1 /*
2 * Copyright (c) 2001, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/symbolTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc_implementation/concurrentMarkSweep/cmsAdaptiveSizePolicy.hpp"
31 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
32 #include "gc_implementation/concurrentMarkSweep/cmsGCAdaptivePolicyCounters.hpp"
33 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
34 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
36 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
37 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
38 #include "gc_implementation/parNew/parNewGeneration.hpp"
39 #include "gc_implementation/shared/collectorCounters.hpp"
40 #include "gc_implementation/shared/isGCActiveMark.hpp"
41 #include "gc_interface/collectedHeap.inline.hpp"
42 #include "memory/cardTableRS.hpp"
43 #include "memory/collectorPolicy.hpp"
44 #include "memory/gcLocker.inline.hpp"
45 #include "memory/genCollectedHeap.hpp"
46 #include "memory/genMarkSweep.hpp"
47 #include "memory/genOopClosures.inline.hpp"
48 #include "memory/iterator.hpp"
49 #include "memory/referencePolicy.hpp"
50 #include "memory/resourceArea.hpp"
51 #include "memory/tenuredGeneration.hpp"
52 #include "oops/oop.inline.hpp"
53 #include "prims/jvmtiExport.hpp"
54 #include "runtime/globals_extension.hpp"
55 #include "runtime/handles.inline.hpp"
56 #include "runtime/java.hpp"
57 #include "runtime/vmThread.hpp"
58 #include "services/memoryService.hpp"
59 #include "services/runtimeService.hpp"
60
61 // statics
62 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
63 bool CMSCollector::_full_gc_requested = false;
64
65 //////////////////////////////////////////////////////////////////
66 // In support of CMS/VM thread synchronization
67 //////////////////////////////////////////////////////////////////
68 // We split use of the CGC_lock into 2 "levels".
69 // The low-level locking is of the usual CGC_lock monitor. We introduce
70 // a higher level "token" (hereafter "CMS token") built on top of the
71 // low level monitor (hereafter "CGC lock").
72 // The token-passing protocol gives priority to the VM thread. The
73 // CMS-lock doesn't provide any fairness guarantees, but clients
74 // should ensure that it is only held for very short, bounded
75 // durations.
76 //
77 // When either of the CMS thread or the VM thread is involved in
78 // collection operations during which it does not want the other
79 // thread to interfere, it obtains the CMS token.
80 //
81 // If either thread tries to get the token while the other has
82 // it, that thread waits. However, if the VM thread and CMS thread
83 // both want the token, then the VM thread gets priority while the
84 // CMS thread waits. This ensures, for instance, that the "concurrent"
85 // phases of the CMS thread's work do not block out the VM thread
86 // for long periods of time as the CMS thread continues to hog
87 // the token. (See bug 4616232).
88 //
89 // The baton-passing functions are, however, controlled by the
90 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
91 // and here the low-level CMS lock, not the high level token,
92 // ensures mutual exclusion.
93 //
94 // Two important conditions that we have to satisfy:
95 // 1. if a thread does a low-level wait on the CMS lock, then it
96 // relinquishes the CMS token if it were holding that token
97 // when it acquired the low-level CMS lock.
98 // 2. any low-level notifications on the low-level lock
99 // should only be sent when a thread has relinquished the token.
100 //
101 // In the absence of either property, we'd have potential deadlock.
102 //
103 // We protect each of the CMS (concurrent and sequential) phases
104 // with the CMS _token_, not the CMS _lock_.
105 //
106 // The only code protected by CMS lock is the token acquisition code
107 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
108 // baton-passing code.
109 //
110 // Unfortunately, i couldn't come up with a good abstraction to factor and
111 // hide the naked CGC_lock manipulation in the baton-passing code
112 // further below. That's something we should try to do. Also, the proof
113 // of correctness of this 2-level locking scheme is far from obvious,
114 // and potentially quite slippery. We have an uneasy supsicion, for instance,
115 // that there may be a theoretical possibility of delay/starvation in the
116 // low-level lock/wait/notify scheme used for the baton-passing because of
117 // potential intereference with the priority scheme embodied in the
118 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
119 // invocation further below and marked with "XXX 20011219YSR".
120 // Indeed, as we note elsewhere, this may become yet more slippery
121 // in the presence of multiple CMS and/or multiple VM threads. XXX
122
123 class CMSTokenSync: public StackObj {
124 private:
125 bool _is_cms_thread;
126 public:
127 CMSTokenSync(bool is_cms_thread):
128 _is_cms_thread(is_cms_thread) {
129 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
130 "Incorrect argument to constructor");
131 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
132 }
133
134 ~CMSTokenSync() {
135 assert(_is_cms_thread ?
136 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
137 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
138 "Incorrect state");
139 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
140 }
141 };
142
143 // Convenience class that does a CMSTokenSync, and then acquires
144 // upto three locks.
145 class CMSTokenSyncWithLocks: public CMSTokenSync {
146 private:
147 // Note: locks are acquired in textual declaration order
148 // and released in the opposite order
149 MutexLockerEx _locker1, _locker2, _locker3;
150 public:
151 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
152 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
153 CMSTokenSync(is_cms_thread),
154 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
155 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
156 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
157 { }
158 };
159
160
161 // Wrapper class to temporarily disable icms during a foreground cms collection.
162 class ICMSDisabler: public StackObj {
163 public:
164 // The ctor disables icms and wakes up the thread so it notices the change;
165 // the dtor re-enables icms. Note that the CMSCollector methods will check
166 // CMSIncrementalMode.
167 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
168 ~ICMSDisabler() { CMSCollector::enable_icms(); }
169 };
170
171 //////////////////////////////////////////////////////////////////
172 // Concurrent Mark-Sweep Generation /////////////////////////////
173 //////////////////////////////////////////////////////////////////
174
175 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
176
177 // This struct contains per-thread things necessary to support parallel
178 // young-gen collection.
179 class CMSParGCThreadState: public CHeapObj<mtGC> {
180 public:
181 CFLS_LAB lab;
182 PromotionInfo promo;
183
184 // Constructor.
185 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
186 promo.setSpace(cfls);
187 }
188 };
189
190 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
191 ReservedSpace rs, size_t initial_byte_size, int level,
192 CardTableRS* ct, bool use_adaptive_freelists,
193 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
194 CardGeneration(rs, initial_byte_size, level, ct),
195 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
196 _debug_collection_type(Concurrent_collection_type),
197 _did_compact(false)
198 {
199 HeapWord* bottom = (HeapWord*) _virtual_space.low();
200 HeapWord* end = (HeapWord*) _virtual_space.high();
201
202 _direct_allocated_words = 0;
203 NOT_PRODUCT(
204 _numObjectsPromoted = 0;
205 _numWordsPromoted = 0;
206 _numObjectsAllocated = 0;
207 _numWordsAllocated = 0;
208 )
209
210 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
211 use_adaptive_freelists,
212 dictionaryChoice);
213 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
214 if (_cmsSpace == NULL) {
215 vm_exit_during_initialization(
216 "CompactibleFreeListSpace allocation failure");
217 }
218 _cmsSpace->_gen = this;
219
220 _gc_stats = new CMSGCStats();
221
222 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
223 // offsets match. The ability to tell free chunks from objects
224 // depends on this property.
225 debug_only(
226 FreeChunk* junk = NULL;
227 assert(UseCompressedKlassPointers ||
228 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
229 "Offset of FreeChunk::_prev within FreeChunk must match"
230 " that of OopDesc::_klass within OopDesc");
231 )
232 if (CollectedHeap::use_parallel_gc_threads()) {
233 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
234 _par_gc_thread_states =
235 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
236 if (_par_gc_thread_states == NULL) {
237 vm_exit_during_initialization("Could not allocate par gc structs");
238 }
239 for (uint i = 0; i < ParallelGCThreads; i++) {
240 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
241 if (_par_gc_thread_states[i] == NULL) {
242 vm_exit_during_initialization("Could not allocate par gc structs");
243 }
244 }
245 } else {
246 _par_gc_thread_states = NULL;
247 }
248 _incremental_collection_failed = false;
249 // The "dilatation_factor" is the expansion that can occur on
250 // account of the fact that the minimum object size in the CMS
251 // generation may be larger than that in, say, a contiguous young
252 // generation.
253 // Ideally, in the calculation below, we'd compute the dilatation
254 // factor as: MinChunkSize/(promoting_gen's min object size)
255 // Since we do not have such a general query interface for the
256 // promoting generation, we'll instead just use the mimimum
257 // object size (which today is a header's worth of space);
258 // note that all arithmetic is in units of HeapWords.
259 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
260 assert(_dilatation_factor >= 1.0, "from previous assert");
261 }
262
263
264 // The field "_initiating_occupancy" represents the occupancy percentage
265 // at which we trigger a new collection cycle. Unless explicitly specified
266 // via CMSInitiatingOccupancyFraction (argument "io" below), it
267 // is calculated by:
268 //
269 // Let "f" be MinHeapFreeRatio in
270 //
271 // _intiating_occupancy = 100-f +
272 // f * (CMSTriggerRatio/100)
273 // where CMSTriggerRatio is the argument "tr" below.
274 //
275 // That is, if we assume the heap is at its desired maximum occupancy at the
276 // end of a collection, we let CMSTriggerRatio of the (purported) free
277 // space be allocated before initiating a new collection cycle.
278 //
279 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
280 assert(io <= 100 && tr <= 100, "Check the arguments");
281 if (io >= 0) {
282 _initiating_occupancy = (double)io / 100.0;
283 } else {
284 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
285 (double)(tr * MinHeapFreeRatio) / 100.0)
286 / 100.0;
287 }
288 }
289
290 void ConcurrentMarkSweepGeneration::ref_processor_init() {
291 assert(collector() != NULL, "no collector");
292 collector()->ref_processor_init();
293 }
294
295 void CMSCollector::ref_processor_init() {
296 if (_ref_processor == NULL) {
297 // Allocate and initialize a reference processor
298 _ref_processor =
299 new ReferenceProcessor(_span, // span
300 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
301 (int) ParallelGCThreads, // mt processing degree
302 _cmsGen->refs_discovery_is_mt(), // mt discovery
303 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
304 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
305 &_is_alive_closure, // closure for liveness info
306 false); // next field updates do not need write barrier
307 // Initialize the _ref_processor field of CMSGen
308 _cmsGen->set_ref_processor(_ref_processor);
309
310 }
311 }
312
313 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
314 GenCollectedHeap* gch = GenCollectedHeap::heap();
315 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
316 "Wrong type of heap");
317 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
318 gch->gen_policy()->size_policy();
319 assert(sp->is_gc_cms_adaptive_size_policy(),
320 "Wrong type of size policy");
321 return sp;
322 }
323
324 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
325 CMSGCAdaptivePolicyCounters* results =
326 (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
327 assert(
328 results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
329 "Wrong gc policy counter kind");
330 return results;
331 }
332
333
334 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
335
336 const char* gen_name = "old";
337
338 // Generation Counters - generation 1, 1 subspace
339 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
340
341 _space_counters = new GSpaceCounters(gen_name, 0,
342 _virtual_space.reserved_size(),
343 this, _gen_counters);
344 }
345
346 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
347 _cms_gen(cms_gen)
348 {
349 assert(alpha <= 100, "bad value");
350 _saved_alpha = alpha;
351
352 // Initialize the alphas to the bootstrap value of 100.
353 _gc0_alpha = _cms_alpha = 100;
354
355 _cms_begin_time.update();
356 _cms_end_time.update();
357
358 _gc0_duration = 0.0;
359 _gc0_period = 0.0;
360 _gc0_promoted = 0;
361
362 _cms_duration = 0.0;
363 _cms_period = 0.0;
364 _cms_allocated = 0;
365
366 _cms_used_at_gc0_begin = 0;
367 _cms_used_at_gc0_end = 0;
368 _allow_duty_cycle_reduction = false;
369 _valid_bits = 0;
370 _icms_duty_cycle = CMSIncrementalDutyCycle;
371 }
372
373 double CMSStats::cms_free_adjustment_factor(size_t free) const {
374 // TBD: CR 6909490
375 return 1.0;
376 }
377
378 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
379 }
380
381 // If promotion failure handling is on use
382 // the padded average size of the promotion for each
383 // young generation collection.
384 double CMSStats::time_until_cms_gen_full() const {
385 size_t cms_free = _cms_gen->cmsSpace()->free();
386 GenCollectedHeap* gch = GenCollectedHeap::heap();
387 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
388 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
389 if (cms_free > expected_promotion) {
390 // Start a cms collection if there isn't enough space to promote
391 // for the next minor collection. Use the padded average as
392 // a safety factor.
393 cms_free -= expected_promotion;
394
395 // Adjust by the safety factor.
396 double cms_free_dbl = (double)cms_free;
397 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
398 // Apply a further correction factor which tries to adjust
399 // for recent occurance of concurrent mode failures.
400 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
401 cms_free_dbl = cms_free_dbl * cms_adjustment;
402
403 if (PrintGCDetails && Verbose) {
404 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
405 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
406 cms_free, expected_promotion);
407 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
408 cms_free_dbl, cms_consumption_rate() + 1.0);
409 }
410 // Add 1 in case the consumption rate goes to zero.
411 return cms_free_dbl / (cms_consumption_rate() + 1.0);
412 }
413 return 0.0;
414 }
415
416 // Compare the duration of the cms collection to the
417 // time remaining before the cms generation is empty.
418 // Note that the time from the start of the cms collection
419 // to the start of the cms sweep (less than the total
420 // duration of the cms collection) can be used. This
421 // has been tried and some applications experienced
422 // promotion failures early in execution. This was
423 // possibly because the averages were not accurate
424 // enough at the beginning.
425 double CMSStats::time_until_cms_start() const {
426 // We add "gc0_period" to the "work" calculation
427 // below because this query is done (mostly) at the
428 // end of a scavenge, so we need to conservatively
429 // account for that much possible delay
430 // in the query so as to avoid concurrent mode failures
431 // due to starting the collection just a wee bit too
432 // late.
433 double work = cms_duration() + gc0_period();
434 double deadline = time_until_cms_gen_full();
435 // If a concurrent mode failure occurred recently, we want to be
436 // more conservative and halve our expected time_until_cms_gen_full()
437 if (work > deadline) {
438 if (Verbose && PrintGCDetails) {
439 gclog_or_tty->print(
440 " CMSCollector: collect because of anticipated promotion "
441 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
442 gc0_period(), time_until_cms_gen_full());
443 }
444 return 0.0;
445 }
446 return work - deadline;
447 }
448
449 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
450 // amount of change to prevent wild oscillation.
451 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
452 unsigned int new_duty_cycle) {
453 assert(old_duty_cycle <= 100, "bad input value");
454 assert(new_duty_cycle <= 100, "bad input value");
455
456 // Note: use subtraction with caution since it may underflow (values are
457 // unsigned). Addition is safe since we're in the range 0-100.
458 unsigned int damped_duty_cycle = new_duty_cycle;
459 if (new_duty_cycle < old_duty_cycle) {
460 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
461 if (new_duty_cycle + largest_delta < old_duty_cycle) {
462 damped_duty_cycle = old_duty_cycle - largest_delta;
463 }
464 } else if (new_duty_cycle > old_duty_cycle) {
465 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
466 if (new_duty_cycle > old_duty_cycle + largest_delta) {
467 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
468 }
469 }
470 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
471
472 if (CMSTraceIncrementalPacing) {
473 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
474 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
475 }
476 return damped_duty_cycle;
477 }
478
479 unsigned int CMSStats::icms_update_duty_cycle_impl() {
480 assert(CMSIncrementalPacing && valid(),
481 "should be handled in icms_update_duty_cycle()");
482
483 double cms_time_so_far = cms_timer().seconds();
484 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
485 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
486
487 // Avoid division by 0.
488 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
489 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
490
491 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
492 if (new_duty_cycle > _icms_duty_cycle) {
493 // Avoid very small duty cycles (1 or 2); 0 is allowed.
494 if (new_duty_cycle > 2) {
495 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
496 new_duty_cycle);
497 }
498 } else if (_allow_duty_cycle_reduction) {
499 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
500 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
501 // Respect the minimum duty cycle.
502 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
503 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
504 }
505
506 if (PrintGCDetails || CMSTraceIncrementalPacing) {
507 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
508 }
509
510 _allow_duty_cycle_reduction = false;
511 return _icms_duty_cycle;
512 }
513
514 #ifndef PRODUCT
515 void CMSStats::print_on(outputStream *st) const {
516 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
517 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
518 gc0_duration(), gc0_period(), gc0_promoted());
519 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
520 cms_duration(), cms_duration_per_mb(),
521 cms_period(), cms_allocated());
522 st->print(",cms_since_beg=%g,cms_since_end=%g",
523 cms_time_since_begin(), cms_time_since_end());
524 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
525 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
526 if (CMSIncrementalMode) {
527 st->print(",dc=%d", icms_duty_cycle());
528 }
529
530 if (valid()) {
531 st->print(",promo_rate=%g,cms_alloc_rate=%g",
532 promotion_rate(), cms_allocation_rate());
533 st->print(",cms_consumption_rate=%g,time_until_full=%g",
534 cms_consumption_rate(), time_until_cms_gen_full());
535 }
536 st->print(" ");
537 }
538 #endif // #ifndef PRODUCT
539
540 CMSCollector::CollectorState CMSCollector::_collectorState =
541 CMSCollector::Idling;
542 bool CMSCollector::_foregroundGCIsActive = false;
543 bool CMSCollector::_foregroundGCShouldWait = false;
544
545 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
546 CardTableRS* ct,
547 ConcurrentMarkSweepPolicy* cp):
548 _cmsGen(cmsGen),
549 _ct(ct),
550 _ref_processor(NULL), // will be set later
551 _conc_workers(NULL), // may be set later
552 _abort_preclean(false),
553 _start_sampling(false),
554 _between_prologue_and_epilogue(false),
555 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
556 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
557 -1 /* lock-free */, "No_lock" /* dummy */),
558 _modUnionClosure(&_modUnionTable),
559 _modUnionClosurePar(&_modUnionTable),
560 // Adjust my span to cover old (cms) gen
561 _span(cmsGen->reserved()),
562 // Construct the is_alive_closure with _span & markBitMap
563 _is_alive_closure(_span, &_markBitMap),
564 _restart_addr(NULL),
565 _overflow_list(NULL),
566 _stats(cmsGen),
567 _eden_chunk_array(NULL), // may be set in ctor body
568 _eden_chunk_capacity(0), // -- ditto --
569 _eden_chunk_index(0), // -- ditto --
570 _survivor_plab_array(NULL), // -- ditto --
571 _survivor_chunk_array(NULL), // -- ditto --
572 _survivor_chunk_capacity(0), // -- ditto --
573 _survivor_chunk_index(0), // -- ditto --
574 _ser_pmc_preclean_ovflw(0),
575 _ser_kac_preclean_ovflw(0),
576 _ser_pmc_remark_ovflw(0),
577 _par_pmc_remark_ovflw(0),
578 _ser_kac_ovflw(0),
579 _par_kac_ovflw(0),
580 #ifndef PRODUCT
581 _num_par_pushes(0),
582 #endif
583 _collection_count_start(0),
584 _verifying(false),
585 _icms_start_limit(NULL),
586 _icms_stop_limit(NULL),
587 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
588 _completed_initialization(false),
589 _collector_policy(cp),
590 _should_unload_classes(false),
591 _concurrent_cycles_since_last_unload(0),
592 _roots_scanning_options(0),
593 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
594 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding)
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) {
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 // Choose what strong roots should be scanned depending on verification options
782 if (!CMSClassUnloadingEnabled) {
783 // If class unloading is disabled we want to include all classes into the root set.
784 add_root_scanning_option(SharedHeap::SO_AllClasses);
785 } else {
786 add_root_scanning_option(SharedHeap::SO_SystemClasses);
787 }
788
789 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
790 _gc_counters = new CollectorCounters("CMS", 1);
791 _completed_initialization = true;
792 _inter_sweep_timer.start(); // start of time
793 }
794
795 const char* ConcurrentMarkSweepGeneration::name() const {
796 return "concurrent mark-sweep generation";
797 }
798 void ConcurrentMarkSweepGeneration::update_counters() {
799 if (UsePerfData) {
800 _space_counters->update_all();
801 _gen_counters->update_all();
802 }
803 }
804
805 // this is an optimized version of update_counters(). it takes the
806 // used value as a parameter rather than computing it.
807 //
808 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
809 if (UsePerfData) {
810 _space_counters->update_used(used);
811 _space_counters->update_capacity();
812 _gen_counters->update_all();
813 }
814 }
815
816 void ConcurrentMarkSweepGeneration::print() const {
817 Generation::print();
818 cmsSpace()->print();
819 }
820
821 #ifndef PRODUCT
822 void ConcurrentMarkSweepGeneration::print_statistics() {
823 cmsSpace()->printFLCensus(0);
824 }
825 #endif
826
827 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
828 GenCollectedHeap* gch = GenCollectedHeap::heap();
829 if (PrintGCDetails) {
830 if (Verbose) {
831 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
832 level(), short_name(), s, used(), capacity());
833 } else {
834 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
835 level(), short_name(), s, used() / K, capacity() / K);
836 }
837 }
838 if (Verbose) {
839 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
840 gch->used(), gch->capacity());
841 } else {
842 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
843 gch->used() / K, gch->capacity() / K);
844 }
845 }
846
847 size_t
848 ConcurrentMarkSweepGeneration::contiguous_available() const {
849 // dld proposes an improvement in precision here. If the committed
850 // part of the space ends in a free block we should add that to
851 // uncommitted size in the calculation below. Will make this
852 // change later, staying with the approximation below for the
853 // time being. -- ysr.
854 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
855 }
856
857 size_t
858 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
859 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
860 }
861
862 size_t ConcurrentMarkSweepGeneration::max_available() const {
863 return free() + _virtual_space.uncommitted_size();
864 }
865
866 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
867 size_t available = max_available();
868 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
869 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
870 if (Verbose && PrintGCDetails) {
871 gclog_or_tty->print_cr(
872 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
873 "max_promo("SIZE_FORMAT")",
874 res? "":" not", available, res? ">=":"<",
875 av_promo, max_promotion_in_bytes);
876 }
877 return res;
878 }
879
880 // At a promotion failure dump information on block layout in heap
881 // (cms old generation).
882 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
883 if (CMSDumpAtPromotionFailure) {
884 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
885 }
886 }
887
888 CompactibleSpace*
889 ConcurrentMarkSweepGeneration::first_compaction_space() const {
890 return _cmsSpace;
891 }
892
893 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
894 // Clear the promotion information. These pointers can be adjusted
895 // along with all the other pointers into the heap but
896 // compaction is expected to be a rare event with
897 // a heap using cms so don't do it without seeing the need.
898 if (CollectedHeap::use_parallel_gc_threads()) {
899 for (uint i = 0; i < ParallelGCThreads; i++) {
900 _par_gc_thread_states[i]->promo.reset();
901 }
902 }
903 }
904
905 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
906 blk->do_space(_cmsSpace);
907 }
908
909 void ConcurrentMarkSweepGeneration::compute_new_size() {
910 assert_locked_or_safepoint(Heap_lock);
911
912 // If incremental collection failed, we just want to expand
913 // to the limit.
914 if (incremental_collection_failed()) {
915 clear_incremental_collection_failed();
916 grow_to_reserved();
917 return;
918 }
919
920 // The heap has been compacted but not reset yet.
921 // Any metric such as free() or used() will be incorrect.
922
923 CardGeneration::compute_new_size();
924
925 // Reset again after a possible resizing
926 if (did_compact()) {
927 cmsSpace()->reset_after_compaction();
928 }
929 }
930
931 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
932 assert_locked_or_safepoint(Heap_lock);
933
934 // If incremental collection failed, we just want to expand
935 // to the limit.
936 if (incremental_collection_failed()) {
937 clear_incremental_collection_failed();
938 grow_to_reserved();
939 return;
940 }
941
942 double free_percentage = ((double) free()) / capacity();
943 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
944 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
945
946 // compute expansion delta needed for reaching desired free percentage
947 if (free_percentage < desired_free_percentage) {
948 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
949 assert(desired_capacity >= capacity(), "invalid expansion size");
950 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
951 if (PrintGCDetails && Verbose) {
952 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
953 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
954 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
955 gclog_or_tty->print_cr(" Desired free fraction %f",
956 desired_free_percentage);
957 gclog_or_tty->print_cr(" Maximum free fraction %f",
958 maximum_free_percentage);
959 gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000);
960 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
961 desired_capacity/1000);
962 int prev_level = level() - 1;
963 if (prev_level >= 0) {
964 size_t prev_size = 0;
965 GenCollectedHeap* gch = GenCollectedHeap::heap();
966 Generation* prev_gen = gch->_gens[prev_level];
967 prev_size = prev_gen->capacity();
968 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
969 prev_size/1000);
970 }
971 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
972 unsafe_max_alloc_nogc()/1000);
973 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
974 contiguous_available()/1000);
975 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
976 expand_bytes);
977 }
978 // safe if expansion fails
979 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
980 if (PrintGCDetails && Verbose) {
981 gclog_or_tty->print_cr(" Expanded free fraction %f",
982 ((double) free()) / capacity());
983 }
984 } else {
985 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
986 assert(desired_capacity <= capacity(), "invalid expansion size");
987 size_t shrink_bytes = capacity() - desired_capacity;
988 // Don't shrink unless the delta is greater than the minimum shrink we want
989 if (shrink_bytes >= MinHeapDeltaBytes) {
990 shrink_free_list_by(shrink_bytes);
991 }
992 }
993 }
994
995 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
996 return cmsSpace()->freelistLock();
997 }
998
999 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
1000 bool tlab) {
1001 CMSSynchronousYieldRequest yr;
1002 MutexLockerEx x(freelistLock(),
1003 Mutex::_no_safepoint_check_flag);
1004 return have_lock_and_allocate(size, tlab);
1005 }
1006
1007 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
1008 bool tlab /* ignored */) {
1009 assert_lock_strong(freelistLock());
1010 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1011 HeapWord* res = cmsSpace()->allocate(adjustedSize);
1012 // Allocate the object live (grey) if the background collector has
1013 // started marking. This is necessary because the marker may
1014 // have passed this address and consequently this object will
1015 // not otherwise be greyed and would be incorrectly swept up.
1016 // Note that if this object contains references, the writing
1017 // of those references will dirty the card containing this object
1018 // allowing the object to be blackened (and its references scanned)
1019 // either during a preclean phase or at the final checkpoint.
1020 if (res != NULL) {
1021 // We may block here with an uninitialized object with
1022 // its mark-bit or P-bits not yet set. Such objects need
1023 // to be safely navigable by block_start().
1024 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1025 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1026 collector()->direct_allocated(res, adjustedSize);
1027 _direct_allocated_words += adjustedSize;
1028 // allocation counters
1029 NOT_PRODUCT(
1030 _numObjectsAllocated++;
1031 _numWordsAllocated += (int)adjustedSize;
1032 )
1033 }
1034 return res;
1035 }
1036
1037 // In the case of direct allocation by mutators in a generation that
1038 // is being concurrently collected, the object must be allocated
1039 // live (grey) if the background collector has started marking.
1040 // This is necessary because the marker may
1041 // have passed this address and consequently this object will
1042 // not otherwise be greyed and would be incorrectly swept up.
1043 // Note that if this object contains references, the writing
1044 // of those references will dirty the card containing this object
1045 // allowing the object to be blackened (and its references scanned)
1046 // either during a preclean phase or at the final checkpoint.
1047 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1048 assert(_markBitMap.covers(start, size), "Out of bounds");
1049 if (_collectorState >= Marking) {
1050 MutexLockerEx y(_markBitMap.lock(),
1051 Mutex::_no_safepoint_check_flag);
1052 // [see comments preceding SweepClosure::do_blk() below for details]
1053 //
1054 // Can the P-bits be deleted now? JJJ
1055 //
1056 // 1. need to mark the object as live so it isn't collected
1057 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1058 // 3. need to mark the end of the object so marking, precleaning or sweeping
1059 // can skip over uninitialized or unparsable objects. An allocated
1060 // object is considered uninitialized for our purposes as long as
1061 // its klass word is NULL. All old gen objects are parsable
1062 // as soon as they are initialized.)
1063 _markBitMap.mark(start); // object is live
1064 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1065 _markBitMap.mark(start + size - 1);
1066 // mark end of object
1067 }
1068 // check that oop looks uninitialized
1069 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1070 }
1071
1072 void CMSCollector::promoted(bool par, HeapWord* start,
1073 bool is_obj_array, size_t obj_size) {
1074 assert(_markBitMap.covers(start), "Out of bounds");
1075 // See comment in direct_allocated() about when objects should
1076 // be allocated live.
1077 if (_collectorState >= Marking) {
1078 // we already hold the marking bit map lock, taken in
1079 // the prologue
1080 if (par) {
1081 _markBitMap.par_mark(start);
1082 } else {
1083 _markBitMap.mark(start);
1084 }
1085 // We don't need to mark the object as uninitialized (as
1086 // in direct_allocated above) because this is being done with the
1087 // world stopped and the object will be initialized by the
1088 // time the marking, precleaning or sweeping get to look at it.
1089 // But see the code for copying objects into the CMS generation,
1090 // where we need to ensure that concurrent readers of the
1091 // block offset table are able to safely navigate a block that
1092 // is in flux from being free to being allocated (and in
1093 // transition while being copied into) and subsequently
1094 // becoming a bona-fide object when the copy/promotion is complete.
1095 assert(SafepointSynchronize::is_at_safepoint(),
1096 "expect promotion only at safepoints");
1097
1098 if (_collectorState < Sweeping) {
1099 // Mark the appropriate cards in the modUnionTable, so that
1100 // this object gets scanned before the sweep. If this is
1101 // not done, CMS generation references in the object might
1102 // not get marked.
1103 // For the case of arrays, which are otherwise precisely
1104 // marked, we need to dirty the entire array, not just its head.
1105 if (is_obj_array) {
1106 // The [par_]mark_range() method expects mr.end() below to
1107 // be aligned to the granularity of a bit's representation
1108 // in the heap. In the case of the MUT below, that's a
1109 // card size.
1110 MemRegion mr(start,
1111 (HeapWord*)round_to((intptr_t)(start + obj_size),
1112 CardTableModRefBS::card_size /* bytes */));
1113 if (par) {
1114 _modUnionTable.par_mark_range(mr);
1115 } else {
1116 _modUnionTable.mark_range(mr);
1117 }
1118 } else { // not an obj array; we can just mark the head
1119 if (par) {
1120 _modUnionTable.par_mark(start);
1121 } else {
1122 _modUnionTable.mark(start);
1123 }
1124 }
1125 }
1126 }
1127 }
1128
1129 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1130 {
1131 size_t delta = pointer_delta(addr, space->bottom());
1132 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1133 }
1134
1135 void CMSCollector::icms_update_allocation_limits()
1136 {
1137 Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1138 EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1139
1140 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1141 if (CMSTraceIncrementalPacing) {
1142 stats().print();
1143 }
1144
1145 assert(duty_cycle <= 100, "invalid duty cycle");
1146 if (duty_cycle != 0) {
1147 // The duty_cycle is a percentage between 0 and 100; convert to words and
1148 // then compute the offset from the endpoints of the space.
1149 size_t free_words = eden->free() / HeapWordSize;
1150 double free_words_dbl = (double)free_words;
1151 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1152 size_t offset_words = (free_words - duty_cycle_words) / 2;
1153
1154 _icms_start_limit = eden->top() + offset_words;
1155 _icms_stop_limit = eden->end() - offset_words;
1156
1157 // The limits may be adjusted (shifted to the right) by
1158 // CMSIncrementalOffset, to allow the application more mutator time after a
1159 // young gen gc (when all mutators were stopped) and before CMS starts and
1160 // takes away one or more cpus.
1161 if (CMSIncrementalOffset != 0) {
1162 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1163 size_t adjustment = (size_t)adjustment_dbl;
1164 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1165 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1166 _icms_start_limit += adjustment;
1167 _icms_stop_limit = tmp_stop;
1168 }
1169 }
1170 }
1171 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1172 _icms_start_limit = _icms_stop_limit = eden->end();
1173 }
1174
1175 // Install the new start limit.
1176 eden->set_soft_end(_icms_start_limit);
1177
1178 if (CMSTraceIncrementalMode) {
1179 gclog_or_tty->print(" icms alloc limits: "
1180 PTR_FORMAT "," PTR_FORMAT
1181 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1182 _icms_start_limit, _icms_stop_limit,
1183 percent_of_space(eden, _icms_start_limit),
1184 percent_of_space(eden, _icms_stop_limit));
1185 if (Verbose) {
1186 gclog_or_tty->print("eden: ");
1187 eden->print_on(gclog_or_tty);
1188 }
1189 }
1190 }
1191
1192 // Any changes here should try to maintain the invariant
1193 // that if this method is called with _icms_start_limit
1194 // and _icms_stop_limit both NULL, then it should return NULL
1195 // and not notify the icms thread.
1196 HeapWord*
1197 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1198 size_t word_size)
1199 {
1200 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1201 // nop.
1202 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1203 if (top <= _icms_start_limit) {
1204 if (CMSTraceIncrementalMode) {
1205 space->print_on(gclog_or_tty);
1206 gclog_or_tty->stamp();
1207 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1208 ", new limit=" PTR_FORMAT
1209 " (" SIZE_FORMAT "%%)",
1210 top, _icms_stop_limit,
1211 percent_of_space(space, _icms_stop_limit));
1212 }
1213 ConcurrentMarkSweepThread::start_icms();
1214 assert(top < _icms_stop_limit, "Tautology");
1215 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1216 return _icms_stop_limit;
1217 }
1218
1219 // The allocation will cross both the _start and _stop limits, so do the
1220 // stop notification also and return end().
1221 if (CMSTraceIncrementalMode) {
1222 space->print_on(gclog_or_tty);
1223 gclog_or_tty->stamp();
1224 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1225 ", new limit=" PTR_FORMAT
1226 " (" SIZE_FORMAT "%%)",
1227 top, space->end(),
1228 percent_of_space(space, space->end()));
1229 }
1230 ConcurrentMarkSweepThread::stop_icms();
1231 return space->end();
1232 }
1233
1234 if (top <= _icms_stop_limit) {
1235 if (CMSTraceIncrementalMode) {
1236 space->print_on(gclog_or_tty);
1237 gclog_or_tty->stamp();
1238 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1239 ", new limit=" PTR_FORMAT
1240 " (" SIZE_FORMAT "%%)",
1241 top, space->end(),
1242 percent_of_space(space, space->end()));
1243 }
1244 ConcurrentMarkSweepThread::stop_icms();
1245 return space->end();
1246 }
1247
1248 if (CMSTraceIncrementalMode) {
1249 space->print_on(gclog_or_tty);
1250 gclog_or_tty->stamp();
1251 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1252 ", new limit=" PTR_FORMAT,
1253 top, NULL);
1254 }
1255 }
1256
1257 return NULL;
1258 }
1259
1260 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1261 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1262 // allocate, copy and if necessary update promoinfo --
1263 // delegate to underlying space.
1264 assert_lock_strong(freelistLock());
1265
1266 #ifndef PRODUCT
1267 if (Universe::heap()->promotion_should_fail()) {
1268 return NULL;
1269 }
1270 #endif // #ifndef PRODUCT
1271
1272 oop res = _cmsSpace->promote(obj, obj_size);
1273 if (res == NULL) {
1274 // expand and retry
1275 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1276 expand(s*HeapWordSize, MinHeapDeltaBytes,
1277 CMSExpansionCause::_satisfy_promotion);
1278 // Since there's currently no next generation, we don't try to promote
1279 // into a more senior generation.
1280 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1281 "is made to pass on a possibly failing "
1282 "promotion to next generation");
1283 res = _cmsSpace->promote(obj, obj_size);
1284 }
1285 if (res != NULL) {
1286 // See comment in allocate() about when objects should
1287 // be allocated live.
1288 assert(obj->is_oop(), "Will dereference klass pointer below");
1289 collector()->promoted(false, // Not parallel
1290 (HeapWord*)res, obj->is_objArray(), obj_size);
1291 // promotion counters
1292 NOT_PRODUCT(
1293 _numObjectsPromoted++;
1294 _numWordsPromoted +=
1295 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1296 )
1297 }
1298 return res;
1299 }
1300
1301
1302 HeapWord*
1303 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1304 HeapWord* top,
1305 size_t word_sz)
1306 {
1307 return collector()->allocation_limit_reached(space, top, word_sz);
1308 }
1309
1310 // IMPORTANT: Notes on object size recognition in CMS.
1311 // ---------------------------------------------------
1312 // A block of storage in the CMS generation is always in
1313 // one of three states. A free block (FREE), an allocated
1314 // object (OBJECT) whose size() method reports the correct size,
1315 // and an intermediate state (TRANSIENT) in which its size cannot
1316 // be accurately determined.
1317 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1318 // -----------------------------------------------------
1319 // FREE: klass_word & 1 == 1; mark_word holds block size
1320 //
1321 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1322 // obj->size() computes correct size
1323 //
1324 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1325 //
1326 // STATE IDENTIFICATION: (64 bit+COOPS)
1327 // ------------------------------------
1328 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1329 //
1330 // OBJECT: klass_word installed; klass_word != 0;
1331 // obj->size() computes correct size
1332 //
1333 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1334 //
1335 //
1336 // STATE TRANSITION DIAGRAM
1337 //
1338 // mut / parnew mut / parnew
1339 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1340 // ^ |
1341 // |------------------------ DEAD <------------------------------------|
1342 // sweep mut
1343 //
1344 // While a block is in TRANSIENT state its size cannot be determined
1345 // so readers will either need to come back later or stall until
1346 // the size can be determined. Note that for the case of direct
1347 // allocation, P-bits, when available, may be used to determine the
1348 // size of an object that may not yet have been initialized.
1349
1350 // Things to support parallel young-gen collection.
1351 oop
1352 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1353 oop old, markOop m,
1354 size_t word_sz) {
1355 #ifndef PRODUCT
1356 if (Universe::heap()->promotion_should_fail()) {
1357 return NULL;
1358 }
1359 #endif // #ifndef PRODUCT
1360
1361 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1362 PromotionInfo* promoInfo = &ps->promo;
1363 // if we are tracking promotions, then first ensure space for
1364 // promotion (including spooling space for saving header if necessary).
1365 // then allocate and copy, then track promoted info if needed.
1366 // When tracking (see PromotionInfo::track()), the mark word may
1367 // be displaced and in this case restoration of the mark word
1368 // occurs in the (oop_since_save_marks_)iterate phase.
1369 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1370 // Out of space for allocating spooling buffers;
1371 // try expanding and allocating spooling buffers.
1372 if (!expand_and_ensure_spooling_space(promoInfo)) {
1373 return NULL;
1374 }
1375 }
1376 assert(promoInfo->has_spooling_space(), "Control point invariant");
1377 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1378 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1379 if (obj_ptr == NULL) {
1380 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1381 if (obj_ptr == NULL) {
1382 return NULL;
1383 }
1384 }
1385 oop obj = oop(obj_ptr);
1386 OrderAccess::storestore();
1387 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1388 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1389 // IMPORTANT: See note on object initialization for CMS above.
1390 // Otherwise, copy the object. Here we must be careful to insert the
1391 // klass pointer last, since this marks the block as an allocated object.
1392 // Except with compressed oops it's the mark word.
1393 HeapWord* old_ptr = (HeapWord*)old;
1394 // Restore the mark word copied above.
