Source code: edu/emory/mathcs/util/concurrent/AlarmClock.java
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2 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
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4 * The contents of this file are subject to the Mozilla Public License Version
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14 * The Original Code is the Emory Utilities.
15 *
16 * The Initial Developer of the Original Code is
17 * The Distributed Computing Laboratory, Emory University.
18 * Portions created by the Initial Developer are Copyright (C) 2002
19 * the Initial Developer. All Rights Reserved.
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34
35 package edu.emory.mathcs.util.concurrent;
36
37 import java.util.*;
38
39 /**
40 * This class provide some value-added over java.util.Timer: that is,
41 * it enables rescheduling of previously scheduled tasks.
42 *
43 * @author Dawid Kurzyniec
44 * @version 1.0
45 */
46 public class AlarmClock {
47 final Timer engine;
48 final Runnable task;
49 TimerTask timerTask;
50
51 public AlarmClock(Timer engine, Runnable task) {
52 this.engine = engine;
53 this.task = task;
54 }
55
56 /**
57 * Reschedule previously scheduled task unless it would postpone it.
58 * In other words, if the requested delay is longer than the time remaining
59 * until the previously scheduled execution, the request is ignored.
60 *
61 * @param delay the new delay before the task is to be executed,
62 * measured from the moment the method is invoked.
63 * @returns true if successful, false otherwise (i.e. if task is already
64 * running or complete)
65 */
66 public synchronized void setAlarmDelayIfSooner(long delay) {
67 if (delay < 0) {
68 // infinite; can't be more restrictive than anything
69 return;
70 }
71 if (timerTask != null) {
72 long oldDelay = timerTask.scheduledExecutionTime() - System.currentTimeMillis();
73 if (delay >= oldDelay) {
74 // not more restrictive; ignore request
75 return;
76 }
77 }
78 setAlarmDelay(delay);
79 }
80
81 /**
82 * Reschedule previously scheduled task.
83 *
84 * @param delay the new delay before the task is to be executed,
85 * measured from the moment the method is invoked.
86 * @returns true if successful, false otherwise (i.e. if task is already
87 * running or complete)
88 */
89 public synchronized boolean setAlarmDelay(long delay) {
90 if (timerTask != null) {
91 if (!cancel()) {
92 // task is running at the moment
93 return false;
94 }
95 }
96 // start timer
97 timerTask = new TimerTask() {
98 public void run() {
99 task.run();
100 synchronized (AlarmClock.this) {
101 // job done; suicide
102 AlarmClock.this.timerTask = null;
103 }
104 }
105 };
106
107 engine.schedule(timerTask, delay);
108 return true;
109 }
110
111 /**
112 * Cancel the scheduled task.
113 *
114 * @return true if successful, false otherwise.
115 * @see TimerTask#cancel
116 */
117 public synchronized boolean cancel() {
118 if (timerTask != null) {
119 boolean result = timerTask.cancel();
120 timerTask = null;
121 return result;
122 }
123 return false;
124 }
125 }