Improve exception handling for background processes

There were a bunch of places where we fire off a process to happen in the
background, but don't have any exception handling on it - instead relying on
the unhandled error being logged when the relevent deferred gets
garbage-collected.

This is unsatisfactory for a number of reasons:
 - logging on garbage collection is best-effort and may happen some time after
   the error, if at all
 - it can be hard to figure out where the error actually happened.
 - it is logged as a scary CRITICAL error which (a) I always forget to grep for
   and (b) it's not really CRITICAL if a background process we don't care about
   fails.

So this is an attempt to add exception handling to everything we fire off into
the background.

1 files changed, 16 insertions, 6 deletions

diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py

index 21628a8540..d168ff5b86 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -857,15 +857,25 @@ class EventCreationHandler(object):
         @defer.inlineCallbacks
         def _notify():
             yield run_on_reactor()
-            self.notifier.on_new_room_event(
-                event, event_stream_id, max_stream_id,
-                extra_users=extra_users
-            )
+            try:
+                self.notifier.on_new_room_event(
+                    event, event_stream_id, max_stream_id,
+                    extra_users=extra_users
+                )
+            except Exception:
+                logger.exception("Error notifying about new room event")
 
         preserve_fn(_notify)()
 
         if event.type == EventTypes.Message:
-            presence = self.hs.get_presence_handler()
             # We don't want to block sending messages on any presence code. This
             # matters as sometimes presence code can take a while.
-            preserve_fn(presence.bump_presence_active_time)(requester.user)
+            run_in_background(self._bump_active_time, requester.user)
+
+    @defer.inlineCallbacks
+    def _bump_active_time(self, user):
+        try:
+            presence = self.hs.get_presence_handler()
+            yield presence.bump_presence_active_time(user)
+        except Exception:
+            logger.exception("Error bumping presence active time")