Fix "db txn 'update_presence' from sentinel context" log messages (#5275)

Fixes #4414.

changelog.d/5275.bugfix

@@ -0,0 +1 @@
+Fix "db txn 'update_presence' from sentinel context" log messages.

synapse/handlers/presence.py

@@ -182,17 +182,27 @@ class PresenceHandler(object):
         # Start a LoopingCall in 30s that fires every 5s.
         # The initial delay is to allow disconnected clients a chance to
         # reconnect before we treat them as offline.
+        def run_timeout_handler():
+            return run_as_background_process(
+                "handle_presence_timeouts", self._handle_timeouts
+            )
+
         self.clock.call_later(
             30,
             self.clock.looping_call,
-            self._handle_timeouts,
+            run_timeout_handler,
             5000,
         )
 
+        def run_persister():
+            return run_as_background_process(
+                "persist_presence_changes", self._persist_unpersisted_changes
+            )
+
         self.clock.call_later(
             60,
             self.clock.looping_call,
-            self._persist_unpersisted_changes,
+            run_persister,
             60 * 1000,
         )
 
@@ -229,6 +239,7 @@ class PresenceHandler(object):
         )
 
         if self.unpersisted_users_changes:
+
             yield self.store.update_presence([
                 self.user_to_current_state[user_id]
                 for user_id in self.unpersisted_users_changes
@@ -240,30 +251,18 @@ class PresenceHandler(object):
         """We periodically persist the unpersisted changes, as otherwise they
         may stack up and slow down shutdown times.
         """
-        logger.info(
-            "Performing _persist_unpersisted_changes. Persisting %d unpersisted changes",
-            len(self.unpersisted_users_changes)
-        )
-
         unpersisted = self.unpersisted_users_changes
         self.unpersisted_users_changes = set()
 
         if unpersisted:
+            logger.info(
+                "Persisting %d upersisted presence updates", len(unpersisted)
+            )
             yield self.store.update_presence([
                 self.user_to_current_state[user_id]
                 for user_id in unpersisted
             ])
 
-        logger.info("Finished _persist_unpersisted_changes")
-
-    @defer.inlineCallbacks
-    def _update_states_and_catch_exception(self, new_states):
-        try:
-            res = yield self._update_states(new_states)
-            defer.returnValue(res)
-        except Exception:
-            logger.exception("Error updating presence")
-
     @defer.inlineCallbacks
     def _update_states(self, new_states):
         """Updates presence of users. Sets the appropriate timeouts. Pokes
@@ -338,8 +337,6 @@ class PresenceHandler(object):
         logger.info("Handling presence timeouts")
         now = self.clock.time_msec()
 
-        try:
-            with Measure(self.clock, "presence_handle_timeouts"):
         # Fetch the list of users that *may* have timed out. Things may have
         # changed since the timeout was set, so we won't necessarily have to
         # take any action.
@@ -374,9 +371,7 @@ class PresenceHandler(object):
             now=now,
         )
 
-            run_in_background(self._update_states_and_catch_exception, changes)
+        return self._update_states(changes)
-        except Exception:
-            logger.exception("Exception in _handle_timeouts loop")
 
     @defer.inlineCallbacks
     def bump_presence_active_time(self, user):