Using blocking portal with a loitering event loop thread

example.py

import asyncio
import atexit
from contextlib import ExitStack

from anyio.from_thread import start_blocking_portal

exit_stack = ExitStack()
portal = exit_stack.enter_context(start_blocking_portal())
atexit.register(exit_stack.close)

portal.call(asyncio.sleep, 1)

I think I see the problem. start_blocking_portal() is using a concurrent.futures.ThreadPoolExecutor behind the scenes, and these started using non-daemonic threads in Python 3.9, so atexit callbacks aren't run, leading to a deadlock. I'll need to make it use plain daemonic Thread instead for consistency.

I think I see the problem. start_blocking_portal() is using a concurrent.futures.ThreadPoolExecutor behind the scenes, and these started using non-daemonic threads in Python 3.9, so atexit callbacks aren't run, leading to a deadlock. I'll need to make it use plain daemonic Thread instead for consistency.

Nothing is ever as easy as it should be! 😅 I'm glad you could see the root cause as debugging that was definitely outside my experience/expertise!