Fixed #21952 -- signals deadlock due to locking + weakref interaction (c29d6f76) · Commits · Dom Sekotill / django

django/dispatch/dispatcher.py

+23 −14

Original line number	Diff line number	Diff line
		@@ -48,6 +48,7 @@ class Signal(object):
		# 'sender_receivers_cache'. The cache is cleaned when .connect() or
		# .disconnect() is called and populated on send().
		self.sender_receivers_cache = weakref.WeakKeyDictionary() if use_caching else {}
		self._dead_receivers = False

		def connect(self, receiver, sender=None, weak=True, dispatch_uid=None):
		"""
		@@ -127,6 +128,7 @@ class Signal(object):
		receiver_id = _make_id(receiver)

		with self.lock:
		self._clear_dead_receivers()
		for r_key, _, _ in self.receivers:
		if r_key == lookup_key:
		break
		@@ -162,6 +164,7 @@ class Signal(object):
		lookup_key = (_make_id(receiver), _make_id(sender))

		with self.lock:
		self._clear_dead_receivers()
		for index in xrange(len(self.receivers)):
		(r_key, _, _) = self.receivers[index]
		if r_key == lookup_key:
		@@ -237,6 +240,17 @@ class Signal(object):
		responses.append((receiver, response))
		return responses

		def _clear_dead_receivers(self):
		# Note: caller is assumed to hold self.lock.
		if self._dead_receivers:
		self._dead_receivers = False
		new_receivers = []
		for r in self.receivers:
		if isinstance(r[1], weakref.ReferenceType) and r[1]() is None:
		continue
		new_receivers.append(r)
		self.receivers = new_receivers

		def _live_receivers(self, sender):
		"""
		Filter sequence of receivers to get resolved, live receivers.
		@@ -245,7 +259,7 @@ class Signal(object):
		live receivers.
		"""
		receivers = None
		if self.use_caching:
		if self.use_caching and not self._dead_receivers:
		receivers = self.sender_receivers_cache.get(sender)
		# We could end up here with NO_RECEIVERS even if we do check this case in
		# .send() prior to calling _live_receivers() due to concurrent .send() call.
		@@ -253,6 +267,7 @@ class Signal(object):
		return []
		if receivers is None:
		with self.lock:
		self._clear_dead_receivers()
		senderkey = _make_id(sender)
		receivers = []
		for (receiverkey, r_senderkey), receiver, _ in self.receivers:
		@@ -276,19 +291,13 @@ class Signal(object):
		return non_weak_receivers

		def _remove_receiver(self, receiver=None, receiver_id=None, _make_id=_make_id):
		"""
		Remove dead receivers from connections.

		`receiver_id` is used by python 3.4 and up. `receiver` is used in older
		versions and is the weakref to the receiver (if the connection was defined
		as `weak`). We also need to pass on `_make_id` since the original reference
		will be None during module shutdown.
		"""
		with self.lock:
		if receiver is not None:
		receiver_id = _make_id(receiver)
		self.receivers[:] = [val for val in self.receivers if val[2] != receiver_id]
		self.sender_receivers_cache.clear()
		# Mark that the self.receivers list has dead weakrefs. If so, we will
		# clean those up in connect, disconnect and _live_receivers while
		# holding self.lock. Note that doing the cleanup here isn't a good
		# idea, _remove_receiver() will be called as side effect of garbage
		# collection, and so the call can happen while we are already holding
		# self.lock.
		self._dead_receivers = True


		def receiver(signal, **kwargs):

tests/dispatch/tests/test_dispatcher.py

+4 −3

Original line number	Diff line number	Diff line
		@@ -46,11 +46,12 @@ class DispatcherTests(unittest.TestCase):

		def _testIsClean(self, signal):
		"""Assert that everything has been cleaned up automatically"""
		# Note that dead weakref cleanup happens as side effect of using
		# the signal's receivers through the signals API. So, first do a
		# call to an API method to force cleanup.
		self.assertFalse(signal.has_listeners())
		self.assertEqual(signal.receivers, [])

		# force cleanup just in case
		signal.receivers = []

		def testExact(self):
		a_signal.connect(receiver_1_arg, sender=self)
		expected = [(receiver_1_arg, "test")]