✨ feat(lru): LRU 缓存淘汰策略

Cache New Get RemoveOldest Add Len

.gitignore

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+*.jpg
+*.png

.vscode/settings.json

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+{
+ "go.inferGopath": false
+}

go.mod

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+module geecache
+
+go 1.18

lru/lru.go

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+package lru
+
+import (
+ "container/list"
+)
+
+// 核心数据结构
+// map + double linked list
+
+// Cache is a LRU cache. Not safe for ocncurrent access.
+type Cache struct {
+ maxBytes int64 // 允许的最大内存
+ nbytes int64 // 已使用内存
+ ll *list.List // 双向链表
+ cache map[string]*list.Element
+ OnEvicted func(key string, value Value) // 某条记录被移除时的回调，可以为 nil
+}
+
+type entry struct {
+ key string
+ value Value
+}
+
+type Value interface {
+ Len() int
+}
+
+// New 实例化
+func New(maxBytes int64, onEvicted func(string, Value)) *Cache {
+ return &Cache{
+ maxBytes: maxBytes,
+ ll: list.New(),
+ cache: make(map[string]*list.Element),
+ OnEvicted: onEvicted,
+ }
+}
+
+// Get 查找
+//
+// 如果键对应的链表结点存在，将对应节点移动到队首，并返回找到的值
+func (c *Cache) Get(key string) (value Value, ok bool) {
+ if ele, ok := c.cache[key]; ok {
+ c.ll.MoveToFront(ele)
+ kv := ele.Value.(*entry)
+ return kv.value, true
+ }
+ return
+}
+
+// RemoveOldest 缓存淘汰
+//
+// 移除最近最少访问的节点（尾节点）
+func (c *Cache) RemoveOldest() {
+ ele := c.ll.Back()
+ if ele != nil {
+ c.ll.Remove(ele)
+ kv := ele.Value.(*entry)
+ //TODO
+ delete(c.cache, kv.key)
+ c.nbytes -= int64(len(kv.key)) + int64(kv.value.Len())
+ if c.OnEvicted != nil {
+ c.OnEvicted(kv.key, kv.value)
+ }
+ }
+}
+
+// Add 添加一个值到缓存中
+func (c *Cache) Add(key string, value Value) {
+ // 已存在，修改值，并将该节点移动到队首
+ if ele, ok := c.cache[key]; ok {
+ c.ll.MoveToFront(ele)
+ kv := ele.Value.(*entry)
+ c.nbytes += int64(value.Len()) - int64(kv.value.Len())
+ kv.value = value
+ } else {
+ ele := c.ll.PushFront(&entry{key, value})
+ c.cache[key] = ele
+ c.nbytes += int64(len(key)) + int64(value.Len())
+ }
+ for c.maxBytes != 0 && c.maxBytes < c.nbytes {
+ c.RemoveOldest()
+ }
+}
+
+// Len 获取已添加数据条数
+func (c *Cache) Len() int {
+ return c.ll.Len()
+}

lru/lru_test.go

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+package lru
+
+import (
+ "reflect"
+ "testing"
+)
+
+type String string
+
+func (s String) Len() int {
+ return len(s)
+}
+
+func TestGet(t *testing.T) {
+ lru := New(int64(0), nil)
+ lru.Add("key1", String("1234"))
+ if v, ok := lru.Get("key1"); !ok || string(v.(String)) != "1234" {
+ t.Fatalf("cache hit key1=1234 failed")
+ }
+ if _, ok := lru.Get("key2"); ok {
+ t.Fatalf("cache miss key2 failed")
+ }
+}
+
+func TestRemoveOldest(t *testing.T) {
+ k1, k2, k3 := "key1", "key2", "k3"
+ v1, v2, v3 := "value1", "value2", "v3"
+ cap := len(k1 + k2 + v1 + v2)
+ lru := New(int64(cap), nil)
+ lru.Add(k1, String(v1))
+ lru.Add(k2, String(v2))
+ lru.Add(k3, String(v3))
+
+ if _, ok := lru.Get("key1"); ok || lru.Len() != 2 {
+ t.Fatalf("RemoveOldest key1 failed")
+ }
+}
+
+func TestOnEvicted(t *testing.T) {
+ keys := make([]string, 0)
+ callback := func(key string, value Value) {
+ keys = append(keys, key)
+ }
+ lru := New(int64(10), callback)
+ lru.Add("key1", String("123456"))
+ lru.Add("k2", String("k2"))
+ lru.Add("k3", String("k3"))
+ lru.Add("k4", String("k4"))
+
+ expect := []string{"key1", "k2"}
+
+ if !reflect.DeepEqual(expect, keys) {
+ t.Fatalf("Call OnEvicted failed, expect keys equals to %s", expect)
+ }
+}