1395 obj->set_mark(m);
1396 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1397 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1398 OrderAccess::storestore();
1399
1400 if (UseCompressedKlassPointers) {
1401 // Copy gap missed by (aligned) header size calculation below
1402 obj->set_klass_gap(old->klass_gap());
1403 }
1404 if (word_sz > (size_t)oopDesc::header_size()) {
1405 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1406 obj_ptr + oopDesc::header_size(),
1407 word_sz - oopDesc::header_size());
1408 }
1409
1410 // Now we can track the promoted object, if necessary. We take care
1411 // to delay the transition from uninitialized to full object
1412 // (i.e., insertion of klass pointer) until after, so that it
1413 // atomically becomes a promoted object.
1414 if (promoInfo->tracking()) {
1415 promoInfo->track((PromotedObject*)obj, old->klass());
1416 }
1417 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1418 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1419 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1420
1421 // Finally, install the klass pointer (this should be volatile).
1422 OrderAccess::storestore();
1423 obj->set_klass(old->klass());
1424 // We should now be able to calculate the right size for this object
1425 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1426
1427 collector()->promoted(true, // parallel
1428 obj_ptr, old->is_objArray(), word_sz);
1429
1430 NOT_PRODUCT(
1431 Atomic::inc_ptr(&_numObjectsPromoted);
1432 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1433 )
1434
1435 return obj;
1436 }
1437
1438 void
1439 ConcurrentMarkSweepGeneration::
1440 par_promote_alloc_undo(int thread_num,
1441 HeapWord* obj, size_t word_sz) {
1442 // CMS does not support promotion undo.
1443 ShouldNotReachHere();
1444 }
1445
1446 void
1447 ConcurrentMarkSweepGeneration::
1448 par_promote_alloc_done(int thread_num) {
1449 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1450 ps->lab.retire(thread_num);
1451 }
1452
1453 void
1454 ConcurrentMarkSweepGeneration::
1455 par_oop_since_save_marks_iterate_done(int thread_num) {
1456 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1457 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1458 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1459 }
1460
1461 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1462 size_t size,
1463 bool tlab)
1464 {
1465 // We allow a STW collection only if a full
1466 // collection was requested.
1467 return full || should_allocate(size, tlab); // FIX ME !!!
1468 // This and promotion failure handling are connected at the
1469 // hip and should be fixed by untying them.
1470 }
1471
1472 bool CMSCollector::shouldConcurrentCollect() {
1473 if (_full_gc_requested) {
1474 if (Verbose && PrintGCDetails) {
1475 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1476 " gc request (or gc_locker)");
1477 }
1478 return true;
1479 }
1480
1481 // For debugging purposes, change the type of collection.
1482 // If the rotation is not on the concurrent collection
1483 // type, don't start a concurrent collection.
1484 NOT_PRODUCT(
1485 if (RotateCMSCollectionTypes &&
1486 (_cmsGen->debug_collection_type() !=
1487 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1488 assert(_cmsGen->debug_collection_type() !=
1489 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1490 "Bad cms collection type");
1491 return false;
1492 }
1493 )
1494
1495 FreelistLocker x(this);
1496 // ------------------------------------------------------------------
1497 // Print out lots of information which affects the initiation of
1498 // a collection.
1499 if (PrintCMSInitiationStatistics && stats().valid()) {
1500 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1501 gclog_or_tty->stamp();
1502 gclog_or_tty->print_cr("");
1503 stats().print_on(gclog_or_tty);
1504 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1505 stats().time_until_cms_gen_full());
1506 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1507 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1508 _cmsGen->contiguous_available());
1509 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1510 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1511 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1512 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1513 gclog_or_tty->print_cr("metadata initialized %d",
1514 MetaspaceGC::should_concurrent_collect());
1515 }
1516 // ------------------------------------------------------------------
1517
1518 // If the estimated time to complete a cms collection (cms_duration())
1519 // is less than the estimated time remaining until the cms generation
1520 // is full, start a collection.
1521 if (!UseCMSInitiatingOccupancyOnly) {
1522 if (stats().valid()) {
1523 if (stats().time_until_cms_start() == 0.0) {
1524 return true;
1525 }
1526 } else {
1527 // We want to conservatively collect somewhat early in order
1528 // to try and "bootstrap" our CMS/promotion statistics;
1529 // this branch will not fire after the first successful CMS
1530 // collection because the stats should then be valid.
1531 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1532 if (Verbose && PrintGCDetails) {
1533 gclog_or_tty->print_cr(
1534 " CMSCollector: collect for bootstrapping statistics:"
1535 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1536 _bootstrap_occupancy);
1537 }
1538 return true;
1539 }
1540 }
1541 }
1542
1543 // Otherwise, we start a collection cycle if
1544 // old gen want a collection cycle started. Each may use
1545 // an appropriate criterion for making this decision.
1546 // XXX We need to make sure that the gen expansion
1547 // criterion dovetails well with this. XXX NEED TO FIX THIS
1548 if (_cmsGen->should_concurrent_collect()) {
1549 if (Verbose && PrintGCDetails) {
1550 gclog_or_tty->print_cr("CMS old gen initiated");
1551 }
1552 return true;
1553 }
1554
1555 // We start a collection if we believe an incremental collection may fail;
1556 // this is not likely to be productive in practice because it's probably too
1557 // late anyway.
1558 GenCollectedHeap* gch = GenCollectedHeap::heap();
1559 assert(gch->collector_policy()->is_two_generation_policy(),
1560 "You may want to check the correctness of the following");
1561 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1562 if (Verbose && PrintGCDetails) {
1563 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1564 }
1565 return true;
1566 }
1567
1568 if (MetaspaceGC::should_concurrent_collect()) {
1569 if (Verbose && PrintGCDetails) {
1570 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1571 }
1572 return true;
1573 }
1574
1575 return false;
1576 }
1577
1578 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1579
1580 // Clear _expansion_cause fields of constituent generations
1581 void CMSCollector::clear_expansion_cause() {
1582 _cmsGen->clear_expansion_cause();
1583 }
1584
1585 // We should be conservative in starting a collection cycle. To
1586 // start too eagerly runs the risk of collecting too often in the
1587 // extreme. To collect too rarely falls back on full collections,
1588 // which works, even if not optimum in terms of concurrent work.
1589 // As a work around for too eagerly collecting, use the flag
1590 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1591 // giving the user an easily understandable way of controlling the
1592 // collections.
1593 // We want to start a new collection cycle if any of the following
1594 // conditions hold:
1595 // . our current occupancy exceeds the configured initiating occupancy
1596 // for this generation, or
1597 // . we recently needed to expand this space and have not, since that
1598 // expansion, done a collection of this generation, or
1599 // . the underlying space believes that it may be a good idea to initiate
1600 // a concurrent collection (this may be based on criteria such as the
1601 // following: the space uses linear allocation and linear allocation is
1602 // going to fail, or there is believed to be excessive fragmentation in
1603 // the generation, etc... or ...
1604 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1605 // the case of the old generation; see CR 6543076):
1606 // we may be approaching a point at which allocation requests may fail because
1607 // we will be out of sufficient free space given allocation rate estimates.]
1608 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1609
1610 assert_lock_strong(freelistLock());
1611 if (occupancy() > initiating_occupancy()) {
1612 if (PrintGCDetails && Verbose) {
1613 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1614 short_name(), occupancy(), initiating_occupancy());
1615 }
1616 return true;
1617 }
1618 if (UseCMSInitiatingOccupancyOnly) {
1619 return false;
1620 }
1621 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1622 if (PrintGCDetails && Verbose) {
1623 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1624 short_name());
1625 }
1626 return true;
1627 }
1628 if (_cmsSpace->should_concurrent_collect()) {
1629 if (PrintGCDetails && Verbose) {
1630 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1631 short_name());
1632 }
1633 return true;
1634 }
1635 return false;
1636 }
1637
1638 void ConcurrentMarkSweepGeneration::collect(bool full,
1639 bool clear_all_soft_refs,
1640 size_t size,
1641 bool tlab)
1642 {
1643 collector()->collect(full, clear_all_soft_refs, size, tlab);
1644 }
1645
1646 void CMSCollector::collect(bool full,
1647 bool clear_all_soft_refs,
1648 size_t size,
1649 bool tlab)
1650 {
1651 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1652 // For debugging purposes skip the collection if the state
1653 // is not currently idle
1654 if (TraceCMSState) {
1655 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1656 Thread::current(), full, _collectorState);
1657 }
1658 return;
1659 }
1660
1661 // The following "if" branch is present for defensive reasons.
1662 // In the current uses of this interface, it can be replaced with:
1663 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1664 // But I am not placing that assert here to allow future
1665 // generality in invoking this interface.
1666 if (GC_locker::is_active()) {
1667 // A consistency test for GC_locker
1668 assert(GC_locker::needs_gc(), "Should have been set already");
1669 // Skip this foreground collection, instead
1670 // expanding the heap if necessary.
1671 // Need the free list locks for the call to free() in compute_new_size()
1672 compute_new_size();
1673 return;
1674 }
1675 acquire_control_and_collect(full, clear_all_soft_refs);
1676 _full_gcs_since_conc_gc++;
1677 }
1678
1679 void CMSCollector::request_full_gc(unsigned int full_gc_count) {
1680 GenCollectedHeap* gch = GenCollectedHeap::heap();
1681 unsigned int gc_count = gch->total_full_collections();
1682 if (gc_count == full_gc_count) {
1683 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1684 _full_gc_requested = true;
1685 CGC_lock->notify(); // nudge CMS thread
1686 } else {
1687 assert(gc_count > full_gc_count, "Error: causal loop");
1688 }
1689 }
1690
1691
1692 // The foreground and background collectors need to coordinate in order
1693 // to make sure that they do not mutually interfere with CMS collections.
1694 // When a background collection is active,
1695 // the foreground collector may need to take over (preempt) and
1696 // synchronously complete an ongoing collection. Depending on the
1697 // frequency of the background collections and the heap usage
1698 // of the application, this preemption can be seldom or frequent.
1699 // There are only certain
1700 // points in the background collection that the "collection-baton"
1701 // can be passed to the foreground collector.
1702 //
1703 // The foreground collector will wait for the baton before
1704 // starting any part of the collection. The foreground collector
1705 // will only wait at one location.
1706 //
1707 // The background collector will yield the baton before starting a new
1708 // phase of the collection (e.g., before initial marking, marking from roots,
1709 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1710 // of the loop which switches the phases. The background collector does some
1711 // of the phases (initial mark, final re-mark) with the world stopped.
1712 // Because of locking involved in stopping the world,
1713 // the foreground collector should not block waiting for the background
1714 // collector when it is doing a stop-the-world phase. The background
1715 // collector will yield the baton at an additional point just before
1716 // it enters a stop-the-world phase. Once the world is stopped, the
1717 // background collector checks the phase of the collection. If the
1718 // phase has not changed, it proceeds with the collection. If the
1719 // phase has changed, it skips that phase of the collection. See
1720 // the comments on the use of the Heap_lock in collect_in_background().
1721 //
1722 // Variable used in baton passing.
1723 // _foregroundGCIsActive - Set to true by the foreground collector when
1724 // it wants the baton. The foreground clears it when it has finished
1725 // the collection.
1726 // _foregroundGCShouldWait - Set to true by the background collector
1727 // when it is running. The foreground collector waits while
1728 // _foregroundGCShouldWait is true.
1729 // CGC_lock - monitor used to protect access to the above variables
1730 // and to notify the foreground and background collectors.
1731 // _collectorState - current state of the CMS collection.
1732 //
1733 // The foreground collector
1734 // acquires the CGC_lock
1735 // sets _foregroundGCIsActive
1736 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1737 // various locks acquired in preparation for the collection
1738 // are released so as not to block the background collector
1739 // that is in the midst of a collection
1740 // proceeds with the collection
1741 // clears _foregroundGCIsActive
1742 // returns
1743 //
1744 // The background collector in a loop iterating on the phases of the
1745 // collection
1746 // acquires the CGC_lock
1747 // sets _foregroundGCShouldWait
1748 // if _foregroundGCIsActive is set
1749 // clears _foregroundGCShouldWait, notifies _CGC_lock
1750 // waits on _CGC_lock for _foregroundGCIsActive to become false
1751 // and exits the loop.
1752 // otherwise
1753 // proceed with that phase of the collection
1754 // if the phase is a stop-the-world phase,
1755 // yield the baton once more just before enqueueing
1756 // the stop-world CMS operation (executed by the VM thread).
1757 // returns after all phases of the collection are done
1758 //
1759
1760 void CMSCollector::acquire_control_and_collect(bool full,
1761 bool clear_all_soft_refs) {
1762 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1763 assert(!Thread::current()->is_ConcurrentGC_thread(),
1764 "shouldn't try to acquire control from self!");
1765
1766 // Start the protocol for acquiring control of the
1767 // collection from the background collector (aka CMS thread).
1768 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1769 "VM thread should have CMS token");
1770 // Remember the possibly interrupted state of an ongoing
1771 // concurrent collection
1772 CollectorState first_state = _collectorState;
1773
1774 // Signal to a possibly ongoing concurrent collection that
1775 // we want to do a foreground collection.
1776 _foregroundGCIsActive = true;
1777
1778 // Disable incremental mode during a foreground collection.
1779 ICMSDisabler icms_disabler;
1780
1781 // release locks and wait for a notify from the background collector
1782 // releasing the locks in only necessary for phases which
1783 // do yields to improve the granularity of the collection.
1784 assert_lock_strong(bitMapLock());
1785 // We need to lock the Free list lock for the space that we are
1786 // currently collecting.
1787 assert(haveFreelistLocks(), "Must be holding free list locks");
1788 bitMapLock()->unlock();
1789 releaseFreelistLocks();
1790 {
1791 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1792 if (_foregroundGCShouldWait) {
1793 // We are going to be waiting for action for the CMS thread;
1794 // it had better not be gone (for instance at shutdown)!
1795 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1796 "CMS thread must be running");
1797 // Wait here until the background collector gives us the go-ahead
1798 ConcurrentMarkSweepThread::clear_CMS_flag(
1799 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1800 // Get a possibly blocked CMS thread going:
1801 // Note that we set _foregroundGCIsActive true above,
1802 // without protection of the CGC_lock.
1803 CGC_lock->notify();
1804 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1805 "Possible deadlock");
1806 while (_foregroundGCShouldWait) {
1807 // wait for notification
1808 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1809 // Possibility of delay/starvation here, since CMS token does
1810 // not know to give priority to VM thread? Actually, i think
1811 // there wouldn't be any delay/starvation, but the proof of
1812 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1813 }
1814 ConcurrentMarkSweepThread::set_CMS_flag(
1815 ConcurrentMarkSweepThread::CMS_vm_has_token);
1816 }
1817 }
1818 // The CMS_token is already held. Get back the other locks.
1819 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1820 "VM thread should have CMS token");
1821 getFreelistLocks();
1822 bitMapLock()->lock_without_safepoint_check();
1823 if (TraceCMSState) {
1824 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1825 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1826 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1827 }
1828
1829 // Check if we need to do a compaction, or if not, whether
1830 // we need to start the mark-sweep from scratch.
1831 bool should_compact = false;
1832 bool should_start_over = false;
1833 decide_foreground_collection_type(clear_all_soft_refs,
1834 &should_compact, &should_start_over);
1835
1836 NOT_PRODUCT(
1837 if (RotateCMSCollectionTypes) {
1838 if (_cmsGen->debug_collection_type() ==
1839 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1840 should_compact = true;
1841 } else if (_cmsGen->debug_collection_type() ==
1842 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1843 should_compact = false;
1844 }
1845 }
1846 )
1847
1848 if (PrintGCDetails && first_state > Idling) {
1849 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1850 if (GCCause::is_user_requested_gc(cause) ||
1851 GCCause::is_serviceability_requested_gc(cause)) {
1852 gclog_or_tty->print(" (concurrent mode interrupted)");
1853 } else {
1854 gclog_or_tty->print(" (concurrent mode failure)");
1855 }
1856 }
1857
1858 set_did_compact(should_compact);
1859 if (should_compact) {
1860 // If the collection is being acquired from the background
1861 // collector, there may be references on the discovered
1862 // references lists that have NULL referents (being those
1863 // that were concurrently cleared by a mutator) or
1864 // that are no longer active (having been enqueued concurrently
1865 // by the mutator).
1866 // Scrub the list of those references because Mark-Sweep-Compact
1867 // code assumes referents are not NULL and that all discovered
1868 // Reference objects are active.
1869 ref_processor()->clean_up_discovered_references();
1870
1871 do_compaction_work(clear_all_soft_refs);
1872
1873 // Has the GC time limit been exceeded?
1874 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1875 size_t max_eden_size = young_gen->max_capacity() -
1876 young_gen->to()->capacity() -
1877 young_gen->from()->capacity();
1878 GenCollectedHeap* gch = GenCollectedHeap::heap();
1879 GCCause::Cause gc_cause = gch->gc_cause();
1880 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1881 young_gen->eden()->used(),
1882 _cmsGen->max_capacity(),
1883 max_eden_size,
1884 full,
1885 gc_cause,
1886 gch->collector_policy());
1887 } else {
1888 do_mark_sweep_work(clear_all_soft_refs, first_state,
1889 should_start_over);
1890 }
1891 // Reset the expansion cause, now that we just completed
1892 // a collection cycle.
1893 clear_expansion_cause();
1894 _foregroundGCIsActive = false;
1895 return;
1896 }
1897
1898 // Resize the tenured generation
1899 // after obtaining the free list locks for the
1900 // two generations.
1901 void CMSCollector::compute_new_size() {
1902 assert_locked_or_safepoint(Heap_lock);
1903 FreelistLocker z(this);
1904 MetaspaceGC::compute_new_size();
1905 _cmsGen->compute_new_size_free_list();
1906 }
1907
1908 // A work method used by foreground collection to determine
1909 // what type of collection (compacting or not, continuing or fresh)
1910 // it should do.
1911 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1912 // and CMSCompactWhenClearAllSoftRefs the default in the future
1913 // and do away with the flags after a suitable period.
1914 void CMSCollector::decide_foreground_collection_type(
1915 bool clear_all_soft_refs, bool* should_compact,
1916 bool* should_start_over) {
1917 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1918 // flag is set, and we have either requested a System.gc() or
1919 // the number of full gc's since the last concurrent cycle
1920 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1921 // or if an incremental collection has failed
1922 GenCollectedHeap* gch = GenCollectedHeap::heap();
1923 assert(gch->collector_policy()->is_two_generation_policy(),
1924 "You may want to check the correctness of the following");
1925 // Inform cms gen if this was due to partial collection failing.
1926 // The CMS gen may use this fact to determine its expansion policy.
1927 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1928 assert(!_cmsGen->incremental_collection_failed(),
1929 "Should have been noticed, reacted to and cleared");
1930 _cmsGen->set_incremental_collection_failed();
1931 }
1932 *should_compact =
1933 UseCMSCompactAtFullCollection &&
1934 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1935 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1936 gch->incremental_collection_will_fail(true /* consult_young */));
1937 *should_start_over = false;
1938 if (clear_all_soft_refs && !*should_compact) {
1939 // We are about to do a last ditch collection attempt
1940 // so it would normally make sense to do a compaction
1941 // to reclaim as much space as possible.
1942 if (CMSCompactWhenClearAllSoftRefs) {
1943 // Default: The rationale is that in this case either
1944 // we are past the final marking phase, in which case
1945 // we'd have to start over, or so little has been done
1946 // that there's little point in saving that work. Compaction
1947 // appears to be the sensible choice in either case.
1948 *should_compact = true;
1949 } else {
1950 // We have been asked to clear all soft refs, but not to
1951 // compact. Make sure that we aren't past the final checkpoint
1952 // phase, for that is where we process soft refs. If we are already
1953 // past that phase, we'll need to redo the refs discovery phase and
1954 // if necessary clear soft refs that weren't previously
1955 // cleared. We do so by remembering the phase in which
1956 // we came in, and if we are past the refs processing
1957 // phase, we'll choose to just redo the mark-sweep
1958 // collection from scratch.
1959 if (_collectorState > FinalMarking) {
1960 // We are past the refs processing phase;
1961 // start over and do a fresh synchronous CMS cycle
1962 _collectorState = Resetting; // skip to reset to start new cycle
1963 reset(false /* == !asynch */);
1964 *should_start_over = true;
1965 } // else we can continue a possibly ongoing current cycle
1966 }
1967 }
1968 }
1969
1970 // A work method used by the foreground collector to do
1971 // a mark-sweep-compact.
1972 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1973 GenCollectedHeap* gch = GenCollectedHeap::heap();
1974 TraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, gclog_or_tty);
1975 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
1976 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
1977 "collections passed to foreground collector", _full_gcs_since_conc_gc);
1978 }
1979
1980 // Sample collection interval time and reset for collection pause.
1981 if (UseAdaptiveSizePolicy) {
1982 size_policy()->msc_collection_begin();
1983 }
1984
1985 // Temporarily widen the span of the weak reference processing to
1986 // the entire heap.
1987 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1988 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1989 // Temporarily, clear the "is_alive_non_header" field of the
1990 // reference processor.
1991 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1992 // Temporarily make reference _processing_ single threaded (non-MT).
1993 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1994 // Temporarily make refs discovery atomic
1995 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1996 // Temporarily make reference _discovery_ single threaded (non-MT)
1997 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1998
1999 ref_processor()->set_enqueuing_is_done(false);
2000 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
2001 ref_processor()->setup_policy(clear_all_soft_refs);
2002 // If an asynchronous collection finishes, the _modUnionTable is
2003 // all clear. If we are assuming the collection from an asynchronous
2004 // collection, clear the _modUnionTable.
2005 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
2006 "_modUnionTable should be clear if the baton was not passed");
2007 _modUnionTable.clear_all();
2008 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
2009 "mod union for klasses should be clear if the baton was passed");
2010 _ct->klass_rem_set()->clear_mod_union();
2011
2012 // We must adjust the allocation statistics being maintained
2013 // in the free list space. We do so by reading and clearing
2014 // the sweep timer and updating the block flux rate estimates below.
2015 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
2016 if (_inter_sweep_timer.is_active()) {
2017 _inter_sweep_timer.stop();
2018 // Note that we do not use this sample to update the _inter_sweep_estimate.
2019 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
2020 _inter_sweep_estimate.padded_average(),
2021 _intra_sweep_estimate.padded_average());
2022 }
2023
2024 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2025 ref_processor(), clear_all_soft_refs);
2026 #ifdef ASSERT
2027 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2028 size_t free_size = cms_space->free();
2029 assert(free_size ==
2030 pointer_delta(cms_space->end(), cms_space->compaction_top())
2031 * HeapWordSize,
2032 "All the free space should be compacted into one chunk at top");
2033 assert(cms_space->dictionary()->total_chunk_size(
2034 debug_only(cms_space->freelistLock())) == 0 ||
2035 cms_space->totalSizeInIndexedFreeLists() == 0,
2036 "All the free space should be in a single chunk");
2037 size_t num = cms_space->totalCount();
2038 assert((free_size == 0 && num == 0) ||
2039 (free_size > 0 && (num == 1 || num == 2)),
2040 "There should be at most 2 free chunks after compaction");
2041 #endif // ASSERT
2042 _collectorState = Resetting;
2043 assert(_restart_addr == NULL,
2044 "Should have been NULL'd before baton was passed");
2045 reset(false /* == !asynch */);
2046 _cmsGen->reset_after_compaction();
2047 _concurrent_cycles_since_last_unload = 0;
2048
2049 // Clear any data recorded in the PLAB chunk arrays.
2050 if (_survivor_plab_array != NULL) {
2051 reset_survivor_plab_arrays();
2052 }
2053
2054 // Adjust the per-size allocation stats for the next epoch.
2055 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2056 // Restart the "inter sweep timer" for the next epoch.
2057 _inter_sweep_timer.reset();
2058 _inter_sweep_timer.start();
2059
2060 // Sample collection pause time and reset for collection interval.
2061 if (UseAdaptiveSizePolicy) {
2062 size_policy()->msc_collection_end(gch->gc_cause());
2063 }
2064
2065 // For a mark-sweep-compact, compute_new_size() will be called
2066 // in the heap's do_collection() method.
2067 }
2068
2069 // A work method used by the foreground collector to do
2070 // a mark-sweep, after taking over from a possibly on-going
2071 // concurrent mark-sweep collection.
2072 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2073 CollectorState first_state, bool should_start_over) {
2074 if (PrintGC && Verbose) {
2075 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2076 "collector with count %d",
2077 _full_gcs_since_conc_gc);
2078 }
2079 switch (_collectorState) {
2080 case Idling:
2081 if (first_state == Idling || should_start_over) {
2082 // The background GC was not active, or should
2083 // restarted from scratch; start the cycle.
2084 _collectorState = InitialMarking;
2085 }
2086 // If first_state was not Idling, then a background GC
2087 // was in progress and has now finished. No need to do it
2088 // again. Leave the state as Idling.
2089 break;
2090 case Precleaning:
2091 // In the foreground case don't do the precleaning since
2092 // it is not done concurrently and there is extra work
2093 // required.
2094 _collectorState = FinalMarking;
2095 }
2096 collect_in_foreground(clear_all_soft_refs);
2097
2098 // For a mark-sweep, compute_new_size() will be called
2099 // in the heap's do_collection() method.
2100 }
2101
2102
2103 void CMSCollector::getFreelistLocks() const {
2104 // Get locks for all free lists in all generations that this
2105 // collector is responsible for
2106 _cmsGen->freelistLock()->lock_without_safepoint_check();
2107 }
2108
2109 void CMSCollector::releaseFreelistLocks() const {
2110 // Release locks for all free lists in all generations that this
2111 // collector is responsible for
2112 _cmsGen->freelistLock()->unlock();
2113 }
2114
2115 bool CMSCollector::haveFreelistLocks() const {
2116 // Check locks for all free lists in all generations that this
2117 // collector is responsible for
2118 assert_lock_strong(_cmsGen->freelistLock());
2119 PRODUCT_ONLY(ShouldNotReachHere());
2120 return true;
2121 }
2122
2123 // A utility class that is used by the CMS collector to
2124 // temporarily "release" the foreground collector from its
2125 // usual obligation to wait for the background collector to
2126 // complete an ongoing phase before proceeding.
2127 class ReleaseForegroundGC: public StackObj {
2128 private:
2129 CMSCollector* _c;
2130 public:
2131 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2132 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2133 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2134 // allow a potentially blocked foreground collector to proceed
2135 _c->_foregroundGCShouldWait = false;
2136 if (_c->_foregroundGCIsActive) {
2137 CGC_lock->notify();
2138 }
2139 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2140 "Possible deadlock");
2141 }
2142
2143 ~ReleaseForegroundGC() {
2144 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2145 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2146 _c->_foregroundGCShouldWait = true;
2147 }
2148 };
2149
2150 // There are separate collect_in_background and collect_in_foreground because of
2151 // the different locking requirements of the background collector and the
2152 // foreground collector. There was originally an attempt to share
2153 // one "collect" method between the background collector and the foreground
2154 // collector but the if-then-else required made it cleaner to have
2155 // separate methods.
2156 void CMSCollector::collect_in_background(bool clear_all_soft_refs) {
2157 assert(Thread::current()->is_ConcurrentGC_thread(),
2158 "A CMS asynchronous collection is only allowed on a CMS thread.");
2159
2160 GenCollectedHeap* gch = GenCollectedHeap::heap();
2161 {
2162 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2163 MutexLockerEx hl(Heap_lock, safepoint_check);
2164 FreelistLocker fll(this);
2165 MutexLockerEx x(CGC_lock, safepoint_check);
2166 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2167 // The foreground collector is active or we're
2168 // not using asynchronous collections. Skip this
2169 // background collection.
2170 assert(!_foregroundGCShouldWait, "Should be clear");
2171 return;
2172 } else {
2173 assert(_collectorState == Idling, "Should be idling before start.");
2174 _collectorState = InitialMarking;
2175 // Reset the expansion cause, now that we are about to begin
2176 // a new cycle.
2177 clear_expansion_cause();
2178
2179 // Clear the MetaspaceGC flag since a concurrent collection
2180 // is starting but also clear it after the collection.
2181 MetaspaceGC::set_should_concurrent_collect(false);
2182 }
2183 // Decide if we want to enable class unloading as part of the
2184 // ensuing concurrent GC cycle.
2185 update_should_unload_classes();
2186 _full_gc_requested = false; // acks all outstanding full gc requests
2187 // Signal that we are about to start a collection
2188 gch->increment_total_full_collections(); // ... starting a collection cycle
2189 _collection_count_start = gch->total_full_collections();
2190 }
2191
2192 // Used for PrintGC
2193 size_t prev_used;
2194 if (PrintGC && Verbose) {
2195 prev_used = _cmsGen->used(); // XXXPERM
2196 }
2197
2198 // The change of the collection state is normally done at this level;
2199 // the exceptions are phases that are executed while the world is
2200 // stopped. For those phases the change of state is done while the
2201 // world is stopped. For baton passing purposes this allows the
2202 // background collector to finish the phase and change state atomically.
2203 // The foreground collector cannot wait on a phase that is done
2204 // while the world is stopped because the foreground collector already
2205 // has the world stopped and would deadlock.
2206 while (_collectorState != Idling) {
2207 if (TraceCMSState) {
2208 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2209 Thread::current(), _collectorState);
2210 }
2211 // The foreground collector
2212 // holds the Heap_lock throughout its collection.
2213 // holds the CMS token (but not the lock)
2214 // except while it is waiting for the background collector to yield.
2215 //
2216 // The foreground collector should be blocked (not for long)
2217 // if the background collector is about to start a phase
2218 // executed with world stopped. If the background
2219 // collector has already started such a phase, the
2220 // foreground collector is blocked waiting for the
2221 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2222 // are executed in the VM thread.
2223 //
2224 // The locking order is
2225 // PendingListLock (PLL) -- if applicable (FinalMarking)
2226 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2227 // CMS token (claimed in
2228 // stop_world_and_do() -->
2229 // safepoint_synchronize() -->
2230 // CMSThread::synchronize())
2231
2232 {
2233 // Check if the FG collector wants us to yield.
2234 CMSTokenSync x(true); // is cms thread
2235 if (waitForForegroundGC()) {
2236 // We yielded to a foreground GC, nothing more to be
2237 // done this round.
2238 assert(_foregroundGCShouldWait == false, "We set it to false in "
2239 "waitForForegroundGC()");
2240 if (TraceCMSState) {
2241 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2242 " exiting collection CMS state %d",
2243 Thread::current(), _collectorState);
2244 }
2245 return;
2246 } else {
2247 // The background collector can run but check to see if the
2248 // foreground collector has done a collection while the
2249 // background collector was waiting to get the CGC_lock
2250 // above. If yes, break so that _foregroundGCShouldWait
2251 // is cleared before returning.
2252 if (_collectorState == Idling) {
2253 break;
2254 }
2255 }
2256 }
2257
2258 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2259 "should be waiting");
2260
2261 switch (_collectorState) {
2262 case InitialMarking:
2263 {
2264 ReleaseForegroundGC x(this);
2265 stats().record_cms_begin();
2266
2267 VM_CMS_Initial_Mark initial_mark_op(this);
2268 VMThread::execute(&initial_mark_op);
2269 }
2270 // The collector state may be any legal state at this point
2271 // since the background collector may have yielded to the
2272 // foreground collector.
2273 break;
2274 case Marking:
2275 // initial marking in checkpointRootsInitialWork has been completed
2276 if (markFromRoots(true)) { // we were successful
2277 assert(_collectorState == Precleaning, "Collector state should "
2278 "have changed");
2279 } else {
2280 assert(_foregroundGCIsActive, "Internal state inconsistency");
2281 }
2282 break;
2283 case Precleaning:
2284 if (UseAdaptiveSizePolicy) {
2285 size_policy()->concurrent_precleaning_begin();
2286 }
2287 // marking from roots in markFromRoots has been completed
2288 preclean();
2289 if (UseAdaptiveSizePolicy) {
2290 size_policy()->concurrent_precleaning_end();
2291 }
2292 assert(_collectorState == AbortablePreclean ||
2293 _collectorState == FinalMarking,
2294 "Collector state should have changed");
2295 break;
2296 case AbortablePreclean:
2297 if (UseAdaptiveSizePolicy) {
2298 size_policy()->concurrent_phases_resume();
2299 }
2300 abortable_preclean();
2301 if (UseAdaptiveSizePolicy) {
2302 size_policy()->concurrent_precleaning_end();
2303 }
2304 assert(_collectorState == FinalMarking, "Collector state should "
2305 "have changed");
2306 break;
2307 case FinalMarking:
2308 {
2309 ReleaseForegroundGC x(this);
2310
2311 VM_CMS_Final_Remark final_remark_op(this);
2312 VMThread::execute(&final_remark_op);
2313 }
2314 assert(_foregroundGCShouldWait, "block post-condition");
2315 break;
2316 case Sweeping:
2317 if (UseAdaptiveSizePolicy) {
2318 size_policy()->concurrent_sweeping_begin();
2319 }
2320 // final marking in checkpointRootsFinal has been completed
2321 sweep(true);
2322 assert(_collectorState == Resizing, "Collector state change "
2323 "to Resizing must be done under the free_list_lock");
2324 _full_gcs_since_conc_gc = 0;
2325
2326 // Stop the timers for adaptive size policy for the concurrent phases
2327 if (UseAdaptiveSizePolicy) {
2328 size_policy()->concurrent_sweeping_end();
2329 size_policy()->concurrent_phases_end(gch->gc_cause(),
2330 gch->prev_gen(_cmsGen)->capacity(),
2331 _cmsGen->free());
2332 }
2333
2334 case Resizing: {
2335 // Sweeping has been completed...
2336 // At this point the background collection has completed.
2337 // Don't move the call to compute_new_size() down
2338 // into code that might be executed if the background
2339 // collection was preempted.
2340 {
2341 ReleaseForegroundGC x(this); // unblock FG collection
2342 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2343 CMSTokenSync z(true); // not strictly needed.
2344 if (_collectorState == Resizing) {
2345 compute_new_size();
2346 _collectorState = Resetting;
2347 } else {
2348 assert(_collectorState == Idling, "The state should only change"
2349 " because the foreground collector has finished the collection");
2350 }
2351 }
2352 break;
2353 }
2354 case Resetting:
2355 // CMS heap resizing has been completed
2356 reset(true);
2357 assert(_collectorState == Idling, "Collector state should "
2358 "have changed");
2359
2360 MetaspaceGC::set_should_concurrent_collect(false);
2361
2362 stats().record_cms_end();
2363 // Don't move the concurrent_phases_end() and compute_new_size()
2364 // calls to here because a preempted background collection
2365 // has it's state set to "Resetting".
2366 break;
2367 case Idling:
2368 default:
2369 ShouldNotReachHere();
2370 break;
2371 }
2372 if (TraceCMSState) {
2373 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2374 Thread::current(), _collectorState);
2375 }
2376 assert(_foregroundGCShouldWait, "block post-condition");
2377 }
2378
2379 // Should this be in gc_epilogue?
2380 collector_policy()->counters()->update_counters();
2381
2382 {
2383 // Clear _foregroundGCShouldWait and, in the event that the
2384 // foreground collector is waiting, notify it, before
2385 // returning.
2386 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2387 _foregroundGCShouldWait = false;
2388 if (_foregroundGCIsActive) {
2389 CGC_lock->notify();
2390 }
2391 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2392 "Possible deadlock");
2393 }
2394 if (TraceCMSState) {
2395 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2396 " exiting collection CMS state %d",
2397 Thread::current(), _collectorState);
2398 }
2399 if (PrintGC && Verbose) {
2400 _cmsGen->print_heap_change(prev_used);
2401 }
2402 }
2403
2404 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs) {
2405 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2406 "Foreground collector should be waiting, not executing");
2407 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2408 "may only be done by the VM Thread with the world stopped");
2409 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2410 "VM thread should have CMS token");
2411
2412 NOT_PRODUCT(TraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2413 true, gclog_or_tty);)
2414 if (UseAdaptiveSizePolicy) {
2415 size_policy()->ms_collection_begin();
2416 }
2417 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2418
2419 HandleMark hm; // Discard invalid handles created during verification
2420
2421 if (VerifyBeforeGC &&
2422 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2423 Universe::verify();
2424 }
2425
2426 // Snapshot the soft reference policy to be used in this collection cycle.
2427 ref_processor()->setup_policy(clear_all_soft_refs);
2428
2429 bool init_mark_was_synchronous = false; // until proven otherwise
2430 while (_collectorState != Idling) {
2431 if (TraceCMSState) {
2432 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2433 Thread::current(), _collectorState);
2434 }
2435 switch (_collectorState) {
2436 case InitialMarking:
2437 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2438 checkpointRootsInitial(false);
2439 assert(_collectorState == Marking, "Collector state should have changed"
2440 " within checkpointRootsInitial()");
2441 break;
2442 case Marking:
2443 // initial marking in checkpointRootsInitialWork has been completed
2444 if (VerifyDuringGC &&
2445 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2446 Universe::verify("Verify before initial mark: ");
2447 }
2448 {
2449 bool res = markFromRoots(false);
2450 assert(res && _collectorState == FinalMarking, "Collector state should "
2451 "have changed");
2452 break;
2453 }
2454 case FinalMarking:
2455 if (VerifyDuringGC &&
2456 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2457 Universe::verify("Verify before re-mark: ");
2458 }
2459 checkpointRootsFinal(false, clear_all_soft_refs,
2460 init_mark_was_synchronous);
2461 assert(_collectorState == Sweeping, "Collector state should not "
2462 "have changed within checkpointRootsFinal()");
2463 break;
2464 case Sweeping:
2465 // final marking in checkpointRootsFinal has been completed
2466 if (VerifyDuringGC &&
2467 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2468 Universe::verify("Verify before sweep: ");
2469 }
2470 sweep(false);
2471 assert(_collectorState == Resizing, "Incorrect state");
2472 break;
2473 case Resizing: {
2474 // Sweeping has been completed; the actual resize in this case
2475 // is done separately; nothing to be done in this state.
2476 _collectorState = Resetting;
2477 break;
2478 }
2479 case Resetting:
2480 // The heap has been resized.
2481 if (VerifyDuringGC &&
2482 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2483 Universe::verify("Verify before reset: ");
2484 }
2485 reset(false);
2486 assert(_collectorState == Idling, "Collector state should "
2487 "have changed");
2488 break;
2489 case Precleaning:
2490 case AbortablePreclean:
2491 // Elide the preclean phase
2492 _collectorState = FinalMarking;
2493 break;
2494 default:
2495 ShouldNotReachHere();
2496 }
2497 if (TraceCMSState) {
2498 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2499 Thread::current(), _collectorState);
2500 }
2501 }
2502
2503 if (UseAdaptiveSizePolicy) {
2504 GenCollectedHeap* gch = GenCollectedHeap::heap();
2505 size_policy()->ms_collection_end(gch->gc_cause());
2506 }
2507
2508 if (VerifyAfterGC &&
2509 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2510 Universe::verify();
2511 }
2512 if (TraceCMSState) {
2513 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2514 " exiting collection CMS state %d",
2515 Thread::current(), _collectorState);
2516 }
2517 }
2518
2519 bool CMSCollector::waitForForegroundGC() {
2520 bool res = false;
2521 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2522 "CMS thread should have CMS token");
2523 // Block the foreground collector until the
2524 // background collectors decides whether to
2525 // yield.
2526 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2527 _foregroundGCShouldWait = true;
2528 if (_foregroundGCIsActive) {
2529 // The background collector yields to the
2530 // foreground collector and returns a value
2531 // indicating that it has yielded. The foreground
2532 // collector can proceed.
