func()

in policies.go [579:689]

• 92 lines of code
• 24 McCabe index (conditional complexity)

func (t *tokenAwareHostPolicy) Pick(qry ExecutableQuery) NextHost {
	if qry == nil {
		return t.fallback.Pick(qry)
	}

	routingKey, err := qry.GetRoutingKey()
	if err != nil {
		return t.fallback.Pick(qry)
	} else if routingKey == nil {
		return t.fallback.Pick(qry)
	}

	meta := t.getMetadataReadOnly()
	if meta == nil || meta.tokenRing == nil {
		return t.fallback.Pick(qry)
	}

	token := meta.tokenRing.partitioner.Hash(routingKey)
	ht := meta.replicas[qry.Keyspace()].replicasFor(token)

	var replicas []*HostInfo
	if ht == nil {
		host, _ := meta.tokenRing.GetHostForToken(token)
		replicas = []*HostInfo{host}
	} else {
		replicas = ht.hosts
		if t.shuffleReplicas {
			replicas = shuffleHosts(replicas)
		}
	}

	var (
		fallbackIter NextHost
		i, j, k      int
		remote       [][]*HostInfo
		tierer       HostTierer
		tiererOk     bool
		maxTier      uint
	)

	if tierer, tiererOk = t.fallback.(HostTierer); tiererOk {
		maxTier = tierer.MaxHostTier()
	} else {
		maxTier = 1
	}

	if t.nonLocalReplicasFallback {
		remote = make([][]*HostInfo, maxTier)
	}

	used := make(map[*HostInfo]bool, len(replicas))
	return func() SelectedHost {
		for i < len(replicas) {
			h := replicas[i]
			i++

			var tier uint
			if tiererOk {
				tier = tierer.HostTier(h)
			} else if t.fallback.IsLocal(h) {
				tier = 0
			} else {
				tier = 1
			}

			if tier != 0 {
				if t.nonLocalReplicasFallback {
					remote[tier-1] = append(remote[tier-1], h)
				}
				continue
			}

			if h.IsUp() {
				used[h] = true
				return (*selectedHost)(h)
			}
		}

		if t.nonLocalReplicasFallback {
			for j < len(remote) && k < len(remote[j]) {
				h := remote[j][k]
				k++

				if k >= len(remote[j]) {
					j++
					k = 0
				}

				if h.IsUp() {
					used[h] = true
					return (*selectedHost)(h)
				}
			}
		}

		if fallbackIter == nil {
			// fallback
			fallbackIter = t.fallback.Pick(qry)
		}

		// filter the token aware selected hosts from the fallback hosts
		for fallbackHost := fallbackIter(); fallbackHost != nil; fallbackHost = fallbackIter() {
			if !used[fallbackHost.Info()] {
				used[fallbackHost.Info()] = true
				return fallbackHost
			}
		}

		return nil
	}
}