问题
I understand that in order for a ASP.Net handler to support session state you need to implement both IHttpHandler and IRequireSessionState, but why isn't session state provided by default? If for performance reasons, then wouldn't it be better to have an interface like IDoesNotRequireSessionState?
回答1:
Its because the session is block the asynchronous operations, and the handle is usually used for long time operations, like the making and download of a file - if you keep the session on long time operation you block the rest of your pages.
Also the handle is made with the idea of the minimum required to get a response.
About the session lock:
Web app blocked while processing another web app on sharing same session
jQuery Ajax calls to web service seem to be synchronous
ASP.NET Server does not process pages asynchronously
Replacing ASP.Net's session entirely
回答2:
If for performance reasons, then wouldn't it be better to have an interface like IDoesNotRequireSessionState?
Absolutely not, because then everybody implementing a handler must know about the existence of this interface. An HTTP handler is the fastest in terms of performance you might ever get from ASP.NET. So if you want to pollute it with crap like session then you'd better do it explicitly, and taking full responsibility of doing so, by implementing some interface that you should know about.
来源：https://stackoverflow.com/questions/16469673/why-dont-asp-net-handlers-support-session-by-default