You need to understand that one socket is needed to listen for connections, and another different socket is needed for each active client. So ultimately you will need to keep a list of what clients are connected. I modifed your example code to spawn one thread per client. It now has a separate listener thread also. What the code below still lacks is: tracking of client connections (a must-have for a chat program); sending output to all active clients; and many other niceities such as proper naming of clients, etc. Hopefully this will get you started though.

use strict;
use threads;
use threads::shared;
use IO::Socket;

my $keep_running : shared = 1;
my $sender_thread = threads->new(\&do_send);
my $listener_thread = threads->new(\&do_listen);

$sender_thread->detach();
$listener_thread->join();

sub do_listen {
        my $listener_sock = IO::Socket::INET->new(LocalHost => "127.0.
+0.1", LocalPort => 8080, Type => SOCK_STREAM, Proto =>
'tcp', Listen => 1);
        my $client_sock;
        my $ClientNumber = 0;

        STDOUT->autoflush(1);
        print "Starting listener\n";

        while ($keep_running) {
                my $client_sock = $listener_sock->accept();
                my $reader_thread = threads->new(\&do_read, $client_so
+ck, $ClientNumber);
                last unless defined($client_sock);
                $ClientNumber++;
                $reader_thread->detach();
                print "Accepted a connection\n";
        }
        print "Listener stopped\n";
}

sub do_read {
        my $sock = shift;                         
        my $ClientNumber = shift;
        while (<$sock>) {
                print $ClientNumber . ":" . $_;
        }
        print "Client " . $ClientNumber . " disconnected\n";
}

sub do_send {

        # any messages that the local user types
        while (my $line = <STDIN>) {
        # TODO: you need to iterate through all active clients and sen
+d them
        #       , not just one
#               $sock->print($line);
#               $sock->flush();
        # patch for development
        sleep 1;
        }

        $keep_running = 0;
}
[download]

I tested it myself with two clients and got this output:

Starting listener
Accepted a connection
0:hi
Accepted a connection
1:hi
0:Yo #1
1:Whaddup #0!
[download]