how to synchronize multiple requests from a client in php
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i use xampp with apache php server

i send request A to the server and keep it busy. then before the server finish the execution i send another immediate request B. but the server won't response to B until it finish the previous execution requested by A, make B on client side keep waiting. so i expect that the server doesn't automatically multithread the request came from a client. my question is

 1. is that
    
     the client is meant to receive the response of previous request before the
    next request can be sent? i try to set the ajax to synchronous and it still doesnt work
    
     OR 
    
     we can use php multithreading feature to deal with it


 2. if there is a way, can we share the resource among the requests? let say req A put some value into $_SESSION and req B want to read it