32 |
|
* zero, and advancing when all parties reach the barrier (wrapping |
33 |
|
* around to zero after reaching {@code Integer.MAX_VALUE}). |
34 |
|
* |
35 |
< |
* <li> Like a CyclicBarrier, a Phaser may be repeatedly awaited. |
36 |
< |
* Method {@code arriveAndAwaitAdvance} has effect analogous to |
37 |
< |
* {@code CyclicBarrier.await}. However, Phasers separate two |
38 |
< |
* aspects of coordination, that may also be invoked independently: |
35 |
> |
* <li> Like a {@code CyclicBarrier}, a phaser may be repeatedly |
36 |
> |
* awaited. Method {@link #arriveAndAwaitAdvance} has effect |
37 |
> |
* analogous to {@link java.util.concurrent.CyclicBarrier#await |
38 |
> |
* CyclicBarrier.await}. However, phasers separate two aspects of |
39 |
> |
* coordination, which may also be invoked independently: |
40 |
|
* |
41 |
|
* <ul> |
42 |
|
* |
43 |
< |
* <li> Arriving at a barrier. Methods {@code arrive} and |
44 |
< |
* {@code arriveAndDeregister} do not block, but return |
43 |
> |
* <li> Arriving at a barrier. Methods {@link #arrive} and |
44 |
> |
* {@link #arriveAndDeregister} do not block, but return |
45 |
|
* the phase value current upon entry to the method. |
46 |
|
* |
47 |
< |
* <li> Awaiting others. Method {@code awaitAdvance} requires an |
47 |
> |
* <li> Awaiting others. Method {@link #awaitAdvance} requires an |
48 |
|
* argument indicating the entry phase, and returns when the |
49 |
|
* barrier advances to a new phase. |
50 |
|
* </ul> |
51 |
|
* |
52 |
|
* |
53 |
|
* <li> Barrier actions, performed by the task triggering a phase |
54 |
< |
* advance while others may be waiting, are arranged by overriding |
55 |
< |
* method {@code onAdvance}, that also controls termination. |
56 |
< |
* Overriding this method may be used to similar but more flexible |
57 |
< |
* effect as providing a barrier action to a CyclicBarrier. |
54 |
> |
* advance, are arranged by overriding method {@link #onAdvance(int, |
55 |
> |
* int)}, which also controls termination. Overriding this method is |
56 |
> |
* similar to, but more flexible than, providing a barrier action to a |
57 |
> |
* {@code CyclicBarrier}. |
58 |
|
* |
59 |
|
* <li> Phasers may enter a <em>termination</em> state in which all |
60 |
|
* actions immediately return without updating phaser state or waiting |
61 |
|
* for advance, and indicating (via a negative phase value) that |
62 |
< |
* execution is complete. Termination is triggered by executing the |
63 |
< |
* overridable {@code onAdvance} method that is invoked each time the |
64 |
< |
* barrier is about to be tripped. When a Phaser is controlling an |
65 |
< |
* action with a fixed number of iterations, it is often convenient to |
66 |
< |
* override this method to cause termination when the current phase |
67 |
< |
* number reaches a threshold. Method {@code forceTermination} is also |
68 |
< |
* available to abruptly release waiting threads and allow them to |
68 |
< |
* terminate. |
62 |
> |
* execution is complete. Termination is triggered when an invocation |
63 |
> |
* of {@code onAdvance} returns {@code true}. When a phaser is |
64 |
> |
* controlling an action with a fixed number of iterations, it is |
65 |
> |
* often convenient to override this method to cause termination when |
66 |
> |
* the current phase number reaches a threshold. Method {@link |
67 |
> |
* #forceTermination} is also available to abruptly release waiting |
68 |
> |
* threads and allow them to terminate. |
69 |
|
* |
70 |
|
* <li> Phasers may be tiered to reduce contention. Phasers with large |
71 |
|
* numbers of parties that would otherwise experience heavy |
75 |
|
* |
76 |
|
* <li> By default, {@code awaitAdvance} continues to wait even if |
77 |
|
* the waiting thread is interrupted. And unlike the case in |
78 |
< |
* CyclicBarriers, exceptions encountered while tasks wait |
78 |
> |
* {@code CyclicBarrier}, exceptions encountered while tasks wait |
79 |
|
* interruptibly or with timeout do not change the state of the |
80 |
|
* barrier. If necessary, you can perform any associated recovery |
81 |
|
