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/licenses/publicdomain
 */

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>
 * 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>
 * 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>
 * class SerialExecutor implements Executor {
 *     final Queue&lt;Runnable&gt; tasks = new ArrayDeque&lt;Runnable&gt;();
 *     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.
 *
 * Memory consistency effects: State changes to a <tt>Runnable</tt>
 * object made prior to submission to an <tt>Executor</tt> <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
 * its execution.
 *
 * @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:	1.23
Committed:	Thu Sep 8 00:04:00 2005 UTC (18 years, 8 months ago) by dl
Branch:	MAIN
Changes since 1.22:	+1 -1 lines
Log Message:	Edit pass for happens-before descriptions
#	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			* http://creativecommons.org/licenses/publicdomain
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			* <pre>
31			* class DirectExecutor implements Executor {
32			* public void execute(Runnable r) {
33			* r.run();
34			* }
35			* }</pre>
36			*
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			* <pre>
42			* class ThreadPerTaskExecutor implements Executor {
43			* public void execute(Runnable r) {
44			* new Thread(r).start();
45			* }
46			* }</pre>
47			*
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			* <pre>
54			* class SerialExecutor implements Executor {
55	dl	1.20	* final Queue<Runnable> tasks = new ArrayDeque<Runnable>();
56	tim	1.14	* final Executor executor;
57	tim	1.1	* 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	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	dl	1.23	* Memory consistency effects: State changes to a <tt>Runnable</tt>
92	brian	1.22	* object made prior to submission to an <tt>Executor</tt> <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
93	brian	1.21	* its execution.
94			*
95	tim	1.1	* @since 1.5
96	dl	1.7	* @author Doug Lea
97	tim	1.1	*/
98			public interface Executor {
99
100			/**
101			* Executes the given command at some time in the future. The command
102			* may execute in a new thread, in a pooled thread, or in the calling
103			* thread, at the discretion of the <tt>Executor</tt> implementation.
104			*
105	jozart	1.6	* @param command the runnable task
106	dl	1.10	* @throws RejectedExecutionException if this task cannot be
107			* accepted for execution.
108	dl	1.12	* @throws NullPointerException if command is null
109	tim	1.1	*/
110	jozart	1.6	void execute(Runnable command);
111	tim	1.1	}