- /*
- * @(#)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 <tt>take</tt>.
- * The class is lightweight enough to be suitable for transient use
- * when processing groups of tasks.
- *
- * <p>
- *
- * <b>Usage Examples.</b>
- *
- * Suppose you have a set of solvers for a certain problem, each
- * returning a value of some type <tt>Result</tt>, and would like to
- * run them concurrently, processing the results of each of them that
- * return a non-null value, in some method <tt>use(Result r)</tt>. You
- * could write this as:
- *
- * <pre>
- * 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);
- * }
- * }
- * </pre>
- *
- * 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:
- *
- * <pre>
- * 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);
- * }
- * </pre>
- */
- public class ExecutorCompletionService<V> implements CompletionService<V> {
- private final Executor executor;
- private final BlockingQueue<Future<V>> completionQueue;
-
- /**
- * FutureTask extension to enqueue upon completion
- */
- private class QueueingFuture extends FutureTask<V> {
- QueueingFuture(Callable<V> c) { super(c); }
- QueueingFuture(Runnable t, V r) { super(t, r); }
- protected void done() { completionQueue.add(this); }
- }
-
- /**
- * Creates an ExecutorCompletionService using the supplied
- * executor for base task execution and a
- * {@link LinkedBlockingQueue} as a completion queue.
- * @param executor the executor to use
- * @throws NullPointerException if executor is <tt>null</tt>
- */
- public ExecutorCompletionService(Executor executor) {
- if (executor == null)
- throw new NullPointerException();
- this.executor = executor;
- this.completionQueue = new LinkedBlockingQueue<Future<V>>();
- }
-
- /**
- * Creates an ExecutorCompletionService using the supplied
- * executor for base task execution and the supplied queue as its
- * completion queue.
- * @param executor the executor to use
- * @param completionQueue the queue to use as the completion queue
- * normally one dedicated for use by this service
- * @throws NullPointerException if executor or completionQueue are <tt>null</tt>
- */
- public ExecutorCompletionService(Executor executor,
- BlockingQueue<Future<V>> completionQueue) {
- if (executor == null || completionQueue == null)
- throw new NullPointerException();
- this.executor = executor;
- this.completionQueue = completionQueue;
- }
-
- public Future<V> submit(Callable<V> task) {
- if (task == null) throw new NullPointerException();
- QueueingFuture f = new QueueingFuture(task);
- executor.execute(f);
- return f;
- }
-
- public Future<V> submit(Runnable task, V result) {
- if (task == null) throw new NullPointerException();
- QueueingFuture f = new QueueingFuture(task, result);
- executor.execute(f);
- return f;
- }
-
- public Future<V> take() throws InterruptedException {
- return completionQueue.take();
- }
-
- public Future<V> poll() {
- return completionQueue.poll();
- }
-
- public Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException {
- return completionQueue.poll(timeout, unit);
- }
-
- }
-
-