wayland: Untie MetaWindowXwayland lifetime from the wl_surface

For the most part, a MetaWindow is expected to live roughly as long as
the associated wl_surface, give or take asynchronous API discrepancies.

The exception to this rule is handling of reparenting when decorating or
undecorating a window, when a MetaWindow on X11 is made to survive the
unmap/map cycle. The fact that this didn't hold on Wayland caused
various issues, such as a feedback loop where the X11 window kept being
remapped. By making the MetaWindow lifetime for Xwayland windows being
the same as they are on plain X11, we remove the different semantics
here, which seem to lower the risk of hitting the race condition causing
the feedback loop mentioned above.

What this commit do is separate MetaWindow lifetime handling between
native Wayland windows and Xwayland windows. Wayland windows are handled
just as they were, i.e. unmanaged together as part of the wl_surface
destruction; while during the Xwayland wl_surface destruction, the
MetaWindow <-> MetaWaylandSurface association is simply broken.

Related: https://gitlab.freedesktop.org/xorg/xserver/issues/740
Fixes: https://gitlab.gnome.org/GNOME/mutter/issues/762

https://gitlab.gnome.org/GNOME/mutter/merge_requests/774

src/wayland/meta-wayland-legacy-xdg-shell.c

@@ -165,9 +165,10 @@ zxdg_toplevel_v6_destructor (struct wl_resource *resource)
 {
   MetaWaylandZxdgToplevelV6 *xdg_toplevel =
     wl_resource_get_user_data (resource);
-  MetaWaylandSurface *surface = surface_from_xdg_toplevel_resource (resource);
+  MetaWaylandShellSurface *shell_surface =
+    META_WAYLAND_SHELL_SURFACE (xdg_toplevel);
 
-  meta_wayland_surface_destroy_window (surface);
+  meta_wayland_shell_surface_destroy_window (shell_surface);
   xdg_toplevel->resource = NULL;
 }
 
@@ -549,17 +550,15 @@ handle_popup_parent_destroyed (struct wl_listener *listener,
     META_WAYLAND_ZXDG_SURFACE_V6 (xdg_popup);
   struct wl_resource *xdg_shell_resource =
     meta_wayland_zxdg_surface_v6_get_shell_resource (xdg_surface);
-  MetaWaylandSurfaceRole *surface_role =
+  MetaWaylandShellSurface *shell_surface =
-    META_WAYLAND_SURFACE_ROLE (xdg_popup);
+    META_WAYLAND_SHELL_SURFACE (xdg_popup);
-  MetaWaylandSurface *surface =
-    meta_wayland_surface_role_get_surface (surface_role);
 
   wl_resource_post_error (xdg_shell_resource,
                           ZXDG_SHELL_V6_ERROR_NOT_THE_TOPMOST_POPUP,
                           "destroyed popup not top most popup");
   xdg_popup->parent_surface = NULL;
 
-  meta_wayland_surface_destroy_window (surface);
+  meta_wayland_shell_surface_destroy_window (shell_surface);
 }
 
 static void
@@ -944,7 +943,7 @@ finish_popup_setup (MetaWaylandZxdgPopupV6 *xdg_popup)
       if (popup == NULL)
         {
           zxdg_popup_v6_send_popup_done (xdg_popup->resource);
-          meta_wayland_surface_destroy_window (surface);
+          meta_wayland_shell_surface_destroy_window (shell_surface);
           return;
         }
 
@@ -1099,6 +1098,8 @@ meta_wayland_zxdg_popup_v6_dismiss (MetaWaylandPopupSurface *popup_surface)
     META_WAYLAND_ZXDG_SURFACE_V6 (xdg_popup);
   struct wl_resource *xdg_shell_resource =
     meta_wayland_zxdg_surface_v6_get_shell_resource (xdg_surface);
+  MetaWaylandShellSurface *shell_surface =
+    META_WAYLAND_SHELL_SURFACE (xdg_popup);
   MetaWaylandSurfaceRole *surface_role = META_WAYLAND_SURFACE_ROLE (xdg_popup);
   MetaWaylandSurface *surface =
     meta_wayland_surface_role_get_surface (surface_role);
@@ -1114,7 +1115,7 @@ meta_wayland_zxdg_popup_v6_dismiss (MetaWaylandPopupSurface *popup_surface)
 
   xdg_popup->popup = NULL;
 
