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

[Jeff Squyres]

This is related to -- but different from -- MPI 2.2 ticket #55  
("MPI-2.1 Cross-language attribute example is wrong").  Explicitly  
adding all the #55 CC members to this mail, plus a few others.

I cannot find any text in MPI-2.1 (e.g., p223-225) describing specific  
behavior regarding the EXTRA_STATE arguments passed to the Fortran  
keyval copy and delete functions (both the ADDRESS_KIND and deprecated  
flavors).  I see two choices:

1. pass the user's original EXTRA_STATE argument by reference to the  
callbacks, or
2. copy the user's original EXTRA_STATE into internal MPI storage and  
pass *that* value by reference to the callbacks

==> Open MPI currently does #1.  What do other implementations do?

I raise this issue because the text does not indicate which way is  
right.  And I just ran across an old Sun test that assumed #2.  But  
our internal copy of the Intel MPI tests assume #1 (to be fair: I have  
no idea if the Intel tests originally assumed #2 and we changed them  
to #1 over time).  Indeed, #2 is actually in-line with the philosophy  
of storing attribute values in internal MPI storage.  E.g.:

   INTEGER foo = 4
   INTEGER bar
   CALL MPI_COMM_SET_ATTR(comm, keyval, foo, ierr)
   foo = 5
   CALL MPI_COMM_GET_ATTR(comm, keyval, bar, flag, ierr)

bar should equal 4, not 5 (right?).

So what does that mean (or imply) about the EXTRA_STATE value passed  
to the Fortran callbacks?


-- 
Jeff Squyres
Cisco Systems