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| 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 | ||
| 22 | * questions. | ||
| 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 | |||
| 36 | package 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 | * <tt>submit</tt> tasks for execution. Consumers <tt>take</tt> | ||
| 42 | * completed tasks and process their results in the order they | ||
| 43 | * complete. A <tt>CompletionService</tt> can for example be used to | ||
| 44 | * manage asynchronous IO, 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 <tt>CompletionService</tt> relies on a separate | ||
| 50 | * {@link Executor} to actually execute the tasks, in which case the | ||
| 51 | * <tt>CompletionService</tt> 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 | */ | ||
| 62 | public interface CompletionService<V> { | ||
| 63 | /** | ||
| 64 | * Submits a value-returning task for execution and returns a Future | ||
| 65 | * representing the pending results of the task. Upon completion, | ||
| 66 | * this task may be taken or polled. | ||
| 67 | * | ||
| 68 | * @param task the task to submit | ||
| 69 | * @return a Future representing pending completion of the task | ||
| 70 | * @throws RejectedExecutionException if the task cannot be | ||
| 71 | * scheduled for execution | ||
| 72 | * @throws NullPointerException if the task is null | ||
| 73 | */ | ||
| 74 | Future<V> submit(Callable<V> task); | ||
| 75 | |||
| 76 | /** | ||
| 77 | * Submits a Runnable task for execution and returns a Future | ||
| 78 | * representing that task. Upon completion, this task may be | ||
| 79 | * taken or polled. | ||
| 80 | * | ||
| 81 | * @param task the task to submit | ||
| 82 | * @param result the result to return upon successful completion | ||
| 83 | * @return a Future representing pending completion of the task, | ||
| 84 | * and whose <tt>get()</tt> method will return the given | ||
| 85 | * result value upon completion | ||
| 86 | * @throws RejectedExecutionException if the task cannot be | ||
| 87 | * scheduled for execution | ||
| 88 | * @throws NullPointerException if the task is null | ||
| 89 | */ | ||
| 90 | Future<V> submit(Runnable task, V result); | ||
| 91 | |||
| 92 | /** | ||
| 93 | * Retrieves and removes the Future representing the next | ||
| 94 | * completed task, waiting if none are yet present. | ||
| 95 | * | ||
| 96 | * @return the Future representing the next completed task | ||
| 97 | * @throws InterruptedException if interrupted while waiting | ||
| 98 | */ | ||
| 99 | Future<V> take() throws InterruptedException; | ||
| 100 | |||
| 101 | |||
| 102 | /** | ||
| 103 | * Retrieves and removes the Future representing the next | ||
| 104 | * completed task or <tt>null</tt> if none are present. | ||
| 105 | * | ||
| 106 | * @return the Future representing the next completed task, or | ||
| 107 | * <tt>null</tt> 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 | * <tt>unit</tt> | ||
| 118 | * @param unit a <tt>TimeUnit</tt> determining how to interpret the | ||
| 119 | * <tt>timeout</tt> parameter | ||
| 120 | * @return the Future representing the next completed task or | ||
| 121 | * <tt>null</tt> 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 | } | ||