MetOffice · Ed Hone (EdHone) · Feb 27, 2026 · Mar 3, 2026 · Mar 3, 2026 · Mar 4, 2026
@@ -46,9 +46,15 @@ coord_system='native'
   counter_output_suffix = 'counter.txt'
   checkpoint_read       = .false.
   checkpoint_write      = .false.
+  end_of_run_checkpoint = .false.
+  checkpoint_times      = 10, 20
   file_convention       = 'UGRID'
 /
 
+&files
+  checkpoint_stem_name  = 'restart-io_demo-'
+/
+
 &io_demo
   multifile_io          = .false.
   io_benchmark          = .false.

@@ -1,5 +1,22 @@
 import=lfric-driver/HEAD
 
+[namelist:files]
+compulsory=true
+description=Configuration options for file reading and writing
+help=Configuration options for file reading and writing
+ns=namelist/Job/IO
+sort-key=Section-A03
+title=Files
+
+[namelist:files=checkpoint_stem_name]
+compulsory=true
+description=Filename stem for checkpoint files
+help=Where this app writes and reads checkpoint files.
+ns=namelist/Job/IO/Checkpointing & Restart
+sort-key=A-007
+!string_length=filename
+type=character
+
 [namelist:io_demo]
 compulsory=true
 description=Provides options for configuring the runtime behaviour of the IO_Demo app

@@ -16,7 +16,7 @@ module init_io_demo_mod
   use driver_modeldb_mod,                     only : modeldb_type
   use field_collection_mod,                   only : field_collection_type
   use field_mod,                              only : field_type
-  use field_parent_mod,                       only : write_interface
+  use field_parent_mod,                       only : write_interface, read_interface
   use function_space_collection_mod,          only : function_space_collection
   use function_space_mod,                     only : function_space_type
   use fs_continuity_mod,                      only : Wtheta
@@ -25,6 +25,7 @@ module init_io_demo_mod
                                                      LOG_LEVEL_TRACE, &
                                                      LOG_LEVEL_ERROR
   use mesh_mod,                               only : mesh_type
+  use lfric_xios_read_mod,                    only : read_field_generic
   use lfric_xios_write_mod,                   only : write_field_generic
   use io_demo_constants_mod,                  only : create_io_demo_constants
   use random_number_generator_mod,            only : random_number_generator_type
@@ -53,7 +54,8 @@ subroutine init_io_demo(modeldb, mesh, chi, panel_id)
     type(random_number_generator_type), pointer :: rng
     type(field_type)                            :: diffusion_field
     type(field_collection_type), pointer        :: depository
-    procedure(write_interface), pointer         :: tmp_ptr
+    procedure(read_interface), pointer          :: tmp_read_ptr
+    procedure(write_interface), pointer         :: tmp_write_ptr
     real(kind=r_def), parameter                 :: min_val = 280.0_r_def
     real(kind=r_def), parameter                 :: max_val = 330.0_r_def
 
@@ -89,11 +91,10 @@ subroutine init_io_demo(modeldb, mesh, chi, panel_id)
     fs => function_space_collection%get_fs(mesh, order_h, order_v, Wtheta)
     call diffusion_field%initialise(fs, name="diffusion_field")
 
-    ! Set up field with an IO behaviour (XIOS only at present)
-    if (write_diag .and. use_xios_io) then
-       tmp_ptr => write_field_generic
-       call diffusion_field%set_write_behaviour(tmp_ptr)
-    end if
+    tmp_read_ptr => read_field_generic
+    tmp_write_ptr => write_field_generic
+    call diffusion_field%set_read_behaviour(tmp_read_ptr)
+    call diffusion_field%set_write_behaviour(tmp_write_ptr)
 
     ! Add field to modeldb
     depository => modeldb%fields%get_field_collection("depository")

