Codeigniter LongPolling "while(true)" does not work? - php

Question

I am currently implementing a long polling function in Codeigniter and have come up a problem.
Lets say I have a normal PHP Controller:
function longpolling()
{
//PHP Timelimit infinite
set_time_limit(0);
while(true){
echo "test";
//Sleep 3 Seconds
sleep(3);
}
}
The page is just saying loading when called and does not return "test" instead you get 404 Error after a while.
What am I doing wrong?
Thank you!

Answer 1

You aren't doing anything 'wrong' it's just that php doesn't work the way you're expecting it to.
If you did it like this:
$i = 0;
while ($i < 10)
{
echo "Hi There!";
sleep(2);
$i++;
}
It will eventually output lots of Hi There, but not one at a time, rather it will all display at the end of the while loop.
You could even throw a flush() in there
$i = 0;
while ($i < 10)
{
echo "Hi There!";
flush();
sleep(2);
$i++;
}
And you still wont get anything until the very end.
Because your while(true) never ends you will never see any output, and I assume the browser timeout kicks in? Or the max_execution_time setting is reached?
Just popped into my head now: It might work if you wrote some data to a file in an infinite loop I have never tried it myself.

Answer 2

I've ran into issues like this myself. You'll have to look into flushing the output out as php and/or the webserver might be buffering the data until a certain threshold is met. I had a horrible time struggling with IIS over this, I think Apache is a lot easier to manage. Plus there's telling the webserver what to do as well. For apache, here's a snippet found on php.net:
I just had some problems with flush() and ob_flush(). What I did to
resolve this problem took me some time to figure out so I'd like to
share what I came up with.
The main problem is the php setting "output_buffering" which can be
set too large and will prevent your text from outputting. To change
this value you can either set it in php.ini or you can add the line
php_value output_buffering "0"
to your .htaccess file. It will not work with ini_set() since it is
PHP_INI_PERDIR.
This is combined with the flush() function used before sleep(). I also had to output over a number of characters before it started flushing properly:
public function longpolling()
{
echo str_repeat(" ", 1024); flush();
for( $i = 0; $i < 10; $i++) {
echo $i."<br/>";
flush();
sleep(1);
}
}
Also. I just tried this on my server and it wouldn't work until I added the php_value line to my htaccess file. Once I did, it worked as expected.

Answer 3

The page will keep loading until the PHP file execution has reached the end of the file. PHP doesn't work like C or C++. You make a request and when everything is done you get the output. Once the page is loaded no PHP is executing anymore.
And sleep() is just used to slow PHP down in some cases. In this case:
echo "Something";
sleep(30);
echo " else";
"Something" and " else" will be printed at the same moment while the total execution will take 30 seconds more.