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;
import java.util.concurrent.*; // for javadoc (till 6280605 is fixed)

/**
 * 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 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 <tt>null</tt>
     */
    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
     * @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.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:	1.15
Committed:	Fri Aug 26 22:58:57 2005 UTC (18 years, 9 months ago) by jsr166
Branch:	MAIN
Changes since 1.14:	+47 -40 lines
Log Message:	whitespace
#	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	jsr166	1.15	import java.util.concurrent.*; // for javadoc (till 6280605 is fixed)
9	dl	1.1
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	jsr166	1.15	* void solve(Executor e,
29			* Collection<Callable<Result>> solvers)
30			* throws InterruptedException, ExecutionException {
31			* CompletionService<Result> ecs
32			* = new ExecutorCompletionService<Result>(e);
33			* for (Callable<Result> s : solvers)
34			* ecs.submit(s);
35			* int n = solvers.size();
36			* for (int i = 0; i < n; ++i) {
37			* Result r = ecs.take().get();
38			* if (r != null)
39			* use(r);
40			* }
41			* }
42	dl	1.5	* </pre>
43			*
44			* Suppose instead that you would like to use the first non-null result
45	dl	1.9	* of the set of tasks, ignoring any that encounter exceptions,
46	dl	1.6	* and cancelling all other tasks when the first one is ready:
47	dl	1.5	*
48			* <pre>
49	jsr166	1.15	* void solve(Executor e,
50			* Collection<Callable<Result>> solvers)
51			* throws InterruptedException {
52			* CompletionService<Result> ecs
53			* = new ExecutorCompletionService<Result>(e);
54			* int n = solvers.size();
55			* List<Future<Result>> futures
56			* = new ArrayList<Future<Result>>(n);
57			* Result result = null;
58			* try {
59			* for (Callable<Result> s : solvers)
60			* futures.add(ecs.submit(s));
61			* for (int i = 0; i < n; ++i) {
62			* try {
63			* Result r = ecs.take().get();
64			* if (r != null) {
65			* result = r;
66			* break;
67			* }
68			* } catch (ExecutionException ignore) {}
69			* }
70			* }
71			* finally {
72			* for (Future<Result> f : futures)
73			* f.cancel(true);
74			* }
75			*
76			* if (result != null)
77			* use(result);
78			* }
79	dl	1.5	* </pre>
80	dl	1.1	*/
81			public class ExecutorCompletionService<V> implements CompletionService<V> {
82	jozart	1.2	private final Executor executor;
83	dl	1.13	private final AbstractExecutorService aes;
84	dl	1.3	private final BlockingQueue<Future<V>> completionQueue;
85	dl	1.1
86			/**
87			* FutureTask extension to enqueue upon completion
88			*/
89	dl	1.13	private class QueueingFuture extends FutureTask<Void> {
90			QueueingFuture(RunnableFuture<V> task) {
91			super(task, null);
92			this.task = task;
93			}
94			protected void done() { completionQueue.add(task); }
95			private final Future<V> task;
96			}
97
98			private RunnableFuture<V> newTaskFor(Callable<V> task) {
99			if (aes == null)
100			return new FutureTask<V>(task);
101			else
102			return aes.newTaskFor(task);
103			}
104
105			private RunnableFuture<V> newTaskFor(Runnable task, V result) {
106			if (aes == null)
107			return new FutureTask<V>(task, result);
108			else
109			return aes.newTaskFor(task, result);
110	dl	1.1	}
111
112			/**
113			* Creates an ExecutorCompletionService using the supplied
114	dl	1.3	* executor for base task execution and a
115			* {@link LinkedBlockingQueue} as a completion queue.
116	jsr166	1.15	*
117	dl	1.5	* @param executor the executor to use
118	dl	1.10	* @throws NullPointerException if executor is <tt>null</tt>
119	dl	1.1	*/
120	jozart	1.2	public ExecutorCompletionService(Executor executor) {
121	jsr166	1.12	if (executor == null)
122	dl	1.1	throw new NullPointerException();
123			this.executor = executor;
124	dl	1.13	this.aes = (executor instanceof AbstractExecutorService) ?
125			(AbstractExecutorService) executor : null;
126	dl	1.3	this.completionQueue = new LinkedBlockingQueue<Future<V>>();
127	dl	1.1	}
128
129			/**
130	dl	1.3	* Creates an ExecutorCompletionService using the supplied
131			* executor for base task execution and the supplied queue as its
132			* completion queue.
133	jsr166	1.15	*
134	dl	1.5	* @param executor the executor to use
135	dl	1.7	* @param completionQueue the queue to use as the completion queue
136	dl	1.3	* normally one dedicated for use by this service
137	dl	1.10	* @throws NullPointerException if executor or completionQueue are <tt>null</tt>
138	dl	1.1	*/
139	dl	1.3	public ExecutorCompletionService(Executor executor,
140			BlockingQueue<Future<V>> completionQueue) {
141	jsr166	1.12	if (executor == null \|\| completionQueue == null)
142	dl	1.3	throw new NullPointerException();
143			this.executor = executor;
144	dl	1.13	this.aes = (executor instanceof AbstractExecutorService) ?
145			(AbstractExecutorService) executor : null;
146	dl	1.3	this.completionQueue = completionQueue;
147	dl	1.1	}
148
149			public Future<V> submit(Callable<V> task) {
150	dl	1.7	if (task == null) throw new NullPointerException();
151	dl	1.13	RunnableFuture<V> f = newTaskFor(task);
152			executor.execute(new QueueingFuture(f));
153	dl	1.1	return f;
154			}
155
156			public Future<V> submit(Runnable task, V result) {
157	dl	1.7	if (task == null) throw new NullPointerException();
158	dl	1.13	RunnableFuture<V> f = newTaskFor(task, result);
159			executor.execute(new QueueingFuture(f));
160	dl	1.1	return f;
161			}
162
163			public Future<V> take() throws InterruptedException {
164	dl	1.3	return completionQueue.take();
165	dl	1.1	}
166
167			public Future<V> poll() {
168	dl	1.3	return completionQueue.poll();
169	dl	1.1	}
170
171			public Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException {
172	dl	1.3	return completionQueue.poll(timeout, unit);
173	dl	1.1	}
174	dl	1.5
175	dl	1.1	}