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