tryDrainReferenceQueues();
        return null;
      }

      return value;
    }

    /**
     * Performs routine cleanup following a read. Normally cleanup happens during writes, or from
     * the cleanupExecutor. If cleanup is not observed after a sufficient number of reads, try
     * cleaning up from the read thread.
     */
    void postReadCleanup() {

      // structure for them.  Also, some implementations rely on this running prior to listeners
      // so that the cleanup work is visible to listeners.
      // afterDone() should be generally fast and only used for cleanup work... but in theory can
      // also be recursive and create StackOverflowErrors
      future.afterDone();
      // push the current set of listeners onto next

    }

    default void setDayForCleanup(final int value) {
        setSystemPropertyAsInt(Constants.DAY_FOR_CLEANUP_PROPERTY, value);
    }

    default int getDayForCleanup() {
        return getSystemPropertyAsInt(Constants.DAY_FOR_CLEANUP_PROPERTY, Constants.DEFAULT_DAY_FOR_CLEANUP);
    }

    default void setCrawlingThreadCount(final int value) {

 * entries may be counted in {@link Cache#size}, but will never be visible to read or write
 * operations.
 *
 * <p>Certain cache configurations will result in the accrual of periodic maintenance tasks which
 * will be performed during write operations, or during occasional read operations in the absence of

   * href="http://goo.gl/iz2Wi">"diamond" syntax</a>. One caveat to this is that the {@code TreeSet}
   * constructor uses a null {@code Comparator} to mean "natural ordering," whereas this factory
   * rejects null. Clean your code accordingly.
   *
   * @param comparator the comparator to use to sort the set
   * @return a new, empty {@code TreeSet}
   * @throws NullPointerException if {@code comparator} is null
   */

    // that represent a verification of a specification item needs to be a couple lines at most.
    // The expressions help a lot, but we need a clean to pick up a directory of POMs, automatically load
    // them into a resolver, create the expression to extract the data to validate the Model, and the URI