NSTimer some times getting fired before the fire date? - iphone

Question

I'm setting up a timer to fire at an interval of 13 mins. But the timer seems to be getting fired at irregular intervals. This is an intermittent issue. Some users reported the issue and I'm not able to reproduce the same.
- (void)resetIdleTimer
{
if (_idleTimer)
{
[_idleTimer invalidate];
[_idleTimer release];
_idleTimer = nil;
}
_idleTimer = [[NSTimer scheduledTimerWithTimeInterval:13*60.0
target:self
selector:#selector(idleTimerExceeded)
userInfo:nil
repeats:NO] retain];
}
- (void)idleTimerExceeded
{
// do some processing
[_idleTimer release];
_idleTimer = nil;
}
Timer will be reset (resetIdleTimer) depending on some conditions, but that's anyhow resets the timer with 13 mins.
When I looked into code, I can see only the issue that is not passing timer parameter to the selector. I'm not sure whether that's the reason for this issue or not ? Did anyone come across this kind of weird ness ? (Any how I will be updating the code to to have timer as an argument).
One user reported that its just happened after 4 mins itself.

Answer 1

Let confirm one thing,not passing timer parameter to the selector will not cause any issues.
Here is the updated code which works fine
#property(nonatomic,strong)NSTimer *myTimer;
or
#property(nonatomic,retain)NSTimer *myTimer;
Methods
- (void)resetIdleTimer
{
if ([self.myTimer isValid])
[self.myTimer invalidate];
self.myTimer = [NSTimer scheduledTimerWithTimeInterval:13*60.0
target:self
selector:#selector(idleTimerExceeded)
userInfo:nil
repeats:NO];
}
- (void)idleTimerExceeded
{
NSLog(#"tiggered");
}

Answer 2

i don't find any error in your code, the only idea about is that a user enter your class creating an instance, let's call it instance "A", then start the timer, then exit your class before 13 minutes, then enter again with a new instance "B", a new timer starts...
at this point user expects your timer methods fires after 13 minutes... but timer of "A" is still pending (because there may be an error in the way you close your class) and executes...
You may try to add some logs and try to do as i said, and check all logs (in particular if you enter the dealloc, and that the log in idleTimerExceeded print instances equals to the last instances printed in resetIdleTimer):
-(void)resetIdleTimer {
if (_idleTimer)
{
[_idleTimer invalidate];
[_idleTimer release];
_idleTimer = nil;
}
NSLog(#"...resetIdleTimer: instance: %p", self);
_idleTimer = [[NSTimer scheduledTimerWithTimeInterval:13*60.0
target:self
selector:#selector(idleTimerExceeded)
userInfo:nil
repeats:NO] retain];
NSLog(#"...resetIdleTimer: _idleTimer: %p", _idleTimer);
}
- (void)idleTimerExceeded
{
// do some processing
NSLog(#"...idleTimerExceeded: instance: %p", self);
NSLog(#"...idleTimerExceeded: _idleTimer: %p", _idleTimer);
[_idleTimer release];
_idleTimer = nil;
}
-(void) dealloc
{
NSLog(#"...dealloc: instance: %p", self);
[super dealloc];
}
just an idea... but you may have forgotten that timers retain the instance passed in target:parameter (you pass "self", so your class instance is retained), so a common error is to forget to close the timer when closing the class instance.
a correct way should be:
-a root class (AAA) instantiate your class (BBB) with timer
-BBB start its timer
-AAA wanna dealloc/resetIdleTimer class BBB: before to release it must stop/invalidate BBB.timer (if not timer retain BBB, and BBB won't be released until timer fires/executes its method)
so, if it's your case... add a method that could be called from class AAA that stop/invalidate the timer, something like:
-(void)stopTimer{
if (_idleTimer)
{
[_idleTimer invalidate];
[_idleTimer release];
_idleTimer = nil;
}
}

Answer 3

If you want your timer to fire in exact 13 minutes, maybe this will help:
https://stackoverflow.com/a/3519913/1226304