SIGCHLD, fork, listen

[D'Arcy J.M. Cain]

bill <bill at rfa.org> wrote:
> I'm trying to set up a fairly "simple"
> server that listens for a socket connection,
> forks off a process and goes back to listening.
> This works fine for multiple clients, except
> I get zombies.  I try redefining SIGCHLD as
> SIG_IGN, but this doesn't work (as apparently
> is what's expected under POSIX).  I then
> try redefining it with my own function that
> includes a WAIT.  Fine, except "listen"
> doesn't get signalled when the child process
> dies, only when the next socket connection
> occurs.  (which could be hours later, not
> good).

How are you creating your server?  Are you using SocketServer?  This
supposedly does what you want.  Here is a simple echo server using it.

---------------------------- echod ----------------------------
#! /usr/bin/env python

HOST = ''
PORT = 51000

from SocketServer import *

class echohandler(ForkingMixIn, StreamRequestHandler):
    def handle(self):
        self.wfile.write(self.rfile.readline(16384))

if __name__=='__main__':
    from socket import *
    server = TCPServer((HOST, PORT), echohandler)
    server.serve_forever()
---------------------------------------------------------------

However, on a simple test, I find that this doesn't actually fork.
If someone can suggest why this doesn't fork, you should be able
to use this instead.  Note I tried reversing the order of the inherited
classes with no difference.

The simple test, btw, is to telnet to the port from two windows and type
a line into the second one then the first.  The second one doesn't echo
until I type in something into the first session.

-- 
D'Arcy J.M. Cain <darcy at caingang.com>      |  Democracy is three wolves
http://www.druid.net/darcy/                |  and a sheep voting on         
+1 416 425 1212     (DoD#0082)    (eNTP)   |  what's for dinner.