7、JUC--JUC线程高级_生产者消费者案例-虚假唤醒

等待唤醒案例最经典的的就是：生产者消费者案例

 首先定义一个店员进行买卖产品：

//店员
class Clerk{
    private int product =0;
    
    //进货
    public synchronized void get(){
        if(product >=10){
            System.out.println("产品已满！");
        }else{
            System.out.println(Thread.currentThread().getName()+":"+ ++product);
        }
    }
    
    //卖货
    public synchronized void sale(){
        if(product <=0){
            System.out.println("产品卖完");
        }else{
            System.out.println(Thread.currentThread().getName()+":"+ --product);
        }
    }
}

此时是对共享数据进行操作使用synchronized进行操作！！

生产者进行生产产品：

class Product implements Runnable{

    private Clerk clerk;
    
    public Product(Clerk clerk){
        this.clerk = clerk;
    }
    
    @Override
    public void run() {
        //进行生产产品
        for(int i=0;i<20;i++){
            clerk.get();
        }
    }
}

消费者进行购买产品：

class Consumer implements Runnable{

    private Clerk clerk;
    
    public Consumer(Clerk clerk){
        this.clerk = clerk;
    }
    
    @Override
    public void run() {
        //消费者进行消费产品
        //进行生产产品
                for(int i=0;i<20;i++){
                    clerk.sale();
                }
    }
}

public static void main(String[] args) {
        
        Clerk clerk = new Clerk();
        　　
        Product product=new Product(clerk);
        Consumer consumer = new Consumer(clerk);
        
        new Thread(product,"生产者").start();
        new Thread(consumer,"消费者").start();
    }

 执行结果如下

此时可以发现是线程不安全的

生产者消费者过快都会影响数据

进行数据的等待和唤醒

class Clerk{
    private int product =0;
    
    //进货
    public synchronized void get(){
        if(product >=10){
            System.out.println("产品已满！");
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }else{
            System.out.println(Thread.currentThread().getName()+":"+ ++product);
            this.notifyAll();
        }
    }
    
    //卖货
    public synchronized void sale(){
        if(product <=0){
            System.out.println("产品卖完");
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }else{
            System.out.println(Thread.currentThread().getName()+":"+ --product);
            this.notifyAll();
        }
    }
}

 此时的数据是可以进行正常进行

对于数据不会一致重复的请求

对代码在进行修改发现问题：

//店员
class Clerk{
    private int product =0;
    
    //进货
    public synchronized void get(){
        if(product >=1){
            System.out.println("产品已满！");
            try {
                this.wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }else{
            System.out.println(Thread.currentThread().getName()+":"+ ++product);
            this.notifyAll();
        }
    }
    
    //卖货
    public synchronized void sale(){
        if(product <=0){
            System.out.println("产品卖完");
            try {
                this.wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }else{
            System.out.println(Thread.currentThread().getName()+":"+ --product);
            this.notifyAll();
        }
    }
}


//生产者
class Product implements Runnable{

    private Clerk clerk;
    
    public Product(Clerk clerk){
        this.clerk = clerk;
    }
    
    @Override
    public void run() {
        //进行生产产品
        for(int i=0;i<20;i++){
            try {
                Thread.sleep(200);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            clerk.get();
        }
    }
}

//消费者
class Consumer implements Runnable{

    private Clerk clerk;
    
    public Consumer(Clerk clerk){
        this.clerk = clerk;
    }
    
    @Override
    public void run() {
        //消费者进行消费产品
        //进行生产产品
                for(int i=0;i<20;i++){
                    clerk.sale();
                }
    }
}

此时的运行结果：

运行结束之后，线程并未关闭

此时出现问题的位置：

此时的程序执行位置再wait()处，没有代码进行唤醒

程序会处于等待唤醒的状态

解决方法去点else

class Clerk{
    private int product =0;
    
    //进货
    public synchronized void get(){
        if(product >=1){
            System.out.println("产品已满！");
            try {
                this.wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
            System.out.println(Thread.currentThread().getName()+":"+ ++product);
            this.notifyAll();
        
    }
    
    //卖货
    public synchronized void sale(){
        if(product <=0){
            System.out.println("产品卖完");
            try {
                this.wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
            System.out.println(Thread.currentThread().getName()+":"+ --product);
            this.notifyAll();
        
    }
}

增加生产者消费者

    public static void main(String[] args) {
        
        Clerk clerk = new Clerk();
        
        Product product=new Product(clerk);
        Consumer consumer = new Consumer(clerk);
        
        new Thread(product,"生产者").start();
        new Thread(consumer,"消费者").start();
        new Thread(product,"生产者1").start();
        new Thread(consumer,"消费者1").start();
    }

 查看Java API中的wait()方法

 

为了避免虚假唤醒问题，应当总是在循环中使用

代码进行升级

class Clerk{
    private int product =0;
    
    //进货
    public synchronized void get(){
        
        while(product >=1){
            System.out.println("产品已满！");
            try {
                this.wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
            System.out.println(Thread.currentThread().getName()+":"+ ++product);
            this.notifyAll();
        
    }
    
    //卖货
    public synchronized void sale(){
        
        while(product <=0){
            System.out.println("产品卖完");
            try {
                this.wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
            System.out.println(Thread.currentThread().getName()+":"+ --product);
            this.notifyAll();
    }
}