int VisibleDeviceCount() const override {
    int visible_device_count = 0;
    tensorflow::TF_StatusPtr c_status(TF_NewStatus());
    platform_fns_.get_device_count(&platform_, &visible_device_count,
                                   c_status.get());
    if (TF_GetCode(c_status.get()) != TF_OK) {
      LOG(ERROR) << TF_Message(c_status.get());
      return 0;
    }
    return visible_device_count;
  }