1 /*
2 * Copyright (c) 2001, 2018, 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
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7 * published by the Free Software Foundation.
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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13 * accompanied this code).
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23 */
24
25 #ifndef SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP
26 #define SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP
27
28 #include "gc/shared/referenceDiscoverer.hpp"
29 #include "gc/shared/referencePolicy.hpp"
30 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
31 #include "gc/shared/referenceProcessorStats.hpp"
32 #include "memory/referenceType.hpp"
33 #include "oops/instanceRefKlass.hpp"
34
35 class GCTimer;
36
37 // ReferenceProcessor class encapsulates the per-"collector" processing
38 // of java.lang.Reference objects for GC. The interface is useful for supporting
39 // a generational abstraction, in particular when there are multiple
40 // generations that are being independently collected -- possibly
41 // concurrently and/or incrementally.
42 // ReferenceProcessor class abstracts away from a generational setting
43 // by using a closure that determines whether a given reference or referent are
44 // subject to this ReferenceProcessor's discovery, thus allowing its use in a
45 // straightforward manner in a general, non-generational, non-contiguous generation
46 // (or heap) setting.
47 //
48
49 // forward references
50 class ReferencePolicy;
51 class AbstractRefProcTaskExecutor;
52
53 // List of discovered references.
54 class DiscoveredList {
55 public:
56 DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { }
57 inline oop head() const;
58 HeapWord* adr_head() {
59 return UseCompressedOops ? (HeapWord*)&_compressed_head :
60 (HeapWord*)&_oop_head;
61 }
62 inline void set_head(oop o);
63 inline bool is_empty() const;
64 size_t length() { return _len; }
65 void set_length(size_t len) { _len = len; }
66 void inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); }
67 void dec_length(size_t dec) { _len -= dec; }
68 private:
69 // Set value depending on UseCompressedOops. This could be a template class
70 // but then we have to fix all the instantiations and declarations that use this class.
71 oop _oop_head;
72 narrowOop _compressed_head;
73 size_t _len;
74 };
75
76 // Iterator for the list of discovered references.
77 class DiscoveredListIterator {
78 private:
79 DiscoveredList& _refs_list;
80 HeapWord* _prev_next;
81 oop _prev;
82 oop _ref;
83 HeapWord* _discovered_addr;
84 oop _next;
85 HeapWord* _referent_addr;
86 oop _referent;
87 OopClosure* _keep_alive;
88 BoolObjectClosure* _is_alive;
89
90 DEBUG_ONLY(
91 oop _first_seen; // cyclic linked list check
92 )
93
94 NOT_PRODUCT(
95 size_t _processed;
96 size_t _removed;
97 )
98
99 public:
100 inline DiscoveredListIterator(DiscoveredList& refs_list,
101 OopClosure* keep_alive,
102 BoolObjectClosure* is_alive);
103
104 // End Of List.
105 inline bool has_next() const { return _ref != NULL; }
106
107 // Get oop to the Reference object.
108 inline oop obj() const { return _ref; }
109
110 // Get oop to the referent object.
111 inline oop referent() const { return _referent; }
112
113 // Returns true if referent is alive.
114 inline bool is_referent_alive() const {
115 return _is_alive->do_object_b(_referent);
116 }
117
118 // Loads data for the current reference.
119 // The "allow_null_referent" argument tells us to allow for the possibility
120 // of a NULL referent in the discovered Reference object. This typically
121 // happens in the case of concurrent collectors that may have done the
122 // discovery concurrently, or interleaved, with mutator execution.
123 void load_ptrs(DEBUG_ONLY(bool allow_null_referent));
124
125 // Move to the next discovered reference.
126 inline void next() {
127 _prev_next = _discovered_addr;
128 _prev = _ref;
129 move_to_next();
130 }
131
132 // Remove the current reference from the list
133 void remove();
134
135 // Make the referent alive.
136 inline void make_referent_alive() {
137 if (UseCompressedOops) {
138 _keep_alive->do_oop((narrowOop*)_referent_addr);
139 } else {
140 _keep_alive->do_oop((oop*)_referent_addr);
141 }
142 }
143
144 // NULL out referent pointer.
145 void clear_referent();
146
147 // Statistics
148 NOT_PRODUCT(
149 inline size_t processed() const { return _processed; }
150 inline size_t removed() const { return _removed; }
151 )
152
153 inline void move_to_next() {
154 if (_ref == _next) {
155 // End of the list.
