1 /*
2 * Copyright (c) 2002, 2012, 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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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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24
25 #ifndef SHARE_VM_GC_IMPLEMENTATION_PARALLELSCAVENGE_GCTASKMANAGER_HPP
26 #define SHARE_VM_GC_IMPLEMENTATION_PARALLELSCAVENGE_GCTASKMANAGER_HPP
27
28 #include "runtime/mutex.hpp"
29 #include "utilities/growableArray.hpp"
30
31 //
32 // The GCTaskManager is a queue of GCTasks, and accessors
33 // to allow the queue to be accessed from many threads.
34 //
35
36 // Forward declarations of types defined in this file.
37 class GCTask;
38 class GCTaskQueue;
39 class SynchronizedGCTaskQueue;
40 class GCTaskManager;
41 class NotifyDoneClosure;
42 // Some useful subclasses of GCTask. You can also make up your own.
43 class NoopGCTask;
44 class BarrierGCTask;
45 class ReleasingBarrierGCTask;
46 class NotifyingBarrierGCTask;
47 class WaitForBarrierGCTask;
48 class IdleGCTask;
49 // A free list of Monitor*'s.
50 class MonitorSupply;
51
52 // Forward declarations of classes referenced in this file via pointer.
53 class GCTaskThread;
54 class Mutex;
55 class Monitor;
56 class ThreadClosure;
57
58 // The abstract base GCTask.
59 class GCTask : public ResourceObj {
60 public:
61 // Known kinds of GCTasks, for predicates.
62 class Kind : AllStatic {
63 public:
64 enum kind {
65 unknown_task,
66 ordinary_task,
67 barrier_task,
68 noop_task,
69 idle_task
70 };
71 static const char* to_string(kind value);
72 };
73 private:
74 // Instance state.
75 const Kind::kind _kind; // For runtime type checking.
76 const uint _affinity; // Which worker should run task.
77 GCTask* _newer; // Tasks are on doubly-linked ...
78 GCTask* _older; // ... lists.
79 public:
80 virtual char* name() { return (char *)"task"; }
81
82 // Abstract do_it method
83 virtual void do_it(GCTaskManager* manager, uint which) = 0;
84 // Accessors
85 Kind::kind kind() const {
86 return _kind;
87 }
88 uint affinity() const {
89 return _affinity;
90 }
91 GCTask* newer() const {
92 return _newer;
93 }
94 void set_newer(GCTask* n) {
95 _newer = n;
96 }
97 GCTask* older() const {
98 return _older;
99 }
100 void set_older(GCTask* p) {
101 _older = p;
102 }
103 // Predicates.
104 bool is_ordinary_task() const {
105 return kind()==Kind::ordinary_task;
106 }
107 bool is_barrier_task() const {
108 return kind()==Kind::barrier_task;
109 }
110 bool is_noop_task() const {
111 return kind()==Kind::noop_task;
112 }
113 bool is_idle_task() const {
114 return kind()==Kind::idle_task;
115 }
116 void print(const char* message) const PRODUCT_RETURN;
117 protected:
118 // Constructors: Only create subclasses.
119 // An ordinary GCTask.
120 GCTask();
121 // A GCTask of a particular kind, usually barrier or noop.
122 GCTask(Kind::kind kind);
123 // An ordinary GCTask with an affinity.
124 GCTask(uint affinity);
125 // A GCTask of a particular kind, with and affinity.
126 GCTask(Kind::kind kind, uint affinity);
127 // We want a virtual destructor because virtual methods,
128 // but since ResourceObj's don't have their destructors
129 // called, we don't have one at all. Instead we have
130 // this method, which gets called by subclasses to clean up.
131 virtual void destruct();
132 // Methods.
133 void initialize();
134 };
135
136 // A doubly-linked list of GCTasks.
137 // The list is not synchronized, because sometimes we want to
138 // build up a list and then make it available to other threads.
139 // See also: SynchronizedGCTaskQueue.
