You could have the parent send a "GO AWAY" message to the child. That would be done in sequence and not kill the child in the middle of processing something else.

Something like this:

#!/usr/bin/perl

use strict; # https://www.perlmonks.org/?node_id=11154445
use warnings;
use IO::Socket;
$SIG{__WARN__} = sub { die @_ };

my $port = 3333; # FIXME
my $listen = IO::Socket::INET->new( LocalPort => $port,
  Listen => 100, ReusePort => 1,) or die $&;

if( my $pid = fork ) # parent
  {
  print "Hit <ENTER> to quit\n";
  <STDIN>;
  print "parent starting shutdown\n";
  my $child = IO::Socket::INET->new("localhost:$port") or die $@;
  print $child "GO AWAY\n\n";
  close $child;
  print "parent waiting for child to exit\n";
  1 while wait > 0;
  print "parent exiting\n";
  exit;
  }
elsif( defined $pid ) # child
  {
  my $more = 1;
  while( $more )
    {
    my $live_socket = $listen->accept;
    if( $live_socket )
      {
      my $input = '';
      while( <$live_socket> )
        {
        $input .= $_;
        /^\r?\n?\z/ and shutdown($live_socket, 1), last;
        }
      if( $input eq "GO AWAY\n\n" )
        {
        $more = 0;
        }
      else
        {
        print "process 'do stuff' here with:\n$input";
        }
      }
    else
      {
      print "child got $!\n";
      }
    }
  print "child exiting\n";
  exit;
  }
else # bummer
  {
  die "fork failed $!";
  }
[download]