pytest fails while using version asyncio-0.15.0

[Kruszylo]

Python: 3.8 (docker image)

My pytest setup:

...
============================= test session starts ==============================
platform linux -- Python 3.8.9, pytest-6.2.3, py-1.10.0, pluggy-0.13.1 -- /builds/.../venv/bin/python3
cachedir: .pytest_cache
hypothesis profile 'default' -> database=DirectoryBasedExampleDatabase('/builds/.../.hypothesis/examples')
rootdir: /builds/..., configfile: pytest.ini
plugins: hypothesis-6.9.2, asyncio-0.15.0
...

an error:

...
==================================== ERRORS ====================================
_____________________ ERROR at setup of test_async_ticker ______________________

fixturedef = <FixtureDef argname='event_loop' scope='function' baseid=''>
request = <SubRequest 'event_loop' for <Function test_async_ticker>>

    @pytest.hookimpl(hookwrapper=True)
    def pytest_fixture_setup(fixturedef, request):
        """Adjust the event loop policy when an event loop is produced."""
        if fixturedef.argname == "event_loop":
            outcome = yield
            loop = outcome.get_result()
            policy = asyncio.get_event_loop_policy()
>           old_loop = policy.get_event_loop()

venv/lib/python3.8/site-packages/pytest_asyncio/plugin.py:94: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <asyncio.unix_events._UnixDefaultEventLoopPolicy object at 0x7f07326b2bb0>

    def get_event_loop(self):
        """Get the event loop for the current context.
    
        Returns an instance of EventLoop or raises an exception.
        """
        if (self._local._loop is None and
                not self._local._set_called and
                isinstance(threading.current_thread(), threading._MainThread)):
            self.set_event_loop(self.new_event_loop())
    
        if self._local._loop is None:
>           raise RuntimeError('There is no current event loop in thread %r.'
                               % threading.current_thread().name)
E           RuntimeError: There is no current event loop in thread 'MainThread'.

/usr/local/lib/python3.8/asyncio/events.py:639: RuntimeError
...

The error appears when I run:

python -m pytest tests/test_dates.py::test_async_ticker -vv -duration=6  

where the test_async_ticker is:

import asyncio

import pytest

@pytest.mark.asyncio
async def test_async_ticker():
    async with dates.AsyncTicker() as ticker:
        await asyncio.sleep(0.001)

    assert ticker.time_elapsed().total_seconds() > 0

and AsyncTicker:

class AsyncTicker:
    '''Measures time between entering and exiting `async with` block.'''
    def __init__(self):
        self._start = None
        self._end = None

    async def __aenter__(self, *args, **kwargs):
        self._start = current_utc_instant()
        return self

    async def __aexit__(self, *args, **kwargs):
        self._end = current_utc_instant()

    def time_elapsed(self):
        return self._end - self._start

[barend]

I have this exact same problem, and from the looks of it, I've been diagnosing it at the exact same time. I can make the problem occur both in the docker image and in a local virtualenv, and I can reliably toggle it off or on by pip installing pytest-asyncio versions 0.14.0 or 0.15.0.

[Tinche]

Ah, must have been caused by the loop cleanup changes in 0.15.0. Can be fixed relatively easily, just need to understand what exactly is going on first.

[barend]

Thank you for the swift response!

[Tinche]

I cannot repro this with this test (tried 3.8.9 and 3.9.2):

import asyncio

import pytest

class AsyncTicker:
    '''Measures time between entering and exiting `async with` block.'''
    def __init__(self):
        self._start = None
        self._end = None

    async def __aenter__(self, *args, **kwargs):
        self._start = 1
        return self

    async def __aexit__(self, *args, **kwargs):
        self._end = 2

    def time_elapsed(self):
        return self._end - self._start

@pytest.mark.asyncio
async def test_async_ticker():
    async with AsyncTicker() as ticker:
        await asyncio.sleep(0.001)

    assert True

So would appreciate a minimal repro example!

[barend]

I'm dealing with a client's proprietary code base and cannot easily extract a reproducible sample. The most exciting thing here afaict is an asyncio.gather of a bunch of network calls issued at the same time.

