19 |
|
* |
20 |
|
* <ul> |
21 |
|
* |
22 |
< |
* <li> The number of parties synchronizing on a phaser may vary over |
23 |
< |
* time. A task may register to be a party at any time, and may |
24 |
< |
* deregister upon arriving at the barrier. As is the case with most |
25 |
< |
* basic synchronization constructs, registration and deregistration |
26 |
< |
* affect only internal counts; they do not establish any further |
27 |
< |
* internal bookkeeping, so tasks cannot query whether they are |
22 |
> |
* <li> The number of parties <em>registered</em> to synchronize on a |
23 |
> |
* phaser may vary over time. Tasks may be registered at any time |
24 |
> |
* (using methods {@link #register}, {@link #bulkRegister}, or forms |
25 |
> |
* of constructors establishing initial numbers of parties), and may |
26 |
> |
* optionally be deregistered upon any arrival (using {@link |
27 |
> |
* #arriveAndDeregister}). As is the case with most basic |
28 |
> |
* synchronization constructs, registration and deregistration affect |
29 |
> |
* only internal counts; they do not establish any further internal |
30 |
> |
* bookkeeping, so tasks cannot query whether they are |
31 |
|
* registered. (However, you can introduce such bookkeeping by |
32 |
|
* subclassing this class.) |
33 |
|
* |
34 |
< |
* <li> Each generation has an associated phase value, starting at |
35 |
< |
* zero, and advancing when all parties reach the barrier (wrapping |
36 |
< |
* around to zero after reaching {@code Integer.MAX_VALUE}). |
34 |
> |
* <li> Each generation has an associated phase number. The phase |
35 |
> |
* number starts at zero, amd advances when all parties arrive at the |
36 |
> |
* barrier, wrapping around to zero after reaching {@code |
37 |
> |
* Integer.MAX_VALUE}. |
38 |
|
* |
39 |
|
* <li> Like a {@code CyclicBarrier}, a phaser may be repeatedly |
40 |
|
* awaited. Method {@link #arriveAndAwaitAdvance} has effect |
41 |
|
* analogous to {@link java.util.concurrent.CyclicBarrier#await |
42 |
|
* CyclicBarrier.await}. However, phasers separate two aspects of |
43 |
< |
* coordination, that may also be invoked independently: |
43 |
> |
* coordination, which may also be invoked independently: |
44 |
|
* |
45 |
|
* <ul> |
46 |
|
* |
47 |
|
* <li> Arriving at a barrier. Methods {@link #arrive} and |
48 |
|
* {@link #arriveAndDeregister} do not block, but return |
49 |
< |
* the phase value current upon entry to the method. |
49 |
> |
* an associated <em>arrival phase number</em>; |
50 |
> |
* that is, the phase number of the barrier to which the |
51 |
> |
* arrival applied. |
52 |
|
* |
53 |
|
* <li> Awaiting others. Method {@link #awaitAdvance} requires an |
54 |
< |
* argument indicating the entry phase, and returns when the |
55 |
< |
* barrier advances to a new phase. |
54 |
> |
* argument indicating an arrival phase number, and returns |
55 |
> |
* when the barrier advances to a new phase. |
56 |
|
* </ul> |
57 |
|
* |
52 |
– |
* |
58 |
|
* <li> Barrier actions, performed by the task triggering a phase |
59 |
< |
* advance while others may be waiting, are arranged by overriding |
60 |
< |
* method {@link #onAdvance}, that also controls termination. |
61 |
< |
* Overriding this method may be used to similar but more flexible |
62 |
< |
* effect as providing a barrier action to a {@code CyclicBarrier}. |
59 |
> |
* advance, are arranged by overriding method {@link #onAdvance(int, |
60 |
> |
* int)}, which also controls termination. Overriding this method is |
61 |
> |
* similar to, but more flexible than, providing a barrier action to a |
62 |
> |
* {@code CyclicBarrier}. |
63 |
|
* |
64 |
|
* <li> Phasers may enter a <em>termination</em> state in which all |
65 |
|
* actions immediately return without updating phaser state or waiting |
66 |
|
* for advance, and indicating (via a negative phase value) that |
67 |
< |
* execution is complete. Termination is triggered by executing the |
68 |
< |
* overridable {@code onAdvance} method that is invoked each time the |
69 |
< |
* barrier is about to be tripped. When a phaser is controlling an |
70 |
< |
* action with a fixed number of iterations, it is often convenient to |
71 |
< |
* override this method to cause termination when the current phase |
72 |
< |
* number reaches a threshold. Method {@link #forceTermination} is also |
73 |
< |
* available to abruptly release waiting threads and allow them to |
