CompletionService


1   /*
2    * @(#)CompletionService.java   1.1 04/01/12
3    *
4    * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
5    * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6    */
7   
8   package java.util.concurrent;
9   
10  /**
11   * A service that decouples the production of new asynchronous tasks
12   * 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  
21   * <p>
22   *
23   * Typically, a <tt>CompletionService</tt> relies on a separate {@link
24   * Executor} to actually execute the tasks, in which case the
25   * <tt>CompletionService</tt> only manages an internal completion
26   * queue. The {@link ExecutorCompletionService} class provides an
27   * implementation of this approach.
28   *
29   */
30  public interface CompletionService<V> {
31      /**
32       * Submits a value-returning task for execution and returns a Future
33       * representing the pending results of the task. Upon completion,
34       * this task may be taken or polled.
35       *
36       * @param task the task to submit
37       * @return a Future representing pending completion of the task
38       * @throws RejectedExecutionException if task cannot be scheduled
39       * for execution
40       * @throws NullPointerException if task null     
41       */
42      Future  <V> submit(Callable  <V> task);
43  
44  
45      /**
46       * Submits a Runnable task for execution and returns a Future 
47       * representing that task.Upon completion,
48       * this task may be taken or polled.
49       *
50       * @param task the task to submit
51       * @param result the result to return upon successful completion
52       * @return a Future representing pending completion of the task,
53       * and whose <tt>get()</tt> method will return the given result value 
54       * upon completion
55       * @throws RejectedExecutionException if task cannot be scheduled
56       * for execution
57       * @throws NullPointerException if task null     
58       */
59      Future  <V> submit(Runnable   task, V result);
60  
61      /**
62       * Retrieves and removes the Future representing the next
63       * completed task, waiting if none are yet present.
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       * @param timeout how long to wait before giving up, in units of
84       * <tt>unit</tt>
85       * @param unit a <tt>TimeUnit</tt> determining how to interpret the
86       * <tt>timeout</tt> parameter
87       * @return the Future representing the next completed task or
88       * <tt>null</tt> if the specified waiting time elapses before one
89       * is present.
90       * @throws InterruptedException if interrupted while waiting.
91       */
92      Future  <V> poll(long timeout, TimeUnit   unit) throws InterruptedException  ;
93  }
94
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