public @NotNull ActionCallback getWhenProcessed() {
      if (myCallbacks.isEmpty()) {
        return DONE;
      }
      
      ActionCallback result = new ActionCallback(myCallbacks.size());
      Runnable setDoneRunnable = result.createSetDoneRunnable();
      for (ActionCallback each : myCallbacks) {
        each.doWhenProcessed(setDoneRunnable);
      }
      return result;
    }
public @NotNull ActionCallback getWhenProcessed()