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/licenses/publicdomain
 */

package java.util.concurrent;
import java.util.concurrent.atomic.*;
import java.util.*;

/**
 * An {@link ExecutorService} that can schedule commands to run after a given
 * delay, or to execute periodically.
 *
 * <p> The <tt>schedule</tt> methods create tasks with various delays
 * and return a task object that can be used to cancel or check
 * execution. The <tt>scheduleAtFixedRate</tt> and
 * <tt>scheduleWithFixedDelay</tt> methods create and execute tasks
 * that run periodically until cancelled.
 *
 * <p> Commands submitted using the {@link Executor#execute} and
 * {@link ExecutorService} <tt>submit</tt> methods are scheduled with
 * a requested delay of zero. Zero and negative delays (but not
 * periods) are also allowed in <tt>schedule</tt> methods, and are
 * treated as requests for immediate execution.
 *
 * <p>All <tt>schedule</tt> 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 <tt>date</tt>, you can use: <tt>schedule(task,
 * date.getTime() - System.currentTimeMillis(),
 * TimeUnit.MILLISECONDS)</tt>. Beware however that expiration of a
 * relative delay need not coincide with the current <tt>Date</tt> at
 * which the task is enabled due to network time synchronization
 * protocols, clock drift, or other factors.
 *
 * 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>
 * 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&lt;?&gt; 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 <tt>get()</tt> method will return
     *         <tt>null</tt> 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
     * @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
     * <tt>initialDelay</tt> then <tt>initialDelay+period</tt>, then
     * <tt>initialDelay + 2 * period</tt>, 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 <tt>get()</tt> 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 <tt>get()</tt> 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:	1.16
Committed:	Thu Aug 25 04:49:33 2005 UTC (18 years, 9 months ago) by jsr166
Branch:	MAIN
Changes since 1.15:	+38 -34 lines
Log Message:	javadoc style cleanup
#	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			* http://creativecommons.org/licenses/publicdomain
5	tim	1.1	*/
6
7			package java.util.concurrent;
8	tim	1.2	import java.util.concurrent.atomic.*;
9			import java.util.*;
10	tim	1.1
11			/**
12	tim	1.2	* An {@link ExecutorService} that can schedule commands to run after a given
13	jsr166	1.14	* delay, or to execute periodically.
14	tim	1.1	*
15	tim	1.2	* <p> The <tt>schedule</tt> methods create tasks with various delays
16			* and return a task object that can be used to cancel or check
17			* execution. The <tt>scheduleAtFixedRate</tt> and
18			* <tt>scheduleWithFixedDelay</tt> methods create and execute tasks
19	jsr166	1.14	* that run periodically until cancelled.
20	dl	1.4	*
21			* <p> Commands submitted using the {@link Executor#execute} and
22			* {@link ExecutorService} <tt>submit</tt> methods are scheduled with
23			* a requested delay of zero. Zero and negative delays (but not
24			* periods) are also allowed in <tt>schedule</tt> methods, and are
25			* treated as requests for immediate execution.
26	tim	1.2	*
27	dl	1.11	* <p>All <tt>schedule</tt> methods accept <em>relative</em> delays and
28	tim	1.2	* periods as arguments, not absolute times or dates. It is a simple
29			* matter to transform an absolute time represented as a {@link
30			* java.util.Date} to the required form. For example, to schedule at
31			* a certain future <tt>date</tt>, you can use: <tt>schedule(task,
32			* date.getTime() - System.currentTimeMillis(),
33			* TimeUnit.MILLISECONDS)</tt>. Beware however that expiration of a
34			* relative delay need not coincide with the current <tt>Date</tt> at
35			* which the task is enabled due to network time synchronization
36	jsr166	1.14	* protocols, clock drift, or other factors.
37	tim	1.1	*
38	dl	1.7	* The {@link Executors} class provides convenient factory methods for
39			* the ScheduledExecutorService implementations provided in this package.
40			*
41	dl	1.8	* <h3>Usage Example</h3>
42	jsr166	1.14	*
43	dl	1.8	* Here is a class with a method that sets up a ScheduledExecutorService
44			* to beep every ten seconds for an hour:
45			*
46			* <pre>
47	dl	1.12	* import static java.util.concurrent.TimeUnit.*;
48	dl	1.8	* class BeeperControl {
49	jsr166	1.14	* private final ScheduledExecutorService scheduler =
50	dl	1.10	* Executors.newScheduledThreadPool(1);
51	dl	1.8	*
52			* public void beepForAnHour() {
53			* final Runnable beeper = new Runnable() {
54			* public void run() { System.out.println("beep"); }
55			* };
56	jsr166	1.14	* final ScheduledFuture<?> beeperHandle =
57	dl	1.8	* scheduler.scheduleAtFixedRate(beeper, 10, 10, SECONDS);
58			* scheduler.schedule(new Runnable() {
59			* public void run() { beeperHandle.cancel(true); }
60			* }, 60 * 60, SECONDS);
61			* }
62			* }
63			* </pre>
64			*
65	tim	1.1	* @since 1.5
66			* @author Doug Lea
67			*/
68	tim	1.2	public interface ScheduledExecutorService extends ExecutorService {
69
70			/**
71			* Creates and executes a one-shot action that becomes enabled
72			* after the given delay.
