Nodejs基于LRU算法实现的缓存处理操作示例

function CacheLRU(capacity) {/* 利用Buffer写的一个LRU缓存，capacity为缓存容量，为0时不限容量。myCache = new CacheLRU(capacity); //构造缓存myCache.get(key); //读取名为key的缓存值myCache.put(key, value); //写入名为key的缓存值myCache.remove(key); //删除名为key的缓存值myCache.removeAll(); //清空缓存myCache.info(); //返回myCache缓存信息LRU原理：对所有缓存数据的key构建hash链表，当对某一数据进行get或put操作时，将其key提到链表前端（最新）。当进行put数据超出容量时，删除链表尾端（最旧）的缓存数据。hash链表操作可直接定位key，无需历遍整个hash对象，故读写极快。缓存容量不再影响读写速度。*/  this.capacity = capacity || Number.MAX_VALUE;  this.data = {};  this.hash = {};  this.linkedList = {    length: 0,    head: null,    end: null  }  if (capacity <= 0) this.capacity = Number.MAX_VALUE;};CacheLRU.prototype.get = function(key) {  key = '_' + key;  var lruEntry = this.hash[key];  if (!lruEntry) return;  refresh(this.linkedList, lruEntry);  return JSON.parse(this.data[key].toString());};CacheLRU.prototype.put = function(key, value) {  key = '_' + key;  var lruEntry = this.hash[key];  if (value === undefined) return this;  if (!lruEntry) {    this.hash[key] = {key: key};    this.linkedList.length += 1;    lruEntry = this.hash[key];  }  refresh(this.linkedList, lruEntry);  this.data[key] = new Buffer(JSON.stringify(value));  if (this.linkedList.length > this.capacity) this.remove(this.linkedList.end.key.slice(1));  return this;};CacheLRU.prototype.remove = function(key) {  key = '_' + key;  var lruEntry = this.hash[key];  if (!lruEntry) return this;  if (lruEntry === this.linkedList.head) this.linkedList.head = lruEntry.p;  if (lruEntry === this.linkedList.end) this.linkedList.end = lruEntry.n;  link(lruEntry.n, lruEntry.p);  delete this.hash[key];  delete this.data[key];  this.linkedList.length -= 1;  return this;};CacheLRU.prototype.removeAll = function() {  this.data = {};  this.hash = {};  this.linkedList = {    length: 0,    head: null,    end: null  }  return this;};CacheLRU.prototype.info = function() {  var size = 0,    data = this.linkedList.head;  while (data){    size += this.data[data.key].length;    data = data.p;  }  return {    capacity: this.capacity,    length: this.linkedList.length,    size: size  };};// 更新链表，把get或put方法操作的key提到链表head，即表示最新function refresh(linkedList, entry) {  if (entry != linkedList.head) {    if (!linkedList.end) {      linkedList.end = entry;    } else if (linkedList.end == entry) {      linkedList.end = entry.n;    }    link(entry.n, entry.p);    link(entry, linkedList.head);    linkedList.head = entry;    linkedList.head.n = null;  }}// 对两个链表对象建立链接，形成一条链function link(nextEntry, prevEntry) {  if (nextEntry != prevEntry) {    if (nextEntry) nextEntry.p = prevEntry;    if (prevEntry) prevEntry.n = nextEntry;  }}module.exports = CacheLRU;// test:/*var user = new CacheLRU(5);user.put('user1', {name:'admin', age: 30});user.put('user2', {name:'user', age: 31});user.put('user3', {name:'guest', age: 32});user.put('user4', {name:'guest', age: 34});user.put('user5', {name:'guest', age: 35});console.log(user.get('user1'));console.log(user.get('user2'));console.log(user.get('user3'));user.put('user6', {name:'guest', age: 36});console.log(user.info());*/