UltraSonic update rate

When polling an Ultrasonic sensor, does RobotC do this in the background with an interrupt (non-blocking), or does it hold the processor (blocking) until the echo is returned?

It all happens in the background, ROBOTC does not block, the update rate is determined by the way the ultrasonic sensor works and the number of sensors installed.

There’s a little more detail on how the ultrasonic works in this thread.