Re: asynchronous socket communication with perl tk

[kcott]

G'day simonz,

You took that code from this thread (which has exactly the same name): asynchronous socket comunication with perl tk

In that thread, the request was for: "... an example of asynchronous socket communication happening through a perl tk application. A very simple and primitive one."

When I wrote that code last month, I included links to related documentation. If you follow those links, particularly the ones to sections of perlipc, you'll find examples of more complex socket I/O (including multiple clients).

[simonz]

Hi, I have made the following modifications in the server code for asynchronous communication, but the server gui hangs as I start the client.

use strict;
use warnings;

use Tk;
use IO::Socket;
use IO::Select;

my $status = '';

my $mw = MainWindow->new;
$mw->geometry("200x200");
my $buttonFrame = $mw->Frame()->pack(-side => 'bottom');
$buttonFrame->Button(-text => 'Start',
                   -command => sub { init_server(\$mw, \$status) }
    )->pack(-side => 'left');

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

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

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

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

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

#my $client = $server->accept();
$$mw_ref->fileevent($server, 'readable', sub {


    my $readable_handles = new IO::Select();
    $readable_handles->add($server);
    my $buf;
    while (1) {  #Infinite loop
    # select() blocks until a socket is ready to be read or written
    my ($new_readable) = IO::Select->select($readable_handles,
                                         undef, undef, 0);
 print "Inside while \n";
    # If it comes here, there is at least one handle
    # to read from or write to. For the moment, worry only about 
    # the read side.
    foreach my $sock (@$new_readable) {
 print "Inside foreach $sock \n";
        if ($sock == $server) {
            my $new_sock = $sock->accept();
            # Add it to the list, and go back to select because the 
            # new socket may not be readable yet.
            $readable_handles->add($new_sock);
        } else {
            # It is an ordinary client socket, ready for reading.
            $buf = <$sock>;
            if ($buf) {
                # .... Do stuff with $buf
                $$status_ref = $buf;
            } else {
                # Client closed socket. We do the same here, and remov
+e
                # it from the readable_handles list
                $readable_handles->remove($sock);
                close($sock);
            }
        }
    }   
}

}
);



}

[simonz]

Hi
I even modified the server code to make it working, i removed the gui portion. Now when i am starting the server and then starting the client from another terminal , it works. However, the first time when I start client.pl, it prints msg1, then stops. Again when i start client.pl , it prints msg1 amd msg2. Similarly third time msg1, msg2,msg3 .

My question is

1. why not all the five messages msg1..msg5 are getting printed in one go when i start client.pl

The client code remains as it is as posted before
Can someone please explain me the flow of the code.

my $server;
    $server = IO::Socket::INET::->new(
        Proto     => 'tcp',
        LocalPort => 55555,
        Listen    => 1,
        Reuse     => 1
    ) or die "Server can't start: $!";
my $readable_handles = new IO::Select();
    
    my $buf;
    while (my $client = $server->accept) {  #Infinite loop

    
    # select() blocks until a socket is ready to be read or written
    my ($new_readable) = IO::Select->select($readable_handles,
                                         undef, undef, 0);
 # print "Inside while \n";
    # If it comes here, there is at least one handle
    # to read from or write to. For the moment, worry only about 
    # the read side.

$readable_handles->add($client);
    foreach my $sock (@$new_readable) {
         if ($sock == $server) {
            my $new_sock = $sock->accept();
            # Add it to the list, and go back to select because the 
            # new socket may not be readable yet.
            $readable_handles->add($new_sock);
        } else {
            # It is an ordinary client socket, ready for reading.
            $buf = <$sock>;
            if ($buf) {
                # .... Do stuff with $buf
                #$$status_ref = $buf;
                print $buf ;
            } else {
                # Client closed socket. We do the same here, and remov
+e
                # it from the readable_handles list
                $readable_handles->remove($sock);
                #close($sock);
            }
        }
    }   
}