[Tinche]

To me it looks like something in your codebase is making asyncio produce the event loop for the main thread and then setting it to None. Then when pytest-asyncio takes over the event loop management the error pops out. Any chance of something like this happening?

[Kruszylo]

I have extracted the test, in the same docker image with necessary requirements it works without error, but when I run it in my project it fails. I'll investigate further to find out what is happening.

[stevepentland]

I have a similar issue. So far I have noted that prior tests on code that calls asyncio.run(...) leaves the loop on main closed and self._local._set_called set to True. The first time this plugin tries to setup for the marked function, get_event_loop fails due to set having already been called by the prior call to run. I did not experience this previously using this combo however

Edit: subsequent tests using the decorator do still pass though, it is only the first time it is used after asyncio.run(...) was used elsewhere

Edit 2: Swapped back to 0.14.0 and the tests pass in the same run order & environment

[Kruszylo]

I think I have a code that reproduces the error. You will need to write docker file:

Dockerfile:

FROM python:3.8 as base

RUN apt-get update

RUN python3 -m venv venv
RUN /bin/bash -c "source venv/bin/activate"

RUN pip3 install pytest
RUN pip3 install hypothesis==6.9.2
RUN pip3 install pytest-asyncio==0.15.0

RUN /bin/bash -c "source venv/bin/activate"

# fix stdout & stderr missing from `docker logs`
ENV PYTHONUNBUFFERED=1

COPY tests.py .
CMD ["python3", "-m", "pytest", "tmp.py"]

write python script for tests:

tests.py:

import datetime
import asyncio
import queue
import threading

import pytest


def current_utc_instant() -> datetime.datetime:
    '''Datetime representing current UTC instant, with time zone'''
    return datetime.datetime.now(datetime.timezone.utc)



def _run_in_fresh_loop(coro, result_queue):
    loop = asyncio.new_event_loop()
    asyncio.set_event_loop(loop)

    try:
        result = loop.run_until_complete(coro)
        msg = {'success': True,
               'result': result}
    except Exception as e:
        msg = {'success': False,
               'exception': e}

    loop.close()
    result_queue.put(msg)


def run_in_thread(coro):
    '''Workaround for running async coroutine from a synchronous context  inside other async code,
    like `async(sync(async ()))`.

    Runs the coroutine in a separate thread with new event loop and blocks until the coroutine is completed.
    '''
    result_queue = queue.Queue()
    th = threading.Thread(target=_run_in_fresh_loop, args=(coro, result_queue))
    th.start()
    th.join()

    msg = result_queue.get()

    if msg['success']:
        return msg['result']
    else:
        raise msg['exception']


async def _async_division(x, y):
    await asyncio.sleep(0.001)
    return x / y


async def _async_wrapper_fn(x, y):
    # do async stuff
    await asyncio.sleep(0.001)

    # call sync subroutine that triggers a coroutine in another thread
    result = run_in_thread(_async_division(x, y))

    # do async stuff
    await asyncio.sleep(0.001)

    return result


class TestRunInThread:
    # def test_with_no_loop_success(self):
    #     assert 2 == run_in_thread(_async_division(6, 3))

    # def test_no_loop_exception(self):
    #     with pytest.raises(ZeroDivisionError):
    #         run_in_thread(_async_division(1, 0))

    def test_already_present_loop_success(self):
        assert 2 == asyncio.run(_async_wrapper_fn(6, 3))

    # def test_already_present_loop_exception(self):
    #     with pytest.raises(ZeroDivisionError):
    #         asyncio.run(_async_wrapper_fn(1, 0))


class AsyncTicker:
    '''Measures time between entering and exiting `async with` block.'''
    def __init__(self):
        self._start = None
        self._end = None

    async def __aenter__(self, *args, **kwargs):
        self._start = current_utc_instant()
        return self

    async def __aexit__(self, *args, **kwargs):
        self._end = current_utc_instant()

    def time_elapsed(self):
        return self._end - self._start

@pytest.mark.asyncio
async def test_async_ticker():
    async with AsyncTicker() as ticker:
        await asyncio.sleep(0.001)

    assert ticker.time_elapsed().total_seconds() > 0

build the image:

docker build -f Dockerfile -t 'pytest-issue-209' .

