static ForkJoinTask<?> adapt(Runnable runnable)
Returns a new
ForkJoinTask
that performs the
run
method of the given
Runnable
as its action, and returns a null result upon
join()
.
static <T> ForkJoinTask<T> adapt(Runnable runnable, T result)
Returns a new
ForkJoinTask
that performs the
run
method of the given
Runnable
as its action, and returns the given result upon
join()
.
static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable)
Returns a new
ForkJoinTask
that performs the
call
method of the given
Callable
as its action, and returns its result upon
join()
, translating any checked exceptions encountered into
RuntimeException
.
boolean cancel(boolean mayInterruptIfRunning)
Attempts to cancel execution of this task.
boolean compareAndSetForkJoinTaskTag(short expect, short update)
Atomically conditionally sets the tag value for this task.
void complete(V value)
Completes this task, and if not already aborted or cancelled, returning the given value as the result of subsequent invocations of join and related operations.
void completeExceptionally(Throwable ex)
Completes this task abnormally, and if not already aborted or cancelled, causes it to throw the given exception upon join and related operations.
protected abstract boolean exec()
Immediately performs the base action of this task and returns true if, upon return from this method, this task is guaranteed to have completed normally.
ForkJoinTask<V> fork()
Arranges to asynchronously execute this task in the pool the current task is running in, if applicable, or using the
ForkJoinPool.commonPool()
if not
inForkJoinPool()
.
V get()
Waits if necessary for the computation to complete, and then retrieves its result.
V get(long timeout, TimeUnit unit)
Waits if necessary for at most the given time for the computation to complete, and then retrieves its result, if available.
Throwable getException()
Returns the exception thrown by the base computation, or a CancellationException if cancelled, or null if none or if the method has not yet completed.
short getForkJoinTaskTag()
Returns the tag for this task.
static ForkJoinPool getPool()
Returns the pool hosting the current thread, or null if the current thread is executing outside of any ForkJoinPool.
static int getQueuedTaskCount()
Returns an estimate of the number of tasks that have been forked by the current worker thread but not yet executed.
abstract V getRawResult()
Returns the result that would be returned by
join()
, even if this task completed abnormally, or
null
if this task is not known to have been completed.
static int getSurplusQueuedTaskCount()
Returns an estimate of how many more locally queued tasks are held by the current worker thread than there are other worker threads that might steal them, or zero if this thread is not operating in a ForkJoinPool.
static void helpQuiesce()
Possibly executes tasks until the pool hosting the current task
is quiescent.
static boolean inForkJoinPool()
Returns
true
if the current thread is a
ForkJoinWorkerThread
executing as a ForkJoinPool computation.
V invoke()
Commences performing this task, awaits its completion if necessary, and returns its result, or throws an (unchecked) RuntimeException or Error if the underlying computation did so.
static <T extends ForkJoinTask<?>>
Collection<T> invokeAll(Collection<T> tasks)
Forks all tasks in the specified collection, returning when isDone holds for each task or an (unchecked) exception is encountered, in which case the exception is rethrown.
static void invokeAll(ForkJoinTask<?>... tasks)
Forks the given tasks, returning when isDone holds for each task or an (unchecked) exception is encountered, in which case the exception is rethrown.
static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2)
Forks the given tasks, returning when isDone holds for each task or an (unchecked) exception is encountered, in which case the exception is rethrown.
boolean isCompletedAbnormally()
Returns true if this task threw an exception or was cancelled.
boolean isCompletedNormally()
Returns true if this task completed without throwing an exception and was not cancelled.
