[Mpi3-tools] Standardized MPI_COMM_WORLD rank environment variable?

[Jeffrey Squyres]

On Apr 24, 2012, at 4:24 PM, William Gropp 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.

That would defeat the use-case that I proposed (tools needing a unique ID for the process).  Other options:

- provide a comma-delimited list of MCW ranks in the OS process
- provide the lowest (or highest? or median? or ...?) MCW rank in the OS process
- ...some other unique value

Any kind of unique value would allow the tool to have a unique, safe filename.

The MPI (or runtime) is in a good position to provide this unique value because it has global knowledge of the entire MPI job, where the tool does/may not.

-- 
Jeff Squyres
jsquyres at cisco.com
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