lock（）类型转换是否安全？(Is lock() type-cast safe?)

public class A { }
public class B:A { }

void foo()
{
   A a = new B();
   B b = a as B;
}
 
 对于给定的实例设置，将lock(a)等同于lock(b) ？ 
 
 我的意思是，锁定是互斥的吗？ 如果我在一个线程中lock(b)在另一个线程中lock(b) ，我是否会获得对之前创建的B单个实例的互斥访问？ 

public class A { }
public class B:A { }

void foo()
{
   A a = new B();
   B b = a as B;
}
 
for a given instance setup, will lock(a) be equivalent to lock(b) ?
 
I mean, will locking be mutually exclusive? If I lock(a) in one thread and lock(b) in another thread, will I get a mutually exclusive access to that single instance of B created earlier?

原文：https://stackoverflow.com/questions/2838814