Nonblocking send and receive

mpi_isend_irecv.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;
	MPI_Request req;

	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;

	MPI_Isend(&ID, 1, MPI_INT, next, 0, MPI_COMM_WORLD, &req);
	MPI_Irecv(&buf, 1, MPI_INT, prev, 0, MPI_COMM_WORLD, &req);
	//MPI_Irecv(&buf, 1, MPI_INT, MPI_ANY_SOURCE, 0, MPI_COMM_WORLD, &req);
	MPI_Wait(&req, NULL);

	printf("Worker %d: %d\n", ID, buf);

	MPI_Finalize();

	return 0;
}