code: func (pool *ReaderPool) setSharedRates() {
  	if len(pool.givenOut) == 0 {
  		return
  	}
  	perSecPerReader := pool.maxRate / len(pool.givenOut)
  	for reader := range pool.givenOut {
  		reader.SetRate(perSecPerReader)
  	}
  }
docs: // must be called with a lock held on `pool.mu`