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jsr166 |
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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/licenses/publicdomain |
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*/ |
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package java.util.concurrent; |
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import java.util.concurrent.atomic.AtomicReference; |
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import java.util.concurrent.locks.LockSupport; |
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/** |
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1.10 |
* 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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* <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> <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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* <p> <b>Termination.</b> A {@code Phaser} may enter a |
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* <em>termination</em> state in which all synchronization methods |
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* immediately return without updating phaser state or waiting for |
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* advance, and indicating (via a negative phase value) that execution |
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* is complete. Termination is triggered when an invocation of {@code |
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* onAdvance} returns {@code true}. As illustrated below, when |
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* 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 |
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* #forceTermination} is also available to abruptly release waiting |
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* threads and allow them to terminate. |
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* |
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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 |
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* synchronization contention costs may instead be set up so that |
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* groups of sub-phasers share a common parent. This may greatly |
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* increase throughput even though it incurs greater per-operation |
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* overhead. |
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* |
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* <p><b>Monitoring.</b> While synchronization methods may be invoked |
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* only by registered parties, the current state of a phaser may be |
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* monitored by any caller. At any given moment there are {@link |
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* #getRegisteredParties} parties in total, of which {@link |
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* #getArrivedParties} have arrived at the current phase ({@link |
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* #getPhase}). When the remaining ({@link #getUnarrivedParties}) |
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* parties arrive, the phase advances. The values returned by these |
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* methods may reflect transient states and so are not in general |
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* useful for synchronization control. Method {@link #toString} |
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* returns snapshots of these state queries in a form convenient for |
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* informal monitoring. |
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* |
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* <p><b>Sample usages:</b> |
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* |
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* <p>A {@code Phaser} may be used instead of a {@code CountDownLatch} |
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* to control a one-shot action serving a variable number of |
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* parties. The typical idiom is for the method setting this up to |
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* first register, then start the actions, then deregister, as in: |
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1.1 |
* |
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* <pre> {@code |
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1.8 |
* void runTasks(List<Runnable> tasks) { |
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1.1 |
* final Phaser phaser = new Phaser(1); // "1" to register self |
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1.7 |
* // create and start threads |
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* for (Runnable task : tasks) { |
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* phaser.register(); |
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* new Thread() { |
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* public void run() { |
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* phaser.arriveAndAwaitAdvance(); // await all creation |
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* task.run(); |
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* } |
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* }.start(); |
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* } |
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* |
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* // allow threads to start and deregister self |
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* phaser.arriveAndDeregister(); |
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1.1 |
* }}</pre> |
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* |
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* <p>One way to cause a set of threads to repeatedly perform actions |
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* for a given number of iterations is to override {@code onAdvance}: |
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* |
