MPI_Comm_split以及worker_id的關係

第九章利用MPI_Comm_split產生出新的communicator叫做worker_comm

MPI_UNDEFINED: CPU=0的color沒有分類到worker_comm的communicator

//CPU=0

if (!id) {  

  MPI_Comm_split (MPI_COMM_WORLD, MPI_UNDEFINED, id, &worker_comm);

  manager (&argc, &argv, p);

}

//非CPU=0的processors

else {  

  MPI_Comm_split (MPI_COMM_WORLD, 0, id, &worker_comm);

  worker (&argc, &argv, worker_comm);

}

$ mpicc check_worker.c

$ mpirun -np 4 a.out

/* check_worker.c */

#include "stdio.h"

#include <mpi.h>

void manager (int argc, char *argv[], int p) {

  int id;

  MPI_Comm_rank (MPI_COMM_WORLD, &id);

  printf("manager id=%d\n", id);

  fflush (stdout);

}

void worker (int argc, char *argv[], MPI_Comm worker_comm) {

  int id;

  int worker_id;

  MPI_Comm_rank (MPI_COMM_WORLD, &id);

  printf("manager id=%d\n", id);

  fflush (stdout);

  MPI_Comm_rank (worker_comm, &worker_id);

  if (!worker_id) printf("worker id=%d\n", worker_id);

  if (worker_id) printf("worker id=%d\n", worker_id);

  fflush (stdout);

  //printf("%d", worker_id);

}

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

{

  int id, p;  

  MPI_Comm worker_comm; 

  MPI_Init (&argc, &argv);

  MPI_Comm_rank (MPI_COMM_WORLD, &id);

  MPI_Comm_size (MPI_COMM_WORLD, &p);

  if (!id) {  

    MPI_Comm_split (MPI_COMM_WORLD, MPI_UNDEFINED, id, &worker_comm);

    manager (&argc, &argv, p);

  }

  else {  

    MPI_Comm_split (MPI_COMM_WORLD, 0, id, &worker_comm);

    worker (&argc, &argv, worker_comm);

  }

  printf ("%d\n",prime[7]);

  return 0;

}

out:

manager id=0

manager id=1

worker id=0

manager id=2

worker id=1

manager id=3

worker id=2

從螢幕輸出可以發現

CPU1在worker_comm communicator的id變成0

CPU2在worker_comm communicator的id變成1

以此類推