Class ForkJoinPool
- All Implemented Interfaces:
AutoCloseable
,Executor
,ExecutorService
ExecutorService
for running ForkJoinTask
s.
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 ForkJoinTask
s), as well as when many small
tasks are submitted to the pool from external clients. Especially
when setting asyncMode to true in constructors,
ForkJoinPool
s 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 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 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 aForkJoinPool.ForkJoinWorkerThreadFactory
. The system class loader is used to load this class.java.util.concurrent.ForkJoinPool.common.exceptionHandler
- the class name of aThread.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).
SecurityManager
is present, then
the common pool uses a factory supplying threads that have no
Permissions
enabled, and are not guaranteed to preserve
the values of ThreadLocal
variables across tasks.
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 Note:
- This implementation restricts the maximum number of
running threads to 32767. Attempts to create pools with greater
than the maximum number result in
IllegalArgumentException
. Also, 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
Modifier and TypeClassDescriptionstatic interface
Factory for creating newForkJoinWorkerThread
s.static interface
Interface for extending managed parallelism for tasks running inForkJoinPool
s. -
Field Summary
Modifier and TypeFieldDescriptionstatic final ForkJoinPool.ForkJoinWorkerThreadFactory
Creates a new ForkJoinWorkerThread. -
Constructor Summary
ConstructorDescriptionCreates aForkJoinPool
with parallelism equal toRuntime.availableProcessors()
, using defaults for all other parameters (seeForkJoinPool(int, ForkJoinWorkerThreadFactory, UncaughtExceptionHandler, boolean, int, int, int, Predicate, long, TimeUnit)
).ForkJoinPool
(int parallelism) Creates aForkJoinPool
with the indicated parallelism level, using defaults for all other parameters (seeForkJoinPool(int, ForkJoinWorkerThreadFactory, UncaughtExceptionHandler, boolean, int, int, int, Predicate, long, TimeUnit)
).ForkJoinPool
(int parallelism, ForkJoinPool.ForkJoinWorkerThreadFactory factory, Thread.UncaughtExceptionHandler handler, boolean asyncMode) Creates aForkJoinPool
with the given parameters (using defaults for others -- seeForkJoinPool(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 aForkJoinPool
with the given parameters. -
Method Summary
Modifier and TypeMethodDescriptionboolean
awaitQuiescence
(long timeout, TimeUnit unit) If called by a ForkJoinTask operating in this pool, equivalent in effect toForkJoinTask.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.void
close()
Unless this is thecommonPool()
, initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted, and waits until all tasks have completed execution and the executor has terminated.static ForkJoinPool
Returns the common pool instance.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.void
Executes the given command at some time in the future.void
execute
(ForkJoinTask<?> task) Arranges for (asynchronous) execution of the given task.<T> ForkJoinTask
<T> externalSubmit
(ForkJoinTask<T> task) Submits the given task as if submitted from a non-ForkJoinTask
client.int
Returns an estimate of the number of threads that are currently stealing or executing tasks.boolean
Returnstrue
if this pool uses local first-in-first-out scheduling mode for forked tasks that are never joined.static int
Returns the targeted parallelism level of the common pool.Returns the factory used for constructing new workers.int
Returns the targeted parallelism level of this pool.int
Returns the number of worker threads that have started but not yet terminated.int
Returns an estimate of the number of tasks submitted to this pool that have not yet begun executing.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).int
Returns an estimate of the number of worker threads that are not blocked waiting to join tasks or for other managed synchronization.long
Returns an estimate of the total number of completed tasks that were executed by a thread other than their submitter.Returns the handler for internal worker threads that terminate due to unrecoverable errors encountered while executing tasks.boolean
Returnstrue
if there are any tasks submitted to this pool that have not yet begun executing.<T> T
invoke
(ForkJoinTask<T> task) Performs the given task, returning its result upon completion.invokeAllUninterruptibly
(Collection<? extends Callable<T>> tasks) Uninterrupible version ofinvokeAll
.boolean
Returnstrue
if all worker threads are currently idle.boolean
Returnstrue
if this pool has been shut down.boolean
Returnstrue
if all tasks have completed following shut down.boolean
Returnstrue
if the process of termination has commenced but not yet completed.<T> ForkJoinTask
<T> lazySubmit
(ForkJoinTask<T> task) Submits the given task without guaranteeing that it will eventually execute in the absence of available active threads.static void
managedBlock
(ForkJoinPool.ManagedBlocker blocker) Runs the given possibly blocking task.protected ForkJoinTask
<?> Removes and returns the next unexecuted submission if one is available.int
setParallelism
(int size) Changes the target parallelism of this pool, controlling the future creation, use, and termination of worker threads.void
shutdown()
Possibly initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted.Possibly attempts to cancel and/or stop all tasks, and reject all subsequently submitted tasks.ForkJoinTask
<?> Submits a Runnable task for execution and returns a Future representing that task.<T> ForkJoinTask
<T> Submits a Runnable task for execution and returns a Future representing that task.<T> ForkJoinTask
<T> 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.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 declared in class java.util.concurrent.AbstractExecutorService
invokeAll, invokeAll, invokeAny, invokeAny, newTaskFor, newTaskFor
-
Field Details
-
defaultForkJoinWorkerThreadFactory
Creates a new ForkJoinWorkerThread. This factory is used unless overridden in ForkJoinPool constructors.
