code: func newRetrieveManager(peers *peerSet, dist *requestDistributor, serverPool peerSelector) *retrieveManager {
  	return &retrieveManager{
  		peers:      peers,
  		dist:       dist,
  		serverPool: serverPool,
  		sentReqs:   make(map[uint64]*sentReq),
  	}
  }
docs: // newRetrieveManager creates the retrieve manager