140 class GCTaskQueue : public ResourceObj {
141 private:
142 // Instance state.
143 GCTask* _insert_end; // Tasks are enqueued at this end.
144 GCTask* _remove_end; // Tasks are dequeued from this end.
145 uint _length; // The current length of the queue.
146 const bool _is_c_heap_obj; // Is this a CHeapObj?
147 public:
148 // Factory create and destroy methods.
149 // Create as ResourceObj.
150 static GCTaskQueue* create();
151 // Create as CHeapObj.
152 static GCTaskQueue* create_on_c_heap();
153 // Destroyer.
154 static void destroy(GCTaskQueue* that);
155 // Accessors.
156 // These just examine the state of the queue.
157 bool is_empty() const {
158 assert(((insert_end() == NULL && remove_end() == NULL) ||
159 (insert_end() != NULL && remove_end() != NULL)),
160 "insert_end and remove_end don't match");
161 assert((insert_end() != NULL) || (_length == 0), "Not empty");
162 return insert_end() == NULL;
163 }
164 uint length() const {
165 return _length;
166 }
167 // Methods.
168 // Enqueue one task.
169 void enqueue(GCTask* task);
170 // Enqueue a list of tasks. Empties the argument list.
171 void enqueue(GCTaskQueue* list);
172 // Dequeue one task.
173 GCTask* dequeue();
174 // Dequeue one task, preferring one with affinity.
175 GCTask* dequeue(uint affinity);
176 protected:
177 // Constructor. Clients use factory, but there might be subclasses.
178 GCTaskQueue(bool on_c_heap);
179 // Destructor-like method.
180 // Because ResourceMark doesn't call destructors.
181 // This method cleans up like one.
182 virtual void destruct();
183 // Accessors.
184 GCTask* insert_end() const {
185 return _insert_end;
186 }
187 void set_insert_end(GCTask* value) {
188 _insert_end = value;
189 }
190 GCTask* remove_end() const {
191 return _remove_end;
192 }
193 void set_remove_end(GCTask* value) {
194 _remove_end = value;
195 }
196 void increment_length() {
197 _length += 1;
198 }
199 void decrement_length() {
200 _length -= 1;
201 }
202 void set_length(uint value) {
203 _length = value;
204 }
205 bool is_c_heap_obj() const {
206 return _is_c_heap_obj;
207 }
208 // Methods.
209 void initialize();
210 GCTask* remove(); // Remove from remove end.
211 GCTask* remove(GCTask* task); // Remove from the middle.
212 void print(const char* message) const PRODUCT_RETURN;
213 // Debug support
214 void verify_length() const PRODUCT_RETURN;
215 };
216
217 // A GCTaskQueue that can be synchronized.
218 // This "has-a" GCTaskQueue and a mutex to do the exclusion.
219 class SynchronizedGCTaskQueue : public CHeapObj<mtGC> {
220 private:
221 // Instance state.
222 GCTaskQueue* _unsynchronized_queue; // Has-a unsynchronized queue.
223 Monitor * _lock; // Lock to control access.
224 public:
225 // Factory create and destroy methods.
226 static SynchronizedGCTaskQueue* create(GCTaskQueue* queue, Monitor * lock) {
227 return new SynchronizedGCTaskQueue(queue, lock);
228 }
229 static void destroy(SynchronizedGCTaskQueue* that) {
230 if (that != NULL) {
231 delete that;
232 }
233 }
234 // Accessors
235 GCTaskQueue* unsynchronized_queue() const {
236 return _unsynchronized_queue;
237 }
238 Monitor * lock() const {
239 return _lock;
240 }
241 // GCTaskQueue wrapper methods.
242 // These check that you hold the lock
243 // and then call the method on the queue.
