1use std::mem::size_of;
2
3use once_cell::sync::OnceCell;
4
5const N_THREADS: usize = 32;
6const N_ROUNDS: usize = 100_000_000;
7
8static CELL: OnceCell<usize> = OnceCell::new();
9
10fn main() {
11    let start = std::time::Instant::now();
12    let threads =
13        (0..N_THREADS).map(|i| std::thread::spawn(move || thread_main(i))).collect::<Vec<_>>();
14    for thread in threads {
15        thread.join().unwrap();
16    }
17    println!("{:?}", start.elapsed());
18    println!("size_of::<OnceCell<()>>()   = {:?}", size_of::<OnceCell<()>>());
19    println!("size_of::<OnceCell<bool>>() = {:?}", size_of::<OnceCell<bool>>());
20    println!("size_of::<OnceCell<u32>>()  = {:?}", size_of::<OnceCell<u32>>());
21}
22
23fn thread_main(i: usize) {
24    for _ in 0..N_ROUNDS {
25        let &value = CELL.get_or_init(|| i);
26        assert!(value < N_THREADS)
27    }
28}
29