Question

What whould be the best way to prevent multiple users on a page?

For example if a user is at the page “Home.aspx”, no other users should be allowed to go there.

I’m using asp.net on the server and the js-frameword jQuery on the client side.

Answer 1

The easy part is only allowing one user to access a page. You can for example store a session id in an application variable to keep track of who’s on the page.

The hard part is to know when the user leaves the page. The HTTP protocol only handles requests, so the server only knows when a user enters the page. There is no concept of “being on” a page in the protocol.

You can use the onunload event in client code to catch when a user goes somewhere else, however this will not always work. If the user loses the internet connection, there is no way to communicate back to the server that the user leaves the page. If the browser or computer crashes, there will naturally be no onunload event.

You can keep requesting data from the server, by for example reloading an image on the page. That way the server can know if the user is still on the page at certain intervals. However, if the user loses the internet connection, the server will think that the user has left, while the user thinks that he/she is still on the page.

Another problem is browser history and cache. A user might leave the page, then go back to the page again. You have to make sure that the page is not cached, or the browser will just use the cached page and the server has no idea that the user thinks that he/she is on the page again.