[Mpi3-tools] Standardized MPI_COMM_WORLD rank environment variable?

Dries Kimpe dkimpe at mcs.anl.gov
Tue Apr 24 16:36:41 CDT 2012

* Jeffrey Squyres <jsquyres at cisco.com> [2012-04-24 16:52:55]:

> 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.

What about a tmpnam for MPI then :-)

No need to bring details like rank->thread->process mapping into this if
all you want is a guaranteed unique filename among the MPI ranks of the


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