[mpich-discuss] Have constants available in shared library

[Erik Schnetter]

Rajeev

Apologies; I sent an identical request to the OpenMPI developers as
well. I meant the MPICH library here.

In Julia, it is straightforward to call a function in a shared
library, but it is not possible to access constants that are defined
in a C header file, as this would require parsing C code. It would
thus be convenient to access these constant in a different manner,
e.g. by looking at the value of a global variable or constant.

-erik

On Thu, Apr 14, 2016 at 1:50 PM, Thakur, Rajeev <thakur at mcs.anl.gov> wrote:
>> Could you add similar constants to the OpenMPI shared library?
>
> This list is for MPICH. Open MPI has a different mailing list.
>
> In MPICH, these constants are defined in the mpi.h header file.
>
> Rajeev
>
>
>> On Apr 14, 2016, at 9:04 AM, Erik Schnetter <schnetter at gmail.com> wrote:
>>
>> I am one of the maintainers of the MPI wrapper package for Julia
>> <https://github.com/JuliaParallel/MPI.jl>. This package provides Julia
>> language bindings for MPI, essentially wrapping various MPI functions,
>> comparable to what mpi4py <http://pythonhosted.org/mpi4py/> does for
>> Python.
>>
>> It is in Julia straightforward to call C functions in a shared
>> library. The MPI API is standardized, so that part is straightforward.
>> What is not standardized are the values of various constants, such as
>> e.g. MPI_INT, MPI_MAX, or MPI_ANY_TAG.
>>
>> We currently use a cmake function that builds and runs a small
>> executable that outputs the (implementation-specific) values of these
>> constants, and auto-generates Julia code that defines these constants.
>> We do this when the Julia MPI package is installed or updated. This
>> works fine, but I think there could be a better way.
>>
>> The HDF5 library <https://www.hdfgroup.org/HDF5/> puts global
>> constants into the data section of their library, with names derived
>> from the preprocessor constants (with a _g suffix, I believe). This
>> makes it straightforward to access the values of these constants at
>> run time. For example, there exists a constant H5T_NATIVE_INT_g.
>>
>> Could you add similar constants to the OpenMPI shared library? This
>> would simplify wrapping the library.
>>
>> Thanks,
>> -erik
>>
>> --
>> Erik Schnetter <schnetter at gmail.com>
>> http://www.perimeterinstitute.ca/personal/eschnetter/
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-- 
Erik Schnetter <schnetter at gmail.com>
http://www.perimeterinstitute.ca/personal/eschnetter/
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