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* <pre> {@code |
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1.8 |
* void startTasks(List<Runnable> tasks, final int iterations) { |
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1.1 |
* final Phaser phaser = new Phaser() { |
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* protected boolean onAdvance(int phase, int registeredParties) { |
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1.1 |
* return phase >= iterations || registeredParties == 0; |
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* } |
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* }; |
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* phaser.register(); |
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* for (final Runnable task : tasks) { |
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1.1 |
* phaser.register(); |
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* new Thread() { |
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* public void run() { |
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* do { |
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* task.run(); |
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* phaser.arriveAndAwaitAdvance(); |
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* } while (!phaser.isTerminated()); |
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* } |
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* }.start(); |
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* } |
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* phaser.arriveAndDeregister(); // deregister self, don't wait |
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* }}</pre> |
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* |
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* 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 |
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* // ... |
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* phaser.register(); |
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* while (!phaser.isTerminated()) |
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* phaser.arriveAndAwaitAdvance();}</pre> |
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* |
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* <p>Related constructions may be used to await particular phase numbers |
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* in contexts where you are sure that the phase will never wrap around |
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* {@code Integer.MAX_VALUE}. For example: |
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* |
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* <pre> {@code |
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* void awaitPhase(Phaser phaser, int phase) { |
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* int p = phaser.register(); // assumes caller not already registered |
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* while (p < phase) { |
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* if (phaser.isTerminated()) |
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* // ... deal with unexpected termination |
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* else |
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* p = phaser.arriveAndAwaitAdvance(); |
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* } |
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* phaser.arriveAndDeregister(); |
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* }}</pre> |
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* |
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* |
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1.5 |
* <p>To create a set of tasks using a tree of phasers, |
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1.1 |
* you could use code of the following form, assuming a |
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1.4 |
* Task class with a constructor accepting a phaser that |
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1.1 |
* it registers for upon construction: |
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1.10 |
* |
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1.1 |
* <pre> {@code |
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1.10 |
* void build(Task[] actions, int lo, int hi, Phaser ph) { |
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* if (hi - lo > TASKS_PER_PHASER) { |
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* for (int i = lo; i < hi; i += TASKS_PER_PHASER) { |
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* int j = Math.min(i + TASKS_PER_PHASER, hi); |
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* build(actions, i, j, new Phaser(ph)); |
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1.1 |
* } |
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* } else { |
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* for (int i = lo; i < hi; ++i) |
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1.10 |
* actions[i] = new Task(ph); |
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* // assumes new Task(ph) performs ph.register() |
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1.1 |
* } |
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* } |
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* // .. initially called, for n tasks via |
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* build(new Task[n], 0, n, new Phaser());}</pre> |
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* |
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* The best value of {@code TASKS_PER_PHASER} depends mainly on |
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* expected barrier synchronization rates. A value as low as four may |
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* be appropriate for extremely small per-barrier task bodies (thus |
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* high rates), or up to hundreds for extremely large ones. |
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* |
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* </pre> |
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* |
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* <p><b>Implementation notes</b>: This implementation restricts the |
