[Mpi-22] MPI_Aint/MPI_ADDRESS_KIND equivalence and ticket #18

[Jeff Squyres]

On Mar 9, 2009, at 2:34 PM, Rajeev Thakur wrote:

> Address-sized variables in MPI can be passed from C to Fortran or vice
> versa, and I know of no c2f or f2c conversion functions for them. So  
> I think
> MPI_Aint and integer (kind=MPI_ADDRESS_KIND) are assumed to be of  
> the same
> size at least implicitly.
>

I agree.  Should we state this explicitly somewhere (if we didn't  
already)?

>
> Rajeev
>
>
> > -----Original Message-----
> > From: mpi-22-bounces_at_[hidden]
> > [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Dave  
> Goodell
> > Sent: Friday, March 06, 2009 1:09 PM
> > To: MPI 2.2
> > Subject: [Mpi-22] MPI_Aint/MPI_ADDRESS_KIND equivalence and ticket  
> #18
> >
> > At the last meeting in San Jose, Rolf brought up a good point w.r.t.
> > ticket #18 [1].  Part of the proposal for ticket #18 is to add
> > MPI_AINT and MPI_OFFSET types corresponding to MPI_Aint/
> > MPI_ADDRESS_KIND and MPI_Offset/MPI_OFFSET_KIND language types.
> > Rolf's point was that it isn't defined in the standard
> > whether or not
> > MPI_Aint and INTEGER(KIND=MPI_ADDRESS_KIND) are exactly the same
> > type.  Obviously we cannot define a new predefined datatype
> > corresponding to two different language types.  I believe
> > Rolf's view
> > (correct me if I'm misrepresenting you, Rolf) was that the
> > forum ought
> > to make their equivalence explicit, irrespective of what
> > happens with
> > ticket #18.  I'm ambivalent about this issue, but I need a
> > resolution
> > on it in order to get #18 into a final voteable state.
> >
> > So the larger question to the Forum is: Are these types exactly the
> > same between the two languages?
> >
> > Looking at MPICH2 it seems that we try to make them the same
> > size but
> > there are some convoluted code paths in the build logic that might
> > result in different sizes.  I would not consider this to be a
> > compelling argument that they are permitted to differ because the
> > logic in question may simply be buggy or never exercised.
> > Does anyone
> > have an example from other MPI implementations where the
> > types do/may
> > differ?  Do any Fortran experts out there know of instances where
> > MPI_ADDRESS_KIND would be different from MPI_Aint?
> >
> > As for the impact on ticket #18, there are several ways to deal with
> > this:
> >
> > 1) If the Forum decides that the types are always equivalent,
> > add text
> > to that effect (probably in a separate ticket) and otherwise stick
> > with the current proposal.
> > 2) If the Forum decides that the type equivalence is undefined, drop
> > the new MPI_AINT/MPI_OFFSET types from the proposal.
> > 3) If the Forum decides that the type equivalence is
> > undefined, create
> > four types instead of just two: MPI_AINT, MPI_OFFSET, MPI_F_AINT,
> > MPI_F_OFFSET (or some such names).
> > 4) If the Forum decides that the type equivalence is undefined, make
> > MPI_AINT/MPI_OFFSET only correspond to the C types.
> >
> > I'm inclined towards either #1 or #2, depending on what the Forum
> > decides about the type equivalence.  I also can separate the
> > MPI_AINT/
> > MPI_OFFSET types out into a separate ticket if this becomes too
> > contentious of an issue, but I'd like to keep it together for now
> > since the text changes are easier to describe correctly in just one
> > place.
> >
> > -Dave
> >
> > [1] https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/18
> > _______________________________________________
> > mpi-22 mailing list
> > mpi-22_at_[hidden]
> > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-22
> >
>
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-- 
Jeff Squyres
Cisco Systems