Long Polling using PHP and JQuery

longpolling.php

<?php
include 'init.php';
if (!logged_in()){header('Location: index.php'); exit();}
include 'template/header.php';
?>

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.6.4/jquery.min.js" type="text/javascript" ></script>
<script src="http://cdn.jquerytools.org/1.2.6/jquery.tools.min.js"></script>
<style type="text/css" media="screen">
.msg{ background:#aaa;padding:.2em; border-bottom:1px #99FF99 solid}
.old{ background-color:#99FFCC;}
.new{ background-color:#A3FFD1;}
.error{ background-color:#992E36;}
</style>

<link rel="stylesheet" type="text/css" href="http://static.flowplayer.org/tools/css/standalone.css"/>
<link rel="stylesheet" type="text/css" href="http://static.flowplayer.org/tools/css/overlay-basic.css"/>

<script type="text/javascript" charset="utf-8">
var lastMessage;
    function addmsg(type, data){
        var msg = data.substring(0, data.length-5) + "<img id='ajax-loader' src='images/ajax-loader.gif'/><br/>";
        console.log(msg);
        $("#log").html(msg);
    }

   function waitForMsg(){
        /* This requests the url "msgsrv.php"
        When it complete (or errors)*/
        $.ajax({
            type: "GET",
            url: "getprogress.php",
            async: true, /* If set to non-async, browser shows page as "Loading.."*/
            cache: false,
            timeout:500, /* Timeout in ms */
            success: function(data){ /* called when request to barge.php completes */
                //if(data!=''){
                if( data.split('\r\n\r\n')[1] != 'Complete'){
                        addmsg("new", data); 
                        lastMessage=data; 
                        setTimeout('waitForMsg()',2000);
                }else{
                        
                        console.log(data);
                        $("#ajax-loader").replaceWith("");
                        $("#messages").append("<div class='msg new'>Resist has completed. Please wait for the plot.</div>");
                        //abort();
                }
                //}
            },
            error: function(XMLHttpRequest, textStatus, errorThrown){
                        //addmsg("error", textStatus + " (" + errorThrown + ")");
                        setTimeout(
                        'waitForMsg()', /* Try again after.. */
                        "15000"); /* milliseconds (15seconds) */
                },
                });
        };


  $(document).ready(function(){
        $("#start").show();
        $("#messages").hide();
        $("button").click(function(){   
                $("button").hide();
                $("#messages").show();
                $.post("process.php",{cmd:"start"});
                waitForMsg();
        });
        $("img[rel]").overlay();                
    });
    </script>

        <button >Start</button>

    <div id="messages">
        <div class="msg old">Stated RESIST</div>
        <div id='log' class='msg new'></div>
    </div>