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(Runnable)}
 * 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.
 *
 * <p>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
     * @param <V> the type of the callable's result
     * @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.
     *
     * <p>The sequence of task executions continues indefinitely until
     * one of the following exceptional completions occur:
     * <ul>
     * <li>The task is {@linkplain Future#cancel explicitly cancelled}
     * via the returned future.
     * <li>The executor terminates, also resulting in task cancellation.
     * <li>An execution of the task throws an exception.  In this case
     * calling {@link Future#get() get} on the returned future will
     * throw {@link ExecutionException}.
     * </ul>
     * Subsequent executions are suppressed.  Subsequent calls to
     * {@link Future#isDone isDone()} on the returned future will
     * return {@code true}.
     *
     * <p>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 series of repeated tasks.  The future's {@link
     *         Future#get() get()} method will never return normally,
     *         and will throw an exception upon task cancellation or
     *         abnormal termination of a task execution.
     * @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.
     *
     * <p>The sequence of task executions continues indefinitely until
     * one of the following exceptional completions occur:
     * <ul>
     * <li>The task is {@linkplain Future#cancel explicitly cancelled}
     * via the returned future.
     * <li>The executor terminates, also resulting in task cancellation.
     * <li>An execution of the task throws an exception.  In this case
     * calling {@link Future#get() get} on the returned future will
     * throw {@link ExecutionException}.
     * </ul>
     * Subsequent executions are suppressed.  Subsequent calls to
     * {@link Future#isDone isDone()} on the returned future will
     * return {@code true}.
     *
     * @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 series of repeated tasks.  The future's {@link
     *         Future#get() get()} method will never return normally,
     *         and will throw an exception upon task cancellation or
     *         abnormal termination of a task execution.
     * @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:	1.26
Committed:	Tue Feb 18 16:44:35 2014 UTC (10 years, 3 months ago) by jsr166
Branch:	MAIN
Changes since 1.25:	+43 -16 lines
Log Message:	improve docs for scheduleAtFixedRate and scheduleWithFixedDelay
#	User	Rev	Content
1	tim	1.1	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3	dl	1.6	* Expert Group and released to the public domain, as explained at
4	jsr166	1.19	* http://creativecommons.org/publicdomain/zero/1.0/
5	tim	1.1	*/
6
7			package java.util.concurrent;
8
9			/**
10	tim	1.2	* An {@link ExecutorService} that can schedule commands to run after a given
11	jsr166	1.14	* delay, or to execute periodically.
12	tim	1.1	*
13	jsr166	1.22	* <p>The {@code schedule} methods create tasks with various delays
14	tim	1.2	* and return a task object that can be used to cancel or check
15	jsr166	1.22	* execution. The {@code scheduleAtFixedRate} and
16			* {@code scheduleWithFixedDelay} methods create and execute tasks
17	jsr166	1.14	* that run periodically until cancelled.
18	dl	1.4	*
19	jsr166	1.23	* <p>Commands submitted using the {@link Executor#execute(Runnable)}
20			* and {@link ExecutorService} {@code submit} methods are scheduled
21			* with a requested delay of zero. Zero and negative delays (but not
22	jsr166	1.22	* periods) are also allowed in {@code schedule} methods, and are
23	dl	1.4	* treated as requests for immediate execution.
24	tim	1.2	*
25	jsr166	1.22	* <p>All {@code schedule} methods accept <em>relative</em> delays and
26	tim	1.2	* 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	1.22	* a certain future {@code date}, you can use: {@code schedule(task,
30	tim	1.2	* date.getTime() - System.currentTimeMillis(),
31	jsr166	1.22	* TimeUnit.MILLISECONDS)}. Beware however that expiration of a
32			* relative delay need not coincide with the current {@code Date} at
33	tim	1.2	* which the task is enabled due to network time synchronization
34	jsr166	1.14	* protocols, clock drift, or other factors.
35	tim	1.1	*
36	jsr166	1.24	* <p>The {@link Executors} class provides convenient factory methods for
37	dl	1.7	* the ScheduledExecutorService implementations provided in this package.
38			*
39	dl	1.8	* <h3>Usage Example</h3>
40	jsr166	1.14	*
41	dl	1.8	* Here is a class with a method that sets up a ScheduledExecutorService
42			* to beep every ten seconds for an hour:
43			*
44	jsr166	1.18	* <pre> {@code
45	dl	1.12	* import static java.util.concurrent.TimeUnit.*;
46	dl	1.8	* class BeeperControl {
47	jsr166	1.18	* private final ScheduledExecutorService scheduler =
48			* Executors.newScheduledThreadPool(1);
49	dl	1.8	*
50	jsr166	1.18	* 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	dl	1.8	*
62	tim	1.1	* @since 1.5
63			* @author Doug Lea
64			*/
65	tim	1.2	public interface ScheduledExecutorService extends ExecutorService {
66
67			/**
68			* Creates and executes a one-shot action that becomes enabled
69			* after the given delay.
70	jsr166	1.16	*
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	1.22	* the task and whose {@code get()} method will return
76			* {@code null} upon completion
77	jsr166	1.16	* @throws RejectedExecutionException if the task cannot be
78			* scheduled for execution
79	tim	1.2	* @throws NullPointerException if command is null
80			*/
81	jsr166	1.16	public ScheduledFuture<?> schedule(Runnable command,
82	jsr166	1.17	long delay, TimeUnit unit);
83	tim	1.2
84			/**
85			* Creates and executes a ScheduledFuture that becomes enabled after the
86			* given delay.
87	jsr166	1.16	*
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	jsr166	1.25	* @param <V> the type of the callable's result
92	jsr166	1.16	* @return a ScheduledFuture that can be used to extract result or cancel
93			* @throws RejectedExecutionException if the task cannot be
94			* scheduled for execution
95	tim	1.2	* @throws NullPointerException if callable is null
96			*/
97	jsr166	1.16	public <V> ScheduledFuture<V> schedule(Callable<V> callable,
98	jsr166	1.17	long delay, TimeUnit unit);
99	tim	1.2
100			/**
101			* Creates and executes a periodic action that becomes enabled first
102			* after the given initial delay, and subsequently with the given
103	jsr166	1.26	* period; that is, executions will commence after
104			* {@code initialDelay}, then {@code initialDelay + period}, then
105	jsr166	1.22	* {@code initialDelay + 2 * period}, and so on.
106	jsr166	1.26	*
107			* <p>The sequence of task executions continues indefinitely until
108			* one of the following exceptional completions occur:
109			* <ul>
110			* <li>The task is {@linkplain Future#cancel explicitly cancelled}
111			* via the returned future.
112			* <li>The executor terminates, also resulting in task cancellation.
113			* <li>An execution of the task throws an exception. In this case
114			* calling {@link Future#get() get} on the returned future will
115			* throw {@link ExecutionException}.
116			* </ul>
117			* Subsequent executions are suppressed. Subsequent calls to
118			* {@link Future#isDone isDone()} on the returned future will
119			* return {@code true}.
120			*
121			* <p>If any execution of this task takes longer than its period, then
122			* subsequent executions may start late, but will not concurrently
123			* execute.
124	jsr166	1.15	*
125	jsr166	1.16	* @param command the task to execute
126			* @param initialDelay the time to delay first execution
127			* @param period the period between successive executions
128	dl	1.4	* @param unit the time unit of the initialDelay and period parameters
129	jsr166	1.16	* @return a ScheduledFuture representing pending completion of
130	jsr166	1.26	* the series of repeated tasks. The future's {@link
131			* Future#get() get()} method will never return normally,
132			* and will throw an exception upon task cancellation or
133			* abnormal termination of a task execution.
134	jsr166	1.16	* @throws RejectedExecutionException if the task cannot be
135			* scheduled for execution
136	tim	1.2	* @throws NullPointerException if command is null
137	jsr166	1.16	* @throws IllegalArgumentException if period less than or equal to zero
138	tim	1.2	*/
139	jsr166	1.15	public ScheduledFuture<?> scheduleAtFixedRate(Runnable command,
140	jsr166	1.17	long initialDelay,
141			long period,
142			TimeUnit unit);
143	jsr166	1.14
144	tim	1.2	/**
145			* Creates and executes a periodic action that becomes enabled first
146			* after the given initial delay, and subsequently with the
147			* given delay between the termination of one execution and the
148	jsr166	1.26	* commencement of the next.
149			*
150			* <p>The sequence of task executions continues indefinitely until
151			* one of the following exceptional completions occur:
152			* <ul>
153			* <li>The task is {@linkplain Future#cancel explicitly cancelled}
154			* via the returned future.
155			* <li>The executor terminates, also resulting in task cancellation.
156			* <li>An execution of the task throws an exception. In this case
157			* calling {@link Future#get() get} on the returned future will
158			* throw {@link ExecutionException}.
159			* </ul>
160			* Subsequent executions are suppressed. Subsequent calls to
161			* {@link Future#isDone isDone()} on the returned future will
162			* return {@code true}.
163	jsr166	1.15	*
164	jsr166	1.16	* @param command the task to execute
165			* @param initialDelay the time to delay first execution
166	tim	1.2	* @param delay the delay between the termination of one
167	jsr166	1.16	* execution and the commencement of the next
168	dl	1.4	* @param unit the time unit of the initialDelay and delay parameters
169	jsr166	1.16	* @return a ScheduledFuture representing pending completion of
170	jsr166	1.26	* the series of repeated tasks. The future's {@link
171			* Future#get() get()} method will never return normally,
172			* and will throw an exception upon task cancellation or
173			* abnormal termination of a task execution.
174	jsr166	1.16	* @throws RejectedExecutionException if the task cannot be
175			* scheduled for execution
176	tim	1.2	* @throws NullPointerException if command is null
177	jsr166	1.16	* @throws IllegalArgumentException if delay less than or equal to zero
178	tim	1.2	*/
179	jsr166	1.15	public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command,
180	jsr166	1.17	long initialDelay,
181			long delay,
182			TimeUnit unit);
183	tim	1.2
184	tim	1.1	}