Closing a httpx client results in a "RuntimeError: Event loop is closed"

[BabakAmini]

I initially raised this issue on Stack Overflow, but unfortunately, I haven't received a solution. Therefore, I'm bringing it up here again.

I need to maintain a persistent httpx client in my code to utilize its connection pool throughout the lifespan of my application. Below is a simplified version of my implementation:

import asyncio
import weakref
from threading import Lock

import nest_asyncio
from httpx import AsyncClient


class Request:
    _instance = None
    _lock = Lock()
    _loop: asyncio.AbstractEventLoop = None
    _new_loop = False
    _session = None

    def __new__(cls):
        if not cls._instance:
            with cls._lock:
                if not cls._instance:
                    instance = super().__new__(cls)
                    cls._instance = instance
                    weakref.finalize(instance, instance._close)

                    if cls._loop is None:
                        try:
                            cls._loop = asyncio.get_running_loop()
                        except RuntimeError:
                            cls._loop = asyncio.new_event_loop()
                            cls._new_loop = True
                            asyncio.set_event_loop(cls._loop)

                if cls._new_loop:
                    # nest_asyncio.apply()
                    cls._loop.run_until_complete(cls.create_client())
                else:
                    cls._loop.create_task(cls.create_client())

        return cls._instance

    @classmethod
    async def create_client(cls):
        cls._session = AsyncClient()

    @classmethod
    def _close(cls):
        cls._loop.run_until_complete(cls.close())

        if cls._new_loop:
            cls._loop.close()

    @classmethod
    async def close(cls):
        if cls._session:
            await cls._session.aclose()

    async def get(self, url):
        try:
            return await self._session.get(url)

        except Exception:
            return None


req = Request()


async def main():
    result = await req.get('https://www.google.com')
    if result:
        print(result.text[:100])


asyncio.run(main())

This results in a RuntimeError: Event loop is closed:

...
    await self._pool.aclose()
  File "/home/user/.cache/pypoetry/virtualenvs/app-gEFTwlce-py3.12/lib/python3.12/site-packages/httpcore/_async/connection_pool.py", line 313, in aclose
    await self._close_connections(closing_connections)
  File "/home/user/.cache/pypoetry/virtualenvs/app-gEFTwlce-py3.12/lib/python3.12/site-packages/httpcore/_async/connection_pool.py", line 305, in _close_connections
    await connection.aclose()
  File "/home/user/.cache/pypoetry/virtualenvs/app-gEFTwlce-py3.12/lib/python3.12/site-packages/httpcore/_async/connection.py", line 171, in aclose
    await self._connection.aclose()
  File "/home/user/.cache/pypoetry/virtualenvs/app-gEFTwlce-py3.12/lib/python3.12/site-packages/httpcore/_async/http11.py", line 265, in aclose
    await self._network_stream.aclose()
  File "/home/user/.cache/pypoetry/virtualenvs/app-gEFTwlce-py3.12/lib/python3.12/site-packages/httpcore/_backends/anyio.py", line 55, in aclose
    await self._stream.aclose()
  File "/home/user/.cache/pypoetry/virtualenvs/app-gEFTwlce-py3.12/lib/python3.12/site-packages/anyio/streams/tls.py", line 201, in aclose
    await self.transport_stream.aclose()
  File "/home/user/.cache/pypoetry/virtualenvs/app-gEFTwlce-py3.12/lib/python3.12/site-packages/anyio/_backends/_asyncio.py", line 1287, in aclose
    self._transport.close()
  File "/nix/store/gmx7bwrwy6s0kk89ij5yj8r8ayai95x1-python3-3.12.5/lib/python3.12/asyncio/selector_events.py", line 1210, in close
    super().close()
  File "/nix/store/gmx7bwrwy6s0kk89ij5yj8r8ayai95x1-python3-3.12.5/lib/python3.12/asyncio/selector_events.py", line 875, in close
    self._loop.call_soon(self._call_connection_lost, None)
  File "/nix/store/gmx7bwrwy6s0kk89ij5yj8r8ayai95x1-python3-3.12.5/lib/python3.12/asyncio/base_events.py", line 795, in call_soon
    self._check_closed()
  File "/nix/store/gmx7bwrwy6s0kk89ij5yj8r8ayai95x1-python3-3.12.5/lib/python3.12/asyncio/base_events.py", line 541, in _check_closed
    raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed

The only way to resolve this issue is to uncomment the line containing nest_asyncio.apply(). However, since the nest_asyncio package is heavily based on asyncio internal functions and is no longer maintained, I'm not interested in using it in my code.

My question is: Why is the loop closed when I call run_until_complete() (from within the _close() function), which creates a new event loop and immediately calls the AyncClient.aclose() function? How can I fix this?

For your reference, the same code works for aiohttp.ClientSession without the need to use nest_asyncio.