* within handlers of those exceptions, often after invoking |
82 |
|
* {@code forceTermination}. |
83 |
|
* |
84 |
< |
* <li>Phasers ensure lack of starvation when used by ForkJoinTasks. |
84 |
> |
* <li>Phasers may be used to coordinate tasks executing in a {@link |
85 |
> |
* ForkJoinPool}, which will ensure sufficient parallelism to execute |
86 |
> |
* tasks when others are blocked waiting for a phase to advance. |
87 |
|
* |
88 |
|
* </ul> |
89 |
|
* |
90 |
|
* <p><b>Sample usages:</b> |
91 |
|
* |
92 |
< |
* <p>A Phaser may be used instead of a {@code CountDownLatch} to control |
93 |
< |
* a one-shot action serving a variable number of parties. The typical |
94 |
< |
* idiom is for the method setting this up to first register, then |
95 |
< |
* start the actions, then deregister, as in: |
92 |
> |
* <p>A {@code Phaser} may be used instead of a {@code CountDownLatch} |
93 |
> |
* to control a one-shot action serving a variable number of |
94 |
> |
* parties. The typical idiom is for the method setting this up to |
95 |
> |
* first register, then start the actions, then deregister, as in: |
96 |
|
* |
97 |
|
* <pre> {@code |
98 |
|
* void runTasks(List<Runnable> list) { |
99 |
|
* final Phaser phaser = new Phaser(1); // "1" to register self |
100 |
+ |
* // create and start threads |
101 |
|
* for (Runnable r : list) { |
102 |
|
* phaser.register(); |
103 |
|
* new Thread() { |
104 |
|
* public void run() { |
105 |
|
* phaser.arriveAndAwaitAdvance(); // await all creation |
106 |
|
* r.run(); |
104 |
– |
* phaser.arriveAndDeregister(); // signal completion |
107 |
|
* } |
108 |
|
* }.start(); |
109 |
|
* } |
110 |
|
* |
111 |
< |
* doSomethingOnBehalfOfWorkers(); |
112 |
< |
* phaser.arrive(); // allow threads to start |
111 |
< |
* int p = phaser.arriveAndDeregister(); // deregister self ... |
112 |
< |
* p = phaser.awaitAdvance(p); // ... and await arrival |
113 |
< |
* otherActions(); // do other things while tasks execute |
114 |
< |
* phaser.awaitAdvance(p); // await final completion |
111 |
> |
* // allow threads to start and deregister self |
112 |
> |
* phaser.arriveAndDeregister(); |
113 |
|
* }}</pre> |
114 |
|
* |
115 |
|
* <p>One way to cause a set of threads to repeatedly perform actions |
137 |
|
* phaser.arriveAndDeregister(); // deregister self, don't wait |
138 |
|
* }}</pre> |
139 |
|
* |
140 |
< |
* <p> To create a set of tasks using a tree of Phasers, |
140 |
> |
* <p>To create a set of tasks using a tree of phasers, |
141 |
|
* you could use code of the following form, assuming a |
142 |
< |
* Task class with a constructor accepting a Phaser that |
142 |
> |
* Task class with a constructor accepting a phaser that |
143 |
|
* it registers for upon construction: |
144 |
|
* <pre> {@code |
145 |
|
* void build(Task[] actions, int lo, int hi, Phaser b) { |
169 |
|
* |
170 |
|
* <p><b>Implementation notes</b>: This implementation restricts the |
171 |
|
* maximum number of parties to 65535. Attempts to register additional |
172 |
< |
* parties result in IllegalStateExceptions. However, you can and |
172 |
> |
* parties result in {@code IllegalStateException}. However, you can and |
173 |
|
* should create tiered phasers to accommodate arbitrarily large sets |
174 |
|
* of participants. |
175 |
|
* |
247 |
|
private final Phaser parent; |
248 |
|
|
249 |
|
/** |
250 |
< |
* The root of Phaser tree. Equals this if not in a tree. Used to |
250 |
> |
* The root of phaser tree. Equals this if not in a tree. Used to |
251 |
|
* support faster state push-down. |
252 |
|
*/ |
253 |
|
private final Phaser root; |
298 |
|
} |
299 |
|
|
300 |
|
/** |
301 |
< |
* Creates a new Phaser without any initially registered parties, |
301 |
> |
* Creates a new phaser without any initially registered parties, |
302 |
|
* initial phase number 0, and no parent. Any thread using this |
303 |
< |
* Phaser will need to first register for it. |
303 |
> |
* phaser will need to first register for it. |
304 |
|
*/ |
305 |
|
public Phaser() { |
306 |
|
this(null); |
307 |
|
} |
308 |
|
|
309 |
|
/** |
310 |
< |
* Creates a new Phaser with the given numbers of registered |
