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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.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_PARTIES = 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 int UNARRIVED_MASK = 0xffff; |
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private static final int PARTIES_MASK = 0xffff0000; |
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private static final long LPARTIES_MASK = 0xffff0000L; // long version |
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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_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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for (;;) { |
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long s = state; |
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int phase = (int)(s >>> PHASE_SHIFT); |
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if (phase < 0) |
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return phase; |
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int unarrived = (int)s & UNARRIVED_MASK; |
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if (unarrived == 0) |
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checkBadArrive(s); |
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else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s-=adj)) { |
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if (unarrived == 1) { |
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long p = s & LPARTIES_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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final Phaser parent = this.parent; |
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if (parent == null) { |
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if (onAdvance(phase, u)) |
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next |= TERMINATION_PHASE; // obliterate phase |
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UNSAFE.compareAndSwapLong(this, stateOffset, s, next); |
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releaseWaiters(phase); |
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} |
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else { |
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parent.doArrive((u == 0) ? |
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ONE_ARRIVAL|ONE_PARTY : ONE_ARRIVAL); |
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if ((int)(parent.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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return phase; |
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} |
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} |
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} |
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|
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/** |
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* Rechecks state and throws bounds exceptions on arrival -- called |
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* only if unarrived is apparently zero. |
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*/ |
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private void checkBadArrive(long s) { |
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if (reconcileState() == s) |
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throw new IllegalStateException |
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("Attempted arrival of unregistered party for " + |
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stateToString(s)); |
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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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// assert registrations > 0; |
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// adjustment to state |
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long adj = ((long)registrations << PARTIES_SHIFT) | registrations; |
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final Phaser parent = this.parent; |
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for (;;) { |
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long s = (parent == null) ? state : reconcileState(); |
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int phase = (int)(s >>> PHASE_SHIFT); |
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if (phase < 0) |
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return phase; |
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int parties = (int)s >>> PARTIES_SHIFT; |
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if (parties != 0 && ((int)s & UNARRIVED_MASK) == 0) |
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internalAwaitAdvance(phase, null); // wait for onAdvance |
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else if (registrations > MAX_PARTIES - parties) |
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throw new IllegalStateException(badRegister(s)); |
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else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s + adj)) |
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return phase; |
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} |
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} |
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|
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/** |
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* Returns message string for out of bounds exceptions on registration. |
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*/ |
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private String badRegister(long s) { |
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return "Attempt to register more than " + |
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MAX_PARTIES + " parties for " + stateToString(s); |
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} |
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|
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/** |
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* Recursively resolves lagged phase propagation from root if 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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for (;;) { |
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long s, u; |
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int phase, rPhase, pPhase; |
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if ((phase = (int)((s = state)>>> PHASE_SHIFT)) < 0 || |
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(rPhase = (int)(rt.state >>> PHASE_SHIFT)) == phase) |
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return s; |
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long pState = par.parent == null? par.state : par.reconcileState(); |
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if (state == s) { |
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if ((rPhase < 0 || ((int)s & UNARRIVED_MASK) == 0) && |
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((pPhase = (int)(pState >>> PHASE_SHIFT)) < 0 || |
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pPhase == ((phase + 1) & MAX_PHASE))) |
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UNSAFE.compareAndSwapLong |
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(this, stateOffset, s, |
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(((long) pPhase) << PHASE_SHIFT) | |
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(u = s & LPARTIES_MASK) | |
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(u >>> PARTIES_SHIFT)); // reset unarrived to parties |
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else |
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releaseWaiters(phase); // help release others |
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} |
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} |
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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 |
433 |
*/ |
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public Phaser(int parties) { |
435 |
this(null, parties); |
436 |
} |
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|
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/** |
439 |
* Creates a new phaser with the given parent, without any |
440 |
* 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. |
443 |
* |
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* @param parent the parent phaser |
445 |
*/ |
446 |
public Phaser(Phaser parent) { |
447 |
this(parent, 0); |
448 |
} |
449 |
|
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/** |
451 |
* Creates a new phaser with the given parent and number of |
452 |
* registered unarrived parties. If parent is non-null, this phaser |
453 |
* is registered with the parent and its initial phase number is |
454 |
* the same as that of parent phaser. |
455 |
* |
