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.
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5 * This code is free software; you can redistribute it and/or modify it
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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).
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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/referencePolicy.hpp"
29 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
30 #include "gc/shared/referenceProcessorStats.hpp"
31 #include "memory/referenceType.hpp"
32 #include "oops/instanceRefKlass.hpp"
33
34 class GCTimer;
35
36 // ReferenceProcessor class encapsulates the per-"collector" processing
37 // of java.lang.Reference objects for GC. The interface is useful for supporting
38 // a generational abstraction, in particular when there are multiple
39 // generations that are being independently collected -- possibly
40 // concurrently and/or incrementally.
41 // ReferenceProcessor class abstracts away from a generational setting
42 // by using a closure that determines whether a given reference or referent are
43 // subject to this ReferenceProcessor's discovery, thus allowing its use in a
44 // straightforward manner in a general, non-generational, non-contiguous generation
45 // (or heap) setting.
46 //
47
48 // forward references
49 class ReferencePolicy;
50 class AbstractRefProcTaskExecutor;
51
52 // List of discovered references.
53 class DiscoveredList {
54 public:
55 DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { }
56 inline oop head() const;
57 HeapWord* adr_head() {
58 return UseCompressedOops ? (HeapWord*)&_compressed_head :
59 (HeapWord*)&_oop_head;
60 }
61 inline void set_head(oop o);
62 inline bool is_empty() const;
63 size_t length() { return _len; }
64 void set_length(size_t len) { _len = len; }
65 void inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); }
66 void dec_length(size_t dec) { _len -= dec; }
67 private:
68 // Set value depending on UseCompressedOops. This could be a template class
69 // but then we have to fix all the instantiations and declarations that use this class.
70 oop _oop_head;
71 narrowOop _compressed_head;
72 size_t _len;
73 };
74
75 // Iterator for the list of discovered references.
76 class DiscoveredListIterator {
77 private:
78 DiscoveredList& _refs_list;
79 HeapWord* _prev_discovered_addr;
80 oop _prev_discovered;
81 oop _current_discovered;
82 HeapWord* _discovered_addr;
83 oop _next_discovered;
84
85 HeapWord* _referent_addr;
86 oop _referent;
87
88 OopClosure* _keep_alive;
89 BoolObjectClosure* _is_alive;
90
91 DEBUG_ONLY(
92 oop _first_seen; // cyclic linked list check
93 )
94
95 NOT_PRODUCT(
96 size_t _processed;
97 size_t _removed;
98 )
99
100 public:
101 inline DiscoveredListIterator(DiscoveredList& refs_list,
102 OopClosure* keep_alive,
103 BoolObjectClosure* is_alive);
104
105 // End Of List.
106 inline bool has_next() const { return _current_discovered != NULL; }
107
108 // Get oop to the Reference object.
109 inline oop obj() const { return _current_discovered; }
110
111 // Get oop to the referent object.
112 inline oop referent() const { return _referent; }
113
114 // Returns true if referent is alive.
115 inline bool is_referent_alive() const {
116 return _is_alive->do_object_b(_referent);
117 }
118
119 // Loads data for the current reference.
120 // The "allow_null_referent" argument tells us to allow for the possibility
121 // of a NULL referent in the discovered Reference object. This typically
122 // happens in the case of concurrent collectors that may have done the
123 // discovery concurrently, or interleaved, with mutator execution.
124 void load_ptrs(DEBUG_ONLY(bool allow_null_referent));
125
126 // Move to the next discovered reference.
127 inline void next() {
128 _prev_discovered_addr = _discovered_addr;
129 _prev_discovered = _current_discovered;
130 move_to_next();
131 }
132
133 // Remove the current reference from the list
134 void remove();
135
136 // Make the referent alive.
137 inline void make_referent_alive() {
138 if (UseCompressedOops) {
139 _keep_alive->do_oop((narrowOop*)_referent_addr);
140 } else {
141 _keep_alive->do_oop((oop*)_referent_addr);
142 }
143 }
144
145 // NULL out referent pointer.
