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

[Anthony Skjellum]

Shouldn't it just be a trivial request -- why map to null ? - shortcut should of course happen internally but the request should be valid --- undesirable side effects possible Imho with a literal mapping !

Anthony Skjellum, PhD
205-807-4968


> On Dec 11, 2014, at 3:30 PM, Jeff Hammond <jeff.science at gmail.com> wrote:
> 
> 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
> trivial.
> 
> 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.
> 
> Jeff
> 
>> 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
> http://jeffhammond.github.io/
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