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;
import java.util.concurrent.*; // for javadoc (till 6280605 is fixed)

/**
 * 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.
 *
 * <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 <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:	1.12
Committed:	Wed Sep 14 22:51:10 2005 UTC (18 years, 8 months ago) by jsr166
Branch:	MAIN
Changes since 1.11:	+8 -7 lines
Log Message:	happens-before
#	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	jsr166	1.12	import java.util.concurrent.*; // for javadoc (till 6280605 is fixed)
9	dl	1.1
10			/**
11			* A service that decouples the production of new asynchronous tasks
12	dl	1.3	* from the consumption of the results of completed tasks. Producers
13			* <tt>submit</tt> tasks for execution. Consumers <tt>take</tt>
14			* completed tasks and process their results in the order they
15			* complete. A <tt>CompletionService</tt> can for example be used to
16			* manage asynchronous IO, in which tasks that perform reads are
17			* submitted in one part of a program or system, and then acted upon
18			* in a different part of the program when the reads complete,
19			* possibly in a different order than they were requested.
20	brian	1.10	*
21	jsr166	1.12	* <p>Typically, a <tt>CompletionService</tt> relies on a separate
22			* {@link Executor} to actually execute the tasks, in which case the
23	dl	1.2	* <tt>CompletionService</tt> only manages an internal completion
24			* queue. The {@link ExecutorCompletionService} class provides an
25			* implementation of this approach.
26			*
27	jsr166	1.12	* <p>Memory consistency effects: Actions in a thread prior to
28			* submitting a task to a {@code CompletionService}
29			* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
30			* actions taken by that task, which in turn <i>happen-before</i>
31			* actions following a successful return from the corresponding {@code take()}.
32	brian	1.9	*
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	1.8	* and whose <tt>get()</tt> method will return the given
57			* 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			/**
75			* Retrieves and removes the Future representing the next
76			* completed task or <tt>null</tt> if none are present.
77			*
78			* @return the Future representing the next completed task, or
79	jsr166	1.8	* <tt>null</tt> if none are present
80	dl	1.1	*/
81			Future<V> poll();
82
83			/**
84			* Retrieves and removes the Future representing the next
85			* completed task, waiting if necessary up to the specified wait
86			* time if none are yet present.
87	jsr166	1.8	*
88	dl	1.1	* @param timeout how long to wait before giving up, in units of
89	jsr166	1.8	* <tt>unit</tt>
90	dl	1.1	* @param unit a <tt>TimeUnit</tt> determining how to interpret the
91	jsr166	1.8	* <tt>timeout</tt> parameter
92	dl	1.1	* @return the Future representing the next completed task or
93	jsr166	1.8	* <tt>null</tt> if the specified waiting time elapses
94			* before one is present
95			* @throws InterruptedException if interrupted while waiting
96	dl	1.1	*/
97			Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException;
98			}