/*  Program fence.c  */
#include "mpi.h" 
#include <stdio.h> 
int main(int argc, char **argv) {
    int rank, i, buf[2];

    //Start up MPI...
    MPI_Init(&argc,&argv);
    MPI_Comm_rank(MPI_COMM_WORLD,&rank);
    MPI_Comm comm;
    MPI_Group comm_group, group;
    MPI_Win win;
    comm = MPI_COMM_WORLD;

    for(i=0;i<2;i++) buf[i]=0; //Initialize all buffers to 0

    if (rank == 0) {
        /* Only rank 0 has a nonzero buffer at start */
        for(i=0;i<2;i++) buf[i]=(i+1)*3;
        /* Everyone will retrieve from the buffer on root */
        int soi = sizeof(int);
        MPI_Win_create(buf,soi*2,soi,MPI_INFO_NULL,comm,&win);
    }
    else {
        /* Others only retrieve, so these windows can be size 0 */
        MPI_Win_create(NULL,0,sizeof(int),MPI_INFO_NULL,comm,&win);
    }
    printf("Before Get on %d: %d %d\n",rank,buf[0],buf[1]);

    /* No local operations prior to this epoch, so give an assertion */
    MPI_Win_fence(MPI_MODE_NOPRECEDE,win);

    /* Inside the fence, ranks make RMA calls to GET from rank 0 */
    if (rank != 0) {
        MPI_Get(buf,2,MPI_INT,0,0,2,MPI_INT,win);
    }

    /* Complete the epoch - this blocks until the MPI_Get is complete -
       all done with the window, so tell MPI there are no more epochs */
    MPI_Win_fence(MPI_MODE_NOSUCCEED,win);

    printf("After Get on %d: %d %d\n",rank,buf[0],buf[1]);

    /* Free up our window */
    MPI_Win_free(&win);

    //Shut down...
    MPI_Finalize();
    return(0);
}