2533 res = true;
2534 _foregroundGCShouldWait = false;
2535 ConcurrentMarkSweepThread::clear_CMS_flag(
2536 ConcurrentMarkSweepThread::CMS_cms_has_token);
2537 ConcurrentMarkSweepThread::set_CMS_flag(
2538 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2539 // Get a possibly blocked foreground thread going
2540 CGC_lock->notify();
2541 if (TraceCMSState) {
2542 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2543 Thread::current(), _collectorState);
2544 }
2545 while (_foregroundGCIsActive) {
2546 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2547 }
2548 ConcurrentMarkSweepThread::set_CMS_flag(
2549 ConcurrentMarkSweepThread::CMS_cms_has_token);
2550 ConcurrentMarkSweepThread::clear_CMS_flag(
2551 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2552 }
2553 if (TraceCMSState) {
2554 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2555 Thread::current(), _collectorState);
2556 }
2557 return res;
2558 }
2559
2560 // Because of the need to lock the free lists and other structures in
2561 // the collector, common to all the generations that the collector is
2562 // collecting, we need the gc_prologues of individual CMS generations
2563 // delegate to their collector. It may have been simpler had the
2564 // current infrastructure allowed one to call a prologue on a
2565 // collector. In the absence of that we have the generation's
2566 // prologue delegate to the collector, which delegates back
2567 // some "local" work to a worker method in the individual generations
2568 // that it's responsible for collecting, while itself doing any
2569 // work common to all generations it's responsible for. A similar
2570 // comment applies to the gc_epilogue()'s.
2571 // The role of the varaible _between_prologue_and_epilogue is to
2572 // enforce the invocation protocol.
2573 void CMSCollector::gc_prologue(bool full) {
2574 // Call gc_prologue_work() for the CMSGen
2575 // we are responsible for.
2576
2577 // The following locking discipline assumes that we are only called
2578 // when the world is stopped.
2579 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2580
2581 // The CMSCollector prologue must call the gc_prologues for the
2582 // "generations" that it's responsible
2583 // for.
2584
2585 assert( Thread::current()->is_VM_thread()
2586 || ( CMSScavengeBeforeRemark
2587 && Thread::current()->is_ConcurrentGC_thread()),
2588 "Incorrect thread type for prologue execution");
2589
2590 if (_between_prologue_and_epilogue) {
2591 // We have already been invoked; this is a gc_prologue delegation
2592 // from yet another CMS generation that we are responsible for, just
2593 // ignore it since all relevant work has already been done.
2594 return;
2595 }
2596
2597 // set a bit saying prologue has been called; cleared in epilogue
2598 _between_prologue_and_epilogue = true;
2599 // Claim locks for common data structures, then call gc_prologue_work()
2600 // for each CMSGen.
2601
2602 getFreelistLocks(); // gets free list locks on constituent spaces
2603 bitMapLock()->lock_without_safepoint_check();
2604
2605 // Should call gc_prologue_work() for all cms gens we are responsible for
2606 bool duringMarking = _collectorState >= Marking
2607 && _collectorState < Sweeping;
2608
2609 // The young collections clear the modified oops state, which tells if
2610 // there are any modified oops in the class. The remark phase also needs
2611 // that information. Tell the young collection to save the union of all
2612 // modified klasses.
2613 if (duringMarking) {
2614 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2615 }
2616
2617 bool registerClosure = duringMarking;
2618
2619 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2620 &_modUnionClosurePar
2621 : &_modUnionClosure;
2622 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2623
2624 if (!full) {
2625 stats().record_gc0_begin();
2626 }
2627 }
2628
2629 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2630
2631 _capacity_at_prologue = capacity();
2632 _used_at_prologue = used();
2633
2634 // Delegate to CMScollector which knows how to coordinate between
2635 // this and any other CMS generations that it is responsible for
2636 // collecting.
2637 collector()->gc_prologue(full);
2638 }
2639
2640 // This is a "private" interface for use by this generation's CMSCollector.
2641 // Not to be called directly by any other entity (for instance,
2642 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2643 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2644 bool registerClosure, ModUnionClosure* modUnionClosure) {
2645 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2646 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2647 "Should be NULL");
2648 if (registerClosure) {
2649 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2650 }
2651 cmsSpace()->gc_prologue();
2652 // Clear stat counters
2653 NOT_PRODUCT(
2654 assert(_numObjectsPromoted == 0, "check");
2655 assert(_numWordsPromoted == 0, "check");
2656 if (Verbose && PrintGC) {
2657 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2658 SIZE_FORMAT" bytes concurrently",
2659 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2660 }
2661 _numObjectsAllocated = 0;
2662 _numWordsAllocated = 0;
2663 )
2664 }
2665
2666 void CMSCollector::gc_epilogue(bool full) {
2667 // The following locking discipline assumes that we are only called
2668 // when the world is stopped.
2669 assert(SafepointSynchronize::is_at_safepoint(),
2670 "world is stopped assumption");
2671
2672 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2673 // if linear allocation blocks need to be appropriately marked to allow the
2674 // the blocks to be parsable. We also check here whether we need to nudge the
2675 // CMS collector thread to start a new cycle (if it's not already active).
2676 assert( Thread::current()->is_VM_thread()
2677 || ( CMSScavengeBeforeRemark
2678 && Thread::current()->is_ConcurrentGC_thread()),
2679 "Incorrect thread type for epilogue execution");
2680
2681 if (!_between_prologue_and_epilogue) {
2682 // We have already been invoked; this is a gc_epilogue delegation
2683 // from yet another CMS generation that we are responsible for, just
2684 // ignore it since all relevant work has already been done.
2685 return;
2686 }
2687 assert(haveFreelistLocks(), "must have freelist locks");
2688 assert_lock_strong(bitMapLock());
2689
2690 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2691
2692 _cmsGen->gc_epilogue_work(full);
2693
2694 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2695 // in case sampling was not already enabled, enable it
2696 _start_sampling = true;
2697 }
2698 // reset _eden_chunk_array so sampling starts afresh
2699 _eden_chunk_index = 0;
2700
2701 size_t cms_used = _cmsGen->cmsSpace()->used();
2702
2703 // update performance counters - this uses a special version of
2704 // update_counters() that allows the utilization to be passed as a
2705 // parameter, avoiding multiple calls to used().
2706 //
2707 _cmsGen->update_counters(cms_used);
2708
2709 if (CMSIncrementalMode) {
2710 icms_update_allocation_limits();
2711 }
2712
2713 bitMapLock()->unlock();
2714 releaseFreelistLocks();
2715
2716 if (!CleanChunkPoolAsync) {
2717 Chunk::clean_chunk_pool();
2718 }
2719
2720 set_did_compact(false);
2721 _between_prologue_and_epilogue = false; // ready for next cycle
2722 }
2723
2724 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2725 collector()->gc_epilogue(full);
2726
2727 // Also reset promotion tracking in par gc thread states.
2728 if (CollectedHeap::use_parallel_gc_threads()) {
2729 for (uint i = 0; i < ParallelGCThreads; i++) {
2730 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2731 }
2732 }
2733 }
2734
2735 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2736 assert(!incremental_collection_failed(), "Should have been cleared");
2737 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2738 cmsSpace()->gc_epilogue();
2739 // Print stat counters
2740 NOT_PRODUCT(
2741 assert(_numObjectsAllocated == 0, "check");
2742 assert(_numWordsAllocated == 0, "check");
2743 if (Verbose && PrintGC) {
2744 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2745 SIZE_FORMAT" bytes",
2746 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2747 }
2748 _numObjectsPromoted = 0;
2749 _numWordsPromoted = 0;
2750 )
2751
2752 if (PrintGC && Verbose) {
2753 // Call down the chain in contiguous_available needs the freelistLock
2754 // so print this out before releasing the freeListLock.
2755 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2756 contiguous_available());
2757 }
2758 }
2759
2760 #ifndef PRODUCT
2761 bool CMSCollector::have_cms_token() {
2762 Thread* thr = Thread::current();
2763 if (thr->is_VM_thread()) {
2764 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2765 } else if (thr->is_ConcurrentGC_thread()) {
2766 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2767 } else if (thr->is_GC_task_thread()) {
2768 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2769 ParGCRareEvent_lock->owned_by_self();
2770 }
2771 return false;
2772 }
2773 #endif
2774
2775 // Check reachability of the given heap address in CMS generation,
2776 // treating all other generations as roots.
2777 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2778 // We could "guarantee" below, rather than assert, but i'll
2779 // leave these as "asserts" so that an adventurous debugger
2780 // could try this in the product build provided some subset of
2781 // the conditions were met, provided they were intersted in the
2782 // results and knew that the computation below wouldn't interfere
2783 // with other concurrent computations mutating the structures
2784 // being read or written.
2785 assert(SafepointSynchronize::is_at_safepoint(),
2786 "Else mutations in object graph will make answer suspect");
2787 assert(have_cms_token(), "Should hold cms token");
2788 assert(haveFreelistLocks(), "must hold free list locks");
2789 assert_lock_strong(bitMapLock());
2790
2791 // Clear the marking bit map array before starting, but, just
2792 // for kicks, first report if the given address is already marked
2793 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2794 _markBitMap.isMarked(addr) ? "" : " not");
2795
2796 if (verify_after_remark()) {
2797 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2798 bool result = verification_mark_bm()->isMarked(addr);
2799 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2800 result ? "IS" : "is NOT");
2801 return result;
2802 } else {
2803 gclog_or_tty->print_cr("Could not compute result");
2804 return false;
2805 }
2806 }
2807
2808
2809 void
2810 CMSCollector::print_on_error(outputStream* st) {
2811 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2812 if (collector != NULL) {
2813 CMSBitMap* bitmap = &collector->_markBitMap;
2814 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, bitmap);
2815 bitmap->print_on_error(st, " Bits: ");
2816
2817 st->cr();
2818
2819 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2820 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, mut_bitmap);
2821 mut_bitmap->print_on_error(st, " Bits: ");
2822 }
2823 }
2824
2825 ////////////////////////////////////////////////////////
2826 // CMS Verification Support
2827 ////////////////////////////////////////////////////////
2828 // Following the remark phase, the following invariant
2829 // should hold -- each object in the CMS heap which is
2830 // marked in markBitMap() should be marked in the verification_mark_bm().
2831
2832 class VerifyMarkedClosure: public BitMapClosure {
2833 CMSBitMap* _marks;
2834 bool _failed;
2835
2836 public:
2837 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2838
2839 bool do_bit(size_t offset) {
2840 HeapWord* addr = _marks->offsetToHeapWord(offset);
2841 if (!_marks->isMarked(addr)) {
2842 oop(addr)->print_on(gclog_or_tty);
2843 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2844 _failed = true;
2845 }
2846 return true;
2847 }
2848
2849 bool failed() { return _failed; }
2850 };
2851
2852 bool CMSCollector::verify_after_remark(bool silent) {
2853 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2854 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2855 static bool init = false;
2856
2857 assert(SafepointSynchronize::is_at_safepoint(),
2858 "Else mutations in object graph will make answer suspect");
2859 assert(have_cms_token(),
2860 "Else there may be mutual interference in use of "
2861 " verification data structures");
2862 assert(_collectorState > Marking && _collectorState <= Sweeping,
2863 "Else marking info checked here may be obsolete");
2864 assert(haveFreelistLocks(), "must hold free list locks");
2865 assert_lock_strong(bitMapLock());
2866
2867
2868 // Allocate marking bit map if not already allocated
2869 if (!init) { // first time
2870 if (!verification_mark_bm()->allocate(_span)) {
2871 return false;
2872 }
2873 init = true;
2874 }
2875
2876 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2877
2878 // Turn off refs discovery -- so we will be tracing through refs.
2879 // This is as intended, because by this time
2880 // GC must already have cleared any refs that need to be cleared,
2881 // and traced those that need to be marked; moreover,
2882 // the marking done here is not going to intefere in any
2883 // way with the marking information used by GC.
2884 NoRefDiscovery no_discovery(ref_processor());
2885
2886 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2887
2888 // Clear any marks from a previous round
2889 verification_mark_bm()->clear_all();
2890 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2891 verify_work_stacks_empty();
2892
2893 GenCollectedHeap* gch = GenCollectedHeap::heap();
2894 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2895 // Update the saved marks which may affect the root scans.
2896 gch->save_marks();
2897
2898 if (CMSRemarkVerifyVariant == 1) {
2899 // In this first variant of verification, we complete
2900 // all marking, then check if the new marks-verctor is
2901 // a subset of the CMS marks-vector.
2902 verify_after_remark_work_1();
2903 } else if (CMSRemarkVerifyVariant == 2) {
2904 // In this second variant of verification, we flag an error
2905 // (i.e. an object reachable in the new marks-vector not reachable
2906 // in the CMS marks-vector) immediately, also indicating the
2907 // identify of an object (A) that references the unmarked object (B) --
2908 // presumably, a mutation to A failed to be picked up by preclean/remark?
2909 verify_after_remark_work_2();
2910 } else {
2911 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2912 CMSRemarkVerifyVariant);
2913 }
2914 if (!silent) gclog_or_tty->print(" done] ");
2915 return true;
2916 }
2917
2918 void CMSCollector::verify_after_remark_work_1() {
2919 ResourceMark rm;
2920 HandleMark hm;
2921 GenCollectedHeap* gch = GenCollectedHeap::heap();
2922
2923 // Get a clear set of claim bits for the strong roots processing to work with.
2924 ClassLoaderDataGraph::clear_claimed_marks();
2925
2926 // Mark from roots one level into CMS
2927 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2928 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2929
2930 gch->gen_process_strong_roots(_cmsGen->level(),
2931 true, // younger gens are roots
2932 true, // activate StrongRootsScope
2933 false, // not scavenging
2934 SharedHeap::ScanningOption(roots_scanning_options()),
2935 ¬Older,
2936 true, // walk code active on stacks
2937 NULL,
2938 NULL); // SSS: Provide correct closure
2939
2940 // Now mark from the roots
2941 MarkFromRootsClosure markFromRootsClosure(this, _span,
2942 verification_mark_bm(), verification_mark_stack(),
2943 false /* don't yield */, true /* verifying */);
2944 assert(_restart_addr == NULL, "Expected pre-condition");
2945 verification_mark_bm()->iterate(&markFromRootsClosure);
2946 while (_restart_addr != NULL) {
2947 // Deal with stack overflow: by restarting at the indicated
2948 // address.
2949 HeapWord* ra = _restart_addr;
2950 markFromRootsClosure.reset(ra);
2951 _restart_addr = NULL;
2952 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2953 }
2954 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2955 verify_work_stacks_empty();
2956
2957 // Marking completed -- now verify that each bit marked in
2958 // verification_mark_bm() is also marked in markBitMap(); flag all
2959 // errors by printing corresponding objects.
2960 VerifyMarkedClosure vcl(markBitMap());
2961 verification_mark_bm()->iterate(&vcl);
2962 if (vcl.failed()) {
2963 gclog_or_tty->print("Verification failed");
2964 Universe::heap()->print_on(gclog_or_tty);
2965 fatal("CMS: failed marking verification after remark");
2966 }
2967 }
2968
2969 class VerifyKlassOopsKlassClosure : public KlassClosure {
2970 class VerifyKlassOopsClosure : public OopClosure {
2971 CMSBitMap* _bitmap;
2972 public:
2973 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2974 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2975 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2976 } _oop_closure;
2977 public:
2978 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2979 void do_klass(Klass* k) {
2980 k->oops_do(&_oop_closure);
2981 }
2982 };
2983
2984 void CMSCollector::verify_after_remark_work_2() {
2985 ResourceMark rm;
2986 HandleMark hm;
2987 GenCollectedHeap* gch = GenCollectedHeap::heap();
2988
2989 // Get a clear set of claim bits for the strong roots processing to work with.
2990 ClassLoaderDataGraph::clear_claimed_marks();
2991
2992 // Mark from roots one level into CMS
2993 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2994 markBitMap());
2995 CMKlassClosure klass_closure(¬Older);
2996
2997 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2998 gch->gen_process_strong_roots(_cmsGen->level(),
2999 true, // younger gens are roots
3000 true, // activate StrongRootsScope
3001 false, // not scavenging
3002 SharedHeap::ScanningOption(roots_scanning_options()),
3003 ¬Older,
3004 true, // walk code active on stacks
3005 NULL,
3006 &klass_closure);
3007
3008 // Now mark from the roots
3009 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
3010 verification_mark_bm(), markBitMap(), verification_mark_stack());
3011 assert(_restart_addr == NULL, "Expected pre-condition");
3012 verification_mark_bm()->iterate(&markFromRootsClosure);
3013 while (_restart_addr != NULL) {
3014 // Deal with stack overflow: by restarting at the indicated
3015 // address.
3016 HeapWord* ra = _restart_addr;
3017 markFromRootsClosure.reset(ra);
3018 _restart_addr = NULL;
3019 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3020 }
3021 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3022 verify_work_stacks_empty();
3023
3024 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
3025 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
3026
3027 // Marking completed -- now verify that each bit marked in
3028 // verification_mark_bm() is also marked in markBitMap(); flag all
3029 // errors by printing corresponding objects.
3030 VerifyMarkedClosure vcl(markBitMap());
3031 verification_mark_bm()->iterate(&vcl);
3032 assert(!vcl.failed(), "Else verification above should not have succeeded");
3033 }
3034
3035 void ConcurrentMarkSweepGeneration::save_marks() {
3036 // delegate to CMS space
3037 cmsSpace()->save_marks();
3038 for (uint i = 0; i < ParallelGCThreads; i++) {
3039 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3040 }
3041 }
3042
3043 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3044 return cmsSpace()->no_allocs_since_save_marks();
3045 }
3046
3047 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3048 \
3049 void ConcurrentMarkSweepGeneration:: \
3050 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3051 cl->set_generation(this); \
3052 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3053 cl->reset_generation(); \
3054 save_marks(); \
3055 }
3056
3057 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3058
3059 void
3060 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
3061 {
3062 // Not currently implemented; need to do the following. -- ysr.
3063 // dld -- I think that is used for some sort of allocation profiler. So it
3064 // really means the objects allocated by the mutator since the last
3065 // GC. We could potentially implement this cheaply by recording only
3066 // the direct allocations in a side data structure.
3067 //
3068 // I think we probably ought not to be required to support these
3069 // iterations at any arbitrary point; I think there ought to be some
3070 // call to enable/disable allocation profiling in a generation/space,
3071 // and the iterator ought to return the objects allocated in the
3072 // gen/space since the enable call, or the last iterator call (which
3073 // will probably be at a GC.) That way, for gens like CM&S that would
3074 // require some extra data structure to support this, we only pay the
3075 // cost when it's in use...
3076 cmsSpace()->object_iterate_since_last_GC(blk);
3077 }
3078
3079 void
3080 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3081 cl->set_generation(this);
3082 younger_refs_in_space_iterate(_cmsSpace, cl);
3083 cl->reset_generation();
3084 }
3085
3086 void
3087 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, ExtendedOopClosure* cl) {
3088 if (freelistLock()->owned_by_self()) {
3089 Generation::oop_iterate(mr, cl);
3090 } else {
3091 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3092 Generation::oop_iterate(mr, cl);
3093 }
3094 }
3095
3096 void
3097 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
3098 if (freelistLock()->owned_by_self()) {
3099 Generation::oop_iterate(cl);
3100 } else {
3101 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3102 Generation::oop_iterate(cl);
3103 }
3104 }
3105
3106 void
3107 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3108 if (freelistLock()->owned_by_self()) {
3109 Generation::object_iterate(cl);
3110 } else {
3111 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3112 Generation::object_iterate(cl);
3113 }
3114 }
3115
3116 void
3117 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3118 if (freelistLock()->owned_by_self()) {
3119 Generation::safe_object_iterate(cl);
3120 } else {
3121 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3122 Generation::safe_object_iterate(cl);
3123 }
3124 }
3125
3126 void
3127 ConcurrentMarkSweepGeneration::post_compact() {
3128 }
3129
3130 void
3131 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3132 // Fix the linear allocation blocks to look like free blocks.
3133
3134 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3135 // are not called when the heap is verified during universe initialization and
3136 // at vm shutdown.
3137 if (freelistLock()->owned_by_self()) {
3138 cmsSpace()->prepare_for_verify();
3139 } else {
3140 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3141 cmsSpace()->prepare_for_verify();
3142 }
3143 }
3144
3145 void
3146 ConcurrentMarkSweepGeneration::verify() {
3147 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3148 // are not called when the heap is verified during universe initialization and
3149 // at vm shutdown.
3150 if (freelistLock()->owned_by_self()) {
3151 cmsSpace()->verify();
3152 } else {
3153 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3154 cmsSpace()->verify();
3155 }
3156 }
3157
3158 void CMSCollector::verify() {
3159 _cmsGen->verify();
3160 }
3161
3162 #ifndef PRODUCT
3163 bool CMSCollector::overflow_list_is_empty() const {
3164 assert(_num_par_pushes >= 0, "Inconsistency");
3165 if (_overflow_list == NULL) {
3166 assert(_num_par_pushes == 0, "Inconsistency");
3167 }
3168 return _overflow_list == NULL;
3169 }
3170
3171 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3172 // merely consolidate assertion checks that appear to occur together frequently.
3173 void CMSCollector::verify_work_stacks_empty() const {
3174 assert(_markStack.isEmpty(), "Marking stack should be empty");
3175 assert(overflow_list_is_empty(), "Overflow list should be empty");
3176 }
3177
3178 void CMSCollector::verify_overflow_empty() const {
3179 assert(overflow_list_is_empty(), "Overflow list should be empty");
3180 assert(no_preserved_marks(), "No preserved marks");
3181 }
3182 #endif // PRODUCT
3183
3184 // Decide if we want to enable class unloading as part of the
3185 // ensuing concurrent GC cycle. We will collect and
3186 // unload classes if it's the case that:
3187 // (1) an explicit gc request has been made and the flag
3188 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3189 // (2) (a) class unloading is enabled at the command line, and
3190 // (b) old gen is getting really full
3191 // NOTE: Provided there is no change in the state of the heap between
3192 // calls to this method, it should have idempotent results. Moreover,
3193 // its results should be monotonically increasing (i.e. going from 0 to 1,
3194 // but not 1 to 0) between successive calls between which the heap was
3195 // not collected. For the implementation below, it must thus rely on
3196 // the property that concurrent_cycles_since_last_unload()
3197 // will not decrease unless a collection cycle happened and that
3198 // _cmsGen->is_too_full() are
3199 // themselves also monotonic in that sense. See check_monotonicity()
3200 // below.
3201 void CMSCollector::update_should_unload_classes() {
3202 _should_unload_classes = false;
3203 // Condition 1 above
3204 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3205 _should_unload_classes = true;
3206 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3207 // Disjuncts 2.b.(i,ii,iii) above
3208 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3209 CMSClassUnloadingMaxInterval)
3210 || _cmsGen->is_too_full();
3211 }
3212 }
3213
3214 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3215 bool res = should_concurrent_collect();
3216 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3217 return res;
3218 }
3219
3220 void CMSCollector::setup_cms_unloading_and_verification_state() {
3221 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3222 || VerifyBeforeExit;
3223 const int rso = SharedHeap::SO_Strings | SharedHeap::SO_CodeCache;
3224
3225 if (should_unload_classes()) { // Should unload classes this cycle
3226 remove_root_scanning_option(rso); // Shrink the root set appropriately
3227 set_verifying(should_verify); // Set verification state for this cycle
3228 return; // Nothing else needs to be done at this time
3229 }
3230
3231 // Not unloading classes this cycle
3232 assert(!should_unload_classes(), "Inconsitency!");
3233 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3234 // Include symbols, strings and code cache elements to prevent their resurrection.
3235 add_root_scanning_option(rso);
3236 set_verifying(true);
3237 } else if (verifying() && !should_verify) {
3238 // We were verifying, but some verification flags got disabled.
3239 set_verifying(false);
3240 // Exclude symbols, strings and code cache elements from root scanning to
3241 // reduce IM and RM pauses.
3242 remove_root_scanning_option(rso);
3243 }
3244 }
3245
3246
3247 #ifndef PRODUCT
3248 HeapWord* CMSCollector::block_start(const void* p) const {
3249 const HeapWord* addr = (HeapWord*)p;
3250 if (_span.contains(p)) {
3251 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3252 return _cmsGen->cmsSpace()->block_start(p);
3253 }
3254 }
3255 return NULL;
3256 }
3257 #endif
3258
3259 HeapWord*
3260 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3261 bool tlab,
3262 bool parallel) {
3263 CMSSynchronousYieldRequest yr;
3264 assert(!tlab, "Can't deal with TLAB allocation");
3265 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3266 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3267 CMSExpansionCause::_satisfy_allocation);
3268 if (GCExpandToAllocateDelayMillis > 0) {
3269 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3270 }
3271 return have_lock_and_allocate(word_size, tlab);
3272 }
3273
3274 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3275 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3276 // to CardGeneration and share it...
3277 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3278 return CardGeneration::expand(bytes, expand_bytes);
3279 }
3280
3281 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3282 CMSExpansionCause::Cause cause)
3283 {
3284
3285 bool success = expand(bytes, expand_bytes);
3286
3287 // remember why we expanded; this information is used
3288 // by shouldConcurrentCollect() when making decisions on whether to start
3289 // a new CMS cycle.
3290 if (success) {
3291 set_expansion_cause(cause);
3292 if (PrintGCDetails && Verbose) {
3293 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3294 CMSExpansionCause::to_string(cause));
3295 }
3296 }
3297 }
3298
3299 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3300 HeapWord* res = NULL;
3301 MutexLocker x(ParGCRareEvent_lock);
3302 while (true) {
3303 // Expansion by some other thread might make alloc OK now:
3304 res = ps->lab.alloc(word_sz);
3305 if (res != NULL) return res;
3306 // If there's not enough expansion space available, give up.
3307 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3308 return NULL;
3309 }
3310 // Otherwise, we try expansion.
3311 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3312 CMSExpansionCause::_allocate_par_lab);
3313 // Now go around the loop and try alloc again;
3314 // A competing par_promote might beat us to the expansion space,
3315 // so we may go around the loop again if promotion fails agaion.
3316 if (GCExpandToAllocateDelayMillis > 0) {
3317 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3318 }
3319 }
3320 }
3321
3322
3323 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3324 PromotionInfo* promo) {
3325 MutexLocker x(ParGCRareEvent_lock);
3326 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3327 while (true) {
3328 // Expansion by some other thread might make alloc OK now:
3329 if (promo->ensure_spooling_space()) {
3330 assert(promo->has_spooling_space(),
3331 "Post-condition of successful ensure_spooling_space()");
3332 return true;
3333 }
3334 // If there's not enough expansion space available, give up.
3335 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3336 return false;
3337 }
3338 // Otherwise, we try expansion.
3339 expand(refill_size_bytes, MinHeapDeltaBytes,
3340 CMSExpansionCause::_allocate_par_spooling_space);
3341 // Now go around the loop and try alloc again;
3342 // A competing allocation might beat us to the expansion space,
3343 // so we may go around the loop again if allocation fails again.
3344 if (GCExpandToAllocateDelayMillis > 0) {
3345 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3346 }
3347 }
3348 }
3349
3350
3351 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3352 assert_locked_or_safepoint(ExpandHeap_lock);
3353 // Shrink committed space
3354 _virtual_space.shrink_by(bytes);
3355 // Shrink space; this also shrinks the space's BOT
3356 _cmsSpace->set_end((HeapWord*) _virtual_space.high());
3357 size_t new_word_size = heap_word_size(_cmsSpace->capacity());
3358 // Shrink the shared block offset array
3359 _bts->resize(new_word_size);
3360 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3361 // Shrink the card table
3362 Universe::heap()->barrier_set()->resize_covered_region(mr);
3363
3364 if (Verbose && PrintGC) {
3365 size_t new_mem_size = _virtual_space.committed_size();
3366 size_t old_mem_size = new_mem_size + bytes;
3367 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3368 name(), old_mem_size/K, new_mem_size/K);
3369 }
3370 }
3371
3372 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3373 assert_locked_or_safepoint(Heap_lock);
3374 size_t size = ReservedSpace::page_align_size_down(bytes);
3375 if (size > 0) {
3376 shrink_by(size);
3377 }
3378 }
3379
3380 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3381 assert_locked_or_safepoint(Heap_lock);
3382 bool result = _virtual_space.expand_by(bytes);
3383 if (result) {
3384 size_t new_word_size =
3385 heap_word_size(_virtual_space.committed_size());
3386 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3387 _bts->resize(new_word_size); // resize the block offset shared array
3388 Universe::heap()->barrier_set()->resize_covered_region(mr);
3389 // Hmmmm... why doesn't CFLS::set_end verify locking?
3390 // This is quite ugly; FIX ME XXX
3391 _cmsSpace->assert_locked(freelistLock());
3392 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3393
3394 // update the space and generation capacity counters
3395 if (UsePerfData) {
3396 _space_counters->update_capacity();
3397 _gen_counters->update_all();
3398 }
3399
3400 if (Verbose && PrintGC) {
3401 size_t new_mem_size = _virtual_space.committed_size();
3402 size_t old_mem_size = new_mem_size - bytes;
3403 gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3404 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3405 }
3406 }
3407 return result;
3408 }
3409
3410 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3411 assert_locked_or_safepoint(Heap_lock);
3412 bool success = true;
3413 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3414 if (remaining_bytes > 0) {
3415 success = grow_by(remaining_bytes);
3416 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3417 }
3418 return success;
3419 }
3420
3421 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
3422 assert_locked_or_safepoint(Heap_lock);
3423 assert_lock_strong(freelistLock());
3424 if (PrintGCDetails && Verbose) {
3425 warning("Shrinking of CMS not yet implemented");
3426 }
3427 return;
3428 }
3429
3430
3431 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3432 // phases.
3433 class CMSPhaseAccounting: public StackObj {
3434 public:
3435 CMSPhaseAccounting(CMSCollector *collector,
3436 const char *phase,
3437 bool print_cr = true);
3438 ~CMSPhaseAccounting();
3439
3440 private:
3441 CMSCollector *_collector;
3442 const char *_phase;
3443 elapsedTimer _wallclock;
3444 bool _print_cr;
3445
3446 public:
3447 // Not MT-safe; so do not pass around these StackObj's
3448 // where they may be accessed by other threads.
3449 jlong wallclock_millis() {
3450 assert(_wallclock.is_active(), "Wall clock should not stop");
3451 _wallclock.stop(); // to record time
3452 jlong ret = _wallclock.milliseconds();
3453 _wallclock.start(); // restart
3454 return ret;
3455 }
3456 };
3457
3458 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3459 const char *phase,
3460 bool print_cr) :
3461 _collector(collector), _phase(phase), _print_cr(print_cr) {
3462
3463 if (PrintCMSStatistics != 0) {
3464 _collector->resetYields();
3465 }
3466 if (PrintGCDetails) {
3467 gclog_or_tty->date_stamp(PrintGCDateStamps);
3468 gclog_or_tty->stamp(PrintGCTimeStamps);
3469 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
3470 _collector->cmsGen()->short_name(), _phase);
3471 }
3472 _collector->resetTimer();
3473 _wallclock.start();
3474 _collector->startTimer();
3475 }
3476
3477 CMSPhaseAccounting::~CMSPhaseAccounting() {
3478 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3479 _collector->stopTimer();
3480 _wallclock.stop();
3481 if (PrintGCDetails) {
3482 gclog_or_tty->date_stamp(PrintGCDateStamps);
3483 gclog_or_tty->stamp(PrintGCTimeStamps);
3484 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3485 _collector->cmsGen()->short_name(),
3486 _phase, _collector->timerValue(), _wallclock.seconds());
3487 if (_print_cr) {
3488 gclog_or_tty->print_cr("");
3489 }
3490 if (PrintCMSStatistics != 0) {
3491 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3492 _collector->yields());
3493 }
3494 }
3495 }
3496
3497 // CMS work
3498
3499 // Checkpoint the roots into this generation from outside
3500 // this generation. [Note this initial checkpoint need only
3501 // be approximate -- we'll do a catch up phase subsequently.]
3502 void CMSCollector::checkpointRootsInitial(bool asynch) {
3503 assert(_collectorState == InitialMarking, "Wrong collector state");
3504 check_correct_thread_executing();
3505 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3506
3507 ReferenceProcessor* rp = ref_processor();
3508 SpecializationStats::clear();
3509 assert(_restart_addr == NULL, "Control point invariant");
3510 if (asynch) {
3511 // acquire locks for subsequent manipulations
3512 MutexLockerEx x(bitMapLock(),
3513 Mutex::_no_safepoint_check_flag);
3514 checkpointRootsInitialWork(asynch);
3515 // enable ("weak") refs discovery
3516 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3517 _collectorState = Marking;
3518 } else {
3519 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3520 // which recognizes if we are a CMS generation, and doesn't try to turn on
3521 // discovery; verify that they aren't meddling.
3522 assert(!rp->discovery_is_atomic(),
3523 "incorrect setting of discovery predicate");
3524 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3525 "ref discovery for this generation kind");
3526 // already have locks
3527 checkpointRootsInitialWork(asynch);
3528 // now enable ("weak") refs discovery
3529 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3530 _collectorState = Marking;
3531 }
3532 SpecializationStats::print();
3533 }
3534
3535 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3536 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3537 assert(_collectorState == InitialMarking, "just checking");
3538
3539 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3540 // precede our marking with a collection of all
3541 // younger generations to keep floating garbage to a minimum.
3542 // XXX: we won't do this for now -- it's an optimization to be done later.
3543
3544 // already have locks
3545 assert_lock_strong(bitMapLock());
3546 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3547
3548 // Setup the verification and class unloading state for this
3549 // CMS collection cycle.
3550 setup_cms_unloading_and_verification_state();
3551
3552 NOT_PRODUCT(TraceTime t("\ncheckpointRootsInitialWork",
3553 PrintGCDetails && Verbose, true, gclog_or_tty);)
3554 if (UseAdaptiveSizePolicy) {
3555 size_policy()->checkpoint_roots_initial_begin();
3556 }
3557
3558 // Reset all the PLAB chunk arrays if necessary.
3559 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3560 reset_survivor_plab_arrays();
3561 }
3562
3563 ResourceMark rm;
3564 HandleMark hm;
3565
3566 FalseClosure falseClosure;
3567 // In the case of a synchronous collection, we will elide the
3568 // remark step, so it's important to catch all the nmethod oops
3569 // in this step.
3570 // The final 'true' flag to gen_process_strong_roots will ensure this.
3571 // If 'async' is true, we can relax the nmethod tracing.
3572 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3573 GenCollectedHeap* gch = GenCollectedHeap::heap();
3574
3575 verify_work_stacks_empty();
3576 verify_overflow_empty();
3577
3578 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3579 // Update the saved marks which may affect the root scans.
3580 gch->save_marks();
3581
3582 // weak reference processing has not started yet.
3583 ref_processor()->set_enqueuing_is_done(false);
3584
3585 // Need to remember all newly created CLDs,
3586 // so that we can guarantee that the remark finds them.
3587 ClassLoaderDataGraph::remember_new_clds(true);
3588
3589 // Whenever a CLD is found, it will be claimed before proceeding to mark
3590 // the klasses. The claimed marks need to be cleared before marking starts.
3591 ClassLoaderDataGraph::clear_claimed_marks();
3592
3593 CMKlassClosure klass_closure(¬Older);
3594 {
3595 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3596 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3597 gch->gen_process_strong_roots(_cmsGen->level(),
3598 true, // younger gens are roots
3599 true, // activate StrongRootsScope
3600 false, // not scavenging
3601 SharedHeap::ScanningOption(roots_scanning_options()),
3602 ¬Older,
3603 true, // walk all of code cache if (so & SO_CodeCache)
3604 NULL,
3605 &klass_closure);
3606 }
3607
3608 // Clear mod-union table; it will be dirtied in the prologue of
3609 // CMS generation per each younger generation collection.
3610
3611 assert(_modUnionTable.isAllClear(),
3612 "Was cleared in most recent final checkpoint phase"
3613 " or no bits are set in the gc_prologue before the start of the next "
3614 "subsequent marking phase.");
3615
3616 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3617
3618 // Save the end of the used_region of the constituent generations
3619 // to be used to limit the extent of sweep in each generation.
3620 save_sweep_limits();
3621 if (UseAdaptiveSizePolicy) {
3622 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3623 }
3624 verify_overflow_empty();
3625 }
3626
3627 bool CMSCollector::markFromRoots(bool asynch) {
3628 // we might be tempted to assert that:
3629 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3630 // "inconsistent argument?");
3631 // However that wouldn't be right, because it's possible that
3632 // a safepoint is indeed in progress as a younger generation
3633 // stop-the-world GC happens even as we mark in this generation.
3634 assert(_collectorState == Marking, "inconsistent state?");
3635 check_correct_thread_executing();
3636 verify_overflow_empty();
3637
3638 bool res;
3639 if (asynch) {
3640
3641 // Start the timers for adaptive size policy for the concurrent phases
3642 // Do it here so that the foreground MS can use the concurrent
3643 // timer since a foreground MS might has the sweep done concurrently
3644 // or STW.
3645 if (UseAdaptiveSizePolicy) {
3646 size_policy()->concurrent_marking_begin();
3647 }
3648
3649 // Weak ref discovery note: We may be discovering weak
3650 // refs in this generation concurrent (but interleaved) with
3651 // weak ref discovery by a younger generation collector.
3652
3653 CMSTokenSyncWithLocks ts(true, bitMapLock());
3654 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3655 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3656 res = markFromRootsWork(asynch);
3657 if (res) {
3658 _collectorState = Precleaning;
3659 } else { // We failed and a foreground collection wants to take over
3660 assert(_foregroundGCIsActive, "internal state inconsistency");
3661 assert(_restart_addr == NULL, "foreground will restart from scratch");
3662 if (PrintGCDetails) {
3663 gclog_or_tty->print_cr("bailing out to foreground collection");
3664 }
3665 }
3666 if (UseAdaptiveSizePolicy) {
3667 size_policy()->concurrent_marking_end();
3668 }
3669 } else {
3670 assert(SafepointSynchronize::is_at_safepoint(),
3671 "inconsistent with asynch == false");
3672 if (UseAdaptiveSizePolicy) {
3673 size_policy()->ms_collection_marking_begin();
3674 }
3675 // already have locks
3676 res = markFromRootsWork(asynch);
3677 _collectorState = FinalMarking;
3678 if (UseAdaptiveSizePolicy) {
3679 GenCollectedHeap* gch = GenCollectedHeap::heap();
3680 size_policy()->ms_collection_marking_end(gch->gc_cause());
3681 }
3682 }
3683 verify_overflow_empty();
3684 return res;
3685 }
3686
3687 bool CMSCollector::markFromRootsWork(bool asynch) {
3688 // iterate over marked bits in bit map, doing a full scan and mark
3689 // from these roots using the following algorithm:
3690 // . if oop is to the right of the current scan pointer,
3691 // mark corresponding bit (we'll process it later)
3692 // . else (oop is to left of current scan pointer)
3693 // push oop on marking stack
3694 // . drain the marking stack
3695
3696 // Note that when we do a marking step we need to hold the
3697 // bit map lock -- recall that direct allocation (by mutators)
3698 // and promotion (by younger generation collectors) is also
3699 // marking the bit map. [the so-called allocate live policy.]
3700 // Because the implementation of bit map marking is not
3701 // robust wrt simultaneous marking of bits in the same word,
3702 // we need to make sure that there is no such interference
3703 // between concurrent such updates.
3704
3705 // already have locks
3706 assert_lock_strong(bitMapLock());
3707
3708 verify_work_stacks_empty();
3709 verify_overflow_empty();
3710 bool result = false;
3711 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3712 result = do_marking_mt(asynch);
3713 } else {
3714 result = do_marking_st(asynch);
3715 }
3716 return result;
3717 }
3718
3719 // Forward decl
3720 class CMSConcMarkingTask;
3721
3722 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3723 CMSCollector* _collector;
3724 CMSConcMarkingTask* _task;
3725 public:
3726 virtual void yield();
3727
3728 // "n_threads" is the number of threads to be terminated.
