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gh-117536: Fix asyncio _asyncgen_finalizer_hook()#117751

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25 changes: 21 additions & 4 deletionsLib/asyncio/base_events.py
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Original file line numberDiff line numberDiff line change
Expand Up@@ -444,6 +444,11 @@ def __init__(self):
# A weak set of all asynchronous generators that are
# being iterated by the loop.
self._asyncgens = weakref.WeakSet()

# Strong references to asynchronous generators which are being being
# closed by the loop: see _asyncgen_finalizer_hook().
self._close_asyncgens = set()

# Set to True when `loop.shutdown_asyncgens` is called.
self._asyncgens_shutdown_called = False
# Set to True when `loop.shutdown_default_executor` is called.
Expand DownExpand Up@@ -555,10 +560,22 @@ def _check_default_executor(self):
if self._executor_shutdown_called:
raise RuntimeError('Executor shutdown has been called')

async def _asyncgen_close(self, agen):
await agen.aclose()
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this is just side-stepping the actual bug by delaying the creation of the async_generator_aclose object to avoid the incorrect warning

self._close_asyncgens.discard(agen)

def _asyncgen_finalizer_hook(self, agen):
if self.is_closed():
self._asyncgens.discard(agen)
return

# gh-117536: Store a strong reference to the asynchronous generator
# to make sure that shutdown_asyncgens() can close it even if
# asyncio.run() cancels all tasks.
self._close_asyncgens.add(agen)
self._asyncgens.discard(agen)
if not self.is_closed():
self.call_soon_threadsafe(self.create_task,agen.aclose())

self.call_soon_threadsafe(self.create_task,self._asyncgen_close(agen))

def _asyncgen_firstiter_hook(self, agen):
if self._asyncgens_shutdown_called:
Expand All@@ -573,12 +590,12 @@ async def shutdown_asyncgens(self):
"""Shutdown all active asynchronous generators."""
self._asyncgens_shutdown_called = True

if not len(self._asyncgens):
closing_agens = list(set(self._asyncgens) | self._close_asyncgens)
if not closing_agens:
# If Python version is <3.6 or we don't have any asynchronous
# generators alive.
return

closing_agens = list(self._asyncgens)
self._asyncgens.clear()

results = await tasks.gather(
Expand Down
11 changes: 1 addition & 10 deletionsLib/test/test_asyncgen.py
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Original file line numberDiff line numberDiff line change
Expand Up@@ -1570,13 +1570,8 @@ async def main():

message, = messages
self.assertIsInstance(message['exception'], ZeroDivisionError)
self.assertIn('unhandled exceptionduringasyncio.run() shutdown',
self.assertIn('an error occurredduringclosing of asynchronous generator',
message['message'])
with self.assertWarnsRegex(RuntimeWarning,
f"coroutine method 'aclose' of '{async_iterate.__qualname__}' "
f"was never awaited"):
del message, messages
gc_collect()

def test_async_gen_expression_01(self):
async def arange(n):
Expand DownExpand Up@@ -1630,10 +1625,6 @@ async def main():
asyncio.run(main())

self.assertEqual([], messages)
with self.assertWarnsRegex(RuntimeWarning,
f"coroutine method 'aclose' of '{async_iterate.__qualname__}' "
f"was never awaited"):
gc_collect()

def test_async_gen_await_same_anext_coro_twice(self):
async def async_iterate():
Expand Down
37 changes: 37 additions & 0 deletionsLib/test/test_asyncio/test_base_events.py
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Original file line numberDiff line numberDiff line change
Expand Up@@ -1044,6 +1044,43 @@ def test_asyncgen_finalization_by_gc_in_other_thread(self):
test_utils.run_briefly(self.loop)
self.assertTrue(status['finalized'])

def test_shutdown_asyncgens(self):
# gh-117536: Test shutdown_asyncgens() using asyncio.run() which
# may cancel the task which closes the asynchronous generator before
# calling shutdown_asyncgens().

ns = {'state': 'not started'}
async def agen_basic():
try:
ns['state'] = 'started'
yield 0
yield 1
finally:
ns['state'] = 'finalized'
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This should await something to prove it's getting aclosed properly

Suggested change
ns['state']='finalized'
awaitasyncio.sleep(0)
ns['state']='finalized'

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Right. I added a second test. I prefer to have two tests, since having 'await' also changes the behavior in a subtle way.


async def reproducer(agen):
async for item in agen():
break

asyncio.run(reproducer(agen_basic))
self.assertEqual(ns['state'], 'finalized')

# Similar than previous test, but the generator uses 'await' in the
# finally block.
ns['state'] = 'not started'
async def agen_await():
try:
ns['state'] = 'started'
yield 0
yield 1
finally:
ns['state'] = 'await'
await asyncio.sleep(0)
ns['state'] = 'finalized'

asyncio.run(reproducer(agen_await))
self.assertEqual(ns['state'], 'finalized')


class MyProto(asyncio.Protocol):
done = None
Expand Down
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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,2 @@
:mod:`asyncio`: Make the finalization of asynchronous generators more
reliable. Patch by Victor Stinner.
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