diff --git a/changelog.d/6291.misc b/changelog.d/6291.misc
new file mode 100644
index 0000000000..7b1bb4b679
--- /dev/null
+++ b/changelog.d/6291.misc
@@ -0,0 +1 @@
+Change cache descriptors to always return deferreds.
diff --git a/synapse/util/async_helpers.py b/synapse/util/async_helpers.py
index 7659eaeb42..b60a604474 100644
--- a/synapse/util/async_helpers.py
+++ b/synapse/util/async_helpers.py
@@ -86,11 +86,12 @@ class ObservableDeferred(object):
deferred.addCallbacks(callback, errback)
- def observe(self):
+ def observe(self) -> defer.Deferred:
"""Observe the underlying deferred.
- Can return either a deferred if the underlying deferred is still pending
- (or has failed), or the actual value. Callers may need to use maybeDeferred.
+ This returns a brand new deferred that is resolved when the underlying
+ deferred is resolved. Interacting with the returned deferred does not
+ effect the underdlying deferred.
"""
if not self._result:
d = defer.Deferred()
@@ -105,7 +106,7 @@ class ObservableDeferred(object):
return d
else:
success, res = self._result
- return res if success else defer.fail(res)
+ return defer.succeed(res) if success else defer.fail(res)
def observers(self):
return self._observers
diff --git a/tests/storage/test__base.py b/tests/storage/test__base.py
index dd49a14524..9b81b536f5 100644
--- a/tests/storage/test__base.py
+++ b/tests/storage/test__base.py
@@ -197,7 +197,7 @@ class CacheDecoratorTestCase(unittest.TestCase):
a.func.prefill(("foo",), ObservableDeferred(d))
- self.assertEquals(a.func("foo"), d.result)
+ self.assertEquals(a.func("foo").result, d.result)
self.assertEquals(callcount[0], 0)
@defer.inlineCallbacks
diff --git a/tests/util/caches/test_descriptors.py b/tests/util/caches/test_descriptors.py
index f907903511..39e360fe24 100644
--- a/tests/util/caches/test_descriptors.py
+++ b/tests/util/caches/test_descriptors.py
@@ -310,14 +310,14 @@ class DescriptorTestCase(unittest.TestCase):
obj.mock.return_value = ["spam", "eggs"]
r = obj.fn(1, 2)
- self.assertEqual(r, ["spam", "eggs"])
+ self.assertEqual(r.result, ["spam", "eggs"])
obj.mock.assert_called_once_with(1, 2)
obj.mock.reset_mock()
# a call with different params should call the mock again
obj.mock.return_value = ["chips"]
r = obj.fn(1, 3)
- self.assertEqual(r, ["chips"])
+ self.assertEqual(r.result, ["chips"])
obj.mock.assert_called_once_with(1, 3)
obj.mock.reset_mock()
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