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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 | +} | |