Session locking - non-blocking read-only sessions in PHP

session-readonly.php

<?php
    function session_readonly(){
        if(version_compare(PHP_VERSION, '7.0.0') >= 0){
            session_start(array('read_and_close' => true));
        } else {
            $session_name = preg_replace('/[^\da-z]/i', '', $_COOKIE[session_name()]);
            $session_data = file_get_contents(session_save_path() . '/sess_' . $session_name);

            $return_data = array();
            $offset = 0;

            while($offset < strlen($session_data)){
                if(!strstr(substr($session_data, $offset), '|')){
                    break;
                }

                $pos = strpos($session_data, '|', $offset);
                $num = $pos - $offset;
                $varname = substr($session_data, $offset, $num);
                $offset += $num + 1;
                $data = unserialize(substr($session_data, $offset));
                $return_data[$varname] = $data;
                $offset += strlen(serialize($data));
            }

            $_SESSION = $return_data;
        }
    }