long polling (php+ajax)

longpolling.js

function waitForDisc(){
  $.ajax({
		type: "POST",
		url: "/longpolling.php",
		data: "timestamp="+timestamp_d+"&mid="+jt,
		async: true,
		cache: false,
		
		success: function(feed){
		
			var json = eval('('+feed+')');

			//do whatever you want with json

			setTimeout('waitForDisc()',1000);			
		},
		
		error: function(XMLHttpRequest, textStatus, errorThrown){
			alert("error: " + textStatus + " (waitForD error" + errorThrown + ")");
			setTimeout('waitForDisc()',15000);
		}
	});
}

longpolling.php

<?php

$mid = isset($_POST['mid']) ? $_POST['mid'] : null;

if($mid == null){
  echo "error";
}else{

	$dir = '/your-customized-directory/';
	$filename = $dir.$mid.".txt";
	
	$lastmodif = isset($_POST['timestamp']) ? $_POST['timestamp'] : 0;
	$currentmodif = filemtime($filename);
	
	while($currentmodif <= $lastmodif){
		usleep(10000);
		clearstatcache();
		$currentmodif = filemtime($filename);
	}
	
	$response['msg'] = get_new_discussion($mid);
	$response['timestamp'] = $currentmodif;
	echo json_encode($response);
}