[mpich-discuss] Have constants available in shared library

[Balaji, Pavan]

Erik,

I'm curious why you need this to be done in the MPI library (MPICH or Open MPI).  Is creating your own library, that essentially does exactly the same thing (JULIA_MPI_INT_g = MPI_INT), and linking that as well, not an option?

  -- Pavan

> On Apr 14, 2016, at 1:44 PM, Erik Schnetter <schnetter at gmail.com> wrote:
> 
> 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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>> 
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> 
> 
> -- 
> Erik Schnetter <schnetter at gmail.com>
> http://www.perimeterinstitute.ca/personal/eschnetter/
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