Arc

Arc allows shared read-only access via Arc::clone:

use std::sync::Arc;
use std::thread;
fn main() {
    let v = Arc::new(vec![10, 20, 30]);
    let mut handles = Vec::new();
    for _ in 0..5 {
        let v = Arc::clone(&v);
        handles.push(thread::spawn(move || {
            let thread_id = thread::current().id();
            println!("{thread_id:?}: {v:?}");
        }));
    }
    handles.into_iter().for_each(|h| h.join().unwrap());
    println!("v: {v:?}");
}

This slide should take about 5 minutes.

• Arc stands for “Atomic Reference Counted”, a thread safe version of Rc that uses atomic operations.
• Arc<T> implements Clone whether or not T does. It implements Send and Sync if and only if T implements them both.
• Arc::clone() has the cost of atomic operations that get executed, but after that the use of the T is free.
• Beware of reference cycles, Arc does not use a garbage collector to detect them.
  • std::sync::Weak can help.