bpo-32734: Fix asyncio.Lock multiple acquire safety issue (GH-5466) (#5501)
(cherry picked from commit 2f79c014931cbb23b08a7d16c534a3cc9607ae14)
Co-authored-by: Bar Harel <bzvi7919@gmail.com>
diff --git a/Lib/asyncio/locks.py b/Lib/asyncio/locks.py
index 6193837..508a214 100644
--- a/Lib/asyncio/locks.py
+++ b/Lib/asyncio/locks.py
@@ -183,16 +183,22 @@
fut = self._loop.create_future()
self._waiters.append(fut)
+
+ # Finally block should be called before the CancelledError
+ # handling as we don't want CancelledError to call
+ # _wake_up_first() and attempt to wake up itself.
try:
- await fut
- self._locked = True
- return True
+ try:
+ await fut
+ finally:
+ self._waiters.remove(fut)
except futures.CancelledError:
if not self._locked:
self._wake_up_first()
raise
- finally:
- self._waiters.remove(fut)
+
+ self._locked = True
+ return True
def release(self):
"""Release a lock.
@@ -212,11 +218,17 @@
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
+ """Wake up the first waiter if it isn't done."""
+ try:
+ fut = next(iter(self._waiters))
+ except StopIteration:
+ return
+
+ # .done() necessarily means that a waiter will wake up later on and
+ # either take the lock, or, if it was cancelled and lock wasn't
+ # taken already, will hit this again and wake up a new waiter.
+ if not fut.done():
+ fut.set_result(True)
class Event: