生產者消費者問題（thinking in java 709 ）

一個跳不出的死循環出現在生產者消費者問題上

import java.util.concurrent.*;

class Meal {
    private final int orderNum;

    public Meal(int orderNum) {
        this.orderNum = orderNum;
    }

    public String toString() {
        return "Meal" + orderNum;
    }
}

class WaitPerson implements Runnable {
    private Restaurant restaurant;

    public WaitPerson(Restaurant r) {
        restaurant = r;
    }

    public void run() {
        try {
            while (!Thread.interrupted()) {
                synchronized (this) {
                    while (restaurant.meal == null)
                        wait();
                }
            }
            System.out.println("Waitpersion got " + restaurant.meal);
            synchronized (restaurant.chef) {
                restaurant.meal = null;
                restaurant.chef.notifyAll();
            }

        } catch (InterruptedException e) {
            System.out.println("WaitPerson interrupted");
        }
    }
}

class Chef implements Runnable {
    private Restaurant restaurant;
    private int count = 0;

    public Chef(Restaurant r) {
        restaurant = r;
    }

    public void run() {
        try {
            while (!Thread.interrupted()) {
                synchronized (this) {
                    while (restaurant.meal != null)
                        wait();
                }
                if (++count == 10) {
                    System.out.println("Out of food,closing");
                    restaurant.exec.shutdownNow();
                }
                System.out.print("Order up! ");
                synchronized (restaurant.waitPerson) {
                    restaurant.meal = new Meal(count);
                    restaurant.waitPerson.notifyAll();
                }
                TimeUnit.MILLISECONDS.sleep(100);
            }
        } catch (InterruptedException e) {
            System.out.printf("Chef interrupted");
        }
    }
}

public class Restaurant {
    Meal meal;
    ExecutorService exec = Executors.newCachedThreadPool();
    WaitPerson waitPerson = new WaitPerson(this);
    Chef chef = new Chef(this);

    public Restaurant() {
        exec.execute(chef);
        exec.execute(waitPerson);
    }

    public static void main(String[] args) {
        new Restaurant();
    }
}

問題出現在哪？WaitPerson的run得到資源有被捲入外層的while。就這麼一點點耽誤我好幾小時。。。
應該是這樣

while (!Thread.interrupted()) {
                synchronized (this) {
                    while (restaurant.meal == null)
                        wait();
                }

                System.out.println("Waitpersion got " + restaurant.meal);
                synchronized (restaurant.chef) {
                    restaurant.meal = null;
                    restaurant.chef.notifyAll();
                }
}