Concurrent user notification

<?php
/**
 * PHP Grid Component
 *
 * @author Abu Ghufran <gridphp@gmail.com> - http://www.phpgrid.org
 * @version 1.5.2
 * @license: see license.txt included in package
 */

// include db config
include_once("../../config.php");

// set up DB
mysql_connect(PHPGRID_DBHOST, PHPGRID_DBUSER, PHPGRID_DBPASS);
mysql_select_db(PHPGRID_DBNAME);

// include and create object
include(PHPGRID_LIBPATH."inc/jqgrid_dist.php");

$grid = new jqgrid();

$opt["caption"] = "Data";
$grid->set_options($opt);

$e["on_update"] = array("update_client", null, true);
$grid->set_events($e);

function update_client($data)
{
    $str = "SELECT * FROM invheader WHERE id = {$data["id"]}";
    $rs = mysql_fetch_assoc(mysql_query($str));
    if ( strtotime($rs["invdate"]) > strtotime($data["params"]["invdate"]) )
        phpgrid_error('Already Edited, Kindly refresh grid!');

    // update new timestamp
    $data["params"]["invdate"] = date("Y-m-d H:i:s");

    // continue normal grid update ... by grid lib
}

$grid->table = "invheader";
$out = $grid->render("list1");
?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html>
<head>
    <link rel="stylesheet" type="text/css" media="screen" href="../../lib/js/themes/redmond/jquery-ui.custom.css"></link>
    <link rel="stylesheet" type="text/css" media="screen" href="../../lib/js/jqgrid/css/ui.jqgrid.css"></link>

    <script src="../../lib/js/jquery.min.js" type="text/javascript"></script>
    <script src="../../lib/js/jqgrid/js/i18n/grid.locale-en.js" type="text/javascript"></script>
    <script src="../../lib/js/jqgrid/js/jquery.jqGrid.min.js" type="text/javascript"></script>
    <script src="../../lib/js/themes/jquery-ui.custom.min.js" type="text/javascript"></script>
</head>
<body>
    <div style="margin:10px">
    <?php echo $out?>
    </div>
</body>
</html>