146 void clear_referent();
147
148 // Statistics
149 NOT_PRODUCT(
150 inline size_t processed() const { return _processed; }
151 inline size_t removed() const { return _removed; }
152 )
153
154 inline void move_to_next() {
155 if (_current_discovered == _next_discovered) {
156 // End of the list.
157 _current_discovered = NULL;
158 } else {
159 _current_discovered = _next_discovered;
160 }
161 assert(_current_discovered != _first_seen, "cyclic ref_list found");
162 NOT_PRODUCT(_processed++);
163 }
164 };
165
166 class ReferenceProcessor : public CHeapObj<mtGC> {
167 size_t total_count(DiscoveredList lists[]) const;
168
169 // The SoftReference master timestamp clock
170 static jlong _soft_ref_timestamp_clock;
171
172 BoolObjectClosure* _is_subject_to_discovery; // determines whether a given oop is subject
173 // to this ReferenceProcessor's discovery
174 // (and further processing).
175
176 bool _discovering_refs; // true when discovery enabled
177 bool _discovery_is_atomic; // if discovery is atomic wrt
178 // other collectors in configuration
179 bool _discovery_is_mt; // true if reference discovery is MT.
180
181 bool _enqueuing_is_done; // true if all weak references enqueued
182 bool _processing_is_mt; // true during phases when
183 // reference processing is MT.
184 uint _next_id; // round-robin mod _num_queues counter in
185 // support of work distribution
186
187 // For collectors that do not keep GC liveness information
188 // in the object header, this field holds a closure that
189 // helps the reference processor determine the reachability
190 // of an oop. It is currently initialized to NULL for all
191 // collectors except for CMS and G1.
192 BoolObjectClosure* _is_alive_non_header;
193
194 // Soft ref clearing policies
195 // . the default policy
196 static ReferencePolicy* _default_soft_ref_policy;
197 // . the "clear all" policy
198 static ReferencePolicy* _always_clear_soft_ref_policy;
199 // . the current policy below is either one of the above
200 ReferencePolicy* _current_soft_ref_policy;
201
202 // The discovered ref lists themselves
203
204 // The active MT'ness degree of the queues below
205 uint _num_queues;
206 // The maximum MT'ness degree of the queues below
207 uint _max_num_queues;
208
209 // Master array of discovered oops
210 DiscoveredList* _discovered_refs;
211
212 // Arrays of lists of oops, one per thread (pointers into master array above)
213 DiscoveredList* _discoveredSoftRefs;
214 DiscoveredList* _discoveredWeakRefs;
215 DiscoveredList* _discoveredFinalRefs;
216 DiscoveredList* _discoveredPhantomRefs;
217
218 public:
219 static int number_of_subclasses_of_ref() { return (REF_PHANTOM - REF_OTHER); }
220
221 uint num_queues() const { return _num_queues; }
222 uint max_num_queues() const { return _max_num_queues; }
223 void set_active_mt_degree(uint v);
224
225 DiscoveredList* discovered_refs() { return _discovered_refs; }
226
227 ReferencePolicy* setup_policy(bool always_clear) {
228 _current_soft_ref_policy = always_clear ?
229 _always_clear_soft_ref_policy : _default_soft_ref_policy;
230 _current_soft_ref_policy->setup(); // snapshot the policy threshold
231 return _current_soft_ref_policy;
232 }
233
234 // Process references with a certain reachability level.
235 void process_discovered_reflist(DiscoveredList refs_lists[],
236 ReferencePolicy* policy,
237 bool clear_referent,
238 BoolObjectClosure* is_alive,
239 OopClosure* keep_alive,
240 VoidClosure* complete_gc,
241 AbstractRefProcTaskExecutor* task_executor,
242 ReferenceProcessorPhaseTimes* phase_times);
243
244 // Work methods used by the method process_discovered_reflist
245 // Phase1: keep alive all those referents that are otherwise
246 // dead but which must be kept alive by policy (and their closure).
