gistfile1.cs

    class A
    {
        private object _locker = new object();

        public event EventHandler Bang;

        public void Foo()
        {
            new Thread(() =>
                         {
                             lock (_locker)
                             {
                                 if (Bang != null) Bang(this, EventArgs.Empty);
                             }
                         }).Start();
            Thread.Sleep(10);
            lock (_locker)
            {
                Console.WriteLine("Locked!");
            }
        }
    }

    class B
    {
        static B()
        {
            var a = new A();
            a.Bang += (o, e) => Console.WriteLine("Handled");
            a.Foo();
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            B b = new B();
        }
    }