理解volatitle带来的可见性

public class VolatileTest {
    volatile int value1;
    int value2;

    public static void main(String[] args) {
        final VolatileTest main=new VolatileTest();
        new Thread(()->{
            int value=0;
            while(true){
                value++;
                main.value2=value;//1
                main.value1=value;//2
            }
        }).start();
        new Thread(()->{
            while(true){

                int v1=main.value1;//3
                int v2=main.value2;//4
                if(v2<v1){
                    System.out.println(String.format("error v1=%d v2=%d",v1,v2));
                }
            }
        }).start();
    }
}