can a timer trigger during another timer's callback?

Question

I have two timers running simultaneously. The first timer triggers every 1 second and takes 0.2 seconds to run. The second timer triggers every 20 minutes and takes 5 minutes to run. I would like to have the first timer continue triggering during the 5 minutes it takes the second timer execute its callback. In practice, during the second timer's callback the first timer does not trigger. Is it possible to configure the timers to execute the way I want?

Answer 1

There is a workaround, depending on how your timer callbacks' work is structured. If the long timer callback is running a long loop or sequence of calls to different functions, you can insert drawnow() or pause(0.01) calls to make it yield to Matlab's event dispatch queue, which will handle pending handle graphics and timer events, including your other Timer's trigger.

It's sort of like old-school cooperative multitasking where each thread had to explicitly yield control to other threads, instead of being pre-empted by the system's scheduler. Matlab is single-threaded with respect to M-code execution. When a Matlab function is running, events that get raised are put on an event queue and wait until the function finishes and returns to the command prompt, or drawnow(), pause(), uiwait() or a similar function is called. This is how you keep a Matlab GUI responsive, and is documented under their Handle Graphics stuff. But Matlab timer objects use the same event queue for their callbacks. (At least as of a couple versions ago; this is only semi-documented and might change.) So you can manage their liveness with the same functions. You may also need to tweak BusyMode on your timers.

This is kind of a hack but it should get you basic functionality as long as you don't need precise timing, and don't need the callbacks' code to actually run in parallel. (Whichever timer callback has yielded will wait for the other one to finish before proceeding with its own work.)

If the long callback is really blocked on a long operation that you can't stick drawnow calls in to, you're out of luck with basic Matlab and will need to use one of the workarounds the commenters suggest.