Timer event in viztask

[GiudiceLab]

I am trying to detect when a timer has expired in order to capture the time it takes a person to respond to a change. Using viztask, my code looks something like

# Start a timer
viz.starttimer(0, 1, viz.PERPETUAL)

# define our changing function
def changeThing():
        # change the thing
        thing = thing + change

# Register the timer callback
viz.callback(viz.TIMER_EVENT, changeThing)

# Define the experimental loop
def experiment():
	# Initialize trial number
	trial = 1
	# Wait for spacebar to begin experiment
	yield viztask.waitKeyDown(' ')
	while trial <= numTrials:
		# Update the instructions
		msgbox.message('Trial ' + str(trial))
		# Wait for the timer
                yield viztask.waitEvent( viz.TIMER_EVENT )
		# Wait for response
		yield viztask.waitKeyDown(' ')
		# Increment the trial number
		trial = trial + 1

# Schedule the experiment
viztask.schedule( experiment() )

which I thought would work, but never gets past the waitEvent. I have tried using a timer callback and vizact.ontimer, but neither works to move the script forward (although the function that is called with the timer works fine). Am I doing something wrong, or is this not possible to do? Or do I need a different approach? This was supposed to be a simple example for class, and I don't want to cover custom events yet. Any help is appreciated.
Thanks!

[farshizzo]

Timer events behave differently than all other events. They are only sent to the event handler that started the timer. Also, waiting for any timer event doesn't seem very useful, since a lot of other vizard modules use timer events internally.

I would suggest using viztask.Signal objects. The documentation contains sample code for using task signals. The following code shows how to create a task signal:

timer_signal = viztask.Signal()

In your timer callback you can trigger the signal:

timer_signal.send()

And in your task you can wait for the signal to be triggered using this code:

yield timer_signal.wait()