use IO::Select;

    $s = IO::Select->new();
...

    $s->add($some_handle);

    my $outbuffer;
    while( $running ) {
        if( length $outbuffer ) {
            my @writeable = $s->can_write($timeout);
            for my $client (@writeable) {
                print {$client} $outbuffer;
                # In reality, we'd need to maintain an outbuffer per client, but
                # that's not the point here
            };
            undef $outbuffer;
        } else {
            $outbuffer = refill_outbuffer;
        };
    };