Question

There appears to be a limit on the number of concurrent scripts for a php session. I say session and not IP / client because I can start up another browser and load the second script. Is there a parameter limiting to one concurrent script?

You have to wait for one to complete before the other one starts loading.

Answer 1

The default session handler uses files, and will lock the session file for the duration of the request. If you have a long-running script, then you should force it to relinquish the session lock by doing a session_write_close() before entering the “long running” part of the script.

You can always re-open the session with session_start() again later on, if you need to modify session data after the long-running portion completes.