244 bool is_empty() const {
245 guarantee(own_lock(), "don't own the lock");
246 return unsynchronized_queue()->is_empty();
247 }
248 void enqueue(GCTask* task) {
249 guarantee(own_lock(), "don't own the lock");
250 unsynchronized_queue()->enqueue(task);
251 }
252 void enqueue(GCTaskQueue* list) {
253 guarantee(own_lock(), "don't own the lock");
254 unsynchronized_queue()->enqueue(list);
255 }
256 GCTask* dequeue() {
257 guarantee(own_lock(), "don't own the lock");
258 return unsynchronized_queue()->dequeue();
259 }
260 GCTask* dequeue(uint affinity) {
261 guarantee(own_lock(), "don't own the lock");
262 return unsynchronized_queue()->dequeue(affinity);
263 }
264 uint length() const {
265 guarantee(own_lock(), "don't own the lock");
266 return unsynchronized_queue()->length();
267 }
268 // For guarantees.
269 bool own_lock() const {
270 return lock()->owned_by_self();
271 }
272 protected:
273 // Constructor. Clients use factory, but there might be subclasses.
274 SynchronizedGCTaskQueue(GCTaskQueue* queue, Monitor * lock);
275 // Destructor. Not virtual because no virtuals.
276 ~SynchronizedGCTaskQueue();
277 };
278
279 // This is an abstract base class for getting notifications
280 // when a GCTaskManager is done.
281 class NotifyDoneClosure : public CHeapObj<mtGC> {
282 public:
283 // The notification callback method.
284 virtual void notify(GCTaskManager* manager) = 0;
285 protected:
286 // Constructor.
287 NotifyDoneClosure() {
288 // Nothing to do.
289 }
290 // Virtual destructor because virtual methods.
291 virtual ~NotifyDoneClosure() {
292 // Nothing to do.
293 }
294 };
295
296 // Dynamic number of GC threads
297 //
298 // GC threads wait in get_task() for work (i.e., a task) to perform.
299 // When the number of GC threads was static, the number of tasks
300 // created to do a job was equal to or greater than the maximum
301 // number of GC threads (ParallelGCThreads). The job might be divided
302 // into a number of tasks greater than the number of GC threads for
303 // load balancing (i.e., over partitioning). The last task to be
304 // executed by a GC thread in a job is a work stealing task. A
305 // GC thread that gets a work stealing task continues to execute
306 // that task until the job is done. In the static number of GC threads
307 // case, tasks are added to a queue (FIFO). The work stealing tasks are
308 // the last to be added. Once the tasks are added, the GC threads grab
309 // a task and go. A single thread can do all the non-work stealing tasks
310 // and then execute a work stealing and wait for all the other GC threads
311 // to execute their work stealing task.
312 // In the dynamic number of GC threads implementation, idle-tasks are
313 // created to occupy the non-participating or "inactive" threads. An
314 // idle-task makes the GC thread wait on a barrier that is part of the
315 // GCTaskManager. The GC threads that have been "idled" in a IdleGCTask
316 // are released once all the active GC threads have finished their work
317 // stealing tasks. The GCTaskManager does not wait for all the "idled"
318 // GC threads to resume execution. When those GC threads do resume
319 // execution in the course of the thread scheduling, they call get_tasks()
320 // as all the other GC threads do. Because all the "idled" threads are
321 // not required to execute in order to finish a job, it is possible for
322 // a GC thread to still be "idled" when the next job is started. Such
323 // a thread stays "idled" for the next job. This can result in a new
324 // job not having all the expected active workers. For example if on
325 // job requests 4 active workers out of a total of 10 workers so the
326 // remaining 6 are "idled", if the next job requests 6 active workers
327 // but all 6 of the "idled" workers are still idle, then the next job
328 // will only get 4 active workers.