-
-
Constructor Details
-
ForkJoinPool
public ForkJoinPool()Creates aForkJoinPool
with parallelism equal toRuntime.availableProcessors()
, using defaults for all other parameters (seeForkJoinPool(int, ForkJoinWorkerThreadFactory, UncaughtExceptionHandler, boolean, int, int, int, Predicate, long, TimeUnit)
).- Throws:
SecurityException
- if a security manager exists and the caller is not permitted to modify threads because it does not holdRuntimePermission
("modifyThread")
-
ForkJoinPool
public ForkJoinPool(int parallelism) Creates aForkJoinPool
with the indicated parallelism level, using defaults for all other parameters (seeForkJoinPool(int, ForkJoinWorkerThreadFactory, UncaughtExceptionHandler, boolean, int, int, int, Predicate, long, TimeUnit)
).- Parameters:
parallelism
- the parallelism level- Throws:
IllegalArgumentException
- if parallelism less than or equal to zero, or greater than implementation limitSecurityException
- if a security manager exists and the caller is not permitted to modify threads because it does not holdRuntimePermission
("modifyThread")
-
ForkJoinPool
public ForkJoinPool(int parallelism, ForkJoinPool.ForkJoinWorkerThreadFactory factory, Thread.UncaughtExceptionHandler handler, boolean asyncMode) Creates aForkJoinPool
with the given parameters (using defaults for others -- seeForkJoinPool(int, ForkJoinWorkerThreadFactory, UncaughtExceptionHandler, boolean, int, int, int, Predicate, long, TimeUnit)
).- Parameters:
parallelism
- the parallelism level. For default value, useRuntime.availableProcessors()
.factory
- the factory for creating new threads. For default value, usedefaultForkJoinWorkerThreadFactory
.handler
- the handler for internal worker threads that terminate due to unrecoverable errors encountered while executing tasks. For default value, usenull
.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, usefalse
.- Throws:
IllegalArgumentException
- if parallelism less than or equal to zero, or greater than implementation limitNullPointerException
- if the factory is nullSecurityException
- if a security manager exists and the caller is not permitted to modify threads because it does not holdRuntimePermission
("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 aForkJoinPool
with the given parameters.- Parameters:
parallelism
- the parallelism level. For default value, useRuntime.availableProcessors()
.factory
- the factory for creating new threads. For default value, usedefaultForkJoinWorkerThreadFactory
.handler
- the handler for internal worker threads that terminate due to unrecoverable errors encountered while executing tasks. For default value, usenull
.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, usefalse
.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 example0
) 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, use256
plus theparallelism
level. (By default, the common pool allows a maximum of 256 spare threads.) Using a value (for exampleInteger.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 orForkJoinPool.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, use1
, 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 orForkJoinPool.ManagedBlocker
, but cannot be replaced because the maximumPoolSize would be exceeded, aRejectedExecutionException
is thrown. But if this predicate returnstrue
, 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, use60, TimeUnit.SECONDS
.unit
- the time unit for thekeepAliveTime
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 nullSecurityException
- if a security manager exists and the caller is not permitted to modify threads because it does not holdRuntimePermission
("modifyThread")
- Since:
- 9
-
-
Method Details
-
commonPool
Returns the common pool instance. This pool is statically constructed; its run state is unaffected by attempts toshutdown()
orshutdownNow()
. However this pool and any ongoing processing are automatically terminated upon programSystem.exit(int)
. Any program that relies on asynchronous task processing to complete before program termination should invokecommonPool().
