[gnome-settings-daemon] common: avoid loading Adwaita CSS theme into memory

[Bastien Nocera <hadess src gnome org>]

commit 2088d637743373b753145a4f500787d6c339e0d5
Author: Christian Hergert <chergert redhat com>
Date:   Mon Mar 27 00:17:59 2017 -0700

    common: avoid loading Adwaita CSS theme into memory
    
    The various Gtk programs are not dependent on any specific theme being
    loaded. Therefore, the parsing the Adwaita CSS theme (which is quite a
    detailed theme) is unnecessary and a few MB of overhead to each gsd
    subprocess.
    
    By setting the GTK_THEME environment variable in main() and providing an
    alternate CSS file (which is empty), we can force Gtk to never load the
    default theme, but instead our empty theme. This is important as otherwise
    GtkSettings can force-load Adwaita upon first use, and that fragments the
    heap.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=780555

 configure.ac                          |    1 +
 plugins/common/Makefile.am            |   10 +++++++++
 plugins/common/Makefile.am.gresources |   34 +++++++++++++++++++++++++++++++++
 plugins/common/daemon-skeleton-gtk.h  |   28 +++++++++++++++++++++++++++
 plugins/common/gsd.gresources.xml     |    6 +++++
 5 files changed, 79 insertions(+), 0 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 7688d87..ff6ebb3 100644
--- a/configure.ac
+++ b/configure.ac
@@ -73,6 +73,7 @@ AC_SUBST([GSD_PLUGIN_LDFLAGS])
 
 AC_PATH_PROG(GLIB_GENMARSHAL, glib-genmarshal)
 AC_PATH_PROG([GLIB_MKENUMS],[glib-mkenums])
+AC_PATH_PROG([GLIB_COMPILE_RESOURCES], [glib-compile-resources])
 
 LT_LIB_M
 AC_SUBST(LIBM)
diff --git a/plugins/common/Makefile.am b/plugins/common/Makefile.am
index 239c601..706be12 100644
--- a/plugins/common/Makefile.am
+++ b/plugins/common/Makefile.am
@@ -33,6 +33,8 @@ libcommon_la_SOURCES = \
        gsd-device-mapper.h     \
        gsd-input-helper.c      \
        gsd-input-helper.h      \
+       gsd-resources.c         \
+       gsd-resources.h         \
        gsd-settings-migrate.c  \
        gsd-settings-migrate.h  \
        gsd-shell-helper.c      \
@@ -68,3 +70,11 @@ EXTRA_DIST = $(scripts_DATA) daemon-skeleton.h daemon-skeleton-gtk.h
 
 CLEANFILES = \
        $(GSD_COMMON_ENUM_FILES)
+
+DISTCLEANFILES =
+
+glib_resources_c = gsd-resources.c
+glib_resources_h = gsd-resources.h
+glib_resources_xml = gsd.gresources.xml
+glib_resources_namespace = gsd
+include Makefile.am.gresources
diff --git a/plugins/common/Makefile.am.gresources b/plugins/common/Makefile.am.gresources
new file mode 100644
index 0000000..1441d0e
--- /dev/null
+++ b/plugins/common/Makefile.am.gresources
@@ -0,0 +1,34 @@
+resources_xml=$(addprefix $(srcdir)/,$(glib_resources_xml))
+resources_srcdir=$(dir $(resources_xml))
+
+DISTCLEANFILES += $(glib_resources_h) $(glib_resources_c)
+BUILT_SOURCES += $(glib_resources_h) $(glib_resources_c)
+CLEANFILES += stamp-resources $(glib_resources_c) $(glib_resources_h)
+EXTRA_DIST += \
+       $(glib_resources_xml) \
+       $(shell $(GLIB_COMPILE_RESOURCES) --sourcedir=$(resources_srcdir) --generate-dependencies 
$(resources_xml)) \
+       $(NULL)
+
+stamp-resources: $(glib_resources_c) $(resources_xml)
+       $(AM_V_GEN)$(GLIB_COMPILE_RESOURCES) \
+               --target=xgen-gr.h \
+               --sourcedir=$(resources_srcdir) \
+               --generate-header \
+               --c-name $(glib_resources_namespace) \
+               $(resources_xml) \
+       && (cmp -s xgen-gr.h $(glib_resources_h) || cp -f xgen-gr.h $(glib_resources_h)) \
+       && rm -f xgen-gr.h \
+       && echo timestamp > $(@F)
+
+$(glib_resources_h): stamp-resources
+       @true
+
+$(glib_resources_c): $(resources_xml) $(shell $(GLIB_COMPILE_RESOURCES) --sourcedir=$(resources_srcdir) 
--generate-dependencies $(resources_xml))
+       $(AM_V_GEN)$(GLIB_COMPILE_RESOURCES) \
+               --target=xgen-gr.c \
+               --sourcedir=$(resources_srcdir) \
+               --generate-source \
+               --c-name $(glib_resources_namespace) \
+               $(resources_xml) \
+       && (cmp -s xgen-gr.c $(glib_resources_c) || cp -f xgen-gr.c $(glib_resources_c)) \
+       && rm -f xgen-gr.c
diff --git a/plugins/common/daemon-skeleton-gtk.h b/plugins/common/daemon-skeleton-gtk.h
index 714e48b..d68ad37 100644
--- a/plugins/common/daemon-skeleton-gtk.h
+++ b/plugins/common/daemon-skeleton-gtk.h
@@ -163,6 +163,30 @@ register_with_gnome_session (void)
                           NULL);
 }
 
+static void
+set_empty_gtk_theme (gboolean set)
+{
+       static char *old_gtk_theme = NULL;
+
+       if (set) {
+               /* Override GTK_THEME to reduce overhead of CSS engine. By using
+                * GTK_THEME environment variable, GtkSettings is not allowed to
+                * initially parse the Adwaita theme.
+                *
+                * https://bugzilla.gnome.org/show_bug.cgi?id=780555 */
+               old_gtk_theme = g_strdup (g_getenv ("GTK_THEME"));
+               g_setenv ("GTK_THEME", "Disabled", TRUE);
+       } else {
+               /* GtkSettings has loaded, so we can drop GTK_THEME used to initialize
+                * our internal theme. Only the main thread accesses the GTK_THEME
+                * environment variable, so this is safe to release. */
+               if (old_gtk_theme != NULL)
+                       g_setenv ("GTK_THEME", old_gtk_theme, TRUE);
+               else
+                       g_unsetenv ("GTK_THEME");
+       }
+}
+
 int
 main (int argc, char **argv)
 {
@@ -172,6 +196,8 @@ main (int argc, char **argv)
         bind_textdomain_codeset (GETTEXT_PACKAGE, "UTF-8");
         textdomain (GETTEXT_PACKAGE);
 
+        set_empty_gtk_theme (TRUE);
+
         /* Work around https://bugzilla.gnome.org/show_bug.cgi?id=674885 */
         g_type_ensure (G_TYPE_DBUS_CONNECTION);
         g_type_ensure (G_TYPE_DBUS_PROXY);
@@ -187,6 +213,8 @@ main (int argc, char **argv)
                 exit (1);
         }
 
+        set_empty_gtk_theme (FALSE);
+
         if (verbose)
                 g_setenv ("G_MESSAGES_DEBUG", "all", TRUE);
 
diff --git a/plugins/common/gsd.gresources.xml b/plugins/common/gsd.gresources.xml
new file mode 100644
index 0000000..e4ac1cd
--- /dev/null
+++ b/plugins/common/gsd.gresources.xml
@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<gresources>
+  <gresource prefix="/org/gtk/libgtk/theme/Disabled">
+    <file>gtk.css</file>
+  </gresource>
+</gresources>
diff --git a/plugins/common/gtk.css b/plugins/common/gtk.css
new file mode 100644
index 0000000..e69de29