[bjourne]

Because their gc is a proof-of-concept created specifically for this research. It doesn't even deallocate memory. Most likely, they didn't have their students write any threaded code so thread-safety wasn't a concern. For a production ready tracing gc, of course they would add thread safety, it's not a big problem.

[dahfizz]

No, this is the fundamental tradeoff they made to make the Bronze'd Rust easy to use:

> Rust permits only one mutable reference to a value at a time... With Bronze, mutation is permitted through all references to each garbage-collected object, with no extra effort. A key tradeoff is that Bronze does not guarantee thread safety; as in other garbage collected languages, it is the programmer’s responsibility to ensure safety.

Allowing mutability anywhere is what fundamentally makes Bronze easier to learn, and more error-prone.

[bjourne]

The paper's author has already explained to you how thread safety can be achieved in a production-ready gc. This is not something that is particularly difficult to engineer and is quite orthogonal to whether one chooses to use tracing gc, ref counting or Rust-like borrow checking.