stack.go
func (s *SegmentStack) Push(id int64) {
	s.Lock()
	defer s.Unlock()
	s.s = append(s.s, id)
}
func (s *SegmentStack) Push(id int64) {
	s.Lock()
	defer s.Unlock()
	s.s = append(s.s, id)
}
// Push pushes a segment id onto the segment stack.