Reference-counting `AdvisoryLockGuard` about sqlx

[abonander]

If the key string you pass to PgAdvisoryLock is constant, you could put it in a smol::lock::OnceCell or a std::sync::LazyLock inside a static which would give you &'static references to it.

We could probably promote with_key() to a const fn so that it can be constructed directly in a static.

Otherwise, I'm not against .acquire_owned()/.try_acquire_owned() methods taking Arc<Self>. There's no real reason it doesn't exist already besides "I didn't think of it".

Couple bikeshedding things:

• I'd prefer the _owned suffix to match Tokio: https://docs.rs/tokio/latest/tokio/sync/struct.RwLock.html#method.write_owned
• It's a judgement call whether to take Arc<Self> or &Arc<Self>. The latter would increment the reference count lazily for less thrashing on highly contended locks, but the former would allow even the acquire() call itself to be moved into a task if desired.
  • I'm leaning toward Arc<Self> since it's strictly more flexible at the minor cost of requiring an explicit .clone(). Thrashing the refcount doesn't really matter since it's going to be dwarfed by the network overhead anyway. It also matches Tokio's API.

[bonsairobo]

Unfortunately my keys are not constant. But I appreciate the idea.

I agree with your design thoughts.

I might have time to try implementing this feature if you're open to that.

[abonander]

Yeah, I'd appreciate it!