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 10 use once_cell::sync::OnceCell; 11 12 const N_THREADS: usize = 32; 13 const N_ROUNDS: usize = 1_000_000; 14 15 static CELLS: OnceCell<Vec<OnceCell<usize>>> = OnceCell::new(); 16 static RESULT: OnceCell<usize> = OnceCell::new(); 17 main()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 thread_main(i: usize)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