[Mpi3-hybridpm] First cut at slides

[Pavan Balaji]

On 06/22/2013 08:27 AM, Jeff Squyres (jsquyres) wrote:
> On Jun 22, 2013, at 9:03 AM, Pavan Balaji <balaji at mcs.anl.gov> wrote:
>
>> 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).
>
> How so?  I thought slide 13 was fairly explicit about that:
>
> - INIT and FINALIZE still collective
>     - Continue to not specify if they synchronize or not

Ok, thanks.  I might have missed that.

>> 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.
>
> I guess my point is that process A must wait for the *actual*
> finalization in process B (which is the 2nd one), and if Finalize
> synchronizes (which most.. but not all.. MPI implementations do),
> then A will block until B calls the 2nd Finalize.

Eh?  My reading was that they *might* synchronize on every FINALIZE 
call, but will *finalize* only when ref-count is zero.

> But I think I'm coming to the conclusion that if you want to not be
> affected by Finalize-possibly-blocking semantics, then you should
> just call MPI_COMM_DISCONNECT first.

I don't think so.

-- 
Pavan Balaji
http://www.mcs.anl.gov/~balaji