[Mpi-forum] behavior of NBC for intracommunicators when root == MPI_PROC_NULL

Jeff Hammond jeff.science at gmail.com
Thu Dec 11 14:29:40 CST 2014

I would hope that the Ianything is matched with a corresponding
Test/Wait* call on every process that calls it.  To allow otherwise
seems pretty odd.

Presumably, if Ibcast is a no-op when root=MPI_PROC_NULL, then the
request can be set to MPI_REQUEST_NULL and thus completing it is

If the standard says that completing a request known to be
MPI_REQUEST_NULL is not required, then I suppose the user can avoid
making the completion call, but I don't like that style.


On Thu, Dec 11, 2014 at 11:30 AM, Fab Tillier <ftillier at microsoft.com> wrote:
> Hi Folks,
> I can’t find anything in the standard document that explains the behavior
> for NBC requests on intercommunicators when root == MPI_PROC_NULL.  Taking
> MPI_Ibcast as an example, what is the output value of request?  Is it
> MPI_REQUEST_NULL?  Is it not set at all?  Is it a valid request that must be
> completed?
> Thanks,
> -Fab
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Jeff Hammond
jeff.science at gmail.com

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