On Sep 23, 2008, at 19:20 , Dan Birns wrote:
I'm trying to convert from Carbon to Cocoa for a number of reasons which I won't go into here.My application needs to set a timer that causes a function to be called at a time in the future. This is non-repeating, and sometimes has be immediate. I need it to be as efficient as possible, because it's called frequently.In Carbon I'm using: EventLoopTimerUPP upp; upp = NewEventLoopTimerUPP(macTimerCallback); InstallEventLoopTimer(GetMainEventLoop(),0, kEventDurationForever, upp,0,&macTimer); Then, when I need to set the timer: nextTimerTime = CFAbsoluteTimeGetCurrent() + nextTimer; SetEventLoopTimerNextFireTime(macTimer, nextTimer);In Cocoa, the system I'm using requires me to allocate a new NSTimer every time I need to set a timer:self.timer = [NSTimer scheduledTimerWithTimeInterval: t // seconds target: self selector: @selector (mainLoopTimer:) userInfo: nil repeats: NO];
In your example, what is the value of t? There is some time required to set up the timer and get it scheduled, so you should take that into account. Did you want it to fire again at some point or did you want to schedule a new timer in mainLoopTimer: ?
This is working fine, but our performance is poor. It's not so poor that it's obviously broken, but I'm looking for ways to improve it. I've been try to alloc one NSTimer that I reuse, and I've had no success doing so.I've tried timer = [NSTimer alloc];[timer initWithFireDate:[NSDate date] interval:t target:self selector:@selector(mainLoopTimer:) userInfo:halTimer repeats:NO]; [[NSRunLoop currentRunLoop] addTimer:timer forMode:NSDefaultRunLoopMode];This has failed. Investigating, I called [timer isValid] and it returns false. I've tried altering the args in various ways without success. I've also had various problems retain'ing this timer. When I add [timer retain];, it crashes having exhausted the stack, where it's calling retain over and over.
That's because the timer fires NOW when done this way and interval is ignored since repeats is NO. Once the timer fires it is invalidated (again, since repeats is NO). To create a non-repeating timer that fires in t seconds using the init method, try this:
timer = [[NSTimer alloc] initWithFireDate:[NSDate dateWithTimeIntervalSinceNow:t] interval:0 target:self selector:@selector(mainLoopTimer:) userInfo:halTimer repeats:NO]; [[NSRunLoop currentRunLoop] addTimer:timer forMode:NSDefaultRunLoopMode];
What you might want to do is create a repeating timer which fires every so often (whatever granularity you need). Then in the timer function, if nextTimer's time hasn't yet been reached, return immediately. If it has, do whatever you need to do and reset nextTimer to some time in the future. That should be more efficient (or at least get you better granularity after the initial firing of the timer). You can also manually fire a repeating timer (without worrying about it getting invalidated) if you want it to start AS SOON AS POSSIBLE without waiting for it to get scheduled and fired from the run loop (the initial firing can be a bit delayed in that case...)
Jason
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