3729 // "queue_set" is a set of work queues of other threads.
3730 // "collector" is the CMS collector associated with this task terminator.
3731 // "yield" indicates whether we need the gang as a whole to yield.
3732 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3733 ParallelTaskTerminator(n_threads, queue_set),
3734 _collector(collector) { }
3735
3736 void set_task(CMSConcMarkingTask* task) {
3737 _task = task;
3738 }
3739 };
3740
3741 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3742 CMSConcMarkingTask* _task;
3743 public:
3744 bool should_exit_termination();
3745 void set_task(CMSConcMarkingTask* task) {
3746 _task = task;
3747 }
3748 };
3749
3750 // MT Concurrent Marking Task
3751 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3752 CMSCollector* _collector;
3753 int _n_workers; // requested/desired # workers
3754 bool _asynch;
3755 bool _result;
3756 CompactibleFreeListSpace* _cms_space;
3757 char _pad_front[64]; // padding to ...
3758 HeapWord* _global_finger; // ... avoid sharing cache line
3759 char _pad_back[64];
3760 HeapWord* _restart_addr;
3761
3762 // Exposed here for yielding support
3763 Mutex* const _bit_map_lock;
3764
3765 // The per thread work queues, available here for stealing
3766 OopTaskQueueSet* _task_queues;
3767
3768 // Termination (and yielding) support
3769 CMSConcMarkingTerminator _term;
3770 CMSConcMarkingTerminatorTerminator _term_term;
3771
3772 public:
3773 CMSConcMarkingTask(CMSCollector* collector,
3774 CompactibleFreeListSpace* cms_space,
3775 bool asynch,
3776 YieldingFlexibleWorkGang* workers,
3777 OopTaskQueueSet* task_queues):
3778 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3779 _collector(collector),
3780 _cms_space(cms_space),
3781 _asynch(asynch), _n_workers(0), _result(true),
3782 _task_queues(task_queues),
3783 _term(_n_workers, task_queues, _collector),
3784 _bit_map_lock(collector->bitMapLock())
3785 {
3786 _requested_size = _n_workers;
3787 _term.set_task(this);
3788 _term_term.set_task(this);
3789 _restart_addr = _global_finger = _cms_space->bottom();
3790 }
3791
3792
3793 OopTaskQueueSet* task_queues() { return _task_queues; }
3794
3795 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3796
3797 HeapWord** global_finger_addr() { return &_global_finger; }
3798
3799 CMSConcMarkingTerminator* terminator() { return &_term; }
3800
3801 virtual void set_for_termination(int active_workers) {
3802 terminator()->reset_for_reuse(active_workers);
3803 }
3804
3805 void work(uint worker_id);
3806 bool should_yield() {
3807 return ConcurrentMarkSweepThread::should_yield()
3808 && !_collector->foregroundGCIsActive()
3809 && _asynch;
3810 }
3811
3812 virtual void coordinator_yield(); // stuff done by coordinator
3813 bool result() { return _result; }
3814
3815 void reset(HeapWord* ra) {
3816 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3817 _restart_addr = _global_finger = ra;
3818 _term.reset_for_reuse();
3819 }
3820
3821 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3822 OopTaskQueue* work_q);
3823
3824 private:
3825 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3826 void do_work_steal(int i);
3827 void bump_global_finger(HeapWord* f);
3828 };
3829
3830 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3831 assert(_task != NULL, "Error");
3832 return _task->yielding();
3833 // Note that we do not need the disjunct || _task->should_yield() above
3834 // because we want terminating threads to yield only if the task
3835 // is already in the midst of yielding, which happens only after at least one
3836 // thread has yielded.
3837 }
3838
3839 void CMSConcMarkingTerminator::yield() {
3840 if (_task->should_yield()) {
3841 _task->yield();
3842 } else {
3843 ParallelTaskTerminator::yield();
3844 }
3845 }
3846
3847 ////////////////////////////////////////////////////////////////
3848 // Concurrent Marking Algorithm Sketch
3849 ////////////////////////////////////////////////////////////////
3850 // Until all tasks exhausted (both spaces):
3851 // -- claim next available chunk
3852 // -- bump global finger via CAS
3853 // -- find first object that starts in this chunk
3854 // and start scanning bitmap from that position
3855 // -- scan marked objects for oops
3856 // -- CAS-mark target, and if successful:
3857 // . if target oop is above global finger (volatile read)
3858 // nothing to do
3859 // . if target oop is in chunk and above local finger
3860 // then nothing to do
3861 // . else push on work-queue
3862 // -- Deal with possible overflow issues:
3863 // . local work-queue overflow causes stuff to be pushed on
3864 // global (common) overflow queue
3865 // . always first empty local work queue
3866 // . then get a batch of oops from global work queue if any
3867 // . then do work stealing
3868 // -- When all tasks claimed (both spaces)
3869 // and local work queue empty,
3870 // then in a loop do:
3871 // . check global overflow stack; steal a batch of oops and trace
3872 // . try to steal from other threads oif GOS is empty
3873 // . if neither is available, offer termination
3874 // -- Terminate and return result
3875 //
3876 void CMSConcMarkingTask::work(uint worker_id) {
3877 elapsedTimer _timer;
3878 ResourceMark rm;
3879 HandleMark hm;
3880
3881 DEBUG_ONLY(_collector->verify_overflow_empty();)
3882
3883 // Before we begin work, our work queue should be empty
3884 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3885 // Scan the bitmap covering _cms_space, tracing through grey objects.
3886 _timer.start();
3887 do_scan_and_mark(worker_id, _cms_space);
3888 _timer.stop();
3889 if (PrintCMSStatistics != 0) {
3890 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3891 worker_id, _timer.seconds());
3892 // XXX: need xxx/xxx type of notation, two timers
3893 }
3894
3895 // ... do work stealing
3896 _timer.reset();
3897 _timer.start();
3898 do_work_steal(worker_id);
3899 _timer.stop();
3900 if (PrintCMSStatistics != 0) {
3901 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3902 worker_id, _timer.seconds());
3903 // XXX: need xxx/xxx type of notation, two timers
3904 }
3905 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3906 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3907 // Note that under the current task protocol, the
3908 // following assertion is true even of the spaces
3909 // expanded since the completion of the concurrent
3910 // marking. XXX This will likely change under a strict
3911 // ABORT semantics.
3912 // After perm removal the comparison was changed to
3913 // greater than or equal to from strictly greater than.
3914 // Before perm removal the highest address sweep would
3915 // have been at the end of perm gen but now is at the
3916 // end of the tenured gen.
3917 assert(_global_finger >= _cms_space->end(),
3918 "All tasks have been completed");
3919 DEBUG_ONLY(_collector->verify_overflow_empty();)
3920 }
3921
3922 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3923 HeapWord* read = _global_finger;
3924 HeapWord* cur = read;
3925 while (f > read) {
3926 cur = read;
3927 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3928 if (cur == read) {
3929 // our cas succeeded
3930 assert(_global_finger >= f, "protocol consistency");
3931 break;
3932 }
3933 }
3934 }
3935
3936 // This is really inefficient, and should be redone by
3937 // using (not yet available) block-read and -write interfaces to the
3938 // stack and the work_queue. XXX FIX ME !!!
3939 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3940 OopTaskQueue* work_q) {
3941 // Fast lock-free check
3942 if (ovflw_stk->length() == 0) {
3943 return false;
3944 }
3945 assert(work_q->size() == 0, "Shouldn't steal");
3946 MutexLockerEx ml(ovflw_stk->par_lock(),
3947 Mutex::_no_safepoint_check_flag);
3948 // Grab up to 1/4 the size of the work queue
3949 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3950 (size_t)ParGCDesiredObjsFromOverflowList);
3951 num = MIN2(num, ovflw_stk->length());
3952 for (int i = (int) num; i > 0; i--) {
3953 oop cur = ovflw_stk->pop();
3954 assert(cur != NULL, "Counted wrong?");
3955 work_q->push(cur);
3956 }
3957 return num > 0;
3958 }
3959
3960 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3961 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3962 int n_tasks = pst->n_tasks();
3963 // We allow that there may be no tasks to do here because
3964 // we are restarting after a stack overflow.
3965 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3966 uint nth_task = 0;
3967
3968 HeapWord* aligned_start = sp->bottom();
3969 if (sp->used_region().contains(_restart_addr)) {
3970 // Align down to a card boundary for the start of 0th task
3971 // for this space.
3972 aligned_start =
3973 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3974 CardTableModRefBS::card_size);
3975 }
3976
3977 size_t chunk_size = sp->marking_task_size();
3978 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3979 // Having claimed the nth task in this space,
3980 // compute the chunk that it corresponds to:
3981 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3982 aligned_start + (nth_task+1)*chunk_size);
3983 // Try and bump the global finger via a CAS;
3984 // note that we need to do the global finger bump
3985 // _before_ taking the intersection below, because
3986 // the task corresponding to that region will be
3987 // deemed done even if the used_region() expands
3988 // because of allocation -- as it almost certainly will
3989 // during start-up while the threads yield in the
3990 // closure below.
3991 HeapWord* finger = span.end();
3992 bump_global_finger(finger); // atomically
3993 // There are null tasks here corresponding to chunks
3994 // beyond the "top" address of the space.
3995 span = span.intersection(sp->used_region());
3996 if (!span.is_empty()) { // Non-null task
3997 HeapWord* prev_obj;
3998 assert(!span.contains(_restart_addr) || nth_task == 0,
3999 "Inconsistency");
4000 if (nth_task == 0) {
4001 // For the 0th task, we'll not need to compute a block_start.
4002 if (span.contains(_restart_addr)) {
4003 // In the case of a restart because of stack overflow,
4004 // we might additionally skip a chunk prefix.
4005 prev_obj = _restart_addr;
4006 } else {
4007 prev_obj = span.start();
4008 }
4009 } else {
4010 // We want to skip the first object because
4011 // the protocol is to scan any object in its entirety
4012 // that _starts_ in this span; a fortiori, any
4013 // object starting in an earlier span is scanned
4014 // as part of an earlier claimed task.
4015 // Below we use the "careful" version of block_start
4016 // so we do not try to navigate uninitialized objects.
4017 prev_obj = sp->block_start_careful(span.start());
4018 // Below we use a variant of block_size that uses the
4019 // Printezis bits to avoid waiting for allocated
4020 // objects to become initialized/parsable.
4021 while (prev_obj < span.start()) {
4022 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4023 if (sz > 0) {
4024 prev_obj += sz;
4025 } else {
4026 // In this case we may end up doing a bit of redundant
4027 // scanning, but that appears unavoidable, short of
4028 // locking the free list locks; see bug 6324141.
4029 break;
4030 }
4031 }
4032 }
4033 if (prev_obj < span.end()) {
4034 MemRegion my_span = MemRegion(prev_obj, span.end());
4035 // Do the marking work within a non-empty span --
4036 // the last argument to the constructor indicates whether the
4037 // iteration should be incremental with periodic yields.
4038 Par_MarkFromRootsClosure cl(this, _collector, my_span,
4039 &_collector->_markBitMap,
4040 work_queue(i),
4041 &_collector->_markStack,
4042 _asynch);
4043 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4044 } // else nothing to do for this task
4045 } // else nothing to do for this task
4046 }
4047 // We'd be tempted to assert here that since there are no
4048 // more tasks left to claim in this space, the global_finger
4049 // must exceed space->top() and a fortiori space->end(). However,
4050 // that would not quite be correct because the bumping of
4051 // global_finger occurs strictly after the claiming of a task,
4052 // so by the time we reach here the global finger may not yet
4053 // have been bumped up by the thread that claimed the last
4054 // task.
4055 pst->all_tasks_completed();
4056 }
4057
4058 class Par_ConcMarkingClosure: public CMSOopClosure {
4059 private:
4060 CMSCollector* _collector;
4061 CMSConcMarkingTask* _task;
4062 MemRegion _span;
4063 CMSBitMap* _bit_map;
4064 CMSMarkStack* _overflow_stack;
4065 OopTaskQueue* _work_queue;
4066 protected:
4067 DO_OOP_WORK_DEFN
4068 public:
4069 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4070 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
4071 CMSOopClosure(collector->ref_processor()),
4072 _collector(collector),
4073 _task(task),
4074 _span(collector->_span),
4075 _work_queue(work_queue),
4076 _bit_map(bit_map),
4077 _overflow_stack(overflow_stack)
4078 { }
4079 virtual void do_oop(oop* p);
4080 virtual void do_oop(narrowOop* p);
4081
4082 void trim_queue(size_t max);
4083 void handle_stack_overflow(HeapWord* lost);
4084 void do_yield_check() {
4085 if (_task->should_yield()) {
4086 _task->yield();
4087 }
4088 }
4089 };
4090
4091 // Grey object scanning during work stealing phase --
4092 // the salient assumption here is that any references
4093 // that are in these stolen objects being scanned must
4094 // already have been initialized (else they would not have
4095 // been published), so we do not need to check for
4096 // uninitialized objects before pushing here.
4097 void Par_ConcMarkingClosure::do_oop(oop obj) {
4098 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4099 HeapWord* addr = (HeapWord*)obj;
4100 // Check if oop points into the CMS generation
4101 // and is not marked
4102 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4103 // a white object ...
4104 // If we manage to "claim" the object, by being the
4105 // first thread to mark it, then we push it on our
4106 // marking stack
4107 if (_bit_map->par_mark(addr)) { // ... now grey
4108 // push on work queue (grey set)
4109 bool simulate_overflow = false;
4110 NOT_PRODUCT(
4111 if (CMSMarkStackOverflowALot &&
4112 _collector->simulate_overflow()) {
4113 // simulate a stack overflow
4114 simulate_overflow = true;
4115 }
4116 )
4117 if (simulate_overflow ||
4118 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4119 // stack overflow
4120 if (PrintCMSStatistics != 0) {
4121 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4122 SIZE_FORMAT, _overflow_stack->capacity());
4123 }
4124 // We cannot assert that the overflow stack is full because
4125 // it may have been emptied since.
4126 assert(simulate_overflow ||
4127 _work_queue->size() == _work_queue->max_elems(),
4128 "Else push should have succeeded");
4129 handle_stack_overflow(addr);
4130 }
4131 } // Else, some other thread got there first
4132 do_yield_check();
4133 }
4134 }
4135
4136 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4137 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4138
4139 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4140 while (_work_queue->size() > max) {
4141 oop new_oop;
4142 if (_work_queue->pop_local(new_oop)) {
4143 assert(new_oop->is_oop(), "Should be an oop");
4144 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4145 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4146 new_oop->oop_iterate(this); // do_oop() above
4147 do_yield_check();
4148 }
4149 }
4150 }
4151
4152 // Upon stack overflow, we discard (part of) the stack,
4153 // remembering the least address amongst those discarded
4154 // in CMSCollector's _restart_address.
4155 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4156 // We need to do this under a mutex to prevent other
4157 // workers from interfering with the work done below.
4158 MutexLockerEx ml(_overflow_stack->par_lock(),
4159 Mutex::_no_safepoint_check_flag);
4160 // Remember the least grey address discarded
4161 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4162 _collector->lower_restart_addr(ra);
4163 _overflow_stack->reset(); // discard stack contents
4164 _overflow_stack->expand(); // expand the stack if possible
4165 }
4166
4167
4168 void CMSConcMarkingTask::do_work_steal(int i) {
4169 OopTaskQueue* work_q = work_queue(i);
4170 oop obj_to_scan;
4171 CMSBitMap* bm = &(_collector->_markBitMap);
4172 CMSMarkStack* ovflw = &(_collector->_markStack);
4173 int* seed = _collector->hash_seed(i);
4174 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4175 while (true) {
4176 cl.trim_queue(0);
4177 assert(work_q->size() == 0, "Should have been emptied above");
4178 if (get_work_from_overflow_stack(ovflw, work_q)) {
4179 // Can't assert below because the work obtained from the
4180 // overflow stack may already have been stolen from us.
4181 // assert(work_q->size() > 0, "Work from overflow stack");
4182 continue;
4183 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4184 assert(obj_to_scan->is_oop(), "Should be an oop");
4185 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4186 obj_to_scan->oop_iterate(&cl);
4187 } else if (terminator()->offer_termination(&_term_term)) {
4188 assert(work_q->size() == 0, "Impossible!");
4189 break;
4190 } else if (yielding() || should_yield()) {
4191 yield();
4192 }
4193 }
4194 }
4195
4196 // This is run by the CMS (coordinator) thread.
4197 void CMSConcMarkingTask::coordinator_yield() {
4198 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4199 "CMS thread should hold CMS token");
4200 // First give up the locks, then yield, then re-lock
4201 // We should probably use a constructor/destructor idiom to
4202 // do this unlock/lock or modify the MutexUnlocker class to
4203 // serve our purpose. XXX
4204 assert_lock_strong(_bit_map_lock);
4205 _bit_map_lock->unlock();
4206 ConcurrentMarkSweepThread::desynchronize(true);
4207 ConcurrentMarkSweepThread::acknowledge_yield_request();
4208 _collector->stopTimer();
4209 if (PrintCMSStatistics != 0) {
4210 _collector->incrementYields();
4211 }
4212 _collector->icms_wait();
4213
4214 // It is possible for whichever thread initiated the yield request
4215 // not to get a chance to wake up and take the bitmap lock between
4216 // this thread releasing it and reacquiring it. So, while the
4217 // should_yield() flag is on, let's sleep for a bit to give the
4218 // other thread a chance to wake up. The limit imposed on the number
4219 // of iterations is defensive, to avoid any unforseen circumstances
4220 // putting us into an infinite loop. Since it's always been this
4221 // (coordinator_yield()) method that was observed to cause the
4222 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4223 // which is by default non-zero. For the other seven methods that
4224 // also perform the yield operation, as are using a different
4225 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4226 // can enable the sleeping for those methods too, if necessary.
4227 // See 6442774.
4228 //
4229 // We really need to reconsider the synchronization between the GC
4230 // thread and the yield-requesting threads in the future and we
4231 // should really use wait/notify, which is the recommended
4232 // way of doing this type of interaction. Additionally, we should
4233 // consolidate the eight methods that do the yield operation and they
4234 // are almost identical into one for better maintenability and
4235 // readability. See 6445193.
4236 //
4237 // Tony 2006.06.29
4238 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4239 ConcurrentMarkSweepThread::should_yield() &&
4240 !CMSCollector::foregroundGCIsActive(); ++i) {
4241 os::sleep(Thread::current(), 1, false);
4242 ConcurrentMarkSweepThread::acknowledge_yield_request();
4243 }
4244
4245 ConcurrentMarkSweepThread::synchronize(true);
4246 _bit_map_lock->lock_without_safepoint_check();
4247 _collector->startTimer();
4248 }
4249
4250 bool CMSCollector::do_marking_mt(bool asynch) {
4251 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4252 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4253 conc_workers()->total_workers(),
4254 conc_workers()->active_workers(),
4255 Threads::number_of_non_daemon_threads());
4256 conc_workers()->set_active_workers(num_workers);
4257
4258 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4259
4260 CMSConcMarkingTask tsk(this,
4261 cms_space,
4262 asynch,
4263 conc_workers(),
4264 task_queues());
4265
4266 // Since the actual number of workers we get may be different
4267 // from the number we requested above, do we need to do anything different
4268 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4269 // class?? XXX
4270 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4271
4272 // Refs discovery is already non-atomic.
4273 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4274 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4275 conc_workers()->start_task(&tsk);
4276 while (tsk.yielded()) {
4277 tsk.coordinator_yield();
4278 conc_workers()->continue_task(&tsk);
4279 }
4280 // If the task was aborted, _restart_addr will be non-NULL
4281 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4282 while (_restart_addr != NULL) {
4283 // XXX For now we do not make use of ABORTED state and have not
4284 // yet implemented the right abort semantics (even in the original
4285 // single-threaded CMS case). That needs some more investigation
4286 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4287 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4288 // If _restart_addr is non-NULL, a marking stack overflow
4289 // occurred; we need to do a fresh marking iteration from the
4290 // indicated restart address.
4291 if (_foregroundGCIsActive && asynch) {
4292 // We may be running into repeated stack overflows, having
4293 // reached the limit of the stack size, while making very
4294 // slow forward progress. It may be best to bail out and
4295 // let the foreground collector do its job.
4296 // Clear _restart_addr, so that foreground GC
4297 // works from scratch. This avoids the headache of
4298 // a "rescan" which would otherwise be needed because
4299 // of the dirty mod union table & card table.
4300 _restart_addr = NULL;
4301 return false;
4302 }
4303 // Adjust the task to restart from _restart_addr
4304 tsk.reset(_restart_addr);
4305 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4306 _restart_addr);
4307 _restart_addr = NULL;
4308 // Get the workers going again
4309 conc_workers()->start_task(&tsk);
4310 while (tsk.yielded()) {
4311 tsk.coordinator_yield();
4312 conc_workers()->continue_task(&tsk);
4313 }
4314 }
4315 assert(tsk.completed(), "Inconsistency");
4316 assert(tsk.result() == true, "Inconsistency");
4317 return true;
4318 }
4319
4320 bool CMSCollector::do_marking_st(bool asynch) {
4321 ResourceMark rm;
4322 HandleMark hm;
4323
4324 // Temporarily make refs discovery single threaded (non-MT)
4325 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4326 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4327 &_markStack, CMSYield && asynch);
4328 // the last argument to iterate indicates whether the iteration
4329 // should be incremental with periodic yields.
4330 _markBitMap.iterate(&markFromRootsClosure);
4331 // If _restart_addr is non-NULL, a marking stack overflow
4332 // occurred; we need to do a fresh iteration from the
4333 // indicated restart address.
4334 while (_restart_addr != NULL) {
4335 if (_foregroundGCIsActive && asynch) {
4336 // We may be running into repeated stack overflows, having
4337 // reached the limit of the stack size, while making very
4338 // slow forward progress. It may be best to bail out and
4339 // let the foreground collector do its job.
4340 // Clear _restart_addr, so that foreground GC
4341 // works from scratch. This avoids the headache of
4342 // a "rescan" which would otherwise be needed because
4343 // of the dirty mod union table & card table.
4344 _restart_addr = NULL;
4345 return false; // indicating failure to complete marking
4346 }
4347 // Deal with stack overflow:
4348 // we restart marking from _restart_addr
4349 HeapWord* ra = _restart_addr;
4350 markFromRootsClosure.reset(ra);
4351 _restart_addr = NULL;
4352 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4353 }
4354 return true;
4355 }
4356
4357 void CMSCollector::preclean() {
4358 check_correct_thread_executing();
4359 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4360 verify_work_stacks_empty();
4361 verify_overflow_empty();
4362 _abort_preclean = false;
4363 if (CMSPrecleaningEnabled) {
4364 _eden_chunk_index = 0;
4365 size_t used = get_eden_used();
4366 size_t capacity = get_eden_capacity();
4367 // Don't start sampling unless we will get sufficiently
4368 // many samples.
4369 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4370 * CMSScheduleRemarkEdenPenetration)) {
4371 _start_sampling = true;
4372 } else {
4373 _start_sampling = false;
4374 }
4375 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4376 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4377 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4378 }
4379 CMSTokenSync x(true); // is cms thread
4380 if (CMSPrecleaningEnabled) {
4381 sample_eden();
4382 _collectorState = AbortablePreclean;
4383 } else {
4384 _collectorState = FinalMarking;
4385 }
4386 verify_work_stacks_empty();
4387 verify_overflow_empty();
4388 }
4389
4390 // Try and schedule the remark such that young gen
4391 // occupancy is CMSScheduleRemarkEdenPenetration %.
4392 void CMSCollector::abortable_preclean() {
4393 check_correct_thread_executing();
4394 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4395 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4396
4397 // If Eden's current occupancy is below this threshold,
4398 // immediately schedule the remark; else preclean
4399 // past the next scavenge in an effort to
4400 // schedule the pause as described avove. By choosing
4401 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4402 // we will never do an actual abortable preclean cycle.
4403 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4404 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4405 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4406 // We need more smarts in the abortable preclean
4407 // loop below to deal with cases where allocation
4408 // in young gen is very very slow, and our precleaning
4409 // is running a losing race against a horde of
4410 // mutators intent on flooding us with CMS updates
4411 // (dirty cards).
4412 // One, admittedly dumb, strategy is to give up
4413 // after a certain number of abortable precleaning loops
4414 // or after a certain maximum time. We want to make
4415 // this smarter in the next iteration.
4416 // XXX FIX ME!!! YSR
4417 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4418 while (!(should_abort_preclean() ||
4419 ConcurrentMarkSweepThread::should_terminate())) {
4420 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4421 cumworkdone += workdone;
4422 loops++;
4423 // Voluntarily terminate abortable preclean phase if we have
4424 // been at it for too long.
4425 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4426 loops >= CMSMaxAbortablePrecleanLoops) {
4427 if (PrintGCDetails) {
4428 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4429 }
4430 break;
4431 }
4432 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4433 if (PrintGCDetails) {
4434 gclog_or_tty->print(" CMS: abort preclean due to time ");
4435 }
4436 break;
4437 }
4438 // If we are doing little work each iteration, we should
4439 // take a short break.
4440 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4441 // Sleep for some time, waiting for work to accumulate
4442 stopTimer();
4443 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4444 startTimer();
4445 waited++;
4446 }
4447 }
4448 if (PrintCMSStatistics > 0) {
4449 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4450 loops, waited, cumworkdone);
4451 }
4452 }
4453 CMSTokenSync x(true); // is cms thread
4454 if (_collectorState != Idling) {
4455 assert(_collectorState == AbortablePreclean,
4456 "Spontaneous state transition?");
4457 _collectorState = FinalMarking;
4458 } // Else, a foreground collection completed this CMS cycle.
4459 return;
4460 }
4461
4462 // Respond to an Eden sampling opportunity
4463 void CMSCollector::sample_eden() {
4464 // Make sure a young gc cannot sneak in between our
4465 // reading and recording of a sample.
4466 assert(Thread::current()->is_ConcurrentGC_thread(),
4467 "Only the cms thread may collect Eden samples");
4468 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4469 "Should collect samples while holding CMS token");
4470 if (!_start_sampling) {
4471 return;
4472 }
4473 if (_eden_chunk_array) {
4474 if (_eden_chunk_index < _eden_chunk_capacity) {
4475 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4476 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4477 "Unexpected state of Eden");
4478 // We'd like to check that what we just sampled is an oop-start address;
4479 // however, we cannot do that here since the object may not yet have been
4480 // initialized. So we'll instead do the check when we _use_ this sample
4481 // later.
4482 if (_eden_chunk_index == 0 ||
4483 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4484 _eden_chunk_array[_eden_chunk_index-1])
4485 >= CMSSamplingGrain)) {
4486 _eden_chunk_index++; // commit sample
4487 }
4488 }
4489 }
4490 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4491 size_t used = get_eden_used();
4492 size_t capacity = get_eden_capacity();
4493 assert(used <= capacity, "Unexpected state of Eden");
4494 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4495 _abort_preclean = true;
4496 }
4497 }
4498 }
4499
4500
4501 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4502 assert(_collectorState == Precleaning ||
4503 _collectorState == AbortablePreclean, "incorrect state");
4504 ResourceMark rm;
4505 HandleMark hm;
4506
4507 // Precleaning is currently not MT but the reference processor
4508 // may be set for MT. Disable it temporarily here.
4509 ReferenceProcessor* rp = ref_processor();
4510 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4511
4512 // Do one pass of scrubbing the discovered reference lists
4513 // to remove any reference objects with strongly-reachable
4514 // referents.
4515 if (clean_refs) {
4516 CMSPrecleanRefsYieldClosure yield_cl(this);
4517 assert(rp->span().equals(_span), "Spans should be equal");
4518 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4519 &_markStack, true /* preclean */);
4520 CMSDrainMarkingStackClosure complete_trace(this,
4521 _span, &_markBitMap, &_markStack,
4522 &keep_alive, true /* preclean */);
4523
4524 // We don't want this step to interfere with a young
4525 // collection because we don't want to take CPU
4526 // or memory bandwidth away from the young GC threads
4527 // (which may be as many as there are CPUs).
4528 // Note that we don't need to protect ourselves from
4529 // interference with mutators because they can't
4530 // manipulate the discovered reference lists nor affect
4531 // the computed reachability of the referents, the
4532 // only properties manipulated by the precleaning
4533 // of these reference lists.
4534 stopTimer();
4535 CMSTokenSyncWithLocks x(true /* is cms thread */,
4536 bitMapLock());
4537 startTimer();
4538 sample_eden();
4539
4540 // The following will yield to allow foreground
4541 // collection to proceed promptly. XXX YSR:
4542 // The code in this method may need further
4543 // tweaking for better performance and some restructuring
4544 // for cleaner interfaces.
4545 rp->preclean_discovered_references(
4546 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl);
4547 }
4548
4549 if (clean_survivor) { // preclean the active survivor space(s)
4550 assert(_young_gen->kind() == Generation::DefNew ||
4551 _young_gen->kind() == Generation::ParNew ||
4552 _young_gen->kind() == Generation::ASParNew,
4553 "incorrect type for cast");
4554 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4555 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4556 &_markBitMap, &_modUnionTable,
4557 &_markStack, true /* precleaning phase */);
4558 stopTimer();
4559 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4560 bitMapLock());
4561 startTimer();
4562 unsigned int before_count =
4563 GenCollectedHeap::heap()->total_collections();
4564 SurvivorSpacePrecleanClosure
4565 sss_cl(this, _span, &_markBitMap, &_markStack,
4566 &pam_cl, before_count, CMSYield);
4567 dng->from()->object_iterate_careful(&sss_cl);
4568 dng->to()->object_iterate_careful(&sss_cl);
4569 }
4570 MarkRefsIntoAndScanClosure
4571 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4572 &_markStack, this, CMSYield,
4573 true /* precleaning phase */);
4574 // CAUTION: The following closure has persistent state that may need to
4575 // be reset upon a decrease in the sequence of addresses it
4576 // processes.
4577 ScanMarkedObjectsAgainCarefullyClosure
4578 smoac_cl(this, _span,
4579 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4580
4581 // Preclean dirty cards in ModUnionTable and CardTable using
4582 // appropriate convergence criterion;
4583 // repeat CMSPrecleanIter times unless we find that
4584 // we are losing.
4585 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4586 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4587 "Bad convergence multiplier");
4588 assert(CMSPrecleanThreshold >= 100,
4589 "Unreasonably low CMSPrecleanThreshold");
4590
4591 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4592 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4593 numIter < CMSPrecleanIter;
4594 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4595 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4596 if (Verbose && PrintGCDetails) {
4597 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4598 }
4599 // Either there are very few dirty cards, so re-mark
4600 // pause will be small anyway, or our pre-cleaning isn't
4601 // that much faster than the rate at which cards are being
4602 // dirtied, so we might as well stop and re-mark since
4603 // precleaning won't improve our re-mark time by much.
4604 if (curNumCards <= CMSPrecleanThreshold ||
4605 (numIter > 0 &&
4606 (curNumCards * CMSPrecleanDenominator >
4607 lastNumCards * CMSPrecleanNumerator))) {
4608 numIter++;
4609 cumNumCards += curNumCards;
4610 break;
4611 }
4612 }
4613
4614 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4615
4616 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4617 cumNumCards += curNumCards;
4618 if (PrintGCDetails && PrintCMSStatistics != 0) {
4619 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4620 curNumCards, cumNumCards, numIter);
4621 }
4622 return cumNumCards; // as a measure of useful work done
4623 }
4624
4625 // PRECLEANING NOTES:
4626 // Precleaning involves:
4627 // . reading the bits of the modUnionTable and clearing the set bits.
4628 // . For the cards corresponding to the set bits, we scan the
4629 // objects on those cards. This means we need the free_list_lock
4630 // so that we can safely iterate over the CMS space when scanning
4631 // for oops.
4632 // . When we scan the objects, we'll be both reading and setting
4633 // marks in the marking bit map, so we'll need the marking bit map.
4634 // . For protecting _collector_state transitions, we take the CGC_lock.
4635 // Note that any races in the reading of of card table entries by the
4636 // CMS thread on the one hand and the clearing of those entries by the
4637 // VM thread or the setting of those entries by the mutator threads on the
4638 // other are quite benign. However, for efficiency it makes sense to keep
4639 // the VM thread from racing with the CMS thread while the latter is
4640 // dirty card info to the modUnionTable. We therefore also use the
4641 // CGC_lock to protect the reading of the card table and the mod union
4642 // table by the CM thread.
4643 // . We run concurrently with mutator updates, so scanning
4644 // needs to be done carefully -- we should not try to scan
4645 // potentially uninitialized objects.
4646 //
4647 // Locking strategy: While holding the CGC_lock, we scan over and
4648 // reset a maximal dirty range of the mod union / card tables, then lock
4649 // the free_list_lock and bitmap lock to do a full marking, then
4650 // release these locks; and repeat the cycle. This allows for a
4651 // certain amount of fairness in the sharing of these locks between
4652 // the CMS collector on the one hand, and the VM thread and the
4653 // mutators on the other.
4654
4655 // NOTE: preclean_mod_union_table() and preclean_card_table()
4656 // further below are largely identical; if you need to modify
4657 // one of these methods, please check the other method too.
4658
4659 size_t CMSCollector::preclean_mod_union_table(
4660 ConcurrentMarkSweepGeneration* gen,
4661 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4662 verify_work_stacks_empty();
4663 verify_overflow_empty();
4664
4665 // strategy: starting with the first card, accumulate contiguous
4666 // ranges of dirty cards; clear these cards, then scan the region
4667 // covered by these cards.
4668
4669 // Since all of the MUT is committed ahead, we can just use
4670 // that, in case the generations expand while we are precleaning.
4671 // It might also be fine to just use the committed part of the
4672 // generation, but we might potentially miss cards when the
4673 // generation is rapidly expanding while we are in the midst
4674 // of precleaning.
4675 HeapWord* startAddr = gen->reserved().start();
4676 HeapWord* endAddr = gen->reserved().end();
4677
4678 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4679
4680 size_t numDirtyCards, cumNumDirtyCards;
4681 HeapWord *nextAddr, *lastAddr;
4682 for (cumNumDirtyCards = numDirtyCards = 0,
4683 nextAddr = lastAddr = startAddr;
4684 nextAddr < endAddr;
4685 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4686
4687 ResourceMark rm;
4688 HandleMark hm;
4689
4690 MemRegion dirtyRegion;
4691 {
4692 stopTimer();
4693 // Potential yield point
4694 CMSTokenSync ts(true);
4695 startTimer();
4696 sample_eden();
4697 // Get dirty region starting at nextOffset (inclusive),
4698 // simultaneously clearing it.
4699 dirtyRegion =
4700 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4701 assert(dirtyRegion.start() >= nextAddr,
4702 "returned region inconsistent?");
4703 }
4704 // Remember where the next search should begin.
4705 // The returned region (if non-empty) is a right open interval,
4706 // so lastOffset is obtained from the right end of that
4707 // interval.
4708 lastAddr = dirtyRegion.end();
4709 // Should do something more transparent and less hacky XXX
4710 numDirtyCards =
4711 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4712
4713 // We'll scan the cards in the dirty region (with periodic
4714 // yields for foreground GC as needed).
4715 if (!dirtyRegion.is_empty()) {
4716 assert(numDirtyCards > 0, "consistency check");
4717 HeapWord* stop_point = NULL;
4718 stopTimer();
4719 // Potential yield point
4720 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4721 bitMapLock());
4722 startTimer();
4723 {
4724 verify_work_stacks_empty();
4725 verify_overflow_empty();
4726 sample_eden();
4727 stop_point =
4728 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4729 }
4730 if (stop_point != NULL) {
4731 // The careful iteration stopped early either because it found an
4732 // uninitialized object, or because we were in the midst of an
4733 // "abortable preclean", which should now be aborted. Redirty
4734 // the bits corresponding to the partially-scanned or unscanned
4735 // cards. We'll either restart at the next block boundary or
4736 // abort the preclean.
4737 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4738 "Should only be AbortablePreclean.");
4739 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4740 if (should_abort_preclean()) {
4741 break; // out of preclean loop
4742 } else {
4743 // Compute the next address at which preclean should pick up;
4744 // might need bitMapLock in order to read P-bits.
4745 lastAddr = next_card_start_after_block(stop_point);
4746 }
4747 }
4748 } else {
4749 assert(lastAddr == endAddr, "consistency check");
4750 assert(numDirtyCards == 0, "consistency check");
4751 break;
4752 }
4753 }
4754 verify_work_stacks_empty();
4755 verify_overflow_empty();
4756 return cumNumDirtyCards;
4757 }
4758
4759 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4760 // below are largely identical; if you need to modify
4761 // one of these methods, please check the other method too.
4762
4763 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4764 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4765 // strategy: it's similar to precleamModUnionTable above, in that
4766 // we accumulate contiguous ranges of dirty cards, mark these cards
4767 // precleaned, then scan the region covered by these cards.
4768 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4769 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4770
4771 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4772
4773 size_t numDirtyCards, cumNumDirtyCards;
4774 HeapWord *lastAddr, *nextAddr;
4775
4776 for (cumNumDirtyCards = numDirtyCards = 0,
4777 nextAddr = lastAddr = startAddr;
4778 nextAddr < endAddr;
4779 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4780
4781 ResourceMark rm;
4782 HandleMark hm;
4783
4784 MemRegion dirtyRegion;
4785 {
4786 // See comments in "Precleaning notes" above on why we
4787 // do this locking. XXX Could the locking overheads be
4788 // too high when dirty cards are sparse? [I don't think so.]
4789 stopTimer();
4790 CMSTokenSync x(true); // is cms thread
4791 startTimer();
4792 sample_eden();
4793 // Get and clear dirty region from card table
4794 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4795 MemRegion(nextAddr, endAddr),
4796 true,
4797 CardTableModRefBS::precleaned_card_val());
4798
4799 assert(dirtyRegion.start() >= nextAddr,
4800 "returned region inconsistent?");
4801 }
4802 lastAddr = dirtyRegion.end();
4803 numDirtyCards =
4804 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4805
4806 if (!dirtyRegion.is_empty()) {
4807 stopTimer();
4808 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4809 startTimer();
4810 sample_eden();
4811 verify_work_stacks_empty();
4812 verify_overflow_empty();
4813 HeapWord* stop_point =
4814 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4815 if (stop_point != NULL) {
4816 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4817 "Should only be AbortablePreclean.");
4818 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4819 if (should_abort_preclean()) {
4820 break; // out of preclean loop
4821 } else {
4822 // Compute the next address at which preclean should pick up.
4823 lastAddr = next_card_start_after_block(stop_point);
4824 }
4825 }
4826 } else {
4827 break;
4828 }
4829 }
4830 verify_work_stacks_empty();
4831 verify_overflow_empty();
4832 return cumNumDirtyCards;
4833 }
4834
4835 class PrecleanKlassClosure : public KlassClosure {
4836 CMKlassClosure _cm_klass_closure;
4837 public:
4838 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4839 void do_klass(Klass* k) {
4840 if (k->has_accumulated_modified_oops()) {
4841 k->clear_accumulated_modified_oops();
4842
4843 _cm_klass_closure.do_klass(k);
4844 }
4845 }
4846 };
4847
4848 // The freelist lock is needed to prevent asserts, is it really needed?
