kawashima-fj
commented
8 years ago Fujitsu MPI, which is based on Open MPI, also provides multiple compiler support unofficially (not general product).
The issue is not specific to Fortran (and removed C++). Even for C, OpenMP support is not ABI compatible. So Fujitsu MPI provides mpifcc/mpiFCC/mpifrt for Fujitsu compiler, mpigcc/mpig++/mpigfortran for GCC, and mpiicc/mpicpc/mpiifort for Intel compiler.
The implementation is not same as the one which @jeffhammond suggested. But if someone need this, I can contribute it to Open MPI.
User's view
All MPI wrapper compilers are installed in the same directory (/opt/FJSVpclang/bin). Users don't need to switch the PATH environment variable but need to switch command names.
All shared libraries have distinct names (e.g. libmpi_gnu.so) and installed in the same directory (/opt/FJSVpclang/lib64). Include files and module files are installed separately with the same file names (e.g. /opt/FJSVpclang/include/mpi/gnu/mpi.h). All are hidden by the wrapper compilers and users don't need to know the file names or directory paths.
mpiexec and other files are shared. When user executes a MPI program using mpiexec, appropriate libraries are linked automatically.
Developer's view
Developers need to run configure and make all install for each compiler product. On each configure run, --enable-extra-named-lib=COMPILER_NAME option must be supplied and CC/CXX/FC must be set appropriately. The --prefix option must be same.
Though this does not save sysadmin's time, but saves filesystem metadata.
jeffhammond
ggouaillardet
jjhursey
Summary
Please support the ability to build Open-MPI Fortran bindings for multiple Fortran compilers in the same build. This will dramatically improve user experience.
I recognize this is not a small thing to implement, but at least two vendors do this already, and since some vendors use Open-MPI as the basis for their MPI product, it might be the sort of thing that makes sense for the project to support.
Alternative / Workaround
The current solution for multiple Fortran compilers is to build the MPI library once for every toolchain, e.g. one has installation directories
open-mpi-intel15,open-mpi-intel16,open-mpi-gcc5,open-mpi-gcc6, etc. This naturally leads tompi.modandmpi_f08.modfor every Fortran compiler.While simple, the current solution is a waste of sysadmin time, processor cycles, filesystem metadata, etc. given that one could instead build Open-MPI once with the preferred C compiler once and then support O(n) Fortran compiler wrappers and modules.
Future Workaround
In theory, there could be an implementation-agnostic implementation of the MPI Fortran 2008 bindings that could be compiled independent of the MPI C library, but such a project does not yet exist and in any case, very few users have adopted
use mpi_f08.Background
The Fortran bindings are largely if not completely independent of the internals of MPI, which are compiled with a C compiler, and C allows for a standard ABI. On the other hand, Fortran does not have a standard ABI and modules must be generated for every compiler vendor, and possibly also multiple (major) versions of the compiler from a single vendor.
Suggested implementation
FCnfor n=1,2,... as an alternative toFC. The build system would then generate MPI Fortran scripts namedmpi$FC1,mpi$FC2, etc., assumingFCndo not have the full paths, otherwise they will be stripped.-enable-fortran-compilers=$FC1,$FC2. This is just different syntax for option 1.Ideally, the user can do something like
$PATH_TO_OMPI/configure FC1=ifort FC2=gfortranand get$OMPI_PREFIX/bin/mpiifort,$OMPI_PREFIX/bin/mpigfortran,$OMPI_PREFIX/include/ifort/mpi.mod,$OMPI_PREFIX/include/gfortran/mpi.mod,$OMPI_PREFIX/include/ifort/mpi_f08.mod,$OMPI_PREFIX/include/gfortran/mpi_f08.mod, and any companion files.Prior Engineering / Proof-of-Principle
Intel MPI
Intel MPI packages the wrappers and modules for Intel Fortran and GNU Fortran.
IBM Blue Gene/Q
IBM supported this on Blue Gene/Q. I do not know the implementation details but can demonstrate the results if anyone needs to see it.