Use a real Volatile struct

[gkoz]

We might want to import Volatile from the volatile crate in the sys crates. It doesn't have a constructor though, so @antoyo you might still not be entirely happy with it.
gtk-rs/sys#25 (comment)

[antoyo]

I am not sure why we need a wrapper for the ref_count volatile fields.
Could you please explain me why?

I believe most of the time, the user of the API will not change this value directly: it will be updated by the g_object_ref function.
And if an update is needed, perhaps write_volatile from the standard library could be used.

Moreover, it seems to be used only in the sys crates, right?

Am I missing something?

[gkoz]

Generally, it seemed a good idea to statically prevent inappropriate accesses to volatile fields at the sys crates level. The higher level crates so far haven't touched such fields because the API functions take care of that indeed.

I suspect mem::swap can subvert that restriction anyway so it may be a bit pointless. Still, like in the privacy issue it seems wrong to just ignore the volatile thing. Do you think we can find some middle ground here?

[gkoz]

I guess changing Volatile to be a transparent wrapper could provide some notice while leaving the users with responsibility to actually do the right thing. Something like

#[repr(C)]
pub struct Volatile<T> {
    pub volatile: T,
}

[antoyo]

Having a public field would help me.

I have another idea, but I am not sure if it is good thought and it only works for the ref_count field.

My issue is that I want to create a const struct with a ref_count of -1 (meaning not ref counted).
So perhaps we could create an enum like the following:

enum RefCount {
    NoRefCount,
    RefCount(Volatile),
}

I don't think creating a const struct with a ref count make sense, so the Volatile field could stay abstract.

[gkoz]

Eh, I don't think this kind of special treatment for some fields in the sys crates is going to work.

[antoyo]

Ok, then if we could make the field public, this code would work.

[EPashkin]

Volatible break ABI on at minimum on Windows 32, so it was removed in #579 completely.