You don't even need your own mainloop, as AnyEvent brings its own main loop with it.

I would rewrite your main loop as follows:

my $loop = AnyEvent->condvar;
my $a = 0;

sub heartbeat {
    open( $fh, '>>', $msg_log );
        print $fh "looping $a\n";
    close $fh;
};

AnyEvent->timer( interval => 5, cb => \&heartbeat );
$loop->recv;
exit 0;
[download]

I would move reacting to IO out of the main loop as well:

$iocv->cb( \&on_io );

sub on_io {
    open( $fh, '>>', $msg_log );
        print $fh "loop data: $data\n";
    close $fh;
    undef( $iocv );
    $iocv = AnyEvent->condvar;
    $iocv->cb( \&on_io );
};
[download]

Ideally, you don't have your own main loop and only have callbacks and let AnyEvent decide, which callback to run, depending on what kind of event has arrived.

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.