ch2-10-id-allocation-subtract-before-panic.rs

use std::sync::atomic::AtomicU32;
use std::sync::atomic::Ordering::Relaxed;

fn allocate_new_id() -> u32 {
    static NEXT_ID: AtomicU32 = AtomicU32::new(0);
    let id = NEXT_ID.fetch_add(1, Relaxed);
    if id >= 1000 {
        NEXT_ID.fetch_sub(1, Relaxed);
        panic!("too many IDs!");
    }
    id
}

fn main() {
    dbg!(allocate_new_id());
    dbg!(allocate_new_id());
    dbg!(allocate_new_id());
    // TODO
}