}

    private TimedSemaphore(long countdownInMillis) {
      this.semaphore = new Semaphore(0);
      this.completed = new Completion(countdownInMillis);
      scheduleRelease(countdownInMillis);
    }

    /**
     * Requests a permit from the semaphore with a timeout and asserts that operation completed in
     * the expected timeframe.
     */