Question

I try to write a daemon in python. But I have no idea how can I use a thread to start parallel tcp server in this daemon. And even what type of server I should use : asyncore?SocketServer?socket?

this is part of my code:

import os
def demonized():
   child_pid = os.fork()
   if child_pid == 0:
       child_pid = os.fork()
       if child_pid == 0:          #fork twice for demonize
           file = open('###', "r") # open file
           event = file.read()
           while event:
               #TODO check for changes put changes in list variable
               event = file.read()
       file.close()
       else:
           sys.exit(0)
   else:
       sys.exit(0)


if __name__ == "__main__":
  demonized()

So in a loop I have a list variable with some data appended every circle, and I want to start a thread with tcp server that wait for connection in the loop and if client connects send it this data(with zeroing variable). So I do not need to handle multiple clients, the client will be only one at time. What is the optimal way to implement this?

Thank you.

Answer 1

In case you want to avoid repeating boilerplate, Python will soon have a standard module that does the fork() pair and standard-I/O manipulations (which you have not added to your program yet?) that make it a daemon. You can download and use this module right now, from:

http://pypi.python.org/pypi/python-daemon

Running a TCP server in a separate thread is often as simple as:

import threading

def my_tcp_server():
    sock = socket.socket(...)
    sock.bind(...)
    sock.listen()
    while True:
        conn, address = sock.accept()
        ...
        ... talk on the connection ...
        ...
        conn.close()

def main():
    ...
    threading.Thread(target=my_tcp_server).start()
    ...

I strongly recommend against trying to get your file-reader thread and your socket-answering thread talking with a list and lock of your own devising; such schemes are hard to get working and hard to keep working. Instead, use the standard library’s Queue.Queue() class which does all of the locking and appending correctly for you.