Cell and RefCell are both !Sync, as they don't prevent dataraces. You would still need to wrap them in a Mutex to actually make them threadsafe. But Rc<RefCell<

Cell and RefCell are both !Sync, as they don't prevent dataraces. You would still need to wrap them in a Mutex to actually make them threadsafe. But Rc<RefCell<Ppu>> would forego the need for unsafe{} here, at the cost of runtime enforcement of unique mutable access, without making it threadsafe. Or Arc<Mutex<Ppu>> for the thread safe variation.