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 <t>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.newSingleThreadScheduledExecutor();
 *
 *    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 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:	1.8
Committed:	Fri Jan 9 18:40:03 2004 UTC (20 years, 5 months ago) by dl
Branch:	MAIN
Changes since 1.7:	+24 -0 lines
Log Message:	Added usage example
#	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/licenses/publicdomain
5	*/
6
7	package java.util.concurrent;
8	import java.util.concurrent.atomic.*;
9	import java.util.*;
10
11	/**
12	* An {@link ExecutorService} that can schedule commands to run after a given
13	* delay, or to execute periodically.
14	*
15	* <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	* 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	*
27	* <p>All <t>schedule</tt> methods accept <em>relative</em> delays and
28	* 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	* protocols, clock drift, or other factors.
37	*
38	* The {@link Executors} class provides convenient factory methods for
39	* the ScheduledExecutorService implementations provided in this package.
40	*
41	* <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	* Executors.newSingleThreadScheduledExecutor();
51	*
52	* public void beepForAnHour() {
53	* final Runnable beeper = new Runnable() {
54	* public void run() { System.out.println("beep"); }
55	* };
56	* final ScheduledFuture<?> beeperHandle =
57	* 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	* @since 1.5
66	* @author Doug Lea
67	*/
68	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	* and whose <tt>get()</tt> method will return <tt>null</tt>
78	* upon completion.
79	* @throws RejectedExecutionException if task cannot be scheduled
80	* for execution.
81	* @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	* for execution.
94	* @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	* <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	* @param command the task to execute.
109	* @param initialDelay the time to delay first execution.
110	* @param period the period between successive executions.
111	* @param unit the time unit of the initialDelay and period parameters
112	* @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	* for execution.
117	* @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	* 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	* @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	* @param unit the time unit of the initialDelay and delay parameters
135	* @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	* for execution.
140	* @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	}