Normally i have a static class that reads and writes to HttpContext.Current.Cache
However since adding threading to my project, the threads all get null reference exceptions when trying to retrieve this object.
Is there any other way i can access it, workarounds or another cache i can use?
The System.Web.Cache object itself is thread safe.
The issue is how to obtain a reference to it in a way that works throughout your application. HttpContext.Current returns null unless it is called on a thread that is handling an ASP.NET request. An alternative way to get the Cache is through the static property System.Web.HttpRuntime.Cache. This will avoid the problems with the HttpContext.
If your project is an ASP.NET project, then it was multithreaded even before you "added threading".
Check to see if HttpContext.Current is non-null before referencing HttpContext.Current.Cache.
Also, please post the complete exception you're receiving, and show us the code that references the cache.
System.Web.Caching.Cacheis thread-safe. Nolockneeded here.HttpContext.Currentis thread-local and read-only so basically, yes, it is thread-safe, although it's also wrong for the reasons pointed out by binarycoder below.HttpRuntime.Cacheis the same, but globally-accessible; it's not synchronized but it's also immutable, so you don't need to use any explicit locks. In fact, the ASP.NETHttpContext.Cacheis just a reference toHttpRuntime.Cache, so it has to be thread-safe, otherwise ASP.NET requests would steamroll each other constantly.