def count_down(self):
return self._encode_invoke(count_down_latch_count_down_codec)<EOL>
Decrements the count of the latch, releasing all waiting threads if the count reaches zero.

If the current count is greater than zero, then it is decremented. If the new count is zero:
    * All waiting threads are re-enabled for thread scheduling purposes, and
    * Countdown owner is set to ``None``.

If the current count equals zero, nothing happens.