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, 11 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
#	User	Rev	Content
1	jsr166	1.1	/*
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	jsr166	1.2	* = new ExecutorCompletionService<>(e);
32	jsr166	1.1	* 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	jsr166	1.2	* = new ExecutorCompletionService<>(e);
52	jsr166	1.1	* 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	jsr166	1.3	*
77			* @since 1.5
78	jsr166	1.1	*/
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			}