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* maximum number of parties to 65535. Attempts to register additional |
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1.8 |
* parties result in {@code IllegalStateException}. However, you can and |
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1.1 |
* should create tiered phasers to accommodate arbitrarily large sets |
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* of participants. |
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* |
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* @since 1.7 |
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* @author Doug Lea |
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*/ |
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public class Phaser { |
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/* |
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* This class implements an extension of X10 "clocks". Thanks to |
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* Vijay Saraswat for the idea, and to Vivek Sarkar for |
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* enhancements to extend functionality. |
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*/ |
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/** |
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* Barrier state representation. Conceptually, a barrier contains |
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* four values: |
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* |
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* * parties -- the number of parties to wait (16 bits) |
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* * unarrived -- the number of parties yet to hit barrier (16 bits) |
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* * phase -- the generation of the barrier (31 bits) |
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* * terminated -- set if barrier is terminated (1 bit) |
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* |
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* However, to efficiently maintain atomicity, these values are |
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* packed into a single (atomic) long. Termination uses the sign |
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* bit of 32 bit representation of phase, so phase is set to -1 on |
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* termination. Good performance relies on keeping state decoding |
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* and encoding simple, and keeping race windows short. |
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* |
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* Note: there are some cheats in arrive() that rely on unarrived |
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* count being lowest 16 bits. |
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*/ |
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private volatile long state; |
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private static final int ushortMask = 0xffff; |
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private static final int phaseMask = 0x7fffffff; |
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private static int unarrivedOf(long s) { |
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return (int) (s & ushortMask); |
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} |
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private static int partiesOf(long s) { |
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return ((int) s) >>> 16; |
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} |
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private static int phaseOf(long s) { |
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return (int) (s >>> 32); |
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} |
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private static int arrivedOf(long s) { |
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return partiesOf(s) - unarrivedOf(s); |
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} |
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private static long stateFor(int phase, int parties, int unarrived) { |
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return ((((long) phase) << 32) | (((long) parties) << 16) | |
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(long) unarrived); |
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} |
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private static long trippedStateFor(int phase, int parties) { |
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long lp = (long) parties; |
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return (((long) phase) << 32) | (lp << 16) | lp; |
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} |
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/** |
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* Returns message string for bad bounds exceptions. |
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*/ |
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private static String badBounds(int parties, int unarrived) { |
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return ("Attempt to set " + unarrived + |
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" unarrived of " + parties + " parties"); |
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} |
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/** |
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* The parent of this phaser, or null if none |
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*/ |
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private final Phaser parent; |
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/** |
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1.4 |
* The root of phaser tree. Equals this if not in a tree. Used to |
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1.1 |
* support faster state push-down. |
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*/ |
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private final Phaser root; |
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// Wait queues |