V join()
Returns the result of the computation when it
is done.
protected static ForkJoinTask<?> peekNextLocalTask()
Returns, but does not unschedule or execute, a task queued by the current thread but not yet executed, if one is immediately available.
protected static ForkJoinTask<?> pollNextLocalTask()
Unschedules and returns, without executing, the next task queued by the current thread but not yet executed, if the current thread is operating in a ForkJoinPool.
protected static ForkJoinTask<?> pollSubmission()
If the current thread is operating in a ForkJoinPool, unschedules and returns, without executing, a task externally submitted to the pool, if one is available.
protected static ForkJoinTask<?> pollTask()
If the current thread is operating in a ForkJoinPool, unschedules and returns, without executing, the next task queued by the current thread but not yet executed, if one is available, or if not available, a task that was forked by some other thread, if available.
void quietlyComplete()
Completes this task normally without setting a value.
void quietlyInvoke()
Commences performing this task and awaits its completion if necessary, without returning its result or throwing its exception.
void quietlyJoin()
Joins this task, without returning its result or throwing its exception.
void reinitialize()
Resets the internal bookkeeping state of this task, allowing a subsequent fork.
short setForkJoinTaskTag(short newValue)
Atomically sets the tag value for this task and returns the old value.
protected abstract void setRawResult(V value)
Forces the given value to be returned as a result.
boolean tryUnfork()
Tries to unschedule this task for execution.
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, waitisCancelled, isDonepublic final ForkJoinTask<V> fork()
Arranges to asynchronously execute this task in the pool the current task is running in, if applicable, or using the
ForkJoinPool.commonPool()
if not
inForkJoinPool()
. While it is not necessarily enforced, it is a usage error to fork a task more than once unless it has completed and been reinitialized. Subsequent modifications to the state of this task or any data it operates on are not necessarily consistently observable by any thread other than the one executing it unless preceded by a call to
join()
or related methods, or a call to
Future.isDone()
returning
true
.
this, to simplify usage
public final V join()
Returns the result of the computation when it
is done. This method differs from
get()
in that abnormal completion results in
RuntimeException
or
Error
, not
ExecutionException
, and that interrupts of the calling thread do
notcause the method to abruptly return by throwing
InterruptedException
.
public final V invoke()
Commences performing this task, awaits its completion if necessary, and returns its result, or throws an (unchecked) RuntimeException or Error if the underlying computation did so.
public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2)
Forks the given tasks, returning when
isDone
holds for each task or an (unchecked) exception is encountered, in which case the exception is rethrown. If more than one task encounters an exception, then this method throws any one of these exceptions. If any task encounters an exception, the other may be cancelled. However, the execution status of individual tasks is not guaranteed upon exceptional return. The status of each task may be obtained using
getException()
and related methods to check if they have been cancelled, completed normally or exceptionally, or left unprocessed.
t1 - the first task
t2 - the second task
NullPointerException - if any task is null
public static void invokeAll(ForkJoinTask<?>... tasks)
Forks the given tasks, returning when
isDone
holds for each task or an (unchecked) exception is encountered, in which case the exception is rethrown. If more than one task encounters an exception, then this method throws any one of these exceptions. If any task encounters an exception, others may be cancelled. However, the execution status of individual tasks is not guaranteed upon exceptional return. The status of each task may be obtained using
getException()
and related methods to check if they have been cancelled, completed normally or exceptionally, or left unprocessed.
tasks - the tasks
NullPointerException - if any task is null
public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks)
Forks all tasks in the specified collection, returning when
isDone
holds for each task or an (unchecked) exception is encountered, in which case the exception is rethrown. If more than one task encounters an exception, then this method throws any one of these exceptions. If any task encounters an exception, others may be cancelled. However, the execution status of individual tasks is not guaranteed upon exceptional return. The status of each task may be obtained using
getException()
and related methods to check if they have been cancelled, completed normally or exceptionally, or left unprocessed.
T - the type of the values returned from the tasks
tasks - the collection of tasks
NullPointerException - if tasks or any element are null
public boolean cancel(boolean mayInterruptIfRunning)
Attempts to cancel execution of this task. This attempt will fail if the task has already completed or could not be cancelled for some other reason. If successful, and this task has not started when
cancel
is called, execution of this task is suppressed. After this method returns successfully, unless there is an intervening call to
reinitialize()
, subsequent calls to
Future.isCancelled()
,
Future.isDone()
, and
cancel
will return
true
and calls to
join()
and related methods will result in
CancellationException
.
This method may be overridden in subclasses, but if so, must still ensure that these properties hold. In particular, the cancel method itself must not throw exceptions.
