Create an Rc<T> from an Arc<T>?

1

I could not find anything skimming through Arc in std::sync - Rust

I have an Arc<T> . Without cloning the T itself, is there a way to produce an Rc<T> ?

EDIT: Some context. I have some single threaded functions that take Rc<T> as argument. I am now writing some multi threaded code, which is passing Arc<T>'s around.

2

If the Arc is unique you could move the value out and into an Rc.

if let Ok(inner) = Arc::try_unwrap(arc) {
    let rc = Rc::new(inner);
}
3

Definitely not unique. Multiple threads have Arcs to it.

4

If the Arc is not unique, the conversion is unsound, because an Rc's ref counts are not atomic. So when the Rc was cloned or dropped you would create a data race with other threads, even though the Rc itself did not cross a thread boundary.

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5

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