René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"JIT x Free-Threading","articleBody":"# Feature or enhancement\n\n### Proposal:\n\nThis provides an alternative design to https://github.com/python/cpython/issues/133171. I have a branch where all tests (including FT) pass.\n\n**Part 1:**\nFor the first and simplest part, we could add a watcher/callback to thread creation. When multiple threads are created, we simply invalidate the executor as _CHECK_VALIDITY fails.\n\nThis means single threaded code gets all the benefits of JIT in the future, while multi-threaded code will lose all the benefits. However, both can coexist at the same time in the same build. We will finally get JIT + FT in a limited form. Pending part 2.\n\n**Part 2:**\nIf we detect multiple threads are running, we turn off the non-thread safe optimizations, and redo the trace with those optimizations off. If we detect only a single thread, we follow part 1 and run till we get invalidated. This allows single threaded code to run faster, while multi-threaded code will run a little slower. Note that all optimizations I've proposed for the JIT in the past 6 months and in the future are FT safe (in theory. whether they are implemented in practice is different).\n\nTogether, part 1 and part 2 get the best of both worlds: for single-threaded code, we get max performance, even recovering some of the perf single-threaded perf lost from FT. In part 2, we get max compatibility with multiple threads.\n\n**We need both parts to get the max perf out of the JIT on FT**.\n\nFollow-up after this:\n* Lock/unlock removal in FT code.\n\n### Has this already been discussed elsewhere?\n\nNo response given\n\n### Links to previous discussion of this feature:\n\nhttps://github.com/python/cpython/issues/133171\n\n\u003c!-- gh-linked-prs -->\n### Linked PRs\n* gh-141595\n\u003c!-- /gh-linked-prs -->\n","author":{"url":"https://github.com/Fidget-Spinner","@type":"Person","name":"Fidget-Spinner"},"datePublished":"2025-11-15T16:25:55Z","url":"https://github.com/python/cpython/issues/141594"}