st: Track stylesheet changes on the StThemeContext

Instead of every individual StThemeNode. There are essentially two kinds
of theme nodes: Those we create for lookups, and those interned by the
theme context and used by StWidgets. Listening to the signal on the former
is pointless as they are short lived and not meant to be really used for
drawing. So it is only essential to track stylesheet changes in those we
intern for later use.

This change does precisely that, it lets the StThemeContext track the
stylesheet changes and let all known theme nodes reset their state for
it.

The internal array holding all connected handlers for this signal in glib
was about the biggest single allocation made in gnome-shell, as interned
theme nodes nodes are around the 4 to 5 digit numbers. This essentially
makes it disappear.

This however means that widgets that are explicitly set a theme through
st_widget_set_theme() don't get their theme node implicitly updated.
There's little reasons to use that API, so perhaps this is an acceptable
tradeoff.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/779

src/st/st-theme-context.c

@@ -25,6 +25,7 @@
 #include "st-texture-cache.h"
 #include "st-theme.h"
 #include "st-theme-context.h"
+#include "st-theme-node-private.h"
 
 struct _StThemeContext {
   GObject parent;
@@ -36,6 +37,8 @@ struct _StThemeContext {
   /* set of StThemeNode */
   GHashTable *nodes;
 
+  gulong stylesheets_changed_id;
+
   int scale_factor;
 };
 
@@ -83,6 +86,8 @@ st_theme_context_finalize (GObject *object)
                                         (gpointer) st_theme_context_changed,
                                         context);
 
+  g_clear_signal_handler (&context->stylesheets_changed_id, context->theme);
+
   if (context->nodes)
     g_hash_table_unref (context->nodes);
   if (context->root_node)
@@ -254,6 +259,19 @@ on_icon_theme_changed (StTextureCache *cache,
   g_source_set_name_by_id (id, "[gnome-shell] changed_idle");
 }
 
+static void
+on_custom_stylesheets_changed (StTheme        *theme,
+                               StThemeContext *context)
+{
+  GHashTableIter iter;
+  StThemeNode *node;
+
+  g_hash_table_iter_init (&iter, context->nodes);
+
+  while (g_hash_table_iter_next (&iter, (gpointer *) &node, NULL))
+    _st_theme_node_reset_for_stylesheet_change (node);
+}
+
 /**
  * st_theme_context_get_for_stage:
  * @stage: a #ClutterStage
@@ -299,12 +317,17 @@ st_theme_context_set_theme (StThemeContext          *context,
   if (context->theme != theme)
     {
       if (context->theme)
-        g_object_unref (context->theme);
+        g_clear_signal_handler (&context->stylesheets_changed_id, context->theme);
 
-      context->theme = theme;
+      g_set_object (&context->theme, theme);
 
       if (context->theme)
-        g_object_ref (context->theme);
+        {
+          context->stylesheets_changed_id =
+            g_signal_connect (context->theme, "custom-stylesheets-changed",
+                              G_CALLBACK (on_custom_stylesheets_changed),
+                              context);
+        }
 
       st_theme_context_changed (context);
     }

src/st/st-theme-node-private.h

@@ -123,6 +123,7 @@ void _st_theme_node_ensure_background (StThemeNode *node);
 void _st_theme_node_ensure_geometry (StThemeNode *node);
 void _st_theme_node_apply_margins (StThemeNode *node,
                                    ClutterActor *actor);
+void _st_theme_node_reset_for_stylesheet_change (StThemeNode *node);
 
 G_END_DECLS
 

src/st/st-theme-node.c

@@ -77,16 +77,13 @@ maybe_free_properties (StThemeNode *node)
     }
 }
 
-static void
+void
-on_custom_stylesheets_changed (StTheme *theme,
+_st_theme_node_reset_for_stylesheet_change (StThemeNode *node)
-                               gpointer data)
 {
-  StThemeNode *node = data;
   maybe_free_properties (node);
   node->properties_computed = FALSE;
 }
 
-
 static void
 st_theme_node_dispose (GObject *gobject)
 {
@@ -110,12 +107,6 @@ st_theme_node_dispose (GObject *gobject)
       node->icon_colors = NULL;
     }
 
-  if (node->theme && node->stylesheets_changed_id)
-    {
-      g_signal_handler_disconnect (node->theme, node->stylesheets_changed_id);
-      node->stylesheets_changed_id = 0;
-    }
-
   st_theme_node_paint_state_free (&node->cached_state);
 
   g_clear_object (&node->theme);
@@ -228,14 +219,7 @@ st_theme_node_new (StThemeContext    *context,
   if (theme == NULL && parent_node != NULL)
     theme = parent_node->theme;
 
-  if (theme != NULL)
+  g_set_object (&node->theme, theme);
-    {
-      node->theme = g_object_ref (theme);
-      node->stylesheets_changed_id =
-        g_signal_connect (node->theme, "custom-stylesheets-changed",
-                          G_CALLBACK (on_custom_stylesheets_changed), node);
-    }
-
   node->element_type = element_type;
   node->element_id = g_strdup (element_id);
   node->element_classes = split_on_whitespace (element_class);