The sched module defines a class which implements a general
purpose event scheduler:
The scheduler class defines a generic interface to scheduling
events. It needs two functions to actually deal with the ``outside world''
-- timefunc should be callable without arguments, and return
a number (the ``time'', in any units whatsoever). The delayfunc
function should be callable with one argument, compatible with the output
of timefunc, and should delay that many time units.
delayfunc will also be called with the argument 0 after
each event is run to allow other threads an opportunity to run in