PHP MYSQL JQuery Long Polling - Not working as expected - php

Question

My long polling implementation isn't working. Been having a very difficult time understanding where to look toward debugging said code.
Key Points
No Errors
Long polling working randomly (only responds to some changes in MySQL with no distinct pattern)
MySQL is updating correctly
I'm testing this via Localhost WAMP and two browsers with two different sessions
PHP Portion -
$path= $_SERVER[ 'DOCUMENT_ROOT'];
$path .= "/config.php" ;
require_once($path);
require_once(PHP_PATH . "/classes/user.php");
session_start();
require_once(PHP_PATH . "/functions/database.php");
// Return to Login if no Session
if(!isset($_SESSION['user'])){
header("Location: /login");
die();
}
$db = connectdatabase();
$timeout = 40;
// if no post ids kill the script // Should never get here
if(!isset($_POST['post_ids'])){
die();
}
if(!isset($_POST['timestamp'])){
die();
}
$last_ajax_call = $_POST['timestamp'];
$post_ids = trim(strip_tags($_POST['post_ids']));
$id = $_SESSION['user']->getID();
// Check if there are posts from the last search that need to be updated with a comments or the like number has to be updated
$query = "SELECT posts.*, users.first_name, users.last_name, users.picture
FROM posts
LEFT JOIN users
ON users.id = posts.user_id
WHERE ((UNIX_TIMESTAMP(posts.date) > :last_ajax_call OR UNIX_TIMESTAMP(posts.last_modified) > :last_ajax_call)
AND posts.parent IN (:post_ids)) OR (posts.id IN (:post_ids) AND UNIX_TIMESTAMP(posts.last_modified) > :last_ajax_call)";
while ($timeout > 0) {
$check_for_updates = $db->prepare($query);
$check_for_updates->bindParam(':post_ids', $post_ids);
$check_for_updates->bindParam(':last_ajax_call', $last_ajax_call);
$check_for_updates->execute();
$r = $check_for_updates->fetchAll();
if(!empty($r)){
// Get current date time in mysql format
$unix_timestamp = time();
// Cofigure result array to pass back
$result = array(
'timestamp' => $unix_timestamp,
'updates' => $r
);
$json = json_encode($result);
echo $json;
return;
} else {
$timeout --;
usleep( 250000 );
clearstatcache();
}
}
// you only get here if no data found
$unix_timestamp = time();
// Cofigure result array to pass back
$result = array(
'timestamp' => $unix_timestamp
);
$json = json_encode($result);
echo $json;
JQuery Ajax -
function getUpdates(timestamp) {
var post_ids = $("#newsfeed").find("#post_ids").attr('data-post-ids');
var data = {'timestamp' : timestamp,
'post_ids' : post_ids};
poll = $.ajax({
type: 'POST',
url: '/php/check_for_updates.php',
data: data,
async: true, /* If set to non-async, browser shows page as "Loading.."*/
cache: false,
success: function(data) {
try {
// put result data into "obj"
var obj = jQuery.parseJSON(data);
// put the data_from_file into #response
//$('#response').html(obj.data_from_file);
// repeat
console.log("SQL: " + obj['timestamp']);
setTimeout( function() {
// call the function again, this time with the timestamp we just got from server.php
getUpdates(obj['timestamp']);
}, 1000 );
} catch( e ) {
// repeat
// Get mysql formated date
var unix_timestamp = Math.floor(Date.now() / 1000);
console.log("JS: " + unix_timestamp);
setTimeout( function() {
getUpdates(unix_timestamp);
}, 1000 );
}
}
}
);
}

Answer 1

Thanks for all the help guys! I asked around a lot of people and got a bunch of great places to look to debug the code.
I finally found the answer here -
http://blog.preinheimer.com/index.php?/archives/416-PHP-and-Async-requests-with-file-based-sessions.html
http://konrness.com/php5/how-to-prevent-blocking-php-requests/
It looks like I the PHP checking for updates was blocking any updates from happening till the PHP stop checking for updates.

Answer 2

Couple things you can do is:
1.) Open the Chrome Developer tools and then click on the Network tab and clear everything out. Then click on submit. Look at the network tab and see what is being posted and what isn't. Then adjust accordingly from there.
2.) Echo out different steps in your php script and do the same thing with the Network tab and then click on the "results" area and see what's being echoed out and if it's as expected.
From there, you should be able to debug what's happening and figure out where it's going wrong.