FunkyFunc.cs

class Program
{

        static void Main(string[] args)
        {

            Func<string> getStuff = () =>
                {
                    Console.WriteLine("Called!");
                    return Guid.NewGuid().ToString();
                };

            var concurrentDictionary = new ConcurrentDictionary<int, string>();
            concurrentDictionary.GetOrAdd(1, _ => "casd");
            concurrentDictionary.GetOrAdd(1, _ => getStuff());


            Console.WriteLine("You do not see a 'Called!' above");
            Console.Read();
        }
}

class ProgramContention
{

    static void Main(string[] args)
    {
        var color = Console.ForegroundColor;
        int counter = 0;

        Func<string> getStuff = () =>
            {
                Interlocked.Increment(ref counter);
                return Guid.NewGuid().ToString();
            };

        var concurrentDictionary = new ConcurrentDictionary<int, string>();
        concurrentDictionary.GetOrAdd(1, _ => "casd");
        Parallel.For((int) 1, 90000, (i) => concurrentDictionary.GetOrAdd(i/3, _ => getStuff()));

        //Console.WriteLine("You do not see a 'Called!' above");
        Console.ForegroundColor = ConsoleColor.DarkGreen;
        Console.Write("Expected 30000 but was ");
        Console.ForegroundColor = ConsoleColor.Red;
        Console.WriteLine(counter);
        Console.ForegroundColor = color;

        Console.Read();
    }       
}