* @since 16.0 (present in 13.0 with {@code void} return type})
   */
  @CanIgnoreReturnValue
  public double acquire(int permits) {
    long microsToWait = reserve(permits);
    stopwatch.sleepMicrosUninterruptibly(microsToWait);
    return 1.0 * microsToWait / SECONDS.toMicros(1L);
  }

  /**
   * Reserves the given number of permits from this {@code RateLimiter} for future use, returning

      instant += MICROSECONDS.toNanos(micros);
      events.add(caption + String.format(Locale.ROOT, "%3.2f", (micros / 1000000.0)));
    }

    @Override
    protected void sleepMicrosUninterruptibly(long micros) {
      sleepMicros("R", micros);
    }

    String readEventsAndClear() {
      try {
        return events.toString();
      } finally {
        events.clear();
      }

      instant += MICROSECONDS.toNanos(micros);
      events.add(caption + String.format(Locale.ROOT, "%3.2f", (micros / 1000000.0)));
    }

    @Override
    protected void sleepMicrosUninterruptibly(long micros) {
      sleepMicros("R", micros);
    }

    String readEventsAndClear() {
      try {
        return events.toString();
      } finally {
        events.clear();
      }