Hello,
I'm trying to use the neighborhood collective communication capabilities
(MPI_Ineighbor_x) of MPI coupled with the distributed graph constructor
(MPI_Dist_graph_create_adjacent) but I'm encountering a segmentation fault
on a test case.
I have attached a 'working' example where I create a MPI communicator with
a simple distributed graph topology where Rank 0 contains Node 0 that
communicates bi-directionally (receiving from and sending to) with Node 1
located on Rank 1. I then attempt to send integer messages using the
neighborhood collective MPI_Ineighbor_alltoall. The program run with the
command 'mpirun -n 2 ./simpleneighborhood' compiled with the latest
OpenMPI (1.10.2) encounters a segmentation fault during the non-blocking
call. The same program compiled with MPICH (3.2) runs without any problems
and with the expected results. To muddy the waters a little more, the same
program compiled with OpenMPI but using the blocking neighborhood
collective, MPI_Neighbor_alltoall, seems to run just fine as well.
I'm not really sure at this point if I'm making a simple mistake in the
construction of my test or if something is more fundamentally wrong. I
would appreciate any insight into my problem!
Thanks ahead of the time for help and let me know if I can provide anymore
information.
Sincerely,
Jun
#include <mpi.h>
#include <iostream>
int main (int argc, char* argv[]) {
MPI_Init(nullptr, nullptr);
//--> Connect graph to my mpi communicator
bool reorder = false;
int indegree = 1;
int outdegree = 1;
int sources[indegree];
int sweights[indegree];
int destinations[outdegree];
int dweights[outdegree];
int my_rank;
MPI_Comm_rank(MPI_COMM_WORLD, &my_rank); //get my rank
if (my_rank == 0) {
sources[0] = 1;
sweights[0] = 1;
destinations[0] = 1;
dweights[0] = 1;
}else if (my_rank == 1) {
sources[0] = 0;
sweights[0] = 1;
destinations[0] = 0;
dweights[0] = 1;
}
MPI_Info mpi_info = MPI_INFO_NULL;
MPI_Info_create(&mpi_info);
MPI_Comm mpi_comm_with_graph;
MPI_Dist_graph_create_adjacent(MPI_COMM_WORLD, indegree, sources,
sweights, outdegree,
destinations, dweights,
mpi_info, reorder, &mpi_comm_with_graph);
MPI_Comm_rank(mpi_comm_with_graph, &my_rank); //get my rank
//----------------------------------------------------------------------------
//---> Send and receive messages
int send_number[1];
int recv_number[1];
if (my_rank == 0) {
send_number[0] = 123;
recv_number[0] = -1;
}else if (my_rank == 1) {
send_number[0] = 456;
recv_number[0] = -1;
}
MPI_Request request_array[1];
request_array[0] = MPI_REQUEST_NULL;
int error_code = MPI_Ineighbor_alltoall
(send_number, 1, MPI::INT,
recv_number, 1, MPI::INT,
mpi_comm_with_graph, request_array);
MPI_Status status[1];
MPI_Wait(request_array, status);
MPI_Finalize();
std::cout << "Rank : " << my_rank << " send of " << send_number[0] << "\n";
std::cout << "Rank : " << my_rank << " recv of " << recv_number[0] << "\n";
return 0; //--> End simulation
}// End Main
