C# DiagnosticSource and DiagnosticListener

  class Program
    {
        private static readonly DiagnosticSource testDiagnosticListener = new DiagnosticListener("TestDiagnosticListener");
        public static void Main()
        {
            DiagnosticListener.AllListeners.Subscribe(new CurrentConditionDisplay());
            testDiagnosticListener.Write("RequestStart", "hello world");
            var httpClient =new HttpClient();
            var response =  httpClient.GetAsync("http://www.mingdao.com").Result;
            var result =  response.Content.ReadAsStringAsync().Result;
        }
    }

    class CurrentConditionDisplay : IObserver<DiagnosticListener>
    {
        public void OnCompleted()
        {

        }

        public void OnError(Exception error)
        {
            // Method intentionally left empty.
        }
        public void OnNext(DiagnosticListener value)
        {
            value.Subscribe(new DiagnosticEventObserver());
        }
    }

    public class DiagnosticEventObserver : IObserver<KeyValuePair<string, object>>
    { 

        public void OnCompleted()
        {
            // Method intentionally left empty.
        }

        public void OnError(Exception error)
        {
            // Method intentionally left empty.
        }

        public void OnNext(KeyValuePair<string, object> value)
        {

        }
    }

reference -> https://www.jianshu.com/p/a1eb1c0aa1ef