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 com.google.common.annotations.Beta;
020import com.google.common.annotations.GwtCompatible;
021
022import java.util.concurrent.CancellationException;
023import java.util.concurrent.ExecutionException;
024import java.util.concurrent.Future;
025import java.util.concurrent.TimeUnit;
026import java.util.concurrent.TimeoutException;
027
028/**
029 * A {@code CheckedFuture} is a {@link ListenableFuture} that includes versions
030 * of the {@code get} methods that can throw a checked exception.  This makes it
031 * easier to create a future that executes logic which can throw an exception.
032 *
033 * <p><b>Warning:</b> We recommend against using {@code CheckedFuture} in new
034 * projects. {@code CheckedFuture} is difficult to build libraries atop. {@code
035 * CheckedFuture} ports of methods like {@link Futures#transformAsync} have
036 * historically had bugs, and some of these bugs are necessary, unavoidable
037 * consequences of the {@code CheckedFuture} API. Additionally, {@code
038 * CheckedFuture} encourages users to take exceptions from one thread and
039 * rethrow them in another, producing confusing stack traces.
040 *
041 * <p>A common implementation is {@link Futures#immediateCheckedFuture}.
042 *
043 * <p>Implementations of this interface must adapt the exceptions thrown by
044 * {@code Future#get()}: {@link CancellationException},
045 * {@link ExecutionException} and {@link InterruptedException} into the type
046 * specified by the {@code X} type parameter.
047 *
048 * <p>This interface also extends the ListenableFuture interface to allow
049 * listeners to be added. This allows the future to be used as a normal
050 * {@link Future} or as an asynchronous callback mechanism as needed. This
051 * allows multiple callbacks to be registered for a particular task, and the
052 * future will guarantee execution of all listeners when the task completes.
053 *
054 * <p>For a simpler alternative to CheckedFuture, consider accessing Future
055 * values with {@link Futures#getChecked(Future, Class) Futures.getChecked()}.
056 *
057 * @author Sven Mawson
058 * @since 1.0
059 */
060@Beta
061@GwtCompatible
062public interface CheckedFuture<V, X extends Exception>
063    extends ListenableFuture<V> {
064
065  /**
066   * Exception checking version of {@link Future#get()} that will translate
067   * {@link InterruptedException}, {@link CancellationException} and
068   * {@link ExecutionException} into application-specific exceptions.
069   *
070   * @return the result of executing the future.
071   * @throws X on interruption, cancellation or execution exceptions.
072   */
073  V checkedGet() throws X;
074
075  /**
076   * Exception checking version of {@link Future#get(long, TimeUnit)} that will
077   * translate {@link InterruptedException}, {@link CancellationException} and
078   * {@link ExecutionException} into application-specific exceptions.  On
079   * timeout this method throws a normal {@link TimeoutException}.
080   *
081   * @return the result of executing the future.
082   * @throws TimeoutException if retrieving the result timed out.
083   * @throws X on interruption, cancellation or execution exceptions.
084   */
085  V checkedGet(long timeout, TimeUnit unit) throws TimeoutException, X;
086}