读写锁ReadWriteLock

86 阅读 0 评论 57 点赞

我是靠谱客的博主矮小毛豆，最近开发中收集的这篇文章主要介绍读写锁ReadWriteLock，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

适用场景：并发读写场景，且读多写少

为什么要用：提高读场景的性能，对应读远远大于写的场景，性能优化显著

性能提升原因：同步锁或者重入锁在读写时都锁定，并发访问实际是串行处理。改用读写锁后，仅在写操作会锁定并阻塞，并发线程访问仅有读操作时不堵塞

	读	写
读	不阻塞	阻塞
写	阻塞	阻塞

测试代码

public class ReadThread implements Runnable {
	
	Resources resources;
	
	Lock lock;
	
	public ReadThread(Resources resources,Lock lock) {
		this.resources=resources;
		this.lock=lock;
		
	}
	

	public void run() {
	
		int value=0;
		try {
			value = resources.handleRead(lock);
		} catch (InterruptedException e) {	
			e.printStackTrace();
		}
		System.out.println(DateUtils.getCurrentTime("yyyy-MM-dd HH:mm:ss:SSS")+ "]---read value="+value);

	}

}

public class WriteThread implements Runnable {

	Resources resources;
	
	Lock lock;
	
	public WriteThread(Resources resources,Lock lock) {
		this.resources=resources;
		this.lock=lock;
		
	}
	

	public void run() {
	
		   try {
			resources.handleWirte(lock);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		}

}

public class Resources {

	private int value = 0;

	public int handleRead(Lock lock) throws InterruptedException {
		try {
			lock.lock();

			Thread.sleep(10);
			return this.value;
		} finally {
			lock.unlock();
		}
	}

	public void handleWirte(Lock lock) throws InterruptedException {
		try {
			lock.lock();
			
			
			int newValue = Math.abs(new Random().nextInt() % 10 + 2);
			int old = this.value;
			this.value = newValue;
			String currTime=DateUtils.getCurrentTime("yyyy-MM-dd HH:mm:ss:SSS");
			System.out.println(currTime+ "]-old=" + old + ",newValue=" + value);

			Thread.sleep(50);

		} finally {
			lock.unlock();
		}
	}

}

	public static void main(String[] args) {

		ReentrantReadWriteLock readWriteLock = new ReentrantReadWriteLock();

		Lock lock = new ReentrantLock();

		Lock readLock = readWriteLock.readLock();
		Lock writeLock = readWriteLock.writeLock();

		Resources rs = new Resources();

		ExecutorService es = Executors.newFixedThreadPool(100);

		//普通同步锁
		for (int i = 0; i < 10; i++) {
			es.submit(new ReadThread(rs, lock));//普通同步锁
		}

		for (int i = 0; i < 2; i++) {
			es.submit(new WriteThread(rs, lock));//普通同步锁
		}
		
		for (int i = 0; i < 10; i++) {
			es.submit(new ReadThread(rs, lock));//普通同步锁
		}
		
		//读写锁
/*		for (int i = 0; i < 10; i++) {
			es.submit(new ReadThread(rs, readLock)); //读写分离锁
		}

		for (int i = 0; i < 2; i++) {
			es.submit(new WriteThread(rs, writeLock));//读写分离锁
		}
		
		for (int i = 0; i < 10; i++) {
			es.submit(new ReadThread(rs, readLock)); //读写分离锁
		}*/
	}

前置条件

1. 先启动10个读线程，接着启动2个写线程，最后启动10个读线程

2.每个读线程获取锁后，睡眠10ms模拟读过程

3.每个写线程获取锁后，先写，再睡眠50ms，再释放锁

结果对比（已剔除写耗时）

同步锁，读总耗时：286ms

2018-12-07 21:21:34:147]---read value=0
2018-12-07 21:21:34:147]---read value=0
2018-12-07 21:21:34:147]---read value=0
2018-12-07 21:21:34:162]---read value=0
2018-12-07 21:21:34:178]---read value=0
2018-12-07 21:21:34:194]---read value=0
2018-12-07 21:21:34:209]---read value=0
2018-12-07 21:21:34:225]---read value=0
2018-12-07 21:21:34:240]---read value=0
2018-12-07 21:21:34:256]---read value=0
2018-12-07 21:21:34:256]-old=0,newValue=1
2018-12-07 21:21:34:319]-old=1,newValue=2
2018-12-07 21:21:34:397]---read value=2
2018-12-07 21:21:34:412]---read value=2
2018-12-07 21:21:34:428]---read value=2
2018-12-07 21:21:34:444]---read value=2
2018-12-07 21:21:34:459]---read value=2
2018-12-07 21:21:34:475]---read value=2
2018-12-07 21:21:34:491]---read value=2
2018-12-07 21:21:34:506]---read value=2
2018-12-07 21:21:34:522]---read value=2
2018-12-07 21:21:34:533]---read value=2

读写锁，读总耗时：34ms

2018-12-07 21:22:48:815]---read value=0
2018-12-07 21:22:48:815]---read value=0
2018-12-07 21:22:48:815]---read value=0
2018-12-07 21:22:48:815]---read value=0
2018-12-07 21:22:48:815]---read value=0
2018-12-07 21:22:48:815]-old=0,newValue=4
2018-12-07 21:22:48:815]---read value=0
2018-12-07 21:22:48:815]---read value=0
2018-12-07 21:22:48:815]---read value=0
2018-12-07 21:22:48:815]---read value=0
2018-12-07 21:22:48:815]---read value=0
2018-12-07 21:22:48:877]-old=4,newValue=10
2018-12-07 21:22:48:949]---read value=10
2018-12-07 21:22:48:949]---read value=10
2018-12-07 21:22:48:949]---read value=10
2018-12-07 21:22:48:949]---read value=10
2018-12-07 21:22:48:949]---read value=10
2018-12-07 21:22:48:949]---read value=10
2018-12-07 21:22:48:949]---read value=10
2018-12-07 21:22:48:949]---read value=10
2018-12-07 21:22:48:949]---read value=10
2018-12-07 21:22:48:949]---read value=10