Hi Min, I will have a look into it when I get a bit of time, but it's strange, because I still see it. I've tested similar c++ code as well, and the same problem is there - I see 3 processes running during the computation in main program, after the workers should be finished. Also, I have tested on Debian 8.7 in VirtualBox with mpich from distro repositories v3.1-5+b2 with the same outcome. I'll try to get back with new info asap. If interested, here's the c++ code with removed calculation from worker but added to the main program:mpi.cpp:#include <mpi.h>#include <math.h>#include <iostream> int main(int argc, char *argv[]){ MPI_Comm everyone; MPI_Init(&argc, &argv); double c = 0.; std::cout << "starting worker\n"; for(int i=0;i<2;i++){ MPI_Comm_spawn("./worker",MPI_ARGV_NULL,1,MPI_INFO _NULL,0,MPI_COMM_SELF, &everyone,MPI_ERRCODES_IGNORE); MPI_Barrier(everyone); } std::cout << "parent rolling again & doing stuff" << "\n"; for(int i=0;i<50000000;i++){ c = i*i+1- (i*10) + sin(pow(i,i%8)); } std::cout << "parent finished stuff: " << c << "\n"; MPI_Finalize(); return 0;} worker.cpp:#include <mpi.h>#include <iostream>using namespace std; int main(int argc, char *argv[]){ double c; MPI_Init(&argc, &argv); MPI_Comm parent; MPI_Comm_get_parent(&parent); cout << "worker inside worker finished stuff: " << c << "\n"; if(parent != MPI_COMM_NULL){ MPI_Barrier(parent); } MPI_Finalize(); return 0;} best,stanislav. On Tue, 2017-09-05 at 16:27 -1000, Min Si wrote:

Hi Stanislav,

I apologize for the late update. After a while I finally find chance to try this test. I could not reproduce this problem on my side.

Here is my environment:

- MPICH version: version 3.3a2 (using the same configure options as shown in your config.log)

- mpi4py: version 2.0.0

- platform: a Fedora25 VM and a Centos7 VM

If you are still facing this problem, please try the following steps to narrow down:

1. Try remove the computation in child.py

2. Try MPICH test suite under <your MPICH build directory>/test/mpi/spawn/

make

make testing V=1

Regards,

Min

On 8/13/17 11:07 AM, Stanislav Simko wrote:

...

Hi Min, attached are configure and make logs for the build that I did for myself on our local cluster with Intel compilers. I.e., build is definitely not guaranteed to be perfect/optimal. But please keep in mind that I get the same behaviour with standard MPICH package in Fedora distribution - I think that configuration options should be available online, maybe prepared by someone from MPICH?

Also, I tested with simple c++ hello world like program and it's the same.

Thank you. best, stanislav.

On Sun, 2017-08-13 at 19:58 +0100, Min Si wrote:

...

Hi Stanislav,

This seems interesting. Could you please also attach the MPICH config.log ? You can find under the directory where you build MPICH. I will look into this problem then and keep you updated.

Min

On 8/11/17 1:31 PM, Stanislav Simko wrote:

...

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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