// 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

        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() {

 * 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