| 19 |
|
* |
| 20 |
|
* <ul> |
| 21 |
|
* |
| 22 |
< |
* <li> The number of parties synchronizing on a phaser may vary over |
| 23 |
< |
* time. A task may register to be a party at any time, and may |
| 24 |
< |
* deregister upon arriving at the barrier. As is the case with most |
| 25 |
< |
* basic synchronization constructs, registration and deregistration |
| 26 |
< |
* affect only internal counts; they do not establish any further |
| 27 |
< |
* internal bookkeeping, so tasks cannot query whether they are |
| 22 |
> |
* <li> The number of parties <em>registered</em> to synchronize on a |
| 23 |
> |
* phaser may vary over time. Tasks may be registered at any time |
| 24 |
> |
* (using methods {@link #register}, {@link #bulkRegister}, or forms |
| 25 |
> |
* of constructors establishing initial numbers of parties), and may |
| 26 |
> |
* optionally be deregistered upon any arrival (using {@link |
| 27 |
> |
* #arriveAndDeregister}). As is the case with most basic |
| 28 |
> |
* synchronization constructs, registration and deregistration affect |
| 29 |
> |
* only internal counts; they do not establish any further internal |
| 30 |
> |
* bookkeeping, so tasks cannot query whether they are |
| 31 |
|
* registered. (However, you can introduce such bookkeeping by |
| 32 |
|
* subclassing this class.) |
| 33 |
|
* |
| 34 |
< |
* <li> Each generation has an associated phase value, starting at |
| 35 |
< |
* zero, and advancing when all parties reach the barrier (wrapping |
| 36 |
< |
* around to zero after reaching {@code Integer.MAX_VALUE}). |
| 34 |
> |
* <li> Each generation has an associated phase number. The phase |
| 35 |
> |
* number starts at zero, amd advances when all parties arrive at the |
| 36 |
> |
* barrier, wrapping around to zero after reaching {@code |
| 37 |
> |
* Integer.MAX_VALUE}. |
| 38 |
|
* |
| 39 |
< |
* <li> Like a {@code CyclicBarrier}, a Phaser may be repeatedly |
| 39 |
> |
* <li> Like a {@code CyclicBarrier}, a phaser may be repeatedly |
| 40 |
|
* awaited. Method {@link #arriveAndAwaitAdvance} has effect |
| 41 |
|
* analogous to {@link java.util.concurrent.CyclicBarrier#await |
| 42 |
|
* CyclicBarrier.await}. However, phasers separate two aspects of |
| 43 |
< |
* coordination, that may also be invoked independently: |
| 43 |
> |
* coordination, which may also be invoked independently: |
| 44 |
|
* |
| 45 |
|
* <ul> |
| 46 |
|
* |
| 47 |
|
* <li> Arriving at a barrier. Methods {@link #arrive} and |
| 48 |
|
* {@link #arriveAndDeregister} do not block, but return |
| 49 |
< |
* the phase value current upon entry to the method. |
| 49 |
> |
* an associated <em>arrival phase number</em>; |
| 50 |
> |
* that is, the phase number of the barrier to which the |
| 51 |
> |
* arrival applied. |
| 52 |
|
* |
| 53 |
|
* <li> Awaiting others. Method {@link #awaitAdvance} requires an |
| 54 |
< |
* argument indicating the entry phase, and returns when the |
| 55 |
< |
* barrier advances to a new phase. |
| 54 |
> |
* argument indicating an arrival phase number, and returns |
| 55 |
> |
* when the barrier advances to a new phase. |
| 56 |
|
* </ul> |
| 57 |
|
* |
| 52 |
– |
* |
| 58 |
|
* <li> Barrier actions, performed by the task triggering a phase |
| 59 |
< |
* advance while others may be waiting, are arranged by overriding |
| 60 |
< |
* method {@link #onAdvance}, that also controls termination. |
| 61 |
< |
* Overriding this method may be used to similar but more flexible |
| 62 |
< |
* effect as providing a barrier action to a {@code CyclicBarrier}. |
| 59 |
> |
* advance, are arranged by overriding method {@link #onAdvance(int, |
| 60 |
> |
* int)}, which also controls termination. Overriding this method is |