This method is designed to be invoked by other tasks. To terminate the current task, you can just return or throw an unchecked exception from its computation method, or invoke completeExceptionally(Throwable).
public final boolean isCompletedAbnormally()
Returns true if this task threw an exception or was cancelled.
true if this task threw an exception or was cancelled
public final boolean isCompletedNormally()
Returns true if this task completed without throwing an exception and was not cancelled.
true if this task completed without throwing an exception and was not cancelled
public final Throwable getException()
Returns the exception thrown by the base computation, or a CancellationException if cancelled, or null if none or if the method has not yet completed.
null if none
public void completeExceptionally(Throwable ex)
Completes this task abnormally, and if not already aborted or cancelled, causes it to throw the given exception upon join and related operations. This method may be used to induce exceptions in asynchronous tasks, or to force completion of tasks that would not otherwise complete. Its use in other situations is discouraged. This method is overridable, but overridden versions must invoke super implementation to maintain guarantees.
ex - the exception to throw. If this exception is not a RuntimeException or Error, the actual exception thrown will be a RuntimeException with cause ex.
public void complete(V value)
Completes this task, and if not already aborted or cancelled, returning the given value as the result of subsequent invocations of join and related operations. This method may be used to provide results for asynchronous tasks, or to provide alternative handling for tasks that would not otherwise complete normally. Its use in other situations is discouraged. This method is overridable, but overridden versions must invoke super implementation to maintain guarantees.
value - the result value for this task
public final void quietlyComplete()
Completes this task normally without setting a value. The most recent value established by
setRawResult(V)
(or
null
by default) will be returned as the result of subsequent invocations of
join
and related operations.
public final V get() throws InterruptedException, ExecutionException
Waits if necessary for the computation to complete, and then retrieves its result.
get in interface Future<V>
CancellationException - if the computation was cancelled
ExecutionException - if the computation threw an exception
InterruptedException - if the current thread is not a member of a ForkJoinPool and was interrupted while waiting
public final V get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException
Waits if necessary for at most the given time for the computation to complete, and then retrieves its result, if available.
get in interface Future<V>
timeout - the maximum time to wait
unit - the time unit of the timeout argument
CancellationException - if the computation was cancelled
ExecutionException - if the computation threw an exception
InterruptedException - if the current thread is not a member of a ForkJoinPool and was interrupted while waiting
TimeoutException - if the wait timed out
public final void quietlyJoin()
Joins this task, without returning its result or throwing its exception. This method may be useful when processing collections of tasks when some have been cancelled or otherwise known to have aborted.
public final void quietlyInvoke()
Commences performing this task and awaits its completion if necessary, without returning its result or throwing its exception.
public static void helpQuiesce()
Possibly executes tasks until the pool hosting the current task
is quiescent. This method may be of use in designs in which many tasks are forked, but none are explicitly joined, instead executing them until all are processed.
public void reinitialize()
Resets the internal bookkeeping state of this task, allowing a subsequent
fork
. This method allows repeated reuse of this task, but only if reuse occurs when this task has either never been forked, or has been forked, then completed and all outstanding joins of this task have also completed. Effects under any other usage conditions are not guaranteed. This method may be useful when executing pre-constructed trees of subtasks in loops.
Upon completion of this method, isDone() reports false, and getException() reports null. However, the value returned by getRawResult is unaffected. To clear this value, you can invoke setRawResult(null).
public static ForkJoinPool getPool()
Returns the pool hosting the current thread, or
null
if the current thread is executing outside of any ForkJoinPool.
This method returns null if and only if inForkJoinPool() returns false.
null if none
public static boolean inForkJoinPool()
Returns
true
if the current thread is a
ForkJoinWorkerThread
executing as a ForkJoinPool computation.
true if the current thread is a ForkJoinWorkerThread executing as a ForkJoinPool computation, or false otherwise
public boolean tryUnfork()
Tries to unschedule this task for execution. This method will typically (but is not guaranteed to) succeed if this task is the most recently forked task by the current thread, and has not commenced executing in another thread. This method may be useful when arranging alternative local processing of tasks that could have been, but were not, stolen.
true if unforked
public static int getQueuedTaskCount()
Returns an estimate of the number of tasks that have been forked by the current worker thread but not yet executed. This value may be useful for heuristic decisions about whether to fork other tasks.
public static int getSurplusQueuedTaskCount()
Returns an estimate of how many more locally queued tasks are held by the current worker thread than there are other worker threads that might steal them, or zero if this thread is not operating in a ForkJoinPool. This value may be useful for heuristic decisions about whether to fork other tasks. In many usages of ForkJoinTasks, at steady state, each worker should aim to maintain a small constant surplus (for example, 3) of tasks, and to process computations locally if this threshold is exceeded.
public abstract V getRawResult()
Returns the result that would be returned by
join()
, even if this task completed abnormally, or
null
if this task is not known to have been completed. This method is designed to aid debugging, as well as to support extensions. Its use in any other context is discouraged.
null if not completed
protected abstract void setRawResult(V value)
Forces the given value to be returned as a result. This method is designed to support extensions, and should not in general be called otherwise.
value - the value
protected abstract boolean exec()
Immediately performs the base action of this task and returns true if, upon return from this method, this task is guaranteed to have completed normally. This method may return false otherwise, to indicate that this task is not necessarily complete (or is not known to be complete), for example in asynchronous actions that require explicit invocations of completion methods. This method may also throw an (unchecked) exception to indicate abnormal exit. This method is designed to support extensions, and should not in general be called otherwise.
true if this task is known to have completed normally
protected static ForkJoinTask<?> peekNextLocalTask()
Returns, but does not unschedule or execute, a task queued by the current thread but not yet executed, if one is immediately available. There is no guarantee that this task will actually be polled or executed next. Conversely, this method may return null even if a task exists but cannot be accessed without contention with other threads. This method is designed primarily to support extensions, and is unlikely to be useful otherwise.
null if none are available
protected static ForkJoinTask<?> pollNextLocalTask()
Unschedules and returns, without executing, the next task queued by the current thread but not yet executed, if the current thread is operating in a ForkJoinPool. This method is designed primarily to support extensions, and is unlikely to be useful otherwise.
null if none are available
protected static ForkJoinTask<?> pollTask()
If the current thread is operating in a ForkJoinPool, unschedules and returns, without executing, the next task queued by the current thread but not yet executed, if one is available, or if not available, a task that was forked by some other thread, if available. Availability may be transient, so a null result does not necessarily imply quiescence of the pool this task is operating in. This method is designed primarily to support extensions, and is unlikely to be useful otherwise.
null if none are available
protected static ForkJoinTask<?> pollSubmission()
If the current thread is operating in a ForkJoinPool, unschedules and returns, without executing, a task externally submitted to the pool, if one is available. Availability may be transient, so a null result does not necessarily imply quiescence of the pool. This method is designed primarily to support extensions, and is unlikely to be useful otherwise.
null if none are available
public final short getForkJoinTaskTag()
Returns the tag for this task.
public final short setForkJoinTaskTag(short newValue)
Atomically sets the tag value for this task and returns the old value.
newValue - the new tag value
public final boolean compareAndSetForkJoinTaskTag(short expect,
short update)
Atomically conditionally sets the tag value for this task. Among other applications, tags can be used as visit markers in tasks operating on graphs, as in methods that check: if (task.compareAndSetForkJoinTaskTag((short)0, (short)1)) before processing, otherwise exiting because the node has already been visited.
expect - the expected tag value
update - the new tag value
true if successful; i.e., the current value was equal to expect and was changed to update.
public static ForkJoinTask<?> adapt(Runnable runnable)
Returns a new
ForkJoinTask
that performs the
run
method of the given
Runnable
as its action, and returns a null result upon
join()
.
runnable - the runnable action
public static <T> ForkJoinTask<T> adapt(Runnable runnable, T result)
Returns a new
ForkJoinTask
that performs the
run
method of the given
Runnable
as its action, and returns the given result upon
join()
.
T - the type of the result
runnable - the runnable action
result - the result upon completion
public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable)
Returns a new
ForkJoinTask
that performs the
call
method of the given
Callable
as its action, and returns its result upon
join()
, translating any checked exceptions encountered into
RuntimeException
.
T - the type of the callable's result
callable - the callable action
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