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/** |
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* Heads of Treiber stacks for waiting threads. To eliminate |
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* contention while releasing some threads while adding others, we |
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* use two of them, alternating across even and odd phases. |
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*/ |
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private final AtomicReference<QNode> evenQ = new AtomicReference<QNode>(); |
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private final AtomicReference<QNode> oddQ = new AtomicReference<QNode>(); |
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private AtomicReference<QNode> queueFor(int phase) { |
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return ((phase & 1) == 0) ? evenQ : oddQ; |
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} |
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/** |
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* Returns current state, first resolving lagged propagation from |
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* root if necessary. |
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*/ |
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private long getReconciledState() { |
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return (parent == null) ? state : reconcileState(); |
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} |
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/** |
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* Recursively resolves state. |
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*/ |
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private long reconcileState() { |
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Phaser p = parent; |
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long s = state; |
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if (p != null) { |
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while (unarrivedOf(s) == 0 && phaseOf(s) != phaseOf(root.state)) { |
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long parentState = p.getReconciledState(); |
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int parentPhase = phaseOf(parentState); |
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int phase = phaseOf(s = state); |
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if (phase != parentPhase) { |
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long next = trippedStateFor(parentPhase, partiesOf(s)); |
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if (casState(s, next)) { |
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releaseWaiters(phase); |
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s = next; |
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} |
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} |
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} |
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} |
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return s; |
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} |
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/** |
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jsr166 |
1.4 |
* Creates a new phaser without any initially registered parties, |
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jsr166 |
1.1 |
* initial phase number 0, and no parent. Any thread using this |
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jsr166 |
1.4 |
* phaser will need to first register for it. |
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jsr166 |
1.1 |
*/ |
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public Phaser() { |
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this(null); |
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} |
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/** |
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jsr166 |
1.4 |
* Creates a new phaser with the given numbers of registered |
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jsr166 |
1.1 |
* unarrived parties, initial phase number 0, and no parent. |
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* |
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* @param parties the number of parties required to trip barrier |
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* @throws IllegalArgumentException if parties less than zero |
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* or greater than the maximum number of parties supported |
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*/ |
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public Phaser(int parties) { |
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this(null, parties); |
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} |
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/** |
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jsr166 |
1.4 |
* Creates a new phaser with the given parent, without any |
362 |
jsr166 |
1.1 |
* initially registered parties. If parent is non-null this phaser |
363 |
|
|
* is registered with the parent and its initial phase number is |
364 |
|
|
* the same as that of parent phaser. |
365 |
|
|
* |
366 |
|
|
* @param parent the parent phaser |
367 |
|
|
*/ |
368 |
|
|
public Phaser(Phaser parent) { |
369 |
|
|
int phase = 0; |
370 |
|
|
this.parent = parent; |
371 |
|
|
if (parent != null) { |
372 |
|
|
this.root = parent.root; |
373 |
|
|
phase = parent.register(); |
374 |
|
|
} |
375 |
|
|
else |
376 |
|
|
this.root = this; |
377 |
|
|
this.state = trippedStateFor(phase, 0); |
378 |
|
|
} |
379 |
|
|
|
380 |
|
|
/** |
381 |
jsr166 |
1.4 |
* Creates a new phaser with the given parent and numbers of |
382 |
jsr166 |
1.1 |
* registered unarrived parties. If parent is non-null, this phaser |
383 |
|
|
* is registered with the parent and its initial phase number is |
384 |
|
|
* the same as that of parent phaser. |
385 |
|
|
* |
386 |
|
|
* @param parent the parent phaser |
387 |
|
|
* @param parties the number of parties required to trip barrier |
388 |
|
|
* @throws IllegalArgumentException if parties less than zero |
389 |
|
|
* or greater than the maximum number of parties supported |
