PHP - Multiple scripts at once (AJAX) -

after asking this question, pointed on right direction of not being able execute second script @ if 1 running.

i make apps rely on execution of ajax calls php pages, , today found trying write on file fwrite() on php script , trying read same file fread() (to progress feedback) on ajax call ended in the second script being executed when first 1 had finished.

even trying echo simple "hello" (echo "hello"; exit;) not show nothing on page until first script finished.

so, i'm asking: normal configuration? same on every installation of php default? configuration on php.ini that can change?

or has server (in case, microsoft iis 10)? can shed light on how able execute multiple php scripts on different ajax calls at once (or before others finish)?

i know i'm not giving information settings of context, don't know neither into.

thank time , help!

as luis said write-lock on file you're trying modify. possibility if you're using sessions use files (rather database), or framework uses file-based-sessions - behavior result of session-locking. money on luis' answer though - should using database rather file unless have solid reason not to.