问文件会话:是否总是生成？

EN

function session_start() {
     if (isset($_COOKIE[ini_get('session.name')])) {
           // session ID was sent from client, get it
           $id = $_COOKIE[ini_get('session.name')];
     } else {
           // no session ID received, generate one
           $id = generate_new_id();
           setcookie(ini_get('session.name'), $id, ......);
     }
     $session_file = ini_get('session.save_path') . '/sess_' . $id;
     if (file_exists($session_file)) {
        // found a session file, load it
        $raw_data = file_get_contents($session_file);
        $_SESSION = unserialize($raw_data);
     } else {
        // brand new session, create file and initialize empty session
        file_put_contents($session_file, serialize(array());
        $_SESSION = array();
     }
     // lock the session file to prevent parallel overwrites.
     flock($session_file);
}