How to stop subprocesses from copying listening sockets

[Rick van Hattem]

Hi everyone,

Recently I've started building a program that spawns new processes when
requested via http, since the http interface doesn't need to be fancy I've
just used the BaseHTTPServer module for this, but... it seems I'm running
into a little problem. When spawning a new process (which forks itself into a
daemon, but isn't too relevant in this case) the listening socket is copied
to the new process. Evidently this results in the base process not being able
to restart since the new spawned process starts listening on the port.

Here's a simple example of what I mean.
Assuming we've got the server like this:
import subprocess
import BaseHTTPServer

server = BaseHTTPServer.HTTPServer(('', 1234),
BaseHTTPServer.BaseHTTPRequestHandler)

subprocess.Popen(['python', 'the_daemon.py'])


With the_daemon.py being this:
import time
time.sleep(60)

And we run the main server and kill it after that (i.e. using netstat to find
the PID), we'll see that the new process which does nothing besides wait for
60 second will listen on port 1234 (use netstat to confirm).

Anyone has an idea on how to circumvent this issue?

Kind regards,

Rick van Hattem

PS: tested both on Fedora 8 using Python 2.5.1 and Gentoo Linux 2008 using
Python 2.5.2

 

[Roy Smith]

Recently I've started building a program that spawns new processes when
requested via http, since the http interface doesn't need to be fancy I've
just used the BaseHTTPServer module for this, but... it seems I'm running
into a little problem. When spawning a new process (which forks itself into a
daemon, but isn't too relevant in this case) the listening socket is copied
to the new process.

The standard solution to this problem is to close all descriptors after
forking and before doing the exec. You can tell subprocess.Popen() to do
this by call it with "close_fds=True".

 

[Rick van Hattem]

The standard solution to this problem is to close all descriptors after
forking and before doing the exec. You can tell subprocess.Popen() to do
this by call it with "close_fds=True".

Thank you very much, I completely forgot about the close_fds argument.

That will fix the problem nicely