247 void process_phase1(DiscoveredList& refs_list,
248 ReferencePolicy* policy,
249 BoolObjectClosure* is_alive,
250 OopClosure* keep_alive,
251 VoidClosure* complete_gc);
252 // Phase2: remove all those references whose referents are
253 // reachable.
254 void process_phase2(DiscoveredList& refs_list,
255 BoolObjectClosure* is_alive,
256 OopClosure* keep_alive,
257 VoidClosure* complete_gc);
258 // Work methods in support of process_phase2
259 void pp2_work(DiscoveredList& refs_list,
260 BoolObjectClosure* is_alive,
261 OopClosure* keep_alive);
262 void pp2_work_concurrent_discovery(
263 DiscoveredList& refs_list,
264 BoolObjectClosure* is_alive,
265 OopClosure* keep_alive,
266 VoidClosure* complete_gc);
267 // Phase3: process the referents by either clearing them
268 // or keeping them alive (and their closure), and enqueuing them.
269 void process_phase3(DiscoveredList& refs_list,
270 bool clear_referent,
271 BoolObjectClosure* is_alive,
272 OopClosure* keep_alive,
273 VoidClosure* complete_gc);
274
275 // Enqueue references with a certain reachability level
276 void enqueue_discovered_reflist(DiscoveredList& refs_list);
277
278 // "Preclean" all the discovered reference lists
279 // by removing references with strongly reachable referents.
280 // The first argument is a predicate on an oop that indicates
281 // its (strong) reachability and the second is a closure that
282 // may be used to incrementalize or abort the precleaning process.
283 // The caller is responsible for taking care of potential
284 // interference with concurrent operations on these lists
285 // (or predicates involved) by other threads. Currently
286 // only used by the CMS collector.
287 void preclean_discovered_references(BoolObjectClosure* is_alive,
288 OopClosure* keep_alive,
289 VoidClosure* complete_gc,
290 YieldClosure* yield,
291 GCTimer* gc_timer);
292
293 // Returns the name of the discovered reference list
294 // occupying the i / _num_queues slot.
295 const char* list_name(uint i);
296
297 void enqueue_discovered_reflists(AbstractRefProcTaskExecutor* task_executor,
298 ReferenceProcessorPhaseTimes* phase_times);
299
300 // "Preclean" the given discovered reference list
301 // by removing references with strongly reachable referents.
302 // Currently used in support of CMS only.
303 void preclean_discovered_reflist(DiscoveredList& refs_list,
304 BoolObjectClosure* is_alive,
305 OopClosure* keep_alive,
306 VoidClosure* complete_gc,
307 YieldClosure* yield);
308 private:
309 // round-robin mod _num_queues (not: _not_ mod _max_num_queues)
310 uint next_id() {
311 uint id = _next_id;
312 assert(!_discovery_is_mt, "Round robin should only be used in serial discovery");
313 if (++_next_id == _num_queues) {
314 _next_id = 0;
315 }
316 assert(_next_id < _num_queues, "_next_id %u _num_queues %u _max_num_queues %u", _next_id, _num_queues, _max_num_queues);
317 return id;
318 }
319 DiscoveredList* get_discovered_list(ReferenceType rt);
320 inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
321 HeapWord* discovered_addr);
322
323 void clear_discovered_references(DiscoveredList& refs_list);
324
325 void log_reflist_counts(DiscoveredList ref_lists[], uint active_length, size_t total_count) PRODUCT_RETURN;
326
327 // Balances reference queues.
328 void balance_queues(DiscoveredList ref_lists[]);
329
330 // Update (advance) the soft ref master clock field.
331 void update_soft_ref_master_clock();
332
333 template <class T>
334 bool is_subject_to_discovery(T const obj) const;
335 public:
336 // Default parameters give you a vanilla reference processor.
