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import java.util.concurrent.locks.LockSupport; |
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/** |
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* A reusable synchronization barrier, similar in functionality to a |
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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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* <ul> |
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* |
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* <li> The number of parties synchronizing on a phaser may vary over |
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* time. A task may register to be a party at any time, and may |
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* deregister upon arriving at the barrier. As is the case with most |
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* basic synchronization constructs, registration and deregistration |
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* affect only internal counts; they do not establish any further |
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* internal bookkeeping, so tasks cannot query whether they are |
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* registered. (However, you can introduce such bookkeeping by |
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* subclassing this class.) |
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* |
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* <li> Each generation has an associated phase value, starting at |
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* zero, and advancing when all parties reach the barrier (wrapping |
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* around to zero after reaching {@code Integer.MAX_VALUE}). |
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* <li> The number of parties <em>registered</em> to synchronize on a |
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* phaser may vary over time. Tasks may be registered at any time |
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* (using methods {@link #register}, {@link #bulkRegister}, or forms |
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* of constructors establishing initial numbers of parties), and may |
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* optionally be 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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* <li> Each generation has an associated phase number. The phase |
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* number starts at zero, amd advances when all parties arrive at the |
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* barrier, wrapping around to zero after reaching {@code |
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* Integer.MAX_VALUE}. |
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* |
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* <li> Like a {@code CyclicBarrier}, a phaser may be repeatedly |
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* awaited. Method {@link #arriveAndAwaitAdvance} has effect |
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* |
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* <li> Arriving at a barrier. Methods {@link #arrive} and |
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* {@link #arriveAndDeregister} do not block, but return |
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* the phase value current upon entry to the method. |
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* an associated <em>arrival phase number</em>; |
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* that is, the phase number of the barrier to which the |
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* arrival applied. |
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* |
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* <li> Awaiting others. Method {@link #awaitAdvance} requires an |
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* argument indicating the entry phase, and returns when the |
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* barrier advances to a new phase. |
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* argument indicating an arrival phase number, and returns |
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* when the barrier advances to a new phase. |
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* </ul> |
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* |
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* |
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* <li> Barrier actions, performed by the task triggering a phase |
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* advance, are arranged by overriding method {@link #onAdvance(int, |
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* int)}, which also controls termination. Overriding this method is |
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* ForkJoinPool}, which will ensure sufficient parallelism to execute |
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* tasks when others are blocked waiting for a phase to advance. |
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* |
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* <li>The current state of a phaser may be monitored. At any given |
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* moment there are {@link #getRegisteredParties}, where {@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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* arrive, the phase advances. Method {@link #toString} returns |
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* snapshots of these state queries in a form convenient for |
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* informal monitoring. |
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* |
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* </ul> |
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* |
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* <p><b>Sample usages:</b> |
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* first 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> list) { |
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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 r : list) { |
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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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* r.run(); |
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* task.run(); |
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* } |
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* }.start(); |
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* } |
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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> list, final int iterations) { |
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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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* public 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 (Runnable r : list) { |
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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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* do { |
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* r.run(); |
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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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* |
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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 IllegalStateExceptions. However, you can and |
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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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/** |
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* Adds a new unarrived party to this phaser. |
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* |
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* @return the current barrier phase number upon registration |
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* @return the arrival phase number to which this registration applied |
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* @throws IllegalStateException if attempting to register more |
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* than the maximum supported number of parties |
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*/ |
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* Adds the given number of new unarrived parties to this phaser. |
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* |
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* @param parties the number of parties required to trip barrier |
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* @return the current barrier phase number upon registration |
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* @return the arrival phase number to which this registration applied |
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* @throws IllegalStateException if attempting to register more |
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* than the maximum supported number of parties |
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*/ |
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* Arrives at the barrier, but does not wait for others. (You can |
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* in turn wait for others via {@link #awaitAdvance}). |
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* |
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* @return the barrier phase number upon entry to this method, or a |
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* negative value if terminated |
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* @return the arrival phase number, or a negative value if terminated |
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* @throws IllegalStateException if not terminated and the number |
