#!/usr/bin/perl

use v5.12;
use strict;
use warnings;
use Data::Dumper;

package SpyHash;

use Tie::Hash; # for Tie::StdHash
use Carp qw( carp );

our @ISA=qw( Tie::StdHash );

sub STORE{
        my ($self,$key,$value)=@_;
        $key=~/^CH?LD$/ and carp "Assign to key $key";
        return $self->SUPER::STORE($key,$value);
    }

sub DELETE
    {
        my ($self,$key)=@_;
        $key=~/^CH?LD$/ and carp "Delete key $key";
        return $self->SUPER::DELETE($key);
    }

   1;


package main;

sub info
{
        my $where=shift;
        print $where,": ",Dumper($SIG{'CHLD'}),"\n";
}

info('start');
tie %SIG,'SpyHash';
info('after tie');
$SIG{'CHLD'}=sub { 'just a dummy' }; # this line should be reported
info('after set handler');
require Net::DNS; # Any module messing with $SIG{'CHLD'} should be reported from here
info('after require');
Net::DNS->import(); # ... or here
info('after import');
# For some extra paranoia, pretend to do some work with Net::DNS:
my $dns=Net::DNS::Resolver->new();
info('after creating instance');
my $reply=$dns->search('localhost');
info('after resolving localhost');
$reply=$dns->search('no.such.host.anywhere.invalid.');
info('after resolving junk');