关于codeigniter即ci的session关闭浏览器不能自动失效的问题

/**

ci的session有很多问题，包括关闭浏览器不能失效，这是因为ci的session用cookie来保存的问题，除此之外就是unset_userdata函数有问题，我们可以重写sessio类，在application/library/文件夹下建立Session.php文件，写入如下code

*/

<?php if (!defined('BASEPATH')) exit('No direct script access allowed');
//> makes dw cs4 happy

/**
* Session class using native PHP session features and hardened against session fixation.
*
* @package CodeIgniter
* @subpackage Libraries
* @category Sessions
* @author Dariusz Debowczyk, Matthew Toledo
* @link http://www.philsbury.co.uk/index.php/blog/code-igniter-sessions/
*/
class CI_Session {

var $flashdata_key = 'flash'; // prefix for "flash" variables (eg. flash:new:message)

function CI_Session()
{
$this->object =& get_instance();
log_message('debug', "Native_session Class Initialized");
$this->_sess_run();
}

/**
* Regenerates session id
*/
function regenerate_id()
{
// copy old session data, including its id
$old_session_id = session_id();
$old_session_data = $_SESSION;

// regenerate session id and store it
session_regenerate_id();
$new_session_id = session_id();

// switch to the old session and destroy its storage
session_id($old_session_id);
session_destroy();

// switch back to the new session id and send the cookie
session_id($new_session_id);
session_start();

// restore the old session data into the new session
$_SESSION = $old_session_data;

// update the session creation time
$_SESSION['regenerated'] = time();

// session_write_close() patch based on this thread
// http://www.codeigniter.com/forums/viewthread/1624/
// there is a question mark ?? as to side affects

// end the current session and store session data.
session_write_close();
}

/**
* Destroys the session and erases session storage
*/
function destroy()
{
unset($_SESSION);
if ( isset( $_COOKIE[session_name()] ) )
{
setcookie(session_name(), '', time()-42000, '/');
}
session_destroy();
}

/**
* Alias for destroy(), makes 1.7.2 happy.
*/
function sess_destroy()
{
$this->destroy();
}

/**
* Reads given session attribute value
*/
function userdata($item)
{
if($item == 'session_id'){ //added for backward-compatibility
return session_id();
}else{
return ( ! isset($_SESSION[$item])) ? false : $_SESSION[$item];
}
}

/**
* Sets session attributes to the given values
*/
function set_userdata($newdata = array(), $newval = '')
{
if (is_string($newdata))
{
$newdata = array($newdata => $newval);
}

if (count($newdata) > 0)
{
foreach ($newdata as $key => $val)
{
$_SESSION[$key] = $val;
}
}
}

/**
* Erases given session attributes
*/
function unset_userdata($newdata = array())
{
if (is_string($newdata))
{
$newdata = array($newdata => '');
}

if (count($newdata) > 0)
{
foreach ($newdata as $key => $val)
{
unset($_SESSION[$key]);
}
}
}

/**
* Starts up the session system for current request
*/
function _sess_run()
{
session_start();

$session_id_ttl = $this->object->config->item('sess_expiration');

if (is_numeric($session_id_ttl))
{
if ($session_id_ttl > 0)
{
$this->session_id_ttl = $this->object->config->item('sess_expiration');
}
else
{
$this->session_id_ttl = (60*60*24*365*2);
}
}

// check if session id needs regeneration
if ( $this->_session_id_expired() )
{
// regenerate session id (session data stays the
// same, but old session storage is destroyed)
$this->regenerate_id();
}

// delete old flashdata (from last request)
$this->_flashdata_sweep();

// mark all new flashdata as old (data will be deleted before next request)
$this->_flashdata_mark();
}

/**
* Checks if session has expired
*/
function _session_id_expired()
{
if ( !isset( $_SESSION['regenerated'] ) )
{
$_SESSION['regenerated'] = time();
return false;
}

$expiry_time = time() - $this->session_id_ttl;

if ( $_SESSION['regenerated'] <= $expiry_time )
{
return true;
}

return false;
}

/**
* Sets "flash" data which will be available only in next request (then it will
* be deleted from session). You can use it to implement "Save succeeded" messages
* after redirect.
*/
function set_flashdata($newdata = array(), $newval = '')
{
if (is_string($newdata))
{
$newdata = array($newdata => $newval);
}

if (count($newdata) > 0)
{
foreach ($newdata as $key => $val)
{
$flashdata_key = $this->flashdata_key.':new:'.$key;
$this->set_userdata($flashdata_key, $val);
}
}
}


/**
* Keeps existing "flash" data available to next request.
*/
function keep_flashdata($key)
{
$old_flashdata_key = $this->flashdata_key.':old:'.$key;
$value = $this->userdata($old_flashdata_key);

$new_flashdata_key = $this->flashdata_key.':new:'.$key;
$this->set_userdata($new_flashdata_key, $value);
}

/**
* Returns "flash" data for the given key.
*/
function flashdata($key)
{
$flashdata_key = $this->flashdata_key.':old:'.$key;
return $this->userdata($flashdata_key);
}

/**
* PRIVATE: Internal method - marks "flash" session attributes as 'old'
*/
function _flashdata_mark()
{
foreach ($_SESSION as $name => $value)
{
$parts = explode(':new:', $name);
if (is_array($parts) && count($parts) == 2)
{
$new_name = $this->flashdata_key.':old:'.$parts[1];
$this->set_userdata($new_name, $value);
$this->unset_userdata($name);
}
}
}

/**
* PRIVATE: Internal method - removes "flash" session marked as 'old'
*/
function _flashdata_sweep()
{
foreach ($_SESSION as $name => $value)
{
$parts = explode(':old:', $name);
if (is_array($parts) && count($parts) == 2 && $parts[0] == $this->flashdata_key)
{
$this->unset_userdata($name);
}
}
}
}