156 _ref = NULL;
157 } else {
158 _ref = _next;
159 }
160 assert(_ref != _first_seen, "cyclic ref_list found");
161 NOT_PRODUCT(_processed++);
162 }
163 };
164
165 class ReferenceProcessor : public ReferenceDiscoverer {
166 size_t total_count(DiscoveredList lists[]) const;
167
168 // The SoftReference master timestamp clock
169 static jlong _soft_ref_timestamp_clock;
170
171 BoolObjectClosure* _is_subject_to_discovery; // determines whether a given oop is subject
172 // to this ReferenceProcessor's discovery
173 // (and further processing).
174
175 bool _discovering_refs; // true when discovery enabled
176 bool _discovery_is_atomic; // if discovery is atomic wrt
177 // other collectors in configuration
178 bool _discovery_is_mt; // true if reference discovery is MT.
179
180 bool _enqueuing_is_done; // true if all weak references enqueued
181 bool _processing_is_mt; // true during phases when
182 // reference processing is MT.
183 uint _next_id; // round-robin mod _num_q counter in
184 // support of work distribution
185
186 // For collectors that do not keep GC liveness information
187 // in the object header, this field holds a closure that
188 // helps the reference processor determine the reachability
189 // of an oop. It is currently initialized to NULL for all
190 // collectors except for CMS and G1.
191 BoolObjectClosure* _is_alive_non_header;
192
193 // Soft ref clearing policies
194 // . the default policy
195 static ReferencePolicy* _default_soft_ref_policy;
196 // . the "clear all" policy
197 static ReferencePolicy* _always_clear_soft_ref_policy;
198 // . the current policy below is either one of the above
199 ReferencePolicy* _current_soft_ref_policy;
200
201 // The discovered ref lists themselves
202
203 // The active MT'ness degree of the queues below
204 uint _num_q;
205 // The maximum MT'ness degree of the queues below
206 uint _max_num_q;
207
208 // Master array of discovered oops
209 DiscoveredList* _discovered_refs;
210
211 // Arrays of lists of oops, one per thread (pointers into master array above)
212 DiscoveredList* _discoveredSoftRefs;
213 DiscoveredList* _discoveredWeakRefs;
214 DiscoveredList* _discoveredFinalRefs;
215 DiscoveredList* _discoveredPhantomRefs;
216
217 public:
218 static int number_of_subclasses_of_ref() { return (REF_PHANTOM - REF_OTHER); }
219
220 uint num_q() { return _num_q; }
221 uint max_num_q() { return _max_num_q; }
222 void set_active_mt_degree(uint v);
223
224 DiscoveredList* discovered_refs() { return _discovered_refs; }
225
226 ReferencePolicy* setup_policy(bool always_clear) {
227 _current_soft_ref_policy = always_clear ?
228 _always_clear_soft_ref_policy : _default_soft_ref_policy;
229 _current_soft_ref_policy->setup(); // snapshot the policy threshold
230 return _current_soft_ref_policy;
231 }
232
233 // Process references with a certain reachability level.
234 void process_discovered_reflist(DiscoveredList refs_lists[],
235 ReferencePolicy* policy,
236 bool clear_referent,
237 BoolObjectClosure* is_alive,
238 OopClosure* keep_alive,
239 VoidClosure* complete_gc,
240 AbstractRefProcTaskExecutor* task_executor,
241 ReferenceProcessorPhaseTimes* phase_times);
242
243 // Work methods used by the method process_discovered_reflist
244 // Phase1: keep alive all those referents that are otherwise
245 // dead but which must be kept alive by policy (and their closure).
246 void process_phase1(DiscoveredList& refs_list,
247 ReferencePolicy* policy,
248 BoolObjectClosure* is_alive,
249 OopClosure* keep_alive,
250 VoidClosure* complete_gc);
251 // Phase2: remove all those references whose referents are
252 // reachable.
253 void process_phase2(DiscoveredList& refs_list,
254 BoolObjectClosure* is_alive,
255 OopClosure* keep_alive,
256 VoidClosure* complete_gc);
257 // Work methods in support of process_phase2
258 void pp2_work(DiscoveredList& refs_list,
259 BoolObjectClosure* is_alive,
260 OopClosure* keep_alive);
261 void pp2_work_concurrent_discovery(
262 DiscoveredList& refs_list,
263 BoolObjectClosure* is_alive,
264 OopClosure* keep_alive,
265 VoidClosure* complete_gc);
266 // Phase3: process the referents by either clearing them
267 // or keeping them alive (and their closure)
268 void process_phase3(DiscoveredList& refs_list,
269 bool clear_referent,
270 BoolObjectClosure* is_alive,
271 OopClosure* keep_alive,
272 VoidClosure* complete_gc);
273
274 // Enqueue references with a certain reachability level
275 void enqueue_discovered_reflist(DiscoveredList& refs_list);
276
277 // "Preclean" all the discovered reference lists
278 // by removing references with strongly reachable referents.
