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[3.8] bpo-34767: Do not always create a collections.deque() in asyncio.Lock() (GH-13834) #13837

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Merged
miss-islington merged 1 commit into from
Jun 5, 2019
Merged

[3.8] bpo-34767: Do not always create a collections.deque() in asyncio.Lock() (GH-13834) #13837

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9 changes: 7 additions & 2 deletions Lib/asyncio/locks.py
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Original file line number Diff line number Diff line change
Expand Up @@ -158,7 +158,7 @@ class Lock(_ContextManagerMixin):
"""

def __init__(self, *, loop=None):
self._waiters = collections.deque()
self._waiters = None
self._locked = False
if loop is not None:
self._loop = loop
Expand All @@ -182,10 +182,13 @@ async def acquire(self):
This method blocks until the lock is unlocked, then sets it to
locked and returns True.
"""
if not self._locked and all(w.cancelled() for w in self._waiters):
if (not self._locked and (self._waiters is None or
all(w.cancelled() for w in self._waiters))):
self._locked = True
return True

if self._waiters is None:
self._waiters = collections.deque()
fut = self._loop.create_future()
self._waiters.append(fut)

Expand Down Expand Up @@ -224,6 +227,8 @@ def release(self):

def _wake_up_first(self):
"""Wake up the first waiter if it isn't done."""
if not self._waiters:
return
try:
fut = next(iter(self._waiters))
except StopIteration:
Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2019-06-04-23-44-52.bpo-34767.BpDShN.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Do not always create a :class:`collections.deque` in :class:`asyncio.Lock`.