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akka.dispatch.forkjoin

ForkJoinPool

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.

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 ManagedBlocker interface enables extension of the kinds of synchronization accommodated.

In addition to execution and lifecycle control methods, this class provides status check methods (for example #getStealCount) that are intended to aid in developing, tuning, and monitoring fork/join applications. Also, method #toString 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.

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 common pool is by default constructed with default parameters, but these may be controlled by setting three `[[ System#getProperty system properties]]` with prefix java.util.concurrent.ForkJoinPool.common: parallelism -- an integer greater than zero, threadFactory -- the class name of a `[[ForkJoinWorkerThreadFactory]]`, and exceptionHandler -- the class name of a `[[ java.lang.Thread.UncaughtExceptionHandler Thread.UncaughtExceptionHandler]]`. Upon any error in establishing these settings, default parameters are used. Implementation notes: This implementation restricts the maximum number of running threads to 32767. Attempts to create pools with greater than the maximum number result in IllegalArgumentException. This implementation rejects submitted tasks (that is, by throwing `[[RejectedExecutionException]]`) only when the pool is shut down or internal resources have been exhausted.

Source
ForkJoinPool.java
Since

1.7

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  1. ForkJoinPool
  2. AbstractExecutorService
  3. ExecutorService
  4. Executor
  5. AnyRef
  6. Any
Implicitly
  1. by any2stringadd
  2. by StringFormat
  3. by Ensuring
  4. by ArrowAssoc
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Instance Constructors

  1. new ForkJoinPool(parallelism: Int, factory: ForkJoinWorkerThreadFactory, handler: UncaughtExceptionHandler, asyncMode: Boolean)

    Creates a ForkJoinPool with the given parameters.

    Creates a ForkJoinPool with the given parameters.

    parallelism

    the parallelism level. For default value, use java.lang.Runtime#availableProcessors.

    factory

    the factory for creating new threads. For default value, use #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.

    Exceptions thrown

    IllegalArgumentException if parallelism less than or equal to zero, or greater than implementation limit

    NullPointerException if the factory is null

    SecurityException if a security manager exists and the caller is not permitted to modify threads because it does not hold java.lang.RuntimePermission("modifyThread")

  2. new ForkJoinPool(parallelism: Int)

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

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

    parallelism

    the parallelism level

    Exceptions thrown

    IllegalArgumentException if parallelism less than or equal to zero, or greater than implementation limit

    SecurityException if a security manager exists and the caller is not permitted to modify threads because it does not hold java.lang.RuntimePermission("modifyThread")

  3. new ForkJoinPool()

Value Members

  1. final def !=(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  2. final def ##(): Int
    Definition Classes
    AnyRef → Any
  3. def +(other: String): String
    Implicit
    This member is added by an implicit conversion from ForkJoinPool to any2stringadd[ForkJoinPool] performed by method any2stringadd in scala.Predef.
    Definition Classes
    any2stringadd
  4. def ->[B](y: B): (ForkJoinPool, B)
    Implicit
    This member is added by an implicit conversion from ForkJoinPool to ArrowAssoc[ForkJoinPool] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
    ArrowAssoc
    Annotations
    @inline()
  5. final def ==(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  6. final def asInstanceOf[T0]: T0
    Definition Classes
    Any
  7. def awaitQuiescence(timeout: Long, unit: TimeUnit): Boolean

    If called by a ForkJoinTask operating in this pool, equivalent in effect to ForkJoinTask#helpQuiesce.

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

    timeout

    the maximum time to wait

    unit

    the time unit of the timeout argument

    returns

    true if quiescent; false if the timeout elapsed.

  8. def awaitTermination(timeout: Long, unit: TimeUnit): Boolean

    Blocks until all tasks have completed execution after a shutdown request, or the timeout occurs, or the current thread is interrupted, whichever happens first.

    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 but always returns false.

    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

    Definition Classes
    ForkJoinPool → ExecutorService
    Exceptions thrown

    InterruptedException if interrupted while waiting

  9. def clone(): AnyRef
    Attributes
    protected[java.lang]
    Definition Classes
    AnyRef
    Annotations
    @native() @HotSpotIntrinsicCandidate() @throws( ... )
  10. def drainTasksTo(c: Collection[_ >: ForkJoinTask[_]]): Int

    Removes all available unexecuted submitted and forked tasks from scheduling queues and adds them to the given collection, without altering their execution status.

    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.

    c

    the collection to transfer elements into

    returns

    the number of elements transferred

    Attributes
    protected[akka.dispatch.forkjoin]
  11. def ensuring(cond: (ForkJoinPool) ⇒ Boolean, msg: ⇒ Any): ForkJoinPool
    Implicit
    This member is added by an implicit conversion from ForkJoinPool to Ensuring[ForkJoinPool] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  12. def ensuring(cond: (ForkJoinPool) ⇒ Boolean): ForkJoinPool
    Implicit
    This member is added by an implicit conversion from ForkJoinPool to Ensuring[ForkJoinPool] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  13. def ensuring(cond: Boolean, msg: ⇒ Any): ForkJoinPool
    Implicit
    This member is added by an implicit conversion from ForkJoinPool to Ensuring[ForkJoinPool] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  14. def ensuring(cond: Boolean): ForkJoinPool
    Implicit
    This member is added by an implicit conversion from ForkJoinPool to Ensuring[ForkJoinPool] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  15. final def eq(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  16. def equals(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  17. def execute(task: Runnable): Unit

    Definition Classes
    ForkJoinPool → Executor
    Exceptions thrown

    NullPointerException if the task is null

    RejectedExecutionException if the task cannot be scheduled for execution

  18. def execute(task: ForkJoinTask[_]): Unit

    Arranges for (asynchronous) execution of the given task.

    Arranges for (asynchronous) execution of the given task.

    task

    the task

    Exceptions thrown

    NullPointerException if the task is null

    RejectedExecutionException if the task cannot be scheduled for execution

  19. def formatted(fmtstr: String): String
    Implicit
    This member is added by an implicit conversion from ForkJoinPool to StringFormat[ForkJoinPool] performed by method StringFormat in scala.Predef.
    Definition Classes
    StringFormat
    Annotations
    @inline()
  20. def getActiveThreadCount(): Int

    Returns an estimate of the number of threads that are currently stealing or executing tasks.

    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

  21. def getAsyncMode(): Boolean

    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 local first-in-first-out scheduling mode for forked tasks that are never joined.

    returns

    true if this pool uses async mode

  22. final def getClass(): Class[_]
    Definition Classes
    AnyRef → Any
    Annotations
    @native() @HotSpotIntrinsicCandidate()
  23. def getFactory(): ForkJoinWorkerThreadFactory

    Returns the factory used for constructing new workers.

    Returns the factory used for constructing new workers.

    returns

    the factory used for constructing new workers

  24. def getParallelism(): Int

    Returns the targeted parallelism level of this pool.

    Returns the targeted parallelism level of this pool.

    returns

    the targeted parallelism level of this pool

  25. def getPoolSize(): Int

    Returns the number of worker threads that have started but not yet terminated.

    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.

    returns

    the number of worker threads

  26. def getQueuedSubmissionCount(): Int

    Returns an estimate of the number of tasks submitted to this pool that have not yet begun executing.

    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

  27. def getQueuedTaskCount(): Long

    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).

    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

  28. def getRunningThreadCount(): Int

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

    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

  29. def getStealCount(): Long

    Returns an estimate of the total number of tasks stolen from one thread's work queue by another.

    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

  30. def getUncaughtExceptionHandler(): UncaughtExceptionHandler

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

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

    returns

    the handler, or null if none

  31. def hasQueuedSubmissions(): Boolean

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

    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

  32. def hashCode(): Int
    Definition Classes
    AnyRef → Any
    Annotations
    @native() @HotSpotIntrinsicCandidate()
  33. def invoke[T](task: ForkJoinTask[T]): T

    Performs the given task, returning its result upon completion.

    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.

    task

    the task

    returns

    the task's result

    Exceptions thrown

    NullPointerException if the task is null

    RejectedExecutionException if the task cannot be scheduled for execution

  34. def invokeAll[T](tasks: Collection[_ <: Callable[T]]): List[Future[T]]

    Definition Classes
    ForkJoinPool → AbstractExecutorService → ExecutorService
    Exceptions thrown

    NullPointerException <invalid inheritdoc annotation>

    RejectedExecutionException <invalid inheritdoc annotation>

  35. def invokeAll[T](arg0: Collection[_ <: Callable[T]], arg1: Long, arg2: TimeUnit): List[Future[T]]
    Definition Classes
    AbstractExecutorService → ExecutorService
    Annotations
    @throws( ... )
  36. def invokeAny[T](arg0: Collection[_ <: Callable[T]], arg1: Long, arg2: TimeUnit): T
    Definition Classes
    AbstractExecutorService → ExecutorService
    Annotations
    @throws( ... ) @throws( ... ) @throws( ... )
  37. def invokeAny[T](arg0: Collection[_ <: Callable[T]]): T
    Definition Classes
    AbstractExecutorService → ExecutorService
    Annotations
    @throws( ... ) @throws( ... )
  38. final def isInstanceOf[T0]: Boolean
    Definition Classes
    Any
  39. def isQuiescent(): Boolean

    Returns true if all worker threads are currently idle.

    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

  40. def isShutdown(): Boolean

    Returns true if this pool has been shut down.

    Returns true if this pool has been shut down.

    returns

    true if this pool has been shut down

    Definition Classes
    ForkJoinPool → ExecutorService
  41. def isTerminated(): Boolean

    Returns true if all tasks have completed following shut down.

    Returns true if all tasks have completed following shut down.

    returns

    true if all tasks have completed following shut down

    Definition Classes
    ForkJoinPool → ExecutorService
  42. def isTerminating(): Boolean

    Returns true if the process of termination has commenced but not yet completed.

    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.)

    returns

    true if terminating but not yet terminated

  43. final def ne(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  44. def newTaskFor[T](callable: Callable[T]): RunnableFuture[T]
    Attributes
    protected[akka.dispatch.forkjoin]
    Definition Classes
    ForkJoinPool → AbstractExecutorService
  45. def newTaskFor[T](runnable: Runnable, value: T): RunnableFuture[T]
    Attributes
    protected[akka.dispatch.forkjoin]
    Definition Classes
    ForkJoinPool → AbstractExecutorService
  46. final def notify(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native() @HotSpotIntrinsicCandidate()
  47. final def notifyAll(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native() @HotSpotIntrinsicCandidate()
  48. def pollSubmission(): ForkJoinTask[_]

    Removes and returns the next unexecuted submission if one is available.

    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

    Attributes
    protected[akka.dispatch.forkjoin]
  49. def shutdown(): Unit

    Possibly initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted.

    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.

    Definition Classes
    ForkJoinPool → ExecutorService
    Exceptions thrown

    SecurityException if a security manager exists and the caller is not permitted to modify threads because it does not hold java.lang.RuntimePermission("modifyThread")

  50. def shutdownNow(): List[Runnable]

    Possibly attempts to cancel and/or stop all tasks, and reject all subsequently submitted tasks.

    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).

    returns

    an empty list

    Definition Classes
    ForkJoinPool → ExecutorService
    Exceptions thrown

    SecurityException if a security manager exists and the caller is not permitted to modify threads because it does not hold java.lang.RuntimePermission("modifyThread")

  51. def submit(task: Runnable): ForkJoinTask[_]

    Definition Classes
    ForkJoinPool → AbstractExecutorService → ExecutorService
    Exceptions thrown

    NullPointerException if the task is null

    RejectedExecutionException if the task cannot be scheduled for execution

  52. def submit[T](task: Runnable, result: T): ForkJoinTask[T]

    Definition Classes
    ForkJoinPool → AbstractExecutorService → ExecutorService
    Exceptions thrown

    NullPointerException if the task is null

    RejectedExecutionException if the task cannot be scheduled for execution

  53. def submit[T](task: Callable[T]): ForkJoinTask[T]

    Definition Classes
    ForkJoinPool → AbstractExecutorService → ExecutorService
    Exceptions thrown

    NullPointerException if the task is null

    RejectedExecutionException if the task cannot be scheduled for execution

  54. def submit[T](task: ForkJoinTask[T]): ForkJoinTask[T]

    Submits a ForkJoinTask for execution.

    Submits a ForkJoinTask for execution.

    task

    the task to submit

    returns

    the task

    Exceptions thrown

    NullPointerException if the task is null

    RejectedExecutionException if the task cannot be scheduled for execution

  55. final def synchronized[T0](arg0: ⇒ T0): T0
    Definition Classes
    AnyRef
  56. def toString(): String

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

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

    returns

    a string identifying this pool, as well as its state

    Definition Classes
    ForkJoinPool → AnyRef → Any
  57. final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  58. final def wait(arg0: Long): Unit
    Definition Classes
    AnyRef
    Annotations
    @native() @throws( ... )
  59. final def wait(): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  60. def [B](y: B): (ForkJoinPool, B)
    Implicit
    This member is added by an implicit conversion from ForkJoinPool to ArrowAssoc[ForkJoinPool] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
    ArrowAssoc

Deprecated Value Members

  1. def finalize(): Unit
    Attributes
    protected[java.lang]
    Definition Classes
    AnyRef
    Annotations
    @Deprecated @deprecated @throws( classOf[java.lang.Throwable] )
    Deprecated

    (Since version ) see corresponding Javadoc for more information.

Inherited from AbstractExecutorService

Inherited from ExecutorService

Inherited from Executor

Inherited from AnyRef

Inherited from Any

Inherited by implicit conversion any2stringadd from ForkJoinPool to any2stringadd[ForkJoinPool]

Inherited by implicit conversion StringFormat from ForkJoinPool to StringFormat[ForkJoinPool]

Inherited by implicit conversion Ensuring from ForkJoinPool to Ensuring[ForkJoinPool]

Inherited by implicit conversion ArrowAssoc from ForkJoinPool to ArrowAssoc[ForkJoinPool]

Ungrouped