Partitioned communications hang #12969
Description
This issue was initially reported on Stack Overflow at https://stackoverflow.com/questions/79258925/openmpi5-partitioned-communication-with-multiple-neighbors
With the main branch, the following program running on 3 MPI tasks hang:
#include <mpi.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
int main(int argc, char *argv[]) {
MPI_Init(&argc, &argv);
int rank, size;
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
MPI_Comm_size(MPI_COMM_WORLD, &size);
if (size != 3) {
if (rank == 0)
printf("Need 3 workers, you have %d\n", size);
return -1;
}
/*
* Topology
* 0 <-> 1 <-> 2
* */
const int partitions = 1;
const int count = 16;
int buffer[partitions * count];
MPI_Request request[2];
memset(buffer, 0, sizeof(int) * partitions * count);
if (rank == 1) {
for (int i = 0; i < partitions * count; i++) {
buffer[i] = i;
}
}
int nor = 0;
if (rank == 0) {
MPI_Precv_init(buffer, partitions, count, MPI_INT, 1, 0, MPI_COMM_WORLD, MPI_INFO_NULL, &request[nor++]);
} else if (rank == 1) {
MPI_Psend_init(buffer, partitions, count, MPI_INT, 0, 0, MPI_COMM_WORLD, MPI_INFO_NULL, &request[nor++]);
MPI_Psend_init(buffer, partitions, count, MPI_INT, 2, 0, MPI_COMM_WORLD, MPI_INFO_NULL, &request[nor++]);
} else if (rank == 2) {
MPI_Precv_init(buffer, partitions, count, MPI_INT, 1, 0, MPI_COMM_WORLD, MPI_INFO_NULL, &request[nor++]);
}
MPI_Startall(nor, request);
if (rank == 1) {
MPI_Pready(0, request[0]);
MPI_Pready(0, request[1]);
}
MPI_Waitall(nor, request, MPI_STATUS_IGNORE);
MPI_Barrier(MPI_COMM_WORLD);
for (int i = 0; i < nor; i++) {
MPI_Request_free(request + i);
}
MPI_Finalize();
return 0;
}