390 |
|
|
*/ |
391 |
|
|
public Phaser(Phaser parent, int parties) { |
392 |
|
|
if (parties < 0 || parties > ushortMask) |
393 |
|
|
throw new IllegalArgumentException("Illegal number of parties"); |
394 |
|
|
int phase = 0; |
395 |
|
|
this.parent = parent; |
396 |
|
|
if (parent != null) { |
397 |
|
|
this.root = parent.root; |
398 |
|
|
phase = parent.register(); |
399 |
|
|
} |
400 |
|
|
else |
401 |
|
|
this.root = this; |
402 |
|
|
this.state = trippedStateFor(phase, parties); |
403 |
|
|
} |
404 |
|
|
|
405 |
|
|
/** |
406 |
|
|
* Adds a new unarrived party to this phaser. |
407 |
|
|
* |
408 |
jsr166 |
1.10 |
* @return the arrival phase number to which this registration applied |
409 |
jsr166 |
1.1 |
* @throws IllegalStateException if attempting to register more |
410 |
|
|
* than the maximum supported number of parties |
411 |
|
|
*/ |
412 |
|
|
public int register() { |
413 |
|
|
return doRegister(1); |
414 |
|
|
} |
415 |
|
|
|
416 |
|
|
/** |
417 |
|
|
* Adds the given number of new unarrived parties to this phaser. |
418 |
|
|
* |
419 |
|
|
* @param parties the number of parties required to trip barrier |
420 |
jsr166 |
1.10 |
* @return the arrival phase number to which this registration applied |
421 |
jsr166 |
1.1 |
* @throws IllegalStateException if attempting to register more |
422 |
|
|
* than the maximum supported number of parties |
423 |
|
|
*/ |
424 |
|
|
public int bulkRegister(int parties) { |
425 |
|
|
if (parties < 0) |
426 |
|
|
throw new IllegalArgumentException(); |
427 |
|
|
if (parties == 0) |
428 |
|
|
return getPhase(); |
429 |
|
|
return doRegister(parties); |
430 |
|
|
} |
431 |
|
|
|
432 |
|
|
/** |
433 |
|
|
* Shared code for register, bulkRegister |
434 |
|
|
*/ |
435 |
|
|
private int doRegister(int registrations) { |
436 |
|
|
int phase; |
437 |
|
|
for (;;) { |
438 |
|
|
long s = getReconciledState(); |
439 |
|
|
phase = phaseOf(s); |
440 |
|
|
int unarrived = unarrivedOf(s) + registrations; |
441 |
|
|
int parties = partiesOf(s) + registrations; |
442 |
|
|
if (phase < 0) |
443 |
|
|
break; |
444 |
|
|
if (parties > ushortMask || unarrived > ushortMask) |
445 |
|
|
throw new IllegalStateException(badBounds(parties, unarrived)); |
446 |
|
|
if (phase == phaseOf(root.state) && |
447 |
|
|
casState(s, stateFor(phase, parties, unarrived))) |
448 |
|
|
break; |
449 |
|
|
} |
450 |
|
|
return phase; |
451 |
|
|
} |
452 |
|
|
|
453 |
|
|
/** |
454 |
|
|
* Arrives at the barrier, but does not wait for others. (You can |
455 |
jsr166 |
1.10 |
* in turn wait for others via {@link #awaitAdvance}). It is an |
456 |
|
|
* unenforced usage error for an unregistered party to invoke this |
457 |
|
|
* method. |
458 |
jsr166 |
1.1 |
* |
459 |
jsr166 |
1.10 |
* @return the arrival phase number, or a negative value if terminated |
460 |
jsr166 |
1.1 |
* @throws IllegalStateException if not terminated and the number |
461 |
|
|
* of unarrived parties would become negative |
462 |
|
|
*/ |
463 |
|
|
public int arrive() { |
464 |
|
|
int phase; |
465 |
|
|
for (;;) { |
466 |
|
|
long s = state; |
467 |
|
|
phase = phaseOf(s); |
468 |
|
|
if (phase < 0) |
469 |
|
|
break; |
470 |
|
|
int parties = partiesOf(s); |
471 |
|
|
int unarrived = unarrivedOf(s) - 1; |
472 |
|
|
if (unarrived > 0) { // Not the last arrival |
473 |
|
|
if (casState(s, s - 1)) // s-1 adds one arrival |
474 |
|
|
break; |
475 |
|
|
} |
476 |
|
|
else if (unarrived == 0) { // the last arrival |
477 |
|
|
Phaser par = parent; |
478 |
|
|
if (par == null) { // directly trip |
479 |
|
|
if (casState |
480 |
|
|
(s, |
481 |
|
|
trippedStateFor(onAdvance(phase, parties) ? -1 : |
482 |
|
|
((phase + 1) & phaseMask), parties))) { |
483 |
|
|
releaseWaiters(phase); |
484 |
|
|
break; |
485 |
|
|
} |
486 |
|
|
} |
487 |
|
|
else { // cascade to parent |
488 |
|
|
if (casState(s, s - 1)) { // zeroes unarrived |
489 |
|
|
par.arrive(); |
490 |
|
|
reconcileState(); |
491 |
|
|
break; |
492 |
|
|
} |
493 |
|
|
} |
494 |
|
|
} |
495 |
|
|
else if (phase != phaseOf(root.state)) // or if unreconciled |
496 |
|
|
reconcileState(); |
497 |
|
|
else |
498 |
|
|
throw new IllegalStateException(badBounds(parties, unarrived)); |
499 |
|
|
} |
500 |
|
|
return phase; |
501 |
|
|
} |
502 |
|
|
|
503 |
|
|
/** |
504 |
jsr166 |
1.7 |
* Arrives at the barrier and deregisters from it without waiting |
505 |
|
|
* for others. Deregistration reduces the number of parties |
506 |
jsr166 |
1.1 |
* required to trip the barrier in future phases. If this phaser |
507 |
|
|
* has a parent, and deregistration causes this phaser to have |
508 |
jsr166 |
1.7 |
* zero parties, this phaser also arrives at and is deregistered |
509 |
jsr166 |
1.10 |
* from its parent. It is an unenforced usage error for an |
510 |
|
|
* unregistered party to invoke this method. |
511 |
jsr166 |
1.1 |
* |
512 |
jsr166 |
1.10 |
* @return the arrival phase number, or a negative value if terminated |
513 |
jsr166 |
1.1 |
* @throws IllegalStateException if not terminated and the number |
514 |
|
|
* of registered or unarrived parties would become negative |
515 |
|
|
*/ |
516 |
|
|
public int arriveAndDeregister() { |
517 |
|
|
// similar code to arrive, but too different to merge |
518 |
|
|
Phaser par = parent; |
519 |
|
|
int phase; |
520 |
|
|
for (;;) { |
521 |
|
|
long s = state; |
522 |
|
|
phase = phaseOf(s); |
523 |
|
|
if (phase < 0) |
524 |
|
|
break; |
525 |
|
|
int parties = partiesOf(s) - 1; |
526 |
|
|
int unarrived = unarrivedOf(s) - 1; |
527 |
|
|
if (parties >= 0) { |
528 |
|
|
if (unarrived > 0 || (unarrived == 0 && par != null)) { |
529 |
|
|
if (casState |
530 |
|
|
(s, |
531 |
|
|
stateFor(phase, parties, unarrived))) { |
532 |
|
|
if (unarrived == 0) { |
533 |
|
|
par.arriveAndDeregister(); |
534 |
|
|
reconcileState(); |
535 |
|
|
} |
536 |
|
|
break; |
537 |
|
|
} |
538 |
|
|
continue; |
539 |
|
|
} |
540 |
|
|
if (unarrived == 0) { |
541 |
|
|
if (casState |
542 |
|
|
(s, |
543 |
|
|
trippedStateFor(onAdvance(phase, parties) ? -1 : |
544 |
|
|
((phase + 1) & phaseMask), parties))) { |
545 |
|
|
releaseWaiters(phase); |
546 |
|
|
break; |
547 |
|
|
} |
548 |
|
|
continue; |
549 |
|
|
} |
550 |
|
|
if (par != null && phase != phaseOf(root.state)) { |
551 |
|
|
reconcileState(); |
552 |
|
|
continue; |
553 |
|
|
} |
554 |
|
|
} |
555 |
|
|