329 // The implementation for the parallel old compaction phase has an
330 // added complication. In the static case parold partitions the chunks
331 // ready to be filled into stacks, one for each GC thread. A GC thread
332 // executing a draining task (drains the stack of ready chunks)
333 // claims a stack according to it's id (the unique ordinal value assigned
334 // to each GC thread). In the dynamic case not all GC threads will
335 // actively participate so stacks with ready to fill chunks can only be
336 // given to the active threads. An initial implementation chose stacks
337 // number 1-n to get the ready chunks and required that GC threads
338 // 1-n be the active workers. This was undesirable because it required
339 // certain threads to participate. In the final implementation a
340 // list of stacks equal in number to the active workers are filled
341 // with ready chunks. GC threads that participate get a stack from
342 // the task (DrainStacksCompactionTask), empty the stack, and then add it to a
343 // recycling list at the end of the task. If the same GC thread gets
344 // a second task, it gets a second stack to drain and returns it. The
345 // stacks are added to a recycling list so that later stealing tasks
346 // for this tasks can get a stack from the recycling list. Stealing tasks
347 // use the stacks in its work in a way similar to the draining tasks.
348 // A thread is not guaranteed to get anything but a stealing task and
349 // a thread that only gets a stealing task has to get a stack. A failed
350 // implementation tried to have the GC threads keep the stack they used
351 // during a draining task for later use in the stealing task but that didn't
352 // work because as noted a thread is not guaranteed to get a draining task.
353 //
354 // For PSScavenge and ParCompactionManager the GC threads are
355 // held in the GCTaskThread** _thread array in GCTaskManager.
356
357
358 class GCTaskManager : public CHeapObj<mtGC> {
359 friend class ParCompactionManager;
360 friend class PSParallelCompact;
361 friend class PSScavenge;
362 friend class PSRefProcTaskExecutor;
363 friend class RefProcTaskExecutor;
364 friend class GCTaskThread;
365 friend class IdleGCTask;
366 private:
367 // Instance state.
368 NotifyDoneClosure* _ndc; // Notify on completion.
369 const uint _workers; // Number of workers.
370 Monitor* _monitor; // Notification of changes.
371 SynchronizedGCTaskQueue* _queue; // Queue of tasks.
372 GCTaskThread** _thread; // Array of worker threads.
373 uint _active_workers; // Number of active workers.
374 uint _busy_workers; // Number of busy workers.
375 uint _blocking_worker; // The worker that's blocking.
376 bool* _resource_flag; // Array of flag per threads.
377 uint _delivered_tasks; // Count of delivered tasks.
378 uint _completed_tasks; // Count of completed tasks.
379 uint _barriers; // Count of barrier tasks.
380 uint _emptied_queue; // Times we emptied the queue.
381 NoopGCTask* _noop_task; // The NoopGCTask instance.
382 uint _noop_tasks; // Count of noop tasks.
383 WaitForBarrierGCTask* _idle_inactive_task;// Task for inactive workers
384 volatile uint _idle_workers; // Number of idled workers
385 public:
386 // Factory create and destroy methods.
387 static GCTaskManager* create(uint workers) {
388 return new GCTaskManager(workers);
389 }
390 static GCTaskManager* create(uint workers, NotifyDoneClosure* ndc) {
391 return new GCTaskManager(workers, ndc);
392 }
393 static void destroy(GCTaskManager* that) {
394 if (that != NULL) {
395 delete that;
396 }
397 }
398 // Accessors.
399 uint busy_workers() const {
400 return _busy_workers;
401 }
402 volatile uint idle_workers() const {
403 return _idle_workers;
404 }
405 // Pun between Monitor* and Mutex*
406 Monitor* monitor() const {
407 return _monitor;
408 }
409 Monitor * lock() const {
410 return _monitor;
411 }
412 WaitForBarrierGCTask* idle_inactive_task() {
413 return _idle_inactive_task;
414 }
415 // Methods.
416 // Add the argument task to be run.
417 void add_task(GCTask* task);
418 // Add a list of tasks. Removes task from the argument list.
419 void add_list(GCTaskQueue* list);
420 // Claim a task for argument worker.
421 GCTask* get_task(uint which);
422 // Note the completion of a task by the argument worker.
423 void note_completion(uint which);
424 // Is the queue blocked from handing out new tasks?
425 bool is_blocked() const {
426 return (blocking_worker() != sentinel_worker());
427 }
428 // Request that all workers release their resources.