4849 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4850
4851 cl->set_freelistLock(freelistLock);
4852
4853 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4854
4855 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4856 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4857 PrecleanKlassClosure preclean_klass_closure(cl);
4858 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4859
4860 verify_work_stacks_empty();
4861 verify_overflow_empty();
4862 }
4863
4864 void CMSCollector::checkpointRootsFinal(bool asynch,
4865 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4866 assert(_collectorState == FinalMarking, "incorrect state transition?");
4867 check_correct_thread_executing();
4868 // world is stopped at this checkpoint
4869 assert(SafepointSynchronize::is_at_safepoint(),
4870 "world should be stopped");
4871 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4872
4873 verify_work_stacks_empty();
4874 verify_overflow_empty();
4875
4876 SpecializationStats::clear();
4877 if (PrintGCDetails) {
4878 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4879 _young_gen->used() / K,
4880 _young_gen->capacity() / K);
4881 }
4882 if (asynch) {
4883 if (CMSScavengeBeforeRemark) {
4884 GenCollectedHeap* gch = GenCollectedHeap::heap();
4885 // Temporarily set flag to false, GCH->do_collection will
4886 // expect it to be false and set to true
4887 FlagSetting fl(gch->_is_gc_active, false);
4888 NOT_PRODUCT(TraceTime t("Scavenge-Before-Remark",
4889 PrintGCDetails && Verbose, true, gclog_or_tty);)
4890 int level = _cmsGen->level() - 1;
4891 if (level >= 0) {
4892 gch->do_collection(true, // full (i.e. force, see below)
4893 false, // !clear_all_soft_refs
4894 0, // size
4895 false, // is_tlab
4896 level // max_level
4897 );
4898 }
4899 }
4900 FreelistLocker x(this);
4901 MutexLockerEx y(bitMapLock(),
4902 Mutex::_no_safepoint_check_flag);
4903 assert(!init_mark_was_synchronous, "but that's impossible!");
4904 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4905 } else {
4906 // already have all the locks
4907 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4908 init_mark_was_synchronous);
4909 }
4910 verify_work_stacks_empty();
4911 verify_overflow_empty();
4912 SpecializationStats::print();
4913 }
4914
4915 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4916 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4917
4918 NOT_PRODUCT(TraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, gclog_or_tty);)
4919
4920 assert(haveFreelistLocks(), "must have free list locks");
4921 assert_lock_strong(bitMapLock());
4922
4923 if (UseAdaptiveSizePolicy) {
4924 size_policy()->checkpoint_roots_final_begin();
4925 }
4926
4927 ResourceMark rm;
4928 HandleMark hm;
4929
4930 GenCollectedHeap* gch = GenCollectedHeap::heap();
4931
4932 if (should_unload_classes()) {
4933 CodeCache::gc_prologue();
4934 }
4935 assert(haveFreelistLocks(), "must have free list locks");
4936 assert_lock_strong(bitMapLock());
4937
4938 if (!init_mark_was_synchronous) {
4939 // We might assume that we need not fill TLAB's when
4940 // CMSScavengeBeforeRemark is set, because we may have just done
4941 // a scavenge which would have filled all TLAB's -- and besides
4942 // Eden would be empty. This however may not always be the case --
4943 // for instance although we asked for a scavenge, it may not have
4944 // happened because of a JNI critical section. We probably need
4945 // a policy for deciding whether we can in that case wait until
4946 // the critical section releases and then do the remark following
4947 // the scavenge, and skip it here. In the absence of that policy,
4948 // or of an indication of whether the scavenge did indeed occur,
4949 // we cannot rely on TLAB's having been filled and must do
4950 // so here just in case a scavenge did not happen.
4951 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4952 // Update the saved marks which may affect the root scans.
4953 gch->save_marks();
4954
4955 {
4956 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4957
4958 // Note on the role of the mod union table:
4959 // Since the marker in "markFromRoots" marks concurrently with
4960 // mutators, it is possible for some reachable objects not to have been
4961 // scanned. For instance, an only reference to an object A was
4962 // placed in object B after the marker scanned B. Unless B is rescanned,
4963 // A would be collected. Such updates to references in marked objects
4964 // are detected via the mod union table which is the set of all cards
4965 // dirtied since the first checkpoint in this GC cycle and prior to
4966 // the most recent young generation GC, minus those cleaned up by the
4967 // concurrent precleaning.
4968 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
4969 TraceTime t("Rescan (parallel) ", PrintGCDetails, false, gclog_or_tty);
4970 do_remark_parallel();
4971 } else {
4972 TraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4973 gclog_or_tty);
4974 do_remark_non_parallel();
4975 }
4976 }
4977 } else {
4978 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
4979 // The initial mark was stop-world, so there's no rescanning to
4980 // do; go straight on to the next step below.
4981 }
4982 verify_work_stacks_empty();
4983 verify_overflow_empty();
4984
4985 {
4986 NOT_PRODUCT(TraceTime ts("refProcessingWork", PrintGCDetails, false, gclog_or_tty);)
4987 refProcessingWork(asynch, clear_all_soft_refs);
4988 }
4989 verify_work_stacks_empty();
4990 verify_overflow_empty();
4991
4992 if (should_unload_classes()) {
4993 CodeCache::gc_epilogue();
4994 }
4995 JvmtiExport::gc_epilogue();
4996
4997 // If we encountered any (marking stack / work queue) overflow
4998 // events during the current CMS cycle, take appropriate
4999 // remedial measures, where possible, so as to try and avoid
5000 // recurrence of that condition.
5001 assert(_markStack.isEmpty(), "No grey objects");
5002 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5003 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
5004 if (ser_ovflw > 0) {
5005 if (PrintCMSStatistics != 0) {
5006 gclog_or_tty->print_cr("Marking stack overflow (benign) "
5007 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5008 ", kac_preclean="SIZE_FORMAT")",
5009 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5010 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5011 }
5012 _markStack.expand();
5013 _ser_pmc_remark_ovflw = 0;
5014 _ser_pmc_preclean_ovflw = 0;
5015 _ser_kac_preclean_ovflw = 0;
5016 _ser_kac_ovflw = 0;
5017 }
5018 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5019 if (PrintCMSStatistics != 0) {
5020 gclog_or_tty->print_cr("Work queue overflow (benign) "
5021 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5022 _par_pmc_remark_ovflw, _par_kac_ovflw);
5023 }
5024 _par_pmc_remark_ovflw = 0;
5025 _par_kac_ovflw = 0;
5026 }
5027 if (PrintCMSStatistics != 0) {
5028 if (_markStack._hit_limit > 0) {
5029 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5030 _markStack._hit_limit);
5031 }
5032 if (_markStack._failed_double > 0) {
5033 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5034 " current capacity "SIZE_FORMAT,
5035 _markStack._failed_double,
5036 _markStack.capacity());
5037 }
5038 }
5039 _markStack._hit_limit = 0;
5040 _markStack._failed_double = 0;
5041
5042 if ((VerifyAfterGC || VerifyDuringGC) &&
5043 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5044 verify_after_remark();
5045 }
5046
5047 // Change under the freelistLocks.
5048 _collectorState = Sweeping;
5049 // Call isAllClear() under bitMapLock
5050 assert(_modUnionTable.isAllClear(),
5051 "Should be clear by end of the final marking");
5052 assert(_ct->klass_rem_set()->mod_union_is_clear(),
5053 "Should be clear by end of the final marking");
5054 if (UseAdaptiveSizePolicy) {
5055 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
5056 }
5057 }
5058
5059 // Parallel remark task
5060 class CMSParRemarkTask: public AbstractGangTask {
5061 CMSCollector* _collector;
5062 int _n_workers;
5063 CompactibleFreeListSpace* _cms_space;
5064
5065 // The per-thread work queues, available here for stealing.
5066 OopTaskQueueSet* _task_queues;
5067 ParallelTaskTerminator _term;
5068
5069 public:
5070 // A value of 0 passed to n_workers will cause the number of
5071 // workers to be taken from the active workers in the work gang.
5072 CMSParRemarkTask(CMSCollector* collector,
5073 CompactibleFreeListSpace* cms_space,
5074 int n_workers, FlexibleWorkGang* workers,
5075 OopTaskQueueSet* task_queues):
5076 AbstractGangTask("Rescan roots and grey objects in parallel"),
5077 _collector(collector),
5078 _cms_space(cms_space),
5079 _n_workers(n_workers),
5080 _task_queues(task_queues),
5081 _term(n_workers, task_queues) { }
5082
5083 OopTaskQueueSet* task_queues() { return _task_queues; }
5084
5085 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5086
5087 ParallelTaskTerminator* terminator() { return &_term; }
5088 int n_workers() { return _n_workers; }
5089
5090 void work(uint worker_id);
5091
5092 private:
5093 // Work method in support of parallel rescan ... of young gen spaces
5094 void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
5095 ContiguousSpace* space,
5096 HeapWord** chunk_array, size_t chunk_top);
5097
5098 // ... of dirty cards in old space
5099 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5100 Par_MarkRefsIntoAndScanClosure* cl);
5101
5102 // ... work stealing for the above
5103 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5104 };
5105
5106 class RemarkKlassClosure : public KlassClosure {
5107 CMKlassClosure _cm_klass_closure;
5108 public:
5109 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
5110 void do_klass(Klass* k) {
5111 // Check if we have modified any oops in the Klass during the concurrent marking.
5112 if (k->has_accumulated_modified_oops()) {
5113 k->clear_accumulated_modified_oops();
5114
5115 // We could have transfered the current modified marks to the accumulated marks,
5116 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
5117 } else if (k->has_modified_oops()) {
5118 // Don't clear anything, this info is needed by the next young collection.
5119 } else {
5120 // No modified oops in the Klass.
5121 return;
5122 }
5123
5124 // The klass has modified fields, need to scan the klass.
5125 _cm_klass_closure.do_klass(k);
5126 }
5127 };
5128
5129 // work_queue(i) is passed to the closure
5130 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5131 // also is passed to do_dirty_card_rescan_tasks() and to
5132 // do_work_steal() to select the i-th task_queue.
5133
5134 void CMSParRemarkTask::work(uint worker_id) {
5135 elapsedTimer _timer;
5136 ResourceMark rm;
5137 HandleMark hm;
5138
5139 // ---------- rescan from roots --------------
5140 _timer.start();
5141 GenCollectedHeap* gch = GenCollectedHeap::heap();
5142 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5143 _collector->_span, _collector->ref_processor(),
5144 &(_collector->_markBitMap),
5145 work_queue(worker_id));
5146
5147 // Rescan young gen roots first since these are likely
5148 // coarsely partitioned and may, on that account, constitute
5149 // the critical path; thus, it's best to start off that
5150 // work first.
5151 // ---------- young gen roots --------------
5152 {
5153 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5154 EdenSpace* eden_space = dng->eden();
5155 ContiguousSpace* from_space = dng->from();
5156 ContiguousSpace* to_space = dng->to();
5157
5158 HeapWord** eca = _collector->_eden_chunk_array;
5159 size_t ect = _collector->_eden_chunk_index;
5160 HeapWord** sca = _collector->_survivor_chunk_array;
5161 size_t sct = _collector->_survivor_chunk_index;
5162
5163 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5164 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5165
5166 do_young_space_rescan(worker_id, &par_mrias_cl, to_space, NULL, 0);
5167 do_young_space_rescan(worker_id, &par_mrias_cl, from_space, sca, sct);
5168 do_young_space_rescan(worker_id, &par_mrias_cl, eden_space, eca, ect);
5169
5170 _timer.stop();
5171 if (PrintCMSStatistics != 0) {
5172 gclog_or_tty->print_cr(
5173 "Finished young gen rescan work in %dth thread: %3.3f sec",
5174 worker_id, _timer.seconds());
5175 }
5176 }
5177
5178 // ---------- remaining roots --------------
5179 _timer.reset();
5180 _timer.start();
5181 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5182 false, // yg was scanned above
5183 false, // this is parallel code
5184 false, // not scavenging
5185 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5186 &par_mrias_cl,
5187 true, // walk all of code cache if (so & SO_CodeCache)
5188 NULL,
5189 NULL); // The dirty klasses will be handled below
5190 assert(_collector->should_unload_classes()
5191 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache),
5192 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5193 _timer.stop();
5194 if (PrintCMSStatistics != 0) {
5195 gclog_or_tty->print_cr(
5196 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5197 worker_id, _timer.seconds());
5198 }
5199
5200 // ---------- unhandled CLD scanning ----------
5201 if (worker_id == 0) { // Single threaded at the moment.
5202 _timer.reset();
5203 _timer.start();
5204
5205 // Scan all new class loader data objects and new dependencies that were
5206 // introduced during concurrent marking.
5207 ResourceMark rm;
5208 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5209 for (int i = 0; i < array->length(); i++) {
5210 par_mrias_cl.do_class_loader_data(array->at(i));
5211 }
5212
5213 // We don't need to keep track of new CLDs anymore.
5214 ClassLoaderDataGraph::remember_new_clds(false);
5215
5216 _timer.stop();
5217 if (PrintCMSStatistics != 0) {
5218 gclog_or_tty->print_cr(
5219 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
5220 worker_id, _timer.seconds());
5221 }
5222 }
5223
5224 // ---------- dirty klass scanning ----------
5225 if (worker_id == 0) { // Single threaded at the moment.
5226 _timer.reset();
5227 _timer.start();
5228
5229 // Scan all classes that was dirtied during the concurrent marking phase.
5230 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
5231 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5232
5233 _timer.stop();
5234 if (PrintCMSStatistics != 0) {
5235 gclog_or_tty->print_cr(
5236 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
5237 worker_id, _timer.seconds());
5238 }
5239 }
5240
5241 // We might have added oops to ClassLoaderData::_handles during the
5242 // concurrent marking phase. These oops point to newly allocated objects
5243 // that are guaranteed to be kept alive. Either by the direct allocation
5244 // code, or when the young collector processes the strong roots. Hence,
5245 // we don't have to revisit the _handles block during the remark phase.
5246
5247 // ---------- rescan dirty cards ------------
5248 _timer.reset();
5249 _timer.start();
5250
5251 // Do the rescan tasks for each of the two spaces
5252 // (cms_space) in turn.
5253 // "worker_id" is passed to select the task_queue for "worker_id"
5254 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5255 _timer.stop();
5256 if (PrintCMSStatistics != 0) {
5257 gclog_or_tty->print_cr(
5258 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5259 worker_id, _timer.seconds());
5260 }
5261
5262 // ---------- steal work from other threads ...
5263 // ---------- ... and drain overflow list.
5264 _timer.reset();
5265 _timer.start();
5266 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5267 _timer.stop();
5268 if (PrintCMSStatistics != 0) {
5269 gclog_or_tty->print_cr(
5270 "Finished work stealing in %dth thread: %3.3f sec",
5271 worker_id, _timer.seconds());
5272 }
5273 }
5274
5275 // Note that parameter "i" is not used.
5276 void
5277 CMSParRemarkTask::do_young_space_rescan(int i,
5278 Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
5279 HeapWord** chunk_array, size_t chunk_top) {
5280 // Until all tasks completed:
5281 // . claim an unclaimed task
5282 // . compute region boundaries corresponding to task claimed
5283 // using chunk_array
5284 // . par_oop_iterate(cl) over that region
5285
5286 ResourceMark rm;
5287 HandleMark hm;
5288
5289 SequentialSubTasksDone* pst = space->par_seq_tasks();
5290 assert(pst->valid(), "Uninitialized use?");
5291
5292 uint nth_task = 0;
5293 uint n_tasks = pst->n_tasks();
5294
5295 HeapWord *start, *end;
5296 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5297 // We claimed task # nth_task; compute its boundaries.
5298 if (chunk_top == 0) { // no samples were taken
5299 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5300 start = space->bottom();
5301 end = space->top();
5302 } else if (nth_task == 0) {
5303 start = space->bottom();
5304 end = chunk_array[nth_task];
5305 } else if (nth_task < (uint)chunk_top) {
5306 assert(nth_task >= 1, "Control point invariant");
5307 start = chunk_array[nth_task - 1];
5308 end = chunk_array[nth_task];
5309 } else {
5310 assert(nth_task == (uint)chunk_top, "Control point invariant");
5311 start = chunk_array[chunk_top - 1];
5312 end = space->top();
5313 }
5314 MemRegion mr(start, end);
5315 // Verify that mr is in space
5316 assert(mr.is_empty() || space->used_region().contains(mr),
5317 "Should be in space");
5318 // Verify that "start" is an object boundary
5319 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5320 "Should be an oop");
5321 space->par_oop_iterate(mr, cl);
5322 }
5323 pst->all_tasks_completed();
5324 }
5325
5326 void
5327 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5328 CompactibleFreeListSpace* sp, int i,
5329 Par_MarkRefsIntoAndScanClosure* cl) {
5330 // Until all tasks completed:
5331 // . claim an unclaimed task
5332 // . compute region boundaries corresponding to task claimed
5333 // . transfer dirty bits ct->mut for that region
5334 // . apply rescanclosure to dirty mut bits for that region
5335
5336 ResourceMark rm;
5337 HandleMark hm;
5338
5339 OopTaskQueue* work_q = work_queue(i);
5340 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5341 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5342 // CAUTION: This closure has state that persists across calls to
5343 // the work method dirty_range_iterate_clear() in that it has
5344 // imbedded in it a (subtype of) UpwardsObjectClosure. The
5345 // use of that state in the imbedded UpwardsObjectClosure instance
5346 // assumes that the cards are always iterated (even if in parallel
5347 // by several threads) in monotonically increasing order per each
5348 // thread. This is true of the implementation below which picks
5349 // card ranges (chunks) in monotonically increasing order globally
5350 // and, a-fortiori, in monotonically increasing order per thread
5351 // (the latter order being a subsequence of the former).
5352 // If the work code below is ever reorganized into a more chaotic
5353 // work-partitioning form than the current "sequential tasks"
5354 // paradigm, the use of that persistent state will have to be
5355 // revisited and modified appropriately. See also related
5356 // bug 4756801 work on which should examine this code to make
5357 // sure that the changes there do not run counter to the
5358 // assumptions made here and necessary for correctness and
5359 // efficiency. Note also that this code might yield inefficient
5360 // behaviour in the case of very large objects that span one or
5361 // more work chunks. Such objects would potentially be scanned
5362 // several times redundantly. Work on 4756801 should try and
5363 // address that performance anomaly if at all possible. XXX
5364 MemRegion full_span = _collector->_span;
5365 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5366 MarkFromDirtyCardsClosure
5367 greyRescanClosure(_collector, full_span, // entire span of interest
5368 sp, bm, work_q, cl);
5369
5370 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5371 assert(pst->valid(), "Uninitialized use?");
5372 uint nth_task = 0;
5373 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5374 MemRegion span = sp->used_region();
5375 HeapWord* start_addr = span.start();
5376 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5377 alignment);
5378 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5379 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5380 start_addr, "Check alignment");
5381 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5382 chunk_size, "Check alignment");
5383
5384 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5385 // Having claimed the nth_task, compute corresponding mem-region,
5386 // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5387 // The alignment restriction ensures that we do not need any
5388 // synchronization with other gang-workers while setting or
5389 // clearing bits in thus chunk of the MUT.
5390 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5391 start_addr + (nth_task+1)*chunk_size);
5392 // The last chunk's end might be way beyond end of the
5393 // used region. In that case pull back appropriately.
5394 if (this_span.end() > end_addr) {
5395 this_span.set_end(end_addr);
5396 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5397 }
5398 // Iterate over the dirty cards covering this chunk, marking them
5399 // precleaned, and setting the corresponding bits in the mod union
5400 // table. Since we have been careful to partition at Card and MUT-word
5401 // boundaries no synchronization is needed between parallel threads.
5402 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5403 &modUnionClosure);
5404
5405 // Having transferred these marks into the modUnionTable,
5406 // rescan the marked objects on the dirty cards in the modUnionTable.
5407 // Even if this is at a synchronous collection, the initial marking
5408 // may have been done during an asynchronous collection so there
5409 // may be dirty bits in the mod-union table.
5410 _collector->_modUnionTable.dirty_range_iterate_clear(
5411 this_span, &greyRescanClosure);
5412 _collector->_modUnionTable.verifyNoOneBitsInRange(
5413 this_span.start(),
5414 this_span.end());
5415 }
5416 pst->all_tasks_completed(); // declare that i am done
5417 }
5418
5419 // . see if we can share work_queues with ParNew? XXX
5420 void
5421 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5422 int* seed) {
5423 OopTaskQueue* work_q = work_queue(i);
5424 NOT_PRODUCT(int num_steals = 0;)
5425 oop obj_to_scan;
5426 CMSBitMap* bm = &(_collector->_markBitMap);
5427
5428 while (true) {
5429 // Completely finish any left over work from (an) earlier round(s)
5430 cl->trim_queue(0);
5431 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5432 (size_t)ParGCDesiredObjsFromOverflowList);
5433 // Now check if there's any work in the overflow list
5434 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5435 // only affects the number of attempts made to get work from the
5436 // overflow list and does not affect the number of workers. Just
5437 // pass ParallelGCThreads so this behavior is unchanged.
5438 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5439 work_q,
5440 ParallelGCThreads)) {
5441 // found something in global overflow list;
5442 // not yet ready to go stealing work from others.
5443 // We'd like to assert(work_q->size() != 0, ...)
5444 // because we just took work from the overflow list,
5445 // but of course we can't since all of that could have
5446 // been already stolen from us.
5447 // "He giveth and He taketh away."
5448 continue;
5449 }
5450 // Verify that we have no work before we resort to stealing
5451 assert(work_q->size() == 0, "Have work, shouldn't steal");
5452 // Try to steal from other queues that have work
5453 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5454 NOT_PRODUCT(num_steals++;)
5455 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5456 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5457 // Do scanning work
5458 obj_to_scan->oop_iterate(cl);
5459 // Loop around, finish this work, and try to steal some more
5460 } else if (terminator()->offer_termination()) {
5461 break; // nirvana from the infinite cycle
5462 }
5463 }
5464 NOT_PRODUCT(
5465 if (PrintCMSStatistics != 0) {
5466 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5467 }
5468 )
5469 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5470 "Else our work is not yet done");
5471 }
5472
5473 // Return a thread-local PLAB recording array, as appropriate.
5474 void* CMSCollector::get_data_recorder(int thr_num) {
5475 if (_survivor_plab_array != NULL &&
5476 (CMSPLABRecordAlways ||
5477 (_collectorState > Marking && _collectorState < FinalMarking))) {
5478 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5479 ChunkArray* ca = &_survivor_plab_array[thr_num];
5480 ca->reset(); // clear it so that fresh data is recorded
5481 return (void*) ca;
5482 } else {
5483 return NULL;
5484 }
5485 }
5486
5487 // Reset all the thread-local PLAB recording arrays
5488 void CMSCollector::reset_survivor_plab_arrays() {
5489 for (uint i = 0; i < ParallelGCThreads; i++) {
5490 _survivor_plab_array[i].reset();
5491 }
5492 }
5493
5494 // Merge the per-thread plab arrays into the global survivor chunk
5495 // array which will provide the partitioning of the survivor space
5496 // for CMS rescan.
5497 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5498 int no_of_gc_threads) {
5499 assert(_survivor_plab_array != NULL, "Error");
5500 assert(_survivor_chunk_array != NULL, "Error");
5501 assert(_collectorState == FinalMarking, "Error");
5502 for (int j = 0; j < no_of_gc_threads; j++) {
5503 _cursor[j] = 0;
5504 }
5505 HeapWord* top = surv->top();
5506 size_t i;
5507 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5508 HeapWord* min_val = top; // Higher than any PLAB address
5509 uint min_tid = 0; // position of min_val this round
5510 for (int j = 0; j < no_of_gc_threads; j++) {
5511 ChunkArray* cur_sca = &_survivor_plab_array[j];
5512 if (_cursor[j] == cur_sca->end()) {
5513 continue;
5514 }
5515 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5516 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5517 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5518 if (cur_val < min_val) {
5519 min_tid = j;
5520 min_val = cur_val;
5521 } else {
5522 assert(cur_val < top, "All recorded addresses should be less");
5523 }
5524 }
5525 // At this point min_val and min_tid are respectively
5526 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5527 // and the thread (j) that witnesses that address.
5528 // We record this address in the _survivor_chunk_array[i]
5529 // and increment _cursor[min_tid] prior to the next round i.
5530 if (min_val == top) {
5531 break;
5532 }
5533 _survivor_chunk_array[i] = min_val;
5534 _cursor[min_tid]++;
5535 }
5536 // We are all done; record the size of the _survivor_chunk_array
5537 _survivor_chunk_index = i; // exclusive: [0, i)
5538 if (PrintCMSStatistics > 0) {
5539 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5540 }
5541 // Verify that we used up all the recorded entries
5542 #ifdef ASSERT
5543 size_t total = 0;
5544 for (int j = 0; j < no_of_gc_threads; j++) {
5545 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5546 total += _cursor[j];
5547 }
5548 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5549 // Check that the merged array is in sorted order
5550 if (total > 0) {
5551 for (size_t i = 0; i < total - 1; i++) {
5552 if (PrintCMSStatistics > 0) {
5553 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5554 i, _survivor_chunk_array[i]);
5555 }
5556 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5557 "Not sorted");
5558 }
5559 }
5560 #endif // ASSERT
5561 }
5562
5563 // Set up the space's par_seq_tasks structure for work claiming
5564 // for parallel rescan of young gen.
5565 // See ParRescanTask where this is currently used.
5566 void
5567 CMSCollector::
5568 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5569 assert(n_threads > 0, "Unexpected n_threads argument");
5570 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5571
5572 // Eden space
5573 {
5574 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5575 assert(!pst->valid(), "Clobbering existing data?");
5576 // Each valid entry in [0, _eden_chunk_index) represents a task.
5577 size_t n_tasks = _eden_chunk_index + 1;
5578 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5579 // Sets the condition for completion of the subtask (how many threads
5580 // need to finish in order to be done).
5581 pst->set_n_threads(n_threads);
5582 pst->set_n_tasks((int)n_tasks);
5583 }
5584
5585 // Merge the survivor plab arrays into _survivor_chunk_array
5586 if (_survivor_plab_array != NULL) {
5587 merge_survivor_plab_arrays(dng->from(), n_threads);
5588 } else {
5589 assert(_survivor_chunk_index == 0, "Error");
5590 }
5591
5592 // To space
5593 {
5594 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5595 assert(!pst->valid(), "Clobbering existing data?");
5596 // Sets the condition for completion of the subtask (how many threads
5597 // need to finish in order to be done).
5598 pst->set_n_threads(n_threads);
5599 pst->set_n_tasks(1);
5600 assert(pst->valid(), "Error");
5601 }
5602
5603 // From space
5604 {
5605 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5606 assert(!pst->valid(), "Clobbering existing data?");
5607 size_t n_tasks = _survivor_chunk_index + 1;
5608 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5609 // Sets the condition for completion of the subtask (how many threads
5610 // need to finish in order to be done).
5611 pst->set_n_threads(n_threads);
5612 pst->set_n_tasks((int)n_tasks);
5613 assert(pst->valid(), "Error");
5614 }
5615 }
5616
5617 // Parallel version of remark
5618 void CMSCollector::do_remark_parallel() {
5619 GenCollectedHeap* gch = GenCollectedHeap::heap();
5620 FlexibleWorkGang* workers = gch->workers();
5621 assert(workers != NULL, "Need parallel worker threads.");
5622 // Choose to use the number of GC workers most recently set
5623 // into "active_workers". If active_workers is not set, set it
5624 // to ParallelGCThreads.
5625 int n_workers = workers->active_workers();
5626 if (n_workers == 0) {
5627 assert(n_workers > 0, "Should have been set during scavenge");
5628 n_workers = ParallelGCThreads;
5629 workers->set_active_workers(n_workers);
5630 }
5631 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5632
5633 CMSParRemarkTask tsk(this,
5634 cms_space,
5635 n_workers, workers, task_queues());
5636
5637 // Set up for parallel process_strong_roots work.
5638 gch->set_par_threads(n_workers);
5639 // We won't be iterating over the cards in the card table updating
5640 // the younger_gen cards, so we shouldn't call the following else
5641 // the verification code as well as subsequent younger_refs_iterate
5642 // code would get confused. XXX
5643 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5644
5645 // The young gen rescan work will not be done as part of
5646 // process_strong_roots (which currently doesn't knw how to
5647 // parallelize such a scan), but rather will be broken up into
5648 // a set of parallel tasks (via the sampling that the [abortable]
5649 // preclean phase did of EdenSpace, plus the [two] tasks of
5650 // scanning the [two] survivor spaces. Further fine-grain
5651 // parallelization of the scanning of the survivor spaces
5652 // themselves, and of precleaning of the younger gen itself
5653 // is deferred to the future.
5654 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5655
5656 // The dirty card rescan work is broken up into a "sequence"
5657 // of parallel tasks (per constituent space) that are dynamically
5658 // claimed by the parallel threads.
5659 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5660
5661 // It turns out that even when we're using 1 thread, doing the work in a
5662 // separate thread causes wide variance in run times. We can't help this
5663 // in the multi-threaded case, but we special-case n=1 here to get
5664 // repeatable measurements of the 1-thread overhead of the parallel code.
5665 if (n_workers > 1) {
5666 // Make refs discovery MT-safe, if it isn't already: it may not
5667 // necessarily be so, since it's possible that we are doing
5668 // ST marking.
5669 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5670 GenCollectedHeap::StrongRootsScope srs(gch);
5671 workers->run_task(&tsk);
5672 } else {
5673 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5674 GenCollectedHeap::StrongRootsScope srs(gch);
5675 tsk.work(0);
5676 }
5677
5678 gch->set_par_threads(0); // 0 ==> non-parallel.
5679 // restore, single-threaded for now, any preserved marks
5680 // as a result of work_q overflow
5681 restore_preserved_marks_if_any();
5682 }
5683
5684 // Non-parallel version of remark
5685 void CMSCollector::do_remark_non_parallel() {
5686 ResourceMark rm;
5687 HandleMark hm;
5688 GenCollectedHeap* gch = GenCollectedHeap::heap();
5689 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5690
5691 MarkRefsIntoAndScanClosure
5692 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5693 &_markStack, this,
5694 false /* should_yield */, false /* not precleaning */);
5695 MarkFromDirtyCardsClosure
5696 markFromDirtyCardsClosure(this, _span,
5697 NULL, // space is set further below
5698 &_markBitMap, &_markStack, &mrias_cl);
5699 {
5700 TraceTime t("grey object rescan", PrintGCDetails, false, gclog_or_tty);
5701 // Iterate over the dirty cards, setting the corresponding bits in the
5702 // mod union table.
5703 {
5704 ModUnionClosure modUnionClosure(&_modUnionTable);
5705 _ct->ct_bs()->dirty_card_iterate(
5706 _cmsGen->used_region(),
5707 &modUnionClosure);
5708 }
5709 // Having transferred these marks into the modUnionTable, we just need
5710 // to rescan the marked objects on the dirty cards in the modUnionTable.
5711 // The initial marking may have been done during an asynchronous
5712 // collection so there may be dirty bits in the mod-union table.
5713 const int alignment =
5714 CardTableModRefBS::card_size * BitsPerWord;
5715 {
5716 // ... First handle dirty cards in CMS gen
5717 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5718 MemRegion ur = _cmsGen->used_region();
5719 HeapWord* lb = ur.start();
5720 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5721 MemRegion cms_span(lb, ub);
5722 _modUnionTable.dirty_range_iterate_clear(cms_span,
5723 &markFromDirtyCardsClosure);
5724 verify_work_stacks_empty();
5725 if (PrintCMSStatistics != 0) {
5726 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5727 markFromDirtyCardsClosure.num_dirty_cards());
5728 }
5729 }
5730 }
5731 if (VerifyDuringGC &&
5732 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5733 HandleMark hm; // Discard invalid handles created during verification
5734 Universe::verify();
5735 }
5736 {
5737 TraceTime t("root rescan", PrintGCDetails, false, gclog_or_tty);
5738
5739 verify_work_stacks_empty();
5740
5741 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5742 GenCollectedHeap::StrongRootsScope srs(gch);
5743 gch->gen_process_strong_roots(_cmsGen->level(),
5744 true, // younger gens as roots
5745 false, // use the local StrongRootsScope
5746 false, // not scavenging
5747 SharedHeap::ScanningOption(roots_scanning_options()),
5748 &mrias_cl,
5749 true, // walk code active on stacks
5750 NULL,
5751 NULL); // The dirty klasses will be handled below
5752
5753 assert(should_unload_classes()
5754 || (roots_scanning_options() & SharedHeap::SO_CodeCache),
5755 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5756 }
5757
5758 {
5759 TraceTime t("visit unhandled CLDs", PrintGCDetails, false, gclog_or_tty);
5760
5761 verify_work_stacks_empty();
5762
5763 // Scan all class loader data objects that might have been introduced
5764 // during concurrent marking.
5765 ResourceMark rm;
5766 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5767 for (int i = 0; i < array->length(); i++) {
5768 mrias_cl.do_class_loader_data(array->at(i));
5769 }
5770
5771 // We don't need to keep track of new CLDs anymore.
5772 ClassLoaderDataGraph::remember_new_clds(false);
5773
5774 verify_work_stacks_empty();
5775 }
5776
5777 {
5778 TraceTime t("dirty klass scan", PrintGCDetails, false, gclog_or_tty);
5779
5780 verify_work_stacks_empty();
5781
5782 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5783 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5784
5785 verify_work_stacks_empty();
5786 }
5787
5788 // We might have added oops to ClassLoaderData::_handles during the
5789 // concurrent marking phase. These oops point to newly allocated objects
5790 // that are guaranteed to be kept alive. Either by the direct allocation
5791 // code, or when the young collector processes the strong roots. Hence,
5792 // we don't have to revisit the _handles block during the remark phase.
5793
5794 verify_work_stacks_empty();
5795 // Restore evacuated mark words, if any, used for overflow list links
5796 if (!CMSOverflowEarlyRestoration) {
5797 restore_preserved_marks_if_any();
5798 }
5799 verify_overflow_empty();
5800 }
5801
5802 ////////////////////////////////////////////////////////
5803 // Parallel Reference Processing Task Proxy Class
5804 ////////////////////////////////////////////////////////
5805 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5806 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5807 CMSCollector* _collector;
5808 CMSBitMap* _mark_bit_map;
5809 const MemRegion _span;
5810 ProcessTask& _task;
5811
5812 public:
5813 CMSRefProcTaskProxy(ProcessTask& task,
5814 CMSCollector* collector,
5815 const MemRegion& span,
5816 CMSBitMap* mark_bit_map,
5817 AbstractWorkGang* workers,
5818 OopTaskQueueSet* task_queues):
5819 // XXX Should superclass AGTWOQ also know about AWG since it knows
5820 // about the task_queues used by the AWG? Then it could initialize
5821 // the terminator() object. See 6984287. The set_for_termination()
5822 // below is a temporary band-aid for the regression in 6984287.
5823 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5824 task_queues),
5825 _task(task),
5826 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5827 {
5828 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5829 "Inconsistency in _span");
5830 set_for_termination(workers->active_workers());
5831 }
5832
5833 OopTaskQueueSet* task_queues() { return queues(); }
5834
5835 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5836
5837 void do_work_steal(int i,
5838 CMSParDrainMarkingStackClosure* drain,
5839 CMSParKeepAliveClosure* keep_alive,
5840 int* seed);
5841
5842 virtual void work(uint worker_id);
5843 };
5844
5845 void CMSRefProcTaskProxy::work(uint worker_id) {
5846 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5847 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5848 _mark_bit_map,
5849 work_queue(worker_id));
5850 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5851 _mark_bit_map,
5852 work_queue(worker_id));
5853 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5854 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5855 if (_task.marks_oops_alive()) {
5856 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5857 _collector->hash_seed(worker_id));
5858 }
5859 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5860 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5861 }
5862
5863 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5864 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5865 EnqueueTask& _task;
5866
5867 public:
5868 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5869 : AbstractGangTask("Enqueue reference objects in parallel"),
5870 _task(task)
5871 { }
5872
5873 virtual void work(uint worker_id)
5874 {
5875 _task.work(worker_id);
5876 }
5877 };
5878
5879 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5880 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5881 _span(span),
5882 _bit_map(bit_map),
5883 _work_queue(work_queue),
5884 _mark_and_push(collector, span, bit_map, work_queue),
5885 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5886 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5887 { }
5888
5889 // . see if we can share work_queues with ParNew? XXX
5890 void CMSRefProcTaskProxy::do_work_steal(int i,
5891 CMSParDrainMarkingStackClosure* drain,
5892 CMSParKeepAliveClosure* keep_alive,
5893 int* seed) {
5894 OopTaskQueue* work_q = work_queue(i);
5895 NOT_PRODUCT(int num_steals = 0;)
5896 oop obj_to_scan;
5897
5898 while (true) {
5899 // Completely finish any left over work from (an) earlier round(s)
5900 drain->trim_queue(0);
5901 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5902 (size_t)ParGCDesiredObjsFromOverflowList);
5903 // Now check if there's any work in the overflow list
5904 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5905 // only affects the number of attempts made to get work from the
5906 // overflow list and does not affect the number of workers. Just
5907 // pass ParallelGCThreads so this behavior is unchanged.
5908 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5909 work_q,
5910 ParallelGCThreads)) {
5911 // Found something in global overflow list;
5912 // not yet ready to go stealing work from others.
5913 // We'd like to assert(work_q->size() != 0, ...)
5914 // because we just took work from the overflow list,
5915 // but of course we can't, since all of that might have
5916 // been already stolen from us.
5917 continue;
5918 }
5919 // Verify that we have no work before we resort to stealing
5920 assert(work_q->size() == 0, "Have work, shouldn't steal");
5921 // Try to steal from other queues that have work
5922 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5923 NOT_PRODUCT(num_steals++;)
5924 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5925 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5926 // Do scanning work
5927 obj_to_scan->oop_iterate(keep_alive);
5928 // Loop around, finish this work, and try to steal some more
5929 } else if (terminator()->offer_termination()) {
5930 break; // nirvana from the infinite cycle
5931 }
5932 }
5933 NOT_PRODUCT(
5934 if (PrintCMSStatistics != 0) {
5935 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5936 }
5937 )
5938 }
5939
5940 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5941 {
5942 GenCollectedHeap* gch = GenCollectedHeap::heap();
5943 FlexibleWorkGang* workers = gch->workers();
5944 assert(workers != NULL, "Need parallel worker threads.");
5945 CMSRefProcTaskProxy rp_task(task, &_collector,
5946 _collector.ref_processor()->span(),
5947 _collector.markBitMap(),
5948 workers, _collector.task_queues());
5949 workers->run_task(&rp_task);
5950 }
5951
5952 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5953 {
5954
5955 GenCollectedHeap* gch = GenCollectedHeap::heap();
5956 FlexibleWorkGang* workers = gch->workers();
5957 assert(workers != NULL, "Need parallel worker threads.");
5958 CMSRefEnqueueTaskProxy enq_task(task);
5959 workers->run_task(&enq_task);
5960 }
5961
5962 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5963
5964 ResourceMark rm;
5965 HandleMark hm;
5966
5967 ReferenceProcessor* rp = ref_processor();
5968 assert(rp->span().equals(_span), "Spans should be equal");
5969 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5970 // Process weak references.
5971 rp->setup_policy(clear_all_soft_refs);
5972 verify_work_stacks_empty();
5973
5974 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5975 &_markStack, false /* !preclean */);
5976 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5977 _span, &_markBitMap, &_markStack,
5978 &cmsKeepAliveClosure, false /* !preclean */);
5979 {
5980 TraceTime t("weak refs processing", PrintGCDetails, false, gclog_or_tty);
5981 if (rp->processing_is_mt()) {
5982 // Set the degree of MT here. If the discovery is done MT, there
5983 // may have been a different number of threads doing the discovery
5984 // and a different number of discovered lists may have Ref objects.
5985 // That is OK as long as the Reference lists are balanced (see
5986 // balance_all_queues() and balance_queues()).
