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/**
* LRU (Least Recently Used) 缓存实现
* 用于缓存解密结果，提高性能同时控制内存使用
*/
class LRUCache {
constructor(maxSize = 500) {
this.maxSize = maxSize
this.cache = new Map()
this.hits = 0
this.misses = 0
this.evictions = 0
this.lastCleanup = Date.now()
this.cleanupInterval = 5 * 60 * 1000 // 5分钟清理一次过期项
}
/**
* 获取缓存值
* @param {string} key - 缓存键
* @returns {*} 缓存的值，如果不存在则返回 undefined
*/
get(key) {
// 定期清理
if (Date.now() - this.lastCleanup > this.cleanupInterval) {
this.cleanup()
}
const item = this.cache.get(key)
if (!item) {
this.misses++
return undefined
}
// 检查是否过期
if (item.expiry && Date.now() > item.expiry) {
this.cache.delete(key)
this.misses++
return undefined
}
// 更新访问时间，将元素移到最后（最近使用）
this.cache.delete(key)
this.cache.set(key, {
...item,
lastAccessed: Date.now()
})
this.hits++
return item.value
}
/**
* 设置缓存值
* @param {string} key - 缓存键
* @param {*} value - 要缓存的值
* @param {number} ttl - 生存时间（毫秒），默认5分钟
*/
set(key, value, ttl = 5 * 60 * 1000) {
// 如果缓存已满，删除最少使用的项
if (this.cache.size >= this.maxSize && !this.cache.has(key)) {
const firstKey = this.cache.keys().next().value
this.cache.delete(firstKey)
this.evictions++
}
this.cache.set(key, {
value,
createdAt: Date.now(),
lastAccessed: Date.now(),
expiry: ttl ? Date.now() + ttl : null
})
}
/**
* 清理过期项
*/
cleanup() {
const now = Date.now()
let cleanedCount = 0
for (const [key, item] of this.cache.entries()) {
if (item.expiry && now > item.expiry) {
this.cache.delete(key)
cleanedCount++
}
}
this.lastCleanup = now
if (cleanedCount > 0) {
console.log(`🧹 LRU Cache: Cleaned ${cleanedCount} expired items`)
}
}
/**
* 清空缓存
*/
clear() {
const { size } = this.cache
this.cache.clear()
this.hits = 0
this.misses = 0
this.evictions = 0
console.log(`🗑️ LRU Cache: Cleared ${size} items`)
}
/**
* 获取缓存统计信息
*/
getStats() {
const total = this.hits + this.misses
const hitRate = total > 0 ? ((this.hits / total) * 100).toFixed(2) : 0
return {
size: this.cache.size,
maxSize: this.maxSize,
hits: this.hits,
misses: this.misses,
evictions: this.evictions,
hitRate: `${hitRate}%`,
total
}
}
/**
* 打印缓存统计信息
*/
printStats() {
const stats = this.getStats()
console.log(
`📊 LRU Cache Stats: Size: ${stats.size}/${stats.maxSize}, Hit Rate: ${stats.hitRate}, Hits: ${stats.hits}, Misses: ${stats.misses}, Evictions: ${stats.evictions}`
)
}
}
module.exports = LRUCache
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