Question

I have an issue while working with NSTimer.
Let’s assume I have this architecture :

ThreadedClass.m (contains a NSTimer* timer;)

- (id) init {
  if (self = [super init]) {
    // do blablabla
    [self launchAThread];
  }
  return self;
}


- (void) launchAThread {
    [NSThread detachNewThreadSelector:@selector(selectorToMyThreadFunction)
                             toTarget:self
                           withObject:nil];
}


- (void) selectorToMyThreadFunction {
    //I do my stuff in here
    //Then i relaunch a Timer to call this function
    //periodically but it has to be "atomic" so no
    //repeating timer since i don't know the time
    //this function will take

    //I do some [self changeSomething];

    [self restartTimer];

    //MyThread ends here (and might be recreated by the Timer's bip
}

- (void)restartTimer {
    if (![NSThread isMainThread]) {
      [self performSelectorOnMainThread:@selector(restartTimer)
                             withObject:nil
                          waitUntilDone:NO];
      return;
    }

    [timer invalidate];
    [timer release];
    timer = [[NSTimer scheduledTimerWithTimeInterval:interval
                                              target:self
                                            selector:@selector(launchWithTimer:)
                                            userInfo:nil
                                             repeats:NO] retain];
}

- (void) launchWithTimer:(NSTimer *)theTimer {
  if (theTimer == timer)
  {
    [timer release];
    timer = nil;
    [self launchAThread];
  }
  else
  {
    //Nothing to be done in here, a user launch a thread manually
  }
}

So let’s assume the user of the class alloc it and release it right after. My timer will still be alive and the object too (since there is a retain made by the timer).
When the timer will fire, it will do [self launchAThread] and then the timer will invalidate and release itself AND it will release my object which now has a retainCount = 0… Let’s assume, one more time, the object is deallocted right after, this will cause crash and there is nothing i can do to stop it that comes right to my mind.

I agree, this is a lot of assumptions but i’m curious to know if someone already had this issue and how he solved it.

Thanks for reading and I hope I was clear ! 🙂

Answer 1

Since I’m making a library, i can’t assume that the user will call a cleanUp function anytime.

So to solve my problem, I added a new “layer” : a new class that will do the thread and timer part so that I am the user of this class and I know I have to cleanUp !