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Producer and Consumer Problems in Concurrent Programming

2022-08-04 09:03:00 【51CTO】

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();
       
    }
       
}
      
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测试

Producer and Consumer Problems in Concurrent Programming_开发文档

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();
       
    }
       
}
       
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测试结果

Producer and Consumer Problems in Concurrent Programming_线程通信_02

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

Producer and Consumer Problems in Concurrent Programming_i++_03

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();
       
    }
       
}
      
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