How to reload code changes in CodeIgniter with RabbitMQ? - php

Question

I am using CodeIgniter framework with RabbitMQ for doing time consuming activities such as sending emails, generating PDFs.
Whenever I change a code in the PHP files, say library or controller, until I restart the Apache, the old code is being executed by the RabbitMQ. How to resolve this?
The function in Controller,
public function receive()
{
$this->db->reconnect();
$connection = new AMQPStreamConnection('localhost', 5672, 'guest', 'guest');
$channel = $connection->channel();
$channel->queue_declare('generate_pdf', false, false, false, false);
echo "[*] Started listening to connections... To exit press CTRL+C\n";
$generate_pdf = function ($data)
{
$this->generatepdf->generate($data); // Generatepdf.php library -> generate() function
};
$channel->basic_qos(null, 1, null);
$channel->basic_consume('generate_pdf', '', false, true, false, false, $generate_pdf)
while ($channel->is_consuming())
{
$channel->wait();
}
}
Starting this in termimal,
php index.php Controllerfile.php receive
This works fine as expected. So when a job is pushed to the queue, the generate() function in the library file Generatepdf.php is called and the execution is done.
However, if I modify the generate() function thru an editor or I re-upload the file with changes, the changes does not reflect until I restart the Apache server.
Function definition before changes:
public function generate()
{
echo "Hello the data is 250";
}
Output: Hello the data is 250
Function definition after the change:
public function generate()
{
echo "Hello the data is 251";
}
Output before restarting Apache: Hello the data is 250
Output after restarting Apache: Hello the data is 251
Why does this happen? How can I made the execution to refresh the changes in the file?

Answer 1

The code you've shown contains this loop:
while ($channel->is_consuming())
{
$channel->wait();
}
What that's saying is "unless the connection to RabbitMQ breaks, wait for a new message, process it, and then wait again, forever". In other words, it's an infinite loop, and the PHP process running it won't exit unless you kill it.
Contrary to some descriptions I've seen, PHP is a compiled language, not an interpreted one: when a PHP process is asked to load a file of PHP code, it looks at it once, compiles it to a machine-friendly representation (called "op codes") and then doesn't need to look at it again to execute the code in it any number of times. So when you edit the file, a process that's already running won't notice, and won't compile your new code.
If you want to have the new code loaded, you need to exit the infinite loop, so the process ends, and then start a new one, which will compile your new code. For instance, you can have a check in the loop for a particular file, measure the time it's been running, or listen for a special message telling it to exit. You can then use something like "supervisord" to ensure the script is re-run whenever it exits, or just have a "cron" task to regularly start a new copy.
As one extra point: there is a feature of PHP called "OpCache" which reuses the compiled version of files even between processes, for better performance. By default, it will look at the timestamp of the file to decide whether to recompile it, so will "notice" if you edit a file, but that check can be turned off, for maximum performance. If that was the problem, you'd see this with all PHP code, though, not just your RabbitMQ loop.