def wait_on(event)
      $shreduler.shredule(Shred.current, event, $shreduler.event_clock)
      Shred.current.pause
    end
def wait_on(event)
      $shreduler.shredule(Shred.current, event, $shreduler.event_clock)
      Shred.current.pause
    end
sleeps, waiting on the given event on the default EventClock of
 the global Shreduler