appnope crashes with segfault from subrocess

[impact27]

Steps:

1. Add this code in a file:

from multiprocessing import Pool
import appnope

def f(x):
    appnope.nope()

if __name__ == '__main__':
    with Pool(5) as p:
        print(p.map(f, [1]))

2. Run with ipython crash.py
3. Crash with a segfault and prints:

objc[2560]: +[NSString initialize] may have been in progress in another thread when fork() was called.
objc[2560]: +[NSString initialize] may have been in progress in another thread when fork() was called. We cannot safely call it or ignore it in the fork() child process. Crashing instead. Set a breakpoint on objc_initializeAfterForkError to debug.

[impact27]

Interestingly, using python instead of ipython doesn't trigger the crash.

[impact27]

Also printing the PIDs:

Main Process PID: 2688
Subprocess PID: 2691
objc[2691]: +[NSString initialize] may have been in progress in another thread when fork() was called.
objc[2691]: +[NSString initialize] may have been in progress in another thread when fork() was called. We cannot safely call it or ignore it in the fork() child process. Crashing instead. Set a breakpoint on objc_initializeAfterForkError to debug.

[impact27]

https://stackoverflow.com/questions/50168647/multiprocessing-causes-python-to-crash-and-gives-an-error-may-have-been-in-progr:
This solves it:
export OBJC_DISABLE_INITIALIZE_FORK_SAFETY=YES
ipython crash.py

[impact27]

Maybe relevant https://github.com/python/cpython/pull/13849/files

[impact27]

I think this is the relevant issue https://bugs.python.org/issue33725

[impact27]

I am closing this as this is a python bug and not appnope related. I suspect that any objc code called in a subprocess will create the same issue.