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.
 *
 * <h2>Usage Example</h2>
 *
 * 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() {
 *     Runnable beeper = () -> System.out.println("beep");
 *     ScheduledFuture<?> beeperHandle =
 *       scheduler.scheduleAtFixedRate(beeper, 10, 10, SECONDS);
 *     Runnable canceller = () -> beeperHandle.cancel(false);
 *     scheduler.schedule(canceller, 1, HOURS);
 *   }
 * }}</pre>
 *
 * @since 1.5
 * @author Doug Lea
 */
public interface ScheduledExecutorService extends ExecutorService {

    /**
     * Submits a one-shot task 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 or unit is null
     */
    public ScheduledFuture<?> schedule(Runnable command,
                                       long delay, TimeUnit unit);

    /**
     * Submits a value-returning one-shot task 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 or unit is null
     */
    public <V> ScheduledFuture<V> schedule(Callable<V> callable,
                                           long delay, TimeUnit unit);

    /**
     * Submits 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}, holding the exception as its cause.
     * </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 or unit is null
     * @throws IllegalArgumentException if period less than or equal to zero
     */
    public ScheduledFuture<?> scheduleAtFixedRate(Runnable command,
                                                  long initialDelay,
                                                  long period,
                                                  TimeUnit unit);

    /**
     * Submits 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}, holding the exception as its cause.
     * </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 or unit is null
     * @throws IllegalArgumentException if delay less than or equal to zero
     */
    public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command,
                                                     long initialDelay,
                                                     long delay,
                                                     TimeUnit unit);

