On: Python interpreter written in rust reaches 10000 c...

[Joker_vD]

It's not a "flag", really: it's a fundamental, implicit underlying assumption about the execution environment. The C extensions assume (roughly) that if they're executing, they can touch any part of the runtime without any synchronization whatsoever, because nobody else is executing (that's what GIL ensures).

[jerf → Joker_vD]

Or, to put it another way, it's the first letter of the acronym: "Global Interpreter Lock".

You can't really "fake" a global lock. Either you're globally locking everywhere with the global lock or you aren't.