ForkJoinPool

defaultForkJoinWorkerThreadFactory

ForkJoinPool.ForkJoinWorkerThreadFactory defaultForkJoinWorkerThreadFactory

Creates a new ForkJoinWorkerThread. This factory is used unless overridden in ForkJoinPool constructors.

ForkJoinPool

ForkJoinPool ()

Creates a ForkJoinPool with parallelism equal to availableProcessors(), using the default thread factory, no UncaughtExceptionHandler, and non-async LIFO processing mode.

ForkJoinPool

ForkJoinPool (int parallelism)

Creates a ForkJoinPool with the indicated parallelism level, the default thread factory, no UncaughtExceptionHandler, and non-async LIFO processing mode.

ForkJoinPool

ForkJoinPool (int parallelism, 
                ForkJoinPool.ForkJoinWorkerThreadFactory factory, 
                Thread.UncaughtExceptionHandler handler, 
                boolean asyncMode)

Creates a ForkJoinPool with the given parameters.

awaitQuiescence

boolean awaitQuiescence (long timeout, 
                TimeUnit unit)

If called by a ForkJoinTask operating in this pool, equivalent in effect to helpQuiesce(). Otherwise, waits and/or attempts to assist performing tasks until this pool isQuiescent() or the indicated timeout elapses.

awaitTermination

boolean awaitTermination (long timeout, 
                TimeUnit unit)

Blocks until all tasks have completed execution after a shutdown request, or the timeout occurs, or the current thread is interrupted, whichever happens first. Because the commonPool() never terminates until program shutdown, when applied to the common pool, this method is equivalent to awaitQuiescence(long, TimeUnit) but always returns false.

commonPool

ForkJoinPool commonPool ()

Returns the common pool instance. This pool is statically constructed; its run state is unaffected by attempts to shutdown() or shutdownNow(). However this pool and any ongoing processing are automatically terminated upon program exit(int). Any program that relies on asynchronous task processing to complete before program termination should invoke commonPool().awaitQuiescence, before exit.

execute

void execute (Runnable task)

execute

void execute (ForkJoinTask<?> task)

Arranges for (asynchronous) execution of the given task.

getActiveThreadCount

int getActiveThreadCount ()

Returns an estimate of the number of threads that are currently stealing or executing tasks. This method may overestimate the number of active threads.

getAsyncMode

boolean getAsyncMode ()

Returns true if this pool uses local first-in-first-out scheduling mode for forked tasks that are never joined.

getCommonPoolParallelism

int getCommonPoolParallelism ()

Returns the targeted parallelism level of the common pool.

getFactory

ForkJoinPool.ForkJoinWorkerThreadFactory getFactory ()

Returns the factory used for constructing new workers.

getParallelism

int getParallelism ()

Returns the targeted parallelism level of this pool.

getPoolSize

int getPoolSize ()

Returns the number of worker threads that have started but not yet terminated. The result returned by this method may differ from getParallelism() when threads are created to maintain parallelism when others are cooperatively blocked.

getQueuedSubmissionCount

int getQueuedSubmissionCount ()

Returns an estimate of the number of tasks submitted to this pool that have not yet begun executing. This method may take time proportional to the number of submissions.

getQueuedTaskCount

long getQueuedTaskCount ()

Returns an estimate of the total number of tasks currently held in queues by worker threads (but not including tasks submitted to the pool that have not begun executing). This value is only an approximation, obtained by iterating across all threads in the pool. This method may be useful for tuning task granularities.

getRunningThreadCount

int getRunningThreadCount ()

Returns an estimate of the number of worker threads that are not blocked waiting to join tasks or for other managed synchronization. This method may overestimate the number of running threads.

getStealCount

long getStealCount ()

Returns an estimate of the total number of tasks stolen from one thread's work queue by another. The reported value underestimates the actual total number of steals when the pool is not quiescent. This value may be useful for monitoring and tuning fork/join programs: in general, steal counts should be high enough to keep threads busy, but low enough to avoid overhead and contention across threads.

getUncaughtExceptionHandler

Thread.UncaughtExceptionHandler getUncaughtExceptionHandler ()

Returns the handler for internal worker threads that terminate due to unrecoverable errors encountered while executing tasks.

hasQueuedSubmissions

boolean hasQueuedSubmissions ()

Returns true if there are any tasks submitted to this pool that have not yet begun executing.

invoke

T invoke (ForkJoinTask<T> task)

Performs the given task, returning its result upon completion. If the computation encounters an unchecked Exception or Error, it is rethrown as the outcome of this invocation. Rethrown exceptions behave in the same way as regular exceptions, but, when possible, contain stack traces (as displayed for example using ex.printStackTrace()) of both the current thread as well as the thread actually encountering the exception; minimally only the latter.

invokeAll

List<Future<T>> invokeAll (Collection<? extends Callable<T>> tasks)

Executes the given tasks, returning a list of Futures holding their status and results when all complete. isDone() is true for each element of the returned list. Note that a completed task could have terminated either normally or by throwing an exception. The results of this method are undefined if the given collection is modified while this operation is in progress.

isQuiescent

boolean isQuiescent ()

Returns true if all worker threads are currently idle. An idle worker is one that cannot obtain a task to execute because none are available to steal from other threads, and there are no pending submissions to the pool. This method is conservative; it might not return true immediately upon idleness of all threads, but will eventually become true if threads remain inactive.

isShutdown

boolean isShutdown ()

Returns true if this pool has been shut down.

isTerminated

boolean isTerminated ()

Returns true if all tasks have completed following shut down.

isTerminating

boolean isTerminating ()

Returns true if the process of termination has commenced but not yet completed. This method may be useful for debugging. A return of true reported a sufficient period after shutdown may indicate that submitted tasks have ignored or suppressed interruption, or are waiting for I/O, causing this executor not to properly terminate. (See the advisory notes for class ForkJoinTask stating that tasks should not normally entail blocking operations. But if they do, they must abort them on interrupt.)

managedBlock

void managedBlock (ForkJoinPool.ManagedBlocker blocker)

Runs the given possibly blocking task. When running in a ForkJoinPool, this method possibly arranges for a spare thread to be activated if necessary to ensure sufficient parallelism while the current thread is blocked in blocker.block().

This method repeatedly calls blocker.isReleasable() and blocker.block() until either method returns true. Every call to blocker.block() is preceded by a call to blocker.isReleasable() that returned false.

If not running in a ForkJoinPool, this method is behaviorally equivalent to

 while (!blocker.isReleasable())
   if (blocker.block())
     break;

shutdown

void shutdown ()

Possibly initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted. Invocation has no effect on execution state if this is the commonPool(), and no additional effect if already shut down. Tasks that are in the process of being submitted concurrently during the course of this method may or may not be rejected.

shutdownNow

List<Runnable> shutdownNow ()

Possibly attempts to cancel and/or stop all tasks, and reject all subsequently submitted tasks. Invocation has no effect on execution state if this is the commonPool(), and no additional effect if already shut down. Otherwise, tasks that are in the process of being submitted or executed concurrently during the course of this method may or may not be rejected. This method cancels both existing and unexecuted tasks, in order to permit termination in the presence of task dependencies. So the method always returns an empty list (unlike the case for some other Executors).

submit

ForkJoinTask<T> submit (Callable<T> task)

Submits a value-returning task for execution and returns a Future representing the pending results of the task. The Future's get method will return the task's result upon successful completion.

If you would like to immediately block waiting for a task, you can use constructions of the form result = exec.submit(aCallable).get();

Note: The Executors class includes a set of methods that can convert some other common closure-like objects, for example, PrivilegedAction to Callable form so they can be submitted.

submit

ForkJoinTask<T> submit (ForkJoinTask<T> task)

Submits a ForkJoinTask for execution.

submit

ForkJoinTask<?> submit (Runnable task)

Submits a Runnable task for execution and returns a Future representing that task. The Future's get method will return null upon successful completion.

submit

ForkJoinTask<T> submit (Runnable task, 
                T result)

Submits a Runnable task for execution and returns a Future representing that task. The Future's get method will return the given result upon successful completion.

toString

String toString ()

Returns a string identifying this pool, as well as its state, including indications of run state, parallelism level, and worker and task counts.

drainTasksTo

int drainTasksTo (Collection<? super ForkJoinTask<?>> c)

Removes all available unexecuted submitted and forked tasks from scheduling queues and adds them to the given collection, without altering their execution status. These may include artificially generated or wrapped tasks. This method is designed to be invoked only when the pool is known to be quiescent. Invocations at other times may not remove all tasks. A failure encountered while attempting to add elements to collection c may result in elements being in neither, either or both collections when the associated exception is thrown. The behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

newTaskFor

RunnableFuture<T> newTaskFor (Runnable runnable, 
                T value)

Returns a RunnableFuture for the given runnable and default value.

newTaskFor

RunnableFuture<T> newTaskFor (Callable<T> callable)

Returns a RunnableFuture for the given callable task.

pollSubmission

ForkJoinTask<?> pollSubmission ()

Removes and returns the next unexecuted submission if one is available. This method may be useful in extensions to this class that re-assign work in systems with multiple pools.