reload: simplify execution pathway

* The reload code was spread around four places:
  * Scheduler.command_reload_workflow
  * Scheduler.main_loop
  * Pool.set_do_reload
  * Pool.reload_taskdefs
* This commit co-locates the Scheduler/Pool parts and turns them into a
  single synchronous operation (no main-loop moving parts) to simplify
  the pathway.
* This removes the need for the `do_reload` pool flag.

cylc/flow/scheduler.py

@@ -1071,7 +1071,7 @@ def command_reload_workflow(self) -> None:
         # reload the workflow definition
         LOG.info("Reloading the workflow definition.")
         try:
-            cfg = self.load_flow_file(is_reload=True)
+            config = self.load_flow_file(is_reload=True)
         except (ParsecError, CylcConfigError) as exc:
             if cylc.flow.flags.verbosity > 1:
                 # log full traceback in debug mode
@@ -1092,10 +1092,13 @@ def command_reload_workflow(self) -> None:
             self.workflow_db_mgr.pri_dao.select_workflow_params(
                 self._load_workflow_params
             )
-            self.apply_new_config(cfg, is_reload=True)
+            self.apply_new_config(config, is_reload=True)
             self.broadcast_mgr.linearized_ancestors = (
                 self.config.get_linearized_ancestors())
-            self.pool.set_do_reload(self.config)
+
+            # OLD
+            # self.pool.set_do_reload(self.config)
+
             self.task_events_mgr.mail_interval = self.cylc_config['mail'][
                 'task event batch interval']
             self.task_events_mgr.mail_smtp = self._get_events_conf("smtp")
@@ -1113,6 +1116,28 @@ def command_reload_workflow(self) -> None:
             self.is_updated = True
             self.is_reloaded = True
 
+            # NEW
+
+            # Re-initialise data model on reload
+            self.data_store_mgr.initiate_data_model(reloaded=True)
+
+            # Reset the remote init map to trigger fresh file installation
+            self.task_job_mgr.task_remote_mgr.remote_init_map.clear()
+            self.task_job_mgr.task_remote_mgr.is_reload = True
+            self.pool.reload_taskdefs(config)
+            # Load jobs from DB
+            self.workflow_db_mgr.pri_dao.select_jobs_for_restart(
+                self.data_store_mgr.insert_db_job
+            )
+            if self.pool.compute_runahead(force=True):
+                self.pool.release_runahead_tasks()
+            self.is_reloaded = True
+            self.is_updated = True
+
+
+
+            LOG.info("Reload completed.")
+
         # resume the workflow if previously paused
         self.reload_pending = False
         if not was_paused:
@@ -1618,21 +1643,6 @@ async def main_loop(self) -> None:
             # self.pool.log_task_pool(logging.CRITICAL)
             if self.incomplete_ri_map:
                 self.manage_remote_init()
-            if self.pool.do_reload:
-                # Re-initialise data model on reload
-                self.data_store_mgr.initiate_data_model(reloaded=True)
-                # Reset the remote init map to trigger fresh file installation
-                self.task_job_mgr.task_remote_mgr.remote_init_map.clear()
-                self.task_job_mgr.task_remote_mgr.is_reload = True
-                self.pool.reload_taskdefs()
-                # Load jobs from DB
-                self.workflow_db_mgr.pri_dao.select_jobs_for_restart(
-                    self.data_store_mgr.insert_db_job)
-                LOG.info("Reload completed.")
-                if self.pool.compute_runahead(force=True):
-                    self.pool.release_runahead_tasks()
-                self.is_reloaded = True
-                self.is_updated = True
 
             self.process_command_queue()
             self.proc_pool.process()

cylc/flow/task_pool.py

@@ -111,7 +111,6 @@ def __init__(
         self.data_store_mgr: 'DataStoreMgr' = data_store_mgr
         self.flow_mgr: 'FlowMgr' = flow_mgr
 
