Tk_MainLoop man page
Tk_MainLoop — loop for events until all windows are deleted
#include <tk.h> Tk_MainLoop()
Tk_MainLoop is a procedure that loops repeatedly calling Tcl_DoOneEvent. It returns only when there are no applications left in this process (i.e. no main windows exist anymore). Most windowing applications will call Tk_MainLoop after initialization; the main execution of the application will consist entirely of callbacks invoked via Tcl_DoOneEvent.
application, event, main loop