...;
my $thr1 = threads->new(\&sock_io);
stdio_io();
...;

##</code><code>##

...;
use IO::Handle;
STDOUT->autoflush(1);
$socket->autoflush(1);
...;

##</code><code>##

while (<STDIN>) {
  chomp;
  print $socket $_ . CRLF;
}