presto-main/src/main/java/io/prestosql/server/remotetask/ContinuousTaskStatusFetcher.java/ContinuousTaskStatusFetcher/start
class ContinuousTaskStatusFetcher:    public synchronized void start()
    {
        if (running) {
            // already running
            return;
        }
        running = true;
        scheduleNextRequest();
    }