Horovod 사용시 에러 : getting local rank failed, orte_ess_init failed, ompi_rte_init failed

horovodrun -np 1 python train.py

위의 방식으로 Horovod를 사용한 deep learning코드 실행시 아래와 같은 에러가 발생했다.

--------------------------------------------------------------------------
It looks like orte_init failed for some reason; your parallel process is
likely to abort.  There are many reasons that a parallel process can
fail during orte_init; some of which are due to configuration or
environment problems.  This failure appears to be an internal failure;
here's some additional information (which may only be relevant to an
Open MPI developer):

  getting local rank failed
  --> Returned value No permission (-17) instead of ORTE_SUCCESS
--------------------------------------------------------------------------
--------------------------------------------------------------------------
It looks like orte_init failed for some reason; your parallel process is
likely to abort.  There are many reasons that a parallel process can
fail during orte_init; some of which are due to configuration or
environment problems.  This failure appears to be an internal failure;
here's some additional information (which may only be relevant to an
Open MPI developer):

  orte_ess_init failed
  --> Returned value No permission (-17) instead of ORTE_SUCCESS
--------------------------------------------------------------------------
--------------------------------------------------------------------------
It looks like MPI_INIT failed for some reason; your parallel process is
likely to abort.  There are many reasons that a parallel process can
fail during MPI_INIT; some of which are due to configuration or environment
problems.  This failure appears to be an internal failure; here's some
additional information (which may only be relevant to an Open MPI
developer):

  ompi_mpi_init: ompi_rte_init failed
  --> Returned "No permission" (-17) instead of "Success" (0)
--------------------------------------------------------------------------
[1,0]<stderr>:*** An error occurred in MPI_Init_thread
[1,0]<stderr>:*** on a NULL communicator
[1,0]<stderr>:*** MPI_ERRORS_ARE_FATAL (processes in this communicator will now abort,
[1,0]<stderr>:***    and potentially your MPI job)
[1,0]<stderr>:[K0878P2:12600] Local abort before MPI_INIT completed completed successfully, but am not able to aggregate error messages, and not able to guarantee that all other processes were killed!

에러의 근원은 생각지도 못한 것에서 발견됐다.

train.py 맨 상위단에서 horovod로 만들어진 함수를 호출하는 부분이 있는데, 이 부분을

if __name__ == "__main__":

으로 묶어주기만 하니까 해당 에러가 사라졌다... 응?

혹시라도 같은 에러로 고생하는 분들에게 도움이 되길 바람.