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, 10 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.2:	+5 -4 lines
Log Message:	sync javadoc fixes from src/main
#	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	jsr166	1.3	* <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	1.2	* 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	jsr166	1.3	* <p>The {@link Executors} class provides convenient factory methods for
37	dl	1.1	* 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	jsr166	1.3	* @param <V> the type of the callable's result
92	dl	1.1	* @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	jsr166	1.2	* {@code initialDelay} then {@code initialDelay+period}, then
105			* {@code initialDelay + 2 * period}, and so on.
106	dl	1.1	* 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	jsr166	1.2	* the task, and whose {@code get()} method will throw an
119	dl	1.1	* 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	jsr166	1.2	* the task, and whose {@code get()} method will throw an
146	dl	1.1	* 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			}