halo_async_init Subroutine

   subroutine halo_async_init(ha, decomp, nghost, nx_local, ny_local)
      !! Pre-allocate halo buffers for all 4 fields
      type(halo_async_t), intent(out) :: ha
      type(decomp_t), intent(in) :: decomp
      integer, intent(in) :: nghost, nx_local, ny_local

      integer :: nx_total, ny_total

      ha%decomp = decomp
      ha%nghost = nghost
      ha%nx_local = nx_local
      ha%ny_local = ny_local
      nx_total = nx_local + 2*nghost
      ny_total = ny_local + 2*nghost
      ha%nx_total = nx_total
      ha%ny_total = ny_total

      ! Per-field strip sizes, multiplied by NFIELDS for combined buffers
      ha%strip_ew = NFIELDS*nghost*ny_total
      ha%strip_sn = NFIELDS*nx_total*nghost

      if (.not. decomp%has_west) then
         ha%rank_west = decomp_rank_from_coords(decomp%px, decomp%rx - 1, decomp%ry)
         allocate (ha_buf_send_west(ha%strip_ew), ha_buf_recv_west(ha%strip_ew))
         !$acc enter data create( ha_buf_send_west, ha_buf_recv_west)
      end if
      if (.not. decomp%has_east) then
         ha%rank_east = decomp_rank_from_coords(decomp%px, decomp%rx + 1, decomp%ry)
         allocate (ha_buf_send_east(ha%strip_ew), ha_buf_recv_east(ha%strip_ew))
         !$acc enter data create( ha_buf_send_east, ha_buf_recv_east)
      end if
      if (.not. decomp%has_south) then
         ha%rank_south = decomp_rank_from_coords(decomp%px, decomp%rx, decomp%ry - 1)
         allocate (ha_buf_send_south(ha%strip_sn), ha_buf_recv_south(ha%strip_sn))
         !$acc enter data create( ha_buf_send_south, ha_buf_recv_south)
      end if
      if (.not. decomp%has_north) then
         ha%rank_north = decomp_rank_from_coords(decomp%px, decomp%rx, decomp%ry + 1)
         allocate (ha_buf_send_north(ha%strip_sn), ha_buf_recv_north(ha%strip_sn))
         !$acc enter data create( ha_buf_send_north, ha_buf_recv_north)
      end if

      ha%initialised = .true.

   end subroutine halo_async_init