When a widget is destroyed, you need to free up any resources it has allocated. The resources associated with attributes are cleaned up by Tk_FreeOptions. The others you must take care of yourself. The ClockDestroy procedure is called as a result of the Tk_EventuallyFree call in the ClockEventProc. The Tk_EventuallyFree procedure is part of a protocol that is needed for widgets that might get deleted when in the middle of processing. Typically the Tk_Preserve and Tk_Release procedures are called at the beginning and end of the widget instance command to mark the widget as being in use. Tk_EventuallyFree will wait until Tk_Release is called before calling the cleanup procedure. The next example shows ClockDestroy:

static void
ClockDestroy(clientData)
   ClientData clientData;      /* Info about entry widget. */
{
   register Clock *clockPtr = (Clock *) clientData;

   /*
    * Free up all the stuff that requires special handling,
    * then let Tk_FreeOptions handle resources associated
    * with the widget attributes.
    */
   if (clockPtr->textGC != None) {
      Tk_FreeGC(clockPtr->display, clockPtr->textGC);
   }
   if (clockPtr->clock != NULL) {
      Tcl_Free(clockPtr->clock);
   }
   if (clockPtr->flags & TICKING) {
      Tk_DeleteTimerHandler(clockPtr->token);
   }
   if (clockPtr->flags & REDRAW_PENDING) {
      Tk_CancelIdleCall(ClockDisplay,
         (ClientData) clockPtr);
   }
   /*
    * This frees up colors and fonts and any allocated
    * storage associated with the widget attributes.
    */
   Tk_FreeOptions(configSpecs, (char *) clockPtr,
      clockPtr->display, 0);
   Tcl_Free((char *) clockPtr);
}

void
ClockObjDelete(ClientData clientData)
{
   Tk_OptionTable optionTable = (Tk_OptionTable) clientData;
   if (optionTable != NULL) {
      Tk_DeleteOptionTable(optionTable);
   }
}