Can't run simple pytest session in a thread while using labgrid

[MaroMetelski]

Hi, While trying to invoke pytest in a thread with labgrid plugin in use RuntimeError is raised. Maybe the exeption should be catched in the module?

Example code:

from threading import Thread
import pytest

def tt():
    pytest.main(['-s', f'--lg-env=../qemu.yaml'])

t = Thread(target=tt, args=())
t.start()
t.join()

Can be worked around by adding this to the thread target function:

loop = asyncio.new_event_loop()
asyncio.set_event_loop(loop)

The line at fault: https://github.com/labgrid-project/labgrid/blob/d11a5ecc86decd74d3ff86b6fb8b730c9ea4a962/labgrid/remote/client.py#L30

The error log:

Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/lib/python3.7/threading.py", line 926, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3.7/threading.py", line 870, in run
    self._target(*self._args, **self._kwargs)
  File "hm.py", line 5, in tt
    pytest.main(['-s', f'--lg-env=../qemu.yaml'])
  File "/home/marek/.local/lib/python3.7/site-packages/_pytest/config/__init__.py", line 105, in main
    config = _prepareconfig(args, plugins)
  File "/home/marek/.local/lib/python3.7/site-packages/_pytest/config/__init__.py", line 258, in _prepareconfig
    pluginmanager=pluginmanager, args=args
  File "/home/marek/.local/lib/python3.7/site-packages/pluggy/hooks.py", line 286, in __call__
    return self._hookexec(self, self.get_hookimpls(), kwargs)
  File "/home/marek/.local/lib/python3.7/site-packages/pluggy/manager.py", line 93, in _hookexec
    return self._inner_hookexec(hook, methods, kwargs)
  File "/home/marek/.local/lib/python3.7/site-packages/pluggy/manager.py", line 87, in <lambda>
    firstresult=hook.spec.opts.get("firstresult") if hook.spec else False,
  File "/home/marek/.local/lib/python3.7/site-packages/pluggy/callers.py", line 203, in _multicall
    gen.send(outcome)
  File "/home/marek/.local/lib/python3.7/site-packages/_pytest/helpconfig.py", line 90, in pytest_cmdline_parse
    config = outcome.get_result()
  File "/home/marek/.local/lib/python3.7/site-packages/pluggy/callers.py", line 80, in get_result
    raise ex[1].with_traceback(ex[2])
  File "/home/marek/.local/lib/python3.7/site-packages/pluggy/callers.py", line 187, in _multicall
    res = hook_impl.function(*args)
  File "/home/marek/.local/lib/python3.7/site-packages/_pytest/config/__init__.py", line 836, in pytest_cmdline_parse
    self.parse(args)
  File "/home/marek/.local/lib/python3.7/site-packages/_pytest/config/__init__.py", line 1044, in parse
    self._preparse(args, addopts=addopts)
  File "/home/marek/.local/lib/python3.7/site-packages/_pytest/config/__init__.py", line 992, in _preparse
    self.pluginmanager.load_setuptools_entrypoints("pytest11")
  File "/home/marek/.local/lib/python3.7/site-packages/pluggy/manager.py", line 299, in load_setuptools_entrypoints
    plugin = ep.load()
  File "/home/marek/.local/lib/python3.7/site-packages/importlib_metadata/__init__.py", line 95, in load
    module = import_module(match.group('module'))
  File "/usr/lib/python3.7/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
  File "<frozen importlib._bootstrap>", line 983, in _find_and_load
  File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
  File "/home/marek/.local/lib/python3.7/site-packages/_pytest/assertion/rewrite.py", line 152, in exec_module
    exec(co, module.__dict__)
  File "/home/marek/.local/lib/python3.7/site-packages/labgrid/pytestplugin/__init__.py", line 1, in <module>
    from .fixtures import pytest_addoption, env, target
  File "<frozen importlib._bootstrap>", line 983, in _find_and_load
  File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
  File "/home/marek/.local/lib/python3.7/site-packages/_pytest/assertion/rewrite.py", line 152, in exec_module
    exec(co, module.__dict__)
  File "/home/marek/.local/lib/python3.7/site-packages/labgrid/pytestplugin/fixtures.py", line 6, in <module>
    from ..remote.client import UserError
  File "<frozen importlib._bootstrap>", line 983, in _find_and_load
  File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
  File "/home/marek/.local/lib/python3.7/site-packages/_pytest/assertion/rewrite.py", line 152, in exec_module
    exec(co, module.__dict__)
  File "/home/marek/.local/lib/python3.7/site-packages/labgrid/remote/client.py", line 30, in <module>
    txaio.config.loop = asyncio.get_event_loop()
  File "/usr/lib/python3.7/asyncio/events.py", line 644, in get_event_loop
    % threading.current_thread().name)
RuntimeError: There is no current event loop in thread 'Thread-1'.

[jluebbe]

With you workaround, txaio and asyncio have different event loops, right? Are you sure there are no issues with this? So far, we've not looked into what would need to be done to support this properly. Note that the integration of autobahn via txaio is not really straight forward.

[MaroMetelski]

No, I don't have any issues with this workaround. The error happens without using any of the 'Remote' functionalities or even any labgrid environment. It crashes while pytest loads all the modules in its plugins, and the mentioned line is invoked. Maybe this line from the Traceback is a problem here?

File "/home/marek/.local/lib/python3.7/site-packages/labgrid/pytestplugin/fixtures.py", line 6, in <module>
    from ..remote.client import UserError