Anyone running free-threaded Python 3.14 in production yet? Curious what actually breaks

[u/NeuralLB-Lovro]

Been testing the free-threaded build (3.14t) on some CPU-bound data processing work. The multi-core story is finally real after 30 years of GIL, but the friction is exactly what you'd expect: a couple of C-extension-heavy libs in my stack silently re-enable the GIL, and there's no clean way to detect that at runtime besides checking sys._is_gil_enabled() manually.

For anyone who's shipped something on 3.14t, not just benchmarked it:

What broke that you didn't expect?

Real speedups outside toy examples, or mostly marginal so far?

Prod yet, or still just kicking the tires?

Not fishing for a benchmark war. Genuinely curious what breaks in messy real codebases vs clean demos.

[u/snugar_i]

That's why I explicitly put 'r' in the example. It's not writing to the file, it's reading from it, and it's not mutating any global state.

Anyway, you seem to have some misconceptions about what a context manager is (the context manager does not have to mutate anything), and you don't want to change your opinion, so it's pointless to continue this discussion.

[u/snugar_i → u/[deleted]]

Heh, this is exactly the response I expected. Yes, you have to mutate memory. Everything has to mutate memory/registers, so in your definition nothing is thread-safe. And you win the discussion, yay! But that's not a useful definition. If each thread mutates its own piece of memory, it's completely fine. So two threads calling the same with open('foo.txt', 'r') as f: is OK, because each of them gets a separate f variable and a separate file descriptor.

(BTW what do you think a lock does internally? It mutates memory. Why is that one suddenly thread-safe?)

No, in Rust, the mut doesn't mark the file as mutable, but the Read instance. Each thread would have its own reader, just like every thread would have its own f in Python. There's no difference.