ForkJoinPool (Java SE 9 & JDK 9 ) (original) (raw)

All Implemented Interfaces:
[Executor](../../../java/util/concurrent/Executor.html "interface in java.util.concurrent"), [ExecutorService](../../../java/util/concurrent/ExecutorService.html "interface in java.util.concurrent")

public class ForkJoinPool
extends AbstractExecutorService
An ExecutorService for running ForkJoinTasks. A ForkJoinPool provides the entry point for submissions from non-ForkJoinTask clients, as well as management and monitoring operations.
A ForkJoinPool differs from other kinds of ExecutorService mainly by virtue of employing_work-stealing_: all threads in the pool attempt to find and execute tasks submitted to the pool and/or created by other active tasks (eventually blocking waiting for work if none exist). This enables efficient processing when most tasks spawn other subtasks (as do most ForkJoinTasks), as well as when many small tasks are submitted to the pool from external clients. Especially when setting asyncMode to true in constructors, ForkJoinPools may also be appropriate for use with event-style tasks that are never joined. All worker threads are initialized with Thread.isDaemon() set true.
A static commonPool() is available and appropriate for most applications. The common pool is used by any ForkJoinTask that is not explicitly submitted to a specified pool. Using the common pool normally reduces resource usage (its threads are slowly reclaimed during periods of non-use, and reinstated upon subsequent use).
For applications that require separate or custom pools, a ForkJoinPool may be constructed with a given target parallelism level; by default, equal to the number of available processors. The pool attempts to maintain enough active (or available) threads by dynamically adding, suspending, or resuming internal worker threads, even if some tasks are stalled waiting to join others. However, no such adjustments are guaranteed in the face of blocked I/O or other unmanaged synchronization. The nested ForkJoinPool.ManagedBlocker interface enables extension of the kinds of synchronization accommodated. The default policies may be overridden using a constructor with parameters corresponding to those documented in class ThreadPoolExecutor.
In addition to execution and lifecycle control methods, this class provides status check methods (for examplegetStealCount()) that are intended to aid in developing, tuning, and monitoring fork/join applications. Also, methodtoString() returns indications of pool state in a convenient form for informal monitoring.
As is the case with other ExecutorServices, there are three main task execution methods summarized in the following table. These are designed to be used primarily by clients not already engaged in fork/join computations in the current pool. The main forms of these methods accept instances of ForkJoinTask, but overloaded forms also allow mixed execution of plain Runnable- or Callable- based activities as well. However, tasks that are already executing in a pool should normally instead use the within-computation forms listed in the table unless using async event-style tasks that are not usually joined, in which case there is little difference among choice of methods.
Summary of task execution methods

Call from non-fork/join clients	Call from within fork/join computations
Arrange async execution	execute(ForkJoinTask)	ForkJoinTask.fork()
Await and obtain result	invoke(ForkJoinTask)	ForkJoinTask.invoke()
Arrange exec and obtain Future	submit(ForkJoinTask)	ForkJoinTask.fork() (ForkJoinTasks are Futures)
The parameters used to construct the common pool may be controlled by setting the following system properties:

java.util.concurrent.ForkJoinPool.common.parallelism - the parallelism level, a non-negative integer
java.util.concurrent.ForkJoinPool.common.threadFactory - the class name of a ForkJoinPool.ForkJoinWorkerThreadFactory. The system class loader is used to load this class.
java.util.concurrent.ForkJoinPool.common.exceptionHandler - the class name of a Thread.UncaughtExceptionHandler. The system class loader is used to load this class.
java.util.concurrent.ForkJoinPool.common.maximumSpares - the maximum number of allowed extra threads to maintain target parallelism (default 256).
If no thread factory is supplied via a system property, then the common pool uses a factory that uses the system class loader as thethread context class loader. In addition, if a SecurityManager is present, then the common pool uses a factory supplying threads that have noPermissions enabled. Upon any error in establishing these settings, default parameters are used. It is possible to disable or limit the use of threads in the common pool by setting the parallelism property to zero, and/or using a factory that may return null. However doing so may cause unjoined tasks to never be executed.
Implementation notes: This implementation restricts the maximum number of running threads to 32767. Attempts to create pools with greater than the maximum number result inIllegalArgumentException.
This implementation rejects submitted tasks (that is, by throwingRejectedExecutionException) only when the pool is shut down or internal resources have been exhausted.
Since:
1.7

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static interface	ForkJoinPool.ForkJoinWorkerThreadFactory	Factory for creating new ForkJoinWorkerThreads.
static interface	ForkJoinPool.ManagedBlocker	Interface for extending managed parallelism for tasks running in ForkJoinPools.

Field Summary

Fields

Modifier and Type	Field	Description
static ForkJoinPool.ForkJoinWorkerThreadFactory	defaultForkJoinWorkerThreadFactory	Creates a new ForkJoinWorkerThread.

