code: public int iterateKeys(HashtableAction action, int index, int length)
                      throws IOException,
                      EOFException,
                      FileManagerException,
                      ClassNotFoundException,
                      HashtableOnDiskException {
          return walkHash(action, RETRIEVE_KEY, index, length);
      }
docs: ************************************************************************
  This invokes the action's "execute" method once for every
  object passing only the key to the method, to avoid the
  overhead of reading the object if it is not necessary.
  
  The iteration is synchronized with concurrent get and put operations
  to avoid locking the HTOD for long periods of time. Some objects which
  are added during iteration may not be seen by the iteration.
  
  @param action The object to be "invoked" for each object.
  
  ***********************************************************************