(j3.2006) Preparing for the Tokyo meeting

[Van Snyder]

On Wed, 2008-11-05 at 12:15 -0800, John Wallin wrote:
> Here is a simple example of an MPI coding horror.  I have to pass a
> Fortran derived type between nodes.
> 
> Here is the code I need to use to even make this exchange possible.
> Please note that a lot of code has been deleted so I don't overwhelm
> everyone's email.[...]
> 
> You might wonder what the 37 is the sphblock_counts.  It is the number
> of double precision numbers in a row within this particular data
> structure.
> 
> The important thing to note is that every time a grad student adds a
> single element to the data structure, you have to alter the block
> counts and sizes by hand.   This leads to huge problems debugging and
> maintaining the code if the base structures are modified.  (And this
> code is the best way I have found for doing it.)

I remarked on this problem before m185, and proposed a trivial addition
to the OPEN statement to allow message passing using I/O statements,
which already know how to do DTIO and asynchronous, in 08-204.  Subgroup
didn't even consider it.

If coarrays are kicked off the train in Tokyo, we really should go back
and look at the directions proposed in 08-204 and 08-205.  At least for
the basic functionality provided by MPI, Fortran I/O applied to message
passing should be far clearer.

Within a single SMP, say a dual quad-core PC, one can already accomplish
what's proposed in 08-204 with a pipe, but I haven't met a system yet
where pipes work across NFS.  08-204 provides syntax for users to hook
to stuff that vendors provide that go beyond NFS.  08-205 provides a way
for users to roll their own.

-- 
Van Snyder                    |  What fraction of Americans believe 
Van.Snyder at jpl.nasa.gov       |  Wrestling is real and NASA is fake?
Any alleged opinions are my own and have not been approved or
disapproved by JPL, CalTech, NASA, the President, or anybody else.