1. 对多线程的一点理解

多线程之间的竞争实际上是对公共资源的一个竞争，在竞争这个资源的时候，我们需要保护好这个公共资源。所以才对竞争的地方进行加锁操作。

2. 基于synchronize + wait + notifyAll的代码实现

/**
 * 生产者消费者模式：利用synchronize、wait、notifyAll
 *
 * @date 2021/12/8 17:03
 */
public class Resource {

    public static void main(String[] args) {

        Resource resource = new Resource();

        Producer producer = new Producer(resource);
        Consumer consumer = new Consumer(resource);

        new Thread(producer).start();
        new Thread(consumer).start();

    }


    private int num = 0;

    public synchronized void produce() {
        // condition does not hold
        while (num >= 10) {
            try {
                System.out.println("当前生产者 < " + Thread.currentThread().getName() + " > 进入等待");
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        num++;
        System.out.println("生产者 - < " + Thread.currentThread().getName() + " >, 当前资源数量为：" + num);
        // 生产完数据后，唤醒等待的消费线程消费数据
        this.notifyAll();
    }

    public synchronized void consume() {
        while (num <= 0) {
            try {
                System.out.println("当前消费者 < " + Thread.currentThread().getName() + " > 进入等待");
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        num--;
        System.out.println("消费者 - < " + Thread.currentThread().getName() + " >, 当前资源数量为：" + num);
        // 消费完数据，唤醒等待的生产线程生产数据
        this.notifyAll();
    }
}

class Producer implements Runnable {

    Resource resource;

    public Producer(Resource resource) {
        this.resource = resource;
    }

    @Override
    public void run() {
        while (true) {
            resource.produce();
        }
    }
}

class Consumer implements Runnable {

    Resource resource;

    public Consumer(Resource resource) {
        this.resource = resource;
    }

    @Override
    public void run() {
        while (true) {
            resource.consume();
        }
    }
}