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Subject: Re: [OMPI devel] Fortran 90 Interface
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2009-01-23 06:53:58

On Jan 23, 2009, at 12:30 AM, David Robertson wrote:

>>> I don't know how helpful this code will be unless you happen to
>>> have HDF5/NetCDF4 already installed. I looked at the code NetCDF4
>>> uses to test parallel IO but it is all in C so it wasn't very
>>> helpful. If you have the NetCDF4 source code the parallel IO tests
>>> are in the nc_test4 directory.
>> Mm, yes, that would be difficult for me to build/run. Can you or
>> your developer trim it down to a small independent example?
> I will talk to the developer tomorrow to see if he can come up with
> an independent example.


>> FWIW, this is not happening for me -- I can call subroutines or
>> functions with MPI_COMM_WORLD and then use that value (which should
>> be 0, btw) to call an MPI function such as MPI_COMM_DUP.
>> Per your prior comment about the debugging not being able to find
>> MPI_COMM_WORLD -- perhaps the compiler is optimizing it out...? Or
>> perhaps it was transmorgified to lower case (i.e., try seeing if
>> "mpi_comm_world" exists -- I see it in your mpi.mod file)...?
> I have looked for both MPI_COMM_WORLD and mpi_comm_world but neither
> can be found by totalview (the parallel debugger we use) when I
> compile with "USE mpi". When I use "include 'mpif.h'" both
> MPI_COMM_WORLD and mpi_comm_world are zero.

I'm afraid I don't know why that would be. :-(

> MPI_COMM_WORLD is set to a large integer (1140850688) in MPICH2 so I
> wonder if there is something in HDF5 and/or NetCDF4 that doesn't
> like 0 for the communicator handle. At any rate, you have given me
> some ideas of things to check in the debugger tomorrow. Is there a
> safe way to change what MPI_COMM_WORLD is set to in OpenMPI?

No. Open MPI's Fortran MPI_COMM_WORLD is pretty much hard-wired to 0.

One question: you *are* using different HDF5/NetCDF4 installations for
Open MPI and MPICH2, right? I.e., all the software that uses MPI
needs to be separately compiled/installed against different MPI
implementations. Case in point: if you have HDF5 compiled against
MPICH2, it will not work properly with Open MPI-compiled MPI

Jeff Squyres
Cisco Systems