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 task cannot be scheduled
     * for execution
     * @throws NullPointerException if task 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 task cannot be scheduled
     * for execution
     * @throws NullPointerException if task 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:	1.7
Committed:	Mon May 2 18:38:53 2005 UTC (19 years, 1 month ago) by jsr166
Branch:	MAIN
Changes since 1.6:	+4 -4 lines
Log Message:	remove trailing whitespace
#	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			* http://creativecommons.org/licenses/publicdomain
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			* <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	dl	1.2
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	dl	1.1	*/
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 task cannot be scheduled
38			* for execution
39	jsr166	1.7	* @throws NullPointerException if task null
40	dl	1.1	*/
41			Future<V> submit(Callable<V> task);
42
43
44			/**
45	jsr166	1.7	* Submits a Runnable task for execution and returns a Future
46	dl	1.6	* representing that task. Upon completion,
47	dl	1.1	* this task may be 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	jsr166	1.7	* and whose <tt>get()</tt> method will return the given result value
53	dl	1.1	* upon completion
54			* @throws RejectedExecutionException if task cannot be scheduled
55			* for execution
56	jsr166	1.7	* @throws NullPointerException if task null
57	dl	1.1	*/
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			* @return the Future representing the next completed task
64			* @throws InterruptedException if interrupted while waiting.
65			*/
66			Future<V> take() throws InterruptedException;
67
68
69			/**
70			* Retrieves and removes the Future representing the next
71			* completed task or <tt>null</tt> if none are present.
72			*
73			* @return the Future representing the next completed task, or
74			* <tt>null</tt> if none are present.
75			*/
76			Future<V> poll();
77
78			/**
79			* Retrieves and removes the Future representing the next
80			* completed task, waiting if necessary up to the specified wait
81			* time if none are yet present.
82			* @param timeout how long to wait before giving up, in units of
83			* <tt>unit</tt>
84			* @param unit a <tt>TimeUnit</tt> determining how to interpret the
85			* <tt>timeout</tt> parameter
86			* @return the Future representing the next completed task or
87			* <tt>null</tt> if the specified waiting time elapses before one
88			* is present.
89			* @throws InterruptedException if interrupted while waiting.
90			*/
91			Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException;
92			}