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gh-148489: Lazy-init _waiters in asyncio Event and Condition #148490

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gh-148489: Lazy-init _waiters in asyncio Event and Condition #148490

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19 changes: 13 additions & 6 deletions Lib/asyncio/locks.py
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Original file line number Diff line number Diff line change
Expand Up @@ -165,7 +165,7 @@ class Event(mixins._LoopBoundMixin):
"""

def __init__(self):
self._waiters = collections.deque()
self._waiters = None
self._value = False

def __repr__(self):
Expand All @@ -187,9 +187,10 @@ def set(self):
if not self._value:
self._value = True

for fut in self._waiters:
if not fut.done():
fut.set_result(True)
if self._waiters:
for fut in self._waiters:
if not fut.done():
fut.set_result(True)

def clear(self):
"""Reset the internal flag to false. Subsequently, tasks calling
Expand All @@ -207,6 +208,8 @@ async def wait(self):
if self._value:
return True

if self._waiters is None:
self._waiters = collections.deque()
fut = self._get_loop().create_future()
self._waiters.append(fut)
try:
Expand Down Expand Up @@ -236,7 +239,7 @@ def __init__(self, lock=None):
self.acquire = lock.acquire
self.release = lock.release

self._waiters = collections.deque()
self._waiters = None

def __repr__(self):
res = super().__repr__()
Expand All @@ -263,6 +266,8 @@ async def wait(self):
if not self.locked():
raise RuntimeError('cannot wait on un-acquired lock')

if self._waiters is None:
self._waiters = collections.deque()
fut = self._get_loop().create_future()
self.release()
try:
Expand Down Expand Up @@ -331,6 +336,8 @@ def notify(self, n=1):
self._notify(n)

def _notify(self, n):
if not self._waiters:
return
idx = 0
for fut in self._waiters:
if idx >= n:
Expand All @@ -346,7 +353,7 @@ def notify_all(self):
calling task has not acquired the lock when this method is called,
a RuntimeError is raised.
"""
self.notify(len(self._waiters))
self.notify(len(self._waiters or ()))


class Semaphore(_ContextManagerMixin, mixins._LoopBoundMixin):
Expand Down
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