watch/watcher.go
func (w *Watcher) Size() int {
	w.Lock()
	defer w.Unlock()
	return len(w.depViewMap)
}
func (w *Watcher) Size() int {
	w.Lock()
	defer w.Unlock()
	return len(w.depViewMap)
}
// Size returns the number of views this watcher is watching.