public void start() {
    if (this.started.compareAndSet(false, true)) {
      this.streamPartitionCountMonitor.ifPresent(StreamPartitionCountMonitor::start);
      this.streamRegexMonitor.ifPresent(StreamRegexMonitor::start);
    } else {
      LOG.warn("Monitors already started");
    }
  }
Utility class for managing multiple monitors.
samza-core/src/main/java/org/apache/samza/coordinator/JobModelMonitors.java