Rust Shared State: Arc and Mutex

use std::sync::{Arc, Mutex};
use std::sync::atomic::{AtomicU64, Ordering};
use std::thread;

fn main() {
    let inventory = Arc::new(Mutex::new(vec![10, 10, 10]));
    let requests = Arc::new(AtomicU64::new(0));
    let mut handles = Vec::new();
    for slot in 0..3 {
        let inventory = Arc::clone(&inventory);
        let requests = Arc::clone(&requests);
        handles.push(thread::spawn(move || {
            for _ in 0..4 {
                let mut stock = inventory.lock().unwrap();   // guard unlocks at end of scope
                stock[slot] -= 1;
                requests.fetch_add(1, Ordering::Relaxed);
            }
        }));
    }
    for h in handles { h.join().unwrap(); }
    println!("stock: {:?}, requests: {}", inventory.lock().unwrap(), requests.load(Ordering::Relaxed));
}