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:

        .....

        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