use std::thread;

#[derive(Copy, Clone)]
struct UnsafeIntPtr(*mut i32);

unsafe impl Send for UnsafeIntPtr {}

fn main() {
    let mut n = 0;
    let n = UnsafeIntPtr(&mut n);

    let a = thread::spawn(move || add_500_000(n.0));
    let b = thread::spawn(move || add_500_000(n.0));

    a.join().unwrap();
    b.join().unwrap();

    println!("{}", unsafe { *n.0 } );
}

fn add_500_000(n: *mut i32) {
    for _ in 0..500_000 {
        unsafe { *n += 1; }
    }
}