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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