MPI_Win_fence(MPI_MODE_NOPRECEDE, dyn_win);
MPI_Accumulate(&one, 1, MPI_INT, i%nproc, val_ptrs[i%nproc], 1, MPI_INT, MPI_SUM, dyn_win);
MPI_Win_fence(MPI_MODE_NOSUCCEED, dyn_win);
MPI_Win_fence(MPI_MODE_NOPRECEDE, dyn_win);
MPI_Accumulate(&one, 1, MPI_INT, i%nproc, val_ptrs[i%nproc], 1, MPI_INT, MPI_SUM, dyn_win);
MPI_Win_fence(MPI_MODE_NOSUCCEED, dyn_win);