---
minutes: 8
---

# Example

Let us see `Arc` and `Mutex` in action:

```rust,editable,compile_fail
use std::thread;
// use std::sync::{Arc, Mutex};

fn main() {
    let v = vec![10, 20, 30];
    let handle = thread::spawn(|| {
        v.push(10);
    });
    v.push(1000);

    handle.join().unwrap();
    println!("v: {v:?}");
}
```

<details>

Possible solution:

```rust,editable
use std::sync::{Arc, Mutex};
use std::thread;

fn main() {
    let v = Arc::new(Mutex::new(vec![10, 20, 30]));

    let v2 = Arc::clone(&v);
    let handle = thread::spawn(move || {
        let mut v2 = v2.lock().unwrap();
        v2.push(10);
    });

    {
        let mut v = v.lock().unwrap();
        v.push(1000);
    }

    handle.join().unwrap();

    println!("v: {v:?}");
}
```

Notable parts:

- `v` is wrapped in both `Arc` and `Mutex`, because their concerns are
  orthogonal.
  - Wrapping a `Mutex` in an `Arc` is a common pattern to share mutable state
    between threads.
- `v: Arc<_>` needs to be cloned as `v2` before it can be moved into another
  thread. Note `move` was added to the lambda signature.
- Blocks are introduced to narrow the scope of the `LockGuard` as much as
  possible.

</details>