shell/app-system: Monitor for icon theme changes

Whenever an app is installed, the usual routine is
to run 'gtk-update-icon-cache' after installing all
of the app's files.

The side effect of that is that the .desktop file of
the application is installed before the icon theme
is updated. By the time GAppInfoMonitor emits the
'changed' signal, the icon theme is not yet updated,
leading to StIcon use the fallback icon.

Under some circumstances (e.g. on very slow spinning
disks) the app icon is never actually loaded, and we
see the fallback icon forever.

Monitor the icon theme for changes when an app is
installed. Try as many as 6 times before giving up
on detecting an icon theme update.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/661

src/shell-app-system.c

@@ -14,6 +14,14 @@
 #include "shell-app-system-private.h"
 #include "shell-global.h"
 #include "shell-util.h"
+#include "st.h"
+
+/* Rescan for at most RESCAN_TIMEOUT_MS * MAX_RESCAN_RETRIES. That
+ * should be plenty of time for even a slow spinning drive to update
+ * the icon cache.
+ */
+#define RESCAN_TIMEOUT_MS 2500
+#define MAX_RESCAN_RETRIES 6
 
 /* Vendor prefixes are something that can be preprended to a .desktop
  * file name.  Undo this.
@@ -51,6 +59,9 @@ struct _ShellAppSystemPrivate {
   GHashTable *id_to_app;
   GHashTable *startup_wm_class_to_id;
   GList *installed_apps;
+
+  guint rescan_icons_timeout_id;
+  guint n_rescan_retries;
 };
 
 static void shell_app_system_finalize (GObject *object);
@@ -157,12 +168,54 @@ stale_app_remove_func (gpointer key,
   return app_is_stale (value);
 }
 
+static gboolean
+rescan_icon_theme_cb (gpointer user_data)
+{
+  ShellAppSystemPrivate *priv;
+  ShellAppSystem *self;
+  StTextureCache *texture_cache;
+  gboolean rescanned;
+
+  self = (ShellAppSystem *) user_data;
+  priv = self->priv;
+
+  texture_cache = st_texture_cache_get_default ();
+  rescanned = st_texture_cache_rescan_icon_theme (texture_cache);
+
+  priv->n_rescan_retries++;
+
+  if (rescanned || priv->n_rescan_retries >= MAX_RESCAN_RETRIES)
+    {
+      priv->n_rescan_retries = 0;
+      priv->rescan_icons_timeout_id = 0;
+      return G_SOURCE_REMOVE;
+    }
+
+  return G_SOURCE_CONTINUE;
+}
+
+static void
+rescan_icon_theme (ShellAppSystem *self)
+{
+  ShellAppSystemPrivate *priv = self->priv;
+
+  priv->n_rescan_retries = 0;
+
+  if (priv->rescan_icons_timeout_id > 0)
+    return;
+
+  priv->rescan_icons_timeout_id = g_timeout_add (RESCAN_TIMEOUT_MS,
+                                                 rescan_icon_theme_cb,
+                                                 self);
+}
+
 static void
 installed_changed (GAppInfoMonitor *monitor,
                    gpointer         user_data)
 {
   ShellAppSystem *self = user_data;
 
+  rescan_icon_theme (self);
   scan_startup_wm_class_to_id (self);
 
   g_hash_table_foreach_remove (self->priv->id_to_app, stale_app_remove_func, NULL);
@@ -200,6 +253,7 @@ shell_app_system_finalize (GObject *object)
   g_hash_table_destroy (priv->id_to_app);
   g_hash_table_destroy (priv->startup_wm_class_to_id);
   g_list_free_full (priv->installed_apps, g_object_unref);
+  g_clear_handle_id (&priv->rescan_icons_timeout_id, g_source_remove);
 
   G_OBJECT_CLASS (shell_app_system_parent_class)->finalize (object);
 }

src/st/st-texture-cache.c

@@ -1567,3 +1567,11 @@ st_texture_cache_get_default (void)
     instance = g_object_new (ST_TYPE_TEXTURE_CACHE, NULL);
   return instance;
 }
+
+gboolean
+st_texture_cache_rescan_icon_theme (StTextureCache *cache)
+{
+  StTextureCachePrivate *priv = cache->priv;
+
+  return gtk_icon_theme_rescan_if_needed (priv->icon_theme);
+}

src/st/st-texture-cache.h

@@ -113,4 +113,6 @@ CoglTexture * st_texture_cache_load (StTextureCache       *cache,
                                      void                 *data,
                                      GError              **error);
 
+gboolean st_texture_cache_rescan_icon_theme (StTextureCache *cache);
+
 #endif /* __ST_TEXTURE_CACHE_H__ */