[Mpi-comments] Use of MPI_DATATYPE_NULL

[Jim Edwards]

There seems to be some ambiguity in the standard with respect to usage of
the MPI_DATATYPE_NULL variable.
It would seem to me that if an MPI routine such as MPI_Send or
MPI_ALLTOALLW has a data count argument of 0
then MPI_DATATYPE_NULL should be an acceptable value for the datatype.
Here is a discussion from several years
ago with openmpi developers.  It references a discussion in the standards
forum but I can no longer find it.

http://lists.mpi-forum.org/mpi-forum/2016/01/3152.php

Would it be possibly to clarify this case in the next iteration of the
standard?


-- 
Jim Edwards

CESM Software Engineer
National Center for Atmospheric Research
Boulder, CO
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