c# - How do I clear a System.Runtime.Caching.MemoryCache

Question

I use a System.Runtime.Caching.MemoryCache to hold items which never expire. However, at times I need the ability to clear the entire cache. How do I do that?

I asked a similar question here concerning whether I could enumerate the cache, but that is a bad idea as it needs to be synchronised during enumeration.

I've tried using .Trim(100) but that doesn't work at all.

I've tried getting a list of all the keys via Linq, but then I'm back where I started because evicting items one-by-one can easily lead to race conditions.

I thought to store all the keys, and then issue a .Remove(key) for each one, but there is an implied race condition there too, so I'd need to lock access to the list of keys, and things get messy again.

I then thought that I should be able to call .Dispose() on the entire cache, but I'm not sure if this is the best approach, due to the way it's implemented.

Using ChangeMonitors is not an option for my design, and is unnecassarily complex for such a trivial requirement.

So, how do I completely clear the cache?

Answer 1

I was struggling with this at first. MemoryCache.Default.Trim(100) does not work (as discussed). Trim is a best attempt, so if there are 100 items in the cache, and you call Trim(100) it will remove the ones least used.

Trim returns the count of items removed, and most people expect that to remove all items.

This code removes all items from MemoryCache for me in my xUnit tests with MemoryCache.Default. MemoryCache.Default is the default Region.

foreach (var element in MemoryCache.Default)
{
    MemoryCache.Default.Remove(element.Key);
}