}
Revision:	1.30
Committed:	Thu Mar 7 00:50:36 2019 UTC (5 years, 3 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.29:	+1 -1 lines
Log Message:	8220248: fix headings in java.util.concurrent
#	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	jsr166	1.30	* <h2>Usage Example</h2>
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	1.27	* <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	jsr166	1.28	* Runnable beeper = () -> System.out.println("beep");
52			* ScheduledFuture<?> beeperHandle =
53	jsr166	1.18	* scheduler.scheduleAtFixedRate(beeper, 10, 10, SECONDS);
54	jsr166	1.29	* Runnable canceller = () -> beeperHandle.cancel(false);
55	jsr166	1.28	* scheduler.schedule(canceller, 1, HOURS);
56	jsr166	1.18	* }
57			* }}</pre>
58	dl	1.8	*
59	tim	1.1	* @since 1.5
60			* @author Doug Lea
61			*/
62	tim	1.2	public interface ScheduledExecutorService extends ExecutorService {
63
64			/**
65	jsr166	1.29	* Submits a one-shot task that becomes enabled after the given delay.
66	jsr166	1.16	*
67			* @param command the task to execute
68			* @param delay the time from now to delay execution
69			* @param unit the time unit of the delay parameter
70			* @return a ScheduledFuture representing pending completion of
71	jsr166	1.22	* the task and whose {@code get()} method will return
72			* {@code null} upon completion
73	jsr166	1.16	* @throws RejectedExecutionException if the task cannot be
74			* scheduled for execution
75	jsr166	1.29	* @throws NullPointerException if command or unit is null
76	tim	1.2	*/
77	jsr166	1.16	public ScheduledFuture<?> schedule(Runnable command,
78	jsr166	1.17	long delay, TimeUnit unit);
79	tim	1.2
80			/**
81	jsr166	1.29	* Submits a value-returning one-shot task that becomes enabled
82			* after the given delay.
83	jsr166	1.16	*
84			* @param callable the function to execute
85			* @param delay the time from now to delay execution
86			* @param unit the time unit of the delay parameter
87	jsr166	1.25	* @param <V> the type of the callable's result
88	jsr166	1.16	* @return a ScheduledFuture that can be used to extract result or cancel
89			* @throws RejectedExecutionException if the task cannot be
90			* scheduled for execution
91	jsr166	1.29	* @throws NullPointerException if callable or unit is null
92	tim	1.2	*/
93	jsr166	1.16	public <V> ScheduledFuture<V> schedule(Callable<V> callable,
94	jsr166	1.17	long delay, TimeUnit unit);
95	tim	1.2
96			/**
97	jsr166	1.29	* Submits a periodic action that becomes enabled first after the
98			* given initial delay, and subsequently with the given period;
99			* that is, executions will commence after
100	jsr166	1.26	* {@code initialDelay}, then {@code initialDelay + period}, then
101	jsr166	1.22	* {@code initialDelay + 2 * period}, and so on.
102	jsr166	1.26	*
103			* <p>The sequence of task executions continues indefinitely until
104			* one of the following exceptional completions occur:
105			* <ul>
106			* <li>The task is {@linkplain Future#cancel explicitly cancelled}
107			* via the returned future.
108			* <li>The executor terminates, also resulting in task cancellation.
109			* <li>An execution of the task throws an exception. In this case
110	jsr166	1.29	* calling {@link Future#get() get} on the returned future will throw
111			* {@link ExecutionException}, holding the exception as its cause.
112	jsr166	1.26	* </ul>
113			* Subsequent executions are suppressed. Subsequent calls to
114			* {@link Future#isDone isDone()} on the returned future will
115			* return {@code true}.
116			*
117			* <p>If any execution of this task takes longer than its period, then
118			* subsequent executions may start late, but will not concurrently
119			* execute.
120	jsr166	1.15	*
121	jsr166	1.16	* @param command the task to execute
122			* @param initialDelay the time to delay first execution
123			* @param period the period between successive executions
124	dl	1.4	* @param unit the time unit of the initialDelay and period parameters
125	jsr166	1.16	* @return a ScheduledFuture representing pending completion of
126	jsr166	1.26	* the series of repeated tasks. The future's {@link
127			* Future#get() get()} method will never return normally,
128			* and will throw an exception upon task cancellation or
129			* abnormal termination of a task execution.
130	jsr166	1.16	* @throws RejectedExecutionException if the task cannot be
131			* scheduled for execution
132	jsr166	1.29	* @throws NullPointerException if command or unit is null
133	jsr166	1.16	* @throws IllegalArgumentException if period less than or equal to zero
134	tim	1.2	*/
135	jsr166	1.15	public ScheduledFuture<?> scheduleAtFixedRate(Runnable command,
136	jsr166	1.17	long initialDelay,
137			long period,
138			TimeUnit unit);
139	jsr166	1.14
140	tim	1.2	/**
141	jsr166	1.29	* Submits a periodic action that becomes enabled first after the
142			* given initial delay, and subsequently with the given delay
143			* between the termination of one execution and the commencement of
144			* the next.
145	jsr166	1.26	*
146			* <p>The sequence of task executions continues indefinitely until
147			* one of the following exceptional completions occur:
148			* <ul>
149			* <li>The task is {@linkplain Future#cancel explicitly cancelled}
150			* via the returned future.
151			* <li>The executor terminates, also resulting in task cancellation.
152			* <li>An execution of the task throws an exception. In this case
153	jsr166	1.29	* calling {@link Future#get() get} on the returned future will throw
154			* {@link ExecutionException}, holding the exception as its cause.
155	jsr166	1.26	* </ul>
156			* Subsequent executions are suppressed. Subsequent calls to
157			* {@link Future#isDone isDone()} on the returned future will
158			* return {@code true}.
159	jsr166	1.15	*
160	jsr166	1.16	* @param command the task to execute
161			* @param initialDelay the time to delay first execution
162	tim	1.2	* @param delay the delay between the termination of one
163	jsr166	1.16	* execution and the commencement of the next
164	dl	1.4	* @param unit the time unit of the initialDelay and delay parameters
165	jsr166	1.16	* @return a ScheduledFuture representing pending completion of
166	jsr166	1.26	* the series of repeated tasks. The future's {@link
167			* Future#get() get()} method will never return normally,
168			* and will throw an exception upon task cancellation or
169			* abnormal termination of a task execution.
170	jsr166	1.16	* @throws RejectedExecutionException if the task cannot be
171			* scheduled for execution
172	jsr166	1.29	* @throws NullPointerException if command or unit is null
173	jsr166	1.16	* @throws IllegalArgumentException if delay less than or equal to zero
174	tim	1.2	*/
175	jsr166	1.15	public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command,
176	jsr166	1.17	long initialDelay,
177			long delay,
178			TimeUnit unit);
179	tim	1.2
180	tim	1.1	}