1 /*
2 * Copyright (c) 2001, 2015, 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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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/gcTrace.hpp"
29 #include "gc/shared/referencePolicy.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 oop head() const {
62 return UseCompressedOops ? oopDesc::decode_heap_oop(_compressed_head) :
63 _oop_head;
64 }
65 HeapWord* adr_head() {
66 return UseCompressedOops ? (HeapWord*)&_compressed_head :
67 (HeapWord*)&_oop_head;
68 }
69 void set_head(oop o) {
70 if (UseCompressedOops) {
71 // Must compress the head ptr.
72 _compressed_head = oopDesc::encode_heap_oop(o);
73 } else {
74 _oop_head = o;
75 }
76 }
77 bool is_empty() const { return head() == NULL; }
78 size_t length() { return _len; }
79 void set_length(size_t len) { _len = len; }
80 void inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); }
81 void dec_length(size_t dec) { _len -= dec; }
82 private:
83 // Set value depending on UseCompressedOops. This could be a template class
84 // but then we have to fix all the instantiations and declarations that use this class.
85 oop _oop_head;
86 narrowOop _compressed_head;
87 size_t _len;
88 };
89
90 // Iterator for the list of discovered references.
91 class DiscoveredListIterator {
92 private:
93 DiscoveredList& _refs_list;
94 HeapWord* _prev_next;
95 oop _prev;
96 oop _ref;
97 HeapWord* _discovered_addr;
98 oop _next;
99 HeapWord* _referent_addr;
100 oop _referent;
101 OopClosure* _keep_alive;
102 BoolObjectClosure* _is_alive;
103
104 DEBUG_ONLY(
105 oop _first_seen; // cyclic linked list check
106 )
107
108 NOT_PRODUCT(
109 size_t _processed;
110 size_t _removed;
111 )
112
113 public:
114 inline DiscoveredListIterator(DiscoveredList& refs_list,
115 OopClosure* keep_alive,
116 BoolObjectClosure* is_alive):
117 _refs_list(refs_list),
118 _prev_next(refs_list.adr_head()),
119 _prev(NULL),
120 _ref(refs_list.head()),
121 #ifdef ASSERT
122 _first_seen(refs_list.head()),
123 #endif
124 #ifndef PRODUCT
125 _processed(0),
126 _removed(0),
127 #endif
128 _next(NULL),
129 _keep_alive(keep_alive),
130 _is_alive(is_alive)
131 { }
132
133 // End Of List.
134 inline bool has_next() const { return _ref != NULL; }
135
136 // Get oop to the Reference object.
137 inline oop obj() const { return _ref; }
138
139 // Get oop to the referent object.
140 inline oop referent() const { return _referent; }
141
142 // Returns true if referent is alive.
143 inline bool is_referent_alive() const {
144 return _is_alive->do_object_b(_referent);
145 }
146
147 // Loads data for the current reference.
148 // The "allow_null_referent" argument tells us to allow for the possibility
149 // of a NULL referent in the discovered Reference object. This typically
150 // happens in the case of concurrent collectors that may have done the
151 // discovery concurrently, or interleaved, with mutator execution.
152 void load_ptrs(DEBUG_ONLY(bool allow_null_referent));
153
154 // Move to the next discovered reference.
155 inline void next() {
156 _prev_next = _discovered_addr;
157 _prev = _ref;
158 move_to_next();
159 }
160
161 // Remove the current reference from the list
162 void remove();
163
164 // Make the referent alive.
165 inline void make_referent_alive() {
166 if (UseCompressedOops) {
167 _keep_alive->do_oop((narrowOop*)_referent_addr);
168 } else {
169 _keep_alive->do_oop((oop*)_referent_addr);
170 }
171 }
172
173 // NULL out referent pointer.
174 void clear_referent();
175
176 // Statistics
177 NOT_PRODUCT(
178 inline size_t processed() const { return _processed; }
179 inline size_t removed() const { return _removed; }
180 )
181
182 inline void move_to_next() {
183 if (_ref == _next) {
184 // End of the list.
