Fix logcontexts for running pushers

First of all, avoid resetting the logcontext before running the pushers, to fix
the "Starting db txn 'get_all_updated_receipts' from sentinel context" warning.

Instead, give them their own "background process" logcontexts.

synapse/app/pusher.py

@@ -162,11 +162,11 @@ class PusherReplicationHandler(ReplicationClientHandler):
                     else:
                         yield self.start_pusher(row.user_id, row.app_id, row.pushkey)
             elif stream_name == "events":
-                yield self.pusher_pool.on_new_notifications(
+                self.pusher_pool.on_new_notifications(
                     token, token,
                 )
             elif stream_name == "receipts":
-                yield self.pusher_pool.on_new_receipts(
+                self.pusher_pool.on_new_receipts(
                     token, token, set(row.room_id for row in rows)
                 )
         except Exception:

synapse/handlers/federation.py

@@ -2386,8 +2386,7 @@ class FederationHandler(BaseHandler):
             extra_users=extra_users
         )
 
-        logcontext.run_in_background(
-            self.pusher_pool.on_new_notifications,
+        self.pusher_pool.on_new_notifications(
             event_stream_id, max_stream_id,
         )
 

synapse/handlers/message.py

@@ -774,11 +774,8 @@ class EventCreationHandler(object):
             event, context=context
         )
 
-        # this intentionally does not yield: we don't care about the result
-        # and don't need to wait for it.
-        run_in_background(
-            self.pusher_pool.on_new_notifications,
-            event_stream_id, max_stream_id
+        self.pusher_pool.on_new_notifications(
+            event_stream_id, max_stream_id,
         )
 
         def _notify():

synapse/handlers/receipts.py

@@ -18,7 +18,6 @@ from twisted.internet import defer
 
 from synapse.types import get_domain_from_id
 from synapse.util import logcontext
-from synapse.util.logcontext import PreserveLoggingContext
 
 from ._base import BaseHandler
 
@@ -116,13 +115,12 @@ class ReceiptsHandler(BaseHandler):
 
         affected_room_ids = list(set([r["room_id"] for r in receipts]))
 
-        with PreserveLoggingContext():
         self.notifier.on_new_event(
             "receipt_key", max_batch_id, rooms=affected_room_ids
         )
         # Note that the min here shouldn't be relied upon to be accurate.
         self.hs.get_pusherpool().on_new_receipts(
-                min_batch_id, max_batch_id, affected_room_ids
+            min_batch_id, max_batch_id, affected_room_ids,
         )
 
         defer.returnValue(True)

synapse/push/pusherpool.py

@@ -18,6 +18,7 @@ import logging
 
 from twisted.internet import defer
 
+from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.push.pusher import PusherFactory
 from synapse.util.logcontext import make_deferred_yieldable, run_in_background
 
@@ -122,8 +123,14 @@ class PusherPool:
                     p['app_id'], p['pushkey'], p['user_name'],
                 )
 
-    @defer.inlineCallbacks
     def on_new_notifications(self, min_stream_id, max_stream_id):
+        run_as_background_process(
+            "on_new_notifications",
+            self._on_new_notifications, min_stream_id, max_stream_id,
+        )
+
+    @defer.inlineCallbacks
+    def _on_new_notifications(self, min_stream_id, max_stream_id):
         try:
             users_affected = yield self.store.get_push_action_users_in_range(
                 min_stream_id, max_stream_id
@@ -147,8 +154,14 @@ class PusherPool:
         except Exception:
             logger.exception("Exception in pusher on_new_notifications")
 
-    @defer.inlineCallbacks
     def on_new_receipts(self, min_stream_id, max_stream_id, affected_room_ids):
+        run_as_background_process(
+            "on_new_receipts",
+            self._on_new_receipts, min_stream_id, max_stream_id, affected_room_ids,
+        )
+
+    @defer.inlineCallbacks
+    def _on_new_receipts(self, min_stream_id, max_stream_id, affected_room_ids):
         try:
             # Need to subtract 1 from the minimum because the lower bound here
             # is not inclusive