Use Lock And Unlock, Or Not

I have a single asp page that interacts with the client via the post method. Four arrays are created and passed back to the client when the form is submitted.

Question, when the form is being processed server side, should I be locking and unlocking aplication variables and arrays? or can I declare ordinary variables and arrays because its a single page? will ordinary variables get changed by multiple clients on a single page? Im confused what has to be locked down! and what does not.