objective-c - NSTimer falling more and more behind

Question

I have a NSTimer (running on main thread) that is supposed to go off every 0.02s. However, I notice that as memory usage start going up (the app captures a frame every tick and stores in an array) subsequent ticks begin to take more then 0.02s.

How can I solve this issue? I'm starting to think NSTimer is not suited for high-frequency tasks like this.

Answer 1

As the docs state,

A timer is not a real-time mechanism; it fires only when one of the run loop modes to which the timer has been added is running and able to check if the timer’s firing time has passed. Because of the various input sources a typical run loop manages, the effective resolution of the time interval for a timer is limited to on the order of 50-100 milliseconds.

Since 100 milliseconds = .1 seconds and your timer is supposed to run every 0.02 seconds, your timer schedule is far shorter than the timer's effective resolution and so you timer can easily get out of sync.