1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
|
package compbio.stat.servlet.util;
import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;
/**
* A facility for threads to schedule recurring tasks for future
* execution in a background thread.
* <p>
* This class is thread-safe: multiple threads can share a single
* <code>Scheduler</code> object without the need for external synchronization.
* <p>
* Implementation note: internally <code>Scheduler</code> uses a
* <code>java.util.Timer</code> to schedule tasks.
*/
public class Scheduler {
class SchedulerTimerTask extends TimerTask {
private SchedulerTask schedulerTask;
private ScheduleIterator iterator;
public SchedulerTimerTask(SchedulerTask schedulerTask,
ScheduleIterator iterator) {
this.schedulerTask = schedulerTask;
this.iterator = iterator;
}
public void run() {
schedulerTask.run();
reschedule(schedulerTask, iterator);
}
}
private final Timer timer = new Timer();
public Scheduler() {
}
/**
* Terminates this <code>Scheduler</code>, discarding any currently scheduled tasks.
* Does not interfere with a currently executing task (if it exists). Once a scheduler
* has been terminated, its execution thread terminates gracefully, and no more tasks
* may be scheduled on it.
* <p>
* Note that calling this method from within the run method of a scheduler task that was
* invoked by this scheduler absolutely guarantees that the ongoing task execution is the
* last task execution that will ever be performed by this scheduler.
* <p>
* This method may be called repeatedly; the second and subsequent calls have no effect.
*/
public void cancel() {
timer.cancel();
}
/**
* Schedules the specified task for execution according to the specified schedule. If times
* specified by the <code>ScheduleIterator</code> are in the past they are scheduled for
* immediate execution.
* <p>
*
* @param schedulerTask task to be scheduled
* @param iterator iterator that describes the schedule
* @throws IllegalStateException if task was already scheduled or cancelled, scheduler was
* cancelled, or scheduler thread terminated.
*/
public void schedule(SchedulerTask schedulerTask,
ScheduleIterator iterator) {
Date time = iterator.next();
if (time == null) {
schedulerTask.cancel();
} else {
synchronized (schedulerTask.lock) {
if (schedulerTask.state != SchedulerTask.VIRGIN) {
throw new IllegalStateException("Task already scheduled " +
"or cancelled");
}
schedulerTask.state = SchedulerTask.SCHEDULED;
schedulerTask.timerTask =
new SchedulerTimerTask(schedulerTask, iterator);
timer.schedule(schedulerTask.timerTask, time);
}
}
}
private void reschedule(SchedulerTask schedulerTask,
ScheduleIterator iterator) {
Date time = iterator.next();
if (time == null) {
schedulerTask.cancel();
} else {
synchronized (schedulerTask.lock) {
if (schedulerTask.state != SchedulerTask.CANCELLED) {
schedulerTask.timerTask =
new SchedulerTimerTask(schedulerTask, iterator);
timer.schedule(schedulerTask.timerTask, time);
}
}
}
}
}
|
