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Commit32e7715

Browse files
bpo-45997: Fix asyncio.Semaphore re-acquiring order (GH-31910)
Co-authored-by: Kumar Aditya <59607654+kumaraditya303@users.noreply.github.com>
1 parent673755b commit32e7715

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3 files changed

+36
-6
lines changed

3 files changed

+36
-6
lines changed

‎Lib/asyncio/locks.py‎

Lines changed: 10 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -6,6 +6,7 @@
66

77
from .importexceptions
88
from .importmixins
9+
from .importtasks
910

1011

1112
class_ContextManagerMixin:
@@ -346,6 +347,7 @@ def __init__(self, value=1):
346347
raiseValueError("Semaphore initial value must be >= 0")
347348
self._value=value
348349
self._waiters=collections.deque()
350+
self._wakeup_scheduled=False
349351

350352
def__repr__(self):
351353
res=super().__repr__()
@@ -359,6 +361,7 @@ def _wake_up_next(self):
359361
waiter=self._waiters.popleft()
360362
ifnotwaiter.done():
361363
waiter.set_result(None)
364+
self._wakeup_scheduled=True
362365
return
363366

364367
deflocked(self):
@@ -374,16 +377,17 @@ async def acquire(self):
374377
called release() to make it larger than 0, and then return
375378
True.
376379
"""
377-
whileself._value<=0:
380+
# _wakeup_scheduled is set if *another* task is scheduled to wakeup
381+
# but its acquire() is not resumed yet
382+
whileself._wakeup_scheduledorself._value<=0:
378383
fut=self._get_loop().create_future()
379384
self._waiters.append(fut)
380385
try:
381386
awaitfut
382-
except:
383-
# See the similar code in Queue.get.
384-
fut.cancel()
385-
ifself._value>0andnotfut.cancelled():
386-
self._wake_up_next()
387+
# reset _wakeup_scheduled *after* waiting for a future
388+
self._wakeup_scheduled=False
389+
exceptexceptions.CancelledError:
390+
self._wake_up_next()
387391
raise
388392
self._value-=1
389393
returnTrue

‎Lib/test/test_asyncio/test_locks.py‎

Lines changed: 25 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -917,6 +917,31 @@ async def test_release_no_waiters(self):
917917
sem.release()
918918
self.assertFalse(sem.locked())
919919

920+
asyncdeftest_acquire_fifo_order(self):
921+
sem=asyncio.Semaphore(1)
922+
result= []
923+
924+
asyncdefcoro(tag):
925+
awaitsem.acquire()
926+
result.append(f'{tag}_1')
927+
awaitasyncio.sleep(0.01)
928+
sem.release()
929+
930+
awaitsem.acquire()
931+
result.append(f'{tag}_2')
932+
awaitasyncio.sleep(0.01)
933+
sem.release()
934+
935+
asyncwithasyncio.TaskGroup()astg:
936+
tg.create_task(coro('c1'))
937+
tg.create_task(coro('c2'))
938+
tg.create_task(coro('c3'))
939+
940+
self.assertEqual(
941+
['c1_1','c2_1','c3_1','c1_2','c2_2','c3_2'],
942+
result
943+
)
944+
920945

921946
if__name__=='__main__':
922947
unittest.main()
Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1 @@
1+
Fix:class:`asyncio.Semaphore` re-aquiring FIFO order.

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