69 |
< |
* terminate. |
67 |
> |
* execution is complete. Termination is triggered when an invocation |
68 |
> |
* of {@code onAdvance} returns {@code true}. When a phaser is |
69 |
> |
* controlling an action with a fixed number of iterations, it is |
70 |
> |
* often convenient to override this method to cause termination when |
71 |
> |
* the current phase number reaches a threshold. Method {@link |
72 |
> |
* #forceTermination} is also available to abruptly release waiting |
73 |
> |
* threads and allow them to terminate. |
74 |
|
* |
75 |
|
* <li> Phasers may be tiered to reduce contention. Phasers with large |
76 |
|
* numbers of parties that would otherwise experience heavy |
86 |
|
* within handlers of those exceptions, often after invoking |
87 |
|
* {@code forceTermination}. |
88 |
|
* |
89 |
< |
* <li>Phasers ensure lack of starvation when used by ForkJoinTasks. |
89 |
> |
* <li>Phasers may be used to coordinate tasks executing in a {@link |
90 |
> |
* ForkJoinPool}, which will ensure sufficient parallelism to execute |
91 |
> |
* tasks when others are blocked waiting for a phase to advance. |
92 |
> |
* |
93 |
> |
* <li>The current state of a phaser may be monitored. At any given |
94 |
> |
* moment there are {@link #getRegisteredParties}, where {@link |
95 |
> |
* #getArrivedParties} have arrived at the current phase ({@link |
96 |
> |
* #getPhase}). When the remaining {@link #getUnarrivedParties}) |
97 |
> |
* arrive, the phase advances. Method {@link #toString} returns |
98 |
> |
* snapshots of these state queries in a form convenient for |
99 |
> |
* informal monitoring. |
100 |
|
* |
101 |
|
* </ul> |
102 |
|
* |
108 |
|
* first register, then start the actions, then deregister, as in: |
109 |
|
* |
110 |
|
* <pre> {@code |
111 |
< |
* void runTasks(List<Runnable> list) { |
111 |
> |
* void runTasks(List<Runnable> tasks) { |
112 |
|
* final Phaser phaser = new Phaser(1); // "1" to register self |
113 |
< |
* for (Runnable r : list) { |
113 |
> |
* // create and start threads |
114 |
> |
* for (Runnable task : tasks) { |
115 |
|
* phaser.register(); |
116 |
|
* new Thread() { |
117 |
|
* public void run() { |
118 |
|
* phaser.arriveAndAwaitAdvance(); // await all creation |
119 |
< |
* r.run(); |
105 |
< |
* phaser.arriveAndDeregister(); // signal completion |
119 |
> |
* task.run(); |
120 |
|
* } |
121 |
|
* }.start(); |
122 |
|
* } |
123 |
|
* |
124 |
< |
* doSomethingOnBehalfOfWorkers(); |
125 |
< |
* phaser.arrive(); // allow threads to start |
112 |
< |
* int p = phaser.arriveAndDeregister(); // deregister self ... |
113 |
< |
* p = phaser.awaitAdvance(p); // ... and await arrival |
114 |
< |
* otherActions(); // do other things while tasks execute |
115 |
< |
* phaser.awaitAdvance(p); // await final completion |
124 |
> |
* // allow threads to start and deregister self |
125 |
> |
* phaser.arriveAndDeregister(); |
126 |
|
* }}</pre> |
127 |
|
* |
128 |
|
* <p>One way to cause a set of threads to repeatedly perform actions |
129 |
|
* for a given number of iterations is to override {@code onAdvance}: |
130 |
|
* |
131 |
|
* <pre> {@code |
132 |
< |
* void startTasks(List<Runnable> list, final int iterations) { |
132 |
> |
* void startTasks(List<Runnable> tasks, final int iterations) { |
133 |
|
* final Phaser phaser = new Phaser() { |
134 |
|
* public boolean onAdvance(int phase, int registeredParties) { |
135 |
|
* return phase >= iterations || registeredParties == 0; |
136 |
|
* } |
137 |
|
* }; |
138 |
|
* phaser.register(); |
139 |
< |
* for (Runnable r : list) { |
139 |
> |
* for (Runnable task : tasks) { |
140 |
|
* phaser.register(); |
141 |
|
* new Thread() { |
142 |
|
* public void run() { |
143 |
|
* do { |
144 |
< |
* r.run(); |
144 |
> |
* task.run(); |
145 |
|
* phaser.arriveAndAwaitAdvance(); |
146 |
|
* } while(!phaser.isTerminated(); |
147 |
|
* } |
182 |
|
* |
183 |
|
* <p><b>Implementation notes</b>: This implementation restricts the |
184 |
|
* maximum number of parties to 65535. Attempts to register additional |
185 |
< |
* parties result in IllegalStateExceptions. However, you can and |
185 |
> |
* parties result in {@code IllegalStateException}. However, you can and |
186 |
|
* should create tiered phasers to accommodate arbitrarily large sets |
187 |
|
* of participants. |
188 |
|
* |
379 |
|
/** |
380 |
|
* Adds a new unarrived party to this phaser. |
381 |
|
* |
382 |
< |
