mpich/examples/spawn_merge_parent.c

/*
 * Copyright (C) by Argonne National Laboratory
 *     See COPYRIGHT in top-level directory
 */

#include <stdio.h>
#include "mpi.h"

int main(int argc, char *argv[])
{
    char str[10];
    int err = 0, errcodes[256], rank, rank1, nprocs;
    MPI_Comm intercomm1, intercomm2, intracomm;

    MPI_Init(&argc, &argv);

    MPI_Comm_size(MPI_COMM_WORLD, &nprocs);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank1);

    if (nprocs != 2) {
        printf("Run this program with 2 processes\n");
        MPI_Abort(MPI_COMM_WORLD, 1);
    }

    if (rank1 == 0) {
        printf("Parents spawning 2 children...\n");
        fflush(stdout);
    }

    err = MPI_Comm_spawn("spawn_merge_child1", MPI_ARGV_NULL, 2,
                         MPI_INFO_NULL, 1, MPI_COMM_WORLD, &intercomm1, errcodes);
    if (err)
        printf("Error in MPI_Comm_spawn\n");

    if (rank1 == 0) {
        printf("Parents and children merging to form new intracommunicator...\n");
        fflush(stdout);
    }

    MPI_Intercomm_merge(intercomm1, 0, &intracomm);

    if (rank1 == 0) {
        printf("Merged parents spawning 2 more children and communicating with them...\n");
        fflush(stdout);
    }

    err = MPI_Comm_spawn("spawn_merge_child2", MPI_ARGV_NULL, 2,
                         MPI_INFO_NULL, 2, intracomm, &intercomm2, errcodes);
    if (err)
        printf("Error in MPI_Comm_spawn\n");

    MPI_Comm_rank(intercomm2, &rank);

    if (rank == 2) {
        err = MPI_Recv(str, 3, MPI_CHAR, 1, 0, intercomm2, MPI_STATUS_IGNORE);
        printf("Parent received from child: %s\n", str);
        fflush(stdout);

        err = MPI_Send("bye", 4, MPI_CHAR, 1, 0, intercomm2);
    }

    MPI_Finalize();

    return 0;
}