return (list instanceof RandomAccess)
        ? new SynchronizedRandomAccessList<E>(list, mutex)
        : new SynchronizedList<E>(list, mutex);
  }

  static class SynchronizedList<E extends @Nullable Object> extends SynchronizedCollection<E>
      implements List<E> {
    SynchronizedList(List<E> delegate, @CheckForNull Object mutex) {
      super(delegate, mutex);
    }

    @Override

    return (list instanceof RandomAccess)
        ? new SynchronizedRandomAccessList<E>(list, mutex)
        : new SynchronizedList<E>(list, mutex);
  }

  static class SynchronizedList<E extends @Nullable Object> extends SynchronizedCollection<E>
      implements List<E> {
    SynchronizedList(List<E> delegate, @CheckForNull Object mutex) {
      super(delegate, mutex);
    }

    @Override

    protected int indexUpdaterPriority = Thread.MAX_PRIORITY;

    protected int crawlerPriority = Thread.NORM_PRIORITY;

    protected final List<Crawler> crawlerList = Collections.synchronizedList(new ArrayList<>());

    public void crawl(final String sessionId, final List<String> webConfigIdList, final List<String> fileConfigIdList) {
        final boolean runAll = webConfigIdList == null && fileConfigIdList == null;