多线程, 当使用共有变量时, 保持计算结果正确很重要:

看下面的例子:

private static int count = 10;
        //private static object objlock = new object();

        public static void Main(string[] args)
        {
            try
            {
                for (int i = 0; i < 20; i++)
                {
                    Thread t1 = new Thread(new ThreadStart(WriteNumber));
                    t1.Name = "Name-" + i.ToString();
                    t1.Start();
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }

            Console.ReadLine();
        }

        public static void WriteNumber()
        {
            //lock (objlock)
            //{
                count--;
                Thread.Sleep(1000);
                Console.WriteLine("Name:" + Thread.CurrentThread.Name + " count:" + count.ToString());
            //}
        }

结果这样,全错了。

 

加上lock之后, 代码修改为这样

private static int count = 10;
        private static object objlock = new object();

        public static void Main(string[] args)
        {
            try
            {
                for (int i = 0; i < 20; i++)
                {
                    Thread t1 = new Thread(new ThreadStart(WriteNumber));
                    t1.Name = "Name-" + i.ToString();
                    t1.Start();
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }

            Console.ReadLine();
        }

        public static void WriteNumber()
        {
            lock (objlock)
            {
                count--;
                Thread.Sleep(1000);
                Console.WriteLine("Name:" + Thread.CurrentThread.Name + " count:" + count.ToString());
            }
        }

运行结果是这样:

 

注意:private static object objlock = new object();  //定义这个变量的位置,

各线程运行先后, 由CPU随机执行, 每次运行都可能看到不同的先后顺序。

 

posted on 2019-01-17 18:57  风浪  阅读(438)  评论(0编辑  收藏  举报