1 /*
2 * Copyright (c) 2001, 2016, 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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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 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[]);
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
248 void process_phaseJNI(BoolObjectClosure* is_alive,
249 OopClosure* keep_alive,
250 VoidClosure* complete_gc);
251
252 // Work methods used by the method process_discovered_reflist
253 // Phase1: keep alive all those referents that are otherwise
254 // dead but which must be kept alive by policy (and their closure).
255 void process_phase1(DiscoveredList& refs_list,
256 ReferencePolicy* policy,
257 BoolObjectClosure* is_alive,
258 OopClosure* keep_alive,
259 VoidClosure* complete_gc);
260 // Phase2: remove all those references whose referents are
261 // reachable.
262 inline void process_phase2(DiscoveredList& refs_list,
263 BoolObjectClosure* is_alive,
264 OopClosure* keep_alive,
265 VoidClosure* complete_gc) {
266 if (discovery_is_atomic()) {
267 // complete_gc is ignored in this case for this phase
268 pp2_work(refs_list, is_alive, keep_alive);
269 } else {
270 assert(complete_gc != NULL, "Error");
271 pp2_work_concurrent_discovery(refs_list, is_alive,
272 keep_alive, complete_gc);
273 }
274 }
275 // Work methods in support of process_phase2
276 void pp2_work(DiscoveredList& refs_list,
277 BoolObjectClosure* is_alive,
278 OopClosure* keep_alive);
279 void pp2_work_concurrent_discovery(
280 DiscoveredList& refs_list,
281 BoolObjectClosure* is_alive,
282 OopClosure* keep_alive,
283 VoidClosure* complete_gc);
284 // Phase3: process the referents by either clearing them
285 // or keeping them alive (and their closure)
286 void process_phase3(DiscoveredList& refs_list,
287 bool clear_referent,
288 BoolObjectClosure* is_alive,
289 OopClosure* keep_alive,
290 VoidClosure* complete_gc);
291
292 // Enqueue references with a certain reachability level
293 void enqueue_discovered_reflist(DiscoveredList& refs_list);
294
295 // "Preclean" all the discovered reference lists
296 // by removing references with strongly reachable referents.
297 // The first argument is a predicate on an oop that indicates
298 // its (strong) reachability and the second is a closure that
299 // may be used to incrementalize or abort the precleaning process.
300 // The caller is responsible for taking care of potential
301 // interference with concurrent operations on these lists
302 // (or predicates involved) by other threads. Currently
303 // only used by the CMS collector.
304 void preclean_discovered_references(BoolObjectClosure* is_alive,
305 OopClosure* keep_alive,
306 VoidClosure* complete_gc,
307 YieldClosure* yield,
308 GCTimer* gc_timer);
309
310 // Returns the name of the discovered reference list
311 // occupying the i / _num_q slot.
312 const char* list_name(uint i);
313
314 void enqueue_discovered_reflists(AbstractRefProcTaskExecutor* task_executor);
315
316 protected:
317 // "Preclean" the given discovered reference list
318 // by removing references with strongly reachable referents.
319 // Currently used in support of CMS only.
320 void preclean_discovered_reflist(DiscoveredList& refs_list,
321 BoolObjectClosure* is_alive,
322 OopClosure* keep_alive,
323 VoidClosure* complete_gc,
324 YieldClosure* yield);
325
326 // round-robin mod _num_q (not: _not_ mode _max_num_q)
327 uint next_id() {
328 uint id = _next_id;
329 assert(!_discovery_is_mt, "Round robin should only be used in serial discovery");
330 if (++_next_id == _num_q) {
331 _next_id = 0;
332 }
333 assert(_next_id < _num_q, "_next_id %u _num_q %u _max_num_q %u", _next_id, _num_q, _max_num_q);
334 return id;
335 }
336 DiscoveredList* get_discovered_list(ReferenceType rt);
337 inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
338 HeapWord* discovered_addr);
339
340 void clear_discovered_references(DiscoveredList& refs_list);
341
342 // Calculate the number of jni handles.
343 size_t count_jni_refs();
344
345 void log_reflist_counts(DiscoveredList ref_lists[], uint active_length, size_t total_count) PRODUCT_RETURN;
346
347 // Balances reference queues.
348 void balance_queues(DiscoveredList ref_lists[]);
349
350 // Update (advance) the soft ref master clock field.
351 void update_soft_ref_master_clock();
352
353 public:
354 // Default parameters give you a vanilla reference processor.
355 ReferenceProcessor(MemRegion span,
356 bool mt_processing = false, uint mt_processing_degree = 1,
357 bool mt_discovery = false, uint mt_discovery_degree = 1,
358 bool atomic_discovery = true,
359 BoolObjectClosure* is_alive_non_header = NULL);
360
361 // RefDiscoveryPolicy values
362 enum DiscoveryPolicy {
363 ReferenceBasedDiscovery = 0,
364 ReferentBasedDiscovery = 1,
365 DiscoveryPolicyMin = ReferenceBasedDiscovery,
366 DiscoveryPolicyMax = ReferentBasedDiscovery
367 };
368
369 static void init_statics();
370
371 public:
372 // get and set "is_alive_non_header" field
373 BoolObjectClosure* is_alive_non_header() {
374 return _is_alive_non_header;
375 }
376 void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
377 _is_alive_non_header = is_alive_non_header;
378 }
379
380 // get and set span
381 MemRegion span() { return _span; }
382 void set_span(MemRegion span) { _span = span; }
383
384 // start and stop weak ref discovery
385 void enable_discovery(bool check_no_refs = true);
386 void disable_discovery() { _discovering_refs = false; }
387 bool discovery_enabled() { return _discovering_refs; }
388
389 // whether discovery is atomic wrt other collectors
390 bool discovery_is_atomic() const { return _discovery_is_atomic; }
391 void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
392
393 // whether discovery is done by multiple threads same-old-timeously
394 bool discovery_is_mt() const { return _discovery_is_mt; }
395 void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
396
397 // Whether we are in a phase when _processing_ is MT.
398 bool processing_is_mt() const { return _processing_is_mt; }
399 void set_mt_processing(bool mt) { _processing_is_mt = mt; }
400
401 // whether all enqueueing of weak references is complete
402 bool enqueuing_is_done() { return _enqueuing_is_done; }
403 void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
404
405 // iterate over oops
406 void weak_oops_do(OopClosure* f); // weak roots
407
408 // Balance each of the discovered lists.
409 void balance_all_queues();
410 void verify_list(DiscoveredList& ref_list);
411
412 // Discover a Reference object, using appropriate discovery criteria
413 bool discover_reference(oop obj, ReferenceType rt);
414
415 // Has discovered references that need handling
416 bool has_discovered_references();
417
418 // Process references found during GC (called by the garbage collector)
419 ReferenceProcessorStats
420 process_discovered_references(BoolObjectClosure* is_alive,
421 OopClosure* keep_alive,
422 VoidClosure* complete_gc,
423 AbstractRefProcTaskExecutor* task_executor,
424 GCTimer *gc_timer);
425
426 // Enqueue references at end of GC (called by the garbage collector)
427 void enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor = NULL);
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 // debugging
435 void verify_no_references_recorded() PRODUCT_RETURN;
436 void verify_referent(oop obj) PRODUCT_RETURN;
437 };
438
439 // A utility class to disable reference discovery in
440 // the scope which contains it, for given ReferenceProcessor.
441 class NoRefDiscovery: StackObj {
442 private:
443 ReferenceProcessor* _rp;
444 bool _was_discovering_refs;
445 public:
446 NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
447 _was_discovering_refs = _rp->discovery_enabled();
448 if (_was_discovering_refs) {
449 _rp->disable_discovery();
450 }
451 }
452
453 ~NoRefDiscovery() {
454 if (_was_discovering_refs) {
455 _rp->enable_discovery(false /*check_no_refs*/);
456 }
457 }
458 };
459
460
461 // A utility class to temporarily mutate the span of the
462 // given ReferenceProcessor in the scope that contains it.
463 class ReferenceProcessorSpanMutator: StackObj {
464 private:
465 ReferenceProcessor* _rp;
466 MemRegion _saved_span;
467
468 public:
469 ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
470 MemRegion span):
471 _rp(rp) {
472 _saved_span = _rp->span();
473 _rp->set_span(span);
474 }
475
476 ~ReferenceProcessorSpanMutator() {
477 _rp->set_span(_saved_span);
478 }
479 };
480
481 // A utility class to temporarily change the MT'ness of
482 // reference discovery for the given ReferenceProcessor
483 // in the scope that contains it.
