public CashDesk getCashDesk(long maxWaitMillis) throws StoreServiceException {
        locking.lock();
        try {
            if(semaphore.tryAcquire(maxWaitMillis, TimeUnit.MILLISECONDS)) { //// just Acquire (if no reason to try)
                return cashDesks.poll();
            }
        } catch (InterruptedException e) {
            throw new StoreServiceException(e);
        } finally {
            locking.unlock();
        }
        throw new StoreServiceException("Maximum waiting time exceeded");
    }