Constructor Summary

Constructors

Constructor	Description
ForkJoinPool()	Creates a ForkJoinPool with parallelism equal to Runtime.availableProcessors(), using defaults for all other parameters (see ForkJoinPool(int, ForkJoinWorkerThreadFactory, UncaughtExceptionHandler, boolean, int, int, int, Predicate, long, TimeUnit)).
ForkJoinPool(int parallelism)	Creates a ForkJoinPool with the indicated parallelism level, using defaults for all other parameters (see ForkJoinPool(int, ForkJoinWorkerThreadFactory, UncaughtExceptionHandler, boolean, int, int, int, Predicate, long, TimeUnit)).
ForkJoinPool(int parallelism,ForkJoinPool.ForkJoinWorkerThreadFactory factory,Thread.UncaughtExceptionHandler handler, boolean asyncMode)	Creates a ForkJoinPool with the given parameters (using defaults for others -- see ForkJoinPool(int, ForkJoinWorkerThreadFactory, UncaughtExceptionHandler, boolean, int, int, int, Predicate, long, TimeUnit)).
ForkJoinPool(int parallelism,ForkJoinPool.ForkJoinWorkerThreadFactory factory,Thread.UncaughtExceptionHandler handler, boolean asyncMode, int corePoolSize, int maximumPoolSize, int minimumRunnable,Predicate<? super ForkJoinPool> saturate, long keepAliveTime,TimeUnit unit)	Creates a ForkJoinPool with the given parameters.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods

Modifier and Type	Method	Description
boolean	awaitQuiescence(long timeout,TimeUnit unit)	If called by a ForkJoinTask operating in this pool, equivalent in effect to ForkJoinTask.helpQuiesce().
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.
static ForkJoinPool	commonPool()	Returns the common pool instance.
protected int	drainTasksTo(Collection> c)	Removes all available unexecuted submitted and forked tasks from scheduling queues and adds them to the given collection, without altering their execution status.
void	execute(Runnable task)	Executes the given command at some time in the future.
void	execute(ForkJoinTask<?> task)	Arranges for (asynchronous) execution of the given task.
int	getActiveThreadCount()	Returns an estimate of the number of threads that are currently stealing or executing tasks.
boolean	getAsyncMode()	Returns true if this pool uses local first-in-first-out scheduling mode for forked tasks that are never joined.
static int	getCommonPoolParallelism()	Returns the targeted parallelism level of the common pool.
ForkJoinPool.ForkJoinWorkerThreadFactory	getFactory()	Returns the factory used for constructing new workers.
int	getParallelism()	Returns the targeted parallelism level of this pool.
int	getPoolSize()	Returns the number of worker threads that have started but not yet terminated.
int	getQueuedSubmissionCount()	Returns an estimate of the number of tasks submitted to this pool that have not yet begun executing.
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).
int	getRunningThreadCount()	Returns an estimate of the number of worker threads that are not blocked waiting to join tasks or for other managed synchronization.
long	getStealCount()	Returns an estimate of the total number of tasks stolen from one thread's work queue by another.
Thread.UncaughtExceptionHandler	getUncaughtExceptionHandler()	Returns the handler for internal worker threads that terminate due to unrecoverable errors encountered while executing tasks.
boolean	hasQueuedSubmissions()	Returns true if there are any tasks submitted to this pool that have not yet begun executing.
T	invoke(ForkJoinTask task)	Performs the given task, returning its result upon completion.
List<Future>	invokeAll(Collection<? extends Callable> tasks)	Executes the given tasks, returning a list of Futures holding their status and results when all complete.
boolean	isQuiescent()	Returns true if all worker threads are currently idle.
boolean	isShutdown()	Returns true if this pool has been shut down.
boolean	isTerminated()	Returns true if all tasks have completed following shut down.
boolean	isTerminating()	Returns true if the process of termination has commenced but not yet completed.
static void	managedBlock(ForkJoinPool.ManagedBlocker blocker)	Runs the given possibly blocking task.
protected RunnableFuture	newTaskFor(Runnable runnable, T value)	Returns a RunnableFuture for the given runnable and default value.
protected RunnableFuture	newTaskFor(Callable callable)	Returns a RunnableFuture for the given callable task.
protected ForkJoinTask<?>	pollSubmission()	Removes and returns the next unexecuted submission if one is available.
void	shutdown()	Possibly initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted.
List<Runnable>	shutdownNow()	Possibly attempts to cancel and/or stop all tasks, and reject all subsequently submitted tasks.
ForkJoinTask<?>	submit(Runnable task)	Submits a Runnable task for execution and returns a Future representing that task.
ForkJoinTask	submit(Runnable task, T result)	Submits a Runnable task for execution and returns a Future representing that task.
ForkJoinTask	submit(Callable task)	Submits a value-returning task for execution and returns a Future representing the pending results of the task.
ForkJoinTask	submit(ForkJoinTask task)	Submits a ForkJoinTask for execution.
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.

   * ### Methods inherited from class java.util.concurrent.[AbstractExecutorService](../../../java/util/concurrent/AbstractExecutorService.html "class in java.util.concurrent")  
   `[invokeAll](../../../java/util/concurrent/AbstractExecutorService.html#invokeAll-java.util.Collection-long-java.util.concurrent.TimeUnit-), [invokeAny](../../../java/util/concurrent/AbstractExecutorService.html#invokeAny-java.util.Collection-), [invokeAny](../../../java/util/concurrent/AbstractExecutorService.html#invokeAny-java.util.Collection-long-java.util.concurrent.TimeUnit-)`  
   * ### Methods inherited from class java.lang.[Object](../../../java/lang/Object.html "class in java.lang")  
   `[clone](../../../java/lang/Object.html#clone--), [equals](../../../java/lang/Object.html#equals-java.lang.Object-), [finalize](../../../java/lang/Object.html#finalize--), [getClass](../../../java/lang/Object.html#getClass--), [hashCode](../../../java/lang/Object.html#hashCode--), [notify](../../../java/lang/Object.html#notify--), [notifyAll](../../../java/lang/Object.html#notifyAll--), [wait](../../../java/lang/Object.html#wait--), [wait](../../../java/lang/Object.html#wait-long-), [wait](../../../java/lang/Object.html#wait-long-int-)`

Field Detail

 * #### defaultForkJoinWorkerThreadFactory  
 public static final [ForkJoinPool.ForkJoinWorkerThreadFactory](../../../java/util/concurrent/ForkJoinPool.ForkJoinWorkerThreadFactory.html "interface in java.util.concurrent") defaultForkJoinWorkerThreadFactory  
 Creates a new ForkJoinWorkerThread. This factory is used unless overridden in ForkJoinPool constructors.

Constructor Detail

* #### ForkJoinPool  
public ForkJoinPool()  
Creates a `ForkJoinPool` with parallelism equal to [Runtime.availableProcessors()](../../../java/lang/Runtime.html#availableProcessors--), using defaults for all other parameters (see [ForkJoinPool(int, ForkJoinWorkerThreadFactory, UncaughtExceptionHandler, boolean, int, int, int, Predicate, long, TimeUnit)](../../../java/util/concurrent/ForkJoinPool.html#ForkJoinPool-int-java.util.concurrent.ForkJoinPool.ForkJoinWorkerThreadFactory-java.lang.Thread.UncaughtExceptionHandler-boolean-int-int-int-java.util.function.Predicate-long-java.util.concurrent.TimeUnit-)).  
Throws:  
`[SecurityException](../../../java/lang/SecurityException.html "class in java.lang")` \- if a security manager exists and the caller is not permitted to modify threads because it does not hold [RuntimePermission](../../../java/lang/RuntimePermission.html "class in java.lang")`("modifyThread")`  
* #### ForkJoinPool  
public ForkJoinPool(int parallelism)  
Creates a `ForkJoinPool` with the indicated parallelism level, using defaults for all other parameters (see [ForkJoinPool(int, ForkJoinWorkerThreadFactory, UncaughtExceptionHandler, boolean, int, int, int, Predicate, long, TimeUnit)](../../../java/util/concurrent/ForkJoinPool.html#ForkJoinPool-int-java.util.concurrent.ForkJoinPool.ForkJoinWorkerThreadFactory-java.lang.Thread.UncaughtExceptionHandler-boolean-int-int-int-java.util.function.Predicate-long-java.util.concurrent.TimeUnit-)).  
Parameters:  
`parallelism` \- the parallelism level  
Throws:  
`[IllegalArgumentException](../../../java/lang/IllegalArgumentException.html "class in java.lang")` \- if parallelism less than or equal to zero, or greater than implementation limit  
`[SecurityException](../../../java/lang/SecurityException.html "class in java.lang")` \- if a security manager exists and the caller is not permitted to modify threads because it does not hold [RuntimePermission](../../../java/lang/RuntimePermission.html "class in java.lang")`("modifyThread")`  
* #### ForkJoinPool  
public ForkJoinPool(int parallelism,  
                    [ForkJoinPool.ForkJoinWorkerThreadFactory](../../../java/util/concurrent/ForkJoinPool.ForkJoinWorkerThreadFactory.html "interface in java.util.concurrent") factory,  
                    [Thread.UncaughtExceptionHandler](../../../java/lang/Thread.UncaughtExceptionHandler.html "interface in java.lang") handler,  
                    boolean asyncMode)  
Parameters:  
`parallelism` \- the parallelism level. For default value, use [Runtime.availableProcessors()](../../../java/lang/Runtime.html#availableProcessors--).  
`factory` \- the factory for creating new threads. For default value, use [defaultForkJoinWorkerThreadFactory](../../../java/util/concurrent/ForkJoinPool.html#defaultForkJoinWorkerThreadFactory).  
`handler` \- the handler for internal worker threads that terminate due to unrecoverable errors encountered while executing tasks. For default value, use `null`.  
`asyncMode` \- if true, establishes local first-in-first-out scheduling mode for forked tasks that are never joined. This mode may be more appropriate than default locally stack-based mode in applications in which worker threads only process event-style asynchronous tasks. For default value, use `false`.  
Throws:  
`[IllegalArgumentException](../../../java/lang/IllegalArgumentException.html "class in java.lang")` \- if parallelism less than or equal to zero, or greater than implementation limit  
`[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang")` \- if the factory is null  
`[SecurityException](../../../java/lang/SecurityException.html "class in java.lang")` \- if a security manager exists and the caller is not permitted to modify threads because it does not hold [RuntimePermission](../../../java/lang/RuntimePermission.html "class in java.lang")`("modifyThread")`  
* #### ForkJoinPool  
public ForkJoinPool(int parallelism,  
                    [ForkJoinPool.ForkJoinWorkerThreadFactory](../../../java/util/concurrent/ForkJoinPool.ForkJoinWorkerThreadFactory.html "interface in java.util.concurrent") factory,  
                    [Thread.UncaughtExceptionHandler](../../../java/lang/Thread.UncaughtExceptionHandler.html "interface in java.lang") handler,  
                    boolean asyncMode,  
                    int corePoolSize,  
                    int maximumPoolSize,  
                    int minimumRunnable,  
