使用wait和notifyAll实现生产者消费者模型

悠悠 2022-06-16 06:11 135阅读 0赞

wait和notifyAll是JDK中Object类的两个方法，主要用来线程间通讯，最经典的应用场景就是【生产者-消费者】，下面给出简单示例。

/** * @Auothor wzx * @Date 2017/5/7 0007 */
    public class ProducerConsumer { 
    
        public static void main(String[] args) {
            Queue<Integer> buffer = new LinkedList<>();
            int maxSize = 10;
            Thread producer = new Thread(new Producer(buffer, maxSize));
            Thread consumer = new Thread(new Consumer(buffer));
            producer.start();
            consumer.start();
        }
    
    
        static class Producer implements Runnable { 
    
            private Queue<Integer> queue;
    
            private int maxSize;
    
            Producer(Queue<Integer> queue, int maxSize) {
                this.queue = queue;
                this.maxSize = maxSize;
            }
    
            @Override
            public void run() {
                while (true) {
                    synchronized (queue) {
                        while (queue.size() == maxSize) {
                            System.out.println("Queue is full,producer thread waiting for "
                                    + " consumer to take something from queue");
                            try {
                                queue.wait();
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                            }
                        }
                        Random random = new Random();
                        int i = random.nextInt();
                        System.out.println("Producing value :" + i);
                        queue.add(i);
                        queue.notifyAll();
                    }
                }
            }
        }
    
        static class Consumer implements Runnable { 
    
            private Queue<Integer> queue;
    
            Consumer(Queue<Integer> queue) {
                this.queue = queue;
            }
    
            @Override
            public void run() {
                while (true) {
                    synchronized (queue) {
                        while (queue.isEmpty()) {
                            System.out.println("Queue is empty,Consumer thread is waiting"
                                + " for producer thread to put something in queue");
                            try {
                                queue.wait();
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                            }
                        }
    
                        System.out.println("Consuming value :" + queue.remove());
                        queue.notifyAll();
    
                    }
                }
            }
    
        }
    
    }

执行结果如下：

Producing value :-306191693
    Producing value :1230823506
    Producing value :-1295070113
    Producing value :-330157665
    Producing value :1580771896
    Producing value :571342129
    Producing value :1798066124
    Producing value :247966176
    Producing value :1149189440
    Producing value :-1506596231
    Queue is full,producer thread waiting for  consumer to take something from queue
    Consuming value :-306191693
    Consuming value :1230823506
    Consuming value :-1295070113
    Consuming value :-330157665
    Consuming value :1580771896
    Consuming value :571342129
    Consuming value :1798066124
    Consuming value :247966176
    Consuming value :1149189440
    Consuming value :-1506596231
    Queue is empty,Consumer thread is waiting for producer thread to put something in queue

使用wait和notifyAll方法需要注意：  
1.一定要在synchronized 方法或synchronized 代码块中使用，否则JVM或抛出IllegalMonitorStateException异常；  
2.使用wait方法使用while循环判断条件，避免被假唤醒；  
3.synchronized 使用的一定是同个锁对象；

> 参考  
> [http://javarevisited.blogspot.com/2015/07/how-to-use-wait-notify-and-notifyall-in.html\#axzz4gOjkc8Yu][http_javarevisited.blogspot.com_2015_07_how-to-use-wait-notify-and-notifyall-in.html_axzz4gOjkc8Yu]  
> [http://javarevisited.blogspot.com/2011/05/wait-notify-and-notifyall-in-java.html][http_javarevisited.blogspot.com_2011_05_wait-notify-and-notifyall-in-java.html]

[http_javarevisited.blogspot.com_2015_07_how-to-use-wait-notify-and-notifyall-in.html_axzz4gOjkc8Yu]: http://javarevisited.blogspot.com/2015/07/how-to-use-wait-notify-and-notifyall-in.html#axzz4gOjkc8Yu
[http_javarevisited.blogspot.com_2011_05_wait-notify-and-notifyall-in-java.html]: http://javarevisited.blogspot.com/2011/05/wait-notify-and-notifyall-in-java.html