Dear all,

I'm just trying some very basic stuff with MPI_COMM_SPAWN in python (i.e. I use mpi4py package), but I see behaviour that I do not understand - the child process gets spawned, does its stuff and then "should" finish. I see though, that the process created for the child stays alive. I see this only with the MPICH, OPENMPI does what I would (naively) expect. In this way I can end up with N "ghost" process, after calling SPAWN N-times. My minimal working example is following:

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parent.py

from __future__ import print_function

from mpi4py import MPI

comm = MPI.COMM_WORLD

spawned = MPI.COMM_SELF.Spawn(sys.executable,args=['child.py'],maxprocs=1)

print("parent process is waiting for child")

spawned.Barrier()

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child.py

from __future__ import print_function

from mpi4py import MPI

parent = MPI.Comm.Get_parent()

# just do some stupid stuff that takes a bit of time

for i in range(5000000):

    a = i*i+1-(i*10) + math.sin(math.pow(i,i%8))

parent.Barrier()

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I run with e.g.:

mpirun -n 1 python mpi.py

Do I miss something with SPAWN method?

(I tested on two independent systems, our local cluster with mpich v3.0.4, and my laptop - fedora 26, mpich v3.2.8 from repositories)

thank you very much for suggestions.

Regards,

stanislav.

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