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 {@code Executor} is normally used
 * instead of explicitly creating threads. For example, rather than
 * invoking {@code new Thread(new(RunnableTask())).start()} 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 {@code Executor} 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 {@code Executor} 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<>();
 *   final Executor executor;
 *   Runnable active;
 *
 *   SerialExecutor(Executor executor) {
 *     this.executor = executor;
 *   }
 *
 *   public synchronized void execute(final Runnable r) {
 *     tasks.add(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 {@code Executor} 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 {@code Executor} 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:	1.5
Committed:	Sun May 25 01:20:22 2014 UTC (10 years ago) by jsr166
Branch:	MAIN
Changes since 1.4:	+1 -1 lines
Log Message:	use <> in code sample
#	User	Rev	Content
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	jsr166	1.2	* use, scheduling, etc. An {@code Executor} is normally used
14	dl	1.1	* instead of explicitly creating threads. For example, rather than
15	jsr166	1.2	* invoking {@code new Thread(new(RunnableTask())).start()} for each
16	dl	1.1	* 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	jsr166	1.2	* However, the {@code Executor} interface does not strictly
26	dl	1.1	* 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	jsr166	1.2	* Many {@code Executor} implementations impose some sort of
49	dl	1.1	* 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	jsr166	1.5	* final Queue<Runnable> tasks = new ArrayDeque<>();
56	dl	1.1	* 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	jsr166	1.4	* tasks.add(new Runnable() {
65	dl	1.1	* 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	jsr166	1.2	* The {@code Executor} implementations provided in this package
86	dl	1.1	* 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	jsr166	1.2	* thread, at the discretion of the {@code Executor} implementation.
105	dl	1.1	*
106			* @param command the runnable task
107			* @throws RejectedExecutionException if this task cannot be
108	jsr166	1.3	* accepted for execution
109	dl	1.1	* @throws NullPointerException if command is null
110			*/
111			void execute(Runnable command);
112			}