code: public void addSample(final T item, final long hash, final int value)
      {
          if (enabled)
          {
              final Object lock = this;
              samplerExecutor.execute(new Runnable()
              {
                  public void run()
                  {
                      // samplerExecutor is single threaded but still need
                      // synchronization against jmx calls to finishSampling
                      synchronized (lock)
                      {
                          if (enabled)
                          {
                              try
                              {
                                  summary.offer(item, value);
                                  hll.offerHashed(hash);
                              } catch (Exception e)
                              {
                                  logger.debug("Failure to offer sample", e);
                              }
                          }
                      }
                  }
              });
          }
      }
docs: Adds a sample to statistics collection. This method is non-blocking and will
  use the "Sampler" thread pool to record results if the sampler is enabled.  If not
  sampling this is a NOOP