mirror of https://github.com/python/cpython
bpo-45997: Fix asyncio.Semaphore re-acquiring order (GH-31910)
Co-authored-by: Kumar Aditya <59607654+kumaraditya303@users.noreply.github.com>
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@ -6,6 +6,7 @@ import collections
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from . import exceptions
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from . import mixins
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from . import tasks
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class _ContextManagerMixin:
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@ -346,6 +347,7 @@ class Semaphore(_ContextManagerMixin, mixins._LoopBoundMixin):
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raise ValueError("Semaphore initial value must be >= 0")
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self._value = value
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self._waiters = collections.deque()
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self._wakeup_scheduled = False
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def __repr__(self):
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res = super().__repr__()
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@ -359,6 +361,7 @@ class Semaphore(_ContextManagerMixin, mixins._LoopBoundMixin):
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waiter = self._waiters.popleft()
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if not waiter.done():
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waiter.set_result(None)
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self._wakeup_scheduled = True
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return
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def locked(self):
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@ -374,15 +377,16 @@ class Semaphore(_ContextManagerMixin, mixins._LoopBoundMixin):
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called release() to make it larger than 0, and then return
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True.
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"""
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while self._value <= 0:
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# _wakeup_scheduled is set if *another* task is scheduled to wakeup
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# but its acquire() is not resumed yet
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while self._wakeup_scheduled or self._value <= 0:
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fut = self._get_loop().create_future()
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self._waiters.append(fut)
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try:
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await fut
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except:
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# See the similar code in Queue.get.
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fut.cancel()
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if self._value > 0 and not fut.cancelled():
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# reset _wakeup_scheduled *after* waiting for a future
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self._wakeup_scheduled = False
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except exceptions.CancelledError:
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self._wake_up_next()
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raise
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self._value -= 1
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@ -917,6 +917,31 @@ class SemaphoreTests(unittest.IsolatedAsyncioTestCase):
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sem.release()
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self.assertFalse(sem.locked())
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async def test_acquire_fifo_order(self):
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sem = asyncio.Semaphore(1)
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result = []
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async def coro(tag):
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await sem.acquire()
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result.append(f'{tag}_1')
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await asyncio.sleep(0.01)
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sem.release()
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await sem.acquire()
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result.append(f'{tag}_2')
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await asyncio.sleep(0.01)
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sem.release()
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async with asyncio.TaskGroup() as tg:
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tg.create_task(coro('c1'))
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tg.create_task(coro('c2'))
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tg.create_task(coro('c3'))
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self.assertEqual(
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['c1_1', 'c2_1', 'c3_1', 'c1_2', 'c2_2', 'c3_2'],
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result
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)
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if __name__ == '__main__':
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unittest.main()
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@ -0,0 +1 @@
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Fix :class:`asyncio.Semaphore` re-aquiring FIFO order.
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