-        self.do_reload = False
         self.max_future_offset: Optional['IntervalBase'] = None
         self._prev_runahead_base_point: Optional['PointBase'] = None
         self._prev_runahead_sequence_points: Optional[Set['PointBase']] = None
@@ -132,7 +131,6 @@ def __init__(
         self.abort_task_failed = False
         self.expected_failed_tasks = self.config.get_expected_failed_tasks()
 
-        self.orphans: List[str] = []
         self.task_name_list = self.config.get_task_name_list()
         self.task_queue_mgr = IndepQueueManager(
             self.config.cfg['scheduling']['queues'],
@@ -913,25 +911,7 @@ def set_max_future_offset(self):
         if max_offset != orig and self.compute_runahead(force=True):
             self.release_runahead_tasks()
 
-    def set_do_reload(self, config: 'WorkflowConfig') -> None:
-        """Set the task pool to reload mode."""
-        self.config = config
-        self.stop_point = config.stop_point or config.final_point
-        self.do_reload = True
-
-        # find any old tasks that have been removed from the workflow
-        old_task_name_list = self.task_name_list
-        self.task_name_list = self.config.get_task_name_list()
-        for name in old_task_name_list:
-            if name not in self.task_name_list:
-                self.orphans.append(name)
-        for name in self.task_name_list:
-            if name in self.orphans:
-                self.orphans.remove(name)
-        # adjust the new workflow config to handle the orphans
-        self.config.adopt_orphans(self.orphans)
-
-    def reload_taskdefs(self) -> None:
+    def reload_taskdefs(self, config: 'WorkflowConfig') -> None:
         """Reload the definitions of task proxies in the pool.
 
         Orphaned tasks (whose definitions were removed from the workflow):
@@ -941,18 +921,33 @@ def reload_taskdefs(self) -> None:
         Otherwise: replace task definitions but copy over existing outputs etc.
 
         """
+        self.config = config
+        self.stop_point = config.stop_point or config.final_point
+
+        # find any old tasks that have been removed from the workflow
+        old_task_name_list = self.task_name_list
+        self.task_name_list = self.config.get_task_name_list()
+        orphans = [
+            task
+            for task in old_task_name_list
+            if task not in self.task_name_list
+        ]
+
+        # adjust the new workflow config to handle the orphans
+        self.config.adopt_orphans(orphans)
+
         LOG.info("Reloading task definitions.")
         tasks = self.get_all_tasks()
         # Log tasks orphaned by a reload but not currently in the task pool.
-        for name in self.orphans:
+        for name in orphans:
             if name not in (itask.tdef.name for itask in tasks):
                 LOG.warning("Removed task: '%s'", name)
         for itask in tasks:
-            if itask.tdef.name in self.orphans:
+            if itask.tdef.name in orphans:
                 if (
-                        itask.state(TASK_STATUS_WAITING)
-                        or itask.state.is_held
-                        or itask.state.is_queued
+                    itask.state(TASK_STATUS_WAITING)
+                    or itask.state.is_held
+                    or itask.state.is_queued
                 ):
                     # Remove orphaned task if it hasn't started running yet.
                     self.remove(itask, 'task definition removed')
@@ -1007,8 +1002,6 @@ def reload_taskdefs(self) -> None:
             if all(ready_check_items) and not itask.state.is_runahead:
                 self.queue_task(itask)
 
-        self.do_reload = False
-
     def set_stop_point(self, stop_point: 'PointBase') -> bool:
         """Set the workflow stop cycle point.
 

tests/integration/test_task_pool.py

@@ -828,7 +828,6 @@ async def test_reload_prereqs(
 
         # Reload the workflow config
         schd.command_reload_workflow()
-        schd.pool.reload_taskdefs()
         assert list_tasks(schd) == expected_3
 
         # Check resulting dependencies of task z
@@ -959,6 +958,5 @@ async def test_graph_change_prereq_satisfaction(
 
             # Reload the workflow config
             schd.command_reload_workflow()
-            schd.pool.reload_taskdefs()
 
             await test.asend(schd)