* @return the current barrier phase number upon registration |
382 |
> |
* @return the arrival phase number to which this registration applied |
383 |
|
* @throws IllegalStateException if attempting to register more |
384 |
|
* than the maximum supported number of parties |
385 |
|
*/ |
391 |
|
* Adds the given number of new unarrived parties to this phaser. |
392 |
|
* |
393 |
|
* @param parties the number of parties required to trip barrier |
394 |
< |
* @return the current barrier phase number upon registration |
394 |
> |
* @return the arrival phase number to which this registration applied |
395 |
|
* @throws IllegalStateException if attempting to register more |
396 |
|
* than the maximum supported number of parties |
397 |
|
*/ |
428 |
|
* Arrives at the barrier, but does not wait for others. (You can |
429 |
|
* in turn wait for others via {@link #awaitAdvance}). |
430 |
|
* |
431 |
< |
* @return the barrier phase number upon entry to this method, or a |
422 |
< |
* negative value if terminated |
431 |
> |
* @return the arrival phase number, or a negative value if terminated |
432 |
|
* @throws IllegalStateException if not terminated and the number |
433 |
|
* of unarrived parties would become negative |
434 |
|
*/ |
473 |
|
} |
474 |
|
|
475 |
|
/** |
476 |
< |
* Arrives at the barrier, and deregisters from it, without |
477 |
< |
* waiting for others. Deregistration reduces number of parties |
476 |
> |
* Arrives at the barrier and deregisters from it without waiting |
477 |
> |
* for others. Deregistration reduces the number of parties |
478 |
|
* required to trip the barrier in future phases. If this phaser |
479 |
|
* has a parent, and deregistration causes this phaser to have |
480 |
< |
* zero parties, this phaser is also deregistered from its parent. |
480 |
> |
* zero parties, this phaser also arrives at and is deregistered |
481 |
> |
* from its parent. |
482 |
|
* |
483 |
< |
* @return the current barrier phase number upon entry to |
474 |
< |
* this method, or a negative value if terminated |
483 |
> |
* @return the arrival phase number, or a negative value if terminated |
484 |
|
* @throws IllegalStateException if not terminated and the number |
485 |
|
* of registered or unarrived parties would become negative |
486 |
|
*/ |
530 |
|
|
531 |
|
/** |
532 |
|
* Arrives at the barrier and awaits others. Equivalent in effect |
533 |
< |
* to {@code awaitAdvance(arrive())}. If you instead need to |
534 |
< |
* await with interruption of timeout, and/or deregister upon |
535 |
< |
* arrival, you can arrange them using analogous constructions. |
533 |
> |
* to {@code awaitAdvance(arrive())}. If you need to await with |
534 |
> |
* interruption or timeout, you can arrange this with an analogous |
535 |
> |
* construction using one of the other forms of the awaitAdvance |
536 |
> |
* method. If instead you need to deregister upon arrival use |
537 |
> |
* {@code arriveAndDeregister}. |
538 |
|
* |
539 |
< |
* @return the phase on entry to this method |
539 |
> |
* @return the arrival phase number, or a negative number if terminated |
540 |
|
* @throws IllegalStateException if not terminated and the number |
541 |
|
* of unarrived parties would become negative |
542 |
|
*/ |
545 |
|
} |
546 |
|
|
547 |
|
/** |
548 |
< |
* Awaits the phase of the barrier to advance from the given |
549 |
< |
* value, or returns immediately if argument is negative or this |
550 |
< |
* barrier is terminated. |
551 |
< |
* |
552 |
< |
* @param phase the phase on entry to this method |
553 |
< |
* @return the phase on exit from this method |
548 |
> |
* Awaits the phase of the barrier to advance from the given phase |
549 |
> |
* value, returning immediately if the current phase of the |
550 |
> |
* barrier is not equal to the given phase value or this barrier |
551 |
> |
* is terminated. |
552 |
> |
* |
553 |
> |
* @param phase an arrival phase number, or negative value if |
554 |
> |
* terminated; this argument is normally the value returned by a |
555 |
> |
* previous call to {@code arrive} or its variants |
556 |
> |
* @return the next arrival phase number, or a negative value |
557 |
> |
* if terminated or argument is negative |
558 |
|
*/ |
559 |
|
public int awaitAdvance(int phase) { |
560 |
|
if (phase < 0) |
570 |
|
} |
571 |
|
|
572 |
|
/** |
573 |
< |
* Awaits the phase of the barrier to advance from the given |
574 |
< |
