* <p>This always holds: {@code 0 <= permitsToTake <= storedPermits}
   */
  abstract long storedPermitsToWaitTime(double storedPermits, double permitsToTake);

  /**
   * Returns the number of microseconds during cool down that we have to wait to get a new permit.
   */
  abstract double coolDownIntervalMicros();

  /** Updates {@code storedPermits} and {@code nextFreeTicketMicros} based on the current time. */