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 Future representing pending completion of the task,
     * and whose <tt>get()</tt> method will return <tt>null</tt>
     * upon completion.
     * @throws RejectedExecutionException if 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 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.
     * @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 Future representing pending completion of the task,
     * and whose <tt>get()</tt> method will throw an exception upon
     * cancellation.
     * @throws RejectedExecutionException if 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 Future representing pending completion of the task,
     * and whose <tt>get()</tt> method will throw an exception upon
     * cancellation.
     * @throws RejectedExecutionException if 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:	1.11
Committed:	Mon Jan 19 15:49:02 2004 UTC (20 years, 4 months ago) by dl
Branch:	MAIN
CVS Tags:	JSR166_PFD
Changes since 1.10:	+1 -1 lines
Log Message:	Javadoc fixes
#	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			* 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	dl	1.4	* that run periodically until cancelled.
20			*
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	dl	1.4	* 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			*
43			* 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			* import static java.util.concurrent.TimeUnit;
48			* class BeeperControl {
49			* 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	dl	1.9	* 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			* @param command the task to execute.
74			* @param delay the time from now to delay execution.
75			* @param unit the time unit of the delay parameter.
76			* @return a Future representing pending completion of the task,
77	dl	1.3	* and whose <tt>get()</tt> method will return <tt>null</tt>
78	tim	1.2	* upon completion.
79			* @throws RejectedExecutionException if task cannot be scheduled
80	dl	1.5	* for execution.
81	tim	1.2	* @throws NullPointerException if command is null
82			*/
83			public ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit);
84
85			/**
86			* Creates and executes a ScheduledFuture that becomes enabled after the
87			* given delay.
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			* @return a ScheduledFuture that can be used to extract result or cancel.
92			* @throws RejectedExecutionException if task cannot be scheduled
93	dl	1.5	* for execution.
94	tim	1.2	* @throws NullPointerException if callable is null
95			*/
96			public <V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit);
97
98			/**
99			* Creates and executes a periodic action that becomes enabled first
100			* after the given initial delay, and subsequently with the given
101			* period; that is executions will commence after
102			* <tt>initialDelay</tt> then <tt>initialDelay+period</tt>, then
103	dl	1.5	* <tt>initialDelay + 2 * period</tt>, and so on.
104			* If any execution of the task
105			* encounters an exception, subsequent executions are suppressed.
106			* Otherwise, the task will only terminate via cancellation or
107			* termination of the executor.
108	tim	1.2	* @param command the task to execute.
109			* @param initialDelay the time to delay first execution.
110			* @param period the period between successive executions.
111	dl	1.4	* @param unit the time unit of the initialDelay and period parameters
112	tim	1.2	* @return a Future representing pending completion of the task,
113			* and whose <tt>get()</tt> method will throw an exception upon
114			* cancellation.
115			* @throws RejectedExecutionException if task cannot be scheduled
116	dl	1.5	* for execution.
117	tim	1.2	* @throws NullPointerException if command is null
118			* @throws IllegalArgumentException if period less than or equal to zero.
119			*/
120			public ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit);
121
122			/**
123			* Creates and executes a periodic action that becomes enabled first
124			* after the given initial delay, and subsequently with the
125			* given delay between the termination of one execution and the
126	dl	1.5	* commencement of the next. If any execution of the task
127			* encounters an exception, subsequent executions are suppressed.
128			* Otherwise, the task will only terminate via cancellation or
129			* termination of the executor.
130	tim	1.2	* @param command the task to execute.
131			* @param initialDelay the time to delay first execution.
132			* @param delay the delay between the termination of one
133			* execution and the commencement of the next.
134	dl	1.4	* @param unit the time unit of the initialDelay and delay parameters
135	tim	1.2	* @return a Future representing pending completion of the task,
136			* and whose <tt>get()</tt> method will throw an exception upon
137			* cancellation.
138			* @throws RejectedExecutionException if task cannot be scheduled
139	dl	1.5	* for execution.
140	tim	1.2	* @throws NullPointerException if command is null
141			* @throws IllegalArgumentException if delay less than or equal to zero.
142			*/
143			public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit);
144
145	tim	1.1	}