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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Type slots are not thread-safe in free-threaded builds","articleBody":"# Bug report\n\n### Bug description:\n\nModification of type slots is protected by the global type lock, however, type slots are read non-atomically without holding the type lock. For example, in `PyObject_SetItem`:\n\nhttps://github.com/python/cpython/blob/5bb059fe606983814a445e4dcf9e96fd7cb4951a/Objects/abstract.c#L231-L235\n\nIt's not clear how we want to address this. From @colesbury in https://github.com/python/cpython/pull/127169#discussion_r1857029790:\n\n```\nI'd lean towards doing a stop-the-world pause when modifying the slot so that we don't need \nto change every read. I expect that to be a bit tricky since class definitions look like they're mutating \nthe class.\n```\n\n\n### CPython versions tested on:\n\n3.13, 3.14, CPython main branch\n\n### Operating systems tested on:\n\nLinux\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-131174\n* gh-133177\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/mpage","@type":"Person","name":"mpage"},"datePublished":"2024-11-25T21:07:34.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/127266/cpython/issues/127266"}