2 files changed, 12 insertions, 3 deletions
diff --git a/synapse/util/caches/response_cache.py b/synapse/util/caches/response_cache.py
index 36686b479e..00af539880 100644
--- a/synapse/util/caches/response_cache.py
+++ b/synapse/util/caches/response_cache.py
@@ -24,9 +24,12 @@ class ResponseCache(object):
     used rather than trying to compute a new response.
     """
 
-    def __init__(self):
+    def __init__(self, hs, timeout_ms=0):
         self.pending_result_cache = {}  # Requests that haven't finished yet.
 
+        self.clock = hs.get_clock()
+        self.timeout_sec = timeout_ms / 1000.
+
     def get(self, key):
         result = self.pending_result_cache.get(key)
         if result is not None:
@@ -39,7 +42,13 @@ class ResponseCache(object):
         self.pending_result_cache[key] = result
 
         def remove(r):
-            self.pending_result_cache.pop(key, None)
+            if self.timeout_sec:
+                self.clock.call_later(
+                    self.timeout_sec,
+                    self.pending_result_cache.pop, key, None,
+                )
+            else:
+                self.pending_result_cache.pop(key, None)
             return r
 
         result.addBoth(remove)
diff --git a/synapse/util/retryutils.py b/synapse/util/retryutils.py
index 43cf11f3f6..49527f4d21 100644
--- a/synapse/util/retryutils.py
+++ b/synapse/util/retryutils.py
@@ -128,7 +128,7 @@ class RetryDestinationLimiter(object):
             )
 
         valid_err_code = False
-        if exc_type is CodeMessageException:
+        if exc_type is not None and issubclass(exc_type, CodeMessageException):
             valid_err_code = 0 <= exc_val.code < 500
 
         if exc_type is None or valid_err_code: