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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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|
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package java.util.concurrent; |
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|
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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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/** |
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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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* <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 parties. |
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* The typical idiom is for the method setting this up to first |
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* register, then start the actions, then deregister, as in: |
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* |
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* <pre> {@code |
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* void runTasks(List<Runnable> tasks) { |
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* final Phaser phaser = new Phaser(1); // "1" to register self |
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* // 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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* }}</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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* void startTasks(List<Runnable> tasks, final int iterations) { |
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* final Phaser phaser = new Phaser() { |
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* protected boolean onAdvance(int phase, int registeredParties) { |
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* 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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* 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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* <p>To create a set of tasks using a tree of phasers, |
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* you could use code of the following form, assuming a |
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* Task class with a constructor accepting a phaser that |
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* it registers with upon construction: |
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* |
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* <pre> {@code |
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* 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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* } |
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* } else { |
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* for (int i = lo; i < hi; ++i) |
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* actions[i] = new Task(ph); |
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* // assumes new Task(ph) performs ph.register() |
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* } |
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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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* <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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* parties result in {@code IllegalStateException}. However, you can and |
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* 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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/** |
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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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|
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private static final int ushortBits = 16; |
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private static final int ushortMask = (1 << ushortBits) - 1; |
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private static final int phaseMask = 0x7fffffff; |
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|
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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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|
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private static int partiesOf(long s) { |
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return ((int) s) >>> ushortBits; |
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} |
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|
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private static int phaseOf(long s) { |
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return (int) (s >>> (2 * ushortBits)); |
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} |
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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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|
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private static long stateFor(int phase, int parties, int unarrived) { |
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return ((((long) phase) << (2 * ushortBits)) | |
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(((long) parties) << ushortBits) | |
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(long) unarrived); |
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} |
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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) << (2 * ushortBits)) | (lp << ushortBits) | lp; |
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} |
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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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/** |
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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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/** |
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* The root of phaser tree. Equals this if not in a tree. Used to |
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* support faster state push-down. |
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*/ |
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private final Phaser root; |
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|
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// Wait queues |
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|
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/** |
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* Heads of Treiber stacks for waiting threads. To eliminate |
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* contention when 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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* Subphasers share queues with root to speed up releases. |
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*/ |
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private final AtomicReference<QNode> evenQ; |
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private final AtomicReference<QNode> oddQ; |
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|
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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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/** |
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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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/** |
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* Recursively resolves state. |
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*/ |
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private long reconcileState() { |
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Phaser par = parent; |
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long s = state; |
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if (par != null) { |
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int phase, rootPhase; |
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while ((phase = phaseOf(s)) >= 0 && |
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(rootPhase = phaseOf(root.state)) != phase && |
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(rootPhase < 0 || unarrivedOf(s) == 0)) { |
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int parentPhase = phaseOf(par.getReconciledState()); |
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if (parentPhase != phase) { |
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long next = trippedStateFor(parentPhase, partiesOf(s)); |
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if (state == s) |
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UNSAFE.compareAndSwapLong(this, stateOffset, s, next); |
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} |
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s = state; |
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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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/** |
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* Creates a new phaser without any initially registered parties, |
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* initial phase number 0, and no parent. Any thread using this |
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* phaser will need to first register for it. |
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*/ |
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public Phaser() { |
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this(null, 0); |
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} |
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|
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/** |
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* Creates a new phaser with the given number of registered |
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* 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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/** |
