【Golang】实现lru（Least recently used）最近最少使用缓存淘汰算法

首先需要一个数据结构：

type Cache struct {
	maxBytes int64
	nbytes int64
	ll *list.List
	cache map[string]*list.Element
	OnEvicted func(key string,value Value)
}

maxBytes：缓存最大存储字节
nbytes：当前存储字节
ll：数据结构
cache：元素
OnEvicted：元素被丢弃后的操作

注意：存了两份，一份在ll链表中，一份在cache中。

定义元素的键值对类型：

type entry struct {
	key string
	value Value
}

元素值类型所占字节获取函数：

type Value interface {
	Len() int
}

创建操作：

func New(maxBytes int64, onEvicted func(key string,value Value)) *Cache {
	return &Cache{
		maxBytes: maxBytes,
		ll: list.New(),
		cache: make(map[string]*list.Element)
		OnEvicted: onEvicted,
	}
}

缓存的大小：

func (c *Cache) Len() int {
	return c.ll.Len()
}

被淘汰的元素操作：

func (c *Cache) RemoveOldest() {
	ele := c.ll.Back()
	if ele != nil {
		c.ll.Remove(ele)
		kv := ele.Value.(*entry)
		c.nbytes -= int64(len(kv.key)) + int64(kv.value.Len())
		if c.OnEvicted != nil {
			c.OnEvicted(kv.key, kv.value)
		}
	}
}

添加元素：

func (c *Cache) Add(key string, value Value) {
	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: key, value: value})
		c.cache[key] = ele
		c.nbytes += int64(len(key)) + int64(value.Len())
	}
	for c.maxBytes != 0 && c.nbytes > c.maxBytes {
		c.RemoveOldest()
	}
}

获取元素：

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, ok
	}
	return
}

全部代码

package lru

import "container/list"

type Cache struct {
	maxBytes int64
	nbytes int64
	ll *list.List
	cache map[string]*list.Element
	OnEvicted func(key string,value Value)
}

type entry struct {
	key string
	value Value
}

type Value interface {
	Len() int
}

func New(maxBytes int64, onEvicted func(key string,value Value)) *Cache {
	return &Cache{
		maxBytes: maxBytes,
		ll: list.New(),
		cache: make(map[string]*list.Element)
		OnEvicted: onEvicted,
	}
}

func (c *Cache) Add(key string, value Value) {
	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: key, value: value})
		c.cache[key] = ele
		c.nbytes += int64(len(key)) + int64(value.Len())
	}
	for c.maxBytes != 0 && c.nbytes > c.maxBytes {
		c.RemoveOldest()
	}
}

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, ok
	}
	return
}

func (c *Cache) RemoveOldest() {
	ele := c.ll.Back()
	if ele != nil {
		c.ll.Remove(ele)
		kv := ele.Value.(*entry)
		c.nbytes -= int64(len(kv.key)) + int64(kv.value.Len())
		if c.OnEvicted != nil {
			c.OnEvicted(kv.key, kv.value)
		}
	}
}

func (c *Cache) Len() int {
	return c.ll.Len()
}