worker.c

/****************************************************************
 ****************************************************************
 ****
 **** This program file is part of the book and course
 **** "Parallel Computing"
 **** by Victor Eijkhout, copyright 2013-6
 ****
 **** spawn_worker.c : worker code for spawn example
 ****
 ****************************************************************
 ****************************************************************
 */

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

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

#define ASSERT(p)                                                              \
  if (!(p)) {                                                                  \
    printf("Assertion failed for proc %d at line %d\n", procno, __LINE__);     \
    return -1;                                                                 \
  }
#define ASSERTm(p, m)                                                          \
  if (!(p)) {                                                                  \
    printf("Message<<%s>> for proc %d at line %d\n", m, procno, __LINE__);     \
    return -1;                                                                 \
  }

  MPI_Comm comm;
  int procno = -1, nprocs;
  MPI_Init(&argc, &argv);
  comm = MPI_COMM_WORLD;
  MPI_Comm_rank(comm, &procno);
  MPI_Comm_size(comm, &nprocs);
  MPI_Comm_set_errhandler(comm, MPI_ERRORS_RETURN);

  int nworkers, workerno;
  MPI_Comm parent;

  // codesnippet spawnworker
  MPI_Comm_size(MPI_COMM_WORLD, &nworkers);
  MPI_Comm_rank(MPI_COMM_WORLD, &workerno);
  MPI_Comm_get_parent(&parent);
  // codesnippet end
  ASSERTm(parent != MPI_COMM_NULL, "No parent!");

  /*
   * To investigate process placement, get host name
   */
  {
    int namelen = MPI_MAX_PROCESSOR_NAME;
    char procname[namelen];
    MPI_Get_processor_name(procname, &namelen);
    printf("[%d] worker process runs on <<%s>>\n", workerno, procname);
  }

  /*
   * Parallel code here.
   * The manager is represented as the process with rank 0 in (the remote
   * group of) MPI_COMM_PARENT.  If the workers need to communicate among
   * themselves, they can use MPI_COMM_WORLD.
   */

  char hostname[256];
  int namelen = 256;
  MPI_Get_processor_name(hostname, &namelen);
  printf("worker %d running on %s\n", workerno, hostname);

  MPI_Finalize();
  return 0;
}