awaitQuiescence
, before exit.- Returns:
- the common pool instance
- Since:
- 1.8
-
invoke
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 usingex.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
- if the task is nullRejectedExecutionException
- if the task cannot be scheduled for execution
-
execute
Arranges for (asynchronous) execution of the given task.- Parameters:
task
- the task- Throws:
NullPointerException
- if the task is nullRejectedExecutionException
- if the task cannot be scheduled for execution
-
execute
Description copied from interface:Executor
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 theExecutor
implementation.- Parameters:
task
- the runnable task- Throws:
NullPointerException
- if the task is nullRejectedExecutionException
- if the task cannot be scheduled for execution
-
submit
Submits a ForkJoinTask for execution.- Implementation Requirements:
- This method is equivalent to
externalSubmit(ForkJoinTask)
when called from a thread that is not in this pool. - Type Parameters:
T
- the type of the task's result- Parameters:
task
- the task to submit- Returns:
- the task
- Throws:
NullPointerException
- if the task is nullRejectedExecutionException
- if the task cannot be scheduled for execution
-
submit
Description copied from interface:ExecutorService
Submits a value-returning task for execution and returns a Future representing the pending results of the task. The Future'sget
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
toCallable
form so they can be submitted.- Specified by:
submit
in interfaceExecutorService
- Overrides:
submit
in classAbstractExecutorService
- 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
- if the task is nullRejectedExecutionException
- if the task cannot be scheduled for execution
-
submit
Description copied from interface:ExecutorService
Submits a Runnable task for execution and returns a Future representing that task. The Future'sget
method will return the given result upon successful completion.- Specified by:
submit
in interfaceExecutorService
- Overrides:
submit
in classAbstractExecutorService
- Type Parameters:
T
- the type of the result- Parameters:
task
- the task to submitresult
- the result to return- Returns:
- a Future representing pending completion of the task
- Throws:
NullPointerException
- if the task is nullRejectedExecutionException
- if the task cannot be scheduled for execution
-
submit
Description copied from interface:ExecutorService
Submits a Runnable task for execution and returns a Future representing that task. The Future'sget
method will returnnull
upon successful completion.- Specified by:
submit
in interfaceExecutorService
- Overrides:
submit
in classAbstractExecutorService
- Parameters:
task
- the task to submit- Returns:
- a Future representing pending completion of the task
- Throws:
NullPointerException
- if the task is nullRejectedExecutionException
- if the task cannot be scheduled for execution
-
externalSubmit
Submits the given task as if submitted from a non-ForkJoinTask
client. The task is added to a scheduling queue for submissions to the pool even when called from a thread in the pool.- Implementation Requirements:
- This method is equivalent to
submit(ForkJoinTask)
when called from a thread that is not in this pool. - Type Parameters:
T
- the type of the task's result- Parameters:
task
- the task to submit- Returns:
- the task
- Throws:
NullPointerException
- if the task is nullRejectedExecutionException
- if the task cannot be scheduled for execution- Since:
- 20
-
lazySubmit
Submits the given task without guaranteeing that it will eventually execute in the absence of available active threads. In some contexts, this method may reduce contention and overhead by relying on context-specific knowledge that existing threads (possibly including the calling thread if operating in this pool) will eventually be available to execute the task.- Type Parameters:
T
- the type of the task's result- Parameters:
task
- the task- Returns:
- the task
- Throws:
NullPointerException
- if the task is nullRejectedExecutionException
- if the task cannot be scheduled for execution- Since:
- 19
-
setParallelism
public int setParallelism(int size) Changes the target parallelism of this pool, controlling the future creation, use, and termination of worker threads. Applications include contexts in which the number of available processors changes over time.- Implementation Note:
- This implementation restricts the maximum number of running threads to 32767
- Parameters:
size
- the target parallelism level- Returns:
- the previous parallelism level.
- Throws:
IllegalArgumentException
- if size is less than 1 or greater than the maximum supported by this pool.UnsupportedOperationException
- this is thecommonPool()
and parallelism level was set by System propertyjava.util.concurrent.ForkJoinPool.common.parallelism
.SecurityException
- if a security manager exists and the caller is not permitted to modify threads because it does not holdRuntimePermission
("modifyThread")
- Since:
- 19
-
invokeAllUninterruptibly
Uninterrupible version ofinvokeAll
. Executes the given tasks, returning a list of Futures holding their status and results when all complete, ignoring interrupts.Future.isDone()
istrue
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.- API Note:
- This method supports usages that previously relied on an
incompatible override of
ExecutorService.invokeAll(java.util.Collection)
. - 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
- if tasks or any of its elements arenull
RejectedExecutionException
- if any task cannot be scheduled for execution- Since:
- 22
-
getFactory
Returns the factory used for constructing new workers.- Returns:
- the factory used for constructing new workers
-
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 fromgetParallelism()
when threads are created to maintain parallelism when others are cooperatively blocked.- Returns:
- the number of worker threads
-
getAsyncMode
public boolean getAsyncMode()Returnstrue
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()Returnstrue
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 returntrue
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 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:
- 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
- See Also:
-
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()Returnstrue
if there are any tasks submitted to this pool that have not yet begun executing.- Returns:
true
if there are any queued submissions
-
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
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 collectionc
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
-
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 thecommonPool()
, 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 holdRuntimePermission
("modifyThread")
-
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 thecommonPool()
, 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
- if a security manager exists and the caller is not permitted to modify threads because it does not holdRuntimePermission
("modifyThread")
-
isTerminated
public boolean isTerminated()Returnstrue
if all tasks have completed following shut down.- Returns:
true
if all tasks have completed following shut down
-
isTerminating
public boolean isTerminating()Returnstrue
if the process of termination has commenced but not yet completed. This method may be useful for debugging. A return oftrue
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 classForkJoinTask
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()Returnstrue
if this pool has been shut down.- Returns:
true
if this pool has been shut down
-
awaitTermination
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 thecommonPool()
never terminates until program shutdown, when applied to the common pool, this method is equivalent toawaitQuiescence(long, TimeUnit)
but always returnsfalse
.- Parameters:
timeout
- the maximum time to waitunit
- the time unit of the timeout argument- Returns:
true
if this executor terminated andfalse
if the timeout elapsed before termination- Throws:
InterruptedException
- if interrupted while waiting
-
awaitQuiescence
If called by a ForkJoinTask operating in this pool, equivalent in effect toForkJoinTask.helpQuiesce()
. Otherwise, waits and/or attempts to assist performing tasks until this poolisQuiescent()
or the indicated timeout elapses.- Parameters:
timeout
- the maximum time to waitunit
- the time unit of the timeout argument- Returns:
true
if quiescent;false
if the timeout elapsed.
-
close
public void close()Unless this is thecommonPool()
, initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted, and waits until all tasks have completed execution and the executor has terminated.If already terminated, or this is the
commonPool()
, this method has no effect on execution, and does not wait. Otherwise, if interrupted while waiting, this method stops all executing tasks as if by invokingshutdownNow()
. It then continues to wait until all actively executing tasks have completed. Tasks that were awaiting execution are not executed. The interrupt status will be re-asserted before this method returns.- Throws:
SecurityException
- if a security manager exists and shutting down this ExecutorService may manipulate threads that the caller is not permitted to modify because it does not holdRuntimePermission
("modifyThread")
, or the security manager'scheckAccess
method denies access.- Since:
- 19
-
managedBlock
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 inblocker.block()
.This method repeatedly calls
blocker.isReleasable()
andblocker.block()
until either method returnstrue
. Every call toblocker.block()
is preceded by a call toblocker.isReleasable()
that returnedfalse
.If not running in a ForkJoinPool, this method is behaviorally equivalent to
while (!blocker.isReleasable()) if (blocker.block()) break;
blocker.block()
.- Parameters:
blocker
- the blocker task- Throws:
InterruptedException
- ifblocker.block()
did so
-