CODEWITHSUNDEEP
c++cmpibroadcast
Aymeric
Aymeric

Reputation: 199

How to broadcast or send a single value to multiple processes (but not all of them)?

What I'm trying to do is to broadcast a value (my pivot) to a sub domain of my hypercube communicator. So that for example process 0 sends to process 1,2 & 3 when process 4 sends to 4,5 & 6. Does it require that I create communicators before hand or is there a way to do a broadcast/send to selected processes?

int broadcaster = 0;    
if(isBroadcaster)
{
    cout << "rank " << mpiRank << " currentd:" << currentd << " selecting pivot: " << pivot << endl;
    pivot = currentValues[0];
    broadcaster = mpiRank;
}

//TODO: Broadcast to processes 0 to 4 only.
//here, MPI_COMM_HYPERCUBE contains process 0 to 8
MPI_Bcast(&pivot, 1, MPI_INT, broadcaster, MPI_COMM_HYPERCUBE);

Upvotes: 1

Views: 417

Answers (2)

Wesley Bland
Wesley Bland

Reputation: 9072

The best solution probably is to use MPI_COMM_SPLIT to break up your processes into sub-communicators. That is the way of describing communication domains.

The MPI_GROUP object is used for describing groups, but for the most part can't be used to perform communication.

Another option would be to use MPI_ALLTOALLV. That's pretty nasty though, and lots of overkill.

Upvotes: 1

VAndrei
VAndrei

Reputation: 5590

You can use mpi_comm_split but if the group members change too often you have to repeat this.

Another solution (dirty but effective in my opinion) would be broadcasting something like a process mask before issuing a compute command. So process 0 will broadcast an array of 8 bool like values with true being set only for mask1, mask[2], mask[3] ...

Upvotes: 0

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