*Patches for nonBous_OBCs to prevent blocking

  This adds logical tests to determine the global OBC data update patterns to
allow for halo updates related to these updates without having the model hang
up with inconsistently blocked message passing calls.  This commit corrects a
bug with some test cases that was introduced with the halo update after the
call to thicknesses_to_dz in update_OBC_segment_data two commits previously.

src/core/MOM_boundary_update.F90

@@ -156,7 +156,7 @@ subroutine update_OBC_data(OBC, G, GV, US, tv, h, CS, Time)
       call shelfwave_set_OBC_data(OBC, CS%shelfwave_OBC_CSp, G, GV, US, h, Time)
   if (CS%use_dyed_channel) &
       call dyed_channel_update_flow(OBC, CS%dyed_channel_OBC_CSp, G, GV, US, Time)
-  if (OBC%needs_IO_for_data .or. OBC%add_tide_constituents)  &
+  if (OBC%any_needs_IO_for_data .or. OBC%add_tide_constituents)  &
       call update_OBC_segment_data(G, GV, US, OBC, tv, h, Time)
 
 end subroutine update_OBC_data

src/core/MOM_open_boundary.F90

@@ -278,7 +278,9 @@ module MOM_open_boundary
   logical :: update_OBC = .false.                     !< Is OBC data time-dependent
   logical :: update_OBC_seg_data = .false.            !< Is it the time for OBC segment data update for fields that
                                                       !! require less frequent update
-  logical :: needs_IO_for_data = .false.              !< Is any i/o needed for OBCs
+  logical :: needs_IO_for_data = .false.              !< Is any i/o needed for OBCs on the current PE
+  logical :: any_needs_IO_for_data = .false.          !< Is any i/o needed for OBCs globally
+  logical :: some_need_no_IO_for_data = .false.       !< Are there any PEs with OBCs that do not need i/o.
   logical :: zero_vorticity = .false.                 !< If True, sets relative vorticity to zero on open boundaries.
   logical :: freeslip_vorticity = .false.             !< If True, sets normal gradient of tangential velocity to zero
                                                       !! in the relative vorticity on open boundaries.
@@ -736,6 +738,7 @@ subroutine initialize_segment_data(G, GV, US, OBC, PF)
   integer, dimension(1) :: single_pelist
   type(external_tracers_segments_props), pointer :: obgc_segments_props_list =>NULL()
   !will be able to dynamically switch between sub-sampling refined grid data or model grid
+  integer :: IO_needs(3) ! Sums to determine global OBC data use and update patterns.
 
   is = G%isc ; ie = G%iec ; js = G%jsc ; je = G%jec
 
@@ -1045,6 +1048,15 @@ subroutine initialize_segment_data(G, GV, US, OBC, PF)
 
   call Set_PElist(saved_pelist)
 
+  ! Determine global IO data requirement patterns.
+  IO_needs(1) = 0 ; if (OBC%needs_IO_for_data) IO_needs(1) = 1
+  IO_needs(2) = 0 ; if (OBC%update_OBC) IO_needs(2) = 1
+  IO_needs(3) = 0 ; if (.not.OBC%needs_IO_for_data) IO_needs(3) = 1
+  call sum_across_PES(IO_needs, 3)
+  OBC%any_needs_IO_for_data = (IO_needs(1) > 0)
+  OBC%update_OBC = (IO_needs(2) > 0)
+  OBC%some_need_no_IO_for_data = (IO_needs(3) > 0)
+
 end subroutine initialize_segment_data
 
 !> Return an appropriate dimensional scaling factor for input data based on an OBC segment data
@@ -1909,7 +1921,7 @@ logical function open_boundary_query(OBC, apply_open_OBC, apply_specified_OBC, a
                                                         OBC%Flather_v_BCs_exist_globally
   if (present(apply_nudged_OBC)) open_boundary_query = OBC%nudged_u_BCs_exist_globally .or. &
                                                        OBC%nudged_v_BCs_exist_globally
-  if (present(needs_ext_seg_data)) open_boundary_query = OBC%needs_IO_for_data
+  if (present(needs_ext_seg_data)) open_boundary_query = OBC%any_needs_IO_for_data
 
 end function open_boundary_query
 
@@ -5755,6 +5767,8 @@ subroutine rotate_OBC_config(OBC_in, G_in, OBC, G, turns)
   OBC%brushcutter_mode = OBC_in%brushcutter_mode
   OBC%update_OBC = OBC_in%update_OBC
   OBC%needs_IO_for_data = OBC_in%needs_IO_for_data
+  OBC%any_needs_IO_for_data = OBC_in%any_needs_IO_for_data
+  OBC%some_need_no_IO_for_data = OBC_in%some_need_no_IO_for_data
 
   OBC%ntr = OBC_in%ntr
 

src/initialization/MOM_state_initialization.F90

@@ -18,6 +18,7 @@ module MOM_state_initialization
 use MOM_get_input, only : directories
 use MOM_grid, only : ocean_grid_type, isPointInCell
 use MOM_interface_heights, only : find_eta, dz_to_thickness, dz_to_thickness_simple
+use MOM_interface_heights, only : calc_derived_thermo
 use MOM_io, only : file_exists, field_size, MOM_read_data, MOM_read_vector, slasher
 use MOM_open_boundary, only : ocean_OBC_type, open_boundary_init, set_tracer_data
 use MOM_open_boundary, only : OBC_NONE
@@ -607,8 +608,10 @@ subroutine MOM_initialize_state(u, v, h, tv, Time, G, GV, US, PF, dirs, &
     call initialize_segment_data(G, GV, US, OBC, PF)
 !     call open_boundary_config(G, US, PF, OBC)
     ! Call this once to fill boundary arrays from fixed values
-    if (.not. OBC%needs_IO_for_data)  &
+    if (OBC%some_need_no_IO_for_data) then
+      call calc_derived_thermo(tv, h, G, GV, US)
       call update_OBC_segment_data(G, GV, US, OBC, tv, h, Time)
+    endif
 
     call get_param(PF, mdl, "OBC_USER_CONFIG", config, &
                  "A string that sets how the user code is invoked to set open boundary data: \n"//&