Merge pull request #2842 from matrix-org/rav/state_resolution_handler

Factor out resolve_state_groups to a separate handler

4 files changed, 116 insertions, 65 deletions

diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 677532c87b..8ee9434c9b 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -808,13 +808,12 @@ class FederationHandler(BaseHandler):
         event_ids = list(extremities.keys())
 
         logger.debug("calling resolve_state_groups in _maybe_backfill")
+        resolve = logcontext.preserve_fn(
+            self.state_handler.resolve_state_groups_for_events
+        )
         states = yield logcontext.make_deferred_yieldable(defer.gatherResults(
-            [
-                logcontext.preserve_fn(self.state_handler.resolve_state_groups)(
-                    room_id, [e]
-                )
-                for e in event_ids
-            ], consumeErrors=True,
+            [resolve(room_id, [e]) for e in event_ids],
+            consumeErrors=True,
         ))
         states = dict(zip(event_ids, [s.state for s in states]))
 
diff --git a/synapse/server.py b/synapse/server.py
index ff8a8fbc46..3173aed1d0 100644
--- a/synapse/server.py
+++ b/synapse/server.py
@@ -66,7 +66,7 @@ from synapse.rest.media.v1.media_repository import (
     MediaRepository,
     MediaRepositoryResource,
 )
-from synapse.state import StateHandler
+from synapse.state import StateHandler, StateResolutionHandler
 from synapse.storage import DataStore
 from synapse.streams.events import EventSources
 from synapse.util import Clock
@@ -102,6 +102,7 @@ class HomeServer(object):
         'v1auth',
         'auth',
         'state_handler',
+        'state_resolution_handler',
         'presence_handler',
         'sync_handler',
         'typing_handler',
@@ -224,6 +225,9 @@ class HomeServer(object):
     def build_state_handler(self):
         return StateHandler(self)
 
+    def build_state_resolution_handler(self):
+        return StateResolutionHandler(self)
+
     def build_presence_handler(self):
         return PresenceHandler(self)
 
diff --git a/synapse/server.pyi b/synapse/server.pyi
index 41416ef252..c3a9a3847b 100644
--- a/synapse/server.pyi
+++ b/synapse/server.pyi
@@ -34,6 +34,9 @@ class HomeServer(object):
     def get_state_handler(self) -> synapse.state.StateHandler:
         pass
 
+    def get_state_resolution_handler(self) -> synapse.state.StateResolutionHandler:
+        pass
+
     def get_deactivate_account_handler(self) -> synapse.handlers.deactivate_account.DeactivateAccountHandler:
         pass
 
diff --git a/synapse/state.py b/synapse/state.py
index 037f24dd79..273f9911ca 100644
--- a/synapse/state.py
+++ b/synapse/state.py
@@ -85,31 +85,19 @@ class _StateCacheEntry(object):
 
 
 class StateHandler(object):
-    """ Responsible for doing state conflict resolution.
+    """Fetches bits of state from the stores, and does state resolution
+    where necessary
     """
 
     def __init__(self, hs):
         self.clock = hs.get_clock()
         self.store = hs.get_datastore()
         self.hs = hs
-
-        # dict of set of event_ids -> _StateCacheEntry.
-        self._state_cache = None
-        self.resolve_linearizer = Linearizer(name="state_resolve_lock")
+        self._state_resolution_handler = hs.get_state_resolution_handler()
 
     def start_caching(self):
-        logger.debug("start_caching")
-
-        self._state_cache = ExpiringCache(
-            cache_name="state_cache",
-            clock=self.clock,
-            max_len=SIZE_OF_CACHE,
-            expiry_ms=EVICTION_TIMEOUT_SECONDS * 1000,
-            iterable=True,
-            reset_expiry_on_get=True,
-        )
-
-        self._state_cache.start()
+        # TODO: remove this shim
+        self._state_resolution_handler.start_caching()
 
     @defer.inlineCallbacks
     def get_current_state(self, room_id, event_type=None, state_key="",
@@ -131,7 +119,7 @@ class StateHandler(object):
             latest_event_ids = yield self.store.get_latest_event_ids_in_room(room_id)
 
         logger.debug("calling resolve_state_groups from get_current_state")
-        ret = yield self.resolve_state_groups(room_id, latest_event_ids)
+        ret = yield self.resolve_state_groups_for_events(room_id, latest_event_ids)
         state = ret.state
 
         if event_type:
@@ -168,7 +156,7 @@ class StateHandler(object):
             latest_event_ids = yield self.store.get_latest_event_ids_in_room(room_id)
 
         logger.debug("calling resolve_state_groups from get_current_state_ids")
-        ret = yield self.resolve_state_groups(room_id, latest_event_ids)
+        ret = yield self.resolve_state_groups_for_events(room_id, latest_event_ids)
         state = ret.state
 
         defer.returnValue(state)
@@ -178,7 +166,7 @@ class StateHandler(object):
         if not latest_event_ids:
             latest_event_ids = yield self.store.get_latest_event_ids_in_room(room_id)
         logger.debug("calling resolve_state_groups from get_current_user_in_room")
-        entry = yield self.resolve_state_groups(room_id, latest_event_ids)
+        entry = yield self.resolve_state_groups_for_events(room_id, latest_event_ids)
         joined_users = yield self.store.get_joined_users_from_state(room_id, entry)
         defer.returnValue(joined_users)
 
@@ -187,7 +175,7 @@ class StateHandler(object):
         if not latest_event_ids:
             latest_event_ids = yield self.store.get_latest_event_ids_in_room(room_id)
         logger.debug("calling resolve_state_groups from get_current_hosts_in_room")
-        entry = yield self.resolve_state_groups(room_id, latest_event_ids)
+        entry = yield self.resolve_state_groups_for_events(room_id, latest_event_ids)
         joined_hosts = yield self.store.get_joined_hosts(room_id, entry)
         defer.returnValue(joined_hosts)
 
@@ -245,7 +233,7 @@ class StateHandler(object):
             defer.returnValue(context)
 
         logger.debug("calling resolve_state_groups from compute_event_context")
-        entry = yield self.resolve_state_groups(
+        entry = yield self.resolve_state_groups_for_events(
             event.room_id, [e for e, _ in event.prev_events],
         )
 
@@ -287,8 +275,7 @@ class StateHandler(object):
         defer.returnValue(context)
 
     @defer.inlineCallbacks
-    @log_function
-    def resolve_state_groups(self, room_id, event_ids):
+    def resolve_state_groups_for_events(self, room_id, event_ids):
         """ Given a list of event_ids this method fetches the state at each
         event, resolves conflicts between them and returns them.
 
@@ -308,13 +295,7 @@ class StateHandler(object):
             room_id, event_ids
         )
 
-        logger.debug(
-            "resolve_state_groups state_groups %s",
-            state_groups_ids.keys()
-        )
-
-        group_names = frozenset(state_groups_ids.keys())
-        if len(group_names) == 1:
+        if len(state_groups_ids) == 1:
             name, state_list = state_groups_ids.items().pop()
 
             prev_group, delta_ids = yield self.store.get_state_group_delta(name)
@@ -326,6 +307,92 @@ class StateHandler(object):
                 delta_ids=delta_ids,
             ))
 
+        result = yield self._state_resolution_handler.resolve_state_groups(
+            room_id, state_groups_ids, self._state_map_factory,
+        )
+        defer.returnValue(result)
+
+    def _state_map_factory(self, ev_ids):
+        return self.store.get_events(
+            ev_ids, get_prev_content=False, check_redacted=False,
+        )
+
+    def resolve_events(self, state_sets, event):
+        logger.info(
+            "Resolving state for %s with %d groups", event.room_id, len(state_sets)
+        )
+        state_set_ids = [{
+            (ev.type, ev.state_key): ev.event_id
+            for ev in st
+        } for st in state_sets]
+
+        state_map = {
+            ev.event_id: ev
+            for st in state_sets
+            for ev in st
+        }
+
+        with Measure(self.clock, "state._resolve_events"):
+            new_state = resolve_events_with_state_map(state_set_ids, state_map)
+
+        new_state = {
+            key: state_map[ev_id] for key, ev_id in new_state.items()
+        }
+
+        return new_state
+
+
+class StateResolutionHandler(object):
+    """Responsible for doing state conflict resolution.
+
+    Note that the storage layer depends on this handler, so all functions must
+    be storage-independent.
+    """
+    def __init__(self, hs):
+        self.clock = hs.get_clock()
+
+        # dict of set of event_ids -> _StateCacheEntry.
+        self._state_cache = None
+        self.resolve_linearizer = Linearizer(name="state_resolve_lock")
+
+    def start_caching(self):
+        logger.debug("start_caching")
+
+        self._state_cache = ExpiringCache(
+            cache_name="state_cache",
+            clock=self.clock,
+            max_len=SIZE_OF_CACHE,
+            expiry_ms=EVICTION_TIMEOUT_SECONDS * 1000,
+            iterable=True,
+            reset_expiry_on_get=True,
+        )
+
+        self._state_cache.start()
+
+    @defer.inlineCallbacks
+    @log_function
+    def resolve_state_groups(self, room_id, state_groups_ids, state_map_factory):
+        """Resolves conflicts between a set of state groups
+
+        Always generates a new state group (unless we hit the cache), so should
+        not be called for a single state group
+
+        Args:
+            room_id (str): room we are resolving for (used for logging)
+            state_groups_ids (dict[int, dict[(str, str), str]]):
+                 map from state group id to the state in that state group
+                (where 'state' is a map from state key to event id)
+
+        Returns:
+            Deferred[_StateCacheEntry]: resolved state
+        """
+        logger.debug(
+            "resolve_state_groups state_groups %s",
+            state_groups_ids.keys()
+        )
+
+        group_names = frozenset(state_groups_ids.keys())
+
         with (yield self.resolve_linearizer.queue(group_names)):
             if self._state_cache is not None:
                 cache = self._state_cache.get(group_names, None)
@@ -356,15 +423,17 @@ class StateHandler(object):
                 with Measure(self.clock, "state._resolve_events"):
                     new_state = yield resolve_events_with_factory(
                         state_groups_ids.values(),
-                        state_map_factory=lambda ev_ids: self.store.get_events(
-                            ev_ids, get_prev_content=False, check_redacted=False,
-                        ),
+                        state_map_factory=state_map_factory,
                     )
             else:
                 new_state = {
                     key: e_ids.pop() for key, e_ids in state.items()
                 }
 
+            # if the new state matches any of the input state groups, we can
+            # use that state group again. Otherwise we will generate a state_id
+            # which will be used as a cache key for future resolutions, but
+            # not get persisted.
             state_group = None
             new_state_event_ids = frozenset(new_state.values())
             for sg, events in state_groups_ids.items():
@@ -401,30 +470,6 @@ class StateHandler(object):
 
             defer.returnValue(cache)
 
-    def resolve_events(self, state_sets, event):
-        logger.info(
-            "Resolving state for %s with %d groups", event.room_id, len(state_sets)
-        )
-        state_set_ids = [{
-            (ev.type, ev.state_key): ev.event_id
-            for ev in st
-        } for st in state_sets]
-
-        state_map = {
-            ev.event_id: ev
-            for st in state_sets
-            for ev in st
-        }
-
-        with Measure(self.clock, "state._resolve_events"):
-            new_state = resolve_events_with_state_map(state_set_ids, state_map)
-
-        new_state = {
-            key: state_map[ev_id] for key, ev_id in new_state.items()
-        }
-
-        return new_state
-
 
 def _ordered_events(events):
     def key_func(e):