Asp – What’s the difference between recycling an app pool manually vs automatically

Classic mode (the only mode in IIS6 and below) is a mode where IIS only works with ISAPI extensions and ISAPI filters directly. In fact, in this mode, ASP.NET is just an ISAPI extension (aspnet_isapi.dll) and an ISAPI filter (aspnet_filter.dll). IIS just treats ASP.NET as an external plugin implemented in ISAPI and works with it like a black box (and only when it's needs to give out the request to ASP.NET). In this mode, ASP.NET is not much different from PHP or other technologies for IIS.

Integrated mode, on the other hand, is a new mode in IIS7 where IIS pipeline is tightly integrated (i.e. is just the same) as ASP.NET request pipeline. ASP.NET can see every request it wants to and manipulate things along the way. ASP.NET is no longer treated as an external plugin. It's completely blended and integrated in IIS. In this mode, ASP.NET HttpModules basically have nearly as much power as an ISAPI filter would have had and ASP.NET HttpHandlers can have nearly equivalent capability as an ISAPI extension could have. In this mode, ASP.NET is basically a part of IIS.

The following might be a little bit of a hack but you could use the application Cache to figure it out. Everytime a page loads you could check the cache for a specific key, if the key doesn't exist then you can consider it a 'recycle' and then add the key. Not the best method but might just work for what you need.

Eg. In your base page's Page_Load or somewhere that will run with every request, you could do the following:

if (HttpContext.Current.Cache["RecycleCheck"] != null)
{ 
    // Add flag to cache
    HttpContext.Current.Cache.Insert("RecycleCheck", "1", null,
        DateTime.UtcNow.AddDays(2),  // 2 days (most will recycle by then)
        System.Web.Caching.Cache.NoSlidingExpiration);

    // Do what you need because a recycle has happened
}

This method will not pick it up as the recycle happens. It will only identify a recycle on the first request after the recycle.

The Application_Start would be the most reliable place to do this but it suffers from the same issue as the hack with the fact that it happens after the recycle on the first request.