C# - Async & await - a simple example

  class Program
  {
      static void Main(string[] args)
      {
          var p = new Program();
          p.Run();
      }
  
      void Run()
      {
          var task = CalculatePiAsync();
          task.Wait();
      }
  
      async Task CalculatePiAsync()
      {
          var task = new Task(CalculatePi);
          task.Start();
          await task;
      }
  
      void CalculatePi()
      {
          Thread.Sleep(2000);
      }
  }
  

  // with comments and logging
  class Program
  {
      static void Main(string[] args)
      {
          var p = new Program();
          p.Run();
      }
  
      // this method runs synchronously, because it does not call await
      void Run()
      {
          Log($"Run() - begin");
  
          var task = CalculatePiAsync();
  
          // force a blocking wait to prevent console app exit
          Log($"Run() - waiting");
          task.Wait();
  
          Log($"Run() - end");
      }
  
      // async method
      async Task CalculatePiAsync()
      {
          Log($"CalculatePiAsync() - begin");
          var task = new Task(CalculatePi);
          task.Start();
  
          // 'await' does NOT block the program thread
          // Execution of this method IS suspended until after CalculatePi completes, but this 'soft block' is managed
          // by the C# generated async state machine via a method callback.
          // When the task completes, the line after await task will execute.
          await task;
  
          Log($"CalculatePiAsync() - end");
      }
  
      void CalculatePi()
      {
          Log("CalculatePi() - begin");
          Thread.Sleep(2000);
          Log($"CalculatePi() - end");
      }
  
      void Log(string message)
      {
          Console.WriteLine($"{Thread.CurrentThread.ManagedThreadId}: {message}");
      }
  

  class Program
  {
      static void Main(string[] args)
      {
          var p = new Program();
          p.Run();
      }
  
      void Run()
      {
          var task = CalculatePiAsync();
          task.Wait();
      }
  
      async Task CalculatePiAsync()
      {
          var task = new Task(CalculatePi);
          task.Start();
          await task;
      }
  
      void CalculatePi()
      {
          Thread.Sleep(2000);
      }
  }
  

  1: Run() - begin
  1: CalculatePiAsync() - begin
  3: CalculatePi() - begin
  
  1: Run() - waiting
  
  3: CalculatePi() - end
  3: CalculatePiAsync() - end
  1: Run() - end