presto-atop/src/main/java/io/prestosql/plugin/atop/AtopPageSource.java/AtopPageSource/close
class AtopPageSource:    @Override
    public void close()
    {
        finished = true;
        if (atop != null) {
            try {
                atop.close();
            }
            finally {
                atop = null;
                readerPermits.release();
            }
        }
    }