CGI fork() Difficulty

lacertus has asked for the wisdom of the Perl Monks concerning the following question:

Hey Folks,

I'm greatly hoping someone can indicate what precisely I am doing wrong with the following code. I believe the problem lies in the manner in which my fork() and exec() are interacting. The code is as follows:

sub do_work {
        my($query) = @_;

        return if( $query->param('password') ne 'pass' );

        if($query->param('which_bot') eq 'chump') {

                if($pid = fork()) {
                        return;
                } elsif(defined $pid) {
                        my @args = ("/bin/killall", "-TERM", "python")
+;
                        #system(@args);

                        exec('/usr/bin/python /usr/share/chump-1.3/src
+/dailychumpbot.py -i -s "neutron.oftc.net" -n chumpy --channel="#iitl
+ug" -d /httpd/htdocs/www/chump -e /chump/churn_html.xsl');
                        exit;
                }
        }

}
[download]

The child process does indeed execute the exec, and a python process begins. Within a second, or so (the script ends shortly after this do_work() function), the python execution ends ... this should not be as it is executing a bot that should be persistent.

Let me give everyone a preemptive thanks for your assitance with this!

Cheers,

Lacertus

------------------------------------
"There is more in heaven and earth
than is dreamt of in your philosophy"

Comment on CGI fork() Difficulty Download Code

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Re: CGI fork() Difficulty by sgifford (Prior) on Oct 26, 2004 at 02:28 UTC
Try doing a "double-fork" to detach the long-running process from the Web server. Something like: `if (my $pid1 = fork()) { wait; return; } elsif (defined($pid1)) { # Child if (my $pid2 = fork()) { # Still Child exit(0); } elsif (defined($pid2)) { # Grandchild exec(...); } else { die "Fork error: $!\n"; } } else { die "Fork error: $!\n"; }` [download] You may also want to do things like `POSIX::setsid` and `setpgrp`. Search the archives for `daemon` for some sample code.	[reply] [d/l] [select]

Replies are listed 'Best First'.

Re: CGI fork() Difficulty
by sgifford (Prior) on Oct 26, 2004 at 02:28 UTC

if (my $pid1 = fork())
{
  wait;
  return;
}
elsif (defined($pid1))
{
  # Child
  if (my $pid2 = fork())
  {
    # Still Child
    exit(0);
  }
  elsif (defined($pid2))
  {
    # Grandchild
    exec(...);
  }
  else
  {
    die "Fork error: $!\n";
  }
}
else
{
  die "Fork error: $!\n";
}
[download]

You may also want to do things like POSIX::setsid and setpgrp. Search the archives for daemon for some sample code.

[reply]
[d/l]
[select]