[gnome-flashback] desktop: check if other application is managing desktop

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 2486fdc96081ab2a695599d33bd50fc2be0a2541
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Thu Nov 14 16:56:27 2019 +0200

    desktop: check if other application is managing desktop
    
    Do not create desktop window if another desktop manager is running.

 gnome-flashback/libdesktop/gf-desktop-window.c | 85 ++++++++++++++++++++++----
 gnome-flashback/libdesktop/gf-desktop-window.h | 11 ++--
 gnome-flashback/libdesktop/gf-desktop.c        | 12 +++-
 3 files changed, 91 insertions(+), 17 deletions(-)
---
diff --git a/gnome-flashback/libdesktop/gf-desktop-window.c b/gnome-flashback/libdesktop/gf-desktop-window.c
index 25cbdd3..2800b8e 100644
--- a/gnome-flashback/libdesktop/gf-desktop-window.c
+++ b/gnome-flashback/libdesktop/gf-desktop-window.c
@@ -67,7 +67,11 @@ enum
 
 static guint window_signals[LAST_SIGNAL] = { 0 };
 
-G_DEFINE_TYPE (GfDesktopWindow, gf_desktop_window, GTK_TYPE_WINDOW)
+static void initable_iface_init (GInitableIface *iface);
+
+G_DEFINE_TYPE_WITH_CODE (GfDesktopWindow, gf_desktop_window, GTK_TYPE_WINDOW,
+                         G_IMPLEMENT_INTERFACE (G_TYPE_INITABLE,
+                                                initable_iface_init))
 
 static gboolean
 get_representative_color (GfDesktopWindow *self,
@@ -463,6 +467,54 @@ monitor_removed_cb (GdkDisplay      *display,
   queue_move_resize (self);
 }
 
+static gboolean
+gf_desktop_window_initable_init (GInitable     *initable,
+                                 GCancellable  *cancellable,
+                                 GError       **error)
+{
+  GtkWidget *widget;
+  GdkDisplay *display;
+  Display *xdisplay;
+  char *atom_name;
+  Atom atom;
+  GdkWindow *window;
+  Window xwindow;
+
+  widget = GTK_WIDGET (initable);
+
+  display = gtk_widget_get_display (widget);
+  xdisplay = gdk_x11_display_get_xdisplay (display);
+
+  atom_name = g_strdup_printf ("_NET_DESKTOP_MANAGER_S%d",
+                               XDefaultScreen (xdisplay));
+
+  atom = XInternAtom (xdisplay, atom_name, False);
+  g_free (atom_name);
+
+  if (XGetSelectionOwner (xdisplay, atom) != None)
+    {
+      g_set_error_literal (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                           "Another desktop manager is running.");
+
+      return FALSE;
+    }
+
+  gtk_widget_realize (widget);
+
+  window = gtk_widget_get_window (widget);
+  xwindow = gdk_x11_window_get_xid (window);
+
+  XSetSelectionOwner (xdisplay, atom, xwindow, CurrentTime);
+
+  return TRUE;
+}
+
+static void
+initable_iface_init (GInitableIface *iface)
+{
+  iface->init = gf_desktop_window_initable_init;
+}
+
 static void
 gf_desktop_window_constructed (GObject *object)
 {
@@ -690,16 +742,27 @@ gf_desktop_window_init (GfDesktopWindow *self)
 }
 
 GtkWidget *
-gf_desktop_window_new (gboolean draw_background,
-                       gboolean show_icons)
-{
-  return g_object_new (GF_TYPE_DESKTOP_WINDOW,
-                       "app-paintable", TRUE,
-                       "type", GTK_WINDOW_TOPLEVEL,
-                       "type-hint", GDK_WINDOW_TYPE_HINT_DESKTOP,
-                       "draw-background", draw_background,
-                       "show-icons", show_icons,
-                       NULL);
+gf_desktop_window_new (gboolean   draw_background,
+                       gboolean   show_icons,
+                       GError   **error)
+{
+  GtkWidget *window;
+
+  window = g_object_new (GF_TYPE_DESKTOP_WINDOW,
+                         "app-paintable", TRUE,
+                         "type", GTK_WINDOW_TOPLEVEL,
+                         "type-hint", GDK_WINDOW_TYPE_HINT_DESKTOP,
+                         "draw-background", draw_background,
+                         "show-icons", show_icons,
+                         NULL);
+
+  if (!g_initable_init (G_INITABLE (window), NULL, error))
+    {
+      gtk_widget_destroy (window);
+      return NULL;
+    }
+
+  return window;
 }
 
 gboolean
diff --git a/gnome-flashback/libdesktop/gf-desktop-window.h b/gnome-flashback/libdesktop/gf-desktop-window.h
index 38a47f1..56e9e1f 100644
--- a/gnome-flashback/libdesktop/gf-desktop-window.h
+++ b/gnome-flashback/libdesktop/gf-desktop-window.h
@@ -26,14 +26,15 @@ G_BEGIN_DECLS
 G_DECLARE_FINAL_TYPE (GfDesktopWindow, gf_desktop_window,
                       GF, DESKTOP_WINDOW, GtkWindow)
 
-GtkWidget *gf_desktop_window_new        (gboolean         draw_background,
-                                         gboolean         show_icons);
+GtkWidget *gf_desktop_window_new        (gboolean          draw_background,
+                                         gboolean          show_icons,
+                                         GError          **error);
 
-gboolean   gf_desktop_window_is_ready   (GfDesktopWindow *self);
+gboolean   gf_desktop_window_is_ready   (GfDesktopWindow  *self);
 
-int        gf_desktop_window_get_width  (GfDesktopWindow *self);
+int        gf_desktop_window_get_width  (GfDesktopWindow  *self);
 
-int        gf_desktop_window_get_height (GfDesktopWindow *self);
+int        gf_desktop_window_get_height (GfDesktopWindow  *self);
 
 G_END_DECLS
 
diff --git a/gnome-flashback/libdesktop/gf-desktop.c b/gnome-flashback/libdesktop/gf-desktop.c
index 014d094..6a582ba 100644
--- a/gnome-flashback/libdesktop/gf-desktop.c
+++ b/gnome-flashback/libdesktop/gf-desktop.c
@@ -68,13 +68,23 @@ gf_desktop_init (GfDesktop *self)
 {
   gboolean draw_background;
   gboolean show_icons;
+  GError *error;
 
   self->settings = g_settings_new ("org.gnome.gnome-flashback.desktop");
 
   draw_background = g_settings_get_boolean (self->settings, "draw-background");
   show_icons = g_settings_get_boolean (self->settings, "show-icons");
 
-  self->window = gf_desktop_window_new (draw_background, show_icons);
+  error = NULL;
+  self->window = gf_desktop_window_new (draw_background, show_icons, &error);
+
+  if (error != NULL)
+    {
+      g_warning ("%s", error->message);
+      g_error_free (error);
+
+      return;
+    }
 
   g_settings_bind (self->settings, "draw-background",
                    self->window, "draw-background",