util/concurrent/ScheduledExecutorService.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 {@link ExecutorService} that can schedule commands to run after a given
 * delay, or to execute periodically.
 *
 * <p>The {@code schedule} methods create tasks with various delays
 * and return a task object that can be used to cancel or check
 * execution. The {@code scheduleAtFixedRate} and
 * {@code scheduleWithFixedDelay} methods create and execute tasks
 * that run periodically until cancelled.
 *
 * <p>Commands submitted using the {@link Executor#execute} and
 * {@link ExecutorService} {@code submit} methods are scheduled with
 * a requested delay of zero. Zero and negative delays (but not
 * periods) are also allowed in {@code schedule} methods, and are
 * treated as requests for immediate execution.
 *
 * <p>All {@code schedule} methods accept <em>relative</em> delays and
 * periods as arguments, not absolute times or dates. It is a simple
 * matter to transform an absolute time represented as a {@link
 * java.util.Date} to the required form. For example, to schedule at
 * a certain future {@code date}, you can use: {@code schedule(task,
 * date.getTime() - System.currentTimeMillis(),
 * TimeUnit.MILLISECONDS)}. Beware however that expiration of a
 * relative delay need not coincide with the current {@code Date} at
 * which the task is enabled due to network time synchronization
 * protocols, clock drift, or other factors.
 *
 * The {@link Executors} class provides convenient factory methods for
 * the ScheduledExecutorService implementations provided in this package.
 *
 * <h3>Usage Example</h3>
 *
 * Here is a class with a method that sets up a ScheduledExecutorService
 * to beep every ten seconds for an hour:
 *
 *  <pre> {@code
 * import static java.util.concurrent.TimeUnit.*;
 * class BeeperControl {
 *   private final ScheduledExecutorService scheduler =
 *     Executors.newScheduledThreadPool(1);
 *
 *   public void beepForAnHour() {
 *     final Runnable beeper = new Runnable() {
 *       public void run() { System.out.println("beep"); }
 *     };
 *     final ScheduledFuture<?> beeperHandle =
 *       scheduler.scheduleAtFixedRate(beeper, 10, 10, SECONDS);
 *     scheduler.schedule(new Runnable() {
 *       public void run() { beeperHandle.cancel(true); }
 *     }, 60 * 60, SECONDS);
 *   }
 * }}</pre>
 *
 * @since 1.5
 * @author Doug Lea
 */
public interface ScheduledExecutorService extends ExecutorService {

    /**
     * Creates and executes a one-shot action that becomes enabled
     * after the given delay.
     *
     * @param command the task to execute
     * @param delay the time from now to delay execution
     * @param unit the time unit of the delay parameter
     * @return a ScheduledFuture representing pending completion of
     *         the task and whose {@code get()} method will return
     *         {@code null} upon completion
     * @throws RejectedExecutionException if the task cannot be
     *         scheduled for execution
     * @throws NullPointerException if command is null
     */
    public ScheduledFuture<?> schedule(Runnable command,
                                       long delay, TimeUnit unit);

    /**
     * Creates and executes a ScheduledFuture that becomes enabled after the
     * given delay.
     *
     * @param callable the function to execute
     * @param delay the time from now to delay execution
     * @param unit the time unit of the delay parameter
     * @return a ScheduledFuture that can be used to extract result or cancel
     * @throws RejectedExecutionException if the task cannot be
     *         scheduled for execution
     * @throws NullPointerException if callable is null
     */
    public <V> ScheduledFuture<V> schedule(Callable<V> callable,
                                           long delay, TimeUnit unit);

    /**
     * Creates and executes a periodic action that becomes enabled first
     * after the given initial delay, and subsequently with the given
     * period; that is executions will commence after
     * {@code initialDelay} then {@code initialDelay+period}, then
     * {@code initialDelay + 2 * period}, and so on.
     * If any execution of the task
     * encounters an exception, subsequent executions are suppressed.
     * Otherwise, the task will only terminate via cancellation or
     * termination of the executor.  If any execution of this task
     * takes longer than its period, then subsequent executions
     * may start late, but will not concurrently execute.
     *
     * @param command the task to execute
     * @param initialDelay the time to delay first execution
     * @param period the period between successive executions
     * @param unit the time unit of the initialDelay and period parameters
     * @return a ScheduledFuture representing pending completion of
     *         the task, and whose {@code get()} method will throw an
     *         exception upon cancellation
     * @throws RejectedExecutionException if the task cannot be
     *         scheduled for execution
     * @throws NullPointerException if command is null
     * @throws IllegalArgumentException if period less than or equal to zero
     */
    public ScheduledFuture<?> scheduleAtFixedRate(Runnable command,
                                                  long initialDelay,
                                                  long period,
                                                  TimeUnit unit);

    /**
     * Creates and executes a periodic action that becomes enabled first
     * after the given initial delay, and subsequently with the
     * given delay between the termination of one execution and the
     * commencement of the next.  If any execution of the task
     * encounters an exception, subsequent executions are suppressed.
     * Otherwise, the task will only terminate via cancellation or
     * termination of the executor.
     *
     * @param command the task to execute
     * @param initialDelay the time to delay first execution
     * @param delay the delay between the termination of one
     * execution and the commencement of the next
     * @param unit the time unit of the initialDelay and delay parameters
     * @return a ScheduledFuture representing pending completion of
     *         the task, and whose {@code get()} method will throw an
     *         exception upon cancellation
     * @throws RejectedExecutionException if the task cannot be
     *         scheduled for execution
     * @throws NullPointerException if command is null
     * @throws IllegalArgumentException if delay less than or equal to zero
     */
    public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command,
                                                     long initialDelay,
                                                     long delay,
                                                     TimeUnit unit);

