Start using the monotonic API in GLib ≥ 2.27

Starting from the 2.27 cycle, GLib is exposing a monotonic clock with
microseconds granularity throughout the time-based API. We can start
using it, given that the old, non-monotonic version is going to be
deprecated by the same cycle.

clutter/clutter-frame-source.c

@@ -144,11 +144,17 @@ clutter_frame_source_prepare (GSource *source,
                               gint    *delay)
 {
   ClutterFrameSource *frame_source = (ClutterFrameSource *) source;
-  GTimeVal source_time;
   gint64 current_time;
 
-  g_source_get_current_time (source, &source_time);
+#if GLIB_CHECK_VERSION (2, 27, 3)
-  current_time = source_time.tv_sec * 1000 + source_time.tv_usec / 1000;
+  current_time = g_source_get_time (source) / 1000;
+#else
+  {
+    GTimeVal source_time;
+    g_source_get_current_time (source, &source_time);
+    current_time = source_time.tv_sec * 1000 + source_time.tv_usec / 1000;
+  }
+#endif
 
   return _clutter_timeout_interval_prepare (current_time,
                                             &frame_source->timeout,

clutter/clutter-master-clock.c

@@ -170,7 +170,6 @@ master_clock_is_running (ClutterMasterClock *master_clock)
 static gint
 master_clock_next_frame_delay (ClutterMasterClock *master_clock)
 {
-  GTimeVal source_time;
   gint64 now, next;
 
   if (!master_clock_is_running (master_clock))
@@ -207,8 +206,16 @@ master_clock_next_frame_delay (ClutterMasterClock *master_clock)
   /* Otherwise, wait at least 1/frame_rate seconds since we last
    * started a frame
    */
-  g_source_get_current_time (master_clock->source, &source_time);
+#if GLIB_CHECK_VERSION (2, 27, 3)
-  now = source_time.tv_sec * 1000000L + source_time.tv_usec;
+  now = g_source_get_time (master_clock->source);
+#else
+  {
+    GTimeVal source_time;
+    g_source_get_current_time (master_clock->source, &source_time);
+    now = source_time.tv_sec * 1000000L + source_time.tv_usec;
+  }
+#endif
+
   next = master_clock->prev_tick;
 
   /* If time has gone backwards then there's no way of knowing how
@@ -301,7 +308,6 @@ clutter_clock_dispatch (GSource     *source,
   ClutterMasterClock *master_clock = clock_source->master_clock;
   ClutterStageManager *stage_manager = clutter_stage_manager_get_default ();
   gboolean stages_updated = FALSE;
-  GTimeVal source_time;
   GSList *stages, *l;
 
   CLUTTER_STATIC_TIMER (master_dispatch_timer,
@@ -322,9 +328,16 @@ clutter_clock_dispatch (GSource     *source,
   clutter_threads_enter ();
 
   /* Get the time to use for this frame */
-  g_source_get_current_time (source, &source_time);
+#if GLIB_CHECK_VERSION (2, 27, 3)
-  master_clock->cur_tick = source_time.tv_sec * 1000000L
+  master_clock->cur_tick = g_source_get_time (source);
-                         + source_time.tv_usec;
+#else
+  {
+    GTimeVal source_time;
+    g_source_get_current_time (source, &source_time);
+    master_clock->cur_tick = source_time.tv_sec * 1000000L
+                           + source_time.tv_usec;
+  }
+#endif
 
   /* We need to protect ourselves against stages being destroyed during
    * event handling

clutter/clutter-timeout-interval.c

@@ -34,12 +34,17 @@ void
 _clutter_timeout_interval_init (ClutterTimeoutInterval *interval,
                                 guint                   fps)
 {
-  GTimeVal start_time;
+#if GLIB_CHECK_VERSION (2, 27, 3)
+  interval->start_time = g_get_monotonic_time () / 1000;
+#else
+  {
+    GTimeVal start_time;
+    g_get_current_time (&start_time);
+    interval->start_time = start_time.tv_sec * 1000
+                         + start_time.tv_usec / 1000;
+  }
+#endif
 
-  g_get_current_time (&start_time);
-
-  interval->start_time = start_time.tv_sec * 1000
-                       + start_time.tv_usec / 1000;
   interval->fps = fps;
   interval->frame_count = 0;
 }

clutter/clutter-timeout-pool.c

@@ -136,11 +136,18 @@ clutter_timeout_prepare (ClutterTimeoutPool *pool,
                          ClutterTimeout     *timeout,
                          gint               *next_timeout)
 {
-  GTimeVal source_time;
+  GSource *source = (GSource *) pool;
   gint64 now;
 
-  g_source_get_current_time (&pool->source, &source_time);
+#if GLIB_CHECK_VERSION (2, 27, 3)
-  now = source_time.tv_sec * 1000 + source_time.tv_usec / 1000;
+  now = g_source_get_time (source) / 1000;
+#else
+  {
+    GTimeVal source_time;
+    g_source_get_current_time (source, &source_time);
+    now = source_time.tv_sec * 1000 + source_time.tv_usec / 1000;
+  }
+#endif
 
   return _clutter_timeout_interval_prepare (now,
                                             &timeout->interval,