Is this a true long polling? - php

Question

After a lot of trials, I am successfully able to maintain continuous server connection with a database.
Now code keep checking and show the messages, if there are new in database.
Please review and tell:
if there is true long polling technique used in this code? If it is not, then please suggest, where I am wrong(deviating from long polling) and how this can be made a true long polling.
Currently, I am getting these errors. However still it maintains the continous connection with database.
**each time only one message is pulled instead of all **(I used each loop but it stops the long polling)
After every 10/15 seconds, token error appeares (Parse error (syntax error=unexpected token)).
var last_msg_id = 2;
function load_msgs() {
$.ajax({
type:"Post",
url:"getdata.php",
data:{
last_msg_id:last_msg_id
},
dataType:"json",
async:true,
cache:false,
success:function(data) {
var json = data;
$("#commidwin").append(json['msg']);
last_msg_id = json["last_msg_id_db"];
setTimeout("load_msgs()", 1000);
},
error:function(XMLhttprequest, textstatus, errorthrown) {
alert("error:" + textstatus + "(" + errorthrown + ")");
setTimeout("load_msgs()", 15000);
}
});
}
Php file is here
$last_msg_id=$_POST['last_msg_id'];
$last_msg_id_db=1;
while($last_msg_id>$last_msg_id_db){
usleep(10000);
clearstatcache();
$sql=mysqli_query($db3->connection,"SELECT * FROM chat_com where id>'$last_msg_id' ORDER by id ASC");
$sql_m=mysqli_query($db3->connection,"SELECT max(id) as maxid FROM chat_com");
$row_m=mysqli_fetch_array($sql_m);
$last_msg_id_db=$row_m['maxid'];
while($row=mysqli_fetch_array($sql)){
$textt=$row['mesg'];
$last_msg_id_db=$last_msg_id_db;
$response=array();
$response['msg']=$textt;
$response['last_msg_id_db']=$last_msg_id_db;
}
}
echo json_encode($response);

Answer 1

Polling is a bit harder than a simple while : just because generally all things you output to the browser will be interpreted when complete. Your example is quite clear :
success:function(data) {
var json = data;
$("#commidwin").append(json['msg']);
last_msg_id = json["last_msg_id_db"];
setTimeout("load_msgs()", 1000);
},
jQuery will wait until the response is complete to build your data variable and then will call your success callback.
One way to create long-polling is to have a task and a follower :
the task is the "infinite" loop, it displays nothing but just catch and trigger events, put in a "box".
the follower is an ajax call made every X seconds, it looks inside the "box" filled by the task, and immediately act inside the page.
Here is an example of long-polling, there is no follower, just an event (release) that stops the poll, but you'll get the idea :
<?php
// For this demo
if (file_exists('poll.txt') == false)
{
file_put_contents('poll.txt', '');
}
// If this variable is set, a long-polling is starting...
if (isset($_GET['poll']))
{
// Don't forget to change the default time limit
set_time_limit(120);
date_default_timezone_set('Europe/Paris');
$time = time();
// We loop until you click on the "release" button...
$poll = true;
$number_of_tries = 1;
while ($poll)
{
// Here we simulate a request (last mtime of file could be a creation/update_date field on a base)
clearstatcache();
$mtime = filemtime('poll.txt');
if ($mtime > $time)
{
$result = htmlentities(file_get_contents('poll.txt'));
$poll = false;
}
// Of course, else your polling will kill your resources!
$number_of_tries++;
sleep(1);
}
// Outputs result
echo "Number of tries : {$number_of_tries}<br/>{$result}";
die();
}
// Here we catch the release form
if (isset($_GET['release']))
{
$data = '';
if (isset($_GET['data']))
{
$data = $_GET['data'];
}
file_put_contents('poll.txt', $data);
die();
}
?>
<!-- click this button to begin long-polling -->
<input id="poll" type="button" value="Click me to start polling" />
<br/><br/>
Give me some text here :
<br/>
<input id="data" type="text" />
<br/>
<!-- click this button to release long-polling -->
<input id="release" type="button" value="Click me to release polling" disabled="disabled" />
<br/><br/>
Result after releasing polling :
<div id="result"></div>
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js"></script>
<script type="text/javascript">
// Script to launch polling
$('#poll').click(function() {
$('#poll').attr('disabled', 'disabled');
$('#release').removeAttr('disabled');
$.ajax({
url: 'poll.php',
data: {
poll: 'yes' // sets our $_GET['poll']
},
success: function(data) {
$('#result').html(data);
$('#poll').removeAttr('disabled');
$('#release').attr('disabled', 'disabled');
}
});
});
// Script to release polling
$('#release').click(function() {
$.ajax({
url: 'poll.php',
data: {
release: 'yes', // sets our $_GET['release']
data: $('#data').val() // sets our $_GET['data']
}
});
});
</script>
Demonstration : here.