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

#define NUM_SLAVES	2		/* create NUM_SLAVES processes	*/


int main (int argc, char *argv[])
{
  MPI_Comm COMM_ALL_PROCESSES,		/* intra-communicator		*/
	   COMM_CHILD_PROCESSES,	/* inter-communicator		*/
	   COMM_PARENT_PROCESSES;	/* inter-communicator		*/
  int	   ntasks_world,		/* # of tasks in MPI_COMM_WORLD	*/
	   ntasks_local,		/* COMM_CHILD_PROCESSES local	*/
	   ntasks_remote,		/* COMM_CHILD_PROCESSES remote	*/
	   ntasks_all,			/* tasks in COMM_ALL_PROCESSES	*/
	   mytid_world,			/* my task id in MPI_COMM_WORLD	*/
	   mytid_all,			/* id in COMM_ALL_PROCESSES	*/
	   namelen;			/* length of processor name	*/
  char	   processor_name[MPI_MAX_PROCESSOR_NAME];

  MPI_Init (&argc, &argv);
  MPI_Comm_rank (MPI_COMM_WORLD, &mytid_world);
  /* At first we must decide if this program is executed from a parent
   * or child process because only a parent is allowed to spawn child
   * processes (otherwise the child process with rank 0 would spawn
   * itself child processes and so on). "MPI_Comm_get_parent ()"
   * returns the parent inter-communicator for a spawned MPI rank and
   * MPI_COMM_NULL if the process wasn't spawned, i.e. it was started
   * statically via "mpiexec" on the command line.
   */
  MPI_Comm_get_parent (&COMM_PARENT_PROCESSES);
  if (COMM_PARENT_PROCESSES == MPI_COMM_NULL)
  {
    /* All parent processes must call "MPI_Comm_spawn ()" but only
     * the root process (in our case the process with rank 0) will
     * spawn child processes. All other processes of the
     * intra-communicator (in our case MPI_COMM_WORLD) will ignore
     * the values of all arguments before the "root" parameter.
     */
    if (mytid_world == 0)
    {
      printf ("Parent process 0: I create %d slave processes\n",
	      NUM_SLAVES);
    }
    MPI_Comm_spawn (argv[0], MPI_ARGV_NULL, NUM_SLAVES,
		    MPI_INFO_NULL, 0, MPI_COMM_WORLD,
		    &COMM_CHILD_PROCESSES, MPI_ERRCODES_IGNORE);
  }
  /* Merge all processes into one intra-communicator. The "high" flag
   * determines the order of the processes in the intra-communicator.
   * If parent and child processes use the same flag the order may
   * be arbitray otherwise the processes with "high == 0" will have
   * a lower rank than the processes with "high == 1".
   */
  if (COMM_PARENT_PROCESSES == MPI_COMM_NULL)
  {
    /* parent processes							*/
    MPI_Intercomm_merge (COMM_CHILD_PROCESSES, 0, &COMM_ALL_PROCESSES);
  }
  else
  {
    /* spawned child processes						*/
    MPI_Intercomm_merge (COMM_PARENT_PROCESSES, 1, &COMM_ALL_PROCESSES);
  }
  MPI_Comm_size	(MPI_COMM_WORLD, &ntasks_world);
  MPI_Comm_size (COMM_ALL_PROCESSES, &ntasks_all);
  MPI_Comm_rank (COMM_ALL_PROCESSES, &mytid_all);
  MPI_Get_processor_name (processor_name, &namelen);
  /* With the following printf-statement every process executing this
   * code will print some lines on the display. It may happen that the
   * lines will get mixed up because the display is a critical section.
   * In general only one process (mostly the process with rank 0) will
   * print on the display and all other processes will send their
   * messages to this process. Nevertheless for debugging purposes
   * (or to demonstrate that it is possible) it may be useful if every
   * process prints itself.
   */
  if (COMM_PARENT_PROCESSES == MPI_COMM_NULL)
  {
    MPI_Comm_size	 (COMM_CHILD_PROCESSES, &ntasks_local);
    MPI_Comm_remote_size (COMM_CHILD_PROCESSES, &ntasks_remote);
    printf ("\nParent process %d running on %s\n"
	    "    MPI_COMM_WORLD ntasks:              %d\n"
	    "    COMM_CHILD_PROCESSES ntasks_local:  %d\n"
	    "    COMM_CHILD_PROCESSES ntasks_remote: %d\n"
	    "    COMM_ALL_PROCESSES ntasks:          %d\n"
	    "    mytid in COMM_ALL_PROCESSES:        %d\n",
	    mytid_world, processor_name, ntasks_world, ntasks_local,
	    ntasks_remote, ntasks_all, mytid_all);
  }
  else
  {
    printf ("\nChild process %d running on %s\n"
	    "    MPI_COMM_WORLD ntasks:              %d\n"
	    "    COMM_ALL_PROCESSES ntasks:          %d\n"
	    "    mytid in COMM_ALL_PROCESSES:        %d\n",
	    mytid_world, processor_name, ntasks_world, ntasks_all,
	    mytid_all);
  }
  MPI_Finalize ();
  return EXIT_SUCCESS;
}