1//! Test if the OnceCell properly synchronizes.
2//! Needs to be run in release mode.
3//!
4//! We create a `Vec` with `N_ROUNDS` of `OnceCell`s. All threads will walk the `Vec`, and race to
5//! be the first one to initialize a cell.
6//! Every thread adds the results of the cells it sees to an accumulator, which is compared at the
7//! end.
8//! All threads should end up with the same result.
9
10use once_cell::sync::OnceCell;
11
12const N_THREADS: usize = 32;
13const N_ROUNDS: usize = 1_000_000;
14
15static CELLS: OnceCell<Vec<OnceCell<usize>>> = OnceCell::new();
16static RESULT: OnceCell<usize> = OnceCell::new();
17
18fn main() {
19 let start = std::time::Instant::now();
20 CELLS.get_or_init(|| vec![OnceCell::new(); N_ROUNDS]);
21 let threads =
22 (0..N_THREADS).map(|i| std::thread::spawn(move || thread_main(i))).collect::<Vec<_>>();
23 for thread in threads {
24 thread.join().unwrap();
25 }
26 println!("{:?}", start.elapsed());
27 println!("No races detected");
28}
29
30fn thread_main(i: usize) {
31 let cells = CELLS.get().unwrap();
32 let mut accum = 0;
33 for cell in cells.iter() {
34 let &value = cell.get_or_init(|| i);
35 accum += value;
36 }
37 assert_eq!(RESULT.get_or_init(|| accum), &accum);
38}
39