-  meta_wayland_surface_destroy_window (surface);
+  meta_wayland_shell_surface_destroy_window (shell_surface);
 }
 
 static MetaWaylandSurface *

src/wayland/meta-wayland-shell-surface.c

@@ -212,6 +212,37 @@ meta_wayland_shell_surface_sync_actor_state (MetaWaylandActorSurface *actor_surf
     actor_surface_class->sync_actor_state (actor_surface);
 }
 
+void
+meta_wayland_shell_surface_destroy_window (MetaWaylandShellSurface *shell_surface)
+{
+  MetaWaylandSurfaceRole *surface_role =
+    META_WAYLAND_SURFACE_ROLE (shell_surface);
+  MetaWaylandSurface *surface =
+    meta_wayland_surface_role_get_surface (surface_role);
+  MetaWindow *window;
+  MetaDisplay *display;
+  uint32_t timestamp;
+
+  window = surface->window;
+  if (!window)
+    return;
+
+  display = meta_window_get_display (window);
+  timestamp = meta_display_get_current_time_roundtrip (display);
+  meta_window_unmanage (surface->window, timestamp);
+  g_assert (!surface->window);
+}
+
+static void
+meta_wayland_shell_surface_finalize (GObject *object)
+{
+  MetaWaylandShellSurface *shell_surface = META_WAYLAND_SHELL_SURFACE (object);
+
+  meta_wayland_shell_surface_destroy_window (shell_surface);
+
+  G_OBJECT_CLASS (meta_wayland_shell_surface_parent_class)->finalize (object);
+}
+
 static void
 meta_wayland_shell_surface_init (MetaWaylandShellSurface *role)
 {
@@ -220,11 +251,14 @@ meta_wayland_shell_surface_init (MetaWaylandShellSurface *role)
 static void
 meta_wayland_shell_surface_class_init (MetaWaylandShellSurfaceClass *klass)
 {
+  GObjectClass *object_class = G_OBJECT_CLASS (klass);
   MetaWaylandSurfaceRoleClass *surface_role_class =
     META_WAYLAND_SURFACE_ROLE_CLASS (klass);
   MetaWaylandActorSurfaceClass *actor_surface_class =
     META_WAYLAND_ACTOR_SURFACE_CLASS (klass);
 
+  object_class->finalize = meta_wayland_shell_surface_finalize;
+
   surface_role_class->commit = meta_wayland_shell_surface_surface_commit;
 
   actor_surface_class->get_geometry_scale =

src/wayland/meta-wayland-shell-surface.h

@@ -71,4 +71,6 @@ void meta_wayland_shell_surface_determine_geometry (MetaWaylandShellSurface *she
 void meta_wayland_shell_surface_set_window (MetaWaylandShellSurface *shell_surface,
                                             MetaWindow              *window);
 
+void meta_wayland_shell_surface_destroy_window (MetaWaylandShellSurface *shell_surface);
+
 #endif /* META_WAYLAND_SHELL_SURFACE_H */

src/wayland/meta-wayland-surface.c

@@ -367,20 +367,6 @@ meta_wayland_surface_queue_pending_state_frame_callbacks (MetaWaylandSurface
   wl_list_init (&pending->frame_callback_list);
 }
 
-void
-meta_wayland_surface_destroy_window (MetaWaylandSurface *surface)
-{
-  if (surface->window)
-    {
-      MetaDisplay *display = meta_get_display ();
-      guint32 timestamp = meta_display_get_current_time_roundtrip (display);
-
-      meta_window_unmanage (surface->window, timestamp);
-    }
-
-  g_assert (surface->window == NULL);
-}
-
 MetaWaylandBuffer *
 meta_wayland_surface_get_buffer (MetaWaylandSurface *surface)
 {
@@ -1364,12 +1350,6 @@ wl_surface_destructor (struct wl_resource *resource)
 
   g_clear_object (&surface->role);
 