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* @param parent the parent phaser |
457 |
* @param parties the number of parties required to trip barrier |
458 |
* @throws IllegalArgumentException if parties less than zero |
459 |
* or greater than the maximum number of parties supported |
460 |
*/ |
461 |
public Phaser(Phaser parent, int parties) { |
462 |
if (parties >>> PARTIES_SHIFT != 0) |
463 |
throw new IllegalArgumentException("Illegal number of parties"); |
464 |
int phase; |
465 |
this.parent = parent; |
466 |
if (parent != null) { |
467 |
Phaser r = parent.root; |
468 |
this.root = r; |
469 |
this.evenQ = r.evenQ; |
470 |
this.oddQ = r.oddQ; |
471 |
phase = parent.register(); |
472 |
} |
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else { |
474 |
this.root = this; |
475 |
this.evenQ = new AtomicReference<QNode>(); |
476 |
this.oddQ = new AtomicReference<QNode>(); |
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phase = 0; |
478 |
} |
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long p = (long)parties; |
480 |
this.state = (((long)phase) << PHASE_SHIFT) | p | (p << PARTIES_SHIFT); |
481 |
} |
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|
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/** |
484 |
* Adds a new unarrived party to this phaser. |
485 |
* If an ongoing invocation of {@link #onAdvance} is in progress, |
486 |
* this method may wait until its completion before registering. |
487 |
* |
488 |
* @return the arrival phase number to which this registration applied |
489 |
* @throws IllegalStateException if attempting to register more |
490 |
* than the maximum supported number of parties |
491 |
*/ |
492 |
public int register() { |
493 |
return doRegister(1); |
494 |
} |
495 |
|
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/** |
497 |
* Adds the given number of new unarrived parties to this phaser. |
498 |
* If an ongoing invocation of {@link #onAdvance} is in progress, |
499 |
* this method may wait until its completion before registering. |
500 |
* |
501 |
* @param parties the number of additional parties required to trip barrier |
502 |
* @return the arrival phase number to which this registration applied |
503 |
* @throws IllegalStateException if attempting to register more |
504 |
* than the maximum supported number of parties |
505 |
* @throws IllegalArgumentException if {@code parties < 0} |
506 |
*/ |
507 |
public int bulkRegister(int parties) { |
508 |
if (parties < 0) |
509 |
throw new IllegalArgumentException(); |
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 |
long s = (parent == null) ? state : reconcileState(); |
579 |
int p = (int)(s >>> PHASE_SHIFT); |
580 |
return (p != phase) ? p : internalAwaitAdvance(phase, null); |
581 |
} |
582 |
|
583 |
/** |
584 |
* Awaits the phase of the barrier to advance from the given phase |
585 |
* value, throwing {@code InterruptedException} if interrupted |
586 |
* while waiting, or returning immediately if the current phase of |
587 |
* the barrier is not equal to the given phase value or this |
588 |
* barrier is terminated. |
589 |
* |
590 |
* @param phase an arrival phase number, or negative value if |
591 |
* terminated; this argument is normally the value returned by a |
592 |
* previous call to {@code arrive} or its variants |
593 |
* @return the next arrival phase number, or a negative value |
594 |
* if terminated or argument is negative |
595 |
* @throws InterruptedException if thread interrupted while waiting |
596 |
*/ |
597 |
public int awaitAdvanceInterruptibly(int phase) |
598 |
throws InterruptedException { |
599 |
if (phase < 0) |
600 |
return phase; |
601 |
long s = (parent == null) ? state : reconcileState(); |
602 |
int p = (int)(s >>> PHASE_SHIFT); |
603 |
if (p == phase) { |
604 |
QNode node = new QNode(this, phase, true, false, 0L); |
605 |
p = internalAwaitAdvance(phase, node); |
606 |
if (node.wasInterrupted) |
607 |
throw new InterruptedException(); |
608 |
} |
609 |
return p; |
610 |
} |
611 |
|
612 |
/** |
613 |
* Awaits the phase of the barrier to advance from the given phase |
614 |
* value or the given timeout to elapse, throwing {@code |
615 |
* InterruptedException} if interrupted while waiting, or |
616 |
* returning immediately if the current phase of the barrier is |
617 |
* not equal to the given phase value or this barrier is |
618 |
* terminated. |
619 |
* |
620 |
* @param phase an arrival phase number, or negative value if |
621 |
* terminated; this argument is normally the value returned by a |
622 |
* previous call to {@code arrive} or its variants |
623 |
* @param timeout how long to wait before giving up, in units of |
624 |
* {@code unit} |
625 |
* @param unit a {@code TimeUnit} determining how to interpret the |
626 |
* {@code timeout} parameter |
627 |
* @return the next arrival phase number, or a negative value |
628 |
* if terminated or argument is negative |
629 |
* @throws InterruptedException if thread interrupted while waiting |
630 |
* @throws TimeoutException if timed out while waiting |
631 |
*/ |
632 |
public int awaitAdvanceInterruptibly(int phase, |
633 |
long timeout, TimeUnit unit) |
634 |
throws InterruptedException, TimeoutException { |
635 |
if (phase < 0) |
636 |
return phase; |
637 |
long s = (parent == null) ? state : reconcileState(); |
638 |
int p = (int)(s >>> PHASE_SHIFT); |
639 |
if (p == phase) { |
640 |
long nanos = unit.toNanos(timeout); |
641 |
QNode node = new QNode(this, phase, true, true, nanos); |
642 |
p = internalAwaitAdvance(phase, node); |
643 |
if (node.wasInterrupted) |
644 |
throw new InterruptedException(); |
645 |
else if (p == phase) |
646 |
throw new TimeoutException(); |
647 |
} |
648 |
return p; |
649 |
} |
650 |
|
651 |
/** |
652 |
* Forces this barrier to enter termination state. Counts of |
653 |
* arrived and registered parties are unaffected. If this phaser |
654 |
* is a member of a tiered set of phasers, then all of the phasers |
655 |
* in the set are terminated. If this phaser is already |
656 |
* terminated, this method has no effect. This method may be |
657 |
* useful for coordinating recovery after one or more tasks |
658 |
* encounter unexpected exceptions. |
659 |
*/ |
660 |
public void forceTermination() { |
661 |
// Only need to change root state |
662 |
final Phaser root = this.root; |
663 |
long s; |
664 |
while ((s = root.state) >= 0) { |
665 |
if (UNSAFE.compareAndSwapLong(root, stateOffset, |
666 |
s, s | TERMINATION_PHASE)) { |
667 |
releaseWaiters(0); // signal all threads |
668 |
releaseWaiters(1); |
669 |
return; |
670 |
} |
671 |
} |
672 |
} |
673 |
|
674 |
/** |
675 |
* Returns the current phase number. The maximum phase number is |
676 |
* {@code Integer.MAX_VALUE}, after which it restarts at |
677 |
* zero. Upon termination, the phase number is negative. |
678 |
* |
679 |
* @return the phase number, or a negative value if terminated |
680 |
*/ |
681 |
public final int getPhase() { |
682 |
return (int)((parent==null? state : reconcileState()) >>> PHASE_SHIFT); |
683 |
} |
684 |
|
685 |
/** |
686 |
* Returns the number of parties registered at this barrier. |
687 |
* |
688 |
* @return the number of parties |
689 |
*/ |
690 |
public int getRegisteredParties() { |
691 |
return partiesOf(parent==null? state : reconcileState()); |
692 |
} |
693 |
|
694 |
/** |
695 |
* Returns the number of registered parties that have arrived at |
696 |
* the current phase of this barrier. |
697 |
* |
698 |
* @return the number of arrived parties |
699 |
*/ |
700 |
public int getArrivedParties() { |
701 |
return arrivedOf(parent==null? state : reconcileState()); |
702 |
} |
703 |
|
704 |
/** |
705 |
* Returns the number of registered parties that have not yet |
706 |
* arrived at the current phase of this barrier. |
707 |
* |
708 |
* @return the number of unarrived parties |
709 |
*/ |
710 |
public int getUnarrivedParties() { |
711 |
return unarrivedOf(parent==null? state : reconcileState()); |
712 |
} |
713 |
|
714 |
/** |
715 |
* Returns the parent of this phaser, or {@code null} if none. |
716 |
* |
717 |
* @return the parent of this phaser, or {@code null} if none |
718 |
*/ |
719 |
public Phaser getParent() { |
720 |
return parent; |
721 |
} |
722 |
|
723 |
/** |
724 |
* Returns the root ancestor of this phaser, which is the same as |
725 |
* this phaser if it has no parent. |
726 |
* |
727 |
* @return the root ancestor of this phaser |
728 |
*/ |
729 |
public Phaser getRoot() { |
730 |
return root; |
731 |
} |
732 |
|
733 |
/** |
734 |
* Returns {@code true} if this barrier has been terminated. |
735 |
* |
736 |
* @return {@code true} if this barrier has been terminated |
737 |
*/ |
738 |
public boolean isTerminated() { |
739 |
return (parent == null? state : reconcileState()) < 0; |
740 |
} |
741 |
|
742 |
/** |
743 |
* Overridable method to perform an action upon impending phase |
744 |
* advance, and to control termination. This method is invoked |
745 |
* upon arrival of the party tripping the barrier (when all other |
746 |
* waiting parties are dormant). If this method returns {@code |
747 |
* true}, then, rather than advance the phase number, this barrier |
748 |
* will be set to a final termination state, and subsequent calls |
749 |
* to {@link #isTerminated} will return true. Any (unchecked) |
750 |
* Exception or Error thrown by an invocation of this method is |
751 |
* propagated to the party attempting to trip the barrier, in |
752 |
* which case no advance occurs. |
753 |
* |
754 |
* <p>The arguments to this method provide the state of the phaser |
755 |
* prevailing for the current transition. The effects of invoking |
756 |
* arrival, registration, and waiting methods on this Phaser from |
757 |
* within {@code onAdvance} are unspecified and should not be |
758 |
* relied on. |
759 |
* |
760 |
* <p>If this Phaser is a member of a tiered set of Phasers, then |
761 |
* {@code onAdvance} is invoked only for its root Phaser on each |
762 |
* advance. |
763 |
* |
764 |
* <p>The default version returns {@code true} when the number of |
765 |
* registered parties is zero. Normally, overrides that arrange |
766 |
* termination for other reasons should also preserve this |
767 |
* property. |
768 |
* |
769 |
* @param phase the phase number on entering the barrier |
770 |
* @param registeredParties the current number of registered parties |
771 |
* @return {@code true} if this barrier should terminate |
772 |
*/ |
773 |
protected boolean onAdvance(int phase, int registeredParties) { |
774 |
return registeredParties <= 0; |
775 |
} |
776 |
|
777 |
/** |
778 |
* Returns a string identifying this phaser, as well as its |
779 |
* state. The state, in brackets, includes the String {@code |
780 |
* "phase = "} followed by the phase number, {@code "parties = "} |
781 |
* followed by the number of registered parties, and {@code |
782 |
* "arrived = "} followed by the number of arrived parties. |
783 |
* |
784 |
* @return a string identifying this barrier, as well as its state |
785 |
*/ |
786 |
public String toString() { |
787 |
return stateToString(reconcileState()); |
788 |
} |
789 |
|
790 |
/** |
791 |
* Implementation of toString and string-based error messages |
792 |
*/ |
793 |
private String stateToString(long s) { |
794 |
return super.toString() + |
795 |
"[phase = " + phaseOf(s) + |
796 |
" parties = " + partiesOf(s) + |
797 |
" arrived = " + arrivedOf(s) + "]"; |
798 |
} |
799 |
|
800 |
// Waiting mechanics |
801 |
|
802 |
/** |
803 |
* Removes and signals threads from queue for phase |
804 |
*/ |
805 |
private void releaseWaiters(int phase) { |
806 |
AtomicReference<QNode> head = queueFor(phase); |
807 |
QNode q; |
808 |
int p; |
809 |
while ((q = head.get()) != null && |
810 |
((p = q.phase) == phase || |
811 |
(int)(root.state >>> PHASE_SHIFT) != p)) { |
812 |
if (head.compareAndSet(q, q.next)) |
813 |
q.signal(); |
814 |
} |
815 |
} |
816 |
|
817 |
/** |
818 |
* Tries to enqueue given node in the appropriate wait queue. |
819 |
* |
820 |
* @return true if successful |
821 |
*/ |
822 |
private boolean tryEnqueue(int phase, QNode node) { |
823 |
releaseWaiters(phase-1); // ensure old queue clean |
824 |
AtomicReference<QNode> head = queueFor(phase); |
825 |
QNode q = head.get(); |
826 |
return ((q == null || q.phase == phase) && |
827 |
(int)(root.state >>> PHASE_SHIFT) == phase && |
828 |
head.compareAndSet(node.next = q, node)); |
829 |
} |
830 |
|
831 |
/** The number of CPUs, for spin control */ |
832 |
private static final int NCPU = Runtime.getRuntime().availableProcessors(); |
833 |
|
834 |
/** |
835 |
* The number of times to spin before blocking while waiting for |
836 |
* advance, per arrival while waiting. On multiprocessors, fully |
837 |
* blocking and waking up a large number of threads all at once is |
838 |
* usually a very slow process, so we use rechargeable spins to |
839 |
* avoid it when threads regularly arrive: When a thread in |
840 |
* internalAwaitAdvance notices another arrival before blocking, |
841 |
* and there appear to be enough CPUs available, it spins |
842 |
* SPINS_PER_ARRIVAL more times before blocking. Plus, even on |
843 |
* uniprocessors, there is at least one intervening Thread.yield |
844 |
* before blocking. The value trades off good-citizenship vs big |
845 |
* unnecessary slowdowns. |
846 |
*/ |
847 |
static final int SPINS_PER_ARRIVAL = (NCPU < 2) ? 1 : 1 << 8; |
848 |
|
849 |
/** |
850 |
* Possibly blocks and waits for phase to advance unless aborted. |
851 |
* |
852 |
* @param phase current phase |
853 |
* @param node if non-null, the wait node to track interrupt and timeout; |
854 |
* if null, denotes noninterruptible wait |
855 |
* @return current phase |
856 |
*/ |
857 |
private int internalAwaitAdvance(int phase, QNode node) { |
858 |
Phaser current = this; // to eventually wait at root if tiered |
859 |
boolean queued = false; // true when node is enqueued |
860 |
int lastUnarrived = -1; // to increase spins upon change |
861 |
int spins = SPINS_PER_ARRIVAL; |
862 |
for (;;) { |
863 |
int p, unarrived; |
864 |
Phaser par; |
865 |
long s = current.state; |
866 |
if ((p = (int)(s >>> PHASE_SHIFT)) != phase) { |
867 |
if (node != null) |
868 |
node.onRelease(); |
869 |
releaseWaiters(phase); |
870 |
return p; |
871 |
} |
872 |
else if ((unarrived = (int)s & UNARRIVED_MASK) == 0 && |
873 |
(par = current.parent) != null) { |
874 |
current = par; // if all arrived, use parent |
875 |
par = par.parent; |
876 |
lastUnarrived = -1; |
877 |
} |
878 |
else if (unarrived != lastUnarrived) { |
879 |
if ((lastUnarrived = unarrived) < NCPU) |
880 |
spins += SPINS_PER_ARRIVAL; |
881 |
} |
882 |
else if (spins > 0) { |
883 |
if (--spins == (SPINS_PER_ARRIVAL >>> 1)) |
884 |
Thread.yield(); // yield midway through spin |
885 |
} |
886 |
else if (node == null) // must be noninterruptible |
887 |
node = new QNode(this, phase, false, false, 0L); |
888 |
else if (node.isReleasable()) { |
889 |
if ((int)(reconcileState() >>> PHASE_SHIFT) == phase) |
890 |
return phase; // aborted |
891 |
} |
892 |
else if (!queued) |
893 |
queued = tryEnqueue(phase, node); |
894 |
else { |
895 |
try { |
896 |
ForkJoinPool.managedBlock(node); |
897 |
} catch (InterruptedException ie) { |
898 |
node.wasInterrupted = true; |
899 |
} |
900 |
} |
901 |
} |
902 |
} |
903 |
|
904 |
/** |
905 |
* Wait nodes for Treiber stack representing wait queue |
906 |
*/ |
907 |
static final class QNode implements ForkJoinPool.ManagedBlocker { |
908 |
final Phaser phaser; |
909 |
final int phase; |
910 |
final boolean interruptible; |
911 |
final boolean timed; |
912 |
boolean wasInterrupted; |
913 |
long nanos; |
914 |
long lastTime; |
915 |
volatile Thread thread; // nulled to cancel wait |
916 |
QNode next; |
917 |
|
918 |
QNode(Phaser phaser, int phase, boolean interruptible, |
919 |
boolean timed, long nanos) { |
920 |
this.phaser = phaser; |
921 |
this.phase = phase; |
922 |
this.interruptible = interruptible; |
923 |
this.nanos = nanos; |
924 |
this.timed = timed; |
925 |
this.lastTime = timed? System.nanoTime() : 0L; |
926 |
thread = Thread.currentThread(); |
927 |
} |
928 |
|
929 |
public boolean isReleasable() { |
930 |
Thread t = thread; |
931 |
if (t != null) { |
932 |
if (phaser.getPhase() != phase) |
933 |
t = null; |
934 |
else { |
935 |
if (Thread.interrupted()) |
936 |
wasInterrupted = true; |
937 |
if (interruptible && wasInterrupted) |
938 |
t = null; |
939 |
else if (timed) { |
940 |
if (nanos > 0) { |
941 |
long now = System.nanoTime(); |
942 |
nanos -= now - lastTime; |
943 |
lastTime = now; |
944 |
} |
945 |
if (nanos <= 0) |
946 |
t = null; |
947 |
} |
948 |
} |
949 |
if (t != null) |
950 |
return false; |
951 |
thread = null; |
952 |
} |
953 |
return true; |
954 |
} |
955 |
|
956 |
public boolean block() { |
957 |
if (isReleasable()) |
958 |
return true; |
959 |
else if (!timed) |
960 |
LockSupport.park(this); |
961 |
else if (nanos > 0) |
962 |
LockSupport.parkNanos(this, nanos); |
963 |
return isReleasable(); |
964 |
} |
965 |
|
966 |
void signal() { |
967 |
Thread t = thread; |
968 |
if (t != null) { |
969 |
thread = null; |
970 |
LockSupport.unpark(t); |
971 |
} |
972 |
} |
973 |
|
974 |
void onRelease() { // actions upon return from internalAwaitAdvance |
975 |
if (!interruptible && wasInterrupted) |
976 |
Thread.currentThread().interrupt(); |
977 |
if (thread != null) |
978 |
thread = null; |
979 |
} |
980 |
|
981 |
} |
982 |
|
983 |
// Unsafe mechanics |
984 |
|
985 |
private static final sun.misc.Unsafe UNSAFE = sun.misc.Unsafe.getUnsafe(); |
986 |
private static final long stateOffset = |
987 |
objectFieldOffset("state", Phaser.class); |
988 |
|
989 |
private static long objectFieldOffset(String field, Class<?> klazz) { |
990 |
try { |
991 |
return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field)); |
992 |
} catch (NoSuchFieldException e) { |
993 |
// Convert Exception to corresponding Error |
994 |
NoSuchFieldError error = new NoSuchFieldError(field); |
995 |
error.initCause(e); |
996 |
throw error; |
997 |
} |
998 |
} |
999 |
} |