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    }