docs: def start(self):
          """Start thread."""
          if not self._thread:
              logging.info("Starting asterisk mbox thread")
              # Ensure signal queue is empty
              try:
                  while True:
                      self.signal.get(False)
              except queue.Empty:
                  pass
              self._thread = threading.Thread(target=self._loop)
              self._thread.setDaemon(True)
              self._thread.start()