                    [Predicate](../../../java/util/function/Predicate.html "interface in java.util.function")<? super [ForkJoinPool](../../../java/util/concurrent/ForkJoinPool.html "class in java.util.concurrent")> saturate,  
                    long keepAliveTime,  
                    [TimeUnit](../../../java/util/concurrent/TimeUnit.html "enum in java.util.concurrent") unit)  
Creates a `ForkJoinPool` with the given parameters.  
Parameters:  
`parallelism` \- the parallelism level. For default value, use [Runtime.availableProcessors()](../../../java/lang/Runtime.html#availableProcessors--).  
`factory` \- the factory for creating new threads. For default value, use [defaultForkJoinWorkerThreadFactory](../../../java/util/concurrent/ForkJoinPool.html#defaultForkJoinWorkerThreadFactory).  
`handler` \- the handler for internal worker threads that terminate due to unrecoverable errors encountered while executing tasks. For default value, use `null`.  
`asyncMode` \- if true, establishes local first-in-first-out scheduling mode for forked tasks that are never joined. This mode may be more appropriate than default locally stack-based mode in applications in which worker threads only process event-style asynchronous tasks. For default value, use ` false`.  
`corePoolSize` \- the number of threads to keep in the pool (unless timed out after an elapsed keep-alive). Normally (and by default) this is the same value as the parallelism level, but may be set to a larger value to reduce dynamic overhead if tasks regularly block. Using a smaller value (for example`0`) has the same effect as the default.  
`maximumPoolSize` \- the maximum number of threads allowed. When the maximum is reached, attempts to replace blocked threads fail. (However, because creation and termination of different threads may overlap, and may be managed by the given thread factory, this value may be transiently exceeded.) To arrange the same value as is used by default for the common pool, use `256` plus the `parallelism` level. (By default, the common pool allows a maximum of 256 spare threads.) Using a value (for example ` Integer.MAX_VALUE`) larger than the implementation's total thread limit has the same effect as using this limit (which is the default).  
`minimumRunnable` \- the minimum allowed number of core threads not blocked by a join or [ForkJoinPool.ManagedBlocker](../../../java/util/concurrent/ForkJoinPool.ManagedBlocker.html "interface in java.util.concurrent"). To ensure progress, when too few unblocked threads exist and unexecuted tasks may exist, new threads are constructed, up to the given maximumPoolSize. For the default value, use ` 1`, that ensures liveness. A larger value might improve throughput in the presence of blocked activities, but might not, due to increased overhead. A value of zero may be acceptable when submitted tasks cannot have dependencies requiring additional threads.  
`saturate` \- if non-null, a predicate invoked upon attempts to create more than the maximum total allowed threads. By default, when a thread is about to block on a join or [ForkJoinPool.ManagedBlocker](../../../java/util/concurrent/ForkJoinPool.ManagedBlocker.html "interface in java.util.concurrent"), but cannot be replaced because the maximumPoolSize would be exceeded, a [RejectedExecutionException](../../../java/util/concurrent/RejectedExecutionException.html "class in java.util.concurrent") is thrown. But if this predicate returns `true`, then no exception is thrown, so the pool continues to operate with fewer than the target number of runnable threads, which might not ensure progress.  
`keepAliveTime` \- the elapsed time since last use before a thread is terminated (and then later replaced if needed). For the default value, use `60, TimeUnit.SECONDS`.  
`unit` \- the time unit for the `keepAliveTime` argument  
Throws:  
`[IllegalArgumentException](../../../java/lang/IllegalArgumentException.html "class in java.lang")` \- if parallelism is less than or equal to zero, or is greater than implementation limit, or if maximumPoolSize is less than parallelism, of if the keepAliveTime is less than or equal to zero.  
`[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang")` \- if the factory is null  
`[SecurityException](../../../java/lang/SecurityException.html "class in java.lang")` \- if a security manager exists and the caller is not permitted to modify threads because it does not hold [RuntimePermission](../../../java/lang/RuntimePermission.html "class in java.lang")`("modifyThread")`  
Since:  
9

Method Detail

* #### commonPool  
public static [ForkJoinPool](../../../java/util/concurrent/ForkJoinPool.html "class in java.util.concurrent") commonPool()  
Returns the common pool instance. This pool is statically constructed; its run state is unaffected by attempts to [shutdown()](../../../java/util/concurrent/ForkJoinPool.html#shutdown--) or [shutdownNow()](../../../java/util/concurrent/ForkJoinPool.html#shutdownNow--). However this pool and any ongoing processing are automatically terminated upon program[System.exit(int)](../../../java/lang/System.html#exit-int-). Any program that relies on asynchronous task processing to complete before program termination should invoke `commonPool().`[awaitQuiescence](../../../java/util/concurrent/ForkJoinPool.html#awaitQuiescence-long-java.util.concurrent.TimeUnit-), before exit.  
Returns:  
the common pool instance  
Since:  
1.8  
* #### invoke  
public <T> T invoke([ForkJoinTask](../../../java/util/concurrent/ForkJoinTask.html "class in java.util.concurrent")<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.  
Type Parameters:  
`T` \- the type of the task's result  
Parameters:  
`task` \- the task  
Returns:  
the task's result  
Throws:  
`[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang")` \- if the task is null  
`[RejectedExecutionException](../../../java/util/concurrent/RejectedExecutionException.html "class in java.util.concurrent")` \- if the task cannot be scheduled for execution  
* #### execute  
public void execute([ForkJoinTask](../../../java/util/concurrent/ForkJoinTask.html "class in java.util.concurrent")<?> task)  
Arranges for (asynchronous) execution of the given task.  
Parameters:  
`task` \- the task  
Throws:  
`[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang")` \- if the task is null  
`[RejectedExecutionException](../../../java/util/concurrent/RejectedExecutionException.html "class in java.util.concurrent")` \- if the task cannot be scheduled for execution  
* #### execute  
public void execute([Runnable](../../../java/lang/Runnable.html "interface in java.lang") task)  
Description copied from interface: `[Executor](../../../java/util/concurrent/Executor.html#execute-java.lang.Runnable-)`  
Executes the given command at some time in the future. The command may execute in a new thread, in a pooled thread, or in the calling thread, at the discretion of the `Executor` implementation.  
Parameters:  
`task` \- the runnable task  
Throws:  
`[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang")` \- if the task is null  
`[RejectedExecutionException](../../../java/util/concurrent/RejectedExecutionException.html "class in java.util.concurrent")` \- if the task cannot be scheduled for execution  
* #### submit  
public <T> [ForkJoinTask](../../../java/util/concurrent/ForkJoinTask.html "class in java.util.concurrent")<T> submit([ForkJoinTask](../../../java/util/concurrent/ForkJoinTask.html "class in java.util.concurrent")<T> task)  
Submits a ForkJoinTask for execution.  
Type Parameters:  
`T` \- the type of the task's result  
Parameters:  
`task` \- the task to submit  
Returns:  
the task  
Throws:  
`[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang")` \- if the task is null  
`[RejectedExecutionException](../../../java/util/concurrent/RejectedExecutionException.html "class in java.util.concurrent")` \- if the task cannot be scheduled for execution  
* #### submit  
public <T> [ForkJoinTask](../../../java/util/concurrent/ForkJoinTask.html "class in java.util.concurrent")<T> submit([Callable](../../../java/util/concurrent/Callable.html "interface in java.util.concurrent")<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](../../../java/util/concurrent/Executors.html "class in java.util.concurrent") class includes a set of methods that can convert some other common closure-like objects, for example, [PrivilegedAction](../../../java/security/PrivilegedAction.html "interface in java.security") to[Callable](../../../java/util/concurrent/Callable.html "interface in java.util.concurrent") form so they can be submitted.  
Specified by:  
`[submit](../../../java/util/concurrent/ExecutorService.html#submit-java.util.concurrent.Callable-)` in interface `[ExecutorService](../../../java/util/concurrent/ExecutorService.html "interface in java.util.concurrent")`  
Overrides:  
`[submit](../../../java/util/concurrent/AbstractExecutorService.html#submit-java.util.concurrent.Callable-)` in class `[AbstractExecutorService](../../../java/util/concurrent/AbstractExecutorService.html "class in java.util.concurrent")`  
Type Parameters:  
`T` \- the type of the task's result  
Parameters:  
`task` \- the task to submit  
Returns:  
a Future representing pending completion of the task  
Throws:  
`[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang")` \- if the task is null  
`[RejectedExecutionException](../../../java/util/concurrent/RejectedExecutionException.html "class in java.util.concurrent")` \- if the task cannot be scheduled for execution  
* #### submit  
public <T> [ForkJoinTask](../../../java/util/concurrent/ForkJoinTask.html "class in java.util.concurrent")<T> submit([Runnable](../../../java/lang/Runnable.html "interface in java.lang") 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.  
Specified by:  
`[submit](../../../java/util/concurrent/ExecutorService.html#submit-java.lang.Runnable-T-)` in interface `[ExecutorService](../../../java/util/concurrent/ExecutorService.html "interface in java.util.concurrent")`  
Overrides:  
`[submit](../../../java/util/concurrent/AbstractExecutorService.html#submit-java.lang.Runnable-T-)` in class `[AbstractExecutorService](../../../java/util/concurrent/AbstractExecutorService.html "class in java.util.concurrent")`  
Type Parameters:  
`T` \- the type of the result  
Parameters:  
`task` \- the task to submit  
`result` \- the result to return  
Returns:  
a Future representing pending completion of the task  
Throws:  
`[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang")` \- if the task is null  
`[RejectedExecutionException](../../../java/util/concurrent/RejectedExecutionException.html "class in java.util.concurrent")` \- if the task cannot be scheduled for execution  
* #### submit  
public [ForkJoinTask](../../../java/util/concurrent/ForkJoinTask.html "class in java.util.concurrent")<?> submit([Runnable](../../../java/lang/Runnable.html "interface in java.lang") 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.  
Specified by:  
`[submit](../../../java/util/concurrent/ExecutorService.html#submit-java.lang.Runnable-)` in interface `[ExecutorService](../../../java/util/concurrent/ExecutorService.html "interface in java.util.concurrent")`  
Overrides:  
`[submit](../../../java/util/concurrent/AbstractExecutorService.html#submit-java.lang.Runnable-)` in class `[AbstractExecutorService](../../../java/util/concurrent/AbstractExecutorService.html "class in java.util.concurrent")`  
Parameters:  
`task` \- the task to submit  
Returns:  
a Future representing pending completion of the task  
Throws:  
`[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang")` \- if the task is null  
`[RejectedExecutionException](../../../java/util/concurrent/RejectedExecutionException.html "class in java.util.concurrent")` \- if the task cannot be scheduled for execution  
* #### invokeAll  
public <T> [List](../../../java/util/List.html "interface in java.util")<[Future](../../../java/util/concurrent/Future.html "interface in java.util.concurrent")<T>> invokeAll([Collection](../../../java/util/Collection.html "interface in java.util")<? extends [Callable](../../../java/util/concurrent/Callable.html "interface in java.util.concurrent")<T>> tasks)  
Executes the given tasks, returning a list of Futures holding their status and results when all complete.[Future.isDone()](../../../java/util/concurrent/Future.html#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.  
Specified by:  
`[invokeAll](../../../java/util/concurrent/ExecutorService.html#invokeAll-java.util.Collection-)` in interface `[ExecutorService](../../../java/util/concurrent/ExecutorService.html "interface in java.util.concurrent")`  
Overrides:  
`[invokeAll](../../../java/util/concurrent/AbstractExecutorService.html#invokeAll-java.util.Collection-)` in class `[AbstractExecutorService](../../../java/util/concurrent/AbstractExecutorService.html "class in java.util.concurrent")`  
Type Parameters:  
`T` \- the type of the values returned from the tasks  
Parameters:  
`tasks` \- the collection of tasks  
Returns:  
a list of Futures representing the tasks, in the same sequential order as produced by the iterator for the given task list, each of which has completed  
Throws:  
`[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang")` \- if tasks or any of its elements are `null`  
`[RejectedExecutionException](../../../java/util/concurrent/RejectedExecutionException.html "class in java.util.concurrent")` \- if any task cannot be scheduled for execution  
* #### getFactory  
public [ForkJoinPool.ForkJoinWorkerThreadFactory](../../../java/util/concurrent/ForkJoinPool.ForkJoinWorkerThreadFactory.html "interface in java.util.concurrent") getFactory()  
Returns the factory used for constructing new workers.  
Returns:  
the factory used for constructing new workers  
* #### getUncaughtExceptionHandler  
public [Thread.UncaughtExceptionHandler](../../../java/lang/Thread.UncaughtExceptionHandler.html "interface in java.lang") getUncaughtExceptionHandler()  
Returns the handler for internal worker threads that terminate due to unrecoverable errors encountered while executing tasks.  
Returns:  
the handler, or `null` if none  
* #### getParallelism  
public int getParallelism()  
Returns the targeted parallelism level of this pool.  
Returns:  
the targeted parallelism level of this pool  
* #### getCommonPoolParallelism  
public static int getCommonPoolParallelism()  
Returns the targeted parallelism level of the common pool.  
Returns:  
the targeted parallelism level of the common pool  
Since:  
1.8  
* #### getPoolSize  
public 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()](../../../java/util/concurrent/ForkJoinPool.html#getParallelism--) when threads are created to maintain parallelism when others are cooperatively blocked.  
Returns:  
the number of worker threads  
* #### getAsyncMode  
public boolean getAsyncMode()  
Returns `true` if this pool uses local first-in-first-out scheduling mode for forked tasks that are never joined.  
Returns:  
`true` if this pool uses async mode  
* #### getRunningThreadCount  
public 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.  
Returns:  
the number of worker threads  
* #### getActiveThreadCount  
public 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.  
Returns:  
the number of active threads  
* #### isQuiescent  
public 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.  
Returns:  
`true` if all threads are currently idle  
* #### getStealCount  
public 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.  
Returns:  
the number of steals  
* #### getQueuedTaskCount  
public 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.  
Returns:  
the number of queued tasks  
* #### getQueuedSubmissionCount  
public 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.  
Returns:  
the number of queued submissions  
* #### hasQueuedSubmissions  
public boolean hasQueuedSubmissions()  
Returns `true` if there are any tasks submitted to this pool that have not yet begun executing.  
Returns:  
`true` if there are any queued submissions  
* #### pollSubmission  
protected [ForkJoinTask](../../../java/util/concurrent/ForkJoinTask.html "class in java.util.concurrent")<?> 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.  
Returns:  
the next submission, or `null` if none  
* #### drainTasksTo  
protected int drainTasksTo([Collection](../../../java/util/Collection.html "interface in java.util")<? super [ForkJoinTask](../../../java/util/concurrent/ForkJoinTask.html "class in java.util.concurrent")<?>> 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.  
Parameters:  
`c` \- the collection to transfer elements into  
Returns:  
the number of elements transferred  
* #### toString  
public [String](../../../java/lang/String.html "class in java.lang") toString()  
Returns a string identifying this pool, as well as its state, including indications of run state, parallelism level, and worker and task counts.  
Overrides:  
`[toString](../../../java/lang/Object.html#toString--)` in class `[Object](../../../java/lang/Object.html "class in java.lang")`  
Returns:  
a string identifying this pool, as well as its state  
* #### shutdown  
public 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()](../../../java/util/concurrent/ForkJoinPool.html#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.  