}
Revision:	1.2
Committed:	Wed Jan 16 01:39:37 2013 UTC (11 years, 4 months ago) by jsr166
Branch:	MAIN
Changes since 1.1:	+15 -15 lines
Log Message:	<tt> -> {@code
#	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 {@link ExecutorService} that can schedule commands to run after a given
11			* delay, or to execute periodically.
12			*
13	jsr166	1.2	* <p>The {@code schedule} methods create tasks with various delays
14	dl	1.1	* and return a task object that can be used to cancel or check
15	jsr166	1.2	* execution. The {@code scheduleAtFixedRate} and
16			* {@code scheduleWithFixedDelay} methods create and execute tasks
17	dl	1.1	* that run periodically until cancelled.
18			*
19			* <p>Commands submitted using the {@link Executor#execute} and
20	jsr166	1.2	* {@link ExecutorService} {@code submit} methods are scheduled with
21	dl	1.1	* a requested delay of zero. Zero and negative delays (but not
22	jsr166	1.2	* periods) are also allowed in {@code schedule} methods, and are
23	dl	1.1	* treated as requests for immediate execution.
24			*
25	jsr166	1.2	* <p>All {@code schedule} methods accept <em>relative</em> delays and
26	dl	1.1	* periods as arguments, not absolute times or dates. It is a simple
27			* matter to transform an absolute time represented as a {@link
28			* java.util.Date} to the required form. For example, to schedule at
29	jsr166	1.2	* a certain future {@code date}, you can use: {@code schedule(task,
30	dl	1.1	* date.getTime() - System.currentTimeMillis(),
31	jsr166	1.2	* TimeUnit.MILLISECONDS)}. Beware however that expiration of a
32			* relative delay need not coincide with the current {@code Date} at
33	dl	1.1	* which the task is enabled due to network time synchronization
34			* protocols, clock drift, or other factors.
35			*
36			* The {@link Executors} class provides convenient factory methods for
37			* the ScheduledExecutorService implementations provided in this package.
38			*
39			* <h3>Usage Example</h3>
40			*
41			* Here is a class with a method that sets up a ScheduledExecutorService
42			* to beep every ten seconds for an hour:
43			*
44			* <pre> {@code
45			* import static java.util.concurrent.TimeUnit.*;
46			* class BeeperControl {
47			* private final ScheduledExecutorService scheduler =
48			* Executors.newScheduledThreadPool(1);
49			*
50			* public void beepForAnHour() {
51			* final Runnable beeper = new Runnable() {
52			* public void run() { System.out.println("beep"); }
53			* };
54			* final ScheduledFuture<?> beeperHandle =
55			* scheduler.scheduleAtFixedRate(beeper, 10, 10, SECONDS);
56			* scheduler.schedule(new Runnable() {
57			* public void run() { beeperHandle.cancel(true); }
58			* }, 60 * 60, SECONDS);
59			* }
60			* }}</pre>
61			*
62			* @since 1.5
63			* @author Doug Lea
64			*/
65			public interface ScheduledExecutorService extends ExecutorService {
66
67			/**
68			* Creates and executes a one-shot action that becomes enabled
69			* after the given delay.
70			*
71			* @param command the task to execute
72			* @param delay the time from now to delay execution
73			* @param unit the time unit of the delay parameter
74			* @return a ScheduledFuture representing pending completion of
75	jsr166	1.2	* the task and whose {@code get()} method will return
76			* {@code null} upon completion
77	dl	1.1	* @throws RejectedExecutionException if the task cannot be
78			* scheduled for execution
79			* @throws NullPointerException if command is null
80			*/
81			public ScheduledFuture<?> schedule(Runnable command,
82			long delay, TimeUnit unit);
83
84			/**
85			* Creates and executes a ScheduledFuture that becomes enabled after the
86			* given delay.
87			*
88			* @param callable the function to execute
89			* @param delay the time from now to delay execution
90			* @param unit the time unit of the delay parameter
91			* @return a ScheduledFuture that can be used to extract result or cancel
92			* @throws RejectedExecutionException if the task cannot be
93			* scheduled for execution
94			* @throws NullPointerException if callable is null
95			*/
96			public <V> ScheduledFuture<V> schedule(Callable<V> callable,
97			long delay, TimeUnit unit);
98
99			/**
100			* Creates and executes a periodic action that becomes enabled first
101			* after the given initial delay, and subsequently with the given
102			* period; that is executions will commence after
103	jsr166	1.2	* {@code initialDelay} then {@code initialDelay+period}, then
104			* {@code initialDelay + 2 * period}, and so on.
105	dl	1.1	* If any execution of the task
106			* encounters an exception, subsequent executions are suppressed.
107			* Otherwise, the task will only terminate via cancellation or
108			* termination of the executor. If any execution of this task
109			* takes longer than its period, then subsequent executions
110			* may start late, but will not concurrently execute.
111			*
112			* @param command the task to execute
113			* @param initialDelay the time to delay first execution
114			* @param period the period between successive executions
115			* @param unit the time unit of the initialDelay and period parameters
116			* @return a ScheduledFuture representing pending completion of
117	jsr166	1.2	* the task, and whose {@code get()} method will throw an
118	dl	1.1	* exception upon cancellation
119			* @throws RejectedExecutionException if the task cannot be
120			* scheduled for execution
121			* @throws NullPointerException if command is null
122			* @throws IllegalArgumentException if period less than or equal to zero
123			*/
124			public ScheduledFuture<?> scheduleAtFixedRate(Runnable command,
125			long initialDelay,
126			long period,
127			TimeUnit unit);
128
129			/**
130			* Creates and executes a periodic action that becomes enabled first
131			* after the given initial delay, and subsequently with the
132			* given delay between the termination of one execution and the
133			* commencement of the next. If any execution of the task
134			* encounters an exception, subsequent executions are suppressed.
135			* Otherwise, the task will only terminate via cancellation or
136			* termination of the executor.
137			*
138			* @param command the task to execute
139			* @param initialDelay the time to delay first execution
140			* @param delay the delay between the termination of one
141			* execution and the commencement of the next
142			* @param unit the time unit of the initialDelay and delay parameters
143			* @return a ScheduledFuture representing pending completion of
144	jsr166	1.2	* the task, and whose {@code get()} method will throw an
145	dl	1.1	* exception upon cancellation
146			* @throws RejectedExecutionException if the task cannot be
147			* scheduled for execution
148			* @throws NullPointerException if command is null
149			* @throws IllegalArgumentException if delay less than or equal to zero
150			*/
151			public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command,
152			long initialDelay,
153			long delay,
154			TimeUnit unit);
155
156			}