java volatile.

public class TestVolatile1{
    public volatile static int i=0;
    /**
     * 0 getstatic #2 <online/githuboy/concurrent/TestVolatile1.i>
     * 3 iconst_1
     * 4 iadd
     * 5 putstatic #2 <online/githuboy/concurrent/TestVolatile1.i>
     * 8 return
     */
    public void add(){
        i++;
    }
     public static void main(String[] args) throws InterruptedException {
        Thread t1 = new Thread(() -> {
            for (int i = 0; i < 10000; i++) {
                add();
            }
        });
        Thread t2 = new Thread(() -> {
            for (int i = 0; i < 10000; i++) {
                add();
            }
        });
        t1.start();
        t2.start();
        t1.join();
        t2.join();
        System.out.println(i);
    }
}

i = 10
t1
int temp = i + 1
//ThreadContextSwitch t2
t2
int tmep = i+ 1
i = 11
//write result to main memory

t1
continue execute
reread from temp
write i = 11
sync to main memory