HttpRuntime Close does not remove items from the Cache as advertised.

Question

I've created my own cache manager for a web site I'm developing and I was looking to find the best way to clear the cache under certain circumstances.

I found many articles saying the proper way to clear the cache is to call HttpRuntime.Close()

However, in my unit tests setup I call the encapsulated function HttpRuntime.Close() and the cache is NOT being cleared out.

I expected it to perform something similar to

foreach (DictionaryEntry cacheItem in HttpRuntime.Cache)
{
    HttpRuntime.Cache.Remove(cacheItem.Key.ToString());
}

The foreach loop works great in my encapsulated function, but the Close() never works right.

Am I misunderstanding the purpose of HttpRuntime.Close() or is there something more sinister going on here?

Answer 1

Don't use Close, it does more than the docs say. And the docs also say not to use it while processing normal requests...

This is the reflected source of Close():

[SecurityPermission(SecurityAction.Demand, Unrestricted=true)]
public static void Close() {
    if (_theRuntime.InitiateShutdownOnce()) {
        SetShutdownReason(ApplicationShutdownReason.HttpRuntimeClose, "HttpRuntime.Close is called");
        if (HostingEnvironment.IsHosted) {
            HostingEnvironment.InitiateShutdown();
        } else {
            _theRuntime.Dispose();
        }
    }
}

Also, you cannot iterate over a collection and remove items from it at the same time, as this renders the enumeration invalid.

List<string> toRemove = new List<string>();
foreach (DictionaryEntry cacheItem in HttpRuntime.Cache) {
    toRemove.Add(cacheItem.Key.ToString());
}
foreach (string key in toRemove) {
    HttpRuntime.Cache.Remove(key);
}

But you should try to use cache dependencies to have the invalid cache entries cleared automatically for you...