生产者和消费者问题中锁定的问题？

[moon197896]

public class ManufactureConsume {
	public static void main(String[] args) {
		CommodityStack cs = new CommodityStack();
		Manufacture m = new Manufacture(cs);
		Consumer c = new Consumer(cs);
		//new Thread(m).start();
		new Thread(m).start();
		new Thread(m).start();
		new Thread(c).start();
		
	}
}
class Commodity {
	public int id = 0;
	Commodity (int id) {
		this.id = id;
	}
	public String toString() {
		return "Commodity:" + id; 
	}	
}
class CommodityStack {
	static int index = 0;
	static Commodity[] c = new Commodity[6];
	public synchronized void push (Commodity cd) {
		while (index == c.length) {
			try{
				this.wait();
			}catch (InterruptedException e) {}			
		}
		this.notifyAll();
		c[index] = cd;
		index++;
	}	
	public synchronized Commodity pop () {
		while (index == 0) {
			try{
				this.wait();
			}catch (InterruptedException e) {}
		}
		this.notifyAll();
		index--;
		return c[index];
	}
}
class Manufacture implements Runnable {
	CommodityStack cs = null;
	Manufacture (CommodityStack cs) {
		this.cs = cs;
	}
	public void run() {
		for (int i = 0; i < 10; i++) {
			Commodity cd = new Commodity(cs.index);
			cs.push(cd);
			System.out.println("制造" + cd);
			try {
				Thread.sleep(300);
			} catch (InterruptedException e ) {}			
		}
	}
}
class Consumer implements Runnable {
	CommodityStack cs = null;
	Consumer (CommodityStack cs) {
		this.cs = cs;
	}
	public void run() {
		while (cs.index != 0) {
			System.out.println("吃掉了" + cs.pop());
			try {
				Thread.sleep(200);
			} catch (InterruptedException e ) {}	
		}
	}
}

问题是，在实际运行中，会出现同生产了两个同样ID的Commodity。也会出现同时消费了两个相同ID的Commodity的问题。

也就是说，会出现一下的输出：
“
制造Commodity:3
制造Commodity:3
制造Commodity:4
吃掉了Commodity：4
制造Commodity:4
吃掉了Commodity：4
吃掉了Commodity：3
吃掉了Commodity：3
”

这种情况是不是意味着生产和消费进程未能被独占锁定。有什么方法可以解决呢？

[moon197896]

呵呵，我知道20分少了点，不过念在在下论坛新人的份儿上，请大家不吝赐教阿。

[漫无目的行走的月亮]

给你贴一个生产-消费者的例子，是《java编程思想》上的例子，应该对你有用：

import java.util.concurrent.*;
import static net.mindview.util.Print.*;
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(); // ... for the chef to produce a meal
}
print("Waitperson got " + restaurant.meal);
synchronized(restaurant.chef) {
restaurant.meal = null;
restaurant.chef.notifyAll(); // Ready for another
}
}
} catch(InterruptedException e) {
print("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(); // ... for the meal to be taken
}
if(++count == 10) {
print("Out of food, closing");
restaurant.exec.shutdownNow();
}
printnb("Order up! ");
synchronized(restaurant.waitPerson) {
restaurant.meal = new Meal(count);
restaurant.waitPerson.notifyAll();
}
TimeUnit.MILLISECONDS.sleep(100);
}
} catch(InterruptedException e) {
print("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();
}
} 

[Miracle1216]

太长了，都不想看。。。