Blocking send and receive

mpi_send_recv.c

#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>

#define WORKER(id) if (ID == (id))
#define MASTER WORKER(0)

int main(int argc, char *argv[])
{
	int numprocs, ID;
	int next, prev;
	int buf, i;

	MPI_Init(&argc, &argv);
	MPI_Comm_size(MPI_COMM_WORLD, &numprocs);
	MPI_Comm_rank(MPI_COMM_WORLD, &ID);
	next = (ID + 1) % numprocs;
	prev = (ID - 1 + numprocs) % numprocs;

	for (i = 0; i < 2; i++) {
		if ((ID + i) % 2 == 0) {
			MPI_Send(&ID, 1, MPI_INT, next, 0, MPI_COMM_WORLD);
			//MPI_Send(&ID, sizeof(ID), MPI_BYTE, next, 0, MPI_COMM_WORLD);
		} else {
			MPI_Recv(&buf, 1, MPI_INT, prev, 0, MPI_COMM_WORLD, NULL);
			//MPI_Recv(&buf, sizeof(buf), MPI_BYTE, prev, 0, MPI_COMM_WORLD, NULL);
		}
	}
	
	printf("Worker %d: %d\n", ID, buf);

	MPI_Finalize();

	return 0;
}