#include "mpi.h"
#define N 50000		/* N is the number of rounds */
#define B 5000		/* B is the buffer size for the message, in bytes */

/* This is a ping-pong program. */
/* It sends a message back and forth "N" times between two processes. */

main(int argc, char *argv[])
{	int myid, opponent, trips;
	char ball[B];
	MPI_Status stat;

	if (MPI_Init(&argc, &argv)!=MPI_SUCCESS)
	{	printf("Error, you bonehead!\n");
		exit(1);
	}

	MPI_Comm_rank(MPI_COMM_WORLD, &myid);       /* Get rank */
	opponent = (myid+1)%2;
	
	/* First player starts the game */

	if (myid==1)
	   MPI_Send(ball, B, MPI_CHAR, opponent, 0, MPI_COMM_WORLD);

	/* Wait for the message then send it back to opponent */

	for (trips=0; trips<N;++trips)
	{      MPI_Recv(ball, B, MPI_CHAR, opponent, 0, MPI_COMM_WORLD, &stat);
	       /* printf("Ball %d got from player %d!\n", trips, myid); */
	       MPI_Send(ball, B, MPI_CHAR, opponent, 0, MPI_COMM_WORLD);
	}

	/* Game over -- don't return message */

	if (myid==0)
	{ printf ("Game over after %d rounds and a %d byte ball size!\n", N,B);
	  MPI_Recv(ball, B, MPI_CHAR, opponent, 0, MPI_COMM_WORLD, &stat);
	}  
	MPI_Finalize();
}