What did you do?

make debug or make install

What did you expect to happen?

Expect compilation to happen across all the cores, taking ~ 2-3 seconds.

What actually happened?

Single threaded, taking ~15 seconds. There are something like 60 compilation units, and I have at least 8 cores.

What are your OS, Python and Pillow versions?

• OS: Mac + Linux
• Python: 3.12
• Pillow: 11.2, main

Sometime between ~6 years ago and now, probably when the setuptools migrated around or we went to the newer build tool specifications, the parallel option here: https://github.com/python-pillow/Pillow/blob/main/setup.py#L381 stopped working.

I can confirm that the code there is running, self.parallel is set correctly, but setuptools is apparently not using it anymore.