presto-main/src/main/java/io/prestosql/execution/SqlTaskExecution.java/DriverSplitRunner/close
class DriverSplitRunner:        @Override
        public void close()
        {
            Driver driver;
            synchronized (this) {
                closed = true;
                driver = this.driver;
            }

            if (driver != null) {
                driver.close();
            }
        }