Java使用wait和notify实现生产者和消费者

1. 使用注意事项

1. 永远在synchronized的函数或对象里使用wait、notify和notifyAll，不然Java虚拟机会生成IllegalMonitorStateException。
2. 永远在while循环里而不是if语句下使用wait。这样，循环会在线程睡眠前后都检查wait的条件，并在条件实际上并未改变的情况下处理唤醒通知。
3. 永远在多线程间共享的对象上使用wait。
4. notify随机通知一个阻塞在对象上的线程；notifyAll通知阻塞在对象上所有的线程。

2. 代码示例

2.1 生产者

public class Producer implements Runnable{

    private Queue<Integer> queue;
    private int maxSize;

    public Producer(Queue<Integer> queue, int maxSize){
        this.queue = queue;
        this.maxSize = maxSize;
    }

    @Override
    public void run() {
        while (true){
            synchronized (queue){
                while (queue.size() == maxSize){
                    try{
                        System.out.println("Queue is Full");
                        queue.wait();
                    }catch (InterruptedException ie){
                        ie.printStackTrace();
                    }
                }
                Random random = new Random();
                int i = random.nextInt();
                System.out.println("Produce " + i);
                queue.add(i);
                queue.notifyAll();
            }
        }
    }
}

2.2 消费者

public class Consumer implements Runnable{

    private Queue<Integer> queue;
    private int maxSize;

    public Consumer(Queue<Integer> queue, int maxSize){
        this.queue = queue;
        this.maxSize = maxSize;
    }

    @Override
    public void run() {
        while (true){
            synchronized (queue){
                while (queue.isEmpty()){
                    System.out.println("Queue is Empty");
                    try{
                        queue.wait();
                    }catch (InterruptedException ie){
                        ie.printStackTrace();
                    }
                }
                int v = queue.remove();
                System.out.println("Consume " + v);
                queue.notifyAll();
            }
        }
    }
}

2.3 Main

public class Main {
    public static void main(String[] args){
        Queue<Integer> queue = new LinkedList<>();
        int maxSize = 10;
        Producer p = new Producer(queue, maxSize);
        Consumer c = new Consumer(queue, maxSize);
        Thread pT = new Thread(p);
        Thread pC = new Thread(c);
        pT.start();
        pC.start();
    }
}