JAVA的读写锁

Posted 2023-02-02

我们都知道锁分共享锁和排他锁，实际使用中我们一般将锁机制分为读和写两种场景，即我们期望写入排他，读取共享。Java由此提供了包转后的读写锁工具类。

//创建对象
 ReadWriteLock readWriteLock=new ReentrantReadWriteLock();
 //创建写锁
 readWriteLock.writeLock().lock();
 //解锁
 readWriteLock.writeLock().unlock();
 //创建读锁
 readWriteLock.readLock().lock();

特点

1. 读锁可以访问，操作资源，而写锁将阻塞其他线程
2. 加入读锁无法加锁
3. 并发性更好
4. 可重入
   ps ：可重入锁是指该线程a获取锁，可重新申请获取锁
   ​​​重入锁的介绍​​

package day2.读写锁;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

public class Book 
    private ReadWriteLock readWriteLock=new ReentrantReadWriteLock();

    int num=10;
    void buy() throws InterruptedException 
        readWriteLock.writeLock().lock();
        System.out.println("正在清算 购入图书"+Thread.currentThread().getName()+" 当前 "+num);
        TimeUnit.SECONDS.sleep(3);
        num = num +1;
        readWriteLock.writeLock().unlock();


    
    void find()
        readWriteLock.readLock().lock();

        System.out.println("查看当前图书"+Thread.currentThread().getName()+"当前   "+num);
        readWriteLock.readLock().unlock();


    
    void sale() throws InterruptedException 
        readWriteLock.writeLock().lock();
        System.out.println("当前可售卖图书  "+Thread.currentThread().getName()+" 当前  "+num);
        if(num>=1)
        num = num -1;
        readWriteLock.writeLock().unlock();


    

package day2.读写锁;

import java.util.concurrent.TimeUnit;

public class test 



    public static void main(String args[]) throws InterruptedException 
        Book book=new Book();

        new Thread(()->
            for(int i=0;i<=100;i++)
            book.find();
        ).start();
        new Thread(()->
            while(true)
                try 
                    book.find();
                    book.sale();
                    //TimeUnit.SECONDS.sleep(1);

                 catch (InterruptedException e) 
                    e.printStackTrace();
                
            
        ).start();

        new Thread(()->
            while(true)
                try 
                    book.find();
                    book.buy();
                   // TimeUnit.SECONDS.sleep(1);
                 catch (InterruptedException e) 
                    e.printStackTrace();
                
            
        ).start();

        new Thread(()->
            while(true)
                try 
                    book.find();
                    book.buy();
                   // TimeUnit.MILLISECONDS.sleep(1);
                 catch (InterruptedException e) 
                    e.printStackTrace();
                
            
        ).start();