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.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
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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. 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 void process_phaseJNI(BoolObjectClosure* is_alive,
250 OopClosure* keep_alive,
251 VoidClosure* complete_gc);
252
253 size_t process_phaseHeapSampling(BoolObjectClosure* is_alive,
254 OopClosure* keep_alive,
255 VoidClosure* complete_gc);
256
257 // Work methods used by the method process_discovered_reflist
258 // Phase1: keep alive all those referents that are otherwise
259 // dead but which must be kept alive by policy (and their closure).
260 void process_phase1(DiscoveredList& refs_list,
261 ReferencePolicy* policy,
262 BoolObjectClosure* is_alive,
263 OopClosure* keep_alive,
264 VoidClosure* complete_gc);
265 // Phase2: remove all those references whose referents are
266 // reachable.
267 inline void process_phase2(DiscoveredList& refs_list,
268 BoolObjectClosure* is_alive,
269 OopClosure* keep_alive,
270 VoidClosure* complete_gc) {
271 if (discovery_is_atomic()) {
272 // complete_gc is ignored in this case for this phase
273 pp2_work(refs_list, is_alive, keep_alive);
274 } else {
275 assert(complete_gc != NULL, "Error");
276 pp2_work_concurrent_discovery(refs_list, is_alive,
277 keep_alive, complete_gc);
278 }
279 }
280 // Work methods in support of process_phase2
281 void pp2_work(DiscoveredList& refs_list,
282 BoolObjectClosure* is_alive,
283 OopClosure* keep_alive);
284 void pp2_work_concurrent_discovery(
285 DiscoveredList& refs_list,
286 BoolObjectClosure* is_alive,
287 OopClosure* keep_alive,
288 VoidClosure* complete_gc);
289 // Phase3: process the referents by either clearing them
290 // or keeping them alive (and their closure)
291 void process_phase3(DiscoveredList& refs_list,
292 bool clear_referent,
293 BoolObjectClosure* is_alive,
294 OopClosure* keep_alive,
295 VoidClosure* complete_gc);
296
297 // Enqueue references with a certain reachability level
298 void enqueue_discovered_reflist(DiscoveredList& refs_list);
299
300 // "Preclean" all the discovered reference lists
301 // by removing references with strongly reachable referents.
302 // The first argument is a predicate on an oop that indicates
303 // its (strong) reachability and the second is a closure that
304 // may be used to incrementalize or abort the precleaning process.
305 // The caller is responsible for taking care of potential
306 // interference with concurrent operations on these lists
307 // (or predicates involved) by other threads. Currently
308 // only used by the CMS collector.
309 void preclean_discovered_references(BoolObjectClosure* is_alive,
310 OopClosure* keep_alive,
311 VoidClosure* complete_gc,
312 YieldClosure* yield,
313 GCTimer* gc_timer);
314
315 // Returns the name of the discovered reference list
316 // occupying the i / _num_q slot.
317 const char* list_name(uint i);
318
319 void enqueue_discovered_reflists(AbstractRefProcTaskExecutor* task_executor,
320 ReferenceProcessorPhaseTimes* phase_times);
321
322 protected:
323 // "Preclean" the given discovered reference list
324 // by removing references with strongly reachable referents.
325 // Currently used in support of CMS only.
326 void preclean_discovered_reflist(DiscoveredList& refs_list,
327 BoolObjectClosure* is_alive,
328 OopClosure* keep_alive,
329 VoidClosure* complete_gc,
330 YieldClosure* yield);
331
332 // round-robin mod _num_q (not: _not_ mode _max_num_q)
333 uint next_id() {
334 uint id = _next_id;
335 assert(!_discovery_is_mt, "Round robin should only be used in serial discovery");
336 if (++_next_id == _num_q) {
337 _next_id = 0;
338 }
339 assert(_next_id < _num_q, "_next_id %u _num_q %u _max_num_q %u", _next_id, _num_q, _max_num_q);
340 return id;
341 }
342 DiscoveredList* get_discovered_list(ReferenceType rt);
343 inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
344 HeapWord* discovered_addr);
345
346 void clear_discovered_references(DiscoveredList& refs_list);
347
348 // Calculate the number of jni handles.
349 size_t count_jni_refs();
350
351 void log_reflist_counts(DiscoveredList ref_lists[], uint active_length, size_t total_count) PRODUCT_RETURN;
352
353 // Balances reference queues.
354 void balance_queues(DiscoveredList ref_lists[]);
355
356 // Update (advance) the soft ref master clock field.
357 void update_soft_ref_master_clock();
358
359 public:
360 // Default parameters give you a vanilla reference processor.
361 ReferenceProcessor(MemRegion span,
362 bool mt_processing = false, uint mt_processing_degree = 1,
363 bool mt_discovery = false, uint mt_discovery_degree = 1,
364 bool atomic_discovery = true,
365 BoolObjectClosure* is_alive_non_header = NULL);
366
367 // RefDiscoveryPolicy values
368 enum DiscoveryPolicy {
369 ReferenceBasedDiscovery = 0,
370 ReferentBasedDiscovery = 1,
371 DiscoveryPolicyMin = ReferenceBasedDiscovery,
372 DiscoveryPolicyMax = ReferentBasedDiscovery
373 };
374
375 static void init_statics();
376
377 public:
378 // get and set "is_alive_non_header" field
379 BoolObjectClosure* is_alive_non_header() {
380 return _is_alive_non_header;
381 }
382 void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
383 _is_alive_non_header = is_alive_non_header;
384 }
385
386 // get and set span
387 MemRegion span() { return _span; }
388 void set_span(MemRegion span) { _span = span; }
389
390 // start and stop weak ref discovery
391 void enable_discovery(bool check_no_refs = true);
392 void disable_discovery() { _discovering_refs = false; }
393 bool discovery_enabled() { return _discovering_refs; }
394
395 // whether discovery is atomic wrt other collectors
396 bool discovery_is_atomic() const { return _discovery_is_atomic; }
397 void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
398
399 // whether discovery is done by multiple threads same-old-timeously
400 bool discovery_is_mt() const { return _discovery_is_mt; }
401 void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
402
403 // Whether we are in a phase when _processing_ is MT.
404 bool processing_is_mt() const { return _processing_is_mt; }
405 void set_mt_processing(bool mt) { _processing_is_mt = mt; }
406
407 // whether all enqueueing of weak references is complete
408 bool enqueuing_is_done() { return _enqueuing_is_done; }
409 void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
410
411 // iterate over oops
412 void weak_oops_do(OopClosure* f); // weak roots
413
414 // Balance each of the discovered lists.
415 void balance_all_queues();
416 void verify_list(DiscoveredList& ref_list);
417
418 // Discover a Reference object, using appropriate discovery criteria
419 bool discover_reference(oop obj, ReferenceType rt);
420
421 // Has discovered references that need handling
422 bool has_discovered_references();
423
424 // Process references found during GC (called by the garbage collector)
425 ReferenceProcessorStats
426 process_discovered_references(BoolObjectClosure* is_alive,
427 OopClosure* keep_alive,
428 VoidClosure* complete_gc,
429 AbstractRefProcTaskExecutor* task_executor,
430 ReferenceProcessorPhaseTimes* phase_times);
431
432 // Enqueue references at end of GC (called by the garbage collector)
433 void enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor,
434 ReferenceProcessorPhaseTimes* phase_times);
435
436 // If a discovery is in process that is being superceded, abandon it: all
437 // the discovered lists will be empty, and all the objects on them will
438 // have NULL discovered fields. Must be called only at a safepoint.
439 void abandon_partial_discovery();
440
441 size_t total_reference_count(ReferenceType rt) const;
442
443 // debugging
444 void verify_no_references_recorded() PRODUCT_RETURN;
445 void verify_referent(oop obj) PRODUCT_RETURN;
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
470 // A utility class to temporarily mutate the span of the
471 // given ReferenceProcessor in the scope that contains it.
472 class ReferenceProcessorSpanMutator: StackObj {
473 private:
474 ReferenceProcessor* _rp;
475 MemRegion _saved_span;
476
477 public:
478 ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
479 MemRegion span):
480 _rp(rp) {
481 _saved_span = _rp->span();
482 _rp->set_span(span);
483 }
484
485 ~ReferenceProcessorSpanMutator() {
486 _rp->set_span(_saved_span);
487 }
488 };
489
490 // A utility class to temporarily change the MT'ness of
491 // reference discovery for the given ReferenceProcessor
492 // in the scope that contains it.
493 class ReferenceProcessorMTDiscoveryMutator: StackObj {
494 private:
495 ReferenceProcessor* _rp;
496 bool _saved_mt;
497
498 public:
499 ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp,
500 bool mt):
501 _rp(rp) {
502 _saved_mt = _rp->discovery_is_mt();
503 _rp->set_mt_discovery(mt);
504 }
505
506 ~ReferenceProcessorMTDiscoveryMutator() {
507 _rp->set_mt_discovery(_saved_mt);
508 }
509 };
510
511
512 // A utility class to temporarily change the disposition
513 // of the "is_alive_non_header" closure field of the
514 // given ReferenceProcessor in the scope that contains it.
515 class ReferenceProcessorIsAliveMutator: StackObj {
516 private:
517 ReferenceProcessor* _rp;
518 BoolObjectClosure* _saved_cl;
519
520 public:
521 ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
522 BoolObjectClosure* cl):
523 _rp(rp) {
524 _saved_cl = _rp->is_alive_non_header();
525 _rp->set_is_alive_non_header(cl);
526 }
527
528 ~ReferenceProcessorIsAliveMutator() {
529 _rp->set_is_alive_non_header(_saved_cl);
530 }
531 };
532
533 // A utility class to temporarily change the disposition
534 // of the "discovery_is_atomic" field of the
535 // given ReferenceProcessor in the scope that contains it.
536 class ReferenceProcessorAtomicMutator: StackObj {
537 private:
538 ReferenceProcessor* _rp;
539 bool _saved_atomic_discovery;
540
541 public:
542 ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
543 bool atomic):
544 _rp(rp) {
545 _saved_atomic_discovery = _rp->discovery_is_atomic();
546 _rp->set_atomic_discovery(atomic);
547 }
548
549 ~ReferenceProcessorAtomicMutator() {
550 _rp->set_atomic_discovery(_saved_atomic_discovery);
551 }
552 };
553
554
555 // A utility class to temporarily change the MT processing
556 // disposition of the given ReferenceProcessor instance
557 // in the scope that contains it.
558 class ReferenceProcessorMTProcMutator: StackObj {
559 private:
560 ReferenceProcessor* _rp;
561 bool _saved_mt;
562
563 public:
564 ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
565 bool mt):
566 _rp(rp) {
567 _saved_mt = _rp->processing_is_mt();
568 _rp->set_mt_processing(mt);
569 }
570
571 ~ReferenceProcessorMTProcMutator() {
572 _rp->set_mt_processing(_saved_mt);
573 }
574 };
575
576
577 // This class is an interface used to implement task execution for the
578 // reference processing.
579 class AbstractRefProcTaskExecutor {
580 public:
581
582 // Abstract tasks to execute.
583 class ProcessTask;
584 class EnqueueTask;
585
586 // Executes a task using worker threads.
587 virtual void execute(ProcessTask& task) = 0;
588 virtual void execute(EnqueueTask& 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 // Abstract reference processing task to execute.
624 class AbstractRefProcTaskExecutor::EnqueueTask {
625 protected:
626 EnqueueTask(ReferenceProcessor& ref_processor,
627 DiscoveredList refs_lists[],
628 int n_queues,
629 ReferenceProcessorPhaseTimes* phase_times)
630 : _ref_processor(ref_processor),
631 _refs_lists(refs_lists),
632 _n_queues(n_queues),
633 _phase_times(phase_times)
634 { }
635
636 public:
637 virtual void work(unsigned int work_id) = 0;
638
639 protected:
640 ReferenceProcessor& _ref_processor;
641 DiscoveredList* _refs_lists;
642 ReferenceProcessorPhaseTimes* _phase_times;
643 int _n_queues;
644 };
645
646 #endif // SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP