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import java.util.concurrent.locks.LockSupport; |
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|
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/** |
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* A reusable synchronization barrier, similar in functionality to a |
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* A reusable synchronization barrier, similar in functionality to |
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* {@link java.util.concurrent.CyclicBarrier CyclicBarrier} and |
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* {@link java.util.concurrent.CountDownLatch CountDownLatch} |
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* but supporting more flexible usage. |
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* |
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* <ul> |
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* |
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* <li> The number of parties synchronizing on a phaser may vary over |
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* time. A task may register to be a party at any time, and may |
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* deregister upon arriving at the barrier. As is the case with most |
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* basic synchronization constructs, registration and deregistration |
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* affect only internal counts; they do not establish any further |
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* internal bookkeeping, so tasks cannot query whether they are |
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* registered. (However, you can introduce such bookkeeping by |
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* subclassing this class.) |
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* |
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* <li> Each generation has an associated phase value, starting at |
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* zero, and advancing when all parties reach the barrier (wrapping |
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* around to zero after reaching {@code Integer.MAX_VALUE}). |
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* |
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* <li> Like a {@code CyclicBarrier}, a phaser may be repeatedly |
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* awaited. Method {@link #arriveAndAwaitAdvance} has effect |
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* analogous to {@link java.util.concurrent.CyclicBarrier#await |
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* CyclicBarrier.await}. However, phasers separate two aspects of |
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* coordination, which may also be invoked independently: |
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* <p> <b>Registration.</b> Unlike the case for other barriers, the |
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* number of parties <em>registered</em> to synchronize on a phaser |
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> |
* may vary over time. Tasks may be registered at any time (using |
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> |
* methods {@link #register}, {@link #bulkRegister}, or forms of |
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* constructors establishing initial numbers of parties), and |
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> |
* optionally deregistered upon any arrival (using {@link |
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> |
* #arriveAndDeregister}). As is the case with most basic |
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* synchronization constructs, registration and deregistration affect |
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* only internal counts; they do not establish any further internal |
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> |
* bookkeeping, so tasks cannot query whether they are registered. |
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* (However, you can introduce such bookkeeping by subclassing this |
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* class.) |
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> |
* |
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> |
* <p> <b>Synchronization.</b> Like a {@code CyclicBarrier}, a {@code |
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* Phaser} may be repeatedly awaited. Method {@link |
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> |
* #arriveAndAwaitAdvance} has effect analogous to {@link |
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> |
* java.util.concurrent.CyclicBarrier#await CyclicBarrier.await}. Each |
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> |
* generation of a {@code Phaser} has an associated phase number. The |
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> |
* phase number starts at zero, and advances when all parties arrive |
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> |
* at the barrier, wrapping around to zero after reaching {@code |
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> |
* Integer.MAX_VALUE}. The use of phase numbers enables independent |
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* control of actions upon arrival at a barrier and upon awaiting |
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* others, via two kinds of methods that may be invoked by any |
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* registered party: |
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* |
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* <ul> |
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* |
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* <li> Arriving at a barrier. Methods {@link #arrive} and |
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* {@link #arriveAndDeregister} do not block, but return |
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* the phase value current upon entry to the method. |
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* |
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* <li> Awaiting others. Method {@link #awaitAdvance} requires an |
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* argument indicating the entry phase, and returns when the |
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* barrier advances to a new phase. |
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< |
* </ul> |
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> |
* <li> <b>Arrival.</b> Methods {@link #arrive} and |
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* {@link #arriveAndDeregister} record arrival at a |
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* barrier. These methods do not block, but return an associated |
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* <em>arrival phase number</em>; that is, the phase number of |
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* the barrier to which the arrival applied. When the final |
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* party for a given phase arrives, an optional barrier action |
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* is performed and the phase advances. Barrier actions, |
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* performed by the party triggering a phase advance, are |
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* arranged by overriding method {@link #onAdvance(int, int)}, |
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* which also controls termination. Overriding this method is |
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> |
* similar to, but more flexible than, providing a barrier |
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* action to a {@code CyclicBarrier}. |
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> |
* |
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> |
* <li> <b>Waiting.</b> Method {@link #awaitAdvance} requires an |
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> |
* argument indicating an arrival phase number, and returns when |
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> |
* the barrier advances to (or is already at) a different phase. |
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> |
* Unlike similar constructions using {@code CyclicBarrier}, |
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> |
* method {@code awaitAdvance} continues to wait even if the |
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> |
* waiting thread is interrupted. Interruptible and timeout |
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* versions are also available, but exceptions encountered while |
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> |
* tasks wait interruptibly or with timeout do not change the |
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> |
* state of the barrier. If necessary, you can perform any |
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> |
* associated recovery within handlers of those exceptions, |
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* often after invoking {@code forceTermination}. Phasers may |
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* also be used by tasks executing in a {@link ForkJoinPool}, |
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* which will ensure sufficient parallelism to execute tasks |
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> |
* when others are blocked waiting for a phase to advance. |
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* |
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+ |
* </ul> |
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* |
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< |
* <li> Barrier actions, performed by the task triggering a phase |
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< |
* advance, are arranged by overriding method {@link #onAdvance(int, |
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< |
* int)}, which also controls termination. Overriding this method is |
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< |
* similar to, but more flexible than, providing a barrier action to a |
| 81 |
< |
* {@code CyclicBarrier}. |
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< |
* |
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< |
* <li> Phasers may enter a <em>termination</em> state in which all |
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< |
* 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 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 |
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> |
* <p> <b>Termination.</b> A {@code Phaser} may enter a |
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> |
* <em>termination</em> state in which all synchronization methods |
| 79 |
> |
* immediately return without updating phaser state or waiting for |
| 80 |
> |
* advance, and indicating (via a negative phase value) that execution |
| 81 |
> |
* is complete. Termination is triggered when an invocation of {@code |
| 82 |
> |
* onAdvance} returns {@code true}. As illustrated below, when |
| 83 |
> |
* phasers control actions with a fixed number of iterations, it is |
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* often convenient to override this method to cause termination when |
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* the current phase number reaches a threshold. Method {@link |
| 86 |
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* #forceTermination} is also available to abruptly release waiting |
| 87 |
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* threads and allow them to terminate. |
| 88 |
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* |
| 89 |
< |
* <li> Phasers may be tiered to reduce contention. Phasers with large |
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> |
* <p> <b>Tiering.</b> Phasers may be <em>tiered</em> (i.e., arranged |
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> |
* in tree structures) to reduce contention. Phasers with large |
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* 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 |
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< |
* 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 |
| 105 |
< |
* ForkJoinPool}, which will ensure sufficient parallelism to execute |
| 106 |
< |
* tasks when others are blocked waiting for a phase to advance. |
| 107 |
< |
* |
| 108 |
< |
* </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} parties in total, of which {@link |
| 101 |
> |
* #getArrivedParties} have arrived at the current phase ({@link |
| 102 |
> |
* #getPhase}). When the remaining ({@link #getUnarrivedParties}) |
| 103 |
> |
* parties arrive, the phase advances; thus, this value is always |
| 104 |
> |
* greater than zero if there are any registered parties. The values |
| 105 |
> |
* returned by these methods may reflect transient states and so are |
| 106 |
> |
* not in general useful for synchronization control. Method {@link |
| 107 |
> |
* #toString} returns snapshots of these state queries in a form |
| 108 |
> |
* convenient for informal monitoring. |
| 109 |
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* |
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* <p><b>Sample usages:</b> |
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* |
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* <pre> {@code |
| 139 |
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* void startTasks(List<Runnable> tasks, final int iterations) { |
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* final Phaser phaser = new Phaser() { |
| 141 |
< |
* public boolean onAdvance(int phase, int registeredParties) { |
| 141 |
> |
* protected boolean onAdvance(int phase, int registeredParties) { |
| 142 |
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* return phase >= iterations || registeredParties == 0; |
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* } |
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* }; |
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* phaser.arriveAndDeregister(); // deregister self, don't wait |
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* }}</pre> |
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* |
| 160 |
+ |
* If the main task must later await termination, it |
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+ |
* may re-register and then execute a similar loop: |
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+ |
* <pre> {@code |
| 163 |
+ |
* // ... |
| 164 |
+ |
* phaser.register(); |
| 165 |
+ |
* while (!phaser.isTerminated()) |
| 166 |
+ |
* phaser.arriveAndAwaitAdvance(); |
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+ |
* }</pre> |
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+ |
* |
| 169 |
+ |
* Related constructions may be used to await particular phase numbers |
| 170 |
+ |
* in contexts where you are sure that the phase will never wrap around |
| 171 |
+ |
* {@code Integer.MAX_VALUE}. For example: |
| 172 |
+ |
* |
| 173 |
+ |
* <pre> {@code |
| 174 |
+ |
* void awaitPhase(Phaser phaser, int phase) { |
| 175 |
+ |
* int p = phaser.register(); // assumes caller not already registered |
| 176 |
+ |
* while (p < phase) { |
| 177 |
+ |
* if (phaser.isTerminated()) |
| 178 |
+ |
* // ... deal with unexpected termination |
| 179 |
+ |
* else |
| 180 |
+ |
* p = phaser.arriveAndAwaitAdvance(); |
| 181 |
+ |
* } |
| 182 |
+ |
* phaser.arriveAndDeregister(); |
| 183 |
+ |
* } |
| 184 |
+ |
* }</pre> |
| 185 |
+ |
* |
| 186 |
+ |
* |
| 187 |
|
* <p>To create a set of tasks using a tree of phasers, |
| 188 |
|
* you could use code of the following form, assuming a |
| 189 |
|
* Task class with a constructor accepting a phaser that |
| 250 |
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*/ |
| 251 |
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private volatile long state; |
| 252 |
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|
| 206 |
– |
private static final int ushortBits = 16; |
| 253 |
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private static final int ushortMask = 0xffff; |
| 254 |
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private static final int phaseMask = 0x7fffffff; |
| 255 |
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|
| 412 |
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/** |
| 413 |
|
* Adds a new unarrived party to this phaser. |
| 414 |
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* |
| 415 |
< |
* @return the current barrier phase number upon registration |
| 415 |
> |
* @return the arrival phase number to which this registration applied |
| 416 |
|
* @throws IllegalStateException if attempting to register more |
| 417 |
|
* than the maximum supported number of parties |
| 418 |
|
*/ |
| 424 |
|
* Adds the given number of new unarrived parties to this phaser. |
| 425 |
|
* |
| 426 |
|
* @param parties the number of parties required to trip barrier |
| 427 |
< |
* @return the current barrier phase number upon registration |
| 427 |
> |
* @return the arrival phase number to which this registration applied |
| 428 |
|
* @throws IllegalStateException if attempting to register more |
| 429 |
|
* than the maximum supported number of parties |
| 430 |
|
*/ |
| 459 |
|
|
| 460 |
|
/** |
| 461 |
|
* Arrives at the barrier, but does not wait for others. (You can |
| 462 |
< |
* in turn wait for others via {@link #awaitAdvance}). |
| 462 |
> |
* in turn wait for others via {@link #awaitAdvance}). It is an |
| 463 |
> |
* unenforced usage error for an unregistered party to invoke this |
| 464 |
> |
* method. |
| 465 |
|
* |
| 466 |
< |
* @return the barrier phase number upon entry to this method, or a |
| 419 |
< |
* negative value if terminated |
| 466 |
> |
* @return the arrival phase number, or a negative value if terminated |
| 467 |
|
* @throws IllegalStateException if not terminated and the number |
| 468 |
|
* of unarrived parties would become negative |
| 469 |
|
*/ |
| 513 |
|
* required to trip the barrier in future phases. If this phaser |
| 514 |
|
* has a parent, and deregistration causes this phaser to have |
| 515 |
|
* zero parties, this phaser also arrives at and is deregistered |
| 516 |
< |
* from its parent. |
| 516 |
> |
* from its parent. It is an unenforced usage error for an |
| 517 |
> |
* unregistered party to invoke this method. |
| 518 |
|
* |
| 519 |
< |
* @return the current barrier phase number upon entry to |
| 472 |
< |
* this method, or a negative value if terminated |
| 519 |
> |
* @return the arrival phase number, or a negative value if terminated |
| 520 |
|
* @throws IllegalStateException if not terminated and the number |
| 521 |
|
* of registered or unarrived parties would become negative |
| 522 |
|
*/ |
| 570 |
|
* interruption or timeout, you can arrange this with an analogous |
| 571 |
|
* construction using one of the other forms of the awaitAdvance |
| 572 |
|
* method. If instead you need to deregister upon arrival use |
| 573 |
< |
* {@code arriveAndDeregister}. |
| 573 |
> |
* {@code arriveAndDeregister}. It is an unenforced usage error |
| 574 |
> |
* for an unregistered party to invoke this method. |
| 575 |
|
* |
| 576 |
< |
* @return the phase on entry to this method |
| 576 |
> |
* @return the arrival phase number, or a negative number if terminated |
| 577 |
|
* @throws IllegalStateException if not terminated and the number |
| 578 |
|
* of unarrived parties would become negative |
| 579 |
|
*/ |
| 585 |
|
* Awaits the phase of the barrier to advance from the given phase |
| 586 |
|
* value, returning immediately if the current phase of the |
| 587 |
|
* barrier is not equal to the given phase value or this barrier |
| 588 |
< |
* is terminated. |
| 588 |
> |
* is terminated. It is an unenforced usage error for an |
| 589 |
> |
* unregistered party to invoke this method. |
| 590 |
|
* |
| 591 |
< |
* @param phase the phase on entry to this method |
| 592 |
< |
* @return the current barrier phase number upon exit of |
| 593 |
< |
* this method, or a negative value if terminated or |
| 594 |
< |
* argument is negative |
| 591 |
> |
* @param phase an arrival phase number, or negative value if |
| 592 |
> |
* terminated; this argument is normally the value returned by a |
| 593 |
> |
* previous call to {@code arrive} or its variants |
| 594 |
> |
* @return the next arrival phase number, or a negative value |
| 595 |
> |
* if terminated or argument is negative |
| 596 |
|
*/ |
| 597 |
|
public int awaitAdvance(int phase) { |
| 598 |
|
if (phase < 0) |
| 609 |
|
|
| 610 |
|
/** |
| 611 |
|
* Awaits the phase of the barrier to advance from the given phase |
| 612 |
< |
* value, throwing {@code InterruptedException} if interrupted while |
| 613 |
< |
* waiting, or returning immediately if the current phase of the |
| 614 |
< |
* barrier is not equal to the given phase value or this barrier |
| 615 |
< |
* is terminated. |
| 616 |
< |
* |
| 617 |
< |
* @param phase the phase on entry to this method |
| 618 |
< |
* @return the current barrier phase number upon exit of |
| 619 |
< |
* this method, or a negative value if terminated or |
| 620 |
< |
* argument is negative |
| 612 |
> |
* value, throwing {@code InterruptedException} if interrupted |
| 613 |
> |
* while waiting, or returning immediately if the current phase of |
| 614 |
> |
* the barrier is not equal to the given phase value or this |
| 615 |
> |
* barrier is terminated. It is an unenforced usage error for an |
| 616 |
> |
* unregistered party to invoke this method. |
| 617 |
> |
* |
| 618 |
> |
* @param phase an arrival phase number, or negative value if |
| 619 |
> |
* terminated; this argument is normally the value returned by a |
| 620 |
> |
* previous call to {@code arrive} or its variants |
| 621 |
> |
* @return the next arrival phase number, or a negative value |
| 622 |
> |
* if terminated or argument is negative |
| 623 |
|
* @throws InterruptedException if thread interrupted while waiting |
| 624 |
|
*/ |
| 625 |
|
public int awaitAdvanceInterruptibly(int phase) |
| 637 |
|
|
| 638 |
|
/** |
| 639 |
|
* Awaits the phase of the barrier to advance from the given phase |
| 640 |
< |
* value or the given timeout to elapse, throwing |
| 641 |
< |
* {@code InterruptedException} if interrupted while waiting, or |
| 642 |
< |
* returning immediately if the current phase of the barrier is not |
| 643 |
< |
* equal to the given phase value or this barrier is terminated. |
| 644 |
< |
* |
| 645 |
< |
* @param phase the phase on entry to this method |
| 640 |
> |
* value or the given timeout to elapse, throwing {@code |
| 641 |
> |
* InterruptedException} if interrupted while waiting, or |
| 642 |
> |
* returning immediately if the current phase of the barrier is |
| 643 |
> |
* not equal to the given phase value or this barrier is |
| 644 |
> |
* terminated. It is an unenforced usage error for an |
| 645 |
> |
* unregistered party to invoke this method. |
| 646 |
> |
* |
| 647 |
> |
* @param phase an arrival phase number, or negative value if |
| 648 |
> |
* terminated; this argument is normally the value returned by a |
| 649 |
> |
* previous call to {@code arrive} or its variants |
| 650 |
|
* @param timeout how long to wait before giving up, in units of |
| 651 |
|
* {@code unit} |
| 652 |
|
* @param unit a {@code TimeUnit} determining how to interpret the |
| 653 |
|
* {@code timeout} parameter |
| 654 |
< |
* @return the current barrier phase number upon exit of |
| 655 |
< |
* this method, or a negative value if terminated or |
| 600 |
< |
* argument is negative |
| 654 |
> |
* @return the next arrival phase number, or a negative value |
| 655 |
> |
* if terminated or argument is negative |
| 656 |
|
* @throws InterruptedException if thread interrupted while waiting |
| 657 |
|
* @throws TimeoutException if timed out while waiting |
| 658 |
|
*/ |
| 715 |
|
} |
| 716 |
|
|
| 717 |
|
/** |
| 718 |
< |
* Returns the number of parties that have arrived at the current |
| 719 |
< |
* phase of this barrier. |
| 718 |
> |
* Returns the number of registered parties that have arrived at |
| 719 |
> |
* the current phase of this barrier. |
| 720 |
|
* |
| 721 |
|
* @return the number of arrived parties |
| 722 |
|
*/ |