| 61 |
> |
* similar to, but more flexible than, providing a barrier action to a |
| 62 |
> |
* {@code CyclicBarrier}. |
| 63 |
|
* |
| 64 |
|
* <li> Phasers may enter a <em>termination</em> state in which all |
| 65 |
|
* actions immediately return without updating phaser state or waiting |
| 66 |
|
* for advance, and indicating (via a negative phase value) that |
| 67 |
< |
* execution is complete. Termination is triggered by executing the |
| 68 |
< |
* overridable {@code onAdvance} method that is invoked each time the |
| 69 |
< |
* barrier is about to be tripped. When a phaser is controlling an |
| 70 |
< |
* action with a fixed number of iterations, it is often convenient to |
| 71 |
< |
* override this method to cause termination when the current phase |
| 72 |
< |
* number reaches a threshold. Method {@link #forceTermination} is also |
| 73 |
< |
* available to abruptly release waiting threads and allow them to |
| 69 |
< |
* terminate. |
| 67 |
> |
* execution is complete. Termination is triggered when an invocation |
| 68 |
> |
* of {@code onAdvance} returns {@code true}. When a phaser is |
| 69 |
> |
* controlling an action with a fixed number of iterations, it is |
| 70 |
> |
* often convenient to override this method to cause termination when |
| 71 |
> |
* the current phase number reaches a threshold. Method {@link |
| 72 |
> |
* #forceTermination} is also available to abruptly release waiting |
| 73 |
> |
* threads and allow them to terminate. |
| 74 |
|
* |
| 75 |
|
* <li> Phasers may be tiered to reduce contention. Phasers with large |
| 76 |
|
* numbers of parties that would otherwise experience heavy |
| 86 |
|
* within handlers of those exceptions, often after invoking |
| 87 |
|
* {@code forceTermination}. |
| 88 |
|
* |
| 89 |
< |
* <li>Phasers ensure lack of starvation when used by ForkJoinTasks. |
| 89 |
> |
* <li>Phasers may be used to coordinate tasks executing in a {@link |
| 90 |
> |
* ForkJoinPool}, which will ensure sufficient parallelism to execute |
| 91 |
> |
* tasks when others are blocked waiting for a phase to advance. |
| 92 |
> |
* |
| 93 |
> |
* <li>The current state of a phaser may be monitored. At any given |
| 94 |
> |
* moment there are {@link #getRegisteredParties}, where {@link |
| 95 |
> |
* #getArrivedParties} have arrived at the current phase ({@link |
| 96 |
> |
* #getPhase}). When the remaining {@link #getUnarrivedParties}) |
| 97 |
> |
* arrive, the phase advances. Method {@link #toString} returns |
| 98 |
> |
* snapshots of these state queries in a form convenient for |
| 99 |
> |
* informal monitoring. |
| 100 |
|
* |
| 101 |
|
* </ul> |
| 102 |
|
* |
| 108 |
|
* first register, then start the actions, then deregister, as in: |
| 109 |
|
* |
| 110 |
|
* <pre> {@code |
| 111 |
< |
* void runTasks(List<Runnable> list) { |
| 111 |
> |
* void runTasks(List<Runnable> tasks) { |
| 112 |
|
* final Phaser phaser = new Phaser(1); // "1" to register self |
| 113 |
< |
* for (Runnable r : list) { |
| 113 |
> |
* // create and start threads |
| 114 |
> |
* for (Runnable task : tasks) { |
| 115 |
|
* phaser.register(); |
| 116 |
|
* new Thread() { |
| 117 |
|
* public void run() { |
| 118 |
|
* phaser.arriveAndAwaitAdvance(); // await all creation |
| 119 |
< |
* r.run(); |
| 105 |
< |
* phaser.arriveAndDeregister(); // signal completion |
| 119 |
> |
* task.run(); |
| 120 |
|
* } |
| 121 |
|
* }.start(); |
| 122 |
|
* } |
| 123 |
|
* |
| 124 |
< |
* doSomethingOnBehalfOfWorkers(); |
| 125 |
< |
* phaser.arrive(); // allow threads to start |
| 112 |
< |
* int p = phaser.arriveAndDeregister(); // deregister self ... |
| 113 |
< |
