(j3.2006) (SC22WG5.3839) [ukfortran] Ballot on the technical content of the TR

N.M. Maclaren nmm1
Thu Jan 8 10:26:04 EST 2009


On Dec 10 2008, Craig Rasmussen wrote:
>
>> The vast bulk of N1761 doesn't help even existing MPI,
>
>You are correct, the vast bulk of N1761 was designed to target a set  
>of library developers different from MPI.  In fact when it was voted  
>to proceed with improved C interoperability at Delft, I don't recall  
>that MPI was mentioned.  However, the assumed-shape dummy portion of  
>N1761 would allow "real" (i.e., much better) Fortran interfaces to be  
>developed (as I discuss further below).

Actually, that is in dispute. I have indicated why not in previous 
messages, but will attempt to get back to this area when I have time.

>> let alone help MPI to
>> provide a real Fortran 2003 interface.
>
>There are two thrusts regarding new Fortran MPI interfaces.  The  
>official one is simply to provide interfaces that are safe to use,  
>that map as closely as possible to the existing C interfaces and don't  
>require recoding of existing applications.  The other thrust is to  
>provide "real Fortran" MPI interfaces.  ...

Right.  N1761 is marginal on the first, and poor on the second.  That is
why I think that it needs rethinking.

>> It is pretty clear that MPI will
>> continue to say (more-or-less explicitly, as has been done on its  
>> mailing
>> list) "Don't use assumed-shape arrays, because they aren't portable  
>> - stick
>> to explicit-size ones."  I.e. don't use Fortran 90 - stick to  
>> Fortran 77!
>
>I don't want to put words in your mouth but it sounds like you are in  
>favor of the vast majority of parallel Fortran programmers using the  
>old unsafe Fortran 77 interfaces.  (The Fortran 90 interfaces are  
>awful and should be dropped from the MPI standard as far as I'm  
>concerned.)  N1761 provides the mechanisms for both a new 3.0 MPI  
>interface for Fortran that is safe to use and also for "real" Fortran  
>interfaces with vendor independent implementations that take advantage  
>of the full features of Fortran.

No, absolutely NOT!  That is the converse of what I am saying.  What I am
saying is that the above situation (which IS what MPI says, like it or
not) will continue unless the interface is improved enough to encourage
people to make the paradigm jump.

>Frankly, the current Fortran interfaces are embarrassment to the  
>Fortran community.  They are unsafe to use as described in 3 to 4  
>pages of the MPI standard.  I strongly believe that we must fix this  
>situation.  If you don't like the current proposal, please suggest an  
>alternative that meet the requirements of the MPI community.

I shall try to.  But I have been away and have some urgent, major work
to do.


Regards,
Nick Maclaren,
University of Cambridge Computing Service,
New Museums Site, Pembroke Street, Cambridge CB2 3QH, England.
Email:  nmm1 at cam.ac.uk
Tel.:  +44 1223 334761    Fax:  +44 1223 334679




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