René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Checking for `sys.is_finalizing` before thread.start() still yields \"can't create new thread at interpreter shutdown\"","articleBody":"# Bug report\n\n### Bug description:\n\nWe have code in [pymongo](https://github.com/mongodb/mongo-python-driver) Our `MongoClient` object immediately spawns a new daemon thread to run some periodic check operations from the moment it is initialized. When run on python 3.12, we've run into the issue `can't create new thread at interpreter shutdown` because we have cases `thread.start()` that can execute as the interpreter is shutting down.\n\nTo mitigate this issue we attempted checking `sys.is_finalizing` before issuing the `start()` call: \n```python\nif not sys.is_finalizing():\n    thread.start()\n```\nThis still generated the same runtime error. \n\nWe tried catching the `RuntimeError` exception:\n```python\ntry:\n    thread.start()\nexcept RuntimeError:\n    pass\n```\nThis worked. This feels too broad a solution than the above since it will catch and ignore all `RuntimeError`s. \n\nFinally we decided to see if we could check `sys.is_finalizing` after the exception is raised.\n\n```python\ntry:\n    thread.start()\nexcept RuntimeError:\n    if sys.is_finalizing():\n        self._thread = None\n        return\n    raise\n```\nTo our surprise, this also failed. I can understand that starting a thread on interpreter shutdown should be avoided, but this also feels misleading if the system isn't correctly seeing--which is my assumption on what `sys.is_finalizing()`--that it is experiencing interpreter shutdown. \n\nShould the expectation not be that `sys.is_finalizing` is updated before the `thread.start()` is called OR by the time the `RuntimeError` is raised? This way we can safely catch or preempt the error before triggering?\n\nAs a general inquiry, though, what should be the general best practice for patching issues like this on our end as it has introduced somewhat breaking behavior from 3.11 -\u003e 3.12? Should we do like above with catching the `RuntimeError` but additionally check the exception string for the exact type of `RuntimeError`?\n\n### CPython versions tested on:\n\n3.12\n\n### Operating systems tested on:\n\nmacOS\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-115352\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/Jibola","@type":"Person","name":"Jibola"},"datePublished":"2024-01-25T22:30:16.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":11},"url":"https://github.com/114570/cpython/issues/114570"}