throw new IllegalStateException(badBounds(parties, unarrived)); |
556 |
|
|
} |
557 |
|
|
return phase; |
558 |
|
|
} |
559 |
|
|
|
560 |
|
|
/** |
561 |
|
|
* Arrives at the barrier and awaits others. Equivalent in effect |
562 |
jsr166 |
1.7 |
* to {@code awaitAdvance(arrive())}. If you need to await with |
563 |
|
|
* interruption or timeout, you can arrange this with an analogous |
564 |
|
|
* construction using one of the other forms of the awaitAdvance |
565 |
|
|
* method. If instead you need to deregister upon arrival use |
566 |
jsr166 |
1.10 |
* {@code arriveAndDeregister}. It is an unenforced usage error |
567 |
|
|
* for an unregistered party to invoke this method. |
568 |
jsr166 |
1.1 |
* |
569 |
jsr166 |
1.10 |
* @return the arrival phase number, or a negative number if terminated |
570 |
jsr166 |
1.1 |
* @throws IllegalStateException if not terminated and the number |
571 |
|
|
* of unarrived parties would become negative |
572 |
|
|
*/ |
573 |
|
|
public int arriveAndAwaitAdvance() { |
574 |
|
|
return awaitAdvance(arrive()); |
575 |
|
|
} |
576 |
|
|
|
577 |
|
|
/** |
578 |
jsr166 |
1.7 |
* Awaits the phase of the barrier to advance from the given phase |
579 |
jsr166 |
1.8 |
* value, returning immediately if the current phase of the |
580 |
|
|
* barrier is not equal to the given phase value or this barrier |
581 |
jsr166 |
1.10 |
* is terminated. It is an unenforced usage error for an |
582 |
|
|
* unregistered party to invoke this method. |
583 |
jsr166 |
1.1 |
* |
584 |
jsr166 |
1.10 |
* @param phase an arrival phase number, or negative value if |
585 |
|
|
* terminated; this argument is normally the value returned by a |
586 |
|
|
* previous call to {@code arrive} or its variants |
587 |
|
|
* @return the next arrival phase number, or a negative value |
588 |
|
|
* if terminated or argument is negative |
589 |
jsr166 |
1.1 |
*/ |
590 |
|
|
public int awaitAdvance(int phase) { |
591 |
|
|
if (phase < 0) |
592 |
|
|
return phase; |
593 |
|
|
long s = getReconciledState(); |
594 |
|
|
int p = phaseOf(s); |
595 |
|
|
if (p != phase) |
596 |
|
|
return p; |
597 |
|
|
if (unarrivedOf(s) == 0 && parent != null) |
598 |
|
|
parent.awaitAdvance(phase); |
599 |
|
|
// Fall here even if parent waited, to reconcile and help release |
600 |
|
|
return untimedWait(phase); |
601 |
|
|
} |
602 |
|
|
|
603 |
|
|
/** |
604 |
jsr166 |
1.8 |
* Awaits the phase of the barrier to advance from the given phase |
605 |
jsr166 |
1.10 |
* value, throwing {@code InterruptedException} if interrupted |
606 |
|
|
* while waiting, or returning immediately if the current phase of |
607 |
|
|
* the barrier is not equal to the given phase value or this |
608 |
|
|
* barrier is terminated. It is an unenforced usage error for an |
609 |
|
|
* unregistered party to invoke this method. |
610 |
|
|
* |
611 |
|
|
* @param phase an arrival phase number, or negative value if |
612 |
|
|
* terminated; this argument is normally the value returned by a |
613 |
|
|
* previous call to {@code arrive} or its variants |
614 |
|
|
* @return the next arrival phase number, or a negative value |
615 |
|
|
* if terminated or argument is negative |
616 |
jsr166 |
1.1 |
* @throws InterruptedException if thread interrupted while waiting |
617 |
|
|
*/ |
618 |
|
|
public int awaitAdvanceInterruptibly(int phase) |
619 |
|
|
throws InterruptedException { |
620 |
|
|
if (phase < 0) |
621 |
|
|
return phase; |
622 |
|
|
long s = getReconciledState(); |
623 |
|
|
int p = phaseOf(s); |
624 |
|
|
if (p != phase) |
625 |
|
|
return p; |
626 |
|
|
if (unarrivedOf(s) == 0 && parent != null) |
627 |
|
|
parent.awaitAdvanceInterruptibly(phase); |
628 |
|
|
return interruptibleWait(phase); |
629 |
|
|
} |
630 |
|
|
|
631 |
|
|
/** |
632 |
jsr166 |
1.8 |
* Awaits the phase of the barrier to advance from the given phase |
633 |
jsr166 |
1.10 |
* value or the given timeout to elapse, throwing {@code |
634 |
|
|
* InterruptedException} if interrupted while waiting, or |
635 |
|
|
* returning immediately if the current phase of the barrier is |
636 |
|
|
* not equal to the given phase value or this barrier is |
637 |
|
|
* terminated. It is an unenforced usage error for an |
638 |
|
|
* unregistered party to invoke this method. |
639 |
|
|
* |
640 |
|
|
* @param phase an arrival phase number, or negative value if |
641 |
|
|
* terminated; this argument is normally the value returned by a |
642 |
|
|
* previous call to {@code arrive} or its variants |
643 |
jsr166 |
1.8 |
* @param timeout how long to wait before giving up, in units of |
644 |
|
|
* {@code unit} |
645 |
|
|
* @param unit a {@code TimeUnit} determining how to interpret the |
646 |
|
|
* {@code timeout} parameter |
647 |
jsr166 |
1.10 |
* @return the next arrival phase number, or a negative value |
648 |
|
|
* if terminated or argument is negative |
649 |
jsr166 |
1.1 |
* @throws InterruptedException if thread interrupted while waiting |
650 |
|
|
* @throws TimeoutException if timed out while waiting |
651 |
|
|
*/ |
652 |
|
|
public int awaitAdvanceInterruptibly(int phase, |
653 |
|
|
long timeout, TimeUnit unit) |
654 |
|
|
throws InterruptedException, TimeoutException { |
655 |
|
|
if (phase < 0) |
656 |
|
|
return phase; |
657 |
|
|
long s = getReconciledState(); |
658 |
|
|
int p = phaseOf(s); |
659 |
|
|
if (p != phase) |
660 |
|
|
return p; |
661 |
|
|
if (unarrivedOf(s) == 0 && parent != null) |
662 |
|
|
parent.awaitAdvanceInterruptibly(phase, timeout, unit); |
663 |
|
|
return timedWait(phase, unit.toNanos(timeout)); |
664 |
|
|
} |
665 |
|
|
|
666 |
|
|
/** |
667 |
|
|
* Forces this barrier to enter termination state. Counts of |
668 |
|
|
* arrived and registered parties are unaffected. If this phaser |
669 |
|
|
* has a parent, it too is terminated. This method may be useful |
670 |
|
|
* for coordinating recovery after one or more tasks encounter |
671 |
|
|
* unexpected exceptions. |
672 |
|
|
*/ |
673 |
|
|
public void forceTermination() { |
674 |
|
|
for (;;) { |
675 |
|
|
long s = getReconciledState(); |
676 |
|
|
int phase = phaseOf(s); |
677 |
|
|
int parties = partiesOf(s); |
678 |
|
|
int unarrived = unarrivedOf(s); |
679 |
|
|
if (phase < 0 || |
680 |
|
|
casState(s, stateFor(-1, parties, unarrived))) { |
681 |
|
|
releaseWaiters(0); |
682 |
|
|
releaseWaiters(1); |
683 |
|
|
if (parent != null) |
684 |
