Cache stampede doesn't work in free threading

[ddorian]

Hello,

Looking at the readme, the library provides cache stampede, but it doesn't work in free threading.
Is this issue valid?

❯ uv run --python 3.14.6t --no-project cachebox_freethreading_repro.py
Installed 1 package in 2ms
burst 1: cached(lock=True) ran the body 2x, expected 1x

# /// script
# requires-python = "==3.14.6"
# dependencies = ["cachebox==6.1.2"]
# ///

import sys
import threading

import cachebox

THREADS = 32
BURSTS = 10  # one burst reproduces ~96% of the time; ten make a false negative unlikely


def cold_burst() -> int:
    """Race THREADS threads into one cold cached() key. Return how often the body ran."""
    calls: list[int] = []  # list.append is atomic without the GIL; `calls += 1` would not be
    barrier = threading.Barrier(THREADS)

    @cachebox.cached(cachebox.LRUCache(maxsize=1), lock=True)
    def build() -> dict[int, str]:
        calls.append(1)
        return {i: str(i) for i in range(20_000)}  # slow enough that every thread misses

    def worker() -> None:
        barrier.wait()
        build()

    threads = [threading.Thread(target=worker) for _ in range(THREADS)]
    for thread in threads:
        thread.start()
    for thread in threads:
        thread.join()
    return len(calls)


if sys._is_gil_enabled():
    print("note: the GIL hides this race; expect it to pass here", file=sys.stderr)

for burst in range(1, BURSTS + 1):
    body_calls = cold_burst()
    if body_calls > 1:
        raise SystemExit(f"burst {burst}: cached(lock=True) ran the body {body_calls}x, expected 1x")

print(f"body ran exactly once in all {BURSTS} bursts of {THREADS} threads")