Fix waiter cancellation in asyncio.Lock (#1031) (#2037)
Avoid a deadlock when the waiter who is about to take the lock is
cancelled
Issue #27585
diff --git a/Lib/asyncio/locks.py b/Lib/asyncio/locks.py
index deefc93..9266183 100644
--- a/Lib/asyncio/locks.py
+++ b/Lib/asyncio/locks.py
@@ -176,6 +176,10 @@
yield from fut
self._locked = True
return True
+ except futures.CancelledError:
+ if not self._locked:
+ self._wake_up_first()
+ raise
finally:
self._waiters.remove(fut)
@@ -192,14 +196,17 @@
"""
if self._locked:
self._locked = False
- # Wake up the first waiter who isn't cancelled.
- for fut in self._waiters:
- if not fut.done():
- fut.set_result(True)
- break
+ self._wake_up_first()
else:
raise RuntimeError('Lock is not acquired.')
+ def _wake_up_first(self):
+ """Wake up the first waiter who isn't cancelled."""
+ for fut in self._waiters:
+ if not fut.done():
+ fut.set_result(True)
+ break
+
class Event:
"""Asynchronous equivalent to threading.Event.