ping_pong.c

//code adapted from http://mpitutorial.com/tutorials/mpi-send-and-receive/ 
#include <stdio.h>
#include <mpi.h>
#include <stdlib.h>

#define PING_PONG_LIMIT 8

int main(int argc, char *argv[]){
	MPI_Init (&argc, &argv);//initilization
	//find out the rank and size;
	int world_rank, world_size;
	//GET THE RANK OF THE PROCESS
	MPI_Comm_rank(MPI_COMM_WORLD, &world_rank);
	//GET THE SIZE OF THE WORLD
	MPI_Comm_size(MPI_COMM_WORLD, &world_size);
	double t1, t2;
	int ping_pong_count = 0;
	while(ping_pong_count < PING_PONG_LIMIT){
		if(world_rank == ping_pong_count%world_size){
			 // Increment the ping pong count before you send it
			int next_partner_rank = (world_rank+1)%world_size;
			int a = PING_PONG_LIMIT-ping_pong_count;
			ping_pong_count++;
			if(world_rank == 0)
				t1 = MPI_Wtime();//start counter
			MPI_Send(&ping_pong_count, 
					1,
					MPI_INT, next_partner_rank,
					0,
					MPI_COMM_WORLD);
			printf("%d sent and incremented ping_pong_count "
               "%d to %d\n", world_rank, ping_pong_count,
               next_partner_rank);
			if(a < world_size){
				break;
			}
		}else{
			MPI_Status status;
			MPI_Recv(&ping_pong_count, 1, MPI_INT, MPI_ANY_SOURCE, MPI_ANY_TAG,
                 MPI_COMM_WORLD, &status);
			//take the timer it just received the message
			if(world_rank == 0){
				t2 = MPI_Wtime();
				printf("Time taken before receiving the  ping pong is %f\n", (t2-t1));
			}
        printf("%d received ping_pong_count %d from %d\n",
               world_rank, ping_pong_count, status.MPI_SOURCE);
		}
	}
	MPI_Finalize(); //clean up 
	return 0;
}