[asterisk-users] AGI and forking

[Tilghman Lesher]

On Wednesday 13 April 2011 08:08:03 A J Stiles wrote:
> Hi.  I just want to make sure I understand this before doing something
> that might break things spectacularly for our users and customers  :)
> 
> We are using Asterisk 1.6.2.9 and my programming language of choice is
> Perl.
> 
> I want, when a call comes in on someone's DDI number  (which the person
> who dialled it can only possibly have obtained by dialling 1471 after
> we called them),  to be able to look up the caller's details from one
> of our databases (where the number ought to be stored, because we
> already dialled it).
> 
> Now, this search is going to take some time; so I'd like for the AGI
> script to fork a clone of itself, so the parent process can exit and
> the dialplan continue on to ring the person's phone, while the database
> lookup is done in the background  (the script doesn't need to have any
> further contact with Asterisk -- it will initiate any necessary future
> communication via other channels).
> 
> 
> Is this the sort of thing I need?
> 
> ##########  begin code snippet  ##########
> 
> #!/usr/bin/perl -w
> use strict;
> use Asterisk::AGI;
> 
> my $AGI = new Asterisk::AGI;
> my %params = $AGI->ReadParse();
> 
> $SIG{CHLD} = "IGNORE";
> 
> if (my $child_pid = fork) {
>     #  This is executed in the parent process
>     exit;
> }
> elsif (defined $child_pid) {
>     #  This is executed in the child process
> 
>     close STDIN;
>     close STDOUT;
>     close STDERR;
> 
>     #  Load some more modules and do some stuff
>     #   that will take a long time
> 
>     exit;
> }
> else {
>     die "Could not fork: $!";
> };
> 
> ##########  end code snippet  ##########
> 
> Am I right in thinking I shouldn't have to worry about zombie processes,
> because the parent exits before the child and the init in modern Linux
> distros is smart enough to deal with orphaned processes itself?

Almost.  You should also set a new session ID to ensure that the child gets
a new processgroup.  Otherwise, on some systems, it will still wait for the
child to also exit).  In Perl, this is accessible from the POSIX module,
function setsid().

-- 
Tilghman