One-sided communication

mpi_put.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 *buf;
	MPI_Win win;

	MPI_Init(&argc, &argv);
	MPI_Comm_size(MPI_COMM_WORLD, &numprocs);
	MPI_Comm_rank(MPI_COMM_WORLD, &ID);

	MASTER {
		MPI_Alloc_mem(sizeof(int), MPI_INFO_NULL, &buf);
		*buf = 0;
	}

	// Collective call
	// Expose a window of one integer
	MASTER MPI_Win_create(buf, sizeof(int), 1, MPI_INFO_NULL, MPI_COMM_WORLD, &win);
	// Expose nothing
	else MPI_Win_create(buf, 0, 1, MPI_INFO_NULL, MPI_COMM_WORLD, &win);

	// Passive target communication
	// Cooperation from target process not needed for communication  
	MASTER {
		MPI_Barrier(MPI_COMM_WORLD);
		printf("Master %d: %d\n", ID, *buf);
	} else {
		int n = 42;
		// Starts access epoch for window win
		MPI_Win_lock(MPI_LOCK_EXCLUSIVE, 0, 0, win);
		MPI_Put(&n, 1, MPI_INT, 0, 0, 1, MPI_INT, win);
		// Ends access epoch for window win
		MPI_Win_unlock(0, win);
		MPI_Barrier(MPI_COMM_WORLD);
	}

	// Collective call
	MPI_Win_free(&win);

	MASTER MPI_Free_mem(buf);

	MPI_Finalize();

	return 0;
}