[Mpi3-hybridpm] First cut at slides

Pavan Balaji balaji at mcs.anl.gov
Sat Jun 22 08:03:38 CDT 2013

Hi Jeff,

Thanks.  The slides seem to be confusing collective vs. synchronizing. 
I think you mean to say that INIT/FINALIZE are always collective, and 
they *might* be synchronizing (though we expect most implementations to 
not be synchronizing when they are not actually initializing or finalizing).

Also, doesn't IS_THREAD_MAIN need to be thread safe as well, like 

#pragma omp parallel for
for (i = 0 to gazillion) {
	if (IS_THREAD_MAIN()) {

I agree with JeffH that CONNECT/DISCONNECT is not a problem.  MPI cannot 
actually finalize in the first call to MPI_FINALIZE in your example, 
since the ref-count didn't reach zero.

  -- Pavan

On 06/18/2013 07:47 AM, Jeff Squyres (jsquyres) wrote:
> For comment...
> Here's a first cut at slides that we discussed yesterday.  It's meant to be a rollup of all the issues surrounding:
> - thread safe INIT / FINALIZE
> - reference-counting INIT / FINALIZE
> - nesting of INIT / FINALIZE
> I discovered a new issue when making up these slides: with ref-counting INIT/FINALIZE, since INIT/FINALIZE are collective, we have the same ref counts in all procs in MPI_COMM_WORLD.  But the ref counts may be different in non-COMM_WORLD connected processes.  What happens when they try to finalize over all connected processes?  See slide 12 for an example.  I'm not sure what the right answer is yet.
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Pavan Balaji

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