[JBL]

The documentation on NSTimer says "Because of the various input sources a typical run loop manages, the effective resolution of the time interval for an NSTimer is limited to on the order of 50-100 milliseconds." Is there some way of doing more accurate timing?

[Mooseyard]

NSTimers, like the EventLoopTimers in Carbon, are run from the event loop (runloop), so they're limited in accuracy by the length of time that your other event handlers take. If handling a window resize takes 200ms of drawing, no timers will run during that time because the flow of control hasn't returned back to the main runloop.
More accurate timing will require starting another thread and using thread primitives to schedule an exact delay or wakeup time. Unfortunately I know very little about doing that in Cocoa/BSD/Mach, but hopefully this post has been of some use...

[JBL]

I think that is helpful. I am pretty new to this so let me make sure I have it straight. Every thread has its own event loop. The limit on the accuracy comes from the amount of time spent checking other events on the loop (the timer only gets checked once on each pass through the loop so you can't be any more accurate than the maximum amount of time taken to pass through the loop). This seems to mean that a) the simpler the application the more accurate the timing, and b) the fewer events generated by the program, the more accurate the timing.

[Mooseyard]

That's basically correct except that not every thread has its own event loop (runloop). You have to explicitly start a runloop on a new thread if you want one, using CFRunLoop or NSRunLoop. They are very useful for managing inter-thread messaging, but not necessary in all cases.
In your case if you're very concerned about accurate timing, I would simply have a raw thread whose main function uses lower level timing primitives to block until an exact time. (You can tell I'm getting vague here, since I've never done any of this myself. But I'm pretty sure there are POSIX/BSD APIs to do this.)

[JBL]

Thanks! Clearly I have a lot to learn here but I think I know the direction to look at now.