code: func (s *SeriesIDSet) SetCOW(b bool) {
  	s.Lock()
  	defer s.Unlock()
  	s.bitmap.SetCopyOnWrite(b)
  }
docs: // SetCOW sets the copy-on-write status of the underlying bitmap. When SetCOW(true)
  // is called, modifications to the bitmap will result in copies of the relevant
  // data structures being made, preventing consumers of clones of the bitmap from
  // seeing those modifications.