Re: [mpi-21] F90 bindings

[Jeff Squyres <jsquyres@xxxxxxxxx>]

On Dec 7, 2007, at 2:32 PM, Steven Ericsson-Zenith wrote:

> I fear the by virtue of the beast Fortran will have to live with the  
> large number of function profiles. 7 million, however, is  
> surprisingly large. I assume that this is for all the permutations  
> of type.

Yes -- mainly because of the collectives that have 2 choice buffers.   
The math goes something like this:

- 15 fortran intrinsic types
- max of 7 array dimensions
- 50 MPI functions with 1 choice buffer
- 25 MPI functions with 2 choice buffers

Total = (one choice buffer combos) + (two choice buffer combos)
      = (15 * 7 * 50) + (15 * 7 * 25)^2
      = 5,250 + 6,890,625
      = 6,895,875

Yoinks.  :-(

> If that is the case, then it simply is what it is.

Unfortunately, it's not tenable.  There's no F90 compiler that can  
handle ~7M functions in a single module (not even close).  Even if  
they did, I can't imagine trying to compile a large F90 app that has  
"use mpi" all over the place -- the compiler would continually have to  
load ~7M signatures from the mpi module file, search to find the  
desired signature, etc.

In short: 7M signatures is just [way] too many.

Sun's F90 compiler has a "ignore the type" attribute similar to what  
was proposed for NEC.  Others may, too (I'm not a Fortran expert).   
But it doesn't seem good form that the MPI Standard *requires* a  
vendor-specific addition to the F90 compiler in order to work...

--
Jeff Squyres
Cisco Systems