问MPI_Comm_size总是在代码块上返回1

EN

#include <iostream>
#include "mpi.h"
#include <string>

using namespace std;

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

    int  my_rank;       /* rank of process */
    int  noProcesses;   /* number of processes */
    int  nameSize;      /* length of name */

    char computerName[MPI_MAX_PROCESSOR_NAME];

    MPI_Init(&argc, &argv); /*START MPI */

    /*Determines the size of the group associated with a communicator */
    MPI_Comm_size(MPI_COMM_WORLD, &noProcesses);

    /*Determines the rank of the calling process in the communicator*/
    MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);

    /*Gets the name of the processor*/
    MPI_Get_processor_name(computerName, &nameSize);

    printf("Hello from process %d of %d processor on %s\n", my_rank, noProcesses, computerName);

    MPI_Finalize(); /* EXIT MPI */

    return 0;
}