MPI C逐行向所有进程子进程发送一个矩阵（MPI_COMM_SPAWN）

Question

I have a parent process and a matrix and I want to create for each line a child process and send it the corresponding line for process.

Parent process code:

int tag = 0;
MPI_Status status;

int random(int n) {
    return rand() % n;
}

float** generate_matrix(int n, int m) {
    int i, j;
    float **x;
    x = (float **) malloc(m * sizeof(float));
    for (i = 0; i < m; i++) {
        x[i] = (float *) malloc(n * sizeof(float));
    }
    for (i = 0; i < m; i++) {
        for (j = 0; j < n; j++) {
            x[i][j] = random(100);
        }
    }
    return x;
}
int main(int argc, char** argv) {

    int my_rank;
    int num_procs;
    MPI_Comm workercomm;
    int n = 4, m = 5;
    float**matrix = generate_matrix(n, m);

    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
    MPI_Comm_size(MPI_COMM_WORLD, &num_procs);

    MPI_Comm_spawn("C:/Users/colegnou/workspace/worker/Debug/worker.exe",
    MPI_ARGV_NULL, m,
    MPI_INFO_NULL, 0, MPI_COMM_SELF, &workercomm, MPI_ERRCODES_IGNORE);

    for (int i = 0; i < m; i++) {
        MPI_Bcast(matrix[i], n, MPI_FLOAT, MPI_ROOT, workercomm);
    }
    MPI_Finalize();
    return 0;
}

And worker code:

int tag = 0;
MPI_Status status;

int main(int argc, char** argv) {

    MPI_Init(&argc, &argv);
    MPI_Comm parent;
    MPI_Comm_get_parent(&parent);
    int myid;
    MPI_Comm_rank(MPI_COMM_WORLD, &myid);

    int n = 4;
    float*vector = (float *) malloc(n * sizeof(float));

    if (parent != MPI_COMM_NULL) {
        MPI_Bcast(vector, n, MPI_FLOAT, MPI_ROOT, parent);
    }
    printf("%d ->", myid);
    for (int i = 0; i < n; i++) {
        printf("%f ", vector[i]);
    }
    printf("\n");

    MPI_Comm_free(&parent);
    free(vector);
    MPI_Finalize();
    return 0;
}

But I expecting every child process to print his corresponding line by line in matrix , instead the output is: ....................................................................................

  4 ->0.000000 0.000000 0.000000 0.000000
    1 ->0.000000 0.000000 0.000000 0.000000
    3 ->0.000000 0.000000 0.000000 0.000000
    0 ->0.000000 0.000000 0.000000 0.000000
    2 ->0.000000 0.000000 0.000000 0.000000

Thnaks!!

Answer 1

In the worker code, you should use root=0 instead of MPI_ROOT .

Feel free to re-read the definition of MPI_Bcast() when an inter-communicator is used https://www.open-mpi.org/doc/v2.1/man3/MPI_Bcast.3.php

Note the allocation of the matrix is incorrect, you should malloc(m * sizeof(float *)) instead.

You should also perform m broadcasts in the worker, unless MPI_Scatter() is what you are looking for (and in that case, you should allocate a contiguous 2D matrix)