code: func (ipp *intPoolPool) put(ip *intPool) {
  	ipp.lock.Lock()
  	defer ipp.lock.Unlock()
  
  	if len(ipp.pools) < cap(ipp.pools) {
  		ipp.pools = append(ipp.pools, ip)
  	}
  }
docs: // put a pool that has been allocated with get.