[sr-dev] Developing kamailio module - Forking issue

[Timo Reimann]

Hey Luis,


Am 17.09.2011 um 17:44 schrieb Luis Martin Gil:
> This is Luis Martin. I am developing a new module for Kamailio. This module will include some functions which will allow Kamailio to connect to another servers and retrieve information. I'm thinking on creating a couple of child from my main function, each child will execute a query to an specific server. I read this file "doc/modules_init.txt", but I'm having some troubles and I would appreciate if you could please help me with this.
> 
> This is the how the the first draft of the forking code looks like:
> http://pastebin.com/MLXDN9p9
> I call the "mod_child" function from my function like this:
> int myFunction () {
>   (...)
>   mod_child(randomNUMBER);
>   (...)
> }
> 
> But nothing happens, neither during the compilation process, nor the execution. Nothing is printed on the logs. Can you please point me out any suggestion or example?
> - How I am supposed to call the "mod_child()" function?

You do not call it. It's called automatically by Kamailio for every child configured. That is, if you have 16 workers set in your server configuration, the function is called 16 times. Place initialization code per child (e.g., establishing database connections) in that function, and Kamailio will make sure the code will be carried out for each child.


> - Which should be the rank_number: PROC_MAIN?

Again, you do not set the rank number, you use (read) it. As the documentation states, the child initialization function is called multiple times at different steps in the initialization process. By means of comparing the rank number to PROC_MAIN and other constants, you can make sure that you are doing specific tasks at the right time in the initialization life cycle.

The concept is the same as the way you do forking in Linux: fork()'s return value of 0 indicates you're in a child process, anything else means you're in the parent process. You do the comparison in the very same function, just like you do in Kamailio's mod_child(). I noticed you fork off some children yourself in your example code; not sure if that is supposed to work within Kamailio, I've never done (or needed) it myself. If you're good with having as many worker processes as there are configured in the Kamailio configuration, you should be fine working with that.


> - How I am supposed to cal the "mod_init()" function?

You don't. (I believe you got the idea by now. :) ). Just put your non-child-specific initialization code there and let it get called by Kamailio.


> - Again, could you please provide my any example?

Pick a non-trivial module, many of them require child-based initialization. Examples are the dialog or p_usrloc module.


HTH,

--Timo