429 void release_all_resources();
430 // Ask if a particular worker should release its resources.
431 bool should_release_resources(uint which); // Predicate.
432 // Note the release of resources by the argument worker.
433 void note_release(uint which);
434 // Create IdleGCTasks for inactive workers and start workers
435 void task_idle_workers();
436 // Release the workers in IdleGCTasks
437 void release_idle_workers();
438 // Constants.
439 // A sentinel worker identifier.
440 static uint sentinel_worker() {
441 return (uint) -1; // Why isn't there a max_uint?
442 }
443
444 // Execute the task queue and wait for the completion.
445 void execute_and_wait(GCTaskQueue* list);
446
447 void print_task_time_stamps();
448 void print_threads_on(outputStream* st);
449 void threads_do(ThreadClosure* tc);
450
451 protected:
452 // Constructors. Clients use factory, but there might be subclasses.
453 // Create a GCTaskManager with the appropriate number of workers.
454 GCTaskManager(uint workers);
455 // Create a GCTaskManager that calls back when there's no more work.
456 GCTaskManager(uint workers, NotifyDoneClosure* ndc);
457 // Make virtual if necessary.
458 ~GCTaskManager();
459 // Accessors.
460 uint workers() const {
461 return _workers;
462 }
463 void set_active_workers(uint v) {
464 assert(v <= _workers, "Trying to set more workers active than there are");
465 _active_workers = MIN2(v, _workers);
466 assert(v != 0, "Trying to set active workers to 0");
467 _active_workers = MAX2(1U, _active_workers);
468 }
469 // Sets the number of threads that will be used in a collection
470 void set_active_gang();
471
472 NotifyDoneClosure* notify_done_closure() const {
473 return _ndc;
474 }
475 SynchronizedGCTaskQueue* queue() const {
476 return _queue;
477 }
478 NoopGCTask* noop_task() const {
479 return _noop_task;
480 }
481 // Bounds-checking per-thread data accessors.
482 GCTaskThread* thread(uint which);
483 void set_thread(uint which, GCTaskThread* value);
484 bool resource_flag(uint which);
485 void set_resource_flag(uint which, bool value);
486 // Modifier methods with some semantics.
487 // Is any worker blocking handing out new tasks?
488 uint blocking_worker() const {
489 return _blocking_worker;
490 }
491 void set_blocking_worker(uint value) {
492 _blocking_worker = value;
493 }
494 void set_unblocked() {
495 set_blocking_worker(sentinel_worker());
496 }
497 // Count of busy workers.
498 void reset_busy_workers() {
499 _busy_workers = 0;
500 }
501 uint increment_busy_workers();
502 uint decrement_busy_workers();
503 // Count of tasks delivered to workers.
504 uint delivered_tasks() const {
505 return _delivered_tasks;
506 }
507 void increment_delivered_tasks() {
508 _delivered_tasks += 1;
509 }
510 void reset_delivered_tasks() {
511 _delivered_tasks = 0;
512 }
513 // Count of tasks completed by workers.
514 uint completed_tasks() const {
515 return _completed_tasks;
516 }
517 void increment_completed_tasks() {
518 _completed_tasks += 1;
519 }
520 void reset_completed_tasks() {
521 _completed_tasks = 0;
522 }
523 // Count of barrier tasks completed.
524 uint barriers() const {
525 return _barriers;
526 }
527 void increment_barriers() {
528 _barriers += 1;
529 }
530 void reset_barriers() {
531 _barriers = 0;
532 }
533 // Count of how many times the queue has emptied.
534 uint emptied_queue() const {
535 return _emptied_queue;
536 }
537 void increment_emptied_queue() {
538 _emptied_queue += 1;
539 }
540 void reset_emptied_queue() {
541 _emptied_queue = 0;
542 }
543 // Count of the number of noop tasks we've handed out,
544 // e.g., to handle resource release requests.
