code: def _start_beacon(port=None):
      
      global _beacon
      if _beacon is None:
          _logger.debug("About to start beacon with port %s", port)
          try:
              _beacon = _Beacon(port)
          except (OSError, socket.error) as exc:
              if exc.errno == errno.EADDRINUSE:
                  _logger.warn("Beacon already active on this machine")
                  #
                  # _remote_beacon is simply a not-None sentinel value
                  # to distinguish between the case where we have not
                  # yet started a beacon and where we have found one
                  # in another process.
                  #
                  _beacon = _remote_beacon
              else:
                  raise
          else:
              _beacon.start()
docs: Start a beacon thread within this process if no beacon is currently
      running on this machine.
      
      In general this is called automatically when an attempt is made to
      advertise or discover. It might be convenient, though, to call this
      function directly if you want to have a process whose only job is
      to host this beacon so that it doesn't shut down when other processes
      shut down.