prevent multiple simultaneous page editors

[eluser]MaxPar[/eluser]
I'm sure that this question has been answered multiple times, but I was unable to find it in the forums.

I developed a custom CMS system, and I need to manage what happens when multiple people try to edit the page at once. I wouldn't want one person to make a bunch of edits and submit them, and then have another person unintentionally overwrite all their hard work.

I think the easiest thing to do is probably just to allow only one person to edit a page at a time, but I'm not exactly sure how to go about doing this- and I know it's been done before, so I thought it would be wise to ask.

My current best guess is that I should keep track of all the pages that are being edited (in a database, with three columns: page name, time started editing and user cookie info). Every time someone wants to edit a page, I check to make sure it isn't already open in the database.

Any thoughts? Is there already a library that would help with this?