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* Creates a new phaser with the given parent, without any |
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* initially registered parties. If parent is non-null this phaser |
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* is registered with the parent and its initial phase number is |
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* the same as that of parent phaser. |
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* |
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* @param parent the parent phaser |
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*/ |
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public Phaser(Phaser parent) { |
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this(parent, 0); |
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} |
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|
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/** |
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* Creates a new phaser with the given parent and number of |
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* registered unarrived parties. If parent is non-null, this phaser |
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* is registered with the parent and its initial phase number is |
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* the same as that of parent phaser. |
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* |
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* @param parent the parent phaser |
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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(Phaser parent, int parties) { |
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if (parties >>> ushortBits != 0) |
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throw new IllegalArgumentException("Illegal number of parties"); |
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int phase; |
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this.parent = parent; |
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if (parent != null) { |
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Phaser r = parent.root; |
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this.root = r; |
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this.evenQ = r.evenQ; |
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this.oddQ = r.oddQ; |
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phase = parent.register(); |
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} |
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else { |
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this.root = this; |
398 |
this.evenQ = new AtomicReference<QNode>(); |
399 |
this.oddQ = new AtomicReference<QNode>(); |
400 |
phase = 0; |
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} |
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this.state = trippedStateFor(phase, parties); |
403 |
} |
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|
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/** |
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* Adds a new unarrived party to this phaser. |
407 |
* If an ongoing invocation of {@link #onAdvance} is in progress, |
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* this method may wait until its completion before registering. |
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* |
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* @return the arrival phase number to which this registration applied |
411 |
* @throws IllegalStateException if attempting to register more |
412 |
* than the maximum supported number of parties |
413 |
*/ |
414 |
public int register() { |
415 |
return doRegister(1); |
416 |
} |
417 |
|
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/** |
419 |
* Adds the given number of new unarrived parties to this phaser. |
420 |
* If an ongoing invocation of {@link #onAdvance} is in progress, |
421 |
* this method may wait until its completion before registering. |
422 |
* |
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* @param parties the number of additional parties required to trip barrier |
424 |
* @return the arrival phase number to which this registration applied |
425 |
* @throws IllegalStateException if attempting to register more |
426 |
* than the maximum supported number of parties |
427 |
* @throws IllegalArgumentException if {@code parties < 0} |
428 |
*/ |
429 |
public int bulkRegister(int parties) { |
430 |
if (parties < 0) |
431 |
throw new IllegalArgumentException(); |
432 |
if (parties == 0) |
433 |
return getPhase(); |
434 |
return doRegister(parties); |
435 |
} |
436 |
|
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/** |
438 |
* Shared code for register, bulkRegister |
439 |
*/ |
440 |
private int doRegister(int registrations) { |
441 |
Phaser par = parent; |
442 |
long s; |
443 |
int phase; |
444 |
while ((phase = phaseOf(s = par==null? state:reconcileState())) >= 0) { |
445 |
