美文网首页Spring Cloud
如何用Redlock实现分布式锁

如何用Redlock实现分布式锁

作者: 方志朋 | 来源:发表于2017-04-22 15:09 被阅读292次

    转载请标明出处:
    http://blog.csdn.net/forezp/article/details/70305336
    本文出自方志朋的博客

    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:

    <!-- redis-->
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-data-redis</artifactId>
            </dependency>
            <!-- redisson-->
            <dependency>
                <groupId>org.redisson</groupId>
                <artifactId>redisson</artifactId>
                <version>3.3.2</version>
            </dependency>
    
    

    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> {
         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 <T>
          * @return 处理完具体的业务逻辑要返回的数据
          * @throws UnableToAquireLockException
          * @throws Exception
          */
         <T> T lock(String resourceName, AquiredLockWorker<T> worker) throws UnableToAquireLockException, Exception;
    
         <T> T lock(String resourceName, AquiredLockWorker<T> 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.springframework.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> T lock(String resourceName, AquiredLockWorker<T> worker) throws InterruptedException, UnableToAquireLockException, Exception {
    
            return lock(resourceName, worker, 100);
        }
    
        @Override
        public <T> T lock(String resourceName, AquiredLockWorker<T> 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<Object>() {
    
                        @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。有什么问题欢迎留言。

    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)

    优秀文章推荐:

    相关文章

      网友评论

        本文标题:如何用Redlock实现分布式锁

        本文链接:https://www.haomeiwen.com/subject/paeszttx.html