|
|
parent.forceTermination(); |
685 |
|
|
return; |
686 |
|
|
} |
687 |
|
|
} |
688 |
|
|
} |
689 |
|
|
|
690 |
|
|
/** |
691 |
|
|
* Returns the current phase number. The maximum phase number is |
692 |
|
|
* {@code Integer.MAX_VALUE}, after which it restarts at |
693 |
|
|
* zero. Upon termination, the phase number is negative. |
694 |
|
|
* |
695 |
|
|
* @return the phase number, or a negative value if terminated |
696 |
|
|
*/ |
697 |
|
|
public final int getPhase() { |
698 |
|
|
return phaseOf(getReconciledState()); |
699 |
|
|
} |
700 |
|
|
|
701 |
|
|
/** |
702 |
|
|
* Returns the number of parties registered at this barrier. |
703 |
|
|
* |
704 |
|
|
* @return the number of parties |
705 |
|
|
*/ |
706 |
|
|
public int getRegisteredParties() { |
707 |
|
|
return partiesOf(state); |
708 |
|
|
} |
709 |
|
|
|
710 |
|
|
/** |
711 |
jsr166 |
1.10 |
* Returns the number of registered parties that have arrived at |
712 |
|
|
* the current phase of this barrier. |
713 |
jsr166 |
1.1 |
* |
714 |
|
|
* @return the number of arrived parties |
715 |
|
|
*/ |
716 |
|
|
public int getArrivedParties() { |
717 |
|
|
return arrivedOf(state); |
718 |
|
|
} |
719 |
|
|
|
720 |
|
|
/** |
721 |
|
|
* Returns the number of registered parties that have not yet |
722 |
|
|
* arrived at the current phase of this barrier. |
723 |
|
|
* |
724 |
|
|
* @return the number of unarrived parties |
725 |
|
|
*/ |
726 |
|
|
public int getUnarrivedParties() { |
727 |
|
|
return unarrivedOf(state); |
728 |
|
|
} |
729 |
|
|
|
730 |
|
|
/** |
731 |
jsr166 |
1.4 |
* Returns the parent of this phaser, or {@code null} if none. |
732 |
jsr166 |
1.1 |
* |
733 |
jsr166 |
1.4 |
* @return the parent of this phaser, or {@code null} if none |
734 |
jsr166 |
1.1 |
*/ |
735 |
|
|
public Phaser getParent() { |
736 |
|
|
return parent; |
737 |
|
|
} |
738 |
|
|
|
739 |
|
|
/** |
740 |
|
|
* Returns the root ancestor of this phaser, which is the same as |
741 |
|
|
* this phaser if it has no parent. |
742 |
|
|
* |
743 |
|
|
* @return the root ancestor of this phaser |
744 |
|
|
*/ |
745 |
|
|
public Phaser getRoot() { |
746 |
|
|
return root; |
747 |
|
|
} |
748 |
|
|
|
749 |
|
|
/** |
750 |
|
|
* Returns {@code true} if this barrier has been terminated. |
751 |
|
|
* |
752 |
|
|
* @return {@code true} if this barrier has been terminated |
753 |
|
|
*/ |
754 |
|
|
public boolean isTerminated() { |
755 |
|
|
return getPhase() < 0; |
756 |
|
|
} |
757 |
|
|
|
758 |
|
|
/** |
759 |
jsr166 |
1.10 |
* Overridable method to perform an action upon impending phase |
760 |
|
|
* advance, and to control termination. This method is invoked |
761 |
|
|
* upon arrival of the party tripping the barrier (when all other |
762 |
|
|
* waiting parties are dormant). If this method returns {@code |
763 |
|
|
* true}, then, rather than advance the phase number, this barrier |
764 |
|
|
* will be set to a final termination state, and subsequent calls |
765 |
|
|
* to {@link #isTerminated} will return true. Any (unchecked) |
766 |
|
|
* Exception or Error thrown by an invocation of this method is |
767 |
|
|
* propagated to the party attempting to trip the barrier, in |
768 |
|
|
* which case no advance occurs. |
769 |
|
|
* |
770 |
|
|
* <p>The arguments to this method provide the state of the phaser |
771 |
|
|
* prevailing for the current transition. (When called from within |
772 |
|
|
* an implementation of {@code onAdvance} the values returned by |
773 |
|
|
* methods such as {@code getPhase} may or may not reliably |
774 |
|
|
* indicate the state to which this transition applies.) |
775 |
jsr166 |
1.1 |
* |
776 |
jsr166 |
1.5 |
* <p>The default version returns {@code true} when the number of |
777 |
jsr166 |
1.1 |
* registered parties is zero. Normally, overrides that arrange |
778 |
|
|
* termination for other reasons should also preserve this |
779 |
|
|
* property. |
780 |
|
|
* |
781 |
jsr166 |
1.5 |
* <p>You may override this method to perform an action with side |
782 |
jsr166 |
1.10 |
* effects visible to participating tasks, but it is only sensible |
783 |
|
|
* to do so in designs where all parties register before any |
784 |
|
|
* arrive, and all {@link #awaitAdvance} at each phase. |
785 |
jsr166 |
1.7 |
* Otherwise, you cannot ensure lack of interference from other |
786 |
jsr166 |
1.10 |
* parties during the invocation of this method. Additionally, |
787 |
|
|
* method {@code onAdvance} may be invoked more than once per |
788 |
|
|
* transition if registrations are intermixed with arrivals. |
789 |
jsr166 |
1.1 |
* |
790 |
|
|
* @param phase the phase number on entering the barrier |
791 |
|
|
* @param registeredParties the current number of registered parties |
792 |
|
|
* @return {@code true} if this barrier should terminate |
793 |
|
|
*/ |
794 |
|
|
protected boolean onAdvance(int phase, int registeredParties) { |
795 |
|
|
return registeredParties <= 0; |
796 |
|
|
} |
797 |
|
|
|
798 |
|
|
/** |
799 |
|
|
* Returns a string identifying this phaser, as well as its |
800 |
|
|
* state. The state, in brackets, includes the String {@code |
801 |
|
|
* "phase = "} followed by the phase number, {@code "parties = "} |
802 |
|
|
* followed by the number of registered parties, and {@code |
803 |
|
|
* "arrived = "} followed by the number of arrived parties. |
804 |
|
|
* |
805 |
|
|
* @return a string identifying this barrier, as well as its state |
806 |
|
|
*/ |
807 |
|
|
public String toString() { |
808 |
|
|
long s = getReconciledState(); |
809 |
|
|
return super.toString() + |
810 |
|
|
"[phase = " + phaseOf(s) + |
811 |
|
|
" parties = " + partiesOf(s) + |
812 |
|
|
" arrived = " + arrivedOf(s) + "]"; |
813 |
|
|
} |
814 |
|
|
|
815 |
|
|
// methods for waiting |
816 |
|
|
|
817 |
|
|
/** |
818 |
|
|
* Wait nodes for Treiber stack representing wait queue |
819 |
|
|
*/ |
820 |
|
|
static final class QNode implements ForkJoinPool.ManagedBlocker { |
821 |
|
|
final Phaser phaser; |
822 |
|
|
final int phase; |
823 |
|
|
final long startTime; |
824 |
|
|
final long nanos; |
825 |
|
|
final boolean timed; |
826 |
|
|
final boolean interruptible; |
827 |
|
|
volatile boolean wasInterrupted = false; |
828 |
|
|
volatile Thread thread; // nulled to cancel wait |
829 |
|
|
QNode next; |
830 |
|
|
QNode(Phaser phaser, int phase, boolean interruptible, |
831 |
|
|
