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