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Question

In a custom razor engine, derived from RazorViewEngine, I've spotted what I think is unstable code:

    public override ViewEngineResult FindView(ControllerContext controllerContext, string viewName, string masterName, bool useCache)
    {
        ViewLocationFormats = AddViewDynamicFormat(controllerContext, viewName).ToArray();
        AreaViewLocationFormats = AddAreaViewDynamicFormat(controllerContext, viewName).ToArray();
        return base.FindView(controllerContext, viewName, masterName, useCache);
    }

My concern is that when two requests are being processed "at the same time," the first will set the location formats as it needs, but before it can use them - the second threaded request might have a chance to set the location formats a different way. The rest gets ugly.

Is this a valid concern? Said differently, does ASP.NET MVC guarantee that the Razor View engine will handle exactly one request at a time? I doubt that is the case.

Likewise, if there was one razor view engine object per request, then this would be ok. But I also don't believe that is the case.

UPDATE I have confirmed that this is a race condition. I have also found an article showing a dynamic expansive razor search example , which solves the problem without a race condition (though I still wonder if it has a caching issue).

Answer 1

Are ViewLocationFormats and AreaViewLocationFormats virtual? If so, you can put that value in the HttpContext.Current.Items collection and retrieve it from the overridden properties.

Answer 2

I'm nearly positive that the RazorViewEngine isn't meant to be modified at run-time, but merely configured in Global.asax Application_Start. I believe the RazorViewEngine instance exists for the life of the App Domain after startup.

If you need to add additional ViewLocationFormats or AreaViewLocationFormats do it in Application_Start. Application_Start is guaranteed to run only once per App Domain.