[Mpi-22] Another MPI-2.2 attribute ambiguity?

[William Gropp]

Silly me, I missed that.

In Fortran (particularly thinking in terms of Fortran 77, since that  
was the original design), the Fortran callback should be able to do  
things like increment the "extra data" - i.e., if the extra data is a  
counter, the Fortran callback should be able to increment it.  Since  
Fortran 77 has no pointers (and pointers in Fortran 90 aren't the same  
as addresses), having an address is worthless in a Fortran 77  
program.  So if the MPI implementation stores the address of the extra  
data and passes that to the call back (by value, so Fortran sees the  
address of the extra data), users should get what they expect in  
Fortran.

Bill

On May 19, 2009, at 12:22 PM, Iain Bason wrote:

>
> On May 19, 2009, at 1:16 PM, William Gropp wrote:
>
>> MPICH2 passes the value of the extra_state that was saved in the
>> internal storage to the callback routine, which is case 2 (the copy
>> is implicit as the value is passed to the routine and C semantics
>> ensures that the value isn't changed).
>
> But this is the Fortran interface, not the C interface.
>
> Iain
>

William Gropp
Deputy Director for Research
Institute for Advanced Computing Applications and Technologies
Paul and Cynthia Saylor Professor of Computer Science
University of Illinois Urbana-Champaign