springcloud如何用Redlock实现分布式锁

springcloud如何用Redlock实现分布式锁

目录一、redlock简介二、怎么用java使用 redlock三、参考资料

之前写过一篇文章《如何在springcloud分布式系统中实现分布式锁？ 》，由于自己仅仅是阅读了相关的书籍，和查阅了相关的资料，就认为那样的是可行的。那篇文章实现的大概思路是用setNx命令和setEx配合使用。 setNx是一个耗时操作，因为它需要查询这个键是否存在，就算redis的百万的qps，在高并发的场景下，这种操作也是有问题的。关于redis实现分布式锁，redis官方推荐使用redlock。

一、redlock简介

在不同进程需要互斥地访问共享资源时，分布式锁是一种非常有用的技术手段。实现高效的分布式锁有三个属性需要考虑：

安全属性：互斥，不管什么时候，只有一个客户端持有锁

效率属性A:不会死锁

效率属性B：容错，只要大多数redis节点能够正常工作，客户端端都能获取和释放锁。

Redlock是redis官方提出的实现分布式锁管理器的算法。这个算法会比一般的普通方法更加安全可靠。关于这个算法的讨论可以看下官方文档。

二、怎么用java使用 redlock

在pom文件引入redis和redisson依赖：

org.springframework.boot

spring-boot-starter-data-redis

org.redisson

redisson

3.3.2

AquiredLockWorker接口类，，主要是用于获取锁后需要处理的逻辑：

/**

* Created by fangzhipeng on 2017/4/5.

* 获取锁后需要处理的逻辑

*/

public interface AquiredLockWorker {

T invokeAfterLockAquire() throws Exception;

}

DistributedLocker 获取锁管理类：

/**

* Created by fangzhipeng on 2017/4/5.

* 获取锁管理类

*/

public interface DistributedLocker {

/**

* 获取锁

* @param resourceName 锁的名称

* @param worker 获取锁后的处理类

* @param

* @return 处理完具体的业务逻辑要返回的数据

* @throws UnableToAquireLockException

* @throws Exception

*/

T lock(String resourceName, AquiredLockWorker worker) throws UnableToAquireLockException, Exception;

T lock(String resourceName, AquiredLockWorker worker, int lockTime) throws UnableToAquireLockException, Exception;

}

UnableToAquireLockException ，不能获取锁的异常类：

/**

* Created by fangzhipeng on 2017/4/5.

* 异常类

*/

public class UnableToAquireLockException extends RuntimeException {

public UnableToAquireLockException() {

}

public UnableToAquireLockException(String message) {

super(message);

}

public UnableToAquireLockException(String message, Throwable cause) {

super(message, cause);

}

}

RedissonConnector 连接类：

/**

* Created by fangzhipeng on 2017/4/5.

* 获取RedissonClient连接类

*/

@Component

public class RedissonConnector {

RedissonClient redisson;

@PostConstruct

public void init(){

redisson = Redisson.create();

}

public RedissonClient getClient(){

return redisson;

}

}

RedisLocker 类，实现了DistributedLocker：

import org.redisson.api.RLock;

import org.redisson.api.RedissonClient;

import org.springframework.beans.factory.annotation.Autowired;

import org.springuYMpnframework.stereotype.Component;

import java.util.concurrent.TimeUnit;

/**

* Created by fangzhipeng on 2017/4/5.

*/

@Component

public class RedisLocker implements DistributedLocker{

private final static String LOCKER_PREFIX = "lock:";

@Autowired

RedissonConnector redissonConnector;

@Override

public T lock(String resourceName, AquiredLockWorker worker) throws InterruptedException, UnableToAquireLockException, Exception {

return lock(resourceName, worker, 100);

}

@Override

public T lock(String resourceName, AquiredLockWorker worker, int lockTime) throws UnableToAquireLockException, Exception {

RedissonClient redisson= redissonConnector.getClient();

RLock lock = redisson.getLock(LOCKER_PREFIX + resourceName);

// Wait for 100 seconds seconds and automatically unlock it after lockTime seconds

boolean success = lock.tryLock(100, lockTime, TimeUnit.SECONDS);

if (success) {

try {

return worker.invokeAfterLockAquire();

} finally {

lock.unlock();

}

}

throw new UnableToAquireLockException();

}

}

测试类：

@Autowired

RedisLocker distributedLocker;

@RequestMapping(value = "/redlock")

public String testRedlock() throws Exception{

CountDownLatch startSignal = new CountDownLatch(1);

CountDownLatch doneSignal = new CountDownLatch(5);

for (int i = 0; i < 5; ++i) { // create and start threads

new Thread(new Worker(startSignal, doneSignal)).start();

}

startSignal.countDown(); // let all threads proceed

doneSignal.await();

System.out.println("All processors done. Shutdown connection");

return "redlock";

}

class Worker implements Runnable {

private final CountDownLatch startSignal;

private final CountDownLatch doneSignal;

Worker(CountDownLatch startSignal, CountDownLatch doneSignal) {

this.startSignal = startSignal;

this.doneSignal = doneSignal;

}

public void run() {

try {

startSignal.await();

distributedLocker.lock("test",new AquiredLockWorker

@Override

public Object invokeAfterLockAquire() {

doTask();

return null;

}

});

}catch (Exception e){

}

}

void doTask() {

System.out.println(Thread.currentThread().getName() + " start");

Random random = new Random();

int _int = random.nextInt(200);

System.out.println(Thread.currentThread().getName() + " sleep " + _int + "millis");

try {

Thread.sleep(_int);

} catch (InterruptedException e) {

e.printStackTrace();

}

System.out.println(Thread.currentThread().getName() + " end");

doneSignal.countDown();

}

}

运行测试类：

Thread-48 start

Thread-48 sleep 99millis

Thread-48 end

Thread-49 start

Thread-49 sleep 118millis

Thread-49 end

Thread-52 start

Thread-52 sleep 141millis

Thread-52 end

Thread-50 start

Thread-50 sleep 28millis

Thread-50 end

Thread-51 start

Thread-51 sleep 145millis

Thread-51 end

从运行结果上看，在异步任务的情况下，确实是获取锁之后才能运行线程。不管怎么样，这是redis官方推荐的一种方案，可靠性比较高。

三、参考资料

https://github.com/redisson/redisson

《Redis官方文档》用Redis构建分布式锁

A Look at the Java Distributed In-Memory Data Model (Powered by Redis)

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