On Oct 7, 2004, at 2:17 AM, Vinod Kannan wrote:
> I want a single parent process to spawn off say 4 child processes
> (preferably using spawn and not spawn_multiple). I then want the child
> processes to be communicate with
Random note: the output of SPAWN and SPAWN_MULTIPLE are the same: an
intecommunicator spanning *all* the children and parents. The main
difference between SPAWN and SPAWN_MULTIPLE is that SPAWN only allows
one command line (i.e., argv). SPAWN_MULTIPLE allows multiple command
lines (i.e., you can specify multiple different executables --
MPMPD-style). Regardless of which you use, the processes that are
started are all in one MPI_COMM_WORLD after they finish MPI_INIT.
> each other using an individual communicator for each pair of
> children. Say process parent spawns of child1, child2, child3. I want
> child1 to be able to communicate with child2 using an
> intercommunicator (or an intracommunicator with only child1 and child2
> as members) and similarly child2<->child3 and child3<->child1.
Yes, this is possible.
> From what I understand of Communicators, I can use Spawn_multiple to
> create the children and then use Intercomm_create passing COMM_SELF &
> COMM_WORLD with peer group leaders rank as the one who I want to
> communicate with. Am I correct? Is there a more elegant and insulated
> way than using Spawn_multiple?
In your example, SPAWN_MULTIPLE will return a single intercomm with two
groups:
group 1: parent
group 2: child1, child2, child3
There are a variety of ways to split this into process-pair
communicators. One way, for example, is to INTERCOMM_MERGE this down
to an intracommunicator and then creatively use an ordered sequence of
MPI_COMM_SPLIT's to generate the process-pair comms (note that if you
put in MPI_UNDEFINED for the color, that process will not be included
in the output communicator). For example, use the following color
values for COMM_SPLIT:
time parent child1 child2 child3
0 UNDEFINED 1 1 UNDEFINED
1 UNDEFINED 1 UNDEFINED 1
2 UNDEFINED UNDEFINED 1 1
Hope that helps.
--
{+} Jeff Squyres
{+} jsquyres_at_[hidden]
{+} http://www.lam-mpi.org/
|
