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> {@code
 * Executor executor = anExecutor();
 * 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(Runnable r) {
 *     tasks.add(() -> {
 *       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:	1.37
Committed:	Sat Oct 8 20:37:20 2016 UTC (7 years, 7 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.36:	+6 -8 lines
Log Message:	code sample modernization
#	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/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 {@code Executor} is normally used
14	* instead of explicitly creating threads. For example, rather than
15	* invoking {@code new Thread(new RunnableTask()).start()} for each
16	* of a set of tasks, you might use:
17	*
18	* <pre> {@code
19	* Executor executor = anExecutor();
20	* executor.execute(new RunnableTask1());
21	* executor.execute(new RunnableTask2());
22	* ...}</pre>
23	*
24	* However, the {@code Executor} interface does not strictly require
25	* that execution be asynchronous. In the simplest case, an executor
26	* can run the submitted task immediately in the caller's thread:
27	*
28	* <pre> {@code
29	* class DirectExecutor implements Executor {
30	* public void execute(Runnable r) {
31	* r.run();
32	* }
33	* }}</pre>
34	*
35	* More typically, tasks are executed in some thread other than the
36	* caller's thread. The executor below spawns a new thread for each
37	* task.
38	*
39	* <pre> {@code
40	* class ThreadPerTaskExecutor implements Executor {
41	* public void execute(Runnable r) {
42	* new Thread(r).start();
43	* }
44	* }}</pre>
45	*
46	* Many {@code Executor} implementations impose some sort of
47	* limitation on how and when tasks are scheduled. The executor below
48	* serializes the submission of tasks to a second executor,
49	* illustrating a composite executor.
50	*
51	* <pre> {@code
52	* class SerialExecutor implements Executor {
53	* final Queue<Runnable> tasks = new ArrayDeque<>();
54	* final Executor executor;
55	* Runnable active;
56	*
57	* SerialExecutor(Executor executor) {
58	* this.executor = executor;
59	* }
60	*
61	* public synchronized void execute(Runnable r) {
62	* tasks.add(() -> {
63	* try {
64	* r.run();
65	* } finally {
66	* scheduleNext();
67	* }
68	* });
69	* if (active == null) {
70	* scheduleNext();
71	* }
72	* }
73	*
74	* protected synchronized void scheduleNext() {
75	* if ((active = tasks.poll()) != null) {
76	* executor.execute(active);
77	* }
78	* }
79	* }}</pre>
80	*
81	* The {@code Executor} implementations provided in this package
82	* implement {@link ExecutorService}, which is a more extensive
83	* interface. The {@link ThreadPoolExecutor} class provides an
84	* extensible thread pool implementation. The {@link Executors} class
85	* provides convenient factory methods for these Executors.
86	*
87	* <p>Memory consistency effects: Actions in a thread prior to
88	* submitting a {@code Runnable} object to an {@code Executor}
89	* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
90	* its execution begins, perhaps in another thread.
91	*
92	* @since 1.5
93	* @author Doug Lea
94	*/
95	public interface Executor {
96
97	/**
98	* Executes the given command at some time in the future. The command
99	* may execute in a new thread, in a pooled thread, or in the calling
100	* thread, at the discretion of the {@code Executor} implementation.
101	*
102	* @param command the runnable task
103	* @throws RejectedExecutionException if this task cannot be
104	* accepted for execution
105	* @throws NullPointerException if command is null
106	*/
107	void execute(Runnable command);
108	}