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author | Andrew Svetlov <andrew.svetlov@gmail.com> | 2022-03-22 14:02:51 (GMT) |
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committer | GitHub <noreply@github.com> | 2022-03-22 14:02:51 (GMT) |
commit | 32e77154ddfc514a3144d5912bffdd957246fd6c (patch) | |
tree | 862472617c97dc822ea1dbc33cd3e0396090ebb1 /Lib | |
parent | 673755bfbac46b3cd2c84d7e0d68c2c488e039c3 (diff) | |
download | cpython-32e77154ddfc514a3144d5912bffdd957246fd6c.zip cpython-32e77154ddfc514a3144d5912bffdd957246fd6c.tar.gz cpython-32e77154ddfc514a3144d5912bffdd957246fd6c.tar.bz2 |
bpo-45997: Fix asyncio.Semaphore re-acquiring order (GH-31910)
Co-authored-by: Kumar Aditya <59607654+kumaraditya303@users.noreply.github.com>
Diffstat (limited to 'Lib')
-rw-r--r-- | Lib/asyncio/locks.py | 16 | ||||
-rw-r--r-- | Lib/test/test_asyncio/test_locks.py | 25 |
2 files changed, 35 insertions, 6 deletions
diff --git a/Lib/asyncio/locks.py b/Lib/asyncio/locks.py index 0fbccfa..9b46121 100644 --- a/Lib/asyncio/locks.py +++ b/Lib/asyncio/locks.py @@ -6,6 +6,7 @@ import collections from . import exceptions from . import mixins +from . import tasks class _ContextManagerMixin: @@ -346,6 +347,7 @@ class Semaphore(_ContextManagerMixin, mixins._LoopBoundMixin): raise ValueError("Semaphore initial value must be >= 0") self._value = value self._waiters = collections.deque() + self._wakeup_scheduled = False def __repr__(self): res = super().__repr__() @@ -359,6 +361,7 @@ class Semaphore(_ContextManagerMixin, mixins._LoopBoundMixin): waiter = self._waiters.popleft() if not waiter.done(): waiter.set_result(None) + self._wakeup_scheduled = True return def locked(self): @@ -374,16 +377,17 @@ class Semaphore(_ContextManagerMixin, mixins._LoopBoundMixin): called release() to make it larger than 0, and then return True. """ - while self._value <= 0: + # _wakeup_scheduled is set if *another* task is scheduled to wakeup + # but its acquire() is not resumed yet + while self._wakeup_scheduled or self._value <= 0: fut = self._get_loop().create_future() self._waiters.append(fut) try: await fut - except: - # See the similar code in Queue.get. - fut.cancel() - if self._value > 0 and not fut.cancelled(): - self._wake_up_next() + # reset _wakeup_scheduled *after* waiting for a future + self._wakeup_scheduled = False + except exceptions.CancelledError: + self._wake_up_next() raise self._value -= 1 return True diff --git a/Lib/test/test_asyncio/test_locks.py b/Lib/test/test_asyncio/test_locks.py index d8b164a..920b3b5 100644 --- a/Lib/test/test_asyncio/test_locks.py +++ b/Lib/test/test_asyncio/test_locks.py @@ -917,6 +917,31 @@ class SemaphoreTests(unittest.IsolatedAsyncioTestCase): sem.release() self.assertFalse(sem.locked()) + async def test_acquire_fifo_order(self): + sem = asyncio.Semaphore(1) + result = [] + + async def coro(tag): + await sem.acquire() + result.append(f'{tag}_1') + await asyncio.sleep(0.01) + sem.release() + + await sem.acquire() + result.append(f'{tag}_2') + await asyncio.sleep(0.01) + sem.release() + + async with asyncio.TaskGroup() as tg: + tg.create_task(coro('c1')) + tg.create_task(coro('c2')) + tg.create_task(coro('c3')) + + self.assertEqual( + ['c1_1', 'c2_1', 'c3_1', 'c1_2', 'c2_2', 'c3_2'], + result + ) + if __name__ == '__main__': unittest.main() |