As written, your server is going to leak memory. The rate of leakage will depend upon the number of clients you are monitoring.

• You are never closing the inbound sockets.

  This means you are never recycling filenos within your server, which will become a problem over time.

• You are never cleaning up (detach or join), the threads that you are spawning to handle the inbound connections.

  Although the threads will become dormant once the client disconnects, the threads memory will never be recycled which will become a problem over time.

• I'm not sure that this is doing anything for your application as it stands?

  #ignore child processes to prevent zombies
  $SIG{CHLD} = 'IGNORE';
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  It will have no useful affect on a threaded process under Win32, but that may not be true for other OSs.

Both of these are fairly easy to correct.

Detach your client threads (I've ditched the my $client as you never do anything with it):

threads->create ("read_data", $queue, $connection)->detach;
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and close the client socket once your done with it

sub read_data {
    # accept data from the socket and put it on the queue
    my ($queue, $socket) = @_;
    while (<$socket>) {
        print "listener got: $_";
        $queue -> enqueue(time." $_");
    }
    close $socket;
}
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In my quick test with 100 clients, fileno 4 was re-used for all inbound connections which fixes that problem.

With these measures in place, the server process shows a miniscule growth. After 5 cycles of reconnections from 100 clients, it showed ~ 16k extra memory used. This may well be just the normal process of memory acquisition required by Perl's memory manager. This was true for both AS811(5.8.6) and AS817(5.8.8) on my system (XP).