线程，交换器java

Question

请帮帮我一点。我在使用Exchanger时遇到问题。当乘客试图改变公共汽车时，程序阻塞。任务：如果两辆公共汽车在同一车站，乘客可以换乘公共汽车。

班级Bus：

public class Bus implements Runnable {
    private Lock lock = new ReentrantLock();
    private Exchanger<Passengers> exchanger;
    private Passengers passengers;
    private ArrayList<BusStation> busStations;
    private int number;
    private BeforeState beforeState = new BeforeState();
    private AfterState afterState = new AfterState();

    public Bus(ArrayList busStations, int number, Passengers passengers, Exchanger<Passengers> exchanger) {
        this.busStations = busStations;
        this.number = number;
        this.passengers = passengers;
        this.exchanger = exchanger;
    }

    public void addExchanger(Exchanger exchanger) {
        this.exchanger = exchanger;
    }

    public Exchanger getExchanger() {
        return exchanger;
    }

    public Bus(ArrayList busStations) {
        this.busStations = busStations;
    }

    public void run() {
        for (int i = 0; i < busStations.size(); i++) {
            beforeState.doAction(this, busStations.get(i));
            busStations.get(i).addBus(this);
            afterState.doAction(this, busStations.get(i));
            busStations.get(i).getSemaphore().release();
        }
    }

    public int getNumber() {
        return number;
    }

    public void setPassengers(Passengers passengers) {
        lock.lock();
        if (passengers.getQuantity() < 0)
            passengers = new Passengers(0);
        try {
            this.passengers = passengers;
        } finally {
            lock.unlock();
        }
    }

    public Passengers getPassengers() {
        lock.lock();
        try {
            return passengers;
        } finally {
            lock.unlock();
        }
    }
}

班级BusStation：

public class BusStation {

 private final static Logger logger = Logger.getLogger(BusStation.class);
    private String name;
    private final int busLimit = 2;
    private Semaphore semaphore = new Semaphore(busLimit);

    public BusStation(String name) {
        this.name = name;
    }

    public String getName(){
        return name;
    }

    public void addBus(Bus bus){
        try {
            semaphore.acquire();
        } catch (InterruptedException e) {
            logger.error("Semaphore error", e);
        }
        new InState().doAction(bus, this);
    }
    public Semaphore getSemaphore(){
        return semaphore;
    }
}

控制公交车站活动的班级：

public class InState implements IState {
    private final static Logger logger = Logger.getLogger(InState.class);

    @Override
    public void doAction(Bus bus, BusStation busStation) {
        logger.info("Bus number " + bus.getNumber() + " is on the station " + busStation.getName());
        Random rand = new Random();
        if (busStation.getSemaphore().availablePermits() == 0) {
            if (rand.nextInt(10) > 5) {
                try {
                    Passengers tmpPassengers = bus.getPassengers();                               //
                    tmpPassengers = (Passengers) bus.getExchanger().exchange(bus.getPassengers()); //  Here programm`s blocking
                 //   bus.setPassengers(tmpPassengers);                                               //
                } catch (InterruptedException e) {
                    logger.error("Exchanger mistake", e);
                }

            }
                else
                bus.setPassengers(new Passengers(bus.getPassengers().getQuantity() - rand.nextInt(10)));
            }
        }

    public String toString() {
        return "In state";
    }
}