At least from looking at the SockJS documentation, it is based on ( or compatible with) AnyEvent.

Wow, I think you've nailed it! After reading your post, I started digging into that and came across this, discussing this exact issue:

I'm posting the modified code here so as not to make the OP confusing. The new code no longer closes the connection immediately, but the timer, for some reason only fires ONCE (the first time), whereas I would like it to keep going. I'm guessing this has something to do with the line undef $w; but when I get rid of it, the timer doesn't fire at all.

#!/usr/bin/perl

use strict;
use warnings;

use Plack::Builder;
use SockJS;
use AnyEvent;

builder {
    mount '/echo' => SockJS->new(
        handler => sub {
            my ($session) = @_;

            $session->on(
                'data' => sub {
                    my $session = shift;

                    $session->write('got your message');
                }
            );

            $session->write('connected');

            my $w_cond = AnyEvent->condvar;
            $w_cond->cb( sub { warn $_[0]->recv } );
            my $w; $w = AnyEvent->timer(
                after => 0,
                interval => 5,
                cb => sub {
                    undef $w; # cleanup
                    $session->write('5 seconds have passed');
                    $w_cond->send();
                }
            );
        };
    );
};
[download]

You need to mention the timer variable $w inside the subroutine to keep it alive.

Either move it into a global variable or just mention it in the subroutine so it closes over the value. Even better would be to clean up the timer based on some condition.

So this is the final version of the timer code that works:

...
            my $w_cond = AnyEvent->condvar;
            $w_cond->cb( sub { warn $_[0]->recv } );
            my $w; $w = AnyEvent->timer(
                after => 0,
                interval => 5,
                cb => sub {
                    undef $w if (0);
                    $session->write('5 seconds have passed');
                    $w_cond->send();
                }
            );
...
[download]

I changed undef $w; to undef $w if (0);. Now the big question is why does this work, but simply commenting out undef $w; causes the timer to not work? Is there a logical reason here, or is it voodoo? By "voodoo" I mean, code that has to be typed a certain way "just because".