[issue42600] Cancelling tasks waiting for asyncio.Conditions crashes w/ RuntimeError: Lock is not acquired.

[Daniele Varrazzo]

Daniele Varrazzo  added the comment:

I have stumbled in this bug, or something similar, implementing psycopg3 async 
connection pool. A function such as the following fails but only in Python 3.6 
(tested 3.6.12):

async def wait(self, timeout: float) -> AsyncConnection:
"""Wait for a connection to be set and return it.
Raise an exception if the wait times out or if fail() is called.
"""
async with self._cond:
if not (self.conn or self.error):
try:
await asyncio.wait_for(self._cond.wait(), timeout)
except asyncio.TimeoutError:
# HERE
self.error = PoolTimeout(
f"couldn't get a connection after {timeout} sec"
)

In python 3.6, printing self._cond.locked() in the HERE position gives False, 
even if it's inside the with block. Everything grinds to a halt afterwards.

However I don't have the same problem in other Python versions (3.7.10, 3.8.5 
among the ones tested) so I'm not sure it is the same issue.

Is this a manifestation of the same bug or a different one? Is there any 
workaround or should I make the async pool just not supported on Python 3.6?

--
nosy: +piro

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[issue42600] Cancelling tasks waiting for asyncio.Conditions crashes w/ RuntimeError: Lock is not acquired.

[Yury Selivanov]

Yury Selivanov  added the comment:

This has been actually first fixed in #41891 but somehow wasn't yet merged. 
Yurii, thanks so much for working on this and making a PR, there was just 
another PR to fix the same issue that was there first, so I had to merge that 
one.

--
resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed
superseder:  -> asyncio.wait_for does not wait for task/future to be completed 
in all cases

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[issue42600] Cancelling tasks waiting for asyncio.Conditions crashes w/ RuntimeError: Lock is not acquired.

[Yurii Karabas]

Yurii Karabas <1998uri...@gmail.com> added the comment:

Hey Yurii, I have fixed this issue.
The actual problem was that `wait_for` cancels passed future but doesn't wait 
until it finished.

--

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[issue42600] Cancelling tasks waiting for asyncio.Conditions crashes w/ RuntimeError: Lock is not acquired.

[Yurii Karabas]

Change by Yurii Karabas <1998uri...@gmail.com>:


--
keywords: +patch
nosy: +uriyyo
nosy_count: 4.0 -> 5.0
pull_requests: +22689
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/23829

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[issue42600] Cancelling tasks waiting for asyncio.Conditions crashes w/ RuntimeError: Lock is not acquired.

[Yury Selivanov]

Yury Selivanov  added the comment:

Hey Hynek! :) Can you submit a PR?

--

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[issue42600] Cancelling tasks waiting for asyncio.Conditions crashes w/ RuntimeError: Lock is not acquired.

[Hynek Schlawack]

New submission from Hynek Schlawack :

This is something I've been procrastinating on for almost a year and working 
around it using my own version of asyncio.Condition because I wasn't sure how 
to describe it. So here's my best take:

Consider the following code:

```
import asyncio


async def tf(con):
async with con:
await asyncio.wait_for(con.wait(), 60)


async def f(loop):
con = asyncio.Condition()

t = loop.create_task(tf(con))

await asyncio.sleep(1)
t.cancel()

async with con:
con.notify_all()

await t


loop = asyncio.get_event_loop()
loop.run_until_complete(f(loop))
```

(I'm using old-school APIs because I wanted to verify whether it was a 
regression. I ran into the bug with new-style APIs: 
https://gist.github.com/hynek/387f44672722171c901b8422320e8f9b)

`await t` will crash with:


```
Traceback (most recent call last):
  File "/Users/hynek/t.py", line 6, in tf
await asyncio.wait_for(con.wait(), 60)
  File 
"/Users/hynek/.asdf/installs/python/3.9.0/lib/python3.9/asyncio/tasks.py", line 
466, in wait_for
await waiter
asyncio.exceptions.CancelledError

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/hynek/t.py", line 24, in 
loop.run_until_complete(f(loop))
  File 
"/Users/hynek/.asdf/installs/python/3.9.0/lib/python3.9/asyncio/base_events.py",
 line 642, in run_until_complete
return future.result()
  File "/Users/hynek/t.py", line 20, in f
await t
  File "/Users/hynek/t.py", line 6, in tf
await asyncio.wait_for(con.wait(), 60)
  File 
"/Users/hynek/.asdf/installs/python/3.9.0/lib/python3.9/asyncio/locks.py", line 
20, in __aexit__
self.release()
  File 
"/Users/hynek/.asdf/installs/python/3.9.0/lib/python3.9/asyncio/locks.py", line 
146, in release
raise RuntimeError('Lock is not acquired.')
RuntimeError: Lock is not acquired.

```

If you replace wait_for with a simple await, it works and raises an 
asyncio.exceptions.CancelledError:

```
Traceback (most recent call last):
  File "/Users/hynek/t.py", line 6, in tf
await con.wait()
  File 
"/Users/hynek/.asdf/installs/python/3.9.0/lib/python3.9/asyncio/locks.py", line 
290, in wait
await fut
asyncio.exceptions.CancelledError

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/hynek/t.py", line 20, in f
await t
asyncio.exceptions.CancelledError

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/hynek/t.py", line 24, in 
loop.run_until_complete(f(loop))
  File 
"/Users/hynek/.asdf/installs/python/3.9.0/lib/python3.9/asyncio/base_events.py",
 line 642, in run_until_complete
return future.result()
asyncio.exceptions.CancelledError
```

I have verified, that this has been broken at least since 3.5.10. The current 
3.10.0a3 is affected too.

--
components: asyncio
messages: 382732
nosy: asvetlov, hynek, lukasz.langa, yselivanov
priority: normal
severity: normal
status: open
title: Cancelling tasks waiting for asyncio.Conditions crashes w/ RuntimeError: 
Lock is not acquired.
versions: Python 3.10, Python 3.8, Python 3.9

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