[mpich-discuss] mpi_comm_spawn - process not destroyed

[Stanislav Simko]

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:


______________________________________________
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()


______________________________________________
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()

______________________________________________

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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