Not at all the same thing I admit, but the company I work for has a product that limits the number of transactions (per user) to 1. Where "transaction" is roughly equivalent to an HTTP request. So if you run a query that takes 30 seconds, get bored, open up a new tab to do something else in the product, your new tab will hang until the transaction in the previous tab has completed.

I hate it.

There is a special URL that will kill your running transaction. All of the engineers know it and have it bookmarked, but it's undocumented.