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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 <tt>Future</tt> represents the result of an asynchronous | ||
| 40 | * computation. Methods are provided to check if the computation is | ||
| 41 | * complete, to wait for its completion, and to retrieve the result of | ||
| 42 | * the computation. The result can only be retrieved using method | ||
| 43 | * <tt>get</tt> when the computation has completed, blocking if | ||
| 44 | * necessary until it is ready. Cancellation is performed by the | ||
| 45 | * <tt>cancel</tt> method. Additional methods are provided to | ||
| 46 | * determine if the task completed normally or was cancelled. Once a | ||
| 47 | * computation has completed, the computation cannot be cancelled. | ||
| 48 | * If you would like to use a <tt>Future</tt> for the sake | ||
| 49 | * of cancellability but not provide a usable result, you can | ||
| 50 | * declare types of the form {@code Future<?>} and | ||
| 51 | * return <tt>null</tt> as a result of the underlying task. | ||
| 52 | * | ||
| 53 | * <p> | ||
| 54 | * <b>Sample Usage</b> (Note that the following classes are all | ||
| 55 | * made-up.) <p> | ||
| 56 | * <pre> {@code | ||
| 57 | * interface ArchiveSearcher { String search(String target); } | ||
| 58 | * class App { | ||
| 59 | * ExecutorService executor = ... | ||
| 60 | * ArchiveSearcher searcher = ... | ||
| 61 | * void showSearch(final String target) | ||
| 62 | * throws InterruptedException { | ||
| 63 | * Future<String> future | ||
| 64 | * = executor.submit(new Callable<String>() { | ||
| 65 | * public String call() { | ||
| 66 | * return searcher.search(target); | ||
| 67 | * }}); | ||
| 68 | * displayOtherThings(); // do other things while searching | ||
| 69 | * try { | ||
| 70 | * displayText(future.get()); // use future | ||
| 71 | * } catch (ExecutionException ex) { cleanup(); return; } | ||
| 72 | * } | ||
| 73 | * }}</pre> | ||
| 74 | * | ||
| 75 | * The {@link FutureTask} class is an implementation of <tt>Future</tt> that | ||
| 76 | * implements <tt>Runnable</tt>, and so may be executed by an <tt>Executor</tt>. | ||
| 77 | * For example, the above construction with <tt>submit</tt> could be replaced by: | ||
| 78 | * <pre> {@code | ||
| 79 | * FutureTask<String> future = | ||
| 80 | * new FutureTask<String>(new Callable<String>() { | ||
| 81 | * public String call() { | ||
| 82 | * return searcher.search(target); | ||
| 83 | * }}); | ||
| 84 | * executor.execute(future);}</pre> | ||
| 85 | * | ||
| 86 | * <p>Memory consistency effects: Actions taken by the asynchronous computation | ||
| 87 | * <a href="package-summary.html#MemoryVisibility"> <i>happen-before</i></a> | ||
| 88 | * actions following the corresponding {@code Future.get()} in another thread. | ||
| 89 | * | ||
| 90 | * @see FutureTask | ||
| 91 | * @see Executor | ||
| 92 | * @since 1.5 | ||
| 93 | * @author Doug Lea | ||
| 94 | * @param <V> The result type returned by this Future's <tt>get</tt> method | ||
| 95 | */ | ||
| 96 | public interface Future<V> { | ||
| 97 | |||
| 98 | /** | ||
| 99 | * Attempts to cancel execution of this task. This attempt will | ||
| 100 | * fail if the task has already completed, has already been cancelled, | ||
| 101 | * or could not be cancelled for some other reason. If successful, | ||
| 102 | * and this task has not started when <tt>cancel</tt> is called, | ||
| 103 | * this task should never run. If the task has already started, | ||
| 104 | * then the <tt>mayInterruptIfRunning</tt> parameter determines | ||
| 105 | * whether the thread executing this task should be interrupted in | ||
| 106 | * an attempt to stop the task. | ||
| 107 | * | ||
| 108 | * <p>After this method returns, subsequent calls to {@link #isDone} will | ||
| 109 | * always return <tt>true</tt>. Subsequent calls to {@link #isCancelled} | ||
| 110 | * will always return <tt>true</tt> if this method returned <tt>true</tt>. | ||
| 111 | * | ||
| 112 | * @param mayInterruptIfRunning <tt>true</tt> if the thread executing this | ||
| 113 | * task should be interrupted; otherwise, in-progress tasks are allowed | ||
| 114 | * to complete | ||
| 115 | * @return <tt>false</tt> if the task could not be cancelled, | ||
| 116 | * typically because it has already completed normally; | ||
| 117 | * <tt>true</tt> otherwise | ||
| 118 | */ | ||
| 119 | boolean cancel(boolean mayInterruptIfRunning); | ||
| 120 | |||
| 121 | /** | ||
| 122 | * Returns <tt>true</tt> if this task was cancelled before it completed | ||
| 123 | * normally. | ||
| 124 | * | ||
| 125 | * @return <tt>true</tt> if this task was cancelled before it completed | ||
| 126 | */ | ||
| 127 | boolean isCancelled(); | ||
| 128 | |||
| 129 | /** | ||
| 130 | * Returns <tt>true</tt> if this task completed. | ||
| 131 | * | ||
| 132 | * Completion may be due to normal termination, an exception, or | ||
| 133 | * cancellation -- in all of these cases, this method will return | ||
| 134 | * <tt>true</tt>. | ||
| 135 | * | ||
| 136 | * @return <tt>true</tt> if this task completed | ||
| 137 | */ | ||
| 138 | boolean isDone(); | ||
| 139 | |||
| 140 | /** | ||
| 141 | * Waits if necessary for the computation to complete, and then | ||
| 142 | * retrieves its result. | ||
| 143 | * | ||
| 144 | * @return the computed result | ||
| 145 | * @throws CancellationException if the computation was cancelled | ||
| 146 | * @throws ExecutionException if the computation threw an | ||
| 147 | * exception | ||
| 148 | * @throws InterruptedException if the current thread was interrupted | ||
| 149 | * while waiting | ||
| 150 | */ | ||
| 151 | V get() throws InterruptedException, ExecutionException; | ||
| 152 | |||
| 153 | /** | ||
| 154 | * Waits if necessary for at most the given time for the computation | ||
| 155 | * to complete, and then retrieves its result, if available. | ||
| 156 | * | ||
| 157 | * @param timeout the maximum time to wait | ||
| 158 | * @param unit the time unit of the timeout argument | ||
| 159 | * @return the computed result | ||
| 160 | * @throws CancellationException if the computation was cancelled | ||
| 161 | * @throws ExecutionException if the computation threw an | ||
| 162 | * exception | ||
| 163 | * @throws InterruptedException if the current thread was interrupted | ||
| 164 | * while waiting | ||
| 165 | * @throws TimeoutException if the wait timed out | ||
| 166 | */ | ||
| 167 | V get(long timeout, TimeUnit unit) | ||
| 168 | throws InterruptedException, ExecutionException, TimeoutException; | ||
| 169 | } | ||