nested mpirun commands

okkebas · ‎06-03-2015

Hi,

I have an mpi program that calls another mpi program (written by someone else) using a fortran system call

driver.f90

call MPI_INIT(..)

system('mpirun -np 2 ./mpi_prog.x')

call MPI_FINALIZE(...)

When I run it (e.g. mpirun -np 4 ./driver.x) it crashes inside mpi_prog.x (at a barrier). When I build it using mpich it works fine though. Any hints on what might be wrong (I realize nested mpirun's are completely beyond the mpi standard and highly dependent on implementation)

NOTE: when I do something like:

mpirun -hosts hostA,hostB -perhost 1 -np 2 mpirun -np 4 hostname

it works perfectly fine and returns the correct output.

John_D_6 · ‎06-03-2015

Hi,

good that you realize that this violates the MPI standard in so many ways.

Luckily, there is a solution in MPI-2 and it's called MPI_COMM_SPAWN:

integer ierr,intercomm
integer errcodes(2)

call MPI_COMM_SPAWN("./mpi_prog.x","",2,MPI_INFO_NULL,0,MPI_COMM_WORLD,intercomm,errcodes,ierr)
if (.not.all(errcodes.eq.MPI_SUCCESS)) then
  print*,'Error!'
  call MPI_Abort(MPI_COMM_WORLD,1,ierr)
endif

Quite some magic happens in the MPI_Init routine, so I expect your NOTE seems to work fine because you're not running an actual MPI-program.