Open MPI logo

Open MPI User's Mailing List Archives

  |   Home   |   Support   |   FAQ   |   all Open MPI User's mailing list

From: Bert Wesarg (wesarg_at_[hidden])
Date: 2006-07-18 12:57:06


hi,

yes sorry for my first reply, my words were to rough.

a bcast for a intercomm works this way (in your words):

- your masters want to send a buffer to your slaves
- one of the masters must provide the MPI_ROOT as root in the MPI_BCAST call
- all slaves must provide the rank of this MPI_ROOT as the root argument
- all others ranks from the masters, must provide MPI_PROC_NULL as root

so the buffer will be send from MPI_ROOT to all slaves

if this isn't that clear, you should understand the concept of mpi
intercomms. a good starting point could be the standard:
http://www.mpi-forum.org/docs/mpi-11-html/node111.html

by the way:
* your one_int is never intitialized
* i don't know if the MPI_COMM_SELF is the right comm for the MPI_COMM_SPAWN

by
bert wesarg

s anwar wrote:
> 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]
> <mailto: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 <http://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
>
> _______________________________________________
> users mailing list
> users_at_[hidden] <mailto:users_at_[hidden]>
> http://www.open-mpi.org/mailman/listinfo.cgi/users
>
>
>
> ------------------------------------------------------------------------
>
> _______________________________________________
> users mailing list
> users_at_[hidden]
> http://www.open-mpi.org/mailman/listinfo.cgi/users