Static constructors are guaranteed to be run only once per application domain.How?

Question

Static constructors are guaranteed to be run only once per application domain. It is called automatically before the first instance is created or any static members are referenced. How does the CLR guarantee this?
Suppose there are two threads visit a class which has a static constructor simultaneously. And both these two threads are at very first time. As below:

class SomeType
{
    Static SomeType()
    {
      Console.Write("hello");
    }
}

So because of the simultaneity, how does the CLR guarantee console write only once? Use the Lock or other things??

Answer 1

The CLR takes out a lock before entering into a static constructor to guarantee it is only executed once by a single thread.

This makes it easy to deadlock your application if you go creating threads within the static constructor.

See this MSDN blog post for an example. Basically though, this deadlocks:

using System.Threading;
class MyClass
{
    static void Main() { /* Won't run... the static constructor deadlocks */  }

    static MyClass()
    {
        Thread thread = new Thread(arg => { });
        thread.Start();
        thread.Join();
    }
}