static inline void lock_sync(void)
{
   if (vrend_state.sync_thread && vrend_state.use_async_fence_cb)
      mtx_lock(&vrend_state.fence_mutex);
}
static inline void lock_sync(void)
{
   if (vrend_state.sync_thread && vrend_state.use_async_fence_cb)
      mtx_lock(&vrend_state.fence_mutex);
}