New upstream version 1.63.0+dfsg1

[rustc.git] / src / doc / rust-by-example / src / std / arc.md

# Arc

When shared ownership between threads is needed, `Arc`(Atomically Reference
Counted) can be used. This struct, via the `Clone` implementation can create
a reference pointer for the location of a value in the memory heap while
increasing the reference counter. As it shares ownership between threads, when
the last reference pointer to a value is out of scope, the variable is dropped.

```rust,editable
use std::time::Duration;
use std::sync::Arc;
use std::thread;

fn main() {
    // This variable declaration is where its value is specified.
    let apple = Arc::new("the same apple");

    for _ in 0..10 {
        // Here there is no value specification as it is a pointer to a
        // reference in the memory heap.
        let apple = Arc::clone(&apple);

        thread::spawn(move || {
            // As Arc was used, threads can be spawned using the value allocated
            // in the Arc variable pointer's location.
            println!("{:?}", apple);
        });
    }

    // Make sure all Arc instances are printed from spawned threads.
    thread::sleep(Duration::from_secs(1));
}
```