29.3.1 易变构造

    public class ThreadsSharingData
    {
        private volatile int flag = 0;
        private int value = 0;
        public void Thread1()
        {
            //注意在将1写入flag之前，必须先将5写入value
            value = 5;
            flag = 1;
        }
        public void Thread2()
        {
            //注意在value必须在读取了flag之后才能读取
            if (flag == 1)
                Console.WriteLine(value);
        }
    }