<?php

     class session

     {

         private static $handle = null;

         private static $ip = null;

         private static $lifetime = null;

         private static $time = null;

         static function init($pdo)

         {

             self::$handle = $pdo;

             self::$ip = !empty($_SERVER["REMOTE_ADDR"]) ? $_SERVER["REMOTE_ADDR"] : "unknow";

             self::$lifetime = ini_get('session.gc_maxlifetime');

             self::$time = time();

         }

         static function start($pdo)

         {

             self::init($pdo);

             session_set_save_handler(

                 array(__CLASS__,'open'),

                 array(__CLASS__,'close'),

                 array(__CLASS__,'read'),

                 array(__CLASS__,'write'),

                 array(__CLASS__,'destroy'),

                 array(__CLASS__,'gc')

             );

             session_start();

         }

         public static function open($path, $name)

         {

             return true;

         }

         public static function close()

         {

             return true;

         }

         public static function read($PHPSESSID)

         {

             $sql = "select * from session where PHPSESSID = ?";

             $smit = self::$handle->prepare($sql);

             $smit->execute(array($PHPSESSID));

             if(!$result = $smit->fetch(PDO::FETCH_ASSOC))

             {

                 return '';

             }

             if(self::$ip != $result['client_ip'])

             {

                 self::destroy($PHPSESSID);

                 return '';

             }

             if( ($result['update_time'] + self::$lifetime) < self::$time)

             {

                 self::destroy($PHPSESSID);

                 return '';

             }

             return $result['data'];

         }

         public static function write($PHPSESSID,$data)

         {

             $sql = "select * from session where PHPSESSID = ?";

             $stmt = self::$handle->prepare($sql);

             $stmt->execute(array($PHPSESSID));

             if($result = $stmt->fetch(PDO::FETCH_ASSOC))

             {

                 if($result['data'] != $data || self::$time-30 > $result['update_time'])

                 {

                     $sql="update session set update_time = ?, data =? where PHPSESSID = ?";

                     $stmt = self::$handle->prepare($sql);

                     $stmt->execute(array(self::$time,$data,$PHPSESSID));

                 }

             }else

             {

                 if(!empty($data))

                 {

                     $sql="insert into session(PHPSESSID, update_time, client_ip, data) values(?,?,?,?)";

                     $sth = self::$handle->prepare($sql);

                     $sth->execute(array($PHPSESSID,self::$time,self::$ip,$data));

                 }

             }

             return true;

         }

         public static function destroy($PHPSESSID)

         {

             $sql = "delete from session where PHPSESSID = ?";

             $sth = self::$handle->prepare($sql);

             $sth->execute(array($PHPSESSID));

             return true;

         }

         public static function gc($lifetime)

         {

             $sql = "delete from session where update_time < ?";

             $stmt=self::$handler->prepare($sql);

             $stmt->execute(array(self::$time-self::$lifetime));

             return true;

         }

     }

     try{

         $pdo = new PDO("mysql:host=localhost;dbname=test", "root" ,"");

     }catch(PDOException $e)

     {

         echo $e->getMessage();

     }

     session::start($pdo);