presto-main/src/main/java/io/prestosql/server/remotetask/ContinuousTaskStatusFetcher.java/ContinuousTaskStatusFetcher/stop
class ContinuousTaskStatusFetcher:    public synchronized void stop()
    {
        running = false;
        if (future != null) {
            future.cancel(true);
            future = null;
        }
    }