server.pl:
use IO::Socket::INET;
use threads;

use strict;

my $server = new IO::Socket::INET(Proto => "tcp", LocalPort => 7001, Listen => 5)
          || die "failed to establish socket\n";
while (1) {
	my $client = $server->accept;
	threads->create(\&client_handle, $client);
}

sub client_handle {
	my $client = shift;
	while (1) {
		my $line = <$client>;
		chomp $line;
		print $client $line + 1, "\n";
	}
}

client.pl:
use strict;
use IO::Socket;
use threads;
use threads::shared;

my $numClients = shift;
my %thread_status : shared;
my $server_status : shared = 'threading';
$| = 1;

print "Creating $numClients clients\n";
for (my $i=0; $i<$numClients; $i++) {
    my $socket = IO::Socket::INET->new(Proto => "tcp", PeerAddr => "localhost", PeerPort => 7001) || print "Socket creation error: $!\n";
    threads->new(\&handle_client,$socket,$i)->detach;
	print ".";
}
print "\nAll Created\n";

sleep 1;
$server_status = 'ready';

<STDIN>;

#<------------------------------------------------------------ handle_client -->
sub handle_client {
    my ($socket,$clientNum) = @_;
 
    while ($server_status eq 'threading') { sleep 1 }
	
	print $socket "1\n";
	while (1) {
		my $line = <$socket>;
		chomp $line;
		print "$clientNum <<== $line\n";
		print $socket $line + 1, "\n";
		sleep 1;
	}
    return;
}