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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 jsr166y; |
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|
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import java.util.concurrent.TimeUnit; |
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import java.util.concurrent.TimeoutException; |
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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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* * unarrived -- the number of parties yet to hit barrier (bits 0-15) |
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* * parties -- the number of parties to wait (bits 16-31) |
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* * phase -- the generation of the barrier (bits 32-62) |
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* * terminated -- set if barrier is terminated (bit 63 / sign) |
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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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private volatile long state; |
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|
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private static final int MAX_COUNT = 0xffff; |
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private static final int MAX_PHASE = 0x7fffffff; |
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private static final int PARTIES_SHIFT = 16; |
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private static final int PHASE_SHIFT = 32; |
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private static final long UNARRIVED_MASK = 0xffffL; |
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private static final long PARTIES_MASK = 0xffff0000L; |
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private static final long ONE_ARRIVAL = 1L; |
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private static final long ONE_PARTY = 1L << PARTIES_SHIFT; |
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private static final long TERMINATION_PHASE = -1L << PHASE_SHIFT; |
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|
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// The following unpacking methods are usually manually inlined |
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|
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private static int unarrivedOf(long s) { |
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return (int) (s & UNARRIVED_MASK); |
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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 & PARTIES_MASK)) >>> PARTIES_SHIFT; |
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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 >>> PHASE_SHIFT); |
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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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/** |
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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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/** |
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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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* Main implementation for methods arrive and arriveAndDeregister. |
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* Manually tuned to speed up and minimize race windows for the |
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* common case of just decrementing unarrived field. |
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* |
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* @param adj - adjustment to apply to state -- either |
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* ONE_ARRIVAL (for arrive) or |
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* ONE_ARRIVAL|ONE_PARTY (for arriveAndDeregister) |
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*/ |
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private int doArrive(long adj) { |
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long s; |
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int phase, unarrived; |
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while ((phase = (int)((s = state) >>> PHASE_SHIFT)) >= 0) { |
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if ((unarrived = (int)(s & UNARRIVED_MASK)) != 0) { |
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if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s -= adj)) { |