@@ -0,0 +1,137 @@
+!-----------------------------------------------------------------------------
+! (c) Crown copyright Met Office. All rights reserved.
+! The file LICENCE, distributed with this code, contains details of the terms
+! under which the code may be used.
+!-----------------------------------------------------------------------------
+!> @brief Sets up checkpointing for the IO_demo app
+!> @details Creates an IO context for checkpointing and adds the appropriate
+!!          files and fields to it
+module io_demo_checkpoint_mod
+
+  use constants_mod,          only: i_def, str_max_filename, r_second
+  use driver_modeldb_mod,     only: modeldb_type
+  use event_mod,              only: event_action
+  use event_actor_mod,        only: event_actor_type
+  use field_mod,              only: field_type
+  use field_collection_mod,   only: field_collection_type
+  use file_mod,               only: FILE_MODE_WRITE, FILE_MODE_READ
+  use io_context_mod,         only: io_context_type, callback_clock_arg
+  use linked_list_mod,        only: linked_list_type
+  use lfric_xios_action_mod,  only: advance
+  use lfric_xios_context_mod, only: lfric_xios_context_type
+  use lfric_xios_file_mod,    only: lfric_xios_file_type, OPERATION_ONCE
+  use log_mod,                only: log_event, log_scratch_space, &
+                                    LOG_LEVEL_DEBUG, LOG_LEVEL_ERROR
+
+  implicit none
+
+  private
+  public :: setup_checkpoint_io
+
+contains
+
+  !> @details Sets up checkpointing for the IO_demo app
+  !> @param[in,out] modeldb   The model database
+  !> @param[in]     chi       The co-ordinate field
+  !> @param[in]     panel_id  The panel id field
+  subroutine setup_checkpoint_io(modeldb, chi, panel_id)
+
+    type(modeldb_type), intent(inout) :: modeldb
+    type(field_type),   intent(in)    :: chi(:)
+    type(field_type),   intent(in)    :: panel_id
+
+    type(lfric_xios_context_type) :: tmp_io_context
+    type(lfric_xios_context_type), pointer :: cp_context, io_context
+    type(linked_list_type),        pointer :: file_list
+    type(field_collection_type),   pointer :: checkpoint_fields
+    real(r_second), allocatable            :: checkpoint_times(:)
+
+    class(event_actor_type), pointer :: event_actor_ptr
+    procedure(event_action), pointer :: context_advance
+    procedure(callback_clock_arg), pointer :: before_close
+
+    character(len=str_max_filename) :: checkpoint_write_filename, checkpoint_read_filename
+    integer(i_def) :: ts_start, ts_end, t_cp, freq_ts
+
+    call log_event( 'io_demo: Setting up checkpoint I/O', LOG_LEVEL_DEBUG )
+
+    ts_start = modeldb%calendar%parse_instance(modeldb%config%time%timestep_start())
+    ts_end   = modeldb%calendar%parse_instance(modeldb%config%time%timestep_end())
+    checkpoint_fields => modeldb%fields%get_field_collection("depository")
+
+    call tmp_io_context%initialise( "checkpoint_context", start=ts_start, stop=ts_end )
+    call modeldb%io_contexts%add_context(tmp_io_context)
+
+    ! Get pointer to persistent context
+    call modeldb%io_contexts%get_io_context("checkpoint_context", cp_context)
+    file_list => cp_context%get_filelist()
+
+    if (modeldb%config%io%checkpoint_write()) then
+      if (modeldb%config%io%end_of_run_checkpoint()) then
+        write(checkpoint_write_filename, '(A,I0)') &
+              trim(modeldb%config%files%checkpoint_stem_name()), ts_end
+        call file_list%insert_item( lfric_xios_file_type( checkpoint_write_filename, &
+                                          xios_id = "checkpoint_io_demo",            &
+                                          io_mode = FILE_MODE_WRITE,                 &
+                                          freq = ts_end - ts_start + 1,              &
+                                          operation = OPERATION_ONCE,                &
+                                          fields_in_file = checkpoint_fields ) )
+      end if
+
+      checkpoint_times = modeldb%config%io%checkpoint_times()
+      if (size(checkpoint_times) > 0) then
+        do t_cp = 1, size(checkpoint_times)
+
+          if (mod(checkpoint_times(t_cp), modeldb%clock%get_seconds_per_step()) /= 0) then
+            write(log_scratch_space, '(A,F6.1, A)') "io_demo: Checkpoint time ", &
+                                      checkpoint_times(t_cp),                    &
+                                      " is not an integer multiple of the model timestep."
+            call log_event(log_scratch_space, LOG_LEVEL_ERROR)
+          else
+              freq_ts = int(checkpoint_times(t_cp) / modeldb%clock%get_seconds_per_step())
+              write(checkpoint_write_filename, '(A,I0)') &
+                    trim(modeldb%config%files%checkpoint_stem_name()), freq_ts
+              call file_list%insert_item( lfric_xios_file_type( trim(checkpoint_write_filename), &
+                                                xios_id = trim(checkpoint_write_filename), &
+                                                io_mode = FILE_MODE_WRITE,                 &
+                                                freq = freq_ts,                            &
+                                                operation = OPERATION_ONCE,                &
+                                                fields_in_file = checkpoint_fields ) )
+          end if
+        end do
+      end if
+    end if
+
+    if (modeldb%config%io%checkpoint_read()) then
+      write(checkpoint_read_filename, '(A,I0)') &
+            trim(modeldb%config%files%checkpoint_stem_name()), ts_start - 1
+      call file_list%insert_item( lfric_xios_file_type( checkpoint_read_filename,  &
+                                        xios_id = "restart_io_demo",               &
+                                        io_mode = FILE_MODE_READ,                  &
+                                        freq = 1,                                  &
+                                        operation = OPERATION_ONCE,                &
+                                        fields_in_file = checkpoint_fields ) )
+    end if
+
+    event_actor_ptr => cp_context
+    context_advance => advance
+
+    before_close => null()
+    call cp_context%initialise_xios_context( modeldb%mpi%get_comm(), chi, panel_id, &
+                                             modeldb%clock, modeldb%calendar, before_close )
+
+    call modeldb%clock%add_event(context_advance, event_actor_ptr)
+    call cp_context%set_active(.true.)
+
+    ! Set current context back to main
+    call modeldb%io_contexts%get_io_context("io_demo", io_context)
+    call io_context%set_current()
+
+    nullify(cp_context)
+    nullify(file_list)
+    nullify(checkpoint_fields)
+    nullify(io_context)
+
+  end subroutine setup_checkpoint_io
+
+end module io_demo_checkpoint_mod
@@ -38,6 +38,7 @@ module io_demo_driver_mod
   use multifile_io_mod,           only : init_multifile_io, step_multifile_io
   use io_benchmark_setup_mod,     only : create_io_benchmark_fields, setup_io_benchmark_files
   use io_benchmark_step_mod,      only : step_io_benchmark
+  use io_demo_checkpoint_mod,     only : setup_checkpoint_io
   use io_demo_alg_mod,            only : io_demo_alg
   use sci_field_minmax_alg_mod,   only : log_field_minmax
 
