What is the X11 lock?

[Shachar Shemesh]

Hi list,

Can anyone please explain to me what the x11 lock is used for? I can see
that SOME X11 functions (e.g. - read description on
X11DRV_KEYBOARD_DetectLayout) require a lock, while others seem to call
X11 functions with no lock.

I can see that sometimes the x11 lock is obtained around a single X11 call.

Is there any guideline I can follow that will tell me whether I need a
lock for code I'm writing? What is the race this lock was designed to fix?

Thanks,
Shachar