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.  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, 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) {
        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:	1.7
Committed:	Sun Dec 21 12:24:48 2003 UTC (20 years, 5 months ago) by dl
Branch:	MAIN
Changes since 1.6:	+7 -2 lines
Log Message:	Documentation improvments; support two-arg submit
#	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	1.7	* 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	1.6	* Suppose you have a set of solvers for a certain problem (each returning
21			* a value of some type <tt>Result</tt>),
22	dl	1.5	* and would like to run them concurrently, using the results of each of them
23			* that return a non-null value. You could write this as:
24			*
25			* <pre>
26	dl	1.6	* void solve(Executor e, Collection<Callable<Result>> solvers)
27			* throws InterruptedException, ExecutionException {
28			* CompletionService<Result> ecs = new ExecutorCompletionService<Result>(e);
29	dl	1.5	* for (Callable<Result> s : solvers)
30			* ecs.submit(s);
31			* int n = solvers.size();
32			* for (int i = 0; i < n; ++i) {
33			* Result r = ecs.take().get();
34			* if (r != null)
35			* use(r);
36			* }
37			* }
38			* </pre>
39			*
40			* Suppose instead that you would like to use the first non-null result
41	dl	1.6	* of the set of tasks, ignoring any of those that encounter exceptions,
42			* and cancelling all other tasks when the first one is ready:
43	dl	1.5	*
44			* <pre>
45			* void solve(Executor e, Collection<Callable<Result>> solvers)
46	dl	1.6	* throws InterruptedException {
47			* CompletionService<Result> ecs = new ExecutorCompletionService<Result>(e);
48	dl	1.5	* int n = solvers.size();
49	dl	1.6	* List<Future<Result>> futures = new ArrayList<Future<Result>>(n);
50	dl	1.5	* Result result = null;
51			* try {
52			* for (Callable<Result> s : solvers)
53			* futures.add(ecs.submit(s));
54			* for (int i = 0; i < n; ++i) {
55			* try {
56			* Result r = ecs.take().get();
57			* if (r != null) {
58			* result = r;
59			* break;
60			* }
61			* } catch(ExecutionException ignore) {}
62			* }
63			* }
64			* finally {
65			* for (Future<Result> f : futures)
66			* f.cancel(true);
67			* }
68			*
69			* if (result != null)
70			* use(result);
71			* }
72			* </pre>
73	dl	1.1	*/
74			public class ExecutorCompletionService<V> implements CompletionService<V> {
75	jozart	1.2	private final Executor executor;
76	dl	1.3	private final BlockingQueue<Future<V>> completionQueue;
77	dl	1.1
78			/**
79			* FutureTask extension to enqueue upon completion
80			*/
81	dl	1.4	private class QueueingFuture extends FutureTask<V> {
82			QueueingFuture(Callable<V> c) { super(c); }
83			QueueingFuture(Runnable t, V r) { super(t, r); }
84			protected void done() { completionQueue.add(this); }
85	dl	1.1	}
86
87			/**
88			* Creates an ExecutorCompletionService using the supplied
89	dl	1.3	* executor for base task execution and a
90			* {@link LinkedBlockingQueue} as a completion queue.
91	dl	1.5	* @param executor the executor to use
92	dl	1.3	8 @throws NullPointerException if executor is <tt>null</tt>
93	dl	1.1	*/
94	jozart	1.2	public ExecutorCompletionService(Executor executor) {
95	dl	1.1	if (executor == null)
96			throw new NullPointerException();
97			this.executor = executor;
98	dl	1.3	this.completionQueue = new LinkedBlockingQueue<Future<V>>();
99	dl	1.1	}
100
101			/**
102	dl	1.3	* Creates an ExecutorCompletionService using the supplied
103			* executor for base task execution and the supplied queue as its
104			* completion queue.
105	dl	1.5	* @param executor the executor to use
106	dl	1.7	* @param completionQueue the queue to use as the completion queue
107	dl	1.3	* normally one dedicated for use by this service
108			8 @throws NullPointerException if executor or completionQueue are <tt>null</tt>
109	dl	1.1	*/
110	dl	1.3	public ExecutorCompletionService(Executor executor,
111			BlockingQueue<Future<V>> completionQueue) {
112			if (executor == null \|\| completionQueue == null)
113			throw new NullPointerException();
114			this.executor = executor;
115			this.completionQueue = completionQueue;
116	dl	1.1	}
117
118			public Future<V> submit(Callable<V> task) {
119	dl	1.7	if (task == null) throw new NullPointerException();
120	dl	1.4	QueueingFuture f = new QueueingFuture(task);
121	dl	1.1	executor.execute(f);
122			return f;
123			}
124
125			public Future<V> submit(Runnable task, V result) {
126	dl	1.7	if (task == null) throw new NullPointerException();
127	dl	1.4	QueueingFuture f = new QueueingFuture(task, result);
128	dl	1.1	executor.execute(f);
129			return f;
130			}
131
132			public Future<V> take() throws InterruptedException {
133	dl	1.3	return completionQueue.take();
134	dl	1.1	}
135
136			public Future<V> poll() {
137	dl	1.3	return completionQueue.poll();
138	dl	1.1	}
139
140			public Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException {
141	dl	1.3	return completionQueue.poll(timeout, unit);
142	dl	1.1	}
143	dl	1.5
144	dl	1.1	}
145
146