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

[Jeff Hammond]

On Fri, Sep 21, 2012 at 1:19 PM, N.M. Maclaren <nmm1 at cam.ac.uk> wrote:
> MPI had no option but to go outside the Fortran and C standards for
> choice arguments (in the former) and non-blocking transfer for both, but
> both standards have been updated to enable those aspects of MPI to
> operate cleanly (though, in the case of C, it's the interpretation, not
> the wording).  But it is very disturbing the way that MPI has started to
> specify facilities that are seriously incompatible with both language
> standards and many implementations of them.

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?

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.

The notion that MPI nonblocking send/recv are seriously incompatible
with the C language and its implementation in a reasonable C compiler
(e.g. GCC) is completely inconsistent with enormous quantities of
empirical evidence and sounds like "the sky is falling!" to me.

Jeff

-- 
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/parts/index.php/User:Jhammond