public class ProgressDialog : System.IDisposable  

var progDlg = new ProgressDialog("Running Geoprocessing Tool", "Cancel", 100, true);
      progDlg.Show();
      
      var progSrc = new CancelableProgressorSource(progDlg);

      // prepare input parameter values to CopyFeatures tool
      string input_data = @"C:\data\california.gdb\ca_highways";
      string out_workspace = ArcGIS.Desktop.Core.Project.Current.DefaultGeodatabasePath;
      string out_data = System.IO.Path.Combine(out_workspace, "ca_highways2");

      // make a value array of strings to be passed to ExecuteToolAsync
      var parameters = Geoprocessing.MakeValueArray(input_data, out_data);

      // execute the tool
      await Geoprocessing.ExecuteToolAsync("management.CopyFeatures", parameters,
          null, new CancelableProgressorSource(progDlg).Progressor, GPExecuteToolFlags.Default);

      // dialog hides itself once the execution is complete
      progDlg.Hide();