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Subject: Re: [OMPI users] Problem with MPI_Barrier (Inter-communicator)
From: Edgar Gabriel (gabriel_at_[hidden])
Date: 2012-04-04 16:04:44


did you try to start the program with the --mca coll ^inter switch that
I mentioned? Collective dup for intercommunicators should work, its
probably again the bcast over a communicator of size 1 that is causing
the hang, and you could avoid it with the flag that I mentioned above.

Also, if you could attach your test code, that would help in hunting
things down.

Thanks
Edgar

On 4/4/2012 2:18 PM, Thatyene Louise Alves de Souza Ramos wrote:
> Hi there.
>
> I've made some tests related to the problem reported by Rodrigo. And I
> think, I'd rather be wrong, that /collective calls like Create and Dup
> do not work with Inter communicators. I've try this in the client group:/
>
> *MPI::Intercomm tmp_inter_comm;*
> *
> *
> *tmp_inter_comm = server_comm.Create (server_comm.Get_group().Excl(1,
> &rank));*
> *
> *
> *if(server_comm.Get_rank() != rank)*
> *server_comm = tmp_inter_comm.Dup();*
> *else*
> *server_comm = MPI::COMM_NULL;*
> *
> *
> The server_comm is the original inter communicator with the server group.
>
> I've noticed that the program hangs in the Dup call. It seems that the
> tmp_inter_comm created without one process still has this process,
> because the other processes are waiting for it call the Dup too.
>
> What do you think?
>
> On Wed, Mar 28, 2012 at 6:03 PM, Edgar Gabriel <gabriel_at_[hidden]
> <mailto:gabriel_at_[hidden]>> wrote:
>
> it just uses a different algorithm which avoids the bcast on a
> communicator of 1 (which is causing the problem here).
>
> Thanks
> Edgar
>
> On 3/28/2012 12:08 PM, Rodrigo Oliveira wrote:
> > Hi Edgar,
> >
> > I tested the execution of my code using the option -mca coll ^inter as
> > you suggested and the program worked fine, even when I use 1 server
> > instance.
> >
> > What is the modification caused by this parameter? I did not find an
> > explanation about the utilization of the module coll inter.
> >
> > Thanks a lot for your attention and for the solution.
> >
> > Best regards,
> >
> > Rodrigo Oliveira
> >
> > On Tue, Mar 27, 2012 at 1:10 PM, Rodrigo Oliveira
> > <rsilva.oliveira_at_[hidden] <mailto:rsilva.oliveira_at_[hidden]>
> <mailto:rsilva.oliveira_at_[hidden]
> <mailto:rsilva.oliveira_at_[hidden]>>> wrote:
> >
> >
> > Hi Edgar.
> >
> > Thanks for the response. I just did not understand why the Barrier
> > works before I remove one of the client processes.
> >
> > I tryed it with 1 server and 3 clients and it worked properly.
> After
> > I removed 1 of the clients, it stops working. So, the removal is
> > affecting the functionality of Barrier, I guess.
> >
> > Anyone has an idea?
> >
> >
> > On Mon, Mar 26, 2012 at 12:34 PM, Edgar Gabriel
> <gabriel_at_[hidden] <mailto:gabriel_at_[hidden]>
> > <mailto:gabriel_at_[hidden] <mailto:gabriel_at_[hidden]>>> wrote:
> >
> > I do not recall on what the agreement was on how to treat
> the size=1
> >
> >
> >
> >
> >
> > _______________________________________________
> > users mailing list
> > users_at_[hidden] <mailto:users_at_[hidden]>
> > http://www.open-mpi.org/mailman/listinfo.cgi/users
>
>
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-- 
Edgar Gabriel
Associate Professor
Parallel Software Technologies Lab      http://pstl.cs.uh.edu
Department of Computer Science          University of Houston
Philip G. Hoffman Hall, Room 524        Houston, TX-77204, USA
Tel: +1 (713) 743-3857                  Fax: +1 (713) 743-3335