sclass BackgroundProcessesUI<A> {

  Set<A> processes = syncLinkedHashSet();

  SimpleLiveValue<Int> lvCount = new SimpleLiveValue<Int>(Int, 0);

  JLabel shortLabel() {

    var lbl = bindToolTipToTransformedLiveValue(

      n -> makeToolTip(), lvCount,

        simpleTransformedLiveValueLabel(n -> n2(n), lvCount));

    addPopupTrigger(lbl, e -> {

      var l = cloneList(processes);

      new JPopupMenu menu;

      int n = componentCount(menu);

      for (A a : l)

        addMenuItem(menu, processToMenuItem(a));

      if (componentCount(menu) != n)

        showPopupMenu(menu, e);

    });

    ret lbl;

  }

  void add(A process) {

    if (processes.add(process))

      lvCount.set(l(processes));

  }

  void remove(A process) {

    if (processes.remove(process))

      lvCount.set(l(processes));

  }

  void addOrRemove(bool add, A process) {

    if (add) add(process); else remove(process);

  }

  S makeToolTip() {

    var l = cloneList(processes);

    ret empty(l) ? "No background processes"

      : n2(l, "background process", "background processes")

      + ": " + joinWithComma(processes);

  }

  swappable JMenuItem processToMenuItem(A process) {

    ret null;

  }

}