kubernetes client-go之expiration_cache实现带过期时间的缓存

灰太狼 2022-12-05 10:23 132阅读 0赞

client-go中带过期时间的cache实现,具体在：client-go\\tools\\cache\\expiration\_cache.go  
cache包下有各种数据结构的实现。本节看一下NewTTLStore创建并返回带有TTLPolicy的ExpirationCache实现：

package main
    
    import (
    	"k8s.io/client-go/tools/cache"
    	"log"
    	"time"
    )
    
    func stringKeyFunc(obj interface{ }) (string, error) { 
    	key := obj.(string)
    	return key, nil
    }
    
    func main() { 
    	sto := cache.NewTTLStore(stringKeyFunc, 5*time.Second)
    	sto.Add("key1")
    
    	time.Sleep(2 * time.Second)
    
    	item, exists, err := sto.Get("key1")
    	log.Printf("2s item: %v, exists: %v, err: %v", item, exists, err)
    
    	for { 
    		time.Sleep(7 * time.Second)
    		item, exists, err := sto.Get("key1")
    		log.Printf("time: %v item: %v, exists: %v, err: %v", time.Now(), item, exists, err)
    	}
    }

部分输出如下：

2020/09/09 21:04:51 2s item: key1, exists: true, err: <nil>
    2020/09/09 21:04:58 time: 2020-09-09 21:04:58.8331777 +0800 CST m=+9.134970501 item: <nil>, exists: false, err: <nil>
    2020/09/09 21:05:05 time: 2020-09-09 21:05:05.8332772 +0800 CST m=+16.135070001 item: <nil>, exists: false, err: <nil>

可以看到5s之后exists为false。  
具体实现为：  
每次Get的时候都会执行getOrExpire方法，getOrExpire如果过期，则会将其删除。当且仅当它尚未过期时才从timestampedEntry中检索对象。它在删除过程中拥有写锁定。

// getOrExpire retrieves the object from the timestampedEntry if and only if it hasn't
    // already expired. It holds a write lock across deletion.
    func (c *ExpirationCache) getOrExpire(key string) (interface{ }, bool) { 
    	// Prevent all inserts from the time we deem an item as "expired" to when we
    	// delete it, so an un-expired item doesn't sneak in under the same key, just
    	// before the Delete.
    	c.expirationLock.Lock()
    	defer c.expirationLock.Unlock()
    	timestampedItem, exists := c.getTimestampedEntry(key)
    	if !exists { 
    		return nil, false
    	}
    	if c.expirationPolicy.IsExpired(timestampedItem) { 
    		klog.V(4).Infof("Entry %v: %+v has expired", key, timestampedItem.obj)
    		c.cacheStorage.Delete(key)
    		return nil, false
    	}
    	return timestampedItem.obj, true
    }