OK, here's a version with a low switch interval. Of course it's also
contrived, but it works.

Generally I'd appreciate the RuntimeError, since it's a hint that 
something needs to be rewritten in an application.


It might be a problem if this started to occur sporadically in a
production app under a high system load. But I haven't managed to
trigger the exception just by increasing the system load. I always
had to use the same low switch interval.