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if (unarrived == 1) { |
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Phaser par; |
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long p = s & PARTIES_MASK; // unshifted parties field |
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long lu = p >>> PARTIES_SHIFT; |
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int u = (int)lu; |
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int nextPhase = (phase + 1) & MAX_PHASE; |
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long next = ((long)nextPhase << PHASE_SHIFT) | p | lu; |
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if ((par = parent) == null) { |
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UNSAFE.compareAndSwapLong |
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(this, stateOffset, s, onAdvance(phase, u)? |
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next | TERMINATION_PHASE : next); |
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releaseWaiters(phase); |
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} |
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else { |
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par.doArrive(u == 0? |
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ONE_ARRIVAL|ONE_PARTY : ONE_ARRIVAL); |
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if ((int)(par.state >>> PHASE_SHIFT) != nextPhase || |
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((int)(state >>> PHASE_SHIFT) != nextPhase && |
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!UNSAFE.compareAndSwapLong(this, stateOffset, |
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s, next))) |
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reconcileState(); |
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} |
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} |
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break; |
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} |
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} |
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else if (state == s && reconcileState() == s) // recheck |
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throw new IllegalStateException(badArrive()); |
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} |
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return phase; |
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} |
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|
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/** |
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* Returns message string for bounds exceptions on arrival. |
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* Declared out of-line from doArrive to reduce string op bulk. |
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*/ |
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private String badArrive() { |
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return ("Attempted arrival of unregistered party for " + |
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this.toString()); |
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} |
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|
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/** |
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* Implementation of register, bulkRegister |
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* |
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* @param registrations number to add to both parties and unarrived fields |
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*/ |
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private int doRegister(int registrations) { |
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long adj = (long)registrations; // adjustment to state |
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adj |= adj << PARTIES_SHIFT; |
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Phaser par = parent; |
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long s; |
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int phase; |
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while ((phase = (int)((s = (par == null? state : reconcileState())) |
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>>> PHASE_SHIFT)) >= 0) { |
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int parties = ((int)(s & PARTIES_MASK)) >>> PARTIES_SHIFT; |
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if (parties != 0 && (s & UNARRIVED_MASK) == 0) |
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internalAwaitAdvance(phase, null); // wait for onAdvance |
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else if (parties + registrations > MAX_COUNT) |
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throw new IllegalStateException(badRegister()); |
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else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s + adj)) |
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break; |
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} |
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return phase; |
373 |
} |
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|
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/** |
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* Returns message string for bounds exceptions on registration |
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*/ |
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private String badRegister() { |
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return ("Attempt to register more than " + MAX_COUNT + " parties for "+ |
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this.toString()); |
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} |
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|
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/** |
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* Recursively resolves lagged phase propagation from root if |
385 |
* necessary. |
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*/ |
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private long reconcileState() { |
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Phaser par = parent; |
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if (par == null) |
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return state; |
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Phaser rt = root; |
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long s; |
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int phase, rPhase; |
394 |
while ((phase = (int)((s = state) >>> PHASE_SHIFT)) >= 0 && |
395 |
(rPhase = (int)(rt.state >>> PHASE_SHIFT)) != phase) { |
396 |
if (rPhase < 0 || (s & UNARRIVED_MASK) == 0) { |
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long ps = par.parent == null? par.state : par.reconcileState(); |
398 |
int pPhase = (int)(ps >>> PHASE_SHIFT); |
399 |
if (pPhase < 0 || pPhase == ((phase + 1) & MAX_PHASE)) { |
400 |
if (state != s) |
401 |
continue; |
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long p = s & PARTIES_MASK; |
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long next = ((((long) pPhase) << PHASE_SHIFT) | |
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(p >>> PARTIES_SHIFT) | p); |
405 |
if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next)) |
406 |
return next; |
407 |
} |
408 |
} |
409 |
if (state == s) |
410 |
releaseWaiters(phase); // help release others |
411 |
} |
412 |
return s; |
413 |
} |
414 |
|
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/** |
416 |
* Creates a new phaser without any initially registered parties, |
417 |
* initial phase number 0, and no parent. Any thread using this |
418 |
* phaser will need to first register for it. |
419 |
*/ |
420 |
public Phaser() { |
421 |
this(null, 0); |
422 |
} |
423 |
|
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/** |
425 |
* Creates a new phaser with the given number of registered |
426 |
* unarrived parties, initial phase number 0, and no parent. |
427 |
* |
428 |
* @param parties the number of parties required to trip barrier |
429 |
* @throws IllegalArgumentException if parties less than zero |
430 |
* or greater than the maximum number of parties supported |
431 |
*/ |
432 |
public Phaser(int parties) { |
433 |
this(null, parties); |
434 |
} |
435 |
|
436 |
/** |
437 |
* Creates a new phaser with the given parent, without any |
438 |
* initially registered parties. If parent is non-null this phaser |
439 |
* is registered with the parent and its initial phase number is |
440 |
* the same as that of parent phaser. |
441 |
* |
442 |
* @param parent the parent phaser |
443 |
*/ |
444 |
public Phaser(Phaser parent) { |
445 |
this(parent, 0); |
446 |
} |
447 |
|
448 |
/** |
449 |
* Creates a new phaser with the given parent and number of |
450 |
* registered unarrived parties. If parent is non-null, this phaser |
451 |
* is registered with the parent and its initial phase number is |
452 |
* the same as that of parent phaser. |
453 |
* |
454 |
* @param parent the parent phaser |
455 |
