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 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:	1.13
Committed:	Tue Feb 7 20:54:24 2006 UTC (18 years, 3 months ago) by jsr166
Branch:	MAIN
Changes since 1.12:	+0 -1 lines
Log Message:	6378729: Remove workaround for 6280605
#	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>Typically, a <tt>CompletionService</tt> relies on a separate
21	* {@link Executor} to actually execute the tasks, in which case the
22	* <tt>CompletionService</tt> only manages an internal completion
23	* queue. The {@link ExecutorCompletionService} class provides an
24	* implementation of this approach.
25	*
26	* <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	*
32	*/
33	public interface CompletionService<V> {
34	/**
35	* Submits a value-returning task for execution and returns a Future
36	* representing the pending results of the task. Upon completion,
37	* this task may be taken or polled.
38	*
39	* @param task the task to submit
40	* @return a Future representing pending completion of the task
41	* @throws RejectedExecutionException if the task cannot be
42	* scheduled for execution
43	* @throws NullPointerException if the task is null
44	*/
45	Future<V> submit(Callable<V> task);
46
47	/**
48	* Submits a Runnable task for execution and returns a Future
49	* representing that task. Upon completion, this task may be
50	* taken or polled.
51	*
52	* @param task the task to submit
53	* @param result the result to return upon successful completion
54	* @return a Future representing pending completion of the task,
55	* and whose <tt>get()</tt> method will return the given
56	* result value upon completion
57	* @throws RejectedExecutionException if the task cannot be
58	* scheduled for execution
59	* @throws NullPointerException if the task is null
60	*/
61	Future<V> submit(Runnable task, V result);
62
63	/**
64	* Retrieves and removes the Future representing the next
65	* completed task, waiting if none are yet present.
66	*
67	* @return the Future representing the next completed task
68	* @throws InterruptedException if interrupted while waiting
69	*/
70	Future<V> take() throws InterruptedException;
71
72
73	/**
74	* Retrieves and removes the Future representing the next
75	* completed task or <tt>null</tt> if none are present.
76	*
77	* @return the Future representing the next completed task, or
78	* <tt>null</tt> if none are present
79	*/
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	*
87	* @param timeout how long to wait before giving up, in units of
88	* <tt>unit</tt>
89	* @param unit a <tt>TimeUnit</tt> determining how to interpret the
90	* <tt>timeout</tt> parameter
91	* @return the Future representing the next completed task or
92	* <tt>null</tt> if the specified waiting time elapses
93	* before one is present
94	* @throws InterruptedException if interrupted while waiting
95	*/
96	Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException;
97	}