原子性 与 可见性

public class NoVisibility {
    private static boolean ready;
    private static int number;
    
    private static class ReaderThread extends Thread{
        public void run(){
            while(!ready){
                Thread.yield();
            }
            System.out.println(number);
        }
    }
    
    public static void main(String[] args){
        new ReaderThread().start();
        number = 45;
        ready = true;
    }
}