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/licenses/publicdomain
 */

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&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 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) {
        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);
    }

}


Revision:	1.9
Committed:	Wed Jan 21 15:20:35 2004 UTC (20 years, 4 months ago) by dl
Branch:	MAIN
Changes since 1.8:	+7 -5 lines
Log Message:	doc improvements; consistent conventions for nested classes
#	User	Rev	Content
1	dl	1.1	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3	dl	1.8	* Expert Group and released to the public domain, as explained at
4			* http://creativecommons.org/licenses/publicdomain
5	dl	1.1	*/
6
7			package java.util.concurrent;
8
9
10			/**
11	jozart	1.2	* A {@link CompletionService} that uses a supplied {@link Executor}
12	dl	1.7	* to execute tasks. This class arranges that submitted tasks are,
13			* upon completion, placed on a queue accessible using <tt>take</tt>.
14			* The class is lightweight enough to be suitable for transient use
15			* when processing groups of tasks.
16	dl	1.5	*
17			* <p>
18			*
19			* <b>Usage Examples.</b>
20	dl	1.9	*
21			* Suppose you have a set of solvers for a certain problem, each
22			* returning a value of some type <tt>Result</tt>, and would like to
23			* run them concurrently, processing the results of each of them that
24			* return a non-null value, in some method <tt>use(Result r)</tt>. You
25			* could write this as:
26	dl	1.5	*
27			* <pre>
28	dl	1.6	* void solve(Executor e, Collection<Callable<Result>> solvers)
29			* throws InterruptedException, ExecutionException {
30			* CompletionService<Result> ecs = new ExecutorCompletionService<Result>(e);
31	dl	1.5	* for (Callable<Result> s : solvers)
32			* ecs.submit(s);
33			* int n = solvers.size();
34			* for (int i = 0; i < n; ++i) {
35			* Result r = ecs.take().get();
36			* if (r != null)
37			* use(r);
38			* }
39			* }
40			* </pre>
41			*
42			* Suppose instead that you would like to use the first non-null result
43	dl	1.9	* of the set of tasks, ignoring any that encounter exceptions,
44	dl	1.6	* and cancelling all other tasks when the first one is ready:
45	dl	1.5	*
46			* <pre>
47			* void solve(Executor e, Collection<Callable<Result>> solvers)
48	dl	1.6	* throws InterruptedException {
49			* CompletionService<Result> ecs = new ExecutorCompletionService<Result>(e);
50	dl	1.5	* int n = solvers.size();
51	dl	1.6	* List<Future<Result>> futures = new ArrayList<Future<Result>>(n);
52	dl	1.5	* Result result = null;
53			* try {
54			* for (Callable<Result> s : solvers)
55			* futures.add(ecs.submit(s));
56			* for (int i = 0; i < n; ++i) {
57			* try {
58			* Result r = ecs.take().get();
59			* if (r != null) {
60			* result = r;
61			* break;
62			* }
63			* } catch(ExecutionException ignore) {}
64			* }
65			* }
66			* finally {
67			* for (Future<Result> f : futures)
68			* f.cancel(true);
69			* }
70			*
71			* if (result != null)
72			* use(result);
73			* }
74			* </pre>
75	dl	1.1	*/
76			public class ExecutorCompletionService<V> implements CompletionService<V> {
77	jozart	1.2	private final Executor executor;
78	dl	1.3	private final BlockingQueue<Future<V>> completionQueue;
79	dl	1.1
80			/**
81			* FutureTask extension to enqueue upon completion
82			*/
83	dl	1.4	private class QueueingFuture extends FutureTask<V> {
84			QueueingFuture(Callable<V> c) { super(c); }
85			QueueingFuture(Runnable t, V r) { super(t, r); }
86			protected void done() { completionQueue.add(this); }
87	dl	1.1	}
88
89			/**
90			* Creates an ExecutorCompletionService using the supplied
91	dl	1.3	* executor for base task execution and a
92			* {@link LinkedBlockingQueue} as a completion queue.
93	dl	1.5	* @param executor the executor to use
94	dl	1.3	8 @throws NullPointerException if executor is <tt>null</tt>
95	dl	1.1	*/
96	jozart	1.2	public ExecutorCompletionService(Executor executor) {
97	dl	1.1	if (executor == null)
98			throw new NullPointerException();
99			this.executor = executor;
100	dl	1.3	this.completionQueue = new LinkedBlockingQueue<Future<V>>();
101	dl	1.1	}
102
103			/**
104	dl	1.3	* Creates an ExecutorCompletionService using the supplied
105			* executor for base task execution and the supplied queue as its
106			* completion queue.
107	dl	1.5	* @param executor the executor to use
108	dl	1.7	* @param completionQueue the queue to use as the completion queue
109	dl	1.3	* normally one dedicated for use by this service
110			8 @throws NullPointerException if executor or completionQueue are <tt>null</tt>
111	dl	1.1	*/
112	dl	1.3	public ExecutorCompletionService(Executor executor,
113			BlockingQueue<Future<V>> completionQueue) {
114			if (executor == null \|\| completionQueue == null)
115			throw new NullPointerException();
116			this.executor = executor;
117			this.completionQueue = completionQueue;
118	dl	1.1	}
119
120			public Future<V> submit(Callable<V> task) {
121	dl	1.7	if (task == null) throw new NullPointerException();
122	dl	1.4	QueueingFuture f = new QueueingFuture(task);
123	dl	1.1	executor.execute(f);
124			return f;
125			}
126
127			public Future<V> submit(Runnable task, V result) {
128	dl	1.7	if (task == null) throw new NullPointerException();
129	dl	1.4	QueueingFuture f = new QueueingFuture(task, result);
130	dl	1.1	executor.execute(f);
131			return f;
132			}
133
134			public Future<V> take() throws InterruptedException {
135	dl	1.3	return completionQueue.take();
136	dl	1.1	}
137
138			public Future<V> poll() {
139	dl	1.3	return completionQueue.poll();
140	dl	1.1	}
141
142			public Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException {
143	dl	1.3	return completionQueue.poll(timeout, unit);
144	dl	1.1	}
145	dl	1.5
146	dl	1.1	}
147
148