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.
     * 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:	1.3
Committed:	Sat Jul 20 20:15:46 2013 UTC (10 years, 9 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.2:	+5 -4 lines
Log Message:	sync javadoc fixes from src/main
#	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	* <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	* the task and whose {@code get()} method will return
76	* {@code null} upon completion
77	* @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	* @param <V> the type of the callable's result
92	* @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	* @throws NullPointerException if callable is null
96	*/
97	public <V> ScheduledFuture<V> schedule(Callable<V> callable,
98	long delay, TimeUnit unit);
99
100	/**
101	* Creates and executes a periodic action that becomes enabled first
102	* after the given initial delay, and subsequently with the given
103	* period; that is executions will commence after
104	* {@code initialDelay} then {@code initialDelay+period}, then
105	* {@code initialDelay + 2 * period}, and so on.
106	* If any execution of the task
107	* encounters an exception, subsequent executions are suppressed.
108	* Otherwise, the task will only terminate via cancellation or
109	* termination of the executor. If any execution of this task
110	* takes longer than its period, then subsequent executions
111	* may start late, but will not concurrently execute.
112	*
113	* @param command the task to execute
114	* @param initialDelay the time to delay first execution
115	* @param period the period between successive executions
116	* @param unit the time unit of the initialDelay and period parameters
117	* @return a ScheduledFuture representing pending completion of
118	* the task, and whose {@code get()} method will throw an
119	* exception upon cancellation
120	* @throws RejectedExecutionException if the task cannot be
121	* scheduled for execution
122	* @throws NullPointerException if command is null
123	* @throws IllegalArgumentException if period less than or equal to zero
124	*/
125	public ScheduledFuture<?> scheduleAtFixedRate(Runnable command,
126	long initialDelay,
127	long period,
128	TimeUnit unit);
129
130	/**
131	* Creates and executes a periodic action that becomes enabled first
132	* after the given initial delay, and subsequently with the
133	* given delay between the termination of one execution and the
134	* commencement of the next. If any execution of the task
135	* encounters an exception, subsequent executions are suppressed.
136	* Otherwise, the task will only terminate via cancellation or
137	* termination of the executor.
138	*
139	* @param command the task to execute
140	* @param initialDelay the time to delay first execution
141	* @param delay the delay between the termination of one
142	* execution and the commencement of the next
143	* @param unit the time unit of the initialDelay and delay parameters
144	* @return a ScheduledFuture representing pending completion of
145	* the task, and whose {@code get()} method will throw an
146	* exception upon cancellation
147	* @throws RejectedExecutionException if the task cannot be
148	* scheduled for execution
149	* @throws NullPointerException if command is null
150	* @throws IllegalArgumentException if delay less than or equal to zero
151	*/
152	public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command,
153	long initialDelay,
154	long delay,
155	TimeUnit unit);
156
157	}