C# asynchronous delegates, thread scheduling

Question

I'm absolutely new to threads and trying to understand the very basics. I've got this code with asynchronous delegates invocation:

static void Main(string[] args)
{      
   Action<Thread, string> action = (mainThread, name) =>
        {
            Thread.CurrentThread.Name = name;
            Thread.CurrentThread.IsBackground = false;
            Console.WriteLine("Thread {0} starts", Thread.CurrentThread.Name);
            while (true)
            {
                var input = Console.ReadLine();
                Console.WriteLine("Thread {0} catches an input. User's input is: \"{1}\""
                                  +"\nMain thread is alive = {2}",
                                  Thread.CurrentThread.Name, input, mainThread.IsAlive);
            }
        };
    action.BeginInvoke(Thread.CurrentThread,"First", null, null);
    action.BeginInvoke(Thread.CurrentThread, "Second", null, null);
    Thread.Sleep(2000);
}

And whatever I do, the output result always goes in the following order: First->Second->First->Second->First...

As far as I understand, the output order should be nondetermenistic. Bu in this case it is. How the thread queue is processed? What am I missing? Please, explain

Answer 1

When you wait for input from the user on var input = Console.ReadLine(); you are basically locking your threads. the first one waits for input and when received prints it. The other thread at the exact time already asked for input and waiting for it. So you get one line for each one.

If you remove the ReadLine and use this line instead:

var input = "Hamster";

You will get the results you want: