*/
  @J2ktIncompatible
  @GwtIncompatible // concurrency
  @IgnoreJRERequirement // Users will use this only if they're already using Duration.
  public static void sleepUninterruptibly(Duration sleepFor) {
    sleepUninterruptibly(toNanosSaturated(sleepFor), TimeUnit.NANOSECONDS);
  }

  // TODO(user): Support Sleeper somehow (wrapper or interface method)?