presto-main/src/main/java/io/prestosql/failuredetector/HeartbeatFailureDetector.java/HeartbeatFailureDetector/getFailed
class HeartbeatFailureDetector:    @Override
    public Set<ServiceDescriptor> getFailed()
    {
        return tasks.values().stream()
                .filter(MonitoringTask::isFailed)
                .map(MonitoringTask::getService)
                .collect(toImmutableSet());
    }