login che salva le sessioni nel db ma non l elimina

[rocco.mod]

salve ragazzi volevo chiedervi un aiuto ho fatto un login con sessioni, e ho provato ad iserire una classe che salva le sessioni nel db, adesso succede che , la sessione la salva nel db, pero quando effettuo il logut non distrugge la sessione ,secondo voi cosa devo fare? questo e il logind

if($_POST['xxx']=="verific"){


if(!isset($_POST['login'])){$login="";}else{$login = trim($_POST['login']);}
if(!isset($_POST['pass'])){$pass="";}else{$pass = trim($_POST['pass']);}
if(!isset($login)or $login ==''){
echo"inserire illogin";
return;
}if(!isset($pass) or $pass==''){
echo"inserirela password";
}
else
{
$login = trim(addslashes($_POST['login']));
$pass = trim(addslashes($_POST['pass']));
echo  $pass."non criptata
";
$pass = md5($pass);
echo  $pass." criptata
";
$DB = new DB();
$DB->connect();
$controllo_dati_utente = mysql_query("select * from utenti where user = '$login' and pass = '$pass' and stato = 1 ");
if(@mysql_num_rows($controllo_dati_utente) !=1){
echo"nome non trovato";
}else{
$_SESSION['login']="$login";
echo"loggin effettuato con successo".$_SESSION['login'];
echo"
";
echo session_id();

}
}
} 

questa e la classe per salvare le sessioni nel db

class session {
    // session-lifetime
    var $lifeTime;
    // mysql-handle
    var $dbHandle;
    function open($savePath, $sessName) {
       // get session-lifetime
       $this->lifeTime = get_cfg_var("session.gc_maxlifetime");
       // open database-connection
       $dbHandle = @mysql_connect("localhost","root","maurizio");
       $dbSel = @mysql_select_db("test",$dbHandle);
       // return success
       if(!$dbHandle || !$dbSel)
           return false;
       $this->dbHandle = $dbHandle;
       return true;
    }
    function close() {
        $this->gc(ini_get('session.gc_maxlifetime'));
        // close database-connection
        return @mysql_close($this->dbHandle);
    }
    function read($sessID) {
        // fetch session-data
        $res = mysql_query("SELECT session_data AS d FROM ws_sessions
                            WHERE session_id = '$sessID'
                            AND session_expires > ".time(),$this->dbHandle);
        // return data or an empty string at failure
        if($row = mysql_fetch_assoc($res))
            return $row['d'];
        return "";
    }
    function write($sessID,$sessData) {
        // new session-expire-time
        $newExp = time() + $this->lifeTime;
        // is a session with this id in the database?
        $res = mysql_query("SELECT * FROM ws_sessions
                            WHERE session_id = '$sessID'",$this->dbHandle);
        // if yes,
        if(mysql_num_rows($res)) {
            // ...update session-data
            mysql_query("UPDATE ws_sessions
                         SET session_expires = '$newExp',
                         session_data = '$sessData'
                         WHERE session_id = '$sessID'",$this->dbHandle);
            // if something happened, return true
            if(mysql_affected_rows($this->dbHandle))
                return true;
        }
        // if no session-data was found,
        else {
            // create a new row
            mysql_query("INSERT INTO ws_sessions (
                         session_id,
                         session_expires,
                         session_data)
                         VALUES(
                         '$sessID',
                         '$newExp',
                         '$sessData')",$this->dbHandle);
            // if row was created, return true
            if(mysql_affected_rows($this->dbHandle))
                return true;
        }
        // an unknown error occured
        return false;
    }
    function destroy($sessID) {
        // delete session-data
        mysql_query("DELETE FROM ws_sessions WHERE session_id = '$sessID'",$this->dbHandle);
        // if session was deleted, return true,
        if(mysql_affected_rows($this->dbHandle))
            return true;
        // ...else return false
        return false;
    }
    function gc($sessMaxLifeTime) {
        // delete old sessions
        mysql_query("DELETE FROM ws_sessions WHERE session_expires < ".time(),$this->dbHandle);
        // return affected rows
        return mysql_affected_rows($this->dbHandle);
    }
}
$session = new session();
session_set_save_handler(array(&$session,"open"),
                         array(&$session,"close"),
                         array(&$session,"read"),
                         array(&$session,"write"),
                         array(&$session,"destroy"),
                         array(&$session,"gc"));