1 |
dl |
1.1 |
/* |
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/publicdomain/zero/1.0/ |
5 |
|
|
*/ |
6 |
|
|
|
7 |
|
|
package java.util.concurrent; |
8 |
|
|
|
9 |
|
|
/** |
10 |
|
|
* An object that executes submitted {@link Runnable} tasks. This |
11 |
|
|
* interface provides a way of decoupling task submission from the |
12 |
|
|
* mechanics of how each task will be run, including details of thread |
13 |
|
|
* use, scheduling, etc. An <tt>Executor</tt> is normally used |
14 |
|
|
* instead of explicitly creating threads. For example, rather than |
15 |
|
|
* invoking <tt>new Thread(new(RunnableTask())).start()</tt> for each |
16 |
|
|
* of a set of tasks, you might use: |
17 |
|
|
* |
18 |
|
|
* <pre> |
19 |
|
|
* Executor executor = <em>anExecutor</em>; |
20 |
|
|
* executor.execute(new RunnableTask1()); |
21 |
|
|
* executor.execute(new RunnableTask2()); |
22 |
|
|
* ... |
23 |
|
|
* </pre> |
24 |
|
|
* |
25 |
|
|
* However, the <tt>Executor</tt> interface does not strictly |
26 |
|
|
* require that execution be asynchronous. In the simplest case, an |
27 |
|
|
* executor can run the submitted task immediately in the caller's |
28 |
|
|
* thread: |
29 |
|
|
* |
30 |
|
|
* <pre> {@code |
31 |
|
|
* class DirectExecutor implements Executor { |
32 |
|
|
* public void execute(Runnable r) { |
33 |
|
|
* r.run(); |
34 |
|
|
* } |
35 |
|
|
* }}</pre> |
36 |
|
|
* |
37 |
|
|
* More typically, tasks are executed in some thread other |
38 |
|
|
* than the caller's thread. The executor below spawns a new thread |
39 |
|
|
* for each task. |
40 |
|
|
* |
41 |
|
|
* <pre> {@code |
42 |
|
|
* class ThreadPerTaskExecutor implements Executor { |
43 |
|
|
* public void execute(Runnable r) { |
44 |
|
|
* new Thread(r).start(); |
45 |
|
|
* } |
46 |
|
|
* }}</pre> |
47 |
|
|
* |
48 |
|
|
* Many <tt>Executor</tt> implementations impose some sort of |
49 |
|
|
* limitation on how and when tasks are scheduled. The executor below |
50 |
|
|
* serializes the submission of tasks to a second executor, |
51 |
|
|
* illustrating a composite executor. |
52 |
|
|
* |
53 |
|
|
* <pre> {@code |
54 |
|
|
* class SerialExecutor implements Executor { |
55 |
|
|
* final Queue<Runnable> tasks = new ArrayDeque<Runnable>(); |
56 |
|
|
* final Executor executor; |
57 |
|
|
* Runnable active; |
58 |
|
|
* |
59 |
|
|
* SerialExecutor(Executor executor) { |
60 |
|
|
* this.executor = executor; |
61 |
|
|
* } |
62 |
|
|
* |
63 |
|
|
* public synchronized void execute(final Runnable r) { |
64 |
|
|
* tasks.offer(new Runnable() { |
65 |
|
|
* public void run() { |
66 |
|
|
* try { |
67 |
|
|
* r.run(); |
68 |
|
|
* } finally { |
69 |
|
|
* scheduleNext(); |
70 |
|
|
* } |
71 |
|
|
* } |
72 |
|
|
* }); |
73 |
|
|
* if (active == null) { |
74 |
|
|
* scheduleNext(); |
75 |
|
|
* } |
76 |
|
|
* } |
77 |
|
|
* |
78 |
|
|
* protected synchronized void scheduleNext() { |
79 |
|
|
* if ((active = tasks.poll()) != null) { |
80 |
|
|
* executor.execute(active); |
81 |
|
|
* } |
82 |
|
|
* } |
83 |
|
|
* }}</pre> |
84 |
|
|
* |
85 |
|
|
* The <tt>Executor</tt> implementations provided in this package |
86 |
|
|
* implement {@link ExecutorService}, which is a more extensive |
87 |
|
|
* interface. The {@link ThreadPoolExecutor} class provides an |
88 |
|
|
* extensible thread pool implementation. The {@link Executors} class |
89 |
|
|
* provides convenient factory methods for these Executors. |
90 |
|
|
* |
91 |
|
|
* <p>Memory consistency effects: Actions in a thread prior to |
92 |
|
|
* submitting a {@code Runnable} object to an {@code Executor} |
93 |
|
|
* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a> |
94 |
|
|
* its execution begins, perhaps in another thread. |
95 |
|
|
* |
96 |
|
|
* @since 1.5 |
97 |
|
|
* @author Doug Lea |
98 |
|
|
*/ |
99 |
|
|
public interface Executor { |
100 |
|
|
|
101 |
|
|
/** |
102 |
|
|
* Executes the given command at some time in the future. The command |
103 |
|
|
* may execute in a new thread, in a pooled thread, or in the calling |
104 |
|
|
* thread, at the discretion of the <tt>Executor</tt> implementation. |
105 |
|
|
* |
106 |
|
|
* @param command the runnable task |
107 |
|
|
* @throws RejectedExecutionException if this task cannot be |
108 |
|
|
* accepted for execution. |
109 |
|
|
* @throws NullPointerException if command is null |
110 |
|
|
*/ |
111 |
|
|
void execute(Runnable command); |
112 |
|
|
} |