Go中實現Sieve快取

package main

import (
 <font>"fmt"
 "sync"
 "time"
)

// CacheItem represents an individual item in the cache<i>
type CacheItem struct {
 Value      interface{}
 Expiration int64 // Unix timestamp for expiration<i>
}

//SieveCache 表示篩選快取<i>
type SieveCache struct {
 store        sync.Map
 ttl          time.Duration
 sieveFilter  func(key string, value interface{}) bool //自定義過濾邏輯<i>
 cleanupTicker *time.Ticker
 stopCleanup  chan struct{}
}

// NewSieveCache 建立 SieveCache 的新例項<i>
func NewSieveCache(ttl time.Duration, sieveFilter func(key string, value interface{}) bool) *SieveCache {
 cache := &SieveCache{
  ttl:         ttl,
  sieveFilter: sieveFilter,
  stopCleanup: make(chan struct{}),
 }
 cache.cleanupTicker = time.NewTicker(ttl / 2) // Cleanup runs at half the TTL interval<i>
 go cache.cleanupExpiredItems()
 return cache
}

// 如果透過了篩選過濾器，則 Set 將新專案新增到快取中<i>
func (c *SieveCache) Set(key string, value interface{}) {
 if c.sieveFilter(key, value) {
  c.store.Store(key, CacheItem{
   Value:      value,
   Expiration: time.Now().Add(c.ttl).Unix(),
  })
 }
}

// Get retrieves an item from the cache if it exists and is not expired<i>
func (c *SieveCache) Get(key string) (interface{}, bool) {
 item, exists := c.store.Load(key)
 if !exists {
  return nil, false
 }

 cacheItem := item.(CacheItem)
 if time.Now().Unix() > cacheItem.Expiration {
  c.store.Delete(key)
  return nil, false
 }
 return cacheItem.Value, true
}

// Delete removes an item from the cache<i>
func (c *SieveCache) Delete(key string) {
 c.store.Delete(key)
}

//cleanupExpiredItems 定期從快取中刪除過期專案<i>
func (c *SieveCache) cleanupExpiredItems() {
 for {
  select {
  case <-c.cleanupTicker.C:
   c.store.Range(func(key, value interface{}) bool {
    cacheItem := value.(CacheItem)
    if time.Now().Unix() > cacheItem.Expiration {
     c.store.Delete(key)
    }
    return true
   })
  case <-c.stopCleanup:
   return
  }
 }
}

// Stop stops the cleanup goroutine<i>
func (c *SieveCache) Stop() {
 close(c.stopCleanup)
 c.cleanupTicker.Stop()
}

func main() {
 // 自定義篩選過濾器：僅快取長度 > 3 的字串<i>
 filter := func(key string, value interface{}) bool {
  str, ok := value.(string)
  return ok && len(str) > 3
 }

 //  建立一個具有 10 秒 TTL 的篩選快取 cache<i>
 cache := NewSieveCache(10*time.Second, filter)
 defer cache.Stop()

 // Add items to the cache<i>
 cache.Set("key1", "short")         // Won't be cached (length <= 3)<i>
 cache.Set("key2", "longerString") // Will be cached<i>

 // Retrieve items from the cache<i>
 if value, ok := cache.Get("key2"); ok {
  fmt.Println("Found key2:", value)
 } else {
  fmt.Println("key2 not found")
 }

 // 等待 11 秒測試過期<i>
 time.Sleep(11 * time.Second)
 if _, ok := cache.Get("key2"); !ok {
  fmt.Println("key2 expired")
 }
}