let (user_sender, user_receiver) = spsc::channel();

// You can use any runtime you like:
// tokio, smol, pollster, ... it works with everything!
let rx = tokio::spawn(async {
    // Receiving is async:
    // the call only returns once a value was sent,
    // or the sender was dropped.
    let user = user_receiver.await.unwrap();
    assert_eq!(user, "Max Mustermann");
});

// Sending is synchronous:
// The call does not need to happen inside a runtime.
user_sender.send("Max Mustermann").unwrap();

rx.await.unwrap();