Why does tokio::sync::broadcast::channel not have a Send requirement?

[pretzelhammer]

The function signature of tokio::sync::broadcast::channel is this:

pub fn channel<T: Clone>(capacity: usize) -> (Sender<T>, Receiver<T>)

But why is it T: Clone and not T: Clone + Send? Say I create a broadcast channel with something like:

let (tx, rx) = broadcast::channel::<Rc<RefCell<String>>(8);

And then I spawn a bunch of tasks give each of them an rx, and then I tx.send(Rc::new(RefCell::new(String::from("whatever"))), and then each of the tasks calls clone and borrow_mut a bunch of times on the received value concurrently... wouldn't that cause some kind of data race or undefined behavior?

[sfackler]

Sender and Receiver are only Send if T is.

[pretzelhammer]

huh, it never occurred to me that a broadcast channel could be in a single-threaded context, but that makes sense, thanks for clarifying!