int p = partiesOf(s); |
446 |
int u = unarrivedOf(s); |
447 |
int unarrived = u + registrations; |
448 |
int parties = p + registrations; |
449 |
if (u == 0 && p != 0) // if tripped, wait for advance |
450 |
untimedWait(phase); |
451 |
else if (parties >>> ushortBits != 0) |
452 |
throw new IllegalStateException(badBounds(parties, unarrived)); |
453 |
else if (par == null || phaseOf(root.state) == phase) { |
454 |
long next = stateFor(phase, parties, unarrived); |
455 |
if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next)) |
456 |
break; |
457 |
} |
458 |
} |
459 |
return phase; |
460 |
} |
461 |
|
462 |
/** |
463 |
* Arrives at the barrier, but does not wait for others. (You can |
464 |
* in turn wait for others via {@link #awaitAdvance}). It is an |
465 |
* unenforced usage error for an unregistered party to invoke this |
466 |
* method. |
467 |
* |
468 |
* @return the arrival phase number, or a negative value if terminated |
469 |
* @throws IllegalStateException if not terminated and the number |
470 |
* of unarrived parties would become negative |
471 |
*/ |
472 |
public int arrive() { |
473 |
Phaser par = parent; |
474 |
long s; |
475 |
int phase; |
476 |
while ((phase = phaseOf(s = par==null? state:reconcileState())) >= 0) { |
477 |
int parties = partiesOf(s); |
478 |
int unarrived = unarrivedOf(s) - 1; |
479 |
if (unarrived > 0) { // Not the last arrival |
480 |
if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s - 1)) |
481 |
break; // s-1 adds one arrival |
482 |
} |
483 |
else if (unarrived < 0) |
484 |
throw new IllegalStateException(badBounds(parties, unarrived)); |
485 |
else if (par == null) { // directly trip |
486 |
long next = trippedStateFor(onAdvance(phase, parties) ? -1 : |
487 |
((phase + 1) & phaseMask), |
488 |
parties); |
489 |
if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next)) { |
490 |
releaseWaiters(phase); |
491 |
break; |
492 |
} |
493 |
} |
494 |
else if (phaseOf(root.state) == phase && |
495 |
UNSAFE.compareAndSwapLong(this, stateOffset, s, s - 1)) { |
496 |
par.arrive(); // cascade to parent |
497 |
reconcileState(); |
498 |
break; |
499 |
} |
500 |
} |
501 |
return phase; |
502 |
} |
503 |
|
504 |
/** |
505 |
* Arrives at the barrier and deregisters from it without waiting |
506 |
* for others. Deregistration reduces the number of parties |
507 |
* required to trip the barrier in future phases. If this phaser |
508 |
* has a parent, and deregistration causes this phaser to have |
509 |
* zero parties, this phaser also arrives at and is deregistered |
510 |
* from its parent. It is an unenforced usage error for an |
511 |
* unregistered party to invoke this method. |
512 |
* |
513 |
* @return the arrival phase number, or a negative value if terminated |
514 |
* @throws IllegalStateException if not terminated and the number |
515 |
* of registered or unarrived parties would become negative |
516 |
*/ |
517 |
public int arriveAndDeregister() { |
518 |
// similar to arrive, but too different to merge |
519 |
Phaser par = parent; |
520 |
long s; |
521 |
int phase; |
522 |
while ((phase = phaseOf(s = par==null? state:reconcileState())) >= 0) { |
523 |
int parties = partiesOf(s) - 1; |
524 |
int unarrived = unarrivedOf(s) - 1; |
525 |
if (unarrived > 0) { |
526 |
long next = stateFor(phase, parties, unarrived); |
527 |
if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next)) |
528 |
break; |
529 |
} |
530 |
else if (unarrived < 0) |
531 |
throw new IllegalStateException(badBounds(parties, unarrived)); |
532 |
else if (par == null) { |
533 |
long next = trippedStateFor(onAdvance(phase, parties)? -1: |
534 |
(phase + 1) & phaseMask, |
535 |
parties); |
536 |
if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next)) { |
537 |
releaseWaiters(phase); |
538 |
break; |
539 |
} |
540 |
} |
541 |
else if (phaseOf(root.state) == phase) { |
542 |
long next = stateFor(phase, parties, 0); |
543 |
if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next)) { |
544 |
if (parties == 0) |
545 |
par.arriveAndDeregister(); |
546 |
else |
547 |
par.arrive(); |
548 |
reconcileState(); |
549 |
break; |
550 |
} |
551 |
} |
552 |
} |
553 |
return phase; |
554 |
} |
555 |
|
556 |
/** |
557 |
* Arrives at the barrier and awaits others. Equivalent in effect |
558 |
* to {@code awaitAdvance(arrive())}. If you need to await with |
559 |
* interruption or timeout, you can arrange this with an analogous |
560 |
* construction using one of the other forms of the {@code |
561 |
* awaitAdvance} method. If instead you need to deregister upon |
562 |
* arrival, use {@link #arriveAndDeregister}. It is an unenforced |
563 |
* usage error for an unregistered party to invoke this method. |
564 |
* |
565 |
* @return the arrival phase number, or a negative number if terminated |
566 |
* @throws IllegalStateException if not terminated and the number |
567 |
* of unarrived parties would become negative |
568 |
*/ |
569 |
public int arriveAndAwaitAdvance() { |
570 |
return awaitAdvance(arrive()); |
571 |
} |
572 |
|
573 |
/** |
574 |
* Awaits the phase of the barrier to advance from the given phase |
575 |
* value, returning immediately if the current phase of the |
576 |
* barrier is not equal to the given phase value or this barrier |
577 |
* is terminated. |
578 |
* |
579 |
* @param phase an arrival phase number, or negative value if |
580 |
* terminated; this argument is normally the value returned by a |
581 |
* previous call to {@code arrive} or its variants |
582 |
* @return the next arrival phase number, or a negative value |
583 |
* if terminated or argument is negative |
584 |
*/ |
585 |
public int awaitAdvance(int phase) { |
586 |
if (phase < 0) |
587 |
return phase; |
588 |
int p = getPhase(); |
589 |
if (p != phase) |
590 |
return p; |
591 |
return untimedWait(phase); |
592 |
} |
593 |
|
594 |
/** |
595 |
* Awaits the phase of the barrier to advance from the given phase |
596 |
* value, throwing {@code InterruptedException} if interrupted |
597 |
* while waiting, or returning immediately if the current phase of |
598 |
* the barrier is not equal to the given phase value or this |
599 |
* barrier is terminated. |
600 |
* |
601 |
* @param phase an arrival phase number, or negative value if |
602 |
* terminated; this argument is normally the value returned by a |
603 |
* previous call to {@code arrive} or its variants |
604 |
* @return the next arrival phase number, or a negative value |
605 |
* if terminated or argument is negative |
606 |
* @throws InterruptedException if thread interrupted while waiting |
607 |
*/ |
608 |
public int awaitAdvanceInterruptibly(int phase) |
609 |
throws InterruptedException { |
610 |
if (phase < 0) |
611 |
return phase; |
612 |
int p = getPhase(); |
613 |
if (p != phase) |
614 |
return p; |
615 |
return interruptibleWait(phase); |
616 |
} |
617 |
|
618 |
/** |
619 |
* Awaits the phase of the barrier to advance from the given phase |
620 |
* value or the given timeout to elapse, throwing {@code |
621 |
* InterruptedException} if interrupted while waiting, or |
622 |
* returning immediately if the current phase of the barrier is |
623 |
* not equal to the given phase value or this barrier is |
624 |
* terminated. |
625 |
* |
626 |
* @param phase an arrival phase number, or negative value if |
627 |
* terminated; this argument is normally the value returned by a |
628 |
* previous call to {@code arrive} or its variants |
629 |
* @param timeout how long to wait before giving up, in units of |
630 |
* {@code unit} |
631 |
* @param unit a {@code TimeUnit} determining how to interpret the |
632 |
* {@code timeout} parameter |
633 |
* @return the next arrival phase number, or a negative value |
634 |
* if terminated or argument is negative |
635 |
* @throws InterruptedException if thread interrupted while waiting |
636 |
* @throws TimeoutException if timed out while waiting |
637 |
*/ |
638 |
public int awaitAdvanceInterruptibly(int phase, |
639 |
long timeout, TimeUnit unit) |
640 |
throws InterruptedException, TimeoutException { |
641 |
long nanos = unit.toNanos(timeout); |
642 |
if (phase < 0) |
643 |
return phase; |
644 |
int p = getPhase(); |
645 |
if (p != phase) |
646 |
return p; |
647 |
return timedWait(phase, nanos); |
648 |
} |
649 |
|
650 |
/** |
651 |
* Forces this barrier to enter termination state. Counts of |
652 |
* arrived and registered parties are unaffected. If this phaser |
653 |
* has a parent, it too is terminated. This method may be useful |
654 |
* for coordinating recovery after one or more tasks encounter |
655 |
* unexpected exceptions. |
656 |
*/ |
657 |
public void forceTermination() { |
658 |
Phaser r = root; // force at root then reconcile |
659 |
long s; |
660 |
while (phaseOf(s = r.state) >= 0) |
661 |
UNSAFE.compareAndSwapLong(r, stateOffset, s, |
662 |
stateFor(-1, partiesOf(s), |
663 |
unarrivedOf(s))); |
664 |
reconcileState(); |
665 |
releaseWaiters(0); // ensure wakeups on both queues |
666 |
releaseWaiters(1); |
667 |
} |
668 |
|
669 |
/** |
670 |
* Returns the current phase number. The maximum phase number is |
671 |
* {@code Integer.MAX_VALUE}, after which it restarts at |
672 |
* zero. Upon termination, the phase number is negative. |
673 |
* |
674 |
* @return the phase number, or a negative value if terminated |
675 |
*/ |
676 |
public final int getPhase() { |
677 |
return phaseOf(getReconciledState()); |
678 |
} |
679 |
|
680 |
/** |
681 |
* Returns the number of parties registered at this barrier. |
682 |
* |
683 |
* @return the number of parties |
684 |
*/ |
685 |
public int getRegisteredParties() { |
686 |
return partiesOf(getReconciledState()); |
687 |
} |
688 |
|
689 |
/** |
690 |
* Returns the number of registered parties that have arrived at |
691 |
* the current phase of this barrier. |
692 |
* |
693 |
* @return the number of arrived parties |
694 |
*/ |
695 |
public int getArrivedParties() { |
696 |
return arrivedOf(getReconciledState()); |
697 |
} |
698 |
|
699 |
/** |
700 |
* Returns the number of registered parties that have not yet |
701 |
* arrived at the current phase of this barrier. |
702 |
* |
703 |
* @return the number of unarrived parties |
704 |
*/ |
705 |
public int getUnarrivedParties() { |
706 |
return unarrivedOf(getReconciledState()); |
707 |
} |
708 |
|
709 |
/** |
710 |
* Returns the parent of this phaser, or {@code null} if none. |
711 |
* |
712 |
* @return the parent of this phaser, or {@code null} if none |
713 |
*/ |
714 |
public Phaser getParent() { |
715 |
return parent; |
716 |
} |
717 |
|
718 |
/** |
719 |
* Returns the root ancestor of this phaser, which is the same as |
720 |
* this phaser if it has no parent. |
721 |
* |
722 |
* @return the root ancestor of this phaser |
723 |
*/ |
724 |
public Phaser getRoot() { |
725 |
return root; |
726 |
} |
727 |
|
728 |
/** |
729 |
* Returns {@code true} if this barrier has been terminated. |
730 |
* |
731 |
* @return {@code true} if this barrier has been terminated |
732 |
*/ |
733 |
public boolean isTerminated() { |
734 |
return getPhase() < 0; |
735 |
} |
736 |
|
737 |
/** |
738 |
* Overridable method to perform an action upon impending phase |
739 |
* advance, and to control termination. This method is invoked |
740 |
* upon arrival of the party tripping the barrier (when all other |
741 |
* waiting parties are dormant). If this method returns {@code |
742 |
* true}, then, rather than advance the phase number, this barrier |
743 |
* will be set to a final termination state, and subsequent calls |
744 |
* to {@link #isTerminated} will return true. Any (unchecked) |
745 |
* Exception or Error thrown by an invocation of this method is |
746 |
* propagated to the party attempting to trip the barrier, in |
747 |
* which case no advance occurs. |
748 |
* |
749 |
* <p>The arguments to this method provide the state of the phaser |
750 |
* prevailing for the current transition. The results and effects |
751 |
* of invoking phase-related methods (including {@code getPhase} |
752 |
* as well as arrival, registration, and waiting methods) from |
753 |
* within {@code onAdvance} are unspecified and should not be |
754 |
* relied on. Similarly, while it is possible to override this |
755 |
* method to produce side-effects visible to participating tasks, |
756 |
* it is in general safe to do so only in designs in which all |
757 |
* parties register before any arrive, and all {@link |
758 |
* #awaitAdvance} at each phase. |
759 |
* |
760 |
* <p>The default version returns {@code true} when the number of |
761 |
* registered parties is zero. Normally, overrides that arrange |
762 |
* termination for other reasons should also preserve this |
763 |
* property. |
764 |
* |
765 |
* @param phase the phase number on entering the barrier |
766 |
* @param registeredParties the current number of registered parties |
767 |
* @return {@code true} if this barrier should terminate |
768 |
*/ |
769 |
protected boolean onAdvance(int phase, int registeredParties) { |
770 |
return registeredParties <= 0; |
771 |
} |
772 |
|
773 |
/** |
774 |
* Returns a string identifying this phaser, as well as its |
775 |
* state. The state, in brackets, includes the String {@code |
776 |
* "phase = "} followed by the phase number, {@code "parties = "} |
777 |
* followed by the number of registered parties, and {@code |
778 |
* "arrived = "} followed by the number of arrived parties. |
779 |
* |
780 |
* @return a string identifying this barrier, as well as its state |
781 |
*/ |
782 |
public String toString() { |
783 |
long s = getReconciledState(); |
784 |
return super.toString() + |
785 |
"[phase = " + phaseOf(s) + |
786 |
" parties = " + partiesOf(s) + |
787 |
" arrived = " + arrivedOf(s) + "]"; |
788 |
} |
789 |
|
790 |
// methods for waiting |
791 |
|
792 |
/** |
793 |
* Wait nodes for Treiber stack representing wait queue |
794 |
*/ |
795 |
static final class QNode implements ForkJoinPool.ManagedBlocker { |
796 |
final Phaser phaser; |
797 |
final int phase; |
798 |
final long startTime; |
799 |
final long nanos; |
800 |
final boolean timed; |
801 |
final boolean interruptible; |
802 |
volatile boolean wasInterrupted = false; |
803 |
volatile Thread thread; // nulled to cancel wait |
804 |
QNode next; |
805 |
|
806 |
QNode(Phaser phaser, int phase, boolean interruptible, |
807 |
boolean timed, long startTime, long nanos) { |
808 |
this.phaser = phaser; |
809 |
this.phase = phase; |
810 |
this.timed = timed; |
811 |
this.interruptible = interruptible; |
812 |
this.startTime = startTime; |
813 |
this.nanos = nanos; |
814 |
thread = Thread.currentThread(); |
815 |
} |
816 |
|
817 |
public boolean isReleasable() { |
818 |
return (thread == null || |
819 |
phaser.getPhase() != phase || |
820 |
(interruptible && wasInterrupted) || |
821 |
(timed && (nanos - (System.nanoTime() - startTime)) <= 0)); |
822 |
} |
823 |
|
824 |
public boolean block() { |
825 |
if (Thread.interrupted()) { |
826 |
wasInterrupted = true; |
827 |
if (interruptible) |
828 |
return true; |
829 |
} |
830 |
if (!timed) |
831 |
LockSupport.park(this); |
832 |
else { |
833 |
long waitTime = nanos - (System.nanoTime() - startTime); |
834 |
if (waitTime <= 0) |
835 |
return true; |
836 |
LockSupport.parkNanos(this, waitTime); |
837 |
} |
838 |
return isReleasable(); |
839 |
