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|
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/** |
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* An {@link ExecutorService} for running {@link ForkJoinTask}s. |
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< |
* A ForkJoinPool provides the entry point for submissions from |
| 25 |
< |
* non-ForkJoinTasks, as well as management and monitoring operations. |
| 26 |
< |
* Normally a single ForkJoinPool is used for a large number of |
| 27 |
< |
* submitted tasks. Otherwise, use would not usually outweigh the |
| 28 |
< |
* construction and bookkeeping overhead of creating a large set of |
| 29 |
< |
* threads. |
| 24 |
> |
* A {@code ForkJoinPool} provides the entry point for submissions |
| 25 |
> |
* from non-{@code ForkJoinTask}s, as well as management and |
| 26 |
> |
* monitoring operations. Normally a single {@code ForkJoinPool} is |
| 27 |
> |
* used for a large number of submitted tasks. Otherwise, use would |
| 28 |
> |
* not usually outweigh the construction and bookkeeping overhead of |
| 29 |
> |
* creating a large set of threads. |
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* |
| 31 |
< |
* <p>ForkJoinPools differ from other kinds of Executors mainly in |
| 32 |
< |
* that they provide <em>work-stealing</em>: all threads in the pool |
| 33 |
< |
* attempt to find and execute subtasks created by other active tasks |
| 34 |
< |
* (eventually blocking if none exist). This makes them efficient when |
| 35 |
< |
* most tasks spawn other subtasks (as do most ForkJoinTasks), as well |
| 36 |
< |
* as the mixed execution of some plain Runnable- or Callable- based |
| 37 |
< |
* activities along with ForkJoinTasks. When setting {@linkplain |
| 38 |
< |
* #setAsyncMode async mode}, a ForkJoinPool may also be appropriate |
| 39 |
< |
* for use with fine-grained tasks that are never joined. Otherwise, |
| 40 |
< |
* other ExecutorService implementations are typically more |
| 31 |
> |
* <p>{@code ForkJoinPool}s differ from other kinds of {@link |
| 32 |
> |
* Executor}s mainly in that they provide <em>work-stealing</em>: all |
| 33 |
> |
* threads in the pool attempt to find and execute subtasks created by |
| 34 |
> |
* other active tasks (eventually blocking if none exist). This makes |
| 35 |
> |
* them efficient when most tasks spawn other subtasks (as do most |
| 36 |
> |
* {@code ForkJoinTask}s), as well as the mixed execution of some |
| 37 |
> |
* plain {@code Runnable}- or {@code Callable}- based activities along |
| 38 |
> |
* with {@code ForkJoinTask}s. When setting {@linkplain #setAsyncMode |
| 39 |
> |
* async mode}, a {@code ForkJoinPool} may also be appropriate for use |
| 40 |
> |
* with fine-grained tasks that are never joined. Otherwise, other |
| 41 |
> |
* {@code ExecutorService} implementations are typically more |
| 42 |
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* appropriate choices. |
| 43 |
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* |
| 44 |
< |
* <p>A ForkJoinPool may be constructed with a given parallelism level |
| 45 |
< |
* (target pool size), which it attempts to maintain by dynamically |
| 46 |
< |
* adding, suspending, or resuming threads, even if some tasks are |
| 47 |
< |
* waiting to join others. However, no such adjustments are performed |
| 48 |
< |
* in the face of blocked IO or other unmanaged synchronization. The |
| 49 |
< |
* nested {@link ManagedBlocker} interface enables extension of |
| 50 |
< |
* the kinds of synchronization accommodated. The target parallelism |
| 51 |
< |
* level may also be changed dynamically ({@link #setParallelism}) |
| 52 |
< |
* and thread construction can be limited using methods |
| 53 |
< |
* {@link #setMaximumPoolSize} and/or |
| 54 |
< |
* {@link #setMaintainsParallelism}. |
| 44 |
> |
* <p>A {@code ForkJoinPool} may be constructed with a given |
| 45 |
> |
* parallelism level (target pool size), which it attempts to maintain |
| 46 |
> |
* by dynamically adding, suspending, or resuming threads, even if |
| 47 |
> |
* some tasks are waiting to join others. However, no such adjustments |
| 48 |
> |
* are performed in the face of blocked IO or other unmanaged |
| 49 |
> |
* synchronization. The nested {@link ManagedBlocker} interface |
| 50 |
> |
* enables extension of the kinds of synchronization accommodated. |
| 51 |
> |
* The target parallelism level may also be changed dynamically |
| 52 |
> |
* ({@link #setParallelism}) and thread construction can be limited |
| 53 |
> |
* using methods {@link #setMaximumPoolSize} and/or {@link |
| 54 |
> |
* #setMaintainsParallelism}. |
| 55 |
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* |
| 56 |
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* <p>In addition to execution and lifecycle control methods, this |
| 57 |
|
* class provides status check methods (for example |
| 63 |
|
* <p><b>Implementation notes</b>: This implementation restricts the |
| 64 |
|
* maximum number of running threads to 32767. Attempts to create |
| 65 |
|
* pools with greater than the maximum result in |
| 66 |
< |
* IllegalArgumentExceptions. |
| 66 |
> |
* {@code IllegalArgumentException}. |
| 67 |
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* |
| 68 |
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* @since 1.7 |
| 69 |
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* @author Doug Lea |
| 82 |
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private static final int MAX_THREADS = 0x7FFF; |
| 83 |
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|
| 84 |
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/** |
| 85 |
< |
* Factory for creating new ForkJoinWorkerThreads. A |
| 86 |
< |
* ForkJoinWorkerThreadFactory must be defined and used for |
| 87 |
< |
* ForkJoinWorkerThread subclasses that extend base functionality |
| 88 |
< |
* or initialize threads with different contexts. |
| 85 |
> |
* Factory for creating new {@link ForkJoinWorkerThread}s. |
| 86 |
> |
* A {@code ForkJoinWorkerThreadFactory} must be defined and used |
| 87 |
> |
* for {@code ForkJoinWorkerThread} subclasses that extend base |
| 88 |
> |
* functionality or initialize threads with different contexts. |
| 89 |
|
*/ |
| 90 |
|
public static interface ForkJoinWorkerThreadFactory { |
| 91 |
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/** |
| 579 |
|
* @throws NullPointerException if task is null |
| 580 |
|
* @throws RejectedExecutionException if pool is shut down |
| 581 |
|
*/ |
| 582 |
< |
public <T> void execute(ForkJoinTask<T> task) { |
| 582 |
> |
public void execute(ForkJoinTask<?> task) { |
| 583 |
|
doSubmit(task); |
| 584 |
|
} |
| 585 |
|
|
| 788 |
|
* Setting this value has no effect on current pool size. It |
| 789 |
|
* controls construction of new threads. |
| 790 |
|
* |
| 791 |
< |
* @throws IllegalArgumentException if negative or greater then |
| 791 |
> |
* @throws IllegalArgumentException if negative or greater than |
| 792 |
|
* internal implementation limit |
| 793 |
|
*/ |
| 794 |
|
public void setMaximumPoolSize(int newMax) { |
| 1736 |
|
|
| 1737 |
|
/** |
| 1738 |
|
* Interface for extending managed parallelism for tasks running |
| 1739 |
< |
* in ForkJoinPools. A ManagedBlocker provides two methods. |
| 1739 |
> |
* in {@link ForkJoinPool}s. |
| 1740 |
> |
* |
| 1741 |
> |
* <p>A {@code ManagedBlocker} provides two methods. |
| 1742 |
|
* Method {@code isReleasable} must return {@code true} if |
| 1743 |
|
* blocking is not necessary. Method {@code block} blocks the |
| 1744 |
|
* current thread if necessary (perhaps internally invoking |
| 1781 |
|
|
| 1782 |
|
/** |
| 1783 |
|
* Blocks in accord with the given blocker. If the current thread |
| 1784 |
< |
* is a ForkJoinWorkerThread, this method possibly arranges for a |
| 1785 |
< |
* spare thread to be activated if necessary to ensure parallelism |
| 1786 |
< |
* while the current thread is blocked. If |
| 1787 |
< |
* {@code maintainParallelism} is {@code true} and the pool supports |
| 1788 |
< |
* it ({@link #getMaintainsParallelism}), this method attempts to |
| 1789 |
< |
* maintain the pool's nominal parallelism. Otherwise it activates |
| 1790 |
< |
* a thread only if necessary to avoid complete starvation. This |
| 1791 |
< |
* option may be preferable when blockages use timeouts, or are |
| 1792 |
< |
* almost always brief. |
| 1784 |
> |
* is a {@link ForkJoinWorkerThread}, this method possibly |
| 1785 |
> |
* arranges for a spare thread to be activated if necessary to |
| 1786 |
> |
* ensure parallelism while the current thread is blocked. |
| 1787 |
> |
* |
| 1788 |
> |
* <p>If {@code maintainParallelism} is {@code true} and the pool |
| 1789 |
> |
* supports it ({@link #getMaintainsParallelism}), this method |
| 1790 |
> |
* attempts to maintain the pool's nominal parallelism. Otherwise |
| 1791 |
> |
* it activates a thread only if necessary to avoid complete |
| 1792 |
> |
* starvation. This option may be preferable when blockages use |
| 1793 |
> |
* timeouts, or are almost always brief. |
| 1794 |
|
* |
| 1795 |
< |
* <p> If the caller is not a ForkJoinTask, this method is behaviorally |
| 1796 |
< |
* equivalent to |
| 1795 |
> |
* <p>If the caller is not a {@link ForkJoinTask}, this method is |
| 1796 |
> |
* behaviorally equivalent to |
| 1797 |
|
* <pre> {@code |
| 1798 |
|
* while (!blocker.isReleasable()) |
| 1799 |
|
* if (blocker.block()) |
| 1800 |
|
* return; |
| 1801 |
|
* }</pre> |
| 1802 |
< |
* If the caller is a ForkJoinTask, then the pool may first |
| 1803 |
< |
* be expanded to ensure parallelism, and later adjusted. |
| 1802 |
> |
* |
| 1803 |
> |
* If the caller is a {@code ForkJoinTask}, then the pool may |
| 1804 |
> |
* first be expanded to ensure parallelism, and later adjusted. |
| 1805 |
|
* |
| 1806 |
|
* @param blocker the blocker |
| 1807 |
|
* @param maintainParallelism if {@code true} and supported by |
| 1838 |
|
// implement RunnableFuture. |
| 1839 |
|
|
| 1840 |
|
protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) { |
| 1841 |
< |
return (RunnableFuture<T>)ForkJoinTask.adapt(runnable, value); |
| 1841 |
> |
return (RunnableFuture<T>) ForkJoinTask.adapt(runnable, value); |
| 1842 |
|
} |
| 1843 |
|
|
| 1844 |
|
protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) { |
| 1845 |
< |
return (RunnableFuture<T>)ForkJoinTask.adapt(callable); |
| 1845 |
> |
return (RunnableFuture<T>) ForkJoinTask.adapt(callable); |
| 1846 |
|
} |
| 1847 |
|
|
| 1848 |
|
// Unsafe mechanics |
