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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Multithreaded subinterpreters can be running during finalization","articleBody":"# Crash report\n\n### What happened?\n\n(Found while investigating a fix for #125920.)\n\nSubinterpreters that are running in a different thread can still be running upon the finalization of the main interpreter, depending on what the thread was doing. Take the following script:\n\n```py\nfrom threading import Thread\nimport _interpreters\n\n\ndef silly():\n    interp = _interpreters.create()\n    _interpreters.run_string(interp, \"import time; time.sleep(100)\")\n\n\nif __name__ == \"__main__\":\n    Thread(target=silly).start()\n```\n\nOn 3.13 and 3.14, killing the process with CTRL+C results in an assertion failure:\n\n```\npython: Python/pylifecycle.c:2480: finalize_subinterpreters: Assertion `!_PyInterpreterState_IsRunningMain(interp)' failed.\n```\n\nHowever, if the thread is daemon, then the interpreter fully segfaults:\n\n```py\nfrom threading import Thread\nimport _interpreters\n\n\ndef silly():\n    interp = _interpreters.create()\n    _interpreters.run_string(interp, \"import time; time.sleep(100)\")\n\n\nif __name__ == \"__main__\":\n    Thread(target=silly, daemon=True).start()\n```\n\nI'm going to investigate possible fixes.\n\ncc @ericsnowcurrently\n\n### CPython versions tested on:\n\n3.13, CPython main branch\n\n### Operating systems tested on:\n\nLinux\n\n### Output from running 'python -VV' on the command line:\n\n_No response_\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-126026\n* gh-139158\n* gh-139219\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/ZeroIntensity","@type":"Person","name":"ZeroIntensity"},"datePublished":"2024-10-26T19:10:23.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":7},"url":"https://github.com/126016/cpython/issues/126016"}