com.google.common.util.concurrent

Class SettableFuture<V>

java.lang.Object

com.google.common.util.concurrent.internal.InternalFutureFailureAccess

com.google.common.util.concurrent.AbstractFuture<V>

com.google.common.util.concurrent.SettableFuture<V>

All Implemented Interfaces:

ListenableFuture<V>, Future<V>

@GwtCompatible
public final class SettableFuture<V>
extends AbstractFuture<V>

A ListenableFuture whose result can be set by a set(Object), setException(Throwable) or setFuture(ListenableFuture) call. It can also, like any other Future, be cancelled.

SettableFuture is the recommended ListenableFuture implementation when your task cannot be implemented with ListeningExecutorService, the various Futures utility methods, or ListenableFutureTask. Those APIs have less opportunity for developer error. If your needs are more complex than SettableFuture supports, use AbstractFuture, which offers an extensible version of the API.

Since:

9.0 (in 1.0 as ValueFuture)

Author:

Sven Mawson

Method Summary

Modifier and Type	Method and Description
void	addListener(Runnable listener, Executor executor) Registers a listener to be run on the given executor.
boolean	cancel(boolean mayInterruptIfRunning) Attempts to cancel execution of this task.
static <V> SettableFuture<V>	create() Creates a new SettableFuture that can be completed or cancelled by a later method call.
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.
boolean	isCancelled() Returns true if this task was cancelled before it completed normally.
boolean	isDone() Returns true if this task completed.
boolean	set(V value) Sets the result of this Future unless this Future has already been cancelled or set (including set asynchronously).
boolean	setException(Throwable throwable) Sets the failed result of this Future unless this Future has already been cancelled or set (including set asynchronously).
boolean	setFuture(ListenableFuture<? extends V> future) Sets the result of this Future to match the supplied input Future once the supplied Future is done, unless this Future has already been cancelled or set (including "set asynchronously," defined below).

Methods inherited from class com.google.common.util.concurrent.AbstractFuture

afterDone, interruptTask, pendingToString, toString, tryInternalFastPathGetFailure, wasInterrupted

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Method Detail

create

public static <V> SettableFuture<V> create()

Creates a new SettableFuture that can be completed or cancelled by a later method call.

set

@CanIgnoreReturnValue
public boolean set(V value)

Description copied from class: AbstractFuture

Sets the result of this Future unless this Future has already been cancelled or set (including set asynchronously). When a call to this method returns, the Future is guaranteed to be done only if the call was accepted (in which case it returns true). If it returns false, the Future may have previously been set asynchronously, in which case its result may not be known yet. That result, though not yet known, cannot be overridden by a call to a set* method, only by a call to AbstractFuture.cancel(boolean).

Overrides:

set in class AbstractFuture<V>

Parameters:

value - the value to be used as the result

Returns:

true if the attempt was accepted, completing the Future

setException

@CanIgnoreReturnValue
public boolean setException(Throwable throwable)

Description copied from class: AbstractFuture

Sets the failed result of this Future unless this Future has already been cancelled or set (including set asynchronously). When a call to this method returns, the Future is guaranteed to be done only if the call was accepted (in which case it returns true). If it returns false, the Future may have previously been set asynchronously, in which case its result may not be known yet. That result, though not yet known, cannot be overridden by a call to a set* method, only by a call to AbstractFuture.cancel(boolean).

Overrides:

setException in class AbstractFuture<V>

Parameters:

throwable - the exception to be used as the failed result

Returns:

true if the attempt was accepted, completing the Future

setFuture

@CanIgnoreReturnValue
public boolean setFuture(ListenableFuture<? extends V> future)

Description copied from class: AbstractFuture

Sets the result of this Future to match the supplied input Future once the supplied Future is done, unless this Future has already been cancelled or set (including "set asynchronously," defined below).

If the supplied future is done when this method is called and the call is accepted, then this future is guaranteed to have been completed with the supplied future by the time this method returns. If the supplied future is not done and the call is accepted, then the future will be set asynchronously. Note that such a result, though not yet known, cannot be overridden by a call to a set* method, only by a call to AbstractFuture.cancel(boolean).

If the call setFuture(delegate) is accepted and this Future is later cancelled, cancellation will be propagated to delegate. Additionally, any call to setFuture after any cancellation will propagate cancellation to the supplied Future.

Note that, even if the supplied future is cancelled and it causes this future to complete, it will never trigger interruption behavior. In particular, it will not cause this future to invoke the AbstractFuture.interruptTask() method, and the AbstractFuture.wasInterrupted() method will not return true.

Overrides:

setFuture in class AbstractFuture<V>

Parameters:

future - the future to delegate to

Returns:

true if the attempt was accepted, indicating that the Future was not previously cancelled or set.

get

@CanIgnoreReturnValue
public final V get()
                                  throws InterruptedException,
                                         ExecutionException

Description copied from class: AbstractFuture

Waits if necessary for the computation to complete, and then retrieves its result.

The default AbstractFuture implementation throws InterruptedException if the current thread is interrupted during the call, even if the value is already available.

Specified by:

get in interface Future<V>

Overrides:

get in class AbstractFuture<V>

Returns:

the computed result

Throws:

InterruptedException - if the current thread was interrupted while waiting

ExecutionException - if the computation threw an exception

get

@CanIgnoreReturnValue
public final V get(long timeout,
                                         TimeUnit unit)
                                  throws InterruptedException,
                                         ExecutionException,
                                         TimeoutException

Description copied from class: AbstractFuture

Waits if necessary for at most the given time for the computation to complete, and then retrieves its result, if available.

The default AbstractFuture implementation throws InterruptedException if the current thread is interrupted during the call, even if the value is already available.

Specified by:

get in interface Future<V>

Overrides:

get in class AbstractFuture<V>

Parameters:

timeout - the maximum time to wait

unit - the time unit of the timeout argument

Returns:

the computed result

Throws:

InterruptedException - if the current thread was interrupted while waiting

ExecutionException - if the computation threw an exception

TimeoutException - if the wait timed out

isDone

public final boolean isDone()

Description copied from interface: java.util.concurrent.Future

Returns true if this task completed. Completion may be due to normal termination, an exception, or cancellation -- in all of these cases, this method will return true.

Specified by:

isDone in interface Future<V>

Overrides:

isDone in class AbstractFuture<V>

Returns:

true if this task completed

isCancelled

public final boolean isCancelled()

Description copied from interface: java.util.concurrent.Future

Returns true if this task was cancelled before it completed normally.

Specified by:

isCancelled in interface Future<V>

Overrides:

isCancelled in class AbstractFuture<V>

Returns:

true if this task was cancelled before it completed

addListener

public final void addListener(Runnable listener,
                              Executor executor)

Description copied from class: AbstractFuture

Registers a listener to be run on the given executor. The listener will run when the Future's computation is complete or, if the computation is already complete, immediately.

There is no guaranteed ordering of execution of listeners, but any listener added through this method is guaranteed to be called once the computation is complete.

Exceptions thrown by a listener will be propagated up to the executor. Any exception thrown during Executor.execute (e.g., a RejectedExecutionException or an exception thrown by direct execution) will be caught and logged.

Note: For fast, lightweight listeners that would be safe to execute in any thread, consider MoreExecutors.directExecutor(). Otherwise, avoid it. Heavyweight directExecutor listeners can cause problems, and these problems can be difficult to reproduce because they depend on timing. For example:

• The listener may be executed by the caller of addListener. That caller may be a UI thread or other latency-sensitive thread. This can harm UI responsiveness.
• The listener may be executed by the thread that completes this Future. That thread may be an internal system thread such as an RPC network thread. Blocking that thread may stall progress of the whole system. It may even cause a deadlock.
• The listener may delay other listeners, even listeners that are not themselves directExecutor listeners.

This is the most general listener interface. For common operations performed using listeners, see Futures. For a simplified but general listener interface, see addCallback().

Memory consistency effects: Actions in a thread prior to adding a listener happen-before its execution begins, perhaps in another thread.

Guava implementations of ListenableFuture promptly release references to listeners after executing them.

Specified by:

addListener in interface ListenableFuture<V>

Overrides:

addListener in class AbstractFuture<V>

Parameters:

listener - the listener to run when the computation is complete

executor - the executor to run the listener in

cancel

@CanIgnoreReturnValue
public final boolean cancel(boolean mayInterruptIfRunning)

Description copied from class: AbstractFuture

Attempts to cancel execution of this task. This attempt will fail if the task has already completed, has already been cancelled, or could not be cancelled for some other reason. If successful, and this task has not started when cancel is called, this task should never run. If the task has already started, then the mayInterruptIfRunning parameter determines whether the thread executing this task should be interrupted in an attempt to stop the task.

After this method returns, subsequent calls to Future.isDone() will always return true. Subsequent calls to Future.isCancelled() will always return true if this method returned true.

If a cancellation attempt succeeds on a Future that had previously been set asynchronously, then the cancellation will also be propagated to the delegate Future that was supplied in the setFuture call.

Rather than override this method to perform additional cancellation work or cleanup, subclasses should override AbstractFuture.afterDone(), consulting AbstractFuture.isCancelled() and AbstractFuture.wasInterrupted() as necessary. This ensures that the work is done even if the future is cancelled without a call to cancel, such as by calling setFuture(cancelledFuture).

Specified by:

cancel in interface Future<V>

Overrides:

cancel in class AbstractFuture<V>

Parameters:

mayInterruptIfRunning - true if the thread executing this task should be interrupted; otherwise, in-progress tasks are allowed to complete

Returns:

false if the task could not be cancelled, typically because it has already completed normally; true otherwise