545 uint noop_tasks() const {
546 return _noop_tasks;
547 }
548 void increment_noop_tasks() {
549 _noop_tasks += 1;
550 }
551 void reset_noop_tasks() {
552 _noop_tasks = 0;
553 }
554 void increment_idle_workers() {
555 _idle_workers++;
556 }
557 void decrement_idle_workers() {
558 _idle_workers--;
559 }
560 // Other methods.
561 void initialize();
562
563 public:
564 // Return true if all workers are currently active.
565 bool all_workers_active() { return workers() == active_workers(); }
566 uint active_workers() const {
567 return _active_workers;
568 }
569 };
570
571 //
572 // Some exemplary GCTasks.
573 //
574
575 // A noop task that does nothing,
576 // except take us around the GCTaskThread loop.
577 class NoopGCTask : public GCTask {
578 private:
579 const bool _is_c_heap_obj; // Is this a CHeapObj?
580 public:
581 // Factory create and destroy methods.
582 static NoopGCTask* create();
583 static NoopGCTask* create_on_c_heap();
584 static void destroy(NoopGCTask* that);
585
586 virtual char* name() { return (char *)"noop task"; }
587 // Methods from GCTask.
588 void do_it(GCTaskManager* manager, uint which) {
589 // Nothing to do.
590 }
591 protected:
592 // Constructor.
593 NoopGCTask(bool on_c_heap) :
594 GCTask(GCTask::Kind::noop_task),
595 _is_c_heap_obj(on_c_heap) {
596 // Nothing to do.
597 }
598 // Destructor-like method.
599 void destruct();
600 // Accessors.
601 bool is_c_heap_obj() const {
602 return _is_c_heap_obj;
603 }
604 };
605
606 // A BarrierGCTask blocks other tasks from starting,
607 // and waits until it is the only task running.
608 class BarrierGCTask : public GCTask {
609 public:
610 // Factory create and destroy methods.
611 static BarrierGCTask* create() {
612 return new BarrierGCTask();
613 }
614 static void destroy(BarrierGCTask* that) {
615 if (that != NULL) {
616 that->destruct();
617 delete that;
618 }
619 }
620 // Methods from GCTask.
621 void do_it(GCTaskManager* manager, uint which);
622 protected:
623 // Constructor. Clients use factory, but there might be subclasses.
624 BarrierGCTask() :
625 GCTask(GCTask::Kind::barrier_task) {
626 // Nothing to do.
627 }
628 // Destructor-like method.
629 void destruct();
630
631 virtual char* name() { return (char *)"barrier task"; }
632 // Methods.
633 // Wait for this to be the only task running.
634 void do_it_internal(GCTaskManager* manager, uint which);
635 };
636
637 // A ReleasingBarrierGCTask is a BarrierGCTask
638 // that tells all the tasks to release their resource areas.
639 class ReleasingBarrierGCTask : public BarrierGCTask {
640 public:
641 // Factory create and destroy methods.
642 static ReleasingBarrierGCTask* create() {
643 return new ReleasingBarrierGCTask();
644 }
645 static void destroy(ReleasingBarrierGCTask* that) {
646 if (that != NULL) {
647 that->destruct();
648 delete that;
649 }
650 }
651 // Methods from GCTask.
652 void do_it(GCTaskManager* manager, uint which);
653 protected:
654 // Constructor. Clients use factory, but there might be subclasses.
655 ReleasingBarrierGCTask() :
656 BarrierGCTask() {
657 // Nothing to do.
658 }
659 // Destructor-like method.
660 void destruct();
661 };
662
663 // A NotifyingBarrierGCTask is a BarrierGCTask
664 // that calls a notification method when it is the only task running.
665 class NotifyingBarrierGCTask : public BarrierGCTask {
666 private:
667 // Instance state.
668 NotifyDoneClosure* _ndc; // The callback object.
669 public:
670 // Factory create and destroy methods.
671 static NotifyingBarrierGCTask* create(NotifyDoneClosure* ndc) {
672 return new NotifyingBarrierGCTask(ndc);
673 }
674 static void destroy(NotifyingBarrierGCTask* that) {
675 if (that != NULL) {
676 that->destruct();
677 delete that;
678 }
679 }
680 // Methods from GCTask.
681 void do_it(GCTaskManager* manager, uint which);
682 protected:
683 // Constructor. Clients use factory, but there might be subclasses.
684 NotifyingBarrierGCTask(NotifyDoneClosure* ndc) :
685 BarrierGCTask(),
686 _ndc(ndc) {
687 assert(notify_done_closure() != NULL, "can't notify on NULL");
688 }
689 // Destructor-like method.
690 void destruct();
691 // Accessor.
692 NotifyDoneClosure* notify_done_closure() const { return _ndc; }
693 };
694
695 // A WaitForBarrierGCTask is a BarrierGCTask
696 // with a method you can call to wait until
697 // the BarrierGCTask is done.
698 // This may cover many of the uses of NotifyingBarrierGCTasks.
699 class WaitForBarrierGCTask : public BarrierGCTask {
700 friend class GCTaskManager;
701 friend class IdleGCTask;
702 private:
703 // Instance state.
704 Monitor* _monitor; // Guard and notify changes.
705 volatile bool _should_wait; // true=>wait, false=>proceed.
706 const bool _is_c_heap_obj; // Was allocated on the heap.
707 public:
708 virtual char* name() { return (char *) "waitfor-barrier-task"; }
709
710 // Factory create and destroy methods.
711 static WaitForBarrierGCTask* create();
712 static WaitForBarrierGCTask* create_on_c_heap();
713 static void destroy(WaitForBarrierGCTask* that);
714 // Methods.
715 void do_it(GCTaskManager* manager, uint which);
716 void wait_for(bool reset);
717 void set_should_wait(bool value) {
718 _should_wait = value;
719 }
720 protected:
721 // Constructor. Clients use factory, but there might be subclasses.
722 WaitForBarrierGCTask(bool on_c_heap);
723 // Destructor-like method.
724 void destruct();
725 // Accessors.
726 Monitor* monitor() const {
727 return _monitor;
728 }
729 bool should_wait() const {
730 return _should_wait;
731 }
732 bool is_c_heap_obj() {
733 return _is_c_heap_obj;
734 }
735 };
736
737 // Task that is used to idle a GC task when fewer than
738 // the maximum workers are wanted.
739 class IdleGCTask : public GCTask {
740 const bool _is_c_heap_obj; // Was allocated on the heap.
741 public:
742 bool is_c_heap_obj() {
743 return _is_c_heap_obj;
744 }
745 // Factory create and destroy methods.
746 static IdleGCTask* create();
747 static IdleGCTask* create_on_c_heap();
748 static void destroy(IdleGCTask* that);
749
750 virtual char* name() { return (char *)"idle task"; }
751 // Methods from GCTask.
752 virtual void do_it(GCTaskManager* manager, uint which);
753 protected:
754 // Constructor.
755 IdleGCTask(bool on_c_heap) :
756 GCTask(GCTask::Kind::idle_task),
757 _is_c_heap_obj(on_c_heap) {
758 // Nothing to do.
759 }
760 // Destructor-like method.
761 void destruct();
762 };
763
764 class MonitorSupply : public AllStatic {
765 private:
766 // State.
767 // Control multi-threaded access.
768 static Mutex* _lock;
769 // The list of available Monitor*'s.
770 static GrowableArray<Monitor*>* _freelist;
771 public:
772 // Reserve a Monitor*.
773 static Monitor* reserve();
774 // Release a Monitor*.
775 static void release(Monitor* instance);
776 private:
777 // Accessors.
778 static Mutex* lock() {
779 return _lock;
780 }
781 static GrowableArray<Monitor*>* freelist() {
782 return _freelist;
783 }
784 };
785
786 #endif // SHARE_VM_GC_IMPLEMENTATION_PARALLELSCAVENGE_GCTASKMANAGER_HPP