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Subject: Re: [OMPI users] How to specify hosts for MPI_Comm_spawn
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2008-08-04 10:02:57

On Aug 4, 2008, at 12:59 AM, Mark Borgerding wrote:

>> You should be able to merge each child communicator from each
>> accept thread into a global comm anyway.
> Can you elaborate? I am struggling to see how to implement this. A
> pointer to sample code would be helpful.

> Specifically, I'd like to be able to have a single process merge/
> join/aggregate a bunch of intercommunicators into one group and have
> a single communicator for it. FWIW, the intercommunicators are
> point-to-point from several calls to MPI_Comm_join.

I *think* George Bosilca sent some sample code about this across one
of the OMPI lists (users or devel) a long time ago. I'm not 100% sure
about that, though...

I unfortunately forget the trick that he used. :-\

> MPI_Group_union looks promising, but I cannot see any way of
> retrieving the communicator given a group.

A communicator contains a group, not the other way around. You can
make a communicator from a group, though (see MPI_COMM_CREATE), but I
don't think it'll do what you want in this case.

Jeff Squyres
Cisco Systems