Move start_doing_background_updates() to HomeServer.start_background_tasks()

synapse/app/homeserver.py

@@ -317,11 +317,6 @@ class SynapseHomeServer(HomeServer):
                 # during parsing
                 logger.warning("Unrecognized listener type: %s", listener.type)
 
-    def start_background_tasks(self) -> None:
-        super().start_background_tasks()
-
-        self.get_datastores().main.db_pool.updates.start_doing_background_updates()
-
 
 def load_or_generate_config(argv_options: List[str]) -> HomeServerConfig:
     """

synapse/server.py

@@ -640,12 +640,16 @@ class HomeServer(metaclass=abc.ABCMeta):
         Some handlers have side effects on instantiation (like registering
         background updates). This function causes them to be fetched, and
         therefore instantiated, to run those side effects.
+
+        We assume these background tasks are only run on a single Synapse instance at a
+        time.
         """
         for i in self.REQUIRED_ON_BACKGROUND_TASK_STARTUP:
             getattr(self, "get_" + i + "_handler")()
         self.get_task_scheduler()
         self.get_common_usage_metrics_manager().setup()
         start_phone_stats_home(self)
+        self.get_datastores().main.db_pool.updates.start_doing_background_updates()
 
     def get_reactor(self) -> ISynapseReactor:
         """