// 5a. Update `ctx_0` with updated `server_def_0`.
  {
    server_def_0.set_task_index(0);
    string serialized_update = server_def_0.SerializeAsString();
    TF_Status* status = TF_NewStatus();
    TFE_ContextUpdateServerDef(ctx_0, 0, serialized_update.data(),
                               serialized_update.size(), status);
    ASSERT_EQ(TF_OK, TF_GetCode(status)) << TF_Message(status);
    TF_DeleteStatus(status);
  }