#include <stddef.h>
#include <mpi.h>

// Ping Pong program

int main(int argc, char** argv) 
{
	MPI_Init(NULL, NULL);
	int nb_mpi_processes;
	MPI_Comm_size(MPI_COMM_WORLD, &nb_mpi_processes);
	int rank;
	MPI_Comm_rank(MPI_COMM_WORLD, &rank);
 
	if(nb_mpi_processes != 2) { printf("This program is design to be run with 2 processes only"); return 0;}

	int tag = 7777;
	int ball = 0;
	int n;
	int niter = 6;
	for (n=1;n<=niter;n++) 
	{
		if(rank==0) {
			MPI_Send ( &ball , 1 , MPI_INTEGER , 1 , tag , MPI_COMM_WORLD ); // 0 send ball to 1, and wait for transfer to be finished
			MPI_Recv ( &ball , 1 , MPI_INTEGER , 1 , tag , MPI_COMM_WORLD, MPI_STATUS_IGNORE); // 0 receive ball from 1, and wait for transfer to be finished
			ball = ball + 2;
    	}

		if(rank==1) {
			MPI_Recv ( &ball , 1 , MPI_INTEGER , 0 , tag , MPI_COMM_WORLD, MPI_STATUS_IGNORE );
			ball = ball + 1;
			MPI_Send ( &ball , 1 , MPI_INTEGER , 0 , tag , MPI_COMM_WORLD );
		}

		printf("Process %d iter %d ball value is : %d\n",rank,n,ball);

		MPI_Barrier(MPI_COMM_WORLD); // A barrier. processes stop here, and can pass it only if ALL processes are here. Useful for debug, can impact performances
	}

	MPI_Finalize(); // Close MPI

	return 0;
}