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. An <tt>ExecutorCompletionService</tt> can be
 * useful as an add-on to solve task coordination problems.
 *
 * <p>
 *
 * <b>Usage Examples.</b>
 * Suppose you have a set of solvers for a certain problem,
 * 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 {
 *        ExecutorCompletionService&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 a set of tasks, ignoring any of those that encounter exceptions
 * and cancelling all of the other tasks when the first one is ready:
 *
 * <pre>
 *    void solve(Executor e, Collection&lt;Callable&lt;Result&gt;&gt; solvers) 
 *        throws InterruptedException {
 *        ExecutorCompletionService&lt;Result&gt; ecs = 
 *            new ExecutorCompletionService&lt;Result&gt;(e);
 *        int n = solvers.size();
 *        ArrayList&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:	1.5
Committed:	Wed Dec 17 17:00:24 2003 UTC (20 years, 5 months ago) by dl
Branch:	MAIN
Changes since 1.4:	+64 -5 lines
Log Message:	Export delegation wrappers; fix/add documentation
#	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	1.5	* to execute tasks. An <tt>ExecutorCompletionService</tt> can be
13			* useful as an add-on to solve task coordination problems.
14			*
15			* <p>
16			*
17			* <b>Usage Examples.</b>
18			* Suppose you have a set of solvers for a certain problem,
19			* 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			* void solve(Executor e, Collection<Callable<Result>> solvers)
24			* throws InterruptedException, ExecutionException {
25			* ExecutorCompletionService<Result> ecs = new
26			* ExecutorCompletionService<Result>(e);
27			* for (Callable<Result> s : solvers)
28			* ecs.submit(s);
29			* int n = solvers.size();
30			* for (int i = 0; i < n; ++i) {
31			* Result r = ecs.take().get();
32			* if (r != null)
33			* use(r);
34			* }
35			* }
36			* </pre>
37			*
38			* Suppose instead that you would like to use the first non-null result
39			* of a set of tasks, ignoring any of those that encounter exceptions
40			* and cancelling all of the other tasks when the first one is ready:
41			*
42			* <pre>
43			* void solve(Executor e, Collection<Callable<Result>> solvers)
44			* throws InterruptedException {
45			* ExecutorCompletionService<Result> ecs =
46			* new ExecutorCompletionService<Result>(e);
47			* int n = solvers.size();
48			* ArrayList<Future<Result>> futures =
49			* new ArrayList<Future<Result>>(n);
50			* 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	1.3	* @param completionQueue the queue to use as the completion queue;
107			* 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	1.4	QueueingFuture f = new QueueingFuture(task);
120	dl	1.1	executor.execute(f);
121			return f;
122			}
123
124			public Future<V> submit(Runnable task, V result) {
125	dl	1.4	QueueingFuture f = new QueueingFuture(task, result);
126	dl	1.1	executor.execute(f);
127			return f;
128			}
129
130			public Future<V> take() throws InterruptedException {
131	dl	1.3	return completionQueue.take();
132	dl	1.1	}
133
134			public Future<V> poll() {
135	dl	1.3	return completionQueue.poll();
136	dl	1.1	}
137
138			public Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException {
139	dl	1.3	return completionQueue.poll(timeout, unit);
140	dl	1.1	}
141	dl	1.5
142	dl	1.1	}
143
144