[Mpi-forum] overloading MPI_Init etc.

[Bronis R. de Supinski]

Um, it is standard practice when using the profiling
interface to redefine MPI_* functions. I think this
question is one for the C and C++ standards, not MPI...

On Sun, 4 Mar 2012, Jeff Hammond wrote:

> What was ambiguous to me - looking at 2.6.3-4 - was if using MPI_ was
> still a protected namespace in C++.  The standard really only says
> explicitly that it is so in C.  It is only with an indirect argument
> that mpi.h can define both C and C++ bindings that I can see C++ code
> not being able to define MPI_ functions.
>
> Note that MyMPI_ was ~exactly~ how I fixed the user's code :-)
>
> Jeff
>
> On Sun, Mar 4, 2012 at 9:39 PM, Fab Tillier <ftillier at microsoft.com> wrote:
>> I don't think defining one's own mpi.h is an issue from a compliance perspective.  However, overloading MPI_Init definitely is - the standard reserves the MPI_ namespace, so if it isn't in the standard, it's not standard compliant.  Now, if they named it MyMPI_Init, it'd be fine.
>>
>> -Fab
>>
>> Jeff Hammond wrote on Sun, 4 Mar 2012 at 18:22:40
>>
>>> I have a user who insists it is MPI-compliant to do the following:
>>>
>>> user file mpi.h, which is included in the application with #include
>>> "mpi.h": ================================== #include <mpi.h>
>>>
>>> <snip>
>>>
>>> void MPI_Init(int argc, char* argv[], int& my_rank, int& mpi_size, int&
>>> Master) {
>>>   MPI::Init(argc, argv);
>>>   my_rank = MPI::COMM_WORLD.Get_rank();
>>>   mpi_size = MPI::COMM_WORLD.Get_size();
>>>   Master = 0;
>>>
>>>   std::cout << "Hello World! I am " << my_rank << " of " << mpi_size
>>> << std::endl;
>>> }
>>>
>>> void MPI_finalize()
>>> {MPI::Finalize();}
>>>
>>> ==================================
>>>
>>> I believe that it is a terrible practice, if not a violation of the
>>> MPI standard to:
>>> (1) define one's own mpi.h, since this may confuse the preprocessor
>>> (or are there precedence rules in the ANSI C standard?) as to which to
>>> include first (especially if CC=mpicc or CXX=mpicxx), and
>>> (2) overload MPI_Init, even if one is using C++ and relying upon C++
>>> name-mangling to avoid a symbol conflict.
>>>
>>> The user believes that the inability to overload MPI_Init in C++ means
>>> that MPI is not compliant with the C++ standard.
>>>
>>> Thanks,
>>>
>>> Jeff
>>>
>>
>>
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>
>
>
> -- 
> Jeff Hammond
> Argonne Leadership Computing Facility
> University of Chicago Computation Institute
> jhammond at alcf.anl.gov / (630) 252-5381
> http://www.linkedin.com/in/jeffhammond
> https://wiki.alcf.anl.gov/old/index.php/User:Jhammond
> https://wiki-old.alcf.anl.gov/index.php/User:Jhammond
>
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