Summary: We had a report of crashes in parallel compile subprocesses linked to reading justknobs. See https://fburl.com/workplace/14a4mcbh internally. This is a known issue with justknobs. It looks like we don't have a lot of control over evaluating knobs. Some are read in inductor (`"pytorch/remote_cache:autotune_memcache_version`), but many are read by the triton compiler. According to this advice https://fburl.com/workplace/imx9lsx3, we can import thread_safe_fork which installs some functionality to destroy some singletons before forking and re-enable them after. This apporach works for the failing workload.
Test Plan: See D63719673 where the reporting user was kind enough to provide us with a local repro. Without the relevant import, we can reproduce the crash. With the import, the training runs successfully to completion.
Differential Revision: D63736829
Pull Request resolved: https://github.com/pytorch/pytorch/pull/137155
Approved by: https://github.com/xmfan, https://github.com/eellison
