[mpiwg-ft] Proposal Feedback

Bland, Wesley B. wbland at anl.gov
Tue Feb 25 09:43:41 CST 2014

On Feb 23, 2014, at 7:20 AM, Jim Dinan <james.dinan at gmail.com> wrote:

> Hi Aurelien,
> > (1) Are the semantics for the MPI probe operations (probe, iprobe, mprobe) well defined?  Including when MPI_ANY_SOURCE is used?
> >
> Yes, they are exactly the same as for normal recv operations. We had a WG phone call issue on mprobe alone, sometime last september,  to verify that it was not problematic.
> We state that non-blocking operations must not raise an error when they are initiated.  We may need an exception to this rule for MPI_Iprobe to state that it has MPI_Test semantics.  An Iprobe could be polling with MPI_ANY_SOURCE and lead to deadlock if it does not return an error.

Hmm, that’s a good point. I guess the probe functions wouldn’t be covered under the text about the completion functions. I guess we do need to add text here. It’s inside the two week deadline so I’m not sure what the right thing to do here would be.

> > (2) For comm_shrink, what happens when the remote group in an intercommunicator becomes empty?  Is it valid to get back an intercommunicator with an empty remote group?
> That’s a pretty bizarre case. It is to be noted that the semantic for the shrink is well defined: the outcome is the same as if the user had called split with colors set to MPI_UNDEFINED at all remote group processes.  From the definition of SPLIT stated page 247, the well defined outcome is that MPI_COMM_NULL is returned when a color is used on only one side of the intercomm.
> Ok, thanks!  Just wanted to make sure that this was defined.
> > (3) In 15.2 (pg. 594:21), can we replace the sentence "always complete in a finite amount of time" with the simpler "eventually complete”?
> I believe the original formulation carries the argument more visibly by being pedantic; but if you feel strongly about it, I don't.
> The wording isn't incorrect, this is just word smithing.  Strong words "always" and "finite" imply something about when a thing will occur, when in fact the semantic is not any stronger than "eventually".  "Eventually" is used for semantics like this in the RMA chapter.
>  ~Jim.
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