device-manager-xi2: Fix core pointer retrieval race

The core pointer concept doesn't really exist anymore in an XI2 world,
so the clutter API is a bit of a mismatch with what X provides. Using
XIGetClientPointer doesn't really help, as far as i can tell the
semantics of XIGetClientPointer are essentially: Whatever the X server
picked when it had to reply with device-dependant data to a query
without a device specifier. Not very useful...

To make matters worse, whether XIGetClientPointer returns a valid
pointer depends on whether there has been a query that forced it to pick
one in the first place, making the whole thing pretty non-deterministic.

This patch changes things around such that instead of using
XIGetClientPointer to determine the core pointer, we simply pick the
first master pointer device. In practise this will essentially always
be the X virtual core pointer.

https://bugzilla.gnome.org/show_bug.cgi?id=729462

clutter/x11/clutter-device-manager-xi2.c

@@ -222,21 +222,6 @@ is_touch_device (XIAnyClassInfo         **classes,
   return FALSE;
 }
 
-static void
-update_client_pointer (ClutterDeviceManagerXI2 *manager_xi2)
-{
-  ClutterBackendX11 *backend_x11;
-  int device_id;
-
-  backend_x11 =
-    CLUTTER_BACKEND_X11 (_clutter_device_manager_get_backend (CLUTTER_DEVICE_MANAGER (manager_xi2)));
-
-  XIGetClientPointer (backend_x11->xdpy, None, &device_id);
-
-  manager_xi2->client_pointer = g_hash_table_lookup (manager_xi2->devices_by_id,
-                                                     GINT_TO_POINTER (device_id));
-}
-
 static ClutterInputDevice *
 create_device (ClutterDeviceManagerXI2 *manager_xi2,
                ClutterBackendX11       *backend_x11,
@@ -816,7 +801,6 @@ clutter_device_manager_xi2_translate_event (ClutterEventTranslator *translator,
         XIHierarchyEvent *xev = (XIHierarchyEvent *) xi_event;
 
         translate_hierarchy_event (backend_x11, manager_xi2, xev);
-        update_client_pointer (manager_xi2);
       }
       retval = CLUTTER_TRANSLATE_REMOVE;
       break;
@@ -840,8 +824,6 @@ clutter_device_manager_xi2_translate_event (ClutterEventTranslator *translator,
 
         if (source_device)
           _clutter_input_device_reset_scroll_info (source_device);
-
-        update_client_pointer (manager_xi2);
       }
       retval = CLUTTER_TRANSLATE_REMOVE;
       break;
@@ -1391,17 +1373,29 @@ clutter_device_manager_xi2_get_core_device (ClutterDeviceManager   *manager,
                                             ClutterInputDeviceType  device_type)
 {
   ClutterDeviceManagerXI2 *manager_xi2 = CLUTTER_DEVICE_MANAGER_XI2 (manager);
+  ClutterInputDevice *pointer = NULL;
+  GList *l;
+
+  for (l = manager_xi2->master_devices; l != NULL ; l = l->next)
+    {
+      ClutterInputDevice *device = l->data;
+      if (clutter_input_device_get_device_type (device) == CLUTTER_POINTER_DEVICE)
+        {
+          pointer = device;
+          break;
+        }
+    }
+
+  if (pointer == NULL)
+    return NULL;
 
   switch (device_type)
     {
     case CLUTTER_POINTER_DEVICE:
-      if (manager_xi2->client_pointer == NULL)
+      return pointer;
-        update_client_pointer (manager_xi2);
-
-      return manager_xi2->client_pointer;
 
     case CLUTTER_KEYBOARD_DEVICE:
-      return clutter_input_device_get_associated_device (manager_xi2->client_pointer);
+      return clutter_input_device_get_associated_device (pointer);
 
     default:
       break;
@@ -1505,7 +1499,6 @@ clutter_device_manager_xi2_constructed (GObject *gobject)
                                             &event_mask);
 
   XSync (backend_x11->xdpy, False);
-  update_client_pointer (manager_xi2);
 
   if (G_OBJECT_CLASS (clutter_device_manager_xi2_parent_class)->constructed)
     G_OBJECT_CLASS (clutter_device_manager_xi2_parent_class)->constructed (gobject);

clutter/x11/clutter-device-manager-xi2.h

@@ -49,8 +49,6 @@ struct _ClutterDeviceManagerXI2
   GList *master_devices;
   GList *slave_devices;
 
-  ClutterInputDevice *client_pointer;
-
   int opcode;
 };