Thread safety metadata in Rust is surprisingly condensed! POSIX has more fine-grained MT-unsafe concepts than Rust.

Rust data types can be "Send" (can be moved to another thread) and "Sync" (multiple threads can access them at the same time). Everything else is derived from these properties (structs are Send if their fields are Send. Wrapping non-Sync data in a Mutex makes it Sync, thread::spawn() requires Send args, etc.)

Rust doesn't even reason about thread-safety of functions themselves, only the data they access, and that is sufficient if globals are required to be "Sync".