com.google.common.util.concurrent

Class ListenableFutureTask<V>

java.lang.Object

java.util.concurrent.FutureTask<V>

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

All Implemented Interfaces:

ListenableFuture<V>, Runnable, Future<V>, RunnableFuture<V>

@GwtIncompatible
public class ListenableFutureTask<V>
extends FutureTask<V>
implements ListenableFuture<V>

A FutureTask that also implements the ListenableFuture interface. Unlike FutureTask, ListenableFutureTask does not provide an overrideable done() method. For similar functionality, call addListener(java.lang.Runnable, java.util.concurrent.Executor).

Few users should use this class. It is intended primarily for those who are implementing an ExecutorService. Most users should call ListeningExecutorService.submit on a service obtained from MoreExecutors.listeningDecorator(java.util.concurrent.ExecutorService).

Since:

1.0

Author:

Sven Mawson

Method Summary

Modifier and Type	Method and Description
void	addListener(Runnable listener, Executor exec) Registers a listener to be run on the given executor.
static <V> ListenableFutureTask<V>	create(Callable<V> callable) Creates a ListenableFutureTask that will upon running, execute the given Callable.
static <V> ListenableFutureTask<V>	create(Runnable runnable, V result) Creates a ListenableFutureTask that will upon running, execute the given Runnable, and arrange that get will return the given result on successful completion.
protected void	done() Internal implementation detail used to invoke the listeners.

Methods inherited from class java.util.concurrent.FutureTask

cancel, get, get, isCancelled, isDone, run, runAndReset, set, setException

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.concurrent.Future

cancel, get, get, isCancelled, isDone

Method Detail

create

public static <V> ListenableFutureTask<V> create(Callable<V> callable)

Creates a ListenableFutureTask that will upon running, execute the given Callable.

Parameters:

callable - the callable task

Since:

10.0

create

public static <V> ListenableFutureTask<V> create(Runnable runnable,
                                                 V result)

Creates a ListenableFutureTask that will upon running, execute the given Runnable, and arrange that get will return the given result on successful completion.

Parameters:

runnable - the runnable task

result - the result to return on successful completion. If you don't need a particular result, consider using constructions of the form: ListenableFuture<?> f = ListenableFutureTask.create(runnable, null)

Since:

10.0

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 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>

Parameters:

listener - the listener to run when the computation is complete

exec - the executor to run the listener in

done

protected void done()

Internal implementation detail used to invoke the listeners.

Overrides:

done in class FutureTask<V>