Why does this simple .NET console app have so many threads?

This simple program starts with 15 threads - according to the count. Sometimes during its lifetime it drops a few, but they come back.

class Program
 {
     static void Main(string[] args)
     {
         while (true)
         {
             Console.WriteLine(Process.GetCurrentProcess().Threads.Count);
             Thread.Sleep(500);
         }
     }
 }

I was expecting the process to just have one thread (and my intuition was backed up by this)

Without the debugger, the process has only (!) 4 threads. Surely any CLR stuff would be hidden from my process?

What count is this? Does the process really have that many threads? Why?

Try running it outside the debugger (i.e. press Ctrl+F5 instead of F5). You should only see three threads - the main thread, the GC thread & the finalizer thread IIRC. The other threads you see are debugger-related threads.

Project + Properties, Debugging, untick "Enable the Visual Studio hosting process". I can't discover what it is doing. As soon as I tick the "Enabled unmanaged code debugging" option to try to get a peek at these threads, they no longer get started. No clue. But I'm sure it's for our benefit :)

If you run it without a debugger attached, there are significantly fewer threads. And those would presumably be the finalizer thread, and other house-keeping CLR stuff.

Try running it without the debugger (Visual Studio) attached (Ctrl+F5). You'll see that there will be less (probably 3) threads. Most of those threads have to do with the debugger.