Fix some looping_call calls which were broken in #3604

It turns out that looping_call does check the deferred returned by its
callback, and (at least in the case of client_ips), we were relying on this,
and I broke it in #3604.

Update run_as_background_process to return the deferred, and make sure we
return it to clock.looping_call.

changelog.d/3610.feature

@@ -0,0 +1 @@
+Add metrics to track resource usage by background processes

synapse/app/homeserver.py

@@ -429,7 +429,7 @@ def run(hs):
     stats_process = []
 
     def start_phone_stats_home():
-        run_as_background_process("phone_stats_home", phone_stats_home)
+        return run_as_background_process("phone_stats_home", phone_stats_home)
 
     @defer.inlineCallbacks
     def phone_stats_home():
@@ -502,7 +502,7 @@ def run(hs):
             )
 
     def generate_user_daily_visit_stats():
-        run_as_background_process(
+        return run_as_background_process(
             "generate_user_daily_visits",
             hs.get_datastore().generate_user_daily_visits,
         )

synapse/groups/attestations.py

@@ -153,7 +153,7 @@ class GroupAttestionRenewer(object):
         defer.returnValue({})
 
     def _start_renew_attestations(self):
-        run_as_background_process("renew_attestations", self._renew_attestations)
+        return run_as_background_process("renew_attestations", self._renew_attestations)
 
     @defer.inlineCallbacks
     def _renew_attestations(self):

synapse/handlers/profile.py

@@ -256,7 +256,7 @@ class ProfileHandler(BaseHandler):
                 )
 
     def _start_update_remote_profile_cache(self):
-        run_as_background_process(
+        return run_as_background_process(
             "Update remote profile", self._update_remote_profile_cache,
         )
 

synapse/metrics/background_process_metrics.py

@@ -151,13 +151,19 @@ def run_as_background_process(desc, func, *args, **kwargs):
     This should be used to wrap processes which are fired off to run in the
     background, instead of being associated with a particular request.
 
+    It returns a Deferred which completes when the function completes, but it doesn't
+    follow the synapse logcontext rules, which makes it appropriate for passing to
+    clock.looping_call and friends (or for firing-and-forgetting in the middle of a
+    normal synapse inlineCallbacks function).
+
     Args:
         desc (str): a description for this background process type
         func: a function, which may return a Deferred
         args: positional args for func
         kwargs: keyword args for func
 
-    Returns: None
+    Returns: Deferred which returns the result of func, but note that it does not
+        follow the synapse logcontext rules.
     """
     @defer.inlineCallbacks
     def run():
@@ -176,4 +182,4 @@ def run_as_background_process(desc, func, *args, **kwargs):
                 _background_processes[desc].remove(proc)
 
     with PreserveLoggingContext():
-        run()
+        return run()

synapse/rest/media/v1/media_repository.py

@@ -106,7 +106,7 @@ class MediaRepository(object):
         )
 
     def _start_update_recently_accessed(self):
-        run_as_background_process(
+        return run_as_background_process(
             "update_recently_accessed_media", self._update_recently_accessed,
         )
 

synapse/rest/media/v1/preview_url_resource.py

@@ -373,7 +373,7 @@ class PreviewUrlResource(Resource):
         })
 
     def _start_expire_url_cache_data(self):
-        run_as_background_process(
+        return run_as_background_process(
             "expire_url_cache_data", self._expire_url_cache_data,
         )
 

synapse/storage/client_ips.py

@@ -102,7 +102,7 @@ class ClientIpStore(background_updates.BackgroundUpdateStore):
                 to_update,
             )
 
-        run_as_background_process(
+        return run_as_background_process(
             "update_client_ips", update,
         )
 

synapse/storage/devices.py

@@ -712,7 +712,7 @@ class DeviceStore(SQLBaseStore):
 
             logger.info("Pruned %d device list outbound pokes", txn.rowcount)
 
-        run_as_background_process(
+        return run_as_background_process(
             "prune_old_outbound_device_pokes",
             self.runInteraction,
             "_prune_old_outbound_device_pokes",

synapse/storage/event_federation.py

@@ -549,7 +549,7 @@ class EventFederationStore(EventFederationWorkerStore):
                 sql,
                 (self.stream_ordering_month_ago, self.stream_ordering_month_ago,)
             )
-        run_as_background_process(
+        return run_as_background_process(
             "delete_old_forward_extrem_cache",
             self.runInteraction,
             "_delete_old_forward_extrem_cache",

synapse/storage/event_push_actions.py

@@ -460,7 +460,7 @@ class EventPushActionsWorkerStore(SQLBaseStore):
             )
 
     def _find_stream_orderings_for_times(self):
-        run_as_background_process(
+        return run_as_background_process(
             "event_push_action_stream_orderings",
             self.runInteraction,
             "_find_stream_orderings_for_times",
@@ -790,7 +790,7 @@ class EventPushActionsStore(EventPushActionsWorkerStore):
         """, (room_id, user_id, stream_ordering))
 
     def _start_rotate_notifs(self):
-        run_as_background_process("rotate_notifs", self._rotate_notifs)
+        return run_as_background_process("rotate_notifs", self._rotate_notifs)
 
     @defer.inlineCallbacks
     def _rotate_notifs(self):

synapse/storage/transactions.py

@@ -273,7 +273,9 @@ class TransactionStore(SQLBaseStore):
         return self.cursor_to_dict(txn)
 
     def _start_cleanup_transactions(self):
-        run_as_background_process("cleanup_transactions", self._cleanup_transactions)
+        return run_as_background_process(
+            "cleanup_transactions", self._cleanup_transactions,
+        )
 
     def _cleanup_transactions(self):
         now = self._clock.time_msec()

synapse/util/caches/expiringcache.py

@@ -64,7 +64,7 @@ class ExpiringCache(object):
             return
 
         def f():
-            run_as_background_process(
+            return run_as_background_process(
                 "prune_cache_%s" % self._cache_name,
                 self._prune_cache,
             )