I don't think you're right on this one. His code works fine as long as you just replace

my @rhSet = IO::Select->select($readSet, undef, undef, 0);
foreach my $rh (@{$rhSet[0]}) {
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with (as in your example)

my @rhSet = IO::Select->select($readSet, undef, undef, 0);
foreach my $rh (@{$rhSet[0]}) {
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The

my $connection = $sock->accept();
$readSet->add($connection);
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you added are not needed, and I'd personally consider doing that more harmful than useful.

I also don't understand your comment about $sock not being an "active channel". After you create a server socket you can add it to the read set perfectly fine, and the select will return the socket when there's a connection to accept.