J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 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. Sun designates this |
| 7 | * particular file as subject to the "Classpath" exception as provided |
| 8 | * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 21 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 22 | * have any 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/licenses/publicdomain |
| 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) throws InterruptedException { |
| 201 | return completionQueue.poll(timeout, unit); |
| 202 | } |
| 203 | |
| 204 | } |