Why Thread 2 not available?

Question

In below little console application, I'm printing main thread Id and the 5 other thread, it's printing 1, 3,4,5,6,7, but not 2. Is thread 2 not available and how this number is generated?

static void Main(string[] args)
    {
        Console.WriteLine($"Thread {Thread.CurrentThread.ManagedThreadId}");

        Enumerable.Range(0, 5).ToList().ForEach(f =>
        {
            new Thread(() =>
            {
                Console.WriteLine($"Thread {Thread.CurrentThread.ManagedThreadId}");
                Thread.Sleep(1000);
            }).Start();

        });
        Console.ReadLine();
    }

Thread 1 Thread 3 Thread 4 Thread 5 Thread 6 Thread 7

Answer 1

Thread with Id=2 is garbage collector thread. You can check its Id by running finalizer:

class Test
{
    ~Test()
    {
        Console.WriteLine(Thread.CurrentThread.ManagedThreadId);
    }
}

static void Main(string[] args)
{
    Console.WriteLine(Thread.CurrentThread.ManagedThreadId);

    var test = new Test();
    test = null;
    GC.Collect();
}

Prints:

1
2