[MPI3 Fortran] Issues with Fortran bindings for MPI_Pcontrol

[N.M. Maclaren]

On Apr 14 2013, Schulz, Martin wrote:
>
> We ran into this, when one developer added Pcontrol calls with ierr 
> arguments, which led to a seg fault and then he pointed to the statement 
> that all MPI routines require that argument.
>
> We (Jeff S., Dave G., Bill, and I) had a brief discussion on this and it 
> turns out that MPICH and Open MPI actually implement this differently: 
> MPICH includes ierr (following the general rule) and Open MPI does not 
> (following the specified prototype). This does cause problems for codes 
> that are used on both implementations (as we had in our case that led to 
> this discussion) and hence breaks portability.
>
> The two options seem to be to either change the prototype or allow for 
> exceptions to the general rule and there are obvious pros and cons for 
> either option. That's why we thought it would be better to get both 
> working groups involved.
>
>Any comments or other good ideas on how to fix this?

My main comment isn't particularly helpful for a solution, and is
probably well-known.  When I first looked at MPI_Pcontrol, I tried to
work out what it could be used for, and failed.  If anyone is writing a
PMPI-based tool and needs programmatic control, it is both unlikely to
be just a single integer and is absolutely trivial to provide extra
tool-dependent functions.  Because MPI_Pcontrol had no defined semantics
in MPI 2.2, it couldn't be used by any program that wants to interoperate
with arbitrary PMPI-based tools.  So there is unlikely to be a significant
amount of old code using it, and changes should not be a big deal.

I would favour restoring IERR as an optional argument.


Regards,
Nick Maclaren.