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From: s anwar (sanwar_at_[hidden])
Date: 2006-07-18 12:36:52


I don't think I blamed the implementation in any way in my original email.
My intent is to gain understanding of why my code does/should not work. I
assumed that I was not passing the correct intercommunicator. However, I am
at a loss on how to construct a proper intercommunicator in this case. You
have mentioned that I haven't defined any group to be the root group. Could
you care to elaborate on how can I make a group a root group?

Thanks.

On 7/18/06, Bert Wesarg <wesarg_at_[hidden]> wrote:
>
> Hi,
>
> s anwar wrote:
> > Please see attached source file.
> >
> > According to my understanding of MPI_Comm_spawn(), the intercommunicator
> > returned is the same as it is returned by MPI_Comm_get_parent() in the
> > spawned processes. I am assuming that there is one intercommunicator
> > which contains all the (spawned) child processes as well as the parent
> > process. If this is the case, then why does an MPI_Bcast() using such an
> > intercommunicator wait indefinately?
>
> your code from line 75:
>
> MPI_Bcast(&one_int, 1, MPI_INT, 0, intercomm);
>
> from the mpi 2 standard "7.3.2.1. Broadcast"
>
> "If comm is an intercommunicator, then the call involves all processes in
> the intercommunicator, but with one group (group A) defining the root
> process. All processes in the other group (group B) pass the same value in
> argument root, which is the rank of the root in group A. The root passes
> the value MPI_ROOT in root. All other processes in group A pass the value
> MPI_PROC_NULL in root. Data is broadcast from the root to all processes in
> group B. The receive buffer arguments of the processes in group B must be
> consistent with the send buffer argument of the root."
>
> so, you define no group to be the root group (group A). i don't know what
> schould happen, when no root group is defined, but your code firstly don't
> conform to the standard, so don't blame the implementation first.
>
> by
> bert wesarg
>
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