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