1 |
/* |
2 |
* Written by Doug Lea with assistance from members of JCP JSR-166 |
3 |
* Expert Group and released to the public domain. Use, modify, and |
4 |
* redistribute this code in any way without acknowledgement. |
5 |
*/ |
6 |
|
7 |
package java.util.concurrent; |
8 |
|
9 |
/** |
10 |
* A <tt>Future</tt> represents the result of an asynchronous |
11 |
* computation. Methods are provided to check if the computation is |
12 |
* complete, to wait for its completion, and to retrieve the result of |
13 |
* the computation. The result can only be retrieved using method |
14 |
* <tt>get</tt> when the computation has completed, blocking if |
15 |
* necessary until it is ready. Cancellation is performed by the |
16 |
* <tt>cancel</tt> method. Additional methods are provided to |
17 |
* determine if the task completed normally or was cancelled. Once a |
18 |
* computation has completed, the computation cannot be cancelled. |
19 |
* |
20 |
* <p> |
21 |
* <b>Sample Usage</b> (Note that the following classes are all |
22 |
* made-up.) <p> |
23 |
* <pre> |
24 |
* interface ArchiveSearcher { String search(String target); } |
25 |
* class App { |
26 |
* ExecutorService executor = ... |
27 |
* ArchiveSearcher searcher = ... |
28 |
* void showSearch(final String target) throws InterruptedException { |
29 |
* Future<String> future = executor.submit(new Callable<String>() { |
30 |
* public String call() { return searcher.search(target); } |
31 |
* }); |
32 |
* displayOtherThings(); // do other things while searching |
33 |
* try { |
34 |
* displayText(future.get()); // use future |
35 |
* } catch (ExecutionException ex) { cleanup(); return; } |
36 |
* } |
37 |
* } |
38 |
* </pre> |
39 |
* |
40 |
* The {@link FutureTask} class is an implementation of <tt>Future</tt> that |
41 |
* implements <tt>Runnable</tt>, and so may be executed by an <tt>Executor</tt>. |
42 |
* For example, the above construction with <tt>submit</tt> could be replaced by: |
43 |
* <pre> |
44 |
* FutureTask<String> future = |
45 |
* new FutureTask<String>(new Callable<String>() { |
46 |
* public String call() { |
47 |
* return searcher.search(target); |
48 |
* }}); |
49 |
* executor.execute(future); |
50 |
* </pre> |
51 |
* @see FutureTask |
52 |
* @see Executor |
53 |
* @since 1.5 |
54 |
* @author Doug Lea |
55 |
* @param <V> The result type returned by this Future's <tt>get</tt> method |
56 |
*/ |
57 |
public interface Future<V> { |
58 |
|
59 |
/** |
60 |
* Attempts to cancel execution of this task. This attempt will |
61 |
* fail if the task has already completed, already been cancelled, |
62 |
* or could not be cancelled for some other reason. If successful, |
63 |
* and this task has not started when <tt>cancel</tt> is called, |
64 |
* this task should never run. If the task has already started, |
65 |
* then the <tt>interruptIfRunning</tt> parameter determines |
66 |
* whether the thread executing this task should be interrupted in |
67 |
* an attempt to stop the task. |
68 |
* |
69 |
* @param mayInterruptIfRunning <tt>true</tt> if the thread executing this |
70 |
* task should be interrupted; otherwise, in-progress tasks are allowed |
71 |
* to complete |
72 |
* @return <tt>false</tt> if the task could not be cancelled, |
73 |
* typically because is has already completed normally; |
74 |
* <tt>true</tt> otherwise |
75 |
*/ |
76 |
boolean cancel(boolean mayInterruptIfRunning); |
77 |
|
78 |
/** |
79 |
* Returns <tt>true</tt> if this task was cancelled before it completed |
80 |
* normally. |
81 |
* |
82 |
* @return <tt>true</tt> if task was cancelled before it completed |
83 |
*/ |
84 |
boolean isCancelled(); |
85 |
|
86 |
/** |
87 |
* Returns <tt>true</tt> if this task completed. |
88 |
* |
89 |
* Completion may be due to normal termination, an exception, or |
90 |
* cancellation -- in all of these cases, this method will return |
91 |
* <tt>true</tt>. |
92 |
* |
93 |
* @return <tt>true</tt> if this task completed. |
94 |
*/ |
95 |
boolean isDone(); |
96 |
|
97 |
/** |
98 |
* Waits if necessary for computation to complete, and then |
99 |
* retrieves its result. |
100 |
* |
101 |
* @return computed result |
102 |
* @throws CancellationException if this future was cancelled. |
103 |
* @throws ExecutionException if underlying computation threw an |
104 |
* exception |
105 |
* @throws InterruptedException if current thread was interrupted |
106 |
* while waiting |
107 |
*/ |
108 |
V get() throws InterruptedException, ExecutionException; |
109 |
|
110 |
/** |
111 |
* Waits if necessary for at most the given time for the computation |
112 |
* to complete, and then retrieves its result. |
113 |
* |
114 |
* @param timeout the maximum time to wait |
115 |
* @param unit the time unit of the timeout argument |
116 |
* @return computed result |
117 |
* @throws ExecutionException if underlying computation threw an |
118 |
* exception |
119 |
* @throws InterruptedException if current thread was interrupted |
120 |
* while waiting |
121 |
* @throws TimeoutException if the wait timed out |
122 |
*/ |
123 |
V get(long timeout, TimeUnit unit) |
124 |
throws InterruptedException, ExecutionException, TimeoutException; |
125 |
} |
126 |
|
127 |
|
128 |
|