337 ReferenceProcessor(BoolObjectClosure* is_subject_to_discovery,
338 bool mt_processing = false, uint mt_processing_degree = 1,
339 bool mt_discovery = false, uint mt_discovery_degree = 1,
340 bool atomic_discovery = true,
341 BoolObjectClosure* is_alive_non_header = NULL);
342
343 // RefDiscoveryPolicy values
344 enum DiscoveryPolicy {
345 ReferenceBasedDiscovery = 0,
346 ReferentBasedDiscovery = 1,
347 DiscoveryPolicyMin = ReferenceBasedDiscovery,
348 DiscoveryPolicyMax = ReferentBasedDiscovery
349 };
350
351 static void init_statics();
352
353 public:
354 // get and set "is_alive_non_header" field
355 BoolObjectClosure* is_alive_non_header() {
356 return _is_alive_non_header;
357 }
358 void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
359 _is_alive_non_header = is_alive_non_header;
360 }
361
362 BoolObjectClosure* is_subject_to_discovery_closure() const { return _is_subject_to_discovery; }
363 void set_is_subject_to_discovery_closure(BoolObjectClosure* cl) { _is_subject_to_discovery = cl; }
364
365 // start and stop weak ref discovery
366 void enable_discovery(bool check_no_refs = true);
367 void disable_discovery() { _discovering_refs = false; }
368 bool discovery_enabled() { return _discovering_refs; }
369
370 // whether discovery is atomic wrt other collectors
371 bool discovery_is_atomic() const { return _discovery_is_atomic; }
372 void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
373
374 // whether discovery is done by multiple threads same-old-timeously
375 bool discovery_is_mt() const { return _discovery_is_mt; }
376 void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
377
378 // Whether we are in a phase when _processing_ is MT.
379 bool processing_is_mt() const { return _processing_is_mt; }
380 void set_mt_processing(bool mt) { _processing_is_mt = mt; }
381
382 // whether all enqueueing of weak references is complete
383 bool enqueuing_is_done() { return _enqueuing_is_done; }
384 void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
385
386 // iterate over oops
387 void weak_oops_do(OopClosure* f); // weak roots
388
389 // Balance each of the discovered lists.
390 void balance_all_queues();
391 void verify_list(DiscoveredList& ref_list);
392
393 // Discover a Reference object, using appropriate discovery criteria
394 bool discover_reference(oop obj, ReferenceType rt);
395
396 // Has discovered references that need handling
397 bool has_discovered_references();
398
399 // Process references found during GC (called by the garbage collector)
400 ReferenceProcessorStats
401 process_discovered_references(BoolObjectClosure* is_alive,
402 OopClosure* keep_alive,
403 VoidClosure* complete_gc,
404 AbstractRefProcTaskExecutor* task_executor,
405 ReferenceProcessorPhaseTimes* phase_times);
406
407 // Enqueue references at end of GC (called by the garbage collector)
408 void enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor,
409 ReferenceProcessorPhaseTimes* phase_times);
410
411 // If a discovery is in process that is being superceded, abandon it: all
412 // the discovered lists will be empty, and all the objects on them will
413 // have NULL discovered fields. Must be called only at a safepoint.
414 void abandon_partial_discovery();
415
416 size_t total_reference_count(ReferenceType rt) const;
417
418 // debugging
419 void verify_no_references_recorded() PRODUCT_RETURN;
420 void verify_referent(oop obj) PRODUCT_RETURN;
421 };
422
423 // A reference processor that uses a single memory span to determine the area that
424 // is subject to discovery. Useful for collectors which have contiguous generations.
425 class SpanReferenceProcessor : public ReferenceProcessor {
426 class SpanBasedDiscoverer : public BoolObjectClosure {
427 public:
428 MemRegion _span;
429
430 SpanBasedDiscoverer(MemRegion span) : BoolObjectClosure(), _span(span) { }
431
432 virtual bool do_object_b(oop obj) {
433 return _span.contains(obj);
434 }
435 };
436
437 SpanBasedDiscoverer _span_based_discoverer;
438 public:
439 SpanReferenceProcessor(MemRegion span,
440 bool mt_processing = false, uint mt_processing_degree = 1,
441 bool mt_discovery = false, uint mt_discovery_degree = 1,
442 bool atomic_discovery = true,
443 BoolObjectClosure* is_alive_non_header = NULL);
444
445 // get and set span
446 MemRegion span() { return _span_based_discoverer._span; }
447 void set_span(MemRegion span) { _span_based_discoverer._span = span; }
448 };
449
450 // A utility class to disable reference discovery in
451 // the scope which contains it, for given ReferenceProcessor.
452 class NoRefDiscovery: StackObj {
453 private:
454 ReferenceProcessor* _rp;
455 bool _was_discovering_refs;
456 public:
457 NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
458 _was_discovering_refs = _rp->discovery_enabled();
459 if (_was_discovering_refs) {
460 _rp->disable_discovery();
461 }
462 }
463
464 ~NoRefDiscovery() {
465 if (_was_discovering_refs) {
466 _rp->enable_discovery(false /*check_no_refs*/);
467 }
468 }
469 };
470
471 // A utility class to temporarily mutate the subject discovery closure of the
472 // given ReferenceProcessor in the scope that contains it.
473 class ReferenceProcessorSubjectToDiscoveryMutator : StackObj {
474 private:
475 ReferenceProcessor* _rp;
476 BoolObjectClosure* _saved_cl;
477
478 public:
479 ReferenceProcessorSubjectToDiscoveryMutator(ReferenceProcessor* rp, BoolObjectClosure* cl):
480 _rp(rp) {
481 _saved_cl = _rp->is_subject_to_discovery_closure();
482 _rp->set_is_subject_to_discovery_closure(cl);
483 }
484
485 ~ReferenceProcessorSubjectToDiscoveryMutator() {
486 _rp->set_is_subject_to_discovery_closure(_saved_cl);
487 }
488 };
489
490 // A utility class to temporarily mutate the span of the
491 // given ReferenceProcessor in the scope that contains it.
492 class ReferenceProcessorSpanMutator: StackObj {
493 private:
494 SpanReferenceProcessor* _rp;
495 MemRegion _saved_span;
496
497 public:
498 ReferenceProcessorSpanMutator(SpanReferenceProcessor* rp,
499 MemRegion span):
500 _rp(rp) {
501 _saved_span = _rp->span();
502 _rp->set_span(span);
503 }
504
505 ~ReferenceProcessorSpanMutator() {
506 _rp->set_span(_saved_span);
507 }
508 };
509
510 // A utility class to temporarily change the MT'ness of
511 // reference discovery for the given ReferenceProcessor
512 // in the scope that contains it.
513 class ReferenceProcessorMTDiscoveryMutator: StackObj {
514 private:
515 ReferenceProcessor* _rp;
516 bool _saved_mt;
517
518 public:
519 ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp,
520 bool mt):
521 _rp(rp) {
522 _saved_mt = _rp->discovery_is_mt();
523 _rp->set_mt_discovery(mt);
524 }
525
526 ~ReferenceProcessorMTDiscoveryMutator() {
527 _rp->set_mt_discovery(_saved_mt);
528 }
529 };
530
531 // A utility class to temporarily change the disposition
532 // of the "is_alive_non_header" closure field of the
533 // given ReferenceProcessor in the scope that contains it.
