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
#	Content
1	/*
2	* Written by Doug Lea with assistance from members of JCP JSR-166
3	* Expert Group and released to the public domain, as explained at
4	* http://creativecommons.org/licenses/publicdomain
5	*/
6
7	package java.util.concurrent;
8	import java.util.concurrent.*; // for javadoc (till 6280605 is fixed)
9
10	/**
11	* A {@link CompletionService} that uses a supplied {@link Executor}
12	* 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	*
17	* <p>
18	*
19	* <b>Usage Examples.</b>
20	*
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	*
27	* <pre>
28	* 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	* </pre>
43	*
44	* Suppose instead that you would like to use the first non-null result
45	* of the set of tasks, ignoring any that encounter exceptions,
46	* and cancelling all other tasks when the first one is ready:
47	*
48	* <pre>
49	* 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	* </pre>
80	*/
81	public class ExecutorCompletionService<V> implements CompletionService<V> {
82	private final Executor executor;
83	private final AbstractExecutorService aes;
84	private final BlockingQueue<Future<V>> completionQueue;
85
86	/**
87	* FutureTask extension to enqueue upon completion
88	*/
89	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	}
111
112	/**
113	* Creates an ExecutorCompletionService using the supplied
114	* executor for base task execution and a
115	* {@link LinkedBlockingQueue} as a completion queue.
116	*
117	* @param executor the executor to use
118	* @throws NullPointerException if executor is <tt>null</tt>
119	*/
120	public ExecutorCompletionService(Executor executor) {
121	if (executor == null)
122	throw new NullPointerException();
123	this.executor = executor;
124	this.aes = (executor instanceof AbstractExecutorService) ?
125	(AbstractExecutorService) executor : null;
126	this.completionQueue = new LinkedBlockingQueue<Future<V>>();
127	}
128
129	/**
130	* Creates an ExecutorCompletionService using the supplied
131	* executor for base task execution and the supplied queue as its
132	* completion queue.
133	*
134	* @param executor the executor to use
135	* @param completionQueue the queue to use as the completion queue
136	* normally one dedicated for use by this service
137	* @throws NullPointerException if executor or completionQueue are <tt>null</tt>
138	*/
139	public ExecutorCompletionService(Executor executor,
140	BlockingQueue<Future<V>> completionQueue) {
141	if (executor == null \|\| completionQueue == null)
142	throw new NullPointerException();
143	this.executor = executor;
144	this.aes = (executor instanceof AbstractExecutorService) ?
145	(AbstractExecutorService) executor : null;
146	this.completionQueue = completionQueue;
147	}
148
149	public Future<V> submit(Callable<V> task) {
150	if (task == null) throw new NullPointerException();
151	RunnableFuture<V> f = newTaskFor(task);
152	executor.execute(new QueueingFuture(f));
153	return f;
154	}
155
156	public Future<V> submit(Runnable task, V result) {
157	if (task == null) throw new NullPointerException();
158	RunnableFuture<V> f = newTaskFor(task, result);
159	executor.execute(new QueueingFuture(f));
160	return f;
161	}
162
163	public Future<V> take() throws InterruptedException {
164	return completionQueue.take();
165	}
166
167	public Future<V> poll() {
168	return completionQueue.poll();
169	}
170
171	public Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException {
172	return completionQueue.poll(timeout, unit);
173	}
174
175	}