Deprecated (undocumented) g_thread_gettime

g_thread_gettime() is an undocumented public function pointer that
points to a function that returns the monotonic time in nanoseconds.
g_get_monotonic_time() does the same in microseconds, so it can be used
instead.

GLib had one internal user in GFileMonitor that only cared about
millisecond accuracy; it has been ported to g_get_monotonic_time().

gio/gfilemonitor.c

@@ -439,7 +439,7 @@ emit_in_idle (GFileMonitor      *monitor,
 static guint32
 get_time_msecs (void)
 {
-  return g_thread_gettime() / (1000 * 1000);
+  return g_get_monotonic_time () / G_TIME_SPAN_MILLISECOND;
 }
 
 static guint32