G'day ghosh123,

"Can anybody please give me (or point me to) an example of asynchronous socket communication happening through a perl tk application. A very simple and primitive one.
The gui should be a server which will open a listening socket and some other processing application should connect to it and send info. The gui status should change according to the message received."

This is simple and primitive. :-)

The server (pm_asynch_sock_server_tk.pl):

#!/usr/bin/env perl

use strict;
use warnings;

use Tk;
use IO::Socket;

my $status = '';

my $mw = MainWindow->new;

my $control_F = $mw->Frame()->pack(-side => 'bottom');
$control_F->Button(-text => 'Listen',
                   -command => sub { start_server(\$mw, \$status) }
    )->pack(-side => 'left');
$control_F->Button(-text => 'Quit', -command => sub { exit }
    )->pack(-side => 'left');

my $status_F = $mw->Frame()->pack(-side => 'top');
$status_F->Label(-text => 'Status:')->pack(-side => 'left');
$status_F->Label(-textvariable => \$status)->pack(-side => 'left');

MainLoop;

sub start_server {
    my ($mw_ref, $status_ref) = @_;

    my $server = IO::Socket::INET::->new(
        Proto     => 'tcp',
        LocalPort => 55555,
        Listen    => SOMAXCONN,
        Reuse     => 1
    ) or die "Server can't start: $!";

    my $client = $server->accept();
    $client->autoflush;

    $$mw_ref->fileevent($client, 'readable', sub {
        if (defined(my $read = <$client>)) {
            chomp $read;
            $$status_ref = $read;
        }
    });
}
[download]

The client (pm_asynch_sock_client.pl):

#!/usr/bin/env perl

use strict;
use warnings;

use IO::Socket;

my $client = IO::Socket::INET::->new(
    Proto    => 'tcp',
    PeerAddr => 'localhost',
    PeerPort => 55555
) or die "Client can't connect: $!";

my @msgs = 'A' .. 'Z';

for (@msgs) {
    print $client "$_\n";
    sleep 1;
}
[download]

To run, start the GUI (I ran it in the background):

$ pm_asynch_sock_server_tk.pl &
[download]

Then start the server (click the Listen button) followed by the client (again, I ran this in the background):

$ pm_asynch_sock_client.pl &
[download]

You'll see the letters of the alphabet appear one at a time every second as the Status: value. That's just my test: you probably want something entirely different but gave no hint as to what that might be.

Notes:

• The socket-related code came (mostly verbatim) from perlipc. See the TCP Clients with IO::Socket and TCP Servers with IO::Socket sections if you have questions with any of that.
• See Tk::fileevent for questions about the file event handler.
• See Tk for links to any of the other GUI code.
• There's no requirement to run either the server or client in the background: that's just my preference as it frees up the command-line for other work.

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