Revert "Revert accidental fast-forward merge from v1.49.0rc1"

This reverts commit 158d73ebdd.

tests/storage/test_background_update.py

@@ -1,8 +1,26 @@
-from unittest.mock import Mock
+# 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.
+
+# Use backported mock for AsyncMock support on Python 3.6.
+from mock import Mock
+
+from twisted.internet.defer import Deferred, ensureDeferred
 
 from synapse.storage.background_updates import BackgroundUpdater
 
 from tests import unittest
+from tests.test_utils import make_awaitable
 
 
 class BackgroundUpdateTestCase(unittest.HomeserverTestCase):
@@ -20,10 +38,10 @@ class BackgroundUpdateTestCase(unittest.HomeserverTestCase):
 
     def test_do_background_update(self):
         # the time we claim it takes to update one item when running the update
-        duration_ms = 4200
+        duration_ms = 10
 
         # the target runtime for each bg update
-        target_background_update_duration_ms = 5000000
+        target_background_update_duration_ms = 100
 
         store = self.hs.get_datastore()
         self.get_success(
@@ -48,10 +66,8 @@ class BackgroundUpdateTestCase(unittest.HomeserverTestCase):
         self.update_handler.side_effect = update
         self.update_handler.reset_mock()
         res = self.get_success(
-            self.updates.do_next_background_update(
-                target_background_update_duration_ms
-            ),
-            by=0.1,
+            self.updates.do_next_background_update(False),
+            by=0.01,
         )
         self.assertFalse(res)
 
@@ -74,16 +90,93 @@ class BackgroundUpdateTestCase(unittest.HomeserverTestCase):
 
         self.update_handler.side_effect = update
         self.update_handler.reset_mock()
-        result = self.get_success(
-            self.updates.do_next_background_update(target_background_update_duration_ms)
-        )
+        result = self.get_success(self.updates.do_next_background_update(False))
         self.assertFalse(result)
         self.update_handler.assert_called_once()
 
         # third step: we don't expect to be called any more
         self.update_handler.reset_mock()
-        result = self.get_success(
-            self.updates.do_next_background_update(target_background_update_duration_ms)
-        )
+        result = self.get_success(self.updates.do_next_background_update(False))
         self.assertTrue(result)
         self.assertFalse(self.update_handler.called)
+
+
+class BackgroundUpdateControllerTestCase(unittest.HomeserverTestCase):
+    def prepare(self, reactor, clock, homeserver):
+        self.updates: BackgroundUpdater = self.hs.get_datastore().db_pool.updates
+        # the base test class should have run the real bg updates for us
+        self.assertTrue(
+            self.get_success(self.updates.has_completed_background_updates())
+        )
+
+        self.update_deferred = Deferred()
+        self.update_handler = Mock(return_value=self.update_deferred)
+        self.updates.register_background_update_handler(
+            "test_update", self.update_handler
+        )
+
+        # Mock out the AsyncContextManager
+        self._update_ctx_manager = Mock(spec=["__aenter__", "__aexit__"])
+        self._update_ctx_manager.__aenter__ = Mock(
+            return_value=make_awaitable(None),
+        )
+        self._update_ctx_manager.__aexit__ = Mock(return_value=make_awaitable(None))
+
+        # Mock out the `update_handler` callback
+        self._on_update = Mock(return_value=self._update_ctx_manager)
+
+        # Define a default batch size value that's not the same as the internal default
+        # value (100).
+        self._default_batch_size = 500
+
+        # Register the callbacks with more mocks
+        self.hs.get_module_api().register_background_update_controller_callbacks(
+            on_update=self._on_update,
+            min_batch_size=Mock(return_value=make_awaitable(self._default_batch_size)),
+            default_batch_size=Mock(
+                return_value=make_awaitable(self._default_batch_size),
+            ),
+        )
+
+    def test_controller(self):
+        store = self.hs.get_datastore()
+        self.get_success(
+            store.db_pool.simple_insert(
+                "background_updates",
+                values={"update_name": "test_update", "progress_json": "{}"},
+            )
+        )
+
+        # Set the return value for the context manager.
+        enter_defer = Deferred()
+        self._update_ctx_manager.__aenter__ = Mock(return_value=enter_defer)
+
+        # Start the background update.
+        do_update_d = ensureDeferred(self.updates.do_next_background_update(True))
+
+        self.pump()
+
+        # `run_update` should have been called, but the update handler won't be
+        # called until the `enter_defer` (returned by `__aenter__`) is resolved.
+        self._on_update.assert_called_once_with(
+            "test_update",
+            "master",
+            False,
+        )
+        self.assertFalse(do_update_d.called)
+        self.assertFalse(self.update_deferred.called)
+
+        # Resolving the `enter_defer` should call the update handler, which then
+        # blocks.
+        enter_defer.callback(100)
+        self.pump()
+        self.update_handler.assert_called_once_with({}, self._default_batch_size)
+        self.assertFalse(self.update_deferred.called)
+        self._update_ctx_manager.__aexit__.assert_not_called()
+
+        # Resolving the update handler deferred should cause the
+        # `do_next_background_update` to finish and return
+        self.update_deferred.callback(100)
+        self.pump()
+        self._update_ctx_manager.__aexit__.assert_called()
+        self.get_success(do_update_d)