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consistenthash.go
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consistenthash.go
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package hash
import (
"fmt"
"sort"
"strconv"
"sync"
"github.com/zeromicro/go-zero/core/lang"
)
const (
// TopWeight is the top weight that one entry might set.
TopWeight = 100
minReplicas = 100
prime = 16777619
)
type (
// Func defines the hash method.
Func func(data []byte) uint64
// A ConsistentHash is a ring hash implementation.
ConsistentHash struct {
hashFunc Func
replicas int
keys []uint64
ring map[uint64][]any
nodes map[string]lang.PlaceholderType
lock sync.RWMutex
}
)
// NewConsistentHash returns a ConsistentHash.
func NewConsistentHash() *ConsistentHash {
return NewCustomConsistentHash(minReplicas, Hash)
}
// NewCustomConsistentHash returns a ConsistentHash with given replicas and hash func.
func NewCustomConsistentHash(replicas int, fn Func) *ConsistentHash {
if replicas < minReplicas {
replicas = minReplicas
}
if fn == nil {
fn = Hash
}
return &ConsistentHash{
hashFunc: fn,
replicas: replicas,
ring: make(map[uint64][]any),
nodes: make(map[string]lang.PlaceholderType),
}
}
// Add adds the node with the number of h.replicas,
// the later call will overwrite the replicas of the former calls.
func (h *ConsistentHash) Add(node any) {
h.AddWithReplicas(node, h.replicas)
}
// AddWithReplicas adds the node with the number of replicas,
// replicas will be truncated to h.replicas if it's larger than h.replicas,
// the later call will overwrite the replicas of the former calls.
func (h *ConsistentHash) AddWithReplicas(node any, replicas int) {
h.Remove(node)
if replicas > h.replicas {
replicas = h.replicas
}
nodeRepr := repr(node)
h.lock.Lock()
defer h.lock.Unlock()
h.addNode(nodeRepr)
for i := 0; i < replicas; i++ {
hash := h.hashFunc([]byte(nodeRepr + strconv.Itoa(i)))
h.keys = append(h.keys, hash)
h.ring[hash] = append(h.ring[hash], node)
}
sort.Slice(h.keys, func(i, j int) bool {
return h.keys[i] < h.keys[j]
})
}
// AddWithWeight adds the node with weight, the weight can be 1 to 100, indicates the percent,
// the later call will overwrite the replicas of the former calls.
func (h *ConsistentHash) AddWithWeight(node any, weight int) {
// don't need to make sure weight not larger than TopWeight,
// because AddWithReplicas makes sure replicas cannot be larger than h.replicas
replicas := h.replicas * weight / TopWeight
h.AddWithReplicas(node, replicas)
}
// Get returns the corresponding node from h base on the given v.
func (h *ConsistentHash) Get(v any) (any, bool) {
h.lock.RLock()
defer h.lock.RUnlock()
if len(h.ring) == 0 {
return nil, false
}
hash := h.hashFunc([]byte(repr(v)))
index := sort.Search(len(h.keys), func(i int) bool {
return h.keys[i] >= hash
}) % len(h.keys)
nodes := h.ring[h.keys[index]]
switch len(nodes) {
case 0:
return nil, false
case 1:
return nodes[0], true
default:
innerIndex := h.hashFunc([]byte(innerRepr(v)))
pos := int(innerIndex % uint64(len(nodes)))
return nodes[pos], true
}
}
// Remove removes the given node from h.
func (h *ConsistentHash) Remove(node any) {
nodeRepr := repr(node)
h.lock.Lock()
defer h.lock.Unlock()
if !h.containsNode(nodeRepr) {
return
}
for i := 0; i < h.replicas; i++ {
hash := h.hashFunc([]byte(nodeRepr + strconv.Itoa(i)))
index := sort.Search(len(h.keys), func(i int) bool {
return h.keys[i] >= hash
})
if index < len(h.keys) && h.keys[index] == hash {
h.keys = append(h.keys[:index], h.keys[index+1:]...)
}
h.removeRingNode(hash, nodeRepr)
}
h.removeNode(nodeRepr)
}
func (h *ConsistentHash) removeRingNode(hash uint64, nodeRepr string) {
if nodes, ok := h.ring[hash]; ok {
newNodes := nodes[:0]
for _, x := range nodes {
if repr(x) != nodeRepr {
newNodes = append(newNodes, x)
}
}
if len(newNodes) > 0 {
h.ring[hash] = newNodes
} else {
delete(h.ring, hash)
}
}
}
func (h *ConsistentHash) addNode(nodeRepr string) {
h.nodes[nodeRepr] = lang.Placeholder
}
func (h *ConsistentHash) containsNode(nodeRepr string) bool {
_, ok := h.nodes[nodeRepr]
return ok
}
func (h *ConsistentHash) removeNode(nodeRepr string) {
delete(h.nodes, nodeRepr)
}
func innerRepr(node any) string {
return fmt.Sprintf("%d:%v", prime, node)
}
func repr(node any) string {
return lang.Repr(node)
}