[mpich-discuss] Fortran 2008 MPI Interface Bug

Pedro Ricardo Souza eng.pedro.ricardo at gmail.com
Wed Nov 13 13:59:32 CST 2019

Hi there, My name is Pedro Ricardo and I'm currently a researcher at a
Fluid Dynamics Laboratory in Brazil.
We have a CFD software with 12 continuous years of development mostly in
Fortran, and we've been using Mpich and Openmpi since the very beginning.

Recently we started to refactor the code and write it using Fortran2008
standard and this includes the usage of the the newest MPI module for
Fortran "*mpi_f08*".

So far no errors were present in Openmpi implementations and everything
worked like a charm, but when we started compiling with Mpich lots of
errors happened during execution.

I was able so isolate and reproduce the error in a simpler code. Whenever "*use
mpi_f08*" is present, the arrays passed to a MPI subroutine return
with *C*-like
indexes. If I allocate an standard array in Fortran (that starts with index
*1*), after the call of some MPI routine this array come back starting with
index *0*.
And you can imagine that all access to this array will be wrong after that.
It is a funny behavior because if you put  "*use mpi*" instead of "*use
mpi_f08*", the indexes do not change.

The test is simple, allocate and array, print it's bound indexes, calls a
*MPI_Reduce* routine and print the array bounds again. I've also tested
other routines like *MPI_ISend* and the error also happens.

program check_bounds
>     !Check Works
>     ! use mpi
>     !Check Fails
>     use mpi_f08
>     implicit none
>     integer:: mpi_ierr, proc_id, n_proc
>     real, allocatable, dimension(:):: t1, t1_0

>     call MPI_Init(mpi_ierr)
>     call MPI_Comm_rank(MPI_COMM_WORLD, proc_id, mpi_ierr)
>     call MPI_Comm_size(MPI_COMM_WORLD, n_proc, mpi_ierr)

>     allocate(t1(5), t1_0(5))
>     t1 = 1.0; t1_0 = 1.0

>     if (proc_id==0) then
>         write(*,*)'Array Configuration Before:'
>         write(*,'(a6,2(1x,i2))')'Low:',lbound(t1),lbound(t1_0)
>         write(*,'(a6,2(1x,i2))')'Upper:',ubound(t1),ubound(t1_0)
>     end if

> mpi_ierr)

>     if (proc_id==0) then
>         write(*,*)'Array Configuration After:'
>         write(*,'(a6,2(1x,i2))')'Low:',lbound(t1),lbound(t1_0)
>         write(*,'(a6,2(1x,i2))')'Upper:',ubound(t1),ubound(t1_0)
>     end if

>     deallocate(t1, t1_0)
>     call MPI_Finalize(mpi_ierr)

> end program check_bounds

Thanks for the attention,

Best regards,
M.Sc.Eng. Pedro Ricardo C. Souza
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