/* -*- Mode: C; c-basic-offset:4 ; indent-tabs-mode:nil ; -*- */

/*

 *  (C) 2005 by Argonne National Laboratory.

 *      See COPYRIGHT in top-level directory.

 */

/* A very simple program that performs only a send and a receive.  This

   program can be use with logging enabled (configure with 

   --enable-g=dbg,log) and run with -mpich-dbg-class=routine to get

   a trace of the execution of the functions in MPICH */

#include <stdio.h>

#include "mpi.h"

#define SENDER_RANK 0

#define RECEIVER_RANK 1

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

{

    int rank, size, val;

    MPI_Status status;

    MPI_Init( &argc, &argv );

    MPI_Comm_size( MPI_COMM_WORLD, &size );

    MPI_Comm_rank( MPI_COMM_WORLD, &rank );

    if (size < 2) {

	fprintf( stderr, "This program requires at least 2 processes\n" );

	MPI_Abort( MPI_COMM_WORLD, 1 );

    }

    if (rank == SENDER_RANK) {

	MPI_Send( &rank, 1, MPI_INT, RECEIVER_RANK, 0, MPI_COMM_WORLD );

    }

    else if (rank == RECEIVER_RANK) {

	/* This may or may not post the receive before the send arrives */

	MPI_Recv( &val, 1, MPI_INT, SENDER_RANK, 0, MPI_COMM_WORLD, &status );

    }

    /* Perform a second send/receive to allow the first pair to handle

       any connection logic */

#if 1

    if (rank == SENDER_RANK) {

	MPI_Send( &rank, 1, MPI_INT, RECEIVER_RANK, 0, MPI_COMM_WORLD );

    }

    else if (rank == RECEIVER_RANK) {

	/* This may or may not post the receive before the send arrives */

	MPI_Recv( &val, 1, MPI_INT, SENDER_RANK, 0, MPI_COMM_WORLD, &status );

    }

#endif

    MPI_Finalize( );

    return 0;

}