How to get rid of lag when working with multi threading

Question

Refer to: How to animate a spinner while performing a workload via threading

I am working with a Delphi xe5 Application for iOS. While performing a SQL query, I have a TAniIndicator spinning. I am using threads - for specific code, see article stated above.

Everything works, however, when using the code I was helped with in the previous question, I've noticed added lag. When ran under the debugger, the application hangs between the lines:

Thread.DoTerminate;
Thread.FFinished := True;

under the ThreadProc Function of System.Classes Unit

Any clue as to why ? Or what I can do to prevent that added 5 second lag? Thank you

Update reply to TLama:

procedure TForm_Login.WorkIsDone(Sender : TObject);
begin
  Form_Login.LoadSpinnerFrame.visible := False;
  Form_Login.LoadSpinner.Visible := False;
  Form_Login.LoadSpinner.Enabled := False;
  Form_Login.btnLogin.Text := 'Logout';
  Form_Login.btnLogin.Enabled := True;
  if GoodLogin = 1 then
    Main_Form.show;
end;

My onTerminate() is linked to the above procedure.

Answer 1

TThread.DoTerminate() calls TThread.Synchronize() to fire the TThread.OnTerminate event handler in the main thread. TThread is then blocked until the main thread processes that request - which does not happen instantaneously as the main thread has to detect and process new messages first - and the OnTerminate handler exits. Only then is control returned to TThread so it can finish its logic. So if you are encountering a 5s lag in DoTerminate(), then it mean the main thread is taking 5s to detect and process the Synchronize() request.