* implementation. Using a reconstruction of the default Object.toString() prevents OOMs and stack
   * overflows, and helps avoid sensitive data inadvertently ending up in exception messages.
   */
  private void appendResultObject(StringBuilder builder, @CheckForNull Object o) {
    if (o == null) {
      builder.append("null");
    } else if (o == this) {

   * tasks. Second, the returned list will always be empty, as any submitted task is considered to
   * have started execution. This applies also to tasks given to {@code invokeAll} or {@code
   * invokeAny} which are pending serial execution, even the subset of the tasks that have not yet
   * started execution. It is unclear from the {@code ExecutorService} specification if these should