datetime: Use GnomeWallClock instead of periodic timeout

We don't actually use the ::clock property string here - this
is just making it so we don't need to wake up once a second.

https://bugzilla.gnome.org/show_bug.cgi?id=658011

configure.ac

@@ -77,6 +77,7 @@ POLKIT_REQUIRED_VERSION=0.97
 GSD_REQUIRED_VERSION=2.91.94
 NETWORK_MANAGER_REQUIRED_VERSION=0.8.992
 LIBNOTIFY_REQUIRED_VERSION=0.7.3
+GNOME_DESKTOP_REQUIRED_VERSION=3.1.91
 
 COMMON_MODULES="gtk+-3.0 >= $GTK_REQUIRED_VERSION
  glib-2.0 >= $GLIB_REQUIRED_VERSION
@@ -93,6 +94,7 @@ PKG_CHECK_MODULES(SHELL, $COMMON_MODULES libgnome-menu-3.0 gio-unix-2.0)
 PKG_CHECK_MODULES(BACKGROUND_PANEL, $COMMON_MODULES libxml-2.0 gnome-desktop-3.0
                   gdk-pixbuf-2.0 >= $GDKPIXBUF_REQUIRED_VERSION)
 PKG_CHECK_MODULES(DATETIME_PANEL, $COMMON_MODULES dbus-glib-1
+                  gnome-desktop-3.0 >= $GNOME_DESKTOP_REQUIRED_VERSION
                   polkit-gobject-1 >= $POLKIT_REQUIRED_VERSION
                   gdk-pixbuf-2.0 >= $GDKPIXBUF_REQUIRED_VERSION)
 PKG_CHECK_MODULES(DISPLAY_PANEL, $COMMON_MODULES dbus-glib-1 gnome-desktop-3.0 >= 3.1.0)

panels/datetime/cc-datetime-panel.c

@@ -26,11 +26,14 @@
 #include "cc-timezone-map.h"
 #include "dtm.h"
 #include "date-endian.h"
+#define GNOME_DESKTOP_USE_UNSTABLE_API
 
 #include <gdesktop-enums.h>
 #include <string.h>
 #include <stdlib.h>
 #include <libintl.h>
+
+#include <libgnome-desktop/gnome-wall-clock.h>
 #include <polkit/polkit.h>
 
 /* FIXME: This should be "Etc/GMT" instead */
@@ -77,7 +80,7 @@ struct _CcDateTimePanelPrivate
   GSettings *settings;
   GDesktopClockFormat clock_format;
 
-  guint update_id;
+  GnomeWallClock *clock_tracker;
 
   DateTimeMechanism *dtm;
   GCancellable *cancellable;
@@ -86,7 +89,6 @@ struct _CcDateTimePanelPrivate
 };
 
 static void update_time (CcDateTimePanel *self);
-static void queue_clock_update (CcDateTimePanel *self);
 
 static void
 cc_date_time_panel_get_property (GObject    *object,
@@ -119,10 +121,10 @@ cc_date_time_panel_dispose (GObject *object)
 {
   CcDateTimePanelPrivate *priv = CC_DATE_TIME_PANEL (object)->priv;
 
-  if (priv->update_id != 0)
+  if (priv->clock_tracker != NULL)
     {
-      g_source_remove (priv->update_id);
+      g_object_unref (priv->clock_tracker);
-      priv->update_id = 0;
+      priv->clock_tracker = NULL;
     }
 
   if (priv->builder)
@@ -753,6 +755,14 @@ month_year_changed (GtkWidget       *widget,
   change_date (panel);
 }
 
+static void
+on_clock_changed (GnomeWallClock  *clock,
+		  GParamSpec      *pspec,
+		  CcDateTimePanel *panel)
+{
+  update_time (panel);
+}
+
 static void
 change_time (GtkButton       *button,
              CcDateTimePanel *panel)
@@ -803,31 +813,6 @@ change_ntp (GObject         *gobject,
   queue_set_ntp (self);
 }
 
-static gboolean
-update_time_timer (CcDateTimePanel *self)
-{
-  g_date_time_unref (self->priv->date);
-  self->priv->date = g_date_time_new_now_local ();
-  update_time (self);
-  queue_clock_update (self);
-  return FALSE;
-}
-
-static void
-queue_clock_update (CcDateTimePanel *self)
-{
-  int timeouttime;
-  struct timeval tv;
-
-  gettimeofday (&tv, NULL);
-  timeouttime = (G_USEC_PER_SEC - tv.tv_usec) / 1000 + 1;
-
-  /* timeout of one minute if we don't care about the seconds */
-  timeouttime += 1000 * (59 - tv.tv_sec % 60);
-
-  self->priv->update_id = g_timeout_add (timeouttime, (GSourceFunc)update_time_timer, self);
-}
-
 static void
 on_permission_changed (GPermission *permission,
                        GParamSpec  *pspec,
@@ -998,6 +983,9 @@ cc_date_time_panel_init (CcDateTimePanel *self)
 
 
   /* setup the time itself */
+  priv->clock_tracker = g_object_new (GNOME_TYPE_WALL_CLOCK, NULL);
+  g_signal_connect (priv->clock_tracker, "notify::clock", G_CALLBACK (on_clock_changed), self);
+
   priv->settings = g_settings_new (CLOCK_SCHEMA);
   clock_settings_changed_cb (priv->settings, CLOCK_FORMAT_KEY, self);
   g_signal_connect (priv->settings, "changed::" CLOCK_FORMAT_KEY,
@@ -1035,8 +1023,6 @@ cc_date_time_panel_init (CcDateTimePanel *self)
                                          get_timezone_cb,
                                          self);
 
-  queue_clock_update (self);
-
   /* add the lock button */
   priv->permission = polkit_permission_new_sync ("org.gnome.settingsdaemon.datetimemechanism.configure", NULL, NULL, NULL);
   if (priv->permission == NULL)