@@ -92,6 +93,8 @@ subroutine initialise(program_name, modeldb)
     logical        :: check_partitions
     logical        :: multifile_io
     logical        :: io_benchmark
+    logical        :: checkpoint_write
+    logical        :: checkpoint_read
 
     integer(i_def), parameter :: one_layer = 1_i_def
     integer(i_def) :: i
@@ -111,6 +114,10 @@ subroutine initialise(program_name, modeldb)
     scaled_radius    = modeldb%config%planet%scaled_radius()
     multifile_io     = modeldb%config%io_demo%multifile_io()
     io_benchmark     = modeldb%config%io_demo%io_benchmark()
+    checkpoint_write = modeldb%config%io%checkpoint_write()
+    checkpoint_read  = modeldb%config%io%checkpoint_read()
+
+     ! Log the configuration
 
     !=======================================================================
     ! Mesh
@@ -214,6 +221,13 @@ subroutine initialise(program_name, modeldb)
     call panel_id_inventory%get_field(mesh, panel_id)
     call init_io_demo(modeldb, mesh, chi, panel_id)
 
+    !=======================================================================
+    ! Set up checkpointing
+    !=======================================================================
+    if (checkpoint_write .or. checkpoint_read) then
+      call setup_checkpoint_io(modeldb, chi, panel_id)
+    end if
+
     nullify(mesh, chi, panel_id)
     deallocate(base_mesh_names)
 

@@ -185,8 +185,12 @@ subroutine finalise_xios_context( this )
     type(lfric_xios_file_type),  pointer :: file => null()
     integer(tik) :: timing_idlx, timing_idxc
 
