code: public void pushMetric(final MetricsRecord mr) {
      lock.lock();
      try {
        intervalHeartBeat();
        try {
          mr.incrMetric(getName(), getPreviousIntervalValue());
        } catch (Exception e) {
          LOG.info("pushMetric failed for " + getName() + "\n" +
              StringUtils.stringifyException(e));
        }
      } finally {
        lock.unlock();
      }
      
    }
docs: Push the delta  metrics to the mr.
  The delta is since the last push/interval.
  
  Note this does NOT push to JMX
  (JMX gets the info via {@link #previousIntervalValue}
  
  @param mr