1 files changed, 37 insertions, 1 deletions
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index fff0b5fa12..187dedae7d 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -53,6 +53,7 @@ from synapse.events.snapshot import EventContext, UnpersistedEventContextBase
 from synapse.events.utils import SerializeEventConfig, maybe_upsert_event_field
 from synapse.events.validator import EventValidator
 from synapse.handlers.directory import DirectoryHandler
+from synapse.handlers.worker_lock import DELETE_ROOM_LOCK_NAME
 from synapse.logging import opentracing
 from synapse.logging.context import make_deferred_yieldable, run_in_background
 from synapse.metrics.background_process_metrics import run_as_background_process
@@ -485,6 +486,7 @@ class EventCreationHandler:
         self._events_shard_config = self.config.worker.events_shard_config
         self._instance_name = hs.get_instance_name()
         self._notifier = hs.get_notifier()
+        self._worker_lock_handler = hs.get_worker_locks_handler()
 
         self.room_prejoin_state_types = self.hs.config.api.room_prejoin_state
 
@@ -1010,6 +1012,37 @@ class EventCreationHandler:
                         event.internal_metadata.stream_ordering,
                     )
 
+        async with self._worker_lock_handler.acquire_read_write_lock(
+            DELETE_ROOM_LOCK_NAME, room_id, write=False
+        ):
+            return await self._create_and_send_nonmember_event_locked(
+                requester=requester,
+                event_dict=event_dict,
+                allow_no_prev_events=allow_no_prev_events,
+                prev_event_ids=prev_event_ids,
+                state_event_ids=state_event_ids,
+                ratelimit=ratelimit,
+                txn_id=txn_id,
+                ignore_shadow_ban=ignore_shadow_ban,
+                outlier=outlier,
+                depth=depth,
+            )
+
+    async def _create_and_send_nonmember_event_locked(
+        self,
+        requester: Requester,
+        event_dict: dict,
+        allow_no_prev_events: bool = False,
+        prev_event_ids: Optional[List[str]] = None,
+        state_event_ids: Optional[List[str]] = None,
+        ratelimit: bool = True,
+        txn_id: Optional[str] = None,
+        ignore_shadow_ban: bool = False,
+        outlier: bool = False,
+        depth: Optional[int] = None,
+    ) -> Tuple[EventBase, int]:
+        room_id = event_dict["room_id"]
+
         # If we don't have any prev event IDs specified then we need to
         # check that the host is in the room (as otherwise populating the
         # prev events will fail), at which point we may as well check the
@@ -1923,7 +1956,10 @@ class EventCreationHandler:
         )
 
         for room_id in room_ids:
-            dummy_event_sent = await self._send_dummy_event_for_room(room_id)
+            async with self._worker_lock_handler.acquire_read_write_lock(
+                DELETE_ROOM_LOCK_NAME, room_id, write=False
+            ):
+                dummy_event_sent = await self._send_dummy_event_for_room(room_id)
 
             if not dummy_event_sent:
                 # Did not find a valid user in the room, so remove from future attempts