php出现session_start()错误

<?php
    function my_session_start()
    {
        if (ini_get('session.use_cookies') && isset($_COOKIE['PHPSESSID'])) {
            $sessid = $_COOKIE['PHPSESSID'];
        } elseif (!ini_get('session.use_only_cookies') && isset($_GET['PHPSESSID'])) {
            $sessid = $_GET['PHPSESSID'];
        } else {
            session_start();
            return false;
        }

        if (!preg_match('/^[a-z0-9]{32}$/', $sessid)) {
            return false;
        }
        session_start();

        return true;
    }
?>

try {
   session_start();
} catch(ErrorExpression $e) {
   session_regenerate_id();
   session_start();
}

function my_session_start()
{
      $sn = session_name();
      if (isset($_COOKIE[$sn])) {
          $sessid = $_COOKIE[$sn];
      } else if (isset($_GET[$sn])) {
          $sessid = $_GET[$sn];
      } else {
          return session_start();
      }

     if (!preg_match('/^[a-zA-Z0-9,\-]{22,40}$/', $sessid)) {
          return false;
      }
      return session_start();
}

if ( !my_session_start() ) {
    session_id( uniqid() );
    session_start();
    session_regenerate_id();
}

<?php
    function my_session_start()
    {
        $sn = session_name();
        if (isset($_COOKIE[$sn])) {
            $sessid = $_COOKIE[$sn];
        } else if (isset($_GET[$sn])) {
            $sessid = $_GET[$sn];
        } else {
            session_start();
            return false;
        }

       if (!preg_match('/^[a-zA-Z0-9,\-]{22,40}$/', $sessid)) {
            return false;
        }
        session_start();

       return true;
    }
?>

$ok = @session_start();
if(!$ok){
session_regenerate_id(true); // replace the Session ID
session_start(); 
}