How do you prevent a new event handling to start when an event handling is already running? I press a button1 and event handler start e.g. slow printing job. There are several controls in form buttons, edits, combos and I want that a new event allowed only after running handler is finnished. I have used fRunning variable to lock handler in shared event handler. Is there more clever way to handle this? procedure TFormFoo.Button_Click(Sender: TObject); begin if not fRunning then try fRunning := true; if (Sender = Button1) then // Call something slow ... if (Sender = Button2) then // Call something ... if (Sender = Button3) then // Call something ... finally fRunning := false; end; end;