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(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:	1.1
Committed:	Sat Mar 26 06:22:50 2016 UTC (8 years, 1 month ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Log Message:	fork jdk8 maintenance branch for source and jtreg tests
#	User	Rev	Content
1	jsr166	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			* 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(final Runnable r) {
62			* tasks.add(new Runnable() {
63			* public void run() {
64			* try {
65			* r.run();
66			* } finally {
67			* scheduleNext();
68			* }
69			* }
70			* });
71			* if (active == null) {
72			* scheduleNext();
73			* }
74			* }
75			*
76			* protected synchronized void scheduleNext() {
77			* if ((active = tasks.poll()) != null) {
78			* executor.execute(active);
79			* }
80			* }
81			* }}</pre>
82			*
83			* The {@code Executor} implementations provided in this package
84			* implement {@link ExecutorService}, which is a more extensive
85			* interface. The {@link ThreadPoolExecutor} class provides an
86			* extensible thread pool implementation. The {@link Executors} class
87			* provides convenient factory methods for these Executors.
88			*
89			* <p>Memory consistency effects: Actions in a thread prior to
90			* submitting a {@code Runnable} object to an {@code Executor}
91			* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
92			* its execution begins, perhaps in another thread.
93			*
94			* @since 1.5
95			* @author Doug Lea
96			*/
97			public interface Executor {
98
99			/**
100			* Executes the given command at some time in the future. The command
101			* may execute in a new thread, in a pooled thread, or in the calling
102			* thread, at the discretion of the {@code Executor} implementation.
103			*
104			* @param command the runnable task
105			* @throws RejectedExecutionException if this task cannot be
106			* accepted for execution
107			* @throws NullPointerException if command is null
108			*/
109			void execute(Runnable command);
110			}