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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 phaser has an associated phase number. The phase |
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* number starts at zero, and advances when all parties arrive at the |
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* phaser, 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 phaser 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. These methods |
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* do not block, but return an associated <em>arrival phase |
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* number</em>; that is, the phase number of the phaser to which |
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* the arrival applied. When the final party for a given phase |
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* arrives, an optional action is performed and the phase |
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* advances. These actions are performed by the party |
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* triggering a phase advance, and are arranged by overriding |
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* method {@link #onAdvance(int, int)}, which also controls |
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* termination. Overriding this method is similar to, but more |
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* flexible than, providing a barrier action to a {@code |
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* 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 phaser 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 phaser. 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 phaser may enter a <em>termination</em> |
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* state, that may be checked using method {@link #isTerminated}. Upon |
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* termination, all synchronization methods immediately return without |
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* waiting for advance, as indicated by a negative return |
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* value. Similarly, attempts to register upon termination have no |
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* effect. Termination is triggered when an invocation of {@code |
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* onAdvance} returns {@code true}. The default implementation returns |
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* {@code true} if a deregistration has caused the number of |
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* registered parties to become zero. 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., |
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* constructed in tree structures) to reduce contention. Phasers with |
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* large 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>In a tree of tiered phasers, registration and deregistration of |
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* child phasers with their parent are managed automatically. |
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* Whenever the number of registered parties of a child phaser becomes |
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* non-zero (as established in the {@link #Phaser(Phaser,int)} |
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* constructor, {@link #register}, or {@link #bulkRegister}), the |
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* child phaser is registered with its parent. Whenever the number of |
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* registered parties becomes zero as the result of an invocation of |
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* {@link #arriveAndDeregister}, the child phaser is deregistered |
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* from its parent. |
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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 {@code n} tasks using a tree of phasers, you |
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* could use code of the following form, assuming a Task class with a |
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* constructor accepting a {@code Phaser} that it registers with upon |
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* construction. After invocation of {@code build(new Task[n], 0, n, |
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* new Phaser())}, these tasks could then be started, for example by |
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* submitting to a pool: |
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* |
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* <pre> {@code |
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* void build(Task[] tasks, 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(tasks, 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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* tasks[i] = new Task(ph); |
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* // assumes new Task(ph) performs ph.register() |
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* } |
