public void Fail()
 {
     if (_status != CalculateContextStatus.InProcess)
     {
         throw new InvalidOperationException();
     }
     _status = CalculateContextStatus.Fail;
 }
 public void Process()
 {
     if (_status != CalculateContextStatus.None)
     {
         throw new InvalidOperationException();
     }
     _status = CalculateContextStatus.InProcess;
 }