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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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24
25 #ifndef SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP
26 #define SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP
27
28 #include "memory/referencePolicy.hpp"
29 #include "oops/instanceRefKlass.hpp"
30
31 // ReferenceProcessor class encapsulates the per-"collector" processing
32 // of java.lang.Reference objects for GC. The interface is useful for supporting
33 // a generational abstraction, in particular when there are multiple
34 // generations that are being independently collected -- possibly
35 // concurrently and/or incrementally. Note, however, that the
36 // ReferenceProcessor class abstracts away from a generational setting
37 // by using only a heap interval (called "span" below), thus allowing
38 // its use in a straightforward manner in a general, non-generational
39 // setting.
40 //
41 // The basic idea is that each ReferenceProcessor object concerns
42 // itself with ("weak") reference processing in a specific "span"
43 // of the heap of interest to a specific collector. Currently,
44 // the span is a convex interval of the heap, but, efficiency
45 // apart, there seems to be no reason it couldn't be extended
46 // (with appropriate modifications) to any "non-convex interval".
47
48 // forward references
49 class ReferencePolicy;
50 class AbstractRefProcTaskExecutor;
51 class DiscoveredList;
52
53 class ReferenceProcessor : public CHeapObj {
54 protected:
55 MemRegion _span; // (right-open) interval of heap
56 // subject to wkref discovery
57 bool _discovering_refs; // true when discovery enabled
58 bool _discovery_is_atomic; // if discovery is atomic wrt
59 // other collectors in configuration
60 bool _discovery_is_mt; // true if reference discovery is MT.
61 // If true, setting "next" field of a discovered refs list requires
62 // write barrier(s). (Must be true if used in a collector in which
63 // elements of a discovered list may be moved during discovery: for
64 // example, a collector like Garbage-First that moves objects during a
65 // long-term concurrent marking phase that does weak reference
66 // discovery.)
67 bool _discovered_list_needs_barrier;
68 BarrierSet* _bs; // Cached copy of BarrierSet.
69 bool _enqueuing_is_done; // true if all weak references enqueued
70 bool _processing_is_mt; // true during phases when
71 // reference processing is MT.
72 int _next_id; // round-robin mod _num_q counter in
73 // support of work distribution
74
75 // For collectors that do not keep GC marking information
76 // in the object header, this field holds a closure that
77 // helps the reference processor determine the reachability
78 // of an oop (the field is currently initialized to NULL for
79 // all collectors but the CMS collector).
80 BoolObjectClosure* _is_alive_non_header;
81
82 // Soft ref clearing policies
83 // . the default policy
84 static ReferencePolicy* _default_soft_ref_policy;
85 // . the "clear all" policy
86 static ReferencePolicy* _always_clear_soft_ref_policy;
87 // . the current policy below is either one of the above
88 ReferencePolicy* _current_soft_ref_policy;
89
90 // The discovered ref lists themselves
91
92 // The active MT'ness degree of the queues below
93 int _num_q;
94 // The maximum MT'ness degree of the queues below
95 int _max_num_q;
96 // Arrays of lists of oops, one per thread
97 DiscoveredList* _discoveredSoftRefs;
98 DiscoveredList* _discoveredWeakRefs;
99 DiscoveredList* _discoveredFinalRefs;
100 DiscoveredList* _discoveredPhantomRefs;
101
102 public:
103 int num_q() { return _num_q; }
104 int max_num_q() { return _max_num_q; }
105 void set_active_mt_degree(int v) { _num_q = v; }
106 DiscoveredList* discovered_soft_refs() { return _discoveredSoftRefs; }
107 ReferencePolicy* setup_policy(bool always_clear) {
108 _current_soft_ref_policy = always_clear ?
109 _always_clear_soft_ref_policy : _default_soft_ref_policy;
110 _current_soft_ref_policy->setup(); // snapshot the policy threshold
111 return _current_soft_ref_policy;
112 }
113
114 public:
115 // Process references with a certain reachability level.
116 void process_discovered_reflist(DiscoveredList refs_lists[],
117 ReferencePolicy* policy,
118 bool clear_referent,
119 BoolObjectClosure* is_alive,
120 OopClosure* keep_alive,
121 VoidClosure* complete_gc,
122 AbstractRefProcTaskExecutor* task_executor);
123
124 void process_phaseJNI(BoolObjectClosure* is_alive,
125 OopClosure* keep_alive,
126 VoidClosure* complete_gc);
127
128 // Work methods used by the method process_discovered_reflist
129 // Phase1: keep alive all those referents that are otherwise
130 // dead but which must be kept alive by policy (and their closure).
