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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 {@link CompletionService} that uses a supplied {@link Executor} | ||
| 40 | * to execute tasks. This class arranges that submitted tasks are, | ||
| 41 | * upon completion, placed on a queue accessible using {@code take}. | ||
| 42 | * The class is lightweight enough to be suitable for transient use | ||
| 43 | * when processing groups of tasks. | ||
| 44 | * | ||
| 45 | * <p> | ||
| 46 | * | ||
| 47 | * <b>Usage Examples.</b> | ||
| 48 | * | ||
| 49 | * Suppose you have a set of solvers for a certain problem, each | ||
| 50 | * returning a value of some type {@code Result}, and would like to | ||
| 51 | * run them concurrently, processing the results of each of them that | ||
| 52 | * return a non-null value, in some method {@code use(Result r)}. You | ||
| 53 | * could write this as: | ||
| 54 | * | ||
| 55 | * <pre> {@code | ||
| 56 | * void solve(Executor e, | ||
| 57 | * Collection<Callable<Result>> solvers) | ||
| 58 | * throws InterruptedException, ExecutionException { | ||
| 59 | * CompletionService<Result> ecs | ||
| 60 | * = new ExecutorCompletionService<Result>(e); | ||
| 61 | * for (Callable<Result> s : solvers) | ||
| 62 | * ecs.submit(s); | ||
| 63 | * int n = solvers.size(); | ||
| 64 | * for (int i = 0; i < n; ++i) { | ||
| 65 | * Result r = ecs.take().get(); | ||
| 66 | * if (r != null) | ||
| 67 | * use(r); | ||
| 68 | * } | ||
| 69 | * }}</pre> | ||
| 70 | * | ||
| 71 | * Suppose instead that you would like to use the first non-null result | ||
| 72 | * of the set of tasks, ignoring any that encounter exceptions, | ||
| 73 | * and cancelling all other tasks when the first one is ready: | ||
| 74 | * | ||
| 75 | * <pre> {@code | ||
| 76 | * void solve(Executor e, | ||
| 77 | * Collection<Callable<Result>> solvers) | ||
| 78 | * throws InterruptedException { | ||
| 79 | * CompletionService<Result> ecs | ||
| 80 | * = new ExecutorCompletionService<Result>(e); | ||
| 81 | * int n = solvers.size(); | ||
| 82 | * List<Future<Result>> futures | ||
| 83 | * = new ArrayList<Future<Result>>(n); | ||
| 84 | * Result result = null; | ||
| 85 | * try { | ||
| 86 | * for (Callable<Result> s : solvers) | ||
| 87 | * futures.add(ecs.submit(s)); | ||
| 88 | * for (int i = 0; i < n; ++i) { | ||
| 89 | * try { | ||
| 90 | * Result r = ecs.take().get(); | ||
| 91 | * if (r != null) { | ||
| 92 | * result = r; | ||
| 93 | * break; | ||
| 94 | * } | ||
| 95 | * } catch (ExecutionException ignore) {} | ||
| 96 | * } | ||
| 97 | * } | ||
| 98 | * finally { | ||
| 99 | * for (Future<Result> f : futures) | ||
| 100 | * f.cancel(true); | ||
| 101 | * } | ||
| 102 | * | ||
| 103 | * if (result != null) | ||
| 104 | * use(result); | ||
| 105 | * }}</pre> | ||
| 106 | */ | ||
| 107 | public class ExecutorCompletionService<V> implements CompletionService<V> { | ||
| 108 | private final Executor executor; | ||
| 109 | private final AbstractExecutorService aes; | ||
| 110 | private final BlockingQueue<Future<V>> completionQueue; | ||
| 111 | |||
| 112 | /** | ||
| 113 | * FutureTask extension to enqueue upon completion | ||
| 114 | */ | ||
| 115 | private class QueueingFuture extends FutureTask<Void> { | ||
| 116 | QueueingFuture(RunnableFuture<V> task) { | ||
| 117 | super(task, null); | ||
| 118 | this.task = task; | ||
| 119 | } | ||
| 120 | protected void done() { completionQueue.add(task); } | ||
| 121 | private final Future<V> task; | ||
| 122 | } | ||
| 123 | |||
| 124 | private RunnableFuture<V> newTaskFor(Callable<V> task) { | ||
| 125 | if (aes == null) | ||
| 126 | return new FutureTask<V>(task); | ||
| 127 | else | ||
| 128 | return aes.newTaskFor(task); | ||
| 129 | } | ||
| 130 | |||
| 131 | private RunnableFuture<V> newTaskFor(Runnable task, V result) { | ||
| 132 | if (aes == null) | ||
| 133 | return new FutureTask<V>(task, result); | ||
| 134 | else | ||
| 135 | return aes.newTaskFor(task, result); | ||
| 136 | } | ||
| 137 | |||
| 138 | /** | ||
| 139 | * Creates an ExecutorCompletionService using the supplied | ||
| 140 | * executor for base task execution and a | ||
| 141 | * {@link LinkedBlockingQueue} as a completion queue. | ||
| 142 | * | ||
| 143 | * @param executor the executor to use | ||
| 144 | * @throws NullPointerException if executor is {@code null} | ||
| 145 | */ | ||
| 146 | public ExecutorCompletionService(Executor executor) { | ||
| 147 | if (executor == null) | ||
| 148 | throw new NullPointerException(); | ||
| 149 | this.executor = executor; | ||
| 150 | this.aes = (executor instanceof AbstractExecutorService) ? | ||
| 151 | (AbstractExecutorService) executor : null; | ||
| 152 | this.completionQueue = new LinkedBlockingQueue<Future<V>>(); | ||
| 153 | } | ||
| 154 | |||
| 155 | /** | ||
| 156 | * Creates an ExecutorCompletionService using the supplied | ||
| 157 | * executor for base task execution and the supplied queue as its | ||
| 158 | * completion queue. | ||
| 159 | * | ||
| 160 | * @param executor the executor to use | ||
| 161 | * @param completionQueue the queue to use as the completion queue | ||
| 162 | * normally one dedicated for use by this service. This | ||
| 163 | * queue is treated as unbounded -- failed attempted | ||
| 164 | * {@code Queue.add} operations for completed taskes cause | ||
| 165 | * them not to be retrievable. | ||
| 166 | * @throws NullPointerException if executor or completionQueue are {@code null} | ||
| 167 | */ | ||
| 168 | public ExecutorCompletionService(Executor executor, | ||
| 169 | BlockingQueue<Future<V>> completionQueue) { | ||
| 170 | if (executor == null || completionQueue == null) | ||
| 171 | throw new NullPointerException(); | ||
| 172 | this.executor = executor; | ||
| 173 | this.aes = (executor instanceof AbstractExecutorService) ? | ||
| 174 | (AbstractExecutorService) executor : null; | ||
| 175 | this.completionQueue = completionQueue; | ||
| 176 | } | ||
| 177 | |||
| 178 | public Future<V> submit(Callable<V> task) { | ||
| 179 | if (task == null) throw new NullPointerException(); | ||
| 180 | RunnableFuture<V> f = newTaskFor(task); | ||
| 181 | executor.execute(new QueueingFuture(f)); | ||
| 182 | return f; | ||
| 183 | } | ||
| 184 | |||
| 185 | public Future<V> submit(Runnable task, V result) { | ||
| 186 | if (task == null) throw new NullPointerException(); | ||
| 187 | RunnableFuture<V> f = newTaskFor(task, result); | ||
| 188 | executor.execute(new QueueingFuture(f)); | ||
| 189 | return f; | ||
| 190 | } | ||
| 191 | |||
| 192 | public Future<V> take() throws InterruptedException { | ||
| 193 | return completionQueue.take(); | ||
| 194 | } | ||
| 195 | |||
| 196 | public Future<V> poll() { | ||
| 197 | return completionQueue.poll(); | ||
| 198 | } | ||
| 199 | |||
| 200 | public Future<V> poll(long timeout, TimeUnit unit) | ||
| 201 | throws InterruptedException { | ||
| 202 | return completionQueue.poll(timeout, unit); | ||
| 203 | } | ||
| 204 | |||
| 205 | } | ||