This code is not intended as a good example of using threads, but is intended to show how to do bi-directional communications via a single socket under Win32.

It looks a little complicated because it is both client and server:

#! perl -slw
use strict;
use threads;
use IO::Socket;

$| = 1;

## The server.

async {
    ## Create the listening port
    my $server = IO::Socket::INET->new(
        LocalHost => 'localhost',
        LocalPort => 9999,
        Listen => 5,
        Reuse => 1,
    ) or die $!;

    ## Accept connections 
    while( my $client = $server->accept ) {
        ## Set the socket non-blocking
        ioctl( $client, 0x8004667e, \1 ) or die $^E;

        ## Start a thread to receive and display inbound packets
        async {
            my $in = '';
            while( 1 ) {

                ## Use to accumulate whatever is available
                sysread( $client, $in, 100, length( $in ) );

                ## When we've accumulated a complete line
                if( my $p = 1 + index $in, "\n" ) {
                    ## display it and remove it from the buffer
                    printf 'S: %s', substr $in, 0, $p+1, '';
                }
                ## Stop the non-blocking read from running away with t
+he cpu
                Win32::Sleep 100;
            }
        };

        ## Start another thread to simulate input from other clients
        async {
            print $client 'Some text' while sleep 1;
        };
    }
};


## The client

## Connect to the server
my $server = IO::Socket::INET->new(
    'localhost:9999'
) or die $!;

## Set the socket non-blocking
ioctl( $server, 0x8004667e, \1 );

## Start a thread to recieve and display input from the server
async {
    my $in = '';
    while( 1 ) {
        ## Accumulate input and display when we've got a full line
        sysread( $server, $in, 100, length( $in ) );
        if( my $p = 1 + index $in, "\n" ) {
            printf 'C: %s', substr $in, 0, $p+1, '';
        }
        Win32::Sleep 100;
    }
};

## Give the threads a chance to start
sleep 2;

## The main thread reads from the keyboard and sends to the server.
while( <STDIN> ) {
    print $server $_;
}

[download]

NOTE: No 'select' in sight.