René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Abort in free-threaded build due to mutation of `ChainMap` of a `Counter` in threads","articleBody":"### What happened?\r\n\r\nThe code below, in a no-gil debug build with `PYTHON_GIL=0`, results in the following abort:\r\n```\r\npython: ./Include/internal/pycore_stackref.h:99: _PyStackRef_FromPyObjectSteal: Assertion `obj != NULL' failed.\r\nAborted\r\n```\r\n\r\n```python\r\nfrom threading import Thread\r\nfrom collections import ChainMap, Counter\r\n\r\ncounter = Counter(range(100))\r\nchainmap = ChainMap(counter)\r\nchainmap2 = ChainMap(counter)\r\n\r\ndef mutate_removing():\r\n    for x in range(10):\r\n        chainmap.pop(list(chainmap.keys()).pop())\r\n        chainmap2.pop(list(chainmap2.keys()).pop())\r\n\r\ndef mutate_adding():\r\n    for x in range(50):\r\n        chainmap[max(chainmap) + x + 1] = x\r\n        chainmap2[max(chainmap2) + x + 1] = x\r\n\r\nalive = []\r\n\r\nfor x in range(55):\r\n    alive.append(Thread(target=mutate_removing, args=()))\r\n    alive.append(Thread(target=mutate_adding, args=()))\r\n\r\nfor obj in alive:\r\n    try:\r\n        print('START', obj)\r\n        obj.start()\r\n    except Exception:\r\n        pass\r\n```\r\n\r\nFound using fusil by @vstinner.\r\n\r\n\r\n### CPython versions tested on:\r\n\r\nCPython main branch\r\n\r\n### Operating systems tested on:\r\n\r\nLinux\r\n\r\n### Output from running 'python -VV' on the command line:\r\n\r\nPython 3.14.0a1+ experimental free-threading build (heads/main:556dc9b8a7, Nov  3 2024, 10:09:47) [GCC 11.4.0]\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-126369\n* gh-126371\n* gh-132693\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/devdanzin","@type":"Person","name":"devdanzin"},"datePublished":"2024-11-03T15:28:49.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":6},"url":"https://github.com/126366/cpython/issues/126366"}