1 /*
2 * Copyright (c) 2001, 2017, 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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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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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. Note, however, that the
41 // ReferenceProcessor class abstracts away from a generational setting
42 // by using only a heap interval (called "span" below), thus allowing
43 // its use in a straightforward manner in a general, non-generational
44 // setting.
45 //
46 // The basic idea is that each ReferenceProcessor object concerns
47 // itself with ("weak") reference processing in a specific "span"
48 // of the heap of interest to a specific collector. Currently,
49 // the span is a convex interval of the heap, but, efficiency
50 // apart, there seems to be no reason it couldn't be extended
51 // (with appropriate modifications) to any "non-convex interval".
52
53 // forward references
54 class ReferencePolicy;
55 class AbstractRefProcTaskExecutor;
56
57 // List of discovered references.
58 class DiscoveredList {
59 public:
60 DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { }
61 inline oop head() const;
62 HeapWord* adr_head() {
63 return UseCompressedOops ? (HeapWord*)&_compressed_head :
64 (HeapWord*)&_oop_head;
65 }
66 inline void set_head(oop o);
67 inline bool is_empty() const;
68 size_t length() { return _len; }
69 void set_length(size_t len) { _len = len; }
70 void inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); }
71 void dec_length(size_t dec) { _len -= dec; }
72 private:
73 // Set value depending on UseCompressedOops. This could be a template class
74 // but then we have to fix all the instantiations and declarations that use this class.
75 oop _oop_head;
76 narrowOop _compressed_head;
77 size_t _len;
78 };
79
80 // Iterator for the list of discovered references.
81 class DiscoveredListIterator {
82 private:
83 DiscoveredList& _refs_list;
84 HeapWord* _prev_next;
85 oop _prev;
86 oop _ref;
87 HeapWord* _discovered_addr;
88 oop _next;
89 HeapWord* _referent_addr;
90 oop _referent;
91 OopClosure* _keep_alive;
92 BoolObjectClosure* _is_alive;
93
94 DEBUG_ONLY(
95 oop _first_seen; // cyclic linked list check
96 )
97
98 NOT_PRODUCT(
99 size_t _processed;
100 size_t _removed;
101 )
102
103 public:
104 inline DiscoveredListIterator(DiscoveredList& refs_list,
105 OopClosure* keep_alive,
106 BoolObjectClosure* is_alive);
107
108 // End Of List.
109 inline bool has_next() const { return _ref != NULL; }
110
111 // Get oop to the Reference object.
112 inline oop obj() const { return _ref; }
113
114 // Get oop to the referent object.
115 inline oop referent() const { return _referent; }
116
117 // Returns true if referent is alive.
118 inline bool is_referent_alive() const {
119 return _is_alive->do_object_b(_referent);
120 }
121
122 // Loads data for the current reference.
123 // The "allow_null_referent" argument tells us to allow for the possibility
124 // of a NULL referent in the discovered Reference object. This typically
125 // happens in the case of concurrent collectors that may have done the
126 // discovery concurrently, or interleaved, with mutator execution.
127 void load_ptrs(DEBUG_ONLY(bool allow_null_referent));
128
129 // Move to the next discovered reference.
130 inline void next() {
131 _prev_next = _discovered_addr;
132 _prev = _ref;
133 move_to_next();
134 }
135
136 // Remove the current reference from the list
137 void remove();
138
139 // Make the referent alive.
140 inline void make_referent_alive() {
141 if (UseCompressedOops) {
142 _keep_alive->do_oop((narrowOop*)_referent_addr);
143 } else {
144 _keep_alive->do_oop((oop*)_referent_addr);
145 }
146 }
147
148 // NULL out referent pointer.
149 void clear_referent();
150
151 // Statistics
152 NOT_PRODUCT(
153 inline size_t processed() const { return _processed; }
154 inline size_t removed() const { return _removed; }
155 )
156
157 inline void move_to_next() {
158 if (_ref == _next) {
159 // End of the list.
160 _ref = NULL;
161 } else {
162 _ref = _next;
163 }
164 assert(_ref != _first_seen, "cyclic ref_list found");
165 NOT_PRODUCT(_processed++);
166 }
167 };
168
169 class ReferenceProcessor : public CHeapObj<mtGC> {
170
171 private:
172 size_t total_count(DiscoveredList lists[]) const;
173
174 protected:
175 // The SoftReference master timestamp clock
176 static jlong _soft_ref_timestamp_clock;
177
178 MemRegion _span; // (right-open) interval of heap
179 // subject to wkref discovery
180
181 bool _discovering_refs; // true when discovery enabled
182 bool _discovery_is_atomic; // if discovery is atomic wrt
183 // other collectors in configuration
184 bool _discovery_is_mt; // true if reference discovery is MT.
185
186 bool _enqueuing_is_done; // true if all weak references enqueued
187 bool _processing_is_mt; // true during phases when
188 // reference processing is MT.
189 uint _next_id; // round-robin mod _num_q counter in
190 // support of work distribution
191
192 // For collectors that do not keep GC liveness information
193 // in the object header, this field holds a closure that
194 // helps the reference processor determine the reachability
195 // of an oop. It is currently initialized to NULL for all
196 // collectors except for CMS and G1.
197 BoolObjectClosure* _is_alive_non_header;
198
199 // Soft ref clearing policies
200 // . the default policy
201 static ReferencePolicy* _default_soft_ref_policy;
202 // . the "clear all" policy
203 static ReferencePolicy* _always_clear_soft_ref_policy;
204 // . the current policy below is either one of the above
205 ReferencePolicy* _current_soft_ref_policy;
206
207 // The discovered ref lists themselves
208
209 // The active MT'ness degree of the queues below
210 uint _num_q;
211 // The maximum MT'ness degree of the queues below
212 uint _max_num_q;
213
214 // Master array of discovered oops
215 DiscoveredList* _discovered_refs;
216
217 // Arrays of lists of oops, one per thread (pointers into master array above)
218 DiscoveredList* _discoveredSoftRefs;
219 DiscoveredList* _discoveredWeakRefs;
220 DiscoveredList* _discoveredFinalRefs;
221 DiscoveredList* _discoveredPhantomRefs;
222
223 public:
224 static int number_of_subclasses_of_ref() { return (REF_PHANTOM - REF_OTHER); }
225
226 uint num_q() { return _num_q; }
227 uint max_num_q() { return _max_num_q; }
228 void set_active_mt_degree(uint v);
229
230 DiscoveredList* discovered_refs() { return _discovered_refs; }
231
232 ReferencePolicy* setup_policy(bool always_clear) {
233 _current_soft_ref_policy = always_clear ?
234 _always_clear_soft_ref_policy : _default_soft_ref_policy;
235 _current_soft_ref_policy->setup(); // snapshot the policy threshold
236 return _current_soft_ref_policy;
237 }
238
239 // Process references with a certain reachability level.
240 void process_discovered_reflist(DiscoveredList refs_lists[],
241 ReferencePolicy* policy,
242 bool clear_referent,
243 BoolObjectClosure* is_alive,
244 OopClosure* keep_alive,
245 VoidClosure* complete_gc,
246 AbstractRefProcTaskExecutor* task_executor,
247 ReferenceProcessorPhaseTimes* phase_times);
248
249 size_t process_phaseHeapSampling(BoolObjectClosure* is_alive,
250 OopClosure* keep_alive,
251 VoidClosure* complete_gc);
252
253 // Work methods used by the method process_discovered_reflist
254 // Phase1: keep alive all those referents that are otherwise
255 // dead but which must be kept alive by policy (and their closure).
256 void process_phase1(DiscoveredList& refs_list,
257 ReferencePolicy* policy,
258 BoolObjectClosure* is_alive,
259 OopClosure* keep_alive,
260 VoidClosure* complete_gc);
261 // Phase2: remove all those references whose referents are
262 // reachable.
263 inline void process_phase2(DiscoveredList& refs_list,
264 BoolObjectClosure* is_alive,
265 OopClosure* keep_alive,
266 VoidClosure* complete_gc) {
267 if (discovery_is_atomic()) {
268 // complete_gc is ignored in this case for this phase
269 pp2_work(refs_list, is_alive, keep_alive);
270 } else {
271 assert(complete_gc != NULL, "Error");
272 pp2_work_concurrent_discovery(refs_list, is_alive,
273 keep_alive, complete_gc);
274 }
275 }
276 // Work methods in support of process_phase2
277 void pp2_work(DiscoveredList& refs_list,
278 BoolObjectClosure* is_alive,
279 OopClosure* keep_alive);
280 void pp2_work_concurrent_discovery(
281 DiscoveredList& refs_list,
282 BoolObjectClosure* is_alive,
283 OopClosure* keep_alive,
284 VoidClosure* complete_gc);
285 // Phase3: process the referents by either clearing them
286 // or keeping them alive (and their closure)
287 void process_phase3(DiscoveredList& refs_list,
288 bool clear_referent,
289 BoolObjectClosure* is_alive,
290 OopClosure* keep_alive,
291 VoidClosure* complete_gc);
292
293 // Enqueue references with a certain reachability level
294 void enqueue_discovered_reflist(DiscoveredList& refs_list);
295
296 // "Preclean" all the discovered reference lists
297 // by removing references with strongly reachable referents.
298 // The first argument is a predicate on an oop that indicates
299 // its (strong) reachability and the second is a closure that
300 // may be used to incrementalize or abort the precleaning process.
301 // The caller is responsible for taking care of potential
302 // interference with concurrent operations on these lists
303 // (or predicates involved) by other threads. Currently
304 // only used by the CMS collector.
305 void preclean_discovered_references(BoolObjectClosure* is_alive,
306 OopClosure* keep_alive,
307 VoidClosure* complete_gc,
308 YieldClosure* yield,
309 GCTimer* gc_timer);
310
311 // Returns the name of the discovered reference list
312 // occupying the i / _num_q slot.
313 const char* list_name(uint i);
314
315 void enqueue_discovered_reflists(AbstractRefProcTaskExecutor* task_executor,
316 ReferenceProcessorPhaseTimes* phase_times);
317
318 protected:
319 // "Preclean" the given discovered reference list
320 // by removing references with strongly reachable referents.
321 // Currently used in support of CMS only.
322 void preclean_discovered_reflist(DiscoveredList& refs_list,
323 BoolObjectClosure* is_alive,
324 OopClosure* keep_alive,
325 VoidClosure* complete_gc,
326 YieldClosure* yield);
327
328 // round-robin mod _num_q (not: _not_ mode _max_num_q)
329 uint next_id() {
330 uint id = _next_id;
331 assert(!_discovery_is_mt, "Round robin should only be used in serial discovery");
332 if (++_next_id == _num_q) {
333 _next_id = 0;
334 }
335 assert(_next_id < _num_q, "_next_id %u _num_q %u _max_num_q %u", _next_id, _num_q, _max_num_q);
336 return id;
337 }
338 DiscoveredList* get_discovered_list(ReferenceType rt);
339 inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
340 HeapWord* discovered_addr);
341
342 void clear_discovered_references(DiscoveredList& refs_list);
343
344 void log_reflist_counts(DiscoveredList ref_lists[], uint active_length, size_t total_count) PRODUCT_RETURN;
345
346 // Balances reference queues.
347 void balance_queues(DiscoveredList ref_lists[]);
348
349 // Update (advance) the soft ref master clock field.
350 void update_soft_ref_master_clock();
351
352 public:
353 // Default parameters give you a vanilla reference processor.
354 ReferenceProcessor(MemRegion span,
355 bool mt_processing = false, uint mt_processing_degree = 1,
356 bool mt_discovery = false, uint mt_discovery_degree = 1,
357 bool atomic_discovery = true,
358 BoolObjectClosure* is_alive_non_header = NULL);
359
360 // RefDiscoveryPolicy values
361 enum DiscoveryPolicy {
362 ReferenceBasedDiscovery = 0,
363 ReferentBasedDiscovery = 1,
364 DiscoveryPolicyMin = ReferenceBasedDiscovery,
365 DiscoveryPolicyMax = ReferentBasedDiscovery
366 };
367
368 static void init_statics();
369
370 public:
371 // get and set "is_alive_non_header" field
372 BoolObjectClosure* is_alive_non_header() {
373 return _is_alive_non_header;
374 }
375 void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
376 _is_alive_non_header = is_alive_non_header;
377 }
378
379 // get and set span
380 MemRegion span() { return _span; }
381 void set_span(MemRegion span) { _span = span; }
382
383 // start and stop weak ref discovery
384 void enable_discovery(bool check_no_refs = true);
385 void disable_discovery() { _discovering_refs = false; }
386 bool discovery_enabled() { return _discovering_refs; }
387
388 // whether discovery is atomic wrt other collectors
389 bool discovery_is_atomic() const { return _discovery_is_atomic; }
390 void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
391
392 // whether discovery is done by multiple threads same-old-timeously
393 bool discovery_is_mt() const { return _discovery_is_mt; }
394 void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
395
396 // Whether we are in a phase when _processing_ is MT.
397 bool processing_is_mt() const { return _processing_is_mt; }
398 void set_mt_processing(bool mt) { _processing_is_mt = mt; }
399
400 // whether all enqueueing of weak references is complete
401 bool enqueuing_is_done() { return _enqueuing_is_done; }
402 void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
403
404 // iterate over oops
405 void weak_oops_do(OopClosure* f); // weak roots
406
407 // Balance each of the discovered lists.
408 void balance_all_queues();
409 void verify_list(DiscoveredList& ref_list);
410
411 // Discover a Reference object, using appropriate discovery criteria
412 bool discover_reference(oop obj, ReferenceType rt);
413
414 // Has discovered references that need handling
415 bool has_discovered_references();
416
417 // Process references found during GC (called by the garbage collector)
418 ReferenceProcessorStats
419 process_discovered_references(BoolObjectClosure* is_alive,
420 OopClosure* keep_alive,
421 VoidClosure* complete_gc,
422 AbstractRefProcTaskExecutor* task_executor,
423 ReferenceProcessorPhaseTimes* phase_times);
424
425 // Enqueue references at end of GC (called by the garbage collector)
426 void enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor,
427 ReferenceProcessorPhaseTimes* phase_times);
428
429 // If a discovery is in process that is being superceded, abandon it: all
430 // the discovered lists will be empty, and all the objects on them will
431 // have NULL discovered fields. Must be called only at a safepoint.
432 void abandon_partial_discovery();
433
434 size_t total_reference_count(ReferenceType rt) const;
435
436 // debugging
437 void verify_no_references_recorded() PRODUCT_RETURN;
438 void verify_referent(oop obj) PRODUCT_RETURN;
439 };
440
441 // A utility class to disable reference discovery in
442 // the scope which contains it, for given ReferenceProcessor.
443 class NoRefDiscovery: StackObj {
444 private:
445 ReferenceProcessor* _rp;
446 bool _was_discovering_refs;
447 public:
448 NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
449 _was_discovering_refs = _rp->discovery_enabled();
450 if (_was_discovering_refs) {
451 _rp->disable_discovery();
452 }
453 }
454
455 ~NoRefDiscovery() {
456 if (_was_discovering_refs) {
457 _rp->enable_discovery(false /*check_no_refs*/);
458 }
459 }
460 };
461
462
463 // A utility class to temporarily mutate the span of the
464 // given ReferenceProcessor in the scope that contains it.
465 class ReferenceProcessorSpanMutator: StackObj {
466 private:
467 ReferenceProcessor* _rp;
468 MemRegion _saved_span;
469
470 public:
471 ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
472 MemRegion span):
473 _rp(rp) {
474 _saved_span = _rp->span();
475 _rp->set_span(span);
476 }
477
478 ~ReferenceProcessorSpanMutator() {
479 _rp->set_span(_saved_span);
480 }
481 };
482
483 // A utility class to temporarily change the MT'ness of
484 // reference discovery for the given ReferenceProcessor
485 // in the scope that contains it.
486 class ReferenceProcessorMTDiscoveryMutator: StackObj {
487 private:
488 ReferenceProcessor* _rp;
489 bool _saved_mt;
490
491 public:
492 ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp,
493 bool mt):
494 _rp(rp) {
495 _saved_mt = _rp->discovery_is_mt();
496 _rp->set_mt_discovery(mt);
497 }
498
499 ~ReferenceProcessorMTDiscoveryMutator() {
500 _rp->set_mt_discovery(_saved_mt);
501 }
502 };
503
504
505 // A utility class to temporarily change the disposition
506 // of the "is_alive_non_header" closure field of the
507 // given ReferenceProcessor in the scope that contains it.
508 class ReferenceProcessorIsAliveMutator: StackObj {
509 private:
510 ReferenceProcessor* _rp;
511 BoolObjectClosure* _saved_cl;
512
513 public:
514 ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
515 BoolObjectClosure* cl):
516 _rp(rp) {
517 _saved_cl = _rp->is_alive_non_header();
518 _rp->set_is_alive_non_header(cl);
519 }
520
521 ~ReferenceProcessorIsAliveMutator() {
522 _rp->set_is_alive_non_header(_saved_cl);
523 }
524 };
525
526 // A utility class to temporarily change the disposition
527 // of the "discovery_is_atomic" field of the
528 // given ReferenceProcessor in the scope that contains it.
529 class ReferenceProcessorAtomicMutator: StackObj {
530 private:
531 ReferenceProcessor* _rp;
532 bool _saved_atomic_discovery;
533
534 public:
535 ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
536 bool atomic):
537 _rp(rp) {
538 _saved_atomic_discovery = _rp->discovery_is_atomic();
539 _rp->set_atomic_discovery(atomic);
540 }
541
542 ~ReferenceProcessorAtomicMutator() {
543 _rp->set_atomic_discovery(_saved_atomic_discovery);
544 }
545 };
546
547
548 // A utility class to temporarily change the MT processing
549 // disposition of the given ReferenceProcessor instance
550 // in the scope that contains it.
551 class ReferenceProcessorMTProcMutator: StackObj {
552 private:
553 ReferenceProcessor* _rp;
554 bool _saved_mt;
555
556 public:
557 ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
558 bool mt):
559 _rp(rp) {
560 _saved_mt = _rp->processing_is_mt();
561 _rp->set_mt_processing(mt);
562 }
563
564 ~ReferenceProcessorMTProcMutator() {
565 _rp->set_mt_processing(_saved_mt);
566 }
567 };
568
569
570 // This class is an interface used to implement task execution for the
571 // reference processing.
572 class AbstractRefProcTaskExecutor {
573 public:
574
575 // Abstract tasks to execute.
576 class ProcessTask;
577 class EnqueueTask;
578
579 // Executes a task using worker threads.
580 virtual void execute(ProcessTask& task) = 0;
581 virtual void execute(EnqueueTask& task) = 0;
582
583 // Switch to single threaded mode.
584 virtual void set_single_threaded_mode() { };
585 };
586
587 // Abstract reference processing task to execute.
588 class AbstractRefProcTaskExecutor::ProcessTask {
589 protected:
590 ProcessTask(ReferenceProcessor& ref_processor,
591 DiscoveredList refs_lists[],
592 bool marks_oops_alive,
593 ReferenceProcessorPhaseTimes* phase_times)
594 : _ref_processor(ref_processor),
595 _refs_lists(refs_lists),
596 _phase_times(phase_times),
597 _marks_oops_alive(marks_oops_alive)
598 { }
599
600 public:
601 virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
602 OopClosure& keep_alive,
603 VoidClosure& complete_gc) = 0;
604
605 // Returns true if a task marks some oops as alive.
606 bool marks_oops_alive() const
607 { return _marks_oops_alive; }
608
609 protected:
610 ReferenceProcessor& _ref_processor;
611 DiscoveredList* _refs_lists;
612 ReferenceProcessorPhaseTimes* _phase_times;
613 const bool _marks_oops_alive;
614 };
615
616 // Abstract reference processing task to execute.
617 class AbstractRefProcTaskExecutor::EnqueueTask {
618 protected:
619 EnqueueTask(ReferenceProcessor& ref_processor,
620 DiscoveredList refs_lists[],
621 int n_queues,
622 ReferenceProcessorPhaseTimes* phase_times)
623 : _ref_processor(ref_processor),
624 _refs_lists(refs_lists),
625 _n_queues(n_queues),
626 _phase_times(phase_times)
627 { }
628
629 public:
630 virtual void work(unsigned int work_id) = 0;
631
632 protected:
633 ReferenceProcessor& _ref_processor;
634 DiscoveredList* _refs_lists;
635 ReferenceProcessorPhaseTimes* _phase_times;
636 int _n_queues;
637 };
638
639 #endif // SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP