[mpi-21] Ballot 4 proposal: INOUT arguments

[Jeff Squyres]

On Jan 31, 2008, at 8:46 AM, Rolf Rabenseifner wrote:

>> 1. Why do we need to indicate the INOUT status of the back-end MPI
>> object in the language neutral bindings?  All the bindings --
>> regardless of language -- only deal with the MPI handles, not the  
>> back-
>> end MPI objects.
>>
>> 2. Adding qualifiers on what is supposed to happen to the back-end  
>> MPI
>> object would seem to require additional semantics on the back-end MPI
>> object.  Should we really be specifying what the implementation must/
>> must not do with the back-end MPI object?  Who benefits from that?
>
> After all the MPI_BOTTOM discussion and not knowing what future
> languages will bring, I didn't want to remove existing information
> from the standard. An opaque object in MPI consists always
> of two things: the handle and the object itself.
>
> The language independent interface should reflect this.
>
> I thought that especially for the const discussion it would be good
> to see the IN for the handle.

I agree.

> For future HPCS languages, it may be
> also necessary see the INOUT for the object itself.

I guess my point is that the language bindings don't specify anything  
about the object itself anywhere else.

If we also want to specify the behavior of the object, then a) that's  
a huge change (and not one that I'm convinced we need), and b) we need  
to add a second IN/OUT/INOUT to every language-neutral binding  
representing what happens to the object.  Adding it to only a few of  
the bindings doesn't seem consistent to me.


-- 
Jeff Squyres
Cisco Systems