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.
8 *
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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).
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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_enqueue();
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 // Phase3: process the referents by either clearing them
266 // or keeping them alive (and their closure), and enqueuing them.
267 void process_phase3(DiscoveredList& refs_list,
268 bool clear_referent,
269 BoolObjectClosure* is_alive,
270 OopClosure* keep_alive,
271 VoidClosure* complete_gc);
272
273 // "Preclean" all the discovered reference lists by removing references that
274 // are active (e.g. due to the mutator calling enqueue()) or with NULL or
275 // strongly reachable referents.
276 // The first argument is a predicate on an oop that indicates
277 // its (strong) reachability and the fourth is a closure that
278 // may be used to incrementalize or abort the precleaning process.
279 // The caller is responsible for taking care of potential
280 // interference with concurrent operations on these lists
281 // (or predicates involved) by other threads.
282 void preclean_discovered_references(BoolObjectClosure* is_alive,
283 OopClosure* keep_alive,
284 VoidClosure* complete_gc,
285 YieldClosure* yield,
286 GCTimer* gc_timer);
287
288 // Returns the name of the discovered reference list
289 // occupying the i / _num_queues slot.
290 const char* list_name(uint i);
291
292 private:
293 // "Preclean" the given discovered reference list by removing references with
294 // the attributes mentioned in preclean_discovered_references().
295 // Supports both normal and fine grain yielding.
296 // Returns whether the operation should be aborted.
297 bool preclean_discovered_reflist(DiscoveredList& refs_list,
298 BoolObjectClosure* is_alive,
299 OopClosure* keep_alive,
300 VoidClosure* complete_gc,
301 YieldClosure* yield);
302
303 // round-robin mod _num_queues (not: _not_ mod _max_num_queues)
304 uint next_id() {
305 uint id = _next_id;
306 assert(!_discovery_is_mt, "Round robin should only be used in serial discovery");
307 if (++_next_id == _num_queues) {
308 _next_id = 0;
309 }
310 assert(_next_id < _num_queues, "_next_id %u _num_queues %u _max_num_queues %u", _next_id, _num_queues, _max_num_queues);
311 return id;
312 }
313 DiscoveredList* get_discovered_list(ReferenceType rt);
314 inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
315 HeapWord* discovered_addr);
316
317 void clear_discovered_references(DiscoveredList& refs_list);
318
319 void log_reflist(const char* prefix, DiscoveredList list[], uint num_active_queues);
320 void log_reflist_counts(DiscoveredList ref_lists[], uint num_active_queues) PRODUCT_RETURN;
321
322 // Balances reference queues.
323 void balance_queues(DiscoveredList ref_lists[]);
324
325 // Update (advance) the soft ref master clock field.
326 void update_soft_ref_master_clock();
327
328 bool is_subject_to_discovery(oop const obj) const;
329
330 public:
331 // Default parameters give you a vanilla reference processor.
332 ReferenceProcessor(BoolObjectClosure* is_subject_to_discovery,
333 bool mt_processing = false, uint mt_processing_degree = 1,
334 bool mt_discovery = false, uint mt_discovery_degree = 1,
335 bool atomic_discovery = true,
336 BoolObjectClosure* is_alive_non_header = NULL);
337
338 // RefDiscoveryPolicy values
339 enum DiscoveryPolicy {
340 ReferenceBasedDiscovery = 0,
341 ReferentBasedDiscovery = 1,
342 DiscoveryPolicyMin = ReferenceBasedDiscovery,
343 DiscoveryPolicyMax = ReferentBasedDiscovery
344 };
345
346 static void init_statics();
347
348 public:
349 // get and set "is_alive_non_header" field
350 BoolObjectClosure* is_alive_non_header() {
351 return _is_alive_non_header;
352 }
353 void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
354 _is_alive_non_header = is_alive_non_header;
355 }
356
357 BoolObjectClosure* is_subject_to_discovery_closure() const { return _is_subject_to_discovery; }
358 void set_is_subject_to_discovery_closure(BoolObjectClosure* cl) { _is_subject_to_discovery = cl; }
359
360 // start and stop weak ref discovery
361 void enable_discovery(bool check_no_refs = true);
362 void disable_discovery() { _discovering_refs = false; }
363 bool discovery_enabled() { return _discovering_refs; }
364
365 // whether discovery is atomic wrt other collectors
366 bool discovery_is_atomic() const { return _discovery_is_atomic; }
367 void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
368
369 // whether discovery is done by multiple threads same-old-timeously
370 bool discovery_is_mt() const { return _discovery_is_mt; }
371 void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
372
373 // Whether we are in a phase when _processing_ is MT.
374 bool processing_is_mt() const { return _processing_is_mt; }
375 void set_mt_processing(bool mt) { _processing_is_mt = mt; }
376
377 // whether all enqueueing of weak references is complete
378 bool enqueuing_is_done() { return _enqueuing_is_done; }
379 void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
380
381 // iterate over oops
382 void weak_oops_do(OopClosure* f); // weak roots
383
384 void verify_list(DiscoveredList& ref_list);
385
386 // Discover a Reference object, using appropriate discovery criteria
387 virtual bool discover_reference(oop obj, ReferenceType rt);
388
389 // Has discovered references that need handling
390 bool has_discovered_references();
391
392 // Process references found during GC (called by the garbage collector)
393 ReferenceProcessorStats
394 process_discovered_references(BoolObjectClosure* is_alive,
395 OopClosure* keep_alive,
396 VoidClosure* complete_gc,
397 AbstractRefProcTaskExecutor* task_executor,
398 ReferenceProcessorPhaseTimes* phase_times);
399
400 // If a discovery is in process that is being superceded, abandon it: all
401 // the discovered lists will be empty, and all the objects on them will
402 // have NULL discovered fields. Must be called only at a safepoint.
403 void abandon_partial_discovery();
404
405 size_t total_reference_count(ReferenceType rt) const;
406
407 // debugging
408 void verify_no_references_recorded() PRODUCT_RETURN;
409 void verify_referent(oop obj) PRODUCT_RETURN;
410 };
411
412 // A subject-to-discovery closure that uses a single memory span to determine the area that
413 // is subject to discovery. Useful for collectors which have contiguous generations.
414 class SpanSubjectToDiscoveryClosure : public BoolObjectClosure {
415 MemRegion _span;
416
417 public:
418 SpanSubjectToDiscoveryClosure() : BoolObjectClosure(), _span() { }
419 SpanSubjectToDiscoveryClosure(MemRegion span) : BoolObjectClosure(), _span(span) { }
420
421 MemRegion span() const { return _span; }
422
423 void set_span(MemRegion mr) {
424 _span = mr;
425 }
426
427 virtual bool do_object_b(oop obj) {
428 return _span.contains(obj);
429 }
430 };
431
432 // A utility class to disable reference discovery in
433 // the scope which contains it, for given ReferenceProcessor.
434 class NoRefDiscovery: StackObj {
435 private:
436 ReferenceProcessor* _rp;
437 bool _was_discovering_refs;
438 public:
439 NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
440 _was_discovering_refs = _rp->discovery_enabled();
441 if (_was_discovering_refs) {
442 _rp->disable_discovery();
443 }
444 }
445
446 ~NoRefDiscovery() {
447 if (_was_discovering_refs) {
448 _rp->enable_discovery(false /*check_no_refs*/);
449 }
450 }
451 };
452
453 // A utility class to temporarily mutate the subject discovery closure of the
454 // given ReferenceProcessor in the scope that contains it.
455 class ReferenceProcessorSubjectToDiscoveryMutator : StackObj {
456 ReferenceProcessor* _rp;
457 BoolObjectClosure* _saved_cl;
458
459 public:
460 ReferenceProcessorSubjectToDiscoveryMutator(ReferenceProcessor* rp, BoolObjectClosure* cl):
461 _rp(rp) {
462 _saved_cl = _rp->is_subject_to_discovery_closure();
463 _rp->set_is_subject_to_discovery_closure(cl);
464 }
465
466 ~ReferenceProcessorSubjectToDiscoveryMutator() {
467 _rp->set_is_subject_to_discovery_closure(_saved_cl);
468 }
469 };
470
471 // A utility class to temporarily mutate the span of the
472 // given ReferenceProcessor in the scope that contains it.
473 class ReferenceProcessorSpanMutator : StackObj {
474 ReferenceProcessor* _rp;
475 SpanSubjectToDiscoveryClosure _discoverer;
476 BoolObjectClosure* _old_discoverer;
477
478 public:
479 ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
480 MemRegion span):
481 _rp(rp),
482 _discoverer(span),
483 _old_discoverer(rp->is_subject_to_discovery_closure()) {
484
485 rp->set_is_subject_to_discovery_closure(&_discoverer);
486 }
487
488 ~ReferenceProcessorSpanMutator() {
489 _rp->set_is_subject_to_discovery_closure(_old_discoverer);
490 }
491 };
492
493 // A utility class to temporarily change the MT'ness of
494 // reference discovery for the given ReferenceProcessor
495 // in the scope that contains it.
496 class ReferenceProcessorMTDiscoveryMutator: StackObj {
497 private:
498 ReferenceProcessor* _rp;
499 bool _saved_mt;
500
501 public:
502 ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp,
503 bool mt):
504 _rp(rp) {
505 _saved_mt = _rp->discovery_is_mt();
506 _rp->set_mt_discovery(mt);
507 }
508
509 ~ReferenceProcessorMTDiscoveryMutator() {
510 _rp->set_mt_discovery(_saved_mt);
511 }
512 };
513
514 // A utility class to temporarily change the disposition
515 // of the "is_alive_non_header" closure field of the
516 // given ReferenceProcessor in the scope that contains it.
517 class ReferenceProcessorIsAliveMutator: StackObj {
518 private:
519 ReferenceProcessor* _rp;
520 BoolObjectClosure* _saved_cl;
521
522 public:
523 ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
524 BoolObjectClosure* cl):
525 _rp(rp) {
526 _saved_cl = _rp->is_alive_non_header();
527 _rp->set_is_alive_non_header(cl);
528 }
529
530 ~ReferenceProcessorIsAliveMutator() {
531 _rp->set_is_alive_non_header(_saved_cl);
532 }
533 };
534
535 // A utility class to temporarily change the disposition
536 // of the "discovery_is_atomic" field of the
537 // given ReferenceProcessor in the scope that contains it.
538 class ReferenceProcessorAtomicMutator: StackObj {
539 private:
540 ReferenceProcessor* _rp;
541 bool _saved_atomic_discovery;
542
543 public:
544 ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
545 bool atomic):
546 _rp(rp) {
547 _saved_atomic_discovery = _rp->discovery_is_atomic();
548 _rp->set_atomic_discovery(atomic);
549 }
550
551 ~ReferenceProcessorAtomicMutator() {
552 _rp->set_atomic_discovery(_saved_atomic_discovery);
553 }
554 };
555
556
557 // A utility class to temporarily change the MT processing
558 // disposition of the given ReferenceProcessor instance
559 // in the scope that contains it.
560 class ReferenceProcessorMTProcMutator: StackObj {
561 private:
562 ReferenceProcessor* _rp;
563 bool _saved_mt;
564
565 public:
566 ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
567 bool mt):
568 _rp(rp) {
569 _saved_mt = _rp->processing_is_mt();
570 _rp->set_mt_processing(mt);
571 }
572
573 ~ReferenceProcessorMTProcMutator() {
574 _rp->set_mt_processing(_saved_mt);
575 }
576 };
577
578
579 // This class is an interface used to implement task execution for the
580 // reference processing.
581 class AbstractRefProcTaskExecutor {
582 public:
583
584 // Abstract tasks to execute.
585 class ProcessTask;
586
587 // Executes a task using worker threads.
588 virtual void execute(ProcessTask& task) = 0;
589
590 // Switch to single threaded mode.
591 virtual void set_single_threaded_mode() { };
592 };
593
594 // Abstract reference processing task to execute.
595 class AbstractRefProcTaskExecutor::ProcessTask {
596 protected:
597 ProcessTask(ReferenceProcessor& ref_processor,
598 DiscoveredList refs_lists[],
599 bool marks_oops_alive,
600 ReferenceProcessorPhaseTimes* phase_times)
601 : _ref_processor(ref_processor),
602 _refs_lists(refs_lists),
603 _phase_times(phase_times),
604 _marks_oops_alive(marks_oops_alive)
605 { }
606
607 public:
608 virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
609 OopClosure& keep_alive,
610 VoidClosure& complete_gc) = 0;
611
612 // Returns true if a task marks some oops as alive.
613 bool marks_oops_alive() const
614 { return _marks_oops_alive; }
615
616 protected:
617 ReferenceProcessor& _ref_processor;
618 DiscoveredList* _refs_lists;
619 ReferenceProcessorPhaseTimes* _phase_times;
620 const bool _marks_oops_alive;
621 };
622
623 #endif // SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP