Looks like you need a separate program (a "daemon") to process the data. Keep it running in the server computer, checking for new data, and make it write appropriate "status" files. Your CGI program will only "monitor" what the "daemon" is doing.

I've used this approach some times under Windows, I think it is the easier (and maybe the best) approach.

If you let the CGI program do all the processing, you may run out of server processes and your clients will get "500 server error" because they can't connect until everything is done.

such as onLoad

Looks like Activestate perl has support for that, but you must have installed on the client side.