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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"asyncio.Server.wait_closed() appears to hang indefinitely in 3.12.0a7","articleBody":"# Bug report\r\n\r\nI have some code in the [qemu.qmp package](https://pypi.org/project/qemu.qmp/) that appears to work correctly in Python 3.6 (RIP~) through to Python 3.11. I've started testing against 3.12 and I'm finding that waiting on `asyncio.Server.wait_closed()` is creating a deadlock/hang.\r\n\r\nHere's a minimal-ish reproducer:\r\n\r\n```py\r\n#!/usr/bin/env python3\r\nimport asyncio\r\n\r\nasync def cause_problems():\r\n    accepted = asyncio.Event()\r\n\r\n    async def _incoming(reader, writer):\r\n        print(\"entered _incoming\")\r\n        print(\"signaling outer context; we accepted a client\")\r\n        accepted.set()\r\n        print(\"left _incoming\")\r\n\r\n    print(\"starting server\")\r\n    server = await asyncio.start_unix_server(\r\n        _incoming,\r\n        path=\"problems.sock\",\r\n        backlog=1,\r\n    )\r\n    print(\"created server; waiting on a client\")\r\n    await accepted.wait()\r\n    print(\"got a client\")\r\n\r\n    print(\"closing server\")\r\n    server.close()\r\n    print(\"issued close()\")\r\n    await server.wait_closed()\r\n    print(\"finished waiting on server to close\")\r\n\r\n\r\nif __name__ == '__main__':\r\n    asyncio.run(cause_problems())\r\n```\r\n\r\nYou can test a simple connection using whatever you'd like; `socat` works to trigger the accept code, e.g. from the same directory that you run the above code, try:\r\n\r\n```sh\r\nsocat UNIX-CONNECT:problems.sock stdout\r\n```\r\n\r\nHere's what happens in python 3.11.3\r\n```\r\njsnow@scv ~\u003e python3.11 hang.py \r\nstarting server\r\ncreated server; waiting on a client\r\nentered _incoming\r\nsignaling outer context; we accepted a client\r\nleft _incoming\r\ngot a client\r\nclosing server\r\nissued close()\r\nfinished waiting on server to close\r\n```\r\n\r\nAnd here's 3.12.0a7:\r\n```\r\njsnow@scv ~\u003e python3.12 hang.py\r\nstarting server\r\ncreated server; waiting on a client\r\nentered _incoming\r\nsignaling outer context; we accepted a client\r\nleft _incoming\r\ngot a client\r\nclosing server\r\nissued close()\r\n```\r\n\r\nWhen I issue ^C, we get this traceback:\r\n\r\n```\r\n^CTraceback (most recent call last):\r\n  File \"/usr/lib64/python3.12/asyncio/runners.py\", line 118, in run\r\n    return self._loop.run_until_complete(task)\r\n           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\r\n  File \"/usr/lib64/python3.12/asyncio/base_events.py\", line 664, in run_until_complete\r\n    return future.result()\r\n           ^^^^^^^^^^^^^^^\r\n  File \"/home/jsnow/hang2.py\", line 26, in cause_problems\r\n    await server.wait_closed()\r\n  File \"/usr/lib64/python3.12/asyncio/base_events.py\", line 384, in wait_closed\r\n    await waiter\r\nasyncio.exceptions.CancelledError\r\n\r\nDuring handling of the above exception, another exception occurred:\r\n\r\nTraceback (most recent call last):\r\n  File \"/home/jsnow/hang2.py\", line 31, in \u003cmodule\u003e\r\n    asyncio.run(cause_problems())\r\n  File \"/usr/lib64/python3.12/asyncio/runners.py\", line 194, in run\r\n    return runner.run(main)\r\n           ^^^^^^^^^^^^^^^^\r\n  File \"/usr/lib64/python3.12/asyncio/runners.py\", line 123, in run\r\n    raise KeyboardInterrupt()\r\nKeyboardInterrupt\r\n```\r\n\r\n\r\n# Your environment\r\n\r\n- Python 3.12.0a7 (as packaged on Fedora 37)\r\n- `Linux 6.2.12-200.fc37.x86_64 #1 SMP PREEMPT_DYNAMIC Thu Apr 20 23:38:29 UTC 2023`\r\n- Tested on CPython 3.6 through 3.12 as available on Fedora 37. Works on 3.6, 3.7, 3.8, 3.9, 3.10 and 3.11 but fails on the 3.12 alpha package.\r\n","author":{"url":"https://github.com/jnsnow","@type":"Person","name":"jnsnow"},"datePublished":"2023-05-09T23:21:15.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":17},"url":"https://github.com/104344/cpython/issues/104344"}