34 |
|
* awaited. Method {@link #arriveAndAwaitAdvance} has effect |
35 |
|
* analogous to {@link java.util.concurrent.CyclicBarrier#await |
36 |
|
* CyclicBarrier.await}. However, phasers separate two aspects of |
37 |
< |
* coordination, that may also be invoked independently: |
37 |
> |
* coordination, which may also be invoked independently: |
38 |
|
* |
39 |
|
* <ul> |
40 |
|
* |
49 |
|
* |
50 |
|
* |
51 |
|
* <li> Barrier actions, performed by the task triggering a phase |
52 |
< |
* advance while others may be waiting, are arranged by overriding |
53 |
< |
* method {@link #onAdvance}, that also controls termination. |
54 |
< |
* Overriding this method may be used to similar but more flexible |
55 |
< |
* effect as providing a barrier action to a {@code CyclicBarrier}. |
52 |
> |
* advance, are arranged by overriding method {@link #onAdvance(int, |
53 |
> |
* int)}, which also controls termination. Overriding this method is |
54 |
> |
* similar to, but more flexible than, providing a barrier action to a |
55 |
> |
* {@code CyclicBarrier}. |
56 |
|
* |
57 |
|
* <li> Phasers may enter a <em>termination</em> state in which all |
58 |
|
* actions immediately return without updating phaser state or waiting |
59 |
|
* for advance, and indicating (via a negative phase value) that |
60 |
< |
* execution is complete. Termination is triggered by executing the |
61 |
< |
* overridable {@code onAdvance} method that is invoked each time the |
62 |
< |
* barrier is about to be tripped. When a phaser is controlling an |
63 |
< |
* action with a fixed number of iterations, it is often convenient to |
64 |
< |
* override this method to cause termination when the current phase |
65 |
< |
* number reaches a threshold. Method {@link #forceTermination} is also |
66 |
< |
* available to abruptly release waiting threads and allow them to |
67 |
< |
* terminate. |
60 |
> |
* execution is complete. Termination is triggered when an invocation |
61 |
> |
* of {@code onAdvance} returns {@code true}. When a phaser is |
62 |
> |
* controlling an action with a fixed number of iterations, it is |
63 |
> |
* often convenient to override this method to cause termination when |
64 |
> |
* the current phase number reaches a threshold. Method {@link |
65 |
> |
* #forceTermination} is also available to abruptly release waiting |
66 |
> |
* threads and allow them to terminate. |
67 |
|
* |
68 |
|
* <li> Phasers may be tiered to reduce contention. Phasers with large |
69 |
|
* numbers of parties that would otherwise experience heavy |
79 |
|
* within handlers of those exceptions, often after invoking |
80 |
|
* {@code forceTermination}. |
81 |
|
* |
82 |
< |
* <li>Phasers ensure lack of starvation when used by ForkJoinTasks. |
82 |
> |
* <li>Phasers may be used to coordinate tasks executing in a {@link |
83 |
> |
* ForkJoinPool}, which will ensure sufficient parallelism to execute |
84 |
> |
* tasks when others are blocked waiting for a phase to advance. |
85 |
|
* |
86 |
|
* </ul> |
87 |
|
* |
95 |
|
* <pre> {@code |
96 |
|
* void runTasks(List<Runnable> list) { |
97 |
|
* final Phaser phaser = new Phaser(1); // "1" to register self |
98 |
+ |
* // create and start threads |
99 |
|
* for (Runnable r : list) { |
100 |
|
* phaser.register(); |
101 |
|
* new Thread() { |
102 |
|
* public void run() { |
103 |
|
* phaser.arriveAndAwaitAdvance(); // await all creation |
104 |
|
* r.run(); |
103 |
– |
* phaser.arriveAndDeregister(); // signal completion |
105 |
|
* } |
106 |
|
* }.start(); |
107 |
|
* } |
108 |
|
* |
109 |
< |
* doSomethingOnBehalfOfWorkers(); |
110 |
< |
* phaser.arrive(); // allow threads to start |
110 |
< |
* int p = phaser.arriveAndDeregister(); // deregister self ... |
111 |
< |
* p = phaser.awaitAdvance(p); // ... and await arrival |
112 |
< |
* otherActions(); // do other things while tasks execute |
113 |
< |
* phaser.awaitAdvance(p); // await final completion |
109 |
> |
* // allow threads to start and deregister self |
110 |
> |
* phaser.arriveAndDeregister(); |
111 |
|
* }}</pre> |
112 |
|
* |
113 |
|
* <p>One way to cause a set of threads to repeatedly perform actions |
459 |
|
} |
460 |
|
|
461 |
|
/** |
462 |
< |
* Arrives at the barrier, and deregisters from it, without |
463 |
< |
* waiting for others. Deregistration reduces number of parties |
462 |
> |
* Arrives at the barrier and deregisters from it without waiting |
463 |
> |
* for others. Deregistration reduces the number of parties |
464 |
|
* required to trip the barrier in future phases. If this phaser |
465 |
|
* has a parent, and deregistration causes this phaser to have |
466 |
< |
* zero parties, this phaser is also deregistered from its parent. |
466 |
> |
* zero parties, this phaser also arrives at and is deregistered |
467 |
> |
* from its parent. |
468 |
|
* |
469 |
|
* @return the current barrier phase number upon entry to |
470 |
|
* this method, or a negative value if terminated |
517 |
|
|
518 |
|
/** |
519 |
|
* Arrives at the barrier and awaits others. Equivalent in effect |
520 |
< |
* to {@code awaitAdvance(arrive())}. If you instead need to |
521 |
< |
* await with interruption of timeout, and/or deregister upon |
522 |
< |
* arrival, you can arrange them using analogous constructions. |
520 |
> |
* to {@code awaitAdvance(arrive())}. If you need to await with |
521 |
> |
* interruption or timeout, you can arrange this with an analogous |
522 |
> |
* construction using one of the other forms of the awaitAdvance |
523 |
> |
* method. If instead you need to deregister upon arrival use |
524 |
> |
* {@code arriveAndDeregister}. |
525 |
|
* |
526 |
|
* @return the phase on entry to this method |
527 |
|
* @throws IllegalStateException if not terminated and the number |
532 |
|
} |
533 |
|
|
534 |
|
/** |
535 |
< |
* Awaits the phase of the barrier to advance from the given |
536 |
< |
* value, or returns immediately if argument is negative or this |
537 |
< |
* barrier is terminated. |
535 |
> |
* Awaits the phase of the barrier to advance from the given phase |
536 |
> |
* value, or returns immediately if the current phase of the barrier |
537 |
> |
* is not equal to the given phase value or this barrier is |
538 |
> |
* terminated. |
539 |
|
* |
540 |
|
* @param phase the phase on entry to this method |
541 |
|
* @return the phase on exit from this method |
636 |
|
} |
637 |
|
|
638 |
|
/** |
638 |
– |
* Returns {@code true} if the current phase number equals the given phase. |
639 |
– |
* |
640 |
– |
* @param phase the phase |
641 |
– |
* @return {@code true} if the current phase number equals the given phase |
642 |
– |
*/ |
643 |
– |
public final boolean hasPhase(int phase) { |
644 |
– |
return phaseOf(getReconciledState()) == phase; |
645 |
– |
} |
646 |
– |
|
647 |
– |
/** |
639 |
|
* Returns the number of parties registered at this barrier. |
640 |
|
* |
641 |
|
* @return the number of parties |
710 |
|
* effects visible to participating tasks, but it is in general |
711 |
|
* only sensible to do so in designs where all parties register |
712 |
|
* before any arrive, and all {@link #awaitAdvance} at each phase. |
713 |
< |
* Otherwise, you cannot ensure lack of interference. In |
714 |
< |
* particular, this method may be invoked more than once per |
724 |
< |
* transition if other parties successfully register while the |
725 |
< |
* invocation of this method is in progress, thus postponing the |
726 |
< |
* transition until those parties also arrive, re-triggering this |
727 |
< |
* method. |
713 |
> |
* Otherwise, you cannot ensure lack of interference from other |
714 |
> |
* parties during the invocation of this method. |
715 |
|
* |
716 |
|
* @param phase the phase number on entering the barrier |
717 |
|
* @param registeredParties the current number of registered parties |