《Java 編程思想》中，使用 廚師-服務員 來表示：生產者、消費者。

思路

chef 在 有 meal 的時候，會釋放鎖；在制作 meal 時，會獲取 waitPerson 的鎖，制作完 meal 后，喚醒所有的 waitPerson；

waitPerson 在 沒有 meal 的時候，會釋放鎖；在消費 meal 后，會將 meal 置為 null，操作期間需要獲得 chef 的鎖。

實現

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();
    }
}

public class Meal {
    
    private final int orderNum;
    
    public Meal(int orderNum) {
        this.orderNum = orderNum;
    }
    
    @Override
    public String toString() {
        return "Meal " + orderNum;
    }
}

public class Chef implements Runnable{
    private int count = 0;
    private Restaurant restaurant;
    
    public Chef(Restaurant restaurant) {
        this.restaurant = restaurant;
    }
    
    @Override
    public void run() {
        try {
            while (!Thread.interrupted()) { // shutdownNow 后，會退出循環
                synchronized (this) {
                    // 如果有 meal，則釋放鎖，等待
                    while (restaurant.meal != null) {
                        wait();
                    }
                }
                if (++ count == 10) {
                    System.out.println("Out of 10");
                    restaurant.exec.shutdownNow();
                }
                synchronized (restaurant.waitPerson) {
                    restaurant.meal = new Meal(count);
                    restaurant.waitPerson.notifyAll();
                }
                TimeUnit.SECONDS.sleep(1);
            }
            
        } catch (Exception e) {
            System.out.println("Chef interrupted");
        }
    }
}

public class WaitPerson implements Runnable{
    
    private Restaurant restaurant;
    
    public WaitPerson(Restaurant restaurant) {
        this.restaurant = restaurant;
    }
    
    @Override
    public void run() {
        try {
            while (!Thread.interrupted()) {
                synchronized (this) {
                    while (restaurant.meal == null) {
                        wait();
                    }
                }
                System.out.println("WaitPerson got " + restaurant.meal);
                synchronized (restaurant.chef) {
                    restaurant.meal = null;
                    restaurant.chef.notifyAll();
                }
            }
        } catch (Exception e) {
            System.out.println("WaitPerson interrupted");
        }
    }
}