[Mpi-forum] Discussion points from the MPI-<next> discussion today

N.M. Maclaren nmm1 at cam.ac.uk
Fri Sep 21 14:38:00 CDT 2012

On Sep 21 2012, Jeff Hammond wrote:

I said that I wouldn't follow up, but I can't let this pass.

>I only use MPI from C but I have never seen or heard any evidence to
>justify this concern.  Can you state exactly which MPI functions and
>semantics are "seriously incompatible with C89 and/or C99"?  Exactly
>which C compilers do not work with MPI?

Passive one-sided communication, for a start.  I no longer have
access to the sort of systems on which that would fail, and I have
never seen it used.  When I did have such access, I did write code
that caused its underlying assumptions to break, while investigating
problems on the systems I managed.

>At least in C89 and C99, C doesn't have a memory model but instead
>inherits this from the hardware.  I think this ambiguity is a far
>bigger issue than anything MPI nonblocking is doing and somehow C
>manages to be used in many places.

That is total nonsense.  I was involved in both standardisation
efforts, including as a UK expert on that very area.  The model was
defined in terms of sequence points, though C99 also added effective
types.  What you say was true for K&R C, but has not been since.

Nick Maclaren.

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