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/publicdomain/zero/1.0/
 */

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 {@code take}.
 * 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 {@code Result}, and would like to
 * run them concurrently, processing the results of each of them that
 * return a non-null value, in some method {@code use(Result r)}. You
 * could write this as:
 *
 * <pre> {@code
 * void solve(Executor e,
 *            Collection<Callable<Result>> solvers)
 *     throws InterruptedException, ExecutionException {
 *   CompletionService<Result> cs
 *       = new ExecutorCompletionService<>(e);
 *   solvers.forEach(cs::submit);
 *   for (int i = solvers.size(); i > 0; i--) {
 *     Result r = cs.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> {@code
 * void solve(Executor e,
 *            Collection<Callable<Result>> solvers)
 *     throws InterruptedException {
 *   CompletionService<Result> cs
 *       = new ExecutorCompletionService<>(e);
 *   int n = solvers.size();
 *   List<Future<Result>> futures = new ArrayList<>(n);
 *   Result result = null;
 *   try {
 *     solvers.forEach(solver -> futures.add(cs.submit(solver)));
 *     for (int i = n; i > 0; i--) {
 *       try {
 *         Result r = cs.take().get();
 *         if (r != null) {
 *           result = r;
 *           break;
 *         }
 *       } catch (ExecutionException ignore) {}
 *     }
 *   } finally {
 *     futures.forEach(future -> future.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 static class QueueingFuture<V> extends FutureTask<Void> {
        QueueingFuture(RunnableFuture<V> task,
                       BlockingQueue<Future<V>> completionQueue) {
            super(task, null);
            this.task = task;
            this.completionQueue = completionQueue;
        }
        private final Future<V> task;
        private final BlockingQueue<Future<V>> completionQueue;
        protected void done() { completionQueue.add(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 {@code null}
     */
    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. This
     *        queue is treated as unbounded -- failed attempted
     *        {@code Queue.add} operations for completed tasks cause
     *        them not to be retrievable.
     * @throws NullPointerException if executor or completionQueue are {@code null}
     */
    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<V>(f, completionQueue));
        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<V>(f, completionQueue));
        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:	1.28
Committed:	Sun Nov 6 22:15:01 2016 UTC (7 years, 7 months ago) by jsr166
Branch:	MAIN
Changes since 1.27:	+2 -2 lines
Log Message:	elide parens in unary lambdas
#	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/publicdomain/zero/1.0/
5	*/
6
7	package java.util.concurrent;
8
9	/**
10	* A {@link CompletionService} that uses a supplied {@link Executor}
11	* to execute tasks. This class arranges that submitted tasks are,
12	* upon completion, placed on a queue accessible using {@code take}.
13	* The class is lightweight enough to be suitable for transient use
14	* when processing groups of tasks.
15	*
16	* <p>
17	*
18	* <b>Usage Examples.</b>
19	*
20	* Suppose you have a set of solvers for a certain problem, each
21	* returning a value of some type {@code Result}, and would like to
22	* run them concurrently, processing the results of each of them that
23	* return a non-null value, in some method {@code use(Result r)}. You
24	* could write this as:
25	*
26	* <pre> {@code
27	* void solve(Executor e,
28	* Collection<Callable<Result>> solvers)
29	* throws InterruptedException, ExecutionException {
30	* CompletionService<Result> cs
31	* = new ExecutorCompletionService<>(e);
32	* solvers.forEach(cs::submit);
33	* for (int i = solvers.size(); i > 0; i--) {
34	* Result r = cs.take().get();
35	* if (r != null)
36	* use(r);
37	* }
38	* }}</pre>
39	*
40	* Suppose instead that you would like to use the first non-null result
41	* of the set of tasks, ignoring any that encounter exceptions,
42	* and cancelling all other tasks when the first one is ready:
43	*
44	* <pre> {@code
45	* void solve(Executor e,
46	* Collection<Callable<Result>> solvers)
47	* throws InterruptedException {
48	* CompletionService<Result> cs
49	* = new ExecutorCompletionService<>(e);
50	* int n = solvers.size();
51	* List<Future<Result>> futures = new ArrayList<>(n);
52	* Result result = null;
53	* try {
54	* solvers.forEach(solver -> futures.add(cs.submit(solver)));
55	* for (int i = n; i > 0; i--) {
56	* try {
57	* Result r = cs.take().get();
58	* if (r != null) {
59	* result = r;
60	* break;
61	* }
62	* } catch (ExecutionException ignore) {}
63	* }
64	* } finally {
65	* futures.forEach(future -> future.cancel(true));
66	* }
67	*
68	* if (result != null)
69	* use(result);
70	* }}</pre>
71	*/
72	public class ExecutorCompletionService<V> implements CompletionService<V> {
73	private final Executor executor;
74	private final AbstractExecutorService aes;
75	private final BlockingQueue<Future<V>> completionQueue;
76
77	/**
78	* FutureTask extension to enqueue upon completion.
79	*/
80	private static class QueueingFuture<V> extends FutureTask<Void> {
81	QueueingFuture(RunnableFuture<V> task,
82	BlockingQueue<Future<V>> completionQueue) {
83	super(task, null);
84	this.task = task;
85	this.completionQueue = completionQueue;
86	}
87	private final Future<V> task;
88	private final BlockingQueue<Future<V>> completionQueue;
89	protected void done() { completionQueue.add(task); }
90	}
91
92	private RunnableFuture<V> newTaskFor(Callable<V> task) {
93	if (aes == null)
94	return new FutureTask<V>(task);
95	else
96	return aes.newTaskFor(task);
97	}
98
99	private RunnableFuture<V> newTaskFor(Runnable task, V result) {
100	if (aes == null)
101	return new FutureTask<V>(task, result);
102	else
103	return aes.newTaskFor(task, result);
104	}
105
106	/**
107	* Creates an ExecutorCompletionService using the supplied
108	* executor for base task execution and a
109	* {@link LinkedBlockingQueue} as a completion queue.
110	*
111	* @param executor the executor to use
112	* @throws NullPointerException if executor is {@code null}
113	*/
114	public ExecutorCompletionService(Executor executor) {
115	if (executor == null)
116	throw new NullPointerException();
117	this.executor = executor;
118	this.aes = (executor instanceof AbstractExecutorService) ?
119	(AbstractExecutorService) executor : null;
120	this.completionQueue = new LinkedBlockingQueue<Future<V>>();
121	}
122
123	/**
124	* Creates an ExecutorCompletionService using the supplied
125	* executor for base task execution and the supplied queue as its
126	* completion queue.
127	*
128	* @param executor the executor to use
129	* @param completionQueue the queue to use as the completion queue
130	* normally one dedicated for use by this service. This
131	* queue is treated as unbounded -- failed attempted
132	* {@code Queue.add} operations for completed tasks cause
133	* them not to be retrievable.
134	* @throws NullPointerException if executor or completionQueue are {@code null}
135	*/
136	public ExecutorCompletionService(Executor executor,
137	BlockingQueue<Future<V>> completionQueue) {
138	if (executor == null \|\| completionQueue == null)
139	throw new NullPointerException();
140	this.executor = executor;
141	this.aes = (executor instanceof AbstractExecutorService) ?
142	(AbstractExecutorService) executor : null;
143	this.completionQueue = completionQueue;
144	}
145
146	public Future<V> submit(Callable<V> task) {
147	if (task == null) throw new NullPointerException();
148	RunnableFuture<V> f = newTaskFor(task);
149	executor.execute(new QueueingFuture<V>(f, completionQueue));
150	return f;
151	}
152
153	public Future<V> submit(Runnable task, V result) {
154	if (task == null) throw new NullPointerException();
155	RunnableFuture<V> f = newTaskFor(task, result);
156	executor.execute(new QueueingFuture<V>(f, completionQueue));
157	return f;
158	}
159
160	public Future<V> take() throws InterruptedException {
161	return completionQueue.take();
162	}
163
164	public Future<V> poll() {
165	return completionQueue.poll();
166	}
167
168	public Future<V> poll(long timeout, TimeUnit unit)
169	throws InterruptedException {
170	return completionQueue.poll(timeout, unit);
171	}
172
173	}