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.
 *
 * <p>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:	1.24
Committed:	Tue Sep 13 10:45:51 2005 UTC (18 years, 8 months ago) by dl
Branch:	MAIN
Changes since 1.23:	+1 -1 lines
Log Message:	Add newline
#	Content
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/licenses/publicdomain
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>
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>
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>
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: State changes to a <tt>Runnable</tt>
92	* object made prior to submission to an <tt>Executor</tt> <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
93	* its execution.
94	*
95	* @since 1.5
96	* @author Doug Lea
97	*/
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	* @param command the runnable task
106	* @throws RejectedExecutionException if this task cannot be
107	* accepted for execution.
108	* @throws NullPointerException if command is null
109	*/
110	void execute(Runnable command);
111	}