[Discuss-gnuradio] Source block question: internal sleep loop or let GR scheduler handle empty read?

[Monahan-Mitchell, Tim]

Looking at some source block examples (audio jack, comedi, file source, etc.), 
sometimes I see a sleep() called inside the work function when there is no data 
to read, sometimes not (noutputitems = 0).

For a real file, not sleeping and returning noutputitems = 0 makes perfect 
sense.

For a stream device, using fread(), what are the pros/cons of the work loop 
sleeping if fread is empty, or letting the scheduler decide?

If I can influence the implementation of the device driver, similar question on 
pros/cons if the driver sleeps (or schedules) instead if there is no data yet, 
or just returns an empty read?

(ignore endless looping for these questions, that could be detected)

I will be using GR v3.7 when available.

Thanks in advance,
Tim