* p = phaser.awaitAdvance(p); // ... and await arrival |
| 114 |
< |
* otherActions(); // do other things while tasks execute |
| 115 |
< |
* phaser.awaitAdvance(p); // await final completion |
| 124 |
> |
* // allow threads to start and deregister self |
| 125 |
> |
* phaser.arriveAndDeregister(); |
| 126 |
|
* }}</pre> |
| 127 |
|
* |
| 128 |
|
* <p>One way to cause a set of threads to repeatedly perform actions |
| 129 |
|
* for a given number of iterations is to override {@code onAdvance}: |
| 130 |
|
* |
| 131 |
|
* <pre> {@code |
| 132 |
< |
* void startTasks(List<Runnable> list, final int iterations) { |
| 132 |
> |
* void startTasks(List<Runnable> tasks, final int iterations) { |
| 133 |
|
* final Phaser phaser = new Phaser() { |
| 134 |
|
* public boolean onAdvance(int phase, int registeredParties) { |
| 135 |
|
* return phase >= iterations || registeredParties == 0; |
| 136 |
|
* } |
| 137 |
|
* }; |
| 138 |
|
* phaser.register(); |
| 139 |
< |
* for (Runnable r : list) { |
| 139 |
> |
* for (Runnable task : tasks) { |
| 140 |
|
* phaser.register(); |
| 141 |
|
* new Thread() { |
| 142 |
|
* public void run() { |
| 143 |
|
* do { |
| 144 |
< |
* r.run(); |
| 144 |
> |
* task.run(); |
| 145 |
|
* phaser.arriveAndAwaitAdvance(); |
| 146 |
|
* } while(!phaser.isTerminated(); |
| 147 |
|
* } |
| 182 |
|
* |
| 183 |
|
* <p><b>Implementation notes</b>: This implementation restricts the |
| 184 |
|
* maximum number of parties to 65535. Attempts to register additional |
| 185 |
< |
* parties result in IllegalStateExceptions. However, you can and |
| 185 |
> |
* parties result in {@code IllegalStateException}. However, you can and |
| 186 |
|
* should create tiered phasers to accommodate arbitrarily large sets |
| 187 |
|
* of participants. |
| 188 |
|
* |
| 379 |
|
/** |
| 380 |
|
* Adds a new unarrived party to this phaser. |
| 381 |
|
* |
| 382 |
< |
* @return the current barrier phase number upon registration |
| 382 |
> |
* @return the arrival phase number to which this registration applied |
| 383 |
|
* @throws IllegalStateException if attempting to register more |
| 384 |
|
* than the maximum supported number of parties |
| 385 |
|
*/ |
| 391 |
|
* Adds the given number of new unarrived parties to this phaser. |
| 392 |
|
* |
| 393 |
|
* @param parties the number of parties required to trip barrier |
| 394 |
< |
* @return the current barrier phase number upon registration |
| 394 |
> |
* @return the arrival phase number to which this registration applied |
| 395 |
|
* @throws IllegalStateException if attempting to register more |
| 396 |
|
* than the maximum supported number of parties |
| 397 |
|
*/ |
| 428 |
|
* Arrives at the barrier, but does not wait for others. (You can |
| 429 |
|
* in turn wait for others via {@link #awaitAdvance}). |
| 430 |
|
* |
| 431 |
< |
* @return the barrier phase number upon entry to this method, or a |
| 422 |
< |
* negative value if terminated |
| 431 |
> |
* @return the arrival phase number, or a negative value if terminated |
| 432 |
|
* @throws IllegalStateException if not terminated and the number |
| 433 |
|
* of unarrived parties would become negative |
| 434 |
|
*/ |
| 473 |
|
} |
| 474 |
|
|
| 475 |
|
/** |
| 476 |
< |
* Arrives at the barrier, and deregisters from it, without |
| 477 |
< |
* waiting for others. Deregistration reduces number of parties |
| 476 |
> |
* Arrives at the barrier and deregisters from it without waiting |
| 477 |
> |
* for others. Deregistration reduces the number of parties |
| 478 |
|
* required to trip the barrier in future phases. If this phaser |
| 479 |
|
* has a parent, and deregistration causes this phaser to have |
| 480 |
< |
