Slothy isn't inherently thread-safe

[bswck]

Because it patches the built-in scope, which is often a globally reused object (the builtins module).'
That means that a change of a built-in name in a frame may affect outer and inner and unrelated frames.

Here's an example:

from functools import partial
from sys import _getframe
from threading import Thread
from time import sleep


@partial(Thread, None)
def t1_patch() -> None:
    _getframe(0).f_builtins["foo"] = "bar"
    sleep(1)


@partial(Thread, None)
def t2_read() -> None:
    sleep(0.5)
    print(foo)


if __name__ == "__main__":
    t1_patch.start()
    t2_read.start()

    t1_patch.join()
    t2_read.join()

(outputs bar in the console).

@pawamoy I think this was the reason why slothy broke tests in Griffe.
Though it was when combined with xdist, so I'll have to investigate further.

[pawamoy]

Yup, would have to read xdist's code to understand why it was causing issues.