code: private void help_copy( ) {
      // Read the top-level CHM only once.  We'll try to help this copy along,
      // even if it gets promoted out from under us (i.e., the copy completes
      // and another KVS becomes the top-level copy).
      CHM topchm = _chm;
      if( topchm._newchm == null ) return; // No copy in-progress
      topchm.help_copy_impl(false);
    }
docs: copies in progress.