534 class ReferenceProcessorIsAliveMutator: StackObj {
535 private:
536 ReferenceProcessor* _rp;
537 BoolObjectClosure* _saved_cl;
538
539 public:
540 ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
541 BoolObjectClosure* cl):
542 _rp(rp) {
543 _saved_cl = _rp->is_alive_non_header();
544 _rp->set_is_alive_non_header(cl);
545 }
546
547 ~ReferenceProcessorIsAliveMutator() {
548 _rp->set_is_alive_non_header(_saved_cl);
549 }
550 };
551
552 // A utility class to temporarily change the disposition
553 // of the "discovery_is_atomic" field of the
554 // given ReferenceProcessor in the scope that contains it.
555 class ReferenceProcessorAtomicMutator: StackObj {
556 private:
557 ReferenceProcessor* _rp;
558 bool _saved_atomic_discovery;
559
560 public:
561 ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
562 bool atomic):
563 _rp(rp) {
564 _saved_atomic_discovery = _rp->discovery_is_atomic();
565 _rp->set_atomic_discovery(atomic);
566 }
567
568 ~ReferenceProcessorAtomicMutator() {
569 _rp->set_atomic_discovery(_saved_atomic_discovery);
570 }
571 };
572
573
574 // A utility class to temporarily change the MT processing
575 // disposition of the given ReferenceProcessor instance
576 // in the scope that contains it.
577 class ReferenceProcessorMTProcMutator: StackObj {
578 private:
579 ReferenceProcessor* _rp;
580 bool _saved_mt;
581
582 public:
583 ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
584 bool mt):
585 _rp(rp) {
586 _saved_mt = _rp->processing_is_mt();
587 _rp->set_mt_processing(mt);
588 }
589
590 ~ReferenceProcessorMTProcMutator() {
591 _rp->set_mt_processing(_saved_mt);
592 }
593 };
594
595
596 // This class is an interface used to implement task execution for the
597 // reference processing.
598 class AbstractRefProcTaskExecutor {
599 public:
600
601 // Abstract tasks to execute.
602 class ProcessTask;
603 class EnqueueTask;
604
605 // Executes a task using worker threads.
606 virtual void execute(ProcessTask& task) = 0;
607 virtual void execute(EnqueueTask& task) = 0;
608
609 // Switch to single threaded mode.
610 virtual void set_single_threaded_mode() { };
611 };
612
613 // Abstract reference processing task to execute.
614 class AbstractRefProcTaskExecutor::ProcessTask {
615 protected:
616 ProcessTask(ReferenceProcessor& ref_processor,
617 DiscoveredList refs_lists[],
618 bool marks_oops_alive,
619 ReferenceProcessorPhaseTimes* phase_times)
620 : _ref_processor(ref_processor),
621 _refs_lists(refs_lists),
622 _phase_times(phase_times),
623 _marks_oops_alive(marks_oops_alive)
624 { }
625
626 public:
627 virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
628 OopClosure& keep_alive,
629 VoidClosure& complete_gc) = 0;
630
631 // Returns true if a task marks some oops as alive.
632 bool marks_oops_alive() const
633 { return _marks_oops_alive; }
634
635 protected:
636 ReferenceProcessor& _ref_processor;
637 DiscoveredList* _refs_lists;
638 ReferenceProcessorPhaseTimes* _phase_times;
639 const bool _marks_oops_alive;
640 };
641
642 // Abstract reference processing task to execute.
643 class AbstractRefProcTaskExecutor::EnqueueTask {
644 protected:
645 EnqueueTask(ReferenceProcessor& ref_processor,
646 DiscoveredList refs_lists[],
647 int n_queues,
648 ReferenceProcessorPhaseTimes* phase_times)
649 : _ref_processor(ref_processor),
650 _refs_lists(refs_lists),
651 _n_queues(n_queues),
652 _phase_times(phase_times)
653 { }
654
655 public:
656 virtual void work(unsigned int work_id) = 0;
657
658 protected:
659 ReferenceProcessor& _ref_processor;
660 DiscoveredList* _refs_lists;
661 ReferenceProcessorPhaseTimes* _phase_times;
662 int _n_queues;
663 };
664
665 #endif // SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP