In asyncio.locks.Lock.acquire(): Avoid deadlock when a cancelled future is in self._waiters.

gvanrossum · gvanrossum · commit 83f5a3846cf6 · 2016-08-23T09:39:03.000-07:00
diff --git a/Lib/asyncio/locks.py b/Lib/asyncio/locks.py
@@ -166,7 +166,7 @@ def acquire(self):
         This method blocks until the lock is unlocked, then sets it to
         locked and returns True.
         """
-        if not self._waiters and not self._locked:
+        if not self._locked and all(w.cancelled() for w in self._waiters):
             self._locked = True
             return True
 
