com.google.common.util.concurrent

Class ForwardingListenableFuture<V>

java.lang.Object

com.google.common.collect.ForwardingObject

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

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

Type Parameters:

V - The result type returned by this Future's get method

All Implemented Interfaces:

ListenableFuture<V>, Future<V>

Direct Known Subclasses:

ForwardingCheckedFuture, ForwardingListenableFuture.SimpleForwardingListenableFuture

public abstract class ForwardingListenableFuture<V>
extends ForwardingFuture<V>
implements ListenableFuture<V>

A ListenableFuture which forwards all its method calls to another future. Subclasses should override one or more methods to modify the behavior of the backing future as desired per the decorator pattern.

Most subclasses can just use ForwardingListenableFuture.SimpleForwardingListenableFuture.

Since:

4.0

Author:

Shardul Deo

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	ForwardingListenableFuture.SimpleForwardingListenableFuture<V> A simplified version of ForwardingListenableFuture where subclasses can pass in an already constructed ListenableFuture as the delegate.

Nested classes/interfaces inherited from class com.google.common.util.concurrent.ForwardingFuture

ForwardingFuture.SimpleForwardingFuture<V>

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	ForwardingListenableFuture() Constructor for use by subclasses.

Method Summary

Methods

Modifier and Type	Method and Description
void	addListener(Runnable listener, Executor exec) Registers a listener to be run on the given executor.
protected abstract ListenableFuture<V>	delegate() Returns the backing delegate instance that methods are forwarded to.

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

cancel, get, get, isCancelled, isDone

Methods inherited from class com.google.common.collect.ForwardingObject

toString

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.concurrent.Future

cancel, get, get, isCancelled, isDone

Constructor Detail

ForwardingListenableFuture

protected ForwardingListenableFuture()

Constructor for use by subclasses.

Method Detail

delegate

protected abstract ListenableFuture<V> delegate()

Description copied from class: ForwardingObject

Returns the backing delegate instance that methods are forwarded to. Abstract subclasses generally override this method with an abstract method that has a more specific return type, such as ForwardingSet.delegate(). Concrete subclasses override this method to supply the instance being decorated.

Specified by:

delegate in class ForwardingFuture<V>

addListener

public void addListener(Runnable listener,
               Executor exec)

Description copied from interface: ListenableFuture

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 inline execution) will be caught and logged.

Note: For fast, lightweight listeners that would be safe to execute in any thread, consider MoreExecutors.sameThreadExecutor(). For heavier listeners, sameThreadExecutor() carries some caveats. For example, the listener may run on an unpredictable or undesirable thread:

• If the input Future is done at the time addListener is called, addListener will execute the listener inline.
• If the input Future is not yet done, addListener will schedule the listener to be run by the thread that completes the input Future, which may be an internal system thread such as an RPC network thread.

Also note that, regardless of which thread executes the listener, all other registered but unexecuted listeners are prevented from running during its execution, even if those listeners are to run in other executors.

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

Specified by:

addListener in interface ListenableFuture<V>

Parameters:

listener - the listener to run when the computation is complete

exec - the executor to run the listener in