Add a batching queue implementation. (#10017)

1 files changed, 169 insertions, 0 deletions

diff --git a/tests/util/test_batching_queue.py b/tests/util/test_batching_queue.py
new file mode 100644
index 0000000000..5def1e56c9
--- /dev/null
+++ b/tests/util/test_batching_queue.py
@@ -0,0 +1,169 @@
+# Copyright 2021 The Matrix.org Foundation C.I.C.
+#
+# 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 twisted.internet import defer
+
+from synapse.logging.context import make_deferred_yieldable
+from synapse.util.batching_queue import BatchingQueue
+
+from tests.server import get_clock
+from tests.unittest import TestCase
+
+
+class BatchingQueueTestCase(TestCase):
+    def setUp(self):
+        self.clock, hs_clock = get_clock()
+
+        self._pending_calls = []
+        self.queue = BatchingQueue("test_queue", hs_clock, self._process_queue)
+
+    async def _process_queue(self, values):
+        d = defer.Deferred()
+        self._pending_calls.append((values, d))
+        return await make_deferred_yieldable(d)
+
+    def test_simple(self):
+        """Tests the basic case of calling `add_to_queue` once and having
+        `_process_queue` return.
+        """
+
+        self.assertFalse(self._pending_calls)
+
+        queue_d = defer.ensureDeferred(self.queue.add_to_queue("foo"))
+
+        # The queue should wait a reactor tick before calling the processing
+        # function.
+        self.assertFalse(self._pending_calls)
+        self.assertFalse(queue_d.called)
+
+        # We should see a call to `_process_queue` after a reactor tick.
+        self.clock.pump([0])
+
+        self.assertEqual(len(self._pending_calls), 1)
+        self.assertEqual(self._pending_calls[0][0], ["foo"])
+        self.assertFalse(queue_d.called)
+
+        # Return value of the `_process_queue` should be propagated back.
+        self._pending_calls.pop()[1].callback("bar")
+
+        self.assertEqual(self.successResultOf(queue_d), "bar")
+
+    def test_batching(self):
+        """Test that multiple calls at the same time get batched up into one
+        call to `_process_queue`.
+        """
+
+        self.assertFalse(self._pending_calls)
+
+        queue_d1 = defer.ensureDeferred(self.queue.add_to_queue("foo1"))
+        queue_d2 = defer.ensureDeferred(self.queue.add_to_queue("foo2"))
+
+        self.clock.pump([0])
+
+        # We should see only *one* call to `_process_queue`
+        self.assertEqual(len(self._pending_calls), 1)
+        self.assertEqual(self._pending_calls[0][0], ["foo1", "foo2"])
+        self.assertFalse(queue_d1.called)
+        self.assertFalse(queue_d2.called)
+
+        # Return value of the `_process_queue` should be propagated back to both.
+        self._pending_calls.pop()[1].callback("bar")
+
+        self.assertEqual(self.successResultOf(queue_d1), "bar")
+        self.assertEqual(self.successResultOf(queue_d2), "bar")
+
+    def test_queuing(self):
+        """Test that we queue up requests while a `_process_queue` is being
+        called.
+        """
+
+        self.assertFalse(self._pending_calls)
+
+        queue_d1 = defer.ensureDeferred(self.queue.add_to_queue("foo1"))
+        self.clock.pump([0])
+
+        queue_d2 = defer.ensureDeferred(self.queue.add_to_queue("foo2"))
+
+        # We should see only *one* call to `_process_queue`
+        self.assertEqual(len(self._pending_calls), 1)
+        self.assertEqual(self._pending_calls[0][0], ["foo1"])
+        self.assertFalse(queue_d1.called)
+        self.assertFalse(queue_d2.called)
+
+        # Return value of the `_process_queue` should be propagated back to the
+        # first.
+        self._pending_calls.pop()[1].callback("bar1")
+
+        self.assertEqual(self.successResultOf(queue_d1), "bar1")
+        self.assertFalse(queue_d2.called)
+
+        # We should now see a second call to `_process_queue`
+        self.clock.pump([0])
+        self.assertEqual(len(self._pending_calls), 1)
+        self.assertEqual(self._pending_calls[0][0], ["foo2"])
+        self.assertFalse(queue_d2.called)
+
+        # Return value of the `_process_queue` should be propagated back to the
+        # second.
+        self._pending_calls.pop()[1].callback("bar2")
+
+        self.assertEqual(self.successResultOf(queue_d2), "bar2")
+
+    def test_different_keys(self):
+        """Test that calls to different keys get processed in parallel."""
+
+        self.assertFalse(self._pending_calls)
+
+        queue_d1 = defer.ensureDeferred(self.queue.add_to_queue("foo1", key=1))
+        self.clock.pump([0])
+        queue_d2 = defer.ensureDeferred(self.queue.add_to_queue("foo2", key=2))
+        self.clock.pump([0])
+
+        # We queue up another item with key=2 to check that we will keep taking
+        # things off the queue.
+        queue_d3 = defer.ensureDeferred(self.queue.add_to_queue("foo3", key=2))
+
+        # We should see two calls to `_process_queue`
+        self.assertEqual(len(self._pending_calls), 2)
+        self.assertEqual(self._pending_calls[0][0], ["foo1"])
+        self.assertEqual(self._pending_calls[1][0], ["foo2"])
+        self.assertFalse(queue_d1.called)
+        self.assertFalse(queue_d2.called)
+        self.assertFalse(queue_d3.called)
+
+        # Return value of the `_process_queue` should be propagated back to the
+        # first.
+        self._pending_calls.pop(0)[1].callback("bar1")
+
+        self.assertEqual(self.successResultOf(queue_d1), "bar1")
+        self.assertFalse(queue_d2.called)
+        self.assertFalse(queue_d3.called)
+
+        # Return value of the `_process_queue` should be propagated back to the
+        # second.
+        self._pending_calls.pop()[1].callback("bar2")
+
+        self.assertEqual(self.successResultOf(queue_d2), "bar2")
+        self.assertFalse(queue_d3.called)
+
+        # We should now see a call `_pending_calls` for `foo3`
+        self.clock.pump([0])
+        self.assertEqual(len(self._pending_calls), 1)
+        self.assertEqual(self._pending_calls[0][0], ["foo3"])
+        self.assertFalse(queue_d3.called)
+
+        # Return value of the `_process_queue` should be propagated back to the
+        # third deferred.
+        self._pending_calls.pop()[1].callback("bar4")
+
+        self.assertEqual(self.successResultOf(queue_d3), "bar4")