Function async_increment

src/queue.rs:345–351

(queue: &Queue, num: &Arc<Mutex<i32>>)

    use super::*;

    fn async_increment(queue: &Queue, num: &Arc<Mutex<i32>>) {
        let num = num.clone();
        queue.exec_async(move || {
            let mut num = num.lock().unwrap();
            *num += 1;
        });
    }

    #[test]
    fn test_serial_queue() {