util/concurrent/CompletionService.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 service that decouples the production of new asynchronous tasks
 * from the consumption of the results of completed tasks.  Producers
 * {@code submit} tasks for execution. Consumers {@code take}
 * completed tasks and process their results in the order they
 * complete.  A {@code CompletionService} can for example be used to
 * manage asynchronous I/O, in which tasks that perform reads are
 * submitted in one part of a program or system, and then acted upon
 * in a different part of the program when the reads complete,
 * possibly in a different order than they were requested.
 *
 * <p>Typically, a {@code CompletionService} relies on a separate
 * {@link Executor} to actually execute the tasks, in which case the
 * {@code CompletionService} only manages an internal completion
 * queue. The {@link ExecutorCompletionService} class provides an
 * implementation of this approach.
 *
 * <p>Memory consistency effects: Actions in a thread prior to
 * submitting a task to a {@code CompletionService}
 * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
 * actions taken by that task, which in turn <i>happen-before</i>
 * actions following a successful return from the corresponding {@code take()}.
 */
public interface CompletionService<V> {
    /**
     * Submits a value-returning task for execution and returns a Future
     * representing the pending results of the task.  Upon completion,
     * this task may be taken or polled.
     *
     * @param task the task to submit
     * @return a Future representing pending completion of the task
     * @throws RejectedExecutionException if the task cannot be
     *         scheduled for execution
     * @throws NullPointerException if the task is null
     */
    Future<V> submit(Callable<V> task);

    /**
     * Submits a Runnable task for execution and returns a Future
     * representing that task.  Upon completion, this task may be
     * taken or polled.
     *
     * @param task the task to submit
     * @param result the result to return upon successful completion
     * @return a Future representing pending completion of the task,
     *         and whose {@code get()} method will return the given
     *         result value upon completion
     * @throws RejectedExecutionException if the task cannot be
     *         scheduled for execution
     * @throws NullPointerException if the task is null
     */
    Future<V> submit(Runnable task, V result);

    /**
     * Retrieves and removes the Future representing the next
     * completed task, waiting if none are yet present.
     *
     * @return the Future representing the next completed task
     * @throws InterruptedException if interrupted while waiting
     */
    Future<V> take() throws InterruptedException;

    /**
     * Retrieves and removes the Future representing the next
     * completed task or {@code null} if none are present.
     *
     * @return the Future representing the next completed task, or
     *         {@code null} if none are present
     */
    Future<V> poll();

    /**
     * Retrieves and removes the Future representing the next
     * completed task, waiting if necessary up to the specified wait
     * time if none are yet present.
     *
     * @param timeout how long to wait before giving up, in units of
     *        {@code unit}
     * @param unit a {@code TimeUnit} determining how to interpret the
     *        {@code timeout} parameter
     * @return the Future representing the next completed task or
     *         {@code null} if the specified waiting time elapses
     *         before one is present
     * @throws InterruptedException if interrupted while waiting
     */
    Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException;
}
Revision:	1.2
Committed:	Wed Jan 16 01:39:37 2013 UTC (11 years, 4 months ago) by jsr166
Branch:	MAIN
Changes since 1.1:	+11 -11 lines
Log Message:	<tt> -> {@code
#	User	Rev	Content
1	dl	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 service that decouples the production of new asynchronous tasks
11			* from the consumption of the results of completed tasks. Producers
12	jsr166	1.2	* {@code submit} tasks for execution. Consumers {@code take}
13	dl	1.1	* completed tasks and process their results in the order they
14	jsr166	1.2	* complete. A {@code CompletionService} can for example be used to
15	dl	1.1	* manage asynchronous I/O, in which tasks that perform reads are
16			* submitted in one part of a program or system, and then acted upon
17			* in a different part of the program when the reads complete,
18			* possibly in a different order than they were requested.
19			*
20	jsr166	1.2	* <p>Typically, a {@code CompletionService} relies on a separate
21	dl	1.1	* {@link Executor} to actually execute the tasks, in which case the
22	jsr166	1.2	* {@code CompletionService} only manages an internal completion
23	dl	1.1	* queue. The {@link ExecutorCompletionService} class provides an
24			* implementation of this approach.
25			*
26			* <p>Memory consistency effects: Actions in a thread prior to
27			* submitting a task to a {@code CompletionService}
28			* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
29			* actions taken by that task, which in turn <i>happen-before</i>
30			* actions following a successful return from the corresponding {@code take()}.
31			*/
32			public interface CompletionService<V> {
33			/**
34			* Submits a value-returning task for execution and returns a Future
35			* representing the pending results of the task. Upon completion,
36			* this task may be taken or polled.
37			*
38			* @param task the task to submit
39			* @return a Future representing pending completion of the task
40			* @throws RejectedExecutionException if the task cannot be
41			* scheduled for execution
42			* @throws NullPointerException if the task is null
43			*/
44			Future<V> submit(Callable<V> task);
45
46			/**
47			* Submits a Runnable task for execution and returns a Future
48			* representing that task. Upon completion, this task may be
49			* taken or polled.
50			*
51			* @param task the task to submit
52			* @param result the result to return upon successful completion
53			* @return a Future representing pending completion of the task,
54	jsr166	1.2	* and whose {@code get()} method will return the given
55	dl	1.1	* result value upon completion
56			* @throws RejectedExecutionException if the task cannot be
57			* scheduled for execution
58			* @throws NullPointerException if the task is null
59			*/
60			Future<V> submit(Runnable task, V result);
61
62			/**
63			* Retrieves and removes the Future representing the next
64			* completed task, waiting if none are yet present.
65			*
66			* @return the Future representing the next completed task
67			* @throws InterruptedException if interrupted while waiting
68			*/
69			Future<V> take() throws InterruptedException;
70
71			/**
72			* Retrieves and removes the Future representing the next
73	jsr166	1.2	* completed task or {@code null} if none are present.
74	dl	1.1	*
75			* @return the Future representing the next completed task, or
76	jsr166	1.2	* {@code null} if none are present
77	dl	1.1	*/
78			Future<V> poll();
79
80			/**
81			* Retrieves and removes the Future representing the next
82			* completed task, waiting if necessary up to the specified wait
83			* time if none are yet present.
84			*
85			* @param timeout how long to wait before giving up, in units of
86	jsr166	1.2	* {@code unit}
87			* @param unit a {@code TimeUnit} determining how to interpret the
88			* {@code timeout} parameter
89	dl	1.1	* @return the Future representing the next completed task or
90	jsr166	1.2	* {@code null} if the specified waiting time elapses
91	dl	1.1	* before one is present
92			* @throws InterruptedException if interrupted while waiting
93			*/
94			Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException;
95			}