/* -----------------------------------------------------------------------
 * Code:   nbrecv.c
 * Lab:    MPI Point-to-Point Communication
 *         Solution program demonstrating that replacing a blocking receive
 *         with a non-blocking receive earlier in the program can decrease
 *         the synchronization time on the corresponding send.
 * Usage:  nbrecv
 *         Run on two nodes
 * Author: Roslyn Leibensperger  Last revised: 8/30/95 RYL
 * ------------------------------------------------------------------------ */
#include <stdio.h>
#include <sys/time.h>
#include "mpi.h"
#define MSGLEN 2048
#define TAG 100
void print_time ( struct timeval tbegin, struct timeval tend );

main( argc, argv ) 
     int argc;
     char **argv;
{
  float message [MSGLEN];    /* message buffer                   */
  int rank,                  /* rank of task in communicator     */
      i;
  MPI_Status status;         /* status of communication          */
  MPI_Request request;       /* handle for pending communication */
  struct timeval tbegin,     /* used to measure elapsed time     */
                 tend;

  MPI_Init( &argc, &argv );
  MPI_Comm_rank( MPI_COMM_WORLD, &rank );
  printf ( " Process %d initialized\n", rank );

  /* -----------------------------------------------------------------
   * task 0 will report the elapsed time for a blocking send
   * ----------------------------------------------------------------- */
  if ( rank == 0 )  {
    for (i=0; i<MSGLEN; i++) message[i] = 100;
    printf ( " Task %d sending message\n", rank );
    gettimeofday ( &tbegin, (struct timezone*)0 );
    MPI_Send ( message, MSGLEN, MPI_FLOAT, 1, TAG, MPI_COMM_WORLD );
    gettimeofday ( &tend, (struct timezone*)0 );   
    print_time ( tbegin, tend );
  }

  /* ------------------------------------------------------------------
   * task 1 calls a non-blocking receive, sleeps for 10 seconds, and
   * then waits for the receive to complete.
   * the sleep is intended to simulate time spent in useful computation
   * ------------------------------------------------------------------ */
  else if ( rank == 1)  {
    for (i=0; i<MSGLEN; i++) message[i] = -100;
    MPI_Irecv ( message, MSGLEN, MPI_FLOAT, 0, TAG, MPI_COMM_WORLD,
	       &request);
/*    MPI_Sleep(10); */
/*    new_sleep(10); */
    sleep(10);
    MPI_Wait ( &request, &status);
    printf ( " Task %d received message\n", rank );
  }

  MPI_Finalize();
  return 0;
}

/* -------------------------------------------------------------------
 * calculate elapsed time and print results
 * ------------------------------------------------------------------- */
void print_time ( struct timeval tbegin, struct timeval tend )
{
  int dt;
  dt = ( tend.tv_sec - tbegin.tv_sec ) * 1000000 + tend.tv_usec 
    - tbegin.tv_usec;
  printf ( " Elapsed time for send = %8d uSec\n", dt );
}