docs: @Override
      public boolean shouldSchedule(Queue.Task p, List<Action> actions) {
          Item item = Tasks.getItemOf(p);
          if (item != null) {
              lock.readLock().lock();
              try {
                  return !_contains(item);
              } finally {
                  lock.readLock().unlock();
              }
          }
          return true;
      }