* @param parties the number of parties required to trip barrier |
456 |
* @throws IllegalArgumentException if parties less than zero |
457 |
* or greater than the maximum number of parties supported |
458 |
*/ |
459 |
public Phaser(Phaser parent, int parties) { |
460 |
if (parties < 0 || parties > MAX_COUNT) |
461 |
throw new IllegalArgumentException("Illegal number of parties"); |
462 |
int phase; |
463 |
this.parent = parent; |
464 |
if (parent != null) { |
465 |
Phaser r = parent.root; |
466 |
this.root = r; |
467 |
this.evenQ = r.evenQ; |
468 |
this.oddQ = r.oddQ; |
469 |
phase = parent.register(); |
470 |
} |
471 |
else { |
472 |
this.root = this; |
473 |
this.evenQ = new AtomicReference<QNode>(); |
474 |
this.oddQ = new AtomicReference<QNode>(); |
475 |
phase = 0; |
476 |
} |
477 |
long p = (long)parties; |
478 |
this.state = (((long) phase) << PHASE_SHIFT) | p | (p << PARTIES_SHIFT); |
479 |
} |
480 |
|
481 |
/** |
482 |
* Adds a new unarrived party to this phaser. |
483 |
* If an ongoing invocation of {@link #onAdvance} is in progress, |
484 |
* this method may wait until its completion before registering. |
485 |
* |
486 |
* @return the arrival phase number to which this registration applied |
487 |
* @throws IllegalStateException if attempting to register more |
488 |
* than the maximum supported number of parties |
489 |
*/ |
490 |
public int register() { |
491 |
return doRegister(1); |
492 |
} |
493 |
|
494 |
/** |
495 |
* Adds the given number of new unarrived parties to this phaser. |
496 |
* If an ongoing invocation of {@link #onAdvance} is in progress, |
497 |
* this method may wait until its completion before registering. |
498 |
* |
499 |
* @param parties the number of additional parties required to trip barrier |
500 |
* @return the arrival phase number to which this registration applied |
501 |
* @throws IllegalStateException if attempting to register more |
502 |
* than the maximum supported number of parties |
503 |
* @throws IllegalArgumentException if {@code parties < 0} |
504 |
*/ |
505 |
public int bulkRegister(int parties) { |
506 |
if (parties < 0) |
507 |
throw new IllegalArgumentException(); |
508 |
if (parties > MAX_COUNT) |
509 |
throw new IllegalStateException(badRegister()); |
510 |
if (parties == 0) |
511 |
return getPhase(); |
512 |
return doRegister(parties); |
513 |
} |
514 |
|
515 |
/** |
516 |
* Arrives at the barrier, but does not wait for others. (You can |
517 |
* in turn wait for others via {@link #awaitAdvance}). It is an |
518 |
* unenforced usage error for an unregistered party to invoke this |
519 |
* method. |
520 |
* |
521 |
* @return the arrival phase number, or a negative value if terminated |
522 |
* @throws IllegalStateException if not terminated and the number |
523 |
* of unarrived parties would become negative |
524 |
*/ |
525 |
public int arrive() { |
526 |
return doArrive(ONE_ARRIVAL); |
527 |
} |
528 |
|
529 |
/** |
530 |
* Arrives at the barrier and deregisters from it without waiting |
531 |
* for others. Deregistration reduces the number of parties |
532 |
* required to trip the barrier in future phases. If this phaser |
533 |
* has a parent, and deregistration causes this phaser to have |
534 |
* zero parties, this phaser also arrives at and is deregistered |
535 |
* from its parent. It is an unenforced usage error for an |
536 |
* unregistered party to invoke this method. |
537 |
* |
538 |
* @return the arrival phase number, or a negative value if terminated |
539 |
* @throws IllegalStateException if not terminated and the number |
540 |
* of registered or unarrived parties would become negative |
541 |
*/ |
542 |
public int arriveAndDeregister() { |
543 |
return doArrive(ONE_ARRIVAL|ONE_PARTY); |
544 |
} |
545 |
|
546 |
/** |
547 |
* Arrives at the barrier and awaits others. Equivalent in effect |
548 |
* to {@code awaitAdvance(arrive())}. If you need to await with |
549 |
* interruption or timeout, you can arrange this with an analogous |
550 |
* construction using one of the other forms of the {@code |
551 |
* awaitAdvance} method. If instead you need to deregister upon |
552 |
* arrival, use {@link #arriveAndDeregister}. It is an unenforced |
553 |
* usage error for an unregistered party to invoke this method. |
554 |
* |
555 |
* @return the arrival phase number, or a negative number if terminated |
556 |
* @throws IllegalStateException if not terminated and the number |
557 |
* of unarrived parties would become negative |
558 |
*/ |
559 |
public int arriveAndAwaitAdvance() { |
560 |
return awaitAdvance(arrive()); |
561 |
} |
562 |
|
563 |
/** |
564 |
