1 files changed, 34 insertions, 2 deletions
diff --git a/synapse/util/caches/treecache.py b/synapse/util/caches/treecache.py
index 3b58860910..29d02f7e95 100644
--- a/synapse/util/caches/treecache.py
+++ b/synapse/util/caches/treecache.py
@@ -8,6 +8,7 @@ class TreeCache(object):
     Keys must be tuples.
     """
     def __init__(self):
+        self.size = 0
         self.root = {}
 
     def __setitem__(self, key, value):
@@ -20,7 +21,8 @@ class TreeCache(object):
         node = self.root
         for k in key[:-1]:
             node = node.setdefault(k, {})
-        node[key[-1]] = value
+        node[key[-1]] = _Entry(value)
+        self.size += 1
 
     def get(self, key, default=None):
         node = self.root
@@ -28,9 +30,10 @@ class TreeCache(object):
             node = node.get(k, None)
             if node is None:
                 return default
-        return node.get(key[-1], default)
+        return node.get(key[-1], _Entry(default)).value
 
     def clear(self):
+        self.size = 0
         self.root = {}
 
     def pop(self, key, default=None):
@@ -57,4 +60,33 @@ class TreeCache(object):
                 break
             node_and_keys[i+1][0].pop(k)
 
+        popped, cnt = _strip_and_count_entires(popped)
+        self.size -= cnt
         return popped
+
+    def __len__(self):
+        return self.size
+
+
+class _Entry(object):
+    __slots__ = ["value"]
+
+    def __init__(self, value):
+        self.value = value
+
+
+def _strip_and_count_entires(d):
+    """Takes an _Entry or dict with leaves of _Entry's, and either returns the
+    value or a dictionary with _Entry's replaced by their values.
+
+    Also returns the count of _Entry's
+    """
+    if isinstance(d, dict):
+        cnt = 0
+        for key, value in d.items():
+            v, n = _strip_and_count_entires(value)
+            d[key] = v
+            cnt += n
+        return d, cnt
+    else:
+        return d.value, 1