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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Starting new thread during finalization leads to call to `PyMem_Free` without holding the GIL","articleBody":"# Crash report\n\n### What happened?\n\nSince #109135, `thread_run` checks if it is called during finalization, and in this case it frees thread bootstate in `thread_bootstate_free` and returns. The problem is that  `PyMem_Free` shouldn't be called if GIL is not held.\n\nRepro and error message (just in case):\n```python\nimport os\nimport random\nimport signal\nimport subprocess\nimport sys\nimport time\n\nscript = \"\"\"\nimport threading\nwhile True:\n    t = threading.Thread()\n    t.start()\n    t.join()\n\"\"\"\n\nwhile True:\n    p = subprocess.Popen([sys.executable, '-c', script], stderr=subprocess.PIPE)\n    time.sleep(random.random())\n    os.kill(p.pid, signal.SIGINT)\n    _, err = p.communicate()\n    if p.returncode == -signal.SIGABRT:\n        print(err.decode('utf-8'))\n        break\n```\n\n```\nTraceback (most recent call last):\n  File \"\u003cstring\u003e\", line 5, in \u003cmodule\u003e\n  File \"/home/radislav/projects/cpython/Lib/threading.py\", line 983, in start\n    self._started.wait()\n  File \"/home/radislav/projects/cpython/Lib/threading.py\", line 641, in wait\n    signaled = self._cond.wait(timeout)\n               ^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/home/radislav/projects/cpython/Lib/threading.py\", line 341, in wait\n    waiter.acquire()\nKeyboardInterrupt\nFatal Python error: _PyMem_DebugFree: Python memory allocator called without holding the GIL\nPython runtime state: finalizing (tstate=0x0000561b61b67338)\n\nThread 0x00007f8f890b8280 (most recent call first):\n  \u003cno Python frame\u003e\n```\n\ncc @vstinner\n\n### CPython versions tested on:\n\nCPython main branch\n\n### Operating systems tested on:\n\nLinux\n\n### Output from running 'python -VV' on the command line:\n\nPython 3.13.0a0 (heads/main:3e8fcb7df7, Sep 23 2023, 01:43:45) [GCC 10.2.1 20210110]\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-109808\n* gh-109852\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/chgnrdv","@type":"Person","name":"chgnrdv"},"datePublished":"2023-09-23T21:12:20.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":5},"url":"https://github.com/109795/cpython/issues/109795"}