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.
 *
 * <p> Memory visibility effects: State changes to the value returned from
 * a <tt>Callable</tt> <a
 * href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
 * actions following a successful return from <tt>take()</tt>.
 *
 */
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:	1.9
Committed:	Fri Sep 2 01:03:08 2005 UTC (18 years, 9 months ago) by brian
Branch:	MAIN
Changes since 1.8:	+5 -0 lines
Log Message:	Happens-before markup
#	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	* <p> Memory visibility effects: State changes to the value returned from
29	* a <tt>Callable</tt> <a
30	* href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
31	* actions following a successful return from <tt>take()</tt>.
32	*
33	*/
34	public interface CompletionService<V> {
35	/**
36	* Submits a value-returning task for execution and returns a Future
37	* representing the pending results of the task. Upon completion,
38	* 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	* @throws RejectedExecutionException if the task cannot be
43	* scheduled for execution
44	* @throws NullPointerException if the task is null
45	*/
46	Future<V> submit(Callable<V> task);
47
48
49	/**
50	* Submits a Runnable task for execution and returns a Future
51	* representing that task. Upon completion, this task may be
52	* taken or polled.
53	*
54	* @param task the task to submit
55	* @param result the result to return upon successful completion
56	* @return a Future representing pending completion of the task,
57	* and whose <tt>get()</tt> method will return the given
58	* result value upon completion
59	* @throws RejectedExecutionException if the task cannot be
60	* scheduled for execution
61	* @throws NullPointerException if the task is null
62	*/
63	Future<V> submit(Runnable task, V result);
64
65	/**
66	* Retrieves and removes the Future representing the next
67	* completed task, waiting if none are yet present.
68	*
69	* @return the Future representing the next completed task
70	* @throws InterruptedException if interrupted while waiting
71	*/
72	Future<V> take() throws InterruptedException;
73
74
75	/**
76	* Retrieves and removes the Future representing the next
77	* completed task or <tt>null</tt> if none are present.
78	*
79	* @return the Future representing the next completed task, or
80	* <tt>null</tt> if none are present
81	*/
82	Future<V> poll();
83
84	/**
85	* Retrieves and removes the Future representing the next
86	* completed task, waiting if necessary up to the specified wait
87	* time if none are yet present.
88	*
89	* @param timeout how long to wait before giving up, in units of
90	* <tt>unit</tt>
91	* @param unit a <tt>TimeUnit</tt> determining how to interpret the
92	* <tt>timeout</tt> parameter
93	* @return the Future representing the next completed task or
94	* <tt>null</tt> if the specified waiting time elapses
95	* before one is present
96	* @throws InterruptedException if interrupted while waiting
97	*/
98	Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException;
99	}