Forked processes on MacOS v26 die when setting proc title

[iamkhav]

Hi all,
got an issue with an interaction between this lib and the newest MacOS version.

Description

With MacOS v26 (Tahoe), forked processes die silently when setting the process title.
Example to reproduce this:

import multiprocessing
import setproctitle
import time


def print_square(num):
    print("Getting proc title")
    print(setproctitle.getproctitle())
    print("Setting proc title")
    setproctitle.setproctitle(f"hi-i-square-{num}")  # <- this is where the process quits silently
    print(f"Square: {num * num}")
    time.sleep(2)
    print("Ran successfully")


def main() -> None:
    multiprocessing.set_start_method("fork")

    import sys
    print(sys.version)
    print("Starting process")

    p1 = multiprocessing.Process(target=print_square, args=(1,))
    p2 = multiprocessing.Process(target=print_square, args=(2,))
    p3 = multiprocessing.Process(target=print_square, args=(3,))

    processes = [p1, p2, p3]
    for process in processes:
        process.start()
    for process in processes:
        process.join()


if __name__ == "__main__":
    main()

Note: Getting the proc title still works. Only setting a proc title makes things break.

Unfortunately, I don't even get a good error message to put into this issue.

Anyone got an idea what the issue could be here?

[iamkhav]

This test should actually catch this

py-setproctitle/tests/setproctitle_test.py

Lines 486 to 502 in d19c673

	def test_fork_segfault():
	run_script(
	"""\
	import multiprocessing as mp
	from setproctitle import setproctitle
	def foo():
	setproctitle('title in child')
	setproctitle('title in parent')
	mp.set_start_method("fork")
	p = mp.Process(target=foo)
	p.start()
	p.join()
	assert p.exitcode == 0, f"p.exitcode is {p.exitcode}"
	"""
	)

But macos-latest is not yet mapped to macos-26 if I'm not mistaken so the unit tests successfully run through.

Edit: Can confirm this breaks on my local.