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skiplist.go
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skiplist.go
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package container
import (
"math/rand"
"sync"
"sync/atomic"
)
const (
PROBABILITY = 0.25
)
// 定义跳表节点
type SkipNode struct {
index uint64
value interface{}
nextNodes []*SkipNode
}
func newSkipNode(index uint64, value interface{}, level int) *SkipNode {
return &SkipNode{
index: index,
value: value,
nextNodes: make([]*SkipNode, level, level),
}
}
func (s *SkipNode) Value() interface{} {
return s.value
}
func (s *SkipNode) Index() uint64 {
return s.index
}
//==========================================================================
// 定义跳表
type SkipList struct {
level int
length int32
head *SkipNode
tail *SkipNode
mutex sync.RWMutex
}
func NewSkipList(level int) *SkipList {
head := newSkipNode(0, nil, level)
var tail *SkipNode
for i := 0; i < len(head.nextNodes); i++ {
head.nextNodes[i] = tail
}
return &SkipList{
level: level,
length: 0,
head: head,
tail: tail,
}
}
func (s *SkipList) Insert(index uint64, value interface{}) {
s.mutex.Lock()
defer s.mutex.Unlock()
previousNodes, _ := s.searchWithPreviousNodes(index)
// 默认可以插入相同index的节点
// if currentNode != s.head && currentNode.index == index {
// currentNode.value = value
// return
// }
newNode := newSkipNode(index, value, s.randLevel())
for i := len(newNode.nextNodes) - 1; i >= 0; i-- {
newNode.nextNodes[i] = previousNodes[i].nextNodes[i]
previousNodes[i].nextNodes[i] = newNode
previousNodes[i] = nil
}
atomic.AddInt32(&s.length, 1)
for i := len(newNode.nextNodes); i < len(previousNodes); i++ {
previousNodes[i] = nil
}
}
func (s *SkipList) Delete(index uint64) {
s.mutex.Lock()
defer s.mutex.Unlock()
previousNodes, currentNode := s.searchWithPreviousNodes(index)
if currentNode != s.head && currentNode.index == index {
for i := 0; i < len(currentNode.nextNodes); i++ {
previousNodes[i].nextNodes[i] = currentNode.nextNodes[i]
currentNode.nextNodes[i] = nil
previousNodes[i] = nil
}
atomic.AddInt32(&s.length, -1)
}
for i := len(currentNode.nextNodes); i < len(previousNodes); i++ {
previousNodes[i] = nil
}
}
func (s *SkipList) Search(index uint64) (*SkipNode, bool) {
s.mutex.RLock()
defer s.mutex.RUnlock()
result := s.searchWithoutPreviousNodes(index)
return result, result != nil
}
func (s *SkipList) SearchRagne(minIndex, maxIndex uint64) ([]*SkipNode, bool) {
s.mutex.RLock()
defer s.mutex.RUnlock()
if maxIndex <= minIndex {
minIndex, maxIndex = maxIndex, minIndex
}
node := s.searchWithoutPreviousNodes(minIndex)
if node == nil {
return nil, false
}
var nodes []*SkipNode
nodes = append(nodes, node)
for {
node = node.nextNodes[0]
if node == nil || node.index > maxIndex {
break
}
nodes = append(nodes, node)
}
return nodes, true
}
func (s *SkipList) ForEach(f func(node *SkipNode) bool) {
s.mutex.RLock()
defer s.mutex.RUnlock()
nodes := s.Snapshot()
for _, node := range nodes {
if !f(node) {
break
}
}
}
func (s *SkipList) Length() int32 {
return atomic.LoadInt32(&s.length)
}
func (s *SkipList) Level() int {
return s.level
}
func (s *SkipList) searchWithPreviousNodes(index uint64) ([]*SkipNode, *SkipNode) {
previousNodes := make([]*SkipNode, s.level)
currentNode := s.head
for l := s.level - 1; l >= 0; l-- {
for currentNode.nextNodes[l] != s.tail && currentNode.nextNodes[l].index < index {
currentNode = currentNode.nextNodes[l]
}
previousNodes[l] = currentNode
}
if currentNode.nextNodes[0] != s.tail {
currentNode = currentNode.nextNodes[0]
}
return previousNodes, currentNode
}
func (s *SkipList) searchWithoutPreviousNodes(index uint64) *SkipNode {
currentNode := s.head
for l := s.level - 1; l >= 0; l-- {
for currentNode.nextNodes[l] != s.tail && currentNode.nextNodes[l].index < index {
currentNode = currentNode.nextNodes[l]
}
}
currentNode = currentNode.nextNodes[0]
if currentNode != s.tail && currentNode.index >= index {
return currentNode
}
return nil
}
func (s *SkipList) Snapshot() []*SkipNode {
result := make([]*SkipNode, s.length)
i := 0
currentNode := s.head.nextNodes[0]
for currentNode != s.tail {
node := &SkipNode{
index: currentNode.index,
value: currentNode.value,
nextNodes: nil,
}
result[i] = node
currentNode = currentNode.nextNodes[0]
i++
}
return result
}
func (s *SkipList) randLevel() int {
level := 1
for rand.Float64() <= PROBABILITY && level < s.level {
level++
}
return level
}