484 class ReferenceProcessorMTDiscoveryMutator: StackObj {
485 private:
486 ReferenceProcessor* _rp;
487 bool _saved_mt;
488
489 public:
490 ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp,
491 bool mt):
492 _rp(rp) {
493 _saved_mt = _rp->discovery_is_mt();
494 _rp->set_mt_discovery(mt);
495 }
496
497 ~ReferenceProcessorMTDiscoveryMutator() {
498 _rp->set_mt_discovery(_saved_mt);
499 }
500 };
501
502
503 // A utility class to temporarily change the disposition
504 // of the "is_alive_non_header" closure field of the
505 // given ReferenceProcessor in the scope that contains it.
506 class ReferenceProcessorIsAliveMutator: StackObj {
507 private:
508 ReferenceProcessor* _rp;
509 BoolObjectClosure* _saved_cl;
510
511 public:
512 ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
513 BoolObjectClosure* cl):
514 _rp(rp) {
515 _saved_cl = _rp->is_alive_non_header();
516 _rp->set_is_alive_non_header(cl);
517 }
518
519 ~ReferenceProcessorIsAliveMutator() {
520 _rp->set_is_alive_non_header(_saved_cl);
521 }
522 };
523
524 // A utility class to temporarily change the disposition
525 // of the "discovery_is_atomic" field of the
526 // given ReferenceProcessor in the scope that contains it.
527 class ReferenceProcessorAtomicMutator: StackObj {
528 private:
529 ReferenceProcessor* _rp;
530 bool _saved_atomic_discovery;
531
532 public:
533 ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
534 bool atomic):
535 _rp(rp) {
536 _saved_atomic_discovery = _rp->discovery_is_atomic();
537 _rp->set_atomic_discovery(atomic);
538 }
539
540 ~ReferenceProcessorAtomicMutator() {
541 _rp->set_atomic_discovery(_saved_atomic_discovery);
542 }
543 };
544
545
546 // A utility class to temporarily change the MT processing
547 // disposition of the given ReferenceProcessor instance
548 // in the scope that contains it.
549 class ReferenceProcessorMTProcMutator: StackObj {
550 private:
551 ReferenceProcessor* _rp;
552 bool _saved_mt;
553
554 public:
555 ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
556 bool mt):
557 _rp(rp) {
558 _saved_mt = _rp->processing_is_mt();
559 _rp->set_mt_processing(mt);
560 }
561
562 ~ReferenceProcessorMTProcMutator() {
563 _rp->set_mt_processing(_saved_mt);
564 }
565 };
566
567
568 // This class is an interface used to implement task execution for the
569 // reference processing.
570 class AbstractRefProcTaskExecutor {
571 public:
572
573 // Abstract tasks to execute.
574 class ProcessTask;
575 class EnqueueTask;
576
577 // Executes a task using worker threads.
578 virtual void execute(ProcessTask& task) = 0;
579 virtual void execute(EnqueueTask& task) = 0;
580
581 // Switch to single threaded mode.
582 virtual void set_single_threaded_mode() { };
583 };
584
585 // Abstract reference processing task to execute.
586 class AbstractRefProcTaskExecutor::ProcessTask {
587 protected:
588 ProcessTask(ReferenceProcessor& ref_processor,
589 DiscoveredList refs_lists[],
590 bool marks_oops_alive)
591 : _ref_processor(ref_processor),
592 _refs_lists(refs_lists),
593 _marks_oops_alive(marks_oops_alive)
594 { }
595
596 public:
597 virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
598 OopClosure& keep_alive,
599 VoidClosure& complete_gc) = 0;
600
601 // Returns true if a task marks some oops as alive.
602 bool marks_oops_alive() const
603 { return _marks_oops_alive; }
604
605 protected:
606 ReferenceProcessor& _ref_processor;
607 DiscoveredList* _refs_lists;
608 const bool _marks_oops_alive;
609 };
610
611 // Abstract reference processing task to execute.
612 class AbstractRefProcTaskExecutor::EnqueueTask {
613 protected:
614 EnqueueTask(ReferenceProcessor& ref_processor,
615 DiscoveredList refs_lists[],
616 int n_queues)
617 : _ref_processor(ref_processor),
618 _refs_lists(refs_lists),
619 _n_queues(n_queues)
620 { }
621
622 public:
623 virtual void work(unsigned int work_id) = 0;
624
625 protected:
626 ReferenceProcessor& _ref_processor;
627 DiscoveredList* _refs_lists;
628 int _n_queues;
629 };
630
631 #endif // SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP