/*************************************************************************
* Copyright 2009-2012 Eucalyptus Systems, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
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*
* Please contact Eucalyptus Systems, Inc., 6755 Hollister Ave., Goleta
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* and permission notice:
*
* Software License Agreement (BSD License)
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* Copyright (c) 2008, Regents of the University of California
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*
* This file may incorporate work covered under the following copyright
* and permission notice:
*
* Copyright (C) 2009 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
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* or implied. See the License for the specific language governing
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************************************************************************/
package com.eucalyptus.util.concurrent;
import java.util.concurrent.Callable;
import java.util.concurrent.Executor;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import com.eucalyptus.util.async.CheckedListenableFuture;
/**
* <p>
* This interface defines a future that has listeners attached to it, which is useful for asynchronous workflows. Each listener has an associated executor, and
* is invoked using this executor once the {@code Future}'s computation is {@linkplain Future#isDone() complete}. The listener will be executed even if it is
* added after the computation is complete.
*
* <p>
* Usage:
*
* <pre>
* {
* @code
* final ListenableFuture<?> future = myService.async( myRequest );
* future.addListener( new Runnable( ) {
* public void run( ) {
* System.out.println( "Operation Complete." );
* try {
* System.out.println( "Result: " + future.get( ) );
* } catch ( Exception e ) {
* System.out.println( "Error: " + e.message( ) );
* }
* }
* }, exec );
* }
* </pre>
*
* @author Sven Mawson
* @author Nishant Thakkar
* @author chris grzegorczyk <grze@eucalyptus.com> Adopted and repurposed to support callable chaining.
*/
public interface ListenableFuture<V> extends Future<V> {
/**
* <p>
* Adds a listener and executor to the ListenableFuture. The listener will be {@linkplain Executor#execute(Runnable) passed
* to the executor} for execution when the {@code Future}'s computation is {@linkplain Future#isDone() complete}.
*
* <p>
* There is no guaranteed ordering of execution of listeners, they may get called in the order they were added and they may get called out of order, but any
* listener added through this method is guaranteed to be called once the computation is complete.
*
* @param listener the listener to run when the computation is complete.
* @param exec the executor to run the listener in.
* @throws NullPointerException if the executor or listener was null.
* @throws RejectedExecutionException if we tried to execute the listener
* immediately but the executor rejected it.
*/
void addListener( Runnable listener, ExecutorService exec );
void addListener( Runnable listener );
<T> CheckedListenableFuture<T> addListener( Callable<T> listener, ExecutorService exec );
<T> CheckedListenableFuture<T> addListener( Callable<T> listener );
}