Rust: What is the difference between Send and Sync?

Send — can move to another thread. Sync — can share between threads.

Send:

• Value can be transferred.
• Most types are Send.
• Rc is not Send.

Sync:

• Reference can be shared.
• &T is Sync if T is Sync.
• Cell is not Sync.

1fn require_send<T: Send>(val: T) {
2    thread::spawn(move || {
3        println!("{:?}", val);
4    });
5}
6
7fn require_sync<T: Sync>(val: &T) {
8    let handle = thread::spawn(move || {
9        println!("{:?}", val);
10    });
11}

Key: Send for moving, Sync for sharing.