/*
    * Copyright (C) 2008 The Guava Authors
    *
    * 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,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package com.google.common.util.concurrent;
  
  import java.util.concurrent.Callable;
  import java.util.concurrent.Executor;
  import java.util.concurrent.FutureTask;
  
  import javax.annotation.Nullable;
  
  /**
   * A {@link FutureTask} that also implements the {@link ListenableFuture}
   * interface.  Unlike {@code FutureTask}, {@code ListenableFutureTask} does not
   * provide an overrideable {@link FutureTask#done() done()} method.  For similar
   * functionality, call {@link #addListener}.
   * 
   * <p>
   *
   * @author Sven Mawson
   * @since 1.0
   */
  public class ListenableFutureTask<V> extends FutureTask<V>
      implements ListenableFuture<V> {
    // TODO(cpovirk): explore ways of making ListenableFutureTask final. There are
    // some valid reasons such as BoundedQueueExecutorService to allow extends but it
    // would be nice to make it final to avoid unintended usage.
  
    // The execution list to hold our listeners.
    private final ExecutionList executionList = new ExecutionList();
  
    /**
     * Creates a {@code ListenableFutureTask} that will upon running, execute the
     * given {@code Callable}.
     *
     * @param callable the callable task
     * @since 10.0
     */
    public static <V> ListenableFutureTask<V> create(Callable<V> callable) {
      return new ListenableFutureTask<V>(callable);
    }
  
    /**
     * Creates a {@code ListenableFutureTask} that will upon running, execute the
     * given {@code Runnable}, and arrange that {@code get} will return the
     * given result on successful completion.
     *
     * @param runnable the runnable task
     * @param result the result to return on successful completion. If you don't
     *     need a particular result, consider using constructions of the form:
     *     {@code ListenableFuture<?> f = ListenableFutureTask.create(runnable,
     *     null)}
     * @since 10.0
     */
    public static <V> ListenableFutureTask<V> create(
        Runnable runnable, @Nullable V result) {
      return new ListenableFutureTask<V>(runnable, result);
    }
  
    ListenableFutureTask(Callable<V> callable) {
      super(callable);
    }
  
    ListenableFutureTask(Runnable runnable, @Nullable V result) {
      super(runnable, result);
    }
  
    @Override
    public void addListener(Runnable listener, Executor exec) {
      executionList.add(listener, exec);
    }
  
    /**
     * Internal implementation detail used to invoke the listeners.
     */
    @Override
    protected void done() {
      executionList.execute();
    }
  }