* Awaits the phase of the barrier to advance from the given phase |
565 |
* value, returning immediately if the current phase of the |
566 |
* barrier is not equal to the given phase value or this barrier |
567 |
* is terminated. |
568 |
* |
569 |
* @param phase an arrival phase number, or negative value if |
570 |
* terminated; this argument is normally the value returned by a |
571 |
* previous call to {@code arrive} or its variants |
572 |
* @return the next arrival phase number, or a negative value |
573 |
* if terminated or argument is negative |
574 |
*/ |
575 |
public int awaitAdvance(int phase) { |
576 |
if (phase < 0) |
577 |
return phase; |
578 |
int p = (int)((parent==null? state : reconcileState()) >>> PHASE_SHIFT); |
579 |
if (p != phase) |
580 |
return p; |
581 |
return internalAwaitAdvance(phase, null); |
582 |
} |
583 |
|
584 |
/** |
585 |
* Awaits the phase of the barrier to advance from the given phase |
586 |
* value, throwing {@code InterruptedException} if interrupted |
587 |
* while waiting, or returning immediately if the current phase of |
588 |
* the barrier is not equal to the given phase value or this |
589 |
* barrier is terminated. |
590 |
* |
591 |
* @param phase an arrival phase number, or negative value if |
592 |
* terminated; this argument is normally the value returned by a |
593 |
* previous call to {@code arrive} or its variants |
594 |
* @return the next arrival phase number, or a negative value |
595 |
* if terminated or argument is negative |
596 |
* @throws InterruptedException if thread interrupted while waiting |
597 |
*/ |
598 |
public int awaitAdvanceInterruptibly(int phase) |
599 |
throws InterruptedException { |
600 |
if (phase < 0) |
601 |
return phase; |
602 |
int p = (int)((parent==null? state : reconcileState()) >>> PHASE_SHIFT); |
603 |
if (p != phase) |
604 |
return p; |
605 |
QNode node = new QNode(this, phase, true, false, 0L); |
606 |
p = internalAwaitAdvance(phase, node); |
607 |
if (node.wasInterrupted) |
608 |
throw new InterruptedException(); |
609 |
else |
610 |
return p; |
611 |
} |
612 |
|
613 |
/** |
614 |
* Awaits the phase of the barrier to advance from the given phase |
615 |
* value or the given timeout to elapse, throwing {@code |
616 |
* InterruptedException} if interrupted while waiting, or |
617 |
* returning immediately if the current phase of the barrier is |
618 |
* not equal to the given phase value or this barrier is |
619 |
* terminated. |
620 |
* |
621 |
* @param phase an arrival phase number, or negative value if |
622 |
* terminated; this argument is normally the value returned by a |
623 |
* previous call to {@code arrive} or its variants |
624 |
* @param timeout how long to wait before giving up, in units of |
625 |
* {@code unit} |
626 |
* @param unit a {@code TimeUnit} determining how to interpret the |
627 |
* {@code timeout} parameter |
628 |
* @return the next arrival phase number, or a negative value |
629 |
* if terminated or argument is negative |
630 |
* @throws InterruptedException if thread interrupted while waiting |
631 |
* @throws TimeoutException if timed out while waiting |
632 |
*/ |
633 |
public int awaitAdvanceInterruptibly(int phase, |
634 |
long timeout, TimeUnit unit) |
635 |
throws InterruptedException, TimeoutException { |
636 |
long nanos = unit.toNanos(timeout); |
637 |
if (phase < 0) |
638 |
return phase; |
639 |
int p = (int)((parent==null? state : reconcileState()) >>> PHASE_SHIFT); |
640 |
if (p != phase) |
641 |
return p; |
642 |
QNode node = new QNode(this, phase, true, true, nanos); |
643 |
p = internalAwaitAdvance(phase, node); |
644 |
if (node.wasInterrupted) |
645 |
throw new InterruptedException(); |
646 |
else if (p == phase) |
647 |
throw new TimeoutException(); |
648 |
else |
649 |
return p; |
650 |
} |
651 |
|
652 |
/** |
653 |
* Forces this barrier to enter termination state. Counts of |
654 |
* arrived and registered parties are unaffected. If this phaser |
655 |
* has a parent, it too is terminated. This method may be useful |
656 |
* for coordinating recovery after one or more tasks encounter |
657 |
* unexpected exceptions. |
658 |
*/ |
659 |
public void forceTermination() { |
660 |
Phaser r = root; // force at root then reconcile |
661 |
long s; |
662 |
while ((s = r.state) >= 0) |
663 |
UNSAFE.compareAndSwapLong(r, stateOffset, s, s | TERMINATION_PHASE); |
664 |
reconcileState(); |
665 |
releaseWaiters(0); // signal all threads |
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 (int)((parent == null? state : reconcileState()) >>> PHASE_SHIFT); |
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(parent == null? state : reconcileState()); |
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(parent == null? state : reconcileState()); |
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(parent == null? state : reconcileState()); |
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 (parent == null? state : reconcileState()) < 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 effects of invoking |
751 |
* arrival, registration, and waiting methods on this Phaser from |
752 |
* within {@code onAdvance} are unspecified and should not be |
753 |
* relied on. |
754 |
* |
755 |
* <p>If this Phaser is a member of a tiered set of Phasers, then |
756 |
* {@code onAdvance} is invoked only for its root Phaser on each |
757 |
* advance. |
758 |
* |
759 |
* <p>The default version returns {@code true} when the number of |
760 |
* registered parties is zero. Normally, overrides that arrange |
761 |
* termination for other reasons should also preserve this |
762 |
* property. |
763 |
* |
764 |
* @param phase the phase number on entering the barrier |
765 |
* @param registeredParties the current number of registered parties |
766 |
* @return {@code true} if this barrier should terminate |
767 |
*/ |
768 |
protected boolean onAdvance(int phase, int registeredParties) { |
769 |
return registeredParties <= 0; |
770 |
} |
771 |
|
772 |
/** |
773 |
* Returns a string identifying this phaser, as well as its |
774 |
* state. The state, in brackets, includes the String {@code |
775 |
* "phase = "} followed by the phase number, {@code "parties = "} |
776 |
* followed by the number of registered parties, and {@code |
777 |
* "arrived = "} followed by the number of arrived parties. |
778 |
* |
779 |
* @return a string identifying this barrier, as well as its state |
780 |
*/ |
781 |
public String toString() { |
782 |
long s = reconcileState(); |
783 |
return super.toString() + |
784 |
"[phase = " + phaseOf(s) + |
785 |
" parties = " + partiesOf(s) + |
786 |
" arrived = " + arrivedOf(s) + "]"; |
787 |
} |
788 |
|
789 |
/** |
790 |
* Removes and signals threads from queue for phase |
791 |
*/ |
792 |
private void releaseWaiters(int phase) { |
793 |
AtomicReference<QNode> head = queueFor(phase); |
794 |
QNode q; |
795 |
int p; |
796 |
while ((q = head.get()) != null && |
797 |
((p = q.phase) == phase || |
798 |
(int)(root.state >>> PHASE_SHIFT) != p)) { |
799 |
if (head.compareAndSet(q, q.next)) |
800 |
q.signal(); |
801 |
} |
802 |
} |
803 |
|
804 |
/** |
805 |
* Tries to enqueue given node in the appropriate wait queue. |
806 |
* |
807 |
* @return true if successful |
808 |
*/ |
809 |
private boolean tryEnqueue(int phase, QNode node) { |
810 |
releaseWaiters(phase-1); // ensure old queue clean |
811 |
AtomicReference<QNode> head = queueFor(phase); |
812 |
QNode q = head.get(); |
813 |
return ((q == null || q.phase == phase) && |
814 |
(int)(root.state >>> PHASE_SHIFT) == phase && |
815 |
head.compareAndSet(node.next = q, node)); |
816 |
} |
817 |
|
818 |
/** The number of CPUs, for spin control */ |
819 |
private static final int NCPU = Runtime.getRuntime().availableProcessors(); |
820 |
|
821 |
/** |
822 |
* The number of times to spin before blocking while waiting for |
823 |
* advance, per arrival while waiting. On multiprocessors, fully |
824 |
* blocking and waking up a large number of threads all at once is |
825 |
* usually a very slow process, so we use rechargeable spins to |
826 |
* avoid it when threads regularly arrive: When a thread in |
827 |
* internalAwaitAdvance notices another arrival before blocking, |
828 |
* and there appear to be enough CPUs available, it spins |
829 |
* SPINS_PER_ARRIVAL more times before continuing to try to |
830 |
* block. The value trades off good-citizenship vs big unnecessary |
831 |
* slowdowns. |
832 |
*/ |
833 |
static final int SPINS_PER_ARRIVAL = NCPU < 2? 1 : 1 << 8; |
834 |
|
835 |
/** |
836 |
* Possibly blocks and waits for phase to advance unless aborted. |
837 |
* |
838 |
* @param phase current phase |
839 |
* @param node if non-null, the wait node to track interrupt and timeout; |
840 |
* if null, denotes noninterruptible wait |
841 |
* @return current phase |
842 |
*/ |
843 |
private int internalAwaitAdvance(int phase, QNode node) { |
844 |
Phaser current = this; // to eventually wait at root if tiered |
845 |
Phaser par = parent; |
846 |
boolean queued = false; |
847 |
int spins = SPINS_PER_ARRIVAL; |
848 |
int lastUnarrived = -1; // to increase spins upon change |
849 |
long s; |
850 |
int p; |
851 |
while ((p = (int)((s = current.state) >>> PHASE_SHIFT)) == phase) { |
852 |
int unarrived = (int)(s & UNARRIVED_MASK); |
853 |
if (unarrived != lastUnarrived) { |
854 |
if ((lastUnarrived = unarrived) < NCPU) |
855 |
spins += SPINS_PER_ARRIVAL; |
856 |
} |
857 |
else if (unarrived == 0 && par != null) { |
858 |
current = par; // if all arrived, use parent |
859 |
par = par.parent; |
860 |
} |
861 |
else if (spins > 0) |
862 |
--spins; |
863 |
else if (node == null) |
864 |
node = new QNode(this, phase, false, false, 0L); |
865 |
else if (node.isReleasable()) |
866 |
break; |
867 |
else if (!queued) |
868 |
queued = tryEnqueue(phase, node); |
869 |
else { |
870 |
try { |
871 |
ForkJoinPool.managedBlock(node); |
872 |
} catch (InterruptedException ie) { |
873 |
node.wasInterrupted = true; |
874 |
} |
875 |
} |
876 |
} |
877 |
if (node != null) { |
878 |
if (node.thread != null) |
879 |
node.thread = null; |
880 |
if (!node.interruptible && node.wasInterrupted) |
881 |
Thread.currentThread().interrupt(); |
882 |
} |
883 |
if (p == phase) |
884 |
p = (int)(reconcileState() >>> PHASE_SHIFT); |
885 |
if (p != phase) |
886 |
releaseWaiters(phase); |
887 |
return p; |
888 |
} |
889 |
|
890 |
/** |
891 |
* Wait nodes for Treiber stack representing wait queue |
892 |
*/ |
893 |
static final class QNode implements ForkJoinPool.ManagedBlocker { |
894 |
final Phaser phaser; |
895 |
final int phase; |
896 |
final boolean interruptible; |
897 |
final boolean timed; |
898 |
boolean wasInterrupted; |
899 |
long nanos; |
900 |
long lastTime; |
901 |
volatile Thread thread; // nulled to cancel wait |
902 |
QNode next; |
903 |
|
904 |
QNode(Phaser phaser, int phase, boolean interruptible, |
905 |
boolean timed, long nanos) { |
906 |
this.phaser = phaser; |
907 |
this.phase = phase; |
908 |
this.interruptible = interruptible; |
909 |
this.nanos = nanos; |
910 |
this.timed = timed; |
911 |
this.lastTime = timed? System.nanoTime() : 0L; |
912 |
thread = Thread.currentThread(); |
913 |
} |
914 |
|
915 |
public boolean isReleasable() { |
916 |
Thread t = thread; |
917 |
if (t != null) { |
918 |
if (phaser.getPhase() != phase) |
919 |
t = null; |
920 |
else { |
921 |
if (Thread.interrupted()) |
922 |
wasInterrupted = true; |
923 |
if (interruptible && wasInterrupted) |
924 |
t = null; |
925 |
else if (timed) { |
926 |
if (nanos > 0) { |
927 |
long now = System.nanoTime(); |
928 |
nanos -= now - lastTime; |
929 |
lastTime = now; |
930 |
} |
931 |
if (nanos <= 0) |
932 |
t = null; |
933 |
} |
934 |
} |
935 |
if (t != null) |
936 |
return false; |
937 |
thread = null; |
938 |
} |
939 |
return true; |
940 |
} |
941 |
|
942 |
public boolean block() { |
943 |
if (isReleasable()) |
944 |
return true; |
945 |
else if (!timed) |
946 |
LockSupport.park(this); |
947 |
else if (nanos > 0) |
948 |
LockSupport.parkNanos(this, nanos); |
949 |
return isReleasable(); |
950 |
} |
951 |
|
952 |
void signal() { |
953 |
Thread t = thread; |
954 |
if (t != null) { |
955 |
thread = null; |
956 |
LockSupport.unpark(t); |
957 |
} |
958 |
} |
959 |
} |
960 |
|
961 |
// Unsafe mechanics |
962 |
|
963 |
private static final sun.misc.Unsafe UNSAFE = getUnsafe(); |
964 |
private static final long stateOffset = |
965 |
objectFieldOffset("state", Phaser.class); |
966 |
|
967 |
private static long objectFieldOffset(String field, Class<?> klazz) { |
968 |
try { |
969 |
return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field)); |
970 |
} catch (NoSuchFieldException e) { |
971 |
// Convert Exception to corresponding Error |
972 |
NoSuchFieldError error = new NoSuchFieldError(field); |
973 |
error.initCause(e); |
974 |
throw error; |
975 |
} |
976 |
} |
977 |
|
978 |
/** |
979 |
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. |
980 |
* Replace with a simple call to Unsafe.getUnsafe when integrating |
981 |
* into a jdk. |
982 |
* |
983 |
* @return a sun.misc.Unsafe |
984 |
*/ |
985 |
private static sun.misc.Unsafe getUnsafe() { |
986 |
try { |
987 |
return sun.misc.Unsafe.getUnsafe(); |
988 |
} catch (SecurityException se) { |
989 |
try { |
990 |
return java.security.AccessController.doPrivileged |
991 |
(new java.security |
992 |
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
993 |
public sun.misc.Unsafe run() throws Exception { |
994 |
java.lang.reflect.Field f = sun.misc |
995 |
.Unsafe.class.getDeclaredField("theUnsafe"); |
996 |
f.setAccessible(true); |
997 |
return (sun.misc.Unsafe) f.get(null); |
998 |
}}); |
999 |
} catch (java.security.PrivilegedActionException e) { |
1000 |
throw new RuntimeException("Could not initialize intrinsics", |
1001 |
e.getCause()); |
1002 |
} |
1003 |
} |
1004 |
} |
1005 |
} |