docs: def _poll_trigger(self):
          """
          Trigger activity for the caller by writting a NUL to the self-pipe.
      """
          try:
              os.write(self._poll_send, '\0'.encode('utf-8'))
          except Exception as e:
              log = self._getparam('log', self._discard)
              log.debug("Ignoring self-pipe write error -- %s", e)