Repopulate Cache every 30 mintues with new data

Question

I'm trying to build a process that will repopulate an item that was inserted into cache every 30 minutes. I inserted the item into Cached to expire after 30 minutes. I setup a delegate (http://msdn.microsoft.com/en-us/library/system.web.caching.cacheitemremovedcallback(v=VS.90).aspx) to be called when the cached item expired. My goal was when the delegate was called was to rebuild the item and insert it back into cached.

The issue I found with the MSDN article above was that it was using a holding the page instance open until the delegate was called. Instead of had it call another class that was static (vb shared). This caused a different problem -- the delegate lost context. When I tried to add back into the cache the HttpContext.Current was null.

Is there a way I can repopulate an item in cache every 30 minutes in ASP.NET without keeping page instances around? Note, I cannot use a sliding expiration date because the content will change.

Answer 1

Firstly, you know you could just repopulate the cache whenever you have a new request after the 30 minutes have expired. I mean why bother putting in the cache if you have no requests that need that data.

Secondly, we've had a similar need a while ago and anyway ... the basic ideea was:

1.Keep a reference to the App's cache so we can acces it from an async thread

    public static System.Web.Caching.Cache BackgroundCache;    
    public static System.Web.HttpServerUtility BackgroundServer;

then assign them in Global.asax's Application_Start

 BackgroundCache = System.Web.HttpContext.Current.Cache;
 BackgroundServer = System.Web.HttpContext.Current.Server;

2.Start a Timer also on Application_Start, that will run on an async thread every 30 mins.

3.Populate the cache from there using BackgroundCache and BackgroundServer