and run:

docker run 'pytest-issue-209'

Output:

============================= test session starts ==============================
platform linux -- Python 3.8.9, pytest-6.2.3, py-1.10.0, pluggy-0.13.1
rootdir: /
plugins: asyncio-0.15.0, hypothesis-6.9.2
collected 2 items

tmp.py .E                                                                [100%]

==================================== ERRORS ====================================
_____________________ ERROR at setup of test_async_ticker ______________________

fixturedef = <FixtureDef argname='event_loop' scope='function' baseid=''>
request = <SubRequest 'event_loop' for <Function test_async_ticker>>

    @pytest.hookimpl(hookwrapper=True)
    def pytest_fixture_setup(fixturedef, request):
        """Adjust the event loop policy when an event loop is produced."""
        if fixturedef.argname == "event_loop":
            outcome = yield
            loop = outcome.get_result()
            policy = asyncio.get_event_loop_policy()
>           old_loop = policy.get_event_loop()

usr/local/lib/python3.8/site-packages/pytest_asyncio/plugin.py:94: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <asyncio.unix_events._UnixDefaultEventLoopPolicy object at 0x7eff64c52700>

    def get_event_loop(self):
        """Get the event loop for the current context.
    
        Returns an instance of EventLoop or raises an exception.
        """
        if (self._local._loop is None and
                not self._local._set_called and
                isinstance(threading.current_thread(), threading._MainThread)):
            self.set_event_loop(self.new_event_loop())
    
        if self._local._loop is None:
>           raise RuntimeError('There is no current event loop in thread %r.'
                               % threading.current_thread().name)
E           RuntimeError: There is no current event loop in thread 'MainThread'.

usr/local/lib/python3.8/asyncio/events.py:639: RuntimeError
=========================== short test summary info ============================
ERROR tmp.py::test_async_ticker - RuntimeError: There is no current event loo...
========================== 1 passed, 1 error in 0.10s ==========================

[Tinche]

Could people from this thread try the latest commit on the master branch and report if it fixes it?

[escapewindow]

It looks like 94c2560 results in tests hanging, without any error message.

[EDIT] Trying multiple times to see what's going on, and see if I can isolate the issue. Curious if anyone else is seeing similar issues.

[2nd EDIT] I'm now getting errors, Event loop is closed again, e.g.

tests/test_production.py::test_verify_production_cot[fenix production] Exception ignored in: <function BaseSubprocessTransport.__del__ at 0x10fbb5790>
Traceback (most recent call last):
  File "/Users/asasaki/.pyenv/versions/3.8.0/lib/python3.8/asyncio/base_subprocess.py", line 126, in __del__
    self.close()
  File "/Users/asasaki/.pyenv/versions/3.8.0/lib/python3.8/asyncio/base_subprocess.py", line 104, in close
    proto.pipe.close()
  File "/Users/asasaki/.pyenv/versions/3.8.0/lib/python3.8/asyncio/unix_events.py", line 536, in close
    self._close(None)
  File "/Users/asasaki/.pyenv/versions/3.8.0/lib/python3.8/asyncio/unix_events.py", line 560, in _close
    self._loop.call_soon(self._call_connection_lost, exc)
  File "/Users/asasaki/.pyenv/versions/3.8.0/lib/python3.8/asyncio/base_events.py", line 711, in call_soon
    self._check_closed()
  File "/Users/asasaki/.pyenv/versions/3.8.0/lib/python3.8/asyncio/base_events.py", line 504, in _check_closed
    raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed

This is largely in a complex test decorated with @pytest.mark.asyncio and @pytest.mark.parametrize, without an event_loop fixture, with many coroutines awaiting on other coroutines.

[adilkhash]

Could people from this thread try the latest commit on the master branch and report if it fixes it?

I can confirm that the error disappeared after the introduction of the exception handling.