pingpong.cpp

#include "mpi.h"
#include <cstdio>
#include <unistd.h>

#define INLOOP 0
#define FINISH 1

int main(int argc, char **argv) {
	MPI_Init(&argc, &argv);

	int rank, size;
	MPI_Comm_rank(MPI_COMM_WORLD, &rank);
	MPI_Comm_size(MPI_COMM_WORLD, &size);

	int counter = 0;
	int COUNT = 1;
	int SOURCE = (rank + size - 1) % size;
	int TARGET = (rank + 1) % size;
	int TAG = 0;

	if (rank == 0) { // initialize loop
		MPI_Send(&counter, COUNT, MPI_INT, TARGET, TAG, MPI_COMM_WORLD);
	}

	while (true) {
		MPI_Status status;
		MPI_Recv(&counter, COUNT, MPI_INT, SOURCE, TAG, MPI_COMM_WORLD, &status);

		if (status.MPI_TAG == INLOOP) {
			printf("rank %d: counter: %d\n", rank, counter++);
			usleep(500000);
		}
		if (TAG == INLOOP) {
			MPI_Send(&counter, COUNT, MPI_INT, TARGET, TAG, MPI_COMM_WORLD);
		}
	}

	MPI_Finalize();
	return 0;
}