*/
    protected abstract long readMicros();

    protected abstract void sleepMicrosUninterruptibly(long micros);

    public static SleepingStopwatch createFromSystemTimer() {
      return new SleepingStopwatch() {
        final Stopwatch stopwatch = Stopwatch.createStarted();

        @Override
        protected long readMicros() {
          return stopwatch.elapsed(MICROSECONDS);
        }