[Mpi3-tools] Standardized MPI_COMM_WORLD rank environment variable?

Rayson Ho raysonlogin at gmail.com
Tue Apr 24 15:59:04 CDT 2012

On Tue, Apr 24, 2012 at 4:24 PM, William Gropp <wgropp at illinois.edu> wrote:
> Yes, an MPI process need not be an OS process, and there is in fact a long
> history of such implementations, starting (as far as I know) with TMPI.  An
> easy out is to make this optional and only apply when there is such a
> one-to-one mapping of MPI and OS processes.

I believe in those "threaded MPI task" environments, internally inside
the MPI library there is still a way to tell a process (and the thread
group inside that process) on particular host where to start from. I
think it is more straightforward than communicating the RANK during
MPI_Init() from an MPI implementer point of view. So whoever starts
the MPI tasks on a node should be able to set something unique in the

And BTW, thanks William & Rob Ross for sending me the MPITypes library
2 years ago. I played with it for a while and I will eventually go
back to it!


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> Bill
> William Gropp
> Director, Parallel Computing Institute
> Deputy Director for Research
> Institute for Advanced Computing Applications and Technologies
> Paul and Cynthia Saylor Professor of Computer Science
> University of Illinois Urbana-Champaign
> On Apr 24, 2012, at 12:46 PM, John DelSignore wrote:
> I'm not familiar with any implementations where there are multiple MPI
> processes per OS process. I did read Snir's proposal, but I can't say that
> I'm less confused about what it implies relative to an MPI process's rank in
> MPI_COMM_WORLD. Are you saying that a single OS process may have contain
> multiple MPI processes where each MPI process has a unique rank in
> MPI_COMM_WORLD? And therefore, if we try to use the environment to identify
> an OS process's rank in MPI_COMM_WORLD, it would have to be more like a list
> of ranks rather than a single value?
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