/* roll_call.c  check that processors are available  */
#include "mpi.h"
#include <stdio.h>

int main(int argc, char *argv[])
{
  int proc, myid, numprocs;
  int count = 1;
  int tag = 0;
  int master = 0;
  double esec = 0.0;
  int buf[1000];
  MPI_Status status;

  MPI_Init(&argc,&argv);
  MPI_Comm_size(MPI_COMM_WORLD,&numprocs);
  MPI_Comm_rank(MPI_COMM_WORLD,&myid);

  if(myid == 0)
  {
    printf("roll_call.c  numprocs=%d \n", numprocs);
    for(proc=1; proc<numprocs; proc++)
    {
      buf[0] = 10*proc;
      MPI_Send(buf, count, MPI_INT, proc, tag, MPI_COMM_WORLD);
      buf[0] = 0;
      MPI_Recv(buf, count, MPI_INT, proc, tag, MPI_COMM_WORLD, &status);
      printf("proc %d answers with %d \n", proc, buf[0]);  
    }
    esec = MPI_Wtime();
    printf("roll_call.c took %g seconds \n", esec);
  }
  else /* slaves */
  {
    MPI_Recv(buf, count, MPI_INT, master, tag, MPI_COMM_WORLD, &status);  
    printf("proc %d received %d \n", myid, buf[0]);
    buf[0] = 10*buf[0];
    MPI_Send(buf, count, MPI_INT, master, tag, MPI_COMM_WORLD);
  }
  MPI_Finalize();
  return 0; 
}