docs: def wsgiref_thread_arbiter(wsgi, host, port):
      'probably not suitable for production use; example of threaded server'
      import wsgiref.simple_server
      httpd = wsgiref.simple_server.make_server(host, port, wsgi)
      httpd.socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
  
      def start_server():
          server_thread = threading.Thread(target=httpd.serve_forever)
          server_thread.daemon = True
          server_thread.start()
  
      def close_socket():
          httpd.socket.close()
  
      arbiter = Arbiter(post_fork=start_server, child_pre_exit=httpd.shutdown,
                        parent_pre_stop=close_socket)
      return arbiter