具有多个使用者的生产者使用notify()失败

我有这段代码,它模拟了生产者-消费者问题,在共享的Q类对象上使用一个生产者和多个消费者。我在这里使用notify()而不是notifyAll(),因为我需要理解为什么这段代码会进入死锁或无限等待状态。

我的观点是:如果有一个生产者和多个消费者,那么notify()将只调用一个处于等待状态的线程,而rest将保持在wait()状态。然后,生产者将再次恢复,因此代码将继续执行。

观察:这里所有线程的生产者和消费者都处于无限等待状态。代码如下所示:

public class ProdConsProb {
    public static void main(String[] args) {
        Q q = new Q();
        Thread producerThread = new Thread(new Producer(q), "producerThread");
        Thread consumerThread = new Thread(new Consumer(q), "Consumer1");
        Thread consumerAnotherThread = new Thread(new Consumer(q), "Consumer2");
        Thread consumerYetAnotherThread = new Thread(new Consumer(q), "Consumer3");
        producerThread.start();
        consumerThread.start();
        consumerAnotherThread.start();
        consumerYetAnotherThread.start();
    }
}

class Producer implements Runnable {
    Q q;

    public Producer(Q q) {
        this.q = q;
    }

    @Override
    public void run() {
        int i = 0;
        while (true)
            try {
                q.setN(i++);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

    }

}

class Consumer implements Runnable {
    Q q;

    public Consumer(Q q) {
        this.q = q;
    }

    @Override
    public void run() {
        while (true)
            try {
                q.getN();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
    }

}

class Q {
    private int n = 0;
    boolean valueSet = false;

    public synchronized int getN() throws InterruptedException {
        while (!valueSet) 
        {
            wait();
        }
        valueSet = false;
        notify();
        return n;
    }

    public synchronized void setN(int n) throws InterruptedException {
        while (valueSet == true)
        {
            wait();
        }
        this.n = n;
        valueSet = true;
        notify();

    }
}

我添加了一些系统输出。生成的日志如下所示:

producerThread :: SetN : Valueset is false
producerThread :: Producer inserted 0
producerThread :: SetN : Valueset after is true
producerThread :: SetN : Valueset is true
producerThread wait() ------------ Active 
producerThread :: SetN :Wait() Valueset is true
Consumer3  Start :: GetN : Valueset is true
Consumer3 :: Consumer read 0
Consumer3  End :: GetN : Valueset after is false
Consumer3  Start :: GetN : Valueset is false
Consumer3 wait() ------------ Active 
Consumer3 :: GetN :Wait() Valueset is false
Consumer2  Start :: GetN : Valueset is false
Consumer2 wait() ------------ Active 
Consumer2 :: GetN :Wait() Valueset is false
Consumer1  Start :: GetN : Valueset is false
Consumer1 wait() ------------ Active 
Consumer1 :: GetN :Wait() Valueset is false
producerThread wait()   ------------- left 
producerThread :: Producer inserted 1
producerThread :: SetN : Valueset after is true
producerThread :: SetN : Valueset is true
producerThread wait() ------------ Active 
 -->>   producerThread :: SetN :Wait() Valueset is true
        Consumer3 wait() left 
        Consumer3 :: Consumer read 1
        Consumer3  End :: GetN : Valueset after is false
        Consumer3  Start :: GetN : Valueset is false
        Consumer3 wait() ------------ Active 
        Consumer3 :: GetN :Wait() Valueset is false
 ????   Consumer2 wait() left 
        Consumer2 wait() ------------ Active 
        Consumer2 :: GetN :Wait() Valueset is false

奇怪的是,一旦生产者在插入1后通知消费者,消费者3就会读取数据并通知生产者。现在,生产者3必须从其wait()返回触发器,但customer2线程离开其wait()返回wait()。

注意:这段代码可以与notifyAll()一起使用,但我正在寻找一个原因,说明它在使用notify()时失败的原因。