001 /* 002 * Copyright (C) 2007 The Guava Authors 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * http://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017 package com.google.common.util.concurrent; 018 019 import com.google.common.annotations.Beta; 020 021 import java.util.concurrent.Executor; 022 023 /** 024 * <p>An abstract base implementation of the listener support provided by 025 * {@link ListenableFuture}. This class uses an {@link ExecutionList} to 026 * guarantee that all registered listeners will be executed. Listener/Executor 027 * pairs are stored in the execution list and executed in the order in which 028 * they were added, but because of thread scheduling issues there is no 029 * guarantee that the JVM will execute them in order. In addition, listeners 030 * added after the task is complete will be executed immediately, even if some 031 * previously added listeners have not yet been executed. 032 * 033 * <p>This class uses the {@link AbstractFuture} class to implement the 034 * {@code ListenableFuture} interface and simply delegates the 035 * {@link #addListener(Runnable, Executor)} and {@link #done()} methods to it. 036 * 037 * @author Sven Mawson 038 * @since 1 039 */ 040 @Beta 041 public abstract class AbstractListenableFuture<V> 042 extends AbstractFuture<V> implements ListenableFuture<V> { 043 044 // The execution list to hold our executors. 045 private final ExecutionList executionList = new ExecutionList(); 046 047 /* 048 * Adds a listener/executor pair to execution list to execute when this task 049 * is completed. 050 */ 051 @Override 052 public void addListener(Runnable listener, Executor exec) { 053 executionList.add(listener, exec); 054 } 055 056 /* 057 * Override the done method to execute the execution list. 058 */ 059 @Override 060 protected void done() { 061 executionList.run(); 062 } 063 }