[MPI3 Fortran] MPI non-blocking transfers

Bill Long longb at cray.com
Wed Jan 21 16:29:59 CST 2009

N.M. Maclaren wrote:
> Eh?  No proposal so far has been completely different.  The way that MPI
> is specified, there is no difference between requiring an ASYNCHRONOUS
> attribute and requiring and ASYNCH_EXTERNAL one.  Both need a minor 
> change.

More precisely, no proposals since you have joined the discussion.  
There have been proposals in the past that would create a "real" Fortran 
interface for MPI that was completely different from the C interface.  
It would use assumed-shape dummies. (Solves the copy-in/copy-out 
problem.)  With the associated descriptors, a large number of the 
arguments to MPI routines could be dropped.  (Improves on the difficulty 
of use problem and reduces coding mistakes.)

> As someone with experience of installing and supporting multiple 
> different
> MPI's on multiple different systems, it is thoroughly undesirable.  
> Almost
> every compiler requires special flags to work together with MPI 
> non-blocking
> transfers, those options are only sometimes documented and then typically
> in a place that only the most expert administrator will find (and no 
> users
> that I have met).  That is a BIG problem.

I agree that there are problems with the current arrangement.  I just 
was pointing out that these problems have been solved in some way or 
another (perhaps not elegantly).  MPI *does* work. Every day in real 
production.   It it didn't, there would be no motivation to continue 
improving it.


Bill Long                                   longb at cray.com
Fortran Technical Support    &              voice: 651-605-9024
Bioinformatics Software Development         fax:   651-605-9142
Cray Inc., 1340 Mendota Heights Rd., Mendota Heights, MN, 55120


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