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()}.
 *
 * @since 1.5
 */
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:	1.20
Committed:	Thu Jun 15 22:46:46 2017 UTC (6 years, 11 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.19:	+2 -0 lines
Log Message:	8181082: class-level since tag issues in java.base & java.datatransfer module
#	User	Rev	Content
1	dl	1.1	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3	dl	1.5	* Expert Group and released to the public domain, as explained at
4	jsr166	1.14	* http://creativecommons.org/publicdomain/zero/1.0/
5	dl	1.1	*/
6
7			package java.util.concurrent;
8
9			/**
10			* A service that decouples the production of new asynchronous tasks
11	dl	1.3	* from the consumption of the results of completed tasks. Producers
12	jsr166	1.18	* {@code submit} tasks for execution. Consumers {@code take}
13	dl	1.3	* completed tasks and process their results in the order they
14	jsr166	1.18	* complete. A {@code CompletionService} can for example be used to
15	jsr166	1.17	* manage asynchronous I/O, in which tasks that perform reads are
16	dl	1.3	* 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	brian	1.10	*
20	jsr166	1.18	* <p>Typically, a {@code CompletionService} relies on a separate
21	jsr166	1.12	* {@link Executor} to actually execute the tasks, in which case the
22	jsr166	1.18	* {@code CompletionService} only manages an internal completion
23	dl	1.2	* queue. The {@link ExecutorCompletionService} class provides an
24			* implementation of this approach.
25			*
26	jsr166	1.12	* <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	jsr166	1.20	*
32			* @since 1.5
33	dl	1.1	*/
34			public interface CompletionService<V> {
35			/**
36			* Submits a value-returning task for execution and returns a Future
37	jsr166	1.8	* representing the pending results of the task. Upon completion,
38	dl	1.1	* this task may be taken or polled.
39			*
40			* @param task the task to submit
41			* @return a Future representing pending completion of the task
42	jsr166	1.8	* @throws RejectedExecutionException if the task cannot be
43			* scheduled for execution
44			* @throws NullPointerException if the task is null
45	dl	1.1	*/
46			Future<V> submit(Callable<V> task);
47
48			/**
49	jsr166	1.7	* Submits a Runnable task for execution and returns a Future
50	jsr166	1.8	* representing that task. Upon completion, this task may be
51			* taken or polled.
52	dl	1.1	*
53			* @param task the task to submit
54			* @param result the result to return upon successful completion
55			* @return a Future representing pending completion of the task,
56	jsr166	1.18	* and whose {@code get()} method will return the given
57	jsr166	1.8	* result value upon completion
58			* @throws RejectedExecutionException if the task cannot be
59			* scheduled for execution
60			* @throws NullPointerException if the task is null
61	dl	1.1	*/
62			Future<V> submit(Runnable task, V result);
63
64			/**
65			* Retrieves and removes the Future representing the next
66			* completed task, waiting if none are yet present.
67	jsr166	1.8	*
68	dl	1.1	* @return the Future representing the next completed task
69	jsr166	1.8	* @throws InterruptedException if interrupted while waiting
70	dl	1.1	*/
71			Future<V> take() throws InterruptedException;
72
73			/**
74			* Retrieves and removes the Future representing the next
75	jsr166	1.19	* completed task, or {@code null} if none are present.
76	dl	1.1	*
77			* @return the Future representing the next completed task, or
78	jsr166	1.18	* {@code null} if none are present
79	dl	1.1	*/
80			Future<V> poll();
81
82			/**
83			* Retrieves and removes the Future representing the next
84			* completed task, waiting if necessary up to the specified wait
85			* time if none are yet present.
86	jsr166	1.8	*
87	dl	1.1	* @param timeout how long to wait before giving up, in units of
88	jsr166	1.18	* {@code unit}
89			* @param unit a {@code TimeUnit} determining how to interpret the
90			* {@code timeout} parameter
91	dl	1.1	* @return the Future representing the next completed task or
92	jsr166	1.18	* {@code null} if the specified waiting time elapses
93	jsr166	1.8	* before one is present
94			* @throws InterruptedException if interrupted while waiting
95	dl	1.1	*/
96			Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException;
97			}