util/concurrent/Executor.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/publicdomain/zero/1.0/
 */

package java.util.concurrent;

/**
 * An object that executes submitted {@link Runnable} tasks. This
 * interface provides a way of decoupling task submission from the
 * mechanics of how each task will be run, including details of thread
 * use, scheduling, etc.  An <tt>Executor</tt> is normally used
 * instead of explicitly creating threads. For example, rather than
 * invoking <tt>new Thread(new(RunnableTask())).start()</tt> for each
 * of a set of tasks, you might use:
 *
 * <pre>
 * Executor executor = <em>anExecutor</em>;
 * executor.execute(new RunnableTask1());
 * executor.execute(new RunnableTask2());
 * ...
 * </pre>
 *
 * However, the <tt>Executor</tt> interface does not strictly
 * require that execution be asynchronous. In the simplest case, an
 * executor can run the submitted task immediately in the caller's
 * thread:
 *
 *  <pre> {@code
 * class DirectExecutor implements Executor {
 *   public void execute(Runnable r) {
 *     r.run();
 *   }
 * }}</pre>
 *
 * More typically, tasks are executed in some thread other
 * than the caller's thread.  The executor below spawns a new thread
 * for each task.
 *
 *  <pre> {@code
 * class ThreadPerTaskExecutor implements Executor {
 *   public void execute(Runnable r) {
 *     new Thread(r).start();
 *   }
 * }}</pre>
 *
 * Many <tt>Executor</tt> implementations impose some sort of
 * limitation on how and when tasks are scheduled.  The executor below
 * serializes the submission of tasks to a second executor,
 * illustrating a composite executor.
 *
 *  <pre> {@code
 * class SerialExecutor implements Executor {
 *   final Queue<Runnable> tasks = new ArrayDeque<Runnable>();
 *   final Executor executor;
 *   Runnable active;
 *
 *   SerialExecutor(Executor executor) {
 *     this.executor = executor;
 *   }
 *
 *   public synchronized void execute(final Runnable r) {
 *     tasks.offer(new Runnable() {
 *       public void run() {
 *         try {
 *           r.run();
 *         } finally {
 *           scheduleNext();
 *         }
 *       }
 *     });
 *     if (active == null) {
 *       scheduleNext();
 *     }
 *   }
 *
 *   protected synchronized void scheduleNext() {
 *     if ((active = tasks.poll()) != null) {
 *       executor.execute(active);
 *     }
 *   }
 * }}</pre>
 *
 * The <tt>Executor</tt> implementations provided in this package
 * implement {@link ExecutorService}, which is a more extensive
 * interface.  The {@link ThreadPoolExecutor} class provides an
 * extensible thread pool implementation. The {@link Executors} class
 * provides convenient factory methods for these Executors.
 *
 * <p>Memory consistency effects: Actions in a thread prior to
 * submitting a {@code Runnable} object to an {@code Executor}
 * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
 * its execution begins, perhaps in another thread.
 *
 * @since 1.5
 * @author Doug Lea
 */
public interface Executor {

    /**
     * Executes the given command at some time in the future.  The command
     * may execute in a new thread, in a pooled thread, or in the calling
     * thread, at the discretion of the <tt>Executor</tt> implementation.
     *
     * @param command the runnable task
     * @throws RejectedExecutionException if this task cannot be
     * accepted for execution.
     * @throws NullPointerException if command is null
     */
    void execute(Runnable command);
}
Revision:	1.29
Committed:	Thu Jun 9 07:48:43 2011 UTC (13 years ago) by jsr166
Branch:	MAIN
Changes since 1.28:	+10 -10 lines
Log Message:	consistent style for code snippets
#	User	Rev	Content
1	tim	1.1	/*
2	dl	1.2	* Written by Doug Lea with assistance from members of JCP JSR-166
3	dl	1.15	* Expert Group and released to the public domain, as explained at
4	jsr166	1.28	* http://creativecommons.org/publicdomain/zero/1.0/
5	tim	1.1	*/
6
7			package java.util.concurrent;
8
9			/**
10	dl	1.11	* 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	dl	1.16	* 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	jsr166	1.19	*
25	dl	1.16	* 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	tim	1.1	*
30	jsr166	1.29	* <pre> {@code
31	tim	1.1	* class DirectExecutor implements Executor {
32	jsr166	1.29	* public void execute(Runnable r) {
33			* r.run();
34			* }
35			* }}</pre>
36	tim	1.1	*
37	dl	1.18	* More typically, tasks are executed in some thread other
38	dl	1.16	* than the caller's thread. The executor below spawns a new thread
39			* for each task.
40	tim	1.1	*
41	jsr166	1.29	* <pre> {@code
42	tim	1.1	* class ThreadPerTaskExecutor implements Executor {
43	jsr166	1.29	* public void execute(Runnable r) {
44			* new Thread(r).start();
45			* }
46			* }}</pre>
47	tim	1.1	*
48	dl	1.16	* Many <tt>Executor</tt> implementations impose some sort of
49	dl	1.10	* 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	tim	1.1	*
53	jsr166	1.27	* <pre> {@code
54	tim	1.1	* class SerialExecutor implements Executor {
55	jsr166	1.27	* 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	tim	1.1	* }
71	jsr166	1.27	* }
72			* });
73			* if (active == null) {
74			* scheduleNext();
75	tim	1.1	* }
76	jsr166	1.27	* }
77	tim	1.1	*
78	jsr166	1.27	* protected synchronized void scheduleNext() {
79			* if ((active = tasks.poll()) != null) {
80			* executor.execute(active);
81	tim	1.1	* }
82	jsr166	1.27	* }
83			* }}</pre>
84	tim	1.1	*
85	dl	1.10	* 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	tim	1.1	*
91	jsr166	1.25	* <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	brian	1.21	*
96	tim	1.1	* @since 1.5
97	dl	1.7	* @author Doug Lea
98	tim	1.1	*/
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	jozart	1.6	* @param command the runnable task
107	dl	1.10	* @throws RejectedExecutionException if this task cannot be
108			* accepted for execution.
109	dl	1.12	* @throws NullPointerException if command is null
110	tim	1.1	*/
111	jozart	1.6	void execute(Runnable command);
112	tim	1.1	}