读写锁_aiyongbo-优快云博客

本文链接：https://blog.youkuaiyun.com/aiyongbo123456/article/details/87652750

本文深入探讨了读写锁的工作原理，对比排他锁，读写锁在读多于写的情况下能提供更好的并发性和吞吐量。通过一个Java实现的示例，详细解释了读写锁如何在多线程环境中提升读操作的并发性，同时保证写操作的线程安全。

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我们以前理解的锁，基本都是排他锁，也就是这些锁在同一时刻只允许一个线程进行访问，而读写所在同一时刻可以允许多个线程访问，但是在写线程访问时，所有的读线程和其他写线程都会被阻塞。读写锁维护了一对锁，一个读锁、一个写锁; 一般情况下，读写锁的性能都会比排它锁好，因为大多数场景读是多于写的。在读多于写的情况下，读写锁能够提供比排它锁更好的并发性和吞吐量.

package com.example.demo.morethread;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * 读写锁
 */
public class ReentrantReadWriteDemo {
    static Map<String, Object> cacheMap = new HashMap<String, Object>();
    static ReentrantReadWriteLock rw = new ReentrantReadWriteLock();
    static Lock read = rw.readLock();
    static Lock write = rw.writeLock();

    public static final Object get(String key)  {
        read.lock();
        System.out.println(Thread.currentThread().getName() + ":开始读数据" + key + ":" + cacheMap.get(key));
        try {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return cacheMap.get(key);
        }  finally {
            System.out.println(Thread.currentThread().getName() + ":读取结束" + key + ":" + cacheMap.get(key));
            read.unlock();
        }
    }

    public static final void put(String key,Object value){
        write.lock();
        System.out.println(Thread.currentThread().getName()+":开始写数据"+key+":"+value);
        try {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            cacheMap.put(key, value);
        }finally {
            System.out.println(Thread.currentThread().getName()+":写数据结束"+key+":"+value);
            write.unlock();
        }
    }

}

package com.example.demo.morethread;

import java.util.concurrent.locks.ReentrantReadWriteLock;

public class ReadWriteDemoTest {
    public static void main(String[] args) throws InterruptedException{
        new Thread(()->{ReentrantReadWriteDemo.put("name","xiaoming");
        },"write_thread1").start();
        new Thread(()->{ReentrantReadWriteDemo.put("age","29");
        },"write_thread2").start();
        new Thread(()->{ReentrantReadWriteDemo.get("name");
        },"read_thread1").start();
        new Thread(()->{ReentrantReadWriteDemo.get("name");
        },"read_thread2").start();
        new Thread(()->{ReentrantReadWriteDemo.get("name");
        },"read_thread3").start();
        new Thread(()->{ReentrantReadWriteDemo.put("sex","male");
        },"write_thread3").start();
        new Thread(()->{ReentrantReadWriteDemo.get("age");
        },"read_thread12").start();
        new Thread(()->{ReentrantReadWriteDemo.get("age");
        },"read_thread22").start();
        new Thread(()->{ReentrantReadWriteDemo.get("age");
        },"read_thread32").start();
        new Thread(()->{ReentrantReadWriteDemo.get("sex");
        },"read_thread11").start();
        new Thread(()->{ReentrantReadWriteDemo.get("sex");
        },"read_thread21").start();
        new Thread(()->{ReentrantReadWriteDemo.get("sex");
        },"read_thread31").start();
    }
}

运行结果如下：