alt Hacker NewsOriginal post: https://webkit.org/blog/6161/locking-in-webkit/
Post that mentions the two bit lock: https://webkit.org/blog/7122/introducing-riptide-webkits-ret...
I don’t know the details of the Rust port but I don’t imagine the part that involves the two bits to require unsafe, other than in the ways that any locking algorithm dances with unsafety in Rust (ownership relies on locking algorithms being correct)
This is very similar to how Java's object monitors are implemented. In OpenJDK, the markWord uses two bits to describe the state of an Object's monitor (see markWord.hpp:55). On contention, the monitor is said to become inflated, which basically means revving up a heavier lock and knowing how to find it.
I'm a bit disappointed though, I assumed that you had a way of only using 2 bits of an object's memory somehow, but it seems like the lock takes a full byte?