boolean timed, long startTime, long nanos) { |
832 |
|
|
this.phaser = phaser; |
833 |
|
|
this.phase = phase; |
834 |
|
|
this.timed = timed; |
835 |
|
|
this.interruptible = interruptible; |
836 |
|
|
this.startTime = startTime; |
837 |
|
|
this.nanos = nanos; |
838 |
|
|
thread = Thread.currentThread(); |
839 |
|
|
} |
840 |
|
|
public boolean isReleasable() { |
841 |
|
|
return (thread == null || |
842 |
|
|
phaser.getPhase() != phase || |
843 |
|
|
(interruptible && wasInterrupted) || |
844 |
|
|
(timed && (nanos - (System.nanoTime() - startTime)) <= 0)); |
845 |
|
|
} |
846 |
|
|
public boolean block() { |
847 |
|
|
if (Thread.interrupted()) { |
848 |
|
|
wasInterrupted = true; |
849 |
|
|
if (interruptible) |
850 |
|
|
return true; |
851 |
|
|
} |
852 |
|
|
if (!timed) |
853 |
|
|
LockSupport.park(this); |
854 |
|
|
else { |
855 |
|
|
long waitTime = nanos - (System.nanoTime() - startTime); |
856 |
|
|
if (waitTime <= 0) |
857 |
|
|
return true; |
858 |
|
|
LockSupport.parkNanos(this, waitTime); |
859 |
|
|
} |
860 |
|
|
return isReleasable(); |
861 |
|
|
} |
862 |
|
|
void signal() { |
863 |
|
|
Thread t = thread; |
864 |
|
|
if (t != null) { |
865 |
|
|
thread = null; |
866 |
|
|
LockSupport.unpark(t); |
867 |
|
|
} |
868 |
|
|
} |
869 |
|
|
boolean doWait() { |
870 |
|
|
if (thread != null) { |
871 |
|
|
try { |
872 |
dl |
1.11 |
ForkJoinPool.managedBlock(this); |
873 |
jsr166 |
1.1 |
} catch (InterruptedException ie) { |
874 |
|
|
} |
875 |
|
|
} |
876 |
|
|
return wasInterrupted; |
877 |
|
|
} |
878 |
|
|
|
879 |
|
|
} |
880 |
|
|
|
881 |
|
|
/** |
882 |
|
|
* Removes and signals waiting threads from wait queue. |
883 |
|
|
*/ |
884 |
|
|
private void releaseWaiters(int phase) { |
885 |
|
|
AtomicReference<QNode> head = queueFor(phase); |
886 |
|
|
QNode q; |
887 |
|
|
while ((q = head.get()) != null) { |
888 |
|
|
if (head.compareAndSet(q, q.next)) |
889 |
|
|
q.signal(); |
890 |
|
|
} |
891 |
|
|
} |
892 |
|
|
|
893 |
|
|
/** |
894 |
|
|
* Tries to enqueue given node in the appropriate wait queue. |
895 |
|
|
* |
896 |
|
|
* @return true if successful |
897 |
|
|
*/ |
898 |
|
|
private boolean tryEnqueue(QNode node) { |
899 |
|
|
AtomicReference<QNode> head = queueFor(node.phase); |
900 |
|
|
return head.compareAndSet(node.next = head.get(), node); |
901 |
|
|
} |
902 |
|
|
|
903 |
|
|
/** |
904 |
|
|
* Enqueues node and waits unless aborted or signalled. |
905 |
|
|
* |
906 |
|
|
* @return current phase |
907 |
|
|
*/ |
908 |
|
|
private int untimedWait(int phase) { |
909 |
|
|
QNode node = null; |
910 |
|
|
boolean queued = false; |
911 |
|
|
boolean interrupted = false; |
912 |
|
|
int p; |
913 |
|
|
while ((p = getPhase()) == phase) { |
914 |
|
|
if (Thread.interrupted()) |
915 |
|
|
interrupted = true; |
916 |
|
|
else if (node == null) |
917 |
|
|
node = new QNode(this, phase, false, false, 0, 0); |
918 |
|
|
else if (!queued) |
919 |
|
|
queued = tryEnqueue(node); |
920 |
|
|
else |
921 |
|
|
interrupted = node.doWait(); |
922 |
|
|
} |
923 |
|
|
if (node != null) |
924 |
|
|
node.thread = null; |
925 |
|
|
releaseWaiters(phase); |
926 |
|
|
if (interrupted) |
927 |
|
|
Thread.currentThread().interrupt(); |
928 |
|
|
return p; |
929 |
|
|
} |
930 |
|
|
|
931 |
|
|
/** |
932 |
|
|
* Interruptible version |
933 |
|
|
* @return current phase |
934 |
|
|
*/ |
935 |
|
|
private int interruptibleWait(int phase) throws InterruptedException { |
936 |
|
|
QNode node = null; |
937 |
|
|
boolean queued = false; |
938 |
|
|
boolean interrupted = false; |
939 |
|
|
int p; |
940 |
|
|
while ((p = getPhase()) == phase && !interrupted) { |
941 |
|
|
if (Thread.interrupted()) |
942 |
|
|
interrupted = true; |
943 |
|
|
else if (node == null) |
944 |
|
|
node = new QNode(this, phase, true, false, 0, 0); |
945 |
|
|
else if (!queued) |
946 |
|
|
queued = tryEnqueue(node); |
947 |
|
|
else |
948 |
|
|
interrupted = node.doWait(); |
949 |
|
|
} |
950 |
|
|
if (node != null) |
951 |
|
|
node.thread = null; |
952 |
|
|
if (p != phase || (p = getPhase()) != phase) |
953 |
|
|
releaseWaiters(phase); |
954 |
|
|
if (interrupted) |
955 |
|
|
throw new InterruptedException(); |
956 |
|
|
return p; |
957 |
|
|
} |
958 |
|
|
|
959 |
|
|
/** |
960 |
|
|
* Timeout version. |
961 |
|
|
* @return current phase |
962 |
|
|
*/ |
963 |
|
|
private int timedWait(int phase, long nanos) |
964 |
|
|
throws InterruptedException, TimeoutException { |
965 |
|
|
long startTime = System.nanoTime(); |
966 |
|
|
QNode node = null; |
967 |
|
|
boolean queued = false; |
968 |
|
|
boolean interrupted = false; |
969 |
|
|
int p; |
970 |
|
|
while ((p = getPhase()) == phase && !interrupted) { |
971 |
|
|
if (Thread.interrupted()) |
972 |
|
|
interrupted = true; |
973 |
|
|
else if (nanos - (System.nanoTime() - startTime) <= 0) |
974 |
|
|
break; |
975 |
|
|
else if (node == null) |
976 |
|
|
node = new QNode(this, phase, true, true, startTime, nanos); |
977 |
|
|
else if (!queued) |
978 |
|
|
queued = tryEnqueue(node); |
979 |
|
|
else |
980 |
|
|
interrupted = node.doWait(); |
981 |
|
|
} |
982 |
|
|
if (node != null) |
983 |
|
|
node.thread = null; |
984 |
|
|
if (p != phase || (p = getPhase()) != phase) |
985 |
|
|
releaseWaiters(phase); |
986 |
|
|
if (interrupted) |
987 |
|
|
throw new InterruptedException(); |
988 |
|
|
if (p == phase) |
989 |
|
|
throw new TimeoutException(); |
990 |
|
|
return p; |
991 |
|
|
} |
992 |
|
|
|
993 |
|
|
// Unsafe mechanics |
994 |
|
|
|
995 |
|
|
private static final sun.misc.Unsafe UNSAFE = sun.misc.Unsafe.getUnsafe(); |
996 |
jsr166 |
1.2 |
private static final long stateOffset = |
997 |
jsr166 |
1.3 |
objectFieldOffset("state", Phaser.class); |
998 |
jsr166 |
1.1 |
|
999 |
jsr166 |
1.2 |
private final boolean casState(long cmp, long val) { |
1000 |
jsr166 |
1.1 |
return UNSAFE.compareAndSwapLong(this, stateOffset, cmp, val); |
1001 |
|
|
} |
1002 |
jsr166 |
1.3 |
|
1003 |
|
|
private static long objectFieldOffset(String field, Class<?> klazz) { |
1004 |
|
|
try { |
1005 |
|
|
return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field)); |
1006 |
|
|
} catch (NoSuchFieldException e) { |
1007 |
|
|
// Convert Exception to corresponding Error |
1008 |
|
|
NoSuchFieldError error = new NoSuchFieldError(field); |
1009 |
|
|
error.initCause(e); |
1010 |
|
|
throw error; |
1011 |
|
|
} |
1012 |
|
|
} |
1013 |
jsr166 |
1.1 |
} |