Callback behavior?

jje007

Hi folks,

I hope this hasn't been asked already, but I have a question about callback-eque behavior I'd really like some help with.

Basically, the user will be submitting a very computationally intensive query that I don't want the user having to wait around for at the website. I'd like for him/her to be able submit their query, and then be told they'll be notified when it's ready to be viewed. The users and jobs are being kept track of in a MySQL
DB. Some C code should be constantly taking these queries out of the queue and processing them, and when they're finished, somehow notify some PHP code that it's done and ready, which in turn updates the DB and sends an email to the user. An example of a system with a similar chain of events is karnak.com (http://www.karnak.com/whatis.shtml)

The C code itself works fine in terms of being able to process a query submitted to it directly, and I'm cool with knowing how updating the DB works and emailing the user in PHP and all that. However, I'm not really sure how this callback arrangement could be done in PHP. Does anyone have experience with this? I really have no clue how to even get started with that part, so even if you know of some cursory resources for that sort of operation, it would be much appreciated!

Thanks so much!
Jonathan

swr

The best you can do is have a page that reloads every few seconds.

HTTP is fundamentally a client-driven request/response model. The only time the server can send data to the client is when the client requests it (or shortly thereafter, within whatever timeout). To monitor state changes on the server, the client has to poll the server.

If a page refreshing itself every few seconds is not good enough, consider using email or IM to send the notification.

swr

On re-read, it sounds like email what you want...

The C code can just do something like this:

system("/path/to/php /path/to/php/script.php");

Then the script will be invoked. Using PHP from the command line is described here:
http://www.php.net/manual/en/features.commandline.php

If the script is on another server, or you don't have the PHP command-line stuff on your system, you can invoke wget (or some other command-line HTTP client) to call the PHP:

system("wget -O /dev/null http://example.com/yourscript.php");