Any documentation about Python daemons?

[Erik de Castro Lopo]

gradha at iname.com wrote:
> 
> Hello.
> 
> I would like to write now a program which acts as a server on the same
> machine for other clients in a Linux environment, something in the spirit
> of chronyd, if you know the program.

Sorry, i don't.

> However, I am new both to Python and process' intercommunication. Could
> you suggest me ways of doing this and/or point me to documentation
> explaining such communication methods? I first thought about nice pipes,
> but then I realized that the server program should be running always, not
> being allowed to fork, and clients could mantain multiple communication
> channels at the same time (ej: daemon + 2 clients). How could I do this?

This sounds like a job for sockets. The Python documentation has a very 
good section on the sockets module which I found pretty easy to follow.
There is also a more advanced module called SocketServer but I haven't
used that.

As for having multiple clients connect to one server you have a number
of options:

   - fork - only really of much use if the different server
     processes do not need to share very much data
   - threads - this overcomes the data sharing problems of
     forking but you will need to use locking to protect 
     shared data.
   - one process which uses select to manipulate multiple
     input and output connections

My application was a Tk based logging daemon which displays the 
output of a number of clients graphically. Because the clients 
all had to plot to the same Tk widgets I chode the multi-threaded 
model. I managed to get something working from scratch in about 
10 hours spread over three days.

Hope this helps,
Erik
-- 
-----------------------------------------------------------------
Erik de Castro Lopo     nospam at mega-nerd.com      (Yes its valid)
-----------------------------------------------------------------
"I think there is a world market for maybe five computers." 
 -- Thomas Watson, Chairman of IBM, 1943