lock()类型强制转换安全吗?

lock(a){} 相当于 lock(b){}

The lock() documentation 声明lock语句通过获取给定引用类型对象的互斥锁,将语句块标记为关键部分。

a 和 b 两者都是同一个物体,所以它们是等价的。事实上 一 b

Source .

namespace ConsoleApplication2
{
    public class A { }
    public class B : A { }

    class Program
    {
        static A a = new B();

        static void MyThread()
        {
            B b = a as B;
            lock (b)
            {
                Console.WriteLine("b lock acquired");
                Console.WriteLine("releasing b lock");
            }

        }


        static void Main(string[] args)
        {
            System.Threading.Thread t = new System.Threading.Thread(MyThread);

            lock(a)
            {
                Console.WriteLine("a lock acquired");               
                t.Start();
                System.Threading.Thread.Sleep(10000);
                Console.WriteLine("Releasing a lock");
            }
        }
    }
}

... 10秒通过
释放锁
获得b锁