presto-main/src/main/java/io/prestosql/failuredetector/HeartbeatFailureDetector.java/MonitoringTask/enable
class MonitoringTask:        public synchronized void enable()
        {
            if (future == null) {
                future = executor.scheduleAtFixedRate(new Runnable()
                {
                    @Override
                    public void run()
                    {
                        try {
                            ping();
                            updateState();
                        }
                        catch (Throwable e) {
                            // ignore to avoid getting unscheduled
                            log.warn(e, "Error pinging service %s (%s)", service.getId(), uri);
                        }
                    }
                }, heartbeat.toMillis(), heartbeat.toMillis(), TimeUnit.MILLISECONDS);
                disabledTimestamp = null;
            }
        }