gdk session management support

[Felix Bellaby <felix pooh u-net com>]

Hi all,

Here is a response to a mail that I sent to Owen Taylor 
about three patches needed in gdk in order for it to 
implement ICCCM session management correctly.

Owen suggested that I open the patches to general discussion 
on this list in case anyone else has any comments.

I have tested these patches against gnome-session, gnome-smproxy,
xsm and smproxy. I do not currently have access to a WM that
actually implements the ICCCM (mwm is an example). However, I
see no reason to believe that these patches will result in
any bugs elsewhere in gtk+ / gnome.

Patch 1:
 > > At present, the gdk_leader_window is created on gdk initialisation
 > > and is, therefore, unique to the X client. The X11R6 ICCCM suggests
 > > that each X client has a unique window on which to store its
 > > session management properties. The gnome-client.c code currently 
 > > uses the gdk_leader_window for this purpose and sets the
 > > SM_CLIENT_ID property on the window.
 > > 
 > > However, the X11R6 ICCCM further requires that the client sets a
 > > WM_CLIENT_LEADER property on each of its top level windows 
 > > (i.e. the ones with WM_STATE properties) which provides a
 > > reference to this unique window so that the WM can find the
 > > session manager properties that it contains. 
 > > 
 > > gdk/gdkwindow:gdk_window_new seems like the logical place 
 > > to set this property since it is responsible for setting
 > > the other properties on the top level windows.
 > > 
 > > I can not see any advantage in providing additional 
 > > flexibility to the programmer in how this property is set.

Owen replied:
 > [...] 
 > I think setting the client leader property to point to 
 > the GDK group leader should be fine. (Note that these 
 > _are_ distinct concepts in the ICCCM. But people are
 > more likely to want multiple groups in a single app 
 > than multiple clients in a single app. So if we don't
 > provide the former I don't see any reason to worry about 
 > the latter).

Indeed, the concepts are distinct. gdk already includes the 
ability to set multiple groups (gdk_window_set_group). 
The gdk_leader_window is only used as the DEFAULT group.

Allowing am app to set more than one sm client id would 
violate the protocol. Therefore, I can see no reason whatsoever 
for allowing the creation of more than one WM_CLIENT_LEADER 
window per app.

Patch 2:
 > > In addition, it would be neater if gdk provided a function
 > > to set and unset the SM_CLIENT_ID on the gdk_leader_window 
 > > rather than having gnome-client.c do this using the Xlibs.
 > > This is a FIXME hanging around in gnome_client.c: i.e.
 > 
 > You'll notice that the prototype for such a function is
 > in gdk.h. I put it there, but forget to set the 

Ahh... in that case the patch that I am offering is just
an implementation of this function.

Patch 3:
 > > gdk currently provides partial support for the X11R5 ICCCM
 > > session management protocol. I do not think that providing 
 > > full support for this deprecated protocol is really worth 
 > > the effort. However, there is a bug in the support currently
 > > provided that can be fixed easily.
 > 
 > Hmmm, since KDE uses X11R5 SM and we want to have at least
 > a minimal level of cooperation with KDE apps, I think
 > bugfixes in this area are useful.
 >  
 > > The X smproxy program expects to find the WM_COMMAND
 > > and WM_CLIENT_MACHINE propeties in the same place.
 > > gdk currently sets these properties on distinct windows:
 > > the WM_CLIENT_MACHINE property is set on all the top level 
 > > windows but the WM_COMMAND property goes onto the 
 > > gdk_leader_window which is not a top level window.
 > 
 > Hmmm, I can't find any code that that sets WM_CLIENT_MACHINE
 > anywhere in GDK.

The XmbSetWMProperties function sets the WM_CLIENT_MACHINE
property as a side effect. It is used in gdk_window_new.
My patch uses this function in gdk_init as well to ensure
that the WM_CLIENT_MACHINE is also set on the gdk_leader_window.

Any comments ?

Felix

Unified diffs:
--------------
--- gdk.c	Sat Jan 16 01:08:23 1999
+++ gdk.c~	Sat Jan 16 00:01:52 1999
@@ -382,8 +382,9 @@
       gdk_progclass[0] = toupper (gdk_progclass[0]);
     }
   class_hint->res_class = gdk_progclass;
-  XSetClassHint(gdk_display, gdk_leader_window, class_hint);
-  XSetCommand(gdk_display, gdk_leader_window, argv_orig, argc_orig);
+  XmbSetWMProperties (gdk_display, gdk_leader_window,
+                      NULL, NULL, argv_orig, argc_orig, 
+                      NULL, NULL, class_hint);
   XFree (class_hint);
   
   for (i = 0; i < argc_orig; i++)
@@ -871,6 +872,43 @@
   return_val = DisplayHeightMM (gdk_display, gdk_screen);
   
   return return_val;
+}
+
+/*
+ *--------------------------------------------------------------
+ * gdk_set_sm_client_id
+ *
+ *   Set the SM_CLIENT_ID property on the WM_CLIENT_LEADER window
+ *   so that the window manager can save our state using the
+ *   X11R6 ICCCM session management protocol. A NULL value should 
+ *   be set following disconnection from the session manager to
+ *   remove the SM_CLIENT_ID property.
+ *
+ * Arguments:
+ * 
+ *   "sm_client_id" specifies the client id assigned to us by the
+ *   session manager or NULL to remove the property.
+ *
+ * Results:
+ *
+ * Side effects:
+ *
+ *--------------------------------------------------------------
+ */
+
+void
+gdk_set_sm_client_id (const gchar* sm_client_id)
+{
+  if (sm_client_id && strcmp (sm_client_id, ""))
+    {
+      XChangeProperty (gdk_display, gdk_leader_window,
+	   	       gdk_atom_intern ("SM_CLIENT_ID", FALSE),
+		       XA_STRING, 8, PropModeReplace,
+		       sm_client_id, strlen(sm_client_id));
+    }
+  else
+     XDeleteProperty (gdk_display, gdk_leader_window,
+	   	      gdk_atom_intern ("SM_CLIENT_ID", FALSE));
 }
 
 void
--------------
--- gdkwindow.c	Sat Jan 16 01:08:28 1999
+++ gdkwindow.c~	Sat Jan 16 00:03:19 1999
@@ -233,6 +233,8 @@
   gdk_xid_table_insert (&gdk_root_window, &gdk_root_parent);
 }
 
+static GdkAtom wm_client_leader_atom = GDK_NONE;
+
 GdkWindow*
 gdk_window_new (GdkWindow     *parent,
 		GdkWindowAttr *attributes,
@@ -448,6 +448,14 @@
 
   XSetWMHints (private->xdisplay, private->xwindow, &wm_hints);
 
+  if (!wm_client_leader_atom)
+     wm_client_leader_atom = gdk_atom_intern ("WM_CLIENT_LEADER", FALSE);
+
+  XChangeProperty (private->xdisplay, private->xwindow,
+	   	   wm_client_leader_atom,
+		   XA_WINDOW, 32, PropModeReplace,
+		   (guchar*) &gdk_leader_window, 1);
+
   if (attributes_mask & GDK_WA_TITLE)
     title = attributes->title;
   else
--------------