ObservableDeferred: run observers in order (#11229)

tests/util/test_async_helpers.py

@@ -0,0 +1,173 @@
+# Copyright 2019 New Vector 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 twisted.internet import defer
+from twisted.internet.defer import CancelledError, Deferred
+from twisted.internet.task import Clock
+
+from synapse.logging.context import (
+    SENTINEL_CONTEXT,
+    LoggingContext,
+    PreserveLoggingContext,
+    current_context,
+)
+from synapse.util.async_helpers import ObservableDeferred, timeout_deferred
+
+from tests.unittest import TestCase
+
+
+class ObservableDeferredTest(TestCase):
+    def test_succeed(self):
+        origin_d = Deferred()
+        observable = ObservableDeferred(origin_d)
+
+        observer1 = observable.observe()
+        observer2 = observable.observe()
+
+        self.assertFalse(observer1.called)
+        self.assertFalse(observer2.called)
+
+        # check the first observer is called first
+        def check_called_first(res):
+            self.assertFalse(observer2.called)
+            return res
+
+        observer1.addBoth(check_called_first)
+
+        # store the results
+        results = [None, None]
+
+        def check_val(res, idx):
+            results[idx] = res
+            return res
+
+        observer1.addCallback(check_val, 0)
+        observer2.addCallback(check_val, 1)
+
+        origin_d.callback(123)
+        self.assertEqual(results[0], 123, "observer 1 callback result")
+        self.assertEqual(results[1], 123, "observer 2 callback result")
+
+    def test_failure(self):
+        origin_d = Deferred()
+        observable = ObservableDeferred(origin_d, consumeErrors=True)
+
+        observer1 = observable.observe()
+        observer2 = observable.observe()
+
+        self.assertFalse(observer1.called)
+        self.assertFalse(observer2.called)
+
+        # check the first observer is called first
+        def check_called_first(res):
+            self.assertFalse(observer2.called)
+            return res
+
+        observer1.addBoth(check_called_first)
+
+        # store the results
+        results = [None, None]
+
+        def check_val(res, idx):
+            results[idx] = res
+            return None
+
+        observer1.addErrback(check_val, 0)
+        observer2.addErrback(check_val, 1)
+
+        try:
+            raise Exception("gah!")
+        except Exception as e:
+            origin_d.errback(e)
+        self.assertEqual(str(results[0].value), "gah!", "observer 1 errback result")
+        self.assertEqual(str(results[1].value), "gah!", "observer 2 errback result")
+
+
+class TimeoutDeferredTest(TestCase):
+    def setUp(self):
+        self.clock = Clock()
+
+    def test_times_out(self):
+        """Basic test case that checks that the original deferred is cancelled and that
+        the timing-out deferred is errbacked
+        """
+        cancelled = [False]
+
+        def canceller(_d):
+            cancelled[0] = True
+
+        non_completing_d = Deferred(canceller)
+        timing_out_d = timeout_deferred(non_completing_d, 1.0, self.clock)
+
+        self.assertNoResult(timing_out_d)
+        self.assertFalse(cancelled[0], "deferred was cancelled prematurely")
+
+        self.clock.pump((1.0,))
+
+        self.assertTrue(cancelled[0], "deferred was not cancelled by timeout")
+        self.failureResultOf(timing_out_d, defer.TimeoutError)
+
+    def test_times_out_when_canceller_throws(self):
+        """Test that we have successfully worked around
+        https://twistedmatrix.com/trac/ticket/9534"""
+
+        def canceller(_d):
+            raise Exception("can't cancel this deferred")
+
+        non_completing_d = Deferred(canceller)
+        timing_out_d = timeout_deferred(non_completing_d, 1.0, self.clock)
+
+        self.assertNoResult(timing_out_d)
+
+        self.clock.pump((1.0,))
+
+        self.failureResultOf(timing_out_d, defer.TimeoutError)
+
+    def test_logcontext_is_preserved_on_cancellation(self):
+        blocking_was_cancelled = [False]
+
+        @defer.inlineCallbacks
+        def blocking():
+            non_completing_d = Deferred()
+            with PreserveLoggingContext():
+                try:
+                    yield non_completing_d
+                except CancelledError:
+                    blocking_was_cancelled[0] = True
+                    raise
+
+        with LoggingContext("one") as context_one:
+            # the errbacks should be run in the test logcontext
+            def errback(res, deferred_name):
+                self.assertIs(
+                    current_context(),
+                    context_one,
+                    "errback %s run in unexpected logcontext %s"
+                    % (deferred_name, current_context()),
+                )
+                return res
+
+            original_deferred = blocking()
+            original_deferred.addErrback(errback, "orig")
+            timing_out_d = timeout_deferred(original_deferred, 1.0, self.clock)
+            self.assertNoResult(timing_out_d)
+            self.assertIs(current_context(), SENTINEL_CONTEXT)
+            timing_out_d.addErrback(errback, "timingout")
+
+            self.clock.pump((1.0,))
+
+            self.assertTrue(
+                blocking_was_cancelled[0], "non-completing deferred was not cancelled"
+            )
+            self.failureResultOf(timing_out_d, defer.TimeoutError)
+            self.assertIs(current_context(), context_one)