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* of unarrived parties would become negative |
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*/ |
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* zero parties, this phaser also arrives at and is deregistered |
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* from its parent. |
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* |
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* @return the current barrier phase number upon entry to |
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* this method, or a negative value if terminated |
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* @return the arrival phase number, or a negative value if terminated |
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* @throws IllegalStateException if not terminated and the number |
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* of registered or unarrived parties would become negative |
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*/ |
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* method. If instead you need to deregister upon arrival use |
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* {@code arriveAndDeregister}. |
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* |
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* @return the phase on entry to this method |
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* @return the arrival phase number, or a negative number if terminated |
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* @throws IllegalStateException if not terminated and the number |
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* of unarrived parties would become negative |
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*/ |
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/** |
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* Awaits the phase of the barrier to advance from the given phase |
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* value, or returns immediately if current phase of the barrier |
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* is not equal to the given phase value or this barrier is |
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* terminated. |
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* |
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* @param phase the phase on entry to this method |
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* @return the phase on exit from this method |
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* value, returning immediately if the current phase of the |
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* barrier is not equal to the given phase value or this barrier |
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* is terminated. |
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* |
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* @param phase an arrival phase number, or negative value if |
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* terminated; this argument is normally the value returned by a |
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* previous call to {@code arrive} or its variants |
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* @return the next arrival phase number, or a negative value |
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* if terminated or argument is negative |
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*/ |
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public int awaitAdvance(int phase) { |
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if (phase < 0) |
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} |
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/** |
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* Awaits the phase of the barrier to advance from the given |
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* value, or returns immediately if argument is negative or this |
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* barrier is terminated, or throws InterruptedException if |
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* interrupted while waiting. |
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* |
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* @param phase the phase on entry to this method |
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* @return the phase on exit from this method |
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* Awaits the phase of the barrier to advance from the given phase |
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* value, throwing {@code InterruptedException} if interrupted while |
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* waiting, or returning immediately if the current phase of the |
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* barrier is not equal to the given phase value or this barrier |
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* is terminated. |
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* |
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* @param phase an arrival phase number, or negative value if |
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* terminated; this argument is normally the value returned by a |
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* previous call to {@code arrive} or its variants |
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* @return the next arrival phase number, or a negative value |
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* if terminated or argument is negative |
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* @throws InterruptedException if thread interrupted while waiting |
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*/ |
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public int awaitAdvanceInterruptibly(int phase) |
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} |
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/** |
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* Awaits the phase of the barrier to advance from the given value |
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* or the given timeout elapses, or returns immediately if |
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* argument is negative or this barrier is terminated. |
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* |
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* @param phase the phase on entry to this method |
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* @return the phase on exit from this method |
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* Awaits the phase of the barrier to advance from the given phase |
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* value or the given timeout to elapse, throwing |
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* {@code InterruptedException} if interrupted while waiting, or |
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* returning immediately if the current phase of the barrier is not |
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* equal to the given phase value or this barrier is terminated. |
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* |
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* @param phase an arrival phase number, or negative value if |
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* terminated; this argument is normally the value returned by a |
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* previous call to {@code arrive} or its variants |
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* @param timeout how long to wait before giving up, in units of |
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* {@code unit} |
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* @param unit a {@code TimeUnit} determining how to interpret the |
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* {@code timeout} parameter |
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* @return the next arrival phase number, or a negative value |
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* if terminated or argument is negative |
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* @throws InterruptedException if thread interrupted while waiting |
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* @throws TimeoutException if timed out while waiting |
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*/ |
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} |
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/** |
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* Returns the number of parties that have arrived at the current |
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* phase of this barrier. |
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* Returns the number of registered parties that have arrived at |
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* the current phase of this barrier. |
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* |
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* @return the number of arrived parties |
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*/ |
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* only sensible to do so in designs where all parties register |
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* before any arrive, and all {@link #awaitAdvance} at each phase. |
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* Otherwise, you cannot ensure lack of interference from other |
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* parties during the the invocation of this method. |
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* parties during the invocation of this method. |
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* |
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* @param phase the phase number on entering the barrier |
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* @param registeredParties the current number of registered parties |