using System;

​

public class Program

{

    public static void Main()

    {

        new B();

        new C();

        new B();

    }

}

​

public abstract class A

{

    private static bool _myLock;

    public A()

    {

        Console.WriteLine($"{_myLock} in ctor of {this.GetType()}");

        _myLock = true;

    }

}

​

public class B : A {}

public class C : A {}

​