001/*
002 * Copyright (C) 2008 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
017package com.google.common.util.concurrent;
018
019import java.util.concurrent.Callable;
020import java.util.concurrent.Executor;
021import java.util.concurrent.FutureTask;
022
023import javax.annotation.Nullable;
024
025/**
026 * A {@link FutureTask} that also implements the {@link ListenableFuture}
027 * interface.  Unlike {@code FutureTask}, {@code ListenableFutureTask} does not
028 * provide an overrideable {@link FutureTask#done() done()} method.  For similar
029 * functionality, call {@link #addListener}.
030 * 
031 * <p>
032 *
033 * @author Sven Mawson
034 * @since 1.0
035 */
036public class ListenableFutureTask<V> extends FutureTask<V>
037    implements ListenableFuture<V> {
038  // TODO(cpovirk): explore ways of making ListenableFutureTask final. There are
039  // some valid reasons such as BoundedQueueExecutorService to allow extends but it
040  // would be nice to make it final to avoid unintended usage.
041
042  // The execution list to hold our listeners.
043  private final ExecutionList executionList = new ExecutionList();
044
045  /**
046   * Creates a {@code ListenableFutureTask} that will upon running, execute the
047   * given {@code Callable}.
048   *
049   * @param callable the callable task
050   * @since 10.0
051   */
052  public static <V> ListenableFutureTask<V> create(Callable<V> callable) {
053    return new ListenableFutureTask<V>(callable);
054  }
055
056  /**
057   * Creates a {@code ListenableFutureTask} that will upon running, execute the
058   * given {@code Runnable}, and arrange that {@code get} will return the
059   * given result on successful completion.
060   *
061   * @param runnable the runnable task
062   * @param result the result to return on successful completion. If you don't
063   *     need a particular result, consider using constructions of the form:
064   *     {@code ListenableFuture<?> f = ListenableFutureTask.create(runnable,
065   *     null)}
066   * @since 10.0
067   */
068  public static <V> ListenableFutureTask<V> create(
069      Runnable runnable, @Nullable V result) {
070    return new ListenableFutureTask<V>(runnable, result);
071  }
072
073  ListenableFutureTask(Callable<V> callable) {
074    super(callable);
075  }
076
077  ListenableFutureTask(Runnable runnable, @Nullable V result) {
078    super(runnable, result);
079  }
080
081  @Override
082  public void addListener(Runnable listener, Executor exec) {
083    executionList.add(listener, exec);
084  }
085
086  /**
087   * Internal implementation detail used to invoke the listeners.
088   */
089  @Override
090  protected void done() {
091    executionList.execute();
092  }
093}