| 17 |
|
* {@link java.util.concurrent.CountDownLatch CountDownLatch} |
| 18 |
|
* but supporting more flexible usage. |
| 19 |
|
* |
| 20 |
< |
* <ul> |
| 21 |
< |
* |
| 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 |
| 20 |
> |
* <p> <b>Registration.</b> Unlike the case for other barriers, the |
| 21 |
> |
* number of parties <em>registered</em> to synchronize on a phaser |
| 22 |
> |
* may vary over time. Tasks may be registered at any time (using |
| 23 |
> |
* methods {@link #register}, {@link #bulkRegister}, or forms of |
| 24 |
> |
* constructors establishing initial numbers of parties), and |
| 25 |
> |
* optionally deregistered upon any arrival (using {@link |
| 26 |
|
* #arriveAndDeregister}). As is the case with most basic |
| 27 |
|
* synchronization constructs, registration and deregistration affect |
| 28 |
|
* only internal counts; they do not establish any further internal |
| 30 |
|
* (However, you can introduce such bookkeeping by subclassing this |
| 31 |
|
* class.) |
| 32 |
|
* |
| 33 |
< |
* <li> Each generation has an associated phase number. The phase |
| 34 |
< |
* number starts at zero, amd advances when all parties arrive at the |
| 35 |
< |
* barrier, wrapping around to zero after reaching {@code |
| 36 |
< |
* Integer.MAX_VALUE}. |
| 37 |
< |
* |
| 38 |
< |
* <li> Like a {@code CyclicBarrier}, a phaser may be repeatedly |
| 39 |
< |
* awaited. Method {@link #arriveAndAwaitAdvance} has effect |
| 40 |
< |
* analogous to {@link java.util.concurrent.CyclicBarrier#await |
| 41 |
< |
* CyclicBarrier.await}. However, phasers separate two aspects of |
| 42 |
< |
* coordination, which may also be invoked independently: |
| 33 |
> |
* <p> <b>Synchronization.</b> Like a {@code CyclicBarrier}, a {@code |
| 34 |
> |
* Phaser} may be repeatedly awaited. Method {@link |
| 35 |
> |
* #arriveAndAwaitAdvance} has effect analogous to {@link |
| 36 |
> |
* java.util.concurrent.CyclicBarrier#await CyclicBarrier.await}. Each |
| 37 |
> |
* generation of a {@code Phaser} has an associated phase number. The |
| 38 |
> |
* phase number starts at zero, amd advances when all parties arrive |
| 39 |
> |
* at the barrier, wrapping around to zero after reaching {@code |
| 40 |
> |
* Integer.MAX_VALUE}. The use of phase numbers enables independent |
| 41 |
> |
* control of actions upon arrival at a barrier and upon awaiting |
| 42 |
> |
* others, via two kinds of methods that may be invoked by any |
| 43 |
> |
* registered party: |
| 44 |
|
* |
| 45 |
|
* <ul> |
| 46 |
|
* |
| 47 |
< |
* <li> Arriving at a barrier. Methods {@link #arrive} and |
| 48 |
< |
* {@link #arriveAndDeregister} do not block, but return |
| 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 an arrival phase number, and returns |
| 55 |
< |
* when the barrier advances to a new phase. |
| 47 |
> |
* <li> <b>Arrival.</b> Methods {@link #arrive} and |
| 48 |
> |
* {@link #arriveAndDeregister} record arrival at a |
| 49 |
> |
* barrier. These methods do not block, but return an associated |
| 50 |
> |
* <em>arrival phase number</em>; that is, the phase number of |
| 51 |
> |
* the barrier to which the arrival applied. When the final |
| 52 |
> |
* party for a given phase arrives, an optional barrier action |
| 53 |
> |
* is performed and the phase advances. Barrier actions, |
| 54 |
> |
* performed by the party triggering a phase advance, are |
| 55 |
> |
* arranged by overriding method {@link #onAdvance(int, int)}, |
| 56 |
> |
* which also controls termination. Overriding this method is |
| 57 |
> |
* similar to, but more flexible than, providing a barrier |
| 58 |
> |
* action to a {@code CyclicBarrier}. |
| 59 |
> |
* |
| 60 |
> |
* <li> <b>Waiting.</b> Method {@link #awaitAdvance} requires an |
| 61 |
> |
* argument indicating an arrival phase number, and returns when |
| 62 |
> |
* the barrier advances to (or is already at) a different phase. |
| 63 |
> |
* Unlike similar constructions using {@code CyclicBarrier}, |
| 64 |
> |
* method {@code awaitAdvance} continues to wait even if the |
| 65 |
> |
* waiting thread is interrupted. (Interruptible and timeout |
| 66 |
> |
* versions are also available.) Exceptions encountered while |
| 67 |
> |
* tasks wait interruptibly or with timeout do not change the |
| 68 |
> |
* state of the barrier. If necessary, you can perform any |
| 69 |
> |
* associated recovery within handlers of those exceptions, |
| 70 |
> |
* often after invoking {@code forceTermination}. Phasers may |
| 71 |
> |
* also be used by tasks executing in a {@link ForkJoinPool}, |
| 72 |
> |
* which will ensure sufficient parallelism to execute tasks |
| 73 |
> |
* when others are blocked waiting for a phase to advance. |
| 74 |
> |
* |
| 75 |
|
* </ul> |
| 76 |
|
* |
| 77 |
< |
* <li> Barrier actions, performed by the task triggering a phase |
| 78 |
< |
* advance, are arranged by overriding method {@link #onAdvance(int, |
| 79 |
< |
* int)}, which also controls termination. Overriding this method is |
| 80 |
< |
* similar to, but more flexible than, providing a barrier action to a |
| 81 |
< |
* {@code CyclicBarrier}. |
| 82 |
< |
* |
| 83 |
< |
* <li> Phasers may enter a <em>termination</em> state in which all |
| 84 |
< |
* actions immediately return without updating phaser state or waiting |
| 85 |
< |
* for advance, and indicating (via a negative phase value) that |
| 86 |
< |
* execution is complete. Termination is triggered when an invocation |
| 87 |
< |
* 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. |
| 77 |
> |
* <p> <b>Termination.</b> A {@code Phaser} may enter a |
| 78 |
> |
* <em>termination</em> state in which all actions immediately return |
| 79 |
> |
* without updating phaser state or waiting for advance, and |
| 80 |
> |
* indicating (via a negative phase value) that execution is complete. |
| 81 |
> |
* Termination is triggered when an invocation of {@code onAdvance} |
| 82 |
> |
* returns {@code true}. As illustrated below, when phasers control |
| 83 |
> |
* actions with a fixed number of iterations, it is often convenient |
| 84 |
> |
* to override this method to cause termination when the current phase |
| 85 |
> |
* number reaches a threshold. Method {@link #forceTermination} is |
| 86 |
> |
* also available to abruptly release waiting threads and allow them |
| 87 |
> |
* to terminate. |
| 88 |
|
* |
| 89 |
< |
* <li> Phasers may be tiered to reduce contention. Phasers with large |
| 89 |
> |
* <p> <b>Tiering.</b> Phasers may be <em>tiered</em> (i.e., arranged |
| 90 |
> |
* in tree structures) to reduce contention. Phasers with large |
| 91 |
|
* numbers of parties that would otherwise experience heavy |
| 92 |
< |
* synchronization contention costs may instead be arranged in trees. |
| 93 |
< |
* This will typically greatly increase throughput even though it |
| 94 |
< |
* incurs somewhat greater per-operation overhead. |
| 95 |
< |
* |
| 96 |
< |
* <li> By default, {@code awaitAdvance} continues to wait even if |
| 97 |
< |
* the waiting thread is interrupted. And unlike the case in |
| 98 |
< |
* {@code CyclicBarrier}, exceptions encountered while tasks wait |
| 99 |
< |
* interruptibly or with timeout do not change the state of the |
| 100 |
< |
* barrier. If necessary, you can perform any associated recovery |
| 101 |
< |
* within handlers of those exceptions, often after invoking |
| 102 |
< |
* {@code forceTermination}. |
| 103 |
< |
* |
| 104 |
< |
* <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> |
| 92 |
> |
* synchronization contention costs may instead be set up so that |
| 93 |
> |
* groups of sub-phasers share a common parent. This may greatly |
| 94 |
> |
* increase throughput even though it incurs greater per-operation |
| 95 |
> |
* overhead. |
| 96 |
> |
* |
| 97 |
> |
* <p><b>Monitoring.</b> While synchronization methods may be invoked |
| 98 |
> |
* only by registered parties, the current state of a phaser may be |
| 99 |
> |
* monitored by any caller. At any given moment there are {@link |
| 100 |
> |
* #getRegisteredParties}, where {@link #getArrivedParties} have |
| 101 |
> |
* arrived at the current phase ({@link #getPhase}). When the |
| 102 |
> |
* remaining {@link #getUnarrivedParties}) arrive, the phase |
| 103 |
> |
* advances. Method {@link #toString} returns snapshots of these state |
| 104 |
> |
* queries in a form convenient for informal monitoring. |
| 105 |
|
* |
| 106 |
|
* <p><b>Sample usages:</b> |
| 107 |
|
* |
| 134 |
|
* <pre> {@code |
| 135 |
|
* void startTasks(List<Runnable> tasks, final int iterations) { |
| 136 |
|
* final Phaser phaser = new Phaser() { |
| 137 |
< |
* public boolean onAdvance(int phase, int registeredParties) { |
| 137 |
> |
* protected boolean onAdvance(int phase, int registeredParties) { |
| 138 |
|
* return phase >= iterations || registeredParties == 0; |
| 139 |
|
* } |
| 140 |
|
* }; |
| 153 |
|
* phaser.arriveAndDeregister(); // deregister self, don't wait |
| 154 |
|
* }}</pre> |
| 155 |
|
* |
| 156 |
+ |
* If the main task must later await termination, it |
| 157 |
+ |
* may re-register and then execute a similar loop: |
| 158 |
+ |
* <pre> {@code |
| 159 |
+ |
* // ... |
| 160 |
+ |
* phaser.register(); |
| 161 |
+ |
* while (!phaser.isTerminated()) |
| 162 |
+ |
* phaser.arriveAndAwaitAdvance(); |
| 163 |
+ |
* }</pre> |
| 164 |
+ |
* |
| 165 |
+ |
* Related constructions may be used to await particular phase numbers |
| 166 |
+ |
* in contexts where you are sure that the phase will never wrap around |
| 167 |
+ |
* {@code Integer.MAX_VALUE}. For example: |
| 168 |
+ |
* |
| 169 |
+ |
* <pre> {@code |
| 170 |
+ |
* void awaitPhase(Phaser phaser, int phase) { |
| 171 |
+ |
* int p = phaser.register(); // assumes caller not already registered |
| 172 |
+ |
* while (p < phase) { |
| 173 |
+ |
* if (phaser.isTerminated()) |
| 174 |
+ |
* // ... deal with unexpected termination |
| 175 |
+ |
* else |
| 176 |
+ |
* p = phaser.arriveAndAwaitAdvance(); |
| 177 |
+ |
* } |
| 178 |
+ |
* phaser.arriveAndDeregister(); |
| 179 |
+ |
* } |
| 180 |
+ |
* }</pre> |
| 181 |
+ |
* |
| 182 |
+ |
* |
| 183 |
|
* <p>To create a set of tasks using a tree of phasers, |
| 184 |
|
* you could use code of the following form, assuming a |
| 185 |
|
* Task class with a constructor accepting a phaser that |
| 456 |
|
|
| 457 |
|
/** |
| 458 |
|
* Arrives at the barrier, but does not wait for others. (You can |
| 459 |
< |
* in turn wait for others via {@link #awaitAdvance}). |
| 459 |
> |
* in turn wait for others via {@link #awaitAdvance}). It is an |
| 460 |
> |
* unenforced usage error for an unregistered party to invoke this |
| 461 |
> |
* method. |
| 462 |
|
* |
| 463 |
|
* @return the arrival phase number, or a negative value if terminated |
| 464 |
|
* @throws IllegalStateException if not terminated and the number |