} |
840 |
|
841 |
void signal() { |
842 |
Thread t = thread; |
843 |
if (t != null) { |
844 |
thread = null; |
845 |
LockSupport.unpark(t); |
846 |
} |
847 |
} |
848 |
|
849 |
boolean doWait() { |
850 |
if (thread != null) { |
851 |
try { |
852 |
ForkJoinPool.managedBlock(this); |
853 |
} catch (InterruptedException ie) { |
854 |
wasInterrupted = true; // can't currently happen |
855 |
} |
856 |
} |
857 |
return wasInterrupted; |
858 |
} |
859 |
} |
860 |
|
861 |
/** |
862 |
* Removes and signals waiting threads from wait queue. |
863 |
*/ |
864 |
private void releaseWaiters(int phase) { |
865 |
AtomicReference<QNode> head = queueFor(phase); |
866 |
QNode q; |
867 |
while ((q = head.get()) != null) { |
868 |
if (head.compareAndSet(q, q.next)) |
869 |
q.signal(); |
870 |
} |
871 |
} |
872 |
|
873 |
/** |
874 |
* Tries to enqueue given node in the appropriate wait queue. |
875 |
* |
876 |
* @return true if successful |
877 |
*/ |
878 |
private boolean tryEnqueue(QNode node) { |
879 |
AtomicReference<QNode> head = queueFor(node.phase); |
880 |
return head.compareAndSet(node.next = head.get(), node); |
881 |
} |
882 |
|
883 |
/** |
884 |
* The number of times to spin before blocking waiting for advance. |
885 |
*/ |
886 |
static final int MAX_SPINS = |
887 |
Runtime.getRuntime().availableProcessors() == 1 ? 0 : 1 << 8; |
888 |
|
889 |
/** |
890 |
* Enqueues node and waits unless aborted or signalled. |
891 |
* |
892 |
* @return current phase |
893 |
*/ |
894 |
private int untimedWait(int phase) { |
895 |
QNode node = null; |
896 |
boolean queued = false; |
897 |
boolean interrupted = false; |
898 |
int spins = MAX_SPINS; |
899 |
int p; |
900 |
while ((p = getPhase()) == phase) { |
901 |
if (Thread.interrupted()) |
902 |
interrupted = true; |
903 |
else if (spins > 0) { |
904 |
if (--spins == 0) |
905 |
Thread.yield(); |
906 |
} |
907 |
else if (node == null) |
908 |
node = new QNode(this, phase, false, false, 0, 0); |
909 |
else if (!queued) |
910 |
queued = tryEnqueue(node); |
911 |
else if (node.doWait()) |
912 |
interrupted = true; |
913 |
} |
914 |
if (node != null) |
915 |
node.thread = null; |
916 |
releaseWaiters(phase); |
917 |
if (interrupted) |
918 |
Thread.currentThread().interrupt(); |
919 |
return p; |
920 |
} |
921 |
|
922 |
/** |
923 |
* Interruptible version |
924 |
* @return current phase |
925 |
*/ |
926 |
private int interruptibleWait(int phase) throws InterruptedException { |
927 |
QNode node = null; |
928 |
boolean queued = false; |
929 |
boolean interrupted = false; |
930 |
int spins = MAX_SPINS; |
931 |
int p; |
932 |
while ((p = getPhase()) == phase && !interrupted) { |
933 |
if (Thread.interrupted()) |
934 |
interrupted = true; |
935 |
else if (spins > 0) { |
936 |
if (--spins == 0) |
937 |
Thread.yield(); |
938 |
} |
939 |
else if (node == null) |
940 |
node = new QNode(this, phase, true, false, 0, 0); |
941 |
else if (!queued) |
942 |
queued = tryEnqueue(node); |
943 |
else if (node.doWait()) |
944 |
interrupted = true; |
945 |
} |
946 |
if (node != null) |
947 |
node.thread = null; |
948 |
if (p != phase || (p = getPhase()) != phase) |
949 |
releaseWaiters(phase); |
950 |
if (interrupted) |
951 |
throw new InterruptedException(); |
952 |
return p; |
953 |
} |
954 |
|
955 |
/** |
956 |
* Timeout version. |
957 |
* @return current phase |
958 |
*/ |
959 |
private int timedWait(int phase, long nanos) |
960 |
throws InterruptedException, TimeoutException { |
961 |
long startTime = System.nanoTime(); |
962 |
QNode node = null; |
963 |
boolean queued = false; |
964 |
boolean interrupted = false; |
965 |
int spins = MAX_SPINS; |
966 |
int p; |
967 |
while ((p = getPhase()) == phase && !interrupted) { |
968 |
if (Thread.interrupted()) |
969 |
interrupted = true; |
970 |
else if (nanos - (System.nanoTime() - startTime) <= 0) |
971 |
break; |
972 |
else if (spins > 0) { |
973 |
if (--spins == 0) |
974 |
Thread.yield(); |
975 |
} |
976 |
else if (node == null) |
977 |
node = new QNode(this, phase, true, true, startTime, nanos); |
978 |
else if (!queued) |
979 |
queued = tryEnqueue(node); |
980 |
else if (node.doWait()) |
981 |
interrupted = true; |
982 |
} |
983 |
if (node != null) |
984 |
node.thread = null; |
985 |
if (p != phase || (p = getPhase()) != phase) |
986 |
releaseWaiters(phase); |
987 |
if (interrupted) |
988 |
throw new InterruptedException(); |
989 |
if (p == phase) |
990 |
throw new TimeoutException(); |
991 |
return p; |
992 |
} |
993 |
|
994 |
// Unsafe mechanics |
995 |
|
996 |
private static final sun.misc.Unsafe UNSAFE = sun.misc.Unsafe.getUnsafe(); |
997 |
private static final long stateOffset = |
998 |
objectFieldOffset("state", Phaser.class); |
999 |
|
1000 |
private static long objectFieldOffset(String field, Class<?> klazz) { |
1001 |
try { |
1002 |
return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field)); |
1003 |
} catch (NoSuchFieldException e) { |
1004 |
// Convert Exception to corresponding Error |
1005 |
NoSuchFieldError error = new NoSuchFieldError(field); |
1006 |
error.initCause(e); |
1007 |
throw error; |
1008 |
} |
1009 |
} |
1010 |
} |