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Subject: Re: [OMPI users] Problem with MPI_Barrier (Inter-communicator)
From: Edgar Gabriel (gabriel_at_[hidden])
Date: 2012-03-20 10:47:00


do you have by any chance the actual or a small reproducer? It might be
much easier to hunt the problem down...

Thanks
Edgar

On 3/19/2012 8:12 PM, Rodrigo Oliveira wrote:
> Hi there.
>
> I am facing a very strange problem when using MPI_Barrier over an
> inter-communicator after some operations I describe bellow:
>
> 1) I start a server calling mpirun.
> 2) The server spawns 2 copies of a client using MPI_Comm_spawn, creating
> an inter-communicator between the two groups. The server group with 1
> process (lets name it as A) and the client group with 2 processes (group B).
> 3) After that, I need to detach one of the processes (rank 0) in group B
> from the inter-communicator AB. To do that I do the following steps:
>
> Server side:
> .....
> tmp_inter_comm = client_comm.Create ( client_comm.Get_group ( ) );
> client_comm.Free ( );
> client_comm = tmp_inter_comm;
> .....
> client_comm.Barrier();
> .....
>
> Client side:
> ....
> rank = 0;
> tmp_inter_comm = server_comm.Create ( server_comm.Get_group (
> ).Excl ( 1, &rank ) );
> server_comm.Free ( );
> server_comm = tmp_inter_comm;
> .....
> if (server_comm != MPI::COMM_NULL)
> server_comm.Barrier();
>
>
> The problem: everything works fine until the call to Barrier. In that
> point, the server exits the barrier, but the client at the group B does
> not. Observe that we have only one process inside B, because I used Excl
> to remove one process from the original group.
>
> p.s.: This occurs in the version 1.5.4 and the C++ API.
>
> I am very concerned about this problem because this solution plays a
> very important role in my master thesis.
>
> Is this an ompi problem or am I doing something wrong?
>
> Thanks in advance
>
> Rodrigo Oliveira
>
>
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