#! /usr/bin/perl

use HTML::TreeBuilder::XPath;
use WWW::Mechanize;
use warnings;
use diagnostics;
use constant MAX_CHILDREN => 3;

open(INPUT,"<",$input) || die("Couldn't read from the file, $input with error: $!\n");
open(OUTPUT, ">>", $output) || die("Couldn't open the file, $output with error: $!\n");

$pm = Parallel::ForkManager->new(MAX_CHILDREN);

$mech=WWW::Mechanize->new();
$mech->stack_depth(0);

while(<INPUT>)
{
chomp $_;
$url=$_;

$pm->start() and next;

$mech->get($url);

if($mech->success)
{
    $tree=HTML::TreeBuilder::XPath->new();
    $tree->parse($mech->content);

    # do some processing here on the content and print the results to OUTPUT file

    # once done then delete the root node

    $tree->delete();
}

$pm->finish();

print "Child Processing finished\n"; # it never reaches this point!

}

$pm->wait_all_children;