73	jsr166	1.16	*
74			* @param command the task to execute
75			* @param delay the time from now to delay execution
76			* @param unit the time unit of the delay parameter
77			* @return a ScheduledFuture representing pending completion of
78			* the task and whose <tt>get()</tt> method will return
79			* <tt>null</tt> upon completion
80			* @throws RejectedExecutionException if the task cannot be
81			* scheduled for execution
82	tim	1.2	* @throws NullPointerException if command is null
83			*/
84	jsr166	1.16	public ScheduledFuture<?> schedule(Runnable command,
85			long delay, TimeUnit unit);
86	tim	1.2
87			/**
88			* Creates and executes a ScheduledFuture that becomes enabled after the
89			* given delay.
90	jsr166	1.16	*
91			* @param callable the function to execute
92			* @param delay the time from now to delay execution
93			* @param unit the time unit of the delay parameter
94			* @return a ScheduledFuture that can be used to extract result or cancel
95			* @throws RejectedExecutionException if the task cannot be
96			* scheduled for execution
97	tim	1.2	* @throws NullPointerException if callable is null
98			*/
99	jsr166	1.16	public <V> ScheduledFuture<V> schedule(Callable<V> callable,
100			long delay, TimeUnit unit);
101	tim	1.2
102			/**
103			* Creates and executes a periodic action that becomes enabled first
104			* after the given initial delay, and subsequently with the given
105			* period; that is executions will commence after
106			* <tt>initialDelay</tt> then <tt>initialDelay+period</tt>, then
107	jsr166	1.14	* <tt>initialDelay + 2 * period</tt>, and so on.
108	dl	1.5	* If any execution of the task
109			* encounters an exception, subsequent executions are suppressed.
110			* Otherwise, the task will only terminate via cancellation or
111	jsr166	1.15	* termination of the executor. If any execution of this task
112	dl	1.13	* takes longer than its period, then subsequent executions
113			* may start late, but will not concurrently execute.
114	jsr166	1.15	*
115	jsr166	1.16	* @param command the task to execute
116			* @param initialDelay the time to delay first execution
117			* @param period the period between successive executions
118	dl	1.4	* @param unit the time unit of the initialDelay and period parameters
119	jsr166	1.16	* @return a ScheduledFuture representing pending completion of
120			* the task, and whose <tt>get()</tt> method will throw an
121			* exception upon cancellation
122			* @throws RejectedExecutionException if the task cannot be
123			* scheduled for execution
124	tim	1.2	* @throws NullPointerException if command is null
125	jsr166	1.16	* @throws IllegalArgumentException if period less than or equal to zero
126	tim	1.2	*/
127	jsr166	1.15	public ScheduledFuture<?> scheduleAtFixedRate(Runnable command,
128			long initialDelay,
129			long period,
130			TimeUnit unit);
131	jsr166	1.14
132	tim	1.2	/**
133			* Creates and executes a periodic action that becomes enabled first
134			* after the given initial delay, and subsequently with the
135			* given delay between the termination of one execution and the
136	jsr166	1.15	* commencement of the next. If any execution of the task
137	dl	1.5	* encounters an exception, subsequent executions are suppressed.
138			* Otherwise, the task will only terminate via cancellation or
139			* termination of the executor.
140	jsr166	1.15	*
141	jsr166	1.16	* @param command the task to execute
142			* @param initialDelay the time to delay first execution
143	tim	1.2	* @param delay the delay between the termination of one
144	jsr166	1.16	* execution and the commencement of the next
145	dl	1.4	* @param unit the time unit of the initialDelay and delay parameters
146	jsr166	1.16	* @return a ScheduledFuture representing pending completion of
147			* the task, and whose <tt>get()</tt> method will throw an
148			* exception upon cancellation
149			* @throws RejectedExecutionException if the task cannot be
150			* scheduled for execution
151	tim	1.2	* @throws NullPointerException if command is null
152	jsr166	1.16	* @throws IllegalArgumentException if delay less than or equal to zero
153	tim	1.2	*/
154	jsr166	1.15	public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command,
155			long initialDelay,
156			long delay,
157			TimeUnit unit);
158	tim	1.2
159	tim	1.1	}