Fix "Starting metrics collection from sentinel context" errors (#9053)

changelog.d/9053.bugfix

+Fix bug where we didn't correctly record CPU time spent in 'on_new_event' block.

synapse/notifier.py

@@ -396,31 +396,30 @@ class Notifier:
 
         Will wake up all listeners for the given users and rooms.
         """
-        with PreserveLoggingContext():
-            with Measure(self.clock, "on_new_event"):
-                user_streams = set()
+        with Measure(self.clock, "on_new_event"):
+            user_streams = set()
 
-                for user in users:
-                    user_stream = self.user_to_user_stream.get(str(user))
-                    if user_stream is not None:
-                        user_streams.add(user_stream)
+            for user in users:
+                user_stream = self.user_to_user_stream.get(str(user))
+                if user_stream is not None:
+                    user_streams.add(user_stream)
 
-                for room in rooms:
-                    user_streams |= self.room_to_user_streams.get(room, set())
+            for room in rooms:
+                user_streams |= self.room_to_user_streams.get(room, set())
 
-                time_now_ms = self.clock.time_msec()
-                for user_stream in user_streams:
-                    try:
-                        user_stream.notify(stream_key, new_token, time_now_ms)
-                    except Exception:
-                        logger.exception("Failed to notify listener")
+            time_now_ms = self.clock.time_msec()
+            for user_stream in user_streams:
+                try:
+                    user_stream.notify(stream_key, new_token, time_now_ms)
+                except Exception:
+                    logger.exception("Failed to notify listener")
 
-                self.notify_replication()
+            self.notify_replication()
 
-                # Notify appservices
-                self._notify_app_services_ephemeral(
-                    stream_key, new_token, users,
-                )
+            # Notify appservices
+            self._notify_app_services_ephemeral(
+                stream_key, new_token, users,
+            )
 
     def on_new_replication_data(self) -> None:
         """Used to inform replication listeners that something has happened

synapse/util/metrics.py

@@ -111,7 +111,8 @@ class Measure:
         curr_context = current_context()
         if not curr_context:
             logger.warning(
-                "Starting metrics collection from sentinel context: metrics will be lost"
+                "Starting metrics collection %r from sentinel context: metrics will be lost",
+                name,
             )
             parent_context = None
         else: