qznc puts that better then I do. It saves you from data races, but not from race conditions. Cell and RefCell are both not Sync (that means they can't be used

qznc puts that better then I do. It saves you from data races, but not from race conditions. Cell and RefCell are both not Sync (that means they can't be used from multiple threads) for a reason. RefCell does, however, allow borrow checking at runtime, for wrapping it with something that establishes Sync.