Rust: What is the difference between RefCell and Mutex?

RefCell — single-threaded runtime borrow. Mutex — thread-safe lock.

RefCell:

• Single-threaded.
• Runtime borrow check.
• Can panic.

Mutex:

• Thread-safe.
• Blocking lock.
• Can deadlock.

1// RefCell
2use std::cell::RefCell;
3let r = RefCell::new(5);
4*r.borrow_mut() += 1;
5
6// Mutex
7use std::sync::Mutex;
8let m = Mutex::new(5);
9*m.lock().unwrap() += 1;

Key: RefCell for single thread, Mutex for multi-thread.