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, 2 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
#	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 {@link ExecutorService} that can schedule commands to run after a given
11	* delay, or to execute periodically.
12	*
13	* <p>The {@code schedule} methods create tasks with various delays
14	* and return a task object that can be used to cancel or check
15	* execution. The {@code scheduleAtFixedRate} and
16	* {@code scheduleWithFixedDelay} methods create and execute tasks
17	* that run periodically until cancelled.
18	*
19	* <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	* periods) are also allowed in {@code schedule} methods, and are
23	* treated as requests for immediate execution.
24	*
25	* <p>All {@code schedule} methods accept <em>relative</em> delays and
26	* 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	* a certain future {@code date}, you can use: {@code schedule(task,
30	* date.getTime() - System.currentTimeMillis(),
31	* TimeUnit.MILLISECONDS)}. Beware however that expiration of a
32	* relative delay need not coincide with the current {@code Date} at
33	* which the task is enabled due to network time synchronization
34	* protocols, clock drift, or other factors.
35	*
36	* <p>The {@link Executors} class provides convenient factory methods for
37	* the ScheduledExecutorService implementations provided in this package.
38	*
39	* <h2>Usage Example</h2>
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	* Runnable beeper = () -> System.out.println("beep");
52	* ScheduledFuture<?> beeperHandle =
53	* scheduler.scheduleAtFixedRate(beeper, 10, 10, SECONDS);
54	* Runnable canceller = () -> beeperHandle.cancel(false);
55	* scheduler.schedule(canceller, 1, HOURS);
56	* }
57	* }}</pre>
58	*
59	* @since 1.5
60	* @author Doug Lea
61	*/
62	public interface ScheduledExecutorService extends ExecutorService {
63
64	/**
65	* Submits a one-shot task that becomes enabled after the given delay.
66	*
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	* the task and whose {@code get()} method will return
72	* {@code null} upon completion
73	* @throws RejectedExecutionException if the task cannot be
74	* scheduled for execution
75	* @throws NullPointerException if command or unit is null
76	*/
77	public ScheduledFuture<?> schedule(Runnable command,
78	long delay, TimeUnit unit);
79
80	/**
81	* Submits a value-returning one-shot task that becomes enabled
82	* after the given delay.
83	*
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	* @param <V> the type of the callable's result
88	* @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	* @throws NullPointerException if callable or unit is null
92	*/
93	public <V> ScheduledFuture<V> schedule(Callable<V> callable,
94	long delay, TimeUnit unit);
95
96	/**
97	* 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	* {@code initialDelay}, then {@code initialDelay + period}, then
101	* {@code initialDelay + 2 * period}, and so on.
102	*
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	* calling {@link Future#get() get} on the returned future will throw
111	* {@link ExecutionException}, holding the exception as its cause.
112	* </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	*
121	* @param command the task to execute
122	* @param initialDelay the time to delay first execution
123	* @param period the period between successive executions
124	* @param unit the time unit of the initialDelay and period parameters
125	* @return a ScheduledFuture representing pending completion of
126	* 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	* @throws RejectedExecutionException if the task cannot be
131	* scheduled for execution
132	* @throws NullPointerException if command or unit is null
133	* @throws IllegalArgumentException if period less than or equal to zero
134	*/
135	public ScheduledFuture<?> scheduleAtFixedRate(Runnable command,
136	long initialDelay,
137	long period,
138	TimeUnit unit);
139
140	/**
141	* 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	*
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	* calling {@link Future#get() get} on the returned future will throw
154	* {@link ExecutionException}, holding the exception as its cause.
155	* </ul>
156	* Subsequent executions are suppressed. Subsequent calls to
157	* {@link Future#isDone isDone()} on the returned future will
158	* return {@code true}.
159	*
160	* @param command the task to execute
161	* @param initialDelay the time to delay first execution
162	* @param delay the delay between the termination of one
163	* execution and the commencement of the next
164	* @param unit the time unit of the initialDelay and delay parameters
165	* @return a ScheduledFuture representing pending completion of
166	* 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	* @throws RejectedExecutionException if the task cannot be
171	* scheduled for execution
172	* @throws NullPointerException if command or unit is null
173	* @throws IllegalArgumentException if delay less than or equal to zero
174	*/
175	public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command,
176	long initialDelay,
177	long delay,
178	TimeUnit unit);
179
180	}