util/concurrent/ExecutorCompletionService.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

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 {@code take}.
 * 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 {@code Result}, and would like to
 * run them concurrently, processing the results of each of them that
 * return a non-null value, in some method {@code use(Result r)}. You
 * could write this as:
 *
 * <pre> {@code
 * 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> {@code
 * 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 AbstractExecutorService aes;
    private final BlockingQueue<Future<V>> completionQueue;

    /**
     * FutureTask extension to enqueue upon completion
     */
    private class QueueingFuture extends FutureTask<Void> {
        QueueingFuture(RunnableFuture<V> task) {
            super(task, null);
            this.task = task;
        }
        protected void done() { completionQueue.add(task); }
        private final Future<V> task;
    }

    private RunnableFuture<V> newTaskFor(Callable<V> task) {
        if (aes == null)
            return new FutureTask<V>(task);
        else
            return aes.newTaskFor(task);
    }

    private RunnableFuture<V> newTaskFor(Runnable task, V result) {
        if (aes == null)
            return new FutureTask<V>(task, result);
        else
            return aes.newTaskFor(task, result);
    }

    /**
     * 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 {@code null}
     */
    public ExecutorCompletionService(Executor executor) {
        if (executor == null)
            throw new NullPointerException();
        this.executor = executor;
        this.aes = (executor instanceof AbstractExecutorService) ?
            (AbstractExecutorService) executor : null;
        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. This
     *        queue is treated as unbounded -- failed attempted
     *        {@code Queue.add} operations for completed tasks cause
     *        them not to be retrievable.
     * @throws NullPointerException if executor or completionQueue are {@code null}
     */
    public ExecutorCompletionService(Executor executor,
                                     BlockingQueue<Future<V>> completionQueue) {
        if (executor == null || completionQueue == null)
            throw new NullPointerException();
        this.executor = executor;
        this.aes = (executor instanceof AbstractExecutorService) ?
            (AbstractExecutorService) executor : null;
        this.completionQueue = completionQueue;
    }

    public Future<V> submit(Callable<V> task) {
        if (task == null) throw new NullPointerException();
        RunnableFuture<V> f = newTaskFor(task);
        executor.execute(new QueueingFuture(f));
        return f;
    }

    public Future<V> submit(Runnable task, V result) {
        if (task == null) throw new NullPointerException();
        RunnableFuture<V> f = newTaskFor(task, result);
        executor.execute(new QueueingFuture(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);
    }

}
Revision:	1.2
Committed:	Tue Oct 22 15:21:30 2013 UTC (10 years, 6 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.1:	+1 -1 lines
Log Message:	javadoc typo fixes from Sergey Malenkov; https://bugs.openjdk.java.net/browse/JDK-8022746
#	Content
1	/*
2	* Written by Doug Lea with assistance from members of JCP JSR-166
3	* Expert Group and released to the public domain, as explained at
4	* http://creativecommons.org/publicdomain/zero/1.0/
5	*/
6
7	package java.util.concurrent;
8
9	/**
10	* A {@link CompletionService} that uses a supplied {@link Executor}
11	* to execute tasks. This class arranges that submitted tasks are,
12	* upon completion, placed on a queue accessible using {@code take}.
13	* The class is lightweight enough to be suitable for transient use
14	* when processing groups of tasks.
15	*
16	* <p>
17	*
18	* <b>Usage Examples.</b>
19	*
20	* Suppose you have a set of solvers for a certain problem, each
21	* returning a value of some type {@code Result}, and would like to
22	* run them concurrently, processing the results of each of them that
23	* return a non-null value, in some method {@code use(Result r)}. You
24	* could write this as:
25	*
26	* <pre> {@code
27	* void solve(Executor e,
28	* Collection<Callable<Result>> solvers)
29	* throws InterruptedException, ExecutionException {
30	* CompletionService<Result> ecs
31	* = new ExecutorCompletionService<Result>(e);
32	* for (Callable<Result> s : solvers)
33	* ecs.submit(s);
34	* int n = solvers.size();
35	* for (int i = 0; i < n; ++i) {
36	* Result r = ecs.take().get();
37	* if (r != null)
38	* use(r);
39	* }
40	* }}</pre>
41	*
42	* Suppose instead that you would like to use the first non-null result
43	* of the set of tasks, ignoring any that encounter exceptions,
44	* and cancelling all other tasks when the first one is ready:
45	*
46	* <pre> {@code
47	* void solve(Executor e,
48	* Collection<Callable<Result>> solvers)
49	* throws InterruptedException {
50	* CompletionService<Result> ecs
51	* = new ExecutorCompletionService<Result>(e);
52	* int n = solvers.size();
53	* List<Future<Result>> futures
54	* = new ArrayList<Future<Result>>(n);
55	* Result result = null;
56	* try {
57	* for (Callable<Result> s : solvers)
58	* futures.add(ecs.submit(s));
59	* for (int i = 0; i < n; ++i) {
60	* try {
61	* Result r = ecs.take().get();
62	* if (r != null) {
63	* result = r;
64	* break;
65	* }
66	* } catch (ExecutionException ignore) {}
67	* }
68	* }
69	* finally {
70	* for (Future<Result> f : futures)
71	* f.cancel(true);
72	* }
73	*
74	* if (result != null)
75	* use(result);
76	* }}</pre>
77	*/
78	public class ExecutorCompletionService<V> implements CompletionService<V> {
79	private final Executor executor;
80	private final AbstractExecutorService aes;
81	private final BlockingQueue<Future<V>> completionQueue;
82
83	/**
84	* FutureTask extension to enqueue upon completion
85	*/
86	private class QueueingFuture extends FutureTask<Void> {
87	QueueingFuture(RunnableFuture<V> task) {
88	super(task, null);
89	this.task = task;
90	}
91	protected void done() { completionQueue.add(task); }
92	private final Future<V> task;
93	}
94
95	private RunnableFuture<V> newTaskFor(Callable<V> task) {
96	if (aes == null)
97	return new FutureTask<V>(task);
98	else
99	return aes.newTaskFor(task);
100	}
101
102	private RunnableFuture<V> newTaskFor(Runnable task, V result) {
103	if (aes == null)
104	return new FutureTask<V>(task, result);
105	else
106	return aes.newTaskFor(task, result);
107	}
108
109	/**
110	* Creates an ExecutorCompletionService using the supplied
111	* executor for base task execution and a
112	* {@link LinkedBlockingQueue} as a completion queue.
113	*
114	* @param executor the executor to use
115	* @throws NullPointerException if executor is {@code null}
116	*/
117	public ExecutorCompletionService(Executor executor) {
118	if (executor == null)
119	throw new NullPointerException();
120	this.executor = executor;
121	this.aes = (executor instanceof AbstractExecutorService) ?
122	(AbstractExecutorService) executor : null;
123	this.completionQueue = new LinkedBlockingQueue<Future<V>>();
124	}
125
126	/**
127	* Creates an ExecutorCompletionService using the supplied
128	* executor for base task execution and the supplied queue as its
129	* completion queue.
130	*
131	* @param executor the executor to use
132	* @param completionQueue the queue to use as the completion queue
133	* normally one dedicated for use by this service. This
134	* queue is treated as unbounded -- failed attempted
135	* {@code Queue.add} operations for completed tasks cause
136	* them not to be retrievable.
137	* @throws NullPointerException if executor or completionQueue are {@code null}
138	*/
139	public ExecutorCompletionService(Executor executor,
140	BlockingQueue<Future<V>> completionQueue) {
141	if (executor == null \|\| completionQueue == null)
142	throw new NullPointerException();
143	this.executor = executor;
144	this.aes = (executor instanceof AbstractExecutorService) ?
145	(AbstractExecutorService) executor : null;
146	this.completionQueue = completionQueue;
147	}
148
149	public Future<V> submit(Callable<V> task) {
150	if (task == null) throw new NullPointerException();
151	RunnableFuture<V> f = newTaskFor(task);
152	executor.execute(new QueueingFuture(f));
153	return f;
154	}
155
156	public Future<V> submit(Runnable task, V result) {
157	if (task == null) throw new NullPointerException();
158	RunnableFuture<V> f = newTaskFor(task, result);
159	executor.execute(new QueueingFuture(f));
160	return f;
161	}
162
163	public Future<V> take() throws InterruptedException {
164	return completionQueue.take();
165	}
166
167	public Future<V> poll() {
168	return completionQueue.poll();
169	}
170
171	public Future<V> poll(long timeout, TimeUnit unit)
172	throws InterruptedException {
173	return completionQueue.poll(timeout, unit);
174	}
175
176	}