Can I iterate over the .NET4 MemoryCache?

Question

I'm using the cache provided by System.Runtime.Caching.MemoryCache.

I'd like to enumerate over the cache's items so that I can invalidate (evict then reload) items as such

foreach (var item in MemoryCache.Default) { item.invalidate() }

But the official docs found here state:

!Important: Retrieving an enumerator for a MemoryCache instance is a resource-intensive and blocking operation. Therefore, the enumerator should not be used in production applications.

Surely there must be a simple and efficient way to iterate over the cache's items?

Answer 1

Consider using ChangeMonitors, which allow you to automatically evict stale entries when certain conditions are met.

See Is there some sort of CacheDependency in System.Runtime.Caching?

This is similar to System.Web.Caching CacheDependencys, who allow you to evict entries when files or other cache entries change.

Answer 2

Suggestions made so far have been great, but my need is still as stated: to iterate over the cache's items. It seems like such a simple task, and I expect that the cache internally has some sort of list structure anyway. The docs and the feature set for MemoryCache are wanting.

So as discussed above, I've added a list to my cache adapter class, which holds a reference to each item I place in the cache. If I need to iterate over the cache--not just for invalidation, but for gathering statistics, etc.--then I iterate over my list.

If the number of items placed in the cache does not change, then this is a reasonable solution. If the number does change, then you need to insert/remove via the adapter class, so as to keep the list in sync with the actual cache. Messy but it works, and avoids the perf penalties alluded to in the docs.

Hopefully MemoryCache cache provider will be fleshed-out in the next platform release.

Answer 3

In 2014,

This is the correct way to get all the items:

Dim AllItems = MemoryCache.Default.Select(Of ItemType)(Function(O) O.Value)

Hope this helps someone.