ObservableDeferred: run observers in order (#11229)

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Richard van der Hoff 2021-11-02 00:17:35 +00:00 committed by GitHub
parent 93aa670642
commit 46d0937447
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4 changed files with 88 additions and 20 deletions

1
changelog.d/11229.misc Normal file
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@ -0,0 +1 @@
`ObservableDeferred`: run registered observers in order.

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@ -22,11 +22,11 @@ from typing import (
Any,
Awaitable,
Callable,
Collection,
Dict,
Generic,
Hashable,
Iterable,
List,
Optional,
Set,
TypeVar,
@ -76,12 +76,17 @@ class ObservableDeferred(Generic[_T]):
def __init__(self, deferred: "defer.Deferred[_T]", consumeErrors: bool = False):
object.__setattr__(self, "_deferred", deferred)
object.__setattr__(self, "_result", None)
object.__setattr__(self, "_observers", set())
object.__setattr__(self, "_observers", [])
def callback(r):
object.__setattr__(self, "_result", (True, r))
while self._observers:
observer = self._observers.pop()
# once we have set _result, no more entries will be added to _observers,
# so it's safe to replace it with the empty tuple.
observers = self._observers
object.__setattr__(self, "_observers", ())
for observer in observers:
try:
observer.callback(r)
except Exception as e:
@ -95,12 +100,16 @@ class ObservableDeferred(Generic[_T]):
def errback(f):
object.__setattr__(self, "_result", (False, f))
while self._observers:
# once we have set _result, no more entries will be added to _observers,
# so it's safe to replace it with the empty tuple.
observers = self._observers
object.__setattr__(self, "_observers", ())
for observer in observers:
# This is a little bit of magic to correctly propagate stack
# traces when we `await` on one of the observer deferreds.
f.value.__failure__ = f
observer = self._observers.pop()
try:
observer.errback(f)
except Exception as e:
@ -127,20 +136,13 @@ class ObservableDeferred(Generic[_T]):
"""
if not self._result:
d: "defer.Deferred[_T]" = defer.Deferred()
def remove(r):
self._observers.discard(d)
return r
d.addBoth(remove)
self._observers.add(d)
self._observers.append(d)
return d
else:
success, res = self._result
return defer.succeed(res) if success else defer.fail(res)
def observers(self) -> "List[defer.Deferred[_T]]":
def observers(self) -> "Collection[defer.Deferred[_T]]":
return self._observers
def has_called(self) -> bool:

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@ -47,9 +47,7 @@ class DeferredCacheTestCase(TestCase):
self.assertTrue(set_d.called)
return r
# TODO: Actually ObservableDeferred *doesn't* run its tests in order on py3.8.
# maybe we should fix that?
# get_d.addCallback(check1)
get_d.addCallback(check1)
# now fire off all the deferreds
origin_d.callback(99)

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@ -21,11 +21,78 @@ from synapse.logging.context import (
PreserveLoggingContext,
current_context,
)
from synapse.util.async_helpers import timeout_deferred
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()