Add ability to wait for replication streams (#7542)

The idea here is that if an instance persists an event via the replication HTTP API it can return before we receive that event over replication, which can lead to races where code assumes that persisting an event immediately updates various caches (e.g. current state of the room).

Most of Synapse doesn't hit such races, so we don't do the waiting automagically, instead we do so where necessary to avoid unnecessary delays. We may decide to change our minds here if it turns out there are a lot of subtle races going on.

People probably want to look at this commit by commit.

1 files changed, 45 insertions, 20 deletions

diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index 13850ba672..2698a129ca 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -22,6 +22,7 @@ import logging
 import math
 import string
 from collections import OrderedDict
+from typing import Tuple
 
 from six import iteritems, string_types
 
@@ -518,7 +519,7 @@ class RoomCreationHandler(BaseHandler):
 
     async def create_room(
         self, requester, config, ratelimit=True, creator_join_profile=None
-    ):
+    ) -> Tuple[dict, int]:
         """ Creates a new room.
 
         Args:
@@ -535,9 +536,9 @@ class RoomCreationHandler(BaseHandler):
                 `avatar_url` and/or `displayname`.
 
         Returns:
-            Deferred[dict]:
-                a dict containing the keys `room_id` and, if an alias was
-                requested, `room_alias`.
+                First, a dict containing the keys `room_id` and, if an alias
+                was, requested, `room_alias`. Secondly, the stream_id of the
+                last persisted event.
         Raises:
             SynapseError if the room ID couldn't be stored, or something went
             horribly wrong.
@@ -669,7 +670,7 @@ class RoomCreationHandler(BaseHandler):
         # override any attempt to set room versions via the creation_content
         creation_content["room_version"] = room_version.identifier
 
-        await self._send_events_for_new_room(
+        last_stream_id = await self._send_events_for_new_room(
             requester,
             room_id,
             preset_config=preset_config,
@@ -683,7 +684,10 @@ class RoomCreationHandler(BaseHandler):
 
         if "name" in config:
             name = config["name"]
-            await self.event_creation_handler.create_and_send_nonmember_event(
+            (
+                _,
+                last_stream_id,
+            ) = await self.event_creation_handler.create_and_send_nonmember_event(
                 requester,
                 {
                     "type": EventTypes.Name,
@@ -697,7 +701,10 @@ class RoomCreationHandler(BaseHandler):
 
         if "topic" in config:
             topic = config["topic"]
-            await self.event_creation_handler.create_and_send_nonmember_event(
+            (
+                _,
+                last_stream_id,
+            ) = await self.event_creation_handler.create_and_send_nonmember_event(
                 requester,
                 {
                     "type": EventTypes.Topic,
@@ -715,7 +722,7 @@ class RoomCreationHandler(BaseHandler):
             if is_direct:
                 content["is_direct"] = is_direct
 
-            await self.room_member_handler.update_membership(
+            _, last_stream_id = await self.room_member_handler.update_membership(
                 requester,
                 UserID.from_string(invitee),
                 room_id,
@@ -729,7 +736,7 @@ class RoomCreationHandler(BaseHandler):
             id_access_token = invite_3pid.get("id_access_token")  # optional
             address = invite_3pid["address"]
             medium = invite_3pid["medium"]
-            await self.hs.get_room_member_handler().do_3pid_invite(
+            last_stream_id = await self.hs.get_room_member_handler().do_3pid_invite(
                 room_id,
                 requester.user,
                 medium,
@@ -745,7 +752,7 @@ class RoomCreationHandler(BaseHandler):
         if room_alias:
             result["room_alias"] = room_alias.to_string()
 
-        return result
+        return result, last_stream_id
 
     async def _send_events_for_new_room(
         self,
@@ -758,7 +765,13 @@ class RoomCreationHandler(BaseHandler):
         room_alias=None,
         power_level_content_override=None,  # Doesn't apply when initial state has power level state event content
         creator_join_profile=None,
-    ):
+    ) -> int:
+        """Sends the initial events into a new room.
+
+        Returns:
+            The stream_id of the last event persisted.
+        """
+
         def create(etype, content, **kwargs):
             e = {"type": etype, "content": content}
 
@@ -767,12 +780,16 @@ class RoomCreationHandler(BaseHandler):
 
             return e
 
-        async def send(etype, content, **kwargs):
+        async def send(etype, content, **kwargs) -> int:
             event = create(etype, content, **kwargs)
             logger.debug("Sending %s in new room", etype)
-            await self.event_creation_handler.create_and_send_nonmember_event(
+            (
+                _,
+                last_stream_id,
+            ) = await self.event_creation_handler.create_and_send_nonmember_event(
                 creator, event, ratelimit=False
             )
+            return last_stream_id
 
         config = RoomCreationHandler.PRESETS_DICT[preset_config]
 
@@ -797,7 +814,9 @@ class RoomCreationHandler(BaseHandler):
         # of the first events that get sent into a room.
         pl_content = initial_state.pop((EventTypes.PowerLevels, ""), None)
         if pl_content is not None:
-            await send(etype=EventTypes.PowerLevels, content=pl_content)
+            last_sent_stream_id = await send(
+                etype=EventTypes.PowerLevels, content=pl_content
+            )
         else:
             power_level_content = {
                 "users": {creator_id: 100},
@@ -830,33 +849,39 @@ class RoomCreationHandler(BaseHandler):
             if power_level_content_override:
                 power_level_content.update(power_level_content_override)
 
-            await send(etype=EventTypes.PowerLevels, content=power_level_content)
+            last_sent_stream_id = await send(
+                etype=EventTypes.PowerLevels, content=power_level_content
+            )
 
         if room_alias and (EventTypes.CanonicalAlias, "") not in initial_state:
-            await send(
+            last_sent_stream_id = await send(
                 etype=EventTypes.CanonicalAlias,
                 content={"alias": room_alias.to_string()},
             )
 
         if (EventTypes.JoinRules, "") not in initial_state:
-            await send(
+            last_sent_stream_id = await send(
                 etype=EventTypes.JoinRules, content={"join_rule": config["join_rules"]}
             )
 
         if (EventTypes.RoomHistoryVisibility, "") not in initial_state:
-            await send(
+            last_sent_stream_id = await send(
                 etype=EventTypes.RoomHistoryVisibility,
                 content={"history_visibility": config["history_visibility"]},
             )
 
         if config["guest_can_join"]:
             if (EventTypes.GuestAccess, "") not in initial_state:
-                await send(
+                last_sent_stream_id = await send(
                     etype=EventTypes.GuestAccess, content={"guest_access": "can_join"}
                 )
 
         for (etype, state_key), content in initial_state.items():
-            await send(etype=etype, state_key=state_key, content=content)
+            last_sent_stream_id = await send(
+                etype=etype, state_key=state_key, content=content
+            )
+
+        return last_sent_stream_id
 
     async def _generate_room_id(
         self, creator_id: str, is_public: str, room_version: RoomVersion,