5987 GenCollectedHeap* gch = GenCollectedHeap::heap();
5988 int active_workers = ParallelGCThreads;
5989 FlexibleWorkGang* workers = gch->workers();
5990 if (workers != NULL) {
5991 active_workers = workers->active_workers();
5992 // The expectation is that active_workers will have already
5993 // been set to a reasonable value. If it has not been set,
5994 // investigate.
5995 assert(active_workers > 0, "Should have been set during scavenge");
5996 }
5997 rp->set_active_mt_degree(active_workers);
5998 CMSRefProcTaskExecutor task_executor(*this);
5999 rp->process_discovered_references(&_is_alive_closure,
6000 &cmsKeepAliveClosure,
6001 &cmsDrainMarkingStackClosure,
6002 &task_executor);
6003 } else {
6004 rp->process_discovered_references(&_is_alive_closure,
6005 &cmsKeepAliveClosure,
6006 &cmsDrainMarkingStackClosure,
6007 NULL);
6008 }
6009 }
6010
6011 // This is the point where the entire marking should have completed.
6012 verify_work_stacks_empty();
6013
6014 if (should_unload_classes()) {
6015 {
6016 TraceTime t("class unloading", PrintGCDetails, false, gclog_or_tty);
6017
6018 // Unload classes and purge the SystemDictionary.
6019 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
6020
6021 // Unload nmethods.
6022 CodeCache::do_unloading(&_is_alive_closure, purged_class);
6023
6024 // Prune dead klasses from subklass/sibling/implementor lists.
6025 Klass::clean_weak_klass_links(&_is_alive_closure);
6026 }
6027
6028 {
6029 TraceTime t("scrub symbol table", PrintGCDetails, false, gclog_or_tty);
6030 // Clean up unreferenced symbols in symbol table.
6031 SymbolTable::unlink();
6032 }
6033 }
6034
6035 // CMS doesn't use the StringTable as hard roots when class unloading is turned off.
6036 // Need to check if we really scanned the StringTable.
6037 if ((roots_scanning_options() & SharedHeap::SO_Strings) == 0) {
6038 TraceTime t("scrub string table", PrintGCDetails, false, gclog_or_tty);
6039 // Delete entries for dead interned strings.
6040 StringTable::unlink(&_is_alive_closure);
6041 }
6042
6043 // Restore any preserved marks as a result of mark stack or
6044 // work queue overflow
6045 restore_preserved_marks_if_any(); // done single-threaded for now
6046
6047 rp->set_enqueuing_is_done(true);
6048 if (rp->processing_is_mt()) {
6049 rp->balance_all_queues();
6050 CMSRefProcTaskExecutor task_executor(*this);
6051 rp->enqueue_discovered_references(&task_executor);
6052 } else {
6053 rp->enqueue_discovered_references(NULL);
6054 }
6055 rp->verify_no_references_recorded();
6056 assert(!rp->discovery_enabled(), "should have been disabled");
6057 }
6058
6059 #ifndef PRODUCT
6060 void CMSCollector::check_correct_thread_executing() {
6061 Thread* t = Thread::current();
6062 // Only the VM thread or the CMS thread should be here.
6063 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6064 "Unexpected thread type");
6065 // If this is the vm thread, the foreground process
6066 // should not be waiting. Note that _foregroundGCIsActive is
6067 // true while the foreground collector is waiting.
6068 if (_foregroundGCShouldWait) {
6069 // We cannot be the VM thread
6070 assert(t->is_ConcurrentGC_thread(),
6071 "Should be CMS thread");
6072 } else {
6073 // We can be the CMS thread only if we are in a stop-world
6074 // phase of CMS collection.
6075 if (t->is_ConcurrentGC_thread()) {
6076 assert(_collectorState == InitialMarking ||
6077 _collectorState == FinalMarking,
6078 "Should be a stop-world phase");
6079 // The CMS thread should be holding the CMS_token.
6080 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6081 "Potential interference with concurrently "
6082 "executing VM thread");
6083 }
6084 }
6085 }
6086 #endif
6087
6088 void CMSCollector::sweep(bool asynch) {
6089 assert(_collectorState == Sweeping, "just checking");
6090 check_correct_thread_executing();
6091 verify_work_stacks_empty();
6092 verify_overflow_empty();
6093 increment_sweep_count();
6094 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6095
6096 _inter_sweep_timer.stop();
6097 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6098 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
6099
6100 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6101 _intra_sweep_timer.reset();
6102 _intra_sweep_timer.start();
6103 if (asynch) {
6104 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6105 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
6106 // First sweep the old gen
6107 {
6108 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6109 bitMapLock());
6110 sweepWork(_cmsGen, asynch);
6111 }
6112
6113 // Update Universe::_heap_*_at_gc figures.
6114 // We need all the free list locks to make the abstract state
6115 // transition from Sweeping to Resetting. See detailed note
6116 // further below.
6117 {
6118 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6119 // Update heap occupancy information which is used as
6120 // input to soft ref clearing policy at the next gc.
6121 Universe::update_heap_info_at_gc();
6122 _collectorState = Resizing;
6123 }
6124 } else {
6125 // already have needed locks
6126 sweepWork(_cmsGen, asynch);
6127 // Update heap occupancy information which is used as
6128 // input to soft ref clearing policy at the next gc.
6129 Universe::update_heap_info_at_gc();
6130 _collectorState = Resizing;
6131 }
6132 verify_work_stacks_empty();
6133 verify_overflow_empty();
6134
6135 if (should_unload_classes()) {
6136 ClassLoaderDataGraph::purge();
6137 }
6138
6139 _intra_sweep_timer.stop();
6140 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6141
6142 _inter_sweep_timer.reset();
6143 _inter_sweep_timer.start();
6144
6145 // We need to use a monotonically non-deccreasing time in ms
6146 // or we will see time-warp warnings and os::javaTimeMillis()
6147 // does not guarantee monotonicity.
6148 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6149 update_time_of_last_gc(now);
6150
6151 // NOTE on abstract state transitions:
6152 // Mutators allocate-live and/or mark the mod-union table dirty
6153 // based on the state of the collection. The former is done in
6154 // the interval [Marking, Sweeping] and the latter in the interval
6155 // [Marking, Sweeping). Thus the transitions into the Marking state
6156 // and out of the Sweeping state must be synchronously visible
6157 // globally to the mutators.
6158 // The transition into the Marking state happens with the world
6159 // stopped so the mutators will globally see it. Sweeping is
6160 // done asynchronously by the background collector so the transition
6161 // from the Sweeping state to the Resizing state must be done
6162 // under the freelistLock (as is the check for whether to
6163 // allocate-live and whether to dirty the mod-union table).
6164 assert(_collectorState == Resizing, "Change of collector state to"
6165 " Resizing must be done under the freelistLocks (plural)");
6166
6167 // Now that sweeping has been completed, we clear
6168 // the incremental_collection_failed flag,
6169 // thus inviting a younger gen collection to promote into
6170 // this generation. If such a promotion may still fail,
6171 // the flag will be set again when a young collection is
6172 // attempted.
6173 GenCollectedHeap* gch = GenCollectedHeap::heap();
6174 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6175 gch->update_full_collections_completed(_collection_count_start);
6176 }
6177
6178 // FIX ME!!! Looks like this belongs in CFLSpace, with
6179 // CMSGen merely delegating to it.
6180 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6181 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6182 HeapWord* minAddr = _cmsSpace->bottom();
6183 HeapWord* largestAddr =
6184 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6185 if (largestAddr == NULL) {
6186 // The dictionary appears to be empty. In this case
6187 // try to coalesce at the end of the heap.
6188 largestAddr = _cmsSpace->end();
6189 }
6190 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6191 size_t nearLargestOffset =
6192 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6193 if (PrintFLSStatistics != 0) {
6194 gclog_or_tty->print_cr(
6195 "CMS: Large Block: " PTR_FORMAT ";"
6196 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6197 largestAddr,
6198 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6199 }
6200 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6201 }
6202
6203 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6204 return addr >= _cmsSpace->nearLargestChunk();
6205 }
6206
6207 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6208 return _cmsSpace->find_chunk_at_end();
6209 }
6210
6211 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6212 bool full) {
6213 // The next lower level has been collected. Gather any statistics
6214 // that are of interest at this point.
6215 if (!full && (current_level + 1) == level()) {
6216 // Gather statistics on the young generation collection.
6217 collector()->stats().record_gc0_end(used());
6218 }
6219 }
6220
6221 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6222 GenCollectedHeap* gch = GenCollectedHeap::heap();
6223 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6224 "Wrong type of heap");
6225 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6226 gch->gen_policy()->size_policy();
6227 assert(sp->is_gc_cms_adaptive_size_policy(),
6228 "Wrong type of size policy");
6229 return sp;
6230 }
6231
6232 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6233 if (PrintGCDetails && Verbose) {
6234 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6235 }
6236 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6237 _debug_collection_type =
6238 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6239 if (PrintGCDetails && Verbose) {
6240 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6241 }
6242 }
6243
6244 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6245 bool asynch) {
6246 // We iterate over the space(s) underlying this generation,
6247 // checking the mark bit map to see if the bits corresponding
6248 // to specific blocks are marked or not. Blocks that are
6249 // marked are live and are not swept up. All remaining blocks
6250 // are swept up, with coalescing on-the-fly as we sweep up
6251 // contiguous free and/or garbage blocks:
6252 // We need to ensure that the sweeper synchronizes with allocators
6253 // and stop-the-world collectors. In particular, the following
6254 // locks are used:
6255 // . CMS token: if this is held, a stop the world collection cannot occur
6256 // . freelistLock: if this is held no allocation can occur from this
6257 // generation by another thread
6258 // . bitMapLock: if this is held, no other thread can access or update
6259 //
6260
6261 // Note that we need to hold the freelistLock if we use
6262 // block iterate below; else the iterator might go awry if
6263 // a mutator (or promotion) causes block contents to change
6264 // (for instance if the allocator divvies up a block).
6265 // If we hold the free list lock, for all practical purposes
6266 // young generation GC's can't occur (they'll usually need to
6267 // promote), so we might as well prevent all young generation
6268 // GC's while we do a sweeping step. For the same reason, we might
6269 // as well take the bit map lock for the entire duration
6270
6271 // check that we hold the requisite locks
6272 assert(have_cms_token(), "Should hold cms token");
6273 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6274 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6275 "Should possess CMS token to sweep");
6276 assert_lock_strong(gen->freelistLock());
6277 assert_lock_strong(bitMapLock());
6278
6279 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6280 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6281 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6282 _inter_sweep_estimate.padded_average(),
6283 _intra_sweep_estimate.padded_average());
6284 gen->setNearLargestChunk();
6285
6286 {
6287 SweepClosure sweepClosure(this, gen, &_markBitMap,
6288 CMSYield && asynch);
6289 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6290 // We need to free-up/coalesce garbage/blocks from a
6291 // co-terminal free run. This is done in the SweepClosure
6292 // destructor; so, do not remove this scope, else the
6293 // end-of-sweep-census below will be off by a little bit.
6294 }
6295 gen->cmsSpace()->sweep_completed();
6296 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6297 if (should_unload_classes()) { // unloaded classes this cycle,
6298 _concurrent_cycles_since_last_unload = 0; // ... reset count
6299 } else { // did not unload classes,
6300 _concurrent_cycles_since_last_unload++; // ... increment count
6301 }
6302 }
6303
6304 // Reset CMS data structures (for now just the marking bit map)
6305 // preparatory for the next cycle.
6306 void CMSCollector::reset(bool asynch) {
6307 GenCollectedHeap* gch = GenCollectedHeap::heap();
6308 CMSAdaptiveSizePolicy* sp = size_policy();
6309 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6310 if (asynch) {
6311 CMSTokenSyncWithLocks ts(true, bitMapLock());
6312
6313 // If the state is not "Resetting", the foreground thread
6314 // has done a collection and the resetting.
6315 if (_collectorState != Resetting) {
6316 assert(_collectorState == Idling, "The state should only change"
6317 " because the foreground collector has finished the collection");
6318 return;
6319 }
6320
6321 // Clear the mark bitmap (no grey objects to start with)
6322 // for the next cycle.
6323 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6324 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6325
6326 HeapWord* curAddr = _markBitMap.startWord();
6327 while (curAddr < _markBitMap.endWord()) {
6328 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6329 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6330 _markBitMap.clear_large_range(chunk);
6331 if (ConcurrentMarkSweepThread::should_yield() &&
6332 !foregroundGCIsActive() &&
6333 CMSYield) {
6334 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6335 "CMS thread should hold CMS token");
6336 assert_lock_strong(bitMapLock());
6337 bitMapLock()->unlock();
6338 ConcurrentMarkSweepThread::desynchronize(true);
6339 ConcurrentMarkSweepThread::acknowledge_yield_request();
6340 stopTimer();
6341 if (PrintCMSStatistics != 0) {
6342 incrementYields();
6343 }
6344 icms_wait();
6345
6346 // See the comment in coordinator_yield()
6347 for (unsigned i = 0; i < CMSYieldSleepCount &&
6348 ConcurrentMarkSweepThread::should_yield() &&
6349 !CMSCollector::foregroundGCIsActive(); ++i) {
6350 os::sleep(Thread::current(), 1, false);
6351 ConcurrentMarkSweepThread::acknowledge_yield_request();
6352 }
6353
6354 ConcurrentMarkSweepThread::synchronize(true);
6355 bitMapLock()->lock_without_safepoint_check();
6356 startTimer();
6357 }
6358 curAddr = chunk.end();
6359 }
6360 // A successful mostly concurrent collection has been done.
6361 // Because only the full (i.e., concurrent mode failure) collections
6362 // are being measured for gc overhead limits, clean the "near" flag
6363 // and count.
6364 sp->reset_gc_overhead_limit_count();
6365 _collectorState = Idling;
6366 } else {
6367 // already have the lock
6368 assert(_collectorState == Resetting, "just checking");
6369 assert_lock_strong(bitMapLock());
6370 _markBitMap.clear_all();
6371 _collectorState = Idling;
6372 }
6373
6374 // Stop incremental mode after a cycle completes, so that any future cycles
6375 // are triggered by allocation.
6376 stop_icms();
6377
6378 NOT_PRODUCT(
6379 if (RotateCMSCollectionTypes) {
6380 _cmsGen->rotate_debug_collection_type();
6381 }
6382 )
6383 }
6384
6385 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6386 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6387 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6388 TraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, gclog_or_tty);
6389 TraceCollectorStats tcs(counters());
6390
6391 switch (op) {
6392 case CMS_op_checkpointRootsInitial: {
6393 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6394 checkpointRootsInitial(true); // asynch
6395 if (PrintGC) {
6396 _cmsGen->printOccupancy("initial-mark");
6397 }
6398 break;
6399 }
6400 case CMS_op_checkpointRootsFinal: {
6401 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6402 checkpointRootsFinal(true, // asynch
6403 false, // !clear_all_soft_refs
6404 false); // !init_mark_was_synchronous
6405 if (PrintGC) {
6406 _cmsGen->printOccupancy("remark");
6407 }
6408 break;
6409 }
6410 default:
6411 fatal("No such CMS_op");
6412 }
6413 }
6414
6415 #ifndef PRODUCT
6416 size_t const CMSCollector::skip_header_HeapWords() {
6417 return FreeChunk::header_size();
6418 }
6419
6420 // Try and collect here conditions that should hold when
6421 // CMS thread is exiting. The idea is that the foreground GC
6422 // thread should not be blocked if it wants to terminate
6423 // the CMS thread and yet continue to run the VM for a while
6424 // after that.
6425 void CMSCollector::verify_ok_to_terminate() const {
6426 assert(Thread::current()->is_ConcurrentGC_thread(),
6427 "should be called by CMS thread");
6428 assert(!_foregroundGCShouldWait, "should be false");
6429 // We could check here that all the various low-level locks
6430 // are not held by the CMS thread, but that is overkill; see
6431 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6432 // is checked.
6433 }
6434 #endif
6435
6436 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6437 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6438 "missing Printezis mark?");
6439 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6440 size_t size = pointer_delta(nextOneAddr + 1, addr);
6441 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6442 "alignment problem");
6443 assert(size >= 3, "Necessary for Printezis marks to work");
6444 return size;
6445 }
6446
6447 // A variant of the above (block_size_using_printezis_bits()) except
6448 // that we return 0 if the P-bits are not yet set.
6449 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6450 if (_markBitMap.isMarked(addr + 1)) {
6451 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6452 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6453 size_t size = pointer_delta(nextOneAddr + 1, addr);
6454 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6455 "alignment problem");
6456 assert(size >= 3, "Necessary for Printezis marks to work");
6457 return size;
6458 }
6459 return 0;
6460 }
6461
6462 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6463 size_t sz = 0;
6464 oop p = (oop)addr;
6465 if (p->klass_or_null() != NULL) {
6466 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6467 } else {
6468 sz = block_size_using_printezis_bits(addr);
6469 }
6470 assert(sz > 0, "size must be nonzero");
6471 HeapWord* next_block = addr + sz;
6472 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6473 CardTableModRefBS::card_size);
6474 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6475 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6476 "must be different cards");
6477 return next_card;
6478 }
6479
6480
6481 // CMS Bit Map Wrapper /////////////////////////////////////////
6482
6483 // Construct a CMS bit map infrastructure, but don't create the
6484 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6485 // further below.
6486 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6487 _bm(),
6488 _shifter(shifter),
6489 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6490 {
6491 _bmStartWord = 0;
6492 _bmWordSize = 0;
6493 }
6494
6495 bool CMSBitMap::allocate(MemRegion mr) {
6496 _bmStartWord = mr.start();
6497 _bmWordSize = mr.word_size();
6498 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6499 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6500 if (!brs.is_reserved()) {
6501 warning("CMS bit map allocation failure");
6502 return false;
6503 }
6504 // For now we'll just commit all of the bit map up fromt.
6505 // Later on we'll try to be more parsimonious with swap.
6506 if (!_virtual_space.initialize(brs, brs.size())) {
6507 warning("CMS bit map backing store failure");
6508 return false;
6509 }
6510 assert(_virtual_space.committed_size() == brs.size(),
6511 "didn't reserve backing store for all of CMS bit map?");
6512 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6513 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6514 _bmWordSize, "inconsistency in bit map sizing");
6515 _bm.set_size(_bmWordSize >> _shifter);
6516
6517 // bm.clear(); // can we rely on getting zero'd memory? verify below
6518 assert(isAllClear(),
6519 "Expected zero'd memory from ReservedSpace constructor");
6520 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6521 "consistency check");
6522 return true;
6523 }
6524
6525 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6526 HeapWord *next_addr, *end_addr, *last_addr;
6527 assert_locked();
6528 assert(covers(mr), "out-of-range error");
6529 // XXX assert that start and end are appropriately aligned
6530 for (next_addr = mr.start(), end_addr = mr.end();
6531 next_addr < end_addr; next_addr = last_addr) {
6532 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6533 last_addr = dirty_region.end();
6534 if (!dirty_region.is_empty()) {
6535 cl->do_MemRegion(dirty_region);
6536 } else {
6537 assert(last_addr == end_addr, "program logic");
6538 return;
6539 }
6540 }
6541 }
6542
6543 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6544 _bm.print_on_error(st, prefix);
6545 }
6546
6547 #ifndef PRODUCT
6548 void CMSBitMap::assert_locked() const {
6549 CMSLockVerifier::assert_locked(lock());
6550 }
6551
6552 bool CMSBitMap::covers(MemRegion mr) const {
6553 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6554 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6555 "size inconsistency");
6556 return (mr.start() >= _bmStartWord) &&
6557 (mr.end() <= endWord());
6558 }
6559
6560 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6561 return (start >= _bmStartWord && (start + size) <= endWord());
6562 }
6563
6564 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6565 // verify that there are no 1 bits in the interval [left, right)
6566 FalseBitMapClosure falseBitMapClosure;
6567 iterate(&falseBitMapClosure, left, right);
6568 }
6569
6570 void CMSBitMap::region_invariant(MemRegion mr)
6571 {
6572 assert_locked();
6573 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6574 assert(!mr.is_empty(), "unexpected empty region");
6575 assert(covers(mr), "mr should be covered by bit map");
6576 // convert address range into offset range
6577 size_t start_ofs = heapWordToOffset(mr.start());
6578 // Make sure that end() is appropriately aligned
6579 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6580 (1 << (_shifter+LogHeapWordSize))),
6581 "Misaligned mr.end()");
6582 size_t end_ofs = heapWordToOffset(mr.end());
6583 assert(end_ofs > start_ofs, "Should mark at least one bit");
6584 }
6585
6586 #endif
6587
6588 bool CMSMarkStack::allocate(size_t size) {
6589 // allocate a stack of the requisite depth
6590 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6591 size * sizeof(oop)));
6592 if (!rs.is_reserved()) {
6593 warning("CMSMarkStack allocation failure");
6594 return false;
6595 }
6596 if (!_virtual_space.initialize(rs, rs.size())) {
6597 warning("CMSMarkStack backing store failure");
6598 return false;
6599 }
6600 assert(_virtual_space.committed_size() == rs.size(),
6601 "didn't reserve backing store for all of CMS stack?");
6602 _base = (oop*)(_virtual_space.low());
6603 _index = 0;
6604 _capacity = size;
6605 NOT_PRODUCT(_max_depth = 0);
6606 return true;
6607 }
6608
6609 // XXX FIX ME !!! In the MT case we come in here holding a
6610 // leaf lock. For printing we need to take a further lock
6611 // which has lower rank. We need to recallibrate the two
6612 // lock-ranks involved in order to be able to rpint the
6613 // messages below. (Or defer the printing to the caller.
6614 // For now we take the expedient path of just disabling the
6615 // messages for the problematic case.)
6616 void CMSMarkStack::expand() {
6617 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6618 if (_capacity == MarkStackSizeMax) {
6619 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6620 // We print a warning message only once per CMS cycle.
6621 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6622 }
6623 return;
6624 }
6625 // Double capacity if possible
6626 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6627 // Do not give up existing stack until we have managed to
6628 // get the double capacity that we desired.
6629 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6630 new_capacity * sizeof(oop)));
6631 if (rs.is_reserved()) {
6632 // Release the backing store associated with old stack
6633 _virtual_space.release();
6634 // Reinitialize virtual space for new stack
6635 if (!_virtual_space.initialize(rs, rs.size())) {
6636 fatal("Not enough swap for expanded marking stack");
6637 }
6638 _base = (oop*)(_virtual_space.low());
6639 _index = 0;
6640 _capacity = new_capacity;
6641 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6642 // Failed to double capacity, continue;
6643 // we print a detail message only once per CMS cycle.
6644 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6645 SIZE_FORMAT"K",
6646 _capacity / K, new_capacity / K);
6647 }
6648 }
6649
6650
6651 // Closures
6652 // XXX: there seems to be a lot of code duplication here;
6653 // should refactor and consolidate common code.
6654
6655 // This closure is used to mark refs into the CMS generation in
6656 // the CMS bit map. Called at the first checkpoint. This closure
6657 // assumes that we do not need to re-mark dirty cards; if the CMS
6658 // generation on which this is used is not an oldest
6659 // generation then this will lose younger_gen cards!
6660
6661 MarkRefsIntoClosure::MarkRefsIntoClosure(
6662 MemRegion span, CMSBitMap* bitMap):
6663 _span(span),
6664 _bitMap(bitMap)
6665 {
6666 assert(_ref_processor == NULL, "deliberately left NULL");
6667 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6668 }
6669
6670 void MarkRefsIntoClosure::do_oop(oop obj) {
6671 // if p points into _span, then mark corresponding bit in _markBitMap
6672 assert(obj->is_oop(), "expected an oop");
6673 HeapWord* addr = (HeapWord*)obj;
6674 if (_span.contains(addr)) {
6675 // this should be made more efficient
6676 _bitMap->mark(addr);
6677 }
6678 }
6679
6680 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6681 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6682
6683 // A variant of the above, used for CMS marking verification.
6684 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6685 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6686 _span(span),
6687 _verification_bm(verification_bm),
6688 _cms_bm(cms_bm)
6689 {
6690 assert(_ref_processor == NULL, "deliberately left NULL");
6691 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6692 }
6693
6694 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6695 // if p points into _span, then mark corresponding bit in _markBitMap
6696 assert(obj->is_oop(), "expected an oop");
6697 HeapWord* addr = (HeapWord*)obj;
6698 if (_span.contains(addr)) {
6699 _verification_bm->mark(addr);
6700 if (!_cms_bm->isMarked(addr)) {
6701 oop(addr)->print();
6702 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6703 fatal("... aborting");
6704 }
6705 }
6706 }
6707
6708 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6709 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6710
6711 //////////////////////////////////////////////////
6712 // MarkRefsIntoAndScanClosure
6713 //////////////////////////////////////////////////
6714
6715 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6716 ReferenceProcessor* rp,
6717 CMSBitMap* bit_map,
6718 CMSBitMap* mod_union_table,
6719 CMSMarkStack* mark_stack,
6720 CMSCollector* collector,
6721 bool should_yield,
6722 bool concurrent_precleaning):
6723 _collector(collector),
6724 _span(span),
6725 _bit_map(bit_map),
6726 _mark_stack(mark_stack),
6727 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6728 mark_stack, concurrent_precleaning),
6729 _yield(should_yield),
6730 _concurrent_precleaning(concurrent_precleaning),
6731 _freelistLock(NULL)
6732 {
6733 _ref_processor = rp;
6734 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6735 }
6736
6737 // This closure is used to mark refs into the CMS generation at the
6738 // second (final) checkpoint, and to scan and transitively follow
6739 // the unmarked oops. It is also used during the concurrent precleaning
6740 // phase while scanning objects on dirty cards in the CMS generation.
6741 // The marks are made in the marking bit map and the marking stack is
6742 // used for keeping the (newly) grey objects during the scan.
6743 // The parallel version (Par_...) appears further below.
6744 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6745 if (obj != NULL) {
6746 assert(obj->is_oop(), "expected an oop");
6747 HeapWord* addr = (HeapWord*)obj;
6748 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6749 assert(_collector->overflow_list_is_empty(),
6750 "overflow list should be empty");
6751 if (_span.contains(addr) &&
6752 !_bit_map->isMarked(addr)) {
6753 // mark bit map (object is now grey)
6754 _bit_map->mark(addr);
6755 // push on marking stack (stack should be empty), and drain the
6756 // stack by applying this closure to the oops in the oops popped
6757 // from the stack (i.e. blacken the grey objects)
6758 bool res = _mark_stack->push(obj);
6759 assert(res, "Should have space to push on empty stack");
6760 do {
6761 oop new_oop = _mark_stack->pop();
6762 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6763 assert(_bit_map->isMarked((HeapWord*)new_oop),
6764 "only grey objects on this stack");
6765 // iterate over the oops in this oop, marking and pushing
6766 // the ones in CMS heap (i.e. in _span).
6767 new_oop->oop_iterate(&_pushAndMarkClosure);
6768 // check if it's time to yield
6769 do_yield_check();
6770 } while (!_mark_stack->isEmpty() ||
6771 (!_concurrent_precleaning && take_from_overflow_list()));
6772 // if marking stack is empty, and we are not doing this
6773 // during precleaning, then check the overflow list
6774 }
6775 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6776 assert(_collector->overflow_list_is_empty(),
6777 "overflow list was drained above");
6778 // We could restore evacuated mark words, if any, used for
6779 // overflow list links here because the overflow list is
6780 // provably empty here. That would reduce the maximum
6781 // size requirements for preserved_{oop,mark}_stack.
6782 // But we'll just postpone it until we are all done
6783 // so we can just stream through.
6784 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6785 _collector->restore_preserved_marks_if_any();
6786 assert(_collector->no_preserved_marks(), "No preserved marks");
6787 }
6788 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6789 "All preserved marks should have been restored above");
6790 }
6791 }
6792
6793 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6794 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6795
6796 void MarkRefsIntoAndScanClosure::do_yield_work() {
6797 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6798 "CMS thread should hold CMS token");
6799 assert_lock_strong(_freelistLock);
6800 assert_lock_strong(_bit_map->lock());
6801 // relinquish the free_list_lock and bitMaplock()
6802 _bit_map->lock()->unlock();
6803 _freelistLock->unlock();
6804 ConcurrentMarkSweepThread::desynchronize(true);
6805 ConcurrentMarkSweepThread::acknowledge_yield_request();
6806 _collector->stopTimer();
6807 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6808 if (PrintCMSStatistics != 0) {
6809 _collector->incrementYields();
6810 }
6811 _collector->icms_wait();
6812
6813 // See the comment in coordinator_yield()
6814 for (unsigned i = 0;
6815 i < CMSYieldSleepCount &&
6816 ConcurrentMarkSweepThread::should_yield() &&
6817 !CMSCollector::foregroundGCIsActive();
6818 ++i) {
6819 os::sleep(Thread::current(), 1, false);
6820 ConcurrentMarkSweepThread::acknowledge_yield_request();
6821 }
6822
6823 ConcurrentMarkSweepThread::synchronize(true);
6824 _freelistLock->lock_without_safepoint_check();
6825 _bit_map->lock()->lock_without_safepoint_check();
6826 _collector->startTimer();
6827 }
6828
6829 ///////////////////////////////////////////////////////////
6830 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6831 // MarkRefsIntoAndScanClosure
6832 ///////////////////////////////////////////////////////////
6833 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6834 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6835 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6836 _span(span),
6837 _bit_map(bit_map),
6838 _work_queue(work_queue),
6839 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6840 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6841 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6842 {
6843 _ref_processor = rp;
6844 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6845 }
6846
6847 // This closure is used to mark refs into the CMS generation at the
6848 // second (final) checkpoint, and to scan and transitively follow
6849 // the unmarked oops. The marks are made in the marking bit map and
6850 // the work_queue is used for keeping the (newly) grey objects during
6851 // the scan phase whence they are also available for stealing by parallel
6852 // threads. Since the marking bit map is shared, updates are
6853 // synchronized (via CAS).
6854 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6855 if (obj != NULL) {
6856 // Ignore mark word because this could be an already marked oop
6857 // that may be chained at the end of the overflow list.
6858 assert(obj->is_oop(true), "expected an oop");
6859 HeapWord* addr = (HeapWord*)obj;
6860 if (_span.contains(addr) &&
6861 !_bit_map->isMarked(addr)) {
6862 // mark bit map (object will become grey):
6863 // It is possible for several threads to be
6864 // trying to "claim" this object concurrently;
6865 // the unique thread that succeeds in marking the
6866 // object first will do the subsequent push on
6867 // to the work queue (or overflow list).
6868 if (_bit_map->par_mark(addr)) {
6869 // push on work_queue (which may not be empty), and trim the
6870 // queue to an appropriate length by applying this closure to
6871 // the oops in the oops popped from the stack (i.e. blacken the
6872 // grey objects)
6873 bool res = _work_queue->push(obj);
6874 assert(res, "Low water mark should be less than capacity?");
6875 trim_queue(_low_water_mark);
6876 } // Else, another thread claimed the object
6877 }
6878 }
6879 }
6880
6881 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6882 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6883
6884 // This closure is used to rescan the marked objects on the dirty cards
6885 // in the mod union table and the card table proper.
6886 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6887 oop p, MemRegion mr) {
6888
6889 size_t size = 0;
6890 HeapWord* addr = (HeapWord*)p;
6891 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6892 assert(_span.contains(addr), "we are scanning the CMS generation");
6893 // check if it's time to yield
6894 if (do_yield_check()) {
6895 // We yielded for some foreground stop-world work,
6896 // and we have been asked to abort this ongoing preclean cycle.
6897 return 0;
6898 }
6899 if (_bitMap->isMarked(addr)) {
6900 // it's marked; is it potentially uninitialized?
6901 if (p->klass_or_null() != NULL) {
6902 // an initialized object; ignore mark word in verification below
6903 // since we are running concurrent with mutators
6904 assert(p->is_oop(true), "should be an oop");
6905 if (p->is_objArray()) {
6906 // objArrays are precisely marked; restrict scanning
6907 // to dirty cards only.
6908 size = CompactibleFreeListSpace::adjustObjectSize(
6909 p->oop_iterate(_scanningClosure, mr));
6910 } else {
6911 // A non-array may have been imprecisely marked; we need
6912 // to scan object in its entirety.
6913 size = CompactibleFreeListSpace::adjustObjectSize(
6914 p->oop_iterate(_scanningClosure));
6915 }
6916 #ifdef ASSERT
6917 size_t direct_size =
6918 CompactibleFreeListSpace::adjustObjectSize(p->size());
6919 assert(size == direct_size, "Inconsistency in size");
6920 assert(size >= 3, "Necessary for Printezis marks to work");
6921 if (!_bitMap->isMarked(addr+1)) {
6922 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6923 } else {
6924 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6925 assert(_bitMap->isMarked(addr+size-1),
6926 "inconsistent Printezis mark");
6927 }
6928 #endif // ASSERT
6929 } else {
6930 // an unitialized object
6931 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6932 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6933 size = pointer_delta(nextOneAddr + 1, addr);
6934 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6935 "alignment problem");
6936 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6937 // will dirty the card when the klass pointer is installed in the
6938 // object (signalling the completion of initialization).
6939 }
6940 } else {
6941 // Either a not yet marked object or an uninitialized object
6942 if (p->klass_or_null() == NULL) {
6943 // An uninitialized object, skip to the next card, since
6944 // we may not be able to read its P-bits yet.
6945 assert(size == 0, "Initial value");
6946 } else {
6947 // An object not (yet) reached by marking: we merely need to
6948 // compute its size so as to go look at the next block.
6949 assert(p->is_oop(true), "should be an oop");
6950 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6951 }
6952 }
6953 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6954 return size;
6955 }
6956
6957 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6958 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6959 "CMS thread should hold CMS token");
6960 assert_lock_strong(_freelistLock);
6961 assert_lock_strong(_bitMap->lock());
6962 // relinquish the free_list_lock and bitMaplock()
6963 _bitMap->lock()->unlock();
6964 _freelistLock->unlock();
6965 ConcurrentMarkSweepThread::desynchronize(true);
6966 ConcurrentMarkSweepThread::acknowledge_yield_request();
6967 _collector->stopTimer();
6968 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6969 if (PrintCMSStatistics != 0) {
6970 _collector->incrementYields();
6971 }
6972 _collector->icms_wait();
6973
6974 // See the comment in coordinator_yield()
6975 for (unsigned i = 0; i < CMSYieldSleepCount &&
6976 ConcurrentMarkSweepThread::should_yield() &&
6977 !CMSCollector::foregroundGCIsActive(); ++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 _bitMap->lock()->lock_without_safepoint_check();
6985 _collector->startTimer();
6986 }
6987
6988
6989 //////////////////////////////////////////////////////////////////
6990 // SurvivorSpacePrecleanClosure
6991 //////////////////////////////////////////////////////////////////
6992 // This (single-threaded) closure is used to preclean the oops in
6993 // the survivor spaces.
6994 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6995
6996 HeapWord* addr = (HeapWord*)p;
6997 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6998 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6999 assert(p->klass_or_null() != NULL, "object should be initializd");
7000 // an initialized object; ignore mark word in verification below
7001 // since we are running concurrent with mutators
7002 assert(p->is_oop(true), "should be an oop");
7003 // Note that we do not yield while we iterate over
7004 // the interior oops of p, pushing the relevant ones
7005 // on our marking stack.
7006 size_t size = p->oop_iterate(_scanning_closure);
7007 do_yield_check();
7008 // Observe that below, we do not abandon the preclean
7009 // phase as soon as we should; rather we empty the
7010 // marking stack before returning. This is to satisfy
7011 // some existing assertions. In general, it may be a
7012 // good idea to abort immediately and complete the marking
7013 // from the grey objects at a later time.
7014 while (!_mark_stack->isEmpty()) {
7015 oop new_oop = _mark_stack->pop();
7016 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7017 assert(_bit_map->isMarked((HeapWord*)new_oop),
7018 "only grey objects on this stack");
7019 // iterate over the oops in this oop, marking and pushing
7020 // the ones in CMS heap (i.e. in _span).
7021 new_oop->oop_iterate(_scanning_closure);
7022 // check if it's time to yield
7023 do_yield_check();
7024 }
7025 unsigned int after_count =
7026 GenCollectedHeap::heap()->total_collections();
7027 bool abort = (_before_count != after_count) ||
7028 _collector->should_abort_preclean();
7029 return abort ? 0 : size;
7030 }
7031
7032 void SurvivorSpacePrecleanClosure::do_yield_work() {
7033 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7034 "CMS thread should hold CMS token");
7035 assert_lock_strong(_bit_map->lock());
7036 // Relinquish the bit map lock
7037 _bit_map->lock()->unlock();
7038 ConcurrentMarkSweepThread::desynchronize(true);
7039 ConcurrentMarkSweepThread::acknowledge_yield_request();
7040 _collector->stopTimer();
7041 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7042 if (PrintCMSStatistics != 0) {
7043 _collector->incrementYields();
7044 }
7045 _collector->icms_wait();
7046
7047 // See the comment in coordinator_yield()
7048 for (unsigned i = 0; i < CMSYieldSleepCount &&
7049 ConcurrentMarkSweepThread::should_yield() &&
7050 !CMSCollector::foregroundGCIsActive(); ++i) {
7051 os::sleep(Thread::current(), 1, false);
7052 ConcurrentMarkSweepThread::acknowledge_yield_request();
7053 }
7054
7055 ConcurrentMarkSweepThread::synchronize(true);
7056 _bit_map->lock()->lock_without_safepoint_check();
7057 _collector->startTimer();
7058 }
7059
7060 // This closure is used to rescan the marked objects on the dirty cards
7061 // in the mod union table and the card table proper. In the parallel
7062 // case, although the bitMap is shared, we do a single read so the
7063 // isMarked() query is "safe".
7064 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7065 // Ignore mark word because we are running concurrent with mutators
7066 assert(p->is_oop_or_null(true), "expected an oop or null");
7067 HeapWord* addr = (HeapWord*)p;
7068 assert(_span.contains(addr), "we are scanning the CMS generation");
7069 bool is_obj_array = false;
7070 #ifdef ASSERT
7071 if (!_parallel) {
7072 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7073 assert(_collector->overflow_list_is_empty(),
7074 "overflow list should be empty");
7075
7076 }
7077 #endif // ASSERT
7078 if (_bit_map->isMarked(addr)) {
7079 // Obj arrays are precisely marked, non-arrays are not;
7080 // so we scan objArrays precisely and non-arrays in their
7081 // entirety.
7082 if (p->is_objArray()) {
7083 is_obj_array = true;
7084 if (_parallel) {
7085 p->oop_iterate(_par_scan_closure, mr);
7086 } else {
7087 p->oop_iterate(_scan_closure, mr);
7088 }
7089 } else {
7090 if (_parallel) {
7091 p->oop_iterate(_par_scan_closure);
7092 } else {
7093 p->oop_iterate(_scan_closure);
7094 }
7095 }
7096 }
7097 #ifdef ASSERT
7098 if (!_parallel) {
7099 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7100 assert(_collector->overflow_list_is_empty(),
7101 "overflow list should be empty");
7102
7103 }
7104 #endif // ASSERT
7105 return is_obj_array;
7106 }
7107
7108 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7109 MemRegion span,
7110 CMSBitMap* bitMap, CMSMarkStack* markStack,
7111 bool should_yield, bool verifying):
7112 _collector(collector),
7113 _span(span),
7114 _bitMap(bitMap),
7115 _mut(&collector->_modUnionTable),
7116 _markStack(markStack),
7117 _yield(should_yield),
7118 _skipBits(0)
7119 {
7120 assert(_markStack->isEmpty(), "stack should be empty");
7121 _finger = _bitMap->startWord();
7122 _threshold = _finger;
7123 assert(_collector->_restart_addr == NULL, "Sanity check");
7124 assert(_span.contains(_finger), "Out of bounds _finger?");
7125 DEBUG_ONLY(_verifying = verifying;)
7126 }
7127
7128 void MarkFromRootsClosure::reset(HeapWord* addr) {
7129 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7130 assert(_span.contains(addr), "Out of bounds _finger?");
7131 _finger = addr;
7132 _threshold = (HeapWord*)round_to(
7133 (intptr_t)_finger, CardTableModRefBS::card_size);
7134 }
7135
7136 // Should revisit to see if this should be restructured for
7137 // greater efficiency.
7138 bool MarkFromRootsClosure::do_bit(size_t offset) {
7139 if (_skipBits > 0) {
7140 _skipBits--;
7141 return true;
7142 }
7143 // convert offset into a HeapWord*
7144 HeapWord* addr = _bitMap->startWord() + offset;
7145 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7146 "address out of range");
7147 assert(_bitMap->isMarked(addr), "tautology");
7148 if (_bitMap->isMarked(addr+1)) {
7149 // this is an allocated but not yet initialized object
7150 assert(_skipBits == 0, "tautology");
7151 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7152 oop p = oop(addr);
7153 if (p->klass_or_null() == NULL) {
7154 DEBUG_ONLY(if (!_verifying) {)
7155 // We re-dirty the cards on which this object lies and increase
7156 // the _threshold so that we'll come back to scan this object
7157 // during the preclean or remark phase. (CMSCleanOnEnter)
7158 if (CMSCleanOnEnter) {
7159 size_t sz = _collector->block_size_using_printezis_bits(addr);
7160 HeapWord* end_card_addr = (HeapWord*)round_to(
7161 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7162 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7163 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7164 // Bump _threshold to end_card_addr; note that
7165 // _threshold cannot possibly exceed end_card_addr, anyhow.
7166 // This prevents future clearing of the card as the scan proceeds
7167 // to the right.
7168 assert(_threshold <= end_card_addr,
7169 "Because we are just scanning into this object");
7170 if (_threshold < end_card_addr) {
7171 _threshold = end_card_addr;
7172 }
7173 if (p->klass_or_null() != NULL) {
7174 // Redirty the range of cards...
7175 _mut->mark_range(redirty_range);
7176 } // ...else the setting of klass will dirty the card anyway.
7177 }
7178 DEBUG_ONLY(})
7179 return true;
7180 }
7181 }
7182 scanOopsInOop(addr);
7183 return true;
7184 }
7185
7186 // We take a break if we've been at this for a while,
7187 // so as to avoid monopolizing the locks involved.
7188 void MarkFromRootsClosure::do_yield_work() {
7189 // First give up the locks, then yield, then re-lock
7190 // We should probably use a constructor/destructor idiom to
7191 // do this unlock/lock or modify the MutexUnlocker class to
7192 // serve our purpose. XXX
7193 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7194 "CMS thread should hold CMS token");
7195 assert_lock_strong(_bitMap->lock());
7196 _bitMap->lock()->unlock();
7197 ConcurrentMarkSweepThread::desynchronize(true);
7198 ConcurrentMarkSweepThread::acknowledge_yield_request();
7199 _collector->stopTimer();
7200 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7201 if (PrintCMSStatistics != 0) {
7202 _collector->incrementYields();
7203 }
7204 _collector->icms_wait();
7205
7206 // See the comment in coordinator_yield()
7207 for (unsigned i = 0; i < CMSYieldSleepCount &&
7208 ConcurrentMarkSweepThread::should_yield() &&
7209 !CMSCollector::foregroundGCIsActive(); ++i) {
7210 os::sleep(Thread::current(), 1, false);
7211 ConcurrentMarkSweepThread::acknowledge_yield_request();
7212 }
7213
7214 ConcurrentMarkSweepThread::synchronize(true);
7215 _bitMap->lock()->lock_without_safepoint_check();
7216 _collector->startTimer();
7217 }
7218
7219 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7220 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7221 assert(_markStack->isEmpty(),
7222 "should drain stack to limit stack usage");
7223 // convert ptr to an oop preparatory to scanning
7224 oop obj = oop(ptr);
7225 // Ignore mark word in verification below, since we
7226 // may be running concurrent with mutators.
7227 assert(obj->is_oop(true), "should be an oop");
7228 assert(_finger <= ptr, "_finger runneth ahead");
7229 // advance the finger to right end of this object
7230 _finger = ptr + obj->size();
7231 assert(_finger > ptr, "we just incremented it above");
7232 // On large heaps, it may take us some time to get through
7233 // the marking phase (especially if running iCMS). During
7234 // this time it's possible that a lot of mutations have
7235 // accumulated in the card table and the mod union table --
7236 // these mutation records are redundant until we have
7237 // actually traced into the corresponding card.
7238 // Here, we check whether advancing the finger would make
7239 // us cross into a new card, and if so clear corresponding
7240 // cards in the MUT (preclean them in the card-table in the
7241 // future).
7242
7243 DEBUG_ONLY(if (!_verifying) {)
7244 // The clean-on-enter optimization is disabled by default,
7245 // until we fix 6178663.
7246 if (CMSCleanOnEnter && (_finger > _threshold)) {
7247 // [_threshold, _finger) represents the interval
7248 // of cards to be cleared in MUT (or precleaned in card table).
7249 // The set of cards to be cleared is all those that overlap
7250 // with the interval [_threshold, _finger); note that
7251 // _threshold is always kept card-aligned but _finger isn't
7252 // always card-aligned.
7253 HeapWord* old_threshold = _threshold;
7254 assert(old_threshold == (HeapWord*)round_to(
7255 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7256 "_threshold should always be card-aligned");
7257 _threshold = (HeapWord*)round_to(
7258 (intptr_t)_finger, CardTableModRefBS::card_size);
7259 MemRegion mr(old_threshold, _threshold);
7260 assert(!mr.is_empty(), "Control point invariant");
7261 assert(_span.contains(mr), "Should clear within span");
7262 _mut->clear_range(mr);
7263 }
7264 DEBUG_ONLY(})
7265 // Note: the finger doesn't advance while we drain
7266 // the stack below.
7267 PushOrMarkClosure pushOrMarkClosure(_collector,
7268 _span, _bitMap, _markStack,
7269 _finger, this);
7270 bool res = _markStack->push(obj);
7271 assert(res, "Empty non-zero size stack should have space for single push");
7272 while (!_markStack->isEmpty()) {
7273 oop new_oop = _markStack->pop();
7274 // Skip verifying header mark word below because we are
7275 // running concurrent with mutators.
7276 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7277 // now scan this oop's oops
7278 new_oop->oop_iterate(&pushOrMarkClosure);
7279 do_yield_check();
7280 }
7281 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7282 }
7283
7284 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7285 CMSCollector* collector, MemRegion span,
7286 CMSBitMap* bit_map,
7287 OopTaskQueue* work_queue,
7288 CMSMarkStack* overflow_stack,
7289 bool should_yield):
7290 _collector(collector),
7291 _whole_span(collector->_span),
7292 _span(span),
7293 _bit_map(bit_map),
7294 _mut(&collector->_modUnionTable),
7295 _work_queue(work_queue),
7296 _overflow_stack(overflow_stack),
7297 _yield(should_yield),
7298 _skip_bits(0),
7299 _task(task)
7300 {
7301 assert(_work_queue->size() == 0, "work_queue should be empty");
7302 _finger = span.start();
7303 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7304 assert(_span.contains(_finger), "Out of bounds _finger?");
7305 }
7306
7307 // Should revisit to see if this should be restructured for
7308 // greater efficiency.
7309 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7310 if (_skip_bits > 0) {
7311 _skip_bits--;
7312 return true;
7313 }
7314 // convert offset into a HeapWord*
7315 HeapWord* addr = _bit_map->startWord() + offset;
7316 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7317 "address out of range");
7318 assert(_bit_map->isMarked(addr), "tautology");
7319 if (_bit_map->isMarked(addr+1)) {
7320 // this is an allocated object that might not yet be initialized
7321 assert(_skip_bits == 0, "tautology");
7322 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7323 oop p = oop(addr);
7324 if (p->klass_or_null() == NULL) {
7325 // in the case of Clean-on-Enter optimization, redirty card
7326 // and avoid clearing card by increasing the threshold.
7327 return true;
7328 }
7329 }
7330 scan_oops_in_oop(addr);
7331 return true;
7332 }
7333
7334 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7335 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7336 // Should we assert that our work queue is empty or
7337 // below some drain limit?
7338 assert(_work_queue->size() == 0,
7339 "should drain stack to limit stack usage");
7340 // convert ptr to an oop preparatory to scanning
7341 oop obj = oop(ptr);
7342 // Ignore mark word in verification below, since we
7343 // may be running concurrent with mutators.
7344 assert(obj->is_oop(true), "should be an oop");
7345 assert(_finger <= ptr, "_finger runneth ahead");
7346 // advance the finger to right end of this object
7347 _finger = ptr + obj->size();
7348 assert(_finger > ptr, "we just incremented it above");
7349 // On large heaps, it may take us some time to get through
7350 // the marking phase (especially if running iCMS). During
7351 // this time it's possible that a lot of mutations have
7352 // accumulated in the card table and the mod union table --
7353 // these mutation records are redundant until we have
7354 // actually traced into the corresponding card.
7355 // Here, we check whether advancing the finger would make
7356 // us cross into a new card, and if so clear corresponding
7357 // cards in the MUT (preclean them in the card-table in the
7358 // future).
7359
7360 // The clean-on-enter optimization is disabled by default,
7361 // until we fix 6178663.
7362 if (CMSCleanOnEnter && (_finger > _threshold)) {
7363 // [_threshold, _finger) represents the interval
7364 // of cards to be cleared in MUT (or precleaned in card table).
7365 // The set of cards to be cleared is all those that overlap
7366 // with the interval [_threshold, _finger); note that
7367 // _threshold is always kept card-aligned but _finger isn't
7368 // always card-aligned.
7369 HeapWord* old_threshold = _threshold;
7370 assert(old_threshold == (HeapWord*)round_to(
7371 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7372 "_threshold should always be card-aligned");
7373 _threshold = (HeapWord*)round_to(
7374 (intptr_t)_finger, CardTableModRefBS::card_size);
7375 MemRegion mr(old_threshold, _threshold);
7376 assert(!mr.is_empty(), "Control point invariant");
7377 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7378 _mut->clear_range(mr);
7379 }
7380
7381 // Note: the local finger doesn't advance while we drain
7382 // the stack below, but the global finger sure can and will.
7383 HeapWord** gfa = _task->global_finger_addr();
7384 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7385 _span, _bit_map,
7386 _work_queue,
7387 _overflow_stack,
7388 _finger,
7389 gfa, this);
7390 bool res = _work_queue->push(obj); // overflow could occur here
7391 assert(res, "Will hold once we use workqueues");
7392 while (true) {
7393 oop new_oop;
7394 if (!_work_queue->pop_local(new_oop)) {
7395 // We emptied our work_queue; check if there's stuff that can
7396 // be gotten from the overflow stack.
7397 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7398 _overflow_stack, _work_queue)) {
7399 do_yield_check();
7400 continue;
7401 } else { // done
7402 break;
7403 }
7404 }
7405 // Skip verifying header mark word below because we are
7406 // running concurrent with mutators.
7407 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7408 // now scan this oop's oops
7409 new_oop->oop_iterate(&pushOrMarkClosure);
7410 do_yield_check();
7411 }
7412 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7413 }
7414
7415 // Yield in response to a request from VM Thread or
7416 // from mutators.
7417 void Par_MarkFromRootsClosure::do_yield_work() {
7418 assert(_task != NULL, "sanity");
7419 _task->yield();
7420 }
7421
7422 // A variant of the above used for verifying CMS marking work.
7423 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7424 MemRegion span,
7425 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7426 CMSMarkStack* mark_stack):
7427 _collector(collector),
7428 _span(span),
7429 _verification_bm(verification_bm),
7430 _cms_bm(cms_bm),
7431 _mark_stack(mark_stack),
7432 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7433 mark_stack)
7434 {
7435 assert(_mark_stack->isEmpty(), "stack should be empty");
7436 _finger = _verification_bm->startWord();
7437 assert(_collector->_restart_addr == NULL, "Sanity check");
7438 assert(_span.contains(_finger), "Out of bounds _finger?");
7439 }
7440
7441 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7442 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7443 assert(_span.contains(addr), "Out of bounds _finger?");
7444 _finger = addr;
7445 }
7446
7447 // Should revisit to see if this should be restructured for
7448 // greater efficiency.
7449 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7450 // convert offset into a HeapWord*
7451 HeapWord* addr = _verification_bm->startWord() + offset;
7452 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7453 "address out of range");
7454 assert(_verification_bm->isMarked(addr), "tautology");
7455 assert(_cms_bm->isMarked(addr), "tautology");
7456
7457 assert(_mark_stack->isEmpty(),
7458 "should drain stack to limit stack usage");
7459 // convert addr to an oop preparatory to scanning
7460 oop obj = oop(addr);
7461 assert(obj->is_oop(), "should be an oop");
7462 assert(_finger <= addr, "_finger runneth ahead");
7463 // advance the finger to right end of this object
7464 _finger = addr + obj->size();
7465 assert(_finger > addr, "we just incremented it above");
7466 // Note: the finger doesn't advance while we drain
7467 // the stack below.
7468 bool res = _mark_stack->push(obj);
7469 assert(res, "Empty non-zero size stack should have space for single push");
7470 while (!_mark_stack->isEmpty()) {
7471 oop new_oop = _mark_stack->pop();
7472 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7473 // now scan this oop's oops
7474 new_oop->oop_iterate(&_pam_verify_closure);
7475 }
7476 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7477 return true;
7478 }
7479
7480 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7481 CMSCollector* collector, MemRegion span,
7482 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7483 CMSMarkStack* mark_stack):
7484 CMSOopClosure(collector->ref_processor()),
7485 _collector(collector),
7486 _span(span),
7487 _verification_bm(verification_bm),
7488 _cms_bm(cms_bm),
7489 _mark_stack(mark_stack)
7490 { }
7491
7492 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7493 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7494
7495 // Upon stack overflow, we discard (part of) the stack,
7496 // remembering the least address amongst those discarded
7497 // in CMSCollector's _restart_address.
7498 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7499 // Remember the least grey address discarded
7500 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7501 _collector->lower_restart_addr(ra);
7502 _mark_stack->reset(); // discard stack contents
7503 _mark_stack->expand(); // expand the stack if possible
7504 }
7505
7506 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7507 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7508 HeapWord* addr = (HeapWord*)obj;
7509 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7510 // Oop lies in _span and isn't yet grey or black
7511 _verification_bm->mark(addr); // now grey
7512 if (!_cms_bm->isMarked(addr)) {
7513 oop(addr)->print();
7514 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7515 addr);
7516 fatal("... aborting");
7517 }
7518
7519 if (!_mark_stack->push(obj)) { // stack overflow
7520 if (PrintCMSStatistics != 0) {
7521 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7522 SIZE_FORMAT, _mark_stack->capacity());
7523 }
7524 assert(_mark_stack->isFull(), "Else push should have succeeded");
7525 handle_stack_overflow(addr);
7526 }
7527 // anything including and to the right of _finger
7528 // will be scanned as we iterate over the remainder of the
7529 // bit map
7530 }
7531 }
7532
7533 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7534 MemRegion span,
7535 CMSBitMap* bitMap, CMSMarkStack* markStack,
7536 HeapWord* finger, MarkFromRootsClosure* parent) :
7537 CMSOopClosure(collector->ref_processor()),
7538 _collector(collector),
7539 _span(span),
7540 _bitMap(bitMap),
7541 _markStack(markStack),
7542 _finger(finger),
7543 _parent(parent)
7544 { }
7545
7546 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7547 MemRegion span,
7548 CMSBitMap* bit_map,
7549 OopTaskQueue* work_queue,
7550 CMSMarkStack* overflow_stack,
7551 HeapWord* finger,
7552 HeapWord** global_finger_addr,
7553 Par_MarkFromRootsClosure* parent) :
7554 CMSOopClosure(collector->ref_processor()),
7555 _collector(collector),
7556 _whole_span(collector->_span),
7557 _span(span),
7558 _bit_map(bit_map),
7559 _work_queue(work_queue),
7560 _overflow_stack(overflow_stack),
7561 _finger(finger),
7562 _global_finger_addr(global_finger_addr),
7563 _parent(parent)
7564 { }
7565
7566 // Assumes thread-safe access by callers, who are
7567 // responsible for mutual exclusion.
7568 void CMSCollector::lower_restart_addr(HeapWord* low) {
7569 assert(_span.contains(low), "Out of bounds addr");
7570 if (_restart_addr == NULL) {
7571 _restart_addr = low;
7572 } else {
7573 _restart_addr = MIN2(_restart_addr, low);
7574 }
7575 }
7576
7577 // Upon stack overflow, we discard (part of) the stack,
7578 // remembering the least address amongst those discarded
7579 // in CMSCollector's _restart_address.
7580 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7581 // Remember the least grey address discarded
7582 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7583 _collector->lower_restart_addr(ra);
7584 _markStack->reset(); // discard stack contents
7585 _markStack->expand(); // expand the stack if possible
7586 }
7587
7588 // Upon stack overflow, we discard (part of) the stack,
7589 // remembering the least address amongst those discarded
7590 // in CMSCollector's _restart_address.
7591 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7592 // We need to do this under a mutex to prevent other
7593 // workers from interfering with the work done below.
7594 MutexLockerEx ml(_overflow_stack->par_lock(),
7595 Mutex::_no_safepoint_check_flag);
7596 // Remember the least grey address discarded
7597 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7598 _collector->lower_restart_addr(ra);
7599 _overflow_stack->reset(); // discard stack contents
7600 _overflow_stack->expand(); // expand the stack if possible
7601 }
7602
7603 void CMKlassClosure::do_klass(Klass* k) {
7604 assert(_oop_closure != NULL, "Not initialized?");
7605 k->oops_do(_oop_closure);
7606 }
7607
7608 void PushOrMarkClosure::do_oop(oop obj) {
7609 // Ignore mark word because we are running concurrent with mutators.
7610 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7611 HeapWord* addr = (HeapWord*)obj;
7612 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7613 // Oop lies in _span and isn't yet grey or black
7614 _bitMap->mark(addr); // now grey
7615 if (addr < _finger) {
7616 // the bit map iteration has already either passed, or
7617 // sampled, this bit in the bit map; we'll need to
7618 // use the marking stack to scan this oop's oops.
7619 bool simulate_overflow = false;
7620 NOT_PRODUCT(
7621 if (CMSMarkStackOverflowALot &&
7622 _collector->simulate_overflow()) {
7623 // simulate a stack overflow
7624 simulate_overflow = true;
7625 }
7626 )
7627 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7628 if (PrintCMSStatistics != 0) {
7629 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7630 SIZE_FORMAT, _markStack->capacity());
7631 }
7632 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7633 handle_stack_overflow(addr);
7634 }
7635 }
7636 // anything including and to the right of _finger
7637 // will be scanned as we iterate over the remainder of the
7638 // bit map
7639 do_yield_check();
7640 }
7641 }
7642
7643 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7644 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7645
7646 void Par_PushOrMarkClosure::do_oop(oop obj) {
7647 // Ignore mark word because we are running concurrent with mutators.
7648 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7649 HeapWord* addr = (HeapWord*)obj;
7650 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7651 // Oop lies in _span and isn't yet grey or black
7652 // We read the global_finger (volatile read) strictly after marking oop
7653 bool res = _bit_map->par_mark(addr); // now grey
7654 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7655 // Should we push this marked oop on our stack?
7656 // -- if someone else marked it, nothing to do
7657 // -- if target oop is above global finger nothing to do
7658 // -- if target oop is in chunk and above local finger
7659 // then nothing to do
7660 // -- else push on work queue
7661 if ( !res // someone else marked it, they will deal with it
7662 || (addr >= *gfa) // will be scanned in a later task
7663 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7664 return;
7665 }
7666 // the bit map iteration has already either passed, or
7667 // sampled, this bit in the bit map; we'll need to
7668 // use the marking stack to scan this oop's oops.
7669 bool simulate_overflow = false;
7670 NOT_PRODUCT(
7671 if (CMSMarkStackOverflowALot &&
7672 _collector->simulate_overflow()) {
7673 // simulate a stack overflow
7674 simulate_overflow = true;
7675 }
7676 )
7677 if (simulate_overflow ||
7678 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7679 // stack overflow
7680 if (PrintCMSStatistics != 0) {
7681 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7682 SIZE_FORMAT, _overflow_stack->capacity());
7683 }
7684 // We cannot assert that the overflow stack is full because
7685 // it may have been emptied since.
7686 assert(simulate_overflow ||
7687 _work_queue->size() == _work_queue->max_elems(),
7688 "Else push should have succeeded");
7689 handle_stack_overflow(addr);
7690 }
7691 do_yield_check();
7692 }
7693 }
7694
7695 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7696 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7697
7698 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7699 MemRegion span,
7700 ReferenceProcessor* rp,
7701 CMSBitMap* bit_map,
7702 CMSBitMap* mod_union_table,
7703 CMSMarkStack* mark_stack,
7704 bool concurrent_precleaning):
7705 CMSOopClosure(rp),
7706 _collector(collector),
7707 _span(span),
7708 _bit_map(bit_map),
7709 _mod_union_table(mod_union_table),
7710 _mark_stack(mark_stack),
7711 _concurrent_precleaning(concurrent_precleaning)
7712 {
7713 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7714 }
7715
7716 // Grey object rescan during pre-cleaning and second checkpoint phases --
7717 // the non-parallel version (the parallel version appears further below.)
7718 void PushAndMarkClosure::do_oop(oop obj) {
7719 // Ignore mark word verification. If during concurrent precleaning,
7720 // the object monitor may be locked. If during the checkpoint
7721 // phases, the object may already have been reached by a different
7722 // path and may be at the end of the global overflow list (so
7723 // the mark word may be NULL).
7724 assert(obj->is_oop_or_null(true /* ignore mark word */),
7725 "expected an oop or NULL");
7726 HeapWord* addr = (HeapWord*)obj;
7727 // Check if oop points into the CMS generation
7728 // and is not marked
7729 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7730 // a white object ...
7731 _bit_map->mark(addr); // ... now grey
7732 // push on the marking stack (grey set)
7733 bool simulate_overflow = false;
7734 NOT_PRODUCT(
7735 if (CMSMarkStackOverflowALot &&
7736 _collector->simulate_overflow()) {
7737 // simulate a stack overflow
7738 simulate_overflow = true;
7739 }
7740 )
7741 if (simulate_overflow || !_mark_stack->push(obj)) {
7742 if (_concurrent_precleaning) {
7743 // During precleaning we can just dirty the appropriate card(s)
7744 // in the mod union table, thus ensuring that the object remains
7745 // in the grey set and continue. In the case of object arrays
7746 // we need to dirty all of the cards that the object spans,
7747 // since the rescan of object arrays will be limited to the
7748 // dirty cards.
7749 // Note that no one can be intefering with us in this action
7750 // of dirtying the mod union table, so no locking or atomics
7751 // are required.
7752 if (obj->is_objArray()) {
7753 size_t sz = obj->size();
7754 HeapWord* end_card_addr = (HeapWord*)round_to(
7755 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7756 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7757 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7758 _mod_union_table->mark_range(redirty_range);
7759 } else {
7760 _mod_union_table->mark(addr);
7761 }
7762 _collector->_ser_pmc_preclean_ovflw++;
7763 } else {
7764 // During the remark phase, we need to remember this oop
7765 // in the overflow list.
7766 _collector->push_on_overflow_list(obj);
7767 _collector->_ser_pmc_remark_ovflw++;
7768 }
7769 }
7770 }
7771 }
7772
7773 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7774 MemRegion span,
7775 ReferenceProcessor* rp,
7776 CMSBitMap* bit_map,
7777 OopTaskQueue* work_queue):
7778 CMSOopClosure(rp),
7779 _collector(collector),
7780 _span(span),
7781 _bit_map(bit_map),
7782 _work_queue(work_queue)
7783 {
7784 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7785 }
7786
7787 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7788 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7789
7790 // Grey object rescan during second checkpoint phase --
7791 // the parallel version.
7792 void Par_PushAndMarkClosure::do_oop(oop obj) {
7793 // In the assert below, we ignore the mark word because
7794 // this oop may point to an already visited object that is
7795 // on the overflow stack (in which case the mark word has
7796 // been hijacked for chaining into the overflow stack --
7797 // if this is the last object in the overflow stack then
7798 // its mark word will be NULL). Because this object may
7799 // have been subsequently popped off the global overflow
7800 // stack, and the mark word possibly restored to the prototypical
7801 // value, by the time we get to examined this failing assert in
7802 // the debugger, is_oop_or_null(false) may subsequently start
7803 // to hold.
7804 assert(obj->is_oop_or_null(true),
7805 "expected an oop or NULL");
7806 HeapWord* addr = (HeapWord*)obj;
7807 // Check if oop points into the CMS generation
7808 // and is not marked
7809 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7810 // a white object ...
7811 // If we manage to "claim" the object, by being the
7812 // first thread to mark it, then we push it on our
7813 // marking stack
7814 if (_bit_map->par_mark(addr)) { // ... now grey
7815 // push on work queue (grey set)
7816 bool simulate_overflow = false;
7817 NOT_PRODUCT(
7818 if (CMSMarkStackOverflowALot &&
7819 _collector->par_simulate_overflow()) {
7820 // simulate a stack overflow
7821 simulate_overflow = true;
7822 }
7823 )
7824 if (simulate_overflow || !_work_queue->push(obj)) {
7825 _collector->par_push_on_overflow_list(obj);
7826 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7827 }
7828 } // Else, some other thread got there first
7829 }
7830 }
7831
7832 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7833 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7834
7835 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7836 Mutex* bml = _collector->bitMapLock();
7837 assert_lock_strong(bml);
7838 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7839 "CMS thread should hold CMS token");
7840
7841 bml->unlock();
7842 ConcurrentMarkSweepThread::desynchronize(true);
7843
7844 ConcurrentMarkSweepThread::acknowledge_yield_request();
7845
7846 _collector->stopTimer();
7847 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7848 if (PrintCMSStatistics != 0) {
7849 _collector->incrementYields();
7850 }
7851 _collector->icms_wait();
7852
7853 // See the comment in coordinator_yield()
7854 for (unsigned i = 0; i < CMSYieldSleepCount &&
7855 ConcurrentMarkSweepThread::should_yield() &&
7856 !CMSCollector::foregroundGCIsActive(); ++i) {
7857 os::sleep(Thread::current(), 1, false);
7858 ConcurrentMarkSweepThread::acknowledge_yield_request();
7859 }
7860
7861 ConcurrentMarkSweepThread::synchronize(true);
7862 bml->lock();
7863
7864 _collector->startTimer();
7865 }
7866
7867 bool CMSPrecleanRefsYieldClosure::should_return() {
7868 if (ConcurrentMarkSweepThread::should_yield()) {
7869 do_yield_work();
7870 }
7871 return _collector->foregroundGCIsActive();
7872 }
7873
7874 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7875 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7876 "mr should be aligned to start at a card boundary");
7877 // We'd like to assert:
7878 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7879 // "mr should be a range of cards");
7880 // However, that would be too strong in one case -- the last
7881 // partition ends at _unallocated_block which, in general, can be
7882 // an arbitrary boundary, not necessarily card aligned.
7883 if (PrintCMSStatistics != 0) {
7884 _num_dirty_cards +=
7885 mr.word_size()/CardTableModRefBS::card_size_in_words;
7886 }
7887 _space->object_iterate_mem(mr, &_scan_cl);
7888 }
7889
7890 SweepClosure::SweepClosure(CMSCollector* collector,
7891 ConcurrentMarkSweepGeneration* g,
7892 CMSBitMap* bitMap, bool should_yield) :
7893 _collector(collector),
7894 _g(g),
7895 _sp(g->cmsSpace()),
7896 _limit(_sp->sweep_limit()),
7897 _freelistLock(_sp->freelistLock()),
7898 _bitMap(bitMap),
7899 _yield(should_yield),
7900 _inFreeRange(false), // No free range at beginning of sweep
7901 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7902 _lastFreeRangeCoalesced(false),
7903 _freeFinger(g->used_region().start())
7904 {
7905 NOT_PRODUCT(
7906 _numObjectsFreed = 0;
7907 _numWordsFreed = 0;
7908 _numObjectsLive = 0;
7909 _numWordsLive = 0;
7910 _numObjectsAlreadyFree = 0;
7911 _numWordsAlreadyFree = 0;
7912 _last_fc = NULL;
7913
7914 _sp->initializeIndexedFreeListArrayReturnedBytes();
7915 _sp->dictionary()->initialize_dict_returned_bytes();
7916 )
7917 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7918 "sweep _limit out of bounds");
7919 if (CMSTraceSweeper) {
7920 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7921 _limit);
7922 }
7923 }
7924
7925 void SweepClosure::print_on(outputStream* st) const {
7926 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7927 _sp->bottom(), _sp->end());
7928 tty->print_cr("_limit = " PTR_FORMAT, _limit);
7929 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
7930 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
7931 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7932 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7933 }
7934
7935 #ifndef PRODUCT
7936 // Assertion checking only: no useful work in product mode --
7937 // however, if any of the flags below become product flags,
7938 // you may need to review this code to see if it needs to be
7939 // enabled in product mode.
7940 SweepClosure::~SweepClosure() {
7941 assert_lock_strong(_freelistLock);
7942 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7943 "sweep _limit out of bounds");
7944 if (inFreeRange()) {
7945 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7946 print();
7947 ShouldNotReachHere();
7948 }
7949 if (Verbose && PrintGC) {
7950 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7951 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7952 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7953 SIZE_FORMAT" bytes "
7954 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7955 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7956 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7957 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7958 * sizeof(HeapWord);
7959 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7960
7961 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7962 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7963 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7964 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7965 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7966 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7967 indexListReturnedBytes);
7968 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7969 dict_returned_bytes);
7970 }
7971 }
7972 if (CMSTraceSweeper) {
7973 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7974 _limit);
7975 }
7976 }
7977 #endif // PRODUCT
7978
7979 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7980 bool freeRangeInFreeLists) {
7981 if (CMSTraceSweeper) {
7982 gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n",
7983 freeFinger, freeRangeInFreeLists);
7984 }
7985 assert(!inFreeRange(), "Trampling existing free range");
7986 set_inFreeRange(true);
7987 set_lastFreeRangeCoalesced(false);
7988
7989 set_freeFinger(freeFinger);
7990 set_freeRangeInFreeLists(freeRangeInFreeLists);
7991 if (CMSTestInFreeList) {
7992 if (freeRangeInFreeLists) {
7993 FreeChunk* fc = (FreeChunk*) freeFinger;
7994 assert(fc->is_free(), "A chunk on the free list should be free.");
7995 assert(fc->size() > 0, "Free range should have a size");
7996 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7997 }
7998 }
7999 }
8000
8001 // Note that the sweeper runs concurrently with mutators. Thus,
8002 // it is possible for direct allocation in this generation to happen
8003 // in the middle of the sweep. Note that the sweeper also coalesces
8004 // contiguous free blocks. Thus, unless the sweeper and the allocator
8005 // synchronize appropriately freshly allocated blocks may get swept up.
8006 // This is accomplished by the sweeper locking the free lists while
8007 // it is sweeping. Thus blocks that are determined to be free are
8008 // indeed free. There is however one additional complication:
8009 // blocks that have been allocated since the final checkpoint and
8010 // mark, will not have been marked and so would be treated as
8011 // unreachable and swept up. To prevent this, the allocator marks
8012 // the bit map when allocating during the sweep phase. This leads,
8013 // however, to a further complication -- objects may have been allocated
8014 // but not yet initialized -- in the sense that the header isn't yet
8015 // installed. The sweeper can not then determine the size of the block
8016 // in order to skip over it. To deal with this case, we use a technique
8017 // (due to Printezis) to encode such uninitialized block sizes in the
8018 // bit map. Since the bit map uses a bit per every HeapWord, but the
8019 // CMS generation has a minimum object size of 3 HeapWords, it follows
8020 // that "normal marks" won't be adjacent in the bit map (there will
8021 // always be at least two 0 bits between successive 1 bits). We make use
8022 // of these "unused" bits to represent uninitialized blocks -- the bit
8023 // corresponding to the start of the uninitialized object and the next
8024 // bit are both set. Finally, a 1 bit marks the end of the object that
8025 // started with the two consecutive 1 bits to indicate its potentially
8026 // uninitialized state.
8027
8028 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8029 FreeChunk* fc = (FreeChunk*)addr;
8030 size_t res;
8031
8032 // Check if we are done sweeping. Below we check "addr >= _limit" rather
8033 // than "addr == _limit" because although _limit was a block boundary when
8034 // we started the sweep, it may no longer be one because heap expansion
8035 // may have caused us to coalesce the block ending at the address _limit
8036 // with a newly expanded chunk (this happens when _limit was set to the
8037 // previous _end of the space), so we may have stepped past _limit:
8038 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8039 if (addr >= _limit) { // we have swept up to or past the limit: finish up
8040 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8041 "sweep _limit out of bounds");
8042 assert(addr < _sp->end(), "addr out of bounds");
8043 // Flush any free range we might be holding as a single
8044 // coalesced chunk to the appropriate free list.
8045 if (inFreeRange()) {
8046 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8047 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8048 flush_cur_free_chunk(freeFinger(),
8049 pointer_delta(addr, freeFinger()));
8050 if (CMSTraceSweeper) {
8051 gclog_or_tty->print("Sweep: last chunk: ");
8052 gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") "
8053 "[coalesced:"SIZE_FORMAT"]\n",
8054 freeFinger(), pointer_delta(addr, freeFinger()),
8055 lastFreeRangeCoalesced());
8056 }
8057 }
8058
8059 // help the iterator loop finish
8060 return pointer_delta(_sp->end(), addr);
8061 }
8062
8063 assert(addr < _limit, "sweep invariant");
8064 // check if we should yield
8065 do_yield_check(addr);
8066 if (fc->is_free()) {
8067 // Chunk that is already free
8068 res = fc->size();
8069 do_already_free_chunk(fc);
8070 debug_only(_sp->verifyFreeLists());
8071 // If we flush the chunk at hand in lookahead_and_flush()
8072 // and it's coalesced with a preceding chunk, then the
8073 // process of "mangling" the payload of the coalesced block
8074 // will cause erasure of the size information from the
8075 // (erstwhile) header of all the coalesced blocks but the
8076 // first, so the first disjunct in the assert will not hold
8077 // in that specific case (in which case the second disjunct
8078 // will hold).
8079 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8080 "Otherwise the size info doesn't change at this step");
8081 NOT_PRODUCT(
8082 _numObjectsAlreadyFree++;
8083 _numWordsAlreadyFree += res;
8084 )
8085 NOT_PRODUCT(_last_fc = fc;)
8086 } else if (!_bitMap->isMarked(addr)) {
8087 // Chunk is fresh garbage
8088 res = do_garbage_chunk(fc);
8089 debug_only(_sp->verifyFreeLists());
8090 NOT_PRODUCT(
8091 _numObjectsFreed++;
8092 _numWordsFreed += res;
8093 )
8094 } else {
8095 // Chunk that is alive.
8096 res = do_live_chunk(fc);
8097 debug_only(_sp->verifyFreeLists());
8098 NOT_PRODUCT(
8099 _numObjectsLive++;
8100 _numWordsLive += res;
8101 )
8102 }
8103 return res;
8104 }
8105
8106 // For the smart allocation, record following
8107 // split deaths - a free chunk is removed from its free list because
8108 // it is being split into two or more chunks.
8109 // split birth - a free chunk is being added to its free list because
8110 // a larger free chunk has been split and resulted in this free chunk.
8111 // coal death - a free chunk is being removed from its free list because
8112 // it is being coalesced into a large free chunk.
8113 // coal birth - a free chunk is being added to its free list because
8114 // it was created when two or more free chunks where coalesced into
8115 // this free chunk.
8116 //
8117 // These statistics are used to determine the desired number of free
8118 // chunks of a given size. The desired number is chosen to be relative
8119 // to the end of a CMS sweep. The desired number at the end of a sweep
8120 // is the
8121 // count-at-end-of-previous-sweep (an amount that was enough)
8122 // - count-at-beginning-of-current-sweep (the excess)
8123 // + split-births (gains in this size during interval)
8124 // - split-deaths (demands on this size during interval)
8125 // where the interval is from the end of one sweep to the end of the
8126 // next.
8127 //
8128 // When sweeping the sweeper maintains an accumulated chunk which is
8129 // the chunk that is made up of chunks that have been coalesced. That
8130 // will be termed the left-hand chunk. A new chunk of garbage that
8131 // is being considered for coalescing will be referred to as the
8132 // right-hand chunk.
8133 //
8134 // When making a decision on whether to coalesce a right-hand chunk with
8135 // the current left-hand chunk, the current count vs. the desired count
8136 // of the left-hand chunk is considered. Also if the right-hand chunk
8137 // is near the large chunk at the end of the heap (see
8138 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8139 // left-hand chunk is coalesced.
8140 //
8141 // When making a decision about whether to split a chunk, the desired count
8142 // vs. the current count of the candidate to be split is also considered.
8143 // If the candidate is underpopulated (currently fewer chunks than desired)
8144 // a chunk of an overpopulated (currently more chunks than desired) size may
8145 // be chosen. The "hint" associated with a free list, if non-null, points
8146 // to a free list which may be overpopulated.
8147 //
8148
8149 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8150 const size_t size = fc->size();
8151 // Chunks that cannot be coalesced are not in the
8152 // free lists.
8153 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8154 assert(_sp->verify_chunk_in_free_list(fc),
8155 "free chunk should be in free lists");
8156 }
8157 // a chunk that is already free, should not have been
8158 // marked in the bit map
8159 HeapWord* const addr = (HeapWord*) fc;
8160 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8161 // Verify that the bit map has no bits marked between
8162 // addr and purported end of this block.
8163 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8164
8165 // Some chunks cannot be coalesced under any circumstances.
8166 // See the definition of cantCoalesce().
8167 if (!fc->cantCoalesce()) {
8168 // This chunk can potentially be coalesced.
8169 if (_sp->adaptive_freelists()) {
8170 // All the work is done in
8171 do_post_free_or_garbage_chunk(fc, size);
8172 } else { // Not adaptive free lists
8173 // this is a free chunk that can potentially be coalesced by the sweeper;
8174 if (!inFreeRange()) {
8175 // if the next chunk is a free block that can't be coalesced
8176 // it doesn't make sense to remove this chunk from the free lists
8177 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8178 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8179 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8180 nextChunk->is_free() && // ... which is free...
8181 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8182 // nothing to do
8183 } else {
8184 // Potentially the start of a new free range:
8185 // Don't eagerly remove it from the free lists.
8186 // No need to remove it if it will just be put
8187 // back again. (Also from a pragmatic point of view
8188 // if it is a free block in a region that is beyond
8189 // any allocated blocks, an assertion will fail)
8190 // Remember the start of a free run.
8191 initialize_free_range(addr, true);
8192 // end - can coalesce with next chunk
8193 }
8194 } else {
8195 // the midst of a free range, we are coalescing
8196 print_free_block_coalesced(fc);
8197 if (CMSTraceSweeper) {
8198 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
8199 }
8200 // remove it from the free lists
8201 _sp->removeFreeChunkFromFreeLists(fc);
8202 set_lastFreeRangeCoalesced(true);
8203 // If the chunk is being coalesced and the current free range is
8204 // in the free lists, remove the current free range so that it
8205 // will be returned to the free lists in its entirety - all
8206 // the coalesced pieces included.