-    if ( LPROF ) call start_timing(timing_idlx, 'lfric_xios.finalise_context')
+
     if (this%xios_context_initialised) then
+      if ( LPROF ) call start_timing(timing_idlx, 'lfric_xios.finalise_context')
+      call log_event( 'Finalising XIOS context: ' // this%get_context_name(), LOG_LEVEL_DEBUG )
+      call this%set_current()
+
       ! Perform final write
       if (this%filelist%get_length() > 0) then
         loop => this%filelist%get_head()
@@ -225,10 +229,10 @@ subroutine finalise_xios_context( this )
         end do
       end if
       this%xios_context_initialised = .false.
+      if ( LPROF ) call stop_timing(timing_idlx, 'lfric_xios.finalise_context')
     end if
     nullify(loop)
     nullify(file)
-    if ( LPROF ) call stop_timing(timing_idlx, 'lfric_xios.finalise_context')
 
   end subroutine finalise_xios_context
 

@@ -0,0 +1,6 @@
+[namelist:io]
+!!checkpoint_times=60.0,120.0,240.0
+!!end_of_run_checkpoint=.false.
+
+[namelist:timestepping]
+dt=10.0
@@ -18,6 +18,7 @@ mode=mkdir
 mode=auto
 source=namelist:base_mesh
       =  namelist:extrusion
+      =  namelist:files
       =  namelist:finite_element
       =  namelist:io
       =  namelist:io_demo
@@ -46,6 +47,9 @@ method='uniform'
 number_of_layers=10
 planet_radius=6371229.0
 
+[namelist:files]
+checkpoint_stem_name='$CYLC_SUITE_SHARE_DIR/data/restart-io_demo-$ROSE_TASK_NAME'
+
 [namelist:finite_element]
 cellshape='quadrilateral'
 coord_order=1

@@ -13,6 +13,25 @@
         "tsteps": 10,
     }) %}
 
+{% elif task_ns.conf_name == "default-C24-CP" %}
+
+    {% do task_dict.update({
+        "opt_confs": ["default"],
+        "resolution": "C24",
+        "tsteps": 90,
+        "crun": 2,
+        "kgo_checks": [],
+    }) %}
+
+{% elif task_ns.conf_name == "flexible-CP-C24" %}
+
+    {% do task_dict.update({
+        "opt_confs": ["default", "flex_cp"],
+        "resolution": "C24",
+        "tsteps": 60,
+        "kgo_checks": [],
+    }) %}
+
 {% elif task_ns.conf_name == "multifile-C24" %}
 
     {% do task_dict.update({

@@ -11,6 +11,10 @@
         "io_demo_azspice_canned",
         "io_demo_default-C24_azspice_gnu_fast-debug-32bit",
         "io_demo_default-C24_azspice_gnu_full-debug-64bit",
+        "io_demo_default-C24-CP_azspice_gnu_fast-debug-32bit",
+        "io_demo_default-C24-CP_azspice_gnu_fast-debug-64bit",
+        "io_demo_flexible-CP-C24_azspice_gnu_fast-debug-32bit",
+        "io_demo_flexible-CP-C24_azspice_gnu_fast-debug-64bit",
         "io_demo_multifile-C24_azspice_gnu_fast-debug-64bit",
         "io_demo_multifile-C24_azspice_gnu_fast-debug-32bit",
         "io_demo_benchmark-C24_azspice_gnu_fast-debug-64bit",
@@ -39,6 +43,10 @@
         "io_demo_ex1a_canned",
         "io_demo_default-C24_ex1a_cce_fast-debug-32bit",
         "io_demo_default-C24_ex1a_cce_full-debug-64bit",
+        "io_demo_default-C24-CP_ex1a_cce_fast-debug-32bit",
+        "io_demo_default-C24-CP_ex1a_cce_fast-debug-64bit",
+        "io_demo_flexible-CP-C24_ex1a_gnu_fast-debug-64bit",
+        "io_demo_flexible-CP-C24_ex1a_cce_fast-debug-64bit",
         "io_demo_multifile-C24_ex1a_cce_fast-debug-64bit",
         "io_demo_multifile-C24_ex1a_cce_fast-debug-32bit",
         "io_demo_multifile-C24_ex1a_gnu_fast-debug-64bit",

@@ -60,7 +60,7 @@
             application_build_task,
             crun_task]) %}
         {% do graph_sections.append([
-            mesh_run_task,
+            mesh_run_tasks[0],
             crun_task]) %}
     {% else %}
         {# All other runs depend on the run previously #}