185 _ref = NULL;
186 } else {
187 _ref = _next;
188 }
189 assert(_ref != _first_seen, "cyclic ref_list found");
190 NOT_PRODUCT(_processed++);
191 }
192 };
193
194 class ReferenceProcessor : public CHeapObj<mtGC> {
195
196 private:
197 size_t total_count(DiscoveredList lists[]);
198
199 protected:
200 // The SoftReference master timestamp clock
201 static jlong _soft_ref_timestamp_clock;
202
203 MemRegion _span; // (right-open) interval of heap
204 // subject to wkref discovery
205
206 bool _discovering_refs; // true when discovery enabled
207 bool _discovery_is_atomic; // if discovery is atomic wrt
208 // other collectors in configuration
209 bool _discovery_is_mt; // true if reference discovery is MT.
210
211 bool _enqueuing_is_done; // true if all weak references enqueued
212 bool _processing_is_mt; // true during phases when
213 // reference processing is MT.
214 uint _next_id; // round-robin mod _num_q counter in
215 // support of work distribution
216
217 // For collectors that do not keep GC liveness information
218 // in the object header, this field holds a closure that
219 // helps the reference processor determine the reachability
220 // of an oop. It is currently initialized to NULL for all
221 // collectors except for CMS and G1.
222 BoolObjectClosure* _is_alive_non_header;
223
224 // Soft ref clearing policies
225 // . the default policy
226 static ReferencePolicy* _default_soft_ref_policy;
227 // . the "clear all" policy
228 static ReferencePolicy* _always_clear_soft_ref_policy;
229 // . the current policy below is either one of the above
230 ReferencePolicy* _current_soft_ref_policy;
231
232 // The discovered ref lists themselves
233
234 // The active MT'ness degree of the queues below
235 uint _num_q;
236 // The maximum MT'ness degree of the queues below
237 uint _max_num_q;
238
239 // Master array of discovered oops
240 DiscoveredList* _discovered_refs;
241
242 // Arrays of lists of oops, one per thread (pointers into master array above)
243 DiscoveredList* _discoveredSoftRefs;
244 DiscoveredList* _discoveredWeakRefs;
245 DiscoveredList* _discoveredFinalRefs;
246 DiscoveredList* _discoveredPhantomRefs;
247 DiscoveredList* _discoveredCleanerRefs;
248
249 public:
250 static int number_of_subclasses_of_ref() { return (REF_CLEANER - REF_OTHER); }
251
252 uint num_q() { return _num_q; }
253 uint max_num_q() { return _max_num_q; }
254 void set_active_mt_degree(uint v) { _num_q = v; }
255
256 DiscoveredList* discovered_refs() { return _discovered_refs; }
257
258 ReferencePolicy* setup_policy(bool always_clear) {
259 _current_soft_ref_policy = always_clear ?
260 _always_clear_soft_ref_policy : _default_soft_ref_policy;
261 _current_soft_ref_policy->setup(); // snapshot the policy threshold
262 return _current_soft_ref_policy;
263 }
264
265 // Process references with a certain reachability level.
266 void process_discovered_reflist(DiscoveredList refs_lists[],
267 ReferencePolicy* policy,
268 bool clear_referent,
269 BoolObjectClosure* is_alive,
270 OopClosure* keep_alive,
271 VoidClosure* complete_gc,
272 AbstractRefProcTaskExecutor* task_executor);
273
274 void process_phaseJNI(BoolObjectClosure* is_alive,
275 OopClosure* keep_alive,
276 VoidClosure* complete_gc);
277
278 // Work methods used by the method process_discovered_reflist
279 // Phase1: keep alive all those referents that are otherwise
280 // dead but which must be kept alive by policy (and their closure).
281 void process_phase1(DiscoveredList& refs_list,
282 ReferencePolicy* policy,
283 BoolObjectClosure* is_alive,
284 OopClosure* keep_alive,
285 VoidClosure* complete_gc);
286 // Phase2: remove all those references whose referents are
287 // reachable.
288 inline void process_phase2(DiscoveredList& refs_list,
289 BoolObjectClosure* is_alive,
290 OopClosure* keep_alive,
291 VoidClosure* complete_gc) {
292 if (discovery_is_atomic()) {
293 // complete_gc is ignored in this case for this phase
294 pp2_work(refs_list, is_alive, keep_alive);
295 } else {
296 assert(complete_gc != NULL, "Error");
297 pp2_work_concurrent_discovery(refs_list, is_alive,
298 keep_alive, complete_gc);
299 }
300 }
301 // Work methods in support of process_phase2
302 void pp2_work(DiscoveredList& refs_list,
303 BoolObjectClosure* is_alive,
304 OopClosure* keep_alive);
305 void pp2_work_concurrent_discovery(
306 DiscoveredList& refs_list,
307 BoolObjectClosure* is_alive,
308 OopClosure* keep_alive,
309 VoidClosure* complete_gc);
310 // Phase3: process the referents by either clearing them
311 // or keeping them alive (and their closure)
312 void process_phase3(DiscoveredList& refs_list,
313 bool clear_referent,
314 BoolObjectClosure* is_alive,
315 OopClosure* keep_alive,
316 VoidClosure* complete_gc);
317
318 // Enqueue references with a certain reachability level
319 void enqueue_discovered_reflist(DiscoveredList& refs_list, HeapWord* pending_list_addr);
320
321 // "Preclean" all the discovered reference lists
322 // by removing references with strongly reachable referents.
323 // The first argument is a predicate on an oop that indicates
324 // its (strong) reachability and the second is a closure that
325 // may be used to incrementalize or abort the precleaning process.
326 // The caller is responsible for taking care of potential
327 // interference with concurrent operations on these lists
328 // (or predicates involved) by other threads. Currently
329 // only used by the CMS collector.
330 void preclean_discovered_references(BoolObjectClosure* is_alive,
331 OopClosure* keep_alive,
332 VoidClosure* complete_gc,
333 YieldClosure* yield,
334 GCTimer* gc_timer,
335 GCId gc_id);
336
337 // Returns the name of the discovered reference list
338 // occupying the i / _num_q slot.
339 const char* list_name(uint i);
340
341 void enqueue_discovered_reflists(HeapWord* pending_list_addr, AbstractRefProcTaskExecutor* task_executor);
342
343 protected:
344 // "Preclean" the given discovered reference list
345 // by removing references with strongly reachable referents.
346 // Currently used in support of CMS only.
347 void preclean_discovered_reflist(DiscoveredList& refs_list,
348 BoolObjectClosure* is_alive,
349 OopClosure* keep_alive,
350 VoidClosure* complete_gc,
351 YieldClosure* yield);
352
353 // round-robin mod _num_q (not: _not_ mode _max_num_q)
354 uint next_id() {
355 uint id = _next_id;
356 if (++_next_id == _num_q) {
357 _next_id = 0;
358 }
359 return id;
360 }
361 DiscoveredList* get_discovered_list(ReferenceType rt);
362 inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
363 HeapWord* discovered_addr);
364
365 void clear_discovered_references(DiscoveredList& refs_list);
366
367 // Calculate the number of jni handles.
368 unsigned int count_jni_refs();
369
370 // Balances reference queues.
371 void balance_queues(DiscoveredList ref_lists[]);
372
373 // Update (advance) the soft ref master clock field.
374 void update_soft_ref_master_clock();
375
376 public:
377 // Default parameters give you a vanilla reference processor.
378 ReferenceProcessor(MemRegion span,
379 bool mt_processing = false, uint mt_processing_degree = 1,
380 bool mt_discovery = false, uint mt_discovery_degree = 1,
381 bool atomic_discovery = true,
382 BoolObjectClosure* is_alive_non_header = NULL);
383
384 // RefDiscoveryPolicy values
385 enum DiscoveryPolicy {
386 ReferenceBasedDiscovery = 0,
387 ReferentBasedDiscovery = 1,
388 DiscoveryPolicyMin = ReferenceBasedDiscovery,
389 DiscoveryPolicyMax = ReferentBasedDiscovery
390 };
391
392 static void init_statics();
393
394 public:
395 // get and set "is_alive_non_header" field
396 BoolObjectClosure* is_alive_non_header() {
397 return _is_alive_non_header;
398 }
399 void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
400 _is_alive_non_header = is_alive_non_header;
401 }
402
403 // get and set span
404 MemRegion span() { return _span; }
405 void set_span(MemRegion span) { _span = span; }
406
407 // start and stop weak ref discovery
408 void enable_discovery(bool check_no_refs = true);
409 void disable_discovery() { _discovering_refs = false; }
410 bool discovery_enabled() { return _discovering_refs; }
411
412 // whether discovery is atomic wrt other collectors
413 bool discovery_is_atomic() const { return _discovery_is_atomic; }
414 void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
415
416 // whether discovery is done by multiple threads same-old-timeously
417 bool discovery_is_mt() const { return _discovery_is_mt; }
418 void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
419
420 // Whether we are in a phase when _processing_ is MT.