131 void process_phase1(DiscoveredList& refs_list,
132 ReferencePolicy* policy,
133 BoolObjectClosure* is_alive,
134 OopClosure* keep_alive,
135 VoidClosure* complete_gc);
136 // Phase2: remove all those references whose referents are
137 // reachable.
138 inline void process_phase2(DiscoveredList& refs_list,
139 BoolObjectClosure* is_alive,
140 OopClosure* keep_alive,
141 VoidClosure* complete_gc) {
142 if (discovery_is_atomic()) {
143 // complete_gc is ignored in this case for this phase
144 pp2_work(refs_list, is_alive, keep_alive);
145 } else {
146 assert(complete_gc != NULL, "Error");
147 pp2_work_concurrent_discovery(refs_list, is_alive,
148 keep_alive, complete_gc);
149 }
150 }
151 // Work methods in support of process_phase2
152 void pp2_work(DiscoveredList& refs_list,
153 BoolObjectClosure* is_alive,
154 OopClosure* keep_alive);
155 void pp2_work_concurrent_discovery(
156 DiscoveredList& refs_list,
157 BoolObjectClosure* is_alive,
158 OopClosure* keep_alive,
159 VoidClosure* complete_gc);
160 // Phase3: process the referents by either clearing them
161 // or keeping them alive (and their closure)
162 void process_phase3(DiscoveredList& refs_list,
163 bool clear_referent,
164 BoolObjectClosure* is_alive,
165 OopClosure* keep_alive,
166 VoidClosure* complete_gc);
167
168 // Enqueue references with a certain reachability level
169 void enqueue_discovered_reflist(DiscoveredList& refs_list, HeapWord* pending_list_addr);
170
171 // "Preclean" all the discovered reference lists
172 // by removing references with strongly reachable referents.
173 // The first argument is a predicate on an oop that indicates
174 // its (strong) reachability and the second is a closure that
175 // may be used to incrementalize or abort the precleaning process.
176 // The caller is responsible for taking care of potential
177 // interference with concurrent operations on these lists
178 // (or predicates involved) by other threads. Currently
179 // only used by the CMS collector. should_unload_classes is
180 // used to aid assertion checking when classes are collected.
181 void preclean_discovered_references(BoolObjectClosure* is_alive,
182 OopClosure* keep_alive,
183 VoidClosure* complete_gc,
184 YieldClosure* yield,
185 bool should_unload_classes);
186
187 // Delete entries in the discovered lists that have
188 // either a null referent or are not active. Such
189 // Reference objects can result from the clearing
190 // or enqueueing of Reference objects concurrent
191 // with their discovery by a (concurrent) collector.
192 // For a definition of "active" see java.lang.ref.Reference;
193 // Refs are born active, become inactive when enqueued,
194 // and never become active again. The state of being
195 // active is encoded as follows: A Ref is active
196 // if and only if its "next" field is NULL.
197 void clean_up_discovered_references();
198 void clean_up_discovered_reflist(DiscoveredList& refs_list);
199
200 // Returns the name of the discovered reference list
201 // occupying the i / _num_q slot.
202 const char* list_name(int i);
203
204 void enqueue_discovered_reflists(HeapWord* pending_list_addr, AbstractRefProcTaskExecutor* task_executor);
205
206 protected:
207 // "Preclean" the given discovered reference list
208 // by removing references with strongly reachable referents.
209 // Currently used in support of CMS only.
210 void preclean_discovered_reflist(DiscoveredList& refs_list,
211 BoolObjectClosure* is_alive,
212 OopClosure* keep_alive,
213 VoidClosure* complete_gc,
214 YieldClosure* yield);
215
216 // round-robin mod _num_q (not: _not_ mode _max_num_q)
217 int next_id() {
218 int id = _next_id;
219 if (++_next_id == _num_q) {
220 _next_id = 0;
221 }
222 return id;
223 }
224 DiscoveredList* get_discovered_list(ReferenceType rt);
225 inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
226 HeapWord* discovered_addr);
227 void verify_ok_to_handle_reflists() PRODUCT_RETURN;
228
229 void clear_discovered_references(DiscoveredList& refs_list);
230 void abandon_partial_discovered_list(DiscoveredList& refs_list);
231
232 // Calculate the number of jni handles.
233 unsigned int count_jni_refs();
234
235 // Balances reference queues.
236 void balance_queues(DiscoveredList ref_lists[]);
237
238 // Update (advance) the soft ref master clock field.
239 void update_soft_ref_master_clock();
240
241 public:
242 // constructor
243 ReferenceProcessor():
244 _span((HeapWord*)NULL, (HeapWord*)NULL),
245 _discoveredSoftRefs(NULL), _discoveredWeakRefs(NULL),
246 _discoveredFinalRefs(NULL), _discoveredPhantomRefs(NULL),
247 _discovering_refs(false),
248 _discovery_is_atomic(true),
249 _enqueuing_is_done(false),
250 _discovery_is_mt(false),
251 _discovered_list_needs_barrier(false),
252 _bs(NULL),
253 _is_alive_non_header(NULL),
254 _num_q(0),
255 _max_num_q(0),
256 _processing_is_mt(false),
257 _next_id(0)
258 { }
259
260 // Default parameters give you a vanilla reference processor.
