Question

I have this Python based service daemon which is doing a lot of multiplexed IO (select).

From another script (also Python) I want to query this service daemon about status/information and/or control the processing (e.g. pause it, shut it down, change some parameters, etc).

What is the best way to send control messages (“from now on you process like this!”) and query processed data (“what was the result of that?”) using python?

I read somewhere that named pipes might work, but don’t know that much about named pipes, especially in python – and whether there are any better alternatives.

Both the background service daemon AND the frontend will be programmed by me, so all options are open 🙂

I am using Linux.

Answer 1

Pipes and Named pipes are good solution to communicate between different processes.
Pipes work like shared memory buffer but has an interface that mimics a simple file on each of two ends. One process writes data on one end of the pipe, and another reads that data on the other end.

Named pipes are similar to above , except that this pipe is actually associated with a real file in your computer.

More details at

• http://www.softpanorama.org/Scripting/pipes.shtml

In Python, named pipe files are created with the os.mkfifo call

x = os.mkfifo(filename)

In child and parent open this pipe as file

out = os.open(filename, os.O_WRONLY)
in = open(filename, 'r')

To write

os.write(out, 'xxxx')

To read

lines = in.readline( )

Edit: Adding links from SO

• Create a temporary FIFO (named pipe) in Python?
• https://stackoverflow.com/search?q=python+named+pipes

You may want to read more on “IPC and Python”

• http://www.freenetpages.co.uk/hp/alan.gauld/tutipc.htm