* zero parties, this phaser is also deregistered from its parent. |
| 480 |
> |
* zero parties, this phaser also arrives at and is deregistered |
| 481 |
> |
* from its parent. |
| 482 |
|
* |
| 483 |
< |
* @return the current barrier phase number upon entry to |
| 474 |
< |
* this method, or a negative value if terminated |
| 483 |
> |
* @return the arrival phase number, or a negative value if terminated |
| 484 |
|
* @throws IllegalStateException if not terminated and the number |
| 485 |
|
* of registered or unarrived parties would become negative |
| 486 |
|
*/ |
| 530 |
|
|
| 531 |
|
/** |
| 532 |
|
* Arrives at the barrier and awaits others. Equivalent in effect |
| 533 |
< |
* to {@code awaitAdvance(arrive())}. If you instead need to |
| 534 |
< |
* await with interruption of timeout, and/or deregister upon |
| 535 |
< |
* arrival, you can arrange them using analogous constructions. |
| 533 |
> |
* to {@code awaitAdvance(arrive())}. If you need to await with |
| 534 |
> |
* interruption or timeout, you can arrange this with an analogous |
| 535 |
> |
* construction using one of the other forms of the awaitAdvance |
| 536 |
> |
* method. If instead you need to deregister upon arrival use |
| 537 |
> |
* {@code arriveAndDeregister}. |
| 538 |
|
* |
| 539 |
< |
* @return the phase on entry to this method |
| 539 |
> |
* @return the arrival phase number, or a negative number if terminated |
| 540 |
|
* @throws IllegalStateException if not terminated and the number |
| 541 |
|
* of unarrived parties would become negative |
| 542 |
|
*/ |
| 545 |
|
} |
| 546 |
|
|
| 547 |
|
/** |
| 548 |
< |
* Awaits the phase of the barrier to advance from the given |
| 549 |
< |
* value, or returns immediately if argument is negative or this |
| 550 |
< |
* barrier is terminated. |
| 551 |
< |
* |
| 552 |
< |
* @param phase the phase on entry to this method |
| 553 |
< |
* @return the phase on exit from this method |
| 548 |
> |
* Awaits the phase of the barrier to advance from the given phase |
| 549 |
> |
* value, returning immediately if the current phase of the |
| 550 |
> |
* barrier is not equal to the given phase value or this barrier |
| 551 |
> |
* is terminated. |
| 552 |
> |
* |
| 553 |
> |
* @param phase an arrival phase number, or negative value if |
| 554 |
> |
* terminated; this argument is normally the value returned by a |
| 555 |
> |
* previous call to {@code arrive} or its variants |
| 556 |
> |
* @return the next arrival phase number, or a negative value |
| 557 |
> |
* if terminated or argument is negative |
| 558 |
|
*/ |
| 559 |
|
public int awaitAdvance(int phase) { |
| 560 |
|
if (phase < 0) |
| 570 |
|
} |
| 571 |
|
|
| 572 |
|
/** |
| 573 |
< |
* Awaits the phase of the barrier to advance from the given |
| 574 |
< |
* value, or returns immediately if argument is negative or this |
| 575 |
< |
* barrier is terminated, or throws InterruptedException if |
| 576 |
< |
* interrupted while waiting. |
| 577 |
< |
* |
| 578 |
< |
* @param phase the phase on entry to this method |
| 579 |
< |
* @return the phase on exit from this method |
| 573 |
> |
* Awaits the phase of the barrier to advance from the given phase |
| 574 |
> |
* value, throwing {@code InterruptedException} if interrupted while |
| 575 |
> |
* waiting, or returning immediately if the current phase of the |
| 576 |
> |
* barrier is not equal to the given phase value or this barrier |
| 577 |
> |
* is terminated. |
| 578 |
> |
* |
| 579 |
> |
* @param phase an arrival phase number, or negative value if |
| 580 |
> |
* terminated; this argument is normally the value returned by a |
| 581 |
> |
* previous call to {@code arrive} or its variants |
| 582 |
> |
* @return the next arrival phase number, or a negative value |
| 583 |
> |
* if terminated or argument is negative |
| 584 |
|
* @throws InterruptedException if thread interrupted while waiting |
| 585 |
|
*/ |
| 586 |
|
public int awaitAdvanceInterruptibly(int phase) |
| 597 |
|
} |
| 598 |
|
|
| 599 |
|
/** |
| 600 |
< |
* Awaits the phase of the barrier to advance from the given value |
| 601 |
< |
* or the given timeout elapses, or returns immediately if |
| 602 |
< |
* argument is negative or this barrier is terminated. |
| 603 |
< |
* |
| 604 |
< |
* @param phase the phase on entry to this method |
| 605 |
< |
* @return the phase on exit from this method |
| 600 |
> |
* Awaits the phase of the barrier to advance from the given phase |
| 601 |
> |
* value or the given timeout to elapse, throwing |
| 602 |
> |
* {@code InterruptedException} if interrupted while waiting, or |
| 603 |
> |
* returning immediately if the current phase of the barrier is not |
| 604 |
> |
* equal to the given phase value or this barrier is terminated. |
| 605 |
> |
* |
| 606 |
> |
* @param phase an arrival phase number, or negative value if |
| 607 |
> |
* terminated; this argument is normally the value returned by a |
| 608 |
> |
* previous call to {@code arrive} or its variants |
| 609 |
> |
* @param timeout how long to wait before giving up, in units of |
| 610 |
> |
* {@code unit} |
| 611 |
> |
* @param unit a {@code TimeUnit} determining how to interpret the |
| 612 |
> |
* {@code timeout} parameter |
| 613 |
> |
* @return the next arrival phase number, or a negative value |
| 614 |
> |
* if terminated or argument is negative |
| 615 |
|
* @throws InterruptedException if thread interrupted while waiting |
| 616 |
|
* @throws TimeoutException if timed out while waiting |
| 617 |
|
*/ |
| 665 |
|
} |
| 666 |
|
|
| 667 |
|
/** |
| 640 |
– |
* Returns {@code true} if the current phase number equals the given phase. |
| 641 |
– |
* |
| 642 |
– |
* @param phase the phase |
| 643 |
– |
* @return {@code true} if the current phase number equals the given phase |
| 644 |
– |
*/ |
| 645 |
– |
public final boolean hasPhase(int phase) { |
| 646 |
– |
return phaseOf(getReconciledState()) == phase; |
| 647 |
– |
} |
| 648 |
– |
|
| 649 |
– |
/** |
| 668 |
|
* Returns the number of parties registered at this barrier. |
| 669 |
|
* |
| 670 |
|
* @return the number of parties |
| 674 |
|
} |
| 675 |
|
|
| 676 |
|
/** |
| 677 |
< |
* Returns the number of parties that have arrived at the current |
| 678 |
< |
* phase of this barrier. |
| 677 |
> |
* Returns the number of registered parties that have arrived at |
| 678 |
> |
* the current phase of this barrier. |
| 679 |
|
* |
| 680 |
|
* @return the number of arrived parties |
| 681 |
|
*/ |
| 739 |
|
* effects visible to participating tasks, but it is in general |
| 740 |
|
* only sensible to do so in designs where all parties register |
| 741 |
|
* before any arrive, and all {@link #awaitAdvance} at each phase. |
| 742 |
< |
* Otherwise, you cannot ensure lack of interference. In |
| 743 |
< |
* particular, this method may be invoked more than once per |
| 726 |
< |
* transition if other parties successfully register while the |
| 727 |
< |
* invocation of this method is in progress, thus postponing the |
| 728 |
< |
* transition until those parties also arrive, re-triggering this |
| 729 |
< |
* method. |
| 742 |
> |
* Otherwise, you cannot ensure lack of interference from other |
| 743 |
> |
* parties during the invocation of this method. |
| 744 |
|
* |
| 745 |
|
* @param phase the phase number on entering the barrier |
| 746 |
|
* @param registeredParties the current number of registered parties |
