RwLock and std::box - parking_lot does not allocate ?

[luke-titley]

Hey,
So i've been reading through the docs/notes and parking_lot sounds awesome. I'm using std RwLock a lot and I was surprised to learn a few months back that because pthread primitives are non TM that rust std lib has to box them. You mention in the notes that parking_lot RwLock is just one additional word of space. I just want to clarify, does this means a parking_lot RwLock doesn't not implicitly allocate?

[bjorn3]

Correct. parking_lot only needs a single AtomicUsize as state next to the actual value. This AtomicUsize can be moved together with the rest of the RwLock and as such doesn't need to be boxed.

parking_lot/src/raw_rwlock.rs

Lines 55 to 58 in d763fca

	/// Raw reader-writer lock type backed by the parking lot.
	pub struct RawRwLock {
	state: AtomicUsize,
	}