borg81
asked on
TimerTask change period at runtime
Is there a simple possibility to change the period of TimerTask at runtime?
I know that it can certainly be realised using a thread (sleep).
First I made it with threads and everything worked fine in the
Appletviewer. But when I tested it in a browser the applet was always
stopped with a messag from Security Manager that I have to modify thread and so on.
I tried everything in order to make it run with threads (Priority, ...) but it didn't work.
That's why I want it to do with TimerTask this time and it works so far...
I know that it can certainly be realised using a thread (sleep).
First I made it with threads and everything worked fine in the
Appletviewer. But when I tested it in a browser the applet was always
stopped with a messag from Security Manager that I have to modify thread and so on.
I tried everything in order to make it run with threads (Priority, ...) but it didn't work.
That's why I want it to do with TimerTask this time and it works so far...
The sad thing with Timer is that you cannot use the same TimerTask object. Below are two code snippets from the implementation of Timer.java & TimerTask.java (from JDK 1.3). When you call TimerTask.cancel(), you do indeed cancel the TimerTask. However you cannot use that task in any subsequent schedule operations as Timer.sched() will throw an IllegalStateException when the TimerTask is not a virgin. So if you take this approach, make sure that you create a NEW TimerTask object to set the period.
IMHO the Timer/TimerTask classes should be changed in the future to support:
* Timer: listing scheduled tasks by priority.
* Both: cooperate to allow cancelled tasks to be rescheduled.
* Both: allow adjusting period dynamically. This may include options for allowing the next scheduled run to occur or be pre-empted.
borg81: if you want to take a stab at it, you can always get a copy of the Java source, apply these changes as you see fit, TEST TEST TEST, and then triumphantly return with your improved Timer class. :-)
-----------
Timer.java
-----------
private void sched(TimerTask task, long time, long period) {
if (time < 0)
throw new IllegalArgumentException("
synchronized(queue) {
if (!thread.newTasksMayBeSche
throw new IllegalStateException("Tim
synchronized(task.lock) {
if (task.state != TimerTask.VIRGIN)
throw new IllegalStateException(
"Task already scheduled or cancelled");
task.nextExecutionTime = time;
task.period = period;
task.state = TimerTask.SCHEDULED;
}
queue.add(task);
if (queue.getMin() == task)
queue.notify();
}
}
-------------
TimerTask.java
-------------
public boolean cancel() {
synchronized(lock) {
boolean result = (state == SCHEDULED);
state = CANCELLED;
return result;
}
}
--------------
IMHO the Timer/TimerTask classes should be changed in the future to support:
* Timer: listing scheduled tasks by priority.
* Both: cooperate to allow cancelled tasks to be rescheduled.
* Both: allow adjusting period dynamically. This may include options for allowing the next scheduled run to occur or be pre-empted.
borg81: if you want to take a stab at it, you can always get a copy of the Java source, apply these changes as you see fit, TEST TEST TEST, and then triumphantly return with your improved Timer class. :-)
-----------
Timer.java
-----------
private void sched(TimerTask task, long time, long period) {
if (time < 0)
throw new IllegalArgumentException("
synchronized(queue) {
if (!thread.newTasksMayBeSche
throw new IllegalStateException("Tim
synchronized(task.lock) {
if (task.state != TimerTask.VIRGIN)
throw new IllegalStateException(
"Task already scheduled or cancelled");
task.nextExecutionTime = time;
task.period = period;
task.state = TimerTask.SCHEDULED;
}
queue.add(task);
if (queue.getMin() == task)
queue.notify();
}
}
-------------
TimerTask.java
-------------
public boolean cancel() {
synchronized(lock) {
boolean result = (state == SCHEDULED);
state = CANCELLED;
return result;
}
}
--------------
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ASKER
Thousand Thanks
no probs.
No drama, I just ran into that situation once and was confused with the error message.
What you would do is cancel the task and start a new one with the desired period.