FileCheck / lit hanging on mac builders

Hi all,

I’ve got some internal buildbots running lit tests and occasionally when run on Mac the entire lit test suite deadlocks. If I dump the process list on the machine I can see that lit and FileCheck are both running and deadlocked.

Only happens on Mac, but it doesn’t depend on Python version. I’ve seen this with everything from Python 2.7 to Python 3.8.

Does anyone have any theories on what could be going on? I’ve audited the source code for FileCheck and I don’t even see how it’s possible for FileCheck to deadlock.

Has anyone else ever seen anything like this or have any theories on what might be happening?