code: def run(self):
          
          # localize variable access to minimize overhead
          # and to improve thread safety
          q = self._queue
          delayfunc = self.delayfunc
          timefunc = self.timefunc
          pop = heapq.heappop
          while q:
              # TODO: modified part of grumpy version.
              checked_event = q[0]
              time, priority, action, argument = checked_event.get_fields()
              now = timefunc()
              if now < time:
                  delayfunc(time - now)
              else:
                  event = pop(q)
                  # Verify that the event was not removed or altered
                  # by another thread after we last looked at q[0].
                  if event is checked_event:
                      action(*argument)
                      delayfunc(0)   # Let other threads run
                  else:
                      heapq.heappush(q, event)
docs: 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.