Throws:  
`[SecurityException](../../../java/lang/SecurityException.html "class in java.lang")` \- if a security manager exists and the caller is not permitted to modify threads because it does not hold [RuntimePermission](../../../java/lang/RuntimePermission.html "class in java.lang")`("modifyThread")`  
* #### shutdownNow  
public [List](../../../java/util/List.html "interface in java.util")<[Runnable](../../../java/lang/Runnable.html "interface in java.lang")> 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()](../../../java/util/concurrent/ForkJoinPool.html#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).  
Returns:  
an empty list  
Throws:  
`[SecurityException](../../../java/lang/SecurityException.html "class in java.lang")` \- if a security manager exists and the caller is not permitted to modify threads because it does not hold [RuntimePermission](../../../java/lang/RuntimePermission.html "class in java.lang")`("modifyThread")`  
* #### isTerminated  
public boolean isTerminated()  
Returns `true` if all tasks have completed following shut down.  
Returns:  
`true` if all tasks have completed following shut down  
* #### isTerminating  
public 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](../../../java/util/concurrent/ForkJoinTask.html "class in java.util.concurrent") stating that tasks should not normally entail blocking operations. But if they do, they must abort them on interrupt.)  
Returns:  
`true` if terminating but not yet terminated  
* #### isShutdown  
public boolean isShutdown()  
Returns `true` if this pool has been shut down.  
Returns:  
`true` if this pool has been shut down  
* #### awaitTermination  
public boolean awaitTermination(long timeout,  
                                [TimeUnit](../../../java/util/concurrent/TimeUnit.html "enum in java.util.concurrent") unit)  
                         throws [InterruptedException](../../../java/lang/InterruptedException.html "class in java.lang")  
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()](../../../java/util/concurrent/ForkJoinPool.html#commonPool--) never terminates until program shutdown, when applied to the common pool, this method is equivalent to [awaitQuiescence(long, TimeUnit)](../../../java/util/concurrent/ForkJoinPool.html#awaitQuiescence-long-java.util.concurrent.TimeUnit-) but always returns `false`.  
Parameters:  
`timeout` \- the maximum time to wait  
`unit` \- the time unit of the timeout argument  
Returns:  
`true` if this executor terminated and`false` if the timeout elapsed before termination  
Throws:  
`[InterruptedException](../../../java/lang/InterruptedException.html "class in java.lang")` \- if interrupted while waiting  
* #### awaitQuiescence  
public boolean awaitQuiescence(long timeout,  
                               [TimeUnit](../../../java/util/concurrent/TimeUnit.html "enum in java.util.concurrent") unit)  
If called by a ForkJoinTask operating in this pool, equivalent in effect to [ForkJoinTask.helpQuiesce()](../../../java/util/concurrent/ForkJoinTask.html#helpQuiesce--). Otherwise, waits and/or attempts to assist performing tasks until this pool [isQuiescent()](../../../java/util/concurrent/ForkJoinPool.html#isQuiescent--) or the indicated timeout elapses.  
Parameters:  
`timeout` \- the maximum time to wait  
`unit` \- the time unit of the timeout argument  
Returns:  
`true` if quiescent; `false` if the timeout elapsed.  
* #### managedBlock  
public static void managedBlock([ForkJoinPool.ManagedBlocker](../../../java/util/concurrent/ForkJoinPool.ManagedBlocker.html "interface in java.util.concurrent") blocker)  
                         throws [InterruptedException](../../../java/lang/InterruptedException.html "class in java.lang")  
Runs the given possibly blocking task. When [running in a ForkJoinPool](../../../java/util/concurrent/ForkJoinTask.html#inForkJoinPool--), 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()](../../../java/util/concurrent/ForkJoinPool.ManagedBlocker.html#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;`  
 If running in a ForkJoinPool, the pool may first be expanded to ensure sufficient parallelism available during the call to`blocker.block()`.  
Parameters:  
`blocker` \- the blocker task  
Throws:  
`[InterruptedException](../../../java/lang/InterruptedException.html "class in java.lang")` \- if `blocker.block()` did so  
* #### newTaskFor  
protected <T> [RunnableFuture](../../../java/util/concurrent/RunnableFuture.html "interface in java.util.concurrent")<T> newTaskFor([Runnable](../../../java/lang/Runnable.html "interface in java.lang") runnable,  
                                           T value)  
Returns a `RunnableFuture` for the given runnable and default value.  
Overrides:  
`[newTaskFor](../../../java/util/concurrent/AbstractExecutorService.html#newTaskFor-java.lang.Runnable-T-)` in class `[AbstractExecutorService](../../../java/util/concurrent/AbstractExecutorService.html "class in java.util.concurrent")`  
Type Parameters:  
`T` \- the type of the given value  
Parameters:  
`runnable` \- the runnable task being wrapped  
`value` \- the default value for the returned future  
Returns:  
a `RunnableFuture` which, when run, will run the underlying runnable and which, as a `Future`, will yield the given value as its result and provide for cancellation of the underlying task  
* #### newTaskFor  
protected <T> [RunnableFuture](../../../java/util/concurrent/RunnableFuture.html "interface in java.util.concurrent")<T> newTaskFor([Callable](../../../java/util/concurrent/Callable.html "interface in java.util.concurrent")<T> callable)  
Returns a `RunnableFuture` for the given callable task.  
Overrides:  
`[newTaskFor](../../../java/util/concurrent/AbstractExecutorService.html#newTaskFor-java.util.concurrent.Callable-)` in class `[AbstractExecutorService](../../../java/util/concurrent/AbstractExecutorService.html "class in java.util.concurrent")`  
Type Parameters:  
`T` \- the type of the callable's result  
Parameters:  
`callable` \- the callable task being wrapped  
Returns:  
a `RunnableFuture` which, when run, will call the underlying callable and which, as a `Future`, will yield the callable's result as its result and provide for cancellation of the underlying task

ForkJoinPool (Java SE 9 & JDK 9 ) (original) (raw)

Nested Class Summary

Field Summary

Constructor Summary

Method Summary

Field Detail

Constructor Detail

Method Detail