Deduplicate joins

tests/util/test_linearizer.py

@@ -0,0 +1,44 @@
+# -*- 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 tests import unittest
+
+from twisted.internet import defer
+
+from synapse.util.async import Linearizer
+
+
+class LinearizerTestCase(unittest.TestCase):
+
+    @defer.inlineCallbacks
+    def test_linearizer(self):
+        linearizer = Linearizer()
+
+        key = object()
+
+        d1 = linearizer.queue(key)
+        cm1 = yield d1
+
+        d2 = linearizer.queue(key)
+        self.assertFalse(d2.called)
+
+        with cm1:
+            self.assertFalse(d2.called)
+
+        self.assertTrue(d2.called)
+
+        with (yield d2):
+            pass