message: release GIL while waiting.
diff: @@ -34,7 +34,8 @@ PYBIND11_MODULE(_pywrap_server_lib, m) {
  "DispatchGrpcDataServer")
  .def("start", &tensorflow::data::DispatchGrpcDataServer::Start)
  .def("stop", &tensorflow::data::DispatchGrpcDataServer::Stop)
  - .def("join", &tensorflow::data::DispatchGrpcDataServer::Join)
  + .def("join", &tensorflow::data::DispatchGrpcDataServer::Join,
  + py::call_guard<py::gil_scoped_release>())
  .def("bound_port", &tensorflow::data::DispatchGrpcDataServer::BoundPort)
  .def("num_workers",
  [](tensorflow::data::DispatchGrpcDataServer* server) -> int {
  @@ -47,7 +48,8 @@ PYBIND11_MODULE(_pywrap_server_lib, m) {
  py::class_<tensorflow::data::WorkerGrpcDataServer>(m, "WorkerGrpcDataServer")
  .def("start", &tensorflow::data::WorkerGrpcDataServer::Start)
  .def("stop", &tensorflow::data::WorkerGrpcDataServer::Stop)
  - .def("join", &tensorflow::data::WorkerGrpcDataServer::Join)
  + .def("join", &tensorflow::data::WorkerGrpcDataServer::Join,
  + py::call_guard<py::gil_scoped_release>())
  .def("bound_port", &tensorflow::data::WorkerGrpcDataServer::BoundPort);
  m.def(
  