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