/* nonblockingtest.c SJ

   An example of interleaved communication and communication
*/
   
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <mpi.h>

#define MAXP 32

/* a variable needeed for call, result not used */
static MPI_Status tmpstat;

int main(int argc, char **argv)
{
  int PID,	/* process-ID */
	  P;	/* number of processes */ 

  /* own variables */

  int v1, i;

  /* keep these 3 calls */
  MPI_Init(&argc, &argv);
  MPI_Comm_rank(MPI_COMM_WORLD, &PID);
  MPI_Comm_size(MPI_COMM_WORLD, &P);

  /* actual code */

  if (PID == 0) {

	  /* process 0 is the master */

	  /* an array to control progress of send/recv requests */
	  MPI_Request req[MAXP];

	  /* an array of statuses */
	  MPI_Status stats[MAXP];

	  /* array of messages to send */
	  int rnd[MAXP];

	  int p;

	  /* initiate sends */
	  for (p = 1; p < P; p++) {
		  rnd[p] = 3 + rand()%(2*P);
		  MPI_Isend(&rnd[p], 1, MPI_INT, p, 0, MPI_COMM_WORLD, &req[p]);
	  }

	  printf("0: all sends initiated\n");

	  /* "do" something */
	  sleep(1);

	  /* ensure that all messages were sent */
	  MPI_Waitall(P-1, req+1, stats+1);
	  /* req+1 == &(req[1]), i.e., addr of element at index 1 */

	  printf("0: all sent\n");

	  /* receive from all */

	  /* initiate receive */

	  for (p = 1; p < P; p++) {
		  MPI_Irecv(&rnd[p], 1, MPI_INT, p, 0, MPI_COMM_WORLD, &req[p]);
	  }

	  printf("0: start receiving\n");

	  i = P-1;
	  while(i) { /* exit after all are ready, see below */
		  int which;
		  MPI_Status stat;

		  MPI_Waitany(P-1, req+1, &which, &stat);

		  /* if no request was anymore active, exit loop */
		  if (which == MPI_UNDEFINED)
			  break;

		  printf("0: process %d returned %d\n",
				 stat.MPI_SOURCE, rnd[stat.MPI_SOURCE]);

		  i--;
	  }

	  printf("0: all received\n");

  } else {
	  /* all other processes */

	  /* receive from 0 */
	  MPI_Recv(&v1, 1, MPI_INT, 0, 0, MPI_COMM_WORLD, &tmpstat);

	  /* pretend to work */
	  sleep(v1);

	  /* send to 0 */
	  MPI_Send(&v1, 1, MPI_INT, 0, 0, MPI_COMM_WORLD);

  }

  /* keep this call */
  MPI_Finalize();

  exit(0);

}