-  /* If we still have a window at the time of destruction, that means that
-   * the client is disconnecting, as the resources are destroyed in a random
-   * order. Simply destroy the window in this case. */
-  if (surface->window)
-    meta_wayland_surface_destroy_window (surface);
-
   if (surface->unassigned.buffer)
     {
       meta_wayland_surface_unref_buffer_use_count (surface);

src/wayland/meta-wayland-surface.h

@@ -300,8 +300,6 @@ MetaWaylandSurface * meta_wayland_surface_role_get_surface (MetaWaylandSurfaceRo
 cairo_region_t *    meta_wayland_surface_calculate_input_region (MetaWaylandSurface *surface);
 
 
-void                meta_wayland_surface_destroy_window (MetaWaylandSurface *surface);
-
 gboolean            meta_wayland_surface_begin_grab_op (MetaWaylandSurface *surface,
                                                         MetaWaylandSeat    *seat,
                                                         MetaGrabOp          grab_op,

src/wayland/meta-wayland-wl-shell.c

@@ -591,7 +591,7 @@ wl_shell_surface_role_commit (MetaWaylandSurfaceRole  *surface_role,
       if (wl_shell_surface->popup)
         meta_wayland_popup_dismiss (wl_shell_surface->popup);
       else
-        meta_wayland_surface_destroy_window (surface);
+        meta_wayland_shell_surface_destroy_window (shell_surface);
       return;
     }
 
@@ -680,14 +680,12 @@ meta_wayland_wl_shell_surface_popup_dismiss (MetaWaylandPopupSurface *popup_surf
 {
   MetaWaylandWlShellSurface *wl_shell_surface =
     META_WAYLAND_WL_SHELL_SURFACE (popup_surface);
-  MetaWaylandSurfaceRole *surface_role =
+  MetaWaylandShellSurface *shell_surface =
-    META_WAYLAND_SURFACE_ROLE (popup_surface);
+    META_WAYLAND_SHELL_SURFACE (wl_shell_surface);
-  MetaWaylandSurface *surface =
-    meta_wayland_surface_role_get_surface (surface_role);
 
   wl_shell_surface->popup = NULL;
 
-  meta_wayland_surface_destroy_window (surface);
+  meta_wayland_shell_surface_destroy_window (shell_surface);
 }
 
 static MetaWaylandSurface *

src/wayland/meta-wayland-xdg-shell.c

@@ -171,9 +171,10 @@ static void
 xdg_toplevel_destructor (struct wl_resource *resource)
 {
   MetaWaylandXdgToplevel *xdg_toplevel = wl_resource_get_user_data (resource);
-  MetaWaylandSurface *surface = surface_from_xdg_toplevel_resource (resource);
+  MetaWaylandShellSurface *shell_surface =
+    META_WAYLAND_SHELL_SURFACE (xdg_toplevel);
 
-  meta_wayland_surface_destroy_window (surface);
+  meta_wayland_shell_surface_destroy_window (shell_surface);
   xdg_toplevel->resource = NULL;
 }
 
@@ -488,10 +489,8 @@ static const struct xdg_toplevel_interface meta_wayland_xdg_toplevel_interface =
 static void
 meta_wayland_xdg_popup_unmap (MetaWaylandXdgPopup *xdg_popup)
 {
-  MetaWaylandSurfaceRole *surface_role =
+  MetaWaylandShellSurface *shell_surface =
-    META_WAYLAND_SURFACE_ROLE (xdg_popup);
+    META_WAYLAND_SHELL_SURFACE (xdg_popup);
-  MetaWaylandSurface *surface =
-    meta_wayland_surface_role_get_surface (surface_role);
 
   g_assert (!xdg_popup->popup);
 
@@ -502,7 +501,7 @@ meta_wayland_xdg_popup_unmap (MetaWaylandXdgPopup *xdg_popup)
       xdg_popup->parent_surface = NULL;
     }
 
-  meta_wayland_surface_destroy_window (surface);
+  meta_wayland_shell_surface_destroy_window (shell_surface);
 }
 
 static void
@@ -562,17 +561,15 @@ on_parent_surface_unmapped (MetaWaylandSurface  *parent_surface,
   MetaWaylandXdgSurface *xdg_surface = META_WAYLAND_XDG_SURFACE (xdg_popup);
   struct wl_resource *xdg_wm_base_resource =
     meta_wayland_xdg_surface_get_wm_base_resource (xdg_surface);
-  MetaWaylandSurfaceRole *surface_role =
+  MetaWaylandShellSurface *shell_surface =
-    META_WAYLAND_SURFACE_ROLE (xdg_popup);
+    META_WAYLAND_SHELL_SURFACE (xdg_popup);
-  MetaWaylandSurface *surface =
-    meta_wayland_surface_role_get_surface (surface_role);
 
   wl_resource_post_error (xdg_wm_base_resource,
                           XDG_WM_BASE_ERROR_NOT_THE_TOPMOST_POPUP,
                           "destroyed popup not top most popup");
   xdg_popup->parent_surface = NULL;
 
-  meta_wayland_surface_destroy_window (surface);
+  meta_wayland_shell_surface_destroy_window (shell_surface);
 }
 
 static void
@@ -790,7 +787,7 @@ meta_wayland_xdg_toplevel_reset (MetaWaylandXdgSurface *xdg_surface)
 
   surface = meta_wayland_surface_role_get_surface (surface_role);
 
-  meta_wayland_surface_destroy_window (surface);
+  meta_wayland_shell_surface_destroy_window (shell_surface);
 
   meta_wayland_actor_surface_reset_actor (META_WAYLAND_ACTOR_SURFACE (surface_role));
   window = meta_window_wayland_new (meta_get_display (), surface);
@@ -1010,7 +1007,7 @@ finish_popup_setup (MetaWaylandXdgPopup *xdg_popup)
       if (popup == NULL)
         {
           xdg_popup_send_popup_done (xdg_popup->resource);
-          meta_wayland_surface_destroy_window (surface);
+          meta_wayland_shell_surface_destroy_window (shell_surface);
           return;
         }
 

src/wayland/meta-xwayland.c

@@ -927,6 +927,27 @@ xwayland_surface_sync_actor_state (MetaWaylandActorSurface *actor_surface)
     actor_surface_class->sync_actor_state (actor_surface);
 }
 
+static void
+xwayland_surface_finalize (GObject *object)
+{
+  MetaWaylandSurfaceRole *surface_role =
+    META_WAYLAND_SURFACE_ROLE (object);
+  MetaWaylandSurface *surface =
+    meta_wayland_surface_role_get_surface (surface_role);
+  GObjectClass *parent_object_class =
+    G_OBJECT_CLASS (meta_wayland_surface_role_xwayland_parent_class);
+  MetaWindow *window;
+
+  window = surface->window;
+  if (window)
+    {
+      meta_wayland_surface_set_window (surface, NULL);
+      window->surface = NULL;
+    }
+
+  parent_object_class->finalize (object);
+}
+
 static void
 meta_wayland_surface_role_xwayland_init (MetaWaylandSurfaceRoleXWayland *role)
 {
@@ -935,11 +956,14 @@ meta_wayland_surface_role_xwayland_init (MetaWaylandSurfaceRoleXWayland *role)
 static void
 meta_wayland_surface_role_xwayland_class_init (MetaWaylandSurfaceRoleXWaylandClass *klass)
 {
+  GObjectClass *object_class = G_OBJECT_CLASS (klass);
   MetaWaylandSurfaceRoleClass *surface_role_class =
     META_WAYLAND_SURFACE_ROLE_CLASS (klass);
   MetaWaylandActorSurfaceClass *actor_surface_class =
     META_WAYLAND_ACTOR_SURFACE_CLASS (klass);
 
+  object_class->finalize = xwayland_surface_finalize;
+
   surface_role_class->assigned = xwayland_surface_assigned;
   surface_role_class->commit = xwayland_surface_commit;
   surface_role_class->get_toplevel = xwayland_surface_get_toplevel;