Long polling per verificare gli utenti on line

jQuery( function(){
	if(jQuery.cookie('enable-chat')) {

	function user_longpolling(){
		var t;
				
		jQuery.ajax({
			url: 'php/chat/stream_users.php',
			type: 'GET',
			dataType: 'json',
			success: function( payload ){
				clearInterval( t );
				if( payload.status == 'results' || payload.status == 'no-results' ){
					t=setTimeout( function(){
						user_longpolling();
					}, 1000 );
					if( payload.status == 'results' ){
						jQuery.each( payload.data, function(i,msg){
						//jQuery( '.onlineusers ul li#u-'+  msg.id_user +'' ).removeClass('on');
						jQuery( 'li#u-'+  msg.id_user +'').addClass(msg.stato);
						});
					}
				} else if( payload.status == 'error' ){
					alert('Sono confuso, cortesemente ricarica la pagina!');
				}
			},
			error: function(){
				clearInterval( t );
				t=setTimeout( function(){
					user_longpolling();
				}, 15000 );
			}
		});
	}
	user_longpolling();

	}
});

<?php 
require_once('global.php');
require_once('../functions.php');
sec_session_start();

$id_user 	= $_SESSION['user_id'];
// crea connessione
$conn = mysqli_connect($hostname_alliance, $username_alliance, $password_alliance, $database_alliance);
// verifica connessione
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}

$time_wasted = 0;

//XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
//verifico se l'utente è già nella tabella
$sql = "SELECT * FROM users_online where userid = ".$id_user."";
$result = $conn->query($sql);
	//se è stato già inserito aggiorno l'ora
	$time 		= time()+30;
	if ($result->num_rows > 0) {
			$sql = "UPDATE users_online SET timestamp = ".$time." WHERE userid = ".$id_user."";
	}else{
	//altrimenti lo inserisco nella tabella ed inserisco l'ora
			$sql = "INSERT INTO users_online (userid, timestamp)
			VALUES (".$id_user.", ".$time.")";
	}
//eseguo la query
$conn->query($sql); 

//XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

$old_users_check = mysql_query("SELECT * FROM users_online WHERE timestamp < ".time()." AND stato = 'on' AND userid <> ".$id_user." ORDER BY userid DESC");

$new_users_check = mysql_query("SELECT * FROM users_online WHERE timestamp >= ".time()." AND stato = 'off'  AND userid <> ".$id_user." ORDER BY userid DESC");

$num_rows_old = mysql_num_rows( $old_users_check );

$num_rows = mysql_num_rows( $new_users_check );
//se la prima query non mi da risultati
if( $num_rows <= 0 && $num_rows_old <= 0 ){
	//inizio il ciclo se non ottengo risultati
	while( $num_rows <= 0 && $num_rows_old <= 0 ){
		if( $num_rows <= 0 && $num_rows_old <= 0  ){
			// dopo 19 secondi invio una nuova richiesta
			if( $time_wasted >= 29 ){
				die( json_encode( array( 'status' => 'no-results' ) ) );
				exit;
			}
			sleep( 1 );
			$old_users_check = mysql_query("SELECT * FROM users_online WHERE timestamp < ".time()." AND stato = 'on' AND userid <> ".$id_user." ORDER BY userid DESC");
			$new_users_check = mysql_query("SELECT * FROM users_online WHERE timestamp >= ".time()." AND stato = 'off'  AND userid <> ".$id_user." ORDER BY userid DESC");
			$num_rows_old = mysql_num_rows( $old_users_check );
			$num_rows = mysql_num_rows( $new_users_check );
			
			$time_wasted += 1;
		}
	}
}

$new_user = array();

if( $num_rows_old >= 1):
while ( $row = mysql_fetch_array( $old_users_check, MYSQL_ASSOC ) ):
	$new_user[] = array( 
     'id_user' 	=> $row['userid'],
	 'stato'	=> $row['stato']
	);
endwhile;
mysql_query("UPDATE users_online SET stato = 'off ' WHERE timestamp < ".time()." AND stato = 'on' AND userid <> ".$id_user."");
endif;

if( $num_rows >= 1):
while ( $row = mysql_fetch_array( $new_users_check, MYSQL_ASSOC ) ):
	$new_user[] = array( 
     'id_user' 	=> $row['userid'],
	 'stato'	=> $row['stato']
	);
endwhile;
mysql_query("UPDATE users_online SET stato = 'on ' WHERE timestamp >= ".time()." AND stato = 'off' AND userid <> ".$id_user."");
endif;

mysql_free_result($old_users_check);
mysql_free_result($new_users_check);
die( json_encode( array( 'status' => 'results', 'data' => $new_user ) ) );