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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 | * An object that executes submitted {@link Runnable} tasks. This | ||
| 40 | * interface provides a way of decoupling task submission from the | ||
| 41 | * mechanics of how each task will be run, including details of thread | ||
| 42 | * use, scheduling, etc. An <tt>Executor</tt> is normally used | ||
| 43 | * instead of explicitly creating threads. For example, rather than | ||
| 44 | * invoking <tt>new Thread(new(RunnableTask())).start()</tt> for each | ||
| 45 | * of a set of tasks, you might use: | ||
| 46 | * | ||
| 47 | * <pre> | ||
| 48 | * Executor executor = <em>anExecutor</em>; | ||
| 49 | * executor.execute(new RunnableTask1()); | ||
| 50 | * executor.execute(new RunnableTask2()); | ||
| 51 | * ... | ||
| 52 | * </pre> | ||
| 53 | * | ||
| 54 | * However, the <tt>Executor</tt> interface does not strictly | ||
| 55 | * require that execution be asynchronous. In the simplest case, an | ||
| 56 | * executor can run the submitted task immediately in the caller's | ||
| 57 | * thread: | ||
| 58 | * | ||
| 59 | * <pre> | ||
| 60 | * class DirectExecutor implements Executor { | ||
| 61 | * public void execute(Runnable r) { | ||
| 62 | * r.run(); | ||
| 63 | * } | ||
| 64 | * }</pre> | ||
| 65 | * | ||
| 66 | * More typically, tasks are executed in some thread other | ||
| 67 | * than the caller's thread. The executor below spawns a new thread | ||
| 68 | * for each task. | ||
| 69 | * | ||
| 70 | * <pre> | ||
| 71 | * class ThreadPerTaskExecutor implements Executor { | ||
| 72 | * public void execute(Runnable r) { | ||
| 73 | * new Thread(r).start(); | ||
| 74 | * } | ||
| 75 | * }</pre> | ||
| 76 | * | ||
| 77 | * Many <tt>Executor</tt> implementations impose some sort of | ||
| 78 | * limitation on how and when tasks are scheduled. The executor below | ||
| 79 | * serializes the submission of tasks to a second executor, | ||
| 80 | * illustrating a composite executor. | ||
| 81 | * | ||
| 82 | * <pre> {@code | ||
| 83 | * class SerialExecutor implements Executor { | ||
| 84 | * final Queue<Runnable> tasks = new ArrayDeque<Runnable>(); | ||
| 85 | * final Executor executor; | ||
| 86 | * Runnable active; | ||
| 87 | * | ||
| 88 | * SerialExecutor(Executor executor) { | ||
| 89 | * this.executor = executor; | ||
| 90 | * } | ||
| 91 | * | ||
| 92 | * public synchronized void execute(final Runnable r) { | ||
| 93 | * tasks.offer(new Runnable() { | ||
| 94 | * public void run() { | ||
| 95 | * try { | ||
| 96 | * r.run(); | ||
| 97 | * } finally { | ||
| 98 | * scheduleNext(); | ||
| 99 | * } | ||
| 100 | * } | ||
| 101 | * }); | ||
| 102 | * if (active == null) { | ||
| 103 | * scheduleNext(); | ||
| 104 | * } | ||
| 105 | * } | ||
| 106 | * | ||
| 107 | * protected synchronized void scheduleNext() { | ||
| 108 | * if ((active = tasks.poll()) != null) { | ||
| 109 | * executor.execute(active); | ||
| 110 | * } | ||
| 111 | * } | ||
| 112 | * }}</pre> | ||
| 113 | * | ||
| 114 | * The <tt>Executor</tt> implementations provided in this package | ||
| 115 | * implement {@link ExecutorService}, which is a more extensive | ||
| 116 | * interface. The {@link ThreadPoolExecutor} class provides an | ||
| 117 | * extensible thread pool implementation. The {@link Executors} class | ||
| 118 | * provides convenient factory methods for these Executors. | ||
| 119 | * | ||
| 120 | * <p>Memory consistency effects: Actions in a thread prior to | ||
| 121 | * submitting a {@code Runnable} object to an {@code Executor} | ||
| 122 | * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a> | ||
| 123 | * its execution begins, perhaps in another thread. | ||
| 124 | * | ||
| 125 | * @since 1.5 | ||
| 126 | * @author Doug Lea | ||
| 127 | */ | ||
| 128 | public interface Executor { | ||
| 129 | |||
| 130 | /** | ||
| 131 | * Executes the given command at some time in the future. The command | ||
| 132 | * may execute in a new thread, in a pooled thread, or in the calling | ||
| 133 | * thread, at the discretion of the <tt>Executor</tt> implementation. | ||
| 134 | * | ||
| 135 | * @param command the runnable task | ||
| 136 | * @throws RejectedExecutionException if this task cannot be | ||
| 137 | * accepted for execution. | ||
| 138 | * @throws NullPointerException if command is null | ||
| 139 | */ | ||
| 140 | void execute(Runnable command); | ||
| 141 | } | ||