310 |
> |
* Creates a new phaser with the given numbers of registered |
311 |
|
* unarrived parties, initial phase number 0, and no parent. |
312 |
|
* |
313 |
|
* @param parties the number of parties required to trip barrier |
319 |
|
} |
320 |
|
|
321 |
|
/** |
322 |
< |
* Creates a new Phaser with the given parent, without any |
322 |
> |
* Creates a new phaser with the given parent, without any |
323 |
|
* initially registered parties. If parent is non-null this phaser |
324 |
|
* is registered with the parent and its initial phase number is |
325 |
|
* the same as that of parent phaser. |
339 |
|
} |
340 |
|
|
341 |
|
/** |
342 |
< |
* Creates a new Phaser with the given parent and numbers of |
342 |
> |
* Creates a new phaser with the given parent and numbers of |
343 |
|
* registered unarrived parties. If parent is non-null, this phaser |
344 |
|
* is registered with the parent and its initial phase number is |
345 |
|
* the same as that of parent phaser. |
461 |
|
} |
462 |
|
|
463 |
|
/** |
464 |
< |
* Arrives at the barrier, and deregisters from it, without |
465 |
< |
* waiting for others. Deregistration reduces number of parties |
464 |
> |
* Arrives at the barrier and deregisters from it without waiting |
465 |
> |
* for others. Deregistration reduces the number of parties |
466 |
|
* required to trip the barrier in future phases. If this phaser |
467 |
|
* has a parent, and deregistration causes this phaser to have |
468 |
< |
* zero parties, this phaser is also deregistered from its parent. |
468 |
> |
* zero parties, this phaser also arrives at and is deregistered |
469 |
> |
* from its parent. |
470 |
|
* |
471 |
|
* @return the current barrier phase number upon entry to |
472 |
|
* this method, or a negative value if terminated |
519 |
|
|
520 |
|
/** |
521 |
|
* Arrives at the barrier and awaits others. Equivalent in effect |
522 |
< |
* to {@code awaitAdvance(arrive())}. If you instead need to |
523 |
< |
* await with interruption of timeout, and/or deregister upon |
524 |
< |
* arrival, you can arrange them using analogous constructions. |
522 |
> |
* to {@code awaitAdvance(arrive())}. If you need to await with |
523 |
> |
* interruption or timeout, you can arrange this with an analogous |
524 |
> |
* construction using one of the other forms of the awaitAdvance |
525 |
> |
* method. If instead you need to deregister upon arrival use |
526 |
> |
* {@code arriveAndDeregister}. |
527 |
|
* |
528 |
|
* @return the phase on entry to this method |
529 |
|
* @throws IllegalStateException if not terminated and the number |
534 |
|
} |
535 |
|
|
536 |
|
/** |
537 |
< |
* Awaits the phase of the barrier to advance from the given |
538 |
< |
* value, or returns immediately if argument is negative or this |
539 |
< |
* barrier is terminated. |
537 |
> |
* Awaits the phase of the barrier to advance from the given phase |
538 |
> |
* value, returning immediately if the current phase of the |
539 |
> |
* barrier is not equal to the given phase value or this barrier |
540 |
> |
* is terminated. |
541 |
|
* |
542 |
|
* @param phase the phase on entry to this method |
543 |
|
* @return the phase on exit from this method |
556 |
|
} |
557 |
|
|
558 |
|
/** |
559 |
< |
* Awaits the phase of the barrier to advance from the given |
560 |
< |
* value, or returns immediately if argument is negative or this |
561 |
< |
* barrier is terminated, or throws InterruptedException if |
562 |
< |
* interrupted while waiting. |
559 |
> |
* Awaits the phase of the barrier to advance from the given phase |
560 |
> |
* value, throwing {@code InterruptedException} if interrupted while |
561 |
> |
* waiting, or returning immediately if the current phase of the |
562 |
> |
* barrier is not equal to the given phase value or this barrier |
563 |
> |
* is terminated. |
564 |
|
* |
565 |
|
* @param phase the phase on entry to this method |
566 |
|
* @return the phase on exit from this method |
580 |
|
} |
581 |
|
|
582 |
|
/** |
583 |
< |
* Awaits the phase of the barrier to advance from the given value |
584 |
< |
