java多线程之wait和notify

梦里梦外; 2022-01-31 20:29 266阅读 0赞

### 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();
        }
    }

### 3. 参考 ###

[https://www.cnblogs.com/plmnko/archive/2010/10/15/1851854.html][https_www.cnblogs.com_plmnko_archive_2010_10_15_1851854.html]

[https_www.cnblogs.com_plmnko_archive_2010_10_15_1851854.html]: https://www.cnblogs.com/plmnko/archive/2010/10/15/1851854.html