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
#	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 <tt>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.newScheduledThreadPool(1);
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	*
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	* @throws NullPointerException if command is null
83	*/
84	public ScheduledFuture<?> schedule(Runnable command,
85	long delay, TimeUnit unit);
86
87	/**
88	* Creates and executes a ScheduledFuture that becomes enabled after the
89	* given delay.
90	*
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	* @throws NullPointerException if callable is null
98	*/
99	public <V> ScheduledFuture<V> schedule(Callable<V> callable,
100	long delay, TimeUnit unit);
101
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	* <tt>initialDelay + 2 * period</tt>, and so on.
108	* 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	* termination of the executor. If any execution of this task
112	* takes longer than its period, then subsequent executions
113	* may start late, but will not concurrently execute.
114	*
115	* @param command the task to execute
116	* @param initialDelay the time to delay first execution
117	* @param period the period between successive executions
118	* @param unit the time unit of the initialDelay and period parameters
119	* @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	* @throws NullPointerException if command is null
125	* @throws IllegalArgumentException if period less than or equal to zero
126	*/
127	public ScheduledFuture<?> scheduleAtFixedRate(Runnable command,
128	long initialDelay,
129	long period,
130	TimeUnit unit);
131
132	/**
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	* commencement of the next. If any execution of the task
137	* encounters an exception, subsequent executions are suppressed.
138	* Otherwise, the task will only terminate via cancellation or
139	* termination of the executor.
140	*
141	* @param command the task to execute
142	* @param initialDelay the time to delay first execution
143	* @param delay the delay between the termination of one
144	* execution and the commencement of the next
145	* @param unit the time unit of the initialDelay and delay parameters
146	* @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	* @throws NullPointerException if command is null
152	* @throws IllegalArgumentException if delay less than or equal to zero
153	*/
154	public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command,
155	long initialDelay,
156	long delay,
157	TimeUnit unit);
158
159	}