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

const int tag = 42;         /* Message tag */
  int   id, ntasks, source_id, err, i;
  MPI_Status status;
  char msg[80];                /* Message array */

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


  err = MPI_Init(&argc, &argv); /* Initialize MPI */
  if (err != MPI_SUCCESS) {
    printf("MPI_init failed!\n");
    exit(1);
  }

  err = MPI_Comm_size(MPI_COMM_WORLD, &ntasks); /* Get nr of tasks */
  if (err != MPI_SUCCESS) {
    printf("MPI_Comm_size failed!\n");
    exit(1);
  }

  err = MPI_Comm_rank(MPI_COMM_WORLD, &id);    /* Get id of this process */
  if (err != MPI_SUCCESS) {
    printf("MPI_Comm_rank failed!\n");
    exit(1);
  }

  MPI_Errhandler_set(MPI_COMM_WORLD, MPI_ERRORS_RETURN);

  /* Check that we run on at least two processors */
  if (ntasks < 2) {
    printf("You have to use at least 2 processors to run this program\n");
    MPI_Finalize();        /* Quit if there is only one processor */
    exit(0);
  }

  /* Process 0 (the receiver) does this */
  if (id == 0) {
    for (i=1; i<ntasks; i++) {
      mpi_recv_msg();
    }
  }

  /* Processes 1 to N-1 (the senders) do this */
  else {
    mpi_send_msg(id);
  }

  err = MPI_Finalize();          /* Terminate MPI */
  if (err != MPI_SUCCESS) {
    printf("Error in MPI_Finalize!\n");
    exit(1);
  }
  if (id==0) printf("Ready\n");
  exit(0);
}

void mpi_send_msg(int id){
  sleep(id);
  int length;
  MPI_Get_processor_name(msg, &length);
  err = MPI_Send(msg, length, MPI_CHAR, 0, tag, MPI_COMM_WORLD);
  if (err != MPI_SUCCESS) {
    printf("Process %i: Error in MPI_Send!\n", id);
  }
}

void mpi_recv_msg(){

  int length;
  MPI_Get_processor_name(msg, &length);
  err = MPI_Recv(msg, 80, MPI_CHAR, MPI_ANY_SOURCE, tag, MPI_COMM_WORLD, \
         &status);
  if (err != MPI_SUCCESS) {
    printf("Error in MPI_Recv!\n");
  }
  source_id = status.MPI_SOURCE;
  printf("Hello World from process %d running on %s\n", source_id, msg);

}