import javax.swing.tree.*;

static <A, B extends Collection<A>> JTree jDynamicTree_concurrent(final A root, final F1<A, B> makeChildren, fO... optParams) {

  ret swing(func -> JTree {

    final Q queue = startQ();

    DefaultMutableTreeNode rootNode = new(root);

    rootNode.add(new DefaultMutableTreeNode(jDynamicTree_dummy()));

    final JTree tree = new JTree(rootNode);

    tree.setShowsRootHandles(true);

    tree.collapseRow(0);

    final bool keepChildrenOnCollapse = optParam(optParams, 'keepChildrenOnCollapse, false);

    //final bool makeChildrenIsFast = optParam(optParams, 'makeChildrenIsFast, false);

    final bool debug = boolPar debug(optParams, true);

    tree.addTreeWillExpandListener(new TreeWillExpandListener {

      public void treeWillCollapse(TreeExpansionEvent e) {}

      public void treeWillExpand(TreeExpansionEvent e) {

        if (debug) print("treeWillExpand");

        final DefaultMutableTreeNode node = cast e.getPath().getLastPathComponent();

        if (keepChildrenOnCollapse && !jDynamicTree_isInDummyState(node)) ret;

        queue.add(r {

          print("Calling: " + makeChildren);

          B raw = callF(makeChildren, (A) node.getUserObject());

          print("raw => " + className(raw));

          fL<A> l = asList(raw);

          if (debug) print("Have children: " + l(l));

          swing {

            if (replaceTreeNodeChildren_withDummyChild(node, l, jDynamicTree_dummy()))

              ((DefaultTreeModel) tree.getModel()).nodeStructureChanged(node);

          }

        });

      }

    });

    ret tree;

  });

}