public function isThreadLocked($message_id)
{
$sql = 'SELECT message_thread FROM ' . $this->_threads_table . ' WHERE message_id = ?';
$thread = $this->_db->selectValue($sql, array($message_id));
return $this->_db->selectValue('SELECT locked FROM ' . $this->_threads_table . ' WHERE message_id = ?', array($thread));
}