Tcl_CreateEventSource(Tcl_EventSetupProc , Tcl_EventCheckProc, ClientData)

http://www.tcl.tk/man/tcl8.4/TclLib/Notifier.htm

This function is called to create a new source of events that will be checked by the Tcl event loop. It registers two functions that will be called when [Tcl_DoOneEvent] is called to process events. The SetupProc is called to check for the maximum amount of time to block if there are no events. CheckProc is called to test for a signalled state. The manual page has a good deal to say about the Tcl notifier in general so here is a sample that gets Tcl to process Glib or Gtk+ events.

        #include <gtk/gtk.h>
        
        /* When there are Gtk+ events to process we raise a Tcl event
         * When this event is processed here it flushes the Gtk queue */
        static int EventProc(Tcl_Event *evPtr, int flags)
        {
            if (!(flags & TCL_WINDOW_EVENTS)) {
                return 0;
            }
            while (gtk_events_pending()) {
                gtk_main_iteration();
            }
            return 1;
        }
        /* If there are gtk events in the queue, set the block time to zero
         * otherwise make it short - 10ms */
        static void SetupProc(ClientData clientData, int flags) {
            Tcl_Time block_time = {0, 0};
            if (!(flags & TCL_WINDOW_EVENTS)) {
                return;
            }
            if (!gtk_events_pending()) {
                block_time.usec = 10000;
            }
            Tcl_SetMaxBlockTime(&block_time);
            return;
        }
        /* If there are events to process, raise a Tk event to indicate this */
        static void CheckProc(ClientData clientData, int flags) {
            if (!(flags & TCL_WINDOW_EVENTS)) {
                return;
            }
            if (gtk_events_pending()) {
                Tcl_Event *event = (Tcl_Event *)ckalloc(sizeof(Tcl_Event));
                event->proc = EventProc;
                Tcl_QueueEvent(event, TCL_QUEUE_TAIL);
            }
            return;
        }

Given the above functions we just have to register the new event source when we initialize our package or our interpreter:
  Tcl_CreateEventSource(SetupProc, CheckProc, NULL);

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[[[Category Tcl Library]]]