279 // The first argument is a predicate on an oop that indicates
280 // its (strong) reachability and the second is a closure that
281 // may be used to incrementalize or abort the precleaning process.
282 // The caller is responsible for taking care of potential
283 // interference with concurrent operations on these lists
284 // (or predicates involved) by other threads. Currently
285 // only used by the CMS collector.
286 void preclean_discovered_references(BoolObjectClosure* is_alive,
287 OopClosure* keep_alive,
288 VoidClosure* complete_gc,
289 YieldClosure* yield,
290 GCTimer* gc_timer);
291
292 // Returns the name of the discovered reference list
293 // occupying the i / _num_q slot.
294 const char* list_name(uint i);
295
296 void enqueue_discovered_reflists(AbstractRefProcTaskExecutor* task_executor,
297 ReferenceProcessorPhaseTimes* phase_times);
298
299 // "Preclean" the given discovered reference list
300 // by removing references with strongly reachable referents.
301 // Currently used in support of CMS only.
302 void preclean_discovered_reflist(DiscoveredList& refs_list,
303 BoolObjectClosure* is_alive,
304 OopClosure* keep_alive,
305 VoidClosure* complete_gc,
306 YieldClosure* yield);
307 private:
308 // round-robin mod _num_q (not: _not_ mode _max_num_q)
309 uint next_id() {
310 uint id = _next_id;
311 assert(!_discovery_is_mt, "Round robin should only be used in serial discovery");
312 if (++_next_id == _num_q) {
313 _next_id = 0;
314 }
315 assert(_next_id < _num_q, "_next_id %u _num_q %u _max_num_q %u", _next_id, _num_q, _max_num_q);
316 return id;
317 }
318 DiscoveredList* get_discovered_list(ReferenceType rt);
319 inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
320 HeapWord* discovered_addr);
321
322 void clear_discovered_references(DiscoveredList& refs_list);
323
324 void log_reflist_counts(DiscoveredList ref_lists[], uint active_length, size_t total_count) PRODUCT_RETURN;
325
326 // Balances reference queues.
327 void balance_queues(DiscoveredList ref_lists[]);
328
329 // Update (advance) the soft ref master clock field.
330 void update_soft_ref_master_clock();
331
332 bool is_subject_to_discovery(oop const obj) const;
333
334 public:
335 // Default parameters give you a vanilla reference processor.
336 ReferenceProcessor(BoolObjectClosure* is_subject_to_discovery,
337 bool mt_processing = false, uint mt_processing_degree = 1,
338 bool mt_discovery = false, uint mt_discovery_degree = 1,
339 bool atomic_discovery = true,
340 BoolObjectClosure* is_alive_non_header = NULL);
341
342 // RefDiscoveryPolicy values
343 enum DiscoveryPolicy {
344 ReferenceBasedDiscovery = 0,
345 ReferentBasedDiscovery = 1,
346 DiscoveryPolicyMin = ReferenceBasedDiscovery,
347 DiscoveryPolicyMax = ReferentBasedDiscovery
348 };
349
350 static void init_statics();
351
352 public:
353 // get and set "is_alive_non_header" field
354 BoolObjectClosure* is_alive_non_header() {
355 return _is_alive_non_header;
356 }
357 void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
358 _is_alive_non_header = is_alive_non_header;
359 }
360
361 BoolObjectClosure* is_subject_to_discovery_closure() const { return _is_subject_to_discovery; }
362 void set_is_subject_to_discovery_closure(BoolObjectClosure* cl) { _is_subject_to_discovery = cl; }
363
364 // start and stop weak ref discovery
365 void enable_discovery(bool check_no_refs = true);
366 void disable_discovery() { _discovering_refs = false; }
367 bool discovery_enabled() { return _discovering_refs; }
368
369 // whether discovery is atomic wrt other collectors
370 bool discovery_is_atomic() const { return _discovery_is_atomic; }
371 void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
372
373 // whether discovery is done by multiple threads same-old-timeously
374 bool discovery_is_mt() const { return _discovery_is_mt; }
375 void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
376
377 // Whether we are in a phase when _processing_ is MT.
378 bool processing_is_mt() const { return _processing_is_mt; }
379 void set_mt_processing(bool mt) { _processing_is_mt = mt; }
380
381 // whether all enqueueing of weak references is complete
382 bool enqueuing_is_done() { return _enqueuing_is_done; }
383 void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
384
385 // iterate over oops
386 void weak_oops_do(OopClosure* f); // weak roots
387
388 // Balance each of the discovered lists.
389 void balance_all_queues();
390 void verify_list(DiscoveredList& ref_list);
391
392 // Discover a Reference object, using appropriate discovery criteria
393 virtual bool discover_reference(oop obj, ReferenceType rt);
394
395 // Has discovered references that need handling
396 bool has_discovered_references();
397
398 // Process references found during GC (called by the garbage collector)
399 ReferenceProcessorStats
400 process_discovered_references(BoolObjectClosure* is_alive,
401 OopClosure* keep_alive,
402 VoidClosure* complete_gc,
403 AbstractRefProcTaskExecutor* task_executor,
404 ReferenceProcessorPhaseTimes* phase_times);
405
406 // Enqueue references at end of GC (called by the garbage collector)
407 void enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor,
408 ReferenceProcessorPhaseTimes* phase_times);
409
410 // If a discovery is in process that is being superceded, abandon it: all
411 // the discovered lists will be empty, and all the objects on them will
412 // have NULL discovered fields. Must be called only at a safepoint.
413 void abandon_partial_discovery();
414
415 size_t total_reference_count(ReferenceType rt) const;
416
417 // debugging
418 void verify_no_references_recorded() PRODUCT_RETURN;
419 void verify_referent(oop obj) PRODUCT_RETURN;
420 };
421
422 // A subject-to-discovery closure that uses a single memory span to determine the area that
423 // is subject to discovery. Useful for collectors which have contiguous generations.
424 class SpanSubjectToDiscoveryClosure : public BoolObjectClosure {
425 MemRegion _span;
426
427 public:
428 SpanSubjectToDiscoveryClosure() : BoolObjectClosure(), _span() { }
429 SpanSubjectToDiscoveryClosure(MemRegion span) : BoolObjectClosure(), _span(span) { }
430
431 MemRegion span() const { return _span; }
432
433 void set_span(MemRegion mr) {
434 _span = mr;
435 }
436
437 virtual bool do_object_b(oop obj) {
438 return _span.contains(obj);
439 }
440 };
441
442 // A utility class to disable reference discovery in
443 // the scope which contains it, for given ReferenceProcessor.
444 class NoRefDiscovery: StackObj {
445 private:
446 ReferenceProcessor* _rp;
447 bool _was_discovering_refs;
448 public:
449 NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
450 _was_discovering_refs = _rp->discovery_enabled();
451 if (_was_discovering_refs) {
452 _rp->disable_discovery();
453 }
454 }
455
456 ~NoRefDiscovery() {
457 if (_was_discovering_refs) {
458 _rp->enable_discovery(false /*check_no_refs*/);
459 }
460 }
461 };
462
463 // A utility class to temporarily mutate the subject discovery closure of the
464 // given ReferenceProcessor in the scope that contains it.
465 class ReferenceProcessorSubjectToDiscoveryMutator : StackObj {
466 ReferenceProcessor* _rp;
467 BoolObjectClosure* _saved_cl;
468
469 public:
470 ReferenceProcessorSubjectToDiscoveryMutator(ReferenceProcessor* rp, BoolObjectClosure* cl):
471 _rp(rp) {
472 _saved_cl = _rp->is_subject_to_discovery_closure();
473 _rp->set_is_subject_to_discovery_closure(cl);
474 }
475
476 ~ReferenceProcessorSubjectToDiscoveryMutator() {
477 _rp->set_is_subject_to_discovery_closure(_saved_cl);
478 }
479 };
480
481 // A utility class to temporarily mutate the span of the
482 // given ReferenceProcessor in the scope that contains it.
483 class ReferenceProcessorSpanMutator : StackObj {
484 ReferenceProcessor* _rp;
485 SpanSubjectToDiscoveryClosure _discoverer;
486 BoolObjectClosure* _old_discoverer;
487
488 public:
489 ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
490 MemRegion span):
491 _rp(rp), _discoverer(span) {
492 _old_discoverer = rp->is_subject_to_discovery_closure();
493 rp->set_is_subject_to_discovery_closure(&_discoverer);
494 }
495
496 ~ReferenceProcessorSpanMutator() {
497 _rp->set_is_subject_to_discovery_closure(_old_discoverer);
498 }
499 };
500
501 // A utility class to temporarily change the MT'ness of
502 // reference discovery for the given ReferenceProcessor
503 // in the scope that contains it.
504 class ReferenceProcessorMTDiscoveryMutator: StackObj {
505 private:
506 ReferenceProcessor* _rp;
507 bool _saved_mt;
508
509 public:
510 ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp,
511 bool mt):
512 _rp(rp) {
513 _saved_mt = _rp->discovery_is_mt();
514 _rp->set_mt_discovery(mt);
515 }
516
517 ~ReferenceProcessorMTDiscoveryMutator() {
518 _rp->set_mt_discovery(_saved_mt);
519 }
520 };
521
522 // A utility class to temporarily change the disposition
523 // of the "is_alive_non_header" closure field of the
524 // given ReferenceProcessor in the scope that contains it.
525 class ReferenceProcessorIsAliveMutator: StackObj {
526 private:
527 ReferenceProcessor* _rp;
528 BoolObjectClosure* _saved_cl;
529
530 public:
531 ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
532 BoolObjectClosure* cl):
533 _rp(rp) {
534 _saved_cl = _rp->is_alive_non_header();
535 _rp->set_is_alive_non_header(cl);
536 }
537
538 ~ReferenceProcessorIsAliveMutator() {
539 _rp->set_is_alive_non_header(_saved_cl);
540 }
541 };
542
543 // A utility class to temporarily change the disposition
544 // of the "discovery_is_atomic" field of the
545 // given ReferenceProcessor in the scope that contains it.
546 class ReferenceProcessorAtomicMutator: StackObj {
547 private:
548 ReferenceProcessor* _rp;
549 bool _saved_atomic_discovery;
550
551 public:
552 ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
553 bool atomic):
554 _rp(rp) {
555 _saved_atomic_discovery = _rp->discovery_is_atomic();
556 _rp->set_atomic_discovery(atomic);
557 }
558
559 ~ReferenceProcessorAtomicMutator() {
560 _rp->set_atomic_discovery(_saved_atomic_discovery);
561 }
562 };
563
564
565 // A utility class to temporarily change the MT processing
566 // disposition of the given ReferenceProcessor instance
567 // in the scope that contains it.
568 class ReferenceProcessorMTProcMutator: StackObj {
569 private:
570 ReferenceProcessor* _rp;
571 bool _saved_mt;
572
573 public:
574 ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
575 bool mt):
576 _rp(rp) {
577 _saved_mt = _rp->processing_is_mt();
578 _rp->set_mt_processing(mt);
579 }
580
581 ~ReferenceProcessorMTProcMutator() {
582 _rp->set_mt_processing(_saved_mt);
583 }
584 };
585
586
587 // This class is an interface used to implement task execution for the
588 // reference processing.
589 class AbstractRefProcTaskExecutor {
590 public:
591
592 // Abstract tasks to execute.
593 class ProcessTask;
594 class EnqueueTask;
595
596 // Executes a task using worker threads.
597 virtual void execute(ProcessTask& task) = 0;
598 virtual void execute(EnqueueTask& task) = 0;
599
600 // Switch to single threaded mode.
601 virtual void set_single_threaded_mode() { };
602 };
603
604 // Abstract reference processing task to execute.
605 class AbstractRefProcTaskExecutor::ProcessTask {
606 protected:
607 ProcessTask(ReferenceProcessor& ref_processor,
608 DiscoveredList refs_lists[],
609 bool marks_oops_alive,
610 ReferenceProcessorPhaseTimes* phase_times)
611 : _ref_processor(ref_processor),
612 _refs_lists(refs_lists),
613 _phase_times(phase_times),
614 _marks_oops_alive(marks_oops_alive)
615 { }
616
617 public:
618 virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
619 OopClosure& keep_alive,
620 VoidClosure& complete_gc) = 0;
621
622 // Returns true if a task marks some oops as alive.
623 bool marks_oops_alive() const
624 { return _marks_oops_alive; }
625
626 protected:
627 ReferenceProcessor& _ref_processor;
628 DiscoveredList* _refs_lists;
629 ReferenceProcessorPhaseTimes* _phase_times;
630 const bool _marks_oops_alive;
631 };
632
633 // Abstract reference processing task to execute.
634 class AbstractRefProcTaskExecutor::EnqueueTask {
635 protected:
636 EnqueueTask(ReferenceProcessor& ref_processor,
637 DiscoveredList refs_lists[],
638 int n_queues,
639 ReferenceProcessorPhaseTimes* phase_times)
640 : _ref_processor(ref_processor),
641 _refs_lists(refs_lists),
642 _n_queues(n_queues),
643 _phase_times(phase_times)
644 { }
645
646 public:
647 virtual void work(unsigned int work_id) = 0;
648
649 protected:
650 ReferenceProcessor& _ref_processor;
651 DiscoveredList* _refs_lists;
652 ReferenceProcessorPhaseTimes* _phase_times;
653 int _n_queues;
654 };
655
656 #endif // SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP