private void updateSample() {
    long totalBytes = getSpaceUsed(watchPaths);
    for (Listener listener : listenerSet.keySet()) {
      try {
        listener.onUpdate(totalBytes);
      } catch (Throwable e) {
        // catch an exception thrown by one listener so that it does not impact other listeners.
        log.error("Exception thrown by a listener ", e);
      }
    }
  }
Wait until this service has shutdown. Returns true if shutdown occurred within the timeout
and false otherwise.
<p>
This is currently exposed at the package private level for tests only.
samza-core/src/main/java/org/apache/samza/container/disk/PollingScanDiskSpaceMonitor.java