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/licenses/publicdomain
 */

package java.util.concurrent;

/**
 * A service that decouples the production of new asynchronous tasks
 * from the consumption of the results of completed tasks.  Producers
 * <tt>submit</tt> tasks for execution. Consumers <tt>take</tt>
 * completed tasks and process their results in the order they
 * complete.  A <tt>CompletionService</tt> can for example be used to
 * manage asynchronous IO, 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 <tt>CompletionService</tt> relies on a separate {@link
 * Executor} to actually execute the tasks, in which case the
 * <tt>CompletionService</tt> only manages an internal completion
 * queue. The {@link ExecutorCompletionService} class provides an
 * implementation of this approach.
 *
 */
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 <tt>get()</tt> 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 <tt>null</tt> if none are present.
     *
     * @return the Future representing the next completed task, or
     *         <tt>null</tt> 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
     *        <tt>unit</tt>
     * @param unit a <tt>TimeUnit</tt> determining how to interpret the
     *        <tt>timeout</tt> parameter
     * @return the Future representing the next completed task or
     *         <tt>null</tt> 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:	1.8
Committed:	Fri Aug 26 02:14:54 2005 UTC (18 years, 9 months ago) by jsr166
Branch:	MAIN
Changes since 1.7:	+20 -18 lines
Log Message:	doc fixes
#	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/licenses/publicdomain
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	* <tt>submit</tt> tasks for execution. Consumers <tt>take</tt>
13	* completed tasks and process their results in the order they
14	* complete. A <tt>CompletionService</tt> can for example be used to
15	* manage asynchronous IO, 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	* <p>
21	*
22	* Typically, a <tt>CompletionService</tt> relies on a separate {@link
23	* Executor} to actually execute the tasks, in which case the
24	* <tt>CompletionService</tt> only manages an internal completion
25	* queue. The {@link ExecutorCompletionService} class provides an
26	* implementation of this approach.
27	*
28	*/
29	public interface CompletionService<V> {
30	/**
31	* Submits a value-returning task for execution and returns a Future
32	* representing the pending results of the task. Upon completion,
33	* this task may be taken or polled.
34	*
35	* @param task the task to submit
36	* @return a Future representing pending completion of the task
37	* @throws RejectedExecutionException if the task cannot be
38	* scheduled for execution
39	* @throws NullPointerException if the task is null
40	*/
41	Future<V> submit(Callable<V> task);
42
43
44	/**
45	* Submits a Runnable task for execution and returns a Future
46	* representing that task. Upon completion, this task may be
47	* taken or polled.
48	*
49	* @param task the task to submit
50	* @param result the result to return upon successful completion
51	* @return a Future representing pending completion of the task,
52	* and whose <tt>get()</tt> method will return the given
53	* result value upon completion
54	* @throws RejectedExecutionException if the task cannot be
55	* scheduled for execution
56	* @throws NullPointerException if the task is null
57	*/
58	Future<V> submit(Runnable task, V result);
59
60	/**
61	* Retrieves and removes the Future representing the next
62	* completed task, waiting if none are yet present.
63	*
64	* @return the Future representing the next completed task
65	* @throws InterruptedException if interrupted while waiting
66	*/
67	Future<V> take() throws InterruptedException;
68
69
70	/**
71	* Retrieves and removes the Future representing the next
72	* completed task or <tt>null</tt> if none are present.
73	*
74	* @return the Future representing the next completed task, or
75	* <tt>null</tt> if none are present
76	*/
77	Future<V> poll();
78
79	/**
80	* Retrieves and removes the Future representing the next
81	* completed task, waiting if necessary up to the specified wait
82	* time if none are yet present.
83	*
84	* @param timeout how long to wait before giving up, in units of
85	* <tt>unit</tt>
86	* @param unit a <tt>TimeUnit</tt> determining how to interpret the
87	* <tt>timeout</tt> parameter
88	* @return the Future representing the next completed task or
89	* <tt>null</tt> if the specified waiting time elapses
90	* before one is present
91	* @throws InterruptedException if interrupted while waiting
92	*/
93	Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException;
94	}