我在Microsoft.Extensions.Caching.Memory.MemoryCache中设置了具有滑动过期的缓存项.
我想在每次缓存项到期时触发回调,但在我查询缓存中过期的缓存项之前,不会触发回调.
我想在每次缓存项到期时触发回调,但在我查询缓存中过期的缓存项之前,不会触发回调.
这是代码:
using System; using Microsoft.Extensions.Caching.Memory; namespace Memcache { public class Program { private static MemoryCache _cache; private static int _cacheExpSecs; public static void Main(string[] args) { _cache = new MemoryCache(new MemoryCacheOptions()); _cacheExpSecs = 2; var cacheEntryOptions = new MemoryCacheEntryOptions() .SetSlidingExpiration(TimeSpan.FromSeconds(_cacheExpSecs)) .RegisterPostevictionCallback(callback: evictionCallback); _cache.Set(1,"One",cacheEntryOptions); _cache.Set(2,"Two",cacheEntryOptions); var autoEvent = new System.Threading.AutoResetEvent(false); System.Threading.Timer timer = new System.Threading.Timer(checkCache,autoEvent,1000,6000); Console.Read(); } private static void checkCache(Object o) { if(_cache.Get(1)!=null) { Console.WriteLine(string.Format(@"checkCache: Cache with key {0} will be removed manually and will trigger the callback.",1)); _cache.Remove(1); } else { Console.WriteLine(string.Format("checkCache: Cache with key {0} is expired.",1)); } if(_cache.Get(2) != null) { Console.WriteLine(string.Format("checkCache: Cache with key {0} will expire in {1} seconds,but won't trigger the callback until we check it's value again.",2,_cacheExpSecs)); } else { Console.WriteLine(string.Format("checkCache: Cache with key {0} is expired.",2)); } } private static void evictionCallback(object key,object value,evictionReason reason,object state) { Console.WriteLine(); Console.WriteLine("/*****************************************************/"); Console.WriteLine(string.Format("/* evictionCallback: Cache with key {0} has expired. */",key)); Console.WriteLine("/*****************************************************/"); Console.WriteLine(); } } }
解决方法
这种情况正在发生,因为在您查询该项目并检查到期时,该项目不会被逐出
(来自MemoryCacheStore.Get(MemoryCacheKey key)
的来源)
internal MemoryCacheEntry Get(MemoryCacheKey key) { MemoryCacheEntry entry = _entries[key] as MemoryCacheEntry; // has it expired? if (entry != null && entry.UtcAbsExp <= DateTime.UtcNow) { Remove(key,entry,CacheEntryRemovedReason.Expired); entry = null; } // update outside of lock UpdateExpAndUsage(entry); return entry; }
(来自TrimInternal(int percent)
的来源)
/*SNIP*/ trimmedOrExpired = _expires.FlushExpiredItems(true); if (trimmedOrExpired < toTrim) { trimmed = _usage.FlushUnderUsedItems(toTrim - trimmedOrExpired); trimmedOrExpired += trimmed; } /*SNIP*/
如果您的系统当前内存不足以触发修剪,那么唯一可以驱逐项目的时间是尝试检索它们的时间.
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