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