| 510 |
|
* required to trip the barrier in future phases. If this phaser |
| 511 |
|
* has a parent, and deregistration causes this phaser to have |
| 512 |
|
* zero parties, this phaser also arrives at and is deregistered |
| 513 |
< |
* from its parent. |
| 513 |
> |
* from its parent. It is an unenforced usage error for an |
| 514 |
> |
* unregistered party to invoke this method. |
| 515 |
|
* |
| 516 |
|
* @return the arrival phase number, or a negative value if terminated |
| 517 |
|
* @throws IllegalStateException if not terminated and the number |
| 567 |
|
* interruption or timeout, you can arrange this with an analogous |
| 568 |
|
* construction using one of the other forms of the awaitAdvance |
| 569 |
|
* method. If instead you need to deregister upon arrival use |
| 570 |
< |
* {@code arriveAndDeregister}. |
| 570 |
> |
* {@code arriveAndDeregister}. It is an unenforced usage error |
| 571 |
> |
* for an unregistered party to invoke this method. |
| 572 |
|
* |
| 573 |
|
* @return the arrival phase number, or a negative number if terminated |
| 574 |
|
* @throws IllegalStateException if not terminated and the number |
| 582 |
|
* Awaits the phase of the barrier to advance from the given phase |
| 583 |
|
* value, returning immediately if the current phase of the |
| 584 |
|
* barrier is not equal to the given phase value or this barrier |
| 585 |
< |
* is terminated. |
| 585 |
> |
* is terminated. It is an unenforced usage error for an |
| 586 |
> |
* unregistered party to invoke this method. |
| 587 |
|
* |
| 588 |
|
* @param phase an arrival phase number, or negative value if |
| 589 |
|
* terminated; this argument is normally the value returned by a |
| 606 |
|
|
| 607 |
|
/** |
| 608 |
|
* Awaits the phase of the barrier to advance from the given phase |
| 609 |
< |
* value, throwing {@code InterruptedException} if interrupted while |
| 610 |
< |
* waiting, or returning immediately if the current phase of the |
| 611 |
< |
* barrier is not equal to the given phase value or this barrier |
| 612 |
< |
* is terminated. |
| 609 |
> |
* value, throwing {@code InterruptedException} if interrupted |
| 610 |
> |
* while waiting, or returning immediately if the current phase of |
| 611 |
> |
* the barrier is not equal to the given phase value or this |
| 612 |
> |
* barrier is terminated. It is an unenforced usage error for an |
| 613 |
> |
* unregistered party to invoke this method. |
| 614 |
|
* |
| 615 |
|
* @param phase an arrival phase number, or negative value if |
| 616 |
|
* terminated; this argument is normally the value returned by a |
| 634 |
|
|
| 635 |
|
/** |
| 636 |
|
* Awaits the phase of the barrier to advance from the given phase |
| 637 |
< |
* value or the given timeout to elapse, throwing |
| 638 |
< |
* {@code InterruptedException} if interrupted while waiting, or |
| 639 |
< |
* returning immediately if the current phase of the barrier is not |
| 640 |
< |
* equal to the given phase value or this barrier is terminated. |
| 637 |
> |
* value or the given timeout to elapse, throwing {@code |
| 638 |
> |
* InterruptedException} if interrupted while waiting, or |
| 639 |
> |
* returning immediately if the current phase of the barrier is |
| 640 |
> |
* not equal to the given phase value or this barrier is |
| 641 |
> |
* terminated. It is an unenforced usage error for an |
| 642 |
> |
* unregistered party to invoke this method. |
| 643 |
|
* |
| 644 |
|
* @param phase an arrival phase number, or negative value if |
| 645 |
|
* terminated; this argument is normally the value returned by a |