* value, or returns immediately if argument is negative or this |
575 |
< |
* barrier is terminated, or throws InterruptedException if |
576 |
< |
* interrupted while waiting. |
577 |
< |
* |
578 |
< |
* @param phase the phase on entry to this method |
579 |
< |
* @return the phase on exit from this method |
573 |
> |
* Awaits the phase of the barrier to advance from the given phase |
574 |
> |
* value, throwing {@code InterruptedException} if interrupted while |
575 |
> |
* waiting, or returning immediately if the current phase of the |
576 |
> |
* barrier is not equal to the given phase value or this barrier |
577 |
> |
* is terminated. |
578 |
> |
* |
579 |
> |
* @param phase an arrival phase number, or negative value if |
580 |
> |
* terminated; this argument is normally the value returned by a |
581 |
> |
* previous call to {@code arrive} or its variants |
582 |
> |
* @return the next arrival phase number, or a negative value |
583 |
> |
* if terminated or argument is negative |
584 |
|
* @throws InterruptedException if thread interrupted while waiting |
585 |
|
*/ |
586 |
|
public int awaitAdvanceInterruptibly(int phase) |
597 |
|
} |
598 |
|
|
599 |
|
/** |
600 |
< |
* Awaits the phase of the barrier to advance from the given value |
601 |
< |
* or the given timeout elapses, or returns immediately if |
602 |
< |
* argument is negative or this barrier is terminated. |
603 |
< |
* |
604 |
< |
* @param phase the phase on entry to this method |
605 |
< |
* @return the phase on exit from this method |
600 |
> |
* Awaits the phase of the barrier to advance from the given phase |
601 |
> |
* value or the given timeout to elapse, throwing |
602 |
> |
* {@code InterruptedException} if interrupted while waiting, or |
603 |
> |
* returning immediately if the current phase of the barrier is not |
604 |
> |
* equal to the given phase value or this barrier is terminated. |
605 |
> |
* |
606 |
> |
* @param phase an arrival phase number, or negative value if |
607 |
> |
* terminated; this argument is normally the value returned by a |
608 |
> |
* previous call to {@code arrive} or its variants |
609 |
> |
* @param timeout how long to wait before giving up, in units of |
610 |
> |
* {@code unit} |
611 |
> |
* @param unit a {@code TimeUnit} determining how to interpret the |
612 |
> |
* {@code timeout} parameter |
613 |
> |
* @return the next arrival phase number, or a negative value |
614 |
> |
* if terminated or argument is negative |
615 |
|
* @throws InterruptedException if thread interrupted while waiting |
616 |
|
* @throws TimeoutException if timed out while waiting |
617 |
|
*/ |
665 |
|
} |
666 |
|
|
667 |
|
/** |
640 |
– |
* Returns {@code true} if the current phase number equals the given phase. |
641 |
– |
* |
642 |
– |
* @param phase the phase |
643 |
– |
* @return {@code true} if the current phase number equals the given phase |
644 |
– |
*/ |
645 |
– |
public final boolean hasPhase(int phase) { |
646 |
– |
return phaseOf(getReconciledState()) == phase; |
647 |
– |
} |
648 |
– |
|
649 |
– |
/** |
668 |
|
* Returns the number of parties registered at this barrier. |
669 |
|
* |
670 |
|
* @return the number of parties |
674 |
|
} |
675 |
|
|
676 |
|
/** |
677 |
< |
* Returns the number of parties that have arrived at the current |
678 |
< |
* phase of this barrier. |
677 |
> |
* Returns the number of registered parties that have arrived at |
678 |
> |
* the current phase of this barrier. |
679 |
|
* |
680 |
|
* @return the number of arrived parties |
681 |
|
*/ |
739 |
|
* effects visible to participating tasks, but it is in general |
740 |
|
* only sensible to do so in designs where all parties register |
741 |
|
* before any arrive, and all {@link #awaitAdvance} at each phase. |
742 |
< |
* Otherwise, you cannot ensure lack of interference. In |
743 |
< |
* particular, this method may be invoked more than once per |
726 |
< |
* transition if other parties successfully register while the |
727 |
< |
* invocation of this method is in progress, thus postponing the |
728 |
< |
* transition until those parties also arrive, re-triggering this |
729 |
< |
* method. |
742 |
> |
* Otherwise, you cannot ensure lack of interference from other |
743 |
> |
* parties during the invocation of this method. |
744 |
|
* |
745 |
|
* @param phase the phase number on entering the barrier |
746 |
|
* @param registeredParties the current number of registered parties |