421 bool processing_is_mt() const { return _processing_is_mt; }
422 void set_mt_processing(bool mt) { _processing_is_mt = mt; }
423
424 // whether all enqueueing of weak references is complete
425 bool enqueuing_is_done() { return _enqueuing_is_done; }
426 void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
427
428 // iterate over oops
429 void weak_oops_do(OopClosure* f); // weak roots
430
431 // Balance each of the discovered lists.
432 void balance_all_queues();
433 void verify_list(DiscoveredList& ref_list);
434
435 // Discover a Reference object, using appropriate discovery criteria
436 bool discover_reference(oop obj, ReferenceType rt);
437
438 // Process references found during GC (called by the garbage collector)
439 ReferenceProcessorStats
440 process_discovered_references(BoolObjectClosure* is_alive,
441 OopClosure* keep_alive,
442 VoidClosure* complete_gc,
443 AbstractRefProcTaskExecutor* task_executor,
444 GCTimer *gc_timer,
445 GCId gc_id);
446
447 // Enqueue references at end of GC (called by the garbage collector)
448 bool enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor = NULL);
449
450 // If a discovery is in process that is being superceded, abandon it: all
451 // the discovered lists will be empty, and all the objects on them will
452 // have NULL discovered fields. Must be called only at a safepoint.
453 void abandon_partial_discovery();
454
455 // debugging
456 void verify_no_references_recorded() PRODUCT_RETURN;
457 void verify_referent(oop obj) PRODUCT_RETURN;
458 };
459
460 // A utility class to disable reference discovery in
461 // the scope which contains it, for given ReferenceProcessor.
462 class NoRefDiscovery: StackObj {
463 private:
464 ReferenceProcessor* _rp;
465 bool _was_discovering_refs;
466 public:
467 NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
468 _was_discovering_refs = _rp->discovery_enabled();
469 if (_was_discovering_refs) {
470 _rp->disable_discovery();
471 }
472 }
473
474 ~NoRefDiscovery() {
475 if (_was_discovering_refs) {
476 _rp->enable_discovery(false /*check_no_refs*/);
477 }
478 }
479 };
480
481
482 // A utility class to temporarily mutate the span of the
483 // given ReferenceProcessor in the scope that contains it.
484 class ReferenceProcessorSpanMutator: StackObj {
485 private:
486 ReferenceProcessor* _rp;
487 MemRegion _saved_span;
488
489 public:
490 ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
491 MemRegion span):
492 _rp(rp) {
493 _saved_span = _rp->span();
494 _rp->set_span(span);
495 }
496
497 ~ReferenceProcessorSpanMutator() {
498 _rp->set_span(_saved_span);
499 }
500 };
501
502 // A utility class to temporarily change the MT'ness of
503 // reference discovery for the given ReferenceProcessor
504 // in the scope that contains it.
505 class ReferenceProcessorMTDiscoveryMutator: StackObj {
506 private:
507 ReferenceProcessor* _rp;
508 bool _saved_mt;
509
510 public:
511 ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp,
512 bool mt):
513 _rp(rp) {
514 _saved_mt = _rp->discovery_is_mt();
515 _rp->set_mt_discovery(mt);
516 }
517
518 ~ReferenceProcessorMTDiscoveryMutator() {
519 _rp->set_mt_discovery(_saved_mt);
520 }
521 };
522
523
524 // A utility class to temporarily change the disposition
525 // of the "is_alive_non_header" closure field of the
526 // given ReferenceProcessor in the scope that contains it.
527 class ReferenceProcessorIsAliveMutator: StackObj {
528 private:
529 ReferenceProcessor* _rp;
530 BoolObjectClosure* _saved_cl;
531
532 public:
533 ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
534 BoolObjectClosure* cl):
535 _rp(rp) {
536 _saved_cl = _rp->is_alive_non_header();
537 _rp->set_is_alive_non_header(cl);
538 }
539
540 ~ReferenceProcessorIsAliveMutator() {
541 _rp->set_is_alive_non_header(_saved_cl);
542 }
543 };
544
545 // A utility class to temporarily change the disposition
546 // of the "discovery_is_atomic" field of the
547 // given ReferenceProcessor in the scope that contains it.
548 class ReferenceProcessorAtomicMutator: StackObj {
549 private:
550 ReferenceProcessor* _rp;
551 bool _saved_atomic_discovery;
552
553 public:
554 ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
555 bool atomic):
556 _rp(rp) {
557 _saved_atomic_discovery = _rp->discovery_is_atomic();
558 _rp->set_atomic_discovery(atomic);
559 }
560
561 ~ReferenceProcessorAtomicMutator() {
562 _rp->set_atomic_discovery(_saved_atomic_discovery);
563 }
564 };
565
566
567 // A utility class to temporarily change the MT processing
568 // disposition of the given ReferenceProcessor instance
569 // in the scope that contains it.
570 class ReferenceProcessorMTProcMutator: StackObj {
571 private:
572 ReferenceProcessor* _rp;
573 bool _saved_mt;
574
575 public:
576 ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
577 bool mt):
578 _rp(rp) {
579 _saved_mt = _rp->processing_is_mt();
580 _rp->set_mt_processing(mt);
581 }
582
583 ~ReferenceProcessorMTProcMutator() {
584 _rp->set_mt_processing(_saved_mt);
585 }
586 };
587
588
589 // This class is an interface used to implement task execution for the
590 // reference processing.
591 class AbstractRefProcTaskExecutor {
592 public:
593
594 // Abstract tasks to execute.
595 class ProcessTask;
596 class EnqueueTask;
597
598 // Executes a task using worker threads.
599 virtual void execute(ProcessTask& task) = 0;
600 virtual void execute(EnqueueTask& task) = 0;
601
602 // Switch to single threaded mode.
603 virtual void set_single_threaded_mode() { };
604 };
605
606 // Abstract reference processing task to execute.
607 class AbstractRefProcTaskExecutor::ProcessTask {
608 protected:
609 ProcessTask(ReferenceProcessor& ref_processor,
610 DiscoveredList refs_lists[],
611 bool marks_oops_alive)
612 : _ref_processor(ref_processor),
613 _refs_lists(refs_lists),
614 _marks_oops_alive(marks_oops_alive)
615 { }
616
617 public:
618 virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
619 OopClosure& keep_alive,
620 VoidClosure& complete_gc) = 0;
621
622 // Returns true if a task marks some oops as alive.
623 bool marks_oops_alive() const
624 { return _marks_oops_alive; }
625
626 protected:
627 ReferenceProcessor& _ref_processor;
628 DiscoveredList* _refs_lists;
629 const bool _marks_oops_alive;
630 };
631
632 // Abstract reference processing task to execute.
633 class AbstractRefProcTaskExecutor::EnqueueTask {
634 protected:
635 EnqueueTask(ReferenceProcessor& ref_processor,
636 DiscoveredList refs_lists[],
637 HeapWord* pending_list_addr,
638 int n_queues)
639 : _ref_processor(ref_processor),
640 _refs_lists(refs_lists),
641 _pending_list_addr(pending_list_addr),
642 _n_queues(n_queues)
643 { }
644
645 public:
646 virtual void work(unsigned int work_id) = 0;
647
648 protected:
649 ReferenceProcessor& _ref_processor;
650 DiscoveredList* _refs_lists;
651 HeapWord* _pending_list_addr;
652 int _n_queues;
653 };
654
655 #endif // SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP