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> ecs
 *       = new ExecutorCompletionService<>(e);
 *   for (Callable<Result> s : solvers)
 *     ecs.submit(s);
 *   int n = solvers.size();
 *   for (int i = 0; i < 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> {@code
 * void solve(Executor e,
 *            Collection<Callable<Result>> solvers)
 *     throws InterruptedException {
 *   CompletionService<Result> ecs
 *       = new ExecutorCompletionService<>(e);
 *   int n = solvers.size();
 *   List<Future<Result>> futures = new ArrayList<>(n);
 *   Result result = null;
 *   try {
 *     for (Callable<Result> s : solvers)
 *       futures.add(ecs.submit(s));
 *     for (int i = 0; i < n; ++i) {
 *       try {
 *         Result r = ecs.take().get();
 *         if (r != null) {
 *           result = r;
 *           break;
 *         }
 *       } catch (ExecutionException ignore) {}
 *     }
 *   }
 *   finally {
 *     for (Future<Result> f : futures)
 *       f.cancel(true);
 *   }
 *
 *   if (result != null)
 *     use(result);
 * }}</pre>
 *
 * @since 1.5
 */
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:	1.3
Committed:	Thu Jun 15 22:48:08 2017 UTC (6 years, 10 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.2:	+2 -0 lines
Log Message:	8181082: class-level since tag issues in java.base & java.datatransfer module
#	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> ecs
31	* = new ExecutorCompletionService<>(e);
32	* for (Callable<Result> s : solvers)
33	* ecs.submit(s);
34	* int n = solvers.size();
35	* for (int i = 0; i < n; ++i) {
36	* Result r = ecs.take().get();
37	* if (r != null)
38	* use(r);
39	* }
40	* }}</pre>
41	*
42	* Suppose instead that you would like to use the first non-null result
43	* of the set of tasks, ignoring any that encounter exceptions,
44	* and cancelling all other tasks when the first one is ready:
45	*
46	* <pre> {@code
47	* void solve(Executor e,
48	* Collection<Callable<Result>> solvers)
49	* throws InterruptedException {
50	* CompletionService<Result> ecs
51	* = new ExecutorCompletionService<>(e);
52	* int n = solvers.size();
53	* List<Future<Result>> futures = new ArrayList<>(n);
54	* Result result = null;
55	* try {
56	* for (Callable<Result> s : solvers)
57	* futures.add(ecs.submit(s));
58	* for (int i = 0; i < n; ++i) {
59	* try {
60	* Result r = ecs.take().get();
61	* if (r != null) {
62	* result = r;
63	* break;
64	* }
65	* } catch (ExecutionException ignore) {}
66	* }
67	* }
68	* finally {
69	* for (Future<Result> f : futures)
70	* f.cancel(true);
71	* }
72	*
73	* if (result != null)
74	* use(result);
75	* }}</pre>
76	*
77	* @since 1.5
78	*/
79	public class ExecutorCompletionService<V> implements CompletionService<V> {
80	private final Executor executor;
81	private final AbstractExecutorService aes;
82	private final BlockingQueue<Future<V>> completionQueue;
83
84	/**
85	* FutureTask extension to enqueue upon completion.
86	*/
87	private static class QueueingFuture<V> extends FutureTask<Void> {
88	QueueingFuture(RunnableFuture<V> task,
89	BlockingQueue<Future<V>> completionQueue) {
90	super(task, null);
91	this.task = task;
92	this.completionQueue = completionQueue;
93	}
94	private final Future<V> task;
95	private final BlockingQueue<Future<V>> completionQueue;
96	protected void done() { completionQueue.add(task); }
97	}
98
99	private RunnableFuture<V> newTaskFor(Callable<V> task) {
100	if (aes == null)
101	return new FutureTask<V>(task);
102	else
103	return aes.newTaskFor(task);
104	}
105
106	private RunnableFuture<V> newTaskFor(Runnable task, V result) {
107	if (aes == null)
108	return new FutureTask<V>(task, result);
109	else
110	return aes.newTaskFor(task, result);
111	}
112
113	/**
114	* Creates an ExecutorCompletionService using the supplied
115	* executor for base task execution and a
116	* {@link LinkedBlockingQueue} as a completion queue.
117	*
118	* @param executor the executor to use
119	* @throws NullPointerException if executor is {@code null}
120	*/
121	public ExecutorCompletionService(Executor executor) {
122	if (executor == null)
123	throw new NullPointerException();
124	this.executor = executor;
125	this.aes = (executor instanceof AbstractExecutorService) ?
126	(AbstractExecutorService) executor : null;
127	this.completionQueue = new LinkedBlockingQueue<Future<V>>();
128	}
129
130	/**
131	* Creates an ExecutorCompletionService using the supplied
132	* executor for base task execution and the supplied queue as its
133	* completion queue.
134	*
135	* @param executor the executor to use
136	* @param completionQueue the queue to use as the completion queue
137	* normally one dedicated for use by this service. This
138	* queue is treated as unbounded -- failed attempted
139	* {@code Queue.add} operations for completed tasks cause
140	* them not to be retrievable.
141	* @throws NullPointerException if executor or completionQueue are {@code null}
142	*/
143	public ExecutorCompletionService(Executor executor,
144	BlockingQueue<Future<V>> completionQueue) {
145	if (executor == null \|\| completionQueue == null)
146	throw new NullPointerException();
147	this.executor = executor;
148	this.aes = (executor instanceof AbstractExecutorService) ?
149	(AbstractExecutorService) executor : null;
150	this.completionQueue = completionQueue;
151	}
152
153	public Future<V> submit(Callable<V> task) {
154	if (task == null) throw new NullPointerException();
155	RunnableFuture<V> f = newTaskFor(task);
156	executor.execute(new QueueingFuture<V>(f, completionQueue));
157	return f;
158	}
159
160	public Future<V> submit(Runnable task, V result) {
161	if (task == null) throw new NullPointerException();
162	RunnableFuture<V> f = newTaskFor(task, result);
163	executor.execute(new QueueingFuture<V>(f, completionQueue));
164	return f;
165	}
166
167	public Future<V> take() throws InterruptedException {
168	return completionQueue.take();
169	}
170
171	public Future<V> poll() {
172	return completionQueue.poll();
173	}
174
175	public Future<V> poll(long timeout, TimeUnit unit)
176	throws InterruptedException {
177	return completionQueue.poll(timeout, unit);
178	}
179
180	}