1 files changed, 86 insertions, 0 deletions
diff --git a/synapse/util/caches/room_change_cache.py b/synapse/util/caches/room_change_cache.py
new file mode 100644
index 0000000000..3a873c9c30
--- /dev/null
+++ b/synapse/util/caches/room_change_cache.py
@@ -0,0 +1,86 @@
+# -*- coding: utf-8 -*-
+# Copyright 2016 OpenMarket Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from synapse.util.caches import cache_counter, caches_by_name
+
+
+from blist import sorteddict
+import logging
+
+
+logger = logging.getLogger(__name__)
+
+
+class RoomStreamChangeCache(object):
+    """Keeps track of the stream_id of the latest change in rooms.
+
+    Given a list of rooms and stream key, it will give a subset of rooms that
+    may have changed since that key. If the key is too old then the cache
+    will simply return all rooms.
+    """
+    def __init__(self, name, current_key, size_of_cache=10000):
+        self._size_of_cache = size_of_cache
+        self._room_to_key = {}
+        self._cache = sorteddict()
+        self._earliest_known_key = current_key
+        self.name = name
+        caches_by_name[self.name] = self._cache
+
+    def get_room_has_changed(self, room_id, key):
+        if key <= self._earliest_known_key:
+            return True
+
+        room_key = self._room_to_key.get(room_id, None)
+        if room_key is None:
+            return True
+
+        if key < room_key:
+            return True
+
+        return False
+
+    def get_rooms_changed(self, store, room_ids, key):
+        """Returns subset of room ids that have had new things since the
+        given key. If the key is too old it will just return the given list.
+        """
+        if key > self._earliest_known_key:
+            keys = self._cache.keys()
+            i = keys.bisect_right(key)
+
+            result = set(
+                self._cache[k] for k in keys[i:]
+            ).intersection(room_ids)
+
+            cache_counter.inc_hits(self.name)
+        else:
+            result = room_ids
+            cache_counter.inc_misses(self.name)
+
+        return result
+
+    def room_has_changed(self, store, room_id, key):
+        """Informs the cache that the room has been changed at the given key.
+        """
+        if key > self._earliest_known_key:
+            old_key = self._room_to_key.get(room_id, None)
+            if old_key:
+                key = max(key, old_key)
+                self._cache.pop(old_key, None)
+            self._cache[key] = room_id
+
+            while len(self._cache) > self._size_of_cache:
+                k, r = self._cache.popitem()
+                self._earliest_key = max(k, self._earliest_key)
+                self._room_to_key.pop(r, None)