Start fewer opentracing spans (#8640)

#8567 started a span for every background process. This is good as it means all Synapse code that gets run should be in a span (unless in the sentinel logging context), but it means we generate about 15x the number of spans as we did previously.

This PR attempts to reduce that number by a) not starting one for send commands to Redis, and b) deferring starting background processes until after we're sure they're necessary.

I don't really know how much this will help.

1 files changed, 8 insertions, 12 deletions

diff --git a/tests/handlers/test_appservice.py b/tests/handlers/test_appservice.py
index ee4f3da31c..53763cd0f9 100644
--- a/tests/handlers/test_appservice.py
+++ b/tests/handlers/test_appservice.py
@@ -42,7 +42,6 @@ class AppServiceHandlerTestCase(unittest.TestCase):
         hs.get_clock.return_value = MockClock()
         self.handler = ApplicationServicesHandler(hs)
 
-    @defer.inlineCallbacks
     def test_notify_interested_services(self):
         interested_service = self._mkservice(is_interested=True)
         services = [
@@ -62,14 +61,12 @@ class AppServiceHandlerTestCase(unittest.TestCase):
             defer.succeed((0, [event])),
             defer.succeed((0, [])),
         ]
-        yield defer.ensureDeferred(
-            self.handler.notify_interested_services(RoomStreamToken(None, 0))
-        )
+        self.handler.notify_interested_services(RoomStreamToken(None, 0))
+
         self.mock_scheduler.submit_event_for_as.assert_called_once_with(
             interested_service, event
         )
 
-    @defer.inlineCallbacks
     def test_query_user_exists_unknown_user(self):
         user_id = "@someone:anywhere"
         services = [self._mkservice(is_interested=True)]
@@ -83,12 +80,11 @@ class AppServiceHandlerTestCase(unittest.TestCase):
             defer.succeed((0, [event])),
             defer.succeed((0, [])),
         ]
-        yield defer.ensureDeferred(
-            self.handler.notify_interested_services(RoomStreamToken(None, 0))
-        )
+
+        self.handler.notify_interested_services(RoomStreamToken(None, 0))
+
         self.mock_as_api.query_user.assert_called_once_with(services[0], user_id)
 
-    @defer.inlineCallbacks
     def test_query_user_exists_known_user(self):
         user_id = "@someone:anywhere"
         services = [self._mkservice(is_interested=True)]
@@ -102,9 +98,9 @@ class AppServiceHandlerTestCase(unittest.TestCase):
             defer.succeed((0, [event])),
             defer.succeed((0, [])),
         ]
-        yield defer.ensureDeferred(
-            self.handler.notify_interested_services(RoomStreamToken(None, 0))
-        )
+
+        self.handler.notify_interested_services(RoomStreamToken(None, 0))
+
         self.assertFalse(
             self.mock_as_api.query_user.called,
             "query_user called when it shouldn't have been.",