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

int main() {

  MPI_Init(NULL, NULL);

  int my_rank;
  MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);

  int origin_ranks[2] = {0, 1};
  int target_ranks[1] = {0};

  MPI_Group world_group, origin_group, target_group;
  MPI_Comm_group(MPI_COMM_WORLD, &world_group);
  MPI_Group_incl(world_group, 2, origin_ranks, &origin_group);
  MPI_Group_incl(world_group, 1, target_ranks, &target_group);

  unsigned char *buf;
  MPI_Win win;
  if (my_rank == 0) {
    MPI_Win_allocate(17, sizeof(unsigned char), MPI_INFO_NULL, MPI_COMM_WORLD,
                     &buf, &win);
    MPI_Win_post(origin_group, 0, win); // Expose win on rank 0 to ranks 0 and 1
  } else {
    MPI_Win_allocate(0, sizeof(unsigned char), MPI_INFO_NULL, MPI_COMM_WORLD,
                     &buf, &win);
  }

  MPI_Win_start(target_group, 0, win); // Access win on rank 0
  MPI_Win_complete(win);               // Finish access of win

  if (my_rank == 0) {
    printf("Before wait\n");
    fflush(stdout);
    MPI_Win_wait(win); // Wait until all processes have finished accessing win
    printf("After wait\n");
    fflush(stdout);
  }

  MPI_Barrier(MPI_COMM_WORLD);
  MPI_Win_free(&win);
  MPI_Group_free(&target_group);
  MPI_Group_free(&origin_group);

  MPI_Finalize();
}