René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Segmentation fault, possibly due to a GC issue (tp_subclasses)","articleBody":"# Crash report\n\n### What happened?\n\n```python\nfrom typing import Union\n\n\nclass BaseNode:\n    next: Union[\"BaseNode\", None] = None\n\n    @staticmethod\n    def add(node: \"BaseNode\") -\u003e None:\n        if BaseNode.next is None:\n            BaseNode.next = node\n            return\n        current = BaseNode.next\n        while current.next is not None:\n            current = current.next\n        current.next = node\n\n    @staticmethod\n    def remove(node: \"BaseNode\") -\u003e None:\n        if BaseNode.next is None:\n            return\n        current = BaseNode.next\n        prev = BaseNode\n        while True:\n            if current is None:\n                return\n            if current == node:\n                if current.next is not None:\n                    prev.next = current.next\n                else:\n                    prev.next = None\n                return\n            prev = current\n            current = current.next\n\n\nclass Node(BaseNode):\n    def __init__(self) -\u003e None:\n        self.next = None\n        BaseNode.add(self)\n\n    def __del__(self) -\u003e None:\n        BaseNode.remove(self)\n\n\ndef main() -\u003e None:\n    Node()\n    Node()\n\n\nif __name__ == \"__main__\":\n    main()\n\n```\n\n(Edited by @ZeroIntensity) Shortened repro:\n\n```py\nclass BaseNode:\n    next = None\n\n\nclass Node(BaseNode):\n    def __init__(self) -\u003e None:\n        if BaseNode.next is None:\n            BaseNode.next = self\n            return\n        BaseNode.next.next = self\n\n    def __del__(self) -\u003e None:\n        BaseNode.next = BaseNode.next.next\n\n\nNode()\nNode()\n```\n\n(Edited by @fxeqxmulfx) Use after free example:\n```py\nclass BaseNode:\n    def __del__(self):\n        print(\"next\", BaseNode.next)\n        print(\"del\", self)\n\n\nBaseNode.next = BaseNode()\nBaseNode.next.next = BaseNode()\n```\n```\nnext \u003c__main__.BaseNode object at 0x717fb2d23a10\u003e\ndel \u003c__main__.BaseNode object at 0x717fb2d23a10\u003e\nnext \u003c__main__.BaseNode object at 0x717fb2d23a10\u003e use after free\ndel \u003c__main__.BaseNode object at 0x717fb2d23a50\u003e\n```\n\n### CPython versions tested on:\n\n3.14\n\n### Operating systems tested on:\n\nLinux\n\n### Output from running 'python -VV' on the command line:\n\nPython 3.14.0b2 (main, Jun 12 2025, 12:41:01) [Clang 20.1.4 ]\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-135728\n* gh-136147\n* gh-136151\n* gh-136189\n* gh-136304\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/fxeqxmulfx","@type":"Person","name":"fxeqxmulfx"},"datePublished":"2025-06-16T00:31:24.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":25},"url":"https://github.com/135552/cpython/issues/135552"}