'Execute events until the queue is empty.
When there is a positive delay until the first event, the
delay function is called and the event is left in the queue;
otherwise, the event is removed from the queue and executed
(its action function is called, passing it the argument).  If
the delay function returns prematurely, it is simply
restarted.
It is legal for both the delay function and the action
function to modify the queue or to raise an exception;
exceptions are not caught but the scheduler\'s state remains
well-defined so run() may be called again.
A questionable hack is added to allow other threads to run:
just after an event is executed, a delay of 0 is executed, to
avoid monopolizing the CPU when other threads are also
runnable.'

def run(self):

    q = self._queue
    delayfunc = self.delayfunc
    timefunc = self.timefunc
    pop = heapq.heappop
    while q:
        (time, priority, action, argument) = checked_event = q[0]
        now = timefunc()
        if (now < time):
            delayfunc((time - now))
        else:
            event = pop(q)
            if (event is checked_event):
                action(*argument)
                delayfunc(0)
            else:
                heapq.heappush(q, event)
