Failed to embed another xwindow into GtkSocket in GNOME, but succeed in FVWM/blackbox

[Cloudor Pu <cloudor 126 com>]

Hi, all

In my attached example.c, gtk_socket_add_id() is used to embed another 
existed xwindow into a GtkSocket. It works in fvwm or blackbox but 
failed in GNOME.

Can anybody tell me why this happen? It's funny. Shouldn't gnome support 
gtk better than other wm?

Or maybe I have mis-configured my gnome desktop. Then what should I do 
to make it work? Thank you in advance.

==================
To test my example:
1. gcc `pkg-config --cflags --libs gtk+-2.0` example.c -o example
2. use xwininfo to get a pre-existing window id
3. ./example <that window id>

regards,
cloudor

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <gtk/gtk.h>
#include <gdk/gdk.h>

int main (int argc, char *argv[])
{
        int exWID=0;
        GtkWidget *win = NULL;
        GtkWidget *vbox = NULL;
        GtkWidget *label = NULL;
        GtkWidget *socket = NULL;

        if (argc>1) {
            exWID = strtol(argv[1], NULL, 0);
        }else
        {
            printf("You should specify a wid in cmd line.\n");
        }

        gtk_init(&argc, &argv);

        win = gtk_window_new(GTK_WINDOW_TOPLEVEL);
        g_signal_connect(G_OBJECT(win), "delete_event",
                G_CALLBACK(gtk_main_quit), NULL);
        g_signal_connect(G_OBJECT(win), "destroy",
                G_CALLBACK(gtk_main_quit), NULL);
        gtk_container_set_border_width(GTK_CONTAINER(win), 2);
        gtk_window_set_title(GTK_WINDOW(win), "HELLO RE-PARENT");
        gtk_window_set_default_size(GTK_WINDOW(win), 640, 480);
        gtk_widget_set_size_request(GTK_WIDGET(win), 100, 100);

        vbox = gtk_vbox_new (FALSE, 0);
        gtk_container_add(GTK_CONTAINER (win), vbox);

        label = gtk_label_new ("Xlib window");
        gtk_box_pack_start (GTK_BOX (vbox), label, FALSE, FALSE, 0);

        socket = gtk_socket_new();

        gtk_box_pack_start (GTK_BOX (vbox), socket, TRUE, TRUE, 0);
        gtk_widget_show (socket);

        if(exWID >0)
        {
            gtk_socket_add_id(GTK_SOCKET(socket), exWID);
        }else
        {
            printf("My socket id: %d\n", gtk_socket_get_id(GTK_SOCKET(socket)));
        }

        gtk_widget_show (socket);

        gtk_widget_show_all(win);
        gtk_main();
        exit(0);
}