util/concurrent/ExecutorCompletionService.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain. Use, modify, and
 * redistribute this code in any way without acknowledgement.
 */

package java.util.concurrent;


/**
 * A {@link CompletionService} that uses a supplied {@link Executor}
 * to execute 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, using the results of each of them
 * that return a non-null value. You could write this as:
 *
 * <pre>
 *    void solve(Executor e, Collection&lt;Callable&lt;Result&gt;&gt; solvers)
 *      throws InterruptedException, ExecutionException {
 *        CompletionService&lt;Result&gt; ecs = new ExecutorCompletionService&lt;Result&gt;(e);
 *        for (Callable&lt;Result&gt; s : solvers)
 *            ecs.submit(s);
 *        int n = solvers.size();
 *        for (int i = 0; i &lt; 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 of those that encounter exceptions,
 * and cancelling all other tasks when the first one is ready:
 *
 * <pre>
 *    void solve(Executor e, Collection&lt;Callable&lt;Result&gt;&gt; solvers) 
 *      throws InterruptedException {
 *        CompletionService&lt;Result&gt; ecs = new ExecutorCompletionService&lt;Result&gt;(e);
 *        int n = solvers.size();
 *        List&lt;Future&lt;Result&gt;&gt; futures = new ArrayList&lt;Future&lt;Result&gt;&gt;(n);
 *        Result result = null;
 *        try {
 *            for (Callable&lt;Result&gt; s : solvers)
 *                futures.add(ecs.submit(s));
 *            for (int i = 0; i &lt; n; ++i) {
 *                try {
 *                    Result r = ecs.take().get();
 *                    if (r != null) {
 *                        result = r;
 *                        break;
 *                    }
 *                } catch(ExecutionException ignore) {}
 *            }
 *        }
 *        finally {
 *            for (Future&lt;Result&gt; 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
     8 @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
     8 @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) {
        QueueingFuture f = new QueueingFuture(task);
        executor.execute(f);
        return f;
    }

    public Future<V> submit(Runnable task, V result) {
        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);
    }

}


Revision:	1.6
Committed:	Fri Dec 19 14:42:25 2003 UTC (20 years, 5 months ago) by dl
Branch:	MAIN
Changes since 1.5:	+11 -14 lines
Log Message:	Documentation improvements
#	User	Rev	Content
1	dl	1.1	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3			* Expert Group and released to the public domain. Use, modify, and
4			* redistribute this code in any way without acknowledgement.
5			*/
6
7			package java.util.concurrent;
8
9
10			/**
11	jozart	1.2	* A {@link CompletionService} that uses a supplied {@link Executor}
12	dl	1.6	* to execute tasks.
13	dl	1.5	*
14			* <p>
15			*
16			* <b>Usage Examples.</b>
17	dl	1.6	* Suppose you have a set of solvers for a certain problem (each returning
18			* a value of some type <tt>Result</tt>),
19	dl	1.5	* and would like to run them concurrently, using the results of each of them
20			* that return a non-null value. You could write this as:
21			*
22			* <pre>
23	dl	1.6	* void solve(Executor e, Collection<Callable<Result>> solvers)
24			* throws InterruptedException, ExecutionException {
25			* CompletionService<Result> ecs = new ExecutorCompletionService<Result>(e);
26	dl	1.5	* for (Callable<Result> s : solvers)
27			* ecs.submit(s);
28			* int n = solvers.size();
29			* for (int i = 0; i < n; ++i) {
30			* Result r = ecs.take().get();
31			* if (r != null)
32			* use(r);
33			* }
34			* }
35			* </pre>
36			*
37			* Suppose instead that you would like to use the first non-null result
38	dl	1.6	* of the set of tasks, ignoring any of those that encounter exceptions,
39			* and cancelling all other tasks when the first one is ready:
40	dl	1.5	*
41			* <pre>
42			* void solve(Executor e, Collection<Callable<Result>> solvers)
43	dl	1.6	* throws InterruptedException {
44			* CompletionService<Result> ecs = new ExecutorCompletionService<Result>(e);
45	dl	1.5	* int n = solvers.size();
46	dl	1.6	* List<Future<Result>> futures = new ArrayList<Future<Result>>(n);
47	dl	1.5	* Result result = null;
48			* try {
49			* for (Callable<Result> s : solvers)
50			* futures.add(ecs.submit(s));
51			* for (int i = 0; i < n; ++i) {
52			* try {
53			* Result r = ecs.take().get();
54			* if (r != null) {
55			* result = r;
56			* break;
57			* }
58			* } catch(ExecutionException ignore) {}
59			* }
60			* }
61			* finally {
62			* for (Future<Result> f : futures)
63			* f.cancel(true);
64			* }
65			*
66			* if (result != null)
67			* use(result);
68			* }
69			* </pre>
70	dl	1.1	*/
71			public class ExecutorCompletionService<V> implements CompletionService<V> {
72	jozart	1.2	private final Executor executor;
73	dl	1.3	private final BlockingQueue<Future<V>> completionQueue;
74	dl	1.1
75			/**
76			* FutureTask extension to enqueue upon completion
77			*/
78	dl	1.4	private class QueueingFuture extends FutureTask<V> {
79			QueueingFuture(Callable<V> c) { super(c); }
80			QueueingFuture(Runnable t, V r) { super(t, r); }
81			protected void done() { completionQueue.add(this); }
82	dl	1.1	}
83
84			/**
85			* Creates an ExecutorCompletionService using the supplied
86	dl	1.3	* executor for base task execution and a
87			* {@link LinkedBlockingQueue} as a completion queue.
88	dl	1.5	* @param executor the executor to use
89	dl	1.3	8 @throws NullPointerException if executor is <tt>null</tt>
90	dl	1.1	*/
91	jozart	1.2	public ExecutorCompletionService(Executor executor) {
92	dl	1.1	if (executor == null)
93			throw new NullPointerException();
94			this.executor = executor;
95	dl	1.3	this.completionQueue = new LinkedBlockingQueue<Future<V>>();
96	dl	1.1	}
97
98			/**
99	dl	1.3	* Creates an ExecutorCompletionService using the supplied
100			* executor for base task execution and the supplied queue as its
101			* completion queue.
102	dl	1.5	* @param executor the executor to use
103	dl	1.3	* @param completionQueue the queue to use as the completion queue;
104			* normally one dedicated for use by this service
105			8 @throws NullPointerException if executor or completionQueue are <tt>null</tt>
106	dl	1.1	*/
107	dl	1.3	public ExecutorCompletionService(Executor executor,
108			BlockingQueue<Future<V>> completionQueue) {
109			if (executor == null \|\| completionQueue == null)
110			throw new NullPointerException();
111			this.executor = executor;
112			this.completionQueue = completionQueue;
113	dl	1.1	}
114
115			public Future<V> submit(Callable<V> task) {
116	dl	1.4	QueueingFuture f = new QueueingFuture(task);
117	dl	1.1	executor.execute(f);
118			return f;
119			}
120
121			public Future<V> submit(Runnable task, V result) {
122	dl	1.4	QueueingFuture f = new QueueingFuture(task, result);
123	dl	1.1	executor.execute(f);
124			return f;
125			}
126
127			public Future<V> take() throws InterruptedException {
128	dl	1.3	return completionQueue.take();
129	dl	1.1	}
130
131			public Future<V> poll() {
132	dl	1.3	return completionQueue.poll();
133	dl	1.1	}
134
135			public Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException {
136	dl	1.3	return completionQueue.poll(timeout, unit);
137	dl	1.1	}
138	dl	1.5
139	dl	1.1	}
140
141