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* }}</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 synchronization rates. A value as low as four may |
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* be appropriate for extremely small per-phase 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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* Primary state representation, holding four fields: |
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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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* Except that a phaser with no registered parties is |
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* distinguished with the otherwise illegal state of having zero |
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* parties and one unarrived parties (encoded as EMPTY below). |
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* |
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* To efficiently maintain atomicity, these values are packed into |
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* a single (atomic) long. Good performance relies on keeping |
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* state decoding and encoding simple, and keeping race windows |
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* short. |
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* |
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* All state updates are performed via CAS except initial |
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* registration of a sub-phaser (i.e., one with a non-null |
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* parent). In this (relatively rare) case, we use built-in |
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* synchronization to lock while first registering with its |
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* parent. |
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* |
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* The phase of a subphaser is allowed to lag that of its |
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* ancestors until it is actually accessed. Method reconcileState |
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* is usually attempted only only when the number of unarrived |
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* parties appears to be zero, which indicates a potential lag in |
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* updating phase after the root advanced. |
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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; // to mask ints |
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private static final long PARTIES_MASK = 0xffff0000L; // to mask longs |
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private static final long TERMINATION_BIT = 1L << 63; |
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|
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// some special values |
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private static final int ONE_ARRIVAL = 1; |
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private static final int ONE_PARTY = 1 << PARTIES_SHIFT; |
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private static final int EMPTY = 1; |
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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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int counts = (int)s; |
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return (counts == EMPTY) ? 0 : counts & 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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int counts = (int)s; |
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return (counts == EMPTY) ? 0 : |
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(counts >>> PARTIES_SHIFT) - (counts & UNARRIVED_MASK); |
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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. |
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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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* Returns message string for bounds exceptions on arrival. |
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*/ |
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private String badArrive(long s) { |
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return "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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* Returns message string for 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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* 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 deregister false for arrive, true for arriveAndDeregister |
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*/ |
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private int doArrive(boolean deregister) { |
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int adj = deregister ? ONE_ARRIVAL|ONE_PARTY : ONE_ARRIVAL; |
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final Phaser root = this.root; |
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for (;;) { |
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long s = (root == this) ? state : reconcileState(); |
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int phase = (int)(s >>> PHASE_SHIFT); |
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int counts = (int)s; |
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int unarrived = (counts & UNARRIVED_MASK) - 1; |
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if (phase < 0) |
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return phase; |
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else if (counts == EMPTY || unarrived < 0) { |
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if (root == this || reconcileState() == s) |
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throw new IllegalStateException(badArrive(s)); |
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} |
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else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s-=adj)) { |
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if (unarrived == 0) { |
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long n = s & PARTIES_MASK; // base of next state |
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int nextUnarrived = ((int)n) >>> PARTIES_SHIFT; |
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if (root != this) |
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return parent.doArrive(nextUnarrived == 0); |
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if (onAdvance(phase, nextUnarrived)) |
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n |= TERMINATION_BIT; |
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else if (nextUnarrived == 0) |
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n |= EMPTY; |
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else |
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n |= nextUnarrived; |
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n |= ((long)((phase + 1) & MAX_PHASE)) << PHASE_SHIFT; |
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UNSAFE.compareAndSwapLong(this, stateOffset, s, n); |
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releaseWaiters(phase); |
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} |
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return phase; |
381 |
} |
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} |
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} |
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|
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/** |
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* Implementation of register, bulkRegister |
387 |
* |
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* @param registrations number to add to both parties and |
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* unarrived fields. Must be greater than zero. |
390 |
*/ |
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private int doRegister(int registrations) { |
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// adjustment to state |
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long adj = ((long)registrations << PARTIES_SHIFT) | registrations; |
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Phaser par = parent; |
395 |
int phase; |
396 |
for (;;) { |
397 |
long s = state; |
398 |
int counts = (int)s; |
399 |
int parties = counts >>> PARTIES_SHIFT; |
400 |
int unarrived = counts & UNARRIVED_MASK; |
401 |
if (registrations > MAX_PARTIES - parties) |
402 |
throw new IllegalStateException(badRegister(s)); |
403 |
else if ((phase = (int)(s >>> PHASE_SHIFT)) < 0) |
404 |
break; |
405 |
else if (counts != EMPTY) { // not 1st registration |
406 |
if (par == null || reconcileState() == s) { |
407 |
if (unarrived == 0) // wait out advance |
408 |
root.internalAwaitAdvance(phase, null); |
409 |
else if (UNSAFE.compareAndSwapLong(this, stateOffset, |
410 |
s, s + adj)) |
411 |
break; |
412 |
} |
413 |
} |
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else if (par == null) { // 1st root registration |
415 |
long next = (((long) phase) << PHASE_SHIFT) | adj; |
416 |
if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next)) |
417 |
break; |
418 |
} |
419 |
else { |
420 |
synchronized (this) { // 1st sub registration |
421 |
if (state == s) { // recheck under lock |
422 |
par.doRegister(1); |
423 |
do { // force current phase |
424 |
phase = (int)(root.state >>> PHASE_SHIFT); |
425 |
// assert phase < 0 || (int)state == EMPTY; |
426 |
} while (!UNSAFE.compareAndSwapLong |
427 |
(this, stateOffset, state, |
428 |
(((long) phase) << PHASE_SHIFT) | adj)); |
429 |
break; |
430 |
} |
431 |
} |
432 |
} |
433 |
} |
434 |
return phase; |
435 |
} |
436 |
|
437 |
/** |
438 |
* Resolves lagged phase propagation from root if necessary. |
439 |
*/ |
440 |
private long reconcileState() { |
441 |
Phaser rt = root; |
442 |
long s = state; |
443 |
if (rt != this) { |
444 |
int phase; |
445 |
while ((phase = (int)(rt.state >>> PHASE_SHIFT)) != |
446 |
(int)(s >>> PHASE_SHIFT)) { |
447 |
// assert phase < 0 || unarrivedOf(s) == 0 |
448 |
long t; // to reread s |
449 |
long p = s & PARTIES_MASK; // unshifted parties field |
450 |
long n = (((long) phase) << PHASE_SHIFT) | p; |
451 |
if (phase >= 0) { |
452 |
if (p == 0L) |
453 |
n |= EMPTY; // reset to empty |
454 |
else |
455 |
n |= p >>> PARTIES_SHIFT; // set unarr to parties |
456 |
} |
457 |
if ((t = state) == s && |
458 |
UNSAFE.compareAndSwapLong(this, stateOffset, s, s = n)) |
459 |
break; |
460 |
s = t; |
461 |
} |
462 |
} |
463 |
return s; |
464 |
} |
465 |
|
466 |
/** |
467 |
* Creates a new phaser with no initially registered parties, no |
468 |
* parent, and initial phase number 0. Any thread using this |
469 |
* phaser will need to first register for it. |
470 |
*/ |
471 |
public Phaser() { |
472 |
this(null, 0); |
473 |
} |
474 |
|
475 |
/** |
476 |
* Creates a new phaser with the given number of registered |
477 |
* unarrived parties, no parent, and initial phase number 0. |
478 |
* |
479 |
* @param parties the number of parties required to advance to the |
480 |
* next phase |
481 |
* @throws IllegalArgumentException if parties less than zero |
482 |
* or greater than the maximum number of parties supported |
483 |
*/ |
484 |
public Phaser(int parties) { |
485 |
this(null, parties); |
486 |
} |
487 |
|
488 |
/** |
489 |
* Equivalent to {@link #Phaser(Phaser, int) Phaser(parent, 0)}. |
490 |
* |
491 |
* @param parent the parent phaser |
492 |
*/ |
493 |
public Phaser(Phaser parent) { |
494 |
this(parent, 0); |
495 |
} |
496 |
|
497 |
/** |
498 |
* Creates a new phaser with the given parent and number of |
499 |
* registered unarrived parties. When the given parent is non-null |
500 |
* and the given number of parties is greater than zero, this |
501 |
* child phaser is registered with its parent. |
502 |
* |
503 |
* @param parent the parent phaser |
504 |
* @param parties the number of parties required to advance to the |
505 |
* next phase |
506 |
* @throws IllegalArgumentException if parties less than zero |
507 |
* or greater than the maximum number of parties supported |
508 |
*/ |
509 |
public Phaser(Phaser parent, int parties) { |
510 |
if (parties >>> PARTIES_SHIFT != 0) |
511 |
throw new IllegalArgumentException("Illegal number of parties"); |
512 |
int phase = 0; |
513 |
this.parent = parent; |
514 |
if (parent != null) { |
515 |
final Phaser root = parent.root; |
516 |
this.root = root; |
517 |
this.evenQ = root.evenQ; |
518 |
this.oddQ = root.oddQ; |
519 |
if (parties != 0) |
520 |
phase = parent.doRegister(1); |
521 |
} |
522 |
else { |
523 |
this.root = this; |
524 |
this.evenQ = new AtomicReference<QNode>(); |
525 |
this.oddQ = new AtomicReference<QNode>(); |
526 |
} |
527 |
this.state = (parties == 0) ? (long) EMPTY : |
528 |
((((long) phase) << PHASE_SHIFT) | |
529 |
(((long) parties) << PARTIES_SHIFT) | |
530 |
((long) parties)); |
531 |
} |
532 |
|
533 |
/** |
534 |
* Adds a new unarrived party to this phaser. If an ongoing |
535 |
* invocation of {@link #onAdvance} is in progress, this method |
536 |
* may await its completion before returning. If this phaser has |
537 |
* a parent, and this phaser previously had no registered parties, |
538 |
* this child phaser is also registered with its parent. If |
539 |
* this phaser is terminated, the attempt to register has |
540 |
* no effect, and a negative value is returned. |
541 |
* |
542 |
* @return the arrival phase number to which this registration |
543 |
* applied. If this value is negative, then this phaser has |
544 |
* terminated, in which casem registration has no effect. |
545 |
* @throws IllegalStateException if attempting to register more |
546 |
* than the maximum supported number of parties |
547 |
*/ |
548 |
public int register() { |
549 |
return doRegister(1); |
550 |
} |
551 |
|
552 |
/** |
553 |
* Adds the given number of new unarrived parties to this phaser. |
554 |
* If an ongoing invocation of {@link #onAdvance} is in progress, |
555 |
* this method may await its completion before returning. If this |
556 |
* phaser has a parent, and the given number of parties is greater |
557 |
* than zero, and this phaser previously had no registered |
558 |
* parties, this child phaser is also registered with its parent. |
559 |
* If this phaser is terminated, the attempt to register has no |
560 |
* effect, and a negative value is returned. |
561 |
* |
562 |
* @param parties the number of additional parties required to |
563 |
* advance to the next phase |
564 |
* @return the arrival phase number to which this registration |
565 |
* applied. If this value is negative, then this phaser has |
566 |
* terminated, in which casem registration has no effect. |
567 |
* @throws IllegalStateException if attempting to register more |
568 |
* than the maximum supported number of parties |
569 |
* @throws IllegalArgumentException if {@code parties < 0} |
570 |
*/ |
571 |
public int bulkRegister(int parties) { |
572 |
if (parties < 0) |
573 |
throw new IllegalArgumentException(); |
574 |
if (parties == 0) |
575 |
return getPhase(); |
576 |
return doRegister(parties); |
577 |
} |
578 |
|
579 |
/** |
580 |
* Arrives at this phaser, without waiting for others to arrive. |
581 |
* |
582 |
* <p>It is a usage error for an unregistered party to invoke this |
583 |
* method. However, this error may result in an {@code |
584 |
* IllegalStateException} only upon some subsequent operation on |
585 |
* this phaser, if ever. |
586 |
* |
587 |
* @return the arrival phase number, or a negative value if terminated |
588 |
* @throws IllegalStateException if not terminated and the number |
589 |
* of unarrived parties would become negative |
590 |
*/ |
591 |
public int arrive() { |
592 |
return doArrive(false); |
593 |
} |
594 |
|
595 |
/** |
596 |
* Arrives at this phaser and deregisters from it without waiting |
597 |
* for others to arrive. Deregistration reduces the number of |
598 |
* parties required to advance in future phases. If this phaser |
599 |
* has a parent, and deregistration causes this phaser to have |
600 |
* zero parties, this phaser is also deregistered from its parent. |
601 |
* |
602 |
* <p>It is a usage error for an unregistered party to invoke this |
603 |
* method. However, this error may result in an {@code |
604 |
* IllegalStateException} only upon some subsequent operation on |
605 |
* this phaser, if ever. |
606 |
* |
607 |
* @return the arrival phase number, or a negative value if terminated |
608 |
* @throws IllegalStateException if not terminated and the number |
609 |
* of registered or unarrived parties would become negative |
610 |
*/ |
611 |
public int arriveAndDeregister() { |
612 |
return doArrive(true); |
613 |
} |
614 |
|
615 |
/** |
616 |
* Arrives at this phaser and awaits others. Equivalent in effect |
617 |
* to {@code awaitAdvance(arrive())}. If you need to await with |
618 |
* interruption or timeout, you can arrange this with an analogous |
619 |
* construction using one of the other forms of the {@code |
620 |
* awaitAdvance} method. If instead you need to deregister upon |
621 |
* arrival, use {@code awaitAdvance(arriveAndDeregister())}. |
622 |
* |
623 |
* <p>It is a usage error for an unregistered party to invoke this |
624 |
* method. However, this error may result in an {@code |
625 |
* IllegalStateException} only upon some subsequent operation on |
626 |
* this phaser, if ever. |
627 |
* |
628 |
* @return the arrival phase number, or the (negative) |
629 |
* {@linkplain #getPhase() current phase} if terminated |
630 |
* @throws IllegalStateException if not terminated and the number |
631 |
* of unarrived parties would become negative |
632 |
*/ |
633 |
public int arriveAndAwaitAdvance() { |
634 |
// Specialization of doArrive+awaitAdvance eliminating some reads/paths |
635 |
final Phaser root = this.root; |
636 |
for (;;) { |
637 |
long s = (root == this) ? state : reconcileState(); |
638 |
int phase = (int)(s >>> PHASE_SHIFT); |
639 |
int counts = (int)s; |
640 |
int unarrived = (counts & UNARRIVED_MASK) - 1; |
641 |
if (phase < 0) |
642 |
return phase; |
643 |
else if (counts == EMPTY || unarrived < 0) { |
644 |
if (reconcileState() == s) |
645 |
throw new IllegalStateException(badArrive(s)); |
646 |
} |
647 |
else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, |
648 |
s -= ONE_ARRIVAL)) { |
649 |
if (unarrived != 0) |
650 |
return root.internalAwaitAdvance(phase, null); |
651 |
if (root != this) |
652 |
return parent.arriveAndAwaitAdvance(); |
653 |
long n = s & PARTIES_MASK; // base of next state |
654 |
int nextUnarrived = ((int)n) >>> PARTIES_SHIFT; |
655 |
if (onAdvance(phase, nextUnarrived)) |
656 |
n |= TERMINATION_BIT; |
657 |
else if (nextUnarrived == 0) |
658 |
n |= EMPTY; |
659 |
else |
660 |
n |= nextUnarrived; |
661 |
int nextPhase = (phase + 1) & MAX_PHASE; |
662 |
n |= (long)nextPhase << PHASE_SHIFT; |
663 |
if (!UNSAFE.compareAndSwapLong(this, stateOffset, s, n)) |
664 |
return (int)(state >>> PHASE_SHIFT); // terminated |
665 |
releaseWaiters(phase); |
666 |
return nextPhase; |
667 |
} |
668 |
} |
669 |
} |
670 |
|
671 |
/** |
672 |
* Awaits the phase of this phaser to advance from the given phase |
673 |
* value, returning immediately if the current phase is not equal |
674 |
* to the given phase value or this phaser is terminated. |
675 |
* |
676 |
* @param phase an arrival phase number, or negative value if |
677 |
* terminated; this argument is normally the value returned by a |
678 |
* previous call to {@code arrive} or {@code arriveAndDeregister}. |
679 |
* @return the next arrival phase number, or the argument if it is |
680 |
* negative, or the (negative) {@linkplain #getPhase() current phase} |
681 |
* if terminated |
682 |
*/ |
683 |
public int awaitAdvance(int phase) { |
684 |
final Phaser root = this.root; |
685 |
int p = (int)((root == this? state : reconcileState()) >>> PHASE_SHIFT); |
686 |
if (phase < 0) |
687 |
return phase; |
688 |
if (p == phase) |
689 |
return root.internalAwaitAdvance(phase, null); |
690 |
return p; |
691 |
} |
692 |
|
693 |
/** |
694 |
* Awaits the phase of this phaser to advance from the given phase |
695 |
* value, throwing {@code InterruptedException} if interrupted |
696 |
* while waiting, or returning immediately if the current phase is |
697 |
* not equal to the given phase value or this phaser is |
698 |
* terminated. |
699 |
* |
700 |
* @param phase an arrival phase number, or negative value if |
701 |
* terminated; this argument is normally the value returned by a |
702 |
* previous call to {@code arrive} or {@code arriveAndDeregister}. |
703 |
* @return the next arrival phase number, or the argument if it is |
704 |
* negative, or the (negative) {@linkplain #getPhase() current phase} |
705 |
* if terminated |
706 |
* @throws InterruptedException if thread interrupted while waiting |
707 |
*/ |
708 |
public int awaitAdvanceInterruptibly(int phase) |
709 |
throws InterruptedException { |
710 |
final Phaser root = this.root; |
711 |
int p = (int)((root == this? state : reconcileState()) >>> PHASE_SHIFT); |
712 |
if (phase < 0) |
713 |
return phase; |
714 |
if (p == phase) { |
715 |
QNode node = new QNode(this, phase, true, false, 0L); |
716 |
p = root.internalAwaitAdvance(phase, node); |
717 |
if (node.wasInterrupted) |
718 |
throw new InterruptedException(); |
719 |
} |
720 |
return p; |
721 |
} |
722 |
|
723 |
/** |
724 |
* Awaits the phase of this phaser to advance from the given phase |
725 |
* value or the given timeout to elapse, throwing {@code |
726 |
* InterruptedException} if interrupted while waiting, or |
727 |
* returning immediately if the current phase is not equal to the |
728 |
* given phase value or this phaser is terminated. |
729 |
* |
730 |
* @param phase an arrival phase number, or negative value if |
731 |
* terminated; this argument is normally the value returned by a |
732 |
* previous call to {@code arrive} or {@code arriveAndDeregister}. |
733 |
* @param timeout how long to wait before giving up, in units of |
734 |
* {@code unit} |
735 |
* @param unit a {@code TimeUnit} determining how to interpret the |
736 |
* {@code timeout} parameter |
737 |
* @return the next arrival phase number, or the argument if it is |
738 |
* negative, or the (negative) {@linkplain #getPhase() current phase} |
739 |
* if terminated |
740 |
* @throws InterruptedException if thread interrupted while waiting |
741 |
* @throws TimeoutException if timed out while waiting |
742 |
*/ |
743 |
public int awaitAdvanceInterruptibly(int phase, |
744 |
long timeout, TimeUnit unit) |
745 |
throws InterruptedException, TimeoutException { |
746 |
long nanos = unit.toNanos(timeout); |
747 |
final Phaser root = this.root; |
748 |
int p = (int)((root == this? state : reconcileState()) >>> PHASE_SHIFT); |
749 |
if (phase < 0) |
750 |
return phase; |
751 |
if (p == phase) { |
752 |
QNode node = new QNode(this, phase, true, true, nanos); |
753 |
p = root.internalAwaitAdvance(phase, node); |
754 |
if (node.wasInterrupted) |
755 |
throw new InterruptedException(); |
756 |
else if (p == phase) |
757 |
throw new TimeoutException(); |
758 |
} |
759 |
return p; |
760 |
} |
761 |
|
762 |
/** |
763 |
* Forces this phaser to enter termination state. Counts of |
764 |
* registered parties are unaffected. If this phaser is a member |
765 |
* of a tiered set of phasers, then all of the phasers in the set |
766 |
* are terminated. If this phaser is already terminated, this |
767 |
* method has no effect. This method may be useful for |
768 |
* coordinating recovery after one or more tasks encounter |
769 |
* unexpected exceptions. |
770 |
*/ |
771 |
public void forceTermination() { |
772 |
// Only need to change root state |
773 |
final Phaser root = this.root; |
774 |
long s; |
775 |
while ((s = root.state) >= 0) { |
776 |
long next = (s & ~((long)UNARRIVED_MASK)) | TERMINATION_BIT; |
777 |
if (UNSAFE.compareAndSwapLong(root, stateOffset, s, next)) { |
778 |
// signal all threads |
779 |
releaseWaiters(0); |
780 |
releaseWaiters(1); |
781 |
return; |
782 |
} |
783 |
} |
784 |
} |
785 |
|
786 |
/** |
787 |
* Returns the current phase number. The maximum phase number is |
788 |
* {@code Integer.MAX_VALUE}, after which it restarts at |
789 |
* zero. Upon termination, the phase number is negative, |
790 |
* in which case the prevailing phase prior to termination |
791 |
* may be obtained via {@code getPhase() + Integer.MIN_VALUE}. |
792 |
* |
793 |
* @return the phase number, or a negative value if terminated |
794 |
*/ |
795 |
public final int getPhase() { |
796 |
return (int)(root.state >>> PHASE_SHIFT); |
797 |
} |
798 |
|
799 |
/** |
800 |
* Returns the number of parties registered at this phaser. |
801 |
* |
802 |
* @return the number of parties |
803 |
*/ |
804 |
public int getRegisteredParties() { |
805 |
return partiesOf(state); |
806 |
} |
807 |
|
808 |
/** |
809 |
* Returns the number of registered parties that have arrived at |
810 |
* the current phase of this phaser. |
811 |
* |
812 |
* @return the number of arrived parties |
813 |
*/ |
814 |
public int getArrivedParties() { |
815 |
return arrivedOf(reconcileState()); |
816 |
} |
817 |
|
818 |
/** |
819 |
* Returns the number of registered parties that have not yet |
820 |
* arrived at the current phase of this phaser. |
821 |
* |
822 |
* @return the number of unarrived parties |
823 |
*/ |
824 |
public int getUnarrivedParties() { |
825 |
return unarrivedOf(reconcileState()); |
826 |
} |
827 |
|
828 |
/** |
829 |
* Returns the parent of this phaser, or {@code null} if none. |
830 |
* |
831 |
* @return the parent of this phaser, or {@code null} if none |
832 |
*/ |
833 |
public Phaser getParent() { |
834 |
return parent; |
835 |
} |
836 |
|
837 |
/** |
838 |
* Returns the root ancestor of this phaser, which is the same as |
839 |
* this phaser if it has no parent. |
840 |
* |
841 |
* @return the root ancestor of this phaser |
842 |
*/ |
843 |
public Phaser getRoot() { |
844 |
return root; |
845 |
} |
846 |
|
847 |
/** |
848 |
* Returns {@code true} if this phaser has been terminated. |
849 |
* |
850 |
* @return {@code true} if this phaser has been terminated |
851 |
*/ |
852 |
public boolean isTerminated() { |
853 |
return root.state < 0L; |
854 |
} |
855 |
|
856 |
/** |
857 |
* Overridable method to perform an action upon impending phase |
858 |
* advance, and to control termination. This method is invoked |
859 |
* upon arrival of the party advancing this phaser (when all other |
860 |
* waiting parties are dormant). If this method returns {@code |
861 |
* true}, this phaser will be set to a final termination state |
862 |
* upon advance, and subsequent calls to {@link #isTerminated} |
863 |
* will return true. Any (unchecked) Exception or Error thrown by |
864 |
* an invocation of this method is propagated to the party |
865 |
* attempting to advance this phaser, in which case no advance |
866 |
* occurs. |
867 |
* |
868 |
* <p>The arguments to this method provide the state of the phaser |
869 |
* prevailing for the current transition. The effects of invoking |
870 |
* arrival, registration, and waiting methods on this phaser from |
871 |
* within {@code onAdvance} are unspecified and should not be |
872 |
* relied on. |
873 |
* |
874 |
* <p>If this phaser is a member of a tiered set of phasers, then |
875 |
* {@code onAdvance} is invoked only for its root phaser on each |
876 |
* advance. |
877 |
* |
878 |
* <p>To support the most common use cases, the default |
879 |
* implementation of this method returns {@code true} when the |
880 |
* number of registered parties has become zero as the result of a |
881 |
* party invoking {@code arriveAndDeregister}. You can disable |
882 |
* this behavior, thus enabling continuation upon future |
883 |
* registrations, by overriding this method to always return |
884 |
* {@code false}: |
885 |
* |
886 |
* <pre> {@code |
887 |
* Phaser phaser = new Phaser() { |
888 |
* protected boolean onAdvance(int phase, int parties) { return false; } |
889 |
* }}</pre> |
890 |
* |
891 |
* @param phase the current phase number on entry to this method, |
892 |
* before this phaser is advanced |
893 |
* @param registeredParties the current number of registered parties |
894 |
* @return {@code true} if this phaser should terminate |
895 |
*/ |
896 |
protected boolean onAdvance(int phase, int registeredParties) { |
897 |
return registeredParties == 0; |
898 |
} |
899 |
|
900 |
/** |
901 |
* Returns a string identifying this phaser, as well as its |
902 |
* state. The state, in brackets, includes the String {@code |
903 |
* "phase = "} followed by the phase number, {@code "parties = "} |
904 |
* followed by the number of registered parties, and {@code |
905 |
* "arrived = "} followed by the number of arrived parties. |
906 |
* |
907 |
* @return a string identifying this phaser, as well as its state |
908 |
*/ |
909 |
public String toString() { |
910 |
return stateToString(reconcileState()); |
911 |
} |
912 |
|
913 |
/** |
914 |
* Implementation of toString and string-based error messages |
915 |
*/ |
916 |
private String stateToString(long s) { |
917 |
return super.toString() + |
918 |
"[phase = " + phaseOf(s) + |
919 |
" parties = " + partiesOf(s) + |
920 |
" arrived = " + arrivedOf(s) + "]"; |
921 |
} |
922 |
|
923 |
// Waiting mechanics |
924 |
|
925 |
/** |
926 |
* Removes and signals threads from queue for phase. |
927 |
*/ |
928 |
private void releaseWaiters(int phase) { |
929 |
QNode q; // first element of queue |
930 |
Thread t; // its thread |
931 |
AtomicReference<QNode> head = (phase & 1) == 0 ? evenQ : oddQ; |
932 |
while ((q = head.get()) != null && |
933 |
q.phase != (int)(root.state >>> PHASE_SHIFT)) { |
934 |
if (head.compareAndSet(q, q.next) && |
935 |
(t = q.thread) != null) { |
936 |
q.thread = null; |
937 |
LockSupport.unpark(t); |
938 |
} |
939 |
} |
940 |
} |
941 |
|
942 |
/** |
943 |
* Variant of releaseWaiters that additionally tries to remove any |
944 |
* nodes no longer waiting for advance due to timeout or |
945 |
* interrupt. Currently, nodes are removed only if they are at |
946 |
* head of queue, which suffices to reduce memory footprint in |
947 |
* most usages. |
948 |
* |
949 |
* @return current phase on exit |
950 |
*/ |
951 |
private int abortWait(int phase) { |
952 |
AtomicReference<QNode> head = (phase & 1) == 0 ? evenQ : oddQ; |
953 |
for (;;) { |
954 |
Thread t; |
955 |
QNode q = head.get(); |
956 |
int p = (int)(root.state >>> PHASE_SHIFT); |
957 |
if (q == null || ((t = q.thread) != null && q.phase == p)) |
958 |
return p; |
959 |
if (head.compareAndSet(q, q.next) && t != null) { |
960 |
q.thread = null; |
961 |
LockSupport.unpark(t); |
962 |
} |
963 |
} |
964 |
} |
965 |
|
966 |
/** The number of CPUs, for spin control */ |
967 |
private static final int NCPU = Runtime.getRuntime().availableProcessors(); |
968 |
|
969 |
/** |
970 |
* The number of times to spin before blocking while waiting for |
971 |
* advance, per arrival while waiting. On multiprocessors, fully |
972 |
* blocking and waking up a large number of threads all at once is |
973 |
* usually a very slow process, so we use rechargeable spins to |
974 |
* avoid it when threads regularly arrive: When a thread in |
975 |
* internalAwaitAdvance notices another arrival before blocking, |
976 |
* and there appear to be enough CPUs available, it spins |
977 |
* SPINS_PER_ARRIVAL more times before blocking. The value trades |
978 |
* off good-citizenship vs big unnecessary slowdowns. |
979 |
*/ |
980 |
static final int SPINS_PER_ARRIVAL = (NCPU < 2) ? 1 : 1 << 8; |
981 |
|
982 |
/** |
983 |
* Possibly blocks and waits for phase to advance unless aborted. |
984 |
* Call only from root node. |
985 |
* |
986 |
* @param phase current phase |
987 |
* @param node if non-null, the wait node to track interrupt and timeout; |
988 |
* if null, denotes noninterruptible wait |
989 |
* @return current phase |
990 |
*/ |
991 |
private int internalAwaitAdvance(int phase, QNode node) { |
992 |
releaseWaiters(phase-1); // ensure old queue clean |
993 |
boolean queued = false; // true when node is enqueued |
994 |
int lastUnarrived = 0; // to increase spins upon change |
995 |
int spins = SPINS_PER_ARRIVAL; |
996 |
long s; |
997 |
int p; |
998 |
while ((p = (int)((s = state) >>> PHASE_SHIFT)) == phase) { |
999 |
if (node == null) { // spinning in noninterruptible mode |
1000 |
int unarrived = (int)s & UNARRIVED_MASK; |
1001 |
if (unarrived != lastUnarrived && |
1002 |
(lastUnarrived = unarrived) < NCPU) |
1003 |
spins += SPINS_PER_ARRIVAL; |
1004 |
boolean interrupted = Thread.interrupted(); |
1005 |
if (interrupted || --spins < 0) { // need node to record intr |
1006 |
node = new QNode(this, phase, false, false, 0L); |
1007 |
node.wasInterrupted = interrupted; |
1008 |
} |
1009 |
} |
1010 |
else if (node.isReleasable()) // done or aborted |
1011 |
break; |
1012 |
else if (!queued) { // push onto queue |
1013 |
AtomicReference<QNode> head = (phase & 1) == 0 ? evenQ : oddQ; |
1014 |
QNode q = node.next = head.get(); |
1015 |
if ((q == null || q.phase == phase) && |
1016 |
(int)(state >>> PHASE_SHIFT) == phase) // avoid stale enq |
1017 |
queued = head.compareAndSet(q, node); |
1018 |
} |
1019 |
else { |
1020 |
try { |
1021 |
ForkJoinPool.managedBlock(node); |
1022 |
} catch (InterruptedException ie) { |
1023 |
node.wasInterrupted = true; |
1024 |
} |
1025 |
} |
1026 |
} |
1027 |
|
1028 |
if (node != null) { |
1029 |
if (node.thread != null) |
1030 |
node.thread = null; // avoid need for unpark() |
1031 |
if (node.wasInterrupted && !node.interruptible) |
1032 |
Thread.currentThread().interrupt(); |
1033 |
if (p == phase && (p = (int)(state >>> PHASE_SHIFT)) == phase) |
1034 |
return abortWait(phase); // possibly clean up on abort |
1035 |
} |
1036 |
releaseWaiters(phase); |
1037 |
return p; |
1038 |
} |
1039 |
|
1040 |
/** |
1041 |
* Wait nodes for Treiber stack representing wait queue |
1042 |
*/ |
1043 |
static final class QNode implements ForkJoinPool.ManagedBlocker { |
1044 |
final Phaser phaser; |
1045 |
final int phase; |
1046 |
final boolean interruptible; |
1047 |
final boolean timed; |
1048 |
boolean wasInterrupted; |
1049 |
long nanos; |
1050 |
long lastTime; |
1051 |
volatile Thread thread; // nulled to cancel wait |
1052 |
QNode next; |
1053 |
|
1054 |
QNode(Phaser phaser, int phase, boolean interruptible, |
1055 |
boolean timed, long nanos) { |
1056 |
this.phaser = phaser; |
1057 |
this.phase = phase; |
1058 |
this.interruptible = interruptible; |
1059 |
this.nanos = nanos; |
1060 |
this.timed = timed; |
1061 |
this.lastTime = timed ? System.nanoTime() : 0L; |
1062 |
thread = Thread.currentThread(); |
1063 |
} |
1064 |
|
1065 |
public boolean isReleasable() { |
1066 |
if (thread == null) |
1067 |
return true; |
1068 |
if (phaser.getPhase() != phase) { |
1069 |
thread = null; |
1070 |
return true; |
1071 |
} |
1072 |
if (Thread.interrupted()) |
1073 |
wasInterrupted = true; |
1074 |
if (wasInterrupted && interruptible) { |
1075 |
thread = null; |
1076 |
return true; |
1077 |
} |
1078 |
if (timed) { |
1079 |
if (nanos > 0L) { |
1080 |
long now = System.nanoTime(); |
1081 |
nanos -= now - lastTime; |
1082 |
lastTime = now; |
1083 |
} |
1084 |
if (nanos <= 0L) { |
1085 |
thread = null; |
1086 |
return true; |
1087 |
} |
1088 |
} |
1089 |
return false; |
1090 |
} |
1091 |
|
1092 |
public boolean block() { |
1093 |
if (isReleasable()) |
1094 |
return true; |
1095 |
else if (!timed) |
1096 |
LockSupport.park(this); |
1097 |
else if (nanos > 0) |
1098 |
LockSupport.parkNanos(this, nanos); |
1099 |
return isReleasable(); |
1100 |
} |
1101 |
} |
1102 |
|
1103 |
// Unsafe mechanics |
1104 |
|
1105 |
private static final sun.misc.Unsafe UNSAFE = getUnsafe(); |
1106 |
private static final long stateOffset = |
1107 |
objectFieldOffset("state", Phaser.class); |
1108 |
|
1109 |
private static long objectFieldOffset(String field, Class<?> klazz) { |
1110 |
try { |
1111 |
return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field)); |
1112 |
} catch (NoSuchFieldException e) { |
1113 |
// Convert Exception to corresponding Error |
1114 |
NoSuchFieldError error = new NoSuchFieldError(field); |
1115 |
error.initCause(e); |
1116 |
throw error; |
1117 |
} |
1118 |
} |
1119 |
|
1120 |
/** |
1121 |
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. |
1122 |
* Replace with a simple call to Unsafe.getUnsafe when integrating |
1123 |
* into a jdk. |
1124 |
* |
1125 |
* @return a sun.misc.Unsafe |
1126 |
*/ |
1127 |
private static sun.misc.Unsafe getUnsafe() { |
1128 |
try { |
1129 |
return sun.misc.Unsafe.getUnsafe(); |
1130 |
} catch (SecurityException se) { |
1131 |
try { |
1132 |
return java.security.AccessController.doPrivileged |
1133 |
(new java.security |
1134 |
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
1135 |
public sun.misc.Unsafe run() throws Exception { |
1136 |
java.lang.reflect.Field f = sun.misc |
1137 |
.Unsafe.class.getDeclaredField("theUnsafe"); |
1138 |
f.setAccessible(true); |
1139 |
return (sun.misc.Unsafe) f.get(null); |
1140 |
}}); |
1141 |
} catch (java.security.PrivilegedActionException e) { |
1142 |
throw new RuntimeException("Could not initialize intrinsics", |
1143 |
e.getCause()); |
1144 |
} |
1145 |
} |
1146 |
} |
1147 |
} |