/* 
Jonathan Hauenstein - University of Notre Dame
Center for Applied Mathematics Minicourse on Parallel Computing
April 24, May 1, May 8, 2008
Sample programs are designed for educational use 
*/

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

int main(int argc, char **argv)
{ 
  int my_id, num_proc, flag;
  MPI_Status status;

  // initialize MPI
  MPI_Init(&argc, &argv);

  // find unique id
  MPI_Comm_rank(MPI_COMM_WORLD, &my_id);

  // find the number of processes running
  MPI_Comm_size(MPI_COMM_WORLD, &num_proc);

  // test for message waiting
  MPI_Iprobe(MPI_ANY_SOURCE, MPI_ANY_TAG, MPI_COMM_WORLD, &flag, &status);
  printf("id: %d flag: %d\n", my_id, flag);

  // wait here
  MPI_Barrier(MPI_COMM_WORLD);

  // send from id 0 to id 1
  if (my_id == 0)
  { // construct the things to send
    int i, size = 96, tag = 101;
    int *my_values = (int *)malloc(size * sizeof(int));
    for (i = 0; i < size; i++)
      my_values[i] = i;

    MPI_Send(my_values, size, MPI_INT, 1, tag, MPI_COMM_WORLD);

    free(my_values);
  }
  else if (my_id == 1)
  { // setup a recv buffer
    int recv_size, *my_values = NULL;

    MPI_Probe(MPI_ANY_SOURCE, MPI_ANY_TAG, MPI_COMM_WORLD, &status);
    MPI_Get_count(&status, MPI_INT, &recv_size);

    printf("\nprobe values: recv size: %d MPI_SOURCE: %d MPI_TAG: %d MPI_ERROR: %d\n\n", 
                        recv_size, status.MPI_SOURCE, status.MPI_TAG, status.MPI_ERROR);

    my_values = (int *)malloc(recv_size * sizeof(int));
    MPI_Recv(my_values, recv_size, MPI_INT, MPI_ANY_SOURCE, MPI_ANY_TAG, MPI_COMM_WORLD, &status);
    free(my_values);
  }

  // finalize MPI
  MPI_Finalize();

  return 0;
}