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authorAndrew Svetlov <andrew.svetlov@gmail.com>2022-03-22 14:02:51 (GMT)
committerGitHub <noreply@github.com>2022-03-22 14:02:51 (GMT)
commit32e77154ddfc514a3144d5912bffdd957246fd6c (patch)
tree862472617c97dc822ea1dbc33cd3e0396090ebb1 /Lib
parent673755bfbac46b3cd2c84d7e0d68c2c488e039c3 (diff)
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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.py16
-rw-r--r--Lib/test/test_asyncio/test_locks.py25
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()