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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Missing critical sections for `PyDict_Next` calls in `_functoolsmodule.c`","articleBody":"# Bug report\n\n### Bug description:\n\nAfter some discussion  on PR https://github.com/python/cpython/pull/145362, I noticed that in `Modules/_functoolsmodule.c`, all use cases of `PyDict_Next` do not use a critical section, which is necessary in for the free-threaded build. The [docs](https://docs.python.org/3/c-api/dict.html#c.PyDict_Next) say that for `PyDict_Next`:\n\n\u003e The function is not thread-safe in the [free-threaded](https://docs.python.org/3/glossary.html#term-free-threading) build without external synchronization. You can use [Py_BEGIN_CRITICAL_SECTION](https://docs.python.org/3/c-api/synchronization.html#c.Py_BEGIN_CRITICAL_SECTION) to lock the dictionary while iterating over it\n\nI have not checked if other files are missing a critical section, but it is definitely possible.  I will draft a PR shortly for this issue in the coming days, but if anyone else finds other occurrences of `PyDict_Next` that are not thread-safe, please let me know.\n\n### CPython versions tested on:\n\nCPython main branch\n\n### Operating systems tested on:\n\nLinux\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-145487\n* gh-145879\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/brijkapadia","@type":"Person","name":"brijkapadia"},"datePublished":"2026-03-03T02:19:48.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/145446/cpython/issues/145446"}