访问MemoryCache是​​否会创建副本? [英] Does accessing MemoryCache create a copy?

问题描述

我有这样的缓存服务:

public interface ICacheService {
    T Get<T>(string cacheID, Func<T> getItemCallback, int cacheMinutes = 5) where T : class;
}

public class MemoryCacheService : ICacheService {
    public T Get<T>(string cacheId, Func<T> getItemCallback, int cacheMinutes = 5) where T : class {
        T item = MemoryCache.Default.Get(cacheId) as T;
        if (item == null) {
            item = getItemCallback();
            MemoryCache.Default.Add(cacheId, item,
                new CacheItemPolicy {AbsoluteExpiration = DateTime.Now.AddMinutes(cacheMinutes)});
        }
        return item;
    }
}

并按以下方式检索:

var result = _cache.Get("mylist", () => _database.Fetch<MyList>().AsQueryable(), 600);

该列表很大，并且在每个击键提前键入下拉列表中经常访问.而且查询条件也是动态的，例如

The list is large and accessed frequently in a per keystroke type-ahead dropdown. And the query condition is also dynamic, like

if (this) result = result.Where(x=> this ...)
if (that) result = result.Where(x=> that ...)
finally result.ToList() 

我想知道，每次我从缓存访问列表时，系统是否在开始构建linq查询之前创建数据的副本?如果是这样，那就像按击键复制一样，效率不高.还是因为我正在检索AsQueryable并构建linq而推迟了查询?

I wonder, every time I access the list from cache, does the system create a copy of the data before start building linq query? If so, it's like copy-per-keystroke, not very efficient. Or does the it deferred the query because I'm retrieving AsQueryable and build linq?

还有更好的选择吗?谢谢

Any better alternatives? Thanks

推荐答案

否，MemoryCache不会复制.基本上，您将对某个对象实例的引用存储在缓存中，这就是您访问缓存中的项时所获得的.

No, MemoryCache does not make a copy. You basically store a reference to some object instance in the cache, and that is what you get back when you access an item in the cache.

我没有正式的文档链接，但是在实践中发现了困难的方式"，在那儿，我不小心使用了我返回的引用(不复制它)来修改了缓存的对象.

I don't have a formal documentation link, but found out the "hard way" in practice, where I accidentally modified the cached object by just using the reference I got back (without copying it).

另外，研究参考源( http://referencesource.microsoft.com )显示没有参考源.自动复制.

Also, studying the reference sources (http://referencesource.microsoft.com) shows that there is no automatic copying happening.

根据您的应用程序和需求，您可能想要确保缓存的类型实际上是设计不变的.

Depending on your application and needs, you might to want sure that the types you cache are actually immutable by design.

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