How do I block the current thread until OnComplete has finished executing without the use of traditional threading primitives?

How do I block the current thread until the OnComplete handler of my observer has finished, without the use of threading primitives?

Here is my code. I want that the Console.WriteLine("Press... statement should be executed only after the OnComplete handler, namely ResetCount has finished executing.

class Program { private static long totalItemCount = 0; private static long listCount = 0; static void Main() { Console.WriteLine($"Starting Main on Thread {Thread.CurrentThread.ManagedThreadId}\n"); var o = Observable.Timer(TimeSpan.FromSeconds(3), TimeSpan.FromSeconds(1)) .Take(20) .Concat(Observable.Interval(TimeSpan.FromSeconds(0.01)).Take(200)) .Buffer(TimeSpan.FromSeconds(5), TimeSpan.FromSeconds(5)); o.Subscribe(Print, onCompleted: ResetCount); // How I make sure this line appears only after the OnComplete has fired? // Do I have to use traditional threading primitives such as wait handles? // Or just cause the main thread to sleep long enough? That doesn't seem right. Console.WriteLine("\nPress any key to exit..."); Console.ReadKey(); } private static void ResetCount() { if (listCount > 0) { Console.WriteLine($"{totalItemCount} items processed in {listCount} lists."); } else { Console.WriteLine($"{totalItemCount} items processed."); } Interlocked.Exchange(ref totalItemCount, 0); Interlocked.Exchange(ref listCount, 0); } static void Print<T>(T value) { var threadType = Thread.CurrentThread.IsBackground ? "Background" : "Foreground"; if (value is IList) { var list = value as IList; Console.WriteLine($"{list.Count} items in list #{Interlocked.Increment(ref listCount)}:"); foreach (var item in list) { Console.WriteLine($"{item.ToString()}, ({threadType} #{Thread.CurrentThread.ManagedThreadId}), Item #{Interlocked.Increment(ref totalItemCount)}"); } Console.WriteLine(); } else { Console.WriteLine($"{value.ToString()}, ({threadType} #{Thread.CurrentThread.ManagedThreadId}), Item #{Interlocked.Increment(ref totalItemCount)}"); } } }