Mutable statics are difficult to use correctly

[Diggsey]

The documentation gives an example of "correct" usage of a mutable static, where a hypothetical "atomic_add" function is called.

https://doc.rust-lang.org/reference/items/static-items.html#mutable-statics

However, AIUI this code is incorrect as soon as a mutable reference is created to the static variable, as the lack of synchronization means that the mutable reference may alias.

This means that mutable statics can only be used when you already have some method of synchronization in place. Unfortunately this makes mutable statics quite useless. For example: a typical use of a mutable static might be to store a libc::sem_t semaphore type.

[RustyYato]

There was a motion to deprecate static mut entirely because of how hard it is to use correctly: rust-lang/rust/issues/53639

[RalfJung]

However, AIUI this code is incorrect as soon as a mutable reference is created to the static variable, as the lack of synchronization means that the mutable reference may alias.

Hm, yeah that code should probably use &raw mut instead of &mut (Cc rust-lang/rust#73394).