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my $loop = AnyEvent->condvar;
my $a = 0;
...
AnyEvent->timer( interval => 5, cb => \&heartbeat );
$loop->recv;
exit 0;

$iocv->cb( \&on_io );

...
    $iocv = AnyEvent->condvar;
    $iocv->cb( \&on_io );
};