OpenMPI + mpi4py broken: rank=0

Running this command:

guix shell python python-mpi4py openmpi -- mpirun -n 12 python3 \

-c "from mpi4py import MPI; comm = MPI.COMM_WORLD;

print(comm.Get_rank())"

should print the numbers 0-11. Instead it prints 0 11 times. The same

behavior occurs in a container or pure environment.

This breaks any code using mpi4py, because ranks >0 must be available

for multi-threaded code to work.

The issue seems that openmpi is version 5.x but mpi4py is compiled against version 4.x. You can get a consistent version by using this flag: --with-input=openmpi=openmpi@4.1.6. I could fix the issue with this call:

guix shell python python-mpi4py openmpi \

--with-input=openmpi=openmpi@4.1.6 -- \

mpirun -n 12 python3 ...

Lars Bilke <lars.bilke@ufz.de> writes:

That does fix it, thanks. Maybe packages built against MPI 4.x should

be upgraded to the default MPI version, because the docs say:

"The Open MPI v5.0.x series shared libraries are ABI compatible with

Open MPI v4.0.x and v4.1.x, with a few exceptions for Fortran."