how to add Xorg event handing in g_main_loop - c

Question

I have a lightweight application that catches Xorg and dbus events. In order to do this I initialized dbus loop and started g_main_loop, but I don't know how to add Xorg event handling in a natural way:
GMainLoop * mainloop = NULL;
mainloop = g_main_loop_new(NULL,FALSE);
dbus_g_thread_init ();
dbus_init();
// <<<<<<<<<<<<<<<<<<<<<<<<<
//1 way using timeout
//g_timeout_add(100, kbdd_default_iter, mainloop);
//2nd way using pthread
//GThread * t = g_thread_create(kbdd_default_loop, NULL, FALSE, NULL);
//>>>>>>>>>>>>>>>>>>>>>>>>>>>
g_main_loop_run(mainloop);
in default iter I'm checking if there is waiting X-event and handle them.
Both ways seems bad, first because I have unneeded calls for checking event, second because I make an additional thread and have to make additional locks.
P.S. I know I can use gtk lib, but I don't want to have dependencies on any toolkit.

Answer 1

If you want to add Xorg event handling to the main loop without using a timeout (which as you state is wasteful), you'll need to add a source that polls the X connection. For that, you'll need to get below the Xlib abstraction layer to get the underlying X connection file descriptor. That's what the complete program below does. It is an adaptation of C. Tronche's excellent X11 tutorial to use the glib main loop for polling. I also drew from "Foundations of GTK+ Development" by Andrew Krause.
If this doesn't seem very "natural", that's because I doubt there is a very "natural" way to do this - you're really re-implementing a core part of GDK here.
/* needed to break into 'Display' struct internals. */
#define XLIB_ILLEGAL_ACCESS
#include <X11/Xlib.h> // Every Xlib program must include this
#include <assert.h> // I include this to test return values the lazy way
#include <glib.h>
typedef struct _x11_source {
GSource source;
Display *dpy;
Window w;
} x11_source_t;
static gboolean
x11_fd_prepare(GSource *source,
gint *timeout)
{
*timeout = -1;
return FALSE;
}
static gboolean
x11_fd_check (GSource *source)
{
return TRUE;
}
static gboolean
x11_fd_dispatch(GSource* source, GSourceFunc callback, gpointer user_data)
{
static gint counter = 0;
Display *dpy = ((x11_source_t*)source)->dpy;
Window window = ((x11_source_t*)source)->w;
XEvent e;
while (XCheckWindowEvent(dpy,
window,
EnterWindowMask,
&e))
{
if (e.type == EnterNotify)
g_print("We're in!!! (%d)\n", ++counter);
}
return TRUE;
}
static gboolean
msg_beacon(gpointer data)
{
static gint counter = 0;
g_print("Beacon %d\n", ++counter);
return TRUE;
}
int
main()
{
Display *dpy = XOpenDisplay(NULL);
assert(dpy);
int blackColor = BlackPixel(dpy, DefaultScreen(dpy));
int whiteColor = WhitePixel(dpy, DefaultScreen(dpy));
Window w = XCreateSimpleWindow(dpy, DefaultRootWindow(dpy), 0, 0,
200, 100, 0, blackColor, blackColor);
XSelectInput(dpy, w, StructureNotifyMask | EnterWindowMask);
XMapWindow(dpy, w);
for (;;) {
XEvent e;
XNextEvent(dpy, &e);
if (e.type == MapNotify)
break;
}
GMainLoop *mainloop = NULL;
mainloop = g_main_loop_new(NULL, FALSE);
/* beacon to demonstrate we're not blocked. */
g_timeout_add(300, msg_beacon, mainloop);
GPollFD dpy_pollfd = {dpy->fd,
G_IO_IN | G_IO_HUP | G_IO_ERR,
0};
GSourceFuncs x11_source_funcs = {
x11_fd_prepare,
x11_fd_check,
x11_fd_dispatch,
NULL, /* finalize */
NULL, /* closure_callback */
NULL /* closure_marshal */
};
GSource *x11_source =
g_source_new(&x11_source_funcs, sizeof(x11_source_t));
((x11_source_t*)x11_source)->dpy = dpy;
((x11_source_t*)x11_source)->w = w;
g_source_add_poll(x11_source, &dpy_pollfd);
g_source_attach(x11_source, NULL);
g_main_loop_run(mainloop);
return 0;
}