CODEWITHSUNDEEP
javaandroid
Finder
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Reputation: 1217

Timer triggered unexpectedly in java

I have started timer with fixed rate. When user change system Time at that time task is executed continuously.It doesn't consider about the period time. How to manage this.

timer.scheduleAtFixedRate(task, delay, period);

Note : Now system time is current time.Period is 30 seconds. Now user change system time into after 10 mins from current time.At that time timer task not consider about the period. Within a second it execute the task 20 times.

When I use

 timer.schedule(task, delay, period);

instead of

timer.scheduleAtFixedRate(task, delay, period);

task working normally. If I change system time to 10 mins past time from now task doesn't executed...

How to solve this ? :(

Upvotes: 2

Views: 370

Answers (1)

txtechhelp
txtechhelp

Reputation: 6767

Have a look at this Stack Overflow answer; long story short, using scheduleAtFixedRate will queue up the tasks you have scheduled and fire them relative to the system time that the task was first queued; if anything should delay these tasks from firing, they will play 'catch up' and fire as fast as they can. So in your example of how changing the system time to +10 minutes made the event fire 20 times make since given that your period is 30 seconds (1m/2 = 30s, 10m*2 = 20 events).

Using the schedule function has similar issues, except it does not play 'catch up'; if you had a timer set to fire off every 30 seconds, then change the system time to +10 minutes only 10 seconds after the timer has started, your first event will trigger, then continue to wait the 30 second delay and fire again (unless you change the system clock again).

If you want something that is independent of system time you'll need monotonic clock values. To my knowledge the Java API does not directly contain any monotonic timers (for numerous reasons), but that doesn't stop you from implementing one yourself (albeit at the cost of possible wasted execution time in custom timer class code). Here's a Stack Overflow question regarding this, as well as a Google Group discussion post on it.

If you're really hard pressed for using a monotonic timer you could potentially use the POSIX API's and do some Java->C JNI work.

I hope that can help (at least point in a solid direction).

Upvotes: 1

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