* or the given timeout elapses, or returns immediately if |
585 |
< |
* argument is negative or this barrier is terminated. |
583 |
> |
* Awaits the phase of the barrier to advance from the given phase |
584 |
> |
* value or the given timeout to elapse, throwing |
585 |
> |
* {@code InterruptedException} if interrupted while waiting, or |
586 |
> |
* returning immediately if the current phase of the barrier is not |
587 |
> |
* equal to the given phase value or this barrier is terminated. |
588 |
|
* |
589 |
|
* @param phase the phase on entry to this method |
590 |
+ |
* @param timeout how long to wait before giving up, in units of |
591 |
+ |
* {@code unit} |
592 |
+ |
* @param unit a {@code TimeUnit} determining how to interpret the |
593 |
+ |
* {@code timeout} parameter |
594 |
|
* @return the phase on exit from this method |
595 |
|
* @throws InterruptedException if thread interrupted while waiting |
596 |
|
* @throws TimeoutException if timed out while waiting |
645 |
|
} |
646 |
|
|
647 |
|
/** |
639 |
– |
* Returns {@code true} if the current phase number equals the given phase. |
640 |
– |
* |
641 |
– |
* @param phase the phase |
642 |
– |
* @return {@code true} if the current phase number equals the given phase |
643 |
– |
*/ |
644 |
– |
public final boolean hasPhase(int phase) { |
645 |
– |
return phaseOf(getReconciledState()) == phase; |
646 |
– |
} |
647 |
– |
|
648 |
– |
/** |
648 |
|
* Returns the number of parties registered at this barrier. |
649 |
|
* |
650 |
|
* @return the number of parties |
674 |
|
} |
675 |
|
|
676 |
|
/** |
677 |
< |
* Returns the parent of this phaser, or null if none. |
677 |
> |
* Returns the parent of this phaser, or {@code null} if none. |
678 |
|
* |
679 |
< |
* @return the parent of this phaser, or null if none |
679 |
> |
* @return the parent of this phaser, or {@code null} if none |
680 |
|
*/ |
681 |
|
public Phaser getParent() { |
682 |
|
return parent; |
705 |
|
* Overridable method to perform an action upon phase advance, and |
706 |
|
* to control termination. This method is invoked whenever the |
707 |
|
* barrier is tripped (and thus all other waiting parties are |
708 |
< |
* dormant). If it returns true, then, rather than advance the |
709 |
< |
* phase number, this barrier will be set to a final termination |
710 |
< |
* state, and subsequent calls to {@code isTerminated} will |
711 |
< |
* return true. |
708 |
> |
* dormant). If it returns {@code true}, then, rather than advance |
709 |
> |
* the phase number, this barrier will be set to a final |
710 |
> |
* termination state, and subsequent calls to {@link #isTerminated} |
711 |
> |
* will return true. |
712 |
|
* |
713 |
< |
* <p> The default version returns true when the number of |
713 |
> |
* <p>The default version returns {@code true} when the number of |
714 |
|
* registered parties is zero. Normally, overrides that arrange |
715 |
|
* termination for other reasons should also preserve this |
716 |
|
* property. |
717 |
|
* |
718 |
< |
* <p> You may override this method to perform an action with side |
718 |
> |
* <p>You may override this method to perform an action with side |
719 |
|
* effects visible to participating tasks, but it is in general |
720 |
|
* only sensible to do so in designs where all parties register |
721 |
< |
* before any arrive, and all {@code awaitAdvance} at each phase. |
722 |
< |
* Otherwise, you cannot ensure lack of interference. In |
723 |
< |
* particular, this method may be invoked more than once per |
725 |
< |
* transition if other parties successfully register while the |
726 |
< |
* invocation of this method is in progress, thus postponing the |
727 |
< |
* transition until those parties also arrive, re-triggering this |
728 |
< |
* method. |
721 |
> |
* before any arrive, and all {@link #awaitAdvance} at each phase. |
722 |
> |
* Otherwise, you cannot ensure lack of interference from other |
723 |
> |
* parties during the invocation of this method. |
724 |
|
* |
725 |
|
* @param phase the phase number on entering the barrier |
726 |
|
* @param registeredParties the current number of registered parties |