多线程线性 lock

Posted 2020-08-31 空明流光

有时我们lock一段代码或许要根据某个变量的值，值相同则不允许有两个或以上的方法并行运行，我在工作中就遇到了，有100个值，相同的参数值不能并行运行。

还有就是一个被lock的方法递归调用会不会死锁，因为需要lock同一个变量。答案当然是不会死锁。

下面是一个测试demo

class Program
    {
        private static object a = new object();
        private static object b = new object();
        private static object c = new object();
        private static Hashtable list = Hashtable.Synchronized(new Hashtable());

        static void Main(string[] args)
        {
            //所有i不相等的线程将同步执行并返回结果
            new Thread(new ParameterizedThreadStart(delegate(object obj) {
                Test(0, 2000);
                Console.WriteLine("1");
            })).Start();

            new Thread(new ParameterizedThreadStart(delegate(object obj)
            {
                Test(1, 2000);
                Console.WriteLine("1+");
            })).Start();

            //所有i==2的线程将顺序执行
            new Thread(new ParameterizedThreadStart(delegate(object obj)
            {
                Test(2, 2000);
                Console.WriteLine("2");
            })).Start();

            new Thread(new ParameterizedThreadStart(delegate(object obj)
            {
                Test(2, 2000);
                Console.WriteLine("3");
            })).Start();

            new Thread(new ParameterizedThreadStart(delegate(object obj)
            {
                Test(2, 2000);
                Console.WriteLine("4");
            })).Start();

            new Thread(new ParameterizedThreadStart(delegate(object obj)
            {
                Test(2, 2000);
                Console.WriteLine("5");
            })).Start();

            new Thread(new ParameterizedThreadStart(delegate(object obj)
            {
                Test(2, 2000);
                Console.WriteLine("6");
            })).Start();

            //两次lock同一变量不会死锁
            new Thread(new ParameterizedThreadStart(delegate(object obj)
            {
                Test2(3, 2000);
                Console.WriteLine("7");
            })).Start();

            Console.ReadKey();
        }

        /// <summary>
        /// 对于i相同的线程进行阻塞保证不会并行多个
        /// </summary>
        /// <param name="i"></param>
        /// <param name="j"></param>
        public static void Test(int i,int j)
        {
            if (!list.ContainsKey(i))
                list.Add(i, DateTime.Now);

            lock (list[i])
            {
                Thread.Sleep(j);
            }
        }
        
        //多次lock同一变量测试是否会死锁
        public static void Test2(int i, int j, bool isFirstRun = true)
        {
            if (!list.ContainsKey(i))
                list.Add(i, DateTime.Now);

            lock (list[i])
            {
                Thread.Sleep(j);
                if (isFirstRun)
                    Test2(i, j, false);
            }
        }
    }

程序输出如下：

1+
2
1
3
7
4
5
6