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.

So, try this instead, which doesn’t change what it loops over:

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); } 

That being said, really, you should try to use cache dependencies to have the invalid cache entries cleared automatically for you, and then all this becomes unnecessary.