1/*
2 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
3 *
4 * This code is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 only, as
6 * published by the Free Software Foundation.  Oracle designates this
7 * particular file as subject to the "Classpath" exception as provided
8 * by Oracle in the LICENSE file that accompanied this code.
9 *
10 * This code is distributed in the hope that it will be useful, but WITHOUT
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
17 * 2 along with this work; if not, write to the Free Software Foundation,
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 * or visit www.oracle.com if you need additional information or have any
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23 */
24
25/*
26 * This file is available under and governed by the GNU General Public
27 * License version 2 only, as published by the Free Software Foundation.
28 * However, the following notice accompanied the original version of this
29 * file:
30 *
31 * Written by Doug Lea with assistance from members of JCP JSR-166
32 * Expert Group and released to the public domain, as explained at
33 * http://creativecommons.org/publicdomain/zero/1.0/
34 */
35
36package java.util.concurrent;
37
38/**
39 * A service that decouples the production of new asynchronous tasks
40 * from the consumption of the results of completed tasks.  Producers
41 * {@code submit} tasks for execution. Consumers {@code take}
42 * completed tasks and process their results in the order they
43 * complete.  A {@code CompletionService} can for example be used to
44 * manage asynchronous I/O, in which tasks that perform reads are
45 * submitted in one part of a program or system, and then acted upon
46 * in a different part of the program when the reads complete,
47 * possibly in a different order than they were requested.
48 *
49 * <p>Typically, a {@code CompletionService} relies on a separate
50 * {@link Executor} to actually execute the tasks, in which case the
51 * {@code CompletionService} only manages an internal completion
52 * queue. The {@link ExecutorCompletionService} class provides an
53 * implementation of this approach.
54 *
55 * <p>Memory consistency effects: Actions in a thread prior to
56 * submitting a task to a {@code CompletionService}
57 * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
58 * actions taken by that task, which in turn <i>happen-before</i>
59 * actions following a successful return from the corresponding {@code take()}.
60 *
61 * @since 1.5
62 */
63public interface CompletionService<V> {
64    /**
65     * Submits a value-returning task for execution and returns a Future
66     * representing the pending results of the task.  Upon completion,
67     * this task may be taken or polled.
68     *
69     * @param task the task to submit
70     * @return a Future representing pending completion of the task
71     * @throws RejectedExecutionException if the task cannot be
72     *         scheduled for execution
73     * @throws NullPointerException if the task is null
74     */
75    Future<V> submit(Callable<V> task);
76
77    /**
78     * Submits a Runnable task for execution and returns a Future
79     * representing that task.  Upon completion, this task may be
80     * taken or polled.
81     *
82     * @param task the task to submit
83     * @param result the result to return upon successful completion
84     * @return a Future representing pending completion of the task,
85     *         and whose {@code get()} method will return the given
86     *         result value upon completion
87     * @throws RejectedExecutionException if the task cannot be
88     *         scheduled for execution
89     * @throws NullPointerException if the task is null
90     */
91    Future<V> submit(Runnable task, V result);
92
93    /**
94     * Retrieves and removes the Future representing the next
95     * completed task, waiting if none are yet present.
96     *
97     * @return the Future representing the next completed task
98     * @throws InterruptedException if interrupted while waiting
99     */
100    Future<V> take() throws InterruptedException;
101
102    /**
103     * Retrieves and removes the Future representing the next
104     * completed task, or {@code null} if none are present.
105     *
106     * @return the Future representing the next completed task, or
107     *         {@code null} if none are present
108     */
109    Future<V> poll();
110
111    /**
112     * Retrieves and removes the Future representing the next
113     * completed task, waiting if necessary up to the specified wait
114     * time if none are yet present.
115     *
116     * @param timeout how long to wait before giving up, in units of
117     *        {@code unit}
118     * @param unit a {@code TimeUnit} determining how to interpret the
119     *        {@code timeout} parameter
120     * @return the Future representing the next completed task or
121     *         {@code null} if the specified waiting time elapses
122     *         before one is present
123     * @throws InterruptedException if interrupted while waiting
124     */
125    Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException;
126}
127