Limit one instance per user?

[ZootSuitRyan]

Has anyone created a way that one can only have one open ImageMagick instance active at one time? I am getting server oops (restarts) from users stopping/refreshing an upload form and repeating the process. My first thought is to use $_SESSION as the class variable and to test it's presence or value. I sure there's a better way and some expert has experience with this.

[anthony]

This is a web service usage limiting technique and has nothing to do with IM.
Usually it is done by session id's so that new requests from one user kills off, or otherwise controls older requests.