261 ReferenceProcessor(MemRegion span,
262 bool mt_processing = false, int mt_processing_degree = 1,
263 bool mt_discovery = false, int mt_discovery_degree = 1,
264 bool atomic_discovery = true,
265 BoolObjectClosure* is_alive_non_header = NULL,
266 bool discovered_list_needs_barrier = false);
267
268 // RefDiscoveryPolicy values
269 enum DiscoveryPolicy {
270 ReferenceBasedDiscovery = 0,
271 ReferentBasedDiscovery = 1,
272 DiscoveryPolicyMin = ReferenceBasedDiscovery,
273 DiscoveryPolicyMax = ReferentBasedDiscovery
274 };
275
276 static void init_statics();
277
278 public:
279 // get and set "is_alive_non_header" field
280 BoolObjectClosure* is_alive_non_header() {
281 return _is_alive_non_header;
282 }
283 void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
284 _is_alive_non_header = is_alive_non_header;
285 }
286
287 // get and set span
288 MemRegion span() { return _span; }
289 void set_span(MemRegion span) { _span = span; }
290
291 // start and stop weak ref discovery
292 void enable_discovery() { _discovering_refs = true; }
293 void disable_discovery() { _discovering_refs = false; }
294 bool discovery_enabled() { return _discovering_refs; }
295
296 // whether discovery is atomic wrt other collectors
297 bool discovery_is_atomic() const { return _discovery_is_atomic; }
298 void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
299
300 // whether discovery is done by multiple threads same-old-timeously
301 bool discovery_is_mt() const { return _discovery_is_mt; }
302 void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
303
304 // Whether we are in a phase when _processing_ is MT.
305 bool processing_is_mt() const { return _processing_is_mt; }
306 void set_mt_processing(bool mt) { _processing_is_mt = mt; }
307
308 // whether all enqueuing of weak references is complete
309 bool enqueuing_is_done() { return _enqueuing_is_done; }
310 void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
311
312 // iterate over oops
313 void weak_oops_do(OopClosure* f); // weak roots
314
315 // Balance each of the discovered lists.
316 void balance_all_queues();
317
318 // Discover a Reference object, using appropriate discovery criteria
319 bool discover_reference(oop obj, ReferenceType rt);
320
321 // Process references found during GC (called by the garbage collector)
322 void process_discovered_references(BoolObjectClosure* is_alive,
323 OopClosure* keep_alive,
324 VoidClosure* complete_gc,
325 AbstractRefProcTaskExecutor* task_executor);
326
327 public:
328 // Enqueue references at end of GC (called by the garbage collector)
329 bool enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor = NULL);
330
331 // If a discovery is in process that is being superceded, abandon it: all
332 // the discovered lists will be empty, and all the objects on them will
333 // have NULL discovered fields. Must be called only at a safepoint.
334 void abandon_partial_discovery();
335
336 // debugging
337 void verify_no_references_recorded() PRODUCT_RETURN;
338 void verify_referent(oop obj) PRODUCT_RETURN;
339
340 // clear the discovered lists (unlinking each entry).
341 void clear_discovered_references() PRODUCT_RETURN;
342 };
343
344 // A utility class to disable reference discovery in
345 // the scope which contains it, for given ReferenceProcessor.
346 class NoRefDiscovery: StackObj {
347 private:
348 ReferenceProcessor* _rp;
349 bool _was_discovering_refs;
350 public:
351 NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
352 _was_discovering_refs = _rp->discovery_enabled();
353 if (_was_discovering_refs) {
354 _rp->disable_discovery();
355 }
356 }
357
358 ~NoRefDiscovery() {
359 if (_was_discovering_refs) {
360 _rp->enable_discovery();
361 }
362 }
363 };
364
365
366 // A utility class to temporarily mutate the span of the
367 // given ReferenceProcessor in the scope that contains it.
368 class ReferenceProcessorSpanMutator: StackObj {
369 private:
370 ReferenceProcessor* _rp;
371 MemRegion _saved_span;
372
373 public:
374 ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
375 MemRegion span):
376 _rp(rp) {
377 _saved_span = _rp->span();
378 _rp->set_span(span);
379 }
380
381 ~ReferenceProcessorSpanMutator() {
382 _rp->set_span(_saved_span);
383 }
384 };
385
386 // A utility class to temporarily change the MT'ness of
387 // reference discovery for the given ReferenceProcessor
388 // in the scope that contains it.
389 class ReferenceProcessorMTDiscoveryMutator: StackObj {
390 private:
391 ReferenceProcessor* _rp;
392 bool _saved_mt;
393
394 public:
395 ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp,
396 bool mt):
397 _rp(rp) {
398 _saved_mt = _rp->discovery_is_mt();
399 _rp->set_mt_discovery(mt);
400 }
401
402 ~ReferenceProcessorMTDiscoveryMutator() {
403 _rp->set_mt_discovery(_saved_mt);
404 }
405 };
406
407
408 // A utility class to temporarily change the disposition
409 // of the "is_alive_non_header" closure field of the
410 // given ReferenceProcessor in the scope that contains it.
411 class ReferenceProcessorIsAliveMutator: StackObj {
412 private:
413 ReferenceProcessor* _rp;
414 BoolObjectClosure* _saved_cl;
415
416 public:
417 ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
418 BoolObjectClosure* cl):
419 _rp(rp) {
420 _saved_cl = _rp->is_alive_non_header();
421 _rp->set_is_alive_non_header(cl);
422 }
423
424 ~ReferenceProcessorIsAliveMutator() {
425 _rp->set_is_alive_non_header(_saved_cl);
426 }
427 };
428
429 // A utility class to temporarily change the disposition
430 // of the "discovery_is_atomic" field of the
431 // given ReferenceProcessor in the scope that contains it.
432 class ReferenceProcessorAtomicMutator: StackObj {
433 private:
434 ReferenceProcessor* _rp;
435 bool _saved_atomic_discovery;
436
437 public:
438 ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
439 bool atomic):
440 _rp(rp) {
441 _saved_atomic_discovery = _rp->discovery_is_atomic();
442 _rp->set_atomic_discovery(atomic);
443 }
444
445 ~ReferenceProcessorAtomicMutator() {
446 _rp->set_atomic_discovery(_saved_atomic_discovery);
447 }
448 };
449
450
451 // A utility class to temporarily change the MT processing
452 // disposition of the given ReferenceProcessor instance
453 // in the scope that contains it.
454 class ReferenceProcessorMTProcMutator: StackObj {
455 private:
456 ReferenceProcessor* _rp;
457 bool _saved_mt;
458
459 public:
460 ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
461 bool mt):
462 _rp(rp) {
463 _saved_mt = _rp->processing_is_mt();
464 _rp->set_mt_processing(mt);
465 }
466
467 ~ReferenceProcessorMTProcMutator() {
468 _rp->set_mt_processing(_saved_mt);
469 }
470 };
471
472
473 // This class is an interface used to implement task execution for the
474 // reference processing.
475 class AbstractRefProcTaskExecutor {
476 public:
477
478 // Abstract tasks to execute.
479 class ProcessTask;
480 class EnqueueTask;
481
482 // Executes a task using worker threads.
483 virtual void execute(ProcessTask& task) = 0;
484 virtual void execute(EnqueueTask& task) = 0;
485
486 // Switch to single threaded mode.
487 virtual void set_single_threaded_mode() { };
488 };
489
490 // Abstract reference processing task to execute.
491 class AbstractRefProcTaskExecutor::ProcessTask {
492 protected:
493 ProcessTask(ReferenceProcessor& ref_processor,
494 DiscoveredList refs_lists[],
495 bool marks_oops_alive)
496 : _ref_processor(ref_processor),
497 _refs_lists(refs_lists),
498 _marks_oops_alive(marks_oops_alive)
499 { }
500
501 public:
502 virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
503 OopClosure& keep_alive,
504 VoidClosure& complete_gc) = 0;
505
506 // Returns true if a task marks some oops as alive.
507 bool marks_oops_alive() const
508 { return _marks_oops_alive; }
509
510 protected:
511 ReferenceProcessor& _ref_processor;
512 DiscoveredList* _refs_lists;
513 const bool _marks_oops_alive;
514 };
515
516 // Abstract reference processing task to execute.
517 class AbstractRefProcTaskExecutor::EnqueueTask {
518 protected:
519 EnqueueTask(ReferenceProcessor& ref_processor,
520 DiscoveredList refs_lists[],
521 HeapWord* pending_list_addr,
522 int n_queues)
523 : _ref_processor(ref_processor),
524 _refs_lists(refs_lists),
525 _pending_list_addr(pending_list_addr),
526 _n_queues(n_queues)
527 { }
528
529 public:
530 virtual void work(unsigned int work_id) = 0;
531
532 protected:
533 ReferenceProcessor& _ref_processor;
534 DiscoveredList* _refs_lists;
535 HeapWord* _pending_list_addr;
536 int _n_queues;
537 };
538
539 #endif // SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP