrintEdenSurvivorChunks) {
5026 print_eden_and_survivor_chunk_arrays();
5027 }
5028
5029 {
5030 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
5031
5032 // Note on the role of the mod union table:
5033 // Since the marker in "markFromRoots" marks concurrently with
5034 // mutators, it is possible for some reachable objects not to have been
5035 // scanned. For instance, an only reference to an object A was
5036 // placed in object B after the marker scanned B. Unless B is rescanned,
5037 // A would be collected. Such updates to references in marked objects
5038 // are detected via the mod union table which is the set of all cards
5039 // dirtied since the first checkpoint in this GC cycle and prior to
5040 // the most recent young generation GC, minus those cleaned up by the
5041 // concurrent precleaning.
5042 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
5043 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5044 do_remark_parallel();
5045 } else {
5046 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
5047 _gc_timer_cm, _gc_tracer_cm->gc_id());
5048 do_remark_non_parallel();
5049 }
5050 }
5051 } else {
5052 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
5053 // The initial mark was stop-world, so there's no rescanning to
5054 // do; go straight on to the next step below.
5055 }
5056 verify_work_stacks_empty();
5057 verify_overflow_empty();
5058
5059 {
5060 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
5061 refProcessingWork(asynch, clear_all_soft_refs);
5062 }
5063 verify_work_stacks_empty();
5064 verify_overflow_empty();
5065
5066 if (should_unload_classes()) {
5067 CodeCache::gc_epilogue();
5068 }
5069 JvmtiExport::gc_epilogue();
5070
5071 // If we encountered any (marking stack / work queue) overflow
5072 // events during the current CMS cycle, take appropriate
5073 // remedial measures, where possible, so as to try and avoid
5074 // recurrence of that condition.
5075 assert(_markStack.isEmpty(), "No grey objects");
5076 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5077 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
5078 if (ser_ovflw > 0) {
5079 if (PrintCMSStatistics != 0) {
5080 gclog_or_tty->print_cr("Marking stack overflow (benign) "
5081 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5082 ", kac_preclean="SIZE_FORMAT")",
5083 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5084 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5085 }
5086 _markStack.expand();
5087 _ser_pmc_remark_ovflw = 0;
5088 _ser_pmc_preclean_ovflw = 0;
5089 _ser_kac_preclean_ovflw = 0;
5090 _ser_kac_ovflw = 0;
5091 }
5092 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5093 if (PrintCMSStatistics != 0) {
5094 gclog_or_tty->print_cr("Work queue overflow (benign) "
5095 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5096 _par_pmc_remark_ovflw, _par_kac_ovflw);
5097 }
5098 _par_pmc_remark_ovflw = 0;
5099 _par_kac_ovflw = 0;
5100 }
5101 if (PrintCMSStatistics != 0) {
5102 if (_markStack._hit_limit > 0) {
5103 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5104 _markStack._hit_limit);
5105 }
5106 if (_markStack._failed_double > 0) {
5107 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5108 " current capacity "SIZE_FORMAT,
5109 _markStack._failed_double,
5110 _markStack.capacity());
5111 }
5112 }
5113 _markStack._hit_limit = 0;
5114 _markStack._failed_double = 0;
5115
5116 if ((VerifyAfterGC || VerifyDuringGC) &&
5117 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5118 verify_after_remark();
5119 }
5120
5121 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
5122
5123 // Change under the freelistLocks.
5124 _collectorState = Sweeping;
5125 // Call isAllClear() under bitMapLock
5126 assert(_modUnionTable.isAllClear(),
5127 "Should be clear by end of the final marking");
5128 assert(_ct->klass_rem_set()->mod_union_is_clear(),
5129 "Should be clear by end of the final marking");
5130 }
5131
5132 void CMSParInitialMarkTask::work(uint worker_id) {
5133 elapsedTimer _timer;
5134 ResourceMark rm;
5135 HandleMark hm;
5136
5137 // ---------- scan from roots --------------
5138 _timer.start();
5139 GenCollectedHeap* gch = GenCollectedHeap::heap();
5140 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
5141
5142 // ---------- young gen roots --------------
5143 {
5144 work_on_young_gen_roots(worker_id, &par_mri_cl);
5145 _timer.stop();
5146 if (PrintCMSStatistics != 0) {
5147 gclog_or_tty->print_cr(
5148 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
5149 worker_id, _timer.seconds());
5150 }
5151 }
5152
5153 // ---------- remaining roots --------------
5154 _timer.reset();
5155 _timer.start();
5156
5157 CLDToOopClosure cld_closure(&par_mri_cl, true);
5158
5159 gch->gen_process_roots(_collector->_cmsGen->level(),
5160 false, // yg was scanned above
5161 false, // this is parallel code
5162 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5163 _collector->should_unload_classes(),
5164 &par_mri_cl,
5165 NULL,
5166 &cld_closure);
5167 assert(_collector->should_unload_classes()
5168 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5169 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5170 _timer.stop();
5171 if (PrintCMSStatistics != 0) {
5172 gclog_or_tty->print_cr(
5173 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
5174 worker_id, _timer.seconds());
5175 }
5176 }
5177
5178 // Parallel remark task
5179 class CMSParRemarkTask: public CMSParMarkTask {
5180 CompactibleFreeListSpace* _cms_space;
5181
5182 // The per-thread work queues, available here for stealing.
5183 OopTaskQueueSet* _task_queues;
5184 ParallelTaskTerminator _term;
5185
5186 public:
5187 // A value of 0 passed to n_workers will cause the number of
5188 // workers to be taken from the active workers in the work gang.
5189 CMSParRemarkTask(CMSCollector* collector,
5190 CompactibleFreeListSpace* cms_space,
5191 int n_workers, FlexibleWorkGang* workers,
5192 OopTaskQueueSet* task_queues):
5193 CMSParMarkTask("Rescan roots and grey objects in parallel",
5194 collector, n_workers),
5195 _cms_space(cms_space),
5196 _task_queues(task_queues),
5197 _term(n_workers, task_queues) { }
5198
5199 OopTaskQueueSet* task_queues() { return _task_queues; }
5200
5201 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5202
5203 ParallelTaskTerminator* terminator() { return &_term; }
5204 int n_workers() { return _n_workers; }
5205
5206 void work(uint worker_id);
5207
5208 private:
5209 // ... of dirty cards in old space
5210 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5211 Par_MarkRefsIntoAndScanClosure* cl);
5212
5213 // ... work stealing for the above
5214 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5215 };
5216
5217 class RemarkKlassClosure : public KlassClosure {
5218 KlassToOopClosure _cm_klass_closure;
5219 public:
5220 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
5221 void do_klass(Klass* k) {
5222 // Check if we have modified any oops in the Klass during the concurrent marking.
5223 if (k->has_accumulated_modified_oops()) {
5224 k->clear_accumulated_modified_oops();
5225
5226 // We could have transfered the current modified marks to the accumulated marks,
5227 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
5228 } else if (k->has_modified_oops()) {
5229 // Don't clear anything, this info is needed by the next young collection.
5230 } else {
5231 // No modified oops in the Klass.
5232 return;
5233 }
5234
5235 // The klass has modified fields, need to scan the klass.
5236 _cm_klass_closure.do_klass(k);
5237 }
5238 };
5239
5240 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
5241 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5242 EdenSpace* eden_space = dng->eden();
5243 ContiguousSpace* from_space = dng->from();
5244 ContiguousSpace* to_space = dng->to();
5245
5246 HeapWord** eca = _collector->_eden_chunk_array;
5247 size_t ect = _collector->_eden_chunk_index;
5248 HeapWord** sca = _collector->_survivor_chunk_array;
5249 size_t sct = _collector->_survivor_chunk_index;
5250
5251 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5252 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5253
5254 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
5255 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
5256 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
5257 }
5258
5259 // work_queue(i) is passed to the closure
5260 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5261 // also is passed to do_dirty_card_rescan_tasks() and to
5262 // do_work_steal() to select the i-th task_queue.
5263
5264 void CMSParRemarkTask::work(uint worker_id) {
5265 elapsedTimer _timer;
5266 ResourceMark rm;
5267 HandleMark hm;
5268
5269 // ---------- rescan from roots --------------
5270 _timer.start();
5271 GenCollectedHeap* gch = GenCollectedHeap::heap();
5272 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5273 _collector->_span, _collector->ref_processor(),
5274 &(_collector->_markBitMap),
5275 work_queue(worker_id));
5276
5277 // Rescan young gen roots first since these are likely
5278 // coarsely partitioned and may, on that account, constitute
5279 // the critical path; thus, it's best to start off that
5280 // work first.
5281 // ---------- young gen roots --------------
5282 {
5283 work_on_young_gen_roots(worker_id, &par_mrias_cl);
5284 _timer.stop();
5285 if (PrintCMSStatistics != 0) {
5286 gclog_or_tty->print_cr(
5287 "Finished young gen rescan work in %dth thread: %3.3f sec",
5288 worker_id, _timer.seconds());
5289 }
5290 }
5291
5292 // ---------- remaining roots --------------
5293 _timer.reset();
5294 _timer.start();
5295 gch->gen_process_roots(_collector->_cmsGen->level(),
5296 false, // yg was scanned above
5297 false, // this is parallel code
5298 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5299 _collector->should_unload_classes(),
5300 &par_mrias_cl,
5301 NULL,
5302 NULL); // The dirty klasses will be handled below
5303
5304 assert(_collector->should_unload_classes()
5305 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5306 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5307 _timer.stop();
5308 if (PrintCMSStatistics != 0) {
5309 gclog_or_tty->print_cr(
5310 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5311 worker_id, _timer.seconds());
5312 }
5313
5314 // ---------- unhandled CLD scanning ----------
5315 if (worker_id == 0) { // Single threaded at the moment.
5316 _timer.reset();
5317 _timer.start();
5318
5319 // Scan all new class loader data objects and new dependencies that were
5320 // introduced during concurrent marking.
5321 ResourceMark rm;
5322 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5323 for (int i = 0; i < array->length(); i++) {
5324 par_mrias_cl.do_class_loader_data(array->at(i));
5325 }
5326
5327 // We don't need to keep track of new CLDs anymore.
5328 ClassLoaderDataGraph::remember_new_clds(false);
5329
5330 _timer.stop();
5331 if (PrintCMSStatistics != 0) {
5332 gclog_or_tty->print_cr(
5333 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
5334 worker_id, _timer.seconds());
5335 }
5336 }
5337
5338 // ---------- dirty klass scanning ----------
5339 if (worker_id == 0) { // Single threaded at the moment.
5340 _timer.reset();
5341 _timer.start();
5342
5343 // Scan all classes that was dirtied during the concurrent marking phase.
5344 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
5345 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5346
5347 _timer.stop();
5348 if (PrintCMSStatistics != 0) {
5349 gclog_or_tty->print_cr(
5350 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
5351 worker_id, _timer.seconds());
5352 }
5353 }
5354
5355 // We might have added oops to ClassLoaderData::_handles during the
5356 // concurrent marking phase. These oops point to newly allocated objects
5357 // that are guaranteed to be kept alive. Either by the direct allocation
5358 // code, or when the young collector processes the roots. Hence,
5359 // we don't have to revisit the _handles block during the remark phase.
5360
5361 // ---------- rescan dirty cards ------------
5362 _timer.reset();
5363 _timer.start();
5364
5365 // Do the rescan tasks for each of the two spaces
5366 // (cms_space) in turn.
5367 // "worker_id" is passed to select the task_queue for "worker_id"
5368 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5369 _timer.stop();
5370 if (PrintCMSStatistics != 0) {
5371 gclog_or_tty->print_cr(
5372 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5373 worker_id, _timer.seconds());
5374 }
5375
5376 // ---------- steal work from other threads ...
5377 // ---------- ... and drain overflow list.
5378 _timer.reset();
5379 _timer.start();
5380 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5381 _timer.stop();
5382 if (PrintCMSStatistics != 0) {
5383 gclog_or_tty->print_cr(
5384 "Finished work stealing in %dth thread: %3.3f sec",
5385 worker_id, _timer.seconds());
5386 }
5387 }
5388
5389 // Note that parameter "i" is not used.
5390 void
5391 CMSParMarkTask::do_young_space_rescan(uint worker_id,
5392 OopsInGenClosure* cl, ContiguousSpace* space,
5393 HeapWord** chunk_array, size_t chunk_top) {
5394 // Until all tasks completed:
5395 // . claim an unclaimed task
5396 // . compute region boundaries corresponding to task claimed
5397 // using chunk_array
5398 // . par_oop_iterate(cl) over that region
5399
5400 ResourceMark rm;
5401 HandleMark hm;
5402
5403 SequentialSubTasksDone* pst = space->par_seq_tasks();
5404
5405 uint nth_task = 0;
5406 uint n_tasks = pst->n_tasks();
5407
5408 if (n_tasks > 0) {
5409 assert(pst->valid(), "Uninitialized use?");
5410 HeapWord *start, *end;
5411 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5412 // We claimed task # nth_task; compute its boundaries.
5413 if (chunk_top == 0) { // no samples were taken
5414 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5415 start = space->bottom();
5416 end = space->top();
5417 } else if (nth_task == 0) {
5418 start = space->bottom();
5419 end = chunk_array[nth_task];
5420 } else if (nth_task < (uint)chunk_top) {
5421 assert(nth_task >= 1, "Control point invariant");
5422 start = chunk_array[nth_task - 1];
5423 end = chunk_array[nth_task];
5424 } else {
5425 assert(nth_task == (uint)chunk_top, "Control point invariant");
5426 start = chunk_array[chunk_top - 1];
5427 end = space->top();
5428 }
5429 MemRegion mr(start, end);
5430 // Verify that mr is in space
5431 assert(mr.is_empty() || space->used_region().contains(mr),
5432 "Should be in space");
5433 // Verify that "start" is an object boundary
5434 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5435 "Should be an oop");
5436 space->par_oop_iterate(mr, cl);
5437 }
5438 pst->all_tasks_completed();
5439 }
5440 }
5441
5442 void
5443 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5444 CompactibleFreeListSpace* sp, int i,
5445 Par_MarkRefsIntoAndScanClosure* cl) {
5446 // Until all tasks completed:
5447 // . claim an unclaimed task
5448 // . compute region boundaries corresponding to task claimed
5449 // . transfer dirty bits ct->mut for that region
5450 // . apply rescanclosure to dirty mut bits for that region
5451
5452 ResourceMark rm;
5453 HandleMark hm;
5454
5455 OopTaskQueue* work_q = work_queue(i);
5456 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5457 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5458 // CAUTION: This closure has state that persists across calls to
5459 // the work method dirty_range_iterate_clear() in that it has
5460 // embedded in it a (subtype of) UpwardsObjectClosure. The
5461 // use of that state in the embedded UpwardsObjectClosure instance
5462 // assumes that the cards are always iterated (even if in parallel
5463 // by several threads) in monotonically increasing order per each
5464 // thread. This is true of the implementation below which picks
5465 // card ranges (chunks) in monotonically increasing order globally
5466 // and, a-fortiori, in monotonically increasing order per thread
5467 // (the latter order being a subsequence of the former).
5468 // If the work code below is ever reorganized into a more chaotic
5469 // work-partitioning form than the current "sequential tasks"
5470 // paradigm, the use of that persistent state will have to be
5471 // revisited and modified appropriately. See also related
5472 // bug 4756801 work on which should examine this code to make
5473 // sure that the changes there do not run counter to the
5474 // assumptions made here and necessary for correctness and
5475 // efficiency. Note also that this code might yield inefficient
5476 // behavior in the case of very large objects that span one or
5477 // more work chunks. Such objects would potentially be scanned
5478 // several times redundantly. Work on 4756801 should try and
5479 // address that performance anomaly if at all possible. XXX
5480 MemRegion full_span = _collector->_span;
5481 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5482 MarkFromDirtyCardsClosure
5483 greyRescanClosure(_collector, full_span, // entire span of interest
5484 sp, bm, work_q, cl);
5485
5486 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5487 assert(pst->valid(), "Uninitialized use?");
5488 uint nth_task = 0;
5489 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5490 MemRegion span = sp->used_region();
5491 HeapWord* start_addr = span.start();
5492 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5493 alignment);
5494 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5495 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5496 start_addr, "Check alignment");
5497 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5498 chunk_size, "Check alignment");
5499
5500 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5501 // Having claimed the nth_task, compute corresponding mem-region,
5502 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
5503 // The alignment restriction ensures that we do not need any
5504 // synchronization with other gang-workers while setting or
5505 // clearing bits in thus chunk of the MUT.
5506 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5507 start_addr + (nth_task+1)*chunk_size);
5508 // The last chunk's end might be way beyond end of the
5509 // used region. In that case pull back appropriately.
5510 if (this_span.end() > end_addr) {
5511 this_span.set_end(end_addr);
5512 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5513 }
5514 // Iterate over the dirty cards covering this chunk, marking them
5515 // precleaned, and setting the corresponding bits in the mod union
5516 // table. Since we have been careful to partition at Card and MUT-word
5517 // boundaries no synchronization is needed between parallel threads.
5518 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5519 &modUnionClosure);
5520
5521 // Having transferred these marks into the modUnionTable,
5522 // rescan the marked objects on the dirty cards in the modUnionTable.
5523 // Even if this is at a synchronous collection, the initial marking
5524 // may have been done during an asynchronous collection so there
5525 // may be dirty bits in the mod-union table.
5526 _collector->_modUnionTable.dirty_range_iterate_clear(
5527 this_span, &greyRescanClosure);
5528 _collector->_modUnionTable.verifyNoOneBitsInRange(
5529 this_span.start(),
5530 this_span.end());
5531 }
5532 pst->all_tasks_completed(); // declare that i am done
5533 }
5534
5535 // . see if we can share work_queues with ParNew? XXX
5536 void
5537 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5538 int* seed) {
5539 OopTaskQueue* work_q = work_queue(i);
5540 NOT_PRODUCT(int num_steals = 0;)
5541 oop obj_to_scan;
5542 CMSBitMap* bm = &(_collector->_markBitMap);
5543
5544 while (true) {
5545 // Completely finish any left over work from (an) earlier round(s)
5546 cl->trim_queue(0);
5547 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5548 (size_t)ParGCDesiredObjsFromOverflowList);
5549 // Now check if there's any work in the overflow list
5550 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5551 // only affects the number of attempts made to get work from the
5552 // overflow list and does not affect the number of workers. Just
5553 // pass ParallelGCThreads so this behavior is unchanged.
5554 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5555 work_q,
5556 ParallelGCThreads)) {
5557 // found something in global overflow list;
5558 // not yet ready to go stealing work from others.
5559 // We'd like to assert(work_q->size() != 0, ...)
5560 // because we just took work from the overflow list,
5561 // but of course we can't since all of that could have
5562 // been already stolen from us.
5563 // "He giveth and He taketh away."
5564 continue;
5565 }
5566 // Verify that we have no work before we resort to stealing
5567 assert(work_q->size() == 0, "Have work, shouldn't steal");
5568 // Try to steal from other queues that have work
5569 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5570 NOT_PRODUCT(num_steals++;)
5571 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5572 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5573 // Do scanning work
5574 obj_to_scan->oop_iterate(cl);
5575 // Loop around, finish this work, and try to steal some more
5576 } else if (terminator()->offer_termination()) {
5577 break; // nirvana from the infinite cycle
5578 }
5579 }
5580 NOT_PRODUCT(
5581 if (PrintCMSStatistics != 0) {
5582 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5583 }
5584 )
5585 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5586 "Else our work is not yet done");
5587 }
5588
5589 // Record object boundaries in _eden_chunk_array by sampling the eden
5590 // top in the slow-path eden object allocation code path and record
5591 // the boundaries, if CMSEdenChunksRecordAlways is true. If
5592 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
5593 // sampling in sample_eden() that activates during the part of the
5594 // preclean phase.
5595 void CMSCollector::sample_eden_chunk() {
5596 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
5597 if (_eden_chunk_lock->try_lock()) {
5598 // Record a sample. This is the critical section. The contents
5599 // of the _eden_chunk_array have to be non-decreasing in the
5600 // address order.
5601 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
5602 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
5603 "Unexpected state of Eden");
5604 if (_eden_chunk_index == 0 ||
5605 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
5606 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
5607 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
5608 _eden_chunk_index++; // commit sample
5609 }
5610 _eden_chunk_lock->unlock();
5611 }
5612 }
5613 }
5614
5615 // Return a thread-local PLAB recording array, as appropriate.
5616 void* CMSCollector::get_data_recorder(int thr_num) {
5617 if (_survivor_plab_array != NULL &&
5618 (CMSPLABRecordAlways ||
5619 (_collectorState > Marking && _collectorState < FinalMarking))) {
5620 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5621 ChunkArray* ca = &_survivor_plab_array[thr_num];
5622 ca->reset(); // clear it so that fresh data is recorded
5623 return (void*) ca;
5624 } else {
5625 return NULL;
5626 }
5627 }
5628
5629 // Reset all the thread-local PLAB recording arrays
5630 void CMSCollector::reset_survivor_plab_arrays() {
5631 for (uint i = 0; i < ParallelGCThreads; i++) {
5632 _survivor_plab_array[i].reset();
5633 }
5634 }
5635
5636 // Merge the per-thread plab arrays into the global survivor chunk
5637 // array which will provide the partitioning of the survivor space
5638 // for CMS initial scan and rescan.
5639 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5640 int no_of_gc_threads) {
5641 assert(_survivor_plab_array != NULL, "Error");
5642 assert(_survivor_chunk_array != NULL, "Error");
5643 assert(_collectorState == FinalMarking ||
5644 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
5645 for (int j = 0; j < no_of_gc_threads; j++) {
5646 _cursor[j] = 0;
5647 }
5648 HeapWord* top = surv->top();
5649 size_t i;
5650 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5651 HeapWord* min_val = top; // Higher than any PLAB address
5652 uint min_tid = 0; // position of min_val this round
5653 for (int j = 0; j < no_of_gc_threads; j++) {
5654 ChunkArray* cur_sca = &_survivor_plab_array[j];
5655 if (_cursor[j] == cur_sca->end()) {
5656 continue;
5657 }
5658 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5659 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5660 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5661 if (cur_val < min_val) {
5662 min_tid = j;
5663 min_val = cur_val;
5664 } else {
5665 assert(cur_val < top, "All recorded addresses should be less");
5666 }
5667 }
5668 // At this point min_val and min_tid are respectively
5669 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5670 // and the thread (j) that witnesses that address.
5671 // We record this address in the _survivor_chunk_array[i]
5672 // and increment _cursor[min_tid] prior to the next round i.
5673 if (min_val == top) {
5674 break;
5675 }
5676 _survivor_chunk_array[i] = min_val;
5677 _cursor[min_tid]++;
5678 }
5679 // We are all done; record the size of the _survivor_chunk_array
5680 _survivor_chunk_index = i; // exclusive: [0, i)
5681 if (PrintCMSStatistics > 0) {
5682 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5683 }
5684 // Verify that we used up all the recorded entries
5685 #ifdef ASSERT
5686 size_t total = 0;
5687 for (int j = 0; j < no_of_gc_threads; j++) {
5688 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5689 total += _cursor[j];
5690 }
5691 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5692 // Check that the merged array is in sorted order
5693 if (total > 0) {
5694 for (size_t i = 0; i < total - 1; i++) {
5695 if (PrintCMSStatistics > 0) {
5696 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5697 i, _survivor_chunk_array[i]);
5698 }
5699 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5700 "Not sorted");
5701 }
5702 }
5703 #endif // ASSERT
5704 }
5705
5706 // Set up the space's par_seq_tasks structure for work claiming
5707 // for parallel initial scan and rescan of young gen.
5708 // See ParRescanTask where this is currently used.
5709 void
5710 CMSCollector::
5711 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5712 assert(n_threads > 0, "Unexpected n_threads argument");
5713 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5714
5715 // Eden space
5716 if (!dng->eden()->is_empty()) {
5717 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5718 assert(!pst->valid(), "Clobbering existing data?");
5719 // Each valid entry in [0, _eden_chunk_index) represents a task.
5720 size_t n_tasks = _eden_chunk_index + 1;
5721 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5722 // Sets the condition for completion of the subtask (how many threads
5723 // need to finish in order to be done).
5724 pst->set_n_threads(n_threads);
5725 pst->set_n_tasks((int)n_tasks);
5726 }
5727
5728 // Merge the survivor plab arrays into _survivor_chunk_array
5729 if (_survivor_plab_array != NULL) {
5730 merge_survivor_plab_arrays(dng->from(), n_threads);
5731 } else {
5732 assert(_survivor_chunk_index == 0, "Error");
5733 }
5734
5735 // To space
5736 {
5737 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5738 assert(!pst->valid(), "Clobbering existing data?");
5739 // Sets the condition for completion of the subtask (how many threads
5740 // need to finish in order to be done).
5741 pst->set_n_threads(n_threads);
5742 pst->set_n_tasks(1);
5743 assert(pst->valid(), "Error");
5744 }
5745
5746 // From space
5747 {
5748 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5749 assert(!pst->valid(), "Clobbering existing data?");
5750 size_t n_tasks = _survivor_chunk_index + 1;
5751 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5752 // Sets the condition for completion of the subtask (how many threads
5753 // need to finish in order to be done).
5754 pst->set_n_threads(n_threads);
5755 pst->set_n_tasks((int)n_tasks);
5756 assert(pst->valid(), "Error");
5757 }
5758 }
5759
5760 // Parallel version of remark
5761 void CMSCollector::do_remark_parallel() {
5762 GenCollectedHeap* gch = GenCollectedHeap::heap();
5763 FlexibleWorkGang* workers = gch->workers();
5764 assert(workers != NULL, "Need parallel worker threads.");
5765 // Choose to use the number of GC workers most recently set
5766 // into "active_workers". If active_workers is not set, set it
5767 // to ParallelGCThreads.
5768 int n_workers = workers->active_workers();
5769 if (n_workers == 0) {
5770 assert(n_workers > 0, "Should have been set during scavenge");
5771 n_workers = ParallelGCThreads;
5772 workers->set_active_workers(n_workers);
5773 }
5774 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5775
5776 CMSParRemarkTask tsk(this,
5777 cms_space,
5778 n_workers, workers, task_queues());
5779
5780 // Set up for parallel process_roots work.
5781 gch->set_par_threads(n_workers);
5782 // We won't be iterating over the cards in the card table updating
5783 // the younger_gen cards, so we shouldn't call the following else
5784 // the verification code as well as subsequent younger_refs_iterate
5785 // code would get confused. XXX
5786 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5787
5788 // The young gen rescan work will not be done as part of
5789 // process_roots (which currently doesn't know how to
5790 // parallelize such a scan), but rather will be broken up into
5791 // a set of parallel tasks (via the sampling that the [abortable]
5792 // preclean phase did of EdenSpace, plus the [two] tasks of
5793 // scanning the [two] survivor spaces. Further fine-grain
5794 // parallelization of the scanning of the survivor spaces
5795 // themselves, and of precleaning of the younger gen itself
5796 // is deferred to the future.
5797 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5798
5799 // The dirty card rescan work is broken up into a "sequence"
5800 // of parallel tasks (per constituent space) that are dynamically
5801 // claimed by the parallel threads.
5802 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5803
5804 // It turns out that even when we're using 1 thread, doing the work in a
5805 // separate thread causes wide variance in run times. We can't help this
5806 // in the multi-threaded case, but we special-case n=1 here to get
5807 // repeatable measurements of the 1-thread overhead of the parallel code.
5808 if (n_workers > 1) {
5809 // Make refs discovery MT-safe, if it isn't already: it may not
5810 // necessarily be so, since it's possible that we are doing
5811 // ST marking.
5812 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5813 GenCollectedHeap::StrongRootsScope srs(gch);
5814 workers->run_task(&tsk);
5815 } else {
5816 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5817 GenCollectedHeap::StrongRootsScope srs(gch);
5818 tsk.work(0);
5819 }
5820
5821 gch->set_par_threads(0); // 0 ==> non-parallel.
5822 // restore, single-threaded for now, any preserved marks
5823 // as a result of work_q overflow
5824 restore_preserved_marks_if_any();
5825 }
5826
5827 // Non-parallel version of remark
5828 void CMSCollector::do_remark_non_parallel() {
5829 ResourceMark rm;
5830 HandleMark hm;
5831 GenCollectedHeap* gch = GenCollectedHeap::heap();
5832 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5833
5834 MarkRefsIntoAndScanClosure
5835 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5836 &_markStack, this,
5837 false /* should_yield */, false /* not precleaning */);
5838 MarkFromDirtyCardsClosure
5839 markFromDirtyCardsClosure(this, _span,
5840 NULL, // space is set further below
5841 &_markBitMap, &_markStack, &mrias_cl);
5842 {
5843 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5844 // Iterate over the dirty cards, setting the corresponding bits in the
5845 // mod union table.
5846 {
5847 ModUnionClosure modUnionClosure(&_modUnionTable);
5848 _ct->ct_bs()->dirty_card_iterate(
5849 _cmsGen->used_region(),
5850 &modUnionClosure);
5851 }
5852 // Having transferred these marks into the modUnionTable, we just need
5853 // to rescan the marked objects on the dirty cards in the modUnionTable.
5854 // The initial marking may have been done during an asynchronous
5855 // collection so there may be dirty bits in the mod-union table.
5856 const int alignment =
5857 CardTableModRefBS::card_size * BitsPerWord;
5858 {
5859 // ... First handle dirty cards in CMS gen
5860 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5861 MemRegion ur = _cmsGen->used_region();
5862 HeapWord* lb = ur.start();
5863 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5864 MemRegion cms_span(lb, ub);
5865 _modUnionTable.dirty_range_iterate_clear(cms_span,
5866 &markFromDirtyCardsClosure);
5867 verify_work_stacks_empty();
5868 if (PrintCMSStatistics != 0) {
5869 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5870 markFromDirtyCardsClosure.num_dirty_cards());
5871 }
5872 }
5873 }
5874 if (VerifyDuringGC &&
5875 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5876 HandleMark hm; // Discard invalid handles created during verification
5877 Universe::verify();
5878 }
5879 {
5880 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5881
5882 verify_work_stacks_empty();
5883
5884 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5885 GenCollectedHeap::StrongRootsScope srs(gch);
5886
5887 gch->gen_process_roots(_cmsGen->level(),
5888 true, // younger gens as roots
5889 false, // use the local StrongRootsScope
5890 SharedHeap::ScanningOption(roots_scanning_options()),
5891 should_unload_classes(),
5892 &mrias_cl,
5893 NULL,
5894 NULL); // The dirty klasses will be handled below
5895
5896 assert(should_unload_classes()
5897 || (roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5898 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5899 }
5900
5901 {
5902 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5903
5904 verify_work_stacks_empty();
5905
5906 // Scan all class loader data objects that might have been introduced
5907 // during concurrent marking.
5908 ResourceMark rm;
5909 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5910 for (int i = 0; i < array->length(); i++) {
5911 mrias_cl.do_class_loader_data(array->at(i));
5912 }
5913
5914 // We don't need to keep track of new CLDs anymore.
5915 ClassLoaderDataGraph::remember_new_clds(false);
5916
5917 verify_work_stacks_empty();
5918 }
5919
5920 {
5921 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5922
5923 verify_work_stacks_empty();
5924
5925 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5926 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5927
5928 verify_work_stacks_empty();
5929 }
5930
5931 // We might have added oops to ClassLoaderData::_handles during the
5932 // concurrent marking phase. These oops point to newly allocated objects
5933 // that are guaranteed to be kept alive. Either by the direct allocation
5934 // code, or when the young collector processes the roots. Hence,
5935 // we don't have to revisit the _handles block during the remark phase.
5936
5937 verify_work_stacks_empty();
5938 // Restore evacuated mark words, if any, used for overflow list links
5939 if (!CMSOverflowEarlyRestoration) {
5940 restore_preserved_marks_if_any();
5941 }
5942 verify_overflow_empty();
5943 }
5944
5945 ////////////////////////////////////////////////////////
5946 // Parallel Reference Processing Task Proxy Class
5947 ////////////////////////////////////////////////////////
5948 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5949 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5950 CMSCollector* _collector;
5951 CMSBitMap* _mark_bit_map;
5952 const MemRegion _span;
5953 ProcessTask& _task;
5954
5955 public:
5956 CMSRefProcTaskProxy(ProcessTask& task,
5957 CMSCollector* collector,
5958 const MemRegion& span,
5959 CMSBitMap* mark_bit_map,
5960 AbstractWorkGang* workers,
5961 OopTaskQueueSet* task_queues):
5962 // XXX Should superclass AGTWOQ also know about AWG since it knows
5963 // about the task_queues used by the AWG? Then it could initialize
5964 // the terminator() object. See 6984287. The set_for_termination()
5965 // below is a temporary band-aid for the regression in 6984287.
5966 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5967 task_queues),
5968 _task(task),
5969 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5970 {
5971 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5972 "Inconsistency in _span");
5973 set_for_termination(workers->active_workers());
5974 }
5975
5976 OopTaskQueueSet* task_queues() { return queues(); }
5977
5978 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5979
5980 void do_work_steal(int i,
5981 CMSParDrainMarkingStackClosure* drain,
5982 CMSParKeepAliveClosure* keep_alive,
5983 int* seed);
5984
5985 virtual void work(uint worker_id);
5986 };
5987
5988 void CMSRefProcTaskProxy::work(uint worker_id) {
5989 ResourceMark rm;
5990 HandleMark hm;
5991 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5992 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5993 _mark_bit_map,
5994 work_queue(worker_id));
5995 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5996 _mark_bit_map,
5997 work_queue(worker_id));
5998 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5999 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
6000 if (_task.marks_oops_alive()) {
6001 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
6002 _collector->hash_seed(worker_id));
6003 }
6004 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
6005 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
6006 }
6007
6008 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
6009 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
6010 EnqueueTask& _task;
6011
6012 public:
6013 CMSRefEnqueueTaskProxy(EnqueueTask& task)
6014 : AbstractGangTask("Enqueue reference objects in parallel"),
6015 _task(task)
6016 { }
6017
6018 virtual void work(uint worker_id)
6019 {
6020 _task.work(worker_id);
6021 }
6022 };
6023
6024 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
6025 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
6026 _span(span),
6027 _bit_map(bit_map),
6028 _work_queue(work_queue),
6029 _mark_and_push(collector, span, bit_map, work_queue),
6030 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6031 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
6032 { }
6033
6034 // . see if we can share work_queues with ParNew? XXX
6035 void CMSRefProcTaskProxy::do_work_steal(int i,
6036 CMSParDrainMarkingStackClosure* drain,
6037 CMSParKeepAliveClosure* keep_alive,
6038 int* seed) {
6039 OopTaskQueue* work_q = work_queue(i);
6040 NOT_PRODUCT(int num_steals = 0;)
6041 oop obj_to_scan;
6042
6043 while (true) {
6044 // Completely finish any left over work from (an) earlier round(s)
6045 drain->trim_queue(0);
6046 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
6047 (size_t)ParGCDesiredObjsFromOverflowList);
6048 // Now check if there's any work in the overflow list
6049 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
6050 // only affects the number of attempts made to get work from the
6051 // overflow list and does not affect the number of workers. Just
6052 // pass ParallelGCThreads so this behavior is unchanged.
6053 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
6054 work_q,
6055 ParallelGCThreads)) {
6056 // Found something in global overflow list;
6057 // not yet ready to go stealing work from others.
6058 // We'd like to assert(work_q->size() != 0, ...)
6059 // because we just took work from the overflow list,
6060 // but of course we can't, since all of that might have
6061 // been already stolen from us.
6062 continue;
6063 }
6064 // Verify that we have no work before we resort to stealing
6065 assert(work_q->size() == 0, "Have work, shouldn't steal");
6066 // Try to steal from other queues that have work
6067 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
6068 NOT_PRODUCT(num_steals++;)
6069 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
6070 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
6071 // Do scanning work
6072 obj_to_scan->oop_iterate(keep_alive);
6073 // Loop around, finish this work, and try to steal some more
6074 } else if (terminator()->offer_termination()) {
6075 break; // nirvana from the infinite cycle
6076 }
6077 }
6078 NOT_PRODUCT(
6079 if (PrintCMSStatistics != 0) {
6080 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
6081 }
6082 )
6083 }
6084
6085 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
6086 {
6087 GenCollectedHeap* gch = GenCollectedHeap::heap();
6088 FlexibleWorkGang* workers = gch->workers();
6089 assert(workers != NULL, "Need parallel worker threads.");
6090 CMSRefProcTaskProxy rp_task(task, &_collector,
6091 _collector.ref_processor()->span(),
6092 _collector.markBitMap(),
6093 workers, _collector.task_queues());
6094 workers->run_task(&rp_task);
6095 }
6096
6097 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
6098 {
6099
6100 GenCollectedHeap* gch = GenCollectedHeap::heap();
6101 FlexibleWorkGang* workers = gch->workers();
6102 assert(workers != NULL, "Need parallel worker threads.");
6103 CMSRefEnqueueTaskProxy enq_task(task);
6104 workers->run_task(&enq_task);
6105 }
6106
6107 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
6108
6109 ResourceMark rm;
6110 HandleMark hm;
6111
6112 ReferenceProcessor* rp = ref_processor();
6113 assert(rp->span().equals(_span), "Spans should be equal");
6114 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
6115 // Process weak references.
6116 rp->setup_policy(clear_all_soft_refs);
6117 verify_work_stacks_empty();
6118
6119 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
6120 &_markStack, false /* !preclean */);
6121 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
6122 _span, &_markBitMap, &_markStack,
6123 &cmsKeepAliveClosure, false /* !preclean */);
6124 {
6125 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6126
6127 ReferenceProcessorStats stats;
6128 if (rp->processing_is_mt()) {
6129 // Set the degree of MT here. If the discovery is done MT, there
6130 // may have been a different number of threads doing the discovery
6131 // and a different number of discovered lists may have Ref objects.
6132 // That is OK as long as the Reference lists are balanced (see
6133 // balance_all_queues() and balance_queues()).
6134 GenCollectedHeap* gch = GenCollectedHeap::heap();
6135 int active_workers = ParallelGCThreads;
6136 FlexibleWorkGang* workers = gch->workers();
6137 if (workers != NULL) {
6138 active_workers = workers->active_workers();
6139 // The expectation is that active_workers will have already
6140 // been set to a reasonable value. If it has not been set,
6141 // investigate.
6142 assert(active_workers > 0, "Should have been set during scavenge");
6143 }
6144 rp->set_active_mt_degree(active_workers);
6145 CMSRefProcTaskExecutor task_executor(*this);
6146 stats = rp->process_discovered_references(&_is_alive_closure,
6147 &cmsKeepAliveClosure,
6148 &cmsDrainMarkingStackClosure,
6149 &task_executor,
6150 _gc_timer_cm,
6151 _gc_tracer_cm->gc_id());
6152 } else {
6153 stats = rp->process_discovered_references(&_is_alive_closure,
6154 &cmsKeepAliveClosure,
6155 &cmsDrainMarkingStackClosure,
6156 NULL,
6157 _gc_timer_cm,
6158 _gc_tracer_cm->gc_id());
6159 }
6160 _gc_tracer_cm->report_gc_reference_stats(stats);
6161
6162 }
6163
6164 // This is the point where the entire marking should have completed.
6165 verify_work_stacks_empty();
6166
6167 if (should_unload_classes()) {
6168 {
6169 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6170
6171 // Unload classes and purge the SystemDictionary.
6172 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
6173
6174 // Unload nmethods.
6175 CodeCache::do_unloading(&_is_alive_closure, purged_class);
6176
6177 // Prune dead klasses from subklass/sibling/implementor lists.
6178 Klass::clean_weak_klass_links(&_is_alive_closure);
6179 }
6180
6181 {
6182 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6183 // Clean up unreferenced symbols in symbol table.
6184 SymbolTable::unlink();
6185 }
6186
6187 {
6188 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6189 // Delete entries for dead interned strings.
6190 StringTable::unlink(&_is_alive_closure);
6191 }
6192 }
6193
6194
6195 // Restore any preserved marks as a result of mark stack or
6196 // work queue overflow
6197 restore_preserved_marks_if_any(); // done single-threaded for now
6198
6199 rp->set_enqueuing_is_done(true);
6200 if (rp->processing_is_mt()) {
6201 rp->balance_all_queues();
6202 CMSRefProcTaskExecutor task_executor(*this);
6203 rp->enqueue_discovered_references(&task_executor);
6204 } else {
6205 rp->enqueue_discovered_references(NULL);
6206 }
6207 rp->verify_no_references_recorded();
6208 assert(!rp->discovery_enabled(), "should have been disabled");
6209 }
6210
6211 #ifndef PRODUCT
6212 void CMSCollector::check_correct_thread_executing() {
6213 Thread* t = Thread::current();
6214 // Only the VM thread or the CMS thread should be here.
6215 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6216 "Unexpected thread type");
6217 // If this is the vm thread, the foreground process
6218 // should not be waiting. Note that _foregroundGCIsActive is
6219 // true while the foreground collector is waiting.
6220 if (_foregroundGCShouldWait) {
6221 // We cannot be the VM thread
6222 assert(t->is_ConcurrentGC_thread(),
6223 "Should be CMS thread");
6224 } else {
6225 // We can be the CMS thread only if we are in a stop-world
6226 // phase of CMS collection.
6227 if (t->is_ConcurrentGC_thread()) {
6228 assert(_collectorState == InitialMarking ||
6229 _collectorState == FinalMarking,
6230 "Should be a stop-world phase");
6231 // The CMS thread should be holding the CMS_token.
6232 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6233 "Potential interference with concurrently "
6234 "executing VM thread");
6235 }
6236 }
6237 }
6238 #endif
6239
6240 void CMSCollector::sweep(bool asynch) {
6241 assert(_collectorState == Sweeping, "just checking");
6242 check_correct_thread_executing();
6243 verify_work_stacks_empty();
6244 verify_overflow_empty();
6245 increment_sweep_count();
6246 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6247
6248 _inter_sweep_timer.stop();
6249 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6250
6251 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6252 _intra_sweep_timer.reset();
6253 _intra_sweep_timer.start();
6254 if (asynch) {
6255 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6256 CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
6257 // First sweep the old gen
6258 {
6259 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6260 bitMapLock());
6261 sweepWork(_cmsGen, asynch);
6262 }
6263
6264 // Update Universe::_heap_*_at_gc figures.
6265 // We need all the free list locks to make the abstract state
6266 // transition from Sweeping to Resetting. See detailed note
6267 // further below.
6268 {
6269 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6270 // Update heap occupancy information which is used as
6271 // input to soft ref clearing policy at the next gc.
6272 Universe::update_heap_info_at_gc();
6273 _collectorState = Resizing;
6274 }
6275 } else {
6276 // already have needed locks
6277 sweepWork(_cmsGen, asynch);
6278 // Update heap occupancy information which is used as
6279 // input to soft ref clearing policy at the next gc.
6280 Universe::update_heap_info_at_gc();
6281 _collectorState = Resizing;
6282 }
6283 verify_work_stacks_empty();
6284 verify_overflow_empty();
6285
6286 if (should_unload_classes()) {
6287 // Delay purge to the beginning of the next safepoint. Metaspace::contains
6288 // requires that the virtual spaces are stable and not deleted.
6289 ClassLoaderDataGraph::set_should_purge(true);
6290 }
6291
6292 _intra_sweep_timer.stop();
6293 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6294
6295 _inter_sweep_timer.reset();
6296 _inter_sweep_timer.start();
6297
6298 // We need to use a monotonically non-decreasing time in ms
6299 // or we will see time-warp warnings and os::javaTimeMillis()
6300 // does not guarantee monotonicity.
6301 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6302 update_time_of_last_gc(now);
6303
6304 // NOTE on abstract state transitions:
6305 // Mutators allocate-live and/or mark the mod-union table dirty
6306 // based on the state of the collection. The former is done in
6307 // the interval [Marking, Sweeping] and the latter in the interval
6308 // [Marking, Sweeping). Thus the transitions into the Marking state
6309 // and out of the Sweeping state must be synchronously visible
6310 // globally to the mutators.
6311 // The transition into the Marking state happens with the world
6312 // stopped so the mutators will globally see it. Sweeping is
6313 // done asynchronously by the background collector so the transition
6314 // from the Sweeping state to the Resizing state must be done
6315 // under the freelistLock (as is the check for whether to
6316 // allocate-live and whether to dirty the mod-union table).
6317 assert(_collectorState == Resizing, "Change of collector state to"
6318 " Resizing must be done under the freelistLocks (plural)");
6319
6320 // Now that sweeping has been completed, we clear
6321 // the incremental_collection_failed flag,
6322 // thus inviting a younger gen collection to promote into
6323 // this generation. If such a promotion may still fail,
6324 // the flag will be set again when a young collection is
6325 // attempted.
6326 GenCollectedHeap* gch = GenCollectedHeap::heap();
6327 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6328 gch->update_full_collections_completed(_collection_count_start);
6329 }
6330
6331 // FIX ME!!! Looks like this belongs in CFLSpace, with
6332 // CMSGen merely delegating to it.
6333 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6334 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6335 HeapWord* minAddr = _cmsSpace->bottom();
6336 HeapWord* largestAddr =
6337 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6338 if (largestAddr == NULL) {
6339 // The dictionary appears to be empty. In this case
6340 // try to coalesce at the end of the heap.
6341 largestAddr = _cmsSpace->end();
6342 }
6343 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6344 size_t nearLargestOffset =
6345 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6346 if (PrintFLSStatistics != 0) {
6347 gclog_or_tty->print_cr(
6348 "CMS: Large Block: " PTR_FORMAT ";"
6349 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6350 largestAddr,
6351 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6352 }
6353 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6354 }
6355
6356 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6357 return addr >= _cmsSpace->nearLargestChunk();
6358 }
6359
6360 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6361 return _cmsSpace->find_chunk_at_end();
6362 }
6363
6364 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6365 bool full) {
6366 // The next lower level has been collected. Gather any statistics
6367 // that are of interest at this point.
6368 if (!full && (current_level + 1) == level()) {
6369 // Gather statistics on the young generation collection.
6370 collector()->stats().record_gc0_end(used());
6371 }
6372 }
6373
6374 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6375 if (PrintGCDetails && Verbose) {
6376 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6377 }
6378 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6379 _debug_collection_type =
6380 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6381 if (PrintGCDetails && Verbose) {
6382 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6383 }
6384 }
6385
6386 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6387 bool asynch) {
6388 // We iterate over the space(s) underlying this generation,
6389 // checking the mark bit map to see if the bits corresponding
6390 // to specific blocks are marked or not. Blocks that are
6391 // marked are live and are not swept up. All remaining blocks
6392 // are swept up, with coalescing on-the-fly as we sweep up
6393 // contiguous free and/or garbage blocks:
6394 // We need to ensure that the sweeper synchronizes with allocators
6395 // and stop-the-world collectors. In particular, the following
6396 // locks are used:
6397 // . CMS token: if this is held, a stop the world collection cannot occur
6398 // . freelistLock: if this is held no allocation can occur from this
6399 // generation by another thread
6400 // . bitMapLock: if this is held, no other thread can access or update
6401 //
6402
6403 // Note that we need to hold the freelistLock if we use
6404 // block iterate below; else the iterator might go awry if
6405 // a mutator (or promotion) causes block contents to change
6406 // (for instance if the allocator divvies up a block).
6407 // If we hold the free list lock, for all practical purposes
6408 // young generation GC's can't occur (they'll usually need to
6409 // promote), so we might as well prevent all young generation
6410 // GC's while we do a sweeping step. For the same reason, we might
6411 // as well take the bit map lock for the entire duration
6412
6413 // check that we hold the requisite locks
6414 assert(have_cms_token(), "Should hold cms token");
6415 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6416 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6417 "Should possess CMS token to sweep");
6418 assert_lock_strong(gen->freelistLock());
6419 assert_lock_strong(bitMapLock());
6420
6421 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6422 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6423 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6424 _inter_sweep_estimate.padded_average(),
6425 _intra_sweep_estimate.padded_average());
6426 gen->setNearLargestChunk();
6427
6428 {
6429 SweepClosure sweepClosure(this, gen, &_markBitMap,
6430 CMSYield && asynch);
6431 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6432 // We need to free-up/coalesce garbage/blocks from a
6433 // co-terminal free run. This is done in the SweepClosure
6434 // destructor; so, do not remove this scope, else the
6435 // end-of-sweep-census below will be off by a little bit.
6436 }
6437 gen->cmsSpace()->sweep_completed();
6438 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6439 if (should_unload_classes()) { // unloaded classes this cycle,
6440 _concurrent_cycles_since_last_unload = 0; // ... reset count
6441 } else { // did not unload classes,
6442 _concurrent_cycles_since_last_unload++; // ... increment count
6443 }
6444 }
6445
6446 // Reset CMS data structures (for now just the marking bit map)
6447 // preparatory for the next cycle.
6448 void CMSCollector::reset(bool asynch) {
6449 if (asynch) {
6450 CMSTokenSyncWithLocks ts(true, bitMapLock());
6451
6452 // If the state is not "Resetting", the foreground thread
6453 // has done a collection and the resetting.
6454 if (_collectorState != Resetting) {
6455 assert(_collectorState == Idling, "The state should only change"
6456 " because the foreground collector has finished the collection");
6457 return;
6458 }
6459
6460 // Clear the mark bitmap (no grey objects to start with)
6461 // for the next cycle.
6462 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6463 CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
6464
6465 HeapWord* curAddr = _markBitMap.startWord();
6466 while (curAddr < _markBitMap.endWord()) {
6467 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6468 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6469 _markBitMap.clear_large_range(chunk);
6470 if (ConcurrentMarkSweepThread::should_yield() &&
6471 !foregroundGCIsActive() &&
6472 CMSYield) {
6473 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6474 "CMS thread should hold CMS token");
6475 assert_lock_strong(bitMapLock());
6476 bitMapLock()->unlock();
6477 ConcurrentMarkSweepThread::desynchronize(true);
6478 ConcurrentMarkSweepThread::acknowledge_yield_request();
6479 stopTimer();
6480 if (PrintCMSStatistics != 0) {
6481 incrementYields();
6482 }
6483 icms_wait();
6484
6485 // See the comment in coordinator_yield()
6486 for (unsigned i = 0; i < CMSYieldSleepCount &&
6487 ConcurrentMarkSweepThread::should_yield() &&
6488 !CMSCollector::foregroundGCIsActive(); ++i) {
6489 os::sleep(Thread::current(), 1, false);
6490 ConcurrentMarkSweepThread::acknowledge_yield_request();
6491 }
6492
6493 ConcurrentMarkSweepThread::synchronize(true);
6494 bitMapLock()->lock_without_safepoint_check();
6495 startTimer();
6496 }
6497 curAddr = chunk.end();
6498 }
6499 // A successful mostly concurrent collection has been done.
6500 // Because only the full (i.e., concurrent mode failure) collections
6501 // are being measured for gc overhead limits, clean the "near" flag
6502 // and count.
6503 size_policy()->reset_gc_overhead_limit_count();
6504 _collectorState = Idling;
6505 } else {
6506 // already have the lock
6507 assert(_collectorState == Resetting, "just checking");
6508 assert_lock_strong(bitMapLock());
6509 _markBitMap.clear_all();
6510 _collectorState = Idling;
6511 }
6512
6513 // Stop incremental mode after a cycle completes, so that any future cycles
6514 // are triggered by allocation.
6515 stop_icms();
6516
6517 NOT_PRODUCT(
6518 if (RotateCMSCollectionTypes) {
6519 _cmsGen->rotate_debug_collection_type();
6520 }
6521 )
6522
6523 register_gc_end();
6524 }
6525
6526 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6527 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6528 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6529 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
6530 TraceCollectorStats tcs(counters());
6531
6532 switch (op) {
6533 case CMS_op_checkpointRootsInitial: {
6534 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6535 checkpointRootsInitial(true); // asynch
6536 if (PrintGC) {
6537 _cmsGen->printOccupancy("initial-mark");
6538 }
6539 break;
6540 }
6541 case CMS_op_checkpointRootsFinal: {
6542 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6543 checkpointRootsFinal(true, // asynch
6544 false, // !clear_all_soft_refs
6545 false); // !init_mark_was_synchronous
6546 if (PrintGC) {
6547 _cmsGen->printOccupancy("remark");
6548 }
6549 break;
6550 }
6551 default:
6552 fatal("No such CMS_op");
6553 }
6554 }
6555
6556 #ifndef PRODUCT
6557 size_t const CMSCollector::skip_header_HeapWords() {
6558 return FreeChunk::header_size();
6559 }
6560
6561 // Try and collect here conditions that should hold when
6562 // CMS thread is exiting. The idea is that the foreground GC
6563 // thread should not be blocked if it wants to terminate
6564 // the CMS thread and yet continue to run the VM for a while
6565 // after that.
6566 void CMSCollector::verify_ok_to_terminate() const {
6567 assert(Thread::current()->is_ConcurrentGC_thread(),
6568 "should be called by CMS thread");
6569 assert(!_foregroundGCShouldWait, "should be false");
6570 // We could check here that all the various low-level locks
6571 // are not held by the CMS thread, but that is overkill; see
6572 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6573 // is checked.
6574 }
6575 #endif
6576
6577 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6578 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6579 "missing Printezis mark?");
6580 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6581 size_t size = pointer_delta(nextOneAddr + 1, addr);
6582 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6583 "alignment problem");
6584 assert(size >= 3, "Necessary for Printezis marks to work");
6585 return size;
6586 }
6587
6588 // A variant of the above (block_size_using_printezis_bits()) except
6589 // that we return 0 if the P-bits are not yet set.
6590 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6591 if (_markBitMap.isMarked(addr + 1)) {
6592 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6593 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6594 size_t size = pointer_delta(nextOneAddr + 1, addr);
6595 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6596 "alignment problem");
6597 assert(size >= 3, "Necessary for Printezis marks to work");
6598 return size;
6599 }
6600 return 0;
6601 }
6602
6603 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6604 size_t sz = 0;
6605 oop p = (oop)addr;
6606 if (p->klass_or_null() != NULL) {
6607 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6608 } else {
6609 sz = block_size_using_printezis_bits(addr);
6610 }
6611 assert(sz > 0, "size must be nonzero");
6612 HeapWord* next_block = addr + sz;
6613 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6614 CardTableModRefBS::card_size);
6615 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6616 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6617 "must be different cards");
6618 return next_card;
6619 }
6620
6621
6622 // CMS Bit Map Wrapper /////////////////////////////////////////
6623
6624 // Construct a CMS bit map infrastructure, but don't create the
6625 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6626 // further below.
6627 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6628 _bm(),
6629 _shifter(shifter),
6630 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6631 {
6632 _bmStartWord = 0;
6633 _bmWordSize = 0;
6634 }
6635
6636 bool CMSBitMap::allocate(MemRegion mr) {
6637 _bmStartWord = mr.start();
6638 _bmWordSize = mr.word_size();
6639 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6640 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6641 if (!brs.is_reserved()) {
6642 warning("CMS bit map allocation failure");
6643 return false;
6644 }
6645 // For now we'll just commit all of the bit map up front.
6646 // Later on we'll try to be more parsimonious with swap.
6647 if (!_virtual_space.initialize(brs, brs.size())) {
6648 warning("CMS bit map backing store failure");
6649 return false;
6650 }
6651 assert(_virtual_space.committed_size() == brs.size(),
6652 "didn't reserve backing store for all of CMS bit map?");
6653 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6654 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6655 _bmWordSize, "inconsistency in bit map sizing");
6656 _bm.set_size(_bmWordSize >> _shifter);
6657
6658 // bm.clear(); // can we rely on getting zero'd memory? verify below
6659 assert(isAllClear(),
6660 "Expected zero'd memory from ReservedSpace constructor");
6661 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6662 "consistency check");
6663 return true;
6664 }
6665
6666 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6667 HeapWord *next_addr, *end_addr, *last_addr;
6668 assert_locked();
6669 assert(covers(mr), "out-of-range error");
6670 // XXX assert that start and end are appropriately aligned
6671 for (next_addr = mr.start(), end_addr = mr.end();
6672 next_addr < end_addr; next_addr = last_addr) {
6673 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6674 last_addr = dirty_region.end();
6675 if (!dirty_region.is_empty()) {
6676 cl->do_MemRegion(dirty_region);
6677 } else {
6678 assert(last_addr == end_addr, "program logic");
6679 return;
6680 }
6681 }
6682 }
6683
6684 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6685 _bm.print_on_error(st, prefix);
6686 }
6687
6688 #ifndef PRODUCT
6689 void CMSBitMap::assert_locked() const {
6690 CMSLockVerifier::assert_locked(lock());
6691 }
6692
6693 bool CMSBitMap::covers(MemRegion mr) const {
6694 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6695 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6696 "size inconsistency");
6697 return (mr.start() >= _bmStartWord) &&
6698 (mr.end() <= endWord());
6699 }
6700
6701 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6702 return (start >= _bmStartWord && (start + size) <= endWord());
6703 }
6704
6705 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6706 // verify that there are no 1 bits in the interval [left, right)
6707 FalseBitMapClosure falseBitMapClosure;
6708 iterate(&falseBitMapClosure, left, right);
6709 }
6710
6711 void CMSBitMap::region_invariant(MemRegion mr)
6712 {
6713 assert_locked();
6714 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6715 assert(!mr.is_empty(), "unexpected empty region");
6716 assert(covers(mr), "mr should be covered by bit map");
6717 // convert address range into offset range
6718 size_t start_ofs = heapWordToOffset(mr.start());
6719 // Make sure that end() is appropriately aligned
6720 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6721 (1 << (_shifter+LogHeapWordSize))),
6722 "Misaligned mr.end()");
6723 size_t end_ofs = heapWordToOffset(mr.end());
6724 assert(end_ofs > start_ofs, "Should mark at least one bit");
6725 }
6726
6727 #endif
6728
6729 bool CMSMarkStack::allocate(size_t size) {
6730 // allocate a stack of the requisite depth
6731 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6732 size * sizeof(oop)));
6733 if (!rs.is_reserved()) {
6734 warning("CMSMarkStack allocation failure");
6735 return false;
6736 }
6737 if (!_virtual_space.initialize(rs, rs.size())) {
6738 warning("CMSMarkStack backing store failure");
6739 return false;
6740 }
6741 assert(_virtual_space.committed_size() == rs.size(),
6742 "didn't reserve backing store for all of CMS stack?");
6743 _base = (oop*)(_virtual_space.low());
6744 _index = 0;
6745 _capacity = size;
6746 NOT_PRODUCT(_max_depth = 0);
6747 return true;
6748 }
6749
6750 // XXX FIX ME !!! In the MT case we come in here holding a
6751 // leaf lock. For printing we need to take a further lock
6752 // which has lower rank. We need to recalibrate the two
6753 // lock-ranks involved in order to be able to print the
6754 // messages below. (Or defer the printing to the caller.
6755 // For now we take the expedient path of just disabling the
6756 // messages for the problematic case.)
6757 void CMSMarkStack::expand() {
6758 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6759 if (_capacity == MarkStackSizeMax) {
6760 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6761 // We print a warning message only once per CMS cycle.
6762 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6763 }
6764 return;
6765 }
6766 // Double capacity if possible
6767 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6768 // Do not give up existing stack until we have managed to
6769 // get the double capacity that we desired.
6770 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6771 new_capacity * sizeof(oop)));
6772 if (rs.is_reserved()) {
6773 // Release the backing store associated with old stack
6774 _virtual_space.release();
6775 // Reinitialize virtual space for new stack
6776 if (!_virtual_space.initialize(rs, rs.size())) {
6777 fatal("Not enough swap for expanded marking stack");
6778 }
6779 _base = (oop*)(_virtual_space.low());
6780 _index = 0;
6781 _capacity = new_capacity;
6782 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6783 // Failed to double capacity, continue;
6784 // we print a detail message only once per CMS cycle.
6785 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6786 SIZE_FORMAT"K",
6787 _capacity / K, new_capacity / K);
6788 }
6789 }
6790
6791
6792 // Closures
6793 // XXX: there seems to be a lot of code duplication here;
6794 // should refactor and consolidate common code.
6795
6796 // This closure is used to mark refs into the CMS generation in
6797 // the CMS bit map. Called at the first checkpoint. This closure
6798 // assumes that we do not need to re-mark dirty cards; if the CMS
6799 // generation on which this is used is not an oldest
6800 // generation then this will lose younger_gen cards!
6801
6802 MarkRefsIntoClosure::MarkRefsIntoClosure(
6803 MemRegion span, CMSBitMap* bitMap):
6804 _span(span),
6805 _bitMap(bitMap)
6806 {
6807 assert(_ref_processor == NULL, "deliberately left NULL");
6808 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6809 }
6810
6811 void MarkRefsIntoClosure::do_oop(oop obj) {
6812 // if p points into _span, then mark corresponding bit in _markBitMap
6813 assert(obj->is_oop(), "expected an oop");
6814 HeapWord* addr = (HeapWord*)obj;
6815 if (_span.contains(addr)) {
6816 // this should be made more efficient
6817 _bitMap->mark(addr);
6818 }
6819 }
6820
6821 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6822 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6823
6824 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6825 MemRegion span, CMSBitMap* bitMap):
6826 _span(span),
6827 _bitMap(bitMap)
6828 {
6829 assert(_ref_processor == NULL, "deliberately left NULL");
6830 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6831 }
6832
6833 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6834 // if p points into _span, then mark corresponding bit in _markBitMap
6835 assert(obj->is_oop(), "expected an oop");
6836 HeapWord* addr = (HeapWord*)obj;
6837 if (_span.contains(addr)) {
6838 // this should be made more efficient
6839 _bitMap->par_mark(addr);
6840 }
6841 }
6842
6843 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6844 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6845
6846 // A variant of the above, used for CMS marking verification.
6847 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6848 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6849 _span(span),
6850 _verification_bm(verification_bm),
6851 _cms_bm(cms_bm)
6852 {
6853 assert(_ref_processor == NULL, "deliberately left NULL");
6854 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6855 }
6856
6857 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6858 // if p points into _span, then mark corresponding bit in _markBitMap
6859 assert(obj->is_oop(), "expected an oop");
6860 HeapWord* addr = (HeapWord*)obj;
6861 if (_span.contains(addr)) {
6862 _verification_bm->mark(addr);
6863 if (!_cms_bm->isMarked(addr)) {
6864 oop(addr)->print();
6865 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6866 fatal("... aborting");
6867 }
6868 }
6869 }
6870
6871 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6872 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6873
6874 //////////////////////////////////////////////////
6875 // MarkRefsIntoAndScanClosure
6876 //////////////////////////////////////////////////
6877
6878 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6879 ReferenceProcessor* rp,
6880 CMSBitMap* bit_map,
6881 CMSBitMap* mod_union_table,
6882 CMSMarkStack* mark_stack,
6883 CMSCollector* collector,
6884 bool should_yield,
6885 bool concurrent_precleaning):
6886 _collector(collector),
6887 _span(span),
6888 _bit_map(bit_map),
6889 _mark_stack(mark_stack),
6890 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6891 mark_stack, concurrent_precleaning),
6892 _yield(should_yield),
6893 _concurrent_precleaning(concurrent_precleaning),
6894 _freelistLock(NULL)
6895 {
6896 _ref_processor = rp;
6897 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6898 }
6899
6900 // This closure is used to mark refs into the CMS generation at the
6901 // second (final) checkpoint, and to scan and transitively follow
6902 // the unmarked oops. It is also used during the concurrent precleaning
6903 // phase while scanning objects on dirty cards in the CMS generation.
6904 // The marks are made in the marking bit map and the marking stack is
6905 // used for keeping the (newly) grey objects during the scan.
6906 // The parallel version (Par_...) appears further below.
6907 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6908 if (obj != NULL) {
6909 assert(obj->is_oop(), "expected an oop");
6910 HeapWord* addr = (HeapWord*)obj;
6911 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6912 assert(_collector->overflow_list_is_empty(),
6913 "overflow list should be empty");
6914 if (_span.contains(addr) &&
6915 !_bit_map->isMarked(addr)) {
6916 // mark bit map (object is now grey)
6917 _bit_map->mark(addr);
6918 // push on marking stack (stack should be empty), and drain the
6919 // stack by applying this closure to the oops in the oops popped
6920 // from the stack (i.e. blacken the grey objects)
6921 bool res = _mark_stack->push(obj);
6922 assert(res, "Should have space to push on empty stack");
6923 do {
6924 oop new_oop = _mark_stack->pop();
6925 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6926 assert(_bit_map->isMarked((HeapWord*)new_oop),
6927 "only grey objects on this stack");
6928 // iterate over the oops in this oop, marking and pushing
6929 // the ones in CMS heap (i.e. in _span).
6930 new_oop->oop_iterate(&_pushAndMarkClosure);
6931 // check if it's time to yield
6932 do_yield_check();
6933 } while (!_mark_stack->isEmpty() ||
6934 (!_concurrent_precleaning && take_from_overflow_list()));
6935 // if marking stack is empty, and we are not doing this
6936 // during precleaning, then check the overflow list
6937 }
6938 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6939 assert(_collector->overflow_list_is_empty(),
6940 "overflow list was drained above");
6941 // We could restore evacuated mark words, if any, used for
6942 // overflow list links here because the overflow list is
6943 // provably empty here. That would reduce the maximum
6944 // size requirements for preserved_{oop,mark}_stack.
6945 // But we'll just postpone it until we are all done
6946 // so we can just stream through.
6947 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6948 _collector->restore_preserved_marks_if_any();
6949 assert(_collector->no_preserved_marks(), "No preserved marks");
6950 }
6951 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6952 "All preserved marks should have been restored above");
6953 }
6954 }
6955
6956 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6957 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6958
6959 void MarkRefsIntoAndScanClosure::do_yield_work() {
6960 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6961 "CMS thread should hold CMS token");
6962 assert_lock_strong(_freelistLock);
6963 assert_lock_strong(_bit_map->lock());
6964 // relinquish the free_list_lock and bitMaplock()
6965 _bit_map->lock()->unlock();
6966 _freelistLock->unlock();
6967 ConcurrentMarkSweepThread::desynchronize(true);
6968 ConcurrentMarkSweepThread::acknowledge_yield_request();
6969 _collector->stopTimer();
6970 if (PrintCMSStatistics != 0) {
6971 _collector->incrementYields();
6972 }
6973 _collector->icms_wait();
6974
6975 // See the comment in coordinator_yield()
6976 for (unsigned i = 0;
6977 i < CMSYieldSleepCount &&
6978 ConcurrentMarkSweepThread::should_yield() &&
6979 !CMSCollector::foregroundGCIsActive();
6980 ++i) {
6981 os::sleep(Thread::current(), 1, false);
6982 ConcurrentMarkSweepThread::acknowledge_yield_request();
6983 }
6984
6985 ConcurrentMarkSweepThread::synchronize(true);
6986 _freelistLock->lock_without_safepoint_check();
6987 _bit_map->lock()->lock_without_safepoint_check();
6988 _collector->startTimer();
6989 }
6990
6991 ///////////////////////////////////////////////////////////
6992 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6993 // MarkRefsIntoAndScanClosure
6994 ///////////////////////////////////////////////////////////
6995 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6996 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6997 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6998 _span(span),
6999 _bit_map(bit_map),
7000 _work_queue(work_queue),
7001 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
7002 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
7003 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
7004 {
7005 _ref_processor = rp;
7006 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7007 }
7008
7009 // This closure is used to mark refs into the CMS generation at the
7010 // second (final) checkpoint, and to scan and transitively follow
7011 // the unmarked oops. The marks are made in the marking bit map and
7012 // the work_queue is used for keeping the (newly) grey objects during
7013 // the scan phase whence they are also available for stealing by parallel
7014 // threads. Since the marking bit map is shared, updates are
7015 // synchronized (via CAS).
7016 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
7017 if (obj != NULL) {
7018 // Ignore mark word because this could be an already marked oop
7019 // that may be chained at the end of the overflow list.
7020 assert(obj->is_oop(true), "expected an oop");
7021 HeapWord* addr = (HeapWord*)obj;
7022 if (_span.contains(addr) &&
7023 !_bit_map->isMarked(addr)) {
7024 // mark bit map (object will become grey):
7025 // It is possible for several threads to be
7026 // trying to "claim" this object concurrently;
7027 // the unique thread that succeeds in marking the
7028 // object first will do the subsequent push on
7029 // to the work queue (or overflow list).
7030 if (_bit_map->par_mark(addr)) {
7031 // push on work_queue (which may not be empty), and trim the
7032 // queue to an appropriate length by applying this closure to
7033 // the oops in the oops popped from the stack (i.e. blacken the
7034 // grey objects)
7035 bool res = _work_queue->push(obj);
7036 assert(res, "Low water mark should be less than capacity?");
7037 trim_queue(_low_water_mark);
7038 } // Else, another thread claimed the object
7039 }
7040 }
7041 }
7042
7043 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7044 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7045
7046 // This closure is used to rescan the marked objects on the dirty cards
7047 // in the mod union table and the card table proper.
7048 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
7049 oop p, MemRegion mr) {
7050
7051 size_t size = 0;
7052 HeapWord* addr = (HeapWord*)p;
7053 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7054 assert(_span.contains(addr), "we are scanning the CMS generation");
7055 // check if it's time to yield
7056 if (do_yield_check()) {
7057 // We yielded for some foreground stop-world work,
7058 // and we have been asked to abort this ongoing preclean cycle.
7059 return 0;
7060 }
7061 if (_bitMap->isMarked(addr)) {
7062 // it's marked; is it potentially uninitialized?
7063 if (p->klass_or_null() != NULL) {
7064 // an initialized object; ignore mark word in verification below
7065 // since we are running concurrent with mutators
7066 assert(p->is_oop(true), "should be an oop");
7067 if (p->is_objArray()) {
7068 // objArrays are precisely marked; restrict scanning
7069 // to dirty cards only.
7070 size = CompactibleFreeListSpace::adjustObjectSize(
7071 p->oop_iterate(_scanningClosure, mr));
7072 } else {
7073 // A non-array may have been imprecisely marked; we need
7074 // to scan object in its entirety.
7075 size = CompactibleFreeListSpace::adjustObjectSize(
7076 p->oop_iterate(_scanningClosure));
7077 }
7078 #ifdef ASSERT
7079 size_t direct_size =
7080 CompactibleFreeListSpace::adjustObjectSize(p->size());
7081 assert(size == direct_size, "Inconsistency in size");
7082 assert(size >= 3, "Necessary for Printezis marks to work");
7083 if (!_bitMap->isMarked(addr+1)) {
7084 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
7085 } else {
7086 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
7087 assert(_bitMap->isMarked(addr+size-1),
7088 "inconsistent Printezis mark");
7089 }
7090 #endif // ASSERT
7091 } else {
7092 // An uninitialized object.
7093 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
7094 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7095 size = pointer_delta(nextOneAddr + 1, addr);
7096 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7097 "alignment problem");
7098 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
7099 // will dirty the card when the klass pointer is installed in the
7100 // object (signaling the completion of initialization).
7101 }
7102 } else {
7103 // Either a not yet marked object or an uninitialized object
7104 if (p->klass_or_null() == NULL) {
7105 // An uninitialized object, skip to the next card, since
7106 // we may not be able to read its P-bits yet.
7107 assert(size == 0, "Initial value");
7108 } else {
7109 // An object not (yet) reached by marking: we merely need to
7110 // compute its size so as to go look at the next block.
7111 assert(p->is_oop(true), "should be an oop");
7112 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
7113 }
7114 }
7115 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7116 return size;
7117 }
7118
7119 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
7120 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7121 "CMS thread should hold CMS token");
7122 assert_lock_strong(_freelistLock);
7123 assert_lock_strong(_bitMap->lock());
7124 // relinquish the free_list_lock and bitMaplock()
7125 _bitMap->lock()->unlock();
7126 _freelistLock->unlock();
7127 ConcurrentMarkSweepThread::desynchronize(true);
7128 ConcurrentMarkSweepThread::acknowledge_yield_request();
7129 _collector->stopTimer();
7130 if (PrintCMSStatistics != 0) {
7131 _collector->incrementYields();
7132 }
7133 _collector->icms_wait();
7134
7135 // See the comment in coordinator_yield()
7136 for (unsigned i = 0; i < CMSYieldSleepCount &&
7137 ConcurrentMarkSweepThread::should_yield() &&
7138 !CMSCollector::foregroundGCIsActive(); ++i) {
7139 os::sleep(Thread::current(), 1, false);
7140 ConcurrentMarkSweepThread::acknowledge_yield_request();
7141 }
7142
7143 ConcurrentMarkSweepThread::synchronize(true);
7144 _freelistLock->lock_without_safepoint_check();
7145 _bitMap->lock()->lock_without_safepoint_check();
7146 _collector->startTimer();
7147 }
7148
7149
7150 //////////////////////////////////////////////////////////////////
7151 // SurvivorSpacePrecleanClosure
7152 //////////////////////////////////////////////////////////////////
7153 // This (single-threaded) closure is used to preclean the oops in
7154 // the survivor spaces.
7155 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
7156
7157 HeapWord* addr = (HeapWord*)p;
7158 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7159 assert(!_span.contains(addr), "we are scanning the survivor spaces");
7160 assert(p->klass_or_null() != NULL, "object should be initialized");
7161 // an initialized object; ignore mark word in verification below
7162 // since we are running concurrent with mutators
7163 assert(p->is_oop(true), "should be an oop");
7164 // Note that we do not yield while we iterate over
7165 // the interior oops of p, pushing the relevant ones
7166 // on our marking stack.
7167 size_t size = p->oop_iterate(_scanning_closure);
7168 do_yield_check();
7169 // Observe that below, we do not abandon the preclean
7170 // phase as soon as we should; rather we empty the
7171 // marking stack before returning. This is to satisfy
7172 // some existing assertions. In general, it may be a
7173 // good idea to abort immediately and complete the marking
7174 // from the grey objects at a later time.
7175 while (!_mark_stack->isEmpty()) {
7176 oop new_oop = _mark_stack->pop();
7177 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7178 assert(_bit_map->isMarked((HeapWord*)new_oop),
7179 "only grey objects on this stack");
7180 // iterate over the oops in this oop, marking and pushing
7181 // the ones in CMS heap (i.e. in _span).
7182 new_oop->oop_iterate(_scanning_closure);
7183 // check if it's time to yield
7184 do_yield_check();
7185 }
7186 unsigned int after_count =
7187 GenCollectedHeap::heap()->total_collections();
7188 bool abort = (_before_count != after_count) ||
7189 _collector->should_abort_preclean();
7190 return abort ? 0 : size;
7191 }
7192
7193 void SurvivorSpacePrecleanClosure::do_yield_work() {
7194 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7195 "CMS thread should hold CMS token");
7196 assert_lock_strong(_bit_map->lock());
7197 // Relinquish the bit map lock
7198 _bit_map->lock()->unlock();
7199 ConcurrentMarkSweepThread::desynchronize(true);
7200 ConcurrentMarkSweepThread::acknowledge_yield_request();
7201 _collector->stopTimer();
7202 if (PrintCMSStatistics != 0) {
7203 _collector->incrementYields();
7204 }
7205 _collector->icms_wait();
7206
7207 // See the comment in coordinator_yield()
7208 for (unsigned i = 0; i < CMSYieldSleepCount &&
7209 ConcurrentMarkSweepThread::should_yield() &&
7210 !CMSCollector::foregroundGCIsActive(); ++i) {
7211 os::sleep(Thread::current(), 1, false);
7212 ConcurrentMarkSweepThread::acknowledge_yield_request();
7213 }
7214
7215 ConcurrentMarkSweepThread::synchronize(true);
7216 _bit_map->lock()->lock_without_safepoint_check();
7217 _collector->startTimer();
7218 }
7219
7220 // This closure is used to rescan the marked objects on the dirty cards
7221 // in the mod union table and the card table proper. In the parallel
7222 // case, although the bitMap is shared, we do a single read so the
7223 // isMarked() query is "safe".
7224 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7225 // Ignore mark word because we are running concurrent with mutators
7226 assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
7227 HeapWord* addr = (HeapWord*)p;
7228 assert(_span.contains(addr), "we are scanning the CMS generation");
7229 bool is_obj_array = false;
7230 #ifdef ASSERT
7231 if (!_parallel) {
7232 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7233 assert(_collector->overflow_list_is_empty(),
7234 "overflow list should be empty");
7235
7236 }
7237 #endif // ASSERT
7238 if (_bit_map->isMarked(addr)) {
7239 // Obj arrays are precisely marked, non-arrays are not;
7240 // so we scan objArrays precisely and non-arrays in their
7241 // entirety.
7242 if (p->is_objArray()) {
7243 is_obj_array = true;
7244 if (_parallel) {
7245 p->oop_iterate(_par_scan_closure, mr);
7246 } else {
7247 p->oop_iterate(_scan_closure, mr);
7248 }
7249 } else {
7250 if (_parallel) {
7251 p->oop_iterate(_par_scan_closure);
7252 } else {
7253 p->oop_iterate(_scan_closure);
7254 }
7255 }
7256 }
7257 #ifdef ASSERT
7258 if (!_parallel) {
7259 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7260 assert(_collector->overflow_list_is_empty(),
7261 "overflow list should be empty");
7262
7263 }
7264 #endif // ASSERT
7265 return is_obj_array;
7266 }
7267
7268 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7269 MemRegion span,
7270 CMSBitMap* bitMap, CMSMarkStack* markStack,
7271 bool should_yield, bool verifying):
7272 _collector(collector),
7273 _span(span),
7274 _bitMap(bitMap),
7275 _mut(&collector->_modUnionTable),
7276 _markStack(markStack),
7277 _yield(should_yield),
7278 _skipBits(0)
7279 {
7280 assert(_markStack->isEmpty(), "stack should be empty");
7281 _finger = _bitMap->startWord();
7282 _threshold = _finger;
7283 assert(_collector->_restart_addr == NULL, "Sanity check");
7284 assert(_span.contains(_finger), "Out of bounds _finger?");
7285 DEBUG_ONLY(_verifying = verifying;)
7286 }
7287
7288 void MarkFromRootsClosure::reset(HeapWord* addr) {
7289 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7290 assert(_span.contains(addr), "Out of bounds _finger?");
7291 _finger = addr;
7292 _threshold = (HeapWord*)round_to(
7293 (intptr_t)_finger, CardTableModRefBS::card_size);
7294 }
7295
7296 // Should revisit to see if this should be restructured for
7297 // greater efficiency.
7298 bool MarkFromRootsClosure::do_bit(size_t offset) {
7299 if (_skipBits > 0) {
7300 _skipBits--;
7301 return true;
7302 }
7303 // convert offset into a HeapWord*
7304 HeapWord* addr = _bitMap->startWord() + offset;
7305 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7306 "address out of range");
7307 assert(_bitMap->isMarked(addr), "tautology");
7308 if (_bitMap->isMarked(addr+1)) {
7309 // this is an allocated but not yet initialized object
7310 assert(_skipBits == 0, "tautology");
7311 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7312 oop p = oop(addr);
7313 if (p->klass_or_null() == NULL) {
7314 DEBUG_ONLY(if (!_verifying) {)
7315 // We re-dirty the cards on which this object lies and increase
7316 // the _threshold so that we'll come back to scan this object
7317 // during the preclean or remark phase. (CMSCleanOnEnter)
7318 if (CMSCleanOnEnter) {
7319 size_t sz = _collector->block_size_using_printezis_bits(addr);
7320 HeapWord* end_card_addr = (HeapWord*)round_to(
7321 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7322 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7323 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7324 // Bump _threshold to end_card_addr; note that
7325 // _threshold cannot possibly exceed end_card_addr, anyhow.
7326 // This prevents future clearing of the card as the scan proceeds
7327 // to the right.
7328 assert(_threshold <= end_card_addr,
7329 "Because we are just scanning into this object");
7330 if (_threshold < end_card_addr) {
7331 _threshold = end_card_addr;
7332 }
7333 if (p->klass_or_null() != NULL) {
7334 // Redirty the range of cards...
7335 _mut->mark_range(redirty_range);
7336 } // ...else the setting of klass will dirty the card anyway.
7337 }
7338 DEBUG_ONLY(})
7339 return true;
7340 }
7341 }
7342 scanOopsInOop(addr);
7343 return true;
7344 }
7345
7346 // We take a break if we've been at this for a while,
7347 // so as to avoid monopolizing the locks involved.
7348 void MarkFromRootsClosure::do_yield_work() {
7349 // First give up the locks, then yield, then re-lock
7350 // We should probably use a constructor/destructor idiom to
7351 // do this unlock/lock or modify the MutexUnlocker class to
7352 // serve our purpose. XXX
7353 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7354 "CMS thread should hold CMS token");
7355 assert_lock_strong(_bitMap->lock());
7356 _bitMap->lock()->unlock();
7357 ConcurrentMarkSweepThread::desynchronize(true);
7358 ConcurrentMarkSweepThread::acknowledge_yield_request();
7359 _collector->stopTimer();
7360 if (PrintCMSStatistics != 0) {
7361 _collector->incrementYields();
7362 }
7363 _collector->icms_wait();
7364
7365 // See the comment in coordinator_yield()
7366 for (unsigned i = 0; i < CMSYieldSleepCount &&
7367 ConcurrentMarkSweepThread::should_yield() &&
7368 !CMSCollector::foregroundGCIsActive(); ++i) {
7369 os::sleep(Thread::current(), 1, false);
7370 ConcurrentMarkSweepThread::acknowledge_yield_request();
7371 }
7372
7373 ConcurrentMarkSweepThread::synchronize(true);
7374 _bitMap->lock()->lock_without_safepoint_check();
7375 _collector->startTimer();
7376 }
7377
7378 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7379 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7380 assert(_markStack->isEmpty(),
7381 "should drain stack to limit stack usage");
7382 // convert ptr to an oop preparatory to scanning
7383 oop obj = oop(ptr);
7384 // Ignore mark word in verification below, since we
7385 // may be running concurrent with mutators.
7386 assert(obj->is_oop(true), "should be an oop");
7387 assert(_finger <= ptr, "_finger runneth ahead");
7388 // advance the finger to right end of this object
7389 _finger = ptr + obj->size();
7390 assert(_finger > ptr, "we just incremented it above");
7391 // On large heaps, it may take us some time to get through
7392 // the marking phase (especially if running iCMS). During
7393 // this time it's possible that a lot of mutations have
7394 // accumulated in the card table and the mod union table --
7395 // these mutation records are redundant until we have
7396 // actually traced into the corresponding card.
7397 // Here, we check whether advancing the finger would make
7398 // us cross into a new card, and if so clear corresponding
7399 // cards in the MUT (preclean them in the card-table in the
7400 // future).
7401
7402 DEBUG_ONLY(if (!_verifying) {)
7403 // The clean-on-enter optimization is disabled by default,
7404 // until we fix 6178663.
7405 if (CMSCleanOnEnter && (_finger > _threshold)) {
7406 // [_threshold, _finger) represents the interval
7407 // of cards to be cleared in MUT (or precleaned in card table).
7408 // The set of cards to be cleared is all those that overlap
7409 // with the interval [_threshold, _finger); note that
7410 // _threshold is always kept card-aligned but _finger isn't
7411 // always card-aligned.
7412 HeapWord* old_threshold = _threshold;
7413 assert(old_threshold == (HeapWord*)round_to(
7414 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7415 "_threshold should always be card-aligned");
7416 _threshold = (HeapWord*)round_to(
7417 (intptr_t)_finger, CardTableModRefBS::card_size);
7418 MemRegion mr(old_threshold, _threshold);
7419 assert(!mr.is_empty(), "Control point invariant");
7420 assert(_span.contains(mr), "Should clear within span");
7421 _mut->clear_range(mr);
7422 }
7423 DEBUG_ONLY(})
7424 // Note: the finger doesn't advance while we drain
7425 // the stack below.
7426 PushOrMarkClosure pushOrMarkClosure(_collector,
7427 _span, _bitMap, _markStack,
7428 _finger, this);
7429 bool res = _markStack->push(obj);
7430 assert(res, "Empty non-zero size stack should have space for single push");
7431 while (!_markStack->isEmpty()) {
7432 oop new_oop = _markStack->pop();
7433 // Skip verifying header mark word below because we are
7434 // running concurrent with mutators.
7435 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7436 // now scan this oop's oops
7437 new_oop->oop_iterate(&pushOrMarkClosure);
7438 do_yield_check();
7439 }
7440 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7441 }
7442
7443 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7444 CMSCollector* collector, MemRegion span,
7445 CMSBitMap* bit_map,
7446 OopTaskQueue* work_queue,
7447 CMSMarkStack* overflow_stack,
7448 bool should_yield):
7449 _collector(collector),
7450 _whole_span(collector->_span),
7451 _span(span),
7452 _bit_map(bit_map),
7453 _mut(&collector->_modUnionTable),
7454 _work_queue(work_queue),
7455 _overflow_stack(overflow_stack),
7456 _yield(should_yield),
7457 _skip_bits(0),
7458 _task(task)
7459 {
7460 assert(_work_queue->size() == 0, "work_queue should be empty");
7461 _finger = span.start();
7462 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7463 assert(_span.contains(_finger), "Out of bounds _finger?");
7464 }
7465
7466 // Should revisit to see if this should be restructured for
7467 // greater efficiency.
7468 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7469 if (_skip_bits > 0) {
7470 _skip_bits--;
7471 return true;
7472 }
7473 // convert offset into a HeapWord*
7474 HeapWord* addr = _bit_map->startWord() + offset;
7475 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7476 "address out of range");
7477 assert(_bit_map->isMarked(addr), "tautology");
7478 if (_bit_map->isMarked(addr+1)) {
7479 // this is an allocated object that might not yet be initialized
7480 assert(_skip_bits == 0, "tautology");
7481 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7482 oop p = oop(addr);
7483 if (p->klass_or_null() == NULL) {
7484 // in the case of Clean-on-Enter optimization, redirty card
7485 // and avoid clearing card by increasing the threshold.
7486 return true;
7487 }
7488 }
7489 scan_oops_in_oop(addr);
7490 return true;
7491 }
7492
7493 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7494 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7495 // Should we assert that our work queue is empty or
7496 // below some drain limit?
7497 assert(_work_queue->size() == 0,
7498 "should drain stack to limit stack usage");
7499 // convert ptr to an oop preparatory to scanning
7500 oop obj = oop(ptr);
7501 // Ignore mark word in verification below, since we
7502 // may be running concurrent with mutators.
7503 assert(obj->is_oop(true), "should be an oop");
7504 assert(_finger <= ptr, "_finger runneth ahead");
7505 // advance the finger to right end of this object
7506 _finger = ptr + obj->size();
7507 assert(_finger > ptr, "we just incremented it above");
7508 // On large heaps, it may take us some time to get through
7509 // the marking phase (especially if running iCMS). During
7510 // this time it's possible that a lot of mutations have
7511 // accumulated in the card table and the mod union table --
7512 // these mutation records are redundant until we have
7513 // actually traced into the corresponding card.
7514 // Here, we check whether advancing the finger would make
7515 // us cross into a new card, and if so clear corresponding
7516 // cards in the MUT (preclean them in the card-table in the
7517 // future).
7518
7519 // The clean-on-enter optimization is disabled by default,
7520 // until we fix 6178663.
7521 if (CMSCleanOnEnter && (_finger > _threshold)) {
7522 // [_threshold, _finger) represents the interval
7523 // of cards to be cleared in MUT (or precleaned in card table).
7524 // The set of cards to be cleared is all those that overlap
7525 // with the interval [_threshold, _finger); note that
7526 // _threshold is always kept card-aligned but _finger isn't
7527 // always card-aligned.
7528 HeapWord* old_threshold = _threshold;
7529 assert(old_threshold == (HeapWord*)round_to(
7530 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7531 "_threshold should always be card-aligned");
7532 _threshold = (HeapWord*)round_to(
7533 (intptr_t)_finger, CardTableModRefBS::card_size);
7534 MemRegion mr(old_threshold, _threshold);
7535 assert(!mr.is_empty(), "Control point invariant");
7536 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7537 _mut->clear_range(mr);
7538 }
7539
7540 // Note: the local finger doesn't advance while we drain
7541 // the stack below, but the global finger sure can and will.
7542 HeapWord** gfa = _task->global_finger_addr();
7543 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7544 _span, _bit_map,
7545 _work_queue,
7546 _overflow_stack,
7547 _finger,
7548 gfa, this);
7549 bool res = _work_queue->push(obj); // overflow could occur here
7550 assert(res, "Will hold once we use workqueues");
7551 while (true) {
7552 oop new_oop;
7553 if (!_work_queue->pop_local(new_oop)) {
7554 // We emptied our work_queue; check if there's stuff that can
7555 // be gotten from the overflow stack.
7556 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7557 _overflow_stack, _work_queue)) {
7558 do_yield_check();
7559 continue;
7560 } else { // done
7561 break;
7562 }
7563 }
7564 // Skip verifying header mark word below because we are
7565 // running concurrent with mutators.
7566 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7567 // now scan this oop's oops
7568 new_oop->oop_iterate(&pushOrMarkClosure);
7569 do_yield_check();
7570 }
7571 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7572 }
7573
7574 // Yield in response to a request from VM Thread or
7575 // from mutators.
7576 void Par_MarkFromRootsClosure::do_yield_work() {
7577 assert(_task != NULL, "sanity");
7578 _task->yield();
7579 }
7580
7581 // A variant of the above used for verifying CMS marking work.
7582 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7583 MemRegion span,
7584 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7585 CMSMarkStack* mark_stack):
7586 _collector(collector),
7587 _span(span),
7588 _verification_bm(verification_bm),
7589 _cms_bm(cms_bm),
7590 _mark_stack(mark_stack),
7591 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7592 mark_stack)
7593 {
7594 assert(_mark_stack->isEmpty(), "stack should be empty");
7595 _finger = _verification_bm->startWord();
7596 assert(_collector->_restart_addr == NULL, "Sanity check");
7597 assert(_span.contains(_finger), "Out of bounds _finger?");
7598 }
7599
7600 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7601 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7602 assert(_span.contains(addr), "Out of bounds _finger?");
7603 _finger = addr;
7604 }
7605
7606 // Should revisit to see if this should be restructured for
7607 // greater efficiency.
7608 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7609 // convert offset into a HeapWord*
7610 HeapWord* addr = _verification_bm->startWord() + offset;
7611 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7612 "address out of range");
7613 assert(_verification_bm->isMarked(addr), "tautology");
7614 assert(_cms_bm->isMarked(addr), "tautology");
7615
7616 assert(_mark_stack->isEmpty(),
7617 "should drain stack to limit stack usage");
7618 // convert addr to an oop preparatory to scanning
7619 oop obj = oop(addr);
7620 assert(obj->is_oop(), "should be an oop");
7621 assert(_finger <= addr, "_finger runneth ahead");
7622 // advance the finger to right end of this object
7623 _finger = addr + obj->size();
7624 assert(_finger > addr, "we just incremented it above");
7625 // Note: the finger doesn't advance while we drain
7626 // the stack below.
7627 bool res = _mark_stack->push(obj);
7628 assert(res, "Empty non-zero size stack should have space for single push");
7629 while (!_mark_stack->isEmpty()) {
7630 oop new_oop = _mark_stack->pop();
7631 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7632 // now scan this oop's oops
7633 new_oop->oop_iterate(&_pam_verify_closure);
7634 }
7635 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7636 return true;
7637 }
7638
7639 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7640 CMSCollector* collector, MemRegion span,
7641 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7642 CMSMarkStack* mark_stack):
7643 MetadataAwareOopClosure(collector->ref_processor()),
7644 _collector(collector),
7645 _span(span),
7646 _verification_bm(verification_bm),
7647 _cms_bm(cms_bm),
7648 _mark_stack(mark_stack)
7649 { }
7650
7651 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7652 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7653
7654 // Upon stack overflow, we discard (part of) the stack,
7655 // remembering the least address amongst those discarded
7656 // in CMSCollector's _restart_address.
7657 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7658 // Remember the least grey address discarded
7659 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7660 _collector->lower_restart_addr(ra);
7661 _mark_stack->reset(); // discard stack contents
7662 _mark_stack->expand(); // expand the stack if possible
7663 }
7664
7665 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7666 assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7667 HeapWord* addr = (HeapWord*)obj;
7668 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7669 // Oop lies in _span and isn't yet grey or black
7670 _verification_bm->mark(addr); // now grey
7671 if (!_cms_bm->isMarked(addr)) {
7672 oop(addr)->print();
7673 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7674 addr);
7675 fatal("... aborting");
7676 }
7677
7678 if (!_mark_stack->push(obj)) { // stack overflow
7679 if (PrintCMSStatistics != 0) {
7680 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7681 SIZE_FORMAT, _mark_stack->capacity());
7682 }
7683 assert(_mark_stack->isFull(), "Else push should have succeeded");
7684 handle_stack_overflow(addr);
7685 }
7686 // anything including and to the right of _finger
7687 // will be scanned as we iterate over the remainder of the
7688 // bit map
7689 }
7690 }
7691
7692 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7693 MemRegion span,
7694 CMSBitMap* bitMap, CMSMarkStack* markStack,
7695 HeapWord* finger, MarkFromRootsClosure* parent) :
7696 MetadataAwareOopClosure(collector->ref_processor()),
7697 _collector(collector),
7698 _span(span),
7699 _bitMap(bitMap),
7700 _markStack(markStack),
7701 _finger(finger),
7702 _parent(parent)
7703 { }
7704
7705 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7706 MemRegion span,
7707 CMSBitMap* bit_map,
7708 OopTaskQueue* work_queue,
7709 CMSMarkStack* overflow_stack,
7710 HeapWord* finger,
7711 HeapWord** global_finger_addr,
7712 Par_MarkFromRootsClosure* parent) :
7713 MetadataAwareOopClosure(collector->ref_processor()),
7714 _collector(collector),
7715 _whole_span(collector->_span),
7716 _span(span),
7717 _bit_map(bit_map),
7718 _work_queue(work_queue),
7719 _overflow_stack(overflow_stack),
7720 _finger(finger),
7721 _global_finger_addr(global_finger_addr),
7722 _parent(parent)
7723 { }
7724
7725 // Assumes thread-safe access by callers, who are
7726 // responsible for mutual exclusion.
7727 void CMSCollector::lower_restart_addr(HeapWord* low) {
7728 assert(_span.contains(low), "Out of bounds addr");
7729 if (_restart_addr == NULL) {
7730 _restart_addr = low;
7731 } else {
7732 _restart_addr = MIN2(_restart_addr, low);
7733 }
7734 }
7735
7736 // Upon stack overflow, we discard (part of) the stack,
7737 // remembering the least address amongst those discarded
7738 // in CMSCollector's _restart_address.
7739 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7740 // Remember the least grey address discarded
7741 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7742 _collector->lower_restart_addr(ra);
7743 _markStack->reset(); // discard stack contents
7744 _markStack->expand(); // expand the stack if possible
7745 }
7746
7747 // Upon stack overflow, we discard (part of) the stack,
7748 // remembering the least address amongst those discarded
7749 // in CMSCollector's _restart_address.
7750 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7751 // We need to do this under a mutex to prevent other
7752 // workers from interfering with the work done below.
7753 MutexLockerEx ml(_overflow_stack->par_lock(),
7754 Mutex::_no_safepoint_check_flag);
7755 // Remember the least grey address discarded
7756 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7757 _collector->lower_restart_addr(ra);
7758 _overflow_stack->reset(); // discard stack contents
7759 _overflow_stack->expand(); // expand the stack if possible
7760 }
7761
7762 void PushOrMarkClosure::do_oop(oop obj) {
7763 // Ignore mark word because we are running concurrent with mutators.
7764 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7765 HeapWord* addr = (HeapWord*)obj;
7766 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7767 // Oop lies in _span and isn't yet grey or black
7768 _bitMap->mark(addr); // now grey
7769 if (addr < _finger) {
7770 // the bit map iteration has already either passed, or
7771 // sampled, this bit in the bit map; we'll need to
7772 // use the marking stack to scan this oop's oops.
7773 bool simulate_overflow = false;
7774 NOT_PRODUCT(
7775 if (CMSMarkStackOverflowALot &&
7776 _collector->simulate_overflow()) {
7777 // simulate a stack overflow
7778 simulate_overflow = true;
7779 }
7780 )
7781 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7782 if (PrintCMSStatistics != 0) {
7783 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7784 SIZE_FORMAT, _markStack->capacity());
7785 }
7786 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7787 handle_stack_overflow(addr);
7788 }
7789 }
7790 // anything including and to the right of _finger
7791 // will be scanned as we iterate over the remainder of the
7792 // bit map
7793 do_yield_check();
7794 }
7795 }
7796
7797 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7798 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7799
7800 void Par_PushOrMarkClosure::do_oop(oop obj) {
7801 // Ignore mark word because we are running concurrent with mutators.
7802 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7803 HeapWord* addr = (HeapWord*)obj;
7804 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7805 // Oop lies in _span and isn't yet grey or black
7806 // We read the global_finger (volatile read) strictly after marking oop
7807 bool res = _bit_map->par_mark(addr); // now grey
7808 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7809 // Should we push this marked oop on our stack?
7810 // -- if someone else marked it, nothing to do
7811 // -- if target oop is above global finger nothing to do
7812 // -- if target oop is in chunk and above local finger
7813 // then nothing to do
7814 // -- else push on work queue
7815 if ( !res // someone else marked it, they will deal with it
7816 || (addr >= *gfa) // will be scanned in a later task
7817 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7818 return;
7819 }
7820 // the bit map iteration has already either passed, or
7821 // sampled, this bit in the bit map; we'll need to
7822 // use the marking stack to scan this oop's oops.
7823 bool simulate_overflow = false;
7824 NOT_PRODUCT(
7825 if (CMSMarkStackOverflowALot &&
7826 _collector->simulate_overflow()) {
7827 // simulate a stack overflow
7828 simulate_overflow = true;
7829 }
7830 )
7831 if (simulate_overflow ||
7832 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7833 // stack overflow
7834 if (PrintCMSStatistics != 0) {
7835 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7836 SIZE_FORMAT, _overflow_stack->capacity());
7837 }
7838 // We cannot assert that the overflow stack is full because
7839 // it may have been emptied since.
7840 assert(simulate_overflow ||
7841 _work_queue->size() == _work_queue->max_elems(),
7842 "Else push should have succeeded");
7843 handle_stack_overflow(addr);
7844 }
7845 do_yield_check();
7846 }
7847 }
7848
7849 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7850 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7851
7852 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7853 MemRegion span,
7854 ReferenceProcessor* rp,
7855 CMSBitMap* bit_map,
7856 CMSBitMap* mod_union_table,
7857 CMSMarkStack* mark_stack,
7858 bool concurrent_precleaning):
7859 MetadataAwareOopClosure(rp),
7860 _collector(collector),
7861 _span(span),
7862 _bit_map(bit_map),
7863 _mod_union_table(mod_union_table),
7864 _mark_stack(mark_stack),
7865 _concurrent_precleaning(concurrent_precleaning)
7866 {
7867 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7868 }
7869
7870 // Grey object rescan during pre-cleaning and second checkpoint phases --
7871 // the non-parallel version (the parallel version appears further below.)
7872 void PushAndMarkClosure::do_oop(oop obj) {
7873 // Ignore mark word verification. If during concurrent precleaning,
7874 // the object monitor may be locked. If during the checkpoint
7875 // phases, the object may already have been reached by a different
7876 // path and may be at the end of the global overflow list (so
7877 // the mark word may be NULL).
7878 assert(obj->is_oop_or_null(true /* ignore mark word */),
7879 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7880 HeapWord* addr = (HeapWord*)obj;
7881 // Check if oop points into the CMS generation
7882 // and is not marked
7883 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7884 // a white object ...
7885 _bit_map->mark(addr); // ... now grey
7886 // push on the marking stack (grey set)
7887 bool simulate_overflow = false;
7888 NOT_PRODUCT(
7889 if (CMSMarkStackOverflowALot &&
7890 _collector->simulate_overflow()) {
7891 // simulate a stack overflow
7892 simulate_overflow = true;
7893 }
7894 )
7895 if (simulate_overflow || !_mark_stack->push(obj)) {
7896 if (_concurrent_precleaning) {
7897 // During precleaning we can just dirty the appropriate card(s)
7898 // in the mod union table, thus ensuring that the object remains
7899 // in the grey set and continue. In the case of object arrays
7900 // we need to dirty all of the cards that the object spans,
7901 // since the rescan of object arrays will be limited to the
7902 // dirty cards.
7903 // Note that no one can be interfering with us in this action
7904 // of dirtying the mod union table, so no locking or atomics
7905 // are required.
7906 if (obj->is_objArray()) {
7907 size_t sz = obj->size();
7908 HeapWord* end_card_addr = (HeapWord*)round_to(
7909 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7910 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7911 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7912 _mod_union_table->mark_range(redirty_range);
7913 } else {
7914 _mod_union_table->mark(addr);
7915 }
7916 _collector->_ser_pmc_preclean_ovflw++;
7917 } else {
7918 // During the remark phase, we need to remember this oop
7919 // in the overflow list.
7920 _collector->push_on_overflow_list(obj);
7921 _collector->_ser_pmc_remark_ovflw++;
7922 }
7923 }
7924 }
7925 }
7926
7927 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7928 MemRegion span,
7929 ReferenceProcessor* rp,
7930 CMSBitMap* bit_map,
7931 OopTaskQueue* work_queue):
7932 MetadataAwareOopClosure(rp),
7933 _collector(collector),
7934 _span(span),
7935 _bit_map(bit_map),
7936 _work_queue(work_queue)
7937 {
7938 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7939 }
7940
7941 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7942 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7943
7944 // Grey object rescan during second checkpoint phase --
7945 // the parallel version.
7946 void Par_PushAndMarkClosure::do_oop(oop obj) {
7947 // In the assert below, we ignore the mark word because
7948 // this oop may point to an already visited object that is
7949 // on the overflow stack (in which case the mark word has
7950 // been hijacked for chaining into the overflow stack --
7951 // if this is the last object in the overflow stack then
7952 // its mark word will be NULL). Because this object may
7953 // have been subsequently popped off the global overflow
7954 // stack, and the mark word possibly restored to the prototypical
7955 // value, by the time we get to examined this failing assert in
7956 // the debugger, is_oop_or_null(false) may subsequently start
7957 // to hold.
7958 assert(obj->is_oop_or_null(true),
7959 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7960 HeapWord* addr = (HeapWord*)obj;
7961 // Check if oop points into the CMS generation
7962 // and is not marked
7963 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7964 // a white object ...
7965 // If we manage to "claim" the object, by being the
7966 // first thread to mark it, then we push it on our
7967 // marking stack
7968 if (_bit_map->par_mark(addr)) { // ... now grey
7969 // push on work queue (grey set)
7970 bool simulate_overflow = false;
7971 NOT_PRODUCT(
7972 if (CMSMarkStackOverflowALot &&
7973 _collector->par_simulate_overflow()) {
7974 // simulate a stack overflow
7975 simulate_overflow = true;
7976 }
7977 )
7978 if (simulate_overflow || !_work_queue->push(obj)) {
7979 _collector->par_push_on_overflow_list(obj);
7980 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7981 }
7982 } // Else, some other thread got there first
7983 }
7984 }
7985
7986 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7987 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7988
7989 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7990 Mutex* bml = _collector->bitMapLock();
7991 assert_lock_strong(bml);
7992 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7993 "CMS thread should hold CMS token");
7994
7995 bml->unlock();
7996 ConcurrentMarkSweepThread::desynchronize(true);
7997
7998 ConcurrentMarkSweepThread::acknowledge_yield_request();
7999
8000 _collector->stopTimer();
8001 if (PrintCMSStatistics != 0) {
8002 _collector->incrementYields();
8003 }
8004 _collector->icms_wait();
8005
8006 // See the comment in coordinator_yield()
8007 for (unsigned i = 0; i < CMSYieldSleepCount &&
8008 ConcurrentMarkSweepThread::should_yield() &&
8009 !CMSCollector::foregroundGCIsActive(); ++i) {
8010 os::sleep(Thread::current(), 1, false);
8011 ConcurrentMarkSweepThread::acknowledge_yield_request();
8012 }
8013
8014 ConcurrentMarkSweepThread::synchronize(true);
8015 bml->lock();
8016
8017 _collector->startTimer();
8018 }
8019
8020 bool CMSPrecleanRefsYieldClosure::should_return() {
8021 if (ConcurrentMarkSweepThread::should_yield()) {
8022 do_yield_work();
8023 }
8024 return _collector->foregroundGCIsActive();
8025 }
8026
8027 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
8028 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
8029 "mr should be aligned to start at a card boundary");
8030 // We'd like to assert:
8031 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
8032 // "mr should be a range of cards");
8033 // However, that would be too strong in one case -- the last
8034 // partition ends at _unallocated_block which, in general, can be
8035 // an arbitrary boundary, not necessarily card aligned.
8036 if (PrintCMSStatistics != 0) {
8037 _num_dirty_cards +=
8038 mr.word_size()/CardTableModRefBS::card_size_in_words;
8039 }
8040 _space->object_iterate_mem(mr, &_scan_cl);
8041 }
8042
8043 SweepClosure::SweepClosure(CMSCollector* collector,
8044 ConcurrentMarkSweepGeneration* g,
8045 CMSBitMap* bitMap, bool should_yield) :
8046 _collector(collector),
8047 _g(g),
8048 _sp(g->cmsSpace()),
8049 _limit(_sp->sweep_limit()),
8050 _freelistLock(_sp->freelistLock()),
8051 _bitMap(bitMap),
8052 _yield(should_yield),
8053 _inFreeRange(false), // No free range at beginning of sweep
8054 _freeRangeInFreeLists(false), // No free range at beginning of sweep
8055 _lastFreeRangeCoalesced(false),
8056 _freeFinger(g->used_region().start())
8057 {
8058 NOT_PRODUCT(
8059 _numObjectsFreed = 0;
8060 _numWordsFreed = 0;
8061 _numObjectsLive = 0;
8062 _numWordsLive = 0;
8063 _numObjectsAlreadyFree = 0;
8064 _numWordsAlreadyFree = 0;
8065 _last_fc = NULL;
8066
8067 _sp->initializeIndexedFreeListArrayReturnedBytes();
8068 _sp->dictionary()->initialize_dict_returned_bytes();
8069 )
8070 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8071 "sweep _limit out of bounds");
8072 if (CMSTraceSweeper) {
8073 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
8074 _limit);
8075 }
8076 }
8077
8078 void SweepClosure::print_on(outputStream* st) const {
8079 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
8080 _sp->bottom(), _sp->end());
8081 tty->print_cr("_limit = " PTR_FORMAT, _limit);
8082 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
8083 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
8084 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
8085 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
8086 }
8087
8088 #ifndef PRODUCT
8089 // Assertion checking only: no useful work in product mode --
8090 // however, if any of the flags below become product flags,
8091 // you may need to review this code to see if it needs to be
8092 // enabled in product mode.
8093 SweepClosure::~SweepClosure() {
8094 assert_lock_strong(_freelistLock);
8095 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8096 "sweep _limit out of bounds");
8097 if (inFreeRange()) {
8098 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
8099 print();
8100 ShouldNotReachHere();
8101 }
8102 if (Verbose && PrintGC) {
8103 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
8104 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
8105 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
8106 SIZE_FORMAT" bytes "
8107 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
8108 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
8109 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
8110 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
8111 * sizeof(HeapWord);
8112 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
8113
8114 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
8115 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
8116 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
8117 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
8118 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
8119 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
8120 indexListReturnedBytes);
8121 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
8122 dict_returned_bytes);
8123 }
8124 }
8125 if (CMSTraceSweeper) {
8126 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
8127 _limit);
8128 }
8129 }
8130 #endif // PRODUCT
8131
8132 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
8133 bool freeRangeInFreeLists) {
8134 if (CMSTraceSweeper) {
8135 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
8136 freeFinger, freeRangeInFreeLists);
8137 }
8138 assert(!inFreeRange(), "Trampling existing free range");
8139 set_inFreeRange(true);
8140 set_lastFreeRangeCoalesced(false);
8141
8142 set_freeFinger(freeFinger);
8143 set_freeRangeInFreeLists(freeRangeInFreeLists);
8144 if (CMSTestInFreeList) {
8145 if (freeRangeInFreeLists) {
8146 FreeChunk* fc = (FreeChunk*) freeFinger;
8147 assert(fc->is_free(), "A chunk on the free list should be free.");
8148 assert(fc->size() > 0, "Free range should have a size");
8149 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
8150 }
8151 }
8152 }
8153
8154 // Note that the sweeper runs concurrently with mutators. Thus,
8155 // it is possible for direct allocation in this generation to happen
8156 // in the middle of the sweep. Note that the sweeper also coalesces
8157 // contiguous free blocks. Thus, unless the sweeper and the allocator
8158 // synchronize appropriately freshly allocated blocks may get swept up.
8159 // This is accomplished by the sweeper locking the free lists while
8160 // it is sweeping. Thus blocks that are determined to be free are
8161 // indeed free. There is however one additional complication:
8162 // blocks that have been allocated since the final checkpoint and
8163 // mark, will not have been marked and so would be treated as
8164 // unreachable and swept up. To prevent this, the allocator marks
8165 // the bit map when allocating during the sweep phase. This leads,
8166 // however, to a further complication -- objects may have been allocated
8167 // but not yet initialized -- in the sense that the header isn't yet
8168 // installed. The sweeper can not then determine the size of the block
8169 // in order to skip over it. To deal with this case, we use a technique
8170 // (due to Printezis) to encode such uninitialized block sizes in the
8171 // bit map. Since the bit map uses a bit per every HeapWord, but the
8172 // CMS generation has a minimum object size of 3 HeapWords, it follows
8173 // that "normal marks" won't be adjacent in the bit map (there will
8174 // always be at least two 0 bits between successive 1 bits). We make use
8175 // of these "unused" bits to represent uninitialized blocks -- the bit
8176 // corresponding to the start of the uninitialized object and the next
8177 // bit are both set. Finally, a 1 bit marks the end of the object that
8178 // started with the two consecutive 1 bits to indicate its potentially
8179 // uninitialized state.
8180
8181 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8182 FreeChunk* fc = (FreeChunk*)addr;
8183 size_t res;
8184
8185 // Check if we are done sweeping. Below we check "addr >= _limit" rather
8186 // than "addr == _limit" because although _limit was a block boundary when
8187 // we started the sweep, it may no longer be one because heap expansion
8188 // may have caused us to coalesce the block ending at the address _limit
8189 // with a newly expanded chunk (this happens when _limit was set to the
8190 // previous _end of the space), so we may have stepped past _limit:
8191 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8192 if (addr >= _limit) { // we have swept up to or past the limit: finish up
8193 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8194 "sweep _limit out of bounds");
8195 assert(addr < _sp->end(), "addr out of bounds");
8196 // Flush any free range we might be holding as a single
8197 // coalesced chunk to the appropriate free list.
8198 if (inFreeRange()) {
8199 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8200 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8201 flush_cur_free_chunk(freeFinger(),
8202 pointer_delta(addr, freeFinger()));
8203 if (CMSTraceSweeper) {
8204 gclog_or_tty->print("Sweep: last chunk: ");
8205 gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
8206 "[coalesced:%d]\n",
8207 freeFinger(), pointer_delta(addr, freeFinger()),
8208 lastFreeRangeCoalesced() ? 1 : 0);
8209 }
8210 }
8211
8212 // help the iterator loop finish
8213 return pointer_delta(_sp->end(), addr);
8214 }
8215
8216 assert(addr < _limit, "sweep invariant");
8217 // check if we should yield
8218 do_yield_check(addr);
8219 if (fc->is_free()) {
8220 // Chunk that is already free
8221 res = fc->size();
8222 do_already_free_chunk(fc);
8223 debug_only(_sp->verifyFreeLists());
8224 // If we flush the chunk at hand in lookahead_and_flush()
8225 // and it's coalesced with a preceding chunk, then the
8226 // process of "mangling" the payload of the coalesced block
8227 // will cause erasure of the size information from the
8228 // (erstwhile) header of all the coalesced blocks but the
8229 // first, so the first disjunct in the assert will not hold
8230 // in that specific case (in which case the second disjunct
8231 // will hold).
8232 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8233 "Otherwise the size info doesn't change at this step");
8234 NOT_PRODUCT(
8235 _numObjectsAlreadyFree++;
8236 _numWordsAlreadyFree += res;
8237 )
8238 NOT_PRODUCT(_last_fc = fc;)
8239 } else if (!_bitMap->isMarked(addr)) {
8240 // Chunk is fresh garbage
8241 res = do_garbage_chunk(fc);
8242 debug_only(_sp->verifyFreeLists());
8243 NOT_PRODUCT(
8244 _numObjectsFreed++;
8245 _numWordsFreed += res;
8246 )
8247 } else {
8248 // Chunk that is alive.
8249 res = do_live_chunk(fc);
8250 debug_only(_sp->verifyFreeLists());
8251 NOT_PRODUCT(
8252 _numObjectsLive++;
8253 _numWordsLive += res;
8254 )
8255 }
8256 return res;
8257 }
8258
8259 // For the smart allocation, record following
8260 // split deaths - a free chunk is removed from its free list because
8261 // it is being split into two or more chunks.
8262 // split birth - a free chunk is being added to its free list because
8263 // a larger free chunk has been split and resulted in this free chunk.
8264 // coal death - a free chunk is being removed from its free list because
8265 // it is being coalesced into a large free chunk.
