ValueError: <Token var=<ContextVar name='flask.app_ctx' at 0x7f2ac79c36a0> at 0x7f2ac06b8600> was created in a different Context

[larsderidder]

I am upgrading Flask in an application. All works fine on Flask 2.1.5, but when going to 2.2.5, I get the below exception.

Traceback (most recent call last):
  File "/usr/lib/python3.10/threading.py", line 953, in run
    self._target(*self._args, **self._kwargs)
  File "/home/lars/.virtualenvs/esdl-mapeditor/lib/python3.10/site-packages/socketio/server.py", line 720, in _handle_event_internal
    r = server._trigger_event(data[0], namespace, sid, *data[1:])
  File "/home/lars/.virtualenvs/esdl-mapeditor/lib/python3.10/site-packages/socketio/server.py", line 745, in _trigger_event
    return self.handlers[namespace][event](*args)
  File "/home/lars/.virtualenvs/esdl-mapeditor/lib/python3.10/site-packages/flask_socketio/__init__.py", line 282, in _handler
    return self._handle_event(handler, message, namespace, sid,
  File "/home/lars/.virtualenvs/esdl-mapeditor/lib/python3.10/site-packages/flask_socketio/__init__.py", line 795, in _handle_event
    with app.request_context(environ):
  File "/home/lars/.virtualenvs/esdl-mapeditor/lib/python3.10/site-packages/flask/ctx.py", line 432, in __exit__
    self.pop(exc_value)
  File "/home/lars/.virtualenvs/esdl-mapeditor/lib/python3.10/site-packages/flask/ctx.py", line 415, in pop
    app_ctx.pop(exc)
  File "/home/lars/.virtualenvs/esdl-mapeditor/lib/python3.10/site-packages/flask/ctx.py", line 256, in pop
    _cv_app.reset(self._cv_tokens.pop())
ValueError: <Token var=<ContextVar name='flask.app_ctx' at 0x7f2ac79c36a0> at 0x7f2ac06b8600> was created in a different Context
Exception in thread Thread-179 (_handle_event_internal):
Traceback (most recent call last):
  File "/usr/lib/python3.10/threading.py", line 1016, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3.10/threading.py", line 953, in run
    self._target(*self._args, **self._kwargs)
  File "/home/lars/.virtualenvs/esdl-mapeditor/lib/python3.10/site-packages/socketio/server.py", line 720, in _handle_event_internal
    r = server._trigger_event(data[0], namespace, sid, *data[1:])
  File "/home/lars/.virtualenvs/esdl-mapeditor/lib/python3.10/site-packages/socketio/server.py", line 745, in _trigger_event
    return self.handlers[namespace][event](*args)
  File "/home/lars/.virtualenvs/esdl-mapeditor/lib/python3.10/site-packages/flask_socketio/__init__.py", line 282, in _handler
    return self._handle_event(handler, message, namespace, sid,
  File "/home/lars/.virtualenvs/esdl-mapeditor/lib/python3.10/site-packages/flask_socketio/__init__.py", line 795, in _handle_event
    with app.request_context(environ):
  File "/home/lars/.virtualenvs/esdl-mapeditor/lib/python3.10/site-packages/flask/ctx.py", line 432, in __exit__
    self.pop(exc_value)
  File "/home/lars/.virtualenvs/esdl-mapeditor/lib/python3.10/site-packages/flask/ctx.py", line 415, in pop
    app_ctx.pop(exc)
  File "/home/lars/.virtualenvs/esdl-mapeditor/lib/python3.10/site-packages/flask/ctx.py", line 256, in pop
    _cv_app.reset(self._cv_tokens.pop())
ValueError: <Token var=<ContextVar name='flask.app_ctx' at 0x7f2ac79c36a0> at 0x7f2ac06b8600> was created in a different Context

Anyone have any clue why? I use Flask-SocketIO 5.3.4. Is it too recent?

[miguelgrinberg]

@larsderidder this is a strange error. Are you doing anything related to app or request contexts in the Socket.IO event handler that runs right before this error appears?

[pdecks]

On this note, see also pallets/flask#4734 (comment).