2 files changed, 11 insertions, 2 deletions
diff --git a/synapse/util/async.py b/synapse/util/async.py
index 0d6f48e2d8..40be7fe7e3 100644
--- a/synapse/util/async.py
+++ b/synapse/util/async.py
@@ -102,6 +102,15 @@ class ObservableDeferred(object):
     def observers(self):
         return self._observers
 
+    def has_called(self):
+        return self._result is not None
+
+    def has_succeeded(self):
+        return self._result is not None and self._result[0] is True
+
+    def get_result(self):
+        return self._result[1]
+
     def __getattr__(self, name):
         return getattr(self._deferred, name)
 
diff --git a/synapse/util/caches/descriptors.py b/synapse/util/caches/descriptors.py
index 4bbb16ed3c..5be4097279 100644
--- a/synapse/util/caches/descriptors.py
+++ b/synapse/util/caches/descriptors.py
@@ -311,12 +311,12 @@ class CacheListDescriptor(object):
 
                 try:
                     res = cache.get(tuple(key))
-                    if not res.called:
+                    if not res.has_succeeded():
                         res = res.observe()
                         res.addCallback(lambda r, arg: (arg, r), arg)
                         cached_defers[arg] = res
                     else:
-                        results[arg] = res.result
+                        results[arg] = res.get_result()
                 except KeyError:
                     missing.append(arg)