Add Limiter: limit concurrent access to resource

tests/util/test_limiter.py

@@ -0,0 +1,70 @@
+# -*- 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 Limiter
+
+
+class LimiterTestCase(unittest.TestCase):
+
+    @defer.inlineCallbacks
+    def test_limiter(self):
+        limiter = Limiter(3)
+
+        key = object()
+
+        d1 = limiter.queue(key)
+        cm1 = yield d1
+
+        d2 = limiter.queue(key)
+        cm2 = yield d2
+
+        d3 = limiter.queue(key)
+        cm3 = yield d3
+
+        d4 = limiter.queue(key)
+        self.assertFalse(d4.called)
+
+        d5 = limiter.queue(key)
+        self.assertFalse(d5.called)
+
+        with cm1:
+            self.assertFalse(d4.called)
+            self.assertFalse(d5.called)
+
+        self.assertTrue(d4.called)
+        self.assertFalse(d5.called)
+
+        with cm3:
+            self.assertFalse(d5.called)
+
+        self.assertTrue(d5.called)
+
+        with cm2:
+            pass
+
+        with (yield d4):
+            pass
+
+        with (yield d5):
+            pass
+
+        d6 = limiter.queue(key)
+        with (yield d6):
+            pass