ForkJoinPool
public
class
ForkJoinPool
extends AbstractExecutorService
| java.lang.Object | ||
| ↳ | java.util.concurrent.AbstractExecutorService | |
| ↳ | java.util.concurrent.ForkJoinPool | |
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 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 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(java.util.concurrent.ForkJoinTask) |
ForkJoinTask#fork |
| Await and obtain result | invoke(java.util.concurrent.ForkJoinTask) |
ForkJoinTask#invoke |
| Arrange exec and obtain Future | submit(java.util.concurrent.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 integerjava.util.concurrent.ForkJoinPool.common.threadFactory- the class name of aForkJoinWorkerThreadFactory. The system class loader is used to load this class.java.util.concurrent.ForkJoinPool.common.exceptionHandler- the class name of aUncaughtExceptionHandler. 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).
SecurityManager is present, then
the common pool uses a factory supplying threads that have no
Permissions 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 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.
Summary
Nested classes | |
|---|---|
interface |
ForkJoinPool.ForkJoinWorkerThreadFactory
Factory for creating new |
interface |
ForkJoinPool.ManagedBlocker
Interface for extending managed parallelism for tasks running
in |
Fields | |
|---|---|
public
static
final
ForkJoinPool.ForkJoinWorkerThreadFactory |
defaultForkJoinWorkerThreadFactory
Creates a new ForkJoinWorkerThread. |
Public methods | |
|---|---|
boolean
|
awaitQuiescence(long timeout, TimeUnit unit)
If called by a ForkJoinTask operating in this pool, equivalent
in effect to |
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. |
void
|
execute(Runnable task)
|
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 |
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 completed tasks that were executed by a thread other than their submitter. |
Thread.UncaughtExceptionHandler
|
getUncaughtExceptionHandler()
Returns the handler for internal worker threads that terminate due to unrecoverable errors encountered while executing tasks. |
boolean
|
hasQueuedSubmissions()
Returns |
<T>
T
|
invoke(ForkJoinTask<T> task)
Performs the given task, returning its result upon completion. |
<T>
List<Future<T>>
|
invokeAll(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)
Executes the given tasks, returning a list of Futures holding their status and results when all complete or the timeout expires, whichever happens first. |
<T>
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. |
<T>
T
|
invokeAny(Collection<? extends Callable<T>> tasks)
Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do. |
<T>
T
|
invokeAny(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)
Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do before the given timeout elapses. |
boolean
|
isQuiescent()
Returns |
boolean
|
isShutdown()
Returns |
boolean
|
isTerminated()
Returns |
boolean
|
isTerminating()
Returns |
static
void
|
managedBlock(ForkJoinPool.ManagedBlocker blocker)
Runs the given possibly blocking task. |
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. |
<T>
ForkJoinTask<T>
|
submit(Callable<T> task)
Submits a value-returning task for execution and returns a Future representing the pending results of the task. |
<T>
ForkJoinTask<T>
|
submit(ForkJoinTask<T> task)
Submits a ForkJoinTask for execution. |
ForkJoinTask<?>
|
submit(Runnable task)
Submits a Runnable task for execution and returns a Future representing that task. |
<T>
ForkJoinTask<T>
|
submit(Runnable task, T result)
Submits a Runnable task for execution and returns a Future representing that task. |
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. |
Protected methods | |
|---|---|
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. |
<T>
RunnableFuture<T>
|
newTaskFor(Runnable runnable, T value)
Returns a |
<T>
RunnableFuture<T>
|
newTaskFor(Callable<T> callable)
Returns a |
ForkJoinTask<?>
|
pollSubmission()
Removes and returns the next unexecuted submission if one is available. |
Inherited methods | |
|---|---|
Fields
defaultForkJoinWorkerThreadFactory
public static final ForkJoinPool.ForkJoinWorkerThreadFactory defaultForkJoinWorkerThreadFactory
Creates a new ForkJoinWorkerThread. This factory is used unless overridden in ForkJoinPool constructors.
