stopwatch.cs

        public class S : IDisposable
        {
            private static void Log(string s)
            {
                Console.WriteLine(DateTime.Now + ": " + s);
            }

            private readonly string _caller;
            private readonly System.Diagnostics.Stopwatch _s;

            public S(string caller)
            {
                _s = System.Diagnostics.Stopwatch.StartNew();
                _caller = caller;
                Log("starting " + caller);
            }

            public void Dispose()
            {
                _s.Stop();
                Log($"finished {_caller} in {_s.ElapsedMilliseconds} ms");
            }
        }