DAQ check for accomplished cycles

[horatius]

I've generated a waveform array that is continously outputted to an analog voltage channel with sample clock (picture). Is there any function that checks after every full array cycle if there is any user reaction (button press ...). If no the waveform should be repeated else stopped. In my program the process can be stopped within a 100 ms interval. But the process shall only stop after a cycle is accomplished. How do I have to adapt the program?