8207 if (freeRangeInFreeLists()) {
8208 FreeChunk* ffc = (FreeChunk*) freeFinger();
8209 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8210 "Size of free range is inconsistent with chunk size.");
8211 if (CMSTestInFreeList) {
8212 assert(_sp->verify_chunk_in_free_list(ffc),
8213 "free range is not in free lists");
8214 }
8215 _sp->removeFreeChunkFromFreeLists(ffc);
8216 set_freeRangeInFreeLists(false);
8217 }
8218 }
8219 }
8220 // Note that if the chunk is not coalescable (the else arm
8221 // below), we unconditionally flush, without needing to do
8222 // a "lookahead," as we do below.
8223 if (inFreeRange()) lookahead_and_flush(fc, size);
8224 } else {
8225 // Code path common to both original and adaptive free lists.
8226
8227 // cant coalesce with previous block; this should be treated
8228 // as the end of a free run if any
8229 if (inFreeRange()) {
8230 // we kicked some butt; time to pick up the garbage
8231 assert(freeFinger() < addr, "freeFinger points too high");
8232 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8233 }
8234 // else, nothing to do, just continue
8235 }
8236 }
8237
8238 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8239 // This is a chunk of garbage. It is not in any free list.
8240 // Add it to a free list or let it possibly be coalesced into
8241 // a larger chunk.
8242 HeapWord* const addr = (HeapWord*) fc;
8243 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8244
8245 if (_sp->adaptive_freelists()) {
8246 // Verify that the bit map has no bits marked between
8247 // addr and purported end of just dead object.
8248 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8249
8250 do_post_free_or_garbage_chunk(fc, size);
8251 } else {
8252 if (!inFreeRange()) {
8253 // start of a new free range
8254 assert(size > 0, "A free range should have a size");
8255 initialize_free_range(addr, false);
8256 } else {
8257 // this will be swept up when we hit the end of the
8258 // free range
8259 if (CMSTraceSweeper) {
8260 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
8261 }
8262 // If the chunk is being coalesced and the current free range is
8263 // in the free lists, remove the current free range so that it
8264 // will be returned to the free lists in its entirety - all
8265 // the coalesced pieces included.
8266 if (freeRangeInFreeLists()) {
8267 FreeChunk* ffc = (FreeChunk*)freeFinger();
8268 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8269 "Size of free range is inconsistent with chunk size.");
8270 if (CMSTestInFreeList) {
8271 assert(_sp->verify_chunk_in_free_list(ffc),
8272 "free range is not in free lists");
8273 }
8274 _sp->removeFreeChunkFromFreeLists(ffc);
8275 set_freeRangeInFreeLists(false);
8276 }
8277 set_lastFreeRangeCoalesced(true);
8278 }
8279 // this will be swept up when we hit the end of the free range
8280
8281 // Verify that the bit map has no bits marked between
8282 // addr and purported end of just dead object.
8283 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8284 }
8285 assert(_limit >= addr + size,
8286 "A freshly garbage chunk can't possibly straddle over _limit");
8287 if (inFreeRange()) lookahead_and_flush(fc, size);
8288 return size;
8289 }
8290
8291 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8292 HeapWord* addr = (HeapWord*) fc;
8293 // The sweeper has just found a live object. Return any accumulated
8294 // left hand chunk to the free lists.
8295 if (inFreeRange()) {
8296 assert(freeFinger() < addr, "freeFinger points too high");
8297 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8298 }
8299
8300 // This object is live: we'd normally expect this to be
8301 // an oop, and like to assert the following:
8302 // assert(oop(addr)->is_oop(), "live block should be an oop");
8303 // However, as we commented above, this may be an object whose
8304 // header hasn't yet been initialized.
8305 size_t size;
8306 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8307 if (_bitMap->isMarked(addr + 1)) {
8308 // Determine the size from the bit map, rather than trying to
8309 // compute it from the object header.
8310 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8311 size = pointer_delta(nextOneAddr + 1, addr);
8312 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8313 "alignment problem");
8314
8315 #ifdef ASSERT
8316 if (oop(addr)->klass_or_null() != NULL) {
8317 // Ignore mark word because we are running concurrent with mutators
8318 assert(oop(addr)->is_oop(true), "live block should be an oop");
8319 assert(size ==
8320 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8321 "P-mark and computed size do not agree");
8322 }
8323 #endif
8324
8325 } else {
8326 // This should be an initialized object that's alive.
8327 assert(oop(addr)->klass_or_null() != NULL,
8328 "Should be an initialized object");
8329 // Ignore mark word because we are running concurrent with mutators
8330 assert(oop(addr)->is_oop(true), "live block should be an oop");
8331 // Verify that the bit map has no bits marked between
8332 // addr and purported end of this block.
8333 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8334 assert(size >= 3, "Necessary for Printezis marks to work");
8335 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8336 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8337 }
8338 return size;
8339 }
8340
8341 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8342 size_t chunkSize) {
8343 // do_post_free_or_garbage_chunk() should only be called in the case
8344 // of the adaptive free list allocator.
8345 const bool fcInFreeLists = fc->is_free();
8346 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8347 assert((HeapWord*)fc <= _limit, "sweep invariant");
8348 if (CMSTestInFreeList && fcInFreeLists) {
8349 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8350 }
8351
8352 if (CMSTraceSweeper) {
8353 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8354 }
8355
8356 HeapWord* const fc_addr = (HeapWord*) fc;
8357
8358 bool coalesce;
8359 const size_t left = pointer_delta(fc_addr, freeFinger());
8360 const size_t right = chunkSize;
8361 switch (FLSCoalescePolicy) {
8362 // numeric value forms a coalition aggressiveness metric
8363 case 0: { // never coalesce
8364 coalesce = false;
8365 break;
8366 }
8367 case 1: { // coalesce if left & right chunks on overpopulated lists
8368 coalesce = _sp->coalOverPopulated(left) &&
8369 _sp->coalOverPopulated(right);
8370 break;
8371 }
8372 case 2: { // coalesce if left chunk on overpopulated list (default)
8373 coalesce = _sp->coalOverPopulated(left);
8374 break;
8375 }
8376 case 3: { // coalesce if left OR right chunk on overpopulated list
8377 coalesce = _sp->coalOverPopulated(left) ||
8378 _sp->coalOverPopulated(right);
8379 break;
8380 }
8381 case 4: { // always coalesce
8382 coalesce = true;
8383 break;
8384 }
8385 default:
8386 ShouldNotReachHere();
8387 }
8388
8389 // Should the current free range be coalesced?
8390 // If the chunk is in a free range and either we decided to coalesce above
8391 // or the chunk is near the large block at the end of the heap
8392 // (isNearLargestChunk() returns true), then coalesce this chunk.
8393 const bool doCoalesce = inFreeRange()
8394 && (coalesce || _g->isNearLargestChunk(fc_addr));
8395 if (doCoalesce) {
8396 // Coalesce the current free range on the left with the new
8397 // chunk on the right. If either is on a free list,
8398 // it must be removed from the list and stashed in the closure.
8399 if (freeRangeInFreeLists()) {
8400 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8401 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8402 "Size of free range is inconsistent with chunk size.");
8403 if (CMSTestInFreeList) {
8404 assert(_sp->verify_chunk_in_free_list(ffc),
8405 "Chunk is not in free lists");
8406 }
8407 _sp->coalDeath(ffc->size());
8408 _sp->removeFreeChunkFromFreeLists(ffc);
8409 set_freeRangeInFreeLists(false);
8410 }
8411 if (fcInFreeLists) {
8412 _sp->coalDeath(chunkSize);
8413 assert(fc->size() == chunkSize,
8414 "The chunk has the wrong size or is not in the free lists");
8415 _sp->removeFreeChunkFromFreeLists(fc);
8416 }
8417 set_lastFreeRangeCoalesced(true);
8418 print_free_block_coalesced(fc);
8419 } else { // not in a free range and/or should not coalesce
8420 // Return the current free range and start a new one.
8421 if (inFreeRange()) {
8422 // In a free range but cannot coalesce with the right hand chunk.
8423 // Put the current free range into the free lists.
8424 flush_cur_free_chunk(freeFinger(),
8425 pointer_delta(fc_addr, freeFinger()));
8426 }
8427 // Set up for new free range. Pass along whether the right hand
8428 // chunk is in the free lists.
8429 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8430 }
8431 }
8432
8433 // Lookahead flush:
8434 // If we are tracking a free range, and this is the last chunk that
8435 // we'll look at because its end crosses past _limit, we'll preemptively
8436 // flush it along with any free range we may be holding on to. Note that
8437 // this can be the case only for an already free or freshly garbage
8438 // chunk. If this block is an object, it can never straddle
8439 // over _limit. The "straddling" occurs when _limit is set at
8440 // the previous end of the space when this cycle started, and
8441 // a subsequent heap expansion caused the previously co-terminal
8442 // free block to be coalesced with the newly expanded portion,
8443 // thus rendering _limit a non-block-boundary making it dangerous
8444 // for the sweeper to step over and examine.
8445 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8446 assert(inFreeRange(), "Should only be called if currently in a free range.");
8447 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8448 assert(_sp->used_region().contains(eob - 1),
8449 err_msg("eob = " PTR_FORMAT " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8450 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8451 _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8452 if (eob >= _limit) {
8453 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8454 if (CMSTraceSweeper) {
8455 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8456 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8457 "[" PTR_FORMAT "," PTR_FORMAT ")",
8458 _limit, fc, eob, _sp->bottom(), _sp->end());
8459 }
8460 // Return the storage we are tracking back into the free lists.
8461 if (CMSTraceSweeper) {
8462 gclog_or_tty->print_cr("Flushing ... ");
8463 }
8464 assert(freeFinger() < eob, "Error");
8465 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8466 }
8467 }
8468
8469 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8470 assert(inFreeRange(), "Should only be called if currently in a free range.");
8471 assert(size > 0,
8472 "A zero sized chunk cannot be added to the free lists.");
8473 if (!freeRangeInFreeLists()) {
8474 if (CMSTestInFreeList) {
8475 FreeChunk* fc = (FreeChunk*) chunk;
8476 fc->set_size(size);
8477 assert(!_sp->verify_chunk_in_free_list(fc),
8478 "chunk should not be in free lists yet");
8479 }
8480 if (CMSTraceSweeper) {
8481 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8482 chunk, size);
8483 }
8484 // A new free range is going to be starting. The current
8485 // free range has not been added to the free lists yet or
8486 // was removed so add it back.
8487 // If the current free range was coalesced, then the death
8488 // of the free range was recorded. Record a birth now.
8489 if (lastFreeRangeCoalesced()) {
8490 _sp->coalBirth(size);
8491 }
8492 _sp->addChunkAndRepairOffsetTable(chunk, size,
8493 lastFreeRangeCoalesced());
8494 } else if (CMSTraceSweeper) {
8495 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8496 }
8497 set_inFreeRange(false);
8498 set_freeRangeInFreeLists(false);
8499 }
8500
8501 // We take a break if we've been at this for a while,
8502 // so as to avoid monopolizing the locks involved.
8503 void SweepClosure::do_yield_work(HeapWord* addr) {
8504 // Return current free chunk being used for coalescing (if any)
8505 // to the appropriate freelist. After yielding, the next
8506 // free block encountered will start a coalescing range of
8507 // free blocks. If the next free block is adjacent to the
8508 // chunk just flushed, they will need to wait for the next
8509 // sweep to be coalesced.
8510 if (inFreeRange()) {
8511 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8512 }
8513
8514 // First give up the locks, then yield, then re-lock.
8515 // We should probably use a constructor/destructor idiom to
8516 // do this unlock/lock or modify the MutexUnlocker class to
8517 // serve our purpose. XXX
8518 assert_lock_strong(_bitMap->lock());
8519 assert_lock_strong(_freelistLock);
8520 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8521 "CMS thread should hold CMS token");
8522 _bitMap->lock()->unlock();
8523 _freelistLock->unlock();
8524 ConcurrentMarkSweepThread::desynchronize(true);
8525 ConcurrentMarkSweepThread::acknowledge_yield_request();
8526 _collector->stopTimer();
8527 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8528 if (PrintCMSStatistics != 0) {
8529 _collector->incrementYields();
8530 }
8531 _collector->icms_wait();
8532
8533 // See the comment in coordinator_yield()
8534 for (unsigned i = 0; i < CMSYieldSleepCount &&
8535 ConcurrentMarkSweepThread::should_yield() &&
8536 !CMSCollector::foregroundGCIsActive(); ++i) {
8537 os::sleep(Thread::current(), 1, false);
8538 ConcurrentMarkSweepThread::acknowledge_yield_request();
8539 }
8540
8541 ConcurrentMarkSweepThread::synchronize(true);
8542 _freelistLock->lock();
8543 _bitMap->lock()->lock_without_safepoint_check();
8544 _collector->startTimer();
8545 }
8546
8547 #ifndef PRODUCT
8548 // This is actually very useful in a product build if it can
8549 // be called from the debugger. Compile it into the product
8550 // as needed.
8551 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8552 return debug_cms_space->verify_chunk_in_free_list(fc);
8553 }
8554 #endif
8555
8556 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8557 if (CMSTraceSweeper) {
8558 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8559 fc, fc->size());
8560 }
8561 }
8562
8563 // CMSIsAliveClosure
8564 bool CMSIsAliveClosure::do_object_b(oop obj) {
8565 HeapWord* addr = (HeapWord*)obj;
8566 return addr != NULL &&
8567 (!_span.contains(addr) || _bit_map->isMarked(addr));
8568 }
8569
8570
8571 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8572 MemRegion span,
8573 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8574 bool cpc):
8575 _collector(collector),
8576 _span(span),
8577 _bit_map(bit_map),
8578 _mark_stack(mark_stack),
8579 _concurrent_precleaning(cpc) {
8580 assert(!_span.is_empty(), "Empty span could spell trouble");
8581 }
8582
8583
8584 // CMSKeepAliveClosure: the serial version
8585 void CMSKeepAliveClosure::do_oop(oop obj) {
8586 HeapWord* addr = (HeapWord*)obj;
8587 if (_span.contains(addr) &&
8588 !_bit_map->isMarked(addr)) {
8589 _bit_map->mark(addr);
8590 bool simulate_overflow = false;
8591 NOT_PRODUCT(
8592 if (CMSMarkStackOverflowALot &&
8593 _collector->simulate_overflow()) {
8594 // simulate a stack overflow
8595 simulate_overflow = true;
8596 }
8597 )
8598 if (simulate_overflow || !_mark_stack->push(obj)) {
8599 if (_concurrent_precleaning) {
8600 // We dirty the overflown object and let the remark
8601 // phase deal with it.
8602 assert(_collector->overflow_list_is_empty(), "Error");
8603 // In the case of object arrays, we need to dirty all of
8604 // the cards that the object spans. No locking or atomics
8605 // are needed since no one else can be mutating the mod union
8606 // table.
8607 if (obj->is_objArray()) {
8608 size_t sz = obj->size();
8609 HeapWord* end_card_addr =
8610 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8611 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8612 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8613 _collector->_modUnionTable.mark_range(redirty_range);
8614 } else {
8615 _collector->_modUnionTable.mark(addr);
8616 }
8617 _collector->_ser_kac_preclean_ovflw++;
8618 } else {
8619 _collector->push_on_overflow_list(obj);
8620 _collector->_ser_kac_ovflw++;
8621 }
8622 }
8623 }
8624 }
8625
8626 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8627 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8628
8629 // CMSParKeepAliveClosure: a parallel version of the above.
8630 // The work queues are private to each closure (thread),
8631 // but (may be) available for stealing by other threads.
8632 void CMSParKeepAliveClosure::do_oop(oop obj) {
8633 HeapWord* addr = (HeapWord*)obj;
8634 if (_span.contains(addr) &&
8635 !_bit_map->isMarked(addr)) {
8636 // In general, during recursive tracing, several threads
8637 // may be concurrently getting here; the first one to
8638 // "tag" it, claims it.
8639 if (_bit_map->par_mark(addr)) {
8640 bool res = _work_queue->push(obj);
8641 assert(res, "Low water mark should be much less than capacity");
8642 // Do a recursive trim in the hope that this will keep
8643 // stack usage lower, but leave some oops for potential stealers
8644 trim_queue(_low_water_mark);
8645 } // Else, another thread got there first
8646 }
8647 }
8648
8649 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8650 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8651
8652 void CMSParKeepAliveClosure::trim_queue(uint max) {
8653 while (_work_queue->size() > max) {
8654 oop new_oop;
8655 if (_work_queue->pop_local(new_oop)) {
8656 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8657 assert(_bit_map->isMarked((HeapWord*)new_oop),
8658 "no white objects on this stack!");
8659 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8660 // iterate over the oops in this oop, marking and pushing
8661 // the ones in CMS heap (i.e. in _span).
8662 new_oop->oop_iterate(&_mark_and_push);
8663 }
8664 }
8665 }
8666
8667 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8668 CMSCollector* collector,
8669 MemRegion span, CMSBitMap* bit_map,
8670 OopTaskQueue* work_queue):
8671 _collector(collector),
8672 _span(span),
8673 _bit_map(bit_map),
8674 _work_queue(work_queue) { }
8675
8676 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8677 HeapWord* addr = (HeapWord*)obj;
8678 if (_span.contains(addr) &&
8679 !_bit_map->isMarked(addr)) {
8680 if (_bit_map->par_mark(addr)) {
8681 bool simulate_overflow = false;
8682 NOT_PRODUCT(
8683 if (CMSMarkStackOverflowALot &&
8684 _collector->par_simulate_overflow()) {
8685 // simulate a stack overflow
8686 simulate_overflow = true;
8687 }
8688 )
8689 if (simulate_overflow || !_work_queue->push(obj)) {
8690 _collector->par_push_on_overflow_list(obj);
8691 _collector->_par_kac_ovflw++;
8692 }
8693 } // Else another thread got there already
8694 }
8695 }
8696
8697 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8698 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8699
8700 //////////////////////////////////////////////////////////////////
8701 // CMSExpansionCause /////////////////////////////
8702 //////////////////////////////////////////////////////////////////
8703 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8704 switch (cause) {
8705 case _no_expansion:
8706 return "No expansion";
8707 case _satisfy_free_ratio:
8708 return "Free ratio";
8709 case _satisfy_promotion:
8710 return "Satisfy promotion";
8711 case _satisfy_allocation:
8712 return "allocation";
8713 case _allocate_par_lab:
8714 return "Par LAB";
8715 case _allocate_par_spooling_space:
8716 return "Par Spooling Space";
8717 case _adaptive_size_policy:
8718 return "Ergonomics";
8719 default:
8720 return "unknown";
8721 }
8722 }
8723
8724 void CMSDrainMarkingStackClosure::do_void() {
8725 // the max number to take from overflow list at a time
8726 const size_t num = _mark_stack->capacity()/4;
8727 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8728 "Overflow list should be NULL during concurrent phases");
8729 while (!_mark_stack->isEmpty() ||
8730 // if stack is empty, check the overflow list
8731 _collector->take_from_overflow_list(num, _mark_stack)) {
8732 oop obj = _mark_stack->pop();
8733 HeapWord* addr = (HeapWord*)obj;
8734 assert(_span.contains(addr), "Should be within span");
8735 assert(_bit_map->isMarked(addr), "Should be marked");
8736 assert(obj->is_oop(), "Should be an oop");
8737 obj->oop_iterate(_keep_alive);
8738 }
8739 }
8740
8741 void CMSParDrainMarkingStackClosure::do_void() {
8742 // drain queue
8743 trim_queue(0);
8744 }
8745
8746 // Trim our work_queue so its length is below max at return
8747 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8748 while (_work_queue->size() > max) {
8749 oop new_oop;
8750 if (_work_queue->pop_local(new_oop)) {
8751 assert(new_oop->is_oop(), "Expected an oop");
8752 assert(_bit_map->isMarked((HeapWord*)new_oop),
8753 "no white objects on this stack!");
8754 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8755 // iterate over the oops in this oop, marking and pushing
8756 // the ones in CMS heap (i.e. in _span).
8757 new_oop->oop_iterate(&_mark_and_push);
8758 }
8759 }
8760 }
8761
8762 ////////////////////////////////////////////////////////////////////
8763 // Support for Marking Stack Overflow list handling and related code
8764 ////////////////////////////////////////////////////////////////////
8765 // Much of the following code is similar in shape and spirit to the
8766 // code used in ParNewGC. We should try and share that code
8767 // as much as possible in the future.
8768
8769 #ifndef PRODUCT
8770 // Debugging support for CMSStackOverflowALot
8771
8772 // It's OK to call this multi-threaded; the worst thing
8773 // that can happen is that we'll get a bunch of closely
8774 // spaced simulated oveflows, but that's OK, in fact
8775 // probably good as it would exercise the overflow code
8776 // under contention.
8777 bool CMSCollector::simulate_overflow() {
8778 if (_overflow_counter-- <= 0) { // just being defensive
8779 _overflow_counter = CMSMarkStackOverflowInterval;
8780 return true;
8781 } else {
8782 return false;
8783 }
8784 }
8785
8786 bool CMSCollector::par_simulate_overflow() {
8787 return simulate_overflow();
8788 }
8789 #endif
8790
8791 // Single-threaded
8792 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8793 assert(stack->isEmpty(), "Expected precondition");
8794 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8795 size_t i = num;
8796 oop cur = _overflow_list;
8797 const markOop proto = markOopDesc::prototype();
8798 NOT_PRODUCT(ssize_t n = 0;)
8799 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8800 next = oop(cur->mark());
8801 cur->set_mark(proto); // until proven otherwise
8802 assert(cur->is_oop(), "Should be an oop");
8803 bool res = stack->push(cur);
8804 assert(res, "Bit off more than can chew?");
8805 NOT_PRODUCT(n++;)
8806 }
8807 _overflow_list = cur;
8808 #ifndef PRODUCT
8809 assert(_num_par_pushes >= n, "Too many pops?");
8810 _num_par_pushes -=n;
8811 #endif
8812 return !stack->isEmpty();
8813 }
8814
8815 #define BUSY (oop(0x1aff1aff))
8816 // (MT-safe) Get a prefix of at most "num" from the list.
8817 // The overflow list is chained through the mark word of
8818 // each object in the list. We fetch the entire list,
8819 // break off a prefix of the right size and return the
8820 // remainder. If other threads try to take objects from
8821 // the overflow list at that time, they will wait for
8822 // some time to see if data becomes available. If (and
8823 // only if) another thread places one or more object(s)
8824 // on the global list before we have returned the suffix
8825 // to the global list, we will walk down our local list
8826 // to find its end and append the global list to
8827 // our suffix before returning it. This suffix walk can
8828 // prove to be expensive (quadratic in the amount of traffic)
8829 // when there are many objects in the overflow list and
8830 // there is much producer-consumer contention on the list.
8831 // *NOTE*: The overflow list manipulation code here and
8832 // in ParNewGeneration:: are very similar in shape,
8833 // except that in the ParNew case we use the old (from/eden)
8834 // copy of the object to thread the list via its klass word.
8835 // Because of the common code, if you make any changes in
8836 // the code below, please check the ParNew version to see if
8837 // similar changes might be needed.
8838 // CR 6797058 has been filed to consolidate the common code.
8839 bool CMSCollector::par_take_from_overflow_list(size_t num,
8840 OopTaskQueue* work_q,
8841 int no_of_gc_threads) {
8842 assert(work_q->size() == 0, "First empty local work queue");
8843 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8844 if (_overflow_list == NULL) {
8845 return false;
8846 }
8847 // Grab the entire list; we'll put back a suffix
8848 oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8849 Thread* tid = Thread::current();
8850 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8851 // set to ParallelGCThreads.
8852 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8853 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8854 // If the list is busy, we spin for a short while,
8855 // sleeping between attempts to get the list.
8856 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8857 os::sleep(tid, sleep_time_millis, false);
8858 if (_overflow_list == NULL) {
8859 // Nothing left to take
8860 return false;
8861 } else if (_overflow_list != BUSY) {
8862 // Try and grab the prefix
8863 prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8864 }
8865 }
8866 // If the list was found to be empty, or we spun long
8867 // enough, we give up and return empty-handed. If we leave
8868 // the list in the BUSY state below, it must be the case that
8869 // some other thread holds the overflow list and will set it
8870 // to a non-BUSY state in the future.
8871 if (prefix == NULL || prefix == BUSY) {
8872 // Nothing to take or waited long enough
8873 if (prefix == NULL) {
8874 // Write back the NULL in case we overwrote it with BUSY above
8875 // and it is still the same value.
8876 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8877 }
8878 return false;
8879 }
8880 assert(prefix != NULL && prefix != BUSY, "Error");
8881 size_t i = num;
8882 oop cur = prefix;
8883 // Walk down the first "num" objects, unless we reach the end.
8884 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8885 if (cur->mark() == NULL) {
8886 // We have "num" or fewer elements in the list, so there
8887 // is nothing to return to the global list.
8888 // Write back the NULL in lieu of the BUSY we wrote
8889 // above, if it is still the same value.
8890 if (_overflow_list == BUSY) {
8891 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8892 }
8893 } else {
8894 // Chop off the suffix and rerturn it to the global list.
8895 assert(cur->mark() != BUSY, "Error");
8896 oop suffix_head = cur->mark(); // suffix will be put back on global list
8897 cur->set_mark(NULL); // break off suffix
8898 // It's possible that the list is still in the empty(busy) state
8899 // we left it in a short while ago; in that case we may be
8900 // able to place back the suffix without incurring the cost
8901 // of a walk down the list.
8902 oop observed_overflow_list = _overflow_list;
8903 oop cur_overflow_list = observed_overflow_list;
8904 bool attached = false;
8905 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8906 observed_overflow_list =
8907 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8908 if (cur_overflow_list == observed_overflow_list) {
8909 attached = true;
8910 break;
8911 } else cur_overflow_list = observed_overflow_list;
8912 }
8913 if (!attached) {
8914 // Too bad, someone else sneaked in (at least) an element; we'll need
8915 // to do a splice. Find tail of suffix so we can prepend suffix to global
8916 // list.
8917 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8918 oop suffix_tail = cur;
8919 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8920 "Tautology");
8921 observed_overflow_list = _overflow_list;
8922 do {
8923 cur_overflow_list = observed_overflow_list;
8924 if (cur_overflow_list != BUSY) {
8925 // Do the splice ...
8926 suffix_tail->set_mark(markOop(cur_overflow_list));
8927 } else { // cur_overflow_list == BUSY
8928 suffix_tail->set_mark(NULL);
8929 }
8930 // ... and try to place spliced list back on overflow_list ...
8931 observed_overflow_list =
8932 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8933 } while (cur_overflow_list != observed_overflow_list);
8934 // ... until we have succeeded in doing so.
8935 }
8936 }
8937
8938 // Push the prefix elements on work_q
8939 assert(prefix != NULL, "control point invariant");
8940 const markOop proto = markOopDesc::prototype();
8941 oop next;
8942 NOT_PRODUCT(ssize_t n = 0;)
8943 for (cur = prefix; cur != NULL; cur = next) {
8944 next = oop(cur->mark());
8945 cur->set_mark(proto); // until proven otherwise
8946 assert(cur->is_oop(), "Should be an oop");
8947 bool res = work_q->push(cur);
8948 assert(res, "Bit off more than we can chew?");
8949 NOT_PRODUCT(n++;)
8950 }
8951 #ifndef PRODUCT
8952 assert(_num_par_pushes >= n, "Too many pops?");
8953 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8954 #endif
8955 return true;
8956 }
8957
8958 // Single-threaded
8959 void CMSCollector::push_on_overflow_list(oop p) {
8960 NOT_PRODUCT(_num_par_pushes++;)
8961 assert(p->is_oop(), "Not an oop");
8962 preserve_mark_if_necessary(p);
8963 p->set_mark((markOop)_overflow_list);
8964 _overflow_list = p;
8965 }
8966
8967 // Multi-threaded; use CAS to prepend to overflow list
8968 void CMSCollector::par_push_on_overflow_list(oop p) {
8969 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8970 assert(p->is_oop(), "Not an oop");
8971 par_preserve_mark_if_necessary(p);
8972 oop observed_overflow_list = _overflow_list;
8973 oop cur_overflow_list;
8974 do {
8975 cur_overflow_list = observed_overflow_list;
8976 if (cur_overflow_list != BUSY) {
8977 p->set_mark(markOop(cur_overflow_list));
8978 } else {
8979 p->set_mark(NULL);
8980 }
8981 observed_overflow_list =
8982 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8983 } while (cur_overflow_list != observed_overflow_list);
8984 }
8985 #undef BUSY
8986
8987 // Single threaded
8988 // General Note on GrowableArray: pushes may silently fail
8989 // because we are (temporarily) out of C-heap for expanding
8990 // the stack. The problem is quite ubiquitous and affects
8991 // a lot of code in the JVM. The prudent thing for GrowableArray
8992 // to do (for now) is to exit with an error. However, that may
8993 // be too draconian in some cases because the caller may be
8994 // able to recover without much harm. For such cases, we
8995 // should probably introduce a "soft_push" method which returns
8996 // an indication of success or failure with the assumption that
8997 // the caller may be able to recover from a failure; code in
8998 // the VM can then be changed, incrementally, to deal with such
8999 // failures where possible, thus, incrementally hardening the VM
9000 // in such low resource situations.
9001 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9002 _preserved_oop_stack.push(p);
9003 _preserved_mark_stack.push(m);
9004 assert(m == p->mark(), "Mark word changed");
9005 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9006 "bijection");
9007 }
9008
9009 // Single threaded
9010 void CMSCollector::preserve_mark_if_necessary(oop p) {
9011 markOop m = p->mark();
9012 if (m->must_be_preserved(p)) {
9013 preserve_mark_work(p, m);
9014 }
9015 }
9016
9017 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9018 markOop m = p->mark();
9019 if (m->must_be_preserved(p)) {
9020 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9021 // Even though we read the mark word without holding
9022 // the lock, we are assured that it will not change
9023 // because we "own" this oop, so no other thread can
9024 // be trying to push it on the overflow list; see
9025 // the assertion in preserve_mark_work() that checks
9026 // that m == p->mark().
9027 preserve_mark_work(p, m);
9028 }
9029 }
9030
9031 // We should be able to do this multi-threaded,
9032 // a chunk of stack being a task (this is
9033 // correct because each oop only ever appears
9034 // once in the overflow list. However, it's
9035 // not very easy to completely overlap this with
9036 // other operations, so will generally not be done
9037 // until all work's been completed. Because we
9038 // expect the preserved oop stack (set) to be small,
9039 // it's probably fine to do this single-threaded.
9040 // We can explore cleverer concurrent/overlapped/parallel
9041 // processing of preserved marks if we feel the
9042 // need for this in the future. Stack overflow should
9043 // be so rare in practice and, when it happens, its
9044 // effect on performance so great that this will
9045 // likely just be in the noise anyway.
9046 void CMSCollector::restore_preserved_marks_if_any() {
9047 assert(SafepointSynchronize::is_at_safepoint(),
9048 "world should be stopped");
9049 assert(Thread::current()->is_ConcurrentGC_thread() ||
9050 Thread::current()->is_VM_thread(),
9051 "should be single-threaded");
9052 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9053 "bijection");
9054
9055 while (!_preserved_oop_stack.is_empty()) {
9056 oop p = _preserved_oop_stack.pop();
9057 assert(p->is_oop(), "Should be an oop");
9058 assert(_span.contains(p), "oop should be in _span");
9059 assert(p->mark() == markOopDesc::prototype(),
9060 "Set when taken from overflow list");
9061 markOop m = _preserved_mark_stack.pop();
9062 p->set_mark(m);
9063 }
9064 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9065 "stacks were cleared above");
9066 }
9067
9068 #ifndef PRODUCT
9069 bool CMSCollector::no_preserved_marks() const {
9070 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9071 }
9072 #endif
9073
9074 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
9075 {
9076 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9077 CMSAdaptiveSizePolicy* size_policy =
9078 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
9079 assert(size_policy->is_gc_cms_adaptive_size_policy(),
9080 "Wrong type for size policy");
9081 return size_policy;
9082 }
9083
9084 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
9085 size_t desired_promo_size) {
9086 if (cur_promo_size < desired_promo_size) {
9087 size_t expand_bytes = desired_promo_size - cur_promo_size;
9088 if (PrintAdaptiveSizePolicy && Verbose) {
9089 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9090 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
9091 expand_bytes);
9092 }
9093 expand(expand_bytes,
9094 MinHeapDeltaBytes,
9095 CMSExpansionCause::_adaptive_size_policy);
9096 } else if (desired_promo_size < cur_promo_size) {
9097 size_t shrink_bytes = cur_promo_size - desired_promo_size;
9098 if (PrintAdaptiveSizePolicy && Verbose) {
9099 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9100 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
9101 shrink_bytes);
9102 }
9103 shrink(shrink_bytes);
9104 }
9105 }
9106
9107 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
9108 GenCollectedHeap* gch = GenCollectedHeap::heap();
9109 CMSGCAdaptivePolicyCounters* counters =
9110 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
9111 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
9112 "Wrong kind of counters");
9113 return counters;
9114 }
9115
9116
9117 void ASConcurrentMarkSweepGeneration::update_counters() {
9118 if (UsePerfData) {
9119 _space_counters->update_all();
9120 _gen_counters->update_all();
9121 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9122 GenCollectedHeap* gch = GenCollectedHeap::heap();
9123 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9124 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9125 "Wrong gc statistics type");
9126 counters->update_counters(gc_stats_l);
9127 }
9128 }
9129
9130 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
9131 if (UsePerfData) {
9132 _space_counters->update_used(used);
9133 _space_counters->update_capacity();
9134 _gen_counters->update_all();
9135
9136 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9137 GenCollectedHeap* gch = GenCollectedHeap::heap();
9138 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9139 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9140 "Wrong gc statistics type");
9141 counters->update_counters(gc_stats_l);
9142 }
9143 }
9144
9145 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9146 assert_locked_or_safepoint(Heap_lock);
9147 assert_lock_strong(freelistLock());
9148 HeapWord* old_end = _cmsSpace->end();
9149 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9150 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9151 FreeChunk* chunk_at_end = find_chunk_at_end();
9152 if (chunk_at_end == NULL) {
9153 // No room to shrink
9154 if (PrintGCDetails && Verbose) {
9155 gclog_or_tty->print_cr("No room to shrink: old_end "
9156 PTR_FORMAT " unallocated_start " PTR_FORMAT
9157 " chunk_at_end " PTR_FORMAT,
9158 old_end, unallocated_start, chunk_at_end);
9159 }
9160 return;
9161 } else {
9162
9163 // Find the chunk at the end of the space and determine
9164 // how much it can be shrunk.
9165 size_t shrinkable_size_in_bytes = chunk_at_end->size();
9166 size_t aligned_shrinkable_size_in_bytes =
9167 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9168 assert(unallocated_start <= (HeapWord*) chunk_at_end->end(),
9169 "Inconsistent chunk at end of space");
9170 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9171 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9172
9173 // Shrink the underlying space
9174 _virtual_space.shrink_by(bytes);
9175 if (PrintGCDetails && Verbose) {
9176 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9177 " desired_bytes " SIZE_FORMAT
9178 " shrinkable_size_in_bytes " SIZE_FORMAT
9179 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9180 " bytes " SIZE_FORMAT,
9181 desired_bytes, shrinkable_size_in_bytes,
9182 aligned_shrinkable_size_in_bytes, bytes);
9183 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
9184 " unallocated_start " SIZE_FORMAT,
9185 old_end, unallocated_start);
9186 }
9187
9188 // If the space did shrink (shrinking is not guaranteed),
9189 // shrink the chunk at the end by the appropriate amount.
9190 if (((HeapWord*)_virtual_space.high()) < old_end) {
9191 size_t new_word_size =
9192 heap_word_size(_virtual_space.committed_size());
9193
9194 // Have to remove the chunk from the dictionary because it is changing
9195 // size and might be someplace elsewhere in the dictionary.
9196
9197 // Get the chunk at end, shrink it, and put it
9198 // back.
9199 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9200 size_t word_size_change = word_size_before - new_word_size;
9201 size_t chunk_at_end_old_size = chunk_at_end->size();
9202 assert(chunk_at_end_old_size >= word_size_change,
9203 "Shrink is too large");
9204 chunk_at_end->set_size(chunk_at_end_old_size -
9205 word_size_change);
9206 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9207 word_size_change);
9208
9209 _cmsSpace->returnChunkToDictionary(chunk_at_end);
9210
9211 MemRegion mr(_cmsSpace->bottom(), new_word_size);
9212 _bts->resize(new_word_size); // resize the block offset shared array
9213 Universe::heap()->barrier_set()->resize_covered_region(mr);
9214 _cmsSpace->assert_locked();
9215 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9216
9217 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9218
9219 // update the space and generation capacity counters
9220 if (UsePerfData) {
9221 _space_counters->update_capacity();
9222 _gen_counters->update_all();
9223 }
9224
9225 if (Verbose && PrintGCDetails) {
9226 size_t new_mem_size = _virtual_space.committed_size();
9227 size_t old_mem_size = new_mem_size + bytes;
9228 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
9229 name(), old_mem_size/K, bytes/K, new_mem_size/K);
9230 }
9231 }
9232
9233 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9234 "Inconsistency at end of space");
9235 assert(chunk_at_end->end() == (uintptr_t*) _cmsSpace->end(),
9236 "Shrinking is inconsistent");
9237 return;
9238 }
9239 }
9240
9241 // Transfer some number of overflown objects to usual marking
9242 // stack. Return true if some objects were transferred.
9243 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9244 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9245 (size_t)ParGCDesiredObjsFromOverflowList);
9246
9247 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9248 assert(_collector->overflow_list_is_empty() || res,
9249 "If list is not empty, we should have taken something");
9250 assert(!res || !_mark_stack->isEmpty(),
9251 "If we took something, it should now be on our stack");
9252 return res;
9253 }
9254
9255 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9256 size_t res = _sp->block_size_no_stall(addr, _collector);
9257 if (_sp->block_is_obj(addr)) {
9258 if (_live_bit_map->isMarked(addr)) {
9259 // It can't have been dead in a previous cycle
9260 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9261 } else {
9262 _dead_bit_map->mark(addr); // mark the dead object
9263 }
9264 }
9265 // Could be 0, if the block size could not be computed without stalling.
9266 return res;
9267 }
9268
9269 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9270
9271 switch (phase) {
9272 case CMSCollector::InitialMarking:
9273 initialize(true /* fullGC */ ,
9274 cause /* cause of the GC */,
9275 true /* recordGCBeginTime */,
9276 true /* recordPreGCUsage */,
9277 false /* recordPeakUsage */,
9278 false /* recordPostGCusage */,
9279 true /* recordAccumulatedGCTime */,
9280 false /* recordGCEndTime */,
9281 false /* countCollection */ );
9282 break;
9283
9284 case CMSCollector::FinalMarking:
9285 initialize(true /* fullGC */ ,
9286 cause /* cause of the GC */,
9287 false /* recordGCBeginTime */,
9288 false /* recordPreGCUsage */,
9289 false /* recordPeakUsage */,
9290 false /* recordPostGCusage */,
9291 true /* recordAccumulatedGCTime */,
9292 false /* recordGCEndTime */,
9293 false /* countCollection */ );
9294 break;
9295
9296 case CMSCollector::Sweeping:
9297 initialize(true /* fullGC */ ,
9298 cause /* cause of the GC */,
9299 false /* recordGCBeginTime */,
9300 false /* recordPreGCUsage */,
9301 true /* recordPeakUsage */,
9302 true /* recordPostGCusage */,
9303 false /* recordAccumulatedGCTime */,
9304 true /* recordGCEndTime */,
9305 true /* countCollection */ );
9306 break;
9307
9308 default:
9309 ShouldNotReachHere();
9310 }
9311 }
9312