Re: octave-mpi questions

[John W. Eaton]

On 21-Feb-2003, Martin Siegert <address@hidden> wrote:

| My impression is that MPICH2 is really beta (e.g., the F90 interface does
| not exist yet).

We only need a C interface, so I don't think this matters much.  Other
than missing interfaces, are there serious problems with MPICH2?

| The only MPI-1 compliant way of calling MPI_Init is
| MPI_Init(&argc,&argv);
| The question now is: is there a way to provide octave's command line
| arguments to the mpi_init module?

Sure, they are already available in the argv variable that is defined
when Octave starts.  But this is just a copy in an octave_value
object, so you would need to convert it back to an array of C
character strings.

In the thread starting here:

  http://www.octave.org/octave-lists/archive/help-octave.2001/msg00138.html

a claim was made that the argv/argc passed to MPI_Init must be
pointers to the actual variables passed to main, and that MPI_Init
needs to see them before they are processed by the program that calls
MPI_Init.  The MPI standard may claim that those are requirements, but
so far, no one has been able to explain *why* the standard includes
these requirements.  Also, there was a claim that bad things happen if
the function that calls MPI_Init returns, and I'm not sure whether
that is another limitation of the standard or was simply due to a
buggy implementation.

So, can anyone tell me *why* these things should cause problems?  It
seems to me that we should be able to define  MPI_Init in Octave that
does something like

  mpi_init (argv)

where argv is a cell array of strings that are packaged as appropriate
and passed on to the C MPI_Init.  Then users could pass whatever
arguments they like to the MPI system and we wouldn't have to modify
Octave's main program or argument processing at all (except perhaps we
would need a way start Octave and have it run a function and then
continue processing, so the client processes would know to go into
listener mode, waiting for commands from the server process).

It would also be nice if Octave's mpi_init could start the client
processes, so you wouldn't have to use mpirun (or similar) to do that
when initially starting Octave.

There was another thread about these issues starting here:

  
http://www.octave.org/octave-lists/archive/octave-maintainers.2002/msg00207.html


jwe