8266 // coal birth - a free chunk is being added to its free list because
8267 // it was created when two or more free chunks where coalesced into
8268 // this free chunk.
8269 //
8270 // These statistics are used to determine the desired number of free
8271 // chunks of a given size. The desired number is chosen to be relative
8272 // to the end of a CMS sweep. The desired number at the end of a sweep
8273 // is the
8274 // count-at-end-of-previous-sweep (an amount that was enough)
8275 // - count-at-beginning-of-current-sweep (the excess)
8276 // + split-births (gains in this size during interval)
8277 // - split-deaths (demands on this size during interval)
8278 // where the interval is from the end of one sweep to the end of the
8279 // next.
8280 //
8281 // When sweeping the sweeper maintains an accumulated chunk which is
8282 // the chunk that is made up of chunks that have been coalesced. That
8283 // will be termed the left-hand chunk. A new chunk of garbage that
8284 // is being considered for coalescing will be referred to as the
8285 // right-hand chunk.
8286 //
8287 // When making a decision on whether to coalesce a right-hand chunk with
8288 // the current left-hand chunk, the current count vs. the desired count
8289 // of the left-hand chunk is considered. Also if the right-hand chunk
8290 // is near the large chunk at the end of the heap (see
8291 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8292 // left-hand chunk is coalesced.
8293 //
8294 // When making a decision about whether to split a chunk, the desired count
8295 // vs. the current count of the candidate to be split is also considered.
8296 // If the candidate is underpopulated (currently fewer chunks than desired)
8297 // a chunk of an overpopulated (currently more chunks than desired) size may
8298 // be chosen. The "hint" associated with a free list, if non-null, points
8299 // to a free list which may be overpopulated.
8300 //
8301
8302 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8303 const size_t size = fc->size();
8304 // Chunks that cannot be coalesced are not in the
8305 // free lists.
8306 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8307 assert(_sp->verify_chunk_in_free_list(fc),
8308 "free chunk should be in free lists");
8309 }
8310 // a chunk that is already free, should not have been
8311 // marked in the bit map
8312 HeapWord* const addr = (HeapWord*) fc;
8313 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8314 // Verify that the bit map has no bits marked between
8315 // addr and purported end of this block.
8316 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8317
8318 // Some chunks cannot be coalesced under any circumstances.
8319 // See the definition of cantCoalesce().
8320 if (!fc->cantCoalesce()) {
8321 // This chunk can potentially be coalesced.
8322 if (_sp->adaptive_freelists()) {
8323 // All the work is done in
8324 do_post_free_or_garbage_chunk(fc, size);
8325 } else { // Not adaptive free lists
8326 // this is a free chunk that can potentially be coalesced by the sweeper;
8327 if (!inFreeRange()) {
8328 // if the next chunk is a free block that can't be coalesced
8329 // it doesn't make sense to remove this chunk from the free lists
8330 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8331 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8332 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8333 nextChunk->is_free() && // ... which is free...
8334 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8335 // nothing to do
8336 } else {
8337 // Potentially the start of a new free range:
8338 // Don't eagerly remove it from the free lists.
8339 // No need to remove it if it will just be put
8340 // back again. (Also from a pragmatic point of view
8341 // if it is a free block in a region that is beyond
8342 // any allocated blocks, an assertion will fail)
8343 // Remember the start of a free run.
8344 initialize_free_range(addr, true);
8345 // end - can coalesce with next chunk
8346 }
8347 } else {
8348 // the midst of a free range, we are coalescing
8349 print_free_block_coalesced(fc);
8350 if (CMSTraceSweeper) {
8351 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
8352 }
8353 // remove it from the free lists
8354 _sp->removeFreeChunkFromFreeLists(fc);
8355 set_lastFreeRangeCoalesced(true);
8356 // If the chunk is being coalesced and the current free range is
8357 // in the free lists, remove the current free range so that it
8358 // will be returned to the free lists in its entirety - all
8359 // the coalesced pieces included.
8360 if (freeRangeInFreeLists()) {
8361 FreeChunk* ffc = (FreeChunk*) freeFinger();
8362 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8363 "Size of free range is inconsistent with chunk size.");
8364 if (CMSTestInFreeList) {
8365 assert(_sp->verify_chunk_in_free_list(ffc),
8366 "free range is not in free lists");
8367 }
8368 _sp->removeFreeChunkFromFreeLists(ffc);
8369 set_freeRangeInFreeLists(false);
8370 }
8371 }
8372 }
8373 // Note that if the chunk is not coalescable (the else arm
8374 // below), we unconditionally flush, without needing to do
8375 // a "lookahead," as we do below.
8376 if (inFreeRange()) lookahead_and_flush(fc, size);
8377 } else {
8378 // Code path common to both original and adaptive free lists.
8379
8380 // cant coalesce with previous block; this should be treated
8381 // as the end of a free run if any
8382 if (inFreeRange()) {
8383 // we kicked some butt; time to pick up the garbage
8384 assert(freeFinger() < addr, "freeFinger points too high");
8385 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8386 }
8387 // else, nothing to do, just continue
8388 }
8389 }
8390
8391 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8392 // This is a chunk of garbage. It is not in any free list.
8393 // Add it to a free list or let it possibly be coalesced into
8394 // a larger chunk.
8395 HeapWord* const addr = (HeapWord*) fc;
8396 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8397
8398 if (_sp->adaptive_freelists()) {
8399 // Verify that the bit map has no bits marked between
8400 // addr and purported end of just dead object.
8401 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8402
8403 do_post_free_or_garbage_chunk(fc, size);
8404 } else {
8405 if (!inFreeRange()) {
8406 // start of a new free range
8407 assert(size > 0, "A free range should have a size");
8408 initialize_free_range(addr, false);
8409 } else {
8410 // this will be swept up when we hit the end of the
8411 // free range
8412 if (CMSTraceSweeper) {
8413 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
8414 }
8415 // If the chunk is being coalesced and the current free range is
8416 // in the free lists, remove the current free range so that it
8417 // will be returned to the free lists in its entirety - all
8418 // the coalesced pieces included.
8419 if (freeRangeInFreeLists()) {
8420 FreeChunk* ffc = (FreeChunk*)freeFinger();
8421 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8422 "Size of free range is inconsistent with chunk size.");
8423 if (CMSTestInFreeList) {
8424 assert(_sp->verify_chunk_in_free_list(ffc),
8425 "free range is not in free lists");
8426 }
8427 _sp->removeFreeChunkFromFreeLists(ffc);
8428 set_freeRangeInFreeLists(false);
8429 }
8430 set_lastFreeRangeCoalesced(true);
8431 }
8432 // this will be swept up when we hit the end of the free range
8433
8434 // Verify that the bit map has no bits marked between
8435 // addr and purported end of just dead object.
8436 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8437 }
8438 assert(_limit >= addr + size,
8439 "A freshly garbage chunk can't possibly straddle over _limit");
8440 if (inFreeRange()) lookahead_and_flush(fc, size);
8441 return size;
8442 }
8443
8444 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8445 HeapWord* addr = (HeapWord*) fc;
8446 // The sweeper has just found a live object. Return any accumulated
8447 // left hand chunk to the free lists.
8448 if (inFreeRange()) {
8449 assert(freeFinger() < addr, "freeFinger points too high");
8450 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8451 }
8452
8453 // This object is live: we'd normally expect this to be
8454 // an oop, and like to assert the following:
8455 // assert(oop(addr)->is_oop(), "live block should be an oop");
8456 // However, as we commented above, this may be an object whose
8457 // header hasn't yet been initialized.
8458 size_t size;
8459 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8460 if (_bitMap->isMarked(addr + 1)) {
8461 // Determine the size from the bit map, rather than trying to
8462 // compute it from the object header.
8463 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8464 size = pointer_delta(nextOneAddr + 1, addr);
8465 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8466 "alignment problem");
8467
8468 #ifdef ASSERT
8469 if (oop(addr)->klass_or_null() != NULL) {
8470 // Ignore mark word because we are running concurrent with mutators
8471 assert(oop(addr)->is_oop(true), "live block should be an oop");
8472 assert(size ==
8473 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8474 "P-mark and computed size do not agree");
8475 }
8476 #endif
8477
8478 } else {
8479 // This should be an initialized object that's alive.
8480 assert(oop(addr)->klass_or_null() != NULL,
8481 "Should be an initialized object");
8482 // Ignore mark word because we are running concurrent with mutators
8483 assert(oop(addr)->is_oop(true), "live block should be an oop");
8484 // Verify that the bit map has no bits marked between
8485 // addr and purported end of this block.
8486 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8487 assert(size >= 3, "Necessary for Printezis marks to work");
8488 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8489 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8490 }
8491 return size;
8492 }
8493
8494 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8495 size_t chunkSize) {
8496 // do_post_free_or_garbage_chunk() should only be called in the case
8497 // of the adaptive free list allocator.
8498 const bool fcInFreeLists = fc->is_free();
8499 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8500 assert((HeapWord*)fc <= _limit, "sweep invariant");
8501 if (CMSTestInFreeList && fcInFreeLists) {
8502 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8503 }
8504
8505 if (CMSTraceSweeper) {
8506 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", fc, chunkSize);
8507 }
8508
8509 HeapWord* const fc_addr = (HeapWord*) fc;
8510
8511 bool coalesce;
8512 const size_t left = pointer_delta(fc_addr, freeFinger());
8513 const size_t right = chunkSize;
8514 switch (FLSCoalescePolicy) {
8515 // numeric value forms a coalition aggressiveness metric
8516 case 0: { // never coalesce
8517 coalesce = false;
8518 break;
8519 }
8520 case 1: { // coalesce if left & right chunks on overpopulated lists
8521 coalesce = _sp->coalOverPopulated(left) &&
8522 _sp->coalOverPopulated(right);
8523 break;
8524 }
8525 case 2: { // coalesce if left chunk on overpopulated list (default)
8526 coalesce = _sp->coalOverPopulated(left);
8527 break;
8528 }
8529 case 3: { // coalesce if left OR right chunk on overpopulated list
8530 coalesce = _sp->coalOverPopulated(left) ||
8531 _sp->coalOverPopulated(right);
8532 break;
8533 }
8534 case 4: { // always coalesce
8535 coalesce = true;
8536 break;
8537 }
8538 default:
8539 ShouldNotReachHere();
8540 }
8541
8542 // Should the current free range be coalesced?
8543 // If the chunk is in a free range and either we decided to coalesce above
8544 // or the chunk is near the large block at the end of the heap
8545 // (isNearLargestChunk() returns true), then coalesce this chunk.
8546 const bool doCoalesce = inFreeRange()
8547 && (coalesce || _g->isNearLargestChunk(fc_addr));
8548 if (doCoalesce) {
8549 // Coalesce the current free range on the left with the new
8550 // chunk on the right. If either is on a free list,
8551 // it must be removed from the list and stashed in the closure.
8552 if (freeRangeInFreeLists()) {
8553 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8554 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8555 "Size of free range is inconsistent with chunk size.");
8556 if (CMSTestInFreeList) {
8557 assert(_sp->verify_chunk_in_free_list(ffc),
8558 "Chunk is not in free lists");
8559 }
8560 _sp->coalDeath(ffc->size());
8561 _sp->removeFreeChunkFromFreeLists(ffc);
8562 set_freeRangeInFreeLists(false);
8563 }
8564 if (fcInFreeLists) {
8565 _sp->coalDeath(chunkSize);
8566 assert(fc->size() == chunkSize,
8567 "The chunk has the wrong size or is not in the free lists");
8568 _sp->removeFreeChunkFromFreeLists(fc);
8569 }
8570 set_lastFreeRangeCoalesced(true);
8571 print_free_block_coalesced(fc);
8572 } else { // not in a free range and/or should not coalesce
8573 // Return the current free range and start a new one.
8574 if (inFreeRange()) {
8575 // In a free range but cannot coalesce with the right hand chunk.
8576 // Put the current free range into the free lists.
8577 flush_cur_free_chunk(freeFinger(),
8578 pointer_delta(fc_addr, freeFinger()));
8579 }
8580 // Set up for new free range. Pass along whether the right hand
8581 // chunk is in the free lists.
8582 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8583 }
8584 }
8585
8586 // Lookahead flush:
8587 // If we are tracking a free range, and this is the last chunk that
8588 // we'll look at because its end crosses past _limit, we'll preemptively
8589 // flush it along with any free range we may be holding on to. Note that
8590 // this can be the case only for an already free or freshly garbage
8591 // chunk. If this block is an object, it can never straddle
8592 // over _limit. The "straddling" occurs when _limit is set at
8593 // the previous end of the space when this cycle started, and
8594 // a subsequent heap expansion caused the previously co-terminal
8595 // free block to be coalesced with the newly expanded portion,
8596 // thus rendering _limit a non-block-boundary making it dangerous
8597 // for the sweeper to step over and examine.
8598 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8599 assert(inFreeRange(), "Should only be called if currently in a free range.");
8600 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8601 assert(_sp->used_region().contains(eob - 1),
8602 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
8603 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8604 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8605 eob, eob-1, _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8606 if (eob >= _limit) {
8607 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8608 if (CMSTraceSweeper) {
8609 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8610 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8611 "[" PTR_FORMAT "," PTR_FORMAT ")",
8612 _limit, fc, eob, _sp->bottom(), _sp->end());
8613 }
8614 // Return the storage we are tracking back into the free lists.
8615 if (CMSTraceSweeper) {
8616 gclog_or_tty->print_cr("Flushing ... ");
8617 }
8618 assert(freeFinger() < eob, "Error");
8619 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8620 }
8621 }
8622
8623 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8624 assert(inFreeRange(), "Should only be called if currently in a free range.");
8625 assert(size > 0,
8626 "A zero sized chunk cannot be added to the free lists.");
8627 if (!freeRangeInFreeLists()) {
8628 if (CMSTestInFreeList) {
8629 FreeChunk* fc = (FreeChunk*) chunk;
8630 fc->set_size(size);
8631 assert(!_sp->verify_chunk_in_free_list(fc),
8632 "chunk should not be in free lists yet");
8633 }
8634 if (CMSTraceSweeper) {
8635 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
8636 chunk, size);
8637 }
8638 // A new free range is going to be starting. The current
8639 // free range has not been added to the free lists yet or
8640 // was removed so add it back.
8641 // If the current free range was coalesced, then the death
8642 // of the free range was recorded. Record a birth now.
8643 if (lastFreeRangeCoalesced()) {
8644 _sp->coalBirth(size);
8645 }
8646 _sp->addChunkAndRepairOffsetTable(chunk, size,
8647 lastFreeRangeCoalesced());
8648 } else if (CMSTraceSweeper) {
8649 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8650 }
8651 set_inFreeRange(false);
8652 set_freeRangeInFreeLists(false);
8653 }
8654
8655 // We take a break if we've been at this for a while,
8656 // so as to avoid monopolizing the locks involved.
8657 void SweepClosure::do_yield_work(HeapWord* addr) {
8658 // Return current free chunk being used for coalescing (if any)
8659 // to the appropriate freelist. After yielding, the next
8660 // free block encountered will start a coalescing range of
8661 // free blocks. If the next free block is adjacent to the
8662 // chunk just flushed, they will need to wait for the next
8663 // sweep to be coalesced.
8664 if (inFreeRange()) {
8665 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8666 }
8667
8668 // First give up the locks, then yield, then re-lock.
8669 // We should probably use a constructor/destructor idiom to
8670 // do this unlock/lock or modify the MutexUnlocker class to
8671 // serve our purpose. XXX
8672 assert_lock_strong(_bitMap->lock());
8673 assert_lock_strong(_freelistLock);
8674 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8675 "CMS thread should hold CMS token");
8676 _bitMap->lock()->unlock();
8677 _freelistLock->unlock();
8678 ConcurrentMarkSweepThread::desynchronize(true);
8679 ConcurrentMarkSweepThread::acknowledge_yield_request();
8680 _collector->stopTimer();
8681 if (PrintCMSStatistics != 0) {
8682 _collector->incrementYields();
8683 }
8684 _collector->icms_wait();
8685
8686 // See the comment in coordinator_yield()
8687 for (unsigned i = 0; i < CMSYieldSleepCount &&
8688 ConcurrentMarkSweepThread::should_yield() &&
8689 !CMSCollector::foregroundGCIsActive(); ++i) {
8690 os::sleep(Thread::current(), 1, false);
8691 ConcurrentMarkSweepThread::acknowledge_yield_request();
8692 }
8693
8694 ConcurrentMarkSweepThread::synchronize(true);
8695 _freelistLock->lock();
8696 _bitMap->lock()->lock_without_safepoint_check();
8697 _collector->startTimer();
8698 }
8699
8700 #ifndef PRODUCT
8701 // This is actually very useful in a product build if it can
8702 // be called from the debugger. Compile it into the product
8703 // as needed.
8704 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8705 return debug_cms_space->verify_chunk_in_free_list(fc);
8706 }
8707 #endif
8708
8709 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8710 if (CMSTraceSweeper) {
8711 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8712 fc, fc->size());
8713 }
8714 }
8715
8716 // CMSIsAliveClosure
8717 bool CMSIsAliveClosure::do_object_b(oop obj) {
8718 HeapWord* addr = (HeapWord*)obj;
8719 return addr != NULL &&
8720 (!_span.contains(addr) || _bit_map->isMarked(addr));
8721 }
8722
8723
8724 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8725 MemRegion span,
8726 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8727 bool cpc):
8728 _collector(collector),
8729 _span(span),
8730 _bit_map(bit_map),
8731 _mark_stack(mark_stack),
8732 _concurrent_precleaning(cpc) {
8733 assert(!_span.is_empty(), "Empty span could spell trouble");
8734 }
8735
8736
8737 // CMSKeepAliveClosure: the serial version
8738 void CMSKeepAliveClosure::do_oop(oop obj) {
8739 HeapWord* addr = (HeapWord*)obj;
8740 if (_span.contains(addr) &&
8741 !_bit_map->isMarked(addr)) {
8742 _bit_map->mark(addr);
8743 bool simulate_overflow = false;
8744 NOT_PRODUCT(
8745 if (CMSMarkStackOverflowALot &&
8746 _collector->simulate_overflow()) {
8747 // simulate a stack overflow
8748 simulate_overflow = true;
8749 }
8750 )
8751 if (simulate_overflow || !_mark_stack->push(obj)) {
8752 if (_concurrent_precleaning) {
8753 // We dirty the overflown object and let the remark
8754 // phase deal with it.
8755 assert(_collector->overflow_list_is_empty(), "Error");
8756 // In the case of object arrays, we need to dirty all of
8757 // the cards that the object spans. No locking or atomics
8758 // are needed since no one else can be mutating the mod union
8759 // table.
8760 if (obj->is_objArray()) {
8761 size_t sz = obj->size();
8762 HeapWord* end_card_addr =
8763 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8764 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8765 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8766 _collector->_modUnionTable.mark_range(redirty_range);
8767 } else {
8768 _collector->_modUnionTable.mark(addr);
8769 }
8770 _collector->_ser_kac_preclean_ovflw++;
8771 } else {
8772 _collector->push_on_overflow_list(obj);
8773 _collector->_ser_kac_ovflw++;
8774 }
8775 }
8776 }
8777 }
8778
8779 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8780 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8781
8782 // CMSParKeepAliveClosure: a parallel version of the above.
8783 // The work queues are private to each closure (thread),
8784 // but (may be) available for stealing by other threads.
8785 void CMSParKeepAliveClosure::do_oop(oop obj) {
8786 HeapWord* addr = (HeapWord*)obj;
8787 if (_span.contains(addr) &&
8788 !_bit_map->isMarked(addr)) {
8789 // In general, during recursive tracing, several threads
8790 // may be concurrently getting here; the first one to
8791 // "tag" it, claims it.
8792 if (_bit_map->par_mark(addr)) {
8793 bool res = _work_queue->push(obj);
8794 assert(res, "Low water mark should be much less than capacity");
8795 // Do a recursive trim in the hope that this will keep
8796 // stack usage lower, but leave some oops for potential stealers
8797 trim_queue(_low_water_mark);
8798 } // Else, another thread got there first
8799 }
8800 }
8801
8802 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8803 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8804
8805 void CMSParKeepAliveClosure::trim_queue(uint max) {
8806 while (_work_queue->size() > max) {
8807 oop new_oop;
8808 if (_work_queue->pop_local(new_oop)) {
8809 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8810 assert(_bit_map->isMarked((HeapWord*)new_oop),
8811 "no white objects on this stack!");
8812 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8813 // iterate over the oops in this oop, marking and pushing
8814 // the ones in CMS heap (i.e. in _span).
8815 new_oop->oop_iterate(&_mark_and_push);
8816 }
8817 }
8818 }
8819
8820 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8821 CMSCollector* collector,
8822 MemRegion span, CMSBitMap* bit_map,
8823 OopTaskQueue* work_queue):
8824 _collector(collector),
8825 _span(span),
8826 _bit_map(bit_map),
8827 _work_queue(work_queue) { }
8828
8829 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8830 HeapWord* addr = (HeapWord*)obj;
8831 if (_span.contains(addr) &&
8832 !_bit_map->isMarked(addr)) {
8833 if (_bit_map->par_mark(addr)) {
8834 bool simulate_overflow = false;
8835 NOT_PRODUCT(
8836 if (CMSMarkStackOverflowALot &&
8837 _collector->par_simulate_overflow()) {
8838 // simulate a stack overflow
8839 simulate_overflow = true;
8840 }
8841 )
8842 if (simulate_overflow || !_work_queue->push(obj)) {
8843 _collector->par_push_on_overflow_list(obj);
8844 _collector->_par_kac_ovflw++;
8845 }
8846 } // Else another thread got there already
8847 }
8848 }
8849
8850 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8851 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8852
8853 //////////////////////////////////////////////////////////////////
8854 // CMSExpansionCause /////////////////////////////
8855 //////////////////////////////////////////////////////////////////
8856 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8857 switch (cause) {
8858 case _no_expansion:
8859 return "No expansion";
8860 case _satisfy_free_ratio:
8861 return "Free ratio";
8862 case _satisfy_promotion:
8863 return "Satisfy promotion";
8864 case _satisfy_allocation:
8865 return "allocation";
8866 case _allocate_par_lab:
8867 return "Par LAB";
8868 case _allocate_par_spooling_space:
8869 return "Par Spooling Space";
8870 case _adaptive_size_policy:
8871 return "Ergonomics";
8872 default:
8873 return "unknown";
8874 }
8875 }
8876
8877 void CMSDrainMarkingStackClosure::do_void() {
8878 // the max number to take from overflow list at a time
8879 const size_t num = _mark_stack->capacity()/4;
8880 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8881 "Overflow list should be NULL during concurrent phases");
8882 while (!_mark_stack->isEmpty() ||
8883 // if stack is empty, check the overflow list
8884 _collector->take_from_overflow_list(num, _mark_stack)) {
8885 oop obj = _mark_stack->pop();
8886 HeapWord* addr = (HeapWord*)obj;
8887 assert(_span.contains(addr), "Should be within span");
8888 assert(_bit_map->isMarked(addr), "Should be marked");
8889 assert(obj->is_oop(), "Should be an oop");
8890 obj->oop_iterate(_keep_alive);
8891 }
8892 }
8893
8894 void CMSParDrainMarkingStackClosure::do_void() {
8895 // drain queue
8896 trim_queue(0);
8897 }
8898
8899 // Trim our work_queue so its length is below max at return
8900 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8901 while (_work_queue->size() > max) {
8902 oop new_oop;
8903 if (_work_queue->pop_local(new_oop)) {
8904 assert(new_oop->is_oop(), "Expected an oop");
8905 assert(_bit_map->isMarked((HeapWord*)new_oop),
8906 "no white objects on this stack!");
8907 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8908 // iterate over the oops in this oop, marking and pushing
8909 // the ones in CMS heap (i.e. in _span).
8910 new_oop->oop_iterate(&_mark_and_push);
8911 }
8912 }
8913 }
8914
8915 ////////////////////////////////////////////////////////////////////
8916 // Support for Marking Stack Overflow list handling and related code
8917 ////////////////////////////////////////////////////////////////////
8918 // Much of the following code is similar in shape and spirit to the
8919 // code used in ParNewGC. We should try and share that code
8920 // as much as possible in the future.
8921
8922 #ifndef PRODUCT
8923 // Debugging support for CMSStackOverflowALot
8924
8925 // It's OK to call this multi-threaded; the worst thing
8926 // that can happen is that we'll get a bunch of closely
8927 // spaced simulated overflows, but that's OK, in fact
8928 // probably good as it would exercise the overflow code
8929 // under contention.
8930 bool CMSCollector::simulate_overflow() {
8931 if (_overflow_counter-- <= 0) { // just being defensive
8932 _overflow_counter = CMSMarkStackOverflowInterval;
8933 return true;
8934 } else {
8935 return false;
8936 }
8937 }
8938
8939 bool CMSCollector::par_simulate_overflow() {
8940 return simulate_overflow();
8941 }
8942 #endif
8943
8944 // Single-threaded
8945 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8946 assert(stack->isEmpty(), "Expected precondition");
8947 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8948 size_t i = num;
8949 oop cur = _overflow_list;
8950 const markOop proto = markOopDesc::prototype();
8951 NOT_PRODUCT(ssize_t n = 0;)
8952 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8953 next = oop(cur->mark());
8954 cur->set_mark(proto); // until proven otherwise
8955 assert(cur->is_oop(), "Should be an oop");
8956 bool res = stack->push(cur);
8957 assert(res, "Bit off more than can chew?");
8958 NOT_PRODUCT(n++;)
8959 }
8960 _overflow_list = cur;
8961 #ifndef PRODUCT
8962 assert(_num_par_pushes >= n, "Too many pops?");
8963 _num_par_pushes -=n;
8964 #endif
8965 return !stack->isEmpty();
8966 }
8967
8968 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8969 // (MT-safe) Get a prefix of at most "num" from the list.
8970 // The overflow list is chained through the mark word of
8971 // each object in the list. We fetch the entire list,
8972 // break off a prefix of the right size and return the
8973 // remainder. If other threads try to take objects from
8974 // the overflow list at that time, they will wait for
8975 // some time to see if data becomes available. If (and
8976 // only if) another thread places one or more object(s)
8977 // on the global list before we have returned the suffix
8978 // to the global list, we will walk down our local list
8979 // to find its end and append the global list to
8980 // our suffix before returning it. This suffix walk can
8981 // prove to be expensive (quadratic in the amount of traffic)
8982 // when there are many objects in the overflow list and
8983 // there is much producer-consumer contention on the list.
8984 // *NOTE*: The overflow list manipulation code here and
8985 // in ParNewGeneration:: are very similar in shape,
8986 // except that in the ParNew case we use the old (from/eden)
8987 // copy of the object to thread the list via its klass word.
8988 // Because of the common code, if you make any changes in
8989 // the code below, please check the ParNew version to see if
8990 // similar changes might be needed.
8991 // CR 6797058 has been filed to consolidate the common code.
8992 bool CMSCollector::par_take_from_overflow_list(size_t num,
8993 OopTaskQueue* work_q,
8994 int no_of_gc_threads) {
8995 assert(work_q->size() == 0, "First empty local work queue");
8996 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8997 if (_overflow_list == NULL) {
8998 return false;
8999 }
9000 // Grab the entire list; we'll put back a suffix
9001 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9002 Thread* tid = Thread::current();
9003 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
9004 // set to ParallelGCThreads.
9005 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
9006 size_t sleep_time_millis = MAX2((size_t)1, num/100);
9007 // If the list is busy, we spin for a short while,
9008 // sleeping between attempts to get the list.
9009 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
9010 os::sleep(tid, sleep_time_millis, false);
9011 if (_overflow_list == NULL) {
9012 // Nothing left to take
9013 return false;
9014 } else if (_overflow_list != BUSY) {
9015 // Try and grab the prefix
9016 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9017 }
9018 }
9019 // If the list was found to be empty, or we spun long
9020 // enough, we give up and return empty-handed. If we leave
9021 // the list in the BUSY state below, it must be the case that
9022 // some other thread holds the overflow list and will set it
9023 // to a non-BUSY state in the future.
9024 if (prefix == NULL || prefix == BUSY) {
9025 // Nothing to take or waited long enough
9026 if (prefix == NULL) {
9027 // Write back the NULL in case we overwrote it with BUSY above
9028 // and it is still the same value.
9029 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9030 }
9031 return false;
9032 }
9033 assert(prefix != NULL && prefix != BUSY, "Error");
9034 size_t i = num;
9035 oop cur = prefix;
9036 // Walk down the first "num" objects, unless we reach the end.
9037 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
9038 if (cur->mark() == NULL) {
9039 // We have "num" or fewer elements in the list, so there
9040 // is nothing to return to the global list.
9041 // Write back the NULL in lieu of the BUSY we wrote
9042 // above, if it is still the same value.
9043 if (_overflow_list == BUSY) {
9044 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9045 }
9046 } else {
9047 // Chop off the suffix and return it to the global list.
9048 assert(cur->mark() != BUSY, "Error");
9049 oop suffix_head = cur->mark(); // suffix will be put back on global list
9050 cur->set_mark(NULL); // break off suffix
9051 // It's possible that the list is still in the empty(busy) state
9052 // we left it in a short while ago; in that case we may be
9053 // able to place back the suffix without incurring the cost
9054 // of a walk down the list.
9055 oop observed_overflow_list = _overflow_list;
9056 oop cur_overflow_list = observed_overflow_list;
9057 bool attached = false;
9058 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
9059 observed_overflow_list =
9060 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9061 if (cur_overflow_list == observed_overflow_list) {
9062 attached = true;
9063 break;
9064 } else cur_overflow_list = observed_overflow_list;
9065 }
9066 if (!attached) {
9067 // Too bad, someone else sneaked in (at least) an element; we'll need
9068 // to do a splice. Find tail of suffix so we can prepend suffix to global
9069 // list.
9070 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
9071 oop suffix_tail = cur;
9072 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
9073 "Tautology");
9074 observed_overflow_list = _overflow_list;
9075 do {
9076 cur_overflow_list = observed_overflow_list;
9077 if (cur_overflow_list != BUSY) {
9078 // Do the splice ...
9079 suffix_tail->set_mark(markOop(cur_overflow_list));
9080 } else { // cur_overflow_list == BUSY
9081 suffix_tail->set_mark(NULL);
9082 }
9083 // ... and try to place spliced list back on overflow_list ...
9084 observed_overflow_list =
9085 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9086 } while (cur_overflow_list != observed_overflow_list);
9087 // ... until we have succeeded in doing so.
9088 }
9089 }
9090
9091 // Push the prefix elements on work_q
9092 assert(prefix != NULL, "control point invariant");
9093 const markOop proto = markOopDesc::prototype();
9094 oop next;
9095 NOT_PRODUCT(ssize_t n = 0;)
9096 for (cur = prefix; cur != NULL; cur = next) {
9097 next = oop(cur->mark());
9098 cur->set_mark(proto); // until proven otherwise
9099 assert(cur->is_oop(), "Should be an oop");
9100 bool res = work_q->push(cur);
9101 assert(res, "Bit off more than we can chew?");
9102 NOT_PRODUCT(n++;)
9103 }
9104 #ifndef PRODUCT
9105 assert(_num_par_pushes >= n, "Too many pops?");
9106 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
9107 #endif
9108 return true;
9109 }
9110
9111 // Single-threaded
9112 void CMSCollector::push_on_overflow_list(oop p) {
9113 NOT_PRODUCT(_num_par_pushes++;)
9114 assert(p->is_oop(), "Not an oop");
9115 preserve_mark_if_necessary(p);
9116 p->set_mark((markOop)_overflow_list);
9117 _overflow_list = p;
9118 }
9119
9120 // Multi-threaded; use CAS to prepend to overflow list
9121 void CMSCollector::par_push_on_overflow_list(oop p) {
9122 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
9123 assert(p->is_oop(), "Not an oop");
9124 par_preserve_mark_if_necessary(p);
9125 oop observed_overflow_list = _overflow_list;
9126 oop cur_overflow_list;
9127 do {
9128 cur_overflow_list = observed_overflow_list;
9129 if (cur_overflow_list != BUSY) {
9130 p->set_mark(markOop(cur_overflow_list));
9131 } else {
9132 p->set_mark(NULL);
9133 }
9134 observed_overflow_list =
9135 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
9136 } while (cur_overflow_list != observed_overflow_list);
9137 }
9138 #undef BUSY
9139
9140 // Single threaded
9141 // General Note on GrowableArray: pushes may silently fail
9142 // because we are (temporarily) out of C-heap for expanding
9143 // the stack. The problem is quite ubiquitous and affects
9144 // a lot of code in the JVM. The prudent thing for GrowableArray
9145 // to do (for now) is to exit with an error. However, that may
9146 // be too draconian in some cases because the caller may be
9147 // able to recover without much harm. For such cases, we
9148 // should probably introduce a "soft_push" method which returns
9149 // an indication of success or failure with the assumption that
9150 // the caller may be able to recover from a failure; code in
9151 // the VM can then be changed, incrementally, to deal with such
9152 // failures where possible, thus, incrementally hardening the VM
9153 // in such low resource situations.
9154 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9155 _preserved_oop_stack.push(p);
9156 _preserved_mark_stack.push(m);
9157 assert(m == p->mark(), "Mark word changed");
9158 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9159 "bijection");
9160 }
9161
9162 // Single threaded
9163 void CMSCollector::preserve_mark_if_necessary(oop p) {
9164 markOop m = p->mark();
9165 if (m->must_be_preserved(p)) {
9166 preserve_mark_work(p, m);
9167 }
9168 }
9169
9170 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9171 markOop m = p->mark();
9172 if (m->must_be_preserved(p)) {
9173 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9174 // Even though we read the mark word without holding
9175 // the lock, we are assured that it will not change
9176 // because we "own" this oop, so no other thread can
9177 // be trying to push it on the overflow list; see
9178 // the assertion in preserve_mark_work() that checks
9179 // that m == p->mark().
9180 preserve_mark_work(p, m);
9181 }
9182 }
9183
9184 // We should be able to do this multi-threaded,
9185 // a chunk of stack being a task (this is
9186 // correct because each oop only ever appears
9187 // once in the overflow list. However, it's
9188 // not very easy to completely overlap this with
9189 // other operations, so will generally not be done
9190 // until all work's been completed. Because we
9191 // expect the preserved oop stack (set) to be small,
9192 // it's probably fine to do this single-threaded.
9193 // We can explore cleverer concurrent/overlapped/parallel
9194 // processing of preserved marks if we feel the
9195 // need for this in the future. Stack overflow should
9196 // be so rare in practice and, when it happens, its
9197 // effect on performance so great that this will
9198 // likely just be in the noise anyway.
9199 void CMSCollector::restore_preserved_marks_if_any() {
9200 assert(SafepointSynchronize::is_at_safepoint(),
9201 "world should be stopped");
9202 assert(Thread::current()->is_ConcurrentGC_thread() ||
9203 Thread::current()->is_VM_thread(),
9204 "should be single-threaded");
9205 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9206 "bijection");
9207
9208 while (!_preserved_oop_stack.is_empty()) {
9209 oop p = _preserved_oop_stack.pop();
9210 assert(p->is_oop(), "Should be an oop");
9211 assert(_span.contains(p), "oop should be in _span");
9212 assert(p->mark() == markOopDesc::prototype(),
9213 "Set when taken from overflow list");
9214 markOop m = _preserved_mark_stack.pop();
9215 p->set_mark(m);
9216 }
9217 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9218 "stacks were cleared above");
9219 }
9220
9221 #ifndef PRODUCT
9222 bool CMSCollector::no_preserved_marks() const {
9223 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9224 }
9225 #endif
9226
9227 // Transfer some number of overflown objects to usual marking
9228 // stack. Return true if some objects were transferred.
9229 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9230 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9231 (size_t)ParGCDesiredObjsFromOverflowList);
9232
9233 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9234 assert(_collector->overflow_list_is_empty() || res,
9235 "If list is not empty, we should have taken something");
9236 assert(!res || !_mark_stack->isEmpty(),
9237 "If we took something, it should now be on our stack");
9238 return res;
9239 }
9240
9241 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9242 size_t res = _sp->block_size_no_stall(addr, _collector);
9243 if (_sp->block_is_obj(addr)) {
9244 if (_live_bit_map->isMarked(addr)) {
9245 // It can't have been dead in a previous cycle
9246 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9247 } else {
9248 _dead_bit_map->mark(addr); // mark the dead object
9249 }
9250 }
9251 // Could be 0, if the block size could not be computed without stalling.
9252 return res;
9253 }
9254
9255 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9256
9257 switch (phase) {
9258 case CMSCollector::InitialMarking:
9259 initialize(true /* fullGC */ ,
9260 cause /* cause of the GC */,
9261 true /* recordGCBeginTime */,
9262 true /* recordPreGCUsage */,
9263 false /* recordPeakUsage */,
9264 false /* recordPostGCusage */,
9265 true /* recordAccumulatedGCTime */,
9266 false /* recordGCEndTime */,
9267 false /* countCollection */ );
9268 break;
9269
9270 case CMSCollector::FinalMarking:
9271 initialize(true /* fullGC */ ,
9272 cause /* cause of the GC */,
9273 false /* recordGCBeginTime */,
9274 false /* recordPreGCUsage */,
9275 false /* recordPeakUsage */,
9276 false /* recordPostGCusage */,
9277 true /* recordAccumulatedGCTime */,
9278 false /* recordGCEndTime */,
9279 false /* countCollection */ );
9280 break;
9281
9282 case CMSCollector::Sweeping:
9283 initialize(true /* fullGC */ ,
9284 cause /* cause of the GC */,
9285 false /* recordGCBeginTime */,
9286 false /* recordPreGCUsage */,
9287 true /* recordPeakUsage */,
9288 true /* recordPostGCusage */,
9289 false /* recordAccumulatedGCTime */,
9290 true /* recordGCEndTime */,
9291 true /* countCollection */ );
9292 break;
9293
9294 default:
9295 ShouldNotReachHere();
9296 }
9297 }