/* * @(#)ExecutorCompletionService.java 1.1 04/02/09 * * Copyright 2004 Sun Microsystems, Inc. All rights reserved. * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ package java.util.concurrent; /** * A {@link CompletionService} that uses a supplied {@link Executor} * to execute tasks. This class arranges that submitted tasks are, * upon completion, placed on a queue accessible using take. * The class is lightweight enough to be suitable for transient use * when processing groups of tasks. * *
* * Usage Examples. * * Suppose you have a set of solvers for a certain problem, each * returning a value of some type Result, and would like to * run them concurrently, processing the results of each of them that * return a non-null value, in some method use(Result r). You * could write this as: * *
* void solve(Executor e, Collection<Callable<Result>> solvers) * throws InterruptedException, ExecutionException { * CompletionService<Result> ecs = new ExecutorCompletionService<Result>(e); * for (Callable<Result> s : solvers) * ecs.submit(s); * int n = solvers.size(); * for (int i = 0; i < n; ++i) { * Result r = ecs.take().get(); * if (r != null) * use(r); * } * } ** * Suppose instead that you would like to use the first non-null result * of the set of tasks, ignoring any that encounter exceptions, * and cancelling all other tasks when the first one is ready: * *
* void solve(Executor e, Collection<Callable<Result>> solvers) * throws InterruptedException { * CompletionService<Result> ecs = new ExecutorCompletionService<Result>(e); * int n = solvers.size(); * List<Future<Result>> futures = new ArrayList<Future<Result>>(n); * Result result = null; * try { * for (Callable<Result> s : solvers) * futures.add(ecs.submit(s)); * for (int i = 0; i < n; ++i) { * try { * Result r = ecs.take().get(); * if (r != null) { * result = r; * break; * } * } catch(ExecutionException ignore) {} * } * } * finally { * for (Future<Result> f : futures) * f.cancel(true); * } * * if (result != null) * use(result); * } **/ public class ExecutorCompletionService