Public constructors
ForkJoinPool
public ForkJoinPool ()
Creates a ForkJoinPool with parallelism equal to Runtime.availableProcessors(), using defaults for all
other parameters (see 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 |
if a security manager exists and
the caller is not permitted to modify threads
because it does not hold RuntimePermission("modifyThread") |
ForkJoinPool
public ForkJoinPool (int parallelism)
Creates a ForkJoinPool with the indicated parallelism
level, using defaults for all other parameters (see 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 |
int: the parallelism level |
| Throws | |
|---|---|
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 RuntimePermission("modifyThread") |
ForkJoinPool
public 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, java.util.concurrent.ForkJoinPool.ForkJoinWorkerThreadFactory, java.lang.Thread.UncaughtExceptionHandler, boolean, int, int, int, java.util.function.Predicate, long, java.util.concurrent.TimeUnit)).
| Parameters | |
|---|---|
parallelism |
int: the parallelism level. For default value,
use Runtime.availableProcessors(). |
factory |
ForkJoinPool.ForkJoinWorkerThreadFactory: the factory for creating new threads. For default value,
use defaultForkJoinWorkerThreadFactory. |
handler |
Thread.UncaughtExceptionHandler: the handler for internal worker threads that
terminate due to unrecoverable errors encountered while executing
tasks. For default value, use null. |
asyncMode |
boolean: 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 |
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 RuntimePermission("modifyThread") |
ForkJoinPool
public 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.
| Parameters | |
|---|---|
parallelism |
int: the parallelism level. For default value,
use Runtime.availableProcessors(). |
factory |
ForkJoinPool.ForkJoinWorkerThreadFactory: the factory for creating new threads. For
default value, use defaultForkJoinWorkerThreadFactory. |
handler |
Thread.UncaughtExceptionHandler: the handler for internal worker threads that
terminate due to unrecoverable errors encountered while
executing tasks. For default value, use null. |
asyncMode |
boolean: 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 |
int: 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 |
int: 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 |
int: the minimum allowed number of core
threads not blocked by a join or ManagedBlocker. 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 |
Predicate: 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 ManagedBlocker, but cannot be replaced because the
maximumPoolSize would be exceeded, a RejectedExecutionException 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 |
long: 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 |
TimeUnit: the time unit for the keepAliveTime argument |
| Throws | |
|---|---|
IllegalArgumentException |
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 |
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 RuntimePermission("modifyThread") |
Public methods
awaitQuiescence
public boolean awaitQuiescence (long timeout,
TimeUnit unit)
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.
| Parameters | |
|---|---|
timeout |
long: the maximum time to wait |
unit |
TimeUnit: the time unit of the timeout argument |
| Returns | |
|---|---|
boolean |
true if quiescent; false if the
timeout elapsed. |
awaitTermination
public 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, java.util.concurrent.TimeUnit) but always returns false.
| Parameters | |
|---|---|
timeout |
long: the maximum time to wait |
unit |
TimeUnit: the time unit of the timeout argument |
| Returns | |
|---|---|
boolean |
true if this executor terminated and
false if the timeout elapsed before termination |
| Throws | |
|---|---|
InterruptedException |
if interrupted while waiting |
commonPool
public static 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
System#exit. Any program that relies on asynchronous
task processing to complete before program termination should
invoke commonPool().awaitQuiescence,
before exit.
| Returns | |
|---|---|
ForkJoinPool |
the common pool instance |
execute
public void execute (Runnable task)
| Parameters | |
|---|---|
task |
Runnable |
| Throws | |
|---|---|
NullPointerException |
if the task is null |
RejectedExecutionException |
if the task cannot be scheduled for execution |
execute
public void execute (ForkJoinTask<?> task)
Arranges for (asynchronous) execution of the given task.
| Parameters | |
|---|---|
task |
ForkJoinTask: the task |
| Throws | |
|---|---|
NullPointerException |
if the task is null |
RejectedExecutionException |
if the task cannot be scheduled for execution |
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 | |
|---|---|
int |
the number of active 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 | |
|---|---|
boolean |
true if this pool uses async mode |
getCommonPoolParallelism
public static int getCommonPoolParallelism ()
Returns the targeted parallelism level of the common pool.
| Returns | |
|---|---|
int |
the targeted parallelism level of the common pool |
getFactory
public ForkJoinPool.ForkJoinWorkerThreadFactory getFactory ()
Returns the factory used for constructing new workers.
| Returns | |
|---|---|
ForkJoinPool.ForkJoinWorkerThreadFactory |
the factory used for constructing new workers |
getParallelism
public int getParallelism ()
Returns the targeted parallelism level of this pool.
| Returns | |
|---|---|
int |
the targeted parallelism level of this pool |
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() when threads are created to
maintain parallelism when others are cooperatively blocked.
| Returns | |
|---|---|
int |
the number of worker threads |
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 | |
|---|---|
int |
the number of queued submissions |
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 | |
|---|---|
long |
the number of queued tasks |
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 | |
|---|---|
int |
the number of worker threads |
getStealCount
public long getStealCount ()
Returns an estimate of the total number of completed tasks that were executed by a thread other than their submitter. 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 | |
|---|---|
long |
the number of steals |
getUncaughtExceptionHandler
public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler ()
Returns the handler for internal worker threads that terminate due to unrecoverable errors encountered while executing tasks.
| Returns | |
|---|---|
Thread.UncaughtExceptionHandler |
the handler, or null if none |
hasQueuedSubmissions
public boolean hasQueuedSubmissions ()
Returns true if there are any tasks submitted to this
pool that have not yet begun executing.
| Returns | |
|---|---|
boolean |
true if there are any queued submissions |
invoke
public 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.
| Parameters | |
|---|---|
task |
ForkJoinTask: the task |
| Returns | |
|---|---|
T |
the task's result |
| Throws | |
|---|---|
NullPointerException |
if the task is null |
RejectedExecutionException |
if the task cannot be scheduled for execution |
invokeAll
public List<Future<T>> invokeAll (Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)
Executes the given tasks, returning a list of Futures holding
their status and results
when all complete or the timeout expires, whichever happens first.
Future#isDone is true for each
element of the returned list.
Upon return, tasks that have not completed are cancelled.
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.
| Parameters | |
|---|---|
tasks |
Collection: the collection of tasks |
timeout |
long: the maximum time to wait |
unit |
TimeUnit: the time unit of the timeout argument |
| Returns | |
|---|---|
List<Future<T>> |
a list of Futures representing the tasks, in the same sequential order as produced by the iterator for the given task list. If the operation did not time out, each task will have completed. If it did time out, some of these tasks will not have completed. |
| Throws | |
|---|---|
InterruptedException |
|
invokeAll
public 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.
Future#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.
| Parameters | |
|---|---|
tasks |
Collection: the collection of tasks |
| Returns | |
|---|---|
List<Future<T>> |
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 |
|
RejectedExecutionException |
|
invokeAny
public T invokeAny (Collection<? extends Callable<T>> tasks)
Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do. Upon normal or exceptional return, tasks that have not completed are cancelled. The results of this method are undefined if the given collection is modified while this operation is in progress.
| Parameters | |
|---|---|
tasks |
Collection: the collection of tasks |
| Returns | |
|---|---|
T |
the result returned by one of the tasks |
| Throws | |
|---|---|
ExecutionException |
|
InterruptedException |
|
invokeAny
public T invokeAny (Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)
Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do before the given timeout elapses. Upon normal or exceptional return, tasks that have not completed are cancelled. The results of this method are undefined if the given collection is modified while this operation is in progress.
| Parameters | |
|---|---|
tasks |
Collection: the collection of tasks |
timeout |
long: the maximum time to wait |
unit |
TimeUnit: the time unit of the timeout argument |
| Returns | |
|---|---|
T |
the result returned by one of the tasks |
| Throws | |
|---|---|
ExecutionException |
|
InterruptedException |
|
TimeoutException |
|
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 | |
|---|---|
boolean |
true if all threads are currently idle |
isShutdown
public boolean isShutdown ()
Returns true if this pool has been shut down.
| Returns | |
|---|---|
boolean |
true if this pool has been shut down |
isTerminated
public boolean isTerminated ()
Returns true if all tasks have completed following shut down.
| Returns | |
|---|---|
boolean |
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 stating that
tasks should not normally entail blocking operations. But if
they do, they must abort them on interrupt.)
| Returns | |
|---|---|
boolean |
true if terminating but not yet terminated |
managedBlock
public static 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;
If running in a ForkJoinPool, the pool may first be expanded to
ensure sufficient parallelism available during the call to
blocker.block().
| Parameters | |
|---|---|
blocker |
ForkJoinPool.ManagedBlocker: the blocker task |
| Throws | |
|---|---|
InterruptedException |
if blocker.block() did so |
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(), 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 |
if a security manager exists and
the caller is not permitted to modify threads
because it does not hold RuntimePermission("modifyThread") |
shutdownNow
public 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).
| Returns | |
|---|---|
List<Runnable> |
an empty list |
| Throws | |
|---|---|
SecurityException |
if a security manager exists and
the caller is not permitted to modify threads
because it does not hold RuntimePermission("modifyThread") |
submit
public 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.
| Parameters | |
|---|---|
task |
Callable: the task to submit |
| Returns | |
|---|---|
ForkJoinTask<T> |
a Future representing pending completion of the task |
| Throws | |
|---|---|
NullPointerException |
if the task is null |
RejectedExecutionException |
if the task cannot be scheduled for execution |
submit
public ForkJoinTask<T> submit (ForkJoinTask<T> task)
Submits a ForkJoinTask for execution.
| Parameters | |
|---|---|
task |
ForkJoinTask: the task to submit |
| Returns | |
|---|---|
ForkJoinTask<T> |
the task |
| Throws | |
|---|---|
NullPointerException |
if the task is null |
RejectedExecutionException |
if the task cannot be scheduled for execution |
submit
public 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.
| Parameters | |
|---|---|
task |
Runnable: the task to submit |
| Returns | |
|---|---|
ForkJoinTask<?> |
a Future representing pending completion of the task |
| Throws | |
|---|---|
NullPointerException |
if the task is null |
RejectedExecutionException |
if the task cannot be scheduled for execution |
submit
public 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.
| Parameters | |
|---|---|
task |
Runnable: the task to submit |
result |
T: the result to return |
| Returns | |
|---|---|
ForkJoinTask<T> |
a Future representing pending completion of the task |
| Throws | |
|---|---|
NullPointerException |
if the task is null |
RejectedExecutionException |
if the task cannot be scheduled for execution |
toString
public 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.
| Returns | |
|---|---|
String |
a string identifying this pool, as well as its state |
Protected methods
drainTasksTo
protected 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.
| Parameters | |
|---|---|
c |
Collection: the collection to transfer elements into |
| Returns | |
|---|---|
int |
the number of elements transferred |
newTaskFor
protected RunnableFuture<T> newTaskFor (Runnable runnable, T value)
Returns a RunnableFuture for the given runnable and default
value.
| Parameters | |
|---|---|
runnable |
Runnable: the runnable task being wrapped |
value |
T: the default value for the returned future |
| Returns | |
|---|---|
RunnableFuture<T> |
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 RunnableFuture<T> newTaskFor (Callable<T> callable)
Returns a RunnableFuture for the given callable task.
| Parameters | |
|---|---|
callable |
Callable: the callable task being wrapped |
| Returns | |
|---|---|
RunnableFuture<T> |
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 |
pollSubmission
protected 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.
| Returns | |
|---|---|
ForkJoinTask<?> |
the next submission, or null if none |
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Last updated 2024-04-11 UTC.