并发编程之生产者和消费者问题

简单的线程通信，一个线程对数字进行增加操作、另一个线程对线程进行减少操作。

简单解释：线程A对数字进行减少操作，但不会一直让这个数字减少下去。当减少到设定的条件，让其等待，通知其他线程获得该资源。

package com.ProductAndCustomer;

/**
 * 线程之间的通信,生产者和消费者问题
 */
public class Product {
    public static void main(String[] args) {
        Data data = new Data();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try {
                    data.increment();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

        },"A").start();

        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try {
                    data.decrement();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

        },"B").start();
    }
}


//等待,业务,通知
class Data{
    //资源类
    private int num = 0;

    //增加操作
    public synchronized void increment() throws InterruptedException {
        if(num != 0){
            //等待
            this.wait();
        }
        num ++;
        System.out.println(Thread.currentThread().getName()+"=>"+num);
        //通知其他线程,+1结束
        this.notifyAll();
    }

    //减少操作
    public synchronized void decrement() throws InterruptedException {
        if(num == 0){
            //等待
            this.wait();
        }
        num --;
        System.out.println(Thread.currentThread().getName()+"=>"+num);
        //通知其他线程,-1结束
        this.notifyAll();
    }
}

测试

在多几个线程

package com.ProductAndCustomer;

/**
 * 线程之间的通信,生产者和消费者问题
 */
public class Product {
    public static void main(String[] args) {
        Data data = new Data();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try {
                    data.increment();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

        },"A").start();

        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try {
                    data.decrement();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

        },"B").start();

        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try {
                    data.decrement();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

        },"C").start();

        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try {
                    data.decrement();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

        },"D").start();
    }
}


//等待,业务,通知
class Data{
    //资源类
    private int num = 0;

    //增加操作
    public synchronized void increment() throws InterruptedException {
        if(num != 0){
            //等待
            this.wait();
        }
        num ++;
        System.out.println(Thread.currentThread().getName()+"=>"+num);
        //通知其他线程,+1结束
        this.notifyAll();
    }

    //减少操作
    public synchronized void decrement() throws InterruptedException {
        if(num == 0){
            //等待
            this.wait();
        }
        num --;
        System.out.println(Thread.currentThread().getName()+"=>"+num);
        //通知其他线程,-1结束
        this.notifyAll();
    }
}

测试结果

这里会出现虚假唤醒
查看开发文档可知、需要修改判断语句 if修改为while

修改后的代码

package com.ProductAndCustomer;

/**
 * 线程之间的通信,生产者和消费者问题
 */
public class Product {
    public static void main(String[] args) {
        Data data = new Data();
        new Thread(()->{
            for (int i = 0; i < 5; i++) {
                try {
                    data.increment();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

        },"A").start();

        new Thread(()->{
            for (int i = 0; i < 5; i++) {
                try {
                    data.decrement();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

        },"B").start();

        new Thread(()->{
            for (int i = 0; i < 5; i++) {
                try {
                    data.increment();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

        },"C").start();

        new Thread(()->{
            for (int i = 0; i < 5; i++) {
                try {
                    data.decrement();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

        },"D").start();
    }
}


//等待,业务,通知
class Data{
    //资源类
    private int num = 0;

    //增加操作
    public synchronized void increment() throws InterruptedException {
        while(num != 0){
            //等待
            this.wait();
        }
        num ++;
        System.out.println(Thread.currentThread().getName()+"=>"+num);
        //通知其他线程,+1结束
        this.notifyAll();
    }

    //减少操作
    public synchronized void decrement() throws InterruptedException {
        while(num == 0){
            //等待
            this.wait();
        }
        num --;
        System.out.println(Thread.currentThread().getName()+"=>"+num);
        //通知其他线程,-1结束
        this.notifyAll();
    }
}

测试结果