[3.8 regression] Deadlock with async_to_sync → sync_to_async → async_to_sync → create_task → sync_to_async

[andersk]

This code, minimized from the Zulip server, worked in asgiref 3.7.2, but deadlocks in 3.8.0, 3.8.1, and current main (abc69a0). A Git bisection implicates d920c3c as the first broken commit:

• Allow nesting sync_to_async via asyncio.wait_for #367, cc @jthorniley

import asyncio

from asgiref.sync import async_to_sync, sync_to_async


async def inner() -> asyncio.Task[None]:
    return asyncio.create_task(sync_to_async(print)("inner"))


async def main() -> None:
    task = await sync_to_async(async_to_sync(inner))()
    await task


async_to_sync(main)()